A Method to Estimate the Friction Coefficient and Tire Slip Angle Using Steering Torque

Knowledge of tire forces is important for vehicle control systems that aim to enhance vehicle handling and passenger safety. This paper introduces a nonlinear observer that estimates the coefficient of friction and tire slip angle, both of which are key factors in characterizing the vehicle's lateral tire forces. The observer estimates the friction coefficient and slip angle based on sensor measurements available on many production vehicles. This includes steering torque measurements readily available in steer-by-wire or electric power steering (EPS) systems. Experimental results on a steer-by-wire research vehicle (Fig. 1) demonstrate the observer's ability to provide accurate estimates out to the limits of handling.