FLUID THRUST BEARING

Abstract: A fluid thrust bearing comprising a thrust runner (10), a thrust plate (28) and a compliant foil bearing located between them. The foil bearing comprises a thrust disc 14 having a series of compliant foils (16) and an underspring (22). The underspring (22) has a corresponding series of tabs (32) which are formed with bumps (24) extending towards the thrust disc (14).

Description: Process fluid or gas bearings are now being used in an increasing number of diverse applications. These fluid bearings generally comprise two relatively movable elements with a predetermined spacing therebetween filled with a fluid such as air, which, under dynamic conditions, forms a supporting wedge sufficient to prevent contact between the two relatively movable elements. More recently, improved fluid bearings, particularly gas bearings of the hydrodynamic type, have been developed by providing foils in the space between the relatively movable bearing elements. Such foils, which are generally thin sheets of a compliant material, are deflected by the hydrodynamic film forces between adjacent bearing surfaces and the foils thus enhance the hydrodynamic characteristics of the fluid bearings and also provide improved operation under extreme load conditions when normal bearing failure might otherwise occur. Additionally, these foils provide the added advantage of accommodating eccentricity of the relatively movable elements and further provide a cushioning and dampening effect. The ready availability of relatively clean process fluid or ambient atmosphere as the bearing fluid makes these hydrodynamic, fluid film lubricated, bearings particularly attractive for high speed rotating machinery. While in many cases the hydrodynamic or self-acting fluid bearings provide sufficient load bearing capacity solely from the pressure generated in the fluid film by the relative motion of the two converging surfaces, it is sometimes necessary to pressurise externally the fluid between the bearing surfaces to increase the load carrying capability. While these externally pressurised or hydrostatic fluid bearings increase the load carrying capacity, they do introduce the requirement for an external source of clean fluid under pressure. In order to position the compliant foils properly between the relatively movable bearing elements, a number of mounting means have been devised. In thrust bearings, it is conventional practice to mount a plurality of individually spaced foils on a foil bearing disc such as by spot welds and position the foil bearing disk on one of the bearing elements as shown in US Patent No. 3,635,534. Alternatively, a compliant unitary foil, such as illustrated in US Patent No. 4,247,155, has been proposed. To establish stability of the foils in most of these mounting means, a substantial pre-load is required on the foil. That is, the individual foils must be loaded against the relatively movable bearing element opposed to the bearing elements upon which the foils are mounted. It has been conventional to provide separate compliant stiffener elements or undersprings beneath the foils to supply this required preload as shown in US Patent Nos. 3,893,733 and 4,153,315. According to the invention, there is provided a fluid thrust bearing comprising a pair of members arranged for relative rotation with respect to one another and a compliant foil bearing located between the two relatively rotatable members, characterised in that the compliant foil bearing comprises a thrust disc having a plurality of compliant foils and an underspring including a plurality of protruberances standing proud of the surface of the underspring towards the thrust disc. One of the two members may be arranged to support the other. The two relatively rotating members may be a thrust runner and a thrust plate which rotatably supports the trust runner. Preferably, one protruberance is generally disposed in supporting relationship to an individual compliant foil. Preferably the compliant foils are individually mounted on the thrust disc, though they may be formed integrally. The protuberances may constitute spring bumps which provide improved load capacity and distribution. Preferably, there are a plurality of tabs on the underspring extending in the direction of rotation of the member adjacent the foils. Preferably, the protruberances are constituted by at least one radially extending bump extending across each tab. The bumps are preferably arcuate and their height may be between 0.003 and 0.060 inches (0.076 to 1.52mm). Alternatively, the tabs may be arcuate and thereby constitute the protruberances in themselves. The tabs may each be defined by a generally U-shaped slot. The underspring may be in the form of a foil stiffener disc, and the protruberances may be formed by stamping. The tabs may include two radially extending bumps. Each tab may include a first radially extending bump near the free end of the tab and a second radially extending bump near the base of the tab, the first bump having a height generally between 0.0005 inches and 0.030 inches (0.076 to 1.52mm) greater than the height of the second bump. The bumps may have a radial length generally between 0.2 and 8.0 inches (0.51 cm to 20.3cm). The bumps may diverge radially outwardly and their sides may be radial lines. The tabs may be divided into at least two prongs. Preferably, there are three prongs. There may also be a plurality of second tabs on the underspring extending in a generally radial direction and protruding away from the thrust disc. According to a preferred embodiment therefore, a fluid thrust bearing comprises a thrust runner a fluid thrust bearing comprising: a thrust runner; a thrust plate to rotatably support the thrust runner; and a compliant foil bearing operably disposed between said thrust runner and said thrust plate and mounted on said thrust plate, said compliant foil bearing including a thrust disc having a plurality of converging surface compliant foils disposed towards said thrust runner and a foil stiffener disc disposed between the thrust disc and the thrust plate, the foil stiffener disc including a plurality of first tabs extending in the direction of rotation of said thrust runner toward said thrust disc with an individual tab generally disposed in a supporting relationship towards an individual foil on said thrust disc and said first tabs divided into at least two generally arcuate prongs, said foil stiffener disc also including a plurality of second tabs extending in a generally radial direction towards said thrust plate. Preferably, the stiffness of the first tabs is at least 10² times grcater than the stiffness of the second tabs, more preferably between 10² and 10⁵ times greater. Preferably, the second tabs are arcuate, though they may be generally straight. The present invention also extends to an underspring for a foil thrust bearing as described above in relation to the foil thrust bearing, preferably stamped from a sheet of uniform thickness. In particular, according to a further aspect of the invention, there is provided an underspring for a foil thrust bearing comprising: a compliant ring disc; and a plurality of tabs disposed on said ring disc with each tab having at least one radially extending bump thereacross. According to a still further aspect of the invention, there is provided an underspring for a foil thrust bearing comprising: a compliant ring disc; a plurality of first tabs disposed on said ring disc extending from one surface thereof; and a plurality of second tabs radially disposed on said ring disc extending from the other surface thereof. According to a further aspect of the invention, there is provided a method of rotatively supporting a thrust runner on a thrust plate comprising the steps of: providing a compliant foil bearing between said thrust runner and said thrust plate, said compliant foil bearing including a thrust disc having a plurality of converging surface compliant foils disposed towards said thrust runner; and providing a compliant generally flat ring stiffener disc between the thrust disc and the thrust plate, said foil stiffener disc including a plurality of first tabs extending in the direction or rotation of said thrust runner toward said thrust disc with an individual tab generally disposed in a supporting relationship towards an individual foil on said thrust disc and said first tabs divided into at least two generally arcuate prongs, said foil stiffener disc also including a plurality of second tabs extending in a generally radial direction towards said thrust plate. According to a still further aspect of the invention, there is provided a method of forming an underspring for a foil thrust bearing comprising the steps of: providing a uniform thickness compliant ring disc; chemically etching a plurality of generally U-­ shaped slots in said disk; and stamping a radially extending bump on each of the tabs formed by the U-­ shaped slots. The invention may be carried into practice in various ways and some embodiments will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 is an exploded perspective view of a foil thrust bearing in accordance with the present invention; Figure 2A is an enlarged partial top plan view of the thrust bearing underspring of the foil thrust bearing of Figure 1; Figure 2B is an enlarged partial bottom plan view of the thrust bearing underspring of Figure 2A; Figure 2C is an enlarged perspective view of an individual bump of the thrust bearing underspring of Figure 2A; Figure 3 is an edge view of the thrust bearing underspring of Figure 2A taken along line 3-3 thereof; Figure 4 is an enlarged partial top plan view of a second embodiment of a thrust bearing underspring; Figure 5 is an edge view of the thrust bearing underspring of Figure 4 taken along line 5-5 thereof; Figure 6 is an enlarged partial top plan view of a third embodiment of a thrust bearing underspring; Figure 7A is an enlarged partial top plan view of a fourth embodiment of a thrust bearing underspring; Figure 7B is an enlarged partial perspective view of the thrust bearing underspring of Figure 7A; Figure 8 is an enlarged partial perspective view of a fifth embodiment of a thrust bearing underspring; Figure 9 is a sectional view of the thrust bearing under spring of Figure 8 taken along line 9-9 thereof; Figure 10 is a sectional view of the thrust bearing underspring of Figure 8 taken along line 10-10 thereof; and Figure 11 is a sectional view of an alternative downwardly extending tab. As illustrated in Figure 1, a thrust runner 10, including a shaft 12, is rotatably supported on a thrust plate 28 by means of a thrust bearing disc 14 and a thrust bearing stiffener or underspring 22. The thrust bearing disc 14 includes a plurality of compliant foils 16 while the thrust bearing underspring 22 includes a plurality of bumps 24 thereon to provide stiffness for the thrust bearing disc 14. The underspring 22 may include outer projections 25 having cut outs 29 which can be used to maintain the position of the underspring 22 with respect to the thrust plate 28. Similar projections 27 may be spaced around the thrust bearing disc 14. As shown more fully in Figures 2A-3, the thrust bearing underspring 22 generally comprises a thin compliant ring disc having a thickness generally between 0.001 inches and 0.030 inches (0.025 to 0.076 mm). A plurality of generally U-shaped slots 30, with the open ends thereof facing away from the direction of rotation of the thrust runner 10, extend through the entire thickness of the underspring 22. Each of these generally U-shaped slots 30 defines a tab 32 having its free end facing in the direction of rotation of the thrust runner 10. The bumps 24, which extend generally radially, are formed by stamping the tabs 32. The number of U-shaped slots 30 and hence the number of tabs 32 is equal to the number of thrust bearing foils 16 on the thrust bearing disc 14 which an individual tab disposed generally beneath each individual foil. The height of the bumps 24 is generally between 0.003 inches to 0.060 inches (0.076 to 1.52 mm). The radial length of the bump would depend upon the size of the bearing and would generally be between 0.02 inches to 8 inches (0.51cm to 20.3cm) As illustrated in Figures 4 and 5, the tab 33 may include more than a single bump, such as the two bumps 34 and 36. Also, the bump 36 closest to the free end of the tab 33 may have a height greater than the height of the bump 34 closer to the base of the tab 33. The height of the bump 36 would generally be between 0.005 inches and 0.030inches (0.013 mm to 0.76mm) greater than the height of the bump 34. Figure 6 illustrates a tab 40 having a bump 42 in which the width of the bump increases radially. It should be recognised that for the purposes of illustration, the radial divergence of the bump 42 is shown as exaggerated. The sides of the bump 42 would generally be radial lines. As illustrated in Figure 7A and 7B, the tab produced by U-shaped slot 48 may be divided into more than one prong, for example, an inner prong 50, a middle prong 52 and an outer prong 54, by means of an inner slot 56 and an outer slot 58. This arrangement produces an inner bump 60, a middle bump 62, and an outer bump 64, each of which are generally radially aligned. An alternative underspring 70 is illustrated in Figures 8 to 11. The underspring 70 includes a plurality of upwardly extending tabs, each having an inner prong 72, a middle prong 74, and an outer prong 76. Each of these prongs has a generally arcuate or curved shape. The underspring 70 also includes a plurality of downwardly extending tabs 80 formed in radially extending slots 82. The tabs 80 may also be arcuate or curved in shape as shown in Figure 9 or the tabs 84 may be straight as shown in Figure 11. While existing chemically etched undersprings are difficult to produce in a highly repeatable manner due to the difficulty in controlling the critical thickness dimensions, undersprings stamped in accordance with the present invention using a constant thickness sheet material consistently produce the series of shallow bumps in a highly repeatable manner. This not only results in a much less complex manufacturing process but provides greater control and better load capacity for the underspring. By slotting the tabs, even more load distribution can be produced in the radial direction. Under load conditions the bumps deform to yield a greater support area for the thrust bearing foil and thus generate a higher load capacity. Good bearing damping is also achieved when the bump flares under load and the free end of the tab stretches and rubs against the bearing structure. The bump is generally quite stiff in order to provide a good load capacity. The downwardly extending tabs are much less stiff or weaker than the upwardly extending tabs and are used to provide a proper preload in the bearing assembly. The upwardly extending tabs, which provide primary stiffness for the bearing, generally have a stiffness at least 10² times greater than the stiffness of the downwardly extending tabs and this stiffness may be as much and 10⁵ times greater. In other words in operation, the downwardly extending tabs will yield or deform under load before any yielding or deformation of the upwardly extending tabs. While the invention has been illustrated in relation to a thrust bearing, it is equally applicable to a conical bearing which has a thrust component.

Claims: 1. A fluid thrust bearing comprising a pair of members (10,28) arranged for relative rotation with respect to one another and a compliant foil bearing (14,22) located between the two relatively rotatable members (10,28), characterised in that the compliant foil bearing comprises a thrust disc (14) having a plurality of compliant foils (16) and an underspring (22) including a plurality of protruberances (24) standing proud of the surface of the underspring (22) towards the thrust disc (14). 2. A bearing as claimed in Claim 1 characterised by a plurality of tabs (32) on the underspring extending in the direction of rotation of the member (10) adjacent the foils (16). 3. A bearing as claimed in Claim 2 characterised in that the protruberances are constituted by at least one radially extending bump (24) extending across each tab (32). 4. A bearing as claimed in Claim 2 characterised in that the tabs (72,74,76) are arcuate and thereby constitute the protruberances in themselves. 5. A bearing as claimed in Claim 3 characterised in that each of the tabs includes two radially extending bumps (34,36) thereacross. 6. A bearing as claimed in Claim 5 characterised in that each tab includes a first radially extending bump (36) near the free end of the tab and a second radially extending bump (34) near the base of the tab, the first bump having a height generally between 0.0005 inches and 0.030 inches (0.076 to 1.52mm) greater than the height of the second bump. 7. A bearing as claimed in any of Claims 3 to 6 characterised in that the bumps (42) radially outwardly diverge. 8. A bearing as claimed in any of Claims 2 to 7 characterised in that the tabs are each divided into at least two prongs (50,52,54). 9. A bearing as claimed in any of Claims 2 to 8 characterised by a plurality of second tabs (80) on the underspring (70) extending in a generally radial direction and protruding away from the thrust disc (14). 10. A bearing as claimed in Claim 9 characterised in that the stiffness of the first tabs (72,74,76) is greater than the stiffness of the second tabs (80). 11. A bearing as claimed in any preceding claim characterised in that the underspring is stamped from a sheet of uniform thickness.

Inventors: LEE-VAN GU, ALSTON
Applicants: ALLIED-SIGNAL INC. (A DELAWARE CORPORATION)
Application year: 1986
Main classification: F16C17
IPC codes: F16C27, F16C17