Study On Parameter Design And Shifting Control Strategy For Transmission System Of Electric Vehicle

Electric vehicle transmission system using fixed-gear decelerator or multi-speed transmission directly affects electric vehicle drivability and economy. Moreover, it has some influence on motor parameter matching. Compared with the fixed-gear decelerator, multi-speed transmission system could improve the performance of electric vehicle, lower the requirement of motor performance and extend the diving range. However, it would make the structure of transmission system complex and increase the weight and the cost of electric vehicle if too many gears are installed. In this paper, the parameters of electric vehicle powertrain were matched and two-speed automatic manual transmission scheme was presented. The gear ratios of transmission system were optimized by the established simulation model of electric vehicle. The comparative analysis between fixed-gear decelerator and two-speed transmission for electric vehicle was carried out, and a shifting control strategy for two-speed AMT without clutch was made. It was proved by experiment on a test bench established for this project. The main research work in this paper is as follows:â‘ The structure of electric vehicle driveline is analyzed. The parameters of drive motor, battery packs and transmission were matched according to the analysis of performance characteristics of motor and battery. And, the effect of transmission system is also taken into consideration. The analysis was focused on the effect of gear ratio and gear number on parameter matching of drive motor and performance of electric vehicle. The method of improving efficiency of motor through gear ratio optimization is studied.â‘¡The economy model of electric vehicle is built based on the dynamics theory of gear ratio optimization. It includes driving model, resistance model, transmission model, drive motor model, regenerative brake model, battery model and energy consumption model. The economy model could compute the energy consumption and further work out the driving range. The drivability model is also built to compare the drivability of different transmission systems. It includes maximum vehicle speed model, accelerating time model and grade ability model.â‘¢The gear ratios of fixed-gear decelerator and two-speed AMT are optimized according to the economy model of electric vehicle. The gear ratios are chosen based on the principle of best economy and adequate drivability. And then, the drivability and economy of two schemes are calculated. By comparison, two-speed transmission is much better than fixed-gear transmission and two-speed AMT are chosen to be used as the transmission of the electric vehicle.â‘£The shift process of two-speed AMT is analyzed, the shifting control strategy for the electric vehicle without clutch is made and the drive motor control in different shifting stages is studied. The test bench for two-speed AMT of electric vehicle is established, the simulation model for test is set up based on MATLAB/Simulink and dSPACE, and data acquisition and auto-control of test bench are achieved. The shift control strategy is proved by the test.