Centrifugal compressor

Abstract

To stably support a rotating shaft in a thrust direction, and to suppress the lowering of the operation efficiency of a centrifugal compressor.SOLUTION: For example, when a load in a thrust direction is smaller than a prescribed load, a first strike collar 17 is supported by only a first dynamic pressure thrust bearing 19 out of the first dynamic pressure thrust bearing 19 and a second dynamic pressure thrust bearing 20. Therefore, it is avoided that a support to a rotating shaft 12 in the thrust direction via a second striker collar 18 of the second dynamic pressure thrust bearing 20 is wastefully performed when the load in the thrust direction is smaller than the prescribed load. When the load in the thrust direction is equal to or larger than the prescribed load, the first striker collar 17 is supported by the first dynamic pressure thrust bearing 19, and the second striker collar 18 is supported by the second dynamic pressure thrust bearing 20.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] The centrifugal compressor includes a rotating shaft and an impeller. The impeller rotates integrally with the rotating shaft. The centrifugal compressor also includes a thrust collar and a dynamic pressure thrust bearing, as disclosed in Patent Document 1, for example. The thrust collar protrudes from the outer circumferential surface of the rotating shaft to the outside in the radial direction of the rotating shaft. The thrust collar rotates integrally with the rotating shaft. The thrust collar is disk-shaped. The dynamic pressure thrust bearing is provided to face the thrust collar in the axial direction of the rotating shaft.

[0003] When the rotation speed of the rotating shaft is below the floating rotation speed, the hydrodynamic thrust bearing supports the rotating shaft in the thrust direction via the thrust collar while in contact with the thrust collar. On the other hand, when the rotation speed of the rotating shaft is equal to or higher than the floating rotation speed, the thrust collar floats relative to the hydrodynamic thrust bearing due to the dynamic pressure of the fluid film generated between the hydrodynamic thrust bearing and the thrust collar. As a result, the hydrodynamic thrust bearing supports the rotating shaft in the thrust direction via the thrust collar without coming into contact with the thrust collar. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-127443 A Summary of the Invention [Problem to be solved by the invention]

[0005] In such a centrifugal compressor, in order to stably support the rotating shaft in the thrust direction, it is necessary to increase the load capacity of the dynamic pressure thrust bearing. In order to increase the load capacity of the dynamic pressure thrust bearing, for example, a centrifugal compressor including a first thrust collar, a second thrust collar, a first dynamic pressure thrust bearing, and a second dynamic pressure thrust bearing is conceivable. The first thrust collar protrudes from the outer peripheral surface of the rotating shaft to the outside in the radial direction of the rotating shaft. The first thrust collar rotates integrally with the rotating shaft. The first thrust collar is disk-shaped. The second thrust collar protrudes from the outer peripheral surface of the rotating shaft to the outside in the radial direction of the rotating shaft. The second thrust collar rotates integrally with the rotating shaft. The second thrust collar is disk-shaped. The second thrust collar is disposed at a position separated from the first thrust collar in the axial direction of the rotating shaft. The first dynamic pressure thrust bearing is provided to face the first thrust collar in the axial direction of the rotating shaft. The second dynamic pressure thrust bearing is disposed to face the second thrust collar in the axial direction of the rotating shaft. With this, a thrust load acting on the rotating shaft in the thrust direction can be received by the first dynamic pressure thrust bearing and the second dynamic pressure thrust bearing, so that the rotating shaft can be stably supported in the thrust direction.

[0006] However, when the thrust load acting on the rotating shaft is small, if the thrust load is received by both the first dynamic pressure thrust bearing and the second dynamic pressure thrust bearing, support by one of the first dynamic pressure thrust bearing and the second dynamic pressure thrust bearing is wasted. As a result, the operating efficiency of the centrifugal compressor is reduced. Therefore, it is desired to stably support the rotating shaft in the thrust direction and suppress the decrease in the operating efficiency of the centrifugal compressor. [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, a disk-shaped first thrust collar that protrudes from an outer circumferential surface of the rotating shaft radially outward from the rotating shaft and rotates integrally with the rotating shaft, a disk-shaped second thrust collar that protrudes from an outer circumferential surface of the rotating shaft radially outward from the rotating shaft, is disposed at a position spaced apart from the first thrust collar in the axial direction of the rotating shaft, and rotates integrally with the rotating shaft, a first hydrodynamic thrust bearing provided to face the first thrust collar in the axial direction, and a first thrust bearing that is disposed on the shaft. and a second dynamic pressure thrust bearing arranged to face the second thrust collar in a thrust direction, wherein when a load in the thrust direction is less than a predetermined load, the first thrust collar is supported only by the first dynamic pressure thrust bearing of the first dynamic pressure thrust bearing and the second dynamic pressure thrust bearing, and when the load in the thrust direction is equal to or greater than the predetermined load, the first thrust collar is supported by the first dynamic pressure thrust bearing and the second thrust collar is supported by the second dynamic pressure thrust bearing.

[0008] According to this, for example, when the load in the thrust direction is less than a predetermined load, the first thrust collar is supported only by the first dynamic pressure thrust bearing out of the first dynamic pressure thrust bearing and the second dynamic pressure thrust bearing. Therefore, when the load in the thrust direction is less than a predetermined load, it is possible to avoid unnecessary support of the rotating shaft in the thrust direction via the second thrust collar in the second dynamic pressure thrust bearing. As a result, it is possible to suppress a decrease in the operating efficiency of the centrifugal compressor. When the load in the thrust direction is equal to or greater than a predetermined load, the first thrust collar is supported by the first dynamic pressure thrust bearing, and the second thrust collar is supported by the second dynamic pressure thrust bearing. Therefore, it is possible to stably support the rotating shaft in the thrust direction. As a result, it is possible to stably support the rotating shaft in the thrust direction and suppress a decrease in the operating efficiency of the centrifugal compressor.

[0009] In the above centrifugal compressor, the first hydrodynamic thrust bearing has a first top foil facing the first thrust collar and a first bump foil provided on the opposite side of the first thrust collar with the first top foil in between, and the second hydrodynamic thrust bearing has a second top foil facing the second thrust collar and a second bump foil provided on the opposite side of the second thrust collar with the second top foil in between, and a clearance between the first top foil and the first thrust collar is preferably smaller than a clearance between the second top foil and the second thrust collar.

[0010] According to this, when the load in the thrust direction is less than a predetermined load, the first thrust collar can be supported only by the first dynamic pressure thrust bearing out of the first dynamic pressure thrust bearing and the second dynamic pressure thrust bearing, and when the load in the thrust direction is equal to or greater than the predetermined load, the first thrust collar can be supported by the first dynamic pressure thrust bearing and the second thrust collar can be supported by the second dynamic pressure thrust bearing.

[0011] In the centrifugal compressor, the first top foil may have a coating layer on a portion facing the first thrust collar. The clearance between the first top foil and the first thrust collar is smaller than the clearance between the second top foil and the second thrust collar. Therefore, the first top foil is in contact with the first thrust collar when the rotation speed of the rotating shaft is lower than the floating rotation speed. At this time, the first top foil has a coating layer on a portion facing the first thrust collar. Therefore, wear between the first top foil and the first thrust collar can be suppressed. On the other hand, the second top foil does not contact the second thrust collar even when the rotating shaft is lower than the floating rotation speed. Therefore, the second top foil does not need a coating layer on a portion facing the second thrust collar. And, since the second top foil does not have a coating layer, heat dissipation is good. As a result, the durability of the second hydrodynamic thrust bearing can be improved.

[0012] In the centrifugal compressor, it is preferable that the first dynamic pressure thrust bearing is provided in pair with the first thrust collar sandwiched therebetween, and the second dynamic pressure thrust bearing is provided on only one side with respect to the second thrust collar to support the second thrust collar.

[0013] According to this, the second dynamic pressure thrust bearing is provided on only one side supporting the second thrust collar with respect to the second thrust collar. Therefore, when the thrust load acting on the rotating shaft increases, the second dynamic pressure thrust bearing can receive the thrust load acting on the rotating shaft in addition to the first dynamic pressure thrust bearing. On the other hand, in a centrifugal compressor, the rotating shaft may move in a direction opposite to the direction in which the thrust load acts on the rotating shaft due to external vibrations or the like. At this time, a pair of first dynamic pressure thrust bearings are provided with respect to the first thrust collar with the first thrust collar sandwiched therebetween. Therefore, even if the rotating shaft moves in a direction opposite to the direction in which the thrust load acts on the rotating shaft, the first thrust collar can be received by the first dynamic pressure thrust bearing. As a result, it is not necessary to provide a pair of second dynamic pressure thrust bearings with the second thrust collar sandwiched therebetween, and therefore the number of parts can be reduced. Therefore, the centrifugal compressor can be configured simply.

[0014] In the above centrifugal compressor, it is preferable that the rotating shaft, the impeller, the first thrust collar, the second thrust collar, the first dynamic pressure thrust bearing, and the second dynamic pressure thrust bearing are accommodated in a housing, the impeller is connected only to a first end of the rotating shaft, and the first dynamic pressure thrust bearing is disposed closer to the impeller than the second dynamic pressure thrust bearing.

[0015] The centrifugal compressor needs to be designed taking into consideration the clearance between the first hydrodynamic thrust bearing and the first thrust collar so that the impeller does not interfere with the housing. Here, the greater the distance between the impeller and the first hydrodynamic thrust bearing in the axial direction of the rotating shaft, the greater the effect of the dimensional tolerance of the housing. Also, the greater the distance between the impeller and the first hydrodynamic thrust bearing in the axial direction of the rotating shaft, the greater the effect of the difference between the thermal expansion in the axial direction of the rotating shaft and the thermal expansion in the axial direction of the rotating shaft in the housing. Therefore, the first hydrodynamic thrust bearing is disposed closer to the impeller than the second hydrodynamic thrust bearing. This makes it possible to minimize the effect of the dimensional tolerance of the housing and the effect of the difference between the thermal expansion in the axial direction of the rotating shaft and the thermal expansion in the axial direction of the rotating shaft in the housing. As a result, it is possible to easily design the clearance between the impeller and the housing to be as small as possible so that the impeller does not interfere with the housing. Therefore, it is possible to improve the compression efficiency of the fluid by the rotation of the impeller.

[0016] In the above centrifugal compressor, it is preferable that the rotating shaft, the impeller, the first thrust collar, the second thrust collar, the first dynamic pressure thrust bearing, and the second dynamic pressure thrust bearing are accommodated in a housing, and the impeller includes a first impeller connected to a first end of the rotating shaft, and a second impeller connected to a second end of the rotating shaft and rotates to compress fluid after being compressed by rotation of the first impeller, and the first dynamic pressure thrust bearing is disposed closer to the second impeller than the second dynamic pressure thrust bearing.

[0017] The centrifugal compressor needs to be designed in consideration of the clearance between the first dynamic pressure thrust bearing and the first thrust collar so that the first impeller and the second impeller do not interfere with the housing. Here, since the second impeller rotates to compress the fluid compressed by the rotation of the first impeller, in order to improve the compression efficiency of the centrifugal compressor, it is necessary to narrow the clearance between the second impeller and the housing as much as possible. The greater the distance between the second impeller and the first dynamic pressure thrust bearing in the axial direction of the rotating shaft, the greater the influence of the dimensional tolerance of the housing. Also, the greater the distance between the second impeller and the first dynamic pressure thrust bearing in the axial direction of the rotating shaft, the greater the influence of the difference between the thermal expansion in the axial direction of the rotating shaft and the thermal expansion in the axial direction of the rotating shaft in the housing. Therefore, the first dynamic pressure thrust bearing is disposed closer to the second impeller than the second dynamic pressure thrust bearing. This makes it possible to minimize the influence of the dimensional tolerance of the housing and the influence of the difference between the thermal expansion in the axial direction of the rotating shaft and the thermal expansion in the axial direction of the rotating shaft in the housing. As a result, it is easy to design the clearance between the second impeller and the housing to be as small as possible so that the second impeller does not interfere with the housing. This improves the efficiency of compressing the fluid by the rotation of the second impeller, thereby improving the compression efficiency of the centrifugal compressor.

[0018] In the centrifugal compressor, the second dynamic pressure thrust bearing may have higher rigidity than the first dynamic pressure thrust bearing. According to this, as the displacement of the first dynamic pressure thrust bearing and the displacement of the second dynamic pressure thrust bearing increase, the magnitude of the thrust load received by the second dynamic pressure thrust bearing approaches the magnitude of the thrust load received by the first dynamic pressure thrust bearing. Therefore, the thrust load acting on the rotating shaft can be efficiently received by the second dynamic pressure thrust bearing. As a result, the rotating shaft can be more stably supported in the thrust direction by the first dynamic pressure thrust bearing and the second dynamic pressure thrust bearing. Effect of the Invention

[0019] According to the present invention, the rotating shaft can be stably supported in the thrust direction, and a decrease in the operating efficiency of the centrifugal compressor can be suppressed. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic configuration diagram showing a centrifugal compressor according to an embodiment. [Diagram 2] FIG. 2 is a graph showing characteristics of the first dynamic pressure thrust bearing and the second dynamic pressure thrust bearing. [Diagram 3] FIG. 3 is a schematic configuration diagram showing a centrifugal compressor in a modified example. [Figure 4] FIG. 4 is a schematic configuration diagram showing a centrifugal compressor in a modified example. [Diagram 5] FIG. 5 is a schematic configuration diagram showing a centrifugal compressor in a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] An embodiment of a centrifugal compressor will be described below with reference to Figures 1 and 2. The centrifugal compressor of the embodiment described below is mounted on a fuel cell vehicle. The centrifugal compressor compresses air as a fluid to be supplied to a fuel cell stack.

[0022] <Schematic configuration of centrifugal compressor> As shown in FIG. 1, the centrifugal compressor 10 includes a housing 11, a rotating shaft 12, an impeller 13, and a motor 14. The housing 11 is cylindrical. The housing 11 accommodates the rotating shaft 12, the impeller 13, and the motor 14. Thus, the rotating shaft 12 is accommodated within the housing 11. The rotating shaft 12 is rotated by the driving of the motor 14. The impeller 13 is connected to a first end of the rotating shaft 12. The impeller 13 rotates integrally with the rotating shaft 12 to compress air. In the centrifugal compressor 10 of this embodiment, the impeller 13 is connected only to the first end of the rotating shaft 12.

[0023] The centrifugal compressor 10 includes a first dynamic pressure radial bearing 15 and a second dynamic pressure radial bearing 16. The first dynamic pressure radial bearing 15 and the second dynamic pressure radial bearing 16 are held in the housing 11. The first dynamic pressure radial bearing 15 and the second dynamic pressure radial bearing 16 are disposed on both sides of the motor 14. The first dynamic pressure radial bearing 15 and the second dynamic pressure radial bearing 16 rotatably support the portions of the rotating shaft 12 on both sides of the motor 14. The first dynamic pressure radial bearing 15 and the second dynamic pressure radial bearing 16 support the rotating shaft 12 rotatably in the radial direction. The "radial direction" is a direction perpendicular to the axial direction of the rotating shaft 12.

[0024] The centrifugal compressor 10 includes a first thrust collar 17 and a second thrust collar 18. The first thrust collar 17 protrudes from a portion of the outer circumferential surface of the rotating shaft 12 that is located between the impeller 13 and the first dynamic pressure radial bearing 15. The first thrust collar 17 is disk-shaped. The first thrust collar 17 is fixed to the rotating shaft 12 by being press-fitted into the outer circumferential surface of the rotating shaft 12. The first thrust collar 17 protrudes from the outer circumferential surface of the rotating shaft 12 to the outside in the radial direction of the rotating shaft 12. The first thrust collar 17 rotates integrally with the rotating shaft 12.

[0025] The second thrust collar 18 protrudes from a portion of the outer circumferential surface of the rotating shaft 12 that is located on the opposite side to the motor 14 than the second dynamic pressure radial bearing 16. Therefore, the second thrust collar 18 is disposed at a position spaced apart from the first thrust collar 17 in the axial direction of the rotating shaft 12. The second thrust collar 18 is disk-shaped. The second thrust collar 18 is fixed to the rotating shaft 12 by being press-fitted into the outer circumferential surface of the rotating shaft 12. The second thrust collar 18 protrudes from the outer circumferential surface of the rotating shaft 12 to the outside in the radial direction of the rotating shaft 12. The second thrust collar 18 rotates integrally with the rotating shaft 12.

[0026] The centrifugal compressor 10 includes a first dynamic pressure thrust bearing 19 and a second dynamic pressure thrust bearing 20. The first dynamic pressure thrust bearing 19 is provided to face the first thrust collar 17 in the axial direction of the rotating shaft 12. The first dynamic pressure thrust bearing 19 is held in the housing 11 in a state facing the first thrust collar 17 in the axial direction of the rotating shaft 12. The first dynamic pressure thrust bearing 19 is provided as a pair with respect to the first thrust collar 17, with the first thrust collar 17 sandwiched therebetween. Therefore, the centrifugal compressor 10 includes two first dynamic pressure thrust bearings 19. The two first dynamic pressure thrust bearings 19 support the first thrust collar 17 rotatably in the thrust direction.

[0027] The second dynamic pressure thrust bearing 20 is provided so as to face the second thrust collar 18 in the axial direction of the rotating shaft 12. The second dynamic pressure thrust bearing 20 is held in the housing 11 in a state of facing the second thrust collar 18 in the axial direction of the rotating shaft 12. Therefore, the first dynamic pressure thrust bearing 19 is disposed closer to the impeller 13 than the second dynamic pressure thrust bearing 20. The second dynamic pressure thrust bearing 20 is provided in pair with respect to the second thrust collar 18, with the second thrust collar 18 sandwiched therebetween. Therefore, the centrifugal compressor 10 has two second dynamic pressure thrust bearings 20. The two second dynamic pressure thrust bearings 20 support the second thrust collar 18 rotatably in the thrust direction. The "thrust direction" refers to the axial direction of the rotating shaft 12.

[0028] The first hydrodynamic thrust bearing 19 has a first top foil 19a and a first bump foil 19b. The first top foil 19a faces the first thrust collar 17. The first top foil 19a is configured by disposing fan-shaped top foil pieces (not shown) at equal intervals in the circumferential direction of the rotating shaft 12. The first bump foil 19b is provided on the opposite side of the first thrust collar 17 with the first top foil 19a in between. The first bump foil 19b is configured by disposing fan-shaped bump foil pieces (not shown) at equal intervals in the circumferential direction of the rotating shaft 12. Each bump foil piece is formed by bending a single thin plate into a corrugated shape. The first bump foil 19b elastically supports the first top foil 19a in a state in which it can be displaced in the axial direction of the rotating shaft 12 by elastic deformation.

[0029] The second hydrodynamic thrust bearing 20 has a second top foil 20a and a second bump foil 20b. The second top foil 20a faces the second thrust collar 18. The second top foil 20a is configured by disposing fan-shaped top foil pieces (not shown) at equal intervals in the circumferential direction of the rotating shaft 12. The second bump foil 20b is provided on the opposite side of the second thrust collar 18 with the second top foil 20a in between. The second bump foil 20b is configured by disposing fan-shaped bump foil pieces (not shown) at equal intervals in the circumferential direction of the rotating shaft 12. Each bump foil piece is formed by bending a single thin plate into a corrugated shape. The second bump foil 20b elastically supports the second top foil 20a in a state in which it can be displaced in the axial direction of the rotating shaft 12 by elastic deformation. Such a hydrodynamic thrust bearing is already known.

[0030] The first dynamic pressure thrust bearing 19 elastically deforms to elastically support the rotating shaft 12 in the thrust direction via the first thrust collar 17 while being displaceable in the axial direction of the rotating shaft 12. The second dynamic pressure thrust bearing 20 elastically deforms to elastically support the rotating shaft 12 in the thrust direction via the second thrust collar 18 while being displaceable in the axial direction of the rotating shaft 12.

[0031] The rotating shaft 12 , the impeller 13 , the first thrust collar 17 , the second thrust collar 18 , the first dynamic pressure thrust bearing 19 , and the second dynamic pressure thrust bearing 20 are accommodated in the housing 11 .

[0032] A clearance C1 between the first top foil 19a and the first thrust collar 17 is smaller than a clearance C2 between the second top foil 20a and the second thrust collar 18. The second hydrodynamic thrust bearing 20 has higher rigidity than the first hydrodynamic thrust bearing 19. Specifically, the rigidity of the second bump foil 20b of the second hydrodynamic thrust bearing 20 is higher than the rigidity of the first bump foil 19b of the first hydrodynamic thrust bearing 19. Therefore, the second hydrodynamic thrust bearing 20 is less susceptible to elastic deformation than the first hydrodynamic thrust bearing 19.

[0033] Fig. 2 shows the characteristics of the first dynamic pressure thrust bearing 19 and the second dynamic pressure thrust bearing 20. In Fig. 2, a solid line L1 indicates the relationship between the displacement of the first dynamic pressure thrust bearing 19 in the axial direction of the rotating shaft 12 and the thrust load received by the first dynamic pressure thrust bearing 19. A solid line L2 indicates the relationship between the displacement of the second dynamic pressure thrust bearing 20 in the axial direction of the rotating shaft 12 and the thrust load received by the second dynamic pressure thrust bearing 20. In the following description, the "thrust load" may be simply referred to as the "thrust load".

[0034] As shown by the solid line L1 in Fig. 2, the magnitude of the thrust load received by the first dynamic pressure thrust bearing 19 increases as the axial displacement of the rotating shaft 12 at the first dynamic pressure thrust bearing 19 increases. As shown by the solid line L2 in Fig. 2, the magnitude of the thrust load received by the second dynamic pressure thrust bearing 20 increases as the axial displacement of the rotating shaft 12 at the second dynamic pressure thrust bearing 20 increases.

[0035] As shown in FIG. 2, when the first dynamic pressure thrust bearing 19 reaches the limit load F1 at which it can bear the thrust load, the second dynamic pressure thrust bearing 20 is set to have a rigidity that enables the second dynamic pressure thrust bearing 20 to bear the same thrust load.

[0036] [Operation of the embodiment] Next, the operation of this embodiment will be described. When the rotating shaft 12 is below the floating rotation speed, the first hydrodynamic thrust bearing 19 supports the rotating shaft 12 in the thrust direction via the first thrust collar 17 while in contact with the first thrust collar 17. On the other hand, when the rotation speed of the rotating shaft 12 is equal to or higher than the floating rotation speed, the first thrust collar 17 floats relative to the first hydrodynamic thrust bearing 19 due to the dynamic pressure of the air film generated between the first hydrodynamic thrust bearing 19 and the first thrust collar 17. As a result, the first hydrodynamic thrust bearing 19 supports the rotating shaft 12 in the thrust direction via the first thrust collar 17 without coming into contact with the first thrust collar 17.

[0037] A clearance C1 between the first top foil 19a and the first thrust collar 17 is smaller than a clearance C2 between the second top foil 20a and the second thrust collar 18. Therefore, for example, when the load in the thrust direction acting on the rotating shaft 12 is less than a predetermined load, the first thrust collar 17 is supported only by the first dynamic pressure thrust bearing 19 out of the first dynamic pressure thrust bearing 19 and the second dynamic pressure thrust bearing 20. Therefore, when the load in the thrust direction is less than the predetermined load, it is possible to prevent the second dynamic pressure thrust bearing 20 from needlessly supporting the rotating shaft 12 in the thrust direction via the second thrust collar 18.

[0038] As the thrust load acting on the rotating shaft 12 increases, the displacement of the first dynamic pressure thrust bearing 19 increases. In other words, as the thrust load acting on the rotating shaft 12 increases, the first bump foil 19b of the first dynamic pressure thrust bearing 19 elastically deforms and is gradually crushed. When the thrust load acting on the rotating shaft 12 is equal to or greater than a predetermined load, the first thrust collar 17 is supported by the first dynamic pressure thrust bearing 19, and the second thrust collar 18 is supported by the second dynamic pressure thrust bearing 20.

[0039] The second hydrodynamic thrust bearing 20 supports the rotating shaft 12 in the thrust direction via the second thrust collar 18, with the second thrust collar 18 floating relative to the second hydrodynamic thrust bearing 20 due to the dynamic pressure of the air film generated between the second hydrodynamic thrust bearing 20 and the second thrust collar 18. As the load in the thrust direction acting on the rotating shaft 12 increases, the displacement of the second hydrodynamic thrust bearing 20 increases. In other words, as the load in the thrust direction acting on the rotating shaft 12 increases, the second bump foil 20b of the second hydrodynamic thrust bearing 20 elastically deforms and is gradually crushed.

[0040] At this time, the second dynamic pressure thrust bearing 20 has higher rigidity than the first dynamic pressure thrust bearing 19. For this reason, as shown in Fig. 2, as the displacement of the first dynamic pressure thrust bearing 19 and the displacement of the second dynamic pressure thrust bearing 20 increase, the magnitude of the thrust load received by the second dynamic pressure thrust bearing 20 approaches the magnitude of the thrust load received by the first dynamic pressure thrust bearing 19. Therefore, the load in the thrust direction acting on the rotating shaft 12 is efficiently received by the second dynamic pressure thrust bearing 20.

[0041] In this way, when the load in the thrust direction is less than a predetermined load, the first thrust collar 17 is supported only by the first dynamic pressure thrust bearing 19 out of the first dynamic pressure thrust bearing 19 and the second dynamic pressure thrust bearing 20. When the load in the thrust direction is equal to or greater than the predetermined load, the first thrust collar 17 is supported by the first dynamic pressure thrust bearing 19, and the second thrust collar 18 is supported by the second dynamic pressure thrust bearing 20.

[0042] [Effects of the embodiment] The above embodiment can provide the following effects. (1) For example, when the load in the thrust direction is less than a predetermined load, the first thrust collar 17 is supported only by the first dynamic pressure thrust bearing 19 out of the first dynamic pressure thrust bearing 19 and the second dynamic pressure thrust bearing 20. Therefore, when the load in the thrust direction is less than a predetermined load, the second dynamic pressure thrust bearing 20 is prevented from unnecessarily supporting the rotating shaft 12 in the thrust direction via the second thrust collar 18. As a result, the decrease in the operating efficiency of the centrifugal compressor 10 can be suppressed. When the load in the thrust direction is equal to or greater than a predetermined load, the first thrust collar 17 is supported by the first dynamic pressure thrust bearing 19, and the second thrust collar 18 is supported by the second dynamic pressure thrust bearing 20. Therefore, the rotating shaft 12 can be stably supported in the thrust direction. As a result, the rotating shaft 12 can be stably supported in the thrust direction, and the decrease in the operating efficiency of the centrifugal compressor 10 can be suppressed.

[0043] (2) The clearance C1 between the first top foil 19a and the first thrust collar 17 is smaller than the clearance C2 between the second top foil 20a and the second thrust collar 18. According to this, when the load in the thrust direction is less than a predetermined load, the first thrust collar 17 can be supported only by the first dynamic pressure thrust bearing 19 out of the first dynamic pressure thrust bearing 19 and the second dynamic pressure thrust bearing 20. When the load in the thrust direction is equal to or greater than the predetermined load, the first thrust collar 17 can be supported by the first dynamic pressure thrust bearing 19, and the second thrust collar 18 can be supported by the second dynamic pressure thrust bearing 20.

[0044] (3) The centrifugal compressor 10 needs to be designed in consideration of the clearance C1 between the first top foil 19a of the first hydrodynamic thrust bearing 19 and the first thrust collar 17 so that the impeller 13 does not interfere with the housing 11. Here, the greater the distance between the impeller 13 and the first hydrodynamic thrust bearing 19 in the axial direction of the rotating shaft 12, the greater the effect of the dimensional tolerance of the housing 11. Also, the greater the distance between the impeller 13 and the first hydrodynamic thrust bearing 19 in the axial direction of the rotating shaft 12, the greater the effect of the difference between the thermal expansion in the axial direction of the rotating shaft 12 and the thermal expansion in the axial direction of the rotating shaft 12 in the housing 11. Therefore, the first hydrodynamic thrust bearing 19 is disposed closer to the impeller 13 than the second hydrodynamic thrust bearing 20. This makes it possible to minimize the effect of the dimensional tolerance of the housing 11 and the effect of the difference between the thermal expansion in the axial direction of the rotating shaft 12 and the thermal expansion in the axial direction of the rotating shaft 12 in the housing 11. As a result, it is easy to design the clearance between impeller 13 and housing 11 as small as possible so that impeller 13 does not interfere with housing 11. Therefore, the efficiency of air compression by rotation of impeller 13 can be improved.

[0045] (4) The second dynamic pressure thrust bearing 20 has higher rigidity than the first dynamic pressure thrust bearing 19. Accordingly, as the displacement of the first dynamic pressure thrust bearing 19 and the displacement of the second dynamic pressure thrust bearing 20 increase, the magnitude of the thrust load received by the second dynamic pressure thrust bearing 20 approaches the magnitude of the thrust load received by the first dynamic pressure thrust bearing 19. Therefore, the thrust load acting on the rotating shaft 12 can be efficiently received by the second dynamic pressure thrust bearing 20. As a result, the first dynamic pressure thrust bearing 19 and the second dynamic pressure thrust bearing 20 can support the rotating shaft 12 more stably in the thrust direction.

[0046] (5) The second dynamic pressure thrust bearing 20 is set to a rigidity that enables the second dynamic pressure thrust bearing 20 to bear the same thrust load when the first dynamic pressure thrust bearing 19 reaches the limit load F1 at which the first dynamic pressure thrust bearing 19 can bear the thrust load. Therefore, the first dynamic pressure thrust bearing 19 and the second dynamic pressure thrust bearing 20 can bear the load in the thrust direction acting on the rotating shaft 12 to the maximum extent.

[0047] (6) According to this embodiment, the first thrust collar 17, the second thrust collar 18, the first dynamic pressure thrust bearing 19, and the second dynamic pressure thrust bearing 20 are used. For example, consider a case where the load capacity is increased by using only the first thrust collar 17 and the first dynamic pressure thrust bearing 19 without using the second thrust collar 18 and the second dynamic pressure thrust bearing 20. Compared to this case, it is not necessary to increase the size of the first thrust collar 17 and the first dynamic pressure thrust bearing 19, and the housing 11 in the radial direction of the rotating shaft 12. Therefore, it is possible to prevent the centrifugal compressor 10 from becoming large in the radial direction of the rotating shaft 12. Furthermore, it is possible to prevent the inertia of the first thrust collar 17, the second thrust collar 18, the first dynamic pressure thrust bearing 19, and the second dynamic pressure thrust bearing 20 from increasing, and the windage loss caused by the rotation of the first thrust collar 17 and the second thrust collar 18 from increasing. Therefore, it is possible to suppress a decrease in the operating efficiency of the centrifugal compressor 10.

[0048] [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.

[0049] 3, the first top foil 19a of the first hydrodynamic thrust bearing 19 may have a coating layer 21 on a portion facing the first thrust collar 17. The coating layer 21 is formed, for example, by coating the surface of the first top foil 19a of the first hydrodynamic thrust bearing 19 facing the first thrust collar 17 with a resin.

[0050] The clearance C1 between the first top foil 19a and the first thrust collar 17 is smaller than the clearance C2 between the second top foil 20a and the second thrust collar 18. Therefore, the first top foil 19a is in contact with the first thrust collar 17 when the rotation speed of the rotating shaft 12 is lower than the floating rotation speed. At this time, the first top foil 19a has a coating layer 21 on a portion facing the first thrust collar 17. Therefore, it is possible to suppress wear between the first top foil 19a and the first thrust collar 17. On the other hand, the second top foil 20a does not contact the second thrust collar 18 even when the rotating shaft 12 is lower than the floating rotation speed. Therefore, the second top foil 20a does not need a coating layer on a portion facing the second thrust collar 18. And, since the second top foil 20a does not have a coating layer, it has good heat dissipation properties. As a result, the durability of the second dynamic pressure thrust bearing 20 can be improved.

[0051] As shown in Fig. 4, the second hydrodynamic thrust bearing 20 may be provided on only one side of the second thrust collar 18 to support the second thrust collar 18. The second hydrodynamic thrust bearing 20 is provided only on the side of the second thrust collar 18 in the direction in which a thrust load acts on the rotating shaft 12. The direction in which the thrust load acts on the rotating shaft 12 is determined in advance, for example, by experiments. In Fig. 4, the direction in which the thrust load acts on the rotating shaft 12 is indicated by an arrow F10.

[0052] According to this, when the thrust load acting on the rotating shaft 12 increases, the second dynamic pressure thrust bearing 20 can receive the thrust load acting on the rotating shaft 12 in addition to the first dynamic pressure thrust bearing 19. On the other hand, in the centrifugal compressor 10, the rotating shaft 12 may move in the opposite direction to the direction in which the thrust load acts on the rotating shaft 12 due to external vibrations or the like. At this time, the first dynamic pressure thrust bearing 19 is provided in a pair with respect to the first thrust collar 17, with the first thrust collar 17 sandwiched therebetween. Therefore, even if the rotating shaft 12 moves in the opposite direction to the direction in which the thrust load acts on the rotating shaft 12, the first thrust collar 17 can be received by the first dynamic pressure thrust bearing 19. As a result, there is no need to provide a pair of the second dynamic pressure thrust bearing 20 with the second thrust collar 18 sandwiched therebetween, and therefore the number of parts can be reduced. Therefore, the centrifugal compressor 10 can have a simple configuration.

[0053] As shown in Fig. 5, the centrifugal compressor 10 may include a first impeller 31 connected to a first end of the rotating shaft 12 and a second impeller 32 connected to a second end of the rotating shaft 12. Therefore, the impeller of the centrifugal compressor 10 of the embodiment shown in Fig. 5 includes the first impeller 31 and the second impeller 32. The second impeller 32 rotates to compress the air compressed by the rotation of the first impeller 31. The first dynamic pressure thrust bearing 19 is disposed closer to the second impeller 32 than the second dynamic pressure thrust bearing 20.

[0054] The centrifugal compressor 10 needs to be designed in consideration of the clearance C1 between the first top foil 19a of the first dynamic pressure thrust bearing 19 and the first thrust collar 17 so that the first impeller 31 and the second impeller 32 do not interfere with the housing. Here, the second impeller 32 rotates to compress the air compressed by the rotation of the first impeller 31, so in order to improve the compression efficiency of the centrifugal compressor 10, it is necessary to make the clearance between the second impeller 32 and the housing 11 as narrow as possible. The greater the distance between the second impeller 32 and the first dynamic pressure thrust bearing 19 in the axial direction of the rotating shaft 12, the greater the influence of the dimensional tolerance of the housing 11. In addition, the greater the distance between the second impeller 32 and the first dynamic pressure thrust bearing 19 in the axial direction of the rotating shaft 12, the greater the influence of the difference between the thermal expansion in the axial direction of the rotating shaft 12 and the thermal expansion in the axial direction of the rotating shaft 12 in the housing 11. Therefore, the first hydrodynamic thrust bearing 19 is disposed closer to the second impeller 32 than the second hydrodynamic thrust bearing 20. This can minimize the influence of the dimensional tolerance of the housing 11 and the influence of the difference between the thermal expansion of the rotating shaft 12 in the axial direction and the thermal expansion of the rotating shaft 12 in the housing 11 in the axial direction. As a result, it is easy to design the clearance between the second impeller 32 and the housing 11 to be as small as possible so that the second impeller 32 does not interfere with the housing 11. Therefore, the efficiency of air compression by the rotation of the second impeller 32 can be improved, and the compression efficiency of the centrifugal compressor 10 can be improved.

[0055] In the embodiment, the first dynamic pressure thrust bearing 19 and the second dynamic pressure thrust bearing 20 may be of the same type. This eliminates the need to prepare different types of bearings for the first dynamic pressure thrust bearing 19 and the second dynamic pressure thrust bearing 20, making it possible to provide a centrifugal compressor 10 with a simple design.

[0056] In the embodiment, the number of impellers 13 that rotate integrally with the rotating shaft 12 is not particularly limited. The centrifugal compressor 10 may be configured to include, for example, three or more impellers.

[0057] In the embodiment, the fluid compressed by the impeller 13 is not limited to air. Therefore, the application of the centrifugal compressor 10 and the fluid to be compressed may be any application. For example, the centrifugal compressor 10 may be used in an air conditioner, and the fluid to be compressed may be a refrigerant. Furthermore, the application of the centrifugal compressor 10 is not limited to a vehicle, and may be any application.

[0058] The above embodiment includes the configurations described in the following supplementary notes. <Appendix 1> A rotation axis; An impeller that rotates integrally with the rotating shaft; a first thrust collar having a disk shape that protrudes from an outer circumferential surface of the rotating shaft toward the outside in the radial direction of the rotating shaft and rotates integrally with the rotating shaft; a disk-shaped second thrust collar that protrudes radially outward from an outer circumferential surface of the rotating shaft, is disposed at a position spaced apart from the first thrust collar in the axial direction of the rotating shaft, and rotates integrally with the rotating shaft; a first hydrodynamic thrust bearing provided to face the first thrust collar in the axial direction; A centrifugal compressor comprising: a second dynamic pressure thrust bearing provided to face the second thrust collar in the axial direction, when a load in a thrust direction is less than a predetermined load, the first thrust collar is supported only by the first hydrodynamic thrust bearing out of the first hydrodynamic thrust bearing and the second hydrodynamic thrust bearing; a first dynamic pressure thrust bearing supporting the first thrust collar and a second dynamic pressure thrust bearing supporting the second thrust collar when a load in the thrust direction is equal to or greater than the predetermined load.

[0059] <Appendix 2> The first hydrodynamic thrust bearing comprises: a first top foil facing the first thrust collar; a first bump foil provided on the opposite side of the first thrust collar with the first top foil interposed therebetween; The second hydrodynamic thrust bearing comprises: a second top foil facing the second thrust collar; a second bump foil provided on the opposite side of the second thrust collar with the second top foil interposed therebetween; The centrifugal compressor described in <Appendix 1>, wherein a clearance between the first top foil and the first thrust collar is smaller than a clearance between the second top foil and the second thrust collar.

[0060] <Appendix 3> The centrifugal compressor according to <Appendix 2>, wherein the first top foil has a coating layer on a portion facing the first thrust collar.

[0061] <Appendix 4> the first hydrodynamic thrust bearing is provided in pair with the first thrust collar sandwiched therebetween, The centrifugal compressor according to any one of <Appendix 1> to <Appendix 3>, wherein the second dynamic pressure thrust bearing is provided on only one side of the second thrust collar to support the second thrust collar.

[0062] <Appendix 5> the rotating shaft, the impeller, the first thrust collar, the second thrust collar, the first dynamic pressure thrust bearing, and the second dynamic pressure thrust bearing are accommodated in a housing; The impeller is coupled only to a first end of the rotating shaft; The centrifugal compressor according to any one of <Appendix 1> to <Appendix 4>, wherein the first dynamic pressure thrust bearing is disposed closer to the impeller than the second dynamic pressure thrust bearing.

[0063] <Appendix 6> the rotating shaft, the impeller, the first thrust collar, the second thrust collar, the first dynamic pressure thrust bearing, and the second dynamic pressure thrust bearing are accommodated in a housing; The impeller comprises: a first impeller coupled to a first end of the rotating shaft; a second impeller coupled to a second end of the rotary shaft and rotating to compress the fluid compressed by the rotation of the first impeller; The centrifugal compressor according to any one of <Appendix 1> to <Appendix 4>, wherein the first dynamic pressure thrust bearing is disposed closer to the second impeller than the second dynamic pressure thrust bearing.

[0064] <Appendix 7> The centrifugal compressor according to any one of <Appendix 1> to <Appendix 6>, wherein the second dynamic pressure thrust bearing has higher rigidity than the first dynamic pressure thrust bearing. [Explanation of symbols]

[0065] Reference Signs List 10...centrifugal compressor, 11...housing, 12...rotating shaft, 13...impeller, 17...first thrust collar, 18...second thrust collar, 19...first hydrodynamic thrust bearing, 19a...first top foil, 19b...first bump foil, 20...second hydrodynamic thrust bearing, 20a...second top foil, 20b...second bump foil, 21...coating layer, 31...first impeller, 32...second impeller, C1, C2...clearance.

Claims

1. A rotation axis; An impeller that rotates integrally with the rotating shaft; a first thrust collar having a disk shape that protrudes from an outer circumferential surface of the rotary shaft toward a radially outer side of the rotary shaft and rotates integrally with the rotary shaft; a disk-shaped second thrust collar that protrudes from an outer circumferential surface of the rotating shaft toward a radially outer side of the rotating shaft, is disposed at a position spaced apart from the first thrust collar in the axial direction of the rotating shaft, and rotates integrally with the rotating shaft; a first hydrodynamic thrust bearing provided to face the first thrust collar in the axial direction; a second dynamic pressure thrust bearing provided to face the second thrust collar in the axial direction, when a load in a thrust direction is less than a predetermined load, the first thrust collar is supported only by the first hydrodynamic thrust bearing out of the first hydrodynamic thrust bearing and the second hydrodynamic thrust bearing; a first dynamic pressure thrust bearing supporting the first thrust collar and a second dynamic pressure thrust bearing supporting the second thrust collar when a load in the thrust direction is equal to or greater than the predetermined load.

2. The first hydrodynamic thrust bearing comprises: a first top foil facing the first thrust collar; a first bump foil provided on the opposite side of the first thrust collar with the first top foil interposed therebetween; The second hydrodynamic thrust bearing comprises: a second top foil facing the second thrust collar; a second bump foil provided on the opposite side of the second thrust collar with the second top foil interposed therebetween; 2. The centrifugal compressor according to claim 1, wherein a clearance between the first top foil and the first thrust collar is smaller than a clearance between the second top foil and the second thrust collar.

3. 3. The centrifugal compressor according to claim 2, wherein the first top foil has a coating layer on a portion facing the first thrust collar.

4. the first hydrodynamic thrust bearings are provided in pair with respect to the first thrust collar, with the first thrust collar sandwiched therebetween, 2. The centrifugal compressor according to claim 1, wherein the second hydrodynamic thrust bearing is provided on only one side thereof for supporting the second thrust collar with respect to the second thrust collar.

5. the rotating shaft, the impeller, the first thrust collar, the second thrust collar, the first dynamic pressure thrust bearing, and the second dynamic pressure thrust bearing are accommodated in a housing; The impeller is coupled only to a first end of the rotating shaft; 2. The centrifugal compressor according to claim 1, wherein the first dynamic pressure thrust bearing is disposed closer to the impeller than the second dynamic pressure thrust bearing.

6. the rotating shaft, the impeller, the first thrust collar, the second thrust collar, the first dynamic pressure thrust bearing, and the second dynamic pressure thrust bearing are accommodated in a housing; The impeller comprises: a first impeller coupled to a first end of the rotating shaft; a second impeller coupled to a second end of the rotary shaft and adapted to rotate to compress the fluid compressed by the rotation of the first impeller; 2. The centrifugal compressor according to claim 1, wherein the first dynamic pressure thrust bearing is disposed closer to the second impeller than the second dynamic pressure thrust bearing.

7. 2. The centrifugal compressor according to claim 1, wherein the second dynamic pressure thrust bearing has a higher rigidity than the first dynamic pressure thrust bearing.

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