Optimal Torque Allocation for Distributed Drive Electric Skid-Steered Vehicles Based on Energy Efficiency 2018-01-0579

Steering of skid-steered vehicles without steering mechanism is realized by differential drive/brake torque generated from in-wheel motors at left and right sides. Compared to traditional Ackerman-steered vehicles, skid-steered vehicles consume much more energy while steering due to greater steering resistance. Torque allocation is critical to the distributed drive skid-steered vehicles, since it influences not only steering performance, but also energy efficiency. In this paper, the dynamic characteristics of six-wheeled skid-steered vehicles were analyzed, and a 2-DOF vehicle model was established, which is important for both motion tracking control and torque allocation. Furthermore, a hierarchical controller was proposed. Considering tire force characteristics and tire slip, the upper layer calculates the generalized force and desired yaw moment based on anti-windup PI (proportion-integral) control method. On the fundamental of dynamic characteristics of skid-steered vehicles and electric motor efficiency characteristics, the lower layer utilizes different optimal torque allocation strategies based on energy efficiency at different driving conditions, namely, straight line driving condition and steering condition. The control results show that the motion controller can track the reference yaw rate accurately and at the same time much energy can be saved by proposed torque allocation strategy.