GB2107414A - Multiple-disc electromagnetic clutch - Google Patents

Abstract

An output disc (91) connected to an output hub (107) is mounted between a pair of input discs (16, 18) connected to the input shaft (11). Magnetic flux passing through the output disc and the input disc clamps the output disc between the input discs. The input disc (18) is splined for axial movement on shaft (11) and the output disc floats axially between the input discs by means of formations (89, 90). Disc (18) is spring biased away from engagement. <IMAGE>

Description

SPECIFICATION Multiple-disc electromagnetic clutch This invention relates to a clutch or brake and, more particularly, to an electromagnetic clutch having increased torque capability.

Mechanical clutches for selectively coupling torque from a rotating shaft, powered by a motor or other power source, to a rotatable load, are well known in the art. An input disc connected to the rotating input shaft is mounted parallel to an output disc connected to the load. When the input and output discs are separated the load is isolated from the power source. When the power is to be transferred from the power source to the load the discs are pressed together by various means. If the load connected to the output disc is too large for the amount of friction between the disc, slippage will occur between the disc and the power will not be transferred to the load. Various methods of pressing the discs together to couple the output to the input include using springs, hydraulics or magnetic flux to force the discs together.Prior art electro-magnetic clutches employ an input disc and an output disc and a magnetic structure which forces these discs together when a magnetic flux-links portions of the magnetic structure. Such a clutch is limited in the amount of force which pulls the discs together and limited in the amount of to rque transferred between the input and output shafts connected to these discs.

The present invention aims to alleviate some of the advantages of the prior art by employing an output disc mounted between a pair of input discs.

One of the input discs is slidably connected to a rotatable input shaft and the output disc is connected to an output hub. An energizing coil or other means supplies a magnetic flux which links one input disc to the other through the output disc. LThe magnetic flux through the output disc is generally at right angles to the surface of the output disc to increase the torque which can be coupled from the input shaft to the output hub. The apparatus of the present invention can also be used as an electromagnetically operated brake by modifying the structure to rigidly connect the output disc to a nonmovable member.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings of which: Figure 1 is a longitudinal cross-section of a multiple-disc electromagnetic clutch; Figure 2 is a vertical section of the electromagnetic disc of the clutch shown in Figure 1 and taken along line 2 - 2 in Figure 1; and Figure 3 is a longitudinal cross-section of another electromagnetic clutch according to the present invention.

The electromagnetic clutch shown in Figures 1 and 2 includes an annular hollow body member 10 having an input shaft 11 rotatably mounted through a longitudinal bore 12 in the body member 10. An annular rotor disc 16 having an axially extending flange 17, and a primary disc 18 are mounted about an input shaft 11 and rotate with the shaft 11. A splined drive hub 22 having a plurality of splines 23 (Figure 2) is mounted between the primary disc 18 and the input shaft 11. The splines secured the drive hub 22 to the primary disc 18 and a key 24 mounted in a slot 28 in the shaft 11, secures the primary disc 18 and the rotor disc 16 to the shaft 11 to cause the shaft and the discs 16, 18 to rotate together.

However, the primary disc 18 is free to slide axially along the splines 23 about the shaft 11 to vary the spacing between the discs 16 and 18. A spring 29 biases the disc 18 away from the disc 16 and an annular ring 30, mounted in a groove 34 in the hub 22, limits the distance the primary disc 18 moves away from the rotor disc 16. A bearing 35 having an inner bearing race 36, an outer bearing race 40 and a plurality of balls 41 between the bearing races, rotatably mounts the shaft 11 and the discs 16, 18 to the body member 10.

The body member 10 includes a field coil 42 having a plurality ofwindings 46 which can be secured in place by an epoxy in a well known manner. A restraining bracket 47 which is welded or otherwise secured to the input end of the body 10 includes a bore 48 through which a pin or other fastener can be placed to secure the body member 10 to a device (not shown) which uses the clutch. The fastener must be placed in such a manner to prevent any preloading of the bearings 41.

The output portion of the clutch includes annular output hub 49 having a radially extending flange 50 adjacent one end and an axial bore 52 extending therethrough. A pair of bearings 53, 54 each having an inner bearing race 58, an outer bearing race 59 and a plurality of balls 60, rotatably mount the output hub 49 about the input shaft 11. An annular sleeve 64, and a pair of annular rings 65,66 mounted in a pair of annular grooves 70,71 in the hub 49 position the bearings 53, 54 inside the bore 52 of the hub. A nut 72 threaded on the left end 11 a (Figure 1) of the input shaft 11, and a washer 76 secure the inner race 58 of the bearing 54 against the drive hub 22.An annular end plate 77 is secured against the outer bearing race 59 by a plurality of bolts 78, each bolt extending through a bore 82 in the plate 77 and through a bore 83 in the output hub 49 into a threaded bore 84 in an annular cup 88.

The radially outer portion of the cup 88 includes a plurality of radial fingers 89 (Figures 1 and 2) each extending through a slot 90 in a output disc 91. The output disc 91 is supported and centered about the drive hub 22 by the fingers 89 of the cup 88, and the output disc 91 "floats" between the primary disc 18 and the rotor disc 16 when the discs are in a non-magnetized position as shown in Figure 1.

When the discs are magnetized, the primary disc 18 moves to the right forcing the floating output disc 91 to the right against the disc 16 to clamp the output disc between discs 16 and 18. The disc 91 includes a recessed pocket 95 having a slab of friction material 97 secured in the pocket by a quantity of adhesive material. The friction material decreases the wear between the output disc 91 and the primary disc 18 when the discs are clamped together. The rotor disc 16 also includes a pocket 101 having a slab of friction material 102 secured in the pocket by a quantity of adhesive. The friction material 102 decreases the wear between the rotary disc 16 and the output disc 91 when these discs are clamped together.

An annular output pulley 107 having axial bore 109 is secured to the output hub 49 by a plurality of bolts 112 each mounted through a bore 113 in the pulley and secured in a threaded bore 114 in the flange 50.

A V-belt 115 can be used to transfer power from the pulley 107 to a variety of devices (not shown).

To secure the output hub 49 to the input shaft 11 an electrical current is supplied to the field coil 42, causing a magnetic flux to follow a path through the body member 10 and the discs 16, 18,91 as shown by the arrows 118 (Figure 1). The magnetic flux enters and leaves the disc 91 at approximately right angles to the surface of the disc. This magnetic flux exerts a force which pulls discs 18 and 91 to the right toward the body member 10 to clamp the output disc 91 between input discs 16 and 18. In addition to the clamping action, the flux links the disc 91 to discs 16, 18 to produce a force which causes disc 91 to be pulled through with discs 16, 18. Routing the magnetic flux through the input and output discs produces a large torque from input shaft to output hub, with a relatively small clutch structure.The torque is several times as great as in prior art clutches of the same physical size. The proper routing of the flux is achieved by using non-magnetic weld materials and "soft" magnetic material for the flux carrying members.

Another embodiment of the present invention disclosed in Figure 3 differs from the embodiment of Figure 1 by the inclusion of another axial flange 17a on the rotor disc 16 which combines with the axial flange 17 to form a sleeve 108 extending the length of the clutch. A drive shaft 11' extends through a longitudinal bore 119 in the sleeve 108 and the shaft 11' is secured to the sleeve 108 by one or more setscrews 120 each extending through a threaded bore 124 in the sleeve 108. The pulley 107, the bearing 53, the cup 88 and the discs 18,91 are retained on the sleeve 108 by an annular snap ring 125 mounted in an annular groove 126 in the sleeve 108. The bearing 35 is retained on the sleeve 108 by an annular snap ring 130 mounted in an annular groove 131. A key 24a mounted in a slot 28a in the shaft 11', secures the rotor disc 16 to the shaft 11' to cause the shaft and the discs 16, 18 to rotate together.

The electromagnetic clutch of the present invention uses a magnetic flux to link an output disc to a pair of input discs and to clamp the output disc between the two input discs. The output torque is several times as large as in prior art clutches of the same physical size. The structure can also be used as an electromechanical brake by mounting the output disc in a fixed position to prevent rotation thereof.

Claims (12)

1. A magnetic clutch or brake having first and second input discs which are mounted for rotation with an input shaft and at least one of which is movable relative to the other axially of the shaft, a further output or fixed disc between the two input discs, and magnetic means for developing a magnetic flux which links the first input disc to the second input disc through the said further disc, to selectively clamp the further disc between the input discs.

2. A magnetic clutch or brake according to claim 1 and comprising means biasing the input discs axially away from the said further disc.

3. A magnetic clutch according to claim 1 or claim 2 wherein the magnetic flux through the further disc is generally at right angles to the surface of the further disc.

4. A magnetic clutch according to any one of claims 1 to 3 including means for slidably connecting at least one of the input discs to the input shaft to facilitate moving the input discs tightly against the further disc when the magnetic flux links the input and the further discs.

5. A magnetic clutch according to any one of claims 1 to 4 including a magnetic flux path which is routed through the further disc and through the first and the second input discs to link the further disc to the first and second input discs.

6. A magnetic clutch or brake according to claim 1 and comprising means for sliding the first input disc axially along the input shaft.

7. A magnetic clutch or brake according to claim 6 including means for biasing the first input disc away from the input disc to separate the further disc from the first and the second input discs in the absence of a magnetic flux.

8. A magnetic clutch or brake according to claim 6 or claim 7 including a magnetic flux path which is routed through the first input disc, through the further disc and through the second input disc with the magnetic flux generally at right angles to the surface of the further disc in the portion of the flux path through the further disc.

9. A magnetic clutch according to any one of the preceding claims wherein the said further disc is connected for rotation with a rotatable output member.

10. A magnetic clutch according to claim 9 as appendantto claim 6 including means connecting the further disc to the output member so as to permit axial movement of the further disc relative to the output member.

11. A magnetic clutch or brake having relatively rotatable parts one of which carries a first and a second disc rnounted for rotation with the part and at least one of which is movable relative to the other axially of the part, the other part comprising a further disc disposed between the said first and second discs, and magnetic means for developing a magnetic flux which links the first disc to the second disc through the further disc, to selectively clamp the further disc between the first and second disc, so preventing relative movement of the parts.

12. A magnetic clutch or brake constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.