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Path planning and tracking are two important means for autonomous vehicle in obstacle avoidance in the last decade. In this study, the reference path is planned on the basis of the sigmoid function which represents the driver’s intent in accordance with obstacle information. Meanwhile, a nonlinear model predictive controller for path tracking of autonomous vehicles is proposed. The proposed controller drives vehicle to track the reference path by controlling the front steering angle and braking torques of four wheels. Computer simulation based on CarSim and MATLAB/Simulink was performed to verify the feasibility and effectiveness of the controller.

With motor and reduction mechanism applied to Electric Power Steering (short for EPS) system of automobile, the frictional loss torque of steering system is increased. The common friction compensation control through the sign function of angular velocity or the saturation function of angular velocity is conducted to reduce the frictional loss torque of steering system. However, when the motor used in steering system generates assist torque based on the common friction compensation control, the longitudinal intercepts of steering torque change obviously at different steering wheel angles. The driver will get different frictional loss torque of steering system at different steering wheel angle. The information of steering torque contains the change of steering reaction torque and the frictional loss torque of steering system, so the change of frictional loss torque can cause the fuzzy of road feeling.