JP2003344331A - Gas sensor, failure sensing apparatus for gas sensor and failure sensing method of gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily, surely and timely sense damage and deterioration. <P>SOLUTION: A failure sensing apparatus 1a for gas sensor is constituted by being provided with a reference voltage applying circuit 30 for applying a predetermined reference voltage to a series circuit 29 comprising a detection element 21, a temperature compensation element 22 of the gas sensor 1, and a dummy element 23 equivalent to the detection element 21 serially connected; a detection circuit 31 for detecting a voltage between terminals of the detection element 21; and a control circuit 32. A failure judging part 34 of the control circuit 32 judges whether a detected value of the voltage between the terminals of the detection element 21 is a predetermined failure determination value or less set based on the reference voltage applied to the series circuit 29. If YES, it judges that the gas sensor 1 is out of order and an instruction signal for instructing to switch an output is outputted. If NO, it judges that the gas sensor 1 is normal. An output switching part 35 outputs a predetermined output value to an output circuit 33 instead of the detected value of the voltage between the terminals inputted from the detection circuit 31 based on the instruction signal for switching the output. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor such as a catalytic combustion gas sensor, a failure detection device for the gas sensor, and a failure detection method for the gas sensor.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Unexamined Patent Publication No. 11-271256.
As in the disconnection / short-circuit detection circuit of the catalytic combustion type gas sensor disclosed in Japanese Patent Publication, a reference element whose resistance value changes only depending on the ambient temperature and a resistance value depending on the ambient temperature and the gas concentration of the gas to be detected. A changing sensing element and a constant current source are connected in series, and based on the change in each voltage drop of the reference element and the detection element, the reference element or the detection element is disconnected, the reference element is short-circuited, and the detection element is short-circuited. A disconnection / short circuit detection circuit of a catalytic combustion type gas sensor for detecting is known.
Further, like a gas alarm device disclosed in Japanese Patent Laid-Open No. 2001-235441, for example, a sensing unit for sensing the gas concentration of the gas to be detected and a heater capable of heating the sensing unit are provided, and the gas to be detected is included. 2. Description of the Related Art There is known a gas alarm device that determines abnormality or disconnection of a heater, that is, a failure of a gas sensor, based on a change in a heater resistance value or a heater current that is stable with respect to atmospheric gas.

Conventionally, for example, a solid polymer membrane fuel cell is constructed by stacking a plurality of cells on a cell formed by sandwiching a solid polymer electrolyte membrane between a fuel electrode and an oxygen electrode from both sides. A fuel cell (hereinafter referred to as a fuel cell), hydrogen is supplied as a fuel to the fuel electrode, air is supplied to the oxygen electrode as an oxidant, and hydrogen ions generated by the catalytic reaction at the fuel electrode are solidified. After passing through the polymer electrolyte membrane to the oxygen electrode, the oxygen electrode causes an electrochemical reaction with oxygen to generate electricity. In such a fuel cell as a solid polymer membrane fuel cell, hydrogen is introduced into the exhaust system on the oxygen electrode side of the fuel cell as in the fuel cell protection device disclosed in JP-A-6-223850. A protective device is known which is equipped with a gas sensor for detecting gas, and when this gas sensor detects that hydrogen on the fuel electrode side has leaked to the oxygen electrode side through the solid polymer electrolyte membrane, shuts off the fuel supply. .

[0004]

By the way, in the fuel cell such as the solid polymer membrane fuel cell as described above,
In order to maintain the ionic conductivity of the solid polymer electrolyte membrane, the reaction gas supplied to the fuel cell, for example, air containing hydrogen as a fuel or oxygen as an oxidant, is supplied with water (humidifying water) by a humidifier or the like. It is mixed. In addition, during operation of the fuel cell, reaction product water is generated by an electrochemical reaction.
For this reason, in the fuel cell protection device according to the example of the conventional art described above, dew condensation may occur on the gas sensor arranged in the flow path of the off gas due to the highly moist off gas discharged from the fuel cell. In particular, in the solid polymer membrane fuel cell described above, the normal operating temperature is lower than the vaporization temperature of water, and the offgas is discharged as a gas with a relatively high humidity and a large amount of water. Water is easily condensed.

Here, for example, when the catalytic combustion type gas sensor according to the above-mentioned prior art is provided in the exhaust system on the oxygen electrode side of the fuel cell, etc., if humidifying water, reaction product water or the like adheres to the detecting element, the surface of the detecting element is detected. Non-uniformity of local temperature distribution may occur, resulting in damage such as deterioration of sensitivity and deterioration of sensitivity. In this case, unlike the disconnection or short circuit of the detection element in the above-mentioned conventional technique, the gas sensor can output an appropriate detection signal, but the amount of hydrogen gas contained in the exhaust system increases due to an abnormality in the fuel cell, for example. However, a damaged or deteriorated gas sensor cannot output a detection signal of an appropriate magnitude according to this increase. For example, in a setting that determines that the fuel cell is in an abnormal state when the detection signal output from the gas sensor exceeds a predetermined determination threshold, a detection signal that exceeds the predetermined determination threshold if the gas sensor has no sensitivity decrease For a hydrogen gas amount such that is output, a hydrogen sensor whose sensitivity has decreased may output a detection signal below a predetermined determination threshold, and it may be determined that an abnormal state has not occurred in the fuel cell. is there. Therefore, unlike the case where the detection signal is not output, such as the disconnection or short circuit of the detection element in the above-described conventional technology, even when an appropriate detection signal is output, damage or deterioration caused in the gas sensor It is desirable to reliably detect
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas sensor, a gas sensor failure detection device, and a gas sensor failure detection method capable of easily and reliably detecting damage or deterioration at appropriate timings. And

[0006]

In order to solve the above problems and achieve the object, a gas sensor according to the present invention comprises a detection element (for example, the detection element 21 in the embodiment). A gas sensor capable of detecting a gas to be detected based on a difference in electric resistance value from a compensating element (for example, the temperature compensating element 22 in the embodiment), in which the electric resistance value is changed by the action of the gas to be detected. A series circuit (for example, the series circuit 29 in the embodiment) in which an element (for example, the dummy element 23 in the embodiment) is connected in series to the detection element and the compensation element, and a reference voltage in the series circuit. And a voltage detecting means (for example, the reference voltage applying circuit 30 in the embodiment) that detects the voltage between the terminals of the detection element or the voltage between the terminals of the dummy element. It is characterized in that it comprises a detection circuit 31) and in state.

According to the gas sensor having the above-mentioned configuration, for example, a catalyst that generates heat due to a catalytic combustion reaction of the gas to be detected is carried,
A detection element whose electric resistance value increases depending on the concentration of the gas to be detected and the ambient temperature, and a compensation element whose electric resistance value changes only depending on the ambient temperature, for example, equivalent to the detection element, or compared with the detection element, for example. And a dummy element having a larger increase in electric resistance value depending on the concentration of the gas to be detected, are connected in series to a reference voltage applying means such as a constant voltage source, and the voltage detecting means is used to connect between terminals of the detecting element. Detect the voltage. Here, in the detection element, for example, an increase in the electric resistance value according to the concentration of the gas to be detected does not occur due to damage, or an increase in the electric resistance value according to the concentration of the gas to be detected due to deterioration such as sensitivity decrease If it is reduced below a certain level, the voltage drop at the detection element will be relatively low compared to the voltage drop at the dummy element that is not damaged or deteriorated. The voltage drop at the detection element, that is, the detected value of the voltage between the terminals of the detection element changes in a decreasing tendency. In other words, due to the change characteristics of the inter-terminal voltage that cannot occur for a detection element that is not damaged or deteriorated, unlike the case where the detection signal is not output, such as disconnection or short circuit of the detection element, Even when the element is damaged or deteriorated and an appropriate detection signal is output, it is possible to easily and reliably detect the damage or deterioration of the detection element. Further, similarly, by detecting the terminal voltage of the dummy element by the voltage detecting means, it is possible to easily and surely detect that the dummy element is damaged or deteriorated.

Further, the gas sensor of the present invention according to claim 2 is provided with a gas detection chamber (for example, the gas detection chamber 17 in the embodiment) into which the gas to be detected is introduced, and the detection element and the compensation. The element and the dummy element are arranged in the gas detection chamber. According to the gas sensor having the above configuration, by arranging each element in the gas detection chamber, for example, the wiring structure when connecting each element in series is simplified, or the connection terminals required for connecting each element and the substrate, etc. It is possible to suppress an increase in the number of terminals and the like, and reduce labor and cost required for manufacturing the gas sensor.

A gas sensor failure detection device according to a third aspect of the present invention is a gas sensor failure detection device for detecting a failure of the gas sensor according to the first or second aspect, wherein the voltage detection means is provided. Determination means (for example, the failure determination unit 34 in the embodiment) that determines whether or not the detected value of the inter-terminal voltage detected by is less than or equal to a predetermined determination value (for example, the failure determination value in the embodiment). And an output unit that outputs a predetermined output value as the detected value of the inter-terminal voltage when the detection value of the inter-terminal voltage is less than or equal to the predetermined determination value according to the determination result of the determination unit (for example, Output switching unit 35) in the form.

According to the gas sensor failure detection device having the above structure, the detection element does not increase in electric resistance value depending on the concentration of the gas to be detected due to damage, for example.
For example, if the amount of increase in the electrical resistance value depending on the concentration of the gas to be detected decreases by more than a predetermined degree due to deterioration such as sensitivity decrease, the detected value of the voltage across the terminals of the detection element is In this state, the inter-terminal voltage becomes a value less than the detected value, and it tends to decrease as the concentration of the gas to be detected increases. Therefore, by setting the predetermined determination value in the determination means to, for example, a value less than the detection value of the inter-terminal voltage of the detection element when the concentration of the gas to be detected is zero, the detection element is not damaged or deteriorated. The occurrence can be detected easily and surely. The detected value of the inter-terminal voltage of the detection element when the concentration of the detected gas is zero is the reference voltage applied to the series circuit, and the detection element and the compensating element when the concentration of the detected gas is zero. Since it can be calculated based on the electric resistance value of the dummy element and the electric resistance value of the dummy element, the predetermined judgment value in the judgment means is the electric resistance value of each element in the state where the reference voltage and the concentration of the gas to be detected are zero. The value may be increased or decreased depending on the value. Moreover, when the detection value of the inter-terminal voltage of the detection element is less than or equal to the predetermined determination value in the determination result of the determination means, instead of simply outputting this detection value, for example, detection that damage or deterioration has not occurred By outputting a predetermined output value that deviates from the output range for the detection value of the terminal voltage of the element, it is possible to prevent the gas concentration of the gas to be detected from being erroneously detected, and to reliably detect the failure of the gas sensor. It can be carried out.

Further, in the gas sensor failure detection method of the present invention as set forth in claim 4, a detection element capable of detecting a gas to be detected based on a difference in electric resistance between the detection elements (for example, the detection element 21 in the embodiment). ) And a compensation element (for example, the temperature compensation element 22 in the embodiment), and a dummy element (for example, the dummy element 23 in the embodiment) whose electric resistance value changes due to the action of the gas to be detected are connected in series. A reference voltage is applied to a series circuit (for example, the series circuit 29 in the embodiment) connected to the detection circuit, and the detection value of the terminal voltage of the detection element or the terminal voltage of the dummy element is a predetermined determination value ( For example,
(Fault determination value in the embodiment) or less (for example, step S02 in the embodiment), if the detected value of the inter-terminal voltage is less than or equal to the predetermined determination value, A predetermined output value is output as the detected value of the voltage (for example, step S04 in the embodiment).

According to the above gas sensor failure detection method, by setting the predetermined determination value to a value less than the detection value of the terminal voltage of the detection element when the concentration of the gas to be detected is zero, for example, It is possible to easily and surely detect that the detection element is damaged or deteriorated. Moreover, when the detected value of the terminal voltage of the detection element is less than or equal to the predetermined determination value, instead of simply outputting the detected value, for example, the detection of the terminal voltage of the detection element that is not damaged or deteriorated is detected. By outputting a predetermined output value that deviates from the output range for the value, it is possible to prevent the gas concentration of the gas to be detected from being erroneously detected, and to reliably detect the failure of the gas sensor. Further, similarly, by outputting a predetermined output value that deviates from the output range for this detection value in accordance with the determination result of whether the detection value of the terminal voltage of the dummy element is less than or equal to the predetermined determination value, It is possible to reliably detect the failure of the gas sensor for damage or deterioration of the dummy element.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A gas sensor and a failure detection device for a gas sensor according to an embodiment of the present invention will be described below with reference to the accompanying drawings. The gas sensor 1 according to the present embodiment is, for example, a hydrogen sensor that detects hydrogen. As shown in FIG. 1, the gas sensor 1 includes a control device 2, a storage device 3, an alarm device 4, a fuel cell 5, and a fuel cell 5. In order to confirm that hydrogen is not discharged from the outlet side pipe 9 provided at the oxygen electrode side outlet side pipe 9 in the fuel cell system 10 including the connected pipes 6, 7, 8 and 9. belongs to. The control device 2 is connected to the gas sensor 1 attached to the outlet side pipe 9 on the oxygen electrode side, and compares, for example, a detection signal output from the gas sensor 1 with a predetermined determination threshold value stored in the storage device 3. Depending on the result, it is determined whether or not an abnormal state of the fuel cell 5 has occurred, and when it is determined that the abnormal state is present, the alarm device 4 outputs an alarm or the like. Here, the storage device 3 stores a map of a predetermined determination threshold value with respect to the detection value of the gas sensor 1 according to the operating state of the fuel cell 5, for example, the inter-electrode differential pressure or the operating pressure.

The fuel cell 5 is mounted on a vehicle as a power source of, for example, an electric vehicle, and has an electrolyte electrode structure in which a solid polymer electrolyte membrane such as a cation exchange membrane is sandwiched between a fuel electrode and an oxygen electrode. Further, a large number of fuel cell units (not shown) sandwiched between a pair of separators are further laminated. In the fuel gas such as hydrogen supplied to the fuel electrode from the inlet side pipe 6, hydrogen is ionized on the catalyst electrode of the fuel electrode and moves to the oxygen electrode through the appropriately humidified solid polymer electrolyte membrane. Electrons generated during that time are taken out to an external circuit and used as direct current electrical energy. For example, an oxidant gas such as oxygen or air is supplied to the oxygen electrode via the inlet side pipe 7, so that hydrogen ions, electrons and oxygen react with each other to generate water. . Then, the reacted so-called off-gas is discharged out of the system through the outlet side pipes 8 and 9 on both the fuel electrode side and the oxygen electrode side.

Here, a gas sensor 1 which is a gas contact combustion type hydrogen sensor is attached to the outlet side pipe 9 on the oxygen electrode side in the vertical direction, and the inside of the outlet side pipe 9 on the oxygen electrode side is attached by this gas sensor 1. It is possible to detect hydrogen in off-gas flowing through the. For example, as shown in FIGS. 2 and 3, the gas sensor 1 includes a rectangular parallelepiped case 11 along the longitudinal direction of the outlet side pipe 9. The case 11 is made of polyphenylene sulfide, for example, and has flange portions 12 at both ends in the longitudinal direction. A collar 13 is attached to the flange portion 12, and a bolt 14 is inserted into the collar 13 so that the outlet side pipe 9
The mounting seat 9a is fastened and fixed.
A cylindrical portion 15 is formed on the lower surface of the case 11 so as to be inserted into the through hole 9b of the outlet side pipe 9 from the outside. A circuit board 16 sealed with resin is provided in the case 11. The inside of the tubular portion 15 is formed as a gas detection chamber 17, and a flange portion 18 is formed toward the inside on the inner side surface of the outlet side pipe 9 of the gas detection chamber 17 to form the flange portion 1.
An inner peripheral portion of 8 is formed with an opening as a gas introducing portion 19.

Further, the sealing material 2 is provided on the outer peripheral surface of the tubular portion 15.
0 is attached to the inner wall of the through hole 9b of the outlet side pipe 9 so as to ensure airtightness. Then, for example, in FIG.
As shown in, the detection element 21, the temperature compensation element 22, and the dummy element 23 are mounted inside the tubular portion 15.
For example, as shown in FIG. 4, each element 21, 22, 23 is arranged at a certain distance from the base 25 by a plurality of, for example, six pins 24 connected to the circuit board 9, and for example, the detection element 21. The temperature compensating element 22 and the dummy element 23 are arranged so as to sandwich in the horizontal direction.

The detection element 21 is a well-known element. For example, as shown in FIG. 5, the surface of a coil 26 of a metal wire containing platinum or the like having a high temperature coefficient with respect to electric resistance is exposed to hydrogen as a gas to be detected. On the other hand, a catalyst 27 composed of an active precious metal or the like
It is formed by being coated with a carrier such as alumina which carries. The temperature compensating element 22 is inactive with respect to the gas to be detected, and is provided with, for example, a coil 26 equivalent to the detecting element 21. Then, the detection element 21 that has become high in temperature due to the heat generated by the combustion reaction that occurs when hydrogen, which is the gas to be detected, contacts the catalyst 27 of the detection element 21, and the temperature below the ambient temperature, where the combustion reaction due to the gas to be detected does not occur. Compensation element 22
It is possible to detect the hydrogen concentration by canceling the change in the electric resistance value due to the ambient temperature by utilizing the difference in the electric resistance value between and.

The dummy element 23 is formed in the same manner as the detection element 21, for example. Each element 21, 22, 23
Are connected in series to each other to form a series circuit 29, and a reference voltage application circuit 30 for applying a predetermined reference voltage is connected to the series circuit 29. Further, a detection circuit 31 that detects the voltage between the terminals of the detection element 21 is connected in parallel with the detection element 21, and the detected value of the voltage between the terminals of the detection element 21 detected by the detection circuit 31 is, for example, a control value. It is input to the circuit 32, and the output circuit 33 is connected via the control circuit 32. The gas sensor failure detection device 1a according to the present embodiment includes, for example, the gas sensor 1, a reference voltage application circuit 30, a detection circuit 31, a control circuit 32, and an output circuit 33. .

The control circuit 22 includes, for example, a failure determination section 34.
And an output switching section 35. The failure determination unit 34 uses the detection element 21 output from the detection circuit 31.
It is determined whether or not the detected value of the inter-terminal voltage is less than or equal to a predetermined failure determination value set according to a predetermined reference voltage applied to the series circuit 29 by the reference voltage application circuit 30. Then, in this determination result, when the detected value is less than or equal to the predetermined failure determination value, it is determined that the gas sensor 1 is in failure, and a command signal for instructing output switching described below is output to the output switching unit 35. . On the other hand, in this determination result, when the detected value is larger than the predetermined failure determination value, it is determined that the gas sensor 1 is normal. When the command signal for instructing output switching is input from the failure determination unit 34, the output switching unit 35 has a predetermined output value instead of the detection value of the terminal voltage of the detection element 21 input from the detection circuit 31. To the output circuit 33. On the other hand, when the command signal for instructing the output switching is not input from the failure determination unit 34, the detection value input from the detection circuit 31 is output to the output circuit 33. The output circuit 33 outputs the detected value of the inter-terminal voltage or the predetermined output value input from the output switching unit 35 to the outside of the gas sensor 1, for example, the control device 2 as an output voltage value.

The gas sensor 1 and the gas sensor failure detection device 1a according to the present embodiment have the above-described structure. Next, the operation of the gas sensor 1 and the gas sensor failure detection device 1a will be described. A detection element 21 and a dummy element 23 whose electric resistance value increases as the hydrogen concentration increases;
The temperature compensating element 22 and the temperature compensating element 22 are connected in series, and the series circuit 2
By applying a predetermined reference voltage to the detecting element 2,
The terminal voltage of 1 is, for example, as shown by the solid line A in FIG.
Starting from the normal lower limit inter-terminal voltage V1 set in accordance with a predetermined reference voltage applied to the series circuit 29 for an appropriate detection lower limit threshold concentration d1, the increasing tendency changes with an increase in hydrogen concentration. In this case, the terminal voltage of the dummy element 23 also shows the same change as the terminal voltage of the detection element 21. Here, if the dummy element 23 is damaged or deteriorates such as a decrease in sensitivity due to, for example, moisture adhering to the surface of the dummy element 23, the voltage drop in the dummy element 23 is reduced, and the detection element 21 is reduced. Of the detection element 21 increases as the hydrogen concentration increases, as indicated by the solid line B in FIG. 6, for example. On the other hand, for example, due to water adhering to the surface of the detection element 21, for example, the carrier carrying the catalyst 27 is damaged or broken, and the electric resistance value does not increase according to the increase in hydrogen concentration. For example, when the increase amount of the electric resistance value corresponding to the increase of the hydrogen concentration is reduced by more than a predetermined degree due to the deterioration of the sensitivity or the like, the voltage drop in the detection element 21 decreases and the voltage in the dummy element 23 decreases. The descent increases and the detection element 2
The terminal voltage of 1 is, for example, as shown by the solid line C in FIG.
Starting from the normal lower limit inter-terminal voltage V1 at an appropriate detection lower limit threshold concentration d1, the tendency tends to decrease as the hydrogen concentration increases. That is, in this case, the inter-terminal voltage of the detection element 21 exhibits a characteristic of change peculiar to the abnormal state of the detection element 21. Therefore, for example, by setting a value that is slightly smaller than the normal lower limit terminal voltage V1 as the predetermined failure determination value in the failure determination unit 34, does the detection element 21 have an abnormality such as damage, breakage, or deterioration? Whether or not it can be detected easily and reliably.

A method of detecting a failure of the gas sensor 1 will be described below with reference to the accompanying drawings. First, in step S01 shown in FIG. 7, the detection value of the terminal voltage of the detection element 21 detected by the detection circuit 31 is acquired.
Next, in step S02, it is determined whether the acquired detection value is less than or equal to a predetermined failure determination value. If the result of this determination is “NO”, the flow proceeds to step S03, the acquired detection value is output as a normal output voltage to the outside of the gas sensor 1, for example, the control device 2 or the like, and a series of processing ends. On the other hand, if the result of this determination is "YES", then step S
In step 04, instead of the acquired detection value, a predetermined output value is output to the outside of the gas sensor 1, for example, the control device 2 as a failure output voltage, and the series of processes is ended. Here, the predetermined output value output as the output voltage value at the time of failure is applied to the series circuit 29 with respect to a value less than the voltage V1 between the lower limit terminals at normal time or an appropriate detection upper limit threshold concentration d2 shown in FIG. 6, for example. The detection element 2 in a normal state such as a value exceeding the normal upper limit voltage V2 set according to a predetermined reference voltage
The voltage between terminals 1 is a value that is not detected, that is, a value that is unique to the abnormal state of the detection element 21.

In the following, in the gas sensor 1 and the gas sensor failure detection device 1a according to the present embodiment described above,
The result of the simulation in which the change in the detected value of the terminal voltage of the detection element 21 according to the change in the hydrogen concentration is calculated will be described. Here, in the above-described gas sensor 1 of the present embodiment, the case where the gas sensor 1 is in a normal state is referred to as Example 1, and the hydrogen concentration of the hydrogen concentration of the carrier carrying the catalyst 27 of the detection element 21 is damaged or damaged, for example. The case where the increase of the electric resistance value according to the increase does not occur or the increase amount of the electric resistance value according to the increase of the hydrogen concentration is decreased by more than a predetermined degree due to the deterioration such as the decrease in sensitivity is referred to as Example 2. Example 3 is a case where the dummy element 23 is damaged or broken, and deteriorates such as a decrease in sensitivity. Further, in the above-described gas sensor 1 of the present embodiment, the dummy element 23 is omitted and the detection element 21 is in a normal state as Comparative Example 1, and the detection element 21 is deteriorated such as damage or breakage, sensitivity deterioration, and the like. Comparative Example 2 was the case in which the occurrence of. The results are shown in Fig. 8. In addition,
In FIG. 8, the detected value of the terminal voltage of the detection element 21 is
This is a relative value where the detected value when the hydrogen concentration is zero is "1".

As shown in FIG. 8, in comparison with the first embodiment in which the gas sensor 1 is in a normal state, in the second embodiment in which the detection element 21 is damaged or is damaged or deteriorated, the inter-terminal voltage increases as the hydrogen concentration increases. Since it exhibits a unique change characteristic that the detected value of 1 changes in a decreasing tendency, it is possible to reliably detect the abnormal state of the detection element 21. On the other hand, the detection element 21
In Comparative Example 1 in which is normal, and in Comparative Example 2 in which the detection element 21 is damaged or damaged, and the sensitivity is lowered, the detected value of the inter-terminal voltage changes to increase as the hydrogen concentration increases. Therefore, even if the detection element 21 has an abnormal state, it cannot be distinguished from the case where the hydrogen concentration is lowered. Further, in the third embodiment in which the dummy element 23 is damaged or damaged, and the sensitivity is lowered, a large detection value that is not detected as the inter-terminal voltage of the detection element 21 in the normal state is obtained. Therefore, it can be distinguished from the case where an increase in hydrogen concentration occurs. In the third embodiment, the increase change amount of the inter-terminal voltage of the detection element 21 per predetermined increase change of the hydrogen concentration (that is, the gradient of the detected value of the inter-terminal voltage shown in FIG. 8 with respect to the hydrogen concentration) is determined by the gas sensor 1. Is larger than that of the first embodiment in which the normal state is. Therefore, it is possible to determine whether or not an abnormality has occurred in the dummy element 23 based on the change in the detected value of the terminal voltage according to the change in the hydrogen concentration.

As described above, according to the gas sensor 1 of this embodiment, the detection element 21 and the temperature compensation element 2 are provided.
2 and the dummy element 23 are connected in series with each other, and the detection element 2 is connected to the series circuit 29 with a predetermined reference voltage applied.
By detecting the change in the voltage between the terminals of No. 1, when the detection element 21 is damaged or damaged, or deteriorates in sensitivity or the like, it is possible to detect a characteristic change characteristic in this abnormal state. It is possible to reliably determine whether or not 21 has an abnormal state. Furthermore, according to the gas sensor failure detection device 1a of the present embodiment, the predetermined failure determination value in the failure determination unit 34 is applied to the series circuit 29 for an appropriate detection lower limit threshold concentration d1. By setting the value slightly lower than the normal time lower limit terminal voltage V1 set according to the reference voltage, it is possible to easily and surely detect that the detection element 21 is damaged, damaged, or deteriorated such as a decrease in sensitivity. can do. Moreover, the detection element 21
When the detected value of the inter-terminal voltage of is less than or equal to the predetermined failure determination value, instead of simply outputting the detected value, it is not detected as the inter-terminal voltage of the detection element 21 in the normal state. By outputting a value, that is, a unique value in the abnormal state of the detection element 21, it is possible to prevent the hydrogen concentration from being erroneously detected, and to reliably detect the failure of the gas sensor 1. Further, according to the failure detection method of the gas sensor of the present embodiment, it is possible to easily and reliably detect that the detection element 21 is deteriorated, such as damaged or broken, and the sensitivity is lowered, and the hydrogen concentration is erroneously detected. This can be prevented, and the failure detection of the gas sensor 1 can be reliably performed.

In the above-mentioned embodiment,
The detection circuit 31 for detecting the voltage between the terminals of the detection element 21 is provided, and it is determined whether the detection value of the voltage between the terminals of the detection element 21 output from the detection circuit 31 is less than or equal to a predetermined failure determination value. However, the detection circuit for detecting the voltage between the terminals of the dummy element 23 is provided, and it is determined whether the detection value of the voltage between the terminals of the dummy element 23 output from the detection circuit is less than or equal to a predetermined failure determination value. You may.

In the above-described embodiment,
The elements 21, 22, and 23 are arranged on the base 25 via the two pins 24, but the arrangement is not limited to this, and each element according to the first modification of the gas sensor 1 of the present embodiment shown in FIG. 9, for example. Like the elements 21, 22, and 23, for example, the base 2
5, instead of connecting the elements 21, 22, and 23 in series in the circuit board 16 or the circuit board 16, a plurality of, for example, four pins 24 are provided.
The elements 21, 22, and 23 may be connected in series via the. In this case, the pin 2 required for the configuration of the gas sensor 1
The number of 4 can be reduced.

Further, in the above-mentioned embodiment,
Although the dummy element 23 is equivalent to the detection element 21, the dummy element 23 is not limited to this. For example, a change in the hydrogen concentration of each element 21, 22, 23 according to the second modification of the gas sensor 1 of the present embodiment shown in FIG. As shown in the graph of the change in the electric resistance value, the dummy element 23 shows a change characteristic different from that of the detection element 21, for example, a characteristic that the electric resistance value is higher than that of the detection element 21 as the hydrogen concentration increases. It may be one.

Further, in the above-mentioned embodiment,
The output switching unit 35 may be omitted. In this case, a failure connected to the failure determination unit 34 in addition to the output circuit 33 connected to the detection circuit 31, as in the modified example of the failure detection device 1a for a gas sensor of the present embodiment shown in FIG. A signal output circuit 41 is provided. Here, the failure signal output circuit 4
In the determination result of the failure determination unit 34, when the detected value is less than or equal to a predetermined failure determination value, a failure signal indicating that the gas sensor 1 has failed is provided outside the gas sensor 1, for example, the control device 2. Output to etc. On the other hand, in the determination result of the failure determination unit 34, when the detected value is larger than the predetermined failure determination value, a failure signal indicating that the gas sensor 1 is normal is sent to the outside of the gas sensor 1, for example, the control device 2 or the like. Output. The operation of the gas sensor failure detection device 1a according to this modification will be described below. First, in step S11 shown in FIG. 12, the detection value of the terminal voltage of the detection element 21 detected by the detection circuit 31 is acquired. Next, in step S12, it is determined whether the acquired detection value is less than or equal to a predetermined failure determination value. If the result of this determination is "NO", the flow proceeds to step S13,
A normal signal is output, and a series of processing ends. On the other hand, if the result of this determination is "YES", then the flow proceeds to step S14, a failure signal is output, and a series of processing ends.

In the above-described embodiment,
The hydrogen concentration may be detected based on the signal output from the output circuit 33, or based on the voltage value detected by a well-known bridge circuit including the detection element 21 and the temperature compensation element 22. A configuration for detecting the hydrogen concentration may be provided.

Although the gas sensor 1 is a hydrogen sensor in the above-described embodiment, the present invention is not limited to this.
It may be a gas sensor that detects other gases, for example, flammable gases such as carbon monoxide and methane.

[0031]

As described above, according to the gas sensor of the present invention as defined in claim 1, the detection element is damaged unlike the case where the detection signal is not output due to disconnection or short circuit of the detection element. It is possible to easily and reliably detect the occurrence of damage, deterioration, etc. in the detection element even in the case where a suitable detection signal is output due to deterioration, deterioration, etc.
Furthermore, according to the gas sensor of the present invention as set forth in claim 2, by disposing each element in the gas detection chamber, for example, the wiring structure when connecting each element in series is simplified, each element and the substrate, etc. It is possible to suppress an increase in the number of connection terminals required for connection with, and reduce the labor and cost required for manufacturing the gas sensor.

Further, according to the failure detecting device for a gas sensor of the present invention as defined in claim 3, it is possible to easily and surely detect the occurrence of damage, damage, deterioration in sensitivity, etc. of the detecting element. By preventing the hydrogen concentration from being erroneously detected, it is possible to reliably detect the failure of the gas sensor. Further, according to the gas sensor failure detection method of the present invention as set forth in claim 4, it is possible to easily and reliably detect the occurrence of damage, damage, deterioration in sensitivity, etc. of the detection element, and to determine the hydrogen concentration. It is possible to prevent the gas sensor from being erroneously detected and reliably detect the failure of the gas sensor.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a fuel cell system including a gas sensor according to an embodiment of the present invention.

FIG. 2 is a plan view of the gas sensor shown in FIG.

3 is a schematic cross-sectional view taken along the line AA shown in FIG.

FIG. 4 is a perspective view showing each element.

FIG. 5 is a configuration diagram of a gas sensor failure detection device according to an embodiment of the present invention.

FIG. 6 is a graph showing a change in inter-terminal voltage of the detection element according to hydrogen concentration.

FIG. 7 is a flowchart showing processing of a gas sensor failure detection method according to an embodiment of the present invention.

FIG. 8 is a graph showing a change in the detected value of the terminal voltage of the detection element according to the hydrogen concentration.

FIG. 9 is a perspective view showing each element according to a first modified example of the gas sensor of the present embodiment.

FIG. 10 is a graph showing a change in electric resistance value according to hydrogen concentration of each element according to a second modified example of the gas sensor of the present embodiment.

FIG. 11 is a configuration diagram showing a modified example of the gas sensor failure detection device of the present embodiment.

FIG. 12 is a flowchart showing processing of a gas sensor failure detection method according to a modification of the present embodiment.

[Explanation of symbols]

1 gas sensor 1a Gas sensor failure detection device 17 Gas detection room 21 detector 22 Temperature compensation element (compensation element) 23 Dummy element 29 series circuit 30 Reference voltage application circuit (reference voltage application means) 31 detection circuit (voltage detection means) 34 Failure determination unit (determination means) 35 output switching unit (output means)

Claims (4)

[Claims] 1. A gas sensor capable of detecting a gas to be detected on the basis of a difference in electric resistance value between a detection element and a compensating element, wherein the detection element is a dummy element whose electric resistance value changes by the action of the gas to be detected. And a series circuit connected in series to the compensation element, reference voltage applying means for applying a reference voltage to the series circuit, and voltage detection for detecting the terminal voltage of the detection element or the terminal voltage of the dummy element. And a gas sensor. 2. A gas detection chamber into which the gas to be detected is introduced, wherein the detection element, the compensation element, and the dummy element are arranged in the gas detection chamber. Gas sensor. 3. A gas sensor failure detection device for detecting a failure of the gas sensor according to claim 1, wherein a detection value of the inter-terminal voltage detected by the voltage detection means is a predetermined determination value. If the detection value of the terminal voltage is less than or equal to the predetermined determination value in the determination result of the determination means and the determination result of the determination means, a predetermined output value as the detection value of the terminal voltage A failure detection device for a gas sensor, comprising: output means for outputting. 4. A detection element and a compensating element capable of detecting a gas to be detected based on a difference in electric resistance between them, and a dummy element whose electric resistance value is changed by the action of the gas to be detected are connected in series. Applying a reference voltage to the series circuit consisting of, the detection value of the inter-terminal voltage of the detection element or the inter-terminal voltage of the dummy element is determined whether or not a predetermined determination value, the detection value of the inter-terminal voltage Is less than or equal to the predetermined determination value, a predetermined output value is output as the detection value of the inter-terminal voltage.