Assembly comprising a blade and a system for holding the blade

Abstract

The invention relates to an assembly (101) which comprises a blade (103) and a system (105) for holding the blade (103), and which is intended for an aircraft turbine engine. The blade (103) extends longitudinally along an axis (A) and the system (105) comprises a pivot (113) configured to rotate about the axis (A). The pivot (113) comprises a groove (113a) in which the root (111) is received. The system (105) further comprises a mobile jaw (117), positioned on one side of the root (111). The groove (113a), the root (111) and the mobile jaw (117) together form a dovetail assembly in which the root (111) is kept clamped.

Description

[0001] Description

[0002] TITLE: ASSEMBLY COMPRISING A DAWN AND A DAWN HOLDING SYSTEM

[0003] TECHNICAL FIELD

[0004] The invention relates to the field of fixed blade architecture for aircraft turbomachines. It relates in particular to an assembly comprising a blade and a blade holding system.

[0005] PRIOR ART

[0006] The state of the art includes in particular documents FR-A1-3128972, FR-A1-3126729, EP-B1-4045398 and US-A1-2020063577.

[0007] 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.

[0008] Similarly, 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 moving blades rotating 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 from the fan which has been accelerated by it. This is also referred to as an outlet guide vane or OGV (from the English "Outlet Guide Vane").

[0009] 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 of extension so as to modify their orientation relative to the direction of flow of the stream.

[0010] Figure 1 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 movable in rotation around the axis A and therefore allows its orientation to be modified.

[0011] In recent turbomachines, and particularly in unducted turbomachines, large blades are increasingly frequently made from organic matrix composite materials, as these materials allow a significant weight saving while retaining mechanical properties equivalent to those of materials used previously.

[0012] In the design and manufacture of composite blades, the support to which the blade is attached is generally made of metallic material. It is this metallic part that can rotate in order to orient the composite blade attached above it, and thus modify its incidence relative to the flow.

[0013] 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.

[0014] 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 Figure 2a and Figure 2b in sectional views perpendicular to the axis of the turbomachine of systems 15 for holding the blade 11. Figure 2a thus shows an attachment by clamping (called “radial attachment”) in which the composite parts 17 are shown in light gray and the screws 19 and the metal attachment part 21 are shown in dark gray.

[0015] Figure 2b shows a tangential attachment in which the composite part 17 is shown in light gray and the metal attachment system 19 and 21 is shown in dark gray.

[0016] In the case of fixed blades with radial attachment, it is the lower part of the blade that is most stressed. In addition, the type of stress to which the blade is subjected produces an antisymmetric loading of the attachment, with one side in tension and the other in compression. In particular, it is possible to distinguish two most critical zones linked to this type of stress: the radius of the flanges 17a, whose bending stresses produce forces in the radial direction, favorable to damage modes called type I (i.e. opening (tension) and buckling (compression)); and, the lateral part of the flanges 17a, in correspondence with the attachments, where the forces are concentrated to be transmitted to the components located below the blade.

[0017] In any case, the stresses on the composite part associated with this type of holding system are likely to reduce the life of the part if special arrangements are not made to avoid these drawbacks.

[0018] SUMMARY OF THE INVENTION

[0019] The present invention provides a solution to these drawbacks.

[0020] 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, said blade extending longitudinally along an axis and comprising a blade and a root, and said system comprising a pivot configured to rotate along the axis, said pivot comprising a groove in which the root is housed, said assembly being characterized in that the system further comprises a movable jaw, positioned on one side of the root, said groove, said root and said movable jaw together forming a dovetail assembly in which said root is held clamped between an inclined plane of said groove, the bottom of said groove and an inclined plane of said movable jaw, by means of fixing means passing through said movable jaw, said root and said pivot, and in that the movable jaw and the pivot fit into each other,in the direction transverse to the longitudinal extent of the foot and are connected to each other by a sliding connection. The assembly according to the invention may comprise one or more of the following characteristics, taken in isolation from each other or in combination with each other:,

[0021] - the fixing means are screws, passing through complementary aligned holes in said movable jaw, said foot and said pivot, said screws being tightened by complementary nuts.

[0022] - the fixing means extend parallel to a direction transverse to the longitudinal extent of the foot.

[0023] - the assembly, formed by the pivot and the movable jaw embedded in each other, has a symmetry according to a plane parallel to the longitudinal extent of the groove and passing through the axis.

[0024] - the movable jaw is positioned on the extrados side of the blade.

[0025] - the number of fixing means is between 3 and 8, preferably between 4 and 6, said fixing means being equally distributed along the longitudinal extent of the foot.

[0026] - the system further comprises at least one platform, mounted on the pivot, and the upper face of which is intended to be in contact with a flow flowing around the blade.

[0027] - the movable jaw has the same shape, in its upper part, as one side of the groove to which the inclined plane belongs and, in its lower part, the movable jaw has substantially the shape of an inverted T which fits into a complementary cavity of the pivot so that the movable jaw and the embedded pivot have no projecting part and only the screw heads protrude when the assembly is assembled.

[0028] The invention according to a second aspect further relates to a turbomachine, in particular an aircraft turbomachine, comprising at least one assembly according to the first aspect. 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:

[0029] - the positioning of the foot in the groove; - the embedding of the movable jaw in the pivot by sliding said movable jaw in said pivot in a direction transverse to the longitudinal extent of the foot;

[0030] - the positioning of the fixing means at the level of the movable jaw, the foot and the pivot; and,

[0031] - tightening the fixing means so that the foot is held tight between the inclined plane of the groove, the bottom of said groove and the inclined plane of the movable jaw.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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: Figure 1 is a perspective view of an assembly comprising a blade and a blade holding system according to an embodiment of the prior art; Figure 2a is a schematic representation of a blade holding system according to a first embodiment of the prior art; Figure 2b is a schematic representation of a blade holding system according to a second embodiment of the prior art; Figure 3 is a perspective view of an assembly comprising a blade and a blade holding system according to an embodiment of the invention; Figure 4 is a perspective and sectional view of an assembly comprising a blade and a blade holding system according to an embodiment of the invention;and, Figure 5 is a step diagram of a method of assembling an assembly comprising a blade and a blade holding system according to one embodiment of the invention.;

[0034] DESCRIPTION OF EMBODIMENTS

[0035] With reference to Figure 3 and Figure 4, we will now describe an embodiment of an assembly 101 comprising a blade 103 and a system 105 for holding the blade 103, for an aircraft turbomachine (not shown) according to the invention.

[0036] The blade 103 extends longitudinally along an axis A and comprises a blade 109 and a root 111. The axis A is orthogonal to an axis X of longitudinal extent of the turbomachine around which mobile blades of the 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.

[0037] 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.

[0038] 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.

[0039] Also by way of example, the blade 103 may be made of an organic matrix composite material. It may have been made, for example, by laminating two-dimensional fiber reinforcements, then densified with resin, or by three-dimensional weaving of a single preform which is then densified.

[0040] Advantageously, this type of material allows a significant weight gain while retaining mechanical properties equivalent to those of other heavier materials, or an improvement in mechanical properties for an equivalent weight or even a combination of the two advantages.

[0041] 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 example shown, the pivot 113 cooperates with ball bearings 115 which allow it to rotate along the axis A. In other embodiments, it could be rollers or any other means allowing the rotation of the pivot 113. In the non-limiting example shown, the pivot 113 is a single part, that is to say that it is not an assembly of several separate parts. In addition, the pivot 113 comprises a cylindrical lower part (which is hollow in this example), and an upper part which has a substantially platen shape which comprises a groove 113a in which the foot 111 is housed.

[0042] 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 this are those furthest (radially) from the X axis.

[0043] The system 105 further comprises a movable jaw 117 which is positioned on one side of the foot 111 (relative to the longitudinal extent of said foot 111). The movable jaw 117 is a separate part from the foot 111 and the pivot 113. It is said to be “movable” insofar as it can be moved independently of the pivot 113 and the foot 111.

[0044] In the non-limiting example shown, the movable jaw 117 is positioned on the extrados side of the blade 103 (and by extension of the root 111 as well). Generally speaking, to the extent that the root 111 is straight, the movable jaw 117 can be positioned indifferently on one side or the other.

[0045] Furthermore, the groove 113a, the foot 111 and the movable jaw 117 together form a dovetail assembly in which the foot 111 is held clamped between an inclined plane 113aa of the groove 113a, the bottom 113ab of the groove 113ba and an inclined plane 117a of the movable jaw 117.

[0046] The foot 111 is held tight in the groove 113a by means of fixing means 119 which pass through the movable jaw 117, the foot 111 and the pivot 113.

[0047] In other words, the root 111 is connected to the system 105 by a sliding connection in which the three faces indicated above (the two inclined planes and the bottom of the groove) are supported on three complementary faces of the root 111 when the assembly 101 is assembled so that the root 111 is clamped in the system 105. Advantageously, this arrangement prevents the loss of the blade 103 once the assembly of the assembly 101 has been carried out. In addition, thanks to this arrangement also, the forces undergone by the blade 103, in particular at its root 111, are diffused to the rest of the structure, in particular via the bearings, which avoids their local concentration and the associated risks.

[0048] In the non-limiting example shown, the fixing means 119 are screws, which pass through aligned complementary orifices 121 of the movable jaw 117, the foot 111 and the pivot 113. These screws 119 are tightened by complementary nuts 123. More precisely, the body of each screw 119 passes through the movable jaw 117, the foot 111 and the pivot 113, and emerges at one side of the groove 113a where the emerging part of each screw 119 is tightened by a complementary nut 123.

[0049] Furthermore, the number of screws 119 used is typically between 3 and 8, and preferably between 4 and 6 (5 in the example shown). These screws 119 are equally distributed along the longitudinal extent of the foot 111.

[0050] Generally speaking, a person skilled in the art will be able to adapt the number and spatial distribution of the fixing means 119 of the movable jaw 117 as a function of a desired tightening (and distribution of this tightening).

[0051] Finally, the fixing means 119, whether screws or not, extend parallel to a transverse direction (i.e. orthogonal) to the longitudinal extent of the foot 111.

[0052] Advantageously, due to the inclination of the inclined planes (117a and 113aa) which clamp the foot 111, the fixing means 119 are subjected to very little shear stress and are therefore protected from the associated risks of wear.

[0053] Generally speaking, the adjustment and distribution of the level of tightening of the movable jaw 117, of the foot 111 and of the pivot 113, by the screws 119, makes it possible to determine the intensity of the force which is exerted on said foot 111 and contributes, on the one hand, to its maintenance in the groove 113a and, on the other hand, to the redistribution of the forces undergone by the blade 103 as a whole.

[0054] In the non-limiting example also shown, the movable jaw 117 and the pivot 113 fit into each other, in a direction transverse to the longitudinal extent of the foot 111 and are connected to each other by a sliding connection. In other words, the movable jaw 117 can only slide in one direction (the direction transverse to the longitudinal extent of the foot 111) to fit into the pivot 113. Furthermore, the direction in question is parallel to that of the extent of the fixing means 119.

[0055] Indeed, as can be seen more particularly in Figure 3, the respective shapes of the movable jaw 117 and the pivot 113 are complementary and fit together perfectly.

[0056] Furthermore, the assembly formed by the pivot 113 and the movable jaw 117 embedded in each other, has a symmetry along a plane P parallel to the longitudinal extent of the groove 113a and passing through the axis A.

[0057] In other words, the movable jaw 117 has the shape of a “missing” part of the pivot 113 so that their embedding produces a part whose shape (which allows the dovetail assembly with the foot 111) is symmetrical (along the plane P). In this case, the movable jaw 117 has the same shape, in its upper part, as the side of the groove 113a to which the inclined plane 113aa belongs which allows the clamping of the foot 111. While, in its lower part, the movable jaw 117 has substantially an inverted T shape which is inserted into a complementary cavity of the pivot 113 so that the assembly of the two embedded parts has no projecting part and only the screw heads 119 protrude from the assembly when the assembly 101 is assembled.

[0058] Finally, in a particular embodiment not shown, the system 105 may also comprise at least one platform which is mounted on the pivot 113 and the upper face of which is intended to be in contact with a flow F (typically an air flow) which flows around the blade 109 during use of the aircraft turbomachine.

[0059] Generally, 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 over their surface while limiting their mass (for example via hollow zones within them). Advantageously, the use of several platforms facilitates the assembly of the assembly 101 and the 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.

[0060] Advantageously also, the assembly 101 according to the invention makes it possible to obtain an aerodynamic connection for a fixed blade which results in a reduction in the stress on its critical zones and good mechanical strength, while reducing the mass of the assembly.

[0061] In addition, the person skilled in the art will know how to adapt the shape of the different parts to avoid the concentration of stresses in a given area.

[0062] In addition, a person skilled in the art will be able to adapt the contact surface between the root 111 and the various elements of the system 105 to optimize the distribution of the forces undergone by the blade 103 during its use, for example by increasing the embedding height of the root 111 in the system 105 (i.e. in the groove 113a in particular).

[0063] With reference to Figure 5, we will now describe an embodiment of a method 501 for assembling an assembly 101 such as that shown in Figure 3.

[0064] The first step 503 consists of positioning the foot 111 in the groove 113a. In particular, the base of the foot 111 (i.e. its lower end part) is positioned in the bottom 113ab of the groove 113a, the width of which is complementary to that of the foot 111.

[0065] The following step 505 consists of embedding the movable jaw 117 in the pivot 113 by sliding the movable jaw 117 in said pivot 113 in a direction transverse to the longitudinal extent of the foot 111. As stated above, the shapes of the movable jaw 117 and of the pivot 113 are complementary and configured to allow the translation of the movable jaw 117 (for its embedding) only in this direction until the inclined plane 117a of the movable jaw 117 is supported on the foot 111.

[0066] The next step 507 then consists of positioning the fixing means 119 at the level of the movable jaw 117, the foot 111 and the pivot 113. In the example shown in Figure 3, this involves inserting the screws 119 and positioning the nuts 123 on these screws, but in other embodiments of the invention, it could involve other fixing means making it possible to tighten the three parts (movable jaw 117, foot 111 and pivot 113) together.

[0067] Finally, step 509 consists of tightening the fixing means 119 (in this case tightening the nuts 123 on the screws 119) so that the foot 111 is held tight between the inclined plane 113aa of the groove 113a, the bottom 113ab of the groove 113a and the inclined plane 117a of the movable jaw 117.

[0068] Advantageously, the assembly according to the invention can therefore be assembled in a very simple manner, for example in a workshop prior to its installation on a turbomachine. Maintenance of the blade is therefore also simplified by the easy disassembly of the assembly according to the reverse of the method described here.

Claims

CLAIMS 1. 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), and said system (105) comprising a pivot (113) configured to rotate along the axis (A), said pivot (113) comprising a groove (113a) in which the root (111) is housed, said assembly (101) being characterized in that the system (105) further comprises a movable jaw (117), positioned on one side of the root (111), said groove (113a), said root (111) and said movable jaw (117) together forming a dovetail assembly in which said root (111) is held clamped between an inclined plane (113aa) of said groove (113a), the bottom (113ab) of said groove (113a) and an inclined plane (117a) of said movable jaw (117), by means of fixing means (119) passing through said movable jaw (117), said foot (111) and said pivot (113),and in that the movable jaw (117) and the pivot (113) fit into each other, in the direction transverse to the longitudinal extent of the foot (111) and are connected to each other by a sliding connection.

2. Assembly (101) according to claim 1, in which the fixing means (119, 123) are screws (119), passing through aligned orifices (121) complementary to said movable jaw (117), said foot (111) and said pivot (113), said screws (119) being tightened by complementary nuts (123).

3. Assembly (101) according to claim 1 or claim 2, in which the fixing means (119, 123) extend parallel to a direction transverse to the longitudinal extent of the foot (111).

4. Assembly (101) according to claim 1, in which the assembly, formed by the pivot (113) and the movable jaw (117) embedded in each other, has a symmetry along a plane (P) parallel to the longitudinal extent of the groove (113a) and passing through the axis (A).

5. Assembly (101) according to any one of the preceding claims, in which the movable jaw (117) is positioned on the extrados side of the blade (103).

6. Assembly (101) according to any one of the preceding claims, in which the number of fixing means (119) is between 3 and 8, preferably between 4 and 6, said fixing means (119) being equally distributed along the longitudinal extent of the foot (111).

7. Assembly (101) according to any one of the preceding claims, in which the system (105) further comprises at least one platform, mounted on the pivot (113), and the upper face of which is intended to be in contact with a flow (F) flowing around the blade (109).

8. Assembly (101) according to any one of claims 2 to 7, in which the movable jaw (117) has the same shape, in its upper part, as one side of the groove (113a) to which the inclined plane (113aa) belongs and, in its lower part, the movable jaw (117) has substantially an inverted T shape which is inserted into a complementary cavity of the pivot (113) so that the embedded movable jaw (117) and pivot (113) have no projecting part and only the heads of the screws (119) protrude when the assembly (101) is assembled.

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

10. Method (501) of assembling an assembly (101) according to any one of claims 1 to 6, comprising the following steps: - the positioning (503) of the foot (111) in the groove (113a); - the embedding (505) of the movable jaw (117) in the pivot (113) by sliding said movable jaw (117) in said pivot (113) in a direction transverse to the longitudinal extent of the foot (111); - the positioning (507) of the fixing means (119, 123) at the level of the movable jaw (117), the foot (111) and the pivot (113); and, - the tightening (509) of the fixing means (119, 123) so that the foot (111) is held tight between the inclined plane (113aa) of the groove (113a), the bottom (113ab) of said groove (113a) and the inclined plane (117a) of the movable jaw (117).

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