Patent ID: 7071683

Claim:
A rotation angle sensing device comprising: a first magnetic member, which is made of a magnetic material and has a substantially cylindrical shape; a second magnetic member, which has a substantially cylindrical shape and is disposed inside the first magnetic member; the second magnetic member being divided in a diametrical direction thereof into at least two portions which are spaced from each other by a magnetic detection gap; at least two magnetic sensing elements, which are disposed in the magnetic detection gap and fixed to the second magnetic member and detect magnetic force; and at least one main magnet, which is fixed to the first magnetic member and applies magnetic force to the magnetic sensing elements, the magnetic force being concentrated by the second magnetic member; a supportive magnet which is disposed at a radial center portion of the second magnetic member to contact both the two portions of the second magnetic member, the supportive magnet being magnetized in the diametrical direction of the second magnetic member, a rotation angle of the supportive magnet relative to the magnetic sensing element being constant, and the magnetic sensing elements being symmetrical about a magnetization-direction axis of the supportive magnet; and a magnetic concentration gap, which is formed between the first magnetic member and the second magnetic member, an interval of the magnetic concentration gap becoming smaller in at least one part of the magnetic concentration gap in a predetermined direction, wherein a relative rotation angle between the first magnetic member and the second magnetic member is detected on the basis of magnetic force detected by the magnetic sensing element.