Bladed assembly equipped with a blade disengagement detection ring

Abstract

The invention relates to a bladed turbomachine assembly extending around an axis of rotation and comprising blades (11a, 11b), each blade (11a, 11b) extending in a radial direction with respect to the axis of rotation up to a heel (14a, 14b), characterized in that it comprises: – an electrically conductive rod (26) which passes through the heels (14a, 14b) of the blades (11a, 11b), this rod (26) being subjected to shear stress if a heel (14a, 14b) shifts along the direction of the axis of rotation relative to another circumferentially adjacent heel (14a, 14b); – detection means connected to the ends of the rod (26) to identify that this rod (26) is broken when it is no longer electrically conductive. Figure for the summary: Figure 8

Description

Title of the invention: Bladed assembly equipped with a blade disengagement detection ring Technical field

[0001] The invention relates to the fixed or mobile blades of a turbomachine such as a turbojet. STATE OF THE PRIOR ART

[0002] In a turbojet, outside air is admitted into an inlet sleeve located upstream of it to pass through a fan comprising a series of rotating blades before splitting into a central primary flow and a secondary flow surrounding the primary flow. In such an engine, upstream and downstream are defined in relation to the direction of circulation of the air flow which passes through it when it is in operation.

[0003] The primary flow is then compressed in compressors before arriving in a combustion chamber, after which it expands by passing through turbines before being evacuated downstream, generating thrust. The secondary flow is propelled directly downstream by the fan in a vein delimited by a casing to generate additional thrust.

[0004] Such an engine comprises a rotor rotating around its longitudinal axis, and including several discs each carrying at its external periphery a series of blades or vanes, these discs corresponding to the fan, the compressors and the turbines.

[0005] A blade comprises a root by which it is fixed to a disc, extended by a blade extending in a radial span direction, each blade being terminated by a heel comprising a platform, the blades carried by the same disc having the same morphology.

[0006] The external periphery of a bladed disc is thus delimited by the platforms of the blades that it carries, which jointly delimit a substantially cylindrical peripheral band.

[0007] In operation, these blades are subjected to high temperatures and significant centrifugal forces, which tend to increase their length. Two circumferentially adjacent platforms, which are contiguous when the turbomachine is at a standstill, thus tend to space circumferentially when the turbomachine is in operation.

[0008] Due to the vibration modes present in such a turbomachine, in particular at the level of the rotating blades, the platforms move relative to each other.

[0009] In practice, the beads tend to oscillate by shifting relative to each other in the axial direction, which is problematic because these beads rub on fixed abradable elements which surround them. The friction forces undergone by the heels are thus all the higher as these heels are axially offset from each other.

[0010] To limit these axial offsets, the platforms of the heels have shapes such that two circumferentially adjacent platforms have their edges which fit circumferentially with each other. However, under certain operating conditions, the heels of two circumferentially adjacent blades can shift axially, or even become dislocated.

[0011] In this context, the invention aims to provide a solution for detecting the disengagement of two circumferentially adjacent blades and for reducing the risk of such disengagement. Statement of the invention

[0012] To this end, the invention relates to a turbomachine bladed assembly extending around an axis of rotation and comprising blades arranged circumferentially adjacent around the axis of rotation, each blade extending in a radial direction relative to the axis of rotation to a heel corresponding to a free end of the blade, characterized in that it comprises:

[0013] - a ring which crosses the heels of the circumferentially adjacent blades, this ring being arranged to be stressed in shear if a heel of one of the blades shifts in the direction of the axis of rotation relative to another heel of another circumferentially adjacent blade;

[0014] - the rod is made of an electrically conductive material;

[0015] - means for detecting a break in the rod.

[0016] With this arrangement, the ring provides mechanical resistance to the offset of one heel relative to another, and excessive offset causes the ring to break, which is automatically detected. The invention thus makes it possible to limit the occurrence of blade offsets to improve the operating robustness of the engine and to limit the quantity of maintenance operations required.

[0017] The invention also relates to an assembly thus defined, in which the means for detecting a break in the rod are electrically connected to the ends of the rod.

[0018] The invention also relates to an assembly thus defined, in which the detection means are connected to a computer of the turbomachine.

[0019] The invention also relates to an assembly thus defined, in which each blade heel comprises a platform carrying an upstream lip, a downstream lip, and a rib connecting the two lips, the lips and the rib projecting radially outwards from the platform, and in which each rib comprises a hole through which the ring passes.

[0020] The invention also relates to an assembly thus defined, in which the rod comprises several sectors assembled to each other by welding or crimping.

[0021] The invention also relates to an assembly thus defined, in which each heel comprises, circumferentially around the axis of rotation, a platform, two circumferentially adjacent platforms having circumferentially adjacent edges whose shapes are complementary, one of the edges comprising a notch and the other circumferentially adjacent edge comprising a protuberance fitting into the notch.

[0022] The invention also relates to an assembly thus defined, in which the protuberances and the notches have V-shapes for their fitting together.

[0023] The invention also relates to an assembly thus defined, in which the rod is equipped with an electrically insulating sheath.

[0024] The invention also relates to an assembly thus defined, in which the holes of the ribs are provided with an electrically insulating coating.

[0025] The invention also relates to a turbomachine comprising a bladed assembly thus defined. Brief description of the drawings

[0026] • [Fig.l] is a longitudinal sectional view of a turbojet according to the invention; • [Fig.2] is a perspective view of two circumferentially adjacent blades equipping a rotating disc according to the invention; • [Fig.3] is a view of a blade heel according to the invention shown alone; • [Fig.4] is a view of three blade heels according to the invention when they are nested; • [Fig.5] is a view of three blade heels according to the invention, two of which are axially offset; • [Fig.6] is a view of three blade heels according to the invention, two of which are disengaged; • [Fig.7] is a perspective view of two blade heels according to the invention when they are fitted together; • [Fig.8] is a perspective view of two blade heels according to the invention in the disengaged state; • [Fig.9] is a schematic representation of the electrical circuit integrating the cable surrounding the blade heels in accordance with the invention.

[0027] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0028] In the turbojet 1 shown in [Fig.l], the outside air is admitted into an inlet sleeve 2 located upstream of the engine then passes through a fan 3 comprising a series of rotating blades before splitting into a central primary flow and a secondary flow surrounding the primary flow.

[0029] The primary flow is then compressed in a first and second compression stage 4 and 6 before arriving in a combustion chamber 7, after which it expands by passing through a set of turbines 8 before being evacuated downstream, generating thrust. The secondary flow is propelled directly downstream by the fan in a vein delimited by the casing 9 to generate additional thrust.

[0030] This engine comprises a rotor rotating around its axis of rotation AX, and including several discs each carrying at its external periphery a series of blades or vanes, these discs corresponding to the fan, the compressors and the turbines.

[0031] As shown in [Fig.2], such a blade 11a comprises a root 12a by which it is fixed to a disc (not shown), extended by a blade 13a extending in a radial span direction relative to the axis of rotation AX. This blade 13a is terminated by a heel 14a corresponding to its free end, this heel comprising a platform 16a here carrying an upstream lip portion 17a, and a downstream lip portion 18a intended to provide sealing functions.

[0032] The blades carried by the same disc have the same morphology, so that the circumferentially adjacent blades 11b and 11c of the blade 11a in [Fig.2], comprise the same components identified by the same numerical references but supplemented by the letter “b” or “c” instead of the letter “a”.

[0033] The external periphery of a bladed disc is thus delimited by the platforms of the blades that it carries, which extend contiguous to each other to jointly delimit a cylindrical shell 20, a portion of which appears in [Fig.4].

[0034] As can be seen in [Fig. 3], the platform 16a is delimited by a first circumferential end edge 19a and by a second opposite circumferential end edge 21a which are connected to each other by a substantially rectilinear upstream edge and a downstream edge. The first edge and the second edge extend essentially in the longitudinal direction AX, while the upstream and downstream edges extend circumferentially in planes normal to the axis AX.

[0035] The first edge 19a has a shape delimiting in its central portion a protuberance 22a, and the second edge 21a has a shape delimiting in its central portion a notch 23a. The protuberance 22a and the notch 23a extend in the circumferential direction DC and have the same shape. Thus, the first and second edges 19a and 21a of two circumferentially adjacent platforms fit together, as shown in [Fig.4].

[0036] The protrusion 22a and the notch 23a both have V-shapes, which allows two nested platforms to remain in contact even when they move substantially apart from each other, as for example in the situation of the [Fig.5].

[0037] As visible in Figures 2 and 3, the platform 16a carries the two wipers 17a and 18a which extend parallel to each other in the circumferential direction DC, projecting radially outwards from this platform 16a.

[0038] Additionally, a rib 24a which is also carried by the platform 16a extends from one lip to the other to connect them in order to stiffen them. This rib 24a projects radially outwards from the platform 16a, and it is oriented in a direction substantially oblique to the axis AX.

[0039] In the example of the figures, the downstream lip 18a is further circumferentially offset relative to the upstream lip 17a. These platforms, which are here of the so-called “Z” edge type, jointly form a shroud 20 corresponding to the external periphery of the blading constituted by the blades that these platforms terminate.

[0040] The blades of the same bladed wheel having the same morphology, the three blades shown in Figures 4 to 6 each have a heel 14a-14c comprising a platform 16a-16c, each platform carrying two wipers connected by a central rib 24a-24c.

[0041] The invention is based on the analysis according to which a dislocation of blade roots can occur essentially during the running-in of the engine, because the friction of the moving blade roots on the fixed abradable elements which surround them is then greater. This tends to increase the clearance between two roots, expected that this clearance is accentuated by the fact that all the clearances of the roots can accumulate between two given consecutive roots.

[0042] It follows that the engine running-in phase proves to be the one which is conducive to generating significant axial offsets of the blade heels.

[0043] In this context, the central ribs 24a-24c according to the invention each comprise a through hole 27a-27c oriented in the circumferential direction DC. These holes are crossed according to the invention by a ring 26, that is to say a split ring, surrounding the cylindrical ferrule 20 delimited by the set of platforms, these through holes 27a and 27b appearing more clearly in Figures 7 and 8.

[0044] As illustrated in [Fig. 5], when, for example under the effect of vibrations, a heel such as the heel 14a shifts in the direction AX relative to the neighboring heel 14b, the section of the rod 26 extending between these heels deforms under the effect of the shearing force undergone by this section due to this shift.

[0045] Thus, due to its mechanical characteristics of bending rigidity and resistance to shear forces (shear resistance), the ring 26 exerts, in reaction to the axial offset of the heels 14a and 14b, forces which oppose this offset to limit its amplitude. The ring 26 thus makes it possible, due to its mounting and its rigidity, to reduce the axial offset of the heels when the turbomachine is in service.

[0046] When the forces exerted on the heels, resulting from vibration modes or other factors, are too great, they can lead to the snap ring 26 breaking at the portion extending between the heels. This corresponds to the situation shown in Figures 6 and 8, in which the heel 14a has shifted axially relative to the heel 14b to the point that the circumferentially adjacent edges of their platforms have become dislocated and the snap ring 26 is broken.

[0047] The material of the rod 26 is electrically conductive and its ends are connected to detection means 28 such as an electronic box, as shown schematically in [Fig.9].

[0048] These detection means are configured to continuously test the electrical conductivity of the rod 26 so as to determine whether the rod 26 is electrically conductive or not. These detection means 28 thus make it possible to detect that the rod 26 is broken, as soon as it is no longer electrically conductive.

[0049] The detection means 28 are advantageously connected to a computer (e.g. FADEC) of the turbomachine. Thus, in the situation of [Fig. 6], the detection means 28 immediately detect that the rod is no longer conductive and then send to the computer a signal representative of the fact that this rod 26 is broken, so that this computer stops for example the turbomachine in the case where it is in the running-in phase.

[0050] The detection by the electronic box 28 of the fact that the rod 26 is no longer electrically conductive thus makes it possible to identify a dislocation of blade heels.

[0051] When the blades are formed from an electrically conductive material such as a metal alloy, the through holes 27a-27c have their internal face covered with an electrically insulating coating, and / or the rod 26 is equipped with an electrically insulating sheath which surrounds it, so that the rupture of the rod effectively causes a discontinuity in its electrical conductivity between its ends.

[0052] The rod 26 is advantageously formed of several sectors rigidly secured to each other after assembly, these sectors then being fixed to each other by welding or by crimping.

[0053] The assembly consists, for example, of installing the blades on the disc which carries them and passing each ring sector into the rib holes of several consecutive blades. Once all the ring sectors are in place, they are welded or crimped end-to-end, so as to jointly constitute a ring extending over the entire circumference of the bladed assembly.

[0054] This ring 26, which is provided to be electrically conductive to allow easy detection of its breakage, is advantageously manufactured from a material having significant rigidity and mechanical resistance to shear forces. This ring 26 thus makes it possible to reduce the risk of significant axial displacement of the beads and the risk of dislocation of these heels.

[0055] In the example of the figures, the heels comprise platforms whose edges are provided to fit circumferentially with each other so as to limit their oscillations in the axial direction. The invention also applies to heels whose platforms have straight edges, that is to say not necessarily fitting with each other, since the ring 26 makes it possible, due to its rigidity, to reduce the amplitude of the longitudinal oscillations of the heels, and thereby to reduce the axial offset of the heels relative to each other. In other words, the ring 26 provides an axial holding function for the blade heels which can supplement or replace the fitting of the heels by their platforms.

Claims

Claims

1. A turbomachine bladed assembly extending around an axis of rotation (AX) and comprising blades (11a, 11b) arranged circumferentially adjacent around the axis of rotation (AX), each blade (11a, 11b) extending in a radial direction relative to the axis of rotation (AX) to a heel (14a, 14b) corresponding to a free end of the blade (11a, 11b), characterized in that it comprises: - a ring (26) which passes through the heels (14a, 14b) of the circumferentially adjacent blades (11a, 11b), this ring (26) being arranged to be stressed in shear if a heel (14a, 14b) of one of the blades (11a, 11b) shifts in the direction of the axis of rotation (AX) relative to another heel (14a, 14b) of another blade (11a, 11b circumferentially adjacent; - the ring (26) is formed from an electrically conductive material; - means (28) for detecting a break in the ring (26).

2. Assembly according to claim 1, in which the means (28) for detecting a break in the rod (26) are electrically connected to the ends of the rod (26).

3. Assembly according to one of the preceding claims, in which the detection means (28) are connected to a computer of the turbomachine.

4. A bladed assembly according to one of the preceding claims, in which each blade (11a, 11b) heel (14a, 14b) comprises a platform (16a, 16b) carrying an upstream lip (17a, 17b), a downstream lip (18a, 18b), and a rib (24a, 24b) connecting the two lips, the lips (17a, 18a, 17b, 18b) and the rib (24a, 24b) projecting radially outwards from the platform (16a, 16b), and in which each rib (24a, 24b) comprises a hole through which the ring (26) passes.

5. Assembly according to one of the preceding claims, in which the rod (26) comprises, circumferentially around the axis of rotation (AX), several sectors assembled to each other by welding or by crimping.

6. A bladed assembly according to claim 1, wherein each heel (14a, 14b) comprises a platform (16a, 16b), two circumferentially adjacent platforms (16a, 16b) having circumferentially adjacent edges (21a, 19b) whose shapes are complementary, one of the edges (21a) comprising a notch (23a) and the other circumferentially adjacent edge (19b) comprising a protuberance (22b) fitting into the notch (23a).

7. A bladed assembly according to claim 6, wherein the protrusions (22a, 22b) and the notches (23a) have V-shapes for their interlocking.

8. Assembly according to one of the preceding claims, in which the rod (26) is equipped with an electrically insulating sheath.

9. An assembly according to claim 4, wherein the holes (27a, 27b) of the ribs (24a, 24b) are provided with an electrically insulating coating.

10. Turbomachine comprising a bladed assembly according to one of the preceding claims.