OIL SUPPLY ARRANGEMENT FOR BEARING

Abstract

A gas turbine engine for an aircraft comprises a gearbox that receives an input from a core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft. The gearbox is an epicyclic gearbox comprising planet gears, each of which is rotatable about its own axis on a respective pin, with a journal bearing formed between each planet gear and its respective pin. A first oil supply system is arranged to provide an oil supply to the journal bearing via a first journal bearing supply channel formed through the pin. A second oil supply system is arranged to provide an oil supply to the journal bearing via a second journal bearing supply channel formed through the pin, the second oil system being different to the first oil system.

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 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, wherein: the gearbox comprises an epicyclic gear train comprising a sun gear, a plurality of planet gears and a ring gear, each planet gear being rotatable about its own axis on a respective pin, with a journal bearing formed between each planet gear and its respective pin; a first oil supply system is arranged to provide an oil supply to the journal bearing via a first journal bearing supply channel formed through the pin; a second oil supply system is arranged to provide an oil supply to the journal bearing via a second journal bearing supply channel formed through the pin, the second oil system being different to the first oil system; the second journal bearing supply channel is parallel to the first journal bearing supply channel; and the second journal bearing supply channel is offset from the first journal bearing supply channel in the direction of the axes of the planet gears.

2. A gas turbine engine according to claim 1, wherein at least one of the first journal bearing supply channel and the second journal bearing supply channel is formed through its pin in the radial direction of the pin.

3. A gas turbine engine according to claim 1, wherein both the first journal bearing supply channel and the second journal bearing supply channel are formed through their pin in the radial direction of the pin.

4. A gas turbine engine according to claim 1, wherein: each pin has a passage running therethrough in the axial direction of the pin; and the first journal bearing supply channel and the second journal bearing supply channel extend between the passage and the journal bearing so as to fluidly connect the passage to the journal bearing.

5. A gas turbine engine according to claim 4, wherein: the first oil supply system comprises a first central feed passage running through the central passage of each pin, the first journal bearing supply channel extending between the first central feed passage and the journal bearing; the second oil supply system comprises a second central feed passage running through the central passage of each pin, the second journal bearing supply channel extending between the second central feed passage and the journal bearing; and the first central feed passage is not fluidly coupled to the second central feed passage.

6. A gas turbine engine according to claim 1, wherein: the first oil supply system comprises a first pump arranged to pump oil around the first oil supply system; and the second oil supply system comprises a second pump arranged to pump oil around the second oil supply system.

7. A gas turbine engine according to claim 6, wherein the second pump is a lower power and/or lower capacity pump than the first pump.

8. A gas turbine engine according to claim 1, wherein the first oil supply system has greater capacity than the second oil supply system.

9. A gas turbine engine according to claim 1, wherein the capacity of the second oil supply system is less than 70% of the capacity of the first oil supply system.

10. A gas turbine engine according to claim 1, wherein the second oil supply system is arranged to provide sufficient oil to the journal bearing to allow the fan to operate in a windmill condition in which it is not driven by the turbine.

11. A gas turbine engine according to claim 1, wherein during normal operation, in which the fan is driven by the turbine via the gearbox, oil is provided to the journal bearings by both the first oil supply system and the second oil supply system.

12. A gas turbine engine according to claim 1, wherein during normal operation, in which the fan is driven by the turbine via the gearbox, oil is provided to the journal bearings by only the first oil supply system.

13. A gas turbine engine according to claim 1, wherein: the first oil supply system comprises at least two first journal bearing supply channels formed through the pin, each first journal supply channel being parallel to the others and offset from the others in the direction of the axis of the planet gears.

14. A gas turbine engine according to claim 1, wherein: the second oil supply system comprises at least two second journal bearing supply channels formed through the pin, each second journal supply channel being parallel to the others and offset from the others in the direction of the axis of the planet gears.

15. A gas turbine engine according to claim 1, wherein the diameter of the fan is in the range of from 220 cm to 400 cm, optionally 220 cm to 290 cm or 320 cm to 400 cm.

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

DESCRIPTION OF THE DRAWINGS

[0064] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0065] FIG. 1 is a sectional side view of a gas turbine engine;

[0066] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0067] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

[0068] FIG. 4 is a schematic showing an oil system in accordance with an example of the present disclosure;

[0069] FIG. 5 is a schematic showing an oil system in accordance with an example of the present disclosure;

[0070] FIG. 6 shows an example of an oil system and journal bearing in accordance with an example of the present disclosure; and

[0071] FIG. 7 shows an example of an oil system and journal bearing in accordance with an example of the present disclosure.

DETAILED DESCRIPTION

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0081] 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 18, 20 meaning that the flow through the bypass duct 22 has its own nozzle 18 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.

[0082] 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.

[0083] As shown in FIG. 3, each of the planet gears 32 rotates on (and relative to) a pin 200, about an axis 300. The pin 200 may remain fixed (or stationary) during operation relative to the planet carrier 34. In some arrangements, the pin 200 may remain stationary in absolute terms, whereas in other arrangements the pin 200 may rotate with the planet carrier 34 around the centreline of the gearbox 30. A journal bearing 250 is formed between the pin 200 and respective planet gear 32. The journal bearing may be said to be formed between a radially outer surface (for example a cylindrical radially outer surface) of the pin 200 and a radially inner surface (for example a cylindrical radially inner surface) of the respective planet gear 32. As explained in greater detail below, oil is supplied to the journal bearing 250 during operation.

[0084] An example of an oil system 100 for supplying oil to the journal bearing is shown in FIG. 4. The oil system 100 comprises a first oil supply system 160 and a second oil supply system 170. The oil in the first oil supply system 160 may be separate from the oil in the second oil supply system 170, as in the FIG. 4 example.

[0085] The first oil supply system 160 comprises a pump 120 and an oil reservoir 110, which may be an oil tank 110. The pump 120 is arranged to be able to pump oil around the first oil supply system 160, so as to be able to supply oil to the gearbox 30 in use. In use, oil may flow in the direction of the arrows in FIG. 4, that is from the reservoir 110 through the pump 120, to the gearbox 30 and then back to the reservoir 110.

[0086] The second oil supply system 170 comprises a pump 140 and an oil reservoir 130. The pump 140 is arranged to be able to pump oil around the first oil supply system 170, so as to be able to supply oil to the gearbox 30 in use. In use, oil may flow in the direction of the arrows in FIG. 4, that is from the reservoir 130 through the pump 140, to the gearbox 30 and then back to the reservoir 130.

[0087] The first and/or second oil supply system 160/170 may comprise other components, such as one or more filters, as desired in order to ensure effective and reliable operation. Purely by way of example, a filter may be provided on the oil return path between the gearbox 30 and the respective reservoir 110/130.

[0088] As shown schematically in the FIG. 4 example, the first oil supply system 160 may be larger (for example in terms of total capacity and/or reservoir capacity and/or pump size) than the second oil supply system 170.

[0089] During normal operationin which the fan 23 is driven by the low pressure turbine 19 via the gearbox 30oil may be supplied to the gearbox 30 using just the first oil supply system 160. Alternatively, during normal operationin which the fan 23 is driven by the low pressure turbine 19 via the gearbox 30oil may be supplied to the gearbox 30 using both the first oil supply system 160 and the second oil supply system 170.

[0090] FIG. 5 shows an alternative oil supply arrangement. The FIG. 5 arrangement also comprises a first oil supply system 160 and a second oil supply system 170. However, in contrast to the FIG. 4 arrangement, the first oil supply system 160 and the second oil supply system 170 share a common oil reservoir 150 in the FIG. 5 arrangement. It will be appreciated that arrangements other than those illustrated by way of example in FIGS. 4 and 5 are within the scope of the present disclosure, for example arrangements in which the first oil supply system 160 and the second oil supply system 170 share a common pump.

[0091] Each of the first oil supply system 160 and the second oil supply system 170 is capable of providing sufficient lubrication to the journal bearings 250 in the gearbox 30 on its own at least during windmilling of the fan 23 (i.e. when the fan 23 is not being driven by the turbine 19). Thus, in the event of failure of one of the oil supply systems 160, 170, the other oil supply system 160, 170 can be used alone in order to allow the fan 23 to continue windmilling without seizure of the gearbox 30 due to oil starvation of the journal bearings 250. For example, the engine 10 may be shut down (such that no fuel is burned in the combustor 16), whilst allowing the fan 23 to continue to rotate due to the aerodynamic forces exerted thereon as it moves through the air through lubrication provided by just one of the first oil supply system 160 and the second oil supply system 170.

[0092] In some arrangements, one or both of the first oil supply system 160 and the second oil supply system 170 may not be capable of providing sufficient lubrication to the journal bearings 250 in the gearbox 30 on its own during normal operation of the fan 23.

[0093] If required, a switch may be used (for example an electrical switch or a mechanical (including pneumatic and/or hydraulic) switch) to determine which one or both of the first oil supply system 160 and the second oil supply system 170 is operational at a given time. Such a switch may be in a different state, for example, when the engine 10 is operating normally compared to when then engine 10 is windmilling.

[0094] FIG. 6 shows a close-up view of the delivery of oil to the journal bearing 250 using the first oil supply system 160 and the second oil supply system 170. The first oil supply system 160 comprises a first journal bearing supply channel 214. The first journal bearing supply channel 214 is in fluid connection with the journal bearing 250. Accordingly, in use, the first journal bearing supply channel 214 can supply oil to the journal bearing 250. The first journal bearing supply channel 214 passes through the pin 200. The first journal bearing supply channel 214 passes from a radially inner surface of the pin 200 to a radially outer surface of the pin 200. In the FIG. 6 example, the first journal bearing supply channel 214 is fed from a channel (which may be a cylindrical channel) 310 through the centre of the pin 200. In the FIG. 6 example, the first journal bearing supply channel 214 is fed via a first central feed passage 212 running through the channel 310 through the centre of the pin.

[0095] The second oil supply system 170 comprises a second journal bearing supply channel 224. The second journal bearing supply channel 224 is in fluid connection with the journal bearing 250. Accordingly, in use, the second journal bearing supply channel 224 can supply oil to the journal bearing 250. The second journal bearing supply channel 224 passes through the pin 200. The second journal bearing supply channel 224 passes from a radially inner surface of the pin 200 to a radially outer surface of the pin 200. In the FIG. 6 example, the second journal bearing supply channel 224 is fed from a channel (which may be a cylindrical channel) 310 through the centre of the pin 200. In the FIG. 6 example, the second journal bearing supply channel 224 is fed via a first central feed passage 222 running through the channel 310 through the centre of the pin.

[0096] In order to optimize the efficiency and/or effectiveness of the oil supplied to the journal bearing 250 during operation, the first journal bearing supply channel 214 is parallel to the second journal bearing supply channel 224. Thus, regardless of whether one or both of the first and second oil system systems 160, 170 is in operation, oil can be supplied to the journal bearing efficiently and effectively.

[0097] In the arrangement shown in FIG. 6, the first journal bearing supply channel 214 and the second journal bearing supply channel 224 both lie in respective planes that are perpendicular to the central axis 300 about which the planet gears 32 are rotatable. The central axis 300 is parallel to the central axis 9 of the gas turbine engine 10, and so the first journal bearing supply channel 214 and the second journal bearing supply channel 224 may be said to both lie in respective planes that are perpendicular to the engine axis 9.

[0098] As illustrated in FIG. 6, the first journal bearing supply channel 214 and the second journal bearing supply channel 224 are axially offset from each other. Thus, there is an axial gap (in the direction of the planet gear axis 300 and/or the engine axis 10) between the first journal bearing supply channel 214 and the second journal bearing supply channel 224.

[0099] FIG. 7 shows an alternative arrangement for the delivery of oil to the journal bearing 250 using the first oil supply system 160 and the second oil supply system 170. All compatible aspects and features described in relation to the FIG. 6 arrangement may also be applied to the FIG. 7 arrangement. The FIG. 7 arrangement is substantially the same as the FIG. 6 arrangement, other than in that the first oil supply system 160 comprises two first journal bearing supply channels 216, 218 and the second oil supply system 170 comprises two second journal bearing supply channels 226, 228. Again, in order to optimize the efficiency and/or effectiveness of the oil supplied to the journal bearing 250 during operation, the first journal bearing supply channels 216, 218 are parallel to the second journal bearing supply channels 226, 228. In the FIG. 7 arrangement, the first journal bearing supply channels 216, 218 are also parallel to each other, and the second journal bearing supply channels 226, 228 are also parallel to each other. However, it will be appreciated that it may not be necessary for all of the channels to be parallel to each other. For example, one first journal bearing supply channel 216 may be parallel to one second journal bearing supply channel 226, but not parallel to the other first journal bearing supply channel 218.

[0100] It will be appreciated that oil may be provided into the gearbox 30 (for example into the central channel 300 of the pins 200) and extracted from the gearbox 30 (for example after being used to lubricate the journal bearings 250) from the first and second oil supply systems 160, 170 using suitable couplings and/or scavenge arrangements.

[0101] 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.