ABSTRACT
Thanks to good torque-to-speed characteristics of electric motors, current electric vehicles are normally equipped with single-speed transmission. However, the driving distance is limited due to the low energy capacity of the battery system. This paper tries to reduce the energy consumption and extend the driving distance of electric vehicles by applying multi-speed transmissions. An efficiency-optimised gear shift strategy is developed to keep the electric motor operating in its most efficient range. Through the forward driving simulation in the WLTC (Worldwide Harmonised Light-Duty Test-Cycle) driving cycle, it is found that a two-speed transmission can greatly reduce the energy consumption and extend the maximum driving distance of electric vehicles. The improvement becomes less significant when continuing to increase the transmission speeds. Therefore, electric vehicles are suggested to have a two-speed transmission with respect to energy conservation and driving distance extension.
