JP2009070576A - Fuel cell system and deterioration detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system in which the partial progress of the deterioration of a catalyst layer in a shutdown process of a fuel cell is controlled and the deterioration of the fuel cell is controlled. <P>SOLUTION: The fuel cell system is provided with a wetting processing means for humidifying a reaction gas supplied to a fuel cell and put it into a wet state, and a drying processing means for putting the reaction gas supplied to the fuel cell into a dry state of lower humidity than the wet state. The fuel cells system conducts shutdown processing to supply the reaction gas to the fuel cell when an operation of the fuel cell is shut down. When the shutdown processing is conducted, the fuel cell system can select either a wetting processing mode in which the reaction gas is put into a wetting state or a drying processing mode in which the reaction gas is put into a drying processing condition. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell system and a fuel cell deterioration detection device. More specifically, the present invention relates to a fuel cell system provided with a power generator including an electrolyte membrane and a pair of electrodes disposed on both sides thereof.

  In a fuel cell in which produced water is generated in an electrochemical reaction, such as a fuel cell using an electrochemical reaction between hydrogen and oxygen, in a reaction gas (fuel and air) passage (anode passage and cathode passage) There is a lot of moisture. Therefore, when the operation of the fuel cell is stopped and the temperature becomes low (below freezing point) during the stop, it is conceivable that the water staying in the reaction gas passage is frozen. Such freezing of moisture in the fuel cell may cause damage or deterioration of the power generation unit, or cause a shortage of fuel by inhibiting the flow of reaction gas at the next start of the fuel cell. Conceivable.

  To solve such a problem, for example, when stopping the operation of the fuel cell, the remaining moisture is removed by flowing a dry gas into the reaction gas passage in the fuel cell to prepare for the start-up at the next freezing point. It is considered.

  However, the electrolyte membrane of the fuel cell may be deteriorated by excessive drying, and it is difficult to wet the once dried electrolyte membrane. When the electrolyte membrane is in a state of insufficient moisture, the electrical conductivity of the electrolyte membrane is lowered, and therefore, particularly when the fuel cell is started, the electrochemical reaction cannot be advanced, and the fuel cell cannot be started.

  In order to prevent the electrolyte membrane from drying, it is conceivable to suppress the flow rate of the dry gas when performing a process of scavenging the reaction gas passage with the dry gas when the fuel cell is stopped. However, Japanese Patent Application Laid-Open No. 2004-199988 points out that if the flow rate of the dry gas is suppressed in this way, it takes time to reach an appropriate wet state, and it takes a long time to stop the fuel cell. Yes. In order to solve such a problem, in the fuel cell system of this prior art, it is disclosed that wet gas with adjusted humidity is supplied to each of the anode flow path and the cathode flow path during the stop process.

  Specifically, in this prior art fuel cell system, the relative humidity of the reaction gas can be adjusted to 15 to 95% in each of the supply paths of the reaction gas supplied to the anode electrode and the cathode electrode. A vessel is placed. At the time of stopping the fuel cell, the humidity of the reaction gas supplied to each of the anode electrode and the cathode electrode is humidified to a predetermined humidity by the humidifier so that the water in the electrolyte membrane is in an equilibrium state.

  For example, it is determined that the electrolyte membrane is too dry in the high temperature and high resistance region. In this case, the humidity of the reaction gas is set high so that the electrolyte membrane is in an appropriate wet state. On the other hand, in the case of low temperature and low resistance, it is determined that moisture remains in the gas diffusion layer. In this case, the humidity of the reaction gas is set low, and excess water staying in the diffusion layer or the like is removed, so that the electrolyte membrane is in an appropriate wet state.

Japanese Patent Laid-Open No. 2004-199988 JP-A-2005-251441 JP 2005-317211 A

  According to the above prior art, depending on the temperature, resistance, etc. of the fuel cell, the reaction gas used in the scavenging process at the time of stopping is in a dry state or a wet state, thereby removing moisture in the reaction gas passage, The electrolyte membrane can be in an appropriate wet state. Thus, it is considered that the power generation performance at the next start-up and the deterioration of the electrolyte membrane due to freezing can be prevented to some extent.

  By the way, even when the reaction gas passage is scavenged with dry gas when the fuel cell is stopped, a certain amount of moisture exists in the catalyst layer and the electrolyte membrane. When the fuel cell is exposed to below freezing point, it is considered that the presence of the moisture causes the catalyst layer to deteriorate. As the deterioration of the catalyst layer progresses, it is considered that the power generation performance of the fuel cell is lowered. Therefore, it is desirable that a process for suppressing the deterioration of the catalyst layer is taken when stopping below freezing point. In this respect, the above-described prior art treatment is effective in preventing a decrease in startability due to moisture freezing in the reaction gas passage when the fuel cell is stopped and in preventing deterioration of the electrolyte membrane. It does not relate to prevention of deterioration of the catalyst layer due to exposure to the environment.

  The present invention has been made to solve the above-described problems, and prevents freezing or the like when the fuel cell is stopped to prevent deterioration of the electrolyte membrane or the diffusion layer, and detects deterioration occurring in the catalyst layer. An object of the present invention is to provide an improved fuel cell system that can suppress the deterioration.

In order to achieve the above object, a first invention is a fuel cell system,
Wet treatment means for humidifying the reaction gas supplied to the fuel cell to a wet state;
A drying treatment means for bringing the reaction gas supplied to the fuel cell into a dry state having a lower humidity than the wet state;
Stop control means for performing a stop process for supplying a reaction gas to the fuel cell when stopping the operation of the fuel cell;
A function of controlling the wet processing mode in which the reactive gas is in the wet state and a dry processing mode in which the reactive gas is in the dry state, and when the operation of the fuel cell is stopped, the wet processing mode or Mode control means capable of selecting and switching the drying processing mode;
It is characterized by providing.

According to a second aspect of the present invention, in the first aspect of the present invention, the apparatus further comprises a freeze prediction means for predicting whether or not the water in the fuel cell is in a frozen state during which the fuel cell is stopped,
When it is predicted that the mode control means will be activated in the frozen state at the next activation, the stop process is executed in any one of the drying process mode and the wet process mode. It is characterized by controlling so that.

  According to a third invention, in the first or second invention, the mode control means is configured so that the stop process in the drying mode and the stop process in the wet mode are alternately performed a specified number of times. It is characterized by switching between the drying mode and the wet mode.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, it is detected that a switching state for switching to the stop process in the dry mode or the wet mode is made according to the operating state of the fuel cell. Further comprising a switching state detecting means,
When the switching state is detected, the mode control means switches the mode so that the next stop process is a stop process in a mode different from the mode in the previous stop process. .

  In a fifth aspect based on the fourth aspect, the mode control means sets the wet mode when the stop process is executed in the initial state of the fuel cell, and after the switching state is detected. The mode is switched from the stop process to the stop process in the drying mode.

  In a fourth aspect based on the fourth aspect, the mode control means sets the drying mode when the stop process is executed in the initial state of the fuel cell, and after the switching state is detected. The mode is switched from the stop process to the stop process in the wet mode.

  In a seventh aspect based on the fourth aspect, the switching state detecting means detects the switching state by detecting deterioration of the fuel cell.

An eighth invention according to any one of the fourth to seventh inventions, further comprising voltage detection means for detecting the voltage of the fuel cell,
The switching state detection means detects the switching state when the detected voltage is smaller than a reference voltage.

According to a ninth invention, in the first or second invention, the fuel cell is disposed on both sides of the power generation unit including an electrolyte membrane and a pair of electrodes disposed on both sides of the electrolyte membrane. Equipped with a separator
The separator having a contact surface in contact with one electrode of the pair of electrodes includes a reaction gas channel for supplying a reaction gas to the one electrode on the contact surface,
The fuel cell system includes:
Inlet performance detection means for detecting power generation performance on the inlet side of the reaction gas flow path during operation of the fuel cell;
Outlet performance detection means for detecting power generation performance on the outlet side of the reaction gas flow path during operation of the fuel cell;
By detecting the deterioration of the fuel cell based on the difference between the power generation performance on the inlet side and the power generation performance on the outlet side, the mode is switched to the dry mode or the wet mode. Switching state detecting means for detecting that
When the switching state is detected, the mode control means switches the mode so that the next stop process is a stop process in a mode different from the mode in the previous stop process. .

According to a tenth aspect, in the first or second aspect, the fuel cell is disposed on both sides of the power generation unit including an electrolyte membrane and a pair of electrodes disposed on both sides of the electrolyte membrane. Equipped with a separator
The separator having a contact surface in contact with one electrode of the pair of electrodes includes a reaction gas channel for supplying a reaction gas to the one electrode on the contact surface,
The fuel cell system includes:
An inlet voltage detecting means for detecting an inlet voltage that is a voltage on the inlet side of the reaction gas flow path during operation of the fuel cell;
During operation of the fuel cell, outlet voltage detection means for detecting an outlet voltage which is a voltage on the outlet side of the reaction gas flow path;
An inlet / outlet voltage difference calculating means for calculating an inlet / outlet voltage difference which is a value obtained by subtracting the outlet voltage from the inlet voltage;
A switching state detecting means for detecting that the mode is switched to the drying mode or the wet mode when the absolute value of the inlet / outlet voltage difference is larger than a reference voltage difference; When the switching state is detected, the mode control means switches the mode so that the next stop process is a stop process in a mode different from the mode in the previous stop process. Features.

In an eleventh aspect based on the tenth aspect, the switching state detecting means comprises:
When the inlet / outlet voltage difference is larger than the first inlet / outlet voltage difference, a drying switching state for switching the mode to the drying mode is detected,
When the inlet / outlet voltage difference is smaller than the second inlet / outlet voltage difference, detecting a wet switching state for switching the mode to the wet mode;
The mode control means includes
When the wet switching state is detected, the mode in the next stop process is switched to the wet mode,
When the drying switching state is detected, the mode is switched so that the mode in the next stop process becomes the drying mode.

In a twelfth aspect according to the first or second aspect, during operation of the fuel cell, a first voltage at a first current of the fuel cell and a second voltage at a second current greater than the first current Voltage detecting means for detecting
Voltage difference calculating means for calculating a voltage difference that is a value obtained by subtracting a second voltage from the first voltage;
A drying switching state for controlling the mode to the drying mode when the mode control means selects the wet mode and the voltage difference is greater than a first reference voltage difference; Switching state detecting means for detecting that
The mode control unit controls the mode in the next stop process to be the drying mode when the drying switching state is detected.

In a thirteenth aspect based on the first or second aspect, during the operation of the fuel cell, the first voltage at the first current and the second voltage at the second current larger than the first current of the fuel cell. Voltage detecting means for detecting
Voltage difference calculating means for calculating a voltage difference which is a value obtained by subtracting a second voltage from the first voltage;
When the mode control means selects the drying mode, and the voltage difference is smaller than the second reference voltage difference, the wet switching for controlling the mode to the wet mode Switching state detecting means for detecting that the state is in a state,
The mode control unit controls the mode in the next stop process to be the wet mode when the wet switching state is detected.

In a fourteenth aspect based on the first or second aspect, during operation of the fuel cell, the fuel cell includes a first voltage at a first current and a second voltage at a second current greater than the first current. Voltage detecting means for detecting
Voltage difference calculating means for calculating a voltage difference which is a value obtained by subtracting the second voltage from the first voltage;
A switching state detecting means for detecting a drying switching state for switching the mode to the drying mode when the voltage difference is larger than a first reference voltage difference;
When the voltage difference is smaller than a second reference voltage difference, a wet switching state for switching the mode to the wet mode is detected;
The mode control means includes
When the wet switching state is detected, the mode is controlled so that the mode in the next stop process becomes the wet mode,
When the drying switching state is detected, the mode is controlled so that the mode in the next stop process becomes the drying mode.

According to a fifteenth aspect, in the first or second aspect, voltage detection means for detecting a first voltage in the first current of the fuel cell and a second voltage in a second current larger than the first current;
Voltage difference detection means for detecting a voltage difference which is a value obtained by subtracting the second voltage from the first voltage;
Determining means for determining whether the voltage difference is in a normal state not less than the second reference voltage difference and not more than the first reference voltage difference;
A deterioration detecting means for detecting deterioration of the fuel cell when the voltage difference is not recognized to be in the normal state;
It is characterized by providing.

  According to the first invention, when the fuel cell is stopped, when the stop gas is supplied to the fuel cell and the stop process is performed, the wet mode in which the reaction gas supplied to the fuel cell is humidified to be in a wet state, or It is possible to set the drying process mode to a dry state rather than a wet state. By the way, when the catalyst layer is deteriorated when the fuel cell is stopped or after starting, it is considered that the portion where the deterioration occurs depends on whether the stop process is performed in the wet mode or the dry mode. Therefore, by switching the fuel cell stop processing mode from the wet mode to the dry mode, it is possible to prevent the partial deterioration caused by the dry state or the wet state from proceeding rapidly only in that portion. it can. Therefore, it is possible to suppress the performance deterioration of the entire fuel cell and improve the durability.

  For example, it is considered that the deterioration of the catalyst layer while the fuel cell is stopped is caused by droplets remaining in the catalyst layer, expansion due to freezing of water around the catalyst layer, or growth of ice by taking in surrounding water. Therefore, as in the second aspect of the invention, particularly when it is predicted that the fuel cell is frozen while the fuel cell is stopped, the stop process is executed in either the dry mode or the wet mode. To control. Thereby, the mode can be controlled so that the mode in the stop process does not concentrate on one of the dry mode and the wet mode. Therefore, the progress of partial deterioration of the fuel cell can be suppressed, the performance of the fuel cell can be reduced, and the durability can be improved.

  According to the third aspect of the invention, the mode is switched so that the stop process in the drying mode and the stop process in the wet mode are alternately performed every specified number of times. Thereby, the intensive progress of partial deterioration of the catalyst due to the continued dry state or wet state can be suppressed, and the durability of the fuel cell can be improved.

  According to any one of the fourth to sixth inventions, when the switching state is detected according to the operation state of the fuel cell, the mode in the stop process is switched to a mode different from the previous mode. Thereby, it is possible to suppress partial concentration of catalyst deterioration due to the stop process in the dry mode or the wet mode, and it is possible to improve the durability of the fuel cell.

  By the way, when the stop process in the drying mode or the stop process in the wet mode is continuously performed, deterioration in a portion where the deterioration is likely to occur in the mode is concentrated. Therefore, according to the seventh aspect, it is possible to execute the mode switching at an appropriate timing by detecting that the fuel cell is in the switching state by detecting the deterioration state of the fuel cell.

  Further, when the deterioration progresses, it is considered that the voltage is lowered in the entire fuel cell. Therefore, according to the eighth aspect, by detecting the switching state based on whether or not the voltage is smaller than the reference voltage, switching to the drying mode or the wet mode can be executed at an appropriate timing.

  By the way, the deterioration due to the stop process in the drying mode is particularly likely to occur at a place where the drying is likely to occur, that is, at the inlet side of the reaction gas channel. On the other hand, the deterioration due to the stop process in the wet mode is likely to occur on the outlet side where moisture tends to stay. For this reason, when degradation occurs in an environment where the shutdown process is performed in the dry mode, the power generation performance at the inlet side is greatly reduced, and when degradation occurs in the wet mode, power generation at the outlet side is performed. The performance drop is large. Therefore, according to the eleventh aspect, it is possible to detect that the deterioration in any mode is progressing by detecting the switching state based on the difference in power generation performance between the inlet side and the outlet side. Can be switched at an appropriate timing. Therefore, the progress of partial deterioration can be suppressed, and the durability of the fuel cell can be improved.

  Further, when the deterioration in the dry mode is proceeding, the decrease in the inlet voltage is large, and when the deterioration in the wet mode is caused, the decrease in the outlet voltage is large. That is, in any case, the difference between the inlet voltage and the outlet voltage becomes large. Therefore, according to the tenth aspect, by detecting the switching state when the absolute value of the voltage difference becomes large, it is possible to detect that the deterioration in any of the modes is progressing. The mode can be switched at the timing. Therefore, the progress of partial deterioration can be suppressed, and the durability of the fuel cell can be improved.

  Further, as described above, when the deterioration in the drying mode is proceeding, the inlet voltage becomes small, and when the degradation in the wet state is proceeding, the outlet voltage becomes small. Therefore, according to the eleventh aspect, when the inlet / outlet voltage difference obtained by subtracting the outlet voltage from the inlet voltage is smaller than a predetermined value, the mode is switched to the wet mode in order to suppress the progress of deterioration due to the dry mode. When the inlet / outlet voltage difference is larger than a predetermined value, the mode is switched to the drying mode in order to suppress deterioration due to the wet mode. Thereby, the progress of partial deterioration of the fuel cell can be suppressed and the durability of the fuel cell can be improved.

  Further, the deterioration in the dry mode easily proceeds in a lower current region, and the deterioration in the wet mode easily proceeds in a higher current region. Therefore, a first voltage at a certain first current and a second voltage at a second current larger than the first current are detected, and a voltage difference obtained by subtracting the second voltage from the first voltage is obtained. When the voltage difference is larger than the first voltage difference, it can be determined that the degradation due to the wet mode is progressing. Further, when the voltage difference is smaller than the second reference voltage difference serving as a reference, it can be determined that the deterioration in the drying mode is proceeding. Therefore, according to the twelfth aspect, by detecting the switching state when the voltage difference is larger than the first reference voltage difference, the switching from the wet mode to the dry mode can be executed at an appropriate timing. . In the thirteenth aspect, the switching state is detected when the voltage difference is smaller than the second reference voltage difference, so that the switching from the drying mode to the wetting mode can be executed at an appropriate timing.

  According to the fourteenth aspect, when the voltage difference is larger than the first reference voltage, the mode in the next stop process is set to the dry mode, and when the voltage difference is smaller than the second reference voltage difference, the next stop is performed. The mode in processing is the wet mode. In other words, by detecting the voltage difference as described above, it is possible to detect whether the deterioration due to the dry mode or the wet mode is currently progressing. Therefore, regardless of the current mode, the progress of deterioration can be more effectively suppressed by switching the deterioration state.

  According to the fifteenth aspect, when it is recognized that the voltage difference is outside the range of the second reference voltage difference or more and the first reference voltage difference or less, the deterioration of the fuel cell is detected. By detecting the deterioration based on the voltage difference at different current values as described above, it is possible to determine whether the deterioration is caused by drying or by wetness as well as detecting the deterioration.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment 1 FIG.
[System configuration of the embodiment]
FIG. 1 is a schematic diagram for explaining the overall configuration of a fuel cell system according to Embodiment 1 of the present invention. In the first embodiment, the fuel cell system is mounted on a vehicle. The system shown in FIG. 1 has a fuel cell 2. The fuel cell 2 has a membrane-electrode assembly (MEA) consisting of an electrolyte membrane and a cathode electrode and an anode electrode, which are a pair of electrodes arranged on both sides of the electrolyte membrane, which are stacked via separators. is doing.

  The fuel cell system has an air supply pump 10 for supplying air to the fuel cell 2. An air supply pipe 12 is connected to the air supply pump 10. A bypass switching valve 14 is installed in the air supply pipe 12. The air supply pipe 12 is connected to the air supply pipe 16 via the bypass switching valve 14. The air supply pipe 16 is connected to the humidifier 18. An air supply pipe 20 is connected to the humidifier 18. A check valve 22 is attached to the air supply pipe 20. The check valve 22 has a function of preventing the flow from the humidifier 18 to the air supply pipe 20 side from flowing backward. The air supply pipe 20 is connected to the air supply pipe 24 on the downstream side (fuel cell 2 side) from the check valve 22. The air supply pipe 24 is connected to the air inlet of the fuel cell 2 at the end opposite to the connecting portion with the air supply pipe 20.

  On the other hand, the air supply pipe 12 is connected to one end of the bypass pipe 26 via the bypass switching valve 14. The bypass pipe 26 is connected to the air supply pipe 24 at the other end. That is, the bypass pipe 26 is installed so as to communicate the air supply pipe 12 and the air supply pipe 24, and the humidifier 18 is bypassed by the bypass pipe 26.

  By switching the bypass switching valve 14, the air introduced into the air supply pipe 12 by the air supply pump passes through the air supply pipe 16, the humidifier 18 and the air supply pipe 20, or the humidifier It is possible to switch whether to bypass 18 by the bypass pipe 26. That is, the air supplied to the fuel cell 2 can be switched between a humidified state in which the humidifier 18 is humidified and a dry state in which the humidifier 18 is bypassed by the bypass pipe 26.

  Although not shown, a pipe for discharging the air off-gas discharged from the fuel cell 2 is installed at the air discharge port of the fuel cell 2. A hydrogen supply pipe for supplying hydrogen as fuel to the fuel cell 2 is connected to the hydrogen inlet of the fuel cell 2, and hydrogen for discharging hydrogen off-gas discharged from the fuel cell 2 is connected to the hydrogen outlet. The discharge pipe is connected.

  This fuel cell system has a control unit 30 for controlling the operation of the fuel cell. The control unit 30 is connected to a cell monitor (not shown) that detects the current, voltage, and the like of each cell of the fuel cell 2. The control unit 30 can detect the current, voltage, impedance, etc. of the cell of the fuel cell 2 by receiving the output of the cell monitor. On the other hand, a bypass switching valve 14 is connected to the control unit 30. The control unit 30 controls the bypass switching valve 14 by issuing a predetermined control signal to control whether the connection with the air supply pipe 12 is on the air supply pipe 16 side or the bypass pipe 26 side. be able to.

[Regarding stop processing]
By the way, in the air flow path (reactive gas flow path) of each cell of the fuel cell 2, a lot of moisture generated by the electrochemical reaction exists. During power generation of the fuel cell 2, the temperature in the air channel is kept at a certain high level by the reaction heat, so that the water in the air flow path moves downstream with the air without being frozen. However, when the outside air temperature is low, when the power generation of the fuel cell 2 is stopped, the temperature in the fuel cell 2 may decrease and the water may freeze (freeze state). If water is actually frozen in the air flow path in such a frozen state, the flow of air is hindered by the frozen water when the fuel cell 2 is started, and the startability of the fuel cell 2 is reduced, or the electrolyte membrane is deteriorated. May occur.

  In order to prevent such a situation, in the fuel cell system according to the first embodiment, in order to prepare for a case where the next start-up is a start-up in a frozen state, moisture that remains after scavenging the air flow path when the fuel cell 2 is stopped. Execute stop processing to remove.

[Deterioration of catalyst layer due to stop treatment]
By the way, even when the fuel cell 2 is stopped, the electrolyte membrane and the portion of the catalyst layer applied thereto are maintained in a state of retaining a certain amount of moisture. If the fuel cell 2 is frozen while the fuel cell 2 is stopped, the catalyst layer may be deteriorated by moisture present in the catalyst layer or the electrolyte membrane. However, the deterioration is small when the moisture is high as described below. It is thought that it progresses in a different state depending on the case.

  2 and 3 are diagrams for explaining the deterioration of the catalyst layer when the fuel cell is frozen after the stop process. 2A and 3A show a normal state, and FIGS. 2B and 3B show a deterioration state.

  FIG. 2 shows the progress of deterioration when the stop process is performed using dry air (dry mode). When the stop process is performed in the dry mode, a large amount of moisture is removed by the dry air, so that the electrolyte membrane 40 and the catalyst layer 42 are also dried to some extent. In this state, when the fuel cell 2 is stopped and the temperature is lowered, water drops are present in the catalyst layer 42. When the fuel cell 2 reaches a frozen state, the water drops in the catalyst layer 42 are frozen and the state shown in FIG. As shown in a), ice nuclei 44a are formed.

  When ice nuclei 44a are generated in the catalyst layer 42, moisture is attracted from the diffusion layer or the like to gradually grow large ice crystals 44b. As a result, locally large ice crystals 44b exist in the catalyst layer, and as shown in FIG. 2B, separation of the catalyst layer 42 occurs, and the catalyst layer 42 deteriorates. Hereinafter, such deterioration due to the drying mode is referred to as “drying deterioration”.

  On the other hand, FIG. 3 shows the progress of deterioration when the stop process is performed using wet air (wet mode). When the stop process is performed in the wet mode, a large amount of moisture 46a remains in the vicinity of the catalyst layer 42. When the fuel cell 2 stops in this state and the temperature decreases, a large amount of moisture 46a exists in the catalyst layer 42 as shown in FIG. When the fuel cell 2 is in a frozen state, the moisture 46a freezes and expands as ice 46b. As a result, as shown in FIG. 3B, the catalyst layer 42 is destroyed and deteriorated. Hereinafter, the deterioration in the wet mode is referred to as “wet deterioration”.

  FIG. 4 is a diagram for explaining a change in the voltage maintenance ratio when the stop process of the fuel cell 2 is repeatedly performed in the frozen state. FIG. 4A is a diagram when the stop process in the dry mode is repeated. FIG. 4B shows a case where the wet mode stop process is repeated. 4 (a) and 4 (b), the horizontal axis indicates the number of cooling cycles [times], that is, in a low-temperature environment (below freezing point), the fuel cell is stopped and stopped, and then restarted. The number of cycles when the operation process is one cycle is shown. The vertical axis represents the voltage maintenance rate [%], that is, the ratio of the voltage currently generated to the voltage generated in the initial operation in the same current region.

  FIG. 4A shows a case where the stop process in the drying mode is repeatedly performed. A solid line A represents a voltage maintenance rate [%] near the outlet of the air flow path when operated in a high current region, and a dotted line B represents The voltage maintenance rate [%] in the vicinity of the air flow path inlet when operating in the low current region is shown.

  When the stop process is performed in the drying mode, the moisture is removed by the dry air, particularly on the inlet side of the air flow path, so that the drying of the catalyst layer 42 becomes significant. On the other hand, the air gradually contains moisture in the air flow path as it flows downstream, so that the catalyst layer 42 is maintained in a relatively high wet state on the downstream side of the air flow path. Therefore, when the fuel cell 2 is stopped, the catalyst layer 42 is in a dry state particularly on the upstream side. Therefore, it is considered that the drying deterioration as described in FIG. 2 occurs in the catalyst layer 42 on the air flow path inlet side. .

  Further, when the fuel cell 2 is operated in a high current region, a large amount of water is generated by the power generation reaction, so that the electrolyte membrane 40 and the catalyst layer 42 are also maintained in a high wet state. On the other hand, when the operation is performed in a low current region, since the generated moisture is small, the electrolyte membrane 40 and the catalyst layer 42 are also in a dry state. Therefore, it is considered that drying deterioration is more likely to occur when operated in a low current region.

  Therefore, as shown by the solid line A in FIG. 4A, even when the stop process in the drying mode is repeated below freezing point, the voltage is near the outlet of the air flow path when operated in a high current range. There is no significant change in the maintenance rate [%], and the performance of the fuel cell 2 is maintained. On the other hand, as indicated by the dotted line B, in the vicinity of the air flow path inlet when operated in a low current region, the voltage maintenance rate [%] is significantly reduced when the cooling / heating cycle is repeated to some extent.

  FIG. 4B shows the case where the stop process in the wet mode is repeated, and the solid line A represents the voltage maintenance rate [%] near the outlet of the air flow path when operating in the low current region. The dotted line B represents the voltage maintenance rate [%] in the vicinity of the air flow path inlet when operating in the high current region.

  When the stop process is performed in the wet mode, the electrolyte membrane 40 and the catalyst layer 42 are kept in a relatively high wet state. In particular, since the supplied air causes a large amount of generated water to move to the downstream side due to the flow from the air channel inlet side to the downstream side, the electrolyte membrane 40 and the catalyst layer are located on the air channel outlet side. The inside of 42 is in a state containing a large amount of moisture. Therefore, it is considered that the wet deterioration as described in FIG. 3 is likely to occur particularly in the catalyst layer 42 near the outlet side of the air flow path.

  Further, more water is generated when the fuel cell 2 is operated in the high current region than when the fuel cell 2 is operated in the low current region. For this reason, the electrolyte membrane 40 and the catalyst layer 42 contain a large amount of moisture and are maintained in a high wet state. For this reason, it is considered that the wet deterioration is more likely to occur when the fuel cell 2 is operated in a high current region.

  Therefore, as shown by the dotted line B in FIG. 4B, even when the stop process in the wet mode is repeated below the freezing point, there is a voltage near the inlet of the air flow path when operated in a low current region. There is no significant change in the maintenance rate [%], and the performance of the fuel cell 2 is maintained. On the other hand, as shown by the solid line A, in the vicinity of the air flow path outlet when operated in a high current region, the voltage maintenance rate [%] is significantly reduced when the cooling / heating cycle is repeated to some extent.

[Control of stop processing mode]
As described above, the dry deterioration and the wet deterioration that occur in the respective stop processes in the dry mode and the wet mode have different generation mechanisms, and it is considered that the portions where the deterioration easily proceeds are different. Therefore, in the first embodiment, the deterioration progressing portion is dispersed by switching between the stop process in the dry mode and the stop process in the wet mode. As a result, as the fuel cell 2 as a whole, partial progress of deterioration can be delayed and the durability of the fuel cell 2 can be improved.

  Specifically, in the first embodiment, at the initial stage of the fuel cell 2, the stop process in the wet mode is set. Here, the air is passed through the humidifier 18 by setting the bypass switching valve 14 to the air supply pipe 16 side during the stop process. Thereby, at the time of a stop process, the inside of an air flow path will be scavenged by the air which became the wet state, and the process in a wet mode is performed.

  After that, when the cell voltage detected in the predetermined current range decreases beyond the allowable range and becomes lower than the reference voltage V0, it is determined that the wet deterioration has progressed to some extent, and the dry mode is stopped. Switch to processing. Here, at the time of the stop process, the bypass switching valve 14 is set to the bypass pipe 26 side so that the air bypasses the humidifier 18. Thereby, at the time of a stop process, the inside of an air flow path will be scavenged by the dry air, and the process in dry mode will be performed.

  Here, the reason why the stop process in the wet mode is performed first is that when the power generation is continued, the MEA (the electrolyte membrane 40 and the catalyst layer 42) is gradually in a state of easily containing moisture. That is, after the MEA is likely to contain moisture in this way, it is possible to more effectively suppress the progress of wet deterioration by supplying dry air.

[Specific control of stop processing]
FIG. 5 is a flowchart for illustrating a control routine executed by the control unit 30 in the stop process of the fuel cell 2 in Embodiment 1 of the present invention. The routine of FIG. 5 is a routine that is executed every time the fuel cell 2 is stopped.

  In the routine of FIG. 5, it is first determined whether or not an instruction to end the power generation of the fuel cell 2 has been issued (S10). Specifically, the determination is made based on whether or not the control unit 30 has detected a stop instruction signal indicating a power generation end instruction. If the power generation end instruction is not accepted, the current process ends. On the other hand, if it is determined in step S10 that a power generation end instruction has been issued, it is next determined whether or not the flag is currently ON (S12). This flag is turned on in the initial state, and is turned off when the stop process is performed in the drying mode in a routine described later.

  If it is determined in step S12 that the flag is ON, then the bypass switching valve 14 is switched to the air supply pipe 16 side, that is, the side through which the air passes the humidifier 18 (S14). Here, the bypass switching valve 14 is switched by a control signal from the control unit 30. As a result, the air supply pipe 12 and the air supply pipe 16 communicate with each other, and the supplied air passes through the humidifier 18 to become a humidified state and passes through the air supply pipes 20 and 24 and the fuel cell. 2 is supplied. Thereby, scavenging in the air flow path by the wet air starts.

  Next, the cell resistance R is detected (S16). The cell resistance R is detected by the control unit 30 by taking the output of a cell monitor (not shown). Next, it is determined whether or not the detected cell resistance R is smaller than the reference resistance R1 (S18). The electrolyte membrane 40 has a high resistance in a dry state, while exhibiting a low resistance value in a wet state. Therefore, when the cell resistance R is smaller than a certain reference resistance R1, it can be determined that the electrolyte membrane 40 is sufficiently wetted and the air passage is sufficiently scavenged. Note that the reference resistance R1 as a reference for such determination is obtained in advance by experiments or the like and stored in the control unit 30.

  In the case where the fuel cell 2 has a structure in which a plurality of cells are stacked as in this embodiment, for example, what is described using the cell resistance or the cell voltage as a criterion is, for example, a plurality of cells. Among them, one that is detected and representative of the resistance and voltage of cells that are likely to show significant deterioration, or one that is detected for each of a plurality of stacked cells, or a prescribed number Appropriate methods can be selected, such as one that is approved when a cell satisfies the condition, and one that uses an average value of values detected for a plurality or all of the cells as a criterion for determination.

  Accordingly, in step S18, when the establishment of cell resistance R <reference resistance R1 is not recognized, scavenging with wet air is continued until the establishment is confirmed. On the other hand, if it is recognized in step S18 that cell resistance R <reference resistance R1 is established, it is determined that the scavenging of the air flow path, that is, the stop process has been completed. Accordingly, the power generation of the fuel cell 2 is terminated (S20), and the current process is terminated.

  On the other hand, if it is not recognized in step S12 that the flag is ON, that is, if the flag is OFF, stop processing in the drying mode is performed. Specifically, first, the bypass switching valve 14 is switched to the bypass pipe 26 side (S22). As a result, the humidifier 18 is bypassed, and the dry air is supplied to the fuel cell 2 through the air supply pipe 12, the bypass pipe 26 and the air supply pipe 24. Thereby, scavenging of the air flow path by the dry air is started.

  Next, the cell resistance R is detected (S24). The cell resistance R is detected by the control unit 30 by taking the output of the cell monitor. Next, it is determined whether or not the detected cell resistance R is greater than the reference resistance R2 (S26). Since the cell resistance increases when the electrolyte membrane 40 is dried as described above, when the stop process is performed in the drying mode, the scavenging is completed when the cell resistance increases to some extent. Judgment can be made. The reference resistance R2 serving as a reference for such determination is obtained in advance by experiments or the like and stored in the control unit 30. Therefore, by performing the determination in step S26, it is possible to determine whether or not scavenging of the air flow path has been completed.

  In step S26, when establishment of cell resistance R> reference resistance R2 is not recognized, the stop process in the drying mode is continued. On the other hand, if it is recognized that the cell resistance R> the reference resistance R2 is established, it is recognized that the scavenging has been completed, so that the power generation of the fuel cell is terminated (S20), and the current process is terminated.

[Specific control of mode switching in stop processing]
FIG. 6 is a flowchart for illustrating a control routine executed by the control unit in the mode switching in the stop process in the first embodiment of the present invention. The routine of FIG. 6 is a routine that is periodically executed during operation of the fuel cell 2.

  In the routine of FIG. 6, it is first determined whether or not the fuel cell 2 is generating power (S100). If it is not recognized that power is being generated, the current process is terminated. On the other hand, if it is confirmed that the fuel cell 2 is generating power, then the cell voltage V in a predetermined current region is detected (S102). The cell voltage V is detected by the control unit 30 by taking the output of the cell monitor.

  Next, it is determined whether or not the detected cell voltage V is smaller than the reference voltage V0 (S104). Here, when the establishment of the cell voltage V <the reference voltage V0 is recognized, the flag for performing the stop process in the wet mode is turned OFF (S106). That is, when the cell voltage V is lower than the reference voltage V0, it can be determined that the progress of the wet deterioration has already progressed as a result of repeating the stop process in the wet mode initially. Accordingly, the flag is turned OFF so that the fuel cell 2 is switched to the stop process in the dry mode after the next stop of the fuel cell 2. Thereafter, the current process ends.

  On the other hand, if establishment of cell voltage V <reference voltage V0 is not recognized in step S104, it can be determined that the wet deterioration has not yet occurred. Accordingly, the flag is maintained in the ON state so that the stop process in the wet mode is executed even when the fuel cell 2 is stopped next time (S108). Thereafter, the current process ends.

  As described above, the degradation mechanism of the fuel cell 2 in the frozen environment is different depending on whether the degradation is in the dry mode or in the wet mode. It is thought that the part where is easy to progress is different. Therefore, in the first embodiment, the mode during the stop process is controlled so as to be switched between the stop process in the dry mode and the stop process in the wet mode. Thereby, the part which progresses deterioration can be disperse | distributed, the progress of deterioration can be delayed as the fuel cell 2 whole, and durability of the fuel cell 2 can be improved.

  By the way, in Embodiment 1, when stopping the fuel cell 2, the case where the stop process in the mode based on the determination of mode switching demonstrated in this Embodiment 1 was performed each time was demonstrated. However, the present invention is not limited to this. For example, based on information such as a weather forecast and an outside air temperature, it is predicted whether or not the fuel cell 2 is frozen while the fuel cell 2 is stopped. The processing of the first embodiment may be executed only when expected. The same applies to the following embodiments.

  Further, in the first embodiment, the case where the wet mode is set in the initial stage and then the mode is switched to the dry mode when the voltage drop is recognized is described. However, the present invention is not necessarily limited to this, and the stop process in the dry mode may be performed in the initial stage, and then the wet mode may be switched after the cell voltage is lowered. Even in such a case, it is possible to prevent the progress of deterioration from being partially concentrated, and the durability of the fuel cell 2 can be improved.

  Moreover, in Embodiment 1, after switching to the drying mode once, the case where the stop process in the drying mode was continued after that was demonstrated. However, the present invention is not limited to this, and the mode may be switched to a mode different from the current mode every time it is confirmed that the cell voltage drop has increased to some extent. In this case, for example, if the reference voltage V0, which is a reference for determining the deterioration of the fuel cell 2 in step S104 in FIG. 6, is changed stepwise to a smaller value every time a decrease in the cell voltage is detected, the deterioration As the process proceeds, mode switching can be repeatedly executed.

  Further, a case has been described in which it is determined that the cell voltage has deteriorated when the cell voltage drops below the reference voltage and the mode is switched. However, the present invention is not limited to this, and the mode may be switched by detecting the performance deterioration of the fuel cell by means other than the cell voltage.

  In addition, without determining the deterioration based on the cell voltage, the mode in the stop process of the fuel cell 2 is switched every predetermined number of times, and the stop process in the dry mode and the stop process in the wet mode are alternately performed a predetermined number of times. It can also be set to be done. Also in this case, the progress of partial deterioration can be dispersed, and the durability of the fuel cell 2 can be improved. Note that the predetermined number of times in this case is not limited to the case where the drying mode and the wetting mode are the same number of times, and may be different times. Further, the number of stop processes in each mode may change based on some condition.

  In the first embodiment, the case where the mode switching timing (switching state) is determined based on the voltage drop in a predetermined current region has been described. However, the present invention is not limited to this, and the determination may be made based on other parameters.

  Further, in the first embodiment, the stop process in the wet mode and the stop process in the dry mode are realized by switching the air supplied to the air flow path side on the cathode electrode side in the stop process to the wet state or the dry state. Explained the case. However, in the present invention, the stop process described in the first embodiment is not limited to the process applied to the cathode electrode side, but may be applied to the anode electrode side, or applied to both electrodes. But you can. In this case, on the anode electrode side, instead of air, the fuel may be used as a scavenging gas at the time of stop processing, and the fuel may be supplied by switching to a dry state or a wet state. Further, as a structure in which air can be supplied also to the anode electrode side at the time of stopping, air in a dry state or a wet state may be supplied similarly to the cathode electrode side. The same applies to the following embodiments.

  In the first embodiment, the case has been described in which the humidifier 18 is passed to make the air wet and the humidifier 18 is bypassed to make the air dry. However, the present invention is not limited to this. For example, in this invention, the humidifying means for moistening the air uses another humidifier that can humidify the air to such an extent that the electrolyte membrane 40 and the catalyst layer 42 can be moistened by supplying air. For example, a humidifier that can adjust the humidity of the air may be used. Further, for example, the drying processing means for supplying dry air is not limited to simply bypassing the humidifier 18, and the air is dried to such an extent that the electrolyte membrane 40 and the catalyst layer 42 are dried. A dryer or the like can also be used. The same applies to the following embodiments.

  In the first embodiment, the processing of steps S10 to S26 in FIG. 5 is executed to realize the “stop control means” of the present invention, and step S106 or S108 in FIG. "Mode control means" is realized. Further, the “switching state detecting unit” is realized by executing step S104 of FIG. 5, and the “voltage detecting unit” is realized by executing step S102.

Embodiment 2. FIG.
The system according to the second embodiment performs the same control as the system according to the first embodiment, except that the determination method for switching between the dry mode and the wet mode is different. In addition, for this control, the fuel cell system of Embodiment 2 has a structure in which the voltage at the inlet side and the outlet side of the air flow path of each cell can be detected in an insulated state. Thus, it has the same structure as the fuel cell system of the first embodiment.

  FIG. 7 is a diagram schematically showing the catalyst layer side of the cathode electrode of the MEA of each cell of the fuel cell system according to the second embodiment. As shown in FIG. 7, a cathode electrode catalyst layer 52 is formed on one surface of the MEA 50. The inlet portion 52a near the inlet of the air flow path of the cathode electrode catalyst layer 52 and the outlet portion 52b near the outlet of the air flow path are electrically insulated from the other portion of the cathode catalyst layer 52. Although not shown, the anode electrode catalyst layer is also in a state where the portion of the air flow channel facing the inlet portion 52a and the portion of the air flow channel facing the outlet portion 52b are insulated.

  Terminals are respectively provided at the entrance portion, the exit portion, and the anode electrode of the cathode electrode. The voltage near the cathode electrode inlet 52a of the MEA 50 is detected by connecting the terminals of the inlets of both electrodes and the parts facing the terminals and the terminals of the outlets and the parts facing the terminals to detect the voltage. The (inlet voltage Vin) and the voltage near the outlet 52b (outlet voltage Vout) can be detected in an insulated state.

  The air flow path formed on the surface of the separator in contact with the cathode electrode catalyst layer 52 and the fuel flow path formed on the surface of the separator in contact with the anode electrode catalyst layer are respectively the cathode electrode catalyst layer 52 or the anode electrode. It is common to the entire catalyst layer, and has a structure that continues throughout the entire cell surface including the inlet and outlet.

  By the way, the system of the first embodiment detects the switching state when the deterioration progresses by simply comparing the cell voltage V in a certain current region with the reference voltage V0. However, the cell voltage actually changes due to various other causes. For this reason, if the deterioration caused by each mode of the stop process is determined only by the decrease in the cell voltage, an error may occur in the deterioration determination. For this reason, in the system of the second embodiment, the switching state is detected by the following method.

  As described with reference to FIG. 4, the dry deterioration and the wet deterioration remarkably proceed at different places. Specifically, the drying deterioration proceeds in the vicinity of the air channel inlet. Therefore, when the voltages at the inlet portion 52a and the outlet portion 52b are detected by being insulated by the structure shown in FIG. 7, the voltage drop due to the drying deterioration is noticeably generated at the inlet portion 52a.

  On the other hand, when the wet deterioration proceeds continuously in the stop process in the wet mode, the deterioration proceeds near the cathode outlet. Therefore, when the voltages at the inlet portion 52a and the outlet portion 52b are respectively detected, the voltage drop in the case of wet deterioration appears remarkably on the outlet portion 52b side.

  That is, in the case of dry deterioration, the inlet voltage Vin that is a voltage in the vicinity of the inlet portion 52a is significantly reduced, and in the case of wet deterioration, the outlet voltage Vout that is a voltage in the vicinity of the outlet portion 52b is significantly reduced. Therefore, when the inlet voltage Vin and the outlet voltage Vout are detected, it is considered that the difference between them is large.

  Therefore, in the system of the second embodiment, when the inlet / outlet voltage difference (Vin−Vout) which is the voltage difference between the inlet portion 52a and the outlet portion 52b is obtained, the value (absolute value) of this voltage difference is large. Furthermore, it can be determined that dry deterioration or wet deterioration has progressed. The system of the second embodiment uses this to determine the timing of switching from the wet mode to the dry mode when the inlet / outlet voltage difference (Vin−Vout) is larger than the reference voltage difference ΔV.

  FIG. 8 is a flowchart for illustrating a control routine executed by control unit 30 in the second embodiment of the present invention. The routine of FIG. 8 is a routine executed in place of the routine of FIG. Further, the routine of FIG. 8 is the same as the routine of FIG. 6 except that the processing of steps S202 to S206 is provided instead of steps S102 to S104 of the routine of FIG.

  Specifically, in the routine of FIG. 8, if it is determined in step S100 that the fuel cell is generating power, then the inlet voltage Vin and the outlet voltage Vout are respectively detected in a predetermined current region (S202). . Here, as described above, the inlet portion 52a and the outlet portion 52b are insulated from each other and a terminal is attached, and a cell monitor is connected to the terminal so that the respective voltages can be detected. When the control unit 30 captures the output of the cell monitor, the inlet voltage Vin and the outlet voltage Vout are detected.

  Next, an inlet / outlet voltage difference (Vin−Vout) between the inlet voltage Vin and the outlet voltage Vout is calculated (S204). Specifically, the outlet / inlet voltage difference (Vin−Vout) is calculated by subtracting the outlet voltage Vout from the inlet voltage Vin.

  Next, it is determined whether or not the voltage difference (Vin−Vout) obtained in step S204 is larger than the reference voltage difference ΔV (S206). In the second embodiment, the flag is set to ON so that the stop process in the wet mode is executed in the initial operation state of the fuel cell 2. Accordingly, in this step, it is determined whether or not wet deterioration has occurred as a result of repeated stop processing in the wet mode. The reference voltage difference ΔV that serves as a reference for such determination is obtained in advance through experiments or the like and stored in the control unit 30.

  In step S206, when it is recognized that the inlet / outlet voltage difference (Vin−Vout)> the reference voltage difference ΔV is established, it is determined that the voltage drop in the vicinity of the outlet portion 52b is large and the wet deterioration is progressing. In this case, the flag is turned off (S106). Thereby, the mode of the stop process is switched from the next stop, and the stop process in the drying mode is executed.

  On the other hand, if the establishment of the difference between the inlet and outlet voltage (Vin−Vout)> the reference voltage difference ΔV is not recognized, the difference between the inlet voltage Vin and the outlet voltage Vout is small, and the progress of the wet deterioration is not recognized. In this case, the flag is kept on (S108), and the current process ends.

  As described above, in the second embodiment, the switching state for switching from the wet mode to the dry mode is detected based on the inlet / outlet voltage difference. Therefore, it is possible to accurately detect the deterioration caused by the stop process in each mode, and it is possible to prevent the stop process mode from being switched due to a voltage change caused by another cause. .

  In the second embodiment, the case where it is detected that the drying deterioration or the wet deterioration is progressing by detecting the inlet voltage Vin and the outlet voltage Vout has been described. However, the present invention is not limited to this, and the power generation performance on the inlet side of the cell and the power generation performance on the outlet side are detected, and when the difference exceeds the standard, the wet deterioration or the dry deterioration is detected. It is also possible to detect and switch the mode.

  Further, in the second embodiment, the case where the operation is started from the wet mode as in the first embodiment and then the mode is switched to the dry mode when the progress of the wet deterioration is recognized is described. However, in the present invention, mode switching and selection are not limited to those described in the second embodiment. Specifically, for example, the mode may be switched from the dry mode to the wet mode. However, in the drying mode, deterioration at the entrance 52a proceeds. Therefore, the decrease of the inlet voltage Vin is larger than the outlet voltage Vout. Therefore, when the absolute value of the voltage difference (Vin−Vout) becomes larger than the predetermined reference voltage difference ΔV, that is, the inlet / outlet voltage difference (Vin−Vout) becomes smaller than the predetermined reference value (for example, −ΔV). In some cases, the progress of drying deterioration can be detected.

  In the second embodiment, the case where the wet mode is switched to the dry mode and then the dry mode is repeated has been described. However, in the second embodiment, if the voltage at the inlet portion 52a and the outlet portion 52b of the MEA is detected and the state of the decrease is detected, it is determined whether the dry deterioration or the wet deterioration is currently progressing. can do.

  More specifically, when the inlet / outlet voltage difference (Vin−Vout) is calculated, if the value is on the plus side and is greater than a predetermined first reference voltage difference (for example, the reference voltage difference ΔV), it indicates that the wet deterioration has occurred. I can judge. Further, if the value is on the negative side and smaller than the second reference voltage difference (for example, -ΔV), it can be determined that the deterioration is drying. Therefore, based on this determination, when it is determined that the deterioration is dry, the state is switched to the wet mode (wet switching state), and when it is determined that the deterioration is wet, the state is switched to the drying mode (dry switching state). It is also possible to detect that there is, and when these states are detected, control can be performed so that the mode can be switched to that mode. At this time, for example, it may be set such that the magnitude (absolute value) of the reference voltage difference for determination is increased each time each switching state is detected. Thereby, even after a cell voltage drop occurs due to any deterioration, each mode can be switched without being fixed to one mode, and the durability of the fuel cell 2 can be further improved.

  Here, it is possible to install a humidifier capable of adjusting the humidity instead of the humidifier 18, detect the deterioration while the inlet / outlet voltage difference is small, and supply the air whose humidity is adjusted according to the deterioration state. . For example, it is possible to supply air of intermediate humidity between the dry state and the wet state in the second embodiment, and in a normal case where no deterioration is detected, stop processing is performed with air of intermediate humidity. May be. In this case, when no deterioration is detected, control is performed so that the stop process at the intermediate humidity is performed, and when dry deterioration and wet deterioration are detected according to the inlet / outlet voltage difference (Vin−Vout). The occurrence of deterioration can be more reliably suppressed by switching to the mode corresponding to the control.

  Further, by stopping the mode while switching the mode while the magnitude (absolute value) of the reference voltage difference ΔV is reduced and the progress of deterioration is small, it is possible to execute stop processing that more reliably suppresses the progress of deterioration.

  Further, in the second embodiment, the case has been described in which the determination of deterioration due to the inlet / outlet voltage difference (Vin−Vout) is used only for detecting the switching state to the dry mode or the wet mode in the stop process. However, according to this degradation determination method, the progress of drying degradation and the progress of wet degradation can be identified and detected, so that the degradation portion and degradation state of each cell can be identified to some extent. Therefore, the present invention can also be applied to other controls that use the result of such deterioration determination.

  In the second embodiment, by executing the process of step S202, the “inlet voltage detecting means” and the “exit voltage detecting means” of the present invention are realized, and by executing the process of step S204, “ The “inlet / outlet voltage difference calculating means” is realized, and the “switching state detecting means” is realized by executing the processing of step S206.

Embodiment 3 FIG.
The fuel cell system of Embodiment 3 has the same configuration as the fuel cell system of FIG. The system of the third embodiment performs the same control as the system of the first embodiment except that the method for detecting the switching state between the dry mode and the wet mode is different.

  FIG. 9 is a diagram for explaining the IV characteristics of the fuel cell when the stop process is repeated in each of the dry mode and the wet mode, and FIG. 9A illustrates the stop process in the dry mode, FIG. 9B shows the case of the stop process in the wet mode. In each of FIGS. 9A and 9B, the horizontal axis represents current [I], the vertical axis represents voltage [V], the dotted line A represents the normal IV characteristics, and the solid line B represents the post-degradation. It represents the IV characteristic.

  As described above, the drying deterioration is likely to occur on the low current region side where the operation is performed in a drier state. That is, a voltage drop due to deterioration tends to appear in a low current region. For this reason, as shown in FIG. 9A, when compared with normal IV characteristics (dotted line A), the IV characteristics (solid line B) in the case of dry deterioration are particularly low voltage on the low current region side. The decline is significant.

  On the other hand, the wet deterioration is likely to occur on the high current region side where the wet state becomes higher. For this reason, as shown in FIG. 9 (b), the IV characteristic (solid line B) in the case of wet deterioration is particularly higher in the high current region side than the IV characteristic (dotted line A) before the deterioration occurs. It shows the characteristic that the voltage drops.

  From the above, based on the difference between the first voltage V1 in the first current I1 in the low current region and the second voltage V2 in the second current I2 in the high current region, the dry deterioration has progressed or the wet deterioration has progressed. Can be determined.

  Specifically, since wet degradation appears in a voltage drop on the high current region side, the second voltage V2 is considered to be smaller than a normal value. Accordingly, the value (voltage difference) of the first voltage V1-the second voltage V2 is larger than the difference in the normal case. Therefore, if the reference value (first reference voltage difference ΔV1) is set based on the difference between the normal first voltage and the second voltage, the first reference voltage difference and the voltage difference (V1−V2) are compared. By doing so, it is possible to detect wet deterioration.

  On the other hand, since the drying deterioration appears on the low current region side, the value of the first voltage V1−the second voltage V2 (voltage difference) becomes smaller than the difference in the normal case. Therefore, if the reference value (second reference voltage difference ΔV2) is set based on the difference between the first voltage and the second voltage in the normal case, the second reference voltage difference and the voltage difference (V1−V2) are compared. By doing so, drying deterioration can be detected.

  In the third embodiment, similarly to the first and second embodiments, the stop process in the wet mode is set to be performed in the initial state. Therefore, here, it is only necessary to perform control so that the wet deterioration is detected and the switching to the drying mode is performed. Therefore, the control unit 30 stores the first reference voltage difference ΔV1 in advance, and the voltage difference (Vin−Vout). ) Is larger than the first reference voltage difference ΔV1, the switching state is detected.

  FIG. 10 is a control routine executed by the control unit 30 in the third embodiment of the present invention. The routine of FIG. 10 is a routine that is executed in place of the routine of FIG. The routine in FIG. 10 is the same as the routine in FIG. 6 except that steps S102 and S104 of the routine in FIG. 6 are replaced with steps S302 to S306.

  Specifically, in the routine of FIG. 10, after confirming that the fuel cell is in operation (S100), the first voltage V1 at the first current I1 and the second voltage V2 at the second current I2 are: It is detected at the timing of each current value (S302). Here, the first voltage V1 and the second voltage V2 are detected in the control unit 30 by capturing the output of the cell monitor.

  Next, a voltage difference (V1−V2) that is a difference between the first voltage V1 and the second voltage V2 is calculated (S304). Next, it is determined whether or not the voltage difference (V1−V2) is larger than the first reference voltage difference ΔV1 (S306). In the routine of the third embodiment, since the stop process is initially performed in the wet mode, the progress of deterioration appears as a decrease in the voltage V2 on the high current region side, so that the voltage difference ( V1-V2) is considered to be larger than in the normal case. Therefore, here, the switching state is determined based on whether or not the voltage difference (V1−V2) is larger than the first reference voltage difference ΔV1.

  In step S306, when it is recognized that the voltage difference (V1−V2)> the first reference voltage difference ΔV1 is established, it is determined that the wet deterioration is progressing, and the flag is turned OFF (S106). Thereby, the stop process in the dry mode is performed from the next stop.

  On the other hand, if the establishment of the voltage difference (V1−V2)> the first reference voltage difference ΔV1 is not recognized in step S306, it is considered that the wet deterioration has not progressed, and therefore the flag is kept ON ( S108). Thereby, the stop process in the wet mode is executed even at the next stop.

  As described above, according to the system of the third embodiment, the deterioration can be determined by detecting and comparing voltages in two different current ranges, and it can be determined whether the deterioration is dry or wet. . Accordingly, it is possible to more reliably detect the dry deterioration and the wet deterioration, and it is possible to appropriately select the mode in the stop process. Therefore, the progress of deterioration of the fuel cell 2 can be suppressed, and the durability of the fuel cell 2 can be improved.

  In the third embodiment, the “voltage detection means” of the present invention is realized by executing the process of step S302, and the “voltage difference calculation means” is realized by executing the process of step S304. By executing the processing of step S306, the “switching state detecting means” is realized.

  In the third embodiment, the case where the operation is started from the wet mode and the progress of the wet deterioration is recognized and the mode is switched to the dry mode has been described. However, in the present invention, mode switching and selection are not limited to those described in the third embodiment. Specifically, for example, the mode may be switched from the dry mode to the wet mode. In the dry mode, since the progress of deterioration appears strongly on the low current region side, the voltage drop at the first voltage V1 becomes large. Accordingly, the progress of the drying deterioration is determined by determining whether the voltage difference (V1-V2) is smaller than the second reference voltage difference, and the deterioration can be detected when this condition is recognized.

  In addition, according to the degradation determination method of the third embodiment, it is possible to identify in which mode degradation is currently progressing. Therefore, the mode can be switched from the wet mode to the dry mode, and thereafter, the mode is not limited to the case where the dry mode is repeated, and the mode is switched to the reverse mode according to the progress of the deterioration mode.

  Specifically, when the voltage difference (V1−V2) is calculated, if the value is larger than a predetermined first reference voltage difference ΔV1, it can be determined that the deterioration is wet, and from the predetermined second reference voltage difference ΔV2. If it is small, it can be judged that it is dry deterioration. Therefore, based on this determination, it is possible to control to switch to the wet mode when it is determined to be dry deterioration, and to switch to the dry mode when it is determined to be wet deterioration.

  As another control of the third embodiment, a range between the second reference voltage difference ΔV2 and the first reference voltage difference ΔV2 is set as a normal range, and the voltage difference (V1−V2) is set from the normal range. When there is a deviation, the wet mode and the dry mode can be switched so as to correct the deviation. The control in this case will be described below.

  FIG. 11 is a flowchart for explaining another control routine executed by the system of the third embodiment. The routine of FIG. 11 is the same as the routine of FIG. 10 except that the processing of steps S402 to S406 is performed and the processing of steps S106 and S108 is not performed.

  In this example, in addition to the air supply path on the side of the humidifier 18 and the bypass pipe 26 that bypasses the fuel cell system, air is also dried by the humidified state by the humidifier and the supply by the bypass pipe. It has a device to adjust the intermediate humidity between the states. At the initial stage of operation of the fuel cell 2, the stop process is set in the normal mode in which scavenging is performed with air of intermediate humidity supplied by this device.

  Here, a voltage difference (V1−V2) is detected in step S304, and it is determined whether or not the voltage difference is larger than a first reference voltage difference ΔV1 that is a reference for wet deterioration determination. If it is determined in step S306 that the voltage difference (V1−V2)> the first reference voltage difference ΔV1 is established, it is determined that the wet deterioration is progressing. Therefore, next, switching to the drying mode is set (S402). Thereby, the stop process in the drying mode is executed at the next stop.

  On the other hand, if the establishment of the voltage difference (V1−V2)> the first reference voltage difference ΔV1 is not recognized in step S306, the voltage difference (V1−V2) is the reference for determining the dry deterioration. It is determined whether or not the difference is greater than 2 reference voltage difference ΔV2 (S404). In step S404, if it is recognized that the voltage difference (V1−V2) <the second reference voltage difference ΔV2, it is determined that the drying deterioration has progressed. In this case, next, in step S406, switching to the wet mode is set (S408). As a result, the processing in the wet mode is executed at the next stop.

  On the other hand, if the establishment of the voltage difference (V1−V2) <the second reference voltage difference ΔV2 is not recognized in step S404, it is determined that neither dry deterioration nor wet deterioration is currently in progress. In this state, the next stop process is set such that the stop process in the normal mode adjusted to the intermediate humidity is executed (S410). Thereby, the stop process in the normal mode is executed at the next stop.

  As described above, the stop process between the dry mode and the wet mode is performed only when the voltage difference in the normal state deviates. Here, if the range of the normal voltage difference (more than the second reference voltage difference ΔV2 and less than the first reference voltage difference ΔV1) is set narrowly, the process in the wet mode and the drying mode are performed before the deterioration proceeds. It is possible to switch to the processing in the above, and it is possible to more reliably suppress the progress of deterioration.

  In another example of this control, the process of step S306 is executed to detect the “dry switching state” in the present invention, and the process of step S404 is executed to detect the “wet switching state”. Thus, the “switching state detecting means” is realized by these steps. Further, the “mode switching means” of the present invention is realized by executing the processing of steps S402 and S406.

  In the third embodiment, the case where the determination of deterioration due to the voltage difference is used only for detecting the switching state to the dry mode or the wet mode in the stop process has been described. However, according to this degradation determination method, the progress of drying degradation and the progress of wet degradation can be identified and detected, so that the degradation portion and degradation state of each cell can be identified to some extent. Therefore, the present invention can also be applied to other controls that use the result of such deterioration determination.

  In the above embodiment, when the number of each element, number, quantity, range, etc. is mentioned, it is mentioned unless otherwise specified or clearly specified in principle. The number is not limited. Further, the structures described in the embodiments, steps in the method, and the like are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

It is a schematic diagram for demonstrating the structure of the fuel cell system in Embodiment 1 of this invention. It is a schematic diagram for demonstrating the deterioration state of a fuel cell. It is a schematic diagram for demonstrating the deterioration state of a fuel cell. It is a figure for demonstrating the relationship between the frequency | count of the stop process of a fuel cell, and a voltage maintenance factor. In Embodiment 1 of this invention, it is a flowchart for demonstrating the routine of control which the control unit of a fuel cell system performs. In Embodiment 1 of this invention, it is a flowchart for demonstrating the routine of control which the control unit of a fuel cell system performs. It is a figure for demonstrating the fuel cell in Embodiment 2 of this invention. In Embodiment 2 of this invention, it is a flowchart for demonstrating the routine of control which the control unit of a fuel cell system performs. It is a figure for demonstrating the relationship between the voltage and current of a fuel cell in Embodiment 3 of this invention. In Embodiment 3 of this invention, it is a flowchart for demonstrating the routine of control which the control unit of a fuel cell system performs. In Embodiment 3 of this invention, it is a flowchart for demonstrating the routine of the other control which the control unit of a fuel cell system performs.

Explanation of symbols

2 Fuel Cell 10 Air Supply Pump 12, 16, 20, 24 Air Supply Pipe 14 Bypass Switch Valve 18 Humidifier 22 Check Valve 26 Bypass Pipe 30 Control Unit 40 Electrolyte Membrane 42 Catalyst Layer 50 MEA
52 Catalyst layer

Claims (15)

Wet treatment means for humidifying the reaction gas supplied to the fuel cell to a wet state;
A drying treatment means for bringing the reaction gas supplied to the fuel cell into a dry state having a lower humidity than the wet state;
Stop control means for performing a stop process for supplying a reaction gas to the fuel cell when stopping the operation of the fuel cell;
A function of controlling the wet processing mode in which the reactive gas is in the wet state and a dry processing mode in which the reactive gas is in the dry state, and when the operation of the fuel cell is stopped, the wet processing mode or Mode control means capable of selecting and switching the drying processing mode;
A fuel cell system comprising: Freezing predicting means for predicting whether or not the water in the fuel cell is in a frozen state that can be frozen while the fuel cell is stopped,
When it is predicted that the mode control means will be activated in the frozen state at the next activation, the stop process is executed in any one of the drying process mode and the wet process mode. The fuel cell system according to claim 1, wherein the fuel cell system is controlled to be   The mode control means switches between the dry mode and the wet mode so that the stop process in the dry mode and the stop process in the wet mode are alternately performed a specified number of times. Item 3. The fuel cell system according to Item 1 or 2. According to the operating state of the fuel cell, further comprising a switching state detecting means for detecting that the switching state is switched to the drying mode or the stop processing in the wet mode,
When the switching state is detected, the mode control means switches the mode so that the next stop process is a stop process in a mode different from the mode in the previous stop process. The fuel cell system according to claim 1 or 2.   When the stop process is executed in the initial state of the fuel cell, the mode control means sets the wet mode, and from the stop process after the switching state is detected, to the stop process in the dry mode. The fuel cell system according to claim 4, wherein the mode is switched.   When the stop process is executed in the initial state of the fuel cell, the mode control unit sets the drying mode, and from the stop process after the switching state is detected, to the stop process in the wet mode. The fuel cell system according to claim 4, wherein the mode is switched.   The fuel cell system according to any one of claims 4 to 6, wherein the switching state detection means detects the switching state by detecting deterioration of the fuel cell. Further comprising voltage detection means for detecting the voltage of the fuel cell;
The fuel cell system according to any one of claims 4 to 7, wherein the switching state detection unit detects the switching state when the detected voltage is smaller than a reference voltage. The fuel cell includes a power generation unit composed of an electrolyte membrane and a pair of electrodes disposed on both sides of the electrolyte membrane, and a separator disposed on both sides of the power generation unit,
The separator having a contact surface in contact with one electrode of the pair of electrodes includes a reaction gas channel for supplying a reaction gas to the one electrode on the contact surface,
The fuel cell system includes:
An inlet performance detecting means for detecting the power generation performance on the inlet side of the reaction gas flow path during operation of the fuel cell;
Outlet performance detection means for detecting power generation performance on the outlet side of the reaction gas flow path during operation of the fuel cell;
By detecting the deterioration of the fuel cell based on the difference between the power generation performance on the inlet side and the power generation performance on the outlet side, the mode is switched to the dry mode or the wet mode. Switching state detecting means for detecting that
When the switching state is detected, the mode control means switches the mode so that the next stop process is a stop process in a mode different from the mode in the previous stop process. The fuel cell system according to claim 1 or 2. The fuel cell includes a power generation unit composed of an electrolyte membrane and a pair of electrodes disposed on both sides of the electrolyte membrane, and a separator disposed on both sides of the power generation unit,
The separator having a contact surface in contact with one electrode of the pair of electrodes includes a reaction gas channel for supplying a reaction gas to the one electrode on the contact surface,
The fuel cell system includes:
An inlet voltage detecting means for detecting an inlet voltage that is a voltage on the inlet side of the reaction gas flow path during operation of the fuel cell;
During operation of the fuel cell, outlet voltage detection means for detecting an outlet voltage which is a voltage on the outlet side of the reaction gas flow path;
An inlet / outlet voltage difference calculating means for calculating an inlet / outlet voltage difference which is a value obtained by subtracting the outlet voltage from the inlet voltage;
A switching state detecting means for detecting that the mode is switched to the drying mode or the wet mode when the absolute value of the inlet / outlet voltage difference is larger than a reference voltage difference; When the switching state is detected, the mode control means switches the mode so that the next stop process is a stop process in a mode different from the mode in the previous stop process. The fuel cell system according to claim 1 or 2, characterized in that The switching state detecting means includes
When the inlet / outlet voltage difference is larger than the first inlet / outlet voltage difference, a drying switching state for switching the mode to the drying mode is detected,
When the inlet / outlet voltage difference is smaller than the second inlet / outlet voltage difference, detecting a wet switching state for switching the mode to the wet mode;
The mode control means includes
When the wet switching state is detected, the mode in the next stop process is switched to the wet mode,
11. The fuel cell system according to claim 10, wherein when the drying switching state is detected, the mode is switched so that a mode in a next stop process becomes a drying mode. Voltage detecting means for detecting a first voltage in the first current of the fuel cell and a second voltage in a second current larger than the first current during operation of the fuel cell;
Voltage difference calculating means for calculating a voltage difference that is a value obtained by subtracting a second voltage from the first voltage;
A drying switching state for controlling the mode to the drying mode when the mode control means selects the wet mode and the voltage difference is greater than a first reference voltage difference; Switching state detecting means for detecting that
3. The fuel cell system according to claim 1, wherein when the drying switching state is detected, the mode control unit controls the mode in the next stop process to be the drying mode. 4. . Voltage detecting means for detecting a first voltage at a first current and a second voltage at a second current greater than the first current of the fuel cell during operation of the fuel cell;
Voltage difference calculating means for calculating a voltage difference which is a value obtained by subtracting a second voltage from the first voltage;
When the mode control means selects the drying mode, and the voltage difference is smaller than the second reference voltage difference, the wet switching for controlling the mode to the wet mode Switching state detecting means for detecting that the state is in a state,
3. The fuel cell system according to claim 1, wherein when the wet switching state is detected, the mode control unit performs control so that a mode in a next stop process becomes the wet mode. 4. . Voltage detecting means for detecting a first voltage at a first current and a second voltage at a second current greater than the first current of the fuel cell during operation of the fuel cell;
Voltage difference calculating means for calculating a voltage difference which is a value obtained by subtracting the second voltage from the first voltage;
A switching state detecting means for detecting a drying switching state for switching the mode to the drying mode when the voltage difference is larger than a first reference voltage difference;
When the voltage difference is smaller than a second reference voltage difference, a wet switching state for switching the mode to the wet mode is detected;
The mode control means includes
When the wet switching state is detected, the mode is controlled so that the mode in the next stop process becomes the wet mode,
3. The fuel cell system according to claim 1, wherein when the drying switching state is detected, the mode is controlled so that a mode in a next stop process becomes a drying mode. 4. Voltage detecting means for detecting a first voltage in a first current of the fuel cell and a second voltage in a second current larger than the first current;
Voltage difference detection means for detecting a voltage difference which is a value obtained by subtracting the second voltage from the first voltage;
Determining means for determining whether the voltage difference is in a normal state not less than the second reference voltage difference and not more than the first reference voltage difference;
A deterioration detecting means for detecting deterioration of the fuel cell when the voltage difference is not recognized to be in the normal state;
An apparatus for detecting deterioration of a fuel cell, comprising:

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