FAILSAFE CONTROL METHOD OF A STEERING SYSTEM USING AN AFS(ACTIVE FRONT STEERING) SYSTEM FOR GENERATING SMALLEST STEERING EFFORTS WITHOUT STEERING ASSIST BY SETTING LARGEST STEERING RATIO BY CONTROLLING OPERATION OF A VARIABLE GEAR MECHANISM ACCORDING TO DRIVING OF AN AFS MOTOR

摘要

PURPOSE: A failsafe control method of a steering system using an AFS system is provided to secure smallest steering effort without steering assist of a steering system by controlling an AFS motor and a variable gear mechanism after detecting fail through a communication unit by the AFS system and accordingly changing steering ratio into largest value. CONSTITUTION: In a steering system adopting an AFS system having a variable gear mechanism mounted to a steering gear or a steering column to execute front wheel steering angle compensation controls based on information about vehicle conditions, and executing steering assist controls, a failsafe control method for the steering system is composed of steps for deciding proper steering ratio by the AFS ECU by receiving steering angle, lateral acceleration, yaw rate, and vehicle speed from various vehicle condition information detection sensors(S1); deciding if fail occurs in the AFS system according to self-diagnosis logic by the ECU of the steering system and transmitting information about fail through a communication unit to the ECU(S2); judging if fail occurs in the steering system by the ECU based on the received information(S3); executing normal front wheel steering angle compensation controls based on the set proper steering ratio if fail is not generated in the steering system(S4); and outputting a control signal for setting largest target steering ratio to the AFS driving circuit unit and accordingly controlling driving of the AFS motor and operation of the variable gear mechanism if fail occurs(S5).