JP7124590B2 - Gas concentration measuring device - Google Patents

Description

The present invention relates to a gas concentration measuring device that measures the concentration of a specific gas in a measurement gas.

Various gas sensors are used to measure the concentration of specific gas components contained in the measurement gas. For example, exhaust gas discharged from an internal combustion engine of an automobile contains gas components such as NOx and _O2 , and a NOx sensor is used to measure the NOx concentration, for example.

A gas sensor such as a NOx sensor generally includes an oxygen ion conductive solid electrolyte body and electrodes such as a sensing electrode and a reference electrode formed on the solid electrolyte body. A reference electrode is also called a reference electrode. An electrode that reacts with the gas component to be measured is used as the detection electrode.

Patent Literature 1 discloses a nitrogen oxide sensor including a solid electrolyte, a sensing electrode, and a reference electrode, the sensing electrode being made of various metal oxides. In the technique disclosed in Patent Document 1, by adjusting the material of the detection electrode, the average thickness, and the particle size of the particles that make up the detection electrode, a mixed potential type nitrogen oxide sensor can detect low concentrations even in the presence of oxygen. It is said that the nitrogen oxide gas concentration can be detected with high accuracy.

JP-A-2006-90898

However, the nitrogen oxide sensor of the conventional structure cannot sufficiently prevent the influence of oxygen on the sensing electrode. Furthermore, the sensing electrode is affected not only by oxygen, but also by nitric oxide. Therefore, when the measurement gas contains NO together with NO ₂ , the detected NO ₂ concentration includes the O ₂ concentration and the NO concentration. Therefore, the conventional nitrogen oxide sensor cannot accurately detect the NO ₂ concentration, and further improvement is desired.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a gas concentration measuring apparatus capable of accurately detecting NO ₂ gas in a measurement gas.

One aspect of the present invention is a NO ₂ detector (2) that outputs an output signal α corresponding to the NO ₂ concentration in the measurement gas;
an O ₂ detector (3) that outputs an output signal β corresponding to the O ₂ concentration in the measurement gas;
By correcting the concentration P _α calculated based on the output signal α from the NO ₂ detection unit based on the concentration P _β calculated based on the output signal β from the O ₂ detection unit, NO a NO ₂ concentration calculator (41) configured to calculate a ₂ concentration P _NO2 ;
a NOx detector (6) for outputting an output signal γ corresponding to the NOx concentration in the measured gas;
a NOx concentration calculator (42) for calculating the NOx concentration based on the output signal γ ,
The NO ₂ detection part is formed of a solid electrolyte body (5), and a NO ₂ detection electrode (21) and a reference electrode (100) formed on the solid electrolyte body,
In the gas concentration measuring device (1), the NO ₂ sensing electrode contains an oxide containing at least one of Fe and Ni.
Another aspect of the present invention is a NO ₂ detector (2) that outputs an output signal α corresponding to the NO ₂ concentration in the measurement gas ;
an O ₂ detector (3) that outputs an output signal β corresponding to the O ₂ concentration in the measurement gas ;
By correcting the concentration P _α calculated based on the output signal α from the NO ₂ detection unit based on the concentration P _β calculated based on the output signal β from the O ₂ detection unit, NO a NO ₂ concentration calculator (41) configured to calculate a ₂ concentration P _NO2 ,
The NO ₂ detection part is formed of a solid electrolyte body (5), and a NO ₂ detection electrode (21) and a reference electrode (100) formed on the solid electrolyte body (5),
the NO ₂ sensing electrode contains an oxide containing at least one of Fe and Ni;
In the NO ₂ concentration calculation unit, the gas concentration measurement device performs correction using a correction formula having an interaction term between the concentration P _α and the concentration P _β .

The gas concentration measuring device includes an NO ₂ detection section, an O ₂ detection section, and an NO ₂ concentration calculation section. Then, the NO ₂ detection section has a detection electrode containing the specific oxide. Such a sensing electrode can detect _NO2 with little sensitivity to NO. Therefore, even if the measured gas contains NO, the NO ₂ detector outputs the _output signal α almost unaffected by the NO concentration. Based on this, the NO ₂ concentration P _NO2 is calculated. When the measured gas does not contain NO, the NO ₂ detector naturally outputs the output signal α without being affected by NO. In other words, the gas concentration measuring device can accurately measure the NO ₂ concentration with little influence of NO regardless of whether the gas to be measured contains NO.

When the measurement gas contains oxygen, the O ₂ detector in the gas concentration measuring device detects oxygen and outputs an output signal β corresponding to the oxygen concentration. Then, in the NO ₂ concentration calculator, correction based on the output signal β is performed as described above. Therefore, even if the detection electrode of the NO ₂ detection section outputs the output signal α under the influence of O ₂ , the influence of oxygen contained in the output signal α is corrected by the NO ₂ concentration calculation section. It should be noted that when the measurement gas does not contain oxygen, the NO ₂ detection section naturally outputs the output signal α without being affected by oxygen. That is, the gas concentration measuring device can accurately measure the NO ₂ concentration regardless of whether the measurement gas contains oxygen.

Thus, in the above gas concentration measuring device, the NO ₂ detection section has the detection electrode containing the specific material, and the NO ₂ concentration calculation section corrects the concentration P _α based on the concentration P _β . is configured to Therefore, regardless of whether nitric oxide and oxygen coexist, NO ₂ concentrations in measurement gases of various compositions can be accurately measured.

As described above, according to the above aspect, it is possible to provide a gas concentration measuring device capable of accurately detecting NO ₂ gas in the measurement gas.
It should be noted that the symbols in parentheses described in the claims and the means for solving the problems indicate the corresponding relationship with the specific means described in the embodiments described later, and limit the technical scope of the present invention. not a thing

FIG. 2 is an enlarged cross-sectional view of a main part of the gas sensor element of the gas concentration measuring device according to the first embodiment; FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1; FIG. 1 is a cross-sectional view taken along line III-III in FIG. FIG. 1 is a cross-sectional view taken along line IV-IV of FIG. FIG. 2 is a cross-sectional view taken along the line VV in FIG. 1; FIG. 2 is an enlarged cross-sectional view of a main part of a gas sensor element of a gas concentration measuring device in Modification 1; FIG. 11 is an enlarged cross-sectional view of a main part of a gas sensor element of a gas concentration measuring device according to Modification 2; FIG. 4 is an enlarged cross-sectional view of a main part of a gas sensor element of a gas concentration measuring device according to Embodiment 2; A cross-sectional view taken along the line IX-IX in FIG. FIG. 2 is a cross-sectional view taken along line XX of FIG. FIG. 11 is an enlarged cross-sectional view of a main part of a gas sensor element of a gas concentration measuring device according to Modification 3; 1 is a schematic diagram showing the configuration of a test apparatus used for measuring a detected potential using a test piece for evaluation in Experimental Example 1. FIG. FIG. 10 is an explanatory diagram showing a comparison result of potentials detected by the NO ₂ detection electrode by the test piece for evaluation in Experimental Example 1; FIG. 4 is an explanatory diagram showing the results of comparison between calculated values of NO ₂ concentration based on multiple regression analysis using an interaction term and the actual concentration for the NO ₂ sensing electrode containing Fe ₂ O ₃ in Experimental Example 2; FIG. 4 is an explanatory diagram showing the error between the calculated value of NO ₂ concentration based on the multiple regression analysis using the interaction term and the actual concentration for the NO ₂ sensing electrode containing Fe ₂ O ₃ in Experimental Example 2; Calculation of NO ₂ concentration based on multiple regression analysis using linear combination of oxygen concentration and NO ₂ concentration and actual concentration for NO ₂ sensing electrode containing Fe ₂ O ₃ in Experimental Example 2. Explanatory drawing which shows a comparison result. Error between calculated NO ₂ concentration and actual concentration based on multiple regression analysis using linear combination of oxygen concentration and NO ₂ concentration for NO ₂ sensing electrode containing Fe ₂ O ₃ in Experimental Example 2 An explanatory diagram showing . For the NO ₂ sensing electrode containing Co ₃ O ₄ in Experimental Example 2, the error between the calculated value of the NO ₂ concentration based on the multiple regression analysis using the linear combination of the oxygen concentration and the NO concentration and the actual concentration was calculated. Explanatory diagram showing.

[Embodiment 1]
An embodiment of a gas concentration measuring device 1 will be described with reference to the drawings. As illustrated in FIGS. 1 to 5, the gas concentration measuring device 1 is used to measure the concentration of specific gas components in the measurement gas Gm. The measurement gas Gm is a gas to be measured, such as a mixed gas containing NO ₂ . Specifically, exhaust gas emitted from internal combustion engines such as automobiles is exemplified.

The gas concentration measuring device 1 includes a NO ₂ detection section 2 , an O ₂ detection section 3 and an NO ₂ concentration calculation section 41 . The NO ₂ detector 2 and the O ₂ detector 3 are composed of a solid electrolyte body 5 and electrodes 21 , 22 , 31 and 32 formed on the solid electrolyte body 5 . The gas concentration measuring device 1 is also called a gas sensor.

The gas concentration measuring device 1 includes, for example, a gas sensor element 11E. The gas sensor element 11E has a solid electrolyte body 5 having a measurement gas surface 5m exposed to the measurement gas Gm and a reference gas surface 5b exposed to the reference gas Gb. The measurement gas surface 5m can also be called the first main surface, and the reference gas surface 5b can also be called the second main surface. The shape of the solid electrolyte body 5 is a plate shape such as a flat plate shape as shown in the figure, but it may be a cylindrical shape with a bottom such as a cup shape, and may be rod-shaped, disc-shaped, spherical, particulate, pellet-shaped, or the like. Other shapes such as an irregular shape may be used.

The solid electrolyte body 5 is mainly composed of, for example, an oxygen ion conductive solid electrolyte. The solid electrolyte consists of, for example, yttria-stabilized zirconia. Yttria-stabilized zirconia is hereinafter referred to as “YSZ”. The solid electrolyte is not particularly limited as long as it has oxygen ion conductivity, and may be made of other materials.

It is preferable that the gas sensor element 11E and the gas concentration measuring device 1 having the same have a longitudinal direction Y. As shown in FIG. In this case, the gas concentration measuring device 1 having the gas sensor element 11E can be inserted parallel to the longitudinal direction Y into, for example, a gas pipe containing the measuring gas Gm. Of the two ends in the longitudinal direction Y of the gas sensor element 11E, the end on the side that is inserted into the gas pipe and exposed to the measurement gas is called the front end, and the other end is called the base end. The longitudinal direction Y is the left-right direction in FIG. 1, the left side of the longitudinal direction Y is the distal side of the gas sensor element 11E, and the right side is the proximal side. A direction perpendicular to the longitudinal direction Y of the gas sensor element 11E and parallel to the direction in which the electrodes formed on the surface of the solid electrolyte body 5 and the solid electrolyte body 5 are laminated is called a thickness direction X. A direction orthogonal to both the longitudinal direction Y and the thickness direction X is called a lateral direction Z. In addition, when the surface of the solid electrolyte body 5 is a curved surface, the thickness direction X and the lateral direction Z are included in the radial direction and the normal direction.

A plurality of electrodes are formed on the surface of the solid electrolyte body 5 , and each electrode and the solid electrolyte body 5 form the NO ₂ detection section 2 and the O ₂ detection section 3 . Specifically, the NO ₂ detection unit ₂ is formed from a partial region (specifically, the first region 51) of the solid electrolyte body 5, the NO ₂ detection electrode 21, and the reference electrode 100. The O ₂ detection part 3 is formed by another area (specifically, the second area 52 ) of the solid electrolyte body 5 different from the formation part of the detection part 2 , the O ₂ detection electrode 31 and the reference electrode 100 . . The NO ₂ detection unit 2 and the O ₂ detection unit 3 share one plate-shaped solid electrolyte body 5 in different regions, and are arranged side by side along the longitudinal direction Y, for example. The gas concentration measuring device of this embodiment can be called a multi-sensor because it can detect the concentration of a plurality of gases such as NO ₂ and O ₂ gases.

The NO ₂ detection electrode 21 and the O ₂ detection electrode 31 are formed, for example, on the measurement gas surface 5m, and the reference electrode 100 is formed on the reference gas surface 5b. The NO ₂ detection electrode 21 and the reference electrode 100 , and the O ₂ detection electrode 31 and the reference electrode 100 are formed so as to face each other with the solid electrolyte body 5 interposed therebetween. Specifically, in the first region 51 of the solid electrolyte body 5, the reference electrode 100, the first region 51, and the NO ₂ detection electrode 21 are laminated in order in the thickness direction X. As shown in FIG. In the second region 52 of the solid electrolyte body 5, the reference electrode 100, the second region 52, and the O ₂ detection electrode 31 are sequentially laminated in the thickness direction X. As shown in FIG.

As illustrated in FIGS. 1 and 5, the reference electrode 100 includes, for example, a first reference electrode 22 and a second reference electrode formed at a position different from the first reference electrode 22 on the reference gas plane 5b. 32 can be formed. The first reference electrode 22 forms the reference electrode of the NO ₂ detector 2 and the second reference electrode 32 forms the reference electrode of the O ₂ detector 3 . The first reference electrode 22 and the second reference electrode 32 contain, for example, noble metals such as Pt, Au, Pd, Ag, and Ru. In this embodiment, two reference electrodes, the first reference electrode 22 and the second reference electrode 32, are formed. is also possible. Although illustration of the configuration is omitted, one reference electrode extending in the longitudinal direction Y may be formed.

A reference gas chamber 55b is formed in the reference gas surface 5b. The first reference electrode 22 and the second reference electrode 32 are formed inside the reference gas chamber 55b. The reference gas chamber 55b has a space into which the reference gas Gb is supplied, and an entrance of the reference gas Gb into the space. The position of the inlet of the reference gas Gb is not particularly limited, but for example, it is preferably on the proximal side of the central position in the longitudinal direction Y of the gas sensor element 11E, and more preferably on the proximal end. In this case, by exposing the proximal side to the reference gas Gb, the reference gas Gb is easily supplied from the inlet into the reference gas chamber 55b. The position of the inlet of the reference gas chamber 55b may be on the tip side of the central position in the longitudinal direction Y of the gas sensor element 11E. In this case, the reference gas Gb is supplied to the reference gas chamber 55b, and the measurement gas Gm is supplied to the measurement gas chamber 55m. can form a path of

At least part of the measurement gas surface 5m is exposed to the outside of the gas sensor element 11E. The measurement gas surface 5m has, for example, a measurement gas chamber formation region 10R in which a measurement gas chamber 55m is formed and a measurement gas chamber non-formation region 11R in which the measurement gas chamber 55m is not formed. The measurement gas chamber non-formation region 11R is exposed to the outside of the gas sensor element 11E. A NO ₂ detection electrode 21 is formed in the measurement gas chamber non-formation region 11R.

A protective layer (not shown) may be placed on the surface of the NO ₂ sensing electrode 21 to cover the NO ₂ sensing electrode 21 with the protective layer. In this case, the NO ₂ detection electrode 21 can be protected from poisonous substances in the measurement gas Gm, flying objects, and the like. The protective layer can be composed of, for example, a gas-permeable ceramic porous body. It is desirable to adjust the porosity and pore diameter of the ceramic porous body so that the measurement gas Gm reaches the NO ₂ detection electrode 21 quickly.

The NO ₂ sensing electrode 21 contains oxides containing Fe and/or Ni. That is, the NO ₂ sensing electrode 21 contains an oxide containing at least one of Fe and Ni. NO ₂ can be detected by reacting this oxide with NO ₂ in the measurement gas Gm. Examples of oxides containing Fe include, in addition to _Fe2O3 , oxides containing at _least Fe such as _{FeO , Fe3O4} , _FeTiO3 and _FeAl2O4 . Examples of oxides containing Ni include NiO and composite oxides containing at least Ni such as NiFe ₂ O ₄ and La ₂ NiO ₄ . The NO ₂ sensing electrode 21 may contain a composite oxide containing at least Fe and Ni. Preferably, the Fe-containing oxide is Fe ₂ O ₃ and the Ni-containing oxide is NiO. In the following description, the oxide containing at least one of Fe and Ni is appropriately referred to as "NO ₂ detection component".

_The NO2 sensing electrode 21 can contain a solid electrolyte. In this case, the adhesion between the NO ₂ detection electrode 21 and the solid electrolyte body 5 is improved, and, for example, the three-phase interface between the gas phase (measurement gas Gm), the NO ₂ detection component, and the solid electrolyte increases. . The increased three-phase interface improves the reactivity of the NO ₂ sensing electrode 21 . From the same point of view, other electrodes such as the O ₂ detection electrode 31 and the reference electrode 100 can also contain a solid electrolyte. A specific example of the solid electrolyte contained in each electrode is the same as the solid electrolyte body 5 described above, preferably the same material as the solid electrolyte body 5 .

A measurement gas chamber formation region 10R and a measurement gas chamber non-formation region 11R are present on the measurement gas surface 5m. A measurement gas chamber 55m is provided in the measurement gas chamber forming region 10R, and a measurement gas Gm is supplied into the measurement gas chamber 55m. The measurement gas chamber 55m has, for example, a space to which the measurement gas Gm is supplied, an entrance of the measurement gas Gm into this space, and a diffusion resistance layer 551. As shown in FIG. The formation position of the diffusion resistance layer 551 is formed, for example, at the entrance to the measurement gas chamber 55m. The diffusion resistance layer can be formed so that the measurement gas Gm is supplied through the diffusion resistance layer 551 into the measurement gas chamber 55m. The diffusion resistance layer 551 is made of porous ceramics such as Al ₂ O ₃ , but the material is not particularly limited, and a material having low reactivity with the measurement gas Gm is suitable.

The measuring gas chamber 55 m faces the measuring gas surface 5 m of the second region 52 of the solid electrolyte body 5 . The O ₂ detection electrode 31 is formed within the measurement gas chamber 55m. A measurement gas Gm that has passed through the diffusion resistance layer 551 is supplied into the measurement gas chamber 55m and reaches the O ₂ detection electrode 31 . The O ₂ sensing electrode 31 contains, for example, noble metals such as Pt, Au, Pd, Ag, and Ru.

The measurement gas chamber 55m and the reference gas chamber 55b are formed by insulators 181, 182, 18 made of insulating ceramics such as alumina. Specifically, the measurement gas chamber 55m and the reference gas chamber 55b are formed by arranging insulators 181, 182 and 18 so that a space is formed between them and the solid electrolyte body 5. As shown in FIG.

The NO ₂ detector 2 is preferably of mixed potential type. In this case, the effect that the sensitivity is high when the gas concentration is low can be obtained. However, in the case of the mixed potential type, since it is affected by the O ₂ concentration, it is necessary to separately measure the O ₂ concentration and correct the NO ₂ concentration based on this O ₂ concentration. Therefore, the gas concentration measuring device 1 is provided with the O ₂ detector 3 . The O ₂ detector 3 is preferably of a limiting current type. Similar to commonly used A/F sensors, the potential type has low sensitivity when the _O2 concentration is high, while the limiting current type has high sensitivity and high accuracy even when the _O2 concentration is high. can be measured. By combining the mixed potential type NO ₂ detection unit 2 and the limiting current type O ₂ detection unit 3 in this way, NO ₂ can be detected with high accuracy even when low concentrations of NO ₂ and high concentrations of O ₂ coexist. Concentration measurements are possible.

The formation positions of the NO ₂ detection part 2 and the O ₂ detection part 3 are not particularly limited, but they are preferably formed on the tip side of the gas sensor element 11E. In this case, by exposing the tip side of the gas sensor element 11E to the measurement gas Gm, the NO ₂ detection unit ₂ and the O ₂ detection unit 3 can be exposed to the measurement gas Gm. and O ₂ concentration can be easily measured.

A heater portion 19 can be provided in the gas sensor element 11E. In this case, the heater section 19 can heat the gas sensor element 11E to a temperature suitable for measuring the gas concentration. The heater section 19 is formed integrally with the gas sensor element 11E by, for example, embedding the heating element 17 in the insulator 18 forming the reference gas chamber 55b. The formation position of the heater part 19 can be changed as appropriate, but it is preferably formed near the solid electrolyte body 5 .

The heating element 17 is supplied with electric power from an external power source (not shown) and generates heat when energized. The insulator 18 is made of insulating ceramics such as alumina. The gas sensor element 11E with the built-in heater section 19 can be manufactured by laminating the heating element 17 between a plurality of unfired ceramic plates, further laminating the solid electrolyte body 5, and firing. The temperature of the gas sensor element 11E is monitored by an energization control section (not shown) and controlled to the operating temperature.

In the gas concentration measuring device 1, for example, the outer periphery of the gas sensor element 11E is held by a housing (not shown). It is attached. Although the type of the measurement gas Gm is not particularly limited, exhaust gas from an internal combustion engine of an automobile is suitable, for example. The type of the reference gas Gb is also not particularly limited, but air is suitable, for example.

The NO ₂ detector 2 outputs an output signal α corresponding to the NO ₂ concentration in the measurement gas Gm. The NO ₂ detector 2 specifically outputs a mixed potential signal as the output signal α. The gas concentration measuring device 1 has, for example, a mixed-potential type output circuit that outputs, for example, an output signal α.

The O ₂ detector 3 outputs an output signal β corresponding to the O ₂ concentration in the measurement gas Gm. The O ₂ detector 3 specifically outputs a limit current signal as the output signal β. The gas concentration measuring device 1 has, for example, a limiting current output circuit that outputs an output signal β.

The output circuit for the output signal α and the output circuit for the output signal β can be incorporated in an integrated product (specifically, a gas sensor) in which the gas sensor element 11E is attached with a housing, a cover, etc. (not shown). Each output circuit may be provided in a sensor control unit (SCU) or an engine control unit (ECU) (not shown) provided outside the integrated product.

As illustrated in FIG. 1 , the gas concentration measuring device 1 has a NO ₂ concentration calculator 41 . The NO ₂ concentration calculator 41 is configured to correct the concentration P _α calculated based on the output signal α based on the concentration P _β calculated based on the output signal β. Due to such a configuration, the gas concentration measuring device 1 can be provided with a circuit for performing arithmetic processing for correction, for example.

The output signal is considered to exhibit responsivity according to the Nernst equation. _The correction in the _{NO 2 concentration} calculation unit 41 is calculated based _on , for example, multiple regression _{analysis .} This can be done based on a regression equation with the product of the logarithm of logPO ₂ ×logPNO ₂ terms and a constant term. Also, the term _logPO2 × _logPNO2 , the product of the logarithm of the _O2 concentration and the logarithm of the _NO2 concentration, is not limited to _only the product, and may be the interaction term of the logarithm of the _O2 concentration and the logarithm of the NO2 concentration. Just do it. In other words, in the multiple regression analysis, not only the linear combination of the NO ₂ concentration term and the O ₂ concentration term, but also the interaction term between the NO ₂ concentration term and the O ₂ concentration term is introduced to calculate the correction formula. be able to. A specific example of correction will be described in an experimental example described later.

Since the NO ₂ sensing electrode 21 contains an oxide containing at least one of Fe and Ni (that is, an NO ₂ sensing component), it hardly reacts with NO but reacts with NO ₂ . On the other hand, the NO ₂ sensing electrode 21 with such a configuration can also react with O ₂ . Therefore, the output signal α is, for example, an output signal corresponding to the NO ₂ concentration and the O ₂ concentration, and the concentration P _α can specifically include the NO ₂ concentration and the O ₂ concentration. The output signal β output by the O ₂ detection electrode 31 is an output signal corresponding to the O ₂ concentration, and the concentration P _β is specifically the O ₂ concentration. Therefore, by performing the correction as described above in the NO ₂ concentration calculator 41, it becomes possible to remove the influence of the oxygen concentration from the concentration _Pα .

The formation position of the NO ₂ concentration calculation section 41 is not particularly limited, and as described above, it can be incorporated in an integrated product in which the gas sensor element 11E is attached with a housing, a cover body and the like (not shown). The NO ₂ concentration calculator 41 may be formed separately from this integrated product. When forming the separate NO ₂ concentration calculation unit 41, for example, the NO ₂ concentration calculation unit 41 can be provided in an ECU or the like. More specifically, for example, the output signal α and the output signal β from the SCU are sent to the NO ₂ concentration calculator 41 provided in the ECU, for example, and corrected in the NO ₂ concentration calculator 41 . The NO ₂ concentration calculator 41 can also be formed in the SCU.

A gas concentration measuring device 1 of this embodiment includes a NO ₂ detection section 2 , an O ₂ detection section 3 and an NO ₂ concentration calculation section 41 . The NO ₂ detection unit 2 has an NO ₂ detection electrode 21 containing a specific NO ₂ detection component. This _NO2 sensing component has little reactivity with NO and does react with _NO2 . Therefore, the NO ₂ detector 2 can detect NO ₂ without being affected by NO. As a result, even if the measurement gas Gm contains NO, such as exhaust gas emitted from an automobile engine, the NO ₂ detector 2 can output the output signal α almost without being affected by the NO concentration. can be done. The NO ₂ concentration calculator 41 calculates the NO ₂ concentration P _NO2 based on signals such as the output signal α.

On the other hand, when the measurement gas Gm does not contain NO, the NO ₂ detector 2 naturally outputs the output signal α without being affected by NO. That is, in this case, the output signal α is not affected by the NO concentration at all.

In this manner, the gas concentration measuring device 1 can accurately measure the NO ₂ concentration with little influence of NO regardless of whether the measurement gas Gm contains NO.

Further, when the measurement gas Gm contains oxygen, the O ₂ detector 3 in the gas concentration measuring device 1 detects oxygen and outputs an output signal β corresponding to the oxygen concentration. Then, in the NO ₂ concentration calculator 41, correction based on the output signal β is performed as described above.

Therefore, even if the detection electrode 21 of the NO ₂ detection unit 2 is affected by O ₂ and outputs the output signal α, the NO ₂ concentration calculation unit 41 corrects the influence of oxygen contained in the output signal α. Therefore, even when the measurement gas Gm contains oxygen, the gas concentration measuring device 1 can accurately measure the NO ₂ concentration in the measurement gas Gm.

On the other hand, when the measurement gas Gm does not contain oxygen, the NO ₂ detector 2 naturally outputs the output signal α without being affected by oxygen. That is, in this case, the output signal α is not affected by the oxygen concentration at all.

Thus, the gas concentration measuring device 1 can accurately measure the NO ₂ concentration regardless of whether the measurement gas Gm contains oxygen.

As described above, in the gas concentration measuring device 1, the NO ₂ detection section 2 has the detection electrode 21 containing the specific material. Then, in the gas concentration measuring device 1, the NO ₂ concentration calculator 41 outputs the output signal α from the NO ₂ detector 2 based on the concentration Pβ calculated based on the output signal _β from the O ₂ detector 3 The density P _α calculated based on is corrected. Therefore, regardless of whether nitric oxide and oxygen coexist, the NO ₂ concentration in the measurement gas Gm having various compositions can be measured with high accuracy. Although the gas concentration measuring device 1 of this embodiment is suitable for measuring NO ₂ concentration, it can also be used for measuring O ₂ concentration.

[Modification 1]
This example is an example of a gas concentration measuring device having a mixed potential type gas sensor element as a NO ₂ detection section and an O ₂ detection section separate from the gas sensor element. Note that, of the reference numerals used in Modification 1 and subsequent examples, the same reference numerals as those used in the above-described embodiments represent the same components and the like as those in the above-described embodiments unless otherwise specified.

As illustrated in FIG. 6, the gas concentration measuring device of this example has a gas sensor element 12E and an O ₂ detector 3, and the O ₂ detector 3 is provided separately from the gas sensor element 12E. ing.

Gas sensor element 12</b>E has solid electrolyte body 5 , NO ₂ detection electrode 21 and reference electrode 100 . In other words, the gas sensor element 12E constitutes the NO ₂ detection section 2. As shown in FIG. The NO ₂ detector 2 can have the same configuration as in the first embodiment. The gas sensor element 12E has a heater section 19 as in the first embodiment.

The O ₂ detection unit 3 uses, for example, an oxygen sensor, although the illustration of its configuration is omitted. The oxygen sensor, like the O ₂ detection unit 3 in the first embodiment, comprises, for example, a solid electrolyte body 5, an O ₂ detection electrode 31 formed on its surface, a reference electrode 100, and the like.

In the gas concentration measuring device 1 of this example, based on the output signal β from the O ₂ detector 3 provided separately from the gas sensor element 12E, from the output signal α from the NO ₂ detector 2 of the gas sensor element 12E, The NO ₂ concentration P _NO2 can be calculated by correcting the calculated concentration P _NO2 . Therefore, the gas concentration measuring device 1 of this example can accurately measure the NO ₂ concentration in the measurement gas. Other configurations can be the same as those of the first embodiment, and effects similar to those of the first embodiment can be exhibited.

[Modification 2]
This example is an example in which two solid electrolyte bodies are provided, and the NO ₂ detection part 2 and the O ₂ detection part 3 are formed in each solid electrolyte body. As illustrated in FIG. 7, the gas concentration measuring device 1 of this example has a gas sensor element 13E, and the gas sensor element 13E includes a first solid electrolyte body 53 and a second solid electrolyte body 54 as the solid electrolyte body 5. and

In the gas sensor element 13E, the heater section 19, the second solid electrolyte body 54, and the first solid electrolyte body 53 are laminated in order in the thickness direction X. As shown in FIG. A measurement gas chamber 55m is formed between the heater portion 19 and the second solid electrolyte body 54 . A measurement gas surface 54m of the second solid electrolyte body 54 faces a measurement gas chamber 55m, and an O ₂ detection electrode 31 is formed on the measurement gas surface 54m. At the tip of the gas sensor element 13E in the longitudinal direction Y, there is an inlet for the measurement gas into the measurement gas chamber 55m, and a diffusion resistance layer 551 is formed at this inlet. A measurement gas is supplied into the measurement gas chamber 55m through the diffusion resistance layer 551. As shown in FIG.

The first solid electrolyte body 53 has a measurement gas surface 53m and a reference gas surface 53b, and the second solid electrolyte body 54 has a measurement gas surface 54m and a reference gas surface 54b. The NO ₂ detection electrode 21 is formed on the measurement gas surface 53m of the first solid electrolyte body 53, and the first reference electrode 22 is formed on the reference gas surface 53b. An O ₂ detection electrode 31 is formed on the measurement gas surface 54m of the second solid electrolyte body 54, and a second reference electrode 32 is formed on the reference gas surface 54b.

A reference gas chamber 55 b is formed between the first solid electrolyte body 53 and the second solid electrolyte body 54 . The reference gas surface 53b of the first solid electrolyte body 53 and the reference gas surface 54b of the second solid electrolyte body 54 face the reference gas chamber 55b. A first reference electrode 22 is formed on the reference gas surface 53 b of the first solid electrolyte body 53 , and a second reference electrode 32 is formed on the reference gas surface 54 b of the second solid electrolyte body 54 .

The surface of the first solid electrolyte body 53 opposite to the reference gas surface 53b is at least partially exposed to the outside of the gas sensor element 13E on the front end side in the longitudinal direction Y to form a measurement gas surface 53m. A NO ₂ detection electrode 21 is formed on the measurement gas surface 53m of the first solid electrolyte body 53 .

The NO ₂ detection unit 2 is formed by sequentially stacking the first reference electrode 22 , the first solid electrolyte body 53 and the NO ₂ detection electrode 21 . The O ₂ detection unit 3 is formed by sequentially stacking the second reference electrode 32 , the second solid electrolyte body 54 and the O ₂ detection electrode 31 . The NO ₂ detection unit 2 and the O ₂ detection unit 3 are arranged side by side in a direction parallel to the thickness direction X via the reference gas chamber 55b as illustrated in FIG. may be staggered relative to each other.

In FIG. 7, the insulators 181 and 182 are formed on the base end sides in the longitudinal direction Y of the first solid electrolyte body 53 and the second solid electrolyte body 54, but the insulators are formed in the same manner as in the first embodiment. The first solid electrolyte body 53 and the second solid electrolyte body 54 extending to the base end side may be formed without forming them. Other configurations are similar to those of the first embodiment, and effects similar to those of the first embodiment can be exhibited.

[Embodiment 2]
Next, an embodiment of the gas concentration measuring device 1 having the NOx detector 6 will be described with reference to FIGS. 8 to 10. FIG. The gas concentration measuring device 1 has a gas sensor element 14E, and the gas sensor element 14E of this embodiment has a NO ₂ detection section 2, an O ₂ detection section 3 and a NOx detection section 6. FIG. The NOx detector 6 outputs an output signal γ corresponding to the NOx concentration in the measured gas. The NOx concentration is the total concentration of NO ₂ and NO, and is also called total NOx concentration.

The gas sensor element 14</b>E has a first solid electrolyte body 53 and a second solid electrolyte body 54 as the solid electrolyte body 5 . In the gas sensor element 14E, the heater section 19, the second solid electrolyte body 54, and the first solid electrolyte body 53 are sequentially stacked in the thickness direction X. As shown in FIG. A measurement gas chamber 55m is formed between the heater portion 19 and the second solid electrolyte body 54 . A measuring gas surface 54m of the second solid electrolyte body 54 faces a measuring gas chamber 55m. An O ₂ detection electrode 31 and a NOx detection electrode 611 are formed on the measurement gas surface 54 m of the second solid electrolyte body 54 . The _O2 detection electrode 31 and the NOx detection electrode 611 are formed within the measuring gas chamber 55m.

A reference gas chamber 55 b is formed between the first solid electrolyte body 53 and the second solid electrolyte body 54 . The reference gas surfaces 53b and 54b of the first solid electrolyte body 53 and the second solid electrolyte body 54 face the reference gas chamber 55b. That is, the reference gas surface 53b of the first solid electrolyte body 53 and the reference gas surface 54b of the second solid electrolyte body 54 face each other, and the reference gas chamber 55b is formed therebetween. On the reference gas surface 54b of the second solid electrolyte body 54, the reference electrode 100 (specifically, the second reference electrode 32) forming the O ₂ detection unit 3 and the reference electrode 100 (specifically, the second reference electrode 32) forming the NOx detection unit 6 Specifically, a third reference electrode 612) is formed.

The O ₂ detection part 3 is formed by sequentially stacking the O ₂ detection electrode 31 , the second solid electrolyte body 54 and the second reference electrode 32 . The NOx detection section 6 is formed by laminating the NOx detection electrode 611, the second solid electrolyte body 54, and the third reference electrode 612 in order.

The NOx sensing electrode 611 contains Au, for example. As an electrode component of the NOx detection electrode 611, Pt, Pd, Ag, Ru, etc. are used in addition to Au. Additionally, the NOx sensing electrode 611, like other electrodes such as the _NO2 sensing electrode 21, can contain a solid electrolyte. A noble metal such as Pt is used for the third reference electrode 612, like the first reference electrode 22 and the second reference electrode 32.

A NO ₂ detection electrode 21 is formed on the measurement gas surface 53m of the first solid electrolyte body 53, and a first reference electrode 22 is formed on the reference gas surface 53b of the first solid electrolyte body 53. As shown in FIG. A measurement gas surface 53m of the first solid electrolyte body 53 is exposed to the outside of the gas sensor element 14E and exposed to the atmosphere of the measurement gas. The NO ₂ detection electrode 21 is formed on the measurement gas surface 53m and is exposed to the measurement gas Gm. The NO ₂ detection unit 2 is formed by sequentially stacking the first reference electrode 22 , the first solid electrolyte body 53 and the NO ₂ detection electrode 21 .

The measurement gas chamber 55m is provided with a measurement gas inlet at the tip of the gas sensor element 14E in the longitudinal direction Y, for example. A diffusion resistance layer 551 is formed at the entrance of the measurement gas chamber 55m, and the measurement gas passes through the diffusion resistance layer 551 and is supplied into the measurement gas chamber 55m.

In the measurement gas chamber 55m, the O ₂ detection electrode 31 of the O ₂ detection section 3 is formed on the tip side in the longitudinal direction Y with respect to the NOx detection electrode 611 . That is, the O ₂ detection electrode 31 is formed closer to the inlet side of the measurement gas chamber 55m than the NOx detection electrode 611 is. Since the exhaust gas flows from the inlet of the measuring gas chamber 55m into the interior, the O ₂ detecting electrode 31 is formed upstream of the NOx detecting electrode 611 in the flow direction of the exhaust gas in the measuring gas chamber 55m. As a result, the O ₂ detector 3 is also formed upstream of the NOx detector 6 in the exhaust gas flow direction.

Therefore, the measurement gas Gm in the measurement gas chamber 55m reacts with the O ₂ detection electrode 31 of the O ₂ detection section 3 and then with the NOx detection electrode 611 of the NOx detection section 6 . In other words, the measuring gas that has reacted with the O ₂ detecting electrode 31 reaches the NOx detecting electrode 611 in the measuring gas chamber 55m.

The O ₂ detector 3 outputs an output signal β in response to the oxygen concentration in the measurement gas. Furthermore, in the O ₂ detection unit 3, when a voltage is applied between the O ₂ detection electrode 31 and the second reference electrode 32, the oxygen in the measurement gas is consumed, the oxygen concentration is reduced, and NO ₂ is produced. reduced to NO. That is, the O ₂ detector functions as the pump part 3P, and the pump part 3P discharges O ₂ from the measuring gas around the NOx detecting part 6, and further reduces NO ₂ in the measuring gas Gm to NO. This is because the O ₂ detection electrode 31 functions as a pump electrode, and this O ₂ detection electrode 31 reacts with oxygen and NO ₂ in the measurement gas in the measurement gas chamber 55m, and the oxygen ions generated are, for example, a reference This is for discharging to the gas chamber 55b.

As a result, the NOx detection electrode 611 located downstream of the O ₂ detection electrode 31 in the exhaust gas flow is reached by the measurement gas containing almost no oxygen and NO ₂ but containing NO. Then, the NOx detection unit 6 outputs an output signal γ corresponding to the NO concentration in the measurement gas reaching the NOx detection electrode 611 . NO detected by the NOx detector 6 includes NO originally contained in the measurement gas and NO derived from NO ₂ reduced by the O ₂ detection electrode 31 . Therefore, the output signal γ is the signal output in response to the total concentration of NO and NO ₂ . That is, the NOx detector 6 detects the total NOx concentration in the measurement gas.

The NOx detector 6 outputs, for example, a limit current signal as the output signal γ. The gas concentration measuring device 1 has a NOx concentration calculator 42, and the NOx concentration calculator 42 calculates the NOx concentration based on the output signal γ. The NOx concentration calculator 42 can be built in the gas sensor like the NO ₂ concentration calculator 41, but it can also be provided in the SUC or ECU.

On the other hand, the NO ₂ detection unit 2 has an NO ₂ detection electrode 21 containing an NO ₂ detection component such as iron oxide, as in the first embodiment. The NO ₂ detector 2 outputs an output signal α that is hardly affected by NO. The O ₂ detector 3 outputs an output signal β corresponding to the oxygen concentration. Then, the NO ₂ concentration calculator 41 calculates the NO ₂ concentration P _NO2 based on the output signal α and the output signal β, as in the first embodiment.

Thus, the gas concentration measuring device 1 of the present embodiment can accurately measure the NO ₂ concentration and also measure the total NOx concentration P _NOX of NO ₂ and NO. Since the NO concentration can be calculated from the total NOx concentration P _NOX and the NO ₂ concentration P _NO2 , the gas concentration measuring device 1 of the present embodiment measures the NO ₂ concentration and the NO concentration in the measurement gas, respectively. be able to. Furthermore, since the O ₂ detector 3 is provided, the oxygen concentration can also be measured. Therefore, the gas concentration measuring device 1 can measure the NO ₂ concentration, the NO concentration, and the oxygen concentration from the measurement gas containing gases such as NO ₂ , NO, and oxygen. Otherwise, the configuration can be the same as that of the first embodiment, and the same effect as that of the first embodiment can be exhibited.

[Modification 3]
This example is an example of a gas sensor element having one solid electrolyte body, in which a NO ₂ detection section 2, an O ₂ detection section 3, and a NOx detection section 6 are respectively formed. As illustrated in FIG. 11, the gas sensor element 15E has a heater section 19, a solid electrolyte body 5, a measurement gas chamber 55m, a reference gas chamber 55b, and the like. In the gas sensor element 15E, the heater section 19 and the solid electrolyte body are sequentially laminated. A reference gas chamber 55 b is formed between the heater portion 19 and the solid electrolyte body 5 .

The solid electrolyte body 5 has a measurement gas surface 5m and a reference gas surface 5b. A reference electrode 100 is formed on the reference gas surface 5b. In this example, a first reference electrode 22 and a second reference electrode 32 are formed as the reference electrode 100 . The first reference electrode 22 serves as a reference electrode for the NO ₂ detection section 2 , and the second reference electrode 32 serves also as a reference electrode for the O ₂ detection section 3 and the NOx detection section 6 .

A NO ₂ detection electrode 21, an O ₂ detection electrode 31, and a NOx detection electrode 611 are formed on the measurement gas surface 5m. A measurement gas chamber 55m is formed in the measurement gas surface 5m, and the O ₂ detection electrode 31 and the NOx detection electrode 611 are formed in the measurement gas chamber 55m. The NO ₂ detection electrode 21 is formed in the measurement gas chamber non-formation region 11R on the front end side in the longitudinal direction Y from the measurement gas chamber formation region 10R.

The NO ₂ detection electrode 21, the O ₂ detection electrode 31, and the NOx detection electrode 611 are sequentially arranged from the distal end side to the proximal end side in the longitudinal direction Y of the gas sensor element 15E. The NO ₂ detection part 2 is formed by the NO ₂ detection electrode 21, the first reference electrode 22, and the first region 51 of the solid electrolyte body 5 sandwiched between these electrodes. The O ₂ detection part 3 is formed by the O ₂ detection electrode 31 , the second reference electrode 32 , and the second region 52 of the solid electrolyte body 5 sandwiched between these electrodes. The NOx detection portion 6 is formed by the NOx detection electrode 611, the second reference electrode 32, and the third region 56 of the solid electrolyte body 5 sandwiched between these electrodes.

As exemplified in FIG. 11, the gas sensor element 15E includes a NO ₂ detection portion 2, an O ₂ detection portion 3, and a NOx detection portion 6 which are sequentially formed from the distal end side to the proximal end side in the longitudinal direction Y. , and each of the detection units 2, 3, 6 shares one solid electrolyte body 5. The O ₂ detection unit 3 also serves as the pump unit 3P as in the second embodiment.

In this example, the gas sensor element 15E has one solid electrolyte body 5, and each electrode 21, 22, 31, 32, 611, 612 is formed on this one solid electrolyte body 5. FIG. Therefore, compared to an element such as the gas sensor element 14E of the second embodiment in which a plurality of solid electrolyte bodies 5 are arranged parallel to the thickness direction X, the thickness of the gas sensor element 15E can be reduced. As a result, the size of the gas concentration measuring device 1 can be reduced.

Further, in the gas sensor element 15E of this example, since there is one solid electrolyte body 5, it is easy to make an internal configuration in which the distance between the heater section 19 and the solid electrolyte body 5 is reduced. Therefore, the solid electrolyte body 5 can be rapidly heated to a desired temperature by causing the heater portion 19 to generate heat by, for example, energizing. That is, temperature control of the gas sensor element 15E becomes easier. Other configurations can be the same as those of, for example, the first and second embodiments, and effects similar to those of the first and second embodiments can be exhibited.

(Experimental example 1)
This example is an example of examining the electrode components of the NO ₂ sensing electrode. In this example, simple gas sensor elements having NO ₂ detection electrodes made of different materials are fabricated, and the responsiveness to each gas is comparatively evaluated.

NO ₂ was detected using a testing apparatus for evaluation having the configuration shown in _FIG . examined. The results are shown in FIG. Note that the measurement points in FIG. 13 correspond to the “measured gas No.” in Table 1.

A test piece P1 was produced as follows. First, a disk-shaped oxygen ion conductive solid electrolyte body 5 having a thickness of 0.5 mm was prepared. The NO ₂ detection electrode 21 is formed on the first main surface (that is, the upper end surface of FIG. 12) of the solid electrolyte body 5, and the reference electrode 100 is formed on the opposite second main surface (that is, the lower end surface of FIG. 12). formed.

The solid electrolyte body 5 is made of YSZ, the NO ₂ detection electrode 21 is made of Fe ₂ O ₃ , and the reference electrode 100 is made of Pt--YSZ. The reference electrode 100 is made by mixing Pt and YSZ so that the volume ratio is 3:1 (Pt:YSZ), and printing the mixture on the solid electrolyte body 5 so as to have a diameter of φ8 mm. It was formed by firing at 1400° C. for 9 hours in an air atmosphere. The NO ₂ detection electrode 21 was formed by printing Fe ₂ O ₃ on the solid electrolyte body 5 so as to have a diameter of φ8 mm, and then firing it in an air atmosphere at 900° C. for 9 hours. Thus, a test piece P1 for evaluation was obtained.

Also, a test piece P2 was produced in the same manner as the test piece P1 except that Co ₃ O ₄ was used instead of Fe ₂ O ₃ . The test piece P2 has the same configuration as the test piece P1 except that the NO ₂ detection electrode 21 is made of Co ₃ O ₄ --YSZ.

As shown in FIG. 12, test pieces P1 and P2 for evaluation were housed in an alumina tube placed in an electric furnace and heated to a temperature of 700° C. in the electric furnace. The test pieces P1 and P2 are arranged so as to partition the interior of an alumina tube with both ends open, and the reference electrode 100 side is open to the atmosphere. A measurement gas was supplied to the NO ₂ detection electrode 21 side. Each gas having the composition shown in Table 1 was used as the measurement gas. "%" and "ppm" in the table are respectively "% by mass" and "ppm by mass".

As is known from Table 1 and FIG. 13, when the detection electrode 21 containing Fe ₂ O ₃ is used, the mixed potential changes with changes in the NO ₂ concentration. , the change in the mixed potential is suppressed. That is, the sensing electrode 21 containing Fe ₂ O ₃ has a small voltage dependence on NO. In contrast, when the sensing electrode 21 containing Co ₃ O ₄ is used, the mixed potential changes with changes in both the NO ₂ concentration and the NO concentration.

Therefore, by using the sensing electrode 21 containing Fe ₂ O ₃ in the NO ₂ detection unit 2 of the gas concentration measuring device 1, the NO ₂ detection unit 2 can respond to the NO ₂ concentration without being affected by NO. An output signal can be output. Although not shown in FIG. 13, it was confirmed that the mixed potential of both the detection electrode 21 containing Fe ₂ O ₃ and the detection electrode 21 containing Co ₃ O ₄ changed according to the oxygen concentration. is doing. That is, the mixed potential of _{both Fe2O3} and _Co3O4 depends _on NO2 _{, O2} , and the mixed potential of _Co3O4 further depends _on NO _, while the mixed potential of _Fe2O3 is less dependent on NO. It has been confirmed that even if NiO is used instead of Fe ₂ O ₃ , the same results as those of Fe ₂ O ₃ can be obtained. Fe ₂ O ₃ is preferable from the viewpoint of obtaining higher NO ₂ sensitivity and being an inexpensive material.

By using an oxide containing at least one of Fe and Ni, such as Fe ₂ O ₃ and NiO, for the NO ₂ detection electrode 21 as in this example, the configurations shown in the above embodiments and modifications can be realized. That is, since the NO ₂ detection electrode 21 hardly reacts with NO, the NO ₂ detection section 2 outputs the output signal α without being affected by the NO concentration. As a result, in the _{NO 2} concentration calculating section 41, for example, _{NO 2} By correcting the concentration, it is possible to accurately measure the NO ₂ concentration of the measurement gas containing NO, NO ₂ , O ₂ and the like.

[Experimental example 2]
This example is an example showing an example of derivation of a correction formula in the NO ₂ concentration calculator. Although the actual correction formula varies depending on the configuration of the gas concentration measuring device 1, variables can be determined in the same manner as in this example.

A formula for calculating the concentration of NO ₂ , that is, a correction formula, is calculated by multiple regression analysis from the result of the mixed potential when the NO ₂ detection electrode 21 containing Fe ₂ O ₃ in Experimental Example 1 is used. In this example, the logarithm of the oxygen concentration, the logarithm of the NO _{2 concentration, and the product of the logarithm of the oxygen concentration and the logarithm of the NO 2 concentration} , which are their interaction terms, were introduced as explanatory variables. Therefore, in the multiple regression analysis, the regression equation I represented by (Formula I) below can be derived. Furthermore, by modifying the formula (I), the NO ₂ concentration formula represented by the formula (II) is calculated, and from the results of the multiple regression analysis, by determining the coefficients A to D, the formula (III ) is obtained. In each equation, Emix indicates the mixed potential, P _O2 indicates the oxygen concentration, and P _NO2 indicates the NO ₂ concentration.

In Experimental Example 1, a measurement gas with a known concentration of each gas component is measured. Therefore, in this example, the NO ₂ concentration calculated by the correction formula (that is, the calculated value) was compared with the actual concentration. The results are shown in FIG. Also, the error between the calculated value and the actual density was calculated, and the result is shown in FIG.

As is known from FIGS. 14 and 15, according to the correction formula represented by Formula III, the difference between the calculated value and the actual density is small, and the standard deviation of the error is 9.7%, which means that the variation is small. Therefore, as in Equation III, instead of the linear combination of the oxygen concentration and the NO2 concentration, a _more accurate calculation of the NO2 concentration can be _achieved by introducing an interaction term into these linear combinations and performing multiple regression analysis. becomes possible. In other words, the NO ₂ concentration can be measured more accurately by performing correction based on the correction formula derived by multiple regression analysis using the oxygen concentration, the NO ₂ concentration, and their interaction terms as explanatory variables. be able to.

On the other hand, FIG. 16 and FIG. 17 show the results when the interaction term was not used in the multiple regression analysis. That is, FIGS. 16 and 17 are based on correction formulas obtained by performing multiple regression analysis using logP _O2 and logP _NO2 as explanatory variables and without using an interaction term such as the product of logP _O2 and logP _NO2 . This figure shows the results obtained. That is, the result is based on a correction formula obtained by linearly combining the explanatory variables logP _O2 and logP _NO2 .

As is known from FIGS. 16 and 17, when the interaction term is not used, the difference between the calculated value by the correction formula and the actual concentration is greater than when the interaction term is used. Furthermore, the standard deviation σ of the error was also large. In other words, as can be seen from the results of FIGS. 14 to 17, the NO ₂ concentration can be calculated more accurately by the correction formula obtained using the multiple regression analysis using the interaction term between the oxygen concentration and the NO ₂ concentration. can be done.

FIG. 18 shows the results when the NO ₂ sensing electrode 21 containing Co ₃ O ₄ in Experimental Example 1 was used. FIG. 18 shows the calculated values when using a correction formula obtained using multiple regression analysis using logP 02, logP _{02, and the product of logP 02 and logP 02 as} explanatory variables, as in formula III. Shows the error from the actual concentration. As is known from FIG. 18, the NO ₂ sensing electrode 21 containing Co ₃ O ₄ has a larger error than the NO ₂ sensing electrode 21 containing Fe ₂ O ₃ shown in FIG. σ is also large.

Thus, the introduction of the interaction term in the multiple regression analysis enables more accurate NO ₂ concentration measurement in the gas concentration measuring device having the NO ₂ sensing electrode 21 containing Fe ₂ O ₃ .

In this example, the product of the logarithm of the oxygen concentration and the logarithm of the NO ₂ concentration is used as the interaction term of the multiple regression analysis, but it is not necessarily the product. For example, interaction terms such as logP _NO2 /logP _O2 and log(P _NO2 +logP _O2 ) can be used.

That is, in the gas concentration measurement device 1 including the NO ₂ detection electrode 21 containing an oxide containing at least one of Fe and Ni, such as Fe ₂ O ₃ , the correction in the NO ₂ concentration calculation unit 41 is performed as shown in Equation III. Secondly, it is preferably based on a correction formula having an interaction term between oxygen concentration and NO ₂ concentration. More preferably, it is based on a correction formula having the oxygen concentration, the NO ₂ concentration, and their interaction terms as explanatory variables.

The present invention is not limited to the above embodiments, modifications, and experimental examples, and can be applied to various embodiments without departing from the scope of the invention. Also, the configuration of each embodiment, each modified example, and the configuration of each experimental example in this specification can be combined with each other.

1 gas concentration measuring device 2 NO ₂ detection unit 3 O ₂ detection unit 41 NO ₂ concentration calculation unit 6 NOx detection unit 42 NOx concentration calculation unit

Claims (6)

a NO ₂ detector (2) that outputs an output signal α corresponding to the NO ₂ concentration in the measured gas;
an O ₂ detector (3) that outputs an output signal β corresponding to the O ₂ concentration in the measurement gas;
By correcting the concentration P _α calculated based on the output signal α from the NO ₂ detection unit based on the concentration P _β calculated based on the output signal β from the O ₂ detection unit, NO a NO ₂ concentration calculator (41) configured to calculate a ₂ concentration P _NO2 ;
a NOx detector (6) for outputting an output signal γ corresponding to the NOx concentration in the measured gas;
a NOx concentration calculator (42) for calculating the NOx concentration based on the output signal γ ,
The NO ₂ detection part is formed of a solid electrolyte body (5), and a NO ₂ detection electrode (21) and a reference electrode (100) formed on the solid electrolyte body,
A gas concentration measuring device (1), wherein the NO ₂ sensing electrode contains an oxide containing at least one of Fe and Ni. a NO ₂ detector (2) that outputs an output signal α corresponding to the NO ₂ concentration in the measured gas ;
an O ₂ detector (3) that outputs an output signal β corresponding to the O ₂ concentration in the measurement gas ;
By correcting the concentration P _α calculated based on the output signal α from the NO ₂ detection unit based on the concentration P _β calculated based on the output signal β from the O ₂ detection unit, NO a NO ₂ concentration calculator (41) configured to calculate a ₂ concentration P _NO2 ,
The NO ₂ detection part is formed of a solid electrolyte body (5), and a NO ₂ detection electrode (21) and a reference electrode (100) formed on the solid electrolyte body (5),
the NO ₂ sensing electrode contains an oxide containing at least one of Fe and Ni;
The gas concentration measuring device, wherein the NO ₂ concentration calculating section performs correction using a correction formula having an interaction term between the concentration P _α and the concentration P _β . Further, a pump section (3P) in which the gas concentration measuring device discharges _O2 from the measurement gas around the NOx detection section and reduces _NO2 in the measurement gas around the NOx detection section to NO. The gas concentration measuring device according to claim 1 , comprising: 4. The gas concentration measuring device according to claim 3, wherein the pump section is formed by the _O2 detection section. 5. The gas concentration measuring device has at least one solid electrolyte body, and the NO ₂ detection section, the O ₂ detection section and the NOx detection section are formed in the same solid electrolyte body. The gas concentration measuring device according to 1. The gas concentration measuring device has a first solid electrolyte body (53) and a second solid electrolyte body (54) formed at a position different from the first solid electrolyte body, and the NO ₂ detection part is 5. The gas concentration measuring device according to claim 3, wherein said first solid electrolyte body is formed, and said _O2 detection section and said NOx detection section are formed in said second solid electrolyte body.

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