Simulation Study On Shift Control Of Two-Speed Wet DCT For Electric Vehicle

In the background of today's energy shortages and environmental pollution,electric vehicle has become the focus of automotive companies' competitive research and development rely on its advantage of using clean energy,less pollution,and low noise.With the advancement of electric vehicle powertrain technology,the transmission system in electric vehicle has gradually evolved from a single-speed reducer to a multi-speed transmission,thereby effectively improving the power and economy of the electric vehicle.Because the two-speed wet DCT has the advantages of high transmission efficiency,no power interruption in gear shifting,it has become a hot spot in the research and development of the domestic and foreign automotive industry.In the two-speed wet DCT,in order to make the actual torque of the clutch follow the target torque well during the shifting process,the actual engagement pressure of clutch must follows the variation of target pressure quickly and accurately.And In order to obtain less impact and sliding friction work during the gear shifting,the two-speed wet DCT needs to coordinate and control the target torques of two sets of clutch.Therefore,it is of great significance to study the shift control technology of two-speed DCT for the development of high-performance two-speed DCT transmissions.Through analyzing the research status of the two-speed DCT at home and abroad and combining with the theoretical research and actual engineering needs,this dissertation made an intensive research on how to improve the following character of clutch hydraulic control system and how to determine the control law of two sets of clutch target torque during the gear shifting of two-speed wet DCT.The main contents include:Chapter 1,the background and significance of the dissertation were expounded,the configuration schemes of the electric vehicle power system were introduced,and the characteristics of the electric vehicle transmissions were compared and analyzed.Furthermore,the structure and working principle of the two-speed wet DCT were elaborated.And the research status of the two-speed DCT at home and abroad was summarized,among which the control law of the clutch target torque in the two-speed wet DCT gear shifting and the clutch hydraulic control system were emphatically analyzed.Finally,the main research contents and technical route of this dissertation were listed.Chapter 2,the UDDS cycle model,the driver PID model,the first-order dynamic model of the drive motor,the clutch transfer torque model and the two-speed wet DCT gear shifting dynamic model were established respectively.The models mentioned above were introduced into the dynamics model of electric vehicle that equipped with two-speed wet DCT,which provides a theoretical basis for the following study.Chapter 3,the formulation method of shifting rules of two-speed wet DCT in electric vehicle was analyzed.The method of two-parameter gear shifting rule was adopted to determine the shifting rules of the two-speed wet DCT in electric vehicle after considering the power performance and economy of the whole vehicle.The validity of the models and shifting rules established in this dissertation were verified by the simulation platform.Chapter 4,the control method and following character of the clutch hydraulic control system for two-speed wet DCT was studied.The mathematical model of clutch hydraulic control system was built,and the accuracy of the model was verified by test.On the basis above,the fuzzy PID control and PID control with simple control structure and easy to implement were simulated and compared.The results show that the clutch hydraulic control system controlled by fuzzy PID has better following character.Finally,the influence of relevant parameters on the following character of hydraulic system was analyzed by orthogonal test design,and the optimal combination which makes the following character of clutch hydraulic control system in two-speed DCT relatively better was selected.Chapter 5,the integrated control strategy of the two-speed wet DCT's gear shifting process was developed and the determination of the clutch target torque during the gear shifting was studied.Regarded the impact and sliding friction work as quadratic functional,the objective torque of clutch was determined by the genetic algorithm linear quadratic optimal control.By comparing,the clutch target torque currently applied to the two-speed wet DCT fixed slope change and the clutch target torque based on genetic algorithm linear quadratic optimal control,it is concluded that the latter one can make the two-shift DCT have More comfortable shifting quality.Chapter 6,the research results and conclusions of the dissertation were systematically summarized,and the prospects of further research work were proposed.