ELECTROMAGNETIC CLUTCH

An electromagnetic clutch is configured to achieve a cutoff state by changing a winding diameter of a wrap spring. The electromagnetic clutch includes a driving element connected to a shaft and supporting one end of the wrap spring, an operating element fitted on the shaft and supporting the other end of the wrap spring, and an armature rotatable in unison with the shaft between the driving element and operating element and movable along a rotational axis. A main aperture is formed in the operating element while an auxiliary aperture is formed in the armature to achieve a positional relationship to electrify an electromagnetic solenoid to attract the operating element and then allow rotation of the driving element by dynamic inertia and attract the armature to the operating element with the wrap spring being remote from an inner surface of an input pulley.