Patent ID: 7044264

Claim:
An electrical power steering system for a vehicle comprising: a steering assist electric motor for applying a steering assist torque to a steering device operatively linked with steering wheels; a steering sensor for detecting a steering operation of a driver's wheel; a motor current detecting means for detecting a motor current supplied to the steering assist electric motor; a power steering control unit for calculating a target assist torque based on a steering signal from the steering sensor, and calculating a motor driving current based on the target assist torque; and a driver circuit for driving the steering assist electric motor with the motor driving current calculated by the power steering unit, wherein the power steering control unit calculates a difference between a motor current in a normal operation and the detected motor current by the motor current detecting means, and memorizes the difference as an offset correction amount in a memory device, the power steering control unit comprises a temperature sensor for detecting a temperature of a current detecting circuit of the motor current detecting means, the power steering control unit calculates an upper limit and a lower limit of the offset correction amount depending on the detected temperature of the current detecting circuit, and the power steering control unit determines that the current detecting means is not in a normal operating condition, when the offset amount is not within a range between the lower and upper limits of the offset correction amount.