Abstract: In order to reduce the longitudinal impact of the vehicle caused by engine start and stop during the mode transition process between e-CVT hybrid mode and pure electric mode, an optimal control strategy of engine shutdown is proposed for the power-split hybrid system. Firstly, the power-split hybrid powertrain model is established based on the Matlab/Simulink platform, and the crankshaft angle which is the most conducive to the restart of engine is determined as the optimal engine stop position. Secondly, the optimal speed trajectory during engine shutdown is designed by the dynamic programming algorithm. When the engine speed is less than 200 r/min, the motor and brake are coordinated to dynamically adjust the crank angle in real time, so that the engine stops near the optimal target position. Finally, the optimal control strategy of engine shutdown is verified by simulation and bench test. The results show that the proposed control strategy can make the engine stop within ±6° of the optimal position, ensuring the ride comfort of the vehicle in engine start and stop stages.

Key words: power-split hybrid system, engine shutdown, optimal engine stop position, dynamic programming algorithm