Research On Key Technology Of Electric Oil Pump And Hydraulic System Based On Hybrid CVT

With the development mode of the world economy from high energy consumption to lower,reducing vehicle exhaust emissions and fuel consumption have become the development direction of automobile industry for all countries in the world.On this occasion,most of the vehicle companies such as Volkswagen,Porsche,Geely,and Changan also responded positively to the government's call for energy-saving and emission reduction.They all proposed their own new energy vehicle technology solutions and the deadline to stop selling traditional fuel vehicles.In order to accelerate the development and transformation of the automotive industry,the Chinese government has established a number of industry standards and subsidies in the development of new-generation automotive technologies,including the earliest proposed“eight vertical and eight horizontal”strategy,as well as the recently implemented“double-point integration standard for fuel consumption of passenger car enterprises”,etc.Significant achievements of new energy automotive technology have been obtained after years of development.China has become a world leader in the production and sales volume of new energy vehicles.But there are still many aspects that need to be improved.This project is based on the National 863 Program and the Hybrid CVT Project of the National Defense Science and Technology Industry Bureau.The focus of this article is mainly on the research of the hybrid CVT hydraulic system with the using of EOP(electric oil pump),the development of EOP and its driver,and the control strategy of CVT speed ratio.The verification of using EOP in CVT was implemented through establishing relevant simulation test models,developing the oil pump motor and hybrid CVT prototypes.The completed research works are as follows:(1)The hydraulic supply solutions of different automatic transmission for achieving engine start-stop control and implementing the features of hybrid vehicles are analyzed and compared.Based on the detailed research of hybrid CVT,the hydraulic system and oil supply schemes are determined in this project.Three kinds of oil supply plans:electric oil pump,mechanical oil pump and mechanical oil pump plus auxiliary electric oil pump are analyzed for the purpose of improving the efficiency of the developed hybrid CVT.And the EOP can save much more energy for hydraulic system compared with other schemes.(2)The pressure and flowrate requirements of the designed hybrid CVT are analyzed,and the maximum power and speed of the oil pump motor used for EOP are established.To verify the correctness of the adopted hydraulic system scheme,the hydraulic system model is established and simulated.At the same time,the I-P characteristics of the system solenoid valve,the primary solenoid valve,the secondary solenoid valve,and the clutch solenoid valve in hydraulic system are tested through experiments.And the principle of the solenoid valve controlling pressure is analyzed theoretically.(3)The steady state and transient models of the CVT varitor are established based on the analysis of the mechanism of shifting and controlling CVT speed ratio.The parameters like k_pk_s and K_i needed for designing speed ratio controller are obtained by experimental tests.The flowrate demaned for a given speed ratio change rate on a certain speed ratio is analyzed,considering EOP can adjust its speed to save much more energy.Finally,the speed ratio control strategy of the vehicle's main drive mode is studied.(4)The feasibility of using BLDC motor and PMSM motor on the given space dimensions as EOP drive source is studied with concerning the hydraulic system's power and speed requirements for oil pump motor.To analysis the performance of the designed oil pump motor,the ANSYS Electronics Desktop software is used to simulate the static and dynamic characteristics.And the performance parameters of the designed oil pump motor are obtained.By analyzing the heat-generating mechanism of the oil pump motor,the heat dissipation problem of the oil pump motor is also studied.The maximum working temperature of the oil pump motor is simulated by using ANSYS.And the results show that the cooling method can ensure that the temperature of the oil pump motor does not exceed the permitted temperature.(5)A drive controller is designed for the developed oil pump motor.The controller and the oil pump motor are not designed integrated for the inconvenience of integration.The development process used for designing the controller is the automotive V-mode method.Then the research focused on the speed control strategy of the oil pump motor,and the speed and current controllers are designed.Considering that the oil pump motor is built in the CVT,it is not convenient to use the corresponding speed sensor to measure the rotational speed.A sliding mode observer is designed to identify the speed of the oil pump motor.Finally,the designed control algorithm of speed controller and sliding mode observer are verified by simulation.(6)Based on the developed oil pump motor,drive controller and the designed hydraulic system,the simulations of the system pressure,clutch pressure,primary pressure and secondary pressure controller are conducted using the joint simulation of AMEsim and Simulink.The simulation results show that the designed controllers are stable,and each pressure controller can meet the pressure stability requirements.The pressure controller,oil pump motor speed controller,speed ratio controller and other related control algorithms are verified on the developed hybrid CVT protype by experiment.The test results show the accuracy of the simulation results.Finally,the efficiency of hybrid CVT is compared with the traditional CVT.