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An electric power steering apparatus for a vehicle includes a protection circuit for stopping operation of an electric motor provided to apply a steering assist force to a steering system of the vehicle. The protection circuit is operable to stop operation of the electric motor when an ignition off

An electric power steering apparatus for a vehicle includes a protection circuit for stopping operation of an electric motor provided to apply a steering assist force to a steering system of the vehicle. The protection circuit is operable to stop operation of the electric motor when an ignition off signal is supplied from an ignition sensor and at least one of an engine speed signal supplied from an engine speed sensor and a vehicle velocity signal supplied from a vehicle velocity sensor falls below a corresponding predetermined value. Even if an ignition on signal is not supplied during movement of the vehicle due to a failure in the ignition sensor, when the engine speed signal or the vehicle velocity signal is above the predetermined value, the vehicle is regarded as being in the running state and operation of the electric motor is continued to apply the steering assist force to the steering system. With this arrangement, a good and stable steering feel can be obtained during movement of the vehicle.

대표청구항 ▼

[ What is claimed is:] [1.]1. An electric power steering apparatus for a vehicle, comprising:a battery;an electric motor for applying a steering assist force to a steering system of a vehicle;a control unit for generating a motor control signal on the basis of at least a steering torque applied to t

[ What is claimed is:] [1.]1. An electric power steering apparatus for a vehicle, comprising:a battery;an electric motor for applying a steering assist force to a steering system of a vehicle;a control unit for generating a motor control signal on the basis of at least a steering torque applied to the steering system;a motor drive unit for driving said electric motor on the basis of said motor control signal;an ignition sensor for detecting an operating condition of an ignition switch of the vehicle;an engine running-state sensor for detecting a running state of an engine of the vehicle and generating an engine running-state signal corresponding to the detected running state of the engine; anda protection circuit for said battery including a switching unit arranged to interrupt operation of said electric motor when a signal indicative of an ignition off state of said ignition switch is supplied from said ignition sensor and the engine running-state signal supplied from said engine running-state sensor falls below a predetermined value;wherein the protection circuit prevents the electric motor from being stopped during an off failure where the ignition switch off state signal is erroneously output from the ignition sensor and the engine is still running above a predetermined value, but the protection circuit protects the battery from power drain and stops possible operation of the electric motor when the ignition switch off state signal is output from the ignition sensor and the engine is stopped or running below the predetermined value.