JPH10132782A - Gas-detecting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the concentration of nitrogen oxide in a gas to be measured with a simple constitution accurately with good response without being influenced by the concentration of oxygen. SOLUTION: In an oxygen sensor part 51, an electrode 511 on the inner side of a hollow part 3, to which a gas to be measured is introduced via a measurement gas introduction path 2, is formed near an opening 2a of the introduction path 2. A component gas detection part 6 has an electrode 61 on the side of the hollow part 3 formed at a position separated from the opening 2a more than the electrode 511 of the oxygen sensor part 51. The electrode 61 is overlapped with an electrode 522 of an oxygen pump part 52. In the constitution, in quick response to a change of an oxygen concentration of the gas to be measured which is introduced into the hollow part 3, the oxygen is supplied or discharged by the oxygen pump part 52 in the vicinity of the electrode 61 of the component gas detection part 6. Therefore, the oxygen concentration can be maintained constant without the oxygen separated by the gas to be measured in the vicinity of the electrode 61.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detection device, and more particularly to a gas detection device which is disposed in an exhaust pipe of an internal combustion engine and is used for detecting the concentration of a component gas contained in exhaust gas discharged from the internal combustion engine. .

[0002]

2. Description of the Related Art In an internal combustion engine of a vehicle or the like, in order to improve exhaust emission, for example, a fuel injection amount or the like is feedback-controlled so that an air-fuel ratio of a mixture becomes a stoichiometric air-fuel ratio. An exhaust emission control technology is adopted in which exhaust emissions in the exhaust gas to be removed are removed by a three-way catalytic converter. In recent years, regulations on exhaust emissions have been tightened, and self-diagnosis regulations (abbreviated as OBD-II) have already begun in the United States, obliging drivers to detect failures in exhaust emission control-related components, such as three-way catalytic converters, so that drivers can recognize them. As a result, drivers are now obliged to repair broken exhaust emission control-related parts.

As a technique for diagnosing deterioration of a three-way catalytic converter, a so-called 2O ₂ sensor system in which an oxygen concentration sensor is provided upstream and downstream of a three-way catalytic converter in an exhaust pipe is known. However, the tightening of exhaust gas regulations has led to the above-mentioned OBD-II LEV (Low Emission Vehicle).
le) to ULEV (Ultra Low Emission Vehicl)
Proceeding to e), the detection accuracy is insufficient with the 2O ₂ sensor system that indirectly detects the purification rate from the signal difference between the two oxygen concentration sensors. Therefore, there is an increasing need for a gas detection device that directly detects exhaust emission components such as nitrogen oxides (NOx).

As a gas detecting device for directly detecting a component gas to be detected, such as the above-mentioned exhaust emission, an electrode exposed to a gas to be measured and a reference gas having a standard oxygen concentration are provided on both surfaces of an oxygen ion conductive solid electrolyte material. There have been proposed various solid electrolyte type gas detection devices that form an electrode that is exposed to a gas and uses a change in an electromotive force or the like generated between the electrodes. In these methods, NOx is decomposed by a catalyst or the like and the NOx concentration of the gas to be measured is detected as oxygen concentration.Since NOx is decomposed into oxygen and detected, there is no selectivity for oxygen in the gas to be measured, and It is necessary to keep the oxygen concentration of the gas constant.

[0005] As such a solid electrolyte type gas detector,
Society of Automobile Eng
There is a thick-film ZrO ₂ NOx sensor described in US Pat. This thick film ZrO
_{2 In the} NOx sensor, an oxygen sensor is provided in the first chamber into which the gas to be measured is introduced, and a first pump cell for discharging oxygen from the first chamber is provided so that the oxygen concentration detected by the sensor becomes a predetermined value. ing. A second pump cell for discharging oxygen in the chamber is provided in the second chamber communicating with the first chamber via the diffusion resistance path, and the electrode on the indoor side has a reducing activity for NOx. Since the acidity concentration in the first chamber is detected by the oxygen sensor provided in the first chamber and fed back to the driving voltage of the first pump cell and kept constant,
The oxygen concentration of the gas to be measured diffused into the second chamber is constant.
In the second chamber, oxygen is newly generated by the decomposition of NOx, and the pump current of the second pump cell increases and decreases according to the NOx concentration. The NOx concentration is detected by measuring the increase or decrease of the pump current.

[0006]

However, the above SA
In the thick film ZrO ₂ NOx sensor described in E960334, a diffusion resistance path separating the first chamber and the second chamber is provided in order to keep the oxygen concentration of the gas to be measured diffused into the second chamber constant. However, the structure is complicated and the response and detection gain are not sufficient. If the diffusion resistance path is simply removed, there is a problem that the oxygen concentration near the electrode of the second pump cell fluctuates due to the oxygen flowing in and out, and a detection error occurs.

Accordingly, an object of the present invention is to provide a gas detection device which can obtain high responsiveness and high detection gain with a simple configuration and also has high detection accuracy.

[0008]

According to the first aspect of the present invention, the following structure is provided for controlling the oxygen concentration in the hollow portion through which the gas to be measured is introduced through the gas introduction passage having the diffusion resistance. Let me know. An oxygen sensor section and a pump section, each having a pair of electrodes formed on opposing surfaces of an oxygen ion conductive solid electrolyte material, are provided. The oxygen sensor portion is formed such that one electrode faces the inside of the hollow portion and the other electrode is exposed to a reference gas outside the hollow portion. The oxygen pump section is formed so that one electrode is exposed to the gas to be measured outside the hollow section and the other electrode faces the inside of the hollow section so that a pump current flows through the solid electrolyte material. Oxygen pump control means for performing feedback control of the pump current of the oxygen pump section based on the oxygen concentration detected by the oxygen sensor section. In order to decompose nitrogen oxides, which are to be detected in the gas to be measured in the hollow part, to generate oxygen and to detect NOx concentration as oxygen concentration, a pair of electrodes are provided on opposite surfaces of a solid electrolyte material having oxygen ion conductivity. Is provided. In the pair of electrodes, the electrode inside the hollow portion is an electrode having an activity of reducing NOx. The other electrode is formed so as to be exposed to a reference gas having a reference oxygen concentration. Signal detection means for detecting an output signal between the electrodes of the component gas detection unit is provided. In addition, the electrode inside the hollow part of the oxygen sensor part is formed near the opening position inside the hollow part of the gas introduction path to be measured, and the electrode inside the hollow part of the component gas detecting part is inside the hollow part of the oxygen sensor part. The electrode is formed at a position farther from the opening of the gas introduction path than the electrode of the above and overlaps with the electrode inside the hollow portion of the oxygen pump section.

In the component gas detection section, NOx is decomposed by a reduction reaction on the electrode surface inside the hollow section to generate oxygen, and a detection signal corresponding to the amount of generated oxygen is obtained by signal detection means.

Since the electrode inside the hollow portion of the oxygen sensor portion is located near the opening of the measured gas introduction passage, the oxygen pump portion responds to the change in the oxygen concentration in the measured gas introduced into the hollow portion. Operate. Since the electrode of the component gas detection unit is formed at a position farther from the opening position of the gas introduction path to be measured than the electrode inside the hollow part of the oxygen sensor unit and overlaps with the electrode of the oxygen pump unit, the component Oxygen in the gas to be measured in the vicinity of the electrode inside the hollow portion of the gas detection unit is supplied or discharged by the oxygen pump unit in response to a change in the oxygen concentration of the gas to be measured introduced into the hollow portion. Thus, the measured gas near the electrode inside the hollow part of the component gas detector is
The oxygen concentration is kept constant without being separated by a diffusion resistance path or the like, and the detection accuracy of the NOx concentration is good. Moreover, since the gas to be measured in the vicinity of the electrode inside the hollow portion of the component gas detector is not separated, the structure is simple and the response is good.

According to the second aspect of the present invention, the electrodes facing the hollow portion of the oxygen pump section and the oxygen sensor section are made of a metal inert to NOx to be detected. NOx in the gas to be measured in the hollow portion on the electrode surface is prevented from being decomposed by the reduction reaction, and the occurrence of NOx detection error can be prevented.

According to the third aspect of the present invention, the gas detector penetrates the partition wall that separates the gas to be measured from the atmosphere, and is provided so that its tip protrudes toward the gas to be measured. Inside, a hollow portion communicating with the outside of the gas detector via the measured gas introduction path and a reference gas introduction path into which the reference gas is introduced are provided at the tip. One end of the reference gas introduction passage extends to the vicinity of the hollow portion, and the reference gas is introduced from the other end of the base side of the gas detector. The oxygen pump section is configured such that the solid electrolyte material is formed on a part of a partition wall that separates the hollow portion from the outside of the gas detector, and the first solid electrolyte material faces the inside of the hollow portion and the outside of the hollow portion of the solid electrolyte material. Are formed. The oxygen sensor section forms the solid electrolyte material on a part of a partition wall separating the hollow section and the reference gas introduction path, and forms a second pair of electrodes inside the hollow section of the solid electrolyte material and the reference gas introduction path side. I do. The electrode inside the hollow portion has a smaller area than the electrode inside the hollow portion of the oxygen pump portion and is formed at a position facing the central portion of the electrode. The component gas detection section forms the solid electrolyte material on a part of a partition wall separating the hollow portion and the reference gas introduction path, and forms a third pair of electrodes inside the hollow portion of the solid electrolyte material and the reference gas introduction path side. Form. The electrode inside the hollow portion is formed so as to surround the electrode inside the hollow portion of the oxygen sensor portion by forming a hollow portion at the center portion and to overlap with the electrode inside the hollow portion of the oxygen pump portion.

With such a configuration, the main part of the gas detection device can be integrally and compactly configured.

[0014]

FIG. 1A shows a gas detector according to the present invention applied to the detection of the NOx concentration of exhaust gas discharged from an internal combustion engine. , And a circuit section C. The sensor portion S is formed by screwing a cylindrical housing 91 through an exhaust pipe wall W serving as an isolation wall of the internal combustion engine, and insulating members 921, 922, and 923 inserted into the housing 91 are opened at the upper end of the housing 91. Is fixed to the housing 91 by a lid member 93 that closes the cover. The elongated plate-shaped gas detector 1 is inserted and held in through holes 92a provided in the insulating members 921, 922, and 923, the tip 1a protrudes from the housing 91 inside the exhaust pipe wall W, and the base 1b is a lid member. It projects beyond 93.

The distal end of the gas detector protruding into the exhaust pipe W is housed in a bottomed cylindrical exhaust cover 95 fixed to the lower end of the housing 91. The exhaust cover 95 is made of stainless steel and has a double structure of an inner cover 951 and an outer cover 952.
Gas flow holes 953, 9 for taking in the exhaust gas as the gas to be measured into the exhaust cover 95 are provided on the peripheral walls of the exhaust valves 51, 952.
54 are formed respectively.

A cylindrical air cover 94 is fixed to the upper end of the cover member 93. The air cover 94 is provided in the housing 91.
And a sub-cover 942 covering the rear end of the main cover 941. The air inlets 943, 944 are respectively provided at positions opposing the peripheral walls of the main cover 941. The gas atmosphere is taken into the atmosphere cover 94.
The taken air is led to the base 1b of the gas detector 1,
It is introduced into the base 1b. Atmospheric inlets 943, 94
4, a water-repellent filter 945 is provided between the main cover 941 and the sub-cover 942 for waterproofing. Only the atmosphere is introduced into the sensor unit S, and moisture may enter. Is prevented.

The upper end of the air cover 94 is open, and a lead wire 96 connected to the rear end of the gas detector 1 extends outside from the upper end opening.

FIG. 1B is an enlarged sectional view of the gas detector 1.
FIG. 2 is an exploded view of the gas detector 1. The gas detector 1 has a hollow portion 3, a sensor cell 51 serving as an oxygen sensor portion, a pump cell 52 serving as an oxygen pump portion, and a component at a distal end portion 1a (left side in the figure) protruding into the exhaust pipe W. It is composed of a detection cell 6 or the like as a gas detector, and the members constituting these have a laminated structure.

In FIG. 2, the laminated structure is a flat oxygen ion conductive solid electrolyte material 11, a flat alumina spacer 12, and a flat oxygen ion conductive solid electrolyte material 13 from the upper side in FIG. I have. The intermediate spacer 12 has a rectangular hollow portion 12 a formed at the tip end side, and the space closed by the solid electrolyte materials 11 and 13 forms the hollow portion 3.

On the lower side of the figure, a flat spacer 14 made of alumina and a flat heater section 15 are provided below the solid electrolyte material 13. Intermediate spacer 14
Is formed with an elongated lightening portion 14a, one end of which has the same shape as the lightening portion 12a of the spacer 12 and faces the lightening portion 12a, and the other end has a slit-like shape. 14 bases have been reached. Solid electrolyte material 1
The space of the lightening portion 14a closed by the heater 3 and the heater portion 15 is a duct 4 serving as a reference gas introduction passage for introducing the atmosphere into the gas detector 1 through the air introduction holes 943, 944 (FIG. 1A). It has become.

One of a first pair of electrodes made of Pt--Au having substantially the same shape as the lightened portion 12a of the spacer 12 by screen printing or the like at a position forming the inner surface of the hollow portion 3 on the lower surface of the solid electrolyte material 11. A certain electrode 522 is formed, and the other electrode 521 of the first pair of electrodes made of Pt is formed on the upper surface of the solid electrolyte material 11 so as to face the electrode 522. The pump cell 52 is constituted by the solid electrolyte material 11 and the electrodes 521 and 522.

The solid electrolyte material 11, the electrodes 521, 52
A pinhole 2 is formed at the center of the electrodes 521 and 522 so as to introduce a gas to be measured, which passes through the gas detector 2. Exhaust gas is introduced as a gas to be measured into the hollow portion 3 from outside the gas detector 1. I have. When oxygen is selectively supplied or discharged from the inside of the hollow portion 3 due to the diffusion resistance of the pinhole 2, a difference in oxygen concentration of the gas to be measured between the inside of the hollow portion 3 and the outside of the hollow portion 3 is generated.

On the upper surface of the solid electrolyte material 13, one electrode 511 of the second pair of electrodes made of Pt-Au and the third electrode made of Pt-Rh are formed by screen printing or the like on the inner surface of the hollow portion 3. One electrode 61 of the pair of electrodes is formed.
The electrode 511 has a smaller area than the electrode 522 of the pump cell 52 and is formed at a position facing the opening of the pinhole 2. The electrode 61 is substantially U-shaped and arranged so as to surround the electrode 511, so that the gas to be measured from the opening 2 a of the pinhole 2 reaches each part of the electrode 61 uniformly. The electrode 61 overlaps with the electrode 522 of the pump cell 52,
It is formed immediately below.

On the lower surface of the solid electrolyte material 13, the electrode 51
The other electrodes 512 and 62 of the second and third pair of electrodes made of Pt are formed opposite to the electrodes 1 and 61, respectively. In these, the solid electrolyte material 13 and the electrodes 511 and 512 constitute the sensor cell 51, and the solid electrolyte material 13, the electrodes 61 and 62
Constitute the detection cell 6.

The heater section 15 is formed by forming a Pt wire 17 on the surface of a plate-like substrate 18 made of alumina and coating it with a plate-like coating layer 16 made of alumina. , To increase the detection sensitivity.

At the base of the gas detector 1, each of the electrodes 51
1, 51, 521, 522, 61, 62 and terminals 51a, 51b, 52a, 5 which are electrically connected to both ends of the Pt wire 17.
2b, 6a, 6b, 17a, and 17b are formed and communicate with the lead wire 96 (FIG. 1A).

On the surface of the gas detector 1, a ceramic protective layer 1 is formed by coating the electrode 521 of the pump cell 52 and applying and baking a porous paste made of alumina or the like.
8 are formed to prevent the pinhole 2 from being clogged with particulates having a large particle size such as soot contained in the exhaust gas.

Each of the solid electrolyte materials 11 and 13 is a sheet of yttria-added zirconia formed by a sheet forming method such as a doctor blade method, and the thickness thereof is usually in the range of 50 to 300 μm. Good. However, considering the balance between electric resistance and sheet strength, 10
It is desirable to set it in the range of 0 to 200 μm. The thickness of the electrode is usually in the range of 1 to 20 μm, but is preferably about 5 to 10 μm in consideration of heat resistance and gas diffusivity.

FIG. 3 is a block diagram of the gas detector.
Here, the circuit section C (FIG. 1A) will be described. The oxygen pump control means 7 includes an electromotive force detection circuit 71 that receives a voltage between a pair of electrodes 511 and 512 of the sensor cell 51 and an oxygen pump control circuit 72 that receives an electromotive force signal output therefrom as an input. . The comparison circuit 721 at the preceding stage of the oxygen pump control circuit 72 includes an electromotive force detection circuit 71
Is compared with the reference signal value of the electromotive force signal, and the difference is output to the pump drive unit 722 of the oxygen pump control circuit 72. The pump driver 722 applies a voltage between the electrodes 521 and 522 of the pump cell 52 and applies the difference between the electromotive force signal and the reference signal value between the pair of electrodes 521 and 522 of the pump cell 52 as a necessary correction amount. The voltage is increased or decreased.

The signal detecting means 8 includes a detecting cell driving circuit 81 for applying a voltage between the pair of electrodes 61 and 62 of the detecting cell 6.
And an ion current detection circuit 82 that measures the current flowing into and out of the electrodes 61 and 62 and detects the ion current flowing through the solid electrolyte material 13 of the detection cell 6.

The operation of the gas detector will be described with reference to FIGS. Exhaust gas flowing through the exhaust pipe W is introduced into the cover unit 95 from each gas flow hole 953, 954 of the cover unit 95. The introduced exhaust gas is guided from the ceramic protective layer 18 of the gas detector 1 to the hollow portion 3 through the pinhole 2. On the other hand, air is introduced into the duct 4 in the sensor unit S from the air introduction holes 944 and 945 of the sensor unit S, and the air is introduced into the sensor cell 51 and the electrode 5 of the detection cell 6A.
12,62 are exposed.

When the electrode 521 outside the gas detector 1 has a positive voltage, the pump cell 52 receives oxygen at the electrode 522 from the oxygen in the hollow portion 3 and
1, electrons are emitted from the electrode 521 and are discharged from the ceramic protective layer 18 into the exhaust gas. The pinhole 2 regulates the diffusion of oxygen from the outside of the gas detector 1 toward the hollow portion 3, so that the oxygen concentration in the hollow portion 3 decreases.
On the other hand, in the sensor cell 51, an electromotive force is generated between the electrodes 511 and 512 according to the oxygen partial pressure ratio between the hollow portion 3 and the duct 4. The electromotive force detection circuit 71 detects the electromotive force, and the comparison circuit 721 compares the detected electromotive force signal with the reference signal value. Based on the difference, the pump driving circuit 722 determines The pump cell 52 is supplied to the hollow portion 3 by changing the voltage applied to the pump cell 52 so as to maintain the reference electromotive force corresponding to the reference signal value, that is, when the detected electromotive force deviates from the reference electromotive force. Or the amount of oxygen discharged from the hollow portion 3 is adjusted.

Electrode 51 inside hollow part 3 of sensor cell 51
Since 1 is located near the position of the opening 2 a of the pinhole 2, the pump cell 52 operates in response to a change in the oxygen concentration in the gas to be measured introduced into the hollow portion 3. Since the electrode 61 of the detection cell 6 is separated from the position of the opening 2a of the pinhole 2 and overlaps with the electrode 522 of the pump cell 52, the pumping operation of the pump cell 52 on the lean side causes the hollow portion from the pinhole 2 to move. Oxygen in the gas to be measured in the vicinity of the electrode 61 of the detection cell 6 is quickly discharged without being affected by oxygen in the gas to be measured flowing into the gas 3. The oxygen concentration of the gas to be measured in the vicinity of the electrode 61 of the detection cell 6 is lower than the oxygen concentration of the gas to be measured on the surface of the electrode 51 of the sensor cell 51 formed at a position facing the opening 2 a of the pinhole 2. Thus, the oxygen concentration of the gas to be measured in the vicinity of the electrode 61 of the detection cell 6 is almost zero.
Becomes

In this state, the electrode 6 of the detection cell 6
A constant voltage is applied between the first and the second 62 so that the electrode 62 side becomes positive from the detection cell drive circuit 81.

Since the electrode 61 is made of Pt-Rh, NOx
Shows a reduction activity, and NOx in the gas to be measured is decomposed on the surface by a reduction reaction to generate oxygen. Since the oxygen concentration of the gas to be measured on the surface of the electrode 61 of the detection cell 6 is substantially 0, the oxygen present on the surface of the electrode 61 is oxygen obtained by decomposing NOx in the gas to be measured, and the NOx concentration of the gas to be measured. It corresponds to.

Since a voltage is applied between the electrodes 61 and 62 of the detection cell 6 by the detection cell driving circuit 81, oxygen generated on the surface of the electrode 61 passes through the electrode 61 and the solid electrolyte material 13 to be ducted from the electrode 62. It is discharged to 4. At this time, a current using oxygen ions moving as carriers in the solid electrolyte material 13 is detected by the ion current detection circuit 82. This ion current corresponds to the amount of oxygen decomposed on the surface of the electrode 61 of the detection cell 6, that is, the NOx concentration of the gas to be measured. Thus, the ion current detection circuit 82 outputs a linear current having no offset current with respect to the NOx concentration of the gas to be measured.

In the rich state, the opening 2 of the pinhole 2 is formed.
The oxygen supply amount to the hollow portion 3 by the pump cell 52 is determined based on the oxygen concentration of the gas to be measured flowing from a.
Since the electrode 61 on the hollow portion 3 side of the detection cell 6 is located at a position overlapping the electrode 522 of the pump cell 52, the oxygen concentration near the electrode 61 of the detection cell 6 quickly converges to a constant value.

FIG. 4 shows an example of the measurement result of the ion current detected by the ion current detection circuit 82 with respect to the NOx (here, NO) concentration of the gas to be measured in the gas detection device of the present invention. Since there is no need to provide a diffusion resistance path,
A linear output signal having a detection gain of about 20 times as much as that of the thick film ZrO ₂ NOx sensor described in AE960334 and having no offset current was obtained.

The electrode 522 inside the hollow portion 3 of the pump cell 52 and the electrode 51 inside the hollow portion 3 of the sensor cell 51
Since No. 1 is made of Pt-Au which is inert to NOx, the reduction reaction of NOx on the surface of the electrode 522 of the pump cell 52 and the surface of the electrode 511 of the sensor cell 51 is prevented,
The NOx concentration of the gas to be measured introduced into the hollow portion 3 does not change.

The electrode on the hollow side of the detection cell is a metal (Pt −) having a reducing activity for NOx to be detected.
Rh), but by forming a catalyst layer containing a metal oxide containing one or more noble metal elements on the surface of an electrically conductive thin film serving as the main body of the electrode, the electrode has a reducing activity against NOx. May be provided.

The oxygen pump control means is not limited to the one described in the embodiment as long as it performs feedback control of the operation of the pump cell based on the amount of oxygen detected by the sensor cell. Further, the control of the supply amount and the discharge amount of oxygen may be performed by duty control instead of controlling the magnitude of the applied voltage to the pump cell.

Although the sensor cell and the detection cell share a solid electrolyte material, they may be made of different solid electrolyte materials. In this case, by separating the solid electrolyte material of the sensor cell and the solid electrolyte material of the detection cell with an insulating material, signal interference between the sensor cell and the detection cell is prevented, and the detection accuracy can be further improved. In the above-described embodiment, the cells such as the hollow portion and the detection cell are integrally formed. However, the present invention is not limited to this, and each of them may be configured separately.

The electrode of the sensor cell and the electrode of the detection cell are
Although the electrodes of the detection cells are arranged so as to surround the electrodes of the sensor cells, both electrodes may be arranged as a rectangle having a size approximately half that of the electrodes of the pump cells and arranged directly below the electrodes of the pump cells. In this case, the pinhole is brought to a position facing the electrode of the sensor cell, or formed so as to penetrate from the tip of the gas detector to the side wall of the sensor cell side of the hollow, so that the electrode inside the hollow of the sensor cell has the pinhole. It should be near the opening.

Although oxygen is discharged from the pump cell into the exhaust gas, the invention is not limited to this. The oxygen may be discharged into the atmosphere. In this case, it is preferable that the discharge hole for discharging oxygen from the sensor unit is provided apart from the air introduction hole of the air cover so as not to affect the oxygen concentration of the air introduced from the air introduction hole.

[Brief description of the drawings]

FIG. 1A is an overall cross-sectional view of a gas detection device of the present invention, and FIG. 1B is an enlarged cross-sectional view of a main part of the gas detection device of the present invention.

FIG. 2 is an exploded view of a main part of the gas detection device of the present invention.

FIG. 3 is a block diagram of the gas detection device of the present invention.

FIG. 4 is a graph illustrating the operation of the gas detection device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas detector 11, 13 Solid electrolyte material 1a Tip 1b Base 2 Pinhole (measured gas introduction path) 3 Hollow section 4 Duct (reference gas introduction path) 51 Sensor cell (oxygen sensor section) 511, 512 Electrode of sensor cell 52 Pump cell (oxygen pump section) 521, 522 Electrode of pump cell 6 Detection cell (component gas detection section) 61, 62 Electrode of detection cell 7 Oxygen pump control means 8 Signal detection means W Exhaust pipe wall (isolation wall)

Continued on the front page (72) Inventor: Hironobu Hijikata 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi Pref. Japan Automobile Parts Research Institute (72) (72) Inventor Kanehito Nakamura 1-1-1, Showa-cho, Kariya-shi, Aichi Pref.

Claims (3)

[Claims] 1. A pair of electrodes are provided on one of two opposing surfaces of a hollow portion into which a gas to be measured is introduced via a gas introduction passage having a diffusion resistance and a solid electrolyte material having oxygen ion conductivity. An oxygen sensor section that faces the inside of the hollow section and is formed so that the other electrode is exposed to a reference gas having a standard oxygen concentration outside the hollow section, and an oxygen sensor section that detects the oxygen concentration on the surface of one electrode, A pair of electrodes are formed on opposite sides of the solid electrolyte material, and one electrode is formed facing the inside of the hollow portion so that one electrode is exposed to the gas to be measured outside the hollow portion. An oxygen pump section that sends a pump current to the solid electrolyte material and moves oxygen between the inside and the outside of the hollow portion,
Oxygen pump control means for performing feedback control of the pump current of the oxygen pump section based on the oxygen concentration detected by the oxygen sensor section, and a pair of electrodes on both opposing surfaces of the solid electrolyte material having oxygen ion conductivity, one electrode Has a component gas detector formed so that the other electrode is exposed to the reference gas, and signal detection means for detecting an output signal between the electrodes of the component gas detector. An electrode inside the hollow portion of the sensor portion is formed near the opening position inside the hollow portion of the gas introduction path to be measured, and the electrode inside the hollow portion of the component gas detecting portion is located closer to the electrode inside the hollow portion of the oxygen sensor portion. The electrode inside the hollow part of the oxygen pump part is formed so as to overlap with the electrode inside the hollow part at a position away from the opening of the gas introduction path, and the electrode inside the hollow part of the component gas detecting part has an activity to reduce nitrogen oxides. Specially Gas detecting apparatus according to. 2. The gas detection device according to claim 1, wherein the oxygen pump portion and the electrode inside the hollow portion of the oxygen sensor portion are made of a metal inert to nitrogen oxides. 3. The gas detection device according to claim 1, further comprising a gas detector penetrating through an isolation wall separating the gas to be measured and the atmosphere, and having a tip end projecting toward the gas to be measured. Inside the gas detector, the hollow portion communicating with the outside of the gas detector via the measured gas introduction path is provided at the distal end, and one end side extends to the vicinity of the hollow portion, and the other end has a reference. A reference gas introduction path into which gas is introduced is provided, and the oxygen pump section is a solid electrolyte material that forms a part of a partition wall separating the inside of the hollow section and the outside of the gas detector, and the inside and the hollow section of the hollow section. A first pair of electrodes formed opposite to both sides of the outside, and the oxygen sensor portion is a solid electrolyte material forming a part of a partition separating the inside of the hollow portion from the reference gas introduction path; On both sides of the inside of the hollow part and the reference gas introduction path side A second pair of electrodes formed, the inner electrode of the hollow portion having a smaller area than the inner electrode of the hollow portion of the oxygen pump portion and formed at a position facing the central portion of the electrode, The component gas detection unit is a solid electrolyte material that forms a part of a partition wall separating the hollow portion and the reference gas introduction path, and a third pair of a pair formed on both sides of the inside of the hollow portion and the reference gas introduction path side. The electrode inside the hollow portion is formed with a hollow portion at the center to surround the electrode inside the hollow portion of the oxygen sensor portion and overlap with the electrode inside the hollow portion of the oxygen pump portion. Gas detection device formed at the position.