Optimized control of engine start assisted by the disconnect clutch in a P2 hybrid automatic transmission

Abstract

Abstract Instead of using conventional starter, engine can be started through slipping of the disconnect clutch in P2 hybrid automatic transmission. However, both riding comfort and engine-start time are challenges for control of the starting process. In order to achieve smooth and quick engine start, this paper proposed an optimized control strategy with respect to different engine-start situations. Firstly, a model of P2 hybrid powertrain is developed to characterize the transient behavior during engine start and provide support for developing control strategies. A multiphase control strategy is then proposed to cope with the control objective of either good riding comfort or short starting time depending on different driving situations. A nonlinear feedforward-feedback controller based on differential flatness and proportional-integral-derivative (PID) algorithm is developed to regulate the current of direct operating solenoid valve. Thus the pressure of the disconnect clutch can be fine-tuned and good tracking capability for the reference trajectory of engine speed can be realized. Finally, simulation and test results demonstrate that the proposed control strategy and controller can satisfy different requirements for engine start. Both riding comfort and engine-start time of a P2 hybrid vehicle can be effectively improved in the engine starting process.