Geared compressor for gas turbine engine

Abstract

A booster assembly for a gas turbine engine having a first rotor assembly comprising a low pressure turbine drivingly connected to a fan via a first shaft and a second rotor assembly comprising a second turbine drivingly connected to a high pressure compressor via a second shaft. The first and second rotor assemblies are arranged to undergo relative rotation in use about a common axis. The booster assembly comprises a further compressor arranged to be disposed about said common axis between the fan and high-pressure compressor in a direction of flow and a gearing having first and second input rotors and an output rotor. The first input rotor is arranged to be driven by the first rotor assembly and the second input rotor is arranged to be driven by the second rotor assembly such that the output rotor drives the further compressor in dependence upon the difference in rotational speed between the first and second rotor assemblies.

Claims

1. A gas turbine engine comprising: a first rotor assembly comprising a low pressure turbine drivingly connected to a fan via a first shaft; a second rotor assembly comprising a second turbine drivingly connected to a high pressure compressor via a second shaft, the first and second rotor assemblies arranged to undergo relative rotation in use about a common axis, and a booster assembly having: a further compressor arranged to be disposed about said common axis between the fan and high-pressure compressor in the direction of flow; and a gearing having first and second input rotors and an output rotor, the first input rotor arranged to be driven by the first rotor assembly and the second input rotor arranged to be driven by the second rotor assembly, wherein the gearing is a mechanical epicyclic gearing comprising at least one mechanical coupling including gears and teeth, and the first input rotor comprises a ring gear, the second input rotor comprises a sun gear and the output rotor comprises a planet gear carrier member.

2. The gas turbine engine according to claim 1, wherein the first or second input rotor comprises an extension portion of the respective first or second shaft.

3. The gas turbine engine according to claim 1, wherein the first or second input rotor is connected to the respective first or second shaft by an intermediate wall or arm which is angled with respect to the common axis.

4. The gas turbine engine according to claim 1, wherein the first rotor assembly and the second rotor assembly are co-rotating.

5. The gas turbine engine according to claim 1, wherein the output rotor of the gearing is drivingly connected to an electrical machine.

6. The gas turbine engine according to claim 5, wherein the electrical machine is driven by the output rotor in a generator mode of operation and/or is arranged to drive the output rotor in a starter motor mode of operation.

7. The gas turbine engine according to claim 5, wherein the output rotor is connected to or integral with a rotor of the electrical machine.

8. The gas turbine engine according to claim 7, wherein the electrical machine rotor comprises one or more magnets.

9. The gas turbine engine according to claim 5, wherein the electrical machine is disposed about the common axis.

10. The gas turbine engine according to claim 5, further comprising a brake for any or any combination of the first rotor assembly, second rotor assembly, the first input rotor and/or the second input rotor.

11. A gas turbine engine comprising: a first rotor assembly comprising a low pressure turbine drivingly connected to a fan via a first shaft; a second rotor assembly comprising a second turbine drivingly connected to a high pressure compressor via a second shaft, the first and second rotor assemblies arranged to undergo relative rotation in use about a common axis, and a booster assembly having: a further compressor arranged to be disposed about said common axis between the fan and high-pressure compressor in the direction of flow; and a gearing having first and second input rotors and an output rotor, the first input rotor arranged to be driven by the first rotor assembly and the second input rotor arranged to be driven by the second rotor assembly, wherein the gearing is a mechanical epicyclic gearing comprising at least one mechanical coupling including gears and teeth, the first input rotor comprises a planet gear carrier member, the second input rotor comprises a sun gear and the output rotor comprises a ring gear, the output rotor drives the further compressor, and the first rotor assembly and the second rotor assembly are contra-rotating.

12. The gas turbine engine according to claim 11, wherein the first or second input rotor comprises an extension portion of the respective first or second shaft.

13. The gas turbine engine according to claim 11, wherein the first or second input rotor is connected to the respective first or second shaft by an intermediate wall or arm which is angled with respect to the common axis.

14. The gas turbine engine according to claim 11, wherein the output rotor of the gearing is drivingly connected to an electrical machine.

15. The gas turbine engine according to claim 14, wherein the electrical machine is driven by the output rotor in a generator mode of operation and/or is arranged to drive the output rotor in a starter motor mode of operation.

16. The gas turbine engine according to claim 14, wherein the output rotor is connected to or integral with a rotor of the electrical machine.

17. The gas turbine engine according to claim 16, wherein the electrical machine rotor comprises one or more magnets.

18. The gas turbine engine according to claim 14, wherein the electrical machine is disposed about the common axis.

19. The gas turbine engine according to claim 14, further comprising a brake for any or any combination of the first rotor assembly, second rotor assembly, the first input rotor and/or the second input rotor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Practicable embodiments of the invention are described in further detail below by way of example only with reference to the accompanying drawings, of which:

(2) FIG. 1 shows a half-longitudinal section through a gas turbine engine according to the prior art;

(3) FIG. 2 shows a half-longitudinal section through a compressor according to one example of the invention;

(4) FIG. 3 shows a half-longitudinal section through a compressor according to a second example of the invention;

(5) FIG. 4 shows a half-longitudinal section through a compressor according to a third example of the invention; and

(6) FIG. 5 shows a half-longitudinal section through a compressor according to a further example of the invention, comprising an electrical machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) The present invention derives from the premise that it is possible to drive a booster and/or generator by the difference in relative rotation between the high-pressure and low-pressure spools of a gas turbine engine.

(8) Gas turbine engines using the invention may operate substantially in the manner described above in relation to FIG. 1, with the exception that the intermediate-pressure turbine 18 and shaft may be removed. Accordingly the intermediate-pressure compressor 14 may be replaced with a booster assembly driven by a gearing as will be described below.

(9) Turning to FIG. 2, there is shown a booster (i.e. compressor) arrangement 24 according to one example of the invention. The compressor portion of the arrangement comprises a rotor drum 26 having a plurality of compressor blades 28 depending radially outwardly therefrom at axially spaced locations. The compressor blades 28 are preferably provided as a plurality of rows or circumferential arrays of blades arranged about axis 11.

(10) The blades extend into an annular compressor passageway 29. The passage is defined as the space between the rotor drum 26 (which defines an inner wall of the passage) and a concentric casing structure 32 (which defines an outer wall of the passage).

(11) The compressor blades, which rotate with the drum in use, are axially spaced and intermediate stator vanes 30 are provided therebetween. The stator vanes depend inwardly from the casing 32. The radially inner ends of the stator vanes may terminate at or immediately adjacent sealing formations on the rotor drum 26 to minimise any leakage from therebetween in use.

(12) The passageway 29 defines a portion of the core flow passage extending from a flow splitter 34 (i.e. downstream of the fan 36) to the high-pressure compressor 38 (only the upstream end of which is shown) and onto the combustor (not shown) in FIG. 2). The compressor is thus in the flow path between the fan and the high-pressure compressor.

(13) The high-pressure compressor is driven by a corresponding high-pressure shaft 40. The high pressure shaft has an extension portion 42 connecting it to an input rotor of a gearing 44. In this embodiment the extension portion comprises a wall 46 or other support formation which is obliquely angled relative to the axis 11 and the remainder of the shaft 40 so as to provide an increase in shaft diameter to accommodate the gearing 44.

(14) The shaft extension portion terminates at a ring gear formation 48 disposed about the axis 11 and having radially-inwardly facing teeth.

(15) The gearing 44 comprises an epicyclic or planet gear arrangement in which a plurality of planet gears 52 are arranged between the radially outer ring gear 48 and a radially inner sun gear 50.

(16) The sun gear is provided as a collar formation on the exterior surface of the low-pressure shaft 54 which extends between the fan 36 and the low-pressure turbine. A portion of the low pressure shaft 54 in concentrically inside the high-pressure shaft 40. However the low pressure shaft 54 extends forwardly of the high pressure shaft in the axial direction.

(17) The low pressure shaft 54 may join with (i.e. may be integrally formed with or attached to) a fan shaft portion 56 which drives the fan in rotation in use.

(18) The sun gear 50 comprises a radially-outwardly facing gear teeth arranged circumferentially about the shaft 54 collar. The sun gear may be formed at a rearward portion of the fan shaft 56 or a forward portion of the low-pressure shaft 54 or at an interface or overlapping region there-between.

(19) The planet gears 52 each comprise a set of teeth arranged about their circumferential surface. The teeth thus mesh with the teeth of the ring gear 48 and the sun gear 50 concurrently.

(20) The plurality of planet gears are typically provided as a circumferential array of gears angularly spaced (typically equidistantly) about the axis 11 and sun gear 50.

(21) A planet carrier structure 58 holds the planet gears at the desired relative orientation and spacing. The planet carrier comprises one or more bearings arranged to hold each planet gear at the required location, whilst permitting rotation of the planet gears relative thereto. In this embodiment, the planet gears 52 each have a central hub portion which is maintained at fore and aft ends thereof within carrier structure bearings. An intermediate wall connects the hub portion to the outer circumferential wall on which the teeth are formed. The hub portion may be generally tubular in form.

(22) The circumferential surface/wall of each planet gear is circular in section such that the planet gears each comprise a body of revolution about its own axis. The axis of rotation of each planet gear may be parallel with axis 11 but radially spaced therefrom such that each said axis can follow a circular path about axis 11 in use.

(23) The planet carrier structure 58 defines a rotor, which, in this embodiment, comprises an output rotor of the gearing 44. The planet carrier structure is supported relative to the static engine structure by a bearing.

(24) The planet carrier structure is drivingly connected to the compressor rotor by an interconnecting drive arm 62.

(25) The gearing 44 is located in a cavity or enclosure surrounding the low-pressure shaft. The gearing 44 in this embodiment is located between the fan and high-pressure compressor, and preferably towards the aft of the booster compressor or immediately downstream thereof.

(26) In use all of the components of the gearing, namely the gear ring 48, the sun gear 50, the planet gears 52 and the planet carrier 58 are rotatable about the common axis 11. Thus, when the gas turbine engine is in operation, the difference in rotational speed between the high-pressure shaft 40 and the low-pressure shaft 54 drives rotation of the planet gears 52 between the ring gear 48 and the sun gear 50. The planet gears in turn cause rotation in the planet carrier 58 about the axis 11, which thus drives rotation of the compressor arrangement 24 such that it functions as a booster.

(27) The speed of rotation of the booster is thus adjusted in line with the input conditions according to the low and high-pressure rotors.

(28) The relative dimensions of the ring gear, planet gears and sun gear are selected to ensure optimal speed requirements of the booster can be achieved. Thus the booster may operate at optimal aerodynamic conditions, wherein the optimal working line is matched with that of the high-pressure compressor. Also the gearing can be additionally or alternatively tailored to ensure that the speed variation of the booster (i.e. the gearing output rotor) between idle and maximum speed lies within an acceptable range, for example for driving an electrical machine as will be described below.

(29) Furthermore the use of a booster configuration as shown in any of the embodiments of the invention can provide an increase in inlet pressure to the high-pressure compressor over that of a conventional two-shaft engine configuration (i.e. more akin to that of a three-shaft engine configuration). This enables a reduction in high-pressure compressor stages and a corresponding reduction in core engine size, thereby allowing the high-pressure spool to operate at increased rotational speeds.

(30) Turning now to FIG. 3, there is shown a further embodiment which is similar to the embodiment of FIG. 2 with the exception that the input and output rotors are drivingly connected to different portions of the epicyclic gearbox. In the embodiment of FIG. 3, the booster compressor 24a is drivingly connected to the sun gear 50a, for example by a short intermediate shaft 64. The sun gear may thus be formed as a collar about the intermediate shaft 64. The intermediate shaft and/or sun gear may be supported relative to the static engine structure by bearing 66.

(31) The planet carrier 58a in FIG. 3 depends from (i.e. is supported by) the low-pressure shaft 54 and may be connected thereto by an intermediate wall or arm formation. The ring gear arrangement 48 is substantially unchanged and is driven by the high-pressure shaft 40. Thus the ring gear and planet bearing carrier provide input rotors, whilst the sun gear comprises an output rotor.

(32) In FIG. 4 there is shown a further embodiment which is similar to the embodiment of FIG. 2 or 3 with the exception that the input and output rotors are drivingly connected to different portions of the epicyclic gearbox. In the embodiment of FIG. 4, the booster compressor 24b is drivingly connected to the planet carrier 58b, for example which may comprise a short intermediate shaft portion. The booster drive arm 62b thus connects the planet carrier to the compressor drum. The planet carrier may be supported relative to the engine static structure by a bearing arrangement.

(33) The sun gear 50b in this embodiment is driven by the high pressure shaft 40 and may be formed as a collar about the high pressure shaft extension portion 42b.

(34) The ring gear 48b in FIG. 4 depends from (i.e. is supported by) the low-pressure shaft 54 and may be connected thereto by an intermediate wall or arm formation 66.

(35) In the embodiment of FIG. 4, the gearing 44b may be shifted forward such that it is in front of the booster compressor 24b in an axial direction. Accordingly the high-pressure shaft extension 42b may be elongated and the ring gear may be supported by the fan shaft 56. The gearing may be mounted within a cavity or housing surrounding the low-pressure shaft downstream of the fan, for example within or adjacent the front bearing housing of the engine.

(36) By virtue of the different embodiments shown in FIGS. 2-4, it can be seen that the booster can be driven by any epicyclic gearing configuration in which all primary components are rotating and having any two input rotors driving an output rotor via the planet gears. Thus any of the ring gear, planet carrier and sun gear can be drivingly connected to any of the high-pressure, low pressure and booster output as required. However certain configurations are considered to provide certain benefits (i.e. offering better drive gear ratios and/or mounting configurations) in different engine scenarios.

(37) In developments of the basic concept of the invention, the epicyclic arrangement can provide a speed inversion characteristic that allows the booster to operate at relatively higher speed at lower high and low-pressure spool speeds (i.e. at lower engine speeds) and at a relatively lower speed at higher engine speeds. In any embodiment of the invention there may be defined a normal mode of use in which the booster operates at a speed between that of the low-pressure and high-pressure rotor speeds (e.g. at cruise). A second mode of use may be defined, which may comprise a reduced engine speed (e.g. an idle speed), in which the booster speed may be increased relative to the high-pressure spool speed.

(38) Also it has been found that by using a helical tooth profile within the gearing, for certain epicyclic gearbox arrangements, the meshing teeth in the gearbox the tensile axial loading between the low-pressure shaft and the booster can be at least partially counter-acted, this can reduce the effective axial loading which needs to be borne by the low-pressure spool support system, e.g. the LP location bearing.

(39) Power can be extracted according to any of the above examples of the invention from both the high and low-pressure spools so as to improve engine operability, especially at low engine speeds. Accordingly the invention has been found to offer a beneficial rotor arrangement for driving an electrical generator.

(40) In one such embodiment a conventional accessory gearbox and/or generator configuration may be driven by the gearing output/booster instead of by the high-pressure shaft alone. In such an arrangement a radial and/or angled drive shaft (e.g. via a step-aside gearbox) may be provided as would be understood by the person skilled in the art in order to drive an accessory gearbox mounted in the nacelle.

(41) However in a further embodiment, an electrical machine may be integrated with the output of the gearbox such that it is driven directly thereby. In any of the above-described embodiments, the gearbox output may comprise a rotor of the electrical machine such that the electrical machine is mounted for rotation about the engine axis 11, rather than being offset therefrom.

(42) An example of such an electrical machine 68 is shown in FIG. 5. The electrical machine in this embodiment is driven by the planet gear carrier structure 58c so as to induce rotation between the rotor 68a and stator 68b portions of the electrical machine. In such an embodiment the stator 68b may be supported by a static portion of the engine structure.

(43) The rotor 68a and stator 68b may comprise any conventional rotor or stator of an electric machine, suitable for use in a gas turbine engine, and may comprise for example one or more permanent magnets or one or more current-carrying conductors in the form of coils. Either such rotor or stator may be arranged about engine axis 11.

(44) The electrical machine 68, e.g. the magnet and coil assembly thereof, may be mounted at an axial location between the fan 36 and booster compressor 24, 24a, 24b or HP compressor 38. The electrical machine may be mounted radially inwardly of a bypass duct and/or core engine air intake. The electrical machine may be mounted within a cavity 70 located radially between the engine axis 11 and the annular passage 29 forming the core engine air intake.

(45) The electrical machine may be supported relative to a wall of cavity 70, for example via an internal support member 72.

(46) In alternative embodiments of the invention for use in driving an electrical machine, the circumferential arrangement of rotor 68a and stator 68b may be reversed such that the stator may be radially inside of the rotor.

(47) The electrical machine rotor may be driven by the difference in relative rotational speeds between the high and low pressure spools of the gas turbine engine. Whilst the embodiment of FIG. 5 shows the electrical machine rotor being driven by the planet gear carrier 58c, it will be appreciate that the planet gear arrangement inputs and output could alternatively be arranged, for example as indicated in FIGS. 2-4, such that the electrical machine could alternatively be driven by the outer ring gear or inner sun gear.

(48) The electrical machine in any embodiment can operate as an electrical generator during a normal mode of operation of the engine. However, the electrical machine can also be used as a starter motor during engine start-up, i.e. to drive the high-pressure shaft in rotation using an electrical supply to the stator coils.

(49) Additionally or alternatively to the generator described in relation to FIG. 5, the gearing output of the invention may be used to drive other accessories, such as for example a pump (e.g. an oil pump). Thus pumps may be at least partially driven by the fan.

(50) The principles of the present invention may be applied within a gas turbine engine having two co-rotating or contra-rotating spools.

(51) Whilst the present invention finds a particular application in aircraft engines, the various available gas turbine engine configurations achievable under the present invention may be adapted to suit any conventional gas turbine engine application, which may include aerospace, marine, power generation amongst other propulsion or industrial pumping applications.