Path Tracking Control for Four-Wheel-Steering Autonomous Vehicles based on Adaptive Sliding Mode Control with Control Allocation

This paper presents a path tracking control algorithm for four-wheel steering autonomous vehicles. The proposed controller utilized the direct yaw moment control approach for path tracking of the autonomous vehicle. The path tracking algorithm consists of three parts, desired yaw-rate decision, adaptive sliding mode control, and control allocation. The desired yaw rate has been determined based on the geometric relationship between a reference path and vehicle position. A required yaw-moment to tracking the desired yaw-rate has been decided by using an adaptive sliding mode control approach to compensate for the linear tire model assumption. Since the four-wheel steering vehicle is an overactuated system, the optimization-based control allocation has been introduced to determine the front and rear-wheel steering inputs, respectively, considering a control effort, actuator limit, ride comfort, and body slip. The simulation study has been conducted to compare the path tracking performance of the base controller using front steering and the proposed algorithm. It has been shown from the simulations that the path tracking performance has been improved in a driving situation with a high curvature and a steep road slope.