JP3395957B2 - Carbon monoxide detection sensor and carbon monoxide detection method using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carbon monoxide detection sensor and a carbon monoxide detection method using the same.

[0002]

2. Description of the Related Art For example, in a combustor or an internal combustion engine that uses fossil fuels such as natural gas or petroleum, carbon monoxide detection sensors have been conventionally used to detect carbon monoxide generated during incomplete combustion. Is proposed. For example, in Japanese Unexamined Patent Publication No. 9-152416, a pair of porous electrodes are formed on the surface of an oxygen ion conductive solid electrolyte layer such as partially stabilized zirconia, and the first electrode is exposed to the gas to be measured. On the other hand, a sensor having a structure in which the second electrode is covered with a carbon monoxide oxidation catalyst is disclosed. In the sensor having the structure, carbon monoxide is combined with oxygen adsorbed on the electrode to form carbon dioxide on the side of the first electrode, while on the side of the second electrode, by the oxidation catalyst before carbon monoxide reaches the electrode. Since it is oxidized, a concentration cell electromotive force is generated between both electrodes. By measuring this electromotive force, the concentration of carbon monoxide in the measured gas can be known.

[0003]

However, the carbon monoxide detection sensor having the above structure has a drawback that the sensitivity of the sensor is likely to deteriorate with time due to long-term use. Therefore, Japanese Unexamined Patent Publication No. 9-89835 proposes a technique for recovering the sensor sensitivity by periodically performing a cleaning process in which a voltage for polarization is applied between electrodes for a predetermined time in the sensor having the above configuration. . However, this method has a drawback that continuous carbon monoxide concentration detection is not possible because cleaning must be frequently performed to maintain good sensor sensitivity and measurement cannot be performed during cleaning.

An object of the present invention is to detect carbon monoxide in a gas to be detected with high accuracy, and to continuously detect carbon monoxide without electrode cleaning, and a carbon monoxide using the same. And a detection method.

[0005]

In order to solve the above-mentioned problems, the carbon monoxide detection sensor of the present invention is
The first treatment space and the second treatment space are formed in a state in which the gas under measurement from the atmosphere under measurement containing carbon monoxide and oxygen can enter and exit, and further, with the oxygen ion conductive solid electrolyte, An oxygen concentration battery element in which two electrodes having oxygen permeability are formed on the surface, one of the electrodes is arranged facing the first treatment space, and the other is arranged facing the second treatment space. Two electrodes having oxygen permeability are formed on the surface of the oxygen ion conductive solid electrolyte, and one of the electrodes is arranged so as to face the first treatment space. A sensor in which an oxygen pump element that pumps oxygen in or out of the first processing space in a direction in which the absolute value of the battery electromotive force decreases and an oxygen pump element and an oxygen concentration battery element are predetermined. And a heating element for heating to a dynamic temperature, the electrode on the side facing the first processing space of the oxygen pump element is the first electrode, the electrode on the side facing the first processing space of the oxygen concentration battery element is the second electrode, The electrode facing the second treatment space of the oxygen concentration cell device is used as the third electrode, and the difference in the combustion consumption of carbon monoxide in the introduced gas to be detected between the first treatment space and the second treatment space. So that the oxidation catalytic activities of the first to third electrodes are adjusted, and the oxygen pump element when the absolute value of the concentration cell electromotive force of the oxygen concentration cell element reaches a predetermined electromotive force target value EC. It is characterized in that the value of the current flowing through is extracted as information reflecting the concentration of carbon monoxide in the gas to be detected.

Further, the carbon monoxide detection method of the present invention is characterized in that the first processing space and the second processing space partitioned from the atmosphere to be measured and the carbon monoxide are supplied to the first processing space and the second processing space. It has a first gas introduction part and a second gas introduction part for respectively guiding the measured gas from the measured atmosphere containing oxygen, and is further composed of an oxygen ion conductive solid electrolyte and has oxygen on its surface. Having transparency 2
Two electrodes are formed, one of the electrodes is arranged to face the first treatment space, and the other is arranged to face the second treatment space. In addition, two electrodes having oxygen permeability are formed on the surface, and one of the electrodes is arranged facing the first treatment space, and the absolute value of the concentration cell electromotive force generated in the oxygen concentration cell element is reduced. And an oxygen pump element for pumping or pumping oxygen to and from the first processing space, and a heating element for heating the oxygen pump element and the oxygen concentration battery element to a predetermined sensor operating temperature. The electrode on the side facing the first treatment space of the element is the first electrode, the electrode on the side facing the first treatment space of the oxygen concentration battery element is the second electrode, and the electrode facing the second treatment space of the oxygen concentration battery element. As the third electrode , The oxidation catalytic activity of the first to third electrodes is adjusted so that the combustion consumption of carbon monoxide in the introduced gas to be detected differs between the first processing space and the second processing space. The measured value of the current flowing through the oxygen pump element when the absolute value of the concentration cell electromotive force of the oxygen concentration cell element reaches a predetermined electromotive force target value E C using It is characterized in that the information is extracted as information reflecting the carbon oxide concentration.

According to the present invention, the gas to be detected containing carbon monoxide and oxygen is introduced into the first processing space and the second processing space, while the first gas is disposed facing the first processing space. One electrode and the second electrode, the oxidation catalytic activity for carbon monoxide of the third electrode arranged facing the second treatment space is the combustion consumption of carbon monoxide in the first treatment space and the second treatment space. Adjusted to make the difference. As a result, in the first treatment space and the second treatment space, oxygen is also consumed on the side on which carbon monoxide is consumed a lot, so that an oxygen concentration difference occurs on both sides of the oxygen concentration battery element, and the concentration based on that is generated. Battery electromotive force will be generated. The oxygen pump element, for example, pumps oxygen into the processing space when the first processing space side is on the low oxygen concentration side, and conversely pumps oxygen from the processing space when it is on the high oxygen concentration side. The concentration battery electromotive force is controlled to the electromotive force target value E C. The current flowing through the oxygen pump element when the concentration cell electromotive force reaches the electromotive force target value EC (hereinafter referred to as pump current) is a value that almost reflects the concentration value of carbon monoxide in the gas to be detected. Therefore, the concentration of carbon monoxide can be detected based on this.

According to the carbon monoxide detection sensor having the above structure, the change in the pump current value with respect to the change in the carbon monoxide concentration is large and the sensitivity is good. Further, it is not necessary to clean the electrodes, and carbon monoxide can be detected continuously and accurately for a long period of time. The reason why the above effects are achieved in the carbon monoxide detection sensor of the present invention is presumed as follows. That is, in the conventional carbon monoxide detection sensor, the concentration battery electromotive force generated in the oxygen concentration battery element is taken out as the sensor output, but in this method, the electromotive force is generated in one direction, If the generation state continues for a long time, polarization may occur in the solid electrolyte or the amount of oxygen on the electrode may decrease with time, which is considered to cause the sensor sensitivity to change with time. However, in the configuration of the sensor of the present invention, oxygen is pumped out or pumped into the first processing space by the oxygen pump element to reduce the absolute value of the concentration cell electromotive force generated in the oxygen concentration cell element (that is, Since the concentration cell electromotive force is canceled), it is presumed that the polarization of the solid electrolyte as described above is less likely to occur, the change in output over time is suppressed, and stable operation is realized.

The oxygen pump element and the oxygen concentration cell element are
It is composed of a solid electrolyte having oxygen ion conductivity. As such a solid electrolyte, Y ₂ O ₃ or C may be used.
ZrO ₂ in which aO is solid-dissolved is a typical one, but a solid solution of an oxide of an alkaline earth metal element or a rare earth metal element other than that and ZrO ₂ may be used. Also,
HfO ₂ may be contained in the base ZrO ₂ .

Further, in the above-mentioned sensor of the present invention, a diffusion regulation flow section for guiding the gas to be detected to a certain diffusion resistance can be provided in the first processing space and the second processing space. The diffusion regulation distribution part is, for example, a small hole, a slit,
And a porous communication part made of porous ceramic or porous metal. As a result, even if the concentration of carbon monoxide in the gas to be detected changes suddenly, the concentration of carbon monoxide in each processing space does not change very rapidly, and stable detection is possible.

Next, the oxygen pump element and the oxygen concentration cell element can be formed in a plate shape so as to be opposed to each other. In this case, the first treatment space and the second treatment space are formed adjacent to each other in the plate surface direction between the oxygen pump element and the oxygen concentration battery element, and the first electrode faces the first treatment space. Formed on the corresponding plate surface of the oxygen pump element at the position, and the second electrode and the third electrode on the corresponding plate surface of the oxygen concentration battery element at the positions facing the first processing space and the second processing space, respectively. Can be formed adjacent to. According to this configuration, since the second electrode and the third electrode of the oxygen concentration battery element are formed on one surface of the plate-shaped solid electrolyte layer, when each electrode is formed by thick film printing and firing of the electrode material paste. It has the advantages that it requires less printing and has high manufacturing efficiency.

In the above structure, the heating element can be arranged to face the oxygen concentration battery element from the side opposite to the oxygen pump element. This makes it possible to uniformly heat the oxygen-concentrated battery element and reduce the temperature variation between the second electrode and the third electrode, so that the detection accuracy of carbon monoxide can be improved.

In this case, the above-mentioned diffusion control and flow section makes each processing space communicate with the atmosphere to be measured between the oxygen concentration battery element and the oxygen pump element.
It can be formed in a form along the plate surface direction of the element. According to this configuration, for example, the diffusion control distribution portion can be easily and uniformly formed by thick film printing / burning of the carbon paste pattern or thick film printing / firing of the porous ceramic paste pattern. The adjustment of the forming dimension and the like has an advantage that it can be easily performed by adjusting the area or thickness of the paste pattern.

Further, the oxygen pump element and the oxygen concentration cell element have their opposing plate surfaces joined to each other by an insulating ceramic layer in the remaining region except the formation portion of the first processing space and the second processing space. It can be a structure.
As a result, the number of steps for assembling the oxygen pump element and the oxygen concentration battery element can be reduced, and the mechanical strength thereof can be improved.

On the other hand, the oxygen pump element is provided in the oxygen concentration battery element so that a predetermined amount of a gap as a processing space in which the gas to be detected is allowed to flow is formed between the oxygen concentration element and the oxygen concentration battery element. They can be arranged facing each other. in this case,
The size of the gap is preferably set to 1 mm or less, for example. If the size of the gap exceeds 1 mm, the effect of restricting the inflow of new gas to be detected due to the gap becomes small, and the detection accuracy of the sensor may decrease. Also, the area Sp of the first electrode
If the ratio Sp / Ss between the area Ss of the second electrode and the area Ss of the second electrode is 1 or more, the oxygen concentration near the second electrode can be made constant,
As a result, the accuracy and stability of the sensor output can be improved. In this case, the gap becomes the first processing space,
A space (hereinafter, also referred to as an opposite space) located on the opposite side of the above-mentioned gap with the oxygen concentration battery element interposed therebetween is the second processing space.

Next, in the sensor of the present invention, since the electrode that functions as a catalyst for carbon monoxide oxidation is arranged facing the first treatment space, the side where the amount of carbon monoxide oxidation increases. It becomes easy to use it as a space. Therefore,
If the second electrode is the high-activity side electrode and the third electrode is the low-activity side electrode, it becomes easy to make a difference in the oxygen consumption amount on both sides of the oxygen concentration battery element, which is advantageous in increasing the sensor sensitivity. Further, if the oxidation catalytic activity of the second electrode is made larger than that of the third electrode, the linearity of the sensor output with respect to the concentration of carbon monoxide in the gas to be detected is enhanced, and thus the detection accuracy of carbon monoxide is increased. May be further improved. In this configuration, the oxygen pump element pumps oxygen into the gap so that the absolute value of the concentration cell electromotive force generated in the oxygen concentration cell element decreases. Here, for both the first electrode and the second electrode, when the oxidation catalytic activity for carbon monoxide is made larger than that of the third electrode, the difference in the amount of carbon monoxide consumed between the gap and the opposite space is further increased. Therefore, the detection sensitivity of carbon monoxide can be increased.

More specifically, the second electrode and the third electrode have a difference in the detected component conversion ratio η of 2 defined as follows.
It is desirable to use a combination of 0% or more. That is, a sample in which a disk-shaped porous electrode having a diameter of 8 mm was formed on the disk of an oxygen ion conductive solid electrolyte having a diameter of 12 mm and a thickness of 1 mm by the same material and condition as the second electrode or the third electrode. , Placed in a tubular body having a gas inlet and outlet and heated to a sensor operating temperature, and in that state, the tubular body contains 300 ppm of oxygen, 350 ppm of a component to be detected, and 3% of water vapor. The test gas, the balance of which is argon, is supplied from the inlet at a flow rate of 100 ml /
The concentration of the component to be detected in the test gas after discharge when Cs (unit: pp
As m), the detected component conversion rate η (%) is determined by the following equation: η = {(350-Cs) / 350} × 100 (1).

That is, when the component to be detected contained in the test gas is oxidized and consumed by using the electrode as an oxidation catalyst, the concentration Cs of the component to be detected in the test gas after discharge is reduced, so that the above-mentioned component to be detected is reduced. The conversion rate η increases. Therefore, the η can be used as a parameter indicating the oxidation catalytic activity of each electrode in the sensor with respect to the component to be detected, and further as a parameter reflecting the consumption amount of the component to be detected in the gap or the opposite space. Then, by setting the difference in the value of η between the second electrode and the third electrode to be 20% or more,
The difference in the consumption amount of the detected component between the gap and the opposite space is increased, the sensor output level is increased, and the detection sensitivity of the detected component can be improved. For example, when the second electrode is configured to have a higher oxidation catalytic activity than the third electrode, the second electrode is configured such that the detected component conversion rate η is 20% or more higher than that of the third electrode. Good to do. The difference in the value of η is more preferably 30% or more.

Here, the value of η of the electrode changes depending on the sensor operating temperature. It can be said that it is desirable to set the sensor operating temperature so that the difference in η is 20% or more, preferably 30% or more. In this case, if the sensor operating temperature is set so that the pump current value of the oxygen pump element when the applied voltage is constant is as high as possible,
The detection sensitivity of the component to be detected is further improved.

For example, in the carbon monoxide detection sensor of the present invention, the first electrode and the second electrode are Pt-based porous electrodes whose constituent metal is substantially Pt, and the third electrode is Pt whose metal component is Pt. It is possible to obtain a Pt-Au-based porous electrode made of a Pt-Au alloy containing 2 to 30% by weight of Au as a main component. In this structure, the catalytic activity for the oxidation (combustion) of carbon monoxide in the Pt-based porous electrode is Pt-A.
Since it is considerably larger than the u-based porous electrode, the combustion amount of carbon monoxide, that is, the consumption amount of oxygen is significantly increased on the side of the first treatment space, and the sensitivity of the sensor is improved. When the content of Au in the third electrode is less than 2% by weight, the difference in the oxidation catalytic ability for carbon monoxide between the first electrode and the second electrode becomes too small, and the sensor sensitivity decreases. Leads to. On the other hand, when the content of Au exceeds 30% by weight, the firing temperature of the porous electrode decreases, and simultaneous firing with the first electrode and the second electrode configured as a Pt-based porous electrode becomes impossible, and the production This leads to an increase in man-hours. In addition to the Pt-Au alloy, the constituent metal of the third electrode is a Pd-Au-based alloy, a Pd-Pb-based alloy, or Pt.
-Pb-based alloy, Pt-Pb-Au-based alloy, Pd-Pb-
An Au-based alloy or the like can be suitably used as the porous electrode for detecting carbon monoxide.

Further, in the carbon monoxide detection sensor having the above structure, the oxygen pump element when the absolute value of the concentration cell electromotive force of the oxygen concentration cell element reaches the electromotive force target value EC set to 10 mV or less. It is possible to extract the value of the electric current flowing through as information that reflects the concentration of carbon monoxide in the gas to be detected.

On the other hand, when a test gas containing 1% by volume or more of oxygen and containing substantially no component that reacts with oxygen at the sensor operating temperature is introduced into the gap and the opposite space, the oxygen-concentrated battery element is produced. The absolute value of the offset electromotive force is EOS (unit: mV), and the electromotive force target value EC is (EOS-5.0) mV or more (EOS + 5.
0) It is set within the range of mV or less, and the current value flowing in the oxygen pump element when the absolute value of the concentration battery electromotive force of the oxygen concentration battery element reaches the electromotive force target value EC It can also be taken out as information reflecting the concentration of carbon monoxide.

For example, oxygen is pumped into or pumped out of the gap by the oxygen pump element so that the oxygen concentration becomes equal to each other between the first treatment space side and the second treatment space side with the oxygen concentration battery element sandwiched therebetween. By doing so, since the pump current directly corresponds to the difference in the consumption amount of carbon monoxide in both of these spaces, the concentration of carbon monoxide can be detected more accurately, and Analysis of the detection result becomes easy. In this case, if the oxygen concentrations of the first treatment space side and the second treatment space side are equal, the concentration battery electromotive force of the oxygen concentration battery element is theoretically 0, so the oxygen pump element is Oxygen is pumped in or pumped out of the first processing space so that the electric power becomes zero. However, even if the oxygen concentrations on both sides of the oxygen concentration battery element become equal, the electromotive force of the oxygen concentration battery element usually does not become zero, and a constant offset electromotive force often remains.

The present inventors have found that for most of the commonly used oxygen ion conductive solid electrolytes, the absolute value of the offset electromotive force is within the range of 10 mV or less when the oxygen concentration battery element is formed of the solid electrolyte. In addition to the above, in the configuration of the carbon monoxide detection sensor of the present invention, the electromotive force target value EC is set to 10 mV or less, and the absolute value of the concentration battery electromotive force is the electromotive force target value EC.
It was found that the concentration of carbon monoxide in the gas to be detected can be accurately detected by adopting the value of the current flowing through the oxygen pump element when the temperature reaches 0 as the detection signal.
If you know the oxygen concentration range of the measurement atmosphere,
It is desirable to set the offset electromotive force at the maximum oxygen concentration in that range as the electromotive force target value.

On the other hand, as a result of intensive studies, the inventors of the present invention found the following, and completed the following constitution of the carbon monoxide detection sensor. That is, the offset electromotive force of the oxygen concentration battery element is more likely to fluctuate as the oxygen concentration in the gas to be detected for detection becomes lower, and when the electromotive force target value E C is set with reference to the offset electromotive force at a certain oxygen concentration or less. The sensor output is easily affected by the oxygen concentration in the gas to be detected. In order to solve this, when a test gas containing oxygen in an amount of 1% by volume or more and containing substantially no component that reacts with oxygen at the sensor operating temperature is introduced into the first processing space and the opposite space, The absolute value of the offset electromotive force generated in the oxygen concentration battery element is EOS (unit: mV), and the electromotive force target value EC is (EOS-5.0) mV or more (EOS + 5.
0) It is effective to set within the range of mV or less. Then, by setting the electromotive force target value E C within the above range,
It is possible to obtain a more stable sensor output that is not affected by the oxygen concentration in the gas to be detected. In this case, it is desirable to set the electromotive force target value EC as a value as close to EOS as possible in order to improve the detection accuracy of the sensor. In addition, E
The oxygen concentration in the test gas for determining the OS is preferably 10% or more, or the atmosphere is preferably used. Further, by setting the electromotive force target value E C to 10 mV or less as in the first configuration, it is possible to obtain a more stable and highly accurate sensor output.

In a sensor structure in which an oxygen pump element having electrodes formed on both sides and an oxygen concentration cell element are arranged to face each other, a gap (first processing space) formed between the elements is formed.
In order to improve the detection accuracy of the sensor, it is advantageous to make this as small as possible (preferably 1 mm or less) to enhance the effect of restricting the inflow of new gas to be detected by the gap. Conversely, if the size of the gap is too large, the reaction between carbon monoxide and oxygen on the electrode having catalytic activity becomes unstable, the electromotive force of the oxygen concentration cell becomes small, and the sensor output becomes insufficient. It may not be possible to obtain it.
This tendency becomes particularly remarkable when the oxygen concentration in the gas to be detected, which is the object of measurement, fluctuates greatly or the water vapor concentration in the gas is high. When a gap forming member that forms a predetermined gap (another gap) between the oxygen concentration battery element and the third electrode is formed on the side where the third electrode is formed, the size of the gap is increased. Also for the same reason, it is desirable to make it as small as possible (desirably 1 mm or less).

However, if the amount of the gap between the elements is made too small, a slight deformation at the time of firing produces the amount of the gap when the oxygen pump element, the oxygen concentration battery element or the gap forming member is manufactured by firing. Have a big impact,
There may be a problem that the output tends to vary among the individual sensors. Therefore, in order to solve this, it is effective to use the following sensor structure. That is, the electrode on the gap side of the oxygen pump element is the first electrode, the electrode on the gap side of the oxygen concentration battery element is the second electrode, and the electrode on the opposite space side of the oxygen concentration battery element is the third electrode. A measurement chamber is formed so as to contact at least one of the three electrodes, and a gas communication portion is formed so as to penetrate the wall of the measurement chamber from the measured atmosphere side to the measurement chamber side. And
The gas communication part is configured as a diffusion regulation flow part including at least one of a small hole, a slit, and a porous communication part made of porous ceramic or porous metal.

With this configuration, even when the size of the gap is increased to a certain extent or more, the gas to be detected flows into the measurement chamber from the diffusion control flow section while the diffusion is regulated, and after being introduced into the measurement chamber. Is also discharged into the measured atmosphere while the diffusion is regulated by the diffusion regulation distribution unit. Therefore, even if the composition of the gas to be detected (in particular, the amount of oxygen or water vapor) in the atmosphere to be detected changes during the time that the gas to be detected once introduced stays longer in the chamber, Since the influence is small, a stable and high sensor output can be obtained, which in turn can improve the detection accuracy of the sensor.

The set of the measurement chamber and the diffusion control and flow section may be formed either on the second electrode side or the third electrode side of the oxygen concentration battery element, but the oxygen pump element and the oxygen concentration battery element may be formed. It is more desirable to form the above group at least on the side where the catalytic activity becomes higher, that is, on the side where the reaction between oxygen and carbon monoxide occurs more actively in the gap and the opposite space from the viewpoint of achieving sensor output. It is even better if the pair is formed on both sides.

Next, regarding the formation form of the measurement chamber and the diffusion regulation flow part, when forming it in the gap side between the oxygen concentration battery element and the oxygen pump element, a wall surrounding the second electrode is formed. It is possible to form a portion and form a space surrounded by the inner surface of the wall portion and the respective facing surfaces of the oxygen concentration cell element and the oxygen pump element as a measurement chamber. In addition, the diffusion control and circulation portion is formed in a form that penetrates at least one of the wall portion and the oxygen concentration battery element from the measurement atmosphere side to the measurement chamber side, and connects the measurement atmosphere and the measurement chamber to each other. It can be a slit or a small hole. In addition,
The above-mentioned porous ceramic body (or a porous metal body) which allows the gas to flow between the gap and the atmosphere to be measured can also function as the diffusion regulation and flow section.

In the case of forming the slit as the diffusion regulation flow portion, for example, a wall forming body which constitutes at least a part of the wall is arranged between the oxygen concentration battery element and the oxygen pump element, and the wall portion is formed. The slit may be formed between the formed body and at least one of the oxygen concentration battery element and the oxygen pump element in a form along the plate surface of the oxygen concentration battery element or the oxygen pump element. This allows
The gas to be detected can be smoothly introduced into the measurement chamber through the slit without causing a spatial deviation.

Next, when the width (spacing) of the slit is d and the dimension of the measurement chamber in the opposite direction of the oxygen concentration cell element and the oxygen pump element (hereinafter referred to as the height of the measurement chamber) is h, d / It is preferable to adjust h in the range of 1/100 to 1/4. If d / h exceeds 1/4, the effect of restricting the diffusion of the gas to be detected in the slit becomes insufficient, and the sensor output may not be sufficiently obtained. d / h is 1/100
If it is less than the lower limit, the inflow rate of gas into the measurement chamber or the outflow rate of gas from the measurement chamber becomes too low, and the detection accuracy of the sensor may rather decrease. d / h is
It is more desirable to set it in the range of 1/20 to 1/8. The ratio S / V of the area of the inner surface of the slit to the space volume V in the slit is 4 to 10 for the same reason.
It is preferable to adjust it to 0, preferably 20 to 50.

On the other hand, the absolute value of the slit width d is 0.01
It is preferable to adjust in the range of 1.0 mm. d is 1.0m
If it exceeds m, the effect of restricting the diffusion of the gas to be detected in the slit becomes insufficient, and the sensor output may not be sufficiently obtained. On the other hand, if d is less than 0.01 mm, the inflow speed of gas into the measurement chamber or the outflow speed of gas from the measurement chamber becomes too small, and the detection accuracy of the sensor may deteriorate. It should be noted that d is more preferably set in the range of 0.02 to 0.5 mm.

The slit may be formed in the middle of the wall forming body in the thickness direction (the stacking direction of the oxygen concentration battery element and the oxygen pumping element), but the wall forming body and the oxygen concentration battery element and The structure formed with at least one of the oxygen pump elements is more advantageous in manufacturing the sensor. That is, in the former case, a ceramic molded body to be a wall forming body (hereinafter referred to as a wall forming body) is provided with a gap to be a slit in advance, or the ceramic molded body is thickened. A slight increase in man-hours is unavoidable, such as forming in two portions that are adjacent to each other in the vertical direction and firing in a state where a gap is formed between these portions. On the other hand, in the latter case, a predetermined amount of gap is formed between the wall forming molded body and the ceramic molded body to be the oxygen concentration cell element or the oxygen pump element (hereinafter referred to as element forming molded body). The carbon monoxide detection sensor having the above structure can be easily manufactured only by firing.

The slits are, for example, a layer formed of a material (for example, carbon paste) which is burned out by firing between the wall-forming molded body and the element-forming molded body in a region where the slits are to be formed. It can be formed by sandwiching and firing the laminate to burn off the layer. In this case, the width of the formed slit can be freely adjusted according to the thickness of the layer to be formed.

Next, the wall forming body can be integrated with at least one of the oxygen pump element and the oxygen concentration cell element by firing. By integrating these by firing, the mechanical strength of the sensor can be improved. When the slit is formed only between the wall forming body and one of the oxygen pump element and the oxygen concentration battery element, the wall forming body and the element forming body are formed on the side where the slit is not formed. On the other hand, on the slit forming side,
It is possible to form a slit by partially sandwiching the sheet with respect to the laminated surface, and to integrate the wall forming molded body and the element forming molded body in the laminated surface region where the sheet is not interposed. In this case, the oxygen pump element or the oxygen concentration cell element for forming the wall portion is integrated with each other on the slit forming side in the portion other than the slit forming region, so that the strength of the sensor can be further increased.

On the other hand, in the case of forming the diffusion control and circulation portion by using a small hole instead of the slit, the small hole can be formed, for example, in the wall forming body. In this case, in order to allow the gas to be detected to flow into the measurement chamber without any deviation, it is preferable to form a plurality of small holes at predetermined intervals in the plate surface direction of the plate-shaped oxygen pump element or the oxygen concentration battery element. . Further, the small holes may be formed in a shape penetrating the oxygen concentration battery element in the thickness direction. In this case, a plurality of small holes may be formed at predetermined intervals along the periphery of the second electrode or the third electrode,
It is desirable to form an inflow state of the gas to be detected that is not biased.

Next, the oxygen pump element and the oxygen concentration battery element can be formed in a laterally long plate shape, and the diffusion restricting flow portion has slits or slits formed on both sides of the oxygen pump element and the oxygen concentration battery element in the plate surface width direction. It can be a plurality of small hole groups arranged at a predetermined interval. By doing so, the gas to be detected that has flowed into the measurement chamber from one of the slits or small holes is discharged from the other, so that a smooth flow of the gas to be detected is formed in the measurement chamber, and by extension the sensor. Output responsiveness can be improved.

Next, in the carbon monoxide detection sensor, a measurement chamber may be formed on the side opposite to the side facing the gap of the oxygen concentration battery element. That is,
The above-mentioned gap forming member that forms another gap between the oxygen concentration battery element and the opposite side of the oxygen concentration battery element is arranged, and a gap is formed between the gap formation member and the oxygen concentration battery element. A wall is formed so as to surround the periphery of the three electrodes, and a space surrounded by the inner surface of the wall and the facing surfaces of the gap forming member and the oxygen concentration battery element is used as a measurement chamber.

Also in this case, the diffusion regulation flow section can be formed in a manner substantially similar to the case where the measurement chamber is formed between the oxygen pump element and the oxygen concentration cell element. That is, the diffusion control and circulation portion is formed in such a manner that it penetrates at least one of the wall portion and the gap forming member from the measurement atmosphere side to the measurement chamber side, and the measurement atmosphere and the measurement chamber communicate with each other. It can be configured as a slit or a small hole.
In addition, between the gap forming member and the oxygen concentration battery element, a wall forming body that constitutes at least a part of the wall can be arranged, and at least one of the wall forming body, the gap forming member, and the oxygen concentration battery element. The slits can be formed between the gap forming members or the plate surface of the oxygen concentration battery element.

The wall forming body can be integrated with at least one of the gap forming member and the oxygen concentration battery element by firing. Further, the gap forming member and the oxygen concentration battery element can be formed in a laterally long plate shape, and the diffusion regulation and flow portion is a slit formed on both sides in the plate surface width direction of the gap forming member and the oxygen concentration battery element. You can

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to some examples shown in the drawings. (Embodiment 1) FIG. 1 shows a carbon monoxide detection sensor 1 as one embodiment of the present invention. That is, the carbon monoxide detection sensor 1 is configured such that the oxygen pump element 3, the oxygen concentration battery element 4, and the heating element 5 each formed in a horizontally long plate shape are laminated in this order. The oxygen pump element 3 and the oxygen concentration battery element 4 are composed of a solid electrolyte having oxygen ion conductivity. A typical example of such a solid electrolyte is ZrO _{2 in} which Y ₂ O ₃ or CaO is solid-dissolved, but a solid solution of an oxide of an alkaline earth metal or a rare earth metal and ZrO ₂ other than that is used. May be used. Further, HfO ₂ may be contained in the base ZrO ₂ . In this embodiment, Y
It is assumed that the ZrO ₂ solid electrolyte ceramic in which ₂ O ₃ or CaO is dissolved is used. On the other hand, the heating element 5 is composed of a known ceramic heater.

A cross section taken along the line AA of FIG. 1 is shown in FIG. That is, the oxygen pump element 3 and the oxygen concentration cell element 4 are formed in a horizontally long plate shape so as to be opposed to each other.
Between the oxygen pump element 3 and the oxygen concentration cell element 4, a first processing space 15 and a second processing space 16 are adjacent to each other in the plate surface direction near one end in the longitudinal direction. Has been formed. The first electrode 11 is formed on the corresponding plate surface of the oxygen pump element 3 at the position facing the first processing space 15, and the outer electrode 10 is formed on the opposite side. The second electrode 12 is formed at a position facing the first processing space 15 of the oxygen concentration battery element 4, and the third electrode 13 is formed at a position facing the second processing space 16 as well.

In the oxygen pump element 3 and the oxygen concentration cell element 4, the plate surfaces facing each other are made of alumina, for example, in the remaining regions excluding the portions where the first processing space 15 and the second processing space 6 are formed. The insulating ceramic layers 30 are joined together. The insulating ceramic layer 30 electrically insulates the oxygen pump element 3 and the oxygen concentration battery element 4 from each other, and together with the oxygen pump element 3 and the oxygen concentration battery element 4, the first treatment space 15 and the second treatment space 16 And
It plays the role of a wall forming body that is partitioned from the surroundings.

On the other hand, the porous electrodes 10 to 13 have a function of dissociating or recombining the oxygen molecules, and a binding reaction between carbon monoxide and oxygen in the exhaust gas in contact with the porous electrodes, that is, monoxide. It also functions as an oxidation catalyst that promotes the combustion reaction of carbon. Then, in the carbon monoxide detection sensor of the present invention, among the four electrodes 10 to 13, three of the first electrode 11, the second electrode 12 and the third electrode 13 have an oxidation catalytic activity for carbon monoxide. , The first treatment space 15 and the second treatment space 16 are adjusted so that there is a difference in the consumption amount of carbon monoxide due to the reaction with oxygen.

Specifically, the first electrode 11 and the second electrode 1
2 is a Pt-based porous electrode whose metal component is substantially Pt, and the third electrode 13 is a Pt—Au alloy (Pt—Au alloy, for example, whose main metal component is Pt and which contains 2 to 30 wt% Au). It is a Pt-Au-based porous electrode made of 10 wt% Au alloy). In this case, the Pt-based porous electrode has a higher oxidation catalytic activity for carbon monoxide than the Pt-Au-based porous electrode. That is, the consumption amount of carbon monoxide due to the reaction with oxygen becomes larger on the first processing space 15 side than on the second processing space 16. The outer electrode 10 is composed of a Pt-based porous electrode, but other materials may be used as long as they have catalytic activity for a dissociation reaction with respect to oxygen molecules or a recombination reaction with oxygen atoms.

Next, as shown in FIGS. 2 and 3, from the porous electrodes 10 and 11 of the oxygen pump element 3, the element 3 is removed.
Electrode lead parts 10a and 11a extending toward the mounting base end side of the carbon monoxide detection sensor 1 are integrally formed along the longitudinal direction thereof, and the oxygen pump element 3 has a connection terminal 10b on the base end side. , 11b are joined at one end. Further, as shown in FIG. 4, the electrode lead portion 12a is similarly formed on each of the porous electrodes 12 and 13 of the oxygen concentration battery element 4.
And 13a are integrally formed, and the connection terminals 12b and 13b are attached respectively.

Further, between the oxygen concentration battery element 4 and the oxygen pump element 3, a fine distribution control section for communicating the first measurement space 15 and the second measurement space 16 with the atmosphere to be detected outside is provided. The holes 33 and 35 are formed, for example, in a shape in which a part of the insulating ceramic layer 30 is cut out along the plate surface width direction of each element. In addition, in the present embodiment, each of the pores 33 and 35 is formed one by one, but a plurality of pores may be formed. In this case, the inflow velocity of the gas to be detected into each measurement space can be adjusted by the number of pores formed.

The integral laminated body of the oxygen pump element 3 and the oxygen concentration battery element 4 which is a main part of the carbon monoxide detection sensor 1 is formed by laminating ceramic green sheets (molded bodies) which are to be the respective portions 3 and 4, respectively. It can be manufactured by firing. Hereinafter, an example of the manufacturing method will be described with reference to FIG. 6 (in the parentheses, conditions for manufacturing a test product used in an experimental example described later are also described).

(1) Preparation of oxygen-concentration battery element side laminate CA: Ceramic green sheet 4 '(thickness 0.35 mm, width 5 mm, length 25 mm) to be an oxygen concentration battery element
On the other hand, an insulating coat 30d ′ for insulating between the lead portion and the solid electrolyte layer is formed using an alumina paste in a region other than the electrode forming portion. A second electrode pattern 12 '(width 1.5 mm, length 4 mm; hereinafter, the same dimensions apply to other electrode patterns) and a lead portion pattern 12a' are formed using Pt paste. Further, the third electrode pattern 13 'is formed by using the mixed powder paste of Pt and Au, and the lead portion pattern 13a' is formed by using the Pt paste. In this embodiment, a screen printing method is used for forming each pattern.

The pore patterns 33 'and 35' are formed using carbon paste (thickness: about 40 μm). At the time of firing, the carbon paste patterns 33 'and 35' are burned off to form pores 33 and 35. Second electrode pattern 12 'using carbon paste
And the patterns 15 ', 16' to be the first processing space 15 and the second processing space 16 on the third electrode pattern 13 '.
(Thickness of 30 μm each). Among them, the thickness of the pattern 15 ′ is preferably adjusted within the range of 15 to 80 μm. If the thickness is less than 15 μm, there is a concern that a contraction during firing may cause a short circuit between the first electrode 11 and the second electrode 12. The thickness of the pattern 15 ′ is 40 to 80 μm
It is better to adjust within the range. In addition, the pattern 15 ', 1
The formation thickness of 6'can be adjusted by the number of times the carbon paste is applied. At the ends of the lead part patterns 12a ′ and 13a ′, metal wires 12b ′, 13 to be connection terminals 12b, 13b are formed.
One end of b ′ (Pt-13 wt% Rh alloy wire, wire diameter 2 mm: the same applies to other connection terminals) is overlapped and temporarily fixed using Pt paste.

(2) Production of oxygen pump element side laminate PA. Insulation between the lead part and the solid electrolyte layer is made on one surface of the ceramic green sheet 3 '(thickness 0.35 mm, width 5 mm, length 25 mm) to be the oxygen pump element, in the region excluding the electrode forming part. Insulation coat 40 'for
It is formed using an alumina paste. The outer electrode pattern 10 ′ and the lead portion pattern 10 are formed on the insulating coat 40 ′ using Pt paste.
a'is formed. On the other side of the ceramic green sheet 3 ', P
The first electrode pattern 11 ′ and the lead portion pattern 11a ′ are formed using t paste.

Insulation coat 3 using alumina paste
0b 'is formed to a thickness corresponding to the carbon paste patterns 15' and 16 'on the laminate CA side. The insulating coat 30b ′ becomes a main part of the insulating ceramic layer 30. At the end of the lead pattern 10a ', the connection terminal 10b
One ends of the metal wires 10b 'to be formed are overlapped and temporarily fixed with Pt paste. At the end of the lead pattern 11a ', the connection terminal 11b
One ends of the metal wires 11b 'to be formed are overlapped and temporarily fixed using Pt paste.

(3) Assembling / Baking Oxygen-concentrated battery element side laminated body CA and oxygen pump element side laminated body PA are laminated and coated with alumina paste, and the both laminated bodies are semi-dried. Overlap and crimp together. The laminated body after the bonding is degreased in a degreasing furnace and then fired at a predetermined temperature (1500 ° C.) to obtain an integral laminated body of the oxygen pump element 3 and the oxygen concentration battery element 4. The heating element 5 is joined to the oxygen concentration battery element 4 side of the integrated laminated body by using an inorganic adhesive or the like, and the connection terminals 10b to 13 are connected.
The sensor is completed by attaching the lead wire to b.

The outline of the operating principle of the carbon monoxide detection sensor 1 is as follows. That is, the carbon monoxide detection sensor 1 shown in FIG.
The detector is attached so as to be located inside the exhaust pipe.
As shown in FIG. 7, in this state, the oxygen pump element 3 is
A voltage is applied so that one of the porous electrodes 10 and 11 is positive and the other is negative. Then, in the porous electrode having a positive polarity, oxygen molecules in the exhaust gas in contact with this are dissociated on the electrode, and the applied voltage acts as a driving force to dissociate oxygen in the form of ions. It is fed into the element 3. The oxygen ions transported in the element 3 by the voltage application receive electrons on the porous electrode having a negative polarity, are further recombined with oxygen molecules, and are released into the atmosphere.

In the oxygen concentration battery element 4, no voltage is applied to the porous electrodes 12 and 13, and oxygen molecules in the exhaust gas which come into contact with the electrodes 12 and 13 are dissociated on the electrodes 12 and 13. And diffuse into the element 4 in the form of oxygen ions, respectively. When there is a difference in oxygen concentration between the electrodes 12 and 13 side, a concentration gradient of oxygen ions is generated in the element 4, and a concentration cell electromotive force corresponding to the concentration gradient is generated between the electrodes 12 and 13. Will occur.

When the exhaust gas containing carbon monoxide and oxygen is introduced into the first processing space 15 and the second processing space 16 through the pores 33 and 35, respectively, the exhaust gas containing carbon monoxide and oxygen enters the first processing space 15 side. Since the electrodes 11 and 12 located on both sides have high catalytic activity for the oxidation of carbon monoxide, and the electrode 13 located on the second treatment space 16 side has low catalytic activity, the oxidation of carbon monoxide in the exhaust gas is The consumption amount due to is larger on the first processing space 15 side than on the second processing space 16 side. On the side where the consumption amount of carbon monoxide is large, the consumption amount of oxygen in the exhaust gas also becomes large, so the oxygen concentration in the second processing space 16 becomes higher than that in the first processing space 15, and The concentration cell element 4 has a second processing space 16
A density cell electromotive force with the positive side is generated.

Then, when oxygen is pumped from the gap 14 side to the first treatment space 15 side by the oxygen pump element 3 so that the absolute value of the concentration battery electromotive force becomes a constant value of, for example, 10 mV or less, the oxygen pump The current flowing through the element 3 (hereinafter,
The oxygen pump current or pump current) is a value that reflects the amount of oxygen consumed for the oxidation of carbon monoxide. Further, as the concentration of carbon monoxide in the exhaust gas increases, the amount of oxygen consumed by the oxidation increases, and as a result, the pump current also increases. Therefore, the concentration of carbon monoxide in the exhaust gas can be known by measuring the pump current.

A sensor system using the above carbon monoxide detection sensor will be described below. FIG. 7 is a block diagram showing an electrical configuration of an example of a sensor system using the carbon monoxide detection sensor 1. That is, the sensor system 50 includes the carbon monoxide detection sensor 1, a microprocessor 51, and a peripheral circuit 50a connecting the carbon monoxide detection sensor 1 and the microprocessor 51.

In the oxygen concentration battery element 4 of the carbon monoxide detection sensor 1, the second electrode 12 is grounded, while the third electrode 13 is connected to the negative terminal side of the inverting amplification operational amplifier 61 (pump current control means). ing. On the other hand, on the positive terminal side of the operational amplifier 61, a power supply circuit 6 for giving an electromotive force target value EC
5 is connected. The power supply circuit 65 is configured to be able to change the set value of the electromotive force target value EC within a certain range. For example, in the example shown in the figure, three fixed resistors 66
a to 66c and a variable resistor 66d on each side, and a power supply 67 connected to the bridge circuit 66. Set the resistance range of the variable resistor 66d to Rmin
~ Rmax is a certain resistance value R such that Rmin <Re <Rmax
The fixed resistors 66a to 66c are set so that the bridge is balanced at e and the output voltage to the terminal of the operational amplifier 61 becomes zero.
Each resistance value of is adjusted. And the variable resistor 66d
By shifting the resistance value of R from Re to the Rmin or Rmax side, respectively, the electromotive force target value E C can be changed within a certain range on both positive and negative sides with 0V in between.

Next, the operational amplifier 61 is provided with the peripheral resistor 6
A differential amplifier is configured with 1a to 61d, and its output side is connected to the outer electrode 10 of the oxygen pump element 3 via a resistor 62 for current detection. On the other hand, the first electrode 11 side of the oxygen pump element 3 is commonly grounded with the second electrode 12 of the oxygen concentration battery element 4. As a result, the operational amplifier 6
1 is the concentration cell electromotive force input Em of the oxygen concentration cell element 4
Then, the differential voltage Em−EC from the electromotive force target value EC is inverted and amplified and applied to the first electrode 11 side of the oxygen pump element 3. When the electric resistances of the resistors 61a and 61b are R1 and R2, respectively, the voltage gain of the operational amplifier 61 is A1 = R1 / R2.

As shown in FIG. 8, if Em> EC, then Em-EC> 0. Therefore, the output voltage -A1 (Em-EC) of the operational amplifier 61 becomes negative, and the oxygen pump element 3 has a negative voltage. A voltage is applied so that the first electrode 11 side becomes negative, and a pump current Id flows through the oxygen pump element 3 in a direction in which oxygen is pumped into the first processing space 15. This pump current Id is
In the form of a voltage difference across the current detecting resistor 62 (resistance value R3), it is taken out as a voltage signal by the operational amplifier 64 which constitutes a differential amplifier together with the peripheral resistors 64a to 64d, and as shown in FIG. It is digitized by the dipolar A / D converter 70 and input to the microprocessor 51. Incidentally, 64a and 64b are operational amplifiers 64
Of the gain adjusting resistors (resistance values R5 and R6, respectively).

Next, the third electrode 13 of the oxygen concentration battery element 4
The side voltage signal Vs passes through the voltage follower 73, is digitally converted by the dipolar type A / D converter 71, and is input to the microprocessor 51. Further, the heating element 5 of the carbon monoxide detection sensor 1 is connected to the microprocessor 5 via a common heater energizing circuit 72, for example.
Connected to 1. FIG. 9A shows a heater energizing circuit 72.
Shows an example. The heater energizing circuit 72 includes a D / A converter 80 for converting the heater control value supplied from the microprocessor 51 into an analog signal, and a current amplification transistor 82 connected to the D / A converter 80. The heating element 5 is connected to the transistor 82. Are connected. Transistor 82
Operates in the active region and increases the energizing current of the heating element 5 according to the applied heater control value.

On the other hand, FIG. 9B shows PWM (pulse widt
h energization) heater energizing circuit 72 adopting control method
Is an example of. The main part of this circuit 72 is a PWM control circuit 85, which is a D / which converts the heater control voltage value given from the microprocessor 51 into an analog signal.
The A converter 86, a triangular wave (or sawtooth wave) generating circuit 87, and operational amplifiers 88 to which outputs from the D / A converter 86 and the triangular wave generating circuit 87 are respectively input. The operational amplifier 88 is of a single power supply type, and operates as a comparator that outputs either zero or a predetermined voltage V that is not zero according to the magnitude relationship between the heater control voltage value and the triangular wave input value. In this case, the duty ratio of the comparator output changes according to the heater control voltage value, and the heat generation of the heating element 5 is adjusted. Further, the heating element 5 may be heated to a constant temperature by a constant voltage power supply circuit.

The temperatures of the oxygen pump element 3 and the oxygen concentration battery element 4 can be detected, for example, by measuring the internal resistance of the oxygen concentration battery element 4, and the heat generation control of the heating element 5 can be performed using the detected temperature information. It can be carried out.

Returning to FIG. 7, the microprocessor 51
I / O port 52 serving as an input / output interface with the peripheral circuit 50a, and CPUs 53 and R connected to the I / O port 52
It is composed of an AM 54, a ROM 55, and the like. In the RAM 54, a work area 54a of the CPU 53,
A storage area 54b for storing the calculated concentration of carbon monoxide is formed. The ROM 55 also includes the sensor system 50.
A control program 55a for controlling the output value determination of the detected component and its output control, and a density conversion table 55b used by the control program 55a are stored. The CPU 53 functions as the main body of the density determining unit by the control program 55a stored in the ROM 55.

In FIG. 8, as the sensor 1 comes into contact with the exhaust gas, carbon monoxide and oxygen react with each other in the first processing space 15, so that the oxygen concentration decreases and the oxygen concentration battery element 4 , A concentration battery electromotive force Em having a positive value on the third electrode 13 side is generated. Here, if the electromotive force target value EC input to the operational amplifier 61 is, for example, 0, Em−
Since EC> 0, the output voltage of the operational amplifier 61-A1
(Em-EC) becomes negative, a voltage is applied to the oxygen pump element 3 so that the first electrode 11 side becomes negative, and the oxygen pump element 3 receives a pump current in the direction of pumping oxygen into the first processing space 15. Id flows. Then, oxygen is pumped into the first processing space 15 by the oxygen pump element 3, and the concentration cell electromotive force Em gradually decreases, so that the oxygen pump current Id is controlled to decrease. As a result, the oxygen pump current is finally controlled so that the concentration cell electromotive force Em approaches nearly 0, and the concentration of carbon monoxide can be known from the equilibrium value of the oxygen pump current Id at that time. As described above, the signal of the pump current Id is converted into a voltage signal by taking the difference between the voltage across the resistor 62 for current detection by the operational amplifier 64, digitized by the A / D converter 70, and input to the microprocessor 51. To be done. However,
The electromotive force target value E C is not always set to 0 in practice. The reason will be described below.

First, the fact that the concentration cell electromotive force is 0 means that both sides of the oxygen concentration cell element 4 (ie,
This means that the oxygen concentrations in the first processing spaces 15 and 16) are equal. This also means that the pump current directly corresponds to the difference in the consumption amount of carbon monoxide in the first processing space 15 and the second processing space 16, so that the concentration of carbon monoxide can be accurately measured. It can be detected and the detection result can be easily analyzed. However, normally, even if the oxygen concentrations of the first treatment space 15 and the second treatment space 16 become equal, the electromotive force of the oxygen concentration battery element 4 does not actually become 0, and a constant offset electromotive force remains. There are many. In this case, the electromotive force target value EC corresponding to the offset electromotive force is set in the range of 10 mV or less, and the oxygen pump element 3 flows when the absolute value of the concentration battery electromotive force reaches the electromotive force target value EC. By using the current value as the detection signal, the concentration of carbon monoxide in the exhaust gas can be detected more accurately.

Further, the offset electromotive force of the oxygen concentration battery element 4 tends to fluctuate as the oxygen concentration in the exhaust gas for detection becomes lower, and the electromotive force target value EC When is set, the sensor output is easily affected by the oxygen concentration in the exhaust gas. Therefore, a test gas containing, for example, 1 volume% or more (preferably 10 volume% or more) of oxygen and substantially no component that reacts with oxygen at the sensor operating temperature is used as the first processing space 15 and the second processing space. The absolute value of the offset electromotive force when introduced into 16 is set to EOS (unit: mV), and the electromotive force target value EC is set within the range of (EOS-5) mV or more and (EOS + 5) mV or less based on this. Is effective.

The change / adjustment of the electromotive force target value EC can be performed by adjusting the variable resistor 66d of the power supply circuit 65 as described above. The offset electromotive force of the oxygen concentration battery element 4 shows a stable value over a relatively long period in the same oxygen concentration battery element 4 even though the offset concentration of each oxygen concentration battery element 4 is different from each other. I often continue. Therefore, the variable resistor 66d needs to be changed after the resistance value is once adjusted in accordance with the offset electromotive force peculiar to the oxygen concentration battery element 4 being used, for example, at the time of shipment of the device 50. It is possible that there is no sex. In this case, it is convenient to configure the variable resistor 66d with a semi-fixed resistor.

The operation of the sensor system 50 will be described below with reference to the flow of processing viewed from the CPU 53 of the microprocessor 51. FIG. 10 shows the density conversion table 5
5b shows an example of the contents of 5b, and the oxygen pump element 3 corresponding to each value C1, C2, C3, ... Of the carbon monoxide concentration.
The output current values Id1, Id2, Id3, ... Of are stored. These values are predetermined by experiments or the like. Then, the CPU 53 shown in FIG. 7 uses the RAM 54 as a work area by the control program 55a, as shown in FIG.
The sensor output control as shown in the flow chart 1 is executed.

That is, the measurement timing is measured by a timer (not shown), and when the timing arrives at S1, the output current value (pump current) Id from the oxygen pump element 3 is sampled at S2. Then, in S3, the value of the carbon monoxide concentration corresponding to the sampled value is calculated by the interpolation method with reference to the concentration conversion table 55b in FIG. 10, and the calculated value is stored in the calculated value storage area of the RAM 54 in S4. 54b. In addition, the area 5
The value written in 4b is overwritten and erased. And
In S5, the calculated value written in the area 54b is output from the I / O port 52 as information on the concentration of carbon monoxide in the exhaust gas. It should be noted that this output may be digitally output as it is, or may be analog-converted by the D / A converter 74 connected to the I / O port 52 and then output.

Various modifications of the carbon monoxide detection sensor 1 will be described below. In the carbon monoxide detection sensor 400 shown in FIG. 12, the first heating element 2, the oxygen pump element 3, the oxygen concentration battery element 4, and the second heating element (heating element) 5, which are each formed in a horizontally long plate shape, are arranged in this order. It is configured as being laminated. The oxygen pump element 3 is formed in a laterally long plate shape, and the outer electrode 10 and the first electrode 11 are formed on both surfaces of the oxygen pump element 3 near one end in the longitudinal direction. The oxygen concentration battery element 4 has a second electrode 12 and a third electrode 13 formed on both sides of the oxygen pump element 3 at positions corresponding to the electrodes 10 and 11. The material of each of the electrodes 10 to 13 is the sensor 1 of FIG.
Is the same as.

Then, between the oxygen concentration battery element 4 and the oxygen pump element 3, a spacer portion 40 as a wall portion forming body is formed.
1 is inserted, and the electrodes 11 and 1 of the spacer portion 401 are inserted.
A window portion 401a is formed at a position corresponding to 2 in the thickness direction so as to penetrate therethrough. The spacer portion 401 forms a wall portion 401b surrounding the electrodes 11 and 12 by the window portion 401a. The space surrounded by the inner surface of the wall portion 401b and the opposing surfaces of the oxygen concentration battery element 4 and the oxygen pump element 3 is a measurement chamber 403 (first processing space 15). Then, between the wall portion 401b and the oxygen pump element 3 at a position corresponding to the measurement chamber 403, diffusion is performed so that the measurement chamber 403 and the outer atmosphere to be detected communicate with each other on both sides in the width direction of the oxygen pump element 3. A slit 402 is formed as a flow restricting portion.

As shown in FIG. 12C, the slit 4
02 is a wall portion 401 on both sides of the second electrode 12 in the width direction.
The portion of the oxygen pump element 3 on the side of the laminated surface with the oxygen pump element 3 is formed by cutting out with a constant thickness, and as shown in FIG. It extends in the longitudinal direction. Further, the width d is the measurement chamber 403.
Is set to be smaller than the height h of, and specifically d /
h is 1/100 to 1/4, more preferably 1/20 to 1
It is set in the range of / 8. The absolute value of the slit width d is 0.01 to 1.0 mm, more preferably 0.0.
It is set in the range of 2 to 0.05 mm. Further, the ratio S / V of the area S of the inner surface of the slit to the space volume V in the slit 402 is 4 to 100, preferably 20 to 50.
The range has been adjusted. The slit 402 is
It may be formed between the wall portion 401b and the oxygen concentration battery element 4 in a similar manner.

The spacer portion 401 (wall portion 401b)
For the oxygen-concentrated battery element 4 on almost the entire surface of the laminated surface, and for the oxygen pump element 3 on the almost entire surface of the laminated surface except for the region where the slit 402 is formed. It is integrated by firing.

On the other hand, the first heating element 2 and the oxygen pump element 3
And spacers 6 and 8 made of glass or cement, respectively, are interposed between the oxygen concentration cell element 4 and the second heating element 5, and a predetermined amount of space is provided between the elements. A gap 14 and a gap 16 are formed respectively. Here, the gap 16 corresponds to the second processing space (hereinafter, also referred to as the second processing space 16). The second heating element 5 also plays the role of a gap forming member. The distance between the first processing space 15 and the second processing space 16 (that is, the size of the gap) is adjusted within a range of 1 mm or less. The area Sp of the first electrode 11 is set to be equal to or larger than the area SS of the second electrode 12.

Each porous electrode 10, 1 of the oxygen pump element 3
1, an electrode lead portion 10 extending along the longitudinal direction of the element 3 toward the mounting base end side of the carbon monoxide detection sensor 1.
a and 11a are integrally formed, and the oxygen pump element 3 has connection terminals 10b and 11b on the base end side.
One end of is buried. Then, for example, the connection terminal 1
As shown in FIG. 13, 0b and 11b are electrically connected to the ends of the electrode lead portions 10a and 11a by conductive portions (vias) 10f formed by sintering a metal paste. Further, as shown in FIG. 12, electrode lead portions 12a and 13a are also integrally formed on the porous electrodes 12 and 13 of the oxygen concentration battery element 4, respectively.
Connection terminals 12b and 13b are attached, respectively.

An integral laminated body of the oxygen pump element 3, the spacer portion 401 and the oxygen concentration battery element 4 which is a main part of the carbon monoxide detection sensor 400 is, for example, a ceramic green sheet which should become the respective portions 3, 401 and 4 respectively. It can be manufactured by stacking (molded bodies) and firing. At this time, in a region where the slit 402 is to be formed between the green sheet (ceramic molded body) to be the oxygen pump element 3 and the green sheet to be the spacer part, a material (for example, carbon) that is burned down at the firing temperature is used. If a layer having a predetermined thickness formed of paste or the like is sandwiched, this layer is burnt off during firing, and the slit 402 can be easily formed.

In this way, the height h of the measuring chamber 403
Even when the size (that is, the size of the gap 15) is increased to a certain extent or more, the exhaust gas flows into the measurement chamber 403 while its diffusion is restricted by the slit 402, and the measurement chamber 40
After being introduced into the sample No. 3, it is similarly discharged through the slit 402 into the measured atmosphere while the diffusion is restricted. Therefore,
Even if the residence time of the exhaust gas once introduced in the measurement chamber 403 becomes long and the composition of the exhaust gas (especially the amount of oxygen or water vapor) in the atmosphere to be detected changes during that time, the effect on the gas in the measurement chamber is not affected. Since the size is reduced, the output of the sensor 1 is improved, and the detection accuracy of the sensor 1 can be improved. Further, since the oxygen pump element 3 and the oxygen concentration cell element 4 are integrated via the spacer portion 401,
The mechanical strength of the sensor 400 is increased.

In the carbon monoxide detection sensor 400 shown in FIG. 14, a ceramic plate 406 for forming a gap as a gap forming member is integrated through a spacer portion 404 (having a window portion 404a) similar to that on the second electrode 12 side. The measurement chamber 407 is formed by the inner surface of the wall portion 404b by the spacer portion 404 and the respective facing surfaces of the oxygen concentration battery element 4 and the gap forming ceramic plate 406. In addition, at the position corresponding to the measurement chamber 407, the wall portion 40
A slit 405 similar to that on the second electrode 12 side is formed between 4b and the oxygen concentration battery element 4. The second heating element 5 is laminated on the gap forming ceramic plate 406. With this configuration, a more stable and high output sensor can be realized.

Further, in the example shown in FIG. 15, the small holes 410 penetrating the wall portion 401b in the plate surface direction of the oxygen pump element 3 and the oxygen concentration battery element 4 are the first and second electrodes 1 and 2.
A plurality are formed at predetermined intervals along the circumferential direction of 1 and 12. On the other hand, in the example shown in FIG. 16, a plurality of small holes 410 that penetrate the oxygen concentration battery element 4 in the thickness direction are formed along the peripheral edge of the third electrode 13 at predetermined intervals.

Next, in the structure shown in FIG. 17, the oxygen concentration battery element 4 is integrated with the spacer portion 401 by firing, while the oxygen pump element 3 is not integrated but separated. Show. In this case, the slit 402 is
It is formed between the plate surface of the oxygen pump element 3 and the facing surface of the wall portion 401b. In addition, the first heating element 2, the oxygen pump element 3, the oxygen concentration battery element 4, and the second heating element 5
Are laminated via the spacers 6 to 8 to form a laminated body 31, and a ceramic stopper 32 having a rectangular through hole 32a is fitted to the laminated body 31 from the outside. The spacer 7 is inserted between the spacer portion 401 and the oxygen pump element 3 and plays a role of forming a slit 402 having a predetermined size therebetween.

[0084]

EXAMPLE In order to confirm the effect of the carbon monoxide detection sensor of the present invention, the following experiment was conducted. The carbon monoxide detection sensor 1 shown in FIG. 1 is a ceramic green sheet containing Y ₂ O ₃ powder and ZrO ₂ powder.
It was produced under the above-mentioned conditions as a stabilized ZrO ₂ sintered body containing 5 mol% of Y ₂ O ₃ . The initial characteristics of the sensor 1 were measured under the following conditions. First, the sensor 1 is held in a test gas composed of 0 to 800 ppm of carbon monoxide, 1% of oxygen, 18% of water vapor, 10% of carbon dioxide, and the balance of nitrogen so that the elements 3 and 4 are heated to 700 ° C. Heated by 5. The gas flow rate is 5 l / mi
It was set to n. Then, the electromotive force target value EC of the oxygen concentration battery element 4 was set to 0 mV, the oxygen pump element 3 was operated, and its output current was measured. The measurement results are shown in FIG. 18 (black circles indicate data points in the figure). The output current value increases almost in proportion to the carbon monoxide concentration, and the current value when the carbon monoxide concentration is 800 ppm is as large as 50 mA, showing that the carbon monoxide detection sensor has good characteristics. .

Next, the sensor 1 is replaced with carbon monoxide 100
0ppm, oxygen 1%, water vapor 18%, carbon dioxide 10
%, 100 in a test gas consisting of the balance nitrogen at 250 ° C.
After aging for a day, the sensor characteristics were measured again under the same conditions as above. The results are shown in FIG. 18 (black dots indicate data points in the figure). That is, it can be seen that the sensor 1 has a slight decrease in output after aging and can obtain stable sensor characteristics for a long period of time.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing an external appearance of a main part of an example of a carbon monoxide detection sensor of the present invention.

FIG. 2 is a plan view of the oxygen pump element.

FIG. 3 is a bottom view of the same.

FIG. 4 is a plan view of an oxygen concentration battery element.

5 is an AA cross section of the carbon monoxide sensor of FIG.

6 is an explanatory diagram showing an example of a manufacturing process of the carbon monoxide detection sensor of FIG. 1. FIG.

7 is a block diagram showing an example of the electrical configuration of a carbon monoxide detection sensor system using the sensor of FIG.

FIG. 8 is a block diagram showing an operation system of a main part thereof.

FIG. 9 is a block diagram showing some examples of heater energizing circuits.

FIG. 10 is an explanatory diagram showing an example of the contents of a density conversion table.

11 is a flowchart showing a processing flow of a control program of the carbon monoxide detection sensor system of FIG.

FIG. 12 is a plan view, a side view, and a cross-sectional view taken along the line AA of the first modification of the carbon monoxide detection sensor in FIG.

FIG. 13 is a partial cross-sectional view showing the terminal structure.

FIG. 14 is a plan view, a side view, and a cross-sectional view taken along the line AA of the second modification of the carbon monoxide detection sensor in FIG.

FIG. 15 is a partial plan view showing a third modified example and a BB sectional view thereof.

FIG. 16 is a partial plan view and a bottom view of the fourth modification.

FIG. 17 is a plan view, a side view and a sectional view taken along the line AA of the fifth modification.

FIG. 18 is a graph showing the dependence of the output of the carbon monoxide detection sensor used in the experiment on the carbon monoxide concentration before and after the aging treatment.

[Explanation of symbols]

1,400 Carbon monoxide detection sensor 2 First heating element 3 Oxygen pump element 4 Oxygen concentration battery element 5 Second heating element (heating element) 11 First electrode 12 Second electrode 13 Third electrode 15 First processing space 16 Second processing space

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-10-185868 (JP, A) JP-A-4-359145 (JP, A) JP-A-63-279159 (JP, A) JP-A-10- 239276 (JP, A) JP-A-10-232220 (JP, A) JP-A-11-2620 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 27/416 G01N 27 / 419 G01N 27/409 G01N 27/41

Claims (5)

(57) [Claims] 1. A carbon monoxide detection sensor for detecting carbon monoxide contained in a gas to be detected, wherein the gas to be measured can enter and leave an atmosphere to be measured containing carbon monoxide and oxygen. In this state, the first treatment space and the second treatment space are formed, and further, two electrodes having oxygen permeability are formed on the surface of the solid electrolyte, which is composed of the oxygen ion conductive solid electrolyte, and one of the electrodes is formed. An oxygen concentration battery element arranged facing the first treatment space and the other facing the second treatment space, and composed of an oxygen ion conductive solid electrolyte and having oxygen permeability on the surface thereof. Two electrodes are formed, one of the electrodes is arranged facing the first treatment space, and the first treatment is performed in a direction in which the absolute value of the concentration cell electromotive force generated in the oxygen concentration cell element decreases. An oxygen pump element for pumping or pumping out oxygen into a space, and a heating element for heating the oxygen pump element and the oxygen concentration battery element to a predetermined sensor operating temperature, the oxygen pump element The electrode on the side facing the first treatment space is the first electrode, the electrode on the side facing the first treatment space of the oxygen concentration battery element is the second electrode, and the electrode on the second treatment space of the oxygen concentration battery element is facing the second treatment space. As the third electrode, the first processing space and the second processing space are different from each other so that the combustion consumption of carbon monoxide in the introduced gas to be detected differs. The oxidation catalyst activity of the third electrode is adjusted, the current value flowing in the oxygen pump element when the absolute value of the concentration battery electromotive force of the oxygen concentration battery element reaches a predetermined electromotive force target value E C, Monoxide in the gas to be detected A carbon monoxide detection sensor characterized by being extracted as information reflecting the carbon concentration. 2. The oxygen pump element and the oxygen concentration cell element are formed in a plate shape so as to be opposed to each other, and the first processing space and the second processing space are the oxygen pump element and the oxygen processing element. It is formed adjacent to the plate surface direction between the oxygen concentration battery element, the first electrode is formed on the corresponding plate surface of the oxygen pump element at a position facing the first processing space, The second electrode and the third electrode are formed adjacent to each other on the corresponding plate surfaces of the oxygen concentration battery element at positions facing the first processing space and the second processing space, respectively. Carbon monoxide detection sensor. 3. The oxygen pump element and the oxygen concentration cell element, in the remaining region excluding the formation portion of the first processing space and the second processing space, opposing plate surfaces are formed by an insulating ceramic layer. The carbon monoxide detection sensor according to claim 2, which is bonded to each other. 4. The first electrode and the second electrode are Pt-based porous electrodes in which the metal component is substantially Pt, and the third electrode is mainly composed of Pt in the metal component and contains 2-3 Au.
The carbon monoxide detection sensor according to any one of claims 1 to 3, which is a Pt-Au-based porous electrode made of a Pt-Au alloy containing 0% by weight. 5. A method for detecting carbon monoxide contained in a gas to be detected, comprising: a first processing space and a second processing space partitioned from an atmosphere to be measured; and the first processing space and the second processing space. For the processing space,
It has a first gas introducing part and a second gas introducing part for respectively introducing the measured gas from the measured atmosphere containing carbon monoxide and oxygen, and further comprises an oxygen ion conductive solid electrolyte. An oxygen concentration battery in which two electrodes having oxygen permeability are formed on the surface, one of the electrodes is arranged facing the first processing space, and the other is arranged facing the second processing space. An element and an oxygen ion conductive solid electrolyte are formed, and two electrodes having oxygen permeability are formed on the surface of the element, and one of the electrodes is arranged to face the first treatment space. An oxygen pump element for pumping or pumping oxygen to and from the first processing space in a direction in which the absolute value of the concentration cell electromotive force generated in the battery element decreases; and the oxygen pump element and the oxygen concentration electrode. And a heating element for heating the element to a predetermined sensor operating temperature, the electrode on the side facing the first treatment space of the oxygen pump element is a first electrode, and the first treatment of the oxygen concentration battery element is performed. The electrode facing the space is the second electrode, the electrode facing the second treatment space of the oxygen concentration battery element is the third electrode, and is introduced between the first treatment space and the second treatment space. The carbon monoxide detection sensor in which the oxidation catalytic activities of the first to third electrodes are adjusted so that a difference occurs in the combustion consumption of carbon monoxide in the detected gas, the oxygen concentration battery element The current value flowing through the oxygen pump element when the absolute value of the concentration cell electromotive force reaches a predetermined electromotive force target value E C is taken out as information reflecting the carbon monoxide concentration in the gas to be detected. Charcoal monoxide characterized by Detection method.