Multi-axle land vehicles with independent drive actuation on multiple axles offer improved stability and traction on various road surfaces. This is possible by exploiting the redundancy of the drive system to generate additional yaw moment and to maximize the utilization of individual tire-road contacts without significant extra power consumption by the drive motors. This paper aims at improving the efficiency of torque allocation with the addition of active steering while enhancing the dynamic performance of the independent hub motor driven multi-axle vehicles. The control algorithm outlined here employs a two-level scheme. The higher level computes the desired global control efforts that are needed to track the reference yaw rate and slip angle state responses generated by a reference vehicle model, and the lower level executes optimal control allocation with a cost function that simultaneously takes into account 1) maximization of the tire utilization on all axles considering dominant tire nonlinearities, and 2) minimization of the actuation efforts of the active steering system and the distributed motor torques. The validity of the proposed algorithm is verified via comparison of the simulations of the control allocation scheme applied to a high fidelity multi-axle vehicle under several aggressive test maneuvers with different actuation configurations. The results suggest that the addition of active steering provides lower actuator power consumption and tire usage while ensuring enhanced lateral and longitudinal dynamic performance for the vehicle.

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