GB2181213A - Flexible couplings - Google Patents

Abstract

A flexible coupling comprises first 21 and second 22 annular members each carrying circumferentially spaced load transmitting members 24, 25 which are interengageable to form an annular interlocking array. Each load transmitting member has a resilient pad bonded to it and located between it and the load transmitting member adjacent thereto in the array. Each pad is bonded to an end piece 26 for driving engagement with the adjacent load transmitting member and comprises a generally parallel sided laminar assembly of resilient and less resilient elements. <IMAGE>

Description

SPECIFICATION Flexible couplings This invention relatesto flexible couplings which may be used to transmit a rotational drive between adjacent members of a powertrain.

Flexible couplings are used where there is likelyto be misalignment between the adjacent members of the powertrain and/or one, or both, of the adjacent members is flexibly mounted. Certain designs of flexible coupling can attenuate irregularities in the torque being transmitted, e.g. from the power strokes of internal combustion engines, and so produce a smoother output.

It is known to use rubber or elastomeric elements asthe resilient component of a flexible coupling. The purpose of the resilient component is to transmit a torque from an input member to an output member while acting as a "cushion" to accommodate relative movement between these two members. Like all elastomeric materials, rubber is quite strong in compression, only moderately strong in shear, but very weak in tension. Thus most flexible couplings employ the resilient elements in compression and shear, ratherthan tension.

Under high compression and shear loads, rubber can distort excessively. Also where large errors in alignment have to be accommodated, thick resilient elements are required. Thus for high loads and large misalignment, thick elements under considerable stress are required. Unfortunately, the thicker the rubber element, the greaterthe distortion, particularly if an element of shear is present in the loading. It is thus extremely difficult to produce a flexible coupling able to accommodate large misalignments with resilient elements which do not distort ex cessivelyunderhigh loads.

Such couplings as are available, are eitherex- tremely expensive, or necessarily limited in either powertransmission ormisalignmentcapability.

There is thus a need for an inexpensiveflexiblecoup- ling, able to accommodate large misalignments and transmit high power.

According to the present invention there is provided a flexible coupling device fortransmitting torque between first and second rotational members, said device comprising; a first annular member which issecurableto said first rotational memberfor rotation therewith about a first common axis; a second annular memberwhich issecurableto said second rotational member for rotation therewith about a second common axis, said first and second axes being co-axial or generally co-axial;; first and second sets of load-transmitting members removably mounted on said first annular member and said second annular member respectively, the load-transmitting members of each set being circumferentially spaced from each other and each member of one set being interengageable drivingly with a respective member of the other set; and a plurality of circumferentially spaced resilient pads arranged one between each memberof oneset and the respective drivingly interengaged member ofthe other set; in which: the load transmitting members of each set togetherform a generally annular interlocking array; each load transmitting member of each set has first and second load transmitting end surfaces lying substantially in planes passing through the axis of rotation ofthe respective annular member; each resilient pad has one end tightly bonded to the first end surface of a respective load transmitting member of one set and has its other end tightly bonded to an end piece for driving engagement with the second end surface of an adjacent load transmitting member ofthe other set; and each pad comprises a substantially parallel-sided flexible memberwhich is formed of a plurality of re silient elements which are separated by, and tightly bonded to, a plurality of less resilient elements to form a generally parallel laminarassembly.

Preferably, the resilient elements of each flexible member are made of an elastomeric material, such as rubber, and the less resilient elements are made of a metal such as steel. However, the less resilient elements may be made of suitable non-metallic material.

The flexible member of each pad is readily ableto compensateforanymisalignmentwhich may occur in service between the first and second rotational members, as torque is transmitted therebetween via the flexible coupling, and yet does not undergo any serious permanent distortion in viewofthe manner by which loads will be transmitted through the pad i.e. load forces acting generally perpendicularto the general plane ofthe laminated assembly oftheflexible member.

Tofacilitatetheformation of each pad, it is prefer- red that each pad is moulded by positioning in a mould one ofthe load-transmitting members,asetof the less resilient elements and the end piece, and then casting any suitable elastomeric material into the mould, which thereby forms an integral laminated unit in the form of a load-transmitting assembly comprising the load-transmitting member, the pad and the end piece.

In the laminated unit, the load-transmitting assembly preferably is formed by an asymmetrical load-transmitting member which is adapted for rigid, yet removable, fixing to one of the annular members, and which has an exposed or outer radial end surface which is adapted for load bearing (to be engaged by the end piece of an adjacent pad).The end piece in the assembly is also preferably of asymmetrical form, and has an exposed or outer radial end surface which is adapted for load bearing.

In service, the load-transmitting member of each laminated assembly is fully restrained in all directions, whereas at the other end ofthe assembly i.e.

the asymmetric end piece, there will be no restraint on movement in eitherthe radial, axial or circumferential directions, other than that due to frictional forces due to the torque being transmitted between the abutting surfaces ofthe asymmetric end piece and the adjacent load-transmitting member of an otherassembly. Misalignment between thefirstand second rotational members, and therefore also between the first and second annular members ofthe flexible coupling, can be accommodated solely by compressive and/orshearmovement across the substantially parallel-sided flexible member of each pad.

In order to promote slippage between the outer end surface of an asymmetric load-transmitting member of one assembly and the outer end surface of an asymmetric end piece of another assembly, it is preferred thata lubricant is applied to at least one of these faces where they abut. In this case, misalignment between the first and second rotational members may be accommodated by a combination of compressive deformation and/or shear movement within the flexible member of each pad, as well as by slippage of the outer faces of the asymmetric end pieces across the abutting outer faces of the loadtransmitting members.

In orderto accommodate the shear load transmitted between the first and second annular members of the coupling (forming the input and output members thereof), and the asymmetric load-transmitting members which are rigidly attached to them, it is pre ferred to use closely toleranced dowel pins which are a push fit in holes formed in the input (and output) member and the asymmetric load-transmitting members. Conventional fixing means e.g. bolts may be used in addition to, or instead of, dowel pins to fix the asymmetric load-transmitting members to the inputoroutputmembers.

Preferred embodiments of a flexible coupling according to the invention will now be described in detail, byway of example only, with reference to the accompanying drawings, in which: Figure 1 is an end elevation of a flexible coupling according to the invention, with a partial cut-away to show the arrangement ofthe load-transmitting assemblies ofthe coupling; Figure2 is a developed circumferential elevation of theflexiblecoupling along the section A-A in Figure 1; Figure 3 is an alternative developed circumferential elevation along section A-A in Figure 1; and Figures and 4b are side and end elevations, re spectively of a load transmitting assemblycompris- ing a load-transmitting member, pad and end piece ofthe coupling of Figures 1 and 2.

Referring to the drawings, there is shown a flexible coupling device for transmitting torque between first and second rotational members, in which the device comprisesafirstannularmemberwhich issecurable to the first rotational memberfor rotation therewith about a first common axis, and a second annular memberwhich issecurableto a second rotation member for rotation therewith about a second common axis, in which the first and second axes are coaxialorgenerallycoaxial. Firstand second sets of load-transmitting members are attached to the first annular member and to the second annular member respectively, the load-transmitting members of each set being circumferentially spaced from each other and each member of one set being interengageable drivinglywith a respective member ofthe other set.A plurality of circumferentially spaced parallel sided resilient pads is arranged one between each member of one set and the respective drivingly interengaged memberofthe other set.

In the flexible coupling device shown in Figure 1, two end plates 1 and 2 (denoted as 21,22 and 31,32 in Figures 2 and 3 respectively), which are essentially co-axial and parallel to each other, form thefirstand second annular members which aresecurabletothe first and second rotational members (denoted by reference numerals 101 and 102 in Figures 2 and 3) re spectivelyfor rotation therewith. On the outer sur- faces of each end plate 1,2 i.e. the surface of each end platenotfacingtheotherend plate,there is provision for the attachment ofthe firstand second rotational members (either of which may be the input member with the other being the output member), for example, via flange ring 3.

Between arrows AA, a section of end plate 1 is cutaway to reveal five load-transmitting assemblies.

The load-transmitting assemblies are arranged in two sets with equal numbers in each set. Afirst set of load-transmitting assemblies, of which three are shown and wherein each includes a loadtransmitting member 4, is secured rigidly to end plate 1 by pairs offastening bolts 6 and dowel pins 7.

The second set of load-transmitting assemblies, of which two are shown in cutawayAA and wherein each includes a load-transmitting member 5, is rigidly secured to end plate 2 by similar pairs offastening bolts and dowel pins (not shown). Each assembly of one set is interposed between adjacent assemblies ofthe other set so that together the assemblies form an annular interlocking array of assemblies. As will be apparent from Figure 1, each assembly has two load-transmitting end surfaces, perpendicularto a plane at right angles to the axis of the respective annular member, and each surface is a radially extending surface, or inclined at a small acute angleto a radius, with respect to the rotational axis ofthe respective annular member. Thus the end surfaces lie substantially in planes passing through the rotational axis of the respective annular member.

Figures 4a and 4b show the detailed design and construction of a load-transmitting assembly comprising a load transmitting member and a resilient pad and an end piece co-operating therewith. Preferably, the load-transmitting assemblies are substanti- ally identical to maximise ease of manufacture and so that they are interchangeable with assemblies of their own set or ofthe other set so as to facilitate subsequent maintenance or replacement. Each assembly consists of a load transmitting member in the form of a mild steel wedge-shaped vane 40, a mild steel wedge-shaped end piece 41 and a resili ently flexible pad 42. The resiliently flexible pad 42 consists of a plurality of resilient elements 43 (of which four are shown in Figures 4a and 4b) separated by, but tightly bonded to, a plurality of less resilient elements 44 (ofwhich three are shown in Figures 4a and 4b). Thus the pad 42 is in the form of a generally parallel-sided laminar assembly wherein, in the absence of misalignment, the elements constituting the assembly are substantially parallel to a plane passing through the common axis of rotation of the annular members 1,2.

The resilient elements 43 may be made of an elas tomeric material such as rubber or other suitable polymer, or of any substance which resiliently distorts under load. The modulus of elasticity of the material ofthese resilient elements 43 could be typically in the range 0.7 - 70 MN/m2. The less resilient elements 44 may be made of a material, such as steel, with a modulus of elasticity oftypically 200 - 210 GN/ m2. Non-metallic materials may also have application as the less resilient material.

The use of a laminated construction forthe flexible pads 42 is so that an adequate total thickness ofthe resilient material 43 may be present to provideforthe misalignment requirements, yet not distort excessively under high compressive load. As theresilient material 43 is present in layers of only limited thickness, distortion due to direct compressive loading will be small and uniform across the whole pad area. However, because there is a substantial overall thickness of resilient material 43, a considerable degree of lateral distortion duetoshearloading can be accommodated. The presence ofthe plurality of less resilient elements 44 maintains the overall substantially parallel form of the flexible pads 42.Even though shearing forces due to misalignment will distortthe shape of pads 42, the change of section will be from that of a substantially parallel-sided rectangle to that of a substantially parallel-sided parallelogram.

Thus the combination of resilient elements 43 and less resilient elements 44 may be considered as analogous to the reinforcing of concrete by steel; the steel is strong in tension and bending and supplementstheconcretewhich is strong only in normal compression. In this example, the metal plates 44re- inforce the stiffness of the rubber under compressive loading,yetdo not detract from the overall flexibility ofthe shear. Withoutthis laminar construction, any combination of high compressive and shear loading, caused bya combination of high powertransmission and substantial misalignment, would produce an overturning moment which would otherwise lead to gross distortion of the pads 42 and premature failure.

Referring to Figures4a and 4b, itwill be seen that the overall shape ofthe integral load transmitting assembly is that of a symmetrical truncated sectoral prism. Both vane 40 and end piece 41 arewedgeshaped having an equal, butopposite,wedgeangle so that the inner surfaces, 47 and 48 respectively, are parallel to each other. The units can be made by placing a vane 40, a plurality of less resilient elements 44 and an end piece 41 in a mouldingjig,which holds them in the correct position. The mould is then filled with raw rubber and suitably polymerised.The result isthatthe rubber becomes tightly bonded to end such face47 of vane40 and end surface 48 of end piece41 respectively as well as to the surfaces of the less resilient elements 44. Thus, after polymerisation, the assembly may be removed from the mould as a single, mechanically strong entity ready for use in a flexible coupling.

Substantially parallel sided pads 42 are used as they are easierto manufacture with repeatable properties. Clearly all the pads loaded in the forward sense of rotation must have the same properties in orderto share the load carrying and misalignment duties equally. The pads loaded in the reverse sense of rotation must also have similar properties to each other. If there is to be interchangeability between the pads loaded in the forward and reverse senses of rot- ation,then all must have the same properties.

Afurther advantage of substantially parallel sided pads isthatthe driving torque is applied perpendicularly ofthe end faces ofthe pads. It would be possible to use wedge-shaped pads having a small included angle which would still give rise to a generally parallel laminarassembly. However in this case, the load due to the driving torque would have an el ementofshearwhichwould be additive to the shear loading due to misalignment and so reduce the life of the pads.

Load transmitting end surface 45 of vane 40 and load-transmitting end surface 46 of end piece 41 are ground to afine surfacefinish sincethey are required to act as load bearing surfaces. These surfaces lie substantially in planes passing through the axis of rotation ofthe respective annular memberto which the assembly is fitted.

When sufficient units have been made, the coupling can be assembled. The method of assembly is as follows. End plates 1 and 2 are mounted in a suitable jig so thatthe plates are concentric, parallel to each other and the required distance apart. The jig permits free access to the circumference of the end plates and mayalso allowthem to be rotated.Afirst load- transmitting assembly comprising a load transmitting member (vane 40), pad 42 and end piece 41 (Figure 4) is then placed between the end plates and bolted to, say, end plate 1 by passing fastening bolts 6 (Figure 1 through end plate 1 and screwing into tapped holes 51 in vane 40 (Figure 4A). When this is complete, but the bolts notfully tightened, a second load-transmitting assembly may be positioned adja centto the first and secured in place to end plate 2 by fastening bolts (not shown in Figure 1). Athird loadtransmitting assembly is placed adjacent to the second unit and is secured to end plate 1.

The process is repeated until the full complement of load-transmitting assemblies is in position, after which minor positional adjustments can be made and dowel pins 7 (Figure 1) inserted. The purpose of the dowel pins is to act as the main load-carrying connection between the end plates 1 or 2 and vanes 40 via dowel pin holes 52. The dowel will be closely tolerancedto be a push fit in end plate 1 or 2 and in dowel pin hole 52. It is inserted by a G-shaped compressing tool and removed by a puller, which engages with blind tapped hole 27A in a dowel pin 27 (Figure 2).

Though bolts 6 have been instanced as the primary means of securing the vanes and dowel pins 7 have been instancedasthe primary means ofcarryingthe shear load,these roles could be combined into a single one by the use of specially designed bolts.

Such boltswouldhaveacloselytolerancedshankof asubstantial diameter,to performthefunctionofthe dowel, with a smallerdiameterthreaded portion at the end to engagewith a screwthread inthecentral part ofthe hole in vane 40.

Figure 2 shows a developed circumferential eleva tion oftheflexiblecoupling along section AAin Figure 1. Parts 21,22,24,25 and 27 of Figure 2 cor respondto parts 1,2,4,5and 7 of Figure 1.Three load-transmitting members 24 are shown fast with end plate 21 and two further load-transmitting members 25 are shown fast with end plate 22. Dowel pins 27areshown passingtightlythrough end plates 21 or22 and into dowel holes 28(52 in Figure4a) in members 24and 25 (vane 40 in Figures 4a and 4b).

The fastening bolts (6) and tapped holes (51) in the members 24 and 25 (40) are not shown in Figure 2to avoid obscuring detail ofthe dowel pins 27 and holes 28.

It has already been stated that the loadtransmitting assemblies are symmetrical. This app liestothe elevations shown in both Figures4a and 4b. Also dowel hole 52 and tapped holes 51 pass completely through vane 40. Thus the loadtransmitting assemblies may be fitted to either end plate 21 or22 i.e. they may be used in both left and right hand configurations. Reference to Figure 4b shows that end piece 41 and less resilient elements 44 are (axially) narrowerthan vane 40, so that there is an axial clearance 50 at both sides. Thus when the coupling is assembled (Figure 2), there will be an axial clearance 29 (50) between the end pieces 26 (41) and the end plate 21 (or22)to which they are secured.

Because the separation distance of the end plate 21, 22 is considerably greaterthan the length ofthe members 24 and 25 (40), the clearance 30 between each member 24 (or 25) and the other end plate 22 (or 21) will be much greaterthan clearance 29 (50).

Clearance 29 is the factor limiting the amount of misalignmentwhich can be accommodated because, if the misalignment is too great,the end of end piece 41 will contact intermittently that end plate 21 or 22 to which it is attached. Where large amounts of misalignment are to be accommodated, clearance 29 (50) must be increased. This could be done by casting the flexible elements 43 asymmetrically onto vane 40, i.e. as shown by vanes 34,35 in the modification shown in Figure 3. In this case, left and right handed assemblies would have to be cast; the left and right handed assemblies would not be interchangeable.

Alternatively a spacer 36 may be inserted between the end plate and vane. Spacer36 could be a machined projection on end plates 31 and 32. The end faces49 (Figure 4) of vanes 40 are ground, as arethe mating surfaces ofthe end plates 21,22 and 31,32, so that the adjacent faces abut correctly. The mating surfaces of spacer 36 will be similarly ground.

To understandtheoperation ofthecoupling, assume that end plate 21 is the driving member ofthe coupling and that it is rotating from left to right in Figure 2. The driving torque passes from end plate 21 via the dowel pins 27 and the fastening bolts (6 not shown) into vanes 24. As vanes 24 commence to rotate with end plate 21, the first load transmitting end surface of each vane 24 (surface 47 in Figure4a) will transmitthetorquetothe pad (42 in Figure4) bonded thereto and thence to the end piece 26.The end surface 26a of each end piece 26 (surface46in Figure 4a) will then contactthe second load transmitting end surface 25a (45 in Figure4a) of adjacent vane 25, and so transmitthe drive into vanes 25, and thence via dowel pins 27 and fastening bolts (6 not shown),to end plate 22, i.e.the driven memberofthe coupling. In Figure 2, a circumferential clearance 23 is shown between end surface 26a of end piece 26 and end surface 25a of vane 25; this is necessary to permit assembly of the coupling, but the clearances 23will betaken up as soon asthe coupling startsto rotate.

When in the forward sense of rotation, the drive will be carried from end surface 26A of end piece 26 onto end surface 25A of vane 25. Usually, misalignment between end plates 21 and 22 will be ac commodated bytheshearflexibilityofthepads42.

Under normal conditions, there should be no relative motion between surfaces 26A and 25A. However, where excessive misalignment is likely to occur, a lubricant may be placed on surfaces 26A and/or 25A so that the misalignment can be accommodated buy a combination of shear of the pads 42 and slippage between surfaces 26A and 25A.

When excessive misalignment has to beaccommodated, the alternative design shown in Figure 3, with large clearances at the sides of the pads is preferred, i.e. a clearance equivalenttospacer36 ratherthan clearance 29.

When in the reverse sense ofrotation,the drivewill be from end plate 22, via dowels 27 to vanes 25 and thence to vanes 24 and end plate 21 via end surfaces 25A, the flexible pads (42) and end pieces 26.

Irregularities in the torque being transmitted will be smoothed out by the resilience of the material, e.g. rubber, of elements 43. This property could be important if the motive power is supplied by an internal combustion engine with regular power strokes, as the effect of the coupling would beto smooth the torque from the output member. There are other instances where a coupling of the type disclosed could be advantageous. For example, if the speed of the prime mover is to be varied suddenly or if the reaction against which the prime mover is operating changes in a step-wise fashion, violent changes inthetorquewould result. Resilientelements inthe flexible coupling would also attenuatethe transmis- sion of noise and vibration.

In a practical design ofcoupling,thetorqueto be transmitted would determine the properties ofthe rubber and thickness of elements 43. The amount and nature ofthe misalignment, i.e. magnitude and type (lateral, axial orangular),would determinethe thickness of the pads 42, i.e. the numbers of each el ement43and 44. The magnitude ofthetorqueto be transmitted determines the total pad area required, and hence the number of pads of a given area. This determinestheoverall diameterofthecoupling.As with many designs, there has to be a compromise between two conflicting requirements. "Soft" couplings are preferred with many elements43 and 44. But as the thickness of each pad increases, the radius of the coupling must also increase in orderthatthe same number of pads may be used. However, increasing the magnitude ofthe radiusatwhichthe pads act increases the magnitude of any misalignment present in a proportionate relationship according to geometric laws. One possible solution to this problem could be concentric circles of pads.

Where excessive misalignment has to be ac commodated, either by design or because ofthe large radius at which the pad has to act, thick, multilayered pads would be used. The shearing effect on such pads may be lessened by permitting sliding movement between adjacent load-bearing faces 25A and 26A, 25B and 26B, etc.

Claims (6)

1. Aflexiblecoupling devicefortransmitting torque between first and second rotational members, said device comprising; afirst annular member which is securableto said first rotational member for rotation therewith about a first common axis; a second annular member which issecurableto said second rotational memberfor rotation therewith about a second common axis, said first and second axes being co-axial or generally co-axial; first and second sets of load-transmitting members removably mounted on said first annular member and said second annular member respectively, the load-transmitting members of each set being circumferentially spaced from each other and each member of one set being interengageable drivingly with a respective member of the other set; and a plurality of circumferentially spaced resilient pads arranged one between each member of one set and the respective drivingly interengaged member of the other set; in which: the load transmitting members of each set togetherform a generallyannularinterlocking array; each load transmitting member of each set has first and second load transmitting end surfaces lying substantially in planes passing through the axis of rotation ofthe respective annular member;; each resilient pad has one end tightly bonded to the first end surface of a respective load transmitting member of one setand has its otherendtightly bon- ded to an end piece for driving engagement with the second end surface of an adjacent load transmitting member ofthe other set; and each pad comprises a substantially parallel-sided flexible memberwhich is formed of a plurality of resilient elements which are separated by, and tightly bonded to, a plurality of less resilient elements to form a generally parallel laminarassembly.

2. Adevice as claimed in claim 1 wherein the re silient elements of each flexible member are made of an elastomeric material and the less resilient el ementsoftheflexible memberaremadeofsteel.

3. Adeviceasclaimed in claim 1 or2 including a plurality of load-transmitting assemblies, each assembly comprising one ofthe load-transmitting members, one ofthe pads, and one ofthe end pieces.

4. A device as claimed in claim 3 wherein, in each assembly, the end piece is asymmetrical and the load-transmitting member is in the form of an asymmetrical vane.

5. A device as claimed in claim 4wherein a lubricant is provided between the end piece of one assembly and said second load transmitting surface of the vane ofthe adjacent assembly.

6. A device as claimed in claim 1 substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 4 ofthe accompanying drawings.