Study On Shift Control Strategy Of Wet Dual Clutch Transmission

The choice and design methods of transmission influence the driveablity, the fuel economy, as well as the driving comfort and pleasure of automobiles. With two clutches working alternatively, Dual Clutch Transmission (DCT) not only overcomes the torque interruption of Automated Manual Transmission (AMT), and realizes torque-interruption-free shift, but also inherits the advantage of high efficiency of Manual Transmission (MT), so it has been becoming the development hot spot of car manufactures all over the world. In addition, DCT may be fitted in front, front-longitudinal and rear longitudinal formats, so it can be adapted in small and compact passenger cars. Furthermore, it can be easily adapted to all-wheel-drive vehicles and trucks, which broadens its range of application.Currently, MT still occupies the major market in China, development of DCT can directly make use of the production equipment of MT that would result in less investment and more convenient facilities improvement, therefore, DCT has vast potential for future development in China. Based on building of the dynamic models of wet DCT system and clutch hydraulic pressure control system, the shift control strategies of wet DCT and the control algorithms for the pressure of clutch have been studied deeply in this paper. The main contents of the paper are as follows.(1) The current research status and development trends of DCT have been summarized. The working principle and power transfer routes (i.e., power flows) for each gear position of DCT have been explained in detail.(2) The constituent of wet DCT system and the working principle of its hydraulically actuating system have been introduced briefly. And the dynamic model of the powertrain system of DCT including the engine, torsional damper, wet dual clutches, gearbox, final drive, wheel, etc., has been established.(3) The hydraulic control system of DCT has been designed, and then, the functionality and working principle of main components of the designed hyardulic system have been introduced. And the mathematic model of the hydraulic control system of DCT including gear bump model, clutch vavle model, cylinder model, etc., has been built. Using the method of frequency domain analysis, the stablity of the designed hydraulic control system has been verified with Bode and Nyquist diagrams.(4) The control strategies of dual clutches, synchroniers and engine, especially that of clutch pressure, during the upshift and downshift process, have been studied deeply, using shift time, shift jerk, and friction work as the evaluation indices. To reach the goal of reducing shift jerk and friction work, the control strategy of clutch pressure has been made and the target oil pressure of clutch has been determined. Based on that, a PID controller and a fuzzy controller for clutch pressure control during shift process have been designed, and the simulation models have been built using MATLAB/Simulink/Stateflow platform. These two proposed control algorithms have been compared through simulation experiments. The simulation results show that:PID control algorithm is better than fuzzy control algorithm, which can trace the target oil pressure of clutch better, and produce smaller jerk and less friction work during the upshift and downshift processes of DCT.