Centrifugal compressor and refrigeration device

Abstract

A technique by which the performance of a closed impeller of a centrifugal compressor can be improved is provided. A compressor 10 according to an embodiment of the present disclosure includes an impeller 200, and a casing 100 configured to house the impeller 200. The impeller 200 includes a hub 210 having a meridional plane 211, a plurality of blades 220 provided on the meridional plane 211, and a shroud 230 provided on tips of the plurality of blades 220 so as to cover the meridional plane 211. The shroud 230 has a first passage 235 penetrating between an inner surface of the shroud 230 facing the meridional plane 211 and an outer surface of the shroud 230 facing an inner surface of the casing 100. The first passage 235 has a first opening 235B in the outer surface of the shroud 230 and a second opening 235A in the inner surface of the shroud 230. In a cross section including an axis AX of a rotating shaft 250 of the impeller 200, the first passage 235 is inclined such that a center 235Bc of the first opening 235B is located on an inlet 200in side of the impeller 200 relative to a center 235Ac of the second opening 235A.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a centrifugal compressor.BACKGROUND ART

[0002] Conventionally, a technique related to a closed impeller of a centrifugal compressor is known (for example, see Patent Document 1).RELATED-ART DOCUMENTSPATENT DOCUMENTS

[0003] Patent Document 1: Japanese Laid-open Patent Publication No. 2009-156122SUMMARY OF THE INVENTIONPROBLEM TO BE SOLVED BY THE INVENTION

[0004] It is desirable to suppress deterioration in the performance of a closed impeller of a centrifugal compressor due to, for example, a reverse flow, separation, and the like and improve the performance.

[0005] An object of the present disclosure is to provide a technique by which the performance of a closed impeller of a centrifugal compressor can be improved.MEANS TO SOLVE THE PROBLEM

[0006] In a first aspect of the present disclosure, there is provided a centrifugal compressor including: an impeller (200); and a casing (100) configured to house the impeller (200), wherein the impeller (200) includes a hub (210) having a meridional plane (211), a plurality of blades (220) provided on the meridional plane (211), and a shroud (230) provided on tips of the plurality of blades (220) so as to cover the meridional plane (211), the shroud (230) has a first passage (235) penetrating between an inner surface of the shroud (230) facing the meridional plane (211) and an outer surface of the shroud (230) facing an inner surface of the casing (100), the first passage (235) having a first opening (235B) in the outer surface of the shroud (230) and a second opening (235A) in the inner surface of the shroud (230), and in a cross section including an axis (AX) of a rotating shaft (250) of the impeller(200), the first passage (235) is inclined such that a center (235Bc) of the first opening (235B) is located on an inlet (200in) side of the impeller (200) relative to a center (235Ac) of the second opening (235A).

[0007] According to the first aspect, the centrifugal compressor can cause a portion of fluid passing through the impeller to flow into a gap between the shroud and the casing through the first passage and circulate to the inlet of the impeller through the gap, for example. Therefore, the centrifugal compressor can suppress an upward slope of pressure-flow rate characteristics by slightly decreasing the peak efficiency of the impeller while increasing a work coefficient (that is, impeller work) on the high-pressure and low-flow-rate side. As a result, the centrifugal compressor can increase an operating range (achieve what is known as a wider operating range). Further, the centrifugal compressor can suppress a mild surge caused by the upward slope of the pressure-flow rate characteristics, and can suppress the generation of whining noise due to the mild surge. In addition, the centrifugal compressor can circulate fluid from the outlet of the impeller through a gap between the shroud and the casing and the first passage, for example. Therefore, the centrifugal compressor can suppress a wake in the vicinity of the outlet of the impeller. Accordingly, the centrifugal compressor can improve the performance of a closed impeller.

[0008] Further, according to the first aspect, the first passage is inclined toward the inlet of the impeller. Thus, the centrifugal compressor can reduce pressure loss due to separation when fluid circulates, and can further enhance the effect of improving the performance.

[0009] Further, in a second aspect of the present disclosure, based on the first aspect described above, the plurality of blades (220) include a first blade (220a) and a second blade (220b) located ahead of and adjacent to the first blade (220a) in a rotation direction (RT) of the impeller (200), and when a shortest distance from one end (Ps), serving as a start point, on an inlet (200in) side of the first blade (220a)to a second blade (220b) is defined as a line segment (225), a point spaced 40 percent of a length of the line segment (225) from the one end of the first blade (220a) is defined as a first imaginary point (P1), and a point spaced 60 percent of the length of the line segment (225) from the one end of the first blade (220a) is defined as a second imaginary point (P2), the second opening (235A) may be located between a first imaginary line (VL1) passing through the first imaginary point (P1) and extending in a circumferential direction and a second imaginary line (VL2) passing through the second imaginary point (P2) and extending in the circumferential direction.

[0010] Further, in a third aspect of the present disclosure, based on the first or second aspect described above, an end portion on an inlet (200in) side of the shroud (230) and the casing (100) may face each other in an axial direction so as to form a second passage (110B), and in the cross section including the axis (AX), the second passage (110B) may be inclined, in a direction from an outer surface side to an inner surface side of the shroud (230), toward an outlet (200out) of the impeller (200) with respect to a direction orthogonal to the inner surface of the shroud (230).

[0011] Further, in a fourth aspect of the present disclosure, based on the third aspect described above, the end portion on the inlet (200in) side of the shroud (230) may be chamfered.

[0012] Further, in a fifth aspect of the present disclosure, based on the third or fourth aspect described above, a width of the second passage (110B) in the axial direction may decrease from the outer surface side toward the inner surface side of the shroud (230).

[0013] Further, in a sixth aspect of the present disclosure, based on any one of the third to fifth aspects described above, an inner diameter (D2) of the end portion on the inlet (200in) side of the shroud (230) may be smaller than an inner diameter (D1) of a portion of the casing (100) facing the end portion on the inlet (200in) side of the shroud (230) in the axial direction.

[0014] Further, in a seventh aspect of the present disclosure, based on any one of the first to sixth aspects described above, it is preferable that tip portions on a shroud (230) side of the plurality of blades (220) do not overlap the second opening (235A).

[0015] Further, in an eighth aspect of the present disclosure, based on any one of the first to seventh aspects described above, a seal part (240) may be provided between the outer surface of the shroud (230) and the casing (100).

[0016] Further, in a ninth aspect of the present disclosure, based on the eighth aspect described above, the first opening (235B) may be provided on the inlet (200in) side relative to the seal part (240).

[0017] Further, in a tenth aspect of the present disclosure, based on any one of the first to ninth aspects described above, the first passage (235) may be provided so as to extend in the circumferential direction.

[0018] Further, in an eleventh aspect of the present disclosure, based on any one of the first to tenth aspects described above, the end portion on the inlet (200in) side of the shroud (230) and the casing (100) may face each other in the axial direction along the axis (AX) so as to form the second passage (110B), a third passage (110A) in communication with the first passage (235) and the second passage (110B) may be formed between the outer surface of the shroud (230) and the inner surface of the casing (100), and in the second passage (110B) or the third passage (110A), the inner surface of the casing (100) may have a protrusion (114, 115) extending in a direction orthogonal to the circumferential direction, may have a groove (113) extending in a direction orthogonal to the circumferential direction, or may be a rougher surface than the inner surface of the shroud (230).

[0019] Further, in a twelfth aspect of the present disclosure, based on the eighth aspect described above, the first opening (235B) may be provided on the outlet (200out) side of the impeller (200) relative to the seal part (240).

[0020] Further, in a thirteenth aspect of the present disclosure, based on any one of the first to twelfth aspects described above, the centrifugal compressor may further include: a first compression part configured to compress fluid flowing into the first compression part; and a second compression part configured to compress the fluid discharged from the first compression part and flowing into the second compression part, wherein the first compression part may include another impeller including another shroud that does not have the first passage (235), and the second compression part may include the impeller (200) including the shroud (230) that has the first passage (235).

[0021] Further, in a fourteenth aspect of the present disclosure, a refrigeration apparatus including the centrifugal compressor (10) of any one of the first to thirteenth aspects described above is provided.EFFECTS OF THE INVENTION

[0022] According to an embodiment, the performance of a closed impeller of a centrifugal compressor can be improved.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] [FIG. 1] FIG. 1 is a diagram illustrating an example of a configuration of a refrigeration apparatus; [FIG. 2] FIG. 2 is a diagram illustrating an example of a configuration of a compressor; [FIG. 3] FIG. 3 is a diagram illustrating a first example of a structure of the compressor; [FIG. 4] FIG. 4 is a diagram illustrating the first example of the structure of the compressor; [FIG. 5] FIG. 5 is a diagram illustrating pressure-flow rate characteristics of the compressor according to an embodiment and pressure-flow rate characteristics of a compressor according to a comparative example; [FIG. 6] FIG. 6 is a diagram illustrating a second example of the structure of the compressor; [FIG. 7] FIG. 7 is a diagram illustrating pressure-flow rate characteristics according to the second example of the structure of the compressor; [FIG. 8] FIG. 8 is a diagram illustrating a third example of the structure of the compressor; [FIG. 9] FIG. 9 is a diagram illustrating a fourth example of the structure of the compressor; [FIG. 10] FIG. 10 is a diagram illustrating a fifth example of the structure of the compressor; [FIG. 11] FIG. 11 is a diagram illustrating a sixth example of the structure of the compressor; [FIG. 12] FIG. 12 is a diagram illustrating a seventh example of the structure of the compressor; [FIG. 13] FIG. 13 is a diagram illustrating an eighth example of the structure of the compressor; [FIG. 14] FIG. 14 is a diagram illustrating a ninth example of the structure of the compressor; [FIG. 15] FIG. 15 is a diagram illustrating a tenth example of the structure of the compressor; [FIG. 16] FIG. 16 is a diagram illustrating an eleventh example of the structure of the compressor; [FIG. 17] FIG. 17 is a diagram illustrating a twelfth example of the structure of the compressor; [FIG. 18] FIG. 18 is a diagram illustrating a thirteenth example of the structure of the compressor; [FIG. 19] FIG. 19 is a diagram illustrating a fourteenth example of the structure of the compressor; [FIG. 20] FIG. 20 is a diagram illustrating a fifteenth example of the structure of the compressor; [FIG. 21] FIG. 21 is a diagram illustrating a sixteenth example of the structure of the compressor; [FIG. 22] FIG. 22 is a diagram illustrating a seventeenth example of the structure of the compressor; [FIG. 23] FIG. 23 is a diagram illustrating an eighteenth example of the structure of the compressor; and [FIG. 24] FIG. 24 is a diagram illustrating a nineteenth example of the structure of the compressor. MODE FOR CARRYING OUT THE INVENTION

[0024] Embodiments will be described below with reference to the drawings.[Configuration of Refrigeration Apparatus]

[0025] A configuration of a refrigeration apparatus 1 according to an embodiment will be described with reference to FIG. 1.

[0026] FIG. 1 is a diagram illustrating an example of the configuration of the refrigeration apparatus 1.

[0027] The refrigeration apparatus 1 circulates a refrigerant through a refrigerant circuit RC and utilizes a compression refrigeration cycle to cool and heat a target liquid or a target gas.

[0028] The refrigeration apparatus 1 is, for example, a chiller that cools a target liquid (liquid to be cooled) by heat exchange between a refrigerant and the target liquid via a compression refrigeration cycle. The liquid to be cooled is, for example, water or brine. The refrigeration apparatus 1 may be a water heater that generates hot water by heat exchange between a refrigerant and water via a compression refrigeration cycle. Further, the refrigeration apparatus 1 may be, for example, an air conditioner that cools or heats a target space by heat exchange between a refrigerant and air. A case where the refrigeration apparatus 1 is a chiller will be mainly described below.

[0029] As illustrated in FIG. 1, the refrigerating apparatus 1 includes refrigerant paths L1 to L4, a compressor 10, a heat exchanger 20, an expansion mechanism 30, and a heat exchanger 40 as components of the refrigerant circuit RC.

[0030] The refrigerant paths L1 to L4 are paths through which a refrigerant flows. The refrigerant paths L1 to L4 are, for example, tubes made of metal such as steel.

[0031] The refrigerant path L1 connects the heat exchanger 40 and an inlet of the compressor 10. The refrigerant path L2 connects an outlet of the compressor 10 and the heat exchanger 20. The refrigerant path L3 connects the heat exchanger 20 and the expansion mechanism 30. The refrigerant path L4 connects the expansion mechanism 30 and the heat exchanger 40.

[0032] The compressor 10 compresses a low-pressure refrigerant flowing in from the refrigerant path L1 and discharges a high-pressure refrigerant to the refrigerant path L2.

[0033] The heat exchanger 20 exchanges heat between the refrigerant flowing inside and an external heat medium (for example, cooling water).

[0034] The heat exchanger 20 is what is known as a condenser, and condenses a high-temperature and high-pressure refrigerant, flowing in from the refrigerant path L2 and compressed by the compressor 10, by cooling the refrigerant by heat exchange with the external heat medium, and causes a high-pressure liquid refrigerant to flow out to the refrigerant path L3.

[0035] The expansion mechanism 30 expands the high-pressure liquid refrigerant and discharges a low-pressure gas-liquid mixed refrigerant. The expansion mechanism 30 is, for example, an expansion valve or an orifice.

[0036] The expansion mechanism 30 expands the high-pressure liquid refrigerant flowing in from the refrigerant path L3 and passing through the heat exchanger 20, and causes the low-pressure gas-liquid mixed refrigerant to flow out to the refrigerant path L4.

[0037] The heat exchanger 40 exchanges heat between the refrigerant flowing inside and the liquid to be cooled outside.

[0038] The heat exchanger 40 is what is known as an evaporator, and evaporates the low-pressure gas-liquid mixed refrigerant, flowing in from the refrigerant path L4 and expanded by the expansion mechanism 30, by heat absorption from the liquid to be cooled, and causes a low-pressure gas refrigerant to flow out to the refrigerant path L1. Accordingly, the refrigerating apparatus 1 can cool the liquid to be cooled.[Configuration of Compressor]

[0039] Next, a configuration of the compressor 10 according to the present embodiment will be described with reference to FIG. 2.

[0040] FIG. 2 is a diagram illustrating an example of a configuration of the compressor 10.

[0041] In FIG. 2, a cross-sectional view of a plane including an axis AX of a rotating shaft 250 is illustrated such that the contents inside a casing 100 are exposed.

[0042] Hereinafter, a direction along the axis AX of the rotating shaft 250, that is, a direction parallel to the axis AX is referred to as an "axial direction", and a description may be given by using each of the axial direction, and a "radial direction" and a "circumferential direction" with respect to the axis AX.

[0043] As illustrated in FIG. 2, in this example, the compressor 10 is a centrifugal-type compressor (centrifugal compressor).

[0044] The number of stages of the compressor 10 is, for example, one (a single stage) as illustrated in FIG. 2. Further, the number of stages of the compressor 10 may be two or more. When the compressor 10 is a multistage compressor, compression parts in a plurality of stages including an impeller 200 are provided in series.

[0045] The compressor 10 includes the casing 100, the impeller 200, the rotating shaft 250, an electric motor 300, a radial magnetic bearing 400, a thrust magnetic bearing 500, and a touchdown bearing 600.

[0046] The casing 100 is a housing within which components of the compressor 10 are housed or attached.

[0047] The impeller 200 is housed in an impeller chamber 110 formed inside the casing 100.

[0048] The impeller 200 is attached to the rotating shaft 250 and rotates around the axis AX of the rotating shaft 250. The impeller 200 is formed such that the outer diameter of an outer surface (a meridional plane 211 described later) increases from one end (in this example, the right end in FIG. 2) to the other end (in this example, the left end in FIG. 2) in the axial direction of the impeller 200. The impeller 200 causes a refrigerant, which flows in along the axial direction from a suction pipe 120 at the circumferential center at one axial end of the impeller 200, to flow out radially outward at the other axial end of the impeller 200. A diffuser 111 is provide on the radially outer side of the other end in the radial direction of the impeller 200. In the diffuser 111, a dynamic pressure (that is, kinetic energy) of the refrigerant flowing out from the impeller 200 is converted into a static pressure (that is, pressure energy), and the compressed refrigerant flows out from the diffuser 111 into a discharge pipe 130.

[0049] The electric motor 300 is housed in an electric motor chamber 140 formed inside the casing 100.

[0050] The electric motor 300 rotationally drives the impeller 200 by using power supplied from the outside. The electric motor 300 is, for example, a permanent magnet synchronous motor. The electric motor 300 is an inner-rotor-type electric motor, and includes a rotor 310 attached to the rotating shaft 250 and a stator 320 disposed on the radially outer side of the rotor 310 and fixed to the inner peripheral surface of the electric motor chamber 140 in the casing 100.

[0051] The radial magnetic bearing 400 supports the radial load of the rotating shaft 250 in a non-contact manner by electromagnetic force. Two radial magnetic bearings 400 are provided, and each of the two radial magnetic bearings 400 is fixed to the inner surface of the casing 100. The two radial magnetic bearings 400 are arranged so as to be adjacent to respective ends of the electric motor 300 in the axial direction.

[0052] The thrust magnetic bearing 500 supports the thrust load of the rotating shaft 250 in a non-contact manner by electromagnetic force. The thrust magnetic bearing 500 includes a pair of electromagnets 510, and each of the electromagnets 510 is fixed to the inner surface of the casing 100. The two electromagnets 510 are arranged so as to be adjacent to respective ends in the axial direction of a disk-shaped collar 260 provided on the rotating shaft 250 with an axis AX at its center. The collar 260 is formed of a magnetic material. In the thrust magnetic bearing 500, the position of the rotating shaft 250 integrated with the collar 260 is held in a non-contact manner by magnetic attraction force of the pair of electromagnets 510 to the collar 260.

[0053] The touchdown bearing 600 is provided so as to suppress contact between the rotating shaft 250 and the radial magnetic bearing 400 and contact between the collar 260 and the electromagnets 510 of the thrust magnetic bearing 500. The touchdown bearing 600 is configured mainly with, for example, an angular contact ball bearing.[First Example of Structure of Compressor]

[0054] Next, a first example of a structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 3 to FIG. 5.

[0055] FIG. 3 and FIG. 4 are diagrams illustrating the first example of the compressor 10. Specifically, FIG. 3 is a perspective view of the impeller 200 of the first example of the compressor 10. FIG. 4 is a cross-sectional view of the first example of the compressor 10 taken along a plane including the axis AX of the rotating shaft 250. The same applies to cross-sectional views of FIG. 8 to FIG. 17 and FIG. 20 to FIG. 24, which will be described later. FIG. 5 is a diagram illustrating pressure-flow rate characteristics of the compressor 10 according to the embodiment and pressure-flow rate characteristics of a compressor according to a comparative example. In FIG. 5, a surge line 501 and a pressure-flow rate characteristics 502 are drawn for the compressor according to the comparative example, and a surge line 511 and a pressure-flow rate characteristic line 512 are drawn for the compressor 10 according to the embodiment.

[0056] The compressor according to the comparative example differs from the compressor 10 according to the present embodiment in that a through hole 235 described later is not provided, and is the same as the compressor 10 according to the present embodiment in other respects.

[0057] As illustrated in FIG. 4, the impeller 200 is disposed in the impeller chamber 110 formed inside the casing 100. The impeller 200 is rotationally driven by the electric motor 300 through the rotating shaft 250, and causes a refrigerant in the suction pipe 120 to flow in from an inlet 200in at one axial end and to flow out from an outlet 200out at the other axial end toward the diffuser 111 provided on the radially outer side of the impeller 200.

[0058] As illustrated in FIG. 3 and FIG. 4, in this example, the impeller 200 is what is known as an closed impeller, and includes a hub 210, a blade 220, and a shroud 230.

[0059] The blade 220 is provided on the meridional plane 211 that is the outer surface of the hub 210. A plurality of blades 220 are provided, and the plurality of blades 220 are arranged in the circumferential direction. The plurality of blades 220 may be arranged at equal intervals in the circumferential direction or may be arranged at unequal intervals in the circumferential direction.

[0060] The shroud 230 is provided to be coupled to the tips of the blades 220 so as to cover the meridional plane 211 of the hub 210. The shroud 230 is formed such that the entire outer diameter of the shroud 230 centered on the axis AX increases from the inlet 200in side toward the outlet 200out side of the impeller 200 in the axial direction. For example, as illustrated in FIG. 4, the shroud 230 includes, in the axial direction, a first section having a constant outer diameter centered on the axis AX of the rotating shaft 250, which starts from the inlet 200in of the impeller 200, and a second section having an increased outer diameter centered on the axis AX, which starts from the end of the first section. Further, the shroud 230 may be formed such that the outer diameter of the shroud 230 centered on the axis AX of the rotating shaft 250 continuously increases from the inlet 200in toward the outlet 200out of the impeller 200 in the axial direction.

[0061] In this example, the suction pipe 120 is formed within the casing 100. For example, an inner surface 100A of the casing 100, corresponding to the suction pipe 120, has a constant diameter (inner diameter) centered on the axis AX of the rotating shaft 250. As illustrated in FIG. 4, the inner diameter of the inner surface 100A of the casing 100 is, for example, the same as the inner diameter of the shroud 230 at the inlet 200in of the impeller 200.

[0062] A stepped surface 100C is provided between the inner surface 100A and an inner surface 100B of the casing 100, and the stepped surface 100C faces an end surface 230A on the inlet 200in side of the shroud 230. In this example, the stepped surface 100C is a flat surface perpendicular to the axial direction.

[0063] Similar to the stepped surface 100C, the end surface 230A of the shroud 230 is a flat surface perpendicular to the axial direction. Therefore, the distance between the stepped surface 100C and shroud 230 is constant in the radial direction.

[0064] The shroud 230 has a through hole 235 penetrating between the inner surface and the outer surface of the shroud 230.

[0065] As illustrated in FIG. 4, in a cross section including the axis AX, the through hole 235 is provided in the shroud 230 at a position relatively close to the inlet 200in of the impeller 200, and is formed so as to linearly penetrate between the inner surface and the outer surface of the shroud 230. In this example, the through hole 235 is provided in the above-described first section of the shroud 230. Accordingly, the through hole 235 enables communication between the inner space of the shroud 230 and the inlet 200in of the impeller 200 through a space 110A between the shroud 230 and the inner surface 100B of the casing 100 and a space 110B between the end surface 230A of the shroud 230 and the stepped surface 100C. Therefore, a portion of the refrigerant, which has flowed into the impeller 200, can be circulated to the inlet 200in of the impeller 200 through the through hole 235, the space 110A, and the space 110B, and can merge with the main flow flowing into the impeller 200.

[0066] Accordingly, for example, as illustrated in FIG. 5 (pressure-flow rate characteristic line 512), the compressor 10 can obtain a high pressure in a region where a discharge flow rate Q is a relatively low, as compared to the pressure-flow rate characteristics 502 of the compressor that does not have the through hole 235 according to the comparative example (see a pressure difference 513). In addition, the compressor 10 can increase an operating range (that is, achieve a wider operating range) as compared to the pressure-flow rate characteristics 502 of the compressor that does not have the through hole 235 according to the comparative example (see a region 514).

[0067] Further, for example, as illustrated in FIG. 5, in the pressure-flow rate characteristics 502 of the compressor according to the comparative example, there is a region 503 having a upward slope characteristic in which pressure P increases in response to an increase in the discharge flow rate Q. In the region 503 having the upward slope characteristic, a local reverse flow phenomenon, which is referred to as a mild surge, occurs, resulting in possible generation of whining noise from the impeller 200.

[0068] In contrast, in this example, as described above, the pressure can be increased in the region where the discharge flow rate Q is relatively low, and the work of the impeller 200 can be increased, and as a result, the upward slope characteristic of the region 503 can be suppressed (in the example of FIG. 5, the upward slope characteristic can be eliminated). Therefore, whining noise from the impeller 200 can be reduced.

[0069] As illustrated in FIG. 3, the through hole 235 is provided in the entire circumferential direction, that is, over the entire circumference of the shroud, and is formed in a slit shape so as to extend in the circumferential direction. Accordingly, the flow rate circulating to the inlet 200in of the impeller 200 through the through hole 235 can be increased.

[0070] The through hole 235 has an opening 235A in the inner surface of the shroud 230 and an opening 235B in the outer surface of the shroud 230. In this example, in a cross section including the axis AX, the through hole 235 has a constant width (dimension in the axial direction) and the openings 235A and 235B have the same width.

[0071] A seal member 240 is provided in a gap, corresponding to the impeller chamber 110, between the shroud 230 and the inner surface 100B of the casing 100. The seal member 240 is, for example, a non-contact seal member such as a labyrinth seal. The seal member 240 may be a sliding seal member.

[0072] In this example, the seal member 240 is provided on the outlet 200out side of the impeller 200 relative to the opening 235B of the through hole 235. Accordingly, the seal member 240 can partition a space between the shroud 230 and the inner surface 100B of the casing 100 into a space in communication with the through hole 235 and a space located on the outlet 200out side of the impeller 200 relative to the seal member 240. Therefore, the seal member 240 can suppress the circulation of the refrigerant from the outlet 200out to the inlet 200in of the impeller 200 through the space between the shroud 230 and the inner surface 100B of the casing 100. Thus, the compressor 10 can suppress an increase in loss due to the generation of an excessive circulation flow, and can achieve both the above-described effect of the through hole 235 and the efficiency.

[0073] Further, the through hole 235 is formed such that the through hole 235 is inclined toward the inlet 200in of the impeller 200 with respect to a direction perpendicular to the inner surface of the shroud 230. Specifically, in a cross section including the axis AX, a center 235Bc of the opening 235B of the through hole 235 is located closer to the inlet 200in of the impeller 200 than a center 235Ac of the opening 235A is. Accordingly, when the refrigerant flows into the space 110B through the through hole 235, the occurrence of separation at the outer edge of the opening 235B of the through hole 235 can be minimized. As a result, a decrease in the effective flow path cross-sectional area can be reduced. Therefore, the compressor 10 can increase the flow rate of the refrigerant circulating to the inlet 200in of the impeller 200 through the through hole 235, and can further improve the effect of the through hole 235.

[0074] For example, if the opening 235B of the through hole 235 is located closer to the outlet 200out of the impeller 200 in the axial direction, the seal member 240 would need to be disposed at a position at which the rate of increase in the outer diameter of the shroud 230 along the axial direction is relatively large. In such a case, a gap between the seal member 240 and the outer surface of the shroud 230 would increase, and as a result, the amount of leakage of the refrigerant from the outlet 200out through a gap between the shroud 230 and the inner surface 100B of the casing 100 into the inlet 200in of the impeller 200 would increase, thereby resulting in a decrease in the efficiency of the compressor 10. Further, in order to reduce the gap between the seal member 240 and the outer surface of the shroud 230, it would be necessary to modify the shape of the outer surface of the shroud 230. As a result, inertia of the impeller 200 would be increased and costs would be increased.

[0075] In contrast, in this example, because the through hole 235 is inclined toward the inlet 200in of the impeller 200, the opening 235B of the through hole 235 can be located closer to the inlet 200in of the impeller 200 in the axial direction. Thus, the seal member 240 can be located closer to the inlet 200in of the impeller 200 in the axial direction. As a result, it is possible to suppress a situation in which the seal member 240 is disposed at a position at which the rate of increase in the outer diameter of the shroud 230 along the axial direction is relatively large. Therefore, the compressor 10 can minimize the occurrence of problems, such as a decrease in efficiently due to an increase in the amount of leakage of fluid from the outlet 200out of the impeller 200 through a gap between the shroud 230 and the inner surface 100B of casing 100 into the inlet 200in of the impeller 200, an increase in inertia of the impeller 200, and an increase in costs.

[0076] The degree of inclination (for example, an inclination angle θ1) of the through hole 235 is defined from the viewpoint of, for example, suppressing separation at the outer edge of the opening 235B of the through hole 235, the viewpoint of the ease of flow of the refrigerant from the inside of the impeller 200 into the through hole 235, and the like. This is because as the degree of inclination of the through hole 235 increases, the likelihood of separation at the outer edge of the opening 235B of the through hole 235 decreases, and as the degree of inclination of the through hole 235 decreases, the refrigerant passing through the inside of the shroud 230 is more likely to flow into the through hole 235.

[0077] The inclination angle θ1 is an angle between a straight line (reference line) perpendicular to the inner surface or the outer surface of the shroud 230 at a position at which the through hole 235 is provided and a center line of the through hole 235 in a cross section including the axis AX. The reference line is, for example, a straight line that passes through the center 235Ac of the opening 235A and is orthogonal to a line segment connecting both ends of the opening 235A in a cross section including the axis AX. The center line of the through hole 235 is a line continuously connecting the centers of the through hole 235 at positions, determined with respect to the reference line, between the opening 235A and the opening 235B of the through hole 235 in a cross section including the axis AX. In this example, the center line of the through hole 235 is a straight line connecting the center 235Ac of the opening 235A and the center 235Bc of the opening 235B.

[0078] For example, the inclination angle θ1 of the through hole 235 is defined in a range of 10 degrees or more in order to prioritize the ease of the main flow of the refrigerant into the through hole 235. Further, the inclination angle θ1 of the through hole 235 may be defined in a range of 30 degrees or more in order to prioritize suppression of the occurrence of separation at the outer edge of the opening 235B of the through hole 235. Further, the inclination angle θ1 of the through hole 235 may be defined in a range of 20 degrees or more in order to achieve a balance between the ease of the main flow of the refrigerant into the through hole 235 and suppression of the occurrence of separation at the outer edge of the opening 235B of the through hole 235.

[0079] Further, the compressor 10 may be a multistage compressor as described above. In this case, as the pressure increases, that is, as an operating point is shifted to the low flow rate side, the load of a rear-stage compression part becomes higher than the load of a front-stage compression part. As a result, in general, a mild surge or a surge more easily occurs in the rear-stage compression part than in the front-stage compression part. Therefore, from the viewpoint of increasing the operating range of the compression parts, the impeller 200 of the present embodiment is employed in the rear-stage compression part and also the through hole 235 is provided in the shroud 230. On the other hand, from the viewpoint of improving the efficiency, the through hole 235 is not necessarily required to be provided in a shroud of an impeller of the front-stage compression part. Specifically, the through hole 235 of the shroud 230 may be provided in at least one compression part among compression parts in a plurality of stages following a first-stage compression part. For example, the compressor 10 includes a first compression part into which the refrigerant flows and a second compression part into which the refrigerant discharged from the first compression part flows. An impeller not having a through hole 235 in a shroud is used in the first compression part, and the impeller 200 having the through hole 235 in the shroud 230 is used in the second compression part. Further, in order to prioritize a wider operating range of the compression parts, the impeller 200 having the through hole 235 in the shroud 230 may be used in each of the compression parts in the plurality of stages.[Second Example of Structure of Compressor]

[0080] Next, a second example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 6 and FIG. 7.

[0081] Hereinafter, the same or corresponding components are denoted by the same reference numerals as those of the above-described first example, components different from those of the above-described first example will be mainly described, and descriptions of the same or corresponding components as those of the above-described first example may be omitted. The same applies to third to twentieth examples, which will be described later, with respect to components that have been described in preceding example(s).

[0082] FIG. 6 is a diagram illustrating the second example of the structure of the compressor 10. Specifically, FIG. 6 is a developed view of the impeller 200 in which the meridional plane 211 and base end portions of blades 220 are developed about the axis AX. FIG. 7 is a diagram illustrating pressure-flow rate characteristics according to the second example of the structure of the compressor 10. FIG. 7 includes pressure-flow rate characteristics 701 of the compressor 10 according to the present example and pressure-flow rate characteristics 702 and 703 of compressors according to two comparative examples. The pressure-flow rate characteristics 702 correspond to a comparative example in which an entire opening 235A of a through hole 235 is located in a region 602 that is closer to the inlet 200in of the impeller 200 than a region 601 of FIG. 6 is. The pressure-flow rate characteristics 703 correspond to a comparative example in which an entire opening 235A of a through hole 235 is located in a region 603 that is closer to the outlet 200out of the impeller 200 than the region 601 is. In addition, FIG. 7 includes the pressure-flow rate characteristics 502 of the compressor according to the comparative example of FIG. 5, that is, the compressor having no through hole 235.

[0083] In FIG. 6, from among the plurality of blades 220, two blades 220 are representatively depicted, and for convenience, a blade 220 located behind in a rotation direction RT is referred to as a "blade 220a" and a blade 220 located ahead in the rotation direction RT is referred to as a "blade 220b."

[0084] The second example differs from the above-described first example in that, in the compressor 10, the position of the opening 235A of the through hole 235 is defined by the relationship with the arrangement of the blades 220 of the impeller 200, and may be the same as the above-described first example in other respects.

[0085] As illustrated in FIG. 6, in this example, the through hole 235 is provided such that a part of or the entirety of the opening 235A is located in the region 601 that includes an imaginary line VL0 extending from a center P0 of a throat 225 in the circumferential direction.

[0086] The throat 225 is a line segment that corresponds to the shortest distance from one end (imaginary point Ps), serving as a start point, on the inlet 200in side of the blade 220a to the blade 220b on the meridional plane 211. In other words, the throat 225 is a line segment connecting the imaginary point Ps of the blade 220a to an imaginary point Pe of the blade 220b on the meridional plane 211. The imaginary point Pe corresponds to a position at which the distance from the imaginary point Ps is the shortest.

[0087] The region 601 is a region between imaginary lines VL1 and VL2 extending in the circumferential direction, and the imaginary lines VL1 and VL2 are positioned with the imaginary line VL0 interposed therebetween in the axial direction. For example, the imaginary line VL1 is an imaginary line extending in the circumferential direction from an imaginary point P1 that is spaced 40% of the length of the throat 225 from the imaginary point Ps, serving as a start point, on the throat 225. Further, for example, the imaginary line VL2 is an imaginary line extending in the circumferential direction from the imaginary point P1 that is spaced 60% of the length of the throat 225 from the imaginary point Ps, serving as the start point, on the throat 225.

[0088] For example, as illustrated in FIG. 7, in the pressure-flow rate characteristics 702 and 703 of the comparative examples in which the entire openings 235A of the through holes 235 are included in the region 602 and the region 603, respectively, the pressure in a low flow rate region is relatively low. In a case where the opening 235A of the through hole 235 is located in the region 602, the pressure of the refrigerant circulating through the through hole 235 is relatively low because the region 602 is located relatively close to the inlet 200in of the impeller 200, and thus an effect of increasing the pressure of the impeller 200 by a circulation flow is limited. In addition, in a case where the opening 235A of the through hole 235 is located in the region 603, the pressure of the refrigerant circulating through the through hole 235 is relatively high because the region 603 is located relatively close to the outlet 200out of the impeller 200, and as a result, the efficiency of the impeller 200 is significantly decreased.

[0089] In contrast, in the present example, the flow rate of a circulation flow can be optimized by providing the through hole 235 such that a part of or the entirety of the opening 235A is included in the region 601. Therefore, as illustrated in FIG. 7, in the pressure-flow rate characteristics 701 of the compressor 10, the pressure in the low flow rate region is relatively high. Accordingly, the above-described upward slope characteristic can be suppressed by increasing the pressure in the low flow rate region.[Third Example of Structure of Compressor]

[0090] Next, a third example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 8.

[0091] FIG. 8 is a diagram illustrating the third example of the structure of the compressor 10.

[0092] As illustrated in FIG. 8, the third example differs from the above-described first example and second example in that, in the compressor 10, the through hole 235 formed in a curved shape penetrates between the inner surface and the outer surface of the shroud 230, and may be the same as the above-described first example or second example in other points.

[0093] In this example, the through hole 235 is formed in a curved shape such that the through hole 235 is inclined toward the inlet 200in of the impeller 200 as the center line of the through hole 235 approaches an opening 235B from an opening 235A. In other words, the through hole 235 is formed in a curved shape such that the inclination angle θ1 increases from the opening 235A toward the opening 235B. This makes it possible to set the inclination angle θ1 at the opening 235B to be relatively large. Therefore, separation when the refrigerant inside the shroud 230 flows into the space 110A through the through hole 235 can be further suppressed. Further, the inclination angle θ1 at the opening 235A and the inclination angle θ1 at the opening 235B can be set separately within manufacturing constraints of the through hole 235. Therefore, within the manufacturing constraints of the through hole 235, the inclination angle θ1 at the opening 235A can be set to be relatively small, and the inclination angle θ1 at the opening 235B can be set to be relatively large. Therefore, it is possible to optimize the ease of the main flow of the refrigerant into the through hole 235 and the suppression of the occurrence of separation at the outer edge of the opening 235B of the through hole 235.[Fourth Example of Structure of Compressor]

[0094] Next, a fourth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 9.

[0095] FIG. 9 is a diagram illustrating the fourth example of the compressor 10.

[0096] As illustrated in FIG. 9, the fourth example differs from the above-described first to third examples in that, in the compressor 10, corner portions of the outer edges of the openings 235A and 235B of the through hole 235 are rounded, and may be the same as the above-described first example or second example in other points.

[0097] In this example, chamfers 235C and 235D are formed at corner portions of the outer edges of the openings 235A and 235B of the through hole 235, which are located on the inlet 200in side of the impeller 200. The chamfers 235C and 235D are, for example, rounded chamfers (R-chamfers).

[0098] Accordingly, separation at the outer edge of the opening 235A when the main flow of the refrigerant inside the shroud 230 flows into the through hole 235 can be suppressed, and also separation at the outer edge of the opening 235B when the refrigerant flows into the space 110A from the through hole 235 can be suppressed.[Fifth Example of Structure of Compressor]

[0099] Next, a fifth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 10.

[0100] FIG. 10 is a diagram illustrating the fifth example of the structure of the compressor 10.

[0101] As illustrated in FIG. 10, the fifth example differs from the above-described first to fourth examples in that, in the compressor 10, the end surface 230A of the shroud 230 is inclined toward the inside of the impeller 200, and may be the same as any one of the above-described first to fourth examples in other points.

[0102] In a cross section including the axis AX, the end surface 230A of the shroud 230 is a flat surface that is inclined such that an end point on the inner surface side of the shroud 230 is located on the inside of the impeller 200 (in other words, located on the outlet 200out side of the impeller 200) relative to an end point on the outer surface side of the shroud 230.

[0103] This allows a circulation flow in the space 110B to have a component acting in the same direction as the main flow in the vicinity of the inlet 200in of the impeller 200. Therefore, it is possible to suppress separation at the end surface 230A of the shroud 230 when the circulation flow of the refrigerant, which has passed through the through hole 235, merges with the main flow of the refrigerant in the vicinity of the inlet of the impeller 200 through the space 110B, and also reduce pressure loss. In addition, the circulation flow merging with the main flow in the vicinity of the inlet 200in of the impeller 200 through the space 110B can reduce a reverse flow occurring at the end portions of the blades 220 of the impeller 200.

[0104] As the degree of inclination (for example, an inclination angle θ2) of the end surface 230A of the shroud 230 increases, a difference in the flow direction between the main flow and the circulation flow can be made smaller. As a result, loss due to merging of the main flow and the circulation flow and mixing of the refrigerant due to the merging of the main flow and the circulation flow can be reduced. Conversely, as the degree of inclination of the end surface 230A of the shroud 230 decreases, the turning angle of the circulation flow from the space 110A into the space 110B can be made smaller. As a result, loss due to separation at a corner portion between the outer surface of the shroud 230 and the end surface 230A can be reduced.

[0105] The inclination angle θ2 is an angle between a line perpendicular to the inner surface of the shroud 230 and the end surface 230A of the shroud 230 in a cross section including the axis AX.

[0106] For example, the inclination angle θ2 of the end surface 230A of the shroud 230 is defined in a range of 30 degrees or more in order to prioritize a reduction in loss due to merging of the main flow and the circulation flow. Further, the inclination angle θ2 of the end surface 230A of the shroud 230 may be defined in a range of 10 degrees or more in order to prioritize a reduction in loss due to separation of the circulation flow at a corner portion between the outer surface of the shroud 230 and the end surface 230A. Further, the inclination angle θ2 of the end surface 230A of the shroud 230 may be defined in a range of 20 degrees or more in order to achieve a balance between a reduction in loss due to merging of the main flow and the circulation flow and a reduction in loss due to separation of the circulation flow at a corner portion between the outer surface of the shroud 230 and the end surface 230A.

[0107] The degree of inclination of the end surface 230A of the shroud 230 may be indirectly defined based on conditions of the degree of inclination (for example, an inclination angle θ3) of the space 110B serving as a passage of the refrigerant.

[0108] In this example, the inclination of the end surface 230A of the shroud 230 causes the direction of the circulation flow of the refrigerant passing through the space 110B to be inclined, in a direction from the outer surface side to the inner surface side of the shroud 230, toward the outlet 200out of the impeller 200 with respect to a direction orthogonal to the inner surface of the shroud 230. Therefore, the space 110B serving as the passage of the refrigerant can be regarded as being inclined, in a direction from the outer surface side to the inner surface side of the shroud 230, toward the outlet 200out of the impeller 200 with respect to a direction orthogonal to the inner surface of the shroud 230.

[0109] For example, the inclination angle θ3 is defined as an angle between a line (reference line) orthogonal to the inner surface of the shroud 230 at one end on the inlet 200in side of the impeller 200 and a center line of the space 110B, serving as the passage of the refrigerant, in a cross section including the axis AX. The center line of the space 110B serving as the passage of the refrigerant is a line continuously connecting the centers of the width of the space 110B at positions, determined with respect to the reference line, between one end on the outer surface side of the shroud 230 and the other end on the inner surface side of the shroud 230. The width of the space 110B is the width of the space 110B in a direction orthogonal to the reference line. In this example, the center line of the space 110B serving as the passage of the refrigerant is a straight line connecting the center of the width of the space 110B at one end on the outer surface side of the shroud 230 and the center of the width of the space 110B at the other end on the inner surface side of the shroud 230.

[0110] For example, the inclination angle θ3 of the space 110B serving as the passage of the refrigerant is defined in a range of 30 degrees or more in order to prioritize reduction in loss due to merging of the main flow and the circulation flow. Further, the inclination angle θ3 of the space 110B serving as the passage of the refrigerant may be defined in a range of 10 degrees or more in order to prioritize a reduction in loss due to separation of the circulation flow at a corner portion between the outer surface of the shroud 230 and the end surface 230A. Further, the inclination angle θ3 of the space 110B serving as the passage of the refrigerant may be defined in a range of 20 degrees or more in order to achieve a balance between a reduction in loss due to merging of the main flow and the circulation flow and a reduction in loss due to separation of the circulation flow at a corner portion between the outer surface of the shroud 230 and the end surface 230A.

[0111] In this example, the inclination angle θ2 is twice the inclination angle θ3, and thus, a value that is twice the inclination angle θ3, which is defined prior to the inclination angle θ2, can be defined as the inclination angle θ2.[Sixth Example of Structure of Compressor]

[0112] Next, a sixth example of the compressor 10 according to the present embodiment will be described with reference to FIG. 11.

[0113] FIG. 11 is a diagram illustrating the sixth example of the structure of the compressor 10.

[0114] As illustrated in FIG. 11, the sixth example differs from the above-described fifth example in that, in the compressor 10, the end surface 230A of the shroud 230 is a curved surface, and may be the same as the above-described fifth example in other respects.

[0115] The end surface 230A of the shroud 230 is inclined in a manner similar to the fifth example described above, and has a curved shape such that the degree of inclination (for example, the inclination angle θ2 or θ3) increases from the outer surface toward the inner surface of the shroud 230.

[0116] Accordingly, the compressor 10 can improve the effect of suppressing separation when the circulation flow of the refrigerant merges with the main flow through the space 110B and the effect of reducing a reverse flow at the end portions of the blades 220 of the impeller 200.

[0117] In this example, the degrees of inclination (inclination angles θ2 and θ3) of the end surface 230A of the shroud 230 and the space 110B serving as the passage of the refrigerant may be evaluated at one end on the inner surface side of the shroud 230, that is, in the vicinity of a portion where the flow of the refrigerant merges with the main flow, and may be defined by a method similar to the method in the above-described sixth example.[Seventh Example of Structure of Compressor]

[0118] Next, a seventh example of the compressor 10 according to the present embodiment will be described with reference to FIG. 12.

[0119] FIG. 12 is a diagram illustrating the seventh example of the structure of the compressor 10.

[0120] As illustrated in FIG. 12, the seventh example differs from the above-described first to sixth examples in that, in the compressor 10, corner portions of the end surface 230A of the shroud 230 are rounded, and may be the same as the above-described fifth example in other points.

[0121] A chamfer 230B is formed at a corner portion between the end surface 230A and the outer surface of the shroud 230 and a chamfer 230C is formed at a corner portion between the end surface 230A and the inner surface of the shroud 230.

[0122] Accordingly, separation of the circulation flow of the refrigerant can be suppressed, and also pressure loss can be reduced.[Eighth Example of Structure of Compressor]

[0123] Next, an eighth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 13.

[0124] FIG. 13 is a diagram illustrating the eighth example of the structure of the compressor 10.

[0125] As illustrated in FIG. 13, the eighth example differs from the above-described first to seventh examples in that, in the compressor 10, the stepped surface 100C is inclined from the inner surface 100B toward the inner surface 100A so as to approach the end surface 230A of the shroud 230, and may be the same as any one of the above-described first to fourth examples in other points.

[0126] In this example, the stepped surface 100C is a flat surface that forms an acute angle with respect to both the inner surface 100A, corresponding to the suction pipe 120, and the inner surface 100B, corresponding to the impeller chamber 110, in a plane including the axis AX.

[0127] This allows the circulation flow in the space 110B to have a component acting in the same direction as the main flow in the vicinity of the inlet 200in of the impeller 200. Therefore, it is possible to suppress separation at the end surface 230A of the shroud 230 when the circulation flow of the refrigerant, which has passed through the through hole 235, merges with the main flow of the refrigerant in the vicinity of the inlet of the impeller 200 through the space 110B, and also reduce pressure loss. In addition, the circulation flow merging with the main flow in the vicinity of the inlet 200in of the impeller 200 through the space 110B can reduce a reverse flow at the end portions of the blades 220 of the impeller 200.

[0128] Further, the stepped surface 100C is inclined from the inner surface 100B toward the inner surface 100A so as to approach the end surface 230A of the shroud 230. Thus, the width of the space 110B serving as the passage of the refrigerant decreases as the space 110B approaches a merging portion where the circulation flow of the refrigerant merges with the main flow. More specifically, a width t2 at one end on the inner surface 100A side of the space 110B serving as the passage of the refrigerant is smaller than a width t2 at the other end on the inner surface 100A side of the space 110B.

[0129] Accordingly, the dynamic pressure of the circulation flow can be increased, and merging of the circulation flow with the main flow can be promoted. Further, by increasing the dynamic pressure of the circulation flow, the effect of the circulation flow pushing back the main flow, which is to flow back, can be increased, and as a result, a reverse flow in the main flow can be reduced.

[0130] As the degree of inclination (for example, an inclination angle θ4) of the stepped surface 100C increases, a difference in the flow direction between the main flow and the circulation flow can be made smaller. As a result, loss due to merging of the main flow and the circulation flow and mixing of the refrigerant due to the merging of the flows can be reduced. Conversely, as the degree of inclination of the stepped surface 100C decreases, the turning angle of the circulation flow from the space 110A into the space 110B can be made smaller. As a result, loss due to separation at a corner portion between the outer surface of the shroud 230 and the end surface 230A can be reduced.

[0131] The inclination angle θ4 is an angle between a line perpendicular to the inner surface of the shroud 230 at one end on the inlet 200in side of the impeller 200 and the stepped surface 100C in a cross section including the axis AX.

[0132] For example, the inclination angle θ4 of the stepped surface 100C is defined in a range of 30 degrees or more in order to prioritize a reduction in loss due to merging of the main flow and the circulation flow. Further, the inclination angle θ4 of the stepped surface 100C may be defined in a range of 10 degrees or more in order to prioritize a reduction in loss due to separation of the circulation flow at a corner portion between the outer surface of the shroud 230 and the end surface 230A. Further, the inclination angle θ4 of the stepped surface 100C may be defined in a range of 20 degrees or more in order to achieve a balance between a reduction in loss due to merging of the main flow and the circulation flow and a reduction in loss due to separation of the circulation flow at a corner portion between the outer surface of the shroud 230 and the end surface 230A.

[0133] Further, the degree of inclination of the stepped surface 100C may be indirectly defined based on conditions of the degree of inclination (for example, the inclination angle θ3) of the space 110B serving as the passage of the refrigerant.

[0134] In this example, the inclination of the stepped surface 100C causes the circulation flow of the refrigerant passing through the space 110B to be inclined, in a direction from the outer surface side to the inner surface side of the shroud 230, toward the outlet 200out of the impeller 200 with respect to a direction orthogonal to the inner surface of the shroud 230. Therefore, the space 110B serving as the passage of the refrigerant can be regarded as being inclined, in a direction from the outer surface side to the inner surface side of the shroud 230, toward the outlet 200out of the impeller 200 with respect to a direction orthogonal to the inner surface of the shroud 230.

[0135] For example, the inclination angle θ3 of the space 110B serving as the passage of the refrigerant is defined in a range of 30 degrees or more in order to prioritize a reduction in loss due to merging of the main flow and the circulation flow. Further, the inclination angle θ3 of the space 110B serving as the passage of the refrigerant may be defined in a range of 10 degrees or more in order to prioritize a reduction in loss due to separation of the circulation flow at a corner portion between the outer surface of the shroud 230 and the end surface 230A. Further, the inclination angle θ3 of the space 110B may be defined in a range of 20 degrees or more in order to achieve a balance between the manufacturability of the casing 100 and a reduction in loss due to separation when the circulation flow merges with the main flow.

[0136] In this example, the inclination angle θ4 is twice the inclination angle θ3, and thus, a value that is twice the inclination angle θ3, which is defined prior to the inclination angle θ4, can be defined as the inclination angle θ4.[Ninth Example of Structure of Compressor]

[0137] Next, a ninth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 14.

[0138] FIG. 14 is a diagram illustrating the ninth example of the structure of the compressor 10.

[0139] As illustrated in FIG. 14, the ninth example differs from the above-described first to eighth examples in that, in the compressor 10, the stepped surface 100C is a curved surface, and may be the same as the above-described eighth example in other points.

[0140] In this example, the stepped surface 100C of the casing 100 is inclined in a manner similar to the eighth example described above, and has a curved shape such that the degree of inclination (for example, the inclination angle θ4) increases from the inner surface 100B toward the inner surface 100A in a cross section including the axis AX.

[0141] Accordingly, the compressor 10 can improve the effect of suppressing separation when the circulation flow of the refrigerant merges with the main flow through the space 110B and the effect of reducing a reverse flow at the end portions of the blades 220 of the impeller 200.

[0142] In this example, the degrees of inclination (inclination angles θ3 and θ4) of the end surface 230A of the shroud 230 and the space 110B serving as the passage of the refrigerant may be evaluated at one end on the inner surface side of the shroud 230, that is, in the vicinity of a merging portion where the flow of the refrigerant merges with the main flow, and may be defined by the same method as in the eighth example described above.[Tenth Example of Structure of Compressor]

[0143] Next, a tenth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 15.

[0144] FIG. 15 is a diagram illustrating the tenth example of the structure of the compressor 10.

[0145] As illustrated in FIG. 15, the tenth example differs from the above-described first to ninth examples in that, in the compressor 10, a connection portion between the stepped surface 100C and the inner surface 100A and a connection portion between the stepped surface 100C and the inner surface 100B are each formed in a curved shape, and may be the same as the above-described ninth example in other respects.

[0146] In this example, a curved surface 100D is formed at a corner portion corresponding to the connection portion between the stepped surface 100C and the inner surface 100B, and a chamfer 100E having a curved shape is formed at a corner portion corresponding to the connection portion between the stepped surface 100C and the inner surface 100A.

[0147] Accordingly, separation when the circulation flow of the refrigerant passes through the spaces 110A and 110B can be reduced, and also pressure loss can be reduced.[Eleventh Example of Structure of Compressor]

[0148] Next, an eleventh example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 16.

[0149] FIG. 16 is a diagram illustrating the eleventh example of the structure of the compressor 10.

[0150] As illustrated in FIG. 16, the eleventh example differs from the above-described first to tenth examples in that, in the compressor 10, the end surface 230A and the stepped surface 100C of the shroud 230 are both formed in a curved shape, and may be the same as the above-described sixth example or ninth example in other points.

[0151] In this example, the end surface 230A of the shroud 230 has a curved shape similar to that of the above-described sixth example. The stepped surface 100C of the casing 100 has a curved shape similar to that of the above-described ninth example.

[0152] Accordingly, similar to the above-described sixth example and ninth example, the compressor 10 can improve the effect of suppressing separation when the circulation flow of the refrigerant merges with the main flow through the space 110B, and improve the effect of reducing a reverse flow at the end portions of the blades 220 of the impeller 200.

[0153] In this example, the curved shape of the end surface 230A of the shroud 230 and the curved shape of the stepped surface 100C of the casing 100 are defined such that the width of the space 110B, serving as the passage of the refrigerant, decreases toward a merging portion where the circulation flow of the refrigerant merges with the main flow. For example, in a cross section including the axis AX, the curved shape of the end surface 230A of the shroud 230 and the curved shape of the stepped surface 100C of the casing 100 are defined such that a width t2 of one end on the inner surface 100A side of the space 110B serving as the passage of the refrigerant is smaller than a width t1 of the other end on the inner surface 100B side of the space 110B.

[0154] Accordingly, the dynamic pressure of the circulation flow can be increased, and merging of the circulation flow with the main flow can be promoted. Further, by increasing the dynamic pressure of the circulation flow, it is possible to reduce a reverse flow in the main flow.[Twelfth Example of Structure of Compressor]

[0155] Next, a twelfth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 17.

[0156] FIG. 17 is a diagram illustrating the twelfth example of the structure of the compressor 10.

[0157] As illustrated in FIG. 17, the twelfth example differs from the above-described first to eleventh examples in that a portion of the compressor 10 extending from the suction pipe 120 to the inlet 200in of the impeller 200 is formed in a bell mouth shape, and may be the same as the above-described eleventh example in other respects.

[0158] In this example, the inner surface 100A of the casing 100, corresponding to the suction pipe 120, is formed such that the inner diameter of the inner surface 100A decrease as it approaches the inlet 200in of the impeller 200. For example, as illustrated in FIG. 17, the inner surface 100A of the casing 100 is formed in a bell mouth shape.

[0159] Accordingly, the flow of the refrigerant can be accelerated toward the inlet 200in of the impeller 200. Therefore, the circulation flow of the refrigerant from the space 110B can merge with an acceleration region of the main flow of the refrigerant. As a result, mixing of the main flow of the refrigerant and the circulation flow of the refrigerant merging with the main flow through the space 110B can be promoted, and loss due to interference between the main flow and a recirculation flow can be reduced.

[0160] Further, in this example, the diameter (inner diameter D2) of the inner surface of the shroud 230 at the inlet 200in of the impeller 200 is set to be smaller than the diameter (inner diameter D1) of a connection portion between inner surface 100A and the stepped surface 100C of the casing 100.

[0161] Accordingly, the flow of the refrigerant can be further accelerated between one end of the inner surface 100A of the casing 100 and the inlet 200in of the impeller 200. Therefore, mixing of the main flow of the refrigerant and the circulation flow of the refrigerant merging with the main flow through the space 110B can be further promoted, and the effect of reducing loss due to interference between the main flow and the recirculation flow can be improved.[Thirteenth Example of Structure of Compressor]

[0162] Next, a thirteenth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 18.

[0163] FIG. 18 is a diagram illustrating the thirteenth example of the structure of the compressor 10. Specifically, FIG. 18 is a perspective view of the impeller 200 of the compressor 10 according to the present example.

[0164] As illustrated in FIG. 18, the thirteenth example differs from the above-described first to twelfth examples in that, in the compressor 10, a slit-shaped through hole 235 extending in the circumferential direction of the impeller is provided only in a part in the circumferential direction of the impeller, and may be the same as any one of the above-described first to twelfth examples in other respects.

[0165] In this example, a plurality of through holes 235 are arranged and spaced apart from each other in the circumferential direction of the impeller. A coupling portion 236 that separates through holes 235 adjacent to each other in the circumferential direction couples a portion on the inlet 200in side of the shroud 230 to a portion on the outlet 200out side of the shroud 230 relative to the through holes 235.

[0166] For example, a blade vibration mode in which the leading edges of tip portions of the blades 220 vibrate may occur in the impeller 200.

[0167] In view of the above, in the present example, the coupling portion 236 couples the portion on the inlet 200in side of the shroud 230, which corresponds to the leading edges of the tip portions of the blades 220, is coupled to the portion on the outlet 200out side of the shroud 230 relative to the through holes 235. This makes it possible to suppress a decrease in an eigenvalue and improve the strength against blade vibration.[Fourteenth Example of Structure of Compressor]

[0168] Next, a fourteenth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 19.

[0169] FIG. 19 is a diagram illustrating the fourteenth example of the structure of the compressor 10. Specifically, FIG. 19 is a perspective view of the impeller 200 of the compressor 10 according to the present example.

[0170] As illustrated in FIG. 19, the fourteenth example differs from the above-described thirteenth example in a structure of a coupling portion 236 of the compressor 10, and may be the same as the above-described thirteenth example in other respects.

[0171] In this example, in some or all of a plurality of through holes 235 arranged in the circumferential direction, openings 235B are arranged so as not to overlap the tips of the blades 220. In other words, the inner surfaces of coupling portions 236 may be coupled to the blades 220. For example, as illustrated in FIG. 19, the coupling portions 236 are formed so as to overlap the blades 220 when viewed in a radially outward direction. Accordingly, it is possible to suppress a situation in which the flow path cross-sectional area of the through holes 235 is reduced by the blades 220. As a result, a decrease in the flow rate of the refrigerant circulating into the inlet 200in of the impeller 200 through the through holes 235 can be reduced. Therefore, the flow rate of the refrigerant circulating into the inlet 200in of the impeller 200 through the through holes 235 can be ensured, and the strength against blade vibration can be ensured.[Fifteenth Example of Structure of Compressor]

[0172] Next, a fifteenth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 20.

[0173] FIG. 20 is a diagram illustrating the fifteenth example of the structure of the compressor 10.

[0174] As illustrated in FIG. 20, the fifteenth example differs from the above-described first to sixteenth examples in that, in the compressor 10, a groove portion 113 is provided in the inner surface 100B of the casing 100 corresponding to the space 110A, and may be the same as the above-described twelfth example in other respects.

[0175] The groove portion 113 is provided in the inner surface 100B of the casing 100 corresponding to the space 110A, that is, in a portion of the casing 100 located on the inlet 200in side of the impeller 200 relative to the seal member 240, so as to extend in a direction orthogonal to the circumferential direction. In other words, the groove portion 113 is provided in a portion of the inner surface 100B of the casing 100 located on the inlet 200in side of the impeller 200 relative to the seal member 240 so as to extend along a plane including the axial direction and the radial direction (that is, a plane including the axis AX). In this example, the groove portion 113 is provided in a portion of the inner surface 100B of the casing 100 located on the inlet 200in side of the impeller 200 relative to the seal member 240 so as to extend in the axial direction. For example, a plurality of groove portions 113 are provided, and the plurality of groove portions 113 are arranged in the entire circumferential direction, that is, in the entire circumference. The plurality of groove portions 113 may be arranged at equal intervals or at unequal intervals.

[0176] Accordingly, when the circulation flow of the refrigerant flowing into the space 110A from the through hole 235 passes along the groove portions 113, the groove portions 113 can regulate the flow in the circumferential direction and suppress a velocity component (forward swirl component) in the rotation direction (swirl direction) included in the circulation flow. Therefore, the forward swirl component included in the circulation flow can suppress a reduction in a pressure increase that occurs in the impeller 200 as the circulation flow merges with the main flow.[Sixteenth Example of Structure of Compressor

[0177] Next, a sixteenth example of the structure of the compressor 10 will be described with reference to FIG. 21.

[0178] FIG. 21 is a diagram illustrating the sixteenth example of the structure of the compressor 10.

[0179] As illustrated in FIG. 21, the sixteenth example differs from the above-described first to fifteenth examples in that, in the compressor 10, a protrusion 114 is provided on the inner surface 100B of the casing 100 corresponding to the space 110A, and may be the same as the above-described twelfth example in other respects.

[0180] The protrusion 114 is provided on the inner surface 100B of the casing 100 corresponding to the space 110A, that is, in a portion of the inner surface 100B of the casing 100 located on the inlet 200in side of the impeller 200 relative to the seal member 240, so as to extend in a direction orthogonal to the circumferential direction. In other words, the groove portion 113 is provided in a portion of the inner surface 100B of the casing 100 located on the inlet 200in side of the impeller 200 relative to the seal member 240, so as to extend along a plane including the axial direction and the radial direction (that is, the plane including the axis AX). In this example, the groove portion 113 is provided in a portion of the inner surface 100B of the casing 100 located on the inlet 200in side of the impeller 200 relative to the seal member 240, so as to extend in the axial direction. For example, a plurality of protrusions 114 are provided, and the plurality of protrusions 114 are arranged in the entire circumferential direction, that is, in the entire circumference. The plurality of protrusions 114 may be arranged at equal intervals or at unequal intervals.

[0181] Accordingly, when the circulation flow of the refrigerant flowing into the space 110A from the through hole 235 passes in the vicinity of the protrusions 114, the protrusions 114 can regulate the flow in the circumferential direction and suppress a velocity component (forward swirl component) in the rotation direction (swirl direction) included in the circulation flow. Therefore, the forward swirl component included in the circulation flow can suppress a reduction in an pressure increase that occurs in the impeller 200 as the circulation flow merges with the main flow.[Seventeenth Example of Structure of Compressor]

[0182] Next, a seventeenth example of the structure of the compressor 10 will be described with reference to FIG. 22.

[0183] FIG. 22 is a diagram illustrating the seventeenth example of the structure of the compressor 10.

[0184] As illustrated in FIG. 22, the seventeenth example differs from the above-described first to sixteenth examples in that, in the compressor 10, a protrusion 115 is provided on the stepped surface 100C, and may be the same as the above-described twelfth example in other points.

[0185] The protrusion 115 is provided on the stepped surface 100C so as to extend in the radial direction. For example, a plurality of protrusions 115 are provided, and the plurality of protrusions 115 are arranged in the entire circumferential direction, that is, in the entire circumference. The plurality of protrusions 115 may be arranged at equal intervals or at unequal intervals.

[0186] Accordingly, when the circulation flow of the refrigerant flowing into the space 110A from the space 110B passes in the vicinity of the protrusions 115, the protrusions 115 can regulate the flow in the circumferential direction and suppress a velocity component (forward swirl component) in the rotation direction (swirl direction) included in the circulation flow. Therefore, the forward swirl component included in the circulation flow can suppress a reduction in a pressure increase that occurs in the impeller 200 as the circulation flow merges with the main flow.[Eighteenth Example of Structure of Compressor]

[0187] Next, an eighteenth example of the structure of the compressor 10 will be described with reference to FIG. 23.

[0188] FIG. 23 is a diagram illustrating the eighteenth example of the structure of the compressor 10.

[0189] As illustrated in FIG. 23, the eighteenth example differs from the above-described first to seventeenth examples in that, in the compressor 10, the through hole 235 is provided on the outlet 200out side of the shroud 230 relative to the seal member 240, and may be the same as the above-described first example in other respects.

[0190] The seal member 240 is disposed between the shroud 230 and the inner surface 100B of the casing 100 at an end portion on the inlet 200in side of the impeller 200.

[0191] As described above, the through hole 235 is provided on the outlet 200out side of the shroud 230 relative to the seal member 240 that is located between one end portion on the inlet 200in side of the impeller 200 and the other end portion on the outlet 200out side of the impeller 200. For example, in a cross section including the axis AX, the opening 235A on the inner surface side of the through hole 235 is provided on the outlet 200out side relative to the center between one end portion on the inlet 200in side of the shroud 230 and the other end portion on the outlet 200out side of the shroud 230. In this example, in a cross section including the axis AX, the through hole 235 is provided in the shroud 230 at a position relatively close to the outlet 200out of the impeller 200, and is formed so as to linearly penetrate between the inner surface and the outer surface of the shroud 230.

[0192] Accordingly, as illustrated in FIG. 23, a portion of the refrigerant discharged from the outlet 200out of the impeller 200 can flow into the through hole 235 through a space 110C between the inner surface 100B of the casing 100 and the shroud 230, and can be circulated into the inside of the impeller 200. Therefore, the compressor 10 can suppress a wake, which is a low-energy refrigerant accumulation region, generated in the vicinity of the outlet of the impeller 200 by the circulation flow that merges with the main flow inside the impeller 200 through the through hole 235.

[0193] Further, similar to the above-described first example, the through hole 235 is provided so as to be inclined toward the inlet 200in of the impeller 200 with respect to a direction perpendicular to the inner surface of the shroud 230. In a cross section including the axis AX, the center 235Bc of the opening 235B of the through hole 235 is disposed on the inlet 200in side of the impeller 200 relative to the center 235Ac of the opening 235A. Accordingly, when the refrigerant flows into the main flow inside the impeller 200 through the through hole 235, the occurrence of separation at the outer edge of the opening 235A of the through hole 235 can be suppressed. The compressor 10 can reduce loss when the circulation flow merges with the main flow inside the impeller 200 through the through hole 235, and can further improve the effect of the through hole 235.

[0194] The degree of inclination (for example, the inclination angle θ1) of the through hole 235 is defined from the viewpoint of, for example, suppressing separation at the outer edge of the opening 235A of the through hole 235, the viewpoint of the ease of the circulation flow of the refrigerant from the space 110C into the through hole 235, and the like. This is because as the degree of inclination of the through hole 235 increases, the likelihood of separation at the outer edge of the opening 235A of the through hole 235 decreases, and as the degree of inclination of the through hole 235 decreases, the circulation flow of the refrigerant is more likely to flow into the through hole 235 through the space 110C.

[0195] For example, the inclination angle θ1 of the through hole 235 is defined in a range of 10 degrees or more in order to prioritize the ease of flow of the refrigerant into the through hole 235 through the space 110C. Further, the inclination angle θ1 of the through hole 235 may be defined in a range of 30 degrees or more in order to prioritize suppression of the occurrence of separation at the outer edge of the opening 235A of the through hole 235. Further, the inclination angle θ1 of the through hole 235 may be defined in a range of 20 degrees or more in order to achieve a balance between the ease of flow of the refrigerant into the through hole 235 through the space 110C and the suppression of the occurrence of separation at the outer edge of the opening 235A of the through hole 235.[Nineteenth Example of Structure of Compressor]

[0196] Next, a nineteenth example of the structure of the compressor 10 according to the present embodiment will be described with reference to FIG. 24.

[0197] FIG. 24 is a diagram illustrating the nineteenth example of the structure of the compressor 10.

[0198] As illustrated in FIG. 24, the nineteenth example differs from the above-described first to eighteenth examples in that, in the compressor 10, through holes are provided in the shroud 230 on both the inlet 200in side and the outlet 200out side of the impeller 200 with the seal member 240 interposed therebetween, and may be the same as the above-described twelfth example in other points.

[0199] Thus, the compressor 10 can achieve a higher pressure in a low flow rate region, a wider operating range, and suppression of a mild surge of the impeller 200 by the effect of a through hole 235 on the inlet 200in side of the impeller 200. In addition, the compressor 10 can suppress a wake of the impeller 200 by the effect of a through hole 235 on the outlet 200out side of the impeller 200.

[0200] Further, similar to the above-described first example, in this example, the through hole 235 on the inlet 200in side of the impeller 200 is provided so as to be inclined toward the inlet 200in of the impeller 200 with respect to a direction perpendicular to the inner surface of the shroud 230.

[0201] Accordingly, the compressor 10 can suppress separation at the outer edge of the opening 235B when the refrigerant flows into the space 110B through the through hole 235, and can increase the flow rate of the refrigerant circulating into the inlet 200in of the impeller 200. Therefore, the compressor 10 can further improve the effect of suppressing a mild surge by the effect of the through hole 235.

[0202] Further, similar to the above-described eighteenth example, in this example, the through hole 235 on the outlet 200out side of the impeller 200 is provided so as to be inclined toward the inlet 200in of the impeller 200 with respect to a direction perpendicular to the inner surface of the shroud 230.

[0203] Accordingly, the compressor 10 can suppress separation at the outer edge of the opening 235A when the refrigerant merges with the main flow through the through hole 235 can be suppressed, and the compressor 10 can reduce loss when the circulation flow merges with the main flow inside the impeller 200 through the through hole 235. Therefore, the compressor 10 can further improve the effect of suppressing a wake by the effect of through hole 235.[Other Examples of Structure of Compressor]

[0204] Next, other examples of structure of the compressor 10 will be described.

[0205] The above-described first to nineteenth examples of the structure of the compressor 10 may be modified or changed as appropriate. Hereinafter, for convenience, examples in which modifications or changes have been made are referred to as "modifications".<First Modification>

[0206] In the fourth example (FIG. 9) of the structure of the compressor 10 described above, the chamfers 235C and 235D may be straight chamfers (C-chamfers).<Second Modification>

[0207] In the fourth example (FIG. 9) and the first modification of the structure of the compressor 10 described above, either the chamfer 235C or the chamfer 235D may be omitted.<Third Modification>

[0208] In the third example (FIG. 8) of the structure of the compressor 10 described above, the chamfer 235C or the chamfer 235D of the fourth example (FIG. 9) or the first modification described above may be provided at least one of the outer edge of the opening 235A or the outer edge of the opening 235B.<Fourth Modification>

[0209] In each of the fifth example (FIG. 10) to the twelfth example (FIG. 17) and the fifteenth example (FIG. 20) to the seventeenth example (FIG. 22) of the structure of the compressor 10 described above, the through hole 235 may be replaced with the through hole 235 of the fourth example (FIG. 9) described above.<Fifth Modification>

[0210] In each of the eighteenth example and the nineteenth example of the structure of the compressor 10 described above, the through hole 235 provided on the outlet 200out side of the impeller 200 relative to the seal member 240 may be formed in a curved shape in a cross section including the axis AX. In this case, unlike the through hole 235 of the third example (FIG. 8), the through hole 235 is formed in a curved shape such that center line of the through hole 235 is inclined toward the inlet 200in of the impeller 200 as the through hole 235 approaches the opening 235A from the opening 235B.<Sixth Modification>

[0211] In the seventh example (FIG. 12) of the structure of the compressor 10 described above, the chamfer 230B and the chamfer 230C may be straight chamfers (for example, C-chamfers).<Seventh Modification>

[0212] In the seventh example (FIG. 12) and the sixth modification of the structure of the compressor 10 described above, either the chamfer 230B or the chamfer 230C may be omitted.<Eighth Modification>

[0213] In the sixth example (FIG. 11) of the structure of the compressor 10 described above, the chamfer 230B and the chamfer 230C of the seventh example (FIG. 12) or the fifth modification described above may be provided at a connection portion (corner portion) between the end surface 230A and the outer surface of the shroud 230 and a connection portion (corner portion) between the end surface 230A and the inner surface of the shroud 230.<Ninth Modification>

[0214] In the tenth example (FIG. 15) of the structure of the compressor 10 described above, a flat surface, shaped to conform to the corner portion corresponding to the connection portion between the stepped surface 100C and the inner surface 100B, may be provided at the corner portion in place of the curved surface 100D. Further, in the tenth example of the structure of the compressor 10 described above, the chamfer 100E at the corner portion corresponding to the connection portion between the stepped surface 100C and the inner surface 100A may be a straight chamfer (for example, a C-chamfer).<Tenth Modification>

[0215] In the tenth example (FIG. 15) and the ninth modification of the structure of the compressor 10 described above, either the curved surface 100D (or the flat surface), which is provided at the corner portion corresponding to the connection portion between the stepped surface 100C and the inner surface 100B, or the chamfer 100E may be omitted.<Eleventh Modification>

[0216] In the first example (FIG. 4) to the seventh example (FIG. 12), the ninth example (FIG. 14), the eleventh example (FIG. 16), the twelfth example (FIG. 17), the fifteenth example (FIG. 20) to the seventeenth example (FIG. 22), and the nineteenth example (FIG. 24) of the structure of the compressor 10 described above, the curved surface 100D of the tenth example (FIG. 15) or the flat surface of the ninth modification may be provided at the corner portion corresponding to the connection portion between the stepped surface 100C and the inner surface 100B. Similarly, in the first example (FIG. 4) to the seventh example (FIG. 12), the ninth example (FIG. 14), the eleventh example (FIG. 16), the twelfth example (FIG. 17), the fifteenth example (FIG. 20) to the seventeenth example (FIG. 22), and the nineteenth example (FIG. 24) of the structure of the compressor 10 described above, the chamfer 100E of the tenth example (FIG. 15) or the ninth modification may be provided at the corner portion corresponding to the connection portion between the stepped surface 100C and the inner surface 100A.<Twelfth Modification>

[0217] In the fifteenth example (FIG. 20) and its various modifications of the structure of the compressor 10 described above, a relatively rough surface (roughened surface) may be employed as the inner surface 100B of the casing 100 instead of or in addition to the groove portion 113. For example, the inner surface 100B of the casing 100 is rougher than the inner surface and the outer surface of the shroud 230. The roughness of the inner surface 100B of the casing 100 can suppress a velocity component (forward swirl component) in the rotation direction (swirl direction) included in the circulation flow of the refrigerant flowing into the space 110A through the through hole 235.<Thirteenth Modification>

[0218] In the sixteenth example (FIG. 21) and its various modifications of the structure of the compressor 10 described above, a relatively rough surface may be employed as the inner surface 100B of casing 100 instead of or in addition to the protrusion 114. For example, the inner surface 100B of the casing 100 is rougher than the inner surface and the outer surface of the shroud 230. The roughness of the inner surface 100B of the casing 100 can suppress a velocity component (forward swirl component) in the rotation direction (swirl direction) included in the circulation flow of the refrigerant flowing into the space 110A through the through hole 235.<Fourteenth Modification>

[0219] In each of the first example (FIG. 4) to the nineteenth example (FIG. 24) and the first modification to the eleventh modification of the structure of the compressor 10 described above, the through hole 235 is not necessarily a slit-shaped through hole having a relatively long dimension in the circumferential direction, and may be a through hole having a relatively short dimension in the circumferential direction (for example, a round hole, an oval hole, a rectangular hole, or the like). In this case, a plurality of through holes 235 are provided, and the plurality of through holes 235 are arranged in the circumferential direction at equal intervals or at unequal intervals. Further, in this case, openings 235B of some or all of the plurality of through holes 235 provided in the circumferential direction may be arranged so as not to overlap the tips of the blades 220. Accordingly, the flow path cross-sectional area of the through holes 235 is less likely to be reduced by the blades 220. As a result, a decrease in the flow rate of the refrigerant circulating into the inlet 200in of the impeller 200 through the through holes 235 can be reduced.[Effects]

[0220] Next, effects of the centrifugal compressor and the refrigeration apparatus according to the present embodiment will be described.

[0221] In a first aspect of the present embodiment, a centrifugal compressor includes an impeller, and a casing configured to house the impeller. The centrifugal compressor is, for example, the above-described compressor 10. The impeller is, for example, the above-described impeller 200. The casing is, for example, the above-described casing 100. Specifically, the impeller includes a hub having a meridional plane, a plurality of blades provided on the meridional plane, and a shroud provided on tips of the plurality of blades so as to cover the meridional plane. The meridional plane is, for example, the above-described meridional plane 211. The hub is, for example, the above-described hub 210. The plurality of blades are, for example, the above-described plurality of blades 220. The shroud is, for example, the above-described shroud 230. More specifically, the shroud has a first passage penetrating between an inner surface of the shroud facing the meridional plane and an outer surface of the shroud facing an inner surface of the casing. The first passage has a first opening in the outer surface of the shroud and a second opening in the inner surface of the shroud. The first opening is, for example, the above-described opening 235B. The second opening is, for example, the above-described opening 235A. The first passage is, for example, the above-described through hole 235. In a cross section including an axis of a rotating shaft of the impeller, the first passage is inclined such that a center of the first opening is located on an inlet side of the impeller relative to a center of the second opening. The rotating shaft is, for example, the above-described rotating shaft 250. The axis is, for example, the above-described axis AX. The center of the first opening is, for example, the above-described center 235Bc. The center of the second opening is, for example, the above-described center 235Ac. The inlet is, for example, the above-described inlet 200in.

[0222] Accordingly, the centrifugal compressor can cause a portion of fluid passing through the impeller to flow into a gap between the shroud and the casing through the first passage, and can circulate the fluid to the inlet of the impeller through the gap, for example. Therefore, the centrifugal compressor can suppress an upward slope of pressure-flow rate characteristics by slightly decreasing the peak efficiency of the impeller while increasing a work coefficient (that is, impeller work) on the high-pressure and low-flow-rate side. As a result, the centrifugal compressor can increase an operating range (achieve what is known as a wider operating range). Further, the centrifugal compressor can suppress a mild surge caused by the upward slope of the pressure-flow rate characteristics, and can suppress the generation of whining noise due to the mild surge. In addition, the centrifugal compressor can circulate the fluid from the outlet of the impeller into the impeller through a gap between the shroud and the casing and the first passage, for example. Therefore, the centrifugal compressor can suppress a wake in the vicinity of the outlet of the impeller. Accordingly, the centrifugal compressor can improve the performance of a closed impeller.

[0223] Further, in a second aspect of the present embodiment, based on the first aspect described above, the plurality of blades include a first blade and a second blade located ahead of and adjacent to the first blade in a rotation direction of the impeller. The first blade is, for example, the above-described blade 220a. The rotation direction is, for example, the above-described rotation direction RT. The second blade is, for example, the above-described blade 220b. Specifically, when a shortest distance from one end, serving as a start point, on an inlet side of the first blade to a second blade is defined as a line segment, a point spaced 40 percent of a length of the line segment from the one end of the first blade is defined as a first imaginary point, and a point spaced 60 percent of the length of the line segment from the one end of the first blade is defined as a second imaginary point, the second opening may be located between a first imaginary line passing through the first imaginary point and extending in a circumferential direction and a second imaginary line passing through the second imaginary point and extending in the circumferential direction. The one end on the inlet side of the first blade is, for example, the above-described imaginary point Ps. The line segment is, for example, the above-described throat 225. The first imaginary point is, for example, the above-described imaginary point P1. The second imaginary point is, for example, the above-described second imaginary point P2. The first imaginary line is, for example, the above-described imaginary line VL1. The second imaginary line is, for example, the above-described imaginary line VL2.

[0224] Accordingly, the centrifugal compressor can optimize the flow rate of a refrigerant circulating to the inlet of the impeller through the first passage and appropriately suppress the upward slope of the pressure-flow rate characteristics.

[0225] Further, in a third aspect of the present embodiment, based on the first or second aspect described above, an end portion on an inlet side of the shroud and the casing may face each other in an axial direction so as to form a second passage. The second passage is, for example, the above-described space 110B. In the cross section including the axis, the second passage may be inclined, in a direction from an outer surface side to an inner surface side of the shroud, toward an outlet of the impeller with respect to a direction orthogonal to the inner surface of the shroud. The outlet , for example, the above-described outlet 200out.

[0226] Accordingly, the centrifugal compressor can cause a circulation flow, which flows into the gap between the shroud and the casing through the first passage, to return to the main flow of the fluid at the inlet of the impeller through the second passage. In addition, in the centrifugal compressor, the second passage is inclined toward the outlet of the impeller. Thus, the centrifugal compressor can suppress separation occurring in the circulation flow and reduce pressure loss when the circulation flow merges with the main flow. In addition, in the centrifugal compressor, because the second passage is inclined toward the outlet of the impeller, the circulation flow can flow into the main flow in a state in which the circulation flow has a component in the main flow direction. As a result, a reverse flow phenomenon occurring at the blade end portions of the impeller can be suppressed.

[0227] Further, in a fourth aspect of the present embodiment, based on the third aspect described above, the end portion on the inlet side of the shroud may be chamfered.

[0228] Accordingly, separation occurring in the circulation flow can be suppressed, and pressure loss due to a decrease in the effective flow path cross-sectional area caused by the occurrence of separation can be reduced.

[0229] Further, in a fifth aspect of the present embodiment, based on the third or fourth aspect described above, a width of the second passage in the axial direction may decrease from the outer surface side toward the inner surface side of the shroud.

[0230] Accordingly, in the centrifugal compressor, the second passage is formed in a nozzle shape toward the main flow at the inlet of the impeller. Thus, the dynamic pressure of a recirculation flow can be increased when the recirculation flow merges with the main flow. Therefore, the centrifugal compressor can enhance the effect of suppressing a reverse flow phenomenon occurring at the blade end portions of the impeller.

[0231] Further, in a sixth aspect of the present embodiment, based on any one of the third to fifth aspects described above, an inner diameter of the end portion on the inlet side of the shroud may be smaller than an inner diameter of a portion of the casing facing the end portion on the inlet side of the shroud in the axial direction. The inner diameter of the end portion on the inlet side of the shroud is, for example, the above-described inner diameter D2. The inner diameter of a portion of the casing facing the end portion on the inlet side of the shroud in the axial direction is, for example, the above-described inner diameter D1.

[0232] Accordingly, in the centrifugal compressor, the vicinity of the inlet of the impeller is formed as a flow path having a bell mouth shape. Thus, the main flow can be accelerated at the inlet of the impeller. Therefore, the centrifugal compressor can cause the circulation flow to merge with an acceleration region of the main flow through the second passage. As a result, mixing of the main flow and the circulation flow can be promoted, and the occurrence of loss due to interference between the main flow and the circulation flow can be suppressed.

[0233] Further, in a seventh aspect of the present embodiment, based on any one of the first to sixth aspects described above, it is preferable that tip portions on a shroud side of the plurality of blades do not overlap the second opening.

[0234] Accordingly, the centrifugal compressor can increase the flow path cross-sectional area of the first passage and increase a flow path of the circulation flow.

[0235] Further, in an eighth aspect of the present embodiment, based on any one of the first to seventh aspects described above, a seal part may be provided between the outer surface of the shroud and the casing. The seal part is, for example, the above-described seal member 240.

[0236] Accordingly, the centrifugal compressor can guide the fluid, flowing into a space between the shroud and the casing through the first passage, into the inlet of the impeller, for example. In addition, the centrifugal compressor can guide the fluid, flowing into a space between the shroud and the casing from the outlet of the impeller, into the first passage.

[0237] Further, in the first passage, in a case where the opening (first opening) in the outer surface of the shroud is located closer to the outlet of the impeller in the axial direction, the seal part would need to be disposed at a position at which the rate of increase in the outer diameter of the shroud along the axial direction is relatively large. In such a case, a gap between the seal part and the outer surface of the shroud would increase, and as a result, the amount of leakage of fluid, which flows to the opposite side of the seal part through a gap between the shroud and the casing, would increase, thereby resulting in a decrease in the efficiency of the centrifugal compressor. Further, in order to reduce the gap between the seal part and the outer surface of the shroud, it would be necessary to modify the shape of the outer surface of the shroud. As a result, inertia of the impeller would be increased and costs would be increased.

[0238] In contrast, in this aspect, the first passage is inclined toward the inlet of the impeller. Thus, the opening (first opening) in the outer surface of the first passage can be located closer to the inlet of the impeller in the axial direction. Therefore, the seal part can be disposed closer to the inlet of the impeller in the axial direction. As a result, it is possible to suppress a situation in which the seal part is disposed at a position at which the rate of increase in the outer diameter of the shroud along the axial direction is relatively large. Therefore, it is possible to minimize the occurrence of problems, such as a decrease in efficiently due to an increase in the amount of leakage of fluid from one side of the seal part through a gap between the shroud and the casing to the opposite side of the seal part, an increase in inertia of the impeller, and an increase in costs.

[0239] Further, in a ninth aspect of the present embodiment, based on the eighth aspect described above, the first opening may be provided on the inlet side relative to the seal part.

[0240] Accordingly, the centrifugal compressor can circulate fluid, flowing into a space between the shroud and the casing through the first passage, to the inlet of the impeller. Therefore, the centrifugal compressor can suppress an upward slope of pressure-flow rate characteristics. As a result, the centrifugal compressor can suppress a mild surge and can suppress the generation of whining noise.

[0241] Further, in a tenth aspect of the present embodiment, based on any one of the first to ninth aspects described above, the first passage may be provided so as to extend in the circumferential direction. Further, the first passage may be provided in a part of the entire circumferential direction.

[0242] Accordingly, the centrifugal compressor can increase the flow path cross-sectional area of the first passage. In addition, when the first passage is provided only in a part of the entire circumferential direction, the centrifugal compressor can suppress a situation in which the shroud is divided by the first passage and an eigenvalue is decreased. As a result, an appropriate strength of the impeller against blade vibration can be secured.

[0243] Further, in an eleventh aspect of the present embodiment, based on any one of the first to tenth aspects described above, the end portion on the inlet side of the shroud and the casing may face each other in the axial direction along the axis so as to form the second passage. A third passage in communication with the first passage and the second passage may be formed between the outer surface of the shroud and the inner surface of the casing. The third passage is, for example, the space 110A. In the second passage or the third passage, the inner surface of the casing may have a protrusion extending in a direction orthogonal to the circumferential direction, may have a groove extending in a direction orthogonal to the circumferential direction, or may be a rougher surface than the inner surface of the shroud. The inner surface of the casing is, for example, the inner surface 100B. The protrusion is, for example, the above-described protrusion 114 or 115. The groove is, for example, the above-described groove portion 113.

[0244] Accordingly, the centrifugal compressor can reduce a swirl component (that is, a velocity component in the circumferential direction) of the flow of the fluid flowing into the gap between the casing and the shroud through the first passage. Therefore, the effect of the swirl component included in the circulation flow can suppress a reduction in an pressure increase that occurs in the impeller by the circulation flow.

[0245] Further, in a twelfth aspect of the present embodiment, based on the eighth aspect described above, the first opening may be provided on the outlet side of the impeller relative to the seal part.

[0246] Accordingly, the centrifugal compressor can circulate a portion of the fluid at the outlet of the impeller by causing the fluid to flow into the gap between the casing and the shroud from the outlet side of the impeller and merge with the main flow in the impeller through the first passage. Therefore, the centrifugal compressor can suppress a wake in the vicinity of the outlet of the impeller.

[0247] Further, in a thirteenth aspect of the present embodiment, based on any one of the first to twelfth aspects described above, the centrifugal compressor may further include: a first compression part configured to compress fluid flowing into the first compression part; and a second compression part configured to compress the fluid discharged from the first compression part and flowing into the second compression part. The first compression part may include another impeller including another shroud that does not have the first passage, and the second compression part may include the impeller including the shroud that has the first passage.

[0248] Accordingly, the first passage is provided only in the rear-stage compression part where a mild surge is likely to occur. Thus, by increasing the pressure in a low flow rate region and increasing an operating range, the centrifugal compressor can achieve a balance between suppression of a mild surge and efficiency.

[0249] Further, in a fourteenth aspect of the present disclosure, a refrigeration apparatus may include the centrifugal compressor of any one of the first to thirteenth aspects described above. The refrigeration apparatus is, for example, the above-described refrigeration apparatus 1.

[0250] Accordingly, the performance of a closed impeller of a centrifugal compressor installed in a refrigeration apparatus can be improved.

[0251] Although the embodiments have been described above, it should be understood that various changes in the form and details can be made without departing from the spirit and scope of the claims.

[0252] This application is based on and claims priority to Japanese Patent Application No. 2024-161492, filed on September 18, 2024, the entire contents of which are incorporated herein by reference.DESCRIPTION OF THE REFERENCE NUMERALS

[0253] 1refrigeration apparatus 10compressor 20heat exchanger 30expansion mechanism 40heat exchanger 100casing 100Ainner surface 100Binner surface 100Cstepped surface 100Dcurved surface 110impeller chamber 110Aspace 110Bspace 110Cspace 111diffuser 113groove portion 114protrusion 115protrusion 120suction pipe 130discharge pipe 140electric motor chamber 200impeller 200ininlet 200outoutlet 210hub 211meridional plane 220blade 220ablade 220bblade 225throat 230shroud 230Aend surface 235through hole 235Aopening 235Accenter 235Bopening 235Bccenter 236coupling portion 240seal member 250rotating shaft 260collar 300electric motor 310rotor 320stator 400radial magnetic bearing 500thrust magnetic bearing 510electromagnet 600touchdown bearing AXaxis D1inner diameter D2inner diameter P0center P1imaginary point P2imaginary point Peimaginary point Psimaginary point t1width t2width VL0imaginary line VL1imaginary line VL2imaginary line θ1inclination angle θ2inclination angle θ3inclination angle θ4inclination angle

Claims

1. A centrifugal compressor comprising: an impeller (200); and a casing (100) configured to house the impeller (200), wherein the impeller (200) includes a hub (210) having a meridional plane (211), a plurality of blades (220) provided on the meridional plane (211), and a shroud (230) provided on tips of the plurality of blades (220) so as to cover the meridional plane (211), the shroud (230) has a first passage (235) penetrating between an inner surface of the shroud (230) facing the meridional plane (211) and an outer surface of the shroud (230) facing an inner surface of the casing (100), the first passage (235) having a first opening (235B) in the outer surface of the shroud (230) and a second opening (235A) in the inner surface of the shroud (230), and in a cross section including an axis (AX) of a rotating shaft (250) of the impeller(200), the first passage (235) is inclined such that a center (235Bc) of the first opening (235B) is located on an inlet (200in) side of the impeller (200) relative to a center (235Ac) of the second opening (235A).

2. The centrifugal compressor according to claim 1, wherein the plurality of blades (220) include a first blade (220a) and a second blade (220b) located ahead of and adjacent to the first blade (220a) in a rotation direction (RT) of the impeller (200), and when a shortest distance from one end (Ps), serving as a start point, on an inlet (200in) side of the first blade (220a) to a second blade (220b) is defined as a line segment (225), a point spaced 40 percent of a length of the line segment (225) from the one end of the first blade (220a) is defined as a first imaginary point (P1), and a point spaced 60 percent of the length of the line segment (225) from the one end of the first blade (220a) is defined as a second imaginary point (P2), the second opening (235A) is located between a first imaginary line (VL1) passing through the first imaginary point (P1) and extending in a circumferential direction and a second imaginary line (VL2) passing through the second imaginary point (P2) and extending in the circumferential direction.

3. The centrifugal compressor according to claim 1 or 2, wherein an end portion on an inlet (200in) side of the shroud (230) and the casing (100) face each other in an axial direction so as to form a second passage (110B), and in the cross section including the axis (AX), the second passage (110B) is inclined, in a direction from an outer surface side to an inner surface side of the shroud (230), toward an outlet (200out) of the impeller (200) with respect to a direction orthogonal to the inner surface of the shroud (230).

4. The centrifugal compressor according to claim 3, wherein the end portion on the inlet (200in) side of the shroud (230) is chamfered.

5. The centrifugal compressor according to claim 3 or 4, wherein a width of the second passage (110B) in the axial direction decreases from the outer surface side toward the inner surface side of the shroud (230).

6. The centrifugal compressor according to any one of claims 3 to 5, wherein an inner diameter (D2) of the end portion on the inlet (200in) side of the shroud (230) is smaller than an inner diameter (D1) of a portion of the casing (100) facing the end portion on the inlet (200in) side of the shroud (230) in the axial direction.

7. The centrifugal compressor according to any one of claims 1 to 6, wherein tip portions on a shroud (230) side of the plurality of blades (220) do not overlap the second opening (235A).

8. The centrifugal compressor according to any one of claims 1 to 7, wherein a seal part (240) is provided between the outer surface of the shroud (230) and the casing (100).

9. The centrifugal compressor according to claim 8, wherein the first opening (235B) is provided on the inlet (200in) side relative to the seal part (240).

10. The centrifugal compressor according to any one of claims 1 to 9, wherein the first passage (235) is provided so as to extend in the circumferential direction.

11. The centrifugal compressor according to any one of claims 1 to 10, wherein the end portion on the inlet (200in) side of the shroud (230) and the casing (100) face each other in the axial direction along the axis (AX) so as to form the second passage (110B), a third passage (110A) in communication with the first passage (235) and the second passage (110B) is formed between the outer surface of the shroud (230) and the inner surface of the casing (100), and in the second passage (110B) or the third passage (110A), the inner surface of the casing (100) has a protrusion (114, 115) extending in a direction orthogonal to the circumferential direction, has a groove (113) extending in a direction orthogonal to the circumferential direction, or is a rougher surface than the inner surface of the shroud (230).

12. The centrifugal compressor according to claim 8, wherein the first opening (235B) is provided on the outlet (200out) side of the impeller (200) relative to the seal part (240).

13. The centrifugal compressor according to any one of claims 1 to 12, further comprising: a first compression part configured to compress fluid flowing into the first compression part; and a second compression part configured to compress the fluid discharged from the first compression part and flowing into the second compression part, wherein the first compression part includes another impeller including another shroud that does not have the first passage (235), and the second compression part includes the impeller (200) including the shroud (230) that has the first passage (235).

14. A refrigeration apparatus comprising: the centrifugal compressor (10) of any one of claims 1 to 13.

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