JP5324522B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

A fuel cell includes an anode and a cathode on both sides of a solid polymer electrolyte membrane. When a fuel gas (for example, hydrogen gas) is supplied to the anode and an oxidant gas (for example, air containing oxygen) is supplied to the cathode, Some generate electricity by chemical reaction.
In this fuel cell, if the water content of the solid polymer electrolyte membrane is insufficient, the ionic resistance increases and the output decreases. Therefore, in order to maintain a good power generation state, the solid polymer electrolyte membrane should be in an appropriate wet state. Need to keep on.

  Fuel that stops supplying air to the fuel cell when it detects a decrease in the humidity of the fuel cell in order to prevent a shortage of humidity in the polymer electrolyte membrane (sometimes referred to as fuel cell humidity) A battery system has been proposed (see, for example, Patent Document 1). In this fuel cell system, by stopping the supply of air to the fuel cell, air containing moisture is prevented from being discharged from the fuel cell, and the humidity of the fuel cell is prevented from further decreasing. Yes.

  In the case of a fuel cell system including a humidifier that collects moisture contained in the oxidant off-gas discharged from the cathode of the fuel cell and adds the collected moisture to the oxidant gas supplied to the fuel cell, The amount of condensed water in the oxidant off-gas is increased by reducing the pressure of the oxidant off-gas by increasing the pressure of the oxidant off-gas by reducing the back pressure valve provided in the oxidant off-gas flow path when the humidity drop of the oxidant gas supplied to the There is also proposed a fuel cell system that increases the amount of humidification to the oxidant gas in the humidifier and prevents the fuel cell from deficient in humidity (see, for example, Patent Document 2).

JP 2006-92801 A JP 2008-305700 A

However, the fuel cell system described in Patent Document 1 has a problem that the operation of the fuel cell cannot be continued because the supply of air to the fuel cell is stopped.
On the other hand, in the fuel cell system described in Patent Document 2, it is possible to prevent the fuel cell from being deficient in humidity while continuing the operation of the fuel cell, but when the pressure of the oxidant off-gas is increased by narrowing the back pressure valve, In order to keep the supply amount of oxidant gas to the fuel cell constant at the supply amount before the pressure rise, the load (rotation speed) of the air pump is increased, so the power consumption increases and the NET output (net) (Output) is reduced.

  In view of this, the present invention provides a fuel cell system that can advantageously prevent the fuel cell from deficient in humidity in terms of energy management.

The fuel cell system according to the present invention employs the following means in order to solve the above problems.
The invention according to claim 1 is a fuel cell (for example, a fuel cell 2 in an embodiment to be described later) that is supplied with an oxidant gas and a fuel gas to generate power, and an oxidizer that circulates the oxidant gas to the fuel cell. An oxidant gas flow path (for example, an air flow path 4 in an embodiment described later) and an oxidant off-gas flow path (for example, an air off-gas flow path 6 in an embodiment described later) through which the oxidant gas discharged from the fuel cell flows. ), An oxidant pump (for example, an air pump 3 in an embodiment described later) that is disposed in the oxidant gas flow path and sends an oxidant gas to the fuel cell, and the oxidant gas flow from the oxidant offgas flow path. A humidifier (for example, a humidifier 5 in an embodiment to be described later) that moves moisture to the path, and a back pressure valve (example) that adjusts the pressure of the oxidant gas in the fuel cell disposed in the oxidant offgas flow path. For example, a back pressure valve 7 in an embodiment described later), a temperature sensor that detects a temperature related to the temperature of the fuel cell (for example, an air offgas temperature sensor 23, a cooling water temperature sensor 24 in an embodiment described later), A control unit (for example, an electronic control unit 40 in an embodiment to be described later) that controls the oxidant pump and the back pressure valve based on temperature information detected by a temperature sensor, and the control unit includes the temperature sensor The humidification state value is repeatedly obtained from the cooling water temperature of the fuel cell and the inlet gas temperature of the humidifier detected in the step, and the dry determination value set according to the load state of the fuel cell is determined each time the repetition is performed. was added to the set value set by the fuel cell is judged to humidification shortage when the humidification state value is smaller than the drying judgment value, reduce the output of the oxidant pump Fuel cell system characterized by reducing the oxidizing gas supply amount (e.g., a fuel cell system 1 in the embodiment) is.

According to a second aspect of the present invention, there is provided a fuel cell (for example, a fuel cell 2 in an embodiment to be described later) that is supplied with an oxidant gas and a fuel gas to generate power, and an oxidant that causes the oxidant gas to flow to the fuel cell. An oxidant gas flow path (for example, an air flow path 4 in an embodiment described later) and an oxidant off-gas flow path (for example, an air off-gas flow path 6 in an embodiment described later) through which the oxidant gas discharged from the fuel cell flows. ), An oxidant pump (for example, an air pump 3 in an embodiment described later) that is disposed in the oxidant gas flow path and sends an oxidant gas to the fuel cell, and the oxidant gas flow from the oxidant offgas flow path. A humidifier (for example, a humidifier 5 in an embodiment to be described later) that moves moisture to the path, and a back pressure valve (example) that adjusts the pressure of the oxidant gas in the fuel cell disposed in the oxidant offgas flow path. For example, a back pressure valve 7 in an embodiment described later), a temperature sensor that detects a temperature related to the temperature of the fuel cell (for example, an air offgas temperature sensor 23, a cooling water temperature sensor 24 in an embodiment described later), A control unit (for example, an electronic control unit 40 in an embodiment to be described later) that controls the oxidant pump and the back pressure valve based on temperature information detected by a temperature sensor, and the control unit includes the temperature sensor The humidification state value is repeatedly obtained from the cooling water temperature of the fuel cell and the inlet gas temperature of the humidifier detected in the step, and the dry determination value set according to the load state of the fuel cell is determined each time the repetition is performed. was added to the set value set by the fuel cell is judged to humidification shortage when the humidification state value is smaller than the drying determination value, increases the output of the oxidant pump It not, the fuel cell system, characterized in that the opening of the back pressure valve by reducing to increase the pressure of the oxidant gas (e.g., fuel cell system 1 in the embodiment) is.

According to a third aspect of the present invention, there is provided a fuel cell (for example, a fuel cell 2 in an embodiment to be described later) that is supplied with an oxidant gas and a fuel gas to generate power, and an oxidant that circulates the oxidant gas to the fuel cell An oxidant gas flow path (for example, an air flow path 4 in an embodiment described later) and an oxidant off-gas flow path (for example, an air off-gas flow path 6 in an embodiment described later) through which the oxidant gas discharged from the fuel cell flows. ), An oxidant pump (for example, an air pump 3 in an embodiment described later) that is disposed in the oxidant gas flow path and sends an oxidant gas to the fuel cell, and the oxidant gas flow from the oxidant offgas flow path. A humidifier (for example, a humidifier 5 in an embodiment to be described later) that moves moisture to the path, and a back pressure valve (example) that adjusts the pressure of the oxidant gas in the fuel cell disposed in the oxidant offgas flow path. For example, a back pressure valve 7 in an embodiment described later), a temperature sensor that detects a temperature related to the temperature of the fuel cell (for example, an air offgas temperature sensor 23, a cooling water temperature sensor 24 in an embodiment described later), A control unit (for example, an electronic control unit 40 in an embodiment to be described later) that controls the oxidant pump and the back pressure valve based on temperature information detected by a temperature sensor, and the control unit includes the temperature sensor The humidification state value is repeatedly obtained from the cooling water temperature of the fuel cell and the inlet gas temperature of the humidifier detected in the step, and the dry determination value set according to the load state of the fuel cell is determined each time the repetition is performed. was added to the set value set by the fuel cell is judged to humidification shortage when the humidification state value is smaller than the drying judgment value, reduce the output of the oxidant pump In a fuel cell system (for example, a fuel cell system 1 in an embodiment to be described later), the supply amount of the oxidant gas is reduced and the pressure of the oxidant gas is increased by reducing the opening of the back pressure valve. is there.

According to the invention of claim 1, when the oxidant gas supply amount is reduced, the humidity of the oxidant gas humidified by the humidifier can be increased, and when the oxidant gas supply amount is reduced, The amount of moisture that the oxidant gas takes from the cathode (or solid polymer electrolyte membrane) of the fuel cell can be reduced, and the synergistic effect of these can restore the humidity of the fuel cell (solid polymer electrolyte membrane), The output of the fuel cell can be increased.
Further, since only the control to reduce the output of the oxidant pump so as to reduce the supply amount of the oxidant gas, the output of the fuel cell can be increased only by reducing the load of the oxidant pump, This is advantageous for energy management.

According to the second aspect of the present invention, if the pressure of the oxidant gas in the fuel cell is increased, the amount of condensed water in the oxidant off-gas can be increased. Since it is possible to increase the amount of oxidant gas with high humidity, the humidity of the fuel cell (solid polymer electrolyte membrane) can be recovered and the output of the fuel cell can be increased. .
Further, since the output of the oxidant pump is not increased, it is advantageous in energy management.

According to the third aspect of the invention, when the pressure of the oxidant gas in the fuel cell is increased, the amount of condensed water in the oxidant off-gas can be increased. Since the oxidant gas supply amount can be increased and the oxidant gas supply amount is reduced, the humidity of the oxidant gas humidified by the humidifier can be increased, and when the oxidant gas supply amount is reduced, the oxidant gas is reduced. Since the amount of moisture taken from the cathode (or solid polymer electrolyte membrane) of the fuel cell can be reduced, the synergistic effect of these can recover the humidity of the fuel cell (solid polymer electrolyte membrane), The output can be increased.
In addition, the output of the oxidant pump is reduced to reduce the supply amount of the oxidant gas, and the back pressure valve opening is reduced to increase the pressure of the oxidant gas in the fuel cell. As a result, the output of the fuel cell can be increased while the NET output is reduced. As a result, the NET output of the fuel cell can be increased, which is advantageous in terms of energy management.

1 is a schematic configuration diagram of a fuel cell system according to the present invention. It is the figure which showed typically the effect | action of the humidifier. It is a figure explaining the influence which an air flow rate has on humidity. It is a figure explaining the principle of humidity recovery. It is a flowchart which shows supply air control. It is an example of a humidification characteristic map. It is an example of the map for calculating a cathode dry determination value. It is an example of the time chart when the said supply air control is performed.

  Embodiments of a fuel cell system according to the present invention will be described below with reference to the drawings of FIGS. Note that the fuel cell system in this embodiment is a mode mounted on a fuel cell vehicle that travels by operating a drive motor with electricity generated by the fuel cell.

FIG. 1 is a diagram showing a schematic configuration of a fuel cell system 1 in this embodiment.
The fuel cell 2 is of a type that obtains electric power by chemically reacting a reaction gas. For example, a solid polymer electrolyte membrane made of a solid polymer ion exchange membrane or the like is sandwiched between an anode and a cathode from both sides to form a membrane electrode structure. A plurality of cells each having an anode gas channel and a cathode gas channel are stacked on both sides of the membrane electrode structure to form an FC stack. Hydrogen gas is supplied to the anode gas channel as a fuel gas, When air containing oxygen as an oxidant gas is supplied to the cathode gas flow path, hydrogen ions generated by the catalytic reaction at the anode move to the cathode through the solid polymer electrolyte membrane, and electrochemical reaction with oxygen at the cathode To generate electricity and produce water. Part of the generated water generated on the cathode side permeates the solid polymer electrolyte membrane and back diffuses to the anode side, so that the generated water also exists on the anode side.

Air as the oxidant gas is pressurized to a predetermined pressure by the air pump 3 and supplied to the cathode of the fuel cell 2 through the air flow path (oxidant gas flow path) 4. The air pump 3 uses an electric motor as a drive source, and the electric motor is driven by electricity generated by the fuel cell 2. The electricity generated by the fuel cell 2 can be stored in a battery (not shown), and the electric motor can be driven by electricity supplied from the battery.
After the air supplied to the fuel cell 2 is used for power generation, it is discharged from the fuel cell 2 together with the generated water on the cathode side as an air offgas (oxidant offgas) and passes through an air offgas passage (oxidant offgas passage) 6. It is led to the diluter 8 through.

In the middle of the air flow path 4 and the air off-gas flow path 6, for example, a humidifier 5 having a water permeable membrane is provided. FIG. 2 is a diagram schematically showing the operation of the humidifier 5. Air (supplied as supply air in FIG. 2) supplied to the cathode of the fuel cell 2 with the water permeable membrane 5 a interposed therebetween and the fuel cell 2. By circulating the air off gas discharged from the air, moisture contained in the air off gas passes through the water permeable membrane 5a and moves to the supply air side, and the air supplied to the fuel cell 2 is humidified. That is, the air supplied from the air pump 3 is humidified by the humidifier 5 and supplied to the fuel cell 2, and the air off-gas discharged from the fuel cell 2 is dehumidified by the humidifier 5 and supplied to the diluter 8. The In other words, the humidifier 5 is means for moving moisture from the air off-gas channel 6 to the air channel 4.
A back pressure valve 7 for adjusting the air pressure at the cathode of the fuel cell 2 is provided in the air off-gas flow path 6 downstream from the humidifier 5.

On the other hand, hydrogen gas as fuel gas is supplied from the high-pressure hydrogen tank 10 to the anode of the fuel cell 2 through the fuel gas passage 11. The fuel gas flow path 11 is provided with a shut-off valve 12, a regulator 13, and an ejector 14 in order from the upstream side.
The regulator 13 uses the pressure of the air supplied to the fuel cell 2 (that is, the cathode pressure) as a signal pressure, and the high-pressure hydrogen gas supplied from the hydrogen tank 10 becomes a pressure higher than the signal pressure by a predetermined pressure. Thus, the hydrogen gas regulated by the regulator 13 is supplied to the anode of the fuel cell 2. Thereby, the pressure difference between the cathode and the anode of the fuel cell 2 is maintained at a predetermined pressure. In order to guide the signal pressure to the regulator 13, a pressure guiding path 15 branched from the air flow path 4 on the upstream side of the humidifier 5 is connected to the regulator 13. Reference numeral 16 is a relief valve provided in Shirube圧path 15.

Unreacted hydrogen gas that has not been consumed in the fuel cell 2 is discharged from the fuel cell 2 as fuel off-gas, sucked into the ejector 14 through the fuel off-gas channel 17, and fresh hydrogen gas supplied from the hydrogen tank 10. And are supplied to the anode of the fuel cell 2 again. That is, in the fuel cell system 1, hydrogen gas discharged from the fuel cell 2 is circulated and used as fuel gas.
The fuel off-gas flow path 17 is provided with a catch tank 18 for collecting condensed water contained in the hydrogen off-gas, and the ejector 14 is supplied with hydrogen gas from which condensed water has been removed. The water collected in the catch tank 18 can be discharged to the diluter 8 via the drainage channel 19, and when a predetermined amount of water accumulates in the catch tank 18, a drain valve 20 provided in the drainage channel 19 is provided. It is opened and discharged to the diluter 8.
Further, a purge passage 22 having a discharge valve 21 branches off from the fuel off-gas passage 17 downstream of the catch tank 18. The discharge valve 21 is normally closed during power generation of the fuel cell 2 and opens when a predetermined condition is satisfied, and discharges the fuel off-gas to the diluter 8.
In the diluter 8, the fuel off-gas is diluted by the air off-gas discharged from the back pressure valve 7 and is discharged from the diluter 8.

Further, the fuel cell 2 includes a cooling passage inside, and heat is taken from the fuel cell 2 by circulating cooling water through the cooling passage, and the fuel cell 2 does not exceed a predetermined upper limit temperature due to heat generated by power generation. So cool. This cooling water is circulated between the fuel cell 2 and the cooling device 30.
The cooling device 30 includes a radiator 31, a cooling water supply passage 32 that connects the outlet of the radiator 31 and the cooling passage inlet of the fuel cell 2, and a cooling that connects the cooling water outlet of the fuel cell 2 and the inlet of the radiator 31. A bypass flow that bypasses the radiator 31 and connects the cooling water supply channel 32 and the cooling water return channel 33 by bypassing the water return channel 33, the cooling water pump 34 provided in the middle of the cooling water supply channel 32 A passage 35 and a switching valve 36 for selecting which of the radiator 31 and the bypass passage 35 to flow cooling water are provided.

The cooling water is boosted by a cooling water pump 34 and supplied to the cooling passage of the fuel cell 2, and the cooling water warmed by heat exchange with the fuel cell 2 is discharged from the fuel cell 2 and passes through the cooling water return passage 33. And sent to the radiator 31. Cooling water cooled by heat radiation to the outside in the Raj ethanone 31 returns to the cooling water pump 34 through the cooling water supply passage 32, it is supplied is boosted again with the cooling water pump 34 to the fuel cell 2. Further, when it is desired to raise the temperature of the fuel cell 2, the switching valve 36 is switched so that the cooling water is bypassed through the radiator 31 and circulated through the bypass passage 35, thereby dissipating heat from the radiator 31.

The air flow path 4 upstream of the humidifier 5 is provided with a humidifier inlet gas temperature sensor 23 for detecting the temperature of the air supplied from the air pump 3 to the humidifier 5, and the cooling water return flow path. A cooling water temperature sensor 24 for detecting the temperature of the cooling water discharged from the fuel cell 2 is provided at 33. The cooling water temperature detected by the cooling water temperature sensor 24 is substantially equal to the internal temperature of the fuel cell 2. Furthermore, the fuel cell system 1 includes a current meter 25 for detecting an extraction current extracted from the fuel cell 2. The temperature sensors 23 and 24 and the ammeter 25 output an electrical signal corresponding to the detected value to an electronic control unit (hereinafter abbreviated as ECU) 40.

  The ECU 40 calculates the output required for the fuel cell 2 according to the operating state of the fuel cell vehicle, calculates the target air flow rate and the target air pressure according to the required output, and sets the target air flow rate at the target air pressure. The load (rotation speed) control of the air pump 3 and the opening control of the back pressure valve 7 are performed so that air is supplied to the cathode of the fuel cell 2.

  Further, in the fuel cell system 1, the ECU 40 reduces the humidity in the fuel cell 2 below a predetermined value based on the temperature information detected by the temperature sensors 23 and 24 and the extracted current information detected by the ammeter 25. If it is determined whether the humidity in the fuel cell 2 is not lower than a predetermined value, the normal mode control is performed based on the target air flow rate and the target air pressure in the normal mode. When it is judged that the humidity in the inside is lower than the predetermined value, high-temperature mode control is performed by using the target air flow rate and target air pressure in the high-temperature mode to recover (increase) the humidity and generate power at high temperatures. Improve performance.

Here, a method for increasing the humidity in the fuel cell 2 that has decreased due to the high temperature of the fuel cell 2 will be considered.
The first method is a method of reducing the opening degree of the back pressure valve 7. When the opening of the back pressure valve 7 is narrowed, the pressure of the air supplied to the fuel cell 2 and the pressure of the air off-gas discharged from the fuel cell 2 are increased, both of which make it easy for water to condense. (See FIG. 4A). When the condensed water in the air off gas increases, the amount of water moving from the air off gas to the air side in the humidifier 5 increases, and as a result, the humidity of the air supplied to the fuel cell 2 can be increased (FIG. 4). (See (B)). This high humidity air is supplied to the cathode of the fuel cell 2, and the pressure of this air is also high and it is easy to condense. Therefore, the condensed water supplied to the cathode of the fuel cell 2 together with the air passes through the cathode. At the same time, the moisture in the air is condensed at the cathode to wet the cathode. Thereby, the humidity of the cathode of the fuel cell 2 can be recovered, that is, the humidity of the fuel cell 2 can be recovered. Then, when the humidity of the fuel cell 2 recovers, the voltage of the fuel cell 2 increases and the output can be increased.

However, as in the prior art described above, when the opening of the back pressure valve 7 is throttled, the air flow to be supplied to the fuel cell 2 is set to be the same as before the throttle control of the back pressure valve 7 is throttled. When the load (rotation speed) of the pump 3 is increased, the power consumption in the air pump 3 is increased, and even if the output of the fuel cell 2 is increased, the increase in the NET output is reduced. This is disadvantageous for energy management.
Therefore, when the opening degree of the back pressure valve 7 is reduced, control is performed so as not to increase the power supplied to the air pump 3.

  The second method is a method for reducing the amount of air supplied to the cathode of the fuel cell 2. As shown in FIG. 3, when the humidity of the air off gas is constant and the amount of water moving from the air off gas to the air side in the humidifier 5 (in other words, the amount of condensed water received by the air) is constant. The humidity of the air supplied to the fuel cell 2 can be increased as the flow rate of the air supplied to the fuel cell 2 is smaller than that of the larger one, and the humidification ratio is increased. Further, if the flow rate of air supplied to the fuel cell 2 is small, the amount of water that the air takes away from the cathode of the fuel cell 2 decreases, which acts to increase the humidity of the cathode. Thereby, the humidity of the cathode of the fuel cell 2 can be recovered, that is, the humidity in the fuel cell 2 can be recovered (see FIG. 4C). Then, when the humidity of the fuel cell 2 recovers, the voltage of the fuel cell 2 increases and the output can be increased.

Therefore, in this fuel cell system 1, the process (humidity recovery process) for recovering the humidity in the fuel cell 2 that has decreased due to the high temperature of the fuel cell 2 is the control described in the following (A) to (C). One of them will be executed.
(A) The air pump 3 is controlled so as to reduce the air flow rate to the fuel cell 2. In other words, the output of the air pump 3 is reduced to reduce the air flow rate. This corresponds to the invention according to claim 1.
(B) The back pressure valve 7 is controlled so as to increase the air pressure at the cathode of the fuel cell 2 without increasing the power supplied to the air pump 3. In other words, the air pressure is increased by reducing the opening of the back pressure valve 7 without increasing the output of the air pump 3. This corresponds to the invention according to claim 2.
(C) The air pump 3 is controlled so as to decrease the air flow rate to the fuel cell 2 and the back pressure valve 7 is controlled so as to increase the air pressure at the cathode of the fuel cell 2. In other words, the output of the air pump 3 is reduced to lower the air flow rate, and the opening of the back pressure valve 7 is reduced to increase the air pressure. This corresponds to the invention according to claim 3.

  When the control is performed as in (A) above, the air flow rate to the fuel cell 2 is reduced, and as described above, the humidification ratio with respect to the air in the humidifier 5 increases, so the air supplied to the fuel cell 2 When the air flow rate is lowered, the amount of water taken from the cathode of the fuel cell 2 can be reduced, and the humidity of the fuel cell 2 can be recovered by a synergistic effect thereof. The output of the fuel cell 2 can be increased. Further, in the control (A), since the output of the air pump 3 is only controlled so as to reduce the air flow rate, the output of the fuel cell 2 can be increased only by reducing the load of the air pump 3. As a result, the NET output of the fuel cell 2 can be increased, which is advantageous for energy management.

  When the control is performed as in (B) above, the amount of condensed water in the air off-gas can be increased by increasing the air pressure at the cathode of the fuel cell 2, so that the humidifier 5 increases the amount of humidification to the air. High humidity air can be supplied to the cathode of the fuel cell 2, and condensed water supplied to the cathode together with air and moisture in the air supplied to the cathode are condensed at the cathode. Since the condensed water wets the cathode, the humidity of the fuel cell 2 can be recovered, and the output of the fuel cell 2 can be increased. In the control (B), since the output of the air pump 3 is not increased, the NET output of the fuel cell 2 can be increased, which is advantageous in terms of energy management.

  When the control is performed as in (C) above, the air flow rate to the fuel cell 2 is reduced, so that the humidification ratio with respect to the air in the humidifier 5 is increased, so that the humidity of the air supplied to the fuel cell 2 is increased. If the air flow rate is reduced, the amount of water taken from the cathode of the fuel cell can be reduced, and further, the amount of condensed water in the air off-gas can be increased by increasing the air pressure at the cathode of the fuel cell 2. In the humidifier 5, the humidified air can be increased, high-humidity air can be supplied to the cathode of the fuel cell 2, condensed water supplied to the cathode together with air, and in the air Since the condensed water generated by the condensation of water at the cathode wets the cathode, the humidity of the fuel cell 2 can be restored and the output of the fuel cell 2 can be increased. That. In the control (C), the opening of the back pressure valve 7 is decreased to increase the air pressure at the cathode of the fuel cell 2. At the same time, the output of the air pump 3 is decreased to supply the fuel cell 2 to the fuel cell 2. Since the air flow rate is lowered, the output of the fuel cell 2 can be increased while reducing the load of the air pump 3, and as a result, the NET output of the fuel cell 2 can be increased, which is advantageous in terms of energy management. Become.

Next, a specific example of the control (C) will be described with reference to a flowchart shown in FIG. 5 and a time chart shown in FIG.
First, in step S101, it is determined whether or not the drying determination flag is 1. The initial value of the drying determination flag is set to 0.
If the determination result in step S101 is “NO” (≠ 1), the process proceeds to step S102, the drying determination flag is set to 0, the dry determination finalizing counter is reset, and the process proceeds to step S103.
In step S103, the target air pressure in the normal mode according to the load of the fuel cell 2 is calculated with reference to, for example, a map (not shown).
Next, proceeding to step S104, the target air flow rate in the normal mode according to the current load of the fuel cell 2 is calculated with reference to, for example, a map (not shown).

Next, it progresses to step S105 and the humidification characteristic map according to the present load of the fuel cell 2 is selected. The applicant applies the temperature of air supplied from the air pump 3 to the humidifier 5 (hereinafter referred to as humidifier inlet air temperature) and the temperature of cooling water discharged from the fuel cell 2 (hereinafter referred to as cooling water outlet temperature). And the humidity of the cathode air of the fuel cell 2 (hereinafter abbreviated as “cathode humidity”), and the correlation varies depending on the load state (extraction current I) of the fuel cell 2. I have obtained this as knowledge. Therefore, an experiment is performed in advance, and for each load of the fuel cell 2, as shown in FIG. 6, the relationship between the humidifier inlet air temperature, the cooling water outlet temperature, and the cathode humidity is mapped and prepared as a humidification characteristic map. . In step S105, a humidification characteristic map corresponding to the current load of the fuel cell 2 is selected from the prepared humidification characteristic map for each load.
Next, the process proceeds to step S106, with reference to the selected humidification characteristic map, based on the cooling water temperature detected by the cooling water temperature sensor 24 and the temperature of the supply air detected by the humidifier inlet gas temperature sensor 23. Thus, the cathode humidity A1 of the fuel cell 2 is calculated.

  Next, the process proceeds to step S107, and the cathode drying determination value A2 corresponding to the load of the fuel cell 2 is calculated. Here, the cathode drying determination value A2 is a humidity threshold value for determining that the cathode of the fuel cell 2 is dry when the cathode humidity A1 falls below the cathode drying determination value A2, and the load of the fuel cell 2 It is a variable that changes depending on the state. The load of the fuel cell 2 is determined by the extraction current I detected by the ammeter 25.

FIG. 7 shows a map example when the cathode drying determination value (humidity value) A2 is calculated using a map. FIG. 7A is a map for calculating the drying determination initial setting value A ₂₁ , and FIG. 7B is a map for calculating the drying determination addition rate A ₂₂ .
The dry determination initial setting value A ₂₁ is based on the current I taken out from the fuel cell 2 at the beginning of the normal mode operation or when the normal mode is switched to the high temperature mode. It is set with reference to the drying determination initial setting value map shown in FIG. In the dry determination initialization value map shown in FIG. 7 (A), drying determination the initial setting value A ₂₁ as the obtained current value I is increased is set to a large value.

The drying determination addition rate A ₂₂ is added to the drying determination initial setting value A _{21 when} the temperature of the fuel cell 2 exceeds a predetermined temperature T1 set in advance after the drying determination initial setting value A ₂₁ is set. Based on the extraction current I at that time, it is set with reference to the dry determination addition rate map shown in FIG. In the dry determination addition rate map shown in FIG. 7 (B), drying determination the addition rate A ₂₂ as the extraction current I is increased is set to a large value.

The cathode dry judgment value A2 is dried determined initial set value A ₂₁ dry judgment addition rate A ₂₂ is calculated by adding the dry determination addition rate A ₂₂ continues to be added, i.e. will be accumulated. Then, when switching from the normal mode to the high temperature mode, the integration of the drying determination addition rate A ₂₂ is reset, and the drying determination initial setting value A ₂₁ is reset. Also, during the high temperature mode it is not performed integrated drying determination the addition rate A _22.

Next, the process proceeds from step S107 to step S108, and it is determined whether or not the cathode humidity A1 calculated in step S106 is smaller than the cathode drying determination value A2 calculated in step S107.
If the determination result in step S108 is “NO” (A1 ≧ A2), it is determined that the humidity of the cathode of the fuel cell 2 is appropriate, the process proceeds to step S109, and the air target at the anode of the fuel cell 2 is determined. The pressure (target air pressure) is set to the target air pressure in the normal mode calculated in step S103, and the opening control of the back pressure valve 7 is executed so as to be the target air pressure.
In step S110, the target flow rate of air supplied to the fuel cell 2 (target air flow rate) is set to the target air flow rate in the normal mode calculated in step S104, and the air pump 3 is set to the target air flow rate. The rotational speed control is executed, and the execution of this routine is temporarily terminated.

  On the other hand, if the determination result in step S108 is “YES” (A1 <A2), it is determined that the humidity of the cathode of the fuel cell 2 is insufficient, and the process proceeds to step S111 to set the target air pressure to the fuel cell. The target air pressure in the high temperature mode corresponding to the load of 2 is set, and the opening control of the back pressure valve 7 is executed so as to be the target air pressure. Here, the target air pressure in the high temperature mode corresponding to the load of the fuel cell 2 is set to a value larger by a predetermined pressure than the target air pressure in the normal mode corresponding to the load of the fuel cell 2. The predetermined pressure at this time may be a constant value regardless of the load of the fuel cell 2 or may be a variable that changes according to the load of the fuel cell 2.

Furthermore, it progresses to step S112, the target air flow rate is set to the target air flow rate in the high temperature mode according to the load of the fuel cell 2, and the rotation speed control of the air pump 3 is executed so as to become the target air flow rate. Here, the target air flow rate in the high temperature mode according to the load of the fuel cell 2 is set to a value smaller by a predetermined amount than the target air flow rate in the normal mode according to the load of the fuel cell 2. The predetermined amount at this time may be a constant value regardless of the load of the fuel cell 2 or may be a variable that changes according to the load of the fuel cell 2.
Next, the process proceeds to step S113, the drying determination flag is set to 1. Further, the process proceeds to step S114, 1 is added to the dry determination finalizing counter, and the execution of this routine is temporarily ended.

  If the drying determination flag is set to 1 in step S113, the next time this routine is executed, an affirmative determination is made in step S101. Therefore, the process proceeds from step S101 to step S115, and whether or not the dry determination finalizing counter is greater than or equal to the specified count. Determine whether.

  If the determination result in step S115 is “NO” (less than the specified count), the process proceeds to step S111. That is, the processes in steps S111 to S114 are repeated until the dry determination finalizing counter reaches the predetermined count, and the supply air control (high temperature mode control) based on the target air pressure and the target air flow rate in the high temperature mode is continued.

  On the other hand, if the determination result in step S115 is “YES” (more than the specified count), the process proceeds to step S102, the drying determination flag is set to 0, and the dry determination finalizing counter is reset. That is, when the dry determination finalizing counter reaches the specified count, the high-temperature mode control is temporarily terminated and switched to supply air control (normal mode control) based on the target air pressure and target air flow rate in the normal mode.

The time chart shown in FIG. 8 is an example when the supply air control is performed as described above.
When the normal mode control is performed and the temperature of the cooling water is constant at the predetermined temperature T1 (until time t1 in FIG. 8), the cathode humidity A1 is substantially constant, and the cathode drying determination value A2 is also constant, and the cathode humidity A1 is larger than the cathode drying determination value A2. That is, the cathode of the fuel cell 2 is kept at a sufficient humidity.

When the temperature of the cooling water exceeds the predetermined temperature T1 after the time t1 and the temperature rise continues, the cathode humidity A1 gradually decreases as the temperature of the fuel cell 2 rises. On the other hand, the cathode dried determination value A2, by the temperature of the fuel cell 2 is integrated in the drying determination the addition rate A ₂₂ from the time exceeds the predetermined temperature T1 is started, gradually increases.

When the cathode humidity A1 falls below the cathode drying determination value A2 at time t2, the normal mode control is switched to the high temperature mode control. When the high temperature mode control is entered, the cathode pressure of the fuel cell 2 becomes higher than that in the normal mode by reducing the opening of the back pressure valve 7, and the rotational speed of the air pump 3 is reduced to supply the fuel cell 2. The air flow rate to be reduced is lower than that in the normal mode.
On the other hand, the cathode dried determination value A2 is the integrated value of the dry determination addition rate A ₂₂ immediately after switching from the normal mode to the high temperature mode is reset, dried determined initial set value A ₂₁ is because it is re-set to reduce immediately .

  Further, the cooling water temperature of the fuel cell 2 does not decrease even when the high temperature mode control is entered, and exceeds the maximum value of the cooling water temperature in the normal mode control, but the cathode pressure of the fuel cell 2 is higher than that in the normal mode. As the air flow rate supplied to the fuel cell 2 becomes lower than that in the normal mode, the cathode humidity A1 recovers and exceeds the cathode drying determination value A2.

  In the embodiment described above, the cathode humidity A1 is calculated based on the temperature of the cooling water and the air temperature at the inlet of the humidifier, and when the condition that the cathode humidity A1 is lower than the cathode drying determination value A2 is satisfied, It is determined that the cathode of the fuel cell 2 is deficient in humidity, and the control of (C) described above is executed as the humidity recovery process. However, the humidity recovery process is not limited to the control of (C). ) Or (B).

1 Fuel Cell System 2 Fuel Cell 3 Air Pump (Oxidant Pump)
4 Air channel (oxidant gas channel)
5 Humidifier 6 Air off gas flow path (oxidant off gas flow path)
7 Back pressure valve 23 Humidifier inlet gas temperature sensor (temperature sensor)
24 Cooling water temperature sensor (temperature sensor)
40 Electronic control unit (control unit)

Claims (3)

A fuel cell that is supplied with an oxidant gas and a fuel gas to generate electricity;
An oxidant gas flow path for flowing an oxidant gas to the fuel cell;
An oxidant off-gas flow path for circulating an oxidant gas discharged from the fuel cell;
An oxidant pump that is disposed in the oxidant gas flow path and sends an oxidant gas to the fuel cell;
A humidifier that moves moisture from the oxidant off-gas channel to the oxidant gas channel;
A back pressure valve arranged in the oxidant off-gas flow path to adjust the pressure of the oxidant gas in the fuel cell;
A temperature sensor for detecting a temperature related to the temperature of the fuel cell;
A controller that controls the oxidant pump and the back pressure valve based on temperature information detected by the temperature sensor;
The controller is
Repetitively obtaining a humidification state value from the coolant temperature of the fuel cell detected by the temperature sensor and the inlet gas temperature of the humidifier,
The dryness determination value set according to the load state of the fuel cell is set by adding to the previously set value for each repetition,
When the humidification state value is smaller than the drying determination value , it is determined that the inside of the fuel cell is insufficiently humidified, and the output of the oxidant pump is reduced to reduce the oxidant gas supply amount. . A fuel cell that is supplied with an oxidant gas and a fuel gas to generate electricity;
An oxidant gas flow path for flowing an oxidant gas to the fuel cell;
An oxidant off-gas flow path for circulating an oxidant gas discharged from the fuel cell;
An oxidant pump that is disposed in the oxidant gas flow path and sends an oxidant gas to the fuel cell;
A humidifier that moves moisture from the oxidant off-gas channel to the oxidant gas channel;
A back pressure valve arranged in the oxidant off-gas flow path to adjust the pressure of the oxidant gas in the fuel cell;
A temperature sensor for detecting a temperature related to the temperature of the fuel cell;
A controller that controls the oxidant pump and the back pressure valve based on temperature information detected by the temperature sensor;
The controller is
Repetitively obtaining a humidification state value from the coolant temperature of the fuel cell detected by the temperature sensor and the inlet gas temperature of the humidifier,
The dryness determination value set according to the load state of the fuel cell is set by adding to the previously set value for each repetition,
When the humidification state value is smaller than the drying determination value , it is determined that the inside of the fuel cell is insufficiently humidified, and without increasing the output of the oxidant pump, the opening of the back pressure valve is reduced to reduce the amount of oxidant gas. A fuel cell system characterized by increasing pressure. A fuel cell that is supplied with an oxidant gas and a fuel gas to generate electricity;
An oxidant gas flow path for flowing an oxidant gas to the fuel cell;
An oxidant off-gas flow path for circulating an oxidant gas discharged from the fuel cell;
An oxidant pump that is disposed in the oxidant gas flow path and sends an oxidant gas to the fuel cell;
A humidifier that moves moisture from the oxidant off-gas channel to the oxidant gas channel;
A back pressure valve arranged in the oxidant off-gas flow path to adjust the pressure of the oxidant gas in the fuel cell;
A temperature sensor for detecting a temperature related to the temperature of the fuel cell;
A controller that controls the oxidant pump and the back pressure valve based on temperature information detected by the temperature sensor;
The controller is
Repetitively obtaining a humidification state value from the coolant temperature of the fuel cell detected by the temperature sensor and the inlet gas temperature of the humidifier,
The dryness determination value set according to the load state of the fuel cell is set by adding to the previously set value for each repetition,
When the humidification state value is smaller than the drying determination value , it is determined that the inside of the fuel cell is insufficiently humidified, the output of the oxidant pump is reduced to reduce the oxidant gas supply amount, and the opening of the back pressure valve A fuel cell system characterized in that the pressure of the oxidant gas is increased by reducing the pressure.

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