In this paper, a hierarchical driving force distribution and control strategy for a six-wheel drive (6WD) skid-steering electric unmanned ground vehicle (EUGV) with independent drive motors is presented to improve the vehicle maneuverability and stability. The proposed hierarchical strategy is based on a nine-degrees-of-freedom (DOFs) dynamics model of 6WD skid-steering EUGV with a vehicle system dynamics model, wheel dynamics model, and tire model. In the proposed hierarchical strategy, the upper layer controller calculates the resultant driving force and yaw moment to control the vehicle motion states to track the desired ones by using the integral sliding mode control (ISMC) and proportion–integral–differential (PID) control methods. In the lower layer controllers, the driving force distribution method is adopted to allocate torques to the six motors. An objective function is proposed and composed of the longitudinal tire workload rates and weighting factors, considering the inequality constraints and equality constraints, which is solved by using the active set method. In order to evaluate the effectiveness of the proposed method, experiments with two types of scenarios were conducted. Comparative studies were also conducted with the other two methods used in the literature. The experimental results show that better performance can be achieved with the proposed control strategy in vehicle maneuverability and stability.
Front and Rear Driving Force Distribution Method for Retaining Driving Force on Instantaneous Slippery Roads for Electric Vehicle with In-Wheel Motors