Research On Control Technology Of A Novel Brake-by-Wire System For Electric Vehicle

The braking system is the main device to ensure road safety,its performance directly de-termines the vehicle security.The hydraulic braking system is very mature and reliable after dozens of years development,but its improvement potential is limited because of its structure restrictions.At present,the braking system is gradually converting to brake-by-wire(BBW)system represented by electro-hydraulic brake(EHB)and electro-mechanical brake(EMB).Although EHB and EMB can effectively deal with the insufficient of conventional hydraulic braking system,these new BBW systems still have disadvantages because of their own struc-tural characteristics.EHB is improved from conventional hydraulic braking system,it still keeps hydraulic pump,accumulator,high-pressure pipeline and other hydraulic components,so the further improving potential is still limited.EMB completely abandons the hydraulic structure,the braking performance is significantly improved.But both the motion conversion mechanism and force amplification mechanism are necessary in EMB,the structure is complex and the force control is difficult.In order to deal with the complex structure of EMB and the improving potential of EHB,a novel kind of BBW unit which is called as direct-drive electro-hydraulic brake(DDEHB)unit and based on electro-magnetic linear actuator(EMLA)is presented.A composite braking system include friction braking based on DDEHB and regenerative braking is built for electric vehicle,and the regenerative braking method and slip-rate control method are studied in detail.The main works and fruits of the thesis are as follows:(1)The braking process of electric vehicle is analyzed and the kinematic model of elec-tric vehicle is established.The basic requirements and special requirements for electric vehicle braking system are discussed in detail.The drawbacks using conventional hydraulic braking system in electric vehicle are analyzed by the method of the braking force distribution curve and the utilizing attached coefficient curve.Then the structure and principle of DDEHB are introduced,and a composite braking system including friction braking based on DDEHB and regenerative braking is built for electric vehicle.The unique advantages using DDEHB in electric vehicle are analyzed compared to conventional hydraulic brake system.(2)The structure of EMLA is determined according to the operating environment and the characteristics of DDEHB,and the design index is formulated at the same time.Then the EMLA is manufactured and assembled,and a prototype of DDEHB is modified and trial-manufactured from a certain type of hydraulic brake unit,then its static and dynamic parame-ters are identified.(3)The multi-field model of DDEHB including electric circuit,magnetic circuit,and mechanical-hydraulic system is established.The combined simulation model of DDEHB based on Matlab/Simulink and AMESim is built on the basis of state equation,the actuator parameters are identified and their influence on DDEHB performance is analyzed.(4)The disturbance and the difficulty of controlling braking force of DDEHB are ana-lyzed.A state observer based on Kalman filter is designed for DDEHB to accurately estimate the state variables and a dual-loop controller based on ADRC is proposed for DDEHB to ac-curately regulate braking force.(5)The hardware controller is designed and built,the selection and calibration of sensors are completed,the control software,PC control interface and data analysis tools are wrote.The step response test with 5MPA in hydraulic cylinder and the sinusoidal pressure tracking test with maximum pressure of 4MPa,amplitude of 2MPa and cycle time of 1000ms are designed according to modified prototype.The test results show that the response of DDEHB is fast and the braking force control precision is accurate.(6)The influences of regenerative force are discussed,the optimal braking performance scheme and the optimal recovery efficiency are proposed for electric vehicle which equips D-DEHB.The deceleration control method,slip-rate control method,braking force distribution strategy and the regenerative torque of motor are detailed studied for the proposed two regen-erative schemes.The co-simulation model based on Matlab/Simulink and AMESim is estab-lished for front driving electric vehicle,and the heavy braking and light braking are simulated for the proposed two schemes.The simulation results indicate that there is no significant dif-ference on braking time or braking distance between the two regenerative schemes,and there is no obvious improvement of recovery efficiency in heavy braking.While in light braking,the recovery efficiency of the optimal recovery efficiency scheme is obviously better than the optimal braking performance scheme,but the braking force distribution of the optimal braking performance scheme is more reasonable than the optimal recovery efficiency scheme.