Research On Integrated Electro Hydraulic Braking System And Power Assist Control

Energy-saving,safety,and intelligence are the development direction of future automobiles.For automobile braking systems,it will inevitably develop toward line control to meet the needs of automobile development.The integrated electro-hydraulic braking system(I-EHB)has the advantages of compact structure,high safety redundancy,good braking effect,intelligence and easy integration,which is the main development direction of brake by wire.Therefore,based on the analysis of I-EHB research status at home and abroad,this paper conducted research on I-EHB,established the AMESim simulation model of I-EHB,completed the software and hardware design of I-EHB assist mechanism controller,and studied on the surface-mounted permanent magnet synchronous motor(SPMSM)vector control and field weakening control,brake assist control,under anti-lock brake system(ABS)condition I-EHB and electronic stability control system(ESC)coordinated control and other technologies.The main contents are as follows:(1)The working principle of I-EHB was analyzed,the mathematical model and simulation model of the brake pedal,SPMSM,I-EHB assist mechanism,and hydraulic circuit were established.The correctness of the simulation model was verified by the measured data.(2)According to the functional requirements of I-EHB,the hardware circuit was designed,and the MCU minimum circuit,power supply circuit,communication circuit,signal sampling circuit and drive circuit design were completed.The method based on the Simu Link(?)code generation of the upper-level application combining with the C language of the lower-level code was introduced,and the overall software framework and the lower-level control program were designed.(3)The current control strategy of SPMSM adopted i_d=0 and the seven segment space vector pulse width modulation(SVPWM)algorithm was deduced.Principle of flux weakening control for SPMSM was analyzed.Aiming at the poor dynamic performance of SPMSM caused by slow rise of d axis current in traditional flux weakening control,a compound flux weakening method of SPMSM based on look-up table and negative voltage feedback was proposed.Based on the analysis of the vacuum booster power characteristics,the target displacement difference curve of the main and auxiliary surfaces of the feedback disk and the three closed-loop control strategy based on the displacement difference control of the main and auxiliary surfaces of the feedback disk,the motor position control and the motor current control were designed.The displacement difference of the main and auxiliary surfaces of the feedback disk was controlled by fuzzy PI.The motor bench test results showed that the composite field weakening method had better dynamics and stronger anti-interference ability than the traditional negative d axis field weakening method.The I-EHB boosting mechanism was modified on the JAC IEVS4 test vehicle,and the brake boosting method was debugged and verified.The results showed that I-EHB got a foot feel similar to vacuum booster,and the10MPa pressure build-up time was 180ms when the brake pedal was pressed quickly,and I-EHB brake response was rapid.(4)This paper analyzed the problems existing in the uncoordinated I-EHB and ESC under ABS condition,and proposed a coordinated control strategy based on double closed loops of pressure and current.Taking the relative displacement difference between the main and auxiliary surfaces of the feedback disk,the pressure of the master cylinder and the ABS flag position as the inputs,the switching logic between the power module and the coordination control module was designed.The target master cylinder pressure was determined according to the current master cylinder pressure and the relative displacement difference between the main and auxiliary surfaces of the feedback disk.Finally,it was verified on JAC IEVS4 test vehicle.The results showed that the coordinated control could switch normally,reduced the hydraulic pressure fluctuation of master cylinder,the mechanical load and electrical load of I-EHB,and optimized the pedal feel.In summary,this paper built I-EHB simulation model,completed I-EHB controller hardware and software design,improved SPMSM flux weakening method,and developed I-EHB and ESC coordinated control function under ABS condition,which provided a reference for future I-EHB scheme optimization and control strategy development.