Gas sensor, and method for measuring concentration using gas sensor

Abstract

In the present invention, a sensor element comprises first to third chambers that communicate sequentially from a gas inlet via mutually different diffusion-controlling parts, and a heater that carries out heating such that the vicinity of the first chamber has the highest temperature. Within a range in which H2O and CO2 included in a measurement gas are not broken down, a first adjustment pump cell pumps out the oxygen from the measurement gas introduced into the first chamber. A second adjustment pump cell pumps out oxygen from the second chamber so that all of the H2 and CO2 included in the measurement gas introduced from the first chamber into the second chamber is reduced. A first measurement pump cell pumps the oxygen into the third chamber and selectively oxidizes the H2 located near a first measurement electrode. A second measurement pump cell pumps the oxygen into the third chamber and oxidizes H2 and CO located near a second measurement electrode. The concentration of H2O is identified from the value of a pump-in electric current of the former, and the concentration of CO2 is identified from the value of a pump-in electric current of the latter.

Description

Gas sensor and concentration measurement method using gas sensor

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

[0002] In measurements to control emissions from automobile exhaust gases, water vapor (H ２ O) and carbon dioxide (CO ２ ) is already known (see, for example, Patent Documents 1 to 3). In the gas sensors disclosed in Patent Documents 1 and 2, ２ O) component and carbon dioxide (CO ２ In addition, the gas sensor disclosed in Patent Document 3 can measure carbon dioxide (CO ) components in parallel. ２ ) is included, water vapor (H ２ O) component can be measured with high accuracy.

[0003] In the three-chamber gas sensor disclosed in Patent Document 1, first, a main pump cell, which is a pump cell for the first internal space, is operated to pump O contained in the measurement gas introduced into the first internal space. ２ is pumped out, and H contained in the gas to be measured is also pumped out. ２ O and CO ２ Once everything is returned, ２ and CO. These H ２ The measurement gas containing CO and O is introduced into the second and third internal spaces. ２ H by pumping ２ is selectively oxidized to H ２ O is generated and further O is pumped by the second measurement pump cell, which is a pump cell for the third internal cavity. ２ When CO is pumped in, CO is oxidized and CO ２ are generated. Then, these H ２ and CO are oxidized, based on the magnitude of the pump current flowing through the first measuring pump cell and the second measuring pump cell. ２O and CO ２ The concentration of

[0004] In the gas sensor, H in the first internal space ２ O and CO ２ To reduce the oxygen ion, it is necessary to set a high voltage to be applied to the pump cell for the first internal space. At the same time, it is also necessary to increase the temperature of the main inner pump electrode, which is the pump electrode in the space constituting the main pump cell. However, applying a high voltage and maintaining the pump electrode at a high temperature may cause cracks or blackening of the solid electrolyte ceramic due to reduction of the solid electrolyte ceramic in the sensor element, which is mainly composed of an oxygen ion conductive solid electrolyte ceramic.

[0005] In addition, in the two-chamber gas sensor disclosed in Patent Document 3, H ２ In order to improve the selective oxidation property of the second internal space, the measurement inner pump electrode, which is a pump electrode in the cavity constituting the measurement pump cell, is made of an alloy of Au and another noble metal (e.g., Pt, Rh, Ru), and the abundance ratio of Au on the electrode surface is 25 at % or more.

[0006] At first glance, this electrode material appears to be similar to the H ２ It is also considered that the present invention can be applied to the first inner measuring pump electrode of the first measuring pump cell, which selectively oxidizes .

[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 second measuring inner pump electrode, which is the pump electrode inside the cavity that constitutes the second measuring pump cell.Therefore, if such an electrode material is used, the Au in the electrode may evaporate, and the sensitivity may change during long-term use.

[0008] Patent No. 5918177 Patent No. 6469464 Patent No. 6469462

[0009] The present invention has been made in view of the above problems, and provides a method for treating water vapor (H ２ O) component and carbon dioxide (CO ２The present invention aims to provide a multi-gas sensor that can simultaneously measure the components (a) and (b), that is inhibited from cracking or blackening in the sensor element, that is less susceptible to sensitivity changes even after long-term use, and that has superior long-term reliability compared to conventional multi-gas sensors.

[0010] In order to solve the above-mentioned problems, a first aspect of the present invention is a gas sensor capable of measuring concentrations of a plurality of target gas components contained in a measurement gas containing at least water vapor and carbon dioxide, the gas sensor comprising: a sensor element having a structure made of an oxygen ion conductive solid electrolyte; and a controller for controlling the operation of the gas sensor, the sensor element including a gas inlet through which the measurement gas is introduced; an internal chamber communicating with the gas inlet via a diffusion-controlling part; and a second electrode adjacent to the gas inlet, the second electrode being spaced apart by a predetermined distance from the gas inlet so as to face the internal chamber. a first adjusting electrode, a second adjusting electrode, and a set of a first measuring electrode and a second measuring electrode provided at positions equivalent to each other with respect to the flow of the measurement gas flowing into the internal chamber; a first adjusting pump cell including the first adjusting electrode, an outside-void pump electrode provided at a location other than the internal chamber, and the solid electrolyte present between the first adjusting electrode and the outside-void pump electrode; a second adjusting pump cell including the second adjusting electrode, the outside-void pump electrode, and the solid electrolyte present between the second adjusting electrode and the outside-void pump electrode; a first measurement pump cell including the first measurement electrode, the pump electrode outside the cavity, and the solid electrolyte present between the first measurement electrode and the pump electrode outside the cavity; a second measurement pump cell including the second measurement electrode, the pump electrode outside the cavity, and the solid electrolyte present between the second measurement electrode and the pump electrode outside the cavity; and a heater for heating the sensor element, wherein the first measurement electrode is a cermet electrode containing a Pt—Au alloy as a metal component, and the heater heats the sensor element such that the temperature in the vicinity of the first adjustment electrode in the internal cavity is the highest, the sensor element is heated so that the temperature decreases with increasing distance from the first adjusting electrode in the longitudinal direction of the sensor element, the first adjusting pump cell pumps oxygen from the measurement gas that has reached the first adjusting electrode from the gas inlet to an extent that water vapor and carbon dioxide contained in the measurement gas are not decomposed, the second adjusting pump cell pumps oxygen from the measurement gas that has reached the second adjusting electrode so that water vapor and carbon dioxide contained in the measurement gas from which oxygen has been pumped by the first adjusting pump cell are substantially all reduced, and the first measuring pump cellBy pumping oxygen into the internal chamber, hydrogen produced by reduction of water vapor contained in the measurement gas that has reached the first measurement electrode is selectively oxidized in the vicinity of the first measurement electrode, and the second measurement pump cell pumps oxygen into the internal chamber, thereby oxidizing hydrogen and carbon monoxide produced by reduction of water vapor and carbon dioxide contained in the measurement gas that has reached the second measurement electrode in the vicinity of the second measurement electrode, and the controller controls the first measurement pump cell to pump oxygen so that the hydrogen in the vicinity of the first measurement electrode is selectively oxidized. The gas measuring device is characterized by comprising: a water vapor concentration determining means for determining the concentration of water vapor contained in the measurement gas based on the value of a selective oxidation current, which is an oxygen pump current that flows between the first measurement electrode and the pump electrode outside the cavity when hydrogen and carbon monoxide are oxidized; and a carbon dioxide concentration determining means for determining the concentration of carbon dioxide contained in the measurement gas based on the value of the selective oxidation current and the values ​​of both oxidation currents, which are oxygen pump currents that flow between the second measurement electrode and the pump electrode outside the cavity when hydrogen and carbon monoxide near the second measurement electrode are oxidized by the second measurement pump cell pumping in oxygen.

[0011] A second aspect of the present invention is a gas sensor according to the first aspect, characterized in that the internal chambers are a first chamber, a second chamber, and a third chamber, which are connected in sequence in order of proximity to the gas inlet via different diffusion-controlling sections, the first adjusting electrode is provided in the first chamber, the second adjusting electrode is provided in the second chamber, and the first measuring electrode and the second measuring electrode are provided in the third chamber.

[0012] A third aspect of the present invention is the gas sensor according to the second aspect, characterized in that the water vapor concentration determining means determines the concentration of water vapor contained in the measurement gas based on a proportional relationship between the selective oxidation current and the concentration of water vapor contained in the measurement gas, which is determined in advance, and the carbon dioxide concentration determining means determines the concentration of carbon dioxide contained in the measurement gas based on a proportional relationship between a difference value obtained by subtracting the selective oxidation current from both the oxidation currents, which is determined in advance, and the concentration of carbon dioxide contained in the measurement gas, which is determined in advance.

[0013] A fourth aspect of the present invention is the gas sensor according to the second or third aspect, characterized in that the Au concentration in the Pt—Au alloy is 1 wt % or more and 50 wt % or less.

[0014] A fifth aspect of the present invention is the gas sensor according to the fourth aspect, characterized in that the first adjusting electrode and the second adjusting electrode are cermet electrodes containing Pt but not Au.

[0015] A sixth aspect of the present invention is a gas sensor according to any one of the second to fifth aspects, characterized in that the controller further comprises an oxygen concentration determination means for determining the concentration of oxygen contained in the measured gas based on the magnitude of the current flowing between the first adjusting electrode and the outer-chamber pump electrode when oxygen is pumped out of the first chamber by the first adjusting pump cell.

[0016] A seventh aspect of the present invention is a gas sensor according to any one of the second to sixth aspects, characterized in that the first measurement electrode and the second measurement electrode are arranged opposite each other on a pair of surfaces along the longitudinal direction of the sensor element that define the third chamber.

[0017] An eighth aspect of the present invention is a gas sensor according to any one of the second to sixth aspects, characterized in that the first measurement electrode and the second measurement electrode are arranged in parallel on a surface of the sensor element along the longitudinal direction, which defines the third chamber, so as to be spaced apart from each other in a direction perpendicular to the longitudinal direction.

[0018] A ninth aspect of the present invention is a method for measuring concentrations of a plurality of target gas components contained in a measurement gas containing at least water vapor and carbon dioxide by using a gas sensor, the gas sensor comprising: a sensor element having a long plate-like structure made of an oxygen ion conductive solid electrolyte; and the sensor element comprising: a gas inlet through which the measurement gas is introduced; an internal chamber communicating with the gas inlet via a diffusion-controlling part; and first adjusting electrodes disposed in order from closest to the gas inlet so as to face the internal chamber and spaced apart by a predetermined interval. a second adjusting electrode, and a set of a first measuring electrode and a second measuring electrode provided at equivalent positions relative to the flow of the measurement gas flowing into the internal chamber; a first adjusting pump cell including the first adjusting electrode, an outside-void pump electrode provided at a location other than the internal chamber, and the solid electrolyte present between the first adjusting electrode and the outside-void pump electrode; a second adjusting pump cell including the second adjusting electrode, the outside-void pump electrode, and the solid electrolyte present between the second adjusting electrode and the outside-void pump electrode; a first measurement pump cell including a pump electrode and the solid electrolyte present between the first measurement electrode and the pump electrode outside the cavity; a second measurement pump cell including the second measurement electrode, the pump electrode outside the cavity, and the solid electrolyte present between the second measurement electrode and the pump electrode outside the cavity; and a heater for heating the sensor element, wherein the first measurement electrode is a cermet electrode containing a Pt—Au alloy as a metal component, and a) the heater is configured to heat the first adjustment electrode in the internal cavity such that the temperature is highest in the vicinity of the first adjustment electrode and the temperature is highest in the longitudinal direction of the sensor element. a) heating the sensor element so that the temperature decreases with increasing distance from the first adjusting electrode; b) pumping oxygen from the measurement gas that has reached the first adjusting electrode through the gas inlet by the first adjusting pump cell to an extent that water vapor and carbon dioxide contained in the measurement gas are not decomposed; and c) pumping oxygen from the measurement gas that has reached the second adjusting electrode by the second adjusting pump cell so that substantially all water vapor and carbon dioxide contained in the measurement gas from which oxygen has been pumped by the first adjusting pump cell are reduced.d) pumping oxygen into the internal chamber by the first measurement pump cell, thereby selectively oxidizing hydrogen produced by reduction of water vapor contained in the measurement gas that has reached the first measurement electrode, in the vicinity of the first measurement electrode; e) pumping oxygen into the internal chamber by the second measurement pump cell, thereby oxidizing hydrogen and carbon monoxide produced by reduction of water vapor and carbon dioxide contained in the measurement gas that has reached the second measurement electrode, in the vicinity of the second measurement electrode; and f) pumping oxygen into the first measurement pump cell, thereby selectively oxidizing hydrogen and carbon monoxide produced by reduction of water vapor and carbon dioxide contained in the measurement gas that has reached the second measurement electrode, in the vicinity of the second measurement electrode. g) determining the concentration of water vapor contained in the measurement gas based on the value of a selective oxidation current, which is an oxygen pump current that flows between the first measurement electrode and the pump electrode outside the cavity when hydrogen near the first measurement electrode is selectively oxidized; and g) determining the concentration of carbon dioxide contained in the measurement gas based on the value of the selective oxidation current and the value of both oxidation currents, which are oxygen pump currents that flow between the second measurement electrode and the pump electrode outside the cavity when hydrogen and carbon monoxide near the second measurement electrode are oxidized by the second measurement pump cell pumping in oxygen.

[0019] A tenth aspect of the present invention is a concentration measurement method using a gas sensor according to the ninth aspect, characterized in that the internal chambers are a first chamber, a second chamber, and a third chamber, which are connected in sequence in order of proximity to the gas inlet via different diffusion-controlling sections, the first adjusting electrode is provided in the first chamber, the second adjusting electrode is provided in the second chamber, and the first measurement electrode and the second measurement electrode are provided in the third chamber.

[0020] An eleventh aspect of the present invention is a concentration measurement method using the gas sensor according to the tenth aspect, characterized in that in step f), the concentration of water vapor contained in the measurement gas is determined based on a predetermined proportional relationship between the selective oxidation current and the concentration of water vapor contained in the measurement gas, and in step g), the concentration of carbon dioxide contained in the measurement gas is determined based on a predetermined proportional relationship between a difference value obtained by subtracting the selective oxidation current from both the oxidation currents and the concentration of carbon dioxide contained in the measurement gas.

[0021] A twelfth aspect of the present invention is a concentration measurement method using a gas sensor according to the tenth or eleventh aspect, characterized in that the Au concentration in the Pt—Au alloy is 1 wt % or more and 50 wt % or less.

[0022] A thirteenth aspect of the present invention is a concentration measurement method using a gas sensor according to the twelfth aspect, characterized in that the first adjusting electrode and the second adjusting electrode are cermet electrodes containing Pt but not Au.

[0023] A fourteenth aspect of the present invention is a concentration measurement method using a gas sensor according to any one of the tenth to thirteenth aspects, characterized in that it further comprises the step of: h) determining the concentration of oxygen contained in the measurement gas based on the magnitude of the current flowing between the first adjusting electrode and the outer-chamber pump electrode when oxygen is pumped out of the first chamber by the first adjusting pump cell.

[0024] A fifteenth aspect of the present invention is a concentration measurement method using a gas sensor according to any one of the tenth to fourteenth aspects, characterized in that the first measurement electrode and the second measurement electrode are arranged opposite each other on a pair of surfaces of the sensor element along the longitudinal direction that define the third chamber.

[0025] A sixteenth aspect of the present invention is a concentration measurement method using a gas sensor according to any one of the tenth to fourteenth aspects, characterized in that the first measurement electrode and the second measurement electrode are arranged in parallel on a surface of the sensor element along the longitudinal direction, which defines the third chamber, so as to be spaced apart from each other in a direction perpendicular to the longitudinal direction.

[0026] According to the first to sixteenth aspects of the present invention, the occurrence of cracks and blackening in the sensor element is suppressed, and the evaporation of Au from the electrodes is also suppressed, thereby realizing a multi-gas sensor with better long-term reliability than conventional ones.

[0027] 1 is a diagram schematically illustrating an example of the configuration of a gas sensor 100. FIG. 2 is a block diagram illustrating functional components implemented in a controller 110. FIG. 3 is a schematic diagram illustrating gas flow in and out of three chambers in a sensor element 101 of the gas sensor 100. FIG. 4 is a graph illustrating the relationship between the target value of the electromotive force V0 in the first chamber sensor cell 80 and the oxygen pump current Ip0 flowing through the first adjustment pump cell 21 when three different types of model gas are flowed. FIG. 5 is a diagram illustrating the planar arrangement of a first measurement electrode 44a and a second measurement electrode 44b in a sensor element 101A. FIG. 6 is a diagram illustrating the planar arrangement of a first measurement electrode 44a and a second measurement electrode 44b in a sensor element 101B. FIG. 7 is a diagram illustrating the planar arrangement of a first measurement electrode 44a and a second measurement electrode 44b in a sensor element 101C. FIG. 8 is a diagram schematically illustrating an example of the configuration of a gas sensor 200 according to a modified example.

[0028] <Configuration of Gas Sensor> FIG. 1 is a diagram showing an example of the configuration of a gas sensor 100 according to this embodiment. The gas sensor 100 is a multi-gas sensor that detects multiple types of gas components using a sensor element 101 and measures their concentrations. In this embodiment, at least water vapor (H ２ O) and carbon dioxide (CO ２) are the main gas components to be detected by the gas sensor 100. The gas sensor 100 is attached to an exhaust path of an internal combustion engine such as an automobile engine, and is used in a manner in which the exhaust gas flowing through the exhaust path is used as the measurement gas. FIG. 1 includes a vertical cross-sectional view of the sensor element 101 along the longitudinal direction.

[0029] The sensor element 101 includes a long, plate-shaped structure (base portion) 14 made of an oxygen-ion conductive solid electrolyte, a first diffusion-controlling portion 11 formed at one end (the left end in the drawing) of the structure 14 and serving as a gas inlet 10 through which a gas to be measured is introduced, and a buffer space 12, a first chamber 20, a second chamber 40, and a third chamber 61 formed within the structure 14 and sequentially communicating with the gas inlet 10 (first diffusion-controlling portion 11). The buffer space 12 communicates with the gas inlet 10 (first diffusion-controlling portion 11). The first chamber 20 communicates with the buffer space 12 via the second diffusion-controlling portion 13. The second chamber 40 communicates with the first chamber 20 via the third diffusion-controlling portion 30. The third chamber 61 communicates with the second chamber 40 via the fourth diffusion-controlling portion 60.

[0030] The structure 14 is formed by stacking multiple layers of substrates made of, for example, ceramics. Specifically, the structure 14 has a configuration in which six layers, consisting of a first substrate 1, a second substrate 2, a third substrate 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, are stacked in this order from the bottom up. Each layer is made of, for example, zirconia (ZrO ２ The solid electrolyte is oxygen ion conductive.

[0031] The first diffusion-controlling section 11, which also serves as the gas inlet 10, the buffer space 12, the second diffusion-controlling section 13, the first chamber 20, the third diffusion-controlling section 30, the second chamber 40, the fourth diffusion-controlling section 60, and the third chamber 61 are formed in this order at one end of the structure 14, between the lower surface 6 b of the second solid electrolyte layer 6 and the upper surface 4 a of the first solid electrolyte layer 4. The portion from the gas inlet 10 to the third chamber 61 is also referred to as a gas flow section.

[0032] The buffer space 12, the first cavity 20, the second cavity 40, and the third cavity 61 are formed so as to penetrate the spacer layer 5 in the thickness direction. The lower surface 6b of the second solid electrolyte layer 6 is exposed at the top of each cavity, and the upper surface 4a of the first solid electrolyte layer 4 is exposed at the bottom. The sides of each cavity are defined by the spacer layer 5 or any of the diffusion-controlling portions. The first cavity 20, the second cavity 40, and the third cavity 61 each have a length (size in the longitudinal direction of the element) of, for example, 0.3 mm to 1.0 mm, a width (size in the lateral direction of the element) of, for example, 0.5 mm to 30 mm, and a height (size in the thickness direction of the element) of, for example, 50 μm to 200 μm. However, the sizes of the individual cavities do not need to be the same and may be different.

[0033] Similarly, the gas inlet 10 may be formed so as to penetrate the spacer layer 5 in the thickness direction, separately from the first diffusion rate-controlling part 11. In this case, the first diffusion rate-controlling part 11 is formed adjacent to and inside the gas inlet 10.

[0034] Each of the first diffusion-controlling section 11, the second diffusion-controlling section 13, the third diffusion-controlling section 30, and the fourth diffusion-controlling section 60 has two horizontally elongated slits. That is, each has an opening extending vertically in the direction perpendicular to the plane of the drawing at the top and bottom. The length of the slit (the size in the longitudinal direction of the element) is, for example, 0.2 mm to 1.0 mm, the width of the opening (the size in the lateral direction of the element) is, for example, 0.5 mm to 30 mm, and the height of the opening (the size in the thickness direction of the element) is, for example, 5 μm to 30 μm.

[0035] A reference gas introduction space 43 is provided at the other end (right end in the drawing) of the sensor element 101 opposite to the one end where the gas introduction port 10 is provided. The reference gas introduction space 43 is formed between the upper surface 3a of the third substrate 3 and the lower surface 5b of the spacer layer 5. The sides of the reference gas introduction space 43 are partitioned by the side surfaces of the first solid electrolyte layer 4. The reference gas introduction space 43 is filled with, for example, oxygen (O ２ ) and air are introduced.

[0036] The gas inlet 10 (first diffusion-controlling section 11) is a section that opens to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas inlet 10.

[0037] The first diffusion rate-controlling part 11 is a part that applies a predetermined diffusion resistance to the taken-in measurement gas.

[0038] The buffer space 12 is provided to cancel out fluctuations in the concentration of the measurement gas caused by pressure fluctuations of the measurement gas in the external space, such as pulsations in the exhaust gas pressure of an automobile.

[0039] The second diffusion rate-controlling part 13 is a part that imparts a predetermined diffusion resistance to the measurement gas introduced from the buffer space 12 into the first chamber 20 .

[0040] The first chamber 20 is provided as a space for pumping out oxygen from the measurement gas introduced through the second diffusion-controlling part 13. The pumping out of oxygen is achieved by the operation of the first adjustment pump cell 21.

[0041] The first adjusting pump cell 21 is an electrochemical pump cell composed of a first inner pump electrode (first adjusting electrode) 22, an outer pump electrode (outside the cavity pump electrode) 23, and a solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes.

[0042] In the first adjustment pump cell 21, a voltage Vp0 is applied between the first inner pump electrode 22 and the outer pump electrode 23 by a variable power supply 24 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip0. This makes it possible to pump oxygen from the first chamber 20 to the external space. In this embodiment, the direction of the oxygen pump current Ip0 when oxygen is pumped from the first chamber 20 is defined as the positive direction of the oxygen pump current Ip0.

[0043] The first inner pump electrode 22 is provided as a ceiling electrode portion 22a and a bottom electrode portion 22b on substantially the entire surface of the lower surface 6b of the second solid electrolyte layer 6 and substantially the entire surface of the upper surface 4a of the first solid electrolyte layer 4, which define the first chamber 20. The ceiling electrode portion 22a and the bottom electrode portion 22b are connected by a conductive portion (not shown).

[0044] The first inner pump electrode 22 is provided as a porous cermet electrode having a rectangular shape in plan view, and containing at least one of platinum and rhodium (Rh) as a metal component.

[0045] The outer pump electrode 23 is provided as a porous cermet electrode having a rectangular shape in plan view, for example, containing platinum or an alloy of platinum and gold (Pt—Au alloy) as a metal component, and including platinum or a Pt—Au alloy and zirconia.

[0046] In the sensor element 101, the first inner pump electrode 22, the reference electrode 42, and the solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes form a first chamber sensor cell 80. The first chamber sensor cell 80 is an electrochemical sensor cell for detecting the oxygen partial pressure in the atmosphere in the first chamber 20.

[0047] The reference electrode 42 is an electrode formed between the first solid electrolyte layer 4 and the third substrate 3, and is provided, for example, as a porous cermet electrode containing platinum and zirconia and having a rectangular shape in plan view.

[0048] A reference gas introduction layer 48 made of porous alumina and connected to the reference gas introduction space 43 is provided around the reference electrode 42. The reference gas in the reference gas introduction space 43 is introduced onto the surface of the reference electrode 42 through the reference gas introduction layer 48. In other words, the reference electrode 42 is always in contact with the reference gas.

[0049] In the first chamber sensor cell 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 has a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the first chamber 20 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, since the oxygen concentration (oxygen partial pressure) of the reference gas is basically constant, the electromotive force V0 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the first chamber 20.

[0050] The third diffusion-controlling section 30 controls the H ２ O and CO ２ This is a portion that provides a predetermined diffusion resistance to the measurement gas that contains oxygen and is substantially free of oxygen.

[0051] The second chamber 40 contains H contained as a detection target gas component in the measurement gas introduced through the third diffusion-controlling section 30. ２ O and CO ２ is reduced (decomposed) to hydrogen (H ２ ) and carbon monoxide (CO), and the measurement gas contains not only oxygen but also H ２ O, CO ２ The space is provided so that the H ２ O and CO ２ The reduction (decomposition) of is realized by the operation of the second adjusting pump cell 50.

[0052] The second regulating pump cell 50 is an electrochemical pump cell composed of a second inner pump electrode (second regulating electrode) 51, an outer pump electrode 23, and a solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes.

[0053] In the second adjusting pump cell 50, a voltage Vp1 is applied between the second inner pump electrode 51 and the outer pump electrode 23 by a variable power supply 52 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip1. ２ O and CO ２It is possible to pump out oxygen generated in the second chamber 40 by the reduction of O 3 into the external space. In this embodiment, the direction of the oxygen pump current Ip1 when oxygen is pumped out of the second chamber 40 is set to the positive direction of the oxygen pump current Ip1.

[0054] The second inner pump electrode 51 is provided as a ceiling electrode portion 51a and a bottom electrode portion 51b on substantially the entire surface of the lower surface 6b of the second solid electrolyte layer 6 that defines the second chamber 40 and substantially the entire surface of the upper surface 4a of the first solid electrolyte layer 4. The ceiling electrode portion 51a and the bottom electrode portion 51b are connected by a conductive portion (not shown).

[0055] The second inner pump electrode 51 is provided as a porous cermet electrode having a rectangular shape in plan view and containing Pt as a metal component.

[0056] In the sensor element 101, a second chamber sensor cell 81 is configured by the second inner pump electrode 51, the reference electrode 42, and a solid electrolyte present in a portion of the structure 14 sandwiched between the two electrodes. The second chamber sensor cell 81 is an electrochemical sensor cell for detecting the oxygen partial pressure in the atmosphere in the second chamber 40.

[0057] In the second chamber sensor cell 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 has a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the second chamber 40 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, since the oxygen concentration (oxygen partial pressure) of the reference gas is basically constant, the electromotive force V1 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the second chamber 40.

[0058] The fourth diffusion-controlling section 60 controls the H ２ and CO, while H ２ O, CO ２ and a portion that provides a predetermined diffusion resistance to the measurement gas that is substantially free of oxygen.

[0059] The third chamber 61 contains H contained in the measurement gas introduced through the fourth diffusion-controlling section 60. ２ and CO are all oxidized to H２ O and CO ２ These H ２ and H from the oxidation of CO ２ O and CO ２ The generation of is realized by the operation of the first measuring pump cell 41a and the second measuring pump cell 41b.

[0060] The first measurement pump cell 41a is an electrochemical pump cell that is configured by a first measurement electrode 44a, an outer pump electrode 23, and a solid electrolyte that is present in the portion of the structure 14 that is sandwiched between the two electrodes.

[0061] In the first measurement pump cell 41a, an oxygen pump current (oxygen ion current) Ip2 is generated by applying a voltage Vp2 between the first measurement electrode 44a and the outer pump electrode 23 from a variable power supply 47a provided outside the sensor element 101. This makes it possible to pump oxygen into the third chamber 61 from the external space.

[0062] On the other hand, the second measurement pump cell 41b is an electrochemical pump cell that is configured by a second measurement electrode 44b, an outer pump electrode 23, and a solid electrolyte that is present in the portion of the structure 14 that is sandwiched between the two electrodes.

[0063] In the second measurement pump cell 41b, an oxygen pump current (oxygen ion current) Ip3 is generated by applying a voltage Vp3 between the second measurement electrode 44b and the outer pump electrode 23 from a variable power supply 47b provided outside the sensor element 101. This makes it possible to pump oxygen into the third chamber 61 from the external space.

[0064] In this embodiment, the directions of the oxygen pump current Ip2 and the oxygen pump current Ip3 when oxygen is pumped out of the third chamber 61 are set to be positive directions of the oxygen pump current Ip2 and the oxygen pump current Ip3, respectively.

[0065] The first measurement electrode 44a and the second measurement electrode 44b are provided at equivalent positions relative to the flow of the measurement gas flowing into the third chamber 61 through the fourth diffusion-controlling part 60. In Fig. 1, the first measurement electrode 44a is provided over substantially the entire surface of the lower surface 6b of the second solid electrolyte layer 6 that defines the third chamber 61, and the second measurement electrode 44b is provided over substantially the entire surface of the upper surface 4a of the first solid electrolyte layer 4 that also defines the third chamber 61, but the arrangement of the electrodes is not limited to this.

[0066] The first measurement electrode 44a is provided as a porous cermet electrode that contains a Pt—Au alloy as a metal component, for example, the Pt—Au alloy and zirconia, and has a rectangular shape in plan view. ２ Even when CO coexists, H ２ Only Pt is selectively oxidized, and CO is not oxidized. The Au concentration in the Pt-Au alloy is preferably 1 wt % or more and 50 wt % or less, and more preferably 30 wt % or more and 50 wt % or less. In this case, H at the first measuring electrode 44a ２ Selective oxidation of H in the third chamber 61 ２ When CO coexists, H ２ Only HCl is selectively oxidized by the oxygen pumped in by the first measuring pump cell 41a, and CO is not oxidized, which is more preferably exhibited.

[0067] On the other hand, the second measurement electrode 44b is provided as a porous cermet electrode having a rectangular shape in a plan view and containing Pt as a metal component. ２ When CO coexists, H ２ and CO are both oxidized.

[0068] In the sensor element 101, a first measurement sensor cell 82a is formed by the first measurement electrode 44a, the reference electrode 42, and a solid electrolyte present in a portion of the structure 14 sandwiched between the first and second electrodes. The first measurement sensor cell 82a is an electrochemical sensor cell for detecting the oxygen partial pressure in the atmosphere in the vicinity of the first measurement electrode 44a in the third chamber 61.

[0069] In the first measurement sensor cell 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 has a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the vicinity of the first measurement electrode 44a in the third chamber 61 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, since the oxygen concentration (oxygen partial pressure) of the reference gas is basically constant, the electromotive force V2 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the vicinity of the first measurement electrode 44a.

[0070] Furthermore, in the sensor element 101, a second measurement sensor cell 82b is configured by the second measurement electrode 44b, the reference electrode 42, and the solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes. The second measurement sensor cell 82b is an electrochemical sensor cell for determining the oxygen partial pressure in the atmosphere near the second measurement electrode 44b in the third chamber 61.

[0071] In the second measurement sensor cell 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 has a value corresponding to the difference between the oxygen concentration (oxygen partial pressure) in the vicinity of the second measurement electrode 44b in the third chamber 61 and the oxygen concentration (oxygen partial pressure) of the reference gas. However, since the oxygen concentration (oxygen partial pressure) of the reference gas is basically constant, the electromotive force V3 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the vicinity of the second measurement electrode 44b.

[0072] The sensor element 101 further includes an electrochemical sensor cell 83 that is composed of an outer pump electrode 23, a reference electrode 42, and a solid electrolyte that is present in the portion of the structure 14 that is sandwiched between the two electrodes. The electromotive force Vref generated between the outer pump electrode 23 and the reference electrode 42 in the sensor cell 83 has a value that corresponds to the oxygen partial pressure of the measurement gas that is present outside the sensor element 101.

[0073] In addition to the above, the sensor element 101 is provided with a heater portion 70 that serves to adjust the temperature by heating and keeping the sensor element 101 warm in order to increase the oxygen ion conductivity of the solid electrolyte that constitutes the structure 14.

[0074] The heater section 70 mainly includes a heater electrode 71, a heater element 72, a heater lead 72a, a through hole 73, a heater insulating layer 74, and a heater resistance detection lead (not shown in Fig. 1). Hereinafter, the heater element 72 will also be simply referred to as the heater 72.

[0075] The heater 72 is sandwiched between the second substrate 2 and the third substrate 3, and generates heat when power is supplied from the outside through a heater electrode 71, a through hole 73, and a heater lead 72a provided on the underside 1b of the first substrate 1. The heater 72 is embedded throughout the entire range from the buffer space 12 to the third chamber 61, and is capable of heating the sensor element 101 to a predetermined temperature and maintaining the temperature.

[0076] The heater 72 is provided so that, when heated, the temperature is highest near the first chamber 20 (near the first adjusting electrode 22) and decreases with increasing distance from the first chamber 20 in the element longitudinal direction. In this embodiment, the temperature in the range from one end of the sensor element 101, where the gas inlet 10 is provided, to the third chamber 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 so that the element driving temperature is within the range of 750°C to 950°C.

[0077] Heater insulating layers 74 made of alumina or the like are formed above and below the heater 72 in order to provide electrical insulation between the heater 72 and the second substrate 2 and the third substrate 3. The heater section 70 also has a pressure release hole 75. The pressure release hole 75 is a portion that penetrates the third substrate 3 and is provided so as to communicate with the reference gas introduction space 43, and is provided for the purpose of alleviating an increase in internal pressure that accompanies a temperature rise within the heater insulating layer 74.

[0078] The gas sensor 100 also includes a controller 110 that controls the operation of the sensor element 101 and determines the concentration of the target gas component based on the current flowing through the sensor element 101 .

[0079] 2 is a block diagram showing functional components implemented in the controller 110. The controller 110 is configured with one or more electronic circuits having, for example, one or more central processing units (CPUs) and a storage device. The electronic circuit is also a software function unit in which predetermined functional components are implemented by the CPU executing a predetermined program stored in the storage device. Of course, the controller 110 may also be configured with an integrated circuit such as an FPGA (Field-Programmable Gate Array) in which multiple electronic circuits are connected according to their functions.

[0080] In addition, when the gas sensor 100 is attached to the exhaust path of an automobile engine and the exhaust gas flowing through the exhaust path is used as the measured gas, some or all of the functions of the controller 110 may be realized by the automobile's ECU (electronic control unit).

[0081] The controller 110 has, as functional components realized by the execution of a predetermined program in the CPU, an element operation control unit 120 that controls the operation of each part of the above-mentioned sensor element 101, and a concentration determination unit 130 that is responsible for the process of determining the concentration of the target gas component contained in the measured gas.

[0082] The element operation control unit 120 mainly includes a first adjustment pump cell control unit 121a that controls the operation of the first adjustment pump cell 21, a second adjustment pump cell control unit 121b that controls the operation of the second adjustment pump cell 50, a first measurement pump cell control unit 122a that controls the operation of the first measurement pump cell 41a, a second measurement pump cell control unit 122b that controls the operation of the second measurement pump cell 41b, and a heater control unit 123 that controls the heating operation by the heater 72.

[0083] On the other hand, the concentration specifying unit 130 detects H, which is the main gas component to be detected in the gas sensor 100. ２ O and CO ２ The air conditioning system 100 mainly includes a water vapor concentration specifying unit 130H and a carbon dioxide concentration specifying unit 130C that specify the concentrations of water vapor and carbon dioxide, respectively.

[0084] The water vapor concentration specifying unit 130H determines the water vapor concentration of the H contained in the measurement gas based on the value of the oxygen pump current Ip2 flowing through the first measurement pump cell 41a, which is acquired by the first measurement pump cell control unit 122a. ２ The concentration of O is determined.

[0085] The carbon dioxide concentration specifying unit 130C determines the CO 2 concentration contained in the measurement gas based on the value of the oxygen pump current Ip2 flowing through the first measurement pump cell 41a, which is acquired by the first measurement pump cell control unit 122a, and the value of the oxygen pump current Ip3 flowing through the second measurement pump cell 41b, which is acquired by the second measurement pump cell control unit 122b. ２ Identify the concentration of.

[0086] The concentration specifying unit 130 further includes an oxygen concentration specifying unit 130A that specifies the concentration of oxygen contained in the measurement gas. The oxygen concentration specifying unit 130A specifies the concentration of oxygen contained in the measurement gas based on the value of the oxygen pump current Ip0 flowing through the first adjustment pump cell 21, which is acquired by the first adjustment pump cell control unit 121a. That is, in the gas sensor 100 according to this embodiment, H, which is the main gas component to be detected, is detected. ２ O and CO ２ In addition, oxygen is also detected as an additional target gas component.

[0087] <Multi-gas detection and concentration determination> Next, a method for detecting multiple gas species (multi-gas detection) and determining the concentration of the detected gases, which are realized by the gas sensor 100 having the above-described configuration, will be described. ２ O, and CO ２ The exhaust gas contains

[0088] FIG. 3 is a schematic diagram showing how gas flows in and out of three chambers (internal spaces) in the sensor element 101 of the gas sensor 100. As shown in FIG.

[0089] First, in the sensor element 101 included in the gas sensor 100 according to this embodiment, as described above, the measurement gas is introduced into the first chamber 20 through the gas inlet 10 (first diffusion-controlling part 11), the buffer space 12, and the second diffusion-controlling part 13. In the first chamber 20, the first adjusting pump cell 21 is activated to pump oxygen out of the introduced measurement gas.

[0090] The pumping of oxygen is achieved by the first adjusting pump cell control unit 121a of the controller 110 setting a target value (control voltage) of the electromotive force V0 in the first chamber sensor cell 80 to a value within a range of 400 mV to 700 mV (preferably 400 mV), and then feedback-controlling the voltage Vp0 applied to the first adjusting pump cell 21 by the variable power supply 24 in accordance with the difference between the actual value of the electromotive force V0 and the target value so that the electromotive force V0 is maintained at the target value. For example, when a measurement gas containing a large amount of oxygen reaches the first chamber 20, the value of the electromotive force V0 deviates significantly from the target value. Therefore, the first adjusting pump cell control unit 121a controls the pump voltage Vp0 applied to the first adjusting pump cell 21 by the variable power supply 24 so as to reduce this deviation.

[0091] By pumping oxygen out of the first chamber 20 by the first adjusting pump cell 21 in this manner, the oxygen partial pressure in the first chamber 20 becomes equal to the H ２ O and CO ２ For example, when V0 = 400 mV, the －８ It will be about atm.

[0092] FIG. 4 shows that the target value of the electromotive force V0 is set to a value within the range of 400 mV to 700 mV. ２ O and CO ２ 4 is a graph showing the relationship between the target value (control voltage) of the electromotive force V0 in the first vacant chamber sensor cell 80 and the oxygen pump current Ip0 flowing through the first adjustment pump cell 21 when three different types of model gases are flowed. The three types of model gases are specifically a first gas containing 10% oxygen, a second gas containing 10% oxygen, and a second gas containing 10% oxygen and CO. ２ a second gas containing 10% each of oxygen and H ２ The third gas contains 10% of each of nitrogen (N ２ The element operating temperature was set to 800°C, and the model gas temperature was set to 150°C.

[0093] 4, it can be seen that in the case of the first gas, the oxygen pump current Ip0 is substantially constant in the range of the control voltage of 0.4 V or more, whereas in the case of the second and third gases, the oxygen pump current Ip0 has substantially the same profile as the first gas in the range of the control voltage of 0.7 V or less, but when the control voltage exceeds 0.7 V, it is confirmed that the oxygen pump current Ip0 increases again. This increase is due to the H contained in the measurement gas. ２ O or CO ２ is reduced (decomposed) to generate oxygen, which causes the ２ O or CO ２ This is caused by the superposition of the reduction currents.

[0094] In light of this, in this embodiment, the target value of the electromotive force V0 is set to a value within the range of 400 mV to 700 mV. From the viewpoint of ensuring the durability of the electrode, it is preferable to make the electromotive force V0 as low as possible, and therefore it is determined that the target value of the electromotive force V0 is preferably set to 400 mV.

[0095] As described above, in the gas sensor 100 according to the present embodiment, unlike the gas sensor of the prior art, the first chamber 20, which is the highest temperature in the sensor element 101 during operation, is heated by H ２O and CO ２ Only oxygen is pumped out to the extent that it does not reduce H ２ O and CO ２ The target value of the electromotive force V0 in the first empty chamber sensor cell 80, which is set for such pumping, is 400 mV to 700 mV, and H ２ O and CO ２ This is sufficiently smaller than the target value of 1000 mV to 1500 mV set when reducing H ２ O and CO ２ The increase in the pump voltage Vp0 is suppressed compared to the voltage applied to the corresponding pump cell of a conventional gas sensor, which involves the reduction of the first inner pump electrode 22. As a result, in the gas sensor 100 according to this embodiment, the occurrence of cracks and blackening, which would otherwise occur if a high voltage were applied while the first inner pump electrode 22 is maintained at a high temperature, is suitably suppressed.

[0096] In the first chamber 20, H ２ O and CO ２ The measurement gas from which only oxygen has been pumped out to the extent that H is not reduced is introduced into the second chamber 40. In the second chamber 40, H contained in the measurement gas is ２ O and CO ２ That is, the second adjusting pump cell 50 is operated, oxygen is pumped out from the first chamber 20, and then further oxygen is pumped out from the measurement gas introduced into the second chamber 40, thereby reducing the H contained in the measurement gas. ２ O and CO ２ Reduction (decomposition) reaction of (2H ２ O → 2H ２ +O ２ , 2CO ２ →2CO+O ２ ) progresses, and H ２ O and CO ２ is substantially entirely hydrogen (H ２ ) and carbon monoxide (CO) and oxygen.

[0097] Related H ２ O and CO ２The reduction (decomposition) of and the pumping of the resulting oxygen are achieved by the second adjustment pump cell control section 121b of the controller 110 setting the target value (control voltage) of the electromotive force V1 in the second vacant chamber sensor cell 81 to a value within the range of 1000 mV to 1500 mV (preferably 1000 mV), and feedback-controlling the voltage Vp1 applied to the second adjustment pump cell 50 by the variable power supply 52 in accordance with the difference between the actual value of the electromotive force V1 and the target value so that the electromotive force V1 is maintained at the target value. The graph shown in FIG. 4 also suggests that the target value of the electromotive force V1 should preferably be within the range of 1000 mV to 1500 mV.

[0098] By operating the second adjusting pump cell 50 in this manner, the oxygen partial pressure in the second chamber 40 is maintained at a value lower than the oxygen partial pressure in the first chamber 20. For example, when V1=1000 mV, －２０ As a result, the gas to be measured becomes H ２ O, CO ２ , and becomes substantially free of oxygen.

[0099] H ２ and CO, while H ２ O, CO ２ , and the measurement gas substantially free of oxygen is introduced into the third chamber 61 .

[0100] In the third chamber 61, oxygen is pumped in by the operation of the first measuring pump cell 41a and the second measuring pump cell 41b.

[0101] The pumping of oxygen by the first measurement pump cell 41a is carried out by the first measurement pump cell control unit 122a of the controller 110 setting the target value (control voltage) of the electromotive force V2 in the first measurement sensor cell 82a to a value within the range of 250 mV to 450 mV (preferably 350 mV), and feedback-controlling the voltage Vp2 applied to the first measurement pump cell 41a by the variable power supply 47a in accordance with the difference between the actual value of the electromotive force V2 and the target value so that the electromotive force V2 is maintained at the target value.

[0102] By operating the first measurement pump cell 41a in this manner, a current of 2H is generated in the vicinity of the first measurement electrode 44a in the third chamber 61. ２ +O ２ →2H ２ O oxidation (combustion) reaction is promoted.

[0103] The target value of the electromotive force V2 is set to a value within the range of 250 mV to 450 mV in order to prevent the H ２ This is to selectively oxidize only HCl and prevent CO from being oxidized.

[0104] Thereafter, H generated by pumping oxygen by the first measuring pump cell 41a ２ The amount of O is ２ It is also referred to as the O amount.

[0105] As described above, the first measuring electrode 44a may be provided as a cermet electrode containing a Pt-Au alloy with an Au concentration of 1 wt % or more and 50 wt % or less as a metal component. ２ This contributes to improving the selective oxidation of

[0106] In the conventional gas sensor, a cermet electrode containing a Pt—Au alloy is provided in the second chamber 40, and H ２ In the present invention, the second chamber 40 is provided with a second inner pump electrode 51 that does not contain Au as a metal component, and the second inner pump electrode 51 also contains a Pt-Au alloy as a metal component and is used to selectively oxidize H ２ The first measurement electrode 44a, which is responsible for the selective oxidation of Au, is provided facing the third chamber 61, the temperature of which during operation of the gas sensor 100 is lower than that of the second chamber 40. As a result, in the gas sensor 100 according to this embodiment, evaporation of Au from the electrode is suppressed compared to gas sensors of the prior art.

[0107] In addition, the shape (width, thickness) and arrangement (denseness) of the heater 72 may be devised to further suppress the temperature rise of the first measurement electrode 44a.

[0108] On the other hand, the pumping of oxygen by the second measurement pump cell 41b is carried out by the second measurement pump cell control unit 122b of the controller 110 setting the target value (control voltage) of the electromotive force V3 in the second measurement sensor cell 82b to a value within the range of 100 mV to 300 mV (preferably 200 mV), and feedback-controlling the voltage Vp3 applied to the second measurement pump cell 41b by the variable power supply 47b in accordance with the difference between the actual value of the electromotive force V3 and the target value so that the electromotive force V3 is maintained at the target value.

[0109] By operating the second measurement pump cell 41b in this manner, the following reaction mixture is produced in the vicinity of the second measurement electrode 44b in the third chamber 61: ２ →2CO ２ The oxidation (combustion) reaction ２ +O ２ →2H ２ O oxidation (combustion) reaction is promoted.

[0110] The former reaction causes the CO introduced from the gas inlet 10 to ２ Amount of CO correlated with the amount of ２ is generated again.

[0111] On the other hand, the H produced by the latter reaction ２ The amount of O (hereinafter referred to as the second H ２ The amount of H ２ This is because the first measuring electrode 44a and the second measuring electrode 44b are disposed at equivalent positions relative to the flow of the measurement gas in the third chamber 61, and the amount of H contained in the measurement gas introduced into the third chamber 61 is substantially equal to the amount of O. ２ is due to being oxidized at both electrodes with equal probability.

[0112] Also, the first H ２ O amount and second H ２ The total amount of O is calculated by adding the amount of H introduced from the gas inlet 10 ２ It has a correlation with the amount of O. ２ O or CO ２ The correlation between the amount of H introduced from the gas inlet 10 and the amount of H introduced from the gas inlet 10 is ２ O or CO ２and the amount of H produced by their decomposition ２ and H, which is regenerated by the oxidation of CO. ２ O or CO ２ The amount of the ion is the same as that of the ion or is within a certain tolerance range that is acceptable in terms of measurement accuracy.

[0113] In the gas sensor 100 according to the present embodiment, which operates in the above-described manner, H ２ The oxygen pump current Ip2 flows through the first measurement pump cell 41a, which is an oxygen pumping current for selectively oxidizing H ２ and the oxygen pump current Ip3 flowing through the second measuring pump cell 41b, which is a pumping current for oxygen to oxidize both H and CO. ２ O and CO ２ Hereinafter, the oxygen pump current Ip2 and the oxygen pump current Ip3 measured by the gas sensor 100 will also be referred to as the selective oxidation current Ip2 and the dual oxidation current Ip3, respectively.

[0114] Specifically, H in the measurement gas ２ O and CO ２ The concentrations of Ｈ , C Ｃ When these density values ​​C Ｈ , C Ｃ The following relationship is used between the selective oxidation current Ip2 and the dual oxidation current Ip3: １ , k ２ is the proportionality constant.

[0115] C Ｈ = k １ ・Ip2・・・(1)C Ｃ = k ２ (Ip3-Ip2) (2) Equation (1) is the selective oxidation current Ip2 and the first H ２ There is a proportional relationship between the amount of H and the amount of O. ２ O amount and second H ２ The amount of H in the measurement gas is substantially equal to the amount of O. ２O concentration value C Ｈ This is based on the fact that there is a proportional relationship between ½ of the selective oxidation current Ip2.

[0116] Furthermore, formula (2) is the first H ２ O amount and second H ２ The amount of H in both oxidation currents Ip3 is substantially equal to the amount of O. ２ The contribution of the oxygen pumped by the second measuring pumping cell 41b to the oxidation of CO can be considered to be equal to the selective oxidation current Ip2. Therefore, the difference Ip3-Ip2 corresponds to the contribution of the oxygen pumped by the second measuring pumping cell 41b to the oxidation of CO. Furthermore, the difference Ip3-Ip2 and the CO ２ This is based on the fact that there can be considered a proportional relationship between the concentration of

[0117] proportionality constant k １ , k ２ is determined in advance using a model gas with a known concentration prior to use of the gas sensor 100. １ The equation (1) including the above is stored in the water vapor concentration specifying unit 130H of the controller 110. ２ The formula (2) including the above formula is stored in the carbon dioxide concentration specifying unit 130C of the controller 110.

[0118] The selective oxidation current Ip2 and the dual oxidation current Ip3 are both values ​​that correspond to the diffusion resistance that is applied to the measurement gas from the gas inlet 10 of the sensor element 101 to the third chamber 61. Therefore, strictly speaking, the proportionality constant k １ , k ２ The proportionality constant k １ , k ２ is preferably specified for each individual gas sensor 100. However, if it is confirmed that the error is within the allowable range for gas sensors 100 manufactured under the same conditions and in the same lot, the proportionality constant k obtained for a specific gas sensor 100 can be used as the １ , k ２ The same gas sensor 100 may be applied to another gas sensor 100 in the same lot.

[0119] When the gas sensor 100 actually performs measurement, the measurement gas is introduced into the sensor element 101 heated to the element driving temperature, and the first adjusting pump cell 21, the second adjusting pump cell 50, the first measuring pump cell 41a, and the second measuring pump cell 41b operate in the manner described above. Then, the water vapor concentration specifying unit 130H obtains the selective oxidation current Ip2 from the first measuring pump cell control unit 122a and calculates H ２ Determine the O concentration.

[0120] The carbon dioxide concentration determining unit 130C also obtains the value of the selective oxidation current Ip2 from the first measuring pump cell control unit 122a and the value of the dual oxidation current Ip3 from the second measuring pump cell control unit 122b. ２ Identify the concentration.

[0121] In the gas sensor 100 according to the present embodiment, as described above, H in the measurement gas is ２ O concentration and CO ２ The concentration is specified.

[0122] Also, H ２ O concentration and CO ２ In parallel with the determination of the concentration, the oxygen concentration is also determined using the oxygen pump current Ip0 flowing through the first adjustment pump cell 21.

[0123] In the gas sensor 100 according to this embodiment, as described above, the first adjusting pump cell 21 is operated to pump oxygen from the measurement gas introduced from the gas inlet 10 into the first chamber 20. ２ O and CO ２ Although the oxygen pump current Ip0 (hereinafter also referred to as oxygen detection current Ip0) that flows during this process is approximately proportional to the concentration of oxygen contained in the measurement gas introduced from the gas inlet 10. In other words, a linear relationship is established between the oxygen detection current Ip0 and the oxygen concentration in the measurement gas. Data showing this linear relationship (Ip0-O ２ The oxygen concentration data is determined in advance using a model gas having a known oxygen concentration and stored in the controller 110.

[0124] When the gas sensor 100 actually performs measurement, the oxygen concentration specifying unit 130A obtains the value of the oxygen detection current Ip0 from the first adjustment pump cell control unit 121a. ２ The data is referenced to identify the oxygen concentration value corresponding to the acquired oxygen detection current Ip0, thereby identifying the oxygen concentration in the measurement gas.

[0125] As described above, in the gas sensor according to the present embodiment, the measurement gas is H ２ O and CO ２ When both are present, the concentrations of both can be measured. Furthermore, it is also possible to accurately determine the oxygen concentration.

[0126] In addition, in the case of the gas sensor according to the present embodiment, unlike the gas sensor of the prior art, the first chamber, which is the hottest during operation, contains H ２ O and CO ２ Therefore, the voltage applied to the adjusting pump cell that pumps oxygen from the first chamber is kept lower than that of the gas sensor of the prior art, and therefore the occurrence of cracks and blackening in the sensor element is suitably suppressed.

[0127] Furthermore, the only electrode in the chamber that uses a Pt-Au alloy as its metal component is the second measurement electrode provided in the third chamber, and no electrodes that use a Pt-Au alloy are provided in the first and second chambers, which are hotter than the third chamber. Therefore, evaporation of Au from the electrodes is suppressed compared to conventional technology.

[0128] That is, according to this embodiment, a multi-gas sensor having superior long-term reliability compared to conventional sensors can be realized.

[0129] <Modification of Electrode Arrangement> As described above, in the third chamber 61, H contained in the measurement gas ２ is required to be oxidized at the first measurement electrode 44a and the second measurement electrode 44b with equal probability, both electrodes must be disposed at equivalent positions relative to the flow of the gas to be measured.

[0130] However, in the above-described embodiment, as shown in FIG. 1, the first measurement electrode 44a and the second measurement electrode 44b are respectively arranged on a pair of surfaces along the longitudinal direction of the sensor element 101 that define the third chamber 61, that is, the lower surface 6b of the second solid electrolyte layer 6 that forms the ceiling surface of the third chamber 61, and the upper surface 4a of the first solid electrolyte layer 4 that forms the bottom surface of the third chamber 61. However, the arrangement of both electrodes may be different from that shown in FIG. 1 as long as it is equivalent to the flow of the gas to be measured.

[0131] For example, the arrangement of the first measurement electrode 44a and the second measurement electrode 44b may be reversed from that shown in FIG.

[0132] Alternatively, the first measurement electrode 44a and the second measurement electrode 44b may be arranged opposite each other on two exposed surfaces of the spacer layer 5 that form the sides of the third chamber 61, which are a pair of surfaces that run along the longitudinal direction of the sensor element 101 and also define the third chamber 61.

[0133] 5 to 7 are diagrams illustrating sensor elements 101A to 101C in which the first measurement electrode 44a and the second measurement electrode 44b are arranged in different ways. Each of FIGS. 5 to 7 shows the planar arrangement of the first measurement electrode 44a and the second measurement electrode 44b in the sensor elements 101A to 101C. 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 assumed to be the same as in FIG. 1.

[0134] 5, the first measurement electrode 44a and the second measurement electrode 44b, whose longitudinal directions coincide with the longitudinal direction of the element, are arranged in parallel to each other and spaced apart in a direction perpendicular to the longitudinal direction of the element. Such an arrangement may be made on either the lower surface 6b of the second solid electrolyte layer 6, which forms the ceiling surface of the third cavity 61, or on the upper surface 4a of the first solid electrolyte layer 4, which forms the bottom surface.

[0135] 6, a partition 45 may be provided between the first measurement electrode 44a and the second measurement electrode 44b, which are arranged in the same positions as those of the sensor element 101A. The partition 45 is a portion that protrudes 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 preferably prevented from reaching and adhering to the second measurement electrode 44b.

[0136] The partition 45 may be made of a solid electrolyte like the structure 14, or may be made of alumina or other ceramics.

[0137] It is not preferable for the partition 45 to completely divide the third chamber 61 into two, because CO that has entered the side where the first measurement electrode 44a is provided will remain there and will be less likely to be oxidized at the second measurement electrode 44b.

[0138] 7, the first measurement electrode 44a and the second measurement electrode 44b, which are disposed in the same positions as those of 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 measurement electrode 44a from reaching and adhering to the second measurement electrode 44b.

[0139] The porous bodies 46a and 46b are provided with equal porosities in the range of 5% to 30% and equal thicknesses in the range of 30 μm to 100 μm, for example.

[0140] Alternatively, the porosity and thickness may be suitably adjusted to give the porous bodies 46a and 46b the function of the fourth diffusion rate-controlling section 60, and the fourth diffusion rate-controlling section 60 may be omitted.

[0141] In the gas sensor 100 according to the above-described embodiment, the sensor element 101 is provided with a gas flow section including the first chamber 20, the second chamber 40, and the third chamber 61, which are connected to each other through a diffusion rate-determining section. In the gas flow section, the measurement gas is sequentially introduced into each chamber under a predetermined diffusion resistance. In the first chamber 20, the measurement gas is introduced into each chamber under a predetermined diffusion resistance. In the gas flow section ...２ O and CO ２ The oxygen is pumped out within a range where the reduction of H does not occur, and the H ２ O and CO ２ is reduced, and in the third chamber 61, H ２ H produced by reduction of O ２ Selective oxidation of H by the first measuring pump cell 41a ２ H produced by reduction of O ２ and CO ２ The CO generated by the reduction of H is oxidized by the second measuring pump cell 41b. As a result, the H in the measurement gas is oxidized based on the magnitude of the current flowing through each pump cell. ２ O, CO ２ Furthermore, the concentration of oxygen is measured.

[0142] In this measurement mode of the gas sensor 100, the inflow of the measurement gas from the outside of the element into the first chamber 20 is suppressed by the first diffusion rate-controlling portion 11 and the second diffusion rate-controlling portion 13, the inflow of the measurement gas containing residual oxygen from the first chamber 20 into the second chamber 40 is suppressed by the third diffusion rate-controlling portion 30, and further, H ２ O and CO ２ This can be considered to be achieved by the fourth diffusion rate-controlling part 60 suppressing the inflow of the remaining measurement gas from the second chamber 40 to the third chamber 61. That is, the measurement 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 is suitably controlled by the respective diffusion rate-controlling parts, and gases not targeted by the operation of the respective pump cells are prevented from reaching the respective electrodes, thereby enabling multi-gas detection in the gas sensor 100.

[0143] From another perspective, this means that the H by the first adjusting pump cell 21 is directed to the measurement gas that reaches each of the first inner pump electrode 22, the second inner pump electrode 51, the first measurement electrode 44a, and the second measurement electrode 44b. ２ O and CO ２The pumping of oxygen within a range where reduction of H does not occur, and the pumping of H by the second adjusting pump cell 50 ２ O and CO ２ Reduction of H ２ H produced by reduction of O ２ Selective oxidation of H by the first measuring pump cell 41a ２ H produced by reduction of O ２ and CO ２ This means that, as long as the oxidation of both CO and CO produced by the reduction of HCl by the second measurement pump cell 41b is performed satisfactorily in consideration of ensuring measurement accuracy, a configuration different from that of the gas flow section of the sensor element 101 can be adopted. For example, it is possible to achieve multi-gas detection even with a configuration that does not have three chambers that communicate with each other through a diffusion-controlling section.

[0144] 8 is a diagram showing an example of the configuration of a gas sensor 200 according to a modified example, which is based on the above points. The gas sensor 200 is a multi-gas sensor that detects a plurality of types of gas components using a sensor element 201 and measures their concentrations. As with the gas sensor 100, the gas sensor 200 is also controlled by the controller 110, and as will be described later, detects at least water vapor (H ２ O) and carbon dioxide (CO ２ 8 includes a vertical cross-sectional view of the sensor element 201 along the longitudinal direction.

[0145] The sensor element 201 is a long plate-like structure in which a sensor portion 214 and a heater portion 270 are stacked.

[0146] The sensor unit 214 is configured by stacking multiple substrate layers made of ceramics. Specifically, the sensor unit 214 has a configuration in which four layers, consisting of a first substrate 203, a second substrate 204, a third substrate 205, and a fourth substrate 206, are stacked in this order from bottom to top. Of these, at least the second substrate 204 is configured from an oxygen ion conductive solid electrolyte such as zirconia. The first substrate 203, the third substrate 205, and the fourth substrate 206 may be configured from a solid electrolyte or from an insulating material such as alumina. In the sensor unit 214, the first substrate 203 is adjacent to the heater unit 270.

[0147] A gas inlet 210 through which the gas to be measured is introduced is provided at one end (the left end as viewed in the drawing) of the sensor unit 214. More specifically, a diffusion-controlling portion 211 made of a porous body with a porosity of approximately 10% to 50% is embedded at one end of the third substrate 205, and the exposed portion at one end of the diffusion-controlling portion 211 serves as the gas inlet 210. The length of the diffusion-controlling portion 211 (the size in the longitudinal direction of the element) is, for example, 0.5 mm to 1.0 mm, the width (the size in the lateral direction of the element) is, for example, 1.5 mm to 3 mm, and the height (the size in the thickness direction of the element) is, for example, 10 μm to 20 μm.

[0148] The sensor section 214 is provided with a single internal chamber 220 adjacent to the diffusion-controlling section 211. The internal chamber 220 is formed so as to penetrate the third substrate 205 in the thickness direction. The internal chamber 220 has a length (size in the longitudinal direction of the element) of, for example, 6.0 mm to 12.0 mm, a width (size in the lateral direction of the element) of, for example, 1.5 mm to 2.5 mm, and a height (size in the thickness direction of the element) of, for example, 50 μm to 200 μm.

[0149] That is, in the sensor element 201 , the diffusion rate-controlling portion 211 and the internal chamber 220 form a gas flow portion that communicates with the gas inlet 210 .

[0150] A first adjusting electrode 230, a second adjusting electrode 240, a first measurement electrode 250a, and a second measurement electrode 250b are provided on an exposed surface 204a of the second substrate 204 that faces the internal chamber 220 in the same planar arrangement as 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 Fig. 5. That is, in order from closest to the gas inlet 210 on the left side in the drawing, the first adjusting electrode 230, the second adjusting electrode 240, and the set of the first measurement electrode 250a and the second measurement electrode 250b are provided so as to face the internal chamber 220 while being spaced apart at a predetermined interval. The first adjusting electrode 230, the second adjusting electrode 240, the first measuring electrode 250a, and the second measuring electrode 250b are each provided as porous cermet electrodes similar to the first inner pump electrode 22, the second inner pump electrode 51, the first measuring electrode 44a, and the second measuring electrode 44b of the sensor element 101.

[0151] Furthermore, the sensor section 214 is provided with a reference gas introduction space 260 that opens at the other end of the sensor element 201. The reference gas introduction space 260 is formed so as to penetrate the first substrate 203 in the thickness direction. The reference gas introduction space 260 is filled with a reference gas, such as oxygen (O ２ ) and air are introduced.

[0152] A reference electrode 261 is provided on an exposed surface 204b of the second substrate 204 that faces the reference gas introduction space 260. Preferably, the reference electrode 261 is provided over the entire area where the first adjusting electrode 230, the second adjusting electrode 240, the first measurement electrode 250a, and the second measurement electrode 250b are provided on the exposed surface 204a, which is the surface opposite to the exposed surface 204b. The reference electrode 261 is provided, for example, as a porous cermet electrode that contains platinum and zirconia and has a rectangular shape in a plan view.

[0153] Similar to the heater section 70 of the sensor element 101, the heater section 270 is configured to heat the sensor element 201 to a predetermined temperature and further to keep the temperature by supplying power to a heater element 272 (also simply referred to as heater 272) from outside the element. The heater section 270 can have the same configuration as the heater section 70 of the sensor element 101. Alternatively, the heater section 270 may have a configuration in which the heater element 272 is embedded in an insulator.

[0154] The heater 272 is provided so that the temperature is highest near the first adjusting electrode 230 when heated, and the temperature decreases with increasing distance from the first adjusting electrode 230 in the element longitudinal direction.

[0155] Additionally, the sensor element 201 comprises a first regulating pump cell C0, a second regulating pump cell C1, a first measuring pump cell C2a and a second measuring pump cell C2b.

[0156] The first regulating pump cell C0 is an electrochemical pump cell composed of a first regulating electrode 230, a reference electrode 261, and a second substrate 204 sandwiched between the two electrodes. In the first regulating pump cell C0, an oxygen pump current (oxygen ion current) Ip0 is generated by applying a voltage Vp0 between the first regulating electrode 230 and the reference electrode 261 from a variable power supply 231 provided outside the sensor element 201. The operation of the first regulating pump cell C0 is controlled by a first regulating pump cell control unit 121a of the controller 110.

[0157] The second regulating pump cell C1 is an electrochemical pump cell including a second regulating electrode 240, a reference electrode 261, and a second substrate 204 sandwiched between the two electrodes. In the second regulating pump cell C1, a voltage Vp1 is applied between the second regulating 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 regulating pump cell C1 is controlled by a second regulating pump cell control unit 121b of the controller 110.

[0158] The first measurement pump cell C2a is an electrochemical pump cell including a first measurement electrode 250a, a reference electrode 261, and a second substrate 204 sandwiched between the first and second electrodes. In the first measurement pump cell C2a, a voltage Vp2 is applied between the first measurement 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 measurement pump cell C2a is controlled by a first measurement pump cell control unit 122a of the controller 110.

[0159] The second measurement pump cell C2b is an electrochemical pump cell including a second measurement electrode 250b, a reference electrode 261, and a second substrate 204 sandwiched between the two electrodes. In the second measurement pump cell C2b, a voltage Vp3 is applied between the second measurement 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 measurement pump cell C2b is controlled by a second measurement pump cell control unit 122b of the controller 110.

[0160] As described above, the sensor element 201 differs from the sensor element 101 of the gas sensor 100 in that the first adjusting electrode 230, the second adjusting electrode 240, the first measuring electrode 250a, and the second measuring electrode 250b are provided in one internal chamber 220. However, by providing the diffusion rate-controlling portion 211 and the internal chamber 220 under the conditions described above, the diffusion resistance applied to the measurement gas introduced into the internal chamber 220 can be made suitable, in other words, the flow rate of the measurement gas can be controlled to a suitable value. In the gas sensor 200 including the sensor element 201, similar to the gas sensor 100, at least water vapor (H ２ O) and carbon dioxide (CO ２ ) as the main gas components to be detected, making it possible to perform multi-gas detection.

[0161] Specifically, the measurement gas introduced from the gas inlet 210 into the internal chamber 220 through the diffusion rate-controlling section 211 sequentially reaches the first adjusting electrode 230, the second adjusting electrode 240, and the set of the first measuring electrode 250a and the second measuring electrode 250. The first adjusting pump cell C0 converts H ２ O and CO ２ The second adjusting pump cell C1 pumps out oxygen within a range that does not cause reduction of H contained in the measurement gas that has reached the second adjusting electrode 240. ２ O and CO ２ The first measuring pump cell C2a pumps oxygen so that the H ２ H produced by the reduction of O ２ The second measurement pump cell C2b pumps oxygen into the second adjustment pump cell C1 so that the H2O reaching the second measurement electrode 250b is selectively oxidized. ２ H produced by the reduction of O ２ and CO ２ Oxygen is pumped in so that both the CO produced by the reduction of CO and the CO produced by the reduction of CO are oxidized.

[0162] At this time, the measurement gas from which oxygen has not been pumped passes through the first adjusting electrode 230, and H ２ O and CO ２ Since the gas sensor 200 flows at a flow rate that prevents the remaining measurement gas from passing through the second adjusting electrode 240, the current flowing through each pump cell is equal to the current flowing through each pump cell of the gas sensor 100. Therefore, in the gas sensor 200, as in the gas sensor 100, the H in the measurement gas is detected by the water vapor concentration specifying unit 130H, the carbon dioxide concentration specifying unit 130C, and the oxygen concentration specifying unit 130A. ２ O, CO ２ Furthermore, the oxygen concentration can be determined with high accuracy.

Claims

1. A gas sensor capable of measuring the concentrations of a plurality of target gas components contained in a measurement gas containing at least water vapor and carbon dioxide, comprising: a sensor element having a structure made of an oxygen ion conductive solid electrolyte; and a controller for controlling the operation of the gas sensor, wherein the sensor element comprises: a gas inlet through which the measurement gas is introduced; an internal chamber communicating with the gas inlet via a diffusion-controlling part; a first adjusting electrode and a second adjusting electrode, each facing the internal chamber and arranged in order from closest to the gas inlet while being spaced apart by a predetermined distance; and a pair of first and second measuring electrodes arranged at equivalent positions relative to the flow of the measurement gas flowing into the internal chamber; a first adjusting pump cell consisting of the first adjusting electrode, an external pump electrode arranged at a location other than the internal chamber, and the solid electrolyte present between the first adjusting electrode and the external pump electrode; a second adjusting pump cell composed of the second adjusting electrode, the pump electrode outside the cavity, and the solid electrolyte present between the second adjusting electrode and the pump electrode outside the cavity; a first measurement pump cell composed of the first measurement electrode, the pump electrode outside the cavity, and the solid electrolyte present between the first measurement electrode and the pump electrode outside the cavity; a second measurement pump cell composed of the second measurement electrode, the pump electrode outside the cavity, and the solid electrolyte present between the second measurement electrode and the pump electrode outside the cavity; and a heater for heating the sensor element, wherein the first measurement electrode is a cermet electrode containing a Pt—Au alloy as a metal component, and the heater heats the sensor element so that the temperature is highest in the vicinity of the first adjusting electrode in the internal cavity and decreases with increasing distance from the first adjusting electrode in the longitudinal direction of the sensor element, the first adjusting pump cell pumps oxygen from the measurement gas that has reached the first adjusting electrode through the gas inlet, to a degree that does not decompose water vapor and carbon dioxide contained in the measurement gas;the second adjusting pump cell pumps oxygen from the measurement gas that has reached the second adjusting electrode so that substantially all of the water vapor and carbon dioxide contained in the measurement gas from which oxygen has been pumped by the first adjusting pump cell is reduced; the first measurement pump cell pumps oxygen into the internal chamber, thereby selectively oxidizing hydrogen produced by the reduction of water vapor contained in the measurement gas that has reached the first measurement electrode, in the vicinity of the first measurement electrode; the second measurement pump cell pumps oxygen into the internal chamber, thereby oxidizing hydrogen and carbon monoxide produced by the reduction of water vapor and carbon dioxide contained in the measurement gas that has reached the second measurement electrode, in the vicinity of the second measurement electrode; and the controller comprises: water vapor concentration determining means that determines the concentration of water vapor contained in the measurement gas based on the value of a selective oxidation current, which is an oxygen pump current that flows between the first measurement electrode and the external pump electrode when the first measurement pump cell pumps oxygen and selectively oxidizes hydrogen near the first measurement electrode; and a carbon dioxide concentration determining means for determining the concentration of carbon dioxide contained in the measurement gas based on the value of the selective oxidation current and the value of both oxidation currents, which are oxygen pump currents that flow between the second measurement electrode and the outside-space pump electrode when hydrogen and carbon monoxide near the second measurement electrode are oxidized by the second measurement pump cell pumping in oxygen.

2. A gas sensor as claimed in claim 1, characterized in that the internal chambers are a first chamber, a second chamber and a third chamber which are connected in order of proximity to the gas inlet via different diffusion rate-controlling parts, the first adjusting electrode is provided in the first chamber, the second adjusting electrode is provided in the second chamber, and the first measuring electrode and the second measuring electrode are provided in the third chamber.

3. A gas sensor as claimed in claim 2, characterized in that the water vapor concentration determining means determines the concentration of water vapor contained in the measured gas based on a proportional relationship between the selective oxidation current, which has been determined in advance, and the concentration of water vapor contained in the measured gas, and the carbon dioxide concentration determining means determines the concentration of carbon dioxide contained in the measured gas based on a proportional relationship between a difference value, which has been determined in advance and is obtained by subtracting the selective oxidation current from both oxidation currents, and the concentration of carbon dioxide contained in the measured gas.

4. The gas sensor according to claim 2 or 3, wherein the Au concentration in the Pt-Au alloy is 1 wt % or more and 50 wt % or less.

5. A gas sensor according to claim 4, wherein the first adjusting electrode and the second adjusting electrode are cermet electrodes containing Pt but not Au.

6. A gas sensor as claimed in claim 2 or claim 3, characterized in that the controller further comprises an oxygen concentration determination means for determining the concentration of oxygen contained in the measurement gas based on the magnitude of the current flowing between the first adjusting electrode and the pump electrode outside the cavity when oxygen is pumped out of the first cavity by the first adjusting pump cell.

7. A gas sensor according to claim 2 or 3, characterized in that the first measurement electrode and the second measurement electrode are arranged opposite each other on a pair of surfaces of the sensor element along the longitudinal direction, which define the third chamber.

8. A gas sensor according to claim 2 or claim 3, characterized in that the first measurement electrode and the second measurement electrode are arranged in parallel on a surface of the sensor element along the longitudinal direction, which defines the third chamber, so as to be spaced apart from each other in a direction perpendicular to the longitudinal direction.

9. A method for measuring the concentrations of a plurality of target gas components contained in a measurement gas containing at least water vapor and carbon dioxide using a gas sensor, the gas sensor comprising a sensor element having a long plate-like structure made of an oxygen ion conductive solid electrolyte, the sensor element comprising: a gas inlet through which the measurement gas is introduced; an internal chamber communicating with the gas inlet via a diffusion-controlling part; a first adjusting electrode and a second adjusting electrode provided in order of proximity to the gas inlet, each facing the internal chamber and spaced apart by a predetermined distance; and a pair of a first measuring electrode and a second measuring electrode provided at equivalent positions relative to the flow of the measurement gas flowing into the internal chamber; a first adjusting electrode; an external pump electrode provided at a location other than the internal chamber; and a first adjusting pump cell comprising the first adjusting electrode, an external pump electrode provided at a location other than the internal chamber, and the solid electrolyte present between the first adjusting electrode and the external pump electrode. a second adjusting pump cell comprising the second adjusting electrode, the pump electrode outside the cavity, and the solid electrolyte present between the second adjusting electrode and the pump electrode outside the cavity; a first measurement pump cell comprising the first measurement electrode, the pump electrode outside the cavity, and the solid electrolyte present between the first measurement electrode and the pump electrode outside the cavity; a second measurement pump cell comprising the second measurement electrode, the pump electrode outside the cavity, and the solid electrolyte present between the second measurement electrode and the pump electrode outside the cavity; and a heater for heating the sensor element, wherein the first measurement electrode is a cermet electrode containing a Pt-Au alloy as a metal component, and the heater comprises: a) a step in which the heater heats the sensor element so that the temperature is highest in the vicinity of the first adjusting electrode in the internal cavity and the temperature decreases with increasing distance from the first adjusting electrode in the longitudinal direction of the sensor element; b) pumping oxygen from the measurement gas that has reached the first adjusting electrode through the gas inlet by the first adjusting pump cell to an extent that water vapor and carbon dioxide contained in the measurement gas are not decomposed;c) pumping oxygen from the measurement gas that has reached the second adjusting electrode by the second adjusting pump cell so that substantially all of the water vapor and carbon dioxide contained in the measurement gas from which oxygen has been pumped by the first adjusting pump cell is reduced; d) pumping oxygen into the internal space by the first measurement pump cell, thereby selectively oxidizing hydrogen produced by the reduction of water vapor contained in the measurement gas that has reached the first measurement electrode, in the vicinity of the first measurement electrode; e) pumping oxygen into the internal space by the second measurement pump cell, thereby oxidizing hydrogen and carbon monoxide produced by the reduction of water vapor and carbon dioxide contained in the measurement gas that has reached the second measurement electrode, in the vicinity of the second measurement electrode; f) specifying the concentration of water vapor contained in the measurement gas based on the value of a selective oxidation current, which is an oxygen pump current flowing between the first measurement electrode and the external pump electrode when the first measurement pump cell pumps oxygen and selectively oxidizes hydrogen near the first measurement electrode; g) determining the concentration of carbon dioxide contained in the measurement gas based on the value of the selective oxidation current and the value of both oxidation currents, which are oxygen pump currents that flow between the second measurement electrode and the outside-space pump electrode when hydrogen and carbon monoxide near the second measurement electrode are oxidized by the second measurement pump cell pumping in oxygen.

10. A method for measuring concentration using a gas sensor as described in claim 9, characterized in that the internal chambers are a first chamber, a second chamber, and a third chamber, which are connected in order of proximity to the gas inlet via different diffusion-controlling sections, the first adjusting electrode is provided in the first chamber, the second adjusting electrode is provided in the second chamber, and the first measuring electrode and the second measuring electrode are provided in the third chamber.

11. A method for measuring a concentration using a gas sensor as defined in claim 10, wherein in step f), the concentration of water vapor contained in the measurement gas is determined based on a proportional relationship between the selective oxidation current and the concentration of water vapor contained in the measurement gas, which is determined in advance; and in step g), the concentration of carbon dioxide contained in the measurement gas is determined based on a proportional relationship between a difference value obtained by subtracting the selective oxidation current from both oxidation currents, which is determined in advance, and the concentration of carbon dioxide contained in the measurement gas.

12. A method for measuring concentration 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. A method for measuring a concentration using a gas sensor according to claim 12, characterized in that the first adjusting electrode and the second adjusting electrode are cermet electrodes containing Pt but not Au.

14. A method for measuring a concentration using a gas sensor as claimed in claim 10 or 11, further comprising the step of: h) determining the concentration of oxygen contained in the gas to be measured based on the magnitude of the current flowing between the first adjusting electrode and the pump electrode outside the cavity when oxygen is pumped out of the first cavity by the first adjusting pump cell.

15. A method for measuring concentration using a gas sensor as defined in claim 10 or 11, characterized in that the first measurement electrode and the second measurement electrode are arranged facing each other on a pair of surfaces of the sensor element along the longitudinal direction, which define the third chamber.

16. A method for measuring concentration using a gas sensor as defined in claim 10 or 11, characterized in that the first measurement electrode and the second measurement electrode are arranged in parallel on a surface of the sensor element along the longitudinal direction that defines the third chamber, so as to be spaced apart from each other in a direction perpendicular to the longitudinal direction.