ASSEMBLY INCLUDING A BLADE AND A BLADE RETAINING SYSTEM

Abstract

The invention relates to an assembly (101) comprising a blade (103) and a blade (105) retention system for an aircraft turbomachine. The blade (103) extends longitudinally along an axis (A) and comprises a blade (109) and a foot (111). The system (105) comprises a pivot (113) configured to rotate about the axis (A), a flange (117) mounted on the pivot (113) and configured to retain the foot (111) within it, and at least one platform (123) mounted on the flange (117) configured to cover an external portion of the flange (117). The foot (111) and a groove (131) of the flange (117) form, respectively, a male and a female part of a dovetail joint, and the system (105) includes pressure means (133) exerting a pressure force on a base (135) of the foot (111) so that the foot (111) is compressed against inclined inner faces (137) of the groove (131) of the flange (117). Figure for the abbreviation: Fig. 3

Description

Title of the invention: ASSEMBLY COMPRISING A BLADE AND A BLADE HOLDING SYSTEM Technical field

[0001] The invention relates to the field of the architecture of fixed blades of aircraft turbomachines. It relates in particular to an assembly comprising a blade and a blade holding system. Prior art

[0002] In an unducted turbomachine, so-called fixed blades, i.e. blades that are not mobile in rotation around the longitudinal axis of the turbomachine, are coupled to a propeller and have the function of "straightening" the aerodynamic flow at the outlet of the propeller.

[0003] In the same way, in a ducted turbomachine, such fixed blades are coupled to a fan which is located upstream of these fixed blades in the direction of flow of the flow in the turbomachine and which comprises blades moving in rotation around the axis of the turbomachine. As in the case of the unducted turbomachine, these fixed blades also have the function of straightening the flow coming from the fan which has been accelerated by the latter. This is also referred to as an outlet guide vane or OGV (from the English “Outlet Guide Vane”).

[0004] Furthermore, these fixed blades can be variable-pitch, that is to say they can be part of an assembly which allows their rotation around their longitudinal axis so as to modify their orientation relative to the direction of flow of the stream.

[0005] [Fig.l] thus shows, by way of example, a variable-pitch blade 11 which comprises a blade 13 which is mounted on a system 15 for holding the blade 11 which is mobile in rotation around the axis A and therefore allows its orientation to be modified.

[0006] In recent turbomachines, and in particular in non-ducted turbomachines, large blades are increasingly frequently made from organic matrix composite materials to the extent that these materials allow a significant weight saving while retaining mechanical properties equivalent to those of materials used until now.

[0007] In the context of the design and manufacture of blades made of composite material, the support to which the blade is fixed is generally made of metallic material. It is this metallic part which can exert a rotation in order to orient the composite blade which is fixed above, and thus modify its incidence relative to the flow.

[0008] For such a blade, the main type of stress seen by the part concerns bending movements induced by its incidence, but also by the variation of the pressure field caused by the passage of the fan blades. Significantly larger amplitudes can also be seen in the event of impacts (pieces of propeller, bird, others...) during extreme events.

[0009] The simplest means of attachment between a metal part and a composite part is bolting. For this purpose, two types of fasteners are commonly used, as illustrated in [Fig.2a] and [Fig.2b] in sectional views perpendicular to the axis of the turbomachine of blade holding systems 15.

[0010] [Fig.2a] thus shows a clamping attachment (called a “radial attachment”) in in which the composite parts 17 are shown in light gray and the screws 19 and the metal fixing part 21 are shown in dark gray.

[0011] [Fig.2b] shows a tangential attachment in which the part composite 17 is shown in light gray and the metal fastening system 19 and 21 is shown in dark gray.

[0012] In the case of fixed blades with radial attachment, it is the lower part of the blade which is subjected to the greatest stress. In addition, the type of stress to which the blade is subjected produces an antisymmetrical loading of the attachment, with one side in tension and the other in compression.

[0013] In particular, it is possible to distinguish two most critical zones linked to this type of stress: - the radius of the flanges, the bending stresses of which produce radial forces, favorable to damage modes known as type I (i.e. opening (tension) and buckling (compression)); and, - the lateral part of the flanges, in correspondence with the fixings, where the forces are concentrated to be transmitted to the components located below the blade.

[0014] In all cases, the stresses on the composite part associated with this type of holding system are likely to reduce the service life of the part if special arrangements are not made to avoid these drawbacks. Summary of the invention

[0015] The present invention provides a solution to these drawbacks.

[0016] Thus, one objective of the invention is to improve the distribution of the forces undergone by the blades and to reduce the risks of degradation of said blades linked to their holding system.

[0017] To this end, the invention according to a first aspect relates to an assembly comprising a blade and a blade holding system, for an aircraft turbomachine,

[0018] said blade extending longitudinally along an axis and comprising a blade and a foot,

[0019] said system comprising a pivot configured to rotate along the axis, a strap, mounted on said pivot and configured to hold the foot within it, and at least one platform, mounted on said strap, configured to cover an external part of said strap,

[0020] said assembly being characterized in that the foot and a groove of the flange respectively form a male part and a female part of a dovetail assembly and the system further comprises pressure means exerting a pressure force on a base of the foot, in the direction of the axis, so that the foot is compressed against inclined internal faces of the groove of the flange.

[0021] 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:

[0022] - the pressure means are at least one boss of the pivot passing through at least one hole made in the bottom of the flange groove and resting on the base of the foot.

[0023] - a clearance is provided between the pivot and the flange outside the support zone of the less a boss on the base of the foot.

[0024] - the pressure means comprise screws, inserted into complementary orifices elements passing through the bottom of the groove of the bridle and tightened so as to rest on the base of the foot.

[0025] - the assembly further comprises at least one shim, positioned in the groove, between the flange and the base of the foot, around the screws.

[0026] - the groove is open at a longitudinal end and said assembly comprises in in addition to a plate, fixed to the flange at the said end, so as to block the sliding of the foot in the groove.

[0027] - a plurality of pressure means is distributed along the longitudinal extent from the flange throat.

[0028] - the assembly further comprises a seal, positioned in an area interface between the flange, the foot and the at least one platform, so as to ensure the airtightness of said interface zone.

[0029] - a first platform is positioned on the extrados side of the blade and a second platform is positioned on the intrados side of the blade.

[0030] - the at least one platform is fixed to the flange by means of screws, passing through complementary aligned orifices, provided in said at least one platform and said flange.

[0031] - the flange is fixed on the pivot by means of screws, passing through orifices com additional aligned, arranged in said pivot and said flange.

[0032] - the blade is made of organic matrix composite material, for example made by having a preform made by three-dimensional weaving and impregnated with the organic matrix.

[0033] - the blade is an outlet guide blade.

[0034] The invention according to a second aspect further relates to a turbomachine, in particular for an aircraft, comprising at least one assembly according to the first aspect.

[0035] The invention according to a third aspect further relates to a method of assembling an assembly according to the first aspect, comprising the following steps:

[0036] - positioning the blade in the flange by sliding the foot in the groove;

[0037] - the positioning of the screws in the holes of the groove;

[0038] - tightening the screws so as to exert a determined pressure force on the base from the foot of dawn;

[0039] - inserting at least one shim into the groove of the flange;

[0040] - fixing the plate on the flange so as to block the sliding of the foot in the throat; and,

[0041] - mounting the at least one platform on the flange and said flange on the pivot. Brief description of the drawings

[0042] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which:

[0043] [Fig.l] is a perspective view of an assembly comprising a blade and a blade holding system according to an embodiment of the prior art;

[0044] [Fig.2a] is a schematic representation of a system for holding a blade according to a first embodiment of the prior art;

[0045] [Fig.2b] is a schematic representation of a system for holding a blade according to a second embodiment of the prior art;

[0046] [Fig. 3] is a sectional view of an assembly comprising a blade and a blade holding system according to a first embodiment of the invention;

[0047] [Fig.4] is a sectional view of an assembly comprising a blade and a blade holding system according to a first embodiment of the invention;

[0048] [Fig.5] is a sectional view of an assembly comprising a blade and a blade holding system according to a first embodiment of the invention;

[0049] [Fig.6] is a sectional view of an assembly comprising a blade and a blade holding system according to a second embodiment of the invention;

[0050] [Fig.7] is a step diagram of a method of assembling an assembly comprising a blade and a blade holding system according to the second embodiment of the invention; and,

[0051] [Fig.8] is a schematic representation of the steps of an assembly process of an assembly comprising a blade and a blade holding system according to the second embodiment of the invention. Description of the embodiments

[0052] With reference to [Fig.3], [Fig.4], and [Fig.5], we will now describe a first embodiment of an assembly 101 which comprises a blade 103 and a system 105 for holding the blade 103, for an aircraft turbomachine (not shown). An example of integration of such an assembly in a turbomachine is for example given, in more detail, in application FR-A1-3126729.

[0053] The blade 103 comprises a blade 109 and a root 111 and extends longitudinally along an axis A. The axis A is orthogonal to an axis X of longitudinal extent of the turbomachine around which mobile blades of said turbomachine rotate. The blade 103 is therefore mounted in the turbomachine, typically among other identical blades which belong to a row of so-called fixed blades.

[0054] This is a so-called fixed blade in the sense that it is not rotatable about the longitudinal axis of the turbomachine in which it is mounted. However, as will become more clear in the following, the blade 103 is rotatable about the axis A and can be said to have variable pitch, that is to say that its orientation relative to the flow flowing in the turbomachine can be modified.

[0055] It may thus be, by way of non-limiting example, a blade called an outlet guide vane or OGV (from the English “Outlet Guide Vane”) belonging to a row of OGVs whose function is to straighten a flow coming from a propeller of an unducted turbomachine or from a fan of a ducted turbomachine.

[0056] In a particular embodiment, the blade 103 is made of an organic matrix composite material. It may have been produced, for example, by lamination of two-dimensional fiber reinforcements, then densified by resin, or by three-dimensional weaving, that is to say by having a preform produced by three-dimensional weaving and impregnated by the organic matrix.

[0057] In all cases, this type of material allows a significant gain in mass while retaining mechanical properties equivalent to those of other heavier materials, or an improvement in mechanical properties for an equivalent mass or even a combination of the two advantages.

[0058] In the assembly 101, the system 105 for holding the blade 103 comprises a pivot 113 which is configured to rotate along the axis A. Thus, in the non-limiting example shown, the pivot 113 cooperates with bearings 115 which allow its rotation along the axis A. In other embodiments, these may be rollers or any other means allowing the rotation of the pivot 113.

[0059] The system 105 also comprises a flange 117, mounted on the pivot 113 and configured to hold the root 111 of the blade 103 within it. In the example shown, the lower part of the flange 117 cooperates with the upper part of the pivot 113 so that the flange 117 and the pivot fit into each other.

[0060] The terms "lower" and "upper" are defined relative to the engine axis (i.e. the X axis of rotation of the moving blades of the turbomachine mentioned above). Thus, the lower parts mentioned in the following are those closest (radially) to the X axis while the upper parts mentioned in the following are those furthest (radially) from the X axis.

[0061] Furthermore, the lower part of the pivot 113 has substantially the shape of a cylinder (around which bearings can be mounted) while the upper part of the pivot 113 has substantially the shape of a platform intended to accommodate the flange 117.

[0062] In the non-limiting example shown, the flange 117 is fixed to the pivot 113 by screws 119 (symbolized by dotted lines in [Fig. 3] and visible in [Fig. 6] relating to another embodiment sharing the same flange fixing system) which pass through aligned complementary orifices 121 which are provided in the pivot 113 and in the flange 117. More precisely, four orifices 121 are distributed on each side (intrados and extrados) of the blade 103 and used to allow the flange 117 to be fixed to the pivot 113. Furthermore, in the particular embodiment described, these are screws with a diameter of 12.7 millimeters. In different embodiments, these could be "normal" 12-point screws, 12-point screws with a low head or screws with six hollow lobes.

[0063] Generally speaking, a person skilled in the art will know how to adapt the number, shape and distribution of the screws to a desired tightening force and distribution of this force.

[0064] The system 105 further comprises at least one platform 123 which is mounted on the flange 117 and configured to cover an external portion of the flange 117. The term “external” here designates the portion distinct from the lower portion (i.e. the lateral and upper portion).

[0065] In the non-limiting example shown, the system 105 comprises a first platform 123a positioned on the extrados side of the blade 103 and a second platform 123b positioned on the intrados side of the blade 103. Advantageously, the use of several platforms facilitates the assembly of the assembly 101 and a person skilled in the art will know how to adapt their number, greater than or equal to 1, to the specific geometry of an assembly used.

[0066] Furthermore, the platform(s) used have an aerodynamic role in the sense that their shape (in the example shown, a convex shape) is designed to optimize the flow of the stream in contact with them while limiting their mass (for example via hollow spaces within them).

[0067] In the non-limiting example shown, the platforms 123a and 123b are fixed to the flange 117 by means of screws 125 (visible in [Fig.8] relating to another embodiment sharing the same platform fixing system) which pass through aligned complementary orifices 127 which are provided in the platforms 123a and 123b and in the flange 117.

[0068] In particular, in this example, four countersunk head screws 125, the head of which is buried, are positioned and tightened in each platform 123 and in the threaded holes 127 of the flange 117 so as to fix the platforms 123a and 123b on the flange 117.

[0069] Furthermore, the other orifices 121 mentioned above (passing through the flange 117 and the pivot 113), also pass through the platforms 123a and 123b so that the assembly operations of the assembly 101, in particular the fixing of the flange 117 on the pivot 113 are facilitated.

[0070] As can be seen more particularly in [Fig. 4], in a particular embodiment, the assembly 101 may also comprise a seal 129 which is positioned in an interface zone between the flange 117 and the platforms 123a and 123b on the one hand, and in an interface zone between the foot 111, the flange 117 and the platforms 123a and 123b, so as to ensure the airtightness of these interface zones. This seal also has the function of avoiding the galvanic couple between the flange and the platform(s) and may be, for example, made of EPDM (ethylene-propylene-diene monomer).

[0071] In the example shown in [Fig.4], this seal 129 comprises a first part 129a located in the interface zone between the foot 111, the flange 117 and the platforms 123a and 123b and a second part located in the interface zone between the flange 117 and the platforms 123a and 123b. The two parts 129a and 129b may or may not be integral.

[0072] In addition to the elements described so far, in the assembly 101, the flange 117 comprises a groove 131 (open in its upper part). The foot 111, on the one hand, and this groove 131, on the other hand, respectively form a male part and a female part of a dovetail assembly. This is also referred to as a so-called “broached” foot.

[0073] The foot 111 can thus be assembled with the groove 131 by sliding in the latter, an internal opening of which has a shape complementary to that of the foot 111. The foot 111 and the groove 131 being linked, ultimately, by a sliding connection.

[0074] Advantageously, the foot 111 can thus be held by the flange 117, and generally by the system 105 for holding the blade 103, without requiring recourse to machining in said foot 111 which would be likely to deteriorate its mechanical characteristics.

[0075] Furthermore, the system 105 also comprises pressure means 133 which exert a pressure force on a base 135 of the foot 111, in the direction of the axis A, so that the foot 111 is compressed against inclined internal faces 137 of the groove 131 of the flange 117.

[0076] The term “base” here designates the lower surface of the foot 111 against which the pressure means 133 come to bear so that the pressure is exerted on the foot 111, in the direction of the axis A, from the bottom to the top in the figures, which causes the compression of the foot on the inclined internal faces 137 of the flange 117.

[0077] Advantageously, the root 111 of the blade 103 and the flange 117 are thus subjected to a prestress, that is to say to internal forces which make it possible to redistribute the forces to which the blade 103 is subjected in use (in particular those linked to the circulation of a flow along the blade during operation of the turbomachine) in a favorable manner (i.e. less likely to cause its degradation).

[0078] In particular, in the non-limiting example shown, as illustrated by the arrows 140 visible in [Fig. 5], the forces undergone by the blade 103 at the level of its lower part are transferred to the bearings 115 by means of the flange 117 and the pivot 113 thanks to the prestressing existing in the system 105.

[0079] In this embodiment, the pressure means 133 are at least one boss 133 (also called heel) of the pivot 113 which passes through at least one orifice 138 formed in the bottom of the groove 131 of the flange 117 and which comes to bear on the base 135 of the foot 111.

[0080] The pressure force exerted by this boss 133 on the foot 111 is thus determined by the tightening of the screws 119 which fix the flange 117 to the pivot 113. Furthermore, in the views presented in figures 3, 4 and 5, a single boss (whose length may or may not cover the entire longitudinal extent of the groove) is apparent, but those skilled in the art will appreciate that a number greater than or equal to one of bosses may be distributed along the longitudinal extent of the groove 131 of the flange 117.

[0081] Furthermore, as can be seen in particular in [Fig. 5], a clearance j is provided between the pivot 113 and the flange 117 outside the support zone of the boss 133 on the base 135 of the foot 111. The clearance can also be provided between the flange 117 and the base 135 of the foot 111 outside the orifice 138. In all cases, the presence of this clearance j makes it possible to avoid blocking of the boss 133 and to guarantee that the latter exerts the desired pressure on the foot 111 depending on the tightening of the screws 119.

[0082] With reference to [Fig.6], we will now describe another embodiment of an assembly 101 according to the invention.

[0083] This embodiment incorporates the characteristics of the embodiment described with reference to figures 3, 4 and 5, unlike the pressure means 133 which are used to generate a prestress.

[0084] Indeed, in the embodiment shown in [Fig.6], the pressure means 133 are screws 133 inserted into complementary orifices 139 which pass through the bottom of the groove 131 of the flange 117 and which are tightened so as to come to bear on the base 135 of the foot 111. In this non-limiting example, these are headless screws.

[0085] As in the case of the pressure means 133 described with reference to the previous embodiment, a plurality of screws 133 can be distributed along the longitudinal extent of the groove 131 of the flange 117. Advantageously, the forces generated by the pressure means 133 can be distributed optimally. Thus, in the non-limiting example shown, as seen in [Fig. 8], three screws 133 are equally distributed along the longitudinal extent of the groove 131.

[0086] Furthermore, in this embodiment, at least one shim 141 is positioned in the groove 131, between the flange 117 and the base 135 of the foot 111, around the screws 133. In this example, a single shim in the shape of a flat U is positioned between the flange 117 and the base 135 of the foot 111. Advantageously, this can thus be easily inserted into the desired position during the assembly of the assembly 101 as will appear more clearly below.

[0087] Generally speaking, those skilled in the art will appreciate that the number and shape (the thickness in particular) of the shim(s) can be modified to optimize the distribution of forces at the root 111 of the blade 103.

[0088] In this embodiment also, the groove 131 is open at one longitudinal end and the assembly 101 comprises a plate 143, fixed to the flange 117 at said end, so as to block the sliding of the foot 111 in the groove 131. Here again, the advantage associated with the use of this plate 143 is a simplification of the assembly process of the assembly 101.

[0089] Generally speaking, this embodiment makes it possible to simplify the assembly or disassembly operations (which facilitates possible maintenance) of the assembly. Furthermore, all the assembly steps of this assembly 101 can be carried out in the workshop, prior to mounting the assembly 101 in a turbomachine.

[0090] Thus, with reference to [Fig.7] and [Fig.8], we will now describe a mode of implementation of a method 701 for assembling the assembly 101 as illustrated in [Fig.6].

[0091] The first step 703 consists of positioning the blade 103 in the flange 101 by sliding the foot 111 in the groove 131. As stated above, the groove 131 is open at one of its longitudinal ends so as to allow this insertion during assembly. The dovetail assembly is thus obtained.

[0092] Step 705 then consists of positioning the screws 133 in the orifices 139 of the groove 131. As stated above, the screws 133 are three in number and are equally distributed along the longitudinal extent of the groove 131.

[0093] Step 707 then consists of tightening the screws 133 so as to exert a force of pressure determined on the base 135 of the foot 111 of the blade 103. This operation makes it possible to distribute the pressure force exerted by the screws 133 on the foot 111 to obtain a determined force.

[0094] Step 709 consists of inserting the shim 141 into the groove 131 of the flange 117. As mentioned above, the shape of the shim 141 is adapted to simplify its handling and its insertion while contributing to a determined distribution of the forces generated.

[0095] Step 711 then consists of fixing the plate 143 on the flange 117 so as to block the sliding of the foot 111 in the groove 131. The foot 111 is thus perfectly held in the flange 117.

[0096] Step 713 finally consists of mounting the platforms 123a and 123b on the flange 117 and the flange 117 on the pivot 113 so that all the parts of the assembly are thus assembled.

[0097] In conclusion, for this embodiment as for the previous one, the radial thrust, that is to say the pressure force exerted by the pressure means 133 on the root 111 makes it possible to reduce the stress on critical zones (the forces undergone) of the blade 103 included in the assembly 101.

[0098] In addition, the shape of the various elements which are included in the support system (such as for example their radii of curvature, the heights of the lateral foot-cell spans and / or the inclination of these spans) can be adapted in order to limit the concentration of forces.

Claims

Claims

1. An assembly (101) comprising a blade (103) and a system (105) for holding the blade (103), for an aircraft turbomachine, said blade (103) extending longitudinally along an axis (A) and comprising a blade (109) and a root (111), said system (105) comprising a pivot (113) configured to rotate along the axis (A), a flange (117), mounted on said pivot (113) and configured to hold the root (111) therein, and at least one platform (123), mounted on said flange (117), configured to cover an external portion of said flange (117), said assembly (101) being characterized in that the root (111) and a groove (131) of the flange (117) respectively form a male portion and a female portion of a dovetail assembly and the system (105) further comprises pressure means (133) exerting a pressure force on a base (135) of the foot (111), in the direction of the axis (A),such that the foot (111) is compressed against inclined internal faces (137) of the groove (131) of the flange (117).,

2. Assembly (101) according to claim 1, in which the pressure means (133) are at least one boss (133) of the pivot (113) passing through at least one orifice (138) formed in the bottom of the groove (131) of the flange (117) and coming to bear on the base (131) of the foot (111).

3. Assembly (101) according to claim 2, in which a clearance (j) is provided between the pivot (113) and the flange (117) outside the support zone of the at least one boss (133) on the base (135) of the foot (111).

4. Assembly (101) according to claim 1, in which the pressure means (133) comprise screws (141), inserted into complementary orifices (139) passing through the bottom of the groove (131) of the flange (117) and tightened so as to come to bear on the base (135) of the foot (111).

5. Assembly (101) according to claim 4, further comprising at least one shim (141), positioned in the groove (131), between the flange (117) and the base (135) of the foot (111), around the screws (133).

6. An assembly (101) according to claim 5, wherein the groove (131) is open at a longitudinal end and said assembly (101) further comprises a plate (143), fixed to the flange (117) at said end, so as to block the sliding of the foot (111) in the groove (131).

7. An assembly (101) according to any preceding claim, wherein a plurality of pressure means (133) are distributed along the longitudinal extent of the groove (131) of the flange (117).

8. Assembly (101) according to any one of the preceding claims, further comprising a seal (129), positioned in an interface zone between the flange (117), the foot (111) and the at least one platform (123), so as to ensure the airtightness of said interface zone.

9. An assembly (101) according to any preceding claim, wherein a first platform (123a) is positioned on the suction side of the blade (103) and a second platform (123b) is positioned on the suction side of the blade (103).

10. An assembly (101) according to any one of the preceding claims, wherein the at least one platform (123) is fixed to the flange (117) by means of screws (125), passing through aligned complementary orifices (127), provided in said at least one platform (123) and said flange (117).

11. An assembly (101) according to any preceding claim, wherein the flange (117) is fixed to the pivot (113) by means of screws (119), passing through aligned complementary orifices (121), provided in said pivot (113) and said flange (117).

12. Assembly (101) according to any one of the preceding claims, in which the blade (103) is made of organic matrix composite material, for example made by having a preform made by three-dimensional weaving and impregnated with the organic matrix.

13. An assembly (101) according to any preceding claim, wherein the vane (103) is an outlet guide vane.

14. Turbomachine, in particular for an aircraft, comprising at least one assembly (101) according to any one of the preceding claims.

15. Method (701) for assembling an assembly (101) according to claim 6, comprising the following steps: - positioning (703) the blade (103) in the flange (117) by sliding the foot (111) in the groove (131); - positioning (705) the screws (133) in the orifices (139) of the groove (131); - tightening (707) the screws (133) so as to exert a determined pressure force on the base (135) of the foot (111) of the blade (103); the insertion (709) of the at least one shim (141) into the groove (131) of the flange (117); the fixing (711) of the plate (143) on the flange (117) so as to block the sliding of the foot (111) in the groove (131); and, mounting (713) the at least one platform (123) on the flange (117) and said flange (117) on the pivot (113).

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