Variable-pitch blade for a turbomachine

Abstract

The invention relates to a variable-pitch blade (7) for a turbomachine, comprising: - a tubular metal sleeve (13); - a fibrous structure (20) obtained by three-dimensional weaving of fibers, the fibrous structure (20) comprising a blade root (22) comprising a tubular attachment portion (23) inserted axially into a cavity (17) of the sleeve (13); - an insert (24) centered on the pitch axis (Y) and inserted axially into a recess (20a) of the attachment portion (23) such that the attachment portion (23) is radially interposed between the insert (24) and the inner wall (18) of the sleeve (13), the attachment portion (23) of the fibrous structure (20) having a non-cylindrical first outer surface (23a), and the inner wall (18) of the sleeve (13) covering this first outer surface (23a) and having a shape complementary to this first outer surface (23a).

Description

[0001] DESCRIPTION

[0002] TITLE: VARIABLE TIMING TURBINE BLADE FOR A TURBOMACHINE

[0003] Technical field of the invention

[0004] The invention relates generally to the field of turbomachinery, and in particular to turbomachine blades.

[0005] The invention relates more particularly, but not exclusively, to a variable pitch blade intended for use in an unfaired aircraft engine fan rotor.

[0006] Technical background

[0007] The technical background includes documents FR-A1-3 135 490, US-A1-2023 / 286644 and W0-A1-2022 / 0182353.

[0008] The advantage of unfaired fan engines is that the fan diameter is not limited by the presence of a shroud, making it possible to design an engine with a high bypass ratio (known as BPR), and consequently, reduced fuel consumption. Therefore, in this type of engine, the fan blades can have a large span.

[0009] In addition, these engines generally include a mechanism to change the angle of the blades in order to adapt the thrust generated by the fan according to the different phases of flight.

[0010] However, the design of such blades requires taking into account conflicting constraints.

[0011] On the one hand, the design of these blades must allow for optimal aerodynamic performance, notably maximizing efficiency and providing thrust while minimizing losses. Improving the aerodynamic performance of the fan tends towards an increase in the bypass ratio, which translates into an increase in the external diameter, and therefore the span, of these blades. On the other hand, it is also necessary to guarantee resistance to the mechanical stresses that may be exerted on these blades while limiting their acoustic signature.

[0012] Furthermore, on unshod fan designs, engine start-up is generally performed with a very open valve timing. Indeed, a very open valve timing allows power to be consumed by torque, which ensures machine safety by guaranteeing low fan speeds. However, with a very open valve timing, the blades experience turbulent, completely separated aerodynamic flow, which generates broadband vibrational excitation. In particular, on large-chord, long-span blades, the bending stress is intense, even though the engine speed is not at its maximum.

[0013] In normal operation, that is, during ground and flight phases, the fan pitch is adjusted to a more closed angle. The aerodynamic flow is then perfectly controlled, particularly in relation to the airfoil. Broadband stresses disappear because the rotational speed is higher, and the bending force is controlled. However, since the engine is not enclosed in a cowling, the angle of attack experienced by the various fan blades, depending on their angular position, varies according to the aircraft's angle of attack, creating a cyclic bending moment (commonly called the 1P moment) on the blades. This cyclic bending moment then generates significant bending stresses on the blades in addition to the centrifugal forces due to their rotation.

[0014] These blades can be made of metallic material. While metallic blades have good mechanical resistance, they have the disadvantage of being relatively heavy.

[0015] Manufacturing blades from composite materials is an attractive solution for reducing blade weight. However, composite blades can be fragile due to the intense aerodynamic stresses they are subjected to. These aerodynamic stresses can therefore damage the blades and / or the hub in the interface area between the blades and the fan rotor hub, at the blade root.

[0016] To overcome these drawbacks, various solutions exist in the prior art. Most utilize reinforcing elements, particularly at the blade root, and add various structural elements to allow, for example, the blade to be attached to the stabilization mechanism. Patent documents W0-A1-2022 / 018353 and W0-A1-2022 / 208002 describe the addition of reinforcing and structural elements, especially at the blade roots. However, these solutions have the disadvantage of requiring the manufacture of several elements in potentially different materials and the assembly of these elements using fastening methods. Such blades can therefore be relatively time-consuming to manufacture.

[0017] Summary of the invention

[0018] The invention proposes a variable-pitch blade for a turbomachine comprising:

[0019] - a tubular metal sleeve, this sleeve comprising a fixing part configured to be connected to a variable shimming mechanism, and a recess passing through the sleeve along a shimming axis, the recess being delimited by an internal wall of the sleeve,

[0020] - a fibrous structure comprising a blade root including a tubular attachment portion inserted axially into the sleeve recess, this attachment portion including a housing centered on the alignment axis, the fibrous structure further comprising an aerodynamically profiled blade connected to the blade root,

[0021] - an insert centered on the alignment axis and inserted axially into the housing of the attachment portion so that the attachment portion is radially interposed between the insert and the inner wall of the sleeve,

[0022] - a polymerized resin for solidifying the fibrous structure and for bonding the insert to the fibrous structure and to the inner wall of the sleeve, characterized in that the attachment portion of the fibrous structure has, on at least part of its length along the alignment axis, a first non-cylindrical external surface, and in that the inner wall of the sleeve covers this first external surface and has a shape complementary to this first external surface.

[0023] The problem to be solved concerns the absorption of the torsional moment around the blade's pitch axis. Indeed, the aerodynamic and centrifugal forces acting on the blade generate a resulting torsional moment that must be absorbed at the interface between the blade root and the outer metal sleeve in order to control the blade pitch via the variable pitch mechanism.

[0024] In this application, a non-cylindrical external surface is an external surface whose section perpendicular to the aforementioned axis describes a contour other than a circle.

[0025] By default, this torque is absorbed by the polymerized resin, which ensures bonding between the blade root attachment portion and the sleeve. This bonding provides a default primary load path for the transfer torque. A failure of this interface would lead to a loss of blade pitch control. The invention thus proposes to reinforce this load path through complementary (non-cylindrical) shapes between the blade root attachment portion and the sleeve, the insert being further bonded to the sleeve by the resin. Various shapes are possible for the bonded interface between the attachment portion and the sleeve. The invention also improves fail-safe functionality and compensates for the lack of adhesion, particularly between the attachment portion and the sleeve.

[0026] The blade according to the invention may comprise one or more of the following features, taken individually or in combination with each other:

[0027] - the first external surface of the attachment portion has in cross-section with respect to said alignment axis, a general shape chosen from among a polygon, for example with 4, 5 or 6 sides, an ellipse or an oval, and a star;

[0028] - the shape of the cross-section is devoid of sharp edges and includes, for example, rounded corners at the corners of the polygon or rounded points at the points of the star;

[0029] - the insert has, over at least part of its length along the alignment axis, a second cylindrical external surface, and in which the attachment portion covers this second external surface and has a shape complementary to this second external surface;

[0030] - the insert has, over at least part of its length along the alignment axis, a second non-cylindrical external surface, and in which the attachment portion covers this second external surface and has a shape complementary to this second external surface;

[0031] - the second external surface of the insert has in cross-section with respect to said alignment axis, a general shape chosen from among a polygon, for example with 4, 5 or 6 sides, an ellipse or an oval, and a star;

[0032] - the shape of the cross-section is devoid of sharp edges and includes, for example, rounded corners at the corners of the polygon or rounded points at the points of the star;

[0033] - the first and second external surfaces have the same geometric shape in cross-section with respect to said alignment axis.

[0034] - the first and second external surfaces have:

[0035] - the same elliptical shape in cross-section with respect to said alignment axis, or

[0036] - the same polygonal shape in cross-section with respect to said alignment axis, or

[0037] - the same star shape in cross-section with respect to said alignment axis;

[0038] - the sleeve has, over at least part of its length along the alignment axis, a third cylindrical external surface, this third external surface extending at least in part around said first external surface;

[0039] - the insert has, over at least part of its length along the alignment axis, a cylindrical internal surface, this internal surface extending at least partly radially inside said first external surface;

[0040] - the insert has a minimum radial thickness measured with respect to said alignment axis, which is less than a minimum radial thickness (Emin_por) of the attachment portion of the fibrous structure measured with respect to said alignment axis;

[0041] - the attachment portion of the fibrous structure has a maximum radial thickness measured with respect to said alignment axis, which is greater than or equal to a maximum radial thickness of the sleeve measured with respect to said alignment axis;

[0042] -- rounded corners or points have a radius of curvature between 2 and 20mm, and preferably between 10 and 20mm;

[0043] -- the fibrous structure is obtained by three-dimensional weaving of fibers or superimposing layers of fibers.

[0044] The present invention also relates to a turbomachine, in particular for aircraft, comprising at least one blade as described above.

[0045] Brief description of the figures

[0046] Other features and advantages will become apparent from the following description of a non-limiting embodiment of the invention with reference to the accompanying drawings in which:

[0047] [Fig. 1] Figure 1 schematically represents an example of an engine including an unfaired fan;

[0048] [Fig.2] Figure 2 schematically represents a blower blade according to an embodiment of the invention assembled to a shimming mechanism;

[0049] [Fig. 3] Figure 3 schematically represents a blower blade according to a first embodiment of the invention; [Fig. 4a] Figure 4a schematically represents a sleeve according to a first embodiment of the invention in perspective view

[0050] [Fig. 4b] Figure 4b schematically represents the sleeve of figure 4a in profile view;

[0051] [Fig.4c] Figure 4c schematically represents the sleeve of figures 4a and 4b into which the attachment portion and the insert are inserted;

[0052] [Fig.4d] Figure 4d schematically represents the sleeve / portion of attachment / insert assembly of figure 4c inserted into the shimming mechanism;

[0053] [Fig.5] Figure 5 schematically represents an insert according to one embodiment of the invention;

[0054] [Fig.6] Figure 6 is a partial schematic perspective view of a foot of a blade according to a first embodiment of the invention;

[0055] [Fig.7] Figure 7 is a schematic cross-sectional and perspective view of the dawn of Figure 6, the cross-section being made along line VII-VII of Figure 6;

[0056] [Fig.8] Figure 8 is a schematic perspective view of the blade sleeve of Figure 6;

[0057] [Fig.9] Figure 9 is a schematic perspective view of the attachment portion of the fibrous structure and the blade insert of Figure 6;

[0058] [Fig.10] Figure 10 is a partial schematic perspective view of a foot of a blade according to a second embodiment of the invention;

[0059] [Fig. 11] Figure 11 is a schematic cross-sectional view of the blade of Figure 10, the cross-section being made along line XI-XI of Figure 10;

[0060] [Fig.12] Figure 12 is another schematic cross-sectional view of the blade of Figure 10, the section being made along line XII-XII of Figure 10;

[0061] [Fig.13] Figure 13 is another schematic front view of the end of the foot of a blade according to a third embodiment of the invention;

[0062] [Fig.14] Figure 14 is another schematic front view of the end of the foot of a blade according to the first embodiment of the invention; [Fig.15] Figure 15 is another schematic front view of the end of the foot of a blade according to a fourth embodiment of the invention;

[0063] [Fig.16] Figure 16 is another schematic front view of the end of the foot of a blade according to a fifth embodiment of the invention;

[0064] [Fig.17] Figure 17 is a partial schematic perspective view of a foot of a blade according to the fifth embodiment of the invention;

[0065] [Fig. 18] Figure 18 is a schematic perspective view of the blade sleeve of Figure 17; and

[0066] [Fig.19] Figure 19 is a schematic perspective view of the attachment portion of the fibrous structure of the blade of Figure 17.

[0067] Detailed description of the invention

[0068] In Figure 1, the engine 1 shown is an "Open Rotor" type engine, in a configuration commonly referred to as "pusher" (i.e., the blower is placed at the rear of the power generator with an air inlet located on the side, to the right in Figure 1).

[0069] The engine comprises a nacelle 2 intended to be fixed to an aircraft fuselage, and an unfaired fan 3. The fan 3 comprises two counter-rotating fan rotors 4 and 5. In other words, when the engine 1 is running, the rotors 4 and 5 are driven in rotation relative to the nacelle 2 around the same axis of rotation X (which coincides with a principal axis of the engine), in opposite directions.

[0070] Thus, in the example illustrated in Figure 1, motor 1 is an "Open Rotor" type motor, in a "pusher" configuration, with counter-rotating fan rotors. However, the invention is not limited to this configuration. The invention also applies to "Open Rotor" type motors, in a "puller" configuration (i.e., the fan is placed upstream of the power generator with an air inlet located before, between, or just behind the two fan rotors).

[0071] Furthermore, the invention also applies to motors with different architectures, such as an architecture comprising a blower rotor with moving blades and a blower stator with fixed blades, or a single blower rotor.

[0072] The invention is applicable to turboprop-type architectures (comprising a single fan rotor).

[0073] In Figure 1, each blower rotor 4, 5 comprises a hub 6 mounted rotatably relative to the nacelle 2 and a plurality of blades 7 according to an embodiment of the invention, said blades being fixed to the hub 6. The blades 7 extend substantially radially relative to the axis of rotation X of the hub.

[0074] As illustrated in Figure 2, the fan 3 further includes an actuation mechanism 8 for collectively adjusting the pitch angle of the rotor blades to adapt engine performance to different flight phases. For this purpose, each blade 7 comprises a blade root 9 and an aerodynamically profiled blade 12. The blade root 9 is rotatably mounted relative to the hub 6 around a pitch axis Y. More precisely, the blade root 9 is rotatably mounted within a mounting device 10 formed in the hub 6, via ball bearings 11 or other rolling elements.

[0075] The aerodynamic airfoil blade 12 has a first end connected to the blade root 9 and a second end, opposite the first end. The aerodynamic airfoil portion of the blade 12 is designed to extend into an engine air stream when the engine is running, in order to generate lift. Conversely, the blade root 9 is designed to extend out of the air stream.

[0076] With reference to figures 3, 4a and 4b, the blade 7 includes a sleeve 13 having a fixing part 14 configured to be connected to the mechanism 8, in particular inside the attachment device 10. The sleeve 13 has a recess 17 delimited by an internal wall 18 of the sleeve 13. The recess 17 passes through the sleeve 13 along a shimming axis Y.

[0077] With reference to Figures 3, 5a and 5b, the blade 7 also includes a fibrous structure 20, for example obtained by weaving fibers (UD laminates, 2D, braids and 3D weaves, etc.). The fibrous structure 20 includes a blade root 22 comprising an attachment portion 23 configured to be inserted into the recess 17 formed by the attachment portion 14 of the sleeve 13.

[0078] The fibrous structure 20 has a tubular shape and includes a housing 20a centered on the Y alignment axis.

[0079] The fibrous structure 20 also includes a blade 21 with an aerodynamic profile connected to the blade root 22.

[0080] The blade 7 also includes an insert 24 shown in Figure 5 and which is configured to be inserted into the housing 20a of the attachment portion 23 so that the attachment portion 23 is radially intercalated between the insert 24 and the inner wall 18 of the sleeve 13.

[0081] The blade 7 further includes a polymerized resin for solidifying the fibrous structure 20 and for bonding the insert 24 to the fibrous structure 20 and to the inner wall 18 of the sleeve 13.

[0082] The resin thus makes it possible to form a main force path, called default, when transmitting a torque recovery force around the Y alignment axis between the blade root 22 and the sleeve 13.

[0083] The blade 7 is thus formed from a few elements that fit together to form a single-piece blade. Since the blade 21 and the blade root 22 are formed from the same fibrous structure 20, there is no discontinuity between the blade 21 and the blade root 22. Furthermore, the blade root 22 is wedged between the insert 24 and the sleeve 13, and the fibrous structure 20 is thus securely joined to the blade root 9.

[0084] The blade 7 can therefore withstand significant aerodynamic stresses while maintaining a limited mass, and can thus be used with a variable pitch mechanism and in an "open rotor" type environment. Furthermore, since the components of the blade 7 are limited in number, it is quick to manufacture.

[0085] The resin typically comprises an organic material (thermosetting, thermoplastic, or elastomer) or a carbon matrix. For example, the matrix may comprise a plastic material, typically a polymer, such as epoxy, bismaleimide, or polyimide. The fibers of the fibrous structure 20 comprise at least one of the following materials: carbon, glass, aramid, polypropylene, and / or ceramic.

[0086] With reference to Figures 4a, 4b, and 4c, the attachment portion 23 may have an additional thickness 23” resulting from a progressive thickening of the fibrous structure 20 forming said attachment portion 23, at its free end 23'. This additional thickness 23” is configured to fit into a recessed portion 18' of the inner wall 18. Thus, the portion 18' widens the recess 17, and the remainder of the wall portion 18 narrows the recess 17. In this way, when the insert 24 is positioned in the recess 17, any translation of the attachment portion 23 away from the free end 23' is prevented by the portion of the wall 18 that narrows the recess 17 and forms a stop.

[0087] Indeed, when the fan is rotating, the blade 7 is subjected to centrifugal forces oriented in a radial direction relative to the axis of rotation of the fan, which tend to separate the aerodynamic profile blade 12 from the sleeve 13. The extra thickness 23” helps to prevent the separation of the blade 12 and the sleeve 13. It is the span angle which also contributes to the retention, a composite of constant thickness remaining blocked by the presence of this span.

[0088] With reference to figures 3, 4a to 4d, the fixing part 14 has a rotational symmetry about the Y axis. Furthermore, the fixing part 14 has an external surface with different reliefs.

[0089] The fixing part 14 has at its end through which the attachment portion 23 is inserted a first annular flange 29. This first annular flange 29 forms a stop against which the blade foot 22 is configured to bear.

[0090] The fixing part 14 also includes a second annular flange 29' at its free end opposite the end through which the fibrous structure 20 is inserted. The fixing part 14 also includes a first cylindrical surface 32 and a second cylindrical surface 34, each allowing one of the bearings 11 to be received. The fixing part 14 thus allows the blade foot 9 to be rotatably mounted inside the attachment device 10 provided in the hub 6.

[0091] Sleeve 13 is preferably metallic and monolithic.

[0092] As previously described, the sleeve 13 has an inner wall 18 that defines the recess 17. The recess 17 can form a cylinder of constant diameter that widens as it approaches the free end of the sleeve 13, forming a beveled inner edge. The wall 18 thus has a recessed portion 18' that widens the recess 17 in a radial direction. The extra thickness 23" of the attachment portion 23 is then inserted into the recessed portion 18' so as to prevent any translation of the attachment portion 23 away from the free end 23' when the insert 24 is positioned in the recess 17. The portion of the wall 18 with a constant diameter then acts as a stop for the extra thickness 23".

[0093] The recessed portion can have a different shape and can be placed in a different position along wall 18.

[0094] The wall 18 could alternatively be thickened at its end opposite the free end so as to reduce the diameter of the recess 17 and form a stop allowing the insert 24 to be blocked and the attachment portion 23 to be wedged against the wall 18 in an optimized manner.

[0095] Figure 4d represents the sleeve into which the attachment portion 23 and the insert 24 are inserted, the sleeve being arranged in the attachment device 10, the bearings 11 being arranged on the cylindrical surfaces 32 and 34.

[0096] Referring to Figure 5, the insert 24 comprises a cylindrical body 40 having a free end 41 and a locking end 42 opposite the free end 41. In this embodiment, the locking end 42 is rounded or pointed. According to the variant in which the sleeve 13 has a stop, the rounded locking end 42 allows the insert 24 to wedge the attachment portion 23 against the stop.

[0097] Alternatively, the locking end 42 may have another shape that can adapt to a stop that may also have another shape.

[0098] Insert 24 is preferably metallic.

[0099] Figures 6 and following represent embodiments of the blade 7 according to the invention.

[0100] The distinctive feature of the blade according to the invention lies in the fact that the attachment portion 23 of the fibrous structure 20 has, along at least part of its length along the alignment axis Y, a first non-cylindrical external surface 23a. Furthermore, the inner wall 18 of the sleeve 13 covers this first external surface 23a and has a shape complementary to this first external surface 23a.

[0101] Figures 6 to 9 and 14 illustrate a first embodiment of the blade 7. In this embodiment, the first external surface 23a of the attachment portion 23a, in cross-section with respect to the alignment axis Y, has a generally polygonal shape, in particular a 6-sided one. The internal wall 18 of the sleeve 13 covers this first external surface 23a without clearance and has a complementary generally polygonal shape, in particular a 6-sided one.

[0102] We observe that this shape is devoid of sharp edges and includes, for example, rounded corners at the corners of the polygon. The rounded corners preferably have a radius of curvature between 2 and 20 mm, and preferably between 10 and 20 mm.

[0103] In this embodiment, the insert 24 has, along at least part of its length along the Y-axis, a second cylindrical external surface 24a. Furthermore, the attachment portion 23 covers this second external surface 24a and has a shape complementary to it. In other words, the attachment portion 23 has a cylindrical internal surface 23b that covers the second external surface 24a. In this embodiment, and as is more clearly shown in Figure 14, the insert 24 can have a minimum radial thickness Emin ns measured with respect to the Y-axis that is less than a minimum radial thickness Emin_por of the attachment portion 23 of the fibrous structure 20 measured with respect to said Y-axis.

[0104] The attachment portion 23 of the fibrous structure 20 can have a maximum radial thickness Emax_por measured with respect to the alignment axis Y, which is greater than or equal to a maximum radial thickness Emax_man of the sleeve 13 measured with respect to said alignment axis Y.

[0105] In the example shown, the sleeve 13 may have, over at least part of its length along the Y alignment axis, a third cylindrical external surface 13a, this third external surface extending at least partially around the first external surface 23a. This surface 13a may be a surface for receiving a rolling bearing and for example a ball bearing, as mentioned above.

[0106] The insert 24 may have, over at least part of its length along the Y alignment axis, an internal cylindrical surface 24b, this internal surface 24b extending at least partly radially inside the first external surface 23a.

[0107] Figures 10 to 12 illustrate a second embodiment of the dawn 7.

[0108] In this embodiment, the first external surface 23a of the attachment portion 23a, in cross-section with respect to the alignment axis Y, has a generally elliptical shape. The internal wall 18 of the sleeve 13 covers this first external surface 23a without play and has a complementary generally elliptical shape.

[0109] In this embodiment, the insert 24 has, along at least part of its length along the Y-axis alignment, a second non-cylindrical external surface 24a. Furthermore, the attachment portion 23 covers this second external surface 24a and has a shape complementary to this second external surface 24a. In other words, the attachment portion 23 has a non-cylindrical internal surface 23b that covers the second external surface 24a.

[0110] In the example shown, surfaces 24a and 23b are also elliptical.

[0111] In this embodiment, the insert 24 may have a minimum radial thickness Emin ns measured with respect to the alignment axis Y, which is less than a minimum radial thickness Emin_por of the attachment portion 23 of the fibrous structure 20 measured with respect to said alignment axis Y.

[0112] The attachment portion 23 of the fibrous structure 20 can have a maximum radial thickness Emax_por measured with respect to the alignment axis Y, which is greater than or equal to a maximum radial thickness Emax_man of the sleeve 13 measured with respect to said alignment axis Y.

[0113] In the example shown, the sleeve 13 may have, over at least part of its length along the Y alignment axis, a third cylindrical external surface 13a, this third external surface extending at least partially around the first external surface 23a. This surface 13a may be a surface for receiving a rolling bearing and for example a ball bearing, as mentioned above.

[0114] The insert 24 may have, over at least part of its length along the Y alignment axis, an internal cylindrical surface 24b, this internal surface 24b extending at least partly radially inside the first external surface 23a.

[0115] Figure 12 shows that the elliptical shape of the external surface 24a of the insert 24 is obtained by flaring one end of the insert on two diametrically opposite sides with respect to the alignment axis Y.

[0116] Figure 13 illustrates a third embodiment of the vane 7.

[0117] In this embodiment, the first external surface 23a of the attachment portion 23a, in cross-section with respect to the alignment axis Y, has a generally square shape. The internal wall 18 of the sleeve 13 covers this first external surface 23a without play and has a complementary generally square shape.

[0118] We observe that this shape is devoid of sharp edges and includes, for example, rounded corners at the corners of the square. The rounded corners preferably have a radius of curvature between 2 and 20 mm, and preferably between 10 and 20 mm.

[0119] In this embodiment, the insert 24 has, along at least part of its length along the Y-axis alignment, a second non-cylindrical external surface 24a. Furthermore, the attachment portion 23 covers this second external surface 24a and has a shape complementary to this second external surface 24a. In other words, the attachment portion 23 has a non-cylindrical internal surface 23b that covers the second external surface 24a.

[0120] In the example shown, surfaces 24a and 23b are also squares. This shape is devoid of sharp edges and includes, for example, rounded corners. The rounded corners preferably have a radius of curvature between 2 and 20 mm, and preferably between 10 and 20 mm.

[0121] In this embodiment, the insert 24 may have a minimum radial thickness Emin ns measured with respect to the alignment axis Y, which is less than a minimum radial thickness Emin_por of the attachment portion 23 of the fibrous structure 20 measured with respect to said alignment axis Y.

[0122] The attachment portion 23 of the fibrous structure 20 can have a maximum radial thickness Emax_por measured with respect to the alignment axis Y, which is greater than or equal to a maximum radial thickness Emax_man of the sleeve 13 measured with respect to said alignment axis Y.

[0123] In the example shown, the sleeve 13 may have, along at least part of its length along the Y-axis, a third cylindrical external surface 13a, this third external surface extending at least partially around the first external surface 23a. This surface 13a may be a mounting surface for a rolling bearing, for example a ball bearing, as mentioned above. The insert 24 may have, along at least part of its length along the Y-axis, a cylindrical internal surface 24b, this internal surface 24b extending at least partially radially inside the first external surface 23a.

[0124] Figure 15 illustrates a fourth embodiment of the dawn 7.

[0125] In this embodiment, the first external surface 23a of the attachment portion 23a, in cross-section with respect to the alignment axis Y, has a generally polygonal shape, in particular a 6-sided one. The internal wall 18 of the sleeve 13 covers this first external surface 23a without play and has a complementary generally polygonal shape.

[0126] We observe that this shape is devoid of sharp edges and includes, for example, rounded corners at the corners of the polygon. The rounded corners preferably have a radius of curvature between 2 and 20 mm, and preferably between 10 and 20 mm.

[0127] In this embodiment, the insert 24 has, along at least part of its length along the Y-axis alignment, a second non-cylindrical external surface 24a. Furthermore, the attachment portion 23 covers this second external surface 24a and has a shape complementary to this second external surface 24a. In other words, the attachment portion 23 has a non-cylindrical internal surface 23b that covers the second external surface 24a.

[0128] In the example shown, surfaces 24a and 23b are also polygonal in cross-section, specifically with 6 sides.

[0129] We observe that this shape is devoid of sharp edges and includes, for example, rounded corners at the corners of the polygon. The rounded corners preferably have a radius of curvature between 2 and 20 mm, and preferably between 10 and 20 mm.

[0130] In this embodiment, the insert 24 may have a minimum radial thickness Emin_ns measured with respect to the alignment axis Y, which is less than a minimum radial thickness Emin_por of the attachment portion 23 of the fibrous structure 20 measured with respect to said alignment axis Y. The attachment portion 23 of the fibrous structure 20 may have a maximum radial thickness Emax_por measured with respect to the alignment axis Y, which is greater than or equal to a maximum radial thickness Emax_man of the sleeve 13 measured with respect to said alignment axis Y.

[0131] In the example shown, the sleeve 13 may have, over at least part of its length along the Y alignment axis, a third cylindrical external surface 13a, this third external surface extending at least partially around the first external surface 23a. This surface 13a may be a surface for receiving a rolling bearing and for example a ball bearing, as mentioned above.

[0132] The insert 24 may have, over at least part of its length along the Y alignment axis, an internal cylindrical surface 24b, this internal surface 24b extending at least partly radially inside the first external surface 23a.

[0133] Figures 16 to 19 illustrate a fifth embodiment of the blade 7. In this embodiment, the first external surface 23a of the attachment portion 23a, in cross-section with respect to the alignment axis Y, has a general star shape. The internal wall 18 of the sleeve 13 covers this first external surface 23a without play and has a complementary general star shape.

[0134] It is observed that this shape lacks sharp edges and includes, for example, rounded points at the points of the star. The rounded points preferably have a radius of curvature between 2 and 20 mm, and preferably between 10 and 20 mm.

[0135] In this embodiment, the insert 24 has, along at least part of its length along the Y-axis alignment, a second non-cylindrical external surface 24a. Furthermore, the attachment portion 23 overlaps this second external surface 24a and has a shape complementary to it. In other words, the attachment portion 23 has a non-cylindrical internal surface 23b that overlaps the second external surface 24a. In the example shown, the surfaces 24a and 23b are also star-shaped in cross-section.

[0136] It is observed that this shape lacks sharp edges and includes, for example, rounded points at the points of the star. The rounded points preferably have a radius of curvature between 2 and 20 mm, and preferably between 10 and 20 mm.

[0137] In this embodiment, the insert 24 may have a minimum radial thickness Emin ns measured with respect to the alignment axis Y, which is less than a minimum radial thickness Emin_por of the attachment portion 23 of the fibrous structure 20 measured with respect to said alignment axis Y.

[0138] The attachment portion 23 of the fibrous structure 20 can have a maximum radial thickness Emax_por measured with respect to the alignment axis Y, which is greater than or equal to a maximum radial thickness Emax_man of the sleeve 13 measured with respect to said alignment axis Y.

[0139] In the example shown, the sleeve 13 may have, over at least part of its length along the Y alignment axis, a third cylindrical external surface 13a, this third external surface extending at least partially around the first external surface 23a. This surface 13a may be a surface for receiving a rolling bearing and for example a ball bearing, as mentioned above.

[0140] The insert 24 may have, over at least part of its length along the Y alignment axis, an internal cylindrical surface 24b, this internal surface 24b extending at least partly radially inside the first external surface 23a.

Claims

DEMANDS 1. Variable pitch blade (7) for a turbomachine comprising: - a tubular metal sleeve (13), this sleeve comprising a fixing part (14) configured to be connected to a variable shimming mechanism, and a recess (17) passing through the sleeve (13) along a shimming axis (Y), the recess (17) being delimited by an internal wall (18) of the sleeve (13), - a fibrous structure (20) comprising a blade root (22) including a tubular attachment portion (23) inserted axially into the recess (17) of the sleeve (13), this attachment portion (23) including a housing (20a) centered on the alignment axis (Y), the fibrous structure (20) further including an aerodynamically profiled blade (12) connected to the blade root (22), - an insert (24) centered on the alignment axis (Y) and inserted axially into the housing (20a) of the attachment portion (23) so that the attachment portion (23) is radially intercalated between the insert (24) and the inner wall (18) of the sleeve (13), - a polymerized resin for solidifying the fibrous structure (20) and for bonding the insert (24) to the fibrous structure (20) and to the inner wall (18) of the sleeve (13), characterized in that the attachment portion (23) of the fibrous structure (20) has, on at least part of its length along the alignment axis (Y), a first non-cylindrical external surface (23a), and in that the inner wall (18) of the sleeve (13) covers this first external surface (23a) and has a shape complementary to this first external surface (23a).

2. Blade (7) according to claim 1, wherein the first external surface (23a) of the attachment portion (23) has in cross-section with respect to said alignment axis (Y), a general shape chosen from a polygon, for example with 4, 5 or 6 sides, an ellipse or an oval, and a star.

3. Blade (7) according to claim 2, wherein the shape of the cross section is devoid of sharp edges and includes, for example, rounded corners at the corners of the polygon or rounded points at the points of the star.

4. Blade (7) according to any one of claims 1 to 3, wherein the insert (24) has, over at least part of its length along the alignment axis (Y), a second cylindrical external surface (24a), and wherein the attachment portion (23) covers this second external surface (24a) and has a shape complementary to this second external surface (24a).

5. Blade (7) according to any one of claims 1 to 3, wherein the insert (24) has, over at least part of its length along the alignment axis (Y), a second non-cylindrical external surface (24a), and wherein the attachment portion (23) covers this second external surface (24a) and has a shape complementary to this second external surface (24a).

6. Blade (7) according to claim 5, wherein the second external surface (24a) of the insert (24) has in cross-section with respect to said alignment axis (Y), a general shape chosen from a polygon, for example with 4, 5 or 6 sides, an ellipse or an oval, and a star.

7. Blade according to claim 6, wherein the shape of the cross section is devoid of sharp edges and includes, for example, rounded corners at the corners of the polygon or rounded points at the points of the star.

8. Blade (7) according to any one of claims 5 to 7, wherein the first and second external surfaces (23a, 24a) have the same geometric shape in cross-section with respect to said alignment axis.

9. Blade (7) according to claim 8, wherein the first and second external surfaces (23a, 24a) have: - the same elliptical shape in cross-section with respect to said alignment axis, or - the same polygonal shape in cross-section with respect to said alignment axis, or - the same star shape in cross-section with respect to said alignment axis.

10. Blade (7) according to any one of the preceding claims, wherein the sleeve (13) has, over at least part of its length along the alignment axis (Y), a third cylindrical external surface (13a), this third external surface (13a) extending at least in part around said first external surface (23a).

11. Blade (7) according to any one of the preceding claims, wherein the insert (24) has, over at least part of its length along the alignment axis (Y), a cylindrical internal surface (24b), this internal surface (24b) extending at least partly radially inside said first external surface (23a).

12. Blade (7) according to any one of the preceding claims, wherein the insert (24) has a minimum radial thickness (Emin ns) measured with respect to said alignment axis (Y), which is less than a minimum radial thickness (Emin_por) of the attachment portion (23) of the fibrous structure (20) measured with respect to said alignment axis (Y).

13. Blade (7) according to any one of the preceding claims, wherein the attachment portion (23) of the fibrous structure (20) has a maximum radial thickness (Emax_por) measured with respect to said alignment axis (Y), which is greater than or equal to a maximum radial thickness (Emax_man) of the sleeve (13) measured with respect to said alignment axis (Y).

14. Turbomachine, in particular for aircraft, comprising at least one blade (7) according to any one of the preceding claims.

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