Optimal emergency maneuvers on highways for passenger vehicles with two- and four-wheel active steering

This paper presents and utilizes an optimal-control based method for quantifying the maneuverability of actively-controlled passenger vehicles during emergency highway-speed situations. The research is motivated by the desire to better understand the performance benefits of additional actuated degrees of freedom when compared to a typical vehicle. Specifically, the performance benefits of front-steer vehicles are compared to front-and rear-steer vehicles. In both cases, the vehicle is assumed to be capable of applying independent accelerating/braking torques to the front and rear wheels. The emergency maneuvers considered are obstacle avoidance, barrier avoidance, lane changes, and recovery from an arbitrary state. Necessary conditions for optimality and optimal control laws are found for each case. Solutions are found using a lumped-parameter planar single-track vehicle model and nonlinear tire dynamics are assumed. Front-and rear-steering vehicles are shown to have better maneuver-ability during all emergency maneuvers. Based on the optimal vehicle trajectories, the benefits are quantified using appropriate performance indices.