CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of co¬ pending patent application Serial Number 08/490,976, filed June 15, 1995, in the name of Giridhari L. Agrawal, and entitled "Improved Hydrodynamic Fluid Film Bearing".

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to hydrodynamic flu¬ id film bearings and, more particularly, to such bearings employing a plurality of thin foils lining the inner sur- face of a retaining member within which a high-speed ro¬ tating shaft is receivable, to establish and maintain a lubricating fluid film, e.g., air, between the foils and the rotating shaft.

Related Art

Recent efforts have been made to improve bearings for high speed rotating machinery, such as turbocompressors employed in modern air cycle machines for aircraft cooling and ventilation. Such efforts have led to the development of numerous designs for fluid film hydrodynamic bearings. Generally, fluid film hydrodynamic bearings have been suc¬ cessfully employed in high-speed rotating machines for about the past twenty years. For example, air cycle ma¬ chines used for aircraft cabin environment control systems utilize fluid film hydrodynamic bearings. Such bearings operate on the principle that a high speed rotating mem¬ ber, such as a shaft, is at least slightly eccentric with respect to rotation about its longitudinal axis. There¬ fore, if the shaft is enclosed by a close-fitting, compli- ant, annular element such as a thin foil encased within a stationary retaining member, the eccentricity of rotation within such retaining member will form and maintain a pressurized fluid (e.g., air) film wedge between the shaft

and the compliant foil. The high speed rotation of the shaft generates a high pressure in the fluid film wedge, which fluid film supports the load imposed by the shaft. A spring foil, i.e., a resilient backing member, is dis- posed between the compliant foil and the stationary member (sometimes referred to as a cartridge, retainer or base) to accommodate deflections of the foil resulting from pressurization, centrifugal forces and temperature differ¬ entials in order to maintain optimum or at least adequate film layer geometry. The fluid film hydrodynamic bearing desirably has high load capacity and high coulomb damping for suppression of shaft whirl. Providing such character¬ istics has typically required stringent control of manu¬ facturing tolerances of the fluid film hydrodynamic bear- ing.

One type of known fluid film hydrodynamic bearing is a multi-pad type as described in U.S. Patent 3,615,121 to Barnett et al and U.S. Patents 4,153,315, 4,178,046 and 4,195,395 to Silver et al. Generally, coulomb damping, which is required to suppress whirl of the shaft, is low for such multi-pad bearings, and the low damping has lim¬ ited the utilization of such bearings. The multi-pad bearings have an iris-type construction and the three aforementioned patents to Silver et al show stiffener ele- ments for the foils. U.S. Patent 4,178,046 discloses a foil bearing in which a plurality of foils is mounted within the retaining member or bushing, each subtending a rotational segment, less than all, of the circumferential or inner surface of the bearing. Each foil is mounted at its midpoint with one side or wing of the foil serving as an underfoil for the overfoil of an adjacent member and the other arm or wing serving as an overfoil for the un¬ derfoil of an adjacent member on its opposite side. How¬ ever, the arrangement of the foils is such that the slid- ing travel or shifting of adjacent foils (which results from the forces imposed on the foils by the pressurized fluid film generated by the rotating shaft) is in the same direction. Consequently, the relative sliding travel be-

tween adjacent foils is the difference between the amount of sliding travel of each foil. This limited relative foil movement contributes to the low coulomb damping char¬ acteristic of these multi-pad bearings. Often, in order to compensate for such limited coulomb damping, the art provides multi-pad bearing foils having a preformed diame¬ ter (the foil diameter prior to insertion of the shaft in¬ to the bearing) which is up to 50% less than the diameter of the shaft which is to be received in the bearing. Con- sequently, when the shaft is initially mounted within the bearing, the bearing foils maintain a relatively tight grip on the shaft. This results in a high preloading on the shaft and thereby requires a high starting torque. If any type of contaminant, such as water, is present in the bearing, a still higher starting torque is required. Such high starting torque is of course disadvantageous as it stresses the machine which is being used to drive the shaft and may be severe enough to result in inability to start the engine or motor which drives the shaft and/or cause damage to the engine or motor or to drive compo¬ nents.

Improved bearings were provided by the reverse 360- degree multi-layer hydrodynamic fluid film foil bearings described in U.S. Patents 4,415,280 and 4,415,281 issued to G.L. Agrawal. In these bearings, two layers of flat compliant foils are arranged to shift in opposite rota¬ tional directions and are supported on a layer of corru¬ gated foil which serves as a spring foil and provides high load capacity. Due to the fact that adjacent foils shift in opposite directions, coulomb damping is relatively high because the relative movement between adjacent foils is equal to the sum of the individual foil movements. Ac¬ cordingly, adequate coulomb damping is attained without the necessity of reducing the preformed radius of the foils to significantly less than that of the shaft. Con¬ sequently, preloading imposed on the shaft by the foils is small and the starting torque required is not significant¬ ly increased by the bearing. However, because the foils

are supported at only one end thereof and extend for 360- degrees around the entire circumference of the inner sur¬ face of the stationary member, the foils of these other¬ wise successful bearings occasionally telescope during assembly and operation. If the foils should telescope during operation, the telescoped foils tighten around the shaft and bind it, and the bearing fails. Further, manu¬ facture of such 360-degree foils is expensive as it re¬ quires extensive hand operations to hold the required tol- erances.

Hydrodynamic fluid film foil bearings of conical con¬ figuration which can serve as thrust bearings to sustain axial loads, that is, loads imposed parallel to the longi¬ tudinal axis of the shaft supported by the bearing, are known in the art as evidenced by U.S. Patent 3,382,014 is¬ sued to D. J. Marley. The Marley Patent shows in Figure 2 thereof the overlapping foils of a truncated cone-shaped foil assembly (21) received within a conical recess (19) formed in a bearing housing (17).

SUMMARY OF THE INVENTION

Generally, in accordance with the present invention, there is provided a hydrodynamic fluid film bearing which may be denominated a "reverse multi-pad bearing" and which overcomes the above-noted disadvantages of the known mul¬ ti-pad bearings and 360-degree reverse multi-layer bear¬ ings. The reverse multi-pad bearing of the present in¬ vention is not subject to telescoping failure, exhibits a high coulomb damping friction, has a high load capacity, a small starting torque requirement, is resistant to the presence of contaminants in the bearing and can be easily manufactured at low cost relative to the 360-degree re¬ verse multi-layer bearings.

Specifically, in accordance with the present inven- tion there is provided a hydrodynamic fluid film bearing comprising the following components. A retaining member has an inner surface, e.g., a cylindrical or conical-shap¬ ed inner surface, which defines a shaft opening within

which a rotatable shaft is receivable for rotation. A foil assembly lines the inner surface and comprises a plurality of foil sub-assemblies, the foil sub-assemblies each subtending a rotational segment, less than all, of the inner surface. The foil sub-assemblies comprise com¬ pliant contact foils disposed in overlying contact with spring foils which are disposed radially outwardly of their associated contact foils. The spring foils and the contact foils are affixed to the retaining member in re- spective opposite-facing rotational directions along the inner surface. With this arrangement, sliding travel of the spring foils is in the opposite rotational direction of sliding travel of the contact foils.

In accordance with another aspect of the present in- vention, there is provided a hydrodynamic fluid film bear¬ ing comprising the following components. A retaining mem¬ ber has an inner surface, e.g., a cylindrical- or conical- shaped inner surface, which defines a shaft opening within which a rotatable shaft is receivable for rotation. A foil assembly is affixed to and lines the inner surface and comprises a plurality of foil sub-assemblies, the sub¬ assemblies each subtending a rotational segment, less than all, of the inner surface. The foil sub-assemblies com¬ prise (i) compliant contact foils sandwiched between (ii) spring foils disposed radially outwardly of their associ¬ ated contact foils and (iii) compliant inner foils dis¬ posed radially inwardly of their associated contact foils. The spring foils and the contact foils are affixed to the retaining member in respective opposite-facing rotational directions along the inner surface. With this arrange¬ ment, sliding travel of the spring foils is in the oppo¬ site rotational direction of sliding travel of the contact foils.

One aspect of the invention provides for the follow- ing construction. The spring foils have respective ter¬ minal proximal edges fixed to the retaining member and re¬ spective, opposite terminal distal edges facing in a first rotational direction along the inner surface. The contact

foils are fixed to the retaining member and have respec¬ tive distal edges facing in a second rotational direction opposite to the first rotational direction. With this ar¬ rangement, sliding travel of the spring foils is in the first rotational direction and sliding travel of the con¬ tact foils is in the second, opposite rotational direc¬ tion.

Still another aspect of the present invention pro¬ vides that the bearing further comprises a rotatable shaft received within the shaft opening to define between the shaft and the foil assembly an annular space dimensioned and configured so that a pressurized fluid film layer ca¬ pable of supporting the shaft is maintainable therewithin. Another aspect of the present invention provides that the retaining member has a longitudinal axis and the spring foil is corrugated, the corrugations being disposed substantially parallel to the longitudinal axis of the re¬ taining member.

Other aspects of the present invention will become apparent from the following description and the appended drawings.

As used herein and in the claims, the following terms used in reference to the shape or configuration of the in¬ ner surface of the retaining member and the foil assembly, have the indicated meanings. The term "cylindrical" means a cylinder whose cross sections taken along planes perpen¬ dicular to the longitudinal axis of the cylinder are cir¬ cles of equal size. Stated otherwise, in this context "cylindrical" means a regular, right angle circular cylin- der. The term "conical" means a cone or truncated cone whose longitudinal axis is perpendicular to its base, i.e., a right-angle cone or truncated cone. The term "frusto-conical" refers specifically to a truncated coni¬ cal configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic perspective view, with parts broken away or omitted, of a hydrodynamic bearing in ac-

cordance with one embodiment of the present invention, in¬ cluding a rotatable shaft received therein;

Figure IA is a partial schematic view, enlarged with respect to Figure 1, taken along line A-A of Figure 1; Figure 2 is a schematic end view of the hydrodynamic bearing of Figure 1 with the rotatable shaft omitted;

Figure 2A is a perspective, exploded view, enlarged with respect to Figure 2, of one of the sub-assemblies of Figure 2 and the segment of the retaining member in which the sub-assembly is mounted;

Figure 3 is a partial schematic end view of a hydro¬ dynamic bearing comprising yet another embodiment of the present invention;

Figure 3A is a view corresponding to Figure 3 of still another embodiment of the present invention;

Figure 4 is a schematic end view, with a part broken away, of a hydrodynamic bearing comprising still another embodiment of the present invention;

Figure 4A shows the structure of Figure 4 broken away to show but a single spring foil and compliant foil and an associated segment of the retaining member;

Figure 5 is a view corresponding to that of Figure 3 of still another embodiment of the present invention;

Figure 6 is a partial schematic exploded view, with parts broken away, of a hydrodynamic thrust bearing in ac¬ cordance with yet another embodiment of the present inven¬ tion, and a rotatable shaft to be received therein; and

Figure 6A is a schematic partial end view, with parts broken away and enlarged with respect to Figure 6, of the larger diameter end of the bearing of Figure 6.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

Figure 1 shows a hydrodynamic fluid film bearing 10 comprising a cylindrical retaining member 12 which, in the illustrated embodiment, is of cylindrical configuration and defines a cylindrical opening 14 of circular, constant cross section within which a rotatable shaft 16 (partly

broken away in Figure 1) is received for rotation. A gen¬ erally cylindrical-shaped foil assembly 18 (only partially shown in Figure 1 and better seen in Figure 2) lines the inner surface 20 of retaining member 12. A plurality of circumferentially spaced-apart keyways are formed in inner surface 20 and extend parallel to the longitudinal axis of cylindrical retaining member 12.

In the embodiment illustrated in Figure 2, five iden¬ tical keyways, 22a, 22b, 22c, 22d and 22e are formed in inner surface 20 and are equiangularly spaced apart about the circular cross-sectional circumference of cylindrical opening 14. A plurality, five in the embodiment of Figure 2, of foil sub-assemblies 24 are affixed to retaining mem¬ ber 12 by means of the keyways 22a-22e and corresponding mounting bars 28a, 28b, 28c, 28d and 28e. As best seen in Figure 2, each foil sub-assembly 24 subtends a rotational segment, less than all, of the inner surface 20. That is, each foil sub-assembly 24 overlies a portion, but less than all, of the 360-degree rotational travel path along the circumference of inner surface 20 of a point on the exterior surface of rotatable shaft 16. Inasmuch as the keyways 22a-22e are equiangularly spaced apart along the circumference of inner surface 20, each foil sub-assembly 24 subtends an equal sized rotational segment comprising, in the illustrated embodiment, one-fifth of 360-degrees of rotation, or a rotational segment of 72 degrees. General¬ ly, it is preferred to provide at least three foil sub¬ assemblies, e.g., three to eight such sub-assemblies, to line the entire inner surface 20. Accordingly, each sub- assembly subtends not more than about 120 degrees of ro¬ tation, e.g., from about 45 degrees to 120 degrees of ro¬ tation, of the 360-degree rotational path along inner sur¬ face 20.

Each foil sub-assembly 24 of Figure 2 comprises a spring foil 26, a contact foil 30 and an inner foil 32. In the illustrated embodiment of Figures 1, 2, and 2A, spring foil 26 is corrugated, the corrugation crests and troughs running parallel to the longitudinal axis of re-

taining member 12. As best seen with reference to Figures 2 and 2A, a proximal terminal edge 26a (Figure 2A) of spring foil 26 is received within keyway 22a wherein it is affixed, as by spot welding or by any other suitable means, to a mounting bar 28a which extends through keyway 22a. The opposite edge of spring foil 26 comprises a dis¬ tal terminal edge 26b which is terminated adjacent to key¬ way 22b. (As used herein and in the claims, the terms "proximal" and "distal" have their usual meanings, al- though usually employed in biology wherein "distal" refers to that portion of a member farthest removed from the point of attachment of the member to another body, and "proximal" refers to that point of the member closest to the point of such attachment.) A contact foil 30 has its proximal edge 30a (Figure 2A) affixed to mounting bar 28b for affixation to retain¬ ing member 12 in keyway 22b, which is a keyway adjacent to keyway 22a. The distal edge 30b of contact foil 30 ter¬ minates adjacent to keyway 22a. Sub-assembly 24 is com- pleted by an inner foil 32 having a proximal edge 32a af¬ fixed to mounting bar 28a within keyway 22a, and a distal edge 32b which terminates at keyway 22b. The remaining foil sub-assemblies are identical to the one described.

Contact foil 30 and inner foil 32 generally comprise compliant foils which will tend to flatten along spring foil 26 adjacent to inner surface 20 under the influence of rotation of rotatable shaft 16 (Figure 1). The Figures are all schematic in that the radial thickness of both the foils from which the foil assembly is made, and the radial spacing between foils, as well as the depth of the corru¬ gations in the spring foils, are somewhat exaggerated in the drawings for purposes of clarity of illustration. Typical actual dimensions for the foils would be, for a two-inch (5.1 centimeter) diameter bearing, a foil thick- ness (dimensions t in Figure 2A) for the spring foil 26, contact foil 30 and inner foil 32, of about 3 to 3.5 mils each. (In contrast, the thickness of prior art foils is typically about 6 to 8 mils resulting in relatively rigid

foils. The rigidity of the foils is a function of the cube of the dimension t. ) The spring foil 26 typically has a corrugation depth (dimension d in Figure 2A) of about 15 to 18 mils and a circumferential crest-to-crest (or trough-to-trough) distance (dimension c in Figure 2A) of about 15 to 18 mils. For the above-described typical two-inch diameter bearing, the preform radius of the cyl¬ indrical shaped foil assembly 18 would be less than the radius of the cylindrical opening 14 by only about 21 to 25 mils, which is the sum of the thicknesses (d plus t plus t in Figure 2A) of foils 26, 30 and 32. It is typ¬ ical of the construction of the present invention, de¬ scribed in more detail below, that the inner circumference of the foil assembly 18, defined in the embodiment illu- strated in Figure 2A by the inner foil layer provided by cooperation of the five inner foils 32, will be only slightly smaller than the inside diameter of cylindrical opening 14. The relatively large inside diameter of foil assembly 18 reduces the strength of the gripping action of foil assembly 18 on rotatable shaft 16 (Figure 1) and therefore reduces the required start-up torque.

When rotatable shaft 16 is inserted into retaining member 12 and rotated at high speed, the highly pressur¬ ized fluid film formed between the exterior surface of ro- tatable shaft 16 and foil assembly 18 will tend to flatten foil assembly 18 and cause some "sliding travel" of the foils as they are flattened and stretched by the action of the shaft and the pressurized fluid film, the sliding tra¬ vel being, as is well-known in the art, in the direction moving from the fixed proximal edge of the foil towards the free, distal edge of the foil. Thus, with reference to Figure 2, it will be observed that the sliding travel of spring foil 26 is in the rotational direction which is opposite to the direction of sliding travel of contact foil 30, and the rotational direction of sliding travel of inner foil 32 is opposite to that of the sliding travel of contact foil 30. The direction of sliding travel of spring foil 26, contact foil 30 and inner foil 32 is shown

by the respective arrows 26t, 30t and 32t in Figure 2. It will be appreciated that adjacent foils 26, 30 and 32 therefore travel and rub against each other in respective opposite directions; that is, the sliding travel of each foil is in the rotational direction opposite to the slid¬ ing travel of the foil adjacent to it. The relative move¬ ment between any two adjacent foils is therefore the sum of the sliding travel of the two adjacent foils. The in¬ creased relative sliding travel of adjacent foils, as com- pared to the sliding travel which would be attained if ad¬ jacent foils underwent sliding travel in the same rota¬ tional direction, provides enhanced coulomb damping of the shaft.

As is well-known in the art, suitable coatings may be applied to one or more surfaces of the foils to help con¬ trol the desired degree of friction between adjacent rub¬ bing foils and hence the desired degree of damping.

Any suitable means may be employed to prevent the foil assembly 18 from longitudinally sliding out of the keyways 22. Thus, at each end of the retaining member 12 the keyways may be covered by a small plate or other re¬ taining means affixed to end face 34 (Figure 2) and the corresponding end face (not shown in the drawings) at the opposite longitudinal end of retaining member 12. Such covers or retaining means may be affixed by screws or by any other suitable device. In the construction shown in Figures 1, IA and 2, it will be noted that end face 34 is recessed under end rim 36 to provide a slot within which an annular member, such as metal O-ring 38, only a partial cross-sectional view of which is shown (in Figure IA) , may be inserted within the slot formed by the undercutting of end face 34. Another metal O-ring identical to O-ring 38 is inserted at the other end (not shown) of retaining mem¬ ber 12. Rotatable shaft 16 may, as indicated by the unnumber¬ ed arrows in Figure 1 and the arrow R in Figure 2, be ro¬ tated in either direction. However, with the construction of Figure 2, rotatable shaft 16 is preferably rotated in

the counter-clockwise direction in Figure 2.

A significant advantage accrues from having each foil sub-assembly subtend only a portion, less than all, of the 360-degree path of rotational travel about inner surface 20. As will be appreciated by those skilled in the art, it is necessary to maintain extremely fine tolerances of the manufacture of foils which extend for substantially the full 360-degrees of rotation about the inner surface of the retaining member. Such fine tolerances must be maintained in order to assure that an extremely small and carefully controlled annular space is formed between the generally cylindrical foil assembly and the exterior sur¬ face of a shaft such as rotatable shaft 16 of Figure 1. The maintenance of such fine tolerances in foils which extend for substantially the entire 360-degree path of rotation of the retaining member 12 is extremely diffi¬ cult, requires extensive hand work and incurs very high manufacturing costs. Manufacturing foils and foil sub¬ assemblies which, in accordance with an aspect of the present invention, subtend only a limited portion of the 360-degree path of travel, is much easier and far less expensive. The relatively short lengths of foil are both easier to manufacture and the tolerances may be greater as compared to manufacturing a length of foil which has to wrap around the full 360-degree path of travel. Such re¬ latively short lengths of foil can readily be manufactured by automated machinery.

Referring now to Figure 3 there is illustrated anoth¬ er embodiment of the invention comprising a hydrodynamic fluid film bearing 110 comprised of a retaining member 12, which is identical to that of the embodiments of Figures 1-2A, and in which other parts identical to those of the embodiment of Figures 1-2A are numbered identically there¬ to. The embodiment of Figure 3 differs from that of Fig- ure 2 in that the mounting bars 28a-28e of Figure 2 are omitted and foil sub-assemblies 124 are mounted within the keyways (only keyways 22a, 22b and 22c are shown in the partial view of Figure 3) by providing at least one of the

foils of each foil sub-assembly 124 with a hooked con¬ struction at the proximal edge thereof. In the embodiment of Figure 3, the proximal edges 130a of contact foils 130 are of such hook construction. The sub-assemblies 124 comprise a spring foil 126, a contact foil 130 and an in¬ ner foil 132 and the proximal edges 126a of spring foils 126 and the proximal edges 132a of inner foils 132 are bent at approximately a 90 degree angle from the major surfaces of the respective foils. The proximal edges of each of the foils are inserted into a corresponding one of the keyways 22a, 22b, etc. and the dimensions of the key¬ ways and of the proximal edges of the foils are selected so that the hook-shaped proximal edges 130a of contact foils 130 are compressed sufficiently within the keyways to help retain the foils in place. The use of an end cov¬ ering such as metal O-ring 38 of Figure IA and the close fit provided by the insertion of a rotatable shaft such as rotatable shaft 16 of Figure 1, within cylindrical opening 14 cooperate with the hook construction and key slots to retain foil sub-assemblies 124 in place.

Figure 3A illustrates yet another embodiment of the present invention in which, as in Figure 3, elements iden¬ tical to those of Figure 2 are identically numbered there¬ to. Figure 3A illustrates a hydrodynamic fluid film bear- ing 210 in which each foil sub-assembly 224 is comprised of a spring foil 226, a contact foil 230 and an inner foil 232. In this embodiment, the contact foil 230 of one sub¬ assembly 224 and the inner foil 232 of an adjacent foil sub-assembly 224 are comprised of a unitary foil having a return-bend portion 40 which serves the function of help¬ ing to retain the foil sub-assemblies 224 in place within their associated keyways (only keyways 22a, 22b and 22c are shown in Figure 3A) . The unitary foil 230, 232 thus has its proximal edge, defined in the illustrated embodiment by return-bend portion 40, at its center.

Referring now to Figures 4 and 4A there is shown yet another embodiment of the present invention in which parts identical to the embodiment illustrated in Figure 2 are

identically numbered thereto. Figure 4 shows a hydrody¬ namic fluid film bearing 310 fitted with five foil sub-as¬ semblies 324, each comprising a spring foil 326, a contact foil 330 and an inner foil 332. As best seen in Figure 4A, in this embodiment, the contact foil 330 of a given foil sub-assembly 324 (Figure 4) is formed of a unitary foil which also provides the inner foil 332 of the next adjacent foil sub-assembly 324. In this embodiment, the proximal edge 330a of contact foil 330 is formed in a hook-shaped configuration and, as is clearly shown in Fig¬ ure 4A, the distal edge 330b of contact foil 330 is ad¬ jacent to and connected to the proximal edge 332a of inner foil 332. The unitary foil comprised of contact foil 330 and inner foil 332-is at the free edge of the unitary foil, i.e., at the distal edge 332a of inner foil 332. It will thus be appreciated that in some embodiments, a prox¬ imal or distal "edge" may occur at an intermediate por¬ tion, e.g., at about the center, of a unitary foil.

Referring now to Figure 5, there is shown a hydrody- namic fluid film bearing 410, illustrating yet another em¬ bodiment of the invention which is substantially identical to the embodiment illustrated in Figure 3, except that each foil sub-assembly 424 comprises only a spring foil 426 and a contact foil 430. In this embodiment, an inner foil corresponding to inner foil 132 of the Figure 3 em¬ bodiment is omitted.

The specific embodiments of the invention illustrated in Figures 1-5 all concern bearings having cylindrical shaft-receiving openings, such as opening 14 of Figure 1. Such bearings are well-suited for supporting a load im¬ posed transversely of the longitudinal axis of the shaft supported by the bearing. The present invention, however, also encompasses thrust bearings, which are well-suited for supporting not only loads imposed transversely of the supported shaft, but loads imposed axially along the sup¬ ported shaft towards the thrust bearing. Such thrust bearings made in accordance with the present invention may be constructed similarly or identically to the embodiments

of Figures 1-5 except that the opening corresponding to opening 14 of Figure 1 is of conical, e.g., frusto-conic¬ al, configuration, i.e., the opening has a circular cross section which is of diminishing diameter as sensed moving in the direction in which the axial load is imposed on the shaft supported by the bearing. The foil assembly is sim¬ ilarly of conical, e.g., frusto-conical, configuration in¬ stead of constant diameter but may otherwise be similar or identical to the foil assemblies of the Figures 1-5 embod- iments.

Figures 6 and 6A illustrate such a conical thrust bearing in accordance with another embodiment of the pres¬ ent invention wherein parts which correspond to those of the embodiment of Figures 1 and 2 are identically thereto numbered except for the addition of a prime indicator. Thus, Figure 6 shows a conical, hydrodynamic fluid film bearing 10' comprising a retaining member 12' which de¬ fines a conical opening 14' within which a rotatable shaft 16' (broken away in Figure 6) has a conical-shaped end 16a' which is received for rotation within bearing 10'. A generally conical-shaped foil assembly 18' (seen in .Figure 6 and only partially shown in Figure 6A) lines the inner surface 20' of retaining member 12'. A plurality of cir¬ cumferentially spaced-apart keyways (only keyways 22c', 22d' and 22e' being visible in Figure 6A) are formed in inner surface 20' and extend at an angle to the longi¬ tudinal axis L-L (Figure 6) of retaining member 12'. Conical versions of the foil configurations of Figures 2 through 5 are useable in the conical bearing 10' of Figure 6.

Foil assembly 18' is comprised of a plurality of foil sub-assemblies 24' (Figure 6A) corresponding to foil sub¬ assemblies 24 of Figure 2. At the plane of any given cross section taken perpendicularly to longitudinal axis L-L of Figure 6, the foil sub-assemblies of the fluid film bearing 10 would look identical to the foil sub-assemblies 24 of Figure 2. Thus, as seen in Figure 6A, the foil as¬ sembly 18' is comprised of a plurality of foil sub-assem-

blies, each comprising a spring foil 26', a contact foil 30' and an inner foil 32'. Each foil sub-assembly, like those of the embodiment of Figures 1 and 2, subtends a rotational segment, less than all, of the inner surface 20' and the mounting bars (only mounting bars 28c', 28d' and 28e' being visible in Figure 6A) and the crests and troughs of the corrugation crests and troughs extend along the surface of a truncated right-angle cone. In short, except for the conical configuration of the retaining mem- ber 12' and foil assembly 18', the configuration of the thrust-bearing embodiments of the invention is identical or similar to that of the cylindrical bearings embodiment of the invention, e.g., those illustrated in Figures 1-5. Accordingly, a detailed description of the components of the embodiment of Figures 6 and 6A need not be repeated.

Although the present invention has been described in detail with respect to specific preferred embodiments thereof, various modifications thereto lie within the spirit and scope of the invention and the claims.