Prestudy of a Steering System for Heavy-Duty Trucks
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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...................................................................................