Electromagnetic clutch

Abstract

An electromagnetic clutch assembly for use with a refrigerant compressor for an automotive air-conditioning system includes a first rotatable member, such as a rotor, having an axial end plate of magnetic material and a second rotatable member connected to an outer end of a drive shaft of the compressor. An armature plate of magnetic material is elastically connected to the second rotatable member. The armature plate faces the axial end plate of the rotor with an axial air gap therebetween. An electromagnetic device is disposed within the rotor and is operable to attract the armature plate into contact with the axial end surface of the rotor such that the rotation of the rotor can be transmitted to the drive shaft when the electromagnetic device is activated. The electromagnetic device includes at least first and second electromagnetic coils which are axially aligned so as to generate a thermal difference therebetween when heat is conducted to the electromagnetic device from a contact surface between the axial end plate of the rotor and the armature plate. The first and second coils are connected in series between the battery and ground. A control device controls the connection and disconnection of the electromagnetic device to the battery. The control device disconnects the electromagnetic device to the battery when the thermal difference exceeds a predetermined value while the electromagnetic device is activated.