阅读说明：本技术 包括改进的空气密封和耐火装置的、用于飞行器的双流涡轮发动机的中间壳体的外护罩 (Outer shroud for the intermediate casing of a double flow turbine engine of an aircraft comprising improved air sealing and fire-resistant means ) 是由 布鲁诺·亚历山大·迪迪埃·雅康 巴格达德·阿赤巴利 托马斯·克劳德·布劳格 弗洛伦特·罗伯特· 于 2019-02-13 设计创作，主要内容包括：本发明涉及一种用于飞行器的双流涡轮发动机的中间壳体的外护罩(16),该护罩包括：环形下游部分(24),该环形下游部分设有穿过护罩的环形下游边缘(32)的护罩开口(30)；连接构件(50),该连接构件附接到环形下游部分(24),并用于附接穿过次级流动路径(26)的臂；空气密封和耐火装置(60),该空气密封和耐火装置包括：部分(62),该部分包括：垫(66),该垫被布置在护罩的环形下游边缘(32)的中空环形区域(38)中；叶片(68),该叶片从垫(66)突出并夹紧在臂的周向端部(54)与径向外端部之间；片簧(64),该片簧将垫(66)压入到中空环形区域(38)中。(The invention relates to an outer shroud (16) for the intermediate casing of a double flow turbine engine of an aircraft, comprising: an annular downstream portion (24) provided with a shroud opening (30) through an annular downstream edge (32) of the shroud; a connecting member (50) attached to the annular downstream portion (24) and for attaching an arm through the secondary flow path (26); an air sealing and fire resistant apparatus (60) comprising: a portion (62) comprising: a pad (66) disposed in the hollow annular region (38) of the annular downstream edge (32) of the shroud; a vane (68) projecting from the pad (66) and clamped between the circumferential end (54) and the radially outer end of the arm; a leaf spring (64) that presses the pad (66) into the hollow annular region (38).)

1. An outer shroud (16) for a mid-casing (14) of a double flow turbine engine of an aircraft, the shroud comprising:

-a downstream annular portion (24), the downstream annular portion (24) being provided with a shroud opening (30) passing radially through the shroud and opening axially downstream from the shroud, the downstream portion comprising a downstream annular shroud rim (32) whose radially inner surface (36) delimits a hollow annular region (38) opening radially inwards, the downstream annular rim (32) being interrupted by the shroud opening (30) so as to have two circumferential end surfaces (40) facing each other and delimiting between them a housing space (42) for radially outer ends (44) of arms (22) intended to pass radially through the fan flow (26) of the turbine engine;

-a connecting element (50), preferably formed by a perforated connecting plate (50), fixed to the downstream annular portion (24) of the shroud and arranged radially inwards from the shroud, the element (50) being further designed to be fixed to the arm (22) and to form two circumferential ends (54) fixed to the two circumferential end surfaces (40) of the downstream annular shroud rim (32) to define respectively two joining zones (56),

characterized in that said shield further comprises air sealing and refractory means (60) associated with each junction area (56).

2. The outer shroud of claim 1, wherein said air sealing and fire resisting means (60) comprises:

-an air-tight and refractory component (62) comprising:

-first contact means (66) arranged in a hollow annular region (38) of the downstream annular edge (32) of the shroud, the first contact element having a contact surface (70) with a shape complementary to the shape of the inner surface (36) delimiting the hollow annular region (38);

-a second contact element (68) projecting from the first contact element (66) and extending circumferentially beyond the circumferential end surface (40) of the joint region concerned towards the other circumferential end surface (40), the second contact element bearing on the circumferential end (54) of the joint region concerned and being to be fastened between the radially outer end (44) of the arm (22) and this circumferential end (54).

3. The outer shroud of claim 2, wherein the air sealing and fire resisting means (60) further comprises:

-elastic return means (64) to bring said first contact element (66) into contact within said hollow annular region (38), said elastic return means (64) comprising a first end (64a) fixed on a circumferential end (54) of the relative engagement region and a second opposite end (64b) fixed on said first contact element (66).

4. The outer shroud according to claim 3, characterized in that said first contact element (66) is a pad, said second contact element (68) is a boss and said elastic return means (64) is a leaf spring.

5. The outer shroud according to claim 4, characterized in that the contact surface of the pad (66) locally matches, at the pad (66), the entire angular sector (S) of the radially inner surface (36) delimiting the hollow annular region (38), and the pad (66) has a radially inner portion (74), preferably outside the hollow annular region (38).

6. The outer shroud of claim 4 or claim 5, wherein the pad (66) has a circumferential pad end surface (76) in a portion located radially outward from the boss (68), the circumferential pad end surface (76) lying substantially in the same plane as a circumferential end surface (40) of the downstream annular edge (32) of the shroud.

7. The outer shroud according to any one of claims 4 to 6, characterized in that the boss (68) comprises a connection region (88) of reduced thickness compared to the pad.

8. The outer shroud according to any one of claims 4 to 7, characterized in that said air sealing and fire resistant component (62) is formed in a radial direction (93) by at least one layer of elastomeric material (99), preferably a layer of silicone elastomeric material, and at least one layer of fiber made of ceramic (100b), glass (100a) or meta-aramid (100 c).

9. The outer shroud according to the preceding claim, characterized in that said air sealing and refractory component (62) comprises at least one layer of fiberglass (100a) extending through said mat (66) and said boss (68).

10. The outer shroud according to any one of claims 4 to 9, characterized in that each circumferential end (54) has a spot-facing plane (80) forming a seat for a boss (68) of the air sealing and refractory device (60).

11. The outer shroud according to any one of claims 4 to 10, characterized in that the airtight and refractory component (62) is made by compression moulding and the contact surface (70) of the pad (66) is preferably machined.

12. Double flow turbine engine (1) for an aircraft comprising an outer shroud (16) of an intermediate casing (14) according to any one of the preceding claims, and an arm (22) of a fan flow (26) passing radially through the turbine engine, the turbine engine having a fan compartment (8b) and a flow compartment (8a) connected by the arm (22), the radially outer end (44) of the arm being forced into contact with the radially outer surfaces (82) of the two circumferential ends (54) and with the second contact element (68) associated with these two ends (84).

Technical Field

The invention relates to an air sealing function and a fire resistance function between a fan flow and a fan compartment of a double flow turbine engine for an aircraft. The present invention more particularly relates to performing these functions at the junction between the outer shroud of the intermediate casing of the turbine engine and the arms passing radially through the fan flow.

The invention is applicable to all types of double-flow turbine engines, in particular turbojet engines.

Background

In a dual flow turbine engine for an aircraft, there are typically one or more arms downstream of the fan that pass radially through the blade fan flow. The arms are typically arranged to connect a fan compartment located around an outer shroud of the intermediate housing to the flow compartment. Conventionally, the two compartments house the equipment and the auxiliary equipment, while the arm interposed between the two compartments provides a passage for the different elements (for example cables and/or fluid pipes).

The radially outer end of such an arm is fixed to the outer shroud of the intermediate housing at a through hole in the shroud by means of a perforated connection plate type connection element. The downstream annular edge of the outer shroud is interrupted so that it has two circumferential end surfaces that face each other and between which a space is defined to accommodate the radially outer end of the arm.

However, the presence of the openings on the outer shroud creates air sealing problems and fire resistance problems at both circumferential end surfaces of the downstream annular edge of the shroud. This is explained first by the fact that a gap is observed between each of the two circumferential end surfaces and the radially outer end of the arm. This can also be explained by the fact that the perforated plate is located radially below the downstream annular edge of the shroud, in contact with a hollow annular region open radially inwards and defined by the radially inner surface of the downstream edge. The channels between this radially inner surface of the downstream edge and the perforated plate and the above-mentioned gap form a source of air leakage from the fan to the fan compartment and risk of fire spreading from this compartment to the fan flow.

Disclosure of Invention

In order to at least partially solve the above-mentioned problems arising from solutions according to the prior art, a first object of the invention is an outer shroud for an intermediate casing of a double flow turbine of an aircraft according to the features given in claim 1.

Preferably, the air sealing and fire resistant device comprises:

-an air-tight and refractory component comprising:

-first contact means arranged in a hollow annular region of the downstream annular edge of the shroud, the first contact element having a contact surface with a shape complementary to the shape of said radially inner surface delimiting the hollow annular region;

a second contact element projecting from the first contact element and extending circumferentially beyond the circumferential end surface of the relative joining zone towards the other circumferential end surface, the second contact element bearing on the circumferential end of the relative joining zone and being fastened between the radially outer end of the arm and the circumferential end.

Preferably, the air sealing and fire resisting apparatus further comprises:

-elastic return means for bringing the first contact element into contact within the hollow annular region, the elastic return means comprising a first end fixed to a circumferential end of the relative engagement region and a second opposite end fixed to the first contact element.

Thus, the airtight and refractory device has good performance and is perfectly integrated into its environment without any risk of undue extension in the exclusion zone.

The use of elastic return means ensures correct contact of the first contact means in the hollow region of the downstream edge of the shroud, despite some precision defects due to the dimensional tolerances associated with the elements present. The elastic return means thus provide a contact pressure of the first element in the hollow region, which pressure is then accentuated during operation of the turbine engine by the additional pressure of the air circulating in the fan flow.

The first contact element also forms a physical barrier similar to a plug to prevent air and fire from propagating circumferentially through this hollow region of the downstream edge of the shroud. The second contact means forms a physical barrier to prevent air and fire from propagating radially through a gap defined between the radially outer end of the arm and the circumferential end surface of the interrupted downstream edge of the shroud. The arrangement employed thus advantageously provides air-tightness and fire-resistance between the fan compartment and the fan flow at sensitive joint areas due to interruptions of the downstream annular edge of the shroud.

Finally, this design protects the accommodation space which will contain the radially outer end of the arm, so that the arm can be mounted unrestricted later, for example by a third party.

Preferably, the first contact element is a pad, the second contact element is a boss, and the elastic return means is a leaf spring. However, the first and second contact elements and the elastic return means may be made in other forms without departing from the scope of the invention.

In the following, reference will be made to pads, bosses and leaf springs, but the technical features described below also apply when the first and second contact elements and the elastic return means are made in other forms.

Preferably, the contact surface of the pad locally matches, at the pad, the entire angular sector of the radially inner surface delimiting the hollow annular region, and the pad preferably has a radially inner portion outside said hollow annular region. In other words, at least one corner sector in the hollow annular region is completely filled by the pad to form an even higher performance physical barrier.

Preferably, the gasket has a circumferential gasket end surface in a portion located radially outwardly from the boss, the circumferential gasket end surface lying substantially in the same plane as the circumferential end surface of the downstream annular circumferential edge of the shroud. This makes it possible to maintain as precisely as possible the housing space which holds the outer radial end on the arm.

Preferably, the boss includes a connection region of reduced thickness compared to the pad. Due to this reduced thickness, the connection area is flexible, so that it can pivot between the pad and the boss. Thus, the flexible joint is easily deformed in the elastic domain and only slightly resists the contact force generated by the leaf spring on the pad.

Preferably, said air-tight and fire-resistant part is formed in the radial direction by at least one layer of elastomeric material, preferably a layer of silicone elastomeric material, and at least one layer of fibres made of ceramic, glass or meta-aramid (poly (m-phenylene isophthalamide)). However, other types of layers are possible without departing from the scope of the invention. It will be noted that the ceramic fabric layer is particularly effective for fire-resistant functions, while the glass fibre layer can stiffen the laminate and limit creep of the elastomer in a plane orthogonal to this direction if mechanical stress is applied along the direction of superposition of the layers. Finally, the meta-aramid fiber layer also enables such stiffening and may be placed at the contact surface of the mat to limit the risk of damage when in contact with sharp portions of the outer shroud.

Preferably, the air seal and refractory component comprises at least one layer of fibreglass extending across the pad and boss.

Preferably, each circumferential end has a countersink forming a seat for a boss of the air-tight and refractory device. This makes it easy to obtain a substantially flat surface for the radially outer end support of the arm, consisting of a plurality of distinct superposed elements.

Preferably, the depth of the hollow annular region of the downstream annular edge of the shroud is between 3mm and 5 mm.

Preferably, the air-tight and refractory component is made by compression moulding and the contact surface of the pad is preferably machined.

Another object of the invention is a double flow turbine engine for an aircraft comprising an intermediate casing outer shroud as described above, and an arm of the fan flow radially passing through the turbine engine, the turbine engine having a fan compartment and a flow compartment connected by said arm, the radially outer end of the arm being forced into contact with the radially outer surfaces of the two circumferential ends and with a second contact element associated with the two ends.

Other advantages and features of the present invention will become apparent after reading the following detailed non-limiting description.

Drawings

This description will be given with reference to the accompanying drawings, in which:

figure 1 is a perspective view of a dual flow turbojet according to a preferred embodiment of the invention;

fig. 2 shows a partial perspective view of the outer shroud of the intermediate casing mounted on the turbojet engine shown in fig. 1;

FIG. 3 shows an enlarged perspective view of a portion of the outer shroud shown in the previous figure;

figure 4 shows a perspective view similar to figure 2, in which the arm crosses the fan flow of the turbojet engine;

figure 5 shows a top view of the perspective view of figure 4;

figure 6 shows a perspective view similar to figure 3, in which the arm is shown;

FIG. 7 is a perspective view of the airtight and refractory components of the device forming the main part of the outer shroud;

figure 8 is a perspective view of a leaf spring designed to cooperate with the part shown in figure 7; and

figure 9 shows a cross-sectional view of the component shown in figure 7.

Detailed Description

Referring initially to FIG. 1, an aircraft turbine engine 1 is illustrated in accordance with a preferred embodiment of the present invention. The aircraft turbine engine is preferably a dual-flow twin-shaft turbojet engine.

The turbine engine 1 has a longitudinal centre axis 2 around which the different components of the turbine engine extend. The turbine engine comprises, from upstream to downstream along the main direction 5 of the gas flow through the turbine engine, a fan 3 followed by a gas generator usually consisting of a compressor, a combustion chamber and a turbine. These elements of the gas generator are surrounded by a central casing 6 (also called "core" casing) which radially delimits the interior of the flow compartment 8 a. The compartment 8a is delimited radially outwards by one or more covers comprising an upstream ring 10, which is the only cover shown in fig. 1. The upstream ring 10 is formed in the downstream continuation of the hub 12 of an intermediate casing 14 of the turbojet engine. The intermediate housing 14 also includes an outer shroud 16 located in downstream continuation of the fan housing 18. The intermediate housing also includes outlet guide vanes 20 formed downstream of the fan blades and connecting the hub 12 to the outer shroud 16.

The fan housing 18 and the outer shroud 16 together define a fan compartment 8b in a radially inward direction. This compartment 8b is also delimited in a radially outward direction by one or more covers (not shown), forming part of the turbojet pod. Like the flow compartment 8a, this compartment 8b houses equipment and ancillary equipment, as is well known in the art.

One or more arms 22 are provided to connect the two compartments. For example, there may be two arms 22 mounted on the turbojet engine, arranged at the 12 o 'clock position and at the 6 o' clock position, respectively. The arms 22 are hollow and are used, for example, to circulate electrical cables and/or fluid pipes. More precisely, these arms connect the downstream portion 24 of the outer shroud 16 to the upstream ring 10. To this end, the arms pass through a turbojet fan flow 26, which is delimited in an outward direction by the shroud 16 and by a cover (not shown) located downstream of the shroud, and in an inward direction by the upstream ring 10 of the flow compartment 8 a. The fan flow 26 is in addition to the core engine fan flow 28, which typically passes through the gasifier.

The present invention relates to the engagement between the arms 22 and the outer shroud 16 of the intermediate housing 14. In the remainder of the description, the arm concerned will be the arm at 12 o' clock, but the invention can obviously be applied to any other arm 22 of the turbojet 1.

Referring to fig. 2-6, a preferred embodiment of the outer shroud 16 and its cooperation with the arm 22 will be described. The outer shroud 16 has a circumferential direction 91 and a radial direction 93 relative to the longitudinal center axis 2.

The downstream annular portion 24 of the shroud 16 is provided with a shroud opening 30, similar to a notch that opens in the downstream axial direction. Thus, an opening 30 passes radially through the downstream annular portion 24, the shape of which opening is similar to the shape of the section of the arm 22 to be placed. The openings 30 also pass through a downstream annular edge 32 of the shroud, which is open in the downstream direction, the geometry of which is particularly complex, in particular due to the fact that this edge 32 participates in the structural features of the shroud. The rim 32 has two lips or annular grooves 34 extending radially outwardly, as best seen in fig. 3. The figure also includes an illustration of a radially inner surface 36 of the rim 32 that defines a hollow annular region 38 that opens radially inwardly. The surface 36 is concave, for example having a generally U-shape tapering radially inwardly. The generally U-shape remains shallow, for example, between 3mm and 5mm deep, depending on the large tolerances resulting from the manufacture of the outer shroud 16 by molding.

Thus, the downstream annular edge 32 is not continuous over 360 ° because it is interrupted by the opening 30. Due to this interruption, the edge 32 has two circumferential end surfaces 40 facing each other and spaced apart from each other in the circumferential direction, defining between them an accommodation space 42 which will contain a radially outer end 44 of the arm 22.

In order to form an interface between the downstream portion 24 of the shroud and the arm 22, the shroud further comprises a connection element, in this case a perforated web 50, which is preferably metallic and planar or slightly curved. In the preferred embodiment, the overall shape of the plate 50 is a U-shape or V-shape that generally follows the contour of the opening 30, limits the passage cross-section of the opening, and is circumferentially open at the same height as the opening 30. Perforated plate 50 is secured to downstream portion 24 using conventional attachment means such as bolts 52. Alternatively, the perforated panel 50 may have a shape that follows a closed line, e.g., may have a substantially rectangular shape or a substantially trapezoidal shape.

The plate 50 is radially disposed within the shroud. The plate has two circumferential plate ends 54 which are formed at the two ends of the U-shape or V-shape, respectively, and which in addition extend circumferentially in opposite directions. Each of these two circumferential plate ends 54 is associated with one of the two circumferential end surfaces 40, defining two joining areas 56 sensitive to air and fire respectively. More precisely, steps are taken such that there is no or only little air exchange between the fan compartment 8b and the fan flow 26, in particular to avoid leakage outside the fan flow, and also to prevent a fire induced in the fan compartment 8b from spreading in the fan flow 26.

The invention therefore comprises specific means 60 at each of these two joining zones 56 to satisfy the air-sealing function and the fire-resistant function. In this regard, with respect to air tightness, it may be desirable to limit the leakage to a maximum flow of 0.54g/s, for example. In respect of fire resistance, in addition to complying with the requirements of standards ISO 2685-1998 and AC20-135, the most severe conditions are also considered, namely fire resistance in flight and on the ground. In particular, this means that it is necessary to devise a solution that performs the fire-resistant function under the following conditions:

-flame temperature: 1100 plus or minus 80 ℃;

-amount of vibration: within + -0.4 mm at a frequency of 50 Hz;

-pressure: 0.4 bar in the first 5 minutes of the fire test;

-test time: 15 minutes, divided into 2 phases:

5 minutes: applying positive pressure; and

10 minutes: atmospheric pressure;

self-extinguishment in a limited time.

In the remainder of the description, only one of the two devices 60 will be described, it being understood that these two devices may have the same or similar design, for example designed to be symmetrical with respect to a longitudinal plane of the turbojet engine passing through the axis 2.

Thus, the device 60 will provide air tightness and fire resistance between the fan compartment 8b and the fan flow 26. The device is formed firstly by a part 62 having air-tight and fire-resistant functions and secondly by a leaf spring 64 forcing this part 62 into contact with the outer shroud 16. More precisely, the functional component 62 is divided into two parts, namely a pad 66 and a boss 68, which are fixed to each other. The pad 66 is formed in the hollow annular region 38 of the downstream edge 32. The pad has a contact surface 70 which is of a shape complementary to that of the radially inner surface 36 bounding the region 38, and is therefore convex and has a generally U-shape tapering radially inwardly. The pad 66 functions like a plug and fills all or some of the hollow regions 38 located near the circumferential end surface 40. As best seen in fig. 3 and 6, the contact surface 70 of the pad 66 locally matches the entire surface 36 at least over an angular sector S of the surface, which sector S is centered on the axis 2. Furthermore, at this angular sector S, the pad 66 may have a radially inner portion 74, which radially inner portion 74 extends beyond the hollow annular region 38, in other words, outside this region, as can be seen in fig. 6. This figure shows that for the portion of the pad 66 located radially outward from the boss 68, this portion is terminated by a circumferential end surface 76 formed substantially in the same plane as the associated circumferential end surface 40. The housing space 42 is thus preserved, so that the device 60 does not interfere at all with the subsequent assembly of the outer radial end 44 of the arm 22.

The other circumferential end surface 78 radially inward from the boss 68 is further receded rearward in the circumferential direction 91, thereby forming a recess in which the tip end portion of the circumferential plate end 54 is fitted. The end portion also forms a spot-facing 80 which serves as a seat for the boss 68, on which the boss 68 actually lies. The presence of this spot-facing plane provides the radial outer end support 44 of the arm with a substantially flat surface effectively formed by the radial outer surfaces 82 of the two plate ends 54 and the radial outer surfaces 84 of the two associated bosses 68 located in the spot-facing plane 80 thereof. However, to ensure sealing, the boss 68 projects radially beyond the plate 50 prior to assembly of the arm 22.

The bosses 68 project from the surfaces 76, 78 of the pads 66, extending circumferentially beyond the circumferential end surface 40 of the downstream edge of the shroud 32. The projection is in the direction of the other circumferential end surface 40, so that the boss 68 lies in a countersink 80, which countersink 80 ends near the surface 40, possibly even slightly deeper into the hollow region 38 of the rim 32.

After the arm 22 is assembled on the perforated plate 50 by conventional bolt type means (not shown), the boss 68 is radially clamped between the end portion of the circumferential plate end 54 and the radially outer end 44 of the arm 22.

The boss 68 includes a connection region 88 connected with the pad 66, which is disposed in the circumferential gap J between the end surface 40 of the rim 32 and the outer radial end 44 of the arm 22. In this regard, it should be noted that the end 44 provides continuity of the shape of the downstream edge 32 by reconfiguring the shape in the accommodation space 42 despite the presence of the gap J. However, as best seen in FIG. 4, the end 44 need not be cylindrical like the rim 32, but may have a shape that is adapted to the overall shape of the arm 20.

Returning to the connecting region 88 formed in the gap J, this region has the specific feature of being thinner than the remainder of the boss 68. This reduction in thickness is to give the functional portion 62 flexibility to facilitate pivoting between the boss 68 and the pad 66 on which the force of the leaf spring 64 is exerted.

The spring 64 includes a first end 64a secured to the circumferential plate end 54 by one or more bolts 90 and a second, opposite end 64b secured to a radially inner portion of the pad 66. Thus, the leaf spring 64 urges the pad into contact with the surface 36 in the hollow annular region 38, ensuring a sealing and fire-resistant function. In particular, if the relative positions of the pad 66 and the edge 32 are not satisfactory due to dimensional tolerances, the contact force makes it possible to readjust the relative positions of the pad 66 and the edge 32 and ensure that the pad is squashed in the hollow region. Furthermore, the collapsing force is exacerbated during operation of the turbine engine by pressurizing the air flow circulating in the fan flow of the turbine engine and contacting the air flow with the pad 66.

To assemble the second end 64b on the pad 66, the pad may be provided with a radially inner portion in the shape of a plate 94, as can be seen in fig. 7. The plate 94 is perforated to enable the attachment element to pass through. These channels in the plate open up into wells 96 that extend through the entire thickness of the pad 66, up to the contact surface 70 of the pad 66.

The leaf spring 64 is preferably metallic, for example it may be made of inconel

Is made of alloy. The leaf spring can be obtained by folding/stamping to have the detailed shape shown in fig. 8. The spring has a first bend 95 (in this case S-shaped) from the first end 64 a. The spring then continues with a straight or slightly curved strip 97, which strip 97 will be substantially parallel toBoss 68, perforated plate 50, and ends 64a, 64 b. The strip 97 is then connected to the second end 64b by a second bend 98 (in this case C-shaped). Perforations may be formed in the strip 97 and the ends 64a, 64b to accommodate the longitudinal stiffness and radial stiffness of the spring.

Compression molding techniques are preferably used to fabricate the functional components 62 of the device 60. The functional component may be a simple elastomeric block, but the block is preferably combined with one or more layers having different functions.

In the example shown in fig. 9, the component 62 is formed by superimposing layers made of elastomeric material 99 and preferably of silicone elastomeric material, and a functional layer of fibres, which will now be described, in the radial direction 93.

There will first be one or two glass fabric layers 100a which enhance the rigidity of the component 32 by passing through the pad 66 and boss 68. Two refractory layers 100b are then provided in the pad 66, on each side of the layer 100a, and separated from the pad by a layer 99 of silicon elastomer material. The layer 100b may be made of ceramic fibers, for example. The refractory layer is disposed in the region of the mat most exposed to flame. Since the silicone elastomer material of layer 99 degrades to silica at high temperatures, the mesh of fabric 100b used may retain these degraded particles.

The alternation of layers may be accomplished by one or two aramid fiber layers 100c in the radially outer portion of the mat to enhance the stiffness of the assembly. One of these layers 100c may be coated on the contact surface 70 to limit the risk of damage to the pad 66 by contact with sharp portions of the shield. In all cases, whether or not the contact surface 70 is coated with a protective layer 100c, the contact surface is preferably machined to have a more precise geometry to ensure more reliable contact in the hollow region of the shroud edge.

The layers 99, 100 a-100 c are preferably parallel to each other and substantially parallel to the circumferential direction 91 of the outer shroud 16 on which the device 60 is mounted. The folded orientation of the cloth/fabric 100a to 100c also limits the deformation of the assembly in the circumferential direction 91, keeping the cushion 66 outside the boundaries of the housing space 42 during turbojet operation. When the pad 66 is compressed in the radial direction 93, the functional layers 100a to 100c are subjected to tensile stress, and the stiffness of the functional layers limits the creep of the layer 99 made of silicone elastomer material in the circumferential direction 91.

It is clear that a person skilled in the art can make various modifications to the invention, since it has just been described by way of non-limiting example only, within the scope of the appended claims.