Tire/terrain models for simulating six-wheeled vehicle on soft ground
2006 (English)In: In Proceedings of the 10th European Conference of the ISTVS, 2006Conference paper (Refereed)
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
IdentifiersURN: urn:nbn:se:kth:diva-6847OAI: oai:DiVA.org:kth-6847DiVA: diva2:11669
In Proceedings of the 10th European Conference of the ISTVS, Budapest, Hungary October 3–6, 2006
QC 201010262007-03-012007-03-012010-10-26Bibliographically approved