Electromagnetic connecting device

An electromagnetic connecting device comprising:

• an electromagnetic coil;
• a field core including a first inner cylinder, a first outer cylinder, a bottom that connects an edge of the first inner cylinder and an edge of the first outer cylinder, and a coil storage groove that stores the electromagnetic coil;
• a rotor including a second inner cylinder, a second outer cylinder, a disc that connects an edge of the second inner cylinder and an edge of the second outer cylinder, and a core storage groove that stores the field core inserted from a side of an opening of the coil storage groove;
• and
• an armature facing the disc of the rotor,
• wherein the bottom of the field core wholly projects to an outside of the core storage groove,
• an outer peripheral surface of the first inner cylinder and an inner peripheral surface of the first outer cylinder include a first transition surface and a second transition surface, respectively, on a side of the bottom,
• each of the first transition surface and the second transition surface includes a tilting surface that gradually narrows a groove width of the coil storage groove along with an increase in a distance from the side of the opening of the coil storage groove,
• wherein the outer peripheral surface of the first inner cylinder includes a first tapered surface extending from an opening edge of the coil storage groove toward the bottom, and a second tapered surface that forms the first transition surface,
• the inner peripheral surface of the first outer cylinder includes a third tapered surface extending from the opening edge of the coil storage groove toward the bottom, and a fourth tapered surface that forms the second transition surface, and
• tilt angles of the second tapered surface and the fourth tapered surface with respect to an axis are larger than tilt angles of the first tapered surface and the third tapered surface with respect to the axis, respectively.