Fail safe method and system for motor driven power steering apparatus.

摘要

A fail safe system for a motor driven power steering apparatus comprises a DC motor (13) for subsidiarily energizing said steering apparatus; a handle for generating a steering torque; a torque sensor (3) for producing a signal corresponding to said steering torque which includes a potentiometer (31) having a movable electrode for detecting a torsional angle relating to said steering torque, and a torque neutral region sensor (32) arranged to operate together with said movable electrode to produce a signal indicating whether said steering torque is within said torque neutral region; a motor current detection circuit (94) for detecting a current flowing in said DC motor (13); an electromagnetic clutch (16) for coupling/decoupling an output of said DC motor (13) to/from said steering apparatus; a power supply circuit (11, 108) for suppplying electric power to said DC motor (13) and said electromagnetic clutch; and a fail safe relay (91) being interrupted to remove said subsidiary steering force when a current exceeding that relating to said torque neutral region flows in said motor-current detection circuit (94) while said steering torque is within said torque neutral region.