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. A first 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 a second adjustment 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 first measurement pump unit sucks oxygen into the third cavity to selectively oxidize H2 in the vicinity of the first measurement electrode, the second measurement pump unit sucks oxygen into the third cavity to oxidize H2 and CO in the vicinity of the second measurement electrode, the concentration of H2O is determined on the basis of the value of the suction current of the former, and the concentration of CO2 is determined on the basis of the values of the suction currents of both.

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 would seem 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 changes 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 has been 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, suppresses cracking and blackening of sensor elements, and is less likely to experience sensitivity changes even after long-term use, which has excellent long-term reliability 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, the sensor element comprising: 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; a first adjustment electrode, a second adjustment electrode, and a group of a first measuring electrode and a second measuring electrode arranged at positions equivalent to each other with respect to the flow of the measured gas flowing into the internal cavity, which are separated by a predetermined interval in a manner facing the internal cavity and are spaced at a distance from the gas inlet port. The first pump unit is arranged in the order from near to far; the first adjustment pump unit is composed of the first adjustment electrode, the cavity pump electrode arranged at a position outside the internal cavity, and the solid electrolyte existing between the first adjustment electrode and the cavity pump electrode; the second adjustment pump unit is composed of the second adjustment electrode, the cavity pump electrode, and the solid electrolyte existing between the second adjustment electrode and the cavity pump electrode; 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; the second measurement pump unit is composed of the second measurement electrode, the cavity pump electrode, and the solid electrolyte existing between the second measurement electrode and the cavity pump electrode;and a heater for heating the sensor element, wherein the first measuring electrode is a metal ceramic electrode including a Pt-Au alloy as a metal component, the heater heats the sensor element in such a manner that the temperature is highest near the first adjustment electrode in the internal cavity and the temperature decreases as the temperature increases away from the first adjustment electrode in the longitudinal direction of the sensor element, the first adjustment pump unit absorbs oxygen from the measured gas that reaches the first adjustment electrode from the gas inlet within a range where water vapor and carbon dioxide contained in the measured gas are not decomposed, the second adjustment pump unit absorbs oxygen from the measured gas that reaches the second adjustment electrode in such a manner that water vapor and carbon dioxide contained in the measured gas after the oxygen is absorbed by the first adjustment pump unit are substantially completely reduced, and the first measurement pump unit selectively oxidizes hydrogen generated by the reduction of water vapor contained in the measured gas that reaches the first measurement electrode near the first measurement electrode by sucking oxygen into the internal cavity , the second measuring pump unit absorbs oxygen into the internal cavity to oxidize hydrogen and carbon monoxide generated by reduction of water vapor and carbon dioxide contained in the measured gas reaching the second measuring electrode near the second measuring electrode, and the controller comprises: a water vapor concentration determining mechanism that determines the concentration of water vapor contained in the measured gas based on the value of a selective oxidation current, which is an 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 selectively oxidize hydrogen near the first measuring electrode; and a carbon dioxide concentration determining mechanism that determines the concentration of carbon dioxide contained in the measured gas based on the value of the selective oxidation current and the value of a double oxidation current, which is an oxygen pump current flowing between the second measuring electrode and the pump electrode outside the cavity when the second measuring pump unit absorbs oxygen to oxidize hydrogen and carbon monoxide near the second measuring electrode. ;

[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 first adjustment electrode is arranged in the first cavity, the second adjustment electrode is arranged in the second cavity, and the first measuring electrode and the second measuring electrode are 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 water vapor concentration determining mechanism determines the concentration of water vapor contained in the measured gas based on the proportional relationship between the predetermined selective oxidation current and the concentration of water vapor contained in the measured gas, and the carbon dioxide concentration determining mechanism determines the concentration of carbon dioxide contained in the measured gas based on the proportional relationship between the difference obtained by subtracting the selective oxidation current from the predetermined double oxidation current and the concentration of carbon dioxide contained in the measured gas.

[0017] A fourth aspect of the present invention is the gas sensor according to the second or third aspect, wherein the Au concentration in the Pt—Au alloy is 1 wt % or more and 50 wt % or less.

[0018] A fifth aspect of the present invention is the gas sensor according to the fourth aspect, wherein the first adjustment electrode and the second adjustment electrode are metal ceramic electrodes containing Pt and not containing Au.

[0019] The sixth scheme of the present invention is based on the gas sensor involved in any one of the second to fifth 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 first adjustment electrode and the pump electrode outside the cavity when oxygen is sucked out from the first cavity by using the first adjustment pump unit.

[0020] The seventh scheme of the present invention is based on the gas sensor involved in any one of the second to sixth schemes, characterized in that the first measuring electrode and the second measuring electrode are arranged in a manner opposite to each other on a pair of surfaces along the length direction of the sensor element that divides the third cavity.

[0021] The eighth scheme of the present invention is based on the gas sensor involved in any one of the second to sixth schemes, and is characterized in that the first measuring electrode and the second measuring electrode are arranged in parallel on the surface along the length direction of the sensor element that demarcates the third cavity in a manner isolated from each other in a direction perpendicular to the length direction.

[0022] A ninth 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, the sensor element comprising: a gas inlet port for introducing the measured gas; an internal cavity connected to the gas inlet port via a diffusion rate control unit; a first adjustment electrode, a second adjustment electrode, and a first measuring electrode and a second measuring electrode arranged at positions equivalent to each other with respect to the flow of the measured gas flowing into the internal cavity. groups, which are arranged in a manner facing the internal cavity respectively and separated by a prescribed interval and in order from near to far from the gas inlet; a first adjustment pump unit, which is composed of the first adjustment electrode, an out-of-cavity pump electrode arranged at a position outside the internal cavity, and the solid electrolyte existing between the first adjustment electrode and the out-of-cavity pump electrode; a second adjustment pump unit, which is composed of the second adjustment electrode, the out-of-cavity pump electrode, and the solid electrolyte existing between the second adjustment electrode and the out-of-cavity pump electrode; a first measurement pump unit, which is composed of the first measurement electrode, the out-of-cavity pump electrode, and the solid electrolyte existing between the second adjustment electrode and the out-of-cavity pump electrode. The method comprises the following steps: a) the sensor element is heated by the heater in such a manner that the temperature near the first adjustment electrode in the internal cavity becomes the highest and the temperature decreases as the sensor element moves away from the first adjustment electrode in the longitudinal direction of the sensor element. heating; b) using the first adjustment pump unit to absorb oxygen from the measured gas that reaches the first adjustment electrode from the gas inlet port within a range where water vapor and carbon dioxide contained in the measured gas are not decomposed; c) using the second adjustment pump unit to absorb oxygen from the measured gas that reaches the second adjustment electrode in a manner such that water vapor and carbon dioxide contained in the measured gas after the oxygen is absorbed by the first adjustment pump unit are substantially completely reduced; d) using the first measuring pump unit to selectively oxidize hydrogen generated by the reduction of water vapor contained in the measured gas that reaches the first measuring electrode by sucking oxygen into the internal cavity;e) using the second measuring pump unit to absorb oxygen into the internal cavity so that hydrogen and carbon monoxide generated by the reduction of water vapor and carbon dioxide contained in the measured gas reaching the second measuring electrode are oxidized near the second measuring electrode; f) determining the concentration of water vapor contained in the measured gas based on the value of a selective oxidation current, which is an oxygen pump current flowing between the first measuring electrode and the pump electrode outside the cavity when the first measuring pump unit absorbs oxygen so that hydrogen near the first measuring electrode is selectively oxidized; g) determining the concentration of carbon dioxide contained in the measured gas based on the value of the selective oxidation current and the value of a double oxidation current, which is an oxygen pump current flowing between the second measuring electrode and the pump electrode outside the cavity when the second measuring pump unit absorbs oxygen so that hydrogen and carbon monoxide near the second measuring electrode are oxidized. ;

[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 the internal cavity is a first cavity, a second cavity, and a third cavity that are connected in sequence in order of distance from the gas inlet port via different diffusion rate control parts, the first adjustment electrode is arranged in the first cavity, the second adjustment electrode is arranged in the second cavity, and the first measuring electrode and the second measuring electrode are arranged in the third cavity.

[0024] The eleventh scheme of the present invention is based on the concentration measurement method using a gas sensor involved in the tenth scheme, and is characterized in that in the step f), the concentration of water vapor contained in the measured gas is determined based on the proportional relationship between the predetermined selective oxidation current and the concentration of water vapor contained in the measured gas, and in the step g), the concentration of carbon dioxide contained in the measured gas is determined based on the proportional relationship between the difference obtained by subtracting the selective oxidation current from the predetermined double oxidation current and the concentration of carbon dioxide contained in the measured gas.

[0025] A twelfth aspect of the present invention is the concentration measurement method using a gas sensor according to the tenth or eleventh aspect, wherein the Au concentration in the Pt—Au alloy is set to 1 wt % or more and 50 wt % or less.

[0026] A thirteenth aspect of the present invention is the concentration measurement method using a gas sensor according to the twelfth aspect, wherein the first adjustment electrode and the second adjustment electrode are formed as metal ceramic electrodes containing Pt and not containing 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 tenth to thirteenth schemes, and is characterized in that it also includes the following steps: h) determining the concentration of oxygen contained in the measured gas based on the magnitude of the current flowing between the first adjustment electrode and the pump electrode outside the cavity when oxygen is sucked out of the first cavity by the first adjustment pump unit.

[0028] The fifteenth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in any one of the tenth to fourteenth schemes, and is characterized in that the first measuring electrode and the second measuring electrode are arranged in a manner opposite to each other on a pair of surfaces along the length direction of the sensor element that divides the third cavity.

[0029] The sixteenth scheme of the present invention is based on the concentration measurement method using a gas sensor involved in any one of the tenth to fourteenth schemes, and is characterized in that the first measuring electrode and the second measuring electrode are arranged in parallel on the surface along the length direction of the sensor element that demarcates the third cavity in a manner isolated from each other in a direction perpendicular to the length direction.

[0030] According to the first to sixteenth aspects of the present invention, it is possible to realize a multi-gas sensor which is superior in long-term reliability compared with the related art in that cracking and blackening of the sensor element are suppressed and evaporation of Au from the electrode is also suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a diagram schematically showing an example of the configuration of the gas sensor 100 .

[0032] Figure 2 It is a block diagram showing components of functions implemented in the controller 110 .

[0033] Figure 3 Schematic diagram showing how gases enter and exit the three cavities in the sensor element 101 of the gas sensor 100 .

[0034] Figure 4 Graph 1 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 first adjustment pump unit 21 when three different model gases are flowing.

[0035] Figure 5 1 is a diagram showing the planar arrangement relationship between the first measurement electrode 44 a and the second measurement electrode 44 b in the sensor element 101A.

[0036] Figure 61 is a diagram showing the planar arrangement relationship between the first measurement electrode 44 a and the second measurement electrode 44 b in the sensor element 101B.

[0037] Figure 7 101C is a diagram showing the planar arrangement relationship between the first measurement electrode 44 a and the second measurement electrode 44 b in the sensor element 101C.

[0038] 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

[0039] <Gas sensor configuration>

[0040] 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.

[0041] 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.

[0042] 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).

[0043] 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.

[0044] 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.

[0045] The gas inlet 10 may also be formed to penetrate the spacer layer 5 in the thickness direction, unlike 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.

[0046] 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.

[0047] 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.

[0048] 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 .

[0049] The first diffusion rate control unit 11 is a portion that provides a predetermined diffusion resistance to the introduced gas to be measured.

[0050] 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.

[0051] 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 .

[0052] 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 the operation of the first adjustment pump unit 21.

[0053] The first adjustment pump cell 21 is an electrochemical pump cell composed of a first inner pump electrode (first 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.

[0054] In the first adjustment pump unit 21, a voltage Vp0 is applied between the first 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, 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.

[0055] The first 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 that define the first cavity 20. The top electrode portion 22a and the bottom electrode portion 22b are connected by a conductive portion (not shown).

[0056] The first 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.

[0057] 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.

[0058] In the sensor element 101, the first cavity sensor unit 80 is formed by the first 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 unit 80 is an electrochemical sensor unit for grasping the oxygen partial pressure in the atmosphere in the first cavity 20.

[0059] 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.

[0060] 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.

[0061] In the first cavity sensor unit 80, an electromotive force (Nernst electromotive force) V0 is generated between the first 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.

[0062] The third diffusion rate control unit 30 is a portion that provides a predetermined diffusion resistance to the measurement gas containing H 2 O and CO 2 and substantially not containing oxygen, which is introduced from the first cavity 20 to the second cavity 40 .

[0063] 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 second adjustment pump unit 50.

[0064] The second adjustment pump cell 50 is an electrochemical pump cell composed of a second inner pump electrode (second adjustment electrode) 51 , the outer pump electrode 23 , and a solid electrolyte present in a portion of the structure 14 sandwiched between these two electrodes.

[0065] In the second adjustment pump unit 50, a voltage Vp1 is applied between the second inner pump electrode 51 and the outer pump electrode 23 by using a variable power supply 52 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip1. In this way, 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 sucking oxygen from the second cavity 40 is set to the positive direction of the oxygen pump current Ip1.

[0066] The second inner pump 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).

[0067] The second inner pump electrode 51 is provided as a porous cermet electrode having a rectangular shape in a plan view and containing Pt as a metal component.

[0068] In the sensor element 101, the second inner pump 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 unit 81. The second cavity sensor unit 81 is an electrochemical sensor unit for grasping the oxygen partial pressure in the atmosphere in the second cavity 40.

[0069] In the second cavity sensor unit 81, an electromotive force (Nernst electromotive force) V1 is generated between the second inner pump 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.

[0070] 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 .

[0071] The third cavity 61 is provided as a space for oxidizing all H2 and CO contained in the gas to be measured introduced through the fourth diffusion rate control unit 60 to generate H2O and CO2 again. The oxidation of H2 and CO to generate H2O and CO2 is achieved by the operation of the first measurement pump unit 41a and the second measurement pump unit 41b.

[0072] The first measuring pump cell 41 a is an electrochemical pump cell composed of the first measuring electrode 44 a , the outer pump electrode 23 , and a solid electrolyte present in a portion of the structure 14 sandwiched between the two electrodes.

[0073] In the first measuring pump unit 41a, a voltage Vp2 is applied between the first measuring electrode 44a and the outer pump electrode 23 by a variable power supply 47a provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip2. Thus, oxygen can be taken into the third cavity 61 from the external space.

[0074] On the other hand, the second measuring pump cell 41 b is an electrochemical pump cell composed of the second measuring electrode 44 b , the outer pump electrode 23 , and a solid electrolyte present in a portion of the structure 14 sandwiched between the two electrodes.

[0075] In the second measuring pump unit 41b, a voltage Vp3 is applied between the second measuring electrode 44b and the outer pump electrode 23 by a variable power supply 47b provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip3. Thus, oxygen can be taken into the third cavity 61 from the external space.

[0076] In addition, in the present embodiment, the directions of the oxygen pumping current Ip2 and the oxygen pumping current Ip3 when oxygen is sucked out from the third cavity 61 are set to the positive directions of the oxygen pumping current Ip2 and the oxygen pumping current Ip3, respectively.

[0077] The first measuring electrode 44 a and the second measuring electrode 44 b are provided at positions equivalent to each other with respect to the flow of the gas to be measured flowing into the third cavity 61 through the fourth diffusion rate controlling unit 60 . Figure 1 In the figure, the first measuring electrode 44a is arranged on substantially the entire lower surface 6b of the second solid electrolyte layer 6 which demarcates the third cavity 61, and the second measuring electrode 44b is arranged on substantially the entire upper surface 4a of the first solid electrolyte layer 4 which also demarcates the third cavity 61, but the configuration of the two electrodes is not limited to this.

[0078] The first measuring electrode 44a is set as a porous metal ceramic electrode containing a Pt-Au alloy as a metal component, for example, a rectangular shape in a plan view containing the Pt-Au alloy and zirconium oxide. As a result, in the first measuring electrode 44a, even when H2 and CO coexist in the third cavity 61, only H2 is selectively oxidized, and CO is not oxidized. It should be noted that the Au concentration in the Pt-Au alloy is preferably 1wt% or more and 50wt% or less, and more preferably 30wt% or more and 50wt% or less. In this case, the selective oxidation property of H2 at the first measuring electrode 44a, that is, the property that only H2 is selectively oxidized by oxygen sucked by the first measuring pump unit 41a and CO is not oxidized when H2 and CO coexist in the third cavity 61, is better exhibited.

[0079] On the other hand, the second measuring electrode 44b is provided as a rectangular porous cermet electrode having Pt as a metal component in a plan view. Thus, at the second measuring electrode 44b, when H2 and CO coexist in the third cavity 61, both H2 and CO are oxidized.

[0080] In the sensor element 101, the first measuring electrode 44a, the reference electrode 42, and the solid electrolyte present in the portion sandwiched between the two electrodes in the structure 14 constitute a first measuring sensor unit 82a. The first measuring sensor unit 82a is an electrochemical sensor unit for grasping the oxygen partial pressure of the atmosphere near the first measuring electrode 44a in the third cavity 61.

[0081] In the first measurement sensor unit 82a, an electromotive force (Nernst electromotive force) V2 is generated between the first measurement electrode 44a and the reference electrode 42. The electromotive force V2 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) near the first measurement electrode 44a in the third cavity 61 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 V2 is a value corresponding to the oxygen concentration (oxygen partial pressure) near the first measurement electrode 44a.

[0082] In the sensor element 101, the second measuring electrode 44b, the reference electrode 42, and the solid electrolyte present in the portion sandwiched between the two electrodes in the structure 14 constitute a second measuring sensor unit 82b. The second measuring sensor unit 82b is an electrochemical sensor unit for grasping the oxygen partial pressure of the atmosphere near the second measuring electrode 44b in the third cavity 61.

[0083] In the second measurement sensor unit 82b, an electromotive force (Nernst electromotive force) V3 is generated between the second measurement electrode 44b and the reference electrode 42. The electromotive force V3 is a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) near the second measurement electrode 44b 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 V3 is a value corresponding to the oxygen concentration (oxygen partial pressure) near the second measurement electrode 44b.

[0084] 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 the 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.

[0085] 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 .

[0086] 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.

[0087] 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.

[0088] The heater 72 is set so that when heating, the vicinity of the first cavity 20 (the vicinity of the first 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.

[0089] 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.

[0090] 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 .

[0091] Figure 2 This is a block diagram showing the components of the functions 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 component of a specified function by executing a specified program stored in a storage device, for example, by the 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 the function.

[0092] 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).

[0093] The controller 110 includes, as components for implementing functions by executing a prescribed program in the CPU, an element operation control unit 120 for controlling the operation of each part of the sensor element 101, and a concentration determination unit 130 for determining the concentration of the monitored gas component contained in the measured gas.

[0094] The element action control unit 120 mainly includes: a first adjustment pump unit control unit 121a, which controls the action of the first adjustment pump unit 21; a second adjustment pump unit control unit 121b, which controls the action of the second adjustment pump unit 50; a first measuring pump unit control unit 122a, which controls the action of the first measuring pump unit 41a; a second measuring pump unit control unit 122b, which controls the action of the second measuring pump unit 41b; and a heater control unit 123, which controls the heating action of the heater 72.

[0095] 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 .

[0096] 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 first measuring pump cell 41 a acquired by the first measuring pump cell control unit 122 a .

[0097] The carbon dioxide concentration determination unit 130C determines the concentration of CO2 contained in the measured gas based on the value of the oxygen pump current Ip2 flowing through the first measuring pump cell 41a obtained by the first measuring pump cell control unit 122a and the value of the oxygen pump current Ip3 flowing through the second measuring pump cell 41b obtained by the second measuring pump cell control unit 122b.

[0098] 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 first adjustment pump unit 21 obtained by the first adjustment pump unit control unit 121a. That is, in the gas sensor 100 involved in this embodiment, in addition to H2O and CO2, which are the main monitoring target gas components, oxygen is also monitored as an additional monitoring target gas component.

[0099] <Multi-gas monitoring and concentration determination>

[0100] 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.

[0101] Figure 3 1 is a schematic diagram showing how gases enter and exit three cavities (internal cavities) in the sensor element 101 of the gas sensor 100 .

[0102] 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 (the first diffusion rate control unit 11), the buffer space 12, and the second diffusion rate control unit 13. In the first cavity 20, the first adjustment pump unit 21 operates to absorb oxygen from the introduced gas to be measured.

[0103] The above-mentioned oxygen suction is performed as follows, that is, the first adjustment pump unit control section 121a 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 electromotive force V0 and the target value, feedback control is performed on the voltage Vp0 applied by the variable power supply 24 to the first adjustment pump unit 21 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 changes greatly with respect to the target value, and therefore, the first adjustment pump unit control section 121a controls the pump voltage Vp0 applied by the variable power supply 24 to the first adjustment pump unit 21 so as to reduce the change.

[0104] By sucking oxygen from the first cavity 20 by the first adjustment pump unit 21 in the above manner, the oxygen partial pressure in the first cavity 20 is kept 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 Around atm.

[0105] 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 It is a curve 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 first 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 and the temperature of the model gas is set to 150°C.

[0106] Depend on Figure 4 It 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.

[0107] 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.

[0108] 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 cell 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 cell 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 first inner pump electrode 22 is kept at a high temperature are well suppressed.

[0109] The gas to be measured, from which only oxygen is absorbed within the range where H2O and CO2 are not reduced in the first cavity 20, is introduced into the second cavity 40. Then, H2O and CO2 contained in the gas to be measured are reduced in the second cavity 40. That is, the second adjustment pump unit 50 operates to further absorb oxygen from the gas to be measured, from which oxygen is 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 H2O and CO2 contained in the gas to be measured, and H2O and CO2 are substantially all decomposed into hydrogen (H2), carbon monoxide (CO), and oxygen.

[0110] The reduction (decomposition) of H2O and CO2 and the absorption of the generated oxygen are performed as follows: the second adjustment pump unit control unit 121b 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 second adjustment pump unit 50 is feedback-controlled in such a way 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.

[0111] The second regulating pump unit 50 operates in this way 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.

[0112] 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 .

[0113] Oxygen is sucked into the third cavity 61 by the operation of the first measuring pump cell 41 a and the second measuring pump cell 41 b .

[0114] The first measuring pump unit 41a performs oxygen inhalation as follows: the first measuring pump unit control unit 122a of the controller 110 sets the target value (control voltage) of the electromotive force V2 in the first measuring sensor unit 82a to a value within the range of 250mV to 450mV (preferably 350mV), and based on the difference between the actual electromotive force V2 and the target value, feedback control is performed on the voltage Vp2 applied by the variable power supply 47a to the first measuring pump unit 41a in such a manner that the electromotive force V2 is maintained at the above-mentioned target value.

[0115] As the first measuring pump unit 41 a operates in the above-described manner, the oxidation (combustion) reaction of 2H 2 +O 2 →2H 2 O is promoted in the vicinity of the first measuring electrode 44 a of the third cavity 61 .

[0116] The target value of the electromotive force V2 is set to a value within a range of 250 mV to 450 mV in order to selectively oxidize only H 2 and not oxidize CO among the gas species contained in the gas to be measured present near the first measuring electrode 44 a of the third cavity 61 .

[0117] Hereinafter, the amount of H 2 O generated when oxygen is sucked in by the first measuring pump unit 41 a is also referred to as a first H 2 O amount.

[0118] Furthermore, as described above, providing the first measuring electrode 44 a 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 .

[0119] 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 second inner pump electrode 51 containing no Au in the metal component is provided in the second cavity 40, and a first measuring electrode 44a which is also composed of a Pt-Au alloy and is responsible for selective oxidation of H2 is provided facing the third cavity 61 whose temperature during operation of the gas sensor 100 is lower than that of the second cavity 40. As a result, the gas sensor 100 according to the present embodiment suppresses evaporation of Au from the electrode compared to the conventional gas sensor.

[0120] In addition to this, it is also possible to take measures such as making changes to the shape (width, thickness), arrangement (density), etc. of the heater 72 to further suppress the temperature rise of the first measuring electrode 44 a.

[0121] On the other hand, the second measuring pump unit 41b performs oxygen inhalation as follows: the second measuring pump unit control unit 122b of the controller 110 sets the target value (control voltage) of the electromotive force V3 in the second measuring sensor unit 82b to a value in the range of 100mV to 300mV (preferably 200mV), and based on the difference between the actual electromotive force V3 and the target value, feedback control is performed on the voltage Vp3 applied by the variable power supply 47b to the second measuring pump unit 41b in such a manner that the electromotive force V3 is maintained at the above-mentioned target value.

[0122] By operating the second measuring pump unit 41b in the above-described manner, both the oxidation (combustion) reaction of 2CO+O2→2CO2 and the oxidation (combustion) reaction of 2H2+O2→2H2O are promoted in the vicinity of the second measuring electrode 44b of the third cavity 61.

[0123] Through the former reaction, CO 2 is generated again in an amount correlated with the amount of CO 2 introduced from the gas inlet port 10 .

[0124] On the other hand, the amount of H2O generated by the latter reaction (hereinafter also referred to as the second H2O amount) is substantially equal to the above-mentioned first H2O amount. This is because: in the third cavity 61, the first measuring electrode 44a and the second measuring electrode 44b are arranged at equivalent positions relative to the flow of the measured gas, and the H2 contained in the measured gas introduced into the third cavity 61 is oxidized at the two electrodes with equal probability.

[0125] In addition, the sum of the first H2O amount and the second H2O amount is correlated with the amount of H2O introduced from the gas inlet port 10. It should be noted that in this embodiment, the correlation of the amount of H2O or CO2 means that the amount of H2O or CO2 introduced from the gas inlet port 10 is the same as the amount of H2O or CO2 generated by the decomposition of these H2 and CO and then oxidized and regenerated, or is within a certain error range allowed in terms of measurement accuracy.

[0126] In the gas sensor 100 according to the present embodiment operating in the above manner, the concentrations of H2O and CO2 in the measured gas are determined based on the oxygen intake current for selectively oxidizing H2 at the first measuring electrode 44a, that is, the oxygen pump current Ip2 flowing through the first measuring pump cell 41a, and the oxygen intake current for oxidizing both H2 and CO at the second measuring electrode 44b, that is, the oxygen pump current Ip3 flowing through the second measuring pump cell 41b. Hereinafter, the oxygen pump current Ip2 and the oxygen pump current Ip3 during actual measurement by the gas sensor 100 are also referred to as the selective oxidation current Ip2 and the double oxidation current Ip3, respectively.

[0127] Specifically, the concentrations of H2O and CO2 in the measured gas are respectively set to C H , C C At the above concentration value C H , C C The following relationship holds true between the selective oxidation current Ip2 and the double oxidation current Ip3: Where k1 and k2 are proportional constants.

[0128] C H =k1·Ip2····(1)

[0129] C C =k2·(Ip3-Ip2)····(2)

[0130] Formula (1) is based on the fact that there is a proportional relationship between the selective oxidation current Ip2 and the first H2O amount; and that since the first H2O amount and the second H2O amount are substantially equal, the concentration value C of H2O in the measured gas is considered to be H There is a proportional relationship between 1 / 2 of the selective oxidation current Ip2.

[0131] In addition, formula (2) is based on the fact that the first H2O amount and the second H2O amount are substantially equal, so the portion of the dual oxidation current Ip3 that contributes to the oxidation of H2 is considered to be equal to the selective oxidation current Ip2, so the difference Ip3-Ip2 is equivalent to the portion of the oxygen inhaled by the second measuring pump unit 41b that contributes to the oxidation of CO, and further, it is considered that there is a proportional relationship between the difference Ip3-Ip2 and the concentration of CO2 in the measured gas.

[0132] The proportional constants k1 and k2 are determined in advance using a model gas with a known concentration before using the gas sensor 100. In addition, the equation (1) including the proportional constant k1 is stored in the water vapor concentration determination unit 130H of the controller 110. In addition, the equation (2) including the proportional constant k2 is stored in the carbon dioxide concentration determination unit 130C of the controller 110.

[0133] It should be noted that both the selective oxidation current Ip2 and the double oxidation current Ip3 are values ​​corresponding to the diffusion resistance applied to the measured gas from the gas inlet 10 of the sensor element 101 to the third cavity 61. Therefore, strictly speaking, the proportional constants k1 and k2 are different for each individual sensor element 101 constituting each gas sensor 100. Therefore, the proportional constants k1 and k2 are preferably determined for each gas sensor 100. Among them, for 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 proportional constants k1 and k2 obtained for a certain gas sensor 100 are applied to other gas sensors 100 of the same batch.

[0134] Furthermore, when the gas sensor 100 actually performs measurement, the measured gas is introduced into the sensor element 101 that has been heated to the element driving temperature, and the first adjustment pump unit 21, the second adjustment pump unit 50, the first measurement pump unit 41a, and the second measurement pump unit 41b operate in the above manner. Furthermore, the water vapor concentration determination unit 130H obtains the selective oxidation current Ip2 from the first measurement pump unit control unit 122a, and determines the H2O concentration based on the formula (1).

[0135] The carbon dioxide concentration determination unit 130C obtains the value of the selective oxidation current Ip2 from the first measuring pump unit control unit 122a and the value of the dual oxidation current Ip3 from the second measuring pump unit control unit 122b, and then determines the CO2 concentration based on equation (2).

[0136] In the gas sensor 100 according to the present embodiment, the H 2 O concentration and the CO 2 concentration in the measured gas can be determined through the above operation.

[0137] 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 first adjustment pump cell 21 .

[0138] In the gas sensor 100 involved in this embodiment, as described above, the first adjustment pump unit 21 operates, 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 is stored in the controller 110.

[0139] 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 first adjustment pump unit control unit 121a. Then, referring to the Ip0-O2 data, the value of the oxygen concentration corresponding to the obtained oxygen detection current Ip0 is determined. In this way, the oxygen concentration in the measured gas can be determined.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] <Modification of electrode arrangement>

[0145] As described above, in the third cavity 61, in order to oxidize H2 contained in the measured gas with equal probability at the first measuring electrode 44a and the second measuring electrode 44b, the two electrodes need to be arranged at equivalent positions with respect to the flow of the measured gas.

[0146] Among them, in the above implementation mode, if Figure 1 As shown, the first measuring electrode 44a and the second measuring electrode 44b are respectively arranged on the lower surface 6b of the second solid electrolyte layer 6 constituting the top surface of the third cavity 61 and the upper surface 4a of the first solid electrolyte layer 4 constituting the bottom surface of the third cavity 61, which are a pair of surfaces along the length direction of the sensor element 101 that demarcates the third cavity 61. However, as long as they are equivalent with respect to the flow of the measured gas, the arrangement of the two electrodes may be different. Figure 1 The configuration shown is different.

[0147] For example, the first measurement electrode 44a and the second measurement electrode 44b may be arranged in the same manner as Figure 1 Swap the configuration shown.

[0148] Alternatively, the first measuring electrode 44a and the second measuring electrode 44b may be disposed facing each other on two exposed surfaces of the isolation layer 5 constituting the side portion of the third cavity 61 as a pair of surfaces along the longitudinal direction of the sensor element 101 that also define the third cavity 61.

[0149] Figures 5 to 7 The diagrams respectively illustrate sensor elements 101A to 101C in which the arrangement of the first measurement electrodes 44 a and the second measurement electrodes 44 b is further different. Figures 5 to 7 The planar arrangement relationship of the first measuring electrode 44a and the second measuring electrode 44b in the sensor elements 101A to 101C is shown respectively. It should be noted that for reference, the first inner pump electrode 22 and the second inner pump electrode 51 are also shown, but the arrangement positions of these electrodes are different from Figure 1 The situation is the same.

[0150] Figure 5 In the sensor element 101A shown, the first measuring electrode 44a and the second measuring electrode 44b, whose respective longitudinal directions coincide with the longitudinal direction of the element, are arranged in parallel in a manner separated from each other in a direction perpendicular to the longitudinal direction of the element. This arrangement can be performed on either the lower surface 6b of the second solid electrolyte layer 6 constituting the top surface of the third cavity 61 or the upper surface 4a of the first solid electrolyte layer 4 constituting the bottom surface of the third cavity 61.

[0151] in addition, Figure 6In the sensor element 101B shown, a partition 45 may be provided between the first measurement electrode 44a and the second measurement electrode 44b arranged at the same position as the sensor element 101A. The partition 45 is a portion protruding at a predetermined height from the formation surface of the first measurement electrode 44a and the second measurement electrode 44b. When the partition 45 is provided, Au evaporated from the first measurement electrode 44a is well suppressed from reaching and adhering to the second measurement electrode 44b.

[0152] The separator 45 may be formed of a solid electrolyte similar to the structure 14 , or may be formed of other ceramics such as alumina.

[0153] It should be noted that if the partition 45 completely divides the third cavity 61 into two equal parts, CO entering the side where the first measuring electrode 44a is located will accumulate and will be less likely to be oxidized at the second measuring electrode 44b, which is not ideal.

[0154] in addition, Figure 7 In the sensor element 101C shown, the first measuring electrode 44a and the second measuring electrode 44b arranged at the same position as the sensor element 101A are covered with ceramic porous bodies 46a and 46b, respectively. The porous bodies 46a and 46b are also provided for the purpose of preventing Au evaporated from the first measuring electrode 44a from reaching and adhering to the second measuring electrode 44b.

[0155] The porous bodies 46 a and 46 b are provided with an equal porosity in the range of, for example, 5% to 30% and an equal thickness in the range of 30 μm to 100 μm.

[0156] Alternatively, the following mode may be adopted: the porosity and thickness are optimally adjusted to give the function of the fourth diffusion rate controlling unit 60 to the porous bodies 46 a and 46 b , and the fourth diffusion rate controlling unit 60 may be omitted.

[0157] <Other Modifications>

[0158] In the gas sensor 100 according to the above-mentioned embodiment, the sensor element 101 is provided with a gas flow section having a first cavity 20, a second cavity 40, and a third cavity 61 connected by a diffusion rate control section. In addition, for the gas to be measured that 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 first adjustment pump unit 21 within a range where H2O and CO2 are not reduced, and H2O and CO2 are reduced by the second adjustment pump unit 50 in the second cavity 40. In the third cavity 61, H2 generated by the reduction of H2O is selectively oxidized by the first measurement pump unit 41a, and both H2 generated by the reduction of H2O and CO generated by the reduction of CO2 are oxidized by the second measurement pump unit 41b. 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.

[0159] 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 controlling the measured gas reaching the first inner pump electrode 22 of the first adjustment pump cell 21, the second adjustment electrode 51 of the second adjustment pump cell 50, the first measurement electrode 44a of the first measurement pump cell 41a, and the second measurement electrode 44b of the second measurement pump cell 41b well 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.

[0160] From another perspective, this means that, as long as the oxygen suction by the first adjustment pump cell 21 within the range where H2O and CO2 reduction does not occur is performed for the gas to be measured reaching the first inner pump electrode 22, the second inner pump electrode 51, the first measuring electrode 44a, and the second measuring electrode 44b, the reduction of H2O and CO2 by the second adjustment pump cell 50, the selective oxidation of H2 generated by the reduction of H2O by the first measuring pump cell 41a, and the oxidation of both H2 generated by the reduction of H2O and CO generated by the reduction of CO2 by the second measuring pump cell 41b are performed well in view of ensuring the measurement accuracy, a different configuration from the gas flow portion 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 portion, multi-gas monitoring can be realized.

[0161] 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.

[0162] The sensor element 201 is a long plate-shaped structure in which the sensor portion 214 and the heater portion 270 are stacked.

[0163] 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 including 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.

[0164] 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.

[0165] 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.

[0166] That is, in the sensor element 201 , it can be said that the diffusion rate control section 211 and the internal cavity 220 constitute a gas flow section communicating from the gas introduction port 210 .

[0167] The exposed surface 204a of the second substrate 204 relative to the inner cavity 220 is Figure 5 The first adjustment electrode 230, the second adjustment electrode 240, the first measurement electrode 250a and the second measurement electrode 250b are arranged in the same arrangement as the planar arrangement of the first inner pump electrode 22, the second inner pump electrode 51, the first measurement electrode 44a and the second measurement electrode 44b in the sensor element 101A shown in the figure. That is, in the order of the distance from the gas inlet 210 on the left side of the figure, the first adjustment electrode 230, the second adjustment electrode 240, and the first measurement electrode 250a and the second measurement electrode 250b are arranged in a manner that they are separated by a predetermined interval and face the internal cavity 220. The first adjustment electrode 230, the second adjustment electrode 240, the first measurement electrode 250a and the second measurement electrode 250b are respectively provided as porous metal ceramic electrodes similar to the first inner pump electrode 22, the second inner pump electrode 51, the first measurement electrode 44a and the second measurement electrode 44b of the sensor element 101.

[0168] 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.

[0169] 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 first adjustment electrode 230, the second adjustment electrode 240, the first measurement electrode 250a, and the second measurement electrode 250b provided on the opposite surface 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.

[0170] 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.

[0171] The heater 272 is provided so that, during heating, the temperature near the first adjustment electrode 230 becomes the highest, and the temperature decreases as the distance from the first adjustment electrode 230 increases in the element length direction.

[0172] Furthermore, the sensor element 201 includes a first adjustment pump cell C0 , a second adjustment pump cell C1 , a first measurement pump cell C2 a , and a second measurement pump cell C2 b .

[0173] The first adjustment pump cell C0 is an electrochemical pump cell composed of a first adjustment electrode 230, a reference electrode 261, and a second substrate 204 sandwiched by the two electrodes. In the first adjustment pump cell C0, a voltage Vp0 is applied between the first 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 first adjustment pump cell C0 is controlled by the first adjustment pump cell control unit 121a of the controller 110.

[0174] The second adjustment pump cell C1 is an electrochemical pump cell composed of a second adjustment electrode 240, a reference electrode 261, and a second substrate 204 sandwiched by the two electrodes. In the second adjustment pump cell C1, a voltage Vp1 is applied between the second adjustment 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 second adjustment pump cell C1 is controlled by the second adjustment pump cell control unit 121b of the controller 110.

[0175] The first measuring pump cell C2a is an electrochemical pump cell composed of a first measuring electrode 250a, a reference electrode 261, and a second substrate 204 sandwiched by the two electrodes. In the first measuring pump cell C2a, a voltage Vp2 is applied between the first measuring electrode 250a and the reference electrode 261 by a variable power supply 251a provided outside the sensor element 201, thereby generating an oxygen pump current (oxygen ion current) Ip2. The operation of the first measuring pump cell C2a is controlled by the first measuring pump cell control unit 122a of the controller 110.

[0176] The second measuring pump cell C2b is an electrochemical pump cell composed of a second measuring electrode 250b, a reference electrode 261, and a second substrate 204 sandwiched by the two electrodes. In the second measuring pump cell C2b, a voltage Vp3 is applied between the second measuring electrode 250b and the reference electrode 261 by a variable power supply 251b provided outside the sensor element 201, thereby generating an oxygen pump current (oxygen ion current) Ip3. The operation of the second measuring pump cell C2b is controlled by the second measuring pump cell control unit 122b of the controller 110.

[0177] As described above, in the sensor element 201, unlike the sensor element 101 of the gas sensor 100, the first adjustment electrode 230, the second adjustment electrode 240, the first measurement electrode 250a, and the second measurement electrode 250b 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 gas to be measured introduced into the internal cavity 220 is optimized, in other words, by controlling the flow rate of the gas to be measured to the optimal flow rate, in the gas sensor 200 having the sensor element 201, it is possible to realize multi-gas monitoring with at least water vapor (H2O) and carbon dioxide (CO2) as the main monitoring target gas components under the control of the controller 110, similarly to the gas sensor 100.

[0178] 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 first adjustment electrode 230, the second adjustment electrode 240, the first measuring electrode 250a, and the second measuring electrode 250. In addition, the first adjustment pump cell C0 performs an oxygen suction operation to suck out oxygen from the measured gas reaching the first adjustment electrode 230 within a range where H2O and CO2 are not reduced. The second adjustment pump cell C1 performs an oxygen suction operation in a manner that H2O and CO2 contained in the measured gas reaching the second adjustment electrode 240 are reduced. The first measuring pump cell C2a performs an oxygen suction operation in a manner that H2 generated by reducing H2O by the second adjustment pump cell C1 reaching the first measuring electrode 250a is selectively oxidized. The second measuring pump cell C2b performs an oxygen suction operation in a manner that both H2 generated by reducing H2O and CO generated by reducing CO2 by the second adjustment pump cell C1 reaching the second measuring electrode 250b are oxidized.

[0179] At this time, the measured gas flows at a flow rate at which neither the measured gas from which oxygen is not absorbed passes through the first adjustment electrode 230 nor the measured gas with residual H2O and CO2 passes through the second adjustment 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; a first adjustment electrode, a second adjustment electrode, and a group of a first measuring electrode and a second measuring electrode disposed at positions equivalent to each other with respect to a flow of the measured gas flowing into the internal cavity, which are disposed so as to face the internal cavity, respectively, and are separated by a predetermined interval and disposed in order of distance from the gas inlet port from near to far; a first adjustment pump cell, the first adjustment pump cell comprising the first adjustment electrode, an out-of-cavity pump electrode provided at a location outside the internal cavity, and the solid electrolyte present between the first adjustment electrode and the out-of-cavity pump electrode; a second adjustment pump cell, the second adjustment pump cell being composed of the second adjustment electrode, the out-of-cavity pump electrode, and the solid electrolyte existing between the second 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 first measuring electrode is a cermet electrode containing a Pt-Au alloy as a metal component, The heater heats the sensor element so that the temperature is highest near the first adjustment electrode in the internal cavity and decreases as the temperature is farther from the first adjustment electrode in the longitudinal direction of the sensor element. The first adjustment pump unit absorbs oxygen from the gas to be measured that reaches the first 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 second adjustment pump unit absorbs oxygen from the gas to be measured that reaches the second adjustment 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 first adjustment pump unit are substantially completely reduced. The first measuring pump unit sucks oxygen into the internal cavity to selectively oxidize hydrogen generated by reduction of water vapor contained in the measured gas reaching the first measuring electrode near the first measuring electrode. The second measuring pump unit absorbs oxygen into the internal cavity to oxidize hydrogen and carbon monoxide generated by reduction of water vapor and carbon dioxide contained in the measured gas reaching the second measuring electrode near the second measuring electrode. The controller has: a water vapor concentration determining mechanism that determines the concentration of water vapor contained in the measured gas based on a value of a selective oxidation current, the selective oxidation current being an oxygen pump current flowing between the first measuring electrode and the cavity outer pump electrode when the first measuring pump unit absorbs oxygen so that hydrogen near the first measuring electrode is selectively oxidized; 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 selective oxidation current and the value of the double oxidation current, wherein the double oxidation current is the oxygen pump current flowing between the second measuring electrode and the pump electrode outside the cavity when the second measuring pump unit inhales oxygen so that hydrogen and carbon monoxide near the second measuring electrode are oxidized.

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 first adjustment electrode is disposed in the first cavity. The second adjustment electrode is disposed in the second cavity. The first measurement electrode and the second measurement electrode are disposed in the third cavity.

3. The gas sensor according to claim 2, characterized in that: The water vapor concentration determining means determines the concentration of the water vapor contained in the gas to be measured based on a predetermined proportional relationship between the selective oxidation current and the concentration of the water vapor contained in the gas to be measured, The carbon dioxide concentration determining means determines the concentration of carbon dioxide contained in the measured gas based on a proportional relationship between a predetermined difference value obtained by subtracting the selective oxidation current from the dual oxidation current and the concentration of carbon dioxide contained in the measured gas.

4. The gas sensor according to claim 2 or 3, characterized in that: The Au concentration in the Pt—Au alloy is greater than or equal to 1 wt % and less than or equal to 50 wt %.

5. The gas sensor according to claim 4, characterized in that: The first adjustment electrode and the second adjustment electrode are metal ceramic electrodes containing Pt and not containing Au.

6. The gas sensor according to claim 2 or 3, 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 first adjustment electrode and the pump electrode outside the cavity when the first adjustment pump unit sucks oxygen from the first cavity.

7. The gas sensor according to claim 2 or 3, characterized in that: The first measuring electrode and the second measuring electrode are arranged on a pair of surfaces along the longitudinal direction of the sensor element defining the third cavity so as to face each other.

8. The gas sensor according to claim 2 or 3, characterized in that: The first measuring electrode and the second measuring electrode are arranged in parallel on a surface of the sensor element defining the third cavity along the longitudinal direction so as to be separated from each other in a direction perpendicular to the longitudinal direction.

9. 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; a first adjustment electrode, a second adjustment electrode, and a group of a first measuring electrode and a second measuring electrode disposed at positions equivalent to each other with respect to a flow of the measured gas flowing into the internal cavity, which are disposed so as to face the internal cavity, respectively, and are separated by a predetermined interval and disposed in order of distance from the gas inlet port from near to far; a first adjustment pump cell, the first adjustment pump cell comprising the first adjustment electrode, an out-of-cavity pump electrode provided at a location outside the internal cavity, and the solid electrolyte present between the first adjustment electrode and the out-of-cavity pump electrode; a second adjustment pump cell, the second adjustment pump cell being composed of the second adjustment electrode, the out-of-cavity pump electrode, and the solid electrolyte existing between the second 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 first measuring electrode is a cermet electrode containing a Pt-Au alloy as a metal component, 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 first adjustment electrode in the internal cavity and decreases as the temperature is farther away from the first adjustment electrode in the longitudinal direction of the sensor element; b) using the first adjustment pump unit to absorb oxygen from the gas to be measured that reaches the first 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 second adjustment pump unit to absorb oxygen from the gas to be measured that reaches the second adjustment 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 first adjustment pump unit are substantially completely reduced; d) using the first measuring pump unit to suck oxygen into the internal cavity so that hydrogen generated by reduction of water vapor contained in the measured gas reaching the first measuring electrode is selectively oxidized near the first measuring electrode; e) using the second measuring pump unit to absorb oxygen into the internal cavity so that hydrogen and carbon monoxide generated by reduction of water vapor and carbon dioxide contained in the measured gas reaching the second measuring electrode are oxidized near the second measuring electrode; f) determining the concentration of water vapor contained in the measured gas based on the value of a selective oxidation current, which is an oxygen pump current flowing between the first measuring electrode and the cavity outer pump electrode when the first measuring pump unit absorbs oxygen so that hydrogen near the first measuring electrode is selectively oxidized; g) determining the concentration of carbon dioxide contained in the measured gas based on the value of the selective oxidation current and the value of the double oxidation current, wherein the double oxidation current is the oxygen pump current flowing between the second measuring electrode and the pump electrode outside the cavity when the second measuring pump unit inhales oxygen so that hydrogen and carbon monoxide near the second measuring electrode are oxidized.

10. The concentration measurement method using a gas sensor according to claim 9, 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 first adjustment electrode is disposed in the first cavity. The second adjustment electrode is disposed in the second cavity. The first measurement electrode and the second measurement electrode are disposed in the third cavity.

11. The concentration measurement method using a gas sensor according to claim 10, characterized in that: In the step f), the concentration of water vapor contained in the gas to be measured is determined based on a predetermined proportional relationship between the selective oxidation current and the concentration of water vapor contained in the gas to be measured, In the step g), the concentration of carbon dioxide contained in the gas to be measured is determined based on a predetermined proportional relationship between a difference value obtained by subtracting the selective oxidation current from the dual oxidation current and the concentration of carbon dioxide contained in the gas to be measured.

12. The concentration measurement method using a gas sensor according to claim 10 or 11, characterized in that: The Au concentration in the Pt—Au alloy is set to 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 first adjustment electrode and the second adjustment electrode are metal ceramic electrodes containing Pt and not containing Au.

14. The concentration measurement method using a gas sensor according to claim 10 or 11, characterized in that: It also includes the following steps: h) determining the concentration of oxygen contained in the measured gas based on the magnitude of a current flowing between the first adjustment electrode and the pump electrode outside the cavity when the first adjustment pump unit sucks oxygen from the first cavity.

15. The concentration measurement method using a gas sensor according to claim 10 or 11, characterized in that: The first measuring electrode and the second measuring electrode are arranged on a pair of surfaces along the longitudinal direction of the sensor element defining the third cavity so as to face each other.

16. The concentration measurement method using a gas sensor according to claim 10 or 11, characterized in that: The first measuring electrode and the second measuring electrode are arranged in parallel on a surface of the sensor element defining the third cavity along the longitudinal direction so as to be separated from each other in a direction perpendicular to the longitudinal direction.

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