JP7816066B2 - Hydrogen Circulation System - Google Patents

Description

The present invention relates to a hydrogen circulation system.

For example, the fuel cell system disclosed in Patent Document 1 executes control to prevent the roots-type hydrogen circulation pump from freezing when the fuel cell system is stopped.
The fuel cell system disclosed in Patent Document 1 includes a fuel cell, a gas-liquid separator, a Roots-type hydrogen circulation pump, and a control unit. To prevent the Roots-type hydrogen circulation pump from freezing, the control unit operates the Roots-type hydrogen circulation pump at a first rotation speed when the fuel cell system is stopped. After a predetermined time has elapsed, the control unit operates the Roots-type hydrogen circulation pump at a second rotation speed, which is lower than the first rotation speed.

When the Roots-type hydrogen circulation pump is operated at a first rotation speed, the residual water on the suction side of the Roots-type hydrogen circulation pump is reduced. This reduces the possibility of the gas-liquid separator freezing at low temperatures. Furthermore, after a predetermined time has elapsed, the Roots-type hydrogen circulation pump is operated at a second rotation speed lower than the first rotation speed, which prevents the suction side from being stirred up and reduces the amount of water remaining in the Roots-type hydrogen circulation pump to a specified amount or less. This prevents the Roots-type hydrogen circulation pump from freezing at low temperatures.

Japanese Patent Application Laid-Open No. 2020-68153

When the fuel cell system is stopped, the Roots-type hydrogen circulation pump operates at the first or second rotation speed, allowing hydrogen to flow throughout the entire fuel cell system. For this reason, in Patent Document 1, it is necessary to allow hydrogen to flow throughout the entire fuel cell system in order to prevent the Roots-type hydrogen circulation pump from freezing. Therefore, in Patent Document 1, the system for preventing the Roots-type hydrogen circulation pump from freezing is large-scale.

A hydrogen circulation system that solves the above problems includes a fuel cell, a hydrogen supply path that supplies hydrogen to the fuel cell, a hydrogen circulation path that returns hydrogen discharged from the fuel cell to the hydrogen supply path, a first gas-liquid separator that is provided in the hydrogen circulation path and separates the hydrogen discharged from the fuel cell from water, a pump that is provided in the hydrogen circulation path and takes in hydrogen discharged from the first gas-liquid separator and discharges hydrogen toward the hydrogen supply path, and a control unit that controls the pump. A check valve is provided between the pump and the first gas-liquid separator to regulate the direction of hydrogen flow, a first branch section connected to the hydrogen circulation path so as to branch off from between the pump and the check valve, and a branch path connecting the first branch section to a second branch section connected to the hydrogen circulation path across the pump. A second gas-liquid separator is provided in the closed loop including the pump and the branch path to separate hydrogen and moisture, and a switching valve is provided in the second branch section to switch the flow of hydrogen to the closed loop, and the switching valve is controlled by the control unit.

With this, the control unit can control the switching valve to switch the flow of hydrogen to a closed loop. The hydrogen remaining in the closed loop then flows through the closed loop and into the second gas-liquid separator. The second gas-liquid separator separates moisture from the hydrogen. The hydrogen from which moisture has been separated flows through the closed loop as dry gas. The check valve prevents the dry gas from flowing back through the hydrogen circulation path, so the dry gas flows through the closed loop. As a result, the pump is dried by the dry gas flowing through the closed loop. For example, the hydrogen circulation system can be made smaller than when hydrogen is returned from the hydrogen circulation path to the hydrogen supply path and fuel cell and then flowed through the entire fuel cell system to dry the pump.

In a hydrogen circulation system, when hydrogen is returned from the fuel cell to the hydrogen supply path, the control unit controls the switching valve to return hydrogen discharged from the fuel cell to the hydrogen supply path by driving the pump; when hydrogen is not returned from the fuel cell to the hydrogen supply path, the control unit controls the switching valve to allow hydrogen to flow in the closed loop by driving the pump for a predetermined time, and stops the pump after the predetermined time has elapsed.

By controlling the switching valve with the control unit, hydrogen can be prevented from flowing through the closed loop when returning hydrogen to the hydrogen supply channel. This prevents a decrease in the amount of hydrogen returned to the hydrogen supply channel. On the other hand, when hydrogen is not returned to the hydrogen supply channel, hydrogen can be flowed through the closed loop. This allows all of the hydrogen that flows when the pump is driven to flow through the closed loop. This allows the pump to be dried efficiently using hydrogen from which moisture has been separated. Furthermore, the control unit stops the pump after a predetermined time has elapsed. This prevents the pump from being driven unnecessarily, thereby reducing unnecessary power consumption.

In the hydrogen circulation system, the second gas-liquid separator may be provided on the suction side of the pump in the hydrogen circulation path or in the branch path.
According to this, hydrogen from which water has been separated by the second gas-liquid separator flows into the pump, which makes it easier to dry the pump.

In the hydrogen circulation system, the second gas-liquid separator may be provided integrally with the pump.
This makes it easier to reduce the size of the hydrogen circulation system compared to when the second gas-liquid separator is separate from the pump, for example.

In the hydrogen circulation system, a drainage channel may be connected to the second gas-liquid separator, and the drainage channel may be provided with an on-off valve for opening and closing the drainage channel.
This can prevent moisture from continuing to accumulate in the second gas-liquid separator.

This invention enables the hydrogen circulation system to be downsized.

1 is a cross-sectional view showing a Roots pump according to a first embodiment. FIG. 1 is a block diagram showing a hydrogen circulation system according to a first embodiment; FIG. 2 is a cross-sectional view showing a rotor and a rotor chamber of the first embodiment. FIG. 1 is a diagram illustrating a hydrogen circulation system in a dry mode. FIG. 10 is a partial cross-sectional view showing a Roots pump according to a second embodiment. FIG. 10 is a block diagram showing a hydrogen circulation system according to a second embodiment. FIG. 6 is a cross-sectional view showing a rotor and a rotor chamber according to a second embodiment. FIG. 1 is a diagram illustrating a hydrogen circulation system in a dry mode. FIG. 10 is a block diagram showing another example of a hydrogen circulation system.

(First embodiment)
A first embodiment of a hydrogen circulation system will be described with reference to FIGS. 1 to 4. FIG.
1 and 2, the hydrogen circulation system 51 is provided in a fuel cell system 60. The fuel cell system 60 is mounted on a fuel cell vehicle. The fuel cell system 60 generates electricity using oxygen and hydrogen.

<Roots Pump Overview>
First, the roots pump 10 as a pump provided in the hydrogen circulation system 51 and the fuel cell system 60 will be described.

As shown in FIG. 1, the Roots pump 10 has a cylindrical housing 11. The housing 11 has a motor housing 12, a gear housing 13, a rotor housing 14, a first cover member 15, and a second cover member 40. Each of the motor housing 12, gear housing 13, rotor housing 14, first cover member 15, and second cover member 40 is made of metal.

The motor housing 12 is connected to the gear housing 13. The rotor housing 14 is connected to the gear housing 13. The first cover member 15 is connected to the rotor housing 14. The second cover member 40 is connected to the first cover member 15.

The motor housing 12 has a plate-shaped bottom wall 12a and a peripheral wall 12b that extends cylindrically from the outer periphery of the bottom wall 12a. The gear housing 13 has a plate-shaped bottom wall 13a and a peripheral wall 13b that extends cylindrically from the outer periphery of the bottom wall 13a. A pair of first recesses 13c are formed in the bottom wall 13a of the gear housing 13. Each of the pair of first recesses 13c is recessed circularly from the inner bottom surface of the gear housing 13.

The rotor housing 14 has a plate-shaped bottom wall 14a and a peripheral wall 14b extending cylindrically from the outer periphery of the bottom wall 14a. A pair of second recesses 14c are formed in the bottom wall 14a of the rotor housing 14. Each of the pair of second recesses 14c is circularly recessed from the end face of the bottom wall 14a. Each of the pair of second recesses 14c is positioned coaxially with each of the pair of first recesses 13c. The first cover member 15 is plate-shaped. The first cover member 15 has an inner wall surface 15a and an outer wall surface 15b. The second cover member 40 is cylindrical.

The bottom wall 13a of the gear housing 13 abuts against the peripheral wall 12b of the motor housing 12. The bottom wall 14a of the rotor housing 14 abuts against the peripheral wall 13b of the gear housing 13. The first cover member 15 abuts against the peripheral wall 14b of the rotor housing 14. The second cover member 40 abuts against the first cover member 15.

A gear chamber 24 is defined in the housing 11. The gear chamber 24 is defined by the bottom wall 13a of the gear housing 13, the peripheral wall 13b of the gear housing 13, and the bottom wall 14a of the rotor housing 14.

A rotor chamber 25 is defined in the housing 11. The rotor chamber 25 is defined by the bottom wall 14a of the rotor housing 14, the peripheral wall 14b of the rotor housing 14, and the first cover member 15. The housing 11 has a pair of rotor chamber end faces 26. One of the pair of rotor chamber end faces 26 is formed by the inner wall surface 14e of the bottom wall 14a of the rotor housing 14, and the other of the pair of rotor chamber end faces 26 is defined by the inner wall surface 15a of the first cover member 15. The pair of rotor chamber end faces 26 are located on opposite sides of the rotor chamber 25.

A motor chamber 12c is defined in the housing 11. The motor chamber 12c is defined by the bottom wall 12a of the motor housing 12, the peripheral wall 12b of the motor housing 12, and the bottom wall 13a of the gear housing 13.

A gas-liquid separation chamber 41 is defined in the housing 11. The gas-liquid separation chamber 41 is defined by an outer wall surface 15b of the first cover member 15 and an inner surface of the second cover member 40.
The Roots pump 10 has a drive shaft 16a and a driven shaft 16b as the rotating shaft 16. The drive shaft 16a and the driven shaft 16b are made of metal. The drive shaft 16a and the driven shaft 16b are parallel to each other. The direction in which the axis L of the rotating shaft 16 extends is defined as the axial direction. The drive shaft 16a penetrates the bottom wall 13a of the gear housing 13 and the bottom wall 14a of the rotor housing 14. The driven shaft 16b penetrates the bottom wall 14a of the rotor housing 14.

A pair of first bearings 31 are arranged on the bottom wall 13a of the gear housing 13. One of the pair of first bearings 31 is press-fitted into one of the first recesses 13c, and the other of the pair of first bearings 31 is press-fitted into the other of the first recesses 13c. A pair of second bearings 32 are arranged on the bottom wall 14a of the rotor housing 14. One of the pair of second bearings 32 is press-fitted into one of the second recesses 14c, and the other of the pair of second bearings 32 is press-fitted into the other of the second recesses 14c. A third bearing 33 is arranged on the bottom wall 12a of the motor housing 12. The drive shaft 16a is rotatably supported in the housing 11 via one of the first bearings 31, one of the second bearings 32, and the third bearing 33. The driven shaft 16b is rotatably supported in the housing 11 via the other of the first bearings 31 and the other of the second bearings 32.

The first seal member 17a is provided on the bottom wall 13a of the gear housing 13. The first seal member 17a is press-fitted into one of the first recesses 13c. The first seal member 17a seals between the drive shaft 16a and the bottom wall 13a of the gear housing 13. The first seal member 17a seals between the gear chamber 24 and the motor chamber 12c. The pair of second seal members 17b are provided on the bottom wall 14a of the rotor housing 14. Each of the pair of second seal members 17b is press-fitted into the second recess 14c. The second seal member 17b seals between the rotating shaft 16 and the bottom wall 14a. The second seal member 17b seals between the gear chamber 24 and the rotor chamber 25.

The Roots pump 10 has an electric motor 50 that rotates the drive shaft 16a. The electric motor 50 is housed in the motor chamber 12c. The electric motor 50 rotates the drive shaft 16a.

The Roots pump 10 has a power transmission mechanism G. The power transmission mechanism G has a drive gear 18 and a driven gear 19. The drive gear 18 is fixed to the drive shaft 16a. The driven gear 19 is fixed to the driven shaft 16b. The drive gear 18 and the driven gear 19 are housed in a gear chamber 24. Therefore, the power transmission mechanism G is housed in the housing 11. The driven gear 19 rotates in mesh with the drive gear 18. The driven shaft 16b rotates in the opposite direction to the drive shaft 16a due to the power transmission mechanism G.

The Roots pump 10 has a second gas-liquid separator 39. The first gas-liquid separator 64 will be described later. The second gas-liquid separator 39 is integral with the Roots pump 10. The second gas-liquid separator 39 has a gas-liquid separation chamber 41, a separation tube 42 disposed in the gas-liquid separation chamber 41, and an intake port 43. The separation tube 42 is cylindrical. The intake port 43 is formed in the second cover member 40. The intake port 43 faces the separation tube 42. Hydrogen flows into the gas-liquid separation chamber 41 via the intake port 43. The hydrogen that flows into the gas-liquid separation chamber 41 from the intake port 43 collides with the separation tube 42. The collision of the hydrogen with the separation tube 42 separates the moisture contained in the hydrogen from the hydrogen. Therefore, the second gas-liquid separator 39 separates the moisture from the hydrogen.

The gas-liquid separation performed by the second gas-liquid separator 39 is not limited to a separation method using collision of hydrogen against the separation cylinder 42. For example, the hydrogen that has flowed into the gas-liquid separation chamber 41 may be circulated around a centrifugal cylinder to separate the moisture contained in the hydrogen by centrifugation. In short, any method of gas-liquid separation performed by the second gas-liquid separator 39 can be used as long as it can separate moisture from hydrogen.

As shown in FIG. 3, the Roots pump 10 has a pump section 38. The pump section 38 has a rotor chamber 25, a pair of rotors 22, a pair of rotary shafts 16, an intake hole 45, and a discharge hole 46. The intake hole 45 is formed in the first cover member 15. The discharge hole 46 is formed in the peripheral wall 14b of the rotor housing 14. The intake hole 45 connects the gas-liquid separation chamber 41 of the second gas-liquid separator 39 with the rotor chamber 25. Hydrogen in the gas-liquid separation chamber 41 is drawn into the rotor chamber 25 via the intake hole 45. The hydrogen drawn into the rotor chamber 25 is discharged out of the rotor chamber 25 via the discharge hole 46.

Each of the pair of rotors 22 is a two-lobed cocoon-shaped rotor. The pair of rotors 22 consists of a drive rotor 20 and a driven rotor 21. The drive rotor 20 is rotated by the drive gear 18. The driven rotor 21 is rotated by the driven gear 19. The pair of rotors 22 are housed in a rotor chamber 25. The drive rotor 20 is attached to the drive shaft 16a. The driven rotor 21 is attached to the driven shaft 16b. The driven rotor 21 rotates together with the drive rotor 20. Therefore, the drive rotor 20 and the driven rotor 21 constitute a pair of rotors 22 that rotate in opposite directions within the rotor chamber 25.

As shown in Figures 1 and 3, the rotor 22 has a pair of rotor end faces 22c. The pair of rotor end faces 22c are both axial end faces of the rotor 22. One rotor end face 22c faces the inner wall surface 14e of the bottom wall 14a via a clearance, and the other rotor end face 22c faces the inner wall surface 15a of the first cover member 15 via a clearance. Therefore, a clearance in the axial direction of the rotating shaft 16 is defined between the rotor 22 and the inner surface of the rotor chamber 25.

In the Roots pump 10, when the drive rotor 20 and driven rotor 21 rotate in opposite directions within the rotor chamber 25, hydrogen in the gas-liquid separation chamber 41 is drawn into the rotor chamber 25 through the suction hole 45. The drawn-in hydrogen is trapped by the tip of the rotor 22. The trapped hydrogen remains trapped and is sent toward the discharge hole 46. The trapped hydrogen is discharged from the discharge hole 46.

The drive of the Roots pump 10 is controlled by the control unit 54. The control unit 54 switches the Roots pump 10 between drive and stop.
<Fuel cell system>
Next, a fuel cell system 60 having the above-described Roots pump 10 will be described.

As shown in FIG. 2, the fuel cell system 60 includes a Roots pump 10, a switching valve 52, a branching channel 53, a control unit 54, a check valve 55, a fuel cell 61, a hydrogen tank 62, an air compressor 63, a first gas-liquid separator 64, a hydrogen supply channel 71, a hydrogen circulation channel 72, and an air supply channel 73. The hydrogen circulation system 51 included in the fuel cell system 60 includes the fuel cell 61, the hydrogen supply channel 71, the hydrogen circulation channel 72, the first gas-liquid separator 64, a Roots pump 10 having a second gas-liquid separator 39, a switching valve 52, a branching channel 53, a control unit 54, and a check valve 55. The hydrogen circulation system 51 may also include a drainage channel 65 and a solenoid valve 66.

The fuel cell 61 is a fuel cell stack composed of multiple stacked battery cells. The fuel cell 61 is, for example, a polymer electrolyte fuel cell. The fuel cell 61 has an anode, a cathode, and an electrolyte membrane (not shown). The fuel cell 61 generates electricity by chemically reacting hydrogen, which serves as fuel gas supplied to the anode, with oxygen, which serves as oxidant gas supplied to the cathode. In the fuel cell 61, the chemical reaction between hydrogen and oxygen produces water.

The hydrogen tank 62 stores hydrogen to be supplied to the fuel cell 61. The hydrogen supply path 71 is a pipe connecting the anode of the fuel cell 61 to the hydrogen tank 62. The hydrogen supply path 71 supplies hydrogen to the fuel cell 61. The hydrogen stored in the hydrogen tank 62 is supplied to the anode of the fuel cell 61 via the hydrogen supply path 71. Therefore, hydrogen to be supplied to the fuel cell 61 flows through the hydrogen supply path 71. The hydrogen supply path 71 is provided with an on-off valve 71a and a pressure adjustment valve 71b. The on-off valve 71a opens and closes the hydrogen supply path 71. The pressure adjustment valve 71b adjusts the pressure of the hydrogen supplied to the fuel cell 61.

The air compressor 63 supplies atmospheric air to the fuel cell 61. The air supply path 73 is a pipe connecting the air compressor 63 to the cathode of the fuel cell 61. The air supply path 73 supplies oxygen to the fuel cell 61. Air containing oxygen from the atmosphere is supplied by the air compressor 63 to the cathode of the fuel cell 61 via the air supply path 73.

The hydrogen circulation path 72 connects the hydrogen supply path 71 and the fuel cell 61. The hydrogen circulation path 72 is a pipe. A first end 721 of the hydrogen circulation path 72 is connected to the anode of the fuel cell 61. A second end 722 of the hydrogen circulation path 72 is connected to the hydrogen supply path 71. The hydrogen circulation path 72 is provided to return hydrogen discharged from the fuel cell 61 to the hydrogen supply path 71.

The hydrogen circulation path 72 is provided with a first gas-liquid separator 64, a Roots pump 10, a switching valve 52, and a check valve 55. The pump unit 38 of the Roots pump 10 draws in and discharges hydrogen discharged from the anode of the fuel cell 61 on the hydrogen circulation path 72. The pump unit 38 of the Roots pump 10 sends hydrogen flowing through the hydrogen circulation path 72 to the hydrogen supply path 71. Therefore, the Roots pump 10 is provided on the hydrogen circulation path 72 to cause hydrogen to flow through the hydrogen circulation path 72. The direction in which hydrogen flows through the hydrogen circulation path 72 due to the Roots pump 10 is referred to as the hydrogen flow direction J.

The hydrogen circulation path 72 has a first flow path 72a, a second flow path 72b, a third flow path 72c, and a fourth flow path 72d. The first flow path 72a connects the anode of the fuel cell 61 and the first gas-liquid separator 64. A first end 721 of the first flow path 72a is connected to the anode of the fuel cell 61, and the other end of the first flow path 72a is connected to the first gas-liquid separator 64. Therefore, in the flow direction J, the first gas-liquid separator 64 is located downstream of the fuel cell 61. The first gas-liquid separator 64 is also located in the hydrogen circulation path 72.

Hydrogen discharged from the anode of the fuel cell 61 flows into the first gas-liquid separator 64 via the first flow path 72a. The first gas-liquid separator 64 separates the produced water, which is the moisture contained in the hydrogen, from the hydrogen. Therefore, the first gas-liquid separator 64 separates the hydrogen and moisture discharged from the fuel cell 61. The gas-liquid separation method used by the first gas-liquid separator 64 may be a separation method in which hydrogen collides against a separation cylinder, or a centrifugal separation method in which hydrogen circulates around a centrifugal cylinder. In short, the gas-liquid separation method used by the first gas-liquid separator 64 is arbitrary as long as it can separate moisture from hydrogen.

The second flow path 72b connects the first gas-liquid separator 64 and the Roots pump 10. One end of the second flow path 72b is connected to the first gas-liquid separator 64, and the other end is connected to the suction port 43 of the Roots pump 10. Therefore, the second flow path 72b is connected to the second gas-liquid separator 39, which is on the suction side of the Roots pump 10. Hydrogen, from which moisture has been separated in the first gas-liquid separator 64, flows into the gas-liquid separation chamber 41 of the second gas-liquid separator 39 via the second flow path 72b and the suction port 43. Therefore, the second gas-liquid separator 39 is located on the suction side of the Roots pump 10 in the hydrogen circulation path 72. As described above, moisture contained in hydrogen that flows from the suction port 43 into the gas-liquid separation chamber 41 is separated from the hydrogen by collision of the hydrogen with the separation tube 42.

The third flow path 72c connects the Roots pump 10 and the switching valve 52. One end of the third flow path 72c is connected to the discharge hole 46 of the Roots pump 10, and the other end of the third flow path 72c is connected to the switching valve 52. Therefore, the third flow path 72c is connected to the discharge hole 46 of the pump section 38 and the switching valve 52. As a result, the Roots pump 10 draws in hydrogen discharged from the first gas-liquid separator 64 via the second flow path 72b and the inlet 43, and discharges the hydrogen toward the hydrogen supply path 71 via the third flow path 72c.

In the hydrogen circulation path 72, the second flow path 72b is upstream of the third flow path 72c in the flow direction J. Therefore, the second gas-liquid separator 39 connected to the second flow path 72b is located upstream of the pump unit 38 connected to the third flow path 72c in the hydrogen circulation path 72.

The switching valve 52 is a three-way valve. It has a first port 52a, a second port 52b, and a third port 52c. The other end of the third flow path 72c is connected to the first port 52a. The fourth flow path 72d is connected to the second port 52b. Therefore, the fourth flow path 72d connects the switching valve 52 to the hydrogen supply path 71. Specifically, one end of the fourth flow path 72d is connected to the second port 52b of the switching valve 52, and the other end of the fourth flow path 72d is connected to the hydrogen supply path 71. The fourth flow path 72d and the hydrogen supply path 71 are connected at a confluence point H. Therefore, the switching valve 52 is located downstream of the Roots pump 10 in the flow direction J and upstream of the confluence point H between the hydrogen supply path 71 and the hydrogen circulation path 72. A branch path 53 is connected to the third port 52c of the switching valve 52. The branch path 53 will be described later.

The switching valve 52 can be switched between a first position P1, which connects the first port 52a to the second port 52b, and a second position P2, which connects the first port 52a to the third port 52c. When the switching valve 52 is switched to the first position P1, hydrogen flowing into the switching valve 52 from the first port 52a flows to the fourth flow path 72d via the second port 52b. When the switching valve 52 is switched to the second position P2, hydrogen flowing into the switching valve 52 from the first port 52a flows to the branch path 53 via the third port 52c. The switching of the switching valve 52 between the first position P1 and the second position P2 is performed by the control unit 54. Therefore, the switching valve 52 is controlled by the control unit 54.

When the fuel cell 61 is generating electricity and hydrogen is to be returned from the fuel cell 61 to the hydrogen supply channel 71, the control unit 54 switches the switching valve 52 to the first position P1. When the fuel cell 61 is not generating electricity, that is, when hydrogen is not to be returned from the fuel cell 61 to the hydrogen supply channel 71, the control unit 54 switches the switching valve 52 to the second position P2 so that the Roots pump 10 flows hydrogen into the branch channel 53. Therefore, the switching valve 52 can be switched by the control unit 54 between the first position P1, which allows hydrogen that has flowed into the switching valve 52 to flow into the hydrogen supply channel 71, and the second position P2, which allows hydrogen that has flowed into the switching valve 52 to flow into the branch channel 53. In other words, the control unit 54 switches the switching valve 52 between the first position P1, which returns hydrogen that has flowed into the switching valve 52 to the hydrogen supply channel 71, and the second position P2, which allows hydrogen that has flowed into the switching valve 52 to flow into the branch channel 53.

The branch path 53 is a pipe connecting the switching valve 52 and the second flow path 72b. The first end 53a of the branch path 53 is connected to the third port 52c of the switching valve 52, and the second end 53b of the branch path 53 is connected to the second flow path 72b. The branch path 53 branches off from the second flow path 72b as it moves from the second end 53b to the first end 53a. The end of the branch path 53 that includes the second end 53b is a first branch portion 531 that branches off from the second flow path 72b. The first branch portion 531 is connected to the second flow path 72b in the hydrogen circulation path 72.

The branch path 53 branches off from the switching valve 52 as it moves from the first end 53a to the second end 53b. The end of the branch path 53, including the first end 53a, is the second branch portion 532, which branches off from the hydrogen circulation path 72 via the switching valve 52. Therefore, the second branch portion 532 is connected to the hydrogen circulation path 72 via the switching valve 52. The second branch portion 532 is connected to the hydrogen circulation path 72 from the first branch portion 531, spanning the Roots pump 10.

More specifically, the second end 53b, including the first branch portion 531, is connected to the second flow path 72b of the hydrogen circulation path 72, upstream of the Roots pump 10 and downstream of the check valve 55 in the flow direction J. Therefore, the first branch portion 531 is connected to the hydrogen circulation path 72 so as to branch off between the Roots pump 10 and the check valve 55. Hydrogen flows into the branch path 53 via the switching valve 52, which is in the second position P2. The hydrogen flowing through the branch path 53 is returned to the hydrogen circulation path 72 upstream of the Roots pump 10 in the flow direction J.

When the selector valve 52 is in the second position P2, a closed loop Q including the selector valve 52 and the branch path 53 is formed in the hydrogen circulation system 51. The closed loop Q is formed by the section of the hydrogen circulation path 72 from the first branch 531 to the selector valve 52, the Roots pump 10 provided in that section, the selector valve 52, and the section of the branch path 53 from the second branch 532 to the first branch 531. Therefore, when the closed loop Q is formed, hydrogen discharged from the Roots pump 10 flows into the selector valve 52 from the third flow path 72c of the hydrogen circulation path 72 and then flows into the branch path 53 from the second branch 532. The hydrogen that flows into the branch path 53 flows into the second flow path 72b of the hydrogen circulation path 72 from the first branch 531 and then into the Roots pump 10. Therefore, the second branch 532 is provided with a selector valve 52 that switches the flow of hydrogen to the closed loop Q.

A Roots pump 10 is provided in a portion of the hydrogen circulation path 72 that forms the closed loop Q. A second gas-liquid separator 39 is integrally provided with the Roots pump 10. Therefore, the closed loop Q is provided with the second gas-liquid separator 39 that separates hydrogen and moisture.

When hydrogen is returned from the fuel cell 61 to the hydrogen supply path 71, if the switching valve 52 is switched to the first position P1, hydrogen does not flow through the closed loop Q. On the other hand, when hydrogen is not returned from the fuel cell 61 to the hydrogen supply path 71, if the switching valve 52 is switched to the second position P2, hydrogen flows through the closed loop Q.

The check valve 55 is provided in the second flow path 72b of the hydrogen circulation path 72. The check valve 55 is provided in the second flow path 72b downstream of the fuel cell 61 and first gas-liquid separator 64 in the flow direction J and upstream of the Roots pump 10. The check valve 55 is also provided upstream of the first branch portion 531 of the branch path 53, i.e., the second end 53b. Therefore, the branch path 53 connects the hydrogen circulation path 72 upstream of the Roots pump 10 in the flow direction J and downstream of the check valve 55 with the switching valve 52. The second gas-liquid separator 39 included in the Roots pump 10 is provided in the hydrogen circulation path 72 downstream of the check valve 55 in the flow direction J and upstream of the switching valve 52.

The check valve 55 allows hydrogen to flow in flow direction J through the hydrogen circulation path 72, while preventing hydrogen from flowing in the opposite direction to flow direction J through the hydrogen circulation path 72. Therefore, the check valve 55 is provided between the Roots pump 10 and the first gas-liquid separator 64, and regulates the direction of hydrogen flow through the hydrogen circulation path 72.

The first end 65a of the drainage channel 65 is connected to the second gas-liquid separator 39 of the Roots pump 10. Specifically, the first end 65a of the drainage channel 65 is connected to the bottom of the second cover member 40. The second end 65b of the drainage channel 65 is connected to the first gas-liquid separator 64. In this case, the second gas-liquid separator 39 of the Roots pump 10 is positioned higher than the first gas-liquid separator 64, and the drainage channel 65 is arranged vertically or at a downward angle from the second gas-liquid separator 39 to the first gas-liquid separator 64.

The solenoid valve 66 is an on-off valve that opens and closes the drainage channel 65. The solenoid valve 66 has an open position and a closed position. When the solenoid valve 66 is in the open position, moisture accumulated in the gas-liquid separation chamber 41 is drained from the bottom of the second cover member 40 into the drainage channel 65. The moisture discharged into the drainage channel 65 is then discharged into the first gas-liquid separator 64. When the solenoid valve 66 is in the closed position, moisture is not discharged from the gas-liquid separation chamber 41 and accumulates in the gas-liquid separation chamber 41.

The control unit 54 is a vehicle ECU that controls the fuel cell vehicle, and controls the fuel cell system 60 and the hydrogen circulation system 51.
The control unit 54 has a processor and a memory unit. The memory unit includes a random access memory (RAM) and a read-only memory (ROM). The memory unit stores program code or instructions configured to cause the processor to execute processes. The memory unit, i.e., a computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control unit 54 may be configured with a hardware circuit such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). The control unit 54, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof.

The control unit 54 controls the Roots pump 10, the switching valve 52, and the solenoid valve 66 of the hydrogen circulation system 51. The control unit 54 is signal-connected to the Roots pump 10, the switching valve 52, and the solenoid valve 66. The control unit 54 drives the Roots pump 10 or stops the drive of the Roots pump 10. The control unit 54 switches the switching valve 52 to the first position P1 or the second position P2. The control unit 54 opens and closes the solenoid valve 66.

<When fuel cell generates electricity>
To cause the fuel cell 61 to generate electricity, hydrogen is supplied to the fuel cell 61 from the hydrogen tank 62 via the hydrogen supply line 71. When the fuel cell 61 is generating electricity, hydrogen discharged from the fuel cell 61 is returned to the hydrogen supply line 71. In this case, the on-off valve 71a is opened and the pressure of the hydrogen is adjusted by the pressure adjustment valve 71b. In addition, the air compressor 63 is driven, and compressed air is supplied from the air compressor 63 to the fuel cell 61 via the air supply line 73. The control unit 54 also drives the Roots pump 10.

In the hydrogen circulation system 51, the control unit 54 switches the switching valve 52 to the first position P1. At this time, the switching valve 52 is not in communication with the branch path 53. Furthermore, when the fuel cell 61 is generating power, the control unit 54 closes the solenoid valve 66. In the fuel cell 61, power is generated by the fuel cell, and water is produced by the reaction between oxygen and hydrogen.

As shown by the arrows in Figure 2, when the fuel cell 61 is generating electricity, the Roots pump 10 is driven, causing hydrogen discharged from the anode of the fuel cell 61 to flow into the first gas-liquid separator 64 via the first flow path 72a. Furthermore, water generated in the fuel cell 61 is discharged from the fuel cell 61 along with the hydrogen into the hydrogen circulation path 72. In the first gas-liquid separator 64, water is separated from the hydrogen that has flowed into the first gas-liquid separator 64.

The hydrogen from which moisture has been separated by the first gas-liquid separator 64 flows into the gas-liquid separation chamber 41 of the second gas-liquid separator 39 via the second flow path 72b, the check valve 55, and the intake port 43. The hydrogen that flows into the gas-liquid separation chamber 41 of the second gas-liquid separator 39 is sprayed toward the separation tube 42. When the hydrogen collides with the separation tube 42, some of the moisture is separated from the hydrogen.

The hydrogen from which water has been separated by the second gas-liquid separator 39 flows into the rotor chamber 25 of the pump section 38 via the intake port 45. The hydrogen that flows into the rotor chamber 25 is trapped by the tip of the rotor 22. The trapped hydrogen remains trapped and is sent toward the discharge port 46.

Hydrogen that flows into the pump section 38 may contain residual moisture. This residual moisture may penetrate into the clearance between the rotor end face 22c and the inner wall surface 14e of the rotor housing 14, or the clearance between the rotor end face 22c and the inner wall surface 15a of the first cover member 15.

The trapped hydrogen is discharged from the rotor chamber 25 through the discharge hole 46. This causes the pump section 38 of the Roots pump 10 to discharge hydrogen into the third flow path 72c. The hydrogen discharged into the third flow path 72c passes through the third flow path 72c and flows into the switching valve 52 from the first port 52a of the switching valve 52. The hydrogen that flows into the switching valve 52 flows into the fourth flow path 72d via the second port 52b with the switching valve 52 in the first position P1. With the switching valve 52 in the first position P1, hydrogen does not flow into the branch path 53. No hydrogen flows into the closed loop Q, and hydrogen discharged from the fuel cell 61 is returned to the hydrogen supply path 71 by the operation of the Roots pump 10.

Hydrogen that flows into the fourth flow path 72d via the switching valve 52 flows into the hydrogen supply path 71 at the junction H. The hydrogen that flows into the hydrogen supply path 71 is supplied to the anode of the fuel cell 61 via the hydrogen supply path 71. As a result, the pump unit 38 of the Roots pump 10 sends hydrogen flowing through the hydrogen circulation path 72 to the hydrogen supply path 71.

<Drying mode>
When the fuel cell vehicle is turned off, the on-off valve 71a is closed, stopping the supply of hydrogen to the fuel cell 61. The air compressor 63 is also stopped, stopping the supply of compressed air to the fuel cell 61. As a result, power generation by the fuel cell 61 is stopped.

When the fuel cell vehicle is keyed off, the control unit 54 executes a drying mode to dry the pump unit 38. When the drying mode is executed, the control unit 54 switches the selector valve 52 to the second position P2. This connects the third flow path 72c of the hydrogen circulation path 72 to the branch path 53 via the selector valve 52. Even when power generation by the fuel cell 61 is stopped, the control unit 54 closes the solenoid valve 66. The Roots pump 10 is also driven by the control unit 54.

As shown by arrow Y in Figure 4, when the dry mode is in operation, the Roots pump 10 drives hydrogen remaining in the hydrogen circulation path 72 to flow into the gas-liquid separation chamber 41 of the second gas-liquid separator 39 via the intake port 43. The hydrogen that flows into the gas-liquid separation chamber 41 of the second gas-liquid separator 39 is sprayed toward the separation tube 42. When the hydrogen collides with the separation tube 42, some of the moisture is separated from the hydrogen. The hydrogen that has passed through the second gas-liquid separator 39 contains a reduced amount of moisture compared to before passing through the second gas-liquid separator 39. During the dry mode, the hydrogen that has passed through the second gas-liquid separator 39 is referred to as "dry gas."

Dry gas flows into the rotor chamber 25 of the pump section 38 through the intake port 45. The dry gas that flows into the rotor chamber 25 penetrates the clearance between the rotor 22 and the inner surface of the rotor chamber 25. The dry gas that flows into the rotor chamber 25 is then discharged from the discharge port 46 to the outside of the rotor chamber 25. Therefore, the pump section 38 of the Roots pump 10 discharges the drawn hydrogen as dry gas into the third flow path 72c. The dry gas discharged into the third flow path 72c flows into the selector valve 52 from the first port 52a of the selector valve 52 via the third flow path 72c. With the selector valve 52 in its second position P2, the dry gas that flows into the selector valve 52 flows into the branch path 53 via the third port 52c. In other words, with the selector valve 52 in its second position P2, the dry gas does not flow into the fourth flow path 72d. Therefore, the dry gas is not returned to the hydrogen supply path 71.

The dry gas that flows into the branch line 53 passes through the branch line 53 and is returned to the second flow path 72b upstream of the Roots pump 10 and downstream of the check valve 55 in the hydrogen circulation path 72. At this time, the check valve 55 prevents the dry gas from flowing in the direction opposite to the flow direction J. In other words, the dry gas returned to the second flow path 72b of the hydrogen circulation path 72 is prevented from flowing back into the first gas-liquid separator 64 and the fuel cell 61.

The dry gas returned to the hydrogen circulation path 72 flows again into the second gas-liquid separator 39 of the Roots pump 10. Then, when the drying mode is being executed, the dry gas repeatedly flows through the second gas-liquid separator 39 and pump section 38 of the Roots pump 10, the switching valve 52, and the branch path 53 in the above order. In other words, when the drying mode is being executed, the dry gas flows through the closed loop Q. Therefore, when the drying mode is being executed, hydrogen is not returned to the hydrogen supply path 71. Therefore, when hydrogen is not returned from the fuel cell 61 to the hydrogen supply path 71, hydrogen flows through the closed loop Q when the Roots pump 10 is driven.

Every time dry gas passes through the second gas-liquid separator 39, moisture is removed from the hydrogen, and the pump section 38 of the second gas-liquid separator 39 is dried by the dry gas. When the drying mode is executed, the predetermined time during which dry gas flows through the Roots pump 10, the switching valve 52, and the branch line 53 is defined as the "drying time." The drying time is the time during which dry gas flows through the closed loop Q due to the operation of the Roots pump 10.

The drying time is the time required to remove moisture from the pump section 38 and dry it. The drying time is determined by the rotation speed per unit time of the rotating shaft 16 of the Roots pump 10, the volume of the rotor chamber 25, the size of the rotor 22, and other factors. For example, the lower the rotation speed per unit time of the rotating shaft 16, the longer the drying time. Furthermore, the larger the volume of the rotor chamber 25 and the rotor 22, the longer the drying time. Therefore, the drying time is set by predetermining the volume of the rotor chamber 25, the size of the rotor 22, and the rotation speed of the rotating shaft 16. At the start of the drying mode, the control unit 54 switches the selector valve 52 from the first position P1 to the second position P2 and measures the elapsed time from the start of the drying mode. When the measured elapsed time reaches the predetermined drying time, the control unit 54 returns the selector valve 52 to the first position P1 and stops the operation of the Roots pump 10. In other words, the control unit 54 terminates the drying mode. Therefore, if hydrogen is not returned from the fuel cell 61 to the hydrogen supply path 71, the control unit 54 controls the switching valve 52 to operate the Roots pump 10 to allow hydrogen to flow through the closed loop Q for a predetermined drying time, and stops the Roots pump 10 after the drying time has elapsed.

When the drying mode is executed, the control unit 54 opens the solenoid valve 66 at predetermined intervals or arbitrarily.
[Operation of the First Embodiment]
When the drying mode is executed, dry gas is generated by the second gas-liquid separator 39 of the Roots pump 10. The dry gas flows into the pump unit 38. The dry gas discharged from the pump unit 38 flows through the branch path 53 by the switching valve 52 and is returned from the branch path 53 to the hydrogen circulation path 72. At this time, the check valve 55 prevents the dry gas returned to the hydrogen circulation path 72 from flowing back toward the fuel cell 61 and the first gas-liquid separator 64. This causes the dry gas to flow through the closed loop Q. The dry gas then flows through the closed loop Q repeatedly for a predetermined time. As a result, in the pump unit 38, the dry gas enters the clearance between the rotor 22 and the rotor chamber 25, thereby removing moisture that has entered the clearance and drying the rotor chamber 25.

Therefore, even if the fuel cell system 60 remains stopped for an extended period of time in low temperatures, such as when the fuel cell vehicle is subsequently parked in low temperatures, it is possible to prevent water from freezing between the rotor end surface 22c and the rotor chamber end surface 26.

[Effects of the First Embodiment]
According to the first embodiment, the following effects can be obtained.
(1-1) When the drying mode is executed, the second gas-liquid separator 39 separates water from hydrogen to generate dry gas, and the dry gas is returned to the second flow path 72b of the hydrogen circulation path 72 via the switching valve 52 and the branch path 53. Then, while the switching valve 52 is in the second position P2, the dry gas can flow through the closed loop Q. As a result, the pump section 38 of the Roots pump 10 can be dried by the dry gas. For example, the hydrogen circulation system 51 can be made smaller in size than when hydrogen discharged from the Roots pump 10 is returned from the hydrogen circulation path 72 to the hydrogen supply path 71 and the fuel cell 61, and then returned to the pump section 38 to dry the pump section 38.

As a result, even if the fuel cell system 60 remains stopped for an extended period of time at low temperatures, such as when the fuel cell vehicle is parked in low temperatures for an extended period of time after the dry mode is executed, freezing of moisture between the rotor end face 22c and the rotor chamber end face 26 can be suppressed. As a result, when restarting the fuel cell system 60 at low temperatures, the rotor 22 can be prevented from locking due to freezing, preventing the fuel cell system 60 from starting. Furthermore, since there is no need to increase the clearance between the rotor end face 22c and the rotor chamber end face 26 to suppress freezing of moisture between the rotor end face 22c and the rotor chamber end face 26, there is no degradation in the pumping performance of the Roots pump 10. As a result, the amount of hydrogen returned to the hydrogen supply path 71 by the Roots pump 10 is not reduced, thereby suppressing a decline in the power generation efficiency of the fuel cell 61.

Furthermore, the time required to dry the pump unit 38 can be shortened. Furthermore, when the fuel cell 61 is generating electricity, moisture remaining in the pump unit 38 can be prevented from being returned to the fuel cell 61 from the hydrogen circulation path 72 via the hydrogen supply path 71, thereby preventing moisture from reducing the power generation efficiency of the fuel cell 61.

(1-2) The hydrogen circulation system 51 has a check valve 55. When the dry gas is returned to the hydrogen circulation path 72 via the switching valve 52 and the branch path 53, the check valve 55 prevents the hydrogen returned to the hydrogen circulation path 72 from flowing back. Therefore, the check valve 55 can maintain the closed loop Q and prevent hydrogen from entering the anode of the fuel cell 61 or the first gas-liquid separator 64.

(1-3) When the drying mode is executed, the control unit 54 controls the switching valve 52 and the Roots pump 10 to allow the drying gas to flow through the closed loop Q for a predetermined drying time. Therefore, the control unit 54 controls the switching valve 52 and the Roots pump 10 to optimally dry the pump unit 38 and reduce unnecessary power consumption.

(1-4) When the fuel cell 61 is generating electricity, the control unit 54 controls the switching valve 52 to the first position P1, thereby returning hydrogen to the hydrogen supply path 71. This prevents hydrogen from flowing through the closed loop Q when the fuel cell 61 is generating electricity. This prevents a decrease in the amount of hydrogen returned to the hydrogen supply path 71 when the fuel cell 61 is generating electricity, thereby preventing a decrease in the power generation efficiency of the fuel cell 61.

(1-5) When the drying mode is executed, the control unit 54 controls the switching valve 52 to the second position P2, allowing hydrogen to flow through the closed loop Q. As a result, all of the hydrogen flowing due to the operation of the Roots pump 10 can flow through the closed loop Q. As a result, the pump section 38 of the Roots pump 10 can be efficiently dried using dry gas.

(1-6) The second gas-liquid separator 39 is provided integrally with the Roots pump 10. For example, compared to when the second gas-liquid separator 39 is provided separately from the Roots pump 10, it is easier to reduce the size of the hydrogen circulation system 51.

(1-7) A drainage channel 65 is connected to the second gas-liquid separator 39, and a solenoid valve 66 is provided in the drainage channel 65. When the drying mode is being executed, the control unit 54 opens the solenoid valve 66 at predetermined intervals or at any time. This allows the moisture separated by the second gas-liquid separator 39 to be discharged from the gas-liquid separation chamber 41. As a result, when the drying mode is being executed, it is possible to prevent moisture from continuing to accumulate in the gas-liquid separation chamber 41.

(1-8) In the flow direction J of the hydrogen circulation path 72, the second gas-liquid separator 39 is located on the suction side of the Roots pump 10, i.e., upstream of the pump section 38. Therefore, when the drying mode is being executed, the hydrogen from which water has been separated by the second gas-liquid separator 39 flows into the pump section 38 of the Roots pump 10. Therefore, when the drying mode is being executed, the pump section 38 can be dried efficiently.

Second Embodiment
A second embodiment of the hydrogen circulation system will be described below with reference to Figures 5 to 8. In the description of the second embodiment, detailed descriptions of parts that are the same as those of the first embodiment will be omitted.

As shown in Figures 5, 6, and 7, the intake hole 14d is formed in the peripheral wall 14b of the rotor housing 14. The second flow path 72b of the hydrogen circulation path 72 is connected to the intake hole 14d. The discharge hole 15c is formed in the first cover member 15. The second cover member 40 has a discharge port 44. The third flow path 72c of the hydrogen circulation path 72 is connected to the discharge port 44 of the pump section 38 and the switching valve 52. In the hydrogen circulation path 72, the second flow path 72b is upstream of the third flow path 72c in the flow direction J. Therefore, the pump section 38 connected to the second flow path 72b is upstream of the second gas-liquid separator 39 connected to the third flow path 72c. The second gas-liquid separator 39 included in the Roots pump 10 is located in the hydrogen circulation path 72 downstream of the check valve 55 in the flow direction J and upstream of the switching valve 52.

<When fuel cell generates electricity>
When the fuel cell 61 generates electricity, hydrogen discharged from the anode of the fuel cell 61 flows into the rotor chamber 25 of the pump unit 38 via the first flow path 72a, the first gas-liquid separator 64, the second flow path 72b, the check valve 55, and the suction port 14d. The hydrogen that flows into the rotor chamber 25 of the pump unit 38 is discharged into the gas-liquid separation chamber 41 of the second gas-liquid separator 39 via the discharge port 15c. The hydrogen that flows into the gas-liquid separation chamber 41 of the second gas-liquid separator 39 is separated into gas and liquid and then discharged into the third flow path 72c via the discharge port 44. The hydrogen then flows into the selector valve 52 from the first port 52a of the selector valve 52, which is in the first position P1. The hydrogen that flows into the selector valve 52 flows into the fourth flow path 72d via the second port 52b, due to the selector valve 52 being in the first position P1. With the switching valve 52 in the first position P1, hydrogen does not flow into the branch path 53. Therefore, hydrogen does not flow into the closed loop Q, and the hydrogen that flows into the switching valve 52 flows via the second port 52b of the switching valve 52, through the fourth flow path 72d, the junction H, and the hydrogen supply path 71. In other words, hydrogen discharged from the fuel cell 61 is returned to the hydrogen supply path 71 by the operation of the Roots pump 10. The hydrogen is then supplied to the anode of the fuel cell 61.

<Drying mode>
As shown by arrow Y in FIG. 8 , when the dry mode is executed, the Roots pump 10 is driven, causing hydrogen remaining in the hydrogen circulation path 72 to flow into the rotor chamber 25 of the pump section 38 via the suction port 14d. The hydrogen that flows into the rotor chamber 25 penetrates the clearance between the rotor 22 and the inner surface of the rotor chamber 25. The hydrogen that flows into the rotor chamber 25 is then discharged from the rotor chamber 25 through the discharge port 15c. The pump section 38 of the Roots pump 10 discharges the hydrogen that flows into the second gas-liquid separator 39. The hydrogen that flows into the second gas-liquid separator 39 is sprayed toward the separation tube 42. The hydrogen collides with the separation tube 42, separating some of the moisture from the hydrogen. The hydrogen that has passed through the second gas-liquid separator 39 contains less moisture than the hydrogen that did not pass through the second gas-liquid separator 39. The hydrogen that has passed through the second gas-liquid separator 39 is referred to as "dry gas."

The dry gas is discharged as dry gas into the third flow path 72c via the discharge port 44. The dry gas that flows into the third flow path 72c flows into the switching valve 52 from the first port 52a of the switching valve 52 via the third flow path 72c. With the switching valve 52 in the second position P2, the dry gas that flows into the switching valve 52 flows into the branch path 53 via the third port 52c. In other words, with the switching valve 52 in the second position P2, the dry gas does not flow into the fourth flow path 72d.

The dry gas that flows into the branch line 53 passes through the branch line 53 and is returned to the second flow path 72b upstream of the Roots pump 10 and downstream of the check valve 55 in the hydrogen circulation path 72. At this time, the check valve 55 prevents the dry gas from flowing in the direction opposite to the flow direction J. In other words, the dry gas returned to the second flow path 72b of the hydrogen circulation path 72 is prevented from flowing back into the first gas-liquid separator 64 and the fuel cell 61.

The dry gas returned to the hydrogen circulation path 72 flows back into the pump section 38 of the Roots pump 10. The dry gas that flows into the rotor chamber 25 penetrates the clearance between the rotor 22 and the inner surface of the rotor chamber 25. The dry gas that flows into the rotor chamber 25 is then discharged from the rotor chamber 25 through the discharge hole 15c. When the dry mode is being executed, the dry gas repeatedly flows through the pump section 38 of the Roots pump 10, the second gas-liquid separator 39, the switching valve 52, and the branch path 53 in the above order. In other words, when the dry mode is being executed, the dry gas flows through the closed loop Q. Therefore, when the dry mode is being executed, hydrogen is not returned to the hydrogen supply path 71. Therefore, when hydrogen is not returned from the fuel cell 61 to the hydrogen supply path 71, hydrogen flows through the closed loop Q when the Roots pump 10 is driven.

Each time the dry gas passes through the second gas-liquid separator 39, moisture is removed from the hydrogen and the second gas-liquid separator 39 becomes drier. As a result, in the pump section 38, the dry gas enters the clearance between the rotor 22 and the rotor chamber 25, removing moisture that has entered the clearance and drying the inside of the rotor chamber 25.

According to the second embodiment, it is possible to obtain the same effects as those (1-1) to (1-7) described in the first embodiment.
This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

The drainage channel 65 does not have to be connected to the second gas-liquid separator 39. In this case, the solenoid valve 66 is also omitted. In this case, moisture that has accumulated in the gas-liquid separation chamber 41 of the second gas-liquid separator 39 is directly discharged from the bottom of the second cover member 40 to the outside of the second gas-liquid separator 39.

- Regarding the drainage channel 65 connected to the second gas-liquid separator 39, the second end 65b of the drainage channel 65 may be connected to a drainage tank instead of the first gas-liquid separator 64. When the solenoid valve 66 is opened, moisture accumulated in the gas-liquid separation chamber 41 of the second gas-liquid separator 39 may be discharged to the drainage tank via the drainage channel 65.

The Roots pump 10 does not have to have the second gas-liquid separator 39 integrated into it. In this case, in the first embodiment, the second gas-liquid separator 39 is provided in the second flow path 72b downstream of the check valve 55 in the flow direction J and upstream of the Roots pump 10. In the second embodiment, the second gas-liquid separator 39 is provided in the third flow path 72c downstream of the Roots pump 10 in the flow direction J and upstream of the switching valve 52.

Even when the fuel cell 61 is generating electricity, the control unit 54 may temporarily switch the switching valve 52 to the second position P2 to allow hydrogen to flow through the closed loop Q, or when the drying mode is being executed, the control unit 54 may temporarily switch the switching valve 52 to the first position P1 to prevent hydrogen from flowing through the closed loop Q.

9, the second gas-liquid separator 39 may be provided in the branch passage 53. The second gas-liquid separator 39 is not limited to the configuration described in the embodiment and may be modified as appropriate.
When the drying mode begins, the Roots pump 10 is driven, causing hydrogen remaining in the hydrogen circulation path 72 to be discharged from the pump section 38 of the Roots pump 10 to the third flow path 72c. The hydrogen discharged to the third flow path 72c passes through the third flow path 72c and flows into the switching valve 52 from the first port 52a of the switching valve 52. With the switching valve 52 in the second position P2, the hydrogen that has flowed into the switching valve 52 flows into the branch path 53 via the third port 52c. The hydrogen then flows through the branch path 53 and into the second gas-liquid separator 39. The second gas-liquid separator 39 separates some of the moisture from the hydrogen. After passing through the second gas-liquid separator 39, the hydrogen flows through the branch path 53 as dry gas and is returned to the hydrogen circulation path 72.

The dry gas returned to the hydrogen circulation path 72 flows back into the Roots pump 10. When the drying mode is in operation, the dry gas repeatedly flows through the pump section 38 of the Roots pump 10, the switching valve 52, the branch path 53, and the second gas-liquid separator 39 in the above order. In other words, when the drying mode is in operation, the dry gas flows through the closed loop Q.

The pump may be a screw pump or a scroll pump.
Next, the technical ideas that can be understood from the above-described embodiment and other examples will be described below.
[Aspect 1] A hydrogen circulation system having a fuel cell, a hydrogen supply path that supplies hydrogen to the fuel cell, a hydrogen circulation path that returns hydrogen discharged from the fuel cell to the hydrogen supply path, a first gas-liquid separator that is provided in the hydrogen circulation path and separates hydrogen discharged from the fuel cell from water, a pump that is provided in the hydrogen circulation path and takes in hydrogen discharged from the first gas-liquid separator and discharges hydrogen toward the hydrogen supply path, and a control unit that controls the pump, wherein the hydrogen circulation path includes a first gas-liquid separator that is provided between the pump and the first gas-liquid separator. a check valve that regulates the direction of hydrogen flow, a first branch that is connected to the hydrogen circulation path so as to branch off between the pump and the check valve, and a branch path that connects the first branch to a second branch that straddles the pump and is connected to the hydrogen circulation path, a second gas-liquid separator that separates hydrogen and moisture is provided in a closed loop that includes the pump and the branch path, and a switching valve that switches the flow of hydrogen to the closed loop is provided in the second branch, and the switching valve is controlled by the control unit.

[Aspect 2] A hydrogen circulation system as described in [Aspect 1], wherein the control unit, when returning hydrogen from the fuel cell to the hydrogen supply path, controls the switching valve to return hydrogen discharged from the fuel cell to the hydrogen supply path by driving the pump; when not returning hydrogen from the fuel cell to the hydrogen supply path, controls the switching valve to allow hydrogen to flow in the closed loop by driving the pump for a predetermined time, and stops the pump after the predetermined time has elapsed.

[Aspect 3] A hydrogen circulation system according to [Aspect 1] or [Aspect 2], wherein the second gas-liquid separator is provided on the suction side of the pump in the hydrogen circulation path or in the branch path.
[Aspect 4] A hydrogen circulation system according to any one of [Aspect 1] to [Aspect 3], wherein the second gas-liquid separator is provided integrally with the pump.

[Aspect 5] A hydrogen circulation system according to any one of [Aspects 1] to 4], wherein a drainage channel is connected to the second gas-liquid separator, and the drainage channel is provided with an on-off valve for opening and closing the drainage channel.

Q...closed loop, 10...Roots pump as pump, 39...second gas-liquid separator, 51...hydrogen circulation system, 52...switching valve, 53...branching path, 54...control unit, 55...check valve, 61...fuel cell, 64...first gas-liquid separator, 65...drainage path, 66...solenoid valve, 71...hydrogen supply path, 72...hydrogen circulation path, 531...first branching portion, 532...second branching portion.

Claims (5)

A fuel cell;
a hydrogen supply path for supplying hydrogen to the fuel cell;
a hydrogen circulation path that returns hydrogen discharged from the fuel cell to the hydrogen supply path;
a first gas-liquid separator provided in the hydrogen circulation path for separating hydrogen and water discharged from the fuel cell;
a pump provided in the hydrogen circulation path, which takes in hydrogen discharged from the first gas-liquid separator and discharges the hydrogen toward the hydrogen supply path;
a control unit that controls the pump,
The hydrogen circulation path includes:
a check valve provided between the pump and the first gas-liquid separator to regulate the direction of hydrogen flow;
a first branch portion connected to the hydrogen circulation path so as to branch off between the pump and the check valve, and a branch path connecting the first branch portion to a second branch portion connected to the hydrogen circulation path across the pump,
a second gas-liquid separator for separating hydrogen and water is provided in the closed loop including the pump and the branch path;
a switching valve for switching the flow of hydrogen to the closed loop is provided in the second branch portion;
The switching valve is controlled by the control unit. The control unit
When returning hydrogen from the fuel cell to the hydrogen supply path, the switching valve is controlled so that the hydrogen discharged from the fuel cell is returned to the hydrogen supply path by driving the pump;
2. The hydrogen circulation system according to claim 1, wherein when hydrogen is not returned from the fuel cell to the hydrogen supply path, the switching valve is controlled so that hydrogen flows through the closed loop by driving the pump for a predetermined time, and the pump is stopped after the predetermined time has elapsed. The hydrogen circulation system described in claim 2, wherein the second gas-liquid separator is provided on the suction side of the pump in the hydrogen circulation path or in the branch path. The hydrogen circulation system described in claim 3, wherein the second gas-liquid separator is integrally provided with the pump. The hydrogen circulation system described in claim 3, wherein a drainage channel is connected to the second gas-liquid separator, and the drainage channel is provided with an on-off valve for opening and closing the drainage channel.