TURBOMACHINE STATOR BLADE CONTROL MECHANISM WITH AT LEAST ONE STIFFNER

Abstract

The invention relates to a variable-pitch stator blade control mechanism for a turbomachine, comprising a control ring adapted to be rotated and control levers connecting each stator blade to the control ring so that the rotation of the control ring causes the stator blades to pivot. Each control lever is pivotally mounted on the control ring and comprises a body (21) elongated between a first portion (22) and a second portion (23), the body comprising a central portion (24) connecting the first and second portions. According to the invention, each control lever (20) comprises at least one stiffener (40) to increase the mechanical strength of the control lever (20), each control lever (20) comprising a hole (41) through its wall, and each stiffener (40) being an added component fitted and fixed in the hole (41). Figure for the abstract: Fig. 5

Description

Title of the invention: TURBOMACHINE STATOR BLADE CONTROL MECHANISM WITH AT LEAST ONE STIFFNER Technical field of the invention

[0001] The present invention relates to the field of turbomachinery comprising variable-pitch stator blades. It relates in particular to a control mechanism for variable-pitch stator blades. Technological background

[0002] Aircraft turbomachinery can be equipped with variable-pitch stator vanes that allow the turbomachinery to adapt to various operating conditions. These stator vanes can be located at different points within the turbomachine and are known, for example, as "OGV" for Outlet Guide Vane or "VSV" for Variable Stator Vanes. These stator vanes are arranged radially across the turbomachine's airflow and allow it to be straightened.

[0003] To this end, the turbomachine is equipped with a control mechanism comprising a control ring driven in rotation about the longitudinal axis of the turbomachine and driving the pivoting of the variable-pitch stator blades via control levers. The control levers are connected to the variable-pitch stator blades and to the control ring.

[0004] In the case of variable-pitch stator blades equipping an air inlet guide wheel, which is located upstream of the low-pressure compressor, the control mechanism includes a fusible part positioned between the control ring and a control means acting on the rotation of the control ring. The fusible part is configured to break under high mechanical stresses applied to the variable-pitch blades in order to prevent damage to the control means. The mechanical stresses affect all parts of the control mechanism and are caused, for example, by pumping (violent backflow of air upstream of the turbomachine) or by impacts / ingests of a foreign body known by the acronym "FOD" for "Foreign Object Debris". Such an example of a control mechanism is described in document FR-A1-2794801.

[0005] However, the fusible part may not break under lesser mechanical stress, and this can lead to damage to other parts of the control mechanism. The parts of the mechanism most affected are generally the control levers, which can break, deform, and / or disengage from the control ring.

[0006] Damage to the control levers can lead to misalignment of the variable-pitch stator blades, resulting in a loss of turbomachinery performance and collisions between adjacent variable-pitch stator blades, which can then lead to blade breakage. The breakage of these stator blades can release fragments known as "DOD" (Domestic Object Debris), which can damage nearby components such as a crankcase arm, moving blades, etc.

[0007] There is therefore a need to resolve all or part of the aforementioned drawbacks. Summary of the invention

[0008] The objective of the present invention is to provide a simple and economical solution to reliably ensure the operation of the variable pitch stator blade control mechanism in the event of high mechanical stresses.

[0009] We achieve this objective in accordance with the invention by means of a variable-pitch stator blade control mechanism for a turbomachine, this control mechanism comprising a control ring adapted to be driven in rotation about a longitudinal axis and control levers connecting each variable-pitch stator blade to the control ring such that the rotation of the control ring causes each variable-pitch stator blade to pivot, each control lever being pivotally mounted on the control ring by means of a connecting member and comprising a body elongated along an elongation direction between a first portion and a second portion, the body comprising a central portion connecting the first portion and the second portion, each control lever comprising at least one stiffener configured to increase the mechanical resistance of the control lever,Each control lever includes at least one hole passing through its wall on both sides, and each stiffener is an added piece that is fitted and fixed in the hole.

[0010] Thus, this solution makes it possible to achieve the aforementioned objective. In particular, the stiffener makes it possible to obtain mechanically reinforced and more robust control levers in the event of high mechanical stresses applied to the stator blades. In this description, the expression "high mechanical stresses" refers to a pumping phenomenon that exerts an aerodynamic force on the variable-pitch stator blades due to violent backflows of air and / or the ingestion of foreign bodies that cause impacts on the stator blades. The increased mechanical strength of the control levers will at least limit their deflection under high mechanical stresses, their damage, and their disengagement from the control ring. The reliability of the mechanism The control system is considerably improved, which allows, on the one hand, for the control of the stator blades to be ensured in all circumstances (the other parts of the control mechanism are not impacted), and on the other hand, for the maintenance of the aerodynamic performance of the turbomachine.

[0011] In addition, the stiffening applied to the control levers limits the increase in mass and does not involve significant structural modifications to themselves or even to the surrounding parts.

[0012] The control mechanism also includes one or more of the following features and / or steps, taken alone or in combination: - the control mechanism includes a control means causing the rotation of the control ring via at least one fusible transmission piece connecting the control ring to the control means. - Each control lever is made of titanium, titanium alloy, steel or an organic matrix composite material. - the second portion of each control lever includes an opening receiving at least part of the connecting member. - the hole and the opening of the second portion have the same diameter. - the distance separating the axis of the hole and the axis of the orifice is equal to 1.5*D4. - the stiffener is made of a metallic material different from the material of each control lever and preferably comprising iron or an iron alloy. - each stiffener has a cylindrical body having a first part and a second part which have identical or different diameters. - between two and five stiffeners are added and arranged on each control lever between the first portion and the second portion. - the connecting element is permanently fixed at the level of the second portion. - the connecting element is mounted using a ball joint at the level of the second portion. — the stiffener(s) is a separate added part.

[0013] The invention also relates to a turbomachine comprising variable-pitch stator blades for straightening an airflow circulating in the turbomachine and a stator blade control mechanism having any one of the preceding characteristics.

[0014] According to an advantageous feature, the turbomachine comprises at least one stage formed of an annular row of moving blades and an annular row of stator blades, the stator blades being arranged upstream or downstream of the moving blades.

[0015] According to another advantageous feature, the turbomachine comprises, from upstream to downstream along the longitudinal axis, a low-pressure compressor, a high-pressure compressor pressure, a high-pressure turbine and a low-pressure turbine, at least one of the low-pressure compressor, high-pressure compressor, high-pressure turbine, and low-pressure turbine comprising one or more stages. Brief description of the figures

[0016] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent upon reading the following detailed explanatory description, of embodiments of the invention given by way of purely illustrative and non-limiting examples, with reference to the accompanying schematic drawings in which:

[0017] - Fig. 1 is a perspective view of an example of a turbomachine to which the invention applies;

[0018] - Figure 2 is a partial view of a turbomachine module comprising a control mechanism for a row of stator blades with variable pitch according to the invention;

[0019] - Fig. 3 is a detailed and partial view of an example of a stator blade with a timing mechanism. variable connected to a control ring by means of a control lever according to the invention;

[0020] - Figure 4 illustrates, in perspective, one embodiment of a control lever intended to equip a control mechanism according to the invention;

[0021] - Fig. 5 is a bottom and perspective view of the control lever according to the [Fig.4];

[0022] - Figure 6 illustrates, in an axial cross-sectional view, an example of a stiffener according to the invention; and

[0023] - Figure 7 is a perspective view of another embodiment of a lever order according to the invention. Detailed description of the invention

[0024] Figure 1 represents a turbomachine 1 having a longitudinal axis X and intended to be mounted on an aircraft (not shown). The turbomachine 1 may be a turboshaft engine, a turbojet engine, a turboprop engine, or may include fan rotor blades or rotor blades of at least one propeller, whether shrouded or unshrouded.

[0025] In the present invention, and generally, the terms "upstream" and "downstream" are defined with respect to the circulation of gases or airflows in the turbomachine and here along the longitudinal axis X. The terms "axial" and "axially" are defined with respect to the longitudinal axis X. The terms "external," "outer," "inner," "internal," and "radial" are defined with respect to a radial axis Z extending from the axis longitudinal X and with regard to the distance from the longitudinal axis X. The radial axis is perpendicular to the longitudinal axis X.

[0026] The turbomachine 1 which is represented in [Fig.1] comprises, from upstream to downstream, a low pressure compressor 2, a high pressure compressor 3, a combustion chamber 4, a high pressure turbine 5 and a low pressure turbine 6. The low pressure compressor 2 and low pressure turbine 6 each comprise rotors which are connected by a low pressure shaft while the high pressure compressor 3 and high pressure turbine 5 comprise rotors which are connected by a high pressure shaft.

[0027] The turbomachine advantageously, but not limited to, rotor blades or movable blades which rotate around the longitudinal axis X and which can equip the rotors of the low pressure compressors 2, high pressure compressor 3, low pressure turbine 6 and high pressure turbine 5.

[0028] The turbomachine 1 advantageously, but not exclusively, includes stator blades or fixed blades which equip, for example, the stators of the low pressure compressor 2, high pressure compressor 3, low pressure turbine 5 and high pressure turbine 6.

[0029] In this description, the term "stator blade" or "fixed blade" refers to a blade that is not driven in rotation about the longitudinal axis X of the turbomachine. In other words, the stator blade is distinct from and unlike a rotor blade or moving blade of the turbomachine.

[0030] Advantageously, the stator blades and rotor blades are generally arranged in annular rows. The annular rows of stator blades are positioned upstream and / or downstream of the annular rows of rotor blades along the longitudinal axis X. An annular row of stator blades and an annular row of rotor blades, for example, form a stage.

[0031] Stator vanes are known as "rectifiers" or by the English acronym "VSV" for "Variable Stator Vane". These allow the flow passing through them to be straightened.

[0032] In the embodiment shown in [Fig. 1], the turbomachine 1 comprises a fan 7 or a propeller including an annular row of rotor blades 8 located upstream of the low-pressure compressor 2 and an annular row of stator blades 9 located downstream of the rotor blades 8. The stator blades 9 are outlet guide vanes, also known as OGVs. Both the rotor blades 8 and the stator blades 9 are shrouded. The stator blades 9 advantageously extend through a secondary flow generated by the fan 7 and, in this example, radially outward from the low-pressure compressor 2, which is traversed by a primary flow also generated by the fan 7.

[0033] In another embodiment shown in Figures 2 and 3, the turbomachine 1 comprises an annular row of stator blades 10 which is arranged, for example, upstream of the low-pressure compressor 2 and at the inlet of the turbomachine 1 at the level of an inlet guide wheel 11. The stator blades 10 are surrounded, for example, by a housing 12 on which they are pivotally mounted about a mounting axis A. The housing 12 is advantageously centered on the longitudinal axis X.

[0034] Advantageously, at least one annular row of the stator blades 9, 10 equipping the turbomachine has variable pitch. That is to say, the blades 9, 10 can pivot about an axis so as to modify their angle of incidence relative to the airflow circulating through the casing. Adjusting the angle of incidence increases or decreases the flow rate and thus the velocity of the airflow.

[0035] For this purpose and as shown in [Fig.2], the turbomachine 1 includes a control mechanism 13 which is configured to change the timing of the stator blades 9, 10 according to the operating mode of the turbomachine.

[0036] The control mechanism 13 includes, for example, a control ring 14 which is driven in displacement such that its displacement causes the variable-pitch stator vanes 9, 10 to pivot. The displacement of the control ring 14 in this example is advantageously a rotation about the longitudinal axis X as well as a translation about this same longitudinal axis X. The control ring 14 is advantageously arranged around the housing 12 and is preferably centered on the longitudinal axis X.

[0037] The control mechanism 13 includes a control means 15 that causes the control ring 14 to move. Advantageously, the control means 15 is an actuator such as a cylinder. The control means 15 includes a movable part 16 that moves relative to a fixed body 17. The latter is fixed, for example, to the housing 12. The movable part 16 moves in translation along the longitudinal axis X.

[0038] Advantageously, but not limitingly, the control means 15 is connected to a fluidic power supply source (not shown) to supply chambers (not shown) which are formed between the fixed body 17 and the moving member 16.

[0039] The control mechanism 13 includes a transmission part that is connected via a pivot joint to the control means 15 and to the control ring 14. Advantageously, the transmission part is fusible. The term "fusible" means that the part can break following an impact and / or high mechanical stress. The fusible part may include areas with a restricted cross-section to facilitate its breakage.

[0040] According to one embodiment, the control mechanism 13 comprises a connecting rod 18 or a turnbuckle having a first end 18a articulated for example on the control ring 14 and a second end 18b articulated for example on a first arm 19a of a right-angle lever 19 connected to the control means 15. The connecting rod 18 may have an adjustable length, that is to say that the length measured between its first end 18a and its second end 18b may vary.

[0041] The right-angle lever 19 includes a second arm 19b pivotally articulated on the moving member 16 (for example, a cylinder rod). The fusible transmission element can be the right-angle lever 19 or the connecting rod 18. The connecting rod 18 and the right-angle lever 19 allow the movement of the moving member 16 of the actuator to be transmitted to the control ring 14.

[0042] The control mechanism 13 further advantageously includes control levers 20 which connect each variable-pitch stator blade 10 to the control ring 14 such that the rotation of the control ring 14 (via the control means) causes the stator blades to pivot about the pitch axis A. Advantageously, but not exclusively, the stator blades 10 pivot simultaneously under the action of the control means 15.

[0043] With reference to [Fig. 3], each stator blade 10 extends radially between a first end 10a and a second end 10b. The first end 10a is pivotally mounted, for example, on the housing 12, and the second end 10b is pivotally mounted, for example, on a radially internal annular ferrule (not shown). Advantageously, the first end 10a passes through an opening 12a through the wall of the housing 12 on both sides and extends radially outwards from the housing 12. The first end 10a and the second end 10b are advantageously each in the form of a pivot.

[0044] Figure 4 illustrates an embodiment of a control lever 20. The control lever 20 comprises, for example, a body 21 elongated along an elongation direction DA. Each elongated body 21 extends between a first portion 22 and a second portion 23, which are connected by a central portion 24. The elongated body 21 is generally delimited by a peripheral edge 25. The peripheral edge 25 is connected, for example, to a radially external surface 26 and a radially internal surface 27. The radially internal surface 27 and the radially external surface 26 are here opposite each other along a radial direction DR. In the installed position, the radial direction DR is parallel to the radial axis Z.

[0045] According to the example shown, the first portion 22 is connected to the first end 10a of a variable-pitch stator blade 10. The first portion 22 advantageously comprises an orifice 28 which passes through its wall on both sides and on the other hand along the radial direction DR. The orifice 28 opens in particular onto the radially external surface 26 of the elongated body 21.

[0046] In [Fig. 5], the body 21 in this embodiment includes a recess 29 which opens onto the radially internal surface 27. The orifice 28 also advantageously opens into this recess 29. The latter allows at least a portion of the pivot of the first end 10a to be received. The recess 29 has an overall rectangular cross-section. This allows for a plane-to-plane connection between the recess and the pivot of the first end 10a, which permits improved torque transmission. Of course, other shapes are possible. The orifice 28 advantageously has a circular cross-section with an axis B.

[0047] Advantageously, the first end 10a of the stator blade 10 is fixed to the first portion 22 by means of fasteners. These fasteners may be bolts with, for example, a shank passing through the orifice 28 and the recess 29, and screwing into a threaded bore of the first end 10a. Another type of fastener allowing for quick disassembly and assembly is of course conceivable.

[0048] Advantageously, the first portion 22 comprises a first maximum thickness el measured along the radial direction RD. The first thickness el is between 8 mm and 10 mm. At the level of the first portion 22, a portion of the radially internal surface 27a is defined in a plane (perpendicular to the radial direction DR) which is offset, for example, from the plane in which the radially internal surface portions of the second portion 23 are defined and possibly from the plane of the central portion 24. The first thickness el is advantageously measured between the radially internal surface portion 27a and a radially external surface portion 26 at the level of the first portion 22.

[0049] The first portion 22 may have a predetermined length L1 which may be equal to a length L2 of the second portion 23 or to a length L3 of the central portion 24. Alternatively, the lengths L1, L2 and L3 may be different. By way of example, the length L1 is between 20 mm and 50 mm.

[0050] Advantageously, but not limitingly, the width of the control lever body 20, measured along the transverse direction DT, decreases from the first portion 22 to the second portion 23.

[0051] The second portion 23 comprises a second thickness e2 which is advantageously less than the first thickness el of the first portion 22. The second thickness can be between 0.8 and 4 mm.

[0052] The second portion 23 is advantageously connected to the control ring 14. For this purpose, the second portion 23 comprises, for example, an orifice 30 (shown in [Fig. 5]) passing through the wall on both sides in the radial direction DR and opening onto both the radially internal surface 27 and the radially external surface External 27. The orifice 30 advantageously has a circular cross-section with axis C and a predetermined diameter D3. A connecting member 31 (shown in Figures 4 and 7) passes, for example, at least partially through the orifice 30 so as to allow connection with the control ring 14.

[0053] The connecting member 31 is advantageously, but not exclusively, permanently fixed to the second portion 23. The connecting member 31 may be a pin which comprises, for example, a head 32 (for example, of circular cross-section) from which extends a straight cylindrical body 33 (having an axis D parallel to the radial axis or radial direction DR). The head 32 advantageously has a diameter D32 greater than that of the cylindrical body D33. The head 32 may be crimped, for example, at the orifice 30. The cylindrical body 33 extends on the side of the radially internal surface 27. In other words, the pin is stationary relative to the control lever 20.

[0054] The control lever 20 is made, for example, of a metallic material. Advantageously, but not exclusively, the metallic material may be titanium or a titanium alloy, steel, or an organic matrix composite material (with, for example, a three-dimensionally woven fibrous reinforcement). Titanium or titanium alloy exhibits good thermomechanical properties and very good corrosion resistance.

[0055] The control lever 20 is advantageously made from a single piece (from material or monolithic).

[0056] According to one embodiment, the control lever 20 is manufactured from a block of metal material which is machined.

[0057] Preferably, the control lever 20 is produced by an additive manufacturing or selective powder melting process. Additive manufacturing makes it possible to obtain complex and three-dimensional parts by fusing layers of powder with the least possible material loss.

[0058] There are several additive manufacturing techniques, one of which can be selected from the group comprising selective laser melting (SLM), electron beam melting (EBM), direct laser additive construction (CLAD), electron beam additive manufacturing (EBAM), laser metal deposition (LMD), binder jetting, or selective laser sintering (SLS). English.

[0059] Preferably, the additive manufacturing technique used is laser powder bed fusion “SLM” also known by the acronym “LBM” for “Laser Beam Melting”.

[0060] Advantageously, but not exclusively, the manufacturing process is carried out by an additive manufacturing installation, not shown. Such an additive manufacturing installation comprises, for example, at least one feed hopper containing a powder, here metallic, in particular titanium or a titanium alloy, at least one device for depositing the powder from the feed hopper onto a build platform, and an energy-generating element, such as a laser, for melting layers of powder. In particular, powder is deposited layer by layer on the build platform, and each layer of powder is melted by the energy-generating element, solidified, and then covered by further layers of the material. This operation is repeated multiple times to form the control lever 20.

[0061] In the context of additive manufacturing, the manufacturing direction of the control lever 20 is advantageously oriented in the elongation direction DA, and preferably from the first portion 22 to the second portion 23. In other words, the successive layers of powder are arranged along the elongation direction DA.

[0062] As shown in Figures 4 to 6, the control lever 20 advantageously includes at least one stiffener 40 which is configured to increase the mechanical strength of the control lever.

[0063] In the present example, a single stiffener 40 is advantageously located between the first portion 22 and the second portion 23. The stiffener 40 is preferably located at the level of the second portion 23 of the control lever 20. Alternatively, the stiffener 40 can be located more or less close to the connecting member 31 or more or less close to the first portion 22.

[0064] The control lever 20 includes at least one hole 41 which passes through its wall on both sides along the radial direction DR. The hole 41 advantageously has a circular cross-section.

[0065] Each orifice 30 and hole 41 is formed, for example, by a simple drilling operation after the body of each control lever 20 has been manufactured. Preferably, the drilling of the orifice 30 and hole 41 is carried out in the same step. Alternatively, the orifice 30 and the hole 41 are formed during the additive manufacturing of the control levers.

[0066] Advantageously, but not exclusively, the hole 41 has a diameter D4 which is identical to the diameter D3 of the orifice 30 intended to receive the connecting element, here the pin. This simplifies the manufacture of the reinforced control levers 20 and avoids increasing the manufacturing time.

[0067] According to the embodiment example, the hole 41 is disposed at a predetermined distance d5 from the orifice 30. More precisely, the predetermined distance d5 separating the axis of the orifice 30 and the axis of the hole 41 is advantageously equal to 1.5*D4.

[0068] The stiffener 40 is an added part which is arranged in the hole 41. In this description, we mean "added part" a part which is not produced during the manufacturing process of the control lever 20. The stiffener is, for example, separate from the control lever during its manufacture.

[0069] Advantageously, the stiffener 40 is made of a metallic material that is different from the metallic material of the control lever 20. The metallic material of the stiffener 40 may include iron or an iron alloy.

[0070] With reference to [Fig. 6], the stiffener 40 advantageously, but not exclusively, comprises a cylindrical body 42 having an axis E. The axis E of the cylindrical body 42 is coaxial with the axis of the hole (parallel to the radial direction). The cylindrical body 42 advantageously comprises a first portion 42a and a second portion 42b. In this embodiment, the first portion 42a has a diameter D42a that is larger than the diameter D42b of the second portion 42b. The diameter D42b is, for example, slightly smaller than the diameter D4 of the hole 41, allowing a clearance preferably between 0.05 mm and 0.15 mm. This difference in diameter between the second portion 42 and the hole 41 facilitates the installation of the stiffener 40 within the control lever 20.

[0071] According to another alternative, the diameter D42a of the first part 42a is equal to the diameter D42b of the second part 42b.

[0072] Advantageously, but not exclusively, the diameter D42a of the first part 42a is substantially equal to the diameter D32 of the head 32 of the pin forming the connecting member 31. Similarly, the diameter D42b of the second part 42b of the stiffener 40 is substantially equal to the diameter D33 of the cylindrical body 33 of the pin. Alternatively, the diameter D42a of the first part 42a may be greater than or less than the diameter D32 of the head of the pin. According to yet another alternative, the diameter D42b of the second part 42b of the stiffener 40 may be greater than or less than the diameter D33 of the cylindrical body of the pin.

[0073] According to an advantageous, but optional feature, the stiffener 40 is fixed to the control lever 20. The fixing can be a crimping (as for the pin installed at the level of the second portion of the control lever 20).

[0074] According to another embodiment not shown, the number of stiffeners may be different and may, for example, be between two and five. Preferably, between two and three stiffeners are attached to a control lever 20. The stiffeners 40 may be arranged regularly between the first portion 22 and the second portion 23 along the elongation direction DA.

[0075] According to the embodiment, the radially external surface portions 26 of each portion 22, 23, 24 of the control lever 20 exhibit surface continuity. These are advantageously located in the same plane. Alternatively, each radially external surface portion could be defined in a plane that has a slight inclination, for example on the order of 5°, with respect to the other planes of the adjacent radially external surface portions. Advantageously, the thickness of the central portion 24 (excluding the stiffeners) is identical to the second thickness e2 of the second portion 23.

[0076] Figure 7 illustrates another embodiment of a control lever 20. This control lever 20 differs from the previous embodiments and alternative embodiments in that the connecting member 31 is mounted to move relative to the control lever 20. More specifically, the connecting member 31 is mounted, for example, via a ball joint 44 on the second portion 23. To this end, the ball joint 44 is made by means of an outer ring 45 and an inner ring 46. The outer ring 45 is advantageously crimped into the through hole 30 of the second portion 23, while the head 32 of the connecting member is press-fitted into the inner ring 46 of the ball joint 44. The ball joint 44 allows each control lever 20 to move by deforming without significant effort, since the connecting member 31 (here the pin) and the second portion 23 of each control lever 20 can move relative to each other.The control means 15, with its current power, can be retained to move the reinforced control levers.

[0077] The configuration of the stiffener(s) gives each control lever 20 at least an increased longitudinal stiffness which will increase its resistance to longitudinal deformation.

[0078] With control levers 20 whose shape is optimized with the stiffeners 40, deformations of the control lever and partial or total disengagement of the pin of the control ring 14 are avoided in the event of application of a given mechanical torque (moment), applied (for example in the event of pumping and / or ingestion of a foreign body) on the stator blades.

Claims

Demands

1. A control mechanism (13) for variable-pitch stator blades of a turbomachine (1), said control mechanism (13) comprising a control ring (14) adapted to be driven in rotation about a longitudinal axis (X) and control levers (20) connecting each variable-pitch stator blade (10) to the control ring (14) such that the rotation of the control ring (14) causes each variable-pitch stator blade (10) to pivot, each control lever (20) being pivotally mounted on the control ring (14) by means of a linkage member (31) and comprising a body (21) elongated along an elongation direction between a first portion (22) and a second portion (23), the body (21) comprising a central portion (24) connecting the first portion (22) and the second portion (23),characterized in that each control lever (20) comprises at least one stiffener (40) configured to increase the mechanical strength of the control lever (20), each control lever (20) comprising at least one hole (41) passing through its wall on both sides, and each stiffener (40) being an added part which is arranged and fixed in the hole (41).

2. Control mechanism (13) according to the preceding claim, characterized in that the control mechanism (13) comprises a control means (15) causing the rotation of the control ring (14) via at least one fusible transmission piece connecting the control ring (14) to the control means (15).

3. Control mechanism (13) according to any one of the preceding claims, characterized in that each control lever (20) is made of titanium, titanium alloy, steel or an organic matrix composite material.

4. Control mechanism (13) according to any one of the preceding claims, characterized in that the second portion (23) of each control lever (20) includes an orifice (30) receiving at least part of the linking member (31).

5. Control mechanism (13) according to the preceding claim, characterized in that the hole (41) and the orifice (30) of the second portion have an identical diameter.

6. Control mechanism (13) according to any one of claims 4 to 5, characterized in that the distance (d5) separating the axis of the hole (41) and the orifice (30) is equal to 1.5*D4.

7. Control mechanism (13) according to any one of claims 3 to 6, characterized in that the stiffener (40) is made of a metallic material different from the material of each control lever (20) and preferably comprising iron or an iron alloy.

8. Control mechanism (13) according to any one of the preceding claims, characterized in that each stiffener (40) has a cylindrical body (42) having a first part (42a) and a second part (42a) which have identical or different diameters.

9. Control mechanism (13) according to any one of the preceding claims, characterized in that between two and five stiffeners (40) are attached and arranged on each control lever (20) between the first portion (22) and the second portion (23).

10. Control mechanism (13) according to any one of claims 4 to 9, characterized in that the linking member (31) is permanently fixed at the level of the second portion (23).

11. Control mechanism (13) according to any one of claims 4 to 9, characterized in that the linking member (31) is mounted following a ball joint (44) at the level of the second portion (23).

12. Turbomachine (1) comprising variable-pitch stator blades (10) for straightening an airflow circulating in the turbomachine and a control mechanism (13) for the stator blades (10) according to any one of the preceding claims.

13. Turbomachine (1) according to claim 12, characterized in that it comprises at least one stage formed of an annular row of moving blades and an annular row of stator blades (10), the stator blades (10) being arranged upstream or downstream of the moving blades.

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