Engine operation for the planetary gear hybrid powertrain

The planetary gear hybrid powertrain (PGHP) is considered as a prospective hybrid electric vehicle (HEV) configuration. However, the optimal control of the system remains controversial because the characteristics of this system are much more complicated than those of conventional systems. This paper presents a case study that reveals the ambiguity of the conventionally-defined optimal operation line. Instead of this engine optimal operation line, the system optimal operation point is suggested. This point is determined by considering the engine efficiency and the transmission efficiency simultaneously. With the system optimal operation point, the fuel economy estimate can be simulated. First, the vehicle cruising at constant velocities was simulated. Then, the vehicle was run at various standard emission test schedules and the mileages were estimated. In each case, the engine operation was analysed to comprehend the optimal operation of the PGHP system. Also, the improvements in fuel economy by optimal operation are presented.