Energy Consumption of Electric Powertrain Architectures: a Comparative Study

Battery electric vehicles (BEVs) have the potential to replace conventional vehicles, but the short driving range is currently limiting their diffusion. Using analytical methods this paper compares two electric powertrains with respect to energy consumption and efficiency: the standard single-motor architecture, derived from conventional internal combustion engine vehicles and equipped with a high-speed electric motor and a mechanical reduction system, versus the novel in-wheel direct drive topology. The potential benefits of a two-speed transmission to improve the driving range of battery electric vehicles are also studied. A backwards-simulation model from the wheels (load) to the battery (source) has been developed to simulate an EV during representative drive cycles. The results show superior performance of the in-wheel powertrain, which can provide up to 14% energy saving vs. the single-motor configuration thanks to the absence of mechanical transmission components and related power losses. Furthermore, the adoption of a two-speed gearbox on a single-motor electric vehicle doesn’t provide any effective energy saving benefit versus a fixed reduction gear. On the contrary, it consumes more battery energy during urban driving, up to 7%, due to the lower efficiency of the multi-gear transmission compared to the single-speed type.