Safer car driving by robust steering control

The task of steering a car may be split into two subtasks: (1) Plan a path, starting at the present car position and velocity, and steer the car by preview such that it follows the planned path. (2) Stabilize the yaw motion in order to prevent swerving or skidding caused by disturbance torques around a vertical axis through the center of gravity. The first subtask is simple routine for the driver as long as the problems with the second subtask do not interfere. Safety critical situations primarily arise from the human reaction time followed by panic overreaction in the yaw stabilization task. During the reaction time large tire sideslip angles between the tire direction and the local velocity vector can build up and push the available tire lateral force into saturation. Control systems can react faster, more precisely and without panic to unexpected yaw motions. Nowadays reasonably priced yaw rate sensors for the use in automobiles are available. On the actuator side the addition of a small feedback-controlled steering angle to the main driver-controlled steering angle is required, it needs only ±2 degrees at the front wheels but a higher bandwidth than the driver. What is needed then is a simple and robust control algorithm to connect the yaw rate sensor with the additional steering actuator. "Robust" means that the feedback control system should not only perform well for nominal values of tire and road contact, vehicle velocity and mass, but for a wide range of such varying parameters.