Research On The Key Components And Pressure Control Of Fully-decoupled Regenerative Braking System

Regenerative braking system can transform the vehicle kinetic energy into electric energy and store into the battery during braking,which can realize energy recycling and improve the energy economy of vehicle.With the coordination between motor braking and hydraulic braking,the system should ensure the brake feeling when try to improve energy recovery ratio.With the requirements of cooperation project,this thesis put forward a new hydraulic regenerative braking system which can realize decoupling of both axles,aimed to research on the key components and pressure control of fully-decoupled regenerative braking system.This thesis can provide technical support for the application of the new system.The key components of fully-decoupled regenerative braking system include pump motor,hydraulic pump,high-pressure accumulator,linear solenoid valve and brake stroke simulator.For the research on key components,analyze the structure and working mechanism first,build the simulation model and simulate on the basis of theory,then test the performance of the key components to study the control law.For the research on pressure control,with the requirements of system pressure control states,this thesis studied the control theory of step pressure control and linear pressure control,and finished the validation of pressure control with the control performance of linear solenoid valve.On the basis of research method above,this thesis finished the following research work:1.Analysis on system scheme.With the working principle of RBS,this thesis studied the constraints of the system,which including driving cycle,vehicle configuration,brake system configuration,power system of electric vehicle,braking force distribution,etc.Acquired the best brake intensity during regenerative braking.Analyzed the energy flow during regenerative braking of the electric vehicle,and put forward the energy saving evaluation index of RBS.Analyzed the control requirments and pressure control index of fully-decoupled RBS.2.Research on key components.Built the basic pressure adjusting model of brake cylinder,and studied its PV performance.Mainly researched on the electrical and hydraulic performance,and acquired the relation of electromagnetic force,valve core stroke and coil current.Studied the relation between pressure and valve control duty cycle through bench test,which provided theory and data support for pressure control.Meanwhile,did mechanism analysis,parameter matching and test validation to the high pressure source(pump motor,hydraulic pump and high-pressure accumulator).3.Research on pressure control.Analyzed the basic principle of step and linear pressure control.Mainly researched on the relation between the pressure rate and current rate of linear solenoid valve,and acquired the 3-D curve of coil current,pressure rate and pressure difference,which was used for linear pressure control.Tested the result of the two pressure control methods at last.4.Simulation and test validation.Validated the control results of different brake intensity by using Matlab/Simulink and AMESim co-simulation,and analyzed the relation between energy recovery ratio and brake intensity.HIL test validated the system function and pressure control result further.The following conclusions can be derived from the above research results:1.Through the analysis of system scheme,the range of brake intensity can be set to 0?0.3g during regenerative braking.Fully-decoupled RBS can be applied to AWD electric vehicles and can recover more brake energy.Braking recovery ratio can be applied to evaluate the energy saving of single brake process,and the contribution of RBS to the vehicle consumption or driving range can be appied to evaluate the energy saving of driving cycle.The motor braking force distribution coefficient has proportional relation with energy recovery ratio directly.2.Through the research on the components performance,the pressure change rate is related to the current pressure of the cylinder.The coil current has linear relation with the control singal duty cycle.The pressure difference of the valve port has linear relation with duty cycle within a fixed range.The active pressurization source can realize rapid pressurizing and the pressure is steady.The brake pedal stroke simulator matched can simulate the brake feeling.3,Through the research on pressure control,step and linear pressure control methods both can realize target pressure following,and the deviation is less than 5 bar.Linear pressure control can realize the target pressure change rate following,which can reduce the state change of solenoid valve,with small working noise,and is beneficial to prolong the life of solenoid valve.4.Through simulation and test validation,fully-decoupled regenerative braking system can realize the coordination control between motor brake and hydraulic brake,and test result meet the pressure control index.The energy recovery ratio can reach above 60%below 0.3g.