Trajectory tracking control of four wheel steering under high speed emergency obstacle avoidance

To solve the problem of trajectory tracking for 4WS autonomous vehicles under high speed emergency obstacle avoidance, an improved trajectory tracking controller combining four-wheel steering (4WS) feed-forward control and linear quadratic regulator (LQR) feed-back control is proposed. First, a polynomial obstacle avoidance trajectory of small radius and sharp curve is established and its several variables are analysed. Second, in order to make actual yaw rate follow steady-state value based on reference model, the steering gain of the improved 4WS feed-forward control can change with steering angular frequency and vehicle speed. Third, combined with the LQR feed-back control, the deviations between actual lateral displacement and desired lateral displacement are controlled under 0.05 m. Finally, CarSim® simulation results show that 4WS autonomous vehicles based on the controller can not only avoid obstacles in time, but also improve active safety and handling stability under high speed emergency obstacle avoidance.