The effects of macro and micro road texture on tyre simulations

Abstract

The tyre contact patch is important to vehicle dynamics analysis since this is where the tyre-road interaction forces originate. If the contact patch mechanism is understood in depth and can be simulated accurately, it could improve various aspects of vehicle and tyre design. In this study, emphasis is placed on the effect that a change in macro and micro texture has on the forces generated in the contact patch. This is done by inspecting the effect of the resolution with which the surface is measured, on simulations of a vehicle driving over a rough road. The macro texture largely affects the normal force that is created at the contact patch and influences the ride comfort. This was evaluated with the use of an FTiretyre model on a quarter car and a full-scale model respectively through simulations on a rough road. The quarter car model was used to evaluate the effects of speed, tyre model resolution and road geometry resolution on the reaction forces and moments based on comparing simulation data to each other. This analysis concluded that the speed and tyre resolution had little to no effect on the results. The road profile resolution, however resulted in a 20% error when a 15x15mm resolution was compared to a 1x1mm road resolution. A 10x10mm resolution road is ideal for a quarter car simulation. The Belgian paving, representing the rough road, was created at various resolutions on a macro texture level for full-scale vehicle simulations. This simulation data was then compared to the experimental data. This experiment was solely based on evaluating the road resolution. It was found that the percentage error between the simulations and experimental data differed, depending on the resolution of the road. However, the differences were less than 5%. The simulations were compared to the most accurate road resolution and the percentage error differed by less than 10%. This indicates that a road resolution smaller than 15x15mm is only significant to highly sensitive results or quarter-car studies over a rough road when ride comfort is being evaluated. The micro texture largely has an effect on the friction coefficient at the contact patch in the form of lateral and longitudinal force. The friction coefficient in this case was estimated with the use of a physics based model, which was validated on a flat concrete block. By comparing experimental data with the estimation data, the estimation model was found to be sufficient to estimate the friction coefficient on a rough road. The comparison resulted in a ± 6% error for the estimations. The micro texture resolution, at which the surface was measured, was subsampled to evaluate the effect it had on the estimation. It was determined that the resolution at which the micro texture is measured, influences the friction coefficient estimation. The percentage error of the estimation model changed by up to 10% for an increase of increments of 0.12x0.12mm. the change in micro texture resolution had a larger effect on the rough road than on the flat concrete road. To ensure that the percentage error stays below 10% the road should be sampled at 0.144x0.144 for a rough road and 0.216x0.216mm for a flat road. Since the measuring capability was limited, no conclusion can be drawn for results with a road resolution of smaller than 0.12x0.12mm.