Patent ID: 7663360

Claim:
A rotation angle detecting device comprising: a magnetic member for providing a magnetic field that rotates with a rotating object; a magnetic sensor for sensing a change in the magnetic field when the magnetic member rotates relative to the magnetic sensor about a rotation axis; and means for calculating a rotation angle of the rotating object by converting the output signals of the magnetic sensor to trigonometric functions, wherein: the magnetic member comprises a disk-shaped permanent magnet magnetized in a radial direction to provide a pair of diametrically opposite N and S poles on its outer periphery to form the magnetic field; and the magnetic sensor comprises a pair of sensor elements disposed adjacent to each other on a single plate that is disposed at a place adjacent a circumference of the permanent magnet so as to be perpendicular to the rotation axis, so that said sensor elements are closer to the circumference of the permanent magnet than to the rotation axis, and so that sensing surfaces of the sensor elements are disposed at an angle of 90 degrees to each other; and so that each of the sensing surfaces is inclined by 45 degrees in angle to a line intersecting the rotation axis at a right angle.