GB2315314A - Membrane type flexible coupling - Google Patents

Abstract

A flexible coupling comprises a star shaped membrane fixed by spot welds 7 to an outer ring 3 and by spot welds 8 to an inner disc 10 or to the end of a solid shaft (2, Fig. 1). The other end of the shaft may be fixed to a further coupling (Fig. 1). Alternatively the ends of a tubular spacer (11, Fig. 3) may be bolted to the discs 10 of a pair of couplings using threaded holes 13. The spot welds 7,8 may be produced by resistance welding and provide a fail safe feature. A destructive overload causes the inner weld cluster to shear thus severing the drive but preserving the integrity of the flexible spokes. The coupling may be used in a flammable environment without the need to manufacture the coupling from special non ferrous membrane materials.

Description

IMPROVEMENTS RELATING TO MEMBRANE TYPE FLEXIBLE COUPLINGS The invention relates to power transmission couplings incorporating the use of one or more metallic flexible membranes of the radial spoke type particularly with the means of attachment of the said membranes to the rigid parts of the coupling to ensure, for a given outside diameter, a flexibility not available from the conventional radial spoke types. At the same time ensuring the satety of the connected machinery against a destructive overload by attaching the flexible membranes of the coupling to the rigid members of the coupling in a manner which avoids the shearing of the flexible spokes and the consequent dangerous attrition which follows that event.

In my Patent Application No. GB 2280725A a number of methods are described for achieving the said flexibilty based on the key premiss that whatever the method, the membranes assembly must be fixed at its outer diameter as close as possible to the rim of the Coupling and at its inner diameter, as close as possible to the centre line of the coupling this being the only way of providing the maximum free flexing length of the spokes of the said membrane assembly. In the conventional radial spoke membrane couplings, rivetted rings are attached to the inner and outer annuli in order to accomodate the bolts fixing the said membrane assembly to the hub and spacer respectively, so that for a given coupling diameter the free flexing length of the said spokes is severely restricted, resulting in an overall coupling flexibility which is unacceptable.

In Patent Application No.GB2280725A, the preferred method of attachment of the membrane pack to the rigid coupling members is by frictional drive, obtained at the periphery by a pair of rings applying pressure on a narrow annulus of the membranes adjacent to their outside diameter. The pressure is obtained from bolts located well inside the clamped annulus and out of contact with the membranes.

A similar arrangement is provided for the frictional drive at the inner annulus of the membranes. This method requires four clamping rings on each membrane pack.

According to the present invention the flexible membranes consist of star shaped laminations with at least 2 spokes free at their extremities but joined at their inner extremities to form a circular disc carrying a centralhole locating the membrane pack to solid, flanged spacer shaft or to a disc in the case of a tubular spacer. The purpose of the said central hole being to locate accurately the membranes to the spacer.

Subject to considerations of coupling size, weight, spacer length and critical speeds each membrane pack is attached either to a solid spacer or to a plate acting as carrier of a tubular spacer.

Each membrane pack is then welded, preferably by resistance welding techniques, to the aforesaid solid spacer or carrier plate.

The flexible transmission unit is completed by welding two rings to the outer extremities of the spokes, the said rings are then used for bolting to the hubs attached to the driving and driven shafts.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings noting the following definition of the assemblies described in the text.

"Flexible Transmission unit" as in Figs. 1 and 3, comprising a welded or bolted spacer, the said unit thus being ready for bolting on site to the hubs of the driving and driven machines.

"Module" as in Fig.4, suitable for bolting to a tubular or solid spacer, to form a flexible transmission unit as defined above.

Fig.1 shows a flexible unit comprising flexible membranes welded their inner diameter to a solid spacer and at their outer diameter to two captive rings.

Fig.2 shows by way of example a five spoke membrane pack located at its outer diameter on a ring with five threaded holes used for bolting oii site to a hub (not shown), the said holes being located anywhere in the clear space available between the spokes.

Fig.3 shows two modules as in fig.4, bolted to each end of a tubular spacer, forming a flexible unit as defined above.

Fig.4 shows a module comprising a membrane pack with a ring welded near the outer diameter and a disc welded near the inner diameter.

Fig.5 shows the method used for removing the bending stresses from the root of the outer weld spots to two profiled toroidal chamfers formed by the outer ring and the hub rim, under conditions of angular shaft misalignment.

Referring to Fig.l, the invention in its lightest form comprises two membrane packs 1 welded respectively to the spacer shaft 2 and rings 3. The method used to achieve concentricity between shaft 2, rings 3 and the two coupling hubs (not shown) is as follows: The membrane pack 1 is accurately located on shaft 2 by means of hole 4 (Fig.2) fitting register 4 (Fig.1). Ring 3 is located concentrically before welding by a fixture plate (not shown) at register 4 and at spigot 5 of the ring for which a clearance 6 serves the double purpose of yielding the neccessary float as well as preventing the distortion of the spoke during welding.

Spigot 5 is used to locate the finished flexible transmission unit on the hubs fixed to the two shafts of the connected machines.

Referring to Fig.2 the free flexing length of each spoke is determined by the distance between point 7 at the outer end of the spoke and point 8 at the inner end, this length being considerably greater than is possible by the conventional method of rivetting the membranes to clamping plates. Thus, tbe axial flexibility is much greater than is possible by any other method, other than in my Patent Application No. GD 2280725A.

In Fig.3 the membrane packs are shown welded at their outer diameter to ring 3 and at their inner diameter to a disc 10 thus forming a flat element defined above as the "Module" to which is attached a tubular spacer 11 bolted to item 10. Compared with Fig.l this form allows the module to be attached to any required spacer length and offers considerable logistic advantages, especially in the larger sizes.

Fig.4 shows the module in isolation, consisting of 3 items: The membrane pack 1 locating on plate 10 at its centre Spigot 12.

Ring 3 is centralised before welding by a circular plate fixture (not shown), locating on spigot 12 and register 5, as explained above with reference to Fig.1. It must also be noted that the angular relationship between the threaded holes 13 (Fig.4) and the flexible spokes, is unimportant, thus simplifying manufacture.

With reference to Fig.5 and under conditions of axial membrane deflection or angular hub misalignment, bending stresses will occur1 at the weld 7 Fig.2 and it is within the scope of this invention to provide means of eliminating these stresses by providing toroidal shaped surfaces close to weld 7. The radius of these surfaces is designed to follow tlie deflected contour of the membranes, minimising the stress concentration tis point.

Fig.5 is a radial section through weld spot 7 at the outer end of the spoke showing the spot clamped between face 14 of ring 3 and face 15 of the hub flange. The inner edges of these faces have toroidal reliefs 16 and 17 following the contour of the bent membranes and thus restricting the duty of the weld spot to one of shear only.

In Fig.2 it will be noted that the inner extremities of the spokes are blended at 9A to the circular inner zone of the membranes, with the weld spots 9 well inside the edge 9A. As the flexibility of this inner zone is smaller than that of the spokes at 9A, the axial thrust of the membranes on the weld spot is greatly diminished

Claims (6)

1. CLAIMS 1. A flexible coupling comprising two axially spaced input and output members flexibly connected to a spacer shaft in a way providing maximum flexibility combined with a 'fail safe' feature against destructive torque overload as is available in spoke type flexible membranes. The outer extremities of these spokes are spot welded to a circular ring used for bolting to the coupling hubs, the inner extremities are joined to a commoii circular portion spot welded either to a solid spacer shaft or to a disc which in turn may be bolted to a tubular spacer. When the flexible membrane is welded to the aforesaid disc, a simple flexible unit is formed having a thin flat shape consisting of only 3 parts, the flexible membrane pack, the outer ring and the inner disc resulting in manufacturing cost savings.

   2. A module according to claims 1 and 2 comprising a flexible membrane pack welded at its outer diameter to a ring and at its inner diameter to a concentric disc for the purpose of bolting a tubular or solid spacer shaft.

   3. A flexible coupling according to claims 1 to 3 comprising outer rings welded to the extremities of the spokes incorporating an annular plane surface on which the extremities of the spokes are welded, the inner edge of the said annulus being profiled to support the bending of the spokes under conditions of coupling axial deflection or angular misalignment. A similar profiled chamfer is provided on the hub flange so that when assembled, the welded region of the outer spoke extremities is clamped between the said annuli and bending stresses are removed from the weld spots.

   4. A flexible coupling comprising a flexible membrane pack welded near its inner diameter to a spacer shaft or disc so that in the event of a destructive overload the weld will shear at a predictable torque severing the drive without shearing the spokes thus eliminating the undesirable attrition that would otherwise occur at the fractured edges of the sheared spokes.

   5. A flexible coupling substantially as described herein with reference to Figs.1 to 5 of the accompanying drawings.

   Amendments to the claims have been filed as follows CLAIMS 1. A flexible coupling comprising two axially spaced input and output members flexibly connected to a spacer shaft in a way providing maximum flexibility combined with a "fail safe" feature against destructive torque overload as is available in spoke type flexible membranes. The outer extremities of these spokes are spot welded to'a circular ring used for bolting to the coupling hubs, the inner extremities are joined to a common circular portion spot welded either to a solid spacer shaft or to a disc which in turn may be bolted to a tubular spacer. When the flexible membrane is welded to the aforesaid disc, a simple flexible unit is formed having a thin flat shape consisting of only 3 parts, the flexible membrane pack, the outer ring and the inner disc resulting in manufacturing cost savings.
2. 2. A flexible coupling comprising flexible membranes with an outer profile such that a radial clearance between the membranes' outer edges and the spigot on the clamping ring ensures distortion free welding, and a centre hole locating on the spacer stub and providing accurate concentricity between the membrane packs and the associated rigid parts.

   A further advantage being that it allows the entire membrane profile to be manufactured by water jet technologies eliminating the need of costly press tools.
3. 3. A module according to claims l and 2 comprising .1 flexible membrane pack welded at its outer diameter lo a ring and nl its inner diameter to a concentric disc for Ihe purpose Of bolting n tubular or solid spacer shaft.
4. 4. A flexible coupling according to claims 1 to 3 comprising outer rings welded to the extremities of the spokes incorporating an annular plane surface on whi cli the extremities of the spokes are welded, the inner edge of tlie said annulus being profiled to support the bending of the spokes under conditions of coupl ing axial deflection or angular misalignment. A similar profile chamfer is provided on the hub flange so that when assembled, the welded region of the outer spoke extremities is clamped between the said annull and bending stresses are removed rrom time weld spots.
5. 5. A flexible coupling comprising a flexible membrane pack welded near its inner diameter lo a spacer shaft or disc so that in the event of a destructive overload the weld will shear at a predictable torque severing the drive without shearing the spokes thus eliminating the undesirable attrition that would otherwise occur at the fractured edges of time sheared spokes.
6. 6. A flexible coupling substantially as described herein with reference to Figs. 1 to 5 of the accompanying drawings.