Rotation detection device

An electric power steering apparatus that outputs a steering torque for assisting a steering operation of a vehicle, the electric power steering apparatus comprising:

• a motor for outputting the steering torque for assisting the steering operation of the vehicle;
• a rotation detection device comprising:
• a sensor section configured to detect a rotation of a shaft of the motor by detecting changes in a magnetic field that is caused by rotation of a magnet on the shaft of the motor, and the sensor section configured to output first rotation information that includes a rotation angle of the motor in one rotation of the motor and second rotation information that includes a number of rotations of the motor;
• and
• a control section including:
• a signal acquirer configured to acquire the first rotation information and the second rotation information from the sensor section;
• an absolute angle calculator configured to calculate an absolute angle indicative of a rotation amount from a reference position based on the first rotation information and the second rotation information;
• an abnormality determiner configured to determine an abnormality in a calculation of the absolute angle;
• and
• a communicator configured to transmit and receive absolute angle information for the absolute angle, wherein
• the absolute angle calculator, in response to the abnormality in the calculation of the absolute angle, is further configured to use a pre-abnormality value of the absolute angle to calculate the absolute angle, the pre-abnormality value of the absolute angle being calculated before the abnormality in the calculation of the absolute angle occurs, and wherein
• the absolute angle calculator is further configured to recover from the abnormality in the calculation of the absolute angle after calculating a recovery-time absolute angle and to resume normal absolute angle calculation, the recovery-time absolute angle calculated based on a difference between a rotation angle that is stored in memory before the abnormality is determined and a rotation angle measured when normal absolute angle calculation resumes wherein the motor outputs the steering torque for assisting the steering operation of the vehicle based on a steering angle calculated from the absolute angle.