A flexible hierarchical model-based control methodology for vehicle active safety systems

Abstract

A hierarchical control scheme is applied to the problem of integrated chassis control of a collision avoidance system (CAS). This includes both lateral and longitudinal control, using Active Front Steer in addition to the brake actuators. The inherent flexibility of the control system is provided by the intermediate layer, which employs a form of model predictive control to determine actuator apportionment. The desired vehicle motions in the upper layer, in the form of reference yaw rate and two-dimensional mass center accelerations, are determined using a kinematic policy (KP) for collision avoidance. The KP uses simple information about range and azimuth angles for multiple points that bound the available vehicle trajectory, and prioritises yaw motion response based on the worst case collision threat. This KP approach for CAS is more practical than trajectory tracking approaches because the KP does not need a pre-defined a reference path and does not need any computationally intensive optimisation of the vehicle motion control.