Device for axially retaining the moving blades of an LP turbine in the cells of a rotor disc of the LP turbine and method for mounting these moving blades

Abstract

Device for axially retaining the moving blades of an LP turbine in the cells of a rotor disc of the LP turbine and method for mounting these moving blades One aspect of the invention relates to a device (30) for axially retaining a moving blade (10) of a low pressure turbine in a cell (21) of a rotor disc of axis (X) of said turbine. This device comprises a stop piece (40) intended to extend between an upstream face (11a) of a blade root (11) of the moving blade (10) and a downstream face (11b) of said blade root of the moving blade, said stop piece (40) comprising: a first wall (41) which forms a stop for the upstream face (11a) of the blade root (11), a second wall (42) which forms a stop for the downstream face (11b) of the blade root (11), and a connecting surface (43) intended to extend between the first and second walls (41, 42), along a radially internal end face (11c) of the blade root (11).Other aspects of the invention relate to a turbomachine rotor assembly and a method of mounting the moving blades (10) in the cells (21) of an LP turbine rotor disc. Figure to be published with the abstract: Figure 2.

Description

Title of the invention: Device for axially retaining the moving blades of an LP turbine in the cells of a rotor disc of the LP turbine and method for mounting these moving blades TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a device for axially retaining the moving blades of a low pressure (LP) turbine in the cells of the rotor disc of the LP turbine. It also relates to a method of mounting these moving blades in the rotor disc.

[0002] The invention finds applications in the field of aeronautics and, in particular, in the field of low pressure turbines of aircraft turbomachines. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] In a known manner, a low pressure (LP) turbine comprises several successive bladed wheels, separated by distributor stages. A bladed wheel, also called a wheel, comprises so-called "moving" blades and a rotor disk. The outer periphery of the rotor disk comprises mounting grooves, called cells, which extend in substantially axial directions (i.e. with an angle of up to a few degrees relative to the axial direction). Each cell is designed to receive the root of a moving blade mounted by fitting into said cell.

[0004] Usually, a first axial retention ring, or flange, is provided, arranged on the upstream face of the turbine disk and a second axial retention ring, arranged on the downstream face of the turbine disk. These rings form axial stops for the roots of the blades housed in the cells. An example of a portion of a LP turbine comprising three bladed wheels 1 a, 1 b, according to the state of the art is shown in [Fig.l]. The bladed wheels 1a, 1b, 1c are separated from each other by distributors 7, 8 each equipped with a ferrule 9, 10 forming the internal wall of the flow path F. Each bladed wheel 1a, 1b, 1c comprises a disc rotating around the central axis of the turbine, represented diagrammatically by the axis X, and comprising an external peripheral rim 2a, 2b, 2c, to which the blades are fixed by their roots 3a, 3b, 3c.In particular, a first wheel 1a comprises a movable blade 4a mounted axially, by its root 3a, in a cell 6a of the rim 2a of the disc. The root 3a of the blade 4a is blocked axially, upstream, by an annular flange 13 and, downstream, by an annular flange 14, the flanges 13 and 14 being of different types.

[0005] These flanges and / or rings which allow the axial maintenance of the feet 3a, 3b, 3c of the blades 4a, 4b, 4c must be maintained along said blades. In certain cases, the axial support of the flange or ring is ensured by a spoiler, or hook, whose shape is relatively complex. In other cases, axial support is achieved by means of a dog-grip lock.

[0006] Nowadays, moving blades are often made from a ceramic matrix composite (CMC) material which has the advantage of being lightweight. CMC blades are therefore lighter than conventional metal blades. However, the manufacture of CMC blades with hooks is complex because it involves weaving and requires forming on the blade, at the platform 5a, 5b, 5c located between the blade and the root 3a, 3b, 3c of the blade, two texture layers, one of which constitutes the surface delimiting the air stream and the hook and the other serves as anti-tilt of the blade and downstream overlap. In addition, the absorption of the centrifugal force of a flange or an axial retaining ring by a hook integrated into the blade leads to centrifugal mechanical loading, which is detrimental to the hook made of CMC material.

[0007] In the case of holding by a dog-lock, the sealing of the blade wheel must be advanced to the foot of the low-pressure distributors (DBP), which results in a lack of space for integrating axial stopping solutions at the rear of the blades, i.e. on the downstream face of the blade roots.

[0008] There is therefore a real need for a device for axially retaining the blade roots in the disc cells which does not require the manufacture of a CMC hook, nor the advancement of the seal at the root of the DBP. Summary of the invention

[0009] To address the problems mentioned above of axially holding the root of the moving blade in the cell of the disk, the applicant proposes a stop piece positioned between the root of the blade and the bottom of the cell of the disk and extending between the upstream face and the downstream face of the blade root.

[0010] In the following description, the terms "upstream" and "downstream" are defined with respect to the direction of air flow from the air inlet into the LP turbine to the air outlet from the LP turbine. In other words, upstream and downstream are understood to be along a central axis X with respect to the general direction of the gases in operation.

[0011] In the description, the term "exterior" designates the surfaces or parts of parts furthest from the central axis X of the air stream of the turbomachine (i.e. the axis of rotation of the fan blades), as opposed to the term "interior" which designates the surfaces and parts of parts closest to said central axis X.

[0012] According to a first aspect, the invention relates to a device for axially retaining a moving blade of a low-pressure turbine in a cell of a rotor disk of the axis of said turbine, characterized in that it comprises a stop piece intended to extend between an upstream face of a blade root of the moving blade and a downstream face of said blade root of the moving blade, said stop piece comprising: • a first wall which forms a stop for the upstream face of the blade root, • a second wall which forms a stop for the downstream face of the blade root, and • a connecting surface intended to extend between the first and second walls, along a radially internal end face of the blade root.

[0013] This device allows axial stopping or blocking of the blade roots in the cells of the disc without requiring any hook on the blade, nor any specific part on the downstream face of the blade wheel. It thus avoids the need for an axial stop ring whose centrifugal force would have to be taken up by a hook integrated into the CMC blade. It also has the advantage of having a reduced size, allowing space to be saved downstream of the blade root so as to leave space for achieving axial sealing.

[0014] In addition to the characteristics which have just been mentioned in the preceding paragraph, the axial retaining device according to one aspect of the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations: • the stop piece is a single-piece metal part. • the first wall of the stop piece has a width dimension or of height, which is greater than another dimension of width or height of the second wall, the dimensions being taken in a plane transverse to the bonding surface. • the first wall is configured to extend partially over an upstream face of the rotor disk. • the first wall of the stop piece extends perpendicularly on either side of the connecting surface. • the second wall of the stop piece extends perpendicular to the connecting surface so as to be able to cover a downstream face of a blade root.

[0015] A second aspect of the invention relates to a turbomachine rotor assembly comprising a rotor disc of axis X which has hollowed-out cells at its periphery and moving blades mounted in cells of the disc, two cells circumferentially adjacent around the disc each delimiting a tooth of the disc, characterized in that it comprises: • several stop pieces as defined above, each stop piece being intended to axially hold a moving blade in a corresponding cell of the disc, and, • means of locking the stop pieces against the disc, the first wall of each stop piece extending circumferentially so as to be in contact with at least one upstream face of a tooth of the rotor disc.

[0016] Advantageously, this assembly may include the following characteristics, considered individually or in all technically possible combinations: • the disc comprises a cavity hollowed out in the disc and in that the first wall comprises a hook fitted by fitting into the cavity. • it comprises a plurality of stop pieces each arranged in a cell of the disc and configured so that their first walls are circumferentially arranged end to end, around the X axis. • it comprises a retaining ring fixed to the disc and mounted around the entire circumference of the rotor disc, against the first walls of the stop pieces so as to hold the stop pieces in position in the disc cells. • it further comprises a retaining ring housed in a groove of the rotor disc, at an internal end of the retaining ring, the retaining ring being configured to secure the retaining ring to the disc after mounting the retaining ring on the disc.

[0017] A third aspect of the invention relates to a method for mounting low-pressure turbine moving blades in cells of a rotor disk of said turbine, characterized in that it comprises, for each moving blade, the following steps: • installation of a stop piece as defined previously against a radially internal end face of a blade root, and • installation of the moving blade equipped with the stop piece in a cell of the rotor disc.

[0018] This method has the advantage of being relatively simple to implement.

[0019] Advantageously, the method comprises the following operations: • installation of the snap ring in a groove of the rotor disc, and • installation of a retaining ring on the disc along the first walls of the stop piece, the retaining ring being held in position by a blockage provided by the stop ring. BRIEF DESCRIPTION OF THE FIGURES

[0020] Other advantages and characteristics of the invention will appear on reading the following description, illustrated by the figures in which:

[0021] [Fig.l], already described, represents a schematic view in longitudinal section of a part of an LP turbine with several bladed wheels according to the state of the art;

[0022] [Fig. 2] represents a longitudinal sectional view of the axial retaining device according to the invention, with a stop piece mounted between a blade root and a disc cell;

[0023] [Fig. 3] represents a schematic view of the upstream and a schematic view of the downstream of a stop piece of the axial retaining device according to the invention, mounted between a blade root and a disc cell;

[0024] [Fig. 4] represents several views, in section, from upstream or downstream, of various embodiments of the stop piece according to the invention;

[0025] Figures 5A, 5B and 5C represent, respectively, a cutaway perspective view, an upstream view and a downstream view of an embodiment of the axial retaining device according to the invention;

[0026] [Fig. 6] represents, in perspective views, several stages of the method of mounting the moving blades according to the invention; and

[0027] [Fig. 7] shows a perspective view of several moving blades mounted in a rotor disc with the axial retaining device according to the invention. DETAILED DESCRIPTION

[0028] An exemplary embodiment of a device for axially retaining moving blades of an LP turbine is described in detail below, with reference to the accompanying drawings. This example illustrates the characteristics and advantages of the invention. It is however recalled that the invention is not limited to this example.

[0029] In the figures, identical elements are identified by identical references. For reasons of readability of the figures, the size scales between elements represented are not respected.

[0030] An example of an axial retaining device according to the invention is shown in a sectional view in [Fig. 2]. This axial retaining device 30 comprises, for each moving blade 10, a stop piece 40 configured to be housed between the root 11 of the blade 10 and the cell 21 of the disk 20 of the rotor of the LP turbine. This stop piece 40 extends between the upstream face 11a of the root 11 of the blade and the downstream face 11b of this blade root. For this, the stop piece 40 comprises: • a first wall 41, also called upstream wall, configured to be positioned at least partially along the upstream face 11a of the blade root, • a second wall 42, also called the downstream wall, configured to be positioned at least partially along the downstream face 11b of the blade root, and • a connecting surface 43 axially connecting (i.e. along the central axis (X)) the upstream wall 41 and the downstream wall 42, along the internal face 11c of the blade root.

[0031] The upstream and downstream walls of the stop piece 40 may, for example, be made of metal or an alloy, such as one of the superalloys conventionally used in this area of ​​the turbine. The upstream 41 and downstream 42 walls are, for example, square or rectangular in shape. The connecting surface 43 may be a plate, preferably made of the same metal or alloy as the upstream and downstream walls. The connecting surface 43 is preferably rectangular in shape, with an axial dimension substantially greater than the axial dimension of the root 11 of the blade. The upstream 41 and downstream 42 walls as well as the connecting surface 43 may be made in a single piece so that the stop piece 40 is a single piece.

[0032] According to certain embodiments, the upstream wall 41 and the downstream wall 42 of the stop piece have similar dimensions. According to other embodiments, the upstream wall 41 and the downstream wall 42 have different dimensions, the upstream wall 41 having dimensions greater than those of the downstream wall 42. Indeed, as shown in the example of FIGS. 2 and 3, the upstream wall 41 can extend radially (i.e. along an axis perpendicular to the axis X) in front of the upstream face 11a of the blade root and in front of the part of the upstream face of the disc 20 under the cell. The upstream wall 41 can thus extend parallel to the upstream opening 21a of the cell 21 and to the internal part of the upstream face of the disc 20 (the internal part being the part of the disc devoid of inter-cell teeth 22). In this example, the downstream wall 42 extends radially in front of the downstream opening 21b of the cell 21, that is to say along the downstream face 11b of the blade root.The stop piece 40 thus has, in the example of figures 2 and 3, a section in the shape of an inverted T, with an upstream wall 41 which extends radially on either side of the connecting surface 43 and a downstream wall 42 which extends radially in the direction of the platform 12 of the blade 10. With such a configuration, the upstream wall 41 is blocked, upstream, by the disc 20 so that the stop piece 40 in its entirety is blocked axially upstream.

[0033] The axial retaining device 30 of the invention may comprise, in addition to the stop piece 40, a flange 50, or retaining ring, mounted radially along the upstream face 20a of the disc 20. This flange 50, of annular shape, extends parallel to the cells 21 and to the inter-cell teeth 22 of the disc 20 over the entire circumferential length of the disc. This flange 50, the shape of which is conventional for an LP turbine flange, comprises a hook 51 partially housed in a groove 23 of the disc 20. This hook 51 ensures the attachment of the flange 50 to the disc 20. Thus mounted along the disc 20, the flange 50 extends upstream of the upstream wall 41 of the stop piece 40 so as to prevent any axial movement, from downstream to upstream, of the stop piece 40.

[0034] It is therefore understood that the stop piece 40 is axially blocked in a bidirectional manner, that is to say both from upstream to downstream and from downstream to upstream. Thus, the blade root 11 positioned inside the stop piece 40 is also axially blocked in a bidirectional manner.

[0035] According to certain embodiments, the axial retaining device 30 also comprises an axial stop ring 60 housed in the groove 23 of the disc 20. This axial stop ring 60 is a substantially annular part, made of a flexible, substantially elastic material, such as the superalloys conventionally used in turbines. The axial stop ring 60 comprises a radial slot extending over the entire section of said stop ring. This radial slot allows it to be lowered into the groove 23 to insert (or remove) the flange 50.

[0036] [Fig. 4] represents embodiments in which the stop piece 40 has different shapes. Drawing A of [Fig. 4] shows, in a sectional view, an example of a stop piece 40 comprising an upstream wall 41 equipped with a shoulder 44 inserted inside the disc 20. This shoulder 44, also called a hook, is formed by an axial extension extending at a substantially right angle in the extension of the upstream wall 4L. This axial extension is configured to be inserted into a suitable housing 24 located at the entrance to the groove 23 of the disc 20. Seen in section, the shoulder 44 has the shape of a hook, a portion of which is housed in the disc 20.In other words, the shoulder 44 is inserted into the disc, under the cell 21 receiving the stop piece 40, partially fitting the internal periphery of the cell 21 of the disc 20, so that the centrifugal force of the stop piece 40 is taken up by the disc and the blade 10 is partially relieved of this force.

[0037] Drawing B and drawing C of [Fig.4] show, respectively a sectional view and a schematic view from upstream, an example of a stop piece 40 in which the upstream wall 41 extends radially to the platform 12 of the blade 10 so as to create a partial seal of the cells 21. In this embodiment, the stop piece 40 has a substantially U-shaped section, with an upstream wall 41 extending in a single radial direction from the connecting surface 43; the upstream wall 41 extends further radially than the downstream wall 42, as far as the platform 12 of the blade. The axial blocking, or stopping, towards the downstream is obtained, in this embodiment, by blocking the upstream wall 41 against the teeth 22 of the disc 20.

[0038] Drawing D of [Fig.4] shows, in a schematic view from downstream, an example of the stop piece 40 in which the downstream wall 42 extends radially on either side of the connecting surface 43. In this embodiment, the downstream wall 42 extends not only in front of the upstream face 11a of the blade root, but also in front of the face upstream of the disc 20 under the cell 21. The downstream wall 42 then participates in the axial blocking towards the upstream of the stop piece 40.

[0039] Of course, the various embodiments described above can be combined with each other, such as, for example, the upstream wall 41 of drawing C combined with the downstream wall 42 of drawing D, or the upstream wall with the shoulder 44 of drawing A combined with the downstream wall 42 of drawing D, etc.

[0040] The embodiment of drawing B of [Fig.4] is shown, in a cutaway perspective view, in [Fig.5A], in an upstream view (or front view) in [Fig.5B] and in a downstream view (or rear view) in [Fig.5C]. These views show a stop piece 40 with a substantially U-shaped section, mounted in a cell 21 of the disc 20, under the blade root 11 so as to cover the upstream face 11a of the blade root 11, the downstream face 11b of the blade root and the internal face 11c of said blade root. [Fig.5A] also shows the groove 23 of the disc 20 in which the stop ring 60 and the flange 50 are housed, said stop ring 60 being positioned at the internal end of the flange 50.

[0041] Whatever the shape and dimensions of the upstream and downstream walls of the stop piece 40, the axial retaining device 30 is mounted in the manner shown in [Fig. 6]. The mounting method according to the invention comprises the following steps, represented by drawings E to H: • Drawings E: manufacture of the stop piece 40 with its upstream wall 41 and its downstream wall 42 connected by the connecting surface 43; • Drawings F: installation of the stop piece 40 under the blade root 11, that is to say against the internal face 11c of the root 11 of the blade 10; • Drawing G: installation of the moving blade 10 equipped with the stop piece 40 in a cell 21 of the disc 20, the upstream wall 41 of the stop piece being in contact with the teeth 22 located on either side of the cell 21; and • Drawings H (for the embodiments concerned and after all the blades have been mounted): installation of the flange 50 in the groove 23 of the disc 20, along the upstream wall 41, the flange 50 being installed after the stop ring 60 has been positioned in the groove 23.

[0042] Once all the moving blades 10, each equipped with a stop piece 40, have been mounted in the cells 21 of the disc 20, the upstream walls 41 of all the stop pieces 40 are positioned side by side, circumferentially, one after the other. An example of several juxtaposed upstream walls 41 is shown in [Fig. 7]. Although, for reasons of clarity, only two blade roots 11 have been shown in this [Fig. 7], several upstream walls 41 are shown side by side, each forming part of one of the stop pieces 40 housed in the cells 21 of the disc 20. [Fig. 7] also shows the flange 50 mounted along the upstream walls 41 and forming an axial retainer (from downstream to upstream) of the stop pieces 40 and, consequently, of the blade roots 11. The flange 50 ensures not only the axial stop of the blade roots 11, by means of the stop pieces 40, but also the ventilation of the cells 21 of the disk. Indeed, the ventilation of the cells 21 of the disk 20 is necessary during the operation of the turbomachine given the high temperature of the gases circulating in the flow path of the LP turbine.

[0043] Although described through a certain number of examples, variants and embodiments, the axial retention device according to the invention comprises various variants, modifications and improvements which will be obvious to those skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention.

Claims

Claims

1. Turbomachine rotor assembly comprising a rotor disc (20) of axis (X) which has cells (21) hollowed out at its periphery and moving blades (10) mounted in cells (21) of the disc, two cells circumferentially adjacent around the disc each delimiting a tooth of the disc, characterized in that it comprises several stop pieces (40) intended to extend between an upstream face (11a) of a blade root (11) of the moving blade (10) and a downstream face (11b) of said root of the moving blade, said stop pieces (40) comprising: a first wall (41) which forms a stop for the upstream face (11a) of the blade root (11), a second wall (42) which forms a stop for the downstream face (11b) of the blade root (11), and a connecting surface (43) intended to extend between the first and second walls (41, 42), along a radially internal end face (11e) of the blade root (H), each stop piece (40) being intended to axially hold a movable blade (10) in a corresponding cell of the disc (20), and, means (50, 60) for locking the stop pieces against the disc (20), the first wall (41) of each stop piece (40) extending circumferentially so as to be in contact with at least one upstream face of a tooth (22) of the rotor disc, a plurality of stop pieces (40) each arranged in a cell (21) of the disc (20) and configured so that their first walls (41) are circumferentially arranged end to end, around the axis (X), a retaining ring (50) fixed to the disc and mounted over the entire circumference of the rotor disc (20), against the first walls (41) of the stop pieces (40) so as to hold the stop pieces (40) in position in the cells of the disc.

2. Assembly according to claim 1, characterized in that the stop piece (40) is a single-piece metal piece.

3. Assembly according to claim 1 or 2, characterized in that the first wall (41) of the stop piece (40) has a width or height dimension, which is greater than another width or height dimension of the second wall (42), the dimensions being taken in a plane transverse to the connecting surface (43).

4. Assembly according to any one of claims 1 to 3, characterized in that the first wall (41) is configured to extend partly on an upstream face of the rotor disc (20).

5. Assembly according to any one of claims 1 to 4, characterized in that the first wall (41) of the stop piece (40) extends perpendicularly on either side of the connecting surface (43).

6. Assembly according to any one of claims 1 to 5, characterized in that the second wall (42) of the stop piece (40) extends perpendicular to the connecting surface (43) so as to be able to cover a downstream face of a blade root.

7. Assembly according to claim 1, characterized in that the disc comprises a cavity hollowed out in the disc and in that the first wall (41) comprises a hook (44) mounted by fitting into the cavity.

8. Assembly according to claim 1, characterized in that it further comprises a retaining ring (60) housed in a groove (23) of the rotor disc, at an internal end of the retaining ring (50), the retaining ring being configured to secure the retaining ring (50) to the disc (20) after mounting the retaining ring (50) on the disc.

9. Method for mounting the moving blades (10) of a low-pressure turbine in cells (21) of a rotor disk of said turbine, characterized in that it comprises, for each moving blade, the following steps: - installation of a stop piece (40) of an assembly according to any one of claims 1 to 6 against a radially internal end face (11c) of a blade root (11), and - installation of the moving blade (10) equipped with the stop piece (40) in a cell (21) of the rotor disk.

10. Method according to claim 9, characterized in that it further comprises the following steps: - installation of a retaining ring (60) in a groove (23) of the rotor disc, and - installation of a retaining ring (50) on the disc (20) along the first walls (41) of the stop piece (40), the retaining ring (50) being held in position by a blocking effected by the retaining ring (60).

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