Design and Position Control of a Novel Electric Brake Booster 2018-01-0812
The battery electric vehicles and the intelligent vehicles put forward to new requirements for the braking system, such as the vacuum- independent, automatic or active braking, and regenerative braking, which are the key link for the vehicle’s comfort and economy. However, the traditional vacuum brake booster is no longer able to meet these requirements.
In this paper, a novel integrated electric assisted actuator of brake system is proposed to improve the brake system. This system is designed to achieve the function of boosting pedal force of driver, being independent on vacuum source, supplying autonomous emergency braking (AEB) or active braking. Such an electric brake booster (E-booster) system is mainly composed of a permanent magnet synchronous motor (PMSM), a two-stage reduction transmission (gears and a ball screw), a servo body, and a reaction disk. The precise control from pedal force to hydraulic pressure is the key for such a power assisted brake actuator. Owning to the high cost of force sensor and the requirements for transient response, we translate the control problem of force feedback control to position tracking control. However, the strong nonlinearity and the load-dependent friction make the position tracking control of the electro-mechanical brake booster become more challenging. So, a Karnopp friction model is used in this paper and its parameters are identified by the method of multiple linear regression. Consequently, a modified PI control architecture is presented with techniques of cascaded three closed loop PI controller, friction compensation based on friction model, and gain scheduling. Finally, based on rapid control prototype environment, the bench tests covering multiple kinds of brake conditions are designed and implemented to verify the performance of the controller. Test results show that both the position tracking performance and response time of electro-mechanical brake booster system perform well.