Design and Power-Assisted Braking Control of a Novel Electromechanical Brake Booster 2018-01-0762
As a novel assist actuator of brake system, the electromechanical brake (EMB) booster has played a significant role in the battery electric vehicles and automatic driving vehicles. It has advantages of independent to vacuum source, active braking, and tuning pedal feeling compared with conventional vacuum brake booster. In this article, a novel EMB booster system is proposed, which is consisted of a permanent magnet synchronous motor (PMSM), a two-stage reduction by gears and ball screw, a servo body, and a reaction disk. Together with the hydraulic control unit, it has two working modes: active braking for automatic drive and passive braking for driver intervention. The structure and work principle of the electric brake booster system is first introduced. The precise control from pedal force to hydraulic pressure is the key for such a power-assisted brake actuator. We translate the control problem of force feedback control to position tracking control. Then, a nonlinear control method for power-assisted braking is presented, which could be divided into three parts: (i) signal processing and driver’s braking behavior recognition, (ii) obtaining target position, and (iii) precise position controlling of PMSM. For this, a Kalman filter was designed to do the signal processing firstly. Next, the method of logic threshold is applied to recognize the driver’s braking behavior. At last, the position control of PMSM is achieved by a triple-closed-loop proportional-integral-derivative (PID) controller with the technology of friction compensation and tuning gain. The contrast tests between the electric brake booster and the vacuum brake booster are implemented based on RCP test environment to verify the validity and effectiveness of the mechanism and controller. The wheel cylinder pressure precise control tests in active braking mode are designed and implemented. Test results show that the performance of the EMB booster system behaves well.