DESIGN OF AN INTEGRATED AFS/ACD CONTROL SYSTEM TO ENHANCE 4WD VEHICLES DYNAMICS AND STABILITY

摘要

An integrated vehicle dynamic control system for a four-wheel drive vehicle with an active front steering (AFS) and active centre differential (ACD), based on fuzzy logic control, is developed to improve the vehicle stability and its handling performance. The control system has a hierarchical structure consisting of two layers. A fuzzy logic controller is used in the upper layer to keep the yaw rate in its desired value. The yaw rate error and the side slip angle are applied to the upper controlling layer as the inputs, where the desired traction torque transfer ratio and the steering angle correction of the front wheels are the outputs. However, the ideal control effectors could not directly be the control inputs for the centre differential. Therefore, in the lower control loop, one should map the ideal control effectors to the physical control inputs for the centre differential by optimum dynamic traction force distribution. A nonlinear eight degree-of-freedom (DOF) vehicle model with the traction force distribution being utilized by a PI controller is considered. The simulation results illustrate considerable improvements have been achieved for the vehicle stability and handling performance through the integrated AFS/ACD control system.