Tyre model verification over off-road terrain

Abstract

Vehicle dynamic simulations form a significant part of the design and development process of vehicles. These simulations are used to study and improve the vehicle’s durability, ride comfort and handling capabilities. All forces acting on the vehicle are either generated in the tyre-road interface or are due to aerodynamic effects, where at low speeds the latter one can be ignored. The accuracy of the tyre model describing the forces on the tyre-road interface is thus of exceptional importance. It ensures that the simulation model is an accurate representation of the actual vehicle. Various approaches are adopted when developing mathematical tyre models. Many of these models are developed to study the handling capabilities of passenger cars over a smooth road. Passenger car tyres are the focal point as larger tyres introduce some difficulties due to their size and load rating. Off-road truck tyres also differ in their construction which will influence force and moment generation of the tyre. Research efforts are increasing to meet the need of tyre models that can describe the behaviour of the tyre over uneven terrain with sufficient accuracy. This thesis addresses the question of whether existing mathematical tyre models can accurately describe the forces and moments generated by a large off-road tyre while driving over rough terrain. The complexity of different mathematical tyre models varies greatly, as does the parameterisation efforts required to obtain the model parameters. The parameterization of most tyre models relies on some experimental test data that is used to extract the necessary information to fit model parameters. The selection of a suitable tyre model for a simulation is often dependent on the availability of such experimental data and the effort to identify the required parameters. In this study the parameterisation process for four different tyre models, are discussed in detail to highlight the difficulties in acquiring the test data and the effort to parameterize the model. The models considered are the One Point Contact, 3D Equivalent Volume contact, 3D Enveloping Contact and FTire model. Experimental measurements are conducted on a 16.00R20 Michelin XZL tyre. Laboratory tests, as well as field tests, over discrete obstacles and uneven hard surfaces are used for parameterisation and validation purposes. Simulation results are compared to experimental test data to determine whether the models could be used to describe the tyre road interactions with sufficient accuracy. Recommendations are made for tyre model selection and model accuracy for simulations over rough off-road surfaces.