Turbojet turbine housing equipped with movable cooling tube fixing devices

Abstract

The invention relates to a turbomachine housing comprising a wall of revolution equipped with circumferential tubes (11) for blowing air onto this wall to cool it, these tubes (11) being supported by bars (12) fitted to the housing and extending parallel to its wall of revolution, each tube (11) being secured to a bar (12) by a fastening device (13), wherein at least one fastening device (13) comprises a collar (14) clamping a tube (11) and terminating in two tabs extending parallel to each other, each tab having a hole, in which a bolt (16) passes through the holes in the two tabs and a hole in the bar (12), and wherein the hole in the bar (12) is an oblong hole extending parallel to the tube (11). For abbreviated purposes: Figure 3

Description

Title of the invention: Turbojet turbine housing equipped with movable cooling tube fixing devices. Technical field

[0001] The invention relates to the cooling of a turbojet turbine casing, which is ensured by tubes surrounding this casing and diffusing air towards the external face of this casing to maintain it at a desired temperature. PREVIOUS STATE OF THE ART

[0002] A low-pressure turbine casing 1 of a turbojet engine, part of which is shown in [Fig.1], has a wall of revolution 2, which surrounds a turbine comprising a rotor not visible carrying blades movable relative to this casing 1.

[0003] The radial clearance existing between the ends of the moving blades and the inner face of the casing strongly conditions the efficiency of the engine, because the quantity of losses is all the more limited as this clearance is small, given that these losses correspond to fluid which is propelled into the engine without driving the blades.

[0004] During operation, the thermal fluctuations to which the engine components are subjected cause differential expansions of these components, resulting, among other things, in a modification of the radial clearance existing between the ends of the movable blades and the turbine housing.

[0005] For this reason, the crankcase is cooled, so as to limit its radial expansion, in order to ensure that the radial play remains minimal under the different operating conditions of the engine.

[0006] This cooling is ensured by tubes 3 fixed to the external face of the wall of revolution 2, these tubes being supplied with fresh air which they blow onto the external face of the wall 2 to cool it, the fresh air supplying these tubes being taken from a compressor of the engine.

[0007] As can be seen more clearly in [Fig.2], these tubes 3 are carried by bars 4 to which they are fixed by collars 6. These bars 4 extend longitudinally and are themselves fixed to circumferential ribs located at the ends of the wall of revolution 2.

[0008] Each collar 6 surrounds the tube 3 it carries and is fixed to the bar 4 by a bolt 7. Complementarily, each bar 4 is fixed to the ribs of the wall of revolution 2 by at least two bolts located at its ends.

[0009] Given the differential expansions occurring in such an assembly subjected to cycles of temperature variations, it is necessary that the tubes 3 slide in the collars 6 which support them.

[0010] In practice, this slippage leads to wear on the outer face of the tubes at the clamps that secure them, and this wear can lead to tube rupture. It is then necessary to replace the entire cooling system, which represents a significant maintenance cost.

[0011] One possibility to limit this phenomenon is to equip the collars with sheaths made of anti-friction material including PTFE (polytetrafluoroethylene) to reduce the friction forces of the tube relative to the collar in order to decrease wear.

[0012] However, given the high temperature, combined with significant stresses, these materials deteriorate too quickly, so this solution proves unsatisfactory.

[0013] The aim of the invention is to provide a solution to increase the longevity of such an arrangement while limiting the maintenance operations necessary for its proper functioning. Description of the invention

[0014] To this end, the invention relates to a turbomachine casing, comprising a wall of revolution equipped with tubes for blowing air onto this wall in order to cool it, these tubes being carried by bars equipping the casing by extending parallel to its wall of revolution, each tube being secured to a bar by a fastening device, in which at least one fastening device comprises a collar secured to the bar by a bolt, the collar clamping a tube by having two tabs extending parallel to each other, each tab having a hole, the bolt passing through the holes of the two tabs and a hole in the bar, and in which the hole in the bar is an oblong hole extending parallel to the tube.

[0015] With this arrangement, the entire collar is able to slide relative to the bar thanks to the oblong hole, during the displacements of the tube relative to the bar which result from differential expansions, without the tube slipping in this collar.

[0016] The invention also relates to a casing thus defined, in which the bolt includes a screw receiving a self-locking type nut.

[0017] The invention also relates to a housing thus defined, comprising a first washer surrounding a screw of the bolt by being interposed between a head of this screw and the bar, and a second washer surrounding the screw by being interposed between the bar and the lugs of the collar, and in which these washers carry an anti-friction coating.

[0018] The invention also relates to a housing thus defined, in which the bar has faces bearing an anti-friction coating around the oblong hole.

[0019] The invention also relates to a casing thus defined, the antifriction coating of which is deposited with a physical vapor phase deposition process.

[0020] The invention also relates to a housing thus defined, comprising a ring in placed between the two washers, this ring having an external diameter corresponding to the diameter of the oblong hole, and having a thickness substantially greater than the thickness of the bar.

[0021] The invention also relates to a casing thus defined, in which the oblong hole has a length corresponding to the width of the collar's legs.

[0022] The invention also relates to a turbomachine comprising a casing as defined above. Brief description of the drawings

[0023] The [Fig. 1] is a partial perspective view of a portion of a crankcase according to the prior art;

[0024] The [Fig.2] is a partial perspective view of a tube fixing system according to the prior art;

[0025] Fig. 3 is a perspective view of a tube fixing arrangement according to the invention;

[0026] Fig. 4 is a perspective view showing the collar and the bar of the arrangement according to the invention;

[0027] Fig. 5 is a perspective view showing the bar equipped with a screw of the arrangement according to the invention;

[0028] Fig. 6 is a perspective view showing the collar fixed to the bar by bolting in the arrangement according to the invention.

[0029] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0030] The idea behind the invention is to secure a tube to a bar with a collar which clamps the tube without allowing it to slide, but which is secured to the bar with translational mobility along the longitudinal direction of the tube.

[0031] In [Fig. 3], a tube 11 is fixed to a bar 12 by a fastening device 13 comprising a collar 14 clamping the tube 11, while being supported by a face 15 of the bar 12 to which it is secured by means of a bolt 16. The tube 11 is substantially straight at the point of the device 13, and extends in a circumferential direction denoted DC. This circumferential direction extends at a distance from the outer cylindrical wall of the housing, being centered on the axis of this cylindrical wall.

[0032] This collar 14 is formed of a band which may be metallic which is folded over itself to form a body 17 in the shape of a portion of a cylinder which encloses the tube 11, and which has two ends forming two tabs 18 and 19 appearing more clearly on the [Fig.4].

[0033] These two tabs, which are folded against each other, each have a hole 21, and the collar 14 is secured to the bar 12 by means of a bolt 16 passing through the holes in the tabs and an oblong hole 22 formed in the bar 12. This oblong hole 22, which appears in [Fig. 4], extends along the DC direction of the tube. It has a diameter corresponding to the diameter of the holes in the legs, and a length corresponding approximately to the width of the legs along the AX axis.

[0034] As can be seen in figures 5 and 6, the attachment of the collar 14 to the bar 12 is ensured with a bolt 16 comprising a screw 23 engaged in the oblong hole 22 and in the holes of the lugs, this screw having its head 24 located on the face of the bar 12 which is opposite to the face carrying the collar 14.

[0035] The head 24 bears against the face of the bar 12 by means of a first washer 26 engaged around this screw 23, this washer 26 being interposed between the head and the face. A second washer 27 is engaged around the screw 23 to bear against the face 15 of the bar 12, so as to be interposed between this face 15 and the tab 19 of the collar 14.

[0036] The washers 26 and 27 are antifriction type washers, that is to say, having the lowest possible coefficient of friction with the material of the bar 12, so as to allow easy sliding of these washers on the faces of the bar 12 against which they are applied.

[0037] Advantageously, the faces of the bar 12 are themselves covered with an antifriction coating to further reduce frictional forces when these washers slide on the faces of the bar 12. This antifriction coating can be applied with a physical vapor phase deposition process, generally referred to by the acronym PVD ("Physical Vapor Deposition"), which is a metallization process that allows thin layers of material to be deposited under vacuum using vapor on a surface.

[0038] The assembly of the collar 14 consists of engaging the screw 23 carrying the first washer 26 in the oblong hole 22, then engaging the second washer 27 around the screw 23 on the face 15, before engaging the tabs 18, 19 around the screw 23, through the holes 21 by pressing the tab 19 on the second washer 27, after which a nut 28 can be screwed around the screw 23.

[0039] The collar 14 can be brought onto the bar 12 already surrounding the tube 11, or the tube 11 can also be engaged in the collar once the collar has been installed on the bar 12.

[0040] When the assembly is in place, the nut 28 is tightened so that the collar 14 clamps the tube 11 so that it cannot slide along the collar in the DC direction.

[0041] The tightening torque of the nut 28 is chosen to be not too high so that a sliding of the washers on the bar remains possible so that the assembly formed by the collar with the washers and the bolt is mobile in the oblong hole, while being high enough so that the collar clamps in a way sufficient to prevent movement of the tube relative to the collar.

[0042] The nut 28 is advantageously of the self-locking type, also known as a self-locking nut or locking nut. It is also possible to use instead of nut 28 is a nut associated with a locknut tightened against each other to ensure their locking onto the screw.

[0043] Additionally, two Belleville washers may be provided to reduce the forces exerted by the washers 26 and 27 on the faces of the bar 12, so as to facilitate their sliding. These Belleville washers are then interposed respectively between the head 24 and the first washer 26, and between the second washer 27 and the nut 28.

[0044] Another possibility is to provide around the screw 23 a ring having a thickness slightly greater than that of the bar 12, interposed between the washers 26 and 27, this ring having an internal diameter corresponding to that of the screw 23 and an external diameter substantially less than that of the oblong hole 22.

[0045] In this configuration, tightening the nut 28 allows the collar 14 to be firmly clamped around the tube 11 without the washers 26 and 27 clamping the bar 12, which ensures that the assembly formed by the collar 14 and the bolt 16 is freely mobile in the DC direction while remaining attached to the bar 12.

[0046] During operation, when the engine is started, the increase in its temperature, and in particular that of the crankcase, results in an increase in the diameter of the crankcase, which is hot. Since the tubes 11 are traversed by a flow of cooling air, they experience a much smaller temperature increase than the crankcase.

[0047] Given the significant expansion of the housing relative to the tubes, these tubes tend to slide relative to the housing in the circumferential direction. Thanks to the invention, each fastening device 13 slides relative to the bar 12 in the DC direction along the oblong hole 22, while remaining rigidly attached to the tube it supports.

[0048] Under these conditions, differential expansions do not damage the tubes since they do not slip relative to the collars that support them, because it is only the collars that slide relative to the bars to which they are attached.

Claims

Demands

1. Turbomachine housing, comprising a wall of revolution equipped with tubes (11) for blowing air onto this wall in order to cool it, these tubes (11) being supported by bars (12) equipping the housing and extending parallel to its wall of revolution, each tube (11) being secured to a bar (12) by a fastening device (13), wherein at least one fastening device (13) comprises a collar (14) secured to the bar (12) by a bolt (16), the collar (14) clamping a tube (11) and terminating in two tabs (18, 19) extending parallel to each other, each tab (18, 19) comprising a hole (21), the bolt (16) passing through the holes in the two tabs (18, 19) and a hole (22) in the bar (12), and wherein the hole (22) of the bar (12) is an oblong hole extending parallel to the tube (11).

2. Housing according to claim 1, in which the bolt (16) has a screw (23) receiving a self-locking nut (28).

3. Housing according to claim 1 or 2, comprising a first washer (26) surrounding a screw (23) of the bolt (16) by being interposed between a head (24) of this screw (23) and the bar (12), and a second washer (27) surrounding the screw (23) by being interposed between the bar (12) and the lugs (18, 19) of the collar, and in which these washers (26, 27) have an anti-friction coating.

4. Housing according to any one of the preceding claims, wherein the bar (12) has faces (15) bearing an anti-friction coating around the oblong hole (22).

5. Housing according to claim 3 or 4, wherein the antifriction coating is deposited with a physical vapor phase deposition process.

6. Housing according to claim 3, comprising a ring interposed between the two washers (26, 27), this ring having an external diameter corresponding to the diameter of the oblong hole (22), and having a thickness substantially greater than the thickness of the bar (12).

7. Housing according to claim 1, in which the oblong hole (22) has a length corresponding to the width of the tabs (18, 19) of the collar (14).

8. Turbomachine comprising a casing according to any one of the preceding claims.

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