Abstract:
A sealing device for a chamber including at least one rotary member and at least one static member of a jet engine and can contain a lubricating oil droplet suspension. The sealing device includes at least one brush seal that includes juxtaposed strands and is set to ensure sealing between at least one rotary member and at least one stationary member, a mechanism to recover part of the oil suspended within the inner space of the chamber, and a mechanism to deliver the recovered oil. The delivery mechanism is set up to generate a flow of oil along the strands of the brush seal, the oil flow being oriented in the direction of the rotary member. The brush seal thus provides better resistance to coking.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a turbojet and in particular a sealing device for a turbojet oil enclosure. 
     2. Description of the Related Art 
     A turboshaft for an aircraft generally comprises, arranged in the direction of the gas flow: a fan, one or more compressor stages, for example a low-pressure compressor and a high-pressure compressor, a combustion chamber, one or more turbine stages, for example a high-pressure turbine and a low-pressure turbine, and a gas exhaust nozzle. Each compressor may be associated with a turbine, the two elements being linked by a shaft, thereby forming, for example, a high-pressure core and a low-pressure core. 
     Turbojets generally have, substantially around the upstream extremity of the high-pressure core, an “upstream enclosure” containing bearing and gear members. They also generally have, substantially around the downstream extremity of the high-pressure core, a “downstream enclosure” containing oil-lubricated bearing and gear members. The oil, projected by these rotary parts , forms a mist (or suspension) of suspended droplets within the enclosures. Furthermore, they are traversed by a gas flow (air), in particular for ventilation purposes. To prevent the oil from being carried out of the enclosures by the gas flow, the gases are evacuated into “oil separators” generally formed by radial chimneys arranged in the low-pressure shaft, the oil being captured on the walls thereof and returned to the corresponding enclosure by centrifugal force. The oil separators communicate with a degassing tube (also rotary) concentric to the low-pressure shaft and in the enclosure of which the gases are carried from the oil separators to the outlet of the degassing tube where they are ejected, generally around the turbojet nozzle. 
     The upstream and downstream enclosures are formed and delimited by the walls of the stationary structure of the turbojet, but also by the walls of the rotary elements. They must enable the passage of a gas flow, but retain as much oil as possible therein, and for this reason the seal between the stationary elements and the rotary elements of an oil enclosure is a particularly delicate problem. 
     Traditionally, the seal is effected using a labyrinth joint, i.e. formed by ribs rigidly connected to a rotary part and an abradable material rigidly connected to a stationary part against which the ribs rub. This rubbing occurs with a given clearance to enable the passage of a gas flow coming from the low-pressure or high-pressure compressors; these gases oppose the egress of oil through the labyrinth joint; the flow rate thereof is dimensioned to be sufficient at slow speeds and is therefore excessive in other flight phases (in which the flow rate of the air aspirated by the fan of the turbojet is greater). This excessive flow in the other flight phases has at least two detrimental effects: firstly, it proportionately reduces the efficiency of the engine and, secondly, it tends to draw a greater quantity of oil out of the enclosure, around the oil separators. 
     It has therefore been envisaged to replace the labyrinth joints with “brush” seals, i.e. having a plurality of juxtaposed, substantially radial fibers that are attached to a stationary part, the free extremities of which are in contact with a rotary part (or very close thereto), the fibers being preferably slightly inclined in the direction of rotation of the rotary part; the fibers of the brush seal may for example be made of carbon. Such a device is in particular described in patent application US 2004/0256807 filed by General Electric. 
     Such brush seals have the advantage of needing to be traversed by a gas flow having a flow rate that is not too high to guarantee the oil seal thereof On the other hand, they have the drawback of tending to cause coking of the oil they come into contact with. Coking is the transformation of oil into a solid deposit; it is caused by reheating oil stuck to the carbon fibers; it reduces the effectiveness of the brush seal. Furthermore, the rubbing of the bristles on the track of the rotary part designed to touch the extremities thereof causes them to wear and therefore also reduces the effectiveness thereof over time. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is intended to mitigate these drawbacks and in particular to propose a sealing device for a turbojet oil enclosure that is effective and that has features that are durable over time. 
     Accordingly, the invention relates to a sealing device for an enclosure that is formed by at least one rotary member and at least one static member of a turbojet and that is intended to contain a suspension of lubricating oil droplets, the sealing device comprising at least one brush seal, with juxtaposed strands, arranged to create a seal between at least one rotary member and at least one stationary member (from the rotary member or members and the stationary member or members presented above), the device being characterized in that it comprises means for recovering some of the oil suspended within the internal volume of the enclosure and means for channeling said recovered oil that are arranged such as to generate an oil flow along the strands of said brush seal towards the rotary member. 
     The invention creates a flow of oil along the strands of the brush seal, which guarantees a recirculation of the oil in contact therewith, since said oil is drawn along the strands. The residual oil is therefore drawn by the oil supplied and does not have time to degrade; coking phenomena are thereby reduced, which prevents the strands from sticking together, thereby improving both the effectiveness and longevity of the seal. Furthermore, the strands are lubricated and therefore less degraded by the rotary contact thereof with the members of the turbojet. 
     The invention is particularly notable in that it addresses a problem related to the presence of oil on the joint precisely by supplying said joint with oil; thus, although it could be considered that the best way to protect the joint from oil would be to improve the oil seal thereof, the oil seal of the joint is in fact improved using oil. 
     The means for channeling the recovered oil can be dimensioned to control the oil flow along the strands of the brush seal. 
     The oil flow can thereby be arranged to reduce the temperature of the brush seal, thereby further reducing coking phenomena. 
     In one embodiment, the device has means for returning the oil to the interior of the enclosure after it has flowed over the strands. This encourages the oil to flow, the oil being drawn between the means for channeling the recovered oil and the means for evacuating the oil. 
     In one embodiment in this case, the device is arranged such that the return means include a gas flow passing through the brush seal. The gas-flow evacuation effect may be reinforced by a centrifugal force related to the rotation of the rotary parts. 
     Preferably, if the strands of the brush seal (more specifically the free extremities of the strands thereof) are intended to rub against a track of an opposing part, said channeling means are arranged such that the oil flow along the strands supplies oil to the track. The friction zone between the seal and the track is therefore lubricated, which reduces the wear of these parts. 
     Also preferably, as the lubricating oil is degraded by temperature (oxidation and coking), it includes at least an additive designed to prevent coking. Such an additive is known, but it loses effectiveness over time. The oil supply provided for in the invention recirculates the oil (and therefore the additive thereof), preserving the anti-coking properties thereof. 
     In a preferred embodiment, the means for channeling the recovered oil include at least one gravitational channel for guiding the oil from the recovery means to the brush seal. 
     In an embodiment in this case, as the seal includes an at least partially hollow torus (i.e. having an internal volume) to which the strands are attached, the channeling means include at least one channel for guiding the oil from the recovery means to the interior of the torus (i.e. into the internal volume thereof) to impregnate the strands where they are attached to the torus. This further improves lubrication of the strands of the seal. 
     In one embodiment, the oil recovery means include, in the top of the turbojet, a gravitational recovery tank for the oil in the oil suspension. 
     In one embodiment, the oil recovery means include at least one oil retention rib combined with a slot for guiding the oil from the rib to the brush seal (the slot in this case forming the guide channel). 
     According to a preferred embodiment, the means for channeling the recovered oil include an oil source specific to the brush seal, i.e. dedicated to supply it. 
     The invention also concerns a turbojet with a sealing device having the features of the sealing device disclosed above. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The description can be better understood from the description below of the preferred embodiment of the turbojet according to the invention, with reference to the attached drawings, in which: 
         FIG. 1  is a global axial profile of the turbojet according to the invention; 
         FIG. 2  is a schematic axial profile of the upstream enclosure of the turbojet in  FIG. 1 , in a first embodiment of the invention; 
         FIG. 3  is a partial cross section of the upper part of the enclosure in  FIG. 2 ; 
         FIG. 4  is a schematic axial profile of the upstream enclosure of the turbojet in  FIG. 1 , in a second embodiment of the invention; 
         FIG. 5  is a schematic axial profile of the upstream enclosure of the turbojet in  FIG. 1 , in a third embodiment of the invention; 
         FIG. 6  is a partial cross section of the upper part of the enclosure in  FIGS. 5  and 
         FIG. 7  is a schematic axial profile of the upstream enclosure of the turbojet in  FIG. 1 , in a fourth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , a turbojet  1  according to the first embodiment of the invention conventionally comprises a fan  1   a , a low-pressure compressor  1   b , a high-pressure compressor  1   e , a combustion chamber  1   d , a high-pressure turbine  1   e , a low-pressure turbine  1   f  and an exhaust nozzle  1   g . The high-pressure compressor  1   e  and the high-pressure turbine  1   e  are joined by a high-pressure shaft  2  and form therewith a high-pressure core. The low-pressure compressor  1   b  and the low-pressure turbine if are joined by a low-pressure shaft  3  and form therewith a low-pressure core. 
     The turbojet  1  comprises static (or stationary) members and rotary members, forming the different functional elements above, in a known manner. 
     The turbojet  1  has, close to the upstream extremity of the high-pressure core, an “upstream enclosure”  4  containing the bearing and gear members and, near to the downstream extremity of the high-pressure core, a “downstream enclosure”  5  containing bearing and gear members. These enclosures  4 ,  5  are conventionally referred to by the person skilled in the art as oil enclosures  4 ,  5  as they contain a suspension of oil droplets, as explained below. 
     The turbojet  1  extends globally along an axis A which is the axis of rotation of the rotary members thereof and in particular the axis of the low-pressure and high-pressure shafts  3 ,  2 . In the remainder of the description, the concepts longitudinal, radial, internal and external shall relate to this axis A. 
     The different embodiments of the invention are described in relation to the upstream enclosure  4 , but it shall be understood to apply equally to the downstream enclosure  5  and in general to any other enclosure containing or housing members with an oil suspension for the lubrication thereof. 
     The upstream enclosure  4  defines a volume in which are housed the bearing and gear members. In this case, the upstream enclosure  4  houses a first bearing  6 , a second bearing  7  and a third bearing  8 , these bearings  6 ,  7 ,  8  each having an internal ring  6   a , rigidly connected to the low-pressure shaft  3 , an external ring  6   b , rigidly connected to the stationary structure of the turbojet and rolling means  6   c  such as balls or rollers between the rings  6   a ,  6   b  to enable the rotation of the internal ring  6   a  in relation to the external ring  6   b  (only rings  6   a ,  6   b  and rolling means  6   c  of the first bearing  6  have been referenced in the figures). The upstream enclosure  4  also contains the internal extremity  9  of an output shaft  10  connected to the high-pressure shaft  2 , the external extremity of this shaft  10  being connected to an accessory gearbox (not shown), commonly referred to as an AGB, for Accessory Gear Box, by the person skilled in the art. 
     The upstream enclosure  4  defines an internal volume V delimited by stationary members and rotary members, more specifically by the walls of the stationary members and the rotary members. In this case, the upstream enclosure  4  is notably delimited on the internal side by the upstream extremity portion of the low-pressure shaft  3  and the parts rigidly connected to this shaft, on the upstream external side by a housing  12  rigidly connected to the stationary structure of the turbojet and supporting the external ring  6   b  of the first bearing  6  and on the downstream side by a housing  13  partially delimiting the internal envelope of the gas path (between the low-pressure compressor  1   b  and the high-pressure compressor  1   e ). 
     The bearings contained in the internal volume V of the enclosure  4  are supplied with lubricating oil in a known manner; the oil, projected by the parts in rotation, forms a mist (or suspension) of suspended droplets within the enclosure  4 . This oil supply to the bearings of the enclosure  4  may be accomplished in different ways. In this case, the internal ring  6   a  of the first bearing  6  is provided with orifices (not shown) to enable oil to enter the bearing  6  before moving, by centrifuging, towards the internal volume V of the enclosure  4 , as shown schematically by the arrow F 1  in  FIG. 2 ; the oil is projected into the enclosure  4  and more specifically centrifuged when the internal ring  6   a  rotates. In another embodiment not shown, one or more oil supply sprinklers may be arranged near to the rolling means  6   c  of the first bearing  6 , in a known manner. 
     The upstream enclosure  4  also includes, on the upstream side thereof, a seal  14  used to provide the oil seal of the enclosure  4 , between the rotary members and static members thereof, in this case between the housing  12  and the low-pressure shaft  3 , more specifically between the housing  12  and an intermediate part  15  rigidly connected to the low-pressure shaft  3 , as detailed below. This seal  14  is a brush seal  14 . It includes a ring torus  16 , rigidly connected to a wall of the stationary structure of the turbojet (in this case rigidly connected to the housing  12  of the stationary structure), to which are attached the strands  17  or bristles  17 , in this case made of carbon, arranged to come into contact with a wall of a rotary member of the turbojet. The torus  16  is rigid and for example made of a metal, in this case steel. More specifically in this case, the housing  12  of the stationary structure has, in the upstream portion thereof, a groove in which the torus  16  is seated, this latter being locked in position by a nut  18  in a known manner. 
     The enclosure  4  is located, on the upstream side, close to the upstream extremity of the low-pressure shaft  3 . The internal ring  6   a  of the first bearing  6  is attached directly to the low-pressure shaft  3 . This latter has, upstream of this internal ring  6   a  and separated therefrom, a radial shoulder  3 ′ forming a rim towards the external side. An intermediate part  15  performing a plurality of functions is attached between the internal ring  6   a  and the radial shoulder  3 ′. In this case, this intermediate part  15  is a one-piece part; as a whole, it is a core of revolution; it comprises a first annular longitudinal portion  15   a , on the downstream side, prolonged by a radial portion  15   b  from which are arranged two portions, namely a radial flange  15   c  and a second annular longitudinal portion  15   d , the upstream extremity  15   e  of which is attached to the low-pressure shaft  3 . The first longitudinal downstream portion  15   a  of the intermediate part  15  is attached between the internal ring  6   a  and the shoulder  3 ′ of the low-pressure shaft and is used to attach the intermediate part  15 . The radial portion  15   b  thereof extends along the radial wall of the shoulder  3 ′ and beyond the external side thereof. The radial flange thereof  15   c  forms a screen for the oil supplying the enclosure  4  coming from the internal ring  6   a  of the first bearing  6 , to prevent it from being projected directly onto the seal  14 ; the person skilled in the art conventionally refers to such a flange  15   c  forming a screen for oil droplets as an “oil slinger”. In this case in particular it enables the supply of oil to the seal  14  to be controlled. The second annular longitudinal portion  15   d  has an external surface  15   f  that forms a track for the strands  17  of the brush seal  14 , i.e. this surface  15   f  is arranged such that the free extremities of the strands  17  come into contact therewith; it will be noted that the intermediate part  15  is rigidly connected to the low-pressure shaft  3  and therefore driven in rotation therewith, while the brush seal  14  is static since it is rigidly connected to the housing  12  of the stationary structure. The strands  17  of the seal  14  are preferably inclined in the transversal plane in the direction of rotation of the low-pressure shaft  3 , in a known manner, to accompany the rotation of the track  15   f  with which they are in contact. 
     According to the invention, the seal  14  is supplied with lubricating oil h to generate, guide and draw an oil flow along the strands  17  thereof; thereby guaranteeing a flow of oil along the strands  17  and thus guaranteeing the long-term effectiveness of the seal  14 , as explained above in the introduction of the description. 
     In the first embodiment shown in  FIGS. 2 and 3 , the turbojet  1  includes a gravitational recovery tank  19  for the oil h in the oil suspension of the enclosure  4 . This tank  19  is therefore intended to capture or recover some of the oil in suspension in the internal volume V of the enclosure  4 . The turbojet  1  also has channels  20  for carrying and guiding the oil from the tank  19  to the brush seal  14  and more specifically to the strands  17  thereof. 
     The top and the bottom, as well as the concepts of upper and lower, are defined in relation to the vertical, this latter being defined, for a turbojet, as the vertical direction in the assembly position thereof on a stationary airplane, i.e. an airplane placed on a horizontal plane. A vertical axis B is drawn on the figures. The axis A of the turbojet  1  is therefore horizontal in the figures. 
     More specifically, with reference to  FIG. 3 , the tank  19  is placed at the top of the turbojet  1 . It takes the form of a enclosure closed on all of the faces thereof except the upper face thereof More specifically, it is formed by a downstream wall  19   a  facing an upstream wall  19   b  formed by an internal portion of the housing  12  of the stationary structure, by a lower (internal) wall  19   c  formed by a redirection (towards the downstream side) of the housing  12  of the stationary structure, linking the upstream walls  19   b  and  19   a , and by two sidewalls  19   d ,  19   e  located on either side. The upper face thereof  19   f  is open. The downstream wall  19   a  and the side walls  19   d ,  19   e  are vertical flat walls, the lower wall  19   c  matches the annular shape of the housing and the open upper face  19   f  is horizontal. 
     The oil is projected against the internal surface of the housing  12  of the stationary structure, as shown schematically by the arrow F 1 . Some of the oil is in suspension in the enclosure  4  and on the different members that it contains; some of the oil flows on the internal surface of the housing  12  of the stationary structure and flows by gravity from the top of the turbojet  1  downwards; indeed, the housing  12  is conical and the diameter thereof decreases from the downstream side to the upstream side, thereby enabling such a flow. Some of this oil therefore runs into the tank  19  where it is received, forming a bath of oil h. 
     The channels  20  extend radially and lead firstly to the tank  19  and secondly to near the external side of the strands  17  of the brush seal  14 , the channels  20  surrounding the torus  16  to guide the oil towards the external side of the strands  17 . In this case, and more specifically, the turbojet  1  has two channels  20  located on either side of the tank  19 , as shown in  FIG. 3 . The oil h contained in the tank  19  flows by gravity through the channels  20  and supplies an annular chamber  22  (on 360°) arranged between the internal part of the downstream wall  19   a  forming the tank  19  and the internal part of the torus  16  of the brush seal  14 ; the annular chamber  22  is “flooded” with oil, i.e. the volume thereof is completely filled with oil. A plurality of small channels  23 , in this case equidistant lunules, for carrying oil from the annular chamber  22  to the strands  17 , are formed and enable the distribution of the oil along the strands  17 , through the joint effects of gravity and capillarity. The flow rate of the oil h supplying the brush seal  14  is regulated and defined by the volume of the tank  19  and the dimensions of the annular chamber  22  and of the channels  20 ,  23 . The oil flows along the strands  17  of the seal  14  to the track  15   f  with which these strands  17  are in contact. 
     Furthermore, the brush seal  14  is arranged to enable the passage of a gas flow (air) from the exterior to the interior V of the enclosure  4 , as symbolized by the arrow F 2 . This gas flow prevents oil from leaking out of the enclosure  4 , in a known manner. Furthermore, this gas flow forms a means for evacuating the oil once it has reached the internal extremity of the strands  17  of the seal  14  and the track  15   f , thereby encouraging the oil to flow along the strands  17 . More specifically, the gas flow is combined with the oil slinger  15   c  to evacuate the oil h: the oil is carried by the gas flow F 2  to the oil slinger  15   c  by which it is driven by centrifuging into the enclosure  4  where it is again suspended in the form of droplets. The gas flow F 2  flows through the enclosure  4  and escapes through oil-removal chimneys or oil separators (not shown but known and already presented in the introduction of the description) before being guided into a degassing tube  21  that extends concentrically to the low-pressure shaft  3 , in a known manner. 
     It will be noted incidentally that if the airplane were to adopt a position in which the tank  19  was no longer oriented horizontally, oil could leak from this latter; this may apply for example, in a military application, to an inverted flight of a fighter plane. Where this occurs, it would not have problematic consequences since such situations do not usually last long, and a temporary interruption of the oil supply to the seal is not problematic. 
     Other embodiments of the turbojet according to the invention are described below. These embodiments are very similar to the preceding embodiment, with only the elements related to the oil supply to the brush seal  14  being changed. This is why the references used for the elements of the turbojets in  FIGS. 4 to 7  having identical, equivalent, similar or comparable function or structure to the elements of the turbojet in  FIGS. 1 to 3  are the same, to simplify the description. Furthermore, the entire description of the turbojet in  FIGS. 1 to 3  is not reproduced, this description applying to the turbojets in  FIGS. 4 to 7  where not incompatible. Only notable, structural and functional differences are described. 
     The arrows F 3  show one or more possible trajectories for the droplets of oil h in these embodiments. 
     In the embodiment in  FIG. 4 , the sealing device again includes a tank  19  for the gravitational recovery (or capture or withdrawal) of oil h from the oil suspension of the enclosure  4  and the channels  20  carrying the oil from the tank  19  to the brush seal  14 . The channels  24  are also arranged in the torus  16  holding the strands  17 , which is hollow; they lead at one extremity to the channels  20  carrying the oil from the tank  19  and at the other extremity to an internal volume of the torus  16  communicating with the external radial extremity of the strands  17 . Thus, the channels  20 ,  24  are arranged to fluidly connect the oil tank  19  to the external radial extremity of the strands  17 , thereby enabling the strands  17  to be directly impregnated with the oil, via the external extremities thereof. The flow of oil along the strands  17  is thereby further improved. As previously, the oil h is evacuated from the internal side of the strands  17  to encourage the flow thereof and to prevent the agglomeration thereof on the strands  17 . 
     In the embodiment in  FIG. 5 , the sealing device includes means for recovering oil from the oil suspension of the enclosure  4  comprising at least one set of one oil retention or stopping rib  25  and one slot  26  to guide the oil from the rib  25  towards the strands  17  of the seal  14 ; in this case, it comprises four sets of one rib  25  and one slot  26 , which are arranged at the top of the turbojet, as shown in  FIG. 6 . More specifically, each rib  25  extends radially outwards from the external surface of the internal wall  19   c  formed by a redirection (towards the downstream side) of the housing  12  of the stationary structure; it extends longitudinally along the entire length of this internal wall  19   c ; the function thereof is to form a retaining dam for the oil flowing along the external surface of this wall  19   c ; some of the oil is therefore retained just upstream of each rib  25  and the remainder passes above this latter. Each slot  26  is arranged in the downstream surface of the downstream wall  27  of the groove in which the torus  16  is seated; the slot  26  extends radially along this downstream wall  27 ; it is also arranged just above the rib  25 , level with the oil dam, the oil then being guided in the slot  26  from the retention zone thereof above the rib  25 . The oil is therefore guided towards the internal part of the strands  17  upon which it is distributed by the joint effects of gravity and capillarity; the oil is here evacuated in the same manner as in the previous embodiments. 
     The embodiment in  FIG. 5  is the preferred embodiment of the invention. Indeed, it is simple to manufacture since simple pairs of ribs  25  and slots  26  are required. The operation thereof is also very simple since the oil is drawn by gravity towards the bottom of the turbojet and is held in this movement by the ribs  25  and guided from the ribs  25  to the seal  14  by the slots  26 . 
     In the embodiment in  FIG. 7 , the sealing device comprises means for supplying oil from a source specifically dedicated to supplying the brush seal  14  with oil. More specifically, the device comprises channels  28  for guiding the oil from the low-pressure shaft  3  (supplied from the same oil source as the oil supplying the bearing); these channels  28  form the specific dedicated source of oil. The oil is guided to the orifices  29  provided in the second annular longitudinal portion  15   d  of the intermediate part  15 , at the base of the oil slinger  15   c ; in this case there are two of these orifices  29 , although a different number may be used. The oil is projected centrifugally against a scoop  30  formed by a rounded wall protruding from the downstream wall  27  of the groove in which the torus  16  is seated. Channels  31  are provided in the downstream wall  27  of the groove, beneath the scoop  30 , and they communicate with an annular chamber  22  provided between the internal part of the downstream wall  19   a,  forming the tank  19  and the internal part of the torus  16  of the brush seal  14 ; the scoop  30  is then finally arranged to guide the oil projected thereupon towards the annular chamber  22 , which is thereby “flooded” with oil, i.e. the volume thereof is completely filled with oil. As in the embodiment in  FIG. 2 , a plurality of small channels  23  for carrying oil from the annular chamber  22  to the strands  17  are provided and they enable the distribution of the oil along the strands  17 . In this case, the oil is evacuated in the same manner as in the previous embodiments. 
     The invention is described in relation to the preferred embodiments, but other embodiments are naturally possible. In particular, the features of the different embodiments described may be combined, where they are not incompatible.