Transmission configuration effect on total efficiency of Electric Vehicle powertrain

Abstract

This study investigates the impact of transmission topology on the combined mechanical and electrical efficiency of an Electric Vehicle (EV) by comparing two types of transmissions. In an EV, due to space restrictions, a relatively high-speed electric motor is used with a reduction gear to provide adequate torque production. Since the electric motor's efficiency varies according to the amount of applied torque at different speeds, there is a question of whether a multi-step gearbox capable of increasing the electric efficiency by shifting operation points along constant power curves can also improve the powertrain overall efficiency. A mathematical model is developed for calculating the power losses due to movement of mechanical components. In this study, a geartrain is taken into closer analysis where a single reduction gear and a five-step gearbox are compared from an efficiency point of view.