Patent ID: 9267817
Filing Date: 2016-02-23
CPC Classification: G01D

Claim Text:
1. A rotation angle detection device for detecting a rotation angle of a rotary body, which rotates about a rotation axis center thereof, relative to a support body, the rotation angle detection device comprising: a first magnet spaced apart from the rotation axis center of the rotary body and magnetized in a direction tangential to an imaginary circle, which is coaxial with the rotation axis center; a second magnet positioned oppositely to the first magnet relative to the rotation axis center and magnetized in a same direction as the first magnet; a first yoke fixed to the rotary body and connecting a N-pole of the first magnet and a N-pole of the second magnet; a second yoke fixed to the rotary body to oppose the first yoke relative to the rotation axis center, the second yoke connecting a S-pole of the first magnet and a S-pole of the second magnet; a magnetism detection element positioned on the rotation axis center and fixed to the support body, the magnetism detection element outputting an electric signal varying with a change in a magnetic field generated by relative rotation between the rotary body and the support body, wherein the first magnet and the second magnet are positioned to face each other in a first direction through the rotation axis center, and the first yoke and the second yoke are positioned to face each other in a second direction, which is orthogonal to the first direction, wherein the first yoke has an inside surface, which faces the second yoke and has a first concave curved surface, a second concave curved surface and a first connecting surface, the first concave curved surface extending from the N-pole of the first magnet in a direction different from the second direction such that the first concave curved surface is more spaced apart from the second yoke as more approaching from the first magnet toward the second magnet, the second concave curved surface extending from the N-pole of the second magnet in a direction different from the second direction such that the second concave curved surface is more spaced apart from the second yoke as more approaching from the second magnet toward the first magnet, and the first connecting surface connecting the first concave curved surface and the second concave curved surface and having a flat surface extending in the first direction or a convex curved surface protruding toward the rotation axis center, and wherein the second yoke has an inside surface, which faces the first yoke and has a third concave curved surface, a fourth concave curved surface and a second connecting surface, the third concave curved surface extending from the S-pole of the first magnet in a direction different from the second direction such that the third concave curved surface is more spaced apart from the first yoke as more approaching from the first magnet toward the second magnet, the fourth concave curved surface extending from the S-pole of the second magnet in a direction different from the second direction such that the fourth concave curved surface is more spaced apart from the first yoke as more approaching from the second magnet toward the first magnet, and the second connecting surface connecting the third concave curved surface and the fourth concave curved surface and having a flat surface extending in the first direction or a convex curved surface protruding toward the rotation axis center, wherein the first concave surface and the second concave surface have a center of a radius of curvature at a second yoke side relative to the rotation axis center; and the third concave surface and the fourth concave surface have a center of a radius of curvature at a first yoke side relative to the rotation axis center, the first magnet and the second magnet are spaced apart oppositely in the first direction from the rotation axis center by same distances, the first yoke and the second yoke are shaped to be in a plane symmetry relative to an imaginary plane, which passes the rotation axis center and extends in the second direction, and the center of a radius of curvature of the first concave curved surface and the second concave curved surface is between the second yoke and the rotation axis center, and the center of a radius of curvature of the third concave curved surface and the fourth concave curved surface is between the first yoke and the rotation axis center, wherein the first yoke and the second yoke are shaped to be in a plane symmetry relative to an imaginary plane, which passes the rotation axis center and extends in the first direction.