Patent Publication Number: US-2023160390-A1

Title: Centrifugal compressor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-188834 filed on Nov. 19, 2021, the entire disclosure of which is incorporated herein by reference. 
     The present disclosure relates to a centrifugal compressor. 
     BACKGROUND ART 
     A known centrifugal compressor is mentioned, for example, in Japanese Patent Application Publication No. 2019-127898. The centrifugal compressor includes a rotary shaft and a compressor impeller. The compressor impeller is mounted on the rotary shaft. The compressor impeller is rotated together with the rotary shaft. The compressor impeller is configured to compress a fluid. The centrifugal compressor includes a housing for accommodating the rotary shaft and the compressor impeller. The centrifugal compressor further includes a thrust bearing. The thrust bearing supports the rotary shaft in a thrust direction such that the rotary shaft is rotatable. 
     The housing has an impeller chamber and a thrust bearing accommodation chamber. The impeller chamber accommodates the compressor impeller. The thrust bearing accommodation chamber accommodates the thrust bearing. The housing has a partition wall that separates the impeller chamber from the thrust bearing accommodation chamber. 
     The temperature of the fluid is increased by compression by the compressor impeller. If the heat of the compressed fluid transfers to the thrust bearing accommodated in the thrust bearing accommodation chamber via the partition wall, the heat of the fluid increases the temperature of the thrust bearing, thereby decreasing the durability of the thrust bearing. It is therefore necessary to increase the ability of the centrifugal compressor to cool the thrust bearing. 
     SUMMARY 
     In accordance with an aspect of the present disclosure, there is provided a centrifugal compressor that includes: a rotary shaft; a compressor impeller mounted on the rotary shaft and configured to rotate together with the rotary shaft to compress a fluid; a housing accommodating the rotary shaft and the compressor impeller; and a thrust bearing supporting the rotary shaft in a thrust direction such that the rotary shaft is rotatable. The housing includes: an impeller chamber in which the compressor impeller is accommodated; a thrust bearing accommodation chamber in which the thrust bearing is accommodated; and a partition wall separating the impeller chamber from the thrust bearing accommodation chamber. The partition wall has therein a cooling gas passage through which cooling gas flows to cool the thrust bearing and a cooling water passage through which cooling water flows to cool the partition wall. 
     Other aspects and advantages of the disclosure will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The disclosure, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
         FIG.  1    is a sectional side view of a centrifugal compressor according to an embodiment of the present disclosure; 
         FIG.  2    is a fragmentary enlarged sectional side view of the centrifugal compressor according to the embodiment; and 
         FIG.  3    is a front view of a seal plate. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following will describe an embodiment of a centrifugal compressor with reference to accompanying  FIGS.  1  to  3   . The centrifugal compressor according to the embodiment is mounted on a fuel cell vehicle. 
     &lt;Configuration of Centrifugal Compressor  10 &gt; 
     As illustrated in  FIG.  1   , a centrifugal compressor  10  includes a housing  11 . The housing  11  is made of metal, such as aluminum. The housing  11  includes a motor housing  12 , a compressor housing  13 , a turbine housing  14 , a first plate  15 , a second plate  16 , and a seal plate  17 . 
     The motor housing  12  has a cylindrical shape. The motor housing  12  includes a plate-like end wall  12   a  and a peripheral wall  12   b . The peripheral wall  12   b  has a cylindrical shape and protrudes from an outer peripheral portion of the end wall  12   a . The first plate  15  is connected to an open end of the peripheral wall  12   b  of the motor housing  12  so as to close the opening of the peripheral wall  12   b . The end wall  12   a  and the peripheral wall  12   b  of the motor housing  12  cooperate with the first plate  15  to define a motor chamber S 1 . The motor chamber S 1  accommodates an electric motor  40 . 
     As illustrated in  FIG.  2   , an end face  15   a  of the first plate  15  that is distant from the motor housing  12  has a first recess  15   c  and a second recess  15   d . The first recess  15   c  and the second recess  15   d  each have a circular hole shape. The inner diameter of the first recess  15   c  is greater than that of the second recess  15   d . The first recess  15   c  is formed coaxially with the second recess  15   d . The first recess  15   c  has an inner peripheral surface  15   e  through which the end face  15   a  is connected to a bottom surface  15   f  of the first recess  15   c . The second recess  15   d  has an inner peripheral surface  15   g  through which the bottom surface  15   f  of the first recess  15   c  is connected to a bottom surface  15   h  of the second recess  15   d.    
     The first plate  15  has a first bearing holding portion  20 . The first bearing holding portion  20  has a cylindrical shape. The first bearing holding portion  20  projects from the center portion of an end face  15   b  of the first plate  15  toward the electric motor  40 . On the opposite side, the first bearing holding portion  20  is formed through the first plate  15  to open on the bottom surface  15   h  of the second recess  15   d . The first bearing holding portion  20  is formed coaxially with the first recess  15   c  and the second recess  15   d.    
     As illustrated in  FIG.  1   , the motor housing  12  has a second bearing holding portion  21 . The second bearing holding portion  21  has a cylindrical shape. The second bearing holding portion  21  projects from the center portion of an inner surface  121   a  of the end wall  12   a  of the motor housing  12  toward the electric motor  40 . The cylindrical second bearing holding portion  21  is formed through the end wall  12   a  of the motor housing  12  to open on an outer surface  122   a  of the end wall  12   a . The first beating holding portion  20  is formed coaxially with the second bearing holding portion  21 . 
     The second plate  16  is connected to the outer surface  122   a  of the end wall  12   a  of the motor housing  12 . The second plate  16  has a shaft insertion hole  16   a  at the center portion of the second plate  16 . The shaft insertion hole  16   a  is communicated with the second bearing holding portion  21 . The shaft insertion hole  16   a  is formed coaxially with the second bearing holding portion  21 . 
     As illustrated in  FIG.  2   , the seal plate  17  has a shaft insertion hole  17   a  at the center portion of the seal plate  17 . The shaft insertion hole  17   a  is formed coaxially with the first bearing holding portion  20 . The seal plate  17  has a plurality of bolt insertion holes  17   h  through which a plurality of bolts B 1  is inserted. The bolt insertion holes  17   h  are formed in an outer peripheral portion of the seal plate  17  and spaced apart from each other around the shaft insertion hole  17   a .  FIG.  2    illustrates only one of the bolt insertion holes  17   h . Each of the bolt insertion holes  17   h  has a circular hole shape. The seal plate  17  is fitted in the first recess  15   c  and fixed to the first plate  15  by the bolts B 1  inserted through the bolt insertion holes  17   h . The seal plate  17  closes the opening of the second recess  15   d . The seal plate  17  has an end face  17   b  that is adjacent to the first plate  15  and cooperates with the second recess  15   d  of the first plate  15  to define a thrust bearing accommodation chamber S 2 . 
     The compressor housing  13  has a cylindrical shape. The compressor housing  13  has an inlet  13   a  that has a circular hole shape. The compressor housing  13  is connected to the end face  15   a  of the first plate  15  with the axis of the inlet  13   a  coaxial with the axis of the shaft insertion hole  17   a  of the seal plate  17  and the axis of the first bearing holding portion  20 . The inlet  13   a  is opened on an end face of the compressor housing  13  that is distant from the first plate  15 . 
     An impeller chamber  13   b , a discharge chamber  13   c , and a first diffuser passage  13   d  are formed between the compressor housing  13  and the seal plate  17 . Accordingly, the seal plate  17  serves as a partition wall that separates the impeller chamber  13   b  from the thrust bearing accommodation chamber S 2 . The impeller chamber  13   b  is communicated with the inlet  13   a . The discharge chamber  13   c  extends about the axis of the inlet  13   a  around the impeller chamber  13   b . The impeller chamber  13   b  is communicated with the discharge chamber  13   c  through the first diffuser passage  13   d . The impeller chamber  13   b  is communicated with the shaft insertion hole  17   a  of the seal plate  17 . 
     As illustrated in  FIG.  1   , the turbine housing  14  has a cylindrical shape. The turbine housing  14  has an outlet  14   a  that has a circular hole shape. The turbine housing  14  is connected to an end face  16   b  of the second plate  16  that is distant from the motor housing  12  with the axis of the outlet  14   a  coaxial with the axis of the shaft insertion hole  16   a  of the second plate  16  and the axis of the second bearing holding portion  21 . The outlet  14   a  is opened on an end face of the turbine housing  14  that is distant from the second plate  16 . 
     A turbine chamber  14   b , a suction chamber  14   c , and a second diffuser passage  14   d  are formed between the turbine housing  14  and the end face  16   b  of the second plate  16 . The turbine chamber  14   b  is communicated with the outlet  14   a . The suction chamber  14   c  extends about the axis of the outlet  14   a  around the turbine chamber  14   b . The turbine chamber  14   b  is communicated with the suction chamber  14   c  through the second diffuser passage  14   d . The turbine chamber  14   b  is communicated with the shaft insertion hole  16   a.    
     &lt;Configuration of Rotating Member A 1 &gt; 
     The centrifugal compressor  10  includes a rotating member A 1 . The rotating member A 1  includes a rotary shaft  30 , a first supporting portion  31 , a second supporting portion  32 , and a support plate  33 . That is, the centrifugal compressor  10  includes the rotary shaft  30 . The rotary shaft  30 , the first supporting portion  31 , the second supporting portion  32 , and the support plate  33  are accommodated in the housing  11 . 
     The axis of the rotary shaft  30  accommodated in the housing  11  is coaxial with the axis of the motor housing  12 . The rotary shaft  30  has a first end portion  30   a , and the rotary shaft  30  extends through the motor chamber S 1 , the first bearing holding portion  20 , the thrust bearing accommodation chamber S 2 , and the shaft insertion hole  17   a  so that the first end portion  30   a  protrudes into the impeller chamber  13   b . The rotary shaft  30  has a second end portion  30   b , and the rotary shaft  30  extends through the motor chamber S 1 , the second bearing holding portion  21 , and the shaft insertion hole  16   a  so that the second end portion  30   b  protrudes into the turbine chamber  14   b.    
     A first sealing member  22  is disposed between the shaft insertion hole  17   a  of the seal plate  17  and the rotary shaft  30 . The first sealing member  22  suppresses leak of air from the impeller chamber  13   b  toward the motor chamber S 1 . A second sealing member  23  is disposed between the shaft insertion hole  16   a  of the second plate  16  and the rotary shaft  30 . The second sealing member  23  suppresses leak of air from the turbine chamber  14   b  toward the motor chamber S 1 . The first sealing member  22  and the second sealing member  23  are each a seal ring, for example. 
     The first supporting portion  31  is formed in a part of an outer peripheral surface  300  of the rotary shaft  30  adjacent to the first end portion  30   a . The first supporting portion  31  is disposed inside the first bearing holding portion  20 . The first supporting portion  31  is formed integrally with the rotary shaft  30 . The first supporting portion  31  projects from the outer peripheral surface  300  of the rotary shaft  30 . 
     The second supporting portion  32  is formed in a part of the outer peripheral surface  300  of the rotary shaft  30  adjacent to the second end portion  30   b . The second supporting portion  32  is disposed inside the second bearing holding portion  21 . The second supporting portion  32  is fixed to the outer peripheral surface  300  of the rotary shaft  30 , and extends from the outer peripheral surface  300  of the rotary shaft  30  so as to have a ring shape. The second supporting portion  32  is rotatable together with the rotary shaft  30 . 
     The support plate  33  is accommodated in the thrust bearing accommodation chamber S 2 . The support plate  33  is fixed to the outer peripheral surface  300  of the rotary shaft  30 , and extends radially and outwardly from the outer peripheral surface  300  of the rotary shaft  30  so as to have a ring shape. That is, the support plate  33  is formed separately from the rotary shaft  30 . The support plate  33  is rotatable together with the rotary shaft  30 . 
     &lt;Compressor Impeller  34 &gt; 
     The centrifugal compressor  10  includes a compressor impeller  34 . The compressor impeller  34  is mounted on the first end portion  30   a  of the rotary shaft  30  in the axial direction of the rotary shaft  30 . The compressor impeller  34  is disposed between the support plate  33  and the first end portion  30   a  of the rotary shaft  30 . The compressor impeller  34  is accommodated in the impeller chamber  13   b . That is, the housing  11  has the impeller chamber  13   b  in which the compressor impeller  34  is accommodated. The housing  11  accommodates the rotary shaft  30  and the compressor impeller  34 . That is, the centrifugal compressor  10  includes the housing  11  accommodating the rotary shaft  30  and the compressor impeller  34 . The compressor impeller  34  is rotated together with the rotary shaft  30 . 
     &lt;Turbine Wheel  35 &gt; 
     The centrifugal compressor  10  includes a turbine wheel  35 . The turbine wheel  35  is mounted on the second end portion  30   b  of the rotary shaft  30 . The turbine wheel  35  is disposed between the second supporting portion  32  and the second end portion  30   b  of the rotary shaft  30 . The turbine wheel  35  is accommodated in the turbine chamber  14   b . The turbine wheel  35  is rotated together with the rotary shaft  30 . 
     &lt;Configuration of Electric Motor  40 &gt; 
     The electric motor  40  includes a cylindrical rotor  41  and a cylindrical stator  42 . The rotor  41  is fixed to the rotary shaft  30 . The stator  42  is fixed in the housing  11 . The rotor  41  is disposed radially inside the stator  42  and rotated together with the rotary shaft  30 . The rotor  41  includes a cylindrical rotor core  41   a  fixed to the rotary shaft  30  and a plurality of permanent magnets, which is not illustrated, disposed in the rotor core  41   a . The stator  42  surrounds the rotor  41 . The stator  42  includes a stator core  43  and a coil  44 . The stator core  43  has a cylindrical shape and is fixed to an inner peripheral surface  121   b  of the peripheral wall  12   b  of the motor housing  12 . The coil  44  is wound around the stator core  43 . The coil  44  receives current from a battery (not illustrated) so that the rotor  41  is rotated together with the rotary shaft  30 . That is, the electric motor  40  is configured to rotate the rotary shaft  30 . The electric motor  40  is disposed between the compressor impeller  34  and the turbine wheel  35  in the axial direction of the rotary shaft  30 . 
     &lt;First Radial Bearing  50  and Second Radial Bearing  51 &gt; 
     The centrifugal compressor  10  includes a first radial bearing  50  and a second radial bearing  51 . The first radial bearing  50  has a cylindrical shape. The first radial bearing  50  is held by the first bearing holding portion  20 . The second radial bearing  51  has a cylindrical shape. The second radial bearing  51  is held by the second bearing holding portion  21 . The first radial bearing  50  and the second radial bearing  51  support the rotary shaft  30  in a radial direction such that the rotary shaft  30  is rotatable relative to the housing  11 . The radial direction is a direction perpendicular to the axial direction of the rotary shaft  30 . 
     &lt;First Thrust Bearing  60  and Second Thrust Bearing  61 &gt; 
     As illustrated in  FIG.  2   , the centrifugal compressor  10  includes a thrust bearing, which, in this embodiment, is a first thrust bearing  60  and a second thrust bearing  61 . The first thrust bearing  60  and the second thrust bearing  61  support the support plate  33  in a thrust direction such that the support plate  33  is rotatable relative to the housing  11 . The thrust direction is a direction parallel to the axial direction of the rotary shaft  30 . 
     The first thrust bearing  60  and the second thrust bearing  61  are accommodated in the thrust bearing accommodation chamber S 2 . That is, the housing  11  has the thrust bearing accommodation chamber S 2  in which the first thrust bearing  60  and the second thrust bearing  61  are accommodated. The first thrust bearing  60  and the second thrust bearing  61  are disposed so as to hold therebetween the support plate  33 . The second thrust bearing  61  and the support plate  33  are disposed between the compressor impeller  34  and the first thrust bearing  60 . The second thrust bearing  61  is disposed between the compressor impeller  34  and the support plate  33 . The first thrust bearing  60  has a first thrust bearing main body  60   a  and a first base portion  60   b . The first base portion  60   b  has a disc shape. The first base portion  60   b  has a first through hole  60   c  through which the rotary shaft  30  is inserted. The second thrust bearing  61  has a second thrust bearing main body  61   a  and a second base portion  61   b . The second base portion  61   b  has a disc shape. The second base portion  61   b  has a second through hole  61   c  through which the rotary shaft  30  is inserted. 
     &lt;Fuel Cell System  1 &gt; 
     As illustrated in  FIG.  1   , the centrifugal compressor  10  serves as a part of a fuel cell system  1  mounted on a fuel cell vehicle. The fuel cell system  1  includes the centrifugal compressor  10 , a fuel cell stack  100 , a supply passage L 1 , a discharge passage L 2 , and a branched passage L 3 . The fuel cell stack  100  includes a plurality of fuel cells. For convenience of explanation, individual fuel cells of the fuel cell stack  100  are not illustrated in drawings. The fuel cell stack  100  is connected to the discharge chamber  13   c  through the supply passage L 1 . The fuel cell stack  100  is also connected to the suction chamber  14   c  through the discharge passage L 2 . 
     When the rotary shaft  30  rotates together with the rotor  41 , the compressor impeller  34  and the turbine wheel  35  are rotated together with the rotary shaft  30 . Air, which has been drawn through the inlet  13   a , is compressed by the compressor impeller  34  in the impeller chamber  13   b , and discharged from the discharge chamber  13   c  through the first diffuser passage  13   d . That is, the compressor impeller  34  is rotated together with the rotary shaft  30  to compress air. 
     The air discharged from the discharge chamber  13   c  is supplied to the fuel cell stack  100  through the supply passage L 1 . The air supplied to the fuel cell stack  100  is used for electricity generation by the fuel cell stack  100 . The used air is then discharged as exhaust from the fuel cell stack  100  to the discharge passage L 2 . The exhaust from the fuel cell stack  100  is drawn into the suction chamber  14   c  through the discharge passage L 2 . The exhaust drawn into the suction chamber  14   c  is then discharged to the turbine chamber  14   b  through the second diffuser passage  14   d . The exhaust discharged into the turbine chamber  14   b  rotates the turbine wheel  35 . The rotary shaft  30  is driven to rotate by the electric motor  40 , and also by the rotation of the turbine wheel  35  by the exhaust from the fuel cell stack  100 . The rotation of the turbine wheel  35  by the exhaust from the fuel cell stack  100  assists the rotation of the rotary shaft  30 . The exhaust discharged into the turbine chamber  14   b  is discharged outside from the outlet  14   a.    
     &lt;Cooling Gas Passage G 1  and Air in Cooling Gas Passage G 1 &gt; 
     As illustrated in  FIGS.  2  and  3   , the seal plate  17  further has a recess  17   c  at the center portion of the end face  17   b  of the seal plate  17 . The recess  17   c  has a circular hole shape. Most of the opening of the recess  17   c  is closed by the second base portion  61   b . The recess  17   c  of the seal plate  17  and the second base portion  61   b  cooperate to define a cooling gas passage G 1 . The cooling gas passage G 1  is communicated with the thrust bearing accommodation chamber S 2  through a gap between the second through hole  61   c  of the second base portion  61   b  and the rotary shaft  30 . 
     The seal plate  17  has a communication hole  17   e  and a connecting passage G 2 . The communication hole  17   e  has a circular hole shape. The communication hole  17   e  is opened on the end face  17   b  of the seal plate  17 . The recess  17   c  is connected to the communication hole  17   e  through the connecting passage G 2 . The connecting passage G 2  extends from the cooling gas passage G 1  outwardly in the radial direction of the rotary shaft  30 . 
     The first plate  15  has a through hole  15   i . The through hole  15   i  is formed through the first plate  15  in the thickness direction of the first plate  15 . The through hole  15   i  is formed coaxially with the communication hole  17   e . One end of the through hole  15   i  is communicated with the communication hole  17   e . The other end of the through hole  15   i  is communicated with the motor chamber S 1 . The communication hole  17   e  is communicated with the motor chamber S 1  through the through hole  15   i . The cooling gas passage G 1  is communicated with the motor chamber S 1  through the connecting passage G 2 , the communication hole  17   e , and the through hole  15   i.    
     Cooling gas for cooling the first thrust bearing  60  and the second thrust bearing  61  flows through the cooling gas passage G 1 . Specifically, the first plate  15  has a first passage  71 . The first passage  71  extends in the radial direction of the rotary shaft  30 . One end of the first passage  71  is opened on an outer surface of the first plate  15 . The other end of the first passage  71  is communicated with the thrust bearing accommodation chamber S 2 . The second plate  16  has a second passage  72 . The second passage  72  extends in the radial direction of the rotary shaft  30 . One end of the second passage  72  is opened on an outer surface of the second plate  16 . The other end of the second passage  72  is communicated with a part of the shaft insertion hole  16   a  adjacent to the motor housing  12  with respect to the second sealing member  23 . 
     The branched passage L 3  branches off from the supply passage L 1 . The supply passage L 1  is connected to the first passage  71  through the branched passage L 3 . An intercooler R 1  is disposed in the branched passage L 3 . The intercooler R 1  cools the air flowing through the branched passage L 3 . 
     The air compressed by the compressor impeller  34  and flowed through the supply passage L 1  toward the fuel cell stack  100  partly flows into the first passage  71  through the branched passage L 3 . The air in the first passage  71  has been cooled by the intercooler R 1  while flowing through the branched passage L 3 . The air in the first passage  71  then flows into the thrust bearing accommodation chamber S 2 , and cools the first thrust bearing  60  and the second thrust bearing  61 . That is, cooling gas for cooling the first thrust bearing  60  and the second thrust bearing  61  is part of the air compressed by the compressor impeller  34 . 
     The air in the thrust bearing accommodation chamber S 2  then flows into the cooling gas passage G 1  through the gap between the second through hole  61   c  of the second base portion  61   b  and the rotary shaft  30 . The air in the cooling gas passage G 1  flows into the motor chamber S 1  through the connecting passage G 2 , the communication hole  17   e , and the through hole  15   i.    
     The air flowed into the motor chamber S 1  cools the electric motor  40 . The air in the motor chamber S 1  partly flows into a gap between the first radial bearing  50  and the first supporting portion  31 , and cools the first radial bearing  50 . The air in the motor chamber S 1 , for example, flows through a gap between the rotor  41  and the stator  42 , and the air then flows into a gap between the second radial bearing  51  and the second supporting portion  32  to cool the second radial bearing  51 . The air flows through the gap between the second radial bearing  51  and the second supporting portion  32 , and is discharged to the outside of the housing  11  through the shaft insertion hole  16   a  and the second passage  72 . 
     &lt;Cooling Water Passage W 1 &gt; 
     The end face  17   b  of the seal plate  17  has a groove  17   d . On the end face  17   b  of the seal plate  17 , the groove  17   d  is disposed outward of the recess  17   c  in the radial direction of the rotary shaft  30 , and extends in the circumferential direction of the rotary shaft  30  so as to surround the recess  17   c . The groove  17   d  is meandering about the axis of the shaft insertion hole  17   a . Specifically, the groove  17   d  is formed of parts extending toward the axis of the shaft insertion hole  17   a  and parts extending away from the axis of the shaft insertion hole  17   a , and those parts are alternatingly arranged. The groove  17   d  extends in the circumferential direction of the rotary shaft  30  such that the groove  17   d  is located inside in the radial direction of the rotary shaft  30  with respect to the bolt insertion holes  17   h . The groove  17   d  has a first end  170   d  and a second end  171   d  that circumferentially extend over the whole circumference of the seal plate  17 . The opening of the groove  17   d  is closed by the first plate  15 . The groove  17   d  and the bottom surface  15   f  of the first recess  15   c  of the first plate  15  cooperate to define a cooling water passage W 1 . The cooling water passage W 1  is formed outward of the cooling gas passage G 1  in the radial direction of the rotary shaft  30 . Cooling water flowing through the cooling water passage W 1  is prevented from leaking by a sealing member (not illustrated) disposed between the end face  17   b  of the seal plate  17  and the bottom surface  15   f  of the first recess  15   c  of the first plate  15 . 
     As illustrated in  FIG.  1   , the centrifugal compressor  10  further includes a cooling water jacket  12   c . The cooling water jacket  12   c  is formed in the peripheral wall  12   b  of the motor housing  12 . The cooling water jacket  12   c  circumferentially extends over the whole circumference of the peripheral wall  12   b.    
     As illustrated in  FIG.  2   , the cooling water jacket  12   c  is connected to a first end of the cooling water passage W 1  through a connecting cooling water passage W 2 . The cooling water jacket  12   c  is also connected to a second end of the cooling water passage W 1  through a connecting cooling water passage W 3 . 
     The cooling water jacket  12   c  is further connected to a first end and a second end of an external passage (not illustrated) through which cooling water (long life coolant) flows. The cooling water in the external passage is cooled by heat exchange with outside air by a radiator (not illustrated) disposed in the external passage. The cooling water circulates from the external passage, through the cooling water jacket  12   c , the connecting cooling water passage W 2 , the cooling water passage W 1 , and the connecting cooling water passage W 3  in this order, to the cooling water jacket  12   c . That is, the cooling water flows through the cooling water passage W 1 . The cooling water flowing through the cooling water passage W 1  cools the seal plate  17 . That is, the seal plate  17  has therein the cooling gas passage G 1  through which the cooling gas flows so as to cool the first thrust bearing  60  and the second thrust bearing  61  and the cooling water passage W 1  through which the cooling water flows so as to cool the seal plate  17 . 
     &lt;Operation&gt; 
     Next, the following will explain the operation of the centrifugal compressor according to the embodiment. 
     The seal plate  17  has therein the cooling gas passage G 1 . Air cools the first thrust bearing  60  and the second thrust bearing  61 , and further cools the seal plate  17  while flowing through the cooling gas passage G 1 . The seal plate  17  further has therein the cooling water passage W 1 . The cooling water flowing through the cooling water passage W 1  cools the seal plate  17 . That is, the heat of the air compressed by the compressor impeller  34  is less likely to transfer, via the seal plate  17 , to the first thrust bearing  60  and the second thrust bearing  61  accommodated in the thrust bearing accommodation chamber S 2 . Accordingly, the first thrust bearing  60  and the second thrust bearing  61  are efficiently cooled by the air. Further, the heat of the first thrust bearing  60  and the second thrust bearing  61  transfers to the cooling water flowing through the cooling water passage W 1 . 
     Advantageous Effects 
     The aforementioned embodiment provides following advantageous effects. 
     (1) The seal plate  17  has therein the cooling gas passage G 1 . This allows air to cool the seal plate  17  by flowing through the cooling gas passage G 1 , while cooling the first thrust bearing  60  and the second thrust bearing  61 . The seal plate  17  further has therein the cooling water passage W 1 , so that the cooling water further cools the seal plate  17 . That is, the heat of the air compressed by the compressor impeller  34  is less likely to transfer, via the seal plate  17 , to the first thrust bearing  60  and the second thrust bearing  61  accommodated in the thrust bearing accommodation chamber S 2 . Accordingly, the first thrust bearing  60  and the second thrust bearing  61  are efficiently cooled by the air. Further, the heat of the first thrust bearing  60  and the second thrust bearing  61  transfers to the cooling water flowing through the cooling water passage W 1 . This allows an increase in the ability of the centrifugal compressor to cool the first thrust bearing  60  and the second thrust bearing  61 . 
     (2) The cooling water passage W 1  is formed outward of the cooling gas passage G 1  in the radial direction of the rotary shaft  30 . This configuration allows an increase in area of the cooling water passage W 1 , compared to a case where the cooling water passage W 1  is formed inward of the cooling gas passage G 1  in the radial direction of the rotary shaft  30 . Accordingly, the seal plate  17  is efficiently cooled. That is, the heat of the fluid compressed by the compressor impeller  34  is less likely to transfer, via the seal plate  17 , to the first thrust bearing  60  and the second thrust bearing  61  accommodated in the thrust bearing accommodation chamber S 2 . Further, the heat of the first thrust bearing  60  and the second thrust bearing  61  is more likely to transfer to the cooling water flowing through the cooling water passage W 1 . This allows a further increase in the ability of the centrifugal compressor to cool the first thrust bearing  60  and the second thrust bearing  61 . 
     Modification Example 
     The aforementioned embodiment may be modified as below. The embodiment may be combined with the following modification examples within technically consistent range.
         In the embodiment, the cooling water passage W 1  may be formed inward of the cooling gas passage G 1  in the radial direction of the rotary shaft  30 .   In the embodiment, the groove  17   d  is not necessarily meandering. That is, the shape of the groove  17   d  is not particularly limited.   In the embodiment, the cooling water flowing through the cooling water passage W 1  is not necessarily the same as the cooling water flowing in the cooling water jacket  12   c . That is, the method for supplying cooling water to the cooling water passage W 1  is not particularly limited.   According to the embodiment, air cools the first thrust bearing  60  and the second thrust bearing  61  in the thrust bearing accommodation chamber S 2 , and then flows into the cooling gas passage G 1 . However, the configuration is not limited thereto. For example, the air may flow first into the cooling gas passage G 1 , and then into the thrust bearing accommodation chamber S 2  to cool the first thrust bearing  60  and the second thrust bearing  61 .   According to the embodiment, the air compressed by the compressor impeller  34  partly flows into the cooling gas passage G 1  to serve as a cooling gas, but it is not limited thereto. The cooling gas may be air that is not the air compressed by the compressor impeller  34 .   In the embodiment, the centrifugal compressor  10  does not necessarily include the turbine wheel  35 .   In the embodiment, the centrifugal compressor  10  may include a compressor impeller instead of the turbine wheel  35 . That is, each of the opposite ends of the rotary shaft  30  may have a compressor impeller, and a fluid compressed by one of the compressor impellers may be compressed again by the other of the compressor impellers.   In the embodiment, for example, the drive source of the centrifugal compressor  10  may be an engine.   In the embodiment, the centrifugal compressor  10  is not necessarily mounted on a fuel cell vehicle. For example, the centrifugal compressor  10  may be used for an air conditioner to compress refrigerant as a fluid. The centrifugal compressor  10  is not limited to a compressor mounted on a vehicle.