Foil bearing assembly including segmented inner foil assembly and compressor including same

A bearing system includes a bearing housing and a foil bearing assembly. The bearing housing includes a sleeve that defines a cylindrical bore and includes at least one bearing assembly locking feature, and a mounting structure. The foil bearing assembly includes an outer foil assembly, an inner foil assembly, and a bump foil assembly positioned between the outer foil assembly and the inner foil assembly. The outer foil assembly includes at least one outer foil pad that extends circumferentially from a first end including a bearing retention feature to a second end. The bearing retention feature is cooperatively engaged with the at least one bearing assembly locking feature. The inner foil assembly includes a plurality of circumferentially-spaced inner foil pads. Each inner foil pad extends circumferentially from a tab to a free end. At least one inner foil pad is welded to the outer foil assembly along the tab.

FIELD

The field of the disclosure relates generally to bearing systems, and more particularly, to gas foil bearing assemblies for use in compressors.

BACKGROUND

Some refrigerants used in modern refrigeration and cooling systems, such as R134a or other low global warming potential (GWP) refrigerants, have a relatively low density which requires higher volume flow compressors such as centrifugal compressors.

Centrifugal compressors typically include compressor bearings to support a driveshaft used to transfer power from the motor to the impeller that imparts kinetic energy to incoming refrigerant. The compressor bearings are typically provided with one or more features to reduce friction between the compressor bearing and the driveshaft. The design of these friction-reducing features of the bearings pose an on-going challenge due at least in part to the refrigerant and the challenging operating environment within gas compressors such as air conditioning compressors.

Some compressor bearings in existing refrigerant compressors use oil or alternative compositions as a lubricant, but some refrigerants are incompatible with at least some existing lubricant compositions. Other compressor bearings are oil-free magnetic bearings that levitate the driveshaft within a magnetic field provided by high-strength magnets, but magnetic bearings are typically complex in design, add significant weight, require complicated control, and limit the choice of driveshaft materials to ferromagnetic materials in order to respond to the magnetic fields within the magnetic bearings. Another type of oil-free bearings is a foil bearing that includes compliant foil elements that surround the driveshaft and support the driveshaft on a fluid layer formed between the driveshaft and the foil elements when the rotation speed of the driveshaft exceeds a threshold speed termed liftoff speed. Foil bearings are well-suited for the high-speed operating environment typical of centrifugal compressors, are compatible with all refrigerant compositions, and may be used with a wider variety of driveshaft materials, thereby permitting the use of lighter-weight materials to reduce the amount of energy needed to operate the compressor.

At least one consideration when using foil bearing assemblies in centrifugal compressors is sub-synchronous vibrations—i.e., vibrations occurring at a frequency below that of the rotational frequency of the shaft or other rotor supported by the bearings. Centrifugal compressors that incorporate foil bearing assemblies can be prone to sub-synchronous vibrations, which can reduce the operating envelope of the compressor.

SUMMARY

In one aspect, a bearing system includes a bearing housing and a foil bearing assembly. The bearing housing includes a sleeve that defines a cylindrical bore and includes at least one bearing assembly locking feature, and a mounting structure for connecting the bearing system to a compressor housing. The foil bearing assembly is positioned within the cylindrical bore and includes an outer foil assembly, an inner foil assembly, and a bump foil assembly positioned between the outer foil assembly and the inner foil assembly. The outer foil assembly includes at least one outer foil pad extending circumferentially from a first end including a bearing retention feature to a second end. The bearing retention feature is cooperatively engaged with the at least one bearing assembly locking feature to maintain the foil bearing assembly within the bearing housing at a fixed rotational position. The inner foil assembly includes a plurality of inner foil pads spaced circumferentially about the foil bearing assembly. Each inner foil pad extends circumferentially from a tab to a free end. At least one of the inner foil pads is welded to the outer foil assembly along the tab.

In another aspect, a compressor includes a compressor housing, a driveshaft rotatably supported within the compressor housing, an impeller connected to the driveshaft and operable to impart kinetic energy to incoming refrigerant gas upon rotation of the driveshaft, a bearing housing mounted to the compressor housing, and a foil bearing assembly rotatably supporting the driveshaft. The bearing housing includes a sleeve that defines a cylindrical bore and includes at least one bearing assembly locking feature. The foil bearing assembly is positioned within the cylindrical bore, and includes an outer foil assembly, an inner foil assembly, and a bump foil assembly positioned between the outer foil assembly and the inner foil assembly. The outer foil assembly includes at least one bearing retention feature cooperatively engaged with the at least one bearing assembly locking feature to maintain the foil bearing assembly within the bearing housing at a fixed rotational position. The inner foil assembly includes a plurality of inner foil pads spaced circumferentially about the foil bearing assembly. Each inner foil pad extends circumferentially from a tab to a free end. At least one of the inner foil pads is welded to the outer foil assembly along the tab.

DETAILED DESCRIPTION

Referring toFIG.1, a compressor illustrated in the form of a two-stage refrigerant compressor is indicated generally at100. The compressor100generally includes a compressor housing102forming at least one sealed cavity within which each stage of refrigerant compression is accomplished. The compressor100includes a first refrigerant inlet110to introduce refrigerant vapor into the first compression stage (not labeled inFIG.1), a first refrigerant exit114, a refrigerant transfer conduit112to transfer compressed refrigerant from the first compression stage to the second compression stage, a second refrigerant inlet118to introduce refrigerant vapor into the second compression stage (not labeled inFIG.1), and a second refrigerant exit120. The refrigerant transfer conduit112is operatively connected at opposite ends to the first refrigerant exit114and the second refrigerant inlet118, respectively. The second refrigerant exit120delivers compressed refrigerant from the second compression stage to a cooling system in which compressor100is incorporated. The refrigerant transfer conduit112may further include a refrigerant port122, for example, for economization.

Referring toFIG.2, the compressor housing102encloses a first compression stage124and a second compression stage126at opposite ends of the compressor100. The first compression stage124includes a first impeller106configured to add kinetic energy to refrigerant entering via the first refrigerant inlet110. The kinetic energy imparted to the refrigerant by the first impeller106is converted to increased refrigerant pressure (i.e. compression) as the refrigerant velocity is slowed upon transfer to a diffuser136. Similarly, the second compression stage126includes a second impeller116configured to add kinetic energy to refrigerant transferred from the first compression stage124entering via the second refrigerant inlet118. The kinetic energy imparted to the refrigerant by the second impeller116is converted to increased refrigerant pressure (i.e. compression) as the refrigerant velocity is slowed upon transfer to a diffuser138. Compressed refrigerant exits the second compression stage126via the second refrigerant exit120(not shown inFIG.2).

Referring toFIG.2andFIG.3, the first stage impeller106and second stage impeller116are connected at opposite ends of a driveshaft104. The driveshaft104is operatively connected to a motor108positioned between the first stage impeller106and second stage impeller116such that the first stage impeller106and second stage impeller116are rotated at a rotation speed selected to compress the refrigerant to a pre-selected pressure exiting the second refrigerant exit120. Any suitable motor may be incorporated into the compressor100including, but not limited to, an electrical motor. The driveshaft104is supported by gas foil bearing assemblies300positioned within a sleeve202of each bearing housing200/200a, as described in additional detail below. Each bearing housing200/200aincludes a mounting structure210for connecting the respective bearing housing200/200ato the compressor housing102, as illustrated inFIG.2.

Referring toFIG.4, each bearing housing200/200a(only bearing housing200illustrated inFIG.4) supports the driveshaft104, and the driveshaft104projects through the bearing housing200/200aopposite the sleeve202, and the impeller106is connected to the projecting end of the driveshaft104. Referring toFIG.5andFIG.7, the gas foil bearing assembly300is positioned within a cylindrical bore206within the bearing housing200. The driveshaft104closely fits within the gas foil bearing assembly300, which includes an outer compliant foil assembly or foil layer302positioned adjacent to the inner wall of the sleeve202, an inner compliant foil assembly or foil layer306(also referred to as a “top foil”) positioned adjacent to the driveshaft104, and a bump foil assembly or foil layer310positioned between the inner foil layer306and the outer foil layer302. The foil assemblies or layers302/306/310of the gas foil bearing assembly300form an essentially cylindrical tube sized to receive the driveshaft104with relatively little or no gap design as determined by existing foil bearing design methods. The components of the foil bearing assembly300, such as outer foil layer302, the inner foil layer306, and the bump foil layer310, may be constructed of any suitable material that enables the foil bearing assembly300to function as described herein. Suitable materials include, for example and without limitation, metal alloys. In some embodiments, for example, each of the outer foil layer302, the inner foil layer306, and the bump foil layer310is constructed of stainless steel (e.g., 17-4 stainless steel). The foil layers can be formed from relatively thin sheets or “foils” of material. For example, the foil assemblies or layers302/306/310can be constructed of metal sheets having a thickness in the range of 0.003 inches to 0.007 inches.

Referring again toFIG.5, the foil bearing assembly300in the illustrated embodiment further includes a pair of foil keepers312a/312bpositioned adjacent opposite ends of the layers302/306/310to inhibit sliding of the layers302/306/310in an axial direction within the cylindrical bore206of the sleeve202. A pair of foil retaining clips314a/314bpositioned adjacent to the foil keepers312a/312b, respectively, fix the layers302/306/310in a locked axial position within the cylindrical bore206. Foil retaining clips314a/314bmay be removably connected to bearing housing200.FIG.8further illustrates the arrangement of the foil keeper312aand foil retaining clip314aat one end of the foil bearing assembly300.

In other embodiments, as illustrated inFIG.6, each bearing housing200/200a(only bearing housing200illustrated inFIG.6) includes a foil retaining lip214formed integrally (e.g., cast) with the bearing housing200and projecting radially inward from the radial inner surface204that defines the cylindrical bore206. In the illustrated embodiment, the foil retaining lip214is positioned near an impeller end216of the cylindrical bore206proximal to the impeller116(shown inFIGS.2-3). The foil retaining lip214is sized and dimensioned to project a radial distance from the radial inner surface204that overlaps at least a portion of the layers302/306/310of the foil bearing assembly300. The foil retaining lip214may extend fully around the circumference of the radial inner surface204, or the foil retaining lip can include two or more segments extending over a portion of the circumference of the radial inner surface204and separated by spaces flush with the adjacent radial inner surface204.

The foil bearing assembly300of the embodiment illustrated inFIG.6further includes a single foil retaining clip314positioned adjacent the ends of the layers302/306/310opposite the foil retaining lip214to inhibit axial movement of the layers302/306/310within the cylindrical bore206of the sleeve202. In this embodiment, the foil retaining clip314snaps into a circumferential groove212formed within the radial inner surface204of the cylindrical bore206near a motor end218of the cylindrical bore206.FIG.9andFIG.10further illustrate the arrangement of the foil retaining clip314at one end of the foil bearing assembly300. The foil retaining clip314is sized and dimensioned to provide clearance for the outer layer302, and to overlap with at least one bearing retention feature304that forms a radially outward projecting tab316, as described further below.

The foil retaining lip214may be positioned within any region of the cylindrical bore206near the impeller end216including, without limitation, a position immediately adjacent to the opening of the cylindrical bore206at the impeller end216. Alternatively, the foil retaining lip214may be positioned within any region of the cylindrical bore206near the motor end218including, without limitation, a position immediately adjacent to the opening of the cylindrical bore206at the motor end218. In such embodiments, the foil retaining clip314snaps into a circumferential groove212formed within the radial inner surface204of the cylindrical bore206near the impeller end216, in an arrangement that is essentially the opposite of the arrangement illustrated inFIG.6.

Referring again toFIG.6, the foil bearing assembly300is installed within the bearing housing200by inserting the foil bearing assembly300into the cylindrical bore206of the bearing housing200at the motor end218. The foil bearing assembly300is then advanced axially into the cylindrical bore206toward the impeller end216until the layers302/306/310contact the foil retaining lip214. The foil retaining clip314is then snapped into the circumferential groove212near the motor end218of the cylindrical bore206to lock the foil bearing assembly300in place.

In other embodiments, any suitable method for affixing the foil bearing assembly300within the sleeve202may be used. Non-limiting examples of suitable methods include keepers and retaining clips, adhesives, set screws, and any other suitable affixing method.

Referring toFIG.11,FIG.12, andFIG.13, the mounting structure210of each bearing housing200(only bearing housing200illustrated inFIG.11,FIG.12, andFIG.13)/200aconnects the respective bearing housing200/200ato the compressor housing102(shown inFIGS.1and2). In the illustrated embodiment, the mounting structure210generally projects in a radially outward direction to a dimension matched to the outer dimension of the compressor housing102. The bearing housing200may include any form of mounting structure210including, without limitation, an annular flange. The bearing housings200/200amay further serve as a mounting structure for a variety of elements including, but not limited to, radial bearings, such as the foil bearing assembly300described above, a thrust bearing, and sensing devices250(shown inFIG.4) used as feedback for passive or active control schemes such as proximity probes, pressure transducers, thermocouples, key phasers, and the like. The bearing housing200may further include external coolant conduits or channels220(shown inFIG.11) to enable active cooling of the foil bearing assembly. The coolant channels220can extend, for example, radially outward from the cylindrical bore206to an opening260formed at a radial outer edge222of the bearing housing200/200a(see alsoFIG.7), and can deliver coolant from an external source and/or from the refrigerant system flow to the bearing housing200/200aand foil bearing assembly300. Additional details of coolant channels and coolant delivery methods suitable for use with compressor system100are described, for example, in U.S. patent application Ser. No. 16/809,836, filed Mar. 5, 2020, the disclosure of which is hereby incorporated by reference in its entirety.

Referring toFIG.13andFIG.14, the bearing housing sleeve202has a radial inner surface204that defines the cylindrical bore206. The cross-sectional profile of the cylindrical bore may be essentially circular, or may be any other rounded or polygonal shape without limitation, such as elliptical, square, octagonal, and the like. The radial inner surface204is sized and dimensioned to receive the foil bearing assembly300such that the outer layer302of the foil bearing assembly300contacts the radial inner surface204.

Referring toFIG.13, the radial inner surface204is provided with at least one or more additional features to enable retaining the foil bearing assembly in a fixed axial and rotational position within the sleeve202. In some embodiments, for example, a first circumferential groove212aand a second circumferential groove212bare formed within the radial inner surface204. The first and second circumferential grooves212a/212bare sized and dimensioned to receive foil retaining clips314aand314b, respectively, as illustrated inFIG.5. In other embodiments, the first circumferential groove212amay be replaced by a circumferential foil retaining lip214(seeFIG.6).

Referring toFIG.14, the radial inner surface204of the bearing housing200is further provided with at least one bearing assembly locking feature208. The bearing assembly locking feature208interlocks with one or more bearing retention features provided on the foil bearing assembly300as described below. The bearing assembly locking feature208may be any suitable form of mechanically interlocking feature without limitation. Non-limiting examples of suitable mechanically interlocking features include raised features such as an axial ridge, key, or tab, and axial depressions formed within the radial inner surface204such as an axially-extending slot, an axially-extending keyhole or keeper as illustrated inFIG.14. The bearing housing200illustrated inFIG.14includes a single bearing assembly locking feature208, though it should be understood that the bearing housing200can include more than one bearing assembly locking feature208. In some embodiments, for example, the radial inner surface204of the bearing housing200defines a plurality of axially-extending grooves spaced circumferentially along the radial inner surface, each one of the axially-extending grooves sized and shaped to receive a corresponding bearing retention feature of the foil bearing assembly300.

Referring toFIGS.15and16, the foil bearing assembly300further includes at least one bearing retention feature304to cooperatively engage the bearing assembly locking feature208to maintain the foil bearing assembly within the bearing housing at a fixed rotational position within the cylindrical bore206of the sleeve202. That is, the bearing retention feature304and the bearing assembly locking feature208are sized and shaped complementary to one another such that, when the bearing retention feature304is engaged with the bearing assembly locking feature208, the bearing assembly locking feature208inhibits or limits at least rotational movement of the bearing retention feature304. The at least one bearing retention feature304may include any suitable form of mechanically interlocking feature without limitation. In some embodiments, the at least one bearing retention feature304is selected based on the choice of bearing assembly locking feature208provided within the cylindrical bore206. Non-limiting examples of suitable mechanically interlocking features include raised features such as an axial ridge, key, or tab, as well as axial depressions formed within at least the outer foil layer302of the foil bearing assembly300such as an axial slot, an axial keyhole or keeper.

The foil bearing assembly300of the illustrated embodiment includes a single bearing retention feature304formed along an edge of the outer layer302. The bearing retention feature defines an axial tab316sized and dimensioned to interlock with the bearing assembly locking feature208, provided in the form of an axial slot208, as illustrated inFIG.14. In other embodiments, the foil bearing assembly300may include additional bearing retention features304formed, for example, along an edge of the inner layer306(see, e.g.,FIGS.23and24). In such embodiments, the bearing retention features304formed along the outer and inner layers302and306may be positioned adjacent one another and/or joined together (e.g., by welding) to define the axial tab316.

The foil bearing assembly300may be provided in any suitable form without limitation. For example, the foil bearing assembly300may be provided with two layers, three layers, four layers, or additional layers without limitation.

The outer foil assembly302includes at least one outer foil pad318. In the example embodiment illustrated inFIGS.1-16, the outer foil assembly302includes a single outer foil pad318constructed of a single, unitary foil. In other embodiments, the outer foil assembly302may be constructed of multiple outer foil pads (see, e.g.,FIGS.20-22). The outer foil assembly302can provide a smooth inner surface for support of the adjacent bump foil assembly310for efficient transmission of transient motions caused by radial forces exerted by the driveshaft104to the inner foil assembly306during operation of the compressor100. The outer foil assembly302provides this smooth inner surface independently of the surface smoothness of the underlying radial inner surface204of the cylindrical bore206of the bearing housing200. Thus, in some embodiments, use of the outer foil assembly302facilitates increasing the surface specification of the radial inner surface204of the cylindrical bore206or, stated another way, reducing a surface smoothness requirement of the radial inner surface204. In some embodiments, the foil bearing assembly300is suitable for use with a bearing housing200in an “as-cast” condition without need for further machining, grinding, or any other means to smooth the radial inner surface204of the cylindrical bore206of the bearing housing200. Accordingly, in some embodiments, the radial inner surface204of the cylindrical bore206is an as-cast surface. That is, the radial inner surface204of the cylindrical bore206is a surface of a cast bearing housing200that has not undergone post-cast machining, grinding, or similar means to smooth the radial inner surface204.

The outer foil assembly302can also improve thermal management of the foil bearing assembly300and facilitate reducing space requirements of the foil bearing assembly300, as described for example in in U.S. patent application Ser. No. 16/809,836, filed Mar. 5, 2020, the disclosure of which is hereby incorporated by reference in its entirety.

The bump foil assembly310of the foil bearing assembly300may be formed from a radially elastic structure to provide a resilient surface for the spinning driveshaft104during operation of the compressor100. The bump foil assembly310may be formed from any suitable radially elastic structure without limitation including, but not limited to, an array of deformable bumps or other features designed to deform and rebound under intermittent compressive radial loads, and any other elastically resilient material capable of compressing and rebounding under intermittent compressive radial loads. The bump foil assembly310may be connected to at least one adjacent layer including, but not limited to at least one of the outer foil assembly302and the inner foil assembly306. In some embodiments, the bump foil assembly310may be connected to both the outer foil assembly302and the inner foil assembly306. In other embodiments, the bump foil assembly310may be free-floating and not connected to any layer of the foil bearing assembly300.

As shown inFIG.15, the bump foil assembly310of the example embodiment includes a plurality of bump foils320spaced circumferentially about the foil bearing assembly300. Each bump foil320extends axially the entire length or substantially the entire length of the foil bearing assembly300, and extends circumferentially from a first edge322to a second edge324. Each bump foil320extends or subtends an arc angle of approximately 110° from the first edge322to the second edge324in the illustrated embodiment, although the bump foils320may extend greater than or less than 110° around the foil bearing assembly300in other embodiments. Additionally, the bump foils320can have different arc angles from one another. In other embodiments, the bump foil assembly310may include a single bump foil that extends circumferentially around the entirety or substantially the entirety of the foil bearing assembly300.

Each bump foil320includes an axially-extending land326located between the first edge322and the second edge324. The bump foils320are secured to one or both of the outer foil assembly302and the inner foil assembly306along the land326. In some embodiments, for example, each of the bump foils320is welded to the outer foil assembly302along a respective land326.

The inner foil assembly306forms a cylindrical inner surface that closely fits the surface of the driveshaft104, as illustrated inFIG.15. The inner foil assembly306includes a plurality of separate or segmented inner foil pads328spaced circumferentially about the foil bearing assembly300. The inner foil assembly306can include any suitable number of inner foil pads328that enables the foil bearing assembly300to function as described herein. The illustrated embodiment includes three inner foil pads328, although other embodiments may include greater than or fewer than three inner foil pads328. Each of the inner foil pads328is arcuate and extends circumferentially from a first end330including a tab332(shown inFIG.16) to a second, free end334.

In the embodiment illustrated inFIG.15, each inner foil pad328extends or subtends an arc angle336of approximately 110° around the foil bearing assembly300. In other embodiments, each inner foil pad328may extend an arc angle336greater than or less than 110°. Additionally, in some embodiments, the inner foil pads328can have different arc angles from one another.FIG.17, for example, illustrates a foil bearing assembly400including an inner foil assembly402with inner foil pads404having different arc angles406,408. In particular, the inner foil assembly402ofFIG.17includes a major inner foil pad410that has an arc angle406greater than the arc angle408of the other inner foil pads404. In this embodiment, the major inner foil pad410has an arc angle406of approximately 160°, and the other inner foil pads404have arc angles408of approximately 95°. In other embodiments, the major inner foil pad410can have an arc angle406in the range of 120° to 360°, in the range of 120° to 270°, in the range of 120° to 240°, in the range of 120° to 200°, in the range of 120° to 180°, in the range of 120° to 150°, in the range of 150° to 360°, in the range of 150° to 270°, in the range of 150° to 240°, in the range of 150° to 200°, or in the range of 150° to 180°.

Referring again toFIG.15, each inner foil pad328is connected to the outer foil assembly302in the illustrated embodiment. In the example embodiment, each inner foil pad328is welded to the outer foil assembly302, and the tabs332may therefore be interchangeably referred to as weld tabs. The tabs332may be welded to the outer foil assembly302using suitable welding techniques, such as resistance or spot welding, and laser welding. In other embodiments, the inner foil pads328may be connected to the outer foil assembly302using any other suitable fastening means. In yet other embodiments, one or more of the inner foil pads328may not be connected or fixed to the outer foil assembly302. That is, one or more of the inner foil pads328can be detached from the outer foil assembly302.

The inner foil pads328can be welded or otherwise connected to the outer foil assembly302at any suitable location that enables the foil bearing assembly300to function as described herein. In the example embodiment, each inner foil pad328is welded to the outer foil assembly302along a respective weld tab332of the inner foil pad328. As shown inFIGS.15and16, the weld tab332of each inner foil pad328extends radially outward from the inner foil pad328through an opening defined between two adjacent bump foils320, and into engagement with the outer foil assembly302.FIG.18is an interior view of the foil bearing assembly300prior to the foil bearing assembly300being formed into a cylinder, and illustrates the weld locations337for the weld tabs332of the inner foil pads328(shown schematically inFIG.18) between adjacent bump foils320. The weld tabs332of the inner foil pads328are welded to a radial inner surface338(FIG.15) of the outer foil pad318in the example embodiment. In other embodiments, the tab332of at least one of the inner foil pads328can be welded or positioned adjacent to the bearing retention feature304of the outer foil assembly302.

FIG.19, for example, illustrates the foil bearing assembly300with the tab332of one of the inner foil pads328positioned adjacent to the bearing retention feature304of the outer foil assembly302. In this embodiment, the tab332is not welded or otherwise fixed to the bearing retention feature304. In other embodiments, the tab332may be connected to the bearing retention feature304, for example, by welding.FIGS.23and24also illustrate tabs332of the inner foil pads328positioned adjacent to bearing retention features304of the outer foil assembly302, as described in further detail herein.

In some embodiments, each of the inner foil pads328is secured or fixed to the foil bearing assembly300only along the weld tab332such that the free end334of the inner foil pad328is free to move or deflect. The free end334of the inner foil pad328can improve damping characteristics of the inner foil assembly306, for example, by allowing greater deflection or freedom of movement of the inner foil assembly306. Additionally, as shown inFIG.15, the segmented inner foil pads328of the inner foil assembly306define axially-extending gaps340between adjacent inner foil pads328. These gaps340create discontinuities along the radial inner surface of the inner foil assembly306, which disrupts or interrupts the swirling fluid film around the driveshaft104. These disruptions in the swirling fluid film facilitate reducing cross-coupling within the foil bearing assembly300, and thereby facilitate reducing sub-synchronous vibrations.

The inner foil pads328can be mounted to the outer foil assembly302in any suitable orientation that enables the foil bearing assembly300to function as described herein. For example, the inner foil pads328can be mounted in an orientation that is the same as or opposite to the direction of rotation of the driveshaft104. More specifically, the driveshaft104is configured for rotation about a rotational axis of the driveshaft104in a first direction (indicated by arrow342inFIG.15) In the embodiment illustrated inFIG.15, each of the inner foil pads328extends circumferentially from the tab332to the free end334in a second direction opposite the first direction342. In other embodiments (seeFIGS.20and21, for example), each of the inner foil pads328can extend circumferentially from the tab332to the free end334in the same (first) direction342as the rotational direction of the driveshaft104.

The inner foil pads328can also be mounted in the same orientation as the outer foil assembly302, or in an opposite orientation than that of the outer foil assembly302. For example, the outer foil pad318extends circumferentially from a first end344including the bearing retention feature304to a second end346. In the embodiment illustrated inFIG.15, the outer foil pad318extends circumferentially from the first end344to the second end346in a first direction, and each of the inner foil pads328extends circumferentially from the tab332to the free end334in a second direction opposite the first direction. In other embodiments (seesFIGS.20and21, for example), the inner foil pads328can be oriented in the same direction as the outer foil pad or pads318. That is, each of the inner foil pads328can extend circumferentially from the tab332to the free end334in the same (first) direction as the outer foil pad or pads318.

FIG.22illustrates another embodiment of a foil bearing assembly500suitable for use with the compressor100. In this embodiment, the foil bearing assembly500includes an outer foil assembly502that includes a plurality of separate, outer foil pads504spaced circumferentially about the foil bearing assembly300. More specifically, the outer foil assembly502includes an outer foil pad504for each of the inner foil pads328of the inner foil assembly306. Each of the inner foil pads328is attached or positioned adjacent to a corresponding one of the outer foil pads504, with one of the bump foils320interposed or “sandwiched” between the outer foil pad504and the inner foil pad328. In this arrangement, the outer foil pads504, inner foil pads328, and bump foils320define a plurality of pad modules506, each pad module506including one of the outer foil pads504, one of the inner foil pads328, and one of the bump foils320. The outer foil assembly302of this embodiment includes three outer foil pads504(corresponding to the three inner foil pads328of the inner foil assembly306), although the outer foil assembly302can include greater than or fewer than three outer foil pads504in other embodiments.

Each outer foil pad504is arcuate and extends circumferentially from a first end508including a bearing retention feature510(e.g., bearing retention feature304) to a second end512. Each outer foil pad504extends or subtends an arc angle514approximately equal to the arc angle336of the corresponding inner foil pad328attached to the outer foil pad504. In the embodiment illustrated inFIG.22, for example, each inner foil pad328extends an arc angle336of approximately 110°, and each outer foil pad504extends an arc angle514of approximately 120°. In this embodiment, the second end512of each outer foil pad504overlaps the first end508of an adjacent outer foil pad504. In other embodiments, the outer foil pads504may not overlap one another. In some embodiments, for example, each outer foil pad504may be separated from adjacent foil pads by a gap (e.g., similar to gap340). Additionally, although the outer foil pads504are illustrated as all having the same arc angle514inFIG.22, it should be understood that the outer foil pads504can have different arc angles from one another.

In the illustrated embodiment, each of the inner foil pads328is welded or otherwise connected to one of the outer foil pads504. In the embodiment illustrated inFIG.22, each of the inner foil pads328is welded to one of the outer foil pads504along the weld tab332of the inner foil pad328. Further, in this embodiment, the weld tab332is welded along a radial inner surface516of the corresponding outer foil pad504. In other embodiments, the tab332of each inner foil pad328can be welded or positioned adjacent to a different location of the outer foil pad504. As illustrated inFIGS.23and24, for example, the tab332of each inner foil pad328is positioned adjacent to the bearing retention feature510of the corresponding outer foil pad504. In this embodiment, the tab332of each inner foil pad328acts as part of the bearing retention feature304, defining a part of the axial tab316sized and dimensioned to interlock with a corresponding bearing assembly locking feature208of the bearing housing200. In the embodiment illustrated inFIGS.23and24, the tab332of each inner foil pad328is not welded to the bearing retention feature510of the corresponding outer foil pad504. That is, the tab332of each inner foil pad328is detached from the corresponding outer foil pad504. In such embodiments, the tab332of each inner foil pad328can be positioned adjacent to and/or in engagement with the bearing retention feature510of the corresponding outer foil pad504, and inserted into a corresponding bearing assembly locking feature208of the bearing housing200to function as part of the axial tab316. In other embodiments, the tab332of each inner foil pad328is welded or otherwise connected to the bearing retention feature510.

The bearing housing and foil bearing assemblies of the present disclosure may be used as part of a method of assembling a compressor. The assembly method includes mounting the bearing housing to the compressor housing using the mounting structure of the bearing housing as described above. The assembly method also includes inserting a foil bearing assembly into the cylindrical bore and connecting the foil bearing assembly to the bearing housing by cooperatively engaging a bearing retention feature of the foil bearing assembly with the bearing assembly locking feature to maintain the foil bearing assembly within the bearing housing at a fixed rotational position as described above. In some embodiments, connecting the foil bearing assembly to the bearing housing includes connecting a plurality of separate pad modules, each having a separate bearing retention feature, to the bearing housing. The method further includes inserting at least one foil retaining clip into a circumferential groove formed within the inner surface of the cylindrical bore to retain the foil bearing assembly in a fixed axial position with respect to the cylindrical bore.

Embodiments of the systems and methods described achieve superior results as compared to prior systems and methods. In particular, bearing systems of the present disclosure facilitate reducing sub-synchronous vibrations (e.g., in centrifugal compressor systems) by incorporating segmented or multi-pad inner foil assemblies. Segmented inner foil assemblies of the present disclosure provide improved damping and reduced cross-coupled stiffness as compared to single-piece or unitary inner foil assemblies, thereby reducing sub-synchronous vibrations. For example, embodiments of the segmented inner foil assemblies form axially-extending discontinuities along the radial inner foil bearing surface, which disrupt or interrupt the swirling fluid film around the shaft, thereby reducing cross-coupling within the foil bearing assembly. Additionally, the multi-pad designs of the present disclosure facilitate tailoring characteristics of the inner foil assembly to enhance operation. For example, inner foil pads of the present disclosure may have different circumferential arc lengths, stiffnesses, and/or other characteristics based on a circumferential position of the inner foil pads.

Example embodiments of bearing systems and methods, such as refrigerant compressors that incorporate the disclosed bearing system and methods of assembling compressors that include the disclosed bearing assembly, are described above in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, components of the system and methods may be used independently and separately from other components described herein. For example, the bearing housing and bearing assemblies described herein may be used in compressors other than refrigerant compressors, such as turbocharger compressors and the like.