Foil bearing, drive shaft, and compressor including foil bearing and drive shaft

Abstract

The bearing system (220) includes a foil bearing assembly (226) positioned within a cylindrical bore of a sleeve (224). The foil bearing includes a top foil layer and an outer layer. The bearing system includes a drive shaft (250) including a recess (280) axially aligned with the top foil layer. The recess defines a cavity having a volume and includes a leading end at a first circumferential position and a trailing end at a second circumferential position.

Description

[Technical Field]

[0001] (Reference to Related Application) This application claims priority to U.S. Patent Application No. 18 / 056,218, filed November 16, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0002] (Technical field) The field relates generally to bearings and compressors, and more particularly to foil bearing and driveshaft assemblies used in compressors. [Background technology]

[0003] Centrifugal compressors used in refrigeration and cooling systems may include foil bearings that support a drive shaft used to transfer power from a motor to an impeller, which imparts kinetic energy to the incoming refrigerant. Generally, foil bearings are well suited to the high-speed operating environments typical of centrifugal compressors, are compatible with all refrigerant compositions, and may be used with a wider variety of drive shaft materials, thereby allowing the use of lighter materials to reduce the amount of energy required to operate the compressor.

[0004] Traditionally, foil bearings include compliant foil elements that surround a drive shaft. The foil bearing supports the drive shaft against the pressure profile of a lubricating fluid, e.g., air and / or refrigerant, that builds up between the drive shaft and the foil elements as the drive shaft rotates. When the drive shaft reaches a sufficient speed, referred to as the lift-off speed, the lubricating fluid pressure profile can cause complete radial separation between the drive shaft and the foil elements. However, when the drive shaft rotates at a speed below the lift-off speed, typically during start-up and shutdown of a refrigeration cycle, the pressure profile is not fully developed, resulting in frictional engagement between the drive shaft and the foil elements, potentially leading to wear and / or failure. Therefore, there is a need to improve the performance of drive shaft rotational speed foil bearings, especially at lower drive shaft rotational speeds.

[0005] 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

[0006] In one embodiment, a bearing system includes a sleeve having a radially inner surface defining a cylindrical bore, and a foil bearing assembly positioned within the cylindrical bore. The foil bearing includes a top foil layer and an outer layer positioned between the top foil layer and the radially inner surface. The bearing system includes a drive shaft including a recess axially aligned with the top foil layer. The recess defines a cavity having a volume and includes a forward end at a first circumferential position and an aft end at a second circumferential position.

[0007] In another aspect, a compressor includes a compressor housing, a bearing housing attached to the compressor housing, and a bearing system. The bearing system includes a sleeve having a radially inner surface defining a cylindrical bore, and a foil bearing assembly positioned within the cylindrical bore. The foil bearing includes a top foil layer and an outer layer positioned between the top foil layer and the radially inner surface. The bearing system includes a drive shaft including a recess axially aligned with the top foil layer. The recess defines a cavity having a volume and includes a forward end at a first circumferential position and an aft end at a second circumferential position.

[0008] In yet another aspect, a method of assembling a compressor including a compressor housing includes attaching a bearing housing to the compressor housing. The bearing housing includes a sleeve having a radially inner surface defining a cylindrical bore. The method includes inserting an outer layer into the cylindrical bore and inserting a top foil into the outer layer such that the outer layer is positioned between the cylindrical bore and the top foil. The method also includes inserting a drive shaft into the top foil such that the drive shaft is rotatably supported within the compressor housing, the drive shaft including a recess axially aligned with the top foil layer. The recess defines a cavity having a volume and includes a forward end at a first circumferential position and an aft end at a second circumferential position.

[0009] Various refinements exist in the features noted in connection with the above-described aspects. Additional features may 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 alone or in any combination.

[0010] The following figures illustrate various aspects of the present disclosure. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view of the assembled compressor.

[0012] [Figure 2] 2 is a cross-sectional view of the compressor of FIG. 1 taken along line 2-2, with the external conduit removed.

[0013] [Figure 3] FIG. 3 is a cross-sectional view of the compressor of FIG. 2 with the outer compressor housing removed.

[0014] [Figure 4] FIG. 1 is a side view of an impeller mounted on the end of a drive shaft, the drive shaft being supported by a bearing housing.

[0015] [Figure 5] FIG. 2 is a perspective view of a drive shaft and first and second foil bearing assemblies for use with the compressor shown in FIG. 1;

[0016] [Figure 6] FIG. 10 is an exploded view of a portion of a drive shaft showing the placement of the first foil bearing assembly relative to the drive shaft.

[0017] [Figure 7] 7 is a cross-sectional view of the drive shaft and first and second foil bearings of FIG. 5 taken along line 7-7.

[0018] [Figure 8] FIG. 8 is a detailed view of region 8 shown in FIG. 7.

[0019] [Figure 9] 9 is a cross-sectional view of the drive shaft and first foil bearing assembly of FIG. 5 taken along line 9-9.

[0020] [Figure 10] FIG. 10 is a cross-sectional view of the drive shaft of FIG. 6 taken along line 10-10.

[0021] [Figure 11] FIG. 11 is a detailed view of the region 11 shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0022] Corresponding reference characters indicate corresponding parts throughout the drawings.

[0023] 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 each stage of refrigerant compression is achieved. Compressor 100 includes a first refrigerant inlet 110 for introducing refrigerant vapor into a first compression stage (not labeled in FIG. 1 ), a first refrigerant outlet 114, a refrigerant transfer conduit 112 for transferring compressed refrigerant from the first compression stage to a second compression stage, a second refrigerant inlet 118 for introducing refrigerant vapor into the second compression stage (not labeled in FIG. 1 ), and a second refrigerant outlet 120. Refrigerant transfer conduit 112 is operatively 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 incorporating compressor 100. The refrigerant transport conduit 112 may further include a refrigerant port 122, for example, for economical use.

[0024] Referring to FIG. 2 , the compressor housing 102 encloses a first compression stage 124 and a second compression stage 126 at opposite ends of the compressor 100. The first compression stage 124 includes a first impeller 106 configured to add kinetic energy to the refrigerant entering through the first refrigerant inlet 110. The kinetic energy imparted to the refrigerant by the first impeller 106 is converted to increased refrigerant pressure (i.e., compression) as the refrigerant velocity slows after transitioning to the diffuser 136. Similarly, the second compression stage 126 includes a second impeller 116 configured to add kinetic energy to the refrigerant transferred from the first compression stage 124 entering through the second refrigerant inlet 118. The kinetic energy imparted to the refrigerant by the second impeller 116 is converted to increased refrigerant pressure (i.e., compression) as the refrigerant velocity slows after transitioning to the diffuser 138. The compressed refrigerant exits the second compression stage 126 via a second refrigerant outlet 120 (not shown in FIG. 2).

[0025] 2 and 3, the first stage impeller 106 and the second stage impeller 116 are connected to opposite ends of a drive shaft 104. The drive shaft 104 is operatively connected to a motor 108 positioned 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 are rotated at a selected rotational speed to compress the refrigerant to a preselected pressure that exits a second refrigerant outlet 120. Any suitable motor may be incorporated into the compressor 100, including, but not limited to, an electric motor.

[0026] 3 and 4, the drive shaft 104 is supported by a first foil bearing assembly 220 and a second foil bearing assembly 222 positioned within a sleeve 204 of the first and second bearing housings 200, 202, respectively. Specifically, the sleeve 204 includes a radially inner surface that defines a cylindrical bore 206, and the first and second foil bearing assemblies 220, 222 are positioned within the cylindrical bore 206. Each of the first and second bearing housings 200, 202 includes a mounting structure 210 for connecting the respective first and second bearing housings 200, 202 to the compressor housing 102. Each bearing housing 200, 202 (only bearing housing 200 is shown in FIG. 4) supports a drive shaft 104, which protrudes through the bearing housing 200, 202 opposite the sleeve 204, and the impellers 106, 116 are connected to the protruding end of the drive shaft 104.

[0027] 5 and 6, the first and second foil bearing assemblies 220, 222 include an outer compliant assembly or outer layer 224 positioned adjacent the radially inner surface of the sleeve 204 and an inner compliant foil assembly or inner foil layer 226 (also referred to as the “top foil layer”), visible in FIG. 6, positioned adjacent the drive shaft 104. The first and second foil bearing assemblies 220, 222, including the outer layer 224 and the top foil layer 226, form an essentially cylindrical tube dimensioned to receive the drive shaft 104. Components of the foil bearing assemblies 220, 222, such as the outer layer 224 and / or the top foil layer 226, may be constructed of any suitable material that enables the foil bearing assemblies 220, 222 to function as described herein. Suitable materials include, but are not limited to, metal alloys, for example. In some embodiments, for example, outer layer 224 and top foil layer 226 are each constructed of stainless steel (e.g., 17-4 stainless steel). Top foil layer 226 can be formed from a relatively thin sheet or "foil" of material. For example, foil layer 226 can be constructed of a metal sheet having a thickness in the range of 0.003 inches to 0.007 inches. In some embodiments, first and second foil bearing assemblies 220, 222 include a bump foil layer (not shown) disposed between outer layer 224 and top foil layer 226. The bump foil layer, having a series of corrugations, acts as a biasing mechanism between top foil 226 and outer layer 224. In the illustrated embodiment, foil bearing assemblies 220, 222 do not include a bump foil layer. Outer layer 224 can be constructed of a compliant material and acts as a biasing mechanism between top foil layer 226 and the radially inner surface of sleeve 204. The outer layer 224 may be constructed of polyvinyl chloride (PVC). In other embodiments, the outer layer 224 may be constructed of any suitable material. The outer layer 224 may include a groove 228 sized and shaped to receive the retention feature 230 on the top foil layer 226.The engagement of the retention feature 230 with the groove 228 connects the top foil layer 22 with the outer layer 224 .

[0028] 5-7 , the drive shaft 104 includes a first bearing portion 250 disposed proximate the first impeller 106. The first bearing portion 250 is axially aligned with the first foil bearing assembly 220. The drive shaft 104 includes a second bearing portion 252 disposed proximate the second impeller 116, the second bearing portion 252 being axially aligned with the second foil bearing assembly 222. The drive shaft 104 further includes a drive shaft longitudinal axis A extending between the first and second bearing portions 250, 252. The motor 108 rotates the drive shaft 104 about the longitudinal axis A. The axial direction is oriented along the longitudinal axis A, and the radial direction extends radially outward and / or perpendicular to the axial direction. The drive shaft 104 has a cylindrical shape including an outer surface 254 that extends around the circumference of the drive shaft 104. The drive shaft 104 has a diameter D defined by the outer surface 254. 254 In the illustrated embodiment, the drive shaft 104 has an outer diameter D 254 Generally, the diameter D 254 is the diameter of the first bearing portion 250 and the second bearing portion 252.

[0029] During refrigerant compression, rotation of the drive shaft 104 is induced by a buildup of a pressure profile in the lubricating fluid layer surrounding the outer circumference of the drive shaft 104, causing the top foil layer 226 to move radially outward from the drive shaft 104 due to hydrodynamic pressure. The lubricating fluid may include any medium, such as air or refrigerant, that enables rotation of the drive shaft 104. When the drive shaft 104 rotates at a sufficient rotational speed, the pressure of the lubricating fluid layer is sufficient to create complete radial separation between the top foil layer 226 and the drive shaft 104, e.g., there is no contact between the drive shaft 104 and the top foil layer 226. Similarly, at “lower” rotational speeds, the top foil layer 226 may be radially closer to the drive shaft 104, the lubricating fluid layer may be thin and / or negligible, and in some instances, the top foil layer 226 or a portion of the top foil layer 226 may contact the drive shaft 104.

[0030] 6-8 , the drive shaft 104 includes one or more recesses 260 formed therein, e.g., machined therein. The recesses 260 may be axially aligned with either or both of the foil bearing assemblies 220 and 222. Each of the recesses 260 defines a cavity 266. A volume of fluid, e.g., gas including air and / or refrigerant, may be accommodated within the cavity 266 and radially inward from the top foil layer 226 at any rotational speed of the drive shaft 104. For example, the cavity 266 may contain a volume of fluid during the start-up phase of refrigerant compression when the drive shaft 104 is not yet rotating or when the drive shaft 104 is rotating at a low rotational speed, e.g., less than 5,000 rpm. Additionally, a volume of fluid may be accommodated within the cavity 266 and radially inward from the top foil layer 226 prior to the lift-off speed of the drive shaft 104. Generally, the lift-off speed is the rate at which a layer of fluid develops around the entire circumference of the drive shaft 104. A drive shaft 104 having one or more recesses 260 may develop a full pressure profile of lubricating fluid between the drive shaft 104 and the top foil layer 226 at a lower lift-off speed, for example, below 30,000 rpm, compared to a drive shaft that does not include a recess 260.

[0031] The recess 260 may be tapered such that the volume of the cavity 266 decreases toward one end of the recess 260, e.g., the width and / or depth decreases. The fluid contained within the cavity 266 and / or passing through the drive shaft 104 may be generally stationary and / or may move counter to the direction of rotation of the drive shaft 104, such that the fluid has an opposite relative motion compared to the direction of rotation of the drive shaft 104. Thus, the fluid moves toward the tapered end of the recess 260. The fluid moving into the tapered cavity 266 compresses the fluid, increasing its pressure. The increased fluid pressure pushes the top foil layer 226 radially outward, away from the drive shaft 104, promoting the development of a complete fluid layer around the entire circumference of the drive shaft 104. The volume of fluid contained within the cavity 266 defined by the recess 260 improves the start-up and stop performance of the compressor 100. The recess 260 improves the performance, e.g., stability, of the drive shaft 104 and foil bearing assemblies 220 and 222 at higher rotational speeds of the drive shaft 104, e.g., greater than 30,000 rpm and / or greater than 50,000 rpm. Additionally, the drive shaft 104 including the tapered recess 260 is suitable for use with foil bearing assemblies 220, 222 that do not include a bump foil layer.

[0032] In the illustrated embodiment, the first bearing portion 250 includes a first set 262 of recesses 260 formed therein that are axially aligned with the first foil bearing assembly 220, and the second bearing portion 252 includes a second set 264 of recesses 260 formed therein that are axially aligned with the second foil bearing assembly 222.

[0033] 6 , each of the recesses 260 includes a leading edge 272 disposed at a first radial position and an aft edge 270 disposed at a second radial position circumferentially offset from the leading edge 272. The leading edge 272 and the aft edge 270 of the recess 260 may include walls and / or surfaces that at least partially define the boundary of the cavity 266. The leading edge 272 is disposed forward of the aft edge 270 relative to the direction of rotation of the drive shaft 104. For example, when the drive shaft 104 rotates clockwise, the leading edge 272 is disposed clockwise relative to the aft edge 270. Similarly, when the drive shaft 104 rotates counterclockwise, the leading edge 272 is disposed counterclockwise relative to the aft edge 270. Each of the recesses 260 has a recess arc length L extending between the leading edge 272 and the aft edge 270. arc The recess 260 includes a recess arc angle α 260 between the leading end 272 and the trailing end 270. See FIG.

[0034] The recess 260 includes a first axial end 276 and a second axial end 278 axially offset from the first axial end 276, e.g., a wall and / or surface that at least partially defines a boundary of the cavity 266. The recess 260 includes an axial length Laxial extending between the first axial end 276 and the second axial end 278. In some embodiments, the first axial end 276 and the second axial end 278 are parallel. In some embodiments, the first axial end 276 and the second axial end 278 are not parallel. The top foil layer 226 is spaced apart from the axial length Laxial of the outer layer 224. 224 The axial length L is the same as or substantially the same as 226 The axial length L of the recess 260 axial is the axial length L of the top foil layer 226 226 In the illustrated embodiment, the axial length L of the recess 260 is axial The top foil layer 226 has an axial length L such that the top foil layer 226 extends axially beyond the first and second axial ends 276, 278 with a gap C. 226 See Figure 8. The gap C may be in the range of 1 to 6 mm.

[0035] The recess 260 further includes a base surface 280 recessed from the outer surface 254. The base surface 280 extends axially between the first axial end 276 and the second axial end 278 and circumferentially between the leading end 272 and the trailing end 270. The depth T of the recess 260 260 extends between the outer surface 254 of the drive shaft 104 and the base surface 280 of the recess 260. See FIG. 11. The depth T 260 is the depth T of the recess 260 260 may be variable between the leading end 272 and the trailing end 270 such that the depth T260 of the recess 260 in the radial direction may be defined by the heights of the first and second axial ends 276, 278, which are variable in the radial direction.

[0036] Referring to FIG. 11, the depth T of the recess 260 260 is greatest near the leading edge 272 and is smallest near the trailing edge 270. The depth T 260 is suitably between 0 and 1 mm. In some embodiments, the depth T at the tip 272 260 is suitably between 0.010 and 0.08 mm. In some embodiments, the depth T 260 The depth T of the recess 260 is suitably between 0.013 and 0.076 mm. 260 is the depth T of the recess 260 260 is located at the tip 272, and the peak depth T 260 2. In this embodiment, base surface 280 is arcuate. In some implementations, the radius of curvature of base surface 280 is less than the radius of curvature of drive shaft 104. In some implementations, the center curvature of base surface 280 is not aligned with the center of curvature of drive shaft 104. In some implementations, base surface 280 is arcuate and has a radius of curvature that is substantially the same as the radius of curvature of drive shaft 104.

[0037] The trailing edge 270 has a depth T260 that is substantially zero, approximately zero, or close to zero. In some embodiments, the trailing edge 270 has a depth T260 of 0±0.001 mm. 260 For example, the depth T 260 is negligible in either or both the radial and axial directions. Therefore, the rear end 270 of the recess 260 is located at the diameter D of the drive shaft 104. 254 The depth T decreases toward the rear end 270. 260 The gradual tapering compresses the fluid contained within the cavity 266, compressing the top foil layer 226 radially inward, thereby increasing the pressure of the fluid. The gradual tapering may also create a more laminar flow of fluid surrounding the drive shaft 104. In the illustrated embodiment, the depth T of the recess 260 along the axial direction between the first axial end 276 and the second axial end 278 is 1 / 2 . 260 For example, the depth T of the recess 260 at the tip 272 260 is generally constant along the axial length of the tip 272.

[0038] In an alternative embodiment, the radial depth T 260 may be constant between the leading end 272 and the trailing end 270. In such an embodiment, the base surface 280 is arcuate. In some other alternative embodiments, the base surface 280 may extend substantially planarly along a chord with respect to the circumference of the drive shaft 104. For example, the base surface 280 may be generally perpendicular to the radial direction.

[0039] In another alternative embodiment, both the leading end 272 and the trailing end 270 may be flush with the outer surface 254 of the drive shaft 104. For example, the radial and axial depths T of the recess 260 at the leading end 272 and the trailing end 270 may be 260 may be zero or substantially zero. Therefore, the depth T of the recess at both the leading end 272 and the trailing end 270 260does not have an abrupt change in the outer surface 254 of the drive shaft 104. In some other alternative embodiments, the depth T 260 is the depth T of the recess from the front end 272 and the rear end 270. 260 In an alternative embodiment, the base surface 280 may be concave. In an alternative embodiment, the recess 260 may have a peak, e.g., a maximum depth T, of the recess 260 located at the radial midpoint between the leading end 272 and the trailing end 270. 260 Includes:

[0040] 6, the leading end 272 and the trailing end 270 are straight such that the leading end 272 and the trailing end 270 extend parallel to each other and parallel to the longitudinal axis A. In this embodiment, the lengths of the leading end 272 and the trailing end 270 may be substantially the same, e.g., the axial length of both the leading end 272 and the trailing end 270 is equal to the axial length L of the recess 260. axial is.

[0041] Alternatively, the axial length of the leading end 272 may be different from the axial length of the aft end 270. For example, the axial length of the leading end 272 may be greater than the axial length of the aft end 270 such that the cavity 266 tapers toward the aft end 270. Thus, in some embodiments, the recess 260 tapers from the wider leading end 272 to the narrower aft end 270. Additionally, in some embodiments, the recess 260 tapers in both depth and width from the leading end 272 to the aft end 270. Additionally, in some alternative embodiments, the leading end 272 and / or the aft end 270 may be arcuate relative to the axial direction. In some embodiments, the leading end 272 is arcuate between the first axial end 276 and the second axial end 278. For example, the leading end 272 may be convex, extending forward in the direction of rotation of the drive shaft 104.

[0042] 10 , the first set 262 and the second set 264 of recesses 260 include any suitable number of recesses 260 arranged in any suitable pattern. In the illustrated embodiment, the first set 262 of recesses 260 includes three recesses 260 arranged in a radially symmetric pattern about axis A. In other words, the recesses 260 are spaced apart equidistantly in the radial direction. Specifically, the drive shaft 104 includes one or more spacing portions 286 extending between adjacent recesses 260. For example, the spacing portion 286 extends between the aft end 270 of a first recess and the leading end 272 of a second recess adjacent to the first recess. The spacing distance A 286 is the arc length A 286 The spacing portion 286 is a circumferential distance along the outer surface 254 of the drive shaft 104 having a spacing arc angle α that spans between the first aft end 270 of the recess 260 and the front end 272 of the adjacent recess 260. 286 The radially symmetric pattern of the first set 262 of recesses 260 is such that the spacing distance A 286 is substantially equal between each pair of adjacent recesses 260. In some embodiments, the arc angle α 260 is 50° to 60°. In some embodiments, the arc angle α 260 is 40° to 70°.

[0043] In some embodiments, the second set 264 of recesses 260 has the same number of recesses 260 and the same arrangement of the recesses 260 as the first set 262. In the illustrated embodiment, the second set 264 of recesses 260 includes three recesses 260 and three spacing portions 286. In some embodiments, the recesses 260 in the first set 262 of recesses 260 and the recesses 260 in the second set 264 of recesses 260 are circumferentially aligned. For example, a first recess in the first set 262 of recesses 260 is circumferentially aligned with a first recess in the second set 264 of recesses 260 but is axially offset. Alternatively, the first set 262 of recesses 260 and the second set 264 of recesses 260 may be circumferentially offset. In some embodiments, the first set 262 of recesses 260 includes a different number of recesses 260, more or less than the number of recesses 260 in the second set 264 of recesses 260.

[0044] The number of recesses 260 in the first set 262 and the second set 264, as well as the radial arrangement of the recesses 260, may depend on the characteristics of the drive shaft 104, and / or the rotational speed, drive shaft diameter D 254 , and compressor operating parameters such as compressor load. arc may be selected based on the number of recesses 260 and the circumferential position of the recesses 260. For example, in some embodiments, the first set 262 and the second set 264 of recesses 260 may include four, five, and / or six of the recesses 260. Additionally and / or alternatively, the shape and dimensions of the recesses 260 may be selected based at least in part on the operating conditions of the compressor. In some embodiments, the arc length L arc and axial length L axial is the same for all recesses. In some embodiments, the recesses 260 of the first set 262 and the recesses 260 of the second set all have the same arc length L arc and axial length L axial It has.

[0045] 11 , the trailing end 270 is planar and extends along a radial direction. For example, the trailing end 270 is perpendicular to the longitudinal axis A. In some alternative embodiments, at least one of the leading end 272 and the trailing end 270 may be arcuate and / or oblique to the radial direction, for example.

[0046] The drive shaft 104 having the first set 262 and second set 264 recesses 260 may be used in combination with other bearing systems, standard / conventional foil bearings, bearings, and / or magnetic bearings. Additionally, the drive shaft 104 may be incorporated into other types of compressors, such as scroll compressors, screw compressors, etc. The drive shaft 104 may also be used with other types of machinery.

[0047] The foil bearing assemblies 220, 222 and drive shaft 104 of the present disclosure may be used as part of a method of assembling a compressor, e.g., compressor 100. The assembly method includes attaching a bearing housing, e.g., bearing housings 200, 202, to compressor housing 102 using bearing housing mounting structure 210, as described above. The assembly method also includes inserting a foil bearing assembly, e.g., foil bearing assembly 220, 222, into cylindrical bore 206 and connecting the foil bearing assembly to the bearing housing by cooperatively engaging a bearing retaining feature of the foil bearing assembly with a bearing assembly locking feature to maintain the foil bearing assembly in a fixed rotational position within the bearing housing.

[0048] 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 configuration. The method further includes inserting at least one foil retention clip into a circumferential groove (not shown) formed on the inner surface of the cylindrical bore 206 to retain the foil bearing assembly in a fixed axial position relative to the cylindrical bore 206. The method further includes inserting the drive shaft 104 into the foil bearing assembly such that the plurality of recesses 260 are axially aligned with the foil bearing assembly and / or are axially centered on the top foil layer 226.

[0049] In some embodiments, the assembly method includes assembling the top foil layer 226 and the outer layer 224 by inserting the top foil layer 226 into the opening in the outer layer 224 and axially aligning the top foil layer 226 with the outer layer 224. In some embodiments, the method includes connecting the retention feature 230 of the top foil layer 226 with the groove 228 formed in the outer layer 224.

[0050] The method may further include forming recess 260 in drive shaft 104. Forming recess 260 may include machining, for example, using a computer numerically controlled (CNC) machine and / or a machining tool, to form recess 260 in drive shaft 104. In other embodiments, forming recess 260 in drive shaft 104 includes using an etching process.

[0051] Embodiments of the described systems and methods achieve superior results compared to conventional systems and methods. In particular, the exemplary foil bearing assembly and drive shaft include recesses that facilitate improved aerodynamic performance and improved development of lubricating fluid surrounding the drive shaft. The recesses store fluid and promote the accumulation of a complete fluid layer surrounding the drive shaft. Specifically, a volume of fluid is contained within each recess, radially inward from the top foil layer, at any rotational speed of the drive shaft.

[0052] Exemplary embodiments of systems and methods including drive shafts, such as refrigerant compressors incorporating the disclosed drive shafts, and methods for assembling compressors including the disclosed drive shafts, are described above in detail. The drive shaft systems and methods are not limited to the specific embodiments described herein; rather, the components of the systems and methods are independent of and may be used separately from the other components described herein. For example, the drive shafts described herein may be used in compressors other than refrigerant compressors, such as turbocharger compressors. The drive shafts described herein may be used in other types of bearing assemblies to facilitate the development of a complete radial pressure profile between the drive shaft and the bearing assembly.

[0053] When introducing elements of the present disclosure or embodiments of the present disclosure, the definite articles "a," "an," "the," and "said" are intended to mean that one or more of the elements are present. The terms "comprising," "including," "containing," and "having" are intended to be inclusive and mean that additional elements may be present other than the listed elements. The use of specific orientational terms (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require any particular orientation of the items being described.

[0054] Because various changes can be made in the structures and methods described above without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

Claims

1. a sleeve including a radially inner surface defining a cylindrical bore; a foil bearing assembly positioned within the cylindrical bore of the sleeve, the foil bearing assembly including a top foil layer and an outer layer positioned between the top foil layer and the radially inner surface; a drive shaft including a recess axially aligned with the top foil layer, the recess defining a cavity having a volume, the recess including a forward end at a first circumferential location and an aft end at a second circumferential location; Bearing system.

2. 2. The bearing system of claim 1, wherein the recess includes a recess depth that is greatest at the forward end, and the volume of the cavity decreases from the forward end to the aft end.

3. 3. The bearing system of claim 1, wherein the forward end includes a first axial length and the aft end includes a second axial length, the first axial length being longer than the second axial length.

4. A bearing system according to any preceding claim, wherein the recess includes a recess depth that decreases from the leading end to the trailing end, the recess depth at the trailing end being zero.

5. The bearing system of claim 1 , wherein the drive shaft includes a plurality of recesses arranged in a radially symmetrical pattern about the axis of rotation of the drive shaft.

6. 5. The bearing system of claim 4, wherein the drive shaft includes three of the recesses arranged in a radially symmetric pattern, each of the recesses including a recess arc angle α between the leading end and the trailing end, the recess arc angle α being between 50° and 60°.

7. 2. The bearing system of claim 1, wherein the drive shaft includes a first portion and a second portion axially offset from the first portion, the drive shaft further including a first set of at least one of the recesses formed in the first portion and a second set of at least one of the recesses formed in the second portion.

8. 8. The bearing system of claim 7, wherein the first set includes a plurality of recesses arranged in a radially symmetrical pattern, and the second set includes the same number of recesses as the first set, the second set being arranged in a radially symmetrical pattern that is the same as the radially symmetrical pattern of the first set.

9. 7. The bearing system according to claim 1, wherein the recess has a base surface extending between the front end and the rear end, the base surface being arcuate and having a radius of curvature that is less than a radius of curvature of an outer surface of the drive shaft.

10. A compressor housing; a bearing housing attached to the compressor housing; a bearing system supported by the bearing housing, the bearing system comprising: a sleeve including a radially inner surface defining a cylindrical bore; a foil bearing assembly positioned within the cylindrical bore of the sleeve, the foil bearing assembly including a top foil layer and an outer layer positioned between the top foil layer and the radially inner surface; a drive shaft including a recess axially aligned with the top foil layer, the recess defining a cavity having a volume, the recess including a forward end at a first circumferential location and an aft end at a second circumferential location; Compressor.

11. The compressor of claim 10 , wherein the recess includes a recess depth that is greatest at the front end, and the volume of the cavity decreases from the front end to the rear end.

12. 12. The compressor of claim 10 or 11, wherein the front end includes a first axial length and the rear end includes a second axial length, the first axial length being longer than the second axial length.

13. The compressor of claim 10 , wherein the recess includes a recess depth that decreases from the front end to the rear end, the recess depth at the rear end being zero.

14. A compressor according to any one of claims 10 to 13, wherein the drive shaft includes a plurality of recesses arranged in a radially symmetrical pattern about the axis of rotation of the drive shaft.

15. 15. The compressor of claim 13 or 14, wherein the drive shaft includes three of the recesses arranged in a radially symmetric pattern, each of the three recesses including a recess arc angle α between the front end and the rear end, the recess arc angle α being between 50° and 60°.

16. 11. The compressor of claim 10, wherein the drive shaft includes a first portion and a second portion axially offset from the first portion, the drive shaft further including a first set of at least one of the recesses formed in the first portion and a second set of at least one of the recesses formed in the second portion.

17. 17. The compressor of claim 16, wherein the first set includes a plurality of recesses arranged in a radially symmetrical pattern, and the second set includes the same number of recesses as the first set, the second set arranged in a radially symmetrical pattern that is the same as the radially symmetrical pattern of the first set.

18. 11. The compressor of claim 10, wherein the recess has a base surface extending between the forward end and the aft end, the base surface being arcuate and having a radius of curvature that is the same as a radius of curvature of an outer surface of the drive shaft.

19. 17. The compressor of claim 16, wherein the first set includes a plurality of recesses arranged in a radially symmetrical pattern, and the second set includes a different number of the recesses than the first set, and the second set is arranged in a radially symmetrical pattern.

20. 1. A method of assembling a compressor including a compressor housing, comprising: mounting a bearing housing to the compressor housing, the bearing housing including a sleeve having a radially inner surface defining a cylindrical bore; inserting an outer layer into the cylindrical bore; inserting the top foil into the outer layer such that the outer layer is positioned between the cylindrical bore and the top foil; inserting the drive shaft into the top foil layer such that the drive shaft is rotatably supported within the compressor housing, the drive shaft including a recess axially aligned with the top foil layer, the recess defining a cavity having a volume, the recess including a forward end at a first circumferential position and an aft end at a second circumferential position; method.

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