Patent ID: 8924083

Claim:
A power steering apparatus comprising: a steering mechanism including: a steering shaft including: an input shaft configured to be rotated by steering operation of a steering wheel; an output shaft; and a torsion bar connected between the input shaft and the output shaft, and configured to transmit rotation of the input shaft to the output shaft; and a motion conversion mechanism configured to convert rotation of the output shaft to steering motion of a steerable wheel; an electric motor configured to apply a steering effort to the steering mechanism; a torque sensor including: a first rotation angle sensor configured to sense as a first rotation angle a rotation angle of the input shaft; and a second rotation angle sensor configured to sense as a second rotation angle a rotation angle of the output shaft; wherein the torque sensor is configured to determine a steering torque on a basis of a relative rotation angle between the first rotation angle and the second rotation angle, wherein the steering torque occurs in the steering shaft; a third rotation angle sensor including a first rotation member configured to be rotated by rotation of the steering shaft, wherein the third rotation angle sensor is configured to sense as a third rotation angle a rotation angle of the first rotation member; a fourth rotation angle sensor including a second rotation member configured to be rotated by rotation of the first rotation member at a gear ratio other than one with respect to the first rotation member, wherein the fourth rotation angle sensor is configured to sense as a fourth rotation angle a rotation angle of the second rotation member; and an electrical control unit configured to control operation of the electric motor, wherein the electrical control unit includes: a motor command value calculation section configured to calculate a command value of a current supplied to the electric motor on a basis of the steering torque; a first absolute rotation angle calculation section configured to calculate a first absolute rotation angle as a first estimate of an absolute rotation angle of the steering wheel on a basis of at least one of combinations, wherein so the combinations include a combination of the first rotation angle and the second rotation angle, a combination of the first rotation angle and the third rotation angle, a combination of the first rotation angle and the fourth rotation angle, a combination of the second rotation angle and the third rotation angle, and a combination of the second rotation angle and the fourth rotation angle; a second absolute rotation angle calculation section configured to calculate a second absolute rotation angle as a second estimate of the absolute rotation angle of the steering wheel on a basis of a combination of the third rotation angle and the fourth rotation angle; and an abnormality detection section configured to detect an abnormality by comparison between the first absolute rotation angle and the second absolute rotation angle.