JP2006107998A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of diagnosing an open failure of a purge valve before starting a fuel cell.
A control unit 20 outputs a close command to a purge valve 14 and starts a hydrogen circulation pump 11 before starting supply of hydrogen to a fuel cell stack 2. If the airtightness of the purge valve 14 is normal, the upstream pressure of the purge valve 14 detected by the pressure sensor 12 decreases, and the control unit 20 detects an open failure of the purge valve 14 based on the detected value of the pressure sensor 12. judge.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system, and more particularly to a technique for detecting an open failure of an exhaust gas flow path opening / closing means (purge valve) for discharging fuel gas out of the system.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidizing gas containing oxygen are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, a polymer electrolyte fuel cell using a polymer electrolyte has attracted attention as a power source for electric vehicles because of its low operating temperature and easy handling. That is, a fuel cell vehicle is equipped with a hydrogen storage device such as a high-pressure hydrogen tank, a liquid hydrogen tank, or a hydrogen storage alloy tank in the vehicle, and reacts by supplying hydrogen supplied therefrom and air containing oxygen to the fuel cell. This is the ultimate clean vehicle that drives the motor connected to the drive wheels with the electric energy extracted from the fuel cell, and the only exhaust material is water.

  Normally, the fuel gas is supplied to the fuel cell stack by supplying an excess flow rate from the flow rate obtained by converting the output current into the mass flow rate of the fuel gas so that the fuel gas spreads to every corner of the fuel cell stack. Excess fuel gas discharged is recirculated to the fuel electrode inlet through the fuel circulation path.

  As a fuel gas circulation drive system, an ejector or a hydrogen pump which is a fluid pump using a new hydrogen gas as a driving flow is used. If the hydrogen recirculation is continued for a long time, the concentration of nitrogen or the like that crosses over from the oxidizer electrode in the hydrogen circulation system increases, and the power generation efficiency decreases. In addition, water may accumulate in the hydrogen circulation path, which may deteriorate the flow of hydrogen in the anode piping system of the fuel cell stack. For this reason, many fuel cell systems having a circulation system purge the hydrogen and water mixed with nitrogen and the like by opening the exhaust gas passage opening / closing means (hereinafter also referred to as a purge valve), thereby reducing the hydrogen concentration in the circulation system. The operation of keeping it above a predetermined value is performed. The purged hydrogen is diluted with a diluter to a certain concentration or less or discharged, or converted into combustion steam using a catalytic combustor utilizing a reaction by a catalyst and discharged. It is considered. It is desired that these exhaust gas treatment apparatuses perform treatment of exhaust hydrogen more appropriately by measures for diagnosing the function of the purge valve.

As a conventional failure diagnosis technique for a purge valve, for example, a technique described in Patent Document 1 is known. According to this technique, means for measuring the pressure at the inlet of the fuel electrode of the fuel cell and means for measuring the generated current of the fuel cell are provided, and the current measuring means for the state where the fuel cell system is in the power generation state. The difference between the assumed hydrogen pressure calculated from the generated current measured from the above and the pressure measured by the pressure measuring means is taken, and the failure diagnosis of the purge valve is performed based on the magnitude relationship between this difference and the set value.
JP 2003-92125 A (page 4, FIG. 2)

  However, the purge valve failure diagnosis method in the prior art described above can be diagnosed only in a power generation state in which hydrogen is supplied to the fuel cell, and the purge valve is opened in a special mode such as when the fuel cell is started or when power generation is stopped. It was difficult to determine the failure. In particular, in a fuel cell vehicle using a fuel cell as a power source, it is desirable that a purge valve can be diagnosed before traveling.

  In order to solve the above problems, the present invention is configured by sandwiching an electrolyte membrane between an oxidant electrode and a fuel electrode, an oxidant gas is supplied to the oxidant electrode side, and hydrogen is supplied to the fuel electrode side. A fuel cell that is supplied with a fuel gas as a main component to generate power; a fuel gas circulation means that re-supplys at least part of the fuel gas discharged from the fuel electrode of the fuel cell to the fuel cell; and A fuel gas discharge passage for discharging the fuel gas discharged from the fuel electrode from the fuel electrode outlet or the fuel gas circulation passage to the outside of the system, and an exhaust gas passage opening / closing means for opening and closing the fuel gas discharge passage. An open / close command state detection means for the exhaust gas flow path opening / closing means, a pressure detection means for detecting a pressure in the fuel gas discharge flow path, and the detected exhaust gas flow path open / close command State closed An open failure state determination means for determining an open failure state of the exhaust gas flow path opening / closing means based on a pressure detected by the pressure detection means in an operating state of the fuel gas circulation means at the time of command This is the gist.

  According to the present invention, before starting the fuel cell system, that is, before supplying fuel gas to the fuel cell, the exhaust gas flow path opening / closing command state is set to the close command state, and the fuel gas circulation means is operated. If the purge valve is in a normal state, that is, if a predetermined airtightness is secured, the pressure upstream of the purge valve is reduced due to the pressure difference between the inlet and outlet of the fuel gas circulation means caused by the fuel gas circulation, When the purge valve is in an open failure state, that is, when the predetermined airtightness cannot be ensured, the purge valve upstream pressure becomes a pressure equivalent to the atmospheric pressure after the predetermined time has elapsed. The open failure of the purge valve can be detected based on the magnitude relationship with the upstream pressure of the purge valve in the state.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. Although not particularly limited, each embodiment described below is a fuel cell system suitable for a fuel cell vehicle.

  FIG. 1 is a system configuration diagram illustrating the configuration of a first embodiment of a fuel cell system according to the present invention. In the figure, the fuel cell stack 2 provided in the fuel cell system 1 includes a plurality of fuel cell structures each having a solid polymer electrolyte membrane sandwiched between a fuel electrode 3 and an oxidant electrode 4 via separators. It has a stack structure. Further, inside the fuel cell stack 2, an oxidant gas flow path 4c, a fuel gas flow path 3c, and a cooling water flow path (not shown) are provided.

  In the fuel cell stack 2, air as an oxidant gas is supplied to the oxidant electrode 4, and hydrogen gas as a fuel gas is supplied to the fuel electrode 3. As a result, in the fuel electrode 3 of the fuel cell stack 2, hydrogen is ionized into hydrogen ions and electrons, the hydrogen ions move through the electrolyte membrane to the oxidant electrode 4, and the electrons pass through the external circuit and the fuel electrode 3 To the oxidant electrode 4. In the oxidant electrode 4, hydrogen ions that have moved from the fuel electrode 3, electrons that have passed through the external circuit, and oxygen in the oxidant gas react to generate water.

  The fuel cell system 1 includes a control unit 20 that controls the operation of each unit. As the control unit 20, for example, an information processing apparatus such as a computer configured by various semiconductor elements is used. By controlling each unit by the control unit 20, the operation of the entire fuel cell system is controlled. Is done.

  In the fuel cell system 1, a hydrogen tank 5 for accumulating hydrogen gas supplied to the fuel electrode 3, a regulator 6, and a hydrogen supply regulating valve 8 are disposed on the hydrogen supply flow path 7, and hydrogen as a fuel gas circulation means. A circulation pump 11 is disposed on the hydrogen circulation flow path 10 and a hydrogen discharge flow path 13 and a purge valve 14 are installed as means for discharging the fuel gas in the circulation path from the hydrogen circulation flow path 10 to the oxidant gas flow path. ing.

  Further, a pressure sensor 9 is installed as a pressure detection means at the fuel electrode inlet 3a, and a pressure sensor 12 is installed as a pressure detection means at the hydrogen circulation passage 10 side of the purge valve 14, and these pressure sensors are used to detect the detected pressure. It outputs to the control part 20 as a signal. As a result, the fuel gas pressure detected by the pressure sensor 9 is recognized as the fuel gas pressure in the fuel cell stack 2 by the control unit 20, and the fuel gas pressure detected by the pressure sensor 12 is recognized as the purge valve inlet pressure. Is done.

  The hydrogen supply adjusting valve 8 and the purge valve 14 each include an actuator for adjusting the valve opening, and the valve opening is controlled according to a control signal from the control unit 20.

  Further, the hydrogen circulation pump 11 incorporates an inverter for controlling the rotational speed, and adjusts the rotational speed in accordance with the rotational speed control signal from the control unit 20.

  FIG. 2 is a flowchart for explaining the purge valve opening failure diagnosis process in the present embodiment. This flowchart is executed by the control unit 20 in a state before the fuel cell system is started, that is, in a stage before the hydrogen supply regulating valve 8 is opened and fuel gas is supplied to the fuel gas passage 3c in the fuel cell stack 2. It is what is done. Further, it is assumed that the flag indicating the open failure state of the purge valve is in the reset initial state before the start of this flowchart.

  First, in step S <b> 10, a closing command is transmitted from the control unit 20 to the purge valve 14. Thereafter, after a sufficient time has elapsed for the purge valve 14 to complete its operation, the hydrogen circulation pump 11 is operated as shown in step S2 and driven at a certain rotational speed. In step S3 after this operation, that is, in the state where the value detected by the pressure sensor 12 on the circulation path side of the purge valve 14 and the rotation speed of the hydrogen circulation pump 14 is sufficiently stable, the fuel gas in the hydrogen circulation path 10 The difference between the flow rate and the pressure difference between the inlet and the outlet of the hydrogen circulation pump is expressed by a curve group a indicating the performance of the hydrogen circulation pump and a curve b indicating the pressure loss characteristic of the hydrogen circulation passage 10 on the pressure-flow rate characteristic diagram shown in FIG. Take the value of the intersection of Therefore, a pressure difference corresponding to the pump rotational speed is generated between the upstream and downstream of the hydrogen circulation pump 11.

  At this time, if the airtightness of the purge valve 14 is sufficiently secured, the fuel gas flow path 3c and the hydrogen circulation flow path 10 in the fuel cell stack 2 become a space closed to the outside. Therefore, due to the pressure difference generated by the operation of the hydrogen circulation pump 11, the fuel gas pressure on the downstream side (pump outlet side) of the hydrogen circulation pump 11 becomes higher than that before the operation of the hydrogen circulation pump 11. The fuel gas pressure on the upstream side (pump inlet side) of the hydrogen circulation pump 11 is lower than that before the operation of the hydrogen circulation pump 11.

  On the other hand, when the purge valve 14 is closed and the airtightness of the purge valve 14 is not sufficiently ensured, the upstream side of the hydrogen circulation pump 11 is communicated with an external constant pressure source, that is, the atmosphere. It becomes space. Therefore, the fuel gas pressure on the downstream side of the hydrogen circulation pump 11 is higher than that before the operation of the hydrogen circulation pump 11 due to the pressure difference generated by the operation of the hydrogen circulation pump 11. The fuel gas pressure on the upstream side is almost the same value as before the operation of the hydrogen circulation pump 11.

  In the fuel cell system shown in FIG. 1, the difference in the fuel gas pressure on the downstream side of the hydrogen circulation pump due to the two purge valve states described above can be detected by the pressure sensor 12 shown in FIG.

  Therefore, if the detection value RP of the pressure sensor 12 is read into the control unit 20 in step S13 in FIG. 2, the detection value RP is a value reflecting the operating state of the purge valve 14.

  Next, in step S14, the difference (RP−) between the pressure (TP) on the circulation path side of the purge valve assumed in the normal state of the purge valve 14 and the actual pressure (RP) measured by the pressure sensor 12 in the state of step S3. It is determined whether or not (TP) is less than a predetermined value (DP). Here, TP uses an average value of values measured in a real machine having a normal function of the purge valve 14, and DP is a discriminating value for judging whether or not the sealing performance of the purge valve is normal. Set from measurement using.

  If (RP-TP) is less than (DP) in the determination in step S14, it is determined as normal and the process proceeds to step S18. If it is determined in step S14 that (RP-TP) is equal to or greater than the predetermined value (DP), it is determined that the purge valve 14 is in an open failure state, the process proceeds to step S16, and the purge valve open failure flag is set ( ON), and the process proceeds to step S18.

  In step S18, the hydrogen circulation pump 11 is stopped and the purge valve open failure diagnosis is completed.

  Note that the purge valve open failure flag set in step S16 indicates that the fuel cell is not used when the series of failure diagnosis before starting the fuel cell is completed, or when all the failure diagnosis before starting the fuel cell system is completed by the control unit 20. It is referred to determine whether or not the system is normal, and is used to display the determination result to the user.

  According to the embodiment described above, the open / close command state of the exhaust gas flow path is set to the close command state (purge valve close command) before the fuel cell system is started, that is, before the fuel gas is supplied to the fuel cell. Then, the fuel gas circulation means (hydrogen circulation pump) is operated. If the purge valve is in a normal state, that is, if a predetermined airtightness is secured, the pressure upstream of the purge valve is reduced due to the pressure difference between the inlet and outlet of the fuel gas circulation means caused by the fuel gas circulation, When the purge valve is in an open failure state, that is, when the predetermined airtightness cannot be ensured, the purge valve upstream pressure becomes a pressure equivalent to the atmospheric pressure after the predetermined time has elapsed. There is an effect that the open failure of the purge valve can be detected by the magnitude relationship with the purge valve upstream pressure in the state.

  Next, Embodiment 2 of the fuel cell system according to the present invention will be described with reference to FIGS. FIG. 4 is a system configuration diagram illustrating the configuration of the fuel cell system according to the second embodiment. In addition to the fuel cell system shown in FIG. 1, the fuel cell system 1 shown in FIG. 4 extends from a point connecting to the fuel electrode outlet 3 b of the fuel cell stack 2 of the hydrogen circulation channel 10 to a point branching from the hydrogen discharge channel 13. Between them, a variable circulation flow path cutoff valve 17 is provided. The circulation flow path shutoff valve 17 is installed to shut off the fuel gas circulated in the fuel gas circulation flow path 10. The circulation flow path shut-off valve 17 incorporates an actuator that controls the opening according to the opening command value from the control unit 20.

  FIG. 5 is a flowchart for explaining the purge valve opening failure diagnosis process in the second embodiment. The difference from the first embodiment is that in step S20 corresponding to step S10 of the first embodiment, not only the control unit 20 transmits a close command to the purge valve 14, but also the circulation flow path shut-off valve 17 is closed or closed. This is the point at which the intermediate opening degree command is transmitted. As a result, in step S24, the fuel gas flow rate in the hydrogen circulation channel 10 and the pressure difference between the inlet and outlet of the hydrogen circulation pump are the pressure loss of the hydrogen circulation channel 10 on the pressure-flow rate characteristic diagram shown in FIG. The characteristic changes from the curve b shown in Example 1 to b ′. As a result, it is possible to increase a predetermined pressure difference between the upstream and downstream sides of the hydrogen circulation pump 11, and it is possible to improve the detection by pressure compared to the first embodiment. When the fully closed command is given to the circulation flow path shutoff valve 17 in step S20, it is possible to improve the detectability most.

  According to the present embodiment described above, before the fuel cell system is started, that is, before the fuel gas is supplied, the open / close command state of the exhaust gas passage is the close command state (purge valve close command), and the fuel gas The fuel gas circulation means (hydrogen circulation pump) is operated with the circulation flow path opening / closing means (circulation flow path cutoff valve) fully closed or at an intermediate opening. Since the pressure difference between the inlet and outlet of the fuel gas circulation means caused by the circulation of the fuel gas can be increased when the purge valve is in the normal state, the upstream pressure of the purge valve in the normal state with respect to the first embodiment. Since it is possible to increase the difference between the upstream pressure of the purge valve in the open failure state and the pressure detection means, it is possible to improve the detectability of the open failure of the purge valve by the pressure detection means.

  Next, a third embodiment of the fuel cell system according to the present invention will be described with reference to FIG. In addition to the fuel cell system shown in FIG. 4, the fuel cell system 1 shown in FIG. 6 has an orifice 18 added in parallel to the circulation flow path shut-off valve 17.

  By adding the orifice 18, it is possible to diagnose an open failure of the purge valve 14 through the same processing flow as that of the second embodiment shown in FIG. However, the command given to the circulation flow path shutoff valve 17 in step S20 is a fully closed command. In this embodiment, when the circulation flow path shut-off valve 17 is fully closed, the pressure loss of the hydrogen circulation flow path 10 is determined by the orifice 18 arranged in parallel thereto.

  In the second embodiment, there is a possibility that there is a difference between the opening command given to the circulation flow path shut-off valve 17 and the actual opening, and even when the purge valve 14 is not open, there is a difference between (RP) and (TP). On the other hand, in this embodiment, the use of an orifice that generates a fixed pressure loss makes it difficult to make a misdiagnosis with respect to the second embodiment, and at the same time, provides the same detectability as the second embodiment. In other words, the detectability can be improved as compared with the first embodiment.

  According to the present embodiment described above, before the fuel cell system is started, that is, before the fuel gas is supplied, the open / close command state of the exhaust gas passage is the close command state (purge valve close command), and the fuel gas The circulation passage opening / closing means (circulation passage cutoff valve) is closed, and the fuel gas circulation means (hydrogen circulation pump) is operated. At this time, since the pressure loss in the fuel gas circulation flow path can be set using the orifice, it is difficult to make a misdiagnosis with respect to the second embodiment, and at the same time, it has the same detectability as the second embodiment, that is, compared with the first embodiment. This has the effect of improving the detectability.

1 is a system configuration diagram illustrating the configuration of a first embodiment of a fuel cell system according to the present invention. FIG. 3 is a flowchart illustrating a purge valve open failure diagnosis process according to the first embodiment. It is a pressure-flow rate characteristic figure of a hydrogen circulation system. It is a system block diagram explaining the structure of Example 2 of the fuel cell system which concerns on this invention. 10 is a flowchart for explaining a purge valve open failure diagnosis process according to the second embodiment. It is a system block diagram explaining the structure of Example 3 of the fuel cell system which concerns on this invention.

Explanation of symbols

1: Fuel cell system 2: Fuel cell stack 3: Fuel electrode 3c: Fuel gas channel 4: Oxidant electrode 4c: Oxidant gas channel 5: Hydrogen tank 6: Regulator 7: Hydrogen supply channel 8: Hydrogen supply adjustment Valve 9: Pressure sensor 10: Hydrogen circulation flow path 11: Hydrogen circulation pump 12: Pressure sensor 13: Hydrogen discharge flow path 14: Purge valve 15: Air supply flow path 16: Air discharge flow path 20: Control unit

Claims (3)

An electrolyte membrane is sandwiched between an oxidant electrode and a fuel electrode, and an oxidant gas is supplied to the oxidant electrode side, and a fuel gas mainly composed of hydrogen is supplied to the fuel electrode side to generate power. A fuel cell; fuel gas circulation means for supplying at least part of the fuel gas discharged from the fuel electrode of the fuel cell to the fuel cell again; and a fuel gas discharged from the fuel electrode of the fuel cell. Alternatively, a fuel cell system comprising: a fuel gas discharge channel that discharges out of the system from the fuel gas circulation channel; and an exhaust gas channel opening / closing means that opens and closes the fuel gas discharge channel.
A means for detecting an open / close command state for the exhaust gas flow path opening / closing means;
Pressure detecting means for detecting the pressure in the fuel gas discharge channel;
When the detected opening / closing command state of the exhaust gas passage is a closing command, an open failure state of the exhaust gas passage opening / closing means based on the pressure detected by the pressure detection means in the operating state of the fuel gas circulation means An open failure state determination means for determining A fuel gas circulation channel opening / closing means for opening and closing the fuel gas circulation channel between the fuel gas discharge channel connection part of the fuel gas circulation channel and the fuel electrode outlet;
The open failure state determination means includes
By setting the fuel gas circulation channel opening / closing means to a fully closed position or an intermediate opening, the pressure detection means can be operated while the fuel gas circulation means is in an operating state when the detected opening / closing command state of the exhaust gas channel is a close command. 2. The fuel cell system according to claim 1, wherein a failure state of the exhaust gas flow path opening / closing means is determined based on a pressure detected by the fuel cell system. Fuel gas circulation channel opening and closing means for opening and closing the fuel gas circulation channel between the fuel gas discharge channel connection part of the fuel gas circulation channel and the fuel electrode outlet;
An orifice arranged in parallel with the fuel gas circulation flow path opening and closing means,
The open failure state determination means includes
By fully closing the fuel gas circulation passage opening / closing means, the detected pressure of the fuel gas circulation means is detected by the pressure detection means when the detected opening / closing command state of the exhaust gas passage is a close command. 2. The fuel cell system according to claim 1, wherein a failure state of the exhaust gas flow path opening / closing means is determined based on a pressure.

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