JP2008177116A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely detect a failure when the failure occurs in a control valve controlling a conduction state of an introduction passage for introducing an anode off-gas into a cathode, in relation to a fuel cell system. <P>SOLUTION: This fuel cell system 10 includes: the introduction passage 40 for introducing the anode off-gas discharged from the anode of a fuel cell 12 into the cathode; the control valve 42 controlling the conduction state of the introduction passage 40; and a hydrogen concentration sensor 46 detecting concentration of hydrogen included in a gas flowing into the cathode. An ECU 50 determines that the control valve 42 is in an open failure when the hydrogen concentration detected by the hydrogen concentration sensor 46 is larger than a predetermined value in the case where anode pressure detected by a pressure sensor 36 is higher than cathode pressure detected by a pressure sensor 38, and a closing instruction is output to the control valve 42. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system.

  Japanese Patent Application Laid-Open No. 9-31167 discloses an anode off-gas (fuel electrode exhaust gas) discharged from an anode (fuel electrode) of a fuel cell as a cathode through an introduction passage (closed line) having a control valve (valve means). A system that is introduced into the (air electrode) is disclosed. According to such a system, exhaust gas containing hydrogen gas (fuel gas) can be prevented from being released to the outside air. For this reason, there exists an advantage that the diluter which dilutes exhaust gas becomes unnecessary.

JP 9-31167 A Japanese Patent No. 2541288

  In the above system, the hydrogen in the anode off-gas is combusted in the cathode. For this reason, if an excessive amount of hydrogen flows into the cathode, the temperature of the fuel cell becomes too high. In order to avoid such a situation, it is necessary to prevent an excessive amount of hydrogen from flowing into the cathode by controlling the opening degree of the control valve provided in the introduction passage. However, assuming a case where the control valve fails to open, an excessive amount of hydrogen may flow into the cathode. In the system described in the above publication, since such a problem is not taken into consideration, there is a problem that it is not possible to cope with a control valve failure.

  The present invention has been made to solve the above-described problems. When a failure occurs in the control valve for controlling the conduction state of the introduction passage for introducing the anode off gas to the cathode, the failure is reliably detected. An object of the present invention is to provide a fuel cell system capable of performing the above.

In order to achieve the above object, a first invention is a fuel cell system,
A fuel cell that generates power by receiving supply of fuel gas to the anode and supply of oxidant gas to the cathode; and
An introduction passage for introducing an anode off-gas discharged from the anode into the cathode;
A control valve for controlling the conduction state of the introduction passage;
Fuel gas concentration detection means for detecting the concentration of fuel gas contained in the gas flowing into the cathode;
Valve failure detection means for detecting a failure of the control valve based on the content of the command issued to the control valve and the fuel gas concentration detected by the fuel gas concentration detection means;
It is characterized by providing.

The second invention is the first invention, wherein
A detecting means for detecting that the anode pressure is higher than the cathode pressure;
The valve failure detection means detects that the anode pressure is higher than the cathode pressure and the detected fuel gas concentration is larger than a predetermined value when a close command is issued to the control valve. Includes means for determining that the control valve has an open failure.

The third invention is the first or second invention, wherein
Pressure adjusting means for adjusting the anode pressure and the cathode pressure;
When an open failure of the control valve is detected by the valve failure detection means, the flow rate of the anode off gas flowing into the cathode through the introduction passage is reduced by reducing the differential pressure between the anode pressure and the cathode pressure. A flow rate suppressing means for suppressing,
Is further provided.

  According to the first aspect of the present invention, in the fuel cell system including the introduction passage for introducing the anode off-gas discharged from the anode into the cathode and the control valve for controlling the conduction state of the introduction passage, the gas flowing into the cathode Based on the detected value of the concentration of the contained fuel gas and the content of the command issued to the control valve, it is possible to accurately detect a failure of the control valve. Thereby, when a failure occurs in the control valve, an appropriate measure can be taken quickly. Therefore, for example, a situation in which the temperature of the fuel cell rises abnormally can be avoided, the fuel cell can be reliably protected, and high safety can be obtained.

  According to the second invention, when it is detected that the anode pressure is higher than the cathode pressure and the close command is issued to the control valve, the concentration of the fuel gas contained in the gas flowing into the cathode is predetermined. When the value is larger than the value, it can be determined that the control valve has an open failure. Thereby, when an open failure occurs in the control valve, this can be reliably detected.

  According to the third invention, when an open failure of the control valve is detected, the flow rate of the anode off gas flowing into the cathode through the introduction passage is reduced by reducing the differential pressure between the anode pressure and the cathode pressure. can do. As a result, even when the control valve fails to open, the amount of fuel gas flowing from the anode to the cathode can be reduced. For this reason, the heat_generation | fever by combustion at a cathode can be suppressed and it can avoid reliably that the temperature of a fuel cell rises too much. That is, the fuel cell can be reliably protected and safety can be ensured. Further, even after the control valve has failed to open, the operation of the fuel cell system can be safely continued while securing a certain amount of power generation.

Embodiment 1 FIG.
[Configuration of fuel cell system]
FIG. 1 is a schematic diagram showing a configuration of a fuel cell system 10 according to Embodiment 1 of the present invention. The fuel cell system 10 is mounted on, for example, a fuel cell vehicle. The fuel cell system 10 includes a fuel cell 12. In the present embodiment, the fuel cell 12 is a fuel cell provided with a solid polymer separation membrane, and is composed of two fuel cell stacks 12a and 12b.

  Each of the stacks 12a and 12b is configured by stacking a plurality of unit cells including an electrolyte membrane, an anode, a cathode, and a separator. Each of the stacks 12a and 12b includes, for example, about 200 unit cells.

  The electrolyte membrane provided in the unit cell is a proton conductive ion exchange membrane formed of, for example, a fluorine-based solid polymer material. Both the anode and the cathode are formed of carbon cloth woven with carbon fibers, and include a catalyst layer and a diffusion layer. Further, the separator is formed of a gas-impermeable conductive member such as dense carbon which is compressed by carbon and impermeable to gas. Adjacent unit cells are stacked with the anode of one cell and the cathode of the other cell facing each other via a separator.

  As shown in FIG. 1, an anode gas channel 14 and a cathode gas channel 16 are connected to the fuel cell 12. Hydrogen gas (hydrogen rich gas) as fuel gas (anode gas) is supplied to the anode gas flow path 14 from a hydrogen supply source such as a high-pressure hydrogen tank. The hydrogen gas is sent to the anode in each stack 12a, 12b.

  In the middle of the anode gas flow path 14, a main valve 18, a hydrogen pressure regulating valve 20, and a hydrogen inlet valve 22 are provided in order from the hydrogen supply source side. The hydrogen pressure regulating valve 20 regulates the pressure of the anode gas at the inlet of the fuel cell 12 to a required appropriate pressure.

  An air compressor 24 is provided in the cathode gas flow path 16. The air compressor 24 sends a cathode gas (air) as an oxidizing gas containing oxygen to the cathodes in the stacks 12a and 12b.

  A coolant is circulated in each unit cell of the fuel cell 12. Thereby, the excessive temperature rise of the fuel cell 12 accompanying electric power generation is suppressed, and the temperature of the fuel cell 12 is set to an optimal value.

  The anode gas supplied through the anode gas flow path 14 is sent to the anode of each unit cell of each stack 12a, 12b. Similarly, the cathode gas supplied through the cathode gas flow path 16 is sent to the cathode of each unit cell of each stack 12a, 12b.

In the anode of the fuel cell 12, when an anode gas is sent, hydrogen ions are generated from hydrogen in the anode gas (H ₂ → 2H ⁺ + 2e ⁻ ). On the other hand, when the cathode gas is fed into the cathode, oxygen ions are generated from the oxygen in the cathode gas. At the same time, water (product water) is generated from the hydrogen ions and oxygen ions at the cathode ((1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O). Most of this water absorbs the heat generated in the fuel cell 12 to become water vapor, is contained in the cathode offgas, and is discharged.

  The gas after reacting at the anode of each unit cell is sent to the anode offgas flow path 26 as the anode offgas. A hydrogen pump 28 is provided in the anode off gas passage 26. The anode off gas is returned to the anode gas flow path 14 again by driving the hydrogen pump 28. The anode off gas returned to the anode gas flow path 14 is replenished with hydrogen from the hydrogen supply source and is sent to the fuel cell 12 again. By sending the anode off gas to the fuel cell 12, unreacted hydrogen contained in the anode off gas can be reacted in the fuel cell 12, and the utilization efficiency of hydrogen can be improved. Further, the flow rate of the cathode gas sent to the fuel cell 12 can be controlled by the hydrogen pressure regulating valve 20 or the hydrogen pump 28.

  On the other hand, the gas after reacting at the cathode of each unit cell is sent to the cathode offgas channel 30 as cathode offgas. The cathode off gas is discharged to the outside through the cathode off gas flow path 30. The cathode off gas flow path 30 is provided with an air pressure regulating valve 32 for adjusting the pressure of the cathode off gas. According to the air pressure regulating valve 32, the pressure of the cathode off-gas discharged from the fuel cell 12 can be controlled. The flow rate of the cathode gas sent to the fuel cell 12 can be controlled by the air compressor 24 and the air pressure regulating valve 32.

  Further, a humidification module 34 is provided between the cathode gas channel 16 and the cathode offgas channel 30. The humidification module 34 has a function of absorbing moisture contained in the cathode off-gas, that is, moisture generated in the fuel cell 12, and humidifying the cathode gas in the cathode gas channel 16 with the absorbed moisture.

  A pressure sensor 36 is installed in the anode off gas passage 26. According to the pressure sensor 36, the anode outlet pressure can be detected. A pressure sensor 38 is installed in the cathode gas channel 16. The pressure sensor 38 can detect the cathode inlet pressure.

  Further, the system of the present embodiment includes an introduction passage 40 that connects the anode off-gas passage 26 and the cathode gas passage 16. In the present embodiment, the anode off gas taken out from the anode off gas passage 26 can be introduced into the cathode gas passage 16 through the introduction passage 40 and introduced into the cathode of the fuel cell 12.

  In the middle of the introduction passage 40, a control valve 42 and a condenser 44 are installed. By controlling the opening degree (conduction state) of the control valve 42, the amount of anode off gas introduced into the cathode through the introduction passage 40 can be controlled. Further, according to the condenser 44, moisture in the anode off gas can be collected.

  A hydrogen concentration sensor 46 is installed in the cathode gas flow channel 16 on the downstream side from the joining portion of the cathode gas flow channel 16 and the introduction passage 40. The hydrogen concentration sensor 46 can detect the concentration of hydrogen contained in the gas flowing into the cathode of the fuel cell 12.

  The system of this embodiment further includes an ECU (Electronic Control Unit) 50. The ECU 50 is connected to various sensors (not shown) for detecting the output (voltage value, current value) of the fuel cell 12, the coolant temperature, etc., in order to grasp the operating state of the system. The ECU 50 is connected to various sensors such as the anode pressure sensor 36, the cathode pressure sensor 38, and the hydrogen concentration sensor 46 described above, and various actuators such as the hydrogen pressure regulating valve 20 and the air pressure regulating valve 32. The ECU 50 can operate the fuel cell 12 in a desired operation state by controlling the output of the fuel cell 12, the pressure of each gas, the flow rate of each gas, and the like.

[Operation in Embodiment 1]
The anode off gas contains unreacted hydrogen (residual hydrogen) that has not reacted in the fuel cell 12. According to the system configuration of the present embodiment, the anode off pressure can be sent to the cathode together with the cathode gas through the introduction passage 40 by making the anode outlet pressure higher than the cathode inlet pressure and opening the control valve 42. In that case, by the action of the catalyst supported on the cathode, unreacted hydrogen contained in the anode off gas reacts with oxygen in the cathode gas to generate water.

  In this way, according to the present system, the residual hydrogen contained in the anode off-gas can be combusted in the cathode, and release of hydrogen to the outside can be avoided. For this reason, a diluter or the like for reducing the hydrogen concentration of the exhaust gas is not required, the apparatus can be reduced in size and cost, and safety is excellent.

  If the amount of residual hydrogen burned in the cathode is large, the temperature of the fuel cell 12 tends to rise. On the other hand, it is not preferable that the temperature of the fuel cell 12 rises too much. Therefore, the ECU 50 prevents the temperature of the fuel cell 12 from excessively rising by controlling the timing and amount of the anode off gas introduced into the cathode by adjusting the opening of the control valve 42.

  However, when the control valve 42 is stuck in an open state due to a failure (hereinafter referred to as “open failure”), the amount of anode off-gas introduced to the cathode becomes excessive, resulting in an abnormal temperature of the fuel cell 12. May rise. For this reason, when an open failure of the control valve 42 occurs, it is necessary to reliably detect this and take appropriate measures.

  Therefore, in this embodiment, an open failure of the control valve 42 is detected using the hydrogen concentration sensor 46 installed at the cathode inlet of the fuel cell 12. Specifically, first, it is confirmed that a closing command (command for setting the opening degree to zero) is issued to the control valve 42 and that the anode outlet pressure is higher than the cathode inlet pressure. If these are confirmed, if the control valve 42 is closed as instructed by the ECU 50, the anode off gas does not flow into the cathode inlet, and therefore hydrogen is detected by the hydrogen concentration sensor 46 at the cathode inlet. It will never be done.

  On the other hand, when the control valve 42 has an open failure, the anode off gas flows into the cathode inlet through the introduction passage 40, so that hydrogen is detected by the hydrogen concentration sensor 46. In the above situation, when hydrogen is detected by the hydrogen concentration sensor 46, in principle, it can only be considered that the control valve 42 has an open failure. Therefore, it is possible to accurately detect the presence or absence of an open failure of the control valve 42 based on the detection value of the hydrogen concentration sensor 46.

[Specific Processing in Embodiment 1]
FIG. 2 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. According to the routine shown in FIG. 2, it is first determined whether or not the command for the control valve 42 is a close command (step 100). When the close command is issued to the control valve 42, it is next determined whether or not the anode outlet pressure detected by the pressure sensor 36 is higher than the cathode inlet pressure detected by the pressure sensor 38. (Step 102).

  If it is determined in step 102 that the anode outlet pressure is higher than the cathode inlet pressure, it is next determined whether or not the hydrogen concentration at the cathode inlet detected by the hydrogen concentration sensor 46 is higher than a predetermined value. (Step 104). As a result, when the hydrogen concentration at the cathode inlet is higher than a predetermined value, it can be determined that hydrogen is flowing into the cathode inlet, that is, the control valve 42 is opened against a command from the ECU 50. Therefore, in this case, it is determined that the control valve 42 has an open failure (step 106).

  On the other hand, if the hydrogen concentration at the cathode inlet is lower than the predetermined value in step 104, it can be determined that hydrogen does not flow into the cathode inlet, that is, the control valve 42 is closed as instructed from the ECU 50. . That is, it can be determined that the control valve 42 is normal and no open failure has occurred. In this case, the processing after step 100 is executed again.

  According to the processing of the routine shown in FIG. 2 described above, when the control valve 42 fails to open, it can be detected reliably.

(Process after detection of open failure of control valve 42)
When an open failure of the control valve 42 is detected, the following processing is performed in the present embodiment. First, the hydrogen pressure regulating valve 20 and the air pressure regulating valve 32 are controlled in order to reduce the differential pressure between the anode outlet pressure and the cathode inlet pressure. Thereby, the flow rate of the anode off gas flowing through the introduction passage 40 can be reduced. Further, the air compressor 24 is driven to control the air flow rate so that the hydrogen concentration of the gas flowing into the cathode is below a predetermined value.

  According to the above-described processing, even if the control valve 42 is in an open failure state, the amount of hydrogen flowing from the anode to the cathode can be reduced. For this reason, since it can avoid reliably that the temperature of the fuel cell 12 rises too much, the fuel cell 12 can be protected and safety can be ensured. In addition, even after the control valve 42 has failed to open, the operation of the fuel cell system 10 can be safely continued while securing a certain amount of power generation. For this reason, it is possible to ensure the vehicle's travel capability (evacuation travel capability).

  The processing when the open failure of the control valve 42 is detected is not limited to the above-described processing. For example, the operation of the fuel cell system 10 is stopped by closing the hydrogen main valve 18. May be.

  In the first embodiment described above, the method for detecting an open failure of the control valve 42 has been described. However, a closed failure (adherence in the closed state) of the control valve 42 can also be detected as follows. First, it is confirmed that an open command is issued to the control valve 42 and that the anode outlet pressure is higher than the cathode inlet pressure. In this case, if the control valve 42 is opened as instructed from the ECU 50, the hydrogen concentration sensor 46 detects hydrogen by the anode off gas flowing into the cathode inlet. On the other hand, if the control valve 42 is closed, the anode off gas does not flow into the cathode inlet, so that hydrogen is not detected by the hydrogen concentration sensor 46. Therefore, in the above situation, if hydrogen is not detected by the hydrogen concentration sensor 46, it can be determined that the control valve 42 has a closed failure.

  Further, in the fuel cell system 10 of the present embodiment, when the system is stopped, the scavenging air sent by the air compressor 24 is introduced into the anode of the fuel cell 12 through the introduction passage 40, whereby hydrogen remaining in the anode is removed. You may make it scavenge.

  In the first embodiment described above, the hydrogen concentration sensor 46 corresponds to the “fuel gas concentration detecting means” in the first invention. Further, when the ECU 50 executes the processing of steps 104 and 106, the “valve failure detection means” in the first invention and the “determination means” in the second invention execute the processing of step 102. Thus, the “detecting means” in the second aspect of the present invention is realized.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell system 12 Fuel cell 14 Anode gas flow path 16 Cathode gas flow path 18 Original valve 20 Hydrogen pressure regulating valve 22 Hydrogen inlet valve 24 Air compressor 26 Anode off gas flow path 30 Cathode off gas flow path 32 Air pressure regulating valve 40 Introductory path 42 Control Valve 44 Condenser 46 Hydrogen concentration sensor 50 ECU

Claims (3)

A fuel cell that generates power by receiving supply of fuel gas to the anode and supply of oxidant gas to the cathode; and
An introduction passage for introducing an anode off-gas discharged from the anode into the cathode;
A control valve for controlling the conduction state of the introduction passage;
Fuel gas concentration detection means for detecting the concentration of fuel gas contained in the gas flowing into the cathode;
Valve failure detection means for detecting a failure of the control valve based on the content of the command issued to the control valve and the fuel gas concentration detected by the fuel gas concentration detection means;
A fuel cell system comprising: A detecting means for detecting that the anode pressure is higher than the cathode pressure;
The valve failure detection means detects that the anode pressure is higher than the cathode pressure and the detected fuel gas concentration is larger than a predetermined value when a close command is issued to the control valve. The fuel cell system according to claim 1, further comprising means for determining that the control valve has an open failure. Pressure adjusting means for adjusting the anode pressure and the cathode pressure;
When an open failure of the control valve is detected by the valve failure detection means, the flow rate of the anode off gas flowing into the cathode through the introduction passage is reduced by reducing the differential pressure between the anode pressure and the cathode pressure. A flow rate suppressing means for suppressing,
The fuel cell system according to claim 1, further comprising:

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