GB2191562A - Shaft flexible coupling - Google Patents

Abstract

The coupling comprises two orthogonally orientated Watt parallel linkages, which connect shafts 1 and 3 carrying transverse end members 2 and 4 to an intermediate member 5 sandwiched between them. Links 10 and 11 connect pivot pins 6 and 7 carried by shaft end member 2, to pivot pins 8 and 9 carried by intermediate member 5. Likewise, links 16 and 17 connect pins 12 and 13 on the opposite shaft end member 4 to the other pins 14 and 15 on the intermediate member. The pivot bearings at each end of the links may be of a spherical or elastomer bushed type, accommodating both translational and angular misalignment of the shafts. Resilient elements 30 stabilise the intermediate member 5 by reacting with the shaft end members 2 and 4. The coupling may be locked in the coaxially aligned position when misalignment forces can be tolerated. <IMAGE>

Description

SPECIFICATION Rotating shaft flexible coupling Rotating shaft flexible couplings capable of accomodating angular misalignment may be ofthe Hooke'sjointtypewith solid pivots, or, alternatively, multiple rubber elements can be used to give the same effect as a pair of solid pivots. It is also possible to use a flexible diaphragm fixed at two diametrically opposite points to a driving disc and fixed to a driven disc at two further diametrically opposite points at right angles to the first pair. lftranslational or lateral misalignment is to be accomodated, then a pair of such couplings must be attached to either end of a cardan shaft.

Purely translational or lateral misalignment can be accomodated by an Oldham coupling, which takes up very little space and is extremely short as compared with a pair of Hooke'sjoints separated by a cardan shaft. Oldham couplings are, however, not adapted to taking very high torques because of the low relative sliding speeds of the elements upon one another, unless resort is had to very high pressure hydrostatic forced lubrication, a feature to be avoided if at all possible. Oldham couplings are also incapable of taking any angular misalignment.

The present invention seeks to overcome the disadvantages outlined above concerning known prior art by cascading two orthogonally orientated Watt parallel linkages connecting transverse shaft end membersto a common intermediate member, which is the kinematic equivalent of an Oldham coupling. In addition, the pivot bearings at each end ofthe links may be of a spherical or elastomer bushed type, permitting each linkto move in any plane containing its pivot axis, as well as to rotate in a plane at right angles to that axis. By this means, both translational and angular misalignment may be accomodated.

Means are also provided to lockthe coupling in the coaxially aligned position, for use under conditions in which forces generated by shaft misalignment can be tolerated.

The invention comprisesacouplingforconnecting two rotating shafts, each shaft terminating in a transverse member carrying a pair of pins symmetrically disposed about the axis ofthe shaft and parallel to that axis, with the space between the shaft end members containing an intermediate member carrying two pairs of pins with their axes normal to the plane ofthis member and symmetrically disposed on orthogonal centre lines with respectto the point of intersection ofthese lines, with a pair of links connecting the pins carried by one shaft mounted transverse memberto one pair of pins on the intermediate member and another pair of links connecting the pins carried by the other shaft mounted member to the second pair of pins carried by the intermediate member.

The invention will now be described in detail with reference to the accompanying drawings where: Figure 1 shows an elevation ofthe whole coupling; Figure 2 is an end sectional view on AA of Figure 1; Figure 3 illustrates in perspective, an alternative construction for the intermediate member; Figure4givesthe method of controlling link attitude; Figure 5 shows the method of locking the coupling.

The invention will now be described in detail.

Referring first to Figures 1 and 2, a first shaft I carries at one end a transverse member 2 which can take the form of a circularflange or alternatively that of a transverse beam. A second shaft 3 carries a similar transverse member 4facing the transverse member of the first shaft. An intermediate member 5 is located between the transverse members 2 and 4. Pins 6 and 7 mounted on the transverse member 2 are symmetri cally disposed in relation to the axis of shaft 1 with the pin axes parallel to the shaft axis.Pins 8 and 9 are symmetrically disposed on the side of the intermediate memberS facing the transverse member 2, with their axes normal to the plane containing the intermediate memberS, such that a line joining the pins 8 and 9 will be at right angles to the centre lines of links 10 and 11 joining pins 6 and 8 and 7 and 9 respectively when these links are parallel to one another.

Pins12and l3mountedonthetransversemember4 are symmetrically disposed in relation to the axis of shaft 3 with the pin axes parallel to the shaft axis. Pins 14 and 15 are symmetrically disposed on the side of the intermediate member 5 facing the transverse member4, with their axes normal to the plane containing the intermediate memberS, such that a line through the centres ofthe pins 14 and 15will be at right angles to the centre lines of links 16 and 17 joining pins 12 to 14 and 13 to 15 respectively when these links are parallel to one another. The line through the centres ofthe pins 8 and 9 is at right angles to the line through the centres of the pins 14 and 15.Pins 8 and 9 carried bythe intermediate member S are equidistant from a centre shown as point C in Figure 2, and pins 14 and 15 are equidistant from the same centre.

It will be noted that in the configuation shown in Figures 1 and 2, the centre distance between the pairs of pins associated with the shaft end members is greaterthan that of the pairs of pins carried by the intermediate member. However, it will be appreciated that this configuration is not mandatory and that the kinematic properties of the coupling are unchanged by reversing the size relationship of the pins centre distances.

The configuration of the intermediate member iso far described with cantilever pins Sand 9 projecting from one side and pins 14and 15 projecting from the other side ofthe member gives rise to twisting moments acting in orthogonal planes at right angles to the plane containing the member. This necessitates a much heavier construction than would be the case if these twisting moments could be eliminated. Such an alternative construction is shown in Figure 3 in which the intermediate member5 comprises parallel plates 28 and 29 assembled in spaced relationship with the gap between the plates spanned by the pins 8,9,14 The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

and 15. Holes 19 may be provided in each of plates 28 and 29 to reduce weight, though as noted below, the holes can serve an additional purpose.

In orderto accomodate angular misalignment, all bearings between links and pins must be of type capable of allowing deviations from a 90 angle between the pin axes and the associated link centre lines.

Bearings capable of providing the necessary transi- tionfrom parallel pins 6,7,8,9,12,13,14, lStothe ends of the links 10,11,16, may consist of spherical low friction bushes of sintered metal or plastic such as PTFE, spherical ball or roller races, ora combination of plain ball or roller races and spherical low friction bushes.

Resilient bushes (not illustrated) with a sandwich consisting of one or more layers of elastomeric material interleaved with rigid tubes may also be used to accomodate angular misalignment.

Except in the case where bearings of elastomeric material are used, there is no static restraint on the intermediate memberto compel itto adopt a postiion sensibly parallel to the shaftend members. However, only limited torque can be transmitted through elastomeric bearings of reasonable size, and high torques lead to much more bulky units than is the case if solid sliding or rolling spherical bearings are used. In the cases in which sliding or rolling spherical bearings are used, it is only when the coupling is rotating that centrifugal forces will tend to cause the intermediate member 5 to orientate itself with its plane normal to the axis of rotation. Since these forces are virtually non-existent at very low speeds, resilient static restraint is required to ensure correct operation of the coupling under such conditions.Figures 1 and 2 show the application of resilient restraints in the form of a plurality of suitably disposed elastic elements 30 reacting between each side ofthe intermediate member5 and the adjacent shaft end elements 2 and 4.

Irrespective of speed, where sliding or rolling spherical bearings are used, there is no dynamic force to preventthe links 10,11, 16 and 17from tilting out of the plane nominally at right angles to the pins 6,7,12 and 13, orto pins 8,9, 14and 15, that is, outofthe approximate plane ofthe coupling. A means four providing static link attitude control forces is shown in Figure 4, in which part of transverse member 2 carrying pin 6, together with part ofthe associated link 10 connected to the pin by a spherical bearing 31 is taken asatypicalexampleofa pin, linkand bearing assembly.A further resilient element 32 concentric with the pin 6 and acting between the transverse member2 andthe associated link 10 preventsthe link from tilting, whilst still allowing the necessary freedom of movementto accomodate shaft misalignment.

Analysis ofthe dynamic characteristics of the coupling shows that, in common with the original Oldham coupling, the locus ofthe geometric centre of the intermediate member5 is a circle of diameter equaltothemisalignmentoftheshaftsl and 3, giving rise to a rotating force with a frequency equal to twice the shaft speed. This means that the coupling cannot be balanced by any simple means, though the magnitude ofthe out of balance forces is generally very small compared with the forces transmitted by the links and in any case, can be minimised by making the massofthe intermediate member as small as possible.

The majoradvantagesare compact length, absence of lubrication problems and the relatively small overall diameter required to transmit very high torques. However, there are applications in which a compactflexible coupling is required at low speeds, but not required at high speeds as for instance, in marine applications, where differential structurai distortion causes shaft bearings to become misaligned, giving rise to limitations asto minimum speed at which an installation can be operated and still maintain hydrodynamic lubrication conditions. Thus, if the coupling can be locked up at higher speeds, vibration is no longer a factor against its use underthe conditions in which it is really needed.Such a locking facility can be provided by a simple pressurised fluid operated bolt coaxial with one shaft, which is mounted in the end of that shaft and engages a socket in the end of the other shaft via a clearance hole through the intermediate member ofthe coupling.

For a better understanding of the method of locking the coupling, Figure 5 shows the principles involved.

The shaft 1 carrying the transverse member 2 has a coaxial socket 20, which can be engaged by a bolt 18 coaxial with and carried in the end of the shaft 3. The bolt passes th rough a clearance hole 19 in the intermediate member 5 and is actuated by fluid pressure acting on a piston 22 in a cylinder21.The fluid (either liquid or gaseous) is supplied via duct 23 running through the centre of the shaft and communicating direct with the cylinder 21. The bolt is with- drawn by pressurised fluid supplied via a pipe 24 passing along the duct 23 and into a chamber 25 which communicates with an annular space 26 behind the piston 22 via a short passage 27.

Claims (18)

1. A coupling connecting two rotating shafts each terminating in a transverse member carrying a pair of pins symmetrically disposed upon a diameter through the axis of the shaft and parallel to that axis, with the space between the shaft end members containing a transverse intermediate member carrying two pairs of pins with their axes normal to the plane of this member and symmetrically disposed on orthogonal centre lines with respect to the point of intersection of these lines, with a pair of links connecting the pins carried by one shaft mounted transverse memberto one pair of pins carried on the intermediate member and another pair of links connecting the pins carried by the other shaft end mem ber to the second pair of pins carried bythe intermediate member.

2. A shaft coupling as described in claim 1 in which one link in a pair is parallel to the other link in that pair and the centre lines ofthe links forum a right angle with a linethroughthe centres of one ofthe pairs of associated pins, when the point of intersection ofthe orthogonal pin centre lines on the intermediate member coincides with the axis ofthe shaft associated with the other pair of pins.

3. Ashaftcoupling according to claim 1 in which the intermediate member carries one pair of cantilever pins on each side ofthe member.

4. Ashaftcoupling accordingtociaim 1 in which the intermediate member consists oftwo parallel plates in spaced relationship with two pairs of symmetrically spaced pins spanning the gap between the plates.

5. Ashaftcoupling accordingtoclaim 1 in which spherical ball or roller bearings are used to connect the links to the pins.

6. Ashaft coupling according to claim 1 in which spherical bushes made of metal or plastic are used to connectthe links to the pins.

7. A shaft coupling as described in claim 1 in which plain ball or roller bearings surmounted by spherical bushes are used to connectthe links to the pins.

8. Ashaftcoupling according to claim 1 in which deformable bushes consisting of a coaxial sandwich of one or more layers of elastomer alternating with metal tubes form the bearings connecting the links to the pins.

9. Ashaft coupling as described in any ofthe preceding claims in which the intermediate member is centered in the gap between the shaft end transverse members by resilient elements reacting between the shaft end transverse members and the intermediate member.

10. Ashaftcoupling according to claims 4 and 5 in which resilient elements centred on the pins act between the pin supports and the links.

11. A shaft coupling according to any of the preceding claims in which one shaft carries a coaxial bolt projecting from the shaft end which bolt can pass through a clearance hole in the intermediate member and engage a socket coaxial with and carried in the end ofthe other shaft.

12. Ashaftcoupling as described in claim 10 in which a fluid operated actuating cylinder is housed within and coaxial with the shaft end containing the bolt.

13. Ashaftcoupling as described in claim 11 in which the operating fluid is a liquid.

14. A shaft coupling according to claim 11 in which the operating fluid is a gas.

15. Ashaftcoupling as described in claim 11 in which the coaxial bolt is engaged by fluid pressure acting on one side of a piston carried on the end ofthe bolt and withdrawn by fluid pressure acting upon the other side of the piston.

16. A shaft coupling according to claim 14 in which the operating fluid required to engage the bolt is supplied via duct passing through the centre of the shaft containing the bolt actuating cylinder which duct communicates directly with that cylinder.

17. A shaft coupling as described in claims 14 and 15 in which the bolt is withdrawn by pressurised fluid supplied to an annular space behind the piston via a pipe passing along the duct and in sliding relationship with and co-operating with a pressure resistant gland into a chamber contained within the piston end of the bolt and thence via a short passage through the wall of the chamber into the annular space behind the piston.

18. Ashaft coupling substantially as hereinbefore described with reference to the accompanying drawings.