MOUNTING ARRANGEMENT FOR A TURBINE ENGINE BLADE

Description

DOMAINE DE L'INVENTION

[0001] The present invention relates to an assembly for a turbomachine for attaching a blade of such a turbomachine to a fastener. ETAT DE LA TECHNIQUE

[0002] A conventional fan includes a blade attachment defining a cell for receiving a blade root. The blade attachment includes two facing flanks defining between them a passage opening into the cell and forming stops preventing the root from exiting the cell through the passage. A blade root can be engaged in the cell through two opposite accesses.

[0003] However, in certain fan configurations, a blade may experience a turbulent, completely detached aerodynamic flow, which generates vibrational excitation over a wide band. Due to this vibrational excitation, the blade root is likely to flap in the cell in which this root is received. However, such flapping risks damaging the blade or the attachment defining the cell.

[0004] It has been proposed to insert a shim into such a cell with the blade root, in particular in document EP2425100. The deformable shim is force-fitted into the cell between the blade root and the attachment, either by hand or with a mallet. Such force-fitting allows the shim to bear simultaneously on the blade root and on the attachment with a support force of a mass of the order of 50 kilograms, when the fan is stopped. However, such a shim is not capable of systematically preventing the aforementioned flapping phenomenon.Indeed, when a fan is rotated at a nominal rotation speed, the blade root rises in the cell under the effect of the centrifugal force, thus increasing the space between it and the bottom of the cell, so that the force exerted by the wedge on the attachment decreases when the wedge returns to its initial unstressed geometry, hence the appearance of a flapping of the blade root, or even a swiveling of the blade.

[0005] Document EP3073054 discloses a device for clamping and retaining a dovetail root of a blade of a gas turbine engine in a corresponding cell extending axially in the periphery of a disk, the root being mounted in the cell by inserting a front end of the root into a proximal end of the cell and then sliding the root towards a distal end of the cell. The device comprises a first clamping body having a first inclined surface on which a corresponding inclined front end surface of the root slides when the root is inserted into the cell to push the front end of the root radially outward, and a second clamping body having a second inclined surface, the clamping bodies pushing the blade radially outward and retaining the root axially in the cell.Clamping bodies may have relatively soft outer layers on their angled surfaces for better contact of the bodies with the foot. EXPOSE DE L'INVENTION

[0006] One aim of the invention is to more effectively prevent the root of a turbomachine blade from flapping, particularly at high rotational speed.

[0007] For this purpose, according to a first aspect, there is proposed an assembly according to the independent claim 1 annexed for a turbomachine blade, the assembly comprising: a fastener defining a cell for receiving a blade root, and a clamping device for clamping the blade root against the fastener when the blade root is in the cell, the clamping device comprising: o at least one clamping element adapted to bear simultaneously on the blade root and on the fastener in the cell so as to exert a clamping force on the blade root, the clamping element defining a tapped hole, in which the clamping element comprises an elastic layer arranged to bear in the cell on the blade root, o a rod comprising a thread cooperating with the tapped hole so that a rotation of the rod relative to the clamping element causes a variation in the clamping force exerted by the clamping element on the blade root.

[0008] Varying the force exerted by the clamping element by means of a threaded rod makes it possible to achieve much higher clamping forces than the simple support forces obtained by forcibly inserting a wedge by hand or with a mallet. Thus, even if the clamping element is centrifuged during operation of the turbomachine, thus causing a reduction in the clamping force exerted by the clamping element on the fastener, this reduction is not significant enough to prevent the clamping element from firmly clamping the fastener. Therefore, the clamping element prevents the blade from flapping even at a high rotational speed.

[0009] The elastic layer element is compressible to be stressed against the blade root so as to maintain the stress under stress of the blade whose root moves centrifugally and / or during aerodynamic stresses. The elastic support force for stress under the blade root is approximately 10 times to 20 times greater than the elastic return force of an elastic deformable shim for example as defined in document EP2425100 or in document EP2009245.

[0010] The assembly according to the first aspect may also comprise the following optional features, taken alone or in combination according to the appended dependent claims.

[0011] Preferably: the clamping element is configured to be moved relative to the fastener when the rod is rotated relative to the fastener, the fastener and the clamping element have shapes adapted so that the movement of the clamping element relative to the fastener causes the variation of the clamping force exerted by the clamping element on the foot.

[0012] Preferably, the clamping element rests on a bottom surface of the cell forming a slope inclined relative to the axis of rotation of the rod.

[0013] Preferably, the clamping member comprises a metal part defining the tapped hole.

[0014] Preferably, the elastic layer has a thickness ranging from 1 millimeter to 4 millimeters.

[0015] Preferably, the clamping device comprises a stop limiting a translational travel of the rod along the axis of rotation of the rod, relative to the fastener.

[0016] Preferably, the assembly comprises a first lock preventing the foot from exiting the socket, the first lock comprising the stop.

[0017] Preferably, the rod comprises an end portion adapted to be engaged with a tool and to be rotated by the tool, the end portion being for example grooved.

[0018] Preferably, the assembly includes an anti-rotation device adapted to prevent rotation of the rod relative to the fastener.

[0019] Preferably, the anti-rotation device comprises a second lock preventing the foot from coming out of the socket.

[0020] Preferably, the anti-rotation device further comprises: the end portion of the rod, a removable socket adapted to be engaged with the end portion in place of the tool, and to be simultaneously engaged with the second lock.

[0021] Preferably: the clamping device comprises two clamping elements, each clamping element being adapted to bear simultaneously on the foot and on the attachment in the socket so as to exert a clamping force on the foot, each clamping element defining a tapped hole, the rod comprises two threads cooperating respectively with the two tapped holes so that a rotation of the rod relative to the clamping element causes a variation of the same sign in the clamping forces exerted respectively by the two clamping elements on the foot.

[0022] Preferably: the two clamping elements are configured to be moved relative to the fastener when the rod is rotated relative to the fastener, the fastener and the two clamping elements have shapes adapted so that the respective movements of the two clamping elements relative to the fastener cause variations in the clamping forces exerted respectively by the two clamping elements on the foot.

[0023] Preferably, the two clamping members are configured to move away from or towards each other, when the rod is rotated about the axis of rotation relative to the fastener. DESCRIPTION DES FIGURES

[0024] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which: There figure 1 is a side view of a turbomachine engine. The figure 2 is a side perspective view of an attachment for a turbomachine blade, according to one embodiment. The figure 3 is a side perspective view of a clamping device according to one embodiment and locks cooperating with the fastener shown in figure 2 . There figure 4 is a bottom view of the clamping device and locks shown in figure 3 . There figure 5 is a bottom view detailing part of the clamping device and one of the locks shown in figure 3 . THE figures 6 à 10 are views of the fastener and clamping device at various stages of assembly. The figure 11 is a side view of a blade root cooperating with the clamping device and the locks shown in figure 2 .

[0025] Throughout the figures, similar elements have identical references. DESCRIPTION DETAILLEE DE L'INVENTION

[0026] In reference to the figure 1 , a turbomachine comprises an engine 1 of the Open Rotor type. The engine 1 comprises a nacelle 2 intended to be fixed to a fuselage of an aircraft, and an unducted fan 3. The fan 3 comprises two counter-rotating fan rotors 4 and 5. In other words, when the engine 1 is in operation, 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 main axis of the engine).

[0027] Engine 1 as shown in the figure 1 is in a configuration commonly referred to as a “pusher” (i.e. blower 3 is placed at the rear of a power generator with an air inlet located upstream, on the right on the figure 1 ).

[0028] However, the engine 1 may alternatively be 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). The engine 1 may also have a different architecture, such as an architecture comprising a fan rotor comprising moving blades and a fan stator comprising fixed blades (USF configuration), or a single fan rotor (TP configuration). The invention may also be applied to a turbomachine with a ducted fan but also with variable pitch.

[0029] On the figure 1 , each fan rotor 4, 5 comprises a hub 6 rotatably mounted relative to the nacelle 2 and a plurality of blades 7 fixed to the hub 6. The blades 7 extend substantially radially relative to the axis of rotation X of the hub.

[0030] In the present application, upstream and downstream are defined relative to the normal flow direction of the gas in the rotor 4, 5 and through the turbomachine. Furthermore, the axis A of the rotor 4, 5 is called its axis of rotation. The axial direction corresponds to the direction of the axis A and a radial direction is a direction perpendicular to this axis and passing through it. Furthermore, the circumferential direction corresponds to a direction perpendicular to the axis A and not passing through it. Unless otherwise specified, internal and external, respectively, are used with reference to a radial direction such that the internal part or face of an element is closer to the axis A than the external part or face of the same element.

[0031] In reference to the figure 2 , the fan 3 comprises, for a blade 7, an attachment 9. The attachment 9 is rotatably mounted relative to the hub 6 around a setting axis Y. More precisely, the attachment 9 is rotatably mounted inside a housing provided in the hub 6, by means of balls or other rolling elements.

[0032] The attachment 9, which may also be called a “pivot” in the literature, defines a cell 10 for receiving a foot of the blade 7, the foot having, for example, a dovetail shape.

[0033] The attachment 9 comprises in particular two flanks 12, 14 defining between them an upper radial opening of the cell 10, opposite a bottom of the cell 10. The two flanks 12, 14 are inclined towards each other and form bearing surfaces.

[0034] The cell 10 extends in a Z direction between two opposite accesses 16, 18 defined by the attachment 9. One of the two accesses 16, 18 is located on the side of a leading edge of the blade, and the other access is located on the side of a trailing edge of the blade. It is through one or the other of these opposite accesses 16, 18 that a blade root can be engaged in translation in the cell 10.

[0035] A pair of facing grooves 20 is formed in the flanks 12, 14 at the access 16. It will be seen below that a lock can be engaged in the grooves 20 so as to close the access 16 and prevent a blade root which is located in the cell 10 from leaving the cell 10.

[0036] Another pair of facing grooves 22 is formed in the flanks 12, 14 at the level of the access 18. It will be seen later that another lock can be engaged in the grooves 20 so as to close the access 18 and prevent a blade root which is located in the cell 10 from leaving the cell 10 via this access 18.

[0037] The bottom of the cell 10 comprises two bottom surfaces 24, 26 having different slopes (this is also visible on the figure 11 ).

[0038] Each of the bottom surfaces 24, 26 has, for example, a rectilinear profile in a plane parallel to the plane (Y, Z). In the following, the profile of a part of the attachment in a plane parallel to the plane (Y, Z) will be called a “sagittal” profile.

[0039] In the embodiment illustrated in the figures, the bottom surfaces 24, 26 are inclined relative to each other so as to meet at a peak constituting the point closest to the upper radial opening of the cell. In other words, the bottom surfaces 24, 26 rise towards this upper radial opening when these surfaces are traveled towards the center of the cell 10. In another way, these bottom surfaces 24, 26 descend when they are traveled towards the two opposite accesses 16, 18 of the cell 10.

[0040] The fastener 9 further comprises a wall 28 projecting radially outwards from the bottom of the cell 10. This wall 28 defines the lower half of an orifice.

[0041] The wall 28 has a top delimiting a radially internal edge of the access 18.

[0042] Two blind holes 30 open into the top of this wall 28. The two blind holes 30 are for example tapped.

[0043] The fastener 9 is made of metal, preferably titanium.

[0044] In reference to the figures 3 et 4 , a clamping device 32 has the function of clamping a blade root against the attachment 9 when the blade root is received in the cell 10.

[0045] The clamping device 32 comprises two clamping elements 34, 36 and a rod 38.

[0046] The clamping element 34 comprises a part 40 defining a tapped hole. This part 40 is made of metal or made of a composite material. The part 40 defines a lower bearing surface 42 of the clamping element 34 on the bottom surface 24.

[0047] The clamping element 34 further comprises an elastic layer 44, which defines an upper bearing surface 46 of the clamping element 34 on a blade root received in the cell 10.

[0048] The elastic layer 44 has, for example, a honeycomb shape.

[0049] The elastic layer 44 is preferably made of an elastomeric material or fiberglass.

[0050] The elastic layer 44 can be bonded to the part 40, in particular when this part 40 is made of metal. When the part 40 is made of a composite material, the elastic layer constitutes a part of this part, more particularly in the case of the honeycomb.

[0051] The elastic layer 44 has a thickness ranging from 1 millimeter to 4 millimeters, preferably from 2 to 3 millimeters. The bearing surfaces 42, 46 have rectilinear, non-parallel sagittal profiles.

[0052] The clamping element 34 has an overall “H” shape so as to allow stable support on the blade root with reduced mass.

[0053] The clamping element 36 includes the same features discussed above as the clamping element 34. It will be noted, however, that the lower bearing surface of the element 36 is intended to bear on the bottom surface 26. Furthermore, the tapped hole of the clamping element 36 is threaded in a direction opposite to the tapped hole of the clamping element 34.

[0054] The rod 38 comprises a thread 48 cooperating with the tapped hole of the clamping element 34, and a thread 50 cooperating with the tapped hole of the clamping element 40. The two threads 48, 50 of the rod 38 extend over two separate sections of the rod 38. The two threads are threaded in two opposite directions. Thus, a rotation of the rod 38 relative to the clamping elements 34, 36 causes the two clamping elements 34, 36 to move away from or towards each other in a direction parallel to the axis of rotation of the rod 38.

[0055] The rod has a first end portion suitable for being engaged with a tool, so as to be driven in rotation by this tool. For this purpose, the first end portion is grooved (the grooves are visible on the figure 9 ).

[0056] The rod has a second end portion opposite the first end portion with respect to its two threads 48, 50.

[0057] The second end portion comprises two collars 52, 54 spaced apart from each other. The two collars 52, 54 are spaced apart from each other by a distance greater than the thickness of the wall 28 (this thickness being measured parallel to the Z axis).

[0058] Also illustrated on the figures 3 And 4 two locks 56 and 58.

[0059] The lock 56 has the function of closing the first access 16 to the cell 10. The lock 56 comprises a plate 60 of generally trapezoidal shape adapted to cooperate with the grooves 20 to ensure this closing. The lock 56 comprises two tabs 62 projecting from the plate 60. The two tabs 58 are parallel.

[0060] In reference to the figure 5 , a removable sleeve 64 is adapted to be engaged with the first end portion of the rod 38, by moving it in translation parallel to the axis of the rod 38. The sleeve 64 has a grooved internal surface cooperating with the first end portion of the rod 38, and has a shape adapted to be able to be engaged between the legs 62.

[0061] The legs 62 define two facing grooves.

[0062] Furthermore, a locking element 66, for example in the form of a brake ring (“circlip” in English) can rest in the two facing grooves formed in the tabs 62.

[0063] Back to the figures 3 And 4, the lock 58 has the function of closing the second access 18 of the cell 10. The lock 58 comprises a plate 68 adapted to cooperate with the grooves 22 formed in the fastener 9 to ensure this closing. The lock 58 further comprises a base 70 defining an upper half of the orifice.

[0064] The base 70 further defines two tapped through holes, and two screws 72 engaged in the two tapped through holes.

[0065] The various elements described above are mounted together in the following manner, starting from the attachment 9 as shown in figure 2 .

[0066] In reference to the figure 6 , the clamping device 32 is placed in the cell 10 in such a way that the lower support wall 42 of the clamping element 34 rests on the bottom surface 24, and the lower support wall of the clamping element 36 simultaneously rests on the surface of 26.

[0067] Furthermore, the clamping device 32 is placed such that the rod 38 passes through the half-orifice formed by the wall 28. The wall 28 is then between the two collars 52 and 54. Furthermore, the collar 52 is then located between the wall 28 and the clamping element 36.

[0068] In reference to the figure 7 , the lock 58 is then engaged in the grooves 22, so as to close the access 18 to the cell 10. The screws 72 are engaged in the blind holes 30 and screwed into these holes 30 so as to fix the lock 58 to the fastener 9.

[0069] The base 70 and the wall 24 then together define an orifice crossed by the rod 38, between the two collars 52 and 54. These four elements, in particular the base 70, thus constitute stops which each limit the travel of movement of the rod 38 along the Z axis.

[0070] From this stage, the bottom surfaces 24, 26 form two slopes inclined relative to the axis of rotation of the rod 38.

[0071] In reference to the figure 8 , the foot of the blade 7 is then engaged in the cell 10 via the access 16 left open. The lock 58 prevents the blade foot from leaving the cell 10 via the access 18.

[0072] In reference to the figure 9 , the first end portion of the rod 38 is at this stage still accessible from the access 16.

[0073] A tool (not shown) is engaged with the first end portion of the rod 38. The tool is either hand-operated or motorized. The tool is then used to rotate the rod 38 relative to the fastener 9 and the clamping members 34, 36 in a first direction of rotation.

[0074] The rotation of the rod 38 in the first direction of rotation causes a displacement of the clamping element 34 in the cell 10 relative to the fastener 9. The clamping element 34 then climbs the slope formed by the bottom surface 24, which brings the clamping element 34 closer to the root of the blade 7 engaged in the cell 10 and compresses the elastomer 44 against the blade root. In other words, the clamping force exerted by the clamping element 34 is increased when the rod is rotated in the first direction of rotation. When the slope formed by the bottom surface 24 is of rectilinear profile, the displacement of the clamping element 34 relative to the fastener 9 is a translation parallel to this slope.

[0075] The rotation of the rod 38 in the first direction of rotation also causes a displacement of the clamping element 36 in the cell 10 relative to the fastener 9. The clamping element 36 then climbs the slope formed by the bottom surface 26, which brings the clamping element 36 closer to the blade root engaged in the cell 10 and compresses the elastomer of the clamping element 36 against the blade root. In other words, the clamping force exerted by the clamping element 36 is also increased when the rod is rotated in the first direction of rotation. When the slope formed by the bottom surface 26 is of rectilinear profile, the displacement of the clamping element 36 relative to the fastener 9 is a translation parallel to this slope.

[0076] The rod 38 is thus rotated until a clamping force on the root of the blade 7 is reached which is sufficiently high to prevent the blade root from flapping in the cell when the turbomachine is in operation.

[0077] To reduce this clamping force, it is of course sufficient to rotate the rod 38 in a second direction of rotation opposite to the first direction of rotation mentioned above. In this case, the two clamping elements descend along their respective slopes 24, 26 and move away from each other, which allows the elastomers to relax.

[0078] Ultimately, the variation in the force exerted by the clamping element 34 on the root of the blade 7 and the variation in the force exerted by the clamping element 36 on the root of the blade 7 are of the same sign when the rod 38 is rotated: either these two forces increase simultaneously, or these two forces decrease simultaneously.

[0079] It will also be noted that, when the rod is rotated by a tool, this rod 38 moves slightly in a radial direction, due to the sloping nature of the bottom surfaces 24 and 28. Of course, the orifice crossed by this rod 38 and formed jointly by the wall 28 and the lock 58 is of dimensions adapted to allow this movement.

[0080] In particular, the elastic layer 44 combines advantageously with the rod 38 and the two clamping elements 34, 36. In fact, the stiffness of the rod 38 constitutes a prestress. When the blade root moves away radially, there is a release of the tensile prestress on the rod 38 causing, while remaining under tensile stress, a mutual approach of the clamping elements 34, 36 which then follow the blade root.

[0081] In reference to the figure 10 , the lock 56 is then engaged in the grooves 20 (the engagement is carried out in a centrifugal direction, that is to say from bottom to top on the figure 10 ), so as to reach an engaged position.

[0082] In the engaged position, the lock 56 closes the access 16, and thus prevents the blade root from exiting the cell through the access 16. Furthermore, in this engaged position, the two legs 62 of the lock 56 define between them a passage towards the first end portion of the rod 38.

[0083] The sleeve 64 is engaged in this passage, so as to cooperate with this first end portion of the rod 38, in place of the tool mentioned above. At the same time, the sleeve fixes the plate 68 relative to the fastener 9. Furthermore, the two tabs 62 block the rotation of the sleeve 64 relative to the fastener 9, and consequently the rotation of the rod 38 relative to the fastener 9.

[0084] Ultimately, the first end portion of the rod 38, the lock 58 and the sleeve 64 together form an anti-rotation device adapted to prevent rotation of the rod 38 relative to the attachment 9. This is advantageous, because the functions of locking the blade root in the cell and of anti-rotation of the rod are implemented using a reduced number of parts.

[0085] The locking element 66 is then engaged in the two facing grooves formed in the two tabs 62 to prevent the socket 64 from exiting the passage defined between the two tabs 62.

[0086] Blade 7 is now firmly attached to clip 9, and ready for use.

[0087] In reference to the figure 11 , the following points should be noted: The axis of rotation of the rod 38 is parallel to the surface of the blade root 7 on which the clamping elements 34, 36 bear; The lower bearing surfaces of the clamping elements 34, 36 are inclined relative to the axis of rotation of the rod 38 and relative to the surface of the blade root on which the clamping elements bear.

[0088] The turbomachine assembly described above with regard to the attached figures may be subject to variations. In particular: Although the presence of two clamping elements is advantageous for better distributing the clamping force on the blade root, a single clamping element is sufficient to achieve a very high clamping force. When two clamping elements are present in the cell, it may be provided that the forces exerted by these two clamping elements on the blade root increase when the two clamping elements move closer together, as illustrated, or conversely when they move away from each other, in a variant not illustrated. In this variant not illustrated, the two bottom surfaces on which the two clamping elements respectively bear together form a hollow in the center of the bottom of the cell. In the illustrated embodiment, the elastomer presses against the blade root, which prevents damage to the latter.It could however be provided to arrange this elastomer against the bottom of the cell 10 in a variant not illustrated which is not currently claimed.

Claims

1. An assembly for a turbomachine blade, the assembly comprising: • a fastener (9) defining a recess (10) for receiving a blade root (7), and • a clamping device (32) for clamping the blade root (7) against the clip (9) when the blade root (7) is in the recess (10), the clamping device (32) comprising : o at least one clamping element (34) adapted to bear simultaneously on the blade foot (7) and on the fastener (9) in the recess (10) so as to exert a clamping force on the blade foot (7), the clamping element (34) defining a tapped hole, wherein the clamping element comprises a resilient layer arranged to bear in the recess on the blade root (7) and to be compressed by the blade root (7) when the clamping force is exerted, o a rod (38) comprising a thread cooperating with the tapped hole so that rotation of the rod (38) relative to the clamping element causes a variation in the clamping force exerted by the clamping element on the blade root (7).

2. Assembly according to the preceding claim, in which : • the clamping element (34) is configured to be moved relative to the clamp (9) when the rod (38) is rotated relative to the clamp (9), • the clamp (9) and the clamping element (34) are shaped so that movement of the clamping element (34) relative to the clamp (9) causes the clamping force exerted by the clamping element (34) on the foot to vary.

3. Assembly according to any one of the preceding claims, in which the clamping element (34) rests on a bottom surface (24) of the cell (10) forming a slope inclined with respect to the axis of rotation of the rod (38).

4. An assembly according to any one of the preceding claims, wherein the clamping element (34) comprises a metal part (40) defining the tapped hole.

5. Assembly according to any one of the preceding claims, in which the elastic layer has a thickness ranging from 1 millimetre to 4 millimetres.

6. Assembly according to any one of the preceding claims, in which the clamping device (32) comprises a stop (70) limiting a translational travel of the rod (38) along the axis of rotation of the rod (38), relative to the fastener (9).

7. Assembly according to the preceding claim, comprising a first lock (56) preventing the foot from leaving the recess (10), the first lock (56) comprising the stop (70).

8. An assembly according to any one of the preceding claims, wherein the rod (38) comprises an end portion adapted to be engaged with a tool and rotated by the tool, the end portion being for example splined.

9. Assembly according to any one of the preceding claims, comprising an anti-rotation device adapted to prevent rotation of the rod (38) relative to the fastener (9).

10. Assembly according to the preceding claim, in which the anti-rotation device comprises a second lock (58) preventing the foot from leaving the socket (10).

11. An assembly according to claims 8, 9 and 10 taken in combination, wherein the anti-rotation device further comprises: • the end portion of the rod (38), • a removable sleeve (64) adapted to be engaged with the end portion in place of the tool, and to be simultaneously engaged with the second lock.

12. Assembly according to any one of the preceding claims, in which : • the clamping device (32) comprises two clamping elements (34, 36), each clamping element being adapted to bear simultaneously on the foot and on the fastener (9) in the socket (10) so as to exert a clamping force on the foot, each clamping element defining a threaded hole, • the rod (38) comprises two threads cooperating respectively with the two tapped holes so that rotation of the rod (38) relative to the clamping element causes a variation of the same sign in the clamping forces exerted respectively by the two clamping elements on the foot.

13. Assembly according to the preceding claim, in which : • the two clamping elements (34, 36) are configured to be moved relative to the clamp (9) when the rod (38) is rotated relative to the clamp (9), • the clamp (9) and the two clamping elements have shapes adapted so that the respective displacements of the two clamping elements relative to the clamp (9) cause variations in the clamping forces exerted respectively by the two clamping elements on the foot.

14. Assembly according to any one of claims 12 and 13, in which the two clamping elements (34, 36) are configured to move away from or towards each other when the rod (38) is rotated about the axis of rotation relative to the fastener (9).

15. Assembly according to any one of the preceding claims, in which the elastic layer is made of an elastomer or glass fibre.