VARIABLE TIMING TURBINE ENGINE VANES

Abstract

Variable pitch blade (7) for a turbomachine comprising: - a tubular metal sleeve (13), - a fibrous structure (20), the fibrous structure (20) comprising a blade root (22) including a tubular attachment portion (23) inserted axially into a recess (17) in the sleeve (13), - an insert (24) centered on the pitch axis (Y) and inserted axially into a housing (20a) in 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), and - at least one key (50) to form a circumferential load path around the axis (Y) between the sleeve (13) and the attachment portion (23) of the fibrous structure (20). Figure for abbreviation: Figures 6a-6b

Description

Title of the invention: VARIABLE PITCHING BLADE FOR A TURBOMACHINE Technical field of the invention

[0001] The invention relates generally to the field of turbomachinery, and in particular to turbomachine blades.

[0002] The invention relates more particularly, but not exclusively, to a variable pitch blade intended for use in an unfaired aircraft engine fan rotor. Technical background

[0003] The advantage of engines with unshod fans 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 the "By Pass Ratio" or BPR), and consequently reduced fuel consumption. Thus, in this type of engine, the fan blades can have a large span.

[0004] In addition, these engines generally include a mechanism for changing the angle of the blades in order to adapt the thrust generated by the fan according to the different phases of flight.

[0005] However, the design of such blades requires taking into account opposing constraints.

[0006] On the one hand, the sizing of these blades must allow for optimal aerodynamic performance, in particular 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.

[0007] 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.

[0008] Furthermore, on unshod fan designs, engine starting is generally performed with a very open timing setting. Indeed, a very open timing setting allows power to be consumed by torque, which ensures machine safety by guaranteeing low fan speeds.

[0009] However, with a very open pitch, the blades undergo turbulent, completely separated aerodynamic flow, which generates broadband vibrational excitation. In particular, on blades with a wide chord and large span, the bending stress is intense, even though the engine speed is not at its maximum.

[0010] In normal operation, namely during ground and flight phases, the fan pitch is adjusted so that the pitch angle is more closed. The aerodynamic flow is then perfectly smooth, particularly when aligned with 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 seen 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 IP moment) on the blades. This cyclic bending moment then generates strong bending stresses on the blades in addition to the centrifugal forces due to their rotation.

[0011] These blades can be made of metallic material. If the blades are made of Metallic materials have good mechanical resistance, however they have the disadvantage of having a relatively large mass.

[0012] 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 to which they are subjected. These aerodynamic stresses can therefore damage the blades and / or the hub in the interface zone between the blades and the fan rotor hub, at the blade root.

[0013] To overcome these drawbacks, various solutions exist in the prior art. Most use reinforcing elements, particularly at the blade root, and add various structural elements to allow, for example, the blade to be attached to the leveling mechanism. Patent documents WO-A1-2022 / 018353 and WO-A1-2022 / 208002 describe the addition of reinforcing and structural elements, particularly at the blade roots.

[0014] 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 means. Such blades can therefore be relatively time-consuming to manufacture. Summary of the invention

[0015] The invention provides a variable-pitch blade for a turbomachine comprising:

[0016] - a tubular metal sleeve, this sleeve comprising a fixing portion 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,

[0017] - a fibrous structure, the fibrous structure comprising a blade root comprising a portion of tubular attachment inserted axially into the recess of the sleeve, this attachment portion comprising a housing centered on the alignment axis, the fibrous structure further comprising a blade with an aerodynamic profile connected to the blade root,

[0018] - an insert centered on the alignment axis and inserted axially into the housing of the attachment portion such that the attachment portion is radially interposed between the insert and the inner wall of the sleeve, and

[0019] - a polymerized resin for solidifying the fibrous structure and bonding from the insert to the fibrous structure and the inner wall of the sleeve,

[0020] characterized in that it further comprises at least one key at the attachment portion of the fibrous structure, said at least one key being able to cooperate by complementarity of shapes with a counterform of the inner wall of the sleeve in order to form a force path in a circumferential direction around the axis between the sleeve and the attachment portion of the fibrous structure.

[0021] The problem to be solved concerns the absorption of the torsional moment around the blade 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.

[0022] By default, this torque is absorbed by the polymerized resin, which ensures bonding between the attachment portion of the blade root and the sleeve. This bonding provides an initial load path for the transfer torque. A failure of this interface would result in a loss of control over the blade pitch.

[0023] The invention thus proposes to reinforce this path of effort by complementary shapes between a key housed or formed in the attachment portion of the blade foot and the sleeve.

[0024] The blade according to the invention may comprise one or more of the following features, taken individually or in combination with each other:

[0025] — the fibrous structure is obtained by weaving, preferably three-dimensional, of fibers; - where each key is inserted into a housing in the attachment portion of the fibrous structure; - where each key extends radially with respect to the axis, from the insert to the counterform of the inner wall of the sleeve; - each key comprises a radially internal end in contact with the insert and a radially external end engaged in a recess in the internal wall of the sleeve, this recess forming the aforementioned counter-form; - where each key has an elongated shape along the axis and extends from a longitudinal end of the attachment portion of the fibrous structure opposite the blade; - where each key extends axially to an internal frustoconical surface of the inner wall of the sleeve and is in contact with this surface; - where each key extends axially beyond the internal frustoconical surface, being in contact with the internal wall of the sleeve and at a radial distance from the insert; - where each key extends axially beyond the internal frustoconical surface, being in contact with the insert and at a radial distance from the internal wall of the sleeve; - where each key is made of metal or composite material; - the key or each key is formed by a part of the attachment portion of the fibrous structure, and is therefore integrated into the attachment portion; - where each key is formed by an external radial projection of the attachment portion of the fibrous structure, this projection being engaged in a recess of the internal wall of the sleeve which forms the aforementioned counter-form; - where each key comprises only resin from material with that of the fibrous structure, or even fibers which may also come from the fibrous structure; - where each key has an angular range around the axis which is between 5 and 20°; - the number of key(s) is between 1 and 10 and for example between 2 and 6.

[0026] The present invention also relates to a turbomachine, in particular for aircraft, comprising at least one blade as described above.

[0027] The present invention also relates to a method for manufacturing a blade as described above, in which

[0028] a) the key or each key is inserted into a recess in the attachment portion of the fibrous structure, this recess being cut into the fibrous structure before its solidification by the resin, or

[0029] a) the key or keys are inserted into a recess in the attachment portion of the fibrous structure, this recess being machined into the fibrous structure after its solidification by the resin, or

[0030] a) the or each key is integrated into the attachment portion of the fibrous structure, and comprises only resin from material with that of the fibrous structure, or even also fibers which may also come from the fibrous structure. Brief description of the figures

[0031] 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:

[0032] [Fig. 1] [Fig. 1] schematically represents an example of an engine including an unfaired fan;

[0033] [Fig.2] [Fig.2] schematically represents a blower blade according to an embodiment of the invention assembled to a shimming mechanism;

[0034] [Fig.3] [Fig.3] schematically represents a blower blade according to a first embodiment of the invention;

[0035] [Fig.4a] Fig.4a schematically represents a sleeve according to a first embodiment of the invention in perspective view;

[0036] [Fig.4b] Fig.4b schematically represents the sleeve of Fig.4a in a profile view;

[0037] [Fig.4c] Fig.4c schematically represents the sleeve of figures 4a and 4b into which the attachment portion and the insert are inserted;

[0038] [Fig.4d] Fig.4d schematically represents the sleeve / portion of attachment / insert assembly of Fig.4c inserted into the shimming mechanism;

[0039] [Fig.5] Fig.5 schematically represents an insert according to one embodiment of the invention;

[0040] [Fig. 6a-6b] Figures 6a and 6b are schematic views, respectively in axial and cross-sectional view of the foot of a blade according to a first embodiment of the invention;

[0041] [Fig. 7a-7b] Figures 7a and 7b are schematic views, respectively in axial and cross-sectional view of the foot of a blade according to a second embodiment of the invention;

[0042] [Fig. 8a-8b] Figures 8a and 8b are schematic cross-sectional views, respectively axial and cross-sectional views of the base of a blade according to a third embodiment of the invention; and

[0043] [Fig. 9a-9b] Figures 9a and 9b are schematic cross-sectional views, respectively transverse and axial section, of a foot of a blade according to a fourth embodiment of the invention. Detailed description of the invention

[0044] In [Fig. 1], the motor 1 shown is an "Open Rotor" type motor, 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 [Fig. 1]).

[0045] 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.

[0046] Thus, in the example illustrated in [Fig. 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).

[0047] In addition, the invention also applies to motors having different architectures, such as an architecture comprising a blower rotor including movable blades and a blower stator including fixed blades, or a single blower rotor.

[0048] The invention is applicable to turboprop type architectures (comprising a single fan rotor).

[0049] In [Fig.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.

[0050] As illustrated in [Fig. 2], the fan 3 further comprises 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 about a pitch axis Y. More specifically, 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.

[0051] The aerodynamically profiled blade 12 has a first end connected to the blade root 9 and a second end, opposite the first end. The aerodynamically profiled portion of the blade 12 is designed to extend into an air stream of the engine, when the engine is running, in order to generate lift. Conversely, the blade root 9 is designed to extend out of the air stream.

[0052] With reference to Figures 3, 4a and 4b, the blade 7 comprises a sleeve 13 having a fastening portion 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 crosses the sleeve 13 along a Y alignment axis.

[0053] With reference to Figures 3, 5a and 5b, the blade 7 also comprises a fibrous structure 20 obtained, for example, by three-dimensional weaving of fibers. Other methods could be used as alternatives.

[0054] The fibrous structure 20 includes a blade foot 22 comprising an attachment portion 23 configured to be inserted into the recess 17 formed by the attachment part 14 of the sleeve 13.

[0055] The fibrous structure 20 has a tubular shape and includes a housing 20a centered on the alignment axis Y.

[0056] The fibrous structure 20 also includes a blade 21 with an aerodynamic profile connected to the blade root 22.

[0057] The blade 7 also includes an insert 24 shown in [Fig.5] 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.

[0058] 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.

[0059] The resin thus makes it possible to form a main force path, called default, during the transmission of a torque recovery force around the Y alignment axis between the blade root 22 and the sleeve 13.

[0060] 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.

[0061] The blade 7 can thus withstand significant aerodynamic forces while having a limited mass and can therefore be used with a variable pitch mechanism and in an "open rotor" type environment. Furthermore, since the elements forming the blade 7 are limited in number, the blade 7 is quick to manufacture.

[0062] 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.

[0063] 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 portion of the wall 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.

[0064] Indeed, when the fan is rotating, the blade 7 is subjected to centrifugal forces oriented in a radial direction with respect 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.

[0065] 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 having different reliefs.

[0066] 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.

[0067] The fixing part 14 also includes a second annular flange 29' at its free end opposite to the end through which the fibrous structure 20 is inserted.

[0068] 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 mounted rotatably inside the attachment device 10 provided in the hub 6.

[0069] The sleeve 13 is preferably metallic and monolithic.

[0070] 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 that has a constant diameter then forms a stop for the extra thickness 23".

[0071] The recessed portion may have another shape and may be placed in another position along the wall 18.

[0072] 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.

[0073] Fig. 4d represents the sleeve into which the attachment portion 23 and the insert 24 are inserted, the sleeve being disposed in the attachment device 10, the bearings 11 being disposed on the cylindrical surfaces 32 and 34.

[0074] With reference to [Fig. 5], the insert 24 comprises a cylindrical body 40 having a free end 41 and a locking end 42 opposite the free end 41. The locking end 42 is, in this embodiment, a rounded or pointed end. According to the embodiment 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.

[0075] Alternatively, the locking end 42 may have another shape that can adapt to a stop that may also have another shape.

[0076] The insert 24 is preferably metallic.

[0077] Figures 6a-6b and following represent embodiments of the blade according to the invention.

[0078] The particularity of the blade according to the invention is related to the fact that the blade includes at least one key 50 at the attachment portion 23 of the fibrous structure 20. The key or each key 50 is configured to cooperate by complementary shapes with a counterform 52 of the inner wall 18 of the sleeve 13 in order to form a force path in a circumferential direction around the Y axis between the sleeve 13 and the attachment portion 23 of the fibrous structure 20.

[0079] Two options are possible according to the invention.

[0080] According to a first option, at least one key 50 is housed in the attachment portion 23 of the fibrous structure 20. Figures 6a-6b to 8a-8b illustrate embodiments according to this first option.

[0081] According to a second option, the attachment portion 23 of the fibrous structure 20 forms at least one key 50. Figures 9a and 9b illustrate another embodiment according to this second option.

[0082] According to the first option, the key or each key 50 is brought into a housing 54 of the attachment portion 23 of the fibrous structure 20.

[0083] As can be seen in figures 6a-6b to 8a-8b, the key or each key 50 extends preferably radially with respect to the Y axis, from the insert 24 to the counterform 52 of the inner wall 18 of the sleeve 13.

[0084] The key or keys 50 may comprise a radially internal end 50a in contact with the insert 24 and a radially external end 50b engaged in a recess in the inner wall 18 of the sleeve 13, this recess forming the aforementioned counterform 52.

[0085] The key or each key 50 preferably has an elongated shape along the Y axis and extends from a longitudinal end of the attachment portion 23 of the fibrous structure 20 opposite the blade 21 (see figures 6a-6b to 8a-8b).

[0086] The key or each key 50 can extend axially to an internal frustoconical surface 56 of the internal wall 18 of the sleeve 13 and be in contact with this surface 56 (cf. figures 6a-6b to 8a-8b).

[0087] In the example shown, the inner wall 18 of the sleeve 13 comprises two internal cylindrical surfaces 58, 60 connected to each other by the frustoconical surface 56. The frustoconical surface 56 is flared on the side of the free end of the foot 22 and is connected by its end of larger diameter to the cylindrical surface 60 of larger diameter which opens at the free end of the foot 22. The frustoconical surface 56 is connected by its end of smaller diameter to the cylindrical surface 58 of smaller diameter which opens towards the blade 21.

[0088] The key or each key 50 can extend axially beyond the internal frustoconical surface 56 (see figures 7a to 8b).

[0089] In the embodiment of figures 7a-7b, the key or each key 50 is in contact with the insert 24 and at a radial distance from the inner wall 18 of the sleeve 13.

[0090] In the embodiment of figures 8a-8b, the key or each key 50 is in contact with the inner wall 18 of the sleeve 13 and at a radial distance from the insert 24.

[0091] In the embodiments of Figures 6a to 8b, the key or keys 50 may be made of metal or composite material. In the case of a composite material, the key or keys 50 may be formed from a resin in which long fibers are embedded. Alternatively, the fibers could be short (for example, 1 cm or less in length).

[0092] The present invention also relates to a method of making a blade according to the first option.

[0093] Two choices are possible. Either the key or each key 50 is mounted in the foot 22 before solidification by the resin, or it is mounted in the foot 22 after this solidification.

[0094] The key or keys 50 can thus be inserted into the recess 54 of the attachment portion 23 before it is solidified by the resin. In this case, the recess 54 is cut into the fibrous structure 20 before it is solidified by the resin. After the key or keys 50 are installed, the resin used to solidify the fibrous structure 20 also ensures the bond between the key or keys 50 and the fibrous structure 20. In this solution, the key or keys 50 are preferably designed to withstand a thermal cycle of consolidation (polymerization) of the blade. Surface preparation of each key 50 may be useful, and even a layer of suitable adhesive may be applied to ensure good adhesion to the matrix.

[0095] The key or keys 50 can also be inserted into the recess 54 of the attachment portion 23 after it has solidified with resin. In this case, the recess 54 is machined into the fibrous structure 20 after it has solidified with resin. It is therefore understood that the key or keys 50 are engaged in their recess 54 formed in the fibrous structure 20 solidified by the resin. In this solution, a surface preparation and an adhesive can also be used to hold the key in place during the various stages of blade assembly in its environment.

[0096] According to the second option, the key or each key 50 is formed by a part of the attachment portion 23 of the fibrous structure 20, and is therefore integrated into the attachment portion 23.

[0097] In the embodiment illustrated in figures 9a-9a, the key or each key 50 is for example formed by an external radial projection 62 of the attachment portion 23 of the fibrous structure 20. This projection 62 is engaged in a recess of the internal wall 18 of the sleeve 13 which forms the aforementioned counterform 52.

[0098] Depending on how the blade is made, the key or each key 50 may comprise only resin, or comprise fibers from or not from the fibrous structure 20 and embedded in resin.

[0099] The present invention also relates to a method of making a blade according to the second option.

[0100] The key or each key 50 is integrated into the attachment portion 23 of the fibrous structure 20 and is formed in one piece with this attachment portion 23 or is formed from material with this attachment portion 23.

[0101] The key or keys 50 may then comprise only resin, as described above. This resin is mixed with the material of the fibrous structure, resulting in a monolithic assembly between the attachment portion and the key. Alternatively, the key or keys 50 may comprise resin and fibers from the attachment portion 23 of the fibrous structure 20. In this second case, before solidification by the resin, the fibrous structure 20 may be cut or untied to provide fibers at the level of the key or keys 50 to be formed. In yet another variant, the key or keys 50 may comprise its own fibrous preform, for example, made of glass or carbon fibers. The fibers of the key or keys 50 may be long fibers. Alternatively, the fibers could be short (for example, 1 cm or less in length).

[0102] Generally, regardless of the option, the key or each key 50 preferably has an angular range a around the Y axis which is between 5 and 20°.

[0103] The number of key(s) 50 is for example between 1 and 10 and for example between 2 and 6. When their number is greater than 2, they are preferably regularly distributed around the Y axis.

[0104] Preferably, the key or each key 50 has an elastic modulus greater than 15 GPa (giga Pascal) in the circumferential direction to ensure correct transmission of force.

Claims

Demands

1. Variable pitch blade (7) for an aircraft turbomachine, comprising: - a tubular metal sleeve (13), this sleeve comprising a fastening portion (14) configured to be connected to a variable pitch mechanism, and a recess (17) passing through the sleeve (13) along a pitch axis (Y), the recess (17) being delimited by an internal wall (18) of the sleeve (13), - a fibrous structure (20), the fibrous structure (20) comprising a blade root (22) comprising a tubular attachment portion (23) inserted axially into the recess (17) of the sleeve (13), this attachment portion (23) comprising a housing (20a) centered on the pitch axis (Y), the fibrous structure (20) further comprising 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) such that the attachment portion (23) is radially interposed between the insert (24) and the inner wall (18) of the sleeve (13), and - 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 it further comprises at least one key (50) at the attachment portion (23) of the fibrous structure (20), said at least one key (50) being capable of cooperating by complementary shapes with a counterform (52) of the inner wall (18) of the sleeve (13) in order to form a circumferential load path around the axis (Y) between the sleeve (13) and the attachment portion (23) of the fibrous structure (20).

2. Blade (7) according to claim 1, wherein the key or each key (50) is brought into a housing (54) of the attachment portion (23) of the fibrous structure (20).

3. Blade (7) according to claim 2, wherein the key or each key (50) extends radially with respect to the axis (Y), from the insert (24) to the counterform (52) of the inner wall (28) of the sleeve (13).

4. Blade (7) according to any one of claims 3, wherein the key or each key (50) comprises a radially internal end (50a) in contact with the insert (24) and a radially external end (50b) engaged in a recess in the inner wall (18) of the sleeve (13), this recess forming the aforementioned counterform (52).

5. Blade (7) according to any one of claims 2 to 4, wherein the key or each key (50) has an elongated shape along the axis (Y) and extends from a longitudinal end of the attachment portion (23) of the fibrous structure (20) opposite the blade (21).

6. Blade (7) according to claim 5, wherein the key or each key (50) extends axially to an internal frustoconical surface (56) of the internal wall (18) of the sleeve (13) and is in contact with this surface (56).

7. Blade according to claim 6, wherein the key or each key (50) extends axially beyond the internal frustoconical surface (56) while being in contact with the internal wall (18) of the sleeve (13) and at a radial distance from the insert (24).

8. Blade according to claim 6, wherein the key or each key (50) extends axially beyond the internal frustoconical surface (56) while being in contact with the insert (24) and at a radial distance from the internal wall (18) of the sleeve (13).

9. Blade according to any one of claims 2 to 8, wherein the key or each key (50) is made of metal or composite material.

10. Blade (7) according to claim 1, wherein the key or each key (50) is formed by a part of the attachment portion (23) of the fibrous structure (20), and is therefore integrated into the attachment portion (23).

11. Blade (7) according to claim 10, wherein the key or each key (50) is formed by an external radial projection (62) of the attachment portion (23) of the fibrous structure (20), this projection (62) being engaged in a recess in the inner wall of the sleeve which forms the aforementioned counterform (52).

12. Blade (7) according to claim 10, wherein the key or each key (50) comprises only resin from material with that of the fibrous structure, or even fibers which may also come from the fibrous structure.

13. Blade (7) according to any one of the preceding claims, wherein the key or each key (50) has an angular extent (a) around the axis which is between 5 and 20°.

14. Blade (7) according to any one of the preceding claims, wherein the number of key(s) (50) is between 1 and 10 and for example between 2 and 6.

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

16. A method for making a blade (7) according to any one of claims 1 to 14, wherein: a) the key or each key (50) is brought into a housing (54) in the attachment portion (23) of the fibrous structure (20), this housing (54) being cut in the fibrous structure (20) before its solidification by the resin, or a) the key or each key (50) is brought into a housing (54) in the attachment portion (23) of the fibrous structure (20), this housing (54) being machined in the fibrous structure (20) after its solidification by the resin, or a) the key or each key (50) is integrated into the attachment portion (23) of the fibrous structure (20), and comprises resin made from material with that of the fibrous structure, or even fibers which may also come from the fibrous structure.

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