Comparison of powertrain system configurations for electric passenger vehicles

Electric vehicles (EV) are considered a practical alternative to conventional and hybrid electric passenger vehicles, with higher overall powertrain efficiencies by omitting the internal combustion engine. As a consequence of lower energy density in the battery energy storage as compared to fossil fuels powered vehicles, EVs have limited driving range, leading to a range phobia and limited consumer acceptance. Particularly for larger luxury EVs, electric motors with a single reduction gear typically do not achieve the diverse range of function needs that are present in multi-speed conventional vehicles, most notably acceleration performance and top speed requirements. Subsequently, multi-speed EV powertrains have been suggested for these applications. Through the utilization of multiple gear ratios a more diverse range of functional needs can be realized without increasing the practical size of the electric motor. The major limitation of multi-speed EV powertrains is that the increased transmission complexity introduces additional losses to the vehicle. Through a number of simulations this paper studies the integration of multispeed transmission with EV platforms. Particularly, it investigates the performance improvements of both B and E class vehicle platforms realized through utilization of two and three speed transmissions. Also the potential application of hybrid energy storage systems (i.e. batteries combined with supercapacitors) is studied. Results demonstrate that there can be significant benefits attained for both small and large passenger vehicles through the application of multi-speed transmissions. However, optimization of these ratios must be considered in the analysis.