US Patent 7581628 Electromagnetic clutch

An electromagnetic clutch 1 is disclosed having first and second relative rotary members 3, 5, an electromagnet 11 having a coil 7 and a yoke 9, a rotor 13 placed in close proximity to the electromagnet 11 and permeating magnetic field lines through the yoke 9, a friction clutch 15 operative to transfer drive torque between the first and second relative rotary members 3, 5, and an armature 17 permeating magnetic field lines coming from the rotor 13 for controlling coupling the friction clutch. The rotor 13 includes first and second magnetic members 21, 23 for forming at least one magnetic flux loop 19 and the first and second magnetic members 21, 23 are made of materials different from each other.