Handling Stability Improvement for a Four-Axle Hybrid Electric Ground Vehicle Driven by In-Wheel Motors

The hybrid electric ground vehicle (HEGV), driven by in-wheel motors (IWMs), is a good solution for prolonging vehicle driving range and improving dynamics performance. This paper presents a hierarchical optimization control strategy for a four-axle HEGV driven by IWMs to improve handling stability. In the proposed hierarchical control strategy, the upper layer controller controls the vehicle motion states to track the desired ones, in which the controlled force and moment are considered as resultant of the longitudinal tire force, and is determined by using the nonlinear sliding mode control method. In the lower layer controller, the control allocation method is adopted to assign torque to all actuators, including the IWMs and brakes, to generate the controlled force and moment determined by the upper layer controller. Considering the motor torque capability, tire workload rate, and road adhesion, we establish an objective function with constraints, which is solved by using the optimization algorithm. The software simulation and the hardware-in-loop test results show that the proposed control strategy exhibits excellent performance in terms of vehicle handling stability, compared with the commonly used control strategies, and has the capability of real-time implementation.