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 about a longitudinal axis and control levers connecting each stator blade to the control ring such 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 along an elongation direction 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 comprises stiffeners (40) configured to increase the mechanical strength of the control levers, the stiffeners extending from a radially internal face of the central portion along a radial direction and along the elongation direction.Figure for the abridged version: 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, the control mechanism comprising a control ring adapted to be rotated 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 an elongated body 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 stiffeners configured to increase the mechanical strength of the control levers, the stiffeners extending on the one hand,from a radially internal face of the central portion along a radial direction and, on the other hand, along the direction of elongation.

[0010] Thus, this solution makes it possible to achieve the aforementioned objective. In particular, the stiffeners allow for 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 backflow 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, damage, and disengagement from the control ring. The reliability of the control mechanism is considerably improved. This 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 stiffeners comprise at least two walls which are arranged at the level of portions of peripheral edge of the central portion and one opposite the other, the stiffeners are arranged regularly between portions of peripheral edge of the central portion. - the stiffeners are arranged regularly between portions of the peripheral edge of the central portion. - the number of walls is between two and five. - each wall comprises a thickness measured along a transverse direction which is substantially equal to or greater than a thickness of the second portion. - each wall comprises a thickness measured along a transverse direction which is substantially less than or equal to 50% of a length of the first portion. - each wall has a predetermined length measured along a direction of elongation which is substantially equal to a length of the first portion. - each wall has a predetermined length equal to or less than a length of a part of the control lever, the length of the part of the control lever being equal to a length of the second portion and a length of the central 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.

[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 of the turbomachine, it 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, 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 [Fig. 4] is a perspective view of an embodiment of a lever order according to the invention; and

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

[0022] - Figure 6 represents another embodiment of a control lever according to the invention. Detailed description of the invention

[0023] 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 comprise fan rotor blades or rotor blades of at least one propeller, whether shrouded or unshrouded.

[0024] 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 relative to the longitudinal axis X. The terms "external", "outside", "internal", "internal" and "radial" are defined relative to a radial axis Z which extends from the longitudinal axis X and with regard to the distance from the longitudinal axis X. The radial axis is perpendicular to the longitudinal axis X.

[0025] 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.

[0026] The turbomachine 1 advantageously, but not exclusively, comprises 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] In the exemplary embodiment of [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 blower 7 and in the present example, radially outside the low pressure compressor 2 which is traversed by a primary flow also generated by the blower 7.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The control mechanism 13 comprises a transmission part which is connected via a pivoting joint to the control means 15 and to the control ring 14. Advantageously, the transmission part is fusible. By the term "fusible," it is understood that the part can break following an impact and / or stress. High mechanical strength. The fusible part may include areas with a restricted cross-section to facilitate its rupture.

[0039] 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.

[0040] 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.

[0041] The control mechanism 13 further advantageously comprises 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 limitingly, the stator blades 10 pivot simultaneously under the action of the control means 15.

[0042] 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.

[0043] 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 opposed along a radial direction DR. In the installed position, the radial direction DR is parallel to the radial axis Z.

[0044] Following 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 includes an orifice 28 which passes through its wall on both sides along the radial direction DR. The orifice 28 opens in particular onto the radially external surface 26 of the elongated body 21.

[0045] In [Fig.5], the body 21 includes in this embodiment a recess 29 which opens onto the radially internal surface 27. The orifice 28 also advantageously opens into this recess 29. The latter allows to receive at least a portion of the pivot of the first end 10a.

[0046] 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 facilitates the transmission of torque. 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, for example, between 8 mm and 20 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) which is offset from the plane in which the radially internal surface portions of the second portion 23 and the central portion 24 are defined. The first thickness el is advantageously measured between the radially internal surface portion 27a and an external surface portion 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 e2 can be between 0.8 mm and 4 mm.

[0052] The second portion 23 is advantageously connected to the control ring 14. For this purpose, the second portion 23 includes, for example, a through orifice 30 The wall on either side follows the radial direction DR and opens onto both the radially internal surface 27 and the radially external surface 26. The orifice 30 advantageously has a circular cross-section with axis C and a predetermined diameter. A connecting member 31 (shown in Figures 4 and 6) passes, for example, at least partially through the orifice 30 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 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 through-hole. 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), and binder jetting. "Binder Jetting" in English, or selective laser sintering, also designated by the acronym "SLS" for "Selective Laser Sintering" in 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 and 5, the control lever 20 advantageously includes at least one stiffener 40 which is configured to increase the mechanical strength of the control lever 20.

[0063] In the embodiment of [Fig.4], stiffeners 40 are advantageously located at the central portion 24 of the control lever 20. More precisely, the stiffeners 40 extend, on the one hand, from the radially internal face 27 of the central portion 24 along the radial direction DR, and on the other hand along the elongation direction DA.

[0064] In this embodiment, the stiffeners 40 comprise at least two walls 41 arranged at portions of the peripheral edge of the central portion 24. The two walls 41 extend opposite each other. In other words, a stiffener wall 41 extends at a portion of the peripheral edge 25 of the control lever, and in particular of the central portion. Advantageously, each wall 41 has a median plane that is generally parallel.

[0065] According to another embodiment not shown, the number of stiffeners 40 may be different. For example, the stiffeners 40 may comprise between two and five walls 41 which extend radially from the radially internal face 27 and along the elongation direction DA.

[0066] The stiffeners 40 can be arranged, preferably regularly, between the peripheral edge portions (opposite along the direction DT) of the central portion 24.

[0067] Each wall 41 comprises a thickness e3 measured along the transverse direction DT that is substantially equal to or greater than the second thickness e2 of the second portion 23. This makes it possible to obtain a homogeneous mass and stiffness. Alternatively, the thickness e3 of the stiffener walls can be substantially less than or equal to 50% of the length L1 of the first portion 22. Such a percentage makes it possible, for example, to maintain separate stiffeners, in particular two stiffeners. Moreover, such a configuration of the thicknesses e3 provides stiffness in the direction of the elongation DA but also in the transverse direction DT.

[0068] Advantageously, but not exclusively, each wall 41 of the stiffeners 40 comprises a predetermined length L4 measured along the elongation direction DA, which is substantially equal to the length L1 of the first portion 22. The predetermined length L4 is between 10 mm and 20 mm. This range of values ​​makes it possible to obtain stiffeners that are effective without impacting the mass of the control lever 20. For example, stiffeners with a length that is too short might not prevent deformation of the control lever 20.

[0069] Alternatively, the predetermined length L4 of the stiffeners 40 may be equal to or less than a length L5 of a portion of the control lever. The latter corresponds to the length L2 of the first portion 22 and the predetermined length L3 of the central portion 24. Advantageously, but not limitingly, the predetermined length L4 may be less than or equal to the length L1 or the length L2.

[0070] 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.

[0071] Figure 6 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 movable 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. For this purpose, the ball joint 44 is The assembly 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 31 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 20.

[0072] The configuration of the stiffener(s) 40 gives each control lever 20 at least an increased longitudinal stiffness which will increase its resistance to longitudinal deformation.

[0073] 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 high 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. Control mechanism (13) for variable-pitch stator blades of a turbomachine (1), the 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 linking member (31) and comprising a body (21) elongated along an elongation direction (DA) 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 stiffeners (40) configured to increase the mechanical strength of the control levers (20), the stiffeners (40) extending on the one hand, from a radially internal face of the central portion (24) in a radial direction and on the other hand, in the elongation direction (DA).

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 stiffeners (40) comprise at least two walls (41) which are arranged at the level of peripheral edge portions (25) of the central portion (24) and opposite each other.

5. Control mechanism (13) according to any one of the preceding claims, characterized in that the stiffeners (40) are arranged regularly between portions of peripheral border (25) of the central portion (24).

6. Control mechanism (13) according to claim 4 or 5, characterized in that the number of walls (41) is between two and five.

7. Control mechanism (13) according to any one of claims 4 to 6, characterized in that each wall (41) comprises a thickness (e3) measured along a transverse direction (DT) which is substantially equal to or greater than a thickness (e2) of the second portion (23).

8. Control mechanism (13) according to any one of claims 4 to 6, characterized in that each wall (41) comprises a thickness (e3) measured along a transverse direction (DT) which is substantially less than or equal to 50% of a length (Ll) of the first portion (22).

9. Control mechanism (13) according to any one of claims 4 to 8, characterized in that each wall (41) has a length (L4) measured along an elongation direction (DA) which is substantially equal to a length (L1) of the first portion (22).

10. Control mechanism (13) according to any one of claims 4 to 8, characterized in that each wall (41) has a length (L4) equal to or less than a length (L5) of a portion of the control lever (20), the length (L5) of a portion of the control lever (20) being equal to a length (L2) of the second portion (22) and to a length (L3) of the central portion (23).

11. Control mechanism (13) according to any one of claims 1 to 10, characterized in that the linking member (31) is permanently fixed at the level of the second portion (23).

12. Control mechanism (13) according to any one of claims 1 to 10, characterized in that the linking member (31) is mounted following a ball joint (44) at the level of the second portion (23).

13. 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.

14. Turbomachine (1) according to claim 13, characterized in that it comprises at least one stage formed of an annular row of movable 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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