GB1085370A - Electromagnetic friction coupling - Google Patents

Abstract

1,085,370. Electromagnets. WARNER ELECTRIC BRAKE & CLUTCH CO. April 29, 1965, No. 18148/65. Heading H1P. [Also in Division F2] In a magnetically controlled coupling (see Division F2) comprising first and second members mounted for rotation, one relative to the other and formed by a rotatable armature member 10 and a stationary mounted magnet member 11 in the brake shown in Fig. 1. Opposed surfaces of the brake or clutch are adapted to be brought into or released from frictional engagement, the members defining a series path 17 adapted to carry magnetic flux in a closed loop which extends across the opposed surfaces, one of the members including a permanent magnet 16 which is interposed in the series path to create magnetic flux threading the path and a multiple turn electromagnetic winding 19 being carried by one of the members 11 such that when energized a magnetic flux threading the series path in a direction opposite to the permanent magnet flux substantially neutralizes the latter between the opposed surfaces so as to effectually neutralize the permanent magnet at the pole faces 14 to release the armature 10, a magnetic shunt 50 being provided round that portion of the series path which includes the permanent magnet. The permanent magnet may comprise a single piece annulus or an annulus series of shallow blocks 25 of generally rectangular shape arranged in an annular manner. The armature 10 is mounted for axial sliding movement by means of a sleeve 38 slidable on a collar 42 fixed to the rotatable shaft 30. A constant air gap is maintained between the armature and the pole faces 14 by means of a channel-shaped ring 3 which engages frictionally the collar 42 and, when wear of the friction surfaces takes place abuts the inner portions of bolt heads 39 and adjust the armature 10 such that when the brake is released a distance d equal to the. width of the air gap to be maintained between the armature 10 and the pole faces 14 is achieved. The winding 19 is released by direct current at a voltage of about 84 which may be derived from an alternating current source through a suitable rectifier (not shown). The reluctances of the parallel flux paths through the permanent magnet 16 on the one hand and the magnetic shunt 50 on the other is such that only a small part of the permanent magnet flux is by-passed through the shunt and thus lost when the permanent magnet alone is active while a substantial part of the coil flux required for neutralizing the permanent magnet flux is carried by the shunt to effect proper release of the brake without subjecting the permanent magnet to an undue demagnetizing force. The balance between the reluctances of the permanent magnet 16 and the shunt 50 when the coil 19 is energized may be adjusted by interposing a thin shim of non-magnetic high reluctance material in series with the permanent magnets at any point in the circuit.