Patent ID: 8474570

Claim:
An electric power steering apparatus comprising: a permanent magnet synchronous motor provided in a steering mechanism and adapted to generate steering assist torque; a rotational angle sensor for detecting an electrical angle of the permanent magnet synchronous motor; sensor anomaly detection means for detecting an anomaly of the rotational angle sensor; electrical angle estimation means, operable when the anomaly of the rotational angle sensor is detected by the sensor anomaly detection means, for estimating the electrical angle of the permanent magnet synchronous motor on the basis of an inductive voltage generated in the permanent magnet synchronous motor; and motor control means for driving and controlling the permanent magnet synchronous motor in such a manner that, when the anomaly of the rotational angle sensor is not detected, the motor control means drives and controls the permanent magnet synchronous motor by performing current vector control while using a d-q coordinate system having a d-axis and a q-axis determined on the basis of the electrical angle detected by the rotational angle sensor, the d-axis coinciding with an extending direction of a magnetic field of a permanent magnet of the permanent magnet synchronous motor and the q-axis being orthogonal to the d-axis, and, when the anomaly of the rotational angle sensor is detected, the motor control means drives and controls the permanent magnet synchronous motor by performing current vector control while using a γ-δ coordinate system having a γ-axis and a δ-axis estimated as the d-axis and the q-axis, respectively, on the basis of the estimative electrical angle estimated by the electrical angle estimation means, the electric power steering apparatus comprising: electrical-angle-difference detection means for detecting a γ-axis inductive voltage, which is an inductive voltage generated in the γ-axis direction of the permanent magnet synchronous motor and for detecting a difference in electrical angle between the q-axis and the δ-axis on the basis of at least the γ-axis inductive voltage; and estimative-electrical-angle correction means for correcting the estimative electrical angle estimated by the electrical angle estimation means, on the basis of the electrical angle difference detected by the electrical-angle-difference detection means, such that the electrical angle of the δ-axis lags behind the electrical angle of the q-axis.