AIRCRAFT TURBOMACHINE COMPRISING VARIABLE-PITCH PROPELLER BLADES

Abstract

Assembly comprising a propeller blade (10) and a system (34) for angularly setting the blade (10), for an aircraft turbomachine, the blade (10) having a root (14) extending from an upper end connected to a blade (12) of the blade (10) to a free lower end (28), the root (14) having a swollen section, called a "bulb (32)", the system (34) allowing angular setting of the blade (10) around a setting axis (A) and comprising a mechanism (90) for preloading the blade root equipped with an elastically deformable interface part (120). Figure for the abstract: Figure 6

Description

Title of the invention: AIRCRAFT TURBOMACHINE COMPRISING VARIABLE-PITCH PROPELLER BLADES Technical field of the invention

[0001] The present invention relates to the field of aircraft turbomachines and in particular to the propulsion propellers of these turbomachines which comprise variable-pitch blades. Technical background

[0002] An aircraft turbomachine propeller may be shrouded, as is the case with a fan for example, or unshrouded as is the case with an open-rotor type architecture for example.

[0003] A propeller comprises blades which can be variable pitch. The turbomachine then comprises a mechanism for modifying the pitch angle of the blades in order to adapt the thrust generated by the propeller according to the different phases of flight.

[0004] The design of a propeller blade involves several disciplines whose objectives are generally antagonistic. It must allow optimal aerodynamic performance (i.e. provide thrust while maximizing efficiency), guarantee mechanical strength of the blade (i.e. withstand the mechanical constraints resulting from static and dynamic loadings) while limiting the mass as well as the acoustic signature. In particular, the improvement of the aerodynamic performance of the propeller tends towards an increase in the BPR (By Pass Ratio), which results in an increase in its external diameter and therefore in the span of the blades.

[0005] At the same time, on certain turbomachine architectures, engine start-up is carried out at a very open pitch, known as feather pitch. Indeed, this starting position makes it possible to consume power by the torque, which ensures machine safety by guaranteeing low propeller speeds. More precisely, according to simple considerations, the power is proportional to the product of the speed and the torque. However, the torque increases with the incidence, which can be increased via the pitch. Indeed, those skilled in the art of aerodynamics understand that the resulting force on a blade profile is, as a first approximation, perpendicular to the chord and can be broken down into two components: the thrust along the engine axis and the drag of the blade in the plane of the propeller. Thus, with the increase in the pitch of the blades, the resulting force moves towards the plane of the propeller, which has the effect of increasing the drag of the aerodynamic profile and reducing the thrust.

[0006] Therefore, in the case of a feathered start, the thrust generated by the propeller is zero, the torque is maximum and the rpm is minimum. However, the incidence becomes so high that the blades then undergo a strongly separated turbulent aerodynamic flow which generates a strong vibratory excitation. This excitation is both broadband due to the small vortices of the separated zone, but also intense on certain particular frequencies due to the large Karman recirculations which cause the aerodynamic force to oscillate significantly. In particular, on blades with a wide chord and a large span which generate a lot of drag, this force is intense although the rpm is not high.

[0007] In current technology, it is common to fix a blade to its support by a so-called broached attachment. The blade comprises a foot which has a general dovetail shape and which is intended to be engaged by complementary shapes in a cell of the support, this cell being conventionally produced by broaching.

[0008] For a blade with a pinned attachment, this aerodynamic force is so intense that it can cause rigid solid movements of the blade root in its cell which are similar to swiveling. Indeed, during a feather start, the reduced speed of the fan does not allow sufficient centrifugal force to be generated to prevent these movements induced by the aerodynamic force. This results in frictional damage to the blade and the shim inserted between the root and the bottom of the cell, in just a few cycles. For the same reasons, this problem may arise in a freewheeling situation (or "windmilling") following an engine failure because variable pitch blades are generally equipped with a feather return system.

[0009] In addition, intense vibration excitation can also occur at much higher rotational speeds on unducted architectures due to the effects of engine installation on the aircraft and the direction of the upstream infinite flow. Indeed, an unducted engine is subject to the influence of the ground and the fuselage, which causes a distortion in the supply of the propeller, in flow speed, according to the engine azimuths. This results in a vibration response of the propeller blades on the first engine orders IN, 2N and 3N (possibly more). On the other hand, in the absence of an air intake sleeve, the direction of the air flowing through the blades is not parallel to the engine axis. This sideslip angle results in so-called "IP" forces which cause a vibration response of the propeller blades on the engine order IN.Similarly, these IP forces can also occur during the aircraft's climb or approach phases because the air flows through the blades at an angle of incidence. These high-speed vibration excitations can cause the same friction damage discussed above if the blade attachment is not suitable.

[0010] For all of these reasons, the broached attachment is not a solution as it stands. viable for variable pitch, wide chord, large span propeller blades.

[0011] There is therefore a need for a variable pitch propeller blade attachment technology that limits blade swiveling during all flight phases that are likely to excite blade vibration modes.

[0012] Furthermore, it is also known to encase the blade root in a barrel which matches the shape of the root, generally a metal barrel. Such a barrel makes it possible in particular to ensure the connection between the blade root and the internal ring of a guide bearing to allow the angular setting of the blade relative to the hub. Such a barrel is fixed to the blade root with numerous precautions to limit as much as possible the creation of a swivel between the blade and the barrel.

[0013] However, regardless of the precautions taken, it is often observed that the blade can oscillate with a certain amount of travel in the shaft. There is therefore a need to ensure that the swiveling of the blade is limited as much as possible relative to the internal guide bearing ring.

[0014] The Applicant has proposed in application WO-A1-2022 / 0182355 an assembly formed by a blade and its angular wedging system, which makes it possible to resolve at least some of these drawbacks. In this solution, the wedging system comprises an upper crown and a lower seat between which the root of the blade is clamped. A preload is thus applied to the root of the blade. In this way, it is guaranteed that the root is fixed to the system without play, which prevents the blade from rotating in the system. This differs in particular from prior art embodiments in which the root is enclosed in an attached barrel.

[0015] The preload force must be maintained at the highest rotation speeds which correspond to the maximum loads in centrifugal force. This force is applied in the same direction and in the same sense as the preload force. However, since the solids involved are not non-deformable, the centrifugal force induces a compressive deformation of the blade root. The latter therefore tends to move and potentially lead to the loss of the preload.

[0016] There is therefore a need to improve the assembly to guarantee the durability of the clamping force applied during assembly of the blade, in particular during the different rotation speeds. Summary of the invention

[0017] The invention proposes an assembly comprising a propeller blade and a system for angularly setting the blade, for an aircraft turbomachine, the blade having a root extending from an upper end linked to a blade of the blade to a free lower end, the root having a swollen section, called a "bulb", the system allowing angular setting of the blade around a setting axis and comprising:

[0018] - a bowl which is radially delimited by an annular wall extending around the axis of wedging, the bowl comprising a lower base closed by a base wall and an upper opening through which the bulb is intended to be inserted axially into the bowl;

[0019] - an annular retention ring which extends around the bulb the ring of retention being at least limited in axial movement towards the opening relative to the bowl, the retention ring having an annular bearing face which restricts the passage section of the opening and which is intended to be in axial contact with an upper face of the bulb to block the axial movement of the foot towards the opening; and

[0020] - a lower seat carried by a part separate from the retention ring and the bowl and intended to be in axial contact with a lower face of the bulb to block the axial movement of the foot on the side opposite the opening, the seat being mounted to move in axial translation relative to the bowl by means of at least one clamping mechanism to allow axial clamping of the bulb between the seat and the retention ring,

[0021] characterized in that the clamping mechanism comprises two nuts, respectively internal and external, which are screwed into each other and extend around the wedging axis, the external nut being locked in rotation with respect to the bowl and in axial support on an annular face of the bowl oriented towards the opening, and the internal nut being locked in rotation with respect to the part carrying the seat, this part being in axial support on the internal nut by means of at least one interface part, this interface part being elastically deformable and capable on the one hand of compressing axially during axial tightening of the bulb, and on the other hand of expanding axially when this tightening is released.

[0022] To maintain the preload force of the root regardless of the rotation speed, the system therefore includes an interface part which provides flexibility in the tightening direction to adapt to the deformation undergone by the blade root in order to ensure maximum continuity of the transfer of the preload force.

[0023] The wedging system thus makes it possible on the one hand to provide high elastic resistance in order to transfer the preload force without plasticizing, and on the other hand to provide sufficient flexibility in order to adapt to the deformations of the blade root.

[0024] The assembly according to the invention may comprise one or more of the following characteristics, taken in isolation from one another, or in combination with one another: • the interface part is annular and extends around the wedging axis; • the interface part has a general ring shape; • the interface part is made from a material or from an element chosen from: an elastomer, a laminated structure based on elastomer and metal, an organic matrix composite preferably with short fibers, dry fibers preferably made of aramid, and a Kevlar® nitrile rubber; • the seat is formed by a truncated cone-shaped wall of the part which is flared on the opening side and which includes an internal truncated cone-shaped surface resting on the lower face of the bulb; • the part further comprises a cylindrical wall which is connected to the internal periphery of the frustoconical wall, the interface part being axially interposed between this cylindrical wall and the internal nut, and preferably between this cylindrical wall and an internal annular rim of the internal nut; • the interface part extends in the extension of the cylindrical wall of the part carrying the seat; • the external nut is locked in rotation relative to the bowl by a first dog system, and / or the internal nut is locked in rotation relative to the part by a second dog system; • the first dog system comprises first projecting teeth carried by the external nut and housed in housings of the bowl, these first projecting teeth being oriented radially outwards relative to the wedging axis, and the second dog system comprises second projecting teeth carried by the internal nut and housed in housings of the part carrying the seat, these second projecting teeth being oriented axially towards the opening of the bowl; • the housings of the part carrying the seat are located at the intersection between the truncated and cylindrical parts of this part; • the interface part is capable of being confined radially between two rigid cylindrical skins, respectively of the internal nut and of said part; this configuration is advantageous for continuing to use the properties of the interface part even if the latter is damaged and for example cut to the extent that the interface part is trapped in the mounting position.

[0025] The present invention also relates to an aircraft turbomachine, comprising a propeller comprising assemblies as described above. Brief description of the figures

[0026] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0027] [Fig-1] [Fig.l] is a schematic perspective view of a propeller blade for an aircraft turbomachine, and illustrates the present invention,

[0028] [Fig.2] [Fig.2] is an enlarged view of part of [Fig.l] and shows the foot of dawn,

[0029] [Fig.3] [Fig.3] is a cross-sectional view along the section plane Pb of the [Fig.4] which represents the shape and position of the free lower end of the foot in relation to the wedging axis,

[0030] [Fig.4] [Fig.4] is an axial sectional view showing the root of the blade of the [Fig.l] fixed in a bowl of a wedging system,

[0031] [Fig.5] [Fig.5] is a perspective view showing the bowl of [Fig.4],

[0032] [Fig.6] [Fig.6] is a view similar to that of [Fig.4] and represents a mode of production of an assembly according to the invention,

[0033] [Fig.7] [Fig.7] is an enlarged view of part of [Fig.6],

[0034] [Fig.8] [Fig.8] is a very schematic representation of the force paths at within the assembly according to the invention, and

[0035] [Fig.9] [Fig.9] is a view similar to that of [Fig.7] and illustrates a variant of production of an assembly according to the invention. Detailed description of the invention

[0036] In the remainder of the description, elements having an identical structure or similar functions will be designated by the same reference.

[0037] In the remainder of the description, an axial orientation directed along the blade setting axis "A" will be adopted, without limitation, from the bottom, near the blade root, to the top, near the free end of the blade. Radial directions extending orthogonally to the setting axis will also be adopted from the inside, near the setting axis, to the outside.

[0038] [Fig.l] shows a blade 10 for a propeller of an aircraft turbomachine, this propeller being shrouded or unshrouded.

[0039] The blade 10 comprises a blade 12 connected to a foot 14.

[0040] The blade 12 has an aerodynamic profile and comprises a lower surface 12a and an upper surface 12b which are connected by an upstream leading edge 12c and by a downstream trailing edge 12d, the terms upstream and downstream referring to the flow of gases around the blade 12 in operation.

[0041] The blade 12 has an upper end which is free, called the apex, and a lower end which is connected to the root 14.

[0042] In the example shown, the blade 10 is made of composite material by an injection process called the RTM process (acronym for Resin Transfer Molding). This process consists of preparing a fiber preform 18 by three-dimensional weaving and then placing this preform in a mold and injecting a resin into it. polymerizable such as an epoxy resin, which will impregnate the preform. After polymerization and hardening of the blade 12, its leading edge 12c is generally reinforced by a metal shield 20 added and fixed, for example by gluing.

[0043] The blade 10 here comprises a spar 22. The spar 22 comprises a portion forming a core of the blade 12. The portion of the spar 22 forming the core of the blade 12 is intended to be inserted into the preform 18 before the injection of resin. The spar 22 also comprises a portion which extends on the side opposite the top of the blade 12 to form the root 14.

[0044] The spar 22 is preferably made of composite material. It is, for example, a composite material with an epoxy organic matrix reinforced by 3D woven carbon fibers with the warp direction predominantly oriented radially and the weft predominantly oriented along the chord of the blade 12 at the height of the aerodynamic vein.

[0045] Alternatively, the spar can also be formed by a more mechanically advantageous assembly of different organic matrix composite materials (thermosetting, thermoplastic or elastomer) reinforced with long fibers (carbon, glass, aramid, polypropylene) according to several fiber arrangements (woven, braided, knitted, unidirectional).

[0046] Although not shown, the blade 12 may be hollow or solid and includes an internal cavity filled with a foam or honeycomb type filler material. This filler material is installed around the spar 22 and is covered with a skin made of organic matrix composite material to increase the impact resistance of the blade 12.

[0047] The shield 20 may be titanium or titanium alloy, stainless steel, steel, aluminum, nickel, etc. The intrados 12a or even the extrados 12b of the blade 12 may be covered with a polyurethane film for protection against erosion.

[0048] The foot 14 is here devoid of an annular metal shaft surrounding it.

[0049] The axis "A" is an axis of elongation of the blade 10 and of the blade 12 and in particular a axis "A" of setting of the blade 10, that is to say the axis around which the angular position of the blade 10 is adjusted. It is generally also a radial axis which therefore extends along a radius relative to the axis of rotation of the propeller equipped with this blade 10.

[0050] Foot 14 has a particular shape better visible in [Fig.2]. Foot 14 essentially comprises three parts, namely:

[0051] - a free lower end 28 located on the side opposite the blade 12,

[0052] - an upper stilt 30 located on the side of the blade 12, and

[0053] - a swollen section, called a "bulb" 32, located between the free end 28 and Péchasse 30.

[0054] The free end 28 has a generally parallelepiped shape in the example re presented. As can be seen in [Fig.3], this free end 28 is offset or offset from the "A" alignment axis to achieve keying or indexing, as will be explained in more detail below.

[0055] Referring to [Fig.4], Pb is defined as a transverse plane, that is to say a plane perpendicular to the wedging axis "A", passing substantially through the middle of the free end 28, measured along the wedging axis "A". This plane Pb is called the low or lower plane. [Fig.3] shows the cross-sectional shape of the free end 28 in this plane Pb. This section, called the low section, has a value or an area, for example maximum, noted Sb and has a generally rectangular shape in the example shown.

[0056] As will also be described below, the free end 28 is configured to cooperate with a system 34 for angularly setting the blade 10.

[0057] Referring again to [Fig.2], Péchasse 30 has a relatively complex shape which allows the transition to be made between the foot 14 and the spar part 22 forming the core of the blade 12. The stilt 30 schematically comprises:

[0058] - two lateral flanks 30a, 30b, located respectively on the side of the intrados 12a and the extrados 12b of the blade 12, which converge towards each other along the pitch axis "A" and towards the top of the blade 12, and

[0059] - two edges, respectively upstream 30c and downstream 30d, which on the contrary diverge from one another on the other along the "A" setting axis and towards the top of the blade 12.

[0060] With reference to [Fig.4], we define Ph as a transverse plane passing through Péchasse 30, and in particular the lower end of Péchasse 30. This plane Ph is called the high or upper plane. In this plane, Péchasse 30 may have a non-circular section shape, for example oval, oblong, square or rectangular. This section, called the high section, has a value or an area, for example maximum, noted Sh.

[0061] The bulb 32 has a generally swollen or domed shape, this swollenness or doming extending all around the wedging axis "A".

[0062] Pm is defined as a median plane passing through the bulb 32, and in particular in its part of largest cross-section, subsequently called the middle section, which is noted Sm. This plane Pm is called the mean plane. In this plane, the bulb 32 may have a circular cross-section, although this section is not limiting.

[0063] It is understood that the plane Pm is located between the planes Pb and Ph. The maximum dimensions of the cross-section of the bulb 32 decrease from the plane Pm (Sm) to the plane Ph, as well as from the plane Pm, to the plane Pb. It is therefore understood that Sm is greater than Sb and Sh. Furthermore, in the example shown, Sh is greater than Sb.

[0064] The blade 10 is intended to be mounted in an angular setting system 34 making it possible to modify its angular position around the setting axis "A" relative to a hub 36 of the propeller.

[0065] For this purpose, the angular setting system 34 comprises bearings 54, 56. The bearings 54, 56 are here two in number and are respectively a lower bearing 54 and an upper bearing 56.

[0066] The bearings 54, 56 are of the ball bearing type. In the example shown, they have different diameters and their balls also have different diameters.

[0067] The lower bearing 54 extends substantially between the planes Pm and Pb and therefore around a lower part of the bulb 32. This lower bearing 54 has a smaller diameter than the upper bearing 56, and its balls have a larger diameter than those of the upper bearing 56.

[0068] The lower bearing 54 is also in oblique contact. In the example shown, the bearing points or surfaces of the balls on the raceways of their rings 54a, 54b are located on a frustoconical surface SI which extends along the setting axis "A" and whose largest diameter is located on the side of the tip of the blade 10.

[0069] The upper bearing 56 extends substantially between the planes Pm and Ph and therefore around an upper part of the bulb 32. The upper bearing 56 is also in oblique contact. In the example shown, the bearing points or surfaces of the balls on the raceways of their rings 56a, 56b are located on a frustoconical surface S2 which extends along the setting axis "A" and whose largest diameter is located on the side of the free end 28 of the root 14 of the blade 10.

[0070] Figures 4 and 5 illustrate an exemplary embodiment of the angular setting system 34.

[0071] The angular wedging system 34 comprises a bowl 58. The bowl 58 has an annular wall 58a extending around the wedging axis "A". The annular wall 58a radially delimits an internal volume of the bowl 58. The internal volume of the bowl 58 is closed downwards by a bottom wall 58b which extends opposite the free end 28 of the foot 14. The bowl 58 has at its upper axial end an opening 58c which is radially delimited by an upper end edge of the annular wall 58a. The free end 28 and the bulb 32 of the foot 14 are intended to be inserted axially inside the bowl 58 through the upper opening 58c.

[0072] The annular wall 58a and the bottom wall 58b are made in a single piece.

[0073] The bottom wall 58b is configured to cooperate by complementarity of shapes with the free end 28 of the foot 14 so that the bowl 58 is secured in rotation with the foot 14 around the wedging axis "A" and thus constitutes a pivot for the associated blade 10.

[0074] In the present case, it is understood that the bottom wall 58b comprises a recess 60 having a non-circular, and in particular rectangular, cross-section, and configured to receive the free end 28, as illustrated in Figures 3 and 4. As seen in [Fig. 6], this recess 60 is eccentric relative to the axis "A" of wedging in a similar manner to the free end 28. This eccentricity allows indexing and keying during insertion and assembly of the foot 14 in the bowl 58, only one position of engagement of the free end 28 in the recess 60 being possible.

[0075] The recess 60 is located on an upper or internal face of the bottom wall 58b of the bowl 58, which is therefore located inside the bowl 58 and oriented towards the foot 14.

[0076] The angular setting system 34 generates a torque at the root 14 of the blade 10 which opposes the torsional moment resulting from the aerodynamic forces and the centrifugal forces. It is advantageous to directly fit the free end 28 into the recess 60, without the interposition of an added element, in order to directly constrain the rotation of the root 14. This gives a more direct force path, the torsional moment being applied directly to the root 14. The lower section has dimensions strictly smaller than the maximum dimension of the middle section in order to limit the circumferential size at this height.

[0077] The position of the middle section, the most radially bulky of the bulb 32, between the two bearings 54, 56, is very advantageous in terms of radial size because part of the bearing height between the middle section and the upper section is located inside the bowl 58, unlike the state of the art on broached fasteners integrated in a pivot. This contributes to reducing the radial size of the angular wedging system 34.

[0078] This makes it possible to reduce the diameter of the lower bearing 54 which is located under the middle section. Therefore, the root 14 of the blade 10 can be integrated lower along the timing axis "A", which greatly reduces the theoretical hub ratio associated with the integration of the root 14. However, those skilled in the art know that a low hub ratio improves the performance of the engine, in particular because it is more compact and therefore lighter. This last point is a very important advantage of the technical solution compared to the competition which conventionally offers barrels with a cylindrical external shape.

[0079] The bottom wall 58b comprises a lower or external face, which is located on the side opposite the foot 14, and which comprises a cylindrical extension 62 extending along the setting axis "A" and comprising an external thread or external rectilinear grooves 64 for the rotational coupling of the angular setting system 34 with a pitch change mechanism which is not illustrated and which is common to the different angular setting systems 34 and blades 10 of the propeller.

[0080] As seen in [Fig.4], the bowl 58 is designed to support the bearings 54, 56 which ensure the centering and guiding of the bowl 58 around the alignment axis "A" with respect to the hub 36 of the turbomachine.

[0081] The bearings 54, 56 may be part of the angular setting system 34. In particular, at least one of the guide bearings may have its internal ring integrated into the bowl 58.

[0082] This is the case here of the lower bearing 54 which has its internal ring 54a integrated into the bowl 58. In practice, this means that the bowl 58 comprises a raceway 54aa at its external periphery on which the balls of the lower bearing 54 roll directly. This raceway comprises an annular surface with a concave curved section. This raceway is here located at the lower end of the bowl 58 and the annular wall 58a. The external ring 54b of the lower bearing 54 is fixed to the hub 36, for example by shrink fitting. Furthermore, the bowl 58 is advantageously designed to apply a prestress to the lower bearing 54.

[0083] The outer ring 56b of the upper bearing 56 is fixed to the hub 36, for example by shrink fitting. Its inner ring 56a is engaged on and around the free upper end of the bowl 58 and the annular wall 58a. This end of the annular wall 58a comprises an outer cylindrical surface 76 for mounting the inner ring 56a as well as an external thread for screwing a nut 78 intended to bear axially on the inner ring 56a to keep it axially tightened against an outer cylindrical shoulder 80 of the bowl 58.

[0084] To axially retain the foot 14 inside the bowl 58, in particular against centrifugal force, an annular retention ring 82 is provided which extends inside the bowl 58, around the bulb 32. The retention ring 82 is connected to the bowl 58 so as to be at least limited in axial movement towards the opening 58c relative to the bowl 58.

[0085] The retaining ring 82 has an annular bearing face 84 directed towards the bottom of the bowl 58. The bearing face 84 is intended to restrict the passage section of the opening 58c of the bowl 58 to prevent the foot 14 from being withdrawn through the opening 58c by obstacle with the bulb 32. More particularly, the bearing face 84 is intended to be in axial contact with an upper face 86 of the bulb 32 to block the axial movement of the bulb 32 towards the upper opening 58c.

[0086] It is also important to securely fix the foot 14 in the bowl 58 in order to avoid any swiveling of the blade 10 relative to the bowl 58 during its use. For this purpose, the angular wedging system 34 comprises a lower seat 88, formed by a face facing the opening 58c of the bowl 58, by means of which the foot 14 is axially supported in the bowl 58 in the direction of the bottom.

[0087] The seat 88 belongs to a separate part from the retention ring 82. At least one of the seat 88 and / or the retention ring 82 is mounted to move in axial translation relative to the bowl 58 by means of at least one clamping mechanism 90 to allow axial clamping of the bulb 32, here made of composite material, between the seat 88 and the bearing face 84 of the retention ring 82. Thus, this makes it possible to avoid the appearance of axial play between the bearing face 84 and the blade 10.

[0088] So that such axial play does not appear, whatever the operating conditions operation of the propeller, the bulb 32 is clamped between the seat 88 and the bearing face 84 of the retention ring 82 with a prestress high enough to exceed the maximum axial forces likely to be applied to the blade 10 during operation of the propeller, for example of the order of several tens of thousands of Newtons.

[0089] The retention crown 82 is here made of a metallic material, such as steel, titanium or a titanium alloy such as TA6V.

[0090] The seat 88 is here made of a metallic material, such as steel, titanium or a titanium alloy such as TA6V.

[0091] The bearing face 84 of the retention ring 82 is directly in contact with the bulb 32, without the interposition of an added part. The bearing face 84 of the retention ring 82 more particularly has a shape complementary to the upper face 86 of the bulb 32 to distribute the forces over a large surface of the bulb 32.

[0092] To simultaneously allow the root 14 to be held radially in the bowl 58, the upper face 86 of the bulb 32 has a generally frustoconical shape and the bearing face 84 has a complementary shape. The bearing face 84 extends, for example, generally from the median plane to the opening 58c of the bowl 58. Thus, under the effect of centrifugal force, the root 14 is centered radially in the bearing face 84. This shape therefore makes it possible to obtain a stable position of the blade 10 relative to the setting axis "A" during rotation of the propeller.

[0093] Compared to a broached attachment, the bearing surface 84 is maximized by utilizing the entire circumference of the bottom of the blade 10. On a broached attachment, only two distinct surfaces of the root 14 of the blade 10, respectively located on the intrados and the extrados, are supported on bearing surfaces, while the surfaces of the root 14 of the blade 10 located at the leading edge and the trailing edge are free. Still in comparison with a broached attachment, the height of the bearing surfaces in the direction of the setting axis "A" is much greater, which also contributes to considerably increasing their surface area. This large bearing surface makes it possible to reduce the contact pressure regardless of the operating situation.

[0094] The internal diameter of the retention ring 82, measured at the upper end of the bearing face 84, is substantially smaller than the diameter of the middle section of the bulb 32. To allow its arrangement around the bulb 32 in a simple manner, the retention ring 82 is here produced in several sectors, two of which sectors 82a, 82b are shown in [Fig.4]. These sectors 82a, 82b are distributed regularly around the wedging axis "A".

[0095] These sectors 82a, 82b may be circumferentially in contact with each other so that the bearing face 84 has a continuous annular shape.

[0096] Alternatively, the sectors 82a, 82b are circumferentially spaced apart from each other. others so that the bearing face 84 has an annular shape with discontinuities between two sectors 82a, 82b.

[0097] The foot 14 here rests on the seat 88 by a lower face 92 of the bulb 32. The seat 88 is thus in the form of an annular support face which extends around the wedging axis "A". The seat 88 more particularly matches the lower face 92 opposite the bulb 32, in particular to reduce the contact pressure between the seat 88 and the bulb 32. The seat 88 is directly in contact with the foot 14, here made of composite material.

[0098] To enable the bottom of the foot 14 to be centered in the bowl 58, the lower face 92 of the bulb 32 in contact with the seat 88 has a generally truncated cone shape, here convex, and the seat 88 has a complementary shape. Thus, the foot 14 is not only axially supported towards the bottom of the bowl 58, but it is also held radially in position in the bowl 58.

[0099] As illustrated in [Fig.4], the seat 88 is carried by at least one piece inserted into the bowl 58. The seat 88 is thus interposed between the foot 14 and the bowl 58. The seat 88 is mounted to move in translation by means of at least one clamping mechanism 90.

[0100] The seat 88 is here formed by the upper face of a ring 94 made in a single piece. The seat 88 is intended to bear against a lower annular face of the bulb 32. In this respect, the seat 88 has a continuous annular shape centered on the wedging axis "A".

[0101] The ring 94 carrying the seat 88 is mounted in axial support towards the bottom of the bowl 58 by means of a clamping ring 96 belonging to the clamping mechanism 90. The clamping ring 96 surrounds the seat 88.

[0102] The clamping ring 96 has an external peripheral rim 98 which bears against an annular shoulder face 100 of the bowl 58. The shoulder face 100 extends radially inwardly from the annular wall 58a and faces the opening 58c. This shoulder face is located slightly above the median plane Pm.

[0103] The clamping ring 96 is intended to cooperate with the ring 94 to clamp the seat 88 axially upwards against the bulb 32 by bearing on the shoulder face 100. For this purpose, the clamping ring 96 is integral in axial displacement with an internal thread which is screwed onto a complementary external thread produced on an external face of the ring 94.

[0104] To enable the seat 88 to be tightened against the bulb 32 by turning the tightening ring 96, one of the external thread or the internal thread is locked in rotation relative to the bowl 58.

[0105] As a non-limiting example, this is the internal thread. In this respect, the ring The clamping ring 96 is immobilized in rotation relative to the bowl 58, in particular by fitting complementary shapes between the clamping ring 96 and the bowl 58, for example by means of flats or pins.

[0106] In the example shown in [Fig.4], the external thread is made in one piece with the seat 88.

[0107] Furthermore, the retention ring 82 is here attached to the bowl 58. It is made of several distinct sectors 82a, 82b which are intended to be axially connected to the bowl 58 by a dog clutch device. To facilitate the insertion of the sectors 82a, 82b, the retention ring 82 is made of at least three sectors, only two of which are shown in [Fig.4].

[0108] Thus, each sector 82a, 82b comprises at least one external dog tooth 102 configured to cooperate with complementary internal dog teeth 104 of the annular wall 58a of the bowl 58. The external dog teeth 102 each have, for example, an angular extension around the wedging axis "A", of between approximately 20 and 30°.

[0109] The internal dog teeth 104 of the bowl 58 are better visible in [Fig. 5]. These internal dog teeth 104 are regularly spaced around the wedging axis "A". There are six of them in the non-limiting example shown. For example, they each have an angular extension around the wedging axis "A" of between approximately 20 and 30°.

[0110] The external dog teeth 102 are complementary to the internal dog teeth 104 and are configured to cooperate by dog ​​engagement with these internal dog teeth 104. Dog engagement is a well-known mounting method in the aeronautical field which will be described in more detail later.

[0111] When assembling the assembly formed by the blade 10 and the angular setting system 34, the ring 94 carrying the seat 88 is first inserted into the bowl 58 through its upper opening 58c. The ring 94 is previously screwed with its clamping ring 96 so that the seat 88 occupies its lowest position in the bowl 58 when the ring 96 is pressed against the shoulder face 100. The ring 94 and its clamping ring 96 are positioned so that the rim 98 of the clamping ring 96 is pressed against the shoulder face 100 of the bowl 58.

[0112] Then the foot 14 is inserted by its free end 28 through the upper opening 58c of the bowl 58. The foot 14 is positioned so that the bulb 32 is received in abutment against the seat 88.

[0113] Then the sectors 82a, 82b of the retaining crown 82 are inserted into the bowl 58 through its upper opening 58c. This insertion is facilitated by the fact that the seat 88 occupies its lowest position. This frees up sufficient space for the insertion of the external dog teeth 102 between the internal dog teeth 104 without being hindered by the bulb 32.

[0114] The external dog teeth 102 of the sectors 82a, 82b are arranged axially in coincidence with the spaces located angularly between the internal dog teeth 104. Then the external teeth 102 of each sector 82a, 82b are inserted axially downwards into these spaces so as to be below the level of the internal dog teeth 104. Finally, the sectors 82a, 82b are pivoted about the wedging axis "A" until the external dog teeth 102 are axially in line with the internal dog teeth 104. Thus, the sectors 82a, 82b of the retention ring 82 are limited in axial movement towards the opening 58c by contact of their external dog teeth 102 against the internal dog teeth 104 of the bowl 58.

[0115] Then, the clamping mechanism 90 is actuated to enable the seat 88 to be clamped axially against the bulb 32. This has the effect of lifting the foot 14 relative to the bowl 58 towards its upper opening 58c, until the bulb 32 is in axial contact against the bearing face 84 of the retention ring 82. Thus, the clamping force is transmitted from the seat 88 to the bulb 32, then from the bulb 32 to the retention ring 82, and from the retention ring 82 to the bowl 58 via the dog teeth 102, 104. A reaction force takes place between the clamping ring 96 and the bowl 58 via the shoulder face 100. The foot 14 is thus only in direct contact with the bearing face 84 of the retention ring 82 and with the seat 88 of the ring 94.

[0116] For the actuation of the clamping mechanism 90, an interval is angularly reserved between at least two sectors 82a, 82b of the retaining ring 82 to allow the insertion of a clamping tool (not shown) through the upper opening 58c. The clamping is here carried out by means of a tool comprising at least one pinion which is inserted into the bowl 58. The pinion is intended to be meshed with an external toothing 106 carried by the periphery of the seat 88. The external toothing 106 is here arranged just above the clamping ring 96.

[0117] Figures 6 and 7 illustrate an embodiment in accordance with the invention and which makes it possible to resolve at least some of the problems of the prior art.

[0118] In these figures, the elements already described in the above are designated by the same references.

[0119] The mechanism 90 for clamping the seat 88 of Figures 6 and 7 is different from that described above.

[0120] The seat 88 is formed by a first part of the ring 94 and in particular by a truncated part 94a of the ring 94 which is located on the side of the opening 58c of the bowl 58.

[0121] The ring 94 comprises a second part and in particular a cylindrical part 94b, which is located on the side opposite the opening 58c of the bowl 58.

[0122] The ring 94 is formed from a single piece in the example shown.

[0123] The truncated part 94a of the ring 94 comprises an internal truncated surface 94a 1 which bears, here directly, on the lower face 92 of the bulb 32.

[0124] The clamping mechanism 90 comprises two nuts, respectively internal 110 and external 112.

[0125] The nuts 110, 112 are screwed into each other and extend around the wedging axis A.

[0126] The external nut 112 is locked in rotation with respect to the bowl 58 and in axial support on an annular shoulder face 100 of the bowl 58, which may form part of its bottom wall 58b.

[0127] In the example shown, the external nut 112 is locked in rotation with respect to the bowl 58 by a first dog system 114.

[0128] The first dog clutch system 114 comprises first projecting teeth 114a carried by the external nut 112 and housed in housings 114b of the bowl 58. These first projecting teeth 114a can be oriented radially outwards relative to the setting axis A as in the example shown.

[0129] The external nut 112 is axially supported on the face 100 via its lower end preferably, the first projecting teeth 114a being located at the level of the upper end of the external nut 112 and therefore located on the side of the opening 58c of the bowl 58.

[0130] The external nut 112 may comprise an external cylindrical sliding and centering face 112b cooperating with an internal cylindrical surface 58d of the bowl 58.

[0131] The external nut 112 further comprises an internal thread 112a for screwing the internal nut 110.

[0132] The internal nut 110 is locked in rotation with respect to the part carrying the seat 88 and therefore with respect to the ring 94. In the example shown, this internal nut 110 is locked in rotation with respect to the ring 94 by a second dog system 116.

[0133] The second dog clutch system 116 comprises second projecting teeth 116a carried by the internal nut 110 and housed in housings 116b of the ring 94. These second projecting teeth 116a can be oriented axially on the side of the opening 58c of the bowl 58 as in the example shown.

[0134] In the example shown, the internal nut 110 also comprises an internal annular rim 118 at its lower end, the projecting teeth 116a being located at its upper end and therefore located on the side of the opening 58c of the bowl 58.

[0135] The housings 116b of the ring 94 are located at the intersection between the frustoconical 94a and cylindrical 94b parts in the example shown.

[0136] The internal nut 110 further comprises an external thread 110a for screwing the nut external 112.

[0137] The part carrying the seat 88, namely the ring 94, bears axially on the internal nut 110 by means of at least one elastically deformable interface part 120. This interface part 120 is capable on the one hand of compressing axially during axial tightening of the bulb 32 between the crown 82 and the seat 88, and on the other hand of expanding axially during a release of this tightening.

[0138] It is therefore understood that the interface part 120 makes it possible to guarantee the durability of the preload force even in the event of movement of the bulb 32 inside the bowl 58.

[0139] The interface part 120 is preferably annular and then extends around the wedging axis A.

[0140] As in the example shown, the interface part 120 may have a general ring shape.

[0141] The interface part 120 may be formed from a single part but could alternatively be sectorized and formed from several angular sectors arranged next to each other and around the wedging axis A.

[0142] The interface part 120 may be formed from a single piece and have, for example, the general shape of a ring.

[0143] The interface part 120 is for example made of a material or from an element chosen from: an elastomer, a laminated structure based on elastomer and metal, an organic matrix composite preferably with short fibers, dry fibers preferably made of aramid, and a Kevlar® nitrile rubber.

[0144] In the example shown, the interface part 120 is interposed axially between the cylindrical wall 94b of the ring 94 and the internal nut 110, and preferably between this cylindrical wall 94b and the internal annular rim 118 of the internal nut 110.

[0145] The interface part 120 may extend in the extension of the cylindrical wall 94b of the ring. For this, the interface part 120 may comprise internal 120b and external 120a cylindrical surfaces axially aligned respectively with internal 94b2 and external 94b1 cylindrical surfaces of the cylindrical wall 94b. The external cylindrical surface 120a may further be aligned with an external cylindrical surface 118a of the rim 118 as in the example shown.

[0146] [Fig.8] shows very schematically the force paths in the tangential direction Fl and in the axial direction F2 (with respect to the wedging axis A) between the part carrying the seat 88 and the internal nut 110. It can be seen that:

[0147] - the axial force path is transmitted between the internal nut 110 and the ring 94 by the interface part 120 which provides a flexibility function in the axial direction, and

[0148] - the tangential force path is transmitted by the second dog system 116 between the teeth 116a of the internal nut 110 and the ring 94.

[0149] It is therefore understood that, thanks to the dog system 116, the radial force paths and tangential are separated during tightening in order to maintain the full effectiveness of the preload application without damaging the interface part 120.

[0150] In the embodiment variant of [Fig. 9], the interface part 120 differs from that described above in that it is intended, after assembly, to be interposed radially between a cylindrical skin 124 of the ring 94 and a cylindrical skin 122 of the internal nut 110. In the example shown, the skin 124 extends along the axis A and projects from the wall 94b. The skin 122 can extend along the axis A while projecting from the rim 118 of the internal nut 110. The skin 122 here extends inside the interface part 120, and the skin 124 is here located outside the part 120. The part 120 is thus trapped between the skins 122, 124.

[0151] When assembling the assembly formed by the blade 10 and the angular setting system 34, the steps described above can be reproduced.

[0152] In particular, the ring 94 carrying the seat 88 is first inserted into the bowl 58 through its upper opening 58c. The ring 94 is previously positioned with the interface part 120 on the clamping mechanism 90 so that the seat 88 occupies its lowest position in the bowl 58 when the external nut 112 is pressed against the face 100.

[0153] The interface part 120 can be positioned on the internal nut 110 before its assembly, or can be fixed to the ring 94 for example before its assembly.

[0154] Then the foot 14 is inserted by its free end 28 through the upper opening 58c of the bowl 58. The foot 14 is positioned so that the bulb 32 is received in abutment against the seat.

[0155] Then the sectors 82a, 82b of the retaining crown 82 are inserted into the bowl 58 through its upper opening 58c. This insertion is facilitated by the fact that the seat 88 occupies its lowest position. This frees up sufficient space for the insertion of the external dog teeth 102 between the internal dog teeth 104 without being hindered by the bulb 32.

[0156] The external dog teeth 102 of the sectors 82a, 82b are arranged axially in coincidence with the spaces located angularly between the internal dog teeth 104. Then the external teeth 102 of each sector 82a, 82b are inserted axially downwards into these spaces so as to be below the level of the internal dog teeth 104. Finally, the sectors 82a, 82b are pivoted about the wedging axis "A" until the external dog teeth 102 are axially in line with the internal dog teeth 104. Thus, the sectors 82a, 82b of the retention ring 82 are limited in axial movement towards the opening 58c by contact of their external dog teeth 102 against the internal dog teeth 104 of the bowl 58.

[0157] Then, the clamping mechanism 90 is actuated to allow the seat 88 to be clamped axially against the bulb 32. This has the effect of lifting the foot 14 relative to the bowl 58 towards its upper opening 58c, until the bulb 32 is in axial support against the bearing face 84 of the retention ring 82. Thus, the clamping force is transmitted from the seat 88 to the bulb 32, then from the bulb 32 to the retention ring 82, and from the retention ring 82 to the bowl 58 via the dog teeth 102, 104. A reaction force takes place between the clamping mechanism 90 and the bowl 58 via the shoulder face 100. The foot 14 is thus in direct contact with the bearing face 84 of the retention ring 82 and with the surface 94a 1 of the ring 94.

[0158] For the actuation of the clamping mechanism 90, an interval is angularly reserved between at least two sectors 82a, 82b of the retaining crown 82 to allow the insertion of a clamping tool (not shown) through the upper opening 58c. The clamping is here carried out by means of a tool comprising at least one pinion which is inserted into the bowl 58. The pinion is intended to be meshed with an external toothing 106 carried by the periphery of the seat 88. The external toothing 106 is here arranged just above the mechanism 90.

[0159] The interface part 120 has the function of acting as a shock absorber within the system. When the preload force is applied, the interface part 120 is compressed against the bulb along the setting axis. When the blade is driven at high rotation speed, the blade root is likely to move radially away from the seat, which causes a significant release of the preload force in the original configuration such as that of [Fig.6]. With the interface part 120, the loss of the initial compression of the interface is greatly slowed down since the displacement of the blade root linked to the centrifuge is compensated by the difference in thickness of the interface part 120 between its initial state and its deformed state. Thus, the invention makes it possible to ensure continuity of application of the preload force, even at high rotation speed.

[0160] The preload mechanism 90 transforms a tightening torque into a force applied to the bearing surfaces of the blade root. In this invention, the tangential force path associated with the tightening torque passes through the second dog system 116. This force path is sufficiently steep to limit deformations of the system as much as possible and to transmit the tightening torque without major dissipation of energy.

Claims

Claims

1. Assembly comprising a propeller blade (10) and a system (34) for angularly setting the blade (10), for an aircraft turbomachine, the blade (10) having a root (14) extending from an upper end linked to a blade (12) of the blade (10) to a free lower end (28), the root (14) having a swollen section, called a "bulb (32)", the system (34) allowing angular setting of the blade (10) around a setting axis (A) and comprising: - a bowl (58) which is delimited radially by an annular wall (58a) extending around the wedging axis (A), the bowl (58) comprising a lower bottom closed by a bottom wall (58b) and an upper opening (58c) through which the bulb (32) is intended to be inserted axially into the bowl (58); - an annular retention ring (82) which extends around the bulb (32), the retention ring (82) being at least limited in axial movement towards the opening (58c) relative to the bowl (58), the retention ring (82) having a face (84) of annular bearing which restricts the passage section of the opening (58c) and which is intended to be in axial contact with an upper face (86) of the bulb (32) to block the axial movement of the foot (14) towards the opening (58c); and - a lower seat (88) carried by a part (94) separate from the retention ring (82) and from the bowl (58) and intended to be in axial contact with a lower face (92) of the bulb (32) to block the axial movement of the foot (14) on the side opposite the opening (58c),the retention seat (88) being mounted so as to be able to move in axial translation relative to the bowl (58) by means of at least one clamping mechanism (90) to enable axial clamping of the bulb (32) between the seat (88) and the retention ring (82), characterized in that the clamping mechanism (90) comprises two nuts, respectively internal (110) and external (112), which are screwed into each other and extend around the wedging axis (A), the external nut (112) being locked in rotation relative to the bowl (58) and in axial support on an annular face (100) of the bowl (32) oriented towards the opening (58c), and the internal nut (110) being locked in rotation relative to the part (94) carrying the seat (88), this part (94) being in axial support on the internal nut (110) by means of of at least one interface part (120), this interface part (120) being elastically deformable, and capable on the one hand of compressing axially during axial tightening of the bulb (32), and on the other hand of expanding axially during a release of this tightening.

2. Assembly according to the preceding claim, characterized in that the interface part (120) is annular and extends around the wedging axis (A).

3. Assembly according to any one of the preceding claims, characterized in that the interface part (120) has the general shape of a ring.

4. Assembly according to the preceding claim, characterized in that the interface part (120) is made of a material or from an element chosen from: an elastomer, a laminated structure based on elastomer and metal, an organic matrix composite preferably with short fibers, dry fibers preferably made of aramid, and a Kevlar® nitrile rubber.

5. Assembly according to any one of the preceding claims, characterized in that the seat (88) is formed by a frustoconical wall (94a) of the part (94) which is flared on the side of the opening (58c) and which comprises an internal frustoconical surface (94a 1) bearing on the lower face (92) of the bulb (32).

6. Assembly according to the preceding claim, characterized in that the part (94) further comprises a cylindrical wall (94b) which is connected to the internal periphery of the frustoconical wall (94a), the interface part (120) being interposed axially between this cylindrical wall (94b) and the internal nut (110), and preferably between this cylindrical wall (94b) and an internal annular rim (118) of the internal nut (110).

7. Assembly according to the preceding claim, characterized in that the interface part (120) extends in the extension of the cylindrical wall (94b) of the part (94) carrying the seat (88).

8. Assembly according to any one of the preceding claims, characterized in that the external nut (112) is locked in rotation with respect to the bowl (58) by a first dog system (114), and / or the internal nut (110) is locked in rotation with respect to the part (94) by a second dog system (116).

9. Assembly according to the preceding claim, characterized in that the first dog system (114) comprises first projecting teeth (114a) carried by the external nut (112) and housed in housings (114b) of the bowl (58), these first projecting teeth (114a) being oriented radially outwards relative to the wedging axis (A), and the second dog system (116) comprises second projecting teeth (116b) carried by the internal nut and housed in housings (116b) of the part (94) carrying the seat (88), these second projecting teeth (116a) being oriented axially on the side of the opening (58c) of the bowl (58).

10. Assembly according to the preceding claim in combination with claims 6 and 8 at least, characterized in that the housings (116b) of the part (94) carrying the seat (88) are located at the intersection between the frustoconical (94a) and cylindrical (94b) parts of this part (94).

11. Assembly according to any one of the preceding claims, characterized in that the interface part (120) is capable of being confined radially between two rigid cylindrical skins (122, 124), respectively of the internal nut (110) and of said part (94).

12. Aircraft turbomachine, comprising a propeller comprising assemblies according to one of the preceding claims.

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