Simplified tilt
FRÉDÉRIC ROCHAT
Master of Science Thesis Stockholm, Sweden 2007
Simplified tilt
Frédéric Rochat
Master of Science Thesis MMK 2007:26 MPK 586 KTH Industrial Engineering and Management Machine Design SE-100 44 STOCKHOLM
Examensarbete MMK 2007:26 MPK 586
Enklare korglutning
Frédéric Rochat
Godkänt Examinator Handledare 2007-03-16 Jan-Gunnar Persson Vincent Capponi (EPFL) Paul Xirouchakis (EPFL) Uppdragsgivare Kontaktperson Sebastian Stichel
Sammanfattning
Detta projekt leddes av Bombardier Transportation i Västerås i samarbete med KTH Stockholm och EPFL Lausanne. Projektet syftar till att utveckla en ny och enklare korglutning för spårfordon.
Ökat konkurrens på marknaden beroende på ett bredare utbud av andra transportmedel tvingade tågkompanier att förbättra sin prestanda. En av de mest uppenbara faktorerna för hög prestanda är restiden, som kan minskas genom användning av höghastighetståg. De kräver kurvor med stor radie och långa övergångskurvor för att undvika minskad komfort, vilket är ett andra mått på prestanda. Att bygga nya spår, som är anpassade till höghastighetståg, är mycket dyrbart och kan bara möjliggöras där antalet resenärer är högt.
Tåg som har förmågan att luta korgen inåt i kurvor är ett billigare alternativ. Genom att korglutning minskar sidoaccelerationen passagerarna upplever, kan tågen hålla högre hastighet genom kurvorna med bibehållen komfort. Risken för åksjuka ökar dock.
Fördelar med korglutningståg är förbättrad möjlighet till hög hastighet in i kurvor samt högre passagerarkomfort, men är dyrare både vad gäller inköps- och underhållskostnad. Eftersom konventionella tåg dessutom har ökat hastigheten i kurvor har prestandafördelen med korglutningståg minskat. Skillnaden i pris förblir dock tydlig och tycks vara konstant. Dessutom har korglutningståg dåligt rykte vad gäller pålitlighet och på grund av åksjuka.
Detta arbete presenterar en state of the art av korglutningståg med fokus på deras mekanik, men tar också i övervägande reglersystem och aktuatorer/motorer. Nya och enklare lösningar har hittats och presenteras i jämförelse med nuvarande industriella konstruktioner.
Nuvarande lösningar förväntas förbli fördelaktiga på den framtida marknaden. En ny lösning är föreslagen, men kräver mer detaljerade studier för att utvärdera och bedöma om den är utförbar. Ingen förändring förväntas ske på aktuatorområdet. Komplexa algoritmer som använder lagrad spårinformation och tågpositionen förväntas ta över marknaden inom en snar framtid.
Master of Science Thesis MMK 2007:26 MPK 586
Simplified tilt
Frédéric Rochat
Approved Examiner Supervisor 2007-03-16 Jan-Gunnar Persson Vincent Capponi (EPFL) Paul Xirouchakis (EPFL) Commissioner Contact person Sebastian Stichel
Abstract
This project was led on behalf of Bombardier Transportation in Västerås, Sweden, in collaboration with KTH Stockholm and EPFL Lausanne. This project is connected to the development of a new and simplified tilt system for rail vehicles.
Growing competition from other means of transportation has forced railway companies throughout the world to search for increased performances. Travelling time is the most obvious performance indicator that may be improved by introducing high-speed trains. They require very large curve radii and long transitions curves not to impair ride comfort, another performance indicator. Building new tracks adapted to high speed trains is very costly and can only be justified where the passenger base is large.
Trains with the capability to tilt the carbodies inwards the curve is a more cost efficient alternative. The tilt inwards reduces the lateral force felt by the passengers allowing the train to pass curves at enhanced speed with maintained ride comfort but increases the frequency of motion sickness.
The benefits of tilting trains are improved speed capability in curves and enhanced passengers comfort, but at higher buying and maintenance cost. As the conventional trains increase their speed in curves, the performance advantage of tilting trains is reduced while their prize is still kept significantly higher and constant. Moreover, tilting trains often suffer from bad reputation regarding reliability and motion sickness.
This work presents a state of the art of tilting trains mainly focused on their mechanisms, but also taking in consideration control and activation. New and simplified solutions have been researched and are presented in comparison with existing embodiments.
Existing solutions are expected to stay advantageous and available on the market. A new possible solution is proposed and requires further investigations to verify its feasabilty. No change is expected concerning activation. It is foreseen that complex control algorithms using onboard track data and train position are going to be usual technology. Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Contents
1TU UT IntroductionTU UT ...... 2
1.1TU UT BackgroundTU of this studyUT ...... 2
1.2TU UT ObjectivesTU of this studyUT ...... 3
2TU UT Track,TU trains and tiltUT ...... 4
2.1TU UT InfrastructureTU UT ...... 4
2.2TU UT VehiclesTU UT ...... 11
2.3TU UT StoryTU of tiltingUT ...... 16
2.4TU UT DevelopmentTU trendsUT ...... 18
2.5TU UT RailsTU dynamicsUT ...... 20
2.6TU UT ComfortTU UT ...... 29
2.7TU UT MotionTU sicknessUT ...... 31
2.8TU UT HowTU much to tiltUT ...... 35
2.9TU UT PerformanceTU and advantages of tilting trainsUT ...... 35
2.10TU UT AdditionalTU requirements of tilting trainsUT ...... 36
3TU UT RequirementsTU for the optimal solutionUT ...... 40
4TU UT TiltTU mechanismUT ...... 48
4.2TU UT DifferentTU possible configurationsUT ...... 52
4.3TU UT PatentsTU UT ...... 56
4.4TU UT OverviewTU of existing mechanismsUT ...... 56
4.5TU UT BrainstormingTU & creativityUT ...... 68
4.6TU UT NovelTU designsUT...... 68
4.7TU UT OverviewTU of all possible tilt mechanismsUT ...... 78
4.8TU UT SystemsTU to be assessedUT ...... 79
4.9TU UT AssessmentTU of different mechanismsUT ...... 80
5TU UT ActuatorsTU UT ...... 92
5.1TU UT PneumaticTU actuatorsUT ...... 92
5.2TU UT HydraulicTU actuatorsUT ...... 93
5.3TU UT Electro-mechanicTU actuators...... 93UT
5.4TU UT Electro-hydraulicTU actuatorsUT ...... 94
5.5TU UT AssessmentTU of actuatorsUT ...... 94
6TU UT ControlTU UT ...... 97
6.1TU UT RequirementsTU of tilt controlUT ...... 97
6.2TU UT ReactiveTU tiltUT...... 98
6.3TU UT PredictiveTU tiltUT ...... 101
6.4TU UT ComparativeTU diagramUT ...... 107
7TU UT ConclusionsTU and further workUT ...... 108
7.1TU UT ConclusionsTU UT ...... 108
7.2TU UT FurtherTU workUT ...... 108
8TU UT AcknowledgementsTU UT ...... 110
9TU UT BibliographyTU UT ...... II
9.1TU UT PublicationsTU UT ...... II
9.2TU UT RailwayTU gazette internationalUT ...... IV
9.3TU UT WebsitesTU UT ...... IV
10TU UT AppendicesTU UT ...... VI
10.1TU UT TableTU of illustrationsUT ...... VI
10.2TU UT TableTU of tablesUT ...... X
10.3TU UT ProposedTU taskUT ...... XII
10.4TU UT ProposedTU planningUT ...... XIII
10.5TU UT BrainstromingTU seminarUT ...... XIV
10.6TU UT PatentsTU studyUT ...... XVIII
10.7TU UT ContactsTU informationUT ...... XXVIII
II
Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Preface
This thesis is the last step of my degree in master of science in microtechnical engineering at the Ecole Polytechnique Fédérale de Lausanne – Swiss Institute of Technology - (EPFL). It was carried out in partnership with the Kungliga Tekniska Högskolan – Royal Institute of Technology - (KTH) in Stockholm and on the behalf of Bombardier Transportation in Västerås, Sweden, at the department of Specialist Engineering / Vehicle Dynamics within the division Mainline & Metros (MLN/ESD).
This study is connected to the need of a simplified and cheap tilt for rail vehicles. This work presents an analysis of the state of the art solutions in term of mechanics, control and activation and analyses those solutions from a cost and benefits perspective. The final aim is to propose improvements of actual existing solutions, possible novel designs and areas for further investigations in view of reaching a better ratio between benefits and costs.
Supervising at Bombardier Transportation was provided by PD Dr.-Ing. Sebastian Stichel and by M.Sc. Rickard Persson. Special thanks to them for their great disponibility, help and entousiasm. Thanks to all colleagues at Specialist Engineering for their presence and interesting time in Västerås.
Further on I would like to thank my academic supervisors Prof. Jan-Gunnar Persson at KTH and Prof. Paul Xirouchakis at EPFL and my assistant Dr.-Ing. Vincent Capponi at EPFL for all their comments, ideas, enthousiasm and support during this work.
Finally thanks to my family and friends for their joy, time and support.
rd Västerås, 23P P February 2007,
Frédéric Rochat
IV
Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Simplified tilt
Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
1 Introduction
The tilting function of a train enhances its speed capability in curves without deteriorating comfort, aiming at reduction of the lateral acceleration felt by passengers in curves due to the centrifugal force that would impair comfort otherwise. This additional design has implication on the whole train design. Safety, reliability, and market performances such as travel time, attraction and competitiveness to other means of transport are key figures of its benefits.
1.1 Background of this study
The railway companies have been exposed to growing competition from other means of transport, namely automobiles and airplanes. Set under the pressure of the market shares and profitability needs while the governments tend to lower their financial support and privatize services, the operators were forced to search for improved performance. Travelling time is the most direct and obvious criterion in terms of competition. But riding comfort, reliability, ecological impact and access to service have to be considered as other global performance indicators.
Journey time must be reduced to compete with airlines on middle distance trips ranging from 300 to 600 [km]. The introduction of high-speed trains is the most obvious way to act on the previously named indicator. To operate, they require straight tracks or at least tracks with very large curve radii not to impair the ride comfort, that means radii above 2000 [m], sometimes even higher on recently built tracks. As the historical rail network doesn’t suit those needs, it turns out to be a very costly solution to build such tracks. That can only be justified where the rate of use is extremely large, thus returns on investments are granted, or where the political willing and funding capability are strong. The landmark obstacles, budget constraints or limited passengers’ base simply prohibit the construction of dedicated high-speed tracks in most of the case while airplanes and cars keep pressing the market with continually more attractive price as well as comfort.
On existing lines with a large amount of curves between small and middle radius where in addition infrastructure has in most cases to be shared with freight trains, centrifugal acceleration is a limiting factor to the maximum cruising speed of passengers trains. However the historical railroad network exists and has the major competitive advantage to link the inner heart of the town where airplanes cannot reach and car traffic is increasingly jammed.
A more cost-effective way to cut journey time on the historic winding tracks, where the passenger base can’t justify the construction of a new track is the introduction of tilting trains. Those vehicles have the ability to roll their carbodies floor inwards to reduce the lateral force felt by the passengers, hence they allow passing through bends at increased speed with maintained ride comfort when not even improved.
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Since the commercial introduction of tilting trains in the early eighties, they became a mature technology. But their reputation suffered from low reliability, at least in some cases when introduced to the market, and due to the cause of increased motion sickness. In parallel, the operators and passengers acceptance for increased lateral force made possible to raise the speed of conventional trains in curves, as the result of a trade-off between shorter travelling times at the cost of lower comfort. This reduces the potential for travelling time improvement by tilting trains to approximately 10 – 15% while the purchase cost of a tilting train is kept about 3-5% higher and their maintenance and utilisation costs are also higher. This performance advantage shrinkage puts stronger stress on construction and maintenance cost of tilting trains for staying an advantageous solution. Hence, the need for a cheaper solution would be a major advantage for future tilting trains onto the market.
1.2 Objectives of this study
The actual market situation with strong competition requires exploring new possible constructions or modifications of existing solutions in order to reduce their costs. Better constructive and operative costs would maintain tilting trains in an advantageous market position. In a first part, the present study will list and judge the existing solutions for tilting trains in a state of the art manner. In a second part, this work will focus on proposing novel designs. Afterwards all the different systems will be compared against the objectives they have to fulfil. The goal is to establish which solution would give most advantages. After the mechanism, the situation of activation and control is presented. The final objectives of this study are to propose improvements, new ideas and to guide further investigations.
FigureT 1 : T many ways to the train station, photo Bombardier.
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2 Track, trains and tilt
2.1 Infrastructure
2.1.1 Tracks
FigureT 2 : T track cross section and its components ([1], p. 2.1).
The track can be divided in a substructure and a superstructure. The latter is composed of rails, rail fastenings, pads, sleepers and ballast. A rail is meant to be both a running surface and a load bearing element. The running surface should be smooth and avoid or at least damp vibrations to grant an optimal ride comfort. On the other hand as a load bearing element, rails have to support the static and dynamic loads in all directions and to transfer it to the ballast. As seen in the above illustration, tracks are usually inclined towards the centre of the tracks, this for better load transmission and interaction between rails and wheels profile.
FigureT 3 : T track cross section and its components with explanations and illustrations of their functions ([36], p. 84).
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The friction between rails and wheels generates a high thermal stress that the rails have to withstand. Historically, tracks were composed of segments of rails from 5 to 20 [m], set one after the other with a gap up to 20 [mm] in between. Nowadays rails are continuously welded which allows better cruising comfort and reduces wheel damages. Joints absorb thermal dilatation or shrinkage. Due to increased lateral track stability the tracks very seldom buckle on account of the length dilatation during hot summer days. The profile of the rails is important for rail - wheel interaction. The actual shape is known as the Vignoles profile and is standardized under the appellation UIC60, where 60 stand for 60 [kg/m]. The tendency is to increase the height and weight of the rails to better withstand higher vehicle speed and consequently higher track loads.
Rails requirements can be summarized as follows: • Very tight geometric tolerances regarding straightness • High wear resistance • High hardness • High tensile strength • High toughness • High fatigue strength • Low brittle transition temperature • Easy to weld
The rail fastenings together with rail pads have to withstand the lateral, longitudinal and vertical loads and to transfer them from the rails to the sleepers. Their requirements are: • Easy mounting • Easy maintenance • Electrical isolation • Elasticity • Acoustic damping
The sleepers, traditionally built out of wood, are gradually replaced by concrete on mainlines throughout the world. Concrete sleepers offer longer service life and greater track stability. A concrete sleeper weights about 30 [kg]. Although timber sleepers have good elasticity and are easier to handle due to lower weight, they age much faster. Synthetic sleepers made of hard polyurethane foam and glass fibres are a recent development in Japan. They are designed for very long service life, expected to reach up to 60 years, while maintaining the good properties of timber. They mainly are used where maintenance work is very difficult like on bridges, in tunnels or around turnovers.
Some tracks are built with reinforced concrete slabs instead of sleepers. If the realisation cost is higher, the maintenance work is reduced. Their use is advantageous for tunnels or bridges, where they reduce height and weight of the final construction, which hence can reduce building costs, making this solution profitable in some cases. Another ongoing development is ladder sleepers that consist of about 10 meters long longitudinal concrete members bound by lateral steel tubes. This construction distributes the load lengthwise, which is advantageous in regard to longitudinal rail flexibility. Sleepers are usually distant from 0.5 to 0.65 [m]. If the gap is not constant, this can lead to higher stress, which in turn can lead to plastic deformation and thus track irregularities. Note that the sleepers can be used as an incremental positioning system or as base for the measurement of convoy speed with the help of a map of the track.
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The sleeper’s functions are: • Constraining and keeping the lateral position of the rails • Transferring the load and distribute stress to the ballast • Ensuring flexural resistance to the rails
Finally the ballast should have high friction capability, which is made possible with an approximately constant granulometry and sharp stone edges. To increase lateral stability in tight curves, the ballast shoulder longwise the track can be brightened and slightly elevated.
Furthermore its properties can be listed as follows: • Withstanding the static and dynamic load • Transferring and distributing it to the sub grade • Avoiding sleepers displacement • Stabilizing the track in lateral and vertical directions • Providing some elasticity • Having a good wear resistance • Providing drainage
2.1.2 Nominal track geometry
The nominal track geometry is the ideal alignment design of the track, whose rails are parallel at an ideal distance called track gauge. Track is composed of the following sections:
• Straight lines • Transition curves • Horizontal circular curves • Vertical curves
Any deviation from the nominal track geometry is called track irregularities or misalignments and will be addressed in the next section. All important definitions will be clarified in the following text. Additionally to the previous elements, which compose the ideal central line of the track in space, track can also have a twist in the lateral and vertical plane, which is called cant.
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2.1.2.1 Track gauge
The track gauge is the distance between the inner faces of the rail heads. The standard track gauge is measured 14 [mm] below the top of the rails plane. Standard track gauge is 1435 [mm] (4 feet and 8 ½ inches). It is used on major part of the European railways, USA, Canada, Mexico, China, the newly built high speed lines of Japan among other countries.
FigureT 4 : T diesel powered tilt train cruising on narrow gauge in Queensland, Australia. Such a train derailed in November 2004, causing unbelievably no casualties, source Wikipedia.
Gauges which are less than 1435 [mm] are called narrow gauges. A typical value is 1000 [mm] which is in use in Africa and South America and 1067 [mm] for the Japanese historical lines, in South African and part of Australian rail network. Narrow gauges have a negative impact on the derailment coefficient and are less adapted for speeding, besides the fact of restricted onboard room.
Finally, various broad gauges exist, namely: 1600 [mm] in Finland and Russia, 1668 [mm] in Portugal and parts of Spain and 1678 [mm] in parts of India.
2.1.2.2 Horizontal curves
In a horizontal circular curve the radius, which refers to the centre of the track, is constant. The curvature is the inverse of the radius. On the lines constructed about a century ago, the span of radii was typically between 500 and 2000 [m]. The trend has naturally been to increase this span on new mainlines to cruise faster. Of course, the ideal track for speeding would be totally straight. The last two decades, curve radii were to be counted between 2000 and 5000 [m], sometimes even wider on new built tracks. This leads to higher cost of construction as the lines often count many tunnels or bridges because they often cannot follow the natural terrain or need to get round the constructed area.
T
7 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
T
T
FigureT 5 : T cant ([1], p. 2.8).
In most of the curves, with the exception of turnouts, a super elevation of the outer rail is arranged to mitigate the effect of the centrifugal acceleration. This is named super elevation or cant D = ht . The angle between the horizontal plane and the track plane is defined by the track super elevation and the distance between the two contact points of a wheel set 2 ⋅ b0 which is 1500 [mm] for standard track gauge. Usually the change of cant starts at the entrance and stops at the end of transition curves, so that it is linked with the appearance and end of centrifugal force. Circular curves have a constant cant. ⎛ D ⎞ ⎜ ⎟ ϕT = arcsin⎜ ⎟ ⎝ 2 ⋅ b0 ⎠ A typical limitation value for cant is 150 [mm] but it can go up to 200 [mm] for dedicated passengers lines. The limitation is largely related to the problem of possible derailment of freight convoys stopping in curves. The standard for all values are specified in national specifications. More information can be found in the national standards or the CEN (European committee of standardization).
The cant of equilibrium, D0 , is the cant when the lateral acceleration is zero in the plane of the tracks at a given speed. If the speed is higher than the one of the cant of equilibrium, then appears a cant deficiency, I . It stands for the additional cant required to reach equilibrium at this higher speed. In the opposite situation, a cant excess, E , appears.
The rate of change of cant, also called ramp gradient is limited. Its inverse is named for ramp index. A common restriction is the value 1/400. The rate of change can increase the risk of derailment due to diagonal unloading especially for convoy with stiff vertical suspension. In addition, a high ramp gradient also worsens the risk of buckling due to thermal dilatation.
2.1.2.3 Transition curves Straight tracks and horizontal curves can naturally not be connected directly. They need a soft transition where the radius usually increases linearly. Such sections of track are called transition curves. A curve, when the curvature grows linearly is called clothoïd. Similarly, the cant cannot change abruptly either, but follows a superelevation ramp to change softly. In a common and ideal manner and because the centrifugal force increases linearly with the curvature at a constant speed, both transition curves and super elevation ramps start and finish at the same position along the track. To avoid that the second derivate becomes infinite as it happens with linear ramps, investigations have been made with the use of parabolic change of curvature or cant. However, their theoretical improvement tends to be insignificant in comparison with importance of track irregularities. Like for cant, the regulation can be found in national or European guidelines.
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2.1.2.4 Vertical curves
The longitudinal track gradient is limited to ensure the ability of the traction system to pull the convoy uphill and to ensure slowing down on acceptable distance downhill. Vertical curves are used to ease the transition between different track gradients. Vertical curves are less important considering tilting trains, with minor influence on motion sickness or comfort.
2.1.3 Track irregularities
The frequent passage of trains loosens and deforms the ballast and/or the bed supporting it. In addition, it increases the grade sag at joints and the rails surface roughness. Those modifications of the ideal track geometry are called track irregularities. They are very important for the wheel rail contact, for the dynamics load and of course for the comfort of travellers. The consequences vary with the type of irregularities, whose wave lengths react differently with the natural frequency of the different dynamic parts of the vehicle. Long wave geometry mainly affects the vertical and lateral body vibration resulting in poor ride quality. Short waves cause shock and high frequency vibrations between rail and wheel, creating increased load on track, noise and vibrations.
Several kinds of irregularities exist and are illustrated in the figure just bellow: • Longitudinal level: geometrical error in the vertical direction in the longitudinal vertical plane. • Line: geometrical error in the lateral direction in the horizontal plane. • Gauge: variation of the gauge. • Twist: difference of cant between the ideal and real cross sections in the longitudinal direction, can be named cant irregularity.
FigureT 6 : T the four kinds of track irregularities ([1], p. 2.17).
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An excessive track irregularity can even cause derailment due to climbing or jumping of the wheel over the rail. An increased lateral thrust can spread the rails, leading to the same consequence. Therefore track irregularities are being measured to grant safety and ride quality. Measurements are realized by vehicles designed for this special task. They can be sorted in two different categories. In a first manner, the vehicle measures by means of inertial based sensors with the ability to give the absolute or real track measurements. Another type of vehicle measures relatively to the vehicle. The second technique suffers from its inability to detect irregularities above 5 times its measuring base. For high speed trains however, the irregularities with longer wavelengths count for passenger comfort. For example, at a speed of 250 [km/h], which is around 70 [m/s], wavelengths of at least 140 [m] should be taken into account. Track irregularities measurements are important to plan maintenance works on the line and for security of service.
The guidelines for track irregularities depend on the allowed speed on the line. They are given as standard deviation and maximal mean to peak values. Maximum values are given for different wavelengths of irregularities (more information [7], national and European standards).
In addition of the listed track geometry irregularities cited above, we can also mention rail corrugation which is an irregular wear of the top surface caused by rail - wheel interactions. They consist of wavelengths typically between 20 and 500 [mm] with amplitudes between 0.1 and 1 [mm]. These irregularities can lead to vibrations and noise. They can be removed with track maintenance, practicing grinding.
2.1.4 Rail flexibility
Just like all materials, rails are not perfectly rigid, but more or less flexible. Due to the high performance requirements of today’s railway, this cannot be neglected and need to be carefully studied. The stiffness and damping coefficients of the track are very important to be considered in regards to the dynamic forces and oscillations they generate, which play a key role in the aging process of vehicles, in particular wheels, and tracks. It is quite recent that those phenomena have been looked closely at in a more theoretical manner. However, for the simulation of vehicles, very simple models are still in use in most cases.
The main phenomena are the vertical flexibility, the sleeper passing frequency and lateral flexibility. In general we can say that a stiffer track breeds higher dynamic forces and higher damping decreases oscillations duration. The vertical flexibility is linked to both the load and the frequency of its oscillations. Firstly, the rails have a play with the sleepers. They in turn have a play with the ballast. High variations are observed between a frozen, waterlogged or extremely dry ground. As already discussed, wooden sleepers are more elastic than concrete ones. Due to the spatial variation in track flexibility and to the spacing between sleepers appears a dynamic frequency called sleeper passing frequency. The static deflection is only 0.1 [mm]. However, it leads to high variations in dynamic loads. Note that this phenomenon could be used as an incremental positioning system assisted by a map of the track and position of sleepers. Ladder sleeper construction could remove, or at least strongly reduce the deflection. The lateral flexibility has a higher stiffness; hence it has been less studied.
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2.2 Vehicles
2.2.1 Introduction
Different types of rail vehicles exist, namely, railways, subways or metros, tramways. The tilting function is only believed to have a market for passengers’ railways vehicles but largely from commuters to high speed segments. Vehicles can be subdivided between tractive and rolling stocks, all consisting of two constructive parts: • Running gear: subassembly of usually one or two wheel sets. A wheel set consists of one axle rigidly connecting two wheels. The running gear has suspensions and connecting parts. Its function is to guide and brake, support the car body and drive it if tractive. • Car body: carries the payload, goods or passengers in our case.
Vehicles can be sorted in two types: • Rigid-frame vehicle: its running gears only consist of wheel set and suspension components. • Bogie vehicle: the running gear is a so called bogie, distinctive by the fact that it can rotate relatively to the car body frame. It has a two stages suspension. It generally consists of two wheel sets; suspension elements and a framework, some example with three wheel sets exist, but are very uncommon. Rigid-frame vehicles are simple, cheap and light but suffer from major drawbacks as restricted length of carriage and limited speed because of poor steerability, higher axle load, resulting in limited payload capacity due to only two wheel sets per carriage, poor comfort due to the single level suspension, far below the modern passenger’s expectations. However, they offer an optimal solution for low requirements transport, especially goods. Their speed limitation is around 100-120 [km/h], i.e. far below the speed for a high speed train. Bogie vehicles construction is costly and heavy, but is however a must to increase speed and comfort. As they are of first interest for the present studies, they are further described in the next section.
2.2.2 Bogie
Bogies usually go unnoticed by passengers. Despite their discrete presence, they are a key element of safe and efficient modern trains. They assume the following functions: • Supporting the car body • Ensuring stable run on both curved and straight tracks • Enhancing comfort by absorbing vibrations generated by track irregularities • Minimizing centrifugal force in curves • Minimizing both rails wear and generation of track irregularity • Brake and, only in case of tractive bogie, drive
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Commonly bogies are two-axle, with the main advantage that the distance between the two wheels geometrically halves the disturbance acting on just one wheel as seen in the sketch below. Two axles reduce the load acting on each wheel set. They have two levels of suspensions allowing easier design and higher comfort. The bogie rotates relative to the car body, leading to better curving performance, which lowers the derailment ratio. The inertia of the bogie frame acts as a high frequency filter.
FigureT 7 : T reduction of the negative effect of track irregularities thanks to bogie construction ([36], p. 20).
Bogies can be non-articulated or articulated, which is also known as Jacob’s principle bogie. Articulated bogies suffer from several drawbacks such as more complex construction, higher axle loads and more difficult maintenance. However, they can increase comfort thanks to reduced noise in the area where the passenger are seated, because the bogies are situated under gangways between the carriages.
FigureT 8 : T difference between articulated and non articulated bogies ([36], p. 20).
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Depending on their construction art, bogies can be classified in two types: swing hanger bogie and small lateral stiffness bogie as illustrated hereunder. The first type absorbs the rolling motion, but its complex structure leads to difficult maintenance due to the large number of wearing parts. In the 1960s, bolster bogies with air springs that absorb vibration due to their small lateral stiffness were introduced. Besides having good vertical suspension properties, they offer good lateral suspension and enough flexibility for the bogie to rotate relatively to the car body. It greatly contributes to the bogie simplification and allows reduction both in weight and size. Most recent bogies are of this type.
FigureT 9 : T the two different types of bogies ([36], p. 20).
FigureT 10 : T a bolster bogie on the left and a bolsterless bogie on the right ([36], p. 20).
The bogie must be able to rotate relatively to the car body in curves but at the same time offer high rotational resistance when cruising on straight tracks to avoid wheel set hunting. As a train runs fast, hunting can increase to such an extend that the bogie vibrates severely from side to side, which creates extreme discomfort for passenger, damages the track, and can lead to derailment of the train in severe cases. In the bolster bogie case, rotation is achieved with a centre pivot at the centre of rotation. Friction side bearers are fitted to resist rotation and thus avoid hunting motion. The wheel shape is also carefully designed to avoid wheel hunting. This is achieved with a variable gradient granting good cruising properties on straight tracks and good curving capability.
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FigureT 11 : T a bogie with no car body bolster, but with a tilting bolster under the secondary suspension, constructed by Bombardier.
In the 1980s, a bolsterless bogie was brought to the market, which lead to even easier bogie construction. In a bolsterless bogie, the rotation is allowed through deformation of the air bellies of the secondary suspension, also often called bolster springs. The rotation is restrained by additional longitudinal anti-yawing dampers on both sides of the bogie. The use of dampers offers a better rotational resistance than the friction side bearers’ solution. Additionally, a bolsterless bogie requires a device to transfer longitudinal forces, namely breaking or tractive forces. This can be solved with a monolink or a z-link construction type at the virtual centre of rotation. Note that we were talking about the car body bolster. A bogie can have two bolsters, a tilting one, under the secondary suspension and a car body one above it. Taking away the car body bolster means a weight reduction, but a more complex assembly.
FigureT 12 : T lateral view of a bolsterless bogie with anti-yawing damper, Bombardier.
The wheel set is an essential component of railways. It usually consists of two wheels rigidly connected to an axle. A wheel set weights between 1000 and 1500 [kg]. The wheel radius is to be counted between 0.3 and 0.6 [m]. The wheel part in contact with the rail is composed of a tread and a flange, whose contact is avoided, but offers a security margin. The running tread is conical or circular, with variable gradient respectively angle. This configuration leads to a variation of the wheel diameter at each rails contact point depending on the lateral position of the wheel set onto the track. This steers or centres the wheel set on curved respectively straight track, due to the induced variation of speed. A careful wheel profile design increases robustness against wheel hunting. Note that the flanges only have a safety and security function and no guidance, as often wrongly believed.
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To improve the bogies steerability into curves, some bogies feature radially steerable wheel sets or a link-type forced steering bogie, which aim at decreasing the lateral forces against the rails up from one third to one half and thus cutting maintenance costs both for wheels and rails with especially good results on very winding roads. Special precautions have to be taken not to degrade running performance on tangent tracks, hunting motion born in mind.
FigureT 13 : T wheel hunting on left ([36], p. 20) and a linked-type forced steering bogie on right ([36], p. 33).
It is believed that active suspensions and active steerability could make a break through in the bogie design. This could totally modify the actual construction manner and attenuate the clear line between rigid-frame and bogie vehicles. The wheel sets could be replaced by active steerable and differential driven wheels and active vertical suspensions, making bogies unnecessary ([17][21][22][29]). To temper these enthusiastic assumptions, doubts can be raised that such complicated, costly and high energy consuming systems can turn out to be profitable. Moreover, the safety aspects are difficult to handle, as active elements must be secured by passive ones in case of failure to guarantee security. However active lateral suspension already entered successfully the market just alike bogies with active steering. Firstly this active design solution enhanced the comfort, secondly steerability and reduced maintenance on both wheels and rails.
2.2.3 Gauge The car body cross-section, considering all possible movements like lateral, vertical, roll due to cant, sway due to suspension deformation and tilt motions of either passive or active systems, must never interfere with the structural elements or aside running trains. Therefore, the constructive dimensions of a train are defined as a maximum vehicle construction gauge. Special attention has to be paid in curves for the middle and end of the car body – bear in mind the structure of a carriage with a car body and two bogies. The middle of the car body exceeds inwards the curve while both ends of the car body exceed outwards. Any part must never exceed the allowed gauge. In the same way, all the elements along the track have to be kept away, a so called structure or obstacle gauge. In between, room must be saved for dynamic movements of the trains and safety margins. Therefore, for long car body, the width may have to be reduced both in the middle and at both ends. For a tilting car body, the high or low width of the carriage is critical and must be given special attention at the design stage. At those special points, the profile often has to be shrunk, but it depends of the position of the tilt centre, as will be further developed in section [6.3.2]. Different standards exist, for national like transnational operation.
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2.3 Story of tilting
Shortly and in a very simplified way, tilting systems were researched in the 1960s and 1970s, tested and developed for production during the 1980s, and increasingly introduced into revenue service during the 1990s to become now a standard technology for new high-speed trains.
FigureT 14 : T the first known patent on a tilting system registered in 1938, US 2 225 242.
The development of tilting trains started early with the first exploration of passive tilting which is also called natural tilting, mainly in Japan. That kind of system transforms the centrifugal force into an inwards roll of the car body around a high placed centre of rotation. The first reported experiments on reducing the lateral force felt by the passenger due to the centrifugal force go back to the late thirties. In 1956, Pullman- Standard built two train sets that became the first commercialised tilting train. Due to oscillations in tilting operation, the ride comfort was very poor, leading to motion sickness. In 1973, the Japanese class 381 became the first large series of tilting trains being in revenue. In 1980, the first Talgo train was put into service.
Aside of passive technology, active technology started in 1957 when the SNCF built a first trial vehicle. In the early days, active technology was using hydraulic actuators. The DB followed and put the first actively tilted train in commercial service in 1972. One key development was the Pendolino which entered commercial service in 1988 with the ETR450, only followed 2 years later by the X2000 in Sweden. This era was the break-through for actively tilted trains. At the same time, the JR2000, were introduced, which were the first natural tilted trains with active tilting support of pneumatic actuators. In 1997, AEG put in revenue the first tilting train equipped with electromechanical motors. FigureT 15 : T X2000 cruising, Bombardier
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Table 1 : important vehicles in tilt train development ([7], p.8)
Developer Product Year Top Tilt Comment speed actuation [km/h] Pullman – Train-X 1956 ? Passive First tilting vehicle in service 1) Standard P P SNCF - 1957 ? ? First vehicle with active tilt FS/FIAT Y0160 1969 200 Hydraulic First vehicle of FIAT technology DB 634 1972 140 Pneumatic First vehicle with active tilt in service
BR APT-E 1972 240 Hydraulic The comfort indexes PCTB B and
PDEB B were developed* JR/Hitachi 381 1973 120 Passive First vehicle on Hitachi technology FS/FIAT ETR401 1975 171 Hydraulic First vehicle of FIAT technology in service SJ/ASEA X15 1975 200 Pneum. / First vehicle of ASEA Hydraulic technology Talgo Pendular 1980 180 Passive First tilting Talgo FS/FIAT ETR450 1989 250 Hydraulic Highest top speed of trains in service JR/Hitachi 2000 1989 130 Passive + First vehicle using stored Pneumatic track data ASEA/ABB X2000 1990 200 Hydraulic First vehicle of ASEA technology in service AEG VT611 1997 160 El-Mech. First vehicle with electro- mechanical actuators JR/Hitachi N700 2007 300 Pneumatic First tilting vehicle in service with top speed above 250 km/h?
* Explained in the comfort section
In Europe, research on tilting technologies were initially undertaken by operators in hand of national governments. While the train companies were more and more privatized, the operators joined forces with industrial partners. Nowadays, most research is carried out by train’s suppliers. The operators tend to be more and more interested in function and service than in technology. Standardisation and interoperability strengthen. The tilt technology has matured to such an extent that it has been transferred to sub-suppliers in some cases. Some suppliers propose total “ready to integrate” tilt systems.
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Other solutions than to tilt the whole car have been proposed, like the possibilities to build two different tracks with different cants in curvy sections of a track (see illustration hereunder), so that both the needs of freight and passenger trains can be fulfilled at the same time. This solution is more funny than realistic as its realisation cost might be high in comparison with a tilting train, at reduced benefits. The trains have to switch tracks between the unchanged tangent part and the two possible tracks that are found in curves. High number of turnovers is expected to have strong negative impact on comfort and doesn’t allow high speed service. Another explored way was to make the seat tilt instead of the whole car body.
FigureT 16 : T The hi-lo bitrack system, [46].
2.4 Development trends
The trend is very naturally towards the research on faster trains for revenue service. In the introduction chapter, the requirements for performance due to the actual market shares battle against other means of transport were discussed and explained. Technology improvements have globally made possible to increase the maximum speed, a trend followed by tilting trains with current development for train travelling above 250 [km/h] in the near future with full tilt. The Shinkansen series N700 is expected to enter in revenue in 2007 with a top speed of 300 [km/h] and a very limited tilt of 1° where previous versions of the Shinkansen did not require tilt on Japanese specially designed high speed lines.
] 300
250
200
150
100
50
Maximum service speed [km/h 0 1970 1980 1990 2000 2010 1st year in service
FigureT 17 : T maximum speed for tilting train in function of first year of commercial revenue ([7], p.9)
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Active tilting
Alstom EMU Siemens EMU ITA Cisalpino ETR610 Pendolino2 Venturio 250 [km/h] 250 [km/h]
Siemens + Bombardier + Alstom EMU Bombardier + Alstom locomotive GER DB ICE T USA Amtrak Acela 230 [km/h] 240 [km/h]
Passive tilting
Talgo locomotive Talgo locomotive ESP Renfe Talgo 250 ESP Loco L9202 250 [km/h] 260 [km/h]
FigureT 18 : T Tilting train in the [250 km/h] market segment, source Kjell Sundqvist.
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Trial trains reached even faster speed as you can see in the small table hereunder, that summarizes record speed for different tests in Japan, Germany and France. Note that none of them featured tilt, but it still shows a general view of the trend in research.
Table 2 : different train prototypes speed record around the world, all without tilt..
Year Country Name Speed 1988 Germany ICE 406,6 [km/h] 1990 France TGV 515,3 [km/h] 1992 Japan WIN350 350,4 [km/h] 1993 Japan Star21 425,0 [km/h] 1996 Japan 300x 443,0 [km/h]
Higher operational speeds create a complete collection of new problems including noise, micro pressure waves in tunnels, ground vibrations and aerodynamic problems when trains pass each other at high speed, ballast stones lifting due to ice breaking loose from the car body. Cross wind stability becomes a crucial safety issue for tilting trains safety at the same time.
The need for speed is though limited in an asymptotic manner when different stops are required along the route due to the acceleration and deceleration phases, therefore very high speed services are of interest only when a long distance separate two stops. When many stops at short distances are required, a tractive power for fast acceleration is more important than the maximum speed ([7], page 62-66).
2.5 Rails dynamics
2.5.1 Relative motion
This section introduces briefly the translational and rotational directions that can be used for describing displacements, velocities or accelerations. Motions imply relative motions to track design geometry or nominal vehicle speed. Table 3 : quantities playing a role in dynamics analysis and their names.
NotationT T RelativeT motionT x Longitudinal Translation in direction of travel y Lateral Translation in transverse direction, parallel to the track plan z Vertical, bounce Translation perpendicular to the track plane ϕ Roll, sway Rotation around a longitudinal axis χ Pitch Rotation around a transverse axis, parallel to the track plane ψ Yaw Rotation around an axis perpendicular to the track plane
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2.5.2 Motion conditions There are three different conditions at which forces or movements can be analysed: • Static or nominal condition: vehicle is on a perfectly plane tangent track. • Quasistatic behaviour: this is an idealized physical condition. It represents a situation where all forces are constant in time and where no relative motion ever happens. A typical quasistatic situation is a train running at a constant speed on a curve with constant geometry. • Dynamic behaviour: all the time dependent variations are included. It can be transition curves, track irregularities, dynamics responses and behaviour of the vehicle.
2.5.3 Tilting trains We admit the following assumptions in this section, so to say quasistatics behaviour: • Vehicle is perfect • Track is perfect We neglect track irregularities and all dynamic behaviour.
-1 When a train drives through a horizontal curve at a speed of v [msP ],P which is characterized by a constant radius R [m], two acceleration components act at the centre of mass, the gravity and a horizontal acceleration, named centrifugal acceleration: v 2 a = h R To mitigate the lateral acceleration component parallel to the plane of the car body floor , a twist inwards of the track called super elevation or cant angle is arranged. The horizontal lateral acceleration is compensated at tack and car body plane with the projected component of the ever vertical gravity (see sketches on next page).
The equilibrium cant, D0 , cancels totally the lateral acceleration for a given speed in a given circular curve with the following radius R [m]: ⎛ v 2 ⎞ ⎛ D ⎞ ⎜ 0 ⎟ ϕ0 = arctan⎜ ⎟ ≅ arcsin⎜ ⎟ ⎝ R ⎠ ⎝ 2⋅b0 ⎠
This equilibrium cant angle, ϕ0 , depends on the speed, meaning it is only adapted to one particular situation. Moreover, its magnitude is limited, typically to around 6°, because of the derailment ratio and the general needs of the track to be shared by high speed passengers’ trains and at the same time by heavy freight trains running at much lower speed. Their goods content could be set into motion if the train had to stop suddenly onto a high cant winding section risking overturning of carriages. Because of the low value in radians, the approximation above can be made so it is easy to convert centrifugal force at a given speed to required cant or cant angle. With the help of the previous equation, it makes easy to calculate the lateral acceleration at track level: v 2 D aL,T = − g ⋅ R 2 ⋅ b0 The following equation gives the value of the cant deficiency, I , when speed is higher than the one used for the calculation of the cant of equilibrium:
I= D0 − D If speed is slower, I , becomes negative and is called cant excess, E .
The lateral acceleration at track level can be expressed for a given cant deficiency as : I aL,T = g ⋅ 2⋅b0
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yC yT xT xC
a zT zC h g
ϕt
ϕT
Angle and axis Curve with no cant
aL,C
aL,T
ah
ah g g aV ,C
aV ,T aL,T
aV ,T
Cant only Cant and tilt
FigureT 19 : Lateral acceleration and vertical acceleration at car body and track level for a conventional train with first no cant (right up), the cant effect (left down), and for a tilt train (right down), the sway in the suspensions is not considered.T
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The angle that the tilt system produces is designated by ϕt . The non-compensated lateral acceleration at the passenger level, aL,C , becomes: a }h v 2 aL,C = &y& = ⋅ cos()()ϕt + ϕT − ϕ S − g ⋅ sin ϕt + ϕT − ϕ S R
The vertical acceleration, aV , sensed in the car body, becomes: v 2 aV ,C = &z& = ⋅ sin()()ϕt + ϕT − ϕ S + g ⋅ cos ϕt + ϕT − ϕ S R
A reduction of lateral acceleration by increased track cant or car body tilt is correlated with a slight increase of the vertical acceleration. The higher roll due to the tilting will also increase the experienced yaw and pitch motion in a curve, but their importance is not considered in known motion sickness models. In those expressions, ϕ S stands for the quasistatic deformation of both primary and secondary suspension. This deformation can increase the non-compensated lateral acceleration with 15-30%. This largely reduces the efficiency of the tilt system. This influence is discussed in the next section.
2.5.3.1 Suspension influence
The lateral acceleration felt by the passenger depends on the suspension design and on the tilt system position.
The roll flexibility coefficient of a suspension is defined in a stationary condition on a canted track. It is the ratio of the roll angle due to the action of gravity onto the suspension, ϕc , divided by the cant angle ϕT : ϕ S = c ϕT
This coefficient includes the influence of both the primary and the secondary suspension. It will be helpful to separate their respective action to evaluate the influence of the position of the tilt system on its efficiency:
()()1+ S = 1+ S1 ⋅(1+ S2 )
If S > 0 , then the uncompensated acceleration at the passenger level, aL,C , will be greater than the one at the track level. Basically, if the speed is higher than the speed of the cant of equilibrium in curve, then the car body will lean outwards, pushed by the centrifugal force. This counteracts the effect of the track cant. On other hand if speed is smaller, the car body will lean inwards the curve, increasing the effect of the gravity. If the car body has a passive system, then S < 0 . It has the opposite effect, reducing the accelerations felt by passenger in both previous cases.
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2.5.3.1.1 Passive tilt or conventional train
FigureT 20 : T on the left, a conventional train showing the effect of centrifugal force when it cruises faster than equilibrium of cant allows. On the right, a passive tilting in the same situation, source Talgo.
The non-compensated acceleration at the passenger level, aL,C , is expressed as following for a passive system or a conventional train :
aL,C = ()1+ S ⋅ aL,T = (1+ S1 )⋅ (1+ S2 )⋅ aL,T
2.5.3.1.2 Tilt above the secondary suspension
The angle that the tilt system produces, is designated by ϕT . The uncompensated acceleration at the passenger level, aL,C , becomes:
aL,C = ()1+ S1 ⋅ (1+ S2 )⋅ aT − g ⋅ tan(ϕT ) = (1+ S)()⋅ aT − g ⋅ tan ϕT
2.5.3.1.3 Tilt under the secondary suspension
If the tilt system is now placed under the secondary suspension, aL,C , becomes now :
aL,C = ()1 + S1 ⋅ (1 + S2 )⋅ aL,T − (1 + S2 )⋅ g ⋅ tan(ϕT ) =
()1 + S ⋅ aL,T − (1 + S2 )⋅ g ⋅ tan ()ϕT
2.5.3.2 Conclusion
We note that the position of the tilt system under the secondary suspension is more efficient because of the reduced deformation of the secondary suspension, due to reduced lateral acceleration.
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2.5.4 Transition curves
Transition curves are the key elements for tilting trains. Both radius and cant increase at the same time in the common case. Ideal transition curve geometry is when the quasi- static decomposition of all the section is at cant of equilibrium when travelled at a given speed. On such a transition curve, the lateral acceleration and yaw velocity grow linearly at entrance and decrease in the same way at exit. The roll velocity has a constant value at entrance and an opposite constant value at exit. Please have a look at sketches on the following page.
Table 4 : typical values of acceleration in curves, ([7], page 6).
Speed v Radius R Track cant Carbody tilt Lateral Vertical [km/h] D [mm] acceleration acceleration [m] angle ϕc 2 2 1)
P P P P P P z [m/s ] [degrees] &y& [m/s ] &&
3) 113 1000 0 0 0,98 P P 0 113 1000 150 0 0 0,05
3) 160 1000 150 0 0,98 P P 0,15
2) 166 1000 150 6,5 P P 0 0,23
2) 201 1000 150 6,5 P P 0,98 0,44 1) The vertical acceleration is here given as offset from g 2) This tilt angle corresponds to an actively tilted train 3) The real value is 15 to 30 % higher due to roll in suspensions
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Circular curve
Transition curve Transition curve
Straight track Straight track
Lateral &y& acceleration
Yaw velocity
ψ&
Roll velocity ϕ&
FigureT 21 : T acceleration at the passenger level when cruising on a transition and super elevation curve followed by a canted horizontal curve for a conventional train. Circular curve
Transition curve Transition curve
Straight track Straight track
Lateral &y& acceleration
Yaw velocity ψ&
Roll velocity ϕ&
FigureT 22 : T acceleration at the passenger level in the same situation as above. Speed has been kept constant. We supposed that the tilt system enters in function synchronously with the transition curve. Note the reduction in lateral acceleration and the increase of roll velocity.
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2.5.5 Track forces and derailment Forces between vehicle and track must be limited for at least three reasons: • Forces cause damage and fatigue on track components, leading to cost • Forces also cause damage to wheels, axles and other train components • Risk of derailments
Wheel-rail forces are defined in the track plane in horizontal and vertical direction. All the norms for track forces can be found in the European or national norms.
2.5.5.1 Vertical forces Vertical forces are assumed to cause : • Track irregularities due to deformation of the ballast • Rail fracture caused by fatigue or brittle fracture • Damage on sleepers and pads • Wheel track damage
Vertical forces are composed of 6 different contributions : 1. The static wheel forces are the weight contribution in a static situation. 2. The quasistatic change in wheel load due to curving: when a train is not running at the cant equilibrium speed, weight is transferred from one side to the other. The load difference grows during transition curves where the effect of track twist on the wheel load distribution has also to be taken into account. The higher the cant deficiency is, the higher the change in wheel loads. A high centre of gravity leads to stronger change of wheel load. Displacement of the centre of gravity or in the suspension also leads to wheel load change. 3. Dynamic contributions due to track irregularities are caused by rail joints, rail corrugations or changes in track flexibility. The dynamic force usually increases with track irregularities, track stiffness, speed an unsprung mass. 4. Dynamic load due to the vehicle can be caused by wheel irregularities or corrugation. Note that the activation of the tilt system causes a change of the dynamic load. 5. Change in wheel loads due to traction or braking. 6. Change in wheel loads due to asymmetries or adjusting errors in the vehicle are the source of minor changes. Note that wind hasn’t been taken into account in this section.
2.5.5.2 Lateral forces Lateral forces are also of interest and limits can also be found in European and national standards. Track shift force is the sum of lateral wheel forces acting on a wheel set. They are a major safety related issue as too high forces lead to track irregularities that in turn lead to higher track shift forces. Too high lateral forces could shift the track laterally when a train is passing, causing derailment. The permissible track shift force increases with the axle load, due to friction between sleeper and ballast. Like vertical force above, lateral force can be divided into different parts: 1. Quasistatic forces due to track plane acceleration. 2. Quasistatic forces due to uneven distribution of force between different wheel sets in a bogie. This is mainly influenced by the bogie design, especially the primary suspension stiffness. A bogie with radial steerability has a much better distribution of lateral forces between the wheel sets of a bogie. 3. Dynamic forces due to track irregularities 4. Dynamic forces due to self-generated vehicle motions, that means hunting motion, that occurs on straight tack or possibly in wide curves 5. Forces due to adjusting errors A well damped quite flexible suspension produces lower dynamic forces than a stiffer and less damped suspension. That especially influences the dynamic behaviour.
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The standards for track forces are issued in Europe by CEN. Another limitation is the derailment criteria which is a ratio between lateral and vertical track forces. Other limitations are set to lateral and vertical wheel rail forces having consequence for the axle load (for detailed information please refer to standards and [7]). The lateral forces are key limits for speeding. Note that the vertical force increase on the outer rail has a positive impact on safety preventing the flange coming into contact with the rail thanks to the running tread profile. In worst case, the vertical force prevents the wheel to jump over the rail when the flange comes into contact with the rails.
2.5.5.3 Derailment Derailment can have many causes, among which: • Vehicle turnover due to excessive speed • Rail fracture • Fracture of wheel set axle or wheel tread • Turnout blade shifted during passage of train • Obstacle on the rail • Natural disaster (cross wind, landslide, avalanche, fallen tree, earthquake) • Severe displacement of rail in lateral direction • Rail turnover • Wheel flange climbing • Geometric errors of wheel sets • Geometric errors of turnouts Flange climbing and vehicle turnover will be elaborated on in the two next sections.
2.5.5.3.1 Flange climbing A common reason for derailment is flange climbing. It means that the flange climbs the rail and continues rolling on it. Wheel climbing is prone to happen when running with an attack angle, in particular for a vehicle with stiff wheel set guidance and a rather long wheelbase. However, steerability is modest for most running gear in tight curves and is therefore critical. Flange climbing is due to flange contact, when the flange is pressed against the rail with an attack angle a creep friction lifting force occurs. A high vertical force and a low friction act against rail climbing. Hence flange climbing is prone to occur for light and torsional stiff vehicles in case of wheel unloading occurring especially on twisted tracks. Another risky case where flange climbing can occur is when the front of a convoy suddenly brakes and the train is not perfectly aligned, strong lateral forces may be produced by the misalignment of convoy and its inertia.
2.5.5.3.2 Cross wind turnover Crosswind safety has become one of the major concerns in designing high-speed trains and much research is actually in progress on this theme. Crosswind doesn’t increase the risk of flange climbing, but means a high risk for turnover. The worst case is a train at high cant deficiency with cross wind blowing radially from the centre of the curve.
Wind has higher speed depending on the topographical situation of the track. The most sensitive situations are embankments, bridges on open sea and narrow valleys. Sudden wind gusts, as when exiting tunnel or coming out of a sheltered part of the track have to be taken into account. However the effect of the wind has to be long enough to have an impact. The tendency of light and self-propelled vehicles increases the risk. The front of the train is the most critical part. A heavy weight front vehicle has a positive effect. The risk is particularly pronounced for tilting trains running at increased cant deficiency in curves. Wind has four components influencing overturning: • Lifting forces • Lateral moments at the front of the train • Yaw moment • Pitch moment
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Here is a list of possible measures to counteract the impact of cross wind: • Leading vehicle should not be too light. It can be solved by placing some heavy equipments in leading vehicle as for example tractive equipment • Centre of gravity should be as low as possible • Cars should have a low cross-section • Nose shape should be optimized • The cross section shape should be aerodynamically optimized • Reduced speed in case of storm, development of measurement stations and warning systems • Install wind shields
2.6 Comfort
2.6.1 Introduction
How the passengers appreciate comfort in a train depends on a large number of parameters like light, temperature, air conditioning, noise, vibrations, cruising time, possible service delay, restaurant quality, internet connection, service onboard and access to train stations. In the frame of this work, we focus only on comfort, or discomfort, caused by the dynamic behaviour of the train. For tilting trains, two points are crucial, the comfort during transition curves and the increased risk of motion sickness. Comfort and motion sickness are not optimal at the same time. A situation where fewer passengers feel motion sickness can be judged averagely as less comfortable like for example reducing the average reading capacity. A good comfort is the result of global conception of the train. For example, the car body structural flexibility and related motions and vibrations often reduce the ride comfort. Usually the lowest eigenfrequency is close to frequencies that significantly influence the human ride discomfort and has to be tuned not to deteriorate comfort.
2.6.2 Passenger comfort models
To evaluate comfort due to dynamic behaviour several indices exist: • Frequency weighted accelerations as functions of time • Combinations of weighted accelerations • Special purposes function
2.6.2.1 Frequency weighted accelerations as functions of time
Frequency weighted accelerations in the car body have been used to measure the comfort since the late 50’s. Several methods are known like the Wz-value and the Ride indices. Those methods are the base of today’s most used passenger comfort indices, please refer to the norms ISO and CEN for more information.
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2.6.2.2 Combinations of weighted accelerations The frequency weighted accelerations can be combined into one comfort index; the technique is described in CEN and UIC. Those standards are written for passengers comfort, but their use is common for homologation of new vehicles. Accelerations can be measured on the floor according to a simplified method, or at passengers interface by an advanced method. Guidance is also given on how to select a track section for the test and how to process the measurements signals. 2 2 2 wd wd wb N MV = 6 ⋅ ()a XP95 + (aYP95 )(+ aZP95 )
wd a XP95 : the 95 percentile of the weighted longitudinal root mean square accelerations measured on the floor
wd aYP95 : the 95 percentile of the weighted lateral root mean square accelerations measured on the floor
wb aZP95 : the 95 percentile of the weighted vertical root mean square accelerations measured on the floor
FigureT 23 : T Example of weighting functions. ([38], p 135).
2.6.2.3 Special purposes functions The previously presented indices can be too general to evaluate comfort for discrete events, like curve transitions. The passenger comfort on curve transition index, PCT , is dedicated to transition curves and gives the expected percentage of unsatisfied passenger in this particular situation. This index is part of the European standard for comfort evaluation. It has two different formulations, one for standing passengers, and the second for seated passengers:
2.283 PCT ,sitting = max()28.54 ⋅ &y& + 20.69 ⋅ &y&&−11.1,0 + 0.185⋅ (θ&) 1.626 PCT ,s tan ding = max()8.97 ⋅ &y& + 9.68 ⋅ &y&&− 5.9,0 + 0.120 ⋅ (θ&) where: -2 &y& : maximum magnitude of lateral acceleration [msP ]P -3 &y&& : maximum magnitude of lateral jerk [msP ]P -1 θ& : maximum magnitude of roll velocity in [°sP ]P
A version of this index exists for discrete events known as the PDE . Another known index used to judge discomfort on curve transition is: TCT .
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2.7 Motion sickness
2.7.1 Introduction Motion sickness or kinetosis is the result of the central nervous system receiving mixed messages from different body sensors namely eyes, inner ears and muscles. For example, when sitting on an airplane, the inner ear detects movements which eyes starring the direct environment of the cabin cannot perceive. It can happen in trains, boats, airplanes, cars, fairground rides, submarines, animal rides like camels or elephants and can even be caused in the total absence of real movement in a live- cinema. Turning pale, cold sweat, dizziness, fatigue and nausea are the most common symptoms of motion sickness. In extreme cases, one may drool, faint or vomit. Depending on its causes, motion sickness can be called carsickness, airsickness, space sickness, seasickness, whose name in ancient Greek was nausea.
The most common theory about the origin of motion sickness is that it evolved as a defence mechanism against neurotoxins, whose ingestion causes disorders between balance and vision. So that when the central nervous system detects mismatch in senses, it induces vomiting to increase chances of surviving suspected poison ingestion.
It is believed that approximately one third of the population is susceptible to feel motion sickness in mild circumstances or uneventful trips, such as sailing in mild weather, although as much as twice so many can suffer from it in more severe and extreme environments. Some groups of persons are far more prone to motion sickness like children and pregnant women. Experience showed that people have a learning ability during the first rides [4]. If the motion causing nausea is not resolved, the sufferer will frequently vomit within twenty minutes in extreme cases. Vomiting will not relieve the nausea, if its cause is not stopped.
2.7.2 In trains Motions sickness has been reported in conventional trains, but is less common than in other means of transport. Although, tilting trains increase the occurrence of motion sickness. Roll movements are believed to be a major contributor to motion sickness [4]. But other motions may contribute namely vertical, lateral, yaw and pitch. Motion sickness is probably provoked by the succession of curves and not by only one. Japanese Railways think it is associated with short transition curves with high roll motion. Therefore they -1 -2 introduced both limitations in roll velocities of 5 [°sP ]P and roll acceleration of 15 [°sP ].P Motion sickness has then been reduced but did not disappear.
In the early days, the tendency was to compensate 100% of the lateral acceleration, which caused an increased mismatch of the different body perceptions senses, which was yet increased by high frequency motions due to the localisation of the accelerometers. Undamped tilting motion and untimely tilting in natural tilting trains were also highly nauseous in very winding sections and led to the introduction of actively controlled natural tilt system in Japan. Nowadays, the command only cancels between 50% and 70% of the total centrifugal force in curves, so the senses mismatch is lowered.
To minimize the effect of motion sickness, the tilt must happen timely with the curve, the roll motion must start smoothly, not too slow or too fast. The tilt should avoid saturation before the end of the transition curve. It is possible to reduce the tilt velocity by anticipating the transition curve and continue the tilting after the end of it, current knowledge does not prove yet if it is advantageous or not [47]. The tilt must be generated without oscillation in curves and the ride comfort must not be deteriorated in straight tracks. Any wrong tilt or too fast and abrupt acceleration must be avoided considering the risk of causing various degrees of uncomfortable situations, including passengers loss of balance risking injuries or beverage spilling.
31 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
2.7.3 Motion sickness models
Lateral acceleration, vertical acceleration, roll velocity, roll acceleration have been reported to provoke motion sickness (as summarized in [7], page 40). The interest of a train builder is to find the best match between the lowest possible motion sickness, the highest comfort and best train performance. Results of experiences found in the literature indicate that a reduced tilt velocity of the car body reduces the provocation of motion sickness. However, a reduction in tilt compensation may produce and increased number of comfort disturbances due to lateral acceleration in the carbody [4]. The motion having incidences on motion sickness cannot be reduced at the same time. For example, a reduction of the lateral acceleration has as a consequence an increase of the vertical acceleration. The values during transition curves can be reduced by longer transition curves or reduced constant value during constant curve. Contradictory to previous research, an optimum tilt angle of zero is given by a recent model [48].
Table 5 : Motion quantities that probably influence ride comfort in general. Lateral and vertical acceleration are referenced to the car body ([4], page 22)
Non tilting trains Tilting train Average comfort Lateral acceleration Same as for non-tilting trains Vertical acceleration Longitudinal acceleration Accelertations in seats Comfort disturbances Same as for non-tilting trains • Straight track Lateral acc (peak-peak) Same as for non-tilting trains • Transition curve Lateral acc (max, peak-peak) Time delays in tilting system Jerk Roll velocity ? Yaw velocity ? • Circular curve Lateral acc (mean, peak – peak) Same as for non-tilting trains • Discrete events Lateral acc (mean, peak-peak) Same as for non-tilting trains Motion sickness Lateral acc (<0.5 Hz) Lateral acc (<0.5 Hz) Vertical acc (<0.5 Hz) Horizontal acc (<0.5 Hz) Vertical acc (<0.5 Hz) Roll acc & velocity (Yaw acc & velocity) Time delays in tilt system
2.7.3.1 Motion sickness model with time dependence
Knowing how motion sickness develops on a train section is very interesting as it can be used as a tool to improve tilt strategy and to design the control system. A motion sickness model can be added to a control algorithm to reduce motion sickness cases. Three right curves after each other probably require another control strategy than one right, followed by a left and another right curve.
A motion sickness model can be integrated to the control algorithm or can be used as a tool to tune its parameters. Those parameters could be adapted to the local track geometry. The use of a motion sickness model in a tilt algorithm is only believed to be effective in parallel with a predictive control (please refer to the control part of this report for further explanations).
32 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
2.7.3.1.1 Motion sickness dose value
Motion sickness dose value ( MSDVZ according to ISO 2631-1:1997) is the international standard for prediction of vomiting (VI ) and illness ( IR ) for an unadapted population of adult males and females. It is based on vertical low-frequency acceleration < 0.5 [Hz]. Therefore, this model is better suited for predicting motion sickness where the dominating provocations are in a vertical direction. This index can be used with other weighted accelerations than the vertical one. In any case, its value can only increase – the model does include any recovery schemes.
T MSDV = a 2 t dt ms −1.5 Z ∫ wf () [] o where: awf frequency-weighted accelerations by the filter w f T the integration time is between 20 minutes and 6 hours
VI = K m * MSDVZ []% where: VI is the percentage of persons who may vomit 1 K = for a mixed population of unadaped male and female adults m 3
Illness rating (according to Griffin 1990) 1 IR = * MSDV 50 Z 0 = I felt all right 1 = I felt slightly unwell 2 = I felt quite ill 3 = I felt absolutely dreadful
2.7.3.1.2 Net dose
The net dose includes a recovery possibility with a time constant after having been motion sick, believed that symptoms reduce on a long tangent section, for example [4]. T −C ⋅()τ −1 ND t = C ⋅ A τ ⋅ e L ⋅ dτ ()A ∫ ( ) 0 where :
C A , CL : constants A()τ : any kind of motion description, but root means square values are mainly used
The time constants are difficult to evaluate and vary a lot. An assumption is that the recovery time depends on the severity of the motion sickness. Its span is to be counted between 10 to 20 minutes. The evaluation of motion sickness using this model can be done with a simplified method based on ideal track geometry and quasi static conditions because the quantities of importance counts all a large low-frequency content.
33 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
2.7.4 Preventive measurements and improvements
To prevent motion sickness, sensitive passengers could : • Avoid reading or looking to a movie • Avoid motioning, especially head movements • Relax • Look outside and stare at the horizon • Close one’s eyes and take a nap • Breathe fresh air • Having a ginger tea, as it is a mild anti-emetic • Avoid caffeine, nicotine, salty, greasy or spicy food • Take medication (antihistamine, scopolamine)
To make tilting trains more comfortable, it could be possible to have one wagon with less tilt than the others for sensitive passengers, or having some seats reserved for motion sickness sensitive people with a screen showing the view seen from the head of the train with an information booklet and special service available, like ginger tea.
34 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
2.8 How much to tilt
2.8.1 Introduction The required tilt angle is mainly determined by the occurrence of tight curves on the line and the requested over speed in those curves. The allowed and installed cant on the line, the optimal compensation ratio and the allowed residual lateral acceleration or cant deficiency shape the maximum requested tilt angle. From the early days 100% compensation of the lateral acceleration, modern knowledge about motion sickness would recommend a compensation in the span of 50% to 70%, this of course reduced the required tilt angle. It should be kept in mind that the choice of the tilt system also depends on the choice of bogie and pertinent wheel-rail forces and their limits. The allowed uncompensated maximal lateral acceleration found in standards is between 0.65 -2 -2 [msP ]P and 1 [msP ].P We underline the fact that offering a better comfort is contradictory to offer the lowest possible occurrence of motion sickness, so a trade off is required.
2.8.2 Market needs The maximal tilt angle of 8 [°] has almost become a standard for intercity services as it is proposed by most of the train suppliers. For that kind of services, a low floor is not a decisive selling argument. However a reduced tilt angle of approximately 4 [°] could be interesting for a low end market, that means trains for commuters or regional services with an average travel distance of about 10 [km] with speeds up to around 160 [km/h]. In that situation, tilting would be used essentially for comfort purposes and not to increase speed in curves. This possible market requires a very low cost solution and a low floor construction.
At the other end of the market, high speed yet non tilting trains using dedicated lines could need in the future a reduced tilt as their speed keep increasing, see the example of the new Shinkansen N700 in Japan that will feature a tilt angle of only 1 [°]. In any case, a reduced tilt capability can be justified only if it offers other advantages in terms of building, maintenance and operating costs. If the difference is not strong, a standard solution will be more efficient due to the absence of development costs and a higher tilt angle capability.
2.9 Performance and advantages of tilting trains The maximum speed allowed for tilting train in curves is limited by three factors : • Resilient lateral acceleration endurable by passengers. The limits span is to be 2 2 counted between 0.65 [m/sP ]P and 1 [m/sP ]P • The wheel-rail forces and what the track can withstand • The tilt angle that the system is able to produce
The tilting function reduces the overall travelling time with reduced requirements on track modifications. Moreover, an effective tilting system greatly improves the passengers ride comfort during curve entrance and exit by minimizing the transient accelerations. The cant cannot be increased on the major part of railway corridors because of sharing service with freight service. On curves, a tilting train may travel 25- 30% faster than a normal non-tilting train, if no other comfort or safety limits are violated. This advantage tends to be reduced to approximately 10-15% depending on how winding the track is with new conventional trains cruising faster thanks to 2 acceptance for higher lateral acceleration, which allowance has increased from 0.6 [m/sP ]P 2 to 1.0 [m/sP ]P in some cases. Sometimes, the introduction of tilting trains is interesting even if the time gain is low, as it can increase the capacity of the line, making possible to pass to a higher frequency of service.
35 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
2.10 Additional requirements of tilting trains
The addition of the tilting feature to a train requires the rethinking of many different aspects of the train ; this section lists the major characteristics that need to be modified, or enhanced. Tilting trains demand special attention to fulfil safety requirements.
Tilting trains have to be able to handle the case of hazard of the tilt system without causing any safety issue. This includes avoiding wrong tilt that may lead to injuring some passengers. In case of a hazard, a tilting train has to be able to reduce its overspeeding to conventional speed and to come back to neutral position.
Due to the tilt motion, the vehicle gauge has to be reduced either at the roof or at the floor level depending on the location of the centre of rotation to fit inside the allowed gauge at all time. In many cases, a tilt train needs an active lateral suspension or a hold off device to avoid bump stop and to enhance comfort.
Increased speed means stringent requirements in terms of crash shock absorption. The higher speed requires stronger brakes to be able to stop in a short enough distance. It also requires better tracks – longer wave lengths will become more important. The length of transition curves becomes essential for comfort and protection against motion sickness.
The higher speed makes the trains come closer to the limit for wheel unloading, therefore the train needs a more accurate speed control system or assistance of the driver to be able to use the advantage of the machine, to make the travel safe and the driver task easier. This can be done with the signalling system (ATP, ERTMS) or supervising system thanks to positioning and onboard track data. With higher train speed it may be necessary to remove the level crossings where it has not yet been done.
The previously named higher risk for wheel unloading makes cross wind stability to become an acute issue. To counteract the negative effect of wheel unloading, the wheel set loads have to be kept high and the centre of gravity brought as low as possible.
On other hand, the car body construction is wished to be as light as possible, thus it requires less power to tilt. Keeping the floor low in the car body is made difficult due to restricted space due to the presence of the car body tilt. This has a direct relation on the wheel diameter.
The bogies need special attention to ensure high running stability in curves as in a tangent track. Special attention has to be paid to wheel hunting. The higher speed in curves increases the lateral force. In order to keep them low and to ensure good steerability, a soft wheel set guidance or radial steering may be wished, but at the risk of reducing running stability at straight tracks. Therefore, in some case, an active guidance is added. Integrating the tilt system into the bogie can increase both its length and weight. Sensors have to be placed at suitable positions of the bogie. Control and monitoring wiring have to be installed along all the train.
To decrease journey time it is also necessary to provide the train with adequate traction performance. Although a tilting train does not need to change its speed as often as a conventional train that slows down and reaccelerates at each curve, it has to be able to reach high speed fast enough and maintain it. Tractive performance is of more importance for commuters’ service with many stops at short to middle distance.
36 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
The tilt function due to relative movements is very sensitive to winter problem. Those movements increase the risk of ice breaking loose of the carriage with the risk of ballast lifting that could hurt nearby humans when going through a train station at high speed, or could damage some mechanical part of the bogie. Ice may jam the tilt system, causing a security issue, risking disrupting the service.
An active tilt function requires a power supply without interruptions for obvious reasons. The tilt function requires an additional pantograph mechanism not to lose contact with the catenaries when tilting. In case of failure of the power supply, the tilt function should be provided until the train has reduced its speed to conventional speed and the tilt should return into neutral position. Specifications for the catenaries are higher due to the increased speed.
Finally, we note that an increasing number of subsystems will require improvements of the reliability of all components/subsystems to achieve at least the same system reliability as on a non tilting train.
2.10.1 Pantograph
FigureT 24 : T View of the pantograph of an ICE, Bombardier.
On electrical powered trains, the pantograph is used to collect current from the overhead line. It has the following characteristics : • Remain in continuous contact with the overhead wire while the train is running • Must not abrade the overhead wire • Must neither be subject to excessive wear • Have low aerodynamic resistance Railways have since long used a diamond-shaped pantograph. It has a replaceable contact strip that touches the overhead wire and that is replaced when it becomes worn by the running abrasion. This strip must also be able to withstand the current arc that sometimes occurs between the overhead wire and the contact strip if the two become shortly separated during running or when contact is made or stopped. The strip is fixed to the base called the collector shoe mounted on a frame. A single-arm pantograph has been used to reach better aerodynamic characteristics. A third type of pantograph is called the wing pantograph which was developed to reduce wind noise generated by high-speed trains. It is mainly used on some of the latest Shinkansen in Japan. See pictures on next page.
37 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
FigureT 25 : T from left to right, the traditional diamond-shaped pantograph, a single- armed one and Japanese wing pantograph, [36, p. 8-9].
On tilting trains, a device must be installed to prevent the pantograph from detaching from the overhead catenary due to car body undergoing considerable roll rotations in curves. Various tilting trains’ designers have solved the problem of electrical collection in a number of different ways.
2.10.1.1 Pantograph on a non tilting locomotive
The train consists of a number of tilting passenger cars hauled by a non-tilting locomotive, which is equipped with a conventional pantograph. The major drawback is that the driver undergoes severe lateral accelerations. The non-tilting locomotive is pushed outwards the curve through centrifugal force which also can disconnect the pantograph from the catenaries. Such a train has very unfavourable aerodynamics. A locomotive has higher axle load than an EMU train, which could limit its speed due to increase forces.
2.10.1.2 Pantograph linked to the bogie
A solution can be to connect the pantograph to the non-tilting bogie structure. The pantograph follows the bogie movements at all time. The main drawbacks are that the additional structure reduces the useful space and adds structural weight. The pantograph is undergoing more vibration as it is attached directly to the primary suspension. This solution has the major advantage of being highly reliable (refer to figure 27, left).
2.10.1.3 Pantograph moved passively
Another solution is to connect the pantograph by means of wire cables. This allows keeping it approximately on the vertical axis of the bogie, whilst the car body can tilt freely below it without exerting an influence on its position. The pantograph is then placed on a rolling platform on the roof of the car, which is connected to the bogie frame by a number of wire cables moving along pulleys in the car body. The wires are tensed by drums on the moving platform. This system has two advantages : a substantial weight reduction and an increased useful space for the car body. The major drawback is that this system transfers the high frequency through the secondary suspension reducing the lifespan of the entire system (refer to figure 26 and 27, middle).
38 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
FigureT 26 : T a sectional view of pantograph moved passively by wires, [EP 0 485 273].
2.10.1.4 Pantograph moved actively A last solution is to use a pantograph placed on a platform which is activated by motors. The system becomes active, but suffers from its complexity always having negative consequences on reliability. But its construction is very local with no influence on the carbody (refer to figure T 27,T right).
FigureT 27 : T from left to right, a bogie mounted pantograph, a roof mounted with rope passive isolating from the tilt, and finally an active moving pantograph [42].
FigureT 28 : T ICN cruising in the Neuchâtel area. Attentive viewer can see the pantograph in a vertical orientation on the forth carriage, photo Bombardier.
39 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
3 Requirements for the optimal solution This section lists the objectives and requirements for a tilting system
3.1.1 Objectives tree The idea of an objectives tree is to identify all the requirements the system has to fulfil. It presents only objectives, no solution. It is a good way to have an overview of the all required functions and their importance. It is a secure way to avoid missing some important points for the final system. The different named requirements are developed and explained in the following sections. This step will help us to determine the assessment criteria in the next phase. Tilt system
Cost-effective Safety Reliability Ride quality Maintenability
Affordable system Stable Break down free Timely tilting Simple maintenance
High reliability Resistant construction No traffic disturbance No bump stop contact Easy diagnose
Cut journey time No wrong or harsh tilt Weather resistant Tilt schemes Easy access
High safety No harsh movement
Low maintenance No wrong tilt
Good ride quality
Energy-efficiency
High ratio performance/cost
FigureT 29 : T objective tree of all requirements the tilt system has to fulfil.
40 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
3.1.2 Main function of the objective tree
Tilt system
Cost-effective
Safety
Reliability
Ride quality
Maintenability
FigureT 30 : T major objectives a tilting system has to fulfil.
In another possible view, the main objective could be cost-effective and all other sub criteria of it, because for example an unreliable system is not cost-effective in terms of the image of the service for users. But this way of proceeding gives a clearer view to differentiate the different objectives and where to act to have result, but the impact and relation to cost have to be borne in mind for all points.
41 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
3.1.2.1 The cost effective branch Cost-effective
Affordable system
High reliability
Cut journey time
High safety
Low maintenance
Good ride quality
Energy-efficiency
High ratio performance/cost t/
FigureT 31 : T the cost-effective branch of objective tree.
Affordable system: the system has to have a low life cycle cost, low construction cost so it is cheap to buy and low operating cost so it is cheap to run. The system has to be as simple as possible, use the lowest number of components, which have to be as standardized as possible, the energy consumption has to be low and the maintenance has to be cheap. High reliability: the reliability is important so the train spends 100% time in revenue service, virtually none in the maintenance workshop. Time at the workshop is costly in work hours, infrastructure and loss of income. High reliability is of major importance for the users as well. For example, the system must not generate delay in service or wrong or bad tilt making people feeling bad, degrading the image of the service, having a negative final impact on the share market. The breakdown time has to be minimal and the mean time between failure extremely high. Cut journey time: the journey time is one of the most important performance indices. It is an important factor to increase the market share in competition with other means of transport, but the local situation can vary a lot. Sometimes even a very small reduction of journey time can have an extreme importance when it makes possible to have a higher frequency of service like for example half an hour frequent service instead of every hour. High safety: is extremely important. The tilt system must be able to resist all forces, for example high forces due to emergency braking. In case of failure, it must be able to turn back into neutral position while forcing the train to slow down the train, not to impair comfort or worse, risking for security of passenger that could lose balance. Low maintenance: the system must be simple to look after, reducing personnel and hours of maintenance work. The number of wearing parts must be as low as possible. The maintenance must be simplified and fast. Good ride quality: the ride quality must be as good as possible. The system must avoid wrong, badly synchronized or excessive fast tilt, vibrations, wrong response or reducing ride quality on tangent tracks. It has to avoid motion sickness as much as possible and should offer maximal comfort. Energy-efficiency: for a cost effective performance, the energy consumption must be kept low. That is important from the cost and also from the environmental point of view, which is a more and more important marketing issue where trains have an extremely strong advantage. High ratio performance/cost: this is a performance index that could integrate all the different aspects listed above.
42 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
3.1.2.2 The safety branch
Safety
Stable
Resistant construction
No wrong or harsh tilt
FigureT 32 : T the safety branch of objective tree.
Stable: the train must have high dynamic stability. The tilt system must not impair stability of the whole system. Resistant construction: the link between bogie and car body must be strong enough to transmit forces at all time. No wrong or harsh tilt: the following different mistakes can be seen as wrong or harsh tilt: • Tilt at the wrong moment (turnovers, tangent track) • Tilt in the wrong direction • Tilt with too high velocity • Tilt with too high acceleration • Tilt to much • Not returning into neutral position Wrong operation could affect the balance of onboard passengers risking hurting them, or making luggage fall from above sitting passenger lockers. Wrong operation has to be avoided at any time. We can note here that the need for train passengers to walk or stand in a train can vary a lot between different train categories. The passengers will move much more in a long distance intercity train having a special restaurant carriage, than if there is no restaurant. In a commuter’s service at peak hours, many persons might stand.
43 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
3.1.2.3 The reliability branch
Reliability
Break down free
No traffic disturbance
Weather resistant
FigureT 33 : T the reliability branch of objectives tree.
Break down free: the system must as far as possible be failure free. Failures could cause bad ride quality, cause security issue and high delay in service, or even worse service cancellation. Repair is costly and time consuming for personnel. This point has a link to security. No traffic disturbance: the tilting trains must be able to perform on time. An out of service tilting train can cause delayed train service, having consequences for the entire network if it is tight. On a high density network, a problem with one train creates a chain reaction delaying all trains, ruining the reputations of the operators and inducing costs. Weather resistant: the tilting system must be able to perform in the normal local environment and avoid freezing down during harsh winter conditions.
44 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
3.1.2.4 The ride quality branch
Ride quality
Timely tilting
No bump stop contact
Tilt schemes
No harsh movement
No wrong tilt
FigureT 34 : T major objectives a tilting system has to fulfil.
Timely tilting: tilting must happen at the right moment. A delay in tilting can be very nauseous. No bump stop contact: the whole dynamics of the different moving and suspension elements must avoid any frequent bump stop which would be very uncomfortable for the passengers. Tilt schemes: the tilting must be adapted with the speed of the train. It must not tilt too slow or too fast, but in a very smooth way. Saturation of the tilt during the transition curve has to be avoided. No harsh movement: the rolling movement start should be very smooth and as unnoticeable as possible for the train passengers. No wrong tilt: tilting at the wrong moment or worse wrong direction must be strongly avoided.
45 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
3.1.2.5 The maintainability branch
Maintenability
Simple maintenance
Easy diagnose
Easy access
FigureT 35 : T the maintainability branch of objective tree.
Simple maintenance: the need for maintenance has to be kept as low as possible. Requested control and maintenance tasks must be easy. Easy diagnose: the maintenance must be easy to foresee and to plan. Easy access: the access to the main parts to be maintained must be simple and fast.
FigureT 36 : T Tilting ICE, photo Bombardier.
46 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
3.1.3 Voice of customers
This section presents in a very simple way the different requirements that different stakeholders around a tilt train are expected to have. The objectives that a tilting system has to fulfil vary from the different stakeholders points of view. It can be seen from : • the constructing and selling enterprise • the buying and exploiting one • the owner of the track system (if different from the one owning the train) • the passenger using the train service • the political organisation that sets the guidelines, rules and sells the licences
The presented objectives tree diagram summarized the main properties a tilting system has to fulfil from a global point of view. The objective will be specified and described from the different customers’ point of view.
3.1.3.1 Interest of the builder
The interest of the builder is to sell its product on a very competitive train market. The requirements and knowledge from the buyers are believed to vary a lot. The buying cost is believed to play a major role on decisions though. Safety, reliability, maintenance, proven technology and trends are also expected to be key factors.
3.1.3.2 Voice of the owner
The owner wants a train with the lowest possible maintenance and operating cost, with the highest reliability and comfort. He wants to turn his investment into profit. The first investment cost is expected to have a strong influence on its decision. It is believed that customers buy more and more functions and their interest in mechanics decreases.
3.1.3.3 Voice of the passenger
The passengers of a tilt train want to be on time and fast, pay a fair price for their ride, feel good onboard and have a good comfort sensation. The motion sickness and comfort have the highest importance for passenger, while owner and builder want better performance/cost ratio or trains that have stronger selling arguments than competitors.
47 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
4 Tilt mechanism
Two parallel developments have been observed in tilting systems. The first based on passive or natural tilt which relies on natural laws takes advantage of the centrifugal force to push the car body centre of gravity outwards and tilt the car body floor inwards thanks to a centre of rotation well above the centre of gravity. The active systems force the car body to tilt inwards the curve by means of actuators.
4.1.1 Passive or natural tilting systems The rotation of the body of the railway vehicle can take place in a spontaneous manner under the action of the centrifugal force acting on the centre of gravity of the car body, which, by means of suitable linkages, flexible element or joints and adapted position of the centre of rotation, causes the roll movement of the body floor inwards the curve.
The design of a passive tilt system relies on a rotation centre situated well above the centre of gravity of the car body. They have the disadvantage of reacting with delay and abruptly to curves due to friction and to the high moment of inertia of the car body and because of the magnitude of the couple of the centrifugal force generated. To benefit of a high couple, the rotation centre and the centre of gravity must be separated by a large distance. Due to inertia and undamped sway movements, the tilt can happen suddenly at the end of the transition curve and generate oscillations. The whole is very nauseous, especially in a tight winding road. Gravity and mechanical losses only allow moderate tilt up to a maximum of 3-4 [°]. Due to the position of the centre of rotation, the car body gauge has to be reduced at floor level where space is the most useful.
FigureT 37 : T View of the passive tilt system of a Talgo train, photo Talgo.
On the other hand passive tilt is reliable, simple, cost effective and with no energy consumption. It has modest tilt capacity but can be effective for low requirements service. However, natural tilt has always a negative impact on safety due to the lateral outwards shift of the centre of gravity. Table 6 : advantages and disadvantages table of passive tilt system.
Advantages Disadvantages • Centre of gravity moves outwards • Simple • Gauge is limited at low level • Reliable • Untimely and abruptly tilt • Low cost • The speed possible increase is small • Failure free • Oscillations • Light construction • Motion sickness prone • Small tilt angle capacity
48 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
4.1.1.1 Hybrid system
Passively tilting trains have been greatly improved by the addition of an active tilt support, which enhances train performance anticipating tilting and avoiding undamped swaying, this evolution is typical from Japan. This solution can be called hybrid tilt. They have the advantage of low force requirements to tilt. Additionally they are still able to work passively when the control or activator is out of service, at reduced performances.
FigureT 38 : T Advantage of a hybrid system, source Hitachi.
Table 7 : advantages and disadvantages of hybrid tilt.
Advantages Disadvantages • Centre of gravity moves outwards • Gauge is limited at low level • Low force • Need for control and activator • Small actuator • Higher complexity • Can be use passively in case of failure • The speed increase is small • Small tilt angle capacity
4.1.1.2 Comparison of natural tilt and hybrid solution
Carbody Angular Velocity
Natural Controlled
Carbody Inclination
FigureT 39 : T Comparison of natural tilt and actively supported tilt, source Hitachi.
49 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
4.1.2 Active or forced tilting systems
Active systems use an actuator that controls the tilt between the superstructure and the bogie via a control loop, depending on the track curvature, cant and the trains speed. These systems are generally suitable for a maximum inclination angle of around 8 [°].
In the early days, some active systems were directly lifted, for example air was shifted from one side to the other of the air suspension. This kind of systems had high energy consumption and a slow response. They more or less disappeared. It is though used on the new Shinkansen N700 at a very limited level with a tilt angle of only 1 [°].
FigureT 40 : T Two different embodiments of the pendulum system, source Talgo and Bombardier.
To lower the energy consumption and make the system safer, the system will rely in most cases on pendulums or rollers, which carry the car body load and have one degree of freedom that can be forced by actuators. The pneumatic actuators were succeeded by hydraulic ones in most of the cases, with the major exception of Japan still using pneumatics. Electromechanical actuators made a recent shy appearance on the market, offering an alternative.
Active tilt has normally no negative impact on safety as passive tilt has. They make possible to chose a lower tilt centre and therefore increase the tilt angle with profile reduction at the roof level. Active systems have proven to be quite reliable after some beginners difficulties and intensive prototype testing but to higher maintenance and operating costs.
Table 8 : advantages and disadvantages of active tilt systems.
Advantages Disadvantages • High cost • Controlled tilt • High force and energy consumption • High tilt angle • High maintenance cost • Higher speed possible • Higher complexity
• Heavy
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4.1.3 Passive vs. active
This section summarises the major differences between active and passive systems and compares their advantages and drawbacks.
FigureT 41 : construction comparison between a hybrid Japanese solution and a hanging pendulum active solution, source Hitachi.T
Table 9 : comparison table of passive and active tilt. Advantages Disadvantages Passive • Simplicity, no control, no • Centre of gravity is displaced actuator outwards • Low maintenance • Tilt velocity and timing poor • Lower part of car body must be narrowed, where most useful • Low speed increases Active • Car body can be wide at the • Complexity lower part • Purchase, maintenance and • High tilt angle capability driven cost • Speed increases
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4.2 Different possible configurations
4.2.1 Above or under the secondary suspension
FigureT 42 : two different embodiments of the same tilt system with under or above the secondary suspension tilt mechanism [DE4423636].T
AsT discussed in the dynamics section in the introduction chapter, the tilt mechanism can be fitted below or above the secondary suspension. We saw that the tilt mechanism is more efficient when situated under the secondary suspension. To counter this strong argument, actuators are in friendlier environment with less high frequency vibrations when above the secondary suspension. Dynamic interactions with the suspension happen in both cases. Most of the tilt systems found in the literature and existing embodiment are placed under the secondary suspension; efficiency of the tilt mechanism is a stronger argument than vibrations.
4.2.2 Centre of tilting relative to centre of gravity
The position of the centre of rotation has a strong implication on the shape of the carriage due to the gauge restriction. A low centre of rotation requires a slimmer shape at high level of the car body. On the other hand a high centre of rotation requires slimmer shape at the floor level of the carriage to fit at all time in the gauge. The room lost due to that phenomenon has more impact in term of cost at the low level, because the gangway or chairs need to become narrower, which can reduce comfort and the total number of sitting places in the train. A smaller gangway or corridor is less practical for the passenger and the requirement for handicap sitting places can reduce the number of chairs, though at a small amount believed to be perhaps 4-5 sitting places per train set.
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Figure 43 : illustration of the profile reduction in function of the position of the rotation centre.
53 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Figure 44 : profile reduction in function of the tilt angle, with a central rotation centre.
Figure 45 : profile of a Bombardier’s Regina train untilted and tilted with 6° with gauge limits, source Kjell Sundqvist.
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Figure 46 : different possibilities for positioning of the centre of tilt for passive systems [EP 0 683 081 A1].
Stability of equilibrium requires that the coach centre of mass reaches its lowest position in the central, neutral configuration, because the only restoring force of a passive tilt system is gravitational and, if its potential energy attains a minimum, the equilibrium is stable. Moreover, the stability margin will be larger, the higher the centre of suspension is kept with respect to the mass centre, and thus it is necessary to plan a sufficient distance between the two points.
When the centre of rotation is situated above the centre of mass, the centrifugal force contributes to tilt the carriage. The higher the distance is, then the higher the moment of the centrifugal force is. In a similar way, when the centre of mass is placed under the centre of the bolster springs, the centrifugal force acts in a way to deform the springs in an advantageous manner.
From a force point of view, the closer the centre of rotation is situated to the centre of mass, the less energy the rotation needs. From simple physics, the longer the distance the point of application is situated from the point of rotation, the larger the moment becomes so it is advantageous to place the activation point at higher distance from the rotation point.
From a security point of view, the centre of mass should not be moved, which would also be ineffective from an energy point of view. The displacement of the centre of gravity in the passive system has negative impact on security and wheel unloading.
From a comfort point of view, when the centre of rotation is situated close to the head of the sitting passengers seems advantageous, minimizing speed and movement for the inner ear. A centre of rotation situated very high would give the impression that the feet are gliding sideways.
Mixing the impact of the rotation centre on comfort and car body shape, the most advantageous position is situated around the knee or elbow of sitting passengers, where the largest width is required.
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4.3 Patents
An extensive patent research and study has been made both to summarise state of the art of existing systems and to find room for new ideas and novel designs. The list of studied patents can be found in appendices. An opportunity is that key patents come to end shortly.
4.4 Overview of existing mechanisms
This section presents the actual existing or commercialized tilt systems in a state of the art review. They are presented with regards to a SWOT analysis, where SWOT stands for Strengths, Weaknesses, Opportunities and Threats).
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4.4.1 Passive or natural tilting systems
4.4.1.1 Secondary suspension above the centre of gravity
Description A Placing the secondary suspension above the centre of gravity allows using the deformation induced in the suspension by the centrifugal force to counterbalance partly the lateral acceleration. Note that this deformation acts in the usual design to increase the lateral acceleration. This solution is own by Talgo.
Strength Weakness • Use space in the carriage, this disadvantage is negligible when use of Jacob’s bogie • Minimize carriage gauge at the floor • Simple and cheap level, where room is the most useful • Allows low floor • Need a new design of the carriage whole • Passive structure as force are transmitted at • No need for anti-roll bar another point • Low tilt angle • No high speed increase possible • Delayed tilt • Shift of centre of gravity outwards Opportunities Threats • Suppress the need for an anti-roll bar • Can be turned active cancelling the delay and increasing the tilt angle • Coming after Talgo may be risky for the • Patent will be opened soon company image • Possibility to have all train long very low floor (gangway) • Low end market train
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4.4.1.2 Mechanical or bar mechanism
Description A The centrifugal force naturally pushes the carriage body outwards under curves. Those different pendulum like mechanisms used this effect to force the carriage floor to tilt inwards the curve. A, B, C are different embodiment of a same patent [FR1549521]. D is a suspension derived thanks to genetic algorithms [37]. E is a system based on a double Watt’s mechanism [DE 44 23 638].
Possible variant
B C
D E
Strength Weakness • Complex mechanics, many joints • Many wear parts • Passive • Delayed tilt • Stable • Difficulty to construct a low floor • No wrong tilt possible, failure safe • Snow can blocks the system when packed between moving parts Opportunities Threats • Possibility to actively support a passive system, which make the activation force • High building cost for the mechanic smaller parts and possibly high maintenance • Potential to develop other mechanisms cost due to many parts [37]
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4.4.1.3 Rolling solutions
Description A The conventional roller tilt system is used on the Series 381 electric rail in Japan and consists of a pair of cylindrical rollers which are mounted on the bogie frame and a tilt beam which has a convex arch-shaped form. As the centre of rotation is placed above the centre of mass, the centrifugal force acts to tilt inwards the car body in curves. Due to inertia of carriage and mechanical resistance, the tilt may happen suddenly in the middle of the curve and can oscillate as it is not damped, which can result in bad riding comfort. Cylindrical rollers can be replaced by roll bearing [C] to reduce mechanical resistance. The system can be reversed and placed under the roof in a Talgo manner. Possible variant
B
C
Strength Weakness • Simple and cheap • Bearing guides are uncommon parts • Compact • Possible winter problem • Passive • Reduce passenger room [B] • No wrong tilt possible, failure safe • Instability of neutral point when • Low floor [B] travelling on tangent track Opportunities Threats • Combining rolling guide and under roof secondary suspension • Systems are patented, among which • Possibility for an hybrid roller-pendulum stops for neutral point solution • Availability of bearing guide • The neutral point can be forced with a brake
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4.4.1.4 Anti-roll bar solutions
Description A A modification of an anti-roll bar can produce a very cheap passive tilting system. It only requires inclining the vertical links (1) to the inside on the higher part. The function of the torsion bar for same phase and anti-phase movement 1 remains unchanged. When a centrifugal force happens in curve, the body is forced to tilt by the bent links (1). Those systems suffer from the major drawback of shortcutting the lateral suspension.
A [FR2434739] B [JP2003002193]
Possible variant
B
Strength Weakness • Cheap • Limited tilt • No new components, just modification • Inertia untimely of an existing one • Bad lateral comfort due to shortcutting • No wrong tilt possible, failure safe of the lateral suspension Opportunities Threats • The idea of the torsion bar offers good possibility for an active tilt system • Possibility to use it with an active lateral • Bad lateral comfort turns the solution to suspension, but the simplification of one be impractical in reality system increase the complexity of the other
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4.4.2 Hybrid solutions
In the literature, it lacks a denomination for natural tilting based system improved with an actuator; therefore the term hybrid tilt system is introduced here. Note that all the different solutions mentioned in the previous section can possibly be turned active to increase their competitiveness in terms of comfort. A total passive solution is believed to be insufficient from a comfort point of view for modern high specifications railways. But market niche cannot be excluded.
4.4.2.1 Rolling solutions
Description B The roller passive solution can be upgraded with the help of an active support. To tilt timely, increase the angle of tilt and avoid oscillations.
Strength Weakness • Low energy consumption • Bearing guides are uncommon parts • If active system is out of order, the • Possible winter problem train can still use the reduced comfort of • The system becomes more complex a passive tilt system Opportunities Threats • Not taking advantage of the passive possibility and make coincidence of the centre of rotation and centre of mass to
have very low energy consumption, but this reduces the stability on the other hand.
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4.4.3 Active or forced tilting systems
4.4.3.1 Direct lifting
Description A Actuators lift directly the carriage to make it tilt actively inwards. This was the embodiment of the first Pendolino. Another variant is to place the activator under the secondary suspension or to ship air in the bellies of the secondary suspension to tilt the carriage.
Possible variant
B C
Strength Weakness • High energy consumption • The actuators are situated above the • High forces secondary suspension, where the • Wrong tilt possible vibrations due to track irregularities are • Failure dependent largely filtered [A] • Usually needs an additional lateral • Few mechanical parts control Opportunities Threats • Potential to use the secondary suspension at limited tilt angle like in • Failure of the actuator becomes difficult the embodiment of the new Shinkansen to handle entering service revenue in 2007.
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4.4.3.2 Pendulum
Description A The vehicle body is hung on a bolster supported by inclined links in a pendulum manner. The secondary suspension is usually placed above the bolster, which reduces the deformation due to the centrifugal force, but creates dynamic oscillations. The pendulum can be either hanging (stable) or standing (unstable). Both solutions have been used, but the first seems really advantageous by its stability. Many different embodiments exist, with basically no change of the original idea. Possible variant
B C D
Strength Weakness • High activation force • Proven technology • Need for bolster • Naturally stable return point • Winter trouble • Quite simple • Low floor difficult to realise Opportunities Threats • Utilisation of a variable force transmission to reduce the actuator requirements
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4.4.3.3 Anti-roll bar solutions
A Description The anti-roll bar can be modified to become an active tilt system. Several possibilities exist. A first one is to change the length of the vertical links with one or two linear actuators [A] & [B]. Another is to lean both links as seen in the passive solution. The actuator can then either push the carriage to tilt [C] or pull the torsion bar [D]. Note that [B] & [D] are hybrid.
Possible variant
B C D
Strength Weakness • Low speed application • Modifying an existing element • Failure problem, no torsion bar in case of • Fewer components problem • No bolster • Air bellies are coupled causing problem in • Possible low floor construction case of failure Opportunities Threats • Flexibility of application • Failure is complicated to handle • Bombardier/Talbot patented and used
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4.4.3.4 Rolling solutions
Description A This embodiment of the roller solution consists of setting the rotation point as close as possible to the centre of mass so that the energy requirement to tilt is as low as possible. Possible variant could set the secondary suspension close to the roof to have a low rotation centre that could minimize the acceleration felt by the passenger at the height of their feet. The system becomes though unstable. But the secondary suspension works exactly as on the Talgo version. The tube version is funny, but the room space is very limited. Possible variant
B C D
Strength Weakness • Bearing guides are uncommon parts • Low energy consumption • Possible winter problem • Compact • The system becomes more complex • Reduces passengers space if used on bogies Opportunities Threats • The lowest possible energy consumption • Instability may be unacceptable for a totally active system
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4.4.3.5 Advanced bar mechanism
Description A This system has been found in the literature study, but no realisation is known [35]. It is the only system having two degrees of freedom [B], making possible to balance the wheel unloading.
Possible variant
B C
Strength Weakness • High actuator forces • No stable neutral position • Full flexibility of movement • Security issues as the centre of gravity is actively moved Opportunities Threats • Possible to balance vertical rails forces. • Possibility to make in addition to the tilt function an active lateral suspension with fast actuators • Security issues • Possibility to use the tilt system to • Unacceptance of the market for too adapt the car to the height of the complex system platform in train station • High development costs • Can reduce the constraints on the profile of the car body • The system can be built as hanging pendulum or standing
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4.4.4 Choice of systems for further analysis and comparison
Based on the SWOT analysis made in the previous section, we decided to keep the 4 following systems for further investigations and comparisons. The first one is probably the most used embodiment of an active tilt. The second is mainly used in Japan. The third is almost a niche product sold and owned by Talgo. The last is an original system found in the literature with no known realisation.
1. Hanging pendulum 2. Active roll-bearing
3. Passive high secondary suspension 4. Advanced bar mechanism
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4.5 Brainstorming & creativity During the middle of the project a brainstorm seminar was organized to enhance creativity and find new directions and ideas. The objective of a brainstorming session is to generate the broadest range of ideas about a question. In order to enhance creativity a brainstorming session follows four basic rules: • Focus on finding as many ideas as possible in a divergent way • No criticism or scepticism • Unusual ideas are encouraged • Combine and improve ideas The equation “1+1=3” is a golden maxim for ideas; two good ideas can be combined to an even better novel idea. The process can be repeated without limits. The results of the brainstorming can be found in appendices.
We specially acknowledge the help and ideas of every participant to the brainstorming seminar.
4.5.1 Discussions of ideas of the brainstorming The whole list of ideas of the brainstorming seminar can be found in the appendices. We discuss here some ideas that have not been used any further, but still require more explanations why they haven’t been used.
4.5.1.1 Bennett’s mechanism A three dimensional Bennett’s mechanism allows to transform a rotation in a plane to another rotation in another plane. That could be used to transform the yaw rotation of the bogie into a roll rotation for the car body. However, there is no direct coupling between the yaw rotation at the bogie level and the wished tilt of the car body. For example a stopped train in a curve may tilt outwards while the coupling between movements would force it inwards. Another problem is the variation of the required tilt in function of speed. Additionally, the yaw rotation is small proportionally to the required tilt angle. Another major drawback would be the negative impact onto the lateral force at the track level that would increase, requiring more maintenance on both wheels and rails. Hence, we did not judge this idea having potential in our application. However, this idea would have potential for an urban automatic fast transport system, where speed would be constant and the track specially designed for this kind of vehicles.
4.5.1.2 Energy regeneration To regenerate energy when the car body returns in position appears being a good idea. This idea didn’t bring to new constructive ideas, but could be implemented onto the activation system.
4.5.1.3 Primary suspension The idea to place a possible tilting system at the level of the primary suspension is not considered as interesting, as the room is very small and restricted, so that the placement of a mechanism would be very difficult. Note that there is no torsion bar either at the primary suspension level.
4.6 Novel designs This section presents the different novel designs that have been generated in the creative phase. They are presented in a SWOT analysis format, so the most interesting one can be sorted out, to be compared with the previous elected systems.
4.6.1 New solutions The new solutions can be divided into two groups: the one modifying an existing element of the train to operate the tilt and the other with an additional purposely designed tilt system.
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4.6.1.1 Modification of an existing element
4.6.1.1.1 Suspension as a flexible element
Description A The secondary suspension has a transverse flexibility that could be used for a simple tilt system. It would only be applicable for small tilt angles. It could be used passively [A]. As a variant, it can be activated, the secondary suspension and naturally be composed of springs or air bellies [B]. As another variant, it would be possible to set the springs of the secondary suspension on pins to make the movement easier and bigger [C]. Another possibility is to turn active the solution with a secondary suspension under the roof [D]. All those systems, except the passive one, have the major drawback to shortcut the lateral suspension steps, it could be solved with a fast response actuator. Possible variant B C
D
Strength Weakness • Small possible angle • Simple • Less effective secondary suspension • Stable (lateral) • Cheap • In case of high secondary suspension, • Medium actuator force cut down passengers room [B] • Possibly very compact system • The lateral secondary suspension is shortcut, with greatly reduced comfort Opportunities Threats • Lateral comfort is too bad, except if the • Bogie without torsion bar actuator can have fast response not to worsen the lateral suspension
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4.6.1.1.2 Suspension used as activator
Description A The air bellies of the secondary suspension can easily be turned into actuators. The approach is used in Japan to make a simplified tilt with limited angle of 1 [°] on the new Shinkansen, that enters the market in 2007. This idea could be used to activate a Talgo type system. It is though difficult to move air fast enough to lift the car body. An interesting option is to use three or four air bellies. The one or two in the centre bear the carriage load and the two lateral ones are used as tilting actuators. The bellies can be set in line in a three or four version or in a cross shape with two bearing element in the centre. As the actuators are flexible, there is no need for pins whatsoever and the suspension is not shortcut at all. A drawback is the weight transmission in the central part of the H-shaped bogie, where usually no force is transmitted. Different variants are possible for example dividing air bellies in several rooms with various air pressure compartments. Possible variant
B C
Strength Weakness • Cheap • Difficulties to reshape the air bellies fast • Few components • Safety might be a problem Opportunities Threats • Possibly interesting for a small tilt angle • Development limitation of the bellies • A potential very cheap solution
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4.6.1.1.3 Anti-roll bar
Description A An active anti-roll bar offers a wide variation of possible implementations. We have already seen some examples with variable vertical links or bent links. Another possibility is to have the motor in the middle of the torsion bar, which seems a good alternative, since many electromechanic actuators are meant to be used as rotational [A]. A variant is to place the actuators aside in a longitudinal direction. Embodiment with one or two actuators is possible [B].
Possible variant
B
Strength Weakness • Taking advantage of the already • Medium size force existing torsion bar • Failure problem is sensitive • Simple Opportunities Threats • System is compact • Bombardier owns a patent • Reducing the performance of the • The failure could be easily solved in the secondary suspension and of the torsion rotational centre motor with a brake bar • A good low market solution
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4.6.1.2 Special designed tilt systems
4.6.1.2.1 Flexible radial elements
Description A Flexible elements [C] & [D] can be used instead of pins or joints. Those can be a flexible beams as used in leaf spring, rubber spring [D] or electro-erosion manufactured beams like illustrated below [C]. This use of flexible element is an interesting novel idea, with elements that have been of common use in suspensions on trains. Elastic elements could substitute B the roller guide one. They could be used to make a tilt system and an active lateral suspension as in [F].
C
D
Possible variant
E F
Strength Weakness • Very simple and cheap mechanical design • Small tilt angle • Stable • Fatigue? • Failure safe Opportunities Threats • Seems to be a promising solution for • Difficulties to go for novel design low market • No such systems are known
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4.6.1.2.2 Flexible element in pendulum arrangement
Description A Another possible way to use flexible elements is to set them in a pendulum like manner. The pendulum can be hanging [A] or standing. A fun and advanced idea would be to combine the active lateral suspension and tilt function in one stage [C].
Possible variant
B C
Strength Weakness • Very simple and cheap mechanical • Small tilt angle design • Wrong tilt in case of motor failure • Stable (hanging pendulum) • Fatigue (?) Opportunities Threats • Difficulties to go for novel design • For regional train • No such systems are known
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4.6.1.2.3 Active multiple links mechanism
Description A The multiple links mechanism presented as a passive system seems to offer a good possibility in an active solution.
Strength Weakness • Low forces • Many mechanical parts • Stable • Many wear parts • Can be used as a passive system in case • Difficulty to combine with low floor of failure Opportunities Threats • Possibility to have a low energy novel design • Mechanical complexity can make it • The mechanical complexity could be expensive solved with an electro-erosion made mechanism
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4.6.1.2.4 Different mechanisms
A Description Many mechanical systems are thinkable to tilt a car body. Few seem to be able to be simpler than the pendulum, like you can see with the various illustrations of the possible variants. We consider though the right possibilities with middle longitudinal pins as a possible construction.
B
Possible variant
C D
E F
G H
Strength Weakness • Unstable • Cannot return to neutral position alone • Potentially compact • Medium actuator force • Centre of rotation is low Opportunities Threats • Use rotational motor instead of a linear • Not possible to compete with current one systems
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4.6.1.2.5 Direct drive and roll solution
Description
Based on the roll solution, it would be
possible to create a direct drive solution A with bearing, brake and motor integrated in one element. A direct drive would need a mechanical brake so that the motor is not always in use. The patented tube version is really bad regarding the gauge. But it could be interesting, to make a roller solution as in the figure to the left, with more rollers or bearings [A]. It would also be possible to use more actuators, allowing the use of very standardized and small actuators, which could be much cheaper. So the system could be more reliable being able to work with only 3 out of 4 actuators working for example. A possible variant is to replace the arch-shaped bearing guide by a linear one, to get more standardized components, but with a loss in terms of energy [B]. Possible variant
B
Strength Weakness • Compact [A] • Expensive [A] • Cheap [B] Opportunities Threats • Development cost for direct drive too • No need for unusual bearing guide [B] high
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4.6.2 Choice of systems for further analysis and comparison
Based on the SWOT analysis, we decided to elect the following five systems for further evaluation (in addition to the four systems retained in §4.4.4).
5. Secondary suspension as actuator 6. Flexible radial elements
7. Active flexible trapeze 8. Active multiple links mechanism
9. Torsion bar with central motor
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4.7 Overview of all possible tilt mechanisms Table 10: overview of all possible tilt mechanisms.
Name of mechanism Criteria System is existing? Angle oftilt Utilisation of existing elements? Self Centring? Movement of centrerotation? of Movement of centre ofgravity? Number of motors per bogie Wearing part? Moving mechanical part? freedom of Degree High secondary suspension YES 4° YES YES NO YES 0 NO NO 1
Mechanical or bar mechanism NO 4° NO YES YES YES 0 YES YES 1
Rolling solutions YES 4° NO YES NO YES 0 (YES) (YES) 1
Passive Passive Anti-roll bar solutions NO 3° YES YES YES YES 0 YES YES 1
High secondary suspension NO 6° YES (YES) NO YES 1 NO NO 1
Activated multiple links mechanism NO 8° NO (YES) NO YES 1 YES YES 1
Rolling solutions YES 8° NO (YES) NO YES 1 (YES) YES 1
Hybrid Hybrid Anti-roll bar solutions NO 7° YES (YES) YES YES 1 YES YES 1
Direct lifting YES 8° NO NO NO (YES) 2 YES NO 1
Pendulum YES 8° NO YES YES (YES) 1 (YES) YES 1
Rolling solutions YES 8° NO NO NO NO 1 YES (YES) 1
Advanced bar mechanism NO 8° NO NO YES NO 2 YES YES 2
Suspension as a flexible element NO 4° YES (YES) YES (NO) 1 NO (NO) 1
Suspension used as activator YES 4° YES NO NO YES (2) NO (NO) 1
Anti-roll bar YES 7° YES NO NO YES 1 YES YES 1
Flexible element in a rolling form NO 6° NO YES NO (NO) 1 NO NO 1
Flexible element in pendulum arrangement NO 6° NO (YES) (YES) (YES) 1 NO (YES) 1
Active Direct drive NO 8° NO NO NO NO 1 (YES) NO 1
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4.8 Systems to be assessed Table 11: systems to be assessed. 1. Hanging pendulum 2. Active roll-bearing
3. Passive high secondary suspension 4. Advanced bar mechanism
5. Secondary suspension as actuators 6. Flexible radial elements
7. Active flexible trapeze 8. Active multiple links mechanism
9. Active torsion bar with central motor
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4.9 Assessment of different mechanisms
Based on the discussion, the objectives tree and the ideas that came up during the brainstorming session, we can decide the assessment criteria. We decide to use three different assessment methods. The first is a multicriteria proportional average, the second another judgement on a reduced list of criteria, with only key figures. Lastly we will apply an ELECTRE judgement.
4.9.1 Proportional multicriteria
4.9.1.1 List of criteria
We made a list of criteria based on experience, ideas that come up during the brainstorming session and finally developed it with the help of the objective tree that has been previously presented. The 9 different selected systems will be assessed by the following list of criteria weighted by their importance in a proportional way. Points have been set by Rickard Persson from Bombardier and me, with equal weight. The scale of mark goes from 0 to 10, ten being the best possible mark. Weight basically follows the same scale even if it would be possible to have higher weight if needed.
• Development cost of the project • Feasibility risk of the project • Time to market of the project • Angle of tilt capability • Force requirements • Power consumption • Lateral force in secondary suspension • Tilt centre • Tilting comfort • Profile reduction of the carriage • Complexity of the system • Weight • Low floor • Space in wagon • Bogie space • Self centring • Failure safe • Wheel unloading • Control complexity • Maintenance • Acquisition cost of the tilting mechanism • Winter problem • Opportunities • Potential • Trends • Customers choice
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4.9.1.2 Correlation between criteria The following table summarises the different correlations between different assessment criteria. Multiple correlations makes sensitive to judge the final importance of one criterion. Table 12: correlations between different criteria; 3 marks a strong correlation, 2 a middle, 1 a weak one, empty box none. 23 24 25 26 10 11 12 13 14 15 16 17 18 19 20 21 22 1 2 3 4 5 6 7 8 9
1 Development cost if the project 3 3 2 1 1 1 2 1 3 1 2 1 2 3 2 1 1 3 3 3 2 Feasibility risk of the project 3 3 1 1 1 3 1 3 3 3 3 2 2 3 1 2 3 3 Time to market of the project 3 3 3 1 1 2 2 3 2 2 2 3 4 Angle of tilt capability 2 3 2 3 3 2 1 2 2 1 3 2 3 3 5 Force requirements 2 2 3 3 2 1 2 2 2 6 Power consumptions 1 3 3 3 1 1 1 2 3 2 2 3 7 Lateral force in secondary suspension 1 1 1 1 8 Tilt centre 1 2 3 3 2 3 1 1 2 2 3 1 3 9 Tilting comfort 2 1 3 2 2 3 2 1 2 2 3 10 Profile reduction of the carriage 1 1 3 3 1 1 3 11 Complexity of the system 3 3 3 1 2 2 1 1 1 1 2 3 1 12 Weight 1 2 2 1 1 2 13 Low floor 2 1 1 1 1 3 2 2 2 14 Space in wagon 1 1 1 1 1 15 Bogie space 1 3 1 1 1 1 1 1 1 16 Self centring 2 3 1 2 3 2 2 1 2 1 3 3 17 Failure safe 3 3 2 1 1 2 3 1 3 1 2 3 1 3 3 18 Wheel unloading 3 2 1 3 2 1 1 1 19 Control complexity 2 2 2 2 2 2 1 1 1 2 2 2 20 Maintenance 1 2 1 1 2 1 1 3 1 1 1 2 21 Acquisition cost of mechanism 1 3 3 2 2 2 3 1 1 2 1 1 1 22 Winter problem 1 1 2 1 3 1 1 1 2 23 Opportunities 3 2 2 3 2 3 1 2 1 3 1 1 2 1 2 2 3 24 Potential 3 2 2 2 1 2 1 3 2 1 2 25 Trends 2 3 2 2 2 2 1 3 26 Customers choice 3 3 3 3 2 3 3 3 3 1 2 1 3 3 1 2 2 1 2 3 2 3
81 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
4.9.1.3 Assessment of selected solutions Table 13 : assessment of the 9 selected solutions under the whole criteria procedure. Design denomination denomination Design optimisation for cost Coefficient optimisation safety Coefficient optimisation market Coefficient pendulum Hanging Active roll-bearing High secondary suspension Advanced bar mechanism suspension Secondary Flexible radial elements Flexible trapeze mechanism links Active multiple motor bar with central Torsion
Assessment criteria 1 2 3 4 5 6 7 8 9 Development cost 10.0 1.0 6.5 10.0 6.5 5.5 0.5 4.5 5.0 4.0 3.0 5.5 Feasibility risk 10.0 5.0 2.5 10.0 7.0 8.5 1.0 4.0 7.0 5.0 2.5 5.5 Time to market 10.0 3.5 2.5 10.0 7.0 8.0 0.5 5.5 5.5 4.5 3.0 5.0 Angle of tilt capability 4.5 1.0 8.0 9.5 8.5 5.0 10.0 5.0 4.5 5.5 7.0 6.5 Force requirements 8.5 4.5 6.0 2.0 8.5 10.0 1.5 6.0 5.5 6.5 8.0 5.0 Power consumptions 8.5 5.0 7.5 2.0 8.0 10.0 3.5 4.5 5.5 7.5 8.5 5.0 Lateral force in suspension 2.0 4.0 4.0 8.5 8.5 3.0 9.0 3.0 7.5 7.5 8.0 3.0 Tilt centre 1.0 9.0 5.0 6.5 9.5 2.5 10.0 5.0 9.5 4.5 9.5 4.0 Tilting comfort 4.0 3.5 8.0 8.5 9.5 3.0 10.0 5.0 9.5 6.0 9.0 5.5 Profile reduction 3.5 1.0 7.5 8.0 8.5 1.0 10.0 5.0 9.5 4.5 10.0 4.5 Complexity 9.5 5.5 7.0 5.0 5.5 10.0 0.5 8.0 7.5 6.5 3.0 4.5 Weight 6.0 2.0 6.0 3.0 7.0 5.5 2.5 9.0 7.5 6.0 3.0 6.5 Low floor 2.0 1.0 7.5 5.5 5.5 10.0 5.5 5.0 4.5 4.5 4.0 5.0 Space in wagon 5.5 1.0 6.5 6.5 8.0 2.0 8.0 9.0 7.5 7.5 7.0 8.0 Bogie space 5.0 1.0 4.0 2.0 6.0 9.0 2.5 5.5 6.5 5.5 2.5 5.0 Self centring 5.5 10.0 8.5 10.0 1.5 10.0 0.0 1.0 10.0 9.5 9.0 0.5 Failure safe 6.0 10.0 8.5 10.0 6.0 10.0 0.0 0.5 10.0 6.5 9.5 0.0 Wheel unloading 4.0 10.0 3.5 8.0 8.5 3.5 10.0 5.5 9.5 5.0 7.0 4.5 Control complexity 8.5 8.5 3.5 6.0 4.5 10.0 0.0 4.0 6.0 4.5 6.0 4.0 Maintenance 7.0 1.5 7.5 6.0 5.0 9.5 2.5 7.0 6.5 4.0 4.0 4.0 Acquisition cost 10.0 1.0 7.5 4.5 5.0 8.0 1.0 7.5 5.5 3.5 4.0 5.5 Winter problem 4.0 9.5 4.0 4.5 5.0 10.0 3.5 6.0 8.5 4.0 4.5 6.0 Opportunities 2.5 2.5 5.0 9.5 5.0 0.0 0.5 3.0 6.5 3.0 0.5 3.0 Potential 2.5 1.0 2.5 4.0 5.0 4.5 3.0 7.5 8.5 7.5 4.5 3.0 Trends 1.0 1.0 8.0 9.0 7.5 4.0 2.0 4.5 6.5 3.0 2.0 2.0 Customers choice 7.5 1.0 10.0 10.0 7.5 3.5 0.5 3.0 6.5 5.0 3.0 6.0 Score 6.8 6.5 7.3 2.7 5.3 6.8 5.4 5.2 4.8 Ranking 3 4 1 9 6 2 5 7 8 Score 7.1 6.4 7.3 3.7 4.4 8.0 5.7 6.5 3.9 Ranking 3 5 2 9 7 1 6 4 8 Score 7.0 6.7 6.4 3.8 5.0 7.2 5.5 5.7 4.5 Ranking 2 3 4 9 7 1 6 5 8 Score global 6.9 6.7 6.4 3.8 5.1 7.2 5.4 5.5 4.5 Ranking 2 3 4 9 7 1 6 5 8
82 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
4.9.1.4 Results analysis Globally, the existing systems received very good score, which is not very surprising. One obvious reason is that they are much less risky. The Talgo solution score is surprisingly good, mainly because of its simplicity, but is though not a very interesting solution as it is a brand design and its interest is limited for modern high performance railways as believed that only an active solution can answers today’s demand.
The solution that appears having the most interesting potential out of this extended proportional analysis is the flexible radial elements. Some wonderings remain about the magnitude of its tilt capability. This has to be evaluated in detail in a further study. Those four systems scored very similarly, difficult to judge which one is the best.
The active torsion bar on which we placed much hope, gave very bad and upsetting score. The reason behind this disaster is that the system suffers of high reliability problems. In case of heavy failure, the train has no more torsion bar. The system suffers from too strong functional interactions.
The advanced bar mechanism is judged as the worse selected system. The system is too complicated and has too much impact on safety to have some potential in this application, as the train industry is very sensitive to these questions, sometimes in a conservative manner.
The score of the secondary suspension system is surprisingly low, also due to safety issues. However some potential exists in this solution due to its simplicity.
Some doubts were expressed about the list of criteria because of the many interactions and correlations between them. Because of those doubts, we decide to assess the chosen system with two other different methods, one with fewer criteria to reduce interaction, one with an ELECTRE method that put weight on agreement and conflicting points at the same time.
Note that a careful choice of the weight gives a very fine and adaptive analysis, and can correct the correlation. Moreover, the conclusions are very stable; hence the results appear quite strong. Nevertheless, we have to bear in mind that those assessment criteria and marks setting are always partly subjective.
4.9.1.5 Performance index In order to be able to compare the solution on a cost / performance basis, we calculate a performance index as follows. Firstly, we calculate the mathematical average between market optimisation and safety optimisation. That gives us a general performance index. Finally, we calculate a performance index as following: (average ∗cost) PI = 100 So that the best possible score is 10 and the worst possible one 0. The results are: Table 14 : performance index.
System 1 2 3 4 5 6 7 8 9 Mark for market optimisation 7.0 6.7 6.4 3.8 5.0 7.2 5.5 5.7 4.5 Mark for safety optimisation 7.1 6.4 7.3 3.7 4.4 8.0 5.7 6.5 3.9 Average for market and safety 7.0 6.6 6.8 3.7 4.7 7.6 5.6 6.1 4.2 Mark for cost optimisation 6.8 6.5 7.3 2.7 5.3 6.8 5.4 5.2 4.8 PERFORMANCE INDEX 0.48 0.43 0.50 0.10 0.25 0.52 0.31 0.31 0.20 RANKING 3 4 2 9 7 1 6 5 8
83 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
We can also present the result on a two axis diagram. On the x-axis is found the average of market and safety optimisation while on the y-axis is found the cost optimisation. Note that the scale is from 0 to 10 with 10 standing for the best possible solution.
Figure 47 : diagram presenting the cost in function of the market and safety optimisation.
The results are very clear. The system 1, 2, 3 and 6 are the most promising. Note that system 1, 2 and 3 are the three existing systems. Systems 7 and 8 are placed intermediately. Finally 5 and 9 are less worth while 4 is in very bad position.
4.9.2 Proportional reduced criteria
4.9.2.1 Criteria
Because of the many interactions between criteria, we decided to assess the system in a simplified manner with a reduced number of criteria to minimize interaction. Scales and marks are identical to the ones used in the previous section. The assessment was also performed by Rickard Persson from Bombardier and me in the same manner as in the previous method. For this analysis, we only select the main and global criteria as follows:
• Purchase cost • LCC (Life Cycle Cost) • Safety • Maintenance • Reliability • Comfort • Customers choice
84 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
4.9.2.2 Assessment
Table 15 : table of assessment of the 9 selected solutions under the simplified assessment procedure. Design denomination denomination Design optimisation for cost Coefficient optimisation safety Coefficient optimisation market Coefficient pendulum Hanging Active roll-bearing High secondary suspension bar mechanism Advanced suspension Secondary Flexible radial elements Flexible trapeze mechanism links Active multiple motor bar with central Torsion
Assessment criteria 1. 2. 3. 4. 5. 6. 7. 8. 9. Purchase cost 10.0 4.0 5.0 4.0 5.0 8.0 0.0 6.5 5.5 3.5 2.5 4.0 LCC 5.0 1.0 5.0 1.5 7.5 10.0 3.5 3.5 4.5 7.5 7.5 5.5 Safety 4.5 10.0 5.0 10.0 5.5 10.0 0.0 1.0 10.0 5.0 10.0 0.0 Maintenance 3.0 1.0 5.0 5.5 4.5 10.0 1.5 5.5 6.5 3.5 3.0 3.5 Reliability 4.0 5.5 5.0 4.0 4.0 10.0 1.0 8.0 6.0 6.0 3.0 5.0 Comfort 5.0 2.5 8.0 9.0 9.0 1.5 9.0 3.0 9.0 7.0 9.0 4.0 Customers choice 5.0 3.5 8.0 10.0 7.0 1.5 0.0 2.0 6.5 4.0 2.0 5.0 Score 5.8 5.0 5.8 1.5 3.9 6.1 4.0 4.0 3.2 Ranking 2 4 3 9 7 1 5 6 8 Score 7.3 5.4 7.5 1.1 3.6 7.5 4.8 5.8 2.7 Ranking 3 5 2 9 7 1 6 4 8 Score 6.6 5.4 5.2 2.1 3.5 6.4 4.3 4.4 3.3 Ranking 1 3 4 9 7 2 6 5 8 Score global 6.3 6.1 7.3 2.1 4.2 6.9 5.2 5.3 3.9 Ranking 3 4 1 9 7 2 6 5 8
4.9.2.3 Results comments
Globally the conclusions underlined by the simplified analysis are exactly the same as from the more detailed evaluation above. The four best scoring systems are the 3 existing and the radial flexible element; the two worse are the advanced bar mechanism and the torsion bar.
85 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
4.9.3 ELECTRE
ELECTRE is multicriteria decision-aid method developed since 1968 in France by Bernard Roy and at the EPFL. The method is based on the following concept: • Outclassing: an action outclasses an other if it is at least as good as the other relatively to a majority of criteria and at the same time not clearly worse relatively to the other criteria. • Agreement: a majority of criteria are in favour of a certain solution. • Non contradiction: it does not exist a too strong pressure in favour of the inverse outclassing. • Orderly pair: the solution is compared in orderly pair in a matrix where, as convention, columns outclass rows.
The method works in four stages: 1. Judgements: decide which are the criteria and give them a weight (low: 1, medium: 3, strong: 4). Then each solution is judged with a scale from very good (G), good (g), average (n), bad (b), very bad (B). The weight is integrated in the mark as follows :
Table 16 : scale used for ELECTRE. Low weight Medium weight Strong weight G Very good 7.0 8.0 10.0 g Good 6.0 6.5 7.5 a Average 5.0 5.0 5.0 b Bad 4.0 3.5 2.5 B Very bad 3.0 2.0 0.0
2. Calculation of the indices: for every orderly pair, we make the hypothesis that the first solution outclasses the second. We calculate the agreement indices: n ∑iPi ()a j ≥ ak i=1 ic ()PR jk = n ∑ Pi i=1
(a j ≥ ak )= a j is at least as good as ak . Make a table with all the calculated indices for all the possible pair. After the agreement indices, we continue with the contradiction indices:
a. Look for all criteria where a j < ak b. Find the biggest disagreement ∆ c. Divide the biggest disagreement by the biggest scale of the named criteria. Calculate the contradiction indices for all pairs. Note that it is possible to calculate the second order disagreement. 3. Outclassing level: outclassing is kept if the agreement is high and the contradiction is low. Therefore, two thresholds are chosen :
• Agreement threshold : S A
• Contradictory threshold : SC 4. Iteration and conclusion: draw the result, make the thresholds vary until the results appear clearly.
This method, like the previous, suffers from the judgement of the person setting marks.
86 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
4.9.3.1 Weight, criteria and assessment
This table presents the judgment step, with the scale and criteria’s choice and judgement. The marks have been set by the author, alone.
Table 17 : ELECTRE, weight, scale and assessment main table.
Cost Comfort efficiency Energy Safety Reliability Maintenance Weight 4 4 3 4 3 3 1 Hanging pendulum 2.5 10.0 2.0 10.0 6.5 3.5 2 Active roll-bearing 5.0 10.0 8.0 5.0 6.5 3.5 3 High secondary suspension 10.0 5.0 8.0 10.0 8.0 8.0 4 Advanced bar mechanism 0.0 10.0 2.0 0.0 2.5 2.0 5 Secondary suspension 7.5 2.5 3.5 5.0 2.5 3.5 6 Flexible radial elements 10.0 10.0 3.5 7.5 6.5 6.5 7 Flexible trapeze 5.0 7.5 3.5 5.0 5.0 5.0 8 Active multiple links mechanism 0.0 10.0 8.0 5.0 3.5 2.0 9 Torsion bar with central motor 2.5 5.0 2.0 2.5 3.5 2.0 Low 0.0 0.0 2.0 0.0 2.0 2.0 High 10.0 10.0 8.0 10.0 8.0 8.0
87 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
4.9.3.2 Weight, criteria and assessment
4.9.3.2.1 Concordance 4.9.3.2.2 Discordance
Table 18: ELECTRE concordance table. Table 19: ELECTRE discordance table.
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 1.00 0.81 0.81 0.33 0.48 0.81 0.48 0.33 0.33 1 0.00 0.50 0.50 1.00 0.75 0.25 0.50 0.50 0.75 2 0.67 1.00 0.81 0.19 0.52 0.86 0.52 0.52 0.00 2 0.75 0.00 0.50 0.75 0.75 0.56 0.56 0.50 0.75 3 0.38 0.33 1.00 0.19 0.00 0.38 0.19 0.33 0.19 3 0.75 0.50 0.00 1.00 0.69 0.56 0.50 1.00 0.75 4 1.00 1.00 0.81 1.00 0.81 1.00 0.81 1.00 0.81 4 0.00 0.00 0.50 0.00 0.75 0.00 0.25 0.00 0.50 5 0.67 0.81 1.00 0.33 1.00 1.00 0.81 0.67 0.33 5 0.50 0.25 0.00 0.75 0.00 0.00 0.25 0.75 0.50 6 0.52 0.48 0.81 0.19 0.14 1.00 0.14 0.33 0.00 6 0.75 0.50 0.50 1.00 0.75 0.00 0.50 1.00 0.75 7 0.52 0.86 0.81 0.19 0.52 1.00 1.00 0.52 0.00 7 0.25 0.19 0.25 0.50 0.50 0.00 0.00 0.50 0.38 8 0.86 1.00 0.81 0.52 0.52 0.86 0.67 1.00 0.48 8 0.75 0.00 0.50 0.75 0.75 0.56 0.56 0.00 0.75 9 1.00 1.00 1.00 0.48 0.67 1.00 1.00 0.81 1.00 9 0.00 0.00 0.00 0.25 0.25 0.00 0.00 0.25 0.00
88 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
4.9.3.2.3 Results
Table 20 : S A = 0.4 SC =0.8 Table 22 : S A = 0.4 SC =0.4
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 X X X - X X X - - 1 X - - - - X - - - 2 X X X - X X X X - 2 - X ------3 - - X ------3 - - X ------4 X X X X X X X X X 4 X X - X - X X X - 5 X X X - X X X X - 5 - X X - X X X - - 6 X X X - - X - - - 6 - - - - - X - - - 7 X X X - X X X X - 7 X X X - - X X - - 8 X X X X X X X X X 8 - X - - - - - X - 9 X X X X X X X X X 9 X X X X X X X X X
Table 21 : S = 0.4 S =0.6 A C Table 23 : S A = 0.6 SC =0.4
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 X X X - - X - - - 1 X - - - - X - - - 2 - X X - - X - - - 2 - X ------3 - - X ------3 - - X ------4 X X X X - X X X X 4 X X - X - X X X - 5 X X X - X X X - - 5 - X X - X X X - - 6 - - X - - X - - - 6 - - - - - X - - - 7 - X X - - X X - - 7 - X X - - X X - - 8 - X X - - X X X - 8 - X - - - - - X - 9 X X X - X X X X X 9 X X X - X X X X X
89 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Table 24 : S A = 0.8 SC =0.4 Table 26 : S A = 1.0 SC =0.1
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 X - - - - X - - - 1 X ------2 - X ------2 - X ------3 - - X ------3 - - X ------4 X X - X - X X X - 4 X X - X - X - X - 5 - X X - X X X - - 5 - - X - X X - - - 6 - - - - - X - - - 6 - - - - - X - - - 7 - X X - - X X - - 7 - - - - - X X - - 8 - X - - - - - X - 8 - X - - - - - X - 9 X X X - - X X X X 9 X X X - - X X - X
Table 25 : S A = 0.9 SC =0.4 Table 27 : S A = 1.0 SC =0.0
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 X ------1 X ------2 - X ------2 - X ------3 - - X ------3 - - X ------4 X X - X - X - X - 4 X X - X - X - X - 5 - - X - X X - - - 5 - - X - X X - - - 6 - - - - - X - - - 6 - - - - - X - - - 7 - - - - - X X - - 7 - - - - - X X - - 8 - X - - - - - X - 8 - X - - - - - X - 9 X X X - - X X - X 9 X X X - - X X - X
90 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
We can see from the previous 3 last tables that the results are identical, thus very stable. The agreement threshold can be very high and the contradictory one very low. The results are thus very reliable. Therefore, the results appear very clearly in the following figures.
2
1 5
3 8
4 9
6 7
Good 1 2 3 6
7 Medium 8
Bad 4 9 5
Figure 48 : schema of the route of the ELECTRE analysis, when the thresholds are set
S A = 1.0 and SC =0.1 in two different views.
To summarise, the systems 1, 2, 3 and 6 score best. They are the three existing and the flexible radial element. Both system 7 and 8 have intermediate score. Finally systems 4, 5 and 9 receive bad scores. The results are very similar to previous methods, which give credits to the assessment.
91 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
5 Actuators
In the commercialized tilt systems, all kinds of actuators are in use, namely: pneumatics, hydraulics, electrical and electro-hydraulics. It is known from the tilting trains in operation that actuator forces are ranging up to 8 to 10 [tons] installed at each of the two bogies of a carriage, the force range depends a lot on the mechanical design of the tilting system. Pneumatic and hydraulic were the first historically used actuators type.
The last three decades have shown a constant trend to replace hydraulic actuators by electrics in industrial application. This tendency has been ignited by the technology advances in the late 70’s to put on the market efficient, practical and economical DC brush motor servo amplifiers. The 80’s brought competitive brushless motors. Continuous technology improvements led to better performance in terms of cost, reliability and size.
Those improvements allowed electric motors to replace hydraulic actuators in machine tools in the 70’s, in robotics in the 80’s, for entertainment in the 90’s and this trend continues further with further increased performance. Electric actuators have then become an alternative to hydraulics or pneumatics for tilting trains in the late 90’s but their advantages in this application remain subject to questions due to safety issues.
5.1 Pneumatic actuators
Pneumatic actuators were used in some prototypes in Europe in early days when air was shifted from one side to the other of the air spring. This solution is very energy consuming. As air is compressible, pneumatic systems have a bad response and therefore almost require an onboard data control to anticipate the curves at high speed to give good results (please refer to the control part).
Pneumatic actuators are though of common use in Japan as an active support added to passively tilted train to enhance performance. As said previously, to be effective they require predictive control due to slow response of the actuators, so they can be commanded timely with consideration of the activation delay.
Table 28: Main advantages and drawbacks of pneumatics actuators.
Advantages Disadvantages • Cheap • Slow response • Clean • Predictive control requested • Easy maintenance
92 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
5.2 Hydraulic actuators Hydraulic actuators where introduced by FS/Fiat in the late 60’s. They largely proved their capability for this kind of use. First embodiments consisted of cylinders used to lift the bogies. This solution was used in the early days and is the less energy efficient solution. A more interesting solution from the energy and safety point of view is to activate a hanging pendulum system. Besides the activation cylinder, a hydraulic system is composed of a hydraulics power pack with motor, pump, valves. All the components are placed in the under frame of the carboy. A hydraulic solution, like pneumatics, has the advantage that the actuators at both end of the carriage can be mounted on the same pressure main, which ensures that they have the same output as long as no obstacle is blocking the system at one end. This is a major advantage and a safety protection against diagonal wheel unloading that can be produced by two different tilt angles at both ends of the carriage. But a control loop is necessary to ensure that no obstacle is blocking one actuator movement. It is easy to add a system to make the tilt system return into neutral position. Both last arguments are major competitive advantages for the hydro-pneumatic systems against electromechanical ones.
Table 29: Main advantages and drawbacks of hydraulics actuators.
Advantages Disadvantages • Leaks of hazardous fluid • Lower efficiency • Durable actuators • Heat dissipation • Easy to avoid diagonal wheel unloading • Installation of hydraulic power unit • Smaller actuator • Sensitive servo valves • High load capacity • More complex installation • Cheap buying cost • No usual train technology • Weight • Space
5.3 Electro-mechanic actuators Electro-mechanic motors can be used to activate a hanging pendulum or other solution instead of the hydro-pneumatic solutions. The usual embodiment is a linear drive, which is designed as a combination of an electromotor and a planet roller spindle. The adjusting means is located between the superstructure and the bogie. An electric power pack with converter is placed in the under frame just like in the hydraulics solution. In case of electrical alimentation stop, they need battery power pack to continue working. To ensure that both the electrical motors are in the same position, it requires a control loop. Electromotors are also considered to have an advantage over hydraulic and pneumatic drive units because they don’t need to be maintained as often, are easily available, have lower life cycle costs, are more easily assembled and consume less energy, thus being very environment-friendly.
Table 30: Main advantages and drawbacks of electro-mechanics actuators.
Advantages Disadvantages • Clean • Efficient • Safety issues • Less heat removal • Limited acceleration • Easy maintenance • More complex actuator • Easy installation • More complex abort mechanism • No complex valve • More complex electronics • Environmental friendlier • Peak power demands • Controllable
93 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
5.4 Electro-hydraulic actuators
These systems consist of the same components as the electro-mechanical actuators, but the mechanical gear in the actuator is replaced by a pump and a cylinder. Electro- hydraulics seems to be one of the novel possibilities promising future bright use [43].
Table 31: Main advantages and drawbacks of electro-hydraulic actuators.
Advantages Disadvantages • Easy installation • Easy maintenance • Leaks • Combining advantage of both hydraulics • Big actuator and electro mechanic systems • Controllable
5.5 Assessment of actuators
A common argument to flavour electromechanical actuators is the wish of train owners not to have hydraulics onboard, as they have considerable electrical competences, which would be easily expanded. But this argument is not so strong and the buyers tend to be less and less interested in technical choice, but want efficient working solution. But it seems clear that electrical and electro-hydraulic solutions have higher buying cost but less maintenance and drive cost. The maintenance cost is largely unproven for those systems though. Hydraulics is a proven technology, cheap to buy, but have higher operating cost.
94 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
5.5.1 Actuators evaluations
We decided to assess the four different kinds of actuators in a similar manner like the simplified assessment procedure used for the tilt mechanisms. The same scale and weight possibilities were used. The marks were set by Rickard Persson from Bombardier and me. We chose the following assessment criteria: • Purchase cost • Maintenance • Compactness • Safety • Weight • Performance
The results are presented in the following table.
Table 32: assessment of actuators. Design denomination Design denomination Coefficient for cost optimisation Coefficient for safety optimisation Coefficient for optimisation market Pneumatics Hydraulics Electro mechanics Electrohydraulics
Assessment criteria 1. 2. 3. 4. Purchase cost 10.0 4.5 6.5 8.5 7.0 4.5 4.5 Maintenance 6.0 4.5 5.0 9.0 5.0 6.0 7.0 Compactness 5.0 4.5 4.5 5.5 4.5 8.0 8.5 Safety 5.0 10.0 10.0 6.5 10.0 4.5 6.0 Weight 5.5 4.5 5.0 5.5 5.0 8.5 9.0 Performance 5.0 4.5 6.5 3.0 9.0 8.5 9.0 Score X 5.2 5.9 5.4 5.8 Ranking X 4 1 3 2 Score X 5.1 6.6 5.5 6.1 Ranking X 4 1 3 2 Score X 5.1 6.6 5.5 6.2 Ranking X 4 1 3 2 Score global 1.5 1.6 1.5 1.7 Ranking 4 2 3 1
95 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
We note that hydraulics and electro-hydraulics scored best in the assessment. The difference between the two systems is rather low. This is in total agreement with the actual proposed solutions by Bombardier and the products available on the market. The hydraulic systems have the advantage that the cylinders can be connected together and thus the control signal is the same for the two bogies. The cylinder offers simple design to keep the tilt position or to come back to neutral position in case of failure. The electromechanical solutions suffer from their greater difficulties to ensure safety on this particular point. Note that a different tilt angle applied at each bogie causes a possibly very dangerous diagonal wheel unloading. Pneumatic solutions seem only possible where predictive control is in use.
5.5.2 Possible improvement
Most of the applications use a linear activation, but the common output of an electrical motor is rotational, so it would be much more convenient to be able to use it this way with a reduction box.
An interesting possibility to reduce the size of the actuators would be the use of a variable transmission. The forces are higher for high angle than small. Hence, the transmission can be lower at smaller angles of inclination (pitch) and bigger with increasing angles of inclination. A smaller transmission at smaller angles of inclination is desirable, thus reducing the gear losses and enabling small actuator forces to safely bring the superstructure into the untilted initial position. Since a smaller drive with respect to the required permanent power is sufficient at comparable forces based on the angle of inclination, this has an influence on the drive itself as well as on the power electronics and the wiring, thus enabling a more inexpensive design of the tilting mechanism. A smaller drive also requires less installation space. Rotational movement allows also using very cheap positioning captors. This interesting way to minimize the cost of the actuators is presented in the patent US 6 224 190 B1.
96 Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
6 Control
6.1 Requirements of tilt control
The control has the important purpose to tilt the carriage at the right timing while cruising on winding tracks. The tilt movement has to properly match the vehicle position in the curve, especially at entrance and exit of a transition curve in accordance with train speed. The tilt angle has to be changed at adequate speed, not too fast, not too slow and smoothly. The compensation of lateral acceleration and its command has to be carefully designed regarding comfort and motion sickness indicators, with the consequence they can possibly have on limitations of tilt velocity and tilt acceleration. The tilt control should not impair riding comfort while cruising on straight tracks and should be stable while in horizontal curves, avoiding oscillations or reactions to track irregularities.
The dynamic behaviour must also be taken into account in the design of the control loop. This can be achieved with increased knowledge of the system with for example an inverse kinematics model or a Kalman filter. The control must be reliable and work at any time and be monitored to detect any failure. If the systems stop working, the train has to slow down and the tilt has to come back in a neutral position, absolutely avoiding wrong tilt or wrong response, which is highly nauseous and has strong security issues, like passenger loosing balance and risking being hurt.
The requirements on the tilt control system can be summarized as following: • Adaptation to the train speed and its change • Adaptation to the curves parameters • Determination of the compensation ratio and command • Cope with dynamics behaviour • High reliability • Safe
The determination of tilt needs relative to the curve can basically be solved by two different approaches: • reactive tilt: live detection and analysis of the curves parameters with help of sensors and data processing • predictive tilt: command is calculated by an algorithm on the base of curve parameters extracted from onboard track data thanks to the knowledge of the train position Those two different approaches will be further detailed in the next section.
Figure 49 : British Intercity 225 APT with first and fourth car having no tilt under revenue service, the train was withdrawn from service after three days, unknown source.
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6.2 Reactive tilt
Surprisingly, there have been few rigorous studies about control and the control strategy evolved in a very incremental manner [19] until recently and those solutions are still in use in the major parts of the tilting trains. The result is a controlling strategy that is not optimized from a system point of view. The dynamics of train is highly complex. The inputs to the system can be, as seen in the introduction divided into two categories: • Deterministic : given by the ideal track geometry • Stochastic : coming from track irregularities The aim of the suspension is to filter the irregularities ensuring good ride quality. The difficulties of the control design of the tilt are to reach a fast response to deterministic inputs and to cut the response to stochastic one.
The system can use different information as control signal, like lateral acceleration, roll and yaw velocity. They are measured by different sensors like rate gyros and inertia systems. Usually several references are combined.
6.2.1 Nulling control
The first control strategies were based on a feedback loop having transverse accelerometers placed in the car body as inputs. The actuators were driven in a straightforward way to totally cancel the lateral acceleration. The difficulties is that lateral and roll motion are strongly coupled. The system has no possibility to distinguish if the detected transverse accelerations were due to the centrifugal force or to disturbances caused by track irregularities or hunting motion. To obtain a fast enough response, the stability is degraded. The basic idea of a 100% compensation of the lateral acceleration leads to excessively bad ride quality, due to a lack of knowledge of the motion sickness generation and a largely degraded stability due to fast response and ignored dynamic complexity. The nulling control can be improved and become partial with the additional use of signal in the bogie. It can serve as a base for more advanced control strategies [12]. The body feedback suffers from stability issues due to low-frequency movements in the secondary suspension. Table 33 : quantities playing a role in dynamic analysis and their name.
Signal Relation Lateral acceleration When measured in the bogie, it has a relation to the cant deficiency of the track. Change in transition curve, constant on other parts. Can be used as lead value. Yaw velocity Is related to curve radius and speed. Only change in transition curve as lateral acceleration. Can only be used as lead value for tilting if speed and cant are known, measured. Roll velocity Indicates the rate of change of cant, that means that it receives only a non zero value in transition curves. It can be used to detect a change of cant.
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Figure 50 : schema of controller [18].
6.2.2 Command driven
The next step was to move the sensors onto the bogie to detect the curves, where they are fully exposed to track irregularities, because placed under the secondary suspension. This requires filtering the signal. The delay generated by the filters made the response too slow. The delay can be of the order of 1 [s], which doesn’t sound much, but it must be borne in mind that for a train cruising at 200 [km/h] onto a parabolic transition section whose length is 100 [m], the transition is traversed in about 2 [s]. It’s easy to understand how bad the comfort will be.
6.2.2.1 Command driven with precedence
Since the command driven control strategy has a too slow response but a good delayed control signal, it is desirable to handle the time delay. A simple way of handling this delay is the precedence concept. The first car transmits the signal to its following carriage. The signal can be transmitted to all coupled carriages with a computer delay based on the length of carriage and train speed and thus cancelling the data processing delay. This strategy is currently in use by the major European train suppliers. The major drawback of this system is that the first vehicle of the train still suffers from an important delay and much reduced comfort and that the system becomes more complex, it is sensitive to different parameters like speed, length and direction and signal connection between vehicles are needed.
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6.2.3 Advanced control
Ongoing research [10] [12] [18] shows that more advanced control methods could lead to a simplified system, making possible to make local vehicle control. As the communication between wagons would still be required for supervision of the system, those results could at least be used for better comfort in the heading vehicle. The possible control schemes are named below; more information can be found in the named literature. • Model based output estimation controller [12]
• Nulling-based H ∞ controller [12]
• Multiple objective H ∞ / H 2 controller [33] • Fuzzy PD+I controller [10] • Use of inverse kinematics
Figure 51 : schema for possible advanced controller [18].
6.2.4 SWOT analysis The following table summarises the advantages and disadvantages of reactive tilt.
Table 34 : SWOT analysis on reactive tilt.
Strength Weakness • No need for onboard stored data • Delay due to filtering • Simple and robust • Can react to track irregularities • No need for position knowledge • Worsen behaviour for first car • Known systems • Can’t avoid tilt saturation • Low cost Opportunities Threads • Can be used as failure mode for a more • The market can expect more advance system with onboard track • Onboard track information are available information on the market • Advanced control can slightly improve • Improvement possibilities are low even its properties with advanced control
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6.3 Predictive tilt
To improve the major drawback of the roller-type natural tilt system from its major drawback, which is causing nausea in sections with many frequent tight curves when tilting often occurs delayed or too abruptly, the Japanese engineers add a controlled tilt system. This system incorporates an air cylinder. A pneumatic solution, due to its slow response needs an anticipative or predictive command to give good result. This lead to a predictive tilt. This is done by an onboard controller having map and data about all curves, including for example following information: curve radius, alignment, elevation, distance between Automatic Train Protection (ATP) ground units and starting point of transition curves, lengths of transition and circular curves. The tilting control starts at the beginning of the curves to eliminate the time lag in the controlled tilting action or can even start a certain distance before the curve entrance to minimize the roll velocity.
Figure 52 : a Japanese JR Hokkaidō DC283 DMU entering a curve [Wikipedia].
The tilt angle of the pendulum is controlled as to follow the targeted values expressed as a function of the running distance and speed of the car to make the car body roll gently and smoothly. This allows to control the roll velocity and to elaborate an advanced control algorithm taking for example advantage of a motion sickness model, limitation of the tilt system not to saturate before the end of the transition curve, dynamically adapted present tilt in function of coming or passed curves. Some questions can be asked concerning the opportunity of anticipating tilting before transition curves like on the figure below, but no study on motion sickness has been made with such a strategy, but the result on acceleration can be seen hereunder. In Japan the introduction of the actuator on the previously natural tilt system made possible to increase the speed from 80-110 [km/h] to 85-120 [km/h] on curves with tight curve radius of 300 to 600 [m]. The increase is modest, but the comfort increased with less motion sickness and it has to be underlined than those trains ride on narrow gauge. The system is proposed in Europe, by CAF, for example. Hitachi was the first company to offer it commercially in 2000.
101 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Cant deficiency Cant deficiency Cant angle Cant angle Tilt angle Tilt angle Lateral acceleration Lateral acceleration Roll angle (cant+tilt) Roll angle (cant+tilt)
Distance along the track Distance along the track
Figure 53 : motion quantities when tilt is in phase with the transition curve on left, same motion quantities when the tilt saturates during the transition curves on right. [47].
Figure 54 : reduction of the angular velocity of roll due to anticipation of the transition curve thanks to predictive control [Hitachi].
Cant deficiency Cant angle Tilt angle Lateral acceleration Roll angle (cant+tilt)
Distance along the track
Figure 55 : concept of predictive tilt on left [Hitachi], motion quantities in this case [47].
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6.3.1 Positioning
The exact knowledge of the position of the train in addition to a map with the track characteristics makes possible an advanced control algorithm of the tilting system. In comparison to mobile robotics, the given problem of positioning is rather simpler than driving in an open space. It is more related to the Automated Guided Vehicle application. The system of a train cruising on track is highly constrained. The major difficulties result in the high speed, the accuracy requirements believed in a span of a few meters [10] in longitudinal direction, plus the necessity to know on which track the train is when several tracks are laid in parallel. The exact position can be found for example from exact distance travelled and how the turnouts were set during travel when a map is available. This section presents different possible sensors and techniques that could be used for position detection to control the tilt. The many possible solutions can roughly be categorized into two groups: relative and absolute position measurements. In most cases, both methods are combined.
6.3.1.1 Relative position measurements
6.3.1.1.1 Odometry
Odometry is the most widely used navigation method for positioning in the mobile robotics world. It is inexpensive, good short-term accuracy and allows very high sampling rates. The vehicles linear motion is calculated from measured wheel rotation. However, the idea of odometry is the integration of incremental measured motions over time, which leads to the accumulation of errors through time. The errors are due for example to sensors measurements errors or wheel slippage. Several methods exist to fuse odometric data with absolute position measurements to obtain more reliable position estimation [13]. New algorithms developed with fuzzy techniques can reach good measurement of speed or distance thanks to incremental encoder type sensors. The error is less than 3% [49].
6.3.1.1.2 Inertial navigation
Despite the availability of inertial sensors, namely accelerators and gyroscopes, they are of lesser use for trains than for mobile robots. They can be used to detect the curvatures of the tracks and thus finding the position of the train through map matching. As seen ahead they can drive the tilt system directly in reactive control use.
6.3.1.2 Absolute position measurements
6.3.1.2.1 Magnetic compasses
The use of magnetic compasses provides absolute measurement of heading. Unfortunately the earth magnetic field is disturbed near power lines or steel structures making all kind of magnetic compass useless for a train.
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6.3.1.2.2 Beacons
Active or passive beacon navigation systems are the most common navigation aids on ships and airplanes as well as on commercial mobile robot systems. They are equally largely used in Japan to control the tilt trains. Passive beacons are less costly, but they can only be used as milestones. Active beacons can be detected reliably and provide accurate positioning information with minimal processing. It has high reliability but suffers from high installation and maintenance costs, in particular for active beacons. The beacons could be based on the existing or under construction signalling and communication systems. They represent an interesting tool in combination with map and distance measurements.
Figure 56 : passive beacons, Bombardier.
6.3.1.2.3 Global positioning system (GPS)
The Global Positioning System (GPS) has been developed by the US Department of Defence for outdoor navigation. The system is composed of 24 satellites, including 3 spares, which transmit encoded RF signals – basically it’s an active beacons system. Using advanced triangulation methods, ground-based receivers can compute their position by measuring the travel flight of the satellites RF signals, which include information about the satellites momentary location. Knowing the exact distance from the ground receiver to the three satellites theoretically allows for the calculation of receiver latitude, longitude, and altitude. The US government deliberately applies small errors in timing and satellite position to prevent a hostile use of GPS; this is called for selective availability. This degrades the accuracy to around 100 [m].
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The effect of selective availability can be eliminated through the use of a Differential Global Positioning System (DGPS). The principle is based on the fact that two GPS receivers placed in fairly close proximity, say 10 [km], will experience the same error when reckoning their position based on the same emitter satellites. If one of the two receivers is placed on a known ground position, the difference between the real position and the calculated position will give a vector making possible to increase the accuracy of the positioning of the second receiver with unknown position. Typical accuracy for DGPS is 4-6 meters, and this increases when the distance to the fixed reference ground station is decreased. On a limited area like a harbour or an airport, DGPS has demonstrated capability of 1 meter accuracy in real time for vehicle localisation. Experts use DGPS to achieve centimetre accuracy, but this practice needs significant post processing of the collected data.
The GPS suffers from its owner, who could switch it on or off, or decrease its accuracy when needed. The future realisation of a European positioning system and a project for a Russian one will ease this question. Applied to train technology and due to their high speed of the receiver, the accuracy of GPS alone cannot be expected better than 34 [m] [13], with the major restriction of loosing signal when travelling through tunnels. The believed accuracy required for activating the tilt is 4 [m]. This can be reached when fusing DGPS information with other information like map matching, odometry and/or sideway beacons. Note that a precision of 4 [m] can’t tell you on which line the train is circulating, this precision can be raised with multiple inputs processing.
6.3.1.2.4 Landmark navigation
To determine its position, a mobile vehicle can spy its environment with its sensors. For this purpose, natural or artificial landmarks can be used. Natural means in this context existing before the sensor, it doesn’t mean naturally grown. Artificial are added to the environment just having the purpose of helping positioning, they could be assimilated to passive beacons. In any case, a database of landmarks and their location in the environment must be available and maintained.
Most of the landmark navigation for mobile robotics use video. But it offers no good solutions for a train, where lighting and weather condition change a lot. However, the track is a very structured environment, and the sleepers, fasteners and sleeper passing frequency can be used to detect the localisation. Special beacons could be added to determine absolute position and other could be added at turnouts to detect on which line the train drives and when it changes.
6.3.1.2.5 Map based positioning
A system using map based positioning senses its environment to generate a local map and refers to a global map previously stored in a memory. For a train, the elements for map based positioning could be curvature, cant, orientation change, beacons. The map can be generated by measurements or automatically generated from a previous ride. An advanced thinkable solution would be an artificial intelligent system able to create the most suitable parameters in function of the track and comfort and motion sickness models. In most cases, several sensors information can be fused to give the actual position with higher accuracy.
105 Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
6.3.2 SWOT analysis
The following table summarises the advantages and disadvantages of predictive tilt using route files and positioning.
Table 35 : SWOT analysis of predictive tilt.
Strength Weakness • Use full advantage of the tilt • Allow making complex algorithm • No delays, no saturation, anticipation • Need for a positioning system possible • Higher complexity • Not only the local position, but passed • System can lose its position and coming curves known • Track data needs previously to be • Robust against track irregularities, no stored and updated unintentional tilt motions • No saturation of the tilt system during the transition curve Opportunities Threads • Motion sickness models can be added to advanced algorithm • Positioning systems are affordable and • Competitors already use such systems proven technology • The market may require it • Potential for adaptive algorithm is huge • Self learning train • Synergy with modern signalling systems
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6.4 Comparative diagram
Reactive tilt Predictive tilt
y y eed eed osition p p p uts p Train kinematics Train kinematics Train s Train Train kinematics Train kinematics Stored track data Yaw velocit Train s Lateral acceleration Lateral acceleration Roll velocit In
g Filtering Model sickness & comfort model
Algorithm Advanced algorithm Processin
uts uts Local optimal tilt angle Global optimal tilt angle p Out
Figure 57 : possible inputs and algorithms.
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7 Conclusions and further work
7.1 Conclusions
This work has mainly focused on mechanisms and their possible simplification aiming at a better ratio between performance and costs. It presents a state of the art of the tilt mechanism and proposes some new designs. It is foreseen that the existing systems may continue being the preferred embodiments in the future. However radial flexible elements can offer an extremely interesting new constructive solution that could be very cheap. The active secondary suspension may also have some potential to exploit.
The actuator situation will almost without doubt remain unchanged. The electromechanic motors difficulties to compete with hydraulics on safety issues are remaining, hydraulics and electro-hydraulics will probably stay as the favourite solutions.
Finally, the market dominant reactive control may evolve to predictive. While the figures to improve reactive tilt are much reduced, predictive tilt offers possibilities to improve comfort very efficiently. Because this technology is featured onboard competitors’ products, the market risks demanding it. Positioning technology seems to have matured enough to easily implement such systems and synergy can be made with new signalling systems.
7.2 Further work
As new design showed having good potential, a feasibility study should be conduced on the radial flexible elements to see assess if it is interesting to go further on with this idea.
Advanced performance strategy with improved comfort can become a major selling argument for future tilting train, therefore it would be wise to develop put on the market new products. I believed that investment in realising an efficient predictive tilt will be the most profitable.
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Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
8 Acknowledgements
I want to specially acknowledge Professors Paul Xirouchakis at EPFL and Jan-Gunnar Persson for their efforts to organize and supervise this master thesis project. Special thanks to Bombardier Transportation at Västerås for offering me the chance to work on this interesting and challenging project and for hosting and financial support, with a dedication to Henrik Tengstrand, Director R&D.
A special thank to PD Dr.-Ing. Sebastian Stichel and M.Sc. Rickard Persson for their availabilty, time, advices and support.
I want to thank you everyone that helped me organising and participated to the Brainstorming seminar for your time and inputs, with a special acknowledgement to Stefan Björklund, Reymond Clavel and Ian Anthony Stroud.
Thank you to the persons that helped me to correct my English, Valérie Chavez, Florian Jousset, Raphaël Pythoud and Christophe Roulin.
Thank you to Telly Moussavi for distracting me with several Swiss fondues and an Umeå final vacation to write the final report in calm and cold – ideas grow better below zero.
Västerås, 23rd February 2007
Frédéric ROCHAT, microtechnics engineering.
Figure 58 : View of Öresund Bridge linking Denmark and Sweden, Bombardier.
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Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
9 Bibliography
9.1 Publications
[1] Andersson, E., Berg M., Stichel S. : 2005. Rail vehicle dynamics, KTH Railway Technology, Stockholm. [2] Andersson, E., Berg M. : 2003. Järnväagssystem och spårfordon, Del 1 : Järnvägssystem, KTH Railway Technology, Stockholm. [3] Andersson, E., Berg M. : 2003. Järnväagssystem och spårfordon, Del 2 : Järnvägssystem, KTH Railway Technology, Stockholm. [4] Förstberg, J. : 2000. Ride comfort and motion sickness in tilting trains, KTH Railway Technology, Stockholm. [5] Förstberg, J. : 1996. Motion-related comfort levels in trains, KTH Railway Technology, Stockholm. [6] Förstberg, J. : 1996. Rörelserelaterad komfortnivå på tåg, KTH Railway Technology, Stockholm. [7] Persson, R. : 2006. Tilting trains, a description and analysis of the present situation, not yet published. [8] Thomas, D. : 2006. Introduction of semi active or active lateral suspension in the Regina train, Darmstadt Technische Universität, Darmstadt. [9] UiC : 1998. First report on tilting train technology, the stat of the art. , UiC Paris, High speed division. [10] Zamzuri, H, Zolotas, A. C., Goodall, R. M. : 2005. Tilting control system using fuzzy PD+I controller, Loughboough University, Departement of EEE. [11] Henke, M., Liu-Henke, X., Lückel, J., Grotstollen, H., Jäker, K.-P. : 2000. Design of a railway carriage, driven by a linear motor with active suspension/tilt module. New railway system Paderborn, University of Paderborn, Germany. [12] Zolotas, A. C., Goodall, R. M., Halikias, G. D. : 2003. New control strategies for tilting trains. Loughborough University, Departement of EEE. [13] Sasaki, K : 2005. Position detection system using GPS for carboy tilt control, QR of RTRI, Vol. 46, No. 2, Japan. [14] Enomoto, M. Et al, RTRI : 2005. Development of tilt control system using electro- hydraulic actuators, Japan. [15] Förstberg, J., Andersson, E., Ledin, T. : 1998. Influence of different conditions for tilt compensation on symptoms of motion sickness in tilting trains, Brain Research Bulletin, Vol. 47, No. 5. pp. 525-535, USA. [16] Mei, T. X., Nagy, Z., Goodall, R. M., Wickens, A. H. : 2002. Mechatronic solutions for high-speed railway vehicles, Control Engineering Practice 10, pp. 1023-1028. [17] Goodall, R. M., Kortüm, W. : 2002. Mechatronic developments for railway vehicles of the future, Control Engineering Practice 10, pp. 887-898. [18] Zolotas, A. C., Goodall, R. M. : 2000. Advanced control strategies for tilting railway vehicles, UKACC International Conference on Control, University of Cambridge, 6pp, ISBN : 0 85296 240 1 [19] Goodall, R. M., Zolotas, A. C., Evans, J. : 2000. Assessment of the performance of tilt system controllers, Proc of the Railway Technology Conference, C580/028/2000, ImechE, Birmingham, UK, pp 231-239 [20] Golding, J. F., Bles, W., Bos, J. E., Haynes, T., Gresty, M. A. : 2003. Motion sickness and tilts of the inertial force environment : active suspension systems vs. active passengers, Aviation, Space and Environmental Medicine, Vol. 74, No. 3.
II Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
[21] Goodall, R. : 1999. Tilting trains and beyond – the future for active railway suspension, Part 1 : Improving passenger comfort, Computing & control engineering journal, pp 153-161. [22] Goodall, R. : 1999. Tilting trains and beyond – the future for active railway suspension, Part 2 : Improving stability and guidance, Computing & control engineering journal, pp 221-230. [23] Kent, S., Evans, J. : 1999. Hardware-in-loop simulation of railway vehicles with tilting and active suspension systems, Vehicle system dynamics supplement 33, pp 453-463. [24] Goodal, R. M., Pearson, J. T., Pratt, I : 1996. Design of complex controllers for active secondary suspensions on railway vehicles, Vehicle system dynamics supplement 25, pp 217-228. [25] Stribersky, A., Müller, H., Rath, B. : 1998. The development of an integrated suspension control technology for passenger trains, Proc Instn Mech Engrs; Vol. 221, Part F, pp 33-42. [26] Electromechanical tilting systems for passenger trains, 2006, ESW Extel Systems Wedel, Jenoptik-Group [27] Pratt, I., Goodall, R. M. : 1997. Controlling the ride quality of the central portion of a high-speed railway vehicle, Proceedings of the American control conference, AACC, Albuquerque, New Mexico, USA. [28] Kortüm, W., Goodall, R. M., Hedrick, J. K. : 1998. Mechatronics in ground transportation – current trends and future possibilties, Annual reviews in control 22, pp 133-144. [29] Goodall, R. M. : 1997. Active railway suspensions : implementation status and technical trends, vehicle system and dynamics, 28, pp. 87-117. [30] Pollard, M. G. Simons, N. J. A. : 1984. Passenger comfort – the role of active suspensions, Proc Instn Mech Engrs Vol 198D No 11, pp 161-175. TM [31] The New PendolinoP ,P 2006, Alstom. [32] Graber, C. : 2006. High-speed railways in Spain, www.technologyreview.com/spain/train [33] Zolotas, A. C., Halikias, G. D., Goodall, R. M. : 2000. A comparison of tilt control approaches for high speed railway vehicles, Prc ICSE 2000, Coventry, UK, vol 2, pp 632-636.5 [34] UiC : 2004. Second report on tilting train technology, the stat of the art. , UiC Paris, High speed division, unpublished. [35] Nagai, M., Yoshida, H., Sueki, T., 2004. Study on car body tilting system using variable link mechanism (Perfect tilting condition and tilting control), JSME International Journal, Series C, Vol. 47, No. 2, pp 471-476. [36] Railway technical research institute, East Japan railway culture foundation, 2001. Japanese railway technology today, East Japan railway culture foundation [37] Sorge, F., 2002. Geometrical analysis of self-compensating suspension systems for railcar engineering, Proc Instn Mech Engrs Vol 216 Part F, J Rail and Rapid Transit, IMechE, pp 185-196 [38] Haigermoser, A., 2002. Schienenfahrzeuge, Vorlesungsskriptum, Technischen Universität Graz. [39] Mun, H.-S., You, W.-H, ???. Development for simple tilting mechanism with rounded section car body, Uiwang-City, Kyonggi-Do, Korea [40] Pearson, J. T., Goodall, R. M., Pratt, I., 1998. Control system studies of an active anti-roll bar tilt system for railway vehicles, Proc Instn Mech Engrs Vol 212 Part F, IMechE, pp 43-60
III Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
[41] Borenstein, J., Everett, H.R., Feng, L., Wehe, D., ????. Mobile robot positioning – sensors and techniques, Invite paper for the journal of robotic systems, Special issue on mobile robots, Vol 14, No 4, pp. 231-249. [42] Schneider, R., 1998. Pantograph for tilting trains, Fiat Schienenfahrzeug, IEE- 98.10, FSS 7455 RS: 24.09.98. [43] Enomoto, M., Kamoshita, S., Kamiyama, M., Sasaki, K., Hamada, T., Kazato, A., 2005. Development of the tilt system using electro-hydraulic actuators, Railway Technical Research Institutes, RTRI Report, April 2005. [44] Malvezzi, M., Toni, P., Allotta, B., Colla, V., 2001. Train speed and position evaluation using wheel velocity measurements, IEEE, International conference on advanced intelligent mechatronics proceedings, Como, Italy. [45] Bartel, C., Foster, D., 2002. Life cycle motion base cost comparison : electric vs. hydraulic, Industrial controls division, Moog inc. [46] Scales, B. T., 2004. The hi-lo bi-track system. ASME/IEEE Joint rail conference, USA. [47] Kufver, B., Persson, R. 200?. On enhanced tilt strategies for tilting trains, ??? [48] Förstberg, J., Thorslund, B., Persson, R., 2005. Nordic field tests with tilting trains. European commission competitive and sustainable growth programme – Fast and comfortable trains (FACT), Report D6a. UIC, Paris. [49] Malvezzi, M., Toni, P., Allotta, B., Colla, V., 2001. Train speed and position evaluation using wheel velocity measurements, IEEE/ASME International conference on advanced intelligent mechatronics proceedings.
9.2 Railway gazette international
• TTX is coming, Railway gazette international, June 2006 • French start tests with new tilting TGV Bogie, Railway gazette international, July 1999 • AGV : the next generation – high speed trains, Railway gazett international, May 2000 • CAF tests new compact body tilting system, Railway gazette international, September 1999 • Fastech 360 prototypes prob ultra high speed territory, Railway gazette international, November 2005 • Fastech 360 twins herald speed-up to the north, Railway gazette international, May 2006 • Alstom unveils next generation of Pendolino, Railway gazette international, July 2004 • The complexities of high-speed rail : high speed rail is now well established in western Europe and eastern Asia, but other parts of the world remain to be convinced of the economic benefits that high-speed trains can bring, Railway gazette international, November 2005 • World high-speed rail market set for strong growth, Railway gazette international, May 2005 • Speed records are tumbling, Railway gazette international, October 2006
9.3 Websites
• www.bombardier.com • www.alstom.com • www.siemens.com • www.caf.com • www.talgo.com • www.hitachi.com • www.wikipedia.org
IV
Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
10 Appendices
10.1 Table of illustrations
FigureTU 1 : many ways to the train station, photo Bombardier.UT ...... 3
FigureTU 2 : track cross section and its components ([1], p. 2.1).UT ...... 4
FigureTU 3 : track cross section and its components with explanations and illustrations of their
functions ([36], p. 84).UT ...... 4
FigureTU 4 : diesel powered tilt train cruising on narrow gauge in Queensland, Australia. Such a train
derailed in November 2004, causing unbelievably no casualties, source Wikipedia.UT ...... 7
FigureTU 5 : cant ([1], p. 2.8).UT ...... 8
FigureTU 6 : the four kinds of track irregularities ([1], p. 2.17).UT ...... 9
FigureTU 7 : reduction of the negative effect of track irregularities thanks to bogie construction
([36], p. 20)...... 12UT
FigureTU 8 : difference between articulated and non articulated bogies ([36], p. 20).UT ...... 12
FigureTU 9 : the two different types of bogies ([36], p. 20).UT ...... 13
FigureTU 10 : a bolster bogie on the left and a bolsterless bogie on the right ([36], p. 20).UT ...... 13
FigureTU 11 : a bogie with no car body bolster, but with a tilting bolster under the secondary
suspension, constructed by Bombardier.UT ...... 14
FigureTU 12 : lateral view of a bolsterless bogie with anti-yawing damper, Bombardier.UT...... 14
FigureTU 13 : wheel hunting on left ([36], p. 20) and a linked-type forced steering bogie on right
([36], p. 33)...... 15UT
FigureTU 14 : the first known patent on a tilting system registered in 1938, US 2 225 242.UT ...... 16
FigureTU 15 : X2000 cruising, BombardierUT ...... 16
FigureTU 16 : The hi-lo bitrack system, [46].UT ...... 18
FigureTU 17 : maximum speed for tilting train in function of first year of commercial revenue ([7],
p.9)UT ...... 18
FigureTU 18 : Tilting train in the [250 km/h] market segment, source Kjell Sundqvist.UT ...... 19
FigureTU 19 : Lateral acceleration and vertical acceleration at car body and track level for a conventional train with first no cant (right up), the cant effect (left down), and for a tilt train
(right down), the sway in the suspensions is not considered.UT ...... 22
FigureTU 20 : on the left, a conventional train showing the effect of centrifugal force when it cruises faster than equilibrium of cant allows. On the right, a passive tilting in the same situation,
source Talgo.UT ...... 24
FigureTU 21 : acceleration at the passenger level when cruising on a transition and super elevation
curve followed by a canted horizontal curve for a conventional train.UT ...... 26
FigureTU 22 : acceleration at the passenger level in the same situation as above. Speed has been kept constant. We supposed that the tilt system enters in function synchronously with the
transition curve. Note the reduction in lateral acceleration and the increase of roll velocity.UT ..26
FigureTU 23 : Example of weighting functions. ([38], p 135).UT ...... 30
FigureTU 24 : View of the pantograph of an ICE, Bombardier.UT ...... 37
FigureTU 25 : from left to right, the traditional diamond-shaped pantograph, a single-armed one and
Japanese wing pantograph, [36, p. 8-9].UT ...... 38
FigureTU 26 : a sectional view of pantograph moved passively by wires, [EP 0 485 273].UT...... 39
FigureTU 27 : from left to right, a bogie mounted pantograph, a roof mounted with rope passive
isolating from the tilt, and finally an active moving pantograph [42].UT ...... 39
FigureTU 28 : ICN cruising in the Neuchâtel area. Attentive viewer can see the pantograph in a
vertical orientation on the forth carriage, photo Bombardier.UT ...... 39
FigureTU 29 : objective tree of all requirements the tilt system has to fulfil.UT ...... 40
FigureTU 30 : major objectives a tilting system has to fulfil.UT ...... 41
VI
T
Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
FigureU 31 : the cost-effective branch of objective tree.U ...... 42
FigureU 32 : the safety branch of objective tree.U ...... 43
FigureU 33 : the reliability branch of objectives tree.U ...... 44
FigureU 34 : major objectives a tilting system has to fulfil.U ...... 45
FigureU 35 : the maintainability branch of objective tree.U ...... 46
FigureU 36 : Tilting ICE, photo Bombardier.U ...... 46
FigureU 37 : View of the passive tilt system of a Talgo train, photo Talgo.U ...... 48
FigureU 38 : Advantage of a hybrid system, source Hitachi.U ...... 49
FigureU 39 : Comparison of natural tilt and actively supported tilt, source Hitachi.U ...... 49
FigureU 40 : Two different embodiments of the pendulum system, source Talgo and Bombardier. 50U
UFigure 41 : construction comparison between a hybrid Japanese solution and a hanging pendulum
active solution, source Hitachi.U ...... 51
FigureU 42 : two different embodiments of the same tilt system with under or above the secondary
suspension tilt mechanism [DE4423636].U ...... 52
FigureU 43 : illustration of the profile reduction in function of the position of the rotation centre. .53U
UFigure 44 : profile reduction in function of the tilt angle, with a central rotation centre.U ...... 54
FigureU 45 : profile of a Bombardier’s Regina train untilted and tilted with 6° with gauge limits,
source Kjell Sundqvist.U...... 54
FigureU 46 : different possibilities for positioning of the centre of tilt for passive systems [EP 0 683
081 A1].U ...... 55
FigureU 47 : diagram presenting the cost in function of the market and safety optimisation.U ...... 84
FigureU 48 : schema of the route of the ELECTRE analysis, when the thresholds are set U S A = 1.0 U
and U SC =0.1 in two different views.U ...... 91 U
FigureU 49 : British Intercity 225 APT with first and fourth car having no tilt under revenue service,
the train was withdrawn from service after three days, unknown source.U ...... 97
FigureU 50 : schema of controller [18].U ...... 99
FigureU 51 : schema for possible advanced controller [18].U ...... 100
FigureU 52 : a Japanese JR Hokkaidō DC283 DMU entering a curve [Wikipedia].U ...... 101
FigureU 53 : motion quantities when tilt is in phase with the transition curve on left, same motion
quantities when the tilt saturates during the transition curves on right. [47].U ...... 102
FigureU 54 : reduction of the angular velocity of roll due to anticipation of the transition curve
thanks to predictive control [Hitachi].U ...... 102
FigureU 55 : concept of predictive tilt on left [Hitachi], motion quantities in this case [47].U ...... 102
FigureU 56 : passive beacons, Bombardier.U ...... 104
FigureU 57 : possible inputs and algorithms.U ...... 107
FigureU 58 : View of Öresund Bridge linking Denmark and Sweden, Bombardier.U ...... 110
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Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
10.2 Table of tables
TableU 1 : important vehicles in tilt train development ([7], p.8)U ...... 17
TableU 2 : different train prototypes speed record around the world, all without tilt..U ...... 20
TableU 3 : quantities playing a role in dynamics analysis and their names.U ...... 20
TableU 4 : typical values of acceleration in curves, ([7], page 6).U ...... 25
TableU 5 : Motion quantities that probably influence ride comfort in general. Lateral and vertical
acceleration are referenced to the car body ([4], page 22)U ...... 32
TableU 6 : advantages and disadvantages table of passive tilt system.U ...... 48
TableU 7 : advantages and disadvantages of hybrid tilt.U ...... 49
TableU 8 : advantages and disadvantages of active tilt systems.U ...... 50
TableU 9 : comparison table of passive and active tilt.U ...... 51
TableU 10: overview of all possible tilt mechanisms...... 78U
TableU 11: systems to be assessed.U ...... 79
TableU 12: correlations between different criteria; 3 marks a strong correlation, 2 a middle, 1 a
weak one, empty box none.U ...... 81
TableU 13 : assessment of the 9 selected solutions under the whole criteria procedure.U ...... 82
TableU 14 : performance index.U ...... 83
TableU 15 : table of assessment of the 9 selected solutions under the simplified assessment
procedure.U ...... 85
TableU 16 : scale used for ELECTRE.U ...... 86
TableU 17 : ELECTRE, weight, scale and assessment main table.U ...... 87
TableU 18: ELECTRE concordance table.U ...... 88
TableU 19: ELECTRE discordance table.U ...... 88
TableU 20 : U S A = 0.4U U SC =0.8U U ...... 89
TableU 21 : U S A = 0.4U U SC =0.6U U ...... 89
TableU 22 : U S A = 0.4U U SC =0.4U U ...... 89
TableU 23 : U S A = 0.6U U SC =0.4U U ...... 89
TableU 24 : U S A = 0.8U U SC =0.4U U ...... 90
TableU 25 : U S A = 0.9U U SC =0.4U U ...... 90
TableU 26 : U S A = 1.0U U SC =0.1U U ...... 90
TableU 27 : U S A = 1.0U U SC =0.0U U ...... 90
TableU 28: Main advantages and drawbacks of pneumatics actuators.U ...... 92
TableU 29: Main advantages and drawbacks of hydraulics actuators.U ...... 93
TableU 30: Main advantages and drawbacks of electro-mechanics actuators.U ...... 93
TableU 31: Main advantages and drawbacks of electro-hydraulic actuators.U ...... 94
TableU 32: assessment of actuators.U ...... 95
TableU 33 : quantities playing a role in dynamic analysis and their name.U ...... 98
TableU 34 : SWOT analysis on reactive tilt.U ...... 100
TableU 35 :U SWOTU analysis of predictive tilt.U ...... 106
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Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
10.3 Proposed task
Simplified tilt 2006-10-12
This work proposal is connected to development of a new and simplified tilt for rail vehicles. Background Growing competition from other means of transportation has forced railway companies throughout the world to search for increased performance. Travelling time is the most obvious performance indicator that may be improved by introducing high-speed trains. High-speed trains require straight track or at least tracks with large curve radii and long transition curves not to impair the ride comfort, another performance indicator. Building new tracks with large curve radii is costly and can only be justified where the passenger base is large. Trains with capability to tilt the bodies inwards the curve is a less costly alternative than building new tracks with large curve radii. The tilt inwards reduces the centrifugal force felt by the passengers, allowing the train to pass curves at enhanced speed with maintained ride comfort. The benefit of tilting trains is the improved curve speed capability, but to what cost? New Automatic Train Protections (ATP) systems remove the rigid classes of non-tilted and tilted vehicles can this open for “limited” tilted trains? Are there other solutions that give better ratios between benefit and cost? Main tasks 1. Literature study of existing solutions - mechanics - activation - control 2. Compare existing solutions on cost benefit base 3. Propose improvements. 4. Propose areas for further investigation.
XII Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
10.4 Proposed planning
Master thesis 2006-2007 Titel : Simplified tilt Supervisor at Bombardier : Sebastian Stichel Professor KTH : Jan-Gunnar Persson Professor EPFL : Paul Xirouchakis Assistant : Vincent Capponi Candidate : Frédéric Rochat
Planning : version 27 October 2006 Important dates : Start : 23 October 2006 End and final repport due : 23 Februari 2007 Final presentation : between the 12 March and 19 March 2007
November December January February 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 semaine # 43 44 45 46 47 48 49 50 51 52 1 2 3 4 5 6 7 9 12 Nov 19 Nov 13 Nov 26 Nov 20 Nov 27 Nov 10 Dec 17 Dec 11 Dec 24 Dec 18 Dec 31 Dec 25 Dec 11 Feb 18 Feb 12 Feb 23 Feb 19 Feb 14 Jan 21 Jan 15 Jan 28 Jan 22 Jan 29 Jan 29 Oct 23 Oct 30 Oct 5 Nov 6 Nov 3 Dec 4 Dec 4 Feb 4 Feb 5 Feb 7 Jan 1 Jan 8 Jan dates
Introduction to theme Brainstorming x Possible solutions Litterature study Existing solution
-mechanics
-activation
-control
Comparaison cost benefits Improvement
Spare time
Activity and intermediate repport
Final report
Meeting Professor x x x Persson Meeting Professor Xirouchakis x x x x
XIII Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
10.5 Brainstroming seminar
List of inputs ideas :
A inverse four bar mechanism Transforming a linear movement in rotation The centre of rotation can be tuned
Using a paralellogram structure
A Watt’s mechanism
Using the four bar mechanism with an eccentric
XIV Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
An active torsion bar With inversion of the moment with a motor gear, or just an inversor
Have a close look to automobile vehicle suspension
A possible interesting way to look at to decrease the cost : the use of flexure element.
A mechanism presented in the document : Study on car body tilting system using variable link mechanism (Perfect tilting condition and tilting control)
Another mechanism presented in the document : Geometrical analysis of self-compensating suspension systems for railcar engineering
A possible way is to use coupling between different motions, not only thing in plane. Bennet kinematics
To be creative, it’s proposed to make subclassification of the different existing systems in regards to : • Degrees of freedom • Centre of rotation / centre of mass • Coupling motion • Flexible elements.
XV Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Cost effective : squeeze down the numbers of components
Primary supension ? Torsion bar in the primary suspension ?
Moving the weight ?
To store energy ?
Actuators : • Hydraulics • Electrohydraulics • Piezoelectrics ? • Electromechanics
• Linear • Rotational
Using transmission/reduction from rotary to linear.
Using variable rigidity in the suspension :
Changing the spring constant
Transform a linear pneumatic motion to a rotation :
Rheological fluid.
Active anti-roll in cars.
Use a morphological matrix to sort the generated ideas.
Above or under the secondary suspension ? Possibility in the primary suspension ?
XVI Diploma thesis 2006-2007 Frédéric ROCHAT Simplified tilt
Assessments criteria : • Space • Weight • Angle of tilt • Space • Steered internally/externally • Updating infrastructures / refurbishments of the tracks • Maintenance • Need to return to zero position in case of failure. • Force requirements + rough estimation • Ratio cost/performance • Power consumption • Safety
Bombardiers preferred actuation : compact hydraulics
Patents will be opened shortly
Establishment of the state of the art Possibility for new or simplified system ? Pop up with new ideas ? Identify potential between existing solution ? Preferred solution ?
XVII Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
10.6 Patents study
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Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Classification Title Demander Year Interest Binder 1 EP 0 844 159 A1 Link tilt device and a link tilt bogie Alstom 1997 Mechanism Angular stiffness between the bogie frame and vehicle body is predetermined. US006108596A Process and device for the control and/or regulation of wagon body tilt systems 1998 Control Utilisation of parameters limits in addition to a direct and inverse kinematics model. FR 1 549 521 Dispositif de correction d’assiette pour véhicules ferroviaires 1967 **** Mechanism Passive system EP 0 713 817 A1 Railroad car body rotation control system Fiat 1995 Control Control of hydraulic cylinders with modulated derivative coefficient. DE 0 287 821 Schienenfahrzeug mit Querneiguguseinrichtung 1998 ***** Mechanism Tilt with pendulum realize though the secondary suspension, with anti-roll. DE 44 23 636 A1 Neigevorrichtung für Schienenfahrzeuge Siemens 1996 **** Mechanism Pendulum, vertical activation CH 677763 A5 Wankstützvorrichtung für Fahrzeuge 1988 *** Suspension Anti-roll with damping function DE 37 11 907 A1 Gleisbogenabhängige Wagenkastenneigungsteuerung för Luftfeder-Drehgestelle 1987 Mechanism Lifting system FR 2 102 922 Perfectionnements apportés aux suspensions pour véhicules à grande vitesse, notamment 1970 H ferroviaires. Mechanism Passive and old days mechanics FR 2 028 213 Véhicule ferroviaire pour trains circulant à grande vitesse 1970 H Mechanism Mechanical complex system WO 95/26291 Anti-roll support for rail vehicles with a transverse tilting device Talbot 1995 ***** Anti-roll Talbot EP 0 189 382 High speed railway vehicle with a variable-attitude body Fiat 1986 Mechanism Fiat ferroviata, hydraulic, verticals US005222440 Tilt compensator for high speed vehicles, in particular rail vehicles SIG 1989 Mechanism SIG, passive tilt, with modified roll bar, complex construction US0035947A1 Railway rolling stock 2001 ***** Anti-roll Active anti-roll bar EP 0 693 081 A1 A bogie equipped with a body-tilt system for a railway car 1994 ***** Mechanism Top rolling systems, active US 6,244,190 B1 Tilting mechanism MOOG 2001 ***** Mechanism Transmission coupling, electromotor, crankshaft. FR 2.054.907 Perfectionnements apportés aux véhicules se déplaçant sur une piste 1969 Mechanism Not very interesting… - FR 2 748 979 Dispositif de pendulassions de véhicules articulés, rame de véhicules et véhicule comprenant un tel Alstom 1996 **** dispositif Mechanism Différence angulaire de pendulaisons, véhicules articulés. FR 2 434 739 Véhicule sur rails 1978 Anti-rolls Tilting based on anti-rolls bars. 1978. DE 44 23 638 A1 Vorrichtung zur Steuerung eines Wagenkastens Siemens 1994 *** Mechanism Système de levier, passif ou actif, siemens.
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Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Classification Title Demander Year Interest Binder 2 FR 2 284 495 Dispositif de sécurité pour véhicule inclinable 1974 - Mechanism Not interesting US 3,717,104 Active roll controlling truck stabilizing mechanism 1970 - Mechanism Not very different 4 bars systems, with ressort to pull back the system US 5,295,443 Arrangement for tilting a rail bound vehicule in track curves ASEA 1990 *** Control One control valve, correlation to detect transition curves FR 2 831 126 A1 Procédé de contrôle sécuritaire de la pendulatation d’un véhicule ferroviaire Alstom 2001 **** Control, gabarit Limitation de la pendulation en fonction du canton de voie. WO 01/32491 A1 Comfort monitoring method and system for a tilting train Bombardier 2001 **** Control Monitroing fault. US 6,622,637 B2 Arcuate tilting mechanism for high speed trains 2002 - Mechanism Funny EP 0 557 893 A1 A system for controlling the rotation of the body of a railway vehicle about its longitudinal axis Fiat 1992 ***** Control Fiat Ferroviaria, control unit from the pendolino FR 2 741 026 Système de basculement pour véhicule ferroviaire CAF 1995 ***** Control Description of control with stored track data and inverse kinematics US 845 899 Improvements in or relating to railway cars or carriages 1957 *** Mechanism Suspension with passive trapezoid tilting GB 525 858 Suspension system for vehicles 1938 H Mechanism Talgo similar US 2 225 242 FR 71.34511 Dispositifs pour l’oscillation de la caisse de véhicules sur rails JNR, Japan 1970 *** Mechanism Rolling system, longeron central EP 1 035 000 A2 Neigesteuerung für ein Schienenfahrzeug Daimler 2000 ***** Control Onboard track data and positioning system JP2002264806 [Japanese] 2002 ***** A naturally controlled system adjusting air springs JP6056034 Car body tilting device for rolling stock 1994 ***** Mechanism Active tilting bar FR2122210 Perfectionnements aux véhicules guidés le long d’une voie, notamment aux véhicules de chemins de 1973 - fer - Butée mécanique changeante en fonction de la pendulation JP 8 324 425 Method and device for tilting rolling stock body 1996 * Control Simple control for tilting with the air belly JP 8 156 790 Tilt controller of car body 1996 Control Oil circuit for tilting system JP 9 048 345 Body tilting control method for rolling stock and its device 1995 ** Control Control for tilting realized with the air spring JR 11 278 261 Vehicle body tilting device 1999 ***** Torsion bar Active torsion bar with reduce unsprung weight US 6 273 001 B1 Pantograph for tilting trains 2001 Pantograph Pantograph with ropes EP 0 485 273 B1 Pantograph unmovable with respect to bogie frame 1991 *** Pantograph
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Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Classification Title Demander Year Interest Binder 3 JP11129900 Truck with tilting device of vehicle body for rolling stock 1999 **** Mechanism Hydraulic actuator housed in the primary suspension springs JP2002234437 Vehicle body tilting device Fuji 2002 ***** Mechanism Double sandwich air belly, one for allowing rotational, one for tilting JP2003072543 Rolling stock Hitachi 2003 ***** Anti-roll Anti-roll bar mounted as tilting system with rubber shock absorber. JP2005035321 Body tilting system for railway rolling stock 2005 *** Mechanism Air belly, system not very clear, but probably naturally controlled JP2003002193 Railroad vehicle Hitachi 2003 ***** Anti-roll Torsion bar with sloping links JP2002362361 Body inclination control device for rolling stock Kawasaki 2002 *** Control Use of speed, lateral acceleration, yaw velocity to control air belly in open loop JP2006027444 Body tilt controlling device of railroad car Kawaskai 2006 ** Control Air spring control system JP2005035495 Vehicle body tilting controller and its method 2005 Control Anti-roll bar and tilting, NOT CLEAR... EP 0 818 008 A1 Dispositif de pendulation à vérins, et bogie à pendulation à vérins Alstom 1998 **** Mechanics The actuator are rigidly and vertically bound to the bogie US 6 199 875 B1 Tilting apparatus having actuators, and a tilting bogie having actuators Alstom 2001 **** Mechanics Same as EP 0 818 008 A1 US 6 393 998 Assembly comprising a first chassis and a second chassis tilting laterally with respect to the first Alstom 2002 ** chassis, and corresponding railway vehicle Mech+pant Trapezium pendulum with rotary motor mainly claimed for pantograph. WO 98/26970 Truck frame for railway rolling stock Siemens 1997 ***** Mechanism Compact tilting system with one hydraulic actuator, over the secondary suspension DE 2 145 738 Schienenfahrzezg mit Gleisteuerung 1971 **** Mechanism Rolling mechanism above the secondary suspension DE 2 145 747 Hydraulische Betätigungsvorrichtung für Gleisbogensteuerung bei Schinenefahrzeugen 1971 Actuator Actuation of the previous mechanism EP 0 987 161 A2 Einrichtung zur Neigung eines über eine Federung auf einem Fahrwerk abgestützten Wagenkastens Alstom 1999 **** eines Schinenfahrzeuges um eine Fahrzeuglängsachse, die eine Wankstütze umfasst Anti-roll Special anti-roll bar, active JP06056034A Car body tilting device for rolling stock 1992 ** Anti-roll English summary not very clear to me, but active anti roll bar WO 2004/089716 Running gear for a railway vehicle provided with an improved transversal suspension Bombardier 2003 **** Suspension Lateral suspension, damping US005211116A Bogie for high-speed rail vehicles SIG 1989 *** Radial steering Radially adjusting of the wheel WO96/23515 Guiding mechanism for radially controlling in a curve the wheel sets of rail vehicle bogies Fiat-Sig 1996 *** Radial steering Same as above WO92/20557 Bogie Yaw damping Decoupling to make sure that only the rotary damping of the bogie is damped SIG 1992 **
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Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
Classification Title Demander Year Interest Binder 4 US 2 225 242 Suspension system for vehicles 1938 H Mechanism Talgo similar GB 525 858 US 4 271 765 Railway car tilting stabilizing system 1979 ***** Active anti-roll Active anti-roll bar with two separate selectively rotating bars US 4 355 582 Railway car tilt control system 1980 *** Control Above active ant-roll bar with its control, old fashion. DE 39 35 740 A1 Steuerung för den neigungsfähigen Wagenkasten eines sprugebundenen Fahrzeugs 1989 **** Control Onboard stored data (principle) DE 196 47 461 A1 Deinrichtung und Verfahren för ein Fahrzeugortungs-, Auswerte- und Informationtionssytem DB 1996 ***** Position Modern communication system, train information... JP2005238937 Rolling stock 2005 ***** Mechanism Using a central air belly for sustaining the load dans lateral to tilt JP2005238858 Anti-rolling device for rolling stock 2005 *** Anti-roll bar Internal external double structure torsion bar, variable rigidity US005787815A Storage of track data in a position controlled tilt system ASEA 1998 ***** Track data Real time track data storing in order to use in a next ride (self learning) US005775230A Guidance system and process for controlling the lateral inclination on a rail vehicle Fiat-SIG 1998 ***** Track data Onboard stored data to cancel the lag for control DE44 22 109A1 Kuppelbare Fahrwerkanordnung zum Tragen und Querneigen eines Wagenkastens SIG 1994 - Radial steering Coupled radial steering between wagons US006278914 Adaptive signal conditioning device for train tilting control systems Bombardier 2001 ***** Control Using adaptive flittering depending base on the noise to minimize time delay EP1 527 976A1 Railway car with tilting car body Hitachi 2004 *** Mechanism Natural tilting with two-step bumper DE42 41 929 A1 Anfhängung för einen Wagenkasten an einem Fahrgestell insbesondere an einem Drehgestell eines schinengebundenen 1992 * Fahrzeugs Mechanism Hydraulic mechanism with special feature, but not so interesting EP 0 736 438 A railway vehicle with variable trim body Fiat 1995 ** Control Early day pendolino EP 0 528 783 Einrichtung zur Abstützung eines Wagenkastens auf einem Laufwerk, insbesondere för Schienenfahrzeuge 1992 * Mechanism Three actuator mechanism, high force, problem to fit the secondary suspension DE 41 05 350 Sekundärfederung för Drehgestelle von Schinenfahrzeugen 1991 *** Suspension Secondary suspension swing to the inside of the wagon DE 2 237 638 Einrichtung, insbesondere för Schienenfahrzeuge, zum Hemmen von Drehbewegungen eines Drehgestelles gegenüber einem 1972 * Wagenkasten Yaw Friction element to avoid yaw, special secondary suspension US005107773 Railway trucks 1990 Bogie Just a bogie description US005671683A Railway vehicle with variable trim body Fiat 1996 *** Mechanism Another pendulum mechanism with actuator placed in another position US004526109 Laterally damped railway car 1985 ** Lateral suspension Lateral suspension with variable damping US003977694 Roll stabilization system ASEA 1974 * Mechanism Three actuators for tilting and lateral position. No suspension and movements coupling EP 0 930 211 B1 Drehgestell för ein neigbares Schienenfahrzeug Siemens 2004 ** Detail Hermetically welded pressure vessel in bogie for the secondary suspension EP 1 174 326 A1 Verfahren und Vorrichtung zur Einstellung der Querneigung eines Wagenkastens Fiat-SIG 2000 **** Control Separate corrected tilting angle for each bogie EP 1 038 749 A1 Neigungs-Steuerung för einen Wagenkasten eines spurgebundenen Fahrzeuges Alstom 2000 **** Control Use of data stored to control the tilt EP 0 736 437 A1 A body control system for a railway vehicle with variable trim body Fiat 2000 **** Hydraulic control The same side actuators are controlled together
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Frédéric ROCHAT 2006-2007 Diploma thesis Simplified tilt
10.7 Contacts information
Frédéric Rochat CH-1676 Chavannes-les-Forts Suisse
++41 26 656 14 09 ++41 79 773 86 38 [email protected] [email protected]
Bombardier Huvudkontor Östra Ringvägen 2 S-721 73 Västerås Sverige
++ 46 21 31 70 00 www.bombardier.com
Kungliga Tekniska Högskolan S-100 44 Stockholm Sverige
++ 46 87 90 60 00 www.kth.se
Ecole Polytechnique Fédérale de Lausanne CH-1015 Lausanne Suisse
++ 41 21 693 11 11 www.epfl.ch