DEVICE FOR COUPLING AN OUTPUT SHAFT WITH AN EPICYCLIC GEARBOX, METHOD FOR COUPLING AN OUTPUT SHAFT WITH AN EPICYCLIC GEARBOX AND A GAS TURBINE ENGINE

Abstract

The embodiments relate to devices for coupling, in particular the recoupling an output shaft with an epicyclic gearbox in a gas turbine engine, wherein an axial coupling action between the output shaft and the epicyclic gearbox is generatable through an oil pump and transmitted through an oil transfer coupling. Embodiments also relate to a method for coupling and a gas turbine engine.

Claims

1. A device for coupling, in particular the recoupling an output shaft with an epicyclic gearbox, in particular a planetary gearbox in a gas turbine engine, wherein an axial coupling action between the output shaft and the epicyclic gearbox is generatable through an oil pump and transmitted through an oil transfer coupling.

2. The device according to claim 1, wherein the oil transfer coupling comprises an activating pressure surface for oil pressurized by the oil pump, the activating pressure surface oriented to generate an axial relative movement between the output shaft and the epicyclic gearbox.

3. The device according to claim 2, wherein the activating pressure surface is part of a sealing device.

4. The device according to claim 3, wherein the sealing device comprises two sealing elements, with a first sealing element comprising the activating pressure surface having a larger surface than a second surface of the second sealing element.

5. The device according to claim 1, wherein the oil pump is drivably connected with a turbine of the gas turbine engine.

6. The device according to claim 1, wherein the oil pump is drivable connected with an external drive.

7. The device according to claim 1, wherein the output shaft and the epicyclic gearbox are coupleable through a helical spline connection.

8. The device according to claim 7, wherein splines of the helical spline connection comprise a tapered section at the rim of the helical spline connection

9. The device according to claim 1, with an additional bearing, in particular at a planet carrier of the epicyclic gearbox.

10. A method for coupling, in particular recoupling an output shaft with an epicyclic gearbox, in particular a planetary gearbox in a gas turbine engine, wherein an axial coupling action between the output shaft and the epicyclic gearbox is generated by an oil pump and the coupling action is transmitted through the oil in an oil transfer coupling.

11. The method according to claim 10, wherein the re-coupling is effected after the output shaft and the epicyclic gearbox were decoupled due to malfunction in the gas turbine engine, in particular a seizure in the epicyclic gearbox.

12. A gas turbine engine for an aircraft comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and an epicyclic gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, with a device for coupling, in particular recoupling an output shaft with an epicyclic gearbox in a gas turbine engine, wherein an axial coupling action between the output shaft and the epicyclic gearbox is generatable through an oil pump and transmitted through an oil transfer coupling.

Description

[0041] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0042] FIG. 1 is a sectional side view of a gas turbine engine;

[0043] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0044] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

[0045] FIG. 4 is a schematic sectional view of an embodiment of a device for coupling an output shaft with a planetary gearbox;

[0046] FIG. 5 is a sectional view of a further embodiment of a device for coupling an output shaft with a planetary gearbox in a first working position;

[0047] FIG. 6 is a sectional view of the embodiment shown in FIG. 5 in a second working position;

[0048] FIG. 7 is a perspective view of an oil transfer coupling in the embodiment shown in FIGS. 5 and 6:

[0049] FIG. 8 is a perspective view of helical spline connection in the embodiment shown in FIGS. 5 and 6:

[0050] FIG. 9 is a sectional view of an embodiment of a device for coupling an output shaft with a planetary gear drive.

[0051] FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

[0052] In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive the high pressure and low pressure turbines 17, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0053] An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun wheel, or sun gear 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to precess around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

[0054] Note that the terms low pressure turbine and low pressure compressor as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the low pressure turbine and low pressure compressor referred to herein may alternatively be known as the intermediate pressure turbine and intermediate pressure compressor. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

[0055] The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the claimed invention. Practical applications of a planetary gearbox 30, (i.e. a special case of an epicyclic gearbox) generally comprise at least three planet gears 32.

[0056] The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft 41 (see FIG. 4) via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

[0057] It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft 41 and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts 41 from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2.

[0058] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of epicyclic gearbox styles (for example star or planetary), support structures, input shaft and output shaft 41 arrangement, and bearing locations.

[0059] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0060] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 20, 22 meaning that the flow through the bypass duct 22 has its own nozzle that is separate to and radially outside the core engine nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

[0061] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0062] In FIG. 4 a schematic sectional view is shown of an embodiment for a device for coupling, in particular the recoupling an output shaft 41 with an epicyclic gearbox 30 in a gas turbine engine 10. FIG. 4 only shows a part of the output side of the planetary gearbox 30 and its output shaft 41.

[0063] A helical spline connection 42 connects the output shaft 41 with the planetary gearbox 30. At the other end of the output shaft 41 a straight spline connection 48 connects it with a fan shaft 47. The output shaft 41 has a varying diameter. The helical spline connection 42 is typically lubricated (not shown in FIG. 4 for the sake of simplicity).

[0064] Axial coupling action C (indicated by an arrow) between the output shaft 41 and the planetary gearbox 30 is generatable through an oil pump 50 (only shown schematically in FIG. 4) and transmitted through an oil transfer coupling 53. The oil pressure is provided by a main engine oil pump which is typically driven by an accessory gearbox (not shown in FIG. 4). The oil pump 50 can e.g. be riven by the accessory gear box, which in this embodiment is driven by the high pressure turbine shaft. A main oil tank provides the oil which is pumped into the gearbox 30 cavity and the cavity 54 in particular. The oil pump 54 can also provide oil to other consumers in the engine 10, in particular other consumers coupled to the gearbox 30.

[0065] The oil transfer coupling 53 can be moved by applying oil pressure for coupling (as shown in FIGS. 4 and 5). Therefore, the oil pressure can be used to re-couple the output shaft if it is fully disengaged. If the shaft is partially or fully engaged, the helical splines connection 42 will generate the axial load required to achieve and maintain full engagement. The decoupling would require a reversal of the direction of torque. Such a reversal results when the airstream rather than the turbine drives the fan 23, or should the gearbox 30 seize and momentum drive the fan 23.

[0066] In FIGS. 5 to 9 different operating positions and embodiments are shown in detail.

[0067] FIGS. 5 and 6 show one embodiment in different positions.

[0068] FIG. 5 shows the normal operating configuration on the output side of the planetary gearbox 30 a gas turbine engine 10.

On the right hand side of FIG. 5 the output side of the planetary gearbox 30 is shown. An output element 44 of the planetary gearbox 30 is connected to the planet carrier 34 (not shown in detail in FIG. 5).

[0069] During normal operation, torque is applied by the planetary gearbox 30 via a helical spline connection 42 at the output element 44 to the output shaft 41. The output shaft 41 then drives the fan shaft 47 to drive the propulsive fan 23 (FIG. 1 or 2). The output shaft 41 and the fan shaft 47 are connected via a standard spline connection 48.

[0070] The helical spline connection 42 produces as a result of this torque an axial force along the rotational axis 9 of the gas turbine engine 10. This axial force acts to push the output shaft 41 forward (to the left, indicated by an arrow). Actual motion is prevented by an operating stop 45.

[0071] Pressure from the main oil system (not shown here), supplied via the oil transfer coupling 53, also generates an axial load on the output shaft 41. This load is not required however to maintain engagement as long as the output shaft 41 is driven by the planetary gearbox 30.

[0072] FIG. 6 shows the embodiment shown in FIG. 5 in a decoupled configuration. In order for this configuration to be achieved, the planetary gearbox 30 must stop delivering torque to the output shaft 41. Torque in opposite direction from the normal operating torque must be applied via the standard spline connection 48 to the output shaft 41. Such a torque would be experienced during in-flight e.g. in windmilling. Under this torque, the helical spline connection 42 produces a force along the axis of the engine. This force acts to push the output shaft 41 rearward (to the right, indicated by an arrow) until the helical spline connection 42 become disengaged. A decouple stop 46 ensures that the standard spline connection 48 remains engaged in this configuration. In this configuration, the propulsive fan 23 and the output shaft 41 are free to rotate independently of the planetary gearbox 30.

[0073] Failure to deliver torque to the propulsive fan 23 will result in an gas turbine engine 10 shutdown due to engine overspeed protection activation, the sensing of excessive vibration, or some other means.

[0074] In order to return to the normal operating configuration, i.e. a recoupling from a decoupled configuration, two things must happen.

[0075] First, torque must be applied to the planetary gearbox 30 input exceeding the negative torque being applied to the output shaft 41.

[0076] Second, the main engine oil system must supply pressure to the oil transfer coupling.

[0077] Under these conditions, pressure applied by the main engine oil system will act to move the output shaft forward (to the left) until the ends of the helical spline connection 42 become engaged. The axial force generated on the output shaft 41 by the helical spline connection 42 then also acts to bring the helical spline connection 42 into full engagement as shown in FIG. 5. This is the axial coupling action C shown in FIG. 5.

[0078] This process will also occur on engine start up should the invention be brought into the de-coupled configuration by ground windmilling, maintenance activity, or some other means.

[0079] Therefore, the recoupling of the output shaft 41 with a planetary gearbox 30 is effected by an axial coupling action C between the output shaft 41 and the planetary gearbox 30 generatable through an oil pump 50 and transmitted through an oil transfer coupling 53 (see FIG. 4).

[0080] FIG. 7 shows details of the oil transfer coupling 53 in the previous embodiment. The oil transfer coupling 53 is e.g. a sealing device 60 (see FIG. 9).

[0081] It comprises a cavity 54 which axially is limited by surfaces 51, 52. The first surface, axially in front (i.e. on the left hand side in FIG. 7) is an activating pressure surface 51 for oil in the cavity 54 pressurized by the oil pump 50 (not shown here). The activating pressure surface 51 has an annular shape and is oriented to generate an axial relative movement between the output shaft 41 and the planetary gearbox 30. The surfaces 51, 52 are formed in part by ring-like sealing elements 61, 62 best seen in FIG. 9.

[0082] The second surface 52 is located axially towards the rear. The oil transfer coupling 53 implements differing seal diameters with the result that the areas of the surfaces 51, 52 are different. Therefore, oil pressure in the cavity 54 from the main engine oil system produces an axial load on the output shaft 41.

[0083] Any pressure in the main engine oil system will act to bring the end faces of the helical spline connection 42 into contact with the de-coupled configuration. Such oil pressure may be generated by windmilling loads on the high pressure compressor and turbine, which will apply torque to the high pressure shaft and, via the radial drive shaft to the accessory gearbox.

[0084] In order to minimize damage to the splines under such conditions, a taper is included at the mating faces, i.e. the rim 43 of both the male and female helical splines in the helical spline connection 42. Such a taper is shown in FIG. 8.

[0085] On applications where the output shaft 41 is subject to significant bending loads, an additional bearing 80 can be implemented, in particular around the output shaft 41, relatively close to the connection to the planetary gearbox 30 as shown in FIG. 9.

[0086] The additional bearing 80 would see no rotation of the inner race relative to the outer race during normal operation. Once decoupled, the inner race will begin rotating relative to the outer race. The additional bearing 80 will also allow the output shaft 41 to transfer radial loads.

[0087] FIG. 9 also shows the cavity 54 and the different diameters of the surfaces 51, 52.

[0088] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

LIST OF REFERENCE NUMBERS

[0089] 9 principal rotational axis [0090] 10 gas turbine engine [0091] 11 engine core [0092] 12 air intake [0093] 14 low-pressure compressor [0094] 15 high-pressure compressor [0095] 16 combustion equipment [0096] 17 high-pressure turbine [0097] 18 bypass exhaust nozzle [0098] 19 low-pressure turbine [0099] 20 core exhaust nozzle [0100] 21 nacelle [0101] 22 bypass duct [0102] 23 propulsive fan [0103] 24 stationary support structure [0104] 26 shaft [0105] 27 interconnecting shaft [0106] 28 sun gear [0107] 30 epicyclic gearbox, planetary gearbox [0108] 32 planet gears [0109] 34 planet carrier [0110] 36 linkages [0111] 38 ring gear [0112] 40 linkages [0113] 41 output shaft of epicyclic/planetary gearbox [0114] 42 helical spline connection between output shaft and planetary gearbox [0115] 43 rim of splines [0116] 44 output element planetary gearbox [0117] 45 operating stop [0118] 46 decouple stop [0119] 47 fan shaft [0120] 48 standard spline connection [0121] 48 alternative stop [0122] 50 oil pump [0123] 51 activating pressure surface [0124] 52 second surface [0125] 53 oil transfer coupling [0126] 54 cavity [0127] 60 sealing device [0128] 61 first sealing element [0129] 62 second sealing element [0130] 70 external drive [0131] 80 additional bearing [0132] A core airflow [0133] B bypass airflow [0134] C Coupling action