Improved tie-rod turbine rotor and rotor assembly method

Abstract

Improved tie-rod turbine rotor and rotor assembly method. Turbine rotor (60) comprising a rotation shaft (X), a first disc (61) and at least one second disc (62) downstream of the first disc, each carrying rotor blades (62) mounted on its periphery and each having a radial rim (610, 620), the first disc (61) comprising a downstream ferrule (614) extending downstream from the rim (610) of the first disc (61), and a radial flange (615) extending radially from a downstream end of the downstream ferrule (614) and bearing against the rim (620) of the second disc (62), the first and second discs being fixed to each other by means of a fastening assembly (70) comprising at least one tie rod (71) extending at least through the rim (610) of the first disc, the radial flange (615) and the rim (620) of the second disc. Figure for the abbreviation: Fig. 3.

Description

Title of the invention: Improved tie-rod turbine rotor and rotor assembly method Technical field

[0001] The invention relates to the field of aeronautical turbomachines. More specifically, the invention relates to an aircraft turbomachine turbine rotor, and in particular a device for fixing the rotor discs, and a turbine comprising such a rotor. Prior art

[0002] In aircraft turbomachines, the turbine rotors comprise several discs fixed axially to each other by bolted connections. These discs each comprise a structural rim (or web), these rims forming between them cavities arranged radially under the hot air flow stream.

[0003] Furthermore, it is common to use secondary air circuits, for example to ensure the necessary ventilation flow rates in certain regions of these turbomachines. One of these secondary circuits (called "bore cooling" in English) must in particular be routed from the upstream casing, upstream (called "TRF" casing for "turbine rear frame" in English) of the low-pressure turbine, to downstream of the latter to be purged there. To ensure the flow rate of this secondary circuit, existing solutions propose using labyrinths of enclosures bolted onto a disc or engaged on the turbine shaft.

[0004] However, to meet the need for mechanical strength of the disks of so-called fast turbines, it is necessary to reduce their bore diameters, which reduces the available space and no longer allows the use of the aforementioned labyrinths. To overcome this drawback, it is possible to use sleeves (or caps, or length of barrel upstream or downstream of the bore of the disk) integrated into the disk, in a single piece with the latter, and therefore not requiring bolted connections. These sleeves make it possible to close the inter-disc cavities to ensure the routing of the secondary circuit known as "bore cooling".

[0005] However, the use of these sleeves, partitioning the inter-disc spaces, no longer allows access to said spaces, and to the bolted connections allowing the discs to be fixed axially together, making it impossible to mount the rotor.

[0006] There is therefore a need for a device making it possible to at least partially overcome the aforementioned drawbacks. Statement of the invention

[0007] The present disclosure relates to a turbine rotor comprising an axis of rotation, a first disc and at least one second disc downstream of the first disc, carrying each of the rotor blades mounted at its periphery and each having a radial rim, the first disc comprising a downstream shroud extending downstream from the rim of the first disc, and a radial flange extending radially from a downstream end of the downstream shroud and bearing against the rim of the second disc, the first and second discs being fixed to each other by means of at least one fixing assembly comprising at least one tie rod extending at least through the rim of the first disc, the radial flange and the rim of the second disc.

[0008] In some embodiments, said second disc comprises an upstream sleeve extending upstream from a radial end of the rim of the second disc so as to form a first inter-disc cavity between the respective rims of the first and second discs.

[0009] In the present disclosure, the terms "upstream" and "downstream" are defined with respect to the direction of flow of the gases through the turbomachine turbine. Similarly, the terms "axial", "radial" and their derivatives are defined with reference to the axis of rotation of the rotor.

[0010] The rotor discs each comprise, in a known manner, a plurality of cells for receiving the root of the rotor blades, and a structural rim (or web), radially inside the cells, forming the skeleton of the disc. It is understood that each of the rims are pierced, so as to allow the passage of the fixing means, in the present case of the fixing assembly, allowing the fixing of the discs together. In particular, these discs are connected together by means of the downstream shell extending axially downstream from the rim of the first disc, and the radial flange extending radially from the downstream shell, preferably towards the inside of the disc, the radial flange itself being pierced to allow the passage of the fixing assembly.

[0011] In this regard, the term “fixing assembly” means an assembly which may comprise a single tie rod, two tie rods, three or more, depending in particular on the number of rotor discs, as explained in the remainder of the description.

[0012] It is also understood that the fixing assembly is configured to allow the fixing and tightening of the discs together, by means known per se. For example, an upstream end of the fixing assembly, projecting upstream beyond the drilling of the rim of the first disc into which the fixing assembly is inserted, may be threaded, a nut being screwed onto this thread. Similarly, the opposite downstream end of the fixing assembly projecting downstream beyond the drilling of the rim of the second disc into which the fixing assembly is inserted, may be threaded, a nut being screwed onto this thread.

[0013] Furthermore, the upstream sleeve preferably extends axially from the radially internal end of the rim of the second disc, so as to form the first inter-disc cavity formed between the respective rims of the first and second discs, without necessarily completely closing said first cavity, a clearance possibly existing between the rim of the first disc and the upstream end of the upstream sleeve. It is thus understood that the upstream sleeve preferably extends to the rim of the first disc, in the vicinity of the radially internal end thereof, so as to form a partition limiting leaks from the secondary cooling circuit (called "bore cooling") towards the inside of the first inter-disc cavity. This partition thus makes it possible to guide the fluid of this secondary circuit towards the downstream of the turbine, while maintaining its flow rate.

[0014] Furthermore, when assembling the first and second discs together, the first inter-disc cavity, partitioned axially by the rims of the first and second discs on the one hand, and radially by the downstream ferrule and the upstream sleeve on the other hand, is inaccessible. The use of the fixing assembly extending axially through the rim of the first disc, the radial flange and the rim of the second disc, allows the discs to be fixed together, without requiring access to the interior of the first cavity.

[0015] Furthermore, the fixing assembly makes it possible to fix the discs together via the radial flange, consequently also fixing the downstream shell of the disc, which allows the fixing assembly to be arranged closer to the hot air flow vein of the turbine than to the radially internal end of the rims, in other words than to the bore of the rims, thus improving the stability of the holding of the discs together. This device thus makes it easier to assemble a rotor whose inter-disc cavities are closed, while ensuring reliable holding of the rotor discs.

[0016] In certain embodiments, the at least one tie rod comprises a downstream stop wall disposed upstream of a downstream end of the tie rod and bearing against the radial flange of the first disc.

[0017] The stop wall makes it possible to limit the axial translation of the tie rod downstream, allowing precise axial positioning. This limits in particular the risk of the fixing assembly penetrating completely into the first cavity, and that it is necessary to dismantle the first disc in order to recover it.

[0018] In some embodiments, the stop wall comprises a flat cooperating with a shoulder of the radial flange of the first disc.

[0019] The shoulder may, for example, extend circumferentially in the angle formed between the downstream ferrule and the radial flange. The contact between the flat of the stop wall and this shoulder prevents rotational movement of the tie rod around its axis. This makes it easier to fix the assembly of discs by means of the tie rod and the fixing means, for example the aforementioned nuts. Similarly, when the assembly fixing comprises a second tie rod fixed to a first tie rod comprising this flat, the fixing of the second tie rod on the first tie rod is facilitated by the fact that rotation of the latter is prevented.

[0020] In some embodiments, the turbine rotor comprises a third disc downstream of the second disc, having a radial rim and comprising an upstream shroud extending upstream from said rim, and a radial flange extending radially from an upstream end of the upstream shroud and bearing against the rim of the second disc, the first, second and third discs being fixed to each other by means of said fixing assembly.

[0021] In some embodiments, said second disc comprises a downstream sleeve extending downstream from the radial end of the rim of the second disc so as to form a second inter-disc cavity between the respective rims of the second and third discs.

[0022] It is understood in the same way that the rim of the third disc is pierced, so as to allow the passage of the fixing assembly, allowing the fixing of the discs together. The third disc is connected to the second disc by means of the upstream ferrule extending axially upstream from the rim of the third disc, and the radial flange extending radially from the upstream ferrule, preferably towards the inside of the disc, the radial flange itself being pierced to allow the passage of the fixing assembly.

[0023] Furthermore, the downstream sleeve preferably extends axially from the radially inner end of the rim of the second disc, so as to form the second inter-disc cavity between the respective rims of the second and third discs, without necessarily completely closing said second cavity, a clearance possibly existing between the rim of the third disc and the downstream end of the downstream sleeve. It is thus understood that the downstream sleeve preferably extends to the rim of the third disc, in the vicinity of the radially inner end thereof, so as to form a partition limiting leaks from the secondary cooling circuit towards the inside of the second inter-disc cavity. This partition thus also makes it possible to guide the fluid of this secondary circuit towards the downstream of the turbine, while maintaining its flow rate.

[0024] In the same way also, when assembling the third disc on the second disc, the second inter-disc cavity, partitioned axially by the rims of the second and third discs on the one hand, and radially by the upstream ferrule and the downstream sleeve on the other hand, is inaccessible. The use of the fixing assembly extending axially through the rim of the first, second and third discs, and through the radial flange of the downstream ferrule and the upstream ferrule, allows the discs to be fixed together, without requiring access to the interior of the second cavity, while thus improving the stability of the holding of the discs together.

[0025] In some embodiments, the turbine rotor comprises a fourth disc downstream of the third disc, having a radial rim and comprising an upstream shroud extending upstream from said rim, and a radial flange extending radially from an upstream end of the upstream shroud and bearing against the rim of the third disc, the first, second, third and fourth discs being fixed to each other by means of said fixing assembly.

[0026] In some embodiments, the downstream sleeve of the second disc extends downstream to the fourth disc so as to form a third inter-disc cavity between the respective rims of the third and fourth discs.

[0027] It is understood in this case that the fourth disc is substantially identical to the third disc, including in particular an upstream shroud and a radial flange extending radially from the latter. It is also understood that the downstream sleeve of the second disc extends downstream to the rim of the fourth disc, in the vicinity of the radially internal end thereof, so as to form a partition limiting leaks from the secondary cooling circuit towards the inside of the third inter-disc cavity, thus guiding the fluid of the secondary circuit towards the downstream of the turbine. The downstream sleeve thus also forms the fourth cavity, without necessarily completely closing it, a clearance possibly existing between the rim of the fourth disc and the downstream end of the downstream sleeve.

[0028] In the same way also, when assembling the fourth disc on the third disc, the third inter-disc cavity, partitioned axially by the rims of the third and fourth discs on the one hand, and radially by the upstream ferrule of the third disc and the downstream sleeve on the other hand, is inaccessible. The use of the fixing assembly extending axially through the rim of the first, second, third and fourth discs, and through the radial flanges of the ferrules, allows the discs to be fixed together, without requiring access to the interior of the fourth cavity, while thus improving the stability of the holding of the discs together.

[0029] In some embodiments, the fastening assembly comprises a single tie rod (extending through the rim of the first, second and third discs, and through the radial flange of the first and third discs).

[0030] In other words, whether the rotor comprises two, three or four discs, a single tie rod passes through the rim of each of the discs, as well as the radial flange of the ferrules. This simplifies the process of assembling and fixing the discs together.

[0031] Preferably, the single tie rod comprises intermediate threaded portions axially adjacent to the rim of the intermediate disc(s). By "intermediate threaded portions" is meant portions located along the tie rod between its two ends, and distinct from the latter, themselves threaded. By "intermediate disc", we understand the second disc when the rotor comprises three discs, and the second and third discs when the rotor comprises four discs. The presence of these intermediate threaded portions makes it possible to screw a tightening means such as a nut onto them, and thus improve the support and rigidity of the assembly.

[0032] In some embodiments, the attachment assembly includes a first tie rod and a second tie rod, the second tie rod extending at least partially between the second and third discs, an upstream end of the second tie rod being attached to a downstream end of the first tie rod.

[0033] It is thus understood that when the rotor comprises three discs, the first and second discs are connected to each other by the first tie rod, the second tie rod then serving as a fixing means, and the second and third discs are connected to each other by means of the second tie rod, the first tie rod thus serving as a fixing means. This configuration makes it possible to improve the stability of the holding of the discs together.

[0034] In some embodiments, the attachment assembly comprises a third tie rod extending at least partially between the third and fourth discs, an upstream end of the third tie rod being attached to a downstream end of the second tie rod.

[0035] It is thus understood that when the rotor comprises four discs, the second and third discs are connected to each other by means of the second tie rod, the first and third tie rods thus serving as fixing means, and the third and fourth discs are connected to each other by means of the third tie rod, the second tie rod thus serving as fixing means. This configuration makes it possible to improve the stability of the holding of the discs together.

[0036] Preferably, the downstream end of the second tie rod comprises a threaded female portion, and the upstream end of the third tie rod comprises a threaded male portion, screwed into the female portion of the second tie rod. The third tie rod may also comprise an upstream stop wall and drive slots, in the same way as for the second tie rod, and having the same advantages.

[0037] In some embodiments, the downstream end of the first tie rod comprises a threaded female portion, and the upstream end of the second tie rod comprises a threaded male portion, screwed into the female portion.

[0038] It is thus possible to screw the second tie rod directly onto the first tie rod, without the need to install an additional part such as a nut, thus facilitating the assembly and structure of the rotor.

[0039] In certain embodiments, the second tie rod comprises an upstream stop wall, downstream of the upstream end of the second tie rod, and bearing against the radial flange of the third disc.

[0040] It is understood that the upstream stop wall is located on an upstream portion of the second tie rod, downstream of the upstream end of said second tie rod. In other words, a small portion of the second tie rod, comprising the threaded male part screwing into the female part of the first tie rod, is located upstream of the upstream stop wall. When the second tie rod is screwed onto the first tie rod, the upstream stop wall is pressed against the radial flange of the second disc, itself pressing against the rim of the second disc. The upstream stop wall thus makes it possible to improve the maintenance and rigidity of the attachment of the discs to each other.

[0041] In certain embodiments, the second tie rod comprises drive slots distributed circumferentially around an axis of the second tie rod, downstream of the upstream stop wall and adjacent to the latter.

[0042] It is understood that these drive slots extend radially around the axis of the second tie rod. These slots make it easier to rotate the second tie rod around its axis, allowing it to be screwed onto the first tie rod, for example using a tool provided for this purpose.

[0043] In certain embodiments, the turbine rotor comprises at least one annular flange disposed on an upstream face of the first disc, and comprising at least one cylindrical boss configured to fit into an orifice in the rim of the first disc, in which the fixing assembly is housed.

[0044] It is understood that a diameter of the axis of the tie rod, for example of the first tie rod, is less than the diameter of the hole in the rim of the first disc in which it is housed, to allow for example the downstream stop wall to be inserted therein if necessary. The cylindrical boss forms a tube in which the first tie rod is housed, the cylindrical boss itself being housed in the hole in the rim.

[0045] Thus, the cylindrical boss makes it possible to fill the gap existing between the axis of the first tie rod and the wall of the orifice. It is thus possible to improve the centering of the discs between them, and also the stability of the holding of the discs between them. It will be noted that an annular flange having the same characteristics can also be arranged on a downstream face of the third disc when the rotor comprises three discs, or on a downstream face of the fourth disc when the rotor comprises four discs.

[0046] In some embodiments, the fastening assembly comprises tie rods distributed circumferentially around the axis of rotation so as to fasten the first and second discs together.

[0047] It is understood that the rim of each disc comprises a plurality of holes each crossed by a fixing assembly. It is also understood that each tie rod may comprise one, two or three tie rods, having the characteristics described above, depending on the number of discs.

[0048] The present disclosure also relates to a turbine comprising a turbine rotor according to any one of the preceding embodiments, the turbine being a low pressure turbine.

[0049] The present disclosure also relates to a turbomachine comprising a turbine according to the present disclosure.

[0050] The present disclosure also relates to a method of assembling a turbine rotor according to any one of the preceding embodiments, comprising: - axial positioning of the first disc relative to the second disc, by placing the radial flange in abutment against the rim of the second disc, - inserting the fixing assembly through the rim of the first disc, the radial flange and the rim of the second disc, - fixing the first disc and the second disc to each other by means of the fixing assembly.

[0051] It is understood that when the rotor comprises three discs, the first and third discs are positioned axially relative to the second disc, by placing their respective radial flanges in abutment against the rim of the second disc, on either side thereof, the holes in each of these flanges being aligned with the holes in the rim of the second disc. The single tie rod, if any, is then inserted through the hole in the rim of the first disc. Alternatively, the first tie rod is inserted through said hole, while the second tie rod is inserted through the hole in the rim of the third disc and then fixed to the first tie rod, before fixing the assembly.

[0052] Similarly, it is understood that when the rotor comprises four discs, the first and third discs are positioned axially relative to the second disc and then fixed together by the first and second tie rods as described above. Then, the fourth disc is positioned axially relative to the third disc, by placing the radial flange of the fourth disc in abutment against the rim of the third disc. The third tie rod is then inserted through the hole in the rim of the fourth disc and then screwed onto the second tie rod. Alternatively, when the fixing assembly comprises a single tie rod, the four discs are positioned axially relative to each other initially, then the single tie rod is inserted through the hole in the rim of the first disc through all the discs, before fixing the assembly.

[0053] Regardless of the number of discs, it is thus possible to assemble and fix the discs together, while the inter-disc cavities formed by these assemblies are not accessible. This method thus makes it possible to facilitate assembly, while ensuring reliable maintenance of the rotor discs. Brief description of the drawings

[0054] The invention and its advantages will be better understood upon reading the detailed description given below of different embodiments of the invention given as of non-limiting examples. This description refers to the attached figure pages, on which:

[0055] [Fig. 1] [Fig.l] is a longitudinal sectional view of a turbomachine comprising a turbine according to the present disclosure,

[0056] [Fig.2] [Fig.2] represents a longitudinal and partial sectional view of a turbine rotor without tie rod,

[0057] [Fig.3] [Fig.3] represents, on the left, a longitudinal and partial sectional view of a turbine rotor according to a first embodiment of the invention, and on the right, a detailed view of the tie rods of this rotor,

[0058] [Fig.4] [Fig.4] represents a detailed view of the first end of the first tie rod of [Fig.3],

[0059] [Fig.5] [Fig.5] is a perspective view of the first tie rod of [Fig.3],

[0060] [Fig.6] [Fig.6] is a perspective view of the second tie rod of [Fig.3],

[0061] [Fig.7] [Fig.7] is a perspective and partial view of an annular flange of the rotor of [Fig.3],

[0062] [Fig.8] [Fig.8] represents a longitudinal and partial sectional view of a turbine rotor according to a second embodiment of the invention,

[0063] [Fig.9] [Fig.9] represents a longitudinal and partial sectional view of a turbine rotor according to a third embodiment of the invention,

[0064] [Fig. 10] [Fig. 10] shows a longitudinal and partial sectional view of a modified example of the turbine rotor according to the third embodiment.

[0065] [Fig. 11A-11H] Figures 1 1A to 11H show different steps of a method of assembling a turbine rotor according to the present disclosure. Description of the embodiments

[0066] A first embodiment of the present disclosure will be presented with reference to Figures 1 to 4.

[0067] The terms "upstream" and "downstream" are subsequently defined in relation to the direction of flow of gases through a turbomachine, indicated by the arrow F in [Fig.l]. Similarly, the terms "axial", "radial", "circumference" and their derivatives are defined in relation to the main axis X of rotation of the turbomachine.

[0068] [Fig.l] illustrates a double-flow turbomachine 100 comprising in a known manner from upstream to downstream successively at least one fan 1, an engine part successively comprising at least one low-pressure compressor stage 2, high-pressure compressor stage 3, a combustion chamber 4, at least one high-pressure turbine stage 5 and low-pressure turbine stage 6. The present embodiment is particularly concerned with the low-pressure turbine 6, and the rotor of the latter.

[0069] In a known manner, secondary air circuits are used, and are taken from different locations of the turbomachine 100, in order to ensure the necessary ventilation flow rates in certain regions of this turbomachine. For example, a fraction of air is taken from the high-pressure compressor 3 and is conveyed via a cooling duct C1 in order to cool hotter areas of the turbomachine 100, in particular the high-pressure turbine 5 and the low-pressure turbine 6.

[0070] Furthermore, one of these secondary circuits (called “bore cooling” in English) must in particular be routed from an upstream casing (called “TRF” casing for “turbine rear frame” in English, not visible in the figures), upstream of the low pressure turbine 6, to downstream of the latter to be purged there.

[0071] [Fig.2] represents a detailed and schematic view of the rotor 60 of the low pressure turbine 6 (the stator of said turbine not being shown), illustrating a portion of this “bore cooling” circuit, more simply called “secondary circuit C2” in the remainder of the description.

[0072] In the example shown in [Fig. 2], the rotor 60 comprises four annular discs rotating around the main axis X, in particular, from upstream to downstream, a first disc 61, a second disc 62, a third disc 63 and a fourth disc 64. Each of them comprises an annular rim (or web) and, at a radially external end of the rim, a plurality of cells (only one is visible in [Fig. 2]) for carrying rotor blades 62. More precisely, the first disc 61 comprises a rim 610 and cells 611, the second disc 62 comprises a rim 620 and cells 621, the third disc 63 comprises a rim 630 and cells 631, and the fourth disc 64 comprises a rim 640 and cells 641.

[0073] It will be noted that the first, third and fourth discs 61, 63, 64 respectively comprise, at the radially internal end of the rim 610, 630, 640, a balancing device 612, 632, 642. In addition, each rim 610, 620, 630, 640 respectively comprises a plurality of orifices 613, 623, 633, 643 (only one is visible in [Fig. 2]) distributed circumferentially around the main axis X, and intended to receive the tie rods described in the remainder of the description.

[0074] The space between the rims 610, 620, 630, 640 forms inter-disc cavities (or sub-vein cavities, arranged radially inside the hot air flow vein in which the blades 62 are arranged). In particular, a first inter-disc cavity P1 is formed between the rims 610 and 620 of the first and second discs 61, 62. A second inter-disc cavity P2 is formed between the rims 620 and 630 of the second and third discs 62, 63. A third inter-disc cavity P3 is formed between the rims 630 and 640 of the third and fourth discs 63, 64.

[0075] Furthermore, the first disc 61 comprises a downstream ferrule 614, extending axially downstream from a radially external end of the downstream face of the rim 610, in an area preferably between the orifices 613 and the cells 611. This downstream ferrule 614 carries in particular the wipers intended to cooperate with the abradable tracks of the stator (not shown). A radial flange 615 extends radially inward from the downstream end of the downstream ferrule 614. The radial flange 615 cooperates, directly or via an annular flange, with the upstream face of the rim 620 of the second disc 62. It also comprises a plurality of orifices arranged opposite the orifices 623 of the rim 620, and coaxially with the latter.

[0076] The second disc comprises a flared portion at the radially inner end of its rim 620, from which an upstream sleeve 622a extends upstream, and from which a downstream sleeve 622b extends downstream. The upstream sleeve 622a extends to an upstream end arranged substantially at the same axial position as the first disc 61, in the vicinity of its radially inner end, in particular in the vicinity of the balancing device 612. By “in the vicinity”, it is understood that the upstream sleeve 622a is sufficiently close to the radially inner end of the disc 61 to limit the ingestion of air from the secondary circuit C2 into the first inter-disc cavity PI (this ingestion limitation is symbolized by the cross in [Fig. 2]), without being in contact with the disc 61.

[0077] Similarly, the downstream sleeve 622b extends to a downstream end arranged substantially at the same axial position as the fourth disc 64, in the vicinity of its radially internal end, in particular in the vicinity of the balancing device 642. A labyrinth seal may also be arranged between the downstream sleeve 622b and the balancing device 632, and between the downstream sleeve 622b and the balancing device 642. The rim 620, the upstream sleeve 622a and the downstream sleeve 622b of the second disc 62 are formed in a single piece, without any connecting element. The upstream sleeve 622a and the downstream sleeve 622b thus make it possible to guide the air from the secondary circuit C2 towards the downstream of the rotor 60, limiting the risks of air ingestion into the inter-disc cavities P1, P2 and P3.

[0078] The third disc 63 further comprises an upstream ferrule 634, extending axially upstream from a radially external end of the upstream face of the rim 630, in an area preferably between the orifices 633 and the cells 631. This upstream ferrule 634 carries in particular the wipers intended to cooperate with the abradable tracks of the stator (not shown). A radial flange 635 extends radially inward from the upstream end of the upstream ferrule 634. The radial flange 635 cooperates with the downstream face of the rim 620 of the second disc 62. It also comprises a plurality of orifices arranged opposite the orifices 623 of the rim 620, and coaxially with the latter.

[0079] The fourth disc 64 also comprises an upstream ferrule 644 and a radial flange 645 having the same characteristics as on the third disc 63. In particular, the radial flange 645 cooperates, directly or via an annular flange, with the downstream face of the rim 630 of the third disc 63. It also comprises a plurality of orifices arranged opposite the orifices 633 of the rim 630, and coaxially with the latter.

[0080] Taking into account the assembly illustrated in [Fig.2] and the characteristics above, the inter-disc cavities are closed, on the one hand axially by the rims of the discs, and on the other hand radially by the upstream or downstream ferrules and by the upstream or downstream sleeves. For example, the first inter-disc cavity PI is closed axially by the rims 610 and 620 of the first and second discs 61, 62, and radially by the downstream ferrule 614 and the sleeve 622a. The latter being non-removable, it is not possible to manually access the interior of the first inter-disc cavity PI, in particular to fix the discs together. The tie rods described in the remainder of the description allow such fixing.

[0081] A first embodiment will be described with reference to Figures 3 to 7.

[0082] In this embodiment, the rotor 60 of the low pressure turbine 6 comprises three discs, in particular, from upstream to downstream, a first disc 61, a second disc 62 and a third disc 63. These discs are similar to the first, second and third discs described with reference to [Fig.2], and will not be described again. It will be noted, however, that given the absence of the fourth disc, the downstream sleeve 622b is shorter and extends axially to the third disc 63.

[0083] The left part of [Fig. 3] represents the rotor 60, and the right part of [Fig. 3] is a detailed view of this rotor, at the level of the tie rods. The rotor 60 comprises a plurality of sets of tie rods 70 (only one is visible in [Fig. 3]) distributed circumferentially around the main axis X. In this embodiment, each fixing assembly 70 comprises a first tie rod 71 and a second tie rod 72.

[0084] The first tie rod 71, shown in perspective in [Fig. 5], extends mainly between the rim 610 and the rim 620, and the second tie rod 72, also shown in perspective in [Fig. 6], extends mainly between the rim 620 and the rim 630. A downstream end 712 of the first tie rod 71 is fixed to an upstream end 721 of the second tie rod 72, inside the orifice 623 of the rim 620 of the second disc 62. More precisely, the downstream end 712 of the first tie rod 71 is a female threaded part, inside which is screwed the upstream end 721 of the second tie rod 72, which is a male threaded part.

[0085] Furthermore, an upstream end 711 of the first tie rod 71 projects upstream beyond the orifice 613 of the rim 610, this upstream end 711 being threaded and a nut 74 being screwed therein. [Fig.4] shows a detailed view of the fixing at the level of the upstream end 711 of the first tie rod 71. It will also be noted that an annular flange 80, described in more detail below, is arranged between the nut 74 and the upstream face of the rim 610.

[0086] Similarly, a downstream end 722 of the second tie rod 72 projects downstream beyond the orifice 633 of the rim 630, this downstream end 722 also being threaded and a nut 75 being screwed thereto.

[0087] The first tie rod 71 further comprises a stop wall 714 arranged upstream of the female downstream end 712. This wall corresponds to a radially widened portion of the axis of the first tie rod 71, configured to come into abutment against the radial flange 615, so as to limit the axial travel of the first tie rod 71. It will be noted in this regard that the diameter of the orifices 613 of the first disc 61 is substantially greater than the diameter of the stop wall 714, so as to allow its passage during insertion of the first tie rod 71. Consequently, the diameter of the orifices 613 is greater than the diameter of the orifices 623 of the second disc 62, and also greater than the diameter of the axis of the first tie rod 71, housed in the orifice 613.

[0088] In order to fill the clearance then existing between the first tie rod 71 and the wall of the orifice 613, it is possible to provide the annular flange 80 with cylindrical bosses 82, distributed circumferentially on a downstream face of the annular flange 80, as shown in perspective in [Fig.7]. These cylindrical bosses 82 thus fit into the aforementioned clearance, thus filling the latter ([Fig.4]).

[0089] Furthermore, the stop wall 714 has a flat 715, cooperating with a shoulder 616 formed in the angle between the downstream ferrule 614 and the radial flange 615, making it possible to limit the rotational movements of the first tie rod 71 around its axis.

[0090] Furthermore, the second tie rod 72 also comprises a stop wall 724 arranged downstream of the upstream male end 721. This wall corresponds to a radially widened portion of the axis of the second tie rod 72, configured to come into abutment against the radial flange 635, so as to limit the axial travel of the second tie rod 72.

[0091] In the same way, the diameter of the orifices 633 of the third disc 63 is substantially greater than the diameter of the stop wall 724, so as to allow its passage during the insertion of the second tie rod 72. In doing so, the diameter of the orifices 613 is consequently greater than the diameter of the orifices 623 of the second disc 62. Consequently, in order to fill the clearance then existing between the second tie rod 72 and the wall of the orifice 633, it is possible to provide the annular flange 81 similar to the annular flange 80, comprising bosses to fill this clearance.

[0092] Furthermore, the second tie rod 72 comprises drive slots 726 distributed circumferentially around the axis of the second tie rod 72, downstream of the stop wall 724 and adjacent to the latter, making it easier to screw onto the first tie rod.

[0093] The fixing assembly 70 described above thus makes it possible to fix the discs 61, 62, 63 between them, without needing to access the interior of the inter-disc cavities PI and P2, while being engaged with the radial flanges 615, 635 of the ferrules 614, 634, thus improving the stability of the maintenance of the assembly.

[0094] A second embodiment will be described with reference to [Fig.8], representing a detailed view of a rotor 60, at the level of the tie rods.

[0095] In this embodiment, the rotor 60 of the low-pressure turbine 6 comprises four discs 61, 62, 63, 64. These discs are similar to the discs described with reference to [Fig. 2], and will not be described again. The rotor 60 of [Fig. 8] differs from the rotor of [Fig. 2] only by the presence of the fixing assembly 70, described below. In this embodiment, each fixing assembly 70 comprises a first tie rod 71, a second tie rod 72 and a third tie rod 73.

[0096] The first tie rod 71 is identical to the first tie rod according to the first embodiment, and extends mainly between the rim 610 and the rim 620. The second tie rod 72 extends mainly between the rim 620 and the rim 630. Its upstream end 721 is identical to the upstream end of the second tie rod according to the first embodiment. On the other hand, its downstream end 722 is a female end comprising a thread, in the same way as the downstream end 721 of the first tie rod 71, but does not include a stop wall.

[0097] The third tie rod 73 extends mainly between the rim 630 and the rim 640, and is identical to the second tie rod 72. More precisely, the downstream end 722 of the second tie rod 72 is fixed to an upstream end 731 of the second tie rod 72, which is a threaded male part, inside the orifice 633 of the rim 630 of the third disc 63. It will be noted that a flange 83, similar to the flanges 80 and 81 described below, and comprising bosses, can also be arranged so as to fill the clearance existing between the downstream end 722 of the second tie rod 72, and the wall of the orifice 633 of the rim 630 of the third disc 63.

[0098] Furthermore, a downstream end 732 of the third tie rod 73 projects downstream beyond the orifice 643 of the rim 640, this downstream end 732 also being threaded and a nut 75 being screwed therein. The third tie rod 73 also comprises an upstream stop wall and drive slots in a manner similar to the second tie rod 72.

[0099] A third embodiment will be described with reference to [Fig.9].

[0100] In this embodiment, the rotor 60 of the low-pressure turbine 6 comprises four discs similar to the discs described with reference to [Fig. 2]. The fixing assembly 70 according to this embodiment differs from the fixing assembly according to the second embodiment, in that it comprises a single tie rod 76, extending over the entire length of the rotor 60, passing through the respective orifices of each disc and of each radial flange.

[0101] The tie rod 76 comprises an upstream end 761 projecting upstream beyond of the orifice 613 of the rim 610, this upstream end 761 being threaded and a nut 74 being screwed thereto, and a downstream end 762 projecting downstream beyond the orifice 643 of the rim 640, this downstream end 722 also being threaded and a nut 75 being screwed thereto.

[0102] Furthermore, intermediate portions of the tie rod 76 are also threaded, in particular a first intermediate portion 767 onto which a nut 77 is screwed bearing against the radial flange 635, and a second intermediate portion 768 onto which a nut 78 is screwed bearing against the radial flange 645. It will be noted that a stop wall 764, similar to the stop wall 714 of the first tie rod described above with reference to the first embodiment, may also be present on an intermediate portion of the tie rod 76. This stop wall 764, bearing on the radial flange 615, makes it possible to limit the axial travel of the tie rod 76.

[0103] [Fig. 10] shows a modified example of the third embodiment, in which the fixing assembly 70 also comprises a single tie rod 76', the latter differing from the tie rod 76 in that it does not comprise threaded intermediate portions and an intermediate stop wall bearing against the radial flange 615. In addition, the upstream end 761' is not threaded, but is in the form of an upstream stop wall bearing against the rim 610, directly or via an annular flange 80. Furthermore, in the absence of an intermediate stop wall bearing against the radial flange 615, the orifices 613 of the rim 610 may have a diameter identical to the orifices 623, 633 and 643 of the rims 620, 630, 640 respectively. In this case, the flange 80 can be without a boss. This makes it easier to assemble and center the parts.

[0104] A method of assembling a low-pressure turbine rotor 60 will be described in the remainder of the description, with reference to the figures. This method takes as an example the first embodiment described previously, in which the rotor 60 comprises three discs.

[0105] The second disc 62 is provided initially (image 1 IA of figures 11A-11H). A centering flange 90, making it possible to improve centering of the discs between them, is possibly arranged on the upstream face of the disc.

[0106] The first disc 61 is then positioned axially relative to the second disc 62, by placing the radial flange 615 in abutment against the upstream face of the rim 620 of the second disc 62 (directly, or via the centering flange), so that the orifices of the radial flange 615 are opposite the orifices 623 of the rim 620 (image 11B of figures 11A-11H).

[0107] Then, the third disc 63 is positioned axially relative to the second disc 62, by placing the radial flange 635 in abutment against the downstream face of the rim 620 of the second disc 62, so that the orifices of the radial flange 635 are opposite the holes 623 of the rim 620 (image 11C of figures 11A-11H).

[0108] The sets of tie rods 70 are then inserted, over the entire circumference of the discs, through the rim 610 of the first disc 61, the radial flange 615, the rim 620 of the second disc 62, the radial flange 635 and the rim 630 of the third disc 63.

[0109] More precisely, the first tie rods 71 ​​are inserted into each orifice 613 of the rim 610, and moved axially until the stop wall 714 comes into abutment against the radial flange 615, while orienting the first tie rod 71 around its axis so that the flat 715 is disposed against the shoulder 616 (image 11D of figures 11A-11H). At this stage, the flange 80 can be disposed against the upstream face of the rim 610 by inserting the bosses 82 into the clearances between the first tie rod 71 and the wall of the orifices 613, so as to fill these clearances (image 11E of figures 11A-11H).

[0110] Then, the second tie rods 72 are inserted into each orifice 633 of the rim 630, and moved axially until the upstream end 721 male threaded is at the entrance of the downstream end 712 female threaded of the first tie rod 71. The second tie rod 72 is then turned around its axis, so as to screw the male threaded part into the female threaded part (image 11F of figures 11A-11H). In addition, the presence of the drive slots 726 provides gripping surfaces making it possible to facilitate this screwing, in particular by using a suitable tool. The latter can be inserted into the inter-disc cavity P2 via the clearance existing between the second tie rod 72 and the wall of the orifices 633. The second tie rods 72 are then screwed onto the first tie rods 71 ​​until the stop wall 724 comes into abutment against the radial flange 635.

[0111] After the possible installation of the flange 81 comprising the bosses to fill the aforementioned clearances, against the downstream face of the rim 630, the discs 61, 62, 63 are then fixed to each other, by means of the sets of tie rods 70, by screwing and tightening nuts 74, 75, on the ends of the tie rods 71, 72 projecting beyond the orifices 613, 633 (images 11G and 11H of figures 11A-11H).

[0112] 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.

[0113] It is also obvious that all the characteristics described with reference to a method are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a method.

Claims

Claims

1. A turbine rotor (60) comprising an axis of rotation (X), a first disc (61) and at least one second disc (62) downstream of the first disc, each carrying rotor blades (62) mounted at its periphery and each having a radial rim (610, 620), the first disc (61) comprising a downstream shroud (614) extending downstream from the rim (610) of the first disc (61), and a radial flange (615) extending radially from a downstream end of the downstream shroud (614) and bearing against the rim (620) of the second disc (62), the first and second discs being fixed to each other by means of a fixing assembly (70) comprising at least one tie rod (71) extending at least through the rim (610) of the first disc, the radial flange (615) and the rim (620) of the second disc.

2. Turbine rotor (60) according to claim 1, in which the tie rod (71) comprises a downstream stop wall (714) disposed upstream of a downstream end (712) of the tie rod and bearing against the radial flange (615) of the first disc (61).

3. A turbine rotor (60) according to claim 2, wherein the stop wall (714) comprises a flat (715) cooperating with a shoulder (616) of the radial flange (615) of the first disc (61).

4. A turbine rotor (60) according to any one of claims 1 to 3, comprising a third disc (63) downstream of the second disc (62), having a radial rim (630) and comprising an upstream shroud (634) extending upstream from said rim, and a radial flange (635) extending radially from an upstream end of the upstream shroud (634) and bearing against the rim (620) of the second disc (62), the first, second and third discs (61, 62, 63) being fixed to each other by means of the fixing assembly (70).

5. A turbine rotor (60) according to claim 4, comprising a fourth disc (64) downstream of the third disc (63), having a radial rim (640) and comprising an upstream shroud (644) extending upstream from said rim, and a radial flange (645) extending radially from an upstream end of the upstream shroud (644) and bearing against the rim (630) of the third disc (63), the first, second, third and fourth discs being fixed to each other by means of said fixing assembly (70).

6. A turbine rotor (60) according to claim 4 or 5, wherein the fixing assembly (70) comprises a first tie rod (71) and a second tie rod (72), the second tie rod (72) extending at least partly between the second and third discs (62, 63), an upstream end (721) of the second tie rod (72) being fixed to a downstream end (712) of the first tie rod (71).

7. A turbine rotor (60) according to claims 5 and 6, wherein the attachment assembly (70) comprises a third tie rod (73) extending at least partly between the third and fourth discs (63, 64), an upstream end (731) of the third tie rod (73) being attached to a downstream end (722) of the second tie rod (72).

8. A turbine rotor (60) according to claim 6 or 7, wherein the downstream end (712) of the first tie rod comprises a threaded female portion, and the upstream end (721) of the second tie rod (72) comprises a threaded male portion, screwed into the female portion.

9. Turbine rotor (60) according to any one of claims 6 to 8, in which the second tie rod (72) comprises an upstream stop wall (724), downstream of the upstream end (721) of the second tie rod (72) and bearing against the radial flange (630) of the third disc (63), and drive slots (726) distributed circumferentially around an axis of the second tie rod (72), downstream of the upstream stop wall (724) and adjacent to the latter.

10. Turbine rotor (60) according to any one of claims 1 to 9, comprising at least one annular flange (80) arranged on an upstream face of the first disc (61), and comprising at least one cylindrical boss (82) configured to fit into an orifice (613) of the rim (610) of the first disc (61), in which the fixing assembly (70) is housed.

11. A turbine rotor (60) according to any one of claims 1 to 10, wherein the fixing assembly (70) comprises tie rods distributed circumferentially around the axis of rotation (X) so as to fix the first and second discs together.

12. A turbine (6) comprising a turbine rotor (60) according to any preceding claim, the turbine (6) being a low pressure turbine.

13. Method of assembling a turbine rotor (60) according to any one of claims 1 to 11, comprising: - axial positioning of the first disc (61) relative to the second disc (62), by placing the radial flange (615) in abutment against the rim (620) of the second disc (62), - inserting the fixing assembly (70) through the rim (610) of the first disc (61), the radial flange (615) and the rim (620) of the second disc (62), - fixing the first disc (61) and the second disc (62) to each other by means of the fixing assembly (70).

Images