Assembly comprising a blade and a system for holding the blade

Abstract

The invention relates to an assembly (101) comprising a blade (103) and a system (105) for holding the blade (103) for an aircraft turbine engine. The blade (103) extends longitudinally along an axis (A) and comprises a blade body (109) and a root (111). The system (105) comprises a pivot (113) configured to rotate about the axis (A) and at least one platform (115) mounted on the pivot (113). The pivot (113) and the at least one platform (115) together form a cavity (117), which has a shape that complements the shape of the root (111), and in which the root (111) is clamped and held by attachment means (121, 125).

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-A13087830, FR-A1-3123885 and FR-A1-3126729.

[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 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 2 in sectional views perpendicular to the axis of the turbomachine of systems 15 for holding the blade 11.

[0015] The left part of figure 2 thus shows a clamping attachment (called a “radial attachment”) 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.

[0016] The right part of Figure 2 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.

[0017] 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.

[0018] 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.

[0019] SUMMARY OF THE INVENTION

[0020] The present invention provides a solution to these drawbacks.

[0021] 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, said system comprising a pivot configured to rotate along the axis and 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, said assembly being characterized in that the pivot and the at least one platform together form a cavity, having a shape complementary to the shape of the root, and in which said root is gripped and held by means of fixing means, in that the at least one platform and the pivot comprise first aligned orifices, parallel to the axis, said first orifices being complementary to first means among said fixing means, preferably screws,used to fix said pivot and said at least one platform together, and in that the at least one platform and the foot comprise second aligned through-holes, perpendicular to the axis, said second holes being complementary to second means among said fixing means used to fix said foot and said at least one platform together.,

[0022] 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:

[0023] - the foot has substantially the shape of a rectangular parallelepiped, and the first fixing means and the second fixing means are distributed along the length direction of the foot.

[0024] - the first fixing means and the second fixing means are alternated according to the direction of the length of the foot.

[0025] - the first fixing means are equally distributed along the length direction of the foot and the second fixing means are equally distributed along the length direction of the foot.

[0026] - the second fixing means comprise threaded rods, passing through the second orifices, and nuts, tightening said threaded rods, on either side of said second orifices.

[0027] - the pivot is a single piece comprising a cylindrical lower part, and an upper part having substantially the shape of a plate comprising a groove in which a base of the foot is housed.

[0028] - 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.

[0029] - the blade is made of organic matrix composite material, for example made by three-dimensional weaving.

[0030] - the dawn is an exit guide dawn.

[0031] 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 finally relates to a method of assembling an assembly according to the first aspect, comprising the following steps: - inserting the threaded rods into the second orifices of a platform among the first platform and the second platform;

[0032] - positioning the foot in contact with the platform by inserting the threaded rods into the second holes of said foot;

[0033] - positioning another platform, among the first platform and the second platform, in contact with the foot, by inserting the threaded rods into the second orifices of said other platform;

[0034] - the positioning and tightening of the nuts on the threaded rods so as to fix the first platform, the foot and the second platform together;

[0035] - positioning the assembly formed by the first platform, the foot and the second platform on the upper part of the pivot so that the base of the foot is housed in the groove; and,

[0036] - inserting and tightening the screws in the first holes so as to fix the pivot and the first platform and the second platform together.

[0037] Furthermore, in a particular embodiment of the method, during the step of positioning and tightening the nuts, a marble is used, before tightening the nuts, to align the lower surfaces of the first platform and the second platform.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] 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 4a is a sectional view of an assembly comprising a blade and a blade holding system according to an embodiment of the invention;Figure 4b is a sectional view of an assembly comprising a blade and a blade holding system according to one embodiment of the invention; 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; and, Figure 6 is a schematic representation of steps of assembling an assembly comprising a blade and a blade holding system according to one embodiment of the invention.;

[0040] DESCRIPTION OF EMBODIMENTS

[0041] With reference to Figure 3, Figure 4a and Figure 4b, 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).

[0042] Figures 4a and 4b represent two sectional views of the same assembly along two sectional planes parallel to each other but offset. The elements included in the assembly 101 described below are also visible in Figure 6, which illustrates certain steps of an embodiment of a method of assembling said assembly 101.

[0043] 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.

[0044] 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. It can 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.

[0045] In a particular embodiment, the blade 103 is 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.

[0046] 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.

[0047] 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, by way of example, the pivot 113 can cooperate with bearings (not shown) which allow its rotation along the axis A or with rollers or any other means allowing its rotation.

[0048] 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. Furthermore, the pivot 113 comprises a cylindrical lower part 113a, and an upper part 113b which has substantially the shape of a plate which comprises a groove 113ba in which the base 111a of the foot 111 is housed.

[0049] The term "base" here designates the lower surface of the foot 111. The terms

[0050] "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.

[0051] Furthermore, the root 111 has substantially the shape of a rectangular parallelepiped and the groove 113ba extends longitudinally along the direction of the length of the root 111 (i.e. along the length of the parallelepiped). Generally speaking, the root 111 may have any equivalent elongated shape to easily manufacture the blade root and to allow good support and good force transmission capacity between the blade 109 and the pivot 113) whatever the conditions of use.

[0052] The system 105 also comprises at least one platform 115 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.

[0053] The platform(s) used therefore 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).

[0054] In the non-limiting example also shown, the system 105 comprises a first platform 115a which is positioned on the extrados side of the blade 103 and a second platform 115b which is positioned on the intrados side of the blade 103.

[0055] 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.

[0056] Furthermore, the platforms 115a and 115b on the one hand, and the pivot 113 on the other hand, together form a cavity 117, which has a shape complementary to the shape of the foot 111, and in which the foot 111 is clamped and held by means of fixing means (described below).

[0057] In particular, in this example, the groove 113ba and internal cavities of the platforms 115a and 115b together form the cavity 117 which has substantially a parallelepiped shape, identical to that of the foot 111, so as to enclose the foot 111 when the assembly 101 is assembled. In other embodiments (not shown), the shape of the foot 111 could have tapered faces, or double tapered faces, in order to optimize the transmission of forces, to limit the risks of the foot slipping, and to make the fixing means (described later) work in shear.

[0058] In addition, a person skilled in the art will be able to adapt the contact surface between the platforms 115 and the root 111 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 platforms 115 and the pivot 113).

[0059] In the example shown, the platforms 115a and 115b and the pivot 113 have orifices 119 aligned and parallel to the axis A. The orifices 119 are complementary to fixing means 121, in this case screws, used to fix the pivot 113 and the platforms 115a and 115b together.

[0060] Furthermore, in the example also shown, five screws 121 of 12.7 millimeters in diameter are distributed in each platform 115 in the direction of the length of the foot 111. The screws 121 are buried in the orifices 119 so that they do not protrude from the upper face of the platforms 115a and 115b so as not to hinder the flow of a stream in this zone.

[0061] The platforms 115a and 115b and the foot 111 also have aligned through holes 123 which are perpendicular to the axis A. In the described embodiment, the axis of the holes 123 is also perpendicular to the length of the foot 111. Furthermore, the holes 123 are complementary to fastening means 125 used to fasten the foot 111 and the platforms 115a and 115b together.

[0062] As can be seen in particular in Figure 4a, the orifices 123 which pass through both the foot 111 and the platforms 115a and 115b open out at the level of internal hollow zones of the platforms 115a and 115b.

[0063] Furthermore, in the non-limiting example shown, four fixing means 125 are distributed along the length direction of the foot 111. More precisely, the fixing means 125 comprise threaded rods 125a (also called “tie rods” in the vocabulary of the field of design and use of blades according to the invention) which pass through the orifices 125 and nuts 125b which tighten the threaded rods 125a, on either side of the orifices 123. The threaded rods 125a and the nuts 125b are equally distributed along the length direction of the foot 111.

[0064] As can be seen more particularly in Figure 3 and Figure 6, the fixing means 121 (and consequently the orifices 119) as well as the fixing means 125 (and consequently the orifices 123) are alternated along the direction of the length of the foot 111.

[0065] Finally, in the non-limiting example shown again, the assembly 101 also comprises a nut 127 screwed onto a complementary thread located in the lower part 113a of the pivot 113. The nut 127 retains the assembly on the engine and is not described in more detail here since it is not part of the invention. Advantageously, the invention in general and this arrangement in particular makes it possible to maintain the blade 103 with a system 105 which is compact and lightweight.

[0066] 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, better mechanical strength, and a significant reduction in mass.

[0067] With reference to Figure 5 and Figure 6, we will now describe an embodiment of a method 501 for assembling the assembly 101 as illustrated in Figure 3 and Figure 4.

[0068] The first step 503 consists of inserting the threaded rods 125a into the second orifices 123 of a platform 115 among the first platform 115a and the second platform 115b. In the example shown, this is the platform 115a and the threaded rods 125a therefore open out at a hollow area of ​​the platform 115a.

[0069] The following step 505 consists of positioning the foot 111 (and therefore the blade 103) in contact with the platform 115a by inserting the threaded rods 125a into the orifices 123 of the foot 111.

[0070] The following step 507 consists of positioning another platform 115, among the first platform 115a and the second platform 115b, in contact with the foot 111, by inserting the threaded rods 125a into the orifices 123 of this other platform 115a or 115b. In the example, it is the platform 115b which comes into contact with the foot 111 and the other platform 115a so that the two platforms 115a and 115b enclose the foot 111 and the threaded rods 125a open into internal hollow zones of the two platforms 115a and 115b.

[0071] The next step 509 consists of positioning and tightening the nuts 125b on the threaded rods 125a so as to fix the first platform 115a, the foot 111 and the second platform 125b together. A person skilled in the art will know how to adapt the tightening of the nuts 125b so as to obtain a pinching of the foot 111 by the platforms 115a and 115b with a desired level of pressure.

[0072] Furthermore, in a particular embodiment, during this step, a marble is used, before tightening the nuts 125b, to align the lower surfaces of the first platform 115a and the second platform 115b (as can be seen in the lower part of Figure 6).

[0073] The next step 511 consists of positioning the assembly formed by the first platform 115a, the foot 111 and the second platform 115b (i.e. the assembly which was tightened during the previous step) on the upper part of the pivot 113b so that the base of the foot 111a is housed in the groove 113ba. The foot 111 is therefore gripped by the platforms 115a and 115b and the pivot 113 with, in addition, the presence of a clearance between the lower part of the base 111a and the groove 113ba (i.e. there is no contact between these two parts) to avoid hyper-statics when tightening the screws 121 in the pivot 113.

[0074] Finally, step 513 consists of inserting and tightening the screws 121 into the holes 119 so as to fix the pivot 113, the first platform 115a and the second platform 115b together.

[0075] The method described here is a method of assembling the assembly 101, however, the steps described can be applied to a disassembly by reversing their order and replacing tightening with loosening, positioning with removal and insertion with extraction. Advantageously, the assembly according to the invention therefore has a simplified assembly or disassembly. It is thus in particular possible to assemble the assembly in the workshop before its mounting on a turbomachine. Likewise, maintenance of the blade is thus simplified thanks to its easy disassembly.

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), said system (105) comprising a pivot (113) configured to rotate along the axis (A) and at least one platform (115) 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), said assembly being characterized in that the pivot (113) and the at least one platform (115) together form a cavity (117), having a shape complementary to the shape of the root (111), and in which said root (111) is clamped and held by means of fixing means (121, 125), in that the at least one platform (115) and the pivot (113) comprise first aligned orifices (119), parallel to the axis (A),said first orifices (119) being complementary to first means (121) among said fixing means (121, 125), preferably screws (121), used to fix said pivot (113) and said at least one platform (115) together, and in that the at least one platform (115) and the foot (111) comprise second aligned through orifices (123), perpendicular to the axis (A), said second orifices (123) being complementary to second means (125) among said fixing means (125, 121) used to fix said foot (111) and said at least one platform (115) together., 2. Assembly (101) according to claim 1, in which the foot (111) has substantially the shape of a rectangular parallelepiped, and the first fixing means (121) and the second fixing means (125) are distributed along the length direction of the foot (111).

3. Assembly (101) according to claim 2, wherein the first fixing means (121) and the second fixing means (125) are alternated along the length direction of the foot (111).

4. Assembly (101) according to claim 3, in which the first fixing means (121) are equally distributed along the direction of the length of the foot (111) and the second fixing means (121) are equally distributed along the direction of the length of the foot (111).

5. Assembly (101) according to any one of the preceding claims, in which the second fixing means (125) comprise threaded rods (125a), passing through the second orifices (123), and nuts (125b), tightening said threaded rods (125a), on either side of said second orifices (123).

6. Assembly (101) according to any one of the preceding claims, in which the pivot (113) is a single piece comprising a cylindrical lower part (113a), and an upper part (113b) having substantially the shape of a plate comprising a groove (113ba) in which a base (111a) of the foot (111) is housed.

7. Assembly (101) according to any one of the preceding claims, wherein a first platform (115a) is positioned on the extrados side of the blade (103) and a second platform (115b) is positioned on the intrados side of the blade (103).

8. Assembly (101) according to any one of the preceding claims, in which the blade (103) is made of organic matrix composite material, for example produced by three-dimensional weaving.

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

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

11. Method (501) for assembling an assembly (101) having at least the characteristics of claims 1 to 5 and 7, comprising the following steps: - inserting (503) the threaded rods (125a) into the second holes (123) of a platform (115) among the first platform (115a) and the second platform (115b); - positioning (505) of the foot (111) in contact with the platform (115) by inserting the threaded rods (125a) into the second orifices (123) of said foot (111); - the positioning (507) of another platform (115), among the first platform (115a) and the second platform (115b), in contact with the foot (111), by inserting the threaded rods (125a) into the second orifices (123) of said other platform (115); - positioning and tightening (509) the nuts (125b), on the threaded rods (125a) so as to fix the first platform (115a), the foot (111) and the second platform (115b) together; - the positioning (511) of the assembly formed by the first platform (115a), the foot (111) and the second platform (115b) on the upper part of the pivot (113b) so that the base (111a) of the foot (111) is housed in the groove (113ba); and, - inserting and tightening (513) the screws (121) in the first holes (119) so as to fix the pivot (113) and the first platform (115a) and the second platform (115b) together.

12. Method (501) of assembling an assembly (101) according to claim 11, wherein, during the step of positioning and tightening (509) the nuts (125b), a marble is used, before tightening the nuts (125b), to align the lower surfaces of the first platform (115a) and the second platform (115b).

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