JP2002310985A - NOx SENSOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide NOx concentration measuring technique capable of continuously and accurately measuring the concentration of NOx in gas to be measured without being affected by the concentration of oxygen or the change thereof. SOLUTION: The NOx sensor is provided with a first internal space 6 to which the gas to be measured is guided, a second internal space 8 to which the atmosphere of the gas to be measured is guided, a first oxygen pump means for controlling the partial pressure of oxygen in the first internal space 6, a second oxygen pump means for pumping up oxygen in the second internal space 8 and a current detection means 32 for detecting the pump current flowing by the operation of the second oxygen pump means for the purpose of knowing the concentration of NOx in the gas to be measured. The concentration of NOx in the gas to be measured can be calculated from the value of the pump current Ip detected by the current detection means 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring a predetermined gas component in a gas component to be measured, and more particularly to a method for measuring a gas component to be measured having bound oxygen and various gas sensors. The present invention relates to a sensor for measuring a NOx in a gas as a gas to be measured as a combustion gas and a method for advantageously measuring the NOx.

[0002]

2. Description of the Related Art Conventionally, various measuring methods and apparatuses have been proposed to know the concentration of a desired gas component in a gas to be measured. For example, NO.
As a method of measuring x, a sensor comprising a Pt electrode and a Rh electrode provided on an oxygen ion-conductive solid electrolyte such as zirconia utilizing the NOx reducing property of Rh is used to measure the voltage between the two electrodes. Techniques for measuring power are known. However, such a sensor not only has a large change in electromotive force due to a change in the concentration of oxygen contained in the combustion gas as the gas to be measured, but also has a N
Since the change in electromotive force is small with respect to the change in Ox concentration, there is a problem that it is susceptible to noise. In addition, since reducing gas such as CO is indispensable in order to bring out the reducibility of NOx, a large amount is generally used. Under the combustion condition of insufficient fuel in which NOx is generated, the amount of generated CO becomes lower than the amount of generated NOx. Therefore, there is a disadvantage that measurement cannot be performed with the combustion gas formed under such a combustion condition. there were.

[0003] Also, a set of electrochemical pump cells and sensor cells comprising a Pt electrode and an oxygen ion conductive solid electrolyte, and another set of electrochemical pump cells and sensor cells comprising a Rh electrode and an oxygen ion conductive solid electrolyte. And a method of measuring NOx based on the difference between the respective pump current values is disclosed in JP-A-63-38154 and JP-A-64-39545. Further, Japanese Patent Application Laid-Open Nos. 1-277751 and 2-154
No. 3 discloses two sets of a pair of electrochemical pump cells and sensor cells, and measures a limit current under a partial pressure of oxygen where NOx is not reduced by a sensor including one set of pump cells and sensor cells. The other pair of the pump cell and the sensor cell is used to measure the pump current under the partial pressure of oxygen at which NOx is reduced, and to measure the difference between the respective limit currents. The oxygen partial pressure in the gas to be measured
There has been proposed a method of switching between a partial pressure of oxygen that can be reduced and a partial pressure of oxygen that cannot be reduced, and measuring a difference in limiting current.

FIG. 25 is a diagram showing the principle of these conventional methods. Two independent first and second sensor elements 61 and 6 are shown.
Numeral 2 includes internal cavities 65 and 66, which are connected to the external measured gas existence space via diffusion resistance portions 63 and 64, respectively, and electrochemical pump cells 67 and 68 using a solid electrolyte. The first sensor element 61 pumps only oxygen under diffusion-limited conditions, and the pump current Ip _{1 at} that time.
Is multiplied by the sensitivity coefficient K ₁ to the oxygen concentration is determined. The second sensor element 62 pumps both oxygen and NOx under diffusion-controlled conditions in the presence of an electrode or a catalyst capable of reducing NOx, and the sensitivity coefficient K ₂ to the pump current Ip ₂ at that time.
To obtain the total amount of oxygen concentration and NOx. Therefore, the NOx concentration: Cn is obtained by the following equation. Cn = K ₂ · Ip ₂ -K ₁ · Ip ₁

However, in these NOx measuring methods, the current of oxygen contained in a large amount occupies a large part of the limit current value, and the current based on the target NOx is usually very small. Due to the difference between the values, a small current value corresponding to NOx is determined. In the case of switching and measuring with a set of sensors, continuous measurement cannot be performed, responsiveness is poor, accuracy is poor. In the case of a system using two sets of sensors, if the oxygen concentration in the gas to be measured greatly changes, an error is likely to occur in the measured value. If the oxygen concentration of the gas greatly changed, it could not be used. This is because the oxygen concentration dependency of the pump current of one sensor and the oxygen concentration dependency of the pump current of the other sensor are different from each other. For example, in the case of an automobile, under an operating condition with an air-fuel ratio of 20, the oxygen concentration of exhaust gas is approximately several percent, while the NOx concentration is several hundred ppm, and NOx is 1/100 of oxygen. Since the dependence of the pump current on the oxygen concentration is slightly different because the concentration is about the same, the difference in the limit current value with respect to the oxygen concentration change becomes larger than the limit current change due to NOx to be measured. It is. Also, if the diffusion controlling means of the pump cell becomes clogged with oil combustion substances in the exhaust gas, a change is caused in the pump current, causing loss of accuracy or a large change in the exhaust gas temperature, causing an abnormality in the measured value. Or something that happened. Further, if there is a difference in the change over time of the characteristics of the two sets of sensors, the difference becomes an error as it is, and there is a drawback that it cannot withstand long-term use.

As described above, the oxygen present in the gas to be measured causes various problems when measuring NOx. However, when measuring the components of the gas to be measured other than NOx, Similar problems such as a decrease in measurement accuracy are caused, and it is strongly desired to solve the problems.

[0007]

The present invention relates to the conventional N
The purpose of the present invention is to eliminate all the drawbacks in the measurement method of gas components such as Ox.
A method and apparatus for measuring a desired gas component in a gas to be measured, particularly a bound oxygen-containing gas component, capable of continuously measuring accurately and for a long time without being affected by the oxygen concentration or its change. Is to provide. Further, a further object of the present invention is to measure a wide range of NOx that can be used as a gas to be measured, in a combustion gas having an air-fuel ratio ranging from an excessive fuel region to an excessive air region.
It is an object of the present invention to provide a sensor and a NOx measuring method having such a wide measuring area.

[0008]

According to the present invention, in order to solve the above-described problems, an externally-existing space in which a gas to be measured is present is used.
A gas to be measured containing a gas component to be measured is guided under a predetermined diffusion resistance into the first internal space, and the amount of oxygen in the gas to be measured is controlled in the first internal space. At the very least, the gas to be measured is made to have a predetermined atmosphere that does not substantially affect the measurement of the target gas component amount to be measured and does not change the gas component to be measured. To the second internal space under a predetermined diffusion resistance from the first internal space, and in the second internal space, the atmosphere in the second internal space A gist of the present invention is a method for measuring a predetermined gas component in a measured gas, which comprises measuring an amount of a measured gas component present in the gas.

According to a preferred embodiment of the measuring method according to the present invention, the amount of oxygen in the gas to be measured led to the first internal space is controlled, and the amount of oxygen in the first internal space is controlled. , An atmosphere having a substantially negligible oxygen concentration.

According to another preferred embodiment of the measuring method according to the present invention, the control of the amount of oxygen in the gas to be measured in the first internal space is realized by an oxygen pumping action of an electrochemical cell. Will be done.

According to one of the advantageous aspects of the measuring method of the present invention, the measuring gas is located in
A gas to be measured containing a gas component to be measured having bound oxygen to be measured in the first internal space is guided under a predetermined diffusion resistance, and the oxygen in the gas to be measured is introduced into the first internal space. The amount of the gas to be measured is adjusted to a predetermined atmosphere in which the measurement of the gas component having bound oxygen has substantially no influence and the gas component to be measured cannot be reduced or decomposed substantially. While controlling, the atmosphere in the controlled first internal space is guided into the second internal space under a predetermined diffusion resistance from the first internal space, and in the second internal space, Reducing or decomposing the gas component to be measured existing in the atmosphere of the second internal space, and pumping out the oxygen generated at that time by the oxygen pumping action of the electrochemical cell, thereby producing the electric power. Check the pump current flowing through the chemical cell To, and is characterized in that for obtaining the measurement gas component of the measurement gas than the detected value.

According to another preferred embodiment of the measuring method according to the present invention, the amount of oxygen in the gas to be measured introduced into the first internal space is controlled, and An atmosphere having a substantially negligible oxygen concentration in one internal space is obtained.

According to another preferred embodiment of the measuring method according to the present invention, the control of the amount of oxygen in the gas to be measured in the first internal space is different from that of the electrochemical cell. It will be realized by the pumping action of oxygen by another different electrochemical cell.

In the measuring method according to the present invention, the gas to be measured including the gas component to be measured having the bound oxygen to be measured is supplied to the first internal space from the external gas existing space. And the oxygen partial pressure of the atmosphere in the first internal space is reduced by the pumping action of oxygen by the first electrochemical cell on the first internal space. Under the heating environment of the internal space, the gas component to be measured is controlled to a predetermined low value that cannot be substantially reduced or decomposed, and the atmosphere in the controlled first internal space is changed to a second value. The oxygen is pumped into the internal cavity by a predetermined diffusion resistance, and is further pumped by the oxygen pumping action of the second electrochemical cell to the second internal cavity. Oxygen partial pressure The measurement gas component in a heating environment of the cavity is controlled to a predetermined value reduction or may be decomposed,
By reducing or decomposing the gas component to be measured present in the atmosphere in the second internal space and simultaneously pumping out the oxygen generated at that time, the second electrochemical cell The gist of the present invention is also a measuring method characterized by detecting a pump current flowing by oxygen pumping and obtaining a measured gas component amount in a measured gas from the detected value.

Further, in the measuring method according to the present invention, the gas to be measured containing the gas to be measured having the bound oxygen to be measured is diffused into the first internal space from the external space where the gas to be measured exists. The oxygen partial pressure in the atmosphere in the first internal cavity is reduced by the pumping action of oxygen by the first electrochemical cell on the first internal cavity by conducting the resistance under the resistance.
In the heating environment of the first internal space, the gas component to be measured is controlled to a predetermined low value that cannot be substantially reduced or decomposed, while the atmosphere in the controlled first internal space is The second internal space, which is provided in communication with the first internal space and is filled with a porous body having a predetermined diffusion resistance, is further filled. Oxygen is pumped out by the pumping action of oxygen by the chemical cell, and the oxygen partial pressure in the atmosphere in the second internal space is reduced.
The gas component to be measured present in the atmosphere in the second internal space is reduced by controlling the gas component to be measured to a predetermined value at which the gas component to be measured can be reduced or decomposed under the heating environment of the second internal space. At the same time, by pumping out the oxygen generated at the same time, the pump current flowing when pumping oxygen by the second electrochemical cell is detected, and the detected value in the gas to be measured is determined based on the detected value. The gist of the present invention is also a measuring method characterized by obtaining a measured gas component amount.

According to a preferred aspect of the measuring method according to the present invention, the partial pressure of oxygen in the atmosphere in the first internal space is detected, and the power supply voltage is changed based on the detected value. By controlling the pumping action of oxygen by the first electrochemical cell, the oxygen partial pressure in the atmosphere in the first internal space is controlled to a predetermined constant value.

According to another preferred embodiment of the measuring method according to the present invention, the pumping of oxygen by the second electrochemical cell is performed by applying a voltage having a magnitude giving a diffusion limiting current of the gas component to be measured. Is performed by power supply from a constant voltage power supply that can apply
The oxygen partial pressure in the atmosphere in the second internal space is controlled.

Further, according to one advantageous aspect of the present invention, the heating temperature of the second internal space is equal to or higher than the heating temperature of the first internal space. Become.

According to still another advantageous embodiment of the present invention, the partial pressure of oxygen in the atmosphere in the second internal space is controlled by the partial pressure of oxygen in the atmosphere in the first internal space. It will be equal to or less than the pressure.

In the measuring method according to the present invention, the gas component to be measured having bound oxygen is advantageously any one of NOx, CO ₂ and H ₂ O.

The present invention also provides an apparatus for measuring a predetermined gas component in a gas to be measured as described below. It can be implemented.

That is, the apparatus for measuring a predetermined gas component in a gas to be measured according to the present invention reduces or decomposes a gas component to be measured having bound oxygen in the gas to be measured. A measurement device configured to determine the amount of the measured gas component in the measured gas by measuring the amount of oxygen to be measured, and a first internal space communicated with an external measured gas existing space; From the measured gas existing space,
A first diffusion-controlling means for introducing a gas to be measured containing the gas to be measured into the first internal space under a predetermined diffusion resistance; and a first oxygen ion conductive solid electrolyte and Using an electrochemical cell composed of a pair of electrodes provided, by applying a current between the pair of electrodes, oxygen is pumped into the first internal space, and the atmosphere in the first internal space is First oxygen pump means for controlling the oxygen partial pressure to a predetermined low value at which the measured gas component cannot be substantially reduced or decomposed; and a second oxygen pump means connected to the first internal space. A second internal cavity; second diffusion-controlling means for guiding a controlled atmosphere in the first internal cavity into the second internal cavity under a predetermined diffusion resistance; An electrode consisting of an ion-conductive solid electrolyte and a pair of electrodes provided in contact with it By using a chemical cell and energizing between the pair of electrodes, oxygen in the atmosphere in the second internal space is pumped out, and the oxygen partial pressure in such an atmosphere is reduced or the NOx component is reduced or decomposed. A second oxygen pump configured to control or obtain a predetermined value to reduce or decompose the NOx component present in the atmosphere in the second internal space and to pump out the oxygen generated at the same time. A measuring device for measuring a predetermined gas component in the gas to be measured, comprising: means; and current detecting means for detecting a pump current flowing by a pump operation of the second oxygen pump means. It is.

According to a preferred embodiment of the measuring device according to the present invention, a catalyst for reducing or decomposing the gas component to be measured to generate oxygen is disposed in the second internal space. Is done.

Further, according to another preferred embodiment of the measuring device according to the present invention, the catalyst includes the second internal pump of the pair of electrodes constituting an electrochemical cell in the second oxygen pump means. Also serves as an electrode arranged in the space.

According to still another preferred embodiment of the measuring device according to the present invention, the measuring device further comprises a sensor element having an integrated structure including the first and second oxygen ion conductive solid electrolytes, A structure in which the first and second internal spaces, the first and second diffusion rate controlling means, and the first and second oxygen pumping means are integrally provided in the sensor element. Will be adopted.

According to one of the advantageous aspects of the measuring device of the present invention, the sensor element has a narrow flat surface having a predetermined diffusion resistance and opening to the external space where the gas to be measured exists. Having a space, the first and second diffusion-controlling means are configured in the flat space, and the measured gas existing space opening side portion of the flat space is defined as the first internal space. Then, the first oxygen pump means is provided therein, and a portion of the flat space that is deeper than the first internal space is defined as the second internal space, and the second internal space is provided therein. A second oxygen pump means is provided.

According to another aspect of the measuring device according to the present invention, the first and second oxygen ion conductive solid electrolytes may be constituted by the same oxygen ion conductive solid electrolyte layer. Or different oxygen ion conductive solid electrolyte layers.

Further, in the measuring device according to the present invention, the opening of the flat space in the sensor element is filled with a porous body having a predetermined diffusion resistance, or the inside of the first internal space and A configuration in which the second internal space is filled with a porous body having a predetermined diffusion resistance is appropriately adopted.

In addition, according to a preferred aspect of the above-described measuring device of the present invention, a heating means capable of heating the first internal space and the second internal space to a predetermined temperature respectively is provided. Is advantageously employed, whereby the measuring device can be operated effectively even when the temperature of the gas to be measured is low, and the decomposition of a predetermined gas component in the gas to be measured is also advantageous. You can do it.

Further, in the present invention, in order to solve the above-mentioned problems, a sensor element having an integrated structure containing an oxygen ion conductive solid electrolyte is used, and a sensor to be measured is provided by a catalyst provided in the sensor element. A measuring device that reduces or decomposes a gas component having bound oxygen in a gas and measures the amount of oxygen generated at that time to obtain the gas component content in the gas to be measured. (A) a first internal space provided in the integrated structure of the sensor element and communicating with an external gas-existing space; and (b) a predetermined diffusion resistance from the gas-existing space. A first diffusion-controlling means for guiding a gas to be measured including the gas component to be measured to the first internal space; and (c) the first internal space in an integrated structure of the sensor element. And is provided separately from the first interior space. A second internal space in which the catalyst is disposed, and (d) a second diffusion for guiding an atmosphere in the first internal space to the second internal space under a predetermined diffusion resistance. Rate-controlling means; (e) heating means for heating each of the first and second internal cavities to a predetermined temperature; and (f) oxygen ion conductive solid electrolyte of the sensor element and Using an electrochemical cell consisting of a pair of electrodes provided in contact with, by energizing between the pair of electrodes, oxygen is pumped or pumped into the first internal space, A second step of controlling the oxygen partial pressure in the atmosphere in the one internal space to a predetermined low value at which the measured gas cannot be substantially reduced or decomposed under the heating environment of the first internal space. (G) oxygen ion transmission of the sensor element; Using an electrochemical cell consisting of a pair of electrodes provided in contact with the conductive solid electrolyte, by energizing between the pair of electrodes, oxygen in the atmosphere in the second internal space is pumped out, and the The oxygen partial pressure in the atmosphere is controlled to a predetermined value at which the gas component to be measured can be reduced or decomposed by the catalyst under the heating environment of the second internal space, and the second internal Second oxygen pump means for reducing or decomposing the gas component to be measured present in the atmosphere in the space, and for simultaneously pumping out the oxygen generated at that time; and (h) said second oxygen pump. The present invention also provides a measuring device having a current detecting means for detecting a pump current flowing by a pump operation of the means.

Similarly, in the present invention, an integrated sensor element containing an oxygen ion conductive solid electrolyte is used,
The measured gas component in the measured gas is reduced or decomposed by the catalyst provided in the sensor element, and the amount of oxygen generated at that time is measured to determine the measured gas component amount in the measured gas. (A) a first internal space provided in an integral structure of the sensor element and communicating with an external gas existence space, and (b) a measurement gas existence From a space, under a predetermined diffusion resistance, first diffusion-controlling means for guiding a measured gas containing a measured gas component having bound oxygen to be measured to the first internal space,
(C ′) a second internal space formed in the integral structure of the sensor element and communicating with the first internal space and having the catalyst disposed therein; and (d ′) the second internal space. (E) the first internal space and the second internal space are each filled with a predetermined amount of porous material having a predetermined diffusion resistance and filled in the space. A heating means capable of heating to a temperature, and (f) an electrochemical cell comprising the oxygen ion-conductive solid electrolyte of the sensor element and a pair of electrodes provided in contact with the solid electrolyte, and By energization, oxygen is pumped or pumped into and out of the first internal space, and the oxygen partial pressure in the atmosphere in the first internal space is increased under the heating environment of the first internal space. A predetermined low value at which the gas component to be measured cannot be substantially reduced or decomposed. Using a first oxygen pump means for controlling, and (g) an electrochemical cell comprising the oxygen ion conductive solid electrolyte of the sensor element and a pair of electrodes provided in contact with the solid electrolyte, and between the pair of electrodes. By pumping oxygen in the atmosphere in the second internal space, the oxygen partial pressure in the atmosphere is increased, and under the heating environment of the second internal space, the gas component to be measured is Is controlled to a predetermined value that can be reduced or decomposed, thereby reducing or decomposing the gas component to be measured existing in the atmosphere in the second internal space, and simultaneously pumping out the oxygen generated at that time. The gist of the present invention also relates to a measuring device having the second oxygen pump means as described above and (h) current detecting means for detecting a pump current flowing by the pump operation of the second oxygen pump means. Also It is.

According to a preferred embodiment of the measuring device according to the present invention, the measuring device further has an oxygen partial pressure detecting means for detecting an oxygen partial pressure in the atmosphere in the first internal space, By controlling the amount of electricity between a pair of electrodes of an electrochemical cell in the first oxygen pump means based on the oxygen partial pressure value detected by the oxygen partial pressure detection means, the first oxygen pump means It is configured to control the oxygen partial pressure in the atmosphere in the internal cavity, whereby the control of the oxygen partial pressure in the first internal cavity can be performed more accurately and easily.

According to another preferred embodiment of the measuring device according to the present invention, a reference gas existing space is provided in the integrated structure of the sensor element independently of the first and second internal spaces. And an oxygen ion conductive solid electrolyte extending between the reference gas existing space and the first internal space, and provided in contact with the solid electrolyte located in the reference gas existing space. The oxygen partial pressure detecting means is configured by an electrochemical cell including a reference electrode and a measurement electrode provided in contact with the solid electrolyte located in the first internal space,
At this time, the reference gas presence space is preferably
The sensor element is opened at an exposed portion of the atmosphere, and the atmosphere is introduced as a reference gas into the reference gas existing space through the opening.

Further, according to one preferred embodiment of the present invention, the electrochemical cell in the second oxygen pump means extends between the second internal space and the reference gas existing space. An oxygen ion conductive solid electrolyte present, a first pump electrode provided in contact with the solid electrolyte located in the second internal space, and a contact with the solid electrolyte located in the reference gas existing space. And a second pump electrode provided on the second oxygen pump means, and the oxygen ion-conductive solid electrolyte in the electrochemical cell of the second oxygen pump means and the electrochemical cell of the oxygen partial pressure detecting means. Since the oxygen ion conductive solid electrolyte in the static cell is composed of an integral oxygen ion conductive solid electrolyte, and the second pump electrode and the reference electrode provided on the solid electrolyte are a common electrode. Ah .

According to one advantageous aspect of the measuring device according to the present invention, the first cell disposed in the second internal space of the electrochemical cell constituting the second oxygen pump means. Are the same as those of the above-mentioned catalyst, and the manufacturing process of the device is simplified.

In the present invention, such a first pump electrode is advantageously made of a porous cermet comprising a metal and a ceramic capable of reducing or decomposing the gas component to be measured having the above-mentioned bound oxygen. With such an electrode structure also serving as a catalyst, reduction or decomposition of the gas component to be measured can be effectively performed.

According to one aspect of the present invention,
The catalyst is disposed in the second internal space in the vicinity of a first pump electrode of an electrochemical cell constituting the second oxygen pump means, or the second oxygen pump means It will be provided by being laminated on the first pump electrode of the electrochemical cell to be constituted.

According to another preferred embodiment of the measuring device according to the present invention, the heating means is disposed in the sensor element so as to be biased toward the second internal space. The second internal space is configured to be heated to a higher temperature than the first internal space. By disposing such a heating means, the second internal space can be maintained in an environment (particularly, a temperature) where the measured gas component can be easily reduced or decomposed.

Further, according to another preferred embodiment of the measuring apparatus according to the present invention, the diffusion resistance of the second diffusion-controlling means is made larger than the diffusion resistance of the first diffusion-controlling means. As a result, it is possible to effectively avoid the influence on the measured value of the gas component to be measured due to the clogging of the oil combustion material.

Furthermore, according to another advantageous embodiment of the measuring device according to the present invention, the gas component to be measured having bound oxygen is any one of NOx, CO ₂ and H ₂ O. Or

The present invention also provides a first oxygen pump means for controlling an oxygen partial pressure in a gas to be measured led from a space in which a gas to be measured exists to a predetermined value, and the first oxygen pump means. From the measured gas of the oxygen partial pressure controlled by
Oxygen in the gas to be measured is pumped out, and the oxygen partial pressure in the atmosphere is controlled to a predetermined value at which the NOx component can be reduced or decomposed, so that the oxygen exists in the atmosphere in the second internal space. A second oxygen pump means for reducing or decomposing the NOx component and simultaneously pumping out the oxygen generated at that time, and detecting a pump current flowing by the pump operation of the second oxygen pump means Accordingly, the gist of the present invention is a NOx sensor characterized in that the concentration of NOx present in the gas to be measured is obtained.

Further, the present invention comprises a solid electrolyte and a pair of electrodes provided in contact with the solid electrolyte, and one of the pair of electrodes is disposed in the first internal space into which the gas to be measured is introduced. The first electrochemical pump cell that has been, consisting of a fixed electrolyte and a pair of electrodes provided in contact with it,
One of the pair of electrodes has a second electrochemical pump cell disposed in a second internal cavity for NOx measurement, wherein the second internal electrode of the second electrochemical pump cell is provided. The NOx reducing power of the electrode disposed in the void is configured to be stronger than the NOx reducing power of the electrode disposed in the first internal void, and the NOx reducing power is reduced by the first electrochemical pump cell. A NOx sensor characterized in that the oxygen concentration in the first internal space is adjusted while the NOx concentration in the second internal space is detected by the second electrochemical pump cell. This is the gist.

According to one preferred embodiment of the NOx sensor according to the present invention, the first internal space and the second internal space are communicated with each other, and An atmosphere having an oxygen concentration adjusted by a dynamic pump cell is led from the first internal space to the second internal space.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, in order to clarify the present invention more specifically, the present invention will be described with reference to a specific example of NOx measurement shown in the drawings, which targets NOx as a gas component to be measured. The configuration will be described in detail.

First, FIGS. 1 and 2 show a typical example of a NOx sensor according to a measuring device according to the present invention, in which FIG. 1 is a plan view of such a sensor. FIG. 2 is an enlarged explanatory view of a main part in a section AA in FIG.

In these figures, reference numeral 2 denotes a sensor element having an elongated and long plate-like shape, and as shown in FIG. Solid electrolyte layers 4a, 4b, 4c, 4d,
4e and a plate-like body of an integral structure laminated. Each of the solid electrolyte layers 4a to 4e is formed by using a known oxygen ion conductive solid electrolyte material such as zirconia porcelain. In addition, the sensor element 2 having the integral structure is formed by integrally firing the unfired solid electrolyte layer laminate in the same manner as in the related art.
It will be manufactured.

In the sensor element 2 having such an integral structure, a first internal space 6 and a second internal space 8 each exhibiting a rectangular planar shape are provided on the tip end side of the second internal space. The reference air introduction passage 10 serving as a reference gas-existing space is provided separately from the first and second internal spaces 6 and 8 so as to be located separately from each other. Is provided so as to extend in the longitudinal direction of the sensor element 2, and the reference air introduction passage 10 is opened at an end on the base side of the sensor element 2 and communicates with the atmosphere. Here, the first and second internal spaces 6,
8 and the reference air introduction passage 10, the corresponding voids formed in the solid electrolyte layer 4b have upper and lower solid electrolyte layers 4a, 4c.
The cover is formed in a state where it is located on substantially the same plane. In addition, the first internal space 6
Is provided through the solid electrolyte layer 4a as a first diffusion-controlling means. The first diffusion-controlling passage 12 is a first diffusion-controlling means. An external gas to be measured is introduced into the first internal space 6 under a predetermined diffusion resistance. Further, a second diffusion-controlling means for connecting the two internal cavities 6 and 8 through the solid electrolyte layer 4b located between the first internal cavities 6 and the second internal cavities 8 A second diffusion-controlling passage 14 is provided. Through the second diffusion-controlling passage 14, the atmosphere in the first internal space 6 is
Under a predetermined diffusion resistance, it is guided into the second internal space 8.

Further, a portion of the solid electrolyte layer 4a exposed in the first internal space 6 is provided with an inner electrode (pump electrode) 16 made of a rectangular porous Pt electrode in contact therewith. The solid electrolyte layer 4 corresponding to the inner electrode 16
An outer electrode (pump electrode) 1 made of a porous Pt electrode having a similar rectangular shape so as to be in contact with the outer surface portion of a.
An electrode 8 is provided, and the electrodes 16, 18 and the solid electrolyte layer 4a constitute an electrochemical cell in the first oxygen pump means, that is, a first electrochemical pump cell. Accordingly, by applying a desired voltage between the two electrodes 16 and 18 of the first electrochemical pump cell by the external variable power supply 20 and flowing a current in a predetermined direction, the first internal space is formed. Oxygen in the atmosphere in the internal space 6 is pumped out to the external gas-existing space, or conversely, oxygen is pumped into the first internal space 6 from the external gas-existing space. It has become. Here, the porous Pt electrode is formed of a cermet electrode composed of Pt as an electrode metal and ZrO ₂ as a ceramic.

Further, a portion of the solid electrolyte layer 4c exposed in the first internal space 6 is provided with a measuring electrode 22 made of a rectangular porous Pt electrode in contact therewith, A reference electrode 24 made of a similar porous Pt electrode is provided in contact with a portion of the electrolyte layer 4c exposed in the reference air introduction passage 10, and the measurement electrode 22, the reference electrode 24, and the solid electrolyte layer 4c constitutes an electrochemical cell as an oxygen partial pressure detecting means, that is, an electrochemical sensor cell, and as is well known, the atmosphere in the first internal space 6 and the reference air introduction passage 1
The electromotive force generated between the measurement electrode 22 and the reference electrode 24 is measured by the potentiometer 26 based on the oxygen concentration difference between the reference air in the zero and the first internal space. The oxygen partial pressure in the atmosphere in 6 is detected. Then, the voltage of the variable power supply 20 is controlled based on the value of the oxygen partial pressure in the atmosphere in the first internal space 6 detected by the potentiometer 26, so that the first internal space 6 That is, the oxygen partial pressure in the internal atmosphere can be maintained at a constant value.

Further, a rectangular internal pump electrode (first pump electrode) 28 is provided on and in contact with the solid electrolyte layer 4 c so as to be located in the second internal space 8. I have. The internal pump electrode 28 is formed of a porous cermet composed of Rh, which is a metal capable of reducing NOx, and zirconia as a ceramic, thereby reducing NOx present in the atmosphere in the second internal space 8. While functioning as a NOx reduction catalyst that can be used, a constant voltage is applied from a constant voltage power supply 30 to a reference electrode (second pump electrode) 24 disposed in the reference air introduction passage 10, whereby a second voltage is applied. The oxygen in the atmosphere in the internal space 8 is pumped into the reference air introduction passage 10. Accordingly, the reference electrode 24 also functions as one of the pump electrodes, and the reference electrode 24, the internal pump electrode 28, and the solid electrolyte layer 4c provide an electrochemical cell that provides a second oxygen pump means, that is, a second electrochemical cell. This constitutes an electrochemical pump cell. Then, the pump current flowing by the pump operation of the electrochemical pump cell, in other words, the second oxygen pump means is detected by the ammeter 32. Note that the constant voltage power supply 30 described above supplies a limiting current to pumping of oxygen generated at the time of NOx decomposition in the second electrochemical pump cell under the restricted NOx inflow through the second diffusion control passage 14. A voltage of a given magnitude can be applied.

In the sensor element 2, an alumina insulating layer 34 is integrally laminated in a form sandwiched between the solid electrolyte layers 4c and 4e and surrounded on three sides by the solid electrolyte layer 4d. In this alumina insulating layer 34,
A heater 36 that generates heat by external power supply is embedded. As shown in FIG. 2, the heater 36 is provided in the second internal space 8 located on the tip side of the sensor element 2.
The second internal space 8 has a higher temperature than the first internal space 6, in other words, the internal pump electrode 28 has a higher temperature than the inner electrode 16 and the measurement electrode 22. Is heated to a higher temperature. For example, when the gas temperature of the gas to be measured changes between 300 ° C. and 850 ° C., the inner electrode 16 and the measuring electrode 22 in the first internal space 6 become 400 ° C. to 600 ° C., and 700 ° C. to 900 ° C. when the internal pump electrode 28 in the internal space 8 is
The heater 36 is arranged so that the heater 36 can be heated.

In the sensor element 2 having such a configuration, the tip end side is arranged in the space where the gas to be measured is present. Through the diffusion-controlling passage 12 of
Under a certain diffusion resistance, it is led into the first internal space 6. The gas to be measured guided into the first internal space 6 is generated by applying a predetermined voltage between the two electrodes 16 and 18 constituting the first electrochemical pump cell. Due to the oxygen pumping action, the oxygen partial pressure is controlled to a predetermined value, for example, 10 ⁻⁶ atm.

Incidentally, in order to maintain the oxygen partial pressure in the atmosphere in the first internal space 6 at a predetermined constant value, as described above, based on the well-known Nernst equation,
The electromotive force between the measurement electrode 22 and the reference electrode 24 in the electrochemical sensor cell is measured by a potentiometer 26, and the two electromotive forces of the first electrochemical pump cell are set to, for example, 203 mV (500 ° C.). A method of controlling the voltage (variable power supply 20) applied between the electrodes 16 and 18 is adopted, whereby the target oxygen partial pressure of 10 ⁻⁶ atm can be easily controlled. That is, the voltage of the first electrochemical pump cell may be controlled so that the electromotive force corresponds to the difference between the desired oxygen concentration in the first internal space 6 and the oxygen concentration of the reference air. The first diffusion-controlling passage 12 narrows the amount of oxygen in the gas to be measured that diffuses and flows into the measurement space (first internal space 6) when a voltage is applied to the first electrochemical pump cell. , And functions to suppress the current flowing through the first electrochemical pump cell.

In the first internal space 6, NOx in the atmosphere is reduced by the inner electrode 16 and the measuring electrode 22 even under the heating environment by the external gas to be measured and the heating environment by the heater 36. A state under an oxygen partial pressure that is not performed, for example, a state under an oxygen partial pressure at which a reaction of NO → １ ／ N ₂ + ／ O ₂ does not occur, is formed. Gas to be measured (atmosphere) in the first internal space 6
When NOx in the inside is reduced, N in the second internal space 8 is reduced.
This is because accurate measurement of Ox cannot be performed, and in this sense, components involved in the reduction of NOx (at least components of the inner electrode 16 of the first electrochemical pump cell) in the first internal space 6. Therefore, it is necessary to form a situation where NOx cannot be reduced.

In this way, the first internal space 6
The measured gas whose oxygen partial pressure is controlled
Through the speed passage 14, under a predetermined diffusion resistance,
It will be guided into the space 8. And the second inside
The gas to be measured introduced into the space 8 is
Pump electrode 28 and a reference
Between the pole 24, oxygen is removed from the second internal space 8 by reference air.
A predetermined voltage, for example, in the direction of pumping to the introduction passage 10 side
For example, 449mV (700 ° C) is applied.
Therefore, it is pumped by oxygen,
In the internal space 8 of the internal pump electrode 28, in particular,
At the phase interface, the oxygen concentration further decreases, and the oxygen concentration becomes 1
0^-Ten atm and also functions as a NOx reduction catalyst
NOx is reduced around the internal pump electrode 28.
State, for example, NO → 1 / 2N _Two + 1 / 2O_Two reaction
Is controlled under the circumstances in which is caused. At this time,
The current flowing through the second electrochemical pump cell is
Oxygen concentration in the atmosphere led to the void 8, ie, the first interior
The oxygen concentration in the atmosphere in the space 6 and the internal pump electrode 28
Is proportional to the sum of the concentration of oxygen generated by reduction of NOx
The atmosphere in the first internal space 6 is obtained.
Since the oxygen concentration in the air is controlled at a constant level,
The current flowing through the second electrochemical pump cell is NO
It will be proportional to the concentration of x. And that NOx
The concentration of NOx is restricted in the second diffusion control passage 14.
And thus the NOx concentration
Can be measured.

For example, if the oxygen concentration in the atmosphere in the first internal space 6 is 0.02 ppm and the NO concentration of the gas to be measured is 100 ppm, the oxygen concentration generated by reduction of NO is 50 ppm and the first concentration is 50 ppm. A current corresponding to the sum of the oxygen concentration in the atmosphere in the internal space 6 and the oxygen concentration of 0.02 ppm: 50.02 ppm flows. Therefore, the pump current value in the second electrochemical pump cell is almost NO. It indicates the reduced amount and therefore does not depend on the oxygen concentration in the gas to be measured.

Here, the principle of the present invention will be described in more detail with reference to FIG. In FIG. 24, the gas to be measured is introduced into the first internal space 6 through the first diffusion-controlled passage 12, and the oxygen partial pressure in the first internal space 6 is controlled by the oxygen concentration control means. Barrel first electrochemical pump cell 5
6 is controlled to a predetermined, preferably low value at which NOx is not reduced. Then, the atmosphere in the first internal space 6 whose oxygen partial pressure is controlled becomes the second internal space 8 communicating with the first internal space 6 via the second diffusion-controlling passage 14. And the NOx is reduced in the second internal space 8, and the oxygen generated at that time is converted into the second internal space 8 using the second electrochemical pump cell 58 under gas diffusion controlled conditions. Pumping the second electrochemical pump cell 58
, The amount of NOx in the gas to be measured is measured.

In this method, the NOx concentration: Cn
= K · Ip ₃ -A. Where K is a sensitivity coefficient,
Ip ₃ is a current value flowing through the second electrochemical pump cell 58, and A is a constant caused by a small amount of oxygen remaining in the first internal space 6. Here, most of Ip ₃ is due to oxygen generated by the decomposition of the NOx component in the gas to be measured. Compared with the conventional method, Ip ₃ is obtained in a state in which the influence of oxygen in the gas to be measured is excluded. It can accurately measure even small amounts of NOx. The outer electrode provided opposite to the electrode exposed to the internal space only needs to be in a state capable of releasing oxygen, and may be in air, for example.

By the way, FIG. 3 shows a first embodiment of a control electrode heating temperature and the partial pressure of oxygen in the internal space, where also at a temperature of 1400 ° C., ZrO ₂
A cermet-shaped Pt electrode having a volume ratio of ZrO ₂ and Pt of 40:60 co-fired with the substrate, and ZrO ₂ and R
For cermet-shaped Rh electrodes having a volume ratio of h of 40:60, the reducibility of NO to oxygen partial pressure and temperature of the electrodes is shown. As is apparent from FIG.
It is understood that the electrode does not exhibit reducing properties unless it is under a high temperature and a low oxygen partial pressure, whereas the Rh electrode exhibits a reducing action under a low temperature and a high oxygen partial pressure.

The present invention makes use of the above-mentioned properties, wherein the oxygen concentration in the first internal space 6, the temperature,
Specifically, the temperature of the Pt electrode (the inner electrode 16 and the measurement electrode 22) disposed in the first internal space 6, that is, the temperature of the first electrode is a region where NO is not reduced by the first electrode. Is set and controlled. For example, as shown in the figure, when the oxygen partial pressure in the first internal space ⁶ is set to 10 ⁻⁶ atm, the gas temperature of the gas to be measured becomes 900 ° C. (substantially the highest temperature of the exhaust gas temperature of the automobile). Even so, the arrangement and the electric power of the heater 36 are set so that the temperature in the first internal space 6 becomes 650 ° C. or less. Then, the measured gas whose oxygen partial pressure has been controlled to 10 ⁻⁶ atm passes through the second diffusion-controlled passage 14 and enters the second internal space 8.
In the second internal space 8, a voltage of 450 mV is applied between the internal pump electrode 28 and the reference electrode 24, and oxygen is pumped from the second internal space 8 into the reference air introduction passage 10. The partial pressure of oxygen at the three-phase interface of the internal pump electrode 28 is set to approximately 10 ⁻¹⁰ atm (the electromotive force between the internal pump electrode 28 and the reference electrode 24 corresponds to 450 mV). Thus, as shown in FIG. 3, the Rh electrode as the internal pump electrode 28, that is, the second electrode is 10 ^-10 at.
Under an oxygen partial pressure of m, NO can be reduced at 410 ° C. or higher, and the temperature of the second internal space 8, specifically, the temperature of the internal pump electrode 28 as the second electrode is determined by the temperature of the gas to be measured. Even when the gas temperature is 300 ° C. (substantially the lowest temperature of the exhaust gas of the automobile), the arrangement of the heater 36 and the electric power are set so as to be 410 ° C. or more. Thus, at the three-phase interface of the internal pump electrode 28 as the second electrode, NO is reduced, and a current flows due to the generation of oxygen by the reduction, and the current value is proportional to the NO concentration. .

That is, in the above-mentioned first specific example, the oxygen partial pressure in the first internal space 6 becomes 10 ⁻⁶ atm,
Further, the oxygen partial pressure at the three-phase interface of the second internal space 8, especially the three-phase interface of the internal pump electrode 28 (second electrode) is controlled to 10 ^-10 atm, and the first internal space 8 is controlled. 6, the temperature of the inner electrode 16, the measuring electrode 22, and the temperature of the internal pump electrode 28 provided in the second internal space 8 are determined by the total change width of the exhaust gas temperature of the automobile, for example, 300 ° C. to 900 ° C.
In the range of ° C., the inner electrode 16 and the measuring electrode 22
The arrangement and the power of the heater 36 are set so that the temperature of the internal pump electrode 28 becomes 410 ° C. or higher at 0 ° C. or lower.

The temperature of the sensor element 2 is controlled by the heater 36.
The target temperature can be set to a target temperature by controlling the power of the gas according to the temperature of the gas to be measured, for example, the temperature of the exhaust gas. From where it gets lower towards the end,
When the heater 36 is arranged close to the element tip side, the temperature on the tip side is likely to be higher. Therefore, the second internal space 8 in which the internal pump electrode 28 is arranged is located on the element tip side, and the inner electrode 16 and the measurement electrode 22 are arranged. Is arranged at a distance from the element tip, the above-mentioned temperature setting can be easily performed only by applying a predetermined voltage without controlling the heater power. I can do it.

Further, FIG. 4 shows a specific example for explaining the setting of the arrangement of the heaters in the sensor element. That is, in FIG. 4, width: 4.2 mm, thickness:
In a ZrO ₂ solid electrolyte substrate having a length of 1.3 mm and a length of 62 mm, the size of the heat generating portion is 3.6 mm in width and 5 m in length.
m and a normal temperature resistance: 8 Ω, a platinum heater embedded at a position 1 mm to 6 mm from the tip of the element was attached to an exhaust pipe of an automobile.
The position and temperature from the tip of the sensor element when a voltage of V is applied and the gas is exposed to exhaust gas at 300 ° C. and 900 ° C. are shown.

As is apparent from FIG. 4, the position where the maximum temperature of the exhaust gas is 900 ° C. and the temperature of the sensor element is 650 ° C. or less is 5.2 mm or more from the tip of the element.
In this area, the first electrode (the inner electrode 16, the measuring electrode 2)
2) while the lowest gas temperature of 300 ° C. at 410 ° C.
Since the position where the temperature is higher than 0 ° C. is a position of 0 to 6.2 mm, the second electrode (internal pump electrode 28)
Is arranged, it is possible to realize the NOx sensor according to the present invention capable of setting the temperature as shown in FIG. The setting of the temperature distribution in the sensor element can be arbitrarily performed by appropriately selecting the power (resistance value), the size (length), and the arrangement position of the heater.

FIG. 5 shows the NO concentration and the pump current value (diffusion limit current value: I
The relationship of p) is shown, where the pump current value (Ip) changes linearly with the change in NO concentration. Therefore, the NO concentration can be easily known by measuring the Ip value. in this case,
When NO = 0 ppm, the Ip value is 0.03 μA, which is the oxygen concentration in the atmosphere in the first internal space 6: 10
^This is a pump current required to pump out oxygen corresponding to a difference between ^-6 atm and the atmosphere in the second internal space 8, that is, the oxygen concentration at the three-phase interface of the internal pump electrode 28: 10 ^-10 atm. This pump current has a sensitivity of 30 μA / 2000 pp
Considering m = 0.015 μA / ppm, several tens of ppm
Although it does not hinder the concentration measurement of
The measurement of the pm NO concentration may be a problem as an error factor. For this reason, it is preferable that such a pump current value is as close as possible to zero, and such a pump current value indicates a partial pressure of oxygen in the atmosphere in the first internal space 6 as NO.
In a situation where x cannot be substantially reduced, the oxygen partial pressure in the atmosphere in the first internal space 6 and the oxygen in the atmosphere in the second internal space 8 should be reduced as much as possible. This is realized by making the partial pressure equal to the partial pressure of oxygen at the three-phase interface in the internal pump electrode 28.

FIG. 6 shows a second specific example relating to the control of the oxygen partial pressure in the two internal cavities and the control of the temperature of each electrode heated in those two cavities. There, the oxygen partial pressure in the first internal space 6 and the oxygen partial pressure in the second internal space 8, that is, the oxygen partial pressure at the three-phase interface of the internal pump electrode 28 as the second electrode, are both increased. , Set to 10 ^-8 atm. Then, the heater 3 is set so that the first electrode (the inner electrode 16 and the measurement electrode 22) has a temperature of 490 ° C. or lower and the second electrode (the internal pump electrode 28) has a temperature of 430 ° C. or higher.
6 is set.

FIG. 7 shows the relationship between the NO concentration and the pump current (Ip) in the NOx sensor controlled as described above. Here, the oxygen partial pressure in the first internal space 6 and the oxygen partial pressure at the three-phase interface of the second electrode (internal pump electrode 28) in the second internal space 8 are set to the same value. Therefore, when NO = 0 ppm, the Ip value is 0
μA.

FIG. 8 shows a third specific example relating to the control of the oxygen partial pressure and the electrode heating temperature, in which the first electrode (the inner electrode 16 and the measuring electrode 22) and the second electrode are controlled. The two electrodes (internal pump electrode 28) are both composed of Pt electrodes, and the oxygen partial pressure in the first internal space 6 and the second electrode ( The oxygen partial pressure at the three-phase interface of the internal pump electrode 28) is 10 ⁻⁶ at.
m. And the first electrode is 65
The heater 36 is set so that the temperature is lower than 0 ° C. and the temperature of the second electrode is 650 ° C. or higher.

FIG. 9 shows a fourth specific example relating to the control of the oxygen partial pressure and the electrode heating temperature, in which the first electrode (the inner electrode 16 and the measuring electrode 22) and the second electrode are controlled. The two electrodes (internal pump electrode 28) are both composed of Pt electrodes, and the oxygen partial pressure in the first internal space 6 is set to 10 ⁻⁶ atm and the second internal space 8 Oxygen partial pressure in the
Specifically, the oxygen partial pressure at the three-phase interface of the second electrode (the internal pump electrode 28) is set to 10 ⁻¹⁰ atm. The heater 36 is set so that the temperature of the first electrode is 650 ° C. or lower and the temperature of the second electrode is 430 ° C. or higher.

In the case of the fourth example, NO =
At 0 ppm, the pump current flows as described above. If the oxygen partial pressure at the phase interface is kept constant, it is easy to calibrate since it becomes a constant value. FIG. 10 shows the relationship between the NO concentration and the pump current in the NOx sensor according to the fourth specific example.

As described above, in the above-described embodiment of the present invention, the gas to be measured is introduced into the first internal space, where the oxygen partial pressure at which NOx is not reduced is determined. While setting the temperature, the oxygen concentration in the gas to be measured is controlled to a constant value by the oxygen pumping operation of the first electrochemical pump cell, while the gas to be measured having a constant oxygen concentration in the first internal space. Is introduced into the second internal space, and the temperature and oxygen concentration at which NOx is reduced at the three-phase interface of the NOx reduction catalyst (internal pump electrode = first pump electrode) arranged in the second internal space are determined. Setting, operating the second electrochemical pump cell to perform oxygen pumping, and measuring the pump current proportional to the NOx concentration in the second electrochemical pump cell. NOx without receiving Than it was decided that it is possible to effectively measure.

Further, the above-mentioned N which is a measuring device according to the present invention is
In the Ox sensor, since the first internal space is disposed behind the first diffusion-controlling passage (means), and the second diffusion-controlling passage (means) is further disposed behind the first internal space, the oil combustion Even if clogging by an object occurs in the first diffusion-controlled passage, clogging is unlikely to occur in the second diffusion-controlled passage. Then, the diffusion resistance of the first diffusion-controlled passage: D1
And the diffusion resistance of the second diffusion-controlled passage: D2 by taking into account the change α of the diffusion resistance due to clogging, D1 + α≪
By setting the relationship of D2, the NOx measurement value due to clogging has no effect. In other words, with this setting, even if clogging occurs in the first diffusion-controlled passage, only the pump current for keeping the oxygen concentration in the first internal space constant decreases, and NOx Since the substantial diffusion-controlling section is the second diffusion-controlling path, there is no effect on the measured value.

In the specific example described above, the first electrodes (16, 22) arranged in the first internal space 6 are composed of Pt cermet electrodes, and the second internal space 8 The second electrode (28) disposed therein may be constituted by a Rh cermet electrode, or the first and second electrodes may be both
Although it is composed of a Pt cermet electrode, it is not necessarily limited to such an electrode configuration.
For example, if a cermet electrode of Au or an alloy of Au and Pt is used for the first electrode and a Rh cermet electrode is used for the second electrode, the reducing property of the Au / Pt cermet electrode is reduced,
The degree of freedom in setting the oxygen partial pressure and the temperature in the first internal space is increased, which is preferable. In addition, the electrode metal of such an electrode can be appropriately selected from known ones. For example, the first and second electrodes are both Au electrodes and the second Au electrode And Rh or Pt
The electrode or the porous body of ceramics such as alumina
Laying and arranging a catalyst body supporting Ox reduced metal,
While both the first and second electrodes are Pt electrodes, an Rh catalyst electrode may be disposed on the second Pt electrode, or only the temperature of the first and second electrodes may be different. Is possible.

In any case, it is desirable that the first and second electrodes are cermet electrodes composed of an electrode metal and appropriate ceramics.
When the second electrode also serving as the Ox reduction catalyst is used, it is preferable to use a porous cermet electrode made of a known metal capable of reducing NOx, such as Rh or Pt, and ceramics. Further, the NOx reduction catalyst is close to an internal pump electrode 28 disposed in the second internal space 8 in the second electrochemical pump cell for pumping oxygen in the second internal space 8. As shown in FIG. 11, porous alumina or the like carrying a NOx reduction catalyst made of Rh or the like is laminated on the first pump electrode 28 by printing or the like. May be configured. Further, in the sensor element as shown in FIG. 11, the heater 36 is disposed on the side of the second internal space 8, and the temperature of the second internal space 8 is higher than that of the first internal space 6. From where it is going to be heated,
That is, the NOx reduction catalyst 42 works more effectively.

In the present invention, when the exhaust gas with excess fuel is the target gas,
Since the amount of unburned components such as O and HC becomes large and the reaction with NOx causes a measurement error, for example, as shown in FIG. It is preferable to fill the oxidation catalyst body 38 composed of the following to oxidize unburned components such as CO and HC in the gas to be measured in the first internal space 6. In this case, the polarity of the first electrochemical pump cell is opposite to that in the case of excess air, and the direction is to take oxygen from the gas atmosphere to be measured into the first internal space 6. By arranging the oxidation catalyst body 38 in the first internal space 6 in this manner, even if the gas to be measured is in an atmosphere with excess air, it is possible to eliminate the influence of the reducing gas such as CO and HC. It is valid.

The arrangement of the oxidation catalyst body 38 in the first internal space 6 does not necessarily have to be the filling as shown in the example.
Up to the solid electrolyte layer 4c or the inner electrode 16
It may be printed on top. That is, by the time the gas to be measured reaches the second internal space 8, C
It is only necessary to oxidize unburned components such as O and HC.

Further, in order to realize such an oxidation reaction, it is not always necessary to dispose the oxidation catalyst 38.
It goes without saying that if the inner electrode 16 has an oxidation catalytic property, the oxidation reaction is promoted. It can also be achieved by setting the oxygen partial pressure and temperature of the above and the conditions under which these unburned components can be oxidized. The conditions also include a condition that is advantageous for NOx measurement, that is, an oxygen partial pressure that is as low as possible and is close to the oxygen partial pressure of the second internal space 8 without reducing NOx. For example, at 500 ° C., 10 ^-10 atm or more, 6
If it is 00 ° C., it can be sufficiently oxidized if it is 10 ⁻¹⁵ atm or more.

In such a NOx measuring method, N
Prior to the measurement of the NOx amount by the reduction of Ox, the atmosphere of the gas to be measured is adjusted in the first internal space 6 and the NOx is measured.
By setting the atmosphere effective for measuring the amount of x, specifically, the oxygen is pumped from the atmosphere in the first internal space 6 by the pumping action of oxygen by the first electrochemical cell. Carbon monoxide (CO) or hydrocarbon (H) which is pumped or pumped and has a constant value as close as possible to the oxygen partial pressure of the second internal space 8 and is contained in the gas to be measured.
The value is controlled to a value at which the unburned components such as C) are oxidized.
In this way, oxidation of unburned components such as carbon monoxide (CO), hydrocarbons (HC), etc. is performed, thereby avoiding a reaction between such unburned components and NOx. , NOx concentration can be measured more accurately. When measuring the NOx concentration in the gas burned under the condition of excessive fuel, the unburned components such as carbon monoxide and hydrocarbons become extremely large, and avoidance of the reaction with the unburned components is required. This is particularly effective for the gas to be measured.

The oxidation of the unburned components in the gas to be measured as described above is caused not only in the case of exhaust gas having excess fuel, but also in the case of
It is needless to say that even in the case of exhaust gas with insufficient fuel, it is effective in removing the influence of the slightly remaining unburned component on the measured value.

Further, as shown in FIG. 13, the oxidation catalyst body 38 is disposed on the solid electrolyte layer 4a so as to be located at the portion of the first diffusion-controlled passage 12 on the side of the space under the gas to be measured. It can also be arranged in layers, in which case
In removing errors due to CO and HC when air is excessive,
Mainly effective. However, when the fuel is excessive, the amount of CO and HC cannot be oxidized completely because the amount of oxygen in the gas to be measured is too small. Further, in the arrangement form of the oxidation catalyst as shown in FIG. 14, the solid electrolyte layers 4f and 4g are further laminated on the outside of the solid electrolyte layer 4a, and the gas introduction path 40 is provided. A medium 38 can also be arranged. In this case, since the oxidation catalyst body 38 is arranged at a higher temperature portion than in the example of FIG.
There is an advantage that oxidation of O, HC and the like is further promoted.

Further, in the second internal space 8, N
In order to control the oxygen concentration at the three-phase interface of the second electrode (28) also serving as the Ox reduction catalyst, not only the example of pumping oxygen from the second electrode (28) to the reference electrode 24 side, An electrochemical pump cell is configured between the outer electrode 18 of the first electrochemical pump cell and the second electrode (28), and oxygen in the second internal space 8 is supplied to the outer electrode 18 side. A method of pumping may be employed, or an electrode for pumping oxygen may be provided separately from the NOx reduction catalyst electrode (28) in the second internal space 8, and the NOx reduction catalyst electrode and the reference electrode may be provided. Based on the electromotive force between the NOx reduction catalyst electrode and the pumping electrode, the pumping electrode is pumped from the pumping electrode to the reference electrode 24 side, to the outer electrode 18 side, or to a separately provided pumping-dedicated electrode. Oxygen concentration at the interface Control or the method can also be employed.

Further, as a method of controlling the oxygen partial pressure in the first internal space 6, a method of changing the applied voltage throughout based on the detection value of the electromotive force by the electrochemical sensor cell as in the above example is used. In addition, a method of applying a constant voltage between the pair of electrodes 16 and 18 of the first electrochemical pump cell,
Alternatively, there is no problem even if one electrochemical cell is time-divided and used as a pump cell and a sensor cell.

The reference electrode 24 does not necessarily need to be communicated with the atmosphere through the reference air introduction passage 10, and forms a space for storing oxygen pumped from the second electrode (28). It is also possible to arrange the reference electrode 24 in the space.

Further, in the present invention, the second internal space and the second diffusion-controlling means may be constituted by a space filled with a porous body. More specifically,
Second internal space 8 in sensor element 2 shown in FIG.
Instead of the configuration of the second diffusion control passage 14, the configuration as shown in FIG. 15 can be adopted. That is, a second diffusion-controlling means made of a porous body 44 such as porous alumina is filled in the space following the first inner space so as to be in contact with the first inner space 6. Thereby, a second internal space is formed at the same time, and the shape of the internal space is simplified. Here, the diffusion resistance of the second diffusion-controlling means (44) is configured to be larger than the diffusion resistance of the first diffusion-controlling passage 12, and the atmosphere in the first internal space 6 is controlled. However, it is not affected by the atmosphere in the second internal space.

The filling of the porous body 44 may be performed by printing on the inner pump electrode 28 as shown in FIG. With such a configuration, the porous body 44 serves as the second diffusion-controlling means, and the porous body itself substantially serves as the second internal space and is filled in the internal space.

In the sensor element 2 having such a configuration, the first electromotive force between the measurement electrode 22 and the reference electrode 24 in the first internal space 6 is set to 203 mV (500 ° C.). Two electrodes 1 of one electrochemical pump cell
The voltage applied between the internal pump electrodes 6 and 18 is controlled, and the electromotive force between the internal pump electrode 28 and the reference electrode 24 constituting the second electrochemical pump cell is 449 mV.
In the state where the predetermined voltage is controlled to be (700 ° C.), as shown in FIG. 16, the NO concentration and the pump current (Ip) change linearly. Therefore, the NO concentration can be known by measuring the Ip value.

In addition to the structure of the sensor element shown in FIG. 15, a NOx reduction catalyst may be carried in the porous structure of second diffusion Even if an oxidation catalyst for oxidizing unburned components such as CO and HC is provided, the same NO detection characteristics can be obtained, and various configurations can be added as necessary. It is.

Further, the electrodes (16, 22) arranged in the first internal space 6 and the electrode (28) in the second internal space (second diffusion-controlling means 44) are connected to their NOx. The reducing power is selected and used as appropriate so that the relationship of “reducing (electrode in the first internal space 6) ≦ (electrode in the second internal space) strong” is satisfied. In addition, a NOx reduction catalyst layer may be provided on the electrode (28) in the second internal space.

The position of the reference electrode, the reference gas introduction hole, and the type of the reference gas are such that the electromotive force between the measurement electrode and the reference electrode in the first internal space 6 is in a range according to the Nernst equation. Are appropriately selected.

As for the heating means, the relationship between the electrode temperature in the first internal space 6 and the electrode temperature in the second internal space (second diffusion control means 44) is “low (second). Electrode in one internal space 6) <(electrode in second internal space) higher.

Furthermore, in the NOx sensor according to the present invention, the sensor element is formed in a narrow flat space having a predetermined diffusion resistance and provided in the sensor element so as to open to the external space where the gas to be measured exists. It is also possible to configure the first diffusion rate controlling means and the second diffusion rate controlling means, an example of which is shown in FIG.

That is, in FIG. 17, the sensor element 2 has six oxygen ion conductive solid electrolyte layers 4a, 4b, 4c, 4h,
d and 4e, and is a plate-like body having an integral structure which is laminated, and among the plurality of solid electrolyte layers, the tip of the second solid electrolyte layer 4b from the top in the figure is:
By being cut out in a rectangular shape over a predetermined length, a narrow flat space 50 having a predetermined diffusion resistance and opening at the front end of the sensor element 2 has a predetermined width and a predetermined width. In the direction over a predetermined length. In short, the flat space 50 has a long rectangular plane shape, and one short side of the flat space 50 is opened to the external space where the gas to be measured exists.

An external gas to be measured is introduced into the flat space 50 through the opening, and is allowed to reach a deep portion of the flat space 50 under a predetermined diffusion resistance. Thus, such a flat space 50 itself constitutes the first diffusion rate controlling means and the second diffusion rate controlling means. In addition, the flat space 50 is provided with an inner electrode (pump electrode) 16 constituting the first electrochemical pump cell at an opening side portion thereof, so that the portion becomes the first internal space 6. On the other hand, a portion of the flat space 50 deeper than the first internal space 6 is defined as a second internal space 8, where the internal pump electrode 2 constituting the second electrochemical pump cell is provided.
8 are provided.

In this case, the reference air introduction passage 10
Is formed by a cutout portion of the solid electrolyte layer 4h, is opened at an end on the base side of the sensor element 2, and is communicated with the atmosphere. Further, a reference electrode 24 is disposed in the reference air introduction passage 10, and an electrochemical sensor cell is formed between the reference electrode 24 and the measurement electrode 22 provided in the flat space 50. Also function, and together with the internal pump electrode 28, constitute a second electrochemical pump cell.

The other parts of the NOx sensor shown in FIG. 17 are the same as the sensor element structure of the NOx sensor shown in FIG. 2 described above. It is omitted. Further, the flat space 50 provided in the sensor element 2 and the reference air introduction passage 1
0 is specifically shown in FIG. 10 and FIG. 11 of Japanese Patent Publication No. 5-18059, and with reference to those figures, the sensor element structure of FIG. It should be.

FIG. 18 shows a modification of the sensor element 2 shown in FIG. 17 described above. In the modification, a porous material having a predetermined diffusion resistance The body 52 is filled. Through such a porous body 52, the gas to be measured is supplied from the external gas existence space to the flat space 5 under a predetermined diffusion resistance.
0, and oxygen pumping by the first oxygen pump means is performed in the first internal space 6 formed by the opening side portion of the flat space 50.
A more reliable diffusion control for the first internal space 6 can be realized, and unburned components such as CO and HC
In the method (2), advantages such as effective oxidation can be obtained.

Further, in the above-described specific examples of the operation of the NOx sensor, in each case, a temperature difference is provided between the first internal space 6 and the second internal space 8 to effectively reduce NOx. Although a simple decomposition and reduction operation can be realized, it is not always necessary to provide a difference between the temperature of the atmosphere in the first internal space 6 and the temperature of the atmosphere in the second internal space 8. is there. For example, if it explains based on the example shown in FIG. 3, the temperature of the 1st internal space 6 and the 2nd internal space 8 will be described.
When both are set to 600 ° C., the Pt electrode (16) provided in the first internal space 6 cannot reduce NOx under an oxygen partial pressure of about 10 ⁻⁶ atm or more, while the second internal In the Rh electrode (28) provided in the space 8, 1
NOx is reduced under an oxygen partial pressure of 0 ^-5 atm or less. Therefore, the oxygen partial pressure in the atmosphere in the first internal space 6 is set to 10 ^-6 atm or more, and the oxygen partial pressure in the atmosphere in the second internal space 8 is set to 10 ^-5 atm or less. If set, NOx can be measured even at the same temperature of 600 ° C. in the first and second internal cavities 6 and 8.

As described above, the Au electrode, Au /
If an electrode having no NOx reducing property such as a Pt alloy electrode or an electrode having a low reducing property is employed, the temperature of the first internal space>
It is possible to measure NOx even under the condition of the temperature of the second internal space. For example, in the case of an alloy electrode containing 1% Au in Pt, even if the temperature is 800 ° C., NOx is not reduced at 10 ⁻¹⁵ atm.
By setting the temperature of the second internal space to 600 ° C. and the oxygen partial pressure to 10 ⁻¹⁰ atm at 00 ° C. and the oxygen partial pressure to 10 ⁻¹⁰ atm, NOx can be measured.

FIG. 19 shows the relationship between the electromotive force at 600 ° C. and the oxygen partial pressure. The first internal electrode is set so that the electromotive force of the measuring electrode 22 constituting the electrochemical sensor cell becomes 150 mV. If the oxygen partial pressure in the atmosphere in the space 6 is controlled, the oxygen partial pressure in the first internal space 6 is approximately 10 ^-4 atm, and therefore, the first internal In the space 6, NOx is not reduced. On the other hand, when 450 mV is applied to the internal pump electrode 28 disposed in the second internal space 8 constituting the second electrochemical pump cell, the oxygen partial pressure at the three-phase interface becomes approximately 10 ^-11 atm. Therefore, NOx is reduced at the internal pump electrode 28, and the oxygen generated at the time of the reduction can be detected as the pump current of the second electrochemical pump cell. NO controlled in this way
FIG. 20 shows the relationship between the NO concentration in the x sensor and the pump current (Ip).

In each of the above specific examples, NOx is targeted as the gas component to be measured. However, the present invention is, of course, affected by the oxygen present in the gas to be measured.
Other bound oxygen-containing gas components other than NOx, for example, H ₂ O
It and those that can be effectively applied to the measurement of CO ₂ or the like is of course place.

Incidentally, in the case of measuring H ₂ O (moisture) in the gas to be measured using the sensor element 2 as shown in FIGS. Is controlled to a value at which the oxygen partial pressure is as low as possible and H ₂ O is not decomposed, for example, 10 ⁻¹⁰ atm by pumping out oxygen by the first electrochemical pump cell. Next, the gas to be measured (the atmosphere in the first internal space 6) whose O ₂ concentration is controlled to a constant low value is supplied to the second diffusion-controlled passage 1.
4 to a second internal space 8. The constant voltage power supply 30 for applying a predetermined voltage between the electrodes 24 and 28 of the second electrochemical pump cell is set to 1.5 V, and oxygen is pumped from the internal pump electrode 28 toward the reference electrode 24. . At this time, H ₂ O in the atmosphere in the second internal space 8 is decomposed into H ₂ and O _2, and the decomposed O ₂
Is also pumped at the same time. And in the pump operation by such a second electrochemical pump cell, the ammeter 3
The pump current detected at ₂ is proportional to the H ₂ O concentration in the atmosphere in the second internal space 8. Oxygen in the gas to be measured is 10 ⁻¹ in the first internal space 6.
Since it has been reduced to atm (0.0001 ppm), most of the values are based on the decomposition of H ₂ O. FIG. 22 shows the relationship between the H ₂ O concentration and the pump current (Ip) when both the first internal space 6 and the second internal space 8 are heated to 700 ° C.

In such a measurement of H ₂ O,
In order to decompose H ₂ O in the atmosphere, the pump voltage of the second electrochemical pump cell may be set to 1 V or more. If the voltage is lower than that, H ₂ O cannot be decomposed sufficiently. . Further, it is desirable that the pump voltage be 3 V or less. When the pump is operated at a higher voltage for a long time, the solid electrolyte material (for example, ZrO 2) is used.
₂ ) is decomposed, causing problems such as a decrease in strength. The pump voltage is preferably 1.2 V to 2.5 V
Will be adopted.

[0103] Further, even when the measurement gas component is CO _2, using the sensor element 2 of a configuration such as shown in FIGS. 1 and 2, in the same manner as that in the H ₂ O, Its measurement is possible. That is, when measuring CO ₂ ,
First, when the oxygen partial pressure in the atmosphere in the first internal space 6 is 10
^The oxygen partial pressure is controlled to ^-10 atm so that CO ₂ is not decomposed and the oxygen partial pressure is as low as possible. Then, the atmosphere in which the O ₂ concentration is controlled to a constant low value is led into the second internal space 8 through the second diffusion-controlling passage 14, and the 1.5 V
Oxygen is pumped from the internal pump electrode 28 toward the reference electrode 24 by the pump operation of the second electrochemical pump cell by the power supply from the constant voltage power supply 30 set to. At this time, CO ₂ in the second internal space 8 is CO and O
_2, and the decomposed O ₂ is also pumped out at the same time, and the pump current at this time is proportional to the CO ₂ concentration. The oxygen in the gas to be measured is 10 ⁻¹⁰ atm (0.0001 p.m.) in the first internal space 6.
pm), the second internal space 8
Most of the oxygen that is pumped out of the furnace is based on the decomposition of CO ₂ . FIG. 23 shows the relationship between the CO ₂ concentration and the pump current (Ip) when both the first internal space 6 and the second internal space 8 are heated to 700 ° C.

[0,104] Also in case of such a CO ₂ measurement, the degrades CO ₂ in the atmosphere, may be a pump voltage of the second electrochemical pumping cell above 1V, the voltage than Is too low to decompose CO ₂ sufficiently. Further, it is desirable that the pump voltage be 3 V or less. If the pump is operated for a long time at a higher voltage, problems such as decomposition of the solid electrolyte material are caused. A more desirable range of the pump voltage is as follows.
1.2V to 2.5V.

As described above, even gas components having bound oxygen, such as H ₂ O and CO ₂ , are decomposed in the second internal space 8 as in the case of NOx, thereby being generated. By detecting the pump current value (Ip) when O ₂ is pumped out, the gas component concentrations can be obtained. In order to positively decompose the gas components to be measured such as H ₂ O and CO ₂ , an appropriate decomposition catalyst may be disposed in the second internal space 8 in the same manner as in the case of NOx. It is possible.

Further, the present invention relates to the above-mentioned NOx and H ₂
In the case where the gas component having the binding oxygen such as O and CO _{2 is used as the} gas component to be measured, the gas component is particularly advantageously employed, but is not limited thereto. If the gas component is affected,
The present invention can be applied to any object. Eg, H ₂ and NH _3, upon the measurement, combusted by oxygen in the measurement gas, but the there is a possibility that accurate measurement is difficult, according to the present invention, the oxygen in the measurement gas first If it is removed in the internal space, the concentration of H ₂ or NH ₃ can be accurately measured in the second internal space.

For measuring the concentration of various kinds of gas components to be measured such as H ₂ and NH ₃ existing in the atmosphere in the second internal space, well-known appropriate detection means is selected. ,
For the measurement of H ₂ , a proton pump having the same configuration as the oxygen pump means will be used. Namely, the proton pump, is constituted by a proton ion conductive solid electrolyte layer and a pair of electrodes provided in it in contact, H ₂ by energizing the between those pair of electrodes, to the outside from the second internal space
Is pumped, and the H ₂ concentration is determined by detecting the pump current at that time. Also, NH
Also in the case of the measurement of ₃ , since it decomposes in the second internal space to generate H ₂ and N ₂ , the generated H ₂ is pumped out by the above-mentioned proton pump. By detecting the current, the NH ₃ concentration can be known.

As described above, it goes without saying that the present invention can be embodied in modes in which various changes, modifications, improvements and the like are made based on the knowledge of those skilled in the art. However, it is to be understood that any one of them falls within the scope of the present invention without departing from the spirit of the present invention.

[0109]

As is apparent from the above description, according to the method and apparatus for measuring a predetermined gas component in a gas to be measured according to the present invention, the oxygen concentration in the gas to be measured or its change is not affected. It is possible to accurately measure the concentration of the target gas component to be measured without receiving the In addition, the amount of NOx contained in the combustion gas in a wide range from the fuel-rich region to the air-excess region is measured easily and accurately without being affected by the oil combustion substances, and the NOx amount contained therein is easily and accurately measured. It is possible to find the extremely significant significance in industry.

[Brief description of the drawings]

FIG. 1 is an explanatory plan view showing an example of a sensor element constituting a NOx sensor according to a measuring device according to the present invention.

FIG. 2 is an enlarged explanatory view of a main part in a section AA of the sensor element shown in FIG. 1;

FIG. 3 is a graph showing a specific example of a control method of an electrode heating temperature and an oxygen partial pressure in each internal space.

FIG. 4 is a graph showing a relationship between a heating temperature of a sensor element and a distance from a tip of the sensor element under different exhaust gas temperatures.

FIG. 5 is a graph showing the relationship between the NO concentration and the pump current (Ip) in an example of the control shown in FIG.

FIG. 6 is a graph showing a second specific example relating to control of the electrode heating temperature and the oxygen partial pressure in each internal space.

FIG. 7 is a graph showing the relationship between the NO concentration and the pump current (Ip) in the specific example shown in FIG.

FIG. 8 is a graph showing a third specific example relating to control of the electrode heating temperature and the oxygen partial pressure in each internal space.

FIG. 9 is a graph showing a fourth specific example relating to control of the electrode heating temperature and the oxygen partial pressure in each internal space.

10 is a graph showing the relationship between the NO concentration and the pump current (Ip) in the specific example shown in FIG.

FIG. 11 is a partial view corresponding to FIG. 2, showing an example in which a NOx reduction catalyst is laminated on an internal pump electrode.

FIG. 12 is a partial view corresponding to FIG. 2, showing an example in which an oxidation catalyst is disposed in a first internal space.

FIG. 13 is a partial view corresponding to FIG. 2, showing another example of the arrangement of the oxidation catalyst.

FIG. 14 shows still another different arrangement example of the oxidation catalyst body.
FIG. 3 is a partial view corresponding to FIG. 2.

FIG. 15 is a partial view corresponding to FIG. 2, showing a specific example of a different configuration of the second internal space and the second diffusion-controlling means.

FIG. 16 is a graph showing the relationship between the NO concentration and the pump current (Ip) in the specific example shown in FIG.

FIG. 17 is an explanatory sectional view corresponding to FIG. 2 and showing another example of a sensor element constituting the NOx sensor according to the measuring device according to the present invention.

18 is an explanatory sectional view corresponding to FIG. 17 and showing a modified example of the sensor element shown in FIG. 17;

FIG. 19 is a graph showing the relationship between electromotive force and oxygen partial pressure at 600 ° C.

FIG. 20 shows that the temperatures of the first internal space and the second internal space are 6
It is a graph which shows the relationship between NO density | concentration and the pump current in the Example which made the applied voltage to a 1st electrochemical pump cell and a 2nd electrochemical pump cell different at 00 degreeC.

21 is a partial view corresponding to FIG. 2, showing a specific example of a configuration different from that shown in FIG. 15 for the second internal space and the second diffusion rate controlling means.

FIG. 22 shows that the temperatures of the first internal space and the second internal space are 7
In the 00 ° C., which is a graph showing the relationship between the H ₂ O concentration and the pumping current (Ip) in the embodiment was measured in H ₂ O.

FIG. 23 shows that the temperatures of the first internal space and the second internal space are 7
In the 00 ° C., which is a graph showing the relationship between the CO ₂ concentration and the pumping current (Ip) in the embodiment was measured in CO _2.

FIG. 24 is an explanatory sectional view of a sensor element for explaining the principle of the present invention.

FIG. 25 is an explanatory sectional view of a sensor element for explaining the principle of a conventional method.

[Explanation of symbols]

2 Sensor elements 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h
Solid electrolyte layer 6 First internal space 8 Second internal space 10 Reference air introduction passage 12 First diffusion-controlled passage 14 Second diffusion-controlled passage 16 Inner electrode 18 Outer electrode 20 Variable power supply 22 Measurement electrode 24 Reference Electrode 26 Potentiometer 28 Internal pump electrode 30 Constant voltage power supply 32 Ammeter 34 Alumina insulating layer 36 Heater 38 Oxidation catalyst 40 Gas introduction path 42 NOx reduction catalyst 44, 52 Porous body 50 Flat space 56 First electrochemical pump cell 58 Second electrochemical pump cell

Claims (3)

[Claims] 1. A first oxygen pump means for controlling an oxygen partial pressure in a measured gas introduced from a measured gas existing space to a predetermined value, and an oxygen controlled by the first oxygen pump means. Oxygen in the gas to be measured is pumped from the gas to be measured at a partial pressure, and the oxygen partial pressure in such an atmosphere is controlled to a predetermined value at which the NOx component can be reduced or decomposed, and the second internal A second oxygen pump means for reducing or decomposing NOx components present in the atmosphere in the space and for simultaneously pumping out the oxygen generated at that time; and By detecting the pump current flowing by the pump operation, the NO present in the gas to be measured is detected.
A NOx sensor characterized in that an x concentration is obtained. 2. A semiconductor device comprising a solid electrolyte and a pair of electrodes provided in contact with the solid electrolyte, wherein one of the pair of electrodes is disposed in a first internal space into which a gas to be measured is introduced. One electrochemical pump cell includes a fixed electrolyte and a pair of electrodes provided in contact with the fixed electrolyte, and one of the pair of electrodes is disposed in a second internal space for NOx measurement. A second electrochemical pump cell, wherein the NOx reducing power of the electrode disposed in the second internal space of the second electrochemical pump cell is higher than that of the electrode disposed in the first internal space. The first electrochemical pump cell is configured to be stronger than the NOx reducing power, and the oxygen concentration in the first internal space is adjusted by the first electrochemical pump cell. The second feature is that the concentration of NOx in the internal space is detected. NOx sensor. 3. The first internal space and the second internal space are communicated with each other, and the atmosphere having the oxygen concentration adjusted by the first electrochemical pump cell is provided in the first internal space. 3. The NOx sensor according to claim 2, wherein said NOx sensor is guided from said internal space to said second internal space.