Research On Control Strategy Of Electromechanical Brake System For Dynamic Control

Intelligence and electrification are the main trends of current automotive development.The longitudinal dynamics control system including adaptive cruise control and automatic emergency braking,as an important part of the intelligent technology,has received wide attention and become one of the research hotspots in the industry.At the same time,with the development of vehicle electrification and intelligent technology,the vehicle has higher and higher demand for braking system,on the one hand,it is required to have active braking function and integrate with other control systems in the chassis domain conveniently,on the other hand,it is required to minimize fluid pollution and recover as much braking energy as possible with the upper control strategy to improve the range of electric vehicles under the premise of ensuring pedal force.Electromechanical Brake System(EMB)system is a kind of linear control system,which uses the electric motor as the power source and applies the clamping force directly to the brake disc through the transmission system to brake the vehicle,the system not only eliminates many hydraulic lines,but also is easy to achieve active braking and integration with the longitudinal dynamics control system.In addition,Electromechanical Brake System can also realize the decoupling of the brake pedal force under the premise of ensuring the brake pedal feel,so as to cooperate with the regenerative braking system to achieve a greater energy recovery rate,so the electromechanical brake system can well adapt to the development trend of electrification and intelligent vehicles,has a good application prospects.This paper mainly focuses on the control strategy of the electromechanical braking system.Firstly,the selection,design calculation and system modeling of EMB actuator are completed,then the control strategy of drive motor in EMB actuator is studied,and based on the analysis of the working process of electromechanical braking system,the EMB multi-stage closed-loop control strategy is designed,and the effectiveness of EMB control strategy is verified by Simulink/Amesim joint simulation and hardware-in-the-loop experiment.Finally,a longitudinal dynamics control strategy based on EMB is designed,and the effectiveness of the longitudinal dynamics control strategy including ACC and AEB functions with EMB as the actuator is verified by Simulink/Carsim joint simulation.The specific research contents are as follows:(1)Calculation and modeling of the actuator design of the electromechanical braking system.Then the overall braking requirements of the EMB are determined according to the target vehicle parameters and relevant regulatory requirements,and the design of the two main performance indicators of the EMB actuator,i.e.,the maximum clamping force and the clearance elimination time,are completed,followed by the selection and design calculation of the EMB drive motor,reduction mechanism and motion conversion device,etc.After that the mathematical model of the actuator is analyzed in detail,and the corresponding simulation model is established in Simulink environment based on the mathematical model,which lays the foundation for the development and simulation verification of the EMB control strategy.(2)Research on the control algorithm of EMB drive motor.Firstly,the vector control method of permanent magnet synchronous motor is analyzed,then the three coordinate systems and coordinate transformations involved in vector control,space vector pulse width modulation are carefully studied and the relevant equations are derived,then the overall control strategy of EMB drive motor including current loop,speed loop and position loop is designed,and the current loop control strategy based on MPC is analyzed and theoretically deduced in detail.The simulation results show that the designed MPC-based current loop control strategy can achieve a better current tracking effect.(3)Research on the control strategy of electromechanical braking system.Firstly,the working process of EMB actuator is analyzed,and the EMB multi-stage closed-loop control strategy is designed according to the working characteristics of EMB actuator in three stages,and then the pressure loop that directly affects the braking control effect of the vehicle is designed based on active disturbance rejection,comparative simulation analysis of pressure loop control strategies is carried out in conjunction with actuator model.Finally,a Simulink/Amesim-based joint simulation platform and a d SPACE-based EMB hardware-inthe-loop experimental platform are built,and the joint simulation and hardware-in-the-loop experiments verify the rationality and superiority of the designed EMB multi-stage closed-loop control strategy.(4)EMB-based longitudinal dynamics control strategy research.Based on the EMB control algorithm,the longitudinal dynamics upper and lower control strategies including ACC and AEB systems are studied with EMB as the actuator.First,the overall architecture of the EMB-based longitudinal dynamics control system is introduced,for the lower control part,the longitudinal force analysis of the driving vehicle is carried out,and the target braking pressure control strategy,target drive torque control strategy and drive-brake switching control strategy are designed based on the longitudinal dynamics equation,followed by the design of the upper decision control part of the fixed speed cruise PID controller and autonomous following LQR controller,and then the AEB safety distance model,graded braking control strategy and the switching control strategy between each functional module are studied,Finally,a joint simulation platform based on Carsim/Simulink is built,and the simulation verifies the effectiveness of the EMB-based longitudinal dynamics control strategy.