Moving Horizon Based Coordinated Control Framework for Agile Drifting of Autonomous Vehicles

Most of fatal traffic accidents occur in emergency conditions, for example, unexpected dynamical obstacle, sudden post-impact etc, in which vehicle attitudes are immediately changed due to external circumstances and internal perturbations. It is extremely challenging for autonomous vehicle to effectively and efficiently handle such a dangerous scenario, especially at the friction limit of the tire. Drifting is proven an effective way to augment driving stable domain and maintain vehicle stability at friction limit. To this end, this paper introduces drifting maneuverability strategy into variable curvature path tracking control to further strengthen its mobility by mode switch approach. To begin with, a nonlinear three degree of freedom vehicle dynamic model is constructed to analyze planar dynamical characteristics, and different drift equilibrium points are obtained. After that, a MPC based steady-state drift controller and a LQR based path tracking controller are respectively designed to ensure vehicle driving stability and path tracking capacity, and the influence mechanism of initial longitudinal velocity on steadystate drifting is explored. Based upon, the requirements oriented motion mode switch criterion is designed according to the curvature corresponding to the path reference point that closest to the vehicle's center of mass. Lastly, simulation examples with different curvature path and motion mode performed on Simulink-CarSim joint simulation platform validated the agility and effectiveness of proposed control scheme and approaches subject to mode switching between drift driving and normal driving.