FAILSAFE CONTROL METHOD OF AN AFS(ACTIVE FRONT STEERING) SYSTEM FOR SETTING SLOWEST STEERING RATIO BY MOVING IMMEDIATELY A CONTROL SHAFT OF A THIRD LEVEL TO AN OUTPUT SHAFT IN GENERATING FAIL ACCORDING TO SELF-DIAGNOSIS LOGIC OF AN ECU(ELECTRONIC CONTROL UNIT)

摘要

PURPOSE: A failsafe control method of an AFS system is provided to stabilize unstable behavior of a vehicle caused by fast steering ratio in high-speed traveling by moving a control shaft of a third level to an output shaft at once and setting slowly the steering ratio. CONSTITUTION: An AFS system for compensating steering angle of front wheels comprises a vehicle information detection sensor; an AFS ECU; an AFS driving circuit unit; a variable gear mechanism composed of a first level input shaft, a second level output shaft, and a third level control shaft, and operated by the ECU to make steering ratio slow as the third level control shaft approaches the output shaft and make steering ratio fast as the control shaft gets apart from the output shaft; and an AFS motor. A failsafe control method of the AFS system is composed of steps for deciding proper steering ratio by the AFS ECU by receiving steering angle, vehicle speed, lateral acceleration, and yaw rate detected by a steering angle sensor, a vehicle speed sensor, a lateral acceleration sensor, and a yaw rate sensor(S1); deciding if fail occurs in the AFS system according to self-diagnosis logic by the AFS ECU(S2); outputting a control signal to the AFS driving circuit unit and controlling driving of the AFS motor and operation of the variable gear mechanism to follow and control the decided proper steering ratio, when fail is not generated in the AFS system(S3); and outputting a control signal for setting slowest steering ratio to the AFS driving circuit unit and accordingly controlling the AFS motor and the variable gear mechanism if fail occurs(S4).