STRUCTURAL ASSEMBLY FOR A GAS TURBINE ENGINE

Abstract

A structural subassembly for a gas turbine engine, includes: a bearing mounting a fan shaft, a bearing housing surrounding the bearing, and a bearing support housing surrounding the bearing housing at a radial distance and which is connected to a supporting structure of the engine. Upon loss of a fan blade, the bearing housing contacts the bearing support housing because of an eccentric revolving movement of the bearing housing. The bearing support housing forms an inner surface which faces the bearing housing and has at least two flat contact surfaces which are spaced apart in the circumferential direction. Upon loss of a fan blade, the bearing housing strikes against the at least two flat contact surfaces during each eccentric revolution, and which in regions outside the flat contact surfaces is spaced apart from the bearing housing such that there is no contact with the eccentrically revolving bearing housing.

Claims

1. Structural subassembly for a gas turbine engine, which has: a bearing serving for the mounting of the fan shaft of a gas turbine engine, wherein the bearing comprises a static bearing element, a bearing housing which surrounds the bearing, wherein the bearing housing is connected to the static bearing element or forms the latter, and a bearing support housing which surrounds the bearing housing at a radial distance and which is connected to a supporting structure of the gas turbine engine, wherein, in the event of the loss of a fan blade, the bearing housing enters into contact with the bearing support housing because of an eccentric revolving movement of the bearing housing then occurring, wherein the bearing support housing forms an inner surface which faces the bearing housing and has at least two flat contact surfaces which are spaced apart in the circumferential direction, wherein, in the event of the loss of a fan blade, the bearing housing strikes against the at least two flat contact surfaces during each eccentric revolution, and in regions outside the flat contact surfaces is spaced apart from the bearing housing in such a manner that there is no contact with the eccentrically revolving bearing housing.

2. Structural subassembly according to claim 1, wherein the bearing support housing has a contact sleeve which surrounds the bearing housing in the radial direction and forms the inner surface facing the bearing housing and the at least two flat contact surfaces in said inner surface.

3. Structural subassembly according to claim 2, wherein the contact sleeve surrounds the bearing housing over an angular range of 360 in a plane perpendicular to the axis of rotation of the fan shaft.

4. Structural subassembly according to claim 1, wherein the bearing support housing has two flat contact surfaces which run parallel to each other and are arranged lying opposite with respect to the axis of rotation of the fan shaft.

5. Structural subassembly according to claim 1, wherein the bearing support housing has three flat contact surfaces.

6. Structural subassembly according to claim 5, wherein the three flat contact surfaces in a sectional illustration perpendicular to the axis of rotation of the fan shaft are oriented with respect to one another corresponding to the three sides of an equilateral triangle, wherein the axis of rotation of the fan shaft lies at the center point of the equilateral triangle.

7. Structural subassembly according to claim 1, wherein the bearing support housing has four flat contact surfaces.

8. Structural subassembly according to claim 7, wherein the four flat contact surfaces in a sectional illustration perpendicular to the axis of rotation of the fan shaft are oriented with respect to one another corresponding to the four sides of a square, wherein the axis of rotation of the fan shaft lies at the centre point of the square.

9. Structural subassembly according to claim 4, wherein the contact surfaces are positioned in such a manner that vibrations of the bearing support housing that are produced by the impact of the bearing housing are produced with a defined preferred direction and are transported via the bearing support housing.

10. Structural subassembly according to claim 9, wherein the two flat contact surfaces which are arranged parallel to each other are rotated by a defined angle in relation to a horizontal orientation.

11. Structural subassembly according to claim 1, wherein the bearing housing and the bearing support housing are connected to each other via shearing pins, wherein the shearing pins are designed in such a manner that they shear off in the event of the loss of a fan blade because of an eccentric revolving movement of the bearing housing then occurring.

12. Structural subassembly according to claim 1, wherein the contact surfaces have a Vickers hardness of at least 300 HV 10.

13. Structural subassembly according to claim 1, wherein the contact surfaces are not connected to a damping material or mounted in a floating manner.

14. Structural subassembly according to claim 1, wherein the bearing housing has a bearing housing contact surface which revolves by 360 and enters into contact with the contact surfaces of the bearing support housing during an eccentric revolving movement of the bearing housing.

15. Structural subassembly according to claim 14, wherein the bearing housing contact surface in a sectional illustration perpendicular to the axis of rotation of the fan shaft is circular.

16. Structural subassembly according to claim 14, wherein the bearing housing contact surface is provided with a coating which increases the local yield strength of the bearing housing contact surface.

17. Gas turbine engine having a structural subassembly according to claim 1.

18. Gas turbine engine according to claim 16, which has: an engine core which comprises a turbine, a compressor having a structural subassembly, and a turbine shaft which is configured as a hollow shaft and connects the turbine to the compressor; a fan, which is positioned upstream of the engine core, wherein the fan comprises a plurality of fan blades; and a gearbox that receives an input from the turbine shaft and outputs drive for the fan so as to drive the fan at a lower rotational speed than the turbine shaft.

19. Aircraft with a gas turbine engine according to claim 17, wherein the gas turbine engine is arranged on the fuselage of the aircraft or on a wing of the aircraft via an engine mount, wherein the contact surfaces of the bearing support housing are positioned in such a manner that vibrations of the bearing support housing that are produced by the impact of the bearing housing are introduced with a defined preferred direction into the engine mount.

20. Structural subassembly, which has: a bearing serving for the mounting of a shaft, wherein the bearing comprises a static bearing element, a bearing housing which surrounds the bearing, wherein the bearing housing is connected to the static bearing element or forms the latter, and a bearing support housing which surrounds the bearing housing at a radial distance, wherein the bearing housing enters into contact with the bearing support housing in the event of radial loads acting on the shaft and an associated eccentric revolving movement of the bearing housing, wherein the bearing support housing forms an inner surface which faces the bearing housing and which has at least two flat contact surfaces which are spaced apart in the circumferential direction, wherein, in the event of radial loads acting on the shaft, the bearing housing strikes against the at least two flat contact surfaces during each eccentric revolution, and in regions outside the flat contact surfaces is spaced apart from the bearing housing in such a manner that there is no contact with the eccentrically revolving bearing housing.

Description

[0071] The invention will be explained in more detail below on the basis of a plurality of exemplary embodiments with reference to the figures of the drawing. In the drawing:

[0072] FIG. 1 shows a sectional lateral view of a gas turbine engine;

[0073] FIG. 2 shows a close-up sectional lateral view of an upstream portion of a gas turbine engine;

[0074] FIG. 3 shows a partially cut-away view of a gearbox for a gas turbine engine;

[0075] FIG. 4 schematically shows the arrangement of a structural subassembly for transmitting radial loads acting on a bearing of the fan shaft, in a gas turbine engine;

[0076] FIG. 5 shows an exemplary embodiment of the structural subassembly according to FIG. 4 for transmitting radial loads, wherein the structural subassembly comprises a bearing housing and a bearing support housing;

[0077] FIG. 6 shows a sectional view along the line A-A of FIG. 5 of a first variant embodiment of the design of the contact surfaces of the bearing support housing, against which the bearing housing strikes during an eccentric revolution, wherein the bearing support housing forms two contact surfaces;

[0078] FIG. 7 shows a sectional view along the line A-A of FIG. 5 of a second variant embodiment of the design of the contact surfaces of the bearing support housing, against which the bearing housing strikes during an eccentric revolution, wherein the bearing support housing forms three contact surfaces;

[0079] FIG. 8 shows a sectional view along the line A-A of FIG. 5 of a third variant embodiment of the design of the contact surfaces of the bearing support housing, against which the bearing housing strikes during an eccentric revolution, wherein the bearing support housing forms four contact surfaces; and

[0080] FIG. 9 shows schematically the influencing of a transmission function, which describes the transmission of vibrations between the fan shaft and an engine mount, by a structural subassembly according to FIGS. 4 to 8.

[0081] FIG. 1 illustrates a gas turbine engine 10 having a main axis of rotation 9. The engine 10 comprises an air intake 12 and a thrust fan or fan 23 that generates two air flows: a core air flow A and a bypass air flow B. The gas turbine engine 10 comprises a core 11 which receives the core air flow A. In the sequence of axial flow, the engine core 11 comprises a low-pressure compressor 14, a high-pressure compressor 15, a combustion device 16, a high-pressure turbine 17, a low-pressure turbine 19, and a core thrust nozzle 20. An engine nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass thrust nozzle 18. The bypass air flow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low-pressure turbine 19 by way of a shaft 26 and an epicyclic gearbox 30.

[0082] During use, the core air flow 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 expelled from the high-pressure compressor 15 is directed into the combustion device 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 expelled through the nozzle 20 to provide some thrust force. The high-pressure turbine 17 drives the high-pressure compressor 15 by means of a suitable connecting shaft 27. The fan 23 generally provides the major part of the thrust force. The epicyclic gearbox 30 is a reduction gearbox.

[0083] 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 gear 28 of the epicyclic gearbox assembly 30. Radially to the outside of the sun gear 28 and meshing therewith is a plurality of planet gears 32 that are coupled to one another by a planet carrier 34. The planet carrier 34 limits the planet gears 32 to orbiting around the sun gear 28 in a synchronous manner while enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled by way of linkages 36 to the fan 23 so as to drive the rotation of the latter about the engine axis 9. Radially to the outside of the planet gears 32 and meshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

[0084] It is noted that the terms low-pressure turbine and low-pressure compressor as used herein can be taken to mean the lowest-pressure turbine stage and the lowest-pressure compressor stage (that is to say not including the fan 23) respectively and/or the turbine and compressor stages that are connected to one another by the connecting shaft 26 with the lowest rotational speed in the engine (that is to say not including the gearbox output shaft that drives the fan 23). In some literature, the low-pressure turbine and the 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 can be referred to as a first compression stage or lowest-pressure compression stage.

[0085] The epicyclic gearbox 30 is shown in an exemplary manner in greater detail in FIG. 3. Each of the sun gear 28, the planet gears 32 and the ring gear 38 comprise teeth about their periphery to mesh 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 person skilled in the art that more or fewer planet gears 32 can be provided within the scope of protection of the claimed invention. Practical applications of an epicyclic gearbox 30 generally comprise at least three planet gears 32.

[0086] 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, wherein the ring gear 38 is fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of a further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held so as to be fixed, wherein the ring gear (or annulus) 38 is allowed to rotate. In the case of such an arrangement, the fan 23 is driven by the ring gear 38. By way of a further alternative example, the gearbox 30 can be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

[0087] It is self-evident that the arrangement shown in FIGS. 2 and 3 is merely an example, and various alternatives fall within the scope of protection of the present disclosure. Purely by way of example, any suitable arrangement may be used for positioning the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of a further example, the connections (such as the linkages 36, 40 in the example of FIG. 2) 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 a certain degree of stiffness or flexibility. By way of a further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts of 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 person skilled in the art would readily understand that the arrangement of output and support linkages and bearing positions would typically be different to that shown by way of example in FIG. 2.

[0088] Accordingly, the present disclosure extends to a gas turbine engine having an arbitrary arrangement of gearbox types (for example star-shaped or planetary), support structures, input and output shaft arrangement, and bearing positions.

[0089] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate-pressure compressor and/or a booster compressor).

[0090] Other gas turbine engines to which the present disclosure can be applied may have alternative configurations. For example, engines of this type may have an alternative number of compressors and/or turbines and/or an alternative number of connecting shafts. By way of a 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. While the example described relates to a turbofan engine, the disclosure may be applied, for example, to any type of gas turbine engine, such as an open-rotor engine (in which the fan stage is not surrounded by an engine nacelle) or a turboprop engine. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

[0091] The geometry of the gas turbine engine 10, and components thereof, is/are defined by a conventional axis system, comprising an axial direction (which is aligned with the axis 9 of rotation), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the view in FIG. 1). The axial, radial and circumferential directions run so as to be mutually perpendicular.

[0092] FIG. 2 also shows the fan shaft 7 which is coupled on the output side to the planetary gearbox 30 and is mounted by means of a front bearing 5 and a rear bearing 95. The static components of the bearings 5, 95 are connected here to a fan housing 42 which is part of the stationary support structure 24. It is noted here that the stationary support structure 24 is connected to an engine mount via which the gas turbine engine is secured on the fuselage of the aircraft or on a wing of the aircraft.

[0093] In the context of the present invention, the design and coupling of the front bearing 5 to the fan housing 42 and in general to the stationary support structure 24 is of importance in the event of the loss of a fan blade of the fan 23.

[0094] FIG. 4 clarifies the arrangement of a structural subassembly 100 via which the front bearing 5 of the fan shaft 7 of a gas turbine engine is coupled to a stationary support structure 24 of the gas turbine engine. Unlike in the exemplary embodiment of FIGS. 1 to 3, the gas turbine engine illustrated is not equipped here with a planetary gearbox. On the contrary, the low-pressure shaft driven by the low-pressure turbine drives the fan 23 without a gear reduction. The present invention can be used both in gas turbine engines having a reduction gearbox and in gas turbine engines without a reduction gearbox.

[0095] Corresponding to FIG. 2, FIG. 4 shows the fan shaft 7, the front bearing 5 and the rear bearing 95. The fan shaft 7 forms an outer ring 70 axially at the front, to which the fan blades 230 of the fan 23 are fastened or with which they are integrally formed.

[0096] The front bearing 5 is connected via the structural subassembly 10, merely illustrated as a functional block, to the fan housing 42 which is part of the supporting support structure 24. Further elements of the support structure that are illustrated are a hub 44 which limits the primary flow duct 90 through the core engine radially on the inside, and wall regions 46 via which the static components of the rear bearing 95 are connected to the support structure 24.

[0097] FIG. 5 shows an exemplary embodiment of a structural subassembly 100 via which the front bearing 5 of the fan shaft 7 is coupled to the fan housing 42. The bearing 5 comprises a rotating inner ring 51 connected fixedly to the shaft 7, a static outer ring 52 and rolling bodies 53 which are arranged in between and are designed, for example, as balls. However, this configuration of the bearing 5 should be understood as being merely by way of example.

[0098] The bearing 5 furthermore has a bearing housing 55 which is fixedly connected to the outer ring 52 or is formed integrally therewith. The bearing housing 55 is assigned a bearing support housing 6. Firstly, there is a direct connection here between the bearing housing 55 and the bearing support housing, which connection is produced by shearing pins 85 which extend between a radial extension 57 of the bearing housing 55 and the bearing support housing 6. The shearing pins 85 have a predetermined breaking point which causes the shearing pins 85 to shear off in the event of powerful radial relative movements between the bearing housing 55 and the bearing support housing 6. The shearing pins 85 are designed here to the effect that they shear off whenever, in the event of the loss of a fan blade, the bearing housing 55 revolves eccentrically.

[0099] Secondly, the bearing housing 55 and the bearing support housing 6 are coupled via a mechanism which is used only when the shearing pins 85 shear off. This mechanism comprises a contact sleeve 60 which forms the bearing support housing 6 on the side thereof facing the bearing housing 55. The contact sleeve 60 here forms an inner surface 610 which faces the bearing housing 55.

[0100] Radially opposite and spaced apart from the inner surface 610 of the contact sleeve 60, the bearing housing 55 forms a bearing housing contact surface 56 on its outer side. Said bearing housing contact surface 56 can be provided with a coating 80, for example composed of tungsten carbide, which increases the local yield strength of the bearing housing contact surface.

[0101] The operating principle of the coupling between the bearing housing 55 and the bearing support housing 6 is first apparent in the sectional illustration along the plane A-A, wherein the plane A-A extends perpendicularly to the axis of rotation of the fan or machine axis 9.

[0102] The situation in which, after loss of a blade, powerful revolving radial loads are introduced into the fan shaft 7 because of the imbalance in the fan plane, is considered here. Said radial loads lead to the statically arranged bearing housing 55 carrying out an eccentric revolving movement, which may also be referred to as orbiting. This does not involve a rotation, since the bearing housing 55 is arranged statically, but rather a revolving eccentric deflection in the radial direction. This leads to breaking or shearing off of the shearing pins 85. The shearing off of the shearing pins 85 leads to an interruption of the connection between the bearing 5 and the fan housing 42 or the supporting structure of the engine. A direct transmission of the radial loads which occur into the supporting structure of the engine is therefore prevented.

[0103] Instead, the bearing housing contact surface 56 of the bearing housing 55 now enters intermittently into contact with the contact sleeve 60 of the bearing support housing 6. FIGS. 6 to 8 show three different exemplary embodiments in this regard, wherein these figures each illustrate a sectional illustration along the plane A-A of FIG. 5.

[0104] FIG. 6 shows the bearing support housing 6 which is arranged spaced apart radially from the bearing housing 55. The fan shaft and the components of the bearing 5 which are located radially within the bearing housing contact surface 56 not illustrated in FIG. 6. In this respect, the illustration of FIG. 6 is schematic. Not schematic, however, is the fact that the bearing housing contact surface 56 is circular in the sectional illustration under consideration.

[0105] Corresponding to the illustration of FIG. 5, the bearing support housing 9 forms a contact sleeve 60 which, radially on the inside, forms an inner surface 610 facing the bearing housing 55. In the plane under consideration perpendicular to the axis of rotation of the fan shaft, the contact sleeve 60 surrounds the bearing housing 5 over an angular range of 360, i.e. completely in the circumferential direction.

[0106] The inner surface 610 of the contact sleeve 60, said inner surface encircling in the circumferential direction, comprises a plurality of differently shaped surfaces. It thus comprises two flat contact surfaces 611, 612 which, in a horizontal orientation of the engine, extend in the horizontal direction and are spaced apart in the vertical direction. The two contact surfaces 611, 612 run parallel here. Furthermore, the inner surface comprises two curved surfaces 618, 619 which connect the flat contact surfaces 611, 612. It is the case here that the minimum distance d1 between the bearing housing contact surface 56 and the flat contact surfaces 611, 612 is smaller than the maximum distance d2 between the bearing housing contact surface 56 and the curved surfaces 618, 619. For example, the distance d2 is at least 4 times to 10 times the distance d1.

[0107] Furthermore, it is noted that the contact sleeve 60 is composed of a hard material which has, for example, a Vickers hardness of at least 300 HV 10. The contact sleeve 60 is also not connected to an elastic material or damping material or the like. The contact sleeve 60 thus does not have any significant damping properties.

[0108] During an eccentric revolving movement of the bearing housing 55 after the shearing pins 85 have sheared off, the bearing housing 55 comes intermittently into contact with the bearing support housing 6, specifically to the effect that it strikes alternately by means of its bearing housing contact surface 56 against the two flat contact surfaces 611, 612, wherein, during each eccentric revolution about 360, the bearing housing 55 in each case collides once with said two contact surfaces 611, 612. By contrast, there is no contact with the eccentrically revolving bearing housing 55 in those regions 618, 619 of the inner surface 610 of the contact sleeve 60 which are arranged at a greater radial distance from the surface 56 of the bearing housing 55. This ensures that the respective contact is a radial strike against the respective contact surface 611, 612.

[0109] This repeated exertion of a radial force on the bearing support housing 6 by the bearing housing 55 and therefore in the supporting structure 42, 24 of the engine changes the vibration pattern. The vibration pattern is thus transferred from a first excitation order into a second excitation order since the revolving housing 55 which revolves with a first excitation order exerts two radial impacts per revolution on the bearing support housing 6. The impacts formed by the bearing housing on the contact surfaces 611, 612 therefore form vibrations of a higher order in the supporting structure of the engine.

[0110] The load amplitudes which the engine mount has to sustain are thereby reduced. The vibration energy which, without the invention, is concentrated in the first vibration order is split between vibration orders of a higher order. The maximum loads which act on the engine mount are thereby reduced.

[0111] It is noted here that the orientation of the flat contact surfaces 611, 612 predetermines a direction in which vibrations are transmitted into the engine. In the exemplary embodiment illustrated in FIG. 6, the vibrations are transmitted upwards and downwards in the vertical direction into the supporting structure of the engine. This direction can be predetermined or set by a change in the orientation of the contact surfaces 611, 612. For example, if the flat contact surfaces 611, 612 were arranged rotated by 45 in the clockwise direction in comparison to the illustration of FIG. 6, the vibrations would be transmitted with a correspondingly changed direction into the supporting structure of the engine.

[0112] FIG. 7 shows an alternative exemplary embodiment for the design of contact surfaces on the inner side 610 of the contact sleeve 60 of the bearing support housing 6. The bearing housing 55 which runs coaxially with respect to the axis of rotation 9 and has a circular bearing housing contact surface 56 is again illustrated schematically. The bearing components arranged radially on the inside with respect to the bearing housing 55 and the fan shaft are again not illustrated.

[0113] In the exemplary embodiment of FIG. 7, the contact sleeve 60 forms three flat contact surfaces 613, 614, 615 which are arranged at an angle of 120 to one another, corresponding to the sides of an equilateral triangle. Such an arrangement leads to the bearing housing 55 in each case colliding once with the three contact surfaces 613, 614, 615 during each eccentric revolution through 360. By contrast, there is no contact with the eccentrically revolving bearing housing 55 in those regions of the inner surface 610 of the contact sleeve 60 which lie in between and are arranged at a greater radial distance from the surface 56 of the bearing housing 55.

[0114] This repeated exertion of a radial force on the bearing support housing 6 by the bearing housing 55 and therefore in the supporting structure 42, 24 of the engine again changes the vibration pattern. The vibration pattern is thus transferred from a first excitation order into a third excitation order since the revolving housing 55 exerts three radial impacts per revolution on the bearing support housing 6.

[0115] FIG. 8 shows a further alternative exemplary embodiment. For the basic construction, reference is made to the description of FIGS. 6 and 7. In the exemplary embodiment of FIG. 8, the contact sleeve 6 on its inner surface 610 forms four flat contact surfaces 611, 612, 616, 617 which are arranged at an angle of 90 to one another, corresponding to the four sides of a square. Such an arrangement leads to the bearing housing 55 in each case colliding once with the four contact surfaces 611, 612, 616, 617 during each eccentric revolution through 360. By contrast, there is no contact with the eccentrically revolving bearing housing 55 in those regions of the inner surface 610 of the contact sleeve 60 which lie in between and are arranged at a greater radial distance from the surface 56 of the bearing housing 55.

[0116] This repeated exertion of a radial force on the bearing support housing 6 by the bearing housing 55 and therefore in the supporting structure 42, 24 of the engine again changes the vibration pattern. The vibration pattern is thus transferred from a first excitation order into a fourth excitation order since the revolving housing 55 exerts four radial impacts on the bearing support housing 6 per revolution.

[0117] It is also true for the exemplary embodiments of FIGS. 7 and 8 that a correspondingly rotated positioning of the contact surfaces can define preferred directions in which the radial pulses exerted on the bearing support housing 6 by the gearbox housing 55 are transmitted.

[0118] FIG. 9 schematically shows the effects of the structural subassembly according to the invention on the forces acting on the engine mount. The system comprises an intake I which is formed by the fan shaft 7 with the fan 23. An exit O of the system is formed by an engine mount 66 which connects the engine to a component 65 of an aircraft. Intake I and exit O are coupled to each other via the structural subassembly according to the invention and a support structure which can be described via a transmission function H. A malfunction X in the form of a partial or complete loss of a blade is observed here in the fan 23. The malfunction X causes a vibration in the first vibration order in the system via the bearings 5, 95.

[0119] At the bottom right in the illustration, FIG. 9 shows the frequency components at the intake I for the situations C, D and E, wherein situation C refers to the situation in which there is no coupling according to the invention between the bearing housing and the bearing support housing, situation D refers to the situation in which coupling takes place via two flat contact surfaces, and E refers to the situation in which coupling takes place via three flat contact surfaces.

[0120] In situation C, the entire vibration energy is concentrated in the first vibration order 1. In situation D, the vibration energy is split between the two first vibration orders 1 and 2. It should be noted here that the vibration order 1 furthermore contains energy, for example because corresponding vibrations are transmitted via the rear bearing 95 into the system. In situation E, the vibration energy is split between the three first vibration orders 1, 2 and 3.

[0121] The transmission function H to an increased extent weakens the higher frequencies according to the vibration orders 2 and 3. Accordingly, the amplitudes of the frequencies at the exit O for the frequencies of the vibration orders 2 and 3 are significantly weakened in accordance with the illustration at the top right of FIG. 9. Vibrations of the vibration order 1 that are significantly reduced by the amplitude in comparison to situation C remain. The maximum loads which act on the engine mount 66 are therefore significantly reduced.

[0122] It is self-evident that the invention is not limited to the embodiments described above and that various modifications and improvements may be made without departing from the concepts described herein. It is also pointed out that any of the features described may be used separately or in combination with any other features, unless they are mutually exclusive. The disclosure also extends to and comprises all combinations and sub-combinations of one or a plurality of features which are described here. If ranges are defined, said ranges thus comprise all of the values within said ranges as well as all of the partial ranges that lie in a range.