Measurement and Simulation of Transients in Longitudinal and Lateral Tire Forces 900210
The design of ABS- or vehicle control systems by means of computer simulation needs adequate tire models. Recordings of the wheel speed during ABS control show oscillations caused by the rapid pressure changes in the wheel brake cylinder. Investigations in lateral tire dynamics show a phase shift between the slip angle and the lateral tire force. These transients can not be explained by simulation if the usual stationary tire input-output behaviour is supposed. Thus the investigation of the oscillations requires a different approach to the modelling of the tire.
In a first step measurements with an experimental car equipped with a computer for data acquisition and control and with various sensors - e.g. a Rotating Wheel Dynamometer - were carried out. The measurement results showed a correlation between the oscillations in the wheel speed and the braking force caused by the pressure pulses as well as high frequency oscillations in the lateral tire forces. Also the phase shift between the slip angle and the lateral tire force could be reproduced.
Transients in the tire input-output quantities were expected to result from the elastic deformation of the tire side walls and of the tread in the tire-road contact area. Correspondingly, a tire model with elastic sidewalls and an elastic tread was developed. The deformation distribution of the tread is computed by differential equations which result from the kinematic condition of the belt.
Using this model the simulation results show a tire input-output behaviour which is very similar to that obtained by measurement. It is believed that for the development of high performance ABS- or vehicle control systems this dynamic tire model is adequate.