Slide bearing structure and turbo fluid machine

Abstract

According to the present invention, a sliding bearing structure has a rotating body (24) and sliding bearings (30, 40, 60) that support the rotating body (24). More specifically, the sliding bearings (30, 40, 60) have a bearing surface (60a) formed of a coating layer (61) containing at least a polyamide-imide. The rotating body (24) has a supported surface (24g) that faces the bearing surface (60a) and is formed from a metal material. The aspect ratio Str of surface properties of the supported surface (24g) is 0.020 or more.

Description

Plain bearing structure and turbo fluid machine

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

[0002] Foil bearings are known as hydrodynamic gas bearings that support a rotating body, which is the shaft of a turbo-type fluid machine (see, for example, Patent Document 1). Foil bearings support the rotating body by levitating it using a fluid film, such as an air film, that forms between the bearing surface of the foil bearing and the rotating body. Patent Document 1 discloses forming a coating on the bearing surface of the foil bearing to improve the wear resistance and durability of the bearing surface.

[0003] Japanese Patent Application Laid-Open No. 2019-82195

[0004] To facilitate the floating of the rotor by the fluid film, the bearing surfaces of the foil bearing and the bearing surfaces of the rotor are sometimes smoothed. However, typical smoothing processes for metals do not sufficiently suppress wear on the bearing surfaces of the rotor.

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

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

[0007] The sliding bearing structure includes a rotating body and a sliding bearing that supports the rotating body, the sliding bearing having a bearing surface formed with a coating layer that contains at least polyamideimide, the rotating body having a bearing surface facing the bearing surface and formed of a metallic material, and the aspect ratio Str of the surface texture of the bearing surface is 0.020 or more.

[0008] In the sliding bearing structure, it is preferable that the aspect ratio Str of the surface texture of the bearing surface is 0.80 or less.

[0009] In the sliding bearing structure, it is preferable that the aspect ratio Str of the surface texture of the bearing surface is 0.05 to 0.75, and the protruding peak height Rpk of the bearing surface is 0.3 to 0.7 μm.

[0010] In the sliding bearing structure, it is preferable that the aspect ratio Str of the surface texture 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 sliding bearing structure, it is preferable that the aspect ratio Str of the surface texture 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, it is preferable that the aspect ratio Str of the surface texture 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 above-described sliding bearing structure, the sliding bearing is preferably a dynamic pressure gas bearing.

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

[0015] In the sliding bearing structure, the coating layer preferably 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, the rotating body is preferably made of the metallic material.

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

[0018] The turbo fluid machine includes a rotating body, a working body that rotates integrally with the rotating body to pump a fluid, a housing that accommodates the rotating body and the working body, and a dynamic pressure gas bearing that rotatably supports the rotating body relative to the housing, wherein the dynamic pressure gas bearing has a bearing surface formed with a coating layer that contains at least polyamide-imide, 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 texture of the bearing surface is 0.020 or more.

[0019] In the turbo fluid machine, it is preferable that the aspect ratio Str of the surface texture of the bearing surface is 0.05 to 0.75, and the height Rpk of the protruding peaks of the bearing surface is 0.3 to 0.7 μm.

[0020] In the turbo fluid machine, it is preferable that any of the following [a] to [c] be satisfied: [a] the aspect ratio Str of the surface texture 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, and 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 more, and the load length ratio Mr1 of the bearing surface is 10% or more.

[0021] In the turbo fluid machine, the dynamic pressure gas bearing is preferably a foil bearing.

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

[0023] In the turbo fluid machine, it is preferable that the dynamic pressure gas bearing includes at least one of a thrust bearing that supports the rotating body in an axial direction of the rotating body, and a radial bearing that supports the rotating body in a direction perpendicular to the axial direction.

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

[0025] 1 is a cross-sectional view showing a turbo compressor. FIG. 1 is a cross-sectional view showing an enlarged view of a portion of the turbo compressor shown in FIG. 1. FIG. 2 is a cross-sectional view showing an enlarged view of another portion of the turbo compressor shown in FIG. 1. FIG. 3 is a cross-sectional view showing an enlarged view of a portion of a rotor and a foil bearing of the turbo compressor shown in FIG. 1. FIG. 4 is a cross-sectional view schematically illustrating a state in which a coating layer of a foil bearing of the turbo compressor shown in FIG. 1 wears. FIG. 5 is a perspective view schematically illustrating a frictional wear test. FIG. 6 is a backscattered electron image of the outer peripheral surface of a ring of Test Example 1 before a frictional wear test, observed with a scanning electron microscope. FIG. 7 is a backscattered electron image of the outer peripheral surface of a ring of Test Example 2 before a frictional wear test, observed with a scanning electron microscope. FIG. 8 is a backscattered electron image of the outer peripheral surface of a ring of Test Example 8 before a frictional wear test, observed with a scanning electron microscope. FIG. 9 is a backscattered electron image of the outer peripheral surface of a ring of Test Example 13 before a frictional wear test. FIG. 10 is a backscattered electron image of the outer peripheral surface of a ring of Test Example 14 before a frictional wear test. 1 shows SEM images of the coating layer of the block of Test Example 1 after the friction and wear test, observed with a scanning electron microscope, where (a) is a backscattered electron image and (b) is a secondary electron image. 2 shows SEM images of the coating layer of the block of Test Example 2 after the friction and wear test, observed with a scanning electron microscope, where (a) is a backscattered electron image and (b) is a secondary electron image. 3 shows SEM images of the coating layer of the block of Test Example 8 after the friction and wear test, observed with a scanning electron microscope, where (a) is a backscattered electron image and (b) is a secondary electron image. 4 shows SEM images of the coating layer of the block of Test Example 13 after the friction and wear test, observed with a scanning electron microscope, where (a) is a backscattered electron image and (b) is a secondary electron image. 5 shows SEM images of the coating layer of the block of Test Example 14 after the friction and wear test, observed with a scanning electron microscope, where (a) is a backscattered electron image and (b) is a secondary electron image.

[0026] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification, a numerical range such as "x to y" includes an upper limit and a lower limit unless otherwise specified, and represents a numerical range of "x or more and y or less."

[0027] In this embodiment, a turbo compressor is used as an example of a turbo fluid machine, and a sliding bearing structure is described that has a rotating body and a foil bearing that is a hydrodynamic gas bearing as the sliding bearing.

[0028] <Basic configuration of turbo compressor> Fig. 1 is a cross-sectional view showing a turbo compressor. Figs. 2 and 3 are cross-sectional views showing enlarged portions of the turbo compressor shown in Fig. 1. Fig. 4 is a cross-sectional view showing enlarged portions of a rotor and a foil bearing of the turbo compressor shown in Fig. 1. Fig. 5 is a cross-sectional view schematically illustrating wear of a coating layer on a foil bearing of the turbo compressor shown in Fig. 1.

[0029] The turbo compressor 10 (turbo fluid machinery) is mounted on a fuel cell vehicle equipped with a fuel cell system 1. The fuel cell system 1 supplies oxygen and hydrogen to an on-board fuel cell to generate electricity. The turbo compressor 10 compresses the oxygen-containing air that is supplied to the on-board fuel cell.

[0030] (Housing) As shown in Fig. 1 , the turbo compressor 10 includes 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 periphery of the end wall 12a. The first plate 15 is connected to the end of the peripheral wall 12b on the opening side of the motor housing 12 and closes the opening of the peripheral wall 12b.

[0032] A motor chamber S1 is defined by an inner surface 121a of the end wall 12a of the motor housing 12, an inner peripheral surface 121b of the peripheral wall 12b, and an end surface 15a of the first plate 15 facing the motor housing 12. An electric motor 18 is accommodated in the motor chamber S1.

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

[0034] A recess 15c having a bottom surface 15d is formed in an end surface 15b of the first plate 15 opposite the motor housing 12. The recess 15c is a circular hole. The cylindrical interior of the first bearing holder 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 holder 20 coincide with each other.

[0035] The motor housing 12 has a second bearing retaining portion 22. The second bearing retaining portion 22 protrudes from the center of the inner surface 121a of the end wall 12a of the motor housing 12 toward the electric motor 18. The second bearing retaining portion 22 is cylindrical. The interior of the second bearing retaining portion 22 passes through 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 with each other.

[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 is connected to the inside of 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 holder 20. A thrust bearing accommodating chamber S2 is defined 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 suction port 13a through which air is drawn in. The compressor housing 13 is connected to an end face 16c of the second plate 16 opposite the first plate 15. The axial centers of the suction port 13a of the compressor housing 13, the shaft insertion hole 16a of the second plate 16, and the first bearing holder 20 are aligned. The suction port 13a opens at the end face of the compressor housing 13 opposite the second plate 16.

[0038] A first impeller chamber 13b, a discharge chamber 13c, and a diffuser passage 13d are formed between the compressor housing 13 and an end face 16c of the second plate 16. The first impeller chamber 13b is in communication with the suction port 13a. The discharge chamber 13c extends around the axis of the suction port 13a around the periphery of 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 is in communication 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 cylindrical interior 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 through which air is discharged. The turbine housing 14 is connected to an end face 17b of the third plate 17 opposite the motor housing 12. The axis of the discharge port 14a of the turbine housing 14, the axis of the shaft insertion hole 17a of the third plate 17, and the axis of the second bearing holder 22 are aligned. The discharge port 14a opens into the end face of the turbine housing 14 opposite the third plate 17.

[0041] A second impeller chamber 14b, a suction chamber 14c, and a communication passage 14d are formed between the turbine housing 14 and an end face 17b of the third plate 17. The second impeller chamber 14b is in communication with the discharge port 14a. The suction chamber 14c extends around the axis of the discharge port 14a around the periphery of the second impeller chamber 14b. The communication passage 14d connects the second impeller chamber 14b and the suction chamber 14c. The second impeller chamber 14b is in communication with the shaft insertion hole 17a of the third plate 17.

[0042] (Electric Motor) The electric motor 18 includes a cylindrical rotor 31 and a cylindrical stator 32. The rotor 31 is fixed to a rotating shaft 24a (described later). The stator 32 is fixed to the housing 11. The rotor 31 is disposed radially inward of the stator 32 and rotates integrally with the rotating body 24 (described later). The rotor 31 includes 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 includes 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 a current flows through the coil 34 from a battery (not shown), the rotating body 24 rotates integrally with the rotor 31. The electric motor 18 rotates at 100,000 rpm or more, for example, in the range of 100,000 to 120,000 rpm.

[0043] 1, a rotor 24 is accommodated within the housing 11. The rotor 24 has a rotating shaft 24a as a 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 that is the end portion on the compressor housing 13 side and a second end portion 24f that is the end portion on the turbine housing 14 side.

[0044] The first support portion 24b is provided on an outer peripheral surface 240a of the rotating shaft 24a at a position closer to the first end 24e, and is disposed inside the cylinder of the first bearing holder 20. The first support portion 24b is formed integrally with the rotating shaft 24a, and protrudes in an annular shape from the outer peripheral surface 240a of the rotating shaft 24a.

[0045] The second support portion 24c is provided on the outer peripheral surface 240a of the rotating shaft 24a at a position closer to the second end 24f and is disposed within the cylinder of the second bearing holder 22. The second support portion 24c is cylindrical and fixed to the outer peripheral surface 240a of the rotating shaft 24a in a state where it protrudes in an annular shape from the outer peripheral 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 disposed in the thrust bearing accommodating chamber S2. The third support portion 24d is disk-shaped and fixed to the outer peripheral surface 240a of the rotating shaft 24a in a state where it protrudes annularly from the outer peripheral surface 240a of the rotating shaft 24a. The third support portion 24d can rotate integrally with the rotating shaft 24a. The third support portion 24d is disposed at a position spaced apart from the electric motor 18 in the axial direction of the rotating body 24 (hereinafter simply referred to as the "axial direction").

[0047] A first impeller 25 (actuator) is connected to a first end 24e of the rotary shaft 24a. The first impeller 25 is disposed closer to the first end 24e than the third support portion 24d of the rotary shaft 24a. The first impeller 25 is housed in the first impeller chamber 13b. A second impeller 26 is connected to a second end 24f of the rotary shaft 24a. The second impeller 26 is disposed closer to the second end 24f than the second support portion 24c of the rotary 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 rotor 24.

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

[0049] The rotating body 24 is supported by a foil bearing 60 (described below) so as to be rotatable relative to the housing 11. The rotating body 24 faces a bearing surface 60a (described below) and has a bearing surface 24g formed of a metallic material. As long as at least the bearing surface 24g of the rotating body 24 is formed of a metallic material, the portions of the rotating body 24 other than the bearing surface 24g may be formed of a material other than the metallic material, or 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 resin. Alternatively, the entire rotating body 24 may be formed of a metallic material, and the metallic material of the surfaces that become the bearing surface 24g (the surfaces of the first to third support portions 24b to 24d) may serve as the bearing surface 24g. Examples of metallic materials that form the rotating body 24 or the bearing surface 24g include simple metals such as titanium; metal alloys such as titanium alloys; nickel alloys; and alloy steels such as stainless steel and chromium-molybdenum steel. An example of the stainless steel is SUS. Since the rotor 24 is preferably made of a material that is not easily 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 material, a paramagnetic material, or a diamagnetic material. The metallic material is preferably a metal or alloy containing titanium, or an austenitic stainless steel such as austenitic SUS, and more preferably titanium or a titanium alloy.

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

[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 greater, and may be 0.025 or greater, 0.030 or greater, preferably 0.040 or greater, or 0.050 or greater. The aspect ratio Str of the bearing surface 24g may be 0.020 to 0.80, 0.030 to 0.75, preferably 0.040 to 0.72, 0.045 to 0.60, 0.050 to 0.50, or 0.060 to 0.40. The aspect ratio Str takes a value between 0 and 1, with values ​​closer to 0 indicating a more anisotropic surface with a regular pattern, and values ​​closer to 1 indicating a more 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 a value measured using the following procedure. A sample for measuring the aspect ratio Str is prepared, and 3D shape data is measured in a field of view measuring 290 μm wide x 230 μm long observed at 1000x magnification. Waviness is removed using a cutoff wavelength of 0.20 mm, and the aspect ratio Str in that field of view is obtained. For the same sample, 3D shape data is measured in two to five fields of view using the above procedure, with different observation locations, and the aspect ratio Str in each field of view is obtained. The average of the aspect ratios Str in the obtained fields of view is taken as the aspect ratio Str of the surface texture of the bearing surface 24g of that sample.

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

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

[0055] It is preferable that the aspect ratio Str of the bearing surface 24g and the load length ratio Mr1 of the bearing surface 24g satisfy any one 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, and the load length ratio Mr1 of the bearing surface 24g is 11% or more. [b] The aspect ratio Str of the bearing surface 24g is 0.1 or more and less than 0.6, and the load length ratio Mr1 of the bearing surface 24g is 7.7% or more. [c] The aspect ratio Str of the surface texture of the bearing surface 24g is 0.6 or more, and the load length ratio Mr1 of the bearing surface is 10% or more.

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

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

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

[0059] When 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, or 13% or more, for example, 12 to 18%, 12.5 to 16%, or 13 to 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 determined from the profile curve obtained by measuring the bearing surface 24g. The equivalent line is the line with the gentlest slope, where the secant line passing through two points on the load curve where the difference in load length ratio is 40% is taken as the equivalent line. The core portion is defined as the area between the two height positions where the equivalent line intersects the vertical axis at 0% and 100% of the horizontal axis. The average height of the protruding peaks above the core portion on the profile curve is Rpk, and the load length ratio at the intersection of the profile curve and the dividing line between the peaks and the core portion is Mr1. ​​Therefore, the load length ratio Mr1 is an index representing the proportion of the bearing surface 24g occupied by the protruding peaks, and the protruding peak height Rpk can be said to represent the average height of the protruding peaks on the bearing surface 24g.

[0061] In this specification, the load length ratio Mr1 and the peak height Rpk refer to values ​​measured using the following procedure. Using the 3D shape data obtained for the sample for which the aspect ratio Str is to be 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 peak height Rpk of each shape curve are determined. The load length ratio Mr1 and the peak height Rpk obtained from each shape curve in each field of view are respectively averaged, and the respective average values ​​are used as the load length ratio Mr1 and the peak height Rpk of the bearing surface 24g of the sample. No high-pass or low-pass correction processing is performed 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 used when forming the bearing surface 24g. Grinding methods include a traverse grinding method in which a dressed grinding wheel (described later) is moved to grind the object to be ground while reciprocating, a grinding wheel grinding method in which a grinding wheel is pressed against the surface to be ground, a shot blasting method in which a projectile is sprayed or collided against the surface to be ground, a tape grinding method in which a tape (or film) coated with abrasive grains is pressed against the surface to be ground, and combinations thereof. The grinding method is preferably a traverse grinding method, a grinding wheel grinding method, a shot blasting method, or a combination thereof.

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

[0064] The pair of thrust foil bearings 30 are disposed in the thrust bearing accommodating chamber S2. The pair of thrust foil bearings 30 are disposed so as to sandwich the third support portion 24d, which serves as a thrust collar. The pair of thrust foil bearings 30 face the third support portion 24d in the axial direction of the rotating body 24. One thrust foil bearing 30 is disposed 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 disposed on the second end 24f side of the rotating shaft 24a relative to the third support portion 24d.

[0065] 2, the end face of third support portion 24d on the side of first end 24e of rotating shaft 24a serves as bearing surface 24g that is axially supported by one thrust foil bearing 30. One thrust foil bearing 30 has a bearing surface 60a that faces this bearing surface 24g. Similarly, the end face of third support portion 24d on the side of second end 24f of rotating shaft 24a serves as 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 disposed in the first bearing holder 20, and the other radial foil bearing 40 is disposed in the 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 radial foil bearing 40. The outer peripheral surface of the first support portion 24b serves as a bearing surface 24g that is supported by one radial foil bearing 40 in a direction perpendicular to the axial direction. One radial foil bearing 40 has a bearing surface 60a that faces 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 peripheral surface of the second support portion 24c serves as a bearing surface 24g that is 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 FIG. 4 , the bearing surface 60 a of each foil bearing 60, i.e., the bearing surface 60 a of each thrust foil bearing 30, 30 and the bearing surface 60 a of each radial foil bearing 40, 40, is formed with a coating layer 61. The coating layer 61 is formed to improve the wear resistance and durability of the bearing surface 60 a. The coating layer 61 contains at least polyamideimide (PAI). The PAI is used as a resin binder 61 a. The coating layer 61 preferably further contains polytetrafluoroethylene (PTFE). The coating layer 61 contains molybdenum disulfide (MoS) in addition to PAI or in addition to PAI and PTFE. ２), titanium oxide (TiO ２ ), and calcium fluoride (CaF ２ ) may contain one or more inorganic additives 61b selected from the group consisting of PTFE and MoS ２ is used as a solid lubricant, and TiO ２ and CaF ２ is used as a strengthening agent.

[0068] The content of PTFE 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 relative to 100 parts by mass of PAI. ２ The content of may be 1 to 200 parts by mass, 20 to 150 parts by mass, or 40 to 120 parts by mass relative to 100 parts by mass of PAI.

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

[0070] The foil bearing 60 may have the basic configuration of a hydrodynamic gas bearing. For example, the foil bearing 60 may have a top foil having a bearing surface 60a and a corrugated bump foil that elastically supports the top foil. The foil bearing 60 supports the rotating body 24, which rotates relative to the bearing surface 60a while the bearing surface 60a and the bearing surface 24g are in contact with each other, during low-speed rotation of the rotating body 24 until the rotation speed of the rotating body 24 reaches the floating rotation speed. Once the rotating body 24 rotates at high speed and reaches the floating rotation speed, the bearing surface 60a and the bearing surface 24g are no longer in contact with each other, and the foil bearing 60 supports the rotating body 24 by an air film formed in a 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 with each other refers to the state in which the coating layer 61 of the bearing surface 60a is in contact with the bearing surface 24g.

[0071] 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 in a side wall surface of the second plate 16. The branch passage L3 connects the supply passage L1 to the inlet 51a of the first passage 51. The first passage 51 communicates with the motor chamber S1 via the thrust bearing accommodation 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 a discharge port 52a provided in a side end surface of the third plate 17. The second passage 52 communicates 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 also includes a fuel cell stack 100 as an on-board fuel cell, a supply flow path L1, a discharge flow path L2, and a branch flow path L3. The fuel cell stack 100 is made up of a plurality of fuel cells. The supply flow path L1 connects the discharge chamber 13c to the fuel cell stack 100. The discharge flow path L2 connects the fuel cell stack 100 to the suction chamber 14c. An intercooler 110 is provided midway along the branch flow path L3 that branches off from the supply flow path L1. The intercooler 110 cools the air flowing through the branch flow path L3.

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

[0076] When 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. Air drawn in through the suction 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 is then discharged to the discharge passage L2 as exhaust gas from the fuel cell stack 100. The exhaust gas from the fuel cell stack 100 is drawn into the suction chamber 14c via the discharge passage L2. The exhaust gas from the fuel cell stack 100 drawn into the suction chamber 14c is discharged to the second impeller chamber 14b via the communication passage 14d. The second impeller 26 is rotated by the exhaust gas from the fuel cell stack 100 that is discharged into the second impeller chamber 14b. The rotor 24 is rotated not only by the drive of the electric motor 18 but also by the rotation of the second impeller 26, which is rotated by the exhaust gas from the fuel cell stack 100. Therefore, the first impeller 25 (actuator) rotates integrally with the rotor 24 and pressurizes and delivers air as an external fluid. The exhaust gas from the fuel cell stack 100 that is discharged into the second impeller chamber 14b is discharged to the outside from the discharge port 14a.

[0077] During operation of the turbo compressor 10, a portion of the air flowing through the supply passage L1 toward the fuel cell stack 100 flows into the first passage 51 via the branch passage 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 passage L3. The cooled air that has flowed into the first passage 51 flows into the thrust bearing accommodation chamber S2.

[0078] The cooling air that flows into the thrust bearing accommodation chamber S2 flows from the inner periphery toward the outer periphery mainly via one of the thrust foil bearings 30. After that, the cooling air that passes radially outside the third support portion 24d flows from the outer periphery toward the inner periphery mainly via 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 discharge port 52a.

[0080] In this way, the cooling air flows through the cooling passage 50, whereby 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.

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

[0082] When the rotor 24 rotates at low speeds, initial wear caused by the sliding causes a portion of the coating layer 61 on the bearing surface 60a to be torn off, and the PAI in the coating layer 61 is transferred to the bearing surface 24g ( FIG. 5 ). As described above, the bearing surface 24g of the rotor 24 has an aspect ratio Str within the above-described range, which is thought to create irregular irregularities that easily trap the PAI (hereinafter also referred to as "transferred particles 61c") transferred to the bearing surface 24g. Therefore, even when the rotor 24 rotates at high speeds, it is thought that the transferred particles 61c are unlikely to fall off the bearing surface 24g, making it easier for a coating of the transferred particles 61c to form on the bearing surface 24g. This coating reduces the frictional force when the bearing surface 60a and the bearing surface 24g slide together after initial wear, thereby suppressing wear of the metallic material forming the bearing surface 24g. Furthermore, the coating layer 61 can be prevented from being damaged by wear particles of metallic materials, which would otherwise increase the surface roughness, and therefore the durability of the coating layer 61 can be improved.

[0083] On the other hand, to facilitate the floating of the rotor 24 by the air film, the smoothness of the bearing surface 24g may be improved by traverse grinding using a grinding wheel that has been used without being dressed, 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 above-mentioned range and tends to approach 0. It is believed that the closer the aspect ratio Str is to 0, the more regularly the unidirectional striations are formed on the bearing surface 24g. It is presumed that the transferred particles 61c are less likely to become trapped on the bearing surface 24g having an aspect ratio Str closer to 0 than the above-mentioned range, and that under conditions in which the rotor 24 rotates at high speed, the transferred particles 61c fall off the bearing surface 24g, making it difficult for a coating of the transferred particles 61c to form on the bearing surface 24g. Therefore, after the initial wear, the frictional force when the bearing surface 60a and the bearing surface 24g slide against each other tends to increase, wear powder of metallic material tends to be generated from the bearing surface 24g, and the durability of the coating layer 61 tends to decrease.

[0084] The bearing surface 24g preferably has a protruding peak height Rpk within the above-mentioned range. This provides the bearing surface 24g with protruding peaks at a height that easily catches the transferred particles 61c, making it easier for the transferred particles 61c to become trapped by the irregularities of the bearing surface 24g. Therefore, by setting the protruding peak height Rpk of the bearing surface 24g within the above-mentioned range, wear can be more easily suppressed when the bearing surface 24g and the bearing surface 60a slide against each other. In particular, by setting the aspect ratio Str of the surface texture of the bearing surface 24g to 0.05 to 0.75 and the protruding peak height Rpk of the bearing surface 24g to 0.3 to 0.7 μm, the transferred particles 61c can be more easily trapped by 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 be within the range of [a] to [c] described above, depending on the aspect ratio Str. This results in the bearing surface 24g having an appropriate number of protruding peaks of a height that easily catches the transferred particles 61c, making it easier for the transferred particles 61c to catch on the irregularities of the bearing surface 24g, and facilitating the formation of a coating over the entire bearing surface 24g. Therefore, adjusting the load length ratio Mr1 depending on the aspect ratio Str of the bearing surface 24g makes it easier to suppress wear when the bearing surface 24g and the bearing surface 60a slide against each other.

[0086] As described above, the coating layer 61 may contain PTFE. If PTFE is present in the coating layer 61, the transferred particles of PTFE can adhere to the bearing surface 24g and form a coating upon initial wear. Because the PTFE coating is slippery and tends to achieve low friction, the frictional force when the bearing surface 60a and the bearing surface 24g slide together after initial wear is reduced. This suppresses wear of the metallic material that forms the bearing surface 24g, and also suppresses wear of the coating layer 61.

[0087] As described above, the coating layer 61 is made of MoS ２ , TiO ２ , and CaF ２ The coating layer 61 may contain one or more inorganic additives selected from the group consisting of: The inorganic additives are harder and less tough than the PAI contained in the coating layer 61. If the inorganic additive is present in the coating layer, when the bearing surface 60a and the bearing surface 24g slide against each other, the PAI (transferred particles 61c) that is ripped off from the coating layer 61 is broken up by the inorganic additive, thereby reducing the size of the transferred particles 61c. This makes it possible to prevent the surface roughness of the coating layer 61 from increasing due to initial wear, and to suppress the critical thickness of the air film when levitating the rotating body.

[0088] In particular, the coating layer 61 contains MoS as an inorganic additive. ２ If it contains MoS ２has a layered crystalline structure in which S layers are stacked, which allows for sliding between the S layers and facilitates low friction, thereby reducing the sliding resistance when the bearing surface 60a and the bearing surface 24g slide against each other.

[0089] <Method for Manufacturing a Plain Bearing Structure> As described above, a turbo compressor has a rotating body 24 and a foil bearing 60 as a plain bearing structure. The method for manufacturing this plain bearing structure (hereinafter also referred to as "this manufacturing method") includes: preparing a cylindrical member for forming the rotating body 24, the cylindrical member having a surface on which the bearing surface 24g of the rotating body 24 is formed, which is made of a metallic material; and grinding the surface of the metallic material of the cylindrical member to form the bearing surface 24g. Grinding methods for grinding the surface of the metallic material of the cylindrical member include traverse grinding using the dressed grinding wheel described above, grinding wheel grinding, shot blasting, tape polishing, and combinations thereof. The grinding method is preferably traverse grinding, grinding wheel grinding, shot blasting, or combinations 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 portion other than the bearing surface 24g is made of a material other than a metallic material, it is sufficient that at least the surface of the cylindrical member on which the bearing surface 24g is formed is made of a metallic material, and the portion other than this surface may be made of a material other than a metallic material. Examples of metallic materials that constitute the cylindrical member and the surface of the cylindrical member on which the bearing surface 24g is formed include the metallic materials described for the rotating body 24 and the bearing surface 24g.

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

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

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

[0094] [Modifications] The above embodiment is not limited to the above embodiment, and can be modified as follows, for example.

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

[0096] In the above description, all bearing surfaces 60a of the turbo compressor 10 are coated with the coating layer 61. However, as long as the bearing surfaces 60a that are formed of a metallic material and support the bearing surfaces 24g having the aspect ratio Str within the above-described range are formed with the coating layer 61, some bearing surfaces 60a may not be formed with the coating layer 61. For example, the bearing surfaces 60a of the pair of thrust foil bearings 30, 30 may be formed with a metallic material, and the bearing surfaces 60a of the pair of radial foil bearings 40, 40 may be formed with a material other than a metallic material, or vice versa. When multiple bearing surfaces 60a are formed with the coating layer 61, it is sufficient that any one of the bearing surfaces 60a has the coating layer 61 containing at least PAI. Preferably, all bearing surfaces 60a have the coating layer 61 containing at least PAI. In this case, the compositions of the coating layers 61 may be the same or different, but are preferably the same.

[0097] Although the turbo compressor 10 shown in FIG. 1 has been described as compressing air, 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, it may compress a refrigerant. The refrigerant may change state between gas and liquid depending on pressure and temperature. The turbo compressor may be applied to air conditioning systems such as an automotive cabin air conditioner, a cooling circuit for battery temperature control, and the like.

[0098] 1, the rotating body 24 is supported by an air film generated in the bearing gap 60b between the bearing surface 60a and the bearing surface 24g, but a gas film other than an air film may be generated in the bearing gap 60b. Examples of the gas film include a refrigerant film and a fluid film formed by the fluid compressed by the turbo compressor 10.

[0099] Although a foil bearing structure has been described above as an example of a plain bearing structure, the plain bearing structure may be a hydrodynamic bearing structure other than a foil bearing structure, or may be an oil-free bearing structure.

[0100] When the sliding bearing structure is a hydrodynamic bearing structure, a lubricating film is formed by a fluid lubricant supplied between the rotating body and the sliding bearing, and the bearing surface and the bearing surface are completely separated, resulting in operation in a fluid lubrication state. The fluid lubricant is preferably a lubricant other than lubricating oil or grease, and examples thereof include gas and water. The lubricant is a liquid lubricant containing a base oil. Grease is a lubricant containing a base oil and a thickener based on JIS K 2220:2013, and is a semi-solid or solid lubricant that does not flow when an external force is applied, but flows when an external force is applied.

[0101] When the plain bearing structure is an oil-free bearing structure, a lubricant is not supplied between the rotating body and the plain bearing, but 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 oil-free bearing structure operates in a boundary lubrication state where the bearing surface and the bearing surface are in localized contact.

[0102] In the turbo compressor 10 shown in FIG. 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 between the second impeller 26 and the second support portion 24c on the second end 24f side of the rotating shaft 24a.

[0103] The present invention will be explained in more detail below by showing test examples.

[0104] [Measurement of the aspect ratio Str of the surface texture] The aspect ratio Str of the surface texture of the outer peripheral surface 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, the outer peripheral surface of the ring was observed at 1000x magnification in a field of view measuring 290 μm wide x 230 μm long, and 3D shape data was measured at a pitch of 0.1 μm in the height direction. A waviness removal process with a cutoff wavelength of 0.20 mm was then performed, and the aspect ratio Str in that field of view was obtained. On the outer peripheral surface of the same ring, 3D shape data was measured at 2 to 5 fields of view using the above procedure, changing the observation location, to obtain the aspect ratio Str. The average aspect ratio Str in each field of view was calculated, and this was used as the aspect ratio Str of the surface texture of the outer peripheral surface of the ring.

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

[0106] Test Examples 1 to 14 In order to evaluate the friction and wear properties when the bearing surface of a plain bearing was caused to slide against the bearing surface of a rotating body, a friction and wear test was carried out according to the following procedure. Fig. 6 is a perspective view showing a schematic diagram of the friction and wear test.

[0107] As shown in Figure 6, a block 74 simulating a plain bearing was prepared by forming a 40 µm thick coating layer 74a on the top surface (the 16.5 mm wide x 6.2 mm long surface) of a raw material block made entirely of stainless steel and measuring 16.5 mm wide x 6.2 mm long x 10.2 mm high. The coating layer 74a imitates the coating layer on the bearing surface of a plain bearing, and the top surface of the block and the surface of the coating layer 74a are also flat. The coating layer 74a is made of 100 parts by mass of polyamideimide (PAI), 78 parts by mass of polytetrafluoroethylene (PTFE), and molybdenum disulfide (MoS ２ The upper surface of the raw material block was sprayed with a coating solution containing 114 parts by mass of hydroxybenzoates, followed by firing and polishing.

[0108] The outer peripheral surface of a raw material ring entirely formed with 64 titanium alloy was ground, and the grinding conditions were adjusted to form an outer peripheral surface 73a having the surface texture aspect ratio Str, load length ratio Mr1, and peak height Rpk shown in Table 1, thereby preparing a ring 73 simulating a rotating body. The ring 73 had a ring diameter φ of 35 mm and a width of the outer peripheral surface 73a of the ring of 8.15 mm. The outer peripheral surface of the raw material ring was ground using the following methods: Test Example 1: Lapping method using a liquid lapping agent containing abrasive grains; Test Examples 2-9: Traverse grinding method using a dressed grinding wheel (the dressing conditions and grinding conditions were adjusted); Test Examples 10-12: Grinding method in which a grinding wheel is pressed against the surface to be polished; Test Examples 13-14: Shot blasting method in which the outer peripheral surface of the raw material ring is ground by spraying blasting material.

[0109] With the coating layer 74a of the block 74 prepared above and the outer circumferential surface 73a of the ring 73 in contact (FIG. 6), a friction and wear test was carried out under the following conditions: Testing machine: UMT-TribolaB (manufactured by Bruker) Load: 50 gf Ring 73 rotation speed: 3000 rpm (steady) Test time: 30 seconds Lubrication environment: no lubrication Test start temperature: room temperature (as it happened)

[0110] After the friction and wear test, a scanning electron microscope (SEM) was used to obtain backscattered electron images at 100x magnification of the widthwise center of the outer peripheral surface 73a of the ring 73 of Test Examples 1 to 14. The results of the backscattered electron images obtained for Test Examples 1, 2, 8, 13, and 14 are shown in Figures 7 to 11, respectively. When carbon, oxygen, fluorine, sulfur, and molybdenum were detected by EDS (energy dispersive X-ray spectroscopy) analysis of the substance adhering to the outer peripheral surface 73a of the ring 73 (the black areas in the figures), the substance was determined to be a transfer material transferred from the coating layer 74a. In Test Example 1, highly regular streaks extending in one direction were formed, and as can be seen from the backscattered electron image shown in Figure 7, almost no transfer material transferred from the coating layer 74a was observed. As in Test Examples 2 to 14, when the degree of regularity of the unidirectional striations was small and irregular asperities were observed, particles transferred from the coating layer 74a were observed (see Figures 8 to 11). From this, it can be said that as the aspect ratio Str of the surface texture of the outer peripheral surface 73a of the ring 73 increases, it is more likely that particles transferred from the coating layer 74a will be prevented from falling off the outer peripheral surface 73a of the ring 73. This is thought to make it more likely that wear of the ring 73 will be reduced when the ring 73 slides against the block 74. Furthermore, it can be said that as the load length ratio Mr1 of the outer peripheral surface 73a of the ring 73 increases, it is more likely that particles transferred from the coating layer 74a will be prevented from falling off.

[0111] After the friction and wear test, a scanning electron microscope (SEM) was used to check for deposits on the surface of the coating layer 74a of the block 74, and if titanium was detected by EDS analysis of the deposits, the deposits were determined to be 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 found to be deposited in the form of particles (a small amount of titanium alloy deposits). C: Titanium alloy was found to be deposited in the form of stripes or lumps (a large amount of titanium alloy deposits).

[0112] 12 to 16 show the results of backscattered electron images and secondary electron images taken at 30x magnification using a scanning electron microscope (SEM) for the coating layer 74a of the blocks 74 of Test Examples 1, 2, 8, 13, and 14.

[0113]

[0114] From the results shown in Table 1, in Test Examples 2 to 14, in which the aspect ratio Str of the surface texture of the outer peripheral surface 73a of the ring 73 was 0.020 or more, no or little titanium alloy adhesion was observed on the coating layer 74a after the friction and wear test (FIGS. 14 and 15) (particularly in the areas surrounded by dashed lines in FIG. 13(a) and FIG. 16(a)). This shows that in Test Examples 2 to 14, wear of the outer peripheral surface 73a of the ring 73 was suppressed when the coating layer 74a of the block 74 and the outer peripheral surface 73a of the ring 73 were slid against each other. Furthermore, it can be seen that by having the aspect ratio Str of the surface texture of the outer peripheral surface 73a be 0.05 to 0.75 and the protruding peak height Rpk of the outer peripheral surface 73a be 0.3 to 0.7 μm, wear of the outer peripheral surface 73a of the ring 73 can be further suppressed when the coating layer 74a of the block 74 and the outer peripheral surface 73a of the ring 73 are caused to slide against each other.

[0115] On the other hand, from the results shown in Table 1 and Figures 12(a) and (b), it can be seen that in Test Example 1, in which the aspect ratio of the surface texture of the outer peripheral surface 73a of the ring 73 was smaller than 0.020, adhesion of titanium alloy was observed to the coating layer 74a after the friction and wear test, and the amount of wear of the ring outer peripheral surface 73a was larger than in Test Examples 2 to 14.

[0116] [Additional Notes] It will be understood by those skilled in the art that the exemplary embodiments described above are specific examples of the following embodiments. (Aspect 1) A sliding bearing structure comprising a rotating body and a sliding bearing supporting the rotating body, wherein the sliding bearing has a bearing surface formed with a coating layer containing at least polyamideimide, 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 texture of the bearing surface is 0.020 or more. (Aspect 2) The sliding bearing structure according to Aspect 1, wherein the aspect ratio Str of the surface texture of the bearing surface is 0.80 or less. (Aspect 3) The sliding bearing structure according to Aspect 1 or 2, wherein the aspect ratio Str of the surface texture of the bearing surface is 0.05 to 0.75, and the protruding peak height Rpk of the bearing surface is 0.3 to 0.7 μm. (Aspect 4) The sliding bearing structure according to Aspect 1 or 2, wherein the aspect ratio Str of the surface texture 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. (Aspect 5) The sliding bearing structure according to Aspect 1 or 2, wherein the aspect ratio Str of the surface texture 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. (Aspect 6) The sliding bearing structure according to Aspect 1 or 2, wherein the aspect ratio Str of the surface texture of the bearing surface is 0.6 or more, and the load length ratio Mr1 of the bearing surface is 10% or more. (Aspect 7) The sliding bearing structure according to any of Aspects 1 to 6, wherein the sliding bearing is a hydrodynamic gas bearing. (Aspect 8) The sliding bearing structure according to any of Aspects 1 to 7, wherein the coating layer further contains polytetrafluoroethylene. (Aspect 9) The sliding bearing structure according to any one of Aspects 1 to 8, wherein the coating layer further contains 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 Aspects 1 to 9, wherein the rotating body is formed from the metallic material. (Aspect 11) The sliding bearing structure according to any one of Aspects 1 to 10, wherein the metallic material is one or more selected from the group consisting of titanium, a titanium alloy, and stainless steel.(Aspect 12) A turbo fluid machine comprising: a rotating body; an actuating body that rotates integrally with the rotating body to pump a fluid; a housing that accommodates the rotating body and the actuating body; and a dynamic pressure gas bearing that rotatably supports the rotating body relative to the housing, wherein the dynamic pressure gas bearing has a bearing surface formed with a coating layer that contains at least polyamideimide, the rotating body has a bearing surface facing the bearing surface and formed of a metallic material, and an aspect ratio Str of the surface texture of the bearing surface is 0.020 or more. (Aspect 13) The turbo fluid machine according to Aspect 12, wherein the aspect ratio Str of the surface texture of the bearing surface is 0.05 to 0.75, and a protruding peak height Rpk of the bearing surface is 0.3 to 0.7 μm. (Aspect 14) The turbo fluid machine according to Aspect 12, which satisfies any of the following [a] to [c]: [a] the aspect ratio Str of the surface texture 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, and 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 more, and the load length ratio Mr1 of the bearing surface is 10% or more. (Aspect 15) The turbo fluid machine according to any of Aspects 12 to 14, wherein the hydrodynamic gas bearing is a foil bearing. (Aspect 16) The turbo fluid machine according to any of Aspects 12 to 15, wherein the metallic material is one or more selected from the group consisting of titanium, a titanium alloy, and stainless steel. (Aspect 17) The turbo fluid machine according to any one of Aspects 12 to 16, wherein the dynamic pressure gas bearing includes at least one of a thrust bearing that supports the rotating body in an 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 to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0118] The sliding bearing structure of the present invention can be used, for example, in turbo fluid machines, such as air compressors used in fuel cell systems, air conditioning compressors, turbines, generators, and fans.

[0119] REFERENCE SIGNS LIST 1 fuel cell system 10 turbo compressor (turbo fluid machine) 11 housing 24 rotating body 24b first support portion 24c second support portion 24d third support portion 24g bearing surface 25 first impeller (working body) 30 thrust foil bearing (thrust bearing) 40 radial foil bearing (radial bearing) 60 foil bearing (slide bearing, hydrodynamic gas bearing) 60a bearing surface 61 coating layer 61a resin binder 61b inorganic additive 61c transferred particles

Claims

1. A sliding bearing structure comprising a rotating body and a sliding bearing supporting the rotating body, wherein the sliding bearing has a bearing surface formed with a coating layer containing at least polyamideimide, the rotating body faces the bearing surface and has a bearing surface formed of a metallic material, and the aspect ratio Str of the surface texture of the bearing surface is 0.020 or more.

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

3. A sliding bearing structure according to claim 1, wherein the aspect ratio Str of the surface texture of said bearing surface is 0.05 to 0.75, and the protruding peak height Rpk of said bearing surface is 0.3 to 0.7 μm.

4. A sliding bearing structure according to claim 1, wherein the aspect ratio Str of the surface texture 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.

5. A sliding bearing structure according to claim 1, wherein the aspect ratio Str of the surface texture of the bearing surface is equal to or greater than 0.1 and less than 0.6, and the load length ratio Mr1 of the bearing surface is equal to or greater than 7.7%.

6. A sliding bearing structure according to claim 1, wherein the aspect ratio Str of the surface texture of the bearing surface is 0.6 or more, and 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 hydrodynamic gas bearing.

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

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

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

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

12. A turbo fluid machine comprising: a rotating body; an actuator that rotates integrally with said rotating body to pump a fluid; a housing that accommodates said rotating body and said actuator; and a dynamic pressure gas bearing that rotatably supports said rotating body relative to said housing, wherein said dynamic pressure gas bearing has a bearing surface formed with a coating layer that contains at least polyamideimide, said rotating body has a bearing surface facing said bearing surface and formed of a metallic material, and the aspect ratio Str of the surface texture of said bearing surface is 0.020 or more.

13. A turbo fluid machine according to claim 12, wherein the aspect ratio Str of the surface texture of said bearing surface is 0.05 to 0.75, and the height Rpk of the protruding peaks of said bearing surface is 0.3 to 0.7 μm.

14. A turbo fluid machine according to claim 12, which satisfies any of the following [a] to [c]: [a] the aspect ratio Str of the surface texture 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, and 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 more, and the load length ratio Mr1 of the bearing surface is 10% or more.

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

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

17. A 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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