| Automobile technology is developing in a direction of saving more energy and friendly environment. New technologies are emerging. For the transmission system, from the 1960s, semi automatic mechanical transmission has been made which improved from mechanical clutch and manual transmission into AMT now. Since the 1970s, Automatic transmission (AT), which is composed of torque converter and planetary, is greatly improved. AT is at a dominant position in the market of the United States and Japan. In 1980s, due to metal belt invented, the essence problem of strap transmission was resolved which made rapid increase of market sales. The direct shift gearbox (DSG), developed from ATM, will be one of the major auto transmission to be developed in the future. To develop transmission system in China, there is a common key technology among AMT,AT,CVT,DSG which is wet clutch starting control. The key technologies of CVT wet clutch control researched in this paper include: dynamic models of mechanic transmission and hydraulic system of transmission, the friction characteristics of wet clutch, theory analysis of engaging process of clutch, ECU and engineering software for products. The research achievements are shown below.1) Based on mechanic theory, hydraulic system theory and mathematics model of engine and torque converter, the status-space model X = AX(formats 2.26) is established. And this is the base of engaging process analyze and control strategy optimization. From the simulation results for some working conditions, we can see that, for coefficient of friction with positive slope, the torque is convergence and for the coefficient of friction with negative slope, the torque is the divergence, which is according with actual tests. We can also see that the clutch pressure fluctuations have great influence on torque transfer. The whole system is oscillating with the fluctuated clutch pressure under certain conditions. That is to say, the turbo,primary friction plates and slave friction plates oscillate together.2) The wet clutch of electronic control system is developed which includes hardware system and software system. Software system is composed of two parts: one part is the control method of the hydraulic components, the other is the system control method based on control theory. Pressure sensors, speed sensors, shifting sensors and the oil temperature sensor characteristics are introduced. The drive circuit design of high-speed on-off valve is the key of the control system. The high-speed on-off valve's characteristics is analyzed and simulated, which is the foundation of the drive circuit design of high-speed on-off valve. Driving circuit is designed using three different methods which are the high-side drive and low-side current sensing, low-side drive and high-side current sensing, high-side drive and high-side current sensing. The design of high-side drive and high-side current sensing can meet the requirement of test bench testing and road testing.3) The factors of friction of clutch are researched. A test bench is built and friction coefficient of CVTF-EXx, CVT-Fx,and EZL-7xx three types of oil is tested. By using CVTF-Exx, the impact of oil temperature on friction coefficient is studied. Test data show that when oil temperature is becoming higher, the value of friction coefficient will be smaller. With the test data, the curve of friction coefficient with the temperature is fitted. Researching results of the impact of clutch pressure on the friction coefficient show that the changes of the oil pressure have little impact on friction coefficient. In the study of the impact of temperature on the friction coefficient, we have found that before sliding speed reaches 100r/min, the coefficient of friction rises sharply, but declines after 200r/min, then stabilizes.4) According to the actual process of the wet clutch engagement, we give object control and evaluation for four stages: free-stage, oil-filled stage, slipping-stage and synchronous engaging-stage. The study found that free-stage has no effect on performance, to be end as soon as possible; the pressure and oil-filling time in oil-filled stage are the key, which directly determines the speediness of the starting; slipping-stage decides the comfort of the starting, and the friction coefficient is important for this stage, synchronous engaging-stage don't product slipping loss, and don't impact the jerk of the vehicle, needing to be finished fast. According to control object and evaluate guidelines, the fuzzy control algorithm is developed and different experiments verify the correction of algorithm.5) With the debug of CVT control software, the experiment is finished in two years which includes test bench experiment, 60℃high temperature test in Tulufan of Sinkiang province, 4647 meters high altitude test at Kunlun mountains, as well as the minimum temperature of -32℃test at Heihe. The achievement is useful for software development of clutch control and calibration flow.6)Calibration of wet clutch is the key technology of software product. The basic model of starting wet clutch is calibrated basing on common characteristics. The revised model of circumstance is calibrated basing on asperity working conditions of vehicle. The attenuation model is calibrated basing on key parts attenuation characteristics through fatigue testing (such as, clutch worn, gap between clutch plates, hydraulic valve worn, attenuation of elec-magnetic valve). On the basis of the three calibration work and safety modes, the key technology problems of product are resolved in this paper and this paper contributes a support to the self-design auto electronic technology.
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