Research On Key Technologies Of Three-speed Planetary Transmission System For Pure Electric Bus

With the haze, the greenhouse effect and the other environmental issues becomingincreasingly severe, the development of the automotive industry is facing unprecedentedchallenges. Increasingly scarce of the oil resources makes it an urgent need for a new cardriven approach to replace the traditional internal combustion engine driven mode. Electricvehicles, with the features of high energy efficiency, diversification of energy sources,environment-friendly and so on, become an ideal alternative power source and the futuredirection of the automotive industry.The application of electric drive technology has a bright future in the high-powercommercial vehicles, which puts forward higher requirements for the traction ability of theelectric drive system. As to the direct drive type of pure electric vehicles, raising the ratedpower and rated torque of the drive motor is the only method to achieve the goal. Theapplication of the automatic transmission technology in the pure electric vehicles greatlyreduces the need for the performance of the drive motor, as well as improves the dynamicperformance and the energy efficiency of vehicles. The planetary automatic transmissionsystem, which is widely used in the traditional internal combustion engine vehicles, due toits reliable performance and excellent shift quality, still has a very high value on the pureelectric vehicle transmission system.In this paper, focusing on the pure electric bus, I summarize the key theories andtechniques of planetary gear system when applied to pure electric bus, and do the followingresearch aspects:1) Parameter matching for the pure electric bus power system. According to the givenvehicle parameters and power indicators, the power system component selection andparameter matching is achieved through the analysis with vehicle dynamics. Then thestrengths and weaknesses of various transmissions are compared to determine planetary gearsystem as the shift program for pure electric bus. Then the number of gears and the speedratio range is determined.2) Principle development and function checking of planetary gear system. Accordingto the results of parameter matching, planetary line structure type and shift control logic isdesigned. The shifting principles of planetary transmission system and the operating state ofeach gear are analyzed using leverage method. And a hydraulic system is matchedreasonably. With the parameters of mechanical system and hydraulic system obtained theclutch torque capacity is checked. Then the planetary transmission is modeled three-dimensionally using CATIA software. Then I calculate the moment of inertia of thevarious transmission components. And further the equivalent moment of inertia under eachstate of the transmission gear is obtained.3) The vehicle power system modeling and simulation. With the system parametersmatched and calculated before, pure electric vehicle power system is modeled based on thetoolbox Simdriveline from Simulink, including motor output model, vehicle dynamics model,planetary transmission model and controller model. Then the model is simulated to verifywhether the parameters obtained before can meet the power requirements of electric buses.4) Electric drive powertrain shifting control strategy. The shifting control theory isproposed for electric drive powertrain, namely the transmission output power should alwaysmeet the power requirements drivers express through the accelerator pedal. On this basis,come out of the electric drive powertrain control strategy of shift points and shift process, ofwhich the principles and implementation are analyzed.