1989-02-01

Measurement and Simulation of Transient Tire Forces 890640

High performance Antilock Braking Systems (ABS) are well known to allow for very rapid pressure changes in the wheel brake cylinders. Recordings of the wheel speed during ABS control show oscillations just after the rapid pressure changes. The oscillations can not be explained by simulation if the usual stationary brake force versus slip curves are used. Thus the investigation of the oscillations requires a different approach to the modelling of the tire.
As a first step in the alternative modelling of the tire the forces and moments on the running tire were measured using an experimental car. During the measurement the pressure in the wheel brake cylinder was modulated stepwise. A new Rotating Wheel Dynamometer was used to take those measurements. The results showed that the oscillations which were observed in the wheel speed could also be found in the braking force on the tire. Contrarily, the corresponding oscillations could not be found in the braking torque.
Transients in the tire braking force were expected to result from the elastic deformation of the tire side walls and from the elastic deformation distribution of the rubber tread in the tire-road contact area. Correspondingly, the tire side walls were modelled as linear spring-damper systems while the contact area was with some modifications modelled according to the well known brush model.
Using this model the simulation results showed oscillations in the wheel speed and in the brake force which were much similar to those obtained by measurement. It is believed that for the development of high performance ABS this dynamic tire model is adequate.

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