Emergency braking using two independent steering actuators while maintaining directional control

Abstract

"By-wire" systems are currently an area of significant interest in the automotive industry. In particular, there is substantial work being done to investigate the use of steer-by-wire and brake-by- wire systems in automobiles. Since these systems replace traditional mechanical connections with digital controllers, ensuring the safety of these systems in the event of a failure is critical. In this work, we investigated the feasibility of using two independent steering actuators to provide emergency braking capability in the event of a primary brake system failure. The work conducted consisted of three major areas. First, a vehicle model was developed for predicting vehicle response to various steering and braking inputs. The derivation, implementation and validation of the model are presented. Once validated, this model was used to run simulations of vehicle response while attempting to stop the vehicle with the steering system. Open-loop simulations were run first to determine how the vehicle responds to given inputs. The results of these simulations indicated that it is possible to achieve a reasonable level of deceleration with the steering system while still maintaining some level of directional control. With the understanding obtained from the open-loop simulations, a closed-loop control strategy was developed for achieving desired performance. In this approach the steering wheel and brake pedal inputs from the driver are used to determine the appropriate steer angles at each of the front wheels. The control strategy attempts to provide the driver with the same response as if the braking and steering systems were functioning normally, requiring no change in the inputs from the driver. The results indicate that it is possible, for low to moderate levels of lateral acceleration and longitudinal deceleration, to provide performance similar to that under normal operation. Although further work needs to be done, the results confirm that it is possible to provide a reasonable level of emergency braking capability from the steering system in the event of a brake system failure. The results suggest that this approach could be used to either reduce the level of redundancy needed for such by-wire systems, or to add an additional level of safety to an existing level of redundancy.