Principle design and control of a brake-by-wire actuator featuring magnetorheological clutch

Electro-mechanical brake (EMB), driven by a motor to push the brake pads to clamp the brake disk for braking, is considered as the future of vehicle braking system, because of its simple structure and controllable braking force. However, EMB must face the problem of motor blocking when it works in a long-time continuous braking condition. When the motor is blocking, the current in the coil windings is large enough to burn the motor down, leading to the failure of EMB, which is a great threat to driving safety. To solve the problem, a new brake-by-wire actuator featuring magnetorheological (MR) clutch (MRC) - an EMB combining with an MRC, i.e., BBW-MRC, is presented in this paper. Specifically, the BBW-MRC is composed of a driving motor, an MRC, a planetary gear reducer, a ball screw, brake pads, and a brake disk. The motor output is transmitted to the MRC through the reducer, and it is controlled in real-time, continuously, and as expected by the MRC via controlling its applied current. The ball screw is driven by the MRC and pushes the brake pads to clamp the brake disk to realize braking in time. The small-scaled BBW-MRC system and the corresponding test bench are developed, and a hierarchical control strategy applied to the BBW-MRC system is designed. Based on the test bench, a series of tests are carried out on the BBW-MRC system, including the stability test of the BBW-MRC system under a long-time braking condition, the braking force response test of the BBW-MRC, and the braking force tracking test. Research results show that: (1) the BBW-MRC system has a quick and accurate performance to track desired braking forces; (2) under long-time braking conditions, the braking force keeps stable and the surface temperature of the motor has a normal change; and (3) the braking force response time has a 53.5% improvement over the EMB that driven by the motor directly.