Variable pitch vane control ring bush retention foil and turbojet containing same

Abstract

A flexible metal foil can be fixed on the inside part of a variable pitch vane control ring of a turbojet compressor, so as to close all through holes in which lever pins and their surrounding bushes are housed. As a result, the foil can retain the shank of the bush if the bush breaks. The use of such foil does not impose the development of a new model of control ring and its impact on the mass is small enough so that it does not affect engine performances. Therefore it avoids problems related to the breakage of bushes without having to make major changes to the existing system.

Claims

1. A foil made from a flexible metal material and to be fixed to an inside surface of a vane control ring with variable pitch for a turbojet, said control ring comprising a plurality of through holes each with an internal radial opening on a side of the inside surface of the control ring and an external radial opening on a side of an outside surface of the control ring, in each of which a bush can be housed to hold a pin of a control lever of one of the vanes, through the external radial opening of the hole, the foil having a length along a longitudinal direction and a width along a direction orthogonal to said longitudinal direction that are adapted to close the internal radial opening of at least one through hole in the control ring, said foil length being longer than the developed length of a determined angular sector of the control ring in which at least one pad of the control ring is located, at the angular sector at which the foil is to be fixed, and in which the foil contains an adapted hole to allow a pad support to pass through connecting the pad to the control ring, and wherein the foil adopts a determined shape in a section plane orthogonal to said longitudinal direction by which the foil can be fixed by click fitting onto the control ring at its inner surface.

2. The foil according to claim 1, comprising at least four folds along its longitudinal direction, to adopt a shape in a section plane orthogonal to said longitudinal direction such that it squeezes the internal part of the control ring when the control ring has an I section.

3. The foil according to claim 2, comprising six folds extending along the longitudinal of the foil.

4. The foil according to claim 3, the length of which along the longitudinal direction is approximately equal to the developed length of a 180-degree angular sector of the control ring, on the side of the internal face of said control ring.

5. The foil according to claim 1, wherein one face of the foil to come into contact with the control ring when the foil is fixed to the control ring, is coated with contact varnish.

6. A control assembly for variable pitch vanes of a turbojet comprising a variable pitch vane control ring, said control ring having an inside surface and an outside surface and having: at least one pad located in a determined angular sector of the control ring, at least at its internal surface; and, a plurality of through holes each with an internal radial opening on a side of the inside surface of the control ring and an external radial opening on a side of an outside surface of the control ring, in each of which a bush can be housed to hold a pin of a control lever of one of the vanes, through the external radial opening of the hole, said control assembly comprises comprising a foil made of a flexible material fixed to the inside surface of the control ring, said foil having: a length along a longitudinal direction and a width along a direction orthogonal to said longitudinal direction that are adapted to close the internal radial opening of at least one through hole in the control ring, said foil length being longer than the developed length of a determined angular sector of the control ring in which at least one pad of the control ring is located, at the angular sector at which the foil will be fixed; a determined shape in a section plane orthogonal to the longitudinal direction by which it can be fixed by click fitting onto the control ring at its inner surface, and, a suitable hole through which a support of said pad can pass; to connect said pad to the control ring.

7. A turbojet comprising a compressor stator with variable pitch vanes, a control ring of said variable pitch vanes, and a foil according to claim 1 fixed on an inside surface of the control ring.

8. The turbojet according to claim 7, wherein the bushes are made of a composite material.

9. The turbojet according to claim 7, wherein the inside surface of the control ring to come into contact with the foil when the foil is fixed to the control ring, is coated with contact varnish.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other characteristics and advantages of the invention will become clear after reading the following description of non-limitative embodiments, with reference to the appended figures among which;

[0035] FIG. 1 is a sectional view of the fixed part of a turbojet compressor with a case supporting a set of variable pitch vanes extending in the radial direction inside said case;

[0036] FIG. 2 is a sectional view of a pivot link sliding between a control lever and a control ring;

[0037] FIG. 3 shows the lower part of a control ring closed at its bottom end by bush retention foil in accordance with embodiments of the invention;

[0038] FIGS. 4A, 4B and 4C are sectional views of a control ring centred on a hole and illustrating the different phases associated with the breakage of a bush;

[0039] FIG. 5 is a sectional view of a control ring centred on a hole and having a pin of the lever in the hole surrounded by a broken bush, the lower part of which is retained by the bush retention foil in FIG. 3;

[0040] FIG. 6A and FIG. 6B each show a top view and a sectional elevation view of control rings with one or more pieces of retention foil, namely: [0041] in FIG. 6A, en embodiment of the invention with an implementation comprising only two foil sectors each covering the angular sectors of a ring, at about 180 degrees each, and through which several ring roots pass; [0042] in FIG. 6B, another possible approach as a variant embodiment of the invention with a layout including a set of foil sectors with circumferential lengths approximately equal to the circumferential distances between pads of the ring, and each of which can be installed between two circumferentially adjacent pads without needing to disassemble the pads.

DETAILED PRESENTATION OF EMBODIMENTS

[0043] FIG. 1 illustrates a sectional view of a high pressure compressor stator case 9 supporting a set of variable pitch vanes 3. More particularly, FIG. 1 shows four stator stages arranged in pairs from left to right, along the air flow direction represented by an arrow. The vanes 3 extend in the radial direction inside the case 9 (towards the bottom of FIG. 1) and there is a pivot 10 at the top of each that can be made from the same as the corresponding vane. In the vane position shown in the case 9, the corresponding pivot 10 is coaxial with the longitudinal X axis of a cylindrical orifice 11 passing through the case 9, associated with the vane. The head 12 of the pivot 10 is connected to a control ring 2 through a manoeuvre arm or control lever 6.

[0044] FIG. 2 illustrates a cross-sectional view of a control ring 2 connected to an associated control lever 6, through a “sliding pivot” type mechanical connection. This connection is made by a cylindrical pin 5, said pin is fixed to the lever 6 and is housed in a through orifice 4 provided in the ring 2, also called the “ring hole”. The part of the pin 5 that is in contact with the ring 2 is in contact through a cylindrical bushing 7 that surrounds said pin and is itself in direct contact with the internal walls of the ring hole 4. The head 7a of the bush is folded like a collar hammered flat so as to cover the external surface of the ring 2 around the entry to the hole 4 on the side of the control lever 6.

[0045] The function of the bush 7 is to act as a liner for the hole 4 to restrict the clearance and friction inherent to the sliding pivot type link between the control lever 6 and the control ring 2.

[0046] Translation of the control ring 2 along an axis perpendicular to the section plane in FIG. 2 thus drives the control lever 6 that is fixed to the pin 5 located in the vane hole 4 and thus causes rotation of the pivot 10 of a vane, and therefore rotation of the vane to which said pivot is fixed.

[0047] A control ring 2 comprises a set of ring holes like hole 4 in FIG. 2, that controls all variable pitch vanes in a determined stage of the compressor simultaneously and identically.

[0048] FIG. 3 illustrates an overview of a control ring 2, the inside surface of which is closed by bush retention foil 1 fixed on said ring. Such foil is made, for example, by a flexible metal strip extending along the longitudinal direction of the control ring 2, i.e. along a perimeter of said ring. Since the control ring is in the form of an arc, the terms “internal” and “external” are used in the following with reference to the curvature of the ring; the inside surface of the ring 2 is the surface on the concave side of the ring (bottom, FIG. 3), and the outside surface of the ring 2 is the surface on the convex side of the ring (top, FIG. 3).

[0049] For example, the length of a foil element can cover the entire length of one of the two parts of a two-part control ring corresponding approximately to angular sectors of 180 degrees each. The “length” of the foil or a foil element or control ring in this description refers to the developed length along the longitudinal direction of the foil element extending over an inside perimeter of the control ring, of an angular sector of said foil element or said control ring respectively.

[0050] The external orifices in FIG. 3 of the holes passing through ring 4 are visible over the entire outside surface of said ring and are present over its entire longitudinal length. The foil 1 covers the entire inside surface of the ring 2 except for the housing orifices of the pads 8 of said ring 2. To achieve this, the dimensions of the orifices in the foil 1 are at least the same size as the dimensions of pad housings in the control ring and are aligned with these housings.

[0051] FIG. 4A shows a sectional view of a control ring 2 containing the pin 5 of a control lever and a bush 7 in which said pin 5 fits, inside one of its ring holes 4. The bush may be made of ceramic for its good contact properties, particularly low friction and good resistance to wear.

[0052] In the example illustrated on FIGS. 4A, 4B and 4C, it is represented in section, and grey. In the case in FIG. 4A, the bush 7 is complete, i.e. unbroken. In the case in FIG. 4B, the bush 7 is broken at the edges of the hole 13 opening up on the outside surface of the ring (i.e., at the top on FIG. 4B) causing most of the shank 7b of the bush to drop by gravity (downwards on FIG. 4B) while the head 7a of the bush that is therefore separated from the shank 7b remained in its initial position.

[0053] The internal part of the control ring 2 (i.e., at the bottom on FIG. 5) is squeezed in the transverse direction (i.e. along a direction orthogonal to the longitudinal direction of the ring 2) by flexible metal foil 1 such that the through hole 4 is closed at its projecting end opening up on the inside surface of the ring 2.

[0054] The foil 1 retains the bush 1 particularly by retaining the shank 7b of the bush 7 inside the ring hole 4 if the bush breaks. This is what is shown in FIG. 5. This thus prevents the shank of the bush from dropping into the engine. This also has the advantage that the shank 7b of the bush 7 is kept in contact with a large portion of the surface of the pin 5 of the control lever and the inside wall of the ring hole 4.

[0055] In the example shown in FIG. 5, the shape of the foil section in a plane orthogonal to the longitudinal axis of the ring 2 and the foil 1 (therefore in the plane of the figure) adopts the external contour of the lower part of the “I” section of the ring 2. In this way, the foil squeezes the ring so that it can be fixed on it.

[0056] More particularly, in one embodiment the foil comprises folds along the longitudinal direction to adopt a determined shape in a section plane orthogonal to said longitudinal direction (corresponding to the plane in FIG. 5), so that it can be fixed by click fitting onto the control ring at its internal surface.

[0057] As shown in FIG. 5, the foil can for example include at least four folds, and preferably six folds extending along the longitudinal direction. The result is that the shape in the section plane orthogonal to said longitudinal direction of the foil is such that the internal part of the control ring can be squeezed, for example when the section of the control ring is an “I” section as shown on FIG. 5.

[0058] The invention is not limited by the shape of the foil in the section plane. Curves rather than folds could be envisaged. Moreover, although the shape of the foil in the section plane in FIG. 5 is symmetric, this is not an obligation. Other embodiments can be envisaged depending on the constraints of the envisaged application.

[0059] Advantageously, the natural elasticity of the foil 1 contributes to holding it in place. However, if necessary the foil can slide on the ring when pushed by an operator. The embodiment with six longitudinal folds as shown in FIG. 5 makes it easier, if necessary, to pass a tool between the control ring 2 and the foil 1, to displace or disengage the foil from the control ring. Thus, an operator can make the orifices in which the pads 8 of the ring are housed (FIG. 3) coincide with the orifices in the foil provided to allow said pads to pass through, as in the embodiment shown in FIG. 6A that will now be presented.

[0060] FIGS. 6A and 6B illustrate a method of making the bush retention foil according to the invention and a variant for making the bush retention foil, respectively.

[0061] FIG. 6A shows a bottom view (top image) and a sectional elevation view (bottom image) of a portion of foil fixed on one of two parts of a control ring 2 composed of at least two separate parts, for example each covering an angular sector of about 180 degrees. In other words, the length of the foil along the longitudinal direction is greater than the developed length of a determined angular sector of the control ring in which at least one pad 8 of the control ring is fitted, and the foil will be fixed to said angular sector. Consequently, the foil comprises a suitable hole through which part of the support of the pad connecting the pad to the control ring can pass.

[0062] More particularly, the foil can comprise a number of orifices (or holes) corresponding at least to the number of pads on the ring. These orifices are also placed such that their position matches the pads along the longitudinal axis of the foil and the ring, respectively. The circumferential length of the hole is adapted to allow part of the pad support, or stand, connecting the pad to the control ring, to pass through. With this embodiment, the pads 8 have to be removed to put the foil into position and the orifices provided in the foil have to be aligned with the locations of the pads 8 on the inside surface of the ring 2. The longitudinal and transverse dimensions of the openings in the foil have to be sufficient to be able to lift the pads once the foil has been put into place.

[0063] FIG. 6B shows a bottom view (top picture) and a sectional elevation view (bottom picture) of a portion of a control ring on which several foil elements with different lengths are fixed, each corresponding to the inter-pad distance between two adjacent pads longitudinally along ring 2. Each foil element 1a thus covers an interpad distance specific to it. Thus, an interval is left between two longitudinally adjacent pieces of foil that is more than the longitudinal length of a pad, or at least of its stand or pad support.

[0064] In the embodiment described above with reference to FIG. 6A, the pads are removed so that the foil can be fixed on the inside part of the ring. If necessary, the foil is slid in the longitudinal direction once it has been click fitted onto the ring 2, so as to align existing orifices with orifices existing along the ring. This solution has the advantage of only requiring a small number of additional parts, namely for example two foil parts each covering an angular sector of about 180 degrees when the control ring is itself composed of two angular sectors, each about 180 degrees. The number of part references to be managed is limited.

[0065] On the other hand, in the variant in FIG. 6B, the foil is composed of a larger number of parts, namely each of the foil elements covering a portion of the inter-pad circumferential length of the control ring. In other words, the length of foil along the longitudinal direction covers not more than the developed length of an angular sector between two adjacent pads 8 on the control ring 2. These elements are not necessarily identical to each other, and in particular their longitudinal dimensions may be different. Together, these foil elements inserted between the pads 8 of the ring cover the entire circumference of the ring (about 360 degrees). This embodiment has the advantage that foil can be fixed onto the ring directly without needing to disassemble the pads present on its internal surface.

[0066] It will be noted that the embodiment in FIG. 6A could be combined with the variant embodiment of foil illustrated in FIG. 6B. Thus, part of the foil conforming with the embodiment in FIG. 6A could be used in one or several angular portions of the ring, and a plurality of foil elements conforming with the approach illustrated in FIG. 6B could be used in one or several other angular portions of the ring. Also, in an embodiment of the turbojet according to the third aspect of the invention, the first embodiment could be chosen for a given stage of the compressor, and the variant could be chosen for at least one other stage.

[0067] The invention also discloses a turbojet comprising a compressor stator with variable pitch vanes and also comprising a control ring of said variable pitch vanes. The turbojet can be fitted with foil like that described above. The foil is fixed to an inside surface of the control ring.

[0068] In one embodiment, the inside surface of the control ring that will come into contact with the foil when the foil is fixed to the control ring, is coated with contact varnish. For example, this varnish can be adapted to prevent the foil from slipping relative to the control ring. Due to this varnish, each element of the foil adheres to the inside perimeter of the control ring.

[0069] It will be noted that either as a variant or as a complement, the face of the foil that will come into contact with the control ring when the foil is fixed to the control ring can be coated with contact varnish identical to or similar to that mentioned above.

[0070] This invention is not limited to the embodiments presented herein. Other variants and embodiments can be deduced and implemented by an expert in the subject after reading this description and the appended Figures.