Reducing the Motor Power Losses of a Four-Wheel Drive Fully Electric Vehicle via Wheel Torque Allocation

Individually-controlled electric motors provide opportunities for enhancing the handling characteristics and energy efficiency of fully electric vehicles. Online power loss minimisation schemes based on electric motor efficiency data may, however, be impractical for real-time implementation due to the heavy computational demand. In this paper, the optimal wheel torque distribution for minimal power losses from the electric motor drives is evaluated in an offline optimisation procedure and then approximated using a simple function for online control allocation. The wheel torque allocation scheme is evaluated via a simulation approach incorporating straight-ahead driving at constant speed, ramp and step steer manoeuvres. The energy efficient wheel torque allocation scheme provides motor power loss reductions and yields savings in the total power utilisation compared to a simpler method in which the torques are evenly distributed across the four wheels. The method does not rely on complex online optimisation and can be applied on real electric vehicles in order to improve efficiency and thus reduce power consumption during different types of manoeuvre.