Abstract:
A face seal assembly with internal weep drain is disclosed for use in a turbo-machine, such as a gas turbine engine, for deterring passage of fluids, such as oil and the like, across an interface dividing the turbo-machine into two distinct regions, the interface being defined between one surface of a seal element and a second surface mounted on a rotating shaft. The face seal assembly includes a housing having a first fixed member including a drain opening, a second member supported for axial motion relative to the first member, and a biasing element positioned between the first and second members for urging the second member toward the interface. The second member supports the seal element and defines with the first member a channel through which the fluids that migrate past the interface are directed into the housing and out through the drain opening. Various housing configurations and sealing arrangements are disclosed, all of which effectively control release of oil and smoke into the atmosphere without affecting the axial length or weight of the sealing system.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to sealing arrangements for establishing sealing barriers for rotors extending from an oil-immersed region to an air-immersed region, and more particularly, to a face seal system which incorporates an oil weep drain, secondary seals, and buffer systems into a housing and is operative to shorten the “effective” length of the sealing system, thereby reducing rotor length and weight.  
           [0002]    Air exhaust from turbo-machinery is often released into areas populated by people. Oil, which can leak into this air due to the high pressures, high temperatures, and/or high speeds, under which the turbo-machinery operates, results in an unpleasant smell and sometimes produces smoke to which the people are exposed. This has become a major cause of removal and/or excessive maintenance of propulsion engines and auxiliary power units (APUs).  
           [0003]    The prior art is replete with sealing apparatus for minimizing passage of fluids across barriers. Some of the apparatus focus on using a multiplicity of seals (see U.S. Pat. No. 3,085,808 to Williams, U.S. Pat. No. 4,619,364 to Mitumary, and U.S. Pat. No. 3,360,272 to Blom et al.), while others focus on maintaining pressure control (see U.S. Pat. No. 3,813,103 to Wiese, U.S. Pat. No. 3,926,442 to Muller, and U.S. Pat. No. 4,087,097 to Hossens et al.), but none incorporate provisions for controlling the axial length of the sealing system, nor is there any concern for the resulting weight increase due to the increased length of the turbo-machinery.  
           [0004]    A more recent solution developed by the assignee of the present invention includes a system for oiled sumps which uses a carbon ring seal (primary air-to-oil seal), two oil “weep” drains, secondary air-to-oil seals, and a single air buffer system in conjunction with the stationary housing of the turbo-machinery. This arrangement has proven to be effective in significantly reducing, if not nearly eliminating, oil leakage. However, when used with a carbon face seal, the axial length of the improved system is increased an extensive and unacceptable amount with a corresponding increase in engine weight, and a negative impact on the dynamics of the rotor system.  
           [0005]    Therefore, there exists a need for sealing apparatus using a face seal to keep lubricating oil on one side of turbo-machinery, such as a gas turbine engine, from passing to the air, or compressor, side of the turbo-machinery which will contribute to reduction of the effective overall axial length of the sealing system, achievement of a meaningful reduction of weight in the turbo-machinery, and also improvement of the system&#39;s dynamic characteristics.  
         SUMMARY OF THE INVENTION  
         [0006]    In one aspect of the present invention, a sealing apparatus comprises a housing including a portion for retaining the face seal element and a biasing element for urging the face seal element into sealing engagement with a portion of the rotor of the turbo-machinery, and further comprises an axial extending leg portion which defines, with the portion for retaining the face seal element, a fluid flow path through the housing for removing oil which has breached the face seal element-rotor interface.  
           [0007]    In another aspect of the invention, variations of the structure of the seal housing are disclosed which provide the same oil-air isolation function but which operate with potentially greater efficiencies.  
           [0008]    Other aspects, advantages and features of the invention will become more apparent and better understood, as will equivalent structures, which are intended to be covered herein, with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 shows a cross sectional view of a typical prior art face seal installation;  
         [0010]    [0010]FIG. 2 is a schematic representation of a typical face seal assembly used in the installation of FIG. 1;  
         [0011]    [0011]FIG. 3 shows a cross sectional view of a typical prior art face seal installation with oil weep drains and an air buffer systems to prevent migration of the oil that has leaked past the face seal into the air system;  
         [0012]    [0012]FIG. 4 is a schematic representation a first embodiment of the face seal assembly according to the present invention;  
         [0013]    [0013]FIG. 5 is a schematic representation of a second embodiment of the face seal assembly according to the present invention;  
         [0014]    [0014]FIG. 6 is a schematic representation of a third embodiment of the face seal assembly according to the present invention;  
         [0015]    [0015]FIG. 7 is a schematic representation of a fourth embodiment of the face seal assembly according to the present invention;  
         [0016]    [0016]FIG. 8 is a schematic representation of a fifth embodiment of the face seal assembly according to the present invention; and  
         [0017]    [0017]FIG. 9 is a schematic representation of a sixth embodiment of the face seal assembly according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide a face seal assembly of superior design and performance.  
         [0019]    Generally, the sealing assembly of the present invention is located in a turbo-machine, such as a gas turbine engine, at the interface of rotating components and fixed stationary components to prevent oil used on the rotor support side of the engine, which is located in an oil bath cavity, from passing to the air side of the engine.  
         [0020]    Referring to the accompanying drawings in which like reference numerals indicate like parts throughout the several views, FIGS. 1 and 2 depict a sealing assembly used in a typical prior art turbo-machine installation  10 , as exemplified by U.S. Pat. No. 3,813,103 to Wiese. FIG. 3 depict a sealing assembly using the face seal of Wiese with secondary seals to prevent fluid migration from one cavity to another, as exemplified by U.S. Pat. No. 4,619,354 to Mitumaru.  
         [0021]    Referring more specifically to FIG. 1, there is shown a rotating shaft  12  having a compressor rotor  17  and compressor blades  15  mounted on one end thereof for rotation together with the shaft. An axial mechanical face seal assembly  25 , comprised of a rotating part  26  and stationary part  27 , is operatively positioned about the exterior of the shaft  12  and between the compressor rotor  17  mounted on shaft  12  and bearing  16  which rotatably supports shaft  12  within the casing. Other critical elements of the installation include the compressor air inlet (air cavity), illustrated by arrow  20 , the oil sump drain  18  (which is the primary oil drain), and the oil sump  19 , which serves to remove oil from the sump. The air to oil interface  23  of the face seal assembly  25 , separates the oil side  22  from the air side  24 . Arrow  28  illustrates the potential oil leak path into the compressor air inlet.  
         [0022]    [0022]FIG. 2 is schematic representation of a typical face seal assembly used in the installation of FIG. 1. The face seal assembly comprises a housing  33  arranged radially outwardly of carbon retainer  34 . Both the housing  33  and carbon retainer  34  are non-rotatably mounted to the casing of the turbo-machine. The housing  33  includes a cylindrical wall  33 A and an axial wall  33 B depending from the downstream  31  end of the housing  33 . The carbon retainer  34  includes a first cylindrical wall  34 A for supporting a carbon element  35  having an upstream  30  facing sealing surface, and a second cylindrical wall  34 B disposed parallel to cylindrical wall  33 A of the housing  33  and extending in a downstream  31  direction toward the axial wall  33 B of the housing  33 . The carbon retainer  34  is supported for axial motion relative to the housing  33 . The carbon element  35  is supported by the first cylindrical wall  34 A of the carbon retainer  34  in such a manner that the upstream  30  facing surface of the carbon element  35  is maintained in a substantially contiguous disposition with the downstream  31  facing surface of a seal runner  32  secured about and rotating with the shaft  12 .  
         [0023]    Disposed between the second cylindrical wall  34 B and the housing  33  is bellows  36  which may take the form of an elastomeric body, a coil spring, or a series of bellow springs (the latter being shown in FIG. 2 for purposes of this description), which is secured to the housing  33  and is compressed axially between axial wall  33 B and carbon retainer  34  in the position shown in FIG. 2. The biasing element is provided for axially urging the carbon retainer  34  in an upstream  30  direction to maintain contact between the upstream  30  facing surface of the carbon element  35  and the downstream  31  facing surface of the seal runner  32 .  
         [0024]    The desired sealing function of the invention is achieved by the interface of the mating surfaces of the seal runner  32  and the carbon element  35 . When operative, the sealing assembly substantially eliminates the leakage of harmful or undesired fluids, such as oil, from one side of turbo-machinery, such as a pump chamber, into the chamber on the other side of the interface, such as the air inlet to a compressor. In the FIG. 2 depiction, the region to the left (i.e., the upstream  30  side) of the seal runner  32  constitutes the “oil-filled” side of the turbo-machine, while the region to the right (i.e., the downstream  31  side) of the seal runner  32  constitutes the “air-filled” or oil-cavity side of the turbo-machine. The interfaced carbon element  35  and seal runner  32  work to deter oil from migrating into the “air-filled” or air-cavity side of the apparatus. In the prior art application of U.S. Pat. No. 3,813,103, as shown in FIG. 1, arrow  28  illustrates how oil that migrated past seal runner  32  and carbon element  35  would enter the air-cavity.  
         [0025]    [0025]FIG. 3 shows the approach taken in U.S. Pat. No. 4,619,354 in order to capture oil that migrates past the primary air to oil seal  44  (seal runner  32  and carbon element  35  of FIG. 2) the air to oil interface  23  on the downstream  31 , “air-filled” side of the turbo-machine is evacuated through one or more secondary oil drain  43  openings in the casing of the turbo-machine.  
         [0026]    Still referring to FIG. 3, the face seal assembly  25  is typically positioned upstream from secondary seals, which are shown as labyrinth seals  40 A and  40 B, mounted on the rotating shaft  12 , as well as secondary oil drain openings  43  and a single buffer air supply  46  formed in the stationary housing  42 . Because no seal is fully capable of preventing leakage, especially where the components are operating under high speeds, high temperatures, and high pressures as would be the case in turbo-machines, the machinery is provided with secondary oil drains  43  (commonly known as weep drains to those skilled in the art) downstream of the face seal assembly  40 . The single buffer air supply  46 , which is pressurized air maintained at a higher pressure than the oil-cavity and the air-cavity pressures, is provided to assist in the evacuation of oil (through the secondary oil drains  43 ) which has leaked through the air to oil interface  23  (the potential oil leakage path is shown as arrow  45 ) to the downstream  31 , or “air”, side of the turbo-machine. The labyrinth seals  40 A and  40 B are positioned at strategically located placements on the rotating shaft  12  so as to be in facing relationship with labyrinth seal shrouds  48 A,  48 B and  48 C carried by the machine casing so that secondary seals are formed therebetween.  
         [0027]    The assemblage of elements shown in FIG. 3, representative of the prior art, is deficient and therefore undesirable because all of these elements mandate an increased axial length and a commensurate weight penalty. When compared to FIG. 1, however, the prior art approach shown in FIG. 3 does reduce the potential of oil migration from the oil-cavity into the air-cavity.  
         [0028]    [0028]FIG. 4 schematically depicts a first embodiment of the face seal assembly of the present invention, which comprises a housing  51 , a carbon retainer  50 , a bellows  36 , a seal runner  32 , and a carbon element  35 . The housing  51  includes an axially extending cylindrical wall  51 A, an axial wall  51 B depending radially inward from the downstream  31  end of cylindrical wall  51 A, and a second cylindrical wall  51 C extending in an axial upstream  30  direction from the radially inward end of axial wall  51 B parallel to cylindrical wall  51 A. An inwardly directed short axial leg  51 D which depends from the cylindrical wall  51 A and parallel to axial wall  51 B is located upstream  31  of axial wall  51 B a small distance therefrom. An oil drain hole  55  is provided in cylindrical wall  51 A between axial leg  51 D and axial wall  51 B to provide an oil drain path  54  leading to a oil weep drain in the housing (such as the secondary oil drains  43  shown in FIG. 3).  
         [0029]    The carbon retainer  50  includes a first cylindrical wall  50 A for supporting carbon element  35  having an upstream  31  facing sealing surface, and a second cylindrical wall  50 B disposed parallel to and extending in an axial direction between cylindrical wall  51 A and the second cylindrical wall  51 C. The second cylindrical wall  50 B extends in a downstream  31  direction toward axial wall  51 B. A biasing bellows  36  positioned between the upstream  30  side of axial leg  51 D and the downstream  31  facing surface of the carbon retainer  50  urges first cylindrical wall  50 A in an upstream  30  direction such that the upstream  30  face of carbon element  35  is pressed into sealing engagement with the downstream  31  face of the rotating seal runner  32 .  
         [0030]    The radially inner surface of the second cylindrical wall  51 C carries a labyrinth seal shroud  53  arranged atop labyrinth seal  52  secured to the rotating shaft  12 . The second cylindrical wall  50 B of the carbon retainer  50  is radially spaced from the second cylindrical wall  51 C of the housing  51  so that a oil drain path (indicated by the dotted line  54  running from below the carbon element  35  through the face seal housing) is formed between the two. The flow path runs from the radially innermost region of the seal housing just downstream  31  of the carbon element  35  to oil drain hole  55  in cylindrical wall  51 A. Along with the labyrinth seals  52  which act to block the further migration of oil downstream, the oil drain path  54  allows oil which has migrated past the interface between carbon element  35  and seal runner  32  to be evacuated from the “air” side of the engine before entering any airstream being directed to the passenger compartment, or other occupied areas.  
         [0031]    [0031]FIG. 5 schematically depicts a second embodiment of the face seal assembly according to the present invention, which provides for redundant oil draining capability. In this embodiment, the housing  60  includes a first axial wall  60 B and a second axial wall  60 C spaced from and axially positioned downstream  31  of the first axial wall  60 B. A second oil drain hole  62  is positioned on the housing  60  cylindrical wall  60 A downstream  31  of the first oil drain hole  61 . The radially inward end of the housing  60  second axial wall  60 C has a downstream  31  extending cylindrical leg  60 D which carries a second labyrinth seal shroud  66  in facing relationship to a second labyrinth seal  64  carried on the shaft  12  downstream  31  of the first labyrinth seal  63  and first labyrinth seal shroud  65 .  
         [0032]    [0032]FIG. 6 schematically depicts a third embodiment of the face seal assembly according to the present invention which provides not only the redundant oil draining capability as depicted in FIG. 5, but also includes an air buffer downstream of the oil drains. As shown, the housing&#39;s  70  second axial wall  70 A is formed with an axially extending wall  70 B having two sealing zones defined at the second labyrinth seal pad  71  and third labyrinth seal pad  72  disposed between the radially inward face of the axially extending wall  70 B and a pair of strategically placed labyrinth seals  73  and  74  mounted to the rotating shaft  12 . A channel  75  provided between the second labyrinth seal pad  71  and the third labyrinth seal pad  72  is operatively coupled to a source of pressurized gas, preferably compressed air, for increasing pressure on the downstream  31  side of the face seal assembly to force oil toward oil drain hole  61  and  62 . An o-ring  76  provides a seal between axially extending wall  70 B and the turbo-machine casing (not shown)  
         [0033]    [0033]FIG. 7 schematically depicts a fourth embodiment of the face seal assembly embraced by the present invention which is similar to the third embodiment shown in FIG. 6, but which differs in that the turbo-machine  80  casing is provided with a single cavity or sump  80 A that communicates with oil drain holes  82  and  83  on the housing  81  first cylindrical wall  81 A. The casing sump  80  is preferably operatively coupled with a vacuum source or other apparatus (not shown) communicating with a zone of lower pressure in order to encourage drainage of oil from within the face seal assembly. The housing  81  first axial wall  81 B extends inwardly to an angular wall extension  81 C and then in a upstream  30  direction forming a second cylindrical wall  81 D, having a sealing zone defined at the first labyrinth seal pad  84  and a strategically placed first labyrinth seal  87  mounted on the rotating shaft  12 . The axially extending wall  81 E is spaced from and axially positioned downstream  31  of the first axial wall  81 B, and has two sealing zones defined at the second labyrinth seal pad  85  and third labyrinth seal pad  86  disposed between the radially inward face of the axially extending wall  81 E and a pair of strategically placed labyrinth seals  86  and  87  mounted to the rotating shaft  12 . A channel  90  provided between the second labyrinth seal pad  85  and the third labyrinth seal pad  86  is operatively coupled to a source of pressurized gas, preferably compressed air, for increasing pressure on the downstream  31  side of the face seal assembly to force oil toward oil drain holes  82  and  83 . An o-ring  80 B provides a seal between axially extending wall  81 E and the turbo-machine casing  80 .  
         [0034]    [0034]FIG. 8 schematically depicts a fifth embodiment of the face seal assembly of the present invention in which the first and second axial legs  60 B and  60 C of the seal assembly second embodiment shown in FIG. 5 located downstream  31  of axial leg  51 D, are merged into a large single axial element  91  bearing a first cylindrical wall  92  having an upstream  30  orientation and a second cylindrical wall  93  having a downstream  31  orientation. The first cylindrical wall  92  bears a pair of axially spaced apart labyrinth seal shrouds  94  and  95  disposed between a pair of strategically placed labyrinth seals  97  and  98  mounted to the rotating shaft  12 , between which is an oil drain hole  96  for directing oil into the interior of the face seal assembly  98  that has migrated past the entrance of the primary flow path through the face seal assembly. The second cylindrical wall  93  bears, on a radially inward surface facing the rotating shaft  12 , a third labyrinth seal shroud  99  for mating engagement with labyrinth seal  100  on the shaft. A channel  101  provided in the upstream  31  portion of the second cylindrical wall  93  is operatively coupled to a source of pressurized gas, preferably compressed air, for increasing pressure on the downstream  31  side of the face seal assembly to force oil toward oil drain holes  96  and  82 . An o-ring  102  provides a seal between radial wall  91  and the turbo-machine casing  80 .  
         [0035]    [0035]FIG. 9 shows a sixth embodiment of the face seal assembly of the present invention in which the housing  105  comprises a first cylindrical wall  105 A, a large axial wall  105 B, and a second cylindrical wall  105 C. The first cylindrical wall  105 A includes a first oil drain hole  106  leading to a first sump  107 , and comprises the primary oil flow path. The second cylindrical wall  105 C bears a pair of axially spaced apart labyrinth seal shrouds  109  and  110  disposed between a pair of strategically placed labyrinth seals  111  and  112  mounted to the rotating shaft  12 . Axial wall  105 B includes a second oil drain hole  113  leading from the inner surface of second cylindrical wall  105 C to the second sump  108 , and comprises the secondary oil flow path. The first and second sumps  107  and  108  for the primary and secondary flow paths may be separate or they may constitute a single chamber, shown in FIG. 8. The downstream  31  portion of axial wall  105 B has a shoulder  105 D which engages the casing  114  of the turbo-machine, and which carries an o-ring  115  type seal.  
         [0036]    Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein.