Abstract
A steering command from the driver to an active steering vehicle can be excessive, especially in lower road friction conditions. The present paper discusses protection functions for active steering vehicles. The grip margin is defined as the residual tire force normalized by the radius of friction circle. The isotropic brush model is reanalyzed so that a cubic equation for the estimation of the grip margin can be obtained. A protection function similar to that used in fly-by-wire aircraft is developed for active steering. This protection continuously updates the upper bound for a steering command according to the present vehicle state and the estimated grip margin. The proposed scheme is simulated using CarSim and the numerical results show their basic functionalities.
