Research On Shift Schedule And Motor Control Strategy Of Two-speed Pure Electric Vehicle

In recent years,while electric vehicles are developing at a high speed,there are still some shortcomings that limit their use scenarios.At present,electric vehicles are mainly equipped with single-speed transmissions,and it is difficult to balance the dynamic performance and economy performance,thereby affecting the vehicle’s range.The multi-speed transmission can make the vehicle achieve the same dynamic performance with a smaller motor and improve the efficiency.To further improve the cruising range of the electric vehicle,a multi-speed transmission can be used instead of the single-speed transmission.For electric vehicles equipped with multi-speed transmissions,the shift schedule and motor control strategy will also have an impact on the economy and dynamic performance of the vehicle.The main work done in this paper is as follows:(1)For the defect of the single-speed electric vehicle,the structure of the twospeed electric vehicle powertrain system is determined and the parameters are matched.The design index of the two-speed electric vehicle was formulated,According to the design index,the parameters of the drive motor are matched,and the appropriate drive motor is selected.The boundary conditions of the transmission ratio are determined,in order to improve the economic performance of the vehicle,the high-frequency working area of the mainstream test conditions is analyzed,and the gear ratios of each gear are determined based on this.After the parameters of the powertrain system are determined,the vehicle performance indicators are found to meet the design requirements.(2)The vehicle model of the two-speed electric vehicle was built,and the control strategy of the two-speed electric vehicle was studied.The shift schedule of the internal combustion engine and the pure electric vehicle were compared and analyzed.A twospeed electric vehicle powertrain system including driver model,power battery model,drive motor model,transmission system model and vehicle longitudinal dynamics model was built in LMS AMESim,Establish VCU including MCU,TCU and driver model correction unit in Matlab/Simulink platform.The vehicle control strategy and shifting schedule were established.In addition,in order to compare the dynamic and economic performance of the two-speed electric vehicle and the single-speed electric vehicle,the parameters of the single-speed electric vehicle were matched and the vehicle model was built.(3)Aiming at the phenomenon of frequent shifting,the shift schedule of efficiency difference method is proposed and simulation analysis is carried out.The co-simulation platform of AMESim and Matlab/Simulink was built.Selected the appropriate test conditions.The two-speed electric vehicle and single-speed electric vehicle were simulated respectively.The simulation results show that compared with the single-speed electric vehicle,the dynamic and economic performance are both improved.Aiming at the frequent shifting phenomenon in the simulation process of the two-speed electric vehicle,the efficiency difference of the motor is taken into account,and the efficiency difference based downshift schedule is proposed.Considering the economic performance,the following situation of the vehicle speed and the number of shifts,the most suitable efficiency difference value is determined.The simulation results show that compared with the speed difference,the efficiency difference based downshift schedule is improved in terms of economy,speed following and frequent shifting.(4)In order to better reflect the driver’s intention,improve the dynamics of the vehicle under partial load and further alleviate the frequent shifting of the vehicle,a control strategy of the drive motor based on the torque on the wheel is proposed.The results show that the new motor control strategy can better balance the dynamic shifting rules and economic shifting rules.The simulation results show that compared with the original motor control strategy,the new motor control strategy can greatly reduce the number of shifts and improve the cycle completion,but the power consumption increases.By combining the new motor control strategy with the efficiency difference based downshift schedule,the number of shifts can be further reduced and the cycle completion degree can be improved without significant changes in economics.Finally,based on the simulation results of each combination,the scenarios used by each combination are analyzed.