Electric power steering apparatus

An electric power steering apparatus including an electric motor for providing an assist torque to a steering system, a steering torque detecting unit for detecting a steering torque exerted on said steering system to generate a steering torque signal, a target current determining unit for determining, on the basis of at least said steering torque signal, a target current to be supplied to said electric motor so as to generate a target current signal, a current detecting unit for detecting a current flowing through said electric motor to generate a motor current signal, an offset calculating unit for calculating an offset between said target current signal and said motor current signal to generate an offset signal, a motor operation control unit for generating, on the basis of said offset signal, a drive control signal to drive said electric motor, and a motor drive unit for driving said electric motor on the basis of said drive control signal, said electric power steering apparatus comprising:

• a judgment unit which passes a judgment that a variation of said motor current signal per unit time is smaller than a predetermined value when one of said offset signal and said drive control signal is greater than a preset threshold;
• a forced drive control unit for generating a forced drive control signal tending to forcibly drive said electric motor when said judgment unit has passed said judgment;
• and
• a fault judgment unit which judges said current detecting unit to be at fault if said motor current signal does not vary even though said electric motor is forcibly driven.

An electric power steering apparatus including an electric motor for providing an assist torque to a steering system, a steering torque detecting unit for detecting a steering torque exerted on said steering system to generate a steering torque signal, a target current determining unit for determining, on the basis of at least said steering torque signal, a target current to be supplied to said electric motor so as to generate a target current signal, a current detecting unit for detecting a current flowing through said electric motor to generate a motor current signal, an offset calculating unit for calculating an offset between said target current signal and said motor current signal to generate an offset signal, a motor operation control unit for generating, on the basis of said offset signal, a drive control signal to drive said electric motor, and a motor drive unit for driving said electric motor on the basis of said drive control signal, said electric power steering apparatus comprising:

• a first judgment unit which passes a judgment that a condition in which one of said offset signal and said drive control signal exceeds a first threshold has continued for a preset allowable time;
• a second judgment unit which passes a judgment that a variation of said motor current signal per unit time is smaller than a predetermined value when said drive control signal is greater than a second threshold;
• a forced drive control unit for generating a forced drive control signal tending to forcibly drive said electric motor when said judgment of said first judgment unit and said judgment of said second judgment unit have passed concurrently;
• and
• a fault judgment unit which judges said current detecting unit to be at fault if said motor current signal does not vary even though said electric motor is forcibly driven.