Radial-type magnetic encoder, bearing device provided with radial-type magnetic encoder, and method for manufacturing radial-type magnetic encoder

A radial-type magnetic encoder comprising:

• an annular fixing member including a cylindrical portion to be attached to a rotary body;
• and
• an annular plastic magnet attached to the annular fixing member and magnetized in a multipole form so as to have N poles and S poles at regular intervals in a circumferential direction, wherein
• the annular fixing member includes the cylindrical portion, an outward flange portion extending outward in a radial direction from an edge of the cylindrical portion, and a sensor opposed portion bent from an edge of the outward flange portion and opposed to a magnetic sensor which detects rotation of the magnetic encoder, and the annular fixing member has a substantially U-shaped sectional shape along a plane including the radial direction and an axial direction,
• the annular plastic magnet has a shape that covers a front surface, a back surface, and an end edge of the sensor opposed portion, and an outer-diameter-side part of the outward flange portion,
• the front surface and the back surface of the sensor opposed portion of the annular fixing member are conical surfaces having diameters that reduce from the end edge toward the outward flange portion of the annular fixing member, and
• an outer circumferential surface of the annular plastic magnet, and an axial-direction part, of an inner circumferential surface of the annular plastic magnet, that is on a sensor opposed portion side with respect to the outward flange portion, are conical surfaces having the same inclination direction as the sensor opposed portion.

A method for manufacturing a radial-type magnetic encoder that includes

• an annular fixing member including a cylindrical portion to be attached to a rotary body, and
• an annular plastic magnet attached to the annular fixing member and magnetized in a multipole form so as to have N poles and S poles at regular intervals in a circumferential direction, the method comprising:
• a press working step of manufacturing the annular fixing member by press working, the annular fixing member including the cylindrical portion, an outward flange portion extending outward in a radial direction from an edge of the cylindrical portion, and a sensor opposed portion bent from an edge of the outward flange portion and opposed to a magnetic sensor which detects rotation of the magnetic encoder, the annular fixing member having a substantially U-shaped sectional shape along a plane including the radial direction and an axial direction;
• and
• an injection molding step of, in a state in which the annular fixing member is placed in a mold for injection molding, injecting a melted annular plastic magnet material into a cavity of the mold, to mold the annular plastic magnet having a shape that covers a front surface, a back surface, and an end edge of the sensor opposed portion, and an outer-diameter-side part of the outward flange portion, wherein
• the front surface and the back surface of the sensor opposed portion of the annular fixing member are conical surfaces having diameters that reduce from the end edge toward the outward flange portion of the annular fixing member, and
• an outer circumferential surface of the annular plastic magnet, and an axial-direction part, of an inner circumferential surface of the annular plastic magnet, that is on a sensor opposed portion side with respect to the outward flange portion, are conical surfaces having the same inclination direction as the sensor opposed portion.