Yoke member for torque detection device, torque detection device, and steering device

A yoke member for a torque detection device that includes a multipole magnet, the yoke member comprising:

• a primary yoke and a secondary yoke which are opposed to each other and are configured to be disposed around the multipole magnet, wherein:
• the primary yoke has:
• a primary ring plate, which is shaped in a ring form;
• and
• a plurality of primary teeth, which are arranged at equal intervals along an inner periphery of the primary ring plate and project in a normal direction that is normal to a plane of the primary ring plate;
• the secondary yoke has:
• a secondary ring plate, which is shaped in a ring form;
• and
• a plurality of secondary teeth, which are arranged at equal intervals along an inner periphery of the secondary ring plate and project in a normal direction that is normal to a plane of the secondary ring plate;
• the primary yoke and the secondary yoke are configured such that the plurality of primary teeth and the plurality of secondary teeth are alternately arranged in a circumferential direction of the primary ring plate, and a predetermined gap is maintained between the primary yoke and the secondary yoke;
• the primary yoke
• is configured such that a maximum width of a widest portion of each of the plurality of primary teeth, which is widest along each of the plurality of primary teeth in an alignment direction of the primary yoke and the secondary yoke, is set to be smaller than a width between the inner periphery and an outer periphery of the primary ring plate at a portion of the primary ring plate which is circumferentially centered between adjacent primary teeth of the plurality of primary teeth,
• to, when a central axis of the multipole magnet deviates from a central axis of the yoke member with a maximum amount of eccentricity while the yoke member is in use as part of the torque detection device,
• limit a flow of a magnetic flux flowing from the multipole magnet to the primary ring plate through a corresponding one or more of the plurality of primary teeth, thereby maintaining a maximum density of the magnetic flux generated in the primary ring plate to a level that is smaller than a saturation magnetic flux density of the primary ring plate, and
• generate a change in a magnetic flux density in the primary ring plate in response to relative rotation between the multipole magnet and the primary yoke,
• wherein the alignment direction of the primary yoke and the secondary yoke is a direction along which the primary yoke and the secondary yoke are arranged;
• the secondary yoke
• is configured such that a maximum width of a widest portion of each of the plurality of secondary teeth, which is widest along each of the plurality of secondary teeth in the alignment direction, is set to be smaller than a width between the inner periphery and an outer periphery of the secondary ring plate at a portion of the secondary ring plate which is circumferentially centered between adjacent secondary teeth of the plurality of secondary teeth,
• to, when the central axis of the multipole magnet deviates from the central axis of the yoke member with the maximum amount of eccentricity while the yoke member is in use as part of the torque detection device,
• limit a flow of the magnetic flux flowing from the multipole magnet to the secondary ring plate through a corresponding one or more of the plurality of secondary teeth, thereby maintaining a maximum density of the magnetic flux generated in the secondary ring plate to a level that is smaller than a saturation magnetic flux density of the secondary ring plate, and
• generate a change in a magnetic flux density in the secondary ring plate in response to relative rotation between the multipole magnet and the secondary yoke;
• the maximum width of each of the plurality of primary teeth is a width of a base of each of the plurality of primary teeth which is joined to the primary ring plate, wherein the base of each of the plurality of primary teeth is bent and radially extends in parallel with the primary ring plate;
• and
• the maximum width of each of the plurality of secondary teeth is a width of a base of each of the plurality of secondary teeth which is joined to the secondary ring plate, wherein the base of each of the plurality of secondary teeth is bent and radially extends in parallel with the secondary ring plate.