Foil bearings and fluid machinery

Abstract

To suppress the lowering of the bearing performance of a foil bearing.SOLUTION: A first foil bearing 20 and a second foil bearing 22 have a bearing housing 71, a top foil 72 which has a bearing face 72s, and a bump foil 73 which is arranged between the top foil 72 and the bearing housing 71, and in which a crest part 81 contacting with an external peripheral face 72f of the top foil 72 and a trough part 82 contacting with an internal peripheral face 71g of the bearing housing 71 are alternately arranged along a rotation direction of a rotating shaft 40. When a load which is received by the bearing face 72s from the rotating shaft 40 exceeds a prescribed load, the bump foil 73 supports the top foil 72 by the abutment of the crest part 81 with even the internal peripheral face 71g of the bearing housing 71, and by the abutment of the trough part 82 with even the external peripheral face 72f of the top foil 72, and the top foil 72 and the bump foil 73 locally constitute a plane bearing, thus supporting the rotating shaft 40.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a foil bearing and a fluid machine. [Background technology]

[0002] A foil bearing that rotatably supports a rotating body is known. The foil bearing includes a top foil, a bump foil, and a housing. The housing has an insertion hole through which the rotating body is inserted. The top foil faces the rotating body and has a bearing surface. The bump foil is disposed between the top foil and the housing. The bump foil includes a peak portion that contacts an outer peripheral surface of the top foil and a valley portion that contacts an inner peripheral surface of the housing. The peak portion and the valley portion are disposed alternately along the rotational direction of the rotating body.

[0003] When the rotation speed of the rotor reaches the levitation rotation speed, the rotor is levitated relative to the foil bearing due to the dynamic pressure of the air film generated between the rotor and the bearing surface. As a result, the foil bearing supports the rotor without coming into contact with it.

[0004] Here, if an excessive load is applied to the rotating body, the rotating body may come too close to the bearing surface, which may result in an excessive load acting on the top foil. At this time, the portion of the top foil that receives the excessive load is displaced so as to come closer to the housing, and the top foil presses the peaks of the bump foil. The bump foil is deformed so that the peaks come closer to the housing. If the bump foil is damaged due to such deformation, the bearing performance of the foil bearing may be reduced. In a fluid machine equipped with a foil bearing, if the bearing performance of the foil bearing described above is reduced, the reliability of the fluid machine will be reduced, so it is necessary to suppress such damage to the bump foil.

[0005] The foil bearing described in Patent Document 1 has a protrusion protruding from the inner surface of the housing toward the top foil, in addition to the bump foil. When the above-mentioned excessive load acts on this foil bearing, the part of the top foil that receives the load abuts against the protrusion. This makes it difficult for the bump foil to receive excessive pressure from the top foil, thereby suppressing damage to the bump foil. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent Application Publication No. 2021 / 0010531 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the foil bearing described in Patent Document 1, when the top foil is pressed against the convex portion, the portion of the top foil that contacts the convex portion may deform to conform to the shape of the convex portion. If such deformation of the top foil occurs, the bearing performance of the foil bearing may be degraded. [Means for solving the problem]

[0008] A foil bearing that solves the above problem includes a housing having an insertion hole through which a rotating body is inserted, a cylindrical top foil facing the rotating body and having a bearing surface, and a thin plate-like bump foil that is arranged between the top foil and the housing, in which peaks that contact an outer circumferential surface of the top foil and valleys that contact an inner circumferential surface of the housing are alternately arranged along a rotation direction of the rotating body, and in which the peaks and valleys extend in the rotation direction to elastically support the top foil, wherein the bearing surface is supported by the rotating body. When the load is equal to or less than a predetermined load, the bump foil supports the top foil with the peak portion having a gap between it and the housing and the valley portion having a gap between it and the top foil, and when the load that the bearing surface receives from the rotating body exceeds the predetermined load, the bump foil supports the top foil with the peak portion abutting also the inner surface of the housing and the valley portion abutting also the outer surface of the top foil, and the top foil and the bump foil locally form a plain bearing to support the rotating body.

[0009] According to the above configuration, when the load received by the bearing surface from the rotating body exceeds a predetermined load, the bump foil supports the top foil by contacting the inner peripheral surface of the housing with the peaks and contacting the outer peripheral surface of the top foil with the valleys. This makes it possible to suppress deformation of the bump foil that would cause a deterioration in the bearing performance of the foil bearing. When the load received by the bearing surface from the rotating body exceeds a predetermined load, the top foil and the bump foil locally constitute a plain bearing, so that the foil bearing can support the rotating shaft by dynamic pressure. Therefore, even under a situation where an excessive load acts on the top foil, it is possible to suppress a deterioration in the bearing performance of the foil bearing. Note that "contact" includes an interpretation of coming close to each other in addition to touching each other. Therefore, the outer peripheral surface of the top foil and the peaks may be in contact before the rotating body rotates, or the outer peripheral surface of the top foil and the peaks may not be in contact with each other, and the peaks may come close to the outer peripheral surface of the top foil and touch it after the rotating body rotates. In addition, before the rotating body rotates, the inner surface of the housing and the valley portion may be in contact, or the inner surface of the housing and the valley portion may not be in contact, and the valley portion may approach and touch the inner surface of the housing after the rotating body rotates.

[0010] In a foil bearing, when the load that the bearing surface receives from the rotating body exceeds the predetermined load and then returns to below the predetermined load, the bump foil's own elastic force causes the peak portion to move away from the inner surface of the housing and the valley portion to move away from the outer surface of the top foil.

[0011] According to the above-mentioned configuration, when the load received by the bearing surface from the rotating body returns to a predetermined load or less, the elastic force of the bump foil itself causes the peaks to move away from the inner peripheral surface of the housing and the valleys to move away from the outer peripheral surface of the top foil. Therefore, since a reversible bump foil can be used, the deterioration of the bearing performance of the foil bearing can be further suppressed.

[0012] In a foil bearing, the bump foil is composed of a plurality of divided bodies divided in the rotational direction, each of the divided bodies having a fixed end fixed to the housing and a free end not fixed to the housing in the rotational direction, and each of the divided bodies is arranged so that a gap is formed between adjacent fixed ends and free ends regardless of elongation.

[0013] According to the above-mentioned configuration, even if the bump foil stretches in the rotation direction of the rotor, the adjacent divided bodies do not overlap each other. Therefore, the displacement of the bump foil in the rotation direction of the rotor is not hindered, and the bump foil can suitably elastically support the top foil.

[0014] In the foil bearing, the gap forms a herringbone-shaped groove, and when the load that the bearing surface receives from the rotating body exceeds the specified load, the peak portion also abuts the inner surface of the housing and the valley portion also abuts the outer surface of the top foil to support the top foil, thereby forming a herringbone bearing locally and supporting the rotating body.

[0015] According to the above configuration, when the load received by the bearing surface from the rotating body exceeds a predetermined load, the portion of the top foil located radially inward of the rotating body from the gap between the adjacent fixed end and free end is curved so as to be pressed toward the gap. This allows the foil bearing to support the rotating body by locally forming a herringbone bearing. This further prevents the bearing performance of the foil bearing from deteriorating.

[0016] In the foil bearing, the peaks and valleys are preferably formed so as not to exceed the yield strength limit of the material after the predetermined load is exceeded. According to the above configuration, even after the load that the bearing surface receives from the rotating body exceeds a predetermined load, deformation of the bump foil that would deteriorate the bearing performance of the foil bearing can be suppressed.

[0017] In a foil bearing, when no load from the rotating body acts on the bearing surface, the distance between the adjacent peaks and valleys in the rotational direction is L1, the thickness of the bump foil is h1, and the distance between the outer peripheral surface of the bump foil at the peaks in the radial direction of the rotating body and the inner peripheral surface of the housing is H1. 2 It is preferable that the relationship be / 600h1>H1.

[0018] According to the above configuration, the maximum amount of displacement of the bump foil in the radial direction of the rotating body is H1, which is the amount of displacement when the bump foil moves along the inner peripheral surface of the housing. When the amount of displacement is equal to or less than H1, the bump foil can be elastically deformed. Since the deformed bump foil is not plastically deformed, it can return to the shape of the bump foil when the load received by the bearing surface from the rotating body is equal to or less than a predetermined load. Therefore, since a reversible bump foil can be used, the deterioration of the bearing performance of the foil bearing can be further suppressed.

[0019] The fluid machine that solves the above problem is a fluid machine comprising the rotating body, an impeller that compresses a fluid by rotating integrally with the rotating body, an impeller housing in which the rotating body and the impeller are accommodated, and any one of the foil bearings listed above, wherein the impeller housing has a shroud surface that covers an outer periphery of the impeller, and even when the top foil and the bump foil locally form a plain bearing, the tip clearance between the impeller and the shroud surface is greater than 0.

[0020] According to the above configuration, even if the top foil is displaced so that the top foil and the bump foil locally form a plain bearing, collision of the impeller with the shroud surface can be suppressed.

[0021] The fluid machine that solves the above problem is a fluid machine comprising the rotating body, an impeller that compresses a fluid by rotating integrally with the rotating body, an impeller housing in which the rotating body and the impeller are accommodated, and any one of the foil bearings described above, wherein the impeller housing has a shroud surface that covers the outer periphery of the impeller, and when no load from the rotating body acts on the bearing surface, the distance between the outer periphery of the bump foil at the ridge portion in the radial direction of the rotating body and the inner periphery of the housing is H1, the minimum value of the gap between the impeller and the shroud surface in the radial direction is greater than H1.

[0022] According to the above configuration, the impeller can be prevented from colliding with the shroud surface while the amount of displacement of the bump foil in the radial direction of the rotor is equal to or less than H1. Therefore, even if the top foil is displaced so that the top foil and the bump foil locally form a plain bearing, the impeller can be prevented from colliding with the shroud surface. Effect of the Invention

[0023] According to the present invention, deterioration of the bearing performance of the foil bearing can be suppressed. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a cross-sectional view showing a fluid machine. [Diagram 2] FIG. 2 is an exploded perspective view showing a first foil bearing in the first embodiment. [Diagram 3] FIG. 2 is a cross-sectional view showing a first foil bearing and a rotating shaft in the first embodiment. [Figure 4] FIG. 2 is a cross-sectional view showing a first foil bearing of the first embodiment when in a first state. [Diagram 5] FIG. 2 is a perspective view showing a first foil bearing in a first state according to the first embodiment. [Figure 6] FIG. 4 is a cross-sectional view showing the first foil bearing in the second state of the first embodiment. [Figure 7]FIG. 4 is a perspective view showing the first foil bearing in the second state according to the first embodiment. [Figure 8] FIG. 2 is a schematic diagram showing a bump foil for one pitch. [Figure 9] FIG. 13 is a schematic diagram showing a beam model. [Figure 10] FIG. 11 is a cross-sectional view showing a first foil bearing of a second embodiment in a first state. [Figure 11] FIG. 11 is a cross-sectional view showing the first foil bearing of the second embodiment in a second state. [Figure 12] FIG. 11 is a perspective view showing a first foil bearing of the second embodiment when in a first state. [Figure 13] FIG. 11 is a perspective view showing the first foil bearing of the second embodiment when in a second state. [Figure 14] FIG. 11 is a perspective view showing a first foil bearing of a modified example in a first state. [Figure 15] FIG. 11 is a perspective view showing the first foil bearing in a second state of the modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] (First embodiment) A first embodiment of a foil bearing and a fluid machine will be described below with reference to Figures 1 to 9. For convenience of explanation, the foil bearing will be described after the fluid machine.

[0026] <Basic Configuration of Fluid Machine 10> As shown in Fig. 1, the fluid machine 10 includes a rotating shaft 40 as a rotating body, a first impeller 34 as an impeller, and a second impeller 35 as an impeller. The fluid machine 10 includes a housing 11. The fluid machine 10 includes a first foil bearing 20 as a foil bearing, and a second foil bearing 22 as a foil bearing. The fluid machine 10 includes an electric motor 39. The fluid machine 10 of this embodiment is mounted on a vehicle. The fluid machine 10 can be used, for example, as a centrifugal compressor that compresses air as an oxygen-containing fluid supplied to a fuel cell of a fuel cell vehicle, or a centrifugal compressor that compresses a refrigerant in an on-board refrigeration circuit.

[0027] The housing 11 is made of a metal material. Examples of the material of the housing 11 include aluminum. The housing 11 has a motor housing 12, a first impeller housing 13 as an impeller housing, a second impeller housing 14 as an impeller housing, a first plate 15, a second plate 16, and a third plate 17. In other words, the fluid machine 10 includes the first impeller housing 13 as an impeller housing, and the second impeller housing 14 as an impeller housing. The housing 11 includes a bearing housing 71 (FIG. 2) described later.

[0028] The motor housing 12 has a cylindrical peripheral wall 12a and a flat end wall 12b located at a first end of the peripheral wall 12a. A second end of the peripheral wall 12a is an open end. A first plate 15 closes the second end of the motor housing 12. A motor chamber 51 is defined by the inner surface of the motor housing 12 and the first plate 15. An electric motor 39 is accommodated in the motor chamber 51.

[0029] The first plate 15 has a first bearing retaining portion 18. The first bearing retaining portion 18 is cylindrical. A recess 15c is formed in an end face 15b of the first plate 15 opposite the motor housing 12. The inside of the first bearing retaining portion 18 and the inside of the recess 15c communicate with each other via an opening in a bottom face 15d of the recess 15c. The axis of the recess 15c and the axis of the first bearing retaining portion 18 coincide with each other. A side face 15e of the recess 15c connects the end face 15b and the bottom face 15d.

[0030] The end wall 12b of the motor housing 12 has a second bearing retaining portion 19. The second bearing retaining portion 19 is cylindrical. The second bearing retaining portion 19 is open at both end faces of the end wall 12b. The axis of the second bearing retaining portion 19 coincides with the axis of the first bearing retaining portion 18.

[0031] The second plate 16 is connected to the first plate 15. The second plate 16 extends along the first plate 15. A first shaft insertion hole 16a is formed in the center of the second plate 16. The first shaft insertion hole 16a penetrates the second plate 16. The first shaft insertion hole 16a communicates with the recess 15c. The axis of the first shaft insertion hole 16a coincides with the axis of the recess 15c. A thrust bearing accommodating chamber 52 is defined by the inner surface that defines the recess 15c in the first plate 15 and the second plate 16.

[0032] The first impeller housing 13 is cylindrical and has a circular suction port 13a through which air, for example, is drawn as a working fluid. The first impeller housing 13 is connected to a second plate 16. The axis of the suction port 13a coincides with the axis of a first shaft insertion hole 16a of the second plate 16. The suction port 13a opens at an end face of the first impeller housing 13 opposite to the second plate 16. A first impeller chamber 13b, a discharge chamber 13c, and a first diffuser passage 13d are formed between the first impeller housing 13 and the second plate 16.

[0033] The first impeller chamber 13b communicates with the suction port 13a. The discharge chamber 13c extends around the periphery of the first impeller chamber 13b around the axis of the suction port 13a. The first diffuser passage 13d communicates between the first impeller chamber 13b and the discharge chamber 13c. The first impeller chamber 13b communicates with the first shaft insertion hole 16a of the second plate 16.

[0034] The first impeller housing 13 includes a first shroud surface 53a as a shroud surface. The first shroud surface 53a defines a first impeller chamber 13b in cooperation with the second plate 16. The first shroud surface 53a has a truncated cone shape.

[0035] The third plate 17 is connected to the end wall 12b of the motor housing 12. A second shaft insertion hole 17a is formed in the center of the third plate 17. The second shaft insertion hole 17a communicates with the inside of the second bearing holder 19. The axis of the second shaft insertion hole 17a coincides with the axis of the second bearing holder 19.

[0036] The second impeller housing 14 is cylindrical and has a circular discharge port 14a through which air is drawn. The second impeller housing 14 is connected to an end face of the third plate 17 opposite the motor housing 12. The axis of the discharge port 14a coincides with the axis of a second shaft insertion hole 17a of the third plate 17. The discharge port 14a opens into an end face of the second impeller housing 14 opposite the third plate 17. A second impeller chamber 14b, a suction chamber 14c, and a second diffuser passage 14d are formed between the second impeller housing 14 and the third plate 17.

[0037] The second impeller chamber 14b communicates 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 communicates between the second impeller chamber 14b and the suction chamber 14c. The second impeller chamber 14b communicates with the second shaft insertion hole 17a.

[0038] The second impeller housing 14 includes a second shroud surface 53b as a shroud surface. The second shroud surface 53b defines a second impeller chamber 14b in cooperation with the third plate 17. The second shroud surface 53b has a truncated cone shape.

[0039] <Rotation axis 40> A rotating shaft 40 serving as a rotating body is accommodated in the housing 11. The rotating shaft 40 is rotated by an electric motor 39. A portion of the rotating shaft 40 is located in the first impeller chamber 13b and the second impeller chamber 14b. As a result, the rotating shaft 40 is accommodated in the first impeller housing 13 and the second impeller housing 14.

[0040] The rotating shaft 40 passes through the first impeller chamber 13b, the first shaft insertion hole 16a, the recess 15c of the first plate 15, the inside of the first bearing holder 18, the motor chamber 51, the inside of the second bearing holder 19, the second shaft insertion hole 17a, and the second impeller chamber 14b, in that order. The axis SL of the rotating shaft 40 coincides with the central axes of the first bearing holder 18, the second bearing holder 19, the first shaft insertion hole 16a, the second shaft insertion hole 17a, the suction port 13a, and the discharge port 14a.

[0041] In the following description, the "axial direction of the rotating shaft 40", which is the direction in which the axis SL of the rotating shaft 40 extends, may be referred to as the "thrust direction". The "radial direction of the rotating shaft 40", which is the direction in which the diameter of the rotating shaft 40 extends, may be referred to as the "radial direction". The axial direction of the rotating shaft 40 may also be referred to as the axial direction X. The radial direction of the rotating shaft 40 may also be referred to as the radial direction Y. The radial direction Y corresponds to the radial direction of the rotating body.

[0042] The rotating shaft 40 is provided with a disk-shaped support plate 33. The support plate 33 protrudes from the outer circumferential surface of the rotating shaft 40. The support plate 33 is press-fitted into the outer circumferential surface of the rotating shaft 40. The support plate 33 rotates integrally with the rotating shaft 40. The support plate 33 is disposed in a thrust bearing accommodating chamber 52.

[0043] The support plate 33 is supported by thrust bearings 80. The thrust bearings 80 are disposed between the first plate 15 and the support plate 33, and between the second plate 16 and the support plate 33. When the support plate 33 rotates in conjunction with the rotation of the rotating shaft 40, dynamic pressure is generated between the support plate 33 and both thrust bearings 80. This causes the support plate 33 to float relative to both thrust bearings 80. Both thrust bearings 80 rotatably support the support plate 33 in a non-contact state. Therefore, both thrust bearings 80 are air dynamic pressure bearings that rotatably support the rotating shaft 40 in the thrust direction.

[0044] <First impeller 34> The first impeller 34 is made of metal. An example of the material of the first impeller 34 is aluminum. The first impeller 34 is connected to the first end 30a of the rotary shaft 40. The first impeller 34 is an impeller that rotates integrally with the rotary shaft 40. The first impeller 34 is accommodated in the first impeller chamber 13b. That is, the first impeller 34 is accommodated in the first impeller housing 13.

[0045] The first impeller 34 has a truncated cone shape. The diameter of the first impeller 34 gradually decreases from a first back surface 34a, which is the back surface of the first impeller 34, to a first tip surface 34b, which is the tip surface of the first impeller 34. The first back surface 34a faces the second plate 16 in the axial direction X. A first shroud surface 53a extends along the outer periphery of the first impeller 34 from the first back surface 34a to the first tip surface 34b. As a result, the first shroud surface 53a covers the outer periphery of the first impeller 34. The first impeller 34 compresses air as a fluid by rotating integrally with the rotating shaft 40.

[0046] <Second impeller 35> The second impeller 35 is made of metal. An example of the material of the second impeller 35 is aluminum. The second impeller 35 is connected to the second end 30b of the rotary shaft 40. The second impeller 35 is an impeller that rotates integrally with the rotary shaft 40. The second impeller 35 is accommodated in the second impeller chamber 14b. That is, the second impeller 35 is accommodated in the second impeller housing 14.

[0047] The second impeller 35 has a truncated cone shape. The diameter of the second impeller 35 gradually decreases from a second back surface 35a, which is the back surface of the second impeller 35, to a second tip surface 35b, which is the tip surface of the second impeller 35. The second back surface 35a faces the third plate 17 in the axial direction X. A second shroud surface 53b extends along the outer periphery of the second impeller 35 from the second back surface 35a to the second tip surface 35b. As a result, the second shroud surface 53b covers the outer periphery of the second impeller 35. The second impeller 35 compresses air as a fluid by rotating integrally with the rotating shaft 40.

[0048] <First tip clearance 55> A first tip clearance 55 is formed between the first impeller 34 as an impeller and the first shroud surface 53a as a shroud surface. The first tip clearance 55 is a gap extending from the first front end surface 34b to the first back surface 34a of the first impeller 34 between the outer periphery of the first impeller 34 and the first shroud surface 53a.

[0049] The dimension of the first tip clearance 55 in the radial direction Y is referred to as a first clearance dimension C1. The first clearance dimension C1 is the dimension of the gap between the first impeller 34 and the first shroud surface 53a in the radial direction Y. The first clearance dimension C1 may be the same dimension from the first front end surface 34b to the first back surface 34a of the first impeller 34, or may be different dimensions. For example, the first clearance dimension C1 may become smaller as it approaches from the first front end surface 34b to the first back surface 34a. Note that in FIG. 1, the size of the first clearance dimension C1 is exaggerated compared to the actual size.

[0050] <Second Tip Clearance 56> Between the second impeller 35 as an impeller and the second shroud surface 53b as a shroud surface, a second tip clearance 56 as a tip clearance is formed. The second tip clearance 56 is a gap extending from the second front end surface 35b to the second back surface 35a of the second impeller 35 between the outer periphery of the second impeller 35 and the second shroud surface 53b.

[0051] The dimension of the second tip clearance 56 in the radial direction Y is referred to as the second clearance dimension C2. The second clearance dimension C2 is the dimension of the gap between the second impeller 35 and the second shroud surface 53b in the radial direction Y. The second clearance dimension C2 may be the same dimension from the second front end surface 35b to the second back surface 35a of the second impeller 35, or may be different dimensions. For example, the second clearance dimension C2 may be smaller as it approaches from the second front end surface 35b to the second back surface 35a. In FIG. 1, the size of the second clearance dimension C2 is exaggerated compared to the actual size. In this embodiment, the second clearance dimension C2 is the same size as the first clearance dimension C1.

[0052] <Electric motor 39> The electric motor 39 is disposed between the first impeller 34 and the second impeller 35 in the axial direction X. The electric motor 39 is housed in a motor chamber 51. The electric motor 39 includes a stator 42 and a rotor 41. The stator 42 includes a cylindrical stator core 43 and a coil 44 wound around the stator core 43. The stator core 43 is fixed to the inner surface of the peripheral wall 12a of the motor housing 12.

[0053] The rotor 41 is disposed inside the stator core 43 in the motor chamber 51. The rotor 41 rotates integrally with the rotating shaft 40. The rotor 41 has a rotor core 41a fixed to the rotating shaft 40 and a plurality of permanent magnets (not shown) provided on the rotor core 41a. The rotor 41 rotates when power controlled by an inverter device (not shown) is supplied to the coil 44. The rotating shaft 40 rotates integrally with the rotor 41.

[0054] <Fuel cell system 1> A vehicle on which the fluid machine 10 is mounted includes a fuel cell system 1. The fuel cell system 1 includes a fuel cell stack 99 as an on-vehicle fuel cell, the fluid machine 10, a supply flow path LA, and a discharge flow path LB. The fuel cell stack 99 is composed of a plurality of battery cells. The supply flow path LA connects the discharge chamber 13c and the fuel cell stack 99. The discharge flow path LB connects the fuel cell stack 99 and the suction chamber 14c.

[0055] When the rotating shaft 40 rotates integrally with the rotor 41, the first impeller 34 and the second impeller 35 rotate integrally with the rotating shaft 40. Then, air taken in from the intake port 13a is compressed by the first impeller 34 in the first impeller chamber 13b, passes through the first diffuser flow path 13d, and is discharged from the discharge chamber 13c. The air discharged from the discharge chamber 13c is supplied to the fuel cell stack 99 via the supply flow path LA. The air supplied to the fuel cell stack 99 is used to generate power in the fuel cell stack 99. The air passes through the fuel cell stack 99.

[0056] The air passing through the fuel cell stack 99 is discharged to the discharge passage LB as exhaust air from the fuel cell stack 99. The exhaust air from the fuel cell stack 99 is drawn into the suction chamber 14c via the discharge passage LB. The exhaust air from the fuel cell stack 99 drawn into the suction chamber 14c is discharged into the second impeller chamber 14b through the second diffuser passage 14d. The second impeller 35 is rotated by the exhaust air from the fuel cell stack 99 discharged into the second impeller chamber 14b.

[0057] In addition to being rotated by the drive of electric motor 39, rotating shaft 40 is also rotated by the rotation of second impeller 35 which is rotated by the exhaust air from fuel cell stack 99. The rotation of second impeller 35 by the exhaust air from fuel cell stack 99 assists the rotation of rotating shaft 40. The exhaust air from fuel cell stack 99 discharged into suction chamber 14c is discharged to the outside from discharge port 14a.

[0058] <Configuration of First Foil Bearing 20 and Second Foil Bearing 22> A first foil bearing 20 serving as a foil bearing is held by a first bearing holder 18. A second foil bearing 22 serving as a foil bearing is held by a second bearing holder 19. Therefore, the first foil bearing 20 and the second foil bearing 22 are disposed in the housing 11. The foil bearing in this embodiment includes the first foil bearing 20 and the second foil bearing 22. The first foil bearing 20 and the second foil bearing 22 rotatably support the rotating shaft 40.

[0059] The first foil bearing 20 and the second foil bearing 22 support the rotating shaft 40 in a state of contact with the rotating shaft 40 until the rotation speed of the rotating shaft 40 reaches a floating rotation speed at which the rotating shaft 40 is floated by the first foil bearing 20 and the second foil bearing 22. When the rotating shaft 40 rotates, dynamic pressure is generated between the rotating shaft 40 and the first foil bearing 20 and between the rotating shaft 40 and the second foil bearing 22. When the rotation speed of the rotating shaft 40 reaches the floating rotation speed, the generated dynamic pressure causes the rotating shaft 40 to float relative to the first foil bearing 20 and the second foil bearing 22. As a result, the first foil bearing 20 and the second foil bearing 22 rotatably support the rotating shaft 40 in a state of not contacting the rotating shaft 40. Therefore, the first foil bearing 20 and the second foil bearing 22 support the rotating shaft 40 rotatably in the radial direction.

[0060] Next, a specific configuration of the first foil bearing 20 will be described. The shape of the second foil bearing 22 is the same as the shape of the first foil bearing 20. Therefore, in the configuration of the second foil bearing 22, detailed description of the same configuration as the first foil bearing 20 will be omitted below.

[0061] 2 and 3, the first foil bearing 20 has a bearing housing 71, a top foil 72, and a bump foil 73. Since the housing 11 has the bearing housing 71, it can also be said that the first foil bearing 20 has the housing 11.

[0062] <Bearing housing 71> The bearing housing 71 is cylindrical. The axis of the bearing housing 71 coincides with the axis SL of the rotating shaft 40. Therefore, the axial direction X is also the axial direction of the bearing housing 71. The radial direction Y is also the radial direction of the bearing housing 71. An insertion hole 71h through which the rotating shaft 40 is inserted is formed in the bearing housing 71. The insertion hole 71h is a through hole that penetrates the bearing housing 71 in the axial direction X.

[0063] 1 and 2 , the bearing housing 71 of the first foil bearing 20 is held by the first bearing retaining portion 18. In this embodiment, the bearing housing 71 of the first foil bearing 20 is a separate body from the first bearing retaining portion 18. The bearing housing 71 of the second foil bearing 22 is held by the second bearing retaining portion 19. In this embodiment, the bearing housing 71 of the second foil bearing 22 is a separate body from the second bearing retaining portion 19.

[0064] <Top Foil 72> As shown in Figs. 2 and 3, the top foil 72 is tubular. The top foil 72 in this embodiment is substantially cylindrical. The top foil 72 is located inside the bearing housing 71. The top foil 72 extends in the circumferential direction of the bearing housing 71 inside the bearing housing 71. The top foil 72 is thin plate-like. In detail, the top foil 72 is made of a strip-shaped metal plate material made of a flexible metal such as stainless steel. The top foil 72 is formed by curving this metal plate material into a cylindrical shape such that the longitudinal direction extends in the circumferential direction of the bearing housing 71 and the lateral direction extends in the axial direction X.

[0065] One end of the top foil 72 in the circumferential direction of the bearing housing 71 is fixed to the bearing housing 71 by welding or interference fitting, and the other end is not fixed to the bearing housing 71. The end of the top foil 72 fixed to the bearing housing 71 in this manner is referred to as a first fixed end 72a, and the end of the top foil 72 not fixed to the bearing housing 71 is referred to as a first free end 72b. The first fixed end 72a is bent outward of the top foil 72 in the radial direction Y. The first free end 72b is separated from the base end of the first fixed end 72a in the circumferential direction of the bearing housing 71. Therefore, the top foil 72 is a non-annular shape with a portion cut out from the annular shape.

[0066] The top foil 72 is disposed outward of the rotating shaft 40 in the radial direction Y. The top foil 72 faces the rotating shaft 40. The top foil 72 has a bearing surface 72s. The inner surface of the top foil 72 constitutes the bearing surface 72s facing the rotating shaft 40. The top foil 72 rotatably supports the rotating shaft 40 in a non-contact state when the rotating shaft 40 rotates.

[0067] <Bump Foil 73> The bump foil 73 is substantially cylindrical. The bump foil 73 is disposed between the top foil 72 and the bearing housing 71 in the radial direction Y. The bump foil 73 is thin plate-like. In detail, the bump foil 73 is made of a strip-shaped metal plate material made of a flexible metal such as stainless steel. The bump foil 73 is formed by curving this metal plate material into a cylindrical shape such that the longitudinal direction extends in the circumferential direction of the bearing housing 71 and the lateral direction extends in the axial direction X. The thickness of the bump foil 73 is defined as thickness h1. The thickness h1 may be substantially the same as the thickness of the top foil 72.

[0068] One end of the bump foil 73 in the circumferential direction of the bearing housing 71 is fixed to the bearing housing 71 by welding or interference fitting, and the other end is not fixed to the bearing housing 71. The end of the bump foil 73 fixed to the bearing housing 71 in this manner is called the second fixed end 73a, and the end of the bump foil 73 not fixed to the bearing housing 71 is called the second free end 73b. The second fixed end 73a is bent outward of the bump foil 73 in the radial direction Y. The second free end 73b is separated from the base end of the second fixed end 73a in the circumferential direction of the bearing housing 71. Therefore, the bump foil 73 is non-annular with a portion cut out from the annular shape. The bump foil 73 elastically supports the top foil 72.

[0069] The bump foil 73 has peaks 81 and valleys 82. The peaks 81 contact an outer peripheral surface 72f of the top foil 72. The valleys 82 contact an inner peripheral surface 71g of the bearing housing 71, which is the inner peripheral surface of the housing 11. The peaks 81 and the valleys 82 are alternately arranged along the rotation direction D of the rotating shaft 40.

[0070] The valley portion 82 protrudes in a direction away from the outer peripheral surface 72f of the top foil 72 and is curved in an arc so as to bulge toward the inner peripheral surface 71g of the bearing housing 71. The peak portion 81 protrudes from an end portion 82c of the valley portion 82 in the rotation direction D of the rotating shaft 40 toward the outer peripheral surface 72f of the top foil 72 and is curved in an arc so as to bulge toward the top foil 72. The end portion 82c of the valley portion 82 is a boundary portion between the peak portion 81 and the valley portion 82 in the bump foil 73. The bump foil 73 elastically supports the top foil 72 by the peak portion 81 and the valley portion 82 extending in the rotation direction D of the rotating shaft 40.

[0071] The bump foil 73 of this embodiment is composed of multiple divisional bodies 73c divided in the rotation direction D of the rotating shaft 40. The bump foil 73 of this embodiment has three divisional bodies 73c. ​​All the divisional bodies 73c of the bump foil 73 are also referred to as multiple divisional bodies 73c below. The dimensions of the multiple divisional bodies 73c in the rotation direction D of the rotating shaft 40 may be approximately the same as each other, or some or all of them may have different dimensions. The multiple divisional bodies 73c may have the same number of peak portions 81, or some or all of them may have different numbers of peak portions 81. The multiple divisional bodies 73c may have the same number of valley portions 82, or some or all of them may have different numbers of valley portions 82.

[0072] Each divided body 73c has a fixed end 73d fixed to the bearing housing 71 in the rotation direction D of the rotating shaft 40, and a free end 73e that is not fixed to the bearing housing 71. Of the multiple divided bodies 73c, the fixed end 73d of one divided body 73c is the second fixed end 73a, and the free end 73e of the remaining divided body 73c is the second free end 73b. In each divided body 73c, the end in the rotation direction D of the rotating shaft 40 is the fixed end 73d. In each divided body 73c, the end opposite the fixed end 73d is the free end 73e.

[0073] Of the two adjacent divided bodies 73c, the fixed end 73d of one divided body 73c and the free end 73e of the other divided body 73c are adjacent to each other in the rotational direction D of the rotating shaft 40. In each divided body 73c, the fixed end 73d and the free end 73e extend in the axial direction X between one end and the other end of the divided body 73c in the axial direction X.

[0074] Of the two adjacent divided bodies 73c, the fixed end 73d of one divided body 73c and the free end 73e of the other divided body 73c are spaced apart from each other in the rotation direction D of the rotating shaft 40. Each divided body 73c is disposed such that a gap 83 is formed between the adjacent fixed end 73d and free end 73e regardless of elongation.

[0075] <No load state SN> Next, the first foil bearing 20 in a state where no load is applied from the rotating shaft 40 to the bearing surface 72s will be described with reference to Fig. 3. The state where no load is applied from the rotating shaft 40 to the bearing surface 72s refers to a state where the rotating shaft 40 is not rotating and the entire bearing surface 72s in the circumferential direction of the bearing housing 71 is in contact with the rotating shaft 40. Such a state where no load is applied from the rotating shaft 40 to the bearing surface 72s will be referred to as a no-load state SN below.

[0076] 3, in the no-load state SN, each of the peaks 81 of the bump foil 73 locally contacts the outer peripheral surface 72f of the top foil 72. In the no-load state SN, the tip portions of the peaks 81 in the direction of protrusion toward the top foil 72 contact the outer peripheral surface 72f of the top foil 72. In the no-load state SN, each of the valleys 82 of the bump foil 73 locally contacts the inner peripheral surface 71g of the bearing housing 71. In the no-load state SN, the tip portions of the valleys 82 in the direction of protrusion toward the bearing housing 71 contact the inner peripheral surface 71g of the bearing housing 71.

[0077] In the no-load state SN, the distance between the outer peripheral surface 73f of the bump foil 73 at the peak portion 81 and the inner peripheral surface 71g of the bearing housing 71 in the radial direction Y is defined as a first distance H1. The first distance H1 is smaller than a first clearance dimension C1, which is the dimension of the first tip clearance 55 in the radial direction Y, and a second clearance dimension C2, which is the dimension of the second tip clearance 56 in the radial direction Y. That is, the minimum value of the first clearance dimension C1, which is the dimension of the gap between the first impeller 34 and the first shroud surface 53a in the radial direction Y, is larger than the first distance H1. The minimum value of the second clearance dimension C2, which is the dimension of the gap between the second impeller 35 and the second shroud surface 53b in the radial direction Y, is larger than the first distance H1.

[0078] In the no-load state SN, the distance between adjacent peaks 81 and valleys 82 in the rotation direction D of the rotating shaft 40 is defined as a second distance L1. The second distance L1 is the distance in the rotation direction D between the tip of the peak 81 in the protruding direction and the tip of the valley 82 in the protruding direction of the peaks 81 and the valleys 82 adjacent to each other in the rotation direction D. The thickness h1 of the bump foil 73, the first distance H1, and the second distance L1 are determined by L1. 2 The relationship is / 600h1>H1.

[0079] In the no-load state SN, a gap 83 is formed between adjacent fixed ends 73d and free ends 73e. In other words, in the no-load state SN, a gap 83 in which the bump foil 73 is not positioned is formed between two divided bodies 73c adjacent to each other in the rotational direction D of the rotating shaft 40.

[0080] It should be noted that the no-load state SN is different from a state in which the rotating shaft 40 is simply not rotating. When the rotating shaft 40 is not rotating and is not in the no-load state SN, the rotating shaft 40 contacts a part or the whole of the bearing surface 72s of the top foil 72 in the rotation direction D of the rotating shaft 40. When the rotating shaft 40 is not rotating and is not in the no-load state SN, a load acts from the rotating shaft 40 to the bearing surface 72s at the portion of the top foil 72 with which the rotating shaft 40 contacts.

[0081] <First state S1> Next, the first state S1 will be described with reference to Figures 4 and 5. The first state S1 refers to the state of the first foil bearing 20 when the rotating shaft 40 rotates and floats up from the bearing surface 72s. The first state S1 is a case in which the load that the bearing surface 72s receives from the rotating shaft 40 is equal to or less than a predetermined load P.

[0082] 4, in the first state S1, the top foil 72 elastically deforms outward in the radial direction Y as the rotating shaft 40 rotates. As a result, an air film is formed between the rotating shaft 40 and the top foil 72, generating dynamic pressure. The first foil bearing 20 rotatably supports the rotating shaft 40 in a state where the rotating shaft 40 is not in contact with the top foil 72.

[0083] When the top foil 72 is elastically deformed outward in the radial direction Y by the air film between the rotating shaft 40 and the top foil 72, each peak 81 of the bump foil 73 in contact with the outer peripheral surface 72f of the top foil 72 is pressed by the top foil 72. As a result, the bump foil 73 is elastically deformed outward in the radial direction Y together with the top foil 72. In this way, the top foil 72 is elastically supported by the bump foil 73. As the top foil 72 is displaced outward in the radial direction Y, each peak 81 and each valley 82 is elastically deformed. In the first state S1, a load is applied evenly from the rotating shaft 40 to the entire bearing surface 72s via the air film. Therefore, each peak 81 and each valley 82 is elastically deformed uniformly.

[0084] 5, in the first state S1, each of the peaks 81 of the bump foil 73 locally contacts the outer peripheral surface 72f of the top foil 72. As each peak 81 elastically deforms, in the first state S1, a wider portion of the peak 81 in the circumferential direction of the bearing housing 71 contacts the top foil 72 than in the no-load state SN. In the first state S1, each of the valleys 82 of the bump foil 73 locally contacts the inner surface of the bearing housing 71. As each valley 82 elastically deforms, in the first state S1, a wider portion of the valley 82 in the circumferential direction of the bearing housing 71 contacts the bearing housing 71 than in the no-load state SN.

[0085] In the first state S1, the peak portion 81 has a gap G1 between it and the bearing housing 71. In the first state S1, the valley portion 82 has a gap G2 between it and the top foil 72. In the first state S1, the bump foil 73 supports the top foil 72 with these gaps G1 and G2.

[0086] The dimension of the gap 83 in the circumferential direction of the bearing housing 71 is referred to as gap dimension A. In the first state S1, a gap 83 is formed between adjacent fixed ends 73d and free ends 73e. Two adjacent divided bodies 73c are separated from each other in the rotational direction D of the rotating shaft 40. As each peak portion 81 and each valley portion 82 elastically deforms, the divided bodies 73c deform so that the adjacent fixed ends 73d and free ends 73e approach each other. Therefore, the gap dimension A in the first state S1 is smaller than that in the no-load state SN.

[0087] <Second state S2> Next, the second state S2 will be described with reference to Fig. 6 and Fig. 7. The second state S2 refers to a state of the first foil bearing 20 in which the rotating shaft 40 is closer to a part of the bearing surface 72s in the circumferential direction of the bearing housing 71 than in the first state S1. In the second state S2, the state in which the rotating shaft 40 is closer to the bearing surface 72s than in the first state S1 can be when the rotating shaft 40 is eccentric, for example, when it is displaced in the radial direction Y. Also, the diameter of the rotating shaft 40 increases due to thermal expansion of the rotating shaft 40. The second state S2 is a state in which the load received by the bearing surface 72s from the rotating shaft 40 exceeds a predetermined load P.

[0088] As shown in FIG. 6, a part of the top foil 72 in the circumferential direction of the bearing housing 71 is defined as a first displacement portion 72p. A part of the bump foil 73 located radially Y outward from the first displacement portion 72p is defined as a second displacement portion 73p. The first displacement portion 72p in the second state S2 corresponds to a part where the rotation shaft 40 is closer to the bearing surface 72s than in the first state S1. In this embodiment, the entirety of one divided body 73c is exemplified as the second displacement portion 73p. A part of the top foil 72 located radially Y inward from one divided body 73c as the second displacement portion 73p is exemplified as the first displacement portion 72p.

[0089] In the second state S2, a load larger than that in the first state S1 acts on the first displacement portion 72p from the rotating shaft 40 via the air film. As a result, the first displacement portion 72p is displaced outward in the radial direction Y from its position in the first state S1. Therefore, the second state S2 can also be said to be a state of the first foil bearing 20 when the first displacement portion 72p is displaced outward in the radial direction Y from its position in the first state S1.

[0090] 7, as the first displacement portion 72p is displaced outward in the radial direction Y, the peaks 81 and valleys 82 located in the second displacement portion 73p are elastically deformed to a greater extent than in the first state S1. As a result, the contact area of ​​the second displacement portion 73p with the top foil 72 and the bearing housing 71 in the circumferential direction of the bearing housing 71 in the second state S2 is expanded compared to the first state S1.

[0091] With the elastic deformation of each peak portion 81 and each valley portion 82, the divided body 73c is deformed so that the adjacent fixed end 73d and free end 73e approach each other. Therefore, the divided body 73c including the second displacement portion 73p in the second state S2 is displaced to be larger in the rotation direction D of the rotating shaft 40 compared to the first state S1. In the second state S2, a gap 83 is formed between the adjacent fixed end 73d and free end 73e. In the second state S2, the divided body 73c including the second displacement portion 73p does not overlap with the divided body 73c adjacent to this divided body 73c in the rotation direction D of the rotating shaft 40. That is, the gap dimension A in the first state S1 is set to be equal to or larger than the displacement amount in the rotation direction D of the rotating shaft 40 of the divided body 73c including the second displacement portion 73p in the second state S2.

[0092] In the second state S2, the peaks 81 abut not only against the outer circumferential surface 72f of the top foil 72 but also against the inner circumferential surface 71g of the bearing housing 71. In the second state S2, the valleys 82 abut not only against the inner circumferential surface 71g of the bearing housing 71 but also against the outer circumferential surface 72f of the top foil 72. The bump foil 73 supports the top foil 72 by the abutment of the peaks 81 and the valleys 82.

[0093] In the second state S2, the second displacement portion 73p, which is a part of the bump foil 73, extends along the outer circumferential surface 72f of the top foil 72 and the inner circumferential surface 71g of the bearing housing 71. As a result, in the second state S2, the top foil 72 and the bump foil 73 locally configure a plain bearing 85 to support the rotating shaft 40.

[0094] Even when the top foil 72 and the bump foil 73 locally form a plain bearing 85, the first tip clearance 55 between the first impeller 34 and the first shroud surface 53a is greater than 0. Even when the top foil 72 and the bump foil 73 locally form a plain bearing 85, the second tip clearance 56 between the second impeller 35 and the second shroud surface 53b is greater than 0.

[0095] <Calculation formula using beam model> As shown in Figs. 8 and 9, the deformation amount δ of the bump foil 73 within the elastic deformation range is examined using a first model 100 and a second model 200. The first model 100 is one pitch of the bump foil 73. The first model 100 has a first convex portion 102 that is curved in an arc so as to bulge from both ends. Both ends of the first model 100 correspond to the valley portion 82. The first convex portion 102 corresponds to the mountain portion 81. The second model 200 is one pitch of the bump foil 73 modeled as a beam with both ends fixed. The second model 200 as a beam model is a flat plate material that extends in a flat plate shape between one end and the other end. Both ends of the second model 200 are fixed. In these models, the bump pitch is "2L1" and the bump thickness is "h". In these models, the applied load is "F", the bearing width is "b", the stress is "σ", the deformation amount is "δ", and the Young's modulus is "E". The bearing width b is the length of the bump foil 73 in the axial direction X. The bump pitch "2L1" corresponds to the second distance L1 multiplied by 2. The bump plate thickness "h" corresponds to the thickness h1.

[0096] In the second model 200, the following formulas (Equation 1) and (Equation 2) hold.

[0097]

number

[0098]

number

[0099] From the above (Equation 1) and (Equation 2), the following (Equation 3) can be derived.

[0100]

number

[0101] Generally, alloy steel or stainless steel is used for the bump foil 73, so that the Young's modulus E is generally about 200 [GPa] and the yield strength σmax is about 1000 [MPa]. By substituting these values ​​into (Equation 3), the following (Equation 4) can be derived.

[0102]

number

[0103] From the above (Equation 4), "L1 2 A deformation amount δ of less than "L1 / 600h" is in the elastic region, and a deformation amount δ greater than that is in the plastic region. 2 / 600h" is the maximum displacement in the elastic region. The first distance H1, which is the height of the bump foil 73, is defined as "L1 2 By setting the value such that "H1 / 600h>H1" is satisfied, it becomes possible to use the bump foil 73 in the elastic range.

[0104] As shown in the above formula (4), the bump foil 73 of this embodiment has the first distance H1, the second distance L1, and the thickness h1 set to "L1 2The relationship is preset to "1 / 600h1>H1". This allows the bump foil 73 to be elastically deformed while the amount of displacement of the bump foil 73 in the radial direction Y is equal to or less than the first distance H1. Since the bump foil 73 after deformation is not plastically deformed, it can return to the shape of the bump foil 73 in the no-load state SN or the first state S1. Therefore, the bump foil 73 of this embodiment has reversibility.

[0105] The peaks 81 and the valleys 82 are formed so as not to exceed the material's strength limit after the load P is exceeded, i.e., after the support state of the top foil 72 by the first foil bearing 20 transitions from the first state S1 to the second state S2. When the load that the bearing surface 72s receives from the rotating shaft 40 returns to a load equal to or lower than the predetermined load P after exceeding the predetermined load P, the support state of the top foil 72 by the first foil bearing 20 transitions from the second state S2 to the first state S1. When transitioning from the second state S2 to the first state S1 in this manner, the peaks 81 of the bump foil 73 are separated from the inner peripheral surface 71g of the bearing housing 71, and the valleys 82 are separated from the outer peripheral surface 72f of the top foil 72, due to their own elastic force.

[0106] <Operation of the First Embodiment> Next, the operation of the first embodiment will be described. For example, the top foil 72 may be displaced further outward in the radial direction Y than the first state S1 to a second state S2 due to vibration of the rotating shaft 40 or thermal expansion of the rotating shaft 40. In this case, each peak portion 81 of the bump foil 73 in contact with the outer circumferential surface 72f of the top foil 72 may be excessively pressed by the top foil 72.

[0107] According to this embodiment, the second displacement portion 73p in the second state S2 has a larger contact range with the top foil 72 and the bearing housing 71 in the rotation direction D of the rotating shaft 40 than in the first state S1. The second displacement portion 73p in the second state S2 extends along the outer peripheral surface 72f of the top foil 72 and the inner peripheral surface 71g of the bearing housing 71. As a result, in the first displacement portion 72p and the second displacement portion 73p in the second state S2, the top foil 72 and the bump foil 73 extend from each other in the rotation direction D of the rotating shaft 40 to form a plain bearing. Therefore, the first foil bearing 20 in the second state S2 can support the rotating shaft 40 by dynamic pressure, since the top foil 72 and the bump foil 73 locally constitute a plain bearing 85.

[0108] <Advantages of the First Embodiment> According to the first embodiment, the following effects can be obtained. (1-1) When the load that the bearing surface 72s receives from the rotating shaft 40 exceeds a predetermined load P, the bump foil 73 supports the top foil 72 with the peaks 81 abutting against the inner circumferential surface 71g of the bearing housing 71 and the valleys 82 abutting against the outer circumferential surface 72f of the top foil 72. This makes it possible to suppress deformation of the bump foil 73 that would reduce the bearing performance of the first foil bearing 20 and the second foil bearing 22 as foil bearings. When the load that the bearing surface 72s receives from the rotating shaft 40 exceeds the predetermined load P, the top foil 72 and the bump foil 73 locally constitute a plain bearing 85, so that the first foil bearing 20 and the second foil bearing 22 can support the rotating shaft 40 by dynamic pressure. Therefore, even under a situation in which an excessive load acts on the top foil 72, it is possible to suppress a reduction in the bearing performance of the first foil bearing 20 and the second foil bearing 22 as foil bearings.

[0109] (1-2) When the load that the bearing surface 72s receives from the rotating shaft 40 returns to being equal to or less than the predetermined load P, the elastic force of the bump foil 73 itself causes the peaks 81 to separate from the inner circumferential surface 71g of the bearing housing 71, and the valleys 82 to separate from the outer circumferential surface 72f of the top foil 72. Therefore, since a reversible bump foil 73 can be used, the deterioration of the bearing performance of the first foil bearing 20 and the second foil bearing 22 can be further suppressed.

[0110] (1-3) Each divided body 73c has a fixed end 73d fixed to the bearing housing 71 in the rotation direction D of the rotating shaft 40, and a free end 73e that is not fixed to the bearing housing 71. Each divided body 73c is arranged such that a gap 83 is formed between the adjacent fixed end 73d and free end 73e regardless of elongation. Therefore, even if the bump foil 73 elongates in the rotation direction D of the rotating shaft 40, the adjacent divided bodies 73c do not overlap with each other. Therefore, the displacement of the bump foil 73 in the rotation direction D of the rotating shaft 40 is not hindered, and the bump foil 73 can elastically support the top foil 72 in an appropriate manner.

[0111] (1-4) The peaks 81 and the valleys 82 are formed so as not to exceed the yield strength limit of the material after the load exceeds the predetermined load P. Therefore, even after the load that the bearing surface 72s receives from the rotating shaft 40 exceeds the predetermined load P, deformation of the bump foil 73 that would deteriorate the bearing performance of the first foil bearing 20 and the second foil bearing 22 can be suppressed.

[0112] (1-5) When no load is applied from the rotating shaft 40 to the bearing surface 72s, the second distance L1, the thickness h1, and the first distance H1 are L1 2 / 600h1>H1. Therefore, the maximum displacement of the bump foil 73 in the radial direction Y is the displacement when the bump foil 73 is along the inner circumferential surface 71g of the bearing housing 71, and is the first distance H1. The bump foil 73 can be elastically deformed below the first distance H1. Since the deformed bump foil 73 is not plastically deformed, it can return to the shape of the bump foil 73 when the load received by the bearing surface 72s from the rotating shaft 40 is equal to or less than the predetermined load P. Therefore, since the reversible bump foil 73 can be used, the deterioration of the bearing performance of the first foil bearing 20 and the second foil bearing 22 as foil bearings can be further suppressed.

[0113] (1-6) Even when the top foil 72 and the bump foil 73 locally form a plain bearing 85, the first tip clearance 55 and the second tip clearance 56 are larger than 0. Therefore, even if the top foil 72 is displaced so as to locally form the plain bearing 85, collision of the first impeller 34 with the first shroud surface 53a and collision of the second impeller 35 with the second shroud surface 53b can be suppressed.

[0114] (1-7) The minimum value of the first clearance dimension C1, which is the dimension of the gap between the first impeller 34 and the first shroud surface 53a in the radial direction Y, is greater than the first distance H1. The minimum value of the second clearance dimension C2, which is the dimension of the gap between the second impeller 35 and the second shroud surface 53b in the radial direction Y, is greater than the first distance H1. Therefore, while the displacement amount of the bump foil 73 in the radial direction Y is equal to or less than the first distance H1, the collision of the first impeller 34 with the first shroud surface 53a and the collision of the second impeller 35 with the second shroud surface 53b can be suppressed. Therefore, even if the top foil 72 is displaced so as to locally configure the plain bearing 85, the collision of the first impeller 34 with the first shroud surface 53a and the collision of the second impeller 35 with the second shroud surface 53b can be suppressed.

[0115] (1-8) By increasing the rigidity of the bump foil 73, it is possible to suppress deformation of the bump foil 73, such as damage to the bump foil 73, which would reduce the bearing performance of the first foil bearing 20 and the second foil bearing 22 as foil bearings. However, in this case, even under a situation in which the gap between the rotating shaft 40 and the bearing surface 72s becomes smaller due to thermal expansion caused by the high-speed rotation of the rotating shaft 40, the bump foil 73 is unlikely to deform, and the gap is unlikely to widen. Therefore, when the rotating shaft 40 directly contacts the bearing surface 72s, there is a risk that the rotating shaft 40 and the first foil bearing 20 and the second foil bearing 22 will be burned due to frictional heat. In addition, by increasing the rigidity of the bump foil 73, the resonance frequency of the first foil bearing 20 and the second foil bearing 22 will increase. On the other hand, the excitation force (unbalanced force of the rotating shaft 40) increases in proportion to the square of the rotation speed. For this reason, the resonance points of the first foil bearing 20 and the second foil bearing 22 are passed at high rotation speeds where the excitation force is large, causing vibration of the rotating shaft 40. According to the first embodiment, it is possible to suppress deformation of the bump foil 73 that would deteriorate the bearing performance of the first foil bearing 20 and the second foil bearing 22 as foil bearings, without increasing the rigidity of the bump foil 73. Therefore, it is possible to suppress the occurrence of problems that occur when the rigidity of the bump foil 73 is increased as described above.

[0116] Second embodiment A second embodiment of a foil bearing and a fluid machine will be described below with reference to Figs. 10 to 13. The shape of the foil bearing in the second embodiment is different from that in the first embodiment. The following description will focus on the differences from the first embodiment. Descriptions of configurations similar to those in the first embodiment will be omitted as appropriate.

[0117] <Bump Foil 73> 10 to 12, each divided body 73c is disposed such that a gap 83 is formed between the adjacent fixed end 73d and free end 73e regardless of elongation. The gap 83 is formed when the supporting state of the top foil 72 by the first foil bearing 20 and the second foil bearing 22 is in any of the no-load state SN, the first state S1, and the second state S2.

[0118] In each divided body 73c in this embodiment, the fixed end 73d extends in the axial direction X between one end and the other end of the divided body 73c in the axial direction X, similarly to the first embodiment. In each divided body 73c, the free end 73e is shaped so as to be shifted in the rotation direction D of the rotating shaft 40 as it approaches the middle part from both ends of the divided body 73c in the axial direction X. Due to such shapes of the fixed end 73d and the free end 73e, the gap 83 forms a herringbone-shaped groove 86.

[0119] In this embodiment, when the load-free state SN is changed to the first state S1, the bump foil 73 is deformed in the same manner as in the first embodiment. In this embodiment, similarly to the first embodiment, when no load is applied from the rotating shaft 40 to the bearing surface 72s, the second distance L1, the thickness h1, and the first distance H1 are changed to L1 2 The relationship is / 600h1>H1.

[0120] <Second state S2> 10 and 11, when the load that the bearing surface 72s receives from the rotating shaft 40 exceeds a predetermined load P, the peaks 81 also come into contact with the inner circumferential surface 71g of the bearing housing 71, and the valleys 82 also come into contact with the outer circumferential surface 72f of the top foil 72. With the peaks 81 and the valleys 82 in this state of contact, the bump foil 73 supports the top foil 72.

[0121] In the present embodiment, similarly to the first embodiment, the second displacement portion 73p in the second state S2 extends along the outer peripheral surface 72f of the top foil 72 and the inner peripheral surface 71g of the bearing housing 71. As a result, the first foil bearing 20 in the second state S2 can support the rotating shaft 40 by dynamic pressure, since the top foil 72 and the bump foil 73 locally configure a plain bearing 85.

[0122] 13, in the second state S2, herringbone-shaped grooves 86 are formed by the gaps 83 of the bump foil 73. In the second state S2, the first foil bearing 20 and the second foil bearing 22 locally configure a herringbone bearing 87 to support the rotating shaft 40.

[0123] <Operation of the Second Embodiment> Next, the operation of the second embodiment will be described. According to this embodiment, similarly to the first embodiment, the second displacement portion 73p in the second state S2 extends along the outer circumferential surface 72f of the top foil 72 and the inner circumferential surface 71g of the bearing housing 71. In the first foil bearing 20 in the second state S2, the top foil 72 and the bump foil 73 locally configure a plain bearing 85, so that the first foil bearing 20 can support the rotating shaft 40 by dynamic pressure.

[0124] In this embodiment, a load is applied from the rotating shaft 40 to the first displacement portion 72p in the second state S2 via an air film. A portion of the top foil 72 located radially inward of the gap 83 in the second state S2 is curved so as to be pressed toward the gap 83. As a result, the first foil bearing 20 becomes a herringbone bearing in the first displacement portion 72p. This also allows the first foil bearing 20 in the second state S2 to support the rotating shaft 40 by dynamic pressure.

[0125] <Effects of the second embodiment> According to the second embodiment, in addition to the effects of the first embodiment, the following effects can be obtained.

[0126] (2-1) The gap 83 forms a herringbone-shaped groove 86. When the load that the bearing surface 72s receives from the rotating shaft 40 exceeds a predetermined load P, the first foil bearing 20 and the second foil bearing 22 support the rotating shaft 40 by locally forming a herringbone bearing 87. Therefore, when the load that the bearing surface 72s receives from the rotating shaft 40 exceeds the predetermined load P, a portion of the top foil 72 located on the inside in the radial direction Y of the gap 83 between the adjacent fixed end 73d and free end 73e is curved so as to be pressed toward the gap 83. As a result, the first foil bearing 20 and the second foil bearing 22 can support the rotating shaft 40 by locally forming a herringbone bearing 87. Therefore, it is possible to further suppress a decrease in the bearing performance of the first foil bearing 20 and the second foil bearing 22.

[0127] <Example of change> The above-described embodiments may be modified as follows: The above-described embodiments and the following modifications may be combined with each other to the extent that no technical contradiction occurs.

[0128] 14 and 15 , like the free end 73e, the fixed end 73d may be shifted in the rotational direction D of the rotating shaft 40 from both ends of the divided body 73c in the axial direction X toward the middle part. In other words, the fixed end 73d may be shaped to conform to the free end 73e.

[0129] The minimum value of the first clearance dimension C1 and the minimum value of the second clearance dimension C2 may be the same as the first distance H1 or may be smaller than the first distance H1. When the top foil 72 and the bump foil 73 locally form a plain bearing 85, the first tip clearance 55 and the second tip clearance 56 may be zero.

[0130] After the load P exceeds the predetermined load, the peaks 81 and the valleys 82 may exceed the strength limit of the material. The second distance L1, the thickness h1, and the first distance H1 are expressed as "L1 2 / 600h1>H1" does not have to be satisfied.

[0131] When transitioning from the second state S2 to the first state S1, the elastic force of the bump foil 73 may not cause deformation of the bump foil 73. In this case, for example, the peak portion 81 remains in contact with the inner circumferential surface 71g of the bearing housing 71 even when transitioning from the second state S2 to the first state S1. For example, the valley portion 82 remains in contact with the outer circumferential surface 72f of the top foil 72 even when transitioning from the second state S2 to the first state S1.

[0132] Each divided body 73c may be elongated so that the gap 83 between the adjacent fixed end 73d and free end 73e disappears. In this case, for example, in the second state S2, the fixed end 73d and the free end 73e of two adjacent divided bodies 73c may be in contact with each other.

[0133] The bump foil 73 may be configured as a single member that is integral with the bearing housing 71 in the circumferential direction. The bearing housing 71 may be omitted from the first foil bearing 20 and the second foil bearing 22. In this case, for example, the bearing housing 71 may be integrated with the first bearing retaining portion 18 and the second bearing retaining portion 19, thereby omitting the bearing housing 71 from the first foil bearing 20 and the second foil bearing 22. The bump foil 73 and the top foil 72 may be fixed to the housing 11 by welding or an interference fit.

[0134] For example, the fluid machine 10 does not need to include the second impeller 35. The fluid compressed by the first impeller 34 and the second impeller 35 is not limited to air. The fluid may be, for example, a refrigerant or a freon atmosphere in which a gas state and a liquid state are mixed. Therefore, the fluid machine 10 may compress any fluid. For example, the fluid machine 10 may be used in an air conditioning system. In this case, the fluid machine 10 may compress a refrigerant. The fluid machine 10 may be mounted on any object, and is not limited to a vehicle. [Explanation of symbols]

[0135] D...direction of rotation, G1, G2...gap, h1...thickness, P...specified load, Y...radial direction, 10...fluid machine, 11...housing, 40...rotating shaft, 71...bearing housing, 71g...inner surface, 71h...insertion hole, 72...top foil, 72f...outer surface (of top foil), 72s...bearing surface, 73...bump foil, 73c...divided body, 73d...fixed end, 73e...free end, 73f...outer surface of bump foil, 81...peak portion, 82...valley portion, 83...gap, 85...plain bearing, 86...groove, 87...herringbone bearing.

Claims

1. a housing having an insertion hole through which the rotating body is inserted; A cylindrical top foil facing the rotating body and having a bearing surface; a thin-plate-like bump foil that is disposed between the top foil and the housing, in which peaks in contact with an outer peripheral surface of the top foil and valleys in contact with an inner peripheral surface of the housing are alternately disposed along a rotational direction of the rotating body, and the peaks and valleys extend in the rotational direction to elastically support the top foil, When the load that the bearing surface receives from the rotating body is equal to or smaller than a predetermined load, the bump foil supports the top foil with a gap between the peak portion and the housing and a gap between the valley portion and the top foil, When the load that the bearing surface receives from the rotating body exceeds the predetermined load, the bump foil supports the top foil with the peaks abutting also on the inner circumferential surface of the housing and the valleys abutting also on the outer circumferential surface of the top foil, and the top foil and the bump foil locally constitute a plain bearing to support the rotating body, The bump foil is composed of a plurality of divided bodies divided in the rotation direction, each of the divided bodies has, in the rotational direction, a fixed end fixed to the housing and a free end not fixed to the housing; Each of the divided bodies is arranged such that a gap is formed between the adjacent fixed end and the free end regardless of elongation, The gap forms a herringbone groove; A foil bearing characterized in that, when the load that the bearing surface receives from the rotating body exceeds the specified load, the peak portion also abuts the inner surface of the housing and the valley portion also abuts the outer surface of the top foil to support the top foil, thereby locally forming a herringbone bearing and supporting the rotating body.

2. a housing having an insertion hole through which the rotating body is inserted; A cylindrical top foil facing the rotating body and having a bearing surface; a thin-plate-like bump foil that is disposed between the top foil and the housing, in which peaks in contact with an outer peripheral surface of the top foil and valleys in contact with an inner peripheral surface of the housing are alternately disposed along a rotational direction of the rotating body, and the peaks and valleys extend in the rotational direction to elastically support the top foil, When the load that the bearing surface receives from the rotating body is equal to or smaller than a predetermined load, the bump foil supports the top foil with a gap between the peak portion and the housing and a gap between the valley portion and the top foil, When the load that the bearing surface receives from the rotating body exceeds the predetermined load, the bump foil supports the top foil with the peaks abutting also on the inner circumferential surface of the housing and the valleys abutting also on the outer circumferential surface of the top foil, and the top foil and the bump foil locally constitute a plain bearing to support the rotating body, A foil bearing, characterized in that the peaks and valleys are formed so as not to exceed a yield strength limit of the material after the predetermined load is exceeded.

3. a housing having an insertion hole through which the rotating body is inserted; A cylindrical top foil facing the rotating body and having a bearing surface; a thin-plate-like bump foil that is disposed between the top foil and the housing, in which peaks in contact with an outer peripheral surface of the top foil and valleys in contact with an inner peripheral surface of the housing are alternately disposed along a rotational direction of the rotating body, and the peaks and valleys extend in the rotational direction to elastically support the top foil, When the load that the bearing surface receives from the rotating body is equal to or smaller than a predetermined load, the bump foil supports the top foil with a gap between the peak portion and the housing and a gap between the valley portion and the top foil, When the load that the bearing surface receives from the rotating body exceeds the predetermined load, the bump foil supports the top foil with the peaks abutting also on the inner circumferential surface of the housing and the valleys abutting also on the outer circumferential surface of the top foil, and the top foil and the bump foil locally constitute a plain bearing to support the rotating body, A foil bearing characterized in that, when no load from the rotating body acts on the bearing surface, the distance between adjacent peaks and valleys in the rotational direction is L1, the thickness of the bump foil is h1, and the distance between the outer surface of the bump foil at the peaks in the radial direction of the rotating body and the inner surface of the housing is H1, such that L12 / 600h1>H1.

4. A rotating body, an impeller that compresses a fluid by rotating integrally with the rotor; an impeller housing in which the rotor and the impeller are housed; A fluid machine comprising: The foil bearing comprises: a housing having an insertion hole through which the rotating body is inserted; A cylindrical top foil facing the rotating body and having a bearing surface; a thin-plate-like bump foil that is disposed between the top foil and the housing, in which peaks in contact with an outer peripheral surface of the top foil and valleys in contact with an inner peripheral surface of the housing are alternately disposed along a rotational direction of the rotating body, and the peaks and valleys extend in the rotational direction to elastically support the top foil, When the load that the bearing surface receives from the rotating body is equal to or smaller than a predetermined load, the bump foil supports the top foil with a gap between the peak portion and the housing and a gap between the valley portion and the top foil, When the load that the bearing surface receives from the rotating body exceeds the predetermined load, the bump foil supports the top foil with the peaks abutting also on the inner circumferential surface of the housing and the valleys abutting also on the outer circumferential surface of the top foil, and the top foil and the bump foil locally constitute a plain bearing to support the rotating body, The impeller housing includes a shroud surface that covers an outer periphery of the impeller, A fluid machinery, characterized in that a tip clearance between the impeller and the shroud surface is greater than 0 even when the top foil and the bump foil locally form a plain bearing.

5. A rotating body, an impeller that compresses a fluid by rotating integrally with the rotor; an impeller housing in which the rotor and the impeller are housed; A fluid machine comprising: The foil bearing comprises: a housing having an insertion hole through which the rotating body is inserted; A cylindrical top foil facing the rotating body and having a bearing surface; a thin-plate-like bump foil that is disposed between the top foil and the housing, in which peaks in contact with an outer peripheral surface of the top foil and valleys in contact with an inner peripheral surface of the housing are alternately disposed along a rotational direction of the rotating body, and the peaks and valleys extend in the rotational direction to elastically support the top foil, When the load that the bearing surface receives from the rotating body is equal to or smaller than a predetermined load, the bump foil supports the top foil with a gap between the peak portion and the housing and a gap between the valley portion and the top foil, When the load that the bearing surface receives from the rotating body exceeds the predetermined load, the bump foil supports the top foil with the peaks abutting also on the inner circumferential surface of the housing and the valleys abutting also on the outer circumferential surface of the top foil, and the top foil and the bump foil locally constitute a plain bearing to support the rotating body, The impeller housing includes a shroud surface that covers an outer periphery of the impeller, A fluid machine characterized in that, when no load from the rotating body acts on the bearing surface, a distance H1 between the outer surface of the bump foil at the ridge portion in the radial direction of the rotating body and the inner surface of the housing, a minimum value of a gap between the impeller and the shroud surface in the radial direction is greater than H1.

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