Gas sensor and concentration measuring method using gas sensor

Abstract

The sensor element is provided with: first to third cavities that communicate in order from the gas introduction port via different diffusion rate control units; and a heater that heats the vicinity of the first cavity so that the temperature is the highest. The adjustment pump unit sucks oxygen from the gas to be measured introduced into the first cavity within a range in which H2O and CO2 contained in the gas to be measured are not decomposed, and the first measurement pump unit sucks oxygen from the second cavity such that all H2O and CO2 contained in the gas to be measured introduced into the second cavity from the first cavity are reduced. The second measurement pump unit sucks oxygen into the third cavity to selectively oxidize H2 generated by reduction, the concentration of H2O is determined from the value of the suction current in the second measurement pump unit, and the concentration of CO2 is determined on the basis of the determined concentration of H2O and the value of the suction current in the first measurement pump unit.

Description

Technical Field

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

[0002] As for the measurement for managing the emission amount from automobile exhaust gas, there are known technologies for measuring the concentration of water vapor (H2O) and carbon dioxide (CO2) (for example, see Patent Documents 1 to 3). The gas sensors disclosed in Patent Documents 1 and 2 can measure the water vapor (H2O) component and the carbon dioxide (CO2) component at the same time. In addition, the gas sensor disclosed in Patent Document 3 can also measure the water vapor (H2O) component with good accuracy when the measured gas contains carbon dioxide (CO2).

[0003] In the three-chamber gas sensor disclosed in Patent Document 1, first, the main pump unit, which is a pump unit for the first internal cavity, operates to suck out O2 contained in the measured gas introduced into the first internal cavity, and H2O and CO2 also contained in the measured gas are temporarily reduced to generate H2 and CO. The measured gas containing H2 and CO is introduced into the second and third internal cavities. Next, O2 is sucked in by the first measuring pump unit, which is a pump unit for the second internal cavity, so that H2 is selectively oxidized to generate H2O, and further, O2 is sucked in by the second measuring pump unit, which is a pump unit for the third internal cavity, so that CO is oxidized to generate CO2. And, based on the magnitude of the pump current flowing in the first measuring pump unit and the second measuring pump unit respectively when the H2 and CO are oxidized, the concentrations of H2O and CO2 in the measured gas are measured.

[0004] In this gas sensor, in order to reduce H2O and CO2 in the first internal cavity, it is necessary to set the applied voltage in the pump unit for the first internal cavity to be high. At the same time, it is also necessary to increase the temperature of the main inner pump electrode, which is the cavity pump electrode constituting the main pump unit. However, the high applied voltage and the high temperature maintenance of the pump electrode may cause cracking of the sensor element mainly composed of oxygen ion conductive solid electrolyte ceramics, or blackening of the solid electrolyte ceramics due to reduction.

[0005] In addition, in the two-chamber gas sensor disclosed in Patent Document 3, in order to improve the selective oxidizing property of H2, the material of the intra-cavity pump electrode of the measuring pump unit constituting the pump unit serving as the second internal cavity, that is, the measuring inner pump electrode, is an alloy of Au and other precious metals (such as Pt, Rh, Ru), and the presence ratio of Au on the electrode surface is greater than 25at%.

[0006] At first glance, it seems that this electrode material can also be applied to the first measurement inner pump electrode of the first measurement pump cell that selectively oxidizes H 2 in the gas sensor disclosed in Patent Document 1.

[0007] However, in the gas sensor disclosed in Patent Document 1, the first measuring inner pump electrode is located at a higher temperature than the cavity pump electrode constituting the second measuring pump unit, i.e., the second measuring inner pump electrode. Therefore, when such an electrode material is used, Au in the electrode evaporates, and the sensitivity may change when used for a long time.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent No. 5918177

[0011] Patent Document 2: Japanese Patent No. 6469464

[0012] Patent Document 3: Japanese Patent No. 6469462 Summary of the invention

[0013] The present invention is implemented in view of the above-mentioned problems, and its purpose is to provide a multi-gas sensor that can simultaneously measure water vapor (H2O) components and carbon dioxide (CO2) components, and suppress cracking and blackening of sensor elements. In addition, even if used for a long time, the sensitivity is not likely to change, and the long-term reliability is excellent compared with the past.

[0014] In order to solve the above-mentioned problems, a first scheme of the present invention is a gas sensor capable of measuring the concentrations of multiple monitoring target gas components contained in a measured gas containing at least water vapor and carbon dioxide, characterized in that it comprises: a sensor element having a structure composed of a solid electrolyte with oxygen ion conductivity; and a controller, which controls the operation of the gas sensor, wherein the sensor element comprises: a gas inlet port for introducing the measured gas; an internal cavity, which is connected to the gas inlet port via a diffusion rate control unit; an adjustment electrode, a first measuring electrode and a second measuring electrode, which are arranged at respective surfaces. The inner cavity is isolated at a predetermined interval and arranged in order from near to far from the gas inlet; an adjustment pump unit, which is composed of the adjustment electrode, an outer cavity pump electrode arranged at a position outside the inner cavity, and the solid electrolyte existing between the adjustment electrode and the outer cavity pump electrode; a first measurement pump unit, which is composed of the first measurement electrode, the outer cavity pump electrode, and the solid electrolyte existing between the first measurement electrode and the outer cavity pump electrode; a second measurement pump unit, which is composed of the second measurement electrode, the outer cavity pump electrode, and the solid electrolyte existing between the adjustment electrode and the outer cavity pump electrode. The solid electrolyte is composed of the second measuring electrode and the pump electrode outside the cavity; and a heater, which heats the sensor element, the heater heats the sensor element in a manner that the temperature is highest near the adjustment electrode in the internal cavity and the temperature decreases as it moves away from the adjustment electrode in the length direction of the sensor element, the adjustment pump unit absorbs oxygen from the measured gas that reaches the adjustment electrode from the gas inlet within a range where water vapor and carbon dioxide contained in the measured gas are not decomposed, and the first measuring pump unit uses the oxygen in the measured gas after the oxygen is absorbed by the adjustment pump unit. The controller comprises: a device for determining a water vapor concentration, wherein the device determines the concentration of water vapor contained in the gas to be measured based on the value of a water vapor equivalent current, the water vapor equivalent current being an oxygen pump current flowing between the second measuring electrode and the pump electrode outside the cavity when hydrogen is oxidized by the oxygen sucked by the second measuring pump unit;and a carbon dioxide concentration determination mechanism that determines the concentration of carbon dioxide contained in the gas to be measured based on the value of the water vapor equivalent current and the value of the total reduction current, which is the oxygen pump current flowing between the first measurement electrode and the cavity outer pump electrode when the first measurement pump unit absorbs oxygen to reduce water vapor and carbon dioxide. ;

[0015] The second scheme of the present invention is based on the gas sensor involved in the first scheme, and is characterized in that the internal cavity is a first cavity, a second cavity and a third cavity which are connected in sequence in order of distance from the gas inlet port via different diffusion rate control parts, the adjustment electrode is arranged in the first cavity, the first measuring electrode is arranged in the second cavity, and the second measuring electrode is arranged in the third cavity.

[0016] The third scheme of the present invention is based on the gas sensor involved in the second scheme, and is characterized in that the controller stores: predetermined Ip1-H2O data indicating the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, predetermined Ip1-CO2 data indicating the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains carbon dioxide but does not contain water vapor, and predetermined Ip1-H2O data indicating the relationship between the oxygen pump current flowing through the second measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide. The water vapor concentration determining mechanism determines the concentration of water vapor corresponding to the value of the water vapor equivalent current in the Ip2-H2O data as the concentration of water vapor contained in the measured gas, and the carbon dioxide concentration determining mechanism determines the contribution of water vapor reduction to the total reduction current based on the concentration of water vapor contained in the measured gas determined by the water vapor concentration determining mechanism and the Ip1-H2O data, and then determines the carbon dioxide concentration corresponding to the difference between the total reduction current and the contribution in the Ip1-CO2 data as the concentration of carbon dioxide contained in the measured gas.

[0017] The fourth scheme of the present invention is based on the gas sensor involved in the second scheme, and is characterized in that the controller stores: predetermined Ip1-CO2 data indicating the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains carbon dioxide but does not contain water vapor, predetermined Ip2-H2O data indicating the relationship between the oxygen pump current flowing through the second measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, and predetermined Ip2-H2O data indicating the water vapor equivalent current and the contribution of water vapor to the total reduction current. The water vapor concentration determining mechanism determines the water vapor concentration corresponding to the value of the water vapor equivalent current in the Ip2-H2O data as the concentration of water vapor contained in the measured gas; the carbon dioxide concentration determining mechanism determines the contribution of water vapor reduction to the total reduction current based on the water vapor equivalent current and the H2O characteristic data, and then determines the carbon dioxide concentration corresponding to the difference between the total reduction current and the contribution in the Ip1-CO2 data as the concentration of carbon dioxide contained in the measured gas.

[0018] The fifth scheme of the present invention is based on the gas sensor involved in any one of the second to fourth schemes, and is characterized in that the second measuring electrode is a metal ceramic electrode containing a Pt-Au alloy as a metal component, and the Au concentration in the Pt-Au alloy is greater than 1wt% and less than 50wt%.

[0019] A sixth aspect of the present invention is the gas sensor according to the fifth aspect, wherein the adjustment electrode and the first measuring electrode are metal ceramic electrodes containing Pt but not Au.

[0020] The seventh scheme of the present invention is based on the gas sensor involved in any one of the second to fourth schemes, and is characterized in that the controller also has an oxygen concentration determination mechanism, which determines the concentration of oxygen contained in the measured gas based on the magnitude of the current flowing between the adjustment electrode and the pump electrode outside the cavity when oxygen is sucked out from the first cavity by the adjustment pump unit.

[0021] The eighth scheme of the present invention is a method for measuring the concentrations of multiple monitored gas components contained in a measured gas containing at least water vapor and carbon dioxide using a gas sensor, characterized in that the gas sensor comprises a sensor element having a long plate-shaped structure composed of an oxygen ion conductive solid electrolyte, and the sensor element comprises: a gas inlet port for introducing the measured gas; an internal cavity, the internal cavity being connected to the gas inlet port via a diffusion rate control unit; an adjustment electrode, a first measurement electrode and a second measurement electrode, which are respectively arranged in a manner facing the internal cavity and separated by a prescribed interval and in order of distance from the gas inlet port from near to far; an adjustment electrode A whole pump unit, the adjustment pump unit is composed of the adjustment electrode, the cavity pump electrode arranged at a position outside the internal cavity, and the solid electrolyte existing between the adjustment electrode and the cavity pump electrode; a first measurement pump unit, the first measurement pump unit is composed of the first measurement electrode, the cavity pump electrode, and the solid electrolyte existing between the first measurement electrode and the cavity pump electrode; a second measurement pump unit, the second measurement pump unit is composed of the second measurement electrode, the cavity pump electrode, and the solid electrolyte existing between the first measurement electrode and the cavity pump electrode; and a heater, the heater heats the sensor element, the method includes the following steps :a) the heater heats the sensor element in such a manner that the temperature is highest near the adjustment electrode in the internal cavity and decreases as the temperature moves away from the adjustment electrode in the longitudinal direction of the sensor element; b) using the adjustment pump unit, oxygen is sucked out from the gas to be measured that reaches the adjustment electrode from the gas inlet port within a range where water vapor and carbon dioxide contained in the gas to be measured are not decomposed; c) using the first measuring pump unit, oxygen is sucked out from the gas to be measured that reaches the first measuring electrode in such a manner that water vapor and carbon dioxide contained in the gas to be measured after the oxygen is sucked out by the adjustment pump unit are substantially completely reduced; d) using the second measuring pump unit, by pumping oxygen into the internal cavity, The cavity absorbs oxygen to selectively oxidize hydrogen generated by the reduction of water vapor contained in the measured gas reaching the second measuring electrode; e) determining the concentration of water vapor contained in the measured gas based on the value of the water vapor equivalent current, which is the oxygen pump current flowing between the second measuring electrode and the pump electrode outside the cavity when hydrogen is oxidized by the oxygen absorbed by the second measuring pump unit; f) determining the concentration of carbon dioxide contained in the measured gas based on the value of the water vapor equivalent current and the value of the total reduction current, which is the oxygen pump current flowing between the first measuring electrode and the pump electrode outside the cavity when the first measuring pump unit absorbs oxygen to reduce water vapor and carbon dioxide.

[0022] The ninth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in the eighth scheme, and is characterized in that the internal cavity is a first cavity, a second cavity, and a third cavity which are connected in sequence in order of distance from the gas inlet port via different diffusion rate control parts, the adjustment electrode is arranged in the first cavity, the first measuring electrode is arranged in the second cavity, and the second measuring electrode is arranged in the third cavity.

[0023] The tenth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in the ninth scheme, and is characterized in that it also includes the following steps: g) before the steps a) to f), pre-determining: Ip1-H2O data indicating the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but no carbon dioxide, Ip1-CO2 data indicating the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains carbon dioxide but no water vapor, and Ip1-CO2 data indicating the relationship between the oxygen pump current flowing through the second measuring pump unit when the measured gas contains water vapor but no carbon dioxide. The method comprises the following steps: providing Ip2-H2O data showing the relationship between the oxygen pump current of the element and the concentration of water vapor, wherein in the step e), the concentration of water vapor corresponding to the value of the water vapor equivalent current in the Ip2-H2O data is determined as the concentration of water vapor contained in the measured gas, and in the step f), based on the concentration of water vapor contained in the measured gas determined in the step e) and the Ip1-H2O data, the contribution of water vapor reduction to the total reduction current is determined, and then, the concentration of carbon dioxide corresponding to the difference between the total reduction current and the contribution is determined in the Ip1-CO2 data as the concentration of carbon dioxide contained in the measured gas.

[0024] The eleventh scheme of the present invention is based on the concentration measurement method using a gas sensor involved in the ninth scheme, and is characterized in that it also includes the following steps: g) before the steps a) to f), pre-determining: Ip1-CO2 data representing the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains carbon dioxide but does not contain water vapor, Ip2-H2O data representing the relationship between the oxygen pump current flowing through the second measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, and Ip2-H2O data representing the relationship between the water vapor equivalent current and the total In the process e), the water vapor concentration corresponding to the value of the water vapor equivalent current in the Ip2-H2O data is determined as the concentration of water vapor contained in the measured gas; in the process f), after the contribution part of the total reduction current brought by the reduction of water vapor is determined based on the water vapor equivalent current and the H2O characteristic data, the carbon dioxide concentration corresponding to the difference obtained by subtracting the contribution part from the total reduction current in the Ip1-CO2 data is determined as the concentration of carbon dioxide contained in the measured gas.

[0025] The twelfth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in any one of the ninth to eleventh schemes, and is characterized in that the second measuring electrode is set to a metal ceramic electrode containing a Pt-Au alloy as a metal component, and the Au concentration in the Pt-Au alloy is set to be greater than 1wt% and less than 50wt%.

[0026] A thirteenth aspect of the present invention is the concentration measurement method using a gas sensor according to the twelfth aspect, wherein the adjustment electrode and the first measurement electrode are formed as metal ceramic electrodes containing Pt but not Au.

[0027] The fourteenth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in any one of the ninth to eleventh schemes, and is characterized in that it also includes the following steps: g) determining the concentration of oxygen contained in the measured gas based on the magnitude of the current flowing between the adjustment electrode and the pump electrode outside the cavity when oxygen is sucked out from the first cavity using the adjustment pump unit.

[0028] According to the first to fourteenth aspects of the present invention, it is possible to realize a multi-gas sensor having excellent long-term reliability compared with the related art, in which cracking and blackening of the sensor element are suppressed and evaporation of Au from the electrode is also suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a diagram schematically showing an example of the configuration of the gas sensor 100 .

[0030] Figure 2 It is a block diagram showing functional components implemented in the controller 110 .

[0031] Figure 3 Schematic diagram showing how gases enter and exit the three cavities in the sensor element 101 of the gas sensor 100 .

[0032] Figure 4 It is a graph showing the relationship between the target value of the electromotive force V0 in the first cavity sensor unit 80 and the oxygen pump current Ip0 flowing through the adjustment pump unit 21 when three different model gases are flowing.

[0033] Figure 5 : is a graph showing the dependency of the oxygen pump current Ip1 on the concentration of the monitoring target gas component.

[0034] Figure 6 2 is a diagram showing the dependency of the oxygen pump current Ip2 on the concentration of the monitoring target gas component.

[0035] Figure 7 It is a diagram illustrating H2O characteristic data.

[0036] Figure 8 This is a diagram schematically showing an example of the configuration of a gas sensor 200 according to a modified example. DETAILED DESCRIPTION

[0037] <Gas sensor configuration>

[0038] Figure 1 1 is a diagram schematically showing an example of the configuration of the gas sensor 100 involved in the present embodiment. The gas sensor 100 is a multi-gas sensor that monitors a plurality of gas components and measures their concentrations through a sensor element 101. In the present embodiment, at least water vapor (H2O) and carbon dioxide (CO2) are the main monitoring target gas components in the gas sensor 100. The gas sensor 100 is used in a manner such as being installed in an exhaust path of an internal combustion engine such as an engine of an automobile and using the exhaust gas flowing through the exhaust path as the measured gas. Figure 1 A vertical cross-sectional view along the length direction of the sensor element 101 is included.

[0039] The sensor element 101 comprises: a long plate-shaped structure (base part) 14 formed of a solid electrolyte having oxygen ion conductivity; a first diffusion rate control part 11 formed at one end (the left end in the drawing) of the structure 14 and also serving as a gas inlet 10 for introducing the measured gas; and a buffer space 12, a first cavity 20, a second cavity 40 and a third cavity 61 formed in the structure 14 and connected in sequence from the gas inlet 10 (first diffusion rate control part 11). The buffer space 12 is connected to the gas inlet 10 (first diffusion rate control part 11). The first cavity 20 is connected to the buffer space 12 via the second diffusion rate control part 13. The second cavity 40 is connected to the first cavity 20 via the third diffusion rate control part 30. The third cavity 61 is connected to the second cavity 40 via the fourth diffusion rate control part 60.

[0040] The structure 14 is formed by laminating a plurality of substrates formed of, for example, ceramics. Specifically, the structure 14 has a structure in which six layers are laminated in this order from the bottom, namely, a first substrate 1, a second substrate 2, a third substrate 3, a first solid electrolyte layer 4, a separator 5, and a second solid electrolyte layer 6. Each layer is formed of a solid electrolyte having oxygen ion conductivity, such as zirconium oxide (ZrO2).

[0041] The first diffusion rate control part 11, the buffer space 12, the second diffusion rate control part 13, the first cavity 20, the third diffusion rate control part 30, the second cavity 40, the fourth diffusion rate control part 60 and the third cavity 61, which also serve as the gas introduction port 10, are formed in this order on one end side of the structure 14 and are formed between the lower surface 6b of the second solid electrolyte layer 6 and the upper surface 4a of the first solid electrolyte layer 4. The portion from the gas introduction port 10 to the third cavity 61 is also referred to as a gas flow portion.

[0042] The buffer space 12, the first cavity 20, the second cavity 40 and the third cavity 61 are formed so as to penetrate the isolation layer 5 in the thickness direction. In the above-mentioned cavities, the lower surface 6b of the second solid electrolyte layer 6 is exposed in the upper part in the drawings, and the upper surface 4a of the first solid electrolyte layer 4 is exposed in the lower part in the drawings. The side of the above-mentioned cavities is divided by the isolation layer 5 or any diffusion rate control part. The length (dimension in the element length direction) of the first cavity 20, the second cavity 40 and the third cavity 61 is, for example, 0.3 mm to 1.0 mm, the width (dimension in the element width direction) is, for example, 0.5 mm to 30 mm, and the height (dimension in the element thickness direction) is, for example, 50 μm to 200 μm. However, the dimensions of each cavity do not need to be the same and may be different.

[0043] The gas inlet 10 may also be formed to penetrate the spacer layer 5 in the thickness direction, separately from the first diffusion rate control portion 11. In this case, the first diffusion rate control portion 11 is formed adjacent to the gas inlet 10 at a position inside.

[0044] The first diffusion rate control unit 11, the second diffusion rate control unit 13, the third diffusion rate control unit 30, and the fourth diffusion rate control unit 60 are each provided with two horizontally long slits. That is, the upper and lower parts in the drawing have openings extending long in a direction perpendicular to the drawing. The length of the slit (dimension in the element length direction) is, for example, 0.2 mm to 1.0 mm, the width of the opening (dimension in the element width direction) is, for example, 0.5 mm to 30 mm, and the height of the opening (dimension in the element thickness direction) is, for example, 5 μm to 30 μm.

[0045] In addition, a reference gas introduction space 43 is provided at the other end (right end in the drawing) of the sensor element 101 on the opposite side of the end provided with the gas introduction port 10. 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 isolation layer 5. In addition, the side portion of the reference gas introduction space 43 is partitioned by the side surface of the first solid electrolyte layer 4. For example, oxygen (O2) and the atmosphere are introduced into the reference gas introduction space 43 as the reference gas.

[0046] The gas inlet port 10 (first diffusion rate control unit 11 ) is a portion open to the external space, and the gas to be measured is introduced from the external space into the sensor element 101 through the gas inlet port 10 .

[0047] The first diffusion rate control unit 11 is a portion that provides a predetermined diffusion resistance to the introduced gas to be measured.

[0048] The buffer space 12 is provided to eliminate the concentration fluctuation of the gas to be measured caused by the pressure fluctuation of the gas to be measured in the external space. Examples of the pressure fluctuation of the gas to be measured include the pulsation of the exhaust pressure of automobile exhaust gas.

[0049] The second diffusion rate control unit 13 is a portion that provides a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first cavity 20 .

[0050] The first cavity 20 is provided as a space for sucking out oxygen from the gas to be measured introduced through the second diffusion rate control unit 13. The suction of oxygen is achieved by adjusting the operation of the pump unit 21.

[0051] The adjustment pump cell 21 is an electrochemical pump cell composed of an inner pump electrode (adjustment electrode) 22 , an outer pump electrode (outer-cavity pump electrode) 23 , and a solid electrolyte present in a portion of the structure 14 sandwiched between these two electrodes.

[0052] In the adjustment pump unit 21, a voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 by using a variable power supply 24 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip0. As a result, the oxygen in the first cavity 20 can be sucked out to the external space. It should be noted that in this embodiment, the direction of the oxygen pump current Ip0 when sucking oxygen from the first cavity 20 is set to the positive direction of the oxygen pump current Ip0.

[0053] The inner pump electrode 22 is provided as a top electrode portion 22a and a bottom electrode portion 22b respectively on substantially the entire lower surface 6b of the second solid electrolyte layer 6 and substantially the entire upper surface 4a of the first solid electrolyte layer 4 defining the first cavity 20. The top electrode portion 22a and the bottom electrode portion 22b are connected by a conductive portion not shown.

[0054] The inner pump electrode 22 is provided as a porous cermet electrode having a rectangular shape in a plan view and containing at least one of platinum and rhodium (Rh) as a metal component.

[0055] The outer pump electrode 23 is provided as a porous cermet electrode having platinum or an alloy of platinum and gold (Pt—Au alloy) as a metal component, for example, platinum or a Pt—Au alloy and zirconium oxide and having a rectangular shape in plan view.

[0056] In the sensor element 101, the first cavity sensor cell 80 is formed by the inner pump electrode 22, the reference electrode 42, and the solid electrolyte present in the portion sandwiched by these two electrodes in the structure 14. The first cavity sensor cell 80 is an electrochemical sensor cell for grasping the oxygen partial pressure in the atmosphere in the first cavity 20.

[0057] The reference electrode 42 is an electrode formed between the first solid electrolyte layer 4 and the third substrate 3 and is provided as, for example, a porous cermet electrode containing platinum and zirconium oxide and having a rectangular shape in a plan view.

[0058] A reference gas introduction layer 48 formed 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 into the surface of the reference electrode 42 via the reference gas introduction layer 48. That is, the reference electrode 42 is always in contact with the reference gas.

[0059] In the first cavity sensor unit 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 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the first cavity 20 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, the oxygen concentration (oxygen partial pressure) of the reference gas is substantially constant, so the electromotive force V0 is a value corresponding to the oxygen concentration (oxygen partial pressure) in the first cavity 20.

[0060] The third diffusion rate control unit 30 is a portion that provides a predetermined diffusion resistance to the measurement gas that contains H 2 O and CO 2 and does not substantially contain oxygen and is introduced from the first cavity 20 to the second cavity 40 .

[0061] The second cavity 40 is provided as a space for reducing (decomposing) H2O and CO2 contained in the gas to be measured introduced through the third diffusion rate control unit 30 as the gas component to be monitored to generate hydrogen (H2) and carbon monoxide (CO), so that the gas to be measured does not contain oxygen but also substantially does not contain H2O and CO2. The reduction (decomposition) of H2O and CO2 is achieved by the operation of the first measurement pump unit 50.

[0062] The first measuring pump cell 50 is an electrochemical pump cell composed of a first measuring electrode 51 , an outer pump electrode 23 , and a solid electrolyte present in a portion of the structure 14 sandwiched between these two electrodes.

[0063] In the first measuring pump unit 50, a voltage Vp1 is applied between the first measuring electrode 51 and the outer pump electrode 23 by a variable power supply 52 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip1. Thus, oxygen generated in the second cavity 40 by the reduction of H2O and CO2 can be sucked out to the external space. It should be noted that in this embodiment, the direction of the oxygen pump current Ip1 when oxygen is sucked out from the second cavity 40 is set to the positive direction of the oxygen pump current Ip1.

[0064] The first measuring electrode 51 is provided as a top electrode portion 51a and a bottom electrode portion 51b respectively on substantially the entire lower surface 6b of the second solid electrolyte layer 6 and substantially the entire upper surface 4a of the first solid electrolyte layer 4 defining the second cavity 40. The top electrode portion 51a and the bottom electrode portion 51b are connected by a conductive portion (not shown).

[0065] The first measurement electrode 51 is provided as a porous cermet electrode having a rectangular shape in a plan view and containing Pt as a metal component.

[0066] In the sensor element 101, the first measuring electrode 51, the reference electrode 42, and the solid electrolyte present in the portion sandwiched between the two electrodes in the structure 14 constitute the second cavity sensor cell 81. The second cavity sensor cell 81 is an electrochemical sensor cell for grasping the oxygen partial pressure in the atmosphere in the second cavity 40.

[0067] In the second cavity sensor unit 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 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the second cavity 40 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, the oxygen concentration (oxygen partial pressure) of the reference gas is substantially constant, so the electromotive force V1 is a value corresponding to the oxygen concentration (oxygen partial pressure) in the second cavity 40.

[0068] The fourth diffusion rate control unit 60 is a portion that provides a predetermined diffusion resistance to the measured gas containing H 2 and CO and substantially containing no H 2 O, CO 2 and oxygen, which is introduced from the second cavity 40 into the third cavity 61 .

[0069] The third cavity 61 is provided as a space for selectively oxidizing all H2 contained in the gas to be measured and H2 in CO introduced through the fourth diffusion rate control unit 60 to generate H2O again. The oxidation of H2 to generate H2O is achieved by the operation of the second measurement pump unit 41.

[0070] The second measuring pump cell 41 is an electrochemical pump cell composed of a second measuring electrode 44 , an outer pump electrode 23 , and a solid electrolyte present in a portion of the structure 14 sandwiched between these two electrodes.

[0071] In the second measuring pump unit 41, a voltage Vp2 is applied between the second measuring 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. Thus, oxygen can be sucked from the external space into the third cavity 61. It should be noted that in this embodiment, the direction of the oxygen pump current Ip2 when oxygen is sucked out from the third cavity 61 is set to the positive direction of the oxygen pump current Ip2.

[0072] The second measuring electrode 44 is provided on substantially the entire upper surface 4 a of the first solid electrolyte layer 4 defining the third cavity 61 .

[0073] The second measuring electrode 44 is provided as a porous metal ceramic electrode having a rectangular shape in a plan view and containing a Pt-Au alloy as a metal component, for example, the Pt-Au alloy and zirconium oxide. 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, the selective oxidation property of H2 at the second measuring electrode 44, that is, the property that only H2 is selectively oxidized by oxygen sucked in by the second measuring pump unit 41 and CO is not oxidized when H2 and CO coexist in the third cavity 61, is better exhibited.

[0074] In the sensor element 101, the second measuring electrode 44, the reference electrode 42, and the solid electrolyte present in the portion sandwiched by these two electrodes in the structure 14 constitute the third cavity sensor cell 82. The third cavity sensor cell 82 is an electrochemical sensor cell for grasping the oxygen partial pressure in the atmosphere in the third cavity 61.

[0075] In the third cavity sensor unit 82, an electromotive force (Nernst electromotive force) V2 is generated between the second measuring electrode 44 and the reference electrode 42. The electromotive force V2 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the third cavity 61 and the oxygen concentration (oxygen partial pressure) of the reference gas. The oxygen concentration (oxygen partial pressure) of the reference gas is substantially constant, so the electromotive force V2 is a value corresponding to the oxygen concentration (oxygen partial pressure) in the third cavity 61.

[0076] In addition, the sensor element 101 further includes an electrochemical sensor unit 83 composed of an outer pump electrode 23, a reference electrode 42, and a solid electrolyte present in a portion sandwiched between these two electrodes in the structure 14. The electromotive force Vref generated between the outer pump electrode 23 and the reference electrode 42 in the sensor unit 83 is a value corresponding to the oxygen partial pressure of the measured gas present outside the sensor element 101.

[0077] In addition to the above components, the sensor element 101 includes a heater unit 70 that performs a temperature adjustment function of heating and keeping the sensor element 101 warm in order to improve the oxygen ion conductivity of the solid electrolyte constituting the structure 14 .

[0078] The heater unit 70 mainly includes a heater electrode 71, a heater member 72, a heater lead 72a, a through hole 73, a heater insulating layer 74, and Figure 1 The heater resistance detection lead wire shown in the figure is omitted.

[0079] The heater 72 is provided in a manner of being sandwiched between the second substrate 2 and the third substrate 3, and generates heat by supplying power from the outside through the heater electrode 71, the through hole 73, and the heater lead 72a provided on the lower surface 1b of the first substrate 1. The heater 72 is implanted in the entire area ranging from the buffer space 12 to the third cavity 61, and can heat the sensor element 101 to a predetermined temperature and keep the temperature.

[0080] The heater 72 is set so that when heating, the vicinity of the first cavity 20 (the vicinity of the adjustment electrode 22) becomes the highest temperature, and the temperature becomes lower as it moves away from the first cavity 20 in the element length direction. In this embodiment, the temperature of the range from one end of the sensor element 101 where the gas inlet 10 is located to the third cavity 61 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 heats in such a manner that the element driving temperature reaches a range of 750°C to 950°C.

[0081] A heater insulating layer 74 made of alumina or the like is formed above and below the heater 72 for the purpose of obtaining electrical insulation from the second substrate 2 and the third substrate 3. In addition, the heater portion 70 is provided with a pressure release hole 75. The pressure release hole 75 is a portion provided to penetrate the third substrate 3 and communicate with the reference gas introduction space 43. The purpose of providing the pressure release hole 75 is to mitigate the internal pressure increase accompanying the temperature increase in the heater insulating layer 74.

[0082] The gas sensor 100 further includes a controller 110 that controls the operation of the sensor element 101 and performs processing for determining the concentration of a monitoring target gas component based on the current flowing through the sensor element 101 .

[0083] Figure 2 This is a block diagram showing the functional components implemented in the controller 110. The controller 110 is composed of one or more electronic circuits such as one or more CPUs (central processing units) and a storage device. The electronic circuit is also a software function unit that implements a specified functional component by executing a specified program stored in a storage device such as a CPU. Of course, it can also be composed of an integrated circuit such as an FPGA (Field-Programmable Gate Array) obtained by connecting multiple electronic circuits according to their functions.

[0084] It should be noted that when the gas sensor 100 is installed in the exhaust path of a car engine and the exhaust gas flowing through the exhaust path is used as the measured gas, part or all of the functions of the controller 110 can be implemented by the car's ECU (electronic control unit).

[0085] The controller 110 includes functional components implemented by executing a specified program in the CPU, including: an element action control unit 120, which controls the actions of various parts of the above-mentioned sensor element 101; and a concentration determination unit 130, which determines the concentration of the monitored gas component contained in the measured gas.

[0086] The element action control unit 120 mainly includes: an adjustment pump unit control unit 121, which controls the action of the adjustment pump unit 21; a first measuring pump unit control unit 122a, which controls the action of the first measuring pump unit 50; a second measuring pump unit control unit 122b, which controls the action of the second measuring pump unit 41; and a heater control unit 123, which controls the heating action of the heater 72.

[0087] On the other hand, the concentration determination unit 130 mainly includes a water vapor concentration determination unit 130H and a carbon dioxide concentration determination unit 130C for respectively determining the concentrations of H 2 O and CO 2 , which are main monitoring target gas components in the gas sensor 100 .

[0088] The water vapor concentration determination unit 130H determines the concentration of H 2 O contained in the gas to be measured based on the value of the oxygen pump current Ip2 flowing through the second measuring pump cell 41 acquired by the second measuring pump cell control unit 122 b.

[0089] The carbon dioxide concentration determination unit 130C determines the concentration of CO2 contained in the measured gas based on the concentration of H2O determined in the water vapor concentration determination unit 130H (the value of the oxygen pump current Ip2 serving as the basis for its determination) and the value of the oxygen pump current Ip1 flowing through the first measuring pump unit 50 obtained by the first measuring pump unit control unit 122a.

[0090] The concentration determination unit 130 further includes an oxygen concentration determination unit 130A that determines the concentration of oxygen contained in the measured gas. The oxygen concentration determination unit 130A determines the concentration of oxygen contained in the measured gas based on the value of the oxygen pump current Ip0 flowing through the adjustment pump unit 21 obtained by the adjustment pump unit control unit 121. That is, in the gas sensor 100 involved in this embodiment, in addition to the main monitoring target gas components, that is, H2O and CO2, oxygen is also monitored as an additional monitoring target gas component.

[0091] <Multi-gas monitoring and concentration determination>

[0092] Next, the monitoring of multiple gas types (multi-gas monitoring) and the method of determining the concentration of the monitored gas implemented in the gas sensor 100 having the above-mentioned configuration are described. Hereinafter, the gas to be measured is exhaust gas containing oxygen, H2O, and CO2.

[0093] Figure 3 Schematic diagram showing how gases enter and exit three cavities (internal cavities) in the sensor element 101 of the gas sensor 100 .

[0094] First, in the sensor element 101 of the gas sensor 100 according to the present embodiment, as described above, the gas to be measured is introduced into the first cavity 20 through the gas inlet 10 (first diffusion rate control unit 11), the buffer space 12, and the second diffusion rate control unit 13. In the first cavity 20, the pump unit 21 is adjusted to operate, thereby sucking oxygen from the introduced gas to be measured.

[0095] The above-mentioned oxygen suction is performed as follows, that is, the adjustment pump unit control unit 121 of the controller 110 sets the target value (control voltage) of the electromotive force V0 in the first cavity sensor unit 80 to a value within the range of 400mV to 700mV (preferably 400mV), and based on the difference between the actual value of the electromotive force V0 and the target value, the voltage Vp0 applied by the variable power supply 24 to the adjustment pump unit 21 is feedback-controlled so that the electromotive force V0 is maintained at the target value. For example, when the measured gas containing a large amount of oxygen reaches the first cavity 20, the value of the electromotive force V0 deviates greatly from the target value, and therefore, the adjustment pump unit control unit 121 controls the pump voltage Vp0 applied by the variable power supply 24 to the adjustment pump unit 21 so as to reduce the deviation.

[0096] By adjusting the pump unit 21 to suck oxygen from the first cavity 20 in the above manner, the oxygen partial pressure in the first cavity 20 is maintained at a sufficiently low value within a range where H2O and CO2 contained in the measured gas are not reduced. For example, in the case of V0 = 400 mV, it is 10 －8 Atm or so.

[0097] Figure 4 This is a diagram for explaining the reason why oxygen absorption is performed within a range where H2O and CO2 reduction does not occur by setting the target value of the electromotive force V0 to a value within a range of 400 mV to 700 mV. Specifically, Figure 4 This is a graph showing the relationship between the target value (control voltage) of the electromotive force V0 in the first cavity sensor unit 80 and the oxygen pump current Ip0 flowing through the adjustment pump unit 21 when three different model gases are circulated. Specifically, the three model gases are: a first gas containing 10% oxygen, a second gas containing 10% oxygen and CO2, and a third gas containing 10% oxygen and H2O. The remainder of any gas is nitrogen (N2). It should be noted that the element driving temperature is set to 800°C or above, and the temperature of the model gas is set to 150°C.

[0098] Depend on Figure 4It was confirmed that in the case of the first gas, the oxygen pump current Ip0 was substantially constant within the range of the control voltage being 0.4 V or more, whereas in the case of the second gas and the third gas, within the range of the control voltage being 0.7 V or less, the oxygen pump current Ip0 showed substantially the same curve as that of the first gas, but when the control voltage exceeded 0.7 V, the oxygen pump current Ip0 increased again. This increase was caused by the superposition of the reduction current of H2O or CO2 that was generated by the reduction (decomposition) of H2O or CO2 contained in the measured gas to generate oxygen and flow.

[0099] Based on this, in this embodiment, the target value of electromotive force V0 is set to a value within a range of 400 mV to 700 mV. It should be noted that from the viewpoint of ensuring the durability of the electrode, it is ideal to make electromotive force V0 as low as possible, so the target value of electromotive force V0 is preferably set to 400 mV.

[0100] As described above, in the gas sensor 100 according to the present embodiment, unlike the gas sensor of the prior art, in the first cavity 20 which becomes the highest temperature in the sensor element 101 during operation, only oxygen is sucked out within the range where H2O and CO2 are not reduced, and H2O and CO2 are not reduced. The target value of the electromotive force V0 in the sensor unit 80 for the first cavity set for this sucking out is 400mV to 700mV, which is sufficiently smaller than the target value of 1000mV to 1500mV set when H2O and CO2 are reduced. Thus, the increase of the pump voltage Vp0 is suppressed compared with the voltage applied to the corresponding pump unit of the gas sensor of the prior art accompanied by the reduction of H2O and CO2. As a result, in the gas sensor 100 according to the present embodiment, cracking and blackening caused by applying a high voltage while the inner pump electrode 22 is maintained at a high temperature are well suppressed.

[0101] The gas to be measured, from which only oxygen has been absorbed within the range where H2O and CO2 are not reduced in the first cavity 20, is introduced into the second cavity 40. Then, the H2O and CO2 contained in the gas to be measured are reduced in the second cavity 40. That is, the first measuring pump unit 50 operates to further absorb oxygen from the gas to be measured, from which oxygen has been absorbed in the first cavity 20 and then introduced into the second cavity 40, thereby performing a reduction (decomposition) reaction (2H2O→2H2+O2, 2CO2→2CO+O2) of the H2O and CO2 contained in the gas to be measured, and substantially all of the H2O and CO2 are decomposed into hydrogen (H2), carbon monoxide (CO), and oxygen.

[0102] The reduction (decomposition) of H2O and CO2 and the extraction of generated oxygen are performed as follows: the first measuring pump unit control section 122a of the controller 110 sets the target value (control voltage) of the electromotive force V1 in the second cavity sensor unit 81 to a value within the range of 1000mV to 1500mV (preferably 1000mV), and based on the difference between the actual electromotive force V1 and the target value, the voltage Vp1 applied by the variable power supply 52 to the first measuring pump unit 50 is feedback-controlled so that the electromotive force V1 is maintained at the target value. It should be noted that Figure 4 The graph shown also suggests that it is preferable to set the target value of the electromotive force V1 to a value within the range of 1000 mV to 1500 mV.

[0103] The first measuring pump unit 50 operates in this manner so that the oxygen partial pressure in the second cavity 40 is maintained at a lower value than the oxygen partial pressure in the first cavity 20. For example, in the case of V1=1000 mV, it is 10 －20 Therefore, the measured gas does not substantially contain H2O, CO2 and oxygen.

[0104] The measured gas containing H 2 and CO and substantially containing no H 2 O, CO 2 , and oxygen is introduced into the third cavity 61 .

[0105] Oxygen is sucked into the third cavity 61 by the operation of the second measuring pump unit 41, and only H 2 contained in the introduced measurement gas is selectively oxidized.

[0106] The above-mentioned oxygen inhalation is carried out as follows: the second measuring pump unit control unit 122b of the controller 110 sets the target value (control voltage) of the electromotive force V2 in the third cavity sensor unit 82 to a value in the range of 250mV to 450mV (preferably 350mV), and based on the difference between the actual value of the electromotive force V2 and the target value, the voltage Vp2 applied by the variable power supply 46 to the second measuring pump unit 41 is feedback controlled to keep the electromotive force V2 at the above-mentioned target value.

[0107] By operating the second measuring pump unit 41 in the above-mentioned manner, the oxidation (combustion) reaction of 2H2+O2→2H2O is promoted in the third cavity 61, and H2O is regenerated in an amount correlated with the amount of H2O introduced from the gas inlet port 10. It should be noted that in this embodiment, the amount of H2O is correlated, which means that the amount of H2O introduced from the gas inlet port 10 and the amount of H2O regenerated by oxidation of the H2 generated by their decomposition are the same, or are within a certain error range allowed in terms of measurement accuracy.

[0108] By setting the target value of the electromotive force V2 to a value within the range of 250 mV to 450 mV, the oxygen partial pressure in the third cavity 61 is maintained within a range where almost all H2 is oxidized but CO is not oxidized. For example, when V2 = 350 mV, the oxygen partial pressure in the third cavity 61 is 10 －7 Atm or so.

[0109] Furthermore, as described above, providing the second measuring electrode 44 as a cermet electrode containing, as a metal component, a Pt—Au alloy having an Au concentration of 1 wt % or more and 50 wt % or less also contributes to the improvement of the selective oxidation property of H 2 .

[0110] It should be noted that in the conventional gas sensor, a metal ceramic electrode containing a Pt-Au alloy is provided in the second cavity 40, and oxygen intake for selective oxidation of H2 is performed by a pump unit including the electrode. In contrast, in the case of the present application, a first measuring electrode 51 containing no Au in the metal component is provided in the second cavity 40, and a second measuring electrode 44 containing a Pt-Au alloy as a metal component and responsible for selective oxidation of H2 is provided facing the third cavity 61 whose temperature when the gas sensor 100 is in operation is lower than that of the second cavity 40. As a result, the gas sensor 100 involved in the present embodiment suppresses evaporation of Au from the electrode compared to the conventional gas sensor.

[0111] In addition to this, the following countermeasures may be taken: the temperature rise of the second measuring electrode 44 may be further suppressed by devising the shape (width, thickness), arrangement (density), etc. of the heater 72 .

[0112] In the gas sensor 100 involved in the present embodiment operating in the above manner, the concentrations of H2O and CO2 in the measured gas are determined based on the oxygen pump current Ip1 flowing through the first measuring pump unit 50 during oxygen absorption including reduction of H2O and CO2, and the oxygen pump current Ip2 flowing through the second measuring pump unit 41 during oxygen absorption for H2 oxidation.

[0113] Figure 5 and Figure 6 These are graphs showing the dependence of the oxygen pump current Ip1 and the oxygen pump current Ip2 on the concentration of the monitored gas component when only one of H2O and CO2, which are the main monitored gas components, is contained in the measured gas and when equal concentrations of H2O and CO2 are contained in the measured gas.

[0114] Figure 5 and Figure 6In the figure, the curve in which H2O is included as the monitoring target gas component alone is represented by a circle symbol, the curve in which CO2 is included as the monitoring target gas component alone is represented by a triangle symbol, and the curve in which H2O and CO2 of equal concentration are included as the monitoring target gas components (recorded as "H2O+CO2" in the figure) is represented by a quadrilateral symbol. It should be noted that these curves are obtained by operating the gas sensor 100 in an atmosphere of a model gas in which the concentration of the monitoring target gas component is known and the remainder is oxygen and nitrogen. The element driving temperature is set to 800°C or more, and the temperature of the model gas is set to 200°C.

[0115] Depend on Figure 5 It can be seen that in the case where only H2O is included as the monitoring target gas component and in the case where only CO2 is included as the monitoring target gas component, the curve increases monotonically and is approximately linear.

[0116] In addition, the value of the oxygen pump current Ip1 when H2O and CO2 are contained as monitoring target gas components at equal concentrations is the sum of the oxygen pump currents Ip1 when H2O and CO2 are contained separately. In addition, although the illustration is omitted, it is confirmed that the value of the oxygen pump current Ip1 when the ratio of H2O and CO2 is different is also the sum of the oxygen pump currents Ip1 when H2O and CO2 are contained separately at concentrations corresponding to the respective ratios.

[0117] On the other hand, Figure 6 As shown in FIG. 1 , the curve of the oxygen pump current Ip2 in the case where only H2O is included as the monitoring target gas component is monotonically decreasing (the absolute value is monotonically increasing) and is approximately linear. It should be noted that the oxygen pump current Ip2 is a negative value because: in the second measuring pump unit 41, as described above, the direction of the oxygen suction is the positive direction of the oxygen pump current, and on the other hand, in order to re-oxidize the H2 generated by the reduction in the second cavity 40, the oxygen pump current Ip2 flows in the direction of the suction oxygen.

[0118] In contrast, the value of the oxygen pump current Ip2 when only CO 2 is included as the monitoring target gas component remains substantially zero. This indicates that CO generated by reduction in the second cavity 40 is not reoxidized by the operation of the second measuring pump unit 41 .

[0119] In addition, the curve of the oxygen pump current Ip2 in the case where H2O and CO2 are contained as the monitoring target gas components at equal concentrations is roughly consistent with the curve of the oxygen pump current Ip2 in the case where H2O is contained alone. This is consistent with the fact that the oxygen pump current Ip2 in the case where only CO2 is contained as the monitoring target gas component is substantially zero. It should be noted that, although the illustration is omitted, it is confirmed that the value of the oxygen pump current Ip2 when the ratio of H2O and CO2 is different is also roughly consistent with the curve of the oxygen pump current Ip2 when H2O and CO2 are contained alone. This means that the oxygen pump current Ip2 actually depends only on the concentration of H2O, so if the oxygen pump current Ip2 is known, the concentration of H2O can be determined.

[0120] In this embodiment, the concentrations of H2O and CO2 in the measured gas are measured by using the properties of the oxygen pump current Ip1 and the oxygen pump current Ip2 as described above. Hereinafter, the oxygen pump current Ip1 and the oxygen pump current Ip2 actually measured by the gas sensor 100 are referred to as the full reduction current Ip1 and the water vapor equivalent current Ip2, respectively.

[0121] Specifically, before using the gas sensor 100, a model gas with a known concentration is used to obtain Figure 5 The characteristic data (hereinafter referred to as Ip1-H2O data and Ip1-CO2 data, respectively) showing the relationship between the oxygen pump current Ip1 and the concentration of each gas in each case where the measured gas contains only one of H2O and CO2 but not the other, and Figure 6 Characteristic data (hereinafter referred to as Ip2-H2O data) showing the relationship between the oxygen pump current Ip2 and the concentration of H2O when the measured gas contains H2O but does not contain CO2 is stored in the controller 110. It should be noted that the Ip1-H2O data and the Ip1-CO2 data are values ​​showing the contribution of H2O and the contribution of CO2 in the full reduction current Ip1, respectively.

[0122] It should be noted that the oxygen pump current Ip1 is a value corresponding to the diffusion resistance given to the measured gas from the gas inlet port 10 to the second cavity 40 of the sensor element 101, and the oxygen pump current Ip2 is a value corresponding to the diffusion resistance given to the measured gas from the gas inlet port 10 to the third cavity 61 of the sensor element 101. Therefore, strictly speaking, the Ip1-H2O data, the Ip1-CO2 data, and the Ip2-H2O data are different in the individual sensor elements 101 constituting each gas sensor 100. Therefore, these characteristic data are preferably determined for each gas sensor 100. Among them, with respect to the gas sensors 100 manufactured under the same conditions and the same batch, the following scheme can be adopted: when it is confirmed that the error is within the allowable range, the characteristic data obtained for a certain gas sensor 100 is applied to other gas sensors 100 of the same batch.

[0123] Furthermore, when the gas sensor 100 actually performs measurement, the measured gas is introduced into the sensor element 101 heated to the element driving temperature, and the adjustment pump unit 21, the first measurement pump unit 50, and the second measurement pump unit 41 operate in the above-mentioned manner. Then, the water vapor concentration determination unit 130H obtains the water vapor equivalent current Ip2 from the second measurement pump unit control unit 122b, and determines the H2O concentration corresponding to the obtained value based on the Ip2-H2O data.

[0124] After the H2O concentration is determined, the carbon dioxide concentration determination unit 130C then obtains the value of the total reduction current Ip1 from the first measuring pump unit control unit 122a, and determines the contribution of the determined concentration of H2O in the total reduction current Ip1, that is, the amount of current obtained by the reduction of H2O in the total reduction current Ip1, based on the Ip1-H2O data. The contribution of CO2 in the total reduction current Ip1 is determined by subtracting the obtained value from the value of the total reduction current Ip1. Finally, the CO2 concentration corresponding to the contribution of CO2 is determined based on the Ip1-CO2 data.

[0125] In the gas sensor 100 according to the present embodiment, the H 2 O concentration and the CO 2 concentration in the measured gas are measured by the above operation.

[0126] Alternatively, the relationship between the water vapor equivalent current Ip2 and the oxygen pump current Ip1 equivalent to the H2O contribution portion of the full reduction current Ip1 can be determined in advance, and characteristic data representing the relationship (hereinafter referred to as H2O characteristic data) can be stored in the controller 110. The carbon dioxide concentration determination unit 130C uses the H2O characteristic data and directly determines the H2O contribution portion of the full reduction current Ip1 based on the water vapor equivalent current Ip2.

[0127] Figure 7This is a diagram showing H2O characteristic data. Figure 7 In the figure, the absolute value of the water vapor equivalent current Ip2 is set as the x-axis, and the value of the oxygen pump current Ip1 corresponding to the contribution of H2O in the total reduction current Ip1 is set as the y-axis. Figure 7 As shown in FIG. 1 , there is a linear relationship between the water vapor equivalent current Ip2 and the H 2 O contribution in the full reduction current Ip1 , and therefore, it is sufficient to determine a relational expression representing the linear relationship as the H 2 O characteristic data.

[0128] Alternatively, the value of the y pitch in the relational expression should be zero in principle, and in the case of the gas sensor 100 operating cleanly, it is actually a value so small that it can be regarded as zero. Therefore, only the slope of the expression representing the above linear relationship may be stored in the controller 110 as H2O characteristic data in advance, and the carbon dioxide concentration determination unit 130C uses the product of the slope value and the water vapor equivalent current Ip2 as the H2O contribution portion in the full reduction current Ip1.

[0129] The slope in the H 2 O characteristic data corresponds to the ratio of the diffusion resistance given to the measured gas from the gas inlet 10 to the third cavity 61 to the diffusion resistance given to the measured gas from the gas inlet 10 to the second cavity 40 .

[0130] In addition, when the H 2 O concentration and the CO 2 concentration are determined, the oxygen concentration is also determined simultaneously using the oxygen pump current Ip0 flowing through the adjustment pump cell 21 .

[0131] In the gas sensor 100 involved in the present embodiment, as described above, the pump unit 21 is adjusted to operate, thereby, in the first cavity 20, oxygen is sucked out from the measured gas introduced from the gas inlet port 10. The oxygen suction is performed within a range where H2O and CO2 are not reduced, but the oxygen pump current Ip0 (hereinafter also referred to as the oxygen detection current Ip0) flowing at this time is approximately proportional to the concentration of oxygen contained in the measured gas introduced from the gas inlet port 10. That is, there is a linear relationship between the oxygen detection current Ip0 and the oxygen concentration in the measured gas. The data representing this linear relationship (Ip0-O2 data) is predetermined using a model gas with a known oxygen concentration and stored in the controller 110.

[0132] When the gas sensor 100 actually performs measurement, the oxygen concentration determination unit 130A obtains the value of the oxygen detection current Ip0 from the adjustment pump unit control unit 121. Then, the value of the oxygen concentration corresponding to the obtained oxygen detection current Ip0 is determined by referring to the Ip0-O2 data. In this way, the oxygen concentration in the measured gas can be determined.

[0133] As described above, the gas sensor according to the present embodiment can measure the concentrations of both H 2 O and CO 2 when the measured gas contains both H 2 O and CO 2 , similarly to the conventional gas sensor. In addition, the oxygen concentration can be obtained with high accuracy.

[0134] Furthermore, in the case of the gas sensor involved in the present embodiment, unlike the gas sensor of the prior art, reduction of H2O and CO2 is not performed in the first cavity which reaches the highest temperature during operation. Therefore, the voltage applied to the adjustment pump unit for absorbing oxygen from the first cavity is suppressed to a lower level compared with the gas sensor of the prior art. Therefore, cracking and blackening of the sensor element are well suppressed.

[0135] In addition, the only electrode using Pt-Au alloy as a metal component provided in the cavity is the second measuring electrode disposed in the third cavity. No electrodes using Pt-Au alloy are disposed in the first cavity and the second cavity which are at a higher temperature than the third cavity. Therefore, the evaporation of Au from the electrode is suppressed compared with the prior art.

[0136] That is, according to the present embodiment, it is possible to realize a multi-gas sensor having excellent long-term reliability compared with the related art.

[0137] <Other Modifications>

[0138] In the gas sensor 100 according to the above-mentioned embodiment, a gas flow section including a first cavity 20, a second cavity 40, and a third cavity 61 connected by a diffusion rate control section is provided in the sensor element 101. In addition, for the gas to be measured which is sequentially introduced into each cavity under a predetermined diffusion resistance in the gas flow section, oxygen is sucked out in the first cavity 20 by the adjustment pump unit 21 within a range where H2O and CO2 are not reduced, H2O and CO2 are reduced by the first measurement pump unit 50 in the second cavity 40, and H2 generated by the reduction of H2O is selectively oxidized by the second measurement pump unit 41 in the third cavity 61. As a result, the concentrations of H2O, CO2, and oxygen in the gas to be measured are measured based on the magnitude of the current flowing through each pump unit.

[0139] The above-mentioned measurement method in the gas sensor 100 is realized as follows: the inflow of the measured gas from the outside of the element to the first cavity 20 is suppressed by the first diffusion rate control unit 11 and the second diffusion rate control unit 13, the inflow of the measured gas with residual oxygen from the first cavity 20 to the second cavity 40 is suppressed by the third diffusion rate control unit 30, and the inflow of the measured gas with residual H2O and CO2 from the second cavity 40 to the third cavity 61 is suppressed by the fourth diffusion rate control unit 60. That is, it can be said that by well controlling the measured gas reaching the inner pump electrode 22 of the adjustment pump cell 21, the first measurement electrode 51 of the first measurement pump cell 50, and the second measurement electrode 44 of the second measurement pump cell 41 by each diffusion rate control unit, the non-operation target gas in each pump cell does not reach each electrode, and multi-gas monitoring can be performed in the gas sensor 100.

[0140] From another perspective, this means that, as long as the oxygen suction by the adjustment pump cell 21 within the range where H2O and CO2 reduction does not occur is performed for the gas to be measured reaching each electrode of the inner pump electrode 22, the first measuring electrode 51, and the second measuring electrode 44, the reduction of H2O and CO2 by the first measuring pump cell 50, and the selective oxidation of H2 generated by the reduction of H2O by the second measuring pump cell 41 are performed well in view of ensuring the measurement accuracy, a configuration different from the gas flow section of the sensor element 101 can be adopted. For example, even if the configuration does not include three cavities connected by the diffusion rate control section, multi-gas monitoring can be realized.

[0141] Figure 8 1 is a diagram schematically showing an example of the configuration of a gas sensor 200 of a modified example based on the above points. The gas sensor 200 is a multi-gas sensor that monitors multiple types of gas components and measures their concentrations using a sensor element 201. The gas sensor 200 is controlled by a controller 110 in the same manner as the gas sensor 100, and thus, as described later, it is possible to perform multi-gas monitoring with at least water vapor (H2O) and carbon dioxide (CO2) as the main monitoring target gas components. Figure 8 A vertical cross-sectional view along the length direction of the sensor element 201 is included.

[0142] The sensor element 201 is a long plate-shaped structure in which the sensor portion 214 and the heater portion 270 are stacked.

[0143] The sensor part 214 is formed by stacking a plurality of substrate layers formed of ceramics. Specifically, the sensor part 214 has a structure in which four layers consisting of a first substrate 203, a second substrate 204, a third substrate 205 and a fourth substrate 206 are stacked in sequence from the bottom. Among them, at least the second substrate 204 is composed of a solid electrolyte such as zirconium oxide that is oxygen ion conductive. The first substrate 203, the third substrate 205 and the fourth substrate 206 can be composed of a solid electrolyte or an insulating material such as aluminum oxide. In the sensor part 214, the first substrate 203 is adjacent to the heater part 270.

[0144] A gas inlet 210 for introducing the measured gas is provided at one end (left end in the figure) of the sensor portion 214. More specifically, a diffusion rate control portion 211 composed of a porous body having a porosity of about 10% to 50% is implanted at one end of the third substrate 205, and an exposed portion of the diffusion rate control portion 211 at one end serves as the gas inlet 210. The diffusion rate control portion 211 has a length (dimension in the element length direction) of, for example, 0.5 mm to 1.0 mm, a width (dimension in the element width direction) of, for example, 1.5 mm to 3 mm, and a height (dimension in the element thickness direction) of, for example, 10 μm to 20 μm.

[0145] In addition, the sensor portion 214 is provided with a single internal cavity 220 adjacent to the diffusion rate control portion 211. The internal cavity 220 is formed to penetrate the third substrate 205 in the thickness direction. The length (dimension in the element length direction) of the internal cavity 220 is, for example, 6.0 mm to 12.0 mm, the width (dimension in the element width direction) is, for example, 1.5 mm to 2.5 mm, and the height (dimension in the element thickness direction) is, for example, 50 μm to 200 μm.

[0146] That is, in the sensor element 201 , the diffusion rate control section 211 and the internal cavity 220 may constitute a gas flow section communicating from the gas introduction port 210 .

[0147] On the exposed surface 204a of the second substrate 204 relative to the internal cavity 220, the adjustment electrode 230, the first measurement electrode 240, and the second measurement electrode 250 are arranged in order of distance from the gas inlet 210 on the left side of the drawing, separated by a predetermined interval and facing the internal cavity 220. These electrodes are respectively provided as porous metal ceramic electrodes similar to the inner pump electrode (adjustment electrode) 22, the first measurement electrode 51, and the second measurement electrode 44 of the sensor element 101.

[0148] The sensor unit 214 is provided with a reference gas introduction space 260 which is open at the other end of the sensor element 201. The reference gas introduction space 260 is formed to penetrate the first substrate 203 in the thickness direction. For example, oxygen (O2) or air is introduced into the reference gas introduction space 260 as a reference gas.

[0149] In addition, a reference electrode 261 is provided on the exposed surface 204b of the second substrate 204 relative to the reference gas introduction space 260. Preferably, the reference electrode 261 is provided over the entire arrangement range of the adjustment electrode 230, the first measurement electrode 240, and the second measurement electrode 250 provided on the opposite side of the exposed surface 204b, that is, the exposed surface 204a. The reference electrode 261 is provided as a porous metal ceramic electrode that is rectangular in a plan view and contains platinum and zirconium oxide, for example.

[0150] The heater unit 270 is configured to heat the sensor element 201 to a predetermined temperature and further maintain the temperature by supplying power to a heater member 272 (also referred to as a heater 272) from outside the element, similarly to the heater unit 70 of the sensor element 101. The heater unit 270 may have the same configuration as the heater unit 70 of the sensor element 101. Alternatively, the heater member 272 may be embedded in an insulator.

[0151] The heater 272 is provided so that, during heating, the vicinity of the adjustment electrode 230 becomes the highest temperature, and the temperature decreases as the distance from the adjustment electrode 230 increases in the element length direction.

[0152] Furthermore, the sensor element 201 includes an adjustment pump cell C0 , a first measurement pump cell C1 , and a second measurement pump cell C2 .

[0153] The adjustment pump cell C0 is an electrochemical pump cell composed of an adjustment electrode 230, a reference electrode 261, and a second substrate 204 sandwiched by these two electrodes. In the adjustment pump cell C0, a voltage Vp0 is applied between the adjustment electrode 230 and the reference electrode 261 by a variable power supply 231 provided outside the sensor element 201, thereby generating an oxygen pump current (oxygen ion current) Ip0. The operation of the adjustment pump cell C0 is controlled by the adjustment pump cell control unit 121 of the controller 110.

[0154] The first measuring pump cell C1 is an electrochemical pump cell composed of a first measuring electrode 240, a reference electrode 261, and a second substrate 204 sandwiched by the two electrodes. In the first measuring pump cell C1, a voltage Vp1 is applied between the first measuring electrode 240 and the reference electrode 261 by a variable power supply 241 provided outside the sensor element 201, thereby generating an oxygen pump current (oxygen ion current) Ip1. The operation of the first measuring pump cell C1 is controlled by the first measuring pump cell control unit 122a of the controller 110.

[0155] The second measuring pump unit C2 is an electrochemical pump unit composed of a second measuring electrode 250, a reference electrode 261, and a second substrate 204 sandwiched by these two electrodes. In the second measuring pump unit C2, a voltage Vp2 is applied between the second measuring electrode 250 and the reference electrode 261 by a variable power supply 251 provided outside the sensor element 201, thereby generating an oxygen pump current (oxygen ion current) Ip2. The operation of the second measuring pump unit C2 is controlled by the second measuring pump unit control unit 122b of the controller 110.

[0156] As described above, in the sensor element 201, unlike the sensor element 101 of the gas sensor 100, the adjustment electrode 230, the first measuring electrode 240, and the second measuring electrode 250 are provided in one internal cavity 220. However, by setting the diffusion rate control unit 211 and the internal cavity 220 under the above-mentioned conditions, the diffusion resistance given to the measured gas introduced into the internal cavity 220 is optimized, in other words, the flow rate of the measured gas is controlled to the optimal flow rate. In the gas sensor 200 having the sensor element 201, as in the gas sensor 100, multi-gas monitoring with at least water vapor (H2O) and carbon dioxide (CO2) as the main monitoring target gas components can be achieved under the control of the controller 110.

[0157] Specifically, the measured gas introduced from the gas inlet 210 into the internal cavity 220 through the diffusion rate control unit 211 sequentially reaches the adjustment electrode 230, the first measurement electrode 240, and the second measurement electrode 250. In addition, the adjustment pump unit C0 performs an oxygen suction operation to suck out oxygen from the measured gas reaching the adjustment electrode 230 within a range where H2O and CO2 are not reduced. The first measurement pump unit C1 performs an oxygen suction operation in a manner that H2O and CO2 contained in the measured gas reaching the first measurement electrode 240 are reduced. The second measurement pump unit C2 performs an oxygen suction operation in a manner that H2 generated by reducing H2O by the first measurement pump unit C1 reaching the second measurement electrode 250 is selectively oxidized.

[0158] At this time, the measured gas flows at a flow rate that does not cause the measured gas without oxygen to pass through the adjustment electrode 230 and the measured gas with residual H2O and CO2 to pass through the first measuring electrode 240, so the current flowing through each pump unit is equal to the current flowing through each pump unit of the gas sensor 100. Therefore, in the gas sensor 200, as in the gas sensor 100, the concentrations of H2O, CO2, and oxygen in the measured gas can be determined with good accuracy using the water vapor concentration determination unit 130H, the carbon dioxide concentration determination unit 130C, and the oxygen concentration determination unit 130A.

Claims

1. A gas sensor capable of measuring the concentrations of a plurality of monitoring target gas components contained in a measured gas containing at least water vapor and carbon dioxide, The gas sensor is characterized in that it has: A sensor element having a structure composed of an oxygen ion conductive solid electrolyte; and a controller, the controller controlling the action of the gas sensor, The sensor element comprises: A gas inlet port, the gas inlet port is used to introduce the measured gas; an internal cavity, the internal cavity being in communication with the gas inlet via a diffusion rate control unit; an adjustment electrode, a first measurement electrode, and a second measurement electrode, which are arranged in order from near to far from the gas inlet in such a manner that they face the internal cavity, are separated by a predetermined interval, and are arranged; an adjustment pump cell, the adjustment pump cell comprising the adjustment electrode, an out-of-cavity pump electrode provided at a location outside the internal cavity, and the solid electrolyte existing between the adjustment electrode and the out-of-cavity pump electrode; a first measuring pump cell, the first measuring pump cell being composed of the first measuring electrode, the outer-cavity pump electrode, and the solid electrolyte existing between the first measuring electrode and the outer-cavity pump electrode; a second measuring pump cell, the second measuring pump cell being composed of the second measuring electrode, the outer-cavity pump electrode, and the solid electrolyte existing between the second measuring electrode and the outer-cavity pump electrode; and a heater for heating the sensor element, The heater heats the sensor element in such a manner that the temperature is highest near the adjustment electrode in the internal cavity and decreases as the temperature is farther from the adjustment electrode in the longitudinal direction of the sensor element. The adjustment pump unit absorbs oxygen from the gas to be measured that reaches the adjustment electrode from the gas inlet within a range where water vapor and carbon dioxide contained in the gas to be measured are not decomposed. The first measuring pump unit absorbs oxygen from the gas to be measured that reaches the first measuring electrode in such a manner that water vapor and carbon dioxide contained in the gas to be measured after the oxygen is absorbed by the adjustment pump unit are substantially completely reduced. The second measuring pump unit selectively oxidizes hydrogen generated by reduction of water vapor contained in the measured gas reaching the second measuring electrode by sucking oxygen into the internal cavity. The controller has: a water vapor concentration determining mechanism that determines the concentration of water vapor contained in the gas to be measured based on a value of a water vapor equivalent current, which is an oxygen pump current flowing between the second measuring electrode and the cavity outer pump electrode when hydrogen is oxidized by oxygen sucked by the second measuring pump unit; and A carbon dioxide concentration determining mechanism, which determines the concentration of carbon dioxide contained in the measured gas based on the value of the water vapor equivalent current and the value of the total reduction current, wherein the total reduction current is the oxygen pump current flowing between the first measuring electrode and the pump electrode outside the cavity when the first measuring pump unit absorbs oxygen to reduce water vapor and carbon dioxide.

2. The gas sensor according to claim 1, characterized in that The internal cavity is a first cavity, a second cavity, and a third cavity which are connected in sequence from near to far from the gas inlet via different diffusion rate control parts. The adjustment electrode is disposed in the first cavity. The first measuring electrode is disposed in the second cavity. The second measuring electrode is disposed in the third cavity.

3. The gas sensor according to claim 2, characterized in that: The controller stores: Ip1-H2O data predetermined to indicate the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, Ip1-CO2 data which is predetermined and indicates the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains carbon dioxide but does not contain water vapor, and Ip2-H2O data which is predetermined and indicates the relationship between the oxygen pump current flowing through the second measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, The water vapor concentration determination unit determines the water vapor concentration corresponding to the value of the water vapor equivalent current in the Ip2-H2O data as the water vapor concentration contained in the measured gas. The carbon dioxide concentration determination mechanism determines the contribution of water vapor reduction to the total reduction current based on the concentration of water vapor contained in the measured gas determined by the water vapor concentration determination mechanism and the Ip1-H2O data, and then determines the carbon dioxide concentration corresponding to the difference between the total reduction current and the contribution in the Ip1-CO2 data as the concentration of carbon dioxide contained in the measured gas.

4. The gas sensor according to claim 2, characterized in that: The controller stores: Ip1-CO2 data predetermined to indicate the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains carbon dioxide but does not contain water vapor, Ip2-H2O data which is predetermined and indicates the relationship between the oxygen pump current flowing through the second measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, and predetermined H2O characteristic data indicating the relationship between the water vapor equivalent current and the oxygen pump current equivalent to the portion of the total reduction current contributed by the water vapor, The water vapor concentration determination means determines the water vapor concentration corresponding to the value of the water vapor equivalent current in the Ip2-H2O data as the concentration of water vapor contained in the measured gas, The carbon dioxide concentration determination mechanism determines the contribution of water vapor reduction to the total reduction current based on the water vapor equivalent current and the H2O characteristic data, and then determines the carbon dioxide concentration corresponding to the difference between the total reduction current and the contribution in the Ip1-CO2 data as the concentration of carbon dioxide contained in the measured gas.

5. The gas sensor according to any one of claims 2 to 4, characterized in that: The second measuring electrode is a cermet electrode including 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.

6. The gas sensor according to claim 5, characterized in that: The adjustment electrode and the first measuring electrode are metal ceramic electrodes containing Pt but not Au.

7. The gas sensor according to any one of claims 2 to 4, characterized in that: The controller further includes an oxygen concentration determination mechanism. The oxygen concentration determining means determines the concentration of oxygen contained in the measured gas based on the magnitude of a current flowing between the adjustment electrode and the pump electrode outside the cavity when the adjustment pump unit sucks oxygen from the first cavity.

8. A concentration measurement method using a gas sensor, comprising measuring the concentrations of a plurality of monitoring target gas components contained in a measured gas containing at least water vapor and carbon dioxide using the gas sensor, The concentration determination method is characterized in that The gas sensor includes a sensor element having a long plate-shaped structure composed of an oxygen ion conductive solid electrolyte. The sensor element comprises: A gas inlet port, the gas inlet port is used to introduce the measured gas; an internal cavity, the internal cavity being in communication with the gas inlet via a diffusion rate control unit; an adjustment electrode, a first measurement electrode, and a second measurement electrode, which are arranged in order from near to far from the gas inlet in such a manner that they face the internal cavity, are separated by a predetermined interval, and are arranged; an adjustment pump cell, the adjustment pump cell comprising the adjustment electrode, an out-of-cavity pump electrode provided at a location outside the internal cavity, and the solid electrolyte existing between the adjustment electrode and the out-of-cavity pump electrode; a first measuring pump cell, the first measuring pump cell being composed of the first measuring electrode, the outer-cavity pump electrode, and the solid electrolyte existing between the first measuring electrode and the outer-cavity pump electrode; a second measuring pump cell, the second measuring pump cell being composed of the second measuring electrode, the outer-cavity pump electrode, and the solid electrolyte existing between the second measuring electrode and the outer-cavity pump electrode; as well as a heater for heating the sensor element, The concentration determination method comprises the following steps: a) the heater heats the sensor element in such a manner that the temperature is highest near the adjustment electrode in the internal cavity and decreases as the temperature is farther from the adjustment electrode in the longitudinal direction of the sensor element; b) using the adjustment pump unit to absorb oxygen from the gas to be measured that reaches the adjustment electrode from the gas inlet within a range where water vapor and carbon dioxide contained in the gas to be measured are not decomposed; c) using the first measuring pump unit to absorb oxygen from the gas to be measured that reaches the first measuring electrode in such a manner that water vapor and carbon dioxide contained in the gas to be measured after the oxygen is absorbed by the adjustment pump unit are substantially completely reduced; d) selectively oxidizing hydrogen generated by reduction of water vapor contained in the gas to be measured that reaches the second measuring electrode by sucking oxygen into the internal cavity using the second measuring pump unit; e) determining the concentration of water vapor contained in the measured gas based on the value of the water vapor equivalent current, which is the oxygen pump current flowing between the second measuring electrode and the cavity outer pump electrode when hydrogen is oxidized by oxygen absorbed by the second measuring pump unit; f) determining the concentration of carbon dioxide contained in the measured gas based on the value of the water vapor equivalent current and the value of the total reduction current, wherein the total reduction current is the oxygen pump current flowing between the first measuring electrode and the pump electrode outside the cavity when the first measuring pump unit absorbs oxygen to reduce water vapor and carbon dioxide.

9. The concentration measurement method using a gas sensor according to claim 8, characterized in that: The internal cavity is a first cavity, a second cavity, and a third cavity which are connected in sequence from near to far from the gas inlet via different diffusion rate control parts. The adjustment electrode is disposed in the first cavity. The first measuring electrode is disposed in the second cavity. The second measuring electrode is disposed in the third cavity.

10. The concentration measurement method using a gas sensor according to claim 9, characterized in that: It also includes the following steps: g) Before the steps a) to f), predetermine: Ip1-H2O data indicating the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, Ip1-CO2 data indicating the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains carbon dioxide but does not contain water vapor, and Ip2-H2O data indicating the relationship between the oxygen pump current flowing through the second measuring pump unit and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, In the step e), the concentration of water vapor corresponding to the value of the water vapor equivalent current in the Ip2-H2O data is determined as the concentration of water vapor contained in the measured gas. In the process f), based on the concentration of water vapor contained in the measured gas determined in the process e) and the Ip1-H2O data, the contribution of water vapor reduction in the total reduction current is determined, and then the carbon dioxide concentration corresponding to the difference between the total reduction current and the contribution in the Ip1-CO2 data is determined as the concentration of carbon dioxide contained in the measured gas.

11. The concentration measurement method using a gas sensor according to claim 9, characterized in that: It also includes the following steps: g) Before the steps a) to f), predetermine: Ip1-CO2 data indicating the relationship between the oxygen pump current flowing through the first measuring pump unit and the concentration of water vapor when the measured gas contains carbon dioxide but does not contain water vapor, Ip2-H2O data indicating the relationship between the oxygen pump current flowing through the second measuring pump cell and the concentration of water vapor when the measured gas contains water vapor but does not contain carbon dioxide, and H2O characteristic data indicating the relationship between the water vapor equivalent current and the oxygen pump current equivalent to the portion of the total reduction current contributed by the water vapor, In the step e), the water vapor concentration corresponding to the value of the water vapor equivalent current in the Ip2-H2O data is determined as the concentration of water vapor contained in the measured gas. In the process f), after determining the contribution of water vapor reduction to the total reduction current based on the water vapor equivalent current and the H2O characteristic data, the carbon dioxide concentration corresponding to the difference between the total reduction current and the contribution in the Ip1-CO2 data is determined as the concentration of carbon dioxide contained in the measured gas.

12. The concentration measurement method using a gas sensor according to any one of claims 9 to 11, characterized in that: The second measuring electrode is a cermet electrode containing a Pt—Au alloy as a metal component, and the Au concentration in the Pt—Au alloy is set to be 1 wt % or more and 50 wt % or less.

13. The concentration measurement method using a gas sensor according to claim 12, characterized in that: The adjustment electrode and the first measuring electrode are metal ceramic electrodes containing Pt but not Au.

14. The concentration measurement method using a gas sensor according to any one of claims 9 to 11, characterized in that: It also includes the following steps: g) determining the concentration of oxygen contained in the measured gas based on the magnitude of a current flowing between the adjustment electrode and the pump electrode outside the cavity when the adjustment pump unit sucks oxygen from the first cavity.

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