Tilting technology at AG - Prophecies, reality and necessary innovations

Dr. T. Erpenbeck1, A. Büttner2, Dr. W. Voges3

1Deutsche Bahn AG, Tilting-Body Train Systems, Minden, Germany; 2Deutsche Bahn AG, DB Systemtechnik, , Germany; 3Deutsche Bahn AG

Introduction “Like a motorcyclist leaning into the bend” and “like hurtling down the ice on a bob” - these are two typical images used in advertising by Deutsche Bahn AG to get the benefits of tilting-body travel across to the public. Such advertising pronouncements reflect the self-perception, expectations and promises that Deutsche Bahn AG associates with its tilting-body trains and with faster travel through curves. A journey experience full of “dashing elegance” and technical innovation at top speeds and timings. The ten years and more of experience gained in regional and long-distance services with tilting technology have confirmed the expectations placed in it whilst also underscoring the challenges it has thrown up and clearly pin-pointing what needs to be improved so tilting technology can remain attractive and economical.

1. Expectations With the growth in private motoring, the focus has increasingly shifted to how long journeys take. Germany’s extensive network of motorways has long since led to cars being a faster means of travelling between population centres than trains, thus obliging Deutsche Bahn AG to adopt measures to reduce journey times. Alongside new-build and upgraded lines designed to rival motorway links, tilting technology constitutes a promising and economical means of reducing journey times. Wherever it has proved possible to adapt heavily-curved lines for faster operation through curves, tilting technology has been seen as offering the requisite gain in journey time coupled with economical infrastructural measures on account of the minimal expenditure - relative to new-build lines - required for infrastructural investment. Besides such quantifiable expectations, those of a more qualitative nature were also placed in the cutting- edge innovative technology with regard to increases in ridership. The deployment of new multiple units whose innovative technology additionally conveys a new ride feeling was expected to once again cause passengers to switch from road to rail in greater numbers.

2. Development of tilting-body trains at Deutsche Bahn AG As well as constantly raising the top speed, in the 1990s Deutsche Bahn AG also pushed ahead with tilting technology for local and long-distance services with the aim of reducing timings. The tilting technology era was ushered in at what was then Deutsche Bundesbahn when 12 VT 634 Class trains fitted with a body-tilting mechanism operated by pneumatic springs were presented at the international transport exhibition held in Munich in 1965. However, this initiation into tilting technology was not pursued any further until after the “” (ETR 401) operated by the Italian State Railway (FS) had been successfully tested over the DB network and commissioning commenced in the 1990s, leading to a peak of 352 tilting-body trains currently running at Deutsche Bahn AG [1].

June 1992 saw the beginning of scheduled “faster operation through curves” with VT 610 Class stock. 20 two-car sets featuring an active hydraulic tilt system made by / are being worked in regional services in the Nuremberg area at speeds up to 160km/h (Fig. 1).

Fig. 1: VT 610

Talgo stock with passive tilting technology has been deployed in overnight services by Deutsche Bahn AG since 1994 (Fig. 2). Tilt is achieved passively with this system by means of forces acting centrifugally via a pneumatic spring located significantly above the car-body’s centre of gravity.

Fig. 2:

From 1996, 50 VT 611 Class two-car sets featuring electromechanical tilting technology made by Adtranz and ESW were run in the Ulm area (Fig. 3) . In contrast to VT 610 Class stock, on these trains the tilt mechanism is situated beneath the secondary spring. Trains run at top speeds of 160 km/h.

Fig. 3: VT 611

The VT 612 Class stock that has been used in regional services since 2000 (Fig. 4) is the most recent tilting-body series in the speed range to 160 km/h to be run regionally by Deutsche Bahn AG. 200 of these multiple units are operating in the , Erfurt, Kempten, Hof and Kaiserslautern areas. Theirs is an electromechanical tilt system without an active transverse spring or active transverse centring and with the tilt mechanism beneath the secondary suspension.

Fig. 4: VT 612

Deutsche Bahn AG has also, since 1999 , been running tilting-body trains on long -distance high-speed services in the form of 411/415 Class st ock. There are a total of 43 five-car (Class 415) and seven-car (Class 411) (ICE) sets with a top speed of 230km/h ( Fig. 5) . The multiple units are equipped with an hydraulic tilting technology system made by ALSTOM/FIAT Ferroviaria having active transverse springing and a tilt mechanism above the secondary suspension.

Fig. 5: Classes 411/415 (shown here: Class 411)

A further 28 Class 411 ICEs with enhanced features have been placed into service by Deutsche Bahn AG since the autumn of 2004 [3].

Twenty VT 605 Class four-car diesel multiple units were added to the long-distance tilting technology fleet in 2001. These DMUs feature an ele ctromechanical tilt system with active transverse centring, a tilt mechanism above the secondary suspension and max. speeds of 200km/h.

Fig. 6: VT 605

A comparative synopsis of tilting-body trains run by Deutsche Bahn AG is shown in Table 1

Property Active tilting technology Passive tilting technology Off-centring of the car body via hydraulic cylinder via electromechanical via centrifugal forces actuators (passive) Angle of tilt up to 8 degrees up to 8 degrees up to 3.5 degrees Application Classes 610, 411, 415 Classes 611, 612, 605 Talgo (DB night train) Added speed through curves up to 28 % up to 28 % up to 15 %

Table 1: Tilting-body trains compared

3. Experience gained The primary expectations regarding journey-time reductions can be confirmed. Introduction of the VT 610 in the region around Nuremberg in the early 1990s, for instance, led to timings being cut by 21 % [2]. Deploying tilting-body Class 411 ICEs on long-distance services between Munich and allowed the time for the trip to be reduced by 6 %. The potential for reducing journey times with the aid of tilting technology is obviously limited by the number of winding lines there are in the rail network that can be prepared for tilting-body running. The area of application extends to potential new-build tilt-operation lines in cases where alternative methods of building a high-speed section of line (e.g. tunnels or bridges) are so expensive as to make the tilt variant an economically viable proposition there too.

Tilt operation has greater difficulty adhering to the limit values in force for ride quality and hence necessitates greater input for track inspections and assuring the quality of the permanent way. Thus, whilst considerably reducing the investment required for infrastructure or the building of new lines, tilt operation gives rise to operating costs that are far from negligible. It is also necessary to factor higher vehicle procurement costs for tilting-body rolling stock into the equation, since these make up about 5 % of the total procurement price [4] (cf. Fig. 7)

Power supply 11% Transmission 7% Bogies 13% Auxilaries 8%

Brake system 7% car body 26% Interior fitments other 2% 12% Control and Tilt system 5% communication 9%

Fig. 7: Breakdown of cost of procuring new tilting-body rolling stock

The commissioning of tilting-body rolling stock enabled rail traffic to be markedly increased especially in regions in which winding routes predominate. Thus, the entry into service of the VT 610 in the Nuremberg area caused traffic to grow by 30 % and more (comparing 1992 and 1994) [2]. These increases are undoubtedly in large part attributable to routes having become more attractive and in part to the more innovative rolling stock. It should be noted, however, that these two factors - attractive routes and tilting-body rolling stock - are inter-related and interdependent: the routes are only attractive in conjunction with tilting-body rolling stock whilst the latter requires suitable lines if its potential is to be tapped. It is accordingly possible to state an initial precondition for economical and attractive tilt operations: the trains used must be able to tilt reliably and flawlessly, since it will not otherwise be possible to achieve cuts in journey times. The system’s benefits are then squandered, giving rise to bigger increases in running times than occur when conventional vehicles fail on conventional lines.

The experience gained with regard to tilting-body rolling stock and its infrastructure at Deutsche Bahn AG is as varied as the system and its interfaces are complex. Tilting technology is a complex technical subsystem that impacts both on the entire train and on the rail infrastructure: § control § diagnostics § maintenance (rolling stock and infrastructure) § reliability and availability § safety

3.1 Control and regulation All tilting-body trains run by Deutsche Bahn AG except the Talgo overnight stock, which has a passive system, feature an a ctive tilt system, i.e. body tilt is a ctively controlled. Control and regulation gear guarantees safety -critical functions and comfortable riding by adapting body tilt to the layout of the line instead of its occurring jerkily. If the control system malfunctions, it is necessary to intervene in the tilt system on account of safety- critical functions being affected; this usually results in a return to conventional operation involving slower running through curves. Tilt systems have been constantly improved to reflect operational insights gained

for this reason, with a view, for instance, to raising redundancy levels and guaranteeing greater reliability and availability overall. The number of tilt failures per million kilometres of running is used as a measuring variable at Deutsche Bahn AG to this end. In the case of the tilting-body ICE (Classes 411/415), it proved possible to improve this value from more than 60 in 2001 to less than 15 in 2004. This was decisively due to changes made to the tilt control software. Hardware measures carried out on large numbers of sub- components in the tilt system stabilised the overall system and thus helped reduce technical failures and malfunctioning. These improvements contributed to the realisation that the technic al system had yet to fully tap its potential. When the second series of Class 411 tilting-body ICEs was procured, the emphasis was laid from the start of the concept-drafting phase in 2001 on improving the tilt system, a system conforming to and compatible with that of the first series. Parallel operation of the first series in the context of developing and manufacturing the second delivered the requisite stimuli and verifications. As a consequence, a tilt reliability of max. 10 tilt failures per million kilometres of running was agreed for the second series of Class 411 stock.

3.2 Diagnostics Control and regulation gear ensure s the correct responses by rolling stock to given parameters. This is, however, predicated on diagnostics data indicating what the ruling parameters are - notably as regards malfunctions. Besides malfunctions and support data , the condition of individual components is also diagnosed, thus facilitating condition-based maintenance. Faulty diagnoses in the tilt system lead in this way to tilt failures and unnecessary maintenance input. The basic tenet holds true here which states that, the more complex the system and the more detaile d the diagnosis desired, the more failure and malfunction-prone that system will be. With regard to Class 411/415 stock, therefore, diagnoses were simplified in part and made more resilient to fluctuations, whilst the afore-mentioned software modifications were put to effect as a means of enhancing diagnostic accuracy.

3.3 Maintenance Crucial to the success of any production resource alongside revenues from train journeys sold are outgoings for the resource’s operation and, first and foremost, for its maintenance. Where rail vehicles are concerned this is an item second only in importance to procurement investment, since most trains are worked for 15 years and more. Thus, expenditure on the maintenance of tilting-body rolling stock ultimately has a key role to play in the success of the technology. Maintenance is determined by means of the scheduled works required to guarantee the functioning and reliability of the system. Ideally, the measures thus defined for tilt systems will dovetail into the remaining maintenance schedule for the train, e.g. relating to running gear, brakes and traction c omponents. Here, too, it holds true that, the more complex the system, the shorter the notice given for input-intensive measures designed to ensure this complexity remains in working order. There are many instances in which the tilt systems used at Deutsche Bahn AG require additional maintenance such as the reconditioning of components or the cleaning and replacement of operating supplies between major overhauls. Many of the hardware measures referred to for Classes 411/415 have the aim of reducing maintenance expenditure. With this aim in mind, the operator separately lays down programmes for enhancing maintenance-intensive components with a view to facilitating uniform and greater intervals for scheduled maintenance.

All other maintenance measures between scheduled works serve the purpose of remedying faults, rectifying malfunctions and effecting repairs. Such corrective maintenance determines the quality and availability of tilting technology as well as having a decisive bearing on its cost. To again cite the example of Classes 411/415, corrective maintenance costs for the tilt sy stem amount to approx. 12 % of total corrective maintenance costs. With the tilt system making up 5 % of procurement costs ( cf. Fig. 7 ), a significant imbalance might appear to obtain here . The 5% figure given in Fig. 7 is, however, a mean value for all tilting-body vehicles at Deutsche Bahn AG – the tilt system constitutes a bigger proportion of procurement costs for long-distance trains, the figure being closer to 10 % and more in that sector. The adverse effects of severe weather conditions during the seasons of the year likewise impinge to a particular degree on corrective maintenance. In spring and summer, for instance, there is a considerably

higher need than that scheduled for the cleaning of filters and other protective apparatus serving air coolers in the tilt system. In winter, the tilt action is disabled if there is too great an accumulation of ice or snow or else damage is done to parts that have not been designed sturdily enough (cf. Fig. 8). Additional maintenance is rendered necessary in both instances, with delays arising due to the tilt system not being fully functional.

Fig. 8: Seasonal problems (above left: soiled filter, above right: iced-up bogie)

3.4 Infrastructure One of the main motives for putting tilting technology into practice at Deutsche Bahn AG was the fact that, compared to new-build lines, there is minimal expenditure on infrastructure when preparing a line for faster passage through curves. Mention does, however, need to be made at this juncture of the higher outlay for line inspections and for assuring the quality of the permanent way entailed with tilt-operation lines than with standard types. The far higher degree of unbalanced transverse acceleratio n in tilting-body vehicles leads to their having greater difficulty adhering to the limit values prescribed for ride quality in UIC Leaflet 518 than do conventional vehicles - to which the same Leaflet applies. Lines on which there is faster negotiation of curves are accordingly assessed by means of additional vehicle response measurements [4]. This outlay is plannable in the same way as with vehicle maintenance. But added to this is a corrective portion for maintenance measures to the track caused by tilt operation. One decisive advantage of preparing infrastructure for faster negotiation of curves, however, is the drastically shorter time required to bring a tilt-operation line to fruition as compared with high-speed lines. A telling example of this is the 30 years needed to plan and put to effect the new-build Cologne- line as against the two years taken to prepare the - line for faster curve negotiation. Thus, tilt system offerings can be brought to market more quickly [5].

3.5 Command/control system

The command/control system for lines with faster curve negotiation also has to be adapted for tilt operation. In Germany, the law prescribes that commercial speeds on lines with faster running through curves have to be constantly monitored. This is achieved by means of a stand-alone system known as Speed Monitoring for Tilt Systems (GNT). GNT transmits the permitted speed profile to tilting-body vehicles as they negotiate fixed installations. Given that the running behaviour of the various series of tilting-body trains differs (as regards brake reaction and cross-wind properties for instance), each series has its own speed profile. This has lead to a situation whereby, on lines worked by differing series of tilting-body trains, the “weakest” series defines the speed profile for all the others and hence it has not been possible to fully tap the speed potential of the “faster” series.

Table 2 summarises and evaluates the experience gained by Deutsche Bahn AG with tilting technology.

+ - Journey time Reduction of up to 30 % without

reduction building a new line Outlay for: Minimal costs compared to new- § line inspections Infrastructure build lines § additional command/control system Vehicle procurement Additional cost of tilting trains

Far faster new offerings of Time to market vehicles and lines for passengers than with high-speed lines

Faults Forfeiture of journey time reduction Comparatively young technology Comparatively young technology in Sophistication of in the railway sector with scope for the railway sector with scope for system development development

Diagnostics More complex/fault-prone system

§ has immediate, unfiltered Reliability/availability impact on journey time § determines cost-effectiveness § additional components Maintenance § some lack of congruency with maintenance intervals Table 2: Experience with tilting technology evaluated

4. Necessary innovations The comments made in Column “-“ in Table 2 are not set in stone and are not to be understood as forming part of a case against tilting technology. Rather, they point up means of achieving targeted innovations. If improvements are made on these points, this will be conducive to the lasting success of tilting technology. Notwithstanding the problems and expenses alluded to that running tilting-body rolling stock entails, there remains the major benefit as referred to in Table 2 of being able to reduce journey times with comparatively little outlay and hence achieve a better competitive standing.

The experience gained with regard to the properties demanded of tilting technology as set out above reveals this to be a technology that can only deliver its benefits in actual operation if it works. Any gain in timing is squandered and additional measures become necessary that make the system less economical the moment the system fails or ceases to be fully functional. Hence, reliability and availability are the decisive system requirements not only on cost grounds but also and in particular with regard to harnessing the benefits of tilting technology in actual operation. The complexity of the control, regulation and diagnostics systems referred to needs to be manageable and must not be allowed to condemn tilting technology to becoming a system that is only viable under laboratory conditions.

Ø Further development of existing systems rather than technically ambitious new developments are the innovations that tilting technology requires

Ø Innovative in the sense of constituting progress and further development, therefore, are systems marked by a high degree of reliability and ruggedness. “Simplicity” is the key to success here.

Reliable tilting technology directly gives rise to a reduction in the corrective maintenance it undergoes. Given that it is the central task along with operation, maintenance is a further area in which improvements are needed.

Ø Scheduled maintenance for tilting technology needs to be conceived in such a way that it does not necessitate any extreme measures between the main exams for the train as a whole.

Ø An assured level of quality for the permanent way on lines featuring faster passage through curves is a prerequisite for economical and calculable tilt operation. The further development of tilting technology needs, therefore, to take account of interactions with the infrastructure – simply optimising vehicle engineering will not yield the improvements in availability needed.

Evidence of the interdependencies between vehicle and infrastructure is also provided by the afore- mentioned restrictions brought about by the process of speed monitoring for tilting technology (GNT) as part of the command/control regime. With such restrictions already having been imposed at domestic level, further are to be anticipated for the burgeoning sphere of cross-border services.

Ø Innovative developments are those that integrate tilting technology into command/control systems and make no further separate systems necessary.

Ø The interplay between vehicle and infrastructure needs to be flexibl e and clearly demarcated between the two. Vehicle-related information, for instance, ought to be solely carried on the vehicle and line-related information solely archived in the infrastructure. Any mixing merely leads to a loss of potential.

Ø Ensuring the separation of vehicle and infrastructure data, through international standards for instance, helps remove competitive drawbacks for tilting technology on the international market.

Concluding summary Tilting technology has great potential for very rapidly delivering journey time reductions on existing railway lines as well as requiring very little investment compared to new-build lines. The new and additional engineering relative to conventional rolling stock and lines necessitates additional outlay for the maintenance and operation of tilting-body trains and tilt-operation lines. Only if it can be ensured that this additional outlay does not nullify the system’s investment benefits over the lifetime of the rolling stock from a life-cycle-cost perspective will tilting technology be economical and hence successful. The experience gained from over ten years of tilt operation i n regional and long-distance services at Deutsche Bahn AG points to a need not only for innovation in respect of new systems at the forefront of technical progress but also for further developing existing systems with the aim of achieving greater reliability and availability. It is essential that further development along these lines take account of interactions between tilting-body rolling stock and its environment so as to avoid any sub-optimal outcome. Tilting technology derives its potential from the interplay between vehicle and infrastructure and needs, therefore, to be further developed in a way that also takes account of interactions between the two if its potential is to be harnessed.

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