The Research On Electro-hydraulic Proportional Control System Model And Optimization Of Belt Continuously Variable Transmission

As the driving comfort,dynamics and fuel economy for vehicle have become increasingly demanding by people,the metal belt continuously variable transmission(CVT)with high-power density is becoming more favored by market,for the reason that it can make the engine operates according to the optimum fuel economic or the optimum dynamic characteristic curve at all times.The large automotive and automatic transmission companies from domestic and overseas are committed to develop a new generation of high-power density CVT.The electro-hydraulic proportional control system(EPCS),whose performance directly determines whether the car with CVT can achieve the ideal driving comfort,dynamics and fuel economy,is a key part of CVT.Additionally,there is a big gap between the domestic and foreign countries in the development of EPCS.Therefore,the model and performance optimization for CVT’s EPCS are studied in this paper based on the national and international special cooperation project for science and technology,“Associated Research and Develop a New Generation of High-power Density CVT for Cars”(2014DFA70170).The main works that have been carried out and completed are as follows:(1)The solenoid control strategies of transmission control unit(TCU)are studied.The functional requirements of CVT to EPCS are analyzed.The hydraulic principle diagram of EPCS is designed and the TCU solenoid control strategies are established from the aspect of industrialization.The validity of the established TCU solenoid control strategies is verified through the tests of clutch engagement,torque converter lock-up and Worldwide-harmonized Light vehicles Test Cycle(WLTC)condition.The results show that the established TCU solenoid control strategies can realize the functional requirements of CVT to EPCS very well.(2)The model of pressure spool in throttle area and the influence of clearance to spool’s operating characteristics are studied.The steady flow force mathematical model in throttle area of pressure spool is set up.The flow field calculation model for throttle area of the spool considering fitting clearance between the spool and valve body is constructed.The test platform is built up to verify the correctness of the spool throttle area model considering fitting clearance.The results indicate that the simulation results of the spool throttle area model considering fitting clearance is very consistent with thetest.The effect of fitting clearance on the throttle opening,the inlet jet angle and the steady flow force of spool throttle area are analyzed based on the verified model.(3)The model of proportional solenoid and the effect of dither signal to proportional solenoid’s performance are studied.The proportional solenoid’s structure and working principle are analyzed.The mathematical models of electric,magnetic,mechanical and hydraulic fields in proportional solenoid are established under the consideration of driving circuit.The proportional solenoid model is built up combined Ansoft Maxwell with AMESim software.The result shows that the simulation result of the established proportional solenoid model is in good consistency with the test.The effect of frequency and magnitude of the dither signal on the pressure hysteresis and dynamic response of proportional solenoid are analyzed respectively.(4)The steady flow force compensation of the internal flow spool is studied.The effect of steady flow force on the pressure control accuracy of electro-hydraulic proportional relief valve(EPRV)is analyzed from theoretical and experimental aspects.The turbine bucket profile is designed in spool groove to compensate steady flow force.The turbine bucket profile is optimized based on the response surface method.The effect of optimized spool on the pressure control accuracy improvement of EPRV is verified by test.The results show that the optimized spool can obviously compensate steady flow force and improve the pressure control accuracy of EPRV.(5)The power loss reduction of CVT oil pump is studied.A new hydraulic scheme,which adjusts the effective displacement of oil pump using the pressure of third hydraulic circuit to realize the variable pump and controls the primary and secondary pressures with Smart mode,is proposed.The power matching mathematical model of the new hydraulic scheme is established.The vehicle,TCU solenoid control strategies and hydraulic power amplification module are formed a closed loop through the Silver virtual integration platform to place software in loop simulation.The power matching of single pump,quantitative pump and the new hydraulic scheme are compared in the conditions of full pedal launch,rapid acceleration and New European Driving Cycle(NEDC).The efficiency improvement effect of CVT by the variable pump and Smart mode of the new hydraulic scheme are verified by the bench test respectively.The results indicate that the new hydraulic scheme can obviously decrease the power loss of oil pump and improve the CVT transmission efficiency.