In this paper, a hierarchical input-output decoupling controller is proposed to simultaneously prevent vehicle rollover and keep the input-output stability of vehicle planar motion. A four-degree-of-freedom nonlinear vehicle dynamics model with four-wheel steering (4WS) and four in-wheel motors (4IWMs) is first developed. Then, in the high-level control design, the roll dynamics is decoupled from the planar motion using the general longitudinal and lateral forces. The decoupled roll dynamics is proved to perform as a linear system with an exponentially stable equilibrium. Moreover, the general yaw moment is also determined in the high-level control through the input-output stability analysis for tracking a yaw rate reference. In the low-level control design, the active 4WS control and direct yaw moment control are applied through a control allocation method to satisfy and distribute the virtual control obtained from the high-level control. Demonstrated by co-simulations integrating with CarSim® and MATLAB/Simulink®, the proposed hierarchical input-output decoupling control can successfully prevent the impending rollover and stabilize the vehicle planar motion.
