DRIVING FORCE TRANSMITTING DEVICE AND METHOD OF DESIGNING THE SAME

PROBLEM TO BE SOLVED: To provide a driving force transmitting device which can make an electromagnetic clutch device function surely even though magnetic flux leaking from an armature to a protrusion of a moving cam member occurs.SOLUTION: The moving cam member 52 is formed to protrude on armature 43 side annularly and is provided with the protrusion 130 which regulates move to a direction opposed to yoke 41 side of the armature 43 by abutting against the armature 43. The protrusion 130 is provided with inner peripheral cylindrical surface 131, outer peripheral cylindrical surface 132, annular end face 133 capable of abutting against the armature 43, a tapered inner peripheral chamfering 134 which conects the inner peripheral cylindrical surface 131 to inner peripheral edge of the end face 133 and a tapered outer peripheral chamfering 135 which connects the outer peripheral cylindrical surface 132 to outer peripheral edge of the end face 133. Radial length Wb of the end face 133 is set to range from 1.3 mm to 2.0 mm.