Research on mode transition control for single-shaft parallel hybrid powertrain

During the low vehicle speed condition, engine idling stop plays a remarkable role for single-shaft parallel hybrid powertrain. Due to the structure characteristics of this powertrain, when the powertrain system is working during the switching process from pure electrical driving mode to hybrid mode, the engine needs to be started and engaged into driveline via the clutch. The electric machine (EM) starting engine mode and the clutch engagement control problem might always be a hot issue in the area of hybrid powertrain control. Motivated by this issue, the driveline model and the model of dry clutch with its actuating mechanism are built. Considering the trade-off between the smoothness of mode transition process and the system transmission efficiency, and also combined with the uncertainties of engine resisting torque and load torque, a novel mode transition control method for single-shaft parallel hybrid powertrain is presented. Firstly, robust control theory is used to find a near optimal clutch engaging speed trajectory subject to the above performance index. Secondly, a PID controller is designed to implement the accurate speed tracking of clutch actuating mechanism, which ensures the fast and smooth process of clutch engagement. And then, the simulation works are performed under the conditions of urgent accelerating, slow accelerating, different engine resisting torques, and different vehicle load torques, respectively. Finally, the proposed method is verified in real vehicle test by the automatic code generation technique of vehicle controller. The results show that, the hybrid powertrain can implement fast and smooth mode transition process via the proposed control method, and the vehicle longitudinal jerk can be controller within the given reasonable range, which might ensure the mode transition smoothness. The proposed method might provide the theoretical basis for the control strategy design of real vehicle controller.