Fluid Machinery for Fuel Cells

Abstract

The present invention provides a fluid machine for a fuel cell that can improve the turbine efficiency. The fluid machine for a fuel cell includes a rotating shaft, an electric motor, a compression section, and a rotation assisting section. The rotation assisting section includes a turbine impeller and a turbine housing. The turbine impeller rotates by introducing the exhaust gas discharged from the fuel cell stack and introduced into the turbine chamber in the radial direction of the rotating shaft and discharging the exhaust gas in the axial direction of the rotating shaft. The diameter of the turbine impeller and the diameter of the shroud surface gradually increase from the upstream to the downstream in the flow direction of the exhaust gas.

Description

Technical Field

[0001] The present invention relates to a fluid machine for a fuel cell. Background Art

[0002] Conventionally, a fluid machine for a fuel cell having a rotating shaft, an electric motor, and a compression unit has been known. The electric motor rotates the rotating shaft. The compression unit is driven by the rotation of the rotating shaft. Further, the compression unit compresses the air supplied to the fuel cell stack. In addition, the fluid machine for a fuel cell sometimes includes a rotation assist unit that assists the rotation of the rotating shaft. The rotation assist unit includes, for example, a turbine impeller and a turbine housing as disclosed in Japanese Patent Application Laid-Open No. 2013-204422. The turbine impeller is provided on the rotating shaft. The turbine impeller rotates integrally with the rotating shaft. The turbine housing forms a turbine chamber. The turbine impeller is housed in the turbine chamber. Further, the turbine housing has a shroud surface opposed to the turbine impeller. In such a fluid machine for a fuel cell, the turbine impeller rotates by introducing the exhaust gas discharged from the fuel cell stack and introduced into the turbine chamber from the radial direction of the rotating shaft and discharging it in the axial direction of the rotating shaft.

[0003] In addition, in such a fluid machine for a fuel cell, as Figure 3 shown, there is a relationship between the turbine efficiency η and the speed ratio U / C. The turbine efficiency η has a characteristic of being convex upward with respect to the speed ratio U / C. Therefore, the turbine efficiency η becomes a maximum value ηmax at a prescribed speed ratio U / C0.

[0004] The speed ratio U / C is represented by the ratio of the circumferential speed U of the turbine impeller to the adiabatic speed C. The circumferential speed U of the turbine impeller is the rotational speed in the circumferential direction of the turbine impeller. The circumferential speed U of the turbine impeller is represented by the product of the rotational speed of the turbine impeller and the inlet diameter located upstream in the flow direction of the exhaust gas in the turbine impeller. The adiabatic speed C is represented by a function of the temperature and pressure of the exhaust gas. The adiabatic speed C is the theoretical gas speed obtained when expanding the exhaust gas having a certain temperature and pressure to a prescribed temperature and pressure.

[0005] Here, the temperature and pressure of the exhaust gas discharged from the fuel cell stack are significantly lower than, for example, the exhaust gas of an engine. Therefore, in the fluid machine for a fuel cell, the adiabatic speed C is relatively low, and thus the speed ratio U / C becomes a speed ratio U / Cx larger than the prescribed speed ratio U / C0. As a result, the turbine efficiency η becomes a value ηx lower than the maximum value ηmax.

[0006] The temperature and pressure of the exhaust gas discharged from the fuel cell stack are uniquely determined according to the required flow rate, temperature, and pressure of the air supplied to the fuel cell stack. Therefore, in the fluid machinery for fuel cells, the adiabatic velocity C is uniquely determined according to the required flow rate, temperature, and pressure of the air supplied to the fuel cell stack. Therefore, in order to increase the turbine efficiency η, it is necessary to reduce the circumferential velocity U of the turbine impeller.

[0007] In order to reduce the circumferential velocity U of the turbine impeller, for example, consideration is given to reducing the rotational speed of the turbine impeller. However, in order to assist the rotation of the rotating shaft, it is not preferable to reduce the rotational speed of the turbine impeller. Therefore, consideration is given to reducing the inlet diameter of the turbine impeller located upstream in the flow direction of the exhaust gas. At this time, consider the case of a turbine impeller having a structure in which the diameter of the turbine impeller gradually decreases from the upstream to the downstream in the flow direction of the exhaust gas. In this case, as the inlet diameter of the turbine impeller decreases, the outlet diameter of the turbine impeller located downstream in the flow direction of the exhaust gas also becomes smaller. As a result, the exhaust gas flowing under the action of the rotation of the turbine impeller is difficult to pass through the turbine chamber. Therefore, in the turbine chamber, the pressure upstream in the flow direction of the exhaust gas rises, so that the pressure at the inlet of the fuel cell stack rises. As a result, it is possible to significantly increase the power consumed by the compression section. Summary of the Invention

[0008] A fluid machinery for fuel cells according to one aspect includes: a rotating shaft; an electric motor configured to rotate the rotating shaft; a compression section configured to compress air supplied to the fuel cell stack by the rotation of the rotating shaft; and a rotation assisting section configured to assist the rotation of the rotating shaft. The rotation assisting section includes: a turbine impeller provided on the rotating shaft and configured to rotate integrally with the rotating shaft; and a turbine housing that defines a turbine chamber accommodating the turbine impeller and has a shroud surface facing the turbine impeller. The turbine impeller is configured to rotate by introducing the exhaust gas discharged from the fuel cell stack and introduced into the turbine chamber from the radial direction of the rotating shaft and discharging the exhaust gas in the axial direction of the rotating shaft. The diameter of the turbine impeller and the diameter of the shroud surface gradually increase from the upstream to the downstream in the flow direction of the exhaust gas. Brief Description of the Drawings

[0009] Figure 1 It is a side sectional view for explaining the fluid machinery for fuel cells of the embodiment.

[0010] Figure 2 It is a sectional view showing an enlarged view of the periphery of the turbine impeller.

[0011] Figure 3 It is a graph showing the relationship between the turbine efficiency and the speed ratio.

[0012] Figure 4 This is a cross-sectional view showing an enlarged periphery of the turbine impeller of other embodiments. Detailed Embodiment

[0013] Hereinafter, Figures 1 to 3 an embodiment of embodying the fluid machine for a fuel cell will be described. The fluid machine for a fuel cell in this embodiment is used, for example, in a fuel cell system mounted on a vehicle such as a fuel cell vehicle.

[0014] (Regarding the fuel cell system 10)

[0015] As Figure 1 shown, the fuel cell system 10 includes a fuel cell stack 11 and a fluid machine 12 for a fuel cell. The fluid machine 12 for a fuel cell compresses air as an oxidant gas. The compressed air by the fluid machine 12 for a fuel cell is supplied to the fuel cell stack 11. The fuel cell stack 11 has, for example, a plurality of single cells. Each single cell is formed by laminating an oxygen electrode, a hydrogen electrode, and an electrolyte membrane disposed between the two electrodes.

[0016] Moreover, the fuel cell stack 11 generates electricity by causing hydrogen as a fuel gas to chemically react with oxygen contained in the air. Only about 20% of the oxygen contributing to the power generation of the fuel cell stack 11 exists in the air. Therefore, about 80% of the air supplied to the fuel cell stack 11 does not contribute to the power generation of the fuel cell stack 11 and is discharged from the fuel cell stack 11 as exhaust gas.

[0017] The fuel cell stack 11 is electrically connected to a traveling motor (not shown). The traveling motor is driven using the electric power generated by the fuel cell stack 11 as a power source. The power of the traveling motor is transmitted to an axle via a power transmission mechanism (not shown), and the vehicle travels at a vehicle speed corresponding to the throttle opening of the accelerator pedal.

[0018] (Overall Structure of the Fluid Machine 12 for a Fuel Cell)

[0019] The fluid machine 12 for a fuel cell includes a rotating shaft 13, an electric motor 14, and a compression unit 15. The electric motor 14 rotates the rotating shaft 13. The compression unit 15 is driven by the rotation of the rotating shaft 13. In this embodiment, the compression unit 15 is a compressor impeller connected to the first end of the rotating shaft 13. Moreover, the compression unit 15 compresses the air supplied to the fuel cell stack 11.

[0020] (Structure of the Rotation Assist Unit 16)

[0021] The fluid machinery 12 for a fuel cell includes a rotation assisting portion 16. The rotation assisting portion 16 assists the rotation of the rotating shaft 13. The rotation assisting portion 16 includes a turbine impeller 20 and a turbine housing 30. The turbine impeller 20 is provided on the rotating shaft 13. Specifically, the turbine impeller 20 is connected to the second end portion of the rotating shaft 13. The turbine impeller 20 rotates integrally with the rotating shaft 13.

[0022] The turbine housing 30 forms a turbine chamber 31. The turbine impeller 20 is housed in the turbine chamber 31. The turbine housing 30 is in a cylindrical shape having a discharge port 32 in a circular hole shape. The discharge port 32 communicates with the turbine chamber 31. The axis of the discharge port 32 coincides with the axis L1 of the rotating shaft 13. In addition, the turbine housing 30 has a suction chamber 33 and an inlet port 34. The suction chamber 33 extends around the axis of the discharge port 32 around the turbine chamber 31. The exhaust gas discharged from the fuel cell stack 11 is sucked into the suction chamber 33. The inlet port 34 connects the turbine chamber 31 and the suction chamber 33. The inlet port 34 extends in the radial direction of the rotating shaft 13. And, the inlet port 34 guides the exhaust gas sucked into the suction chamber 33 from the radial direction of the rotating shaft 13 into the turbine chamber 31.

[0023] The turbine impeller 20 rotates by introducing the exhaust gas discharged from the fuel cell stack 11 and introduced into the turbine chamber 31 from the radial direction of the rotating shaft 13 and discharging it in the axial direction of the rotating shaft 13. The turbine impeller 20 rotates by the kinetic energy of the exhaust gas introduced into the turbine chamber 31. Thus, the kinetic energy of the exhaust gas is converted into the rotational energy of the turbine impeller 20. In this way, the rotational energy generated in the turbine impeller 20 assists the rotation of the rotating shaft 13. And, the exhaust gas that has passed through the turbine chamber 31 is discharged to the outside from the discharge port 32.

[0024] (Regarding the shroud surface 35)

[0025] As Figure 2 shown, the turbine housing 30 has a shroud surface 35 opposed to the turbine impeller 20. The shroud surface 35 forms the turbine chamber 31. The shroud surface 35 surrounds the turbine impeller 20. The shroud surface 35 connects the opening edge on the turbine chamber 31 side in the inlet port 34 and the inner peripheral surface of the discharge port 32. The diameter of the shroud surface 35 gradually increases from the inlet port 34 toward the discharge port 32. Therefore, the diameter of the shroud surface 35 gradually increases from the upstream to the downstream in the flow direction of the exhaust gas.

[0026] (Regarding the hub 21)

[0027] The turbine impeller 20 has a hub 21 and a plurality of blades 22. The hub 21 rotates integrally with the rotating shaft 13. The hub 21 is mounted on the second end portion of the rotating shaft 13. The hub 21 has a substantially conical shape with an outer diameter that increases as it goes from the back surface 21a toward the front end surface 21b. The hub 21 has an outer peripheral surface 21c that gradually decreases in diameter as it goes from the back surface 21a toward the front end surface 21b. The flow direction of the exhaust gas flowing in the turbine chamber 31 is from the inlet 34 toward the outlet 32. Therefore, the hub 21 has an outer peripheral surface 21c that gradually decreases in diameter from the upstream to the downstream in the flow direction of the exhaust gas. The outer peripheral surface 21c of the hub 21 is a curved surface that is recessed toward the axis L1 of the rotating shaft 13. The outer diameter of the back surface 21a of the hub 21 is the maximum diameter of the diameter of the hub 21. The outer diameter of the front end surface 21b of the hub 21 is the minimum diameter of the diameter of the hub 21.

[0028] (Regarding the blade 22)

[0029] A plurality of blades 22 are provided on the outer peripheral surface 21c of the hub 21. The plurality of blades 22 project from the outer peripheral surface 21c of the hub 21. The plurality of blades 22 are arranged at equal intervals in the circumferential direction of the hub 21 on the outer peripheral surface 21c of the hub 21. The plurality of blades 22 are arranged in the circumferential direction of the hub 21. The turbine impeller 20 is housed in the turbine chamber 31 in a state where each blade 22 faces the shroud surface 35. The outer edge 23, which is the edge on the shroud surface 35 side among the plurality of blades 22, gradually increases in diameter as it goes from the back surface 21a of the hub 21 toward the front end surface 21b. Therefore, each blade 22 gradually increases in diameter from the upstream to the downstream in the flow direction of the exhaust gas. Thus, the diameter of the turbine impeller 20 and the diameter of the shroud surface 35 gradually increase in diameter from the upstream to the downstream in the flow direction of the exhaust gas.

[0030] The outer edge 23 of the plurality of blades 22 extends along the shroud surface 35. Therefore, the gap C1 between the outer edge 23 of each blade 22 and the shroud surface 35 is constant in the flow direction of the exhaust gas. The inlet 34 faces each blade 22. Therefore, each blade 22 has an opposed edge 24 that faces the inlet 34. And, among the plurality of blades 22, the opposed edge 24 that faces the inlet 34 extends in such a way as to separate from the rotating shaft 13 as the diameter of the hub 21 decreases from the maximum diameter with respect to the axial direction of the rotating shaft 13. The diameter of the opposed edge 24 of each blade 22 is the inlet diameter at the upstream in the flow direction of the exhaust gas in the turbine impeller 20. The diameter of the end portion on the front end surface 21b side of the outer edge 23 of each blade 22 is the outlet diameter at the downstream in the flow direction of the exhaust gas in the turbine impeller 20.

[0031] (Function)

[0032] Next, the function of the present embodiment will be described.

[0033] When the rotating shaft 13 rotates by means of the electric motor 14, the compression part 15 is driven by the rotation of the rotating shaft 13, and the compression part 15 compresses air. The air compressed by the compression part 15 is supplied to the fuel cell stack 11. The oxygen contained in the air supplied to the fuel cell stack 11 contributes to the power generation of the fuel cell stack 11. The exhaust gas discharged from the fuel cell stack 11 is sucked into the suction chamber 33. The exhaust gas sucked into the suction chamber 33 is introduced into the turbine chamber 31 through the inlet 34. Then, the turbine impeller 20 rotates by the kinetic energy of the exhaust gas introduced into the turbine chamber 31. Thereby, the kinetic energy of the exhaust gas is converted into the rotational energy of the turbine impeller 20. Thus, the rotational energy generated in the turbine impeller 20 assists the rotation of the rotating shaft 13. Then, the exhaust gas that has passed through the turbine chamber 31 is discharged to the outside from the discharge port 32.

[0034] Figure 3 The figure shows the relationship between the turbine efficiency η and the speed ratio U / C. As Figure 3 shown, the turbine efficiency η has a characteristic of being convex upward with respect to the speed ratio U / C. Therefore, the turbine efficiency η becomes a maximum value ηmax at a prescribed speed ratio U / C0.

[0035] In addition, in such a fluid machine 12 for a fuel cell, there is a relationship between the turbine efficiency η and the speed ratio U / C. The speed ratio U / C is represented by the ratio of the circumferential speed U of the turbine impeller to the adiabatic speed C. The circumferential speed U of the turbine impeller is the circumferential rotational speed of the turbine impeller 20. The circumferential speed U of the turbine impeller is represented by the product of the rotational speed of the turbine impeller 20 and the inlet diameter located upstream in the flow direction of the exhaust gas in the turbine impeller 20. The adiabatic speed C is represented by a function of the temperature and pressure of the exhaust gas. The adiabatic speed C is the theoretical gas speed obtained when expanding the exhaust gas having a certain temperature and pressure to a prescribed temperature and pressure.

[0036] Here, the temperature and pressure of the exhaust gas discharged from the fuel cell stack 11 are significantly lower than, for example, the exhaust of an engine. Therefore, in the fluid machine 12 for a fuel cell, the adiabatic speed C is relatively low, and thus the speed ratio U / C becomes a speed ratio U / Cx larger than the prescribed speed ratio U / C0. As a result, the turbine efficiency η becomes a value ηx lower than the maximum value ηmax.

[0037] The temperature and pressure of the exhaust gas discharged from the fuel cell stack 11 are uniquely determined according to the required flow rate, temperature, and pressure of the air supplied to the fuel cell stack 11. Therefore, in the fluid machine 12 for a fuel cell, the adiabatic speed C is uniquely determined according to the required flow rate, temperature, and pressure of the air supplied to the fuel cell stack 11. Therefore, in order to increase the turbine efficiency η, it is necessary to reduce the circumferential speed U of the turbine impeller.

[0038] In order to reduce the circumferential velocity U of the turbine impeller, for example, consideration is given to reducing the rotational speed of the turbine impeller 20. However, in order to assist the rotation of the rotating shaft 13, it is not preferable to reduce the rotational speed of the turbine impeller 20. Therefore, consideration is given to reducing the inlet diameter of the turbine impeller 20 that is upstream in the flow direction of the exhaust gas.

[0039] Then, the diameter of the turbine impeller 20 and the diameter of the shroud surface 35 gradually increase from upstream to downstream in the flow direction of the exhaust gas. Accordingly, the inlet diameter of the turbine impeller 20 that is upstream in the flow direction of the exhaust gas becomes smaller, and thus the circumferential velocity U of the turbine impeller becomes smaller. Therefore, the speed ratio U / C approaches the specified speed ratio U / C0, and the turbine efficiency η approaches the maximum value ηmax. As a result, in the fluid machine 12 for a fuel cell, the turbine efficiency η is improved.

[0040] Moreover, even if the inlet diameter of the turbine impeller 20 that is upstream in the flow direction of the exhaust gas is reduced, the outlet diameter of the turbine impeller 20 that is downstream in the flow direction of the exhaust gas does not become smaller than the inlet diameter. Thus, even if the inlet diameter of the turbine impeller 20 is reduced, a situation where the exhaust gas flowing under the action of the rotation of the turbine impeller 20 hardly passes through the turbine chamber 31 is suppressed. As a result, even if the inlet diameter of the turbine impeller 20 is reduced in order to reduce the circumferential velocity U of the turbine impeller, an increase in the pressure upstream in the flow direction of the exhaust gas in the turbine chamber 31 is suppressed. Therefore, an increase in the pressure at the inlet of the fuel cell stack 11 is suppressed. Through the above, the power consumed by the compression unit 15 does not increase, and the turbine efficiency η is improved.

[0041] (Effect)

[0042] The following effects can be obtained in the above-described embodiment.

[0043] (1) The diameter of the turbine impeller 20 and the diameter of the shroud surface 35 gradually increase from the upstream to the downstream in the flow direction of the exhaust gas. Accordingly, the inlet diameter of the turbine impeller 20 located upstream in the flow direction of the exhaust gas becomes smaller, so the circumferential velocity U of the turbine impeller becomes smaller. Therefore, the speed ratio U / C approaches the specified speed ratio U / C0, and the turbine efficiency η approaches the maximum value ηmax. As a result, in the fluid machine 12 for a fuel cell, the turbine efficiency η is improved. And even if the inlet diameter of the turbine impeller 20 located upstream in the flow direction of the exhaust gas is reduced, the outlet diameter of the turbine impeller 20 located downstream in the flow direction of the exhaust gas does not become smaller than the inlet diameter. Thus, even if the inlet diameter of the turbine impeller 20 is reduced, it is possible to suppress the situation where the exhaust gas flowing under the action of the rotation of the turbine impeller 20 is difficult to pass through the turbine chamber 31. As a result, even if the inlet diameter of the turbine impeller 20 is reduced to reduce the circumferential velocity U of the turbine impeller, in the turbine chamber 31, the pressure rise upstream in the flow direction of the exhaust gas is suppressed. Therefore, the pressure rise at the inlet of the fuel cell stack 11 is suppressed. Through the above, the power consumed by the compression unit 15 does not increase, and the turbine efficiency η can be improved.

[0044] (2) The outer edge 23 of the plurality of blades 22, which is the edge on the shroud surface 35 side, extends along the shroud surface 35. Accordingly, the gap C1 between the outer edge 23 of the plurality of blades 22, which is the edge on the shroud surface 35 side, and the shroud surface 35 can be maintained constant. Therefore, the turbine efficiency η can be further improved.

[0045] (3) The opposed edge 24 of the plurality of blades 22 opposed to the inlet 34 extends in a manner that separates from the rotation axis 13 as the diameter of the hub 21 decreases from the maximum diameter in the axial direction of the rotation axis 13. Accordingly, the difference between the inlet diameter of the turbine impeller 20 located upstream in the flow direction of the exhaust gas and the outlet diameter of the turbine impeller 20 located downstream in the flow direction of the exhaust gas in the turbine impeller 20 can be made as large as possible. Therefore, even if the inlet diameter of the turbine impeller 20 is reduced, it is possible to further easily suppress the situation where the exhaust gas flowing under the action of the rotation of the turbine impeller 20 is difficult to pass through the turbine chamber 31.

[0046] (Modification example)

[0047] It should be noted that the above-described embodiment can be modified and implemented as follows. The above-described embodiment and the following modification examples can be implemented in combination with each other within a technically non-contradictory range.

[0048] ○ As Figure 4As shown, the opposing edge 24 of the plurality of blades 22 that faces the inlet port 34 may also extend in the axial direction of the rotary shaft 13 as the diameter of the hub 21 decreases from the maximum diameter. Accordingly, the kinetic energy of the exhaust gas can be easily transferred to the turbine impeller 20. Therefore, the kinetic energy of the exhaust gas can be easily converted into the rotational energy of the turbine impeller 20, and the rotation of the rotary shaft 13 can be easily assisted by using the rotational energy generated in the turbine impeller 20.

[0049] ○ In the embodiment, the outer edge 23 of the plurality of blades 22, which is the edge on the shroud surface 35 side, may not extend along the shroud surface 35. In short, the gap C1 between the outer edge 23 of the plurality of blades 22, which is the edge on the shroud surface 35 side, and the shroud surface 35 may not be constant. For example, the gap C1 between the outer edge 23 of the plurality of blades 22, which is the edge on the shroud surface 35 side, and the shroud surface 35 may gradually narrow as it goes from the upstream to the downstream in the flow direction of the exhaust gas. Additionally, for example, the gap C1 between the outer edge 23 of the plurality of blades 22, which is the edge on the shroud surface 35 side, and the shroud surface 35 may gradually widen as it goes from the upstream to the downstream in the flow direction of the exhaust gas.

[0050] ○ In the embodiment, the fluid machine 12 for a fuel cell is not limited to being mounted on a fuel cell vehicle and used for supplying air to the fuel cell stack 11. For example, the fluid machine 12 for a fuel cell is not limited to being mounted on a vehicle.

Claims

1. A fluid machine for a fuel cell, wherein, the fluid machine for a fuel cell includes: a rotating shaft; an electric motor configured to rotate the rotating shaft; a compression part configured to compress air supplied to a fuel cell stack by rotation of the rotating shaft; and a rotation assisting part configured to assist the rotation of the rotating shaft, the rotation assisting part includes: a turbine impeller provided on the rotating shaft and configured to rotate integrally with the rotating shaft; and a turbine housing that defines a turbine chamber accommodating the turbine impeller and has a shroud surface opposed to the turbine impeller in the radial direction of the rotating shaft, the turbine impeller is configured to rotate by introducing exhaust gas discharged from the fuel cell stack and introduced into the turbine chamber from the radial direction of the rotating shaft and discharging the exhaust gas in the axial direction of the rotating shaft, the turbine housing is cylindrical with a circular hole-shaped discharge port, the discharge port communicates with the turbine chamber, and the axis of the discharge port coincides with the axis of the rotating shaft, the turbine housing has a suction chamber and an inlet, the suction chamber extends around the axis of the discharge port around the turbine chamber, the inlet communicates the turbine chamber with the suction chamber, and the inlet extends in the radial direction of the rotating shaft, the diameter of the turbine impeller and the diameter of the shroud surface gradually increase from the inlet toward the discharge port, the turbine impeller has: a hub having an outer peripheral surface that gradually decreases in diameter from the back surface toward the front end surface; and a plurality of blades provided on the outer peripheral surface, arranged in the circumferential direction of the hub, and gradually increasing in diameter from the back surface of the hub toward the front end surface of the hub, the outer edge of the plurality of blades, which is the edge opposed to the shroud surface, extends along the shroud surface, each of the blades has an opposed edge opposed to the inlet, the diameter of the opposed edge of each blade is the inlet diameter of the turbine impeller located upstream in the flow direction of the exhaust gas, the diameter of the end of the outer edge of each blade located on the front end surface side of the hub is the outlet diameter of the turbine impeller located downstream in the flow direction of the exhaust gas, the outlet diameter is larger than the inlet diameter.

2. The fluid machine for a fuel cell according to claim 1, wherein, the inlet is opposed to the blade and introduces the exhaust gas into the turbine chamber, the opposed edge of the plurality of blades extends away from the rotating shaft in a direction in which the diameter of the hub decreases from the maximum diameter in the axial direction of the rotating shaft with respect to the axis direction of the rotating shaft.

3. The fluid machine for a fuel cell according to claim 1, wherein, the inlet is opposed to the blade and introduces the exhaust gas, the opposed edge of the plurality of blades extends in the axial direction of the rotating shaft in a direction in which the diameter of the hub decreases from the maximum diameter in the axial direction of the rotating shaft with respect to the axis direction of the rotating shaft.

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