VARIABLE TIMING TURBINE ENGINE VANES

Abstract

Variable-pitch blade (7) for a turbomachine comprising: - a tubular metal sleeve (13), - a fibrous structure (20) comprising a tubular attachment portion (23) inserted axially into the sleeve (13) and comprising a housing (20a), - a first insert (24) inserted axially into the housing (20a) of the attachment portion (23) such that the attachment portion (23) is radially interposed between the first insert (24) and the sleeve (13), - a polymerized resin for solidifying the fibrous structure (20) and for bonding the first insert (24) to the fibrous structure (20) and to the inner wall (18) of the sleeve (13), and - a second insert (60) inserted axially into the housing (20a) of the attachment portion (23), and cooperating by complementary shapes with the attachment portion (23) while being separated from the attachment portion (23) by less a circumferential set (J1). Figure for the abbreviation: Figure 6a

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. While blades made of metallic material have good mechanical resistance, they nevertheless have the disadvantage of having a relatively large mass.

[0012] Manufacturing blades from composite material 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 through the sleeve along a shimming axis, the recess being delimited by an internal wall of the sleeve;

[0017] - a fibrous structure obtained by weaving, preferably three-dimensional, fibers, the fibrous structure comprising a blade root including an attachment portion tubular 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 base;

[0018] - a first 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 first insert and the inner wall of the sleeve,

[0019] - a polymerized resin for solidifying the fibrous structure and bonding from the first insert to the fibrous structure and the inner wall of the sleeve, so as to form a main force path, called the default path, during the transmission of a torque reaction force around the alignment axis between the blade root and the sleeve, and

[0020] - a second insert centered on the alignment axis and inserted axially into the housing of the attachment portion, or even in the recess of the sleeve, this second insert cooperating by complementarity of shapes with the attachment portion, or even also with the inner wall of the sleeve, and being separated from the attachment portion, or even also from the inner wall of the sleeve, by at least one circumferential clearance around the alignment axis so as to form a secondary force path, said to be on standby, when transmitting a torque recovery force around the alignment axis between the blade root and the sleeve, the secondary force path being used when the first main force path disappears and said at least one circumferential clearance is eliminated.

[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 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 result in a loss of control over the blade pitch.

[0023] The invention thus proposes to integrate a secondary force path, in standby, in order to take up this torque in the event of a break in the glued interface between the attachment portion of the blade foot and the sleeve.

[0024] This is achieved by means of a second insert which is brought in to ensure a secondary torque recovery path.

[0025] The blade according to the invention may comprise one or more of the following features, taken individually or in combination with each other: • the second insert is also inserted axially into the recess of the sleeve, this second insert cooperating by complementary shapes with the inner wall of the sleeve and being separated from this inner wall by at least a circumferential clearance around the shimming axis so that the secondary force path passes from the attachment portion to the second insert and then from the second insert to the inner wall of the sleeve; • the second insert is inserted both into the housing of the attachment portion and into the recess of the sleeve so that the secondary force path passes from the attachment portion to the second insert and then from the second insert to the inner wall of the sleeve; • the second insert is inserted only into the housing of the attachment portion so that the secondary force path passes from the attachment portion to the second insert, from the second insert to the attachment portion, and then from the attachment portion to the inner wall of the sleeve; • the outer periphery has a polygonal, elliptical, etc. contour; • the second insert includes a second floor engaged in a second female imprint of the attachment portion and comprising an external periphery with a non-circular contour which cooperates by complementary shapes with circumferential play with the second female imprint; • the second insert includes a second stage engaged in the inner wall of the sleeve and having an external periphery with a non-circular contour which cooperates by complementary shapes with circumferential play with the inner wall; • the second floor has a larger diameter than the first floor; • the second insert is glued to the attachment portion and / or to the inner wall of the sleeve; • the blade also includes a locking device for the second insert in the housing of the attachment portion; • the locking device is a split ring which is engaged in an annular groove in the inner wall of the sleeve, which opens radially inwards, this ring being able to cooperate by abutment in the axial direction with the second insert in order to retain it axially in the housing of the attachment portion;

[0026] — an adhesive film can be intercalated between the fibrous structure and the sleeve.

[0027] The present invention also relates to a method for manufacturing a blade as described above, comprising the following steps:

[0028] - to produce the fibrous structure comprising the attachment portion by weaving, of three-dimensional preference,

[0029] - insert the attachment portion into the recess in the sleeve and against the inner wall,

[0030] - position the first insert in the recess so that the portion the attachment is radially interposed between the first insert and the inner wall of the sleeve,

[0031] - insert the fibrous structure, the sleeve and the insert into a mold and inject the resin is placed in the mold to solidify the fibrous structure and to bond the first insert to the fibrous structure and the inner wall of the sleeve.

[0032] - insert and glue the second insert into a hollowed-out part of the attachment portion, or also in the hollowing of the sleeve, so that the second insert cooperates by complementarity of shapes with this hollowed part, or even also with the inner wall of the sleeve, and is separated from this hollowed part, or even from the inner wall, by at least a circumferential gap.

[0033] The method according to the invention may comprise one or more of the following features, taken individually or in combination with each other: • the said hollowed-out part is obtained using the said mold; • before inserting and gluing the second insert, the attachment portion is machined to form the said hollowed-out part; • before inserting the fibrous structure, the sleeve and the insert into the mold, a plug is mounted axially in the sleeve to cover part of the inner wall and prevent it from being covered with resin, this plug being removed before machining the attachment portion; • the plug covers and protects said groove, the process further comprising, after inserting and gluing the second insert, mounting the locking ring in this groove; • before machining the attachment portion, this attachment portion extends axially beyond the sleeve and includes a portion projecting axially outside the sleeve; • before machining the attachment portion, this attachment portion is axially recessed relative to a free end of the sleeve;

[0034] — an adhesive film can be intercalated between the fibrous structure and the inner wall of the sleeve. Brief description of the figures

[0035] 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:

[0036] [Fig. 1] [Fig. 1] schematically represents an example of an engine including an unfaired fan;

[0037] [Fig.2] [Fig.2] schematically represents a blower blade according to an embodiment of the invention assembled to a shimming mechanism;

[0038] [Fig.3] [Fig.3] schematically represents a blower blade according to a first embodiment of the invention;

[0039] [Fig.4a] Fig.4a schematically represents a sleeve according to a first embodiment of the invention in perspective view;

[0040] [Fig.4b] Fig.4b schematically represents the sleeve of Fig.4a in a profile view;

[0041] [Fig.4c] Fig.4c schematically represents the sleeve of figures 4a and 4b into which the attachment portion and the insert are inserted;

[0042] [Fig.4d] Fig.4d schematically represents the sleeve / portion of attachment / insert assembly of Fig.4c inserted into the shimming mechanism;

[0043] [Fig.5] Fig.5 schematically represents an insert according to one embodiment of the invention;

[0044] [Fig.6a] Fig.6a schematically and partially represents a blade according to a first embodiment of the invention;

[0045] [Fig.6b] The [Fig.6b] is a larger scale view of part of the [Fig.6a];

[0046] [Fig.7] Fig.7 schematically represents a manufacturing step of the dawn of the [Fig.6a];

[0047] [Fig.8a] Fig.8a is a schematic cross-sectional view along line AA of the [Fig.6b];

[0048] [Fig.8b] Fig.8b is a schematic cross-sectional view along line BB of the [Fig.6b];

[0049] [Fig.9a] Fig.9a schematically and partially represents a blade according to a second embodiment of the invention;

[0050] [Fig.9b] The [Fig.9b] is a larger scale view of part of the [Fig.9a];

[0051] [Fig. 10] Fig. 10 schematically represents a manufacturing step of the dawn of the [Fig.9a];

[0052] [Fig. 11] Fig. 11 is a schematic cross-sectional view along line CC of the [Fig.9a];

[0053] [Fig. 12] The [Fig. 12] schematically represents a method for manufacturing a blade according to an embodiment of the invention;

[0054] [Fig. 13a] Fig. 13a shows the blade obtained according to the process of Fig. 12 in front view; and

[0055] [Fig. 13b] The [Fig. 13b] represents the blade obtained according to the process of [Fig. 12] in profile view. Detailed description of the invention

[0056] 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]).

[0057] 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.

[0058] 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).

[0059] 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.

[0060] The invention is applicable to turboprop type architectures (comprising a single fan rotor).

[0061] 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.

[0062] 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, by means of balls 11 or other rolling elements.

[0063] 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, it generates lift. Conversely, the blade foot 9 is designed to extend out of the air stream.

[0064] 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 a variable pitching mechanism of a turbomachine, 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 pitching axis Y.

[0065] With reference to Figures 3, 4c and 4d, the blade 7 also comprises a fibrous structure 20 obtained by weaving, preferably three-dimensional. The fibrous structure 20 comprises a blade root 22 including an attachment portion 23 configured to be inserted into the recess 17 formed by the attachment portion 14 of the sleeve 13.

[0066] The fibrous structure 20 has a tubular shape and includes a housing 20a centered on the alignment axis Y.

[0067] The fibrous structure 20 also includes a blade 21 with an aerodynamic profile connected to the blade root 22.

[0068] The blade 7 also includes a first 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 first insert 24 and the inner wall 18 of the sleeve 13.

[0069] The blade 7 further includes a polymerized resin for solidifying the fibrous structure 20 and for bonding the first insert 24 to the fibrous structure 20 and to the inner wall 18 of the sleeve 13.

[0070] 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.

[0071] The blade 7 is thus formed of few elements which fit together to form a single-piece blade. Since the blade 21 and the blade root 22 are formed by 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 first insert 24 and the sleeve 13, and the fibrous structure 20 is thus securely joined to the blade root 9.

[0072] 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.

[0073] 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, by Examples include 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.

[0074] 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 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.

[0075] 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.

[0076] 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 30 having different reliefs.

[0077] The fastening 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.

[0078] 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.

[0079] The mounting portion 14 also includes a first circular groove 32 and a second circular groove 34 for forming a raceway on at least one bearing, for example a ball bearing. The mounting portion 14 thus allows the blade foot 9 to be rotatably mounted inside the attachment device 10 provided in the hub 6.

[0080] The sleeve 13 is preferably metallic and monolithic.

[0081] 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 first insert 24 is positioned in the recess 17. The part of the wall 18 which has a constant diameter then forms a stop for the extra thickness 23”.

[0082] The recessed portion may have another shape and may be placed in another position along the wall 18.

[0083] 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 first insert 24 to be blocked and the attachment portion 23 to be wedged against the wall 18 in an optimized manner.

[0084] Fig. 4d represents the sleeve into which the attachment portion 23 and the first insert 24 are inserted, the sleeve being arranged in the attachment device 10, the rolling elements 11 being arranged in the circular grooves 32 and 34.

[0085] With reference to [Fig. 5], the first 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 end. According to the variant in which the sleeve 13 has a stop, the rounded locking end 42 allows the first insert 24 to wedge the attachment portion 23 against the stop.

[0086] Alternatively, the locking end may have another shape that can adapt to a stop that may also have another shape.

[0087] The first insert 24 is preferably metallic.

[0088] Figures 6a and 6b represent a first embodiment of the blade 7 according to the invention. In [Fig. 6a], the invention is shown to the right of the Y-axis and differs from the configuration described above, which is located to the left of the Y-axis. [Fig. 6b] is a larger-scale view and allows for a better visualization of the features of the invention.

[0089] The blade 7 includes a second insert 60 centered on the alignment axis Y and inserted axially on one side into the housing 20a of the attachment portion 23 ([Fig.6b]).

[0090] The second insert 60 is configured to cooperate by complementarity of shapes with the attachment portion 23 and is separated from the attachment portion 23 by at least one circumferential clearance J1 around the mounting axis Y, as illustrated in [Fig.8a].

[0091] This allows a secondary force path, called standby, to be formed when a torque recovery force is transmitted around the yaw axis Y between the blade root 22 and the sleeve 13. This secondary force path is used when the first main force path disappears and the circumferential play J1 is eliminated.

[0092] In this embodiment, the second insert 60 is also inserted axially into the recess 17 of the sleeve 13. The second insert 60 is further configured to cooperate directly with the inner wall 18 of the sleeve 13 by complementary shapes. sleeve 13 and is separated from this inner wall 18 by at least one circumferential clearance J2 around the shimming axis Y, as illustrated in [Fig.8b].

[0093] This allows the formation of a secondary force path, referred to as a standby force path, during the transmission of a torque reaction force around the yaw axis between the blade root 22 and the sleeve 13. This secondary force path is used when the first primary force path disappears and the circumferential clearances J1, J2 are eliminated. This force path passes from the attachment portion 23 to the second insert 60 and then from the second insert 60 to the inner wall 18 of the sleeve 13 as illustrated by the double-dash arrows in [Fig. 6b].

[0094] In the example shown, the second insert 60 has a stepped shape and includes a first step 60a engaged in a first female impression of the attachment portion 23 and having an external periphery with a non-circular contour which cooperates by complementarity of shapes with circumferential play J1 with the first female impression ([Fig.8a]).

[0095] The outer periphery may have a polygonal, elliptical, etc. contour.

[0096] In the example shown, the second insert 60 comprises a second stage 60b engaged in a second female recess in the inner wall 18 of the sleeve 13 and having an external periphery with a non-circular contour which cooperates by complementary shapes with circumferential clearance J2 with the second female recess ([Fig. 8b]). The second stage 60b here has a diameter greater than the first stage 60a.

[0097] In the embodiment shown in Figures 9a and 9b, the second insert 60 is inserted only in the housing 20a of the attachment portion 23 so that the secondary force path passes from the attachment portion 23 to the second insert 60, from the second insert 60 to the attachment portion 23, and then from the attachment portion 23 to the inner wall 18 of the sleeve 13, as illustrated by the double-lined arrows in [Fig.9b].

[0098] The second insert 60 comprises a second stage 60b engaged in a second female recess of the attachment portion 23 and having a non-circular outer periphery which cooperates by complementary shapes with circumferential clearance J2 with the second female recess ([Fig. 8b]). The second stage 60b has a diameter greater than the first stage 60a.

[0099] The second insert 60 is preferably glued to the attachment portion 23 and / or to the inner wall 18 of the sleeve 13.

[0100] In the embodiment of figures 6a and 6b, the blade 7 further includes a device 62 for locking the second insert 60 in the housing 20a of the attachment portion 23.

[0101] In the example shown, the locking device 62 is a split ring which is engaged in an annular groove 18a of the inner wall 18 of the sleeve 13. The Groove 18a opens radially inwards. Device 62 is able to cooperate by means of an axial stop with the second insert 60 in order to retain it axially in the housing 20a of the attachment portion 23.

[0102] Reference is now made to [Fig. 12] which represents steps of a manufacturing process 50 of a blade 7 according to the invention.

[0103] The process includes a step 51 consisting of producing the fibrous structure 20 comprising the attachment portion 23 by weaving, preferably three-dimensional, the attachment portion 23 being produced by forming, for example, unlinking in the weaving.

[0104] The method 50 then includes step 52 of inserting the attachment portion 23 into the recess 17 of the sleeve 13 and positioning said attachment portion 23 against the inner wall 18. An adhesive film not shown may be intercalated between the attachment portion 23 of the fibrous structure 20 and the inner wall 18 of the sleeve 13.

[0105] In a step 53, the first insert 24 is positioned in the recess 17 so that the attachment portion 23 is intercalated radially between the first insert 24 and the inner wall 18 of the sleeve 13.

[0106] Once the fibrous structure 20, the sleeve 13 and the first insert 24 are assembled, the blade 7 thus formed is inserted into a mold 64 in a step 55, and a liquid resin is then injected into the mold 64 according to the RTM process to obtain the one-piece blade 7 shown in Figures 13a and 13b. The resin can be, in particular, an epoxy resin, a thermoplastic resin or a polybismaleimide (BMI) resin.

[0107] During the injection of the resin, the latter impregnates the entire fibrous structure 20 and thus inserts itself in particular between the first insert 24 and the wall 18 and around the attachment portion 23. The resin thus makes it possible to maintain the various assembled elements, namely the fibrous structure 20, the sleeve 13 and the first insert 24, in a single block.

[0108] In a subsequent step 56, the attachment portion 23 is machined in particular to form the aforementioned impression or impressions intended to cooperate by complementarity of shapes with the second insert 60.

[0109] Alternatively, the hollowed part formed by the aforementioned impression or impressions could be obtained using the mold 64 and thus be obtained directly by the molding step.

[0110] The process then includes a step 57 in which the second insert 60 is inserted and glued into the hollowed / machined part of the attachment portion 23, or even also into the recess 17 of the sleeve 13, so that the second insert 60 cooperates by complementarity of shapes with this hollowed / machined part, or even also with the internal wall 18 of the sleeve 13, and is separated from it or even by the circumferential gap(s) J1, J2, J3 mentioned above.

[0111] The adhesive for fixing the second insert 60 can be of the hot-curing or room-temperature type.

[0112] Before step 55, a plug 70 can be axially mounted in the sleeve 13 as illustrated in Figures 7 and 9. The function of this plug 70 is to cover a portion of the inner wall 18 of the sleeve 13 and to prevent it from being covered with resin during the injection of the latter. The plug 70 is intended to be removed before machining the attachment portion 23 in step 56.

[0113] In the embodiment of figures 6a, 6b, and 7, the plug 70 covers and protects the mounting groove 18a of the device 62. In this embodiment, it is understood that the device 62 is mounted in the groove 18a after inserting and gluing the second insert 60.

[0114] In the examples shown, the plug 70 has a tubular shape and an axially general L-shaped shape. It comprises a cylindrical wall engaged in the sleeve 13 and on the internal wall 18, and an external annular rim which bears axially on the free end 13' of the sleeve 13.

[0115] In [Fig.7], it can be seen that the attachment portion 23 is axially recessed relative to the free end 13' of the sleeve 13. It is this axially recessed portion that will be machined in step 56 during the process.

[0116] In the variant of [Fig. 10], it can be seen that the attachment portion 23 is axially projecting outside the sleeve 13. It is this axially projecting portion that will be machined in step 56 during the process.

Claims

1. Demands 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 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 of the sleeve (13); - a fibrous structure (20) obtained by weaving fibers, 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 alignment axis (Y), the fibrous structure (20) further comprising an aerodynamically profiled blade (12) connected to the blade root (22); - a first 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 interposed between the first insert (24) and the inner wall (18) of the sleeve (13), - a polymerized resin for solidifying the fibrous structure (20) and for bonding the first insert (24) to the fibrous structure (20) and to the inner wall (18) of the sleeve (13), so as to form a principal load path, referred to as the default load path, during the transmission of a torque reaction force around the alignment axis (Y) between the blade root (22) and the sleeve (13), and - a second insert (60) centered on the alignment axis (Y) and inserted axially into the housing (20a) of the attachment portion (23), or even also into the recess (17) of the sleeve (13), this second insert (60) cooperating by complementary shapes with the attachment portion (23), or even also with the inner wall (18) of the sleeve (13), and being separated from the attachment portion (23), or even also from the inner wall (18) of the sleeve (13), by at least one circumferential clearance (J1, J2, J3) around the alignment axis (Y) so as to form a secondary load path, called a standby load path, during the transmission of a torque reaction force around the alignment axis (Y) between the blade root (22) and the sleeve (13), the secondary load path being used when the first load path main disappears and that said at least one circumferential set (J1, J2, J3) is removed.

2. Blade according to claim 1, wherein the second insert (60) is inserted both in the housing (20a) of the attachment portion (23) and in the recess (17) of the sleeve (13) so that the secondary force path passes from the attachment portion (23) to the second insert (60) and then from the second insert (60) to the inner wall (18) of the sleeve (13).

3. Blade according to claim 1, wherein the second insert (60) is inserted only in the housing (20a) of the attachment portion (23) so that the secondary force path passes from the attachment portion (23) to the second insert (60), from the second insert (60) to the attachment portion (23), and then from the attachment portion (23) to the inner wall (18) of the sleeve (13).

4. Blade according to any one of the preceding claims, wherein the second insert (60) has a stepped shape and comprises a first stage (60a) engaged in a first female imprint of the attachment portion (23) and having an external periphery with a non-circular contour which cooperates by complementarity of shapes with circumferential clearance (Jl) with the first female imprint.

5. Blade according to claim 4, wherein the outer periphery has a polygonal or elliptical contour.

6. Blade according to claim 4 or 5, depending on claim 3, wherein the second insert (60) comprises a second stage (60b) engaged in a second female recess of the attachment portion (23) and having an external periphery with a non-circular contour which cooperates by complementarity of shapes with circumferential clearance (J3) with the second female recess.

7. Blade according to claim 4 or 5, depending on claim 2, wherein the second insert (60) comprises a second stage (60b) engaged in the inner wall (18) of the sleeve (13) and having an outer periphery with a non-circular contour which cooperates by complementarity of shapes with circumferential clearance (J2) with the inner wall (18).

8. Blade according to claim 6 or 7, wherein the second stage (60b) has a diameter greater than the first stage (60a).

9. Blade according to any one of the preceding claims, wherein the second insert (60) is glued to the attachment portion (23) and / or to the inner wall (18) of the sleeve (13).

10. Blade according to any one of the preceding claims, wherein it further comprises a device (62) for locking the second insert (60) in the housing (20a) of the attachment portion (23).

11. Blade according to claim 10, wherein the locking device (62) is a split ring which is engaged in an annular groove (18a) of the inner wall (18) of the sleeve (13), which opens radially inwards, this ring being able to cooperate by abutment in the axial direction with the second insert (60) in order to retain it axially in the housing (20a) of the attachment portion (23).

12. A method for manufacturing a blade according to any one of the preceding claims, comprising the following steps: - producing (51) the fibrous structure (20) including the attachment portion (23) by weaving, - inserting (52) the attachment portion (23) into the recess (17) of the sleeve (13) and against the inner wall (18), - positioning (53) the first insert (24) in the recess (17) so that the attachment portion (23) is radially intercalated between the first insert (24) and the inner wall (18) of the sleeve (13), - inserting (55) the fibrous structure (20), the sleeve (13) and the insert (24) into a mold (64) and injecting the resin into the mold (64), so as to solidify the fibrous structure (20) and to bond the first insert (24) to the fibrous structure (20) and to the inner wall (18) of the sleeve (13), - machine (56) the attachment portion (23), - insert (57) and glue the second insert (60) into a hollowed-out part of the attachment portion (23),even also in the recess (17) of the sleeve (13), so that the second insert (60) cooperates by complementary shapes with this recessed part, or even also with the internal wall (18) of the sleeve (13), and is separated from this recessed part, or even from the internal wall (18), by at least one circumferential gap (J1, J2, J3).

13. Manufacturing method according to claim 12, wherein said hollowed part is obtained by means of said mold (64).

14. A manufacturing method according to claim 12, wherein, before inserting (55) and gluing the second insert (60), the attachment portion (23) is machined to form said hollowed part.

15. A manufacturing method according to the preceding claim, wherein, before inserting (55) the fibrous structure (20), the sleeve (13) and the insert (24) into the mold, a plug (70) is mounted axially in the sleeve (13) to cover a part of the inner wall (18) and prevent it from being covered with resin, this plug (70) being removed before machining the attachment portion (23).

16. A manufacturing method according to the preceding claim, the blade (7) being as defined in claim 11, wherein the plug (70) covers and protects said groove (18a), the method further comprising, after inserting and gluing the second insert (60), mounting the locking ring in this groove (18a).

17. A manufacturing method according to claim 15 or 16, wherein, before machining (56) the attachment portion (23), this attachment portion (23) extends axially from the sleeve (13) and includes a portion projecting axially outside the sleeve (13).

18. A manufacturing method according to claim 15 or 16, wherein, before machining (56) the attachment portion (23), this attachment portion (23) is axially recessed relative to a free end of the sleeve (13).

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