Development of a brake by wire system design for car stability controls

Abstract

The paper presents the development of a vehicle stability control system that is able to operate in real time, ensuring to enhance vehicle dynamics and safety in all vehicle motion conditions, even at limit of handling. The commercial cars have an Electronic Stability System, ESC, that acts actuating the brakes autonomously to correct the vehicle dynamics at limit of adhesion conditions. In this study it will be shown how the stability control system proposed can operate autonomously and constantly during vehicle motion, thanks to a controller based on a simplified vehicle model and a brake unit that operates in continuous.The control system consists of a high-level control and four Brake-By-Wire actuators. The high-level control is an Linear Quadratic Regulator, LQR, that ensures to stabilize the yaw rate and the side slip angle minimizing the errors between the actual car values and the values given by a steady state dynamic reference model. To reach this aim the LQR gives the values of longitudinal forces that each wheel has to achieve. These values of force are sent by a CAN signal to the Cornering Brake Actuators, CBA, that with their own logic and proximity to the wheels ensure a vary fast actuation, stabilizing the vehicle and providing safety.To validate the control system a series of manoeuvres have been carried out on a case-study test bench, that has been installed on a static driving simulator equipped with a concurrent real-time machine, the complete vehicle network and the full steering system. The control system has been design to be used as a stability system on commercial cars, requiring of common vehicle sensors, ensuring better performances and stability even in driving at limit of adhesion conditions, but also to be installed in an autonomous vehicle being able to act independently from the driver.