Abstract:
An apparatus for scavenging lubricating oil comprises an integrated slinger/runner rotatable with the turbine engine rotor discourages oil seepage out of an oil sump of a forward bearing for a gas turbine engine during all operating conditions of the gas turbine engine from idle to take-off speeds and during static non-operation. The apparatus includes a runner comprising an axially forward section and a frusto-conical aft section, and a slinger joined coaxially integrally to the aft frusto-conical aft section. The apparatus includes a means for blocking flow of oil from the frusto-conical aft section toward the axially forward section.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to gas turbine engines and, more particularly, to apparatus for scavenging lubricating oil from the structure of a bearing during all operating conditions.  
         [0002]     Gas turbine engines typically include a core engine having a compressor for compressing air entering the core engine, a combustor where fuel is mixed with the compressed air and then burned to create a high energy gas stream, and a first or high pressure turbine which extracts energy from the gas stream to drive the compressor. In aircraft turbofan engines, a second turbine or low pressure turbine located downstream from the high pressure turbine extracts more energy from the gas stream for driving a fan. The fan provides the main propulsive thrust generated by the engine.  
         [0003]     Typically, a rotor shaft is supported within a non-rotating stator by bearings used in the turbine engine to accurately locate and rotatably mount the rotor with respect to the stator. The bearings are typically surrounded by oil sumps which contain lubricating oil which is sprayed onto the bearings. The bearing and sump are isolated from the hot gas path by a seal which prevents oil leakage from the sump and hot gas entry into the sump. The seal is a contact seal, typically a non-metallic brush seal or carbon seal. At low power points in the operation of the engine, lubricating oil tends to seep toward the seal. Any oil accumulation near the contact seal can cause coking or the creation of varnish on the seal surfaces, which can cause deterioration of seal performance.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0004]     One embodiment of an apparatus for scavenging lubricating oil employs a runner comprising a generally cylindrical forward section and an aft generally frusto-conical section and a generally disk-shaped slinger integrally joined coaxially to the axially aft end of the runner. The runner also comprises a means for blocking oil flow in the forward direction along its outer surface, which in the first embodiment comprises a circumferential groove in the outer surface of said runner between said forward section and said aft section.  
         [0005]     In another embodiment of the apparatus as described in the previous paragraph, the means for blocking flow of oil forward along the outer surface of said runner further comprises a radially stepped ring surface downstream of said contact surface.  
         [0006]     In another embodiment an apparatus for scavenging lubricating oil comprises a generally cylindrical forward section a frusto-conical aft section tapered radially outwardly integral with a disk-shaped slinger and having means for blocking flow of oil forward along said runner comprising at least one separating wall extending radially outwardly from said frusto-conical aft section of said runner.  
         [0007]     In yet another embodiment, an apparatus for scavenging lubricating oil, a means for blocking flow of oil forward along said runner comprises an abradable strip mounted on a generally cylindrical extension of a stationary seal holder oriented parallel to the rotor axis of rotation, for contacting at least one separating wall mounted on a tapered section of a runner. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic cross-sectional view of a gas turbine engine incorporating an apparatus for scavenging lubricating oil;  
         [0009]      FIG. 2  is a schematic, partial cross-sectional view of one embodiment of an apparatus for scavenging lubricating oil incorporating an integrated slinger/runner apparatus;  
         [0010]      FIG. 3  is a schematic partial cross-sectional illustration of an alternative embodiment of an apparatus for scavenging lubricating oil incorporating an integrated slinger/runner;  
         [0011]      FIG. 4  is a schematic, partial cross-sectional illustration of another alternative embodiment of an apparatus for scavenging lubricating oil incorporating an integrated slinger/runner; and  
         [0012]      FIG. 5  is a schematic, partial cross-sectional illustration of yet another embodiment of an apparatus for scavenging lubricating oil incorporating an integrated slinger/runner; 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]      FIG. 1  schematically illustrates a gas turbine engine  10  which includes a stationary engine stator structure and a rotor structure mounted for rotation around longitudinal axis  12 . As used herein “forward” refers to the upstream axial direction as shown by arrow  13  and “aft” refers to the downstream axial direction of air flow as shown by arrow  15 . The forward end of the rotor  20  is rotationally supported within stator  18  by forward bearing  14 . An oil sump  16  is defined about the forward bearing  14 , and the oil sump  16  is pressurized by air provided to cavity  24 .  
         [0014]      FIG. 2  schematically illustrates a gas turbine bearing structure which includes one embodiment of an integrated slinger/runner. The stator  18  supports the rotor  20  via forward bearing  14 . Oil lubricating the forward bearing  14  within the oil sump  16  is supplied via conduit  17 . A sump seal  22  including generally annular contact brush seal  23  is located forward of the oil sump  16  to seal the forward end of the oil sump  16 . Pressurized air in the cavity  24  provides a positive air pressure on the exterior of the sump seal  22 . Runner  30  comprises a generally cylindrical axially forward section  31  concentric with the axis of rotation of the rotor  20 , having circumferential radially outer contact surface  46  axially aligned with sump seal  22 , and a frusto-conical aft section  36  having radially outwardly tapered exterior surface  34 . A circumferential groove  38  extends around the radially outer surface of runner  30  axially between of radially outer contact surface  46  of axially forward section  31  and radially outwardly tapered exterior surface  34  of frusto-conical aft section  36 . Slinger  32  comprises a generally circular disk attached to the axially aft end of frusto-conical aft section  36  of runner  30  to form an integrated slinger/runner. Slinger  32  is generally axially aligned with a plurality of scavenge ports  44  in flow communication with the oil sump  16 .  
         [0015]     The stationary seal support structure  26  supports generally annular contact brush seal  23  so that seal surface  33  is axially aligned with radially outer contact surface  46  of runner  30 . O-ring  27  seals the oil sump  16  to block oil leakage out of the sump and hot gas leakage into the oil sump  16 . Stationary seal support structure  26  includes cylindrical sleeve  40  extending axially aftward from stationary seal support structure  26 . The radially exterior surface of cylindrical sleeve  40  is formed as a circumferential scavenger groove  42  and the radially inner circumference thereof includes a circumferential, helical groove  28  in contact with the axially aft portion of radially outer contact surface  46 .  
         [0016]     During rotational operation of the gas turbine engine  10 , lubricating oil is provided to the bearing by spray mechanisms (not shown) and pressurized air is applied to the exterior of sump seal  22  to prevent oil leakage through the sump seal  22 . The oil sump  16  is vented to maintain proper pressure balance between the volume exterior to the oil sump  16  and the interior of the oil sump  16 . In scavenging lubricating oil during normal operation of the gas turbine engine, oil from the forward bearing  14  driven by centrifugal force is pumped away from sump seal  22  by rotation of the runner  30  in contact with circumferential, helical groove  28  and radially outwardly tapered exterior surface  34 , and by slinger  32  toward the scavenge ports  44 . During slow speed operation or when engine rotation is stopped, oil is drawn by gravity forwardly along the surface of runner  30  toward the sump seal  22 , but contact of oil with sump seal  22  is blocked by circumferential groove  38 , which scavenges oil from radially outwardly tapered exterior surface  34  and directs it toward the bottom of the runner  30  where it is drawn by gravity along slinger  32  toward the bottom scavenge port. Circumferential scavenger groove  42  collects oil from the stationary seal support structure  26  at all operating conditions and channels it to scavenge ports  44  at the bottom of the annular structure.  
         [0017]      FIG. 3  is a detailed partial cross-sectional schematic illustration of a modification of an integrated slinger/runner as shown in  FIG. 2 . The axially forward section  31  of runner  30  includes a radially outer contact surface  47 . Axially downstream of radially outer contact surface  47 , runner  30  incorporates a radially outwardly stepped ring  49  having stepped surface  48  projecting radially outwardly from the radially outer contact surface  47 . Circumferential groove  38  is disposed axially between radially outwardly stepped ring  49  and radially outwardly tapered exterior surface  34  which tapers radially outwardly at an angle between one and four degrees in the downstream direction. Stepped surface  48  projects radially outwardly by a height sufficient to block oil from overflowing circumferential groove  38  axially upstream and has a surface roughness sufficient to inhibit flow of oil axially upstream. Slinger  32  is integral with the frusto-conical aft section  36  of runner  30 . During engine operation radially outwardly stepped ring  49  is in contact with circumferential, helical groove  28  and inhibits seepage of oil toward sump seal  22  during rotation of runner  30 . Radially outwardly stepped ring  49  also enhances the effectiveness of circumferential, helical groove  28  in scavenging oil at slow rotation or during static conditions to block oil flow forward along the surface of the runner  30 .  
         [0018]      FIG. 4  schematically illustrates another embodiment of an apparatus for scavenging lubricating oil including an integrated slinger/runner. Generally cylindrical runner  100  includes a generally cylindrical forward section  101  and a frusto-conical aft section  102  from which at least one separating wall projects generally radially and perpendicular to the axis of rotation. Although two separating walls  104 ,  106  are shown, it will be understood that a single separating wall or several may be used depending on material properties of the wall or walls and expected operating conditions of the engine. The stationary contact seal holder  110  supports the contact seal  112  which engages radially exterior surface  114  of generally cylindrical runner  100 . At its axially aft end, frusto-conical aft section  102  is integrally connected to disk-shaped slinger  108 . The stationary contact seal holder  110  further includes a cylindrical axial extension  116  extending axially aft of the contact seal  112  and supports stationary abradable strip  118  on its radially inner frusto-conical surface  128 . The cylindrical axial extension  116  is tapered radially outwardly relative to the axis of rotation in the downstream direction to align stationary abradable strip  118  with the radially outer tips of separating walls  104 ,  106 . The stationary contact seal holder  110  is secured to the stationary seal support structure  120  by welding or other suitably robust technique and O-ring seal  122  prevents air leakage into the sump and oil leakage from the sump. A circumferential groove  124  extends circumferentially around cylindrical axial member  126 . The tapered structure of the frusto-conical aft section  102  in  FIG. 4  with multiple separating walls  104 ,  106  extends generally perpendicularly to the stationary abradable strip  118 , to pump the oil away from the contact seal  112  to block oil flow axially upstream toward contact seal  112  during engine operation. Most of the oil will be contained inside the sump due to the disc pump action of the disk-shaped slinger  108 . Any residual oil or oil/air mixture passing over the disk-shaped slinger  108  will be centrifuged back to a scavenge port (not shown in  FIG. 4 ). The oil/air mixture reaching the tapered surface of stationary abradable strip  118  by whatever mechanism, will contact one of the separating walls  104 ,  106  and drain back into the sump. The proposed design provides a near zero oil leakage possibility even under the situations with little or zero pressurization margins. Circumferential groove  124  scavenges oil from the stationary seal support structure  120  at all operating conditions to direct it toward the bottom of the support structure and oil scavenge ports.  
         [0019]      FIG. 5  is yet another preferred embodiment of an apparatus for scavenging lubricating oil including an integrated slinger/runner. Runner  200  includes generally cylindrical forward section  201  and a frusto-conical aft section  202  having separating walls  204 ,  206  integral with disk-shaped slinger  208 . The  FIG. 5  design requires at least one separating wall. Stationary contact seal holder  210  supports contact seal  212  axially aligned to engage radially exterior contact surface  214  of generally cylindrical forward section  201 . Stationary contact seal holder  210  also includes axially extending hollow cylindrical member  216  with abradable strip  218 , covering the radially inner cylindrical surface  226  of axially extending hollow cylindrical member  216 . The axially extending hollow cylindrical member  216  and abradable strip  218  extend axially generally parallel to the rotor axis of rotation. The radial heights of the respective separating walls  204 ,  206  are selected to maintain contact with the mating abradable strip  218 . The stationary contact seal holder  210  is attached to stationary seal support structure  220 , and O-ring seal  222  prevents leakage between stationary contact seal holder  210  and stationary seal support structure  220 . An axially extending cylindrical member  228  extends axially from stationary seal support structure  220  and provides circumferential groove  224  to scavenge oil from the support structure during all operating conditions.  
         [0020]     The design of  FIG. 5  is preferred in turbine engine designs requiring accommodation of significant axial movement of the rotor components relative to stator components due to thermal cycles, rotational speed variation or other operating conditions. The axially extending hollow cylindrical member  216  accommodates axial movement of frusto-conical aft section  202  and separating walls  204  and  206  relative to abradable strip  218  without exerting significant axial load on separating walls  204 ,  206  or allowing loss of contact between separating walls  204 ,  206  and abradable strip  218 . Air flow which leaks through the contact seal  212  will be diffused in the first separating wall cavity  230 , and the swirling will create resistance to air leakage into the sump. Additionally, use of the abradable strip  218  allows the tighter radial clearances to further reduce the air leakage into the sump. The proposed features eliminate oil collection near the contact seal  212 , and at the same time minimize air flow into the sump. This design also provides the additional feature of continuing to resist lubricating oil leakage even if the primary contact seal  212  failed or the pressurization margins were lost.  
         [0021]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.