Research On Pneumatic Modulating Actuators Of Regenerative Braking System In Electric Bus

With the rising concern in energy crisis and environmental issues,electrified vehicles become a worldwide research topics.As an important energy-saving technology,the regenerative braking system can effectively improve the energy economy of a vehicle.However,the introduction of regenerative brake makes the friction brake changes in real time,so that the pressure regulation on the brake chamber put forward higher requirements,the brake pressure modulator need to adjust the pressure on the friction braking faster and more precise.The brake pressure modulators of regenerative braking system of electric bus are investigated by means of computer simulation and hard-warein-loop(HIL)test in this paper.An electro-magnetic-mechanical-pneumatic coupling model of a solenoid on/off valve,which is widely used for pressure adjustment,is built.The response process is analyzed by simulation,the PFM,PWM and the upstream pressure characteristic of the valve is studied by experiment.Considering the control accuracy,the effective duty,the service life and other factors,the control signal frequency is selected.A logic threshold control algorithm is proposed and verified by experiment.Due to the frequent operation of the solenoid on/off valve will bring noise and life issues,so consider using proportional valve instead of solenoid on/off valve to adjust the brake pressure.A nonlinear mathematic model of proportional relay valve is established and verified through open loop experiment.The effects of main physical and geometrical parameters on characteristics of the valve are analyzed.A PI controller with feedforward and anti-windup compensation is designed.Experiment shows that the designed controller improves the pressure regulation precision and robustness.A new type of regenerative braking system,which use a proportional valve as the pressure modulator,is proposed.A test bench with real-time simulation system xPC target is built,and HIL test is processed to compare the control effect of solenoid on/off valve and proportional valve.The test results shows that the proportional valve has a batter control accuracy,and improves the brake comfort.So proportional valve have an advantage in application of regenerative brake systems.