Development and experimental validation of a novel hybrid powertrain with dual planetary gear sets for transit bus applications

Given that energy conservation and environmental protection are two important goals for the automotive industry, the application of a hybrid electric powertrain can improve vehicle energy efficiency while decreasing fuel consumption and engine emissions. Planetary gear-based power-split hybrid powertrains have become widely used in passenger vehicles, but remain rarely employed on transit buses. This study proposes a novel hybrid powertrain based on two planetary gear sets (CHS) and presents its operating principles along with development of a control strategy for the powertrain. The CHS hybrid powertrain operates in electric mode when the driving power demand is low, and changes to a hybrid electric mode according to the power-split principle of the planetary gear set. To validate the feasibility of the designed CHS hybrid powertrain, a prototype transit bus equipped with the designed hybrid powertrain system was built, and the operating characteristics of the system were analyzed through a performance test conducted on a chassis dynamometer. Compared with a conventional powertrain, the CHS hybrid powertrain can reduce fuel consumption by 39%. Thus, the CHS hybrid powertrain is a good solution for heavy-duty applications such as hybrid transit buses because of its simple structure and excellent fuel efficiency.