Estimation of the Tire Cornering Stiffness and Its Application to Active Car Steering

Active steering systems can help the driver to master critical driving situations, for example aquaplaning and -split braking. In these situations it is likely that the tires reach their performance limits, where nonlinear effects like saturation play an important role. Tires are the part in vehicle dynamics afflicted with the highest degree of nonlinearity – due to saturation – and uncertainty – due to whether conditions. Therefore, active steering systems have to be designed considering the uncertain and nonlinear tire characteristics which are determined by the road-tire-contact. This paper demonstrates how an important tire parameter, the cornering stiffness, can be estimated by measurement of dynamic vehicle parameters like lateral accelerations and yaw rate. This parameter indicates whether the saturation region of the tire is reached or not. Based on the estimate of the tire the robust decoupling control law by Ackermann [1] for active front steering is extended.