Wheel Torque Distribution Criteria for Electric Vehicles With Torque-Vectoring Differentials

The continuous, precise modulation of the driving and braking torque of each wheel is considered to be the ultimate goal for controlling the performance of a vehicle in steady-state and transient conditions. To do so, dedicated torque-vectoring controllers which allow optimal wheel torque distribution under all possible driving conditions have to be developed. Commonly, vehicle torque-vectoring controllers are based on a hierarchical approach, consisting of a high-level supervisory controller which evaluates a corrective yaw moment, and a low-level controller which defines the individual wheel torque reference values. The problem of the optimal individual wheel torque distribution for a particular driving condition can be solved through an optimization-based control allocation algorithm, which must rely on the appropriate selection of the objective function. With a newly developed off-line optimization procedure, this article assesses the performance of alternative objective functions for the optimal wheel torque distribution of a four-wheel-drive fully electric vehicle. Results show that objective functions based on minimum tire slip criterion provide better control performance than functions based on energy efficiency