JP2008034248A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems that there is difficulty in keeping a suitable moisture content since moisture inside a fuel cell has a possibility of becoming a dried-up state by being evaporated and becoming apt to be discharged in a high temperature state, and has a possibility of becoming a flooding state by being condensed and becoming hard to be discharged in a low temperature state. <P>SOLUTION: This is a fuel cell system equipped with the fuel cell which has a membrane electrode assembly and in which power generation is carried out using a reaction gas, a measuring part in which a measured temperature value is obtained by measuring a temperature in the fuel cell, and a switching part to switch a flow direction of the reaction gas in the membrane electrode assembly so that according to the temperature measured value, it becomes either one of the forward direction which is the gravity direction, or the reverse direction reversed to the forward direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for adjusting the amount of water inside a fuel cell.

  Conventionally, in a fuel cell including a membrane electrode assembly (hereinafter referred to as MEA), the electrolyte membrane contained in the MEA exhibits high proton conductivity in a humid environment, and therefore, a reaction used for an electrochemical reaction. Gases (fuel gas and oxidizing gas) are often humidified. At the cathode of the fuel cell, water is generated by an electrochemical reaction using an oxidizing gas. In a state where the generated water and the water used for humidifying the reaction gas are excessively present in the fuel cell (flooding state), the water acts as a resistance to diffusion of the reaction gas, and the reaction gas is sufficiently supplied to the electrolyte membrane. Can not be supplied to. Therefore, various fuel cells have been proposed that discharge water in the fuel cell depending on the flow of the reaction gas to be supplied (see Patent Documents 1 and 2 below).

JP 2003-142133 A JP 2003-249247 A

  In the fuel cell that discharges the water inside the fuel cell by the flow of the reaction gas as described above, the water inside the fuel cell evaporates when the temperature becomes high during operation, so that the water is easily discharged by the flow of the reaction gas. Become. Therefore, moisture is excessively discharged and the electrolyte membrane is dried (dry-up state), which may cause a decrease in power generation capacity in the MEA. On the other hand, when the fuel cell is at a low temperature at the start of operation or the like, the water inside the fuel cell is condensed, and there is a possibility that the water cannot be sufficiently discharged and a flooding state occurs.

  The present invention has been made in order to solve the above-described conventional problems, and an object of the present invention is to provide a technique that makes it possible to appropriately maintain the moisture content inside the fuel cell.

  In order to achieve the above object, a fuel cell system of the present invention has a membrane electrode assembly, and generates a temperature measurement value by measuring the temperature in the fuel cell, which generates power using a reaction gas. Depending on the temperature measurement value, the flow direction of the reaction gas in the measurement unit and the membrane electrode assembly may be any of a forward direction that is a gravitational direction and a reverse direction that is opposite to the forward direction. The gist of the invention is to include a switching unit that switches so as to be in such a direction.

  Thus, in the fuel cell system of the present invention, the flow direction of the reaction gas in the membrane electrode assembly is set to one of the forward direction and the reverse direction according to the temperature measurement value in the fuel cell. For example, when there is a possibility that the fuel cell may be flooded at a low temperature, it is easy to drain moisture in the fuel cell according to gravity, and the fuel cell becomes dry up at a high temperature. When there is a fear, switching in the opposite direction makes it difficult to drain moisture against gravity, and the moisture content inside the fuel cell can be kept appropriate.

  In the fuel cell system, the switching unit switches the flow direction to the forward direction when the temperature measurement value is higher than a first threshold value, and is lower than a second threshold value. Sometimes, the flow direction may be switched to the opposite direction.

  By doing in this way, when the temperature in the fuel cell is higher than the first threshold value, the direction is switched in the reverse direction, so that it is difficult to discharge moisture inside the fuel cell against gravity. Moreover, since it switches to the gravity direction when it is lower than the 2nd threshold value, it can be made easy to discharge | emit water according to gravity.

  In the fuel cell system, the first threshold value may be higher than the second threshold value.

  In this way, by making the first threshold value and the second threshold value different from each other, the flow direction of the reaction gas is frequently switched when the temperature in the fuel cell is near the threshold value. Can be suppressed. Therefore, it is possible to prevent the reaction gas from being hardly supplied to the fuel cell due to frequent switching of the flow of the reaction gas.

  The fuel cell system may further include a control unit capable of controlling the output power of the fuel cell, and the control unit may reduce the output power when the switching unit switches the flow direction. Good.

  In this way, when the flow direction of the reaction gas is switched, the output power of the fuel cell can be reduced even if the amount of the reaction gas supplied to the fuel cell temporarily decreases compared to that during normal operation. Therefore, the power generation operation of the fuel cell can be suppressed, and the deterioration of the fuel cell can be suppressed.

The fuel cell system further includes another power supply unit different from the fuel cell,
The power supply unit may supply power to a load connected to the fuel cell system so as to compensate for the reduced output power.

  In this way, even if the output power of the fuel cell is temporarily reduced by switching the flow direction of the reaction gas, the power is not reduced with respect to the load connected to the fuel cell system. Can be supplied.

  The present invention can be realized in various forms, for example, a reaction gas supply method, a computer program for realizing the function of the reaction gas supply method or the fuel cell system, and the computer program recorded therein. The present invention can be realized in the form of a recording medium, a data signal including the computer program and embodied in a carrier wave, and the like.

Hereinafter, the best mode for carrying out the present invention will be described in the following order based on examples.
A. First embodiment:
B. Second embodiment:
C. Third embodiment:
D. Fourth embodiment:
E. Variation:

A. First embodiment:
A1. Configuration of fuel cell system:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell system to which the fuel cell of the present invention is applied.
This fuel cell system 200 includes a fuel cell stack 10, a hydrogen tank 201, a radiator 202, an air filter 203, circulation pumps 204 and 206, a gas-liquid separator 205, a temperature sensor 207, an air compressor 260, The control unit 50 is provided. The fuel cell stack 10 is configured by stacking a plurality of fuel cell modules 15 in the horizontal direction. Various control operations of the control unit 50 are realized by a CPU (not shown) executing a computer program stored in a memory (not shown) built in the control unit 50. The fuel cell system 200 is mounted on an electric vehicle and supplies electric power as a power source.

  During the operation of the fuel cell system 200, the fuel cell stack 10 is supplied with a reaction gas and a cooling medium used for an electrochemical reaction. Specifically, air that has passed through the air filter 203 is supplied to the fuel cell stack 10 as an oxidizing gas by an air compressor 260. The oxidizing gas supplied to the fuel cell stack 10 is used for an electrochemical reaction at the cathode of each fuel cell module 15. The used oxidizing gas is discharged to the atmosphere as off-gas.

  There are two routes for supplying the oxidizing gas to the fuel cell stack 10. The first supply route is a route supplied from the pipe 250a via the solenoid valve 220a (hereinafter referred to as “supply order route”), and the second supply route is the pipe via the solenoid valve 220b. This is a route supplied from 250b (hereinafter referred to as “supply reverse route”). In addition, there are two cathode-side off-gas discharge routes. The first discharge route is a route for discharging through the pipe 350a and the electromagnetic valve 320a (hereinafter referred to as “discharge order route”), and the second discharge route is through the pipe 350b and the electromagnetic valve 320b. This is a discharge route (hereinafter referred to as “discharge reverse route”). Which of the supply route and the discharge route is used is determined by the control unit 50 in the oxidizing gas supply direction switching process described later. The electromagnetic valves 220a, 220b, 320a, and 330b described above are controlled to be opened and closed by the control unit 50.

  Further, hydrogen gas as fuel gas is supplied from the hydrogen tank 201 to the fuel cell stack 10. The fuel gas is humidified by a humidifier (not shown) and supplied to the fuel cell stack 10. The fuel gas supplied to the fuel cell stack 10 is used for an electrochemical reaction at the anode of each fuel cell module 15 and then discharged as an off gas. In addition to the hydrogen gas discharged without being used for the electrochemical reaction, the off-gas includes water generated by the electrochemical reaction and water used for humidification. The off-gas is removed from the water in the gas-liquid separator 205 and is circulated again to the fuel cell stack 10 by the circulation pump 204.

  Further, water as a cooling medium is supplied from the radiator 202 to the fuel cell stack 10. The cooling water discharged from the fuel cell stack 10 is sent to the radiator 202 by the circulation pump 206 and is circulated again to the fuel cell stack 10. The temperature sensor 207 measures the temperature of the cooling medium discharged from the fuel cell stack 10 and notifies the control unit 50 of the measured value.

  FIG. 2 is an exploded view showing a detailed configuration of the fuel cell module 15 shown in FIG. The fuel cell module 15 includes a seal-integrated MEA 21 and a separator 25. The fuel cell module 15 is configured by alternately laminating these seal-integrated MEAs 21 and separators 25.

  The seal-integrated MEA 21 includes an MEA portion 60 and a seal portion 61 that surrounds the MEA portion. The MEA unit 60 has an electrolyte membrane. As such an electrolyte membrane, Nafion (registered trademark), Flemion (registered trademark), Aciplex (registered trademark) or the like of a fluororesin ion exchange membrane can be used. In FIG. 2, the seal-integrated MEA 21 has a surface on the anode surface and a back surface on the cathode surface. The seal portion 61 includes a plurality of upper oxidizing gas manifold forming portions 211a provided in the upper portion, a plurality of lower oxidizing gas manifold forming portions 211b provided in the lower portion, a fuel gas supply manifold forming portion 212a, and a cooling medium supply manifold. A forming portion 213a, a fuel gas discharge manifold forming portion 212b, and a cooling medium discharge manifold forming portion 213b are provided. Each of these manifold forming portions 211a, 211b, 212a, 212b, 213a, and 213b is formed as a through portion that penetrates the seal portion 61 in the thickness direction. The seal portion 61 is made of silicon rubber.

  The separator 25 includes an anode side plate 22, an intermediate plate 23, and a cathode side plate 24. The anode side plate 22 faces the anode surface of the seal-integrated MEA 21, and the cathode side plate 24 faces the cathode surface of the seal-integrated MEA (not shown) that is adjacent in the lower part of the drawing. The intermediate plate 23 is sandwiched between the anode side plate 22 and the cathode side plate 24.

  The anode side plate 22 is located at the same position as the seal-integrated MEA 21 at an upper oxidizing gas manifold forming portion 221a, a lower oxidizing gas manifold forming portion 221b, a fuel gas supply manifold forming portion 222a, and a fuel gas discharge manifold forming portion 222b. The cooling medium supply manifold forming part 223a and the cooling medium discharge manifold forming part 223b are provided. Each of these manifold forming portions 221a, 221b, 222a, 222b, 223a, and 223b is formed as a through portion that penetrates the anode side plate 22 in the thickness direction. Further, the anode side plate 22 is provided with a fuel gas supply hole 225 and a fuel gas discharge hole 226 which are long holes in a portion facing the MEA portion 60 of the seal-integrated MEA 21. The fuel gas supply hole 225 and the fuel gas discharge hole 226 are formed as through portions that penetrate the anode side plate 22 in the thickness direction.

  The cathode side plate 24 is located at the same position as the seal-integrated MEA 21 at an upper oxidizing gas manifold forming portion 241a, a lower oxidizing gas manifold forming portion 241b, a fuel gas supply manifold forming portion 242a, and a fuel gas discharge manifold forming portion 242b. The cooling medium supply manifold forming portion 243a and the cooling medium discharge manifold forming portion 243b are provided. Each of these manifold forming portions 241a, 241b, 242a, 242b, 243a, 243b is formed as a through portion that penetrates the cathode side plate 24 in the thickness direction. Further, the cathode side plate 24 includes a plurality of oxidizing gas passage holes 245 provided in the upper portion and a plurality of oxidizing gas passage holes 246 provided in the lower portion. These oxidizing gas passage holes 245 and 246 are formed as penetrating portions that penetrate the cathode side plate 24 in the thickness direction.

  The intermediate plate 23 is located at the same position as the anode side plate 22 and the cathode side plate 24, and includes an upper oxidizing gas manifold forming portion 231a, a lower oxidizing gas manifold forming portion 231b, a fuel gas supply manifold forming portion 232a, and a fuel gas discharge manifold. A forming unit 232b, a cooling medium supply manifold forming unit 233a, and a cooling medium discharge manifold forming unit 233b are provided. Each of these manifold forming portions 231a, 231b, 232a, 232b, 233a, and 233b is formed as a through portion that penetrates the intermediate plate 23 in the thickness direction. Further, the intermediate plate 23 includes a plurality of upper oxidizing gas flow path forming portions 235, a lower oxidizing gas flow path forming portion 236, a fuel gas supply flow path forming portion 237, and a fuel gas discharge flow path forming portion 238. I have. One end of each of these flow path forming portions 235 to 238 communicates with each of the manifold forming portions 231a, 231b, 232a, and 232b. Further, the other ends of the upper oxidizing gas channel forming part 235 and the lower oxidizing gas channel forming part 236 are respectively connected to the oxidizing gas channel hole 245 and the oxidizing gas channel hole 246 formed in the cathode side plate 24 in the laminated state. Communicating with Similarly, the other ends of the fuel gas supply flow path forming part 237 and the fuel gas discharge flow path forming part 238 communicate with the fuel gas supply hole 225 and the fuel gas discharge hole 226 formed in the anode side plate 22, respectively. ing. Further, the intermediate plate 23 includes a plurality of cooling medium flow path forming portions 239 that traverse the intermediate plate 23. And each flow-path formation part 235-239 in the intermediate | middle plate 23 mentioned above is all formed as a penetration part which penetrates the intermediate | middle plate 23 in thickness direction. In addition to the intermediate plate 23, the above-described anode side plate 22 and cathode side plate 24 are both manufactured by forming the above-described through portions in a thin titanium plate.

A2. Operation on the cathode side in the fuel cell module 15:
3 is a cross-sectional view showing the AA cross section in FIG. 2 in a state where the seal-integrated MEA 21 and the separator 25 are stacked. Note that two separators 25a and 25b are shown for easy understanding of the stacked state. The MEA portion 60 of the seal-integrated MEA 21 includes a cathode side gas diffusion layer 60a and an anode side gas diffusion layer 60b with an electrolyte membrane 60c interposed therebetween. The MEA unit 60 includes other catalyst layers and electrodes, but is omitted for convenience of explanation.

  In the example of FIG. 3, the upper oxidizing gas manifold is formed by the upper oxidizing gas manifold forming portions 211a, 241a, 231a, and 221a, and the lower oxidizing gas is formed by the lower oxidizing gas manifold forming portions 221b, 241b, 231b, and 221b. A manifold is formed. Here, in each fuel cell module 15 of the fuel cell stack 10, the oxidizing gas (air) is in the direction of gravity (hereinafter referred to as “forward direction”) and the direction opposite to the direction of gravity (hereinafter referred to as “reverse”). The direction is referred to as “direction”. 4 shows a state in which the oxidizing gas is supplied in the forward direction. The oxidizing gas is supplied from the upper oxidizing gas manifold, and the off-gas is discharged from the lower oxidizing gas manifold. The supply direction of the oxidizing gas is determined by the control unit 50 in the oxidizing gas supply direction switching process described later.

  In addition, a space surrounded by the upper oxidizing gas flow path forming portion 235, which is a penetrating portion in the intermediate plate 23, the anode side plate 22, and the cathode side plate 24 (hereinafter referred to as “upper oxidizing gas flow path”). ) Is formed. One end of the upper oxidant gas channel communicates with the oxidant gas channel hole 245 and the other end communicates with the upper oxidant gas manifold. Similarly, a space (hereinafter referred to as “lower oxidant gas flow path”) surrounded by the lower oxidant gas flow path forming part 236, the anode side plate 22, and the cathode side plate 24 is formed. . One end of the lower oxidant gas flow path communicates with the oxidant gas flow path hole 246, and the other end communicates with the lower oxidant gas manifold. Note that a space (hereinafter referred to as “cooling medium flow path”) surrounded by the cooling medium flow path forming portion 239, which is a through-hole in the intermediate plate 23, the anode side plate 22, and the cathode side plate 24. A plurality are formed. Water, which is a cooling medium, flows through the cooling medium flow path to cool each fuel cell module 15.

  Part of the oxidizing gas (air) flowing through the upper oxidizing gas manifold flows into the upper oxidizing gas channel from the upper oxidizing gas manifold forming portion 231a in the intermediate plate 23 of the separator 25b, and passes through the oxidizing gas channel hole 245. It is supplied to the cathode-side gas diffusion layer 60a of the seal-integrated MEA 21. The supplied air is diffused over the entire electrolyte membrane 60c from the top to the bottom in accordance with the gas flow and gravity, and is supplied to the electrochemical reaction. After the electrochemical reaction, surplus air flows into the lower oxidizing gas channel through the oxidizing gas channel hole 246 of the cathode side plate 24 of the separator 25b shown in FIG. 4, and passes through the lower oxidizing gas manifold to the fuel cell stack. 10 is discharged to the outside.

  Here, when the temperature of the fuel cell module 15 becomes high during operation, the water inside the fuel cell module 15 is likely to evaporate, and there is a possibility that a large amount of water is discharged according to the gas flow and gravity, resulting in a dry-up state. Therefore, the fuel cell system 200 is configured to adjust the moisture content in the fuel cell module 15 by performing an oxidizing gas supply direction switching process described later.

A3. Oxidation gas supply direction switching processing:
FIG. 4 is a flowchart showing the procedure of the oxidizing gas supply direction switching process in the fuel cell system 200. When the user turns on the ignition switch of the electric vehicle, the oxidizing gas supply direction switching process is started in the fuel cell system 200. In addition, after the ignition switch is turned on, the reaction gas (hydrogen gas and air) is supplied to the fuel cell stack 10. When the oxidizing gas supply direction switching process shown in FIG. 4 is started, the control unit 50 shown in FIG. 1 controls each electromagnetic valve 220a, 220b, 320a, 320b, and the oxidizing gas supply direction becomes the forward direction. (Step S505).

  FIG. 5 is an explanatory view showing the open / close state of each solenoid valve when the supply direction of the oxidizing gas is the forward direction. As shown in FIG. 5, the control unit 50 controls the solenoid valve 220a to open and closes the solenoid valve 220b, so that the oxidizing gas is supplied to the fuel cell stack 10 through the supply order route. In this case, as shown in FIG. 3, the oxidizing gas is supplied to each fuel cell module 15 through the upper oxidizing gas manifold, and as shown in FIG. 5, the oxidizing gas is present on the cathode side plate 24 (opposite surface of the seal-integrated MEA 21). Are fed in the forward direction (from top to bottom). Then, oxidizing gas (off-gas) is discharged from each fuel cell module 15 through the lower oxidizing gas manifold. At this time, as shown in FIG. 5, the control unit 50 controls the solenoid valve 320a to open and the solenoid valve 320b to close, so that off-gas is discharged from the fuel cell stack 10 in the discharge order route.

  Immediately after the start of the operation of the fuel cell system 200, the temperature of the fuel cell module 15 is low, so that the moisture inside the fuel cell module 15 is condensed, and it is difficult for the moisture to be discharged together with the oxidizing gas as water vapor. However, by setting the supply direction of the oxidizing gas to the forward direction, it is possible to make the water discharge direction and the gravity direction coincide with each other and to easily discharge the condensed water. Therefore, the flooding state can be suppressed.

  After step S505, the control unit 50 acquires the measured value T measured by the temperature sensor 207 (FIG. 1) (step S510). This measured value indicates the temperature of the cooling medium discharged from the fuel cell stack 10 and is considered to be substantially equal to the temperature in the fuel cell module 15. Next, the control unit 50 determines whether or not the ignition switch is turned off (step S515). If the operation is being continued, the control unit 50 determines whether or not the measurement value T acquired earlier is lower than 70 ° C. (step S530). Immediately after the start of operation or in a low temperature environment, the temperature in the fuel cell module 15 is lower than 70 ° C. In this case, the control unit 50 determines whether or not the oxidizing gas is being supplied in the forward direction (step S525). As described above, when the supply direction is not switched after step S505, the control unit 50 returns to step S510 and acquires the measurement value T again.

  When the temperature in the fuel cell module 15 becomes higher than 70 ° C. for a while after the start of operation, the control unit 50 determines in step S520 that the measured value T is not lower than 70 ° C. In this case, the control unit 50 switches the supply direction of the oxidizing gas so as to be the opposite direction (step S545). As described above, when the supply direction of the oxidizing gas is the forward direction, the supply direction is switched to be the reverse direction.

  FIG. 6 is an explanatory diagram showing the open / close state of each solenoid valve when the supply direction of the oxidizing gas is the reverse direction. As shown in FIG. 6, by controlling the electromagnetic valve 220a to be closed and the electromagnetic valve 220b to be opened, the oxidizing gas is supplied to the fuel cell stack 10 through the reverse supply route. In this case, contrary to FIG. 3, the oxidizing gas is supplied to each fuel cell module 15 through the lower oxidizing gas manifold, and as shown in FIG. 6, the oxidizing gas is present on the cathode side plate 24 (surface facing the seal-integrated MEA 21). Are fed in the reverse direction (from bottom to top). Then, oxidizing gas (off-gas) is discharged from each fuel cell module 15 through the upper oxidizing gas manifold. At this time, the control unit 50 performs control so as to close the electromagnetic valve 320a and open the electromagnetic valve 320b, whereby the off-gas is discharged from the fuel cell stack 10 through the reverse discharge route.

  When the temperature of the fuel cell module 15 rises to 70 ° C. or higher, the moisture in the fuel cell module 15 is likely to evaporate due to an increase in the amount of saturated water vapor, and the moisture is easily discharged together with the oxidizing gas. However, by setting the supply direction of the oxidizing gas in the reverse direction, the water discharge direction can be opposite to the direction of gravity, and the discharge of evaporated water can be suppressed. Therefore, the dry-up state can be suppressed.

  In addition, when the temperature of the fuel cell module 15 decreases again to 70 ° C. or lower after the temperature has increased in this way, the control unit 50 determines in step S525 that it is not being supplied in the forward direction. . In this case, since the control unit 50 switches the supply direction in step S545, the supply direction of the oxidizing gas is switched to the forward direction. When the ignition switch is turned off (step S515: YES), the oxidizing gas supply direction switching process ends.

  As described above, in the fuel cell system 200, the supply direction of the oxidizing gas is switched between the forward direction and the reverse direction according to the temperature of the fuel cell module 15, so that the inside of the fuel cell module 15 is in a dry-up state or a flooding state. Can be suppressed, and the amount of water in the fuel cell module 15 can be appropriately maintained.

B. Second embodiment:
FIG. 7 is a flowchart showing the procedure of the oxidizing gas supply direction switching process in the second embodiment. The procedure of the second embodiment is obtained by adding step S519 between steps S515 and S520 of FIG. 4, and the other procedures are the same as those of the first embodiment. In the first example, only “whether or not the measured value T is higher than 70 ° C.” is determined in step S520, but in the second example, “the measured value T is higher than 70 ° C.”. In addition to “whether it is high”, it is a configuration that performs a two-stage determination of “whether the measured value T is lower than 65 ° C.”. The configuration of the fuel cell system in the second embodiment is the same as that of the fuel cell system 200 in the first embodiment.

  Specifically, for example, when the temperature of the fuel cell module 15 rises to 71 ° C. after the start of operation, it is determined in step S519 shown in FIG. 7 that the measured value T is not lower than 65 ° C., and Since it is determined in step S520 that the measured value T is higher than 70 ° C., the supply direction is switched from the forward direction to the reverse direction (step S545). Thereafter, when the temperature of the fuel cell module 15 slightly decreases to 70 ° C., it is determined in step S520 that the measured value T is not higher than 70 ° C. In this case, the process returns to step S510. Further, when the temperature of the fuel cell module 15 decreases and becomes lower than 65 ° C., it is determined in step S525 that the supply direction of the oxidizing gas is not the forward direction, and the supply direction is switched from the reverse direction to the forward direction. (Step S545).

  Thus, in this embodiment, two threshold values (high threshold value and low threshold value) are provided for the measurement value T. The measured value T is higher than the high threshold value (70 ° C.). However, the measured value T decreases as the temperature of the fuel cell module 15 decreases, and the lower threshold value (65 ° C.). The supply direction is switched when the value falls below. Also, the measured value T was lower than 65 ° C., but the measured value T increased with the temperature rise of the fuel cell module 15, and the supply direction when the measured value T exceeded a high threshold (70 ° C.). Is switched. Therefore, when the measured value T is near the threshold value, it is possible to suppress frequent switching of the supply direction of the oxidizing gas. Therefore, it is possible to avoid a state in which the oxidizing gas is not supplied to the fuel cell stack 10 from any supply route due to frequent opening and closing of each electromagnetic valve.

C. Third embodiment:
FIG. 8 is a flowchart showing the procedure of the oxidizing gas supply direction switching process in the third embodiment. The procedure of the third embodiment is such that step S540 is added before step S545 of FIG. 7 and steps S550 and S555 are added after step S545. The other procedures are the same as those of the second embodiment. Is the same. When the supply direction of the oxidizing gas is switched, the supply amount of the oxidizing gas is temporarily lower than the supply amount during normal operation as the supply route is switched. In such a case, if the fuel cell stack 10 is requested to have the same electric power as in normal operation and the power generation is promoted, the fuel cell module 15 is deteriorated. Therefore, in this embodiment, the output power of the fuel cell stack 10 (hereinafter also simply referred to as “FC power”) is reduced when the supply direction is switched. The configuration of the fuel cell system in the third embodiment is the same as that of the fuel cell system 200 in the first embodiment.

  FIG. 9 is an explanatory diagram showing a schematic configuration of a vehicle including the fuel cell system 200 in the third embodiment. The vehicle 100 includes a power supply system 20, a load unit 30, and a control unit 50. The power supply system 20 supplies electric power as a power source for the vehicle 100. The load unit 30 converts the supplied electric power into mechanical power for driving the vehicle 100. The control unit 50 controls the power supply system 20 and the load unit 30.

  The power supply system 20 includes a fuel cell system 200, a secondary battery 26, and a DC-DC converter 27. The load unit 30 includes an accelerator 37, an accelerator sensor 35 that measures the amount of depression (also referred to as accelerator opening) Wt of the accelerator 37, a drive circuit 36, a motor 31, a gear mechanism 32, and wheels 34. Yes. The drive circuit 36 is a circuit for driving the motor 31, and is composed of, for example, a transistor inverter. The power generated by the motor 31 is transmitted to the wheels 34 via the gear mechanism 32. The drive circuit 36 converts the DC power supplied from the power supply system 20 into three-phase AC power and supplies it to the motor 31. The magnitude of the supplied three-phase AC power is determined by the control unit 50 according to the input from the accelerator sensor 35 (accelerator opening Wt). In the first and second embodiments described above, the control unit 50 is a part of the fuel cell system 200. However, in the present embodiment, the control unit 50 exists separately from the fuel cell system 200. The control unit 50 is electrically connected to the DC-DC converter 27 and the drive circuit 36 in addition to the fuel cell system 200, and executes various controls including control of these circuits.

  As shown in FIG. 8, when the measured value T is lower than 65 ° C. and the oxidizing gas supply direction is reverse, or when the measured value T is higher than 70 ° C. and the oxidizing gas supply direction is forward. First, the control unit 50 reduces the FC power before switching the supply direction in step S545 (step S540). Then, the controller 50 determines whether or not a predetermined time has elapsed after switching the supply direction of the oxidizing gas in step S545 (step S550), and returns the reduced FC power when the predetermined time has elapsed ( Step S555). The reason why the FC power is returned after a predetermined time has elapsed is as follows. That is, since the supply amount of the oxidizing gas to each fuel cell module 15 returns to the supply amount during normal operation after a while after the supply direction is switched, the fuel cell module 15 is not deteriorated even if the FC power is returned. . Hereinafter, a specific method for reducing the FC power will be described.

  FIG. 10A shows the relationship between the FC voltage that is the output voltage of the fuel cell system 200 and the FC current that is the output current, and FIG. 10B shows the power supply state of the fuel cell system 200. ing. As shown in FIG. 10A, for the fuel cell system 200 (fuel cell stack 10), as the FC voltage-FC current characteristic, the FC current decreases as the FC voltage increases, and the FC current decreases as the FC voltage decreases. There is a growing relationship. Specifically, when the FC voltage is V0, the FC current is I0 and the FC power is P0. When the FC voltage decreases to V1, the FC current increases to I1, and the FC power increases to P1. However, even if the FC voltage further decreases from V1, the increase in the FC current is being saturated, and the FC power that is the product of the FC current and the FC voltage starts to decrease. The power supply system 20 is configured so that the FC voltage does not become less than the minimum operation voltage Vmin in order to protect the fuel cell system 200. As a result, the fuel cell system 200 is operated at an output voltage between the open circuit voltage OCV and the operation minimum voltage Vmin.

  Utilizing such FC voltage-FC power characteristics, the power supply system 20 reduces the FC power by increasing the FC voltage. For example, if the FC voltage during normal operation is V1, the FC power is reduced by increasing the FC voltage to V0 when switching the oxidizing gas supply direction. The boosting of the FC voltage is performed by adjusting the output voltage of the DC-DC converter 27 connected in parallel with the fuel cell system 200.

  Here, in the power supply system 20 shown in FIG. 9, both the secondary battery 26 and the fuel cell system 200 can supply electric power to the load unit 30 (drive circuit 36). Then, the control unit 50 adjusts the output voltage value of the DC-DC converter 27 to adjust the power supply amount of the secondary battery 26 and the fuel cell system 200, and the drive request power is supplied to the drive circuit 36. Control to supply.

  Specifically, as shown in FIG. 10B, when the output voltage of the DC-DC converter 27 (FC voltage of the fuel cell system 200 connected in parallel) is V1, a drive request is made by FC power P1. The electric power Pt can be sufficiently supplied. Therefore, only the fuel cell system 200 supplies power to the load unit 30. However, as described above, when the output voltage (FC voltage) of the DC-DC converter 27 is boosted to V0 in order to reduce the FC power, the drive request power Pt cannot be supplied with the FC power P0 alone. In this case, when the secondary battery 26 supplies the differential power (Pt−P0), the required drive power Pt can be supplied to the load unit 30. The surplus power (P0-Pt) when the FC voltage is V1 is stored in the secondary battery 26 via the DC-DC converter 27.

  As described above, in the third embodiment, since the FC power is reduced when the oxidant gas supply direction is switched, it is possible to suppress the deterioration of the fuel cell module 15 due to the reduction in the supply amount of the oxidant gas. In addition, even when the FC power is reduced, the required drive power can be supplied to the load unit 30 by supplying power from the secondary battery.

D. Fourth embodiment:
FIG. 11 is an explanatory diagram showing an oxidizing gas flow on the cathode separator surface in the fourth embodiment. In each of the above-described embodiments, as shown in FIGS. 5 and 6, the oxidizing gas flows linearly in either the forward direction or the reverse direction on the cathode side plate 24 (the surface facing the seal-integrated MEA 21). However, in this embodiment, although it is not linear, it is configured to flow in the forward direction or the reverse direction as a whole.

  The cathode side plate 24 ′ shown in FIG. 11 is a so-called serpentine separator, and includes a serpentine channel 249 having a plurality of channels meandering. Both ends of the serpentine channel 249 communicate with the upper oxidizing gas manifold forming portion 241a 'and the lower oxidizing gas manifold forming portion 241b'. When the supply direction of the oxidizing gas is the forward direction, as shown in FIG. 11A, the oxidizing gas supplied from the upper oxidizing gas manifold forming portion 241a ′ is meandering along the serpentine flow path 249 while lowering the oxidizing gas. It flows to the manifold forming portion 241b ′ and is discharged. On the other hand, when the supply direction of the oxidizing gas is the reverse direction, as shown in FIG. 11B, the oxidizing gas supplied from the lower oxidizing gas manifold forming portion 241b ′ meanders along the serpentine flow path 249. It flows and is discharged from the upper oxidizing gas manifold forming portion 241a ′.

  Even in such a configuration, when the temperature of the fuel cell module 15 is relatively low, the oxidant gas supply direction is set to the forward direction, so that the moisture discharge direction as a whole can be set to the forward direction. Can be suppressed. Further, when the temperature of the fuel cell module 15 is relatively high, the supply direction of the oxidizing gas is reversed, so that the moisture discharge direction can be reversed as a whole, and the dry-up state is suppressed. can do.

E. Variation:
In addition, elements other than the elements claimed in the independent claims among the constituent elements in each of the above embodiments are additional elements and can be omitted as appropriate. The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

E1. Modification 1:
In each of the above-described embodiments, the supply direction of the reaction gas (oxidizing gas) is switched only on the cathode side. ) May be switched. Specifically, as in the above-described embodiments, when the temperature of the fuel cell module 15 is relatively low, the fuel gas supply direction on the anode side plate 22 (opposite surface of the seal-integrated MEA 21) is the forward direction, When the temperature of the fuel cell module 15 is relatively high, the supply direction may be reversed. By doing in this way, it can suppress that it becomes a flooding state or a dry-up state also about the anode side, and can keep the moisture content in the fuel cell module 15 appropriately.

E2. Modification 2:
In each of the above-described embodiments, when the ignition switch is turned off, the oxidizing gas supply direction switching processing is completed. However, the present invention is not limited to this, and the oxidizing gas supply direction is forcibly limited. Alternatively, the fuel cell stack 10 may be configured so as to end after supplying the oxidizing gas for a predetermined time without generating power in the forward direction. With such a configuration, water remaining in the fuel cell stack 10 can be sufficiently discharged after the operation of the fuel cell system 200 is completed. Therefore, it is possible to suppress a decrease in gas diffusibility at the time of low-temperature starting due to such residual moisture. The reason why the supply direction is forced to be forward is to discharge a large amount of moisture with the supply direction of the oxidizing gas as the forward direction because the temperature of the fuel cell module 15 decreases as power generation stops.

E3. Modification 3:
In the third embodiment described above, the secondary battery 26 is provided as means for supplying power to the load unit 30 in addition to the fuel cell system 200. However, the present invention is not limited to the secondary battery. It may be the composition provided with other electric power supply means. For example, it can also be set as the structure provided with a capacitor instead of the secondary battery 26. FIG.

E4. Modification 4:
In each of the embodiments described above, a threshold value is provided for the measurement value T, and when the measurement value T becomes higher (or lower) than the threshold value, the supply direction of the oxidizing gas is switched. There is no need to use a threshold value, and the supply direction of the oxidizing gas may be generally switched according to the temperature of the fuel cell module 15. Specifically, for example, when the temperature rises by a predetermined temperature or more compared to the previous measurement value T or when the temperature decreases by a predetermined temperature or more compared to the previous measurement value T, the supply direction of the oxidizing gas is switched. You can also. Even in such a configuration, it is possible to suppress a flooding state or a dry-up state by obtaining and setting an appropriate predetermined temperature through experiments or the like.

E5. Modification 5:
In each of the above-described embodiments, the fuel cell system 200 includes the fuel cell stack 10 in which a plurality of fuel cell modules 15 are stacked. However, the fuel cell system 200 may include only one fuel cell module 15. . Even with such a configuration, the moisture inside the fuel cell module 15 can be appropriately maintained.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows schematic structure of the fuel cell system to which the fuel cell of this invention is applied. FIG. 2 is an exploded view showing a detailed configuration of the fuel cell module 15 shown in FIG. 1. Sectional drawing which shows the AA cross section in FIG. 2 in the state which laminated | stacked seal integrated MEA21 and the separator 25. FIG. 5 is a flowchart showing the procedure of an oxidizing gas supply direction switching process in the fuel cell system. Explanatory drawing which shows the opening / closing state of each solenoid valve when the supply direction of oxidizing gas is a forward direction. Explanatory drawing which shows the opening / closing state of each solenoid valve in case the supply direction of oxidizing gas is a reverse direction. The flowchart which shows the procedure of the oxidizing gas supply direction switching process in a 2nd Example. The flowchart which shows the procedure of the oxidizing gas supply direction switching process in a 3rd Example. Explanatory drawing which shows schematic structure of a vehicle provided with the fuel cell system 200 in a 3rd Example. Explanatory drawing which shows the FC voltage-FC current characteristic and electric power supply state of the fuel cell system 200. FIG. Explanatory drawing which shows the oxidizing gas flow on the cathode side separator surface in a 4th Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell stack 15 ... Fuel cell module 20 ... Power supply system 21 ... Seal-integrated MEA
DESCRIPTION OF SYMBOLS 22 ... Anode side plate 23 ... Intermediate | middle plate 24 ... Cathode side plate 25 ... Separator 30 ... Load part 31 ... Motor 32 ... Gear mechanism 34 ... Wheel 35 ... Accelerator sensor 36 ... Drive circuit 37 ... Accelerator 40 ... Radiator 50 ... Control part 60 DESCRIPTION OF SYMBOLS MEA part 60a ... Cathode side gas diffusion layer 60b ... Anode side gas diffusion layer 60c ... Electrolyte membrane 61 ... Seal part 100 ... Vehicle 200 ... Fuel cell system 201 ... Hydrogen tank 202 ... Radiator 203 ... Air filter 204, 206 ... Circulation pump 205 ... Gas-liquid separator 207 ... Temperature sensor 220a, 220b, 320a, 320b ... Solenoid valve 250a, 250b, 350a, 350b ... Pipe 260 ... Air compressor

Claims (6)

A fuel cell system,
A fuel cell having a membrane electrode assembly and generating power using a reaction gas;
A measurement unit for measuring a temperature in the fuel cell to obtain a temperature measurement value;
Depending on the temperature measurement value, the flow direction of the reaction gas in the membrane electrode assembly may be any one of a forward direction that is a gravity direction and a reverse direction that is opposite to the forward direction. A switching unit that switches so that
A fuel cell system comprising: The fuel cell system according to claim 1, wherein
The switching unit switches the flow direction to the forward direction when the temperature measurement value is higher than a first threshold value, and changes the flow direction when the temperature measurement value is lower than a second threshold value. Switch to the opposite direction,
Fuel cell system. The fuel cell system according to claim 2, wherein
The first threshold value is higher than the second threshold value.
Fuel cell system. The fuel cell system according to any one of claims 1 to 3, further comprising:
A control unit capable of controlling the output power of the fuel cell;
The control unit reduces the output power when the switching unit switches the flow direction.
Fuel cell system. The fuel cell system according to claim 4, further comprising:
Comprising another power supply unit different from the fuel cell,
The power supply unit supplies power to a load connected to the fuel cell system so as to compensate for the reduced output power.
Fuel cell system. A reaction gas supply method for supplying the reaction gas to a fuel cell having a membrane electrode assembly and generating power using the reaction gas,
(A) measuring a temperature in the fuel cell to obtain a temperature measurement value;
(B) according to the temperature measurement value, the flow direction of the reaction gas in the membrane electrode assembly is any one of a forward direction that is a gravity direction and a reverse direction that is opposite to the forward direction. Switching to be in the direction;
A reaction gas supply method comprising:

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