EVALUATION OF WHEEL LOAD FLUCTUATIONS.

Abstract

Unevenness of the road surface impairs ride comfort and vehicle safety. This paper quantifies the influence of wheel load fluctuations which occur in certain circumstances on vehicle handling. The reason for this influence is that wheel load fluctuations produce changes in tyre properties: the average cornering forces decrease and dynamic lateral force fluctuations are produced. In respect to handling, this results in changes to the steering tendency, stability and dynamic response. In addition, it also produces variations from the course. For simulation, a dynamic high frequency tyre model and a non–linear vehicle model are developed. In step two, a quarter vehicle illustrates the main tyre properties changed by wheel load fluctuations. In a third step, the effects of the changed tyre properties on driving behaviour in linear range are discussed by means of a linear single track model. In a final step, the influences of the wheel load fluctuations on driving behaviour into the limit range are shown. In addition, results of measurements are presented and important vehicle parameters are analysed. It is shown that even high fluctuations in wheel load need not significantly impair vehicle safety. This is achieved by evaluating wheel loads separately from axle or body resonance. A proposal for reducing the conflicting aims between vehicle safety and ride comfort is presented.