Patent ID: 7154262

Claim:
A rotation angle detecting device comprising: a columnar permanent magnet having a generally oval cross-section that has a long axis (BL) and a short axis (CL) intersecting right angles at the middle position (O) of the long axis (BL), a front surface magnetized to have one magnetic pole at a front end of the short axis and a rear surface magnetized to have the other magnetic pole at a rear end of the short axis; a yoke disposed radially outer side of said permanent magnet, said yoke having a generally cylindrical inner surface and a circumferential front gap disposed opposite the front surface of said permanent magnet; a rotary shaft fixed to said permanent magnet at a position of the short axis offset from the middle position so that said permanent magnet can turn back and forth within the inside surface of said yoke; and a magnetic sensor disposed in the front gap to detect the magnetic flux density therein.