Off Road Terrain and Tyre Simulation and Optimisation

The selection of tyres for a prototype vehicle is currently expensive and relies on experimental testing in controlled conditions, often involving transport of equipment, drivers and engineers to test sites. Any changes to the prototype vehicle before production starts means that the range of tyres selected are not likely to be optimised for the final vehicle. With off-road capability testing, there is an additional complication from ensuring consistency of the test track and environmental conditions during the testing period, so that one test can be fairly compared to another, or to competitor vehicles tested at different times.

As part of the jointly EPSRC and JLR funded programme for Simulation Innovation (PSi), the capability to simulate automotive tyres off-road has been developed for sandy and clay based surfaces, based on terramechanics research which is often driven by agricultural vehicle design or military applications. The ability to market the optimum balance of off-road capability and on-road handling is paramount, as evidenced in media promotions so while the existing tools which are being developed are needed, further research work is essential in this area to improve the terramechanics prediction for typical automotive vehicles closer to the level attained by tyre and rigid road interaction models.

Loughborough University has developed off-road simulation capability for the automotive tyres currently used on Jaguar Land Rover vehicles and takes the form of two high-fidelity modelling methods. It is proposed that these capabilities be further extended using modifications to the Lyasko and Bekker formulation of soil mechanics and existing shear stress / shear deformation equations.

The data for the tyres which can be considered needs to come from existing data, such as correlating tyre stiffness parameters from the carcass and sidewall to existing magic formula models or FTtire / CDTire models. A detailed description of the tread pattern will be incorporated into the off-road tyre model which can be integrated straight into a vehicle simulator in real time, with steering and braking, driver controls and vehicle models of the traction enhancement modes.

A range of academic questions will be posed, in terms of the modelling detail of the tread pattern, the level of dynamic realism required and the methods to integrate these into a real time simulator. Two principle industrially relevant questions will be addressed in this research study:

The first question is how sensitive are changes to tyre specification and/or final vehicle specification to performance? This will allow the engineering departments to quantify the likely effect of selecting a tyre design earlier in the design process. It will show what the range of effects are likely to be and why. If possible, this will also examine what tests are carried out during development and sign off, to identify what parameters are being optimised. This section will allow a comparison of the tyre tread across the whole section of the tyre (inc shoulders). The tyre performance will also be measured relative to initial conditions (sinkage depth) and geometric considerations (static toe and camber and vertical loads). Considerations can also be made of the effects of both drive and braking torque delivery on the performance of the tyre.

The second; research question related to how tyre performance changes over different surfaces. This will focus on the range of soils (triangle). This section will look at modifying the model to operate across the range of the soils triangle, allowing assessments to be made across the range of these surfaces.