GAS SENSOR AND METHOD FOR CONCENTRATION MEASUREMENT USING A GAS SENSOR

Abstract

A sensor element comprises: first to third chambers sequentially connected from a gas inlet via various diffusion control parts;and a heating device that performs heating so that a temperature near the first chamber is the highest, an adjusting pump cell pumps oxygen from a measurement gas introduced into the first chamber to such an extent that the H2O and CO2 contained in the measurement gas are not decomposed, a first measuring pump cell pumps oxygen from the second chamber so that all of the H2O and CO2 contained in the measurement gas introduced from the first chamber into the second chamber is reduced, a second measuring pump cell pumps oxygen into the third chamber to selectively oxidize the H2 generated by reduction, a concentration of H2O is determined from a value of a current generated by the pumping in by the second measuring pump cell, and a concentration of CO2 is determined from the determined concentration of H2O and a value of a current generated by the pumping out by the first measuring pump cell;

Description

TECHNICAL FIELD

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

[0002] In the measurement for managing the amount of exhaust gas emitted by a vehicle, the technology for measuring the concentrations of water vapor (H2O) and carbon dioxide (CO2) is already known (see, for example, Patent Documents 1 to 3). Each of the gas sensors disclosed in Patent Documents 1 and 2 can measure a water vapor (H2O) component and a carbon dioxide (CO2) component in parallel. A gas sensor disclosed in Patent Document 3 can accurately measure a water vapor (H2O) component even when a measurement gas contains carbon dioxide (CO2).

[0003] In the gas sensor having a three-chamber configuration disclosed in Patent Document 1, first, a main pumping cell operates as a pumping cell for a first internal space to pump out O2 contained in a measurement gas introduced into the first internal space, and once reduces all H2O and CO2 also contained in the measurement gas to generate H2 and CO. The measurement gas containing this H2 and CO is introduced into a second internal space and further into a third internal space. A first measuring pumping cell as a pumping cell for the second internal space then pumps in O2 to selectively oxidize H2 and generate H2O, and a second measuring pumping cell as a pumping cell for the third internal space pumps in O2 to oxidize CO and generate CO2. The concentrations of H2O and CO2 in the measurement gas are respectively measured based on the magnitudes of the pumping currents flowing through the first measuring pumping cell and the second measuring pumping cell when H2 and CO are oxidized.

[0004] In the gas sensor, a high applied voltage in the pumping cell for the first internal space must be set to reduce H2O and CO2 in the first internal space. Furthermore, the temperature of a main electrode of the internal pump, a pumping electrode in the intermediate space forming the main pumping cell, must be set to a high temperature. However, such a high applied voltage and maintaining the pumping electrode at a high temperature may cause a sensor element containing an oxygen-ion conductive solid electrolyte ceramic as its main component to crack and turn black, thereby reducing the size of the solid electrolyte ceramic.

[0005] In the gas sensor having a dual-chamber configuration disclosed in Patent Document 3, in order to improve the selective oxidation property of H2, an alloy of Au and another noble metal (for example, Pt, Rh, and Ru) is used as a material for an inner measuring pump electrode as an in-space pump electrode constituting a measuring pump cell as a pump cell for a second internal space, and an abundance ratio of Au in a surface of the electrode is 25 at% or more.

[0006] This electrode material is apparently applicable to a first inner measuring pump electrode of the first measuring pump cell that selectively oxidizes H2 in a similar manner to the gas sensor disclosed in Patent Document 1.

[0007] However, the inner pumping electrode for the first measurement is provided at a position where it has a higher temperature than an inner pumping electrode for the second measurement, which as a pumping electrode in the space constituting the second measuring pumping cell in the gas sensor disclosed in Patent Document 1, so the use of such a material for the electrode may cause Au in the electrode to evaporate and the sensitivity to change during long-term use. PRIOR ART PATENT DOCUMENTS Patent Document 1: Japanese Patent No. 5918177 Patent Document 2: Japanese Patent No. 6469464 Patent Document 3: Japanese Patent No. 6469462 DEPICTION

[0008] The present invention has been conceived in view of the above-mentioned problem, and it is an object of the present invention to provide a multi-gas sensor with higher long-term reliability than heretofore, which is capable of simultaneously measuring a water vapor component (H2O) and a carbon dioxide component (CO2), suppressing cracking and blackening of a sensor element and also being less likely to change the sensitivity during long-term use.

[0009] To solve the above-mentioned problem, a first aspect of the present invention is a gas sensor capable of measuring concentrations of a plurality of sensing target gas components contained in a measurement gas, the measurement gas containing water vapor and carbon dioxide, and the gas sensor comprising: a sensor element having a structure formed of a solid electrolyte conductive to oxygen ions; and a controller that controls the operation of the gas sensor, 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 control part; a setting electrode, a first measuring electrode, and a second measuring electrode, each provided facing the internal chamber and arranged in order of proximity to the gas inlet, spaced apart from each other at predetermined intervals; a setting pump cell including the setting electrode, an outside-the-space pump electrode provided at a location other than a location in the internal chamber, and a portion of the solid electrolyte provided between the setting electrode and the outside-the-space pump electrode; a first measuring pump cell including the first measuring electrode, the outside-the-space pump electrode, and a portion of the solid electrolyte,which is provided between the first measuring electrode and the outside-the-space pumping electrode; a second measuring pumping cell which has the second measuring electrode, the outside-the-space pumping electrode, and a portion of the solid electrolyte which is provided between the second measuring electrode and the outside-the-space pumping electrode; and a heating device which heats the sensor element. The heating device heats the sensor element so that a temperature near the adjusting electrode in the inner chamber is highest and decreases with increasing distance from the adjusting electrode in a longitudinal direction of the sensor element. The adjusting pumping cell pumps out oxygen from the measuring gas which has reached the adjusting electrode through the gas inlet to such an extent that water vapor and carbon dioxide contained in the measuring gas are not decomposed. The first measuring pumping cell pumps out oxygen from the measuring gas which has reached the first measuring electrode to such an extent thatthat substantially all of the water vapor and carbon dioxide contained in the measurement gas from which oxygen has been pumped out by the adjustment pumping cell are reduced, the second measurement pumping cell pumps oxygen into the internal chamber to selectively oxidize hydrogen generated by reducing water vapor and contained in the measurement gas that has reached the second measurement electrode, and the controller comprises: a water vapor concentration identifying means for identifying a concentration of water vapor contained in the measurement gas based on a value of a water vapor equivalent current as an oxygen pumping current flowing between the second measurement electrode and the outside-the-space pumping electrode when hydrogen is oxidized with oxygen,which is pumped through the second measuring pump cell; and a carbon dioxide concentration identification device for identifying a concentration of carbon dioxide contained in the measurement gas based on the value of the water vapor equivalent current and a value of a total reduction current as the oxygen pump current flowing between the first measuring electrode and the outside-the-room pump electrode when water vapor and carbon dioxide are reduced by the first measuring pump cell that pumps out oxygen.

[0010] A second aspect of the present invention is the gas sensor according to the first aspect, wherein the internal chamber has a first chamber, a second chamber, and a third chamber sequentially communicating with each other in the order of their proximity to the gas inlet via different diffusion control parts, wherein the adjustment electrode is arranged in the first chamber, the first measuring electrode is arranged in the second chamber, and the second measuring electrode is arranged in the third chamber.

[0011] A third aspect of the present invention is the gas sensor according to the second aspect, wherein the controller stores: Ip1-H2O data indicating a relationship between an oxygen pumping current flowing through the first measuring pumping cell and a water vapor concentration when the measuring gas contains water vapor and does not contain carbon dioxide, the Ip1-H2O data being identified in advance; Ip1-CO2 data indicating a relationship between an oxygen pumping current flowing through the first measuring pumping cell and a water vapor concentration when the measuring gas contains carbon dioxide and does not contain water vapor, the Ip1-CO2 data being identified in advance; and Ip2-H2O data indicating a relationship between an oxygen pumping current flowing through the second measuring pumping cell and a water vapor concentration when the measuring gas contains water vapor and does not contain carbon dioxide, the Ip2-H2O data being identified in advance.the water vapor concentration identification device identifies a concentration of water vapor corresponding to the value of the water vapor equivalent current in the Ip2-H2O data as the concentration of water vapor contained in the measurement gas, and the carbon dioxide concentration identification device identifies a contribution of water vapor by reducing the total reduction current based on the concentration of water vapor contained in the measurement gas identified by the water vapor concentration identification device and the Ip1-H2O data, and identifies a concentration of carbon dioxide corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the Ip1-CO2 data as the concentration of carbon dioxide contained in the measurement gas.

[0012] A fourth aspect of the present invention is the gas sensor according to the second aspect, wherein the controller stores: Ip1-CO2 data indicating a relationship between an oxygen pumping current flowing through the first measurement pumping cell and a concentration of water vapor when the measurement gas contains carbon dioxide and does not contain water vapor, the Ip1-CO2 data being identified in advance; Ip2-H2O data indicating a relationship between an oxygen pumping current flowing through the second measurement pumping cell and a concentration of water vapor when the measurement gas contains water vapor and does not contain carbon dioxide, the Ip2-H2O data being identified in advance;and H2O characteristic data indicating a relationship between the water vapor equivalent current and an oxygen pumping current corresponding to a contribution of water vapor in the total reduction current, wherein the H2O characteristic data is identified in advance, the water vapor concentration identifying means identifies a concentration of water vapor corresponding to the value of the water vapor equivalent current in the Ip2-H2O data as the concentration of water vapor contained in the measurement gas, and the carbon dioxide concentration identifying means identifies a contribution of water vapor by reducing the total reduction current based on the water vapor equivalent current and the H2O characteristic data, and identifies a concentration of carbon dioxide corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the Ip1-CO2 data as the concentration of carbon dioxide contained in the measurement gas.

[0013] A fifth aspect of the present invention is the gas sensor according to any one of the second to fourth aspects, wherein the second measuring electrode is a cermet electrode containing a Pt-Au alloy as a metal component, and the Pt-Au alloy has an Au concentration of 1 wt% or more and 50 wt% or less.

[0014] A sixth aspect of the present invention is the gas sensor according to the fifth aspect, wherein the adjustment electrode and the first measuring electrode are cermet electrodes containing Pt and not containing Au.

[0015] A seventh aspect of the present invention is the gas sensor according to any one of the second to fourth aspects, wherein the controller further comprises oxygen concentration identifying means for identifying the concentration of oxygen contained in the measurement gas based on the strength of the current flowing between the adjusting electrode and the outside-the-space pumping electrode when the adjusting pumping cell pumps out oxygen from the first chamber.

[0016] An eighth aspect of the present invention is a concentration measurement method for measuring concentrations of a plurality of sensing target gas components contained in a measurement gas using a gas sensor, the measurement gas containing water vapor and carbon dioxide, the gas sensor comprising a sensor element having an elongated planar structure formed 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 control part; a setting electrode, a first measuring electrode, and a second measuring electrode, each provided facing the internal chamber and arranged in order of proximity to the gas inlet, spaced apart from each other at predetermined intervals; a setting pump cell including the setting electrode, an outside-the-space pump electrode provided at a location other than a location in the internal chamber, and a portion of the solid electrolyte provided between the setting electrode and the outside-the-space pump electrode; a first measuring pump cell including the first measuring electrode, the outside-the-space pump electrode, and a portion of the solid electrolyte provided between the first measuring electrode and the outside-the-space pump electrode;a second measuring pumping cell comprising the second measuring electrode, the outside-space pumping electrode, and a portion of the solid electrolyte provided between the second measuring electrode and the outside-space pumping electrode; and a heater that heats the sensor element, and the method for concentration measurement using the gas sensor comprises: a) heating the sensor element using the heater so that a temperature near the adjusting electrode in the internal chamber is the highest and decreases with increasing distance from the adjusting electrode in a longitudinal direction of the sensor element; b) pumping oxygen from the measuring gas, which has reached the adjusting electrode through the gas inlet, through the adjusting pumping cell to such an extent that water vapor and carbon dioxide contained in the measuring gas are not decomposed;c) Pumping oxygen from the measurement gas that has reached the first measurement electrode using the first measurement pumping cell so that substantially all of the water vapor and carbon dioxide contained in the measurement gas from which oxygen has been pumped out using the adjustment pumping cell are reduced; d) Pumping oxygen into the internal chamber using the second measurement pumping cell to selectively oxidize hydrogen generated by reducing water vapor and contained in the measurement gas that has reached the second measurement electrode; e) Identifying a concentration of water vapor contained in the measurement gas based on a value of a water vapor equivalent current as an oxygen pumping current flowing between the second measurement electrode and the outside-the-space pumping electrode when hydrogen is oxidized with oxygen pumped in using the second measurement pumping cell;and f) identifying a concentration of carbon dioxide contained in the measurement gas based on the value of the water vapor equivalent current and a value of a total reduction current as an oxygen pumping current flowing between the first measurement electrode and the outside-the-room pumping electrode when water vapor and carbon dioxide are reduced by pumping out oxygen using the first measurement pumping cell;

[0017] A ninth aspect of the present invention is the method for concentration measurement using the gas sensor according to the eighth aspect, wherein the internal chamber has a first chamber, a second chamber, and a third chamber sequentially communicated in the order of their proximity to the gas inlet via different diffusion control parts, wherein the adjustment electrode is arranged in the first chamber, the first measuring electrode is arranged in the second chamber, and the second measuring electrode is arranged in the third chamber.

[0018] A tenth aspect of the present invention is the method for concentration measurement using the gas sensor according to the ninth aspect, further comprising g) prior to steps a) to f), previously identifying: Ip1-H2O data indicating a relationship between an oxygen pumping current flowing through the first measurement pumping cell and a concentration of water vapor when the measurement gas contains water vapor and does not contain carbon dioxide; Ip1-CO2 data indicating a relationship between an oxygen pumping current flowing through the first measurement pumping cell and a concentration of water vapor when the measurement gas contains carbon dioxide and does not contain water vapor;and Ip2-H2O data indicating a relationship between an oxygen pumping current flowing through the second measuring pumping cell and a concentration of water vapor when the measuring gas contains water vapor and does not contain carbon dioxide, wherein in step e), a concentration of water vapor corresponding to the value of the water vapor equivalent current in the Ip2-H2O data is identified as the concentration of water vapor contained in the measuring gas, and in step f), a contribution of water vapor by reduction in the total reduction current is identified based on the concentration of water vapor contained in the measuring gas identified in step e) and the Ip1-H2O data, and a concentration of carbon dioxide corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the Ip1-CO2 data is identified as the concentration of carbon dioxide contained in the measuring gas.;

[0019] An eleventh aspect of the present invention is the method for concentration measurement using the gas sensor according to claim 9, further comprising g) prior to steps a) to f), previously identifying: Ip1-CO2 data indicating a relationship between an oxygen pumping current flowing through the first measurement pumping cell and a concentration of water vapor when the measurement gas contains carbon dioxide and does not contain water vapor; Ip2-H2O data indicating a relationship between an oxygen pumping current flowing through the second measurement pumping cell and a concentration of water vapor when the measurement gas contains water vapor and does not contain carbon dioxide;and H2O characteristic data indicating a relationship between the water vapor equivalent current and an oxygen pumping current corresponding to a contribution of water vapor to the total reduction current, wherein in step e), a concentration of water vapor corresponding to the value of the water vapor equivalent current in the Ip2-H2O data is identified as the concentration of water vapor contained in the measurement gas, and in step f), a contribution of water vapor by reduction in the total reduction current is identified based on the water vapor equivalent current and the H2O characteristic data, and a concentration of carbon dioxide corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the Ip1-CO2 data is identified as the concentration of carbon dioxide contained in the measurement gas.;

[0020] A twelfth aspect of the present invention is the method for concentration measurement using the gas sensor according to any one of the ninth to eleventh aspects, wherein the second measuring electrode is a cermet electrode containing a Pt-Au alloy as a metal component, and the Pt-Au alloy has an Au concentration of 1 wt% or more and 50 wt% or less.

[0021] A thirteenth aspect of the present invention is the method for concentration measurement using the gas sensor according to the twelfth aspect, wherein the adjustment electrode and the first measuring electrode are cermet electrodes containing Pt and not containing Au.

[0022] A fourteenth aspect of the present invention is the method for concentration measurement using the gas sensor according to any one of the ninth to eleventh aspects, further comprising: g) identifying a concentration of oxygen contained in the measurement gas based on a magnitude of a current flowing between the adjusting electrode and the outside-the-space pumping electrode when oxygen is pumped from the first chamber using the adjusting pumping cell.

[0023] According to the first to fourteenth aspects of the present invention, a multi-gas sensor with higher long-term reliability than before is implemented, which suppresses cracking and blackening of a sensor element and evaporation of Au from an electrode. BRIEF DESCRIPTION OF THE DRAWINGS [ Fig. 1] is a diagram schematically showing an example of a configuration of a gas sensor 100. [ Fig. 2] is a block diagram showing the functional components implemented by a controller 110. [ Fig. 3] is a schematic diagram illustrating the entry and exit of gases into and from three chambers containing a sensor element 101 of the gas sensor 100. [ Fig. 4] is a graph showing a relationship between a target value of the electromotive force V0 in a sensor cell 80 of a first chamber and an oxygen pumping current Ip0 flowing through a setting pumping cell 21 when three different kinds of model gases are caused to flow. [ Fig. 5] is a graph showing the dependence of an oxygen pumping current Ip1 on a concentration of a sensing target gas component. [ Fig. 6] is a graph showing the dependence of the oxygen pumping current Ip2 on the concentration of a sensed component. [ Fig. 7] is a graph showing an example of H2O characteristic data. [ Fig. 8] is a diagram schematically showing an example of a configuration of a gas sensor 200 according to a modification. DESCRIPTION OF THE EMBODIMENTS<Konfiguration des Gassensors>

[0024] Fig. 1 is a diagram schematically showing an example of a configuration of a gas sensor 100 according to the present embodiment. The gas sensor 100 is a multi-gas sensor that senses a variety of gas components and measures their concentrations using a sensor element 101. It is assumed that, in the present embodiment, at least water vapor (H2O) and carbon dioxide (CO2) are the main sensing target gas components sensed by the gas sensor 100. The gas sensor 100 is attached to an exhaust path of an internal combustion engine such as a vehicle engine, and is used, for example, with exhaust gas flowing along the exhaust path as the measurement gas. Fig. 1 includes a vertical cross-sectional view taken along a longitudinal direction of the sensor element 101.

[0025] The sensor element 101 has an elongated planar structure (base part) 14 formed of a solid electrolyte conductive to oxygen ions, a first diffusion control part 11 that duplicates a gas inlet 10 formed in one end portion (a left end portion in the figure) of the structure 14 and through which the measurement gas is introduced, and a buffer space 12, a first chamber 20, a second chamber 40, and a third chamber 61 formed in the structure 14 and sequentially communicating with the gas inlet 10 (first diffusion control part 11). The buffer space 12 communicates with the gas inlet 10 (first diffusion control part 11). The first chamber 20 communicates with the buffer space 12 via a second diffusion control part 13. The second chamber 40 is connected to the first chamber 20 via a third diffusion control part 30.The third chamber 61 is connected to the second chamber 40 via a fourth diffusion control part 60.

[0026] The structure 14 is formed by laminating a plurality of substrates, for example, made of ceramic. Specifically, the structure 14 has a configuration in which six layers, including 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 laminated sequentially from the bottom. Each layer is formed of an oxygen ion-conductive solid electrolyte, such as zirconium dioxide (ZrO2).

[0027] The first diffusion control part 11, which also serves as the gas inlet 10, the buffer space 12, the second diffusion control part 13, the first chamber 20, the third diffusion control part 30, the second chamber 40, the fourth diffusion control part 60, and the third chamber 61 are formed in this order between a lower surface 6b of the second solid electrolyte layer 6 and a surface 4a of the first solid electrolyte layer 4 on one side of the one end portion of the structure 14. A part extending from the gas inlet 10 to the third chamber 61 is also called a gas distribution part.

[0028] The buffer space 12, the first chamber 20, the second chamber 40, and the third chamber 61 are formed to penetrate the spacer layer 5 in the thickness direction. The lower surface 6b of the second solid electrolyte layer 6 is exposed in the upper portions of these chambers and the like in the figure, and the upper surface 4a of the first solid electrolyte layer 4 is exposed in the lower portions of these chambers and the like in the figure. The side portions of these chambers and the like are each defined by the spacer layer 5 or one of the diffusion control members. The first chamber 20, the second chamber 40, and the third chamber 61 each have a length (size in a longitudinal direction of the element) of 0.3 mm to 1.0 mm, for example, a width (size in a transverse direction of the element) of 0.5 mm to 30 mm, for example, and a height (size in a thickness direction of the element) of 50 µm to 200 µm, for example.However, these chambers do not have to be the same size and can be different sizes.

[0029] The gas inlet 10 may similarly be formed so that it penetrates the spacer layer 5 in the thickness direction, separated from the first diffusion control part 11. In this case, the first diffusion control part 11 is formed within and adjacent to the gas inlet 10.

[0030] The first diffusion control member 11, the second diffusion control member 13, the third diffusion control member 30, and the fourth diffusion control member 60 each have two horizontally extending slits. This means that they each have openings extending in a direction perpendicular to the side of the figure at an upper portion and a lower portion in the figure thereof. The slits each have a length (lengthwise dimension of the element) of 0.2 mm to 1.0 mm, for example, an opening width (widthwise dimension of the element) of 0.5 mm to 30 mm, for example, and an opening height (thickness dimension of the element) of 5 µm to 30 µm, for example.

[0031] The sensor element 101 has a reference gas introduction space 43 in the other end portion (a right end portion in the figure) opposite to one end portion where the gas inlet 10 is provided. The reference gas introduction space 43 is formed between an upper surface 3a of the third substrate 3 and a lower surface 5b of the spacer layer 5. A lateral portion of the reference gas introduction space 43 is defined by a side surface of the first solid electrolyte layer 4. Oxygen (O2) and air, for example, are introduced into the reference gas introduction space 43 as reference gases.

[0032] The gas inlet 10, the gas inlet 10 (first part for diffusion control 11), is a part that opens to an outside space, and the measurement gas is introduced from the outside space through the gas inlet 10 into the sensor element 101.

[0033] The first part for diffusion control 11 is a part that opposes a predetermined diffusion resistance to the sample gas taken.

[0034] Buffer chamber 12 is provided to compensate for fluctuations in the concentration of the sample gas caused by pressure fluctuations in the sample gas outside. An example of such pressure fluctuations in the sample gas is the pulsation of the exhaust pressure of the vehicle's exhaust gas.

[0035] The second part for diffusion control 13 is a part that opposes a predetermined diffusion resistance to the measuring gas that is introduced from the buffer space 12 into the first chamber 20.

[0036] The first chamber 20 is provided as a space for pumping oxygen from the measurement gas introduced through the second diffusion control part 13. The oxygen pumping is performed by the operation of a variable-rate pump cell 21.

[0037] The adjustment pumping cell 21 is an electrochemical pumping cell comprising an inner pumping electrode (adjustment electrode) 22, an outer pumping electrode (outside-space pumping electrode) 23, and a solid electrolyte present in a portion of the structure 14 disposed between these electrodes.

[0038] In the adjustable pumping cell 21, a voltage Vp0 is applied across the inner pumping electrode 22 and the outer pumping electrode 23 from a variable current supply 24 arranged outside the sensor element 101 to generate an oxygen pumping current (oxygen ion current) Ip0. Oxygen in the first chamber 20 can thereby be pumped to the outside. It is assumed that the direction of the oxygen pumping current Ip0 when pumping oxygen out of the first chamber 20 is a positive direction of the oxygen pumping current Ip0 in the present embodiment.

[0039] The inner pumping electrode 22 is provided on substantially the entire portions of the lower surface 6b of the second solid electrolyte layer 6 and the upper surface 4a of the first solid electrolyte layer 4, which define the first chamber 20, as the ceiling electrode portion 22a and the bottom electrode portion 22b, respectively. The ceiling electrode portion 22a and the bottom electrode portion 22b are connected by a conductive portion (not shown).

[0040] The inner pumping electrode 22 is provided as a porous cermet electrode containing platinum and / or rhodium (Rh) as a metal component and is rectangular in plan view.

[0041] The outer pumping electrode 23 is provided with platinum or an alloy (a Pt-Au alloy) of platinum and gold as a metal component, as a porous cermet electrode containing platinum or the Pt-Au alloy and zirconium dioxide and is, for example, rectangular in plan view.

[0042] In the sensor element 101, the inner pumping electrode 22, a reference electrode 42, and a solid electrolyte present in a portion of the structure 14 between these 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 an atmosphere in the first chamber 20.

[0043] The reference electrode 42 is an electrode formed between the first solid electrolyte layer 4 and the third substrate 3 and is provided as a porous cermet electrode containing platinum and zirconium dioxide and is, for example, rectangular in plan view.

[0044] A reference gas introduction layer 48 formed of porous aluminum oxide is provided around the reference electrode 42 and leads to the reference gas introduction space 43. A reference gas is introduced into the reference gas introduction space 43 via the reference gas introduction layer 48 into a surface of the reference electrode 42. This means that the reference electrode 42 is always in contact with the reference gas.

[0045] In the sensor cell 80 of the first chamber, an electromotive force (Nernst EMF) V0 is generated between the inner pump electrode 22 and the reference electrode 42. The electromotive force V0 has a value corresponding to a difference between an oxygen concentration (oxygen partial pressure) in the first chamber 20 and an oxygen concentration (oxygen partial pressure) of the reference gas. The oxygen concentration (oxygen partial pressure) of the reference gas is essentially constant, so the electromotive force V0 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the first chamber 20.

[0046] The third diffusion control part 30 is a part that provides a predetermined diffusion resistance to the measurement gas that is introduced from the first chamber 20 into the second chamber 40 and contains H2O and CO2 and essentially contains no oxygen.

[0047] The second chamber 40 is provided as a space for reducing (decomposing) H2O and CO2, which are contained as the sensing target gas components in the measurement gas introduced through the third diffusion control part 30, to generate hydrogen (H2) and carbon monoxide (CO), so that the measurement gas essentially contains no oxygen, H2O, and CO2. The reduction (decomposition) of H2O and CO2 is performed by the operation of a first measurement pump cell 50.

[0048] The first measuring pump cell 50 is an electrochemical pump cell comprising a first measuring electrode 51, the outer pump electrode 23 and a solid electrolyte present in a portion of the structure 14 disposed between these electrodes.

[0049] In the first measuring pumping cell 50, a voltage Vp1 is applied across the first measuring electrode 51 and the outer pumping electrode 23 from a variable current supply 52 arranged outside the sensor element 101 to generate an oxygen pumping current (oxygen ion current) Ip1. Oxygen generated by the reduction of H2O and CO2 in the second chamber 40 can thereby be pumped to the outside. It is assumed that the direction of the oxygen pumping current Ip1 when pumping oxygen from the second chamber 40 is a positive direction of the oxygen pumping current Ip1 in the present embodiment.

[0050] The first measuring electrode 51 is provided on substantially the entire portions of the lower surface 6b of the second solid electrolyte layer 6 and the upper surface 4a of the first solid electrolyte layer 4, which define the second chamber 40, as the ceiling electrode portion 51a and the bottom electrode portion 51b, respectively. The ceiling electrode portion 51a and the bottom electrode portion 51b are connected by a conductive portion (not shown).

[0051] The first measuring electrode 51 is provided as a porous cermet electrode with Pt as the metal component and a rectangular base plan.

[0052] In the sensor element 101, the first measuring electrode 51, the reference electrode 42, and a solid electrolyte present in a portion of the structure 14 between these electrodes form a second chamber sensor cell 81. The second chamber sensor cell 81 is an electrochemical sensor cell for detecting the oxygen partial pressure in an atmosphere in the second chamber 40.

[0053] In the second chamber sensor cell 81, an electromotive force (Nernst electromotive force) V1 is generated between the first measuring electrode 51 and the reference electrode 42. The electromotive force V1 has a value corresponding to a difference between an oxygen concentration (oxygen partial pressure) in the second chamber 40 and the oxygen concentration (oxygen partial pressure) of the reference gas. Since the oxygen concentration (oxygen partial pressure) of the reference gas is substantially constant, the electromotive force V1 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the second chamber 40.

[0054] The fourth diffusion control part 60 is a part that provides a predetermined diffusion resistance to the measurement gas that is introduced from the second chamber 40 into the third chamber 61 and contains H2 and CO while substantially not containing H2O, CO2 and oxygen.

[0055] The third chamber 61 is provided as a space for selectively oxidizing all of the H2 from the H2 and CO contained in the measurement gas introduced through the fourth diffusion control part 60 to regenerate H2O. The generation of H2O by oxidation of H2 is implemented by the operation of a second measurement pumping cell 41.

[0056] The second measuring pump cell 41 is an electrochemical pump cell comprising a second measuring electrode 44, the outer pump electrode 23 and a solid electrolyte present in a portion of the structure 14 disposed between these electrodes.

[0057] In the second measuring pumping cell 41, a voltage Vp2 is applied across the second measuring electrode 44 and the external pumping electrode 23 from a variable current supply 46 arranged outside the sensor element 101 to generate an oxygen pumping current (oxygen ion current) Ip2. This allows oxygen to be pumped from the outside into the third chamber 61. It is assumed that the direction of the oxygen pumping current Ip2 when oxygen is pumped from the third chamber 61 is a positive direction of the oxygen pumping current Ip2 in the present embodiment.

[0058] The second measuring electrode 44 is provided on substantially the entire portion of the upper surface 4a of the first solid electrolyte layer 4 defining the third chamber 61.

[0059] The second measuring electrode 44 contains a Pt-Au alloy as a metal component and is provided as a porous cermet electrode containing the Pt-Au alloy and zirconia, and is rectangular in plan view, for example. The Pt-Au alloy preferably has an Au concentration of 1 wt% or more and 50 wt% or less, and more preferably an Au concentration of 10 wt% or more and 30 wt% or less. In this case, a property for selectively oxidizing H2, that is, a property that when H2 and CO coexist in the third chamber 61, only H2 is selectively oxidized with oxygen pumped in by the second measuring pumping cell 41, and CO is not oxidized, is better developed in the second measuring electrode 44.

[0060] In the sensor element 101, the second measuring electrode 44, the reference electrode 42, and a solid electrolyte present in a portion of the structure 14 between these electrodes form a third-chamber sensor cell 82. The third-chamber sensor cell 82 is an electrochemical sensor cell for detecting the oxygen partial pressure in an atmosphere in the third chamber 61.

[0061] In the sensor cell 82 of the third chamber, the electromotive force (Nernst EMF) V2 is generated between the second measuring electrode 44 and the reference electrode 42. The electromotive force V2 has a value corresponding to a difference between the oxygen concentration (oxygen partial pressure) in the third chamber 61 and the oxygen concentration (oxygen partial pressure) of the reference gas. Since the oxygen concentration (oxygen partial pressure) of the reference gas is essentially constant, the electromotive force V2 has a value corresponding to the oxygen concentration (oxygen partial pressure) in the third chamber 61.

[0062] The sensor element 101 further includes an electrochemical sensor cell 83, which includes the outer pumping electrode 23, the reference electrode 42, and a solid electrolyte present in a portion of the structure 14 sandwiched between these electrodes. The electromotive force Vref generated between the outer pumping electrode 23 and the reference electrode 42 of the sensor cell 83 has a value corresponding to the oxygen partial pressure of the measurement gas present outside the sensor element 101.

[0063] In addition to the above-mentioned embodiments, the sensor element 101 has a heater part 70 which plays a role in temperature adjustment of the heating of the sensor element 101 and maintaining the temperature thereof in order to improve the oxygen ion conductivity of the solid electrolyte forming the structure 14.

[0064] The heater part 70 mainly includes a heater electrode 71, a heater element 72, a heater line 72a, a through-hole 73, a heater insulating layer 74, and a heater resistance detection line arranged in Fig. 1 is not shown. The heating device element 72 is also referred to simply as heating device 72 below.

[0065] The heater 72 is provided so as to be arranged between the second substrate 2 and the third substrate 3 from below and above, and generates heat by being supplied with power from the outside through the heater electrode 71 provided on a lower surface 1b of the first substrate 1, the through-hole 73, and the heater lead 72a. The heater 72 is embedded over the entire area from the buffer space 12 to the third chamber 61 and can heat the sensor element 101 to a predetermined temperature and maintain the temperature thereafter.

[0066] The heater 72 is provided so that the temperature is highest near the first chamber 20 (near the adjustment electrode 22) and decreases with increasing distance from the first chamber 20 in the longitudinal direction of the element during heating. In the present embodiment, a temperature in a range from the one portion of the sensor element 101 where the gas inlet 10 is arranged to the third chamber 61 when the gas sensor 100 is in use (when the sensor element 101 is driven) is referred to as the element driving temperature. The heater 72 performs heating so that the element driving temperature is in a range of 750°C to 950°C.

[0067] The heater insulating layer 74 made of alumina and the like is formed above and below the heater 72 to electrically insulate the heater 72 from the second substrate 2 and the third substrate 3. The heater part 70 also has a pressure relief hole 75. The pressure relief hole 75 is a part provided to penetrate the third substrate 3 and communicate with the reference gas introduction space 43, and is provided to mitigate an increase in internal pressure associated with an increase in temperature in the heater insulating layer 74.

[0068] The gas sensor 100 further includes a controller 110 that controls the operation of the sensor element 101 and performs processing to identify concentrations of the sensing target gas components based on currents flowing through the sensor element 101.

[0069] Fig. Figure 2 is a block diagram showing the functional components implemented by the controller 110. The controller 110 is configured by one or more electronic circuits, including, for example, one or more central processing units (CPUs), a memory device, and the like. Each of the electronic circuits is a functional piece of software that implements a predetermined functional component through a CPU executing a predetermined program stored, for example, in the memory device. Of course, the controller 110 can be configured by an integrated circuit, such as a field-programmable gate array (FPGA), on which a plurality of electronic circuits are connected according to their functions and the like.

[0070] When the gas sensor 100 is connected to the exhaust path of the vehicle's engine and used with the exhaust gas flowing along the exhaust path as the measurement gas, some or all of the functions of the controller 110 may be implemented by an electronic control unit (ECU) of the vehicle.

[0071] The controller 110 includes, as functional components executed by the CPU executing a predetermined program, an element operation control part 120 that controls the operation of each part of the above-described sensor element 101, and a concentration identification part 130 that performs processing to identify the concentrations of the sensing target gas components contained in the measurement gas.

[0072] The element operation control part 120 mainly includes an adjustment pump cell control part 121 that controls the operation of the adjustment pump cell 21, a first measurement pump cell control part 122a that controls the operation of the first measurement pump cell 50, a second measurement pump cell control part 122b that controls the operation of the second measurement pump cell 41, and a heater control part 123 that controls the heating operation performed by the heater 72.

[0073] On the other hand, the concentration identifying part 130 mainly includes a water vapor concentration identifying part 130H and a carbon dioxide concentration identifying part 130C, which respectively identify a concentration of H2O and a concentration of CO2 as the main sensing target gas components of the gas sensor 100.

[0074] The water vapor concentration identifying part 130H identifies the concentration of H2O contained in the measurement gas based on a value of the oxygen pumping current Ip2 flowing through the second measurement pumping cell 41, which is detected by the second measurement pumping cell controlling part 122b.

[0075] The carbon dioxide concentration identifying part 130C identifies the concentration of CO2 contained in the measurement gas based on the concentration of H2O identified by the water vapor concentration identifying part 130H (the value of the oxygen pumping current Ip2 on the basis of which the concentration of H2O is identified) and a value of the oxygen pumping current Ip1 flowing through the first measurement pumping cell 50 and detected by the first measurement pumping cell control part 122a.

[0076] The concentration identification part 130 further includes an oxygen concentration identification part 130A that identifies a concentration of oxygen contained in the measurement gas. The oxygen concentration identification part 130A identifies the concentration of oxygen contained in the measurement gas based on a value of the oxygen pumping current Ip0 flowing through the adjustment pumping cell 21, which is detected by the adjustment pumping cell control part 121. This means that the gas sensor 100 according to the present embodiment senses oxygen as a sensing target gas component in addition to H2O and CO2 as the sensing target gas component. <Multi-Gas-Sensierung und Konzentrationsidentifizierung>

[0077] Next, a method for detecting a plurality of gases (multi-gas sensing) and identifying concentrations of the sensed gases will be described, which is implemented by the gas sensor 100 having a configuration as described above. In the following, it is assumed that the measurement gas is an exhaust gas containing oxygen, H2O, and CO2.

[0078] Fig. 3 is a schematic diagram illustrating the entry and exit of gases into and from the three chambers (internal spaces) included in the sensor element 101 of the gas sensor 100.

[0079] First, in the sensor element 101 of the gas sensor 100 according to the present embodiment, the measurement gas is introduced into the first chamber 20 through the gas inlet 10 (first diffusion control part 11), the buffer chamber 12, and the second diffusion control part 13, as described above. In the first chamber 20, oxygen is pumped out of the introduced measurement gas by actuating the adjustment pump cell 21.

[0080] Oxygen pumping is performed by the pump cell control part 121 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 controlling the voltage supplied from the variable power supply 24 to the pump cell control 21 in accordance with a difference between an actual value and the target value of the electromotive force V0, so that the electromotive force V0 is maintained at the target value. A value of the electromotive force V0 deviates significantly from the target value when the measurement gas containing a large amount of oxygen reaches, for example, the first chamber 20, and thus the pump cell control part 121 controls the pump voltage Vp0 supplied from the variable power supply 24 to the pump cell control 21 to reduce the deviation.

[0081] The adjustable pump cell 21 pumps oxygen out of the first chamber 20 in such a way that the oxygen partial pressure in the first chamber 20 is maintained at a sufficiently low value so that the H2O and CO2 contained in the measurement gas are not reduced. It is approximately 10-8 atm, for example, if the equation V0 = 400 mV applies.

[0082] Fig. Figure 4 is a diagram describing one reason why oxygen is pumped out to such an extent that H2O and CO2 are not reduced by setting the setpoint of the electromotive force V0 to a value in the range of 400 mV to 700 mV. In particular, Fig. 4 is a graph showing a relationship between the set value (control voltage) of the electromotive force V0 in the sensor cell 80 of the first chamber and the oxygen pumping current Ip0 flowing through the adjustment pumping cell 21 when three different types of model gases are flowed. Specifically, the three types of model gases include: a first gas containing 10% oxygen, a second gas containing 10% oxygen and 10% CO, and a third gas containing 10% oxygen and 10% H2O. The remainder of each of the gases is nitrogen (N2). The driving element temperature is 800°C or higher, and the temperature of each of the model gases is 150°C.

[0083] Out of Fig. 4, it can be seen that in the case of the first gas, the oxygen pumping current Ip0 is substantially constant when the control voltage is in a range of 0.4 V or more, while in the case of the second gas and the third gas, a profile is substantially the same as that for the first gas when the control voltage is in a range of 0.7 V or less, but the oxygen pumping current Ip0 increases again when the control voltage exceeds 0.7 V. The increase results from the superposition of reduction currents of H2O or CO2 that flow when H2O or CO2 contained in the measurement gas is reduced (decomposed) to generate oxygen.

[0084] Therefore, in the present embodiment, the target value of the electromotive force V0 is set to a value in the range of 400 mV to 700 mV. In order to ensure the durability of the electrode, the electromotive force V0 is preferably as low as possible, and therefore, the target value of the electromotive force V0 is preferably 400 mV.

[0085] As described above, in the gas sensor 100 according to the present embodiment, in the first chamber 20, which has the highest temperature in the sensor element 101 during operation, only oxygen pumping is performed to the extent that H2O and CO2 are not reduced, and unlike a gas sensor using conventional technology, no reduction of H2O and CO2 is performed. The set value of the electromotive force V0 in the sensor cell 80 of the first chamber, which is set for pumping, is 400 mV to 700 mV, which is sufficiently smaller than the set value of 1000 mV to 1500 mV set when H2O and CO2 are reduced. An increase in the pump voltage Vp0 is thus suppressed compared to a voltage applied to a corresponding pump cell in the gas sensor using conventional technology, which is accompanied by a reduction of H2O and CO2.Thus, cracks and blackening due to the application of a high voltage while maintaining the inner pumping electrode 22 at a high temperature are appropriately suppressed in the gas sensor 100 according to the present embodiment.

[0086] The measurement gas, from which only oxygen was pumped out in the first chamber 20 to the extent that H2O and CO2 are not reduced, is introduced into the second chamber 40. H2O and CO2 contained in the measurement gas are reduced in the second chamber 40. This means that oxygen is further pumped out from the measurement gas from which oxygen was pumped out in the first chamber 20 and which is then introduced into the second chamber 40 by the operation of the first measurement pump cell 50, so that a reduction (decomposition) reaction (2H2O → 2H2 + O2 and 2CO2 → 2CO + O2) of H2O and CO2 contained in the measurement gas proceeds, and substantially all of the H2O and CO2 are decomposed into hydrogen (H2), carbon monoxide (CO), and oxygen.

[0087] The reduction (decomposition) of H2O and CO2 and the pumping out of oxygen are carried out such that the first measuring pump cell control part 122a of the controller 110 sets a target value (control voltage) of the electromotive force V1 in the second chamber sensor cell 81 to a value in the range of 1000 mV to 1500 mV (preferably 1000 mV) and regulates the voltage Vp1 applied from the variable power supply device 52 to the first measuring pump cell 50 according to a difference between an actual value and the target value of the electromotive force V1, so that the electromotive force V1 is maintained at the target value. From the diagram in Fig. 4 also shows that the setpoint of the electromotive force V1 should preferably be set to a value in the range of 1000 mV to 1500 mV.

[0088] The first measuring pump cell 50 operates in this way so that the oxygen partial pressure in the second chamber 40 is maintained at a much lower value than the oxygen partial pressure in the first chamber 20. It is, for example, about 10 -20 atm, if the equation V1 = 1000 mV applies. The sample gas thus essentially contains no more H2O, CO2, or oxygen.

[0089] The measuring gas, which contains H2 and CO but essentially no H2O, CO2 and oxygen, is introduced into the third chamber 61.

[0090] In the third chamber 61, oxygen is pumped in by actuating the second measuring pump cell 41 and only the H2 contained in the introduced measuring gas is selectively oxidized.

[0091] The pumping of oxygen is carried out such that the second part 122b of the measuring pump cell control of the controller 110 sets a target value (control voltage) of the electromotive force V2 in the sensor cell 82 of the third chamber to a value in the range of 250 mV to 450 mV (preferably 350 mV) and the voltage Vp2 applied from the variable power supply device 46 to the second measuring pump cell 41 according to a difference between an actual value and the target value of the electromotive force V2, so that the electromotive force V2 is maintained at the target value.

[0092] The second measuring pumping cell 41 operates in this manner to enable an oxidation reaction (a combustion reaction) 2H2 + O2 → 2H2O, and to regenerate H2O in the third chamber 61 in an amount that correlates with the amount of H2O introduced through the gas inlet 10. In the present embodiment, H2O in the corresponding amount means that the amount of H2O introduced through the gas inlet 10 and the amount of H2O regenerated by oxidation of H2 generated by decomposition of H2O are equal to or within a certain error range allowable in view of measurement accuracy.

[0093] The setpoint of the electromotive force V2 is set to a value in the range of 250 mV to 450 mV, so that the oxygen partial pressure in the third chamber 61 is maintained at a value in a range where almost all of the H2 is oxidized, but not CO. It is approximately 10-7 atm, for example, if the equation V2 = 350 mV applies.

[0094] Providing the second measuring electrode 44 as a cermet electrode containing the Pt-Au alloy having an Au concentration of 1 wt% or more and 50 wt% or less as a metal component as described above also contributes to improving the property of selective oxidation of H2.

[0095] In a conventional technology gas sensor, the cermet electrode containing the Pt-Au alloy is provided in the second chamber 40, and the pumping cell including the electrode pumps pumps oxygen for the selective oxidation of H2. However, here, the first sensing electrode 51, which does not contain Au as a metal component, is provided in the second chamber 40, and the second sensing electrode 44, which contains the Pt-Au alloy as a metal component and is responsible for the selective oxidation of H2, is provided to face the third chamber 61 at a lower temperature than the second chamber 40 during operation of the gas sensor 100. Thus, in the gas sensor 100 according to the present embodiment, the evaporation of Au from the electrode is suppressed compared to that in the conventional technology gas sensor.

[0096] In addition, any measures for designing a shape (a width and a thickness), a placement (a density), and the like of the heater element 72 may be taken to further suppress a temperature rise of the second measuring electrode 44.

[0097] In the gas sensor 100 according to the present embodiment, which operates in the above-mentioned manner, the concentrations of H2O and CO2 in the measurement gas are identified based on the oxygen pumping current Ip1 flowing through the first measurement pumping cell 50 during the pumping out of oxygen, including the reduction of H2O and CO2, and the oxygen pumping current Ip2 flowing through the second measurement pumping cell 41 during the pumping in of oxygen for the oxidation of H2.

[0098] The Fig. 5 and Fig. 6 are diagrams showing, when only one of H2O and CO2 is contained alone in the measurement gas as the main sensing target gas component and when H2O and CO2 with equal concentrations are contained in the measurement gas as the main sensing target gas components, the dependence of the oxygen pumping current Ip1 and the oxygen pumping current Ip2 on a concentration of the sensing target gas component and the concentrations of the sensing target gas components.

[0099] In the Fig. 5 and Fig. 6 is a diagram when H2O alone is included as the sensing target gas component, represented by circles, a diagram when CO2 alone is included as the sensing target gas component, represented by triangles, and a diagram when H2O and CO2 with equal concentrations are included as the sensing target gas components (referred to as "H2O + CO2" in the figure) represented by squares. These diagrams are obtained by operating the gas sensor 100 in an atmosphere of each of the model gases containing a sensing target gas component with a known concentration and oxygen and nitrogen as the balance. The driving element temperature is 800°C or more, and the temperature of each of the model gases is 200°C.

[0100] As from Fig. As can be seen from Figure 5, the curve increases monotonically and is approximately linear when only H2O is included as the sensing target component and when only CO2 is included as the sensing target component.

[0101] Furthermore, a value of the oxygen pumping current Ip1 when H2O and CO2 are included at equal concentrations as the sensing target gas component is the sum of a value of the oxygen pumping current Ip1 when H2O alone is included and a value of the oxygen pumping current Ip1 when CO2 alone is included. It has also been confirmed that a value of the oxygen pumping current Ip1 when H2O and CO2 have different proportions is the sum of a value of the oxygen pumping current Ip1 when H2O alone is included at a concentration according to its proportion and a value of the oxygen pumping current Ip1 when CO2 alone is included at a concentration according to its proportion, although this is not shown.

[0102] On the other hand, as in Fig. As shown in Figure 6, a graph of the oxygen pumping current Ip2 when only H2O is included as the sensing target gas component monotonically decreases (its absolute value increases monotonically) and is approximately linear. The oxygen pumping current Ip2 has a negative value because the oxygen pumping current Ip2 flows in a direction in which oxygen is pumped in to reoxidize the H2 generated by reduction in the second chamber 40, while the direction of the oxygen pumping current when the second measuring pumping cell 41 pumps out oxygen is assumed to be the positive direction of the oxygen pumping current, as described above.

[0103] In contrast, when only CO2 is included as the sensing target gas component, the oxygen pumping current Ip2 is maintained at approximately zero. This means that the CO generated by reduction in the second chamber 40 is not re-oxidized by the operation of the second measuring pumping cell 41.

[0104] A graph of the oxygen pumping current Ip2 when H2O and CO2 are included at equal concentrations as the sensing target gas component is essentially the same as the graph of the oxygen pumping current Ip2 when only H2O is included. This agrees with the oxygen pumping current Ip2 of approximately zero when only CO2 is included as the sensing target gas component. It has also been confirmed that a value of the oxygen pumping current Ip2 when H2O and CO2 have different proportions is essentially the same as the graph of the oxygen pumping current Ip2 when only H2O is included and the graph of the oxygen pumping current Ip2 when only CO2 is included, although this is not shown. This means that the oxygen pumping current Ip2 practically only depends on the concentration of H2O, and thus the concentration of H2O can be determined once the oxygen pumping current Ip2 is known.

[0105] In the present embodiment, the concentrations of H2O and CO2 in the measurement gas are measured using the characteristics of the oxygen pumping current Ip1 and the oxygen pumping current Ip2 as described above. The oxygen pumping current Ip1 and the oxygen pumping current Ip2 during the actual measurement using the gas sensor 100 are hereinafter also referred to as the total reduction current Ip1 and the water vapor equivalent current Ip2.

[0106] Specifically, before using the gas sensor 100, characteristic data showing a relationship between the oxygen pumping current Ip1 and a concentration of each gas when the measurement gas contains only one of H2O and CO2 and not the other of H2O and CO2 as shown in Fig. 5 (hereinafter also referred to as Ip1-H2O data and Ip1-CO2 data) and characteristic data showing a relationship between the oxygen pumping current Ip2 and a concentration of H2O when the measurement gas contains H2O and does not contain CO2, as shown in FIG. 6 (hereinafter also referred to as Ip2-H2O data), are acquired in advance using model gases with known concentrations, and these pieces of characteristic data are stored in the controller 110. The Ip1-H2O data and the Ip1-CO2 data each have a value indicating a contribution of H2O and a value indicating a contribution of CO2 to the total reduction current Ip1.

[0107] The oxygen pumping current Ip1 has a value corresponding to the diffusion resistance provided to the measurement gas from the gas inlet 10 to the second chamber 40 of the sensor element 101, and the oxygen pumping current Ip2 has a value corresponding to the diffusion resistance provided to the measurement gas from the gas inlet 10 to the third chamber 61 of the sensor element 101. Therefore, the Ip1-H2O data, the Ip1-CO2 data, and the Ip2-H2O data strictly vary with each sensor element 101 of the gas sensor 100. These characteristic data are therefore preferably identified for each gas sensor 100. However, for gas sensors 100 manufactured under the same conditions and from the same batch, the characteristic data acquired for a specific gas sensor 100 can be applied to another gas sensor 100 from the same batch if it is confirmed that an error is within the tolerance.

[0108] When an actual measurement is performed using the gas sensor 100, the measurement gas is introduced into the sensor element 101 heated to the element driving temperature, and the adjustment pump cell 21, the first measurement pump cell 50, and the second measurement pump cell 41 operate in the above-mentioned manner. The water vapor concentration identification part 130H detects the water vapor equivalent flow Ip2 from the second measurement pump cell control part 122b and identifies an H2O concentration corresponding to the detected value based on the Ip2-H2O data.

[0109] Once the concentration of H2O is identified, the carbon dioxide concentration identification part 130C acquires a value of the total reduction current Ip1 from the first measuring pump cell control part 122a and identifies a contribution of H2O with the identified concentration in the total reduction current Ip1, that is, the amount of current due to the reduction of H2O in the total reduction current Ip1, based on the Ip1-H2O data. The acquired value is subtracted from the value of the total reduction current Ip1 to determine a contribution of CO2 in the total reduction current Ip1. A concentration of CO2 corresponding to the contribution of CO2 is finally determined based on the Ip1-CO2 data.

[0110] In the gas sensor 100 according to the present embodiment, the concentrations of H2O and CO2 in the measurement gas are measured as described above.

[0111] Alternatively, a relationship between the water vapor equivalent current Ip2 and the oxygen pumping current Ip1 corresponding to the contribution of H2O in the total reduction current Ip1 may be identified in advance, the characteristic data (hereinafter referred to as H2O characteristic data) indicating the relationship may be stored in the controller 110, and the carbon dioxide concentration identifying part 130C may directly determine the contribution of H2O to the total reduction current Ip1 from the water vapor equivalent current Ip2 using the H2O characteristic data.

[0112] Fig. Figure 7 is a graph showing an example of the H2O characteristic data. In Fig. Figure 7 shows the absolute value of the water vapor equivalent current Ip2 on an x-axis, and a value of the oxygen pumping current Ip1, corresponding to the contribution of H2O to the total reduction current Ip1, on a y-axis. As shown in Figure 7, there is a linear relationship between the water vapor equivalent current Ip2 and the contribution of H2O to the total reduction current Ip1, so a relationship expressing the linear relationship only needs to be identified as H2O characteristic data.

[0113] Alternatively, a value of the Y-intercept of the relationship should theoretically be zero, and in the case of a properly operating gas sensor 100, is a value small enough to actually be considered zero. Therefore, only the slope of the relationship expressing the above-mentioned linear relationship can be stored in the controller 110 as the H2O characteristic data, and the carbon dioxide concentration identification part 130C can use the product of the slope value and the water vapor equivalent current Ip2 as the contribution of H2O to the total reduction current Ip1.

[0114] The slope in the H2O characteristic data corresponds to a ratio of the diffusion resistance offered to the sample gas from the gas inlet 10 to the third chamber 61 to the diffusion resistance offered to the sample gas from the gas inlet 10 to the second chamber 40.

[0115] The oxygen concentration is identified using the oxygen pumping current Ip0 flowing through the adjusting pump cell 21 in parallel with the identification of the concentrations of H2O and CO2.

[0116] In the gas sensor 100 according to the present embodiment, oxygen is pumped out from the measurement gas introduced into the first chamber 20 through the gas inlet 10 by the operation of the adjustment pumping cell 21 as described above. The oxygen is pumped out to the extent that H2O and CO2 are not reduced, and the oxygen pumping current Ip0 flowing in this case (hereinafter also referred to as the oxygen detection current Ip0) is substantially proportional to the concentration of oxygen contained in the measurement gas introduced through the gas inlet 10. This means that a linear relationship exists between the oxygen detection current Ip0 and the oxygen concentration in the measurement gas. Data (Ip0-O2 data) indicating the linear relationship is identified in advance using model gases with known oxygen concentrations and stored in the controller 110.

[0117] During the actual measurement using the gas sensor 100, the oxygen concentration identification part 130A detects a value of the oxygen detection current Ip0 from the adjustment pump cell control part 121. An oxygen concentration value corresponding to the detected oxygen detection current Ip0 is identified by referring to the Ip0-O2 data. The oxygen concentration in the measurement gas is thereby identified.

[0118] As described above, in the gas sensor according to the present embodiment, the concentrations of H2O and CO2 can be measured when the measurement gas contains H2O and CO2, just like a conventional gas sensor. Furthermore, the oxygen concentration can also be accurately determined.

[0119] Furthermore, in a gas sensor according to the present embodiment, H2O and CO2 in the first chamber are not reduced to a highest temperature during operation, unlike a gas sensor using conventional technology, so that a voltage applied to the adjusting pump cell that pumps out oxygen from the first chamber is suppressed to be lower than that in the gas sensor using conventional technology, thereby appropriately suppressing cracks and blackening of the sensor element.

[0120] An electrode arranged in a chamber as an electrode containing a Pt-Au alloy as a metal component is only the second measuring electrode provided in the third chamber, and the electrode containing the Pt-Au alloy is not provided in the first chamber and the second chamber to have a higher temperature than the third chamber, so that the evaporation of Au from the electrode is suppressed compared to that in the conventional technology.

[0121] This means that according to the present embodiment, a multi-gas sensor with higher long-term reliability than before is implemented. <modifizierungen>

[0122] In the gas sensor 100 according to the above-mentioned embodiment, the sensor element 101 includes the gas distribution part, which includes the first chamber 20, the second chamber 40, and the third chamber 61, which communicate with each other via the diffusion control parts. With respect to the measurement gas sequentially introduced into the chambers of the gas distribution part under a predetermined diffusion resistance, the adjustment pumping cell 21 pumps out oxygen to such an extent that H2O and CO2 in the first chamber 20 are not reduced, the first measurement pumping cell 50 is used to reduce H2O and CO2 in the second chamber 40, and the second measurement pumping cell 41 is used to selectively oxidize H2 generated by the reduction of H2O in the third chamber 61.As a result, the concentrations of H2O and CO2 and also the concentration of oxygen in the sample gas are measured based on the magnitudes of the currents flowing through the respective pump cells.

[0123] Such a measurement using the gas sensor 100 is considered to be performed by suppressing a flow of the measurement gas from outside the element into the first chamber 20 using the first diffusion control part 11 and the second diffusion control part 13, suppressing a flow of the measurement gas in which oxygen remains from the first chamber 20 into the second chamber 40 using the third diffusion control part 30, and further suppressing a flow of the measurement gas in which H2O and CO2 remain from the second chamber 40 into the third chamber 61 using the fourth diffusion control part 60.That is, the measurement gas reaching the inner pumping electrode 22 of the adjusting pumping cell 21, the first measuring electrode 51 of the first measuring pumping cell 50, and the second measuring electrode 44 of the second measuring pumping cell 41 is appropriately controlled by the respective diffusion control parts so that gases not provided for operation in the respective pumping cells do not reach the respective electrodes, thereby enabling multi-gas sensing using the gas sensor 100.

[0124] In other words, a configuration other than the configuration of the gas distribution part of the sensor element 101 can be adopted as long as the pumping of oxygen to the extent that H2O and CO2 are not reduced using the adjustment pumping cell 21, the reduction of H2O and CO2 using the first measuring pumping cell 50, and the selective oxidation of H2 generated by reducing H2O using the second measuring pumping cell 41 are successfully performed with respect to the measurement gas reaching the inner pumping electrode 22, the first measuring electrode 51, and the second measuring electrode 44, to ensure measurement accuracy. For example, even a configuration in which the three chambers communicate via the diffusion control parts are not included can be adopted to implement multi-gas sensing.

[0125] Fig. 8 is a diagram schematically showing an example of a configuration of a gas sensor 200 according to a modification taking the above into account. The gas sensor 200 is a multi-gas sensor that senses a variety of gas components and measures their concentrations using a sensor element 201. In the gas sensor 200, the control performed by the controller 110 enables multi-gas sensing with at least water vapor (H2O) and carbon dioxide (CO2) as the main sensing target gas components, as described below, as in the gas sensor 100. Fig. 8 includes a vertical cross-sectional view taken along a longitudinal direction of the sensor element 201.

[0126] The sensor element 201 is an elongated planar structure comprising a laminate of a sensor part 214 and a heater part 270.

[0127] The sensor part 214 is formed by laminating a plurality of ceramic substrate layers. Specifically, the sensor part 214 has a configuration in which four layers, including a first substrate 203, a second substrate 204, a third substrate 205, and a fourth substrate 206, are sequentially laminated from the bottom. Of these, at least the second substrate 204 is formed of a solid electrolyte conductive to oxygen ions, such as zirconia. The first substrate 203, the third substrate 205, and the fourth substrate 206 may be formed of a solid electrolyte or an insulating material, such as alumina. In the sensor part 214, the first substrate 203 is adjacent to the heater part 270.

[0128] A gas inlet 210 through which a measurement gas is introduced is provided in one end portion (a left end portion in the figure) of the sensor part 214. More specifically, a diffusion control part 211 made of a porous body with a porosity of about 10% to 50% is embedded in a portion of the third substrate 205, and an exposed portion in a portion of the diffusion control part 211 is the gas inlet 210. The diffusion control part 211 has a length (lengthwise dimension of the element) of, for example, 0.5 mm to 1.0 mm, a width (widthwise dimension of the element) of, for example, 1.5 mm to 3 mm, and a height (thickness dimension of the element) of, for example, 10 μm to 20 μm.

[0129] The sensor part 214 also includes a single internal chamber 220 adjacent to the diffusion control part 211. The internal chamber 220 is formed to penetrate the third substrate 205 in the thickness direction. The internal chamber 220 has a length (lengthwise dimension of the element) of, for example, 6.0 mm to 12.0 mm, a width (transverse dimension of the element) of, for example, 1.5 mm to 2.5 mm, and a height (thickness dimension of the element) of, for example, 50 µm to 200 µm.

[0130] This means that the diffusion control part 211 and the internal chamber 220 form the gas distribution part, which is connected to the gas inlet 210 in the sensor element 201.

[0131] An adjustment electrode 230, a first measuring electrode 240, and a second measuring electrode 250 are arranged on an exposed surface 204a of the second substrate 204 to the internal chamber 220 in order of proximity to the gas inlet 210 on a left side in the figure, so as to face the internal chamber 220 while being spaced apart from each other at predetermined intervals. They are provided as porous cermet electrodes similar to the internal pumping electrode (adjustment electrode) 22, the first measuring electrode 51, and the second measuring electrode 44 of the sensor element 101.

[0132] The sensor part 214 further includes a reference gas introduction space 260, which opens in the other portion of the end of the sensor element 201. The reference gas introduction space 260 is formed to penetrate the first substrate 203 in the thickness direction. Oxygen (O2) and air, for example, are introduced into the reference gas introduction space 260 as reference gases.

[0133] A reference electrode 261 is provided on an exposed surface 204b of the second substrate 204 facing the reference gas introduction space 260. The reference electrode 261 is preferably provided over an entire area of ​​the array of the adjustment electrode 230, the first measuring electrode 240, and the second measuring electrode 250, which are provided on the exposed surface 204a opposite the exposed surface 204b. The reference electrode 261 is provided as a porous cermet electrode containing platinum and zirconium dioxide and is, for example, rectangular in plan view.

[0134] Like the heater part 70 of the sensor element 101, the heater part 270 is configured to heat the sensor element 101 to a predetermined temperature and maintain the temperature by supplying power to the heater element 272 (also referred to simply as the heater 272) from outside the element. A similar configuration to that of the heater element 70 of the sensor element 101 is applicable to the heater part 270. Alternatively, a configuration in which the heater element 272 is embedded in an insulator may be used.

[0135] The heater 272 is provided such that the temperature is highest near the adjustment electrode 230 and decreases with increasing distance from the adjustment electrode 230 in the longitudinal direction of the element during heating.

[0136] In addition, the sensor element 201 has an adjustment pump cell C0, a first measuring pump cell C1 and a second measuring pump cell C2.

[0137] The adjustable pump cell C0 is an electrochemical pump cell comprising the adjustable electrode 230, the reference electrode 261, and the second substrate 204 disposed between these electrodes. In the adjustable pump cell C0, the voltage Vp0 is applied across the adjustable electrode 230 and the reference electrode 261 by a variable power supply 231 disposed outside the sensor element 201 to generate the oxygen pump current (oxygen ion current) Ip0. The operation of the adjustable pump cell C0 is controlled by the adjustable pump cell control section 121 of the controller 110.

[0138] The first measuring pump cell C1 is an electrochemical pump cell comprising the first measuring electrode 240, the reference electrode 261, and the second substrate 204 disposed between these electrodes. In the first measuring pump cell C1, the voltage Vp1 is applied across the first measuring electrode 240 and the reference electrode 261 by a variable power supply 241 disposed outside the sensor element 201 to generate the oxygen pump current (oxygen ion current) Ip1. The operation of the first measuring pump cell C1 is controlled by the first measuring pump cell control part 122a of the controller 110.

[0139] The second measuring pump cell C2 is an electrochemical pump cell comprising the second measuring electrode 250, the reference electrode 261, and the second substrate 204 disposed between these electrodes. In the second measuring pump cell C2, the voltage Vp2 is applied across the second measuring electrode 250 and the reference electrode 261 by a variable power supply 251 disposed outside the sensor element 201 to generate the oxygen pump current (oxygen ion current) Ip2. The operation of the second measuring pump cell C2 is controlled by the second measuring pump cell control part 122b of the controller 110.

[0140] As described above, in the sensor element 201, the adjustment electrode 230, the first measuring electrode 240, and the second measuring electrode 250 are arranged in the single internal chamber 220, unlike the sensor element 101 of the gas sensor 100. However, the diffusion control part 211 and the internal chamber 220 are provided under the conditions described above to provide appropriate diffusion resistance to the measurement gas introduced into the internal chamber 220, in other words, to ensure appropriate control of the flow rate of the measurement gas, and therefore, multi-gas sensing with at least water vapor (H2O) and carbon dioxide (CO2) as sensing target gas components is also enabled in the gas sensor 200 having the sensor element 201 controlled by the controller 110, as performed in the gas sensor 100.

[0141] Specifically, the measurement gas introduced from the gas inlet 210 through the diffusion control part 211 into the internal chamber 220 sequentially reaches the adjustment electrode 230, the first measuring electrode 240, and the second measuring electrode 250. The adjustment pump cell C0 performs an operation to pump oxygen out of the measurement gas that has reached the adjustment electrode 230, unless H2O and CO2 are reduced. The first measuring pump cell C1 performs an operation to pump oxygen out to reduce H2O and CO2 contained in the measurement gas after they reach the first measuring electrode 240. The second measuring pump cell C2 performs an operation to pump oxygen in to selectively oxidize H2 generated by the reduction of H2O performed by the first measuring pump cell C1 and that has reached the second measuring electrode 250.

[0142] In this case, the measurement gas flows at a flow rate such that the measurement gas from which no oxygen has been pumped out does not flow through the adjustment electrode 230, and the measurement gas in which H2O and CO2 remain does not flow through the first measurement electrode 240, so that a current flowing through each pump cell is equivalent to a current flowing through each pump cell of the gas sensor 100. Thus, in the gas sensor 200, the water vapor concentration identification part 130H, the carbon dioxide concentration identification part 130C, and further the oxygen concentration identification part 130A can accurately identify the concentrations of H2O, CO2, and further oxygen in the measurement gas, as in the gas sensor 100. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 6469462

[0007] < / modifizierungen>

Claims

[1] A gas sensor capable of measuring concentrations of a plurality of sensing target gas components contained in a measurement gas, the measurement gas containing water vapor and carbon dioxide, the gas sensor comprising: a sensor element having a structure formed from a solid electrolyte conductive to oxygen ions; and a controller that controls the operation of the gas sensor, wherein the sensor element comprises: a gas inlet through which the measuring gas is introduced; an internal chamber connected to the gas inlet via a diffusion control part; a setting electrode, a first measuring electrode and a second measuring electrode, each provided to face the inner chamber and arranged in the order of proximity to the gas inlet, being spaced apart from each other at predetermined intervals; a tuning pump cell comprising the tuning electrode, an outside-the-space pump electrode provided at a location other than a location in the internal chamber, and a portion of the solid electrolyte provided between the tuning electrode and the outside-the-space pump electrode; a first measuring pumping cell comprising the first measuring electrode, the outside-of-space pumping electrode, and a portion of the solid electrolyte provided between the first measuring electrode and the outside-of-space pumping electrode; a second measuring pump cell comprising the second measuring electrode, the outside-space pump electrode, and a portion of the solid electrolyte present between the second measuring electrode and the outside-space pump electrode; and a heating device that heats the sensor element, the heating device heats the sensor element so that a temperature near the setting electrode in the inner chamber is highest and decreases with increasing distance from the setting electrode in a longitudinal direction of the sensor element, the adjustment pump cell pumps oxygen out of the measuring gas that has reached the adjustment electrode through the gas inlet to such an extent that water vapor and carbon dioxide contained in the measuring gas are not decomposed, the first measuring pump cell pumps oxygen from the measuring gas that has reached the first measuring electrode to such an extent that essentially all of the water vapor and carbon dioxide contained in the measuring gas, from which oxygen was pumped out by the adjusting pump cell, are reduced, the second measuring pump cell pumps oxygen into the inner chamber to selectively oxidise hydrogen produced by the reduction of water vapour and contained in the measuring gas that has reached the second measuring electrode, and the controller has: a water vapor concentration identifying means for identifying a concentration of water vapor contained in the measurement gas based on a value of a water vapor equivalent current as an oxygen pumping current flowing between the second measuring electrode and the outside-the-space pumping electrode when hydrogen is oxidized with oxygen pumped through the second measuring pumping cell; and a carbon dioxide concentration identifying means for identifying a concentration of carbon dioxide contained in the measurement gas based on the value of the water vapor equivalent current and a value of a total reduction current as an oxygen pumping current flowing between the first measurement electrode and the outside-the-room pumping electrode when water vapor and carbon dioxide are reduced by the first measurement pumping cell that pumps out oxygen. [2] Gas sensor according to claim 1, wherein the inner chamber comprises a first chamber, a second chamber and a third chamber, which are connected to each other in succession in the order of their proximity to the gas inlet via various diffusion control parts, the adjustment electrode is arranged in the first chamber, the first measuring electrode is arranged in the second chamber and the second measuring electrode is arranged in the third chamber. [3] The gas sensor of claim 2, wherein the controller stores: Ip1-H2O data indicating a relationship between an oxygen pumping current flowing through the first measuring pumping cell and a concentration of water vapor when the measuring gas contains water vapor and does not contain carbon dioxide, the Ip1-H2O data being identified in advance; Ip1-CO2 data indicating a relationship between an oxygen pumping current flowing through the first measuring pumping cell and a concentration of water vapor when the measuring gas contains carbon dioxide and does not contain water vapor, the Ip1-CO2 data being identified in advance; and Ip2-H2O data indicating a relationship between an oxygen pumping current flowing through the second measuring pumping cell and a concentration of water vapor when the measuring gas contains water vapor and no carbon dioxide, the Ip2-H2O data being identified in advance, the water vapor concentration identification device identifies a concentration of water vapor corresponding to the value of the water vapor equivalent flow in the Ip2-H2O data as the concentration of water vapor contained in the measurement gas, and the carbon dioxide concentration identifying means identifies a contribution of water vapor by reducing the total reduction current based on the concentration of water vapor contained in the measurement gas identified by the water vapor concentration identifying means and the Ip1-H2O data, and identifies a concentration of carbon dioxide corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the Ip1-CO2 data as the concentration of carbon dioxide contained in the measurement gas. [4] The gas sensor of claim 2, wherein the controller stores: Ip1-CO2 data indicating a relationship between an oxygen pumping current flowing through the first measuring pumping cell and a concentration of water vapor when the measuring gas contains carbon dioxide and does not contain water vapor, the Ip1-CO2 data being identified in advance; Ip2-H2O data indicating a relationship between an oxygen pumping current flowing through the second measuring pumping cell and a concentration of water vapor when the measuring gas contains water vapor and no carbon dioxide, the Ip2-H2O data being identified in advance; and H2O characteristic data indicating a relationship between the water vapor equivalent current and an oxygen pumping current corresponding to a contribution of water vapor in the total reduction current, wherein the H2O characteristic data is identified in advance, the water vapor concentration identifying means identifies a concentration of water vapor corresponding to the value of the water vapor equivalent current in the Ip2-H2O data as the concentration of water vapor contained in the measurement gas, and the carbon dioxide concentration identifying means identifies a contribution of water vapor by reducing the total reduction current based on the water vapor equivalent current and the H2O characteristic data, and identifies a concentration of carbon dioxide corresponding to a difference value obtained by subtracting the contribution from the total reduction current in the Ip1-CO2 data as the concentration of carbon dioxide contained in the measurement gas. [5] The gas sensor according to any one of claims 2 to 4, wherein the second measuring electrode is a cermet electrode containing a Pt-Au alloy as a metal component, and the Pt-Au alloy has an Au concentration of 1 wt% or more and 50 wt% or less. [6] The gas sensor according to claim 5, wherein the adjustment electrode and the first measuring electrode are cermet electrodes containing Pt and not containing Au. [7] Gas sensor according to one of claims 2 to 4, wherein the controller further comprises: an oxygen concentration identifying means for identifying the concentration of oxygen contained in the measurement gas based on the strength of the current flowing between the adjusting electrode and the outside-the-space pumping electrode when the adjusting pumping cell pumps oxygen out of the first chamber. [8] A concentration measuring method for measuring concentrations of a plurality of sensing target gas components contained in a measurement gas using a gas sensor, the measurement gas containing water vapor and carbon dioxide, wherein the gas sensor comprises a sensor element with an elongated planar structure formed from a solid electrolyte conductive to oxygen ions, wherein the sensor element comprises: a gas inlet through which the measuring gas is introduced; an internal chamber connected to the gas inlet via a diffusion control part; a setting electrode, a first measuring electrode and a second measuring electrode, each provided so as to face the inner chamber and arranged in the order of their proximity to the gas inlet, being spaced apart from each other at predetermined intervals; a tuning pump cell comprising the tuning electrode, an outside-the-space pump electrode provided at a location other than a location in the internal chamber, and a portion of the solid electrolyte provided between the tuning electrode and the outside-the-space pump electrode; a first measuring pumping cell comprising the first measuring electrode, the outside-of-space pumping electrode, and a portion of the solid electrolyte provided between the first measuring electrode and the outside-of-space pumping electrode; a second measuring pump cell comprising the second measuring electrode, the outside-space pump electrode, and a portion of the solid electrolyte present between the second measuring electrode and the outside-space pump electrode; and a heating device that heats the sensor element, and the method for measuring concentration using the gas sensor comprises: a) heating the sensor element using the heating device so that a temperature near the setting electrode in the inner chamber is highest and decreases with increasing distance from the setting electrode in a longitudinal direction of the sensor element; b) pumping oxygen from the measuring gas which has reached the adjustment electrode through the gas inlet through the adjustment pump cell to such an extent that water vapour and carbon dioxide contained in the measuring gas are not decomposed; c) pumping oxygen from the measurement gas that has reached the first measurement electrode using the first measurement pumping cell so that substantially all of the water vapor and carbon dioxide contained in the measurement gas from which oxygen has been pumped out using the adjustment pumping cell are reduced; d) pumping oxygen into the inner chamber using the second measuring pumping cell to selectively oxidise hydrogen produced by reduction of water vapor and contained in the measuring gas that has reached the second measuring electrode; e) identifying a concentration of water vapor contained in the measurement gas based on a value of a water vapor equivalent current as an oxygen pumping current flowing between the second measurement electrode and the outside-the-space pumping electrode when hydrogen is oxidized with oxygen pumped in using the second measurement pumping cell; and f) identifying a concentration of carbon dioxide contained in the measurement gas based on the value of the water vapor equivalent current and a value of a total reduction current as an oxygen pumping current flowing between the first measurement electrode and the outside-the-room pumping electrode when water vapor and carbon dioxide are reduced by pumping out oxygen using the first measurement pumping cell. [9] A method for measuring concentration using the gas sensor according to claim 8, wherein the inner chamber comprises a first chamber, a second chamber and a third chamber, which are connected in series in the order of their proximity to the gas inlet via various diffusion control parts, the adjustment electrode is arranged in the first chamber, the first measuring electrode is arranged in the second chamber and the second measuring electrode is arranged in the third chamber. [10] A method for measuring concentration using the gas sensor according to claim 9, further comprising: g) before steps a) to f), the prior identification of: Ip1-H2O data indicating a relationship between an oxygen pumping current flowing through the first measuring pumping cell and a concentration of water vapor when the measuring gas contains water vapor and does not contain carbon dioxide; Ip1-CO2 data indicating a relationship between an oxygen pumping current flowing through the first measuring pumping cell and a concentration of water vapor when the measuring gas contains carbon dioxide and does not contain water vapor; and Ip2-H2O data indicating a relationship between an oxygen pumping current flowing through the second measuring pumping cell and a concentration of water vapor when the measuring gas contains water vapor and does not contain carbon dioxide, where in step e) a concentration of water vapor corresponding to the value of the water vapor equivalent flow in the Ip2-H2O data is identified as the concentration of water vapor contained in the measurement gas, and in step f) a contribution of water vapor by reduction in the total reduction flow is identified on the basis of the concentration of water vapor contained in the measurement gas identified in step e) and the Ip1-H2O data, and a concentration of carbon dioxide corresponding to a difference value obtained by subtracting the contribution from the total reduction flow in the Ip1-CO2 data is identified as the concentration of carbon dioxide contained in the measurement gas. [11] A method for measuring concentration using the gas sensor according to claim 9, further comprising: g) before steps a) to f), the prior identification of: Ip1-CO2 data indicating a relationship between an oxygen pumping current flowing through the first measuring pumping cell and a concentration of water vapor when the measuring gas contains carbon dioxide and does not contain water vapor; Ip2-H2O data indicating a relationship between an oxygen pumping current flowing through the second measuring pumping cell and a concentration of water vapor when the measuring gas contains water vapor and no carbon dioxide; and H2O characteristic data indicating a relationship between the water vapor equivalent flow and an oxygen pumping current corresponding to a contribution of water vapor to the total reduction flow, where in step e) a concentration of water vapor corresponding to the value of the water vapor equivalent flow in the Ip2-H2O data is identified as the concentration of water vapor contained in the measurement gas, and in step f) a contribution of water vapor by reduction in the total reduction flow is identified on the basis of the water vapor equivalent flow and the H2O characteristic data, and a concentration of carbon dioxide corresponding to a difference value obtained by subtracting the contribution from the total reduction flow in the Ip1-CO2 data is identified as the concentration of carbon dioxide contained in the measurement gas. [12] A method for measuring concentration using the gas sensor according to any one of claims 9 to 11, wherein the second measuring electrode is a cermet electrode containing a Pt-Au alloy as a metal component, and the Pt-Au alloy has an Au concentration of 1 wt% or more and 50 wt% or less. [13] A method for measuring concentration using the gas sensor according to claim 12, wherein the adjusting electrode and the first measuring electrode are cermet electrodes containing Pt and not containing Au. [14] A method for measuring concentration using the gas sensor according to any one of claims 9 to 11, further comprising: g) identifying a concentration of oxygen contained in the measurement gas based on a magnitude of a current flowing between the adjusting electrode and the outside-the-space pumping electrode when oxygen is pumped out of the first chamber using the adjusting pumping cell.

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