Patent ID: 7642738

Claim:
A power steering apparatus comprising: an electric motor for producing an assist steering effort in a steering system; a temperature sensor for measuring a temperature of a first portion subject to thermal influence of operation of the electric motor; and a control unit configured to: determine an estimated temperature of a second portion in accordance with a value of a motor current flowing through the electric motor, the second portion being subject to thermal influence of operation of the electric motor; determine a first upper limit value in accordance with the measured temperature; determine a second upper limit value in such a manner that when the estimated temperature is below a threshold temperature value, the second upper limit value is larger than or equal to a maximum value of the motor current, and that when the estimated temperature is above the threshold temperature value, the second upper limit value is smaller than the maximum value; determine whether the temperature sensor is normal or abnormal; limit the motor current to a smaller one of the first and second upper limit values, when determining that the temperature sensor is normal; limit the motor current to the second upper limit value, when determining that the temperature sensor is abnormal; and correct at least one of the estimated temperature and the threshold temperature value in such a manner that the estimated temperature increases with respect to the threshold temperature value, when determining that when the estimated temperature is below the threshold temperature value, the temperature sensor becomes abnormal.