An optimal path controller minimizing longitudinal and lateral deviations after light collisions

Abstract

This paper considers the problem of path control for a road vehicle immediately after it is disturbed by an initial light collision. Assuming that the driver cannot adequately control the vehicle during such an event, active chassis controls such as front steering and friction brakes are applied to minimize the risk and/or severity of a secondary impact, e.g. with roadside objects. Statistics have shown that traffic accidents where a vehicle suffers more than one collision comprise about 25% of all passenger car accidents. In this paper, the crash risk for secondary collisions is formulated via a cost function and an optimal controller is developed. The cost function may penalize both longitudinal and lateral deviations from the point of initial impact, and is assumed here to be a time-integrated quadratic function of position. For closed-loop implementation this is further approximated using a simple terminal velocity cost, the direction of which represents predicted locations of maximum risk/harm. A six-state quasi-linear path controller is developed using nonlinear optimal control theory. Example cases are presented, verifying approximate equivalency between cost functions and satisfactory control performance compared with independent open-loop numerical optimizations.