Analysis And Research On High Efficiency And Safety Braking Of Hybrid Electric Vehicle

Regenerative braking is an important way to save energy for HEV or EV.On the one hand,to improve the regenerative braking time of motor,on the other hand,to formulate a reasonable and optimized downgrade strategy can better adapt to the efficient working range of motor and improve the energy saving rate.In order to ensure braking safety,regenerative braking stops working under emergency braking.The ABS braking system is used to control the regenerative braking.The special working conditions of drivers or pavement are considered to ensure braking efficiency.At the same time,the influence of steering system and braking system on stability should be considered in braking process to ensure safe and efficient braking.In this paper,a hardware-in-the-loop simulation platform based on the body stability control system(ESC)and the mechanical automatic transmission system(AMT)is established.The dynamic model and real-time road condition model of the vehicle are established by using Labview and Trucksim.The communication between the system and ESC and AMT is carried out through CAN network.Hardware-in-the-loop simulation platform can accurately calculate the vehicle state,simulate various complex working conditions,and lay the foundation for vehicle verification.Taking a hybrid bus with AMT as the research object,the braking moment statistics analysis is carried out to classify and identify the running status of the vehicle.According to the results of braking moment analysis and operating conditions,three kinds of downshifting strategies to improve regenerative braking efficiency are proposed,which are regular downshifting strategy,stochastic dynamic programming(SDP)based downshifting strategy and dynamic stochastic programming(DP)based downshifting strategy.Regular downshifting strategy depends on the speed of the vehicle according to the agreed rules,and SDP-based downshifting strategy gives the appropriate downshifting gear according to the historical data of the vehicle and the current status of the vehicle.DP-based downgrading strategy needs global information,so it can only be used as a reference value to represent the maximum efficiencyof regenerative braking.The simulation test and hardware-in-the-loop test bench verify the proposed downshifting control strategy.The results show that the regular and SDP-based downshifting strategy improves the efficiency of regenerative braking,but there is still a certain gap with the DP-based downshifting strategy.When the braking intensity required by the driver is too high,the ABS function may be triggered in the process of braking energy recovery.The braking time is short and the vehicle is easy to lose stability.The focus is on the stability control of the vehicle,and the braking energy recovery withdraws from the control.Aiming at ABS process,the problems of speed estimation,wheel speed correction,bumpy road identification and control strategy are analyzed.Vehicle speed is estimated according to the maximum wheel speed and the maximum deceleration that the body may achieve.According to the characteristics of wheel speed during turning,the wheel speed is corrected to the center of axle to effectively reduce the false trigger of ABS.For bumpy pavement,the change range and frequency of wheel deceleration are identified,and the corresponding measures are taken to improve the braking performance.The stability in braking process is analyzed and verified from many aspects.In terms of the coupling structure between braking system and steering system,the method of optimizing the position of ball head is put forward,and the optimization and test are carried out from the aspects of the back inclination angle and the inside inclination angle of the main pin,the structure and stiffness of the leaf spring,etc.The test results show that the proposed improvement measures effectively improve the braking stability.