JP2009146709A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system for preventing a device at a downstream side of a fuel cell from freezing. <P>SOLUTION: The fuel cell system 1 includes a fuel cell stack 10, a compressor 31 (fuel cell scavenging means) for scavenging the fuel cell stack 10 after stopping power generation of the fuel cell stack 10, and a compressor 31 (downstream device scavenging means) for scavenging the device such as a backpressure valve 33 at a downstream of the fuel cell stack 10 after completing scavenging of the fuel cell stack 10 by the fuel cell scavenging means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

  In recent years, a fuel cell such as a polymer electrolyte fuel cell (PEFC) that generates electricity by supplying hydrogen (fuel gas) to the anode and oxygen-containing air (oxidant gas) to the cathode. Development is thriving.

  When such a fuel cell generates power, water (steam) is generated at the cathode. Further, in order to maintain the wet state of the electrolyte membrane (solid polymer membrane), the hydrogen and air toward the fuel cell are humidified by a humidifier equipped with a hollow fiber membrane. Therefore, the inside of the fuel cell, the equipment associated therewith, and the piping connecting them are humid. Therefore, in order to prevent freezing in the fuel cell and the like after power generation is stopped, a technique for scavenging the inside of the fuel cell and the like after power generation is stopped has been proposed (see Patent Document 1).

JP 2003-331893 A (Claim 8)

  However, when the fuel cell is scavenged, a large amount of water is discharged from the fuel cell. After that, when the scavenging is stopped, the water may freeze in a device downstream of the fuel cell (for example, a back pressure valve).

  Therefore, an object of the present invention is to provide a fuel cell system that prevents freezing in a device downstream of the fuel cell.

  As means for solving the problems, the present invention provides a fuel cell, a fuel cell scavenging means for scavenging the fuel cell after power generation of the fuel cell is stopped, and a scavenging of the fuel cell by the fuel cell scavenging means. And a downstream device scavenging means for scavenging a device downstream of the fuel cell after completion.

  Here, the devices (equipment) downstream of the fuel cell include not only equipment such as a back pressure valve, a diluter, and a purge valve, but also piping connecting them. The scavenging of the fuel cell and the downstream device is to push out moisture remaining in the scavenging gas, and air, nitrogen or the like is used as the scavenging gas.

  According to such a fuel cell system, after the fuel cell scavenging means completes the scavenging of the fuel cell, the downstream device scavenging means scavenges the downstream device of the fuel cell, and the water in the downstream device (water vapor, condensed water, etc.) ) To the outside. This prevents the moisture from freezing in the downstream device thereafter. Therefore, piping and the like constituting the downstream device are not blocked by freezing, and the back pressure valve and the like are prevented from becoming inoperable due to freezing. Therefore, even if the fuel cell system is restarted, the downstream device can be operated favorably, the reaction gas (fuel gas, oxidant gas) can be suitably supplied to the fuel cell, and the fuel cell system can be restarted well.

Further, a scavenging condition that is at least one of the scavenging gas total volume flow rate and scavenging time in scavenging by the downstream device scavenging means is set in a device downstream of the fuel cell at the completion of scavenging of the fuel cell by the fuel cell scavenging means. A fuel cell system comprising scavenging condition calculation means for calculating based on a moisture content.
It is.

According to such a fuel cell system, the scavenging condition calculation means sets the scavenging condition that is at least one of the scavenging gas total volume flow rate and the scavenging time in the scavenging by the downstream device scavenging means to complete the scavenging of the fuel cell by the fuel cell scavenging means. Appropriate calculation can be made based on the amount of water in the device downstream of the fuel cell at the time.
Then, by operating the downstream device scavenging means in accordance with the scavenging condition that is the calculation result, it is possible to prevent unnecessary energy consumption (electric power in the embodiment described later) and unnecessary operation noise from being generated by the downstream device scavenging means.

  In addition, the scavenging condition calculation means calculates the water amount as a total of the power generation time of the fuel cell, the integrated power generation amount of the fuel cell, the scavenging time by the fuel cell scavenging means, and the scavenging gas by the fuel cell scavenging means. The fuel cell system is calculated based on at least one of a volume flow rate.

  According to such a fuel cell system, the scavenging condition calculation means determines the amount of water in the downstream device at the completion of scavenging of the fuel cell, the power generation time of the fuel cell, the accumulated power generation amount of the fuel cell, and the fuel cell scavenging means. It can be appropriately calculated based on at least one of the scavenging time and the total volume flow rate of the scavenging gas by the fuel cell scavenging means.

  Further, in the fuel cell system, when it is estimated that the generated water is not substantially generated in the fuel cell before power generation is stopped, the downstream device scavenging means does not perform scavenging.

According to such a fuel cell system, for example, when it is estimated that the generation time before the power generation stop is short and the generated water is not substantially generated in the fuel cell before the power generation stop, the downstream device scavenging means performs the scavenging. do not do. Thereby, wasteful energy consumption by the downstream device scavenging means can be reduced, and generation of unnecessary operating noise can be prevented.
Note that, as in the embodiment described later, when it is estimated that the generated water is not substantially generated in the fuel cell before the power generation is stopped, the fuel cell scavenging means may not perform the scavenging of the fuel cell.

  The device further includes a back pressure valve provided downstream of the oxidant gas flow path of the fuel cell, and the back pressure valve is opened and closed during scavenging by the downstream device scavenging means. System.

  According to such a fuel cell system, during scavenging by the downstream device scavenging means, the back pressure valve opens and closes, that is, the valve body of the back pressure valve is operated to the open side and the close side, so that water droplets adhering to the back pressure valve are shaken. While dropping, pressure fluctuation is caused in the scavenging gas flowing in the downstream device, pulsation is given to the scavenging gas and the like, and the moisture discharging property can be enhanced.

  Further, the scavenging gas from the downstream device scavenging means toward the device includes a bypass passage that bypasses the fuel cell.

  According to such a fuel cell system, when scavenging by the downstream device scavenging means, the scavenging gas bypasses the fuel cell via the bypass passage, so that the scavenging gas toward the downstream device causes a pressure loss from the fuel cell. I will not receive it. This allows the downstream device scavenging means to operate without being overloaded. Moreover, it is possible to prevent the MEA (particularly, the electrolyte membrane) of the fuel cell from being excessively dried.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell system which prevents the freezing in the device downstream of a fuel cell can be provided.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

≪Configuration of fuel cell system≫
A fuel cell system 1 according to this embodiment shown in FIG. 1 is mounted on a fuel cell vehicle (moving body) (not shown). The fuel cell system 1 includes a fuel cell stack 10, an anode system that supplies and discharges hydrogen (fuel gas) to and from the anode of the fuel cell stack 10, and air containing oxygen to the cathode of the fuel cell stack 10 (oxidant) Gas), a scavenging gas system that guides the scavenging gas from the cathode system to the anode system during scavenging, a bypass system that bypasses the cathode passage 12, and power consumption that consumes the power generated by the fuel cell stack 10. A system and an ECU 80 (Electronic Control Unit) that electronically controls these systems are provided.

<Fuel cell stack>
The fuel cell stack 10 is a stack formed by stacking a plurality of (for example, 200 to 400) solid polymer type single cells, and the plurality of single cells are electrically connected in series. The single cell includes an MEA (Membrane Electrode Assembly) and two conductive anode separators and cathode separators sandwiching the MEA.
The MEA includes an electrolyte membrane (solid polymer membrane) made of a monovalent cation exchange membrane or the like, and an anode and a cathode sandwiching the electrolyte membrane. The anode and cathode are mainly composed of a conductive porous material such as carbon paper, and contain a catalyst (Pt, Ru, etc.) for causing an electrode reaction in the anode and cathode.

The anode separator is formed with a through-hole (called an internal manifold) extending in the stacking direction of the single cells and a groove extending in the surface direction of the single cells in order to supply and discharge hydrogen to the anode of each MEA. These through holes and grooves function as the anode channel 11 (fuel gas channel).
The cathode separator is formed with a through-hole (referred to as an internal manifold) extending in the stacking direction of the single cells and a groove extending in the surface direction of the single cells in order to supply and discharge air to and from the cathode of each MEA. These through holes and grooves function as the cathode channel 12 (oxidant gas channel).

When hydrogen is supplied to each anode via the anode flow path 11, the electrode reaction of Formula (1) occurs, and when air is supplied to each cathode via the cathode flow path 12, Formula (2) Thus, a potential difference (OCV (Open Circuit Voltage), open circuit voltage) is generated in each single cell. Next, when the fuel cell stack 10 and an external circuit such as the traveling motor 61 are electrically connected and a current is taken out, the fuel cell stack 10 generates power.
Part of the water (water vapor) generated at the cathode permeates the electrolyte membrane and moves to the anode. Therefore, the cathode off-gas discharged from the cathode and the anode off-gas discharged from the anode are humid.
2H ₂ → 4H ⁺ + 4e ⁻ (1)
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (2)

<Anode system>
The anode system includes a hydrogen tank 21 (fuel gas supply means), a normally closed shut-off valve 22, an ejector 23, a normally closed purge valve 24, and a temperature sensor 25.
The hydrogen tank 21 is connected to the inlet of the anode channel 11 through a pipe 21a, a shutoff valve 22, a pipe 22a, an ejector 23, and a pipe 23a in this order. The piping 22a is provided with a pressure reducing valve (not shown) for reducing hydrogen to a predetermined pressure. When the shutoff valve 22 is opened by the ECU 80, hydrogen in the hydrogen tank 21 is supplied to the anode flow path 11 via the pipe 21a and the like.

  A pipe 23 b is connected to the outlet of the anode channel 11, and the downstream end of the pipe 23 b is connected to the suction port of the ejector 23. Then, the anode off-gas containing unreacted hydrogen discharged from the anode channel 11 is returned to the ejector 23 through the pipe 23b, and after being mixed with hydrogen from the hydrogen tank 21 in the ejector 23, the anode channel 11 is supplied again. As a result, hydrogen circulates through the anode flow path 11 to effectively use hydrogen.

  The middle of the pipe 23b is connected to the diluter 34 through the pipe 24a, the purge valve 24, and the pipe 24b. When the ECU 80 determines that the voltage (cell voltage) of the single cell detected by a voltage sensor (not shown) decreases and the anode off gas contains a large amount of impurities (water vapor, nitrogen, etc.), the purge valve 24 is controlled by the ECU 80. Opened, the anode off gas containing impurities is discharged to the diluter 34 via the pipes 24a and 24b.

The temperature sensor 25 is provided in the pipe 23b through which the anode off gas flows, detects the temperature in the pipe 23b as the fuel cell stack 10 and / or the system temperature, and outputs the detected temperature to the ECU 80. Yes.
However, the position of the temperature sensor 25 is not limited to this, and may be provided in a pipe 32b described later, a pipe (not shown) through which the refrigerant discharged from the fuel cell stack 10 flows, or in the fuel cell stack 10 itself.

<Cathode system>
The cathode system includes a compressor 31 (oxidant gas supply means), a humidifier 32, a back pressure valve 33, and a diluter 34.
The compressor 31 is connected to the inlet of the cathode flow path 12 via the pipe 31a, the humidifier 32, and the pipe 32a. When the compressor 31 operates in accordance with a command from the ECU 80, it takes in oxygen-containing air and supplies it to the cathode flow path 12. It is like that.
The compressor 31 functions as a fuel cell scavenging means when scavenging the anode channel 11 and the cathode channel 12 of the fuel cell stack 10. Then, after the scavenging of the fuel cell stack 10 is completed, it functions as a downstream device scavenging means when scavenging devices downstream of the fuel cell stack 10 (such as the back pressure valve 33).
The compressor 31 is powered by the fuel cell stack 10 and / or a high voltage battery 64 described later.

  The outlet of the cathode channel 12 is connected to the diluter 34 via a pipe 32b, a humidifier 32, a pipe 32c, a back pressure valve 33, and a pipe 33a in this order. The humid cathode off gas discharged from the cathode channel 12 is supplied to the diluter 34 through the pipe 32b and the like.

  The humidifier 32 includes a hollow fiber membrane 32d for exchanging moisture between the air traveling from the compressor 31 toward the cathode flow path 12 and the air flowing toward the cathode flow path 12 and the humid cathode offgas. Further, a bypass pipe (not shown) for connecting the pipe 31a and the pipe 32a is provided, and scavenging from the compressor 31 during scavenging of the fuel cell stack 10 and scavenging of devices such as the back pressure valve 33. Gas flows through the bypass pipe and bypasses the humidifier 32.

The back pressure valve 33 is a valve controlled by the ECU 80 to balance the gas pressure in the anode flow path 11 and the gas pressure in the cathode flow path 12 (back pressure of the back pressure valve 33). Composed.
The diluter 34 is a container for diluting hydrogen in the anode off-gas introduced when the purge valve 24 is opened with the cathode off-gas (dilution gas), and has a dilution space therein. The diluted gas is discharged out of the vehicle through the pipe 34a. The pipe 34a is provided with a silencer (silencer) not shown.

<Devices downstream of the fuel cell stack>
Here, the downstream devices of the fuel cell stack 10 in this embodiment include a downstream device on the anode side and a downstream device on the cathode side. Specifically, the downstream device on the anode side includes a pipe 24a, a purge valve 24, and a pipe 24b. The downstream device on the cathode side includes a pipe 32b, a humidifier 32, a pipe 32c, a back pressure valve 33, a pipe 33a, a diluter 34, and a pipe 34a.

<Scavenging system>
The scavenging system is a system that guides the scavenging gas (non-humidified air) from the compressor 31 to the anode system when scavenging the fuel cell stack 10 and devices downstream of the fuel cell stack 10. I have. The upstream side of the scavenging valve 41 is connected to the pipe 31a via the pipe 41a, and the downstream side of the scavenging valve 41 is connected to the pipe 23a via the pipe 41b.
When scavenging the fuel cell stack 10 or the like, for example, while the system is stopped, if the system temperature detected by the temperature sensor 25 is less than 0 ° C. and the inside of the fuel cell stack 10 is likely to freeze, the ECU 80 causes the compressor 31 to The scavenging valve 41 is set to open while operating.

<Bypass system>
The bypass system (bypass passage) bypasses (bypasses) the scavenging gas from the compressor 31 to the cathode flow path 12 of the fuel cell stack 10 when scavenging a downstream device (back pressure valve 33 or the like) on the cathode side. This system includes a bypass valve 51 that is opened by the ECU 80 during bypass. The upstream of the bypass valve 51 is connected to the pipe 32a via the pipe 51a, and the downstream of the bypass valve 51 is connected to the pipe 32b via the pipe 51b.
In addition, instead of the bypass valve 51, a three-way valve may be provided at the joining position of the pipe 51b and the pipe 32b, and the three-way valve may be appropriately opened and closed to be bypassed.

<Power consumption system>
The power consumption system is a system that consumes the power generated by the fuel cell stack 10, and includes a travel motor 61, a contactor 62, an output detector 63, and a high voltage battery 64.
The travel motor 61 is connected to an output terminal (not shown) of the fuel cell stack 10 via a contactor 62 and an output detector 63, and the high voltage battery 64 is connected between the travel motor 61 and the contactor 62. Yes. The travel motor 61 is a power source of the fuel cell vehicle, and the contactor 62 is a switch for turning on / off the electrical connection between the fuel cell stack 10 and the travel motor 61 by the ECU 80. That is, when the contactor 62 is turned off, no current is taken out from the fuel cell stack 10, and the power generation of the fuel cell stack 10 is stopped.

  The output detector 63 detects an output current and an output voltage of the fuel cell stack 10, and includes a current sensor and a voltage sensor. The output detector 63 is configured to output an output current and an output voltage to the ECU 80. The ECU 80 detects the output current and the output voltage, and generates power (W, power generation) or integrated power generation ( Wh, integrated power generation amount) is appropriately calculated.

  The high-voltage battery 64 is composed of a lithium ion type secondary battery, and stores the surplus generated power of the fuel cell stack 10 and the regenerative power of the travel motor 61, or charges when the generated power of the fuel cell stack 10 is low. Electric power is discharged to assist the fuel cell stack 10.

<IG>
The IG 71 is a start switch for the fuel cell vehicle and the fuel cell system 1 and is provided around the driver's seat. Moreover, IG71 is connected with ECU80, and ECU80 detects the ON / OFF signal of IG71.

<ECU>
The ECU 80 (scavenging condition calculation means) is a control device that electronically controls the fuel cell system 1, and includes a CPU, a ROM, a RAM, various interfaces, an electronic circuit, and the like, and a program stored therein. Accordingly, various devices are controlled and various processes are executed.
The specific control contents by the ECU 80 will be described in detail below with reference to the flowchart of FIG.

≪Operation of fuel cell system≫
Next, the operation of the fuel cell system 1 will be described with reference mainly to FIG.
When the IG 71 is turned off, the processing shown in the flowchart of FIG. 2 starts. Further, before the IG 71 is turned off (initial state), the contactor 62 is turned on, and the fuel cell stack 10 generates power in response to a power generation request from the driver. In addition, here, a case where after the scavenging of the cathode flow path 12 and the anode flow path 11 is performed, the downstream devices (back pressure valve 33, piping 32b, etc.) on the cathode side are scavenged.

  In step S101, the ECU 80 detecting the OFF signal of the IG 71 turns off the contactor 62. Thereby, the power generation of the fuel cell stack 10 is stopped.

In step S102, the ECU 80 determines whether or not the current system temperature detected via the temperature sensor 25 is a low temperature (for example, less than 0 degrees). The determination reference temperature for determining that the temperature is low is a temperature at which the fuel cell stack 10 may be frozen thereafter, and is determined by a preliminary test or the like.
When it is determined that the system temperature is low (S102 / Yes), the process of the ECU 80 proceeds to step S104. On the other hand, when it is determined that the system temperature is not low (S102, No), the process of the ECU 80 proceeds to step S103.

In step S103, the ECU 80 determines whether or not a predetermined time Δt1 (for example, 30 minutes to 1 hour) has elapsed after the determination in step S102.
When it is determined that the predetermined time Δt1 has elapsed (S103: Yes), the processing of the ECU 80 proceeds to step S102. As a result, even if the temperature is not low immediately after the power generation is stopped (No in S102), a determination process for determining whether or not the temperature is low is executed every predetermined time Δt1 (S103 / Yes). Is prevented.
On the other hand, when it is determined that the predetermined time Δt1 has not elapsed (S103, No), the ECU 80 repeats the determination in step S103.

In step S104, the ECU 80 determines whether or not generated water is generated in the fuel cell stack 10 due to the electrode reaction accompanying the power generation in the power generation of the fuel cell stack 10 before the power generation is stopped.
Specifically, due to the power generation time of the fuel cell stack 10 determined by the internal clock of the ECU 80, the IG 71 is turned off in a short time after the IG 71 is turned on (so-called choking), so the power generation time of the fuel cell stack 10 before the stop is If it is short (for example, 3 minutes or less), it is determined that the generated water is hardly generated. Further, even when the power generation is stopped before the warm-up of the fuel cell stack 10 is completed after starting in a low temperature environment (for example, less than 0 ° C.), it is determined that the generated water accompanying the power generation is not substantially generated.

If it is determined that generated water is generated (Yes at S104), the process of the ECU 80 proceeds to step S105.
On the other hand, when it is determined that almost no generated water is generated (S104, No), the process of the ECU 80 proceeds to the end. Thus, when almost no generated water is generated and the process proceeds to the end, the cathode scavenging in step S105, the anode scavenging in step S107, and the scavenging of the downstream device in step S111 are omitted. Thereby, the compressor 31 is not operated unnecessarily, the operation sound of the compressor 31 is reduced, and the power consumption of the high voltage battery 64 can be suppressed.

  In step S105, the ECU 80 starts scavenging the cathode flow path 12 (cathode scavenging). Specifically, the ECU 80 increases the rotational speed of the compressor 31 for the cathode scavenging (see FIG. 6), introduces the scavenging gas from the compressor 31 into the cathode channel 12, and the moisture (product water, etc.) in the cathode channel 12 ). Then, the amount of water in the device downstream of the fuel cell stack 10 once increases and then gradually decreases (see FIG. 6).

  The execution time of the cathode scavenging is calculated based on the power generation time of the fuel cell stack 10 before the stop, the elapsed time after the power generation stop, the temperature of the fuel cell stack 10 when the power generation is stopped, and the map of FIG. . The map of FIG. 3 is obtained by a preliminary test or the like and is stored in the ECU 80 in advance. Then, as shown in FIG. 3, the longer the power generation time of the fuel cell stack 10 is, the longer the cathode scavenging execution time is calculated.

The cathode scavenging execution time calculated in this way is corrected as appropriate based on the temperature of the fuel cell stack 10 when power generation is stopped and / or the elapsed time after power generation is stopped. Specifically, the lower the temperature of the fuel cell stack 10 when power generation is stopped, the easier it is for condensed water to be generated in the fuel cell stack 10, so that the cathode scavenging execution time is corrected. Further, if the elapsed time after the stop of power generation becomes longer, the temperature of the fuel cell stack 10 decreases, and the amount of generated condensed water increases, so that the cathode scavenging execution time is corrected.
The execution time of scavenging (anode scavenging) of the anode flow path 11 to be described later is similarly calculated.

In step S106, the ECU 80 determines whether or not the cathode scavenging has been completed, that is, whether or not the cathode scavenging time determined based on the map of FIG. 3 has elapsed since the start of the cathode scavenging in step S105. .
When it is determined that the cathode scavenging has been completed (S106 / Yes), the processing of the ECU 80 proceeds to step S107. On the other hand, when it is determined that the cathode scavenging has not been completed (No at S106), the ECU 80 repeats the determination at Step S107.

In step S107, the ECU 80 starts scavenging the anode flow path 11 (anode scavenging). Specifically, the ECU 80 increases the rotational speed of the compressor 31 for anode scavenging (see FIG. 6), opens the scavenging valve 41 and the purge valve 24, and introduces the scavenging gas from the compressor 31 into the anode flow path 11. Then, moisture (product water or the like) in the anode channel 11 is pushed out. Then, the amount of water in the device downstream of the fuel cell stack 10 once increases and then gradually decreases (see FIG. 6).
Note that the rotational speed of the compressor 31 during anode scavenging is set higher than during cathode scavenging and during downstream device scavenging (see FIG. 6).

In step S108, the ECU 80 determines whether or not the anode scavenging has been completed, that is, whether or not the anode scavenging time determined based on the map in FIG. 3 has elapsed since the start of the anode scavenging in step S107. .
When it is determined that the anode scavenging has been completed (Yes in S108), the process of the ECU 80 proceeds to step S109. Thus, when progressing to step S109, in this embodiment, it is determined by ECU80 (fuel cell scavenging completion determination means) that scavenging of the fuel cell stack 10 has been completed.
On the other hand, when it is determined that the anode scavenging has not been completed (No at S108), the ECU 80 repeats the determination at Step S108.

In step S109, the ECU 80 (scavenging condition calculation means) calculates the amount of water remaining in the devices (back pressure valve 33, diluter 34, pipe 32b, etc.) downstream of the fuel cell stack 10 when scavenging is completed.
Specifically, the ECU 80 generates power generation time of the fuel cell stack 10 (and / or integrated power generation (Wh, integrated power generation amount) of the fuel cell stack 10), cathode scavenging time, anode scavenging time before stopping, Based on the map in FIG. 4, the amount of moisture remaining in the device downstream of the fuel cell stack 10 is calculated. Further, instead of or in addition to the cathode scavenging time and the anode scavenging time, the moisture content may be calculated based on the total volume flow rate of the scavenging gas during the cathode scavenging and the anode scavenging.
Note that the total volume flow rate of the scavenging gas during the cathode scavenging and the anode scavenging can be obtained, for example, from the product of the discharge amount (L / min) of the scavenging gas discharged from the compressor 31 and the operation time. In addition, a flow rate sensor can be provided in the pipes 23a, 31a and the like.

The map of FIG. 4 is obtained by a preliminary test or the like and is stored in the ECU 80 in advance. As shown in FIG. 4, the longer the power generation time of the fuel cell stack 10, the larger the accumulated power generation (integrated power generation amount), and the shorter the cathode / anode scavenging time (the smaller the total volume flow rate of the scavenging gas), the more the fuel cell. The amount of moisture remaining in the device downstream of the stack 10 is increased.
This is because, as the power generation time of the fuel cell stack 10 is longer and the accumulated power generation (accumulated power generation amount) is larger, the generated water accompanying the power generation is increased and the amount of water remaining in the downstream device is increased. Also, the shorter the cathode / anode scavenging time (the smaller the total volume flow rate of the scavenging gas), the easier it is for the water pushed out of the fuel cell stack 10 to remain in the downstream device.

  In step S110, the ECU 80 (scavenging condition calculating means) determines the scavenging time (and / or the total amount of scavenging gas) of the device downstream of the fuel cell stack 10 based on the moisture amount calculated in step S109 and the map of FIG. Volume flow) is calculated. The map of FIG. 5 is obtained by a preliminary test or the like and is stored in advance in the ECU 80. Further, as shown in FIG. 5, the scavenging time (total volume flow rate of scavenging gas) increases as the amount of water downstream of the fuel cell stack 10 increases.

In step S111, the ECU 80 starts scavenging of the downstream device (such as the back pressure valve 33) on the cathode side of the fuel cell stack 10 (see FIG. 6). Specifically, the ECU 80 operates the compressor 31 at the rotational speed for scavenging the downstream device, opens the back pressure valve 33, supplies the downstream device (back pressure valve 33 and the like), and pushes moisture inside the vehicle out of the vehicle. . As a result, the amount of water in the downstream device gradually decreases (see FIG. 6).
The rotational speed (scavenging gas discharge flow rate) of the compressor 31 is related to the channel cross-sectional area of the downstream device, the water repellency of the channel, and the like, and is obtained by a preliminary test or the like. Further, the rotational speed of the compressor 31 is set higher than the rotational speed (necessary scavenging gas discharge flow rate) necessary for reliably discharging the remaining water (see FIG. 6).

  In this case, the ECU 80 appropriately opens and closes the back pressure valve 33, that is, reciprocates the valve body of the back pressure valve 33 in the open side and the close side. Thereby, the water droplets adhering to the valve body of the back pressure valve 33 are shaken off, and the back pressure valve 33 is prevented from freezing. Further, when the back pressure valve 33 is opened and closed in this manner, the pressure of the scavenging gas passing through the back pressure valve 33 fluctuates, the scavenging gas pulsates, and the pipes 32c and 33a connected to the back pressure valve 33 pulsate. Can increase the sex.

  In this case, the ECU 80 opens the bypass valve 51. Then, the scavenging gas from the compressor 31 bypasses the cathode flow path 12, that is, flows into the pipe 32b from the pipe 32a via the pipe 51a and the pipe 51b. As a result, the scavenging gas can flow into the pipe 32b without receiving pressure loss from the cathode flow path 12, and the compressor 31 can operate without being overloaded. In addition, overdrying of the MEA (particularly the electrolyte membrane) of the fuel cell stack 10 can be prevented.

In step S112, the ECU 80 sets the scavenging time obtained in step S110 (and / or the total volume flow rate of the scavenging gas) and the scavenging time after starting scavenging in step S111 (and / or the total volume flow rate of the scavenging gas). Based on this, it is determined whether or not scavenging of the downstream device on the cathode side of the fuel cell stack 10 has been completed.
Note that erroneous determination can be prevented by determining completion based on both the scavenging time and the total volume flow rate of the scavenging gas.

  If it is determined that scavenging of the device is completed (S112 / Yes), the processing of the ECU 80 proceeds to the end. On the other hand, when it is determined that scavenging of the device has not been completed (No at S112), the ECU 80 repeats the determination at Step S112.

≪Effect of fuel cell system≫
According to such a fuel cell system 1, the following effects are obtained.
After the scavenging of the cathode channel 12 and the anode channel 11 is completed, the devices such as the back pressure valve 33, the diluter 34, and the pipe 32b arranged downstream of the cathode channel 12 are scavenged, and the moisture in the inside is pushed out. Therefore, it is possible to prevent moisture from freezing in these devices.
As a result, the operation of the back pressure valve 33 or the like becomes immobile due to freezing, the inside of the humidifier 32 freezes and cannot be humidified or is damaged, the dilution performance of the diluter 34 decreases due to freezing of the dilution space, piping It is prevented that 32b etc. are blocked by freezing. Therefore, after that, when the IG 71 is turned on and the system is restarted, the back pressure valve 33 and the like can be operated favorably, air can be suitably supplied to the cathode flow path 12, and the fuel cell stack 10 can be regenerated.

Further, the amount of water in the downstream device at the completion of scavenging of the fuel cell stack 10 is determined based on the power generation time of the fuel cell stack 10, the integrated power generation amount, the scavenging time of the fuel cell stack 10, and the total volume flow rate of the scavenging gas. It can be calculated appropriately.
Then, based on the calculated moisture content, the scavenging time (and / or the total volume flow rate of the scavenging gas) of the device downstream of the fuel cell stack 10 is appropriately calculated, and the compressor 31 is appropriately operated accordingly. be able to.

  Further, in the fuel cell stack 10 before power generation is stopped, when generated water is not substantially generated, cathode scavenging, anode scavenging, and downstream device scavenging are not executed, so that unnecessary power consumption and operation noise by the compressor 31 are suppressed. be able to.

  Furthermore, at the time of scavenging the downstream device, by opening and closing the back pressure valve 33, it is possible to improve the water discharging property. Further, since the scavenging gas bypasses the cathode passage 12, it is possible to prevent the MEA from being excessively dried while operating without overloading the compressor 31.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and can be modified, for example, as follows without departing from the spirit of the present invention. May be combined as appropriate.

  In the above-described embodiment, the case where the devices (back pressure valve 33 and the like) downstream of the cathode flow path 12 are scavenged after scavenging of the fuel cell stack 10 is illustrated, but scavenging is performed after scavenging of the fuel cell stack 10 is completed. The valve 41 may also be opened, and devices downstream of the anode channel 11 (such as the purge valve 24) may be scavenged. In this case, the piping 23 a and the piping 23 b may be connected by a bypass piping (bypass passage) so that the scavenging gas bypasses the anode flow path 11.

  In the above-described embodiment, when scavenging the fuel cell stack 10, the case of executing the cathode scavenging and the anode scavenging in this order is exemplified, but the order of the anode scavenging and the cathode scavenging may be used. Further, only one of the cathode scavenging and the anode scavenging may be executed, and then the downstream device may be scavenged.

  In the embodiment described above, the compressor 31 includes the fuel cell scavenging means for scavenging the cathode flow path 12 and the anode flow path 11 of the fuel cell stack 10 and the downstream device scavenging means for scavenging a device downstream of the cathode flow path 12. Although the case where the function is demonstrated was illustrated, it is not limited to this, For example, it is good also as a structure provided with another compressor and a nitrogen tank as a downstream device scavenging means.

  In the above-described embodiment, the case where the fuel cell system 1 is mounted on a fuel cell vehicle has been illustrated. However, for example, a fuel cell system mounted on a motorcycle, a train, or a ship may be used. Moreover, a stationary fuel cell system for home use or a fuel cell system incorporated in a hot water supply system may be used.

It is a figure which shows the structure of the fuel cell system which concerns on this embodiment. It is a flowchart which shows the scavenging operation | movement of the fuel cell system which concerns on this embodiment. It is a map which shows the relationship between the electric power generation time of a fuel cell stack, and cathode / anode scavenging time (scavenging gas total volume flow). It is a map which shows the relationship between the electric power generation time (integrated electric power generation) of a fuel cell stack, a cathode (anode) scavenging time, and the moisture content in the device downstream of a fuel cell stack. It is a map which shows the relationship between the moisture content in the device downstream of a fuel cell stack, and scavenging time (total volume flow rate of scavenging gas). It is a time chart which shows one operation example in the scavenging operation | movement of the fuel cell system which concerns on this embodiment.

Explanation of symbols

1 Fuel Cell System 10 Fuel Cell Stack (Fuel Cell)
24 Purge valve (downstream device)
31 Compressor (fuel cell scavenging means, downstream device scavenging means)
33 Back pressure valve (downstream device)
24a, 24b, 33a, 32c, 33a, 34a Piping (downstream device)
34 Diluter (downstream device)
41 Scavenging valve 51 Bypass valve 51a, 51b Piping (bypass passage)
80 ECU (scavenging condition calculation means)

Claims (6)

A fuel cell;
Fuel cell scavenging means for scavenging the fuel cell after power generation of the fuel cell is stopped;
Downstream device scavenging means for scavenging devices downstream of the fuel cell after completion of scavenging of the fuel cell by the fuel cell scavenging means;
A fuel cell system comprising: The scavenging condition that is at least one of the scavenging gas total volume flow rate and scavenging time in scavenging by the downstream device scavenging means is the amount of water in the device downstream of the fuel cell at the completion of scavenging of the fuel cell by the fuel cell scavenging means The fuel cell system according to claim 1, further comprising a scavenging condition calculation unit that calculates based on The scavenging condition calculating means calculates the water content, the power generation time of the fuel cell, the integrated power generation amount of the fuel cell, the scavenging time by the fuel cell scavenging means, and the total volume flow rate of the scavenging gas by the fuel cell scavenging means. The fuel cell system according to claim 2, wherein the fuel cell system is calculated based on at least one of the following. The downstream device scavenging means does not perform scavenging when it is estimated that the generated water is not substantially generated in the fuel cell before power generation is stopped. The fuel cell system described. The device includes a back pressure valve provided downstream of the oxidant gas flow path of the fuel cell,
The fuel cell system according to any one of claims 1 to 4, wherein the back pressure valve is opened and closed during scavenging by the downstream device scavenging means. The fuel cell system according to any one of claims 1 to 5, wherein the scavenging gas from the downstream device scavenging means toward the device includes a bypass passage that bypasses the fuel cell.

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