Improved variable vane control system

Abstract

Improved variable pitch vane control system Variable pitch vane control system for a turbomachine stator (10), comprising a blade (13) having a radial end (134) movably attached to an outer wall (12), a rotating platform (20) arranged 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 with the vane and comprising at least one slot (23), a masking plate (30) arranged 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 protuberance (33) of a shape complementary to the slot (23), 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 partly from the slot (23). Figure for the abstract: Fig. 6.

Description

Title of the invention: Improved variable-pitch vane control system Technical field

[0001] The present disclosure relates to the field of variable-pitch stators in shrouded aeronautical turbomachines, in particular compressor inlet steering wheel stators, but not only. Prior art

[0002] In a known manner, a turbomachine stator comprises fixed blades extending radially between an inner wall (the hub) and an outer wall (the casing). The inner wall and the outer wall delimit between them an annular flow path for the gases from upstream to downstream of the engine. These stator blades can be variable-pitch, allowing the blades of each of these blades to pivot around a radial axis to modify their angle of incidence. Such a stator with variable-pitch blades can, for example, be an inlet guide wheel (IRW) of high- or low-pressure compressors.

[0003] These variable-pitch blades are, for example, arranged on rotating platforms with a pivot on the casing and / or on the hub, and make it possible to direct the flow at the compressor inlet so that it is aligned with the leading edge of the moving wheel located downstream. The blades may also comprise a cylindrical pivot to which the radial end of the blade is fixed, the rotation of this pivot causing the rotation of the entire blade assembly. In this case, there is generally a clearance between the radial end of the blade and the surface of the casing (or the hub).

[0004] Variable pitch vanes are generally movable between an aligned position and a stalled position. In the aligned position, the angle of incidence, 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 stalled position, the angle of incidence is high, for example greater than 40°. This position allows the flow arriving at the moving wheel located downstream to be redirected. However, changing the angle of incidence of the variable pitch vanes has consequences on the topology of the flow, 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 intrados and the extrados of the blade is low and little flow crosses the clearance between the end of the blade and the surface of the casing (or the hub), which generates few vortices, and therefore little pressure loss.

[0006] In the wedged position, the pressure gradient between the intrados and the extrados is high. This can create a transverse flow at the clearance level, which can generate clearance flows, and in particular a vortex called a clearance vortex, and therefore pressure distortions likely to impact the downstream moving wheel and promote the triggering of the pumping phenomenon.

[0007] To manage these secondary flows, it is known to use surface treatment type technologies, consisting of local modifications in the wall of the hub or the casing delimiting the air flow path. For example, grooves or slots can be made in the wall of the casing and / or the hub to limit the consequences of the appearance of clearance vortices and pressure distortions when the blades are in the stalled position.

[0008] However, while 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 involve 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 making it possible to at least partially overcome the aforementioned drawbacks, and making it possible to improve the performance of the pitched stator regardless of the position of the blades, aligned or pitched, without degrading its performance when they change position. Statement of the invention

[0011] The present disclosure relates to a variable-pitch vane control system for a turbomachine stator, the system comprising: - at least one variable-pitch vane comprising a blade capable of extending radially between an inner wall and an outer wall of the stator, at least one radial end of the blade being movably fixed to the inner wall or to the outer wall, - a rotating platform capable of being arranged in the inner wall or the 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 integral in rotation with the vane and comprising at least one slot passing through the platform from the inner face to an outer face, - a masking plate arranged on the side of the external face of the platform and being able to be fixed in rotation relative to the internal wall or the external wall, the masking plate comprising at least one protuberance of a shape complementary to the slot, the system being configured such that in an aligned position of the blade, the protuberance is inserted entirely into the slot, and in a wedged position of the blade, the protuberance is extracted at least in part from the slot.

[0012] In the present disclosure, the terms "axial direction", "radial direction" and their derivatives are defined relative to the central axis of the stator, which is also the central axis of the turbomachine, around which the moving parts (the rotors) thereof rotate. Preferably, the stator is generally cyclically symmetrical around the central axis. Similarly, the terms "upstream" and "downstream" are understood relative to the normal flow direction of the gases 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 inner wall and the radially outer wall, or to both walls, in a movably manner by being configured to pivot relative to these walls about 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 in particular capable of pivoting about a radial axis passing through the center of the platform. It is thus understood that the inner face of the platform is substantially in continuity with the surface of the inner or outer wall and thus delimits a portion of the annular air flow vein. The platform is furthermore crossed by a slot over its entire thickness, between its inner face and its outer face.

[0015] While the rotating platform is able to pivot, at the same time as 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 when 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, the protuberance having a shape complementary to the slot, it occupies at least part, or even completely, of the volume of the slot when it is inserted into it. This configuration makes it possible to ensure that a slot is present in the profile of the wall when the blade is in the wedged position, and that this slot is masked, by being filled by the protuberance, when the blade is in the aligned position. in this regard by "fully inserted" means the entire protrusion is inserted into the slot. In addition, at least a portion of the protrusion is extracted from the slot in the wedged position, preferably the entire protrusion.

[0017] Thus, when the blade is in the stalled position, the slot makes it possible to limit the consequences of the appearance of clearance 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 partly masked so as not to disturb, or only slightly, the flow. This system thus makes it possible to improve 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 adapted to be compressed between the masking plate and a fixed wall of the inner wall or the outer wall when the blade is in the wedged position, and to exert a return force on the masking plate so as to push the protrusion toward the inside of the slot when the blade and the platform rotate toward the aligned position.

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

[0020] In certain embodiments, when the blade is in the wedged position, the platform is positioned such that the protrusion of the masking plate bears against 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 such as to arrange the slot 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 protuberance bears against a solid portion of the external face of the platform, which is a portion of the platform not comprising a slot. In the wedged position of the blade, the protuberance bears against said solid portion, on the side of the external face of the platform, and is therefore not inserted into the slot, the protuberance then not being radially aligned with the slot. In the aligned position of the blade, the protuberance is radially aligned with the slot such that under the action of the return spring, the protuberance, which was blocked by the solid portion in the wedged position, can be inserted into the slot.

[0022] In some embodiments, the 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 clearance between the radial end of the blade and the platform, the slot extending on either side of a lower surface and an upper surface of the blade.

[0023] The platform being fixed to the cylindrical pivot, the rotation of the blade involves the rotation of the blade and the cylindrical pivot, thus causing an identical rotation of the platform. The fact that the slot formed by the extraction of the protuberance when the blade pivots in the wedged position, extends on either side of the intrados and the extrados of the blade, makes it possible to further limit the consequences of the appearance of clearance vortices and pressure distortions between the intrados and the extrados of the blade.

[0024] In some embodiments, the slot 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 an arc of a circle around the axis of rotation of the blade. Given the circular shape of the platform, this curved shape of the slot makes it easier to guide the protuberance towards the slot, in the direction of insertion or in the direction of extraction thereof. Furthermore, this curved shape makes it possible to ensure that the slot is oriented appropriately regardless of the pitch angle of the blade.

[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. 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 protuberances makes it possible to limit even more effectively the consequences of the appearance of clearance vortices and pressure distortions, and thus to further improve the performance of the stator in the wedged 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 capable of guiding the protrusion from a position of insertion into the slot to a position of extraction from the slot during the passage of the blade from the aligned position to the wedged position.

[0029] The inclined wall constitutes in other words a ramp making it possible to guide the protuberance in the direction of extraction from the slot during rotation of the platform, in other words in the direction of moving away from the internal face towards the external face of the platform. This inclined wall thus makes it easier to extract the protuberance from the slot when the blade moves from the aligned position to the wedged position.

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

[0031] By “flush”, we understand that the end surface of the protuberance is in continuity with the internal face of the platform, without positive or negative difference in level, that is, without step and without recess. Thus, when the blade is in the aligned position and the protrusion is inserted into the slot, the end surface of the protrusion is integrated and merged with the profile of the internal face of the platform. This configuration makes it possible to limit 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 inserted entirely into the slot, and when the pitch angle is between 20 and 80°, the protrusion is extracted at least partially from the slot.

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

[0034] Thus, when the wedging angle 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 disclosure 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 inlet steer wheel of a turbomachine compressor, the inner wall is a hub and the outer wall is an outer casing.

[0037] The present disclosure 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 detailed description given below of different embodiments of the invention given as non-limiting examples. This description refers to the appended pages of figures, in which:

[0039] [Fig.l] [Fig.l] represents a schematic view in longitudinal section of a tur- bomachine,

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

[0041] [Fig.3] [Fig.3] represents a radial section of a pitched stator blade 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 tray and a spring of the control system,

[0044] [Fig.6] [Fig.6] represents a partial and axial 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 bottom view parallel to a radial direction of the control system in the insertion position,

[0047] [Fig.9] [Fig.9] represents an isolated and sectional view, in a sectional plane parallel to the radial direction, from the end of a slot of 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 and sectional view, in a sectional plane parallel to the radial direction, from the end of a slot of 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 and sectional view, in a sectional plane parallel to the radial direction, from the end of a slot of the platform and the masking plate, in the position of [Fig. 12]. Description of the embodiments

[0052] The terms “upstream” and “downstream” are subsequently defined with respect to the direction of flow of gases through a turbomachine, indicated by the arrow F in [Fig.l] and the following. 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 further from the central axis X than its internal wall 11 in the radial direction R.

[0053] [Fig.l] illustrates a dual-flow turbomachine 100 comprising in a manner known from upstream to downstream successively at least one fan S, at least one stage of low pressure compressor 1, high pressure compressor 2, a combustion chamber 3, at least one stage of high pressure turbine 4 and low pressure turbine 5. The rotors of the compressors 1, 2, of the turbines 4, 5 and of the fan 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 making it possible to orient the flow F entering this compressor, in particular to align it with the leading edge of the mobile wheel of the first stage of the high-pressure compressor 2. This example is however not limiting, the invention also applying to any stator comprising variable-pitch blades.

[0055] The stator 10 comprises a hub 11 (the inner wall) and a casing 12 (the outer wall) delimiting between them an annular vein V in which the gas flow F flows. More precisely, the annular vein V is delimited by a radially outer wall 110 of the hub 11 and a radially inner wall 120 of the casing 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 vanes (only one is visible in the figures) extending in the vein 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-section plane parallel to the central axis X, each blade comprises a blade 13 fixed in a movably manner to the casing 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 casing 12, or are fixed both to the hub 11 and to the casing 12 in a movably manner.

[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 casing 12. The cylindrical pivot 135 is rotatable relative to the casing 12, about a radial direction R, by means of a device for controlling the pitch angle of 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 the document EP 1 331 402 B1. The control device is thus able to pivot 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 extrados 131 and a intrados 133. Furthermore, the radially external end 134 of the blade 13 is spaced from the inner wall 120 of the casing by a clearance, or space E, upstream and downstream of the cylindrical pivot 135. The thickness of the space E (intentionally accentuated in [Fig.2]) is between 0.1 and 5 mm. It will be noted that the space 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, taking into account the curved shape of the inner wall 120.

[0059] [Fig. 3] represents a section of a blade 13, at the free end 134, in a left-aligned position, and in a right-set position. The pitch 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 pitch angle [3 is between 0 and 20°, preferably less than 10°, more preferably equal to 0°. The set position corresponds to a situation in which the pitch angle [3 is between 20 and 80°, preferably equal to 60°. Alternatively, the stalled position may correspond to a situation in which the stall angle [3 is strictly greater than 0°, the blade 13 then being aligned when the stall 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 casing 12 and the blades described above, a variable-pitch blade control system, described below with reference to FIGS. 4 to 13.

[0061] The control system comprises at least one blade as described above and a control device (not shown) making it possible to adjust the pitch angle [3 of the blade 13. The control system further comprises a rotating platform 20, integral 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 internal face 21 and an external face 22. The platform 20 is integrated into the wall of the casing 12. In the configuration shown in FIGS. 6 and 7, its internal face 21 is flush with the internal wall 210 of the casing 12, and is intended to be in contact with the gas flow F. It will be noted, however, that FIGS. 6 and 7 are schematic, the internal face 21, which is preferably flat, not necessarily flush with the internal wall 210 over the entire circumference of the platform 20, given the curved shape of the internal wall 210 of the casing 12, which is annular. The distance between the internal face 21 and the external 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. In addition, the platform 20 is circular with a diameter preferably greater than the length of the chord of the blade 13, the diameter however being able to be, alternatively, less than the length of said chord. The platform 20 further comprises a cylindrical sleeve 24 inside which is housed the cylindrical pivot 135 of the blading. On an internal face of the cylindrical sleeve 24, a rectilinear groove 241 extends longitudinally in the direction of the main axis Y of the platform 20, the main axis Y being coincident with the radial direction R when the platform 20 is arranged on the blading.

[0064] The groove 241 is capable of receiving 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 about the radial direction R causes the rotation of the sleeve 24, and therefore of the platform 20 at the same time as the blade 13. The rail 136 can be inserted by force into the groove 241 so as to also block the 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, passing through the thickness of the platform 20, from the internal face 21 to the external 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 main axis Y of the platform, that is to say the radial direction R when the platform 20 is mounted on the stator 10. The slots 23 are arranged on either side of the main axis Y, and symmetrically with respect to the latter. Preferably, the platform 20 is axisymmetric with respect to the main axis Y.

[0066] Preferably, each slot 23 extends over an angular range of between 1° and 170°, preferably between 20° and 100°. More preferably, the curvilinear length of each slot 23 is at least twice as much as the thickness of the blade 13, in particular the thickness of the portion of the blade 13 opposite the slot 23. Its width L may also 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 its two longitudinal ends, an inclined wall 231. Unlike the rest of the slot 23, where the internal face 21 and the external face 22 of the platform 20 are connected by a vertical wall 233, the internal and external 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 internal face 21 to the external face 22, in the reference frame of the figures.

[0068] The control system further comprises a masking plate 30, arranged on the side of the external face 22 of the platform 20, preferably axisymmetric around a main axis Z coinciding with the main 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 in [Fig. 5], comprises an internal face 31 and an external 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 comprises at least one notch 341 capable of receiving a rail 121 of the casing 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 casing 12. Thus, the masking plate 30 is fixed in rotation relative to the casing 12 around the radial direction R, but is free in translation along the radial direction R relative to the casing 12, the notch 341 being able to slide along the rail 121.

[0070] The masking plate 30 also comprises at least one protrusion 33. More specifically, the masking plate 30 comprises as many protrusions 33 as the platform 20 comprises slots 23. In this example, the masking plate 30 comprises two protrusions 33, each having a curved shape. In particular, each protrusion 33 has a shape similar 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 protuberances 33 are slightly smaller than those of the slots 23, in order to allow their insertion into the latter. Thus, when a protuberance 33 is inserted entirely into a slot 23 (hereinafter “insertion position”), it occupies at least 90% of the volume formed by this slot 23, preferably at least 95%, more preferably at least 99%.

[0072] Furthermore, a height H of the protuberances 33 is substantially equal to the thickness of the platform 20, between its internal face 21 and its external face 22. Thus, when the protuberance 33 is in the position of insertion into the slot, an end face 331 of the protuberance 33 is flush with the internal face 21 of the platform 20 (figures 6 and 9).

[0073] The control system also comprises 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 external 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 external face 32 of the masking plate 30 on the one hand, and an internal wall 122 of the casing 12 on the other hand. Preferably, the spring 40 is slightly compressed between the external face 32 and the wall 122. The spring 40 thus maintains the masking plate 30 in the insertion position ([Fig.6]). It will be noted that in this insertion position, the internal face 31 of the masking plate 30 is in plane contact with the external 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 casing 12, and the external face 32 of the masking plate 30. In addition, the end face 331 of the protrusions 33 is pressed by the return force exerted by the spring 40 against the external 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 FIGS. 8 to 13. In particular, FIGS. 8, 10 and 12 represent different phases of the transition from the insertion position to the extraction position in a view from below of the platform 20 (from the side of its internal face 21). By convention, the different longitudinal ends of the slots 23 will be identified by A, B, C and D in these figures. FIGS. 9, 11 and 13 represent these same phases, by an isolated and 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 the 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, with a gap preferably less than 0.5 mm therewith (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 modify the pitch angle [3 of the blade 13, the latter begins a rotation around the radial direction R, in an anti-clockwise direction represented by the arrow in [Fig. 10], so that the pitch angle [3 becomes greater than 0° (Figures 10 and 11). The rotation of the blading, in particular of the blade 13 and of the cylindrical pivot 135, causes the rotation of the platform 20 thanks to 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 against the end 333 of the protuberance 33, then continues its movement beyond said end 333 (this movement is symbolized by the arrow pointing to the right in [Fig. 11]).

[0078] The masking plate 30 being blocked in rotation, but movable in translation along the radial direction R, the rotation of the platform 20 around the radial direction R generates, by means of the inclined wall 231, the translation of the masking plate 30 (this translation is symbolized by the arrow pointing upwards in [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 protuberance 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 FIGS. 9, 11 and 13) during its upward movement.

[0079] It will be noted that, preferably, the longitudinal ends 333 of the protuberances 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 linear 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 further be noted that, while the ends 333 of the protrusions 33 slide along the inclined wall 231 as the platform 20 pivots at the ends A and C, the ends 333 of the protrusions 33, at the ends B and D, move away from the ends 233 of the slots 23, thus gradually releasing said slots 23.

[0081] When the blade 13 continues its rotation to the wedged position, for example a wedge angle [3 of 60°, the masking plate 30 reaches a fully extracted position, in which the protrusions 33 are fully extracted from the slots 23 (Figures 12 and 13). By "fully extracted", it is understood that the volume formed by the slots 23, over their entire length, width and thickness, is entirely freed from 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 different positions thereof, such that the protrusions 33 occupy a portion of the volume of the slots 23.

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

[0083] In the fully extracted position, the inclined wall 231 has passed beyond the end 333 of the protuberance 33 in the azimuthal direction around the radial direction R. The end face 331 of the protuberance 33 is then in abutment against 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 protuberance 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 protuberances 33 respectively move away from each other progressively. 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 protuberances 33 and the external face 22 of the platforms 20, said external face 22 may comprise a guide path (not shown), formed to receive the protuberances, making it possible to reduce the compression of the spring 40 and therefore the friction forces.

[0085] It will be noted that in the example described above, the aligned position corresponds to a setting angle [3 of 0°, and the extraction of the protrusions 33 begins as soon as the setting angle [3 becomes strictly greater than 0°. However, in the insertion position, a greater clearance 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 greater angular range, for example between 0° and 20°, before their extraction begins by the 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 setting angles between 0° and 20°. In this case, however, the filling rate of the volume formed by the slots 23, by the protuberances 33 would be lower in the insertion position.

[0086] Furthermore, the above example has been described considering a control system arranged on the casing 12. However, the invention applies in the same way to a control system arranged on the hub 11, or arranged both on the casing 12 and on the hub 11.

[0087] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that modifications and changes may 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 illustrated / mentioned embodiments may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than 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) adapted to be 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 to exert 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, wherein, 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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