Patent Publication Number: US-11377979-B2

Title: Turbine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of PCT Application No. PCT/JP2019/003908, filed Feb. 4, 2019, which claims the benefit of priority from Japanese Patent Application No. 2018-027167, filed Feb. 19, 2018, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Each of Japanese Unexamined Utility Model Publication No. S60-18233 and Japanese Unexamined Patent Publication No. S60-173316 describes a turbocharger including a turbine and a compressor. 
     For example, Japanese Unexamined Utility Model Publication No. S60-18233 discloses a turbocharger in which a rotary shaft is supported on a journal bearing and a thrust bearing that are formed in a center housing. A flow path and a guide pipe connected to the flow path are provided in the center housing. The guide pipe is connected to a flow path provided in a turbine casing. When a turbine impeller is driven by exhaust gas to thereby cause a compressor outlet pressure to be higher than a compressor inlet pressure, air flows into the center housing from an outlet portion of a compressor impeller to cool the thrust bearing and the journal bearing. A part of the air flows to an outlet flow path of the turbine through the flow path and the guide pipe in the center housing and then through the flow path of the turbine casing. 
     Japanese Unexamined Patent Publication No. S60-173316 discloses a turbocharger in which a rotary shaft is supported on a journal bearing provided in a center housing and a thrust bearing provided between a turbine and the center housing. A guide path that communicates with a large number of air supply holes formed on the inside of the journal bearing is formed in an outer peripheral portion of the journal bearing. Compressed air is supplied to the guide path from a compressor outside via an air supply pipe. A discharge groove having an annular shape is formed in an inner peripheral bearing surface of the journal bearing. A guide hole connected to the discharge groove is formed to penetrate through the journal bearing and the center housing. A distribution groove connected to the guide hole is formed on the circumference of a center housing side of the thrust bearing. Further, the thrust bearing is provided with a blow-out hole that communicates with the distribution groove to open to a turbine side. The compressed air supplied from the compressor causes the journal bearing and the thrust bearing to support the rotary shaft. A part of the compressed air flows into the discharge groove of the journal bearing to be blown out from the distribution groove and the blow-out hole to a back surface side of the turbine. 
     SUMMARY 
     In a turbocharger including a turbine, moist gas (air containing water vapor) may flow into the turbine as exhaust gas. The turbine is operated by such a moist gas. When the water vapor condenses, water may be accumulated in a housing. 
     Here, a turbine housing may be provided with a flow path (discharge path) that discharges the gas flowing into a space where a bearing is provided. If the accumulated water flows into the discharge path to remain, the water can adversely affect the turbine. For example, when the water is frozen due to a decrease in temperature, the discharge path may be blocked, so that a defect may occur in components (for example, a rotary shaft and so on) in the housing. 
     The turbines disclosed herein may be configured to discharge condensate water that is accumulated in a space where a bearing is provided in a housing. 
     An example turbine includes a rotary shaft, a blade attached to the rotary shaft, a housing including a turbine housing that accommodates the blade, and a bearing provided in the housing to rotatably support the rotary shaft. Additionally, the turbine housing may include a discharge path configured to discharge gas in a first space, in which the bearing is provided, to a second space in the turbine housing. The discharge path may include an inlet opening that communicates with the first space and an outlet opening that opens to the second space. A bottom surface of the discharge path may be constituted of an inclined portion descending from the inlet opening toward the outlet opening. The bottom surface of the discharge path may be constituted of the inclined portion and a horizontal portion that continuously extends horizontally from the inclined portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an example electric turbocharger (centrifugal compressor). 
         FIG. 2  is a cross-sectional view illustrating an example electric turbocharger (centrifugal compressor). 
         FIG. 3  is a cross-sectional view illustrating an enlargement of the vicinity of a turbine housing, a seal portion, and a bearing of  FIG. 2 . 
         FIG. 4  is a perspective view illustrating an example assembly in which a seal plate is attached to a center housing. 
         FIG. 5  is a perspective view illustrating the seal plate of  FIG. 4 . 
         FIG. 6  is a perspective view illustrating the seal plate of  FIG. 5  as seen from a back surface side. 
         FIG. 7  is a cross-sectional view of the seal plate of  FIG. 4  as seen from a turbine side in a rotation axis direction. 
         FIG. 8  illustrates the shape of an example discharge path formed in the turbine housing of  FIG. 3  as seen from the turbine side in the rotation axis direction. 
     
    
    
     DETAILED DESCRIPTION 
     An example turbine includes a rotary shaft, a blade attached to the rotary shaft, a housing including a turbine housing that accommodates the blade, and a bearing provided in the housing to rotatably support the rotary shaft. Additionally, the turbine housing may include a discharge path configured to discharge gas in a first space, in which the bearing is provided, to a second space in the turbine housing. The discharge path may include an inlet opening that communicates with the first space and an outlet opening that opens to the second space. A bottom surface of the discharge path may be constituted of an inclined portion descending from the inlet opening toward the outlet opening. The bottom surface of the discharge path may be constituted of the inclined portion and a horizontal portion that continuously extends horizontally from the inclined portion. 
     The gas in the first space where the bearing is provided is discharged to the second space in the turbine housing through the discharge path. If the gas flowing into the turbine contains water vapor and condensate water generated by the condensation of the water vapor is accumulated in the housing, the condensate water may be accumulated also in the first space. When the water level of the condensate water reaches the inlet opening of the discharge path, the condensate water enters the discharge path. The bottom surface of the discharge path is constituted of the inclined portion descending toward the outlet opening or is constituted of the inclined portion and the horizontal portion. Accordingly, the bottom surface of the discharge path does not include an inclined portion ascending toward the outlet opening. Therefore, the condensate water that has entered the discharge path is successfully discharged to the second space. As described above, the turbine can discharge the condensate water that is accumulated in the space where the bearing is provided in the housing. The discharge path serves both as a passage for discharging the gas and as a passage for discharging the condensate water. The discharge path having the above shape avoids being filled with the condensate water. When the turbine is stopped, even in a case where the condensate water is frozen due to a decrease in temperature, the gas flow path is secured in the discharge path. 
     In some examples, the housing includes a center housing in which the bearing is provided and which is connected to the turbine housing, and the center housing includes a communication port that is an outlet of the first space and faces the inlet opening of the discharge path. In this case, the condensate water that is present in the first space in the center housing is readily discharged from the communication port. Additionally, the example configuration facilitates the passage of discharged condensate water into the discharge path via the inlet opening. 
     In some examples, the turbine further includes a seal plate provided between the turbine housing and the center housing, and a guide path extending between the first space and the communication port is formed in an outer peripheral portion of the seal plate. The guide path formed in the seal plate can guide the condensate water, which is present in the first space, to the communication port. Therefore, the discharge of the condensate water through the communication port can be smoothly performed. 
     In some examples, both of a lower end of the communication port of the center housing and a lower end of the inlet opening of the discharge path of the turbine housing are positioned lower than the rotary shaft. In this case, the water level (level) of the condensate water is prohibited from reaching the rotary shaft. Therefore, for example, even in a case where the condensate water is frozen due to a decrease in temperature, the rotary shaft may be prevented from sticking to ice derived from the condensate water. As long as the rotary shaft can rotate in the housing, the turbine can be operated. The operation of the turbine causes an increase in temperature. As a result, the ice melts into water and the water can be discharged from the discharge path. 
     In some examples, a seal portion for the rotary shaft is provided between the bearing and the blade. In this case, for example, gas that has passed through the seal portion from a back surface of the blade, gas that has cooled the bearing, and so on can be collected in the first space to be discharged to the second space through the discharge path. 
     In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. In this specification, the terms such as “upward and downward”, “vertical”, “horizontal”, and “bottom surface” may be understood as being based on a state where a turbine is installed, unless otherwise indicated. Additionally, the terms “ascend” and “descend” may be understood as being based on a state where the turbine is installed and with reference to gravity. 
     An example centrifugal compressor will be described with reference to the electric supercharger  1  illustrated in  FIG. 1 . The electric turbocharger  1  may be applied to, for example, a fuel cell system. The electric turbocharger  1  may be a fuel cell air supply device. The fuel cell system may be, for example, a solid polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), or other type of fuel cell system. 
     As illustrated in  FIGS. 1 and 2 , the example electric turbocharger  1  includes a turbine  2  and a compressor  3 . The turbine  2  is, for example, an exhaust turbine for a fuel cell. The turbine  2  includes a rotary shaft  4  having a rotation axis X. A turbine impeller (blade)  21  is attached to one end of the rotary shaft  4 , and a compressor impeller  31  is attached to the other end of the rotary shaft  4 . A motor  5  that applies a rotational driving force to the rotary shaft  4  is installed between the turbine impeller  21  and the compressor impeller  31 . Compressed air (one example of “compressed gas”) G compressed by the compressor  3  is supplied to the fuel cell system as an oxidant (oxygen). A chemical reaction between a fuel and the oxidant occurs in the fuel cell system to generate electricity. Air containing water vapor is discharged from the fuel cell system, and the air is supplied to the turbine  2 . 
     The electric turbocharger  1  rotates the turbine impeller  21  of the turbine  2  using high-temperature air discharged from the fuel cell system. The rotation of the turbine impeller  21  causes the compressor impeller  31  of the compressor  3  to rotate and the compressed air G to be supplied to the fuel cell system. In the electric turbocharger  1 , a majority of the driving force of the compressor  3  may be applied by the motor  5 . Namely, the electric turbocharger  1  may be a substantially motor-driven turbocharger. 
     The fuel cell system and the electric turbocharger  1  can be mounted in, for example, a vehicle (electric car). Electricity generated by the fuel cell system may be supplied to the motor  5  of the electric turbocharger  1 ; however, electricity may be supplied from an electric power source other than the fuel cell system. 
     The electric turbocharger  1  includes the turbine  2 , the compressor  3 , and an inverter  6  that controls the rotational drive of the motor  5 . The turbine  2  includes a turbine housing  22 , the turbine impeller  21  accommodated in the turbine housing  22 , a motor housing (center housing)  7 , the rotary shaft  4  and the motor  5  disposed in the motor housing  7 , and an air bearing structure  8  which will be described later. 
     The compressor  3  includes a compressor housing  32  and the compressor impeller  31  accommodated in the compressor housing  32 . The motor housing  7  is provided between the turbine housing  22  and the compressor housing  32 . The rotary shaft  4  is rotatably supported by the air bearing structure (gas bearing structure)  8  in the motor housing  7 . In some examples, a housing H of the electric turbocharger  1  includes the turbine housing  22 , the compressor housing  32 , and the motor housing  7 . Among these housings, the turbine housing  22  and the motor housing  7  may constitute a housing of the turbine  2 . 
     The turbine housing  22  is provided with an exhaust gas inlet port and an exhaust gas outlet port  22   a . The air containing water vapor which is discharged from the fuel cell system flows into the turbine housing  22  through the exhaust gas inlet port. The inlet air passes through a turbine scroll  22   b  to be supplied to an inlet side of the turbine impeller  21 . The turbine impeller  21  is, for example, a radial turbine that generates a rotation force using the pressure of the supplied air. Thereafter, the air flows outside the turbine housing  22  through the exhaust gas outlet port  22   a.    
     The compressor housing  32  is provided with a suction port  32   a  and a discharge port  32   b . When the turbine impeller  21  rotates as described above, the rotary shaft  4  and the compressor impeller  31  rotate. The rotating compressor impeller  31  suctions outside air through the suction port  32   a  to compress the air. The compressed air G compressed by the compressor impeller  31  passes through a compressor scroll  32   c  to be discharged from the discharge port  32   b . The compressed air G discharged from the discharge port  32   b  is supplied to the fuel cell system. 
     The motor  5  is, for example, a brushless AC motor, and includes a rotor  51  that is a rotating component and a stator  52  that is a stationary component. The rotor  51  includes one or a plurality of magnets. The rotor  51  is fixed to the rotary shaft  4  and can rotate around the axis, together with the rotary shaft  4 . The rotor  51  is disposed in a central portion of the rotary shaft  4  in an axial direction. The stator  52  includes a plurality of coils and cores. The stator  52  is disposed to surround the rotor  51  in a circumferential direction of the rotary shaft  4 . The stator  52  generates a magnetic field around the rotary shaft  4  to thereby rotate the rotor  51  in cooperation with the rotor  51 . 
     An example cooling structure that cools heat generated inside the turbocharger includes a heat exchanger (cooler)  9  attached to the motor housing  7 , and a refrigerant line  10  and an air cooling line that pass through the heat exchanger  9 . The refrigerant line  10  and the air cooling line are connected or fluidly coupled to each other to enable heat exchange inside the heat exchanger  9 . A part of the compressed air G compressed by the compressor  3  passes through the air cooling line. In some examples, a part of the compressed air G is extracted to flow through the air cooling line as cooling air Ga. A coolant C, which has a lower temperature than the cooling air Ga passing through the air cooling line, passes through the refrigerant line  10 . 
     The refrigerant line  10  is a part of a circulation line that is connected or fluidly coupled to a radiator provided outside the electric turbocharger  1 . The temperature of the coolant C passing through the refrigerant line  10  is, for example, between approximately 50° C. and 100° C. The refrigerant line  10  includes a motor cooling portion  10   a  disposed along the stator  52 , and an inverter cooling portion  10   b  disposed along the inverter  6 . The coolant C that has passed through the heat exchanger  9  flows through the motor cooling portion  10   a  while circulating around the stator  52 , to thereby cool the stator  52 . Thereafter, the coolant C flows through the inverter cooling portion  10   b  along control circuits of the inverter  6 , for example, in a meandering manner, to thereby cool the inverter  6 . In some examples, the control circuit of the inverter  6  may comprise an insulated gate bipolar transistor (IGBT), a bipolar transistor, a MOSFET, a gate turn-off thyristor (GTO), or the like. The configuration of the flow path of the coolant C can be appropriately changed such that the coolant C can cool devices which are to be cooled. 
     The electric turbocharger  1  is configured such that the pressure on a compressor  3  side is higher than the pressure on a turbine  2  side. The air bearing structure  8  is cooled using the pressure difference. A part of the compressed air G compressed by the compressor  3  is extracted, the cooling air Ga is guided to the air bearing structure  8 , and the cooling air Ga that has passed through the air bearing structure  8  is delivered to the turbine  2 . The temperature of the compressed air G is, for example, approximately 170° C. even when the temperature is high, and is lowered to approximately 70 to 80° C. by the heat exchanger  9 . Since the temperature of the air bearing structure  8  is 150° C. or higher without cooling, the air bearing structure  8  is suitably cooled by the supply of the cooling air Ga. In  FIG. 2 , the illustration of the heat exchanger  9  and the inverter  6  is omitted. 
     The motor housing  7  includes a stator housing  71  that accommodates the stator  52  surrounding the rotor  51 , and a bearing housing  72  in which the air bearing structure  8  is provided. A shaft space (a part of a space in the housing H) A through which the rotary shaft  4  penetrates is formed in the stator housing  71  and the bearing housing  72 . Labyrinth seal portions  33   a  and  23   a  that hold airtightness in the shaft space A are provided in both end portions of the shaft space A. 
     The compressor housing  32  accommodating the compressor impeller  31  is connected and fixed to the bearing housing  72  by a fastener such as a bolt or so on. The compressor housing  32  includes an impeller chamber  34  that accommodates the compressor impeller  31 , and a diffuser plate  33  that has a disk shape and forms a diffuser  36  in cooperation with the impeller chamber  34 . A plurality of vanes  37  disposed inside the diffuser  36  are fixed to the diffuser plate  33 . The labyrinth seal portion  33   a  is provided in a central portion (around the rotary shaft  4 ) of the diffuser plate  33 . An extraction hole that is an inlet of the air cooling line to extract a part of the compressed air G may be formed in the diffuser plate  33 . 
     The turbine housing  22  accommodating the turbine impeller  21  is connected and fixed to the stator housing  71  by a fastener such as a bolt or so on. As illustrated in  FIGS. 2 and 3 , a seal plate  23  having a disk shape is provided between the turbine housing  22  and the stator housing  71  (motor housing  7 ). The seal plate  23  forms a gas flow path between the turbine scroll  22   b  and the turbine impeller  21 . The seal plate  23  may be a nozzle ring including a plurality of nozzle vanes disposed in the gas flow path. The labyrinth seal portion  23   a  is provided in a central portion (around the rotary shaft  4 ) of the seal plate  23 . The labyrinth seal portion  23   a  that is a seal portion provided for the rotary shaft  4  holds the airtightness of a space (first space) S where a radial bearing  82  of the air bearing structure  8  is provided. The labyrinth seal portion  23   a  can prevent the air, which is discharged from the fuel cell system and contains water vapor, from flowing into the space S. 
     The example air bearing structure  8  that supports the rotary shaft  4  includes a pair of radial bearings  81  and  82  and a thrust bearing  83 . The pair of radial bearings  81  and  82  restrict the movement of the rotary shaft  4  in a direction perpendicular to the rotary shaft  4  while allowing the rotary shaft  4  to rotate. The pair of radial bearings  81  and  82  are, for example, dynamic pressure air bearings (gas bearings) and are disposed to interpose the rotor  51  therebetween, the rotor  51  being provided in the central portion of the rotary shaft  4 . 
     A first radial bearing  81  is provided in the bearing housing  72  and is disposed between the rotor  51  and the compressor impeller  31 . A second radial bearing  82  is provided in the stator housing  71  and is disposed between the rotor  51  and the turbine impeller  21 . The labyrinth seal portion  23   a  is provided between the second radial bearing  82  and the turbine impeller  21 . The first radial bearing  81  and the second radial bearing  82  have substantially the same structure. As the rotary shaft  4  rotates, ambient air is drawn into a gap between the rotary shaft  4  and the first radial bearing  81  (wedge effect) to increase the pressure to thereby cause the first radial bearing  81  to obtain the load capacity. The first radial bearing  81  rotatably supports the rotary shaft  4  by virtue of the load capacity obtained by the wedge effect. The first radial bearing  81  may comprise, for example, a foil bearing, a tilting pad bearing, a spiral groove bearing or the like 
     The thrust bearing  83  is provided in the bearing housing  72  and is disposed between the radial bearing  81  and the compressor impeller  31 . The thrust bearing  83  restricts the movement of the rotary shaft  4  in the axial direction while allowing the rotary shaft  4  to rotate. The thrust bearing  83  is a dynamic pressure air bearing and is disposed between the first radial bearing  81  and the compressor impeller  31 . The thrust bearing  83  has a structure where, as the rotary shaft  4  rotates, ambient air is drawn into a gap between the rotary shaft  4  and the thrust bearing  83  (wedge effect) to increase the pressure to thereby cause the thrust bearing  83  to obtain the load capacity. The thrust bearing  83  rotatably supports the rotary shaft  4  by virtue of the load capacity obtained by the wedge effect. The thrust bearing  83  may comprise, for example, a foil bearing, a tilting pad bearing, a spiral groove bearing or the like. 
     In some examples, gaps are formed between the rotary shaft  4  and the radial bearing  81 , inside the thrust bearing  83 , between the rotor  51  and the stator  52 , and between the rotary shaft  4  and the radial bearing  82 . The cooling air Ga passes through these gaps to thereby cool the bearings of the air bearing structure  8 . A configuration different from the configuration where a part of the compressed air G is extracted to be introduced as the cooling air Ga may be adopted. For example, a part of the compressed air G discharged from the electric turbocharger  1  may be cooled outside and then return into the electric turbocharger  1  as cooling air. Cooling air other than the compressed air G may be introduced from another air source. 
     The cooling air Ga that has cooled the motor  5  and the radial bearing  82  is introduced to the exhaust gas outlet port (second space)  22   a  via a first flow path  16  formed in the motor housing  7  and a first discharge path  18  formed in the turbine housing  22 . The first discharge path  18  is configured to discharge gas in the space S, in which the radial bearing  82  is provided, to the exhaust gas outlet port  22   a . The cooling air Ga that has cooled the radial bearing  81  and the thrust bearing  83  is introduced to the exhaust gas outlet port  22   a  via a second flow path  15  formed in the motor housing  7  and a second discharge path  17  formed in the turbine housing  22 . Both of the first discharge path  18  and the second discharge path  17  are, for example, flow paths having a circular cross-section. 
     Hereinafter, an example gas flow path provided in the turbine  2  will be described in more detail. Since the turbine  2  receives moist air discharged from the fuel cell system, for example, when the turbine  2  is stopped, condensate water may be accumulated in the motor housing  7 . The gas flow path formed in the turbine housing  22  also serves as a discharge path for the condensate water. The turbine  2  has a structure where the condensate water is successfully discharged to a space downstream of the turbine impeller  21 . 
     The motor housing  7  is provided with the first flow path  16  that connects or fluidly couples the space S of the shaft space A and the turbine housing  22 . The motor housing  7  is also provided with the second flow path  15  that connects or fluidly couples the shaft space A and the turbine housing  22 . The compressed air G that has reached the shaft space A via the heat exchanger  9  branches into a flow toward to the second flow path  15  and a flow toward the first flow path  16 . The second radial bearing  82  is disposed on the flow path toward the first flow path  16 . The cooling air Ga toward the first flow path  16  cools mainly the second radial bearing  82 . The first radial bearing  81  and the thrust bearing  83  are disposed on the flow path toward the second flow path  15 . The cooling air Ga toward the second flow path  15  cools mainly the first radial bearing  81  and the thrust bearing  83 . 
     Additionally, as illustrated in  FIG. 3 , the first flow path  16  is connected or fluidly coupled to the second radial bearing  82 . A bearing main body of the second radial bearing  82  is fixed to the stator housing  71 . The turbine housing  22  is fixed to the stator housing  71 . The seal plate  23  provided with the labyrinth seal portion  23   a  is disposed between the stator housing  71  and the turbine housing  22 . The space S into which the cooling air Ga can flow is formed between the radial bearing  82  and the seal plate  23 . An upstream inlet of the first flow path  16  is connected or fluidly coupled to the space S. 
     The first flow path  16  penetrates through the seal plate  23  and the stator housing  71 . A first communication port  16   a  (refer to  FIG. 7 ) that is an outlet of the first flow path  16  is connected or fluidly coupled to the first discharge path  18  formed in the turbine housing  22 . Accordingly, the first discharge path  18  includes a first inlet opening  18   a  that communicates with the space S via the first flow path  16 , and a first outlet opening  18   b  that opens to the exhaust gas outlet port  22   a  in the turbine housing  22  (refer to  FIG. 8 ). The stator housing  71  includes the first communication port  16   a  (refer to  FIG. 4 ) facing the first inlet opening  18   a  of the first discharge path  18 . In some examples, the first communication port  16   a  is equivalent to an outlet of the space S. An orifice plate  42  that regulates the flow rate of the cooling air Ga may be provided between the first communication port  16   a  and the first inlet opening  18   a.    
     As illustrated in  FIG. 2 , the second flow path  15  is connected or fluidly coupled to a space where the thrust bearing  83  is present. A gap into which the cooling air Ga can flow is present between an outer peripheral surface of a bearing main body of the thrust bearing  83  and the bearing housing  72 . An upstream inlet of the second flow path  15  is connected or fluidly coupled to the gap. As illustrated in  FIG. 3 , the second flow path  15  penetrates the bearing housing  72  and the stator housing  71 . An outlet of the second flow path  15  is connected or fluidly coupled to the second discharge path  17  formed in the turbine housing  22 . Accordingly, the second discharge path  17  includes a second inlet opening  17   a  that faces the outlet of the second flow path  15  and a second outlet opening  17   b  that opens to the exhaust gas outlet port  22   a  in the turbine housing  22  (refer to  FIG. 8 ). The stator housing  71  includes a second communication port  15   a  (refer to  FIG. 4 ) facing the second inlet opening  17   a  of the second discharge path  17 . An orifice plate  41  that regulates the flow rate of the cooling air Ga may be provided between the second communication port  15   a  and the second inlet opening  17   a.    
     With reference to  FIGS. 3 to 8 , it can be seen that a structure related to a fluid (gas and liquid) may be present in the space S where the radial bearing  82  is provided. As illustrated in  FIG. 3 , moist air that has passed through a gap between a back surface  21   a  of the turbine impeller  21  and the seal plate  23  and has further passed through the labyrinth seal portion  23   a  may flow into the space S (refer to a solid-line arrow in the drawing). The cooling air Ga that has cooled the thrust bearing  83  may flow into the space S (refer to a solid-line arrow in the drawing). The air that has flown into the space S can be discharged to the exhaust gas outlet port  22   a  through the first flow path  16  and the first discharge path  18  (refer to the dotted-line arrow in the drawing). 
     As illustrated in  FIGS. 3 and 5 , the seal plate  23  includes a main body portion  23   b  that has an annular shape and includes the labyrinth seal portion  23   a  formed in an inner peripheral surface of the main body portion  23   b , and a flange portion  23   c  that has an annular shape and is connected to an outer periphery of the main body portion  23   b . A step is formed between the main body portion  23   b  and the flange portion  23   c . A protrusion portion  23   d  having a cylindrical shape of the main body portion  23   b  is fitted into an opening that has a circular shape and is formed in the turbine housing  22 . An outer peripheral surface  23   e  of the protrusion portion  23   d  is fitted to an inner peripheral surface  22   e  of the opening of the turbine housing  22 . In some examples, the outer peripheral surface  23   e  may be equivalent to the step between the main body portion  23   b  and the flange portion  23   c . The main body portion  23   b  may be provided with a groove portion  23   f  that has an annular shape and faces the back surface  21   a  of the turbine impeller  21  with a slight gap therebetween. 
     As illustrated in  FIGS. 3 and 4 , the stator housing  71  includes a fitting portion  71   a  that has a cylindrical shape and protrudes toward the turbine housing  22 , and an outer peripheral portion  71   b  that has an annular shape and is connected to an outer periphery of the fitting portion  71   a . The fitting portion  71   a  is fitted into the turbine housing  22 . Additionally, the flange portion  23   c  of the seal plate  23  is fitted into an inner peripheral side of the fitting portion  71   a . The space S is formed on a back surface side of the seal plate  23 , and a flow path constituting a part of the first flow path  16  is formed in the flange portion  23   c  of the seal plate  23 . 
     In some examples, as illustrated in  FIGS. 4 to 6 , a guide path  23   g  that is a notch is formed in the flange portion  23   c  that is an outer peripheral portion of the seal plate  23 . The guide path  23   g  penetrates through the flange portion  23   c  in a radial direction. The guide path  23   g  extends between the space S and the first communication port  16   a  of the first flow path  16 . In some examples, the guide path  23 . g  is configured to guide the condensate water, which is accumulated in the space S, to the first flow path  16 . 
     As illustrated in  FIG. 4 , the first communication port  16   a  of the first flow path  16  opens to an end surface of the fitting portion  71   a  of the stator housing  71  (also refer to  FIG. 3 ). The second communication port  15   a  of the second flow path  15  opens to an end surface of the outer peripheral portion  71   b  of the stator housing  71  (also refer to  FIG. 3 ). 
       FIG. 7  is a cross-sectional view illustrating the structure of an area positioned deeper than the first communication port  16   a  as seen from the turbine  2  side in a rotation axis X direction.  FIG. 8  is a view illustrating the shapes of the first discharge path  18  and the second discharge path  17  formed in the turbine housing  22  as seen from the turbine  2  side in the rotation axis X direction. As illustrated in  FIGS. 7 and 8 , both of the first communication port  16   a  of the first flow path  16  and the first inlet opening  18   a  of the first discharge path  18  have a circular shape and have substantially the same size. The first communication port  16   a  and the first inlet opening  18   a  facing each other are disposed such that the central axes thereof are aligned with each other. When the orifice plate  42  is disposed between the first communication port  16   a  and the first inlet opening  18   a , the diameter of a hole portion of the orifice plate  42  is smaller than the diameter of each of the first communication port  16   a  and the first inlet opening  18   a . Both of the second communication port  15   a  of the second flow path  15  and the second inlet opening  17   a  of the second discharge path  17  have a circular shape and have substantially the same size. The second communication port  15   a  and the second inlet opening  17   a  facing each other are disposed such that the central axes thereof are aligned with each other. When the orifice plate  41  is disposed between the second communication port  15   a  and the second inlet opening  17   a , the diameter of a hole portion of the orifice plate  41  is smaller than the diameter of each of the second communication port  15   a  and the second inlet opening  17   a.    
     In some examples, the first discharge path  18  has a predetermined slope. In  FIGS. 7 and 8 , a virtual vertical plane P 1  and a virtual horizontal plane P 2  based on a state where the electric turbocharger  1  (turbine  2 ) is assembled into an electric car and so on are illustrated. As illustrated in  FIG. 8 , a bottom surface  18   c  of the first discharge path  18  is constituted of a horizontal portion extending horizontally (namely, extending in parallel to the virtual horizontal plane P 2 ) and an inclined portion descending from the first inlet opening  18   a  toward the first outlet opening  18   b . The inclined portion continues downstream of the horizontal portion. Such a downslope in the first discharge path  18  facilitates the discharge of the condensate water to the exhaust gas outlet port  22   a.    
     Additionally, as illustrated in  FIG. 7 , the first flow path  16  in the stator housing  71  ascends from the space S toward the first communication port  16   a . For this reason, the guide path  23   g  of the seal plate  23 , the guide path  23   g  forming a part of the first flow path  16 , forms an angle with respect to the virtual horizontal plane P 2 . However, in the turbine  2 , the height of the first communication port  16   a  is taken into consideration. Both of a lower end  16   ab  of the first flow path  16  and a lower end  42   a  of the orifice plate  42  are positioned lower than the rotary shaft  4 . In some examples, both of the lower end  16   ab  of the first flow path  16  and the lower end  42   a  of the orifice plate  42  are positioned lower than a lower end  4   b  of the rotary shaft  4 . Similarly, also a lower end  18   ab  (refer to  FIG. 8 ) of the first inlet opening  18   a  is positioned lower than the rotary shaft  4 . 
     For this reason, in a case where the orifice plate  42  is provided, the condensate water may be accumulated up to the vicinity of a second level L 2  corresponding to the lower end  42   a  of the orifice plate  42 . In a case where the orifice plate  42  is not provided, the condensate water may be accumulated up to the vicinity of a first level L 1  corresponding to the lower end  16   ab  of the first communication port  16   a . The condensate water at any level does not reach the lower end  4   b  of the rotary shaft  4 . 
     As illustrated in  FIG. 8 , the second discharge path  17  is mainly constituted of an inclined portion ascending from the second inlet opening  17   a  toward the second outlet opening  17   b . Since the air from the compressor  3 , which passes through the second flow path  15  and the second discharge path  17 , is relatively dry, the problem of condensate water does not occur. For this reason, the shape of the second discharge path  17  can be determined without the discharge of a liquid such as water being taken into consideration. 
     A positional relationship between the first discharge path  18  and the second discharge path  17  will be described. As illustrated in  FIG. 3 , both of the first discharge path  18  and the second discharge path  17  are formed on one side with respect to the virtual vertical plane P 1 . Both of the first discharge path  18  and the second discharge path  17  are formed on a lower side with respect to the virtual horizontal plane P 2 . The first outlet opening  18   b  of the first discharge path  18  is positioned farther from the turbine impeller  21  than the second outlet opening  17   b  of the second discharge path  17  in the rotation axis X direction. The example configuration may be understood to secure the downslope of the first discharge path  18 . 
     In some examples, the gas in the space S where the radial bearing  82  is provided is discharged to the exhaust gas outlet port  22   a  in the turbine housing  22  through the first discharge path  18 . If the gas flowing into the turbine  2  contains water vapor and condensate water generated by the condensation of the water vapor is accumulated in the motor housing  7 , the condensate water may be accumulated also in the space S. When the water level of the condensate water reaches the first inlet opening  18   a  of the first discharge path  18 , the condensate water enters the first discharge path  18 . The bottom surface  18   c  of the first discharge path  18  is constituted of the inclined portion descending toward the first outlet opening  18   b  or is constituted of the inclined portion and the horizontal portion. Accordingly, the bottom surface  18   c  of the first discharge path  18  does not include an inclined portion ascending toward the first outlet opening  18   b . Therefore, the condensate water that has entered the first discharge path  18  is successfully discharged to the exhaust gas outlet port  22   a . As described above, the turbine  2  can discharge the condensate water that is accumulated in the space S where the radial bearing  82  is provided in the motor housing  7 . The first discharge path  18  serves both as a passage for discharging the gas and as a passage for discharging the condensate water. The first discharge path  18  may therefore avoid being filled with the condensate water. For example, when the turbine  2  is stopped, even in a case where the condensate water is frozen due to a decrease in temperature, the gas flow path is secured in the first discharge path  18 . 
     Since the motor housing  7  includes the first communication port  16   a  facing the first inlet opening  18   a  of the first discharge path  18 , the condensate water that is present in the space S in the motor housing  7  is readily discharged from the first communication port  16   a . Additionally, the example configuration facilitates the passage of discharged condensate water into the first discharge path  18  via the first inlet opening  18   a.    
     Since the guide path  23   g  is formed in the flange portion  23   c  of the seal plate  23 , the guide path  23   g  can guide the condensate water, which is present in the space S, to the first communication port  16   a . Therefore, the discharge of the condensate water through the first communication port  16   a  can be smoothly performed. 
     Since both of the lower end  16   ab  of the first communication port  16   a  and the lower end  18   ab  of the first inlet opening  18   a  are positioned lower than the rotary shaft  4 , the water level (level) of the condensate water is prohibited from reaching the rotary shaft  4 . Therefore, for example, even in a case where the condensate water is frozen due to a decrease in temperature, the rotary shaft  4  may be prevented from sticking to ice derived from the condensate water. As long as the rotary shaft  4  can rotate in the motor housing  7 , the turbine  2  can be operated. The operation of the turbine  2  causes an increase in temperature. As a result, the ice melts into water and the water can be discharged from the first discharge path  18 . 
     The labyrinth seal portion  23   a  is provided between the radial bearing  82  and the turbine impeller  21 . The gas that has passed through the labyrinth seal portion  23   a  from the back surface  21   a  of the turbine impeller  21 , the cooling air Ga that has cooled the radial bearing  82 , and so on can be collected in the space S to be discharged to the exhaust gas outlet port  22   a  through the first discharge path  18 . 
     It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail. For example, in other examples an axial turbine may include a discharge path having the same structure as that of the first discharge path  18 . When the discharge path is applied to the axial turbine, the discharge path may connect a casing and a downstream side of a blade. When the discharge path is applied to a multi-stage axial turbine, the discharge path may be connected to an intermediate position between one stage and another stage. 
     The seal portion that holds airtightness in the shaft space A is not limited to the labyrinth seal portions  33   a  and  23   a , and may be another type of seal portion. 
     The bottom surface  18   c  of the first discharge path  18  may be constituted of only an inclined portion descending from the first inlet opening  18   a  toward the first outlet opening  18   b.    
     Additionally, the structure of the discharge path may be applied to a turbocharger that does not include a motor. The gas compressed by the centrifugal compressor may be gas other than air. 
     We claim all modifications and variations coming within the spirit and scope of the subject matter claimed herein.