An Optimal Wheel Torque Distribution Controller for Automated Vehicle Trajectory Following

Abstract

This paper proposes an automated vehicle trajectory following system that uses four constrained wheel torques to regulate a vehicle on a reference trajectory. The constrained wheel torques can be achieved using the two-wheel drive and differential brakes. The proposed control algorithm is developed using the following steps. First, the sliding-mode control is used to find stability constraints for trajectory following when the vehicle system is subjected to modeling errors. Second, these stability constraints, along with other actuator constraints, are particularly tuned for the proposed control distribution method. The proposed control distribution method determines four longitudinal tire forces and minimizes actuator control efforts. Finally, these tire forces are converted to traction/braking wheel torques. The proposed method has the following advantages: 1) It achieves both robust trajectory following and optimal control efforts, 2) the optimal control effort is obtained analytically instead of from a numerical search, and 3) the robust performance of this vehicle control system can be theoretically verified. The proposed method is evaluated using numerical simulations on two front-drive vehicle models: a full-state vehicle model and a sedan model from the Carsim commercial software. The simulation results indicate that, in both cases, the proposed method can regulate the vehicle to finish a "double-lane change" when the vehicle is moving at an initial speed of 90 km/h. The maximum lateral acceleration is 6.56 m/s(2), and the regulated position error is less than 6.9 cm.