FLUID-LUBRICATED FOIL BEARINGS, AND FOILS FOR SUCH BEARINGS

Abstract: In a fluid-lubricated foil bearing, the foils (16) are retained in place on one of the bearing members (14) by having an end portion (17) of the foil, which end portion is rolled into a part-cylindrical shape, received in a slot (15) of part-circular cross-section formed in the bearing member (14). The slot (15) is sufficiently deep that its mouth is narrower than its widest part, so that the end portion (17) of the foil (16) cannot escape from the slot (15).

Description: "FOIL MOUNTING ARRANGEMENTS FOR FLUID-LUBRICATED FOIL BEARINGS, AND FOILS FOR SUCH BEARINGS" FIELD OF THE INVENTION This invention relates to fluid-lubricated foil bearings, and more particularly to foil mounting arrangements for such bearings. THE PRIOR ART Process fluid or gas bearings are now being used in an increasing number of applications. These fluid bearings generally comprise two relatively movable elements, such as a shaft and a bushing, with a clea-rance between the elements 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. In many cases, no external supply of lubricant under pressure is required, and the bearing operates purely hydrodynamically. More recently, improved fluid bearings, particularly gas bearings, 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 the fluid between the bearing surfaces from an external source to increase the load carrying capability. In order to keep the compliant foils in their correct positions between the relatively movable bearing elements, a number of mounting means have been devised. For example, U.S. Patent Nos. 3,366,427, 3,375,046 and 3,615,121 show a rod or bar attached to one end of the foil; this rod or bar is retained in a slot or groove in one of the relatively movable bearing elements. Alternatively, a lip or projection at one end of the foil may be restrained in a slot or groove in one of the relatively movable elements, as shown in UIS. Patent Nos. 3,511,544, 3,747,997, 3,809,443 and 3,382,014. U.S. Patent Nos. 3,382,014 and 3,809,443 also suggest mounting a plurality of overlapping foils individually on a foil base by spot welds. The base would then be frictionally held against one of the relatively movable bearing elements. In order to ensure stability of the foils when using most of these known forms of foil mounting, a substantial pre-load is required on the foil, that is to say, the individual foils must be loaded against the relatively movable bearing element opposed to the bearing element upon which the foils are mounted. This pre-load however results in a higher starting torque and can create severe wear on the foils and also will probably reduce the net load carrying capacity of the bearing. SUMMARY OF THE INVENTION According to the present invention, a fluid-lubricated bearing comprising a first member which has a bearing surface, and a second member which carries, on a surface facing the bearing surface of the first member, a plurality of overlapping, compliant foils, each foil being connected to the second member by the engagement of a projection attached to one end of the foil in a slot in the surface of the second member, is characterised in that each slot in the second member has a partcircular cross-section, of sufficient depth that the opening of the slot on to the surface of the second member is narrower than the widest part of the crosssection of the slot, and in that the projection on each foil is formed by an end portion of the foil rolled into a part-circular loop. With such an arrangement, each foil is effectively connected to the second member by a hinge. Since the part-circular loops of the foils cannot readily escape from the slots in the second member, the amount of preload required on the foils is greatly reduced. In addition, the foils will tend to follow the bearing su-rface of the first member even at higher speeds. With the reduced pre-load, less starting torque is required to initiate lift off of the foils from the bearing surface. The net load bearing capability of the foils is also increased as a result of the reduced pre-load. Additional advantages include better stability and the ability to withstand higher surface speeds. Since the foils follow or track better when mounted in this fashion, better damping characteristics will be present. BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a perspective view of a foil journal bearing embodying the present invention; Figure 2 is an enlarged end view of a journal bushing forming part of the foil bearing of Figure 1, and also shows a number of individual foil members mounted in the bushing; Figure 3 is a partial, enlarged end view of a journal bushing forming part of an alternative form of foil journal bearing, incorporating individual foil members and separate stiffener elements; and Figure 4 is a perspective, partially exploded view of a foil thrust bearing embodying the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to Figure 1, there is illustrated a foil journal bearing 10 having a shaft 12 rotatably borne in a bushing 14. Disposed between the shaft 12 and the bushing 14 are a plurality of individual, overlapping arcuate bearing foils 16. Arrows on the end of the shaft 12 and the exterior of the bushing 14 indicate the direction of relative rotation between the shaft and the bushing. It is not necessary that both the shaft and the bushing should rotate; one or other of the shaft or the bushing may be stationary. It is only necessary for correct operation of the bearing that the relative rotation between the shaft and the bushing should be in the direction indicated. As more clearly illustrated in Figure 2, the bushing 14 on its inner surface includes a plurality, in this example eight, of uniformly spaced slots 15, each extending parallel to the axis of the bushing 14. The cross-section of each slot 15 is bounded, except where the slot opens into the bore of the 'bushing 14, by a circular arc of radius r, whose angular extent is rather more than 1800 of a circle, although less than 3600. In other words, the depth h of the slot 15 is less than the diameter d of the circular arc, but is in general greater than the radius r. Each individual bearing foil 16 is formed of a thin, compliant, metallic material. At one end of each bearing foil 16, the material of the foil is rolled to form a part-cylindrical loop 17 which is pivotably received in one of the slots 15 of the bushing 14. The loop 17 can be snapped into or slid into the slot 15 when the bearing is assembled. The outer diameter of the loop 17 is slightly less than the diameter of the circular slot 15, so that the foil 16 is free to pivot, with the loop 17 rotating within the slot 15, without undue force-being required. A mild interference fit between the loops 17 and slots 15 is contemplated. In order that the loops 17 should be captive in the slots 15, the loops 17 extend around at least 1800 of a circle. In the alternative form of bearing shown in Figure 3, each foil 16 is associated with a stiffener or underfoil 18, the underfoil 18 having alternate grooves and ridges so as to provide both a bending and a compressive mode of operation. Such stiffening elements are described in more detail in U.S. Patent No. 4,153,315. Each stiffener 18 includes a rolled loop 19 which is disposed within the loop 17 of the associated foil 16, so that the foil and stiffener can pivot independently within the circular slot 15 of the bushing 14. While the embodiments of Figures 1, 2 and 3 are both journal bearings, it should be recognized that the invention is also applicable to other types of foil bearing, for example, thrust bearings and conical bearings. Figure 4 illustrates a foil thrust bearing 20 embodying the invention. The foil thrust bearing 20 includes a thrust plate 22 and a thrust runner 24, and, positioned between the thrust plate 22 and the thrust runner 24, a plurality of individual, overlapping bearing foils 26. In operation, relative rotation occurs between the thrust plate 22 and the thrust runner 24 in the direction indicated by an arrow on the thrust runner 24. Each individual foil 26 includes a circular loop 28 adapted to be mounted within a corresponding circular slot 30 in the thrust plate 22 in the same manner as described in detail with respect to the journal bearing figures.

Claims: CLAIMS 1. A fluid-lubricated bearing comprising a first member which has a bearing surface, and a second member which carries, on a surface facing the bearing surface of the first member, a plurality of overlapping, compliant foils, each foil being connected to the second member by the engagement of a projection attached to one end of the foil in a slot in the surface of the second member, characterised in that each slot (15, 30) in the second member (14, 22) has a part-circular cross-section, of sufficient depth that the opening of the slot (15, 30) on to the surface of the second member is narrower than the widest part of the cross-section of the slot (15, 30), and in that the projection on each foil (16, 26) is formed by an end portion of the foil rolled into a partcircular loop (17, 28). 2. A bearing as claimed in Claim 1, in which the part-circular loop (l7, 28) extends around at least 0 180 of a circle. 3. A bearing as claimed in Claim 1 or Claim 2, which also includes, for each foil (16), a foil stiffening element (18), which is retained in place by an end portion (19) thereof, which is rolled into a part-circular loop, this loop being received within the part-circular loop (18) of the associated foil (16). 4. A foil for use in a bearing as claimed in Claim 1 or Claim 2 or Claim 3. 5. A fluid bearing comprising: a pair of members arranged for relative movement with respect to one another, one of said pair of members having a plurality of circular slots having a depth less than the diameter but greater than the radius of the slots; and a plurality of compliant foils operably disposed between said pair of relatively movable members, each of said plurality of compliant foils having at one end thereof a circular loop pivotably disposed in a corresponding circular slot of said o-ne of said pair of relatively movable members. 6. A fluid bearing comprising: a bearing support member having an opening to receive a rotatable shaft and having a plurality of circular slots of a depth less than the diameter but greater than the radius of the slots; a rotatable shaft operably disposed within the opening of said bearing support member; and a plurality of compliant overlapping foils operably disposed between the rotatable shaft and the bearing support member, each of said plurality of compliant foils having at one end thereof a circular loop pivotably disposed in a corresponding circular slot in said bearing support member.

Inventors: AGRAWAL, GIRIDHARI L., HOCKEY, EDWARD J.
Applicants: THE GARRETT CORPORATION
Application year: 1980
Main classification: F16C27
IPC codes: F16C27, F16C17