Unified Control of Brake- and Steer-by-Wire Systems Using Optimal Control Allocation Methods

A new optimal control strategy for dealing with braking actuator failures in a vehicle equipped with a brake-by-wire and steer-by- wire system is described. The main objective of the control algorithm during the failure mode is to redistribute the control tasks to the functioning actuators, so that the vehicle performance remains as close as possible to the desired performance in spite of a failure. The desired motion of the vehicle in the yaw plane is determined using driver steering and braking inputs along with vehicle speed. For the purpose of synthesizing the control algorithm, a non-linear vehicle model is developed, which describes the vehicle dynamics in the yaw plane in both linear and non-linear ranges of handling. A control allocation algorithm determines the control inputs that minimize the difference between the desired and actual vehicle motions, while satisfying all actuator constraints. The algorithm can be applied to either vehicles with a brake-by-wire system only or to vehicles with both brake and steer-by-wire systems and can be adapted to specific conditions. The results of simulations using a high fidelity vehicle model demonstrate the benefits of the proposed control method.