A hub motors choice strategy for an electric four independent wheel drive vehicle

Electric vehicles represent a valid solution to solve the air pollution problem. The typical propulsion system of an electric vehicle includes a high speed-low torque electric motor combined with some mechanical parts, such as gearbox, transmission and differential. The indirect coupling between driving wheels and engine allows the electric motor to work close to its maximum operative efficiency point. A different traction system is based on using a hub motor for each wheel drive instead of a single high speed-low torque motor. This allows removing all the mechanical transmission components, reducing weight and increasing space saving. However, in this configuration the hub motor works on all its operating range, affecting adversely the efficiency. The aim of this paper is to analyze efficiency, weight, and cost of different propulsion systems of an electric car designed principally for the urban mobility. The propulsion system is based on hub motors, and two- and four-wheel drive configurations are either evaluated. Furthermore, in the case of the four-wheel drive, configurations with equal or different hub motor features are analysed. The main results of this study points out that hybrid configurations have better performance with respect to the two-wheel drive or the homogenous four-wheel drive solutions.