Fuel Economy Research on Series-Type HEV Intracity Buses with Different Traction Motor Capacity Combinations

Research on HEV (hybrid electric vehicle) intracity buses has become a topic of interest because the well-known service routes of intracity buses and the frequent stop/go pattern make the energy management of the vehicle straightforward. Thus, the energy flow and the energy management of the intracity bus have been studied extensively in order to improve fuel economy. However, the HEV buses that have been studied previously were equipped with a single traction motor or with dual motors with the same capacity for the convenience of the equipment without considering the motoring or generating efficiency of the traction motor. Therefore, the energy flow from the engine/generator unit to the traction motor that has been optimized by many kinds of energy distribution strategies could not be transferred to the wheels in the most efficient manner. This paper investigates this aspect of the energy flow. It studies the traction motor energy distribution by investigating combinations of the different traction motors with the different motoring/generating energy distribution methodology. The research suggests that instead of using a single traction motor or dual motors with the same capacity, dual motors with the different capacity combinations should be used to access the best efficiency distribution map. The different capacity combinations here not only refer to the physical capacity but also to the ratio of electrical energy distributed to the traction motors. Thus, the proposed approach distributes the required motoring/generating energy to the dual motors with the better efficiency. Therefore the system efficiency increases both for motoring and generating and the fuel economy of the system becomes better. The simulation of the proposed method was executed on the Simulink and AMESim co-simulation platform.