Patent ID: 8030917

Claim:
A rotation angle sensor comprising: a gapped magnetic circuit that rotates around an axis-of-rotation while being concurrently moved in an axial direction interlocked with rotation of a rotating body; a magnetic sensing element which detects a magnetic field along the axis-of-rotation being arranged at the axis-of-rotation of the gapped magnet circuit; and a signal-processing unit that detects the number of rotations of the gapped magnet circuit by detecting an angle of rotation based on magnetic field direction detected by a signal from the magnetic sensing element; the gapped magnetic circuit including a magnet that provides a magnetic field and a yoke for strengthening the magnetic field along the axis-of-rotation; wherein the magnet is formed cylindrically from a pair of cylindrical magnets with cut away portions that are arranged facing each other and with the magnetic sensing element disposed therebetween; inner peripheral surfaces of the pair of cylindrical magnets being arranged facing the magnetic sensing element and providing mutually opposite polar magnetic surfaces; the yoke being made of a soft magnetic material in a pipe form arranged surrounding the pair of cylindrical magnets with cut away portions; the yoke delivering and receiving the magnetic flux to and from outer peripheral surfaces of the pair of cylindrical magnets with cut away portions; and the pair of cylindrical magnets with cut away portions being inclined to the axis of rotation such that one end is closer to the axis-of-rotation than the other.