Abstract: An inner peripheral surface of an outer cylindrical tubular portion and an outer peripheral surface of an inner cylindrical tubular portion of a rotor are respectively shaped into a stepped form. A radial distance between the outer cylindrical tubular portion and the inner cylindrical tubular portion at a counter-armature side location is larger than that of an armature side location in the rotor. An outer peripheral surface of an outer cylindrical tubular portion and an inner peripheral surface of an inner cylindrical tubular portion of a stator are respectively shaped into a stepped form. A radial distance between the outer peripheral surface of the outer cylindrical tubular portion and the inner peripheral surface of the inner cylindrical tubular portion at the counter-armature side location is larger than that of the armature side location in the stator.

Abstract: A thermal fuse is covered with a case that has a slit. A capacity of the case is larger than a volume of the thermal fuse, and the case has a space that is formed between an inner wall surface of the case and the thermal fuse. The slit is formed in the case introduce radiant heat, which is generated at a friction surface of a rotor, into an inside of the case. Thereby, the radiant heat, which is inputted into the inside of the case through the slit, can be reflected by the inner wall surface of the case and thereafter can be absorbed by the thermal fuse.

Abstract: An inner peripheral surface of an outer cylindrical tubular portion and an outer peripheral surface of an inner cylindrical tubular portion of a rotor are respectively shaped into a stepped form. A radial distance between the outer cylindrical tubular portion and the inner cylindrical tubular portion at a counter-armature side location is larger than that of an armature side location in the rotor. An outer peripheral surface of an outer cylindrical tubular portion and an inner peripheral surface of an inner cylindrical tubular portion of a stator are respectively shaped into a stepped form. A radial distance between the outer peripheral surface of the outer cylindrical tubular portion and the inner peripheral surface of the inner cylindrical tubular portion at the counter-armature side location is larger than that of the armature side location in the stator.

Abstract: A coil housing has an inner ring, which is shaped into an annular form and is placed on an inner side of an electromagnetic coil in a radial direction of a rotational axis. A thermal fuse is placed on an inner side of a coil inner peripheral end of the electromagnetic coil in the radial direction, so that the thermal fuse can be placed in such a manner that the thermal fuse does not limit a length of the electromagnetic coil in a direction of the rotational axis by using a radial thickness of the inner ring that is indispensable as a part of a structure of a magnetic circuit. Thus, it is possible to sufficiently limit occurrence of limiting of a size of the electromagnetic coil that is caused by the placement of the thermal fuse.

Abstract: An inner peripheral surface of an outer cylindrical tubular portion and an outer peripheral surface of an inner cylindrical tubular portion of a rotor are respectively shaped into a stepped form. A radial distance between the outer cylindrical tubular portion and the inner cylindrical tubular portion at a counter-armature side location is larger than that of an armature side location in the rotor. An outer peripheral surface of an outer cylindrical tubular portion and an inner peripheral surface of an inner cylindrical tubular portion of a stator are respectively shaped into a stepped form. A radial distance between the outer peripheral surface of the outer cylindrical tubular portion and the inner peripheral surface of the inner cylindrical tubular portion at the counter-armature side location is larger than that of the armature side location in the stator.

Abstract: A thermal fuse is covered with a case that has a slit. A capacity of the case is larger than a volume of the thermal fuse, and the case has a space that is formed between an inner wall surface of the case and the thermal fuse. The slit is formed in the case introduce radiant heat, which is generated at a friction surface of a rotor, into an inside of the case. Thereby, the radiant heat, which is inputted into the inside of the case through the slit, can be reflected by the inner wall surface of the case and thereafter can he absorbed by the thermal fuse.

Abstract: A coil housing has an inner ring, which is shaped into an annular form and is placed on an inner side of an electromagnetic coil in a radial direction of a rotational axis. A thermal fuse is placed on an inner side of a coil inner peripheral end of the electromagnetic coil in the radial direction, so that the thermal fuse can be placed in such a manner that the thermal fuse does not limit a length of the electromagnetic coil in a direction of the rotational axis by using a radial thickness of the inner ring that is indispensable as a part of a structure of a magnetic circuit. Thus, it is possible to sufficiently limit occurrence of limiting of a size of the electromagnetic coil that is caused by the placement of the thermal fuse.

Abstract: An end surface portion of a rotor includes a friction surface and an end surface, which are spaced from each other in an axial direction. The armature is attracted and attached to the friction surface of the rotor by an electromagnetic attractive force when a solenoid coil is energized. The stator is opposed to the end surface of the end surface portion. A thermal fuse is held by a portion of a resin member located in an opening of the stator and is melted and disconnected to cut supply of an electric current to the solenoid coil when a temperature of the thermal fuse is equal to or higher than a predetermined temperature. The resin member has a recess that is formed in a predetermined position of a surface of the resin member, which is adjacent to the thermal fuse.

Abstract: An end surface portion of a rotor includes a friction surface and an end surface, which are spaced from each other in an axial direction. The armature is attracted and attached to the friction surface of the rotor by an electromagnetic attractive force when a solenoid coil is energized. The stator is opposed to the end surface of the end surface portion. A thermal fuse is held by a portion of a resin member located in an opening of the stator and is melted and disconnected to cut supply of an electric current to the solenoid coil when a temperature of the thermal fuse is equal to or higher than a predetermined temperature. The resin member has a recess that is formed in a predetermined position of a surface of the resin member, which is adjacent to the thermal fuse.