Integrated Control of AFS and DYC in the Vehicle Yaw Stability Management System Using Fuzzy Logic Control

In this paper, an integrated vehicle dynamics control system is designed to improve vehicle yaw stability by coordinating control of Active Front Steering (AFS) and Direct Yaw-moment Control (DYC) based on a new concept. The control system has a hierarchical structure and consists of two controlling layers. A fuzzy logic controller is used in the upper layer (Yaw Rate Controller) to keep the yaw rate in its desired value. The yaw rate error and its rate of change are applied to upper controlling layer as inputs, where the direct yaw moment control signal and the steering angle correction of the front wheels are built as the outputs. In the lower layer (Fuzzy Integrator), a fuzzy logic controller is designed based on the working region of the lateral tire forces to determine percentage of usage of upper layer controlling inputs. In the next stage, taking into consideration the direction of lateral forces in the front wheels and by accurate analysis of controlling inputs, a switching function is introduced and utilizes in fuzzy integrator. The simulation results by using of nonlinear seven degrees of freedom vehicle model illustrate that considerable improvements are achieved in vehicle handling and driving dynamics through the integrated AFS/DYC control system in comparison with the individual AFS or DYC controllers.