Electromagnetic Clutch

An electromagnetic clutch, comprising:

• a rotor unit provided with a rotor that is rotated with power of a driving source, and rotatably supported to a boss formed on an end surface of a housing of a driven device;
• an armature unit provided with an armature that is magnetically attracted to the rotor when the rotor is excited, and fixed to a rotation shaft of the driven device, which passes through the boss;
• an electromagnetic coil unit including:
• a bobbin having first and second flanges on both sides of a cylindrical portion with an electromagnetic coil wound around an outer circumference of the cylindrical portion positioned between the flanges, the coil serving to excite the rotor in response to electric power supply;
• and
• a ring case provided with a circular bobbin container and accommodated in a circular recess formed in the rotor, the ring case being fixed to the end surface of the housing of the driven device with an opening edge of the bobbin container facing toward the rotor;
• and
• a thermally-actuated element attached to the rotor unit, and displaced toward the electromagnetic coil unit at over a predetermined temperature, the thermally-actuated element serving to cut a cutting wire portion that forms a part of the electromagnetic coil to forcibly interrupt electric power supply to the electromagnetic coil, with the wire being placed toward the electromagnetic coil unit across a movement area of the thermally-actuated element,
• wherein the bobbin includes:
• first and second wall portions extending opposite to each other from the first flange formed on the opening edge in the bobbin container toward a bottom wall in the circular recess of the rotor where the thermally-actuated element is mounted;
• an inner abutment portion extending from an extension end of the first wall portion toward an inner opening edge of the bobbin container;
• and
• an outer abutment portion extending from an extension end of the second wall portion toward an outer opening edge of the bobbin container,
• wherein the bobbin is accommodated into the bobbin container such that the inner abutment portion and the outer abutment portion abut inner and outer opening edges of the bobbin, respectively, and
• wherein the cutting wire portion is stretched between both of the wall portions at a predetermined distance from an end surface of each of the first and second wall portions.