FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& The Patent Rules, 2003
COMPLETE SPECIFICATION
1. TITLE OF THE INVENTION:
SEALING RING FOR A TURBINE STAGE OF AN AIRCRAFT TURBOMACHINE, COMPRISING
SLOTTED ANTI-ROTATION PEGS
2. APPLICANT:
Name: SNECMA
Nationality: France
Address: 2, boulevard du Général Martial Valin, F-75015 Paris, France.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is to be
performed:
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DESCRIPTION
Technical field
This invention relates to the field of turbines for an aircraft turbomachine, in
particular for aircraft turbojets or turboprop engines.
The invention in particular relates to the downstream sealing ring of a turbine
stage, intended to contact in a sealed manner the blades mounted on a rotor disc of the
turbine stage. More precisely, the invention relates to the anti-rotation pegs provided on
this ring, and which prevent the latter from rotating in relation to the rotor disc.
Prior art
The rotor of a turbine stage of an aircraft turbojet comprises a disc, blades
mounted on the disc at its periphery, and a downstream ring mounted downstream of
the turbine disc/blade unit. In a known manner, the rotor is driven in rotation by the
flowing of a gas flow from the upstream to the downstream through the turbine.
For the mounting of the blades, the disc is provided with peripheral teeth
delimiting between them cells wherein the roots of the blades are retained radially.
In prior art, it is known to mount the downstream sealing ring against the
downstream face of the disc/blade unit, in order to obtain the best possible seal.
The ring is moreover provided with a plurality of anti-rotation pegs, for example
three pegs arranged at 120°, protruding axially from a ring body. These pegs prevent the
ring from rotating in relation to the rotor disc. To do this, each peg has two opposite
circumferential-end surfaces, respectively intended to be located facing two directly
consecutive blades carried on the rotor disc. These surfaces therefore constitute
tangential stops provided to come into contact with the blades, and as such prohibit the
relative rotation between the ring and the disc/blade unit.
In operation, the pegs undergo substantial tangential stress, in particular at a high
rotation speed. The most critical zones are constituted by the connecting radii between
the circumferential-end surfaces, and a support surface for pegs provided on the ring
body. These two connecting radii are effectively of very low values, for example close to
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0.1 mm, and undergo a very high tangential stress, rendering these radii critical in the
lifespan of the ring.
In order to solve this problem of stress impacting the lifespan of the ring, it is
possible to increase the value of the aforementioned connecting radii. Nevertheless, this
solution is not satisfactory because it generates interference problems with the root of
the two blades.
Another solution also considered consists in making pits on two connecting radii,
by creating indentations at the base of the two circumferential-end surfaces, in order to
overcome the problem of interferences with the blade roots. However, these pits reduce
the surface area of the circumferential-end surfaces, and render them less effective in
their rotation prevention function. In addition, the machining of these pits is complicated
to implement.
Description of the invention
The invention therefore has for purpose to overcome the problems mentioned
hereinabove at least partially, in relation to the realisations of prior art.
To do this, the invention has first of all for object a sealing ring intended to be
pressed against a rotor disc of a turbine stage for aircraft turbomachine, said ring being
provided with a plurality of anti-rotation pegs which prevent said ring from rotating in
relation to the rotor disc, each peg protruding axially from a ring body and having two
opposite circumferential-end surfaces, respectively intended to be located facing two
directly consecutive blades carried on the rotor disc. According to the invention, an axially
opening slot passes radially through at least one of said anti-rotation pegs.
The invention is therefore remarkable in that it constitutes a solution that is
simple, effective and easy to implement in order to reduce the tangential stress on at
least one of the anti-rotation pegs, and more preferably on all of these pegs. The
presence of the slot passing through the anti-rotation peg makes it possible indeed to
split the latter into two half-pegs each having a lower stiffness, which therefore provides
them with a higher deformation capacity under stress, accompanied by a drop in the
tangential stress to which they are subjected. In this respect, it has been observed that
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the maximum tangential stress, observed on the connecting radii of the tangential-end
surfaces, can be decreased by at least 20% thanks to the simple presence of the slot
specific to this invention.
The invention is particularly advantageous in that it provides a solution that does
not require modifying the value of the aforementioned connecting radii, established in
order to obtain a satisfactory cooperation between the pegs and the blade roots, without
interferences. This solution also does not generate a decrease in the axial length of the
tangential-end surfaces, in such a way that the latter can fulfil their function as a
circumferential stop in a satisfactory manner.
The invention is also advantageous in that it can be implemented on existing rings,
simply by creating slots on their anti-rotation pegs, more preferably by machining.
It is noted that the ring according to the invention is preferably intended to
constitute a downstream sealing ring for the rotor of a turbine stage, but that is could
possibly be used as an upstream ring, without leaving the scope of the invention.
More preferably, each of the two opposite circumferential-end surfaces is
connected to a support surface for pegs, provided on the ring body, by a first connecting
radius. In addition, each of the two lateral flanks of the slot is connected to the bottom of
this slot by a second connecting radius, and it is done in such a way that the second radius
is strictly greater than the first connecting radius. In this way, the second connecting
radius is subjected to a tangential stress that is even lower than that that is applied on the
first connecting radius. As no surrounding element is normally provided to cooperate
directly with the slot, the second connecting radius is therefore not subject to problems
of interferences.
The ratio between the two connecting radii is more preferably greater than eight,
and can go beyond ten.
In order to further increase the effectiveness of the unloading of the stress
procured by the slot, it is more preferably done in such a way that the bottom of the slot
of each peg is located axially at the same level or in the vicinity of the base of said peg.
Moreover, for an entirely optimised compromise in terms of the effectiveness in
unloading the stress, total mass, and mechanical resistance of the half-pegs separated by
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the slot, in particular concerning the resistance to shearing, it is provided that the ratio
between the width of the slot and the total width of said anti-rotation peg, according to
the circumferential direction, is more preferably between 0.3 and 0.4.
More preferably, the slot is centred on said anti-rotation peg. Alternatively, it
could be offset towards one or the other of the circumferential-end surfaces, without
leaving the scope of the invention.
More preferably, the ring has three anti-rotation pegs arranged at 120° in relation
to one another.
Finally, said anti-rotation pegs are more preferably arranged in the vicinity of an
external radial end of said ring body, even if there could be another arrangement, without
leaving the scope of the invention.
The invention also has for object a rotor of a turbine stage of an aircraft
turbomachine, comprising a disc, blades mounted on the disc, and a downstream sealing
ring such as described hereinabove, mounted downstream of the disc and of the blades.
The invention has for object a turbomachine for aircraft, comprising at least one
such turbine comprising at least one turbine stage rotor such as described hereinabove.
Finally, the invention also has for object a method for manufacturing a sealing ring
such as described hereinabove, wherein the slot of said anti-rotation peg is carried out by
machining.
Other advantages and characteristics of the invention shall appear in the detailed
non-restricting description hereinbelow.
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Brief description of the drawings
The invention shall be better understood, and other details, advantages and
characteristics of the latter shall appear when reading the following description given by
way of a non-restricting example and in reference to the annexed drawings wherein:
- figure 1 is a partial diagrammatical axial cross-section view of an aircraft
turbomachine comprising a high-pressure turbine according to a preferred embodiment
of this invention;
- figure 2 is a partial perspective view of the rotor of a stage of the high-pressure
turbine shown in the preceding figure;
- figure 3 is a partial diagrammatical axial cross-section half-view of the rotor
shown in the preceding figure;
- figure 4 is a perspective view of one of the turbine blades of the rotor shown in
the figures 2 and 3;
- figure 5 shows a view similar to that of figure 2, showing in a more precise
manner one of the anti-rotation pegs of the downstream ring;
- figure 6 also shows a partial perspective view of the downstream ring and of one
of its anti-rotation pegs; and
- figure 7 shows a cross-section view of the anti-rotation peg shown in the
preceding figure, taken along the line A-A of this figure 6;
In these figures, identical or similar elements are designated by identical numeric
references.
Detailed description of a preferred embodiment
In reference first of all to figure 1, an aircraft turbomachine 1 can be seen, of the
double-flow and double-body type.
The turbojet comprises, successively according to the direction of thrust shown by
the arrow 2, a low-pressure compressor 4, a high-pressure compressor 6, a combustion
chamber 8, a high-pressure turbine 10 and a low-pressure turbine 12.
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The high-pressure turbine 10, of the single-stage type, is presented in the form of
a preferred embodiment of this invention, for which details shall now be provided in
reference to figures 2 to 7.
The turbine comprises a stage rotor 20 which is located downstream of a highpressure
distributor 24, belonging to the previous stage. Downstream of the rotor 20 is
located a fixed portion 22 of the turbojet, corresponding to the inlet of the low-pressure
turbine.
First of all, the rotor 20 comprises a disc 26 of which the radially external
periphery has teeth 28 each spaced circumferentially from one another. Cells 30 are
defined between the teeth of the disc. They are axial or slanted, open both onto the
upstream face 31 and onto the downstream face 33 of the disc 26. Conventionally, each
cell 30 receives the root 32 of a blade 34, in order to retain it radially towards the exterior,
via cooperation of form.
The root 32 of each blade 34 is located at a distance from the bottom 36 of its
associated cell 30, according to the radial direction. As such, a free space 38 is formed
between the end of the root 32 and the bottom of the cell 36.
Upstream, the root 32 can possibly be extended radially towards the interior by a
first wall 40, downstream as well, the root 32 is extended radially towards the interior by
a second wall 42.
Furthermore, each blade 34 comprises at its base a platform 46 intended in
particular to guide the flow from upstream to downstream in the turbine, i.e. from the
inlet towards the outlet of the turbine, of a primary flow of gas coming from the
combustion chamber. This platform 46, arranged between the root 32 and the
aerodynamic propeller 48 of the blade, extends circumferentially on either side of this
propeller 48. It is conventionally located in the extension of an identical platform
belonging to a directly consecutive blade, as can be seen in figure 2.
The rotor 20 incorporates an upstream sealing ring 44 carried by the disc 26 on the
upstream face 31 of the latter. The upstream ring 44 participates in particular in the axial
retaining of the blades in the cells, towards the front.
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The rotor 20 further incorporates a downstream sealing ring 60 carried by the disc
26 on the downstream face 33 of the latter. The annular ring 60 has an external radial end
in the shape of a peripheral edge 61 intended to press against a tab 62 of downstream
support of the platform 46, which extends under the platform according to a
circumferential length that is longer than that of the foot that carried this tab 62, with this
length being however substantially identical to that of the platform. Free spaces 64 are
then created located under the tabs 62, delimited circumferentially by the upper portion
of the blade roots, and delimited radially between the tabs 62 and the upper face of the
disc teeth 28. Pegs 66 protruding axially upstream from an upstream face 68 of the
downstream ring pass axially through the spaces 64, locally taking the form of a support
surface for these pegs. Three pegs 66 are more preferably provided, distributed at 120°
over the ring body from which they protrude, from the support surface 68 substantially
oriented according to a transverse plane. These pegs 66 make it possible to provide an
anti-rotation function to the downstream ring, in relation to the disc/blade unit. They are
located in the vicinity of the peripheral edge 61 of the ring, by being arranged radially
towards the interior in relation to this edge 61 also protruding axially upstream.
One of the particularities of this invention resides in the design of the anti-rotation
pegs 66, of which a preferred embodiment shall now be described, substantially in
reference to figures 5 to 7.
Each peg 66 has two opposite circumferential-end surfaces 72, respectively
intended to be located facing two directly consecutive feet of blades 34. The two surfaces
72, facing complementary surfaces provided on the blade roots, are used to prevent the
relative rotation between the ring 60 and the disc/blade unit, according to the axis of
rotation of this unit. A mounting clearance is nevertheless provided between these
surfaces cooperating two-by-two, and substantially oriented in parallel to the axial 90 and
circumferential 92 directions. The surfaces 72, used as stops, are also substantially
orthogonal to the support surface for pegs 68, from which they protrude.
Moreover, a slot 70 passes radially through each peg 66, which opens therefore
radially towards the interior and towards the exterior, and which open axially upstream.
In this respect, the slot 70 here has a preferred shape with a generally U-shaped section,
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as can be best seen in figure 7. Other shapes could be nevertheless adopted, without
leaving the scope of the invention.
The slot 70, of which the bottom 74 is oriented axially in the upstream direction,
thus delimits two half-pegs spaced circumferentially from one another. The bottom 74 is
located substantially at the same level, according to the axial direction 90, than the
support surface 68 for pegs, and therefore substantially at the same level as the base of
its associated peg 66, as can be seen in figure 7. In this respect, in the figures 6 and 7, it is
possible to see that the support surface for pegs 68 can have, for reasons of manufacture,
in particular machining of the pegs on the ring carried out as a single part, axial steps 76
protruding upstream, each carrying a peg 66. In such a case, the slot bottom 74 is then
located substantially at the same level as the step 76 of the support surface 68 for pegs.
The slot 70, preferably centred on the peg, therefore has a U-shaped section of
which the two lateral flanks 78 are carried out at the bottom 74 respectively by two
connecting radii 80, more preferably identical, for example of a value of a magnitude of
1 mm.
These radii 80 are high in comparison with the connecting radii 82 between the
surfaces of the stop 72 and the support surface of pegs 68. These radii, more preferably
also identical, have for example a value of a magnitude of 0.1 mm, entirely adapted for
bringing the peg 66 as close as possible to the blade roots, without interferences.
Finally, the slot 66 has a circumferential width "l" between 0.3 and 0.4 times the
total width "L" of the peg, according to this same circumferential direction 92. More
preferably, the ratio between the widths "l" and "L" is one third.
Of course, various modifications can be made by those skilled in the art to the
invention which has just been described, solely by way of non-restricting examples.
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We claim:
1. Sealing ring (60) intended to be pressed against a rotor disc (20) of a turbine
stage (10) for an aircraft turbomachine, said ring being provided with a plurality of antirotation
pegs (66) which prevent said ring from rotating in relation to the rotor disc, each
peg (66) protruding axially from a ring body (63) and having two opposite circumferentialend
surfaces (72), respectively intended to be located facing two directly consecutive
blades carried on the rotor disc, characterised in that an axially opening slot (70) passes
radially through at least one of said anti-rotation pegs (66).
2. Ring according to claim 1, characterised in that each of the two opposite
circumferential-end surfaces (72) is connected to a support surface of pegs (68), provided
on the ring body (63), by a first connecting radius (82), in that each of the two lateral
flanks (78) of the slot is connected at the bottom (74) of this slot by a second connecting
radius (80), and in that the second connecting radius (80) is strictly greater than the first
connecting radius (82).
3. Ring according to claim 1 or claim 2, characterised in that the bottom (74) of the
slot (70) of each peg (66) is located axially at the same level or in the vicinity of the base
of said peg.
4. Ring as claimed in any preceding claim, characterised in that the ratio between
the width (l) of the slot (70) and the total width (L) of said anti-rotation peg (66),
according to the circumferential direction (92), is between 0.3 and 0.4.
5. Ring as claimed in any preceding claim, characterised in that the slot (70) is
centred on said anti-rotation peg (66).
6. Ring as claimed in any preceding claim, characterised in that it has three antirotation
pegs (66) arranged at 120° in relation to one another.
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7. Ring as claimed in any preceding claim, characterised in that said anti-rotation
pegs (66) are arranged in the vicinity of an external radial end (61) of said ring body (63).
8. Rotor (20) of a turbine stage (10) for an aircraft turbomachine, comprising a disc
(26), blades (34) mounted on the disc, and a downstream sealing ring (60) as claimed in
any preceding claim.
9. Turbomachine (1) for aircraft, characterised in that it comprises at least one
turbine (10) comprising at least one rotor (20) of a turbine stage according to claim 8.
10. Method for manufacturing a sealing ring (60) according to any of claims 1 to 7,
characterised in that the slot (70) of said anti-rotation peg (60) is carried out by machining.