Research On Pressure Control Strategy Of Integrated Braking System

With the rapid development of society and continuous progress of technology,electrification and intelligentization have become the major advancement direction of future vehicles.The new development trend also puts forward higher requirements for vehicle braking system.The integrated braking system realizes complete decoupling of pedal force and braking force in structure,as well as integrates the functions of active braking,basic booster braking,regenerative braking,wheel cylinder pressure control and differential braking,which can satisfy the demand of intelligent electric vehicles for braking system.Fast and accurate pressure regulation is the basis of integrated braking system as underlying actuator for intelligent driving and accomplishing target functions.Therefore,it is of great significance to research the pressure control strategy for integrated braking system.This paper is supported by the major technology project "Research and Industrialization for Key Technologies of Braking-By-Wire System " of Changsha City(No.kq2102008)and university-enterprise cooperation project " Research of IBC System Integrated Control ".The configuration,working principle and modeling of system is studied,followed by the research of servo cylinder pressure control strategy and combined pressure control strategy,taking the integrated braking system as research object.The description of research for this paper is specified as follows:(1)Configuration analysis and modeling of integrated braking system.Firstly,the configuration of integrated braking system is analyzed,and three function units of driver handling,servo cylinder and hydraulic regulation in system configuration are introduced,followed by the working state of each component and hydraulic circuit variations in three working modes of system: basic booster braking,active braking and failure backup.Then the system model containing permanent magnet synchronous motor,servo cylinder,braking wheel cylinders and electromagnetic valves is established.Finally,the effectiveness of proposed model is verified by comparing simulation experiment with bench data.(2)Study on servo cylinder pressure control strategy of integrated braking system.Firstly,a servo cylinder pressure control architecture including Driver Braking Requirements Identification(DBR)module,External Braking Requirements(EBR)module and servo cylinder pressure controller is constructed to perform the basic booster and active braking functions of system.The DBR module is designed with three different output characteristics to satisfy the requirements of drivers with different styles,while an input facility for the fusion of pedal displacement and master cylinder pressure is established to derive dynamically varying input weight coefficients based on relationship characteristics of the two parameters to compensate for the shortcomings in reliability of a single sensor for pedal displacement as identification input.For multi-functional EBR module,the deceleration control strategy in module is studied,and a control method with parallel links of dynamic feedforward and variable parameters PI feedback is adopted.Then a pressure loop sub-controller with hydraulic characteristic feedforward and variable PI feedback link in parallel,a position loop sliding mode sub-controller with disturbance compensation and a PI feedback current loop subcontroller with voltage limitation are used to constitute a complete servo cylinder pressure controller.Finally,the proposed servo cylinder pressure controller is simulated and verified with the established system model.(3)Study on combined pressure control strategy of integrated braking system.First of all,combining the research in previous chapter,the bottom combined pressure control architecture containing wheel cylinder pressure control and replenishment control function is established.After that,the pressure increase and decrease experiments of wheel cylinders are carried out,the curves of pressure change are drawn,so as to obtain the working characteristics of inlet and outlet valves for wheel cylinders.Subsequently,the inlet and outlet valve control strategy of characteristic feedforward with pressure feedback is established,and the wheel cylinder pressure regulation logic is further established to independently regulate wheel cylinder pressure by controlling inlet and outlet valves on the basis of servo cylinder pressure control.Lastly,a valve and motor coordinated fluid replenishment control strategy is proposed,which judges the system replenishment demand depending on change of P-V characteristics in servo cylinder,thus controlling the piston to perform reverse motion to draw brake fluid from the reservoir,solving the problem of insufficient brake fluid in hydraulic circuit caused by wheel cylinder depressurization.(4)Experiments verification of integrated braking system pressure control strategy.Based on tools such as MATLAB/Simulink and d SPACE software with hardware,an integrated braking system hardware-in-loop experiment platform is designed and established.Later,depending on the experiment platform,active braking and basic booster braking experiments are conducted to verify the effectiveness of servo cylinder pressure control strategy.Finally,working conditions are designed,differential braking and fluid replenishment control function experiments are carried out using the experiment platform to complete the validation of combined pressure control strategy.