Abstract:
A squeeze-film damper bearing. Squeeze-film damper bearings contain a fluid film captured between two components, typically (1) a bearing race and (2) a housing which supports the race. The fluid film damps vibration of the two components. However, the fluid film also allows movement of the components with respect to each other, which is not always desired. The invention limits the movement, without significantly diminishing the vibration-damping properties of the fluid.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to fluid-film dampers which damp vibration of turbine engines.  
         BACKGROUND OF THE INVENTION  
         [0002]    [0002]FIG. 1 is a partial schematic view of a gas turbine engine  2 , such as that used in a turbo-fan aircraft. A high speed rotor  3  contains a high-pressure compressor  6 , a high-pressure turbine  9 , and a shaft  12  connecting the compressor  6  with the turbine  9 . A low-speed rotor  15  contains a fan  18 , a low-pressure turbine  21 , and a shaft  24  connecting the fan  18  with the turbine  21 .  
           [0003]    Bearings (not shown) support the two rotors  3  and  15 . For example, one set of bearings may be located at the position indicated by dashed box  27 , and allows the shaft  24  to support the high-speed rotor  3 . A similar set may be located aft of this bearing set, which also supports the high-speed rotor  3 .  
           [0004]    Another set of bearings may be located at the position indicated by dashed box  30 , and allows a schematic stationary structure  33  to support the low-speed rotor  15 . A similar set may be located aft of this set, to further support the low-speed rotor. FIG. 2 is an exploded view of one type of bearing, which is shown in assembled form in FIG. 3, which may be located at dashed box  27  in FIG. 1.  
           [0005]    In FIGS. 2 and 3, shaft  24  supports an inner race  36 . Bearing rollers  39  separate the inner race  36  from an outer race  42 . A bearing housing  45  is connected to the stationary structure  33  in FIG. 1, through a connection system which is not shown. The bearing housing  45  is separated from the outer race  42  by a space  46  in FIG. 3.  
           [0006]    The apparatus of FIG. 3 also appears in FIG. 4, which also contains a cross-sectional view of the apparatus. In addition, piston rings  51  are shown at the right side of FIG. 4. The cell  52  is filled with oil (not shown), which acts as a damper.  
           [0007]    The Inventor has identified one, or more, characteristics of the system of FIG. 4 which may be undesirable in certain situations.  
         SUMMARY OF THE INVENTION  
         [0008]    In a fluid-damped bearing of the type shown in FIG. 4, damper blocks, or spacers, are sometimes added between the outer race  42  and the bearing housing  45 . The damper blocks limit travel of the outer race  42 . However, the damper blocks are placed outside of cell  52 , that is, outside the body of damping fluid. This placement provides two features: (1) a firm limit on movement of the outer race  42 , with respect to the housing  45 , and (2) a somewhat softer damping force, compared with certain other placements. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a partial schematic view of a gas turbine engine.  
         [0010]    [0010]FIG. 2 is an exploded view of a bearing which can be used within dashed block  30  in FIG. 1.  
         [0011]    [0011]FIG. 3 shows the bearing of FIG. 2 in assembled form.  
         [0012]    [0012]FIG. 4 shows the bearing of FIG. 3, and also a cross-sectional view of part of the bearing, taken along arrows  4 - 4 .  
         [0013]    [0013]FIG. 5 is a view similar to that of FIG. 4, but containing stops  60 .  
         [0014]    [0014]FIG. 6 is collection of plots showing operating characteristics of three types of squeeze dampers, including one constructed according to the present invention.  
         [0015]    [0015]FIG. 7 illustrates one form of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Prior to explaining the invention, some characteristics of the apparatus of FIG. 4, and a related apparatus, will first be explained. Behavior of the system of FIG. 4 is illustrated by plots  62  and  64  in FIG. 6. These plots are approximations. The damper radial clearance indicated in the plots is represented by dimension  66  in sketch  65 . For the system of FIG. 4, the bumper B in sketch  65  is absent.  
         [0017]    In plot  62 , the static restoring force of the fluid in annular cell  52  in FIG. 4 is approximately zero, as damper radial clearance becomes reduced, and approaches limit  67 . That is, when race  42  contacts housing  45  in sketch  65 , damper radial clearance  66  reaches its minimal limit, represented by point  67  in plot  62 . At this time, the static force becomes very large, because two solid bodies, namely race  42  and housing  45 , are in contact, and oppose each other.  
         [0018]    Plot  64  illustrates the dynamic damping force. This dynamic force is quite complex in nature, and becomes highly non-linear as the gap between race  42  and housing  45  closes.  
         [0019]    The dynamic damping force of plot  64  is rather small in region  70 . That is, the force of the fluid is analogous to a soft spring. In contrast, the opposing force in region  72  becomes rather large, partly because the fluid within chamber, or cell,  52  in FIG. 4 has become dimensionally thin when race  42  approaches housing  45 . The term dimensionally thin is used to distinguish from thinness in the viscous sense.  
         [0020]    Therefore, in the system of FIG. 4, the dynamic force of reaction between the race  42  and the housing  45  rapidly increases as the damper clearance  66  approaches its zero limit, represented by point  67  in plot  64 .  
         [0021]    The plots  75  and  77  of FIG. 6 describe the behavior of a different system, namely, that of FIG. 5. In that Figure, stops, or bumpers  60 , are provided, to limit travel of the race  42 , with respect to the housing  45 . In plot  75  in FIG. 6 for this system, one sees that the static opposing force, which tends to drive the race  42  in sketch  65  in that Figure to a central position within the housing  45 , is approximately zero until point  79  is reached. At that time, bumper B contacts housing  45  in sketch  65 .  
         [0022]    In plot  77 , one sees that the dynamic force fluid rapidly increases in region  70 , compared with region  70  in plot  64 . A primary reason for the rapid increase in plot  77  is that the fluid above bumper  60  becomes dimensionally thin sooner, as race  42  moves toward housing  45  in FIG. 5, compared with the situation in FIG. 4. The dimensionally thin fluid acquires the characteristics of a stiffer spring before damper radial clearance  66  in sketch  65  reaches zero.  
         [0023]    In this connection, the Inventor points out an apparent paradox. In FIG. 5, the surface area of the top T of bumper  60  in contact with the fluid in annular cell  52  is much smaller than the surface area of the remainder of the annular cell  52 , such as that indicated by bracket  78 . One may think that the remainder would therefore dominate the behavior indicated by plot  77  in FIG. 6. However, the Inventor has uncovered evidence which indicates that this dominance is not present: the dynamic force is found to resemble that of plot  77 .  
         [0024]    Therefore, in the system of FIG. 5, travel of the race  42  is limited by bumpers  60 . However, the bumpers  60  provide the stiff spring characteristic shown in plot  77  in FIG. 6. This characteristic may not be desirable in certain situations.  
         [0025]    [0025]FIG. 7 illustrates one form of the invention. Bumpers  82  are provided. However, they are positioned outside annular cell  52 . The bumpers  82  possess a radially outer surface  84 , which is closer to housing  45  than the surface  80  of race  42  within the annular cell  52 . Stated another way, outer surface  84  is radially taller than the inner surface  80  of the race  42 .  
         [0026]    The enlarged view shown at the right side of FIG. 7 illustrates this increased height of the outer surface  84  of bumper  82 , compared with surface  80 . The height of the bumper  82  is indicated by dimension  86 .  
         [0027]    Plots  90  and  95  in FIG. 6 illustrate the approximate behavior of the system of FIG. 7. In plot  90 , static force is approximately zero, until point  92  is reached. At that point, surface  84  in FIG. 7 makes contact with housing  45 .  
         [0028]    In plot  95 , the dynamic force follows a plot which is very similar to that of plot  64 , until point  98  is reached in plot  95 . Point  98  indicates contact between surface  84  in FIG. 7 and housing  45 .  
         [0029]    That is, under the invention, as the race  42  in FIG. 7 moves from its normal, rest position, toward the housing  45 , the dynamic force follows a characteristic curve which is similar to that of plot  64  in FIG. 6. Restated, until point  98  is reached in plot  95 , the dynamic damping force is very similar to that in a system wherein no bumpers B in sketch  65  are present. However, once point  98  is reached, both the static force in plot  90 , and the damping force of plot  95 , increase significantly.  
         [0030]    Restated again, the invention provides the relatively soft dynamic spring force of plot  64 , until the contact represented by point  98  is attained. The contact is between race  42  and housing  45 .  
         [0031]    Some generalized dimensions will now be given. Dimension  46  in FIG. 4 preferably lies between 5 and 20 mils. The term mil refers to a milli-inch, or {fraction (1/1,000)} inch. Dimension  100  in FIG. 5 is preferably similar to dimension  46 . In FIG. 5, dimension  105  preferably lies between 3 and 10 mils.  
         [0032]    In FIG. 7, dimension  108  is similar to dimensions  46  and  100 . Dimension  86  preferably lies between 2 and 10 mils.  
         [0033]    In one embodiment, dimension  110  in FIG. 7 preferably lies between 1 and 2 inches. The axial width  115  of bumper  82  preferably lies between 0.05 and 0.1 inches.  
         [0034]    The invention was described in the context of one, or more, bearings which support the low-speed shaft  24  in FIG. 1, with the bearing itself being supported by stationary structure  33 . Another application of the invention includes the bearing, or bearings, which support the high-speed shaft  12  in FIG. 1. Those bearings are supported by low-speed shaft  24 .  
         [0035]    A third application of the invention includes support of a single-shaft gas turbine engine. A fourth application would include all, or any combination of, shafts in a triple-shaft engine. A fifth application would include support of a high-speed shaft by a stationary structure.  
         [0036]    Numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the invention. What is desired to be secured by Letters Patent is the invention as defined in the following claims.