Improving gear shift quality in a PHEV DCT with integrated PMSM
Conference contribution, 2017
In this paper a hybridized Dual Clutch Transmission (DCT) is presented in which a traction Permanent Magnet Synchronous Motor (PMSM) is mounted on the input side of the even gears. As the motor has high power, it has a high inertia. This leads to increased shift time in Electric Vehicle mode (EV mode). In EV mode, ICE is shut down and both clutches are open and vehicle is driven by PMSM on even gears. Since both off going and oncoming gears are on the same shaft, there will be a torque interrupt during shifts in EV mode.
The main focus of this paper is the speed synchronization phase during torque interrupt shifts. Currently the speed synchronization is done by using PMSM only. This sometimes leads to slower shift times and a degraded drivability due to battery power limitations. The speed synchronization can also not be achieved by synchronizers alone as is done in traditional DCTs due to added inertia of PMSM.
This paper explains the detailed modeling of synchronizers for simulating speed synchronization times during torque interrupt shifts. The PMSM model is based on a loss map and inertia. The effects of the available power from the battery on speed synchronization are also modelled. A high level modeling is done for rest of the powertrain.
Based on simulations, first the increased synchronization time and its main limiting factors are discussed. A prediction model is also created which, before a shift is ordered by high level strategy, creates the speed synchronization trajectories for PMSM and synchronizer.
Based on prediction model, a high level supervisory control strategy is developed that will communicate between synchronizer and motor controller to ensure minimum synchronization time based on the limitations in synchronizer and battery.
The study can be extended to general treatment of clutchless multi-speed transmissions in electric vehicles and their effects on shift quality in general.