FR2877059A1 - Connecting rod for driving variable pitch vane, has drill and opening, where rod is under form of U shaped tongue folded on itself according to single folding along transversal direction so that drill and opening are opposite to each other - Google Patents

Abstract

The rod has a drill (30) centering the rod relative to a pivot (42) of a variable pitch vane (36). An opening (24) has two parallel edges cooperating with flat sections (50) of the pivot to rotatively drive the pivot. The rod is under the form of a U shaped tongue made of thin metal sheet and folded on itself according to single folding along a direction transversal to the rod so that the drill and opening are opposite to each other.

Description

2877059 1

  The invention relates to a control rod.

  It relates more precisely to a control rod intended to drive a variable pitch blade which comprises a pivot rotatably mounted in a turbomachine casing, the end of the pivot having two diametrically opposite flats, the link being made of sheet metal. and comprising: a bore for centering the link relative to the pivot, an opening having two parallel edges capable of cooperating with the two flats to drive the pivot in rotation.

  In a turbomachine compressor, and especially turbojet, one or more crowns of straightening vanes may be variable pitch, that is to say that the angle of attack of these vanes varies depending on the flight conditions, under the control of a servo system that controls the rotation of the vanes of a crown by rods according to predefined parameters.

  In order to reduce the mass of the turbojet engine, it is constantly sought to reduce the mass and cost of production of its constituent elements.

  Often, the rods are cut in the mass therefore have a large mass and a high production cost.

  It has already been imagined to design rods in thin sheet. For example, document US Pat. No. 4,767,264 describes such a link, one end of which comprises a bore intended for centering the pivot, and two parts bent in the longitudinal direction of the link so as to form two edges positioned above the bore intended to cooperate with the pins. two flats of the pivot.

  It will be understood that in order to manufacture this link, we start from a T-shaped thin plate, each of which is folded up to form two edges adapted to cooperate with the two flat portions of the blade pivot.

  It is therefore necessary to carry out two folding operations in order to obtain the desired shape of the link.

  An additional disadvantage is that it is necessary that, when folded, the two ends of the side portions are arranged in the same plane.

  It is therefore understood that, given the smallness of the rod, these folding operations are particularly difficult to implement and, a fortiori, have a high production cost.

  The object of the invention is to provide a rod substantially free of the disadvantages mentioned above.

  The object is achieved according to the invention in that the rod has the form of a thin sheet metal tongue folded on itself in a single folding carried in a direction transverse to the link, so that the drilling and the opening are positioned opposite one another.

  Thus, the rod according to the invention has a single folding, which is a simpler operation, faster and a fortiori less expensive to achieve a double folding as described in the prior art.

  By tab, is meant a thin plate extending predominantly in a single direction, called longitudinal direction.

  Thin sheet refers to any type of material having mechanical properties similar to those of steels commonly encountered in turbojet engines.

  Advantageously, a portion of the rod has the shape of a U whose two branches are substantially parallel.

  In other words, as the folding is carried out in a direction transverse to the link, this means that, once folded, the rod has substantially the shape of a hairpin.

  Advantageously, the drilling is formed in one branch and the opening is formed in the other branch.

  Preferably, the drilling is performed in the folded portion of the tongue and the opening is made in the unfolded portion, which is located opposite the folded portion.

  Advantageously, the branch in which is formed the opening is likely to be supported on the housing while the other leg is locked to the pivot.

  Preferably, when the rod is mounted on the pivot, the portion of the tongue that is not folded is adapted to be locked to the pivot substantially above the housing.

  Advantageously, the U-shaped portion 5 exerting a spring are effort to pull the pivot out of the housing to resume an axial play existing between the pivot and the housing.

  In known manner, it is generally sought to prevent the air which has been brought under pressure by the turbine of a compressor of a turbojet engine to escape into the atmosphere, since, understandably, this reduces the efficiency of the engine. compressor.

  Among the various causes of leakage, those which take place at the level of the blade pivots are particularly known.

  Ideally, a guide disk, also called platinum, located above the thin profile of the blade is wedged against the housing, so as to avoid leakage of compressed air.

  However, because of the vibrations, this guide disc can move in the axial direction of the pivot and, consequently, the compressed air tends to flow through the housing to the outside.

  The rod according to the invention avoids such a disadvantage.

  It is understood that the branch of the U which is folded, forms a spring blade due to the rigidity of the portion of the tongue which tends to resume its U-shape when the two branches are tightened.

  It is also understood that if the blade moves towards the inside of the housing, the two branches of the U are tightened and, consequently, cause an elastic return force tending to bring the blade back to its initial position.

  In this way, the U-shaped portion of the rod advantageously allows to take up the axial play that may exist between the blade and the turbojet engine housing.

  Other advantages and characteristics of the invention will emerge on reading the following description given by way of example and with reference to the appended drawings, in which: FIG. 1 is a view from below of the link according to the invention; , showing the folded part; - Figure 2 is a side view in section of the rod according to the invention; Figure 3 is a perspective view of the rod according to the invention, showing predominantly the non-folded portion of the rod and the bore; Figure 4 is a perspective view of the rod according to the invention, showing predominantly the folded portion and the opening; Figure 5 is a sectional side view of the rod according to the invention attached to the pivot of the blade and the control ring; - Figure 6 is a sectional side view of the rod according to the invention attached to the pivot of the blade and the control ring, when the blade undergoes a vibration; Figure 7 is a bottom view of the rod according to a variant of the invention, showing the folded portion; Figure 8 is a side view in section of the rod according to a variant of the invention; Figure 9 is a perspective view of the rod according to one embodiment of the invention, showing predominantly the non-folded portion of the rod and the bore; Figure 10 is a perspective view of the rod according to one embodiment of the invention, showing predominantly the folded portion and the opening opening; Figure 11 is a sectional side view of the rod according to a variant of the invention, fixed to the pivot of the blade and the control ring; and - Figure 12 is a sectional side view of the rod according to a variant of the invention, attached to the pivot of the blade and the control ring, when the blade is vibrated.

  With the help of Figures 1 to 4, we will now describe a control rod 10 according to the invention.

  The control rod 10 has the general shape of a thin tongue having an upper face 12 and a lower face 14 preferably flat and parallel to each other. The rod has two ends 16,18 between which it extends longitudinally.

  Referring to FIG. 1, it can be seen that said rod 10 comprises a plane of symmetry which extends in the longitudinal direction of the rod while being orthogonal to its upper and lower faces 12 and 14.

  In addition, viewed from above and considered from its first end 16 and towards its second end 18, the control rod 10 has a width which is narrowing.

  As seen in Figure 2, the first end 16 of the control rod 10 according to the invention is advantageously folded on itself to form a U with two branches 20, 22.

  For the sake of convenience, the folded branch will be called the branch 22 of the U which is positioned under the lower face 14 of the control rod 10.

  As can be seen from FIGS. 3 and 4, the end 16 of the control rod 10 according to the invention is folded according to a single folding carried out in a direction transverse to the control rod, so that the two branches 20,22 of the U extend in the longitudinal direction of said control rod 10.

  Preferably, the control rod 10 is bent at its middle part so that the second end 18 of the control rod is disposed substantially in the same plane as the folded branch 22 of the first end 16.

  Referring to FIGS. 1, 2 and 4, it can be seen that the folded branch 22 has a substantially rectangular opening 24 extending in the longitudinal direction of the control rod 10.

  In particular, the opening 24 has two parallel edges 26, 28 which extend in the longitudinal direction of the link 10.

  Referring now to FIGS. 1, 2 and 3, it can be seen that the second branch 20 of the U comprises a bore oriented in a direction orthogonal to the upper face 12 of the control rod 10 which is carried by the plane of symmetry of the link.

  As shown in Figures 1 and 2, the opening 24 is the bore 30 are arranged opposite one another.

  In particular, the diameter of the bore 30 is preferably substantially equal to or slightly less than the distance separating the two parallel edges 26, 28.

  Still preferably, the two branches 20, 22 of the U are substantially parallel to one another so that the axis of the bore is orthogonal to the plane containing the opening 24.

  For reasons explained below, the branches of the U may be slightly spaced apart from each other during manufacture, for example.

  The second end 18 of the control rod 10 comprises a circular orifice 32 oriented in a direction orthogonal to the upper face 12 of the link 10 which is carried by the symmetry plane of the link. The function of the circular orifice 32 will be explained later.

  The control rod 10 according to the invention can be made for example of steel, or any other equivalent material usually used in the field of aeronautics.

  Preferably, the branches of the U are dimensioned such that the folded branch has a certain elasticity in a direction orthogonal to the faces of the control rod 10. The interest of this elasticity is explained below.

  FIG. 5 is a sectional view of a compressor stator of a turbomachine which has an outer casing 34 supporting a plurality of variable blade crowns 36 of variable pitch.

  The blades 36 extend radially inside the housing 34 in the vein of the gas flow. They have in their radially outer region, a plate 38 with circular periphery housed in a cavity formed on the inner face 40 of the housing 34, and surmounted by a pivot 42 coaxial with the axis of the plate 38 housed in a cylindrical orifice 44 through the housing 34. The head 46 of the pivot 42 has a threaded portion 48 ending in two flats 50 diametrically opposed.

  As can be seen in FIG. 5, the lower ends of the two flats 50 are preferably arranged inside the cylindrical orifice 44, so that the neck 45 of the orifice 44 is disposed above the two lower ends of the two flats.

  Each blade crown is generally associated with a control ring 52. The actuation of a control ring causes the pivoting of all the blades 36 of the same ring.

  The control ring 52 is fixed to the pivot 42 of the blade 36 by means of a control rod 10 according to the invention.

  The control rod 10 according to the invention is fixed to the control ring 52 via a pin 54 mounted in the circular orifice 32 and rising from the inner face of the control rod 10.

  The first end 16 of the control rod is fixed integrally to the head of the pivot as follows: The head of the pivot is housed in the U-shaped part of the rod passing through both the opening and the drilling of the rod so that the folded leg comes into abutment against the neck 45 of the orifice 44 and that the two parallel edges of the opening 24 of the control rod surround the two flats of the pivot head.

  Preferably, the bore 30 is intended to allow the centering of the control rod 10 relative to the pivot 42 and the parallel edges of the opening 24 are intended to drive the pivot in rotation.

  It is understood that, preferably, the distance between the two parallel edges of the opening 24 should be substantially equal to the distance between the two flats of the head of the pivot.

  Naturally, the length of the opening 24, viewed along the longitudinal direction of the control rod, must be at least equal to the diameter of the head of the pivot so that it can pass through the folded branch of the U-shaped part.

  It is also understood that the diameter of the bore 30 must be at least equal to the diameter of the threaded portion of the head of the pivot.

  The control rod 10 according to the invention is locked to the pivot head 46 by means of a clamping nut 52 screwed onto the threaded portion of the pivot head.

  Preferably, the pivot head 42 is locked with the branch 20 of the U which is not folded.

  In known manner, it is sought to avoid compressed air leaks which have the effect of reducing the efficiency of the compression. Indeed, the compressed air naturally tends to escape from the inside of the housing 34 through the orifice 44 when there is an axial clearance 3 between the plate 38 of the blade 36 and the inner face 40 of the housing 34.

  This axial clearance 3 may be due in particular to the vibrations experienced by the blade 36.

  The control rod 10 according to the invention overcomes this disadvantage as follows: When the compressor is at rest, the plate 38 of the blade 36 10 bears against the inner face 40 of the housing 34 so that there is no clearance between the casing 34 and the plate 38 of the blade 36.

  In this configuration, the branches 20,22 of the U are arranged substantially parallel to each other, and the folded branch, as already indicated, bears on the neck 45 of the orifice 44.

  As soon as the blade 36 is subjected to a vibration or a force tending to draw it towards the inside of the casing 34, it will be understood that an axial clearance 3 appears between the plate 38 of the blade 36 and the internal face 40 of the housing 34.

  As shown in FIG. 6, the movement of the vane 36 also drives that of the pivot 42 and, consequently, causes the movement of the limb 20 of the U which is locked to the pivot head 42.

  As the folded branch of the U bears on the neck 45 of the orifice 44, it is understood that the internal radial displacement of the blade 36 tends to bring the two branches of the U closer to each other.

  Therefore, because of its elasticity, the U behaves like a spring and tends to bring back its branches in their initial positions. In this case, the unfolded branch 20 of the U tends to return to its original position and, in doing so, moves the blade 36 with it.

  It is therefore understood that, thanks to the particular shape of the control rod 10 according to the invention, a counter-reaction occurs tending to bring the plate 38 against the inner face 40 of the casing 34 in order to eliminate the axial play 3.

  Without departing from the scope of the invention, one could also design a control rod whose U branches are slightly apart from manufacture.

  In this case, when the control rod is locked to the pivot head, the two branches of the U are brought parallel to each other, so that there is an elastic prestress tending to separate the two branches of the U and, consequently, to press the plate 38 against the internal face 40 of the casing 34.

  Therefore, it is understood that despite the vibrations experienced by the blade 36, it tends to remain pressed against the inner face 40 of the housing 34, which has the effect of advantageously avoiding compressed air leaks.

  According to a variant of a control rod according to the invention, represented in FIGS. 7 to 12, the opening 24 opens advantageously to the end of the folded branch 22.

  It will be understood that such an opening is easier to machine than a rectangular opening and also makes it possible to reduce the mass of the control rod by approximately 15% compared to that of the first variant of the control rod.

Claims (9)

  Control rod (10) for driving a variable-pitch blade (36) which comprises a pivot (42) rotatably mounted in a turbomachine casing (34), the end of the pivot (42) having two diametrically opposed flats, the link being made of thin sheet metal and comprising: E a bore (30) for centering the link (10) with respect to the pivot (42), É an opening (24) having two edges (26) , 28) parallel capable of cooperating with the two flats (50) for driving the pivot (42) in rotation, characterized in that it has the form of a thin sheet metal tongue folded on itself in a single folding performed in a direction transverse to the rod (10), so that the bore (30) and the opening (24) are positioned opposite one another.   2. Rod according to claim 1, characterized in that a portion of the link has the shape of a U whose two branches (20, 22) are substantially parallel.   3. Rod according to claim 2, characterized in that the bore (30) is formed in one branch (20) and the opening (24) is formed in the other branch (22).   4. Rod according to any one of claims 1 to 3, characterized in that the two edges (26,28) extend in the longitudinal direction of the link.   5. Rod according to any one of claims 1 to 4, characterized in that the opening (24) is an orifice of substantially rectangular shape.   2877059 11 6. Rod according to any one of claims 1 to 5, characterized in that the opening (24) opens at the end of the folded branch (22).   7. Rod according to any one of claims 1 to 6, characterized in that the rod has a curvature so that the two ends of the link are disposed substantially in the same plane.   8. link according to claim 3 and any one of claims 1 to 7, characterized in that the branch in which is formed the opening (24) is likely to be supported on the housing (34) while the another branch is locked to the pivot (42).   9. Rod according to claim 2 and any one of claims 1 to 8, characterized in that the U-shaped part exerting a spring are effort to pull the pivot (42) out of the housing (34) to resume a axial clearance (J) existing between the pivot (42) and the housing (34).