JP2006308440A - Gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detector for contributing to the stable control of a system. <P>SOLUTION: The gas detector comprises a contact combustion type gas detection element that is arranged under a humidification environment and detects gas to be detected based on at least a current value; a current detection means for detecting current flowing to the gas detection element; and an impurity adhesion determination means for determining the adhesion of impurities to the detection element when the detection value of the current detection means is equal to or higher than a prescribed current value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas detection device that is disposed in a humidified environment and has a gas detection element that detects a gas to be detected based on at least a current value.

In recent years, a system having a fuel cell including an anode and a cathode has a configuration in which a dilution box is provided in an anode-side off-gas flow path to dilute hydrogen in the off-gas.
As this type of technology, a hydrogen detector (gas sensor) that detects hydrogen in the off-gas flow path downstream of the dilution box is provided to detect whether the hydrogen concentration has dropped below a predetermined value. It has been known.

  As this type of gas sensor, for example, a pair of a gas detection element made of a catalyst such as platinum and a temperature compensation element are provided, and the gas detection element is relatively hot due to heat generated by combustion when hydrogen comes into contact with the catalyst such as platinum. Gas contact combustion type hydrogen that detects the concentration of hydrogen gas according to the difference in electrical resistance generated between the temperature compensation element and the temperature compensation element in a relatively low temperature state, for example, at ambient temperature. Detectors are known.

As a technique for detecting an abnormality of this type of hydrogen detector, for example, Patent Document 1 discloses a reference element whose resistance value changes only according to the ambient temperature, a resistance value according to the ambient temperature and the gas concentration of the gas to be detected. Of a catalytic combustion type gas sensor that is connected in series to a sensing element and a constant current source, and detects a disconnection or a short circuit of each of the reference element or the sensing element based on a change in each voltage drop of the reference element or the sensing element. A disconnection / short circuit detection circuit is disclosed.
Further, Patent Document 2 includes a sensing unit that detects the gas concentration of the gas to be detected and a heater that can heat the sensing unit, and the resistance value or heater of the heater that is stable with respect to the atmospheric gas containing the gas to be detected. A gas alarm is disclosed that determines a failure of a gas sensor such as an abnormality or disconnection of a heater based on a change in current.
JP 11-271256 A JP 2001-235441 A

  By the way, in the fuel cell as described above, in order to keep the ionic conductivity of the electrolyte membrane, water (humidified water) is supplied to the reaction gas (for example, hydrogen or air) supplied to the fuel cell by a humidifier or the like. ing. Furthermore, reaction product water is generated by an electrochemical reaction when the fuel cell is operated. For this reason, the exhaust gas of the fuel cell, particularly the cathode side exhaust gas, becomes a highly humid off gas, and as a result, the hydrogen detector disposed in the off gas flow path such as the dilution box described above is being started and stopped. Regardless, condensation may occur. In particular, in solid polymer membrane fuel cells, the normal operating temperature is lower than the vaporization temperature of water, and the off-gas is discharged as a gas with a high humidity and a large amount of moisture. Cheap.

However, in the above-described conventional technology, no consideration is given to dew condensation countermeasures for the hydrogen detector, and if water adheres to the sensor element unit, an erroneous value that temporarily exceeds the upper limit output may be output. There is. If the system is controlled based on this erroneous value, there is a risk that stable control may be hindered. Therefore, it is very important to detect the presence or absence of water adhesion in the hydrogen detector. The same applies when impurities other than water adhere.
An object of this invention is to provide the gas detection apparatus which can contribute to the stable control of a system.

  The invention according to claim 1 is arranged under a humidified environment (for example, the exhaust pipe 14 in the embodiment), and detects a gas to be detected (for example, hydrogen in the embodiment) based on at least a current value. A gas detection element (for example, the detection element 31 in the embodiment) and a current detection means (for example, also serving as a detection signal in the embodiment) for detecting a current flowing through the gas detection element; Impurity attachment determination means for determining that impurities (for example, water in the embodiment) are attached to the detection element when the detection value of the means is equal to or greater than a predetermined current value (for example, the specified current value Ith in the embodiment). (For example, the control device 2 in the embodiment).

  According to the present invention, based on the characteristics of the catalytic combustion type gas detection element, misrecognizing a state where the current value is high due to the adhesion of impurities as a state where the concentration of the detected gas is low, Can be prevented. That is, the catalytic combustion type gas detection element has a characteristic that the output voltage value increases while the current value decreases as the resistance value increases due to the exothermic reaction with the gas to be detected. For this reason, if the contact combustion type gas detection element is in a state in which the gas to be detected can be normally detected, the resistance value due to the reaction with the gas to be detected when the concentration of the gas to be detected is low (including zero). Hardly increases, and the current value remains at a predetermined value. On the other hand, when the concentration of the gas to be detected becomes high, the current value becomes a low value due to an increase in the resistance value due to the reaction with the gas to be detected. On the other hand, when impurities adhere to the catalytic combustion type gas detection element, the present inventors have confirmed that even if the concentration of the gas to be detected is high, the current value shows a high value. Therefore, a state in which the current value is increased due to the adhesion of impurities when the concentration of the detected gas is high is mistakenly recognized as a state in which the concentration of the detected gas is low, and the system (for example, the fuel cell vehicle in the embodiment) Since control of 10) can be prevented, it is possible to contribute to stable control of the system. In other words, during normal operation, when the output voltage of the catalytic combustion type gas detection element is high, it is detected that the concentration of the gas to be detected is high. It can be confirmed that it is possible to contribute to stable control of the system.

The invention according to claim 2 is the apparatus according to claim 1, further comprising voltage detection means (for example, also serving as a detection signal in an embodiment) for detecting an output voltage of the gas detection element, and the impurity The adhesion detection means determines that impurities are adhered to the detection element when a detection value of the voltage detection means is equal to or higher than a predetermined voltage value (for example, a specified voltage value Vth in the embodiment). To do.
According to the present invention, it is possible to prevent a state in which the current value is high due to the characteristic deviation of the gas detection element from being determined as an impurity-attached state. That is, when the catalytic combustion type gas detection element is in a normal state, the current and the concentration of the detected gas are substantially proportional to each other, while the output voltage and the concentration of the detected gas are substantially inversely proportional. . Even if a characteristic deviation occurs in the catalytic combustion type gas detection element, the relationship with the concentration of the gas to be detected does not change, so even if the current value becomes high, the output voltage is a predetermined voltage value. Stay below the value. On the other hand, when impurities adhere to the catalytic combustion type gas detection element, the present inventors have confirmed that not only the current value but also the voltage value shows a high value. Accordingly, since the determination of the adhesion of impurities to the gas detection element can be performed without depending on the characteristic deviation of the gas detection element, the determination of the adhesion of impurities can be performed with high accuracy, and the system can be further stabilized. Can contribute to the control.

The invention according to claim 3 is the one according to claim 1 or 2, wherein the predetermined current value is a maximum current value that can be output when no impurity is attached to the detection element (for example, The current value is larger than the maximum current value Imax in the embodiment.
According to the present invention, it is possible to prevent a state where the concentration of the gas to be detected is low from being determined as an impurity-attached state. Therefore, the determination of the adhesion of impurities to the gas detection element can be performed regardless of the concentration of the gas to be detected. Therefore, the determination of the adhesion of impurities can be performed with high accuracy, and further stability control of the system can be performed. Can contribute.

According to the first aspect of the present invention, it is a characteristic of the catalytic combustion type gas detection element that the state where the current value is high due to the adhesion of impurities is erroneously recognized as the state where the concentration of the detection target gas is low. Therefore, it is possible to contribute to the stable control of the system. In other words, during normal operation, when the output voltage of the catalytic combustion type gas detection element is high, it is detected that the concentration of the gas to be detected is high. It can be confirmed that it is possible to contribute to stable control of the system.
According to the invention of claim 2, since the determination of the adhesion of impurities to the gas detection element can be performed without depending on the characteristic deviation of the gas detection element, the determination of the adhesion of impurities can be performed with high accuracy. Can contribute to further stable control of the system.
According to the invention of claim 3, since the determination of the adhesion of impurities to the gas detection element can be performed regardless of the concentration of the detected gas, the determination of the adhesion of impurities can be performed with high accuracy. It becomes possible, and it can contribute to the further stable control of a system.

Hereinafter, a gas detection apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a fuel cell vehicle equipped with a gas detection device according to an embodiment of the present invention.
The fuel cell 5 is composed of a stack formed by stacking a plurality of cells formed by sandwiching a solid polymer electrolyte membrane made of, for example, a solid polymer ion exchange membrane between an anode and a cathode from both sides. When air containing oxygen as an oxidant is supplied to the cathode, hydrogen ions generated by a 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. Since part of the generated water generated on the cathode side is diffused back to the anode side through the solid polymer electrolyte membrane, the generated water is also present on the anode side.

  The air is pressurized to a predetermined pressure by the compressor 12 and supplied to the cathode of the fuel cell 5 through the air supply passage 7. After the air supplied to the fuel cell 5 is used for power generation, it is discharged from the fuel cell 5 together with the produced water on the cathode side into the air discharge passage 9 and introduced into the purge hydrogen dilution device 13.

On the other hand, hydrogen supplied from the hydrogen tank 11 is supplied to the anode of the fuel cell 5 through the hydrogen supply channel 6. Then, the hydrogen discharged from the fuel cell 5 is discharged to the hydrogen discharge flow path 8. The hydrogen discharge flow path 8 is connected to a purge hydrogen dilution device 13.
Hydrogen discharged from the fuel cell 5 is introduced into the purge hydrogen dilution device 13 via the hydrogen discharge flow path 8. Then, the hydrogen is diluted by the air introduced into the purge hydrogen dilution device 13 via the air discharge flow path 9, and the diluted hydrogen is discharged from the discharge pipe 14 as an exhaust gas.

The exhaust pipe 14 is provided with the gas sensor 1. The gas sensor 1 is for detecting the hydrogen concentration of the exhaust gas flowing through the exhaust pipe 14, and the output signal of the gas sensor 1 is input to the control device 2.
For example, the control device 2 determines whether or not an abnormal state of the fuel cell 5 has occurred according to a comparison result between the detection signal output from the gas sensor 1 and a predetermined determination threshold, and is in an abnormal state. When it is determined, an alarm or the like is output by an alarm device (not shown). Here, the detection signal includes a current value flowing through the gas sensor 1 and information on the output voltage value.

FIG. 2 is a cross-sectional view of a main part of the gas detection device according to the embodiment. FIG. 3 is a schematic sectional view taken along line AA of the gas sensor shown in FIG. As shown in these drawings, the gas sensor 1 includes a case 21 having a rectangular shape that is long in the longitudinal direction of the discharge pipe 14 (see FIG. 3) extending in the horizontal direction, that is, in the horizontal direction. The case 21 is made of, for example, polyphenylene sulfide, and includes flange portions 22 at both ends in the longitudinal direction.
Further, a cylindrical portion 26 is formed on the end surface in the thickness direction of the case 21, the inside of the cylindrical portion 26 is formed as a gas detection portion 27, and an inner side surface of the gas detection portion 27 is flanged inward. A portion 28 is formed, and an inner peripheral portion of the flange portion 28 is formed as an opening as a gas introduction portion 29.

  A circuit board 30 sealed with resin is provided in the case 21, and the detection element 31 and the temperature compensation element 32 disposed inside the cylindrical portion 26 are connected to the circuit board 30. Each element 31, 32 is a resin base material disposed on the bottom surface side of the gas detection unit 27 by a plurality of, for example, four current-carrying stays 33 connected to the circuit board 30 and a platinum wire 33 a as a lead wire. The gas sensor 1 and the gas sensor 1 are arranged so as to form a pair at a predetermined interval at a position separated by a predetermined distance from the gas sensor 1 in the thickness direction. Further, a sealing material 35 is attached to the outer peripheral surface of the cylindrical portion 26, and the sealing material 35 is in close contact with the inner peripheral wall of the through hole 14 a of the discharge pipe 14 to ensure airtightness.

The detection element 31 is a catalytic combustion type element, and the surface of the coil of a metal wire containing platinum or the like having a high temperature coefficient for electric resistance is a catalyst made of a noble metal or the like that is active against hydrogen to be detected gas. It is formed by being covered with a carrier such as alumina to be carried.
The temperature compensation element 32 is inactive with respect to the gas to be detected. For example, the surface of the coil equivalent to the detection element 31 is covered with a carrier such as alumina.

  And the detection element 31 which became high temperature by the heat_generation | fever of the combustion reaction which arises when hydrogen which is to-be-detected gas contacts the catalyst of the detection element 31, and the combustion reaction by a to-be-detected gas does not generate | occur | produce, By utilizing the fact that a difference in electrical resistance value occurs between the temperature compensation element 32 and the temperature compensation element 32, it is possible to detect the hydrogen concentration by offsetting the change in the electrical resistance value due to the ambient temperature.

A heater 36 having a substantially rectangular plate shape is disposed in the gas detection unit 27. The heater 36 is composed of a resistor or the like, and heats the inside of the gas detector 27 and the elements 31 and 32 when energized by the circuit board 30.
In addition, a water repellent filter 19 and a filter 20 are disposed in the gas detection unit 27 in order to reduce environmental influences, for example, the degree of influence of moisture and gas to be detected.

An impurity (in this case, water) adhesion determination process by the gas detection device configured as described above will be described with reference to FIG. FIG. 4 is a flowchart showing the contents of the water adhesion determination process of the gas sensor shown in FIG.
First, in step S12, it is determined whether or not the current value flowing through the detection element 31 is equal to or greater than a specified current value Ith (see FIG. 5). If this determination is YES, the process proceeds to step S14. On the other hand, if this determination result is NO, it is determined that water has not adhered to the detection element 31, and the flow proceeds to step S18.

  This determination process will be described with reference to FIG. FIG. 5 is a graph showing the relationship between the sensor current value and the sensor output voltage value with respect to the hydrogen concentration. As shown in the figure, the gas detection element 31 has a characteristic that the current value Is decreases while the output voltage value Vs increases as the resistance value increases due to an exothermic reaction with the gas to be detected (in this case, hydrogen). Have For this reason, if the gas detection element 31 is in a state where hydrogen can be detected normally, when the concentration of hydrogen is low (including zero), the resistance value due to the reaction with hydrogen hardly increases, and the current value Is Remains at a predetermined value (near Imax). On the other hand, when the concentration of hydrogen increases, the current value Is decreases due to an increase in the resistance value due to the reaction with hydrogen.

  On the other hand, it was found that the current value Im when water is attached to the gas detection element 31 shows a high value regardless of the hydrogen concentration. Therefore, it is possible to prevent the system from being mistakenly recognized as a low hydrogen concentration state when the current value is high due to water adhesion when the hydrogen concentration is high, thereby contributing to stable control of the system. be able to. Here, in the present embodiment, the specified current value Ith is set to be equal to or greater than the maximum current value Imax that can be output when water does not adhere to the detection element 31. For this reason, it can prevent determining the state where the density | concentration of hydrogen is low as the state which the water adhered.

Next, in step S14, it is determined whether or not the output voltage value Vs at the detection element 31 is equal to or greater than a specified voltage value Vth. If this determination result is YES, the process proceeds to step S16, and if this determination result is NO, the process proceeds to step S18.
In step S <b> 16, it is determined that water is attached to the detection element 31, the process of this flowchart is once terminated, and the process is repeated from the beginning. In step S18, it is determined that water is not attached to the detection element 31, and the hydrogen detection process is started. In step S20, the hydrogen detection process is continued for a predetermined time, the process of this flowchart is once ended, and the process is repeated again from the beginning.

  Thus, by determining also about the output voltage value Vs, the determination of water adhesion to the gas detection element 31 can be performed without depending on the characteristic deviation of the gas detection element 31. That is, when the gas detection element 31 is in a normal state, as shown in FIG. 5, the hydrogen concentration and the current Is are approximately proportional to each other, while the hydrogen concentration and the output voltage Vs are approximately inversely proportional. It becomes. This relationship does not change even when the characteristic deviation occurs in the gas detection element 31. Therefore, even when the current value Is increases and exceeds the specified current value Ith, the output voltage Vs is equal to the specified voltage value Vth. Stay below the value.

  On the other hand, when water adhered to the gas detection element 31, it was found that the voltage value showed a high value exceeding the specified voltage value Vth. Therefore, by determining the output voltage value, the determination of water adhesion to the gas detection element 31 can be performed without depending on the characteristic deviation of the gas detection element 31. Can be done.

  FIG. 6 is a graph showing an example of the change over time of the sensor output voltage value when the water adhesion determination of the gas sensor is performed and when the water adhesion determination is not performed. In the same figure, the case where the water adhered to the detection element 31 between the time t1 and t2 is shown. As described above, when water adheres to the detection element 31, the value Vm of the output voltage significantly increases (upper graph in the same figure). If the hydrogen concentration is determined based on the output voltage value Vm, it is determined that the hydrogen concentration is very high. Therefore, if control is performed based on this, stable control of the system becomes difficult.

  On the other hand, at time t1 to t2, water adhesion to the detection element 31 is determined. If it is determined that water is adhered, a dummy voltage value is used instead of the output voltage value Vm. Vs ′ is displayed (graph in the lower part of the figure). By performing such control, it is possible to prevent the system (in this case, the fuel cell vehicle 10) from being controlled based on the high output voltage value Vm due to the adhesion of water, which can contribute to stable control of the system. .

  As described above, in the embodiment, since the determination using the output value of the gas sensor is performed after the determination using the current value of the gas sensor, it is preferable in terms of improving the determination accuracy. The determination may be made using only. That is, as shown in FIG. 7, when it is determined in step S12 that the current value flowing through the detection element 31 is equal to or greater than the specified current value Ith, the process proceeds to step S16, and water is attached to the detection element 31. It is also possible to perform a process for determining. In this case, setting the specified current value Ith to a value larger than that shown in FIG. 4 is preferable in terms of improving the determination accuracy.

  As described above, according to the present invention, it is possible to contribute to stable control of the system by determining whether water adheres to the detection element. Of course, the contents of the present invention are not limited only to the embodiment. For example, in the embodiment, a case where the gas detection device is mounted on a fuel cell vehicle using a fuel cell as a drive source will be described. However, it can also be applied to systems other than vehicles. Further, in the embodiment, the case where water adheres to the gas sensor has been described. However, even when an oil film other than water or impurities such as dust adhere, determination is made in the same manner as the method described in the embodiment. It is possible.

1 is a block diagram of a fuel cell vehicle equipped with a gas detection device in an embodiment of the present invention. It is sectional drawing of the gas sensor shown in FIG. It is a schematic sectional drawing in alignment with the AA of the gas sensor shown in FIG. It is a flowchart figure which shows the content of the water adhesion determination process of the gas sensor shown in FIG. It is a graph which shows the relationship with respect to hydrogen concentration of a sensor electric current value and a sensor output voltage value. It is a graph which shows the example of the time change of the sensor output voltage value in each of the case where the water adhesion determination of a gas sensor is performed, and the case where the water adhesion determination is not performed. It is a flowchart figure which shows the modification of the content of the water adhesion determination process of the gas sensor shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gas sensor 2 ... Control apparatus 10 ... Fuel cell vehicle 14 ... Exhaust pipe 31 ... Detection element

Claims (3)

A contact combustion type gas detection element that is arranged in a humidified environment and detects a gas to be detected based on at least a current value;
Current detection means for detecting a current flowing in the gas detection element,
A gas detection apparatus comprising: an impurity adhesion determination unit that determines that an impurity is adhered to the detection element when a detection value of the current detection unit is equal to or greater than a predetermined current value. Voltage detection means for detecting an output voltage of the gas detection element;
2. The gas detection device according to claim 1, wherein the impurity adhesion detection unit determines that impurities are adhered to the detection element when a detection value of the voltage detection unit is equal to or higher than a predetermined voltage value. . 3. The gas detection device according to claim 1, wherein the predetermined current value is a current value larger than a maximum current value that can be output when impurities are not attached to the detection element.

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