Foil bearing assembly including a perforated inner foil assembly and compressor including the same

Abstract

The bearing system includes a bearing housing and a foil bearing assembly. The bearing housing includes a sleeve defining a cylindrical bore and a mounting structure for connecting the bearing system to the compressor housing. The foil bearing assembly is disposed within the cylindrical bore and includes an inner foil assembly and a bump foil assembly. The bump foil assembly includes a plurality of bump foils circumferentially arranged around the inner foil assembly. Each bump foil is circumferentially spaced from an adjacent bump foil to define a gap therebetween. The inner foil assembly includes a cylindrical inner surface defining a plurality of perforations extending radially through the inner foil assembly. Each perforation is radially aligned with one of the gaps between adjacent bump foils.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. patent application Ser. No. 18 / 162,396, filed January 31, 2023, the contents and disclosure of which are incorporated by reference in their entirety. This application also claims priority to U.S. patent application Ser. No. 18 / 509,780, filed November 15, 2023, which is a continuation of and claims priority to U.S. patent application Ser. No. 18 / 162,396, the contents and disclosure of which are incorporated by reference in their entirety.

[0002] The field relates to bearing systems, and more particularly to gas foil bearing assemblies for compressors. [Background technology]

[0003] Some refrigerants used in modern refrigeration and cooling systems, such as R134a or other low global warming potential (GWP) refrigerants, have relatively low densities and require higher flow rate compressors, such as centrifugal compressors.

[0004] Centrifugal compressors typically include bearings that support a rotor that imparts kinetic energy to the incoming refrigerant. The rotor may include a rotating shaft that transfers power from a motor to additional rotor components, such as an impeller. Compressor bearings typically include one or more features to improve the robustness of the bearing system. 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 rotor within a magnetic field provided by high-strength magnets. However, magnetic bearings are typically complex in design, add significant weight, require complex controls, and limit rotor material choices to ferromagnetic materials that respond to the magnetic field in the magnetic bearing. Another type of oil-free bearing is a foil bearing, which includes compliant foil elements that surround and support the rotor on a gas film. When the shaft rotational speed exceeds a threshold speed, known as the lift-off speed, a gas film forms between the rotor and the foil elements. Foil bearings are well suited to the high speed operating environment typical of centrifugal compressors, are compatible with all refrigerant compositions, and can be used with a wider range of rotor materials.

[0005] At least one consideration when using foil bearing assemblies in centrifugal compressors is sub-synchronous vibrations, i.e., vibrations that occur at frequencies lower than the rotational frequency of the rotor supported by the bearing.

[0006] This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. Summary of the Invention

[0007] In one aspect, the bearing system includes a bearing housing and a foil bearing assembly. The bearing housing includes a sleeve defining a cylindrical bore and a mounting structure for connecting the bearing system to a compressor housing. The foil bearing assembly is disposed within the cylindrical bore and includes an outer foil assembly, an inner foil assembly, and a bump foil assembly disposed between the outer foil assembly and the inner foil assembly. The bump foil assembly includes a plurality of bump foils disposed around the inner foil assembly. Each bump foil is coupled to the outer foil assembly at a respective land and is circumferentially spaced from an adjacent bump foil to define a gap therebetween. The inner foil assembly is disposed radially inward from the outer foil assembly and includes a cylindrical inner surface defining a plurality of openings extending radially therethrough. Each of the plurality of openings is radially aligned with one of the lands or one of the gaps between adjacent bump foils.

[0008] In another aspect, a foil bearing assembly includes an outer foil assembly, an inner foil assembly, and a bump foil assembly disposed between the outer and inner foil assemblies. The bump foil assembly includes a plurality of bump foils circumferentially disposed around the inner foil assembly. Each bump foil is coupled to the outer foil assembly at a land and is circumferentially spaced from an adjacent bump foil to define a gap therebetween. The inner foil assembly is disposed radially inward from the outer foil assembly and includes a cylindrical inner surface defining a plurality of openings extending radially therethrough. Each of the plurality of openings is radially aligned with one of the lands or one of the gaps between adjacent bump foils.

[0009] In another aspect, a compressor includes a compressor housing, a shaft rotatably supported within the compressor housing, an impeller connected to the shaft and operable to impart kinetic energy to an incoming refrigerant gas upon rotation of the shaft, a bearing housing attached to the compressor housing, and a foil bearing assembly rotatably supporting the shaft. The bearing housing includes a sleeve defining a cylindrical bore. The foil bearing assembly is disposed within the cylindrical bore and includes an outer foil assembly, an inner foil assembly, and a bump foil assembly disposed between the outer and inner foil assemblies. The bump foil assembly includes a plurality of bump foils circumferentially disposed around the inner foil assembly. Each bump foil is coupled to the outer foil assembly with a land and is circumferentially spaced from an adjacent bump foil to define a gap therebetween. The inner foil assembly is disposed radially inward from the outer foil assembly and includes a cylindrical inner surface defining a plurality of openings extending radially therethrough. Each of the plurality of openings is radially aligned with one of the lands or one of the gaps between adjacent bump foils.

[0010] Various refinements of the features described in connection with the above-described aspects exist. Additional features may also be incorporated into the above-described aspects. These refinements and additional features may exist individually or in any combination. For example, the various features discussed below in connection with any of the illustrated embodiments may be incorporated into any of the above-described aspects, either alone or in any combination. [Brief explanation of the drawings]

[0011] The following figures illustrate various aspects of the present disclosure.

[0012] [Figure 1] FIG. 1 is a perspective view of the assembled compressor.

[0013] [Figure 2]FIG. 2 is a cross-sectional view taken along line 2-2 of the compressor of FIG. 1 with the external conduit removed.

[0014] [Figure 3] FIG. 2 is a cross-sectional view of the compressor of FIG. 1 with the outer compressor housing removed.

[0015] [Figure 4] FIG. 1 is a side view of an impeller mounted on the end of a shaft, the shaft being supported by a bearing housing.

[0016] [Figure 5] FIG. 5 is a cross-sectional view taken along line 5-5 through the sleeve of the bearing housing shown in FIG. 4, showing a shaft rotatably supported in a foil bearing assembly retained in the sleeve of the bearing housing using a pair of retaining clips.

[0017] [Figure 6] FIG. 2 is a cross-sectional view of another embodiment of a bearing housing suitable for use in the compressor of FIG. 1 , showing a shaft supported in a foil bearing assembly retained within the bearing housing between a retaining lip formed in the bearing housing at one end and a retaining clip at the opposite end.

[0018] [Figure 7] FIG. 1 is an exploded view showing the arrangement of the elements of the foil bearing assembly relative to the bearing housing and shaft.

[0019] [Figure 8] FIG. 8 is a front view of the foil bearing assembly shown in FIGS. 5 and 7.

[0020] [Figure 9] FIG. 8 is a front view of the foil bearing assembly shown in FIGS. 6 and 7.

[0021] [Figure 10] FIG. 10 is an enlarged view of the foil bearing assembly shown in FIG. 9.

[0022] [Figure 11] FIG. 8 is a rear view of the bearing housing shown in FIG. 7.

[0023] [Figure 12] FIG. 8 is a side view of the bearing housing shown in FIG. 7.

[0024] [Figure 13] FIG. 8 is a perspective view of the bearing housing shown in FIG. 7.

[0025] [Figure 14] FIG. 11 is an enlarged view of the sleeve of the bearing housing shown in FIG. 10, illustrating the bearing assembly locking feature.

[0026] [Figure 15] FIG. 9 is a cross-sectional front view of the foil bearing assembly shown in FIG. 8 with the foil keeper and foil retaining clip removed.

[0027] [Figure 16] FIG. 16 is an enlarged view of the foil bearing assembly shown in FIG. 15, showing various features of the foil bearing assembly in more detail.

[0028] [Figure 17] FIG. 2 is a cross-sectional front view of another foil bearing assembly suitable for use in the compressor of FIG. 1.

[0029] [Figure 18] FIG. 16 is an internal view of the bump foil assembly and outer foil assembly of the foil bearing assembly shown in FIG. 15 before being formed into a cylinder.

[0030] [Figure 19] FIG. 16 is a side view of the outer foil assembly, bump foil assembly, and inner foil assembly of the foil bearing assembly shown in FIG. 15 before being formed into a cylinder.

[0031] [Figure 20] FIG. 16 is an internal view of the outer foil assembly, bump foil assembly, and inner foil assembly of the foil bearing assembly shown in FIG. 15 before assembly, showing a plurality of perforations or openings formed along the inner foil assembly.

[0032] [Figure 21] FIG. 16 is an internal view of the outer foil assembly, bump foil assembly, and inner foil assembly of the foil bearing assembly shown in FIG. 15 before assembly, illustrating additional or alternative configurations of perforations or openings formed along the inner foil assembly.

[0033] [Figure 22] FIG. 16 is a cutaway perspective view of the foil bearing assembly shown in FIG. 15 mounted in a bearing housing.

[0034] [Figure 23] FIG. 16 is an enlarged cross-sectional view of a portion of the foil bearing assembly shown in FIG. 15.

[0035] Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0036] Referring to FIG. 1 , a compressor in the form of a two-stage refrigerant compressor is generally designated 100. Compressor 100 generally includes a compressor housing 102 that defines at least one sealed cavity within which stages of refrigerant compression are achieved. Compressor 100 includes a first refrigerant inlet 110 that introduces refrigerant vapor into a first compression stage (not shown in FIG. 1 ), a first refrigerant outlet 114, a refrigerant transfer conduit 112 that transfers compressed refrigerant from the first compression stage to a second compression stage, a second refrigerant inlet 118 that introduces refrigerant vapor into the second compression stage (not shown in FIG. 1 ), and a second refrigerant outlet 120. Refrigerant transfer conduit 112 is operably connected at opposite ends to first refrigerant outlet 114 and second refrigerant inlet 118, respectively. Second refrigerant outlet 120 delivers compressed refrigerant from the second compression stage to a refrigeration system in which compressor 100 is incorporated. The refrigerant transport conduit 112 may further include a refrigerant port 122, for example, for economy.

[0037] Referring to FIG. 2 , compressor housing 102 encloses first and second compression stages 124, 126 at opposite ends of compressor 100. First compression stage 124 includes a first-stage impeller 106 operable to impart kinetic energy to refrigerant entering via first refrigerant inlet 110. The kinetic energy imparted to the refrigerant by first-stage impeller 106 is converted to increased refrigerant pressure (i.e., compression) as the refrigerant velocity is reduced upon transfer to diffuser 136. Similarly, second compression stage 126 includes a second-stage impeller 116 operable to impart kinetic energy to refrigerant transferred from first compression stage 124 via second refrigerant inlet 118. The kinetic energy imparted to the refrigerant by second-stage impeller 116 is converted to increased refrigerant pressure (i.e., compression) as the refrigerant velocity is reduced upon transfer to diffuser 138. The compressed refrigerant exits the second compression stage 126 via a second refrigerant outlet 120 (not shown in FIG. 2).

[0038] 2 and 3, the first-stage impeller 106 and the second-stage impeller 116 are connected to opposite ends of a shaft 104 supported within the compressor housing. In the illustrated embodiment, the shaft 104, the first-stage impeller 106, and the second-stage impeller 116 are coupled together to form a single rotor and may be collectively referred to herein as the rotor. The shaft 104 is operably connected to a motor 108 disposed between the first-stage impeller 106 and the second-stage impeller 116 such that the first-stage impeller 106 and the second-stage impeller 116 rotate at a selected rotational speed to compress the refrigerant to a preselected pressure that exits the second refrigerant outlet 120. Any suitable motor may be incorporated into the compressor 100, including, but not limited to, an electric motor. The shaft 104 is rotatably supported by a gas foil bearing assembly 300 disposed within a sleeve 202 of each bearing housing 200 / 200a, as described in further detail below. Each bearing housing 200 / 200a includes a mounting structure 210 for connecting the respective bearing housing 200 / 200a to the compressor housing 102, as shown in FIG.

[0039] 4, each bearing housing 200 / 200a (only bearing housing 200 is shown in FIG. 4) supports a shaft 104 that protrudes through the bearing housing 200 / 200a opposite the sleeve 202, and an impeller 106 / 116 (only the first stage impeller 106 is shown in FIG. 4) is connected to the protruding end of the shaft 104. Referring to FIGS. 5 and 7, a gas foil bearing assembly 300 is disposed within a cylindrical bore 206 in the bearing housing 200. The shaft 104 fits closely within a gas foil bearing assembly 300, which includes a compliant outer foil assembly 302 or foil layer disposed adjacent the inner wall of the sleeve 202, a compliant inner foil assembly 306 or foil layer (also referred to as the “top foil”) disposed adjacent the shaft 104, and a bump foil assembly 310 or foil layer disposed between the inner foil assembly 306 and the outer foil assembly 302. The foil assemblies or layers 302 / 306 / 310 of the gas foil bearing assembly 300 form an essentially cylindrical tube sized to receive the shaft 104 with a relatively little or no clearance design, as determined by existing foil bearing design methodologies. Components of the foil bearing assembly 300, such as the outer foil assembly 302, inner foil assembly 306, and bump foil assembly 310, may be constructed of any suitable materials that enable the foil bearing assembly 300 to function as described herein. Suitable materials include, for example, but are not limited to, metal alloys. In some embodiments, for example, outer foil assembly 302, inner foil assembly 306, and bump foil assembly 310 are each constructed of stainless steel (e.g., 17-4 stainless steel). The foil assemblies can be formed from relatively thin sheets or "foils" of material. For example, foil assemblies or layers 302 / 306 / 310 can be constructed of metal sheets having thicknesses ranging from 0.003 inches to 0.007 inches.

[0040] 5, the foil bearing assembly 300 of the illustrated embodiment further includes a pair of foil keepers 312a / 312b disposed adjacent to opposite ends of the layers 302 / 306 / 310 to restrain sliding of the layers 302 / 306 / 310 in the axial direction within the cylindrical bore 206 of the sleeve 202. A pair of foil retaining clips 314a / 314b disposed adjacent to the foil keepers 312a / 312b, respectively, secure the layers 302 / 306 / 310 in a locked axial position within the cylindrical bore 206. The foil retaining clips 314a / 314b may be removably connected to the bearing housing 200. FIG. 8 further illustrates the arrangement of the foil keeper 312a and the foil retaining clip 314a at one end of the foil bearing assembly 300.

[0041] 6, each bearing housing 200 / 200a (only bearing housing 200 is shown in FIG. 6) includes a foil retaining lip 214 that is integrally formed (e.g., cast) with bearing housing 200 and that projects radially inward from a radially inner surface 204 that defines cylindrical bore 206. In the illustrated embodiment, foil retaining lip 214 is located near an impeller end 216 of cylindrical bore 206 that is proximate second stage impeller 116 (shown in FIGS. 2-3 ). Foil retaining lip 214 is sized and dimensioned to project a radial distance from radially inner surface 204 that overlaps at least a portion of layers 302 / 306 / 310 of foil bearing assembly 300. The foil retaining lip 214 can extend completely around the radially inner surface 204, or the foil retaining lip can include two or more segments that extend partially around the radially inner surface 204 and are separated by a space that is flush with adjacent radially inner surfaces 204.

[0042] The foil bearing assembly 300 of the embodiment illustrated in FIG. 6 further includes a single foil retaining clip 314 positioned adjacent an end of the layer 302 / 306 / 310 opposite the foil retaining lip 214 to restrain axial movement of the layer 302 / 306 / 310 within the cylindrical bore 206 of the sleeve 202. In this embodiment, the foil retaining clip 314 snaps into a circumferential groove 212 formed in the radially inner surface 204 of the cylindrical bore 206 near the motor end 218 of the cylindrical bore 206. FIGS. 9 and 10 further illustrate the placement of the foil retaining clip 314 at one end of the foil bearing assembly 300. The foil retaining clip 314 is sized and dimensioned to provide clearance for the outer foil assembly 302 and to overlap at least one bearing retention feature 304 forming a radially outwardly protruding axial tab 316, as described further below.

[0043] The foil retaining lip 214 may be positioned within any region of the cylindrical bore 206 near the impeller end 216, including, but not limited to, immediately adjacent the opening of the cylindrical bore 206 at the impeller end 216. Alternatively, the foil retaining lip 214 may be positioned within any region of the cylindrical bore 206 near the motor end 218, including, but not limited to, immediately adjacent the opening of the cylindrical bore 206 at the motor end 218. In such an embodiment, the foil retaining clip 314 snaps into the circumferential groove 212 formed in the radially inner surface 204 of the cylindrical bore 206 near the impeller end 216 in an arrangement essentially opposite to that shown in FIG.

[0044] 6 , the foil bearing assembly 300 is installed within the bearing housing 200 by inserting the foil bearing assembly 300 into the cylindrical bore 206 of the bearing housing 200 at the motor end 218. The foil bearing assembly 300 is then advanced axially into the cylindrical bore 206 toward the impeller end 216 until the layers 302 / 306 / 310 contact the foil retaining lip 214. The foil retaining clip 314 is then snapped into the circumferential groove 212 near the motor end 218 of the cylindrical bore 206 to lock the foil bearing assembly 300 in place. In other embodiments, any suitable method for securing the foil bearing assembly 300 within the sleeve 202 can be used. Non-limiting examples of suitable methods include keepers and retaining clips, adhesives, set screws, and any other suitable fastening method.

[0045] 11, 12, and 13, a mounting structure 210 for each bearing housing 200 / 200a (only bearing housing 200 is shown in FIGS. 11, 12, and 13) connects the respective bearing housing 200 / 200a to the compressor housing 102 (shown in FIGS. 1 and 2). In the illustrated embodiment, the mounting structure 210 projects radially outward to a dimension generally matching the outer dimension of the compressor housing 102. The bearing housing 200 may include any form of mounting structure 210, including, but not limited to, an annular flange. The bearing housing 200 / 200a may further serve as a mounting structure for various elements, including, but not limited to, radial bearings, such as the foil bearing assembly 300 described above, thrust bearings, and sensing devices (not shown) used as feedback for passive or active control schemes, such as proximity probes, pressure transducers, thermocouples, key phasors, etc. The bearing housing 200 may further include external coolant conduits or channels 220 (shown in FIG. 11 ) to enable active cooling of the foil bearing assembly. The coolant channels 220 may extend radially outward from the cylindrical bore 206 to openings 260 formed in the radially outer edge 222 of the bearing housing 200 / 200a (see also FIG. 7 ), for example, and may deliver coolant from an external source and / or refrigerant system flow to the bearing housing 200 / 200a and foil bearing assembly 300. Further details of coolant channels and coolant delivery methods suitable for use with the compressor 100 are described, for example, in U.S. Patent Application No. 16 / 809,836, filed March 5, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0046] 13 and 14 , the bearing housing sleeve 202 has a radially inner surface 204 that defines a cylindrical bore 206. The cross-sectional profile of the cylindrical bore may be essentially circular or may be other rounded or polygonal shapes such as, but not limited to, oval, square, octagon, etc. The radially inner surface 204 is sized and dimensioned to receive the foil bearing assembly 300 such that the outer foil assembly 302 of the foil bearing assembly 300 contacts the radially inner surface 204.

[0047] 13, the radially inner surface 204 includes at least one or more additional features that enable the foil bearing assembly to be retained in a fixed axial and rotational position within the sleeve 202. In some embodiments, for example, a first circumferential groove 212a and a second circumferential groove 212b are formed in the radially inner surface 204. The first and second circumferential grooves 212a / 212b are sized and dimensioned to receive foil retaining clips 314a and 314b, respectively, as shown in FIG. 5. In other embodiments, the first circumferential groove 212a may be replaced by a circumferential foil retaining lip 214 (see FIG. 6).

[0048] 14 , the radially inner surface 204 of the bearing housing 200 further includes at least one bearing assembly locking mechanism 208. The bearing assembly locking mechanism 208 interlocks with one or more bearing retention mechanisms provided on the foil bearing assembly 300, as described below. The bearing assembly locking mechanism 208 can be any suitable form of mechanical interlocking mechanism, without limitation. Non-limiting examples of suitable mechanical interlocking mechanisms include raised features, such as axial ridges, keys, or tabs, and axial recesses formed in the radially inner surface 204, such as axially extending slots, axially extending keyholes, or keepers, as shown in FIG. 14 . While the bearing housing 200 shown in FIG. 14 includes a single bearing assembly locking mechanism 208, it should be understood that the bearing housing 200 can include multiple bearing assembly locking mechanisms 208. In some embodiments, for example, the radially inner surface 204 of the bearing housing 200 defines a plurality of axially extending grooves circumferentially spaced along the radially inner surface, each of the axially extending grooves being sized and shaped to receive a corresponding bearing retention feature of the foil bearing assembly 300.

[0049] 15 and 16 , the foil bearing assembly 300 further includes at least one bearing retention feature 304 for cooperatively engaging with the bearing assembly locking mechanism 208 to maintain the foil bearing assembly within the bearing housing in a fixed rotational position within the cylindrical bore 206 of the sleeve 202. That is, the bearing retention feature 304 and the bearing assembly locking mechanism 208 are sized and shaped to complement one another such that, when the bearing retention feature 304 engages the bearing assembly locking mechanism 208, the bearing assembly locking mechanism 208 inhibits or limits at least rotational movement of the bearing retention feature 304. The bearing retention feature 304 may include, without limitation, any suitable form of mechanical interlocking mechanism. In some embodiments, the at least one bearing retention feature 304 is selected based on the selection of the bearing assembly locking mechanism 208 provided within the cylindrical bore 206. Non-limiting examples of suitable mechanical interlocking mechanisms include raised features such as axial ridges, keys, or tabs, as well as axial recesses formed in at least the outer foil assembly 302 of the foil bearing assembly 300, such as axial slots, axial keyholes, or keepers.

[0050] The foil bearing assembly 300 of the illustrated embodiment includes a single bearing retention feature 304 formed along the edge of the outer foil assembly 302. The bearing retention feature defines an axial tab 316 sized and dimensioned to interlock with the bearing assembly locking feature 208 provided in the form of an axial slot, as shown in FIG. 14 . In other embodiments, the foil bearing assembly 300 may include additional bearing retention features 304 formed, for example, along the edge of the inner foil assembly 306. In such embodiments, the bearing retention features 304 formed along the outer and inner foil assemblies 302, 306 may be positioned adjacent to one another and / or joined together (e.g., by welding) to define the axial tab 316.

[0051] The foil bearing assembly 300 may be provided in any suitable form, without limitation, for example, without limitation, the foil bearing assembly 300 may include two layers, three layers, four layers, or additional layers.

[0052] The outer foil assembly 302 includes at least one outer foil pad 318 circumferentially disposed around the bump foil assembly 310 and the inner foil assembly 306. In the exemplary embodiment shown in FIGS. 1 through 16 , the outer foil assembly 302 includes a single outer foil pad 318 constructed from a single, integral foil. In other embodiments, the outer foil assembly 302 may be constructed from multiple outer foil pads. The outer foil assembly 302 may provide a smooth inner surface that supports the adjacent bump foil assembly 310 to efficiently transmit transient motion caused by radial forces applied to the inner foil assembly 306 by the shaft 104 during operation of the compressor 100. The outer foil assembly 302 provides this smooth inner surface regardless of the surface smoothness of the underlying radial inner surface 204 of the cylindrical bore 206 of the bearing housing 200. Thus, in some embodiments, use of the outer foil assembly 302 facilitates increasing the surface specification of the radially inner surface 204 of the cylindrical bore 206, or, stated differently, reducing the surface smoothness requirements of the radially inner surface 204. In some embodiments, the foil bearing assembly 300 is suitable for use with the bearing housing 200 in an "as-cast" condition, without requiring further machining, grinding, or other means to smooth the radially inner surface 204 of the cylindrical bore 206 of the bearing housing 200. Thus, in some embodiments, the radially inner surface 204 of the cylindrical bore 206 is an as-cast surface. That is, the radially inner surface 204 of the cylindrical bore 206 is a surface of the cast bearing housing 200 that has not undergone post-casting machining, grinding, or similar means to smooth the radially inner surface 204.

[0053] The outer foil assembly 302 can also improve thermal management of the foil bearing assembly 300 and facilitate reducing the space requirements of the foil bearing assembly 300, as described, for example, in U.S. patent application Ser. No. 16 / 809,836, filed March 5, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0054] The bump foil assembly 310 of the foil bearing assembly 300 may be formed from a radially resilient structure to provide a resilient surface for the rotating shaft 104 during operation of the compressor 100. The bump foil assembly 310 may be formed from any suitable radially resilient structure, 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 resilient material capable of compressing and rebounding under intermittent compressive radial loads. The bump foil assembly 310 may be connected to at least one adjacent layer, including, but not limited to, at least one of the outer foil assembly 302 and the inner foil assembly 306. In some embodiments, the bump foil assembly 310 may be connected to both the outer foil assembly 302 and the inner foil assembly 306. In other embodiments, the bump foil assembly 310 may be free-floating and not connected to any layer of the foil bearing assembly 300.

[0055] 15, the bump foil assembly 310 of the exemplary embodiment includes a plurality of bump foils 320 spaced circumferentially around the foil bearing assembly 300. While the bump foil assembly 310 shown in FIG. 15 includes three bump foils 320, the bump foil assembly 310 may include any other suitable number of bump foils 320 that enables the foil bearing assembly 300 to function as described herein, including, but not limited to, one, two, four, or more bump foils. Each bump foil 320 extends the entire axial length or substantially the entire length of the foil bearing assembly 300 and extends circumferentially from a first edge 322 to a second edge 324. In the illustrated embodiment, each bump foil 320 extends or subtends an arc angle 336 of approximately 110° from the first edge 322 to the second edge 324, although the bump foils 320 may extend more or less than 110° around the foil bearing assembly 300 in other embodiments.

[0056] Additionally, the bump foils 320 can have different arc angles. For example, FIG. 17 illustrates a foil bearing assembly 400 including a bump foil assembly 410 with bump foils 415, 420, and 425 having different arc angles 406, 408. In particular, the bump foil assembly 410 of FIG. 17 includes a primary bump foil 415 having an arc angle 406 that is greater than the arc angles 408 of the other bump foils 420 and 425. In this embodiment, the primary bump foil 415 has an arc angle 406 of approximately 160°, and the other bump foils 420 and 425 have arc angles 408 of approximately 95°. In other embodiments, the primary bump foil 415 may have an arc angle 406 in 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°. In other embodiments, the bump foil assembly 310 may include a single bump foil extending circumferentially around the entire or substantially the entire foil bearing assembly 300.

[0057] The inner foil assembly 306 includes at least one inner foil pad 328. In the exemplary embodiment shown in FIGS. 1-17 , the inner foil assembly 306 includes a single inner foil pad 328 constructed from a single, integral foil. In other embodiments, the inner foil assembly 306 may be constructed from multiple separate or segmented inner foil pads spaced circumferentially around the foil bearing assembly 300. In such embodiments, the inner foil assembly 306 may include any suitable number of inner foil pads that enable the foil bearing assembly 300 to function as described herein. Such embodiments are described, for example, in U.S. Patent Application No. 17 / 167,611, filed February 4, 2021, the disclosure of which is incorporated herein by reference in its entirety. The inner foil pad 328 is arcuate and extends circumferentially from a first end 330, including a tab 332, to a second free end 334. The inner foil pad 328 defines a cylindrical inner surface 350 positioned to engage the surface of the shaft 104. The cylindrical inner surface 350 defines a plurality of radially extending openings or perforations 370. As described in more detail herein, the openings 370 extending through the inner foil assembly 306 facilitate reducing sub-synchronous vibrations by, for example, providing improved damping and reduced cross-coupled stiffness throughout the foil bearing assembly 300. The cross-sectional views shown in FIGS. 15-17 are taken through the plurality of openings 370, as indicated by dashed line 500 in FIG. 20.

[0058] 15 and 16 , the inner foil pad 328 is connected to the outer foil assembly 302. A tab 332 of the inner foil pad 328 extends radially outward from the end of the inner foil pad 328 and engages the outer foil assembly 302. In the embodiment shown in FIG. 15 , the tab 332 is nested within the bearing retention feature 304 of the outer foil assembly 302 and is not connected or secured to the outer foil assembly 302. In further embodiments, the inner foil pad 328 can be welded to the outer foil assembly 302 along the tab 332. The tab 332 can be welded to the outer foil assembly 302 using any suitable welding technique, such as resistance or spot welding, and laser welding. In other embodiments, the inner foil pad 328 can be connected to the outer foil assembly 302 using any other suitable fastening means. The inner foil pad 328 can be welded or otherwise connected to the outer foil assembly 302 at any suitable location that enables the foil bearing assembly 300 to function as described herein. In some embodiments, the inner foil pad 328 is clipped or secured to the foil bearing assembly 300 only along the tabs 332, such that the free ends 334 of the inner foil pad 328 are free to move or flex. The free ends 334 of the inner foil pad 328 can improve the damping characteristics of the inner foil assembly 306, for example, by allowing the inner foil assembly 306 greater freedom to flex or move.

[0059] 18 is an internal view of the bump foil assembly 310 and the outer foil assembly 302 prior to assembly into the foil bearing assembly 300. Each bump foil 320 is comprised of multiple bump foil strips 327 extending between a first edge 322 and a second edge 324 of the bump foil 320. In the illustrated embodiment, each bump foil 320 is comprised of four bump foil strips 327. Further embodiments may include any suitable number of bump foil strips 327, for example, one, two, three, five, or more bump foil strips 327. Each bump foil strip 327 is axially spaced from an adjacent bump foil strip 327 to form an axial gap 329 therebetween. Each bump foil strip 327 includes multiple bumps 321 disposed between the first edge 322 and the second edge 324. In the embodiment shown in FIG. 19 , the height of each of the plurality of bumps 321 increases between the first edge 322 and the second edge 324 of the bump foil 320, such that the shortest bump 321 is proximate the first edge 322 and the tallest bump 321 is proximate the second edge 324. In further embodiments, the height of each of the plurality of bumps 321 may vary in any other suitable configuration, or each of the plurality of bumps 321 may have substantially the same height. In some embodiments, the height of each of the plurality of bumps 321 increases in a direction opposite to the direction of rotation of the shaft 104. For example, referring to FIG. 15 , the shaft 104 is configured to rotate in a first direction 342 about the axis of rotation of the shaft 104. The height of each of the plurality of bumps 321 increases in a second direction opposite the first direction 342 from the first edge 322 to the second edge 324 of the bump foil 320. In a further embodiment, the height of each of the plurality of bumps 321 may increase in the same direction as the rotation direction of the shaft 104 .

[0060] Each bump foil 320 includes an axially extending land 326 located between a first edge 322 and a second edge 324. The bump foils 320 are secured to one or both of the outer foil assembly 302 and the inner foil assembly 306. In some embodiments, for example, each of the bump foils 320 is welded to the outer foil assembly 302 along its respective land 326, such that the respective land 326 interconnects the bump foil strips 327 of each bump foil 320. The embodiment shown in FIG. 18 illustrates a bump foil 320 having seven bumps 321 on the left side of the land 326 and three bumps 321 on the right side of the land 326. Other embodiments can have any number of bumps on either side of the land that enables the foil bearing assembly to function as described herein.

[0061] FIG. 20 is an internal view of the foil bearing assembly 300 before assembly. During assembly of the foil bearing assembly 300, the three foil assemblies 302, 310, and 306 are axially aligned and formed into a cylindrical shape. FIG. 20 shows each of the three foil assemblies 302, 310, and 306 at different axial positions for clarity. In the illustrated embodiment, the outer foil assembly 302 includes a single outer foil pad 318 extending from a first end 344 to a second end 346. The bump foil assembly 310 is disposed between the outer foil assembly 302 and the inner foil assembly 306 and, in the illustrated embodiment, includes three bump foils 320. When installed, the bump foil assembly 310 is disposed circumferentially around the inner foil assembly 306, with each bump foil 320 circumferentially spaced from an adjacent bump foil 320 to form a gap 325 therebetween, the gap 325 having a width W. gap It has.

[0062] The inner foil assembly 306 of the first exemplary embodiment includes a single inner foil pad 328 disposed radially inward from the outer foil assembly 302 and the bump foil assembly 310. The cylindrical inner surface 350 of the inner foil assembly 306 extends axially a length L from a first edge of the inner foil assembly 306 to an opposite second edge of the inner foil assembly 306. As described above, the cylindrical inner surface 350 defines a plurality of openings or perforations 370 extending radially therethrough. In the illustrated embodiment, each opening 370 of the plurality of openings 370 is radially aligned with one of the gaps 325 between adjacent bump foils 320 and axially aligned with one of the axial gaps 329 between adjacent bump foil strips 327. The plurality of openings 370 may include at least one subset 375 of openings 370, with each opening 370 in the subset 375 axially aligned with the other openings 370 in the subset 375. While the embodiment illustrated in FIG. 20 includes two subsets 375 of axially aligned openings 370, other embodiments may include more or fewer than two subsets 375. Furthermore, in the illustrated embodiment, each subset 375 includes three axially aligned openings 370. In other embodiments, one or more subsets 375 may include more or fewer than three openings 370, such as one opening, two openings, four openings, five openings, or six or more openings. While the illustrated embodiment includes six openings 370 in total, other embodiments may include more or fewer than six openings 370. For example, the embodiment illustrated in FIG. 21 includes two subsets 375, each with a single opening 370. Each opening is radially aligned with one of the gaps 325 defined between adjacent bump foils 320 and axially aligned with all three axial gaps. In some embodiments, including the embodiment shown in Figures 20 and 21, each of the gaps 325 defined between adjacent bump foils 320 is radially aligned with one subset 375 of the openings 370.

[0063] In other embodiments, the openings 370 may be positioned along the inner foil assembly 306 at locations other than radially aligned with one of the gaps 325 between adjacent bump foils 320. For example, in addition to or as an alternative to being radially aligned with the gaps 325 between the bump foils 320, the openings 370 may be radially aligned with the lands 326 of the bump foils 320. In such embodiments, each subset 375 is radially aligned with one of the lands 326, and the land 326 of each bump foil 320 is radially aligned with one subset 375 of the openings 370.

[0064] Each of the openings 370 may have any suitable size and shape that enables the foil bearing assembly 300 to function as described herein. In the illustrated embodiment, each opening 370 has the same opening shape. In other embodiments, different openings 370 may have different opening shapes. In some embodiments, the opening shape of each of the plurality of openings 370 is at least partially polygonal, including, but not limited to, a rectangle, a triangle, a diamond, or other at least partially polygonal shape that enables the foil bearing assembly 300 to function as described herein. In other embodiments, the opening shape may be fully or partially rounded, such as a circle, an oval, a teardrop, or other fully or partially rounded shape that enables the foil bearing assembly 300 to function as described herein. [Table 1]

[0065] Table 1 shows the total foil area A of 9.312 square inches. foil20 shows dimensions of several example configurations of openings 370 for the inner foil assemblies 306. The inner foil assemblies 306 of Examples 1-6 each include a total of six openings 370, with two subsets 375 each having three openings 370, as shown in FIG. 20. The inner foil assemblies 306 of Examples 7-11 each include a total of four openings, with two subsets 375 each having two openings 370 (not shown). The inner foil assemblies 306 of Examples 12-16 each include a total of two openings 370, with two subsets 375 each having one opening 370, as shown in FIG. 21. Each opening 370 has an axial length L i Extends to width W in the circumferential direction i For example, in Example 1, the inner foil assemblies 306 each have a width W of 0.1 inches. i and a length L of 0.3 inches i In the example listed in Table 1, each opening 370 in the plurality of openings 370 has the same length L i and width W i However, in a further exemplary embodiment, different openings 370 have different lengths L i and / or width W i may have:

[0066] Length L of openings 370 in subset 375 with N openings i The sum of the subset opening length L sub and L1+...+L N In some embodiments, the length L of the subset openings relative to the length L of the cylindrical inner surface 350 of the inner foil assembly 306 is equal to sub In some embodiments, the ratio of the width W of each of the openings 370 in one subset of the openings 370 is between 0.288 and 0.312. i The width W of the gap 325 in which the subsets 375 are radially aligned gap The ratio to is between 0.100 and 0.300.

[0067] Each opening 370 further has an opening area A iIn the examples listed in Table 1, the opening area A i is the length L of the opening 370 i and width W i Total opening area A is equal to the product of total is the opening area A of each of the plurality of openings 370 i For example, Example 3 shows the opening area A of 0.375 square inches each. i and six openings 370 having a total opening area A total is 0.225 square inches. For the example listed in Table 1, the ratio of total aperture area to total foil area, A total / A foil In a further embodiment, the ratio A total / A foil may be in any other suitable range.

[0068] The openings 370 defined along the cylindrical inner surface 350 of the inner foil assembly 306 facilitate reducing subsynchronous vibrations within the centrifugal compressor by, for example, providing improved damping and reduced cross-coupling stiffness by introducing axially extending discontinuities along the cylindrical inner surface 350. With reference to FIGS. 22 and 23 , for example, the openings 370 defined along the cylindrical inner surface 350 of the inner foil assembly 306 are perpendicular to the swirling circumferentially fluid film around the shaft 104 ( FIG. 22 ), thereby disrupting the swirling flow (indicated by arrows 450) and introducing fresh gas (indicated by arrows 460) into the bearing assembly 300. Disrupting the otherwise continuous circumferential flow provides cooling and reduces cross-coupling within the foil bearing assembly 300. The polygonal shape and sharp corners of each opening 370 create additional turbulence that disrupts the swirling fluid film. Drawing additional gas into the bearing membrane further reduces the risk of bearing starvation, and doing so without a pump reduces the complexity, weight and cost of the bearing.

[0069] The openings 370 also allow gas to flow underneath the bump foil assembly 310 and reach each layer of the foil bearing assembly 300. Referring to FIG. 22 , gas (indicated by dashed arrows) can flow through the openings 370, underneath each bump foil 320, and into contact with the outer foil assembly 302. This configuration provides cooling between each layer of the foil bearing assembly 300, improving damping and reducing interconnect stiffness throughout the bearing. Further referring to FIG. 19 , aligning the openings 370 with the gaps 325 between adjacent bump foils 320 advantageously positions the openings 370 between the tallest bump 321 at the second edge 324 of the bump foil 320 and the shortest bump 321 at the first end of the adjacent bump foil 320. During operation, pressure generated by the hydrodynamic film causes the inner foil assembly to flex outward and engage the outer peaks of each bump 321. The changing height of bump foil 320 causes cylindrical inner surface 350 to deflect into a non-cylindrical shape. When shaft 104 rotates in a first direction 342 shown in FIG. 15 , opening 370 is oriented obliquely relative to first direction 342, thus angling the direction of the swirling hydrodynamic film 450 generated by shaft 104, facilitating film 450 flow through opening 370 and facilitating its rupture.

[0070] The bearing housing and foil bearing assembly of the present disclosure can be used as part of a method for assembling a compressor. The assembly method includes attaching the bearing housing to the compressor housing using the bearing housing mounting structure described above. The assembly method also includes inserting the foil bearing assembly into the cylindrical bore and connecting the foil bearing assembly to the bearing housing by cooperatively engaging the bearing retention feature of the foil bearing assembly with the bearing assembly locking mechanism to maintain the foil bearing assembly in a fixed rotational position within the bearing housing, as described above. In some embodiments, connecting the foil bearing assembly to the bearing housing includes connecting a plurality of separate pad modules to the bearing housing, each pad module having a separate bearing retention feature. The method further includes inserting at least one foil retention clip into a circumferential groove formed in the inner surface of the cylindrical bore to hold the foil bearing assembly in a fixed axial position relative to the cylindrical bore.

[0071] Embodiments of the described systems and methods achieve desired results compared to conventional systems and methods. For example, embodiments of the bearing system facilitate reducing subsynchronous vibration (e.g., in centrifugal compressor systems) by incorporating a perforated inner foil assembly into the foil bearing. The perforations formed along the inner foil assembly facilitate breaking up the fluid film swirling around the shaft, thereby reducing cross-coupling within the foil bearing assembly and increasing damping. Furthermore, the disclosed size and orientation of the perforations achieves the described benefits without reducing the load-bearing capacity of the bearing. That is, the hydrodynamic film can be broken up without significantly reducing the hydrodynamic pressure within the bearing.

[0072] Exemplary embodiments of bearing systems and methods, such as refrigerant compressors incorporating the disclosed bearing systems and methods for assembling compressors including the disclosed bearing assemblies, are described above in detail. The systems and methods are not limited to the specific embodiments described herein; rather, components of the systems and methods can be used separately and independently from other components described herein. For example, the bearing housings and bearing assemblies described herein can be used in compressors other than refrigerant compressors, such as turbocharger compressors.

[0073] As used herein, the terms "about," "substantially," "essentially," and "approximately," when used in connection with a dimension, concentration, temperature, or other physical or chemical property or range of properties, are meant to cover the variation that may exist at the upper and / or lower limits of the property or range of properties, including, for example, variation resulting from rounding, measurement method, or other statistical variation.

[0074] When introducing elements of the present disclosure or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," "containing," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terminology indicating a specific orientation (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require a specific orientation of the described items.

[0075] Since various changes can be made in the structures and methods described above without departing from the scope of the disclosure, all matter contained in the above description and shown in the accompanying drawing(s) is intended to be illustrative and not in a limiting sense.

Claims

1. The bearing system is:

1. A bearing housing comprising: a sleeve defining a cylindrical bore; and a mounting structure for connecting the bearing system to a compressor housing; a bearing housing having A foil bearing assembly disposed within the cylindrical bore, comprising: an inner foil assembly including a cylindrical inner surface; and a bump foil assembly disposed radially outward from the inner foil assembly, the bump foil assembly including a plurality of bump foils disposed circumferentially around the inner foil assembly, each of the bump foils being circumferentially spaced from an adjacent bump foil to define a gap therebetween; the cylindrical inner surface of the inner foil assembly defines a plurality of perforations extending radially through the inner foil assembly, each of the plurality of perforations being radially aligned with one of the gaps between adjacent bump foils; a foil bearing assembly; Bearing system.

2. Each of the plurality of perforations has an at least partial polygonal shape.

10. The bearing system of claim 1.

3. each of the plurality of bump foils extends from a first edge to a second edge and includes a plurality of bumps, each of the bumps having a height, the height of each of the plurality of bumps increasing between the first edge and the second edge; 10. The bearing system of claim 1.

4. the plurality of perforations includes at least one subset of perforations, each of the perforations of the at least one subset of perforations being axially aligned with the other perforations of the at least one subset of perforations, and each of the at least one subset of perforations being radially aligned with one of the gaps defined between adjacent bump foils; 10. The bearing system of claim 1.

5. each of the bump foils having a plurality of bump foil strips extending from a first edge to a second edge, each bump foil strip being axially spaced from an adjacent bump foil strip to define an axial gap therebetween; 10. The bearing system of claim 1.

6. each of the plurality of perforations is axially aligned with one of the axial gaps defined between adjacent ones of the bump foil strips; 6. The bearing system of claim 5.

7. the plurality of perforations includes a single perforation radially aligned with one of the gaps defined between adjacent bump foils and axially aligned with each of the axial gaps defined between adjacent bump foil strips.

6. The bearing system of claim 5.

8. each of the plurality of perforations has an open area, the sum of the open areas of each of the plurality of perforations is a total open area, the inner foil assembly has a total foil area, and a ratio of the total open area to the total foil area is between 0.48% and 4.27%.

10. The bearing system of claim 1.

9. each of the plurality of perforations has a width, and a ratio of the width of each of the plurality of perforations to a width of the gap in which the perforations are radially aligned is between 0.100 and 0.300; 10. The bearing system of claim 1.

10. the foil bearing assembly includes an outer foil assembly disposed radially outward from the bump foil assembly such that the bump foil assembly is disposed between the outer foil assembly and the inner foil assembly.

10. The bearing system of claim 1.

11. each of the bump foils is coupled to the outer foil assembly at a respective land; 11. The bearing system of claim 10.

12. each of the bump foils is secured to the outer foil assembly at the respective land; 12. The bearing system of claim 11.

13. 1. A foil bearing assembly comprising: an inner foil assembly including an inner cylindrical surface; a bump foil assembly disposed radially outward from the inner foil assembly, the bump foil assembly including a plurality of bump foils disposed circumferentially around the inner foil assembly, each of the bump foils spaced circumferentially from an adjacent bump foil to define a gap therebetween; the cylindrical inner surface of the inner foil assembly defines a plurality of perforations extending radially through the inner foil assembly, each of the plurality of perforations being radially aligned with one of the gaps between adjacent bump foils; Foil bearing assembly.

14. Each of the plurality of perforations has an at least partial polygonal shape. The foil bearing assembly of claim 13.

15. each of the plurality of bump foils extends from a first edge to a second edge and includes a plurality of bumps, each of the bumps having a height, the height of each of the plurality of bumps increasing between the first edge and the second edge; The foil bearing assembly of claim 13.

16. the plurality of perforations includes at least one subset of perforations, each of the perforations in the at least one subset of perforations being axially aligned with other perforations in the at least one subset of perforations, and each of the at least one subset of perforations being radially aligned with one of the gaps defined between adjacent bump foils; The foil bearing assembly of claim 13.

17. each of the plurality of perforations has an open area, a sum of the open areas of each of the plurality of perforations is a total open area, the inner foil assembly has a total foil area, and a ratio of the total open area to the total foil area is between 0.48% and 4.27%. The foil bearing assembly of claim 13.

18. each of the plurality of perforations has a width, and a ratio of the width of each of the plurality of perforations to a width of the gap in which the perforations are radially aligned is between 0.100 and 0.300; The foil bearing assembly of claim 13.

19. an outer foil assembly disposed radially outward from the bump foil assembly such that the bump foil assembly is disposed between the outer foil assembly and the inner foil assembly; The foil bearing assembly of claim 13.

20. each of the bump foils is coupled to the outer foil assembly at a land; 20. The foil bearing assembly of claim 19.

21. each of the bump foils is secured to the outer foil assembly by a land; 21. The foil bearing assembly of claim 20.

22. A compressor comprising: a compressor housing; a shaft rotatably supported within the compressor housing; an impeller connected to the shaft and operable to impart kinetic energy to an incoming refrigerant gas upon rotation of the shaft; a bearing housing attached to the compressor housing and including a sleeve defining a cylindrical bore; A foil bearing assembly rotatably supporting the shaft and disposed within the cylindrical bore, the foil bearing assembly comprising: an inner foil assembly including a cylindrical inner surface; and a bump foil assembly disposed radially outward from the inner foil assembly, the bump foil assembly including a plurality of bump foils disposed circumferentially around the inner foil assembly, each of the bump foils spaced circumferentially from an adjacent bump foil to define a gap therebetween; the cylindrical inner surface of the inner foil assembly defines a plurality of perforations extending radially through the inner foil assembly, each of the plurality of perforations being radially aligned with one of the gaps between adjacent bump foils; a foil bearing assembly; Compressor.

23. each of the plurality of bump foils extends from a first edge to a second edge and includes a plurality of bumps, each of the bumps having a height, the height of each of the plurality of bumps increasing between the first edge and the second edge; 23. The compressor of claim 22.

24. the shaft is configured to rotate in a first direction about an axis of rotation of the shaft, and the height of each of the plurality of bumps increases between the first edge and the second edge of each of the bump foils in a second direction opposite the first direction; 24. The compressor of claim 23.

25. rotation of the shaft deflects the cylindrical inner surface of the inner foil assembly such that at least one of the plurality of perforations is oriented obliquely with respect to the first direction.

25. The compressor of claim 24.

26. the plurality of perforations includes at least one subset of perforations, each of the perforations in the at least one subset of perforations being axially aligned with other perforations in the at least one subset of perforations, and each of the at least one subset of perforations being radially aligned with one of the gaps defined between adjacent bump foils; 23. The compressor of claim 22.

27. the foil bearing assembly includes an outer foil assembly disposed radially outward from the bump foil assembly such that the bump foil assembly is disposed between the outer foil assembly and the inner foil assembly.

23. The compressor of claim 22.

28. each of the bump foils is coupled to the outer foil assembly at a land; 28. The compressor of claim 27.

29. each of the bump foils is secured to the outer foil assembly at the land; 29. The compressor of claim 28.

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