JPH10177008A - Nox gas concentration detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an NOx gas concentration detector for detecting NOx gas concentration low in oxygen concentration dependency in detecting atmosphere. SOLUTION: The detector has a first oxygen ion pump cell 6 for performing the oxygen concentration control of a gas in a first measurement room 2 and a second oxygen ion pump cell 8 where NOx in a second measurement room 4 where a gas controlled in oxygen concentration is diffused is decomposed, and a current corresponding to the concentration of NOx gas due to the dissociated oxygen flows, a second measurement room external electrode 8b of the second oxygen ion pump cell 8 is arranged so that it does not directly come into contact with the outside air of the detector, and a diffusion resistance means 8d for leading oxygen with a diffusion is provided around the electrode 8b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an automobile, a ship, NO is used to detect the movement, in the exhaust gas of an internal combustion engine for industrial or NO _x gas concentration in the combustion gases of the boiler such as airplanes _x It relates to a gas concentration detector.

[0002]

2. Description of the Related Art In recent years, with the tightening of exhaust gas regulations, research has been conducted to directly measure NO _x in exhaust gas of engines and the like to control engines and catalysts. In particular, using an oxygen ion conductor such as ZrO ₂ , oxygen is pumped out to the extent that NO _x is not decomposed in the first oxygen ion pump cell, and the remaining gas containing NO _x is further pumped in the second oxygen ion pump cell. decomposing NO _x by issuing, NO _x gas concentration detector for detecting the degradation as current,
HC, because it can measure the NO _x gas concentration without being affected by interfering gases such as CO, has recently extensively studied have been made.

As such a NO _x gas concentration detector,
Japanese Patent Application Laid-Open No. 62-276453 discloses a second oxygen ion pump cell in which the oxygen pumping side is exposed to exhaust gas.

[0004]

However, according to the findings of the present inventor, in the above conventional detector, the second detector is used.
The oxygen pumped out side of the oxygen ion pump cell is exposed to the exhaust gas, NO _x concentration measurement value to changes in oxygen concentration depends greatly in the exhaust gas, NO especially at low oxygen concentration atmosphere
It is considered that accurate measurement of _x gas concentration is difficult.

[0005] In view of such circumstances, the present invention aims to provide a NO _X gas concentration detector to enable detection of low NO _x gas concentration oxygen concentration dependency of the atmosphere. Other objects of the present invention will become apparent from the disclosure of the entire specification and drawings.

[0006]

The inventor of the present invention pumps out oxygen to such an extent that NO _x is not decomposed in the first oxygen ion pump cell, and further removes the remaining gas containing NO _x into the second oxygen ion pump cell. If the NO _x gas concentration detector (sensor) for detecting a decomposed current NO _x by pumping oxygen pumped out of the second oxygen ion pump cell is exposed to an exhaust gas atmosphere, (a) the second oxygen Since the oxygen pumping side of the ion pump cell is exposed to the exhaust gas atmosphere, the electromotive force generated in the second oxygen ion pump cell depends on the oxygen concentration change in the exhaust gas atmosphere,
(B) the current (NO _x gas concentration measurement current) Ip2 flowing between the electrodes of the second oxygen ion pump cell, between the voltage Vp2 applied to the second oxygen ion pump cell to decompose the NO _x, Since there is a relationship of “Ip2 = (Vp2-one electromotive force) / R (resistance between the electrodes of the second oxygen ion pump cell)”, the value of Ip2 depends on a change in the oxygen concentration in the exhaust gas.
We noticed that there is a problem.

As a result of further study, the present inventor installed an electrode (oxygen pumping side) opposite to the electrode of the oxygen ion pump cell in the second measurement chamber, inside the element (layer between the stacked solid electrolytes). It has been found that the above problem can be solved by adopting a structure in which oxygen is pumped through the electrode lead portion or a part thereof, and discharging the pumped oxygen by the following various means.

(1) Discharge to the first measuring chamber through a part of the lead portion or through hole. (2) Discharge into the atmosphere or exhaust gas through the lead portion (see FIG. 2). (3) Discharge to the second measurement chamber through a part of the lead portion and the porous portion (see FIG. 3).

With the above structure and means, the external electrode of the second measuring chamber, which is the opposite electrode to the electrode of the oxygen ion pump cell in the second measuring chamber, is shielded from the exhaust gas atmosphere.
Since the oxygen pumped from the second measurement chamber is pooled, the oxygen concentration near the electrodes is stabilized, and the electromotive force generated between the electrodes in the second measurement chamber is stabilized. Therefore, dependence on the oxygen concentration change in the exhaust gas of the pump current (Ip2) flowing through the second oxygen ion pump cell is reduced, thereby enabling accurate measurement of the NO _x gas concentration even in a low oxygen concentration atmosphere.

In order to achieve the above object based on the above findings, the detector according to the first aspect of the present invention is provided outside the second measurement chamber within the pair of electrodes of the second oxygen ion pump cell. The other electrode (hereinafter referred to as the “second measurement chamber external electrode of the second oxygen ion pump cell”) is arranged so as not to directly contact the outside air of the detector, and the second measurement of the second oxygen ion pump cell is performed. Diffusion resistance means for extracting oxygen with diffusion resistance is provided around the outdoor electrode.

The detector having this feature is preferably constructed as follows. A first measurement chamber into which the gas to be measured is introduced via a first diffusion resistor, an oxygen partial pressure detection electrode for measuring the oxygen partial pressure in the gas to be measured in the first measurement chamber, and the oxygen partial pressure Based on the potential of the detection electrode, the oxygen in the gas to be measured is removed from the first measurement chamber to the outside of the measurement chamber by NO.
_A first oxygen ion pump cell that pumps out enough that _X is not decomposed, a second measurement chamber into which gas is introduced from the first measurement chamber via a second diffusion resistor, and an interior of the second measurement chamber. A pair of electrodes provided outside, a voltage is applied to the pair of electrodes to decompose NO _x in the second measurement chamber,
Dissociated NO _X gas concentration detector and a second oxygen ion pump cell current corresponding to NO _x gas concentration by oxygen pumping it. ,

In the detector according to a second aspect of the present invention, based on the first aspect, at least the diffusion resistance means is electrically connected to an external electrode of a second measurement chamber of the second oxygen ion pump cell. It is a lead part or a part thereof.

According to a third aspect of the present invention, the detector according to the first aspect is configured such that, based on the first viewpoint, the external electrode of the second measurement chamber of the second oxygen ion pump cell and the outside air of the detector via the lead portion. Are communicated with a diffusion resistance.

According to a fourth aspect of the present invention, based on the first aspect, the detector of the second oxygen ion pump cell does not directly contact the outside air of the detector based on the first aspect. The diffusion resistance means is disposed between the insulating layer and / or the solid electrolyte layer forming the laminated structure of the detector, and the electrode is connected to the diffusion resistance means.
The measurement chamber external electrode is indirectly connected to the outside air of the detector via the diffusion resistance means.

In the detector according to a fifth aspect of the present invention, based on the first aspect, the diffusion resistance means communicates with a gas passage provided inside the detector, and the gas passage communicates with the first oxygen ion. It is characterized in that it communicates with the electrode of the pump cell, the lead of the electrode or the first measurement chamber.

In the detector according to a sixth aspect of the present invention, based on the first aspect, the diffusion resistance means communicates with a gas passage provided inside the detector, and the gas passage communicates with the second oxygen ion. One of the pair of electrodes of the pump cell, which is provided inside the second measurement chamber (hereinafter referred to as “the second measurement chamber interior electrode of the second oxygen ion pump cell”) or the lead portion of the electrode or the second electrode (2) It is characterized by communicating with a measurement chamber.

According to a seventh aspect of the present invention, in the detector according to the first aspect, the lead portion communicating with the gas passage contacts the outside air based on the first viewpoint.

According to an eighth aspect of the present invention, in the detector according to the first aspect, based on the first aspect, the solid electrolyte layer provided with the pair of electrodes of the second oxygen ion pump cell includes the oxygen partial pressure detection electrode. It is characterized by being laminated between the provided solid electrolyte layer and the second measurement chamber.

In a detector according to a ninth aspect of the present invention, based on the first aspect, the pair of electrodes of the second oxygen ion pump cell are disposed on the same surface of a solid electrolyte layer forming a laminated structure of the detector. It is characterized by being provided.

A detector according to a tenth aspect of the present invention comprises:
Based on the first viewpoint, an electrode inside the second measurement chamber of the second oxygen ion pump cell is provided so as to surround the opening of the second diffusion resistor in the second measurement chamber.

A detector according to an eleventh aspect of the present invention comprises:
A first oxygen ion pump cell that pumps oxygen to such an extent that NO _x is not decomposed from the gas to be measured, and a pair of electrodes provided on the solid electrolyte layer, and a voltage is applied to the pair of electrodes. , NO _x in the residual gas is oxygen is pumped to decompose, and a second oxygen ion pump cell current corresponding to the decomposed amount of NO _x flows, a NO _x gas concentration detector having the first (2) In the pair of electrodes of the oxygen ion pump cell, direct contact between the external electrode of the second measurement chamber and the outside air of the detector is cut off, and oxygen pumped by the second oxygen ion pump cell with a diffusion resistance. And diffusion resistance means for mitigating fluctuations in the oxygen concentration around the electrode.

[0022]

DETAILED DESCRIPTION OF THE INVENTION First, according to an embodiment of the present invention, two pairs of diffusion resistance portion, the oxygen ion pump cell, and the measurement principles of the NO _x gas concentration detector with a measurement chamber as follows is there.

(1) Exhaust gas flows into the first measurement chamber through the first diffusion hole having diffusion resistance. (2) The first oxygen ion pump cell pumps out oxygen in the first measurement chamber to the extent that NO _x is not decomposed (controls the oxygen partial pressure of the first measurement chamber by a signal output from the oxygen partial pressure detection electrode). . (3) second diffusion hole the through a first measurement chamber of a gas having a diffusion resistance (0 ₂ gas + NO _x gas is density control) flows into the second measurement chamber. (4) The NO _x gas in the second measurement chamber is decomposed into N ₂ + O ₂ by further pumping out oxygen by the second oxygen ion pump cell. (5) At this time, since between the pump current Ip2 and NO _x gas concentration flowing through the second oxygen ion pump cell is a linear relationship, it is possible to detect the NO _x gas concentration by detecting the Ip2.

When there is a difference in oxygen concentration between a pair of electrodes of the second oxygen ion pump cell, an electromotive force is generated in the second oxygen ion pump cell, and even if the voltage applied to this cell is controlled to be constant, the effective pump voltage Changes. The effective pump voltage is the "difference between the applied voltage and the electromotive force". Therefore, if the oxygen concentration difference is varied, Ip2 is not the NO _x gas concentration, and thus vary the oxygen concentration. Accordingly, one embodiment of the present invention provides a means for maintaining a constant oxygen concentration difference between a pair of electrodes of a second oxygen ion pump cell, particularly around an electrode provided outside the second measurement chamber of the second oxygen ion pump cell. Means is provided for stabilizing the oxygen concentration of By this means, the electromotive force varies with changes in oxygen concentration is stabilized, the applied voltage will eventually enable pumping voltage from the constant is stabilized, it is accurate NO _X gas concentration detection that does not depend on the oxygen concentration. Preferably, a protective layer (such as an insulating layer of alumina and / or a zirconia-based solid electrolyte layer) is provided as a protection means for blocking the external electrode of the second measurement chamber of the second ion pump cell from the detector outside air to detect the external electrode. As means for cutting off direct contact with the outside air and discharging the pumped oxygen, diffusion resistance means connected to the outer electrode and capable of diffusing oxygen is provided. Therefore, direct contact between the second electrode of the second measurement chamber of the second ion pump cell and the outside air of the detector (atmosphere or gas to be measured such as exhaust gas) is cut off by the solid electrolyte layer, the insulating layer, and the diffusion resistance means. At the same time, oxygen can be led out through the diffusion resistance by the diffusion resistance means, and the oxygen concentration around the electrode is stabilized. Preferably, the diffusion resistance means is made of a porous material (a platinum alloy, a rhodium alloy, an alloy of them and a ceramic, etc.).
With such a lead portion, it is not necessary to separately provide a diffusion resistance means and an electrical connection means for the electrodes, and an effective use of an extremely small space and a reduction in man-hours and raw materials can be achieved.

Preferably, the solid electrolyte layer of the second oxygen ion pump cell provided with a pair of electrodes is replaced with a solid electrolyte layer provided with an oxygen partial pressure detecting electrode (oxygen concentration measuring cell).
And the second measurement chamber. That is, the second
An oxygen ion pump cell is disposed between the oxygen concentration measurement cell and the layer of the second measurement chamber. More preferably, in order to prevent leakage current between the electrodes, an insulating layer is provided between the solid electrolyte layer provided with the pair of electrodes of the second oxygen ion pump cell and the solid electrolyte layer provided with the oxygen partial pressure detection electrode. Distribute.
By arranging the second oxygen ion pump cell in this manner, the solid electrolyte layer is more effectively used than when the second oxygen ion pump cell is arranged between the second measurement chamber and the outside of the detector. Therefore, the number of solid electrolyte layers can be further reduced, and the thickness of the stacked layers can be reduced to make the detector compact.

In the preferred NO _x gas concentration detector of the present invention, the first oxygen ion pump cell 6, the oxygen concentration measuring cell 7, and the second oxygen ion pump cell 8 are all provided on different solid electrolyte layers. (See FIG. 1). Thereby, the leak current flowing between the electrodes of each cell is reduced, and the oxygen concentration in the first measurement chamber can be controlled accurately. More preferably, an insulating film such as alumina or an insulating layer is provided between the cells.

Preferably, a heater layer for heating the detector is laminated between the laminated solid electrolyte layers. By providing the heater layer, the first and second oxygen ion pumping capabilities can be stabilized.

As a solid electrolyte of each cell, a solid solution of zirconia and yttria, a solid solution of zirconia and calcia, and the like are used. As a porous electrode formed by a method such as screen printing and sintering on both surfaces of a thin solid electrolyte layer, it is preferable to use platinum, rhodium, or an alloy thereof having a catalytic action. As the first and second diffusion holes, it is preferable to use porous ceramics, such as porous alumina ceramics. It is preferable that the heat generating portion of the heater be formed of a composite material of ceramics and platinum or a platinum alloy, and the lead portion be formed of platinum or a platinum alloy.

[0029] Incidentally, CO gas is applicable to detectors also present invention to the concentration detection of HC gas, as in the case of the detection of the NO _X gas concentration, precise the target gas concentration is the influence of the oxygen concentration reduced Can be measured.

Other preferable features are as described in Japanese Patent Application No. 8-160812 filed by the present applicant, and the present application can be referred to and incorporated into the present application as necessary.

[0031]

Embodiments of the present invention will be described below with reference to the drawings.

[0032]

Embodiment 1 FIG. 1 is a view for explaining the structure of the NO _X gas concentration detector according to an embodiment of the present invention, is a cross-sectional view taken along the detector in the longitudinal direction.

The detector shown in FIG. 1 has a solid electrolyte layer 5-1.
A first electrode having a pair of electrodes 6a and 6b
An oxygen ion pump cell 6, an oxygen concentration measurement cell 7 including a pair of oxygen partial pressure detection electrodes 7a and 7b provided with a solid electrolyte layer 5-2 interposed therebetween, a solid electrolyte layer 5-3, and a solid electrolyte layer 5-4. A second oxygen ion including a pair of electrodes (electrodes inside the second measurement chamber of the second oxygen ion pump cell 8) 8a and (electrodes outside the second measurement chamber of the second oxygen ion pump cell 8) 8b provided on the surface The pump cells 8 are stacked in this order, and the insulating layers 11-1, 11-1,
11-2 and 11-3 are respectively formed. Then, the first oxygen ion pump cell 6 and the oxygen concentration measuring cell 7
The first measurement chamber 2 is defined by the insulating layers 11-1 on the left and right sides and the solid electrolyte layers 5-1 and 5-2 on the upper and lower sides in the figure, and similarly, the insulating layer 11-3 and the solid electrolyte Layer 5-
A second measurement chamber 4 is defined above the second oxygen ion pump cell 8 by 3, 5-4. Further, the first measurement chamber 2
On the other hand, first diffusion holes 1 having diffusion resistance are provided on both sides in the lateral direction of the detector (the front and back surfaces in FIG. 1), respectively.
In the other side of the first measurement chamber 2, an opening of the second diffusion hole 3 is provided separately from the first diffusion hole 1. The second diffusion hole 3 penetrates through the oxygen concentration measurement cell 7 and the solid electrolyte layer 5-3 to communicate the first and second measurement chambers 2 and 4 with diffusion resistance.

In this detector, porous (platinum, rhodium alloy, etc.) electrodes 8a and 8b are both formed on the same surface of the solid electrolyte layer 5-4 constituting the second oxygen ion pump cell 8. . Although the electrodes 8a and 8b are separated from each other by the insulating layer 11-3, oxygen ions conduct through the solid electrolyte layer 5-4, and the current Ip2 flows. The electrode 8b includes a solid electrolyte layer 5-4, an insulating layer 11-3,
And the lead 8d prevents direct contact with the outside air of the detector, and derives the oxygen pumped by the second oxygen ion pump cell 8 through the porous lead 8d having diffusion resistance. it can. Further, the electrodes 8a, 8
b include lead portions (lines) 8c (not shown) and 8d, respectively.
Are electrically connected, and the lead portion 8d electrically connected to the outer electrode 8b of the second measurement chamber 4 is made porous, and can diffuse oxygen ions. Accordingly, the second oxygen ion pump cell 8, pumped oxygen to 8b from being degraded from NO _X gas electrode 8a (see arrow in FIG. 2), it is discharged via the lead portion 8d.

The oxygen released from the lead portion 8d is
Through the through-hole (or porous hole) 12 which is a gas passage communicating with the lead portion 8d shown in FIG. 1 and the porous lead portion 6c of the first oxygen ion pump cell 6, via the porous lead portion 6c. And discharged into the first measurement chamber 2 and further discharged to the outside of the detector.

The measurement principle of the detector shown in FIG. 1 is the same as that described in the section of the embodiment, and the measurement target gas diffused into the first measurement chamber 2 through the first diffusion hole 1 is introduced. An electromotive force corresponding to the oxygen concentration is generated by a pair of electrodes 7a,
7b, the voltage applied to the first oxygen ion pump cell 6 is controlled so that the voltage due to the electromotive force becomes constant (digital control using a microcomputer, analog control, or the like). Good). Then, surplus oxygen is pumped out and the gas to be measured having a certain oxygen concentration is diffused into the second measurement chamber 4 through the second diffusion hole 3, and a pair of electrodes 8 a and 8 b of the second oxygen ion pump cell 8 The remaining oxygen is further pumped out when a voltage is applied to the electrode, and the catalytic action of the platinum alloy and rhodium alloy electrodes causes
NO _x is decomposed into N ₂ and O _2, by the O ₂ conducts the solid electrolyte layer of the second oxygen ion pump cell 8 as ions, second oxygen provided into the second measurement chamber 4 and outside a pair of electrodes 8a of the ion pump cell 8, current Ip2 flows in accordance with the NO _x amount of gas decomposed between 8b. By measuring the Ip2, it can be measured NO _x gas concentration.

According to this detector, the electrode 8b opposite to the electrode 8a of the second oxygen ion pump cell 8 in the second measurement chamber 4 is installed inside the element (between the stacked solid electrolytes). As a result, the solid electrolyte layer 5-4 and the insulating layer 11-3
Serves as protection means for the electrode 8b, and the lead portion 8d serves as diffusion resistance means, so that the electrode 8b is cut off from the atmosphere of the gas to be measured (exhaust gas) so that it does not come into direct contact with the outside air. The pumped oxygen is pooled, the oxygen concentration around (near) the electrode 8b is stabilized, and the electromotive force generated between the pair of electrodes 8a and 8b of the second oxygen ion pump cell 8 is stabilized. . Furthermore,
By the electromotive force generated is stabilized, the effective pump voltage of the pump voltage Vp2 (VP2 Kazuki power) is stabilized, the oxygen concentration dependency of the NO _x gas concentration measurement that is applied to the second oxygen ion pump cell 8 Decrease.

On the other hand, according to the detector of the comparative example shown in FIG. 6, since the electrode 8b is formed outside the element (detector), the electrode 8b is not affected by the fluctuation of the atmosphere to be measured, especially the fluctuation of the oxygen concentration. A pair of electrodes 8a of the two oxygen ion pump cell 8,
Effective pump voltage varies acting between 8b, so that the oxygen concentration dependency of the NO _x gas concentration measurement is present largely.

The detector of FIG. 1 has an advantage in the process that both electrodes 8a and 8b of the second oxygen ion pump cell 8 can be printed at a time in the manufacturing process.

A pair of electrodes respectively provided in the first oxygen ion pump cell 6, the oxygen concentration measuring cell 7, and the second oxygen ion pump cell 8 can be connected to the outside via leads provided between layers. In the measurement examples described below, the electrodes 6a, 6b, 8a, 8b of the first and second oxygen ion pump cells 6, 8 are used as a power supply and an ammeter, and the electrodes 7a, 7b of the oxygen concentration measurement cell 7 are used as a voltmeter. Connected. Such an embodiment is disclosed in Japanese Patent Application No. 8-160812 filed earlier by the present applicant.
This is illustrated in FIG.

FIGS. 2 and 3 are plan sectional views showing preferred modifications of the NO _x gas concentration detector described above, respectively (corresponding to the plan sectional view taken along line A or B in FIG. 1). ). The detector of FIG. 2 is different from the detector of FIG. 1 in that the lead 8d contacts the detector outside air (in the atmosphere or the atmosphere of the gas to be measured), and communicates the outside air with the electrode 8b via a diffusion resistor. That is the point. Also, the detector of FIG.
The difference from the above detector is that a porous layer (membrane) 12 formed between the solid electrolyte layers communicates between the lead portions 8c and 8d, and oxygen pumped by the second oxygen ion pump cell is It is to recirculate to the second measurement chamber 4 through the layer (film) 12, the porous lead portion 8c and the electrode 8a.

Next, referring to FIGS. 4 to 6, respectively.
Explaining the NO _x gas concentration sensor according to another embodiment of the present invention.

[0043]

Embodiment 2 FIG. 4 is a view showing a NO _{X according} to another embodiment of the present invention.
It is a figure for explaining the structure of a gas concentration detector, and is a sectional view which cut the detector along the longitudinal direction. The difference between the detector shown in FIG. 4 and the detector of the first embodiment is that the solid electrolyte layer (cell) 5-3 which partitions the upper part of the second measurement chamber 4 is shown.
A pair of electrodes 8a and 8b of the second oxygen ion pump cell 8 are provided at positions symmetrical with respect to the
b is electrically connected to the porous lead portion 8d. The lead 8d may be connected to the outside air, and may be connected to the first measurement chamber 2 or the second measurement chamber 4 via a through hole (or a porous hole) as shown in FIG. 1 or FIG. May be. According to such a configuration, it is possible to replace the lowermost solid electrolyte layer in the figure with a layer made of another material.

[0044]

Embodiment 3 FIG. 5, NO _X in accordance with another embodiment of the present invention
It is a figure for explaining the structure of a gas concentration detector, and is a sectional view which cut the detector along the longitudinal direction. 5 is different from the detector of the second embodiment in that the electrode 8a of the second oxygen ion pump cell 8 in the second
The point is that it is formed around (close to) the diffusion hole 3 and the volume of the second measurement chamber 4 is reduced. Other configurations are the same as those of the second embodiment.

Using the NO _x gas concentration detectors of Examples 1 to 3 and Comparative Example, a measurement test of the NO gas concentration in the gas to be measured was performed. First, an example of manufacturing a detector used for measurement will be described with reference to FIG. FIG. 9 is a diagram for explaining a manufacturing example and a layout of the detector used for the measurement.

[0046]

[Production Example] As shown in FIG. 9, a ZrO ₂ green sheet and an electrode paste are laminated in order from the upper left to the lower left and from the upper right to the lower right in the figure to produce an integrated detector. Paste materials such as insulating coats and electrodes are specified Zr
The O ₂ green sheet is screen-printed to form a laminate. Next, an example of manufacturing each component such as a ZrO ₂ green sheet will be described. The porous pores shown in FIG. 1 are produced by the same raw materials and processes as those of the first diffusion holes or the second diffusion holes described below. The porous layer (membrane) shown in FIG. The first diffusion hole or the second diffusion hole is manufactured by the same raw material and process.

[ZrO ₂ sheet molding]

The ZrO ₂ powder was calcined in an atmospheric furnace at 600 ° C. for 2 hours. 30 kg of calcined ZrO ₂ powder, 150 g of a dispersant, and 10 kg of an organic solvent are placed in a trommel together with 60 kg of cobble stones, and the mixture
Mix for 4 hours, disperse, add 4 kg of organic binder dissolved in 10 kg of organic solvent and mix for 20 hours
A slurry having a viscosity of about 10 Pa · s was obtained. A ZrO ₂ green sheet having a thickness of about 0.4 mm was prepared from this slurry by a doctor blade method, and dried at 100 ° C. for 1 hour.

[Printing paste]

(1) For the first oxygen ion pump electrode 6a, oxygen partial pressure detection electrode (oxygen reference electrode) 7b, and second oxygen ion pump electrodes 8a and 8b: platinum powder 20g, ZrO ₂ powder 2.
8 g, an appropriate amount of an organic solvent is placed in a grinder (or pot mill), mixed for 4 hours and dispersed. A solution obtained by dissolving 2 g of an organic binder in 20 g of an organic solvent is added thereto, and 5 g of a viscosity modifier is further added. Add, mix for 4 hours, viscosity 150Pa
・ Approximately s paste was prepared.

(2) First oxygen ion pump electrode 6b, oxygen partial pressure detection electrode (oxygen reference electrode) 7a: platinum powder 19.8
g, ZrO ₂ powder 2.8 g, gold powder 0.2 powder, and an appropriate amount of an organic solvent were placed in a grinder (or pot mill), mixed for 4 hours and dispersed, and 2 g of an organic binder was added to the organic solvent 2.
A solution dissolved in 0 g was added, and 5 g of a viscosity modifier was further added, followed by mixing for 4 hours to prepare a paste having a viscosity of about 150 Pa · s.

(3) For insulating coat and protective coat: 50 g of alumina powder and an appropriate amount of an organic solvent are put in a grinder (or pot mill), mixed for 12 hours, dissolved, and 20 g of a viscosity modifier is added. Mix for 3 hours and viscosity 100Pa · s
A paste of the degree was prepared.

(4) For Pt-containing porous material (for lead wire): Put 10 g of alumina powder, 1.5 g of platinum powder, 2.5 g of organic binder and 20 g of organic solvent in a grinder (or pot mill) and mix for 4 hours. And 10 g of a viscosity modifier, and
After mixing for a time, a paste having a viscosity of about 100 Pa · s was prepared.

(5) For the first diffusion hole: 10 g of alumina powder having an average particle size of about 2 μm, 2 g of organic binder, 20 g of organic solvent
Into a mill (or pot mill), mix,
The mixture was dispersed, 10 g of a viscosity modifier was further added, and mixed for 4 hours to prepare a paste having a viscosity of about 400 Pa · s.

(6) For carbon coating: carbon powder 4
g, 2 g of an organic binder, and 40 g of an organic solvent were placed in a grinder (or pot mill), mixed and dispersed, and 5 g of a viscosity modifier was added, followed by mixing for 4 hours to prepare a paste. In addition, by forming the carbon coat by printing, for example, contact between the first oxygen pump electrode b and the oxygen reference electrode b is prevented. The carbon coat is used to form a first measurement chamber and a second measurement chamber. Since carbon is burned off during firing, the carbon coat layer does not exist in the fired body.

[Pellets]

For the second diffusion hole: 20 g of alumina powder having an average particle size of about 2 μm, 8 g of an organic binder, and 20 g of an organic solvent are put into a grinder (or pot mill) and mixed for 1 hour.
Granulate and apply a pressure of about 2 t / cm ² with a die press to a diameter of 1.3.
A cylindrical press-formed body (green state) having a thickness of 0.8 mm and a thickness of 0.8 mm was produced. The green pressed body is inserted into predetermined portions of the second and third layers of the ZrO ₂ green sheet, pressed and integrated, and then fired to form a second diffusion hole in the detector. .

[ZrO ₂ Laminating Method] After the second and third layers are pressed, a portion (diameter: 1.3 mm) through which the second diffusion hole penetrates is punched. After the punching, a green cylindrical molded body serving as the second diffusion hole is embedded, and 1 to 4 layers of ZrO ₂ green sheets are pressed under a pressure of 5 kg / cm ² and a pressing time of 1 minute.

[Binder Removal and Firing] The pressed compact is debindered at 400 ° C. for 2 hours and fired at 1500 ° C. for 1 hour.

[0060]

[Test Example] NO in the measurement gas using a NO _X gas concentration detector was thus produced in Examples 1 to 3 and Comparative Examples
A gas concentration measurement test was performed. The external dimensions of the detector used for the measurement were 50 mm in length in the longitudinal direction and 4 m in width (transverse direction).
m and thickness (lamination direction) are 1.3 mm. The thickness of the first oxygen ion pump cell is 0.3 mm, the length of the electrodes 6a and 6b in the longitudinal direction is 7 mm, the length in the transverse direction is 2 mm, and the length of the first measurement chamber in the longitudinal direction is 7 mm. The length in the hand direction is 2 mm, the height is 50 μm, and in the case of Examples 1 and 3, the length of the second measurement chamber in the longitudinal direction is 2 mm, and the length in the short direction is 2 m.
m, height 50 μm, in the case of Example 2, the length of the second measurement chamber in the longitudinal direction is 7 mm, and the length of the first diffusion hole in the longitudinal direction is 2 m
m, the length in the lateral direction is 1 mm, the thickness is 50 μm, and the size of the second diffusion hole is 1 mm in diameter.

[0061]

[Table 1]

[0062]

[Table 2]

[0063]

[Test Example] shows these Examples 1-3 and Comparative Examples measured result of NO gas concentration measurement test in the measurement gas using a NO _X gas concentration detector of the Tables 1 and 2, FIG. 7 And FIG. 8 summarizes the measurement results. The common measurement conditions in the test examples described below are as follows.

Gas component to be measured: NO: 0, 1500 pp
_{m, O 2: 0~16%,} CO 2: 10%, N 2: Ba
l. , Measured gas temperature: 300 ° C, heater power: 18
W.

[0065]

Test Example 1 (1) NO: 0 ppm, and the change in the offset value of the current (Ip2) flowing through the second oxygen ion pump cell was measured while changing the oxygen concentration. Note that the offset is the value of Ip2 when NO is not injected into the gas to be measured, and corresponds to the concentration of residual oxygen remaining in the first measurement chamber. Further, it is preferable that the value is smaller, and it is desirable that the value be less insensitive to various external factors, for example, fluctuations in the oxygen concentration and temperature in the atmosphere of the gas to be measured.

FIG. 7 shows the results of Test Example 1. FIG. 7 shows Ip2
It is a graph showing the oxygen concentration dependence of the offset, circle,
Triangles, squares, and diamonds are plotted in Examples 1 and 2, respectively.
It is the measurement data by the conventional type gas concentration detector of 3 and the comparative example. Referring to FIG. 7, according to the gas concentration detectors of Examples 1 to 3, with respect to the change amount of the oxygen concentration of 0 to 16%,
It can be seen that the change amount of the p2 offset is 1 μA or less, and the oxygen concentration dependency is greatly improved, especially on the low oxygen concentration side, as compared with that of the comparative example.

[0067]

Test Example 2 (2) NO: 1500 ppm was introduced into the gas to be measured, and the gain of the current Ip2 flowing through the second oxygen ion pump cell was measured at an oxygen concentration of 0 to 16%. Note that the gain is the amount of change in Ip2 when a constant concentration of NO is supplied (in this test example, the difference between the values of Ip2 flowing when 0 ppm and 1500 ppm of NO are supplied, respectively). To increase the measurement sensitivity of the NO _x gas concentration, the gain is preferably high in Ip2, various external factors, for example, the oxygen concentration in the measurement gas atmosphere, to variations in temperature or the like, varies a less sensitive It is desirable that it is difficult.

FIG. 8 shows the results of Test Example 2. FIG. 8 shows ΔI
It is a graph which shows the oxygen concentration dependence of p2 (Ip2 gain), and a circle, a triangle, a square, and a diamond-shaped plot are measurement data by the conventional type gas concentration detector of Examples 1, 2, 3, and a comparative example, respectively. Referring to FIG. 8, according to the gas concentration detectors of Examples 1 to 3, the change amount of the Ip2 gain is 2 μA or less with respect to the change amount of the oxygen concentration of 0 to 16%. It can be seen that the dependence has been reduced. In particular Ip2 gain is higher as compared with the comparative example in the low oxygen concentration side, it can be seen that the sensitivity of the NO _x gas concentration detection (resolution) is improved.

[0069]

As described above, according to the NO _x gas concentration detector of the present invention, the electromotive force generated between the electrodes of the second oxygen ion pump cell is stabilized, whereby
The oxygen concentration dependency of _x gas concentration detection is greatly improved, and more accurate NO _x gas concentration detection is possible, especially even in a low oxygen concentration atmosphere. Therefore, this detector is excellent as a detector for a gasoline engine that emits exhaust gas with a low oxygen concentration or an internal combustion engine whose air-fuel ratio fluctuates greatly.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a NO _x gas concentration detector according to one embodiment of the present invention, illustrating a structure of the NO _X gas concentration detector cut along a longitudinal direction.

FIG. 2 is a cross-sectional plan view taken along a line A in FIG. 1;

FIG. 3 is a plan sectional view showing a modified example of the NO _x gas concentration detector according to one embodiment of the present invention (corresponding to a plan sectional view shown by an arrow B line in FIG. 1).

[Figure 4] is a view for explaining the structure of the NO _X gas concentration detector according to another embodiment of the present invention, is a cross-sectional view taken along the detector in the longitudinal direction.

FIG. 5 is a further view for explaining the structure of the NO _X gas concentration detector according to another embodiment of the present invention, is a cross-sectional view taken along the detector in the longitudinal direction.

FIG. 6 is a view for explaining the structure of a NO _X gas concentration detector according to a comparative example, and is a cross-sectional view of the detector cut along a longitudinal direction.

FIG. 7 is a graph showing the oxygen concentration dependency of a second oxygen ion pump cell current Ip2 offset, where circles, triangles, squares, and diamonds are measured by the detectors of Examples 1, 2, 3 and Comparative Example, respectively. Show data.

FIG. 8 is a graph showing the oxygen concentration dependency of the second oxygen ion pump cell current ΔIp2 (Ip2 gain), where circles, triangles, squares, and diamonds are plotted in Examples 1, 2, and 3, respectively.
4 shows data measured by a detector of a comparative example.

FIG. 9 is a diagram for explaining a manufacturing method and a layout of a NO _X gas concentration detector used for measurement.

[Explanation of symbols]

 1: First diffusion hole 2: First measurement chamber 3: Second diffusion hole 4: Second measurement chamber 5-1..., 5-4: Solid electrolyte layer 6: First oxygen ion pump cell 6a, 6b: Electrode 6c: Lead portion 7: Oxygen concentration measurement cell 7a, 7b: Electrode 8: Second oxygen ion pump cell 8a, 8b: Electrode 8c, 8d: Lead portion 11-1,..., 11-4: Solid electrolyte layer 12: Through Hole (porous hole), porous layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noboru Ishida 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi Inside Japan Specialty Ceramics Co., Ltd. Inside the corporation

Claims (11)

[Claims] A first measuring chamber into which a gas to be measured is introduced via a first diffusion resistor; an oxygen partial pressure detecting electrode for measuring a partial pressure of oxygen in the gas to be measured in the first measuring chamber; A first oxygen ion pump cell that sufficiently pumps oxygen in the gas to be measured from the first measurement chamber to the outside of the measurement chamber based on the potential of the oxygen partial pressure detection electrode so that NO _x does not decompose, A second measurement chamber into which gas is introduced from the first measurement chamber via a second diffusion resistor; and a pair of electrodes provided inside and outside the second measurement chamber, and a voltage is applied to the pair of electrodes. been applied to decompose the NO _x of the second during the measurement chamber, dissociated and the second oxygen ion pump cell current corresponding to NO _x gas concentration by oxygen pumping it, the NO _X gas concentration detection with A device comprising: a pair of electrodes of the second oxygen ion pump cell; Electrodes of the person who provided outside of the second measuring chamber (hereinafter referred to as "the second measurement chamber outer electrodes of the second oxygen ion pump cell")
Is arranged so as not to come into direct contact with the outside air of the detector, and diffusion resistance means for extracting oxygen with diffusion resistance is provided around the external electrode of the second measurement chamber of the second oxygen ion pump cell. NO _X gas concentration detector to. 2. The apparatus according to claim 1, wherein at least said diffusion resistance means is provided with said second resistor.
NO _X gas concentration detector according to claim 1, characterized in that a lead portion or a portion thereof electrically connected to the second measurement chamber outer electrode of the oxygen ion pump cell. 3. An external electrode of a second measurement chamber of the second oxygen ion pump cell and outside air of a detector are communicated with a diffusion resistance through the lead portion.
NO _X gas concentration detector according to. 4. An external electrode of the second measurement chamber of the second oxygen ion pump cell so as not to directly contact the outside air of the detector.
The diffusion resistance means is arranged between the insulating layer and / or the solid electrolyte layer forming the laminated structure of the detector, and the electrode is connected to the diffusion resistance means. The external electrode of the second measurement chamber of the second oxygen ion pump cell is the diffusion electrode. NO _X gas concentration detector according to any one of claims 1 to 3, characterized in that it is indirectly communicated via the resistance means to the air detector. 5. The diffusion resistance means communicates with a gas passage provided inside the detector, and the gas passage communicates with an electrode of the first oxygen ion pump cell, a lead portion of the electrode, or a first measurement chamber. NO _X gas concentration detector according to any one of claims 1 to 3, characterized in that. 6. The diffusion resistance means communicates with a gas passage provided inside the detector, and the gas passage is provided inside the second measurement chamber within a pair of electrodes of the second oxygen ion pump cell. The electrode connected to the electrode (hereinafter, referred to as an "electrode inside the second measurement chamber of the second oxygen ion pump cell"), a lead portion of the electrode, or the second measurement chamber.
NO _X gas concentration detector according to any one of to 3. 7. The NO _{X according} to claim 5, wherein a lead portion communicating with the gas passage comes into contact with outside air.
Gas concentration detector. 8. A solid electrolyte layer provided with a pair of electrodes of the second oxygen ion pump cell is laminated between the solid electrolyte layer provided with the oxygen partial pressure detection electrode and the second measurement chamber. NO _X gas concentration detector according to any one of claims 1 to 7, characterized in that formed by. 9. The device according to claim 1, wherein the pair of electrodes of the second oxygen ion pump cell are provided on the same surface of a solid electrolyte layer forming a laminated structure of the detector. NO _X gas concentration detector according. 10. An electrode inside the second measurement chamber of the second oxygen ion pump cell surrounding the opening of the second diffusion resistor in the second measurement chamber.
NO _X gas concentration detector according to any one of to 9. 11. A first oxygen ion pump cell for pumping oxygen to such an extent that NO _x is not decomposed from a gas to be measured, and a pair of electrodes provided on a solid electrolyte layer, and a voltage is applied to the pair of electrodes. by being, NO _x in the residual gas is oxygen is pumped to decompose, and a second oxygen ion pump cell current corresponding to the decomposed amount of NO _x flows, there in NO _x gas concentration detector having The second oxygen ion pump cell has a second electrode among the pair of electrodes.
The direct contact between the measurement chamber external electrode and the outside air of the detector is cut off, and the oxygen pumped out by the second oxygen ion pump cell is diffused with a diffusion resistance to reduce the fluctuation of the oxygen concentration around the electrode. NO _X gas concentration detector, characterized in that it comprises a diffusion resistance means mitigating.