JP2002071641A - Complex gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect an excess fuel quantity and oxygen concentration in combustion gas in addition to the detection of NOx concentration. SOLUTION: Air-fuel ratio detecting pump cells 13, 14 and air-fuel ratio sensor parts 23, 26, 27 are added to NOx detecting cells 10, 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor and, more particularly, to a composite gas sensor for detecting an air-fuel ratio of an internal combustion engine by detecting an oxygen concentration or a combustible gas concentration at the same time as a nitrogen oxide concentration in a combustion gas discharged from an internal combustion engine. Things.

[0002]

2. Description of the Related Art In recent years, all-solid-state NOx sensors capable of continuous detection by directly inserting them into combustion exhaust gas such as automobile exhaust gas have attracted attention, and some research results have been reported. For example, a current detection type NOx sensor has been reported as a sensor capable of detecting the NOx concentration in high-temperature exhaust gas from automobiles (SAE TECHNICAL PARER 960334). In this sensor, two spaces are provided by an ion conductor, and the oxygen concentration in the test gas is eliminated to almost zero by using an oxygen pump in the first space.
After x is NO gas, the NO is decomposed into nitrogen and oxygen in the second space by electrolysis, and the total NOx concentration is detected by detecting the decomposition current obtained at this time.

[0003] A mixed potential type total NOx sensor which has a completely different principle has been proposed. For example, JP
In Japanese Patent Application Laid-Open No. 1-72476, a detection electrode having activity simultaneously with NOx and oxygen and a reference electrode having activity only with oxygen are installed in a measurement space formed of an oxygen ion conductor, and the detection electrode and the reference electrode are connected to each other. The total NOx concentration in the test gas is measured by measuring the potential difference between the two. In this NOx sensor, the conversion electrode installed to face the detecting electrode (oxygen pump cell), while electrochemically converted to either the NOx in the test gas NO or NO _2, sensing electrodes of mixed potential Is used to detect the total NOx concentration.

[0004] However, any of the above-mentioned NOx sensors is affected not least by the oxygen concentration in the test gas. Therefore, it is necessary to accurately control the oxygen concentration in the measurement space, but in a test gas such as actual exhaust gas,
When the flow rate is large and the air-fuel ratio changes in a wide range from 10 to 22, it is very difficult to precisely control the oxygen concentration in the measurement space, and the cost increases. Further, in combustion control and exhaust gas purification control of automobiles and the like, it is necessary to detect the oxygen concentration in the combustion gas and perform feedback control, and at the same time, detect the total NOx concentration in the exhaust gas. In particular, in recent years, gasoline direct injection engines and their exhaust gas purification systems are used in a region from an ultra-lean combustion region (lean region) to an excess fuel region (rich region). Therefore, in such a combustion system, it is required to detect the air-fuel ratio (oxygen concentration and excess fuel amount) in a wide range in the actual exhaust gas and to detect the total NOx concentration at the same time.

[0005] In the above-described configuration of the current detection type NOx sensor, the oxygen concentration in the exhaust gas in the lean region where the oxygen is excessive can be simultaneously measured by the oxygen discharge pumping current (limit current value) performed in the preceding space. It has been. That is, by simultaneously measuring the excess oxygen concentration and the total NOx concentration in the exhaust gas, the actual air-fuel ratio state and the NOx concentration in the lean region of the engine can be independently detected. It is desired to control the fuel ratio by feedback. As a result, the NOx concentration can be suppressed within the exhaust gas regulation value, and optimal control of the engine air-fuel ratio with good fuel efficiency can be performed. However, with this sensor configuration, the air-fuel ratio in the rich region where fuel is excessive cannot be detected.

On the other hand, a gas sensor (air-fuel ratio sensor) that detects only a wide-range air-fuel ratio state in actual exhaust gas from a signal of a sensor installed in the exhaust gas is already mounted on a vehicle. This is a previously published paper (SAE TE
According to CHNICAL PARER 850378), a pair of oxygen pumping electrodes and a reference electrode are formed in a can chamber structure made of an oxygen ion conductor. At the time of excess oxygen in the lean region, the oxygen concentration in the exhaust gas is detected from the limiting current value of oxygen pumping, and at the time of excess fuel in the rich region,
The above-described oxygen pump is operated in reverse to detect an oxygen amount (oxygen pumping current value) necessary for burning excess fuel gas. That is, an actual air-fuel ratio state in the engine is detected by the air-fuel ratio sensor. However, it is difficult to directly detect the NOx concentration in the exhaust gas with the air-fuel ratio sensor, and it is necessary to use a plurality of sensors in order to simultaneously measure the NOx concentration and the air-fuel ratio.
In this case, it is clear that there is a limit to miniaturization of the system, and measurement accuracy deteriorates.

[0007]

As described above, in order to accurately measure the total NOx concentration in the combustion gas of an automobile or the like having a wide range of air-fuel ratio fluctuations, the measurement in which the detection electrode of the NOx sensor is installed is performed. It is necessary to precisely control the oxygen concentration in the space, but this involves technical difficulties and high costs. Further, in a combustion control or an exhaust gas treatment system for controlling exhaust gas, it is necessary to detect the total NOx concentration in the combustion gas and the oxygen concentration and the excess fuel amount in the combustion gas at the same time. That is, the present invention provides such a composite gas sensor that can simultaneously detect the total NOx concentration and the oxygen concentration or the excess fuel amount in the exhaust gas, and can improve the total NOx detection accuracy of the NOx sensor itself at low cost. It is an object to provide a composite gas detection device.

[0008]

Means for Solving the Problems The present inventors have made intensive studies in view of the above-mentioned problems, and as a result, have proposed the following solutions. That is, as shown in FIG. 1, a first solid electrolyte substrate 1 having oxygen ion conductivity and a second solid electrolyte substrate 2 are opposed to each other, and a first spacer made of the same kind of ion conductor as the solid electrolyte is used. 6, a first measurement space 4 formed by fixing while maintaining a predetermined distance, a first gas introduction port 8 provided so that the first measurement space 4 and the test gas atmosphere communicate with each other; 1 NOx detection electrode 10 fixed on the first solid electrolyte substrate exposed to the atmosphere in the measurement space and active on NOx and oxygen, and active on oxygen exposed to the atmosphere through the air reference duct 19. A NOx detection cell comprising a reference electrode 11;
A NOx conversion electrode 16 for converting NO in the test gas fixed to the second solid electrolyte substrate exposed to the atmosphere in the measurement space to NO ₂ or NO ₂ to NO; A NOx conversion pump cell as a first oxygen pump including a NOx conversion counter electrode 17 fixed on the electrolyte substrate through an air introduction duct 18 so as to be exposed to the atmosphere, and a NOx detection electrode 10 and a reference electrode 11. A NOx sensor unit comprising a means 21 for measuring a potential difference between the two, and a voltage applying means 25 for driving a NOx conversion pump cell; a first or second solid electrolyte substrate 1 or 2 constituting the NOx sensor unit; The second measurement space 5 formed by the third solid electrolyte substrate 3 having ion conductivity and the second spacer 7, and the second measurement space and the atmosphere of the gas to be detected are controlled by gas diffusion control. A second gas inlet 9 which communicates to the inflow, the second measurement second oxygen electrode 13 activity in a fixed oxygen on the solid electrolyte in the space, the second
An air-fuel ratio detection pump cell as a second oxygen pump including a second oxygen pump counter electrode 14 fixed on a third solid electrolyte substrate paired with the oxygen electrode so as to be exposed to the test gas atmosphere; A voltage application means 26 for driving the fuel ratio detection pump cell and a means 27 for detecting the air-fuel ratio detection pump current; a means 23 for detecting the potential difference between the second oxygen electrode 13 and the reference electrode 11; And a control means for controlling the oxygen concentration in the second measurement space to be constant on the basis of the air-fuel ratio sensor unit.

In the voltage application direction of the conversion pump cell driving external power supply 25 shown in FIGS.
Is converted to NO ₂ , but can be converted to NO by reversing the application direction.

FIG. 1 shows a structural example in which a self-heating heater 20 is attached to the sensor substrate of the present invention. By these means, the total NO in the measurement gas, especially in the combustion exhaust gas,
x concentration and air-fuel ratio can be simultaneously and accurately measured. 1 to 6, the same components are denoted by the same reference numerals.

In the structural example of FIG. 2, a first oxygen electrode active on oxygen is provided on the first solid electrolyte 1 exposed to the atmosphere in the first measurement space 4 in the structural example shown in FIG. 1
2 shows a composite gas detection apparatus characterized in that the apparatus is provided with means for measuring a potential difference between the NOx detection electrode 10 and the first oxygen electrode 12. Thereby, NO
By setting the reference of the x detection electrode under the same atmosphere, even if the oxygen concentration in the vicinity of the NOx detection electrode fluctuates, it is possible to eliminate the influence.

In the structure example of FIG. 3, in the structure example shown in FIG. 1, a first oxygen electrode active on oxygen is provided on the first solid electrolyte 1 exposed to the atmosphere in the first measurement space 4. 1
2 provided with means 21 for measuring a potential difference between the NOx detection electrode 10 and the reference electrode 11, and means 22 for measuring a potential difference between the first oxygen electrode 12 and the reference electrode 11. And a means for performing arithmetic processing using a potential difference. As the means for performing the arithmetic processing, a system using an electronic circuit as hardware or a microcomputer as software can be applied. This makes it possible to correct the NOx detection signal and the like to further improve the accuracy.

According to the present invention, as shown in FIG.
The second oxygen pump counter electrode 14 used in the example of FIG. 3 is also used as the NOx conversion counter electrode 17 used in the example of FIG. 3, and the air-fuel ratio detection pump cell including the NOx conversion counter electrode and the second oxygen electrode 13 is driven. In addition, the number of electrodes and the number of sensor lead wires are reduced, and the manufacturing cost of the sensor can be reduced.

[0014] Further, in the present invention, while converting NOx in the gas to be detected by applying a predetermined voltage to the NOx conversion pumping cell (16, 17) to NO or NO _2, transformed NO or NO ₂ concentration Is detected as the total NOx concentration by the change in the potential difference between the NOx detection electrode 10 and the reference electrode 11 of the NOx detection cell, and the second
It is obtained when the applied voltage of the air-fuel ratio detection pump is adjusted by the air-fuel ratio detection cell controller 28 so that the potential difference between the second oxygen electrode 13 installed in the measurement space 5 and the reference electrode 11 becomes a predetermined value. The current of the air-fuel ratio detection pump is used as a detection signal of the air-fuel ratio in the combustion gas, and thus the total NO in the test gas is
x concentration and air-fuel ratio can be detected simultaneously.

In the air-fuel ratio detection method according to the present invention, the potential of the second oxygen electrode 13 in the second measurement space 5 is set to -300 mV or less with respect to the reference electrode 11 of the NOx detection cell so that the potential becomes the set potential. When the current flowing through the second oxygen electrode flows so as to discharge oxygen in the second measurement space, the current value is calculated as the oxygen concentration in the test gas. As a detection signal, an O signal existing in the test gas atmosphere or the air atmosphere outside the second measurement space.
_When electrolysis of ₂ , H ₂ O or CO ₂ flows into the space so as to pump oxygen, the current value is used as a detection signal for the concentration of the combustible gas excessively present in the test gas. Therefore, depending on the direction of the current flowing through the second oxygen electrode in the second measurement space, the air-fuel ratio detection including the detection of the oxygen concentration or the flammable gas concentration is performed more accurately at the same time as the detection of the total NOx concentration in the test gas. be able to. Here, the air-fuel ratio means a ratio with the amount of air necessary for the fuel agent to burn (oxidize). That is, air-fuel ratio = (air amount)
The amount of air required for complete stoichiometric combustion, indicated by / (fuel agent amount), is called the stoichiometric air-fuel ratio. In the case of gasoline engine combustion, this stoichiometric air-fuel ratio is about 14.6,
Excess air (oxygen) exists in the air-fuel ratio range larger than this value, and fuel (flammable gas) becomes excessive in the air-fuel ratio range smaller than 14.6. That is, the air-fuel ratio in engine combustion can be detected by detecting the oxygen concentration and the combustible gas concentration in the exhaust gas.

In the sensor of the present invention, the NOx conversion pump cell to which a DC voltage is applied allows NOx in the test gas to be measured.
After the gas is converted into NO ₂ or NO, the change in the electromotive force detected by the NOx detection electrode and measured with reference to the reference electrode potential is used as the NOx output detection signal. On the other hand, regarding the detection of the oxygen concentration or the air-fuel ratio, when the electrode potential of the second oxygen electrode in the second measurement space is controlled by an electronic circuit so as to be, for example, −300 mV with respect to the reference electrode of the NOx detection cell, The oxygen concentration in the second measurement space is kept constant at the ppm level, and the oxygen in the test gas flowing into this space becomes excessive, and is detected as a pumping current for oxygen pumping.

Therefore, in the case of excess oxygen, it is detected as an output signal of the oxygen concentration. Conversely, if oxygen in the test gas is insufficient for the amount of coexisting combustible gas, oxygen will be pumped until the output signal of the second oxygen electrode becomes -300 mV. That is, the current value at this time is proportional to the flammable gas concentration in the test gas, and can be used as the output of the flammable gas sensor. The control value of the oxygen concentration in the second measurement space, that is, the setting of the potential difference V'O2 between the second oxygen electrode 13 and the reference electrode 11 is as follows. Becomes large. Preferably, the potential difference V'O2 is set to -5.
It is better not to be less than 00mV. This is because if the control oxygen concentration is extremely reduced due to the delay of the follow-up property of the oxygen pumping, the detection accuracy of the detection signal is reduced due to oscillation or the like.

Further, when the combustible gas is measured, if the combustible gas that has entered the second measurement space is completely burned, the measurement result becomes more accurate. For this reason, if the oxidation catalyst is independently installed in the second measurement chamber, or is fixed as a catalyst film on the second oxygen electrode, the above-described object can be achieved.
This catalyst material includes Pt, Ru, Rh, Ir, P
It is desirable to use d, Ag, Ni, or an alloy, mixed phase, or oxide containing at least one of them. Further, the second oxygen electrode in the second measurement space is also Pt, R
It is desirable to use u, Rh, Ir, Pd, Ag, Ni, or an alloy, mixed phase, or oxide containing at least one of them.

Further, the NOx conversion voltage is controlled by using the oxygen concentration detection signal from the air-fuel ratio detection cell of the composite gas sensor of the present invention, or the output of the NOx sensor is corrected, so that the oxygen concentration of the conventional NOx sensor is controlled. The effect can be greatly reduced. Further, the third oxygen electrode 1 directly exposed to the test gas to the composite gas sensor of the present invention.
By providing 5, the output of the conventional oxygen sensor (λ-sensor) can be extracted by the oxygen concentration electromotive force with the reference electrode 11 as the reference potential. This makes it possible to simultaneously execute the conventional exhaust gas control method and the exhaust gas control using the NOx sensor, thereby enabling more precise combustion control or control of the exhaust gas purification system.

On the other hand, in an actual sensor configuration, FIGS.
In addition to the structure shown in FIG. 6, for example, a derived structure as shown in FIG. That is, in the NOx conversion pump cell as the first oxygen pump, the conversion electrode is divided, and a hydrocarbon gas (HC) or a hydrocarbon gas (HC) coexisting in the test gas in the front part of the first measurement space (the first gas inlet side). Carbon monoxide (C
It can be used as a gas treatment electrode for oxidizing and eliminating a reducing gas such as O). In FIG. 6, the drive power is individually applied to the gas processing pump cells (17, 31) by the external drive power supply 30, but the external power supply 25 for driving the conversion pump cell may be shared (not shown).

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described based on the sensor configuration shown in FIG. The composite gas detector is shown in FIG.
As shown in (1), the first solid electrolyte substrate 1 and the second solid electrolyte substrate 2 having oxygen ion conductivity are opposed to each other,
The first measurement space 4 formed by fixing the first spacer 6 made of the same kind of ion conductor as the above-mentioned solid electrolyte while maintaining a predetermined distance, and the first measurement space 4 and the atmosphere of the test gas are formed. A first gas inlet 8 provided so as to communicate with a NOx and oxygen-active NOx detection electrode 10 fixed on a first solid electrolyte substrate exposed to an atmosphere in a first measurement space; A NOx detection cell comprising a reference electrode 11 exposed to the atmosphere and exposed to oxygen via a reference duct 19, and a test object fixed on a second solid electrolyte substrate exposed to the atmosphere in the first measurement space. N in gas
NOx for converting O to NO ₂ or NO ₂ to NO
Conversion electrode 16 and N fixed on the second solid electrolyte substrate through an air introduction duct so as to be exposed to the atmosphere.
Nx as the first oxygen pump comprising the Ox conversion counter electrode 17
Ox conversion pump cell, NOx detection electrode 10 and reference electrode 1
A NOx sensor unit comprising a means 21 for measuring a potential difference between the NOx sensor 1 and a voltage applying means 25 for driving the NOx conversion pump cell; and a first or second solid electrolyte substrate 1 or 2 constituting the NOx sensor unit. 2 and a third solid electrolyte substrate 3 having oxygen ion conductivity and a second measurement space 5 formed by a second spacer 7, and the second measurement space and the gas atmosphere to be inspected are gas-controlled with gas diffusion control. A second gas inlet 9 that is communicated so as to flow in, a second oxygen electrode 13 that is active on oxygen fixed on the solid electrolyte in the second measurement space, and a second oxygen electrode that is paired with the second oxygen electrode. 3 for driving an air-fuel ratio detection pump cell as a second oxygen pump comprising a second oxygen pump counter electrode 14 fixed on the solid electrolyte substrate so as to be exposed to the test gas atmosphere, and an air-fuel ratio detection pump cell. of Pressure applying means 26 and means 27 for detecting the air-fuel ratio detecting pump current; means 23 for detecting the potential difference between the second oxygen electrode 13 and the reference electrode 11; and the oxygen concentration in the second measurement space based on the potential difference. And an air-fuel ratio sensor unit comprising a control means 28 for keeping the constant.

The oxygen ion conductive solid electrolyte substrates 1, 2, 2,
3 to form a laminated structure, and a sensor element is manufactured. The material of the oxygen ion conductor is not particularly limited, but a zirconia solid electrolyte is generally used. In order to impart ion conductivity, yttria, calcia and the like are usually added as a solid solution, and about 3 to 8 mol is preferably added in consideration of a balance between mechanical strength and ion conductivity. The zirconia green sheet is produced as follows.

That is, a predetermined amount of the zirconia powder and the yttria powder are mixed, or a predetermined number of moles of the solid solution of the yttria-added zirconia powder is mixed with an organic binder (PVA)
Etc.) and a solvent or a dispersant (surfactant) to form a slurry. By forming this zirconia slurry on a PET film by a doctor blade method, a zirconia green sheet having a thickness of several 100 μm is obtained. The green sheet is cut into a predetermined shape, and electrodes, heaters, leads, and the like are applied and formed by screen printing or the like. The green sheets can be adhered to each other by pressing the thus prepared sheets by mechanical pressing or isostatic pressing in warm water.

At this time, in order to form an internal space such as a duct, a vanishing mold is usually loaded. For the disappearing type, theobromine or the like which sublimes at a temperature lower than the temperature at which the organic binder is burned out is used.

[0025] In this way, a device in which zirconia is integrated with each other is obtained by degreasing and firing the laminated green body formed of green sheets. The degreasing temperature is usually selected at around 600 ° C. at which the organic binder is completely burned off, and the firing temperature at around 1400 ° C. at which zirconia is sintered.

The above-described atmospheric duct and measurement space were formed in the sensor element formed of the laminate, and a reference electrode and a conversion pump counter electrode were formed of platinum in each of the air duct and the measurement space. A gas inlet is provided at the front of the gas measurement space, and the gas measurement space is communicated with the atmosphere of the test gas via the gas inlet. The installation position of the gas inlet is not particularly limited. However, in order to control the gas diffusion at the second gas inlet, it is necessary to provide sufficient diffusion resistance. In the first measurement space,
On the opposite side of the solid electrolyte substrate to which the reference electrode is fixed, a first oxygen electrode made of platinum and a NOx-active N
The Ox detection electrode is fixed. As the material of the NOx sensing _{electrode, NiCr 2 O 4, MgCr 2} O 4, FeCr spinel-type metal oxides such as _{2 O 4, NiO, Fe 2} O 4, Cr 2 O single metal oxides such as _3, Pt- Rh, Pt-Ir-Rh, Rh
And other noble metals are used. Further, a conversion electrode was formed of a Pt-Rh alloy on the other side of the ion conductor fixing the Pt counter electrode of the conversion pump in the other air introduction duct.

In such a sensor configuration, as shown in FIG. 1 to FIG.
A measurement space was formed. Diffusion resistance was given to the gas inlet of the second measurement space by reducing the cross-sectional area of the inlet so that gas diffusion was controlled. Further, a second oxygen electrode made of platinum is formed inside the second measurement space. Further, Pt is provided outside the second measurement space as a counter electrode of the second oxygen electrode.
The electrodes were attached.

According to the present invention, as shown in FIG.
The second oxygen pump counter electrode 14 used in the example of FIG. 3 is also used as the NOx conversion counter electrode 17 used in the example of FIG.
By driving the air-fuel ratio detection pump cell including the conversion counter electrode and the second oxygen electrode, the number of electrodes and the number of sensor lead wires are reduced, and the manufacturing cost of the sensor can be further reduced.

In the structural example shown in FIG. 5, a third oxygen electrode made of Pt is provided on the front part of the duct on the reference electrode 11 side (the part that is directly exposed to the test gas atmosphere on the first solid electrolyte substrate). 15 are formed. A means 24 for detecting a potential difference is connected to the third oxygen electrode 15. A self-heatable printing heater 20 of Pt or the like was attached to the outermost part of the composite gas sensor body thus fabricated on the reference electrode side. A measuring circuit as shown in FIGS. 1 to 3 was connected to the composite gas sensor.

[0030]

The present invention will be specifically described below with reference to examples.
The present invention is not limited to these examples.

Example 1 A composite gas sensor having the structure shown in FIG. 3 was manufactured in the following procedure. The NOx detection cell has P on one surface of the zirconia solid electrolyte substrate to which 6 mol of yttria is added.
A t-Rh (3 wt%) NOx detection electrode 10 and a first oxygen electrode 12 made of Pt are placed on a Pt reference electrode 11 on the opposite surface.
Was fixed. The NOx conversion pump cell forms a NOx conversion electrode 16 made of a Pt-Rh (3 wt%) alloy in the first measurement chamber and a NOx conversion electrode 17 made of Pt on the opposite surface so as to face the detection cell of the zirconia solid electrolyte substrate. It was produced. Further, the second measurement space 5 shown in FIG. 3 is formed of a zirconia substrate, and Pt electrodes (the second oxygen electrode 13 and its counter electrode 14) are provided inside and outside this space, respectively.
Was formed. 1400 ° C.
For 5 hours to prepare an integrated element.

In the sensor configuration of this embodiment shown in FIG. 3, the potential difference VNOx between the NOx detecting electrode 10 and the reference electrode 11
And the potential difference VO2 between the first oxygen electrode 12 and the reference electrode 11 was corrected by the arithmetic electronic circuit 29. That is,
An output obtained by adding a correction function value to a difference output between VNOx and VO2 is used as a sensor output.

The characteristics of the composite gas sensor obtained in the simulated gas were evaluated. 200 ppm of NO was allowed to coexist in a nitrogen base gas at a flow rate of 2 L / min, and the oxygen concentration was changed to 0 to 10%. Next, the measurement was performed with the oxygen concentration fixed at 0% and the C ₃ H ₆ gas changed to 10 to 1000 ppm. The sensor operating temperature at this time is fixed at a temperature of 600 ° C. Regarding the control of the air-fuel ratio detection pump cell, the drive voltage of the air-fuel ratio detection pump cell was controlled using an electronic circuit so that the potential of the second oxygen electrode in the second measurement space became -350 mV with respect to the reference electrode. The pump current value obtained at this time was used as the output of the air-fuel ratio sensor. FIG. 7 shows the results. In the region where the oxygen concentration is 0% or more, the current of the air-fuel ratio detection pump cell is proportional to the oxygen concentration, and a negative current flows in the C ₃ H ₆ gas under the 0% oxygen concentration, and the current value is C ₃ H ₆ Was found to be proportional to the concentration of

Example 2 A composite gas sensor having the structure shown in FIG. 4 was manufactured using the same materials and procedures as in Example 1. The difference from the first embodiment is that the second oxygen pump counter electrode 1 in the second measurement space 5 is used.
4 was omitted and shared with the counter electrode 17 of the NOx conversion pump.
The sensor performance of the obtained composite gas sensor was confirmed under the same measurement conditions as in Example 1. FIG. 8 shows the result. It can be seen that almost the same results as in Example 1 were obtained.

Example 3 A composite gas sensor having the structure shown in FIG. 5 was manufactured using the same materials and procedures as in Example 1. The difference from the first embodiment is that the third oxygen electrode 15 made of Pt is installed so as to be directly exposed to the measurement gas atmosphere. The sensor performance of this composite gas sensor was evaluated under the same measurement conditions as in Example 1. In addition, the potential of the third oxygen electrode 15 was measured with respect to the reference electrode 11 of the NOx detection cell to obtain a detection output. FIG. 9 shows the result. From FIG. 9, the total N in the measurement gas
It can be seen that detection outputs indicating the Ox concentration, the oxygen concentration, and the C ₃ H ₆ concentration were obtained. From these results, it is clear that the composite gas sensor of the present invention can obtain an air-fuel ratio in, for example, flue gas.

Example 4 A composite gas sensor having the same configuration as in Example 1 was manufactured. The difference from the first embodiment is that the conversion pump cell voltage of the NOx sensor is controlled using the oxygen detection signal in the second measurement space 5 so that the oxygen concentration dependence of the NOx sensor output is set to be constant. The sensor performance of this composite gas sensor was confirmed under the same measurement conditions as in Example 1.
The result is shown in FIG. Clearly, the oxygen concentration dependence has been improved.

[Embodiment 5] A composite having the same configuration as that of Embodiment 1
A gas sensor was manufactured. However, in this embodiment,
A two-oxygen electrode 13 was produced by changing the materials shown in Table 1. Ma
In addition, the same material system is independently fixed in the second measuring chamber 5.
And the one laminated on the second oxygen electrode 13
did. These composite gas sensors were replaced with oxygen as in Example 1.
Is 0%, C _ThreeH₆Was measured under 4000 ppm. as a result
Are shown in Table 1. No catalyst layer or catalyst body is loaded
Detection output is larger than in the case of
C_ThreeH₆It can be seen that the oxidation of was accelerated.

[0038]

[Table 1]

[0039]

According to the composite sensor of the present invention, the total NOx concentration and the oxygen concentration or the flammable gas concentration in the test gas can be simultaneously measured. That is, the total N in the exhaust gas
Ox concentration and air-fuel ratio can be measured simultaneously.
Furthermore, it is also possible to mount a linear (linear) oxygen sensor and an electromotive force type oxygen sensor as a combined oxygen sensor. If the conversion voltage of the NOx sensor is controlled using the signal of each oxygen sensor, the oxygen concentration of the NOx sensor can be increased. The dependency was found to be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a composite gas sensor showing one example of the present invention.

FIG. 2 is a sectional view of a composite gas sensor showing another example of the present invention.

FIG. 3 is a cross-sectional view of a composite gas sensor showing another example of the present invention.

FIG. 4 is a sectional view of a composite gas sensor showing another example of the present invention.

FIG. 5 is a sectional view of a composite gas sensor showing another example of the present invention.

FIG. 6 is a sectional view of a composite gas sensor showing another example of the present invention.

FIG. 7 is a graph showing measurement results in Example 1 of the present invention.

FIG. 8 is a graph showing measurement results in Example 2 of the present invention.

FIG. 9 is a graph showing measurement results in Example 3 of the present invention.

FIG. 10 is a graph showing measurement results in Example 4 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st solid electrolyte board 2 2nd solid electrolyte board 3 3rd solid electrolyte board 4 1st measurement space 5 2nd measurement space 6 1st spacer 7 2nd spacer 8 1st gas inlet 9 2nd Gas inlet 10 NOx detection electrode 11 Reference electrode 12 First oxygen electrode 13 Second oxygen electrode 14 Second oxygen pump counter electrode 15 Third oxygen electrode 16 NOx conversion electrode 17 NOx conversion counter electrode 18 Atmospheric introduction duct 19 Atmospheric reference duct 20 Self-heating Heater 21 NOx detection electrode output detector 22 First oxygen electrode output detector 23 Second oxygen electrode output detector 24 Third oxygen electrode output detector 25 External power supply for conversion pump cell drive 26 External power supply for air-fuel ratio detection pump cell drive 27 Air-fuel ratio detection pump cell current detector 28 Air-fuel ratio detection pump cell controller 29 NOx sensor output arithmetic processing unit 30 Gas processing External power supply for pump cell drive 31 Gas treatment pump electrode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G01N 27/46 327G 327S 327Z

Claims (12)

[Claims] 1. A first solid electrolyte substrate having oxygen ion conductivity and a second solid electrolyte substrate facing each other, while maintaining a predetermined distance by a first spacer made of the same type of ion conductor as the solid electrolyte. A first measurement space formed by fixing, a first gas inlet provided so that the first measurement space communicates with the test gas atmosphere, and a first measurement space exposed to the atmosphere in the first measurement space. A NOx sensing cell fixed on the first solid electrolyte substrate, the NOx sensing electrode being active on NOx and oxygen, and a reference electrode being exposed to the atmospheric atmosphere and being active on oxygen; A NOx conversion electrode fixed on a second solid electrolyte substrate exposed to an atmosphere for converting NO in a test gas to NO ₂ or NO ₂ to NO, and an NOx conversion electrode on the second solid electrolyte substrate; Exposed to the atmosphere NOx that has been fixed in so that
A NOx conversion pump cell as a first oxygen pump comprising a conversion counter electrode; a unit for measuring a potential difference between the NOx detection electrode and the reference electrode; and a voltage application unit for driving the NOx conversion pump cell. A sensor section; a second measurement space formed by the first or second solid electrolyte substrate constituting the NOx sensor section, a third solid electrolyte substrate having oxygen ion conductivity, and a second spacer; A second gas inlet in which the second measurement space and the test gas atmosphere communicate with each other so as to allow gas to flow in with gas diffusion control; and a second gas introduction port active on oxygen fixed on the solid electrolyte in the second measurement space. A second oxygen electrode comprising a second oxygen electrode and a second oxygen pump counter electrode fixed on the third solid electrolyte substrate paired with the second oxygen electrode so as to be exposed to the test gas atmosphere; An air-fuel ratio detection pump cell as an elementary pump; a voltage application unit for driving the air-fuel ratio detection pump cell; a unit for detecting an air-fuel ratio detection pump current; and a potential difference between the second oxygen electrode and the reference electrode. An air-fuel ratio sensor unit comprising: a detection unit; and a control unit for making the oxygen concentration in the second measurement space constant based on the potential difference. 2. The composite gas detection device according to claim 1, wherein a first oxygen electrode active on oxygen is provided on the first solid electrolyte exposed to the atmosphere in the first measurement space, A composite gas detection device comprising means for measuring a potential difference between the NOx detection electrode and the first oxygen electrode. 3. The composite gas detection device according to claim 1, wherein a first oxygen electrode active on oxygen is provided on the first solid electrolyte exposed to the atmosphere in the first measurement space,
Means for measuring a potential difference between the NOx detection electrode and the reference electrode, and means for measuring a potential difference between the first oxygen electrode and the reference electrode, and means for performing arithmetic processing using the two potential differences A composite gas detection device comprising: 4. The composite gas detection device according to claim 1, wherein the second oxygen pump counter electrode is also used as the NOx conversion counter electrode, and an air-fuel ratio detection pump cell including the NOx conversion counter electrode and the second oxygen electrode is provided. A composite gas detection device having a voltage application unit for driving and a unit for detecting an air-fuel ratio detection pump current. 5. The composite gas sensor according to claim 1, wherein a predetermined voltage is applied to the NOx conversion pump cell to convert NOx in the test gas into NO or NO ₂ while converting NO. or at the same time the NO ₂ concentration detected as total NOx concentration by the potential difference change between the NOx sensing electrode and the reference electrode of the NOx detection cell, between the reference electrode and the second oxygen electrode placed in the second measurement space The current of the air-fuel ratio detection pump obtained when the applied voltage of the air-fuel ratio detection pump is adjusted so that the potential difference becomes a predetermined value is used as a detection signal of the air-fuel ratio in the combustion gas, and thus the total NOx concentration in the test gas A composite gas detection device for simultaneously detecting the air and fuel ratio. 6. The composite gas detection device according to claim 1, wherein a potential of the second oxygen electrode in the second measurement space is set to −300 mV or less with respect to a reference electrode of the NOx detection cell. When the voltage applied to the oxygen detection pump is adjusted to a potential, and the current flowing through the second oxygen electrode flows so as to discharge oxygen in the second measurement space, the current value is measured in the test gas. And the oxygen concentration detection signal
When oxygen flows from outside the second measurement space into this space so as to be pumped into the space, the current value is used as a detection signal of the concentration of combustible gas excessively present in the test gas, and N
A composite gas detection device that performs air-fuel ratio detection including detection of oxygen concentration or flammable gas concentration simultaneously with detection of Ox concentration. 7. The composite gas detection device according to claim 1, wherein an oxidation catalyst is provided in a gas inlet of the second measurement space or inside the measurement space. 8. The composite gas detection device according to claim 4, wherein an oxidation catalyst layer is provided on a surface of the second oxygen electrode provided inside the second measurement space. 9. The composite gas detector according to claim 5, wherein the oxidation catalyst provided inside the second measurement space is Pt, Ru, Rh, Ir, Pd, Ag, Ni, or at least one of them. A composite gas detection device formed using an alloy, an oxide, or a mixture thereof containing one type. 10. The composite gas detection device according to claim 1, wherein the second oxygen electrode provided inside the second measurement space includes Pt, Ru, Rh, Ir, Pd, Ag, Ni,
Alternatively, a composite gas detection device formed using an alloy, an oxide, or a mixture thereof containing at least one of these. 11. The composite gas detecting device according to claim 1, wherein a voltage applied to the NOx conversion pump cell is controlled by using a current flowing through the second oxygen electrode in the second measurement space as a signal. Composite gas detector. 12. The composite gas detection device according to claim 1, wherein a third oxygen electrode active on oxygen is formed on the solid electrolyte substrate where oxygen ion conduction is continuous with the first solid electrolyte substrate. A composite gas detection device, wherein an electromotive force between a third oxygen electrode and a reference electrode of the NOx detection cell is measured to detect an oxygen concentration in a test gas.