ACCESSORY GEARBOX

Abstract

A gas turbine engine has an engine core, a bypass duct, an engine principal rotational axis and a core annulus surrounding the engine principal rotational axis and radially disposed between the engine core and the bypass duct. The engine radial direction is defined as perpendicular to and intersecting the engine principal rotational axis. An accessory gearbox is located in the core annulus. The accessory gearbox has a sequence of spur gears for driving engine accessories. For each spur gear, the spur gear is mounted for rotation about a respective spur gear rotational axis that is non-parallel with the engine principal rotational axis, the spur gear rotating within a respective spur gear rotational plane perpendicular to the spur gear rotational axis, the spur gear rotational plane intersecting said spur gear, wherein the spur gear rotational plane is offset with respect to the engine radial direction.

Claims

1. An accessory gearbox for a ducted fan gas turbine engine, the engine having an engine core, a bypass duct, an engine principal rotational axis and a core annulus surrounding the engine principal rotational axis and radially disposed between the engine core and the bypass duct, wherein an engine radial direction is defined as perpendicular to and intersecting the engine principal rotational axis, wherein: the accessory gearbox is for location in the core annulus, the accessory gearbox has a sequence of spur gears or driving engine accessories, for each spur gear, the spur gear is mounted for rotation about a respective spur gear rotational axis that is non-parallel with the engine principal rotational axis, the spur gear rotating within a respective spur gear rotational plane perpendicular to the spur gear rotational axis, the spur gear rotational plane intersecting said spur gear, wherein the spur gear rotational plane is offset with respect to the engine radial direction.

2. The accessory gearbox according to claim 1, wherein the accessory gearbox has a plurality of engine accessories mounted thereon.

3. The accessory gearbox according to claim 2, wherein a first engine accessory has a first axial length, a second engine accessory has a second axial length, shorter than the first axial length, and the first engine accessory is mounted on a first side of the accessory gearbox and the second engine accessory is mounted on a second side of the accessory gearbox.

4. The accessory gearbox according to claim 3, wherein the first and second engine accessories are driven by respective spur gears of the accessory gearbox.

5. The accessory gearbox according to claim 3, having a group of said first engine accessories, having longer axial lengths than a group of said second engine accessories.

6. The accessory gearbox according to claim 2, wherein the accessories are selected from the group consisting of: starter, fuel pump, oil pump, alternator, breather, generator, hydraulic pump.

7. The accessory gearbox according to claim 1, wherein, for each spur gear, the respective spur gear rotational axis is perpendicular to and offset from the engine principal rotational axis.

8. The accessory gearbox according to claim 7, wherein the spur gear rotational axes are disposed horizontally.

9. The accessory gearbox according to claim 1, wherein the accessory gearbox has a casing having a first side wall at a first side of the casing and a second side wall at a second side of the casing and an average midline defined between the first and second side walls of the casing, the average midline of the casing being parallel to the engine principal axis and offset from the engine radial direction.

10. The accessory gearbox according to claim 1, wherein the accessory gearbox has at least one bevel gear for driving an engine accessory mounted to the accessory gearbox, the at least one bevel gear having a bevel gear rotational axis that extends obliquely with respect to the spur gear rotational axes.

11. A gas turbine engine for an aircraft incorporating an accessory gearbox according to claim 1 in the core annulus of the gas turbine engine.

12. The gas turbine engine according to claim 11, further 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 a 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.

13. The gas turbine engine according to claim 12, wherein: the turbine is a first turbine, the compressor is a first compressor, and the core shaft is a first core shaft; the engine core further comprises a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor; and the second turbine, second compressor, and second core shaft are arranged to rotate at a higher rotational speed than the first core shaft.

14. An accessory gearbox for a ducted fan gas turbine engine, the engine having an engine core, a bypass duct, an engine principal rotational axis and a core annulus surrounding the engine principal rotational axis and radially disposed between the engine core and the bypass duct, wherein an engine radial direction is defined as perpendicular to and intersecting the engine principal rotational axis, wherein: the accessory gearbox is for location in the core annulus, the accessory gearbox has a sequence of spur gears, and for each spur gear, the spur gear is mounted for rotation about a respective spur gear rotational axis that is non-parallel with the engine principal rotational axis, the accessory gearbox has at least one bevel gear for driving an engine accessory mounted to the accessory gearbox, the at least one bevel gear having a bevel gear rotational axis that extends obliquely with respect to the spur gear rotational axes.

Description

DESCRIPTION OF THE DRAWINGS

[0062] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0063] FIG. 1 is a sectional side view of a gas turbine engine;

[0064] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0065] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

[0066] FIG. 4 is a sectional side view of a gas turbine engine, similar to FIG. 1 but showing the lower half of the engine including the accessory gearbox;

[0067] FIG. 5 shows a schematic side view of gears inside an accessory gearbox according to an embodiment, viewed from the side in a direction perpendicular to the principal axis of the engine, as for FIGS. 1 and 4;

[0068] FIG. 6 is a schematic plan view of an accessory gearbox according to an embodiment, viewed from above in a direction perpendicular to the principal axis of the engine; and

[0069] FIG. 7 is a schematic front side view of an accessory gearbox according to an embodiment, viewed from along a direction parallel to the principal axis of the engine.

DETAILED DESCRIPTION

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 epicyclic gearbox 30 generally comprise at least three planet gears 32.

[0075] 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 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.

[0076] 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 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 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.

[0077] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

[0078] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0079] 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.

[0080] 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.

[0081] FIG. 4 is a sectional side view of a gas turbine engine, similar to FIG. 1 but showing the lower half of the engine including the accessory gearbox 62 fitted in the core annulus 64, defined by core annulus inner wall 66 and core annulus outer wall 68. Accessory gearbox 62 provides a mount for accessories (described later) and distributes mechanical power to, or from, each accessory unit. Power is transmitted to the accessory gearbox from the engine typically via an internal gearbox and drive shaft shown schematically as drive 60 in FIG. 4. The internal gearbox includes a bevel gear linked to a rotor of the engine (e.g. at one of the compressor stages of the engine).

[0082] Typical engine-related accessories mounted at the accessory gearbox include the starter, fuel pump, oil pump, alternator and breather. Typical aircraft-related accessories mounted at the accessory gearbox include generators and hydraulic pumps.

[0083] As shown in FIG. 4, accessory gearbox 62 is located in the core annulus 64, which is an enclosed annular space surrounding the core and located internally of the bypass duct 22.

[0084] The curvature of the core annulus is tighter than the curvature outside of the fan casing (which is where an accessory gearbox is conventionally located). Furthermore, the radial width of the core annulus is restricted by the core on one side and by the bypass duct on the other side. Accordingly, there is restricted space available for the accessory gearbox and for the accessories connected to the accessory gearbox.

[0085] As shown in FIG. 4, the engine has an engine core 11, a bypass duct 22, an engine principal rotational axis 9 and a core annulus 64 surrounding the engine principal rotational axis 9 and radially disposed between the engine core 11 and the bypass duct 22. The engine radial direction 13 is defined as perpendicular to and intersecting the engine principal rotational axis 9. Accessory gearbox 62 is located in the core annulus.

[0086] As shown in FIGS. 5 and 6, the accessory gearbox has a sequence of spur gears 80, 82, 84, 86, some for driving engine accessories and some for providing transmission. For each spur gear, the spur gear is mounted for rotation about a respective spur gear rotational axis that is perpendicular to the engine principal rotational axis 9. Each spur gear rotates within a respective spur gear rotational plane 88 (the plane of the page in FIG. 5) perpendicular to the spur gear rotational axis 90. Here, the spur gear rotational plane intersects the spur gear. As shown in FIGS. 6 and 7, the spur gear rotational plane 88 is offset with respect to the engine radial direction by distance 94.

[0087] Engine centre line 92 is shown in FIG. 6.

[0088] The accessory gearbox 62 is driven by the engine by drive shaft 96 and bevel gears 98, 100

[0089] The accessory gearbox 62 has a casing 102. Casing 102 may in part intersect a radial direction of the engine. However, considering the sidewalls 104 and 106 of casing 102, the average midline of the casing 102 may be offset from the engine radial direction.

[0090] As shown in FIG. 7, the effect of this offset position of the accessory gearbox is that a first accessory 110 having a first length may be mounted at a first side of the accessory gearbox (corresponding to side wall 104). However, the same first accessory 110 (shown in ghosted outline 110 in FIG. 7) may not be mounted at the opposing second side (corresponding to side wall 106) of the accessory gearbox because there is not enough space provided at the second side the accessory gearbox without interfering with the outer wall 68 of the core annulus. Therefore a second accessory 112 is mounted at the second side of the accessory gearbox. The second accessory 112 has a second length that is shorter than the first length. The second length is suitable allow the second accessory to fit in the space between the accessory gearbox and the outer wall 68 of the core annulus.

[0091] Note that the curvature of the outer wall 68 of the core annulus in FIG. 7 is exaggerated in order to emphasise the manner in which the first and second accessories fit into the available space. In practice, the core annulus surrounds the engine core, the engine core containing for example a compressor stage axially aligned with the accessory gearbox.

[0092] The effect of the arrangement illustrated in FIG. 7 is that the first length can be relatively long. Therefore accessories of relatively long length can be mounted on the accessory gearbox provided that the accessory gearbox is offset from an engine radial direction. The remaining relatively short second accessories can be mounted on the opposing second side of the accessory gearbox.

[0093] As shown in FIG. 7, the rotational axes 90 of the first and second accessories can be horizontal. This allows the first and second accessories to be drive by spur gears. An advantage of this is that spur gears are relatively simple to manufacture, and are therefore cost-effective. The first accessory 110 and the second accessory 112, driven by spur gears in the accessory gear box, are disposed to extend horizontally from the accessory gearbox.

[0094] FIG. 7 also shows a third accessory 114 mounted obliquely from horizontal at the second side of the accessory gearbox. Third accessory 114 has a relatively long length, similar to or greater than the first length of the first accessory. Its oblique mounting allows it to fit in the available space within the core annulus. In order for the third accessory to be mounted obliquely, it is driven via bevel gears 116, 118 in the accessory gearbox. Bevel gears are relatively complex to manufacture, and are therefore more expensive than spur gears. Thus, from a cost and complexity point of view, it may be preferred to limit the number of accessories mounted in this manner.

[0095] Bevel gear 118 rotates about bevel gear rotational axis 120, which extends obliquely with respect to spur gear rotational axis 90. The angle subtended between the bevel gear rotational axis 120 and the spur gear rotational axis 90 may be about 45. Different angles may be used where convenient, to make use of available space in the core annulus.

[0096] It is possible for there to be one or more further accessories (not shown) driven by bevel gears (not shown). In that case, these further accessories may be driven about rotational axes that are parallel or non-parallel with bevel gear rotational axis 120. As the skilled person will understand, suitable rotational axes directions can be selected depending on the available space in the core annulus for the specific accessories to be driven.

[0097] The accessories may be selected from the group consisting of:

[0098] starter motor, fuel pump, oil pump, alternator, breather, generator, hydraulic pump.

[0099] 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.