Abstract. Electric vehicle (EV) with four independent in-wheel motor is over-actuated systems. The wheel torque distribution can be realized through a large number of methods to satisfy the economic and safety demands. This paper aims at providing a review of the economic-based torque distribution strategies, safety-based torque distribution strategies and coordination control of torque distribution strategies based on both safety and economy. This paper not only provides a comprehensive analysis of torque distribution strategies for in-wheel-motor EVs but also puts forward the future and emphasis of future study, which will promote the development of torque distribution strategy with safety and economy for in-wheel-motor drive EVs.
IntroductionRecently, as a new energy and environment-friendly vehicle, the in-wheel motor drive electric vehicle (EV) has been rapidly developed thanks to its high efficiency, non-pollution, low noise and so on. Differing from the traditional driving manner, the in-wheel motor drives the wheel directly. Thus, the in-wheel motor drive EV has unique advantages, such as simple and compact structure, high energyefficiency, and independent control of the torque [1]. Studying the torque distribution of the drive system is of great significance to the research of four in-wheel motor drive (4IWMD) EV.For the 4IWMD EV, each driving wheel adopts a driving motor as the driving source. And, there is no direct restriction between the mechanical parts between the power sources. The coordinated operation between the driving wheels must be ensured in the control strategy and control method. The torque coordinated control technique is how to control the torque of each driving wheel in order to achieve the goal of stable and safe driving. The wheel torque distribution mainly depends on the working position of each wheel motor under the same torque demand. And, the efficiency of motor and motor controller will be different under different torque demand. The wheel torque distribution also affects the steering characteristics of the vehicle, including the indirect influence of the wheel torque distribution and the direct influence of the left and right wheel torque distribution. The method of moment distribution has an influence on the economy and operation stability of the vehicle, so it is necessary to study both energy saving and safe wheel torque distribution to improve the vehicle's comprehensive performance [2].A large number of literature studied on torque distribution of in-wheel-motored EVs have appeared, the existing articles emphasize on discussing the torque distribution strategy. However, there is no review about torque distribution used in EVs. This study intends to fill this gap. In addition, torque