Improved variable pitch blade control system

Abstract

Improved Variable Pitch Blade Control System: Variable pitch blade control system for a turbomachine stator (10), comprising a blade (13) having a radial end (134) movably fixed to an outer wall (12), a rotating platform (20) disposed in the outer wall (12), an inner face (21) being in contact with the air flowing in the stator (10), the platform (20) being rotationally fixed to the blade and comprising at least one slot (23), a masking plate (30) disposed on the side of an outer face (22) being rotationally fixed relative to the outer wall (12), the masking plate (30) comprising at least one protrusion (33) of a shape complementary to the slot (23), in an aligned position of the blade (13), the protrusion (33) is fully inserted into the slot (23), and in a stalled position of the blade (13), the protuberance (33) is extracted at least in part from the slot (23). Figure for the abstract: Fig. 6.

Description

Title of the invention: Improved variable-pitch blade control system technical field

[0001] The present exposition relates to the field of variable pitch stators in enclosed aeronautical turbomachines, in particular compressor inlet guide wheel stators, but not exclusively. Previous technique

[0002] As is known, a turbomachine stator comprises fixed blades extending radially between an inner wall (the hub) and an outer wall (the casing). The inner and outer walls define an annular gas flow channel from the upstream to the downstream end of the engine. These stator blades may have variable pitch, allowing the blades of each blade to be pivoted around a radial axis to change their angle of incidence. Such a stator with variable pitch blades can, for example, be an inlet guide wheel (IGW) for high- or low-pressure compressors.

[0003] These variable-pitch blades are, for example, mounted on rotating platforms with a pivot on the housing and / or the hub, and allow the flow at the compressor inlet to be directed so that it is aligned with the leading edge of the downstream impeller. The blades may also include a cylindrical pivot to which the radial end of the blade is attached; the rotation of this pivot causes the entire blade assembly to rotate. In this case, some clearance generally exists between the radial end of the blade and the surface of the housing (or the hub).

[0004] Variable-pitch blades are generally movable between an aligned position and a locked position. In the aligned position, the angle of attack, which can be defined as the angle between the blade chord and the engine axis, is zero or small, for example, less than 20°. This position allows the blades to be aligned with the upstream flow. In the locked position, the angle of attack is high, for example, greater than 40°. This position allows the flow arriving at the downstream runner to be redirected. However, changing the angle of attack of variable-pitch blades has consequences for the flow topology, notably involving secondary flows that generate pressure distortion. These unwanted secondary flows must be managed.

[0005] In the aligned position in particular, the pressure differential between the lower and upper surfaces of the blade is small and little flow passes through the gap between the tip of the blade and the surface of the housing (or hub), which generates few vortices, and therefore minimal pressure loss.

[0006] In the locked position, the pressure gradient between the lower and upper surfaces is high. This can create a transverse flow at the level of the play, which can generate play flows, and in particular a vortex known as a play vortex, and therefore pressure distortions likely to impact the moving wheel downstream and promote the onset of the pumping phenomenon.

[0007] To manage these secondary flows, it is known to use surface treatment technologies, consisting of local modifications to the wall of the hub or housing that delimit the airflow channel. For example, grooves or slots can be made in the wall of the housing and / or hub to limit the consequences of the appearance of backlash vortices and pressure distortions when the blades are in the locked position.

[0008] However, although useful for large pitch angles, such slots are less useful when the blades are in an aligned position, and may even degrade stator performance by generating additional losses. Furthermore, while the orientation of the slots may be optimal for certain pitch angles, it is no longer optimal when the blade pitch angle changes.

[0009] In other words, although these technologies have advantages for certain types of flow and certain blade pitch angles, they imply a degradation of stator performance for other types of flow and pitch angles, and are therefore difficult to integrate for variable pitch stator blades.

[0010] There is therefore a need for a system that makes it possible to overcome at least part of the aforementioned disadvantages, and to improve the performance of the stalled stator regardless of the position of the blades, aligned or stalled, without degrading its performance when they change position. Description of the invention

[0011] The present description relates to a variable-pitch turbine blade control system for a turbomachine stator, the system comprising: - at least one variable-pitch blade comprising a blade capable of extending radially between an inner and an outer wall of the stator, at least one radial end of the blade being movably fixed to the inner or outer wall, - a rotating platform capable of being disposed in the inner or outer wall such that an inner face of the platform is capable of being in contact with the air flowing in the stator, the platform being rotationally fixed to the blade and comprising at least one slot passing through the platform from the inner face to an outer face, - a masking plate disposed on the side of the external face of the platform and being able to be fixed in rotation with respect to the internal or external wall, the masking plate comprising at least one protrusion of complementary shape to the slot, the system being configured such that in an aligned position of the blade, the protrusion is fully inserted into the slot, and in a wedged position of the blade, the protrusion is at least partially extracted from the slot.

[0012] In the present description, the terms "axial direction," "radial direction," and their derivatives are defined with respect to the central axis of the stator, which is also the central axis of the turbomachine, around which its moving parts (the rotors) rotate. Preferably, the stator has overall cyclic symmetry about the central axis. Similarly, the terms "upstream" and "downstream" are understood with respect to the normal direction of gas flow in a turbomachine, from the inlet to the outlet nozzle, passing successively through the compressors, the combustion chamber, and the turbines.

[0013] It is understood that the stator blades are fixed to one or the other of the radially internal wall and the radially external wall, or to both walls, in a movable manner by being configured to pivot relative to these walls around a radial axis.

[0014] It is further understood that the platform is a portion of the inner or outer wall, this portion being movable relative to the rest of the inner or outer wall. The platform, which is preferably circular, is notably capable of pivoting around a radial axis passing through the center of the platform. It is thus understood that the inner face of the platform is substantially continuous with the surface of the inner or outer wall and thus delimits a portion of the annular airflow channel. The platform is also traversed by a slot through its entire thickness, between its inner and outer faces.

[0015] While the rotating platform is capable of pivoting, along with the blade, relative to the inner or outer wall, the masking plate is stationary relative to said wall. Thus, when the slot moves, the protrusion remains stationary. Consequently, when the protrusion is inserted into the slot while the platform is in a given angular position corresponding to the aligned position of the blade, it is no longer inserted into the slot when the platform pivots and leaves this angular position.

[0016] Furthermore, since the protrusion has a shape complementary to the slot, it occupies at least part, if not all, of the slot's volume when inserted into it. This configuration ensures that a slot is present in the wall profile when the blade is in the wedged position, and that this slot is concealed, being filled by the protrusion, when the blade is in the aligned position. It is understood In this respect, "fully inserted" means that the entire protrusion is inserted into the slot. Furthermore, at least part of the protrusion is extracted from the slot in a wedged position, preferably the entire protrusion.

[0017] Thus, when the blade is in the stalled position, the slot helps to limit the consequences of the appearance of backlash vortices and pressure distortions. Conversely, when the blade is in the aligned position such that the presence of this slot is no longer necessary, the slot is at least partially masked so as not to disturb, or only minimally disturb, the flow. This system thus improves the performance of the stator in the stalled position, without degrading it in the aligned position. The overall performance of the turbomachine is therefore improved.

[0018] In some embodiments, the system includes a return spring capable of being compressed between the masking plate and a fixed wall of the inner or outer wall when the blade is in the wedged position, and of exerting a return force on the masking plate so as to push the protrusion into the slot when the blade and the platform rotate towards the aligned position.

[0019] The return spring is a simple and inexpensive way of pushing the masking plate in the direction of insertion of the protrusion into the slot, and of holding said protrusion inside said slot when the blade is in the aligned position.

[0020] In certain embodiments, when the blade is in the locked position, the platform is positioned so that the protrusion of the masking plate is in contact with the external face of the platform, the return spring being compressed between the masking plate and the fixed wall, and when the blade is in the aligned position, the platform is positioned so that the slot is opposite the protrusion, the latter then being inserted into the slot by the force exerted by the return spring.

[0021] It is understood that the protrusion rests against a solid portion of the outer face of the platform, which is a portion of the platform without a slot. In the wedged position of the blade, the protrusion rests against said solid portion, on the side of the outer face of the platform, and is therefore not inserted into the slot, the protrusion not being radially aligned with the slot. In the aligned position of the blade, the protrusion is radially aligned with the slot such that, under the action of the return spring, the protrusion, which was blocked by the solid portion in the wedged position, can be inserted into the slot.

[0022] In certain embodiments, at least one radial end of the blade is fixed to the inner wall or to the outer wall by means of a cylindrical pivot of the blade, the platform being fixed to the cylindrical pivot so as to form a gap between the radial end of the blade and the platform, the gap extending on either side of an intrados and an extrados of the blade.

[0023] Since the platform is fixed to the cylindrical pivot, the rotation of the blade implies the rotation of the blade and the cylindrical pivot, thus resulting in an identical rotation of the platform. The fact that the slot formed by the extraction of the protrusion when the blade pivots in the locked position extends on both sides of the lower and upper surfaces of the blade further limits the consequences of the appearance of play vortices and pressure distortions between the lower and upper surfaces of the blade.

[0024] In some embodiments, the slit and the protrusion have a curved shape.

[0025] Preferably, the center of curvature of the slot coincides with the axis of rotation of the platform and the blade. The slot thus has the shape of a circular arc around the axis of rotation of the blade. Given the circular shape of the platform, this curved shape of the slot facilitates guiding the protrusion towards the slot, whether for insertion or extraction. Furthermore, this curved shape ensures that the slot is oriented appropriately regardless of the blade pitch angle.

[0026] In some embodiments, the system comprises at least two slots and at least two protrusions. Preferably, the system comprises as many slots as protrusions. Even more preferably, the system comprises two slots and two protrusions having a curved shape whose center of curvature coincides with the axis of rotation of the blade.

[0027] The presence of at least two slots and at least two protrusions makes it possible to limit even more effectively the consequences of the appearance of play vortices and pressure distortions, and thus to further improve the performance of the stator in the locked position, without degrading it in the aligned position.

[0028] In some embodiments, at least one end of the slot comprises an inclined wall between the inner face and the outer face, the inclined wall being able to guide the protrusion from an insertion position in the slot to an extraction position from the slot when the blade passes from the aligned position to the wedged position.

[0029] In other words, the inclined wall acts as a ramp, guiding the protrusion in the direction of extraction from the slot during platform rotation, that is, in the direction from the inner face to the outer face of the platform. This inclined wall thus facilitates the extraction of the protrusion from the slot as the blade moves from the aligned position to the locked position.

[0030] In certain embodiments, when the blade is in the aligned position, an end face of the protuberance is flush with the inner face of the platform.

[0031] By "flush", it is understood that the end surface of the protuberance is continuous with the inner face of the platform, without any positive or negative difference in level, That is to say, without a step or recess. Thus, when the blade is in the aligned position and the protrusion is inserted into the slot, the protrusion's end surface is integrated and blends seamlessly with the profile of the platform's inner face. This configuration minimizes the impact of the platform and its slot on the incident flow when the blades are in the aligned position.

[0032] In some embodiments, the system is configured such that, when a pitch angle between a chord of the blade at the radial end of the blade and a central axis of the stator is between 0 and 20°, the protrusion is fully inserted into the slot, and when the pitch angle is between 20 and 80°, the protrusion is at least partially extracted from the slot.

[0033] In other words, an aligned blade position corresponds to a situation in which the pitch angle is between 0 and 20°, preferably less than 10°. A set blade position corresponds to a situation in which the pitch angle is between 20 and 80°, for example, equal to 60°. Preferably, an aligned blade position corresponds to a situation in which the pitch angle is equal to 0°, and a set blade position corresponds to a situation in which the pitch angle is strictly greater than 0°. It should be noted that the angle values ​​above are absolute values ​​of the pitch angle around the 0° angle corresponding to the aligned position.

[0034] Thus, when the angle of adjustment is equal to 0°, the protrusion can completely fill the slot, and thus further minimize the impact of the slot on the flow, in the aligned position.

[0035] The present exposition also relates to a turbomachine stator extending around a central axis and comprising an inner wall and an outer wall delimiting an annular vein, and a control system according to any one of the preceding embodiments.

[0036] In some embodiments, the stator is an input guide wheel of a turbomachine compressor, the inner wall is a hub and the outer wall is an outer casing.

[0037] The present description also relates to a turbomachine comprising a stator according to any one of the preceding embodiments. Brief description of the drawings

[0038] The invention and its advantages will be better understood upon reading the following detailed description of various embodiments of the invention, given by way of non-limiting examples. This description refers to the accompanying figure pages, on which:

[0039] [Fig. 1] Fig. 1 represents a schematic longitudinal cross-sectional view of a tur- bomachine,

[0040] [Fig.2] Fig.2 represents a partial view in a half-plane of section parallel to the central axis of a stator with variable timing according to prior art,

[0041] [Fig.3] Fig.3 represents a radial section of a stator blade with a timing variable, at its radial end, in an aligned position (left) and in a wedged position (right),

[0042] [Fig.4] Fig.4 is a perspective view of a rotating platform of a control system according to the invention,

[0043] [Fig. 5] Fig. 5 is a perspective view of a masking plate and a control system spring

[0044] [Fig. 6] Figure 6 shows a partial axial cross-sectional view of a system of control of the invention, in an insertion position,

[0045] [Fig.7] [Fig.7] represents the control system of [Fig.6], in a extraction position,

[0046] [Fig.8] Fig.8 represents a view from below parallel to a radial direction of the control system in the insertion position,

[0047] [Fig.9] Fig.9 represents an isolated, cross-sectional view in a cutting plane parallel to the radial direction, from the end of a slot in the platform and the masking plate, in the position of [Fig.8],

[0048] [Fig. 10] Fig. 10 represents a bottom view parallel to the radial direction of the control system in an intermediate position

[0049] [Fig. 11] Fig. 11 represents an isolated, cross-sectional view in a cutting plane parallel to the radial direction, from the end of a slot in the platform and the masking plate, in the position of [Fig. 10],

[0050] [Fig. 12] Fig. 12 represents a bottom view parallel to the radial direction of the control system in the extraction position,

[0051] [Fig. 13] Fig. 13 represents an isolated, cross-sectional view in a cutting plane parallel to the radial direction, from the end of a slot in the platform and the masking tray, in the position of [Fig. 12]. Description of the implementation methods

[0052] The terms "upstream" and "downstream" are subsequently defined with respect to the direction of gas flow through a turbomachine, indicated by arrow F in [Fig. 1] and subsequent figures. Furthermore, the terms "internal" and "external" are considered in a radial direction R perpendicular to the central axis X of the turbomachine. Thus, the external wall 12 of the stator 10, for example, is farther from the central axis X than its internal wall 11 in the radial direction R.

[0053] Fig. 1 illustrates a double-flow turbomachine 100 comprising in a known from upstream to downstream successively at least one blower S, at least one stage of low pressure compressor 1, of high pressure compressor 2, a combustion chamber 3, at least one stage of high pressure turbine 4 and of low pressure turbine 5. The rotors of the compressors 1, 2, of the turbines 4, 5 and of the blower S rotate around the central axis X of the turbomachine 100.

[0054] The stator 10 considered in the following example is an inlet guide wheel of the high-pressure compressor 2, arranged upstream of the latter and allowing the flow F entering this compressor to be directed, in particular to align it with the leading edge of the moving wheel of the first stage of the high-pressure compressor 2. This example is not limiting however, the invention also applying to any stator comprising variable-pitch vanes.

[0055] The stator 10 comprises a hub 11 (the inner wall) and a housing 12 (the outer wall) delimiting between them an annular channel V in which the gas flow F flows. More precisely, the annular channel V is delimited by a radially external wall 110 of the hub 11 and a radially internal wall 120 of the housing 12, the surfaces of the walls 110, 120 being in contact with the gas flow F. The stator 10 further comprises a plurality of variable-pitch blades (only one is visible in the figures) extending in the channel V and being distributed circumferentially around the central axis X.

[0056] As illustrated in [Fig.2], representing a partial view of a stator 10' according to the prior art in a half-plane of section parallel to the central axis X, each blade comprises a blade 13 movably fixed to the housing 12 and is not in contact with the hub 11. It will be noted that this example is not limiting, the invention also applying to a situation in which the blades 13 are fixed to the hub 11 and are not in contact with the housing 12, or are movably fixed to both the hub 11 and the housing 12.

[0057] More specifically, each blade comprises a cylindrical pivot 135 fixed to a radially external end 134 of the blade 13, the cylindrical pivot 135 being movably fixed to the housing 12. The cylindrical pivot 135 is rotatable relative to the housing 12, about a radial direction R, by means of a blade pitch angle control device for the blade 13. The control device is not the subject of the present invention and is not shown in the figures. Such a control device is, however, described, for example, in document EP 1 331 402 Bl. The control device is thus capable of rotating the cylindrical pivot 135, and therefore the blade 13, about the radial direction R, to adjust the pitch angle of the blade 13.

[0058] Each blade 13 further comprises a leading edge 136, a trailing edge 138, an upper surface 131 and an lower surface 133. Moreover, the radially outer end 134 of the The blade 13 is separated from the inner wall 120 of the housing by a clearance, or gap E, upstream and downstream of the cylindrical pivot 135. The thickness of the gap E (deliberately emphasized in [Fig. 2]) is between 0.1 and 5 mm. It should be noted that the gap E is not necessarily constant and can vary between the leading edge 136 and the trailing edge 138, and also depending on the pitch angle of the blade 13, given the curved shape of the inner wall 120.

[0059] Figure 3 shows a section of a blade 13 at the free end 134, in a left-aligned position and in a right-locked position. The lock angle [3] is the angle formed between the central axis X and the direction G of the chord of the blade 13 at this section, the chord being the straight line connecting the leading edge 136 and the trailing edge 138. The aligned position of the blade 13 corresponds to a situation in which the lock angle [3] is between 0 and 20°, preferably less than 10°, and preferably 0°. The locked position corresponds to a situation in which the lock angle [3] is between 20 and 80°, preferably 60°. Alternatively, the wedged position may correspond to a situation in which the wedge angle [3 is strictly greater than 0°, the blade 13 then being aligned when the wedge angle is equal to 0°.

[0060] The stator 10 according to the invention differs from the stator 10' according to the prior art in that it comprises, in addition to the hub 11, the housing 12 and the blades described above, a variable pitch blade control system, described hereafter with reference to figures 4 to 13.

[0061] The control system includes at least one blade as described above and a control device (not shown) allowing adjustment of the pitch angle [3 of the blade 13. The control system further includes a rotating platform 20, fixed in rotation with the cylindrical pivot 135, and therefore with the blade 13.

[0062] The platform 20, shown alone in perspective in [Fig. 4], comprises an inner face 21 and an outer face 22. The platform 20 is integrated into the wall of the housing 12. In the configuration shown in Figures 6 and 7, its inner face 21 is flush with the inner wall 210 of the housing 12 and is intended to be in contact with the gas flow F. It should be noted, however, that Figures 6 and 7 are schematic; the inner face 21, which is preferably flat, does not necessarily have to be flush with the inner wall 210 around the entire circumference of the platform 20, given the curved shape of the inner wall 210 of the housing 12, which is annular. The distance between the inner face 21 and the outer face 22 of the platform 20 defines the thickness of the platform.

[0063] It is understood that in the stator 10, a platform 20 is fixed to the cylindrical pivot 135 of each blade. Furthermore, the platform 20 is circular with a diameter preferably greater than the chord length of the blade 13, although the diameter may alternatively be less than the length of said chord. The platform 20 It further comprises a cylindrical sleeve 24 within which is housed the cylindrical pivot 135 of the blade. On an inner face of the cylindrical sleeve 24, a straight groove 241 extends longitudinally in the direction of the principal axis Y of the platform 20, the principal axis Y being coincident with the radial direction R when the platform 20 is disposed on the blade.

[0064] The groove 241 is adapted to receive a rail 136 of the cylindrical pivot 135, extending longitudinally in the radial direction R along an external face of the cylindrical pivot 135. Thus, when the rail 136 is engaged in the groove 241, the rotation of the cylindrical pivot 135 around the radial direction R causes the sleeve 24, and therefore the platform 20, to rotate along with the blade 13. The rail 136 can be press-fitted into the groove 241 so as to also block translational movements of the platform 20 along the radial direction R. However, other means can be provided to prevent such translation.

[0065] Furthermore, the platform 20 comprises at least one slot 23, in this example two slots 23, extending through the thickness of the platform 20, from the inner face 21 to the outer face 22. The slots 23 have an elongated and curved shape and extend along a lateral edge 25 of the platform 20. The curvature of the slots 23 is such that their center of curvature coincides with the principal axis Y of the platform, that is, the radial direction R when the platform 20 is mounted on the stator 10. The slots 23 are arranged on either side of the principal axis Y and symmetrically with respect to it. Preferably, the platform 20 is axisymmetric with respect to the principal axis Y.

[0066] Preferably, each slot 23 extends over an angular range between 1° and 170°, preferably between 20° and 100°. Even more preferably, the curvilinear length of each slot 23 is at least twice the thickness of the blade 13, in particular the thickness of the portion of the blade 13 opposite the slot 23. Its width L can further be between 1 mm and 5 mm, for example equal to 2.5 mm.

[0067] Each slot 23 comprises, at at least one of its longitudinal ends (i.e., at the end of the curve formed by the slot 23), in this example at both of its longitudinal ends, an inclined wall 231. Unlike the rest of the slot 23, where the inner face 21 and the outer face 22 of the platform 20 are connected by a vertical wall 233, the inner and outer faces 21, 22 are connected by an inclined wall 231 at the ends of the slot 23. The inclined walls 231 constitute an upward slope, from the inner face 21 to the outer face 22, in the reference frame of the figures.

[0068] The control system further comprises a masking plate 30, disposed on the side of the external face 22 of the platform 20, preferably axisymmetric about a principal axis Z coinciding with the principal axis Y of the platform and the radial direction R when the masking plate is arranged around the cylindrical sleeve 24 in the stator 10. The masking plate 30, shown in isolation (with the return spring 40 described below) in perspective on [Fig.5], comprises an inner face 31 and an outer face 32. The masking plate 30 has the shape of a disc having in its center a circular orifice 34, arranged around the cylindrical sleeve 24 of the platform 20.

[0069] On its lateral edge 35, the masking plate 30 includes at least one notch 341 suitable for receiving a rail 121 of the housing 12. The engagement of the notch 341 in the rail 121 makes it possible to block the rotation of the masking plate 30 around the radial direction R, relative to the housing 12. Thus, the masking plate 30 is fixed in rotation relative to the housing 12 around the radial direction R, but is free in translation along the radial direction R relative to the housing 12, the notch 341 being able to slide along the rail 121.

[0070] The masking platform 30 also includes at least one protrusion 33. More precisely, the masking platform 30 includes as many protrusions 33 as the platform 20 includes slots 23. In this example, the masking platform 30 includes two protrusions 33, each having a curved shape. In particular, each protrusion 33 has a shape similar to and complementary to a slot 23. In other words, each protrusion 33 has substantially the same dimensions as a slot 23, the same angular extent (for example, 60°), the same width L, and the same radius of curvature.

[0071] It is understood, however, that the dimensions of the protrusions 33 are slightly smaller than those of the slots 23, in order to allow their insertion into the latter. Thus, when a protrusion 33 is fully inserted into a slot 23 (hereinafter "insertion position"), it occupies at least 90% of the volume formed by this slot 23, preferably at least 95%, and even more preferably at least 99%.

[0072] In addition, a height H of the protrusions 33 is substantially equal to the thickness of the platform 20, between its inner face 21 and its outer face 22. Thus, when the protrusion 33 is in the insertion position in the slot, an end face 331 of the protrusion 33 is flush with the inner face 21 of the platform 20 (Figures 6 and 9).

[0073] The control system also includes a return spring 40 (hereinafter "spring 40"), in this example a Belleville-type spring washer, elastically deformable. The spring 40 is arranged around the cylindrical sleeve 24 of the platform 20, on the side of the outer face 32 of the masking plate 30. In the insertion position of the masking plate 30, the spring 40 is arranged so as to be in contact with the outer face 32 of the masking plate 30 on one side, and an inner wall 122 of the housing 12 on the other. Preferably, the spring 40 is slightly compressed between the outer face 32 and the wall 122. The spring 40 thus maintains the Masking plate 30 in the insertion position ([Fig. 6]). Note that in this insertion position, the inner face 31 of the masking plate 30 is in planar contact with the outer face 22 of the platform 20.

[0074] In the extraction position, in which the protrusions 33 are extracted from the slots 23 ([Fig.7]), the spring 40 is further compressed between the wall 122 of the housing 12, and the outer face 32 of the masking plate 30. In addition, the end face 331 of the protrusions 33 is pressed by the restoring force exerted by the spring 40 against the outer face 22 of the platform 20, after rotation of the platform 20 as described below.

[0075] The transition from the insertion position to the extraction position is detailed in the remainder of the description with reference to Figures 8 to 13. In particular, Figures 8, 10, and 12 represent different phases of the transition from the insertion position to the extraction position in a bottom view of the platform 20 (from the side of its inner face 21). By convention, the different longitudinal ends of the slots 23 will be identified by A, B, C, and D in these figures. Figures 9, 11, and 13 represent these same phases, in an isolated cross-sectional view of the platform 20 and the masking plate 30 in their thickness, at the level of a longitudinal end 233 of one of the two slots 23, for example, end A.

[0076] When the blade 13 is in the aligned position, for example with a pitch angle [3] of 0°, the masking plate 30 is in the insertion position, the protrusions 33 being fully inserted into the slots 23 (Figures 8 and 9). In this position, the end face 331 of the protrusion 33 is flush with the inner face 21 of the platform 20, and one end 333 of the protrusion 33 is adjacent to one end 233 of the slot 23, preferably with a gap of less than 0.5 mm (the ends 233, 333 are shown in contact in [Fig. 9]). The end 233 of the slot 23 corresponds to the lower base of the inclined wall 231.

[0077] When the control device is actuated to change the pitch angle [3] of the blade 13, the latter begins to rotate around the radial direction R, in a counterclockwise direction represented by the arrow in [Fig. 10], such that the pitch angle [3] becomes greater than 0° (Figures 10 and 11). The rotation of the blade, in particular of the blade 13 and the cylindrical pivot 135, causes the platform 20 to rotate through the interaction between the rail 136 and the groove 241 described previously. On the other hand, the masking plate 30, being blocked in rotation by the interaction between the notch 341 and the rail 121, does not rotate with the platform 20. Given the rotation of the platform 20 around the axis R, the end 233 of the slot 23 comes into contact with the end 333 of the protrusion 33, then continues its movement beyond said end 333 (this movement is symbolized by the arrow pointing to the right on the [Fig.11]).

[0078] Since the masking platform 30 is fixed in rotation, but mobile in translation along the radial direction R, the rotation of the platform 20 around the radial direction R causes, via the inclined wall 231, the translation of the masking platform 30 (this translation is symbolized by the upward-pointing arrow on [Fig. 11]) along the radial direction R. Thus, during its rotation of the platform 20 around the radial direction R, the end 333 of the protrusion 33 slides along the inclined wall 231, gradually shifting upwards. The inner wall 31 of the masking plate 30 therefore also moves away, progressively, from the outer wall 22 of the platform 20, the masking plate 30 thus compressing the spring 40 (not shown in figures 9, 11 and 13) during its upward movement.

[0079] It should be noted that, preferably, the longitudinal ends 333 of the protrusions 33, as well as the longitudinal ends 233 of the slots 23, have a rounded shape, as shown in the figures. The contact between the end 333 and the inclined wall 231 can thus be a point or line contact, limiting the contact surfaces between these parts and consequently facilitating the rotation of the platform and therefore of the blade 13, by reducing friction.

[0080] It will also be noted that, while the ends 333 of the protuberances 33 slide along the inclined wall 231 as the platform 20 pivots at the ends A and C, the ends 333 of the protuberances 33, at the ends B and D, move away from the ends 233 of the slots 23, thus progressively freeing said slots 23.

[0081] When the blade 13 continues its rotation to the locked position, for example a locking angle [3 of 60°], the masking plate 30 reaches a fully extracted position, in which the protrusions 33 are completely extracted from the slots 23 (Figures 12 and 13). By "fully extracted," it is understood that the volume formed by the slots 23, along their entire length, width, and thickness, is completely free of the protrusions 33. Conversely, between the insertion position and the extraction position, a plurality of intermediate partial extraction positions exist, in which the end 333 of the protrusions is in contact with the inclined wall 231 at various positions therein, such that the protrusions 33 occupy a portion of the volume of the slots 23.

[0082] It will also be understood that the extraction position is not necessarily reached when the blade 13 is in the 60° set position, but can be reached from a predetermined set angle [3, for example 20°.

[0083] In the fully extended position, the inclined wall 231 has passed beyond the end 333 of the protrusion 33 in the azimuthal direction around the radial direction R. The end face 331 of the protrusion 33 is then in contact with the external face 22 of the platform 20. The distance between the internal face 31 of the masking plate 30, and the external face 22 of the platform 20 reaches its maximum value, corresponding to the height H of the protrusion 33, and the spring 40 reaches its maximum compression.

[0084] The platform 20 can then continue its rotational movement up to the maximum pitch angle [3] of the blade 13. In this context, at the ends B and D, the ends 233 and 333 of the slots 23 and the protrusions 33 respectively move progressively away from each other. In order to facilitate the rotation of the platform 20 and the blade 13 by limiting the friction forces between the end face 331 of the protrusions 33 and the outer face 22 of the platforms 20, said outer face 22 may include a guide track (not shown), formed to receive the protrusions, making it possible to reduce the compression of the spring 40 and therefore the friction forces.

[0085] It should be noted that in the example described above, the aligned position corresponds to a pitch angle [3] of 0°, and the extraction of the protrusions 33 begins as soon as the pitch angle [3] becomes strictly greater than 0°. However, in the insertion position, a greater gap may exist between the end 233 of the slot 23 and the end 333 of the protrusion 33, such that the protrusions 33 could remain in the insertion position over a larger angular range, for example between 0° and 20°, before their extraction begins by contact between the end 333 and the inclined wall 231. In other words, the aligned position of the blades 13 would correspond to a range of pitch angles between 0° and 20°. In this case however, the filling rate of the volume formed by the slits 23, by the protuberances 33 would be lower in the insertion position.

[0086] Moreover, the above example was described considering a control system disposed in the housing 12. However, the invention applies in the same way to a control system disposed in the hub 11, or disposed both in the housing 12 and in the hub 11.

[0087] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than a restrictive sense.

Claims

Claims

1. A system for controlling variable-pitch vanes for a stator (10) of a turbomachine, the system comprising: - at least one variable-pitch vane comprising a blade (13) capable of extending radially between an inner wall (11) and an outer wall (12) of the stator (10), at least one radial end (134) of the blade (13) being movably fixed to the inner wall (11) or to the outer wall (12), - a rotating platform (20) capable of being arranged in the inner wall (11) or the outer wall (12) such that an inner face (21) of the platform (20) is capable of being in contact with the air flowing in the stator (10), the platform (20) being integral in rotation with the vane and comprising at least one slot (23) passing through the platform (20) from the inner face (21) up to an external face (22),- a masking plate (30) arranged on the side of the external face (22) of the platform (20) and being able to be fixed in rotation relative to the internal wall (11) or the external wall (12), the masking plate (30) comprising at least one protuberance (33) of a shape complementary to the slot (23), the system being configured such that in an aligned position of the blade (13), the protuberance (33) is inserted entirely into the slot (23), and in a wedged position of the blade (13), the protuberance (33) is extracted at least in part from the slot (23).,

2. A system according to claim 1, comprising a return spring (40) capable of being compressed between the masking plate (30) and a fixed wall (122) of the inner wall (11) or the outer wall (12) when the blade (13) is in the wedged position, and of exerting a return force on the masking plate (30) so as to push the protrusion (33) towards the inside of the slot (23) when the blade (13) and the platform (20) rotate towards the aligned position.

3. System according to claim 2, in which, when the blade (13) is in the wedged position, the platform (20) is positioned such that the protuberance (33) of the masking plate (30) is in abutment against the external face (22) of the platform (20), the return spring (40) being compressed between the masking plate (30) and the fixed wall (122), and when the blade (13) is in the aligned position, the platform (20) is positioned such as to arrange the slot (23) opposite the protuberance (33), the latter then being inserted into the slot (23) by the force exerted by the return spring (40).

4. System according to any one of claims 1 to 3, in which the at least one radial end (134) of the blade (13) is fixed to the internal wall (11) or to the external wall (12) by means of a cylindrical pivot (135) of the blade, the platform (20) being fixed to the cylindrical pivot (135) so as to form a clearance (E) between the radial end (134) of the blade (13) and the platform (20), the slot (23) extending on either side of a lower surface (133) and an upper surface (131) of the blade (13).

5. A system according to any one of claims 1 to 4, wherein the slot (23) and the protrusion (33) have a curved shape.

6. System according to any one of claims 1 to 5, comprising at least two slots (23) and at least two protrusions (33).

7. System according to any one of claims 1 to 6, in which at least one end of the slot (23) comprises an inclined wall (231) between the internal face (21) and the external face (22), the inclined wall (231) being capable of guiding the protuberance (33) from a position of insertion into the slot (23) to a position of extraction from the slot (23) during the passage of the blade (13) from the aligned position to the wedged position.

8. A system according to any one of claims 1 to 7, wherein, when the blade (13) is in the aligned position, an end face (331) of the protrusion (33) is flush with the inner face (21) of the platform (20).

9. A system according to any one of claims 1 to 8, configured such that, when a pitch angle (|3) between a chord (G) of the blade (13) at the radial end (134) of the blade and a central axis (X) of the stator is between 0 and 20°, the protrusion (33) is inserted entirely into the slot (23), and when the pitch angle (|3) is between 20 and 80°, the protrusion (33) is extracted at least partly from the slot (23).

10. Stator (10) of a turbomachine extending around a central axis (X) and comprising an internal wall (11) and an external wall (12) delimiting an annular vein (V), and a control system according to any one of claims 1 to 9.

11. A turbomachine (100) comprising a stator (10) according to claim 10.

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