EP3580431B1 - Ring for reducing the overpressure near the upstream seal of a bearing compartment of a turbojet engine - Google Patents

Description

TECHNICAL AREA

The invention relates to the balancing of the pressure in the vicinity of an internal chamber enclosing a lubricated bearing in an aircraft engine of the turbojet type.

STATE OF THE PRIOR ART

A turbojet typically comprises, from upstream to downstream in the direction of the air flow, a low pressure compressor, a high pressure compressor, a combustion chamber, followed by a high pressure turbine and a low turbine. pressure.

In the case of a double-body turbojet, the high pressure compressor and the high pressure turbine form part of a so-called high pressure rotating body which surrounds a low pressure shaft while rotating at a speed different from the latter. The low pressure shaft carries the low pressure compressor and the low pressure turbine.

The low pressure shaft and the high pressure body are carried upstream and downstream by bearings housed in enclosures isolating them from the rest of the engine. Each enclosure contains a bearing in the form of one or more roller bearings interposed between a rotating element such as the shaft or the high pressure body, and a fixed element of the motor.

Each bearing is lubricated by oil circulating in the enclosure which surrounds it, this enclosure being delimited by fixed structural elements of the engine and by the rotating element which passes through it.

More generally, such an enclosure contains at least one bearing while being delimited by walls rotating with respect to one another with a seal between these walls, which limits the leakage section of the enclosure. The oil is moved away from the seal by means of a stream of air entering continuously through this seal, from the outside to the inside of the enclosure.

In the present case, an upstream seal is provided to form a barrier at the junction of the fixed parts delimiting the upstream enclosure with the rotating element, and a downstream seal is provided to form another barrier at the junction of the downstream fixed parts of the enclosure with the rotating element. Thanks to the stream of air entering continuously into each seal, the chamber allows the oil to be circumscribed so that it remains in the vicinity of the bearing without the risk of it polluting the rest of the engine.

Additionally, the air is evacuated out of the enclosure via an oil recovery circuit which is controlled by a volumetric pump pumping both air and oil.

In operation, the pressure prevailing in the enclosure is lower than the pressure surrounding the enclosure, to prevent oil from leaking, because this oil is liable to ignite in hotter parts of the turbojet engine, which would lead to its deterioration. It is this pressure difference which ensures that air continuously enters the enclosure through the seals, and it is continuously evacuated by the pump which thus controls the flow of air passing through the enclosure.

In such an arrangement, a balance is necessary between the pressure difference at the upstream seal and the pressure difference at the downstream seal. If the pressure difference at one of the seals is greater than the pressure difference at the other seal, then only one of the seals is passed by an air stream, so that an oil leak can occur through the other joint.

Thus, in the event of overpressure upstream of the upstream seal relative to the pressure downstream of the downstream seal, this pressure difference tends to cause air to escape from the enclosure via the downstream seal.

In practice, the upstream seal has a significantly larger diameter than the downstream seal. As the air arriving in contact with the rotor in the vicinity of a seal is rotated by this rotor, it undergoes a so-called vortex effect which tends to establish a radial pressure gradient. It follows that the pressure upstream of the upstream seal is more greater than the pressure downstream of the downstream seal, the so-called vortex effect being less important around the downstream seal because its diameter is significantly smaller.

In the patent application FR3016661 for this purpose, provision is made to fix to the fixed casing, around the upstream seal, a plate spaced from the seal along the longitudinal axis, and comprising radial fins delimiting as many radial channels. This arrangement makes it possible to cancel the vortex effect at the level of the upstream seal, and thereby to cancel the pressure difference between the upstream and downstream seals.

In practice, it turns out that mounting this plate and its adjustment is complex and expensive.

The object of the invention is to provide an arrangement making it possible to reduce the pressure in the immediate external environment of the upstream seal which is simple and precise to assemble.

DISCLOSURE OF THE INVENTION

To this end, the invention relates to a turbojet bearing enclosure according to claim 1, comprising in particular a fixed casing through which a rotor passes, this casing comprising a cylindrical end surrounding a seal ensuring the tightness of the cylindrical end with the rotor, this casing being equipped with a ferrule screwed onto its cylindrical end, this ferrule comprising radial channels opening out opposite the seal while being arranged so that a flow of air passing through the seal towards the enclosure originates mainly from these radial channels.

With this arrangement, the mounting of the ferrule is carried out mainly by screwing around the end of the casing, that is to say by adding a limited number of components necessarily positioning themselves precisely with respect to the seal. .

The invention also relates to an enclosure thus defined, comprising a locking ring surrounding the ferrule and comprising on the one hand lugs engaging in corresponding notches in the casing and on the other hand

The invention also relates to an enclosure thus defined, in which the rotor comprises, in the vicinity of the seal, a drip lance located opposite an internal face of the ferrule for centrifuging the oil present on the rotor in the event of seal leakage.

The invention also relates to an enclosure thus defined, in which the ferrule comprises a drainage plate for collecting the oil centrifuged by the drip lance.

The invention also relates to an enclosure thus defined, in which the seal is kept locked axially in the cylindrical end of the casing by the ferrule.

• une étape de positionnement de la bague au niveau de l'extrémité cylindrique de l'enveloppe ;
• une étape d'accostage de la virole entre cette bague et l'extrémité cylindrique de l'enveloppe en vissant un filetage interne de la virole sur un filetage externe de l'extrémité cylindrique ;
• une étape de serrage de la virole jusqu'à mettre en correspondance des encoches frontales de cette virole avec des pattes amont de la bague ;
• une étape de rabattement des pattes amont dans les encoches frontales.

The invention also relates to a method of mounting a ferrule fitted to an enclosure thus defined, comprising:

• a step of positioning the ring at the cylindrical end of the casing;
• a step of docking the ferrule between this ring and the cylindrical end of the casing by screwing an internal thread of the ferrule onto an external thread of the cylindrical end;
• a step of tightening the ferrule until the front notches of this ferrule match upstream tabs of the ring;
• a step of folding the upstream tabs into the front notches.

• une étape d'accostage de la virole portant la bague en vissant un filetage interne de la virole sur un filetage externe de l'extrémité cylindrique ;
• une étape de serrage de la virole jusqu'à mettre en correspondance des encoches frontales de cette virole avec des pattes amont de la bague ;
• une étape de rabattement des pattes amont dans les encoches frontales.

The invention also relates to a method of mounting a ferrule fitted to an enclosure thus defined, comprising:

• a step of docking the ferrule carrying the ring by screwing an internal thread of the ferrule onto an external thread of the cylindrical end;
• a step of tightening the ferrule until the front notches of this ferrule match upstream tabs of the ring;
• a step of folding the upstream tabs into the front notches.

The invention also relates to a turbomachine comprising a bearing enclosure thus defined.

The invention also relates to a turbojet comprising a turbomachine thus defined.

BRIEF DESCRIPTION OF THE DRAWINGS

• The figure 1 is a schematic half-view in section showing the assembled rotor and stator elements of a turbojet at the level of a rear bearing of a high pressure body with its lubrication chamber;
• The figure 2 is a schematic half-view in section showing the rotor and stator elements during assembly of a turbojet at the level of a rear bearing of a high pressure body with its lubrication chamber;
• The figure 3 is a half-sectional view of an upstream seal of a lubrication chamber;
• The figure 4 is a sectional view showing in detail the shape of the section of the ferrule according to the invention;
• The figure 5 is a half-sectional view of an upstream seal of a lubrication chamber during assembly of a ferrule according to the invention;
• The figure 6 is a half-section view of an upstream seal of a lubrication chamber equipped with a ferrule according to the invention;
• The figure 7 is a perspective view of a locking ring shown alone for the ferrule according to the invention;
• The figure 8 is a perspective view of a ferrule shown alone in accordance with the invention;
• The figure 9 is a partial view showing a ferrule equipped with its locking ring according to the invention.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

On the figure 1 , a rear portion 1 of a high pressure body comprises a rotor journal 2 which carries from upstream to downstream a high pressure turbine disc 3, a rotor element 4 inside the upstream seal, an inner ring 6 of a bearing with rollers 7, a wiper holder 8 and a terminal nut 9. The terminal nut 9 maintains in position along the axis of rotation AX of this high pressure body, the rotor 4, the ring 6 and the wiper holder 8 which are thus clamped between an external shoulder 11 of the journal 2 located immediately downstream of the turbine disk 3, and this terminal nut 9 which is at the end of the high pressure body.

This rear portion 1 of the high pressure body is surrounded by a fixed casing 12, which is here a so-called inter-turbine casing, that is to say located along the axis AX between the high pressure turbine 3 and a turbine. low pressure not shown in the figure.

This casing 12 comprises a casing 13 which generally surrounds the inner element 4 of the upstream seal, the bearing 7 and the wiper holder 8, this casing 13 being connected by a radial structure 14 to a fixed structural element 16 of the engine.

The upstream end of this casing 13 receives a circumferential element 17 of the upstream seal which surrounds the inner element 4, to jointly constitute the upstream seal 18. It carries at its downstream end a ring 19 of abradable material which surrounds the wipers 21 of the wiper holder 8 to form therewith the downstream seal 22.

In the example of the figures, the upstream seal is a segmented radial seal, and the downstream seal is a labyrinth-type seal, comprising circumferential wipers whose radial ends run along the internal face of the abradable ring 19.

Other configurations are possible, the segmented radial seal and the labyrinth seal can be reversed; a segmented radial seal or labyrinth seal mountable at each seal; at least one of the seals possibly being a floating ring seal.

The bearing also comprises, halfway between the ends of the casing, an internal structure 23 carrying an outer ring 24 of the roller bearing 7, this structure 23 extending radially towards the inside of the casing 13.

The casing 13 with its upstream and downstream seals 18 and 22 surrounds the journal 2 in order to define with the latter the enclosure 26 which surrounds the bearing 7 to ensure its lubrication.

As shown schematically on the figure 2 , it should be noted that for assembly reasons, the diameters of the rotor 2, 3 and of the casing 13 are increasing, here from downstream to upstream. Thus, in the example of the figures, the diameters of the rotor and of the casing at the level of the upstream seal 18 are greater than the diameters of the rotor and of the casing at the level of the bearing 6, which are themselves greater than the diameters of the rotor and casing at the downstream seal 22.

This increase in diameters, also called stepped dimensioning, allows the engagement of the rotor in the stator, as shown schematically in the figure. figure 2 . The rotor is thus engaged in the stator by being moved from upstream to downstream, without interference thanks to the fact that the diameters are decreasing from upstream to downstream.

It follows that in such an arrangement, the upstream and downstream seals necessarily have significantly different diameters, so that the pressure around these seals is necessarily different taking into account the vortex effect. In the example of the figures, the upstream seal 18 thus has a diameter much greater than the downstream seal 22, so that it is subjected to an external pressure greater than the external pressure of the downstream seal.

Given its large diameter, the upstream seal is here a segmented radial seal whose structure appears more clearly on the figure 3 , this upstream seal 18 corresponds to that described in the patent document EP1055848 . It comprises a ring of segments 27 held together by a circumferential spring 28 and surrounding an upstream end 29 of the inner element 4 of the rotor. The seal is formed at the rotary sliding contact being established between the external face of the rotating end 29, and the internal face of the ring of fixed segments 27 which surrounds this rotating end 29.

The ring 27 is held in a fixed support 31 which is nested and held in an upstream cylindrical end 32 of the casing 13. This support 31 has a cylindrical internal face extended by an internal shoulder defining a flat face against which it bears. the ring 27. A stop ring 33 forming an internal hoop is engaged and locked in an internal groove of the cylindrical face of the support 31, at a distance from its shoulder face.

The ring 27 carries an additional crown 34 to which it is linked by axial springs, to constitute an assembly extending along the axis AX between the stop ring 33 and the shoulder. Thanks to the axial springs, the segment 27 is kept pressed against the shoulder of the support 31, the additional ring 34 resting against the stop ring 33, as visible on the figures. figures 3 to 5 .

As visible on the figure 3 , the upstream cylindrical end 32 of the casing 13 comprises on its outer face a thread marked 36, intended to receive a ferrule 37 having the general shape of a crown, as visible on the figure 6 .

This ferrule comprises 37, seen in section along a plane passing through its axis of revolution AX, comprises a body 38 extended along the axis AX by a threaded cylindrical ring 39, and extended internally by a conical wall 41.

As visible on the figure 4 , the body 38 has a rectangular outline delimiting in particular a radially outer cylindrical face 42 which is extended by the ring 39, and a flat front face 43, of normal orientation to the axis AX, of which the wall 41 constitutes an extension. This body also defines a planar downstream face 44 parallel to the front face 43, and a radially internal face 46.

The wall 41 starts from the edge joining the faces 43 and 46, it has a taper of the order of thirty degrees, and it extends opposite the internal face 46 to extend over approximately half. the length of this face 46 along the axis AX.

As seen more clearly on the figure 8 , the crown-shaped body 38 is crossed by a series of radial channels, identified by 47 contiguous to each other, and each placing the external face 42 in communication with the internal face 46.

When mounted, this ferrule 37 is held tight on the end 32 by a sheet metal locking ring 48 which appears alone on the figure 7 . This locking ring 48 has the general shape of a ring comprising an upstream edge 49 and a downstream edge 51, here with eight downstream tabs 52 projecting from its downstream edge, and six upstream tabs 53 projecting from its upstream edge, all of these tabs. being regularly spaced around the axis of revolution AX. In general, the ring comprises at least two downstream lugs and at least two upstream lugs.

Additionally, the casing 13 has a circumferential edge 54 located opposite the ring 39 when the ferrule is mounted, that is to say set back from the end 32, and which has eight notches. not visible in the figures and each intended to receive one of the downstream tabs 52.

Similarly, the ferrule 37 comprises at least two notches, here six notches identified by 56 which are each intended to receive one of the upstream tabs 53, the number of notches being identical to the number of tabs. Each notch 56 is formed at the edge joining the front face 43 and the outer radial face 42 of this ferrule, each notch being located between two radial channels 47, and also allowing the tightening of the ferrule with a suitable tightening tool.

The locking ring 48 has an internal diameter corresponding to the diameter of the external radial face 42 of the ferrule, so as to surround it when the assembly is in place as in the figure 6 .

The assembly of the assembly may consist in installing the ring 48 in position at the level of the cylindrical end 32 of the casing 13, the tabs 53 then being flat. The ferrule 37 is then docked between this ring 48 and the casing 13 by screwing the internal thread 40 of this ferrule around the external thread 36 of the end 32. Once the ferrule is pressed, having its face 44 in abutment on an upstream end of the support 31, it is tightened until its front notches 56 are facing the upstream tabs 53. The tabs 53 can then be folded towards the axis AX to be folded into the notches 56, so as to completely block the ferrule 37 in rotation relative to the end 32 on which it is clamped, which corresponds to the situation of figures 6 and 9 .

This assembly requires mounting the ferrule 37 between the end 32 and the ring 48 with a small footprint and alignment tolerances, but the ring and the ferrule are mounted relative to the housing.

Another possibility is to mount the ring 48 around the ferrule 37, to screw the ferrule onto the end 32. When the ferrule is pressed, having its face 44 resting on an upstream end of the support 31, it is tightened until 'to put its front notches 56 vis-à-vis the upstream tabs 53. The upstream tabs 53 can then be folded down to ensure complete locking.

This assembly requires the handling of a sub-assembly formed by the ferrule and the non-integral ring, but is simpler in docking.

In this arrangement, the ferrule 37 covers the upstream edge of the end 32 extending radially towards the axis AX to radially cover the majority of the seal 18. Concretely, the internal diameter of this ferrule 37, corresponding to the internal diameter of the wall 41 is very slightly greater than the external diameter of the rotating end 29 in order to allow the mounting of this ferrule 37.

For this purpose, the rotary end 29 has a terminal edge 57 extending radially at a point, and the outer diameter of which is slightly less than the diameter of the free edge 58 of the wall 41, while being located at a short distance from this edge. free 58 along the axis AX.

The annular space located between the terminal edge 57 and the free edge 58 which constitutes an air passage towards the seal 18 is thus provided very small radially and axially, so as to limit the flow rate through this passage.

Conversely, the radial channels 47 have large passage sections so that the passage of air towards the seal 18 occurs mainly via these radial channels, that is to say without undergoing a vortex effect and thereby even without increased pressure.

Furthermore, the terminal edge 57 of the rotor ends in a point oriented radially outwards to constitute a drip lance making it possible to avoid dispersion of oil in the air flow, in the event of an oil leak from the air flow. enclosure 26 through the upstream seal 18.

More concretely, in the event of total or partial failure of the seal 18, a drop of oil running along the outer face of the rotor towards the end 29 of this rotor meets the drop lance 57 which constitutes a radial protuberance in its path. Taking into account the high speed of rotation of the rotor, this drop is then centrifuged by the droplet lance 57, so that it leaves the rotor to join the internal face 46 of the ferrule 37 and the conical wall 41 which constitutes a drainage plate. , which are stationary with the stator.

At this stage, the drop of oil can trickle down along the internal face 46 to reach the bottom of the ferrule and then a lower part of the engine, which allows it to be evacuated. In the case of a drop of oil centrifuged in the upper part of the internal face 46, it can, if necessary, detach itself from this internal face towards the rotor in order to be centrifuged again, so that it ultimately reaches the lower part of the shell and of the engine to be evacuated there.

The drop lance 57 thus makes it possible to confine the oil generated by a leakage from the seal 18 in the region of the shell 37 to finally evacuate it, so as to avoid and at the very least limit a dispersion of this oil in the flow of water. air passing through the engine.

Additionally, an additional casing carried by the rotor may be provided to frontally cover the ferrule 37 and the seal, extending to surround them, so as to further limit the risks of oil dispersion towards the air flow.

Claims (9)

1. Turbojet bearing housing (26) including a fixed envelope (13) traversed by a rotor (2, 4), this envelope (13) including a cylindrical end (32) having an outer thread and surrounding a seal (18) ensuring the leak tightness of this cylindrical end (32) with the rotor (2, 4), this envelope (13) being equipped with a shell (37) having an inner thread screwed onto the outer thread of the cylindrical end (32), this shell (37) including radial channels (47) emerging opposite the seal (18) while being arranged so that an air stream traversing the seal (18) towards the housing mainly comes from these radial channels (47) in which the seal (18) is maintained axially locked in the cylindrical end (32) of the envelope (13) by the shell (37).
2. Housing according to claim 1, including a locking collar (48) surrounding the shell (37) and including on the one hand tabs (52) engaging in corresponding notches of the envelope (13) and on the other hand tabs (53) pulling down into corresponding notches (56) of the shell (37) to rotationally lock this shell with respect to the envelope (13).
3. Housing according to claim 1 or 2, in which the rotor (2, 4) comprises in the vicinity of the seal (18) a drop throwing device (57) situated opposite an inner face of the shell (37) to centrifuge the oil present on the rotor in the event of leakage of the seal (18).
4. Housing according to claim 3, in which the shell (37) comprises a drainage sheet (41) to collect the oil centrifuged by the drop throwing device (57).
5. Housing according to claim 1 or 2, in which the seal (18) is blocked axially in the cylindrical end (32) of the envelope (13) by the shell (37).
6. Method for mounting a shell (37) equipping a housing according to claim 2, including:

   - a step of positioning the collar (48) at the level of the cylindrical end (32) of the envelope (13);

   - a step of docking the shell (37) between this collar (48) and the cylindrical end (32) of the envelope (13) by screwing an inner threading (40) of the shell (37) onto an outer threading (36) of the cylindrical end (32);

   - a step of tightening the shell (37) until frontal notches (56) of this shell (37) are placed in correspondence with upstream tabs (53) of the collar;

   - a step of pulling down the upstream tabs (53) into the frontal notches (56).
7. Method for mounting a shell (37) equipping a housing according to claim 2, including:

   - a step of docking the shell (37) bearing the collar (48) by screwing an inner threading (40) of the shell (37) onto an outer threading (36) of the cylindrical end (32);

   - a step of tightening the shell (37) until frontal notches (56) of this shell (37) are placed in correspondence with upstream tabs (53) of the collar;

   - a step of pulling down the upstream tabs (53) into the frontal notches (56).
8. Turbomachine including a bearing housing according to one of claims 1 to 5.
9. Turbojet including a turbomachine according to claim 8.

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