A permanent-magnet coupling with rapid disconnect capability

A coupling system has been developed for transmitting power from a drive motor to a load. The required torque is produced by the induction of eddy currents in conducting discs due to their relative motion (slip) with nonmagnetic discs which house permanent magnets. In addition to the tangential (torque producing) forces that result from this configuration, forces are produced normal to the disc surfaces. Up to the condition of torque breakdown, the normal (axial) forces between the discs are attractive; these serve to keep the coupling engaged. At slips beyond the breakdown condition the axial forces become repulsive. This paper describes the modeling and testing of a coupling, rated at 74.6 kW, which utilizes the repulsive forces to disengage the coupling; thus, at high slips the motor and load are disconnected. Hence, the coupling serves to protect the motor when excessive loads or jammed loads occur.