GB2280725A - A fail safe flexible coupling having a membrane with a large spoke lenght - Google Patents

Abstract

A flexible membrane has bolts 11, 12 placed in windows so that the spokes effective length 13 is increased and upon the spokes failure no torque is transmitted by the bolts. The membrane or membrane pack is clamped at its outer annulus 8 between a coupling hub and clamping ring 14 and at its inner annulus 10 between ring 15 and drive ring 16. Tightening the bolts 11, 12 generates friction at the inner and outer annuli 9, 10 so that torque is transmitted. A spacer 17 is spigotted and bolted to drive ring 16 and is removed by axially forcing ring 15 against the hub face thus releasing register 18 from ring 16. Ring 15 may be disposed of and the membrane/membrane pack welded, eg laser or electron beam, directly to the drive ring (22, fig 7). Outer annulus 9 may be discarded and the spokes clamped between ring (30, figs 7 and 8) and hub (33, fig 7), thereby reducing clamping stresses. <IMAGE>

Description

IMPROVEMENTS RELATING TO MEMBRANE TYPE FLEXIBLE COUPLINGS The invention relates to power transmission couplings incorporating one or more metallic flexible membrane assemblies particularly with the means fOr providing the flexibility and the means of attachment of the said membranes to the rigid parts of the coupling, The invention relates to the means provided for the safety of the connected machinery in the event of membrane failure from overload or excessive misalignment.

Current designs of membrane couplings may be divided into two broad categories: (a) The peripheral link type in which the driving and driven members are connected by flexible links whose extremities are attached alternately to the driving and driven members. The means of attachment is always by a number of bolts each carrying a substantial nut and and bolt head both of which must be accomodated in clearance holes in the periphery of the driving and driven members.In the event of of link fracture the drive is transferred to the bolt heads and all elastic flexibility is lost. In the event of deep indentation there is a risk of large axial thrusts being transmitted from one machine to the other, compromising the bearings of both.

(b) The radial spoke type in which torque is transmitted from the outer periphery of the membranes via a number of radial spokes to its inner diameter. In the event of a damaging overload, the radial spokes will shear allowing the outer periphery of the driving hub to rotate freely about the inner diameter thus releasing the drive and reducing the torque to zero. The disadvantage of the system is the lack of flexibility of the spokes due to their reduced length.

Attempts to overcome this problem by duplicating the flexible packs have proved unsatisfactory and expensive.

It is the purpose of this invention to divide a form of membrane with the ample flexibility of the peripheral link system combined with the fail safe characteristic of the radial spoke system.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig.l shows the essential elements of the peripheral link type coupling i.e. links and bolt heads with their housing holes.

Fig,2 shows the essential elements of the radial spoke type membrane with the outer annulus driving the inner annulus via the radial spokes.

Fig,3 is a vie* of the flexible membrane claimed in this invention showing a spoke length 13 approximately twice the free length 8 of Fig.2 which represents the existing designs of that type.

Fig.4 shows a radial section of the coupling half comprising the flexible membrane pack clamped between two rings forming a sub assembly mounted on the driving and driven members of the coupling.

Fig.5 shows the friction coefficients on which the drive of the system is based.

Fig.6 shows the cross section of a coupling comprising a membrane pack clamped at its outer rim and welded to the spacer drive ring avoiding the use of the inner clamping ring.

Fig.7 shows in detail the weld of the membrane pack to the drive ring to ensure the preservation of the mechanical properties of the membranes.

Fig.8 shows a coupling design with an alternative form of membrane without an outer rim connecting the extremities of the spokes.

Referring to Fig,1, 6 peripheral links are shown attached to tEle hub I by three bolts 2, the other three extremities attached by bolts 3 to the driven member (not shown) with their bolt heads protruding into the hub flange 1, thus requiring clearance holes 4.

In the event of link fracture the drive will be transferred to the bolts 3 arrested by the clearance holes 4, running the risk of damaging axial forces being transmitted from one driven machine to the other.

Fig.2 shows a conventional radial spoke membrane. Within its outside diameter the outer clamping annulus 5 contains the clamping bnit holes and the inner annulus 6 is subject to two conflicting requirements: Its diameter must be as large as possible in order to minimise the shearing forces in that region, but small enough to provide a reasonable free flexing span 8. A typical value for this length is 16% of tlie outside diameter of the membrane.

Fig.3 shows the shape of the membrane according to the invention: The outer and inner clamping annuli 9 and 10 are narrow and devoid of bolt holes. The torque forces are transmitted by friction generated by the tightening of bolts 11 and 12 located in the windows adjacent to the spokes. For both annuli two bolts are allocated on either side of each spoke, resulting in the following significant advantages.

a. The effective length 13 of the spoke is nearly 30%o of the diameter of the membranes and should be compared with the length of 16% associated with Fig.2. The approximate relationship between the force IFt required to produce an axial deflection tytis

where E=YounRs modulus. L = free sDoke length between annuli

and a ' cross sectional of the spoke. The membrane of Fig.3 is about 5 times more flexible than the membrane of Fig.2, b. The clamping bolts are subject only to tensile stresses without bending.

c. The radial location of the membranes and the suspended masses is made by the outer and inner peripheries and not by the fitting bolts as in Fig.2. As a result, the location of the bolts is not critical, d. It must be borne in mind that a 6-link coupling as in Fig.1 has 3 working and 3 idle links. The minimum number of spokes in the system of Fig.3 is also 3 with the added advantage of overload protection which is absent from the link type of Fig.1.

Fig.4 is a half section of the membrane pack in Fig.3 bolted to the coupling hub at the outer annulus 9 by the clamping ring 14.

Similarly, the inner annulus 10 is clamped between rings 15 and 16 with the clamping bolts 11 and 12 respectively outside the outer and inner annuli. The spacer 17 is shown spigotted and bolted to the inner ring 16 and is removed by jacking ring 15 against the coupling hub face thus releasing the register 18.

Fig.5 shows the friction coefficients on which the size of the clamping bolts is calculated, a typical value of 0.3 being based on shop dry conditions.

Fig.6 shows the method proposed to eliminate the clamping plate 15 of Fig.4 thereby reducing the cost and weight of the coupling as well as reducing the minimum distance between shaft ends.

The flexible membrane pack 19 is clamped between the hub flange 20 and the ring 21 in a manner similar to that of Fig.4.

The membrane pack 19 is welded to the drive ring 22 at their common contact surface 23 using techniques currently available such as Electron Beam Welding or Laser Beam Welding. Spacer 27 is shown located radially by the spigot 26 engaging in register 25. To assemble or remove the spacer, jacking screws are wound into holes 24 withdrawing the ring register 25 from the spacer spigot 26 and releasing the spacer from its radial constraint.

Fig.7 shows an enlarged section of the welded joint between the membrane pack and the ring 22. According to the available techniques the membrane material 28 is fused with the ring material ensuring a continuity at their contact surface which is essential to the preservation of the mechanical properties of the membranes i.e.

maintenance of the shear and tensile strengths required for the transmission of torque under axial deflection or angular shaft misalignment.

Fig.8 shows a 5-spoke membrane without the outer rim connecting the extremities of the spokes shown in item 9 of Fig.3. The spokes are located in the clamping ring 30 with the clamping bolts 31 closer to the outside diameter thus reducing the clamping stresses of the ring as well as its size. A further advantageof this type of membrane is the open apertures which reduce considerably its manufacturing cost.

A spacer type coupling is shown designed with the open membrane described above. Each spoke 32 is clamped between hub 33 and ring 30 with bolts close to the outside diameter thus allowing a maximum hub bore larger than the one shown in Fig.6.

Claims (7)

1. A flexible membrane for use with power transmission couplings comprising an outer and inner annular area forming the surface via which torque may be transmitted from one annulus to the other by friction without the need for bolt holes within the area of the annuli. Torque is transmitted from one annulus to the other via two or more radial spokes connected thereto, in a manner maximising the active length of the spokes and increasing their flexibility above that available from existing designs of the same outside diameter.

Friction forces are generated by bolts crossing the membranes through the open 'windows' available between spokes. In the event of a destructive torque overload the spokes are intended to shear, thereby protecting the connected machinery, a property not available from the peripheral link type.

2. A flexible membrane as in Claim 1 wherein torque is transmitted by friction from the driving member of the coupling to the driven member via a number of radial spokes.

3. A flexible membrane as in Claim 2 with outer and inner circular edges used to locate the membranes to the rigid members of the coupling without recourse to fitting bolts.

4 A flexible membrane as in Claim 1 in which the outer edges of the spokes are not connected by a rim with clamping bolts on either side of each spoke, free of all contact with the membrane.

5. A flexible membrane as in Claim 1 in which the inner rim is welded to a torque transmitting ring or plate, eliminating the need for a third clamping ring.

6. A flexible power transmission membrane described herein with reference to Figs.1 to 7 of the accompanying drawing.

Amendments to the claims have been filed as follows 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 elements but without incurring the severe penalty of poor flexibility typical of the said spoke type flexible elements.The claimed flexible elements have spokes in star form with their inner extremities joined to a common circular rim and with their outer extremities either joined to an outer rim or independent of each other the said extremities clamped to the outer periphery of the adjacent hub by a clamping ring secured by means of bolts clear of any contact with the flexible membranes ensuring that torque is transmitted by friction similarly the inner rim of the said flexible elements is clamped to a pair of rings secured by bolts out of contact with the flexible element alternatively the inner diameter of the inner rim may be welded to the spacer shaft and with either method i.e. clamping or weldingthe disposition of the bolts ensures a free flexing length of the spokes not possible with the conventional spoke type couplings.

2. A flexible coupling according to Claim 1 comprising spoke type flexible elements having a circular outer periphery fitting into corresponding spigots in the hub flanges and ensuring concentricity of the spacer unit not available in couplings where such concentricity relies on the use of fitting bolts.

3. A flexible coupling according to Claims 1 and2 wherein the outer extremities of the flexible spokes are clamped to the hub flange by means of a ring so that the clamped portion of the spokes is a narrow strip close to the outer diameter with the clamping bolts straddling each spoke and ensuring (a) the maximum free spoke length and (b) no contact with the flexible spokes thus allowing the use of standard bolts in pure tension.

4. A flexible coupling according to any of the claims above wherein the inner diameter of the inner rim of the flexible pack is welded to the spacer shaft ensuring that the overall free flexing length of the spokes is greater than would be possible if the flexible element were fixed to the spacer shaft with bolts running through the inner rim of the flexible pack.

5. A flexible coupling according to claim 3 offering an alternative to the welding method in claim 4 whereby the inner rim of the flexible pack is clamped to the spacer with the clamping bolts clear of the said rim in a manner similar to the clamping of the outer extremities of the spokes to the hub flange so as to maintain a free flexing of the spokes equal to that provided by the welding method.

6. A flexible coupling according to claims 3,4 and 5 wherein protection of the connected machines against a destructive overload is provided by the shearing of membrane spokes or the shearing of the weld at the inner diameter of the inner rim.

7. A flexible coupling substantially as described herein with reference to Figs. 1 to 8 of the accompanying drawing.