BE1030541B1 - DEFORMABLE COUPLING FOR VARIABLE PITCH BLADE - Google Patents

Abstract

The invention relates to an assembly (52) for a turbomachine, comprising: a shroud (30); a blade (26); and a control lever (36) for the orientation of the blade (26) relative to the shroud (30); the assembly comprising a deformable coupling (60) between the blade (26) and the ferrule (30), the deformable coupling (60) allowing a single degree of freedom, in rotation, between the blade (26) and the ferrule (30).

Description

1 BE2022/5383

Description

DEFORMABLE COUPLING FOR VARIABLE PITCH BLADE

Technical area

The invention relates to the field of turbomachines and more particularly aircraft turbojet engines. More precisely, the invention relates to the design of the pivoting actuation of stator vanes with variable pitch.

Prior art

In a turbomachine, it is known to provide so-called variable pitch or orientation blades, which pivot on their axis as a function of the load or the rotation speed of the turbomachine in order to optimize its efficiency. Document EP 2 031 188 A1 describes a mechanism for actuating the orientation of a variable-pitch blade. The blade has a head fitted with a rod which is attached to an actuating lever. The rod extends through a hole in an external ferrule. Two bushings are arranged between the rod and the ferrule to ensure the correct positioning of the blade and guarantee the tightness of the air flow.

These sockets are made of softer material than the ferrule or stem. These bushings therefore wear out due to the friction of the rod when the blade pivots. This wear modifies the geometry of the bushings and leads to air leaks and/or blade positioning defects, as well as potentially premature damage to the blade orientation mechanism. The design with a pivoting rod in an orifice in the shell therefore requires maintenance operations.

Summary of the invention

Technical problem

The invention aims to propose a design requiring fewer maintenance operations and guaranteeing precise positioning of the blade which does not deteriorate during use of the turbomachine.

Technical solution

The subject of the invention is an assembly for a turbomachine, comprising: a — shroud; a dawn; and a lever for controlling the orientation of the blade relative to

2 BE2022/5383 on the ferrule; the assembly being remarkable in that it includes a deformable coupling between the blade and the shroud, the deformable coupling allowing a single degree of freedom, in rotation, between the blade and the shroud.

The assembly can be designed to be arranged in a compressor, particularly a low-pressure compressor. The shroud can be an internal shroud cooperating with the root of the blade or an external shroud cooperating with the head of the blade. The control lever can be connected directly or indirectly to the blade.

The deformable coupling in particular prohibits any translation between the blade and the shroud and only allows one rotation. The permitted rotation is that which is desired for the setting of the blade, and which is substantially perpendicular to the main direction of flow of the air flow. This rotation can be done substantially around a radial axis of an axial turbomachine or an axis parallel to the axis of rotation of a centrifugal compressor.

It is thus possible to eliminate friction between a mobile surface attached to the blade and a fixed surface of the shroud. The presence of a socket becomes optional. The lifespan of the whole is therefore longer than that of known systems. In addition, the precision of the positioning of the blade is not affected by the wear of a bushing and therefore remains satisfactory over the entire life of the turbomachine.

According to an advantageous embodiment of the invention, the deformable coupling comprises a fixed part, which is rigid and linked to the ferrule; a mobile part, which is rigid and linked to the blade and the lever; and at least one flexible strip interposed between the fixed part and the mobile part. This design allows easy manufacturing and easy sizing because the mechanics governing the bending deformation of slats are well controlled.

According to an advantageous embodiment of the invention, the deformable coupling is made of a part, preferably metallic and/or obtained by additive manufacturing.

The one-piece design simplifies assembly, makes the whole thing lighter and shortens the manufacturing process (part can be produced on a single machining, electroerosion, additive manufacturing machine, etc.).

According to an advantageous embodiment of the invention, the ferrule comprises a cylindrical orifice in which the deformable coupling is arranged, or is confined.

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This allows for a gain in compactness and also allows the new design to be adapted to an existing shroud and/or blade.

According to an advantageous embodiment of the invention, the deformable coupling is in contact with the ferrule on at least a portion of the cylindrical orifice. The cylinder-on-cylinder attachment is advantageous because it does not present any technical difficulty. Also, tightness is guaranteed since the manufacture of precise cylindrical shapes is easy (boring, turning or drilling).

According to an advantageous embodiment of the invention, the deformable coupling comprises a ring secured to the ferrule; a central pin coaxial with the ring and integral with the blade; and flexible strips connecting the ring to the central pin. In this variant, the rotating part is central.

According to an advantageous embodiment of the invention, a clearance between the deformable coupling and the ferrule is present on an angular portion of the cylindrical orifice. This play, made possible by the precision of the deformable coupling which allows pure rotation of the blade, avoids any friction between a rotating part and a fixed part.

According to an advantageous embodiment of the invention, the deformable coupling comprises a movable part integral with the blade and which is eccentric with respect to the axis of the cylindrical orifice. In this variant, the presence of a journal or a rod at the blade head is not necessary, thereby simplifying the manufacture of the blades.

According to an advantageous embodiment of the invention, the deformable coupling comprises a movable part and the blade comprises a blade which is substantially centered on the movable part, seen in a plane perpendicular to the direction of rotation.

According to advantageous modes of the invention, the assembly comprises a sealing sleeve between the lever and the ferrule, arranged on the side of the deformable coupling opposite the blade. This sleeve is arranged radially externally to the deformable coupling (in the case of an axial turbomachine).

According to an advantageous embodiment of the invention, the assembly comprises a sealing sleeve between the blade and the ferrule, arranged on the side of the deformable coupling opposite the lever. This sleeve is arranged radially internally to the deformable coupling (in the case of an axial turbomachine).

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According to advantageous modes of the invention, the deformable coupling comprises six strips deformable in pure flexion along respective axes parallel to each other.

The invention also relates to a turbomachine comprising a compressor with an annular row of stator vanes with variable orientation; a series of levers for controlling the orientation of the blades connected to a synchronization ring; and an external shroud, the turbomachine being remarkable in that it comprises an annular row of deformable couplings respectively arranged between each stator vane and the shroud, each deformable coupling allowing a single degree of freedom, in rotation, between each vane and the ferrule.

According to an advantageous embodiment of the invention, each deformable coupling comprises a movable part linked to the respective blade and a fixed part linked to the shroud, the movable part being arranged upstream of the fixed part.

Benefits provided

By providing a deformable coupling and not a traditional pivot connection, friction between moving parts and fixed parts is eliminated. This results in a reduction in wear and maintenance needs.

The positioning precision, generally dependent on the wear of the parts in play, is therefore also maintained over a longer lifespan of the turbomachine.

The deformable coupling can be made of metal (e.g. titanium) and can be more resistant to high temperatures than the traditional sealing sleeve (usually made of composite material).

The deformable coupling can be made in a single piece, offering simple manufacturing, particularly with modern additive manufacturing techniques.

Brief description of the drawings

Figure 1 represents an axial turbomachine;

Figure 2 is a diagram of a turbomachine compressor;

Figure 3 illustrates a variable pitch blade according to the state of the art;

Figures 4A to 4C show an assembly for a turbomachine according to a first embodiment;

Figures 5A and 5B represent an assembly for a turbomachine according to a second embodiment; 5 Figures GA and 6B show an assembly for a turbomachine according to a third embodiment.

Description of embodiments

In the description which follows, the terms “internal” and “external” refer to positioning relative to the axis of rotation of an axial turbomachine.

The axial direction corresponds to the direction along the axis of rotation of the turbomachine. The radial direction is perpendicular to the axis of rotation. Upstream and downstream refer to the main flow direction of the flow in the turbomachine.

Figure 1 represents in a simplified manner an example of an axial turbomachine 2. This comprises a low-pressure compressor 4, a high-pressure compressor 6, a combustion chamber 8 and one or more levels of turbines 10. In operation, the mechanical power of the turbine 10 transmitted via the central shaft to the rotor 12 sets in motion the two compressors 4 and 6. The latter comprise several rows of rotor blades associated with rows of stator blades. The rotation of the rotor around its axis of rotation 14 thus makes it possible to generate an air flow and to progressively compress the latter until it enters the combustion chamber 8.

A fan 16 is coupled to the rotor 12 via a gear train 17. This generates an air flow which is divided into a primary flow 18 passing through the different aforementioned levels of the turbomachine, and into a secondary flow 20 passing through a annular conduit (partially shown) along the machine to then join the primary flow at the turbine outlet.

If Figure 1 represents an axial turbomachine, it is understood that the principles of the invention can also be applied to other types of turbomachine, in particular with a centrifugal compressor.

Figure 2 is a sectional view of a low-pressure compressor 4 according to the state of the art. The rotor 12 comprises several rows of rotor blades 24.

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It can consist of a one-piece bladed drum or one-piece bladed discs.

The compressor 4 includes several rectifiers, for example four, which each contain a row of stator vanes 26. Some stator vanes can be adjustable in orientation, also called variable pitch vanes. The rectifiers are associated respectively with a row of rotor blades to straighten the air flow, so as to convert the speed of the flow into pressure, in particular into static pressure.

The stator vanes 26 extend essentially radially from an external shroud 30 towards internal rings 32 which can be sectorized.

The blades 26 generally have rods ("axes" or "journals"), 34, which engage an orifice of the external shroud 30. The external shroud 30 has an internal surface 29 for guiding the flow. In the areas adjacent to the rods 34, sealing should be provided to prevent air leaks escaping from the surface 29.

The rod 34 is generally pivoted by a lever 36 around the axis 38 of the rod 34. The lever 36 is integral with the rod 34, fixed for example by a nut.

The levers 36 of the annular row of blades 26 are all connected to a synchronization ring 40.

Figure 3 illustrates an enlarged view of the arrangement of the variable-pitch blade 26 according to the state of the art.

Each blade 26 comprises a blade 26.1 connected at each of its radially internal and external ends to a rod 34 which extends along the pivot axis 38 of the blade.

The shell 30 comprises a chimney 30.1 pierced with a cylindrical orifice 30.2.

The external rod 34 is engaged in the cylindrical orifice 30.2 and is centered and guided in rotation in this chimney by two identical sealing sleeves 42, 44 mounted head to tail around the rod 34.

The radially outer end of the rod 34 is threaded and is fixed to the lever 36 by means of a nut 46. The control lever 36 carries a finger 48 guided in the synchronization ring 40. An angular movement of the ring 40 around

7 BE2022/5383 of axis 14 results in a rotation of lever 36 and blade 26 around axis 38.

The internal rod 34 is engaged in a cylindrical housing of the internal ring 32 and is centered and guided in rotation in this housing by a cylindrical sleeve 50.

The bushings 42, 44, 50 wear out and affect the positioning precision of the blade. They require maintenance operations. The invention illustrated in the following figures aims to overcome these problems.

Figure 4A shows a star spring 60 which is composed of a stack of several layers 62, each layer 62 comprising two angular portions 64, 66 connected together by an arm 68. The arm 68 can be at least partially under the shape of a strip, that is to say a shape having a preferred direction of bending (around its thickness). The arm 68 may have a thicker non-flexible portion. Optionally, several arms 68 can connect portions 64, 66 of the same layer 62.

The angular portions 64, 66 of each layer 62 are stacked and respectively secured to each other, for example using pins penetrating orifices provided for this purpose (shown but not referenced in Figure 4A). The arms 68 of the different layers 62 are angularly offset, and arranged symmetrically or not with respect to the central axis of the spring 60 and/or with respect to a median plane in the middle of the stack of layers 62.

In a preferred variant, the spring 60 comprises six layers 62.

The spring 60 can be made in one piece (for example produced by additive manufacturing).

The arrangement of the arms 68 has the consequence that only pure flexion of the arms 68 is made possible. The angular portions 66 can therefore have a pure rotational movement relative to the angular portions 64 around the axis of symmetry of the spring 60 (or vice versa). An eccentricity of less than 5 microns is observed for a swept angle of 20° between the two portions 64, 66; an offset of 1 micron of the axis appears for a force of 10 N; a resistant torque of 0.09 Nm is measured for a swept angle of 20°. These results show the level of precision of such a spring 60. In fatigue, this spring 60 withstands approximately 180,000 cycles of +/-10° amplitude.

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This spring 60 constitutes a deformable coupling according to the invention and is implemented in Figure 4B representing an assembly 52 according to the invention. The portion 64 of the spring 60 is fixed to the ferrule 30 and the portion 66 is fixed to the blade 26 and to the lever 36. Thus, under the action of the ring 40, the lever 36 and the blade 26 pivot around axis 38. The portion 64 is fixed and does not cause any wear, and the portion 66 can be at a distance from the ferrule 30, a clearance J being able to be provided between the ferrule 30 and this movable part 66.

The fixed part 64 can be fixed by any suitable means, in particular screws oriented parallel or perpendicular to the axis 14 or by flanges.

A sleeve 70 or a seal may remain but this is no longer responsible for the positioning of the blade and can therefore be made of a material not susceptible to wear. The precision of the positioning of the blade is no longer affected by the wear of a bushing and therefore remains satisfactory over the entire life of the turbomachine.

Only the part at the head of the blade is represented but the same lessons can be applied to the root of the blade.

Figure 4C shows an alternative, with a socket 70 between the lever 36 and the ferrule 30, in a radially external position relative to the deformable coupling 60.

Figure 5A illustrates in isometric view a deformable coupling 160 which can also be implemented between the blade 26 and the shroud 30. This is a butterfly hinge, in one piece. In the same way as for the previous example, this coupling 160 has two portions 164, 166 movable in rotation relative to each other, and separated by more or less fine strips 168. Axis 38 is referenced to illustrate the position that the butterfly takes once mounted.

Each portion 164, 166 is generally triangular in shape, with edges which can be rounded for easy arrangement in a cylindrical orifice.

The angular portions 164, 166 can be fixed respectively to the shroud or to the blade by means, for example, of suitable screws penetrating the holes shown in Figure SA.

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The strips 168 prevent any relative movement between the two portions 164, 166 other than rotation around the axis of symmetry of the part 160 (which coincides with axis 38 once mounted).

Figure 5B shows the implementation of the coupling 160 in a compressor.

The tests show results in precision and lifespan which are equivalent to those of the 60 spring.

Figures GA and 6B show two examples in isometric view of another variant in which the deformable coupling 260 takes the form of a rosette. An external ring 264 is intended to be fixed to the ferrule 30 while the central pin 266 is intended to be fixed to the blade 26 and to the lever 36. Between the ring 264 and the central pin 266 are arranged strips 268.

Radial legs (not referenced) integral with the central pin 266 allow more freedom in the choice of the attachment of the blade 26 and the lever 36.

Figure 6C illustrates an example of implementation of the deformable coupling 260 of Figure GA in a compressor.

The tests show results in precision and lifespan which are equivalent to those of the 60 spring.

It should be noted that the invention is illustrated in relation to an axial turbomachine but the exact same system can be implemented in a centrifugal compressor.

Also, the number of blades 68, 168, 268 of the deformable couplings 60, 160, 260 and their geometry can be chosen so as to obtain a resistant torque or a determined elastic return.

The deformable coupling 60 is represented as a stack of layers 62 but this can also be produced in one piece, in particular by additive manufacturing.

The deformable couplings 160 and 260 are represented as one-pieces but they can be made in several pieces assembled together.

Claims (14)

10 BE2022/5383 Claims 1. Assembly (52) for turbomachine (2), comprising: - a shroud (30); - a blade (26); and - a control lever (36) for the orientation of the blade (26) relative to the shroud (30); the assembly being characterized in that it comprises a deformable coupling (60, 160, 260) between the blade (26) and the ferrule (30), the deformable coupling (60, 160, 260) allowing a single degree of freedom, in rotation, between the blade (26) and the shroud (30). 2. Assembly (52) according to claim 1, characterized in that the deformable coupling (60, 160, 260) comprises a fixed part (64, 164, 264), which is rigid and linked to the ferrule (30); a movable part (66, 166, 266), which is rigid and linked to the blade (26) and the lever (36); and at least one flexible strip (68, 168, 268) interposed between the fixed part (64, 164, 264) and the movable part (66, 166, 266). 3. Assembly (52) according to claim 1 or 2, characterized in that the deformable coupling (60, 160, 260) is made of one part, preferably metallic and/or obtained by additive manufacturing. 4 assembly (52) according to one of claims 1 to 3, characterized in that the ferrule (30) comprises a cylindrical orifice (30.2) in which the deformable coupling (60, 160, 260) is arranged, or is confined. 5. Assembly (52) according to claim 4, characterized in that the deformable coupling (60, 160, 260) is in contact with the ferrule (30) on at least one portion of the cylindrical orifice (30.2). 6. Assembly (52) according to claim 5, characterized in that the deformable coupling (260) comprises a ring (264) secured to the ferrule (30); a central pin (266) coaxial with the ring (264) and secured to the blade (26); and flexible strips (268) connecting the ring (264) to the central pin (266). 11 BE2022/5383 7. Assembly (52, 152) according to one of claims 4 or 5, characterized in that a clearance (J) between the deformable coupling (60, 160) and the ferrule (30) is present on an angular portion of the cylindrical orifice (30.2). 8. Assembly (52, 152) according to claim 7, characterized in that the deformable coupling (60, 160) comprises a movable part (66, 166) integral with the blade (26) and which is eccentric with respect to the axis (38) of the cylindrical orifice (30.2). 9. Assembly (52, 152) according to claim 7 or 8, characterized in that the deformable coupling (60, 160) comprises a movable part (66, 166) and the blade (26) comprises a blade (26.1) which is substantially centered on the movable part (66, 166), seen in a plane perpendicular to the direction of rotation (38). 10. Assembly (52) according to one of claims 1 to 9, characterized in that it comprises a sealing sleeve (70) between the lever (36) and the ferrule (30), arranged on the side of the deformable coupling (60, 160, 260) opposite the blade (26). 11. Assembly (52) according to one of claims 1 to 10, characterized in that it comprises a sealing sleeve (70) between the blade (26) and the ferrule (30), arranged on the side of the deformable coupling (60, 160, 260) opposite the lever (36). 12. Assembly (52) according to one of claims 1 to 11, characterized in that the deformable coupling (60, 160, 260) comprises six strips (68, 168, 268) deformable in pure flexion along respective parallel axes between them. 13. Turbomachine (2) comprising a compressor (4) with an annular row of stator vanes (26) with variable orientation; a series of control levers (36) for the orientation of the blades (26) connected to a synchronization ring (40); and an external shroud (30), the turbomachine being characterized in that it comprises an annular row of couplings 12 deformable BE2022/5383 (60, 160, 260) respectively arranged between each stator blade (26) and the ferrule (30), each deformable coupling (60, 160, 260) allowing a single degree of freedom, in rotation, between each blade (26) and the ferrule (30). 14. Turbomachine (2) according to claim 13, characterized in that each deformable coupling (60, 160, 260) comprises a movable part (66, 166, 266) linked to the respective blade (26) and a fixed part ( 64, 164, 264) linked to the ferrule (30), the movable part (66, 166, 266) being arranged upstream of the fixed part (64, 164, 264).