Research On Clutch Pressure Control For DCT Shifting Process

Dual clutch transmission (DCT) has become the most popular automatic transmis-sion due to its high transmission efciency, quick and no power interrupt shift and gooddriving comfort feeling.DCT’s shifting process is achieved by engaging one clutch while disengaging the other,calling clutch-to-clutch shift, which can be divided into torque phase and inertial phase.Thus DCT’s shift quality is largely determined by the control performance of the twoclutches, especially the control of inertial phase, which is the main period that shiftingshock generates. Besides that, the quickness and precision of clutch actuator’s action alsoshows great influence on shift quality. For DCT with wet clutches, it is the proportionalpressure solenoid valve (PPSV) that plays the role of clutch actuator, which regulates thepressure in clutch chamber to control clutch’s movement. Therefore, a quick and precisepressure response is required for good quality shift. However, considering the fact thatthe clutch’s pressure exists fluctuation and its response speed can be influenced by oil’stemperate and bulk modulus variation, together with PPSV’s high nonlinearity, which allgo against the pressure’s quick and precise response, hence it is essential to apply pressurecontrol for PPSV.To solve the problems above, in this paper, a two-close-loop shift control system isdesigned for wet type DCT, namely introducing PPSV’s pressure control (inner controlloop) into inertial phase control (outer control loop).Firstly，for inner control loop，a control-oriented three order nonlinear model is de-veloped based on PPSV’s dynamics analysis, Newton’s second law of motion and fluiddynamics, and a pressure tracking controller of PPSV is designed nextly using Back-stepping technique. Considering that the information of PPSV’s spool displacement andvelocity can not be measured but is necessary for the pressure tracking controller, a non-linear reduced order observation is thus developed.Secondly, for outer control loop, a clutch slip speed-tracking control scheme is adoptedfor clutch slip control in inertial phase, with controller implementation taken into account. A control-oriented DCT model is developed and the even-flatness technique is used forcontroller design.Finally, both the simulation model of PPSV and vehicle equipped with DCT aredeveloped respectively in AMESim, together with a DCT system HIL (Hard-in-the-Loop)platform established for controller verifcation. Simulation and experience results showthat the observer based pressure tracking controller is efective in PPSV’s quick andprecise pressure control. What’s more, by comparing the shift quality with that withoutpressure control, the pressure-speed two-close-loop shift control demonstrates its excellentperformance in shift quality improving.