GEARED COUPLING

Abstract: A geared coupling comprising a rotatable casing member (10) and a coaxially mounted collector carrier member (25), wherein the collector carrier member has one or more collector portions (20) extending generally radially outwards toward the inner surface of the casing member, and the casing member and the collector carrier member are mechanically arranged such that, in use, the casing rotates relative to the collector carrier member.

Description: GEARED COUPLING The present invention relates to a coupling between two rotary devices, in particular where the two devices rotate at different speeds. In a conventional installation there are typically provided five elements. These include the prime mover, a first spacer type flexible coupling, a gearbox, a second spacer type flexible coupling and finally the driven machine. Normally the prime mover, the gearbox and the driven machine are foot mounted i.e. firmly anchored to a fixed reference usually the ground. Consequently, in order to compensate for any relative misalignment and/or movement of the shaft between the prime mover and the gearbox and the gearbox and the driven machine, it is necessary to provide the flexible couplings between each. Clearly this leads to a complicated and expensive arrangement. It is therefore desirable to reduce the number of these elements preferably to three i.e. the prime mover, the gearbox and the driven machine in order to reduce cost, complexity, overall length/size and to improve reliability. In order to dispense with the spacer couplings, it is necessary to modify the other elements of the drive train in order to make them able to cope with the various deflections of the drive shafts that may be presented. In particular, the gearbox must be able to handle both lateral movements as well as angular flexion of the drive shafts. The gearbox itself may take the form of an epicyclic gearbox or a simple layshaft arrangement having coaxial input and output shafts. An epicyclic gear comprises three nominally coaxial elements: a sun wheel, an annulus and a planet carrier supporting three or more planets. Its main advantage is that, subject to similar gear tooth rating criteria and dependent upon the number of planet wheels sharing the load, it is more compact than a simple parallel shaft gear having only one mesh point carrying the load. In principle it is only necessary to positively locate one of these elements while the other two may be allowed to float and take up a position dictated by their geometric assembly requirements. The load sharing mechanism and the precision with which the respective planet wheels are spaced and matched for size, determines how closely the three elements remain coaxial. Provided they are free to move to an appropriate position there will be no resultant lateral loads on either of the floating elements because their weight will be supported by their mesh points onto the fully located element. This contrasts, with a parallel shaft gear having a simple wheel and pinion which transmits its load through a single mesh point, such that equal and opposite unidirectional lateral loads are produced in their respective shafts which require a pair of bearings with an adequate load capacity on each. This means that whilst a parallel shaft gear is more capable than an epicyclic gear of accepting the parasitic lateral loads and moments generated by so-called flexible couplings, the need for such bearings on each shaft increases the overall cost of the device. However, in practice, epicyclic gears may also need some bearings for the input and output shafts subject to such loads, albeit they may not be so big. A further problem with both epicyclic and parallel shaft gears is that, in addition to both tooth surface and shaft bearing losses, there are significant losses due to the churning of the lubricant and/or cooling fluid. Even in epicyclic gears with a pressurised lubrication oil supply and a dry sump, there tends to be problems with the draining or scavenging of the oil caused by an entraining effect which whips up a whirling mass of emulsified oil that prevents the free flow of oil through a fixed gravity drain or scavenge pickup. Whilst churning losses tend to be worse in parallel shaft gears with their higher pitch line velocities, epicyclic gears have a much smaller surface area through which to dissipate heat generated due to such mechanical losses. The problem is made worse when gears are subject to changes of attitude and/or direction and magnitude of external 'g* loads. Therefore, according to the present invention, there is provided a geared coupling comprising a rotatable casing member and a coaxially mounted collector carrier member, wherein the collector carrier member has one or more collector portions extending generally radially outwards toward the inner surface of the casing member, and the casing member and the collector carrier member are mechanically arranged such that, in use, the casing rotates relative to the collector carrier member. Providing a rotating casing provides a highly effective draining action. Any fluid such as oil, which falls from any of the other parts of the geared coupling is either flung or dropped under gravity towards the casing. As the fluid comes into contact with the casing, it is retained against the inner surface by the centrifugal force generated by the rotation of the casing. The fluid forms a rotating annulus having high static gravitational and dynamic pressure heads. By dipping the collector into the rotating annulus of fluid, the gravitational and dynamic pressure heads cause fluid to be pumped into the collector member. Fluid can then be redistributed to where it is needed within the rest of the coupling. The system is completely independent of the attitude of the device as the pumping pressure is derived by centrifugal force and is effectively independent of normal gravitational force other than at extremely slow speeds. This system enables a pressurised flow of fluid to be continuously re-circulated either internally or, if necessary externally via a stationary reaction member for example for filtering or cooling. The fluid used in the machine is preferably oil but other fluids may be used either alone or in combination for lubrication and/or cooling. However, for simplicity the fluid in the machine will be referred to as oil throughout the rest of this specification. The external surface velocity of the rotating casing also improves heat transferred to the atmosphere when compared to a static casing. The oil is retained as a rotating annulus against the inner surface of the casing, and so it is substantially maintained clear of where the gears mesh so that there is no churning by the gear teeth. Thus only the required amount of oil is directed to the meshing surfaces via the pressurised flow. In addition, the centrifugal action of the rotating casing ensures that any particulate material in the oil is thrust outwards where it will be retained against the inner wall of the casing without being picked up by the collectors. This effectively avoids the need for complex filtration or settling tanks for the oil. A settling tank typically requires around 2 minutes to allow particles to settle out. In a typical machine, the required flow of oil may be 200-250 litres per second. This means the system would need around 400-500 litres of oil. Clearly this is expensive and inconvenient in terms of the need to provide pipework and the settling tank. This is avoided by the present invention. Additionally, in the present invention, any air in the oil is lifted to the surface of the annulus of oil and the oil is rapidly de-aired. The use of a rotating casing not only reduces the amount of heat generated by avoiding the churning of oil but also increases the rate at which heat is dissipated allowing the use of smaller more compact (i.e. coaxial or epicyclic) gears. Preferably, the collector carrier member is maintained stationary by attaching it either to the bed plate or ground or coaxially to either the driving or driven machine. The geared coupling preferably comprises one or more epicyclic trains arranged such that there are effectively three elements: an input, an output and a stationary reaction maintained in a coherent coaxial assembly. The first element is a rotating casing used as either an input or output as appropriate, the second serves vice versa as the output or input while the reaction is kept stationary by coupling it to the bedplate or the ground or one of the stationary casings of the driving or driven machines. If there is misalignment between the driving and driven machine axes, the casing will adopt an arbitrary angular attitude with an axis which is not coaxial with either machine. The casing, the second member and the reaction are preferably all connected to their respective machine shafts and bedplate or stationary casing with couplings which are angularly flexible but with lateral locations which keep them concentric in their coupling planes. The geared coupling assembly can therefore serve effectively as a spacer between the coupling points on the driving and driven machines with the axial distance between these two points analogous to the length of a spacer in a more conventional coupling. This length provides the moment arm required to articulate the rotating couplings through their respective angular amplitudes. A specific embodiment of the present invention will now be described with reference to the drawings in which: Figure 1 shows an example of a coupling arrangement for a conventional geared connection between a prime mover and a driven machine; Figure 2 shows a schematic example of a geared coupling in accordance with the present invention; Figure 3 shows a schematic cross-section through an embodiment of the present invention; Figures 4 A, 4B and 4C show engineering drawings of a more complex practical embodiment of the present invention; Figures 5 A - 5D show examples of the arrangement of the collectors of the present invention; Figure 6 shows an example of a bi-directional collector of the present invention; and Figure 7 shows an example of a radial collector of the present invention. It is commonly required that a mechanical device which needs to be driven by a rotating drive shaft is connected to a separate drive source such as a motor. However, it is also common to find that the rotation speed of the driven machine is not convenient for a speed of operation of a motor and so it is necessary to provide a step-up or step-down gearbox between the two machines. Conventionally, as shown in Figure 1, a gearbox 101 is provided between two machines. The gearbox 101 is connected to the motor 102 by a flexible coupling 104. Similarly, the gearbox 101 is connected to the driven machine 103 by a flexible coupling 105. These couplings 104, 105 are necessary because when the system is running, vibration in both the motor and the driven machine needs to be allowed for to avoid putting unnecessary and probably damaging load on the gearbox, motor or driven machine. The spacer type flexible couplings 104, 105 allow for lateral and angular displacement of the drive shafts 106 preventing damage to the rotating machines including the gearbox. However, these flexible couplings are complex mechanical mechanisms which add considerably to the cost of installing such machinery as well as the maintenance costs. The present invention provides a coupling between a motor and a driven machine which does not require separate couplings and which also provides a step-up or step-down gear between the driving and driven shafts. Thus as shown in Figure 2, the geared coupling 1 of the present invention has input and output shafts connected directly to the shafts of the respective motor 2 and driven machine 3. Figure 3 shows schematically an example of a motor in which the drive shaft is connected to the casing of the geared coupling and the driven shaft is connected to a central shaft within the coupling. In this instance, the geared coupling is an epicyclic arrangement. It is normally necessary to provide a fixed reference to which one of the moving parts of an epicyclic gear train is attached, although this is not shown in Figure 2 for simplicity. The use of an epicyclic gear set using the casing as one of the input or output members allows the casing to act as a coupling member having angular flexibility but with lateral rigidity/location to keep its coupling part concentric with the associated driven machine. The other end of the geared coupling which serves as the output or input respectively also acts as a coupling having angular flexibility and lateral rigidity. The coupling point is free to articulate in an angular sense but not free to move laterally. The third member of the transmission which is the stationary reaction member can then be flexibly connected to the fixed reference such as the bed plate via a lateral coupling arrangement or coaxially to either the driving or driven machine. For compatibility it may be preferable to provide such a coupling with some angular and/or tortional flexibility. Utilising an accessible static reaction member enables both its tortional flexibility and clamping to be varied. This can be used to tune and improve the dynamic characteristics of the combined machine transmission system without modifying either the rotating input or output coupling connections. Positive lateral location keeps the couplings at either end of the rotating casing concentric with the respective driving and driven machines in the planes of their articulation. Thus the effective length of the casing between these planes provides the moment arm required to articulate the coupling through their respective angular amplitudes. Referring to Figure 3, a simplified schematic diagram of a geared coupling in accordance with the present invention is shown. In this case, the motor or driving machine 2 is on the left-hand side and provides a low speed input. The driven machine 3 is connected to the geared coupling via a drive shaft 12 which is the high speed output of the geared coupling. In this instance, the third member of the transmission, i.e. the stationary reaction member 25, is coaxially attached to the frame of the driven machine 3. Thus the member 25 remains substantially stationary at all times providing the support structure for the planet gears 13 inside the geared coupling. At the end of the driven shaft 12 is provided the sun gear 14 and on the inside of the casing 10 is provided a radially inwardly projecting ring 11 of gear teeth which mesh with the planet gears 13. In use, the motor 2 drives the outer casing 10 of the geared coupling 1 such that any oil 15 therein is forced into an annular ring against the inner surface of the casing 10. This oil or fluid in the coupling would normally be used for lubrication of the meshing gear train but may include cooling fluid for cooling the various parts of the geared coupling. As oil is dropped from the surfaces of the parts of the geared coupling, it would either drop vertically down under the action of gravity or be swirled outwardly by the motion of the casing. In either case it will eventually impinge upon the outer surface of the casing and will be assimilated into the annular ring of oil on the inner surface of the casing. The considerable radially outward force on the oil due to the rotation of the casing will retain it in close contact with the inner surface of the casing. This force (centrifugal force) will be far in excess of any normal gravitational force except at very slow speeds of rotation and thus the effect of gravity will be negligible. In the geared coupling of the present invention, in order to provide a pressurised source of oil, for providing oil to the various parts of the coupling, one or more scoop members 20 extend radially from the fixed reaction member 25. These scoop members are provided with an inlet 21 which is generally arranged so that the inlet faces in the opposite direction to which the casing travels. In this way, as the annulus of oil impinges against the inlet 21 of the member 20, the dynamic pressure of the oil causes it to be forced into the inlet and up the collection tube 22. This collection tube then passes along or through the fixed stationary member to provide pressurised oil to those part of the coupling where it is required (the connections are not shown). For example, as shown in Figure 3, the collector tube 22 is connected to a feed pipe 23 which includes an injector 24 for providing oil to the meshing surface between the planet gears 13 and the sun gear 14. Similar arrangements may be provided for providing oil to other parts of the machine as and when necessary. In addition, the collector tube 22 may be extended out of the geared coupling via a further tube 26 which is shown partially in Figure 3 which extends out of the geared coupling for example via an outlet 19 fed from tube 27 connected to the tube 26. The outlet 19 allows the oil to be circulated through an external system for example to remove heat from the oil, to filter the oil, to monitor the characteristics of the oil etc. The inlet tube 21 may take a number of forms as shown in Figures 5a-5d. In Figures 5a and 5b, there are shown examples in which the collector tube member 20 is a generally disc like shape with one or more collector tubes 22 arranged therein. In Figure 5a, the collector tube is angled at the end to form an inlet mouth 21 which is generally flush with the outer circumference of the collector member. In contrast, in Figure 5b, the radius of the collector member increases at the collector mouth 21 so as to present the mouth of the collector tube into the oncoming flow of oil as shown by the arrows in Figures 5a-5d. In Figures 5c and 5d, the collector member comprises one or more radially protruding spoke like members which include the collector tube 22 therein. In Figure 5c, the collector member extends generally radially outwards having a collector inlet provided on the side thereof. In contrast, in Figure 5d, the collector member extends arcuately into the flow with the collector inlet being provided on the end of the collection tube. The embodiments shown in Figures 5a-5d are merely exemplary and any suitable arrangements, whereby the pressurised oil in the annulus outside the casing is caused to pass down the collector tube, can be used. In the examples given above, the collector inlet is generally arranged for a specific direction of rotation of the casing of the geared coupling (as shown). Where it is desirable to rotate the geared coupling in either direction, then additional collector members may be provided for collecting oil when rotation takes place in the opposite direction, arranged so that the collector inlet is directed in the opposite direction to those shown in Figures 5a-5d. The collectors for one direction of rotation may be arranged on a completely separate collector member axially displaced from those for collection in the opposite direction or they may be provided on the same collector member either angularly offset or simply arranged back-to-back as shown in Figure 6. In addition, a flap valve 60 may be included to prevent pressurised fluid escaping out of the collector mouth facing away from the direction of movement of the oil. The collector tubes preferably have a rectangular cross-section for ease of milling. This also makes the use and construction of a flap valve within the tubes easier. At high speeds, the static centrifugal head can be used in conjunction with a single radial intake, see Figure 7, which would be equally effective in both directions of rotation. It is preferable that the collector inlet diverges away from the mouth. In this way the oil enters the mouth at high speed but is slowed as the cross-sectional area increases as the oil moves further into the diverging passsage. This acts as a diffuser to convert velocity to pressure, further enhancing the pressure of the oil. The radially inset gear teeth on the inwardly projecting portion 11 are deliberately set inward from the casing so that the teeth do not lie in the annulus of oil so as not to cause swashing of the oil due to the meshing of the teeth of the casing with the teeth of the planets. One of the advantages of the coupling in the present invention is that, because the oil is held in the annulus around the inner surface of the casing, there is little likelihood of oil leaking through the seals 16 and 17 provided between the geared coupling and the driven machine 3. The seals are principally provided to allow for when the machine is idle or initially turning out low speeds before the annulus of oil is established. Although Figure 3 shows a simplified version of the present invention, it is not intended that the invention should be limited to such construction. In particular, Figure 4a and sections therethrough shown in Figures 4b and 4c (partial section), show a practical construction of a device according to the present invention. In this example the arrangement is similar in principle to the construction shown in Figure 3 but a dual set of epicyclic gears are used in the construction shown in Figure 4. However, the construction still retains the outer casing 10 having a set of gear teeth arranged on the protruding portion 11 which meshes with a first set of planet gears which are rotatably mounted on the fixed planet carrier 405. The oil collection member 20 is also clearly visible with the collection tube 22 also shown. The first set of planet gears 401 are driven by the casing causing an intermediate member 400 to rotate. The intermediate member forms the sun gear of the first epicyclic gear set and the annulus member of the second epicyclic gear set. This annulus member drives the planet gear 402 of the second epicyclic gear set which in turn drives the sun member 403 of the second epicyclic gear set. This sun member is in turn connected by a drive shaft to the driven machine. Again, in this example, the stationary reaction member 405 on which the planet gears of both the first and second epicyclic gear sets are rotatably mounted is connected to the frame of the driven machine shown by the frame connection means 404. Again, it is assumed that the driven machine is on the right-hand side and the motor is on the left-hand side although these may be swapped where step-down instead of step-up gearing is required. In both Figures 3 and 4a it can be seen that fins 18 are provided on the outside of the casing. These fins provide additional cooling of the geared coupling. Heat generated in the geared coupling is naturally transferred to the oil and/or cooling fluid circulating within the machine. This heat will also be transferred to the annulus of oil on the inner surface of the casing. Thus the heat will be transferred to the casing itself and into the fins 18. As the casing is rotating at speed, the air surrounding the casing will be induced to flow enhancing the natural cooling of the geared coupling considerably. Under normal circumstances, this improved natural cooling and the advantageous internal cooling and low heat generation of the geared coupling will avoid the need to provide additional external cooling of the geared coupling. The avoidance of additional external cooling is also more likely because of the avoidance of swashing of the oil within the coupling itself thus further reducing inefficiencies and heat generated within the coupling.

Claims: CLAIMS: 1. A geared coupling comprising a rotatable casing member and a coaxially mounted collector carrier member, wherein the collector carrier member has one or more collector portions extending generally radially outwards toward the inner surface of the casing member, and the casing member and the collector carrier member are mechanically arranged such that, in use, the casing rotates relative to the collector carrier member. 2. A geared coupling according to claim 1 wherein the collector carrier member is attached to a fixed reference such that in use it remains substantially stationary. 3. A geared coupling according to claim 2 wherein the collector carrier member is attached to the ground. 4. A geared coupling according to claim 2 wherein the collector carrier member is arranged to be attached, in use, to the body of a machine which is driving or being driven by the input or the output of the geared coupling. 5. A geared coupling according to any one of the preceding claims wherein the or each collector portion includes an inlet wherein the axis of the inlet is arranged at least partially angled away from a respective radial axis of the coupling. 6. A geared coupling according to claim 5 wherein the axis of the inlet is perpendicular to the radial axis of the coupling. 7. A geared coupling according to claims 5 or 6 wherein the collector carrier member includes pairs of collector portions each having inlets with their axis angled away from the radial axis of the coupling in opposite directions. 8. A geared coupling according to any of the preceding claims wherein the collector carrier member is substantially disc shaped wherein the or each collector portion is a tube within the collector carrier member. 9. A geared coupling according to any one of claims 1-7 wherein the collector carrier member comprises a number of radial spokes, some or all of the spokes comprising a collector portion. 10. A geared coupling according to any one of the preceding claims including one or more epicyclic gear sets wherein the casing forms the annulus of the or the first epicyclic gear set and the collector carrier member forms the planet carrier of at least the or the first epicyclic gear set. 11. A geared coupling according to any one of the preceding claims including one or more epicyclic gear sets wherein the casing is the input or the output of the coupling and the collector carrier member provides the static torque balance between the input and output torques. 12. A method of providing a pressurised oil supply in a rotating machine comprising providing in the machine a rotating outer casing and a coaxially mounted collector carrier member which, in use, rotates relative to the casing comprising: providing oil to the interior of the casing such that an annular ring of oil is formed on the inner surface of the casing and providing a scoop portion on the end of the collector carrier member which is dipped into the annular ring of oil, in use, to force pressurised oil into a tube provided in the interior of the collector carrier member. 13. A geared coupling substantially as described herein with reference to Figures 2- 6 of the drawings.

Applicants: HICKS RAY JOHN, HICKS, RAY, JOHN
Application year: 2001
Main classification: F16H57
IPC codes: F16H1, F16H57