Research On Ratio Optimization And Shift Control Of EV Automatic Transmission System

At present,electric vehicles(EV)are equipped with single-stage reducer.In order to further improve the power and economy of EV,automatic transmission system is a significant research direction.Automated Mechanical Transmission(AMT)has the advantages of simple structure and high transmission efficiency which is very suitable for mounting on EV.Based on an EV with a single-stage reducer,in order to improve the power and economy of the vehicle and match the multi-gear automatic transmission system,the research works have been done as follows:(1)The vehicle dynamics is analyzed according to the characteristics of the power transmission system of EV.The optimization calculation part of the automatic transmission system is modeled in Matlab/Simulink.At the same time,the whole vehicle performance simulation model is established in AVL Cruise.(2)On the basis of preliminary determination of the range of transmission ratio based on dynamic requirements,the optimal transmission ratio and gear number of automatic transmission system are optimized by using dynamic programming algorithm,and the power and efficiency MAP of driving motor are established by using the optimization results,so as to establish the shift law and solve the inaccurate influence of the shift law setting in the general optimization process when the optimal transmission ratio is unknown.The performance simulation in AVL Cruise shows that after matching multi-gear transmission,the power and economy of the vehicle are improved significantly.(3)Aiming at the characteristics of short shift time and rapid change of dynamic characteristics,the appropriate shift performance evaluation index is selected.Through dynamic analysis of the shift process,the function expression of the shift performance evaluation index in each shift process is established.Combining with the configuration of automatic transmission system,based on time logic and space logic,the time-optimal shift control strategy is proposed to improve shift time.Based on the calculation of shift performance function,it is proved that the control strategy in this paper can give consideration to both dynamic performance and ride comfort in the stage of driving motor lifting moment.The AMESim simulation results show that the strategy can effectively reduce the impact force between gears in the gear shifting stage.(4)The vehicle powertrain system bracket,the equivalent inertia flywheel group,and the cooling water circulation system are designed.The vehicle power system test bench is built.A detailed test procedure is developed.The corresponding test control program is written.The static shift test and the dynamic shift test of the automatic shifting system are completed.The test results are analyzed to demonstrate an improvement in the shifting time of the control strategy.