Abstract:
A bearing hub for a gas turbine engine comprises an inner annular member defining a bearing chamber and an outer annular member extending around the inner annular member. Each annular member defines an aperture to receive a conduit which can extend to the bearing chamber. The outer annular member is configured to slidingly engage the conduit at the aperture in the outer annular member.

Description:
FIELD OF THE INVENTION 
   This invention relates to bearing hubs. More particularly, but not exclusively, the invention relates to bearing hubs for use in gas turbine engines, for example the bearing hubs for the bearings supporting the high and intermediate pressure turbines. 
   BACKGROUND OF THE INVENTION 
   In gas turbine engines, the turbine discs for the high and intermediate pressure turbines are supported by bearings held within a common bearing hub. An example of such a bearing hub is an inner annular wall enclosing the bearing, and an outer annular wall surrounding the inner wall. The region between the inner and outer walls accommodates buffer sealing air to prevent leakage of oil out of the bearing chamber. It is important that the inner and outer walls are fixedly held together to provide sufficient rigidity for the respective turbines. 
   The outer wall is subjected to high temperatures, and this can cause considerable expansion. The inner wall is, on the other hand, subjected to much lower temperatures, and expands to a lesser degree. This differential thermal expansion of the inner and outer walls creates stress and can result in failure of the bearing hub. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the invention there is provided a bearing hub for a gas turbine engine comprising an outer annular member surrounding a bearing chamber, the outer annular member defining an aperture to receive a conduit which can extend to the bearing chamber, wherein the outer annular member is configured to slidingly engage the conduit at the aperture therein. 
   According to another aspect of this invention, there is provided a bearing hub for a gas turbine engine comprising an inner annular member defining a bearing chamber, an outer annular member extending around the inner annular member, each annular member defining an aperture for a conduit, which can extend to the bearing chamber, the aperture in the inner annular member allowing communication between the conduit and the bearing chamber, wherein the outer annular member is configured to slidingly engage the conduit at the aperture therein. Thus, the preferred embodiment has the advantage that the sliding engagement of the outer annular member with the conduit at the aperture allows relative thermal expansion between the inner and outer annular members. 
   Preferably, the outer annular member includes sealing means at said aperture, whereby the sealing means can engage the conduit to provide sealing between the outer annular member and the conduit. The sealing means is preferably a sealing ring, a brush seal, or a labyrinth seal. Holding means may be provided to hold the sealing means in engagement with the conduit. In one embodiment, the holding means comprises securing means to secure the sealing means to the outer annular member. The part of the outer annular member surrounding the aperture may include a shoulder defining a circumferentially extending recess to receive the sealing means. The securing means may be mounted on the outer annular member to hold the sealing means in the recess. The securing means may be in the form of an annular retaining element extending around the aperture. The retaining element may be fastened to the outer annular member by fastening means. The fastening means may comprise a plurality of bolts, which may be receivable in threaded bores in the outer annular member, or threaded nuts may be provided to threadably engage the bolts. 
   Alternatively, the holding means comprise a holding member which may be annular and which may extend around the aperture. The holding member preferably defines a recess to receive the sealing means. The holding member may have a C shaped profile to define said recess. 
   Preferably, the inner and outer annular members are connected to each other by connecting means constructed to allow differential thermal expansion of the outer annular member relative to the inner annular member, in use. Preferably, the connecting means may comprise a connecting portion provided at least at one end region, and preferably at both the downstream and upstream end regions of the bearing hub. The, or each, connecting portion is preferably integral with the inner and outer annular members. 
   In one embodiment, the or each connecting portion may be integral with the inner and outer annular members. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a sectional side view of the upper half of a gas turbine engine; 
       FIG. 2  is a sectional side view of the region marked A in  FIG. 1 ; 
       FIG. 3  shows an enlarged view of the bearing chamber shown in  FIG. 2  from the first position; and 
       FIG. 4  shows an enlarged view of an alternative holding means for holding a sealing means. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , a ducted fan gas turbine engine generally indicated at  10  has a principal axis X—X. The engine  10  comprises, in axial flow series, an air intake  11 , a propulsive fan  12 , a compressor region  113  comprising an intermediate pressure compressor  13 , and a high pressure compressor  14 , combustion means  115  comprising a combustor  15 , and a turbine region  116  comprising a high pressure turbine  16 , an intermediate pressure turbine  17 , and a low pressure turbine  18 . An exhaust nozzle  19  is provided at the tail of the engine  10 . 
   The gas turbine engine  10  works in the conventional manner so that air entering the intake  11  is accelerated by the fan to produce two air flows: a first air flow into the intermediate pressure compressor  13  and a second air flow which provides propulsive thrust. The intermediate pressure compressor  13  compresses the air flow directed into it before delivering the air to the high pressure compressor  14  where further compression takes place. 
   The compressed air exhausted from the high pressure compressor  14  is directed into the combustor  15  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low pressure turbine  16 ,  17  and  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low pressure turbines  16 ,  17  and  18  respectively drive the high and intermediate pressure compressors  14  and  13  and the fan  12  by suitable interconnecting shafts. 
     FIG. 2 , is a close-up of the region marked A in  FIG. 1 . In  FIG. 2 , there is shown the high pressure turbine  16 , and the intermediate pressure turbine  17 . A stator vane  20  is arranged between the blades of the high pressure and intermediate pressure turbines  16 ,  17 . 
   The high pressure turbine  16  comprises a plurality of turbine blades  22  mounted on a disc  24 . Similarly, the intermediate pressure turbine  17  comprises a plurality of turbine blades  26  mounted on a support disc  28 . The high pressure turbine support disc  24  and the intermediate pressure turbine support disc  28  are connected to a bearing hub  30 . The bearing hub  30  comprises an outer annular member  36  and an inner annular member  38 . An annular space  40  is provided between the outer and inner annular members  36 ,  38 . The inner annular member  38  defines a bearing chamber  34 . 
   A plurality of bearings  32  are rotatably mounted in the bearing chamber  34  to provide support for the high and intermediate pressure turbine discs  24  and  28 . 
   The outer and inner annular members  36 ,  38  are connected to each other at their upstream and downstream edges by an annular connecting portions  41 ,  42  respectively. The connecting portions  41 ,  42  are sufficiently flexible to accommodate differential thermal expansion of the inner and outer annular members  36 ,  38 , as explained below. 
   Referring to  FIG. 3 , there is shown in more detail, the bearing hub  30 . The view of the bearing hub  30  shown in  FIG. 3  is from a different circumferential position to that shown in  FIG. 2 . In  FIG. 3  a bearing hub service pipe  48  is shown. The outer annular member  36  defines an outer aperture  50  and the inner annular member  38  defines an inner aperture  52 . The pipe  48  extends through the outer aperture  50  and is attached to the inner annular member  38  in the region surrounding the inner aperture  52 , such attachment can be by for example welding the pipe  48  to the inner annular member  38 , for example by butt welding. Thus, the pipe  48  is in communication with the bearing chamber  30  to supply oil thereto as indicated by the arrows X in  FIG. 3 , or remove oil therefrom. 
   The pipe  48  shown is a sliding fit within the aperture  52 . The pipe  48  is held within the aperture  52  by sealing means in the form of a sealing ring  53  which extends around the pipe  50  at the aperture  52 . The bearing hub  30  may include a plurality of pipes  48  at circumferentially spaced regions around the hub  34 . 
   In addition to the service pipe or pipes  48 , there is also provided an air delivery pipe  54  to deliver sealing air to the annular space  40  via an aperture  56  in the inner annular member  36 , as indicated by the arrows Y. The air delivery pipe  54  is fixedly attached, for example by welding, to the outer annular member  36  at the aperture  56 . 
   The sealing ring  53  is held in sealing engagement with the pipe  48  in an annular recess  58  defined by a holding member  60  provided on the outer annular member  36  surrounding the aperture  52 . The holding member  60  has a generally C shaped profile, as shown. 
   A structural member  61  extends radially outwardly from the outer annular member  36  for connection to another feature (not shown) of the engine. The function of the structural member  61  is not material to the operation of the invention and is not described. 
   Referring to  FIG. 4 , there is shown a close up of another embodiment for holding the sealing ring  53  in engagement with the service pipe  48 . As can be seen, an annular recess  62  is defined around the aperture  50  at a shoulder  63  in the radially outer surface of the outer annular member  36 , to receive the sealing ring  56 . An annular retaining member in the form of an annular plate  64  is secured to the outer annular member  36  around the aperture  50  by a plurality of bolts  66  which are received in circumferentially spaced threaded bores  68  in the outer annular member  36 . The retaining member  64  extends over the recess  62  and engages the annular sealing ring  53  to hold the sealing ring  53  in the recess  62 . 
   The above described embodiments will now be described in operation. Referring again to  FIG. 2 , when the gas turbine engine  10  is in operation, air from the compressors is fed in a known manner to a region  70  between the high pressure and intermediate pressure turbine discs  24 ,  28 . The air supplied to the region  70  is bled from the high pressure compressor  14 . Similarly, sealing air is bled from the intermediate compressor  13  via the air delivery pipe  54  to the space  40  between the inner and outer annular members  36 ,  38 . 
   The temperature of the air in the region  70 , is greater than the temperature of the sealing air in the space  40 , which in turn is greater than the temperature of the oil in the bearing chamber  34 . As a result of these temperature differences, the structural member  61  is subjected to large thermal expansion resulting from the high temperature air from the high pressure compressor in the region  70 . This contributes to causing considerable stresses on the outer annular member  36 . The inner annular member  38  is, on the other hand heated to a much lesser degree because of the cooler oil temperature in the bearing chamber  34 . Thus, the inner annular member  38  expands to a much lesser degree and the stresses thereon are also significantly less. 
   The provision of the sealing ring  53 , enables the outer annular member  36 , to reduce the stresses therein by the sliding of the sealing ring  53  over the pipe  48 . In addition, the sealing ring  53  can accommodate circumferential movement of the pipe  48  relative to the sealing ring  53 . This accommodation is effected by a clearance  55  around the sealing ring  53  in the recess  58  in the embodiment shown in  FIG. 3 , and by a clearance  65  around the sealing ring  53  in the recess  62 . This has the advantage in the embodiments shown of allowing the accommodation of movement arising from thermal expansion and from tolerance build-up without compromising the sealing function. This provides an advantage of the elimination of high stresses during such expansion. 
   In addition, the connection of the outer annular member  36  to the inner annular member  38  by the upstream and downstream annular connecting portions  41 ,  42  provides sufficient flexibility to allow the outer annular member  36  to expand with the sealing ring  53  sliding along the pipe  48  without the creation of stresses within the hub  30 . 
   There is thus described a simple but effective arrangement for accommodating the expansion of the outer annular member of a bearing hub preventing stresses in the hub  30  thereby providing for a longer life of the hub. 
   Various modifications can be made without departing from the scope of the invention. For example, the flexibility of the outer annular member  36  relative to the inner annular member  38  can be effected by means other than the connecting portions  41 ,  42 . Also, the attachment of the pipe  50  to the inner annular member can be by any conventional means such as a friction fit, welding, brazing, or being formed as an integral part (e.g. by casting). The sealing ring  53  may be a brush seal or a labyrinth seal. 
   It will be appreciated that an advantageous feature of the upstream and downstream connecting portions  41 ,  42  is that they are sufficiently flexible to accommodate the aforesaid differential thermal expansion of the inner and outer annular members  36 ,  38 . Thus, the connecting portions  41 ,  42  need not be integral with the inner and outer annular members. Instead, the connecting portions could be in the form of separate plates connected to the inner and outer annular members  36 ,  38  by suitable fastening means, such as bolts or the like. 
   Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.