Robust prevention of limit cycles for robustly decoupled car steering dynamics

Considerable safety benefits are achieved by robustly decoupling the lateral and yaw motions of a car with active steering. Robust unilateral decoupling requires an actuator to generate an additional front wheel steering angle. However, introducing actuators to closed loop systems may cause limit cycles due to actuator saturation and rate limits. Such limit cycles are intolerable w.r.t. safety and comfort. By introducing a simple nonlinear modification of the control law, this paper proposes a remedy to significantly reduce the susceptibility to limit cycles for robustly decoupled car steering dynamics. The robustness of the resulting system w.r.t. the avoidance of limit cycles is investigated for varying operating conditions by combining the parameter space approach and the theory of describing functions.