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Six-wheeled vehicle steering
Land Systems Hägglunds.
2005 (English)In: Proceedings of the 15th International Conference of the ISTVS, 2005Conference paper, Published paper (Refereed)
Abstract [en]

Six-wheeled vehicles provide the ability to get high performance both on- and off-road. Ackermannsteering on six-wheeled vehicles is possible to achieve in several ways by steering on differentpair of wheels. The steering system has several contradicting demands such as volume saving wheelhouses, few actuators, small turning radius and fast lateral acceleration response. Some of the demandsare velocity dependent. Fast lateral acceleration response is important at high velocity, while a low turningradius is desired at low velocity. In this paper three different steering methods are considered: (a)steering on front and rear wheels, (b) steering on front and middle wheels and (c) steering only on thefront wheels. The steering methods are evaluated by simulating J-turn maneuvers in Matlab/Simulink andAdams. Considering turning radius, lateral acceleration and yaw rate it is shown that method (a) is best atlow speed, while method (b) gives the best stability at high speeds and method (c) uses few actuators andhas acceptable performance at high velocities. A drawback with method (c) is that the vehicle becomesmore sensitive to the load distribution, i.e. braking, accelerating and moving the load will affect steeringcharacteristics more for method (c) than for the other methods. A steering method using method (a) atlow speeds with a gradually transition to method (c) as the velocity increases is suggested.

Place, publisher, year, edition, pages
2005.
Keyword [en]
Six-wheeled vehicles, steering, modeling, simulation, lateral acceleration, stability
Identifiers
URN: urn:nbn:se:kth:diva-6845OAI: oai:DiVA.org:kth-6845DiVA: diva2:11667
Conference
Proceedings of the 15th International Conference of the ISTVS. Hayama, Japan September 25–29, 2005
Note
QC 20101026Available from: 2007-03-01 Created: 2007-03-01 Last updated: 2010-10-26Bibliographically approved
In thesis
1. Modelling of six-wheeled electric transmission terrain vehicle
Open this publication in new window or tab >>Modelling of six-wheeled electric transmission terrain vehicle
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

In vehicles with electric transmission and independent wheel stations, it is possible to have a possibility to control propulsion, steering and suspension individually for each wheel. This makes it possible to improve mobility, performance and driving safety. The long term goal of this work is to develop a methodt hat can evaluate and improve the mobility of such vehicles in terrain. This contribution concerns how a six wheeled electric transmission vehicle should be modelled to enable evaluation of the dynamic behaviour in different type of terrain. This is made by combining modelling of vehicle, transmission and tire-terrain behaviour.

For wheeled vehicles an electric transmission with hub motors provides the ability to accurately control the torque on every wheel independently, giving a great ability to improve both mobility in terrain and vehicle behaviour on road. In this work the components of a diesel-electric powertrain for off-road vehicles are modelled and a control layout with the possibility to include functions for improved performance both while driving off- and on-road is proposed.

To handle driving on soft ground, a tire/terrain model is needed. The model should include lateral deformation in order to be able to steer. A tire/terrain model is derived based on the ideas of Wong and Reece. The terrain characteristics are chosen to be described by parameters according to the Bekker model, since this data are widely available in literature.

The developed tire/terrain model has been implemented together with a vehicle model. This terrain vehicle model is shown to be able to estimate sinkage, rolling resistance, traction force and steering characteristics, of a six wheeledterrain vehicle using electric transmission.

To conclude, models of a six-wheeled vehicle with electric transmission and tire models both for soft and rigid ground have been developed. These models form a simulation platform, which makes it possible to evaluate control strategies for the electric transmission with the purpose to improve mobility.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. iv, 36 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2007:05
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-4291 (URN)978-91-7178-579-4 (ISBN)
Presentation
2007-02-22, Sal D41, KTH, Lindstedtsvägen 17, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101115Available from: 2007-03-01 Created: 2007-03-01 Last updated: 2010-11-15Bibliographically approved
2. Improving a six-wheeler’sperformance both on- and off-road
Open this publication in new window or tab >>Improving a six-wheeler’sperformance both on- and off-road
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In vehicles with electric transmission and independent wheel stations, there is apossibility to control propulsion, steering and suspension individually for eachwheel. This makes it possible to improve mobility in terrain as well as performanceand driving safety on road. This contribution concerns how a six wheeledelectric transmission vehicle should be modelled to enable evaluation of thedynamic behaviour both in terrain and on road. This is made by combiningmodelling of vehicle, transmission and tyre/terrain behaviour.A tyre/terrain model is needed to simulate driving on soft ground. Heretyre/terrain models for simulating driving with both rigid and pneumatic wheelson soft ground have been developed. A method to measure terrain parametersand drawbar pull for a six-wheeled vehicle on sand is proposed, tested andevaluated.To simulate a six wheeled vehicle at the handling limit on road, a vehicle modelwith a brush tyre model is used in order to get physically reasonable simulationresults during high combined slip conditions. Different vehicle configurationsare considered, where front wheel steering is combined with eithersecond axle steering, rear wheel steering or individual wheel torque control.By applying different vehicle slip angles and thereby limiting the DOF of thevehicle model, the vehicle configurations are evaluated during different drivingconditions. The results show that by applying individual torque control to thefront wheel steered vehicle, the performance is improved for all evaluated manoeuvres,and the achievable aligning torque during a rear wheel skid increasessignificantly if the vehicle slip angle is larger than the maximum front wheelsteering angle.To conclude, models of a six-wheeled vehicle with electric transmission andtyre models both for soft and rigid ground have been developed. These modelsform a simulation platform, which makes it possible to evaluate controlstrategies for the electric transmission with the purpose to improve mobility interrain as well as performance and driving safety on road. Some examples ofapplications of the models are included, e.g. improving at-the-limit handlingand pivot turning performance.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. viii, 69 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2010:61
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-25519 (URN)978-91-7415-766-6 (ISBN)
Public defence
2010-11-09, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101026Available from: 2010-10-26 Created: 2010-10-25 Last updated: 2010-10-26Bibliographically approved

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