Research On The Gearshift Control Strategy For High-power Automatic Transmission

Benefits from excellent torque transmitting capacity, good shifting quality, smooth launch capacity and perfect acceleration performance, the high-power automatic transmission has become the first choice of off-road vehicles, construction vehicles, high-end commercial and other heavy vehicles.Gearshift control strategy is a key technology of the automatic transmission. Based on the Jilin university project in cooperation with China FAW Group Corporation R&D Center, this paper carried out the development of gearshift control strategy of a high-power AT.The gearshift control strategy has four key points. Firstly, build a concise and effective transmission model. Secondly, investigate the working characteristics of friction disks. Thirdly, control the off-going clutch to release in time. Fourthly, get the optimum output torque in inertia phase. Focus on the key points which was pointed just now and aimed on good shifting quality, an automatic transmission gearshift control strategy was developed.Based on a certain automatic transmission, this paper researched on the structure and working principle of solenoid valve, gearshift control valve, clutch and planetary gear mechanism, next Simulink model to research their working characteristics was built, based on that a vehicle dynamics model was built. Further, a test bench was built to get input and output characteristics of the hydraulic system of the automatic transmission, the results proved that the Simulink model was correct. At last, this paper did a test for the friction disks, and the characteristics of coefficient of friction were researched when the rotate speed, temperature and work pressure was different.Chose the vehicle dynamics model to be simulation platform, and take 2 to 3 power on shift for example, the working characteristics of off-going clutch and on-coming clutch was researched when the AT shifting. The AT shifting process was divided into four parts, then in their torque phase and inertial phase, the torque transfer characteristics of off-going and on-coming clutch was researched with the lever analogy method.Based on the torque transfer characteristics of the clutches, a gearshift control strategy was developed; it was made up of off-going clutch control strategy and on-coming clutch control strategy. The two clutch control strategy was divided into several stages respectively, next the control objectives of each stages was researched, and then the control strategy run the each stages in turn. In the torque phase, based on clutch slipping, the off-going clutch control strategy was developed, and the off-going clutch was released in time. In the inertial phase, the shift quality was influenced by the output torque of transmission. the on-coming clutch control strategy was developed based on the optimum output torque. Weight of three shift quality evaluation indexes was researched by Analytic Hierarchy Process; based on the weight, the three shift quality evaluation index was normalized, so that it was convenience to compare different shift quality. Shift quality of different output torque was researched by orthogonal design, an optimum output torque with best shift quality was found, this optimum output torque can be transform into optimum turbine acceleration, and then the error value of actual turbine acceleration and optimum turbine acceleration as an input signal of the PI controller to adjust oil pressure of the on-coming clutch, so an accuracy control process come out. At the end this on-coming clutch control strategy achieves an optimum output torque and optimum shift quality.The gearshift control strategy run on the vehicle dynamics model, it worked, so proved that the strategy was correct; A road test for an high-power off-road vehicle controlled by d SPACE was carried out, next, the transmission working characteristics of parameters and measures in shifting process was researched, take the shifting quality which result from the original TCU’s control strategy as test index, the result of road test indicated that the AT gearshift control strategy could achieve a gearshift function and the shifting quality could reach the test index. So the AT gearshift control strategy was proved works.