GB2335726A - Flexible coupling - Google Patents

Abstract

A coupling for torque transmission between two rotary components, comprising two coupling members 10, 11 for connection respectively to said two components, and a triangular or hexagonal flexible coupling element 12 to which one of the coupling members is connected at a number of circumferentially spaced positions and to which the other coupling member is also connected at an equal number of circumferentially spaced positions between the first said positions. The connections of one of the coupling members to the flexible coupling element are disposed on a pitch circle of different diameter from the connections of the other coupling member, thus, flexure of the coupling element is reduced. If the coupling element fails, the pitch circles are of sufficiently different diameter to allow relative rotation between the coupling members.

Description

2335726 1 PATENTS ACT 1977 GMD/A9321GB Title: FLEXIBLE COUPUNG

Description of Invention

This invention relates to a coupling for torque transmission between two rotary components, able to accommodate relative articulation between the components, i.e. the rotational axes thereof becoming inclined to one another. More particularly the invention relates to such a coupling of the type comprising two coupling members connected or adapted for connection respectively to the two components which are to be coupled, and a flexible coupling element to which one of the coupling members is connected at a C C1 number of circumferentially spaced positions and to which the other coupling member is also connected at an equal number of circumferentially spaced positions between the first said positions.

Such a coupling will hereinafter be referred to as a coupling of the kind specified.

Couplings of the kind specified are well known. Characteristically each coupling member is connected to the flexible coupling element at three positions spaced circumferentially therearound, while the flexible coupling element is in the form of a disc or ring of a material which is able to accommodate articulation between the coupling members by flexing and which, of course, has sufficient strength to transmit the torque for which the couplingo is desioned. More recently, such couplings have become known in which the flexible coupling element, generally annular in form, is made of a fibrereinforced plastics material. Such a flexible coupling element is relatively light in wel-lit and can be made, by suitable choice of the type and quantity of the fibres which make it up, and their orientation and disposition. to provide a high torque transmitting capacity for a given size of coupling and well able to take small angles of articulation (up to about J or so). Typically such couplings are used in machine drives or the like.

It is broadly the object of the present invention to provide all improved coupling of the kind specified, whose advantages will be described hereafter.

According to one aspect of the present invention, we provide a coupling of the kind specified wherein the connections of one of the coupling members to the flexible coupling element are disposed on a pitch cli-cle of different diameter fl-om the connections of the other coupling member thereto.

Hithei-to it has beeii usual ill couplings of the kind specified for the two coupling men-ibers to be connected to the flexible coupling element at connections which all lie oil the saine pitch cli-cle diameter. However, ill a coupling in accordance with the invention two advantages call be obtained over such couplings as known hitherto. One such advantage can be appreciated fi-orn a consideration of the behaviour of such a coupling when it rotates in the articulated condition. As the coupling rotates, the connections of the two coupling members to the flexible coupling eleniew cyclically move axially relative to one another, and the flexin- of the pans of the flexible coupling element between its connections to the coupling members must include components of such axial movement as well as bending. When the pitch circle diameter of the connections of one of the coupling members is reduced, the axial movement of the connectiotis of siicii coupling ineinbei- relative to the other coupling member is reduced. The i-ecliictioii ill relative axial movement means that flexim, of the flexible coupling elenient to accommodate such movement is reduced. Tills has to be balanced a-ainst the increase in force which has to be applied to the flexible coupling element at each of its connections to the coupling niernber of reduced piteli circle dialiletel- ill order to transmit the required torque. The reduction should not be too great, there comes a point at which the beneficial effect ill one respect resulting fl-om the n J reduction in pitch circle diameter is negated by the disadvantageous other effect thereof.

A further advantage of a coupling ill accordance with the invention resides in the fact that it becomes possible to use the coupling as a torquelimiting device. In some drives, it is proposed to incorporate an element which falls in the event of the torque exceeding a predetermined value, in order to prevent damage from such excess torque. In a conventional coupling of the kind specified, even if the flexible coupling element falls under excess torque the two coupling members, since theli, connections to the flexible coupling element are on the same pitch circle diameter and necessarily axially overlapping with one another to some extent, the coupling members come into abutment with one another. Thus the "free-wlieelliig" condition of the two coupling members relative to one another cannot be achieved: when they come into abutment with one another there is the possibility of causing even more dama,,e than would ordinarily result from torque overload.

In a coupling in accordance with tile invention, however, the disposition of the connections of the two coupling members to the flexible coupling element oil different pitch circle diameters means that there is the possibility, after fallure of the flexible joint member, for the two coupling illembers to undergo relative rotation without contacting one another in any way.

The flexible coupling element preferably is generally in the form of a rinQ, havino a central aperture. This enables the two coupling members to have C supporting but non-torque-transmitting engagement with one another in a central reolon of the flexible coupling element. When the couphilo has a torque c C C1 limiting function, it will be appreciated that without such supporting c en,,a(,eiiietit between the coupling members, upon fallure of the flexible t> c 0 coupling element they would be totally unconstrained relative to one another, necessitatilio the provision of some other support means therefor if they did not c relatively, support one another.

4 The flexible coupling element may be generally polygonal in shape comprising limbs which extend between the connection to the coupling members. It may define, at such connections, first apices at which there are the connections which lie on the larger pitch circle diameter and second apices between the first apices and at which there are the connections of smaller pitch circle diameter. Thus in the case of adjacent 11mb portions of a flexible coupling element having a central aperture, the apex angle, subtended internally between the centre lines of adjacent llinabs at each connection point, is greater for the second apices of smaller pitch circle diatileter than it is for the first apices of larger pitch cli-cle diameter.

Alternatively, the flexible coupling element rnay comprise apices at which there are the connections which lie on the lanver pitch circle diameter, with limbs extending therebetween and the connections of smaller pitch circle diameter lying at the mid-points of such limbs.

In what is believed to be a limitina case, wherein the advanta-e obtained c C from the reduction in pitch circle diameter of the connections of one of the coupling members begins to be outweighed by the increase in forces required to be applied at such connections, the connections on the sinaller pitch circle diameter may be afforded at the centre points of substantially straight limbs extendina between the connections of larger pitch circle dianieter. When each C c coupling member has three connections to the flexible coupling element, the latter is of generally triangular configuration.

The invention also provides a flexible coupling eleinent foi- use in a coupling according to the first aspect of the invention. The flexible coupling element according to this second aspect of the invention iflay have any or all of the features thereof which are referred to above in relation to the coupling in accordance with the first aspect of the invention.

The connections of the coupling members to the flexible coupling element may be afforded by bolts or other fastening elements extending through respective apertures ill the flexible coupling element.

The invention will now be described by way of example with reference to the accompanying drawings, of which:- Figures 1 and 2 are respectively a side elevation of a coupling in accordance with the invention and an axial view of the flexible coupling element thereof, Figure -3) is all axial view of a further einbodinient of flexible coupling element ill accordance with the invention.

Referring firstly to Figures 1 and 2 of the drawings, these show a coupling which comprises two couplino members indicated,enerally at 10, 11, respectively connected to a flexible coupling element indicated generally at 12 and shown more clearly ill Figure 2. The COLIPling members 10, 11 are adapted to be connected respectively to two rotary coinponents which are to be coupled to one another, and have respective axes of rotation which in the drawing ci ide with one another and are indicated at 13. Each of the coupling oincl members 10, 11 is in the form of a tliree-leg-ed "spider", coinprising three legs 0C, c which extend radially outwardly relative to the respective rotational axis of the coupling member and also are inclined axially.

Two of such legs are indicated at 14, 15 foi- the coiipllii,, meniber 10 ill Fig-ure 1, and one of such legs is indicated at 16 and part of another at 17 for the couplino, member 11. The legs of the coupling nlernbei- 11 are shorter than those of the coupling member 10. The leg 14 ends at a boss 18 with all aperture extending axially therethrough for receiving a connecting bolt as indicated at 19: each of the other legs as 15, 16, 17 also ends in such a boss as shown at 20, 21, 22 for the legs 15, 16. 17 respectively.

The flexible coupling element 12 is made of coniposite, fibre-reinforced plastics, niaterial and as shown in Figure 2 it is generally triangular in form 6 with a central aperture 25. Its ciangular coil figurati on has three apices indicated at 26, 27, 28, and three straight limbs 29, 30, 31 extend 1 j ing therebetween. The apices 26 to 28 provide for connection of the coupling member 10 to the flexible coupling element, being provided with thickened bosses as indicated at 32 for the apex 26, having apertures as 33 extending axially therethrough. These provide for reception of the fasteners such as bolts 19 by which the ends of the legs of the coupling member are connected to the flexible coupling element.

Midway along each of these limbs 29, 30, 31 there are provided respective thickened bosses with apei-tures extending therethrou 11, as indicated 0 9 at 34, 35, 36. These provide foi- connection of the legs of the coupling member l 1 to the flexible coupling element 12.

Refen-ing now to Floure 3) of the di-a,Iii,,s, this shows, In an axial view as Floure 2, a further embodiment of flexible coupling element in accordance with the invention. The form of this flexible coupling element is a hexagon having six apices 40-45 between which extend limbs 60-65. Each of the apices is adapted for connection of a leg of a coupling member thereto, being provided with a thickened boss havino a central aperture therein, such boss and aperture beine indicated at 46, 47 at the apex 40 and at 48, 49 at the apex 4 1.

The centres of the apertures as 47 at the apices 40, 42, 44 lie on a first pitch circle 50 whose radius is indicated at R]. The centres of the apertures as 49 at the apices 41, 43), 45 lie on a second pitch circle 51 whose radius indicated at R2 is less than the radius R 1. Thus the apex amfle defined between the limbs 60, 65 at the apex 40, bet,,ecii the limbs 61, 62 at the apex 42, and the limbs 63, 64 at the apex 44, is less than the apex angle defined between the limbs 60, 61 at the apex 41, the limbs 62, 63) at the apex 43, and the limbs 64. 65 at the apex 45. The apices 40-45 are equally angularly spaced about the rotational axis of the flexible coupling element in use, which axis extends centrally through the central aperture of the coupling element.

7 In cases where the flexible coupling element is intended to fall if subjected to excess torque, the difference between the pitch circle diameters of the connections of the two coupling members thereto is preferably sufficient to enable the two coupling members to rotate relative to one another without making contact with one another. In the embodiment of coupling element shown in Figure 3, the difference between the radil RI, R2 is sufficient for this purpose.

The flexible coupling element shown in Figures 1 and 2 can be regarded as a limiting case of the difference in pitch circle diameters of the connections of the two couplin- members to the coupling element, at which the advantages of such a difference begin to be outweighed by the disadvantages thereof. Between the configurations of Figure 2 and Figure J3 other configurations are possible, for example the coupling element could have curved limbs with centre lines of fixed or varying radius, with connections to a coupling member at or adjacent the mid-points of such lirnbs.

The features disclosed in the foi-e,,olti,, desci-lptioii, ot. the following claims, or the accompanying drawings, expressed M theli. specific forms or in tenris of a means for performing the disclosed futiction, or a inethod or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof 8

Claims (1)

1. A coupling for torque transmission between two rotary components, 1 respectively to said two comprising two coupling members for connection components, and a flexible coupling element to which one of the coupling members is connected at a number of circurnferen ti ally spaced positions and to which the other coupling member is also connected at all equal number of circumferentially spaced positions between the first said positions, wherein the connections of one of the coupling members to the flexible coupling element are disposed on a pitch circle of different diameter from the connections of the other coupling member thereto.

c 2. A coupling according to Claim 1 wherein each coupling member is C. 11 connected to the flexible coupling element at three circumferentially spaced positions.

1. 1 -d'no to Claim 1 oi- Clafin 2 wherein the flexible coupfi A coupling accoi 1 l 1 1 1 ing C) C element is generally in the foi-m of a fing, having a centi-al aperture.

C) c 4. A coupling according to Claim 3 wherein the flexible coupling element is generally polygonal in shape, comprising linibs which extend between the connections to the couplin- inembers.

c 5. A coupling according to Clairn 4 whereln the flexible coupling element comprises first apices at x,.lilcli there are the connections whiell lie oil tile larger pitch circle diameter and second apices between the first apices and at which there are the connections which lie oil the sinaller plitch circle diaineter.

9 6. A coupling according to Claim 4 wherein the flexible coupling element comprises apices at which there are the connections which lie oil the larger pitch circle diameter, and limbs extending therebetween with the connections at the smaller pitch circle diameter lying at the mid-points of such limbs.

7. A coupling according to Claim 6 wherein said limbs are substantially straight.

8, A coupling according to Claim 7 wherein said flexible couplino element is t Z> Z7 generally triangular in configuration.

9. A coupling according to Claim 5 wherein said flexible coupling element is C c generally hexagonal in configuration.

0 0 10. A flexible coupling element for use in a coupling accordines to ally one of C) c the preceding clairns, said flexible coupling element being generally in the form of 0 a ring having a central aperture and having formations at a plurality of positions spaced anoularly about the ling to have the two coupling members connected c W thereto, said formations for connection of one of the couplin- members being disposed oil a pitch circle of different diameter fl-orn the cotitiections of tile other joint member.

11. A flexible coupling element according to Claim 10 wherein each of said t> c formafions affords an apeiture for receiving a cotiiiectlii,, bolt or other fastener.

c c 12. A flexible coupfijig cletiletit according to Claini 10 or 11 whicl) is generally c 11:1 1 polygonal in shape comprising limbs which extend bet,,.,eeii said positions foi- connection to the coupling members.

13. A flexible coupling element according to any one of Claims 10 to 12 which is of fibre-reinforced plasfics material.

14. A coupling, or a flexible coupling element therefor, substantially as hereinbefore described with reference to the accompanying di-ak%,111(7S.

c 15. Any novel feature or novel combination of features described herein and/or in the accompanying di.awill(IIS.

c c