Centrifugal compressor

Abstract

To reduce unstable force which whirls a rotation shaft while avoiding increase in thrust force which moves an impeller in the axial direction toward an opposing surface of a partition wall.SOLUTION: A swirl breaker 53 suppresses a swirl flow of the air flowing in an insertion hole 27 from a second gap 60b between a second back surface 52a of a second impeller 52 and a second opposing surface 15b of a partition wall 15. Thereby, increase of a swirl direction component in a pressure distribution of a dynamic pressure generating between an inner peripheral surface 27a which partitions the insertion hole 27 and a rotation shaft 40 is suppressed. Also, as the air having a swirl flow rate of the second impeller 52 exit in the second gap 60b directly flows in a concave part 54, the flow rate of the swirl flow of the air decreases, and speed energy of the swirl flow of the air is converted into pressure energy. Thereby, a static pressure generating between the second back surface 52a of the second impeller 52 and the second opposing surface 15b increases, and a pressure acting on the second back surface 52a of the second impeller 52 increases.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] For example, as disclosed in Patent Document 1, a centrifugal compressor includes a rotating shaft, an impeller, and a housing. The impeller rotates integrally with the rotating shaft to compress a fluid. The housing has a partition wall that defines an impeller chamber. The impeller chamber houses the impeller. The partition wall has an opposing surface that faces the back surface of the impeller, and an insertion hole through which the rotating shaft is inserted. The insertion hole opens to the opposing surface.

[0003] In such a centrifugal compressor, a part of the fluid compressed by the rotation of the impeller may flow into the gap between the back surface of the impeller and the opposing surface of the partition wall. The fluid in the gap between the back surface of the impeller and the opposing surface of the partition wall has a swirling flow velocity similar to the circumferential velocity of the impeller, but the swirling flow velocity is further accelerated and increased by the amount of the swirling radius that decreases before reaching the insertion hole, according to the law of conservation of angular momentum. Then, the swirling flow of the fluid in the gap between the back surface of the impeller and the opposing surface of the partition wall flows from the gap into the insertion hole. When the swirling flow of the fluid flows into the insertion hole, the dynamic pressure generated between the inner circumferential surface that defines the insertion hole and the rotating shaft increases. The swirling direction component of the resultant force of this pressure distribution becomes an unstable force, and when it exceeds the damping force of the bearing, it generates a whip that swings the rotating shaft widely. This increases the vibration amplitude of the rotating shaft, and in order to avoid collision between the impeller and the housing, it is necessary to increase the tip clearance, which is the gap between the impeller and the housing, resulting in a decrease in the performance of the centrifugal compressor.

[0004] Therefore, as in Patent Document 2, for example, it is known to form a swirl breaker at the end of the inner circumferential surface that defines the insertion hole on the side of the opposing surface. The swirl breaker suppresses the swirling flow of the fluid that flows into the insertion hole from the gap between the back surface of the impeller and the opposing surface of the partition wall. This prevents the destabilizing force, which is the swirling direction component of the resultant force of dynamic pressure generated between the inner circumferential surface that defines the insertion hole and the rotating shaft, from becoming large, thereby suppressing the occurrence of whip, which increases the vibration amplitude of the rotating shaft. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-57207 [Patent Document 2] US Patent Application Publication No. 2012 / 0183388 Summary of the Invention [Problem to be solved by the invention]

[0006] In this way, when the swirling flow of the fluid flowing into the insertion hole from the gap between the back surface of the impeller and the opposing surface of the partition wall is suppressed by the swirl breaker, the swirling flow of the fluid is less likely to occur between the inner circumferential surface defining the insertion hole and the rotating shaft. As a result, the fluid flowing between the inner circumferential surface defining the insertion hole and the rotating shaft is more likely to flow in the axial direction of the rotating shaft without flowing while swirling around the rotating shaft. Therefore, the flow path length of the fluid flowing between the inner circumferential surface defining the insertion hole and the rotating shaft is shortened. As a result, the sealing performance between the inner circumferential surface defining the insertion hole and the rotating shaft is reduced, so that a part of the fluid compressed by the rotation of the impeller is more likely to flow into the gap between the back surface of the impeller and the opposing surface of the partition wall. Therefore, the flow rate of the fluid flowing through the gap between the back surface of the impeller and the opposing surface of the partition wall is increased, and the static pressure generated between the back surface of the impeller and the opposing surface of the partition wall is reduced. As a result, the pressure acting on the back surface of the impeller decreases, and there is a risk that the thrust force that moves the impeller in the axial direction toward the opposing surface of the partition wall increases. Therefore, it is desirable to reduce the destabilizing force that swings the rotating shaft while avoiding the increase in the thrust force that moves the impeller in the axial direction toward the opposing surface of the partition wall. [Means for solving the problem]

[0007] A centrifugal compressor that solves the above problem includes a rotating shaft, an impeller that rotates integrally with the rotating shaft to compress a fluid, and a housing having a partition wall that defines an impeller chamber that accommodates the impeller, the partition wall having an opposing surface that faces a back surface of the impeller, and an insertion hole that opens into the opposing surface and through which the rotating shaft is inserted, and a swirl breaker that suppresses a swirling flow of fluid that flows into the insertion hole from a gap between the back surface and the opposing surface is formed on an end of an inner circumferential surface that defines the insertion hole on the opposing surface side, and at least one of the back surface and the opposing surface is formed with an annular recess that increases the pressure acting on the back surface, and the swirling flow of the fluid that flows into the gap between the back surface and the opposing surface flows into the recess.

[0008] According to this, the swirl breaker suppresses the swirling flow of the fluid flowing into the insertion hole from the gap between the back surface of the impeller and the opposing surface of the partition wall. Therefore, it is possible to suppress an increase in the swirling direction component of the pressure distribution of the dynamic pressure generated between the inner circumferential surface that defines the insertion hole and the rotating shaft. As a result, it is possible to reduce the destabilizing force that swings the rotating shaft. Furthermore, the fluid having the swirling flow velocity of the impeller outlet flows directly into the recess in the gap between the back surface of the impeller and the opposing surface of the partition wall. Therefore, the flow path cross-sectional area of ​​the swirling flow of the fluid flowing between the back surface of the impeller and the opposing surface of the partition wall is enlarged. Then, the flow velocity of the swirling flow of the fluid flowing between the back surface of the impeller and the opposing surface of the partition wall is reduced. As a result, the velocity energy of the swirling flow of the fluid is converted into pressure energy, and the static pressure generated between the back surface of the impeller and the opposing surface of the partition wall increases. Therefore, the pressure acting on the back surface of the impeller increases, and it is possible to avoid an increase in the thrust force that moves the impeller in the axial direction toward the opposing surface of the partition wall. As a result, it is possible to reduce the destabilizing force that swings the rotating shaft while avoiding an increase in the thrust force that moves the impeller axially toward the opposing surface of the partition wall.

[0009] In the centrifugal compressor, the recess may be formed in the opposing surface. This makes it easier for the swirling flow of fluid flowing into the gap between the back surface of the impeller and the opposing surface of the partition wall to flow into the recess, for example, compared to when the recess is formed on the back surface of the impeller.

[0010] In the centrifugal compressor, an outer peripheral opening edge of the recess may be located radially outward of the rotary shaft with respect to an outer peripheral edge of the back surface. This makes it easier for the swirling flow of fluid flowing into the gap between the back surface of the impeller and the opposing surface of the partition wall to flow into the recess, for example, compared to a case where the outer peripheral opening edge of the recess is located radially inward of the rotating shaft relative to the outer peripheral edge of the back surface of the impeller.

[0011] In the centrifugal compressor, the outer peripheral opening edge of the recess may be located radially outward of the rotating shaft with respect to the outer peripheral edge of the back surface by a distance between the back surface and the opposing surface in the axial direction of the rotating shaft. This configuration is suitable for making it easier for a swirling flow of air flowing into a gap between the back surface of the impeller and the opposing surface of the partition wall to flow into the recess.

[0012] In the above-mentioned centrifugal compressor, an outer peripheral opening edge of the recess is located radially outward of the rotating shaft with respect to an outer peripheral edge of the back surface by a distance greater than a distance between the back surface and the opposing surface in the axial direction of the rotating shaft, and an inner peripheral opening edge of the recess is located radially inward of the rotating shaft with respect to the outer peripheral edge of the back surface.

[0013] According to this, the swirling flow of the fluid flowing into the gap between the back surface of the impeller and the opposing surface of the partition wall is likely to flow directly into the recess without bending. Therefore, pressure loss of the swirling flow of the fluid is unlikely to occur, and the pressure in the recess can be maintained high. As a result, the pressure acting on the back surface of the impeller is likely to increase, making it easier to avoid an increase in the thrust force that moves the impeller axially toward the opposing surface of the partition wall.

[0014] In the centrifugal compressor, an outer peripheral opening edge of the recess may be located radially inward of the rotor shaft with respect to an outer peripheral edge of the back surface, thereby making it possible to reduce the radial size of the rotor shaft in the centrifugal compressor.

[0015] In the centrifugal compressor, the impeller includes a first impeller that rotates integrally with the rotating shaft and a second impeller that rotates integrally with the rotating shaft to compress a fluid compressed by the rotation of the first impeller, the impeller chamber includes a first impeller chamber that accommodates the first impeller and a second impeller chamber that accommodates the second impeller, the partition wall separates the first impeller chamber and the second impeller chamber, a first back surface that is a back surface of the first impeller and a second back surface that is a back surface of the second impeller face each other in an axial direction of the rotating shaft via the partition wall, the opposing surfaces include a first opposing surface that faces the first back surface and a second opposing surface that faces the second back surface, the swirl breaker is formed at an end of an inner circumferential surface that defines the insertion hole on the side of the second opposing surface, and the recess is formed on at least one of the second back surface and the second opposing surface.

[0016] The pressure of the fluid compressed by the rotation of the second impeller is higher than the pressure of the fluid compressed by the rotation of the first impeller. Therefore, air flows from the gap between the second back surface of the second impeller and the second opposing surface of the partition wall through the insertion hole to the gap between the first back surface of the first impeller and the first opposing surface of the partition wall. At this time, a swirl breaker is formed at the end of the inner circumferential surface that defines the insertion hole, on the second opposing surface side. Therefore, the swirl breaker suppresses the swirling flow of the fluid that flows into the insertion hole from the gap between the second back surface of the second impeller and the second opposing surface of the partition wall. Therefore, it is possible to suppress an increase in the swirling direction component of the pressure distribution of the dynamic pressure generated between the inner circumferential surface that defines the insertion hole and the rotating shaft. As a result, it is possible to reduce the unstable force that swings the rotating shaft.

[0017] The thrust force that moves the second impeller in the axial direction toward the second opposing surface of the partition wall is greater than the thrust force that moves the first impeller in the axial direction toward the first opposing surface of the partition wall. Therefore, a recess is formed on at least one of the second back surface of the second impeller and the second opposing surface of the partition wall. This increases the static pressure generated between the second back surface of the second impeller and the second opposing surface of the partition wall. Therefore, the pressure acting on the second back surface of the second impeller increases, making it possible to avoid an increase in the thrust force that moves the second impeller in the axial direction toward the second opposing surface of the partition wall. Effect of the Invention

[0018] According to this invention, it is possible to reduce the destabilizing force that swings the rotating shaft while avoiding an increase in the thrust force that moves the impeller axially toward the opposing surface of the partition wall. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view showing a centrifugal compressor according to an embodiment. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of a portion of the centrifugal compressor. [Diagram 3] FIG. 3 is a front view showing the swirl breaker and the recessed portion. [Figure 4] FIG. 4 is a perspective view showing a swirl breaker and a recess. [Diagram 5] FIG. 5 is an enlarged cross-sectional view showing a part of the centrifugal compressor. [Figure 6] FIG. 6 is a graph showing the relationship between air pressure and the flow velocity of the swirling flow. [Figure 7] FIG. 7 is an enlarged cross-sectional view showing a part of a centrifugal compressor in a modified example. [Figure 8] FIG. 8 is an enlarged cross-sectional view showing a part of a centrifugal compressor in a modified example. [Figure 9] FIG. 9 is a front view showing a swirl breaker and a recess in a modified example. [Figure 10]FIG. 10 is an enlarged cross-sectional view showing a part of a centrifugal compressor in a modified example. [Figure 11] FIG. 11 is an enlarged cross-sectional view showing a part of a centrifugal compressor in a modified example. [Figure 12] FIG. 12 is an enlarged cross-sectional view showing a part of a centrifugal compressor in a modified example. [Figure 13] FIG. 13 is an enlarged cross-sectional view showing a part of a centrifugal compressor in a modified example. [Figure 14] FIG. 14 is an enlarged cross-sectional view showing a part of a centrifugal compressor in a modified example. [Figure 15] FIG. 15 is an enlarged cross-sectional view showing a part of a centrifugal compressor in a modified example. [Figure 16] FIG. 16 is an enlarged cross-sectional view showing a part of a centrifugal compressor in a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, one embodiment of a centrifugal compressor will be described with reference to Figs. 1 to 6. The centrifugal compressor of this embodiment is mounted on a fuel cell vehicle. The fuel cell vehicle is equipped with a fuel cell system that supplies oxygen and hydrogen to a fuel cell to generate electricity. The centrifugal compressor compresses air as a fluid containing oxygen that is supplied to the fuel cell.

[0021] <Basic configuration of a centrifugal compressor> As shown in Fig. 1, the centrifugal compressor 10 includes a cylindrical housing 11. The housing 11 includes a motor housing 12, a first compressor housing 13, a second compressor housing 14, a partition wall 15, a first intermediate housing 16, and a second intermediate housing 17. The motor housing 12, the first compressor housing 13, the second compressor housing 14, the partition wall 15, the first intermediate housing 16, and the second intermediate housing 17 are each made of a metal material, for example, aluminum.

[0022] The motor housing 12 has a disk-shaped end wall 12a and a cylindrical circumferential wall 12b. The circumferential wall 12b extends in a tubular shape from the outer periphery of the end wall 12a. The second intermediate housing 17 is connected to the motor housing 12 with an opening in the circumferential wall 12b opposite to the end wall 12a closed. The end wall 12a, the circumferential wall 12b, and the second intermediate housing 17 of the motor housing 12 define a motor chamber 18.

[0023] The motor housing 12 has a suction hole 12h. The suction hole 12h is formed in a portion of the peripheral wall 12b close to the end wall 12a. The suction hole 12h draws in air. The suction hole 12h communicates with the motor chamber 18. Therefore, air is drawn into the motor chamber 18 through the suction hole 12h.

[0024] The second intermediate housing 17 has a circular shaft insertion hole 17a. The shaft insertion hole 17a is formed in the center of the second intermediate housing 17. The second intermediate housing 17 also has a cylindrical first bearing retaining portion 19. The first bearing retaining portion 19 is formed in the center of the second intermediate housing 17. The inside of the first bearing retaining portion 19 communicates with the shaft insertion hole 17a. The central axis of the first bearing retaining portion 19 and the central axis of the shaft insertion hole 17a coincide with each other. A first foil bearing 20 is retained in the first bearing retaining portion 19.

[0025] Furthermore, the end wall 12a of the motor housing 12 has a cylindrical second bearing retaining portion 21. The second bearing retaining portion 21 is formed in the center of the end wall 12a of the motor housing 12. The central axis of the first bearing retaining portion 19 and the central axis of the second bearing retaining portion 21 coincide with each other. The second bearing retaining portion 21 retains a second foil bearing 22.

[0026] The second intermediate housing 17 has a first chamber forming recess 17b. The first chamber forming recess 17b is formed on the outer surface of the second intermediate housing 17 opposite the motor chamber 18. The inside of the first chamber forming recess 17b communicates with the shaft insertion hole 17a. The second intermediate housing 17 also has a plurality of communication holes 23. Each communication hole 23 is located near the outer periphery of the second intermediate housing 17. Each communication hole 23 penetrates the second intermediate housing 17. Each communication hole 23 communicates between the motor chamber 18 and the inside of the first chamber forming recess 17b.

[0027] The first intermediate housing 16 is connected to the second intermediate housing 17. The first intermediate housing 16 is connected to the second intermediate housing 17 so as to close the opening of the first chamber forming recess 17b. The first intermediate housing 16 and the first chamber forming recess 17b of the second intermediate housing 17 define a thrust bearing accommodating chamber 25.

[0028] The first intermediate housing 16 has a circular shaft insertion hole 16a. The shaft insertion hole 16a is formed in the center of the first intermediate housing 16. The first intermediate housing 16 also has a plurality of communication holes 16b. Each communication hole 16b is located near the outer periphery of the first intermediate housing 16. Each communication hole 16b penetrates the first intermediate housing 16.

[0029] The first intermediate housing 16 has a second chamber forming recess 16c. The second chamber forming recess 16c is formed on the outer surface of the first intermediate housing 16 opposite the thrust bearing accommodating chamber 25. The inside of the second chamber forming recess 16c communicates with the shaft insertion hole 16a. Each communication hole 16b communicates between the thrust bearing accommodating chamber 25 and the inside of the second chamber forming recess 16c.

[0030] The first compressor housing 13 is cylindrical and has a circular first suction port 24 through which air is drawn. The first compressor housing 13 is connected to the first intermediate housing 16 with the central axis of the first suction port 24 coinciding with the central axis of the shaft insertion hole 16a. The first suction port 24 communicates with the inside of the second chamber forming recess 16c.

[0031] The partition wall 15 is connected to an end face of the first compressor housing 13 opposite to the first intermediate housing 16. The partition wall 15 is disk-shaped. The partition wall 15 has a circular insertion hole 27. The insertion hole 27 is formed in the center of the partition wall 15. The insertion hole 27 penetrates the partition wall 15 in the thickness direction of the partition wall 15. The partition wall 15 is connected to the first compressor housing 13 with the central axis of the insertion hole 27 coinciding with the central axis of the first suction port 24. The first suction port 24 faces the partition wall 15 in the direction in which the central axis of the first suction port 24 extends.

[0032] The centrifugal compressor 10 includes a first impeller chamber 28, a first discharge chamber 29, and a first diffuser passage 30. The first impeller chamber 28, the first discharge chamber 29, and the first diffuser passage 30 are formed between the partition wall 15 and the first compressor housing 13. Therefore, the partition wall 15 has a first diffuser surface 30a that defines the first diffuser passage 30.

[0033] The first impeller chamber 28 communicates with the first suction port 24. The first discharge chamber 29 extends around the central axis of the first suction port 24 around the first impeller chamber 28. The first diffuser passage 30 communicates between the first impeller chamber 28 and the first discharge chamber 29.

[0034] The partition wall 15 has a first impeller recess 36. The first impeller recess 36 defines a first impeller chamber 28. An opening edge of the first impeller recess 36 is continuous with the first diffuser surface 30a. The first impeller recess 36 is recessed with respect to the first diffuser surface 30a. The first impeller recess 36 is a circular hole. A first end of the insertion hole 27 opens into a bottom surface of the first impeller recess 36. Therefore, the first end of the insertion hole 27 communicates with the inside of the first impeller recess 36.

[0035] The second compressor housing 14 is cylindrical and has a circular second suction port 32 through which air is drawn. The second compressor housing 14 is connected to an end face of the partition wall 15 opposite to the first compressor housing 13, with the central axis of the second suction port 32 coinciding with the central axis of the first suction port 24. The second suction port 32 faces the partition wall 15 in the direction in which the central axis of the second suction port 32 extends.

[0036] The centrifugal compressor 10 includes a second impeller chamber 33, a second discharge chamber 34, and a second diffuser passage 35. The second impeller chamber 33, the second discharge chamber 34, and the second diffuser passage 35 are formed between the partition wall 15 and the second compressor housing 14. Therefore, the partition wall 15 has a second diffuser surface 35a that defines the second diffuser passage 35.

[0037] The second impeller chamber 33 communicates with the second suction port 32. The second discharge chamber 34 extends around the central axis of the second suction port 32 around the periphery of the second impeller chamber 33. The second diffuser passage 35 communicates between the second impeller chamber 33 and the second discharge chamber 34. The first discharge chamber 29 communicates with the second suction port 32 via a passage (not shown). In this manner, the housing 11 divides the first impeller chamber 28 and the second impeller chamber 33. The partition wall 15 separates the first impeller chamber 28 and the second impeller chamber 33.

[0038] The partition wall 15 has a second impeller recess 37. The second impeller recess 37 defines a second impeller chamber 33. An opening edge of the second impeller recess 37 is continuous with the second diffuser surface 35a. The second impeller recess 37 is recessed with respect to the second diffuser surface 35a. The second impeller recess 37 is in the shape of a circular hole. The second end of the insertion hole 27 opens to a bottom surface of the second impeller recess 37. Therefore, the second end of the insertion hole 27 communicates with the inside of the second impeller recess 37.

[0039] The centrifugal compressor 10 includes a rotating shaft 40 and a motor 41. The motor 41 rotates the rotating shaft 40. The motor 41 is accommodated in the motor chamber 18. The rotating shaft 40 extends in the axial direction of the housing 11. The rotating shaft 40 passes through the motor chamber 18 from the inside of the second bearing holder 21, the inside of the first bearing holder 19, the shaft insertion hole 17a, the thrust bearing accommodating chamber 25, the shaft insertion hole 16a, the first suction port 24, the first impeller chamber 28, the insertion hole 27, and the second impeller chamber 33 in this order. Therefore, the rotating shaft 40 is inserted through the insertion hole 27. The rotating shaft 40 is inserted through the insertion hole 27 and is disposed across the first impeller chamber 28 and the second impeller chamber 33. The axis L of the rotating shaft 40 coincides with the central axes of the first bearing holder 19, the second bearing holder 21, the shaft insertion hole 17a, the shaft insertion hole 16a, the first suction port 24, the insertion hole 27, and the second suction port 32. In this manner, the rotating shaft 40 is accommodated in the housing 11.

[0040] The first foil bearing 20 and the second foil bearing 22 rotatably support the rotating shaft 40. The first foil bearing 20 and the second foil bearing 22 are air dynamic bearings that rotatably support the rotating shaft 40 in the radial direction.

[0041] The centrifugal compressor 10 includes a thrust collar 46. The thrust collar 46 is disk-shaped. The thrust collar 46 protrudes from the outer circumferential surface of the rotating shaft 40. The thrust collar 46 is press-fitted into the outer circumferential surface of the rotating shaft 40. The thrust collar 46 rotates integrally with the rotating shaft 40. The thrust collar 46 is disposed in the thrust bearing accommodating chamber 25.

[0042] The centrifugal compressor 10 includes a thrust bearing 47. The thrust bearing 47 is disposed between the first intermediate housing 16 and the thrust collar 46, and between the second intermediate housing 17 and the thrust collar 46. Both thrust bearings 47 are air dynamic bearings that rotatably support the rotating shaft 40 in the thrust direction.

[0043] In the following description, the "axial direction of the rotating shaft 40", which is the direction in which the axis L of the rotating shaft 40 extends, may be referred to as the "thrust direction", and the "diameter direction of the rotating shaft 40" may be referred to as the "radial direction".

[0044] The motor 41 includes a stator 42 and a rotor 43. The stator 42 has a cylindrical stator core 44 and a coil 45 wound around the stator core 44. The stator core 44 is fixed to the inner circumferential surface of the peripheral wall 12b of the motor housing 12. The rotor 43 is disposed inside the stator core 44 in the motor chamber 18. The rotor 43 rotates integrally with the rotating shaft 40. The rotor 43 has a rotor core 43a fixed to the rotating shaft 40 and a plurality of permanent magnets (not shown) provided on the rotor core 43a. The rotor 43 rotates when power controlled by an inverter device (not shown) is supplied to the coil 45. The rotating shaft 40 rotates integrally with the rotor 43.

[0045] The centrifugal compressor 10 includes a first impeller 51 and a second impeller 52. The first impeller 51 and the second impeller 52 are impellers that rotate integrally with the rotary shaft 40 to compress air. Therefore, the impeller includes the first impeller 51 and the second impeller 52.

[0046] The first impeller 51 and the second impeller 52 are made of, for example, aluminum. The rigidity of the aluminum material forming the first impeller 51 and the second impeller 52 is lower than the rigidity of the aluminum material forming the partition wall 15. The first impeller 51 and the second impeller 52 are connected to a first end of the rotating shaft 40. The second impeller 52 is disposed closer to the first end of the rotating shaft 40 than the first impeller 51.

[0047] The first impeller 51 is accommodated in the first impeller chamber 28. Therefore, the first impeller chamber 28 is an impeller chamber that accommodates the first impeller 51. The first impeller 51 has a truncated cone shape. The first impeller 51 is connected to a first end of the rotating shaft 40. A part of the first impeller 51 fits inside the first impeller recess 36.

[0048] The second impeller 52 is accommodated in the second impeller chamber 33. Therefore, the second impeller chamber 33 is an impeller chamber that accommodates the second impeller 52. Therefore, the impeller chamber includes the first impeller chamber 28 and the second impeller chamber 33. The second impeller 52 has a truncated cone shape. The second impeller 52 is connected to a first end of the rotating shaft 40. A part of the second impeller 52 enters the inside of the second impeller recess 37. The rotating shaft 40, the first impeller 51, and the second impeller 52 are accommodated in the housing 11.

[0049] In the centrifugal compressor 10, air is drawn into the motor chamber 18 through the suction hole 12h. The air drawn into the motor chamber 18 passes through the inside of each communication hole 23, the thrust bearing accommodating chamber 25, each communication hole 16b, and the second chamber forming recess 16c, and is drawn into the first suction port 24. The air drawn into the first suction port 24 is sent from the first impeller chamber 28 to the first diffuser passage 30 by the centrifugal action of the first impeller 51, and is pressurized in the first diffuser passage 30. The air that has passed through the first diffuser passage 30 is then discharged into the first discharge chamber 29.

[0050] The air discharged into the first discharge chamber 29 is drawn into the second suction port 32 from the first discharge chamber 29 through a passage not shown. The air drawn into the second suction port 32 is sent from the second impeller chamber 33 to the second diffuser passage 35 by the centrifugal action of the second impeller 52, and is pressurized in the second diffuser passage 35. The air that has passed through the second diffuser passage 35 is then discharged into the second discharge chamber 34. Therefore, the second impeller 52 rotates to compress the air that has been compressed by the rotation of the first impeller 51.

[0051] As shown in Fig. 2, the first back surface 51a, which is the back surface of the first impeller 51, and the second back surface 52a, which is the back surface of the second impeller 52, face each other in the axial direction of the rotary shaft 40 via the partition wall 15. The partition wall 15 has a first opposing surface 15a, which is an opposing surface facing the first back surface 51a of the first impeller 51, and a second opposing surface 15b, which is an opposing surface facing the second back surface 52a of the second impeller 52. Thus, the partition wall 15 has an opposing surface facing the back surface of the impeller. The opposing surface includes the first opposing surface 15a facing the first back surface 51a and the second opposing surface 15b facing the second back surface 52a.

[0052] The first opposing surface 15a is the bottom surface of the first impeller recess 36. The second opposing surface 15b is the bottom surface of the second impeller recess 37. Therefore, a first end of the insertion hole 27 opens to the first opposing surface 15a. A second end of the insertion hole 27 opens to the second opposing surface 15b. Therefore, the insertion hole 27 opens to the opposing surfaces.

[0053] <Swirl breaker> 3 and 4, a swirl breaker 53 is formed at the end of the inner circumferential surface 27a defining the insertion hole 27 on the second opposing surface 15b side. Therefore, the swirl breaker 53 is formed at the end of the inner circumferential surface 27a defining the insertion hole 27 on the second opposing surface 15b side. The swirl breaker 53 is composed of a plurality of grooves 53a formed at equal intervals in the circumferential direction of the rotating shaft 40 on the end of the inner circumferential surface 27a defining the insertion hole 27 on the second opposing surface 15b side. Each groove 53a opens to the second opposing surface 15b.

[0054] <Concave> An annular recess 54 is formed in the second opposing surface 15b. Therefore, the recess 54 is formed in the second opposing surface 15b. The recess 54 opens to the second opposing surface 15b. When the second opposing surface 15b is viewed in plan, the recess 54 has an annular shape surrounding the insertion hole 27.

[0055] 5, the recess 54 defines a space recessed toward the second opposing surface 15b by a virtual line L100 extending on an extension line of the second opposing surface 15b. An outer peripheral opening edge 54a of the recess 54 is located radially outward of the rotary shaft 40 with respect to an outer peripheral edge 52e of the second back surface 52a of the second impeller 52.

[0056] The outer peripheral opening edge 54a of the recess 54 is located on the same plane as the inner peripheral surface 37a of the second impeller recess 37. Therefore, the outer peripheral opening edge 54a of the recess 54 is continuous with the inner peripheral surface 37a of the second impeller recess 37. In the radial direction of the rotating shaft 40, the distance between the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 and the inner peripheral surface 37a of the second impeller recess 37 is the same as the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotating shaft 40. Therefore, the outer peripheral opening edge 54a of the recess 54 is located radially outward of the rotating shaft 40 by the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotating shaft 40 with respect to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52.

[0057] The inner peripheral opening edge 54b of the recess 54 faces the second back surface 52a of the second impeller 52 in the axial direction of the rotary shaft 40. The inner peripheral opening edge 54b of the recess 54 is located radially inward of the rotary shaft 40 with respect to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52. The outer peripheral opening edge 54a and the inner peripheral opening edge 54b of the recess 54 face each other in the radial direction of the rotary shaft 40. The outer peripheral opening edge 54a surrounds the inner peripheral opening edge 54b. The outer peripheral edge 52e of the second back surface 52a of the second impeller 52 faces a portion of the partition wall 15 located inside the recess 54 in the axial direction of the rotary shaft 40. The width W1 of the recess 54 in the radial direction of the rotary shaft 40 is greater than the depth T1 of the recess 54.

[0058] [Operation of the embodiment] Next, the operation of this embodiment will be described. The pressure of the air compressed by the rotation of the second impeller 52 is higher than the pressure of the air compressed by the rotation of the first impeller 51. In such a centrifugal compressor 10, a part of the air compressed by the rotation of the second impeller 52 flows into the second gap 60b, which is a gap between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15. The air that flows into the second gap 60b flows from the second gap 60b into the insertion hole 27 and passes through the insertion hole 27. The air that passes through the insertion hole 27 flows into the first gap 60a, which is a gap between the first back surface 51a of the first impeller 51 and the first opposing surface 15a of the partition wall 15. Then, the air that flows into the first gap 60a flows toward the first discharge chamber 29. In this way, an air flow is generated from the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 to the first gap 60a between the first back surface 51a of the first impeller 51 and the first opposing surface 15a of the partition wall 15 via the insertion hole 27. The air in the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 has a swirling flow velocity that is approximately the same as the circumferential velocity of the second impeller 52, but the swirling radius becomes smaller before the air reaches the insertion hole 27, and the swirling flow velocity is further accelerated and becomes larger according to the law of conservation of angular momentum.

[0059] 2, the outermost portion of the rotating shaft 40 in the radial direction in the second gap 60b is defined as "point P1." The second end of the insertion hole 27 is defined as "point P2." The first end of the insertion hole 27 is defined as "point P3." The outermost portion of the rotating shaft 40 in the radial direction in the first gap 60a is defined as "point P4."

[0060] FIG. 6 shows the fluctuations in the air pressure and the flow velocity of the swirling air flow from point P1 to point P4 via points P2 and P3. The fluctuations in the air pressure in this embodiment are shown by a thin solid line L1 in FIG. 6, and the fluctuations in the flow velocity of the swirling air flow are shown by a thick solid line L2 in FIG. 6. On the other hand, consider a case where the swirl breaker 53 is not formed at the end of the inner circumferential surface 27a that defines the insertion hole 27 on the second opposing surface 15b side, and the recess 54 is not formed on the second opposing surface 15b. The fluctuations in the air pressure in this case are shown by a two-dot chain line L11 in FIG. 6, and the fluctuations in the flow velocity of the swirling air flow are shown by a dashed line L12 in FIG. 6.

[0061] The swirl breaker 53 suppresses the swirling flow of air flowing into the insertion hole 27 from the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15. This suppresses an increase in the swirling direction component of the dynamic pressure distribution generated between the inner circumferential surface 27a defining the insertion hole 27 and the rotating shaft 40. As a result, the destabilizing force that swings the rotating shaft 40 is reduced.

[0062] As can be seen by comparing the solid line L2 and the dashed line L12 between the points P2 and P4 in FIG. 6, when the swirling flow of air is suppressed by the swirl breaker 53, the swirling flow of air is less likely to occur between the inner circumferential surface 27a that defines the insertion hole 27 and the rotating shaft 40. As a result, the air flowing between the inner circumferential surface 27a that defines the insertion hole 27 and the rotating shaft 40 does not flow while swirling around the rotating shaft 40, but rather flows easily in the axial direction of the rotating shaft 40. Therefore, the flow path length of the air flowing between the inner circumferential surface 27a that defines the insertion hole 27 and the rotating shaft 40 is shortened. As a result, the sealing performance between the inner circumferential surface 27a that defines the insertion hole 27 and the rotating shaft 40 is reduced. For this reason, a part of the air compressed by the rotation of the second impeller 52 is more likely to flow into the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15. Therefore, the flow rate of air flowing through the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 increases.

[0063] Here, consider a case where a swirl breaker 53 is formed at the end of the inner circumferential surface 27a defining the insertion hole 27 on the second opposing surface 15b side, and a recess 54 is not formed on the second opposing surface 15b. Fluctuations in air pressure in this case are indicated by long dashed line L21 in FIG.

[0064] In FIG. 6, the two-dot chain line L11 and the long dashed line L21 between the point P1 and the point P2 are compared. In this way, when the swirl breaker 53 is formed at the end of the inner circumferential surface 27a that defines the insertion hole 27 on the second opposing surface 15b side, the air pressure between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 is reduced. Therefore, the static pressure generated between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 is reduced. As a result, the pressure acting on the second back surface 52a of the second impeller 52 is reduced, and there is a risk that the thrust force that moves the second impeller 52 in the axial direction toward the second opposing surface 15b of the partition wall 15 will increase.

[0065] Therefore, in this embodiment, a recess 54 is formed in the second opposing surface 15b. Air having a swirling flow velocity at the outlet of the second impeller 52 directly flows into the recess 54 into the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15. Therefore, the flow path cross-sectional area of ​​the swirling flow of the air flowing between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 is enlarged. Then, as can be seen by comparing the solid line L2 and the dashed line L12 between the points P1 and P2 in FIG. 6, the flow velocity of the swirling flow of the air flowing between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 is reduced. As a result, the velocity energy of the swirling flow of the air is converted into pressure energy. Therefore, as can be seen by comparing the solid line L1 and the two-dot chain line L11 between the point P1 and the point P2 in FIG. 6, the air pressure between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 increases. Therefore, the static pressure generated between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 increases. Therefore, the pressure acting on the second back surface 52a of the second impeller 52 increases, and an increase in the thrust force that moves the second impeller 52 in the axial direction toward the second opposing surface 15b of the partition wall 15 is avoided. In this way, the recess 54 increases the pressure acting on the second back surface 52a of the second impeller 52.

[0066] [Effects of the embodiment] The above embodiment can provide the following effects. (1) The swirl breaker 53 suppresses the swirling flow of air flowing into the insertion hole 27 from the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15. Therefore, it is possible to suppress an increase in the swirling direction component of the pressure distribution of the dynamic pressure generated between the inner circumferential surface 27a that defines the insertion hole 27 and the rotating shaft 40. As a result, it is possible to reduce the destabilizing force that swings the rotating shaft 40. Furthermore, air having the swirling flow velocity at the outlet of the second impeller 52 flows directly into the recess 54 in the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15. Therefore, the flow path cross-sectional area of ​​the swirling flow of the air flowing between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 is enlarged. Then, the flow velocity of the swirling air flowing between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 decreases. As a result, the velocity energy of the swirling air flow is converted into pressure energy, and the static pressure generated between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 increases. Therefore, the pressure acting on the second back surface 52a of the second impeller 52 increases, and it is possible to avoid an increase in the thrust force that moves the second impeller 52 in the axial direction toward the second opposing surface 15b of the partition wall 15. As a result, it is possible to reduce the destabilizing force that swings the rotating shaft 40 while avoiding an increase in the thrust force that moves the second impeller 52 in the axial direction toward the second opposing surface 15b of the partition wall 15.

[0067] (2) The recess 54 is formed in the second opposing surface 15b of the partition wall 15. This makes it easier for the swirling flow of air flowing into the second gap 60b between the second rear surface 52a of the second impeller 52 and the second opposing surface 15b to flow into the recess 54, for example, compared to a case in which the recess 54 is formed in the second rear surface 52a of the second impeller 52.

[0068] (3) The outer peripheral opening edge 54a of the recess 54 is located radially outward of the rotary shaft 40 with respect to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52. For example, consider a case in which the outer peripheral opening edge 54a of the recess 54 is located radially inward of the rotary shaft 40 with respect to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52. Compared to this case, the swirling flow of air flowing into the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 can be made to flow more easily into the recess 54.

[0069] (4) The outer peripheral opening edge 54a of the recess 54 is located radially outward of the rotating shaft 40 with respect to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 by a distance H1 between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 in the axial direction of the rotating shaft 40. This configuration is suitable for making it easier for the swirling flow of air flowing into the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 to flow into the recess 54.

[0070] (5) The pressure of the air compressed by the rotation of the second impeller 52 is higher than the pressure of the air compressed by the rotation of the first impeller 51. Therefore, an air flow is generated from the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 to the first gap 60a between the first back surface 51a of the first impeller 51 and the first opposing surface 15a of the partition wall 15 through the insertion hole 27. At this time, the swirl breaker 53 is formed at the end of the inner circumferential surface 27a that defines the insertion hole 27 on the second opposing surface 15b side. Therefore, the swirl breaker 53 suppresses the swirling flow of the air flowing into the insertion hole 27 from the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15. This makes it possible to suppress an increase in the rotational direction component of the dynamic pressure distribution generated between the inner circumferential surface 27a defining the insertion hole 27 and the rotating shaft 40. As a result, it is possible to reduce the destabilizing force that swings the rotating shaft 40.

[0071] The thrust force that moves the second impeller 52 in the axial direction toward the second opposing surface 15b of the partition wall 15 is greater than the thrust force that moves the first impeller 51 in the axial direction toward the first opposing surface 15a of the partition wall 15. Therefore, the recess 54 is formed in the second opposing surface 15b of the partition wall 15. This increases the static pressure generated between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15. Therefore, since the pressure acting on the second back surface 52a of the second impeller 52 increases, it is possible to avoid an increase in the thrust force that moves the second impeller 52 in the axial direction toward the second opposing surface 15b of the partition wall 15.

[0072] (6) Since an increase in the thrust force that moves the second impeller 52 in the axial direction toward the second opposing surface 15b of the partition wall 15 is avoided, it is possible to avoid a situation in which an increase in the load on the thrust bearing 47 forces the thrust bearing 47 to be enlarged. As a result, it is possible to prevent the centrifugal compressor 10 from becoming larger.

[0073] (7) As the thrust collar 46 rotates, it stirs up the air around the thrust collar 46, causing windage loss. This windage loss increases as the fifth power of the diameter of the thrust collar 46. However, according to the present embodiment, it is possible to avoid having to increase the size of the thrust bearing 47, and therefore it is possible to suppress an increase in the size of the thrust collar 46. As a result, it is possible to reduce the windage loss caused by the rotation of the thrust collar 46, and therefore it is possible to suppress a decrease in the operating efficiency of the centrifugal compressor.

[0074] [Example of change] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0075] ○ As shown in Figure 7, the outer peripheral opening edge 54a of the recess 54 may be located radially outward of the rotating shaft 40 with respect to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52, and may be located radially inward of the rotating shaft 40 relative to the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotating shaft 40.

[0076] 8, the outer peripheral opening edge 54a of the recess 54 may be located radially inward of the rotating shaft 40 with respect to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52. This makes it possible to reduce the size of the centrifugal compressor 10 in the radial direction of the rotating shaft 40.

[0077] 9, a plurality of recesses 54 may be formed in the second opposing surface 15b. When the second opposing surface 15b is viewed in plan, each recess 54 has an annular shape surrounding the insertion hole 27. Each recess 54 is formed on a concentric circle. In short, the number of recesses 54 is not particularly limited.

[0078] 10, the outer peripheral opening edge 54a of the recess 54 may be located radially inward of the rotating shaft 40 relative to the inner peripheral surface 37a of the second impeller recess 37. Even in this case, the outer peripheral opening edge 54a of the recess 54 may be located radially outward of the rotating shaft 40 relative to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 by the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotating shaft 40. In this case, in the radial direction of the rotating shaft 40, the distance between the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 and the inner peripheral surface 37a of the second impeller recess 37 is larger than the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotating shaft 40.

[0079] As shown in FIG. 11, the outer peripheral opening edge 54a of the recess 54 may be located radially outward of the rotating shaft 40 from the inner peripheral surface 37a of the second impeller recess 37. Even in this case, the outer peripheral opening edge 54a of the recess 54 may be located radially outward of the rotating shaft 40 from the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 by the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotating shaft 40. In this case, in the radial direction of the rotating shaft 40, the distance between the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 and the inner peripheral surface 37a of the second impeller recess 37 is smaller than the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotating shaft 40. The inner peripheral opening edge 54b of the recess 54 is located radially inward of the rotating shaft 40 from the outer peripheral edge 52e of the second back surface 52a of the second impeller 52. The opening of the recess 54 on the outer circumferential side is closed by a part of the partition wall 15 .

[0080] As shown in FIG. 12, the outer peripheral opening edge 54a of the recess 54 may be located radially outward of the rotary shaft 40 with respect to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52, larger than the distance H1 between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 in the axial direction of the rotary shaft 40. The outer peripheral opening edge 54a of the recess 54 is located on the same plane as the inner peripheral surface 37a of the second impeller recess 37. Therefore, the outer peripheral opening edge 54a of the recess 54 is continuous with the inner peripheral surface 37a of the second impeller recess 37. In the radial direction of the rotary shaft 40, the distance between the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 and the inner peripheral surface 37a of the second impeller recess 37 is larger than the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotary shaft 40. Therefore, in the radial direction of the rotating shaft 40, a distance H2 between the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 and the outer peripheral opening edge 54a of the recess 54 is greater than a distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotating shaft 40. The inner peripheral opening edge 54b of the recess 54 is located on the inner side of the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 in the radial direction of the rotating shaft 40.

[0081] According to this, the swirling flow of air flowing into the second gap 60b between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 is likely to flow directly into the recess 54 without bending. Therefore, pressure loss of the swirling flow of air is unlikely to occur, and the pressure in the recess 54 can be maintained high. As a result, the pressure acting on the second back surface 52a of the second impeller 52 is likely to increase, making it easier to avoid an increase in thrust force that moves the second impeller 52 in the axial direction toward the second opposing surface 15b of the partition wall 15.

[0082] As shown in Fig. 13, the outer peripheral opening edge 54a of the recess 54 may be located radially inward of the rotary shaft 40 relative to the inner peripheral surface 37a of the second impeller recess 37. Even in this case, the outer peripheral opening edge 54a of the recess 54 may be located radially outward of the rotary shaft 40 relative to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 by a distance greater than the distance H1 between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 in the axial direction of the rotary shaft 40. Therefore, in the radial direction of the rotary shaft 40, the distance H2 between the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 and the outer peripheral opening edge 54a of the recess 54 is greater than the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotary shaft 40. An inner peripheral opening edge 54b of the recess 54 is located on the inner side in the radial direction of the rotary shaft 40 with respect to an outer peripheral edge 52e of the second back surface 52a of the second impeller 52.

[0083] As shown in Fig. 14, the outer peripheral opening edge 54a of the recess 54 may be located radially outward of the rotary shaft 40 relative to the inner peripheral surface 37a of the second impeller recess 37. Even in this case, the outer peripheral opening edge 54a of the recess 54 may be located radially outward of the rotary shaft 40 relative to the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 by a distance greater than the distance H1 between the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15 in the axial direction of the rotary shaft 40. Therefore, in the radial direction of the rotary shaft 40, the distance H2 between the outer peripheral edge 52e of the second back surface 52a of the second impeller 52 and the outer peripheral opening edge 54a of the recess 54 is greater than the distance H1 between the second back surface 52a and the second opposing surface 15b in the axial direction of the rotary shaft 40. An inner peripheral opening edge 54b of the recess 54 is located radially inward of the rotary shaft 40 with respect to an outer peripheral edge 52e of the second back surface 52a of the second impeller 52. An opening on the outer peripheral side of the recess 54 is closed by a part of the partition wall 15.

[0084] 15, a portion of the recess 54 may have a tapered surface. For example, the recess 54 may have a tapered surface 54c that extends from the outer peripheral opening edge 54a toward the bottom surface of the recess 54 at an angle to the axial direction of the rotation shaft 40. The tapered surface 54c gradually extends inwardly of the rotation shaft 40 as it moves from the outer peripheral opening edge 54a toward the bottom surface of the recess 54.

[0085] 16 , a stepped surface may be provided in a portion of the recess 54. For example, the recess 54 may have an annular stepped surface 54d extending radially inwardly of the rotating shaft 40 from a surface continuous with the outer circumferential opening edge 54a, and a cylindrical stepped surface 54e extending in the axial direction of the rotating shaft 40 from the inner circumferential edge of the stepped surface 54d and connected to the bottom surface of the recess 54.

[0086] In the embodiment, the recess 54 may not be formed on the second opposing surface 15b of the partition wall 15, but may be formed on, for example, the second back surface 52a of the second impeller 52. The recess 54 may be formed on the second back surface 52a of the second impeller 52 in addition to the second opposing surface 15b of the partition wall 15. Therefore, it is sufficient that the recess 54 is formed on at least one of the second back surface 52a of the second impeller 52 and the second opposing surface 15b of the partition wall 15.

[0087] In the above embodiment, the width W1 of the recess 54 in the radial direction of the rotating shaft 40 may be the same as the depth T1 of the recess 54. In an embodiment, the width W1 of the recess 54 in the radial direction of the rotating shaft 40 may be smaller than the depth T1 of the recess 54.

[0088] In the above embodiment, the number of grooves 53a constituting the swirl breaker 53 is not particularly limited. In an embodiment, the swirl breaker 53 may be constituted by a plurality of protrusions formed at equal intervals in the circumferential direction of the rotating shaft 40 on the end portion of the inner circumferential surface 27a that defines the insertion hole 27 on the second opposing surface 15b side.

[0089] In the above embodiment, the centrifugal compressor 10 may be configured such that the second impeller 52 is connected to a first end of the rotating shaft 40 and the first impeller 51 is connected to a second end of the rotating shaft 40.

[0090] In the embodiment, the centrifugal compressor 10 may be configured not to include, for example, the second impeller 52. In this case, it is sufficient that the recess 54 is formed in at least one of the first back surface 51a of the first impeller 51 and the first opposing surface 15a of the partition wall 15. In short, it is sufficient that the recess 54 is formed in at least one of the back surface of the impeller and the opposing surface of the partition wall 15.

[0091] In the embodiment, the fluid compressed by the first impeller 51 and the second impeller 52 is not limited to air. Therefore, the application of the centrifugal compressor 10 and the fluid to be compressed may be any. For example, the centrifugal compressor 10 may be used in an air conditioner, and the fluid to be compressed may be a refrigerant. Furthermore, for example, the centrifugal compressor 10 may be applied to an in-vehicle cabin air conditioner or a refrigerant circuit for battery temperature control. In addition, the application of the centrifugal compressor 10 is not limited to a vehicle, and may be any. [Explanation of symbols]

[0092] Description of the Related Art 10...centrifugal compressor, 11...housing, 15...partition wall, 15a...first opposing surface which is the opposing surface, 15b...second opposing surface which is the opposing surface, 27...insertion hole, 27a...inner circumferential surface, 28...first impeller chamber as impeller chamber, 33...second impeller chamber as impeller chamber, 40...rotating shaft, 51...first impeller as impeller, 51a...first back surface which is the back surface, 52...second impeller as impeller, 52a...second back surface which is the back surface, 52e...outer circumferential edge, 53...swirl breaker, 54...recess, 54a...outer circumferential opening edge, 54b...inner circumferential opening edge.

Claims

1. A rotation axis; an impeller that rotates integrally with the rotary shaft to compress a fluid; a housing having a partition wall that defines an impeller chamber that houses the impeller; The partition wall is An opposing surface facing the back surface of the impeller; an insertion hole that opens in the opposing surface and through which the rotating shaft is inserted, a swirl breaker is formed at an end portion of an inner circumferential surface that defines the insertion hole on the side of the opposing surface to suppress a swirling flow of a fluid that flows into the insertion hole from a gap between the back surface and the opposing surface, At least one of the rear surface and the opposing surface is formed with an annular recess for increasing a pressure acting on the rear surface, A centrifugal compressor, characterized in that a swirling flow of a fluid flowing into a gap between the back surface and the opposing surface flows into the recess.

2. The centrifugal compressor according to claim 1 , wherein the recess is formed in the opposing surface.

3. 3. The centrifugal compressor according to claim 2, wherein an outer peripheral opening edge of the recess is located outside an outer peripheral edge of the back surface in a radial direction of the rotary shaft.

4. 4. The centrifugal compressor according to claim 3, wherein an outer peripheral opening edge of the recess is located radially outward of the rotating shaft with respect to an outer peripheral edge of the back surface by a distance between the back surface and the opposing surface in the axial direction of the rotating shaft.

5. an outer peripheral opening edge of the recess is located radially outward of the rotation shaft with respect to an outer peripheral edge of the back surface by a distance greater than a distance between the back surface and the opposing surface in an axial direction of the rotation shaft, 4. The centrifugal compressor according to claim 3, wherein an inner peripheral opening edge of the recess is located radially inward of an outer peripheral edge of the back surface in the radial direction of the rotary shaft.

6. 3. The centrifugal compressor according to claim 2, wherein an outer peripheral opening edge of the recess is located radially inward of an outer peripheral edge of the back surface in the radial direction of the rotary shaft.

7. The impeller is A first impeller that rotates integrally with the rotary shaft; a second impeller that rotates integrally with the rotary shaft to compress the fluid compressed by the rotation of the first impeller, The impeller chamber is a first impeller chamber that accommodates the first impeller; a second impeller chamber that accommodates the second impeller, The partition wall separates the first impeller chamber and the second impeller chamber, A first back surface that is a back surface of the first impeller and a second back surface that is a back surface of the second impeller face each other in the axial direction of the rotary shaft via the partition wall, The opposing surface is a first opposing surface opposing the first back surface; a second opposing surface opposed to the second back surface, The swirl breaker is formed on an end portion of an inner circumferential surface that defines the insertion hole, the end portion being on the second opposing surface side, The centrifugal compressor according to any one of claims 1 to 6, wherein the recess is formed in at least one of the second back surface and the second opposing surface.

Images