Turbo Fluid Machinery

Abstract

To provide a turbo type fluid machine capable of improving durability of a coating layer formed on a bearing surface of a foil bearing and a borne surface to prolong the product life-time of the foil bearing.SOLUTION: A turbo type fluid machine comprises: a rotary body 24 which has a borne surface 24g; a working body which rotates integrally with the rotary body 24 to pump external fluid; a housing 11 which houses the rotary body 24 and working body; and a foil bearing 60 which has a bearing surface 60a opposed to the borne surface 24g, and supports the rotary body 24 rotatably relative to the housing 11. A coating layer 61 is formed on at least one of the borne surface 24g and bearing surface 60a. The coating layer 61 contains polyamide imide as a resin binder 61a and molybdenum disulfide as a solid lubricant 61b. The molybdenum disulfide is 42 mass% or larger in mass percentage of content for the polyamide imide.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a turbo fluid machine. [Background technology]

[0002] A conventional turbo fluid machine is disclosed in Patent Document 1. This turbo fluid machine includes a rotating body, a working body that rotates integrally with the rotating body to pump an external fluid, a housing that houses the rotating body and the working body, and a foil bearing that rotatably supports the rotating body relative to the housing.

[0003] The rotating body has a bearing surface, while the foil bearing has a bearing surface facing the bearing surface. The foil bearing supports the rotating body rotating at a low speed in a contact manner, and supports the rotating body rotating at a high speed in a non-contact manner. That is, when the rotating body rotates at a low speed, the foil bearing supports the rotating body rotating relatively with the bearing surface and the bearing surface in contact. When the rotating body rotates at a high speed, the bearing surface and the bearing surface are in a non-contact state, and the foil bearing supports the rotating body with a fluid film generated in the bearing gap between the bearing surface and the bearing surface.

[0004] When the foil bearing contacts and supports the rotating body at low speeds, the bearing surface and the supported surface slide against each other, which can easily cause problems such as seizure and damage to the sliding surfaces. For this reason, a coating layer is formed on the bearing surface and the supported surface in order to prevent seizure and damage to the sliding surfaces. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-82195 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the foil bearings in the turbo-type fluid machinery as described above, it is important to improve the durability of the coating layer in order to increase the product life.

[0007] The inventors aimed to improve the durability of the coating layer by using a high-hardness polyamideimide as the material for the coating layer, thereby improving the wear resistance of the coating layer. However, according to the inventors' tests, even if the bearing surface of the foil bearing is coated with a polyamideimide having high wear resistance, the durability of the coating layer is not improved as much as expected.

[0008] The present invention has been made in consideration of the above-mentioned conventional situation, and has as its object to provide a turbo fluid machine that can improve the durability of a coating layer formed on the bearing surface and the bearing surface of a foil bearing, thereby improving the product life of the foil bearing. [Means for solving the problem]

[0009] The turbo fluid machine of the present invention comprises: A rotating body having a bearing surface; an actuator that rotates integrally with the rotor to pump the external fluid; a housing that accommodates the rotating body and the operating body; a foil bearing having a bearing surface facing the bearing surface and supporting the rotor rotatably relative to the housing, a coating layer is formed on at least one of the bearing surface and the bearing surface; The coating layer contains polyamideimide as a resin binder and molybdenum disulfide as a solid lubricant, The mass percentage of the content of the molybdenum disulfide relative to the content of the polyamide-imide is 42 mass% or more. 127% by mass or less, The coating layer further contains polytetrafluoroethylene as a solid lubricant. It is characterized by:

[0010] The inventors have thoroughly studied how to improve the durability of the coating layer, and by changing their approach, have aimed to shorten the time that the coating layer slides against the counter material, i.e., to reduce the chance of the coating layer wearing away, by improving the floating ability of the foil bearing. They believed that in order to improve the floating ability of the foil bearing, it is important to improve the smoothness of the coating layer, and in particular to maintain that smoothness even after the initial wear caused by sliding against the counter material, and completed the present invention after repeated trial and error.

[0011] In the turbo fluid machine of the present invention, a coating layer is formed on at least one of the bearing surface and the bearing surface. In this coating layer, a predetermined amount of molybdenum disulfide as a solid lubricant is mixed with polyamideimide as a resin binder. Therefore, on the surface of the coating layer, a predetermined amount of molybdenum disulfide is dispersed in the polyamideimide.

[0012] Polyamideimide as a resin binder has high hardness and high wear resistance. On the other hand, polyamideimide has high toughness and tenacity. For this reason, during initial wear due to sliding with the counter material, the transferred particles (wear powder) of polyamideimide are largely torn off from the coating layer surface. As a result, the coating layer surface is largely roughened, and the surface roughness of the coating layer increases after initial wear. Then, in the foil bearing, the limit film thickness of the fluid lubrication, that is, the film thickness of the fluid film when the contact support is transferred to the non-contact support, in other words, the film thickness of the fluid film when the foil bearing reaches the floating rotation speed at which the rotor floats, increases, and the floating ability of the foil bearing decreases. If the floating ability of the foil bearing decreases, the coating layer has more opportunities to be worn by sliding with the counter material, leading to a decrease in the durability of the coating layer.

[0013] In this respect, the coating layer in the present invention has a predetermined amount of molybdenum disulfide dispersed in polyamideimide. Molybdenum disulfide is a layered solid lubricant having a sandwich crystal structure in which a Mo layer is sandwiched between S layers. When this molybdenum disulfide slides against a counter material, sliding easily occurs between the S layers, which have a weak bonding force, and low friction is achieved. In addition, in the initial wear, the molybdenum disulfide crushes or cuts the microprotrusions on the surface of the counter material, and fills the grooves, forming a conforming surface early on. Therefore, if molybdenum disulfide is dispersed on the surface of the coating layer, the sliding resistance can be reduced.

[0014] Furthermore, molybdenum disulfide is harder and less tough than polyamideimide. Therefore, the transferred particles of polyamideimide that are torn off from the surface of the coating layer due to initial wear are broken down by molybdenum disulfide, which is harder than polyamideimide. That is, molybdenum disulfide breaks down the transferred particles of polyamideimide. As a result, the transferred particles of polyamideimide during initial wear become smaller. If the transferred particles of polyamideimide become smaller, the surface of the coating layer is prevented from being significantly roughened, and the surface roughness of the coating layer can be prevented from increasing.

[0015] According to the inventors' tests, when the mass percentage of the molybdenum disulfide content relative to the polyamideimide content is 42 mass% or more (when the ratio of the mass of molybdenum disulfide to the mass of polyamideimide is 0.42 or more), the above-mentioned effect of molybdenum disulfide becomes significant.

[0016] If the smoothness of the coating layer after the initial wear is improved in this way, the limit film thickness of the fluid lubrication in the foil bearing can be reduced, and the floating ability can be improved. If the floating ability of the foil bearing is improved, the coating layer has less chance of being worn down by sliding with the counter material, and the durability of the coating layer can be improved.

[0017] Therefore, according to this turbo fluid machine, the durability of the coating layer formed on the bearing surface and the bearing surface of the foil bearing can be improved, thereby improving the product life of the foil bearing.

[0018] The mass percentage of the molybdenum disulfide content relative to the polyamideimide content can be 127 mass% or less. According to tests conducted by the inventors, the above-mentioned effect of molybdenum disulfide has been confirmed when the mass percentage of the molybdenum disulfide content relative to the polyamideimide content is 127 mass%.

[0019] The coating layer further contains polytetrafluoroethylene as a solid lubricant. Is .

[0020] When polytetrafluoroethylene is present on the surface of the coating layer, during initial wear caused by sliding with a counter material, the transferred particles of polytetrafluoroethylene adhere to the counter material to form a coating. Since the polytetrafluoroethylene coating is slippery and has low friction, the formation of this coating reduces the aggressiveness of the counter material against the coating layer. Therefore, the transferred particles of polyamideimide and molybdenum disulfide are prevented from being torn off from the coating layer. As a result, the amount of wear on the surface of the coating layer can be reduced.

[0021] The turbo fluid machine of the present invention is for pumping air to an on-board fuel cell, and preferably includes an electric motor that drives the rotor while rotating at 100,000 rpm or more.

[0022] A turbo fluid machine that pumps air to an on-board fuel cell is required to have a small size and a large gas transfer capacity, and therefore a high rotation speed of 100,000 rpm or more is required. In addition, it is preferable to use an electric motor so that the rotation speed can be changed according to the fluctuation of the power generation amount required for the fuel cell. When the motor drive is stopped at a high rotation speed of 100,000 rpm or more, the inertia of the intake gas acts on the rotor, and as a result, the bearing surface and the bearing surface may come into contact with each other with a large load. If the contact load is large, the transferred particles (abrasion powder) of polyamideimide are torn off in large amounts from the coating layer surface, causing the coating layer surface to be significantly roughened, and there is a risk that the surface roughness of the coating layer will increase after wear.

[0023] In this regard, since the coating layer of the present invention can suppress an increase in surface roughness, the turbo fluid machine of the present invention is suitable for pumping air to an on-board fuel cell. Effect of the Invention

[0024] According to the turbo fluid machine of the present invention, the durability of the coating layer formed on the bearing surface and the bearing surface of the foil bearing can be improved, thereby improving the product life of the foil bearing. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a cross-sectional view of a turbo compressor according to an embodiment. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing a part of the turbo compressor of the embodiment. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of a part of the turbo compressor of the embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view showing an enlarged portion of the coating layer of the rotor and the foil bearing of the turbo compressor of the embodiment. [Diagram 5] FIG. 5 is a schematic cross-sectional view illustrating the state in which the coating layer of the foil bearing is worn away in the turbo compressor of the embodiment. [Figure 6]FIG. 6 is a perspective view that typically illustrates the friction and wear test. [Figure 7] FIG. 7 is a diagram for explaining the test conditions for the friction and wear test. [Figure 8] FIG. 8 is a graph showing the relationship between the surface roughness of the coating layer after friction and wear testing and the molybdenum disulfide content. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0027] (Example) In this embodiment, the turbo fluid machine of the present invention is embodied in a turbo compressor 10. The turbo compressor 10 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 power. The turbo compressor 10 compresses air containing oxygen that is supplied to the on-board fuel cell.

[0028] 1, a turbo compressor 10, which is a turbo fluid machine, includes a housing 11. The housing 11 is made of a metal material, for example, an aluminum alloy. 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.

[0029] The motor housing 12 has a plate-like end wall 12a and a peripheral wall 12b. The peripheral wall 12b extends in a cylindrical shape from the outer periphery of the end wall 12a. The first plate 15 is connected to an end of the peripheral wall 12b of the motor housing 12 on the opening side, and closes the opening of the peripheral wall 12b.

[0030] A motor chamber S1 is defined by an inner surface 121a of the end wall 12a of the motor housing 12, an inner circumferential 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.

[0031] 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.

[0032] A recess 15c having a bottom surface 15d is formed on an end surface 15b of the first plate 15 opposite the motor housing 12. The recess 15c is a circular hole. The inside of the cylinder 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. An inner peripheral surface 15e of the recess 15c connects the end surface 15b and the bottom surface 15d.

[0033] The motor housing 12 has a second bearing retaining portion 22. The second bearing retaining portion 22 protrudes from the center of an inner surface 121a of an end wall 12a of the motor housing 12 toward the electric motor 18. 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 an 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.

[0034] As shown in Fig. 2, the second plate 16 is connected to an 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 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.

[0035] The compressor housing 13 is cylindrical and has a circular suction port 13a through which air is drawn. The compressor housing 13 is connected to an end face 16c of the second plate 16 opposite to the first plate 15. The axis of the suction port 13a of the compressor housing 13, the axis of the shaft insertion hole 16a of the second plate 16, and the axis of the first bearing holder 20 are aligned. The suction port 13a opens into the end face of the compressor housing 13 opposite to the second plate 16.

[0036] 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 first diffuser passage 13d are formed. The first impeller chamber 13b communicates with the suction port 13a. The discharge chamber 13c extends around the axis of the suction port 13a around the first impeller chamber 13b. The first diffuser passage 13d communicates with 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.

[0037] As shown in Fig. 3, the third plate 17 is connected to an 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.

[0038] 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.

[0039] Between the turbine housing 14 and the end face 17b of the third plate 17, a second impeller chamber 14b, a suction chamber 14c, and a second diffuser passage 14d are formed. 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 second diffuser passage 14d is in communication with 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.

[0040] As shown in FIG. 1, a rotor 24 is accommodated in the housing 11. The rotor 24 has a rotor 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 rotor shaft 24a has a first end portion 24e which is an end portion on the compressor housing 13 side, and a second end portion 24f which is an end portion on the turbine housing 14 side. The first support portion 24b is provided at a portion close to the first end portion 24e on the outer circumferential surface 240a of the rotor shaft 24a, and is disposed in the cylinder of the first bearing holder 20. The first support portion 24b is integrally formed with the rotor shaft 24a, and protrudes in an annular shape from the outer circumferential surface 240a of the rotor shaft 24a.

[0041] The rotating body 24 includes a rotating shaft 24a, a first supporting portion 24b, a second supporting portion 24c, and a third supporting portion 24d, all of which are made of a titanium alloy.

[0042] The second support portion 24c is provided on the outer circumferential surface 240a of the rotating shaft 24a at a position close to the second end portion 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 circumferential surface 240a of the rotating shaft 24a in a state where it protrudes in an annular shape from the outer circumferential surface 240a of the rotating shaft 24a. The second support portion 24c is rotatable integrally with the rotating shaft 24a.

[0043] 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 circumferential surface 240a of the rotating shaft 24a in a state where it protrudes in an annular shape from the outer circumferential 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 separated from the electric motor 18 in the axial direction of the rotating body 24. In the following description, the axial direction means the axial direction of the rotating body 24.

[0044] A first impeller 25 serving as an 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 accommodated 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 accommodated in the second impeller chamber 14b. The housing 11 accommodates the first impeller 25, the second impeller 26 and the rotor 24.

[0045] 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.

[0046] The electric motor 18 includes a cylindrical rotor 31 and a cylindrical stator 32. The rotor 31 is fixed to the rotating shaft 24a. The stator 32 is fixed to the housing 11. The rotor 31 is disposed radially inside the stator 32 and rotates integrally with the rotating body 24. 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. The rotating body 24 rotates integrally with the rotor 31 when a current flows from a battery (not shown) to the coil 34. The electric motor 18 rotates in a range of about 100,000 rpm to 120,000 rpm.

[0047] The fuel cell system 1 includes a fuel cell stack 100 as an on-board fuel cell, a turbo compressor 10, a supply flow path L1, a discharge flow path L2, and a branch flow path L3. The fuel cell stack 100 is composed of a plurality of fuel cells. The supply flow path L1 connects the discharge chamber 13c and the fuel cell stack 100. The discharge flow path L2 connects the fuel cell stack 100 and 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.

[0048] 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. Then, air sucked in from the intake port 13a is compressed by the first impeller 25 in the first impeller chamber 13b, passes through the first 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 through the supply passage L1. The air supplied to the fuel cell stack 100 is used to generate power in the fuel cell stack 100, and then discharged to the discharge passage L2 as the exhaust gas of the fuel cell stack 100. The exhaust gas of the fuel cell stack 100 is sucked into the intake chamber 14c through the discharge passage L2. The exhaust gas of the fuel cell stack 100 sucked into the intake chamber 14c is discharged to the second impeller chamber 14b through the second diffuser passage 14d. The second impeller 26 is rotated by the exhaust gas from the fuel cell stack 100 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. Thus, the first impeller 25 as an actuator rotates integrally with the rotor 24 and pumps air as an external fluid. The exhaust gas from the fuel cell stack 100 discharged into the second impeller chamber 14b is discharged to the outside from the discharge port 14a.

[0049] The turbo compressor 10 has a plurality of foil bearings 60 that rotatably support the rotor 24 relative to the housing 11. The plurality of foil bearings 60 include a pair of thrust foil bearings 30, 30 and a pair of radial foil bearings 40, 40. The pair of thrust foil bearings 30, 30 support the third support portion 24d of the rotor 24 in the axial direction of the rotor 24 rotatably relative to the housing 11. The pair of radial foil bearings 40, 40 support the first support portion 24b and the second support portion 24c of the rotor 24 in a direction perpendicular to the axial direction of the rotor 24 rotatably relative to the housing 11.

[0050] The pair of thrust foil bearings 30, 30 are arranged in the thrust bearing accommodating chamber S2. The pair of thrust foil bearings 30, 30 are arranged to sandwich the third support portion 24d serving 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 arranged on the first end portion 24e side of the rotating shaft 24a with respect to the third support portion 24d. The other thrust foil bearing 30 is arranged on the second end portion 24f side of the rotating shaft 24a with respect to the third support portion 24d.

[0051] 2, an end face of the third support portion 24d on the side of the first end 24e of the rotating shaft 24a is a bearing surface 24g that is axially supported by one thrust foil bearing 30. One thrust foil bearing 30 has a bearing surface 60a facing this bearing surface 24g. Similarly, an end face of the third support portion 24d on the side of the second end 24f of the rotating shaft 24a is a 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 facing this bearing surface 24g.

[0052] As shown in FIG. 2 and FIG. 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. In 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 is a bearing surface 24g 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 facing the bearing surface 24g. Similarly, in 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 is a 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 facing the bearing surface 24g.

[0053] As shown in FIG. 4, a coating layer 61 is formed on the bearing surface 60a of each foil bearing 60, that is, the bearing surface 60a of each thrust foil bearing 30, 30 and the bearing surface 60a of each radial foil bearing 40, 40. Each coating layer 61 has basically the same configuration. The coating layer 61 contains polyamideimide (PAI) as a resin binder 61a, molybdenum disulfide (MoS2) as a solid lubricant 61b, and polytetrafluoroethylene (PTFE) as a solid lubricant. In the coating layer 61, molybdenum disulfide and polytetrafluoroethylene as the solid lubricant 61b are contained in a predetermined compounding ratio with respect to polyamideimide as the resin binder 61a. Each coating layer 61 is formed by various methods such as application by spray, brush, knife, or applicator, or screen printing. Each coating layer 61 may be formed either before or after the molding process of the foil bearing 60. Additionally, each coating layer 61 may or may not be polished after formation.

[0054] The basic configuration of the thrust foil bearing 30 and the radial foil bearing 40 is not particularly limited, and the basic configuration of a so-called fluid bearing may be adopted. The thrust foil bearing 30 and the radial foil bearing 40 as the foil bearing 60 support the rotor 24 that rotates relatively with the bearing surface 60a and the bearing surface 24g in contact with each other during low-speed rotation until the rotation speed of the rotor 24 reaches the floating rotation speed, and when the rotor 24 rotates at high speed and reaches the floating rotation speed, the bearing surface 60a and the bearing surface 24g are in a non-contact state and support the rotor 24 with a fluid film generated in the bearing gap 60b between them.

[0055] As shown in Figs. 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.

[0056] 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 and the inlet 51a of the first passage 51. The first passage 51 communicates with the motor chamber S1 via the thrust bearing accommodating chamber S2 and one of the radial foil bearings 40.

[0057] 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.

[0058] 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 by the intercooler 110 while flowing through the branch passage L3. The cooling air that has flowed into the first passage 51 flows into the thrust bearing accommodation chamber S2.

[0059] The cooling air that flows into the thrust bearing accommodation chamber S2 flows mainly from the inner periphery side to the outer periphery side via one of the thrust foil bearings 30. Thereafter, the cooling air that passes radially outside the third support portion 24d flows mainly from the outer periphery side to the inner periphery side via the other thrust foil bearing 30.

[0060] The cooling air that has passed through the thrust bearing accommodating 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 exhaust port 52a.

[0061] In this manner, as the cooling air flows through the cooling passage 50, 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.

[0062] In this turbo compressor 10, a coating layer 61 is formed on a bearing surface 60a of a foil bearing 60. In this coating layer 61, a predetermined amount of molybdenum disulfide as a solid lubricant 61b is mixed with polyamideimide as a resin binder 61a. Therefore, on the surface of the coating layer 61, a predetermined amount of molybdenum disulfide is dispersed in the polyamideimide.

[0063] Polyamideimide as the resin binder 61a has high hardness and high wear resistance. On the other hand, polyamideimide has high toughness and tenacity. For this reason, if a predetermined solid lubricant is not present on the surface of the coating layer 61, the transferred particles (wear powder) of polyamideimide are largely torn off from the surface of the coating layer 61 during initial wear due to sliding with the counter material. As a result, the surface of the coating layer 61 is largely roughened, and the surface roughness of the coating layer 61 increases after initial wear. Then, in the foil bearing 60, the limit film thickness of the fluid lubrication increases, and the floating ability of the foil bearing 60 decreases. If the floating ability of the foil bearing 60 decreases, the coating layer 61 has more opportunities to be worn by sliding with the counter material, leading to a decrease in the durability of the coating layer 61.

[0064] In this regard, the coating layer 61 in the turbo compressor 10 has a predetermined amount of molybdenum disulfide dispersed in polyamideimide. Molybdenum disulfide is a layered solid lubricant having a sandwich crystal structure in which a Mo layer is sandwiched between S layers. When this molybdenum disulfide slides against a counter material, slippage easily occurs between the S layers, which have a weak bonding force, resulting in low friction. In addition, in the initial wear, the molybdenum disulfide crushes or cuts the minute protrusions on the surface of the counter material, and fills in the grooves, forming a conforming surface early on. Therefore, if molybdenum disulfide is dispersed on the surface of the coating layer 61, the sliding resistance can be reduced.

[0065] Furthermore, molybdenum disulfide is harder and less tough than polyamideimide. Therefore, as shown in FIG. 5, the transferred polyamideimide particles 61c torn off from the surface of the coating layer 61 due to initial wear are broken down by molybdenum disulfide, which is harder than polyamideimide. That is, molybdenum disulfide breaks down the transferred polyamideimide particles 61c. As a result, the transferred polyamideimide particles 61c during initial wear become smaller. If the transferred polyamideimide particles 61c become smaller, the surface of the coating layer 61 is prevented from being significantly roughened, and the surface roughness of the coating layer 61 can be prevented from increasing.

[0066] If the smoothness of the coating layer 61 after the initial wear is improved in this way, the limit film thickness of the fluid lubrication in the foil bearing 60 can be reduced, and the flotation capability can be improved. If the flotation capability of the foil bearing 60 is improved, the coating layer 61 has less chance to be worn down by sliding with the counter material, and therefore the durability of the coating layer 61 can be improved.

[0067] Therefore, according to the turbo compressor 10, the durability of the coating layer 61 formed on the bearing surface 60a of the foil bearing 60 can be improved, and the product life of the foil bearing 60 can be improved.

[0068] Moreover, the coating layer 61 in the turbo compressor 10 further contains polytetrafluoroethylene as a solid lubricant. If polytetrafluoroethylene is present on the surface of the coating layer 61, during initial wear due to sliding with a counter material, the transferred particles of polytetrafluoroethylene adhere to the counter material to form a coating. Since the polytetrafluoroethylene coating is slippery and has low friction, the formation of this coating reduces the aggressiveness of the counter material against the coating layer 61. Therefore, the transferred particles of polyamideimide and molybdenum disulfide are prevented from being torn off from the coating layer 61. As a result, the amount of wear on the surface of the coating layer 61 can be reduced.

[0069] A turbo-type fluid machine such as this turbo compressor 10 that compresses air to a fuel cell stack 100 as an on-board fuel cell is required to have a small size and a large flow rate of gas transfer capability, and therefore a high rotation speed of 100,000 rpm or more is required. In addition, an electric turbo-type fluid machine that can change the rotation speed according to the fluctuation of the power generation amount required for the fuel cell stack 100 is preferable. When the electric motor 18 is stopped at a high rotation speed of 100,000 rpm or more, the inertia of the intake gas acts on the rotor 24, and as a result, the bearing surface 60a of the foil bearing 60 and its counterpart bearing surface 24g may come into contact with each other with a large load. If the contact load is large, the transferred particles (wear powder) of polyamideimide are torn off in large amounts from the surface of the coating layer 61, the surface of the coating layer 61 is significantly roughened, and the surface roughness of the coating layer 61 may become large after wear.

[0070] In this regard, the coating layer 61 in the turbo compressor 10 can suppress the surface roughness from increasing. 。

[0071] (Friction and wear test) The evaluation materials for Test Nos. 1 to 5 shown in Table 1 were prepared. That is, a coating layer in which molybdenum disulfide as a solid lubricant was contained in polyamideimide as a resin binder at the compounding ratio shown in Table 1 was formed on the sliding surface of a SUS substrate to prepare the evaluation materials for Test Nos. 1 to 5. In Table 1, Test No. 2 indicates that the ratio of the mass of molybdenum disulfide to the mass of polyamideimide was 0.42, and Test No. 5 indicates that the ratio of the mass of molybdenum disulfide to the mass of polyamideimide was 1.27. The same applies to the other evaluation materials.

[0072] [Table 1]

[0073] For the evaluation materials of Test Nos. 1 to 5, the polyamideimide used as the resin binder 61a is hard and has high strength among polyamideimides. The Vickers hardness of the coating layer 61 in the evaluation materials of Test Nos. 1, 2, 4, and 5 is 20 MHV or more. The average particle size of molybdenum disulfide in the evaluation materials of Test Nos. 1 to 5 is 1.6 μm.

[0074] A block-on-ring friction and wear test was carried out under the following conditions for the evaluation materials of Test Nos. 1 to 5. This test was carried out by rotating a ring 71 as a mating material and sliding the coating layer of a block 72 as an evaluation material against the outer circumferential surface of the ring 71 with a predetermined load, as shown in Fig. 6.

[0075] As shown in Figure 7, the ring rotation speed was increased to 5,000 rpm over 5 seconds, and then decreased to 0 rpm over 5 seconds. This Go-Stop cycle was repeated for 20 minutes.

[0076] <Testing machine> UMT-3 (manufactured by Bruker) <Test mode> Block on Ring (Go-Stop Repeat) <Evaluation material> Block shape: 6.2 x 10.2 x 16.5 mm Material: Each coating layer is formed on a SUS304 base material (spray coating / baking / polishing) <Mating material> Ring shape: Φ35×8.77mm Material: 64 titanium <Load> Approximately 0.5N (50gf) <Contact pressure> 0.04MPa@wear width 2mm <Rotational speed> 5000rpm <Maximum sliding speed> 9.16m / sec (sliding speed equivalent to when foil bearings float) <Acceleration / Deceleration time> 5sec / 5sec <Lubrication environment> No lubrication required <Test start temperature> Room temperature <Exam time> 20min <Notes> Forced air blowing (purpose: to suppress temperature rise due to sliding)

[0077] (Relationship between molybdenum disulfide content and surface roughness) The surface roughness of the coating layer after the friction and wear test was measured for the evaluation materials of Test Nos. 1 to 5. That is, the surface roughness of the coating layer was measured along the rotation direction of ring 71 using a stylus-type roughness meter under measurement conditions conforming to JIS B 0633:2001. The results are shown in FIG.

[0078] As shown in Figure 8, in the evaluation material of Test No. 1, which did not contain molybdenum disulfide, the surface of the coating layer after the initial wear was significantly roughened, whereas in the evaluation materials of Test Nos. 2 to 5, which contained 42 mass% or more of molybdenum disulfide relative to the polyamide-imide content, the surface of the coating layer after the initial wear was prevented from being significantly roughened. This demonstrated the effect of including 42 mass% or more of molybdenum disulfide in polyamide-imide.

[0079] Although the present invention has been described above with reference to the embodiments, it goes without saying that the present invention is not limited to the above embodiments and can be modified as appropriate without departing from the spirit of the present invention.

[0080] For example, in the above embodiment, the coating layer 61 is formed on the bearing surface 60a of the foil bearing 60, but the present invention is not limited to this, and the coating layer 61 may be formed on the bearing surface 24g of the mating material instead of the bearing surface 60a of the foil bearing 60, or the coating layer 61 may be formed on both the bearing surface 60a of the foil bearing 60 and the bearing surface 24g of the mating material.

[0081] In the above embodiment, the coating layer 61 contains molybdenum disulfide and polytetrafluoroethylene as solid lubricants, but the present invention is not limited to this. The coating layer 61 may contain only molybdenum disulfide as a solid lubricant without containing polytetrafluoroethylene, or other solid lubricants, various additives, and fillers may be added as necessary. [Industrial Applicability]

[0082] The present invention can be used in an air compressor or the like used in a fuel cell system. [Explanation of symbols]

[0083] 24...Rotating body 24g…Bearing surface 60...Foil bearing 60a...Bearing surface 61...Coating layer 61a…Resin binder 61b...Solid lubricant

Claims

1. A rotating body having a bearing surface; an actuator that rotates integrally with the rotor to pump the external fluid; a housing that accommodates the rotating body and the operating body; a foil bearing having a bearing surface facing the bearing surface and supporting the rotor rotatably relative to the housing, a coating layer is formed on at least one of the bearing surface and the bearing surface; The coating layer contains polyamideimide as a resin binder and molybdenum disulfide as a solid lubricant, a mass percentage of the content of the molybdenum disulfide relative to the content of the polyamide-imide is 42 mass% or more and 127 mass% or less; The turbo fluid machine, wherein the coating layer further contains polytetrafluoroethylene as a solid lubricant.

2. A turbo-type fluid machine for pumping air to an on-board fuel cell, comprising:

2. The turbo fluid machine according to claim 1, further comprising an electric motor that drives the rotor while rotating at 100,000 rpm or more.

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