Patent ID: 8138752

Claim:
A rotation detection apparatus for detecting a rotation state of a gear, the rotation detection apparatus comprising: a magnetic sensor including: a bias magnet configured to generate a bias magnetic field extending toward the gear; and a magnetic-electric conversion element disposed in the bias magnetic field and configured to sense a change of a direction of the bias magnetic field acting thereon, wherein rotation of the gear changes the direction of the bias magnetic field; a magnetic field generation unit disposed in a vicinity of the magnetic-electric conversion element and configured to generate a diagnosis use magnetic field extending toward the magnetic-electric conversion element, wherein a direction of the diagnosis use magnetic field is different from that of the bias magnetic field; a driving unit configured to apply an electric current to the magnetic field generation unit, and thereby to drive the magnetic field generation unit when the gear is in an stationary state; and a self-diagnosis unit configured to diagnose the magnetic sensor to determine whether the magnetic sensor has a failure, wherein the self-diagnosis unit diagnoses the magnetic sensor based on an output signal from the magnetic-electric conversion element that is subjected to a superposition magnetic field formed by the bias magnetic field and the diagnosis use magnetic field.