Patent GB-677534-A (GB)
Title: Improvements in or relating to a coupling device
IPC: F16D37/02
Filed: 1949-07-04
Abstract: 677,534. Clutches; couplings. EATON MANUFACTURING CO. July 4, 1949 [July 13, 1948; June 4, 1949], Nos. 17594/49 and 17595/49. Class 80 (ii). [Also in Groups XXXIV and XXXV] In a magnetic clutch or coupling, a bonding material comprising a mixture of finely-divided magnetic material (preferably Carbonyl E, though iron may be used) and finelydivided solid dry lubricant (preferably graphite, though mica, soapstone, potstone, steatite, French chalk or lampblack may be used) is provided in the magnetic field across the air gap between opposed faces of relatively rotatable members. The field may be produced by a permanent magnet with an adjustable keeper or by an electromagnet. In the clutch shown in Fig. 1, a shaft 4 carries an electromagnet 24 with alternating poles 26, 28 separated from a surrounding drum 8 by an annular air gap 52, the drum being journalled on the shaft with fluidtight packing 56 but having a breather hole 58 filled with filter material. Labyrinth grooves 64 are arranged between the side faces of the rotor and the drum. As the shaft (or drum) is rotated, the dust-like bonding material in the drum is diffused, and, when the magnet 24 is energised, magnetic flux flowing across the gap 52 sets up solid-like columns of the dust between the poles and the drum to produce a friction drive, aided by the eddy currents set up during slip. It is stated that, with the shaft 4 driving and for a given excitation, a substantially constant torque is transmitted to the drum under overload slip conditions, whereas, with the drum 8 driving, the frictional torque transmitted becomes negligible when overload slip occurs, due to the powder being forced into the inter-pole spaces, transmitted torque being then due almost solely to eddy currents. This may be avoided by filling the inter-pole spaces with a non-magnetic material, such as cast aluminium, or by constructing the rotor of opposed cupshaped members providing opposed annular poles, the axial space between which is filled with non-magnetic material such as a copper tube. In this latter construction, the eddy current effect is greatly reduced. in the plate clutch shown in Fig. 10, a driven plate 156 is disposed between a driving plate 152, carrying a coil 212, and a presser plate 154, the whole being enclosed by a drum 164 secured to the plate 152. Under non-excited conditions, the plates 154, 156 are retracted by springs 176, 194. When the coil is energised, the plate 154 is attracted to reduce the air gaps, engagement being through the interposed layers of bonding material contained in the drum, the axial movement of the plates 154, 156 being limited by studs 180, 192. The presence of adequate quantities of bonding material in the air gaps during non-excited conditions is ensured by providing passages 240, 242, 244, 246, 248 in the plates through which the material circulates, or by making the plates (or the operative surfaces thereof) of material having a pronounced degree of magnetic retentivity, such as cast iron or steel, so that bonding material adheres to the plates, or by both of these expedients. Specification 649,553 is referred to.