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Tire/terrain models for simulating six-wheeled vehicle on soft ground
BAE Systems H¨agglunds AB.
2006 (English)In: In Proceedings of the 10th European Conference of the ISTVS, 2006Conference paper, Published paper (Refereed)
Abstract [en]

This paper is a part of the work in the project “Cross CountryDriving Dynamics”, which is a project within the Swedish“Green Car”initiative.The purpose of the project is to find out how control of the electric transmissionfor terrain vehicles can be used to improve the off-road performance. In thefirst part of the project models for the vehicle are developed in order to beable to use simulations when developing control methods. The steering systemand simulations of the electric transmission were presented as two papers onISTVS in Japan 2005 and together with the tire/terrain models in this paperit is possible to simulate a six-wheeled vehicle with electric transmission onsoft ground. There are a lot of different purposes for tire/terrain models. Thesimplest models are created with the purpose to give a rough estimate of themobility of the vehicle on different terrains. FEM models on the other hand cangive deep insight in the interaction between tire and soil and also features of thetires. However, FEM models are computational intensive and therefore cannotbe practically used for vehicle simulations, but they can assist by providing datawhen developing models for such simulations. In vehicle simulations mainly thevertical force, rolling resistance, torque, sinkage and lateral force are of interest.Based on experimental data, Bekker has proposed a pressure-sinkage model,which can be used when predicting off-road vehicle performance. Beneath atire the soil will flow both in the lateral and longitudinal direction. In thelongitudinal direction, the soil will flow forwards and backwards in differentzones. Due to the two failure zones the pressure in the ground around the tirewill not increase with depth as in the pressure-sinkage model, but instead themaximum pressure will be at the point where the two failure zones join eachother. The position of that point depends on the slip of the wheel. Wongand Reece have proposed models for the pressure in the ground around a rigidwheel based on experimental results. When using pneumatic tires the tires willbe deflected where the pressure in the ground exceeds the sum of the inflationpressure and the pressure exerted by the tire carcass, which in turn affects thegeometry of the tire/terrain interaction and the pressure in the ground. Sincethe shear force in the ground is a function of the pressure, the tire slip and theshear modulus of the soil, it is possible to calculate the torque of the wheel andthe tractive force. It is possible to handle steering by adding a force ellipse tohandle lateral forces. In order to handle transients it is necessary to includedamping characteristics of the soil. The tire/terrain models are implementedtogether with a vehicle model and it is seen that the differential equations forsoft ground simulations are fairly stiff, but simulations show that it is possibleto solve them and get reasonable simulation speeds on a normal PC.

Place, publisher, year, edition, pages
2006.
Keyword [en]
Tire/terrain modeling
Identifiers
URN: urn:nbn:se:kth:diva-6847OAI: oai:DiVA.org:kth-6847DiVA: diva2:11669
Conference
In Proceedings of the 10th European Conference of the ISTVS, Budapest, Hungary October 3–6, 2006
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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