Control strategy for dual-mode power split HEV considering transmission efficiency

In this paper, a control strategy based on transmission efficiency for a dual mode power split-type hybrid electric vehicle (HEV) that considers mechanical loss is developed. Two control strategies, based on the transmission efficiency for the dual mode PST, that consider the TM loss are proposed. An optimal operation line (OOL) control strategy is developed to maintain high engine thermal efficiency by controlling the engine operation point on the OOL of the engine, and by selecting the power split mode - whichever has higher transmission efficiency at a given speed ratio (SR). A SR control strategy is proposed to obtain higher transmission efficiency by shifting the engine operation point. Using the TM loss and the proposed control strategies, a vehicle performance simulation is conducted to evaluate the performance of the two control strategies for dual mode PST, and to investigate the fuel economy for the dual mode PST. It is found from the simulation results that for the SR control strategy, engine efficiency decreased because the engine was operated out of the OOL. However, the transmission efficiency of the dual mode PST increased because the PST was operated near the mechanical point where the PST showed the highest transmission efficiency. Consequently, the fuel economy of the SR control strategy was improved by 3.8% compared to that of the OOL control strategy.