ADAPTIVE YAW RATE FEEDBACK 4WS WITH TIRE ROAD FRICTION COEFFICIENT ESTIMATOR/

This paper proposes an adaptive yaw rate feedback control system for a four-wheel-steering (4WS) vehicle which involves a tire/road friction coefficient estimator. The adaptive 4WS system has been developed so that the vehicle possesses desirable lateral characteristics even on s lippery roads and in critical driving situations. The friction coeffic ient is estimated on real time from the yaw rate response of the contr olled vehicle with the least squares. The control system adopts a two degree of freedom structure which consists of a feedforward compensato r and a feedback control subsystem. The feedforward compensator is det ermined with the estimated friction coefficient to minimize the steady -state and transient vehicle slip angle in spite of changes in tire/ro ad conditions. The feedback subsystem adopts the Internal Model Contro l (IMC) structure in order to compensate for nonlinearities and to rea lize robustness against modelling and estimation errors.