Abstract:
A bearing damper includes: (a) an annular sleeve having spaced-apart grooves formed in a radially-facing surface therein; (b) an annular bearing race received in the sleeve; and (c) a resilient seal ring disposed in each of the grooves, wherein the seal rings cooperate with the sleeve and a radially-facing surface of the bearing race to define a closed annular gap, and further wherein the seal rings are sized so as to urge the bearing race towards a coaxial position relative to the sleeve.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to rotating bearings, and more particularly to squeeze film dampers for bearings associated with high speed turbomachinery. 
         [0002]    In a typical squeeze film shaft damper arrangement, a shaft with its associated rolling element bearing are permitted to have some limited radial motion in the supporting bearing housing. Ordinarily an annular outer race of a rolling element closely fits in an annular chamber in the support housing where two opposing closely adjacent circumferential surfaces of the housing and race define a thin annular squeeze film space into which an oil under pressure is introduced for damping action. 
         [0003]    The use of film dampers in gas turbine engines causes increased clearances for rotor blades and labyrinth seals leading to increased specific fuel consumption (“SFC”) and reduced sealing margins. The effectiveness of the damper is generally improved if the clearance is increased and the damper is sealed. Prior art dampers for turbine engine applications are typically sealed with concentric piston ring type seals which circumferentially engage the bearing housing to seal off the squeeze film space between the rings. 
         [0004]    Some prior art dampers are mounted in a centralized spring structure, such as a squirrel cage. This is effective to limit clearances, but the spring structure increases the bearing cost and weight. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    These and other shortcomings of the prior art are addressed by the present invention, which provides a bearing damper with an integrated centering spring and sealing apparatus. 
         [0006]    According to one aspect of the invention, a bearing damper includes: (a) an annular sleeve having spaced-apart grooves formed in a radially-facing surface therein; (b) an annular bearing race received in the sleeve; and (c) a resilient seal ring disposed in each of the grooves, wherein the seal rings cooperate with the sleeve and a radially-facing surface of the bearing race to define a closed annular gap, and further wherein the seal rings are sized so as to urge the bearing race towards a coaxial position relative to the sleeve. 
         [0007]    According to another aspect of the invention a bearing support apparatus for a gas turbine engine includes: (a) a stationary housing which defines an annular recess; (b) an annular sleeve received in the recess, the sleeve having spaced-apart grooves formed therein; (c) a bearing having annular inner and outer races, the outer race received in the recess; (d) a shaft received in the inner race; and (e) a resilient seal ring disposed in each of the grooves, wherein the seal rings cooperate with the sleeve and the outer race to define a closed annular gap, and the seal rings are sized so as to urge the bearing towards a coaxial position relative to the sleeve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0009]      FIG. 1  is a cross-sectional view of a portion of a gas turbine engine showing a bearing sump thereof; 
           [0010]      FIG. 2  is a perspective cross-sectional view of a portion of the bearing sump shown in  FIG. 1 , illustrating a spring damper seal constructed according to an aspect of the present invention; and 
           [0011]      FIG. 3  is a perspective cross-sectional view of a portion of the bearing sump shown in  FIG. 1 , illustrating an alternative spring damper seal constructed according to an aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  depicts a portion of an enclosed chamber or “sump” of a gas turbine engine, which in this case is a turboshaft engine. This is merely an example of a specific application, and the principles of the present invention are equally applicable to all kinds of turbomachinery such as turbojet, turboprop, and turbofan engines, as well as other types of machinery which use bearing dampers. 
         [0013]    Within the sump, a shaft  10  of the engine is supported for rotation in a rolling-element bearing  12 , in this case a roller bearing. A static annular frame member  14  surrounds the bearing  12 . The bearing  12  is carried by the frame member  14  through a squeeze film bearing damper  16 , which is described in more detail below. The bearing  12  includes an annular inner race  18  mounted on the shaft  10 , a plurality of rollers  20  restrained by a cage  22 , and an annular outer race  24 . 
         [0014]    The frame member  14  incorporates a radially-inwardly extending arm  26 , the inboard end of which defines a housing  28 . The housing  28  includes a recess  30  (see  FIG. 2 ) that receives the bearing damper  16 . In the illustrated example the housing forms the forward end and outer wall of the recess, and the aft end of the recess  30  is closed off by a separate annular retainer  32  which is secured to the housing  28 , for example using threaded studs  34  and nuts  36 , or other fasteners. This configuration facilitates removal and replacement of the damper  16  and/or bearing  12 . 
         [0015]      FIG. 2  illustrates the damper  16  in more detail. The recess  30  of the housing  28  is annular with a generally rectangular cross-sectional shape having forward and aft ends  38  and  40 , respectively. An annular sleeve  42  is received in the recess  30 . The sleeve  42  is stationary in operation and is secured against rotation within the housing  28 , for example through an interference fit. Any alloy which has a suitable life in the application may be used. For weight savings, the sleeve  42  may be made from a lightweight material such as aluminum or titanium alloy. A forward groove  44  having a square cross-section is formed in the inner surface  48  of the sleeve  42  adjacent the forward end  38  of the recess  30 , and an aft groove  46  having a square cross-section is formed in the inner surface  48  of the sleeve  42  adjacent the aft end  40  of the recess  30 . 
         [0016]    The outer race  24  of the bearing  12  is received in the recess  30  inboard of the sleeve  42 . The outer race  24  (and consequently the remainder of the bearing  12 ) is restrained from moving in an axial direction but is free to move radially to some degree. A small annular gap  50  is provided between the inner surface  48  of the sleeve  42  and the outer surface of the outer race  24 . Means are provided, in a known manner, for circulating pressurized oil through this annular gap  50 . For example, oil circulation may be implemented by providing supply and scavenge passages (not shown) in the housing  28  and/or sleeve  42  which are connected to an oil pump (not shown). In a known manner, upon rotation of shaft  10 , any shaft rotor imbalance will cause shaft  10  and bearing  12  to undergo radial motion and subject oil in the annular gap  50  to very high pressure to force viscous flow of the oil and cause a damping action on the outer race  24 . 
         [0017]    An annular seal ring  54  is assembled into each of the forward and aft grooves  44  and  46 . In the illustrated example, the seal ring  54  is a continuous “O”-ring element having a circular cross-section. Any material with appropriate stiffness and fatigue life may be used to construct the seal ring  54 . The geometry of the seal ring cross section, such as the wall thickness, diameter, etc. may be selected to provide desired stiffness characteristics for the seal ring  54 , for example the spring constant “K” in the radial direction. The functional characteristics of the seal ring  54  may be further tuned and optimized by combining a spring (not shown) in series with the seal ring  54 . The seal rings  54  resiliently bear against the outer race  24  and seal off the forward and aft ends of the annular gap, and also provide a radial centering force on the bearing  12  that urges the outer race  24  into a position coaxial with the sleeve  42 . 
         [0018]      FIG. 3  illustrates an alternative damper configuration mounted in a recess  130  of a housing  128  which is identical to the housing  28  described above and which has forward and aft ends  138  and  140 . A sleeve  142  having forward and aft grooves  144  and  146  is received in the recess  130 . The outer race  124  of a bearing  112  is received in the recess  130  inboard of the sleeve  142 . A small annular gap  150  is provided between an inner surface  148  of the sleeve  142  and the outer surface of the outer race  124 . 
         [0019]    Identical annular seal rings  154  are assembled into each of the forward and aft grooves  144  and  146 . The seal ring  154  has a cross-sectional shape which provides a resilient characteristic in the radial direction. Some examples include “Z”, “C”, “I”, or “T” shapes. In this particular example, the cross section is generally “Z” shaped including inner and outer flanges  56  and  58  interconnected by a web  60 . The geometry of the seal ring cross section, such as the material thickness, angle of the web  60 , fillet radii, etc. may be selected to provide desired stiffness characteristics for the forward seal ring  154 , for example the spring constant “K” in the radial direction. The seal rings  154  seal against the outer race  124  to close off the forward and aft ends of the annular gap  150 , and also provide a radial centering force on the bearing  112  that urges the outer race  124  into a position coaxial with the sleeve  142 . 
         [0020]    The damper designs described above can be modified in various ways. For example, the seal rings  54  or  154  and a portion of the sleeve  42  or  142  could be integrated as a single component to further reduce the assembly and part count. Furthermore, the functional characteristics of the seal ring  54  or  154  may be further tuned and optimized by combining a spring (not shown) in series with in the seal ring  54  or  154 . 
         [0021]    The bearing damper configurations described herein provide multiple advantages over prior art film damper sealing technology. Combining the sealing function with the centering spring element eliminates the need for prior art piston rings that are used to seal the end leakage of the annular gap  50 . The sleeve  42  which incorporates grooves for the seal rings  50  will be less expensive to manufacture, maintain, and repair compared to typical designs which require complex machining in a structural outer bearing race. The complete film damper system will be significantly less expensive as well. Sealing via 360° energized rings provides improved squeeze film damping action due to little or no side leakage. This completely eliminates any potential for high side leakage due to mis-assembly or misalignment of piston rings. The overall radial stiffness of the damper can be varied over a wide range. Outer race heat generation will be efficiently balanced by the sealed circumferential cavity that has a continuous circulating lubricant supply. 
         [0022]    The bearing damper will provide improved operating internal radial clearance (IRC) control for the bearing  12 , and the overall reduced clearance range for the engine rotor-stator clearance provides net specific fuel consumption (SFC) improvements. 
         [0023]    The foregoing has described a spring seal damper for a gas turbine engine. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.