Coordinated Control of Trajectory Tracking and Yaw Stability of a Hub-Motor-Driven Vehicle based on Four-Wheel-Steering

In order to improve the trajectory tracking accuracy and yaw stability of vehicles under extreme conditions such as high speed and low adhesion, a coordinated control method of trajectory tracking and yaw stability is proposed based on four-wheel-independent-driving vehicles with four-wheel-steering. The hierarchical structure includes the trajectory tracking control layer, the lateral stability control decision layer, and the four-wheel angle and torque distribution layer. Firstly, the upper layer establishes a three-degree-of-freedom vehicle dynamics model as the controller prediction model, the front wheel steering controller is designed to realize the lateral path tracking based on adaptive model predictive control algorithm and the longitudinal speed controller is designed to realize the longitudinal speed tracking based on PID control algorithm. Then, the middle layer decides the rear wheel steering angle and the additional yaw moment to maintain the vehicle's yaw stability based on the super-twisting sliding mode control algorithm and the improved particle swarm PID (IPSO-PID) control algorithm, respectively. Next, the lower layer allocates the four wheel steering angle according to the Ackermann Angle relation of four-wheel-steering vehicle, and optimally assigns the four wheel hub motor torques using sequential least squares planning with the objective function of minimizing the sum of the four tires' adhesion utilization. Finally, the CarSim/Simulink co-simulation platform is built to carry out the simulation test of medium-speed low-adhesion and high-speed high-adhesion double-lane-change conditions respectively. The simulation results show that the coordinated control strategy of trajectory tracking and yaw stability designed in this paper can improve the path tracking accuracy of the vehicle and meet the yaw stability of the vehicle under dangerous working conditions.