Gas sensor and concentration measurement method using a gas sensor

Abstract

A sensor element includes first to fourth chambers sequentially connected to a gas inlet. An adjusting pump cell pumps oxygen from a measurement gas introduced into the first chamber so that NOx, H2O, and CO2 in the measurement gas are not decomposed. A first measuring pump cell pumps oxygen from the second chamber so that all the NOx in the measurement gas introduced into the second chamber is reduced. A second measuring pump cell pumps oxygen from the third chamber so that all the H2O and CO2 in the measurement gas introduced into the third chamber are reduced. A third measuring pump cell pumps oxygen into the fourth chamber to selectively oxidize the H2 produced by the reduction. A NOx concentration is identified from a current generated by pumping out by the first measuring pump cell. A H2O concentration is identified from a current generated by pumping in by the third measuring pump cell.and a CO2 concentration is identified based on the identified H2O concentration and a current generated by pumping out by the second measuring pump cell.,

Description

Gas sensor and concentration measurement method using gas sensor

[0001] The present invention relates to a multi-gas sensor capable of detecting a plurality of target gas components and measuring their concentrations.

[0002] In measurements to control automobile exhaust gas emissions, water vapor (H ２ O) and carbon dioxide (CO ２ ) is already known (see, for example, Patent Documents 1 and 2). In the gas sensors disclosed in Patent Documents 1 and 2, ２ O) component and carbon dioxide (CO ２ ) components can be measured in parallel.

[0003] In addition, a gas sensor (NOx sensor) that has a sensor element with a configuration similar to that of the gas sensors disclosed in Patent Documents 1 and 2, but is capable of measuring NOx by executing pump cell control different from that of the gas sensors disclosed in Patent Documents 1 and 2, is already known (see, for example, Patent Document 3).

[0004] In the three-chamber gas sensor disclosed in Patent Document 1, first, a main pump cell, which is a pump cell for the first internal space, is operated to pump O contained in the measurement gas introduced into the first internal space. ２ is pumped out, and H contained in the gas to be measured is also pumped out. ２ O and CO ２ Once everything is returned, ２ and CO. These H ２ The measurement gas containing CO and O is introduced into the second and third internal spaces. ２ H by pumping ２ is selectively oxidized to H ２ O is generated and further O is pumped by the second measurement pump cell, which is a pump cell for the third internal cavity. ２ When CO is pumped in, CO is oxidized and CO ２ are generated. Then, these H ２and CO are oxidized, based on the magnitude of the pump current flowing through the first measuring pump cell and the second measuring pump cell. ２ O and CO ２ The concentration of

[0005] In the gas sensor, H in the first internal space ２ O and CO ２ To reduce the oxygen ion, it is necessary to set a high voltage to be applied to the pump cell for the first internal space. At the same time, it is also necessary to increase the temperature of the main inner pump electrode, which is the pump electrode in the space constituting the main pump cell. However, applying a high voltage and maintaining the pump electrode at a high temperature may cause cracks or blackening of the solid electrolyte ceramic due to reduction of the solid electrolyte ceramic in the sensor element, which is mainly composed of an oxygen ion conductive solid electrolyte ceramic.

[0006] In addition, H contained in the exhaust gas ２ In some cases, it is desirable to measure NOx in parallel with the measurement of O and CO. In particular, from the viewpoint of ease of securing installation space and cost reduction, ２ There is a need to simultaneously measure NOx in addition to O and CO in the same gas sensor.

[0007] Patent No. 5918177 Patent No. 6469464 Patent No. 3798412

[0008] The present invention has been made in view of the above problems, and provides a method for treating water vapor (H ２ O) component and carbon dioxide (CO ２ The present invention aims to provide a multi-gas sensor that can simultaneously measure NOx in addition to the benzene (C) component, that is suppressed from cracking or blackening in the sensor element, and that is less susceptible to sensitivity changes even after long-term use, and that has superior long-term reliability compared to conventional multi-gas sensors.

[0009] In order to solve the above-mentioned problems, a first aspect of the present invention is a gas sensor capable of measuring concentrations of a plurality of target gas components, comprising: a sensor element having a structure made of an oxygen ion conductive solid electrolyte; and a controller for controlling the operation of the gas sensor, wherein the sensor element comprises a gas inlet through which a target gas is introduced; a first chamber, a second chamber, a third chamber, and a fourth chamber which are sequentially connected to the gas inlet via different diffusion rate-limiting parts; an inner electrode formed facing the first chamber; and a diffusion rate-limiting part formed between the first chamber, the second chamber, the third chamber, and the fourth chamber. a regulation pump cell including an outside-void pump electrode provided at a location other than the fourth void, and the solid electrolyte present between the inner electrode and the outside-void pump electrode; a first measurement pump cell including a first measurement electrode formed facing the second void, the outside-void pump electrode, and the solid electrolyte present between the first measurement electrode and the outside-void pump electrode; and a second measurement pump cell including a second measurement electrode formed facing the third void, the outside-void pump electrode, and the solid electrolyte present between the second measurement electrode and the outside-void pump electrode. a third measurement pump cell including a constant pump cell, a third measurement electrode formed facing the fourth chamber, the pump electrode outside the cavity, and the solid electrolyte present between the third measurement electrode and the pump electrode outside the cavity; and a heater for heating the sensor element, wherein the inner electrode is a cermet electrode containing a Pt—Au alloy as a metal component and an Au concentration in the Pt—Au alloy is 0.5 wt % or more, the first measurement electrode is another cermet electrode containing a Pt—Rh alloy as a metal component, and the adjusting pump cell is configured to adjust the N contained in the measurement gas. the first measuring pump cell pumps oxygen from the measurement gas introduced into the first chamber through the gas inlet so as not to decompose Oxygen, water vapor, and carbon dioxide; the first measuring pump cell pumps oxygen from the second chamber so as to reduce substantially all of the NOx contained in the measurement gas introduced from the first chamber to the second chamber; the second measuring pump cell pumps oxygen from the third chamber so as to reduce substantially all of the water vapor and carbon dioxide contained in the measurement gas introduced from the second chamber to the third chamber; and the third measuring pump cellBy pumping oxygen into the fourth chamber, hydrogen produced by reduction of water vapor contained in the measurement gas introduced from the third chamber into the fourth chamber is selectively oxidized in the fourth chamber, and the controller includes: a NOx concentration specifying means for specifying the concentration of NOx contained in the measurement gas based on the magnitude of a NOx detection current, which is an oxygen pump current flowing between the first measurement electrode and the pump electrode outside the cavity when oxygen is pumped from the second chamber by the first measurement pump cell; and a NOx concentration specifying means for specifying the concentration of NOx contained in the measurement gas based on the magnitude of a NOx detection current, which is an oxygen pump current flowing between the first measurement electrode and the pump electrode outside the cavity when hydrogen is oxidized by the oxygen pumped into the third chamber by the second measurement pump cell. and a carbon dioxide concentration determining means for determining the concentration of carbon dioxide contained in the measurement gas based on the value of the water vapor equivalent current, which is an oxygen pump current flowing between the second measurement electrode and the pump electrode outside the cavity when the first measurement pump cell pumps oxygen from the second cavity and thereby reduces water vapor and carbon dioxide.

[0010] A second aspect of the present invention is the gas sensor according to the first aspect, characterized in that the controller further stores Ip1-NOx data indicating a relationship between the NOx detection current and the NOx concentration that has been specified in advance, and the NOx concentration specifying means specifies the concentration of NOx contained in the measurement gas based on the NOx detection current and the Ip1-NOx data when NOx contained in the measurement gas is reduced.

[0011] A third aspect of the present invention is the gas sensor according to the second aspect, wherein the controller is configured to calculate Ip2-H, which indicates a relationship between a predetermined oxygen pump current flowing through the second measuring pump cell and a concentration of water vapor when the measurement gas contains water vapor and does not contain carbon dioxide. ２O data and Ip2-CO2, which shows the relationship between the oxygen pump current flowing through the second measuring pump cell and the concentration of water vapor when carbon dioxide is contained in the measurement gas and water vapor is not contained in the measurement gas, which is specified in advance. ２ and Ip3-H, which shows the relationship between the oxygen pump current flowing through the third measuring pump cell and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, as previously specified. ２ and the water vapor concentration specifying means stores the Ip3-H ２ The water vapor concentration corresponding to the value of the water vapor equivalent current in the O data is identified as the concentration of water vapor contained in the measurement target gas, and the carbon dioxide concentration identifying means compares the concentration of water vapor contained in the measurement target gas identified by the water vapor concentration identifying means with the Ip2-H ２ Based on the data and the total reduction current, the contribution of the reduction of water vapor to the total reduction current is identified, and then the Ip2-CO ２ The carbon dioxide concentration corresponding to the difference value obtained by subtracting the contribution from the total reduction current in the data is identified as the concentration of carbon dioxide contained in the measurement gas.

[0012] A fourth aspect of the present invention is the gas sensor according to the second aspect, wherein the controller is configured to calculate Ip2-CO 2 , which indicates a relationship between the oxygen pump current flowing through the second measuring pump cell and the concentration of water vapor when the measurement gas contains carbon dioxide and does not contain water vapor, which is specified in advance. ２ and Ip3-H, which shows the relationship between the oxygen pump current flowing through the third measuring pump cell and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, as previously specified. ２ H showing the relationship between the water vapor equivalent current and the oxygen pump current corresponding to the contribution of water vapor to the total reduction current. ２ and the water vapor concentration specifying means stores the Ip3-H ２The water vapor concentration corresponding to the value of the water vapor equivalent current in the O data is identified as the concentration of water vapor contained in the measurement gas, and the carbon dioxide concentration identifying means is configured to ２ Based on the O characteristic data, the contribution of the reduction of water vapor in the total reduction current is identified, and then the Ip2-CO ２ The carbon dioxide concentration corresponding to the difference value obtained by subtracting the contribution from the total reduction current in the data is identified as the concentration of carbon dioxide contained in the measurement gas.

[0013] A fifth aspect of the present invention is a gas sensor according to any one of the first to fourth aspects, characterized in that the controller further comprises an oxygen concentration determination means for determining the concentration of oxygen contained in the measurement gas based on the magnitude of the current flowing between the inner electrode and the outer pump electrode when oxygen is pumped out of the first chamber by the adjustment pump cell.

[0014] A sixth aspect of the present invention is the gas sensor according to any one of the first to fifth aspects, characterized in that the third measurement electrode is a cermet electrode containing a Pt—Au alloy as a metal component, and the Au concentration in the Pt—Au alloy is 1 wt % or more and 50 wt % or less.

[0015] A seventh aspect of the present invention is a method for measuring the concentrations of a plurality of target gas components using a gas sensor, the gas sensor comprising a sensor element having a long plate-like structure made of an oxygen ion conductive solid electrolyte, the sensor element comprising: a gas inlet through which a gas to be measured is introduced; a first chamber, a second chamber, a third chamber, and a fourth chamber which are sequentially connected to the gas inlet via different diffusion rate-limiting portions; an inner electrode formed facing the first chamber; and diffusion rate-limiting portions provided at locations other than the first chamber, the second chamber, the third chamber, and the fourth chamber. a regulation pump cell including a pump electrode outside the cavity formed by the inner electrode and the solid electrolyte present between the inner electrode and the pump electrode outside the cavity; a first measurement pump cell including a first measurement electrode formed facing the second cavity, the pump electrode outside the cavity, and the solid electrolyte present between the first measurement electrode and the pump electrode outside the cavity; a second measurement pump cell including a second measurement electrode formed facing the third cavity, the pump electrode outside the cavity, and the solid electrolyte present between the second measurement electrode and the pump electrode outside the cavity; a third measurement pump cell including a third measurement electrode formed facing the outer space, the outer space pump electrode, and the solid electrolyte present between the third measurement electrode and the outer space pump electrode; and a heater for heating the sensor element, wherein the inner electrode is a cermet electrode containing a Pt-Au alloy as a metal component and an Au concentration in the Pt-Au alloy is 0.5 wt % or more, and the first measurement electrode is another cermet electrode containing a Pt-Rh alloy as a metal component, and a) the adjustment pump cell adjusts NOx, water vapor, and other gases contained in the measurement target gas to be measured. a) pumping oxygen from the measurement gas introduced into the first chamber through the gas inlet so that NOx and water vapor contained in the measurement gas introduced into the second chamber are not decomposed; b) pumping oxygen from the second chamber by the first measuring pump cell so that substantially all of the NOx contained in the measurement gas introduced into the second chamber from the first chamber is reduced; and c) pumping oxygen from the third chamber by the second measuring pump cell so that substantially all of the water vapor and carbon dioxide contained in the measurement gas introduced into the third chamber from the second chamber are reduced.d) pumping oxygen into the fourth chamber by the third measuring pump cell, thereby selectively oxidizing, in the fourth chamber, hydrogen produced by reduction of water vapor contained in the measurement gas introduced from the third chamber to the fourth chamber; e) determining the concentration of NOx contained in the measurement gas based on the magnitude of a NOx detection current, which is an oxygen pump current flowing between the first measuring electrode and the pump electrode outside the cavity, when NOx is reduced by pumping oxygen from the second chamber by the first measuring pump cell; and f) determining the concentration of NOx contained in the measurement gas based on the magnitude of a NOx detection current, which is an oxygen pump current flowing between the first measuring electrode and the pump electrode outside the cavity, when NOx is reduced by pumping oxygen from the second chamber by the third measuring pump cell. g) determining the concentration of water vapor contained in the measurement gas based on the value of a water vapor equivalent current, which is an oxygen pump current that flows between the third measurement electrode and the pump electrode outside the cavity when hydrogen is oxidized by oxygen pumped into the chamber; and g) determining the concentration of carbon dioxide contained in the measurement gas based on the value of the water vapor equivalent current and the value of a total reduction current, which is an oxygen pump current that flows between the second measurement electrode and the pump electrode outside the cavity when water vapor and carbon dioxide are reduced by the second measurement pump cell pumping oxygen from the third chamber.

[0016] An eighth aspect of the present invention is a concentration measurement method using a gas sensor according to the seventh aspect, comprising: h) a step of specifying Ip1-NOx data indicating the relationship between the NOx detection current and the NOx concentration before steps a) to g), and in step e), specifying the NOx concentration contained in the measurement gas based on the NOx detection current and the Ip1-NOx data when the NOx contained in the measurement gas is reduced.

[0017] A ninth aspect of the present invention is a concentration measurement method using a gas sensor according to the eighth aspect, wherein in the step h), Ip2-H is a relationship between the oxygen pump current flowing through the second measuring pump cell and the concentration of water vapor when the measurement gas contains water vapor but does not contain carbon dioxide. ２and Ip2-CO 2 data, which shows the relationship between the oxygen pump current flowing through the second measuring pump cell and the concentration of water vapor when carbon dioxide is contained in the measurement gas but water vapor is not contained in the measurement gas. ２ and Ip3-H, which shows the relationship between the oxygen pump current flowing through the third measuring pump cell and the concentration of water vapor when the measurement gas contains water vapor but does not contain carbon dioxide. ２ O data, and in the step f), the Ip3-H ２ The water vapor concentration corresponding to the value of the water vapor equivalent current in the O data is identified as the water vapor concentration contained in the measurement target gas, and in step g), the water vapor concentration contained in the measurement target gas identified in step f) and the Ip2-H ２ Based on the data and the total reduction current, the contribution of the reduction of water vapor to the total reduction current is identified, and then the Ip2-CO ２ The carbon dioxide concentration corresponding to the difference value obtained by subtracting the contribution from the total reduction current in the data is identified as the concentration of carbon dioxide contained in the measurement gas.

[0018] A tenth aspect of the present invention is a concentration measurement method using a gas sensor according to the eighth aspect, wherein in the step h), Ip2-CO ２ and Ip3-H, which shows the relationship between the oxygen pump current flowing through the third measuring pump cell and the concentration of water vapor when the measurement gas contains water vapor but does not contain carbon dioxide. ２ 0 data, the water vapor equivalent current, and the oxygen pump current corresponding to the contribution of water vapor to the total reduction current. ２ and a step of identifying the Ip3-H characteristic data. ２ The water vapor concentration corresponding to the value of the water vapor equivalent current in the O data is identified as the concentration of water vapor contained in the measurement gas, and in the step g), the water vapor equivalent current and the H ２Based on the O characteristic data, the contribution of the reduction of water vapor in the total reduction current is identified, and then the Ip2-CO ２ The carbon dioxide concentration corresponding to the difference value obtained by subtracting the contribution from the total reduction current in the data is identified as the concentration of carbon dioxide contained in the measurement gas.

[0019] An eleventh aspect of the present invention is a concentration measurement method using a gas sensor according to any one of the seventh to tenth aspects, characterized in that it further comprises the step of: i) determining the concentration of oxygen contained in the measurement gas based on the magnitude of the current flowing between the inner electrode and the outer pump electrode when oxygen is pumped out of the first chamber by the adjustment pump cell.

[0020] A twelfth aspect of the present invention is a concentration measurement method using a gas sensor according to any one of the seventh to eleventh aspects, characterized in that the third measurement electrode is a cermet electrode containing a Pt—Au alloy as a metal component, and the Au concentration in the Pt—Au alloy is 1 wt % or more and 50 wt % or less.

[0021] According to the first to twelfth aspects of the present invention, a multi-gas sensor is realized which has superior long-term reliability compared to conventional sensors and can simultaneously measure a greater number of gas species.

[0022] 1 is a diagram showing an example of the configuration of the gas sensor 100; FIG. 2 is a block diagram showing functional components realized in the controller 110; FIG. 3 is a schematic diagram showing the flow of gas into and out of four chambers of the sensor element 101 of the gas sensor 100; FIG. 4 is a graph showing the relationship between the target value of the electromotive force V0 in the sensor cell 80 for the first chamber and the oxygen pump current Ip0 flowing through the adjustment pump cell 21 when three different types of model gas are flowed; FIG. 5 is a diagram showing the dependency of the oxygen pump current Ip2 on the concentration of the gas component to be detected; and FIG. 6 is a diagram showing the dependency of the oxygen pump current Ip3 on the concentration of the gas component to be detected. ２ FIG. 10 is a diagram illustrating an example of O characteristic data.

[0023] <Configuration of Gas Sensor> FIG. 1 is a diagram showing an example of the configuration of a gas sensor 100 according to this embodiment. The gas sensor 100 is a multi-gas sensor that detects multiple types of gas components using a sensor element 101 and measures their concentrations. In this embodiment, at least water vapor (H ２ O), carbon dioxide (CO ２ ) and nitrogen oxides (NOx) are the main target gas components to be detected by the gas sensor 100. The gas sensor 100 is attached to an exhaust path of an internal combustion engine such as an automobile engine, and is used in a manner in which the exhaust gas flowing through the exhaust path is used as the target gas to be measured. FIG. 1 includes a vertical cross-sectional view of the sensor element 101 along the longitudinal direction.

[0024] The sensor element 101 includes a long, plate-shaped structure (base portion) 14 made of an oxygen-ion conductive solid electrolyte, a first diffusion-controlling portion 11 formed at one end (the left end in the drawing) of the structure 14 and serving as a gas inlet 10 through which a gas to be measured is introduced, and a buffer space 12, a first chamber 20, a second chamber 40, a third chamber 61, and a fourth chamber 63 formed within the structure 14 and sequentially communicating with the gas inlet 10 (first diffusion-controlling portion 11). The buffer space 12 communicates with the gas inlet 10 (first diffusion-controlling portion 11). The first chamber 20 communicates with the buffer space 12 via the second diffusion-controlling portion 13. The second chamber 40 communicates with the first chamber 20 via the third diffusion-controlling portion 30. The third chamber 61 communicates with the second chamber 40 via the fourth diffusion-controlling portion 60. The fourth chamber 63 communicates with the third chamber 61 via a fifth diffusion-controlling section 62 .

[0025] The structure 14 is formed by stacking multiple layers of substrates made of, for example, ceramics. Specifically, the structure 14 has a configuration in which six layers, consisting of a first substrate 1, a second substrate 2, a third substrate 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, are stacked in this order from the bottom up. Each layer is made of, for example, zirconia (ZrO ２ The solid electrolyte is oxygen ion conductive.

[0026] The first diffusion-controlling section 11, which also serves as the gas inlet 10, the buffer space 12, the second diffusion-controlling section 13, the first cavity 20, the third diffusion-controlling section 30, the second cavity 40, the fourth diffusion-controlling section 60, the third cavity 61, the fifth diffusion-controlling section 62, and the fourth cavity 63 are formed in this order at one end of the structure 14, between the lower surface 6 b of the second solid electrolyte layer 6 and the upper surface 4 a of the first solid electrolyte layer 4. The portion from the gas inlet 10 to the fourth cavity 63 is also referred to as a gas flow section.

[0027] The buffer space 12, the first cavity 20, the second cavity 40, the third cavity 61, and the fourth cavity 63 are formed to penetrate the spacer layer 5 in the thickness direction. The lower surface 6b of the second solid electrolyte layer 6 is exposed at the top of these cavities, and the upper surface 4a of the first solid electrolyte layer 4 is exposed at the bottom. The sides of these cavities are defined by the spacer layer 5 or any of the diffusion-controlling portions. The first cavity 20, the second cavity 40, the third cavity 61, and the fourth cavity 63 each have a length (lengthwise dimension of the element) of, for example, 0.3 mm to 1.0 mm, a width (widthwise dimension of the element) of, for example, 0.5 mm to 30 mm, and a height (thicknesswise dimension of the element) of, for example, 50 μm to 200 μm. However, the sizes of the respective cavities do not need to be the same and may be different.

[0028] Similarly, the gas inlet 10 may be formed so as to penetrate the spacer layer 5 in the thickness direction, separately from the first diffusion rate-controlling part 11. In this case, the first diffusion rate-controlling part 11 is formed adjacent to and inside the gas inlet 10.

[0029] Each of the first diffusion-controlling section 11, the second diffusion-controlling section 13, the third diffusion-controlling section 30, the fourth diffusion-controlling section 60, and the fifth diffusion-controlling section 62 has two horizontally elongated slits. That is, each of the first diffusion-controlling section 11, the second diffusion-controlling section 13, the third diffusion-controlling section 30, the fourth diffusion-controlling section 60, and the fifth diffusion-controlling section 62 has an opening extending vertically in the plane of the drawing at the top and bottom. The length of the slit (the size in the longitudinal direction of the element) is, for example, 0.2 mm to 1.0 mm, the width of the opening (the size in the lateral direction of the element) is, for example, 0.5 mm to 30 mm, and the height of the opening (the size in the thickness direction of the element) is, for example, 5 μm to 30 μm.

[0030] A reference gas introduction space 43 is provided at the other end (right end in the drawing) of the sensor element 101 opposite to the one end where the gas introduction port 10 is provided. The reference gas introduction space 43 is formed between the upper surface 3a of the third substrate 3 and the lower surface 5b of the spacer layer 5. The sides of the reference gas introduction space 43 are partitioned by the side surfaces of the first solid electrolyte layer 4. The reference gas introduction space 43 is filled with, for example, oxygen (O ２ ) and air are introduced.

[0031] The gas inlet 10 (first diffusion-controlling section 11) is a section that opens to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas inlet 10.

[0032] The first diffusion rate-controlling part 11 is a part that applies a predetermined diffusion resistance to the taken-in measurement gas.

[0033] The buffer space 12 is provided to cancel out fluctuations in the concentration of the measurement gas caused by pressure fluctuations of the measurement gas in the external space, such as pulsations in the exhaust gas pressure of an automobile.

[0034] The second diffusion rate-controlling part 13 is a part that imparts a predetermined diffusion resistance to the measurement gas introduced from the buffer space 12 into the first chamber 20 .

[0035] The first chamber 20 is provided as a space for pumping out oxygen from the measurement gas introduced through the second diffusion-controlling part 13. The pumping out of oxygen is realized by the operation of the adjustment pump cell 21.

[0036] The regulating pump cell 21 is an electrochemical pump cell composed of an inner pump electrode (regulating electrode) 22, an outer pump electrode (outside the cavity pump electrode) 23, and a solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes.

[0037] In the adjustment pump cell 21, a voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 by a variable power supply 24 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip0. This makes it possible to pump oxygen from the first chamber 20 to the external space. In this embodiment, the direction of the oxygen pump current Ip0 when oxygen is pumped from the first chamber 20 is defined as the positive direction of the oxygen pump current Ip0.

[0038] The inner pump electrode 22 is provided as a ceiling electrode portion 22a and a bottom electrode portion 22b on substantially the entire surface of the lower surface 6b of the second solid electrolyte layer 6 and substantially the entire surface of the upper surface 4a of the first solid electrolyte layer 4, which define the first chamber 20. The ceiling electrode portion 22a and the bottom electrode portion 22b are connected by a conductive portion (not shown).

[0039] The inner pump electrode 22 is provided as a porous cermet electrode having a rectangular shape in a plan view, for example, containing an alloy of platinum (Pt) and gold (Au) inactive to NOx (Pt—Au alloy) as a metal component, and including a Pt—Au alloy and zirconia. ２ O, and CO ２ From the viewpoint of ensuring that only oxygen contained in the gas to be measured is pumped out without reducing the Pt—Au alloy, it is preferable that the Pt—Au alloy contains Au at a concentration of 0.5 wt % or more.

[0040] The outer pump electrode 23 is provided as a porous cermet electrode having a rectangular shape in plan view, containing platinum or a Pt—Au alloy as a metal component, for example, platinum or a Pt—Au alloy and zirconia.

[0041] In the sensor element 101, the first chamber sensor cell 80 is configured by the inner pump electrode 22, the reference electrode 42, and the solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes. The first chamber sensor cell 80 is an electrochemical sensor cell for detecting the oxygen partial pressure in the atmosphere in the first chamber 20.

[0042] The reference electrode 42 is an electrode formed between the first solid electrolyte layer 4 and the third substrate 3, and is provided, for example, as a porous cermet electrode containing platinum and zirconia and having a rectangular shape in plan view.

[0043] A reference gas introduction layer 48 made of porous alumina and connected to the reference gas introduction space 43 is provided around the reference electrode 42. The reference gas in the reference gas introduction space 43 is introduced onto the surface of the reference electrode 42 through the reference gas introduction layer 48. In other words, the reference electrode 42 is always in contact with the reference gas.

[0044] In the first chamber sensor cell 80, an electromotive force (Nernst electromotive force) V0 is generated between the inner pump electrode 22 and the reference electrode 42. The electromotive force V0 has a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the first chamber 20 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, since the oxygen concentration (oxygen partial pressure) of the reference gas is basically constant, the electromotive force V0 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the first chamber 20.

[0045] The third diffusion rate-controlling portion 30 is a portion that imparts a predetermined diffusion resistance to the measurement gas introduced from the first chamber 20 into the second chamber 40 .

[0046] The second chamber 40 reduces (decomposes) NOx contained as a gas component to be detected in the measurement gas introduced through the third diffusion-controlling part 30, pumps out the oxygen produced by the reduction, and converts the measurement gas into H ２ O, CO ２ The first measuring pump cell 50 is operated to pump out the oxygen.

[0047] The first measurement pump cell 50 is an electrochemical pump cell that is configured by a first measurement electrode 51, an outer pump electrode 23, and a solid electrolyte that is present in the portion of the structure 14 that is sandwiched between the two electrodes.

[0048] In the first measurement pump cell 50, an oxygen pump current (oxygen ion current) Ip1 is generated by applying a voltage Vp1 between the first measurement electrode 51 and the outer pump electrode 23 from a variable power supply 52 provided outside the sensor element 101. This makes it possible to pump oxygen from the second chamber 40 to the external space. In this embodiment, the direction of the oxygen pump current Ip1 when oxygen is pumped from the second chamber 40 is defined as the positive direction of the oxygen pump current Ip1.

[0049] The first measurement electrode 51 is provided as a ceiling electrode portion 51a and a bottom electrode portion 51b on substantially the entire surface of the lower surface 6b of the second solid electrolyte layer 6 that defines the second chamber 40 and substantially the entire surface of the upper surface 4a of the first solid electrolyte layer 4. The ceiling electrode portion 51a and the bottom electrode portion 51b are connected by a conductive portion (not shown).

[0050] The first measuring electrode 51 is provided as a porous cermet electrode having a rectangular shape in plan view, which contains an alloy of platinum and rhodium (Rh) (Pt—Rh alloy) as a metal component, for example, a Pt—Rh alloy and zirconia. The Rh concentration in the Pt—Rh alloy is preferably 30 wt % or more.

[0051] In the sensor element 101, a second chamber sensor cell 81 is configured by the first measurement electrode 51, the reference electrode 42, and a solid electrolyte present in a portion of the structure 14 sandwiched between the first and second electrodes. The second chamber sensor cell 81 is an electrochemical sensor cell for detecting the oxygen partial pressure in the atmosphere in the second chamber 40.

[0052] In the second chamber sensor cell 81, an electromotive force (Nernst electromotive force) V1 is generated between the first measuring electrode 51 and the reference electrode 42. The electromotive force V1 has a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the second chamber 40 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, since the oxygen concentration (oxygen partial pressure) of the reference gas is basically constant, the electromotive force V1 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the second chamber 40.

[0053] The fourth diffusion-controlling section 60 controls the H ２ O and CO２ This section provides a predetermined diffusion resistance to the measurement gas containing NOx and oxygen but not substantially containing NOx and oxygen.

[0054] The third chamber 61 contains H contained as a detection target gas component in the measurement gas introduced through the fourth diffusion-controlling section 60. ２ O and CO ２ is reduced (decomposed) to hydrogen (H ２ ) and carbon monoxide (CO), and the measurement gas contains not only NOx and oxygen but also H ２ O, CO ２ The space is provided so that the H ２ O and CO ２ The reduction (decomposition) of is realized by the operation of the second measuring pumping cell 41 .

[0055] The second measurement pump cell 41 is an electrochemical pump cell that is configured by a second measurement electrode 44, an outer pump electrode 23, and a solid electrolyte that is present in the portion of the structure 14 that is sandwiched between the two electrodes.

[0056] In the second measurement pump cell 41, a voltage Vp2 is applied between the second measurement electrode 44 and the outer pump electrode 23 by a variable power supply 46 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip2. ２ O and CO ２ It is possible to pump out oxygen generated in the third chamber 61 by the reduction of O 3 into the external space. In this embodiment, the direction of the oxygen pump current Ip2 when oxygen is pumped out of the third chamber 61 is set to the positive direction of the oxygen pump current Ip2.

[0057] The second measurement electrode 44 is provided as a ceiling electrode portion 44a and a bottom electrode portion 44b on substantially the entire surface of the lower surface 6b of the second solid electrolyte layer 6 and substantially the entire surface of the upper surface 4a of the first solid electrolyte layer 4, which define the third chamber 61. The ceiling electrode portion 44a and the bottom electrode portion 44b are connected by a conductive portion (not shown).

[0058] The second measurement electrode 44 is provided as a porous cermet electrode having a rectangular shape in plan view and containing Pt as a metal component.

[0059] In the sensor element 101, a third chamber sensor cell 82 is formed by the second measurement electrode 44, the reference electrode 42, and the solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes. The third chamber sensor cell 82 is an electrochemical sensor cell for detecting the oxygen partial pressure in the atmosphere in the third chamber 61.

[0060] In the third chamber sensor cell 82, an electromotive force (Nernst electromotive force) V2 is generated between the second measurement electrode 44 and the reference electrode 42. The electromotive force V2 has a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the third chamber 61 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, since the oxygen concentration (oxygen partial pressure) of the reference gas is basically constant, the electromotive force V2 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the third chamber 61.

[0061] The fifth diffusion-controlling section 62 controls the H ２ and CO, while H ２ O, CO ２ The diffusion resistance is provided to the measurement gas that is substantially free of NOx and oxygen.

[0062] The fourth chamber 63 contains H contained in the measurement gas introduced through the fifth diffusion-controlling section 62. ２ and CO, H ２ Selectively oxidize all of the ２ The space is provided for generating O. ２ H by oxidation of ２ The generation of O is achieved by the operation of the third measuring pump cell 66.

[0063] The third measurement pump cell 66 is an electrochemical pump cell that is configured by a third measurement electrode 64, an outer pump electrode 23, and a solid electrolyte that is present in the portion of the structure 14 that is sandwiched between the two electrodes.

[0064] In the third measurement pump cell 66, a voltage Vp3 is applied between the third measurement electrode 64 and the outer pump electrode 23 by a variable power supply 68 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip3. This makes it possible to pump oxygen from the external space into the fourth chamber 63. In this embodiment, the direction of the oxygen pump current Ip3 when oxygen is pumped out of the fourth chamber 63 is defined as the positive direction of the oxygen pump current Ip3.

[0065] The third measurement electrode 64 is provided on substantially the entire upper surface 4 a of the first solid electrolyte layer 4 that defines the fourth cavity 63 .

[0066] The third measurement electrode 64 is provided as a porous cermet electrode having a rectangular shape in plan view, which contains a Pt—Au alloy as a metal component, for example, the Pt—Au alloy and zirconia. The Au concentration in the Pt—Au alloy is preferably 1 wt % or more and 50 wt % or less, and more preferably 10 wt % or more and 30 wt % or less. In this case, H in the third measurement electrode 64 ２ selective oxidation of H in the fourth chamber 63 ２ When CO coexists, H ２ Only CI is selectively oxidized by the oxygen pumped in by the third measuring pump cell 66, and CO is not oxidized, which is more preferably exhibited.

[0067] In the sensor element 101, a fourth chamber sensor cell 83 is formed by the third measurement electrode 64, the reference electrode 42, and the solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes. The fourth chamber sensor cell 83 is an electrochemical sensor cell for detecting the oxygen partial pressure in the atmosphere in the fourth chamber 63.

[0068] In the fourth chamber sensor cell 83, an electromotive force (Nernst electromotive force) V3 is generated between the third measuring electrode 64 and the reference electrode 42. The electromotive force V3 has a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the fourth chamber 63 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, since the oxygen concentration (oxygen partial pressure) of the reference gas is basically constant, the electromotive force V3 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the fourth chamber 63.

[0069] The sensor element 101 further includes an electrochemical sensor cell 84 that is composed of the outer pump electrode 23, the reference electrode 42, and a solid electrolyte that is present in the portion of the structure 14 that is sandwiched between the two electrodes. The electromotive force Vref generated between the outer pump electrode 23 and the reference electrode 42 in the sensor cell 84 has a value that corresponds to the oxygen partial pressure of the measurement gas that is present outside the sensor element 101.

[0070] In addition to the above, the sensor element 101 is provided with a heater portion 70 that serves to adjust the temperature by heating and keeping the sensor element 101 warm in order to increase the oxygen ion conductivity of the solid electrolyte that constitutes the structure 14.

[0071] The heater section 70 mainly includes a heater electrode 71, a heater element 72, a heater lead 72a, a through hole 73, a heater insulating layer 74, and a heater resistance detection lead (not shown in Fig. 1). Hereinafter, the heater element 72 will also be simply referred to as the heater 72.

[0072] The heater 72 is sandwiched between the second substrate 2 and the third substrate 3, and generates heat when power is supplied from the outside through a heater electrode 71, a through hole 73, and a heater lead 72a provided on the underside 1b of the first substrate 1. The heater 72 is embedded throughout the entire range from the buffer space 12 to the fourth chamber 63, and is capable of heating the sensor element 101 to a predetermined temperature and maintaining the temperature.

[0073] The heater 72 is provided so that the vicinity of the first chamber 20 (near the inner pump electrode 22) becomes the hottest when heated, and the temperature decreases with increasing distance from the first chamber 20 in the element longitudinal direction. In this embodiment, the temperature in the range from one end of the sensor element 101 provided with the gas inlet 10 to the fourth chamber 63 when the gas sensor 100 is used (when the sensor element 101 is driven) is referred to as the element driving temperature. The heater 72 performs heating so that the element driving temperature is within the range of 750°C to 950°C.

[0074] Heater insulating layers 74 made of alumina or the like are formed above and below the heater 72 in order to provide electrical insulation between the heater 72 and the second substrate 2 and the third substrate 3. The heater section 70 also has a pressure release hole 75. The pressure release hole 75 is a portion that penetrates the third substrate 3 and is provided so as to communicate with the reference gas introduction space 43, and is provided for the purpose of alleviating an increase in internal pressure that accompanies a temperature rise within the heater insulating layer 74.

[0075] The gas sensor 100 also includes a controller 110 that controls the operation of the sensor element 101 and determines the concentration of the target gas component based on the current flowing through the sensor element 101 .

[0076] 2 is a block diagram showing functional components implemented in the controller 110. The controller 110 is configured with one or more electronic circuits having, for example, one or more central processing units (CPUs) and a storage device. The electronic circuit is also a software function unit in which predetermined functional components are implemented by the CPU executing a predetermined program stored in the storage device. Of course, the controller 110 may also be configured with an integrated circuit such as an FPGA (Field-Programmable Gate Array) in which multiple electronic circuits are connected according to their functions.

[0077] In addition, when the gas sensor 100 is attached to the exhaust path of an automobile engine and the exhaust gas flowing through the exhaust path is used as the measured gas, some or all of the functions of the controller 110 may be realized by the automobile's ECU (electronic control unit).

[0078] The controller 110 has, as functional components realized by the execution of a predetermined program in the CPU, an element operation control unit 120 that controls the operation of each part of the above-mentioned sensor element 101, and a concentration determination unit 130 that is responsible for the process of determining the concentration of the target gas component contained in the measured gas.

[0079] The element operation control unit 120 mainly comprises an adjustment pump cell control unit 121 that controls the operation of the adjustment pump cell 21, a first measurement pump cell control unit 122a that controls the operation of the first measurement pump cell 50, a second measurement pump cell control unit 122b that controls the operation of the second measurement pump cell 41, a third measurement pump cell control unit 122c that controls the operation of the third measurement pump cell 66, and a heater control unit 123 that controls the heating operation by the heater 72.

[0080] On the other hand, the concentration specifying unit 130 detects NOx, H, and H+, which are the main gas components to be detected by the gas sensor 100. ２ O, and CO ２ The system mainly includes a NOx concentration specifying unit 130N, a water vapor concentration specifying unit 130H, and a carbon dioxide concentration specifying unit 130C that specify the concentrations of NOx, water vapor, and carbon dioxide, respectively.

[0081] The NOx concentration specifying unit 130N specifies the concentration of NOx contained in the measurement gas based on the value of the oxygen pump current Ip1 flowing through the first measurement pump cell 50, which is acquired by the first measurement pump cell control unit 122a.

[0082] The water vapor concentration specifying unit 130H determines the water vapor concentration of the H contained in the measurement gas based on the value of the oxygen pump current Ip3 flowing through the third measurement pump cell 66, which is acquired by the third measurement pump cell control unit 122c. ２ The concentration of O is determined.

[0083] The carbon dioxide concentration specifying unit 130C is configured to calculate the H ２ The CO concentration in the measurement gas is determined based on the O concentration (the value of the oxygen pump current Ip3 that is the basis for determining the concentration) and the value of the oxygen pump current Ip2 that flows through the second measurement pump cell 41 and is acquired by the second measurement pump cell control unit 122b. ２ Identify the concentration of.

[0084] The concentration specifying unit 130 further includes an oxygen concentration specifying unit 130A that specifies the concentration of oxygen contained in the measurement gas. The oxygen concentration specifying unit 130A specifies the concentration of oxygen contained in the measurement gas based on the value of the oxygen pump current Ip0 flowing through the adjustment pump cell 21, which is acquired by the adjustment pump cell control unit 121. That is, in the gas sensor 100 according to this embodiment, the concentration specifying unit 130A specifies the concentration of oxygen contained in the measurement gas based on the value of the oxygen pump current Ip0 flowing through the adjustment pump cell 21, which is acquired by the adjustment pump cell control unit 121. ２ O, and CO ２ In addition, oxygen is also detected as an additional target gas component.

[0085] <Multi-gas detection and concentration determination> Next, a method for detecting multiple gas species (multi-gas detection) and determining the concentration of the detected gases, which are realized by the gas sensor 100 having the above-described configuration, will be described. In the following, the measurement gases are oxygen, NOx, H ２ O, and CO ２ The exhaust gas contains

[0086] FIG. 3 is a schematic diagram showing how gas flows in and out of four chambers (internal spaces) of the sensor element 101 of the gas sensor 100. As shown in FIG.

[0087] First, in the sensor element 101 included in the gas sensor 100 according to this embodiment, as described above, the measurement gas is introduced into the first chamber 20 through the gas inlet 10 (first diffusion-controlling part 11), the buffer space 12, and the second diffusion-controlling part 13. In the first chamber 20, the adjustment pump cell 21 is operated to pump oxygen out of the introduced measurement gas.

[0088] The oxygen is pumped out by the adjustment pump cell control unit 121 of the controller 110 by setting the target value (control voltage) of the electromotive force V0 in the first chamber sensor cell 80 to a value within a range of 300 mV to 500 mV (preferably 350 mV), and then feedback-controlling the voltage Vp0 applied to the adjustment pump cell 21 by the variable power supply 24 in accordance with the difference between the actual value of the electromotive force V0 and the target value so that the electromotive force V0 is maintained at the target value. For example, when a measurement gas containing a large amount of oxygen reaches the first chamber 20, the value of the electromotive force V0 deviates significantly from the target value. Therefore, the adjustment pump cell control unit 121 controls the pump voltage Vp0 applied to the adjustment pump cell 21 by the variable power supply 24 so as to reduce this deviation.

[0089] By pumping oxygen out of the first chamber 20 by the adjusting pump cell 21 in this manner, the oxygen partial pressure (concentration) in the first chamber 20 is adjusted to the H ２ O and CO ２ For example, by operating the adjusting pump cell 21, the oxygen concentration in the first chamber 20 becomes about 0.1 ppm to about 0.00001 ppm.

[0090] FIG. 4 shows that the target value of the electromotive force V0 is set to a value within the range of 300 mV to 500 mV. ２ O and CO ２ 4 is a graph showing the relationship between the target value (control voltage) of the electromotive force V0 in the first vacant chamber sensor cell 80 and the oxygen pump current Ip0 flowing through the adjustment pump cell 21 when three different types of model gases are flowed. The three types of model gases are specifically a first gas containing 10% oxygen, a second gas containing 10% oxygen, and a second gas containing 10% oxygen and CO. ２ a second gas containing 10% each of oxygen and H ２ The third gas contains 10% of each of nitrogen (N ２ The element operating temperature was set to 800°C or higher, and the temperature of the model gas was set to 150°C.

[0091] 4, it can be seen that in the case of the first gas, the oxygen pump current Ip0 is substantially constant in the range of the control voltage of 0.3 V or more, whereas in the case of the second gas and the third gas, the oxygen pump current Ip0 has substantially the same profile as the first gas in the range of the control voltage of 0.7 V or less, but when the control voltage exceeds 0.7 V, it can be seen that the oxygen pump current Ip0 increases again. This increase is due to the H contained in the measurement gas. ２ O or CO ２ is reduced (decomposed) to generate oxygen, which causes the ２ O or CO ２ This is caused by the superposition of the reduction currents.

[0092] Taking this into consideration, in this embodiment, the target value of the electromotive force V0 is set to a value within the range of 300 mV to 500 mV.

[0093] In addition, NOx is also ２ O and CO ２ Similarly, NOx is not reduced as oxygen is pumped out by the regulating pump cell 21. However, this is not due to the way the target value of the electromotive force V0 is set, but rather due to the fact that the inner pump electrode 22 contains Au, which is inactive to NOx, as described above.

[0094] As described above, in the gas sensor 100 according to the present embodiment, unlike the gas sensor of the prior art, the first chamber 20, which is the highest temperature in the sensor element 101 during operation, is heated by H ２ O and CO ２ Only oxygen is pumped out in a manner that does not reduce H ２ O and CO ２ Furthermore, NOx is not reduced.

[0095] The target value of the electromotive force V0 in the first empty chamber sensor cell 80, which is set for pumping out the oxygen, is 300 mV to 500 mV. ２ O and CO ２ This is sufficiently smaller than the target value of 1000 mV to 1500 mV set when reducing H ２ O and CO ２The increase in the pump voltage Vp0 is suppressed compared to the voltage applied to the corresponding pump cell of a conventional gas sensor, which involves the reduction of the pump voltage Vp0. As a result, in the gas sensor 100 according to this embodiment, the occurrence of cracks and blackening due to the application of a high voltage while the inner pump electrode 22 is maintained at a high temperature is suitably suppressed.

[0096] Furthermore, since the inner pump electrode 22 contains Au, which is inactive to NOx, even if the measurement gas contains NOx, the NOx will not be reduced as oxygen is pumped out by the adjustment pump cell 21.

[0097] In the first chamber 20, NOx, H ２ O, and CO ２ The measurement gas from which only oxygen has been pumped out to the extent that NOx is not reduced is introduced into the second chamber 40. Then, in this second chamber 40, reduction of NOx contained in the measurement gas occurs. The first measurement electrode 51 provided in the second chamber 40 and constituting the first measurement pumping cell 50 contains a Pt-Rh alloy as its metal component and does not contain Au, which is inactive to NOx, so that reduction of NOx progresses at the first measurement electrode 51. That is, when the first measurement pumping cell 50 is activated, oxygen is pumped out of the first chamber 20 and then the measurement gas is introduced into the second chamber 40, and further oxygen is pumped out, thereby causing a reduction (decomposition) reaction of NOx contained in the measurement gas (for example, 2NO → 2N ２ +O ２ ) proceeds, and substantially all of the NO is decomposed into nitrogen and oxygen.

[0098] The reduction (decomposition) of NOx and the pumping of the oxygen produced thereby are carried out by the first measurement pump cell control section 122a of the controller 110 setting the target value (control voltage) of the electromotive force V1 in the second empty chamber sensor cell 81 to a value within the range of 350 mV to 700 mV (preferably 400 mV), and feedback-controlling the voltage Vp1 applied by the variable power supply 52 to the first measurement pump cell 50 in accordance with the difference between the actual value of the electromotive force V1 and the target value so that the electromotive force V1 is maintained at the target value.

[0099] By operating the first measuring pump cell 50 in this manner, the oxygen partial pressure in the second chamber 40 is maintained at a value that is approximately the same as or slightly lower than that in the first chamber 20. For example, when V2=400 mV, －８ As a result, the gas to be measured becomes H ２ O and CO ２ (Furthermore, N ２ ) but is substantially free of NOx and oxygen.

[0100] In the gas sensor 100 according to this embodiment, the concentration of NOx in the measurement gas is determined based on the oxygen pump current Ip1 that flows through the first measuring pump cell 50 when oxygen is pumped out, including the reduction of NOx.

[0101] The oxygen pump current Ip1 (hereinafter also referred to as the NOx detection current Ip1) flowing through the first measuring pump cell 50 flows in association with the pumping of oxygen produced by the decomposition of NOx contained in the measurement gas. Therefore, the magnitude of the NOx detection current Ip1 is approximately proportional to the concentration of NOx contained in the measurement gas introduced through the gas inlet 10. That is, a linear relationship is established between the NOx detection current Ip1 and the NOx concentration in the measurement gas. Data indicating this linear relationship (Ip1-NOx data) is determined in advance using a model gas with a known NOx concentration and stored in the controller 110.

[0102] When the gas sensor 100 actually performs measurement, the NOx concentration specifying unit 130N acquires the value of the NOx detection current Ip1 from the first measurement pump cell control unit 122a. Then, by referring to the Ip1-NOx data, the NOx concentration specifying unit 130N specifies the value of the oxygen concentration corresponding to the acquired NOx detection current Ip1. This allows the NOx concentration in the measurement gas to be specified.

[0103] In the second chamber 40, H ２ O and CO ２ The measurement gas in which NOx has been reduced to the extent that H is not reduced is introduced into the third chamber 61. In the third chamber 61, H contained in the measurement gas is ２ O and CO ２That is, by operating the second measuring pump cell 41, the measurement gas in which oxygen has been pumped out from the first chamber 20 and NOx has been reduced in the second chamber 40 is further pumped out, and the H contained in the measurement gas is reduced. ２ O and CO ２ Reduction (decomposition) reaction of (2H ２ O → 2H ２ +O ２ , 2CO ２ →2CO+O ２ ) progresses, and H ２ O and CO ２ is substantially entirely hydrogen (H ２ ) and carbon monoxide (CO) and oxygen.

[0104] Related H ２ O and CO ２ The reduction (decomposition) of and the pumping of the resulting oxygen are achieved by the second measurement pump cell control unit 122b of the controller 110 setting a target value (control voltage) of the electromotive force V2 in the third vacant chamber sensor cell 82 to a value within a range of 1000 mV to 1500 mV (preferably 1000 mV), and then feedback-controlling the voltage Vp2 applied to the second measurement pump cell 41 by the variable power supply 46 in accordance with the difference between the actual value of the electromotive force V2 and the target value, so that the electromotive force V2 is maintained at the target value. The graph shown in FIG. 4 also suggests that the target value of the electromotive force V2 should preferably be within a range of 1000 mV to 1500 mV.

[0105] By operating the second measurement pump cell 41 in this manner, the oxygen partial pressure in the third chamber 61 is maintained at a value lower than the oxygen partial pressures in the first chamber 20 and the second chamber 40. For example, when V2=1000 mV, －２０ As a result, the gas to be measured becomes H ２ and CO (and also N ２ ) including NOx, H ２ O, CO ２ , and becomes substantially free of oxygen.

[0106] H ２ and CO, while NOx, H２ O, CO ２ , and the measurement gas substantially free of oxygen is introduced into the fourth chamber 63 .

[0107] In the fourth chamber 63, oxygen is pumped in by the operation of the third measuring pump cell 66, and H contained in the introduced measurement gas is ２ is selectively oxidized.

[0108] The pumping of oxygen is carried out by the third measurement pump cell control unit 122c of the controller 110 setting the target value (control voltage) of the electromotive force V3 in the fourth vacant chamber sensor cell 83 to a value within the range of 250 mV to 450 mV (preferably 350 mV), and feedback-controlling the voltage Vp3 applied by the variable power supply 68 to the third measurement pump cell 66 in accordance with the difference between the actual value of the electromotive force V3 and the target value so that the electromotive force V3 is maintained at the target value.

[0109] By operating the third measuring pump cell 66 in this manner, the fourth chamber 63 is ２ +O ２ →2H ２ The oxidation (combustion) reaction of H introduced from the gas inlet 10 is promoted. ２ Amount of H correlated with the amount of O ２ O is generated again. ２ The correlation of the amount of O is ２ The amount of O and H produced by their decomposition ２ is oxidized to produce H ２ The amount of O is the same as or within a certain tolerance range that is acceptable in terms of measurement accuracy.

[0110] By setting the target value of the electromotive force V3 to a value within the range of 250 mV to 450 mV, the oxygen partial pressure in the fourth chamber 63 is ２ For example, when V3 = 350 mV, 10 －７ It will be about atm.

[0111] As described above, the third measuring electrode 64 may be provided as a cermet electrode containing a Pt—Au alloy with an Au concentration of 1 wt % or more and 50 wt % or less as a metal component. ２ This contributes to improving the selective oxidation of

[0112] In addition, the temperature rise of the third measurement electrode 64 may be further suppressed by devising the shape (width, thickness) and arrangement (denseness) of the heater 72 .

[0113] In the gas sensor 100 according to the present embodiment, which operates in the above manner, H ２ O and CO ２ the oxygen pump current Ip2 flowing through the second measuring pump cell 41 during the pumping of oxygen, including the reduction of H ２ and the oxygen pump current Ip3 flowing through the third measuring pump cell 66 when oxygen is pumped in for the oxidation of H in the measurement gas. ２ O and CO ２ Identify the concentration of.

[0114] 5 and 6 show the results of the detection of H as the main gas component to be detected. ２ O and CO ２ When only one of these is contained in the measurement gas, and when H ２ O and CO ２ 10 is a diagram showing the dependence of the oxygen pump current Ip2 and the oxygen pump current Ip3 on the concentration of the target gas component when the target gas contains the components Ip2 and Ip3. FIG.

[0115] In FIGS. 5 and 6, H ２ The graph shows the case where O is the only gas component to be detected, and the graph shows the case where CO ２ The graph for when is contained alone as a gas component to be detected is indicated by a triangle, and the graph for when H ２ O and CO ２ When the gas components to be detected include ２ O+CO ２The graphs of the gas sensor 100 are indicated by square marks. These graphs were obtained by operating the gas sensor 100 in an atmosphere of a model gas containing a known concentration of the gas component to be detected and the remainder being oxygen and nitrogen. The element operating temperature was set to 800°C or higher, and the temperature of the model gas was set to 200°C.

[0116] As can be seen from FIG. ２ When only O is contained as the gas component to be detected, and CO ２ In both cases where only the above gas components are included as the detection target gas components, the graph shows a monotonically increasing and approximately linear pattern.

[0117] Furthermore, the same concentration of H ２ O and CO ２ When the gas components to be detected include H, the value of the oxygen pump current Ip2 is ２ O and CO ２ The oxygen pump current Ip2 is the sum of the oxygen pump current Ip2 when the H ２ O and CO ２ The value of the oxygen pump current Ip2 when the ratio is changed also changes depending on the concentration of H ２ O and CO ２ It has been confirmed that the oxygen pump current Ip2 is the sum of the oxygen pump current Ip2 when each of the above is included individually.

[0118] On the other hand, as shown in FIG. ２ The graph of the oxygen pump current Ip3 when only O is included as the detection target gas component monotonically decreases (the absolute value monotonically increases) and is approximately linear. Note that the oxygen pump current Ip3 is a negative value because, as described above, the direction of pumping oxygen in the third measurement pumping cell 66 is set to the positive direction of the oxygen pump current, while the oxygen pump current Ip3 is a negative value because ... ２ This is because the water flows in the direction of drawing in oxygen in order to reoxidize it.

[0119] In contrast, CO ２When only CO is contained as the detection target gas component, the value of the oxygen pump current Ip3 is maintained at approximately zero. This indicates that CO generated by reduction in the third chamber 61 is not reoxidized by the operation of the third measuring pump cell 66.

[0120] Also, the same concentration of H ２ O and CO ２ The graph of the oxygen pump current Ip3 when the gas components to be detected include H ２ This is almost the same as the graph of the oxygen pump current Ip3 when only CO is included. ２ This is consistent with the fact that the oxygen pump current Ip3 is almost zero when only H is contained as the detection target gas component. ２ O and CO ２ The value of the oxygen pump current Ip3 when the ratio of H ２ O and CO ２ It has been confirmed that the graph of the oxygen pump current Ip3 substantially coincides with the graph of the oxygen pump current Ip3 when each of the ２ Therefore, if the oxygen pump current Ip3 is known, ２ This means that the concentration of O can be specified.

[0121] In this embodiment, the above-described properties of the oxygen pump current Ip2 and the oxygen pump current Ip3 are utilized to determine the H ２ O and CO ２ Hereinafter, the oxygen pump current Ip2 and the oxygen pump current Ip3 measured by the gas sensor 100 will also be referred to as the total reduction current Ip2 and the water vapor equivalent current Ip3, respectively.

[0122] Specifically, prior to using the gas sensor 100, a model gas having a known concentration was used to measure the H ２ O and CO ２ The characteristic data showing the relationship between the oxygen pump current Ip2 and the concentration of each gas when only one of the gases is contained in the measurement gas and the other is not contained (hereinafter referred to as Ip2-H ２ O data, Ip2-CO２ data), and H as shown in FIG. ２ O is contained in the measurement gas and CO ２ When the measured gas does not contain H, the oxygen pump current Ip3 and H ２ Characteristic data showing the relationship between the concentration of O (hereinafter referred to as Ip3-H ２ 0 data) and stored in the controller 110. ２ O data and Ip2-CO ２ The data are the H of the total reduction current Ip2. ２ O contribution and CO ２ This is a value that indicates the contribution of

[0123] The oxygen pump current Ip2 is a value corresponding to the diffusion resistance applied to the measurement gas from the gas inlet 10 of the sensor element 101 to the third chamber 61, and the oxygen pump current Ip3 is a value corresponding to the diffusion resistance applied to the measurement gas from the gas inlet 10 of the sensor element 101 to the fourth chamber 63. Therefore, strictly speaking, Ip2-H ２ O data, Ip2-CO ２ Data, and Ip3-H ２ The O data differs for each individual sensor element 101 constituting each gas sensor 100. Therefore, it is preferable that these characteristic data are specified for each individual gas sensor 100. However, for gas sensors 100 manufactured under the same conditions and in the same lot, if it is confirmed that the error is within an allowable range, the characteristic data obtained for a specific gas sensor 100 may be applied to other gas sensors 100 in the same lot.

[0124] When the gas sensor 100 actually performs measurement, the measurement gas is introduced into the sensor element 101 heated to the element driving temperature, and the adjustment pump cell 21, the first measurement pump cell 50, the second measurement pump cell 41, and the third measurement pump cell 66 operate in the manner described above. Then, the water vapor concentration specifying unit 130H acquires the water vapor equivalent current Ip3 from the third measurement pump cell control unit 122c, and calculates the H corresponding to the acquired value. ２ O concentration is Ip3-H ２Identify based on O data.

[0125] H ２ After the O concentration is determined, the carbon dioxide concentration determination unit 130C subsequently obtains the value of the total reduction current Ip2 from the second measurement pump cell control unit 122b and calculates Ip2-H ２ Based on the O data, the specified concentration of H ２ The contribution of H to the total reduction current Ip2 of O, that is, the contribution of H ２ The amount of current due to the reduction of O is determined. The obtained value is subtracted from the value of the total reduction current Ip2 to determine the amount of CO ２ Finally, the contribution of Ip2-CO ２ Based on the data, ２ CO corresponding to the contribution of ２ Identify the concentration.

[0126] In the gas sensor 100 according to the present embodiment, as described above, H in the measurement gas is ２ O concentration and CO ２ The concentration is measured.

[0127] Alternatively, the water vapor equivalent current Ip3 and the total reduction current Ip2 ２ The relationship between the oxygen pump current Ip2 corresponding to the contribution of O and the characteristic data (hereinafter referred to as H ２ The carbon dioxide concentration specifying unit 130C stores the H O characteristic data in the controller 110. ２ Using the O characteristic data, H at the total reduction current Ip2 can be calculated directly from the water vapor equivalent current Ip3. ２ The contribution of O may be specified.

[0128] FIG. 7 shows the H ２ 7 is a diagram illustrating an example of the H O characteristic data. In FIG. 7, the absolute value of the water vapor equivalent current Ip3 is plotted on the x-axis, and the H O characteristic data at the total reduction current Ip2 is plotted on the x-axis. ２ The y-axis indicates the value of the oxygen pump current Ip2, which corresponds to the contribution of O. As shown in FIG. 7, the water vapor equivalent current Ip3 and the H ２ Since a linear relationship exists between the contribution of O and the２ It is sufficient to specify it as O characteristic data.

[0129] Alternatively, the value of the y-intercept in this relational expression should be zero in principle, and in the case of a gas sensor 100 that operates normally, the value is small enough to be considered zero in practice. Therefore, only the slope of the expression showing the linear relationship above is used as the y-intercept. ２ The carbon dioxide concentration specifying unit 130C calculates the product of the slope value and the water vapor equivalent current Ip3 as the H ２ It may be used as the contribution of O.

[0130] In addition, H ２ The slope of the O characteristic data corresponds to the ratio of the diffusion resistance imparted to the measurement gas from the gas inlet 10 to the fourth chamber 63 to the diffusion resistance imparted to the measurement gas from the gas inlet 10 to the third chamber 61.

[0131] In addition, NOx concentration, H ２ O concentration, and CO ２ In parallel with the determination of the concentration, the oxygen concentration is also determined using the oxygen pump current Ip0 flowing through the adjustment pump cell 21.

[0132] In the gas sensor 100 according to this embodiment, as described above, the adjusting pump cell 21 is operated to pump oxygen from the measurement gas introduced from the gas inlet 10 in the first chamber 20. The pumping of oxygen is carried out by the adjustment pump cell 21. ２ O, and CO ２ Although the oxygen pump current Ip0 (hereinafter also referred to as oxygen detection current Ip0) that flows during this process is approximately proportional to the concentration of oxygen contained in the measurement gas introduced through the gas inlet 10. In other words, a linear relationship is established between the oxygen detection current Ip0 and the oxygen concentration in the measurement gas. Data showing this linear relationship (Ip0-O ２ The oxygen concentration data is determined in advance using a model gas having a known oxygen concentration and stored in the controller 110.

[0133] When the gas sensor 100 actually performs measurement, the oxygen concentration specifying unit 130A obtains the value of the oxygen detection current Ip0 from the adjustment pump cell control unit 121. Then, Ip0-O ２ The data is referenced to identify the oxygen concentration value corresponding to the acquired oxygen detection current Ip0, thereby identifying the oxygen concentration in the measurement gas.

[0134] As described above, in the gas sensor according to the present embodiment, the measurement gas is H ２ O and CO ２ When both are present, the concentrations of both can be measured. In addition, the NOx concentration can be measured simultaneously. Furthermore, it is also possible to accurately determine the oxygen concentration.

[0135] In addition, in the case of the gas sensor according to the present embodiment, unlike the gas sensor of the prior art, the first chamber, which is the hottest during operation, contains H ２ O and CO ２ Therefore, the voltage applied to the adjusting pump cell that pumps oxygen from the first chamber is kept lower than that of the gas sensor of the prior art, and therefore the occurrence of cracks and blackening in the sensor element is suitably suppressed.

[0136] That is, according to this embodiment, a multi-gas sensor is realized which has superior long-term reliability compared to conventional sensors and can simultaneously measure a greater number of gas species.

Claims

1. A gas sensor capable of measuring the concentrations of a plurality of target gas components, comprising: a sensor element having a structure made of an oxygen ion conductive solid electrolyte; and a controller for controlling the operation of the gas sensor, wherein the sensor element comprises: a gas inlet through which a gas to be measured is introduced; a first void, a second void, a third void, and a fourth void, which are sequentially connected to the gas inlet via different diffusion-controlling sections; an adjustment pump cell comprising an inner electrode formed facing the first void, an outer-void pump electrode provided in a location other than the first void, the second void, the third void, and the fourth void, and the solid electrolyte present between the inner electrode and the outer-void pump electrode; and a first measurement pump cell comprising a first measurement electrode formed facing the second void, the outer-void pump electrode, and the solid electrolyte present between the first measurement electrode and the outer-void pump electrode. a second measurement pump cell including a second measurement electrode formed facing the third chamber, the pump electrode outside the cavity, and the solid electrolyte present between the second measurement electrode and the pump electrode outside the cavity; a third measurement pump cell including a third measurement electrode formed facing the fourth chamber, the pump electrode outside the cavity, and the solid electrolyte present between the third measurement electrode and the pump electrode outside the cavity; and a heater for heating the sensor element, wherein the inner electrode is a cermet electrode containing a Pt—Au alloy as a metal component, and an Au concentration in the Pt—Au alloy is 0.5 wt % or more, and the first measurement electrode is another cermet electrode containing a Pt—Rh alloy as a metal component, and the adjustment pump cell pumps out oxygen from the measurement gas introduced into the first chamber through the gas inlet so as to prevent decomposition of NOx, water vapor, and carbon dioxide contained in the measurement gas, the first measuring pump cell pumps oxygen from the second chamber so that substantially all of the NOx contained in the measurement gas introduced from the first chamber to the second chamber is reduced, and the second measuring pump cell pumps oxygen from the third chamber so that substantially all of the water vapor and carbon dioxide contained in the measurement gas introduced from the second chamber to the third chamber are reduced,The third measurement pump cell selectively oxidizes, in the fourth chamber, hydrogen produced by reduction of water vapor contained in the measurement gas introduced from the third chamber into the fourth chamber by pumping oxygen into the fourth chamber, and the controller comprises: NOx concentration specifying means for specifying the concentration of NOx contained in the measurement gas based on the magnitude of an NOx detection current which is an oxygen pump current flowing between the first measurement electrode and the pump electrode outside the cavity when oxygen is pumped from the second chamber by the first measurement pump cell; and water vapor concentration specifying means for specifying the concentration of water vapor contained in the measurement gas based on the value of a water vapor equivalent current which is an oxygen pump current flowing between the second measurement electrode and the pump electrode outside the cavity when hydrogen is oxidized by the oxygen pumped into the third chamber by the second measurement pump cell. and a carbon dioxide concentration determining means for determining the concentration of carbon dioxide contained in the measurement gas based on the value of the water vapor equivalent current and the value of a total reduction current, which is an oxygen pump current that flows between the first measurement electrode and the pump electrode outside the cavity when the first measurement pump cell pumps oxygen from the second cavity and thereby reduces water vapor and carbon dioxide.

2. A gas sensor as claimed in claim 1, wherein the controller further stores Ip1-NOx data indicating a relationship between the NOx detection current and the NOx concentration, which is specified in advance, and the NOx concentration specifying means specifies the concentration of NOx contained in the measurement gas based on the NOx detection current and the Ip1-NOx data when NOx contained in the measurement gas is reduced.

3. A gas sensor according to claim 2, wherein the controller: calculates Ip2-H, which indicates a relationship between a predetermined oxygen pump current flowing through the second measuring pump cell and a water vapor concentration when the measurement gas contains water vapor and does not contain carbon dioxide. ２ and Ip2-CO2 data, which indicates the relationship between the oxygen pump current flowing through the second measuring pump cell and the concentration of water vapor when carbon dioxide is contained in the measurement gas and water vapor is not contained in the measurement gas, as previously specified. ２ and Ip3-H, which shows the relationship between the oxygen pump current flowing through the third measuring pump cell and the concentration of water vapor when the measured gas contains water vapor and does not contain carbon dioxide, which is specified in advance. ２ and the water vapor concentration specifying means stores the Ip3-H ２ The water vapor concentration corresponding to the value of the water vapor equivalent current in the O data is identified as the concentration of water vapor contained in the measurement target gas, and the carbon dioxide concentration identifying means compares the concentration of water vapor contained in the measurement target gas identified by the water vapor concentration identifying means with the Ip2-H ２ Based on the data and the total reduction current, the contribution of the reduction of water vapor to the total reduction current is identified, and then the Ip2-CO ２ and determining, as the concentration of carbon dioxide contained in the measurement gas, a carbon dioxide concentration corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the data.

4. A gas sensor according to claim 2, wherein the controller: calculates Ip2-CO 2 , which indicates the relationship between the oxygen pump current flowing through the second measuring pump cell and the concentration of water vapor when the measurement gas contains carbon dioxide and does not contain water vapor, which is specified in advance. ２ and Ip3-H, which shows the relationship between the oxygen pump current flowing through the third measuring pump cell and the concentration of water vapor when the measured gas contains water vapor and does not contain carbon dioxide, which is specified in advance. ２ and H indicating the relationship between the water vapor equivalent current and the oxygen pump current corresponding to the contribution of water vapor to the total reduction current. ２ and the water vapor concentration specifying means stores the Ip3-H ２ the water vapor concentration corresponding to the value of the water vapor equivalent current in the carbon dioxide data is determined as the concentration of water vapor contained in the measurement gas; and ２ Based on the O characteristic data, the contribution of the reduction of water vapor in the total reduction current is identified, and then the Ip2-CO ２ and determining, as the concentration of carbon dioxide contained in the measurement gas, a carbon dioxide concentration corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the data.

5. A gas sensor according to any one of claims 1 to 4, characterized in that the controller further comprises an oxygen concentration determination means for determining the concentration of oxygen contained in the measurement gas based on the magnitude of the current flowing between the inner electrode and the outer pump electrode when oxygen is pumped out of the first chamber by the adjustment pump cell.

6. A gas sensor according to any one of claims 1 to 4, wherein the third measurement electrode is a cermet electrode containing a Pt-Au alloy as a metal component, and the Au concentration in the Pt-Au alloy is 1 wt% or more and 50 wt% or less.

7. A method for measuring the concentrations of a plurality of target gas components using a gas sensor, the gas sensor comprising a sensor element having a long plate-like structure made of an oxygen ion conductive solid electrolyte, the sensor element comprising: a gas inlet through which a gas to be measured is introduced; a first void, a second void, a third void, and a fourth void, which are connected in sequence to the gas inlet via different diffusion rate-limiting sections; an adjustment pump cell comprising an inner electrode formed facing the first void, an outer-space pump electrode provided in a location other than the first void, the second void, the third void, and the fourth void, and the solid electrolyte present between the inner electrode and the outer-space pump electrode; and a first measurement pump cell comprising a first measurement electrode formed facing the second void, the outer-space pump electrode, and the solid electrolyte present between the first measurement electrode and the outer-space pump electrode. a second measurement pump cell including a second measurement electrode formed facing the third chamber, the pump electrode outside the cavity, and the solid electrolyte present between the second measurement electrode and the pump electrode outside the cavity; a third measurement pump cell including a third measurement electrode formed facing the fourth chamber, the pump electrode outside the cavity, and the solid electrolyte present between the third measurement electrode and the pump electrode outside the cavity; and a heater for heating the sensor element, wherein the inner electrode is a cermet electrode containing a Pt-Au alloy as a metal component, and an Au concentration in the Pt-Au alloy is 0.5 wt % or more, and the first measurement electrode is another cermet electrode containing a Pt-Rh alloy as a metal component, and a) pumping oxygen from the measurement gas introduced into the first chamber through the gas inlet by the adjustment pump cell so that NOx, water vapor, and carbon dioxide contained in the measurement gas are not decomposed; b) pumping oxygen from the second chamber by the first measuring pump cell so that substantially all of the NOx contained in the measurement gas introduced from the first chamber into the second chamber is reduced;c) pumping oxygen from the third chamber by the second measurement pump cell so that substantially all of the water vapor and carbon dioxide contained in the measurement gas introduced from the second chamber to the third chamber are reduced; d) pumping oxygen into the fourth chamber by the third measurement pump cell, thereby selectively oxidizing in the fourth chamber hydrogen produced by the reduction of water vapor contained in the measurement gas introduced from the third chamber to the fourth chamber; e) determining the concentration of NOx contained in the measurement gas based on the magnitude of a NOx detection current, which is an oxygen pump current flowing between the first measurement electrode and the pump electrode outside the cavity, when NOx is reduced by the first measurement pump cell pumping oxygen from the second chamber; and f) determining the concentration of water vapor contained in the measurement gas based on the value of a water vapor equivalent current, which is an oxygen pump current flowing between the third measurement electrode and the pump electrode outside the cavity, when hydrogen is oxidized by the oxygen pumped into the fourth chamber by the third measurement pump cell. g) determining the concentration of carbon dioxide contained in the measurement gas based on the value of the water vapor equivalent current and the value of a total reduction current, which is an oxygen pump current that flows between the second measurement electrode and the pump electrode outside the cavity when the second measurement pump cell pumps oxygen from the third cavity and thereby reduces water vapor and carbon dioxide.

8. A method for measuring concentration using a gas sensor as set forth in claim 7, comprising: h) a step of identifying Ip1-NOx data showing the relationship between the NOx detection current and the NOx concentration before steps a) to g), and in step e), identifying the concentration of NOx contained in the measurement gas based on the NOx detection current and the Ip1-NOx data when the NOx contained in the measurement gas is reduced.

9. A concentration measurement method using a gas sensor according to claim 8, wherein in step h), Ip2-H is calculated, which indicates the relationship between the oxygen pump current flowing through the second measuring pump cell and the water vapor concentration when the measurement gas contains water vapor and does not contain carbon dioxide. ２ and Ip2-CO2 data showing the relationship between the oxygen pump current flowing through the second measuring pump cell and the concentration of water vapor when carbon dioxide is contained in the measurement gas but water vapor is not contained in the measurement gas. ２ and Ip3-H, which shows the relationship between the oxygen pump current flowing through the third measuring pump cell and the concentration of water vapor when the measurement gas contains water vapor but does not contain carbon dioxide. ２ O data and further specify, and in the step f), ２ The water vapor concentration corresponding to the value of the water vapor equivalent current in the O data is identified as the water vapor concentration contained in the measurement target gas, and in the step g), the water vapor concentration contained in the measurement target gas identified in the step f) and the Ip2-H ２ Based on the data and the total reduction current, the contribution of the reduction of water vapor to the total reduction current is identified, and then the Ip2-CO ２ and determining, as the concentration of carbon dioxide contained in the measurement gas, a carbon dioxide concentration corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the data.

10. A concentration measurement method using a gas sensor according to claim 8, wherein in step h), Ip2-CO ２ and Ip3-H, which shows the relationship between the oxygen pump current flowing through the third measuring pump cell and the concentration of water vapor when the measurement gas contains water vapor but does not contain carbon dioxide. ２ H O data showing the relationship between the water vapor equivalent current and the oxygen pump current corresponding to the contribution of water vapor to the total reduction current. ２ O characteristic data and a step of identifying, and further identifying, in the step f), ２ The water vapor concentration corresponding to the value of the water vapor equivalent current in the O data is identified as the concentration of water vapor contained in the measurement gas, and in the step g), the water vapor equivalent current and the H ２ Based on the O characteristic data, the contribution of the reduction of water vapor in the total reduction current is identified, and then the Ip2-CO ２ and determining, as the concentration of carbon dioxide contained in the measurement gas, a carbon dioxide concentration corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the data.

11. A method for measuring a concentration using a gas sensor according to any one of claims 7 to 10, further comprising the step of: i) determining the concentration of oxygen contained in the gas to be measured based on the magnitude of the current flowing between the inner electrode and the pump electrode outside the cavity when oxygen is pumped out of the first cavity by the adjusting pump cell.

12. A method for measuring concentration using a gas sensor according to any one of claims 7 to 10, wherein the third measurement electrode is a cermet electrode containing a Pt-Au alloy as a metal component, and the Au concentration in the Pt-Au alloy is 1 wt% or more and 50 wt% or less.

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