| Being as one kind of Brake by Wire(BBW)systems,the Electro-Hydraulic Brake(EHB)system has the advantages of high level of integration,high efficiency and forces control flexibility.However,the high requirement of actuator performance,complex structure and pressure control difficulty retard its marketization.Focused on the self-designed EHB prototype,the paper divided the integrated control of EHB into three layers: the pressure tracking control,the brake force distribution control and the active safety control.Several issues of academic concerns were researched.Due to that the previous version had the deficiencies of unsatisfied brake feel,bad pressure control accuracy and etc.,a new EHB structure is proposed.Through three requirements: regulatory requirements of back up brake mode,performance requirements of normal brake mode and brake pedal feel simulation requirement,the main cylinder,motor,piston-pump,multi-spring pedal feel simulator and dual valve hydraulic control loop are numerical designed and experimental verified.The key point of lower layer control is to drive the actual pressure tracking the reference.The characteristics of non-linear inputs,large delay and narrow high-efficiency range were found in earlier tests.To improve these,a generalized predictive controller(GPC)and a sequential pressurizing scheduling controller are designed to optimize the tracking performance,meanwhile,an error dead-zone controller is introduced to lower on-off frequency of actuators.The works of improving controller framework and parameters are done through simulations and bench tests.Results show that the pressure error and actuator's operating duration are observably decreased when compared to PID controller.When vehicle is stable during braking,the brake forces should be timely calculated tracking to driver's brake intentions.A relation of target longitudinal force and driver's expect deceleration based on PI feedback is modeled.A slide-mode differentiator is introduced,and an emergency braking intention based on pedal movement is defined.In addition,a steering brake model is established,and a brake force distribution strategy based on dynamic I,z curves is proposed.Hi L test results show that,when compared to other distribution strategies,the strategy proposed can have the same longitudinal deceleration.Moreover,in large adhesion conditions,it ensures the enough lateral force on rear wheels,which contributes to a lower sideslip probability.In small adhesion conditions,it has lower slip ratios,which contributes to a later wheel locking time.In aspect of active safety control,the difference between EHB and conventional brake is anti-lock brake system(ABS)control.Therefore,the ABS control method of EHB and tire-road adhesion identification algorithm are proposed.Considering the deficiency that the proposed EHB could not have adequate abilities of pressurizing and depressurizing in short period,the paper presents a hybrid control method based on slip ratio-brake torque and discrete finite-state machine(FSM)controller.Moreover,a 5 parameter exponential sums(ES)model is proposed to linearize Burckhardt friction model,the methods of real-time identification and peak points extracting are designed.Tests show that whether in single or opposite road,when compared to Kiencke linear model,the identified peak points of ES model are more accurate and stable.From the component level to vehicle level,the paper comprehensively researches the layered control of EHB.Several innovative methods are proposed,which contributes reference value to the BBW development. |
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