A flexible coupling

Abstract: A flexible coupling (1,101,201) has an inner member (5,105.205) and a resilient body (4,104,204) mounted on said hub (5,105,205) and connected thereto. A reinforcement ring (8,108,208) is bonded within the resilient body (4,104,204). The ring (8,108,208) has apertures (9,109,209) lined with tapered rubber tubes (10,110,210). Fixing means for connecting the coupling (1,101,201) to the flywheel (3,103,203) are locatable within the rubber tubes (10,110,210). The taper causes the fixing to induce a precompression in the rubber tubes (10,110,210) when the coupling is assembled and fitted in place. The coupling minimises backlash, provides extra torsional flexibility and permits blind assembly.

Description: This invention relates to a flexible coupling and more particularly to a flexible coupling used to interconnect machine components. Known flexible couplings of this kind are often used to connect an engine flywheel to a driven component of the engine for example the gearbox or alternator. These couplings are substantially disc shaped having an inner metallic member connected to an outer metallic ring via a rubber body which is vulcanised to the inner member. The inner member of the coupling is connected to the driven component and the ring is bolted to the engine flywheel. The rubber body provides the torsional flexibility of the coupling. In one particular known coupling the outer ring has a plurality of equiangularly spaced holes by means of which it is bolted to the flywheel. When the bolts are tightened the face of the flywheel engages the ring. Resistance against backlash in this coupling is provided by the friction force between the flywheel face and the outer ring. This coupling is of limited flexibility because the rubber body is confined to the space between the inner member and the outer ring. Blind assembly (in which the flywheel carrying the ring and the driven component with the inner member are brought into engagement by feel without having to fit or tighten any fixing elements which may be difficult to access as a result of housing structures in the engine) is not possible with this design as the bolts connecting the coupling to the flywheel need to be tightened. In another known form of flexible coupling the rubber body has peripheral teeth which engage with corresponding teeth on the outer ring. The teeth on the outer ring and the rubber body allow the coupling to be assembled blind. This type of coupling has several disadvantages. Under load there is a tendency for adjacent engaging teeth to disengage, slip over each other and to re-engage with the next tooth. This causes undesirable wear on the teeth and ultimately ruins the coupling. In transmitting torque the rubber teeth become compressed causing gaps to appear between the two sets of teeth. When the torque reverses the presence of the gap causes backlash in the coupling. Furthermore, as a result of centrifugal forces generated during rotation of the coupling, the rubber teeth on the rubber body tend to swell during rotation and grip tightly the outer ring. This induces friction between them and effectively prevents axial movement between the rubber and the outer ring. Axial movement is desirable in flexible couplings to help provide compensation for any misalignment of the coupled components. GB-A-02235034 describes a flexible coupling member having two concentric coupling members joined by an intermediate coupling element of elastomeric material. The coupling element has a ring of bushes embedded in its inner and outer edges and held immovably with respect to the coupling member by clamping plates urged together by fasteners extending through the bushes. It is an object of the present invention to provide a flexible coupling with improved torsional flexibility. According to the present invention there is provided a flexible coupling for interconnecting machine components, comprising a resilient annular body fixed to rigid inner and outer annular members for connection to respective machine components, said body having angularly spaced holes adjacent its outer periphery and being lined by elements of said outer member, characterised in that said elements have a resilient lining with a tapered bore so that fixing means for connecting the coupling to a machine component can be received in the bore and compresses the lining. The provision of the compressible resilient lining serves to reduce backlash in the coupling to a very low value. Preferably the elements of said outer member are tubular, interconnected by arcuate connecting pieces and are smaller in width than the elements such that the connecting pieces are embedded in the annular body. Hence the annular body extends radially beyond the periphery of the outer member and over the arcuate connecting pieces giving extra torsional flexibility in the coupling. The connecting pieces are preferably T-shaped in section with the stem of the T directed radially outwardly. The bore may be tapered from both ends such that the minimum diameter of the bore is at the centre. According to a second aspect of the present invention there is provided a flexible coupling assembly comprising a flexible coupling as defined above, and fixing means for connecting the outer annular member to its machine component. The fixing means comprises a plurality of drive pins each of which is engageable in a respective one of said elements of said outer member. Advantageously, the drive pins have free ends engageable in said elements so as to permit blind fitting of the coupling with respect to the fixing means. The fixing means may also comprise a locating member adapted to be fixed to said machine component, the locating member having a plurality of recesses which engage with respective spigots on the adjacent ends of the drive pins. In one embodiment of the flexible coupling assembly a failsafe mechanism is provided which comprises at least one inward projection of said locating member and at least one outward projection from said inner member angularly spaced from said inward projection so as to maintain drive transmission in the event of failure of the coupling. Specific embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a part sectioned longitudinal view of half of the flexible coupling according to the present invention together with part of an engine flywheel; Figure 2 is an end view of a quarter of the coupling in the direction of arrow X of Figure 1 (flywheel not shown); Figure 3 is a perspective view of a reinforcement skeleton forming part of the flexible coupling of the present invention; Figure 4 is a sectioned view of the reinforcement skeleton along line A-A of Figure 2; Figure 5 is a part sectioned longitudinal view of a second embodiment of the present invention; Figure 6 is a part sectioned longitudinal view of a third embodiment of the present invention; and Figure 7 is an end view of figure 6 showing a quarter of the coupling. Referring now to Figures 1 and 2 in which for convenience only part of the coupling is shown, the rest of the coupling being the mirror image of the part shown about the centre lines, the flexible coupling generally indicated by arrow 1 is connected between a hub 2 and a flywheel 3 of an internal combustion engine. The hub 2 is machined to fit on to a shaft of a driven component of the engine, for example, the gearbox or the alternator. The coupling has a main body 4 of rubber and is connected at its outer end to the flywheel 3. An inner member 5 of cylindrical shape and having a radially inwardly directed flange 6 is connected to the hub 2 by a plurality of equiangularly spaced screws 7 which pass through the flange 6. The inner member 5 is vulcanised on its outer surface to the main body 4 of rubber. The main body 4 of rubber is of disc-like configuration having faces with radially outward tapers so that the axial thickness of the body 4 diminishes radially outwards. The body 4 has embedded in it, adjacent its outer edge, a metal reinforcement skeleton 8 which is shown in detail in figure 3. The skeleton 8 comprises a plurality of equiangularly spaced tubes 9 which are linked together by arcuate bridges 9a of inverted T-shaped cross section (see figure 4) to form a complete ring. The inside of each tube 9 is lined with a rubber tube 10 formed from rubber which is harder than the rubber of the main body 4. The rubber tube 10 is internally tapered from both ends to a minimum diameter at the centre. Within the rubber tube 10 there is shown a sleeve 11 which is slightly longer than the rubber tube 10. One end of the sleeve 11 has rounded edges 12 and the other end has a spigot formation 13. The minimum inside diameter of the rubber tube 10 is slightly less than the outside diameter of the sleeve 11. A location ring 14 fits into a recess 15 provided in the flywheel 3. The location ring 14 is drilled and counterbored to match the hole pattern in the flywheel 3. The spigot 13 on each sleeve 11 locates in the corresponding counterbore in the location ring 14. The coupling 1 is fixed to the flywheel 3 by means of screws 16 which pass through bores in the sleeves 11 and the location ring 14 to engage in a threaded bore in the flywheel 3. The sleeves 11 may, in an alternative embodiment, be counterbored to receive the head of each screw 16. The coupling 1 is assembled in the following manner. The location ring 14 and sleeves 11 are attached to the flywheel 3 by means of the screws 16 and the hub 2 is connected to the driven machine shaft by means of, for example, a key. The coupling 1 comprising the rubber body 4, the inner member 5, the skeleton 8 and the rubber tubes 10 is then connected to the hub 2 by means of screws 7. The rubber tubes 10 are lubricated with, for example, silicon fluid. The coupling 1 and the flywheel 3 can then be assembled blind by bringing them together and aligning the sleeves 11 to their respective holes in the coupling 1 by feel. The engine and driven machine are then pushed together such that the sleeves 11 enter the rubber tubes 10. The rounded edges 12 of the sleeves 11 and the tapered bores of the rubber tubes 10 facilitate entry of the sleeves 11 into the tubes 10. In manufacture the inner member 5 and skeleton 8 are placed within a mould and the rubber is injected into the mould and vulcanised to them to form the main body 4 and the tubes 10. The rubber body 4 and the rubber tubes 10 are of different rubber compound but are injected simultaneously into the rubber mould. The rubber tubes 10 have a high value of hardness designed to resist deformation and abrasion from the loads imposed by the sleeves 11 whereas the rubber body 4 has a low value of hardness and thus produces a low torsional stiffness in the coupling 1. The rubber body 4 is tapered as described to provide for uniform torsional strength throughout the coupling. By virtue of the minimum internal diameter of the rubber tube 10 being less than the outer diameter of the sleeve 11 a precompression is induced in the rubber tube 10. The arrangement of the sleeves 11 in the tubes 10 provides for a very low axial stiffness in the coupling. As the friction force between the sleeves 11 and the rubber tubes 10 is not great the coupling is allowed to slide axially on the sleeves 11 whilst in use. This axial movement is desirable in couplings to provide compensation for any misalignment of the coupled components. The relatively high radial stiffness of the connection ensures that the torque load or centrifugal stresses do not tend to cause swelling of the rubber tubes 10 and thus they have little or no effect on the axial stiffness. The skeleton 8 is bonded to the rubber body 4 over a large surface area such that the stress of the rubber to metal bond has a relatively low value. The skeleton 8 acts to reinforce the harder rubber of the tubes 10 and provides a strong connection resistant to localised deformation of the rubber. The skeleton 8 and the rubber tubes 10 preloaded by the sleeves 11 act to eliminate virtually all backlash. The provision of a rubber body 4 which entirely encompasses the skeleton 8 and therefore the connection holes gives extra flexibility in the coupling 1 compared with known couplings of this kind. This allows the rubber to have a lower stiffness without overstressing the rubber. The bridges 9a of the skeleton 8 provide restraint from centrifugal forces acting on the connection tubes 9 and the associated fixings as the coupling rotates, and help to reduce the stress concentration in its rubber body near each tube 9. In summary, it can be seen that in the embodiment described the coupling provides extra torsional flexibility whilst minimising backlash and allowing blind assembly. It is to be appreciated that the coupling of the present invention can also be used in applications where blind fitting is not required. In such cases the coupling can be bolted to the flywheel once the tubes 9 of the reinforcement skeleton 8 have been aligned to the holes in the flywheel. The backlash in these cases will be zero. Furthermore, there may be applications where the elimination of backlash is not a significant concern in relation to the torsional flexibility requirement, so couplings may be provided which do not have the rubber tubes 10 lining the tubes 9 of the reinforcement skeleton 8. Figure 5 shows an alternative embodiment of the present invention in which an alternative connection arrangement between the flexible coupling of figs. 1 to 3 and the flywheel is provided to suit other designs of flywheels or driving machines. The same reference numerals but incremented by a value of 100 are used to identify parts common to both embodiments. In this design the location ring 114 is extended radially outwardly. The ring 114 has a plurality of equiangularly spaced outer holes 117a and similarly spaced inner counterbored holes 117b. Each sleeve 111 locates in the counterbored hole 117b as before and the coupling, indicated generally by arrow 101, is connected to the location ring 114 by a nut and bolt arrangement 118. The coupling 101 is connected to the flywheel 103 by a plurality of equiangularly spaced screws 119 which pass through the outer hole 117a in the location ring 114. Figures 6 and 7 show a further alternative embodiment in which parts common to the first embodiment are given the same reference numeral but incremented by a value of 200. For convenience only part of the coupling is shown, the rest of the coupling being the mirror image of the part shown about the centre lines. In this embodiment of the invention the location ring 214 extends radially inwardly from the flywheel connection. An inner limit ring 220 is connected in the same plane as the location ring 214 to the hub 202 and inner member 205 by means of screws 207. The location ring 214 has radially inwardly extending projections 221 which project into the spaces between corresponding outwardly extending projections 222 on the inner limit ring 220. This arrangement acts as a failsafe mechanism. If the rubber of the main body 204 should rupture during rotation the degree of relative rotational motion between the hub 202 and the flywheel 203 is limited by the abutment of the projections 221,222 on the limit ring 220 and location ring 214. Thus despite the rubber failure the projections 221,222 enable the drive to be transmitted by the coupling until the requisite repair action can be taken.

Claims: A flexible coupling (1) for interconnecting machine components (2,3), comprising a resilient annular body (4) fixed to rigid inner and outer annular members (5,8) for connection to respective machine components (2,3), said body (4) having angularly spaced holes adjacent its outer periphery and being lined by elements (9) of said outer member (8), characterised in that said elements (9) have a resilient lining (10) with a tapered bore so that fixing means (11,14,16) for connecting the coupling (1) to a machine component (3) can be received in the bore and compresses the lining (10). A flexible coupling (1) according to claim 1, wherein the elements (9) of said outer member (8) are tubular. A flexible coupling (1) according to any preceding claim, wherein arcuate connecting pieces (9a) interconnect the elements (9) of the outer member (8). A flexible coupling (1) according to claim 3, wherein the arcuate connecting pieces (9a) are smaller in width than the elements (9) such that the connecting pieces (9a) are embedded in the annular body (4). A flexible coupling according to claim 3 or 4, wherein the connecting pieces (9a) are T-shaped in section with the stem of the T directed radially outwardly. A flexible coupling according to any preceding claim, wherein the bore is tapered from both ends such that the minimum diameter of the bore is at the centre. A flexible coupling assembly comprising a flexible coupling (1) as defined in any previous claim, and fixing means (11,14,16) for connecting the outer annular member (8) to its machine component (3). A flexible coupling assembly according to claim 7, wherein the fixing means (11,14,16) comprises a plurality of drive pins (11,16) each of which is engageable in a respective one of said elements (9) of said outer member (8). A flexible coupling assembly according to claim 8, wherein the drive pins (11,16) have free ends engageable in said elements (8) so as to permit blind fitting of the coupling with respect to the fixing means (11,14,16). A flexible coupling assembly according to claim 8 or 9, wherein the fixing means (11,14,16) further comprises a locating member (14) adapted to be fixed to said machine component (3), the locating member (14) having a plurality of recesses (15) which engage with respective spigots (13) on the adjacent ends of the drive pins (11,16). A flexible coupling assembly according to claim 1 wherein a failsafe mechanism comprises at least one inward projection (221) of said locating member (214) and at least one outward projection (222) from said inner member (220) angularly spaced from said inward projection (221) so as to maintain drive transmission in the event of failure of the coupling.

Inventors: HARPIN GRAHAM E, HARPIN, GRAHAM E.
Applicants: RENOLD HOLSET COUPLINGS LIMITE, RENOLD HOLSET COUPLINGS LIMITED
Application year: 1993
Main classification: F16D3
IPC codes: F16D3