Abstract
This study investigates a control strategy using the front steering angle control to improve the handling and stability of heavy-duty vehicles as a possible substitute for four-wheel steering (4WS) system. The effective steering input is regulated through the state feedback computed by the optimal control theory suggested in this research, to adapt the closed system to the changes of some factors depending on running situations, such as velocity and center of the gravity. Direct moment control with a simple auto-tuning proportion controller is also integrated in the compensation system, wherein yaw moment and roll moment are applied to decrease side slip angle and roll angle respectively. A double-cost-function LQR methodology (DLQR) is developed to compute the value of the front steering angle compensation. In addition to traditional LQ cost function, another index called target cost function with a free form is introduced in DLQR to express physical requirements more plainly to determine reasonable weighting matrices. The DLQR extends the concept and the applicable field of LQR to solve an optimal control problem with a general nonlinear cost function. The simulation results show that the integrated system significantly improves the steering characteristics to produce the desired vehicle response in various running conditions.