Centrifugal compressor

Abstract

To reduce a size of a centrifugal compressor.SOLUTION: A branch passage 110 being a part of an introduction passage 109, and branched from a connection passage 108, and a cooling fluid passage 111 in which cooling water for cooling air flowing in the branch passage 110 flows are formed at connection piping 47 having an existing constitution. Therefore, it is not necessary to cool air flowing in the introduction passage 109 by using an intercooler as a conventional technology. Accordingly, a first dynamic pressure slide bearing and a second dynamic pressure slide bearing can be cooled by using a part of air which is compressed by the rotation of a first impeller without using the intercooler.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a centrifugal compressor. [Background technology]

[0002] The centrifugal compressor includes a rotating shaft, a motor, a housing, and a bearing. The centrifugal compressor may also include a first impeller and a second impeller. The first impeller rotates integrally with the rotating shaft to compress a fluid. The second impeller rotates integrally with the rotating shaft to compress the fluid after it has been compressed by the rotation of the first impeller. The motor rotates the rotating shaft. The bearing supports the rotating shaft rotatably relative to the housing.

[0003] The housing has a first impeller chamber, a second impeller chamber, a first intake port, a first discharge port, and a second intake port. The first impeller chamber houses the first impeller. The second impeller chamber houses the second impeller. The first intake port draws fluid into the first impeller chamber. The first discharge port discharges fluid compressed by rotation of the first impeller. The second intake port draws fluid into the second impeller chamber. The centrifugal compressor is provided with a connecting pipe. The connecting pipe connects the first discharge port and the second intake port. The connecting pipe forms a connecting passage that allows the fluid discharged to the first discharge port to flow to the second intake port.

[0004] Incidentally, in such a centrifugal compressor, it is desired to cool the bearing in order to improve the durability of the centrifugal compressor. Therefore, the centrifugal compressor may be provided with, for example, an introduction passage that introduces a part of the fluid compressed by the rotation of the first impeller into the bearing. In order to efficiently cool the bearing, it is desirable that the fluid flowing through the introduction passage is supplied to the bearing at a temperature lower than the temperature of the fluid after being compressed by the rotation of the first impeller. Therefore, as in Patent Document 1, for example, it is conceivable to cool the fluid flowing through the introduction passage by an intercooler and then supply it to the bearing. As a result, the bearing is efficiently cooled by the fluid introduced from the introduction passage. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-7026 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in such a configuration in which an intercooler is used to cool the fluid flowing through the introduction passage, the size of the centrifugal compressor increases by the amount of the intercooler. Therefore, it is desired to reduce the size of the centrifugal compressor by cooling the bearings using part of the fluid compressed by the rotation of the first impeller without using an intercooler. [Means for solving the problem]

[0007] A centrifugal compressor that solves the above problem includes a rotating shaft, a first impeller that rotates integrally with the rotating shaft to compress a fluid, a second impeller that rotates integrally with the rotating shaft to compress the fluid after it has been compressed by the rotation of the first impeller, a motor that rotates the rotating shaft, a first impeller chamber that houses the first impeller, a second impeller chamber that houses the second impeller, a first intake port that draws fluid into the first impeller chamber, a first discharge port through which the fluid compressed by the rotation of the first impeller is discharged, and a second intake port that draws fluid into the second impeller chamber. a bearing that rotatably supports the rotating shaft relative to the housing, a connection pipe that connects the first discharge port and the second suction port and forms a connection passage through which the fluid discharged to the first discharge port flows to the second suction port, and an introduction passage that introduces a portion of the fluid compressed by the rotation of the first impeller into the bearing, wherein the connection pipe is formed with a branch passage that is a portion of the introduction passage and branches off from the connection passage, and a cooling fluid passage through which a cooling fluid flows to cool the fluid flowing through the branch passage.

[0008] According to this, a branch passage that is a part of the introduction passage and branches off from the connection passage, and a cooling fluid passage through which a cooling fluid flows to cool the fluid flowing through the branch passage are formed in the connection pipe, which is an existing configuration. Therefore, unlike the conventional technology, it is not necessary to use an intercooler to cool the fluid flowing through the introduction passage. Therefore, it is possible to cool the bearings by using part of the fluid compressed by the rotation of the first impeller without using an intercooler, and therefore it is possible to reduce the size of the centrifugal compressor.

[0009] In the above centrifugal compressor, the connecting piping has a first cylindrical portion, a second cylindrical portion surrounding the first cylindrical portion, and a third cylindrical portion surrounding the second cylindrical portion, a part of the connecting passage passes inside the first cylindrical portion, a part of the cooling fluid passage passes between an outer peripheral surface of the first cylindrical portion and an inner peripheral surface of the second cylindrical portion, and a part of the branch passage passes between the outer peripheral surface of the second cylindrical portion and an inner peripheral surface of the third cylindrical portion.

[0010] According to this, heat exchange is performed between the cooling fluid flowing between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion and the fluid flowing inside the first cylindrical portion via the first cylindrical portion. As a result, the fluid flowing inside the first cylindrical portion is cooled by the cooling fluid flowing between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion. Also, heat exchange is performed between the cooling fluid flowing between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion and the fluid flowing between the outer peripheral surface of the second cylindrical portion and the inner peripheral surface of the third cylindrical portion via the second cylindrical portion. As a result, the fluid flowing between the outer peripheral surface of the second cylindrical portion and the inner peripheral surface of the third cylindrical portion is cooled by the cooling fluid flowing between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion. In this way, the cooling fluid flowing between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion can cool not only the fluid flowing through the introduction passage but also the fluid flowing through the connection passage. Therefore, the fluid flowing through the connecting passage is cooled, thereby lowering the temperature of the fluid drawn into the second impeller chamber through the second suction port, thereby improving the efficiency of compression of the fluid caused by the rotation of the second impeller.

[0011] In the above centrifugal compressor, the connecting piping may include a first cylindrical member constituting the first cylindrical portion, a second cylindrical member constituting the second cylindrical portion, a third cylindrical member constituting the third cylindrical portion, a first positioning portion that positions the first cylindrical member and the second cylindrical member, and a second positioning portion that positions the second cylindrical member and the third cylindrical member.

[0012] In this manner, the configuration including the first cylindrical member, the second cylindrical member, the third cylindrical member, the first positioning portion, and the second positioning portion is a suitable configuration for manufacturing the connection pipe, which makes it easier to manufacture the connection pipe.

[0013] In the centrifugal compressor, it is preferable that an outer circumferential surface of the second cylindrical portion is formed with fins protruding toward an inner circumferential surface of the third cylindrical portion. According to this, fins protruding toward the inner peripheral surface of the third cylindrical portion are formed on the outer peripheral surface of the second cylindrical portion. Therefore, heat exchange between the cooling fluid flowing between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion and the fluid flowing between the outer peripheral surface of the second cylindrical portion and the inner peripheral surface of the third cylindrical portion is efficiently performed via the second cylindrical portion. Therefore, the fluid flowing between the outer peripheral surface of the second cylindrical portion and the inner peripheral surface of the third cylindrical portion can be more efficiently cooled by the cooling fluid flowing between the outer peripheral surface of the first cylindrical portion and the inner peripheral surface of the second cylindrical portion. As a result, the bearing can be more efficiently cooled.

[0014] The centrifugal compressor may further include a switching valve that is switchable between a first switching state that allows the cooling fluid to flow in the cooling fluid passage and a second switching state that blocks the flow of the cooling fluid in the cooling fluid passage, and the switching valve is switched to the first switching state when the rotation speed of the motor exceeds a predetermined rotation speed and the power consumption of the motor exceeds a predetermined power consumption.

[0015] When the rotation speed of the motor exceeds a predetermined rotation speed, the amount of heat generated by the bearing due to the rotation of the rotating shaft becomes relatively large, and therefore the bearing needs to be cooled. Also, when the power consumption of the motor exceeds a predetermined power consumption, the compression work by the rotation of the first impeller and the second impeller increases relatively. Therefore, the temperature of the fluid compressed by the rotation of the first impeller becomes relatively high. Therefore, when the rotation speed of the motor exceeds a predetermined rotation speed and the power consumption of the motor exceeds the predetermined power consumption, the switching valve switches to the first switching state, and the flow of the cooling fluid in the cooling fluid passage is permitted. As a result, the fluid flowing through the branch passage is cooled by the cooling fluid flowing through the cooling fluid passage. Therefore, the bearing can be efficiently cooled by the fluid introduced from the introduction passage to the bearing.

[0016] In the centrifugal compressor, the switching valve may be a solenoid valve that switches to the first switching state when de-energized and that switches to the second switching state when energized. According to this, since the switching valve is switched to the first switching state when de-energized, the flow of the cooling fluid in the cooling fluid passage can be maintained in an allowable state without supplying power to the switching valve. Then, power is supplied to the switching valve only when there is no need to cool the fluid flowing through the branch passage by the cooling fluid flowing through the cooling fluid passage and when the fluid flowing through the connection passage is not to be heated. Therefore, the fluid flowing through the branch passage can be cooled by the cooling fluid flowing through the cooling fluid passage while minimizing the supply of power to the switching valve. As a result, the bearing can be efficiently cooled while saving energy in the centrifugal compressor. Effect of the Invention

[0017] According to the present invention, the centrifugal compressor can be made smaller in size. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a cross-sectional view of a centrifugal compressor according to an embodiment. [Diagram 2]FIG. 2 is a cross-sectional view for explaining the connection pipe. [Diagram 3] FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. [Diagram 5] FIG. 5 is a cross-sectional view taken along line 5-5 in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. [Figure 8] FIG. 8 is a cross-sectional view taken along line 8-8 in FIG. [Figure 9] FIG. 9 is a cross-sectional view taken along line 9-9 in FIG. [Figure 10] FIG. 10 is a cross-sectional view for explaining the switching valve. [Figure 11] FIG. 11 is a flowchart for explaining the control of the control unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, a centrifugal compressor according to one embodiment will be described with reference to Fig. 1 to Fig. 11. The centrifugal compressor of this embodiment is mounted on a fuel cell vehicle. The centrifugal compressor compresses air. <Basic configuration of a centrifugal compressor> As shown in Fig. 1, the centrifugal compressor 10 includes a housing 11. The housing 11 is made of a metal material. For example, the housing 11 is made of aluminum. The housing 11 includes a motor housing 12, a first compressor housing 13, a second compressor housing 14, a first plate 15, a second plate 16, and a third plate 17.

[0020] The motor housing 12 has an end wall 12a and a peripheral wall 12b. The end wall 12a is plate-shaped. The peripheral wall 12b extends in a cylindrical shape from the outer periphery of the end wall 12a. A water jacket 12w is provided on the peripheral wall 12b. The water jacket 12w is annular.

[0021] The motor housing 12 has a cooling water supply port 12c and a cooling water discharge port 12d. The cooling water supply port 12c and the cooling water discharge port 12d are formed in the peripheral wall 12b. The cooling water supply port 12c and the cooling water discharge port 12d are connected to a water jacket 12w. The cooling water is supplied to the cooling water supply port 12c from a cooling water circuit (not shown). The cooling water supplied to the cooling water supply port 12c flows through the water jacket 12w. The cooling water flowing through the water jacket 12w cools the motor housing 12. The cooling water that has flowed through the water jacket 12w is discharged to the outside of the motor housing 12 from the cooling water discharge port 12d.

[0022] The first plate 15 is connected to an end portion on the opening side of the peripheral wall 12b of the motor housing 12. The first plate 15 closes the opening of the peripheral wall 12b of the motor housing 12. A motor chamber 18 is defined by the motor housing 12 and the first plate 15. Thus, the housing 11 has the motor chamber 18.

[0023] The second plate 16 is connected to the outer surface of the end wall 12a of the motor housing 12. The second plate 16 is attached to the end wall 12a of the motor housing 12 with the thickness direction of the second plate 16 coinciding with the thickness direction of the end wall 12a of the motor housing 12.

[0024] The centrifugal compressor 10 includes a motor 20. The motor 20 is accommodated in a motor chamber 18. Therefore, the motor chamber 18 accommodates the motor 20. The motor housing 12 surrounds the motor 20. Heat generated by the motor 20 is dissipated to the motor housing 12.

[0025] The centrifugal compressor 10 includes a first bearing retaining portion 21. The first bearing retaining portion 21 protrudes from the center of the first plate 15 into the motor chamber 18. Therefore, the first plate 15 has the first bearing retaining portion 21. The first bearing retaining portion 21 is cylindrical.

[0026] The third plate 17 is connected to the end face of the first plate 15 on the opposite side to the motor housing 12. The third plate 17 is attached to the first plate 15 with the thickness direction of the third plate 17 coinciding with the thickness direction of the first plate 15. The third plate 17 has a first insertion hole 23. The first insertion hole 23 is formed in the center of the third plate 17. The axis of the first insertion hole 23 coincides with the axis of the first bearing holder 21. The first insertion hole 23 communicates with the inside of the first bearing holder 21.

[0027] The centrifugal compressor 10 includes a second bearing retaining portion 25. The second bearing retaining portion 25 protrudes from the center of the end wall 12a of the motor housing 12 into the motor chamber 18. Therefore, the motor housing 12 has the second bearing retaining portion 25. The second bearing retaining portion 25 is cylindrical.

[0028] A second insertion hole 26 is formed in the second plate 16. The second insertion hole 26 penetrates the center of the second plate 16. The second insertion hole 26 communicates with the inside of the second bearing holder 25. The axis of the second insertion hole 26 coincides with the axis of the second bearing holder 25.

[0029] The first compressor housing 13 is cylindrical and has a first suction port 35 that is a circular hole through which air is drawn. Therefore, the housing 11 has the first suction port 35. The first compressor housing 13 is connected to an end face of the third plate 17 opposite to the first plate 15 with the axis of the first suction port 35 coinciding with the axis of the first insertion hole 23. The first suction port 35 opens to an end face of the first compressor housing 13 opposite to the third plate 17. Air cleaned by an air cleaner (not shown) flows through the first suction port 35.

[0030] The centrifugal compressor 10 includes a first impeller chamber 36, a first discharge chamber 37, and a first diffuser passage 38. The first impeller chamber 36, the first discharge chamber 37, and the first diffuser passage 38 are formed between the first compressor housing 13 and the third plate 17. Thus, the housing 11 includes the first impeller chamber 36. The first impeller chamber 36 communicates with the first suction port 35. The first suction port 35 draws air into the first impeller chamber 36. The first discharge chamber 37 extends around the axis of the first suction port 35 around the first impeller chamber 36. The first diffuser passage 38 communicates between the first impeller chamber 36 and the first discharge chamber 37. The first impeller chamber 36 communicates with the first insertion hole 23.

[0031] The centrifugal compressor 10 has a first discharge port 39. The first discharge port 39 is formed in the first compressor housing 13. Therefore, the housing 11 has the first discharge port 39. A first end of the first discharge port 39 communicates with the first discharge chamber 37. A second end of the first discharge port 39 opens to the outer circumferential surface of the first compressor housing 13.

[0032] The second compressor housing 14 is cylindrical and has a circular second suction port 40 through which air is drawn. Thus, the housing 11 has the second suction port 40. The second compressor housing 14 is connected to the end face of the second plate 16 opposite the end wall 12a of the motor housing 12 with the axis of the second suction port 40 coinciding with the axis of the second insertion hole 26. The second suction port 40 opens into the end face of the second compressor housing 14 opposite the second plate 16.

[0033] The centrifugal compressor 10 includes a second impeller chamber 41, a second discharge chamber 42, and a second diffuser passage 43. The second impeller chamber 41, the second discharge chamber 42, and the second diffuser passage 43 are formed between the second compressor housing 14 and the second plate 16. Thus, the housing 11 includes the second impeller chamber 41. The second impeller chamber 41 communicates with the second suction port 40. The second suction port 40 draws air into the second impeller chamber 41. The second discharge chamber 42 extends around the axis of the second suction port 40 around the second impeller chamber 41. The second diffuser passage 43 communicates the second impeller chamber 41 and the second discharge chamber 42. The second impeller chamber 41 communicates with the second insertion hole 26.

[0034] The centrifugal compressor 10 has a second discharge port 44. The second discharge port 44 is formed in the second compressor housing 14. A first end of the second discharge port 44 communicates with the second discharge chamber 42. A second end of the second discharge port 44 opens to the outer circumferential surface of the second compressor housing 14.

[0035] A supply pipe 45 is connected to the second outlet 44. The supply pipe 45 is connected to the fuel cell stack 46. A first end of the supply pipe 45 is connected to the second outlet 44. A second end of the supply pipe 45 is connected to the fuel cell stack 46.

[0036] A stack discharge passage 46a is connected to the fuel cell stack 46. The stack discharge passage 46a is, for example, a pipe. Air discharged from the fuel cell stack 46 flows through the stack discharge passage 46a. The stack discharge passage 46a discharges the air discharged from the fuel cell stack 46 to the atmosphere.

[0037] The centrifugal compressor 10 includes a connecting pipe 47. A first end of the connecting pipe 47 is connected to the first discharge port 39. A second end of the connecting pipe 47 is connected to the second suction port 40. Thus, the connecting pipe 47 connects the first discharge port 39 and the second suction port 40.

[0038] The centrifugal compressor 10 includes a rotating shaft 50. The rotating shaft 50 crosses inside the motor chamber 18 with the axis of the rotating shaft 50 coinciding with the axis of the peripheral wall 12b of the motor housing 12. A first end, which is one end in the axial direction of the rotating shaft 50, protrudes from inside the motor chamber 18 to the inside of the first bearing holder 21, through the first insertion hole 23, and into the first impeller chamber 36. A second end, which is the other end in the axial direction of the rotating shaft 50, protrudes from inside the motor chamber 18 to the inside of the second bearing holder 25, through the second insertion hole 26, and into the second impeller chamber 41.

[0039] The motor 20 includes a rotor 51 and a stator 52. The rotor 51 is fixed to a rotating shaft 50. The rotor 51 has a cylindrical rotor core 53 fixed to the rotating shaft 50, and a plurality of permanent magnets (not shown) provided on the rotor core 53. The rotor 51 rotates integrally with the rotating shaft 50.

[0040] The stator 52 is fixed to the motor housing 12. The stator 52 is disposed outside the rotor 51. The stator 52 has a cylindrical stator core 54 and a coil 55. The stator core 54 is fixed to the inner circumferential surface of the peripheral wall 12b of the motor housing 12. The coil 55 is wound around the stator core 54. When a current flows from a battery (not shown) to the coil 55, the rotating shaft 50 rotates integrally with the rotor 51. Thus, the motor 20 rotates the rotating shaft 50.

[0041] The centrifugal compressor 10 includes a first dynamic pressure plain bearing 56 and a second dynamic pressure plain bearing 57. The first dynamic pressure plain bearing 56 is cylindrical. The first dynamic pressure plain bearing 56 is held by the first bearing holder 21. The first dynamic pressure plain bearing 56 supports the rotating shaft 50 rotatably relative to the first plate 15.

[0042] The second dynamic pressure plain bearing 57 is cylindrical. The second dynamic pressure plain bearing 57 is held by the second bearing holder 25. The second dynamic pressure plain bearing 57 supports the rotating shaft 50 rotatably relative to the end wall 12a of the motor housing 12. Therefore, the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 are bearings that support the rotating shaft 50 rotatably relative to the housing 11. The first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 support the rotating shaft 50 rotatably relative to the housing 11 in the radial direction.

[0043] The centrifugal compressor 10 includes a thrust bearing that supports the rotating shaft 50 rotatably in the thrust direction relative to the housing 11. However, a detailed description of the thrust bearing is omitted since it is well known.

[0044] The centrifugal compressor 10 includes a first impeller 61 and a second impeller 62. The first impeller 61 is coupled to a first end of the rotating shaft 50. The first impeller 61 is housed in the first impeller chamber 36. Thus, the first impeller chamber 36 houses the first impeller 61. The first impeller 61 rotates integrally with the rotating shaft 50 to compress air.

[0045] The second impeller 62 is coupled to a second end of the rotating shaft 50. The second impeller 62 is housed in the second impeller chamber 41. Thus, the second impeller chamber 41 houses the second impeller 62. The second impeller 62 rotates integrally with the rotating shaft 50 to compress the air compressed by the rotation of the first impeller 61. The first impeller 61 and the second impeller 62 rotate to compress the air supplied to the fuel cell stack 46.

[0046] The first impeller 61 and the second impeller 62 rotate integrally with the rotary shaft 50 by being driven by the motor 20. Therefore, the motor 20 rotates the first impeller 61 and the second impeller 62.

[0047] The centrifugal compressor 10 includes a first seal member 63. The first seal member 63 is provided between the first insertion hole 23 and the rotating shaft 50. The first seal member 63 suppresses air leakage from the first impeller chamber 36 toward the inside of the motor chamber 18 via the first insertion hole 23 and the inside of the first bearing holder 21. The first seal member 63 is, for example, a seal ring.

[0048] The centrifugal compressor 10 includes a second seal member 64. The second seal member 64 is provided between the second insertion hole 26 and the rotating shaft 50. The second seal member 64 suppresses air leakage from the second impeller chamber 41 toward the inside of the motor chamber 18 via the second insertion hole 26 and the inside of the second bearing holder 25. The second seal member 64 is, for example, a seal ring.

[0049] The air drawn into the first impeller chamber 36 through the first intake port 35 is accelerated by the rotation of the first impeller 61 and sent into the first diffuser passage 38, where it is pressurized as it passes through the first diffuser passage 38. The air that has passed through the first diffuser passage 38 is then discharged into the first discharge chamber 37. The air discharged into the first discharge chamber 37 is then discharged to the first discharge port 39. Therefore, air compressed by the rotation of the first impeller 61 is discharged to the first discharge port 39.

[0050] The air discharged to the first discharge port 39 is drawn into the second impeller chamber 41 via the connecting pipe 47 and the second intake port 40. The air drawn into the second impeller chamber 41 is accelerated by the rotation of the second impeller 62 and sent into the second diffuser passage 43, where it is pressurized by passing through the second diffuser passage 43. The air that has passed through the second diffuser passage 43 is then discharged into the second discharge chamber 42. The air discharged into the second discharge chamber 42 is discharged to the second discharge port 44. Therefore, air compressed by the rotation of the second impeller 62 is discharged to the second discharge port 44.

[0051] The air discharged to the second discharge port 44 is supplied to the fuel cell stack 46 via the supply pipe 45. Thus, the centrifugal compressor 10 supplies air to the fuel cell stack 46. The oxygen contained in the air supplied to the fuel cell stack 46 contributes to power generation in the fuel cell stack 46. The air discharged from the fuel cell stack 46 is released to the atmosphere as exhaust gas via a stack discharge passage 46a.

[0052] An introduction hole 48 is formed in the second plate 16. A first end of the introduction hole 48 opens to the outer circumferential surface of the second plate 16. A second end of the introduction hole 48 communicates with a portion of the second insertion hole 26 closer to the motor chamber 18 than the second seal member 64.

[0053] The centrifugal compressor 10 has a discharge hole 49. The discharge hole 49 is formed in the third plate 17. A first end of the discharge hole 49 communicates with a portion of the first insertion hole 23 that is closer to the motor chamber 18 than the first seal member 63. A second end of the discharge hole 49 opens to the outer circumferential surface of the third plate 17.

[0054] <Connection piping> As shown in FIG. 2, the connection pipe 47 has a first pipe part 65 , a second pipe part 66 , a third pipe part 67 , and a fourth pipe part 68 .

[0055] The first piping part 65 has a first piping main body 69 and a joint portion 70. The first piping main body 69 is cylindrical. The joint portion 70 is cylindrical. The joint portion 70 protrudes from a first end portion of the first piping main body 69 on the outer circumferential surface of the first piping main body 69. The joint portion 70 extends in a direction perpendicular to the axis of the first piping main body 69.

[0056] The first piping part 65 has a first passage 71 and a second passage 72. The first passage 71 is a circular hole. The second passage 72 is a circular hole. The first passage 71 penetrates the inside of the joint part 70 and the first piping main body part 69. The axis of the first passage 71 coincides with the axis of the joint part 70. The second passage 72 passes through the inside of the first piping main body part 69. The axis of the second passage 72 coincides with the axis of the first piping main body part 69. Therefore, the first passage 71 and the second passage 72 extend in directions perpendicular to each other. The axis of the first passage 71 and the axis of the second passage 72 extend in directions perpendicular to each other.

[0057] A first end of the first passage 71 opens into the tip surface of the joint portion 70. The first piping part 65 is disposed relative to the housing 11 with the joint portion 70 connected to the first discharge port 39. Therefore, the first end of the first passage 71 communicates with the first discharge port 39. A second end of the first passage 71 communicates with a first end of the second passage 72. A second end of the second passage 72 opens into an end surface 69a of the first piping main body 69 located on the opposite side to the joint portion 70. The end surface 69a of the first piping main body 69 is flat.

[0058] As shown in FIG. 2 and FIG. 3, the first piping part 65 has two first paths 73. Each of the first paths 73 is formed in the first piping main body 69. Each of the first paths 73 branches off from the second passage 72. The two first paths 73 extend in a direction perpendicular to the axis of the second passage 72 from positions 180 degrees apart in the circumferential direction of the second passage 72. Each of the first paths 73 is in the shape of a circular hole. A first end of each of the first paths 73 communicates with the second passage 72. A second end of each of the first paths 73 opens on the outer circumferential surface of the first piping main body 69. An opening of each of the first paths 73 to the outer circumferential surface of the first piping main body 69 is sealed by a sealing member 73a.

[0059] As shown in FIG. 2, FIG. 3, and FIG. 4, the first piping part 65 has two first axial passages 74. Each first axial passage 74 is formed in the first piping main body 69. Each first axial passage 74 extends along the axis of the second passage 72. Each first axial passage 74 is an arc-shaped hole in cross section. A first end of each first axial passage 74 communicates with each first path 73. As shown in FIG. 3, each first axial passage 74 extends from a communicating portion with each first path 73 to both sides in the circumferential direction of the second passage 72 by the same length. As shown in FIG. 2, a second end of each first axial passage 74 extends toward an end face 69a of the first piping main body 69.

[0060] As shown in Figs. 2 and 5, the first piping part 65 has a first annular passage 75. The first annular passage 75 is formed in an end face 69a of the first piping main body 69. The first annular passage 75 is annular and extends in the circumferential direction of the second passage 72 with the axis of the second passage 72 as its center. The first annular passage 75 is formed by recessing the end face 69a of the first piping main body 69 in an annular shape. The first annular passage 75 is connected to the second ends of the first axial passages 74.

[0061] The first piping part 65 has a second annular passage 76. The second annular passage 76 is formed on an end surface 69a of the first piping main body 69. The second annular passage 76 is annular and extends in the circumferential direction of the second passage 72 with the axis of the second passage 72 as the center. The second annular passage 76 is formed by recessing the end surface 69a of the first piping main body 69 in an annular shape. The second annular passage 76 is disposed inside the first annular passage 75.

[0062] As shown in FIGS. 2, 4, and 5, the first piping part 65 has a second axial passage 77. The second axial passage 77 is formed in the first piping main body 69. The second axial passage 77 extends along the axis of the second passage 72. The second axial passage 77 is an arc-shaped hole in cross section. As shown in FIGS. 2 and 5, a first end of the second axial passage 77 communicates with the second annular passage 76. As shown in FIG. 2, a second end of the second axial passage 77 is located inside the first piping part 65.

[0063] As shown in Figs. 2 and 4, the first piping part 65 has a second path 78. The second path 78 is formed in the first piping main body 69. The second path 78 extends in a direction perpendicular to the axis of the second passage 72. A first end of the second path 78 communicates with a second end of the second axial passage 77. The second path 78 communicates with a portion of the second axial passage 77 that is located in the center of the second axial passage 77 in the circumferential direction of the second passage 72, relative to the second end of the second axial passage 77. The second end of the second path 78 communicates with the outside of the first piping part 65.

[0064] As shown in FIG. 2 and FIG. 5, the connection pipe 47 includes a first seal member 79, a second seal member 80, and a third seal member 81. The first seal member 79, the second seal member 80, and the third seal member 81 are, for example, O-rings. The first seal member 79, the second seal member 80, and the third seal member 81 are respectively attached to the end surface 69a of the first pipe main body 69. The first seal member 79 seals between the first annular passage 75 and the outer circumferential surface of the first pipe main body 69. The second seal member 80 seals between the first annular passage 75 and the second annular passage 76. The third seal member 81 seals between the second annular passage 76 and the second passage 72.

[0065] As shown in FIG. 2 and FIG. 6, the second piping part 66 has a first tubular member 82, a second tubular member 83, and a third tubular member 84. Therefore, the connection piping 47 has a first tubular member 82, a second tubular member 83, and a third tubular member 84. The first tubular member 82 constitutes a first tubular portion. Therefore, the connection piping 47 has a first tubular portion. The second tubular member 83 surrounds the first tubular member 82. Therefore, the second tubular member 83 is a second tubular portion surrounding the first tubular portion. Therefore, the second tubular member 83 constitutes a second tubular portion. The third tubular member 84 surrounds the second tubular member 83. Therefore, the third tubular member 84 is a third tubular portion surrounding the second tubular portion. Therefore, the third tubular member 84 constitutes a third tubular portion.

[0066] As shown in FIG. 2, the first cylindrical member 82, the second cylindrical member 83, and the third cylindrical member 84 have the same axial length. The first end surface of each of the first cylindrical member 82, the second cylindrical member 83, and the third cylindrical member 84 is flat. The second end surface of each of the first cylindrical member 82, the second cylindrical member 83, and the third cylindrical member 84 is flat. The first cylindrical member 82, the second cylindrical member 83, and the third cylindrical member 84 are arranged such that their first end surfaces are located on the same plane and their second end surfaces are located on the same plane. The first end surfaces of each of the first cylindrical member 82, the second cylindrical member 83, and the third cylindrical member 84 form the first end surface of the second piping part 66. The second end surfaces of each of the first cylindrical member 82, the second cylindrical member 83, and the third cylindrical member 84 form the second end surface of the second piping part 66.

[0067] 6, the first cylindrical member 82 has a cylindrical shape. The first cylindrical member 82 forms a third passage 85. The third passage 85 passes through the inside of the first cylindrical member 82. The third passage 85 has a circular hole shape. The axis of the third passage 85 coincides with the axis of the first cylindrical member 82.

[0068] The first cylindrical member 82 has a plurality of first positioning protrusions 86a. Each first positioning protrusion 86a is a rectangular prism-shaped protrusion that protrudes from the outer circumferential surface of the first cylindrical member 82. Each first positioning protrusion 86a extends from the first end to the second end of the first cylindrical member 82. Four first positioning protrusions 86a protrude from the outer circumferential surface of the first cylindrical member 82. The four first positioning protrusions 86a are disposed at equal intervals in the circumferential direction of the first cylindrical member 82.

[0069] The second cylindrical member 83 is cylindrical. A plurality of first positioning recesses 86b are formed on the inner peripheral surface of the second cylindrical member 83. Each of the first positioning recesses 86b is a rectangular hole-shaped groove formed on the inner peripheral surface of the second cylindrical member 83. Each of the first positioning recesses 86b extends from the first end to the second end of the second cylindrical member 83. A first end of each of the first positioning recesses 86b opens on the first end face of the second cylindrical member 83. A second end of each of the first positioning recesses 86b opens on the second end face of the second cylindrical member 83. Four first positioning recesses 86b are formed on the inner peripheral surface of the second cylindrical member 83. The four first positioning recesses 86b are arranged at equal intervals in the circumferential direction of the second cylindrical member 83.

[0070] The first positioning protrusions 86a are fitted into the first positioning recesses 86b. The first positioning protrusions 86a are fitted into the first positioning recesses 86b, thereby positioning the first cylindrical member 82 and the second cylindrical member 83. Therefore, the first positioning protrusions 86a and the first positioning recesses 86b constitute a first positioning portion 86 that positions the first cylindrical member 82 and the second cylindrical member 83. In this way, the connection pipe 47 has the first positioning portion 86 that positions the first cylindrical member 82 and the second cylindrical member 83.

[0071] A plurality of third axial passages 87 are formed between the outer circumferential surface of the first cylindrical member 82 and the inner circumferential surface of the second cylindrical member 83. Each third axial passage 87 is partitioned by each first positioning protrusion 86a. Each third axial passage 87 passes between the outer circumferential surface of the first cylindrical member 82 and the inner circumferential surface of the second cylindrical member 83. Each third axial passage 87 opens to the first end face and the second end face of the second piping part 66, respectively.

[0072] The second cylindrical member 83 has a plurality of second positioning protrusions 88a. Each second positioning protrusion 88a is a rectangular prism-shaped protrusion protruding from the outer circumferential surface of the second cylindrical member 83. Each second positioning protrusion 88a extends from the first end to the second end of the second cylindrical member 83. Four second positioning protrusions 88a protrude from the outer circumferential surface of the second cylindrical member 83. The four second positioning protrusions 88a are disposed at equal intervals in the circumferential direction of the second cylindrical member 83.

[0073] The third tube member 84 is cylindrical. A plurality of second positioning recesses 88b are formed on the inner peripheral surface of the third tube member 84. Each second positioning recess 88b is a rectangular hole-shaped groove formed on the inner peripheral surface of the third tube member 84. Each second positioning recess 88b extends from the first end to the second end of the third tube member 84. A first end of each second positioning recess 88b opens on the first end face of the third tube member 84. A second end of each second positioning recess 88b opens on the second end face of the third tube member 84. Four second positioning recesses 88b are formed on the inner peripheral surface of the third tube member 84. The four second positioning recesses 88b are arranged at equal intervals in the circumferential direction of the third tube member 84.

[0074] The second positioning protrusions 88a are fitted into the second positioning recesses 88b. The second positioning protrusions 88a are fitted into the second positioning recesses 88b, thereby positioning the second cylindrical member 83 and the third cylindrical member 84. Therefore, the second positioning protrusions 88a and the second positioning recesses 88b constitute second positioning portions 88 that position the second cylindrical member 83 and the third cylindrical member 84. In this way, the connection pipe 47 has the second positioning portions 88 that position the second cylindrical member 83 and the third cylindrical member 84.

[0075] A plurality of fourth axial passages 89 are formed between the outer circumferential surface of the second cylindrical member 83 and the inner circumferential surface of the third cylindrical member 84. Each of the fourth axial passages 89 is partitioned by each of the second positioning protrusions 88a. Each of the fourth axial passages 89 passes between the outer circumferential surface of the second cylindrical member 83 and the inner circumferential surface of the third cylindrical member 84. Each of the fourth axial passages 89 opens to the first end face and the second end face of the second piping part 66, respectively.

[0076] A plurality of fins 90 are formed on the outer peripheral surface of the second cylindrical member 83. Each fin 90 protrudes from the outer peripheral surface of the second cylindrical member 83 toward the inner peripheral surface of the third cylindrical member 84. Each fin 90 is a rectangular prism-shaped protrusion protruding from the outer peripheral surface of the second cylindrical member 83. Each fin 90 extends from the first end to the second end of the second cylindrical member 83. The tip surface of each fin 90 is spaced from the inner peripheral surface of the third cylindrical member 84.

[0077] As shown in Fig. 2, the third piping part 67 is cylindrical. A first end surface of the third piping part 67 is flat. A second end surface of the third piping part 67 is flat. A fitting recess 67a is formed in the second end surface of the third piping part 67. The fitting recess 67a is a circular hole.

[0078] The third piping part 67 has a fourth passage 91. The fourth passage 91 is a circular hole. The fourth passage 91 passes through the inside of the third piping part 67. The axis of the fourth passage 91 coincides with the axis of the third piping part 67. A first end of the fourth passage 91 opens into a first end face of the third piping part 67. A second end of the fourth passage 91 opens into a bottom face of the fitting recess 67a.

[0079] 2 and 7, the third piping part 67 has a third annular passage 92. The third annular passage 92 is formed on a first end face of the third piping part 67. The third annular passage 92 has an annular shape extending in the circumferential direction of the fourth passage 91 with the axis of the fourth passage 91 as its center. The third annular passage 92 is formed by recessing the first end face of the third piping part 67 in an annular shape.

[0080] The third piping part 67 has a fourth annular passage 93. The fourth annular passage 93 is formed on a first end face of the third piping part 67. The fourth annular passage 93 is annular and extends in the circumferential direction of the fourth passage 91 with the axis of the fourth passage 91 as the center. The fourth annular passage 93 is formed by recessing the first end face of the third piping part 67 in an annular shape. The fourth annular passage 93 is disposed inside the third annular passage 92.

[0081] As shown in Figures 2, 7, 8 and 9, the third piping part 67 has a fifth axial passage 94. The fifth axial passage 94 extends along the axis of the fourth passage 91. The fifth axial passage 94 is a hole having an arc shape in cross section. As shown in Figures 2 and 7, a first end of the fifth axial passage 94 communicates with the third annular passage 92. As shown in Figure 2, a second end of the fifth axial passage 94 is located inside the third piping part 67.

[0082] 2 and 9, the third piping part 67 has a third path 95. The third path 95 extends in a direction perpendicular to the axis of the fourth passage 91. A first end of the third path 95 communicates with a second end of the fifth axial passage 94. As shown in FIG. 9, the third path 95 communicates with a portion of the fifth axial passage 94 that is located at the center of the fifth axial passage 94 in the circumferential direction of the fourth passage 91, relative to the second end of the fifth axial passage 94. The second end of the third path 95 communicates with the outside of the third piping part 67.

[0083] 2 and 8, the third piping part 67 has a sixth axial passage 96. The sixth axial passage 96 extends along the axis of the fourth passage 91. The sixth axial passage 96 is a hole having an arc shape in cross section. A first end of the sixth axial passage 96 communicates with the fourth annular passage 93. A second end of the sixth axial passage 96 is located inside the third piping part 67.

[0084] The third piping part 67 has a fourth path 97. The fourth path 97 extends in a direction perpendicular to the axis of the fourth passage 91. A first end of the fourth path 97 communicates with a second end of the sixth axial passage 96. The fourth path 97 communicates with a portion located at the center of the sixth axial passage 96 in the circumferential direction of the fourth passage 91 with respect to the second end of the sixth axial passage 96. A second end of the fourth path 97 communicates with the outside of the third piping part 67. As shown in FIG. 2, the second end of the fourth path 97 is located closer to the first end face of the third piping part 67 than the second end of the third path 95. The second end of the third path 95 communicates with a first end of the introduction hole 48. The second end of the fourth path 97 communicates with the cooling water outlet 12d.

[0085] As shown in FIG. 2 and FIG. 7, the connection pipe 47 includes a fourth seal member 98, a fifth seal member 99, and a sixth seal member 100. The fourth seal member 98, the fifth seal member 99, and the sixth seal member 100 are, for example, O-rings. The fourth seal member 98, the fifth seal member 99, and the sixth seal member 100 are respectively attached to a first end surface of the third pipe part 67. The fourth seal member 98 seals between the third annular passage 92 and the outer peripheral surface of the third pipe part 67. The fifth seal member 99 seals between the third annular passage 92 and the fourth annular passage 93. The sixth seal member 100 seals between the fourth annular passage 93 and the fourth passage 91.

[0086] As shown in FIG. 2, the fourth piping part 68 has a first joint part 101, a second joint part 102, and a connecting part 103. The first joint part 101, the second joint part 102, and the connecting part 103 are each cylindrical. The axis of the first joint part 101 and the axis of the second joint part 102 extend parallel to each other. The axis of the connecting part 103 extends in a direction perpendicular to the axis of the first joint part 101 and the axis of the second joint part 102. The connecting part 103 connects the first joint part 101 and the second joint part 102 to each other.

[0087] The fourth piping part 68 has a fifth passage 104, a sixth passage 105, and a seventh passage 106. The fifth passage 104, the sixth passage 105, and the seventh passage 106 are each a circular hole. The fifth passage 104 passes through the inside of the first joint part 101. The axis of the fifth passage 104 coincides with the axis of the first joint part 101. The sixth passage 105 passes through the inside of the connecting part 103. The axis of the sixth passage 105 coincides with the axis of the connecting part 103. The seventh passage 106 passes through the inside of the second joint part 102. The axis of the seventh passage 106 coincides with the axis of the second joint part 102.

[0088] A first end of the fifth passage 104 opens into an end face of the first joint part 101 located opposite the connecting part 103. A second end of the fifth passage 104 communicates with a first end of a sixth passage 105. A second end of the sixth passage 105 communicates with a first end of a seventh passage 106. A second end of the seventh passage 106 opens into an end face of the second joint part 102 located opposite the connecting part 103.

[0089] An end portion of the first joint portion 101 located on the opposite side to the connecting portion 103 can be fitted into a fitting recess 67a of the third piping part 67. The fourth piping part 68 is connected to the third piping part 67 by fitting an end portion of the first joint portion 101 located on the opposite side to the connecting portion 103 into the fitting recess 67a of the third piping part 67. A first end of the fifth passage 104 communicates with a second end of the fourth passage 91. The fourth piping part 68 is disposed relative to the housing 11 with the second joint portion 102 connected to the second suction port 40. A second end of the seventh passage 106 communicates with the second suction port 40.

[0090] The fourth piping part 68 is designed so that, when the second joint part 102 is connected to the second suction port 40, there is a gap between the end face of the first joint part 101 located on the opposite side to the connecting part 103 and the bottom face of the fitting recess 67a. The gap between the first joint part 101 and the bottom face of the fitting recess 67a absorbs the dimensional tolerance between the second joint part 102 and the housing 11. This avoids a problem in which the second joint part 102 becomes unable to be connected to the second suction port 40 when the fourth piping part 68 is connected to the third piping part 67.

[0091] An annular seal member 107 is attached to the outer circumferential surface of the first joint part 101. The seal member 107 is, for example, an O-ring. The seal member 107 provides a seal between the first joint part 101 and the fitting recess 67a.

[0092] The first piping part 65 and the second piping part 66 are connected to each other with a first end face of the second piping part 66 and an end face 69a of the first piping main body 69 of the first piping part 65 butted against each other. A second end of the second passage 72 communicates with a first end of the third passage 85. The first annular passage 75 communicates with a first end of each fourth axial passage 89. The second annular passage 76 communicates with a first end of each third axial passage 87. A first seal member 79, a second seal member 80, and a third seal member 81 seal between the end face 69a of the first piping main body 69 and the first end face of the second piping part 66.

[0093] The second piping part 66 and the third piping part 67 are connected to each other with a second end face of the second piping part 66 and a first end face of the third piping part 67 butted against each other. A second end of the third passage 85 communicates with a first end of the fourth passage 91. A second end of each fourth axial passage 89 communicates with a third annular passage 92. A second end of each third axial passage 87 communicates with a fourth annular passage 93. A fourth seal member 98, a fifth seal member 99, and a sixth seal member 100 seal between the second end face of the second piping part 66 and the first end face of the third piping part 67.

[0094] The first discharge port 39 and the second suction port 40 are in communication with each other through the first passage 71, the second passage 72, the third passage 85, the fourth passage 91, the fifth passage 104, the sixth passage 105, and the seventh passage 106. The first passage 71, the second passage 72, the third passage 85, the fourth passage 91, the fifth passage 104, the sixth passage 105, and the seventh passage 106 allow the air discharged to the first discharge port 39 to flow to the second suction port 40. Therefore, the first passage 71, the second passage 72, the third passage 85, the fourth passage 91, the fifth passage 104, the sixth passage 105, and the seventh passage 106 constitute a connection passage 108 that allows the air discharged to the first discharge port 39 to flow to the second suction port 40. Thus, the connection pipe 47 forms the connection passage 108. The third passage 85, which constitutes a part of the connecting passage 108, passes through the inside of the first cylindrical member 82. Therefore, a part of the connecting passage 108 passes through the inside of the first cylindrical member 82.

[0095] <Entry Passage> A portion of the air compressed by the rotation of the first impeller 61 is introduced into the second insertion hole 26 via the first radial passages 73, the first axial passages 74, the first annular passage 75, the fourth axial passages 89, the third annular passage 92, the fifth axial passage 94, the third radial passage 95, and the introduction hole 48. The air introduced into the second insertion hole 26 passes through the inside of the second bearing holder 25. In this way, a portion of the air compressed by the rotation of the first impeller 61 is introduced into the second hydrodynamic plain bearing 57.

[0096] Furthermore, the air passing inside the second bearing retaining portion 25 is introduced into the motor chamber 18. The air introduced into the motor chamber 18 passes between the rotor 51 and the stator 52, and flows inside the first bearing retaining portion 21. In this way, a portion of the air compressed by the rotation of the first impeller 61 is introduced into the first hydrodynamic bearing 56. Furthermore, the air that has passed inside the first bearing retaining portion 21 is discharged to the outside of the housing 11 via the first insertion hole 23 and the discharge hole 49.

[0097] The first radial passages 73, the first axial passages 74, the first annular passage 75, the fourth axial passages 89, the third annular passage 92, the fifth axial passage 94, the third radial passage 95, and the inlet hole 48 constitute an inlet passage 109. Thus, the centrifugal compressor 10 is provided with the inlet passage 109. The inlet passage 109 introduces a portion of the air compressed by the rotation of the first impeller 61 into the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57. The air from the inlet passage 109 is also introduced into the housing chamber that accommodates the thrust bearing. Thus, the inlet passage 109 introduces air into the thrust bearing as well.

[0098] <Branch Passage> The first passages 73, the first axial passages 74, the first annular passage 75, the fourth axial passages 89, the third annular passage 92, the fifth axial passage 94, and the third passage 95 are part of the introduction passage 109 and constitute a branch passage 110 branching from the connection passage 108. Therefore, the connection pipe 47 is formed with the branch passage 110 which is part of the introduction passage 109 and branches from the connection passage 108. The fourth axial passages 89 which constitute part of the branch passage 110 pass between the outer circumferential surface of the second cylindrical member 83 and the inner circumferential surface of the third cylindrical member 84. Therefore, part of the branch passage 110 passes between the outer circumferential surface of the second cylindrical member 83 and the inner circumferential surface of the third cylindrical member 84.

[0099] <Cooling fluid passage> The cooling water discharged from the cooling water outlet 12d passes through the fourth path 97, the sixth axial path 96, the fourth annular path 93, each third axial path 87, the second annular path 76, the second axial path 77, and the second path 78 in this order, and is discharged outside the first piping part 65. The fourth path 97, the sixth axial path 96, the fourth annular path 93, each third axial path 87, the second annular path 76, the second axial path 77, and the second path 78 form a cooling fluid passage 111 through which the cooling water flows as a cooling fluid. Therefore, the connecting pipe 47 is formed with the cooling fluid passage 111. Each third axial path 87 forming a part of the cooling fluid passage 111 passes between the outer peripheral surface of the first cylindrical member 82 and the inner peripheral surface of the second cylindrical member 83. Therefore, a part of the cooling fluid passage 111 passes between the outer peripheral surface of the first cylindrical member 82 and the inner peripheral surface of the second cylindrical member 83. The cooling water discharged from the first piping part 65 is returned to the cooling water circuit.

[0100] <Switching valve> As shown in FIG. 10, the centrifugal compressor 10 includes a bypass passage 112 branching off from the fourth path 97. The centrifugal compressor 10 includes a switching valve 113. The switching valve 113 is provided at a connection point of the fourth path 97 with the bypass passage 112. The switching valve 113 is an electromagnetic valve. The switching valve 113 is a three-way valve. The switching valve 113 is configured to be switchable to a first switching state that allows the flow of cooling water from the cooling water discharge port 12d to the sixth shaft path 96 via the fourth path 97 and blocks the flow of cooling water from the cooling water discharge port 12d to the bypass passage 112 via the fourth path 97. In addition, the switching valve 113 is configured to be switchable to a second switching state in which the flow of cooling water is blocked from the cooling water discharge port 12d to the sixth axial passage 96 via the fourth path 97, and the flow of cooling water is allowed from the cooling water discharge port 12d to the bypass passage 112 via the fourth path 97.

[0101] When the switching valve 113 is switched to the first switching state, the flow of cooling water is permitted in the cooling fluid passage 111. On the other hand, when the switching valve 113 is switched to the second switching state, the flow of cooling water in the cooling fluid passage 111 is blocked. Therefore, the switching valve 113 is switchable between the first switching state in which the flow of cooling water is permitted in the cooling fluid passage 111 and the second switching state in which the flow of cooling water in the cooling fluid passage 111 is blocked. The cooling water flowing through the bypass passage 112 is returned to the cooling water circuit.

[0102] The centrifugal compressor 10 includes a control unit 114. The control unit 114 is electrically connected to the switching valve 113. The control unit 114 can be realized, for example, by one or more dedicated hardware circuits and / or one or more processors (control circuits) operating according to a computer program (software). The processor includes a CPU and a memory such as a RAM and a ROM, and the memory stores, for example, program codes or instructions configured to cause the processor to execute various processes. The memory, i.e., the computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer.

[0103] When switching the switching valve 113 to the first switching state, the control unit 114 sets the switching valve 113 to a non-energized state. On the other hand, when switching the switching valve 113 to the second switching state, the control unit 114 sets the switching valve 113 to a powered state. Therefore, the switching valve 113 is a solenoid valve that switches to the first switching state when not energized and switches to the second switching state when energized.

[0104] The centrifugal compressor 10 includes a rotation speed sensor 115. The rotation speed sensor 115 is configured to be able to detect the rotation speed of the motor 20. The rotation speed sensor 115 is electrically connected to the control unit 114. Information relating to the rotation speed of the motor 20 detected by the rotation speed sensor 115 is transmitted to the control unit 114.

[0105] A valve control program for controlling the operation of the switching valve 113 is stored in advance in the control unit 114. A program for grasping the power consumption of the motor 20 is stored in advance in the control unit 114. The valve control program controls the operation of the switching valve 113 based on a map in which the rotation speed of the motor 20 detected by the rotation speed sensor 115 and the power consumption of the motor 20 are correlated.

[0106] In the valve control program, when the rotation speed of the motor 20 exceeds a predetermined rotation speed and the power consumption of the motor 20 exceeds a predetermined power consumption, the switching valve 113 is switched to the first switching state. Therefore, when the rotation speed of the motor 20 exceeds a predetermined rotation speed and the power consumption of the motor 20 exceeds a predetermined power consumption, the switching valve 113 is switched to the first switching state. Note that the "predetermined rotation speed" is the rotation speed of the motor 20 at which the amount of heat generated by the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 due to the rotation of the rotating shaft 50 is relatively large and the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 are considered to be highly necessary to be cooled. The "predetermined rotation speed" is appropriately changed depending on the type of the centrifugal compressor 10. Also, the "predetermined power consumption" is the power consumption of the motor 20 at which the compression work by the rotation of the first impeller 61 and the second impeller 62 is relatively increased and the temperature of the air compressed by the rotation of the first impeller 61 is relatively high. The “predetermined power consumption” is changed as appropriate depending on the type of the centrifugal compressor 10.

[0107] [Operation of the embodiment] Next, the operation of the embodiment will be described. 11, first, in step S11, the control unit 114 determines whether or not the rotation speed of the motor 20 detected by the rotation speed sensor 115 exceeds a predetermined rotation speed. If the control unit 114 determines in step S11 that the rotation speed of the motor 20 detected by the rotation speed sensor 115 does not exceed the predetermined rotation speed, the control unit 114 proceeds to step S12, where it switches the switching valve 113 to an energized state. This switches the switching valve 113 to the second switching state, and the flow of cooling water in the cooling fluid passage 111 is blocked.

[0108] On the other hand, if the control unit 114 determines in step S11 that the rotation speed of the motor 20 detected by the rotation speed sensor 115 exceeds a predetermined rotation speed, the process proceeds to step S13. Then, in step S13, the control unit 114 determines whether or not the power consumption of the motor 20 exceeds a predetermined power consumption. If the control unit 114 determines in step S13 that the power consumption of the motor 20 does not exceed the predetermined power consumption, the process proceeds to step S12, where the switching valve 113 is energized. As a result, the switching valve 113 is switched to the second switching state, and the flow of cooling water in the cooling fluid passage 111 is blocked.

[0109] On the other hand, when the control unit 114 determines in step S13 that the power consumption of the motor 20 exceeds the predetermined power consumption, the process proceeds to step S14. Then, in step S14, the control unit 114 de-energizes the switching valve 113. This switches the switching valve 113 to the first switching state, and the flow of cooling water in the cooling fluid passage 111 is permitted.

[0110] When the rotation speed of the motor 20 exceeds a predetermined rotation speed, the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 generate a relatively large amount of heat as the rotating shaft 50 rotates, and therefore it is necessary to cool the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57. Furthermore, when the power consumption of the motor 20 exceeds a predetermined power consumption, the compression work caused by the rotation of the first impeller 61 and the second impeller 62 increases relatively. Therefore, the temperature of the air compressed by the rotation of the first impeller 61 becomes relatively high.

[0111] When the flow of cooling water in the cooling fluid passage 111 is permitted, heat exchange occurs between the cooling water flowing through each third axial passage 87 and the air flowing through the third passage 85 via the first cylindrical member 82. As a result, the air flowing through the third passage 85 is cooled by the cooling water flowing through each third axial passage 87. Then, the air cooled by the cooling water flowing through each third axial passage 87 is sucked into the second impeller chamber 41 via the connecting passage 108 and the second intake port 40.

[0112] In addition, heat exchange is performed between the cooling water flowing through each third axial passage 87 and the air flowing through each fourth axial passage 89 via the second cylindrical member 83, so that the air flowing through each fourth axial passage 89 is cooled by the cooling water flowing through each third axial passage 87. At this time, since a plurality of fins 90 protruding toward the inner circumferential surface of the third cylindrical member 84 are formed on the outer circumferential surface of the second cylindrical member 83, heat exchange is efficiently performed between the cooling water flowing through each third axial passage 87 and the air flowing through each fourth axial passage 89 via the second cylindrical member 83. In this way, the cooling fluid passage 111 is circulated with the cooling water as a cooling fluid for cooling the air flowing through the branch passage 110.

[0113] The air flowing through the branch passage 110 is cooled by the cooling water flowing through the cooling fluid passage 111, and its temperature decreases. As a result, the second dynamic pressure plain bearing 57 is cooled by the air passing inside the second bearing retaining portion 25. The motor 20 is cooled by the air introduced into the motor chamber 18. The first dynamic pressure plain bearing 56 is cooled by the air passing inside the first bearing retaining portion 21. The thrust bearing is also cooled by the air passing through the accommodation chamber that accommodates the thrust bearing.

[0114] [Effects of the embodiment] The embodiment can provide the following effects. (1) In the connecting pipe 47, which is an existing configuration, a branch passage 110 that is part of the introduction passage 109 and branches off from the connecting passage 108, and a cooling fluid passage 111 through which cooling water flows to cool the air flowing through the branch passage 110 are formed. For this reason, unlike the conventional technology, there is no need to use an intercooler to cool the air flowing through the introduction passage 109. Therefore, without using an intercooler, the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 can be cooled by using part of the air compressed by the rotation of the first impeller 61, and therefore the centrifugal compressor 10 can be made more compact.

[0115] (2) Heat exchange between the cooling water flowing through each third axial passage 87 and the air flowing through the third passage 85 is performed via the first cylindrical member 82, so that the air flowing through the third passage 85 is cooled by the cooling water flowing through each third axial passage 87. Also, heat exchange between the cooling water flowing through each third axial passage 87 and the air flowing through each fourth axial passage 89 is performed via the second cylindrical member 83, so that the air flowing through each fourth axial passage 89 is cooled by the cooling water flowing through each third axial passage 87. In this way, the cooling water flowing through each third axial passage 87 can cool not only the air flowing through the introduction passage 109, but also the air flowing through the connection passage 108. Therefore, the air flowing through the connection passage 108 is cooled, so that the temperature of the air sucked into the second impeller chamber 41 from the second intake port 40 can be lowered. Therefore, the efficiency of air compression accompanying the rotation of the second impeller 62 can be improved.

[0116] (3) The configuration including the first cylindrical member 82, the second cylindrical member 83, the third cylindrical member 84, the first positioning portion 86, and the second positioning portion 88 is suitable for manufacturing the connection pipe 47. Therefore, the connection pipe 47 can be easily manufactured.

[0117] (4) Since a plurality of fins 90 that protrude toward the inner circumferential surface of the third cylindrical member 84 are formed on the outer circumferential surface of the second cylindrical member 83, heat exchange between the cooling water flowing through each third axial passage 87 and the air flowing through each fourth axial passage 89 is efficiently carried out via the second cylindrical member 83. Therefore, the air flowing through each fourth axial passage 89 can be more efficiently cooled by the cooling water flowing through each third axial passage 87. As a result, the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 can be more efficiently cooled.

[0118] (5) When the rotation speed of the motor 20 exceeds a predetermined rotation speed, the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 generate a relatively large amount of heat due to the rotation of the rotating shaft 50, and therefore it is necessary to cool the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57. In addition, when the power consumption of the motor 20 exceeds a predetermined power consumption, the compression work due to the rotation of the first impeller 61 and the second impeller 62 increases relatively. Therefore, the temperature of the air compressed by the rotation of the first impeller 61 is relatively high. Therefore, when the rotation speed of the motor 20 exceeds a predetermined rotation speed and the power consumption of the motor 20 exceeds the predetermined power consumption, the switching valve 113 switches to the first switching state, and the flow of cooling water in the cooling fluid passage 111 is permitted. As a result, the air flowing through the branch passage 110 is cooled by the cooling water flowing through the cooling fluid passage 111. Therefore, the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 can be efficiently cooled by the air introduced from the introduction passage 109 to the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57.

[0119] (6) Since the switching valve 113 is switched to the first switching state when de-energized, the flow of cooling water in the cooling fluid passage 111 can be maintained in an allowable state without supplying power to the switching valve 113. Then, power is supplied to the switching valve 113 only when there is no need to cool the air flowing through the branch passage 110 by the cooling water flowing through the cooling fluid passage 111 and when the air flowing through the connection passage 108 is not to be heated. Therefore, the air flowing through the branch passage 110 can be cooled by the cooling water flowing through the cooling fluid passage 111 while minimizing the supply of power to the switching valve 113. As a result, the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 can be efficiently cooled while achieving energy saving in the centrifugal compressor 10.

[0120] (7) For example, consider a case where the power consumption of the motor 20 is small, the operating load of the centrifugal compressor 10 is small, the rotation speed of the motor 20 is low, and the heat generation amount of the first dynamic pressure plain bearing 56 and the second dynamic pressure plain bearing 57 is small. Under such conditions, the temperature of the air compressed by the rotation of the first impeller 61 is relatively low, so there is a risk that the cooling water flowing through the cooling fluid passage 111 will warm the air flowing through the connecting passage 108 and the branch passage 110. Therefore, when the rotation speed of the motor 20 does not exceed a predetermined rotation speed, the switching valve 113 is switched to the second switching state. Furthermore, when the power consumption of the motor 20 does not exceed a predetermined power consumption, the switching valve 113 is switched to the second switching state. This makes it possible to avoid the cooling water flowing through the cooling fluid passage 111 warming the air flowing through the connecting passage 108 and the branch passage 110 when the temperature of the air compressed by the rotation of the first impeller 61 is relatively low.

[0121] (8) By cooling the air flowing through the connecting passage 108, the temperature of the air drawn into the second impeller chamber 41 from the second intake port 40 can be lowered, and as a result, the temperature of the air supplied to the fuel cell stack 46 can be lowered.

[0122] [Example of change] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0123] In the above embodiment, the connection pipe 47 may be configured so that only the air flowing through the introduction passage 109 is cooled by the cooling water flowing through each of the third shaft passages 87. In other words, the connection pipe 47 may be configured so that the air flowing through the connection passage 108 is not cooled by the cooling water flowing through each of the third shaft passages 87.

[0124] In the embodiment, the entire second piping part 66 of the connection piping 47 may be formed by casting. In short, the connection piping 47 may have a first cylindrical portion, a second cylindrical portion surrounding the first cylindrical portion, and a third cylindrical portion surrounding the second cylindrical portion. Also, it is sufficient that a part of the connection passage 108 passes inside the first cylindrical portion, a part of the cooling fluid passage 111 passes between the outer circumferential surface of the first cylindrical portion and the inner circumferential surface of the second cylindrical portion, and a part of the branch passage 110 passes between the outer circumferential surface of the second cylindrical portion and the inner circumferential surface of the third cylindrical portion.

[0125] In the above embodiment, the fins 90 that protrude toward the inner circumferential surface of the third cylindrical member 84 do not necessarily have to be formed on the outer circumferential surface of the second cylindrical member 83 . In the embodiment, for example, a plurality of first positioning recesses may be formed on the outer circumferential surface of the first cylindrical member 82, and a plurality of first positioning protrusions may be formed on the inner circumferential surface of the second cylindrical member 83. Then, the first positioning protrusions may be fitted into the first positioning recesses, thereby positioning the first cylindrical member 82 and the second cylindrical member 83. In this manner, the first positioning recesses formed on the outer circumferential surface of the first cylindrical member 82 and the first positioning protrusions formed on the inner circumferential surface of the second cylindrical member 83 may constitute a first positioning portion 86 that positions the first cylindrical member 82 and the second cylindrical member 83.

[0126] In the embodiment, for example, a plurality of first positioning recesses may be formed on the outer circumferential surface of the first cylindrical member 82, and a plurality of first positioning recesses may be formed on the inner circumferential surface of the second cylindrical member 83. Then, the first cylindrical member 82 and the second cylindrical member 83 may be positioned by fitting a pillar-shaped member into each of the first positioning recesses formed on the outer circumferential surface of the first cylindrical member 82 and the inner circumferential surface of the second cylindrical member 83, respectively. In this manner, a first positioning portion 86 for positioning the first cylindrical member 82 and the second cylindrical member 83 may be configured by the first positioning recesses formed on the outer circumferential surface of the first cylindrical member 82 and the inner circumferential surface of the second cylindrical member 83, respectively, and the pillar-shaped member.

[0127] In the embodiment, for example, a plurality of second positioning recesses may be formed on the outer circumferential surface of the second cylindrical member 83, and a plurality of second positioning protrusions may be formed on the inner circumferential surface of the third cylindrical member 84. Then, the second cylindrical member 83 and the third cylindrical member 84 may be positioned by fitting each of the second positioning protrusions into each of the second positioning recesses. In this manner, the second positioning recesses formed on the outer circumferential surface of the second cylindrical member 83 and the second positioning protrusions formed on the inner circumferential surface of the third cylindrical member 84 may constitute a second positioning portion 88 that positions the second cylindrical member 83 and the third cylindrical member 84.

[0128] In the embodiment, for example, a plurality of second positioning recesses may be formed on the outer circumferential surface of the second cylindrical member 83, and a plurality of second positioning recesses may be formed on the inner circumferential surface of the third cylindrical member 84. Then, the second cylindrical member 83 and the third cylindrical member 84 may be positioned by fitting a pillar-shaped member into each of the second positioning recesses formed on the outer circumferential surface of the second cylindrical member 83 and the inner circumferential surface of the third cylindrical member 84, respectively. In this manner, a second positioning portion 88 for positioning the second cylindrical member 83 and the third cylindrical member 84 may be configured by the second positioning recesses formed on the outer circumferential surface of the second cylindrical member 83 and the inner circumferential surface of the third cylindrical member 84, respectively, and the pillar-shaped member.

[0129] In the above embodiment, the control unit 114 may switch the switching valve 113 to the first switching state when the rotation speed of the motor 20 exceeds a predetermined rotation speed, for example. In the above embodiment, the switching valve 113 may be a solenoid valve that switches to a first switching state when energized and switches to a second switching state when de-energized.

[0130] In an embodiment, the switching valve 113 may be a mechanical valve. In the embodiment, the switching valve 113 does not have to be a three-way valve provided at the connection point of the fourth path 97 with the bypass passage 112. For example, a two-way switching valve may be provided in a portion of the fourth path 97 downstream of the connection point of the fourth path 97 with the bypass passage 112, and a two-way switching valve may also be provided in the bypass passage 112. The two switching valves may be configured to switch between a first switching state that allows the flow of cooling water in the cooling fluid passage 111 and a second switching state that blocks the flow of cooling water in the cooling fluid passage 111.

[0131] In the above embodiment, the centrifugal compressor 10 does not have to include the switching valve 113. In the above embodiment, the cooling fluid flowing through the cooling fluid passage 111 may be, for example, air or a refrigerant.

[0132] In the embodiment, the fluid compressed by the centrifugal compressor 10 is not limited to air. Therefore, the application of the centrifugal compressor 10 and the fluid to be compressed may be any. For example, the centrifugal compressor 10 may be used in an air conditioner, and the fluid to be compressed may be a refrigerant. Furthermore, the application of the centrifugal compressor 10 is not limited to a vehicle, and may be any.

[0133] [Note] The above embodiment includes the configurations described in the following supplementary notes. <Appendix 1> A rotation axis; a first impeller that rotates integrally with the rotary shaft to compress a fluid; a second impeller that rotates integrally with the rotary shaft to compress the fluid compressed by the rotation of the first impeller; A motor that rotates the rotary shaft; a housing having a first impeller chamber that houses the first impeller, a second impeller chamber that houses the second impeller, a first suction port that draws a fluid into the first impeller chamber, a first discharge port through which a fluid compressed by rotation of the first impeller is discharged, and a second suction port that draws a fluid into the second impeller chamber; a bearing that rotatably supports the rotating shaft relative to the housing; a connection pipe that connects the first discharge port and the second suction port and forms a connection passage through which the fluid discharged to the first discharge port flows to the second suction port; An introduction passage that introduces a part of the fluid compressed by the rotation of the first impeller into the bearing, The connecting pipe includes: a branch passage which is a part of the introduction passage and branches off from the connection passage; a cooling fluid passage through which a cooling fluid flows for cooling the fluid flowing through the branch passage.

[0134] <Appendix 2> The connecting pipe is A first cylindrical portion; a second cylindrical portion surrounding the first cylindrical portion; A third cylindrical portion surrounding the second cylindrical portion, A portion of the connecting passage passes through the inside of the first cylindrical portion, a portion of the cooling fluid passage passing between an outer circumferential surface of the first cylindrical portion and an inner circumferential surface of the second cylindrical portion; The centrifugal compressor according to <Appendix 1>, wherein a portion of the branch passage passes between an outer circumferential surface of the second cylindrical portion and an inner circumferential surface of the third cylindrical portion.

[0135] <Appendix 3> The connecting pipe is A first cylindrical member constituting the first cylindrical portion; A second cylindrical member constituting the second cylindrical portion; A third cylindrical member constituting the third cylindrical portion; a first positioning portion that positions the first cylindrical member and the second cylindrical member; The centrifugal compressor according to <Appendix 2>, further comprising: a second positioning portion that positions the second cylindrical member and the third cylindrical member.

[0136] <Appendix 4> The centrifugal compressor according to <Appendix 2> or <Appendix 3>, characterized in that a fin protruding toward an inner circumferential surface of the third cylindrical portion is formed on an outer circumferential surface of the second cylindrical portion.

[0137] <Appendix 5> a switching valve that is switchable between a first switching state that allows the cooling fluid to flow through the cooling fluid passage and a second switching state that blocks the flow of the cooling fluid through the cooling fluid passage; The centrifugal compressor according to any one of <Appendix 1> to <Appendix 4>, wherein the switching valve is switched to the first switching state when the rotation speed of the motor exceeds a predetermined rotation speed and the power consumption of the motor exceeds a predetermined power consumption.

[0138] <Appendix 6> The centrifugal compressor according to <Appendix 5>, wherein the switching valve is an electromagnetic valve that switches to the first switching state when de-energized and switches to the second switching state when energized. [Explanation of symbols]

[0139] DESCRIPTION OF THE REFERENCE NUMERALS 10...centrifugal compressor, 11...housing, 20...motor, 35...first suction port, 36...first impeller chamber, 39...first discharge port, 40...second suction port, 41...second impeller chamber, 47...connecting piping, 50...rotating shaft, 56...first hydrodynamic plain bearing as bearing, 57...second hydrodynamic plain bearing as bearing, 61...first impeller, 62...second impeller, 82...first cylindrical member constituting first cylindrical portion, 83...second cylindrical member constituting second cylindrical portion, 84...third cylindrical member constituting third cylindrical portion, 86...first positioning portion, 88...second positioning portion, 90...fin, 108...connecting passage, 109...introduction passage, 110...branch passage, 111...cooling fluid passage, 113...switching valve.

Claims

1. A rotation axis; a first impeller that rotates integrally with the rotary shaft to compress a fluid; a second impeller that rotates integrally with the rotary shaft to compress the fluid compressed by the rotation of the first impeller; A motor that rotates the rotary shaft; a housing having a first impeller chamber that accommodates the first impeller, a second impeller chamber that accommodates the second impeller, a first suction port that draws a fluid into the first impeller chamber, a first discharge port through which a fluid compressed by rotation of the first impeller is discharged, and a second suction port that draws a fluid into the second impeller chamber; a bearing that rotatably supports the rotating shaft relative to the housing; a connection pipe that connects the first discharge port and the second suction port and forms a connection passage through which the fluid discharged to the first discharge port flows to the second suction port; an introduction passage that introduces a portion of the fluid compressed by rotation of the first impeller into the bearing, The connecting pipe includes: a branch passage which is a part of the introduction passage and branches off from the connection passage; a cooling fluid passage through which a cooling fluid flows for cooling the fluid flowing through the branch passage.

2. The connecting pipe is A first cylindrical portion; a second cylindrical portion surrounding the first cylindrical portion; A third cylindrical portion surrounding the second cylindrical portion, A portion of the connecting passage passes through the inside of the first cylindrical portion, a portion of the cooling fluid passage passing between an outer circumferential surface of the first cylindrical portion and an inner circumferential surface of the second cylindrical portion; 2. The centrifugal compressor according to claim 1, wherein a portion of the branch passage passes between an outer circumferential surface of the second cylindrical portion and an inner circumferential surface of the third cylindrical portion.

3. The connecting pipe is A first cylindrical member constituting the first cylindrical portion; A second cylindrical member constituting the second cylindrical portion; A third cylindrical member constituting the third cylindrical portion; a first positioning portion that positions the first cylindrical member and the second cylindrical member; 3. The centrifugal compressor according to claim 2, further comprising a second positioning portion for positioning the second cylindrical member and the third cylindrical member.

4. 4. The centrifugal compressor according to claim 2, wherein a fin is formed on an outer circumferential surface of the second cylindrical portion so as to protrude toward an inner circumferential surface of the third cylindrical portion.

5. a switching valve that is switchable between a first switching state that allows the cooling fluid to flow through the cooling fluid passage and a second switching state that blocks the flow of the cooling fluid through the cooling fluid passage; 2. The centrifugal compressor according to claim 1, wherein the switching valve is switched to the first switching state when the rotation speed of the motor exceeds a predetermined rotation speed and when the power consumption of the motor exceeds a predetermined power consumption.

6. 6. The centrifugal compressor according to claim 5, wherein the switching valve is an electromagnetic valve that switches to the first switching state when de-energized and that switches to the second switching state when energized.

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