Patent ID: 8235196

Claim:
An electromagnetic clutch comprising: a rotor rotatably surrounding a housing of a driven device; an armature hub fixed to a rotating shaft of the driven device; an armature disposed on said armature hub to be movable in an axial direction; a magnetic body incorporated in said rotor and a first permanent magnet which connects said armature to said rotor; a field core attached to the housing and inserted in said rotor to be in noncontact therewith; an excitation coil which is disposed in said field core and excited, when cutting off power transmission, to cancel a magnetic force of said first permanent magnet, thus releasing said armature from said first permanent magnet; and a second permanent magnet which separates said armature from said rotor, when cutting off power transmission, to move said armature toward said armature hub, wherein said first permanent magnet has a Curie temperature lower than a temperature of heat generated by said rotor upon slip rotation, wherein said rotor comprises an inner cylindrical magnetic path portion and an outer cylindrical magnetic path portion which are concentric, a disc-like magnetic path portion which connects one end of said inner cylindrical magnetic path portion to that of said outer cylindrical magnetic path portion, and an annular groove which accommodates said magnetic body, said first permanent magnet, and said field core, an annular space is defined by an inner surface of said magnet body which is annular, an inner surface of said first permanent magnet, and the inner cylindrical magnetic path portion, and said field core integrally includes an extension to be inserted in the space.