GAS TURBINE ENGINE WITH STAGGERED EPICYCLIC GEARBOX

Abstract

Embodiments of the invention are shown in the figures, where a gas turbine engine for an aircraft includes: an engine core including a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan including 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 about a rotational axis at a lower rotational speed than the core shaft, wherein the gearbox is an epicyclic gearbox with a plurality of planet gears arranged in first and second sets of planet gears, the planet gears of the first set being positioned displaced relative to the planet gears of the second set in a direction parallel to the rotational axis.

Claims

1. 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 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 about a rotational axis at a lower rotational speed than the core shaft, wherein the gearbox is an epicyclic gearbox with a plurality of planet gears arranged in at least first and second sets of planet gears, the planet gears of the first set being positioned displaced relative to the planet gears of the second set in a direction parallel to the rotational axis.

2. The gas turbine engine according to claim 1, wherein the planet gears of the first set are arranged to rotate in a first plane and the planet gears of the second set are arranged to rotate in a second plane, the first plane being parallel to the second plane and displaced relative to the second plane in a direction parallel to the rotational axis.

3. The gas turbine engine according to claim 1, wherein planet gears of the first and second sets overlap one another.

4. The gas turbine engine according to claim 1, wherein the planet gears of the first set are axially offset relative to the planet gears of the second set, so that side faces of planet gears of the first sett are facing side faces of planet gears of the second set.

5. The gas turbine engine according to claim 1, wherein each planet gear is mounted by means of a pin, wherein the pin of a planet gear of one of the first and second sets extends between adjacent planet gears of the other one of the first and second sets.

6. The gas turbine engine according to claim 1, wherein the core shaft is arranged to rotate coaxially with the rotational axis.

7. The gas turbine engine according to claim 1, wherein a planet carrier carries the planet gears of the first and second sets.

8. The gas turbine engine according to claim 7, wherein the planet carrier comprises a first portion and a second portion, wherein the planet gears of the first and second sets are arranged between the first and second portions.

9. The gas turbine engine according to claim 7, wherein the fan is fixedly connected to the planet carrier via one or more linkages.

10. The gas turbine engine according to claim 9, wherein the core shaft is arranged to simultaneously rotate in the same rotational direction as the one or more linkages.

11. The gas turbine engine according to claim 5, wherein one or more of the planet gears are rotatably mounted on the respective pins, the pins being fixed to the planet carrier, and/or one or more of the planet gears are fixed to the respective pins, the pins being rotatably mounted on the planet carrier.

12. The gas turbine engine according to claim 1, wherein each planet gear of the first set comprises a first ring of teeth and each planet gear of the second set comprises a second ring of teeth, the first ring of teeth having an opposite helicity than the second ring of teeth.

13. The gas turbine engine according to claim 1, wherein the first set comprises the same number of planet gears as the second set.

14. The gas turbine engine according to claim 1, wherein the first set and/or the second set comprises at least three, in particular four planet gears.

15. The gas turbine engine according to claim 1, wherein a common oil system provides oil both to the engine core and to the gearbox.

16. The gas turbine engine according to claim 1, 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.

Description

[0052] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0053] FIG. 1 is a perspective view of an aircraft having a plurality of gas turbine engines;

[0054] FIG. 2 is a sectional side view of a gas turbine engine;

[0055] FIG. 3 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0056] FIG. 4 is a partially cut-away view of a gearbox for a gas turbine engine;

[0057] FIG. 5 is a side view of a schematic illustration of a gearbox for the gas turbine engine according to FIGS. 2 and 3;

[0058] FIG. 6 is a perspective view of the gearbox of FIG. 5;

[0059] FIG. 7 is a side view of a sun gear and two planet gears for the gearbox of any of FIGS. 2 to 6;

[0060] FIG. 8 is a schematic illustration of an arrangement of a core engine of the gas turbine engine of FIGS. 2 and 3 with a gearbox and a common oil system; and

[0061] FIG. 9 is a side view of a planet gear mounted on a planet carrier.

[0062] FIG. 1 shows an aircraft 8 in the form of a passenger aircraft. Aircraft 8 comprises several (here two) gas turbine engines 10. In the example shown in FIG. 1, the gas turbine engines 10 are mounted to wings of the aircraft 8. The aircraft 8 wings are fixed to a fuselage of the aircraft 8. Alternatively or in addition, one or more gas turbine engines 10 may be directly mounted to the aircraft body.

[0063] FIG. 2 illustrates one of the gas turbine engines 10 of the aircraft 8. The gas turbine engine 10 has 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 (core) shaft 26 (low-pressure shaft) and an epicyclic gearbox 30; 130.

[0064] 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 (core) shaft 27 (high-pressure shaft). The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30; 130 is a reduction gearbox. Each of the core airflow A and the bypass airflow B flows through an annular channel that surrounds the gearbox 30; 130. The gearbox is integrated between the fan 23 and the engine core 11.

[0065] An exemplary arrangement for the geared fan gas turbine engine 10 is shown in FIG. 3. The low pressure turbine 19 (see FIG. 2) 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.

[0066] The planet gears 32 are disposed in a staggered arrangement as will be described in greater detail below. By the arrangement of the gearbox 30 a maneuver loads reaction path (at least partially) flows through the gearbox 30 and into the engine structure and then into an airframe of the gas turbine engine 10.

[0067] 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 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.

[0068] The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 4. 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. 4. There are four planet gears 32 of a first set S1 of 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. For example, the first set S1 of the (planetary) epicyclic gearbox 30 comprises at least three planet gears 32. The planet gears 32 of the first set S1 are arranged in a first plane. The gearbox 30 further comprises a second set S2 of planet gears 32. The planet gears 32 of the second set S2 are arranged in a second plane that is not shown in the view of FIG. 4.

[0069] Each planet gear 32 is rotatably mounted on the planet carrier 34 (see, e.g., FIG. 3) by means of a pin 35. For example, each planet gear 32 is rotatable with respect to the corresponding pin 35. The pin 35 may then be fixed relative to the planet carrier 34. As another alternative, each of the planet gears 32 may be fixed with respect to the corresponding pin 35, while the pins 35 are rotatably mounted on the planet carrier 34. FIG. 4 shows the pins 35 of the planet gears 32 of the first set S1, as well as the pins 35 of the planet gears 32 of the second set S2 (while the planet gears 32 of the second set S2 themselves are not visible in the view of FIG. 4).

[0070] The epicyclic gearbox 30 illustrated by way of example in FIGS. 3 and 4 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.

[0071] It will be appreciated that the arrangement shown in FIGS. 3 and 4 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, but may particularly be stiff. 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. 3. In particular, however, it may be provided that the shaft 26 (at least its part adjacent the gearbox 30) and/or the linkages 36 is/are stiff, in particular such that during normal use, no movement of parts of the shaft relative to the gearbox are allowed. 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. 3.

[0072] 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.

[0073] Optionally, the gearbox may drive additional components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0074] 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. 2 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.

[0075] 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. 2), and a circumferential direction (perpendicular to the page in the FIG. 2 view). The axial, radial and circumferential directions are mutually perpendicular.

[0076] FIGS. 5 and 6 show a gearbox 130 for the gas turbine engine 10 described above. The gearbox 130 according to FIGS. 5 and 6 is similar to the gearbox 30 described with reference to FIGS. 3 and 4, in that it is an epicyclic gearbox 130, wherein the sun gear 28 is fixed to the shaft 26 and the planet carrier 34 is fixed with respect to the fan 23 by means of the linkages 36, while a ring gear 138 is fixed relative to the engine structure via linkages 40. Also the gearbox 130 of FIG. 5 has a first set S1 and a second set S2 of planet gears 32. The planet gears 32 of the first set S1 are arranged in a first plane and the planet gears 32 of the second set S2 are arranged in a second plane, wherein the first plane and the second plane are displaced relative to one another. To be more precise, according to FIGS. 5 and 6, the first plane and the second plane are parallel to one another and orthogonal to the axis of rotation R of the fan 23. The axis of rotation R of the fan 23 corresponds to the rotational axis of the linkages 36 and the planet carrier 34. Furthermore, the axis of rotation R is coaxial with the principle rotational axis 9. A rotation of the shaft 26 around the principle rotational axis 9 in a given direction leads to a rotation of the fan 23 in the same rotational direction. The first plane and the second plane are offset relative to one another in the direction of the axis of rotation R.

[0077] The ring gear 138 comprises first and second rings of teeth 38A, 38B. The first ring of teeth 38A meshes with the planet gears 32 of the first set S1 (but not with the planet gears 32 of the second set S2). The second ring of teeth 38B meshes with the planet gears 32 of the second set S2 (but not with the planet gears 32 of the first set S1). In the present example, a gap is formed between the first and second rings of teeth 38A, 38B of the ring gear 38. Alternatively, the ring gear 38 could comprise only one (continuous) ring of teeth for the planet gears 32 of all sets S1, S2. This is the case at the gearbox 30 of FIGS. 3 and 4.

[0078] The sun gear 28 comprises only one (continuous in axial direction) ring of teeth for the planet gears 32 of all sets S1, S2. Alternatively, the sun gear 28 could comprise first and second rings of teeth, wherein the first ring of teeth could mesh with the planet gears 32 of the first set S1 (but not with the planet gears 32 of the second set S2) and the second ring of teeth could mesh with the planet gears 32 of the second set S2 (but not with the planet gears 32 of the first set S1).

[0079] The planet carrier 34 comprises a first portion 34A and a second portion 34B. Each planet gear 32 pin 35 is mounted on the first portion 34A as well as on the second portion 34B. The planet gears 32 of both sets S1, S2 are arranged between the first and second portions 34A, 34B of the planet carrier 34. A portion (the first portion 34A) of the planet carrier 34 is fixed to the linkages 36. In the present example, a portion (the second portion 34B) of the planet carrier 34 surrounds the shaft 26.

[0080] Each planet gear 32 according to FIGS. 5 and 6 is rotatably supported on the corresponding pin 35 by means of a roller bearing or a journal bearing. The pins 35 are stiff (and not flexible). The use of a planet carrier 34 with two portions 34A, 34B allows to further increase the stiffness and to avoid deflections of the pins 35.

[0081] As can be seen in FIG. 6, the planet gears 32 of the first and second sets S1, S2 overlap one another so that parts of side faces of the planet gears 32 face one another. The number of planet gears 32 (eight in the example of FIGS. 5 and 6) of the first and second sets S1, S2 would not fit into one plane between the sun gear 28 and the ring gear 138. Therefore, without an increase of the diameter of the gearbox 130 (the same holds for the gearbox 30 according to FIGS. 3 and 4), a larger number of planet gears 32 can be used and, therefore, a higher torque can be transmitted by means of the gearbox 130.

[0082] The teeth of the gears of the gearboxes 30, 130 according to FIGS. 3 and 4, and 5 and 6, respectively, extend parallel to the axis of rotation R. However, alternatively, the teeth may be set at an angle with respect to the axis of rotation R.

[0083] It is worth noting that the rotational axis of each planet gear 32 (of each set S1, S2) are parallel to one another. Further, these rotational axes are all parallel to the rotational axis of the sun gear 28. Each planet gear 32 (of each set S1, S2) is in meshing engagement with the sun gear 28 and with the ring gear 138.

[0084] The staggered epicyclic arrangement allows for an increase of torque splitting (for power density) without an increased diametral space claim. The more planet gears 32, the more the torque can be split and thus each element can be smaller in diameter. In addition, the staggered arrangement allows a relatively small diameter of the gearbox, what helps to reduce centrifugal forces on the gears.

[0085] As can be seen particularly from FIG. 6, two epicyclic gear trains with the same number of planet gears 32 (the first and second sets S1, S2) are clocked (in degrees) corresponding to 360/(2n), where n is the total number planet gears 32 of the first and second sets S1, S2. The planet gears 32 of the first and second sets S1, S2 can be identical. The two epicyclic gear trains are in a stacked arrangement.

[0086] According to FIG. 7, alternatively shaped sun and planet gears 128, 132 for the gearboxes 30, 130 are helical. A corresponding ring gear will be correspondingly helical. Therein, the sun gear 128 comprises a first ring of teeth 28A and a second ring of teeth 28B. The first ring of teeth 28A and the second ring of teeth 28B have opposite helicities. A gap is formed between the first and second rings of teeth 28A, 28B. Correspondingly, each of the planet gears 132 of the first set S1 has a ring of teeth 32A shaped to mesh with the first ring of teeth 28A of the sun gear 128. Each of the planet gears 132 of the second set S2 have a ring of teeth 32B shaped to mesh with the second ring of teeth 28B of the sun gear 128. The different helicities provide an axial fixture of the gears of the gearbox 30; 130.

[0087] It is worth noting that each planet gear 32 has only exactly one type of helicity (either left or right) and does not have different helicities.

[0088] FIG. 8 shows various components of the gas turbine engine according to FIGS. 2 and 3. The engine core 11 is shown schematically and coupled to the gearbox 30; 130, which is a gearbox according to any embodiment described herein, via the shaft 26. The output of the gearbox 30; 130 drives the fan 23.

[0089] Furthermore, FIG. 8 shows an oil system 50. The oil system 50 circulates oil via ducts 51 to the engine core 11 as well as to the gearbox 30; 130. That is, the oil system 50 is one common oil system 50 that is adapted to lubricate both the gearbox 30; 130 and the engine core 11. This allows a simplification of the gas turbine engine 10 and a reduction of weight.

[0090] FIG. 9 shows an example how one or more of the planet gears 32 (e.g. all planet gears 32 of one set S1, S2, or all planet gears 32 of all sets S1, S2) can be rotatably mounted on the planet carrier 34. In this example, the shown planet gear 32 is fixed to the pin 35. The pin 35 (or planet shaft) is rotatably mounted on the planet carrier 34. Therein, the pin 35 is rotatably mounted on one portion 34A of the planet carrier 34 by means of a journal bearing 37A (or, alternatively, by means of a rolling element bearing), in the present example on the first portion 34A facing the fan 23. Further, the pin 35 is rotatably mounted on the other portion 34B of the planet carrier 34 by means of a roller bearing 37B (or rolling element bearing), e.g. a ball bearing (or, alternatively, by means of a journal bearing), in the present example on the second portion 34B facing the engine core 11. It has been found that this configuration allows a particularly robust gearbox 30; 130. However, for a simplified design, it would also be possible to only use journal bearings 37A or only use roller bearings 37B on both sides. Each of the gearboxes 30; 130 described herein may optionally use these kinds of planet gear 32 bearing.

[0091] 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.

[0092] For example, the gearboxes 30, 130 described herein may comprise more than two sets (stages) of planet gears 32.

LIST OF REFERENCE NUMBERS

[0093] 8 aircraft [0094] 9 principal rotational axis [0095] 10 gas turbine engine [0096] 11 engine core [0097] 12 air intake [0098] 14 low-pressure compressor [0099] 15 high-pressure compressor [0100] 16 combustion equipment [0101] 17 high-pressure turbine [0102] 18 bypass exhaust nozzle [0103] 19 low-pressure turbine [0104] 20 core exhaust nozzle [0105] 21 nacelle [0106] 22 bypass duct [0107] 23 propulsive fan [0108] 24 stationary support structure [0109] 26 shaft (first core shaft) [0110] 27 interconnecting shaft (second core shaft) [0111] 28; 128 sun gear [0112] 28A first ring of teeth [0113] 28B second ring of teeth [0114] 30; 130 gearbox [0115] 32; 132 planet gear [0116] 32A (first) ring of teeth [0117] 32B (second) ring of teeth [0118] 34 planet carrier [0119] 34A first portion [0120] 34B second portion [0121] 35 pin [0122] 36 linkages (output) [0123] 37A journal bearing [0124] 37B roller bearing [0125] 38; 138 ring gear [0126] 38A first ring of teeth [0127] 38B second ring of teeth [0128] 40 linkages [0129] 50 oil system [0130] 51 oil duct [0131] A core airflow [0132] B bypass airflow [0133] R rotational axis [0134] S1 first set of planet gears [0135] S2 second set of planet gears