Research On Variable Assisted Characteristics Of Novel Electro-mechanical Brake Booster For Passenger Cars

The brake system has always played a very vital role in the safety of passenger cars.However,with the emergency of environmental pollution,energy shortages and the rapid development of computer technology,the automotive industry is moving towards the direction of electrification,intelligence,networking and sharing.The traditional vacuum assisted brake system can no longer meet the development and requirements of modern cars,while the electro-mechanical brake booster came into being.It has the following characteristics;(1)It uses the motor as the power source,does not need the engine to provide vacuum or vacuum pump,and this meets the requirements of the electric vehicle to cancel the engine and vacuum source gradually;(2)It can achieve rapid response and accuracy of active braking,and meet the requirements of the adaptive cruise control and autonomous emergency braking of the intelligent cars;(3)It can be used with electronic stability program or active accumulator to achieve brake energy recovery;(4)it has adjustable brake pedal characteristics.Nowadays,many features of the car can be adjusted through software,one of which is the adjustable pedal characteristics in the brake system.Through the adjustment of control parameters and software,the assisted characteristic of booster can be changed to form a brake pedal feeling from dynamic sport type to comfortable type,which can meet the requirements of different countries,different vehicle manufacturers,different vehicle platforms and different consumers.This paper makes an in-depth theoretical analysis and research on the variable assisted characteristics of a novel electro-mechanical brake booster,and realizes the variable power assisted control.The strategy can realize three different brake pedal feeling of the brake system,including sports type,normal type and comfortable type.The specific contents are as follows:(1)The principle analysis and modeling of electro-mechanical brake booster.Aiming at a novel electro-mechanical brake booster,this paper introduces its working principle in different working modes in detail.In order to realize the simulation and control parameter optimization of the electro-mechanical brake booster,this paper uses the modular processing method to model the dynamics of the booster,and the corresponding model verification is carries out.In order to realize the control of the brake booster,it is necessary to modify it to some extent.The sensor of motor angle is added and the effectiveness is verified.In this paper,a method of analyzing the single edge nibble transmission protocol is proposed.And also,the protocol analysis and calibration of the displacement difference sensor is completed.(2)Research on the variable assisted characteristics.Starting from the working principle of the vacuum booster,the formation reason,adjustment measures and evaluation indexes at each stage of the assisted characteristics are discussed.The characteristics of the rubber feedback disc are the key to the realize variable assisted power control.Based on two simplified model theories,the influence of the displacement difference of the main and secondary surfaces of the rubber feedback disc on the power assisted characteristic is analyzed.The test platform of the electric cylinder of the rubber feedback disc is built.The test platform is used to test the relationship between the input force,the input displacement and the output force under different working modes and different displacement differences of the main and secondary surfaces of the rubber feedback disc.And it will direct the design of variable assisted control strategy.(3)The variable power assisted control of electro-mechanical brake booster.In this paper,the forming reasons and adjusting measures of the assisted characteristics of the electromechanical brake booster are discussed.According to the requirements of three kinds of ideal assisted characteristics of different brake pedal feeling,the relationship between the input push rod displacement of pedal and the displacement difference between the main and secondary surfaces of the rubber feedback disc is designed by using the test results of the rubber feedback disc and the working principle of the mechanism,so as to obtain the desired target position of the motor indirectly.Three closed-loop control including current loop,speed loop and position loop is adopted for the tracking control of the motor target position.Constant torque angle control method is adopted for the motor in the base speed.In order to improve the maximum speed that the motor can reach,the model free(parameter insensitive)field weakening control method is adopted.In addition,in order to improve the control accuracy,inertia compensation and friction compensation are added.(4)Experimental verification of the variable power assisted control strategy of the electro-mechanical brake booster.Based on the dSPACE rapid prototyping tools MicroAutoBox II and RapidPro,electric cylinders,and inertial navigation RT 3000 and other equipments,a test bench platform and a real vehicle test platform are built,and the software system and hardware system are introduced in detail.The following control strategy of PMSM,basic power assisted control strategy and variable power assisted control strategy of electromechanical brake booster are tested and verified.The results show that the control strategy can realize three different types of brake pedal feeling: dynamic sport type,normal type and comfortable type.In summary,the research in this paper realizes the variable power assisted control of a novel electro-mechanical brake booster,and takes power assisted characteristics of the normal brake pedal feeling as the basic power assisted characteristics of the booster.At the same time,the research results of the variable assisted characteristics in this paper provide a reference for the design of brake assisted characteristics and control strategy for other boosters that use rubber feedback disc as coupling element.