Minimum Lap Time Control for 4WIS&4WID Autonomous Vehicle with a Nonlinear Programming Method

Considering the steering angles and torques of wheels can be controlled independently, a 4-wheel independent steer (4WIS) and 4-wheel independent drive (4WID) vehicle has an advantage for dynamic control in motorsports, and this paper focuses on the minimum lap time control problem of a 4WIS&4WID vehicle. According to the platform vehicle of our lab, a 7-DOF 4WIS&4WID vehicle dynamics model is built in MATLAB with the Magic Formula tire model. In order to better reflect the dynamic performance of the actual vehicle, the response delay of accelerations, steering angles and motor torques are considered as well. Next, based on the boundaries of our self-designed track, and an initial solution provided by an MPC path following controller, the optimal control problem is solved by the nonlinear programming method GPOPS. Moreover, with the abovementioned path following controller, we further evaluate the optimized racing line in Carsim. Through comparison, the GPOPS results have a good correlation with Carsim, in the aspects of control outputs like steering angles and drive torques, which prove the achievability of the optimization and the performance of the controller. And compared to other optimization methods like convex optimization method with quasi steady state vehicle model, the GPOPS results not only have a closer estimation of the actual lap time, but also can reflect the vehicle dynamic behavior better, in the aspect of G-G diagram and tire force.