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 the energy efficiency of fully electric vehicles. Online power loss minimisation schemes based on the electric motor efficiency data may, however, be impractical for real-time implementation owing 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 a constant speed, a ramp manoeuvre and a sequence of step steer manoeuvres. The energy-efficient wheel torque allocation scheme provides motor power loss reductions and yields savings in the total power utilisation compared with 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 the efficiency and thus to reduce power consumption during different manoeuvres.