Cost effective Ftire parameterisation methods for ride simulations with large off-the-road tyres

Abstract

All forces acting on a road vehicle are either generated in the tyre-road interface or are due to aerodynamic effects, where at low speeds the latter can be ignored. The accuracy of the tyre model, describing the forces at the tyre-road interface, is thus of utmost importance in vehicle dynamics simulations. Accurate tyre models are essential to ensure that vehicle dynamics models are an accurate representation of the actual vehicle so that it can be used with confidence to study and improve the vehicle’s safety, durability, ride comfort and handling capabilities. Various tyre models have been developed to describe the forces and moments that are generated in the tyre contact patch. FTire is one of the well-known and widely used nonlinear physics-based models that has been developed for vehicle comfort and handling simulations and the prediction of road loads due to short wave-lengths obstacles. The parameterisation of the FTire model is done by extracting model parameters from experimental results that cover the operational conditions of the tyre. Acquiring these parameterisation datasets, with an acceptable accuracy, is however a challenge. This is especially true for large off-the-road (OTR) tyres. Expensive test equipment is typically required to conduct these tests for passenger car tyres but virtually no test equipment is available to test OTR tyres. Due to a lack of standardisation, the test equipment is often custom built and adapted to the required test conditions. The situation is further complicated due to the large range of possible tyre operating and loading conditions of OTR tyres, as well as the differences in tyre and rim sizes, that the test equipment should be able to accommodate. Alternative methods of obtaining parameterisation data for large OTR tyres thus need to be investigated. This thesis describes two alternative methods that can be used to parameterise an FTire model of a large OTR tyre. Parameterisation methods were investigated that can be applied irrespective of the tyre size and operating load. A baseline parameterisation process, using an experimental data set, was performed. The obtained FTire model was validated against experimental results. The validation process showed that the parameterised model can be used to accurately predict the tyre forces and moments, of large OTR tyres, while driving over uneven terrain. This method can thus successfully be used if the tyre forces and moments, and the applied boundary, as well as environmental conditions, can accurately be measured. Conducting these measurements was however found to be challenging, limited by the available test equipment and problematic to expand to higher loads and larger tyres. One alternative, to experimentally obtained data for the parameterisation process, is to use finite element models to generate the relevant parameterisation data. The required input data of a finite element tyre model can be obtained with the same effort irrespective of the tyre size or operating condition. Geometric and material tests were conducted, and a nonlinear finite element model was created and validated against experimental test. The finite element tyre model was used to replicate the parameterisation tests that are required to parameterise a FTire model without tuning any model parameters. A FTire parameterisation was conducted using FEA data and the model was validated. A second alternative is the use of carcass deformation results to parameterise FTire models. The carcass deformation data can be obtained from experimental testing or from FE simulation results. To obtain the measured carcass deformation data, a set of cameras were mounted to the inside of the test tyre. The stereo vision principle is applied to determine the deformation of the tyre during static tyre tests. Initial results of using the carcass deformation data to parameterise a FTire model is also presented. Carcass deformation measurements can further be used to validate FE tyre models if force and moment measurements are limited or non-existent to improve the confidence in the model. The proposed methods create new possibilities to parameterise FTire models of large off-theroad tyres. These methods are especially useful if experimental results of the tyre are limited or non-existent. This thesis presents results that show that these methods can be used successfully to extract model parameters. More research is however required to extend these capabilities and to standardize these parameterisation methods.