Low Energy-Consuming Load Sensing Truck Cab Suspension

Low energy-consuming load sensing truck cab suspension

Master of Science Thesis TRITA-ITM-EX 2019:721 KTH , Industrial Engineering and Management Machine Design SE-100 44 , STOCKHOLM Intentional left blank

Examensarbete TRITA-ITM-EX 2019:721

Energieffektiv lastkännande fjädring för lastbilshytter

Teodor Hidén

Godkänt Examinator Handledare 2019-12-18 Ulf Sellgren Ulf Sellgren Uppdragsgivare Kontaktperson Scania, RCCB Fredrik Aldebert

Sammanfattning

I utvecklingen av el- och batteridrivna lastbilar är en stor del av utmaning att minimera energianvändningen hos lastbilens alla olika delsystem, där ibland hyttfjädringen.

Dagens lastkännande (aktiva) fjädringssystem på lastbilshytter drivs med tryckluft och arbetar kontinuerligt med att hålla lastbilshytten på rätt höjd. Tryckluften kommer ifrån en stor och tung kompressor som ständigt arbetar för att komprimera luft till lastbilens alla olika delsystem. Alternativet till den aktiva lastkännande hyttfjädringen är att använda en icke lastkännande (passiv) fjädring. Detta begränsar dock lastbilens komfort och utseende, men förbrukar heller ingen energi.

Målet med detta examensarbete var att finna en fjädringslösning som både är lastkännande och energieffektiv. För att hitta en lämplig lastkännande lösning gjordes en grundlig undersökning av hyttfjädringslösningar på andra tunga fordon, samt olika fjädringssystem överlag.

Det visade sig att användandet av hydraulik ger en tillfredsställande justerbarhet, utan att förbruka någon energi när systemet är i vila (inte aktivt justerar). Systemet skulle även kunna göras mycket kompakt. Det är lätt att anpassa dagens befintliga fjädringskomponenter för att kunna fungera ihop med justerbara hydraulcylindrar, och fjädringens hydraulsystem skulle kunna drivas ihop med övriga hydraulsystem på lastbilen.

Nyckelord: Anpassning, Energieffektiv, Fjädring, Komfort, Justerbar

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Master of Science Thesis TRITA-ITM-EX 2019:721

Low energy-consuming load sensing truck cab suspension

Teodor Hidén

Approved Examiner Supervisor 2019-12-18 Ulf Sellgren Ulf Sellgren Commissioner Contact person Scania, RCCB Fredrik Aldebert

Abstract

In the development of battery electric trucks is one of the main concerns how to minimize the energy consumption of all the different subsystems on the truck. One of these energy- consuming systems is the active cab suspension.

The load sensing (active) cab systems used today is using pressurized air, pneumatics, to keep the cab at correct ride height. Currently is this pressurized air produced with a big, bulky and heavy compressor that continuously is running to compress air for multiple different subsystems. The alternative to the load sensing active cab suspension is to use non-load sensing (passive) suspension. This option is limiting the comfort and appearance of the cab but is neither using any energy.

The goal of this master thesis is to find a suspension solution that is both load sensing and energy-efficient. To find a suitable load sensing solution was cab suspension system on other types of heavy machines inspected, together with suspension systems overall.

There could be seen that the use of hydraulics gave the adjustability needed, without consuming any energy when the adjustments had been done. The system could also be very compact. It is easy to adapt the existing suspension components to work together with the hydraulic cylinders, and the hydraulic suspension systems have the possibility to be merged with other hydraulic systems on the truck

Keywords: Adjustability, Comfort, Energy, Spring, Suspension

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5 Acknowledgments and Foreword

I would like to thank Scania with all the employees that have been helping and supporting me both through my summer job and this thesis. It has been a very interesting, learning and pleasant time. Especially thanks to the people at RCCB, the department where I have been based since June 2019.

I would also like to thank Ulf Sellgren at KTH for the support but also the responsibilities and trust that have been given to me.

Teodor Hidén, Stockholm, Autumn, 2019

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7 Table of Content

Sammanfattning ...... 2 Abstract...... 4 Acknowledgments and Foreword ...... 6 Table of Content ...... 8 Introduction ...... 10 Background and Problem Description...... 10 Purpose and Definitions ...... 11 Delimitations ...... 11 Methodology ...... 12 Frame of Reference and State of the Art ...... 14 Suspension Components ...... 14 Suspension System Types ...... 15 Cab Suspension Types on Heavy Machines...... 19 Aftermarket Solutions ...... 31 Implementation ...... 36 Requirements ...... 36 Different Concepts ...... 37 Concept Evaluation ...... 37 Chosen Concepts ...... 38 Existing Solutions ...... 40 Further Design of the Chosen Concept...... 46 Results ...... 50 Conclusion ...... 50 Discussion ...... 52 Future work ...... 54 About Chosen Concept ...... 54 About Other Areas ...... 55 References ...... 56 Appendix ...... 64 Appendix 1, Search Keywords ...... 64 Appendix 2, Gantt schedule ...... 65 Appendix 3, Pugh Weighted Matrix ...... 66 Appendix 4, Risks and Risk Analysis ...... 67 Appendix 5, MATLAB Calculations ...... 68

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9 Introduction

Today is more and more transportations happen in urban areas. This means that noise and exhaust gases are more critical than ever. A more quiet and “clean” transport solutions is requested. One solution for this task is to use electrified trucks. Electrified vehicles fit well in due to the political regulations of exhaust and noise regulations and have a positive association with sustainability among people.

Background and Problem Description Choosing a fully electric driveline on a truck instead of a conventional diesel engine highly affects the cruising range, due to the limitation of the power storage capacity in the batteries. This means that every chance to minimize the power consumption of all the trucks subsystems must be taken.

One subsystem that continuously consumes energy is the pneumatic cab suspension. A set of air bellows sets the ride height and the dampers set the stiffness/comfort of the ride. A compressor must be running more or less continuously to provide the suspension system with pressurized air so the air bellows will keep the cab at the correct height. This system can be replaced with a fully mechanical suspension that does not consume any energy. Here will a coil spring instead set the ride height, and a similar damper as in the pneumatic system sets the comfort of the ride. In both cases is there a sway bar (anti-sway bar / anti-roll bar) connected to the front suspension.

The mechanical system provides less comfort than the pneumatic suspension. This is due to the spring stiffness and to the difference in dampers. The damper in the air suspension setup has a built-in “comfort zone” at optimal ride height. But the biggest downside is its lack of automatic adjustability. The current air suspension system can thanks to its two height sensors, one in the front and one in the rear, detect and adjust for uneven load distribution (but only front to back). There is a possibility to add additional height sensors so that the cab suspension also adjusts left to right, but the more the cab adjusts, the more air will be consumed. The sideway leaning is only limited by the sway bar.

This means that with today's system, if one side of the cab is loaded with a heavy truck driver, snow chains and luggage and the other side of the cab is empty, the cab will be leaning towards one side. The same problem occurs if a lightweight driver has a lot of heavy luggage in the rear of a cab, and the cab is leaning backward (only mechanical system). This looks cheap and is not “premium”, something that does not fit in at a novel electric truck from Scania.

Having 3 or 4 height sensors, a system that can adjust the cab in front/back and left/right, still be comfortable and not use a lot of energy, would be an optimal solution.

10 Purpose and Definitions The goal of this thesis work is to find a solution to the problem described above. It is a conceptual study without testing, simulation or verification.

The aim is to find a cab suspension that does not use a lot of energy but still is automatically adjustable so that the cab can stay level while driving and maintain its ride height. The main focus is on ride height. The example truck that will be fitted with this suspension has a fully electrified driveline. The ride quality must be at least as good as in the current mechanical suspension case.

The design dimensions of one suspension unit that should be fulfilled is: Stroke length of damper 100 mm Minimum length (fully compressed) 250 mm Comfort ride height length 300 mm Maximum length (fully extended) 350 mm Maximum diameter 150 mm

One unit (air bellow and damper) of the current pneumatic systems weighs 2,5 kg One unit (coil spring and damper) of the current mechanical system weighs 3,8 kg

Delimitations All the requirements will not be verified in this paper since it is a conceptual study. The suspension solutions must be estimated to fulfill the criteria.

Because this thesis is a conceptual study, will following parameters not be taken into consideration or be limiting: ● Price ● Type of suspension (air, hydraulic, etc.)

11 Methodology To be able to find relevant data, analyse it, take inspiration and come up with own solutions, was this master thesis done using a qualitative methodology. Background information was gathered through research on company websites, through interviews with Scania employees, etc.

Information and understanding of the purpose of a suspension system, the system components and their effect on the system was the first step. This was followed up with looking at what suspension systems that are on the market for similar applications (cab suspension for heavy duty vehicles like tractors, wheel loaders, forestry machines, etc.). Last of all was an overall vehicle suspension type research done, to get inspiration of different solutions that might work for our application.

All this information was then summarized, shown and discussed with the Scania advisor, and the path for the rest of the work was drawn out. A concept evaluation with a weighted Pugh Matrix with different possible solutions was performed.

The next step was a deeper information and knowledge search about the chosen concepts to see what commercial solution that already exists.

When deeper information search was finished and suitable concepts where analyzed, followed a conceptual design. The conceptual design was more of a double-check that all numbers and solutions seem to be reasonable. Possible positive synergy with other systems and implementation possibilities were also looked at.

No testing was performed due to the early stage of development.

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13 Frame of Reference and State of the Art

Before going into specific solutions for cab suspension will the general function of a suspension system be described.

The goal of a typical vehicle suspension is to maximize the contact and friction between tyres and the ground to provide good handling. This means that the vehicle can provide good braking, steering and acceleration (vehicle control). The suspension shall also provide a good ride, meaning to minimize the negative effect in ride quality, noise and comfort for the passengers created from uneven roads. (Harris, How Stuff Works, CS, 2019).

Why suspension systems and components for cars are as interesting as cab suspension on other heavy machines is due to the similarities between a truck cab and a car seen to; weight, size and 4 point mounting (like 4 tyres).

Suspension Components A typical vehicle suspension contains three main parts; springs, dampers and anti-sway bars. (Collins, 2019).

Spring The main function of the spring is to set the ride height and support the weight of the vehicle. The springs absorb energy when motion from ex. a bump pushes the tyre upwards, but also release the same energy when the pushing motion is over. This means that the vehicle can start to bounce after just hitting one bump. (Harris, How Stuff Works, CS.1, 2019). Different types of springs will be described later on.

Damper or Shock Absorber The main function of the damper is to absorb energy; to convert velocity and motion into heat. This smoothens out the ride. (Harris, How Stuff Works, CS.2, 2019). The ingoing parts in a damper are shown in Figure 1.

Figure 1. An example of a shock absorber. (Upasani, 2019)

14 Anti-sway Bar or Anti-roll Bar The anti-sway bar (often called sway bar) has the main function of keeping the vehicle as stable as possible and help with handling. It connects the left and right side of the vehicle suspension so that the tyres move more similar to each other. This provides a better ride and helps a lot to prevent rolling when entering a curve. (Harris, How Stuff Works, CS.3, 2019). How a sway bar is typically installed on the front of a car is shown in Figure 2.

Figure 2. An example of a sway bar. (Robinson, 2019)

Suspension System Types

Active, Semi-Active and Passive Suspension Active: Active suspension, also known as adaptive suspension, is suspension which can change its properties and behavior due to input from an (often) electric controller. Active suspension has the possibility to both lower and raise the vehicle (often through air- or hydraulic cylinder on top of the spring) and sometimes also to adjust the stiffness of the ride (adjust the dampers). (Shirish, 2019).

Semi-Active: The semi-active suspension is adjustable just like the active suspension, but here can only the firmness/stiffness of the ride be adjusted. This is often through a valve in the damper or magneto-rheological (MR) dampers. (Shirish, 2019).

Passive: Passive suspension is a fully mechanical suspension and does not have any automatic adjustability systems, neither on the spring or the damper. Sometimes there is a valve that can be manually adjusted on the damper, or that the preload on the springs can be set through a special tool. (Shirish, 2019).

In this thesis, the main focus is on the springs and ride height (not damper or sway bar). There are multiple different types of springs, all with their own benefits and downsides.

15 Pneumatic Suspension Pneumatic springs, air springs or air bellows, can lock and work quite differently. They all have in common that they provide a very comfortable ride, but also have a bigger risk of failure than the other spring types and are typically more expensive. (Tan, 2019). Thanks to the increase in spring rate with increased load/pressure can they be soft when the load is low, and stiff when the load is high. When adjusting the air pressure will the ride height and stiffness change, which leads to the ability to keep the ride height constant and independent of the load. Because the need for a compressor, valves, etc. is the system often complex. (Brakster, Your Online Mechanic, AS 2/2, 2019). A section view of an air bellow is shown in Figure 3.

Figure 3. An example of an air bellow. (Gannon, Pneumatic Tips, Air Spring, 2019)

Hydraulic Suspension Hydraulic suspension can be made in two ways, either together with a mechanical suspension or with air suspension. In both applications will the hydraulic cylinder, driven by pressurized oil, sets the ride height. Either will the coil spring and damper do the suspension work and the hydraulic cylinder sets the ride height. This system is mostly used on lowrider cars, sport cars etc. where you want to have the possibility to easy and quick change ride height. (Rowswell, 2019). The other way is when the hydraulic cylinder works as the damper. When the cylinder is moving will the hydraulic fluid be pushed into a pre-pressurized gas chamber. Thanks to the gas ability to compress, will the gas here acts as the spring element. This system is called hydropneumatic and is typically seen on Citroen cars and various luxury cars. The downside with hydraulic systems overall is its complexity, cost and risk of leakage. (Radu, 2019). A simple layout explanation of hydropneumatic is shown in Figure 4.

Figure 4. An example of hydropneumatic suspension. (Marsh, 2019)

Mechanic Suspension Coil Springs: Coil Springs are a helical type of spring that can take heavy loads while still being comfortable. It is a more quiet and comfortable solution than leaf springs and is commonly used on cars. The coil spring can be very bouncy when used together with poor shocks. (Tan, 2019). Why they are so bouncy is because of the lack of internal friction. One of the main benefits with coil springs is that they can be made soft, to get a smooth ride. (Brakster, Your Online Mechanic, AS 1/2, 2019). If the coil spring is mounted around/over/outside of the damper, so they can be mounted as one unit, this unit is called a “coilover” = “coil-over-damper”. (Couchman, 2019). A typical coil spring is shown in Figure 5.

Figure 5. An example of a coil spring with a constant spring rate. (Sales, Moog, Coil springs, 2019)

Leaf Springs: Leaf Springs are one of the oldest suspension solutions that still is used today. They are made up of multiple different steel bands (leaves) that are held together with U-bolts. The longer the leaf the softer it is, and the more leaves in the leaf spring, the more load can it withstand.

17 (Brakster, Your Online Mechanic, AS 1/2, 2019). They are good for heavy-duty applications thanks to its ability to handle heavy loads, but they are heavy, noisy, bulky and provide a pretty rough ride. Still commonly used on trucks and pickups. (Tan, 2019). Some different layouts for leaf springs can be seen here under in Figure 6.

Figure 6. Examples of three different leaf spring setups. (Reimpell, 2019)

Torsion Bars: A Torsion Bar is a steel rod that twists around its own axis and it behaves similar to a coil spring. It is a very simple system that does not behave as good as the coil or leaf springs, but it is compact, affordable and somewhat easy to adjust. (Tan, 2019). It works thanks to its ability to take shear stress. (Bairwa, 2019). Because the torsion bar, just like the coil spring, does not have any internal friction, must they be used together with a damper to provide a non- bouncy ride. (Brakster, Your Online Mechanic, AS 2/2, 2019). A typical setup for torsion bars is shown here under in Figure 7.

Figure 7. Example of how a torsion bar is mounted in a front suspension of a car. (Zahl, 2019)

18 Rubber Springs: Rubber Springs are simple, cheap and compact. They have a good vibration damping property but cannot handle as big of a stroke length as the other spring types. Rubber springs are also less likely to fail than the other systems. There are a few different types of rubber springs. (Bairwa, 2019). The rubber is also quiet when working. They are not suitable for heavy loads, and therefore mainly used as stoppers, bushings, supports, etc. (Brakster, Your Online Mechanic, AS 2/2, 2019). A typical example of a rubber spring is shown in Figure 8.

Figure 8. An example of a rubber spring. (Sales, GMT, 2019)

Cab Suspension Types on Heavy Machines All of the heavy machines, from Scania and other suppliers, that have been looked at have had some type of suspension in the driver's seat. This is an easy, cheap and light way to rapidly improve the driver comfort. This thanks to the principle of sprung- and unsprung mass. Isolating the “light” driver from the “heavy” vehicle is much cheaper and lighter than isolating the whole vehicle from the ground. (Mraz, 2019).

One important factor to take into consideration when comparing the truck cab suspension to other machines is the difference in working conditions; speed, ground surface, tyre size etc. A combine that mostly sees flat fields, low speeds and have big, wide and soft tyres do not need the same type of suspension as a truck that travels fast over sometimes bumpy roads with really stiff tyres.

Agriculture Machines A summary of the different cab suspension types found on agricultural tractors is shown here under, grouped by brand. The characteristics of a tractor can be seen in Figure 9.

Figure 9. Typical example of how an agricultural tractor looks. (Sales, John Deere, 7R (7250) tractor, 2019)

19 Only mid-size and large tractors have been looked at due to the simplicity of smaller tractors most often mean that there is no cab suspension (or even cab). (Sales, John Deere, 5G tractor, 2019)

John Deere: John Deere tractors come with two different types of cab suspension: ● The simpler passive 4 corner solution. This system uses 4 dampers with coil springs (coilover type), one in each corner. The stroke length of the suspension is 100mm. 4 linkage bars control the movements of the cab and a Panhard bar works as a sway bar. (Sales, John Deere, 9R / RT / RX tractor, 2019). The overall suspension layout is shown in Figure 10.

Figure 10. John Deere cab suspension. The letters mark different ingoing components. (Sales, John Deere, 9R / RT / RX tractor, 2019)

● The high-end semi-active HCS+. This is a hydro-pneumatic cab suspension that uses signals from sensors on the front axle suspension and information about the tractors acceleration to increase or decrease the amount of oil in the hydraulic dampers. This gives optimal comfort in all situations. (Sales, John Deere, 6R tractor, 2019). On some models is a Panhard bar used for increased control of the cab movement. The hydraulic cylinders are on the back corners of the cab, and on the front is the cab supported by rubber mounts. (Sales, John Deere, 7R tractor, 2019). The main ingoing components and their positions can be seen in Figure 11.

Figure 11. John Deere cab suspension. The numbers mark different ingoing components. (Sales, John Deere, 7R tractor, 2019)

20 Fendt: The Fendt tractors come with 3 different cab suspension types: ● Their most high-end option, a 3-point air suspension. This is an active cab suspension that compensates for breaking and swaying and is self-leveling. (Sales, Fendt, 700 series tractor, 2019). See Figure 12.

Figure 12. Fendt 3 point active pneumatic suspension. (Sales, Fendt, 700 series tractor, 2019)

This system is even more comfortable on the bigger cab models where a greater difference in height and distance between the mounting point increases the stability and absorption of the rough surface. (Sales, Fendt, 900 series tractor, 2019). See Figure 13

Figure 13. Fendt 3 point active pneumatic suspension. (Sales, Fendt, 900 series tractor, 2019)

● Their mid-end option, 4-point air suspension with automatic leveling feature. (Sales, Fendt, 1000 series tractor, 2019). See Figure 14.

Figure 14. Fendt 4-point active pneumatic suspension. (Sales, Fendt, 1000 series tractor, 2019)

● Their lower-end option, a 4-point suspension with air in the rear and cone-shaped rubber bushings in the front. The system has automatic leveling adjustability in the rear suspension. (Sales, Fendt, 700 series tractor, 2019). See Figure 15 and Figure 16.

Figure 15. Fendt 4-point suspension with cone-shaped rubber bushings in front and active pneumatic suspension in the rear. (Sales, Fendt, 700 series tractor, 2019)

Figure 16. Fendt 4-point suspension with cone-shaped rubber bushings in front and active pneumatic suspension in the rear. (Sales, Fendt, 1000 series tractor, 2019)

22 New Holland: New Holland agricultural tractors come with two different suspension system configurations, both sold under the name “Comfort Ride”: ● A high end fully mechanical system with 4-point suspension. All four ends of the cab are suspended with coil springs and dampers, and then multiple sway bars help to smoothen out and stabilize the ride. (Sales, New Holland, T9 tractor, 2019). See Figure 17 for a better understanding.

Figure 17. New Holland 4-point suspension with dampers and coil springs in each corner. Multiple sway bars ensure a smooth ride. (Sales, New Holland, T9 tractor, 2019)

● An entry-level 4-point system with two rubber isolators in the front and then two coil springs and dampers in the rear working with a sway bar. (Sales, New Holland, T6 tractor, 2019). This simple system can reduce the shock loads that reach the driver with up to 25%. (Sales, New Holland, T8 tractor, 2019).

Case: Case tractors come with two different cab suspension systems. They are used and developed for two different applications: ● For the large articulated steering tractors, the Steiger and Quadtrac tractors, a 4-point cab suspension is used. Each corner is suspended with coil springs and shock absorbers. (Sales, Case, Steiger tractor, 2019). The layout can be seen in Figure 18.

Figure 18. Case 4-point suspension with dampers and coil springs in each corner. (Blog, Case IH Steiger, Cab Suspension, 2011)

23 ● For the more medium sized tractors like their Magnum model, another 4-point suspension system is used. Here are two adjustable damper and coil spring setups in the rear working with a sway bar, and rubber mounts are mounted in the front. (Sales, Case, Magnum tractor, 2019). Figure 19 describes the setup of the suspension.

Figure 19. Case 4-point suspension with adjustable dampers and coil springs in the rear and rubber mounts in front. (Commercial, Case, 2019)

Claas: Claas has two different suspension configurations: ● A semi-active air suspension where the dampers are electrically controlled and adjust automatically to give the perfect ride in all situations. (Sales, Claas, Xerion tractor, 2019). ● A passive 4-point suspension with dampers and coil springs in each corner. Sway bars are mounted to ensure a stable ride. (Sales, Claas, Axion tractor, 2019). Here shown in Figure 20 and Figure 21.

Figure 20. Claas 4-point suspension with dampers and coil springs in each corner. (Sales, Claas, Axion tractor, 2019)

On some of the tractors is an adjustable torsion bar with 3 different stiffness modes mounted. (Sales, Claas, Arion tractor, 2019).

Figure 21. Claas 4-point suspension with dampers and coil springs in each corner. (Sales, Claas, Arion tractor, 2019)

Summary Agriculture Machines A summary is that tractors often use air bellow or coil spring suspension, where the air is the “top of the line” solution.

When looking at other agricultural machines like combines, none of the brands had any type of cab suspension, neither Fendt (Sales, Fendt, Combine, 2019), New Holland (Sales, New Holland, Combine, 2019), Case (Sales, Case, Combine, 2019) or Claas (Sales, Claas, Combine, 2019).

Forestry Machines There are two main types of forestry mechanics, harvesters (Figure 22) and forwarders (Figure 23).

Figure 22. An example of a harvester working. (Sales, Ponsse, Scorpion , 2019)

Figure 23. An example of a forwarder working. (Sales, Ponsse, Elephant King, 2019)

Komatsu: The suspension system on the Komatsu forwarder is called “Comfort Ride”. It is a 4-point hydropneumatic system with integrated automatic leveling features. The system is also fitted with hydraulic sway bar functions. 200mm of travel for the shocks gives great leveling possibilities even in steep hills, see Figure 24. (Commercial, Komatsu, 2019).

Figure 24. Komatsu 4-point suspension with hydraulic cylinders in each corner. (Commercial, Komatsu, 2019)

Rottne: Rottne has its fully automatic leveling hydro-pneumatic suspension system called “Comfort Line”. (Lindman, 2019). 4 hydraulic cylinders make sure that the distance from the cab to the frame always is correct. The cylinders are mounted with rubber mounts to ensure good comfort, and the electronically controlled hydraulics can be turned on and off from the cab. The system described here is mainly suited for forwarders, but there is a variance of the systems that is suitable for harvesters as well. When the hydraulic suspension system was under development was Rottne also considering an air suspension version similar to the one on trucks, but the choice fell on hydraulics. (Sales, Rottne, Comfort Line, 2019).

26 Ponsse: Ponsse is not using cab suspension in the same way as it has been described in previous examples. Instead, they use a 3-piece frame for their harvester, and the cab is mounted on the middle piece (marked red in Figure 25). The front and rear frame pieces are moving according to the terrain. Their hydraulic controlled middle piece is kept level at all times. It is more of a frame control system than an actual suspension system. (Sales, Ponsse, Scorpion King, 2019).

Figure 25. Ponsse hydraulic frame control. (Sales, Ponsse, Scorpion info, 2019)

On the forwarders is the system called “Active frame”. The system mainly protects the driver from sideway swaying, which is the type of motion that is most damaging to the drivers’ body. (Sales, Ponsse, Elephant King, 2019).

John Deere: John Deere provides two options on their forwarders and harvesters, either a fixed cab or a rotating and self-leveling cab. (Sales, John Deere, Forwarder, 2019)

Summary Forestry Machines Summarising, the suspension system on harvesters and forwarders working in the forestry industry more or less all work with hydraulic. This is most likely due to the already existing heavy-duty hydraulic systems on the machines, and the need for long stroke length to compensate for rough terrain.

27 Construction Machines When looking at construction machines like wheel loaders (Figure 26), bulldozers (Figure 27), dump trucks (Figure 28), excavators (Figure 29) etc. almost all of them were missing any type of cab suspension. Some of them had rubber mounts and only a very few had hydraulic cab suspension.

Figure 26. A typical wheel loader. (Sales, CAT, Wheel loader, 2019)

Figure 27. A typical bulldozer. (Sales, CAT, Dozer, 2019)

Figure 28. A typical dump truck. (Sales, CAT, Dump truck, 2019)

Figure 29. A typical excavator. (Sales, CAT, Excavator, 2019)

Hydraulic suspension could be found at: ● Ljungby wheel loaders. Their very sophisticated “Ljungby Maskin Comfort System” is an automatic hydraulic cab suspension system. The system has the option of being manually controlled and raises the cab about 50mm from the standard fixed cab. (Sales, Ljungby, 2019). ● Volvo excavator. The cab is mounted on hydraulic dampers which gives a nicer comfort. (Sales, Volvo CE, Excavator, 2019). ● Volvo mining truck. The truck has hydraulic suspension with viscous damping to provide maximum comfort. (Sales, Volvo CE, Mining truck, 2019).

Rubber mount suspension and fixed cabs will be found at: ● Volvo dump trucks. (Sales, Volvo CE, Dump truck, 2019). ● Volvo wheel loaders. (Sales, Volvo CE, Wheel loader, 2019). ● Claas wheel loaders. (Sales, Claas, Wheel loader, 2019). ● JCB wheel loaders. (Sales, JCB, Wheel loader, 2019). ● JCB excavators. (Sales, JCB, Excavator, 2019). ● JCB rough terrain forklifts. (Sales, JCB, Forklift, 2019). ● CAT bulldozers. (Sales, CAT, Dozer, 2019). ● CAT mining trucks. (Sales, CAT, Mining truck, 2019). ● CAT wheel loaders. (Sales, CAT, Wheel loader, 2019). ● CAT dump trucks. (Sales, CAT, Dump truck, 2019).

Trucks, other brands It was very difficult to find information and good sources about the suspension system on other truck manufactures than Scania.

Volvo: Volvo has multiple different cab suspension combinations: ● Air bellows with dampers front and rear. (Sales, Volvo Trucks FE, 2019). ● Air springs with dampers rear and coil springs with dampers front. (Sales, Volvo Trucks FH, 2019). ● Coil springs with dampers front and rear. (Sales, Volvo Trucks FE, 2019). ● Coil springs with dampers rear and rubber mounts front. (Sales, Volvo Truck FL, 2019).

29 Information about what cab suspension alternatives the other truck manufacturers could provide could not be found on their website. But using information from auction sites, aftermarket and spare parts dealers etc. shows that at least following systems are used:

MAN: Used spare parts for both air bellows and coil springs could be bought. (Sales, Rackstad, spare parts MAN, 2019).

Renault: Used spare parts for both air bellows and coil springs could be bought. (Sales, Bison Parts, spare parts Renault, 2019).

DAF: Used spare parts for both air bellows and coil springs could be bought. (Sales, Bison Parts, spare parts DAF, 2019).

Mercedes: Used spare parts for both air bellows and rubber mounts could be bought. (Sales, Rackstad, spare parts Mercedes Benz, 2019).

Peterbilt: Used spare parts for both air bellows and rubber mounts could be bought. (Sales, Vander Haag's, spare parts Peterbilt, 2019).

International: Used spare parts for both air bellows and rubber mounts could be bought. (Sales, Vander Haag's, spare parts International, 2019).

MACK: Used spare parts for both air bellows and rubber mounts could be bought. (Sales, Vander Haag's, spare parts Mack, 2019).

Freightliner: Used spare parts for both air bellows and rubber mounts could be bought. (Sales, Vander Haag's, spare parts Freightliner, 2019)

Kenworth: Used spare parts for both air bellows and rubber mounts could be bought. (Sales, Vander Haag's, spare parts Kenworth, 2019)

Western Star: Used spare parts for air bellows could be bought. (Sales, Vander Haag's, spare parts Western Star Trucks, 2019)

30 Aftermarket Solutions There are lots of companies making aftermarket custom suspension solution for all kind of applications. Here are some interesting examples of cab suspension companies and their solutions, together with other overall interesting suspension solutions.

Aftermarket Cab Suspensions AgCabSolution: AgCabSolution is an aftermarket alternative to add comfort, safety and longevity to the cab of the tractor. The system contains one air bellow that is pumped up to chosen height and stiffness, and two shocks that control the movement. A drag link is also incorporated. (Sales, AgCabSolution, About Us, 2019). The simple layout is shown in Figure 30.

Figure 30. AgCabSolution. (Sales, AgCabSolution, Photos and Videos, 2019)

Link Manufacturing: The “Cabmate” produced by Link Manufacturing is a premium cab suspension option. It uses air bellows, shock absorbers, air leveling valves and well-designed brackets to give a more comfortable ride for the driver. This system replaces the original solid rear rubber mounts for the cab. (Sales, Link, Cabmate, 2019). See Figure 31.

Figure 31. The Cabmate by Link Manufacturing. (Sales, Link, Cabmate, 2019)

31 Valid Trueline Auto Leveling: The Trueline Auto Leveling system from Valid Manufacturing is an automatic leveling system for RV (campers) and specialty vehicles. It provides anti-dive control, electronic ride enhancement control and electric ride height control. (Sales, Valid Manufacturing, Leveling / Ride Height Systems, 2019). The system layout is shown in Figure 32.

Figure 32. The Trueline Auto Leveling. (Sales, Valid Manufacturing, TRUELINE Leveling System, 2019)

Aftermarket Overall Solutions Roadmaster Active Suspension: The Roadmaster Active Suspension is basically a help coil spring that fits on the standard leaf springs (Figure 33) in the rear of a pickup. It prevents sagging when the pickup is loaded, when pulling a heavy trailer etc. It also absorbs added force from an increase in torque, meaning that it reduces axle wrap and wheel hop. It also reduces body roll. (Sales, Roadmaster Active Suspension, 2019).

Figure 33. The Roadmaster Active Suspension. (Sales, Roadmaster Active Suspension, 2019)

32 Mittler Bros. Hydroshox: The Hydroshox is a coilover suspension with a hydraulic cylinder mounted on top. This hydraulic cylinder can be extended or compressed depending on the wanted ride height. Thanks to that the cylinder is mounted on top of the coilover will the damper and coil spring not be affected by the change in ride height, meaning that the car will behave similarly independent of ride height (except change in center of mass). The design is so compact that the full suspension unit will fit just like a normal coilover would do and gives up to 125mm of ride height change from the hydraulic cylinder, and 75mm of travel in the damper and spring. (Sales, Mittler Bros., Hydroshox, 2019). Better explained in Figure 34.

Figure 34. The Hydroshox Suspension. (Sales, Mittler Bros., Hydroshox, 2019)

JRI shocks: JRi ride height system is a suspension system very similar to the Hydroshox. (Sales, JRI Shocks, Ride Height System, 2019).

Umbrella Auto Design VRH: The Variable Ride Height suspension system from Umbrella Auto Design is basically a coilover with a pneumatic cylinder mounted on top instead of a hydraulic cylinder. (Sales, Umbrella Auto Design, VRH Lift System, 2019). The design is clear when looking at Figure 35.

Figure 35. The Umbrella VRH lift system. (Sales, Umbrella Auto Design, VRH Lift System, 2019)

33 BOSE suspension: The BOSE suspension uses linear electromagnetic motors instead of conventional coilovers. Amplifiers that provide the electricity to the motors are doing it in such a way that the energy from compression also can be regenerated. The BOSE suspension can react much faster than conventional suspension and extract or compress much quicker. The suspension is not yet in production. (Harris, How Stuff Works, CS.9, 2019). Figure 36 shows one way that the suspension can look.

Figure 36. The Bose Suspension. (Harris, How Stuff Works, CS.9, 2019)

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35 Implementation

Requirements Scania has standard requirements that must be fulfilled in order to let the cab suspension system pass and go into their products. Some of these criteria and functions are stated here.

The cab suspension must: ● Carry the cab and keep it in its normal driving position ● Handle a static load of 2300-4100 N (front) and 1800-3200 N (rear) ● Handle compression forces of 20 kN (front) and 15 kN (rear) while driving ● Handle rebound forces of 7 kN (front) and 1 kN (rear) while driving ● Handle compression forces of 25 kN and rebound forces of 20 kN when the cab is tilting (only front suspension) ● Pass the “shake rig test” according to Scanias internal requirements ● Pass the “tilting test” according to Scanias internal requirements ● Pass the legal requirements ECE R29 impact test. This test is made on a complete cab. The cab spring assembly shall resist a vertical compression load, increasing from 0 to 50 kN. Then is the roof pulled upwards with a force of 0 - 30 kN acting on each spring assembly. ● Pass the corrosion test according to Scanias internal requirements ● Handle temperatures tests from -40° C to +100° C ● Have good resistance to multiple liquids; brake fluid, diesel, battery acid, ethanol, etc. ● Be able to be disassembled by one person without the need of special tools ● Be made of as few different materials as possible and the material shall be recyclable ● Work quietly. No disturbing noise from the suspension shall be noticeable for the driver, regardless of driving conditions. ● Be as lightweight as possible given the strength and reliability demands

All the suspension components must be able to fulfill the criteria.

The criteria for the cab suspension system chosen in this study are stated here. The cab suspension must: ● Have adjustable ride height to compensate for change in load and load distribution inside the truck cab ● Be able to fit at the same positions and in similar mounts as current suspension solution ● Be a least as comfortable as the fully mechanical system (coil spring + damper) ● Use less energy than the current pneumatic solution The two criteria for energy and comfort will not be able to confirm. No physical comfort tests will be performed, and the current energy consumption is unknown. This is due to that the current compressor has more applications than just the pneumatic suspension.

It is a bonus if the system also is: ● Lighter than current pneumatic solution ● Smaller than current pneumatic solution

36 Different Concepts A total of ten different cab suspension concepts could be made up thanks to the background information. • The first concept was the current pneumatic air bellow with comfort damper suspension. • The second concept was the current mechanical coil spring with standard damper suspension. • The third concept was a pre-pressurized air bellow with standard damper suspension, similar to the AgCabSolution seen in Figure 30. • The fourth concept was a new version of the current air bellow with comfort damper suspension. The suspension components stay the same, but the pressurized air is created by its own electric compressor instead of the current compressor that is run by the engine to power all pneumatic subsystems on the truck. • The fifth concept was a hydro-pneumatic solution. The amount of hydraulic oil sets the ride height and acts as the damper, and an air accumulator acts as the spring. See Figure 4 for a better understanding of the system layout. • The sixth solution was similar to the current mechanical coil spring and damper solution, but with an extra feature of spring preload adjustment. A hydraulic cylinder can extend or reduce in length to compensate for the coil spring compression. • The seventh solution was also similar to the current mechanical soil spring and damper solution, but here with at hydraulic cylinder on top of the full suspension assembly. This allows for length change of the component without affecting the preload of the coil spring. Similar solution as the Hydroshox solution seen in Figure 34. • The eight solution was the same as the seventh solution but with a pneumatic cylinder instead of a hydraulic cylinder, just like the VRH solution for Umbrella Auto Design seen in Figure 35. • The ninth solution was a similar system to the sixth solution, but with an electrically driven geometric preload adjustment on the spring. An electric motor drives a nut that compresses or slacken the spring to increase preload. • The tenth solution was the same as the seventh and eight solution, but instead of changing the length of the suspension component is the mounting position moved. This could be done electrically with an electric motor that moves an excentre or similar.

Concept Evaluation When all the background information was summarized into different suitable concepts a weighted Pugh matrix (Dermott, 2019) was created to help with the concept evaluation. The complete weighted Pugh matrix can be found in Appendix 3, Pugh Weighted Matrix.

All the weights (priorities) were set in cooperation between Teodor Hidén (thesis author) and a crew of four Scania employees with lots of relevant experience in this subject. The Scania crew was;

- Mattias Hammarwall - Group Manager, RCCB - Cab Body and Suspension - Fredrik Aldebert - Design Engineer, RCCB - Cab Body and Suspension - Micaela Niclasson - Design Engineer, RCCB - Cab Body and Suspension - Mats Hugdahl - Senior Engineer C3, RTCD - Vehicle Dynamics

37 First was all the different concepts worked out. Then were all the different properties and characteristics decided. The current pneumatic (active) suspension was set as the standard or reference system; the system that the others were compared to. The other concept systems were then ranked from -3 (worst possible) up to +3 (best possible) points, where 0 point is as good or bad as the reference system.

The main focus was set on the possibility of adjustable ride height. Then came power consumption, handling, comfort, complexity and robustness.

Some concepts fell straight of the line; the current mechanical system with coil springs and the pre-pressurized air bellow, they were not automatic adjustable. These systems neither consumed any energy, but the adjustability was a must.

Next system to fall out was the hydropneumatic suspension. This system was estimated to be a high energy-consuming, complex, heavy and expensive system.

The different suspension systems where the ride height adjustability is performed outside of the suspension components, e.g. does not affect the preload of the spring or similar, but move the mounting point or extend the total length of the suspension component, has one big downside. These systems do not give the possibility of using a comfort damper (see Figure 37). The systems are about as energy-consuming, complex, heavy and expensive as the similar systems where the ride height adjustment instead is done by compressing a coil spring, changing the preload of the spring, but without the possibility of using comfort dampers. Therefor could not the system with a hydraulic or pneumatic cylinder on top of the coilover make it all the way. The same thing for the concept where the mounting point on the chassis should be moved; these systems can neither allow the possibility of using comfort dampers.

Except for the two chosen systems, deeper described in the following chapter, was there only one concept left. It was the same system as the current pneumatic system, but with its own electric compressor and a new control system. This system should be somewhat easy to implement to current cab suspension and did not need to be further investigated.

Chosen Concepts There could be seen that the best option should be a system that could adjust the height in such a way that the use of “comfort dampers” is possible. This is the type of damper currently used on the air bellow suspension system on Scania trucks.

It is also important that the system is passive when not adjusting. Minimizing the amount of adjustments also minimizes the amount of energy consumed. Maybe only adjust when the truck is started, or a button is pushed. This would be very energy efficient and would hopefully be enough to provide good comfort for the driver. This because the load distribution in the cab almost never changes during driving. It is when loading the cab with driver, passenger, luggage or gods that the load and load distribution in the cab is changed. When the truck is in motions the driver is in his or her seat, the luggage hopefully stored correctly on the shelves, etc. This type of control system would need a suspension system that when not adjusting, is completely passive and can hold its set ride height. No leakage or movement of the adjusters at all can be accepted.

38 (This is why a pneumatic controlled system was not accepted. Due to previous experiences from Scania employees shows that a completely airtight system never is airtight. Another problem is the compressibility of gases). (Hughdal, 2019)

Damper Description The “comfort damper”, ex. Vario Damper from ZF, has a control groove in the cylinder tube. The piston valve will have less resistance when it passes through or moves where this groove is (more area and less resistance for the hydraulic oil to pass through top to bottom or vice versa). This gives a smoother ride compared to when the piston valve is outside the grooved area (or comfort zone), and the oil needs more pressure to pass through the valve. This type of damper is also known as “Stroke-dependent damper”.

The damper is passive and has no adjustability, but thanks to the possibility to keep the ride height constant are this not needed. As long as the ride height is correct will the damper be smooth at cruise height and stiffer when compressed/extended a lot. (Sales, ZF, Axel Dampers, 2019). The damper design with explaining plots is shown in Figure 37.

Figure 37. ZF Vario Damper. Here can be seen how the damping force is less at cruise height and increased when damper compresses or extends a lot. (Sales, ZF, Axel Dampers, 2019)

Concept 1 - Hydraulic Height Control The first chosen system to investigate will be about hydraulically adjusted ride height.

The idea is to have some type of hydraulic cylinder that can lift and adjust the total suspension unit length to compensate for the compression of the coil spring. The coil spring will compress under load. It is important that the ride height stays constant for any load, and then will the damper work in its comfort zone. This meaning that the pre-load on the coil spring will change.

39 Concept 2 - Electronic Height Control The second chosen system to investigate will be about electronically adjusted ride height.

The idea is to have some type of electronically driven motor/ servo/ solenoid that turns a lock nut, excentre, worm gear or similar, that can lift and adjust a coil spring, so that the ride height stays constant for any load, and then will the damper work in its comfort zone. This is also meaning that the pre-load on the coil spring will change.

Example Picture of Idea The suspension unit to the left in Figure 38 is an example of a standard, passive coilover (similar to the mechanical suspension system used on the truck cab today). In the middle is an example of how a hydraulic version could look and to the right how an electric version could look.

Figure 38. Conceptual ideas of how a suspension unit could look like. (Sales, Stage 3 Motorsports, Adjustable Coilover, 2019) (Hidén, 2019)

Existing Solutions KW - HLS: KW is a German brand founded in 1995. They are well known in the car society for making high-quality suspension components. (Sales, KW Suspension, About us, 2019).

KW has a product they call “HLS” - Hydraulic Lift System. It is a system that can lift the vehicle up to 45mm. The hydraulic cylinder is mounted between the spring plate and the spring (Figure 39), and when adjusted to the correct height will the control valve be closed and the cylinder completely solid and hold its position (no leakage or compression). (Sales, KW Suspension, HLS, 2019). The system uses an external hydraulic pump and valve unit. (Sales, Autex, KW HLS, 2019). The required lifting time (from zero to full extent) is 4-5 sec when only the front is lifting. (Sales, Vividracing, KW V3, 2019).

Figure 39. KW HLS suspension unit. (Sales, KW Suspension, HLS, 2019)

TouraTech (similar to TracTive): TouraTech provides aftermarket suspension solutions for motorcycles. Their Extreme Rear shock for KTM 1090/1190/1290 has 50% more adjustments for spring preload compare to a standard solution (up to 15mm). This 15mm on the coilover means that the back of the motorcycle rises up to 50mm. This preload is set by hand while turning a knob to raise the hydraulic cylinder. (Sales, TouraTech, Extreme Shock KTM, 2019). See Figure 40 and Figure 41 for better understanding.

Figure 40. The turning knob and the hydraulic preload adjuster cylinder. (Sales, TouraTech, Extreme Shock KTM, 2019)

Figure 41. Here can be seen how the hydraulic cylinder has been lifted. (Sales, TouraTech, Extreme Shock KTM, 2019)

It is also possible to get the same type of adjustable preload suspension, but instead of turning a knob manually to increase the preload this is done by an electronic stepper motor. (Sales, TouraTech, ESA upgrade BMW, 2019). See Figure 42.

Figure 42. The electric driven preload version only needs electric inputs. (Sales, TouraTech, ESA upgrade BMW, 2019)

TracTive EPA (similar to TouraTech): The Austrian company TracTive Suspension was founded in 2010, coming from WP Suspension. Their suspension products are used in everything from Formula 1 cars to Enduro motorcycles. (Sales, TracTive, History, 2019).

TracTive is producing something they call EPA - Electronic Preload Adjuster. This is a powerful stepper motor (Sales, TracTive, BMW ESA, 2019) that is used to drive and extend a hydraulic cylinder, which then compress the spring and rises the ride height. The hydraulic cylinder can be adjusted about 15mm carrying a load of 10kN. (Commercial, TracTive, 2019). This system does not need any external hydraulic pump. (Sales, TouraTech, Electronic Suspension, 2019). The motor is inside the black plastic cover shown in Figure 43 or the black and gold cylinder shown in Figure 44.

Figure 43. One type of EPA (ESA) suspension, for a BMW motorcycle. (Sales, TracTive, BMW ESA, 2019)

Figure 44. Another type of EPA suspension. (Sales, TouraTech, Electronic Suspension, 2019)

BMW - ESA (org system): BMW motorcycles can be fitted with a system called ESA - Electronic Suspension Adjustment from the factory. This system works thanks to electrohydraulic. The spring rate of the system is changed using two springs connected in series. One of the springs has an elastomer element inside of the coil spring. This elastomer can only expand inwards, and an aluminum sleeve that can be moved up and down thanks to electrohydraulic are changing the amount of expansion possible for the elastomer. This changes the spring stiffness and the ease of compression. (Sales, BMW Motorrad, ESA, 2019).

Aprilia - ADD (org system): Aprilia Dynamic Damping, or ADD, is a truly active motorcycle suspension. The spring preload can be set to 4 predefined settings; driver, driver + luggage, driver + passenger, driver + passenger + luggage, and then will the bike do small adjustments by itself. The spring preload adjuster is only on the rear suspension. (Sales, Aprilia, ADD, 2019). The change in spring preload and damping behavior are possible thanks to electromechanics. (Sales, Aprilia, Caponord, 2019).

KTM - EDS (org system): The Electronic Damping System by WP can be found on various KTM motorcycles. It has the same 4 different predefined preload settings as the Aprilia ADD system. (Sales, KTM, 1190 Adventure, 2019).

RamLiftPro: RamLiftPro provides a system where hydraulic cylinders that lifts up to 40mm can be placed between the spring seat and the coil spring. They are suitable for standard 2” and 2,5” shocks and coilovers. The hydraulic cylinders are run by an external 12v hydraulic pump. (Sales, RamLiftPro, 2019). The ingoing components can be seen in Figure 45.

Figure 45. RamLiftPro cylinders that are fitted on the original coilover. (Sales, RamLiftPro, Shop, 2019)

The pump used for RamLiftPro (Sales, Hy-Pro, Pumps for RamLiftPro, 2019) to drive the system has a working pressure of 55 bar and a flow rating of up to 2,5 l/min. (Sales, Hy-Pro Drive, PR+, 2019).

Mercedes - ABC (org system): The Active Body Control on the high-end Mercedes cars uses a hydraulic cylinder on top of the coil spring to constantly change and adjust the spring preload. This fully active suspension adapts its setting every 10ms. (Commercial, Mercedes-Benz ABC, 2019)

Öhlins - EC: The Electronically Controlled adjustable suspension from Öhlins works just like the other systems above. A DC motor in a remote hydraulic preload adjuster (the silver cylinder in Figure 46) creates the hydraulic pressure needed to expand the hydraulic cylinder and increase the preload on the coil spring. (Sales, Öhlins, TTX EC, 2019)

Figure 46. Example of how the EC hydraulic preload adjuster looks. (Sales, Öhlins, TTX EC, 2019)

Lamborghini - front suspension lift: Lamborghini, who is a well-known producer of supersport cars, equip some of their models with a hydraulic suspension lift in the front. This to improve the driveability and increase the ground clearance when needed, e.g. when passing a speed bump. (Commercial, Street FX Motorsport TV, Lamborghini, 2019). The lifting capacity is up to 40 mm. (AutoBlog Staff, 2011). The hydraulic lift cylinder is placed on top of the coil spring, as a part of the coilover suspension unit. (Dan Edmunds, 2012). See Figure 47 and Figure 48.

Figure 47. Lamborghini pushrod suspension. (Dan Edmunds, 2012)

Figure 48. The Öhlins coilover with hydraulic lift cylinder. (Dan Edmunds, 2012)

Concept Summary There seems that all the existing solutions to this problem are pretty similar; a hydraulic cylinder can expand or compress, changing the preload on the coil spring and in that way rise or lower the vehicle. The hydraulic oil is controlled either manual by turning a knob, electrical where a stepper motor is “turning the knob” or by a separate hydraulic pump. This is the same as concept 1 described in the beginning. There does not seem to be any commercial solution on the market for concept 2.

45 Further Design of the Chosen Concept The chosen design to continue work further with is Concept 1, hydraulic ride height adjustments. The system will be pretty similar to the RamLiftPro system, but with a more advanced control system.

Calculations To be able to lift the cab of a truck will forces similar to lifting a car be needed (up to ~ 1500kg = 15 kN). The maximum load that the suspension components need to withstand is 25 kN over the two front suspension components. (See Scania specifications in Requirements). These 25 kN over the two front suspension components will therefore be the limiting design requirement.

The current coilover suspension used on Scania trucks have the following dimensions:

Figure 49. The current mechanical coilover used in Scania trucks. Dimensions may vary between different load rating options. (Hidén, 2019)

The dimensions shown in Figure 49 shows that a suitable hydraulic lift cylinder should have an inner diameter of ~43 mm and an outer diameter of 88 mm, with an inner collar for the spring of ~ 65 mm. To calculate the needed hydraulic pressure P in the hydraulic cylinder to withstand the force F requirements given from Scania, formula (1.1) can be used:

46 F P = (1.1) A

The area A that will be used is the area difference between the outer and inner dimensions of the hydraulic cylinder, minus the needed wall thickness. To calculate the required wall thickness of the cylinder can the formula from Figure 50 be used.

Figure 50. Wall thickness formula for hydraulic cylinders. (IH Service, 2019)

The values for material property S come from the table in Figure 51.

Figure 51. Material properties for hydraulic cylinder materials. (IH Service, 2019)

Assuming that a wall thickness of 5 mm of the weakest steel C-1010 is used, gives a maximum pressure Pmax of 4550 Bar. This well over any pressure used in any similar application. (only pressure strength calculated).

To calculate the area A that the pressure P will act on is formula (1.2) used.

22 ddout   in  A =−    (1.2) 22   

The area is 15 cm2, which when used in (1.1) leads to a needed maximum hydraulic pressure P of 80 Bar, if the hydraulic cylinder has the dimensions described above.

47 This seems reasonable when a standard hydraulic system can be assumed to handle forces around 2000 to 4000 PSI (~ 140 to 180 Bar). (MD Staff, 2002).

It is possible to decrease the wall thickness of the hydraulic cylinder seen to what pressure they can withstand. This meaning that the area which the lifting pressure act on will be increased, meaning that the pressure needed to lift the cab will decrease.

The currently used hydraulic systems on Scania trucks for steering, lifting the support rear axle and to tilt the cab are using a maximum pressure of 170 Bar for the steering, 150 Bar for lifting the support axle (Karlsson, 2019) and 300 Bar to tilt the cab (Tällberg, 2019). This means that all this system has the capacity of also supporting the hydraulic adjustability ride height systems (seen to pressure).

When calculating the stroke length X needed on the hydraulic cylinder must the spring constant K and the force difference F be known (1.3).

F X = (1.3) K

We can assume that the driver's weight can vary up to 100 kg, and that no driver needs more than 100 kg of luggage. This means that we have a force difference on the springs of about 2000 N. In the worst-case scenario will all this mass be placed just at the driver side front spring. (If there is a passenger with luggage will this of obvious reasons not just affect the suspension on the front driver side). The stiffest coil spring provided by Scania that can handle about 4000 N of static load, has a spring stiffness of about 65 N/mm. (Numbers provided by Scania are rounded due to secretes). Inputting these numbers in MATLAB gives that the stroke length of the hydraulic cylinder needs to be 31 mm. A lift stroke length of 31 mm and an area of 15 cm2 means that each cylinder will have a maximum oil volume V of 0,5 dl (see equation (1.4))

VAL= (1.4)

Additional oil for hoses, reservoir, pump etc. will be needed. All the calculations are done in MATLAB and can be found in Appendix 5, MATLAB Calculations.

A softer coil spring would be compressed more than a stiff one, but the softer springs are also fitted only on lighter and shorter cabs. In a shorter cab is the load inside the cab better distributed between all the suspension components, meaning that less force will act on each of them. This means that the results for needed stroke length on each hydraulic cylinder will be about the same. (Aldebert, 2019). The stroke length of 31 mm also seems very reasonable. Today can the coil pre-tension be done manually from the outside of the cab in 3 steps of 5 mm, a total of 15 mm. (Niclasson, 2019). Similar system for cars like the RamLiftPro is developed for similar forces and has a stroke length of 40 mm. (Sales, RamLiftPro, 2019).

48 Hydraulics is highly independent of temperature in its environment. As long as the temperature is between -40 and +100 degrees Celsius is no additional heating or cooling system required to ensure full functionality. (Gannon, Control Tips, 2017). This makes the hydraulic suspension solution very suitable for our application.

Suspension Control System The idea is to have a system that adjusts as little as possible. Using cab ride height sensors, like potentiometers (Info, Kjell o Co., Potentiometer, 2019), together with some height linkages that can feel the height difference between frame and cab would be a suitable solution. (Engineers Edge, 2019). These components should be placed in each corner of the cab, next to the suspension mounting points.

When the cab is loaded down and the height goes outside its pre-defined preferred value, can the cab-height-ECU (Info, SEAT, ECU, 2019) send signals to the hydraulic valve system to rise that hydraulic cylinder. The cab-height-ECU should only tell the valve package to adjust when the cab has its resting height outside of its height range, not when bouncing. This can be coded into the ECU, that the height must be out of its range for a certain amount of time before height regulation is done.

Minimizing the work for the hydraulic pump is not just beneficial for energy consumption, but also for driver comfort. The noise coming from the hydraulic pump can be perceived as very annoying and unpleasant.

49 Results

Using hydraulic cylinders mounted in series with coil spring makes it possible to adjust the ride height without continuously consuming energy. The hydraulic cylinder extends to compensate for the compression of the coil spring when the load in the cab is increased. The extension of the hydraulic cylinder affects the preload of the spring. The hydraulic system will be able to fit where the current suspension components fit, thanks to the compact size of the hydraulic cylinders. Hydraulics are completely passive and solid when the valves are closed, meaning that the set ride height will hold between adjustments. The adjustable solution also makes it possible to use comfort dampers, which highly improve the comfort for the driver compared to the mechanical suspension used today.

The energy consumption will be less than for the pneumatic suspension system used today. Thanks to the higher pressure in hydraulics all components can also be much smaller in size, which also makes them lighter. The solution where hydraulic cylinders are used to adjust the ride height benefit from the fact that there already are at least 3 other hydraulic systems on the truck; the steering, the support axle lift and the cab tilt. All these 3 systems operate at a higher pressure than what is needed for the cab adjustability systems. Neither of these systems must be able to work simultaneously with the cab height adjustment, meaning that the already used pumps (most likely) could do the job of cab height adjustment as well. Only a larger oil reservoir would be needed.

Conclusion

Developing the hydraulic adjustable ride height systems seems to be possible even with a limited recourse. This is mainly thanks to the usage of conventional components. The dampers and coil springs planned to be used are already tested and used. The only part that must be slightly modified is the lower spring support that has to be lowered so that the hydraulic cylinder can fit in between the spring support and the coil spring. This must be done without changing the “zero” preload on the spring. Only the hydraulic cylinders them self must be designed and tested, but similar sized product with similar properties are already out on the market, proven to work well on other vehicles.

One big challenge will be to implement the control system. This can be done with 3 or maybe 4 separate ride height sensors. If the choice is 3 sensors will these be placed like a triangle (two in each corner in the front and one in the center rear) and if the choice is 4 sensors can they be placed one in each suspension component (in each corner). The 4-sensor system will be over determent if all 4 of them are registering ride height at the same time, but may allow integrated sensors in the suspension components, and a fewer total amount of component. These sensors must communicate with an ECU, that communicates with the electronic valve package that adjusts the pressure and amount of oil in each hydraulic cylinder. The hydraulic pump needs a pressure sensor that makes the pump run as soon as the pressure is too low.

The whole system also needs to be tested for robustness, different environments, etc.

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51 Discussion

The assumption that the pneumatic suspension system used today is more inefficient than the proposed hydraulic suspension solution is mainly based on the fact that the hydraulic system does not have to run continuously. It would be interesting to know how much energy the pneumatic system used today actually consumes, and how much this could be optimized. Maybe just replacing the current compressor that is run by the combustion engine with a separate electric compressor, make a smarter electric control system and optimizing everything is a good option. Especially if this can be done while keeping the current air bellows and dampers. This might be an easy way to implement a more efficient suspension system.

During the information research in the beginning of the thesis, it could be seen that American made, and products made for the American market, more often than their European concurrent, were completely missing or only had simple suspension components. Using rubber mounts instead of air bellows for the rear of truck cabs is a typical example. It could also be seen that there are lots of aftermarket companies that provide this comfort solution afterward. Customizability comfort solutions or “hardworking rough cowboy”-mentality seems to be two totally different camps in this business area.

It was beneficial that a truck cab weighs about as much as a standard small-medium size car. This means that suspensions components designed for handling forces between car and road should be able to handle the forces between the cab and the frame. The amplitudes and frequencies are probably different in these two cases, but the main forces should be similar.

One limitation has been to only look at suspension components that fit in the current suspension mounting position. This means that all components have been of coilover type. If a solution with separate damper and spring was allowed, what other types of suspension options would that give? This will need a big change in the cab structure, both front, floor and rear, but it may be an interesting option for future cab types.

All the heavy machines that have been looked at have in common that they are workstations. The driver spends most of his or her day in the seat of the vehicle, meaning that the seat must be comfortable. That is probably one reason why so much money and engineering have been invested into this area. There are still machines out there used every day without cab suspension, but with advanced suspended seats. Maybe there is time for eg. construction machines to investigate more in cab suspension solutions. The cab suspension is not only providing a better ride, it also isolates the driver from vibrations and sound from the driveline, tracks, hydraulic pumps etc.

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53 Future work

About Chosen Concept How can the overall hydraulic systems on the truck be merged and optimized? The steering may have to have its own closed system due to safety and risk minimization, but can the support axle lift, cab tilt and cab ride height adjustment have the same pump and oil reservoir? This would minimize the total ingoing parts but needs better logistics of hydraulic hoses and controls. How would it work with the hydraulic oil reservoir, does it need to be placed above all the other components?

Sound and driver comfort? How can the noise from the hydraulic pump be minimized? Is it low enough that the adjustments of cab ride height can be done every time the trucks start, or so noisy that the total amount of adjustment needs to be minimized, booth seen to comfort and energy consumption? How can the placement of the pump be optimized?

How should the control be done? Shall there be 4 ride height sensors or is 3 enough? For how long should the cab be out of comfort zone before adjustment? Should the ride height sensors be calibrated using a gyro to compensate for imperfectness in the frame and suspension mounting points? Should there be a possibility to make the cab horizontal to the environment when sleeping even if the truck is parked in an angle?

Possibility to use softer coil springs? Softer springs together with an increase in adjustability would give a comfort increase. Today are there multiple options of coil springs; can the total amount of spring rate options be decreased thanks to the adjustability?

Implementation? Mounting possibilities? How can the production benefit from the new system? Will the assembly time increase or decrease?

Resonance frequencies? Will there be other resonance frequencies produced by the electric engine? How will this affect different systems in the suspension?

Economical value? Is the development of a new hydraulic system financially justifiable? Are the costumers willing to pay for the (assumed) gain in cruising range of the truck?

54 About Other Areas Driver comfort? If the driver comfort is the main focus, more work should be done in the suspended driver seat area. Small improvements here can have larger effect on the comfort than the cab suspension has, to a smaller price.

Choice of dampers? Active dampers were neither in focus during this thesis, but active dampers can make a big improvement in the handling and the truck. Or is the gain in comfort neglectable? Maybe will different gases behave differently in dampers / air bellows / accumulators?

Changes in cab mounting points and sway bars? Is a 4-point cab mounting concept the best, or would a 3-point system be lighter, more comfortable and cheaper? It is hard to implement 3-point suspension mounting systems today because of engine and gearbox placement, will this be different with electric driveline? Active sway bars to improve handling is a big improvement on cars, how would that work for truck cabs?

Have a closed / sealed air system? Using pneumatic cylinders or air bellows, how much would they compress? Is it possible to find or make non-leakage pneumatic systems that are controlled like the hydraulic example here (not adjusting live all the time)?

55 References

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61 excavators/brochures/brochure_ec480e_stagev_sv_12_20057778_a.pdf?v=BNhEP w Sales, Volvo CE, Mining truck. (2019, 9 22). Volov CE. Retrieved from https://www.volvoce.com/-/media/volvoce/global/products/rigid- haulers/brochures/brochure_r100e_t2_sv_12_20055958_c.pdf?v=O4lAPw Sales, Volvo CE, Wheel loader. (2019, 9 22). Volvo CE. Retrieved from https://www.volvoce.com/-/media/volvoce/global/products/wheel-loaders/wheel- loaders/brochures/brochure_l350h_stagev_sv_12_20057499_a.pdf?v=hetDPw Sales, Volvo Truck FL. (2019, 9 22). Volvo Trucks. Retrieved from https://www.volvotrucks.se/sv-se/trucks/volvo-fl/specifications/cab.html Sales, Volvo Trucks FE. (2019, 9 22). Volvo Trucks. Retrieved from https://www.volvotrucks.se/sv-se/trucks/volvo-fe/specifications/cab.html Sales, Volvo Trucks FH. (2019, 9 22). Volvo Trucks. Retrieved from https://www.volvotrucks.se/sv-se/trucks/volvo-fh/specifications/cab.html Sales, ZF, Axel Dampers. (2019, 9 22). ZF. Retrieved from https://www.zf.com/products/en/buses/products_29050.html Sales, Öhlins, TTX EC. (2019, 9 22). Öhlins. Retrieved from https://www.ohlins.eu/download/db/Ohlins_DTC_owners-manual-ttx-ec- stossdaempfer--00001231.pdf Shirish. (2019, 9 19). Car Bike Tech, Active/ Adaptive Suspension. Retrieved from https://carbiketech.com/active-suspension-adaptive-suspension/ Tan, W. (2019, 9 19). Carmudi Insider, CS. Retrieved from https://www.carmudi.com.ph/journal/car-suspension-101-understanding-the-four- types-of-spring-systems/ Tällberg, N. (2019, 9 27). Scania, Object Manager, RTCA - Steering. (T. Hidén, Interviewer) Upasani, H. (2019, 9 19). Quora. Retrieved from https://www.quora.com/What-is-the- difference-between-damper-shock-absorber-and-strut Zahl, T. (2019, 9 19). Car iD, 3 suspension types. Retrieved from https://www.carid.com/articles/coil-leaf-and-torsion-bar-describing-the-3-different- kinds-of-springs.html

62 Intentional left blank

63 Appendix

Appendix 1, Search Keywords Suspension Heavy Duty Suspension Cab suspension Vehicle suspension Comfort Ride Handling Air suspension Pneumatic suspension Mechanical suspension Hydraulic suspension Unique suspension Electric vehicles Electric truck Electric vehicles batteries Spring Damper Shock absorber Active suspension Semi Active suspension Passive suspension Car suspension Tractor cab suspension Forestry machine cab suspension Forklift cab suspension Anti-sway bar Anti-roll bar Sway bar Roll bar Coil spring Leaf spring Torsion Bar Lift kit Lowering kit Adjustable suspension Energy consumption hydraulics

64 Appendix 2, Gantt schedule

65 Appendix 3, Pugh Weighted Matrix

66 Appendix 4, Risks and Risk Analysis Computer crash: All documentation, report writing etc. is done over Google Drive. Everything is saved in the cloud and it makes it easy to work from multiple computers, e.g. Scania work computer and personal laptop.

Internet crash: In the happening of an internet crash or that Google close down, is everything saved and stored on my personal laptop. The laptop continuously syncs with the cloud.

Advisor at Scania disappear for unknown reasons: More than one advisor is used and discussed with. Thanks to having multiple of colleagues at Scania that are up to date with what's happens in the thesis project is this problem minimized.

Project shutdown: The thesis is not a part of an ongoing project, only an independent pre-study. This means that the thesis work is not depending on a project or a budget.

Cannot fulfil deadlines: Scania has not set any hard deadlines for the thesis. This because the thesis is a conceptual pre-study of a solution that would not be put to production in the short run.

67 Appendix 5, MATLAB Calculations % Teodor Hidén, 930331-XXXX % Master Thesis Calculations % KTH and Scania, 2019 close all clear all clc

%% Hydraulics, v2

% Max Pressure in cylinder S = 12500; %[PSI] D = 8.8 / (2.54); %[in] d = 7.8 / (2.54); %[in] P = S*((D^2 * d^2)/(D^2 + d^2)); %[PSI] P = P * 0.0689; %[Bar]

MaxPressureBar = P %[Bar]

% Needed Pressure F = 25000/2; %[N] Aout = (0.083/2 - 0.005)^2 * pi; %[m^2] Ain = (0.048/2 + 0.005)^2 * pi; %[m^2] A = Aout - Ain; %[m^2] P = F/A; %[Pa]

PressureBar = P*10^(-5) %[Bar]

% Spring and stroke length dF = 2000; %[N] K = 65; %[N/mm] for a static load of 3800-4100 N x = dF/K; %[mm]

StrokeLengthMilliMeter = x %[mm]

% Oil volume L = x*10^-3; %[m] V = A * L; %[m^3]

VolumeLiter = V*1000 %[L]