Flexible cage for supporting a rolling bearing in an aircraft turbine engine

Abstract

The invention relates to a flexible cage (44) for an aircraft turbine engine, the cage extending about a longitudinal central axis (3) and comprising a cage outer radial end (50) fastened to a rolling bearing support (42), and a cage inner radial end (52) against which the rolling bearing (32) bears, the outer radial end (50) being connected to the inner radial end (52) by a first connection portion (60a) and by a second connection portion (60b) centred on the longitudinal central axis and connected to the first connection portion (60a) by a curved connecting portion (60c), the first connection portion (60a) comprising first posts (62a) spaced apart from one another in a circumferential direction (C), and the second connection portion (60b) comprising second posts (62b), the curved connecting portion (60c) being equipped with an annular stiffener (70).

Description

[0001] 52287 AP

[0002] Flexible cage for supporting a bearing in an aircraft turbomachine, the cage exhibiting reinforced axial rigidity

[0003] TECHNICAL FIELD

[0004] 5 The present invention relates to the field of aircraft turbomachinery. It relates more particularly to support and guidance systems for turbomachine engine shafts.

[0005] The invention applies to all types of turbomachinery, as well as to all types of aircraft. It relates in particular to turbojet engines with unfaired fans.

[0006] STATE OF PRIOR ART

[0007] Aircraft turbomachinery engine shafts are guided in rotation by bearings. These bearings can be fitted with oil film compression dampers, also known as "squeeze film dampers (SFDs)." This type of damper provides damping to flexible shafts operating at supercritical speeds. The thin film, located between the outer ring of the bearing and a portion of the stator, is not sheared, unlike in a conventional hydrodynamic bearing. This absence of shear limits oil heating and eliminates instabilities.

[0008] The role of such a damper is to dampen the vibrations of the drive shaft caused by its rotation and by the imbalance of its mechanical load, for example, unbalance. This principle of damping by compression of an oil film is known, for example, from document EP 1650449 A1.

[0009] Typically, the outer ring of a damped bearing is integral with and supported by a flexible cage, known as a squirrel cage. This cage comprises columns between which openings are defined, providing the necessary flexibility. This allows for greater orbital movement of the outer ring within the stator portion that houses it, thus ensuring improved efficiency of the oil film compression damper. 52287 AP

[0010] In general, the combination of the flexible cage with the oil film ensures satisfactory dynamic behavior in terms of vibration and acceptable dynamic loads. This combination provides the rotor with a spring-damper system, in which the damping function is performed by the oil film, and the spring function by the flexible cage. The cage must, however, be correctly dimensioned to achieve the target flexibility. In an architecture where the bearing is designed to transmit both radial and axial forces to the flexible cage, the cage must meet several dimensioning criteria. First, axial stiffness must be high, particularly to guarantee the required axial positioning of the rotor. Second, targeted radial flexibility is necessary for good dynamic behavior.Finally, it also concerns the mechanical resistance of the parts to loads, depending on the different phases of flight.

[0011] Meeting all these criteria makes sizing the cage difficult, particularly for 15, as it must be flexible enough to provide good dynamic behavior while also being rigid enough to withstand mechanical loads. However, changing the geometry of the flexible cage's columns does not allow for increased axial rigidity without compromising radial flexibility.

[0012] DESCRIPTION OF THE INVENTION

[0013] To address at least partially the problems mentioned above relating to prior art achievements, the invention first of all relates to a flexible cage for an aircraft turbomachine, according to the characteristics of claim 1.

[0014] The invention thus distinguishes itself from prior art designs by providing a flexible cage with two sets of columns connected by a bent section 25 equipped with a stiffener limiting its deformations. Due to the geometry of such a flexible cage comprising two sets of axial or essentially axial columns, the application of an axial force by the bearing leads to an axial deformation of the cage resulting mainly from the deformation of the bent section, which, for example, tends to become oval, or simply to increase in diameter. Also, 52287 AP

[0015] Reinforcing the rigidity of the angled section of the connection reduces its deformation, thus decreasing the primary axial deformation factor of the cage when it is subjected to an axial load from the bearing. Conversely, the radial flexibility of the cage is only slightly affected, which allows it to meet the criteria described above, particularly with regard to radial flexibility.

[0016] The invention also preferably has at least one of the following optional features, taken individually or in combination.

[0017] Preferably, the ring stiffener extends radially beyond the C, radially inward and / or outward. By moving the free end of the stiffener away from the base of the C, the area moment of inertia of the assembly is increased, thus stiffening the assembly while maintaining a low mass. In this preferred configuration, where the ring stiffener extends radially beyond the C, the stiffener can, of course, also have an axial component.

[0018] Preferably, the annular stiffener extends axially in the opposite direction to that of the first 15 and second columns.

[0019] Preferably, the annular stiffener takes the form of a ring or a truncated conical organ.

[0020] Preferably, the angled connecting portion takes the form of a continuous annular structure, connecting the first columns to the second columns, at their 20 axial ends.

[0021] Preferably, each of the first and second columns satisfies the condition Lt / Hmax > 4, with Hmax corresponding to the maximum height of each column, and Lt corresponding to the total length of each column.

[0022] The invention also relates to an assembly for an aircraft turbomachine, comprising a bearing, a bearing support, and a flexible cage as described above.

[0023] Preferably, a compression-damping oil film is arranged radially between the inner radial end of the cage and the bearing support, and preferably between the inner radial end of the cage and a ring carried internally by the bearing support. 30 52287 AP

[0024] The invention ultimately relates to an aircraft turbomachine, comprising at least one such assembly, or at least one such housing. For example, it could be a turbomachine with an unfaired fan.

[0025] Other advantages and features of the invention will appear in the detailed, non-limiting description 5 below.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] This description will be made with reference to the attached drawings, which include:

[0028] - Figure 1 represents a schematic view in axial half-section of an aircraft turbomachine according to the invention;

[0029] - Figure 2 represents a schematic enlarged view in axial half-section of an assembly equipping the turbomachine shown in the previous figure, the assembly being in the form of a first preferred embodiment of the invention;

[0030] - Figure 3 is a perspective view of a flexible cage belonging to the assembly shown in Figure 2;

[0031] 15 - Figure 4 is a view similar to that of Figure 2, showing a case of axial load on a conventional flexible cage;

[0032] - Figure 5 is a half-axial cross-sectional view of an assembly according to a second preferred embodiment of the invention;

[0033] - Figure 6 is a perspective view showing the flexible cage of the entire assembly of the previous figure;

[0034] - Figure 7 is a half-axial cross-sectional view of an assembly according to a third preferred embodiment of the invention;

[0035] - Figure 8 is a half-axial cross-sectional view of an assembly according to a fourth preferred embodiment of the invention.

[0036] 25 DETAILED PRESENTATION OF PREFERRED METHODS OF IMPLEMENTATION

[0037] Figure 1 represents an aircraft turbomachine 1, corresponding here to a twin- or triple-flow turbojet engine with a single, unfaired fan. However, it could be 52287 AP

[0038] of a ducted turbomachine, for example with a twin body and twin flow, without going out of the scope of the invention.

[0039] Subsequently, the terms "upstream" and "downstream" are considered according to a main direction 14 of gas flow within the turbojet, when it is in 5 normal propulsion configuration.

[0040] The turbojet 1 has a longitudinal axis 3 around which its various components extend. It includes, from upstream to downstream along the direction 14, a single unshod fan 15, and an annular row of OGV blades 30. It also includes, in a conventional manner (but not shown), a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine, and a low-pressure turbine.

[0041] The low-pressure compressor and the low-pressure turbine form a low-pressure unit and are connected to each other by a low-pressure shaft 11 centered on the longitudinal central axis 3. Similarly, the high-pressure compressor and the high-pressure turbine 15 form a high-pressure unit and are connected to each other by a high-pressure shaft 13 also centered on the axis 3 and arranged around the low-pressure shaft 11.

[0042] The blower 15 is preferably driven indirectly by the low-pressure shaft 11, via a drive reduction gear 24, which allows it to rotate at a lower speed. However, a solution with direct drive of the blower 15, by the low-pressure shaft 11, falls within the scope of the invention.

[0043] Furthermore, the turbojet 1 defines a primary flow 16 intended to be traversed by a primary flow 16a, and a secondary flow 18 intended to be traversed by a secondary flow 18a located radially outwards relative to the primary flow, the fan flow thus being divided at a flow separation nozzle 26. The secondary flow 18 is radially delimited outwards by the free end of the fixed OGV blades 30.

[0044] Each of the two shafts 11, 13 is supported and guided in rotation by rolling bearings centered on the axis 3. In Figure 1, a single bearing 32 has been schematically shown in association with each of the two shafts 11, 13.52287 AP

[0045] These bearings are each part of an assembly 40 specific to the present invention, a first preferred embodiment of which will be described with reference to Figures 2 to 4. The assembly 40 is centered on the axis 3, and it comprises, firstly, the bearing housing 32, as well as an annular bearing support 42. It also includes a flexible cage 5 44, specific to the present invention.

[0046] In a conventional manner, the bearing 32 is preferably a ball bearing 45, and it includes an outer ring 46, as well as an inner ring 48 through which one of the two shafts 11, 13 passes.

[0047] The bearing support 42 has a first end fixed on a stator part 49 of the turbojet, for example a turbojet casing, and a second end arranged around the bearing 32.

[0048] The flexible cage 44 also extends centrally around axis 3, and it is defined with respect to an axial direction L parallel to axis 3, a radial direction R, and a circumferential direction C, these three directions forming an orthonormal frame 15 associated with the cage. In this respect, it is noted that this L, R, C frame attached to cage 44 also corresponds to that attached to assembly 40, and even more generally to that attached to the turbojet engine 1.

[0049] Assembly 40 ensures satisfactory dynamic behavior in terms of acceptable vibrations and dynamic loads. It provides the rotor with a spring-damper system 20, in which the damping function is provided by an oil film, which will be described below, and the spring function is provided by the flexible cage 44. The latter has an external radial end 50, fixed to the bearing support 42. For example, this fixing is achieved using fasteners 51, such as screws or bolts, which preferably allow the first end of the bearing support 42 to be fixed to the external radial end of the cage 50 on the housing 49. The external radial end of the cage 50, in the form of an annular or scalloped flange, can be axially clamped between the first end of the bearing support 42 and the housing 49.

[0050] The flexible cage 44 also has an internal radial cage end 52, on which the outer ring 46 of the bearing is supported along the axial direction 52287 AP

[0051] L, and along the radial direction R. To do this, the internal radial end of the cage 52, generally in the form of a ring centered on the axis 3, has an internal radial surface receiving the external radial surface of the outer ring 46. In addition, the internal radial end of the cage 52 has a shoulder 53, possibly interrupted circumferentially, and 5 forming an axial stop for this same outer ring 46 of the bearing 32.

[0052] The cage 44 also includes flexible means connecting its two ends 50, 52, which, in addition to being radially offset from each other, are also axially offset from each other. In this first preferred, non-limiting embodiment, the inner radial end of cage 52 is arranged upstream of the outer radial end of cage 50, but a reversed arrangement remains possible without departing from the scope of the invention. As mentioned previously, a compression-damping oil film 54 is arranged radially between the outer radial surface of the inner radial end of cage 52 and a ring 56 carried internally by the second end of the bearing support 42. This arrangement is known, particularly regarding its implementation and the technical effects it produces. Therefore, this oil film 54, arranged in an axially delimited damping space between two split ring-shaped seals 58, will not be described further.

[0053] The flexible cage 44, the design of which will be detailed below, is preferably made in one piece, i.e. in one piece, for example in casting and / or by machining.

[0054] The flexible means of cage 44 include a first connecting portion 60a, centered on axis 3 and connected to the outer radial end of cage 50, from which this portion 60a projects axially downstream. They also include a second connecting portion 60b, centered on axis 3 and connected to the inner radial end of cage 52, from which this portion 60b also projects axially downstream.

[0055] These two connecting portions 60a, 60b are joined to each other by an angled connecting portion 60c, also centered on axis 3, preferably to form a 180° bend, although other angles of this order of magnitude can also be considered, without departing from the scope of the invention. 52287 AP

[0056] The angled connecting portion 60c then preferably has a longitudinal half-section in the general shape of a C, the hollow of which is axially open. This half-section is preferably the same along the entire length of the portion 60c, which preferably extends continuously over 360°, in the form of a ring centered on axis 3.

[0057] The first connecting portion 60a comprises first columns 62a, spaced from each other along the circumferential direction C, so as to form together an annular structure of first columns 62a, thus extending over 360°. Similarly, the second connecting portion 60b comprises second columns 62b, spaced from each other along the circumferential direction C, so as to form together an annular structure of second columns 62b, thus also extending over 360°.

[0058] The first columns 62a each extend between a first axial column end, here the upstream end connected to the external radial end of cage 50, and 15 a second axial column end, here a downstream end connected to the angled connecting portion 60c.

[0059] The second columns 62b also extend each between a first axial end of column, here the upstream end connected to the external radial end of cage 50, and a second axial end of column, here a downstream end 20 connected to the angled connecting portion 60c.

[0060] In this first preferred embodiment, the first and second columns 62b each extend parallel to axis 3 and axial direction L, or substantially parallel to this direction. They thus form two concentric annular rows of columns arranged around each other.

[0061] Referring now to Figure 4, when an axial force is applied by the bearing 32 to the shoulder 53 of the flexible cage, the second columns 62b are essentially deformed in compression or tension. This leads to stress on the angled connecting portion 60c, which then tends to deform, for example, by becoming oval, or simply by increasing its diameter. Such a deformation of the 30 elements of the cage 44 is shown in dashed lines in Figure 4.52287 AP

[0062] The invention also cleverly provides for reinforcing the rigidity of the angled connecting portion 60c to increase the cage's resistance to axial forces, while advantageously maintaining radial flexibility. Indeed, limiting the deformation of the angled connecting portion 60c, which is preferably annular and continuous over 360°, advantageously reduces the first axial deformation factor of the cage 44 when it is subjected to an axial force from the bearing 32.

[0063] To achieve this stiffening of the angled connecting portion 60c, it is equipped with an annular stiffener 70, which projects outward from the base of the C, for example, in the axial direction L and in the radial direction R. In the first preferred embodiment, the stiffener 70 has a tongue- or finger-shaped axial half-section, preferably straight, which extends axially downstream opposite the columns 62a, 62b, with an outward radial component. Furthermore, it is preferable that the annular stiffener 70 extends radially beyond the C, radially outward. It thus forms a frustoconical element centered on the axis 3, 15 originating from the base of the C formed by the angled connecting portion, and open axially downstream. Alternatively, the truncated conical stiffening organ could not be divergent downstream, but conversely convergent downstream.

[0064] In the second preferred embodiment shown in Figures 5 and 6, the annular stiffener 70 still extends from the base of the C, but only radially outwards, without an axial component. The stiffener 70 then lies in a transverse plane of the assembly 40 and the turbojet engine.

[0065] In Figure 5, the maximum height of each column 62a, 62b, referenced as Hmax, has been identified. This is the maximum height along the radial direction R, which also corresponds to the maximum thickness along the same direction. It is noted that along each column 62a, 62b, its height / thickness ratio varies only slightly. Furthermore, the total length of each column 62a, 62b, referenced as Lt, has been identified. This is the total length along the direction L. In this embodiment, as well as in all other preferred embodiments of the invention, the cage is configured to satisfy the following condition for all 30 columns 62a, 62b: Lt / Hmax > 4.52287 AP 10

[0066] In the third preferred embodiment shown in Figure 7, the annular stiffener 70 is similar to that of Figures 5 and 6, while also extending radially inwards, preferably beyond C. The two radial members formed by the stiffener 70 can preferably be arranged in the same transverse plane 5 of the assembly 40 and the turbojet.

[0067] Finally, in the fourth preferred embodiment shown in Figure 8, the stiffener 70 still extends from the base of the C, but only axially in order to form a stiffening ring projecting downstream, therefore in the opposite direction to that of the first and second columns, while remaining centered on axis 3.

[0068] 10. Of course, various modifications can be made by a person skilled in the art to the invention just described, by way of non-limiting examples only. In particular, in the figures, the elements of the different preferred embodiments that bear the same numerical references are identical or similar elements, and they are interchangeable. Furthermore, these preferred embodiments are combinable.

[0069] 15

Claims

52287 AP DEMANDS 1. Flexible cage (44) for aircraft turbomachine, the cage extending around a central longitudinal axis (3) and comprising an external radial end of cage (50) intended to be fixed on a support (42) of bearing of the turbomachine (32), as well as an internal radial end of cage (52) on which said bearing (32) is intended to be supported in an axial direction (L) and a radial direction (R) relative to the central longitudinal axis (3), the external radial end (50) being connected to the internal radial end (52) by a first connecting portion (60a) centered on the central longitudinal axis (3), and by a second connecting portion (60b) centered on the central longitudinal axis and connected to the first connecting portion (60a) by an angled connecting portion (60c) also centered on the central longitudinal axis (3) and having a longitudinal half-section in the general shape of C, the first connecting portion (60a) comprising first columns (62a) spaced from each other in a circumferential direction (C) in relation to the central longitudinal axis, and the second connecting portion (60b) comprising second columns (62b) spaced from each other in the circumferential direction (C), the first and second columns (62a, 62b) each extending parallel to the central longitudinal axis (3), or substantially parallel to it axis,characterized in that the angled connecting portion (60c) is equipped with an annular stiffener 20 (70) extending projecting from the base of the C in the axial direction (L), and / or in the radial direction (R).

2. Cage according to claim 1, characterized in that the annular stiffener (70) extends radially beyond the C, radially inwards and / or outwards.

3. Cage according to any one of the preceding claims, characterized in that the annular stiffener (70) extends axially in a direction opposite to that of the first and second columns (62a, 62b).

4. Cage according to any one of the preceding claims, characterized in that the annular stiffener (70) takes the form of a ring or a frustoconical element.

5. Cage according to any one of the preceding claims, characterized in that the angled connecting portion (60c) takes the form of a continuous annular structure, 52287 AP connecting the first columns (62a) to the second columns (62b), at their axial ends.

6. Cage according to any one of the preceding claims, characterized in that each of the first and second columns (62a, 62b) satisfies the condition Lt / Hmax 5 > 4, with Hmax corresponding to the maximum height of each column (62a, 62b), and Lt corresponding to the total length of each column (62a, 62b).

7. Assembly (40) for aircraft turbomachine, comprising a bearing (32), a bearing support (42), and a flexible cage (44) according to any one of the preceding claims. 10 8. Assembly according to claim 7, characterized in that a compression damping oil film (50) is arranged radially between the inner radial end of cage (52), and the bearing support (42), and preferably between the inner radial end of cage (52) and a ring (56) carried internally on the bearing support (42).

9. Aircraft turbomachine (1) comprising at least one assembly (40) according to claim 7 or 8, or at least one flexible cage (44) according to any one of claims 1 to 6.

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