2006:257 CIV MASTER’S THESIS

Prestudy of a Steering System for Heavy-Duty Trucks

ALFRED JOHANSSON ROBIN NILSSON

MASTER OF SCIENCE PROGRAMME Mechanical Engineering

Luleå University of Technology Department of Applied Physics and Mechanical Engineering Division of Computer Aided Design

2006:257 CIV • ISSN: 1402 - 1617 • ISRN: LTU - EX - - 06/257 - - SE

Abstract This thesis work was carried out at Volvo 3P, 26200 Advanced Engineering, Gothenburg during the time November 2005 – May 2006. It was a part of the Master of Science in Mechanical Engineering degree at Luleå University of Technology.

The thesis work focused on implementation of the frame-steering concept to an otherwise regular Volvo FM truck. The frame-steering concept was considered interesting in applications where low ground pressure or good off-road performance is important. The performance of the frame-steering concept, mainly in terms of steering capabilities, vehicle stability and off-road performance was to be predicted. Other areas such as transmission layout and axle configuration were also to be considered.

Basic rules and restrictions concerning the design of frame-steered vehicles were set by information given from Volvo Articulated Haulers. These rules and restrictions mainly described the allowed steering angle with maintained vehicle stability. With these restrictions, a mathematical model was constructed. With this model the steering performance could be predicted for any frame-steered vehicle, regardless of its dimensions. During the time of this thesis work, the idea to combine the frame-steering concept with the ordinary wheel-steering Ackerman concept arose. With this “dual steering” concept, high total steering angle could be obtained while maintaining good vehicle stability.

It was found that the steering performance and stability of a frame-steered vehicle is very dependent on the distance between the front axle and the steering joint. To obtain maximum steering angle with maintained stability, this distance should be minimized. On a Volvo FM this distance is dependent on the transmission layout. Two concept vehicles, one 6x6 and one 8x6, were designed in ProEngineer and their performance was studied in detail.

The need of front-wheel drive could not be fully determined and therefore the optimal transmission configuration could not be defined. The idea of utilizing low-speed hydraulic front-wheel drive was presented, but it was often argued that an articulated steered vehicle should always have the front-wheel drive engaged. Otherwise the vehicle could very easy go into an oversteering situation when driving in slippery conditions, something that is very difficult to control with this kind of vehicle. Discussions were held whether this could be solved by an onboard electronic stability system, which could control this behaviour. However, no conclusion could be made on this subject.

Since the 8x6 vehicle where designed with a steered rear axle, the turning ability of this vehicle is slightly superior to the turning ability of the 6x6 vehicle. With a distance between the front axle and the steering joint of 1.6 meters, a turning radius of 7.7 meters could be achieved with the 8x6 and the 6x6 would need a radius of 8.1 meters. If the “dual steering” concept is utilized, the turning radius could be reduced to somewhere between 5.8-7.2 and 6.2-7.5 meters respectively, depending on the wheel steering angle.

The dual steering concept was considered as the most interesting alternative and future work should preferably be focused on this concept. The transmission layout and front axle configuration should be examined with dynamic analysis to fully understand the tractive requirements of the front axle in a frame-steered vehicle.

Alfred Johansson Robin Nilsson

Alfred Johansson Robin Nilsson

Acknowledgements

The authors of this report would like to thank the following persons:

Our examiner at LTU, for giving us the freedom to work confidentially in an authentic project in the commercial vehicle industry: Peter Åström

For support and guidance throughout the project: Roger Andreasson Niklas Börjesson

Our sources at VAH in Braås, for providing experience and highly appreciated information from the world of articulated vehicles: Jörgen Ahlberg Thomas Davidsson Heikki Illerhag

For guidance and companionship during the instructive and inspiring visit to the Volvo Truck customer show in Brno, The Czech Republic: Pavel Prochazka Bartosz Bien

Our technical mentor and supervisor regarding transmission components: Jan Öberg

And finally, for providing the possibility to work with this project, our supervisor and endless source of positive energy and inspiring ideas: Lena Larsson

We would also like to thank everyone else at Volvo 3P who have helped us by providing valuable information about the vehicles and the commercial vehicle industry.

Alfred Johansson Robin Nilsson

Alfred Johansson Robin Nilsson

Alfred Johansson Robin Nilsson

Glossary

Ackerman steering Propeller shaft Wheel steering principle. Longitudinal drive shaft

Articulated steering PTO Wheel alignment controlled by frame Abbreviation of Power Take Off. Power articulation. output in the powertrain, often used to power hydraulic components. Bogie axle A two axles arrangement mounted on a Pusher axle single revolving axle. Individual suspended axle located in front of the rear driven axle. Construction truck Truck equipped with tipper body. Rotation joint Designed for heavy-duty operation. See Hitch.

Drop box Steering joint See Transfer case. Joint used by the articulated steering system. Dump truck See Construction truck. Tag axle Individual suspended axle located behind Hitch the rear driven axle. Rotational bearing enabling rotational freedom between front and rear frame. Transfer case Gearbox distributing the power from one Off-On input axle to multiple output axles. Used Prototype vehicle from the TWINS- on a trucks with both front and rear-wheel project. Designed mainly for off-road drive. operation. Tridem axle configuration On-Off A rear axle arrangement including two Prototype vehicle from the TWINS- bogie suspended axles and a tag or pusher project. Designed mainly for on-road axle. operation. VAH Payload Abbreviation of Volvo Articulated Weight of transported material. Haulers.

Alfred Johansson Robin Nilsson

Alfred Johansson Robin Nilsson

Table of Contents

1. Introduction...... 1 1.1 Background...... 1 1.1.1 Problem definition...... 1 1.2 Objectives ...... 1 1.3 Benchmark of the market...... 2 1.3.1 Articulated haulers...... 2 1.3.2 Construction trucks...... 2 1.3.3 Performance...... 2 1.4 Potential customer sectors...... 3 1.4.1 Urban areas...... 3 1.4.2 Off-road construction sites ...... 3 1.4.3 Russian tundra ...... 3 1.4.4 Agricultural sector...... 4

2. Project description ...... 5 2.1 Frame-steering...... 5 2.1.1 History ...... 5 2.1.2 Applications...... 6 2.1.3 Configurations ...... 6 2.2 TWINS-project ...... 8 2.2.1 General information...... 8 2.2.2 Results ...... 8 2.3 The Volvo FM-FS Concept ...... 10 2.3.1 Volvo’s requirements...... 10 2.3.2 Customer requirements...... 10 2.3.3 Expected market share ...... 10

3. Steering geometry and theory ...... 11 3.1 Theory for frame-steered vehicles ...... 11 3.1.1 Principle of function...... 11 3.1.2 Restrictions considering frame-steered vehicles ...... 12 3.1.3 Comparison to products available on the market ...... 13 3.2 Ackerman steered vehicles...... 14 3.2.1 Principle of function...... 14 3.2.2 Multiple steered axles...... 14 3.2.3 Restrictions of Ackerman steering...... 15 3.3 Combination of Ackerman and frame-steering...... 16 3.4 Mathematical model...... 16 3.4.1 Definitions ...... 16 3.4.2 Results ...... 18

4. Regulations and legal restrictions ...... 25 4.1 Steering ...... 25 4.1.1 Frame-steering...... 25 4.1.2 General steering requirements...... 26 4.1.3 Drive-by-wire ...... 26

Alfred Johansson Robin Nilsson

4.2 Masses and dimensions ...... 27

5. Powertrain and related components ...... 29 5.1 Packaging analysis of the Powertrain ...... 29 5.1.1 Components...... 29 5.1.2 Results ...... 31 5.2 Transmission layouts ...... 31 5.2.1 Differential solutions ...... 31 5.2.2 Transmission layouts...... 32 5.3 Active components...... 34 5.3.1 Existing electronic systems ...... 34 5.3.2 Brake control ...... 34 5.3.3 Torque control ...... 34 5.3.4 Progressive Steering ...... 34 5.3.5 Automatic locking and releasing of differentials...... 34 5.4 The need of front-wheel drive ...... 34 5.5 Tyres for the FM-FS truck ...... 35 5.5.1 Tyres for the FM-FS 6x6 construction truck ...... 35 5.5.2 Tyres for the FM-FS 8x6 “Salix II” agricultural truck ...... 35

6. The FM-FS 6x6 Concept ...... 37 6.1 Drivetrain layout...... 37 6.2 Tipp behaviour ...... 38 6.3 Gross weight and payload ...... 38 6.4 Potential costumers ...... 39

7. FM-FS 8x6...... 41 7.1 Articulated vehicles with four axles ...... 41 7.1.1 Steering Forces ...... 41 7.1.2 Position of load...... 41 7.1.3 Improvement of steering angle...... 42 7.1.4 Articulated haulers in Svalbard...... 42 7.2 Axle Installation...... 43 7.2.1 Steering angles ...... 43 7.3 Volvo FM-FS Salix II ...... 44

8. Results...... 47 8.1 Specifications...... 47 8.1.1 FM-FS 6x6 ...... 47 8.1.2 FM-FS 8x6 ...... 47 8.2 Steering performance ...... 48 8.3 Payload...... 49 8.4 Off-road Performance ...... 49 8.4.1 Ground clearance...... 49 8.4.2 Approach angle ...... 50

9. Conclusion ...... 51

Alfred Johansson Robin Nilsson

10. Discussion and proposals for future work ...... 53

11. References ...... 55

Appendix A. Steering geometry

Appendix B. Hydrostatic Propulsion

Appendix C. Pump-drive-PTO by STIEBEL

Appendix D. Hitch Solutions

Appendix E. Full vehicle test with Off-On truck

Appendix F. Steering Forces on 8x6

Appendix G. Transmission concepts

Appendix H. Michelin XZL 16.00R20

Appendix I. Alliance tyre spec

Alfred Johansson Robin Nilsson

Alfred Johansson Robin Nilsson 1. Introduction

1. Introduction This chapter will describe the background of this report and the targets of the project. A benchmark of competitors will be presented, as well as a description of problems and potential customers.

1.1 Background This report is the result of a master thesis project carried out at Volvo 3P, Gothenburg at department 26200 - Advanced Engineering & Concepts. The project started in November 2005 and the results were presented in May 2006.

It was the final academic assignment for the authors in their Master of Science degrees in Mechanical Engineering at Luleå University of Technology. The supervisor at Volvo 3P was Lena Larsson and examiner at LTU was Peter Åström.

1.1.1 Problem definition The basis of this thesis work was the problem with soil destruction, which occurs when heavy vehicles are used in soft or sensitive terrain. This problem can be experienced in urban areas, where a heavy construction truck can cause soil damage if used in sensitive areas like parks or gardens. The problem is not only a cosmetic issue, since the natural breathing of the soil is destroyed by compaction due to high ground pressures and hence causing long term problems to the environment. In rural areas the problem might transpire as damage to dirt roads or deep wheel tracks when the vehicle is used in soft soil.

Construction trucks are often used in off-road situations, for example during road constructions, where passing abilities and manoeuvrability becomes an important factor. Since numerous transports take place at the same passageway, road conditions get worse and worse and may finally be impassable if the construction site is located in soft or muddy terrain. This is also an economical issue, since the construction company is often responsible to restore the terrain when the work is finished.

The solution to these problems is to use larger and low-pressure tyres, which reduces the ground pressure and hence reducing the ground damage. The downside of using larger wheels is that the manoeuvrability of the truck decreases, since lack of space in the wheelhouse causes a reduction of maximal steering angles to the front wheels.

1.2 Objectives The intention of this master thesis project was to examine the possibilities to design and produce a frame-steered truck, as the steering of this vehicle would be independent of tyre sizes. The trucks performance in terms of manoeuvrability, payload and handling was to be predicted, particularly the turning radius that was considered to be especially important. The truck was to be based on the Volvo FM and the amount of necessary modifications has been examined, as well as how much these modifications improve the performance of the vehicle. In this work, the need and demands from the future costumer were also to be considered.

Alfred Johansson 1 Robin Nilsson 1. Introduction

1.3 Benchmark of the market At the beginning of the project a thorough benchmark of available products, which would compete with a frame-steered truck, was made to get an idea of the performance needed with the new concept. Since the new vehicle would operate on soft and slippery surfaces, mostly all-wheel driven vehicles have been studied.

1.3.1 Articulated haulers The vehicle that resembles the current concept mostly is by no doubts the articulated haulers, or dump trucks. Articulated haulers are frame-steered construction trucks specially designed to work in off-road environment. These articulated dump trucks are robustly built to work in tough environment and are therefore heavier than regular trucks. Thus, due to limitations to the gross weight, the payload when driving on public roads becomes smaller for articulated than for regular construction trucks. Another disadvantage for articulated hauler is that their maximum speeds are limited to around 60 km/h and hence make them uneconomic for longer operational distances. However, when operating in off-road conditions, they have superior performance.

1.3.2 Construction trucks The new concept will primarily focus on the construction market where the need for better manoeuvrability is high, especially when operating in slippery, loose or sensitive terrain where larger tyres must be used. On the market there are a number of different manufacturers competing in the construction sector. Examples of major producers are Volvo, MAN, Scania and Mercedes but also smaller brands as Terberg and Ginaf have very competitive products for certain applications and markets.

Actually, it seems as the main contenders for the concept are the smaller Dutch manufacturers Terberg and Ginaf. The unique Dutch legislation permits a very high vehicle weight of 50 tonnes but a maximum of 10 tonnes per axle. This calls for unusual multiple-axle configurations, which makes the country less interesting for the major manufacturers despite a large demand of construction trucks.

Instead smaller domestic companies as Terberg and Ginaf have specialized on this market and by collaborating with the larger manufacturers they can supply high quality vehicles. An example is Terberg, who is basing most of their construction trucks on the Volvo FM. The multiple-axle configurations demand more advanced steering systems, which have resulted in an all-wheel driven truck with steered rear axle and superior mobility.

1.3.3 Performance From fact sheets published by the manufacturers, some important performance parameters have been collected and can be seen in Table 1.1. Generally, the dumpers have smaller turning radii than the trucks, but the Terberg 6x6 is impressive with its high manoeuvrability. Unfortunately the turning radii will increase significantly for the trucks when larger wheels are mounted. According to sources at Volvo, the steering angle is reduced to 38° (from original 50°) for the FM12 6x6 when 12.00.24 tyres are mounted [1]. This will result in a turning radius above 11 meters, according to equations presented in Appendix A.

Alfred Johansson 2 Robin Nilsson 1. Introduction

Table 1.1 * = restricted by road legislation, ** = total weight restricted to 26 tonnes. Vehicle Wheel base Turning Top speed Payload (mm) radius (mm) (km/h) Bell B18/B20D 5165 6900 65 18

d Cat 725 5519 7605 57 22 e t

a s l r Komatsu HM300 5810 7960 58 27 u e l c i u t 5845 7980 53 24 r a Volvo A25D A H Moxy MT26 5909 8970 51 23

Volvo FM 6x6 5670 9100 >90* 13** n o

i MAN 6x6 5600 9700 >90* n/a** t c

u 5400 7950 >90* n/a** s

r Terberg FM 6x6 t k s c

n Mercedes Actors 6x6 5250 9150 >90* n/a** u o r

C T Renault Kerax 6x6 5200 9600 >90* n/a**

As a conclusion it can be established that articulated haulers have greater mobility than ordinary trucks, especially when considering that the steering performance is practically independent of the tyres mounted to the vehicle. Thus these steering performances will stay unaffected even if the largest wheels that can be fitted are used. So when comparing with regular trucks, it is clear who has the upper hand when the terrain gets tougher.

1.4 Potential customer sectors There are a number of applications where a frame-steered truck would be suitable, a few of those will be presented in this report.

1.4.1 Urban areas As mentioned earlier in this chapter, ground pressure must be kept at a minimum when driving in sensitive terrain to minimize damage to the soil. Truck transports sometimes occur in such areas due to building constructions, services or other operations. In such applications a frame-steered truck might be suitable, especially if high manoeuvrability can be achieved since operating space often is limited.

1.4.2 Off-road construction sites During construction work in difficult terrain articulated haulers is often used. But since they are restricted to about 50-60 km/h they become inefficient if longer transport distances are needed. This sector, where the off-road ability and articulated hauler is needed combined with the high top speed of an ordinary construction truck, would be filled with the frame-steered Volvo FM concept. The payload and productivity are also important parameters in order to give the concept an economic benefit to the buyer. The transmission layout is also an important feature, as the drivers on many markets are used to all-wheel driven trucks and tend to buy this vehicles even if the real need for all-wheel drive can be questioned [2].

1.4.3 Russian tundra In the north of Russia, large amounts of natural resources in form of oil and gas has led to major construction taking place in this vast and remote area of the world. Material and supplies need to be transported over very long distances and in areas where roads hardly

Alfred Johansson 3 Robin Nilsson 1. Introduction exists. During the winter the ground is frozen and the trucks can travel without any major problems, although the truck must be capable of still being functional at 30-40°C below zero. During spring and autumn the soil level above the permafrost is melted and soaked, this make the road conditions almost impassable. In the summer the road are often dry, dusty and the soft sand can some times cause problems, since the average day temperature in summer is around 20-30°C [3]. A truck customized for these working conditions can be seen in Figure 1.1.

With enormous distances between construction sites it might be fatal for the driver to get stucked with the truck. So in this application, soil compaction is not really of interest, instead reliability and off-road performance is of highest importance. The long distances also exclude the use of traditional articulated dump trucks like the Volvo A25D due to their lack of top speed.

Figure 1.1 A Volvo FM truck built for Siberian conditions equipped with lager tyre to increase the performance on soft soil

1.4.4 Agricultural sector The problem with soil compaction caused by heavy machinery is even more important in the agricultural industry since it reduces growth of crops and hence also the economic revenue from the fields. In some agricultural logistic systems trucks are transporting the harvest from the field and must when be able to travel on-field without causing too much soil damage. This sector is of major interest in this thesis work and a frame-steered truck for the agricultural sector is further investigated in chapter 7.

Alfred Johansson 4 Robin Nilsson 2. Project description

2. Project description This chapter will define the project more thoroughly and give a short history in the development of frame-steered machines. It will also describe the chronological position of this master thesis in Volvo Truck Company recent research in articulated steering concepts.

2.1 Frame-steering This steering concept has been used for a long time in several different applications. Due to these numerous applications the frame-steering concept has evolved into different configurations and these will be discussed later in this chapter.

2.1.1 History In the agricultural sector articulated steering has been employed since the beginning of the 20th century, when John Deere introduced a frame-steered one-row cultivator machine in 1916 [4], see Figure 2.1.

Figure 2.1 A John Deere machine from 1916 [4]

In the construction equipment industry the development took longer time, as the worlds first articulated hauler was presented to the world in 1966 when Volvo launched the BM-Volvo DR 631 [5]. Until then, earthmoving applications were often carried out by a wagon pulled by a farm tractor. Early concept vehicles were built, as the Bolinder-Munktell Livab “Moon Rocket” in 1955 which was basically an articulated farm tractor which had the front axle removed, see Figure 2.2. Since then, numerous of other construction vehicles have been developed that also utilize articulated steering.

Figure 2.2 Bolinder-Munktell Livab “Moon Rocket” [5]

Alfred Johansson 5 Robin Nilsson 2. Project description

2.1.2 Applications Articulated steered vehicles can be found in many low-speed applications. As mentioned earlier in this chapter, the concept of articulated steering started in the agricultural sector and it is still used on heavy tractors. It is also very common in the forest industry, as frame- steering almost always is utilized in forest harvesting equipment. Frame-steered products like articulated haulers and wheel loaders are also widely used in the construction industry.

2.1.3 Configurations Different configurations of the articulated steering systems have been developed throughout the years. The configuration used by Volvo CE on their articulated haulers can be seen in Figure 2.3. Two joints are utilised, a steering joint and a rotational joint. The disadvantage of this configuration is the uneven load on the front wheels.

Figure 2.3 The rotational joint is located behind the steering joint

Norwegian dump truck manufacturer Moxy Engineering AS have modified the steering arrangement and are offering a solution that can be seen in Figure 2.4. By locating the rotational joint in front of the steering joint a few benefits are obtained. According to the manufacturer this modification ensures equal weight distribution to the front wheels in all situations [6]. Due to the equal weight distribution the same tractive force can be obtained, which reduces the need to engage the differential lock. However, this concept often deteriorates the weight distribution of the rear frame [7].

Figure 2.4 The rotational joint is positioned in front of the steering joint

Alfred Johansson 6 Robin Nilsson 2. Project description

Not all applications require a fully rotating joint between front and rear frame. Danish company A/S Hydrema is producing dump trucks with a restricted rotation, as shown in Figure 2.5. The rotational degree of freedom is acquired by a linkage of rods connected by spherical bearings. This system may reduce cost and weight since no large rotational bearing is required. But as mentioned before, the rotational degree of freedom is restricted, and the trucks offered by Hydrema have a rotational freedom of ± 15 degrees. A disadvantage of this linkage system is that bump steer can occur during rotational movement [8].

Figure 2.5 A linkage assembly enables a certain degree of rotation

Some vehicles are designed without any rotational freedom at all. This is the case for machines like wheel loaders and agricultural tractors, see Figure 2.6. The frame only incorporates the steering joint and movement in all other directions is restricted. Instead, one of the axles is pivot mounted and neutralizes any vertical differences between the wheels.

Figure 2.6 Rotation is achieved by mounting one of the axles to an oscillating joint

Alfred Johansson 7 Robin Nilsson 2. Project description

2.2 TWINS-project An articulated steered truck with a top speed of 90-100 km/h and good on-road behaviour has during a long time been a dream for engineers at Volvo Articulated Haulers and its market position is illustrated in Figure 2.8. In 1996 Volvo Truck Company were invited to cooperate in a prestudy to make an articulated high-speed hauler and on the 11th of August 1997 the project got a GO-decision for a “common concept study”. The reason for the project was that Volvo Truck Company had an interest in increasing their market share in the construction segment and Volvo Articulated Haulers had to find a replacement truck for the A20C that was put out of production in 2001.

During 1998 to 2001 the concept was further developed and at several occasions during 2001 and 2002 two prototypes were tested and presented to potential costumers. The project was however put to a halt in 2002 due to a number of reasons.

Archived documents from the project have been a starting ground for this master thesis as the same issues regarding articulated steering were dealt with during this project. In this chapter the TWINS-project will be examined further.

2.2.1 General information The “TWINS” project name was inspired by the two concept vehicles, which both were equipped with a rotational hitch as traditionally used in frame-steered dumpers trucks. One of the vehicles was manoeuvred by the traditional Ackerman wheel-steering principle and was designed for mainly on-road operation and given the name “On-Off”. The second vehicle was an articulated hydraulic frame-steered vehicle designed for a higher amount of off-road operation and hence called “Off-On”.

Figure 2.7 The prototypes Off-On (left) and On-Off (right) together for a photo shoot

2.2.2 Results Even if the TWINS-project was called off, it still brought some good results to the companies involved. For instance modifications to the B-ride rear suspension were developed within the TWINS-project, and are today implemented into the standard component. Volvo Articulated Haulers and Volvo Truck Company also gained good experiences of collaboration and working together within the Volvo Group. They shared much information about rigid trucks and articulated haulers and if a new project about building an articulated high-speed off-on hauler would start, much information can be retrieved from the TWINS-project.

In this thesis work the assignment is to make a deeper study of the articulated truck concept and therefore the ideas concerning the On-Off truck will not be mentioned in this report.

Alfred Johansson 8 Robin Nilsson 2. Project description

Figure 2.8 Definition of product need from the TWINS-project As a result of the TWINS-project some of the costumer needs and demands were defined. To allow potential costumers to test the equipment proved to be a superior way to obtain costumer and user requirements.

After testing the costumer agreed that the Off-On would fit “the gap” as defined in Figure 2.8. It would find itself useful, not mainly because of high productivity but rather as a flexible complement to pure articulated haulers like Volvo A25D and on-road rigid trucks. The Off- On would reduce the need of expensive reloading and the total investment per working hour would be less.

According to the costumers some market segments might be:

3-axle: a flexible vehicle, various applications and small contractors a compliment vehicle for large contractors a back-up vehicle partly for articulated dump trucks but mostly to rigid trucks 4-axle: a replacement for 8x8 “off-road” trucks like MB, MAN.

When a new vehicle concept enters the market the costumers and users often find new application areas that the product developer never thought of. The Off-On truck should therefore be possible to equip with for example a towing hitch, hook lift or front attachment plate to fit for example a slow plough. The Off-On truck would be suitable for both small and larger operators. The smaller operators need a flexible truck that allows them to take many different kind of jobs, and larger operators need at truck that can act as a compliment to other equipment on large construction sites.

At the customer clinics concerns about driving license and need for improvement in driver education were raised. Many truck drivers might be a little bit scared and uneasy with the articulated steering and the steering sensitivity might need to be changed. During testing, the truck drivers felt that the steering system were too sensitive around zero. It would be preferred to have some kind of self-centring system so it would behave more like a regular truck.

Alfred Johansson 9 Robin Nilsson 2. Project description

If the Off-On truck is supposed to be a flexible truck and support vehicle the price tag should not be higher than 10-15 % above the price for a comparable rigid truck. To summarize the opinions retrieved from the customers it can be stated that “The interesting thing with the Off- On prototype is not the cost savings, it is the flexibility”.

2.3 The Volvo FM-FS Concept The frame-steered concept truck that this thesis work is based around was throughout the project given the name FM-FS where FS is an abbreviation of “Frame-Steered”. This term will be used in this report frequently when discussing the concept vehicle. FM is the common name for the Volvo’s heavy trucks equipped with cabs of medium height.

The Volvo FM-FS concept is much based on the experience gained by the TWINS- prototypes. One of the main problems with the Off-On prototype was the fact that it had too little in common with the regular product range of Volvo Trucks. Hence, it would have been difficult to fit the frame-steered Off-On into Volvo Truck product family. Although, the idea of a frame-steered Volvo truck is still interesting and this master thesis has examined the possibilities of building a frame-steered vehicle based on the FM chassis.

2.3.1 Volvo’s requirements To minimize the product costs the requirement from Volvo Trucks was that the new concept had to be based on an ordinary Volvo FM truck. Changes to the truck will be made, but the changes must be as few as possible and every modification should be closely examined.

2.3.2 Customer requirements The customer requirements used in this project were adopted from the needs that were defined during the TWINS-project, as discussed previously in this chapter. It was specified based on old experience, visits to potential costumers and, of course, the costumer clinics with the TWINS-prototypes.

The customers really liked the concept with oscillating joint and articulated steering, because the possibilities of high ground clearance and good pass ability. Also, since the rotational joint reduces torsional forces in the frame, the operation cost for repairs of frames and suspension would decrease with this concept. The customers also pointed on the need for payload and price equal to regular rigid truck.

2.3.3 Expected market share The market share for a new vehicle concept is really hard to predict but before and during the development of the TWINS-prototypes Volvo Truck Company and Volvo Articulated Haulers did a deeper international investigation. In the end of 2001 sales volume were predicted to 5000 units (1600 off-on and 3400 on-off). The minimum profitable sales volume where calculated to 2500 units per year. In the long run including additional markets like mining, waste, forestry, military support etc. the sale could be as good as 7500 units a year [9].

Alfred Johansson 10 Robin Nilsson 3. Steering geometry and theory

3. Steering geometry and theory

To be able to estimate the performance of the concept, some theoretical rules and principles have been used and these will be covered in this chapter. A mathematical model of the steering performance for a frame-steered vehicle is presented in chapter 3.4.

3.1 Theory for frame-steered vehicles Frame-steered vehicles are designed with other principles than ordinary wheel-steered machines. The principles for frame-steering will be discussed here and are more thoroughly examined in Appendix A.

3.1.1 Principle of function As visualised in Figure 3.1, frame-steered dump trucks have two joints that the vehicle rotates around, the articulated steering joint (A) and the rotation hitch joint (B). The rotational hitch can be locked in certain situations, such as unloading or when travelling at high speeds. Other type of vehicles sometimes utilizes only a single steering joint (see chapter 2.1.3), but for medium-sized off-road trucks the hitch joint have a number of advantages.

The oscillating joint makes the vehicle more flexible and improves the off-road performance. The front and rear frame can independently tilt when crossing an obstacle and when combined with a rear bogie axle all wheels are ensured to be in contact with the ground. This reduces temporary high-stress situations in the frame, hence makes a weight reduction possible.

The front frame can be suspended by a simple parallel suspension, since all transverse unevenness in the road, or terrain, will be absorbed by the front frame rotational degree of freedom.

Figure 3.1 The articulated steering joint (A) and the oscillating hitch joint (B)

Alfred Johansson 11 Robin Nilsson 3. Steering geometry and theory

3.1.2 Restrictions considering frame-steered vehicles Steering angle According to a Volvo Articulated Haulers in-house rule of thumb, the outer front wheel cannot be allowed to pass the centreline of the rear frame, see Figure 3.2. This is supposed to cause instability and jeopardise the safety. This is discussed further in Appendix A and in Chapter 7.1.2.

Figure 3.2. This vehicle has reached its maximum steering angle, as the outer front wheel is about to pass the centreline of the rear frame.

If this rule is to be obeyed, the steering performance can be predicted by studying the vehicles track width, wheelbase and the location of the steering linkage. How the equations describing the steering performance were derived can be seen in Appendix A.

Payload position In a frame-steered vehicle with three axles the payload centre of gravity should always be located as close to the bogie axis as possible, see Figure 3.3. This is to minimise load transfer to the front axle, as a major momentum otherwise would be acting on the steering assembly. This is not a problem due to mechanical stress, but the stability of the vehicle is reduced. This problem is explained further in Appendix A.

Figure 3.3 Correct position of payload.

Alfred Johansson 12 Robin Nilsson 3. Steering geometry and theory

3.1.3 Comparison to products available on the market Since the steering rule of thumb only is a guideline for how Volvos dump trucks are designed, it is interesting to compare this to the steering geometry of articulated haulers made by other manufacturers.

Equations derived in Appendix A have been used, together with data from specification sheets published by the manufacturers. These data are a bit questionable though, as everyone states that their machines are capable of turning 45°. When comparing the turning radius from the specification sheets and those calculated with equations from Appendix A (for example the Bell B18/B20D), one might think that the data provided by the manufacturer has been slightly “polished”.

Table 3.1 Data provided by specification sheets are listed in the two columns on the left. In the columns on the right results from calculations according to the Volvo rule are listed. Steering Turning radius Max. steering angle Turning radius angle [°] [mm] (Volvo rule) [°] (Volvo rule) [mm] Bell B18/B20D 45 6900 43,8 6888 Cat 725 45 7605 45,4 7218 Komatsu HM300 45 7960 50,4 6998 Volvo A25D 45 7980 49,7 7114 Terex TA25 45 Not available 49,1 7299 Moxy MT26 45 8970 55 7228 Case 325 45 Not available 46,5 7706

The conclusion will be that every manufacturer seems to be fulfilling the Volvo rule that not let the outer front wheel to pass the rear frame centreline, even if someone’s are right on the limit.

An interesting point is that many models seem to be able to accomplish greater steering angles than 45° while maintaining their stability. The reason for restricting the steering angle to 45° might be other aspects, such as drive shafts, hoses etc.

Alfred Johansson 13 Robin Nilsson 3. Steering geometry and theory

3.2 Ackerman steered vehicles Normal wheel steered vehicles are almost always said to be using steering geometry according to something called the Ackerman principle. In this report, the term “Ackerman steering” could be replaced with just “wheel steering”, even though there are a few other principles of aligning the wheels in a wheel steered vehicle.

It should be mentioned that the Ackerman principle is actually more of a theoretical, or mathematical, construction and is rarely fulfilled to perfection in practise, especially not in the trucking industry. It is fairly convenient though, when making theoretical calculations for vehicles turning abilities, as it eliminates tyre slip and the steering performance can be carried out by simple geometric relations between track width, wheelbase and turning angle.

3.2.1 Principle of function The principle of Ackerman steering is visualised in Figure 3.4 (A). In order to turn the vehicle without tyre slip, all wheels must be aligned to the same turning centre. The turning centre is always located in-line with the non-steered axle. In a four-wheeled vehicle, this is fulfilled by using a steering geometry that turns the inner wheel at a greater angle than the outer wheel. Equations for these steering angles can been seen in Appendix A.

When a bogie or multiple non-steered axles are utilized the vehicle cannot turn without tyre slip. The turning centre will now be located in-line with a theoretical “turning axis” located somewhere between the non-steered axles, as can be seen in Figure 3.4 (B)

The lengthwise position of this turning axis may change due to different load distribution, tyre pressure etc between the bogie axles. In this report however, the turning axis is always assumed to be located right in the middle of the two axles.

Assumed turning axis

(A) (B)

Figure 3.4 The basic principle of Ackerman steering on a truck with three axles.

3.2.2 Multiple steered axles As mentioned earlier, if a bogie is used, the rear wheels will experience unhealthy slip and wear when the vehicle is turning. The four aligned wheels unwillingness to turn will also cause higher forces in the front wheels, resulting in a certain slip, leading to higher wear and a minor reduction in manoeuvrability.

Alfred Johansson 14 Robin Nilsson 3. Steering geometry and theory

To eliminate these problems, a second steered axle can replace one of the fixed axles. It is common practice to replace the rear axle, as it will improve the vehicles manoeuvrability. As can be seen in Figure 3.5 (A), the turning centre translated forward and is now located in-line with the non-steered axle and hence reduces the turning radius. The tyre wear will also decrease since no unnecessary slip will take place while cornering.

On Volvo FM trucks these axles are often self-steered or self-aligning and are pneumatically locked at high speeds and during reverse. These can be said to always follow the Ackerman principle. But they can also be hydraulically steered, which gives them the possibility to “oversteer” and improve the turning capability slightly. However, in this report all axles will be assumed to follow the Ackerman principle. Mathematical equations for the steering angles have been constructed and are presented in Appendix A.

If a vehicle is designed for high payloads, a fourth axle might be required. The need for a steerable axle is then considerably increased. Three fixed axles would result in a high amount of tyre slip when turning, leading to increased tyre wear, shearing of the ground surface, and reduced manoeuvrability.

In this case, both front and rear locations of the steerable axle are commonly used. The rear position gives favourable turning abilities [Figure 3.5 (B)], but some applications can lead to very high intermittent loads on the rear-most axle, which makes it more logical to place the more robust bogie at the rear [Figure 3.5 (C)].

(A) (B) (C)

Figure 3.5 Different configurations of the axles can produce significant changes to the turning radius.

3.2.3 Restrictions of Ackerman steering As mentioned before, the major disadvantage for Ackerman steering (or any other type of wheel steering) is that the wheels need space to turn, as opposed to frame-steering.

Alfred Johansson 15 Robin Nilsson 3. Steering geometry and theory

3.3 Combination of Ackerman and frame-steering

It was discussed how the steering performance would be improved if the two principles of steering was combined in a dual-steering system. The vehicle will then behave according to Figure 3.6. As can be seen in the figure, the turning radius can be reduced by a considerable amount with this arrangement.

Figure 3.6 The turning radius is significantly decreased when using a combination of the steering principles.

3.4 Mathematical model By using the equations derived in Appendix A, a mathematical model was created in MATLAB. This is presented here in a comprehensive way by a number of charts by which the steering performance can be predicted for virtually every frame-steered truck within the wheelbase span.

As can be seen in Figure 3.7, the model also takes into consideration the possibility to use a self-aligning auxiliary axle and hence charts to predict the angles “c” and “d” are available.

3.4.1 Definitions To be able to calculate the maximum allowed steering angle “a” according to Volvo, the distance F between the front axle and the steering joint must be known. The theoretical wheelbase (T.W.B.) refers to the distance between the front axle and the rear “turning axis” (se chapter 2.2.1 for definition). All calculations has been carried out with the track width T = 2.495 meters.

Alfred Johansson 16 Robin Nilsson 3. Steering geometry and theory

Figure 3.7 Geometry definitions for the mathematical model

Alfred Johansson 17 Robin Nilsson 3. Steering geometry and theory

3.4.2 Results

Figure 3.8 Maximum allowed steering angle according to Volvo rule.

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Figure 3.9 Turning radii with different turning angles. Note: This graph is only valid if steering angles from Figure 3.8 is used.

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Figure 3.10 The inner turning radius at the rear frame.

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Figure 3.11 Steering angles for the inner wheel on the auxiliary axle with altered distance B. Despite the title of the chart the axle can be located both in front and behind the bogie.

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Figure 3.12 Steering angles for the outer wheel on the auxiliary axle with altered distance B. Despite the title of the chart the axle can be located both in front and behind the bogie.

Alfred Johansson 22 Robin Nilsson 3. Steering geometry and theory

Figure 3.13 Example of how wheel steering will reduce the turning radius. This example is using parameter values of F=1.6 and T.W.B.= 5 meters.

Alfred Johansson 2 3 Robin Nilsson

Alfred Johansson 24 Robin Nilsson 4. Regulations and legal restrictions

4. Regulations and legal restrictions

The transportation industry is restricted by numerous regulations. This chapter will only briefly discuss those of significant importance for the project.

Laws and legislations are unique for every country, but due to the cross-national nature of the transport sector, some instruments are in use to increase the uniformity of regulations concerning this area.

In Europe the European Union, and in particular the European Council, can declare certain directives how the member states should write their legislations. The directives given by the council can often be put in an economic perspective. They are often intended to equalise the situation for the transport industry so the companies can compete on equal conditions, regardless of their nationality.

Uniformed regulations concerning the safety of wheeled vehicles and their equipment are in Europe managed by the Transport Division of the United Nations Economic Commission for Europe (ECE). The ECE is one out of five regional organs connected to the ECOSOC, the Economic and Social Council of the UN.

4.1 Steering In this chapter, legislations concerning the steering system and assisting systems in automotive vehicles are discussed.

4.1.1 Frame-steering As frame-steering is mainly a steering system used for construction and agricultural vehicles and is unproven in on-road high speed applications, a brief examination concerning the legal aspect have been made.

According to sources at Volvo, there are no specific restrictions to frame-steering on motor vehicles [10]. In UN/ECE/R79 this is described as “Buckle steering”.

Quotation from UN/ECE/R79:

2.5.3.3.2 "Buckle steering equipment" in which the movement of chassis parts relative to each other is directly produced by the steering forces.

Hence no specific restrictions against frame-steering exist, although there are a number of demands on a vehicles steering equipment in general.

Alfred Johansson 2 5 Robin Nilsson 4. Regulations and legal restrictions

4.1.2 General steering requirements Even if articulated steering is accepted in a high-speed truck, several demands must be fulfilled in order for the vehicle to be approved by the national transportation government body. Some important requirements according to R79 are listed below.

5.1.1 The steering equipment shall ensure easy and safe handling of the vehicle up to its maximum design speed.

5.3.3.4 In event of a failure within the energy transmission there shall not be any immediate changes in steering angle.

6.2.2 When the vehicle is driven in a circle with its steered wheels at approximately half lock and at a constant speed of at least 10 km/h, the turning circle must remain the same or become larger if the steering control is released.

These requirements must be considered when designing the steering system.

4.1.3 Drive-by-wire Regulations concerning the steering equipment have traditionally required a mechanical link between the steering control and the wheels. A properly dimensioned mechanical link has been regarded as “not being liable to failure”.

Advancement in electronic and data technology, together with the increase in occupant safety by eliminating the steering column have lead to the wish to control the wheels mainly by digital transfer of data. An agreement has been underway since late 90’s and was finally presented in April 2005. In UN/ECE/R79 the agreement is described and where drive-by-wire finally is officially recognized.

The R79 regulation permits fully electronic, but also fully hydraulic, transmission of the steering input from the driver. Hence, the mechanical link is no longer necessary.

Since the signal between the steering input and the wheel now can be digitally transmitted, the steering angle can be easily corrected and manipulated in a number of ways by on-board stability systems. These systems are by R79 described as “Advanced Driver Assistance Steering Systems” and are thoroughly regulated in the document.

Quotation from R79:

Systems whereby the driver remains in primary control of the vehicle but may be helped by the steering system being influenced by signals initiated on-board the vehicle are defined as "Advanced Driver Assistance Steering Systems". Such systems can incorporate an "Automatically Commanded Steering Function", for example, using passive infrastructure features to assist the driver in keeping the vehicle on an ideal path (Lane Guidance, Lane Keeping or Heading Control), to assist the driver in manoeuvring the vehicle at low speed in confined spaces or to assist the driver in coming to rest at a pre-defined point (Bus Stop Guidance).

Advanced Driver Assistance Steering Systems can also incorporate a "Corrective Steering Function" that, for example, warns the driver of any deviation from the chosen lane (Lane Departure Warning), corrects the steering angle to prevent departure from the chosen lane (Lane Departure Avoidance) or corrects the steering angle of one or more wheels to improve the vehicles dynamic behaviour or stability.

In the case of any Advanced Driver Assistance Steering System, the driver can, at all times, choose to override the assistance function by deliberate action, for example, to avoid an unforeseen object in the road.

Alfred Johansson 2 6 Robin Nilsson 4. Regulations and legal restrictions

According to the last paragraph, the assistance system is not allowed to ignore the driver inputs and no restrictions in the steering are permitted. The driver shall at any time be able to override the system.

4.2 Masses and dimensions In compliance to the European Council Directive 96/53/EC the Swedish National Road Administration permits a total gross weight of vehicles according to Table 4.1.

Table 4.1 Total vehicle weight Number of axles Total laden weight 2 18 tonnes 3 25(26*) tonnes 4 31(32*) tonnes *Where the driving axle is fitted with twin tyres and air suspension or suspension recognized as equivalent, or where each driving axle is fitted with twin tyres and the maximum weight of each axle does not exceed 9,5 tonnes (Appendix 1, Trafikförordningen 1998:1276).

In the 96/53/EC the minimum total wheelbase for a four-axle is restricted in terms of legal gross weight.

Quotation from 96/53/EC Annex 1, 4.3:

The maximum authorised weight in tonnes of a four-axle motor vehicle may not exceed five times the distance in metres between the axes of the foremost and rearmost axles of the vehicle.

Swedish, Norwegian and Finnish regulations also restrict the gross weight in respect to the total wheelbase of any vehicle. This is mainly to reduce wear on road structures such as bridges, junctions etc. Swedish regulations can be seen in Table 4.2.

Alfred Johansson 2 7 Robin Nilsson 4. Regulations and legal restrictions

Table 4.2 Demands on vehicle total wheelbase

The EC directives regulate the height of vehicles to 4.0 meters. Swedish national laws do not contain such restrictions, although bridges, viaducts etc. are generally built for vehicles with a maximum height of 4.5 meters.

Alfred Johansson 2 8 Robin Nilsson 5. Powertrain and related components

5. Powertrain and related components

This chapter will investigate the powertrain and other components, which affects the frame- steering concept. The demands of front-wheel drive will be discussed and different transmission layouts will be presented.

5.1 Packaging analysis of the Powertrain

As described in chapter 3 the main parameter when designing a frame-steered truck is the distance “F” between the steering joint and the front axle, see Figure 5.1. As discussed in Chapter 3, the distance F should be minimized in order to increase the steering capability of the vehicle. As can be seen in Figure 5.1, the length of the powertrain restricts this distance. A packaging analysis has been made to examine where the steering joint can be positioned.

Figure 5.1 The transmission components are restricting the location of the steering joint

5.1.1 Components As mentioned before, Volvo FM standard components were to be used as much as possible, and during the analysis the following components have been used.

Engine In the Volvo FM truck program there are several different engine choices, both in displacement and power. In this thesis work the FM-FS is supposed to be a heavy-duty truck and therefore the largest and strongest 13-liter D13 engine was selected.

Gearbox Volvo Truck Company has three different types of gearboxes. In each group there are a handful of variants with different gear ratios and strength to suit the range of different engine power and torque. However, in this analysis the Powertronic automatic gearbox have been used, since it requires the longest over all length.

Alfred Johansson 2 9 Robin Nilsson 5. Powertrain and related components

Transfer case A transfer case, or drop box as it is often called, is a gearbox that divides the engine power between the driven front and rear axles. On Volvo FM trucks, the front-wheel drive is engaged by a pneumatic cylinder that engages the output axle of the front-wheel drive to the input shaft with a dog clutch. The transfer case may also be more advanced with a high and low range gear or a central differential.

In this analysis, three concepts have been examined. In the first concept the transfer case have been excluded. In the second concept an integrated transfer case was used. This transfer case was not fully developed, thus preliminary dimensions given from Volvo Powertrain were used [11]. In the last concept, a standard transfer case was used. It was assumed that it could be mounted in-line directly on the output flange of the gearbox, as can be seen in Figure 5.2.

Figure 5.2 The transfer case is mounted directly to the output flange of the gearbox

Universal Joint To minimize the distance F, a dual universal joint is located directly on the output shaft of the transfer case. This dual joint must be located so that the centreline coincides with the centreline of the steering joint. Thus, since this part is the rearmost component of the transmission unit, the centreline of the dual joint determines the location of the steering joint.

Steering assembly The steering assembly used in the packaging analysis has been retrieved from the TWINS- project and should only be regarded as a visual representation of the steering system.

Front axle Apart from the transmission design, the distance F can be reduced by moving the front axle backwards. It is possible to translate the front axle approximately 200 mm further back before it collides with the flywheel cover (approximately 3340 mm from global zero in Pro/E) [12].

Alfred Johansson 3 0 Robin Nilsson 5. Powertrain and related components

5.1.2 Results With the components listed previously in this chapter, the length between the front axle and the steering joint (distance F) was studied. The results can bee seen in Table 5.1.

Table 5.1 Distances between front axle and steering joint Distance F Maximum Steering angle with relocated Transfer case concept [mm] steering angle front axle (200 mm) Excluded 1600 38 41 Integrated 1850 34 37 Standard in-line 2000 32 35

The steering angles can be significantly improved by relocating the front axle. An additional effect of moving the front axle closer to the steering joint is that it will come closer to the centre of gravity of the front frame. Hence the stability of the front frame will be improved. However, by changing front axle location, new frame brackets for the front suspension is needed due to the change of frame width. The angles of the universal joints of the propeller shaft must also be regarded. For a frame-steered vehicle with no front axle steering, there is no need for steering arms and track rod. Thus, a redesign of the ZF front axle now used can be made, and perhaps the simplest way to do this is to use the wheel hubs from the rear axle [13]. Changing the gear ratio in the transfer case can then compensate for any difference in gear ratio between the ZF and Volvo hubs.

5.2 Transmission layouts With the impacts of different transfer cases established, a number of transmission layouts can be examined. During this thesis work it was often discussed how the transmission should be designed, and most of the ideas discussed will be presented here. A comprehensive summary of the layouts can be seen in Appendix G.

5.2.1 Differential solutions A differential is used to split and distribute the engine power between the wheels. The differential allows some speed difference between the wheels, but if one wheel loses traction and starts to spin, all power will be transferred to this wheel. Therefore many differentials have the possibility of locking and end the allowance of speed diversity between the wheels. The need of a differential between the front axle and the rear tandem bogie on the FM-FS is important to establish since it affects the transmission layouts. A comparison between articulated haulers and regular trucks has been made to explain the different philosophies in this area.

The Volvo A25D is a constant all-wheel driven articulated dump truck equipped with one transversal differential on each axle that divides the power between the right and left wheel, and there are also longitudinal differentials that divide the power between the axles. When large steering angles are applied, large difference in speed between the front and rear wheels occurs. Therefore, on a vehicle equipped with constant all-wheel drive, the first longitudinal differential (between the first and second axle) is very important. The differential saves tyres, fuel and reduces wear in the transmission when driving on high friction surfaces.

Alfred Johansson 3 1 Robin Nilsson 5. Powertrain and related components

However, the all-wheel driven Volvo FM 6x6 truck is not equipped with such a differential. The truck is built around a different philosophy, as it is equipped with constant rear-wheel tandem drive and optional front-wheel drive, which can be engaged manually by the driver. The longitudinal differential can be abandoned, since the only time the optional front-wheel drive is needed is when the truck lacks traction, and then the differential is not necessary because of low friction. Indeed, if the truck had been equipped with a longitudinal differential it may have been locked anyway in such situations.

By studying these solutions, it can be established that the need of a longitudinal differential is dependent of how the front-wheel drive is to be applied. If a constant front-wheel drive is needed, a longitudinal differential is also needed.

An alternative solution is to utilize a clutch on the propeller shaft, which would allow a certain amount of slip during cornering. This would be computer controlled to avoid any power consuming slip while driving forward.

5.2.2 Transmission layouts This chapter will present a brief investigation of several transmission layouts for the FM-FS truck. From the test reports with the Off-On prototype it can be stated that some form of front- wheel drive is needed, see Appendix E. The concepts discussed here will solve this demand with different methods.

Constant 6x6 If constant all-wheel drive is to be used, a longitudinal differential is needed between the front and rear axles. Unfortunately, this will imply a larger and more advanced transfer case compared to the one used in the analysis presented earlier in this chapter. It would be difficult to find space for this in front of the steering joint, and the steering performance of such a vehicle would be dreadful.

An alternative solution would be to position the transfer case on the rear frame. The transfer case could then be placed anywhere between the steering joint and the rear axle.

Another possible solution is to integrate the transfer case into the first rear axle, as visualised in Figure 5.3. This arrangement is good for a truck with short wheelbase, since no space is required for a transfer box between the steering joint and the rear axle. With both these options, it is possible to equip the transfer case with both low-high range gear and differential. A problem with the rear axle installation is the long drive shaft that needs to go from the rear axle to the front axle. This will increase the rotating mass, thus increasing fuel consumption, and also increase the unsprung mass. However, the Dutch truck manufacturer Terberg Benschop uses this rear axle arrangement with success on their FM1350-WDG 6x6 truck.

Unfortunately, these layouts will restrict the movement in the rotational joint since two drive shafts need to pass through the steering assembly in the axis of the steering joint. Some kind of transmission unit is also needed to transfer the torque to the front axle alongside the gearbox and engine. A simple hitch linkage system with a limited degree of rotational can therefore be used on trucks with this type of transmission layout. This is further investigated in Appendix D.

Alfred Johansson 3 2 Robin Nilsson 5. Powertrain and related components

Figure 5.3 Principle layout of a possible driveline configuration with a rear axle mounted transfer case

Torque controlled all-wheel drive If an unrestricted rotational joint is considered vital, the transfer case must be located in front of the steering joint. As described in the analysis earlier in this chapter, a transfer case integrated in the gearbox would then be the best choice in terms of steering performance, since it has the shortest total transmission length achievable. Unfortunately, this alternative requires unique transfer cases specially designed for each gearbox. Also, if maximum steering performance is to be achieved, there is no space for any longitudinal differential.

However, the need for a differential may be solved by mounting a computer controlled clutch on the rear, or front, propeller shaft. The computerised control system would then automatically reduce the torque transmitted through the clutch when the vehicle is turning. If such a clutch is mounted on both propeller shafts, the behaviour of the vehicle could be controlled in a number of ways by altering the torque distribution.

Optional front-wheel drive This concept is utilizing the concept used by Volvo on the FM 6x6 trucks. However, this transfer case is not integrated to the gearbox and will hence require a larger amount of space. As discussed earlier, this problem would be solved by mounting the transfer case on the rear frame. Although, if mounting the transfer case behind the steering joint there would be no problem to mount a more advanced alternative with differential and possibilities to obtain constant all-wheel drive (constant 6x6).

Hydrostatic front-wheel drive Hydrostatic front wheel drive is an optional configuration of the front axle that needs to be considered. The main advantage with this configuration is that no transfer case or drive shaft is needed to the front axle.

This is of major interest for frame-steered vehicles, since the length of the transmission can be kept to a minimum and the turning performance can be optimized without reducing the degree of freedom provided by the rotational joint. Additionally, if a front axle with hydrostatic hub engines is to be used the possibility to relocate the front axle will increase further. The final drive housing and drive shaft can be removed and therefore the distance to the steering joint can be reduced even further. The hydrostatic concept is more thoroughly investigated in Appendix B.

Alfred Johansson 3 3 Robin Nilsson 5. Powertrain and related components

5.3 Active components It is today possible to use electronic systems to control actions like the engagement of the front wheel drive, ABS and different vehicle stability systems. It is of high interest to improve the dynamic stability and safety of a frame-steered vehicle using electronic control systems. A number of applications for such systems will be presented here.

5.3.1 Existing electronic systems The ABS brake system used by Volvo can easily be implemented in a frame-steered vehicle. It is more difficult to implement the other control systems that are available on Volvo FM trucks. The traction control, anti-roll and anti-slide systems use the steering angle of the front wheels as input, and therefore these systems need to be redesigned [14].

5.3.2 Brake control It would be possible to implement a brake control system, which brakes the wheels independently to stabilize the truck.

5.3.3 Torque control If using propeller shafts equipped with clutches as discussed earlier, the engine torque, as well as the engine brake torque, could be totally variable controlled. This would improve the safety when driving on slippery surfaces.

5.3.4 Progressive Steering Customers who had the chance to drive the TWINS vehicle often complained about the sensitivity of the steering system. If an electronic steering system were utilised, it would be possible to use a nonlinear behaviour of the steering output. Since this vehicle will have much higher top speed than regular articulated haulers, too sensitive and nervous steering could cause problems.

5.3.5 Automatic locking and releasing of differentials Volvo Construction Equipment provides an electronic control system to lock and release the differentials on their articulated dump trucks. The system is called ATC - Automatic Traction Control. It locks the differentials immediately if the wheels tend to spin and releases it again instantly. By using an electronic control system, the differential locking only will be used when needed which will lead to reduced wear on drivetrain and tyres and it will also reduce the fuel consumption [15].

5.4 The need of front-wheel drive The need of front-wheel drive is not easy to define. However, it can be stated that some kind of front-wheel drive is necessary to obtain good pass ability and off-road performance. These requirements can be fulfilled with the optional front-wheel drive adopted on the regular Volvo FM.

Alfred Johansson 3 4 Robin Nilsson 5. Powertrain and related components

Generally all-wheel drive is need on surfaces with low traction ice, mud, sand etc. According to VAH a frame-steered vehicle should, from a stability and safety point of view, always be equipped with constant front-wheel drive. Without front-wheel drive a frame-steered vehicle could very easily go into an oversteering situation when driving on slippery surfaces. This can happen with an ordinary truck as well, but it can easily be corrected by the driver. On a frame- steered vehicle, this is very difficult to control because the steering motion will act mostly on the sliding wheels and the vehicle tend to oversteer even more.

If an optional front-wheel drive is used, it must be electronically controlled to engage instantly to avoid such situations. If this is combined with other advanced control systems, as mentioned earlier in this chapter, this might be sufficient to obtain a safe vehicle. Unfortunately, this could not be fully investigated in this thesis project and no complete conclusion has been drawn on this topic.

5.5 Tyres for the FM-FS truck Due to the articulated steering there will be greater possibilities to use larger tyre dimensions compared to a regular truck. Two different tyres has been selected, together with Anders Trygg at 26454 Brake, Hub & Wheel, for the two applications considered in this report, these will be presented in Chapter 6 and 7.

5.5.1 Tyres for the FM-FS 6x6 construction truck Wide tyres that are capable of carrying heavy loads in high speed are uncommon, but for the dump truck application the Michelin XZL-16.00.20 has been selected. The maximum axle load is 13.2 ton per axle if these tyres are single mounted. The overall diameter is 1343 mm and the tyre width is 438 mm. This tyre is 7 mm thinner than the 445.80R25 used on the Off- On TWINS prototype but the XZL tyres can be used at highway speed. The overall diameter is equal for both tyres, and the whole Michelin XZL specification can be read in Appendix H.

5.5.2 Tyres for the FM-FS 8x6 “Salix II” agricultural truck The FM-FS Salix II truck is further investigated in chapter 7. It is an 8x6 truck with a none- driven steered tag axle. The vehicle is to be used on agricultural soil and the ground pressure must therefore be minimized. Since studies have shown that wide super single tyres with low inflation pressure are more suitable than double mounted tyres [16], the Alliance 328 MPF 22.5”series have been selected. Dimensions available can be seen in Table 5.2.

These tyres are restricted to a maximum time in high speed of one hour. This is not optimal for all applications but for the intended work cycle of the Salix II-project it would work fine. The maximum load per axle in high-speed mode is 9000 kg per axle and more detailed specifications can be read in Appendix I.

Alfred Johansson 3 5 Robin Nilsson 5. Powertrain and related components

Table 5.2 Dimensions for Alliance 328 MPF Rim width Tyre Size (inches) 400/55-22.5 13.00 500/60-22.5 16.00 500/45-22.5 16.00 550/45-22.5 16.00 550/60-22.5 16.00 600/50-22.5 20.00

Alfred Johansson 3 6 Robin Nilsson 6. The FM-FS 6x6 Concept

6. The FM-FS 6x6 Concept The all-wheel driven 6x6 truck is thought to be a small truck with good movability. In this thesis assignment a dump truck concept is being used to illustrate the 6x6 FM-FS truck (see Figure 6.2), but of course it is possible to use the chassis layout for other purposes as well. The advantage with the FM-FS concept is that high tyres, giving good ground clearance, or wide tyres with low ground pressure, can be used on all axles because none of them is being used to steer the truck. Therefore, the off-road capabilities will increase.

The rotational degree of freedom in the hitch combined with the large tyres makes the off- road behaviour for this type of truck very good, see Figure 6.1. The on-road maximum legal weight for a three-axle truck will be 26 tons in countries that follows EU agreements (national variation exists).

Figure 6.1 The advantage in terrain pass ability for the frame-steered Off-On vs. an Ackerman steered truck.

6.1 Drivetrain layout The front axle for the FM-FS 6x6 truck will be of a new design, see chapter 5.1.2. The rear bogie installation will be a leaf springed RADD-TR2 tandem drive with a maximum load of 32 tons. The bogie spread needs to be increased from 1370 mm to 1450 mm to make it possible to install tyres with a greater overall diameter. The tyres that has been chosen for the 6x6 FM-FS construction truck is the Michelin XZL 16.00 R20 (chapter 5.5.1) The 1450 mm installation is not a standard Volvo Truck installation, but the same axle spread was used in the TWINS-project [17].

The front axle propulsion is not yet fully determined. There are two different ideas of how the driven front axle would be powered. Either a classic mechanical layout with a transfer case between the gearbox and rear axle or a hydrostatic drive, see Chapter 5.2.

Alfred Johansson 37 Robin Nilsson 6. The FM-FS 6x6 Concept

Figure 6.2 CAD-model of the FM-FS 6x6 truck with tipper body of 14 m³

6.2 Tipp behaviour According to a Volvo Construction Equipment rule of thumb the centre of gravity for the load when tipping is never supposed to move behind the outside of the rear wheel. With this rule the load on the rearmost axle will not increase too much and cause stability problems on soft ground.

Another guideline for this work is that the centre of gravity of the load is located over the bogie joint, see Chapter 3.1.2. The location of the load centre of gravity is calculated in Pro Engineer using a simplified dump body on FM-FS 6x6 model. Maximum tipping angle will therefore be 59° before the centre of gravity will be located behind the rear wheel, see Figure 6.3. Bear in mind that this situation will only occur if no load has left the tipped body earlier in the tipping sequence.

Figure 6.3 Centre of gravity for tipper body 14 m³

6.3 Gross weight and payload The gross weight for this vehicle is hard to predict, but if this concept is to be competitive the gross weight with the mechanical drivetrain can not be more than slightly higher than the

Alfred Johansson 38 Robin Nilsson 6. The FM-FS 6x6 Concept weight of a comparable Volvo FM 6x6. In countries that follow the EU directives the on road legal gross weight with single mounted tyres is 25 tons. The chassis weight is supposed to be 9-10 tons and with a tipper body of 2 tons the on road payload would be 13 tons.

6.4 Potential costumers Before the start of a larger development process, a need must be defined and for the FM-FS 6x6 potential costumers is specified in Chapter 1.4. As mentioned earlier, the FM-FS 6x6 truck is supposed to be a smaller truck with good movability and new vehicle concepts often find market segments that the product developer has not thought of.

The main costumer base for the FM-FS 6x6 is similar to the one that Volvo aimed at with the TWINS-prototypes, construction sites in west and central Europe. In the comparison with the genuine articulated dump trucks the FM-FS lacks in terrain pass ability but has the advantage of better on-road speed. In the costumer clinics with the Off-On prototype, the costumers expressed a need for this type of vehicle.

Alfred Johansson 39 Robin Nilsson

Alfred Johansson 40 Robin Nilsson 7. FM-FS 8x6

7. FM-FS 8x6 To meet the demands for a larger truck, a 4-axle vehicle has been designed. This vehicle is equipped with Volvos “tridem” axle concept that utilizes two driven axles and a steerable, non-driven tag axle at the rear. Due to this additional axle the vehicle is, according to Chapter 3, permitted to operate with a total weight of 32 tonnes.

7.1 Articulated vehicles with four axles To use frame-steering in a 4-axle vehicle is not very common and problems that might arise have been considered. It was also discovered that Volvo already had designed such a vehicle a few years ago.

7.1.1 Steering Forces When turning the steering wheel at standstill a normal articulated hauler behaves according to Figure 7.1 (A); the midsection of the vehicle is “pushed out”[7][8]. It was however feared that, with the 4-axled vehicle, large reaction forces would occur and that it might behave as according to Figure 7.1 (B), where the front frame is dragged sideways. Calculations were made and can be seen in Appendix F. According to this calculation, the vehicle will behave as according to Figure 7.1(B) if assuming an equal load on each axle. This behaviour must be considered when designing the front suspension.

Figure 7.1 Different movements in frame during steering

7.1.2 Position of load Since the rear frame is located on three axles, the stability is greatly improved and hence the payload does not always need to be positioned above the bogie, as stated in Chapter 3.1.2. However, the total load on each axle must be regarded and hence the payload should be positioned as close to the centre of the tridem axle configuration as possible to obtain equal load distribution.

Alfred Johansson 41 Robin Nilsson 7. FM-FS 8x6

7.1.3 Improvement of steering angle Due to the improved stability of the rear frame, the restrictions of the turning angle as presented in Chapter 3.1.2 should be discussed. Since the rear frame is a stable unit by itself, the steering angle could perhaps be increased. However, this is a complicated issue and the dynamic behaviour of the vehicle is difficult to predict. For example, during high-speed turn- in with an ordinary 3-axled articulated hauler, the initial tilt angle of the front frame can reach up to 16° [7]. How a 4-axled vehicle would behave should be analysed in dynamic simulation software such as ADAMS where parameters such as speed, position of payload, turning angles and vehicle geometry can be altered to simulate the truck behaviour.

7.1.4 Articulated haulers in Svalbard In the end of the year 2000, Volvo Articulated Haulers developed and delivered three 4-axled haulers for coal mining operation at Svalbard. The bad road conditions and a very high road inclination made articulated dump trucks the only option. Volvo Articulated Haulers developed an 8x6 A40 hauler as can be seen in Figure 7.2. The axle configuration on these vehicles where very similar to the 8x6 concept presented in this chapter, as the haulers utilized a steered and undriven rearmost axle. According to sources at Volvo Articulated Haulers the A40 8x6 performed very well and no major problems, as those listed previous in this chapter, where discovered with the 8x6 concept. Two of the haulers where still in operation at the time of this report, as the third vehicle was put out of operation due to an engine failure.

Figure 7.2 Svalbard truck in operation

Alfred Johansson 42 Robin Nilsson 7. FM-FS 8x6

7.2 Axle Installation As can be seen in Figure 7.3, the vehicle is equipped with a tridem configuration with a leaf suspended tandem bogie and a steerable air suspended tag axle. However, the vehicle’s undriven auxiliary axle could also be positioned before the bogie, called a “pusher”, if desired by the customer [17]. The difference between “tag” and “pusher” is illustrated in Figure 3.5 (B) and (C).

For dump trucks, a pusher axle is commonly used, since positioning the dual tyres of the bogie at the rearmost location improves the stability while tipping. But since this vehicle is designed for super single tyres on all axles, this argument is now eliminated. Thus a tag axle should be used since, as discussed in Chapter 3.2.2, a tag axle shortens the theoretical wheelbase and improves the turning abilities. To use a fixed auxiliary axle have been discussed but was dismissed due to the increased tyre slip, as discussed in Chapter 3.2.2.

As can be seen in Figure 7.3, the vehicle is also equipped with a container hook lift. The reason for this is presented later in this chapter. For high load applications, the heavy-duty and reinforced tag axle TAD-HD is used, as it is certified for a maximum dynamic load of 9 tons and a static load of 15 tons.

Figure 7.3 CAD-visualisation of the 8x6 rear frame

7.2.1 Steering angles Equations for the steering angles of an auxiliary axle can be found in Chapter 3.2.2. The steering angles are based upon the turning radius and the distance from the auxiliary axle to the turning point of the rear frame, as defined in Appendix A. Since the steering performance of the vehicle cannot be fully predicted, different values are presented in Table 7.1

Alfred Johansson 43 Robin Nilsson 7. FM-FS 8x6

Table 7.1 Steering angles for an auxiliary axle with a distance of 2150 mm to rear “turning point”. Inner turning Steering angle, Steering angle, Mean steering radius (m) inner wheel (°) outer wheel (°) angle (°) 5 23.5 16 19.75 6 20 14.5 17.25 7 17.5 13 15.25 8 15 11.5 13.25

When using the 600/50–22.5 tyres described in Chapter 5.5.2, the maximum angle of the tag axle is about 17°, as can be seen in Figure 7.4. At 17° contact will occur on both the anti-roll bar (A) and the air bellow (B). A project has been carried out where the anti-roll bar has been relocated and hence collision (A) can be solved [18]. The air bellows are more difficult to relocate though. It is possible, but it requires a redesign of the whole axle suspension and a great deal of development work [19]. The air bellows will probably also need some sort of protecting metal plate to prevent damage from the tyres, gravel or other debris.

From Table 7.1 it can then be stated that these tyres should not be used if an inner turning radius of under 6 meters are estimated. However, it should be stated that some degree of tyre slip could be accepted.

Figure 7.4 Collisions occur at a steering angle of 17°.

7.3 Volvo FM-FS Salix II Even though there are many applications where this vehicle can prove to be superior, the SALIX project was the main focus for this vehicle during the thesis work. At the time of this report the first prototype was built and referred to as “SALIX I”. Since the concept vehicle created in this thesis work was considered as the successor of the SALIX I prototype it was often referred to as “SALIX II”. The SALIX vehicle will be able to harvest crops and transport them from the field without any reloading of the cargo. This will provide a new cost effective concept of harvesting to the agricultural industry. In the SALIX project the vehicle

Alfred Johansson 44 Robin Nilsson 7. FM-FS 8x6 will be equipped with a container hook lift as can be seen in Figure 7.5. It will also be equipped with a quick-lock for certain harvesting machinery in front of the cab (not included in Figure 7.5).

Depending on the density of the crops, different container sizes will be preferred. It is clear though that a 20 ft container will be used. Since the width of the vehicle is defined by road legislation, the only way to alter the internal volume it to adjust the height of the container. Two containers will be discussed in this chapter. A splinter container with the dimensions (L*W*H) 6000x2550x3030 giving an internal volume of 40 m3 provided by GMM Container, and a standard 20 ft ISO container with the dimensions (L*W*H) 6058x2438x2591 with a volume of 33 m3. However, since the height of the complete vehicle is restricted, see Chapter 4.2, the 40 m3 container might be to high. As can be seen in Figure 7.6(A), the 40 m3 container make the total height of the vehicle to reach about 4.5 meters depending on tyre pressure, payload etc. However, the lower ISO-container (B) will imply a total height below 4 meters, hence fulfilling the European directive as described in Chapter 4.2.

Figure 7.5 CAD-Visualisation of the complete FM-FS 8x6

Figure 7.6 Height difference between the 40 m3 splinter and ISO 20 ft. container

Alfred Johansson 45 Robin Nilsson

Alfred Johansson 46 Robin Nilsson 8. Results

8. Results Two concept vehicles have been presented in the previous chapters and some important performance parameters of these will be presented in this chapter.

8.1 Specifications Since this thesis work is only a prestudy of the possibilities of the frame-steering concept, some parameters were difficult to predict. For instance, since the transmission design was yet to be established, the distance referred to as “F” could not be fully determined.

8.1.1 FM-FS 6x6 The FM-FS 6x6 was designed as a dump truck equipped with a 14 m3 dump body. The vehicle where designed according to the restrictions regarding payload position, as discussed in Chapter 3.1.2, and the resulting dimensions can be seen in Figure 8.1. The bogie axle spread has been increased to 1450 mm.

Figure 8.1 Key dimensions for FM-FS 6x6 with tipper body

8.1.2 FM-FS 8x6 The 8x6 vehicle was equipped with the tridem axle configuration that utilizes a steerable tag axle at the rear. It has been designed mainly for the SALIX project where a container hook lift is to be used. This has lead to the dimensions that can be seen in Figure 8.2.

Alfred Johansson 4 7 Robin Nilsson 8. Results

Figure 8.2 Key dimension for FM-FS 8x6 with hook lift and container

8.2 Steering performance With the given dimensions, the steering performance can be predicted with the mathematical model presented in Chapter 3. Since the two vehicles have different wheelbases and different axle configurations, their steering performances are presented in two separate tables.

Since the distance F is depending on the transmission layout, two values have been used which both can be associated with certain transmission concepts.

The possibility to use a “dual” steering system including wheel steering has been discussed throughout this thesis work. By using a certain amount of wheel steering, the frame-steering angle could be reduced, which would improve stability. Hence, two values of the frame- steering angle are included in the tables below and these can be combined with different angles of wheel steering.

Table 8.1 Steering performance for 6x6 with different wheel and frame-steering angles. Resulting turning radii are given in the two columns to the right. Distance F (m) Frame-steering Wheel steering Outer turning Inner turning angle (°) angle (°) radius (m) radius (m) 1.4 41.8 (max) 0 7.8 4.6 0 8.7 5.6 38.0 (max) 15 6.7 2.8 1.6 15 7.5 3.8 30 30 6.2 1.6 0 10.2 7.3 33.3 (max) 1.9 15 7.5 3.7 15 8.7 5.1 25 30 6.8 2.3

Alfred Johansson 4 8 Robin Nilsson 8. Results

Table 8.2 Steering performance for 8x6 with different wheel and frame-steering angles. Distance F Frame-steering Wheel steering Outer turning Inner turning Tag mean (m) angle (°) angle (°) radius (m) radius (m) steering angle (°) 1.4 41.8 (max) 0 7.4 4.3 22.4 0 8.2 5.3 19.1 38.0 (max) 15 6.3 2.6 31.6 1.6 15 7.2 3.6 25.7 30 30 5.8 1.4 43.3 0 9.7 6.9 15.3 33.3 (max) 15 7.1 3.5 25.9 1.9 15 8.2 4.7 20.7 25 30 6.5 2.1 35.3

As can be seen in Table 8.2, the necessary steering angles of the tag axle almost always exceeds the 17° which in Chapter 7.2.1 where stated as the limit with the desired tyres.

8.3 Payload No specific study has been made on how the payload will be affected by the frame-steering concept. A brief estimation can however be made based on earlier experience and prototypes.

During the TWINS-project, parts from the Volvo articulated haulers were used. This includes core components as the steering joint and the hitch and the weight of these components were about 400 kg [8]. These parts where used to keep the cost down for the prototype, it can be argued that they are not optimal since they are designed for higher loads and therefore heavier than necessary. However, this weight does not include all components of the steering system. Parts such as hydraulic cylinders, connection flanges etc. must also be considered.

One of the main advantages of the frame-steering concept is the rotational degree of freedom that eliminates the torsional forces in the chassis. This reduces the need of a sub-frame when the vehicle is used as a construction truck or in any other application that normally requires a sub-frame to be mounted. This will result in an increased payload, but also a lower mounting position of the dump body or other equipment.

8.4 Off-road Performance This topic has not been of main priority in this thesis work. But to be able to compare the FM- FS concept with other vehicle two important parameters have been examined.

8.4.1 Ground clearance With the frame-steering concept, wider and larger tyres can be mounted, which significantly improves the ground clearance. With the standard ZF driven front axle and Michelin XZL 16.00R20, the ground clearance is expected to be roughly 480 mm under the front axle housing, see Figure 8.3. This is very good, and even comparable with many articulated haulers in the 20-25 tons payload sector. For instance Volvo A25D got a ground clearance of 456 mm, Bell B20D 440mm and Cat 745 495mm at their lowest points.

Alfred Johansson 4 9 Robin Nilsson 8. Results

Figure 8.3. Ground clearance under front axle 480 mm (with XZL 16.00 R20)

8.4.2 Approach angle The importance of the approach angle can be questioned, but generally it can be said that with low ground clearance, the importance of good approach angle increases. Articulated haulers have an approach angle of about 30°. A standard Volvo FM truck has an approach angle of about 23 degrees. With the XZL 16.00.20 tyres, a modified front bumper and the standard all- wheel drive axle position, the approach angle can reach up to 30°; as good as the articulated haulers, see Figure 8.4. If a larger amount of approach angle is needed, the height of the frame can be improved by mounting a thicker spacer between the leaf spring and the axle. The spacer is today around 30 mm but it could with out any major drawbacks be changed to 90- 100 mm [12].

Figure 8.4. Theoretical angel of attack with front suspension bracket as factor of limitation

Alfred Johansson 5 0 Robin Nilsson 9. Conclusion

9. Conclusion During this thesis work, two concept vehicles have been further investigated, with both mechanical and hydrostatic propulsion. The assignment and goal for this thesis work has been to understand, define and provide ideas of how a frame-steered version of a Volvo FM truck should/could be designed.

The turning radius is a very important parameter when designing a frame-steered truck and therefore the mathematical model for turning performance is of great interest. The MATLAB model made for the FM-FS truck has been really helpful and easy to understand. Different design ideas can through this model straightforwardly be compared and judged on a scientific basis.

The main questions that during the work were defined are the following:

When and under which conditions and circumstances are all-wheel drive needed; - High speed? - Slippery surface? - Off-road?

What is the costumer need and demands; - Steering ability? - Angel of attack? - Ground clearance? - Hitch articulation? - Payload? - Extra low range gear?

The main questions that first need to be solved is the drivetrain layout and much time has been spent trying to come up with a functional and desirable concept.

Optimal steering performance and movability is obtained when no mechanical front wheel drive is used, since this concept do not restricts steering angle or rotational degree of freedom. The alternative solution is hydraulic drive of the front wheels. This does not affect the steering performance, but the maximum torque delivery to the wheels is limited. Hence, both concepts have some customer benefits. The operation environment is important, since this determines the demands on steering performance and amount of front-wheel drive propulsion.

Another conclusion that can be drawn is that for safety reasons trucks with only optional front-wheel drive will need some kind of control system like anti-slide or traction control.

A combined steering concept with both Ackerman and articulated steering was briefly investigated. The concept seems to be the most desirable solution from a Volvo Truck Company point of view, and it would be possible to build a frame-steered all-wheel drive truck with excellent turning ability. It also improves the vehicle stability as the steering angles of the frame can be reduced while maintaining good steering performance.

Alfred Johansson 51 Robin Nilsson

Alfred Johansson 52 Robin Nilsson 10. Discussion and proposals for future work

10. Discussion and proposals for future work During this thesis work much knowledge has been gained, some questions have been answered and other have been raised. The work has been more about collecting and analysing ideas rather than defining a final design.

There has been much discussion about the need of front-wheel drive. A frame-steered vehicle behaves different compared to an Ackerman steered. Since countersteer is very difficult with this type of steering, it was argued by Volvo Articulated Haulers that front-wheel drive is always necessary to avoid oversteer. In this thesis work the starting ground was a rigid Volvo FM truck with only optional front-wheel drive and from a passability perspective all-wheel drive is only needed in low speed where there is a risk to get stucked.

For future work, the arguments concerning constant all-wheel drive need to be investigated. It would be a great advantage if these arguments could be supported with computer simulations where the dynamics of such a vehicle can be tested. With software like ADAMS the importance of parameters like front wheel drive, steering angle, payload, payload distribution and axle configuration could be analysed. ADAMS is used within the Volvo Group and this would probably prove to be an excellent thesis work for two ambitious students.

The dual-steer concept is highly interesting as it could introduce the frame-steering concept into high-speed commercial vehicles. For an initial prototype, the Volvo Truck original ZF driven front axle could be used and it would be supported by an electronic controlled frame- steering system that only is activated at low speeds. At high speed the frame-steering system would be turned off and the vehicle would behave as a regular Volvo FM truck. The high- speed stability concerns on frame-steered vehicles could by this way be ignored.

Electronic stabilisation systems are today accepted within the vehicle industry and in a long time perspective it would be possible to implement such systems to a frame-steered truck. A pure frame-steered truck with only optional front-wheel drive would definitely need some kind of control system from a dynamical high-speed safety point-of-view.

When continuing with this concept, the requirement from the customers needs to be specified in a more detailed way. In this thesis work, the requirements and demands used in the TWINS-project have been used. However, the vehicles presented in this report do not have the same performance and hence the customer basis should be reviewed.

Alfred Johansson 53 Robin Nilsson

Alfred Johansson 54 Robin Nilsson 11. References

11. References

[1] Sten Ragnhult, Front suspension engineer, Dept.26421, Volvo 3P

[2] Pavel Prochazka, Product planner, Dept. 23330, Volvo 3P

[3] Niklas Johansson, Product Manager Region East, Dept.22740, Volvo Trucks AB

[4] Silversides C.R, Use of articulated wheeled tractors in logging. Unasylva No. 83.

[5] http://www.volvo.com/constructionequipment/global/en-gb/AboutUs/history/

[6] http://www.moxy.no

[7] Heikki Illerhag, Dynamic simulation engineer, Dept. 53510, Volvo Articulated Haulers

[8] Jörgen Ahlberg, Senior Engineer, Dept. 53410, Volvo Articulated Haulers

[9] Ivar Aaboen, Vehicle product manager, Dept. 23340, Volvo 3P

[10] Per-Olof Rydberg, Vehicle regulations and certification adviser, Dept. 26710, Volvo 3P

[11] Robert Lundin, Technical consultant, Dept. 24350, Volvo Powertrain

[12] Lorenz Andersson, Platform geometry architecture engineer, Dept. 26940, Volvo 3P

[13] Jan Öberg, Transmission project adviser, Dept. 24350, Volvo Powertrain

[14] Jan-Inge Svensson, Vehicle control systems engineer, Dept. 26452, Volvo 3P

[15] Press release from Volvo CE – 2005-11-24

[16] Braunack M.V, A tyre option for sugarcane haulout trucks to minimise soil compaction. Bureau of Sugar Experiment Stations, Tully Qld., Australia 2004.

[17] Johan Hederstierna, VMT leader suspension, Dept. 23073, Volvo 3P

[18] Roger Andreasson, Technical consultant, Dept. 26200, Volvo 3P

[19] Roland Svensson, Senior engineer, Dept. 26422, Volvo 3P

Alfred Johansson 55 Robin Nilsson Appendix A. Steering geometry

Appendix A. Steering geometry Frame-steering Frame-steering is a rather complex steering configuration and has distinctive dissimilarities with conventional Ackerman steering. These will be discussed in this chapter and a useful mathematical model for predicting the behaviour of a frame-steered vehicle is presented in Chapter 3.

Problems and safety According to a Volvo in-house rule of thumb the outer front wheel cannot be allowed to pass the centreline of the rear frame, see Figure 1. Overrunning this rule is supposed to make the vehicle unstable and affect the safety.

Figure 1. This vehicle has reached its maximum steering angle, as the outer front wheel is about to pass the centreline of the rear frame. Notice the important parameters, the track width T and the distance F.

This is of particular importance if the payload has not been positioned correctly. If the steering linkage is weighed down at a greater steering angle than allowed the front frame can twist around the rotational joint (as shown in Figure 2). The inner front wheel is lifted and the whole front frame can turn over, as seen in Figure 3.

Figure 2. Incorrect position of the payload, load transfer to the front axle will take place. Compare with Figure 2.3 in Chapter 2.1.1

Alfred Johansson A 1 Robin Nilsson Appendix A. Steering geometry

Figure 3.

Theoretical Model From the rule discussed in the previous chapter, a theoretical model for steering performance can be carried out by using the track width (T), wheelbase (R) and the distance between the front axle and the steering joint.

As visualised in Figure 1, the maximum steering angle cannot be greater than ≈ T ’ a = arctan∆ ÷ (1) « 2F ◊

From Figure 4 the outer and inner turning radius can then be expressed as

Alfred Johansson A 2 Robin Nilsson Appendix A. Steering geometry

R F + F + x T T Ro = + = cos a + (2) tan a 2 tan a 2

R F + F + x T T Ri = − y − = cos a − R ⋅ tan a − (3) sin a 2 sin a 2

Definitions: a = steering angle F = Front of joint R = Rear of joint (theoretical turning axis) Ro = Outer radius Ri = Inner radius T = Track width

Figure 4.

This gives a theoretical turning radius that corresponds reasonable well to data sheets published by the manufacturers. It should be remarked that this model does not take in account the different loads on the rear axles, tyre slip and are assuming that the theoretical wheelbase is located right between the rear axles.

Ackerman steering For calculations on different steering angles on a regular truck, similar equations were constructed for Ackerman steering principle. The basic idea with Ackerman steering can be seen in Figure 5. As the inside front wheel must take a more narrow turn it will also turn with a higher steering angle.

According to Figure 5 the outer turning radius ro can be expressed as

L r = (4) o sin a and the inner turning radius ri

L r = − T (5) i tan a

Alfred Johansson A 3 Robin Nilsson Appendix A. Steering geometry

Figure 5.

If the maximum steering angle is only given for the inner wheel (angle b) the angle a can be calculated using the following relationship, see Figure 6. ≈ ’ ∆ ÷ 1 a = arctan∆ ÷ (6) ∆ T 1 ÷ ∆ + ÷ « L tanb ◊

Figure 6.

Alfred Johansson A 4 Robin Nilsson Appendix A. Steering geometry

If self-aligning rear wheel steering is utilized, the steering angle for these wheels can according to Figure 6 be expressed as

B c = arctan (7) ri + T B d = arctan (8) ri

Notice that these two equations can be applied for both rear- and front steered auxiliary axles.

Dual Steering During the work with this master thesis it was found out that a combined steering system with both Ackerman and frame-steering would be really competitive and therefore a mathematical model for the dual-steering concept were examined.

In (2) the equation for outer front wheel turning radius on a frame-steered truck is expressed as: R F + F + x T T R = + = cos a + o tan a 2 tan a 2

If the frame-steering is combined with the Ackerman steering, the equation for the outer turning radius expressed as shown in (9). The relationship is identified by using Figure 7.

T sin a + F⋅ cos a + R R = 2 (9) 1 sin (θ + a)

Figure 7.

Alfred Johansson A 5 Robin Nilsson Appendix B. Hydrostatic Propulsion

Appendix B. Hydrostatic Propulsion

During the time of this report, frequent discussions if to use hydrostatic drive in the FM-FS took place and hence a deeper investigation was made. The investigation will be presented here, as well as suggestions for future development.

High speed assisting hydrostatic drive Due to the restricted distance F referred to in Chapter 5, a hydrostatically driven front axle would save valuable space since the transfer case would be eliminated. This would be very useful in the FM-FS concept, as it would improve the steering performance.

The hydraulic system would be possible to implement in virtually any truck, regardless of it application, since it has a number of advantages. Studies have shown that the all-wheel drive is rarely used in most applications.1 The driver may switch to all-wheel drive when approaching rough terrain or very steep hills but during a normal work cycle the front-wheel drive is often not engaged. Due to the number of rotating transmission parts and added weight, the mechanical all-wheel drive transmission is constantly consuming extra fuel and also reduces the payload. Hence it is not only an articulated steered truck that would benefit from such a propulsion system.

The German competitor MAN had at the time of this report recently presented such a front- wheel hydraulic transmission. They claim to save about 400 kg compared to a standard all- wheel drive truck. Unfortunately no technical specification had been made available. The system was however presented as an “assisting” hydrostatic drive which can be engaged up to 30 km/h.2 The term “assisting” could then be referring to its amount of power, i.e. it may not deliver the same amount of torque as a mechanical all-wheel drive system.

Hydrostatic drive is very interesting for the FM-FS concept, as Volvo Articulated Haulers states that front-wheel drive should always be engaged in an articulated steered vehicle. This is probably a very legitimate demand for an articulated hauler, but for a truck, designed for speeds up to about 90 km/h, this might not be required. If the assisting hydraulic drive can operate up to speeds of about 30 km/h or even higher, this might be enough to fulfil the demands from VAH. When operating in higher speeds the terrain will most likely be rather smooth and hence the VAH demand might be possible to neglect.

1 Arcila M, Bien B, Application of hydraulic motors to drive truck’s steered axles. Chalmers University of Technology, Göteborg, Sweden 2004. 2 http://mis.mn.man.de/

Alfred Johansson B 1 Robin Nilsson Appendix B. Hydrostatic Propulsion

Low speed hydrostatic drive for SALIX vehicle For certain applications a fully hydraulic drive is preferable. This is common when very low speeds are requested, for example when trucks are used for road sweeping. By driving the wheels hydraulically, the speed can be continuously variable, by simply altering the displacement of the pump, from standstill to the hydraulic system’s maximum speed without any clutch slip or significant torque reduction. In such applications the hydraulic motor is often mounted on the propeller shaft and the pump is mounted on an engine PTO.

Background For the SALIX concept vehicle however, this common solution cannot be optimally employed. The vehicle is expected to carry out the harvesting operation at speeds from 5 km/h up to 10 km/h or even higher. At the same time the harvesting equipment is using a large amount of hydraulic power only available when the diesel engine is running at full speed. Due to high speed requirements and a high tractive force produced by the hydraulic propulsion system, no properly dimensioned PTO is available. This resulted in a maximum hydraulic speed of only 3.5 km/h for the prototype vehicle SALIX I. It would perhaps be possible to operate with a manual gearbox, but harvesting should be able to be done at continuously variable speed. Hence a hydrostatic system powered by the driveshaft is required.

Requirements With current equipment, harvesting is expected to be performed at 5-10 km/h depending on the specific crop.3 However, harvesting speeds are generally restricted to about 10 km/h since agricultural machinery often lacks suspension. Higher speeds would result in a very uncomfortable working environment for the driver. The SALIX concept, where the truck is used as the harvesting vehicle, is not restricted by this problem and perhaps higher speeds are possible. If the crop is particularly light and easy to harvest it might be possible to operate at slightly higher speeds. Unfortunately, at the time of this report the harvesting machinery was not tested and no exact values could be used. Hence 10 km/h was regarded as the required speed when driving in fully hydrostatic transmission mode.

According to technicians at Volvo the vehicle should be able to climb an inclination of 25% fully loaded4. The transmitted power can then be calculated according to equation 1.

P = F ⋅ v (1)

P=Power [W] F=Force [N] v=Velocity [m/s]

To fulfil the demands, the hydrostatic system must then be designed to transmit the power listed in Table 1. This amount of power cannot be transmitted trough available PTO’s and hence the pump must be driven by the drive propeller shaft.

3 Wilstrand Mats, project manager, SALIX Maskiner AB 4 Jan Öberg, Technical Adviser, Vendor components and project support, Volvo Powertrain AB

Alfred Johansson B 2 Robin Nilsson Appendix B. Hydrostatic Propulsion

Table 3 Power required to be transmitted trough the hydraulic system. Vehicle gross weight Propulsion force Power (tonnes) (kN) (kW) 26 65 181 32 80 222

Concepts During discussions with supervisor Lena Larsson and other employees at Volvo 3P, several concepts came up and these will be analysed in this chapter.

Scarab Sweepers To provide a simple and cost effective solution to the problem discussed earlier, a short benchmarking of available products was made. It was discovered, that an English company named Scarab Sweepers had developed a concept that would suit the SALIX vehicle perfectly. Scarab Sweepers adapts trucks for road sweeping applications, where problems similar to the ones experienced with the SALIX vehicle. The sweeping machinery consumes a large amount of power requiring the engine to run on high speeds. At the same time the customers want to be able to operate the vehicle in different speeds. This has traditionally been solved by installing a smaller, secondary engine that runs the cleaning equipment. Unfortunately, this secondary engine occupies valuable space and reduces the vehicles efficiency.

The concept developed by Scarab Sweepers solves this problem, the concept is very simple and can be installed in virtually any truck if sufficient space is available. The system is covered in one unit, including a pump, motor and a coupling which enables the drive propeller to be divided when driving in hydrostatic mode. When driving in normal mode, the hydraulic components are disengaged and by reconnecting the drive propeller the vehicle operates like an ordinary truck. A graphic description of the transmission unit can be seen in Figure 1. Another advantage of this product is the PTO used for an additional hydraulic pump that normally drives the sweeping equipment. In the SALIX project, this could be used to power the external harvesting machinery.

Figure 1. (1) Variable displacement pump. (2) Motor. (3) Shaft coupling. (4) Hydraulic pump for external use.

Alfred Johansson B 3 Robin Nilsson Appendix B. Hydrostatic Propulsion

Unfortunately, Scarab Sweepers is currently only installing this transmission unit on small trucks like the Volvo FL and other similar trucks in the 18 tonnes range.

The maximum torque of the diesel engine is restricted to 1000 Nm.5 This is caused by the universal joints, which are stressed when driving in “mechanical” mode. The sizes of these joints are restricted due to space delimitations. The Scandinavian distributor has in recent years discussed this issue with technical spokesmen of Scarab Sweepers and a more robust transmission is under development. However, according to the distributor, it is believed that transmission units for heavy trucks as the FM and FH with engine power of about 300-400 kW are not of interest to Scarab. This is understandable, as they are simply not suitable for ordinary road sweeping applications. The concept is very interesting though, as the system would be very compact and could interact with an assisting front-wheel hydraulic drive, see Figure 2. It might also be used in other applications since it is easy to install.

Figure 2 Layout of the concept developed by Scarab Sweepers assisted by a front-wheel hydraulic system.

Driven front and tag axle During the discussions of developing of a front-wheel hydraulic drive system, the possibility to also mount this system at the tag axle was considered, see Figure 3. If a driven front axle is developed this may be the most cost effective concept since it only utilize of-the-shelves components. In the work done earlier6, a target of 22 kNm at 5 km/h for each axle was set but was not fully accomplished. This torque would produce a total tractive force of 88 kN, which even exceeds the requirements set in Table 1.

However, this torque was set to be produced at speeds of 5 km/h or less. The torque delivered may then drop due to displacement reduction in the hydraulic motor.

Perhaps this is good enough for the SALIX vehicle, as harvesting will mainly be carried out in a relatively horizontal terrain. It might be enough if the hydraulic propulsion system can deliver the amount of torque described above in particular demanding situations, for example to enable driving to the field or to overcome obstacles. If the problems experienced earlier can be solved, this would be a very interesting concept.

5 Clas Andreasson, Ren Väg AB, Scandinavian distributor of Scarab Sweepers. 6 Arcila M, Bien B, Application of hydraulic motors to drive truck’s steered axles. Chalmers University of Technology, Göteborg, Sweden 2004.

Alfred Johansson B 4 Robin Nilsson Appendix B. Hydrostatic Propulsion

Figure 3 Two steered hydraulically driven axles

Rear-mounted motor This is a modification of the Scarab concept, where the hydraulic motor has been positioned behind the third axle, se Figure 4. As can be seen in Chapter 7, the Salix vehicle is planned to be equipped with a tridem axle configuration. With this concept, the third axle would be replaced with an axle similar to the second axle which has a connecting flange on its rear side. Thus an input for the hydraulic power can be arranged by using standard Volvo parts.

Figure 4 Symbolic visualization of the rear-mounted motor concept layout

If the hydraulic motor can operate at the same speed as the drive shaft, no gear reductions will be necessary and hence the system would be lighter and occupy less space. With maximum speed of 10 km/h, an estimated final gear ratio of about 1:4,5 and a wheel radius of 0.5 meters, the motor will experience working conditions as listed in Table 2.

Table 4 Requirements for hydraulic motor Required tractive Max torque (4,5:1) Max speed Theoretical power force (kN) (kNm) (rpm) (kW) 65 7,2 238 181 80 8,9 238 222

Alfred Johansson B 5 Robin Nilsson Appendix B. Hydrostatic Propulsion

However, these values do not take in account a propulsion system at the front axle. If an assisting front hydraulic system is employed, the requirements for the rear hydraulic system naturally decrease.

Still, a PTO mounted on the propeller shaft will be needed. If it features the possibility to disconnect the rear drive shaft axle, as in the Scarab transmission unit, advantages will be gained as there will be no need for an auxiliary shaft coupling. The German transmission manufacturer Stiebel Getriebebau GmbH & Co. KG produces three PTO units of this type with different gear ratios, which together forms the 4496.38 series. A packaging analysis was performed and can be seen in Figure 5 and 6. These transmission units are, according to technicians at Stiebel 7, developed for concrete mixers and direct the torque to either the rear wheels or the PTO. A drawing including brief technical data of these units can be seen in Appendix C.

Figure 5 A simplified visual representation of the Stiebel transmission unit equipped with a variable displacement 180 cc hydraulic pump.

Figure 6. The pump-drive-PTO located in front of the rear axles.

7 Stock R. Product Manager Pump Drive, Stiebel Getriebebau

Alfred Johansson B 6 Robin Nilsson Appendix B. Hydrostatic Propulsion

The different input/output ratios available for the Stiebel PTO are 0.659, 0.825 and 1.054. A higher rotational speed reduces the size of the pump and hence the third ratio, 1.054, seems favourable. Assuming an engine speed of 1500 rpm gives a rotational pump speed of 1581 rpm. According to Table 2, the pump should be able to transmit a total amount of power of about 220 kW. Assuming a system pressure of 350 bar result in a flow of 377 litres/minute. This requires a maximum displacement of 238 cc. In the packaging analysis a Bosch-Rexroth A4VG 250 cc variable displacement pump was used, since this was considered suitable for the application. A summary of the parameters is found in Table 3.

As can be seen in Figure 6, the total height of the transmission unit can cause some problems as it occupies space above the frame. In this analysis, the connection flanges of the unit are placed in the same horizontal plane as the rear axle connection flange.

Table 5 System parameters

P ∆p Q npump Vpump 3 (kW) (bar) (l/min) (rpm) (cm /rev) 220 350 377 1581 238

From table 2 it can be established that the motor should be able to operate at about 240 rpm. This is a rather difficult speed, as it is very high for a radial piston motor, and to low for optimal use of an axial piston motor. After a brief benchmark of the market, including Bosch- Rexroth, Poclain, Denison and Sampo, the Denison MRD/MRV 2800 or the MRD/MRV 1800 was found to be most suitable for this application, since the variable eccentric radial configurations of these motors allow them to reach the speeds required. Specifications for these motors can be seen in Table 3.

Table 6 Specifications of the variable Denison motors. (*=min. displacement) Motor Max. torque Max. speed Power Weight (kNm) (rpm) (kW) (kg) Denison MRD 1800 5,8 250 (400*) 153 209 Denison MRD 2800 8,6 215 (280*) 194 325

The high-speed ability of these pumps would make hydrostatic propulsion possible up to speeds of about 12 km/h and 17 km/h for the MRD 2800 and MRD 1800 respectively.

A packaging study was done in Pro/Engineer and the result can be seen in Figure 7. Since the SALIX vehicle is expected to be equipped with a tridem axle configuration, collision occurs between the hydraulic motor and the air bellow used to lift the tag axle. If the air bellow can be located elsewhere or replaced with another lifting arrangement this concept may be favourable due to its high performance.

Otherwise, a smaller axial piston motor could be mounted together with a gear reduction unit to optimise the speed range of the axial motor. This concept is also very interesting.

Alfred Johansson B 7 Robin Nilsson Appendix B. Hydrostatic Propulsion

Figure 7 The hydraulic motor is marked out as well as the problem with the bogie lift air bellow.

Conclusion The demands on a future hydraulic front-wheel drive in an articulated truck must be thoroughly analysed, with test drives or computer simulations. Dynamic simulations in systems like ADAMS would probably be very helpful, where the vehicles dynamic behaviour with different tractive forces from the hydraulic system can be tested and compared instantly. This could very well be performed in the form of another thesis project, as it is a well defined and certainly a very appealing project for many students.

Also, three different low-speed concepts have been briefly examined in this report. If a hydraulic front axle is developed it will most certainly make the second concept achievable and probably the most suitable since it would also make the vehicle all-wheel driven. Before such an axle is available, only the first or the third concept is possible. Since the first concept, developed by Scarab Sweepers, is a rather complicated and compact unit it might demand extensive development resources. It is probably protected by patent on behalf of Scarab Sweepers and this must be examined. The third concept is probably the most suitable if a quick solution is requested for a prototype vehicle. It has high performance and most parts already exist which should reduce the development time.

Alfred Johansson B 8 Robin Nilsson Appendix C. Pump-drive-PTO by STIEBEL

Appendix C. Pump-drive-PTO by STIEBEL

Alfred Johansson C 1 Robin Nilsson Appendix D. Hitch Solutions

Appendix D. Hitch Solutions On the Off-On twins prototype the Transfer case (that supplies the front axle with power) is placed in front of the articulated steering and rotation hitch. This is similar to the layout on a pure off-road articulated dump truck like the Volvo A25D. On these articulated dump trucks there are only one drive shaft that need to go through the hitch and the truck can therefore be designed to allow the load body (rear of the hitch) to turn over without the front frame to follow in the collapse i.e. a free hitch, see figure 1.

Figure 1. Steering and hitch assembly on the Off-ON prototype.

In this thesis work a truck with the transfer case behind the hitch seems to be the best option for a truck with mechanical front-wheel drive. Therefore the hitch oscillation needed to be limited (figure 2), otherwise the parallel drive shafts would cross each under some circumstances.

Figure 2. A more common hitch system with rear axle mounted transfer case. Ground Clearance 455 mm (front axle)

Perhaps a simpler link system like the one that A/S Hydrema use on their 922C compact dump truck (20 ton payload)8 could be used instead of the Volvo Articulated Haulers solution. The Hydrema 922C is equipped with a simple three-point linkage system that acts both like the hitch and steering system.

8 www.hydrema.com

Alfred Johansson D 1 Robin Nilsson Appendix D. Hitch Solutions

The downside with this system is the bumpsteer that occur when one wheel hit an obstacle. If one front wheel hit an obstacle and lift the wheel the front frame of the truck would tend to turn a little in that direction. Volvo Construction Equipment used a similar three-point link system on their last generation of large backhoe loader the EL 70.

Figure 3. The linkage system on a Hydrema 922C

Figure 4. Link system hitch on forest machine with double drive shafts

A brief investigation of how a three-point hitch concept could be built in on a frame-steered version of a Volvo FM truck was carried out during this thesis work. If the system should be competitive against a regular VAH hitch the ground clearance need to be improved. It could be possible to manage some improvements by lifting both the drive shafts and transfer case higher and place the lower linkage below the drive shafts.

The hitch rotation will not be competitive when compared with a VAH hitch but it will reduce frame twist and may be good enough for many costumers need.

Alfred Johansson D 2 Robin Nilsson Appendix D. Hitch Solutions

Figure 5. Linkage system with Ground Clearance 373 mm

Figure 6 The hitch and steering assembly on the Huddig backhoe loaders

If a linkage system is not favoured, it may be better to use an opened hitch like the one that Huddig AB uses on their large backhoe loaders, see figure 6. On their loaders the hitch is of an opened type and provide space for both the drive shaft and hydraulic hoses. Volvo articulated haulers also used to use an opened hitch design on their articulated haulers.

The work regarding the hitch solution need to be focused on making a simple solution that matches the need of ground clearance a hitch rotation. The lowest part of the truck should always be located under one of the axles and not anywhere between. The hitch should also be equipped with some kind of locking or braking device that can be used to make the chassis stiffer at highway speed.

Alfred Johansson D 3 Robin Nilsson Appendix E. Full vehicle test with Off-On truck Appendix E. Full vehicle test with Off-On truck The test vehicle was the Off-On prototype and the tests were executed in Eskilstuna on Volvo Construction Equipment test facilities on the 28th of February 2002. The comments here below are translated into English from the original test report.

Notes from test with the off-on prototype

With All-Wheel drive on icy surface

1. No differentials locked -

2. Central differential locked It is possible to control the vehicle due to the possibility for the front wheels to pull the vehicle around.

3. Central and differential between rear axles locked. The truck behaves the same way as in case 2.

4. Front axle and central differential locked. The front wheels are forced to turn at equal speed and the truck loses traction.

5. Front axle and differential between rear axles locked. Front axle loses grip and the rear axles got better traction because of locked longitudinal differential and as a consequence the truck tend to under steer.

6. Front axle differential locked The truck still tends to under-steer due to the loss of front axle grip.

With no front-wheel drive and on icy surface

1. No differential locked One wheel often tends to spin and all power goes to this wheel.

2. Differential between rear axles locked The truck move forward, but this case is much worse than test number 2 with all- wheel drive. In this mode it is impossible to control the skid.

3. All three rear differentials locked. Serious under steering, the rear axles are pushing the front axle forward.

Alfred Johansson E 1 Robin Nilsson Appendix E. Full vehicle test with Off-On truck

Conclusion of testing of the Twins off-on prototype In addition to show the TWINS-prototype to potential costumers at clinic tests, there were also some full vehicle tests preformed. Due to lack of guidelines for documentation much information is lost but some reports have been retrieved.

The main task for the test engineers were to test the importance of front-wheel drive for a frame-steered vehicle, and to test the vehicle with and without the differentials locked. When driving with and without the front-wheel drive, the off-on truck behaved as expected on surface with low traction, but the truck was easier to handle when using all- wheel drive. The engine brake was a little bit to rough and tended to lock one of the rear wheels when driving without front-wheel drive.

After the differential tests were carried out the engineers opinion were that they would prefer to have a driveline equipped with differentials between all axles with a differential in the transfer case to get optimal manoeuvrability, i.e. a drive line which is similar to the drive line that Volvo Articulated Haulers uses on their dump trucks. Volvo FM 6x6 truck is not today equipped with such a differential in the drop box.

The test engineers opinion were that to keep good stability and handling in a frame- steered truck which not is equipped with constant all-wheel drive, an advanced control system is required. This would imply a system that the engage the all-wheel drive system and control the looking of the differentials (at least the differential between the rear axles). A frame-steered truck is more unstable than a rigid and has therefore other demands on the driveline layout.

During off-road testing the test team also realized that all-wheel drive would increase manoeuvrability and ability to pass in bad terrain. It is also preferable to have the possibility to lock the differentials. The hill-climbing characteristic also increased while engaging the all-wheel drive system.

As a conclusion the test engineers from Volvo Articulated Haulers were concerned about the safety (in terms of dynamic stability) for this type vehicle and pointed on the fact that this truck has a greater top speed than regular articulated dump trucks and does not have the same driveline layout. Therefore the comparison is quite difficult to perform and they were also worried about the strength of some driveline components. They pointed on the fact that this vehicle is meant to be designed to go 75% off-road, an operation cycle much heavier than the standard components in the FM 6x6 driveline is designed for.

Alfred Johansson E 2 Robin Nilsson Appendix F. Steering Forces on 8x6

Appendix F. Steering Forces on 8x6

The behaviour of the 8x6 when steering during standstill where discussed and thus a quick calculation was made. Two cases where considered as can bee seen in Figure 1. Normally, an articulated steered vehicle behaves as in Case A. It was however feared that a 4-axled vehicle might behave as in Case B.

Figure 1

Alfred Johansson F 1 Robin Nilsson Appendix F. Steering Forces on 8x6

To establish how the vehicle will behave, a comparison between the necessary amount of steering torque was made. Load and friction coefficients are assumed to be equal for each axle. Thus the friction forces are all defined as “Fr”.

Case A Case B

M = Fr ⋅ 4.8 − Fr ⋅ 2 = 2.8⋅ Fr Nm M = 1.7 ⋅ Fr Nm

Figure 2

Conclusion Case B occurs at a lower amount of input torque from the steering system. Hence the vehicle will behave according to this case as long as no obstacle reduces the vehicles rotational freedom. However, this behaviour can alter depending on the axle load. If the vehicle is unloaded, the friction forces will be greatly reduced on the rear frame and the vehicle will tend to behave according to Case A.

Alfred Johansson F 2 Robin Nilsson Appendix G. Transmission Concepts

Appendix G. Transmission Concepts

TC with diff. in front of Simple TC in front of Simple TC, clutch TC with diff. behind Simple TC and clutch steering joint steering joint behind steering joint steering joint behind steering joint

Good Good Good Good Good + Constant all-wheel drive + Acceptable turning radius + Acceptable turning radius + Good turning radius + Good turning radius possible + Unrestricted hitch rotation + Unrestricted hitch rotation + Possible to fit diff. and low + Small needs for control systems range gear +Unrestricted hitch rotation + Possibilities for constant all- wheel drive + TC independent of gearbox + Reduces front axle pressure

Bad Bad Bad Bad Bad - Long distance F, poor turning - Expensive, should be - Expensive, should integrated - Restricted hitch rotation - Restricted hitch rotation radius integrated with gearbox with gearbox - Increased rotating mass - Energy losses in clutch - Expensive, should be integrated - Difficult to fit extra low range - Difficult to fit extra low range - Requires electronic control with gearbox gear gear system for clutch. - Difficult to fit extra low range - No diff., only optional front- - Energy losses in clutch gear wheel drive possible - Requires electronic control - Requires some kind of anti- system for the clutch slip system

TC = Transfer case

Alfred Johansson G1 Robin Nilsson Appendix H. Micheln XZL 16.00R20

Appendix H. Michelin XZL 16.00R20

Technical tyre catalogue

16.00 R 20 XZL TL LRM The actual measurements could change with the creation of new tread patterns. For design of new vehicles, use the ETRTO "box" or consult us.

Michelin reference 123357 Ply rating Unique point Nominal load per axle - single fitment (kg) 13200 Nominal load per axle - twinned fitment (kg) 24000 Nominal pressure in bars (single fitment) 7.60 Nominal pressure in bars (twinned fitment) 7.60 Nominal pressure in bars (unique point) Wheel recommended 10.00W ETRTO section (mm) ETRTO diameter (mm) Free section (mm) 438 Free diameter (mm) 1343 Crushed section (mm) 488 Crushed radius (mm) 609 Rolling circumference (mm) 4060 Minimum distance between axle centres (mm) 495 Tread depth (mm) 27.0 Regrooving depth (mm) 4 Weight in kg Tube 20 V Flap 310-20 LB Sealing ring Regulation 54 0094797 ETRTO approved rims

Single fitment pressure 4.25 4.5 4.75 5.0 5.25 5.5 5.75 6.0 6.25 6.5 6.75 7.0 7.25 7.5 load per axle 8400 8800 9200 9600 10000 10400 10800 11200 11600 12000 12400 12400 12800 13200

Twinned fitment 4.25 4.5 4.75 5.0 5.25 5.5 5.75 6.0 6.25 6.5 6.75 7.0 7.25 7.5 pressure load per axle 15270 16000 16730 17450 18180 18910 19640 20360 21090 21820 22550 22550 23270 24000 Copyright © 2003-2005 Michelin Photos Copyright : Michelin / DPPI www.michelin.com

Alfred Johansson H 1 Robin Nilsson Appendix I. Alliance Tyre Spec.

Appendix I. Alliance Tyre Spec. Date: 21.04.2006

C E R T I F I C A T E

Tire Type MULTI-PURPOSE FAST FLOTATION Tire Size 600/50-22.5 Tread Design 328 MPF

Unloaded Loaded Recommend load, kg (lbs) Rolling Load Infl. dimension Static Circum Index press Speed, km/h (mph) Size Rim SW OD Radius mm mm mm mm Speed bar 15 20 30 40 50 60 70 80 90 in in in in Symbol psi 9 12 19 25 31 37 44 50 56

600 1185 532 3490 600/50-22.5 20.00DC 4 4125 23.6 46.7 20.9 137.4 157G 6810 6190 5160 4740 4620 4540 4410 4290 158F 58 15000 13630 11370 10440 10180 10000 9710 9450 9090

1) Service description: Selfpropelled transport vehicles for Off/On-The-Road cyclic application; Application in agricultural and EM transport activities

2)Maximum travell time with maximum speed on improved surfaces: 60 min

3)Minimum stoping time to permit cooling: 30 min

4)Tire definition is based upon The European Tire and Rim Technical Organization (ETRTO) and The tire & Rim Association of Australia.

5)Reinforced rim is recommended

6)TH2 Rim (with hump) with wider ledge length is recommended

7)Rims without hump is also accepted

Overall Width (+/- 2%) Overall Diameter (+/- 1.5%) Static radius (+/- 2%) Circumference (+/- 2.5%)

Alliance Tire Company (1992) LTD

Alfred Johansson I1 Robin Nilsson