Plain bearing structure and turbo-type fluid machinery

Abstract

The present invention provides a sliding bearing structure that can suppress wear on the bearing surface of a rotating body. [Solution] The sliding bearing structure comprises a rotating body and a sliding bearing that supports the rotating body. The sliding bearing has a bearing surface formed of a coating layer containing at least polyamide-imide. The rotating body has a bearing surface facing the bearing surface and formed of a metallic material. The aspect ratio Str of the surface properties of the bearing surface is 0.020 or greater.

Description

Technical Field

[0001] The present invention relates to a sliding bearing structure and a turbo-type fluid machine.

Background Art

[0002] A foil bearing is known as a hydrodynamic gas bearing that supports a rotating body, which is the shaft of a turbo-type fluid machine (for example, Patent Document 1). The foil bearing floats and supports the rotating body by a fluid film such as an air film generated between the bearing surface of the foil bearing and the rotating body. Patent Document 1 discloses forming a coating on the bearing surface in order to improve the wear resistance and durability of the bearing surface of the foil bearing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to make it easier for the fluid film to float the rotating body, the bearing surface of the foil bearing and the bearing surface of the rotating body may be smoothed. In general metal smoothing processes, wear of the bearing surface of the rotating body cannot be sufficiently suppressed.

[0005] An object of the present invention is to provide a sliding bearing structure and a turbo-type fluid machine that can suppress wear of the bearing surface of a rotating body.

Means for Solving the Problems

[0006] The present invention provides the following sliding bearing structure and turbo-type fluid machine.

[0007] The sliding bearing structure comprises a rotating body and a sliding bearing that supports the rotating body, wherein the sliding bearing has a bearing surface formed of a coating layer containing at least polyamide-imide, and the rotating body has a bearing surface facing the bearing surface and formed of a metallic material, and the aspect ratio Str of the surface properties of the bearing surface is 0.020 or greater.

[0008] In the sliding bearing structure described above, the aspect ratio Str of the surface properties of the bearing surface is preferably 0.80 or less.

[0009] In the sliding bearing structure described above, the aspect ratio Str of the surface properties of the bearing surface is preferably 0.05 to 0.75, and the height Rpk of the protruding peaks on the bearing surface is preferably 0.3 to 0.7 μm.

[0010] In the sliding bearing structure described above, it is preferable that the aspect ratio Str of the surface properties of the bearing surface is 0.040 or more and less than 0.1, and the load length ratio Mr1 of the bearing surface is 11% or more.

[0011] In the aforementioned sliding bearing structure, it is preferable that the aspect ratio Str of the surface properties of the bearing surface is 0.1 or more and less than 0.6, and the load length ratio Mr1 of the bearing surface is 7.7% or more.

[0012] In the sliding bearing structure described above, it is preferable that the aspect ratio Str of the surface properties of the bearing surface is 0.6 or more, and the load length ratio Mr1 of the bearing surface is 10% or more.

[0013] In the aforementioned sliding bearing structure, it is preferable that the sliding bearing is a dynamic pressure gas bearing.

[0014] In the sliding bearing structure described above, it is preferable that the coating layer further contains polytetrafluoroethylene.

[0015] In the sliding bearing structure described above, it is preferable that the coating layer further contains one or more inorganic additives selected from the group consisting of molybdenum disulfide, titanium oxide, and calcium fluoride.

[0016] In the sliding bearing structure described above, it is preferable that the rotating body is made of the metallic material described above.

[0017] In the aforementioned sliding bearing structure, the metallic material is preferably one or more selected from the group consisting of titanium, titanium alloys, and stainless steel.

[0018] The turbo-type fluid machine comprises a rotating body, an actuator that rotates integrally with the rotating body to pump fluid, a housing that accommodates the rotating body and the actuator, and a dynamic pressure gas bearing that rotatably supports the rotating body relative to the housing. The dynamic pressure gas bearing has a bearing surface formed of a coating layer containing at least polyamide-imide, and the rotating body has a bearing surface facing the bearing surface and formed of a metallic material, with an aspect ratio Str of the surface properties of the bearing surface being 0.020 or greater.

[0019] In the turbo-type fluid machine described above, the aspect ratio Str of the surface properties of the bearing surface is preferably 0.05 to 0.75, and the height Rpk of the protruding peaks on the bearing surface is preferably 0.3 to 0.7 μm.

[0020] In the turbo-type fluid machine, the following [a] to [c]: [a] The aspect ratio Str of the surface properties of the bearing surface is 0.040 or more and less than 0.1, and the load length ratio Mr1 of the bearing surface is 11% or more. [b] The aspect ratio Str of the surface texture of the bearing surface is 0.1 or more and less than 0.6. The load length ratio Mr1 of the bearing surface is 7.7% or more, and [c] The aspect ratio Str of the surface properties of the bearing surface is 0.6 or greater. The load length ratio Mr1 of the bearing surface is 10% or more. It is preferable to satisfy any one of the following.

[0021] In the turbo-type fluid machine, the hydrodynamic gas bearing is preferably a foil bearing.

[0022] In the turbo-type fluid machine, the metallic material is preferably at least one selected from the group consisting of titanium, titanium alloy, and stainless steel.

[0023] In the turbo-type fluid machine, the hydrodynamic gas bearing preferably includes at least one of a thrust bearing that supports the rotating body in the axial direction of the rotating body and a radial bearing that supports the rotating body in a direction orthogonal to the axial direction.

Advantages of the Invention

[0024] According to the present invention, it is possible to provide a sliding bearing structure and a turbo-type fluid machine that can suppress wear of the bearing surface of the rotating body.

Brief Description of the Drawings

[0025] [Figure 1] It is a cross-sectional view showing a turbo-type compressor. [Figure 2] It is a cross-sectional view showing an enlarged part of the turbo-type compressor shown in FIG. 1. [Figure 3] It is a cross-sectional view showing an enlarged other part of the turbo-type compressor shown in FIG. 1. [Figure 4] It is a cross-sectional view schematically showing an enlarged part of the rotating body and the foil bearing of the turbo-type compressor shown in FIG. 1. [Figure 5] It is a cross-sectional view schematically explaining how the coating layer of the foil bearing of the turbo-type compressor shown in FIG. 1 wears. [Figure 6] It is a perspective view schematically showing a friction and wear test. [Figure 7] It is a backscattered electron image obtained by observing the outer peripheral surface of the ring before the friction and wear test of Test Example 1 with a scanning electron microscope. [Figure 8]This is a backscattered electron image of the outer surface of the ring before the friction and wear test in Test Example 2, observed with a scanning electron microscope. [Figure 9] This is a backscattered electron image of the outer surface of the ring before the friction and wear test in Test Example 8, observed with a scanning electron microscope. [Figure 10] This is a backscattered electron image of the outer surface of the ring before the friction and wear test in Test Example 13, observed with a scanning electron microscope. [Figure 11] This is a backscattered electron image of the outer surface of the ring in Test Example 14, observed with a scanning electron microscope before the friction and wear test. [Figure 12] These are SEM images of the coating layer of the block after the friction and wear test in Test Example 1, observed with a scanning electron microscope; (a) is a backscattered electron image and (b) is a secondary electron image. [Figure 13] These are SEM images of the coating layer of the block after the friction and wear test in Test Example 2, observed with a scanning electron microscope; (a) is a backscattered electron image and (b) is a secondary electron image. [Figure 14] These are SEM images of the coating layer of the block after the friction and wear test in Test Example 8, observed with a scanning electron microscope; (a) is a backscattered electron image and (b) is a secondary electron image. [Figure 15] These are SEM images of the coating layer of the block after the friction and wear test in Test Example 13, observed with a scanning electron microscope; (a) is a backscattered electron image and (b) is a secondary electron image. [Figure 16] These are SEM images of the coating layer of the block after the friction and wear test in Test Example 14, observed with a scanning electron microscope; (a) is a backscattered electron image and (b) is a secondary electron image. [Modes for carrying out the invention]

[0026] Embodiments of the present invention will be described below with reference to the drawings. In this specification, numerical ranges such as "x~y" include upper and lower limits unless otherwise specified, and represent numerical ranges of "x or greater and y or less".

[0027] In this embodiment, a turbo compressor is given as an example of a turbo-type fluid machine, and the sliding bearing structure is described in an example where it has a rotating body and a foil bearing which is a dynamic pressure gas bearing as the sliding bearing.

[0028] <Basic configuration of a turbo compressor> Figure 1 is a cross-sectional view showing a turbo compressor. Figures 2 and 3 are enlarged cross-sectional views showing a portion of the turbo compressor shown in Figure 1. Figure 4 is a schematic enlarged cross-sectional view showing a portion of the rotating body and foil bearing of the turbo compressor shown in Figure 1. Figure 5 is a schematic cross-sectional view illustrating the wear of the coating layer of the foil bearing of the turbo compressor shown in Figure 1.

[0029] The turbo compressor 10 (turbo fluid machine) is installed in a fuel cell vehicle equipped with a fuel cell system 1. The fuel cell system 1 supplies oxygen and hydrogen to the onboard fuel cell to generate electricity. The turbo compressor 10 compresses the oxygen-containing air supplied to the onboard fuel cell.

[0030] (housing) As shown in Figure 1, the turbo compressor 10 is equipped with a housing 11. The housing 11 is made of metal, for example, an aluminum alloy. The housing 11 is cylindrical. The housing 11 includes a motor housing 12, a compressor housing 13, a turbine housing 14, a first plate 15, a second plate 16, and a third plate 17.

[0031] The motor housing 12 is cylindrical. The motor housing 12 has a plate-shaped end wall 12a and a peripheral wall 12b. The peripheral wall 12b extends cylindrically from the outer circumference of the end wall 12a. The first plate 15 is connected to the open end of the peripheral wall 12b of the motor housing 12, closing the opening of the peripheral wall 12b.

[0032] The motor chamber S1 is partitioned by the inner surface 121a of the end wall 12a of the motor housing 12, the inner circumferential surface 121b of the peripheral wall 12b, and the end surface 15a of the first plate 15 on the motor housing 12 side. An electric motor 18 is housed inside the motor chamber S1.

[0033] The first plate 15 has a first bearing retaining portion 20. The first bearing retaining portion 20 protrudes from the center of the end face 15a of the first plate 15 toward the electric motor 18. The first bearing retaining portion 20 is cylindrical.

[0034] A recess 15c with a bottom surface 15d is formed on the end face 15b of the first plate 15 opposite to the motor housing 12. The recess 15c is circular. The inside of the first bearing retainer 20 penetrates the first plate 15 and opens to the bottom surface 15d of the recess 15c. The axis of the recess 15c and the axis of the first bearing retainer 20 coincide.

[0035] The motor housing 12 has a second bearing retaining portion 22. The second bearing retaining portion 22 protrudes toward the electric motor 18 from the center of the inner surface 121a of the end wall 12a of the motor housing 12. The second bearing retaining portion 22 is cylindrical. The inside of the cylinder of the second bearing retaining portion 22 penetrates the end wall 12a of the motor housing 12 and opens to the outer surface 122a of the end wall 12a. The axis of the first bearing retaining portion 20 and the axis of the second bearing retaining portion 22 coincide.

[0036] As shown in Figure 2, the second plate 16 is connected to the end face 15b of the first plate 15. A shaft insertion hole 16a is formed in the center of the second plate 16. The shaft insertion hole 16a communicates with the recess 15c. The axis of the shaft insertion hole 16a coincides with the axis of the recess 15c and the axis of the first bearing retaining portion 20. The thrust bearing housing chamber S2 is partitioned by the end face 16b of the second plate 16 on the first plate 15 side and the recess 15c of the first plate 15.

[0037] The compressor housing 13 is cylindrical and has a circular air intake port 13a into which air is drawn. The compressor housing 13 is connected to the end face 16c of the second plate 16 opposite to the first plate 15. The axis of the air intake port 13a of the compressor housing 13 coincides with the axis of the shaft insertion hole 16a of the second plate 16 and the axis of the first bearing retaining portion 20. The air intake port 13a opens to the end face of the compressor housing 13 opposite to the second plate 16.

[0038] Between the compressor housing 13 and the end face 16c of the second plate 16, a first impeller chamber 13b, a discharge chamber 13c, and a diffuser passage 13d are formed. The first impeller chamber 13b communicates with the intake port 13a. The discharge chamber 13c extends around the axis of the intake port 13a, surrounding the first impeller chamber 13b. The diffuser passage 13d connects the first impeller chamber 13b and the discharge chamber 13c. The first impeller chamber 13b communicates with the shaft insertion hole 16a of the second plate 16.

[0039] As shown in Figure 3, the third plate 17 is connected to the outer surface 122a of the end wall 12a of the motor housing 12. A shaft insertion hole 17a is formed in the center of the third plate 17. The shaft insertion hole 17a communicates with the inside of the cylinder of the second bearing holder 22. The axis of the shaft insertion hole 17a coincides with the axis of the second bearing holder 22.

[0040] The turbine housing 14 is cylindrical and has a circular discharge port 14a for discharging air. The turbine housing 14 is connected to the end face 17b of the third plate 17 opposite to the motor housing 12. The axis of the discharge port 14a of the turbine housing 14 coincides with the axis of the shaft insertion hole 17a of the third plate 17 and the axis of the second bearing retaining portion 22. The discharge port 14a opens to the end face of the turbine housing 14 opposite to the third plate 17.

[0041] Between the turbine housing 14 and the end face 17b of the third plate 17, a second impeller chamber 14b, an intake chamber 14c, and a communication passage 14d are formed. The second impeller chamber 14b communicates with the discharge port 14a. The intake chamber 14c extends around the axis of the discharge port 14a, surrounding the second impeller chamber 14b. The communication passage 14d connects the second impeller chamber 14b and the intake chamber 14c. The second impeller chamber 14b communicates with the shaft insertion hole 17a of the third plate 17.

[0042] (Electric motor) The electric motor 18 comprises a cylindrical rotor 31 and a cylindrical stator 32. The rotor 31 is fixed to the rotating shaft 24a (described later). The stator 32 is fixed to the housing 11. The rotor 31 is positioned radially inward of the stator 32 and rotates integrally with the rotating body 24 (described later). The rotor 31 has a cylindrical rotor core 31a fixed to the rotating shaft 24a and a plurality of permanent magnets (not shown) provided on the rotor core 31a. The stator 32 surrounds the rotor 31. The stator 32 has a cylindrical stator core 33 fixed to the inner circumferential surface 121b of the peripheral wall 12b of the motor housing 12 and a coil 34 wound around the stator core 33. When current flows from a battery (not shown) to the coil 34, the rotating body 24 rotates integrally with the rotor 31. The electric motor 18 rotates at a speed of 100,000 rpm or more, for example, in the range of 100,000 to 120,000 rpm.

[0043] (Rotating body) As shown in Figure 1, a rotating body 24 is housed inside the housing 11. The rotating body 24 has a rotating shaft 24a as the shaft portion, a first support portion 24b, a second support portion 24c, and a third support portion 24d as a thrust collar. The rotating shaft 24a has a first end portion 24e, which is the end on the compressor housing 13 side, and a second end portion 24f, which is the end on the turbine housing 14 side.

[0044] The first support portion 24b is provided on the outer circumferential surface 240a of the rotating shaft 24a, near the first end portion 24e, and is located inside the cylinder of the first bearing retaining portion 20. The first support portion 24b is integrally formed with the rotating shaft 24a and protrudes annularly from the outer circumferential surface 240a of the rotating shaft 24a.

[0045] The second support portion 24c is provided on the outer circumferential surface 240a of the rotating shaft 24a, near the second end portion 24f, and is positioned inside the cylinder of the second bearing retaining portion 22. The second support portion 24c is cylindrical in shape and is fixed to the outer circumferential surface 240a of the rotating shaft 24a, protruding annularly from the outer circumferential surface 240a of the rotating shaft 24a. The second support portion 24c is rotatable integrally with the rotating shaft 24a.

[0046] The third support portion 24d is located in the thrust bearing housing chamber S2. The third support portion 24d is disc-shaped and is fixed to the outer circumferential surface 240a of the rotating shaft 24a, protruding annularly from the outer circumferential surface 240a of the rotating shaft 24a. The third support portion 24d is rotatable integrally with the rotating shaft 24a. The third support portion 24d is located at a position separated from the electric motor 18 in the axial direction of the rotating body 24 (hereinafter also simply referred to as the "axial direction").

[0047] A first impeller 25 (actuator) is connected to the first end 24e of the rotating shaft 24a. The first impeller 25 is positioned closer to the first end 24e than to the third support portion 24d on the rotating shaft 24a. The first impeller 25 is housed in the first impeller chamber 13b. A second impeller 26 is connected to the second end 24f of the rotating shaft 24a. The second impeller 26 is positioned closer to the second end 24f than to the second support portion 24c on the rotating shaft 24a. The second impeller 26 is housed in the second impeller chamber 14b. The housing 11 houses the first impeller 25, the second impeller 26, and the rotating body 24.

[0048] A first sealing member 27 is provided between the shaft insertion hole 16a of the second plate 16 and the rotating body 24. The first sealing member 27 suppresses air leakage from the first impeller chamber 13b toward the motor chamber S1. A second sealing member 28 is provided between the shaft insertion hole 17a of the third plate 17 and the rotating body 24. The second sealing member 28 suppresses air leakage from the second impeller chamber 14b toward the motor chamber S1. The first sealing member 27 and the second sealing member 28 are, for example, sealing rings.

[0049] The rotating body 24 is supported by a foil bearing 60 (described later) so as to be rotatable relative to the housing 11. The rotating body 24 has a bearing surface 24g facing the bearing surface 60a (described later) and formed of a metallic material. The rotating body 24 may be formed of a material other than the bearing surface 24g, as long as at least the bearing surface 24g is formed of a metallic material, and the parts other than the bearing surface 24g may be formed of a material other than a metallic material, and may be formed of a metallic material different from the metallic material forming the bearing surface 24g. Examples of materials other than metallic materials include ceramics and resins. Alternatively, the entire rotating body 24 may be formed of a metallic material, and the metallic material of the surface that becomes the bearing surface 24g (each surface of the first to third support parts 24b to 24d) may be used as the bearing surface 24g. Examples of metallic materials forming the rotating body 24 or the bearing surface 24g include pure metals such as titanium; metallic alloys such as titanium alloys; nickel alloys; stainless steel and alloy steels such as chromium-molybdenum steel. Examples of stainless steel include SUS. Since the rotating body 24 is preferably made of a material that is less affected by the magnetic field of the electric motor 18, the metallic material is preferably a material other than a ferromagnetic material, such as an antiferromagnetic, paramagnetic, or diamagnetic material. The metallic material is preferably a metal or alloy containing titanium, and an austenitic stainless steel such as austenitic SUS, and more preferably titanium or a titanium alloy.

[0050] The rotating body 24 has bearing surfaces 24g at the third support portion 24d, the first support portion 24b, and the second support portion 24c, and all of these bearing surfaces 24g are formed of a metallic material. The two bearing surfaces 24g at the third support portion 24d are surfaces that are rotatably supported by a pair of thrust foil bearings 30, 30 (described later). The bearing surfaces 24g at the first support portion 24b and the second support portion 24c are surfaces that are rotatably supported by a pair of radial foil bearings 40 (described later).

[0051] The aspect ratio Str of the surface texture of the bearing surface 24g (hereinafter also referred to as "aspect ratio Str") is 0.020 or more, may be 0.025 or more, may be 0.030 or more, preferably 0.040 or more, and may be 0.050 or more. The aspect ratio Str of the bearing surface 24g may be 0.020 to 0.80, may be 0.030 to 0.75, preferably 0.040 to 0.72, may be 0.045 to 0.60, may be 0.050 to 0.50, and may be 0.060 to 0.40. The aspect ratio Str takes a value between 0 and 1, with a value closer to 0 indicating an anisotropic surface with a regular pattern, and a value closer to 1 indicating an isotropic surface with a random pattern.

[0052] The aspect ratio Str of the bearing surface 24g can be measured in accordance with ISO 25178-2 using a shape analysis laser microscope or the like. In this specification, the aspect ratio Str refers to the value measured by the following procedure. A sample for which the aspect ratio Str is to be measured is prepared, and 3D shape data is measured in a field of view of 290 μm horizontally × 230 μm vertically observed at a magnification of 1000x. A waviness removal process with a cutoff wavelength of 0.20 mm is performed to obtain the aspect ratio Str in that field of view. Using the same sample, 3D shape data is measured in 2 to 5 fields of view using the above procedure, changing the observation location, and the aspect ratio Str in each field of view is obtained. The average value of the aspect ratio Str of each obtained field of view is taken as the aspect ratio Str of the surface properties of the bearing surface 24g of the sample.

[0053] The height Rpk of the protruding peaks on the bearing surface 24g is preferably 0.20 μm or more, but may also be 0.28 μm or more, 0.30 μm or more, 0.32 μm or more, 0.35 μm or more, or 0.40 μm or more. The height Rpk of the protruding peaks on the bearing surface 24g is preferably 0.20 to 1.0 μm, but may also be 0.28 to 0.90 μm, more preferably 0.30 to 0.80 μm, but may also be 0.32 to 0.75 μm, 0.35 to 0.70 μm, or 0.40 to 0.65 μm.

[0054] The above range for the height Rpk of the protruding peaks of the bearing surface 24g and the above range for the aspect ratio Str of the bearing surface 24g can be arbitrarily combined. Preferably, the aspect ratio Str of the surface texture of the bearing surface 24g is 0.05 to 0.75, and the height Rpk of the protruding peaks of the bearing surface 24g is 0.3 to 0.7 μm.

[0055] The aspect ratio Str of the bearing surface 24g and the load length ratio Mr1 of the bearing surface 24g preferably satisfy any of the following [a] to [c]. [a] The aspect ratio Str of the bearing surface 24g is 0.040 or more and less than 0.1. The load length ratio Mr1 for the bearing surface of 24g is 11% or more. [b] The aspect ratio Str of the bearing surface 24g is 0.1 or greater and less than 0.6. The load length ratio Mr1 for the bearing surface of 24g is 7.7% or more. [c] The aspect ratio Str of the surface texture of the bearing surface 24g is 0.6 or greater. The load length ratio Mr1 of the bearing surface is 10% or more.

[0056] If the aspect ratio Str of the bearing surface 24g is 0.040 or more and less than 0.1 (as in [a] above), the load length ratio Mr1 of the bearing surface 24g may be 11.5% or more, 12.0% or more, 12.3% or more, 12.5% ​​or more, for example, 11-18%, 11.5-16%, 12.0-14%, 12.3-14%, or 12.5-14%.

[0057] If the aspect ratio Str of the bearing surface 24g is 0.1 or more and less than 0.6 (as in [b] above), the load length ratio Mr1 of the bearing surface 24g may be 8.0% or more, 8.3% or more, 8.5% or more, 9.0% or more, for example, 7.7 to 18%, 8.0 to 16%, 8.3 to 14%, or 8.5 to 14%.

[0058] If the aspect ratio Str of the surface properties of the bearing surface 24g is 0.6 or more (as in [c] above), the load length ratio Mr1 of the bearing surface 24g may be 10.5% or more, 11.0% or more, 11.3% or more, for example, 10-18%, 10.5-16%, 11.0-14%, or 11.3-14%.

[0059] If the aspect ratio Str of the bearing surface 24g is 0.020 or more and less than 0.040, the load length ratio Mr1 of the bearing surface 24g may be 12% or more, 12.5% ​​or more, 13% or more, for example, 12-18%, 12.5-16%, or 13-14%.

[0060] The load length ratio Mr1 and the protruding peak height Rpk are specified in JIS B 0671-2 (2002) and are defined as follows: A load curve (vertical axis: height, horizontal axis: load length ratio) is obtained from the shape curve measured on the bearing surface 24g. The equivalent line is defined as the straight line with the gentlest slope passing through two points on the load curve where the difference in load length ratio is 40%. The core is defined as the area between the two height positions where the equivalent line intersects the vertical axis at the positions where the horizontal axis is 0% and 100%. In the shape curve, Rpk is the average height of the protruding peaks above the core, and Mr1 is the load length ratio at the intersection of the separation line between these peaks and the core and the shape curve. Therefore, the load length ratio Mr1 is an index representing the proportion occupied by the protruding peaks on the bearing surface 24g, and the protruding peak height Rpk represents the average height of the protruding peaks on the bearing surface 24g.

[0061] In this specification, the load length ratio Mr1 and the protruding peak height Rpk refer to the values ​​measured by the following procedure: Using the 3D shape data obtained for the sample to which the aspect ratio Str described above is measured, 60 shape curves are obtained in each field of view in a direction perpendicular to the direction in which friction occurs. The load length ratio Mr1 and the protruding peak height Rpk are determined for each shape curve. The load length ratio Mr1 and the protruding peak height Rpk obtained from each shape curve in each field of view are averaged, and these average values ​​are taken as the load length ratio Mr1 and the protruding peak height Rpk for the bearing surface 24g of the sample. No high-pass or low-pass correction processing is applied when obtaining the shape curves.

[0062] The bearing surface 24g is preferably a ground surface. The aspect ratio Str, load length ratio Mr1, and protruding peak height Rpk of the bearing surface 24g can be adjusted by the grinding method and grinding conditions when forming the bearing surface 24g. Grinding methods include traverse grinding, in which a dressed grinding wheel is moved and the object to be ground is moved back and forth while grinding; grinding wheel grinding, in which a grinding wheel is pressed against the surface to be polished; shot blasting, in which abrasive material is sprayed or impacted onto the surface to be polished; tape polishing, in which a tape (or film) coated with abrasive grains is pressed against the surface to be polished; and combinations thereof. Preferably, the grinding method is traverse grinding, grinding wheel grinding, shot blasting, or a combination thereof.

[0063] (Foil bearing) The turbo compressor 10 has a plurality of foil bearings 60 (sliding bearings, hydrodynamic gas bearings) that rotatably support the rotating body 24 relative to the housing 11. Each foil bearing 60 is not a so-called oil-lubricated bearing, but a hydrodynamic air bearing (hydrodynamic gas bearing) in which air is introduced as a fluid (gas) lubricant into the gap between the bearing surface 60a (described later) and the bearing surface 24g, and the load is supported by the dynamic pressure generated in the gap. The rotating body 24 and the foil bearings 60 constitute a sliding bearing structure (hydrodynamic gas bearing structure). The plurality of foil bearings 60 include a pair of thrust foil bearings 30, 30 (thrust bearings) and a pair of radial foil bearings 40, 40 (radial bearings). The pair of thrust foil bearings 30, 30 are bearings that support the rotating body 24 in the axial direction, and support the third support portion 24d of the rotating body 24 rotatably in the axial direction of the rotating body 24 relative to the housing 11. The pair of radial foil bearings 40, 40 are bearings that support the rotating body 24 in a direction perpendicular to the axial direction, and support the first support portion 24b and the second support portion 24c of the rotating body 24 so that they can rotate relative to the housing 11 in a direction perpendicular to the axial direction of the rotating body 24.

[0064] A pair of thrust foil bearings 30, 30 are arranged in a thrust bearing housing chamber S2. The pair of thrust foil bearings 30, 30 are positioned to sandwich a third support portion 24d, which acts as a thrust collar. The pair of thrust foil bearings 30, 30 face the third support portion 24d in the axial direction of the rotating body 24. One thrust foil bearing 30 is positioned on the first end 24e side of the rotating shaft 24a relative to the third support portion 24d. The other thrust foil bearing 30 is positioned on the second end 24f side of the rotating shaft 24a relative to the third support portion 24d.

[0065] As shown in Figure 2, the end face of the rotating shaft 24a on the first end 24e side of the third support portion 24d is the bearing surface 24g that is axially supported by one of the thrust foil bearings 30. The thrust foil bearing 30 has a bearing surface 60a that faces this bearing surface 24g. Similarly, the end face of the rotating shaft 24a on the second end 24f side of the third support portion 24d is the bearing surface 24g that is axially supported by the other thrust foil bearing 30. The other thrust foil bearing 30 has a bearing surface 60a that faces this bearing surface 24g.

[0066] As shown in Figures 2 and 3, one radial foil bearing 40 is located within a first bearing holder 20, and the other radial foil bearing 40 is located within a second bearing holder 22. Within the first bearing holder 20, the first support portion 24b of the rotating body 24 is rotatably supported by one of the radial foil bearings 40. The outer circumferential surface of the first support portion 24b is the bearing surface 24g supported by one of the radial foil bearings 40 in a direction perpendicular to the axial direction. One of the radial foil bearings 40 has a bearing surface 60a facing this bearing surface 24g. Similarly, within the second bearing holder 22, the second support portion 24c of the rotating body 24 is rotatably supported by the other radial foil bearing 40. The outer circumferential surface of the second support portion 24c is the bearing surface 24g supported by the other radial foil bearing 40 in a direction perpendicular to the axial direction. The other radial foil bearing 40 has a bearing surface 60a that faces the bearing surface 24g.

[0067] As shown in Figure 4, the bearing surfaces 60a of each foil bearing 60, i.e., the bearing surfaces 60a of each thrust foil bearing 30, 30 and the bearing surfaces 60a of each radial foil bearing 40, 40, are each formed with a coating layer 61. The coating layer 61 is formed to improve the wear resistance and durability of the bearing surfaces 60a. The coating layer 61 contains at least polyamide-imide (PAI). PAI is used as a resin binder 61a. Preferably, the coating layer 61 further contains polytetrafluoroethylene (PTFE). In addition to PAI, or in addition to PAI and PTFE, the coating layer 61 may contain one or more inorganic additives 61b selected from the group consisting of molybdenum disulfide (MoS2), titanium oxide (TiO2), and calcium fluoride (CaF2). PTFE and MoS2 are used as solid lubricants, and TiO2 and CaF2 are used as reinforcing agents.

[0068] The PTFE content in each coating layer 61 may be 1 to 150 parts by mass, 20 to 120 parts by mass, or 40 to 80 parts by mass per 100 parts by mass of PAI. The MoS2 content in the coating layer 61 may be 1 to 200 parts by mass, 20 to 150 parts by mass, or 40 to 120 parts by mass per 100 parts by mass of PAI.

[0069] The coating layer 61 can be formed by known methods such as application using a spray, brush, knife, or applicator, or by screen printing. The coating layer 61 may be formed before or after the molding process of the foil bearing 60. Furthermore, the coating layer 61 may or may not be polished after formation.

[0070] The foil bearing 60 can employ the basic configuration of a so-called dynamic pressure gas bearing. For example, the foil bearing 60 may have a top foil having a bearing surface 60a, and a bump foil having a corrugated shape that elastically supports the top foil. When the rotating body 24 is rotating at a low speed until its rotational speed reaches the levitation speed, the foil bearing 60 supports the rotating body 24 as it rotates relative to the bearing surface 24g with the bearing surface 60a in contact with the bearing surface 24g. When the rotating body 24 rotates at high speed and reaches the levitation speed, the bearing surface 60a and the bearing surface 24g are not in contact, and the rotating body 24 is supported by the air film generated in the bearing gap 60b between the bearing surface 60a and the bearing surface 24g. In this specification, the state in which the bearing surface 60a and the bearing surface 24g are in contact means the state in which the coating layer 61 of the bearing surface 60a and the bearing surface 24g are in contact.

[0071] (cooling passage) As shown in Figures 1 to 3, a cooling passage 50 is formed in the housing 11. Air flows as a fluid through the cooling passage 50. The cooling passage 50 is formed across the second plate 16, the first plate 15, the motor housing 12, and the third plate 17. The cooling passage 50 has a first passage 51 and a second passage 52.

[0072] The first passage 51 is provided in the second plate 16. The first passage 51 has an inlet 51a provided on the side wall surface of the second plate 16. The branch passage L3 connects the supply passage L1 and the inlet 51a of the first passage 51. The first passage 51 is in communication with the motor chamber S1 via the thrust bearing housing chamber S2 and one of the radial foil bearings 40.

[0073] The second passage 52 is provided in the third plate 17. The second passage 52 has an outlet 52a provided on the side end face of the third plate 17. The second passage 52 is in communication with the motor chamber S1 via the other radial foil bearing 40.

[0074] (Fuel cell system) As described above, the turbo compressor 10 constitutes part of the fuel cell system 1. In addition to the turbo compressor 10, the fuel cell system 1 includes a fuel cell stack 100 as an on-board fuel cell, a supply channel L1, a discharge channel L2, and a branch channel L3. The fuel cell stack 100 is composed of multiple fuel cells. The supply channel L1 connects the discharge chamber 13c to the fuel cell stack 100. The discharge channel L2 connects the fuel cell stack 100 to the intake chamber 14c. An intercooler 110 is provided in the middle of the branch channel L3, which branches off from the supply channel L1. The intercooler 110 cools the air flowing through the branch channel L3.

[0075] <Operation of Turbo Compressors and Fuel Cell Systems> The turbo compressor 10 and fuel cell system 1 configured as described above operate as follows.

[0076] As the rotating body 24 rotates integrally with the rotor 31, the first impeller 25 and the second impeller 26 rotate integrally with the rotating body 24. As a result, air drawn in from the intake port 13a is compressed by the first impeller 25 in the first impeller chamber 13b, passes through the diffuser passage 13d, and is discharged from the discharge chamber 13c. The air discharged from the discharge chamber 13c is supplied to the fuel cell stack 100 via the supply passage L1. The air supplied to the fuel cell stack 100 is used to generate electricity in the fuel cell stack 100, and then discharged to the discharge passage L2 as exhaust from the fuel cell stack 100. The exhaust from the fuel cell stack 100 is drawn into the intake chamber 14c via the discharge passage L2. The exhaust from the fuel cell stack 100 drawn into the intake chamber 14c is discharged to the second impeller chamber 14b via the communication passage 14d. The exhaust from the fuel cell stack 100 discharged into the second impeller chamber 14b causes the second impeller 26 to rotate. The rotating body 24 rotates not only due to the drive of the electric motor 18, but also due to the rotation of the second impeller 26, which is rotated by the exhaust from the fuel cell stack 100. Therefore, the first impeller 25 (actuator) rotates integrally with the rotating body 24 and also pumps air as an external fluid. The exhaust from the fuel cell stack 100 discharged into the second impeller chamber 14b is discharged to the outside from the discharge port 14a.

[0077] While the turbo compressor 10 is operating, a portion of the air flowing through the supply channel L1 toward the fuel cell stack 100 flows into the first passage 51 via the branch channel L3. The air flowing into the first passage 51 is cooled air that has been cooled by the intercooler 110 while flowing through the branch channel L3. The cooled air that has flowed into the first passage 51 flows into the thrust bearing housing chamber S2.

[0078] The cooling air that flows into the thrust bearing housing chamber S2 flows mainly from the inner circumference to the outer circumference through one of the thrust foil bearings 30. Subsequently, the cooling air that has passed radially outside the third support portion 24d flows mainly from the outer circumference to the inner circumference through the other thrust foil bearing 30.

[0079] The cooling air that has passed through the thrust bearing housing chamber S2 flows into the motor chamber S1 via one of the radial foil bearings 40. The air that has flowed into the motor chamber S1 passes, for example, between the rotor 31 and the stator 32, flows into the second passage 52 via the other radial foil bearing 40, and is discharged from the outlet 52a.

[0080] In this way, the electric motor 18, the pair of thrust foil bearings 30, 30, and the pair of radial foil bearings 40, 40 are directly cooled by the cooling air as it flows through the cooling passage 50.

[0081] In the turbo compressor 10, the rotating body 24 rotates integrally with the rotor 31. At this time, during low-speed rotation until an air film is formed in the bearing gap between the bearing surface 60a and the bearing surface 24g, that is, until the rotational speed of the rotating body 24 reaches the levitation speed, the bearing surface 60a and the bearing surface 24g slide in contact with each other. During high-speed rotation when the rotational speed of the rotating body 24 reaches the levitation speed, the air film that forms in the bearing gap 60b between the bearing surface 60a and the bearing surface 24g causes the bearing surface 60a and the bearing surface 24g to be in a non-contact state, and the rotating body 24 is supported by this air film.

[0082] When the rotating body 24 rotates at a low speed, a portion of the coating layer 61 on the bearing surface 60a is scraped off due to the initial wear caused by the sliding, and the PAI in the coating layer 61 is transferred to the bearing surface 24g (Figure 5). As described above, since the aspect ratio Str of the bearing surface 24g of the rotating body 24 is within the range described above, it is thought that irregular irregularities are formed on the bearing surface 24g, which make it easy for the PAI transferred to the bearing surface 24g (hereinafter also referred to as "transferred particles 61c") to get caught. Therefore, even when the rotating body 24 rotates at high speed, it is presumed that the transferred particles 61c are less likely to fall off the bearing surface 24g, and a film of transferred particles 61c is more likely to form on the bearing surface 24g. This film reduces the frictional force when the bearing surface 60a and the bearing surface 24g slide against each other after the initial wear, thus suppressing wear of the metallic material forming the bearing surface 24g. Furthermore, since it is possible to suppress damage to the coating layer 61 caused by wear particles from metallic materials, which can increase surface roughness, the durability of the coating layer 61 can also be improved.

[0083] On the other hand, in order to make it easier to levitate the rotating body 24 with an air film, the smoothness of the bearing surface 24g may be improved by a traverse grinding method using a grinding wheel that has been used without dressing treatment, or by lapping using a liquid lapping agent containing abrasive grains. The aspect ratio Str of the bearing surface 24g with improved smoothness is smaller than the range described above and tends to approach 0. The closer the aspect ratio Str approaches 0, the more likely it is that the bearing surface 24g has highly regular grooves extending in one direction. It is presumed that the transferred particles 61c are less likely to get caught on the bearing surface 24g with an aspect ratio Str that is closer to 0 than the range described above, and that under conditions where the rotating body 24 is rotating at high speed, the transferred particles 61c will fall off the bearing surface 24g, making it difficult for a film of transferred particles 61c to form on the bearing surface 24g. Therefore, after initial wear, the frictional force when the bearing surface 60a and the bearing surface 24g slide against each other tends to increase, wear particles of metallic material are more likely to be generated from the bearing surface 24g, and the durability of the coating layer 61 tends to decrease.

[0084] Preferably, the height Rpk of the protruding peaks of the bearing surface 24g is within the range described above. This ensures that the bearing surface 24g has protruding peaks of a height that makes it easy for the transferred particles 61c to catch on, thus making it easier for the transferred particles 61c to catch on the irregularities of the bearing surface 24g. Therefore, by setting the height Rpk of the protruding peaks of the bearing surface 24g within the range described above, wear when the bearing surface 24g and the bearing surface 60a slide against each other is made easier to suppress. In particular, by setting the aspect ratio Str of the surface properties of the bearing surface 24g to 0.05 to 0.75 and the height Rpk of the protruding peaks of the bearing surface 24g to 0.3 to 0.7 μm, the transferred particles 61c can easily catch on the irregularities of the bearing surface 24g, making it easier to suppress wear when the bearing surface 24g and the bearing surface 60a slide against each other.

[0085] It is preferable that the load length ratio Mr1 of the bearing surface 24g is within the range of [a] to [c] described above, depending on the magnitude of the aspect ratio Str. This is because the bearing surface 24g has appropriately sized protrusions at a height that makes it easy for the transferred particles 61c to catch on it, thus making it easier for the transferred particles 61c to catch on the irregularities of the bearing surface 24g and for a coating to form on the entire bearing surface 24g. Therefore, by adjusting the load length ratio Mr1 according to the magnitude of the aspect ratio Str of the bearing surface 24g, it is easier to suppress wear when the bearing surface 24g and the bearing surface 60a slide against each other.

[0086] The coating layer 61 may contain PTFE as described above. When PTFE is present in the coating layer 61, the PTFE particles transferred due to initial wear can also adhere to the bearing surface 24g and form a film. Since the PTFE film is slippery and easily achieves low friction, the frictional force when the bearing surface 60a and the bearing surface 24g slide against each other after initial wear is reduced. This suppresses wear of the metallic material forming the bearing surface 24g, and also suppresses wear of the coating layer 61.

[0087] As described above, the coating layer 61 may contain one or more inorganic additives selected from the group consisting of MoS2, TiO2, and CaF2. The inorganic additives have lower toughness and are harder than the PAI contained in the coating layer 61. When the bearing surface 60a and the bearing surface 24g slide against each other, the PAI (transferred particles 61c) that are scraped off from the coating layer 61 are broken up by the inorganic additive, thus reducing the size of the transferred particles 61c. This suppresses the increase in surface roughness of the coating layer 61 due to initial wear and suppresses the limit thickness of the air film when levitating the rotating body.

[0088] In particular, when the coating layer 61 contains MoS2 as an inorganic additive, MoS2 has a layered crystalline structure in which S layers are stacked, so slippage occurs between the S layers, making it easier to achieve low friction. This suppresses the sliding resistance when the bearing surface 60a and the bearing surface 24g slide against each other.

[0089] <Manufacturing method for sliding bearing structure> As described above, the turbo compressor has a rotating body 24 and a foil bearing 60 as a sliding bearing structure. The manufacturing method for this sliding bearing structure (hereinafter also referred to as "this manufacturing method") is as follows: A cylindrical member for forming a rotating body 24 is prepared, wherein the surface on which the bearing surface 24g of the rotating body 24 is formed is made of a metallic material. The bearing surface 24g is formed by grinding the surface of the metallic material of the cylindrical member. Grinding methods for grinding the surface of the metallic material of the cylindrical member include traverse grinding, grinding with abrasive wheels, shot blasting, tape polishing, and combinations thereof, all using the dressed grinding wheels described above. Preferably, the grinding method is traverse grinding, grinding with abrasive wheels, shot blasting, or a combination thereof.

[0090] The cylindrical member is a cylindrical member made of a metallic material when the entire rotating body 24 is made of a metallic material. When the bearing surface 24g of the rotating body 24 is made of a metallic material, and the parts other than the bearing surface 24g are made of a material other than a metallic material, the cylindrical member only needs to have a surface on which the bearing surface 24g is formed made of a metallic material, and the parts other than said surface may be made of a material other than a metallic material. Examples of metallic materials that constitute the cylindrical member and the surface on which the bearing surface 24g of the cylindrical member is formed include the metallic materials described for the rotating body 24 and the bearing surface 24g.

[0091] Dressing is a general term for processes that involve making abrasive grains protrude from the surface of a grinding wheel, removing worn abrasive grains and making new abrasive grains protrude, shaping the surface of a grinding wheel worn down by grinding, and clearing clogging from the surface of a grinding wheel to sharpen it. In this method, using a dressed grinding wheel means using a dressed grinding wheel to grind the surface of a cylindrical member made of metallic material without subjecting it to grinding.

[0092] By adjusting the grinding conditions in the grinding method described above, the aspect ratio Str of the bearing surface 24g can be adjusted to the above range, and the load length ratio Mr1 and the protruding peak height Rpk can also be adjusted.

[0093] The grinding process described above may be applied to the bearing surface 24g of the cylindrical member, but it may also be applied to other surfaces of the cylindrical member.

[0094] [Differentiation] The above embodiments are not limited to those embodiments, and can be implemented with modifications as follows, for example.

[0095] The above describes a case where all bearing surfaces 24g of the turbo compressor 10 are made of metallic material, and the aspect ratio Str, load length ratio Mr1, and protruding peak height Rpk are within the above range, but is not limited to this. If at least one of the bearing surfaces 24g supported by the bearing surface 60a formed of the coating layer 61 is made of metallic material and the aspect ratio Str is within the above range, the other bearing surfaces 24g do not have to be made of metallic material, and the aspect ratio Str may be outside the above range. For example, the bearing surface 24g of the third support portion 24d facing a pair of thrust foil bearings 30, 30 may be within the above range, and the bearing surfaces 24g of the first support portion 24b and the second support portion 24c facing a pair of radial foil bearings 40, 40 may be outside the above range, or vice versa. When multiple bearing surfaces 24g are made of a metallic material and the aspect ratio Str is within the range described above, the metallic material and aspect ratio Str forming each bearing surface 24g may be the same as or different from each other, but preferably they are the same. In this case, the load length ratio Mr1 and the protruding peak height Rpk may also be the same as or different from each other, independently.

[0096] The above describes the case where all bearing surfaces 60a of the turbo compressor 10 are coated with a coating layer 61. However, if the bearing surfaces 60a supporting the bearing surface 24g, which is made of a metallic material and has an aspect ratio Str within the range described above, are formed with a coating layer 61, then bearing surfaces 60a that are not coated with a coating layer 61 may also be included. For example, the bearing surfaces 60a of a pair of thrust foil bearings 30, 30 may be made of a metallic material, and the bearing surfaces 60a of a pair of radial foil bearings 40, 40 may be made of a material other than a metallic material, or vice versa. When multiple bearing surfaces 60a are formed with a coating layer 61, it is sufficient if any of the bearing surfaces 60a have a coating layer 61 containing at least PAI, but preferably all bearing surfaces 60a have a coating layer 61 containing at least PAI. In this case, the composition of each coating layer 61 may be the same as or different from each other, but preferably they are the same.

[0097] Although Figure 1 describes the case of compressing air with the turbo compressor 10, the fluid to be compressed may be a fluid other than air (gas or liquid). For example, when the turbo compressor 10 is used in an air conditioning system, a refrigerant may be compressed. The refrigerant may change its state from gas to liquid depending on the pressure and temperature. The turbo compressor may be applied to air conditioning systems such as cabin air conditioning systems for vehicles and cooling circuits for battery temperature control.

[0098] In the turbo compressor 10 shown in Figure 1, the case in which the rotating body 24 is supported by an air film formed in the bearing gap 60b between the bearing surface 60a and the bearing surface 24g has been described. However, a gaseous film other than an air film may also be formed in the bearing gap 60b. Examples of gaseous films include refrigerant films and fluid films formed by the fluid compressed by the turbo compressor 10.

[0099] In the above explanation, a foil bearing structure was given as an example of a sliding bearing structure, but the sliding bearing structure may also be a hydrodynamic fluid bearing structure other than a foil bearing structure, or it may be a self-lubricating bearing structure.

[0100] When a sliding bearing structure is a hydrodynamic fluid bearing structure, a lubricating film is formed by the fluid lubricant supplied between the rotating body and the sliding bearing, and the bearing surface and the bearing surface are operated in a fluid-lubricated state where they are completely separated. The fluid lubricant is preferably a lubricant other than lubricating oil and grease, and examples include gas and water. Lubricating oil is a liquid lubricant containing a base oil. Grease is a lubricant containing a base oil and a thickener, according to JIS K 2220:2013, and is a semi-solid or solid lubricant that does not flow when no external force is applied, but flows when an external force is applied.

[0101] In the case of a self-lubricating sliding bearing structure, lubricant is not supplied between the rotating body and the sliding bearing. Instead, a thin lubricating film is formed by lubricating oil impregnated into the bearing surface and / or the bearing surface, or by solid lubricant embedded in the bearing surface and / or the bearing surface. Therefore, the self-lubricating sliding bearing structure operates in a boundary lubrication state where the bearing surface and the bearing surface are in local contact.

[0102] In the turbo compressor 10 shown in Figure 1, a pair of thrust foil bearings 30, 30 are provided on the first end 24e side of the rotating shaft 24a, but they may also be provided on the second end 24f side of the rotating shaft 24a, between the second impeller 26 and the second support portion 24c. [Examples]

[0103] The present invention will be described in more detail below with reference to test examples.

[0104] [Measurement of surface texture aspect ratio Str] The aspect ratio Str of the surface texture of the outer periphery of the ring used in the test example was measured in accordance with ISO 25178-2 using a shape analysis laser microscope (VK-X250, manufactured by Keyence Corporation). Specifically, 3D shape data was measured at a height pitch of 0.1 μm in a field of view of 290 μm horizontally × 230 μm vertically, observed at a magnification of 1000x, and the aspect ratio Str for that field of view was obtained after de-wavy processing with a cutoff wavelength of 0.20 mm. On the same outer periphery of the ring, 3D shape data was measured for 2 to 5 fields of view using the above procedure, changing the observation location, and the aspect ratio Str was obtained. The average value of the aspect ratio Str for each field of view was calculated and this was taken as the aspect ratio Str of the surface texture of the outer periphery of the ring.

[0105] [Determination of load length ratio Mr1 and protruding peak height Rpk] Using 3D shape data obtained by measuring the aspect ratio Str of the surface texture, 60 shape curves were acquired in each field of view in a direction perpendicular to the direction in which friction occurs, and the load length ratio Mr1 and protruding peak height Rpk were obtained for each shape curve. The average values ​​of the load length ratio Mr1 and protruding peak height Rpk obtained from each shape curve in each field of view were calculated and used as the load length ratio Mr1 and protruding peak height Rpk of the outer surface of the ring, respectively. No high-pass or low-pass correction processing was applied when acquiring the shape curves.

[0106] [Test Examples 1-14] To evaluate the frictional wear properties when the bearing surface of a sliding bearing slides against the bearing surface of a rotating body, a frictional wear test was conducted using the following procedure. Figure 6 is a schematic perspective view of the frictional wear test.

[0107] As shown in Figure 6, a block 74 simulating a sliding bearing was prepared by forming a 40 μm thick coating layer 74a on the top surface (16.5 mm wide x 6.2 mm high) of a raw material block measuring 16.5 mm wide x 6.2 mm long x 10.2 mm high, which was entirely made of stainless steel. The coating layer 74a is modeled after the coating layer on the bearing surface of a sliding bearing, and both the top surface of the block and the surface of the coating layer 74a are flat. The coating layer 74a was formed by spraying a coating solution containing 100 parts by mass of polyamide-imide (PAI), 78 parts by mass of polytetrafluoroethylene (PTFE), and 114 parts by mass of molybdenum disulfide (MoS2) onto the top surface of the raw material block, firing it, and then polishing it.

[0108] A ring 73 simulating a rotating body was prepared by grinding the outer surface of a raw material ring, which was entirely made of 64 titanium alloy, and adjusting the grinding conditions so that an outer surface 73a with the aspect ratio Str, load length ratio Mr1, and protruding peak height Rpk shown in Table 1 was formed. The ring diameter φ of ring 73 was 35 mm, and the width of the outer surface 73a of the ring was 8.15 mm. The grinding method for the outer surface of the raw material ring was as follows. • Test example 1 A lapping polishing method that uses a liquid lapping agent containing abrasive particles. • Test examples 2-9 A traverse grinding method using a dressed grinding wheel (adjusting the dressing conditions and grinding conditions). • Test examples 10-12 A grinding method using a grinding wheel, where the wheel is pressed against the surface to be polished. • Test examples 13-14 Shot blasting is a method of grinding the outer surface of a raw material ring by spraying it with a projectile.

[0109] With the coating layer 74a of the block 74 prepared above in contact with the outer circumferential surface 73a of the ring 73 (Figure 6), a friction and wear test was conducted under the following conditions. Testing machine: UMT-TriboLab (manufactured by Bruker) Load: 50gf Ring 73 rotation speed: 3000 rpm (steady state) Test time: 30 seconds Lubricated environment: no lubrication Test start temperature: Room temperature (natural temperature)

[0110] After the friction and wear tests, a scanning electron microscope (SEM) was used to obtain backscattered electron images at 100x magnification of the central part in the width direction of the outer surface 73a of the rings 73 in Test Examples 1 to 14. The results of obtaining backscattered electron images for Test Examples 1, 2, 8, 13, and 14 are shown in Figures 7 to 11, respectively. Energy-dispersive X-ray spectroscopy (EDS) analysis of the substance adhering to the outer surface 73a of the rings 73 (black areas in the figures) detected carbon, oxygen, fluorine, sulfur, and molybdenum indicated that the substance was transferred from the coating layer 74a. In Test Example 1, unidirectional streaks were formed in a highly regular manner, and as can be seen from the backscattered electron image in Figure 7, there was almost no transferred material from the coating layer 74a. As shown in Test Examples 2-14, when the degree to which unidirectional grooves are regularly formed becomes small and irregular irregularities are observed, transfer of material from the coating layer 74a was observed (see Figures 8-11). From this, it can be said that when the aspect ratio Str of the surface properties of the outer circumferential surface 73a of the ring 73 increases, the shedding of particles transferred from the coating layer 74a on the outer circumferential surface 73a of the ring 73 is more easily suppressed. This is thought to reduce wear of the ring 73 when it slides against the block 74. Furthermore, it can be said that when the load length ratio Mr1 of the outer circumferential surface 73a of the ring 73 increases, the shedding of particles transferred from the coating layer 74a is more easily suppressed.

[0111] After the friction and wear test, a scanning electron microscope (SEM) was used to examine the deposits on the surface of the coating layer 74a of block 74. If titanium was detected by EDS analysis of these deposits, the deposits were determined to be a titanium alloy and evaluated according to the following criteria. The results are shown in Table 1. A: No titanium alloy deposits were found. B: Titanium alloy was present in granular form (the amount of titanium alloy present was small). C: Titanium alloy was present in streaks or as lumps (large amount of titanium alloy was present).

[0112] Furthermore, using a scanning electron microscope (SEM), backscattered electron images and secondary electron images at 30x magnification were obtained for the coating layer 74a of block 74 in test examples 1, 2, 8, 13, and 14, and the results are shown in Figures 12 to 16.

[0113] [Table 1]

[0114] As shown in Table 1, in Test Examples 2 to 14, where the aspect ratio Str of the surface properties of the outer circumferential surface 73a of the ring 73 is 0.020 or higher, no titanium alloy adhesion was observed on the coating layer 74a after the friction and wear test (Figures 14 and 15) or only a small amount (Figures 13 and 16, especially the areas enclosed by the dashed lines in Figure 13(a) and Figure 16(a)). From this, it can be seen that in Test Examples 2 to 14, wear of the outer circumferential surface 73a of the ring 73 is suppressed when the coating layer 74a of the block 74 and the outer circumferential surface 73a of the ring 73 are slid against each other. Furthermore, it can be seen that the aspect ratio Str of the surface properties of the outer circumferential surface 73a is 0.05 to 0.75, and the height Rpk of the protruding peaks of the outer circumferential surface 73a is 0.3 to 0.7 μm, which further suppresses wear of the outer circumferential surface 73a of the ring 73 when the coating layer 74a of the block 74 slides against the outer circumferential surface 73a of the ring 73.

[0115] On the other hand, the results shown in Table 1 and Figures 12(a) and (b) indicate that in Test Example 1, where the aspect ratio of the surface properties of the outer circumferential surface 73a of the ring 73 is less than 0.020, titanium alloy was observed adhering to the coating layer 74a after the friction and wear test, and the amount of wear on the outer circumferential surface 73a of the ring was greater compared to Test Examples 2 to 14.

[0116] [Note] Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments. (Aspect 1) It comprises a rotating body and a sliding bearing that supports the rotating body, The sliding bearing has a bearing surface formed with a coating layer containing at least polyamide-imide, The rotating body has a bearing surface that faces the bearing surface and is made of a metallic material. A sliding bearing structure in which the aspect ratio Str of the surface properties of the bearing surface is 0.020 or greater. (Aspect 2) The sliding bearing structure according to embodiment 1, wherein the aspect ratio Str of the surface properties of the bearing surface is 0.80 or less. (Aspect 3) The aspect ratio Str of the surface properties of the bearing surface is 0.05 to 0.75. The sliding bearing structure according to embodiment 1 or 2, wherein the height Rpk of the protruding peaks on the bearing surface is 0.3 to 0.7 μm. (Aspect 4) The aspect ratio Str of the surface properties of the bearing surface is 0.040 or more and less than 0.1. The sliding bearing structure according to embodiment 1 or 2, wherein the load length ratio Mr1 of the bearing surface is 11% or more. (Aspect 5) The aspect ratio Str of the surface properties of the bearing surface is 0.1 or more and less than 0.6. The sliding bearing structure according to embodiment 1 or 2, wherein the load length ratio Mr1 of the bearing surface is 7.7% or more. (Aspect 6) The aspect ratio Str of the surface properties of the bearing surface is 0.6 or greater. The sliding bearing structure according to embodiment 1 or 2, wherein the load length ratio Mr1 of the bearing surface is 10% or more. (Aspect 7) The sliding bearing structure according to any one of embodiments 1 to 6, wherein the sliding bearing is a dynamic pressure gas bearing. (Pattern 8) The sliding bearing structure according to any one of embodiments 1 to 7, wherein the coating layer further comprises polytetrafluoroethylene. (Aspect 9) The sliding bearing structure according to any one of embodiments 1 to 8, wherein the coating layer further comprises one or more inorganic additives selected from the group consisting of molybdenum disulfide, titanium oxide, and calcium fluoride. (Aspect 10) The sliding bearing structure according to any one of embodiments 1 to 9, wherein the rotating body is formed of the metallic material. (Aspect 11) The sliding bearing structure according to any one of embodiments 1 to 10, wherein the metallic material is one or more selected from the group consisting of titanium, titanium alloys, and stainless steel. (Aspect 12) A solid of rotation and An actuator that rotates integrally with the aforementioned rotating body to pump fluid, A housing that accommodates the rotating body and the operating body, The rotating body is rotatably supported by a dynamic pressure gas bearing relative to the housing, The aforementioned dynamic pressure gas bearing has a bearing surface formed with a coating layer containing at least polyamide-imide, The rotating body has a bearing surface that faces the bearing surface and is made of a metallic material. A turbo-type fluid machine in which the aspect ratio Str of the surface properties of the bearing surface is 0.020 or greater. (Aspect 13) The aspect ratio Str of the surface properties of the bearing surface is 0.05 to 0.75. The turbo-type fluid machine according to embodiment 12, wherein the height Rpk of the protruding peaks on the bearing surface is 0.3 to 0.7 μm. (Aspect 14) See below [a]~[c]: [a] The aspect ratio Str of the surface properties of the bearing surface is 0.040 or more and less than 0.1. The load length ratio Mr1 of the bearing surface is 11% or more. [b] The aspect ratio Str of the surface texture of the bearing surface is 0.1 or more and less than 0.6. The load length ratio Mr1 of the bearing surface is 7.7% or more, and [c] The aspect ratio Str of the surface properties of the bearing surface is 0.6 or greater. The load length ratio Mr1 of the bearing surface is 10% or more. A turbo-type fluid machine according to embodiment 12, satisfying any of the following conditions. (Aspect 15) The turbo-type fluid machine according to any one of embodiments 12 to 14, wherein the dynamic pressure gas bearing is a foil bearing. (Aspect 16) The turbo-type fluid machine according to any one of embodiments 12 to 15, wherein the metallic material is one or more selected from the group consisting of titanium, titanium alloys, and stainless steel. (Aspect 17) The turbo fluid machine according to any one of embodiments 12 to 16, wherein the dynamic pressure gas bearing includes at least one of a thrust bearing that supports the rotating body in the axial direction of the rotating body and a radial bearing that supports the rotating body in a direction perpendicular to the axial direction.

[0117] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications are intended to be in the meaning and scope equivalent to the claims. [Industrial applicability]

[0118] The sliding bearing structure of the present invention can be used, for example, in turbo-type fluid machinery. The turbo-type fluid machinery of the present invention can be used in air compressors used in fuel cell systems, air conditioning compressors, turbines, generators, blowers, and the like. [Explanation of Symbols]

[0119] 1 Fuel cell system, 10 Turbo compressor (turbo fluid machine), 11 Housing, 24 Rotating body, 24b First support, 24c Second support, 24d Third support, 24g Bearing surface, 25 First impeller (actuator), 30 Thrust foil bearing (thrust bearing), 40 Radial foil bearing (radial bearing), 60 Foil bearing (sliding bearing, hydrodynamic gas bearing), 60a Bearing surface, 61 Coating layer, 61a Resin binder, 61b Inorganic additive, 61c Transfer particles.

Claims

1. It comprises a rotating body and a sliding bearing that supports the rotating body, The sliding bearing has a bearing surface formed with a coating layer containing at least polyamide-imide, The rotating body has a bearing surface that faces the bearing surface and is made of a metallic material. A sliding bearing structure in which the aspect ratio Str of the surface properties of the bearing surface is 0.020 or greater.

2. The sliding bearing structure according to claim 1, wherein the aspect ratio Str of the surface properties of the bearing surface is 0.80 or less.

3. The aspect ratio Str of the surface properties of the bearing surface is 0.05 to 0.

75. The sliding bearing structure according to claim 1, wherein the height Rpk of the protruding peaks on the bearing surface is 0.3 to 0.7 μm.

4. The aspect ratio Str of the surface properties of the bearing surface is 0.040 or more and less than 0.

1. The sliding bearing structure according to claim 1, wherein the load length ratio Mr1 of the bearing surface is 11% or more.

5. The aspect ratio Str of the surface properties of the bearing surface is 0.1 or more and less than 0.

6. The sliding bearing structure according to claim 1, wherein the load length ratio Mr1 of the bearing surface is 7.7% or more.

6. The aspect ratio Str of the surface properties of the bearing surface is 0.6 or greater. The sliding bearing structure according to claim 1, wherein the load length ratio Mr1 of the bearing surface is 10% or more.

7. The sliding bearing structure according to claim 1, wherein the sliding bearing is a dynamic pressure gas bearing.

8. The sliding bearing structure according to claim 1, wherein the coating layer further comprises polytetrafluoroethylene.

9. The sliding bearing structure according to claim 1, wherein the coating layer further comprises one or more inorganic additives selected from the group consisting of molybdenum disulfide, titanium oxide, and calcium fluoride.

10. The sliding bearing structure according to claim 1, wherein the rotating body is formed of the metallic material.

11. The sliding bearing structure according to claim 1, wherein the metallic material is one or more selected from the group consisting of titanium, titanium alloys, and stainless steel.

12. A solid of rotation and An actuator that rotates integrally with the aforementioned rotating body to pump fluid, A housing that accommodates the rotating body and the operating body, The rotating body is rotatably supported by a dynamic pressure gas bearing relative to the housing, The aforementioned dynamic pressure gas bearing has a bearing surface formed with a coating layer containing at least polyamide-imide, The rotating body has a bearing surface that faces the bearing surface and is made of a metallic material. A turbo-type fluid machine in which the aspect ratio Str of the surface properties of the bearing surface is 0.020 or greater.

13. The aspect ratio Str of the surface properties of the bearing surface is 0.05 to 0.

75. The turbo-type fluid machine according to claim 12, wherein the height Rpk of the protruding peaks on the bearing surface is 0.3 to 0.7 μm.

14. See [a] to [c] below: [a] The aspect ratio Str of the surface texture of the bearing surface is 0.040 or more and less than 0.

1. The load length ratio Mr1 of the bearing surface is 11% or more. [b] The aspect ratio Str of the surface texture of the bearing surface is 0.1 or more and less than 0.

6. The load length ratio Mr1 of the bearing surface is 7.7% or more, and [c] The aspect ratio Str of the surface texture of the bearing surface is 0.6 or greater. The load length ratio Mr1 of the bearing surface is 10% or more. A turbo-type fluid machine according to claim 12, satisfying any of the following conditions.

15. The turbo-type fluid machine according to claim 12, wherein the dynamic pressure gas bearing is a foil bearing.

16. The turbo-type fluid machine according to claim 12, wherein the metallic material is one or more selected from the group consisting of titanium, titanium alloys, and stainless steel.

17. The turbo fluid machine according to any one of claims 12 to 16, wherein the dynamic pressure gas bearing includes at least one of a thrust bearing that supports the rotating body in the axial direction of the rotating body and a radial bearing that supports the rotating body in a direction perpendicular to the axial direction.

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