Torque distribution strategy for a front and rear wheel driven electric vehicle

Electric vehicles (EVs) with a distributed drive train configuration offer great potential and flexibility for improving the system efficiency, performance, reliability as well as safety. This paper investigates a torque distribution scheme for a front and rear wheel driven EV in order to improve the drive train efficiency over a wide torque and speed range as a part of the EU funded P-MOB project. It has been shown the maximum efficiency is achieved if the total torque required by the vehicle is shared equally between the two identical motors. In addition, the distribution of the energy consumption over a New European Driving Cycle (NEDC) is analyzed and the regions of high speed, low torque are identified to have a high level of energy consumption, where the motor efficiency improvement in these regions is the most important. Therefore, this paper further proposes to operate just one motor to provide the total required torque in the low torque region. A clutch may be employed between one motor and gearbox (differential), thus “switching off” its idle loss (no-load loss, flux-weakening loss), and improving the drive train efficiency. An online optimized torque distribution algorithm has been devised based on the motor efficiency map to determine whether the second motor should be disengaged by the clutch in the low torque region. With the proposed optimization scheme, the drive train efficiency can be improved by 4% over the NEDC cycle. Experimental test results validate the proposed torque distribution strategy.