| Regenerative Braking System (RBS) is one of the main means to achieve energy savingand improve energy utilization efficiency for electric vehicle. RBS has two sets of brakesystem, hydraulic brake system and motor brake system. In the process of braking energyrecovery, in order to recover the braking energy as much as possible, give priority to usemotor brake. When the braking force of motor cannot meet the needs of the brake, use thebraking force of hydraulic to compensate to meet the total brake demand of driver. Becausethe two sets of brake system work at the same time, so it is necessary to control themcoordinately, which plays an important role in the recovery of braking energy, theconsistency of braking feel and the braking security. In order to achieve the coordinatedcontrol of hydraulic braking force and motor braking force of RBS, it requires the accurateand independent regulation of wheel cylinder pressure along with the change of motorbraking force to meet the total demand of braking. The method of controlling brake pressurehas ladder control and linear control two ways. The linear control can control wheel cylinderpressurization rate more accurately, then the real brake pressure can follow the target brakepressure better. The linear control can avoid the pressure fluctuation and noise due to thefrequent opening and closing of solenoid valve when use the ladder control.Based on the existing RBS of laboratory, analyze the mechanism, characteristics andtest of linear valves and electric hydraulic pump of hydraulic regulate unit which used tocontrol the brake pressure of hydraulic. Then research on the control method of the linearvalve and linear control algorithm for braking pressure. The main contents are as follows:(1) Analyze the regenerative braking system and control needs of braking pressure inthe process of regenerative braking. The key part of controlling the brake pressure-hydraulicregulate unit includes solenoid valves and electric hydraulic pump. Analyze the structure, working principle, mechanical movement, work status and the flow characteristics of linearvalve and the structure and working mechanism of electric hydraulic pump. Study on thePWM control of linear valve and the change rate of the brake pressure, then determine thefactors that influence the change rate of brake pressure. These provide theoretical basis forstudying on the control method of linear valve and developing the linear control algorithmfor braking pressure;(2) Experimental analysis of P_V characteristic of hydraulic brake system, then test theelectrical response characteristic and hydraulic response characteristic of linear inlet valve,linear change-over valve, outlet valve and electric hydraulic pump. The above researchesprovide important experimental basis for studying on the control method of linear valve anddeveloping the linear control algorithm for braking pressure;(3) Study on the control method of linear valve. The method includes the currentgeneration module and feedback correction module two parts. Train the BP neural networkmodel by the test data sample sets. Gain the control current of linear valve by theaccomplished neural network model and determine the duty cycle of the control signal by thefeedback correction module. Then develop the linear control algorithm for braking pressure,firstly to divide the state of pressure control in the process of regenerative braking, secondlyto develop the linear control algorithm for each state of braking pressure control;(4) By the RBS hardware in the loop test bench based on the dSPACE, the effectivenessof the linear control algorithm for braking pressure of regenerative braking system onelectric vehicle is validated. |
