Design And Research Of Automobile Electric Parking Brake Control System

Brake by wire is the inevitable direction of the development of automobile braking system,so the electric parking brake system(EPB)came into being.The development of EPB’s control technology is not only the decisive factor of its excellent performance,but also provides technical reserves for the future application of electronic mechanical braking system(EMB).Therefore,we design and research the EPB control system in this thesis.The most common integrated EPB is taken as the object of the research in this thesis.At first,the control structure,actuator and working principle of the integrated EPB are introduced.In addition,the actuator(brushless dc motor(BLDC),sliding screw nut mechanism and clamping force equivalent model)are modeled and simulated through MATLAB/Simulink software.The processes of clamping and releasing are analyzed.Base on it,we get the curve of BLDC angular displacement-clamping force,which can be used to judge the clamping force.Four kinds of control strategies(EPB button pull up,EPB button press,ramp start assist and EPB automatic startup)are designed.We also analyze the method of downloading the C code of the EPB control strategy to the designated address of the MCU FLASH through CAN bus by using the Bootloader in the MCU.Secondly,the high temperature reclamping function of the brake disc in the EPB automatic startup control strategy is studied.According to the law of conservation of energy and heat calculation formula,the mathematical model of temperature rise of brake disc under emergency braking is derived.Meanwhile,the mathematical model of brake disc cooling is derived based on the lumped parameter method of heat transfer and the Newton cooling formula.The corresponding values of temperature and time during the cooling process of the brake disc at the initial braking speed from 60km/h to 120km/h,every 10 km/h are measured through the real vehicle test.Based on the least square method,the experimental data are fitted according to the cooling formula.The relationship between the cooling coefficient and the initial braking speed is studied.The thermal mechanical coupling analysis of the brake process is carried out by using HyperMesh and ABAQUS software,we mainly study the axial displacement recovery of the high temperature joints of the brake disc material during its cooling process.The mathematical relationship between the amount of axial displacement recovery and the decrease of temperature is deduced.Based on it,we can know the amount of clamping force decrease with the time,which can be used to determine the moment of EPB reclamping.Next,we study the mechanical antilock braking of dynamic emergency braking function,which is led by EPB.The method of controlling the operating state(forward,stop and reverse)of EPB motor by using the T-S fuzzy control algorithm based on the best slip rate is put forward.The best slip rate is obtained by using the recursive least square method to identify the tire road adhesion conditions based on the Burckhardt model.The quantization factor of T-S fuzzy control is optimized by using genetic algorithm,in order to achieve anti-lock and the make full use of the maximum tire road friction coefficient at the same time.Finally,the main part of EPB hardware circuit is designed by using Altium Designer software,including the main MCU and its minimal system circuit,the power switch circuit,the CAN bus communication circuit,the road angle measuring circuit and the BLDC driver circuit.Besides,the correctness of some circuit is verified by using Freescale CodeWarrior and LabVIEW software.The research on the high temperature reclamping function of the brake disc is not only to determine the reclamping time to compensate for the clamping force after the forced brake,but also to improve the control strategy of the conventional parking brake function,that is to get the minimal clamping force to make sure the vehicle that parking in the small slope not slide because of the brake disc cooling,reduce the load of EPB electronic control unit and actuator,prolong its service life.The study on the dynamic emergency braking function is to realize the function of mechanical ABS,which also is one of the core contents of EMB research.