Research On Brake-by-wire Actuator Featuring Magnetorheological Fluid Clutch

With the development of intelligent/automated vehicles,brake-by-wire systems,which transform the control command signals into electric actuation,will definitely replace the bulky hydraulic brake systems.Electro-mechanical brake is a possible solution for brake-by-wire technology.However,the problem of the motor stalling is an inherent defect of the electro-mechanical brakes for long-time braking,which may lead to the failure of the full brake system.In order to solve such problem,this paper proposed a novel method,using a magnetorheological fluid clutch(MRC)with the characteristics of simple structure,fast response and large range of controllable transmission torque to realize continuous and fast braking force output of the electro-mechanical brakes in the whole operation range.The proposed brake-by-wire is mainly composed of an AC servo motor,a planetary gear set,a MRC and a screw set.The planetary gear set amplifies the output torque of the AC servo motor,through controlling the current in the excitation coil of MRC to realize the real-time control of the braking force at the end of the screw set.Specifically,firstly,the structure of the MRC is designed and verified by electromagnetic simulation.The optimization for structural design of the MRC is carried out in ANSYS/Mechanical APDL and the prototype is manufactured using the optimal parameters.Secondly,the mechanical response characteristics of the MRC are tested,including the output torque calibration experiment and the response time test experiment.Thirdly,a small-scale test bench of the proposed brake-by-wire is built,and the hierarchical control strategy is designed with the consideration of the AC servo motor and the MRC.The top layer judges the working mode of the AC servo motor and the MRC according to the desired and actual braking forces.The bottom layer accurately controls the outputs of the two controllable units according to the judgement of the top layer.Meanwhile,the real-time braking force tracking experiment in the whole braking frequency range are evaluated.Finally,on the basis of the hierarchical control strategy,the anti-lock braking system(ABS)function on a quarter car is realized.