Abstract:
A compliant foil fluid thrust bearing has a single sided or two sided thrust disk rotor, an integrally formed compliant foil member, and an underspring member. The non-rotating but compliant foils are located adjacent to the thrust face or faces or the rotatable disk and are formed as arcuate segments on washer-shaped disk members. The underspring member consists of three washer-shaped disk elements that together provide variable spring stiffness in both the circumferential and radial directions.

Description:
TECHNICAL FIELD 
     This invention relates to the general field of compliant foil fluid film bearings. 
     BACKGROUND OF THE INVENTION 
     Compliant foil fluid film thrust bearings are currently being utilized in a variety of high speed rotor applications. These rotor bearing systems generally include a two sided thrust disk rotating element, non-rotating compliant foil members that axially enclose the rotating element, non-rotating compliant underspring members that axially enclose the foil members, and a non-rotating thrust plate element and a non-rotating housing element that axially enclose and provide attachments for the foil members. The space between the rotating element and the thrust plate element on one side of the thrust disk and the space between the rotating element and the thrust surface of the housing element on the other side of the thrust disk are filled with fluid (such as air, natural gas or LPG) that envelops the foils. 
     The rotary motion of the rotating element applies viscous drag forces to the fluid and induces circumferential flow of the fluid between the smooth surface of the rotating element and the foil. The space between the rotating element and the compliant foil is subdivided into a plurality of fluid-dynamic wedge channels. Leading ramps of the compliant foil pads relative to the fluid&#39;s circumferential flow and a smooth surface of the rotating element form the two primary surfaces of the converging wedge channels. Trailing edge and the smooth surface of the rotating element form the primary surfaces of the diverging wedge channels. 
     Fluid flowing circumferentially along a converging wedge channel experiences steadily decreasing flow area, increasing circumferential flow velocity and static fluid pressure. If the rotating element moves toward the non-rotating element, the flow area along the wedge channel decreases, causing the fluid pressure differential along the channel to increase. If the rotating element moves away, the pressure differential along the wedge channel decreases. Thus, the fluid in the wedge channels exerts restoring forces on the rotating element that vary with, and stabilize running clearances, and prevent contact between the rotating and non-rotating elements of the rotor bearing system. Flexing and sliding of the bearing foils cause coulomb damping of any axial or overturning motion of the rotating element of the rotor bearing system. 
     Compliant foil fluid film thrust bearings operate with extremely small running clearances. The clearances between the compliant foil&#39;s converging channel ramp trailing ends and the rotating thrust disk are typically less than 100 micro-inches (2.5 micrometers) when the bearing is heavily loaded at operating conditions. Furthermore, the use of these thrust bearings results in moderate drag and power consumption. 
     Compliant foil fluid film thrust bearings tend to rely on backing or undersprings to preload the compliant foils against the rotating thrust disk so as to control foil position/nesting and to ensure rotor dynamic stability. The bearing starting torque (which should ideally be zero) is directly proportional to these preload forces and/or gravity forces. These preload forces also significantly increase the thrust disk speed at which the hydrodynamic effects in the wedge channels are strong enough to lift the rotating element of the rotor bearing system out of physical contact with the non-rotating members of the rotor bearing system. These preload forces and the high lift-off/touch-down speeds result in significant bearing wear each time the disk is started or stopped. This wear can generally be reduced significantly by coating the compliant foil members with solid film lubricants. 
     SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment of the present invention, a method for rotatably supporting a thrust disk on a thrust plate provides a compliant foil thrust bearing between the thrust disk and the thrust plate, and mounting an underspring member between the compliant foil member and the thrust plate to provide variable spring stiffness to the annular compliant foil member in both circumferential and radial directions. In another embodiment, a compliant foil fluid film thrust bearing includes a thrust disk rotatably supported by a non-rotating thrust bearing surface, and a compliant foil thrust bearing is operably disposed between the thrust disk and the non-rotating thrust bearing surface and mounted on the thrust bearing surface, the compliant foil thrust bearing includes a compliant foil member and an underspring member mounted on the thrust bearing surface and disposed between the thrust bearing surface and compliant foil member, the underspring member includes means to provide variable spring stiffness to the annular compliant foil member in both the circumferential and radial directions. Various shapes and configurations of the bearing members are illustrated and described. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus described the present invention in general terms, reference will now be made to the accompanying drawings in which: 
     FIG. 1 is a sectional view of a turbomachine including a fluid film thrust bearing according to the present invention; 
     FIG. 2 is an enlarged partial view of oval  2  of FIG. 1 illustrating the thrust plate and spacer area of the fluid film thrust bearing according to the present invention; 
     FIG. 3 is a plan view of the support element of an underspring member according to the present invention; 
     FIG. 4 is a plan view of the plate element of underspring member of the present invention; 
     FIG. 5 is a plan view of the anvil element of underspring member according to the present invention; 
     FIG. 6 is a plan view of an aerofoil member according to the present invention; 
     FIG. 7 is an exploded sectional view of an individual pad taken along line  7 — 7  of FIG. 6; 
     FIG. 8 is an exploded plan view of the underspring member and aerofoil member of FIGS. 3-6, with partial sectionals showing aerofoil member and elements of underspring member; 
     FIG. 9 is a partial plan view of an alternate support element of the underspring member of the present invention; 
     FIG. 10 is a plan view of an alternate aerofoil member of the present invention; 
     FIG. 11 is an enlarged sectional view taken along line  11 — 11  of FIG. 8; 
     FIG. 12 is a plan view of the support element of an alternate underspring member according to the present invention; 
     FIG. 13 is a plan view of the plate element of an alternate underspring member according to the present invention; 
     FIG. 14 is a plan view of the anvil element of an alternate underspring member according to the present invention; 
     FIG. 15 is a plan view of an alternate aerofoil member of the present invention for use with the alternate underspring member of FIGS. 12-14; 
     FIG. 16 is an exploded plan view of the underspring member and aerofoil member of FIGS. 12-15, with partial sectionals showing the alternate aerofoil member and elements of the alternate underspring member; 
     FIG. 17 is a plan view of an alternate plate element of alternate underspring member according to the present invention; 
     FIG. 18 is a cross sectional view of the alternate plate element of FIG. 17 taken along line  18 — 18 ; 
     FIG. 19 is a plan view of an alternate support element of alternate underspring member according to the present invention; 
     FIG. 20 is a partial plan view of another alternate aerofoil member according to the present invention; 
     FIG. 21 is a partial plan view of yet another alternate aerofoil member according to the present invention; and 
     FIG. 22 is a partial plan view of still another alternate aerofoil member according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A turbomachine utilizing the fluid film thrust bearing of the present invention is illustrated in FIG.  1 . The turbomachine  10  generally includes a turbine wheel rotor  12  and a compressor wheel rotor  14  at opposite ends of a common shaft or tie bolt  16 . The thrust and radial bearing rotor  18  is disposed around the tie bolt  16  between the turbine wheel rotor  12  and the compressor wheel rotor  14 . A journal bearing cartridge  20  in center bearing housing  22  supports the bearing rotor  18 . 
     The compressor end of the bearing rotor  18  includes a radially ex tending thrust disk  24  which extends into a recess  26  in the compressor end of the center bearing housing  22 . A bearing thrust plate  28  is disposed on the opposite side of the bearing rotor thrust disk  24 . The outer periphery of the compressor end of the center bearing housing  22  engages the compressor housing  30 . 
     With reference to FIG. 2, a thrust bearing spacer  32  is positioned radially outward from the thrust disk  24  of the bearing rotor  18  and is positioned radially by a plurality of circumferentially spaced pins  34  which are fixed in holes  37  in the recess  26  of the center bearing housing  22  and extend into holes  38  in the thrust bearing plate  28 . Alternately, pilots could be utilized to align the various elements. A thrust bearing compliant foil member or aerofoil member  40  and thrust bearing underspring member  42  are disposed on either side of the bearing rotor thrust disk  24  and thrust bearing spacer  32 . On one side, the compliant foil member  40  and underspring member  42  are positioned in the recess  26  of the center bearing housing  22  and on the other side they are adjacent to the bearing thrust plate  28 . The foil member  40  and underspring member  42  are held in position radially and circumferentially by the pins  34  which extend from the center bearing housing  22 , through holes in underspring member  42 , through holes in aerofoil member  40 , through holes in thrust bearing spacer  32 , through holes in the opposite side foil member  40 , holes in the opposite side underspring member  42  and into holes  38  in the bearing thrust plate  28 . The bearing thrust plate  28  is biased towards the center bearing housing  22  by a Belleville washer  23  disposed between the lip  25  on the bearing thrust plate  28  and the compressor housing  30 . 
     The thickness of the thrust bearing spacer  32  is a few thousandths of an inch greater than the thickness of the bearing rotor thrust disk  24 . Variations in the foil or foil coating thicknesses inherently cause compensating variations in the spacing between the thrust plate  28  and the housing  22 . Thus, variations in bearing sway space and bearing compliance due to foil thickness tolerances are prevented. 
     FIGS. 3-5 illustrate the three elements of the underspring member  42 . These are the bottom or support element  50  (FIG.  3 ), the mid or plate element  52  (FIG.  4 ), and the top or anvil element  54  (FIG.  5 ). The compliant foil or aerofoil member  40  is illustrated in FIG.  6 . 
     Each of the support element  50 , plate element  52 , anvil element  54  and aerofoil member  40  is formed from a single flat disk termed a foil blank from the same or different materials. They can be produced by conventional EDM techniques, by fine blanking or stamping techniques, or by chemical etching. 
     The support element  50  includes an outer ring  60  having a plurality of inwardly projecting supports  62 . The number of supports  62  is illustrated by way of example as ten. Each support  62  includes a stem  63  and a wedge or arrow  64  having a leading edge  65  and a trailing edge  66  meeting at point  69 , plus a leading edge base  67  and a trailing edge base  68 . The leading edge base  67  is shorter than the trailing edge base  68  which makes the arrow  64  off centered on the stem  63 . The outer ring  60  includes a plurality of round or oval aligning holes  71  (three shown). 
     The plate element  52  includes an outer ring  60 ′ having similarly situated aligning holes  71 ′. An annular plate ring  75  is supported within the outer ring  60 ′ by a plurality of forwardly slanted webs  78 . The annular plate ring  75  has an outer diameter  76  and an inner diameter  77 . 
     The anvil element  54  also includes an outer ring  60 ″ having aligning holes  71 ″ in the same positions as the support element  50  and plate element  52 . A plurality of anvils  79  extend inward from the outer ring  60 ″ with a stem  80 . The leading edge  81  of the anvil  79  is an extension of the stem  80  while the trailing edge  82  of the anvil  79  extends radially from the anvil base  83 . 
     Likewise, the aerofoil member  40  includes an outer ring  60 ′″ having aligning holes  71 ′″ in the same spatial relationship as the three elements  50 ,  52 , and  54  of the underspring member  42 . An annular aerofoil  89  includes a plurality of pads  90 , having outer diameter  92  and inner diameter  93  supported within the outer ring  60 ′″ by a plurality of forwardly slanted webs  91 . 
     The aligning holes  71 ,  71 ′,  71 ″, and  71 ′″ are equally spaced around the outer rings  60 ,  60 ′,  60 ″, and  60 ′″ respectively, and serve to align the elements  50 ,  52 ,  54  of the underspring member  42  and the aerofoil member  40 . With this equal spacing, a primary or pivotal hole is designated to establish the proper relationship of the aligning holes of the underspring member  42  and aerofoil member  40 . In addition, a triangular arrow, indicating the direction of rotation of the thrust disk, may be etched near this primary hole. 
     With reference to FIG. 7, the pads  90  comprise steeply sloped joggles or steps  94  to function as diverging wedge channels and gradually converging annular wedge channels including flat lands  88  and ramps  95 . The pads  90  each include a leading edge  96  and a trailing edge  97 . 
     FIG. 8 is an enlarged plan view of the assembled underspring member  42  and aerofoil member  40  illustrating the relative positions of the various elements with individual elements partially broken away to show the element underneath. Arc “A” of FIG. 8 shows the support element  50  of FIG. 3 while Arc “B” shows the plate element  52  of FIG. 4 with the support element  50  underneath, partially shown in dotted lines. Arc “C” shows the anvil element  54  of FIG. 5 with both the plate element  52  and support element  50  underneath, with the remainder of FIG. 8 illustrating the aerofoil member  40  of FIG. 6 over the three elements  50 ,  52 , and  54  of the underspring member  42 . 
     The outer radius  76  of the plate ring  75  is slightly less than the radial dimension of the bases  67 ,  68  of arrow  64  of the support element  50  and the base  83  of the anvils  79  of the anvil element  54 . The inner radius  77  of the plate ring  75  generally has the same radial dimension of the point  69  of arrow  64  of the support element  50 . The anvils  79  are spaced between adjacent arrows  64  with the inner diameter  84  of the anvils  70  generally the same as the inner diameter  93  of the aerofoil  89 . The leading edge  81  of the anvil  79  is slightly upstream from the leading edge  96  of the pads  90 . 
     FIG. 9 is an illustration of an alternate support element  50 ′ having outer ring  60 . The alternate support element  50 ′ is generally similar to the support element  50  of FIG. 3 except that the trailing edge of support  64 ′ includes both an arrow portion  98  and a radial portion  99  which results in a shorter trailing edge base  68 ′. In both support element  50 ′ and support element  50 , the arrow point  69  is slightly offset upstream from the radial line through the stem  63 . 
     An alternate aerofoil member  100  is illustrated in FIG.  10 . The aerofoil member  100  is generally similar to aerofoil member  40  of FIG. 6 with an outer ring  101  supporting an aerofoil  103 . The aerofoil  103  includes a plurality of pads  106  having an outer diameter  104  and an inner diameter  105 . 
     As illustrated in FIG. 11, the pads  106  comprise steeply shaped joggles  114  to function as diverging wedge channels and gradually converging annular wedge channels including flat lands  113  and ramps  115 , with each pad having a leading edge  116  and a trailing edge  117 . As illustrated in FIG. 10, the leading edge  116  and trailing edge  117  of pads  106  can be generally curved or arcuate for added rigidity. By curving the leading and trailing edges  116 ,  117  of the pads  106 , the structural strength of the pads can be increased and the potential deflection or deformation of the leading edges of the pads under high temperature load can be significantly reduced, this minimizes loss of load capacity. The three underspring elements are also shown with an exaggerated height beneath the aerofoil in FIG. 11 to illustrate the relative position of the pads  106  with the anvils  79 , the plate  75  and the supports  64 . 
     In the outer ring  101  of aerofoil member  100 , the aligning holes  107 ,  108  and  109  are not equally spaced and accordingly provide a more fail-safe alignment. The circumferential distance between aligning holes  107  and  108  is less than the circumferential distance between aligning holes  107  and  109  and the circumferential distance between aligning holes  108  and  109  is less than the circumferential distance between aligning holes  107  and  108 . Thus, there is only one way for the holes in the aerofoil member to be aligned with the similar holes in the underspring elements. 
     FIGS. 12-14 illustrate the three elements of an alternate underspring member. These are the bottom or support element  150  (FIG.  12 ), the mid or plate element  152  (FIG.  13 ), and the top or anvil element  154  (FIG.  14 ). The alternate compliant foil member  140 , that goes with the underspring elements  150 ,  152  and  154  is illustrated in FIG.  15 . 
     The support element  150  includes an outer ring  160  having a plurality of inwardly projecting supports  162  with each support  162  generally wedge shaped changing width from a greater width at the outer ring  160  to a lesser width at the inner ring  169 . Both the leading edge  165  and trailing edge  166  of the supports  162  would be generally radial. The outer ring  160  includes three unequally spaced round or oval aligning holes  151 ,  153 , and  155 . 
     The plate element  152  includes an outer ring  160 ′ having similarly situated aligning holes  151 ′,  153 ′, and  155 ′. An annular plate ring  175  is supported within the outer ring  160 ′ by a plurality of forwardly slanted webs  178  and includes an outer diameter  176  and an inner diameter  177 . 
     The anvil element  154  also includes an outer ring  160 ″ having aligning holes  151 ″, is  153 ″, and  155 ″, in the same positions as the support element  150  and plate element  152 . An annular ring  180  is supported by a plurality of forwardly slanted webs  185  which also support a plurality of inwardly projecting anvils  179 . Each anvil  179  includes a generally radially extending leading edge  181  and trailing edge  182  and an inner diameter  184 . 
     Likewise, the aerofoil member  140  includes an outer ring  160 ′″ having aligning holes  151 ′″,  153 ′″, and  155 ′″ in the same spatial configuration as the aligning holes in the three elements  150 ,  152 , and  154  of the underspring member. An annular aerofoil  189  includes a plurality of pads  190 , having outer diameter  192  and inner diameter  193  supported within the outer ring  160 ′″ by a plurality of forwardly slanted webs  191 . 
     FIG. 16 is an enlarged plan view of the assembled underspring member and aerofoil member of FIGS. 12-15 illustrating the relative positions of the various elements with individual elements partially broken away to show the element underneath. Arc “L” of FIG. 16 shows the support element  150  of FIG. 12 while Arc “M” shows the plate element  152  of FIG. 13 with the support element  150  underneath, partially in dotted lines. Arc “N” shows the anvil element  154  of FIG. 14 with both the plate element  152  and support element  150  underneath, with the remainder of FIG. 16 illustrating the aerofoil member  140  of FIG. 15 over the three elements of the underspring member. As can be seen, the outer rings  160 ,  160 ′,  160 ″, and  160 ′″ are aligned together with aligning holes therein. 
     The outer diameter  176  of the plate ring  175  is generally the same as the outer diameter  192  of the aerofoil  189 . The anvils  179  are spaced between adjacent supports  162  and the leading edge  181  of the anvil  179  is slightly upstream from the trailing edge of the pads  190 . 
     The alternate plate element  152 ′ of FIGS. 17 and 18 is generally identical to the underspring element  152  of FIG. 13 except for the thickness of the annular plate ring  275  which is now thicker than the rest of the underspring element  152 ′. By increasing the thickness of the annular plate ring  275 , the stiffness of the bearing will be increased. A further alternative would be to taper the thickness of the annular plate ring  275  to have a greater thickness at the outer diameter  176  than at the inner diameter  177 . This will produce a greater stiffness at the outer diameter  176  than at the inner diameter  177  to achieve a mechanical stiffness that approaches in value the hydrodynamic film stiffness which is greater at the outer diameter than the inner diameter. 
     The alternate support element  150 ′ includes an outer ring  260  having a plurality of supports  262  inwardly projecting therefrom. Neither the leading edge  265  or trailing edge  266  are radial but the leading edge  265  of one support  262  is generally parallel with the trailing edge  266  of the next adjacent support. This results in a constant circumferential spring length (of any plate member) from the inner radius to the outer radius. 
     Three alternate aerofoil members are illustrated in FIGS. 20-22. In FIG. 20, aerofoil member  200  is identical to aerofoil member  100  of FIG. 10 except for a plurality of narrow slots  202  at the trailing edge of the pads  106  of the aerofoil  123  which extend a short distance radially inward from the outer diameter  104 . The aerofoil member  220  of FIG. 21 includes a plurality of narrow slots  204  at the trailing edge of the pads  106  of the aerofoil  123  which extend radially outward a short distance from the inner diameter  108 . In FIG. 22, the radially inwardly extending slots  202  alternate with the radially outwardly extending slots  204 . The slots  202  and  204  minimize the deformation of the aerofoil at operating temperatures and thus prevent thermal buckling. 
     While specific embodiments of the invention have been illustrated and described, it is to be understood that these are provided by way of example only and that the invention is not to be construed as being limited thereto but only by the proper scope of the following claims.