Gas sensor and method of measuring concentration with gas sensor

Abstract

In the present invention, a regulation pump cell executes a first pump-out operation for pumping out oxygen so that all of the H2Ｏ and CO2 in a gas under measurement introduced to a first chamber is reduced. A first measurement pump cell selectively oxidizes H2 in a gas under measurement introduced to a second chamber. A second measurement pump cell oxidizes CO in a gas under measurement introduced to a third chamber, identifies the H2O concentration on the basis of a pump-in electrical current to the second chamber, and identifies the CO2 concentration on the basis of a pump-in electrical current to the third chamber. During an ongoing first pump-out operation, the regulation pump cell is furthermore capable of executing a second pump-out operation for pumping out oxygen from the first chamber to an extent whereby the H2O and CO2 are not reduced. Starting the second pump-out operation and interrupting the reduction of the H2O and CO2 in the first chamber causes H2O and CO2 generated in the second chamber or the third chamber to be discharged to the element exterior.

Description

Gas sensor and concentration measurement method using gas sensor

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

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

[0003] In addition, a carbon dioxide detection device is already known in which an air-fuel ratio detection electrode and a carbon dioxide detection electrode are arranged in parallel, and by using the current flowing between each electrode and a reference electrode, the concentration of carbon dioxide can be measured while making corrections that take into account the influence of the air-fuel ratio, and which can also make corrections that take into account the influence of water concentration (see, for example, Patent Document 4).

[0004] In the three-chamber gas sensor disclosed in Patent Document 1, first, a main pump cell, which is a pump cell for the first internal space, is operated to pump O contained in the measurement gas introduced into the first internal space. ２ is pumped out, and H contained in the gas to be measured is also pumped out. ２ O and CO ２ Once everything is returned, ２ and CO. These H ２ The measurement gas containing CO and O is introduced into the second and third internal spaces. ２ H by pumping ２ is selectively oxidized to H２ O is generated and further O is pumped by the second measurement pump cell, which is a pump cell for the third internal cavity. ２ When CO is pumped in, CO is oxidized and CO ２ are generated. Then, these H ２ and CO are oxidized, based on the magnitude of the pump current flowing through the first measuring pump cell and the second measuring pump cell. ２ O and CO ２ The concentration of

[0005] The generated H ２ O and CO ２ However, as the measurement continues, the H ２ O and CO ２ flows back into the first internal cavity and is reduced again, and the H ２ It has been found that a phenomenon can occur in which CO is re-oxidized by pumping oxygen into the second and third internal spaces by the first and second metering pump cells.

[0006] When this phenomenon occurs, the H contained in the measurement gas ２ O and CO ２ The currents due to reoxidation related to the pump currents flowing through the first and second measuring pumping cells are superimposed depending on the amount of H ２ O and CO ２ This is undesirable because it reduces the measurement accuracy of the gas sensor according to Patent Document 1, which measures the concentration of

[0007] In the gas sensor disclosed in Patent Document 4, carbon dioxide is decomposed into carbon and oxygen in the carbon dioxide detection cell, while the electromotive force of the air-fuel ratio detection cell is controlled to be a constant value according to the oxygen concentration of the exhaust gas. However, even in this gas sensor, the CO and oxygen generated in the carbon dioxide detection cell react in the air-fuel ratio detection cell that adjusts the oxygen concentration, resulting in CO ２ is generated and repeatedly detected by the carbon dioxide detection cell, which may reduce the measurement accuracy.

[0008] Japanese Patent No. 5918177 Japanese Patent No. 6469464 Japanese Patent No. 6469462 Japanese Patent Application Laid-Open No. 2020-67432

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a gas sensor that suitably suppresses a decrease in measurement accuracy due to the presence of substances generated during concentration measurement.

[0010] In order to solve the above problems, a first aspect of the present invention is a gas sensor capable of measuring the concentrations of a plurality of target gas components contained in a measurement gas containing at least water vapor and carbon dioxide, the gas sensor comprising: a sensor element having a structure made of an oxygen ion conductive solid electrolyte; and a controller for controlling the operation of the gas sensor, wherein the sensor element comprises: a gas inlet through which the measurement gas is introduced; a plurality of chambers sequentially communicating with the gas inlet via different diffusion rate-limiting portions; and a heater for heating the sensor element; Two of the chambers are a first measuring chamber and a second measuring chamber, the second measuring chamber being the chamber furthest from the gas inlet among the plurality of chambers, and the first measuring chamber being the chamber immediately preceding the second measuring chamber, and the measuring apparatus further comprises: an oxygen pumping means capable of performing a first pumping operation of pumping oxygen contained in the measurement gas so that substantially all of the water vapor and carbon dioxide contained in the measurement gas are reduced before the measurement gas introduced from the gas inlet reaches the first measuring chamber; and an oxygen pumping means facing the first measuring chamber. a first measurement pump cell including a first measurement electrode formed in the second measurement chamber, an outside-void pump electrode provided at a location other than the plurality of voids, and the solid electrolyte present between the first measurement electrode and the outside-void pump electrode; and a second measurement pump cell including a second measurement electrode formed facing the second measurement chamber, the outside-void pump electrode, and the solid electrolyte present between the second measurement electrode and the outside-void pump electrode, wherein the first measurement pump cell pumps oxygen into the first measurement chamber, the second measuring pump cell is configured to be capable of selectively oxidizing, in the first measuring chamber, hydrogen produced by reduction of water vapor during the first pumping operation and contained in the measurement gas introduced into the second measuring chamber; the second measuring pump cell is configured to be capable of oxidizing, in the second measuring chamber, carbon monoxide produced by reduction of carbon dioxide during the first pumping operation and contained in the measurement gas introduced into the second measuring chamber by pumping oxygen into the second measuring chamber; and the controller isand a carbon dioxide concentration determining means for determining the concentration of carbon dioxide contained in the measurement gas based on the magnitude of the current flowing between the second measurement electrode and the pump electrode outside the cavity when oxygen is pumped into the first measurement chamber by the first measurement pump cell, wherein the oxygen pumping means is further configured to be capable of performing a second pumping operation for a predetermined time during the first pumping operation, the second pumping operation being for pumping oxygen contained in the measurement gas to an extent that water vapor and carbon dioxide contained in the measurement gas before it reaches the first measurement chamber are not reduced, and when the second pumping operation is started and the reduction of water vapor and carbon dioxide by the oxygen pumping means is interrupted, the water vapor generated in the first measurement chamber and the carbon dioxide generated in the second measurement chamber are discharged to the outside of the sensor element.

[0011] A second aspect of the present invention is the gas sensor according to the first aspect, wherein the plurality of chambers are a first chamber, a second chamber which is the first measurement chamber, and a third chamber which is the second measurement chamber, and the sensor element further includes an adjustment pump cell as the oxygen pumping means, the adjustment pump cell including an adjustment electrode formed facing the first chamber, the outside-of-cavity pump electrode, and the solid electrolyte present between the adjustment electrode and the outside-of-cavity pump electrode, and the adjustment pump cell pumps oxygen from the first chamber in the first pumping operation so that water vapor and carbon dioxide contained in the measurement gas introduced into the first chamber are substantially all reduced. and a second pumping operation, which pumps oxygen from the first chamber to such an extent that the water vapor and carbon dioxide contained in the measurement gas introduced into the first chamber are not reduced, is performed for a predetermined time during the first pumping operation. When the adjustment pump cell starts the second pumping operation, the reduction of the water vapor and carbon dioxide in the first chamber is interrupted, and the water vapor generated in the second chamber and the carbon dioxide generated in the third chamber are discharged to the outside of the sensor element via the first chamber.

[0012] A third aspect of the present invention is a gas sensor according to the second aspect, characterized in that the adjustment pump cell alternately and periodically performs the first pumping operation and the second pumping operation, and the pumping of oxygen into the second chamber by the first measurement pump cell and the pumping of oxygen into the third chamber by the second measurement pump cell are performed periodically in accordance with the first pumping operation and the second pumping operation by the adjustment pump cell.

[0013] A fourth aspect of the present invention is a gas sensor according to the third aspect, characterized in that the pumping of oxygen into the second chamber by the first measuring pump cell and the pumping of oxygen into the third chamber by the second measuring pump cell are performed in synchronization with the second pumping operation by the adjusting pump cell.

[0014] A fifth aspect of the present invention is a gas sensor according to the third aspect, characterized in that the first measuring pump cell pumps oxygen into the second chamber and the second measuring pump cell pumps oxygen into the third chamber from the middle of the first pumping operation by the adjusting pump cell to the middle of the second pumping operation.

[0015] A sixth aspect of the present invention is the gas sensor according to any one of the second to fifth aspects, wherein the sensor element further comprises: a first chamber sensor cell comprising a reference electrode in contact with a reference gas, the adjusting electrode, the reference electrode, and the solid electrolyte present between the adjusting electrode and the reference electrode, wherein an electromotive force V0 corresponding to the oxygen concentration of the first chamber is generated between the adjusting electrode and the reference electrode; a second chamber sensor cell comprising the first measurement electrode, the reference electrode, and the solid electrolyte present between the first measurement electrode and the reference electrode, wherein an electromotive force V1 corresponding to the oxygen concentration of the second chamber is generated between the first measurement electrode and the reference electrode; and a third chamber sensor cell comprising the second measurement electrode, the reference electrode, and the solid electrolyte present between the second measurement electrode and the reference electrode, wherein an electromotive force V2 corresponding to the oxygen concentration of the third chamber is generated between the second measurement electrode and the reference electrode; The pumping system further comprises: a regulating pump cell control means for controlling a voltage applied between the regulating electrode and the pump electrode outside the cavity in the regulating pump cell so that an electromotive force V0 in the sensor cell is maintained at a predetermined target value within a range of 1000 mV to 1500 mV during the first pumping operation and at a predetermined target value within a range of 400 mV to 700 mV during the second pumping operation; a first measurement pump cell control means for controlling a voltage applied between the first measurement electrode and the pump electrode outside the cavity in the first measurement pump cell so that an electromotive force V1 in the second chamber sensor cell is maintained at a predetermined target value within a range of 250 mV to 450 mV; and a second measurement pump cell control means for controlling a voltage applied between the second measurement electrode and the pump electrode outside the cavity in the second measurement pump cell so that an electromotive force V2 in the third chamber sensor cell is maintained at a predetermined target value within a range of 100 mV to 300 mV.

[0016] A seventh aspect of the present invention is a method for measuring concentrations of a plurality of target gas components contained in a measurement gas containing at least water vapor and carbon dioxide by a gas sensor, the gas sensor comprising a sensor element having a structure made of an oxygen ion conductive solid electrolyte, the sensor element comprising a gas inlet through which the measurement gas is introduced, a plurality of chambers sequentially communicating with the gas inlet via different diffusion rate-limiting parts, and a heater for heating the sensor element, wherein two of the plurality of chambers are used for a first measurement. a chamber and a second measuring chamber, the second measuring chamber being the chamber furthest from the gas inlet among the plurality of chambers, and the first measuring chamber being the chamber immediately preceding the second measuring chamber, and the sensor element includes: an oxygen pumping means capable of performing a first pumping operation of pumping oxygen contained in the measurement gas so that substantially all of the water vapor and carbon dioxide contained in the measurement gas are reduced before the measurement gas introduced from the gas inlet reaches the first measuring chamber; and a first oxygen pumping means formed facing the first measuring chamber. a first measurement pump cell including a measurement electrode, an outside-void pump electrode provided at a location other than the plurality of chambers, and the solid electrolyte present between the first measurement electrode and the outside-void pump electrode; and a second measurement pump cell including a second measurement electrode formed facing the second measurement chamber, the outside-void pump electrode, and the solid electrolyte present between the second measurement electrode and the outside-void pump electrode, and the oxygen pumping device further includes: a) a step in which the oxygen pumping means performs the first pumping operation; and b) a step in which the first measurement pump cell performs the first pumping operation. a step of selectively oxidizing, in the first measuring chamber, hydrogen produced by reduction of water vapor during the first pumping operation and contained in the measurement gas introduced into the first measuring chamber by pumping oxygen into the first measuring chamber; and a step of oxidizing, in the second measuring chamber, carbon monoxide produced by reduction of carbon dioxide during the first pumping operation and contained in the measurement gas introduced into the second measuring chamber by pumping oxygen into the second measuring chamber with the second measuring pump cell.d) determining the concentration of water vapor contained in the measurement gas based on the magnitude of the current flowing between the first measurement electrode and the pump electrode outside the cavity when oxygen is pumped into the first measurement chamber by the first measurement pump cell, and e) determining the concentration of carbon dioxide contained in the measurement gas based on the magnitude of the current flowing between the second measurement electrode and the pump electrode outside the cavity when oxygen is pumped into the second measurement chamber by the second measurement pump cell, wherein during step a), the oxygen pumping means performs a second pumping operation for a predetermined time to pump oxygen contained in the measurement gas to an extent that water vapor and carbon dioxide contained in the measurement gas until it reaches the first measurement chamber are not reduced, thereby interrupting the reduction of water vapor and carbon dioxide by the oxygen pumping means, thereby discharging water vapor generated in the first measurement chamber and carbon dioxide generated in the second measurement chamber to the outside of the sensor element.

[0017] An eighth aspect of the present invention is a concentration measuring method using a gas sensor according to the seventh aspect, wherein the plurality of chambers are a first chamber, a second chamber which is the first measurement chamber, and a third chamber which is the second measurement chamber, and the sensor element further comprises an adjustment pump cell as the oxygen pumping means, the adjustment pump cell comprising an adjustment electrode formed facing the first chamber, the outside-of-void pump electrode, and the solid electrolyte present between the adjustment electrode and the outside-of-void pump electrode, and wherein in the step a), the adjustment pump cell pumps oxygen contained in the measurement gas introduced into the first chamber as the first pumping operation. and performing, as the second pumping operation, an operation of pumping oxygen from the first chamber to such an extent that the water vapor and carbon dioxide contained in the measurement gas introduced into the first chamber are not reduced, for a predetermined time during the first pumping operation, thereby interrupting the reduction of the water vapor and carbon dioxide in the first chamber, and thereby discharging the water vapor generated in the second chamber and the carbon dioxide generated in the third chamber to the outside of the sensor element via the first chamber.

[0018] A ninth aspect of the present invention is a concentration measurement method using a gas sensor according to the eighth aspect, characterized in that in step a), the adjustment pump cell alternately and periodically performs the first pumping operation and the second pumping operation, and the pumping of oxygen into the second chamber by the first measurement pump cell in step b) and the pumping of oxygen into the third chamber by the second measurement pump cell in step c) are periodically performed in accordance with the first pumping operation and the second pumping operation by the adjustment pump cell in step a), respectively.

[0019] A tenth aspect of the present invention is a concentration measurement method using a gas sensor according to the ninth aspect, characterized in that the pumping of oxygen into the second chamber by the first measuring pump cell in step b) and the pumping of oxygen into the third chamber by the second measuring pump cell in step c) are performed in synchronization with the second pumping operation by the regulating pump cell in step a).

[0020] An eleventh aspect of the present invention is a concentration measurement method using a gas sensor according to the ninth aspect, characterized in that the pumping of oxygen into the second chamber by the first measuring pump cell in step b) and the pumping of oxygen into the third chamber by the second measuring pump cell in step c) are performed from the middle of the first pumping operation by the adjusting pump cell in step a) to the middle of the second pumping operation.

[0021] A twelfth aspect of the present invention is a concentration measuring method using a gas sensor according to any one of the eighth to eleventh aspects, wherein the sensor element further comprises a reference electrode in contact with a reference gas, and the step a) comprises controlling a voltage applied between the adjusting electrode and the outer-space pump electrode in the adjusting pump cell so that an electromotive force V0 generated between the adjusting electrode and the reference electrode in accordance with the oxygen concentration in the first space is maintained at a predetermined target value within a range of 1000 mV to 1500 mV during the first pumping operation and at a predetermined target value within a range of 400 mV to 700 mV during the second pumping operation; In step b), the voltage applied between the first measurement electrode and the pump electrode outside the cavity in the first measurement pump cell is controlled so that an electromotive force V1 generated between the first measurement electrode and the reference electrode in response to the oxygen concentration in the second chamber is maintained at a predetermined target value within a range of 250 mV to 450 mV; and in step c), the voltage applied between the second measurement electrode and the pump electrode outside the cavity in the second measurement pump cell is controlled so that an electromotive force V2 generated between the second measurement electrode and the reference electrode in response to the oxygen concentration in the third chamber is maintained at a predetermined target value within a range of 100 mV to 300 mV.

[0022] According to the first to twelfth aspects of the present invention, the degradation of the measurement accuracy of the gas sensor caused by the re-reduction of water vapor and carbon dioxide produced by the oxidation of hydrogen and carbon monoxide is suitably suppressed.

[0023] 1 is a diagram schematically illustrating an example of the configuration of the gas sensor 100. FIG. 2 is a block diagram illustrating functional components implemented in the controller 110. FIG. 3 is a schematic diagram illustrating basic gas inflow and outflow patterns in three chambers provided in the sensor element 101 of the gas sensor 100. FIG. 4 is a diagram for explaining a malfunction that occurs when the gas sensor 100 continuously performs measurements based on the basic operation. FIG. 5 is a diagram for explaining a malfunction that occurs when the gas sensor 100 continuously performs measurements based on the basic operation. FIG. 6 is a diagram illustrating time changes in target values ​​of electromotive forces V0, V1, and V2 in a generated gas discharge operation. FIG. 7 is a schematic diagram illustrating gas inflow and outflow patterns in three chambers during a generated gas discharge operation. FIG. 8 is a diagram illustrating yet another example of a generated gas discharge operation.

[0024] <Configuration of Gas Sensor> FIG. 1 is a diagram showing an example of the configuration of a gas sensor 100 according to this embodiment. The gas sensor 100 is a multi-gas sensor that detects multiple types of gas components using a sensor element 101 and measures their concentrations. In this embodiment, at least water vapor (H ２ O) and carbon dioxide (CO ２ ) are the main gas components to be detected by the gas sensor 100. The gas sensor 100 is attached to an exhaust path of an internal combustion engine such as an automobile engine, and is used in a manner in which the exhaust gas flowing through the exhaust path is used as the measurement gas. FIG. 1 includes a vertical cross-sectional view of the sensor element 101 along the longitudinal direction.

[0025] The sensor element 101 includes a long, plate-shaped structure (base portion) 14 made of an oxygen-ion conductive solid electrolyte, a first diffusion-controlling portion 11 formed at one end (the left end in the drawing) of the structure 14 and serving as a gas inlet 10 through which a gas to be measured is introduced, and a buffer space 12, a first chamber 20, a second chamber 40, and a third chamber 61 formed within the structure 14 and sequentially communicating with the gas inlet 10 (first diffusion-controlling portion 11). The buffer space 12 communicates with the gas inlet 10 (first diffusion-controlling portion 11). The first chamber 20 communicates with the buffer space 12 via the second diffusion-controlling portion 13. The second chamber 40 communicates with the first chamber 20 via the third diffusion-controlling portion 30. The third chamber 61 communicates with the second chamber 40 via the fourth diffusion-controlling portion 60.

[0026] The structure 14 is formed by stacking multiple layers of substrates made of, for example, ceramics. Specifically, the structure 14 has a configuration in which six layers, consisting of a first substrate 1, a second substrate 2, a third substrate 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, are stacked in this order from the bottom up. Each layer is made of, for example, zirconia (ZrO ２ The solid electrolyte is oxygen ion conductive.

[0027] The first diffusion-controlling section 11, which also serves as the gas inlet 10, the buffer space 12, the second diffusion-controlling section 13, the first chamber 20, the third diffusion-controlling section 30, the second chamber 40, the fourth diffusion-controlling section 60, and the third chamber 61 are formed in this order at one end of the structure 14, between the lower surface 6 b of the second solid electrolyte layer 6 and the upper surface 4 a of the first solid electrolyte layer 4. The portion from the gas inlet 10 to the third chamber 61 is also referred to as a gas flow section.

[0028] The buffer space 12, the first cavity 20, the second cavity 40, and the third cavity 61 are formed so as to penetrate the spacer layer 5 in the thickness direction. The lower surface 6b of the second solid electrolyte layer 6 is exposed at the top of each cavity, and the upper surface 4a of the first solid electrolyte layer 4 is exposed at the bottom. The sides of each cavity are defined by the spacer layer 5 or any of the diffusion-controlling portions. The first cavity 20, the second cavity 40, and the third cavity 61 each have a length (size in the longitudinal direction of the element) of, for example, 0.3 mm to 1.0 mm, a width (size in the lateral direction of the element) of, for example, 0.5 mm to 30 mm, and a height (size in the thickness direction of the element) of, for example, 50 μm to 200 μm. However, the sizes of the individual cavities do not need to be the same and may be different.

[0029] Similarly, the gas inlet 10 may be formed so as to penetrate the spacer layer 5 in the thickness direction, separately from the first diffusion rate-controlling part 11. In this case, the first diffusion rate-controlling part 11 is formed adjacent to and inside the gas inlet 10.

[0030] Each of the first diffusion-controlling section 11, the second diffusion-controlling section 13, the third diffusion-controlling section 30, and the fourth diffusion-controlling section 60 has two horizontally elongated slits. That is, each has an opening extending vertically in the direction perpendicular to the plane of the drawing at the top and bottom. The length of the slit (the size in the longitudinal direction of the element) is, for example, 0.2 mm to 1.0 mm, the width of the opening (the size in the lateral direction of the element) is, for example, 0.5 mm to 30 mm, and the height of the opening (the size in the thickness direction of the element) is, for example, 5 μm to 30 μm.

[0031] A reference gas introduction space 43 is provided at the other end (right end in the drawing) of the sensor element 101 opposite to the one end where the gas introduction port 10 is provided. The reference gas introduction space 43 is formed between the upper surface 3a of the third substrate 3 and the lower surface 5b of the spacer layer 5. The sides of the reference gas introduction space 43 are partitioned by the side surfaces of the first solid electrolyte layer 4. The reference gas introduction space 43 is filled with, for example, oxygen (O ２ ) and air are introduced.

[0032] The gas inlet 10 (first diffusion-controlling section 11) is a section that opens to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas inlet 10.

[0033] The first diffusion rate-controlling part 11 is a part that applies a predetermined diffusion resistance to the taken-in measurement gas.

[0034] The buffer space 12 is provided to cancel out fluctuations in the concentration of the measurement gas caused by pressure fluctuations of the measurement gas in the external space, such as pulsations in the exhaust gas pressure of an automobile.

[0035] The second diffusion rate-controlling part 13 is a part that imparts a predetermined diffusion resistance to the measurement gas introduced from the buffer space 12 into the first chamber 20 .

[0036] The first chamber 20 pumps out oxygen from the measurement gas introduced through the second diffusion rate-controlling section 13, and further pumps out H ２ O and CO ２ is reduced (decomposed) to hydrogen (H ２ ) and carbon monoxide (CO), and the measurement gas is oxygen, H ２ O, and CO ２ The pumping of oxygen is realized by the operation of the adjusting pump cell 21.

[0037] The regulating pump cell 21 is an electrochemical pump cell composed of an inner pump electrode (regulating electrode) 22, an outer pump electrode (outside the cavity pump electrode) 23, and a solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes.

[0038] In the adjustment pump cell 21, a voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 by a variable power supply 24 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip0. This makes it possible to pump oxygen from the first chamber 20 to the external space. In this embodiment, the direction of the oxygen pump current Ip0 when oxygen is pumped from the first chamber 20 is defined as the positive direction of the oxygen pump current Ip0.

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

[0040] The inner pump electrode 22 is provided as a porous cermet electrode having a rectangular shape in plan view, and containing at least one of platinum and rhodium (Rh) as a metal component.

[0041] The outer pump electrode 23 is provided as a porous cermet electrode having a rectangular shape in plan view, for example, containing platinum or an alloy of platinum and gold (Pt—Au alloy) as a metal component, and including platinum or a Pt—Au alloy and zirconia.

[0042] In the sensor element 101, the first chamber sensor cell 80 is configured by the inner pump electrode 22, the reference electrode 42, and the solid electrolyte present in the portion of the structure 14 sandwiched between the two electrodes. The first chamber sensor cell 80 is an electrochemical sensor cell for detecting the oxygen partial pressure in the atmosphere in the first chamber 20.

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

[0044] A reference gas introduction layer 48 made of porous alumina and connected to the reference gas introduction space 43 is provided around the reference electrode 42. The reference gas in the reference gas introduction space 43 is introduced onto the surface of the reference electrode 42 through the reference gas introduction layer 48. In other words, the reference electrode 42 is always in contact with the reference gas.

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

[0046] The third diffusion control section 30 controls the diffusion of oxygen, H ２ O, and CO ２ This section provides a predetermined diffusion resistance to the measurement gas that is substantially free of .

[0047] The second chamber 40 contains H contained in the measurement gas introduced through the third diffusion-controlling section 30. ２ and CO, H ２ Selectively oxidize all of the ２ The space is provided for generating O. ２ H by oxidation of ２ The generation of O is achieved by the operation of the first measuring pump cell 50.

[0048] The first measurement pump cell 50 is an electrochemical pump cell that is configured by a first measurement electrode 51, an outer pump electrode 23, and a solid electrolyte that is present in the portion of the structure 14 that is sandwiched between the two electrodes.

[0049] In the first measurement pump cell 50, an oxygen pump current (oxygen ion current) Ip1 is generated by applying a voltage Vp1 between the first measurement electrode 51 and the outer pump electrode 23 from a variable power supply 52 provided outside the sensor element 101. This makes it possible to pump oxygen from the external space into the second chamber 40. In this embodiment, the direction of the oxygen pump current Ip1 when oxygen is pumped out of the second chamber 40 is defined as the positive direction of the oxygen pump current Ip1.

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

[0051] The first measurement electrode 51 is provided as a porous cermet electrode having a rectangular shape in plan view, which contains a Pt—Au alloy as a metal component, for example, the Pt—Au alloy and zirconia. The Au concentration in the Pt—Au alloy is preferably 1 wt % or more and 50 wt % or less, and more preferably 10 wt % or more and 30 wt % or less. In this case, H in the first measurement electrode 51 ２ Selective oxidation of H in the second chamber 40 ２ When CO coexists, H ２ Only CI is selectively oxidized by the oxygen pumped in by the first measuring pump cell 50, and CO is not oxidized, which is more preferably exhibited.

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

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

[0054] The fourth diffusion-controlling section 60 controls the H ２ Contains O and CO, while CO ２ The diffusion resistance is a predetermined value for the measurement gas that is substantially free of oxygen.

[0055] The third chamber 61 oxidizes all of the CO contained in the measurement gas introduced through the fourth diffusion-controlling section 60 and returns to CO ２ The CO generated by the oxidation of CO is ２ The generation of is realized by the operation of the second measuring pump cell 41.

[0056] The second measurement pump cell 41 is an electrochemical pump cell that is configured by a second measurement electrode 44, an outer pump electrode 23, and a solid electrolyte that is present in the portion of the structure 14 that is sandwiched between the two electrodes.

[0057] In the second measurement pump cell 41, a voltage Vp2 is applied between the second measurement electrode 44 and the outer pump electrode 23 by a variable power supply 46 provided outside the sensor element 101, thereby generating an oxygen pump current (oxygen ion current) Ip2. This makes it possible to pump oxygen from the external space into the third chamber 61. In this embodiment, the direction of the oxygen pump current Ip2 when oxygen is pumped out of the third chamber 61 is defined as the positive direction of the oxygen pump current Ip2.

[0058] The second measurement electrode 44 is provided on substantially the entire upper surface 4 a of the first solid electrolyte layer 4 that defines the third cavity 61 .

[0059] The second measurement electrode 44 is provided as a porous cermet electrode that contains Pt as a metal component, for example, Pt and zirconia, and that is rectangular in plan view.

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

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

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

[0063] In addition to the above, the sensor element 101 is provided with a heater portion 70 that serves to adjust the temperature by heating and keeping the sensor element 101 warm in order to increase the oxygen ion conductivity of the solid electrolyte that constitutes the structure 14.

[0064] The heater section 70 mainly includes a heater electrode 71, a heater element 72, a heater lead 72a, a through hole 73, a heater insulating layer 74, and a heater resistance detection lead (not shown in Fig. 1). Hereinafter, the heater element 72 will also be simply referred to as the heater 72.

[0065] The heater 72 is sandwiched between the second substrate 2 and the third substrate 3, and generates heat when power is supplied from the outside through a heater electrode 71, a through hole 73, and a heater lead 72a provided on the underside 1b of the first substrate 1. The heater 72 is embedded throughout the entire range from the buffer space 12 to the third chamber 61, and is capable of heating the sensor element 101 to a predetermined temperature and maintaining the temperature.

[0066] The heater 72 is provided so that, when heated, the temperature is highest near the first chamber 20 (near the adjusting electrode 22) and decreases with increasing distance from the first chamber 20 in the longitudinal direction of the element. In this embodiment, the temperature in the range from one end of the sensor element 101, where the gas inlet 10 is provided, to the third chamber 61 when the gas sensor 100 is used (when the sensor element 101 is driven) is referred to as the element driving temperature. The heater 72 heats so that the element driving temperature is within the range of 750°C to 950°C.

[0067] Heater insulating layers 74 made of alumina or the like are formed above and below the heater 72 in order to provide electrical insulation between the heater 72 and the second substrate 2 and the third substrate 3. The heater section 70 also has a pressure release hole 75. The pressure release hole 75 is a portion that penetrates the third substrate 3 and is provided so as to communicate with the reference gas introduction space 43, and is provided for the purpose of alleviating an increase in internal pressure that accompanies a temperature rise within the heater insulating layer 74.

[0068] The gas sensor 100 also includes a controller 110 that controls the operation of the sensor element 101 and determines the concentration of the target gas component based on the current flowing through the sensor element 101 .

[0069] 2 is a block diagram showing functional components implemented in the controller 110. The controller 110 is configured with one or more electronic circuits having, for example, one or more central processing units (CPUs) and a storage device. The electronic circuit is also a software function unit in which predetermined functional components are implemented by the CPU executing a predetermined program stored in the storage device. Of course, the controller 110 may also be configured with an integrated circuit such as an FPGA (Field-Programmable Gate Array) in which multiple electronic circuits are connected according to their functions.

[0070] In addition, when the gas sensor 100 is attached to the exhaust path of an automobile engine and the exhaust gas flowing through the exhaust path is used as the measured gas, some or all of the functions of the controller 110 may be realized by the automobile's ECU (electronic control unit).

[0071] The controller 110 has, as functional components realized by the execution of a predetermined program in the CPU, an element operation control unit 120 that controls the operation of each part of the above-mentioned sensor element 101, and a concentration determination unit 130 that is responsible for the process of determining the concentration of the target gas component contained in the measured gas.

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

[0073] On the other hand, the concentration specifying unit 130 detects H, which is the main gas component to be detected in the gas sensor 100. ２ O and CO ２ The air conditioning system 100 mainly includes a water vapor concentration specifying unit 130H and a carbon dioxide concentration specifying unit 130C that specify the concentrations of water vapor and carbon dioxide, respectively.

[0074] The water vapor concentration specifying unit 130H determines the water vapor concentration of the H contained in the measurement gas based on the value of the oxygen pump current Ip1 flowing through the first measurement pump cell 50, which is acquired by the first measurement pump cell control unit 122a.２ The concentration of O is specified.

[0075] The carbon dioxide concentration specifying unit 130C determines the CO concentration contained in the measurement gas based on the value of the oxygen pump current Ip2 flowing through the second measurement pump cell 41, which is acquired by the second measurement pump cell control unit 122b. ２ Identify the concentration of.

[0076] The concentration specifying unit 130 further includes an oxygen concentration specifying unit 130A that specifies the concentration of oxygen contained in the measurement gas. The oxygen concentration specifying unit 130A specifies the concentration of oxygen contained in the measurement gas based on the value of the oxygen pump current Ip0 flowing through the adjustment pump cell 21 obtained by the adjustment pump cell control unit 121, the value of the oxygen pump current Ip1 flowing through the first measurement pump cell 50 obtained by the first measurement pump cell control unit 122a, and the value of the oxygen pump current Ip2 flowing through the second measurement pump cell 41 obtained by the second measurement pump cell control unit 122b. That is, in the gas sensor 100 according to this embodiment, H, which is the main gas component to be detected, is used as the oxygen concentration specifying unit 130A. ２ O and CO ２ In addition, oxygen is also detected as an additional target gas component.

[0077] <Basic Concept of Multi-Gas Detection and Concentration Identification> Next, the basic concept of detecting multiple gas species (multi-gas detection) and identifying the concentration of the detected gases, which is realized by the gas sensor 100 having the above-described configuration, will be described. ２ O, and CO ２ The exhaust gas contains

[0078] FIG. 3 is a schematic diagram showing the basic flow of gas in and out of three chambers (internal spaces) provided in the sensor element 101 of the gas sensor 100. As shown in FIG.

[0079] First, in the sensor element 101 included in the gas sensor 100 according to this embodiment, as described above, the measurement gas is introduced into the first chamber 20 through the gas inlet 10 (first diffusion rate-controlling section 11), the buffer space 12, and the second diffusion rate-controlling section 13. In the first chamber 20, the adjustment pump cell 21 is operated to pump out oxygen contained in the introduced measurement gas and to pump out H ２ O and CO ２ That is, the adjusting pump cell 21 is operated to pump out oxygen from the measurement gas introduced into the first chamber 20, and the H contained in the measurement gas is reduced. ２ O and CO ２ Reduction (decomposition) reaction of (2H ２ O → 2H ２ +O ２ , 2CO ２ →2CO+O ２ ) progresses, and H ２ O and CO ２ is substantially entirely hydrogen (H ２ ) and carbon monoxide (CO) and oxygen.

[0080] These oxygen pumping and H ２ O and CO ２ The reduction (decomposition) of is performed by the adjustment pump cell control section 121 of the controller 110 setting the target value (control voltage) of the electromotive force V0 in the first vacant chamber sensor cell 80 to a value within a range of 1000 mV to 1500 mV (preferably 1000 mV), and feedback-controlling the voltage Vp0 applied to the adjustment pump cell 21 by the variable power supply 24 in accordance with the difference between the actual value of the electromotive force V0 and the target value so that the electromotive force V0 is maintained at the target value.

[0081] By operating the adjusting pump cell 21 in this manner, the oxygen partial pressure in the first chamber 20 is kept at a sufficiently low value that it is considered that oxygen is substantially absent. －２０ As a result, the gas to be measured becomes H ２ O, CO ２ , and becomes substantially free of oxygen.

[0082] H ２and CO, while H ２ O, CO ２ , and the measurement gas substantially free of oxygen is introduced into the second chamber 40 .

[0083] In the second chamber 40, oxygen is pumped in by the operation of the first measuring pump cell 50, and H contained in the introduced measurement gas is ２ is selectively oxidized.

[0084] The pumping of oxygen is carried out by the first measurement pump cell control unit 122a of the controller 110 setting the target value (control voltage) of the electromotive force V1 in the second vacant chamber sensor cell 81 to a value within the range of 250 mV to 450 mV (preferably 350 mV), and feedback-controlling the voltage Vp1 applied to the first measurement pump cell 50 by the variable power supply 52 in accordance with the difference between the actual value of the electromotive force V1 and the target value so that the electromotive force V1 is maintained at the target value.

[0085] By operating the first measuring pump cell 50 in this manner, the second chamber 40 ２ +O ２ →2H ２ The oxidation (combustion) reaction of H introduced from the gas inlet 10 is promoted. ２ Amount of H correlated with O ２ O is generated again. ２ The correlation of the amount of O is ２ O and related H ２ H produced by decomposition of O ２ is oxidized to produce H ２ The amount of O is the same as or within a certain tolerance range that is acceptable in terms of measurement accuracy.

[0086] By setting the target value of the electromotive force V1 to a value within the range of 250 mV to 450 mV, the oxygen partial pressure in the second chamber 40 is ２ For example, when V1 = 350 mV, 10 －７ It will be about atm.

[0087] As described above, the first measuring electrode 51 may be provided as a cermet electrode containing a Pt—Au alloy with an Au concentration of 1 wt % or more and 50 wt % or less as a metal component. ２ This contributes to improving the selective oxidation of

[0088] At this time, the oxygen pump current Ip1 (hereinafter also referred to as the water vapor detection current Ip1) flowing through the first measuring pump cell 50 is ２ H produced by the combustion of ２ The water vapor detection current Ip1 is approximately proportional to the concentration of O (the generated H ２ The concentration of H produced by such combustion is linearly related to the concentration of O. ２ The amount of O is determined by the amount of H in the measurement gas that is introduced through the gas inlet 10 and then decomposed in the first chamber 20. ２ Therefore, when the water vapor detection current Ip1 is detected by the first measurement pump cell control unit 122a, the amount of H in the measurement gas can be determined. ２ Therefore, the second chamber 40 is also referred to as a first measurement chamber.

[0089] A linear relationship is also established between the water vapor detection current Ip1 and the water vapor concentration in the measurement gas. Data (water vapor characteristic data) showing this linear relationship is determined in advance using a model gas with a known water vapor concentration and is stored in the water vapor concentration determiner 130H. In the gas sensor 100 according to this embodiment, the water vapor concentration determiner 130H acquires the value of the water vapor detection current Ip1 detected by the first measurement pump cell controller 122a. The water vapor concentration determiner 130H refers to the water vapor characteristic data and determines the value of the water vapor concentration corresponding to the acquired water vapor detection current Ip1. This determines the water vapor concentration in the measurement gas.

[0090] If the measurement gas introduced through the gas inlet 10 contains H ２ If O was not present, the H ２ No decomposition of O occurs, and therefore H ２ is not introduced, the water vapor detection current Ip1 is almost zero.

[0091] H ２ is oxidized to H ２ O, the measurement gas becomes H ２ Contains O and CO and CO ２ The measurement gas is introduced into the third chamber 61. The second measurement pump cell 41 is activated to pump oxygen into the third chamber 61, and the CO contained in the measurement gas is oxidized.

[0092] The pumping of oxygen is achieved by the second measurement pump cell control unit 122b of the controller 110 setting the target value (control voltage) of the electromotive force V2 in the third vacant chamber sensor cell 82 to a value within the range of 100 mV to 300 mV (preferably 200 mV), and feedback-controlling the voltage Vp2 applied to the second measurement pump cell 41 by the variable power supply 46 in accordance with the difference between the actual value of the electromotive force V2 and the target value, so that the electromotive force V2 is maintained at the target value.

[0093] By operating the second measuring pump cell 41 in this manner, the following reaction mixture is produced in the third chamber 61: 2CO+O ２ →2CO ２ The oxidation (combustion) reaction is promoted, and the CO introduced from the gas inlet 10 ２ Amount of CO correlated with the amount of ２ is generated again.

[0094] By setting the target value of the electromotive force V2 to a value within the range of 100 mV to 300 mV, the oxygen partial pressure in the third chamber 61 is maintained within a range in which almost all of the CO is oxidized. －４ It will be about atm.

[0095] At this time, the oxygen pump current Ip2 (hereinafter also referred to as the carbon dioxide detection current Ip2) flowing through the second measurement pump cell 41 is a current Ip1 of CO generated by the combustion of CO in the third chamber 61. ２ is approximately proportional to the concentration of carbon dioxide (the carbon dioxide detection current Ip2 and the generated CO ２ The CO produced by such combustion is ２The amount of CO in the measurement gas that is introduced through the gas inlet 10 and then decomposed in the first chamber 20 is ２ Therefore, when the second measurement pump cell control unit 122b detects the carbon dioxide detection current Ip2, the amount of CO ２ Therefore, the third chamber 61 is also referred to as a second measurement chamber.

[0096] Furthermore, a linear relationship is established between the carbon dioxide detection current Ip2 and the carbon dioxide concentration in the measurement gas. Data (carbon dioxide characteristic data) showing this linear relationship is determined in advance using a model gas with a known carbon dioxide concentration and is stored in the carbon dioxide concentration determination unit 130C. In the gas sensor 100 according to this embodiment, the carbon dioxide concentration determination unit 130C acquires the value of the carbon dioxide detection current Ip2 detected by the second measurement pump cell control unit 122b. The carbon dioxide concentration determination unit 130C refers to the carbon dioxide characteristic data and determines the value of the carbon dioxide concentration corresponding to the acquired carbon dioxide detection current Ip2. This determines the carbon dioxide concentration in the measurement gas.

[0097] If the measurement gas introduced through the gas inlet 10 contains CO ２ If there was no CO in the first chamber 20, ２ No decomposition occurs, and therefore no CO is introduced into the third chamber 61, so the carbon dioxide detection current Ip2 becomes almost zero.

[0098] Hereinafter, the operation mode of the gas sensor 100 as described above with reference to FIG. 3 will also be referred to as the basic operation.

[0099] Furthermore, the gas sensor 100 according to this embodiment is also capable of indirectly determining the concentration of oxygen contained in the measurement gas. Roughly speaking, the difference C=C0-C1-C2 (1) between the concentration of oxygen pumped out of the first chamber 20 (denoted as C0) and the concentrations of oxygen pumped into the second chamber 40 and the third chamber 61 (denoted as C1 and C2, respectively) corresponds to the concentration of oxygen in the measurement gas introduced through the gas inlet 10. C0, C1, and C2 are values ​​approximately proportional to the oxygen pump currents Ip0, Ip1, and Ip2, respectively. In the gas sensor 100, the relationships (proportionality constants) between C0 and Ip0, C1 and Ip1, and C2 and Ip2 are previously determined and stored in the oxygen concentration determination unit 130A. When measurement of the measured gas begins, the oxygen concentration determination unit 130A obtains the detected values ​​of the oxygen pump currents Ip0, Ip1, and Ip2 from the adjustment pump cell control unit 121, the first measurement pump cell control unit 122a, and the second measurement pump cell control unit 122b, respectively, and calculates the concentration of oxygen in the measured gas based on these detected values, the above proportional constant, and equation (1).

[0100] <Concentration Identification Taking Continuous Use into Account> FIGS. 4 and 5 are diagrams for explaining problems that may occur when the gas sensor 100 continuously performs measurements based on the above-described basic operation.

[0101] The gas sensor 100 detects H in the measurement gas according to the basic operation described above. ２ O and CO ２ When measuring the concentration of H and oxygen, the H generated in the second chamber 40 ２ Basically, O is introduced into the third chamber 61 or remains in the second chamber 40. In addition, CO generated in the third chamber 61 ２ Basically, the H 2 in the second chamber 40 and the third chamber 61 remains in the third chamber 61. Therefore, as the measurement is continuously performed, the H 2 in the second chamber 40 and the third chamber 61 ２ O and CO ２ The amount of production will increase.

[0102] When the concentration of the measurement gas newly introduced from the first diffusion rate-controlling section 11 (gas inlet 10) is relatively low, as shown in FIG. 4, in the gas flow section from the gas inlet 10 to the third chamber 61, the concentration of H ２ O and CO ２ A concentration gradient can be formed in which the concentration of

[0103] As a result of this concentration gradient, the H 2 present in the third chamber 61 or the second chamber 40 ２ O and CO ２ Diffusion and migration of H from the third chamber 61 and the second chamber 40 to the first chamber 20 can occur. ２ O and CO ２ A backflow into the first chamber 20 may occur.

[0104] As described above, in the first chamber 20, the adjusting pump cell 21 is operated to pump out oxygen and H ２ O and CO ２ Therefore, as shown in FIG. 5, H ２ O and CO ２ When these gases flow back, they are mixed with the H gas, which is the target gas to be measured at that time and is contained in the gas to be measured introduced from the gas inlet 10. ２ O and CO ２ Without being distinguished from H ２ and CO.

[0105] If such re-reduction occurs, the first measuring pump cell 50 will pump oxygen into the second chamber 40, and the oxidized H ２ is the H produced by re-reduction. ２ The CO generated by re-reduction is included in the CO oxidized by the second measuring pump cell 41 pumping oxygen into the third chamber 61. Therefore, the water vapor detection current Ip1 flowing through the first measuring pump cell 50 and the carbon dioxide detection current Ip2 flowing through the second measuring pump cell 41 contain the CO generated by re-reduction. ２ O and CO ２In other words, the values ​​of the water vapor detection current Ip1 and the carbon dioxide detection current Ip2 are superimposed on each other. ２ O and CO ２ This will no longer correspond to the concentration of the sample, resulting in a decrease in measurement accuracy.

[0106] In the gas sensor 100 according to the present embodiment, such H ２ O and CO ２ The operation of each pump cell is controlled so as not to cause a decrease in measurement accuracy due to the backflow of H. Generally speaking, the H generated in the second chamber 40 and the third chamber 61 ２ O and CO ２ The purpose is not to suppress the occurrence of backflow of H but to suppress the occurrence of backflow of H ２ O and CO ２ Measurement accuracy is ensured by performing an operation to discharge the produced gas to the outside of the sensor element 101. This operation mode is also referred to as a produced gas discharge operation.

[0107] Fig. 6 is a diagram showing the time variations of the target values ​​of electromotive forces V0, V1, and V2 during the generated gas discharge operation, and Fig. 7 is a schematic diagram showing the flow of gas in and out of the three chambers (internal spaces) during the generated gas discharge operation.

[0108] As described above, in the basic operation, the target value of the electromotive force V0 in the first empty chamber sensor cell 80 is set to a value within the range of 1000 mV to 1500 mV, and the voltage Vp0 applied to the adjustment pump cell 21 is feedback-controlled so that the electromotive force V0 is maintained at this target value.

[0109] In contrast, in the generated gas discharge operation, as shown in Figure 6(a), the target value (set value) of the electromotive force V0 in the first vacant chamber sensor cell 80 is temporarily changed from a steady value of V0a to a value of V0b at an appropriate timing.

[0110] Here, the value V0a is a value in the range of 1000 mV to 1500 mV, similar to the target value of the electromotive force V0 in the basic operation. The value V0a may be set to the same value as the target value of the electromotive force V0 in the basic operation.

[0111] While the target value of the electromotive force V0 is set to the value V0a, the adjusting pump cell 21, like in the basic operation, ２ O and CO ２ Oxygen is pumped out of the first chamber 20 so that substantially all of the oxygen is reduced.

[0112] On the other hand, the value V0b is smaller than the value V0a and falls within the range of 400 mV to 700 mV (preferably 400 mV).

[0113] When the target value of the electromotive force V0 is set to the value V0b, the adjusting pump cell 21 ２ O and CO ２ In other words, the adjustment pump cell 21 maintains its function as an oxygen pumping means, while the H ２ O and CO ２ In this case, the partial pressure of oxygen in the first chamber 20 is reduced by the reduction of H contained in the measurement gas. ２ O and CO ２ For example, when V0 = 400 mV, the －８ It will be about atm.

[0114] That is, during the product gas discharge operation, the adjustment pump cell 21 performs a pumping operation (first pumping operation) in which oxygen is pumped from the first chamber 20 so that substantially all of the water vapor and carbon dioxide contained in the measured gas is reduced, and then performs a pumping operation (second pumping operation) in which oxygen is pumped from the first chamber 20 to the extent that the water vapor and carbon dioxide contained in the measured gas introduced into the first chamber 20 are not reduced.

[0115] On the other hand, the target values ​​of the electromotive forces V1 and V2 are set in the same manner as in the basic operation. Specifically, the target value of the electromotive force V1 is set to a value within the range of 250 mV to 450 mV (preferably 350 mV), and the target value of the electromotive force V2 is set to a value within the range of 100 mV to 300 mV (preferably 200 mV).

[0116] In this case, the operation of the gas sensor 100 while the target value of the electromotive force V0 is set to the value V0a is the same as that during the basic operation. However, when the target value of the electromotive force V0 is set to the value V0b, only the oxygen contained in the introduced measurement gas is pumped out from the first chamber 20, and H ２ O and CO ２ Therefore, the H generated in the second chamber 40 and the third chamber 61 is not reduced. ２ O and CO ２ As a result of the accumulation of H, a concentration gradient as shown in FIG. ２ O and CO ２ Even if the reverse flow of H ２ O and CO ２ is discharged directly to the outside of the element without being reduced again in the first chamber 20. As a result, the concentration gradient is weakened, and as a result, the backflow H ２ O and CO ２ That is, in the gas sensor 100 according to the present embodiment, when the second pumping operation is started, the concentration gradient occurring in the gas flow portion inside the sensor element 101 is reduced. ２ and H produced by selective oxidation of CO ２ O and CO ２ is suitably discharged to the outside of the element through the first chamber 20.

[0117] The second pumping operation may be performed at any timing, or may be performed at a predetermined timing. Alternatively, the second pumping operation may be performed when a predetermined condition is satisfied. For example, in the case of the H ２ O and CO２ The longer the measured value of H2O2 continues to be large, the more the H2O2 generated in the second chamber 40 and the third chamber 61 increases. ２ O and CO ２ Therefore, an example of a mode in which the second pumping operation is performed based on the integral value of the measured value is given.

[0118] The target value of the electromotive force V0 is set to a value V0b, and the time during which the second pumping operation is performed is preferably within a range of 1 ms to 1 s. If the set time is shorter than 1 ms, H ２ O and CO ２ This is not preferable because the diffusion from the second chamber 40 or the third chamber 61 does not progress sufficiently, so the concentration gradient does not weaken sufficiently and the measurement accuracy may continue to decrease. ２ O and CO ２ This is undesirable because it lengthens the time during which the amount of time during which the amount of reduction cannot be reduced, in other words, the time during which concentration measurement cannot be performed becomes longer, which reduces the responsiveness.

[0119] Alternatively, the target value of the electromotive force V0 is periodically changed, and the first pumping operation and the second pumping operation are alternately and periodically performed in the adjusting pump cell 21, thereby ２ O and CO ２ The reduction of the oxygen may be periodically stopped, and the target values ​​(set values) of the electromotive force V1 in the second vacant room sensor cell 81 and the electromotive force V2 in the third vacant room sensor cell 82 may also be periodically changed in synchronization with the periodic change in the target value of the electromotive force V0, as shown in Fig. 6(b). In other words, the pumping of oxygen by the first measuring pump cell 50 and the second measuring pump cell 41 may be synchronized with the second pumping operation.

[0120] The target values ​​of the electromotive forces V1 and V2 are set to 0 while the target value of the electromotive force V0 is set to the value V0a, and are set to values ​​within the same range as in the basic operation only while the target value of the electromotive force V0 is set to the value V0b. In this case, the first measuring pump cell 50 and the second measuring pump cell 41 operate only while the regulating pump cell 21 is performing the second pumping operation, and do not operate while the regulating pump cell 21 is performing the first pumping operation. Note that, for simplicity's sake, in Figure 6(b) both are shown on a single graph, but in reality, the electromotive forces V1 and V2 are set to different values.

[0121] In this case, H in the first chamber 20 ２ O and CO ２ and the reduction of H in the second chamber 40 and the third chamber 61. ２ The selective oxidation of H and CO occurs at different times. ２ During the period when CO and CO are reoxidized, only the oxygen contained in the introduced measurement gas is pumped out from the first chamber 20, and H ２ O and CO ２ In this case, the H generated in the second chamber 40 and the third chamber 61 is not reduced. ２ O and CO ２ Even if the concentration gradient shown in FIG. 4 occurs, the H ２ O and CO ２ is not reduced again in the first chamber 20 but is discharged directly to the outside of the element.

[0122] In this case, it is preferable that the time during which the target value of the electromotive force V0 is set to the value V0a is also within the range of 1 ms to 1 s.

[0123] FIG. 8 illustrates another example of the produced gas discharge operation. In this example, as shown in FIG. 8(a), the periodic change in the target value of the electromotive force V0 is the same as in FIG. 6(a). However, as shown in FIG. 8(b), the phase (timing) of the periodic change in the target values ​​of the electromotive forces V1 and V2 is shifted from that in FIG. 6(b). More specifically, the start of oxygen pumping into the second chamber 40 and the third chamber 61 is advanced to the middle of the first pumping operation, and the pumping is terminated in the middle of the second pumping operation. However, the degree of advance in the start time is set to 50% or less of the time Δt during which the first pumping operation is being performed (the time during which the target value of the electromotive force V0 is set to V0a).

[0124] As described above, according to this embodiment, the oxygen contained in the measurement gas is pumped out in the first chamber, and the H ２ O and CO ２ The reduction of H produced by the reduction is carried out in the second and third vacancies, respectively. ２ and CO are oxidized, and the H contained in the measurement gas is calculated based on the magnitude of the oxygen pump current pumped into the second and third chambers during the oxidation. ２ O and CO ２ In a gas sensor for determining the concentration of H in a first chamber, ２ O and CO ２ By temporarily or periodically halting the reduction of H ２ and H produced by oxidation of CO ２ O and CO ２ The concentration gradient is utilized to discharge H from the first chamber to the outside of the sensor element. ２ and H produced by oxidation of CO ２ O and CO ２ Therefore, the decrease in measurement accuracy caused by the re-reduction of the ions is preferably suppressed.

[0125] <Modifications> In the above-described embodiment, the H contained in the measurement gas in the gas sensor 100 having the sensor element 101 with a three-chamber structure is ２ O and CO ２ H produced by reduction of２ and CO, and H generated by oxidation for concentration measurement. ２ O and CO ２ However, the H contained in the measurement gas is ２ O and CO ２ is reduced to H ２ It is not essential that the process of generating CO and CO be performed in only one empty chamber. The sensor element may have a different structure as long as it can perform the same generated gas discharge operation as in the above-described embodiment.

Claims

1. A gas sensor capable of measuring the concentrations of a plurality of target gas components contained in a measurement gas containing at least water vapor and carbon dioxide, comprising: a sensor element having a structure made of an oxygen ion conductive solid electrolyte; and a controller for controlling the operation of the gas sensor, wherein the sensor element comprises: a gas inlet through which the measurement gas is introduced; a plurality of chambers sequentially communicating with the gas inlet via different diffusion rate-limiting sections; and a heater for heating the sensor element, wherein two of the plurality of chambers are a first measurement chamber and a second measurement chamber, the second measurement chamber being the innermost chamber from the gas inlet among the plurality of chambers, and the first measurement chamber being the chamber immediately preceding the second measurement chamber; and oxygen pumping means capable of performing a first pumping operation to pump out oxygen contained in the measurement gas so that substantially all of the water vapor and carbon dioxide contained in the measurement gas is reduced before the measurement gas introduced from the gas inlet reaches the first measurement chamber. a first measurement pump cell including a first measurement electrode formed facing the first measurement chamber, an outside-void pump electrode provided at a location other than the plurality of chambers, and the solid electrolyte present between the first measurement electrode and the outside-void pump electrode; and a second measurement pump cell including a second measurement electrode formed facing the second measurement chamber, the outside-void pump electrode, and the solid electrolyte present between the second measurement electrode and the outside-void pump electrode, wherein the first measurement pump cell is configured to pump oxygen into the first measurement chamber, thereby selectively oxidizing hydrogen in the first measurement chamber, the hydrogen being produced by reduction of water vapor caused by the first pumping operation and being contained in the measurement gas introduced into the first measurement chamber, The second measuring pump cell is configured to pump oxygen into the second measuring chamber, thereby oxidizing, in the second measuring chamber, carbon monoxide that is produced by reduction of carbon dioxide that occurs during the first pumping operation and that is contained in the measurement gas introduced into the second measuring chamber, and the controller is configured to:the oxygen pumping means is further configured to be capable of executing a second pumping operation for a predetermined time during the first pumping operation, pumping oxygen contained in the measurement gas to an extent that water vapor and carbon dioxide contained in the measurement gas are not reduced until the measurement gas reaches the first measurement chamber, and the second pumping operation is stopped when the second pumping operation is started, so that the water vapor generated in the first measurement chamber and the carbon dioxide generated in the second measurement chamber are discharged to the outside of the sensor element. A gas sensor comprising:

2. A gas sensor according to claim 1, wherein the plurality of chambers are a first chamber, a second chamber which is the first measurement chamber, and a third chamber which is the second measurement chamber; and the sensor element further comprises an adjusting pump cell which is the oxygen pumping means and which is composed of an adjusting electrode formed facing the first chamber, the pump electrode outside the cavity, and the solid electrolyte present between the adjusting electrode and the pump electrode outside the cavity; and the adjusting pump cell is configured to be capable of performing, as the first pumping operation, an operation of pumping oxygen from the first chamber so that substantially all of the water vapor and carbon dioxide contained in the measurement gas introduced into the first chamber are reduced, and is configured to be capable of performing, as the second pumping operation, an operation of pumping oxygen from the first chamber to such an extent that the water vapor and carbon dioxide contained in the measurement gas introduced into the first chamber are not reduced, for a predetermined time during the first pumping operation. the adjustment pump cell starts the second pumping operation, interrupting the reduction of water vapor and carbon dioxide in the first chamber, thereby causing the water vapor generated in the second chamber and the carbon dioxide generated in the third chamber to be discharged to the outside of the sensor element via the first chamber.

3. A gas sensor as claimed in claim 2, characterized in that the adjustment pump cell alternately and periodically performs the first pumping operation and the second pumping operation, and the pumping of oxygen into the second chamber by the first measuring pump cell and the pumping of oxygen into the third chamber by the second measuring pump cell are performed periodically in accordance with the first pumping operation and the second pumping operation by the adjustment pump cell.

4. A gas sensor according to claim 3, characterized in that the pumping of oxygen into the second chamber by the first measuring pump cell and the pumping of oxygen into the third chamber by the second measuring pump cell are performed in synchronization with the second pumping operation by the regulating pump cell.

5. A gas sensor as claimed in claim 3, characterized in that the pumping of oxygen into the second chamber by the first measuring pump cell and the pumping of oxygen into the third chamber by the second measuring pump cell are carried out from the middle of the first pumping operation by the adjusting pump cell to the middle of the second pumping operation.

6. A gas sensor according to any one of claims 2 to 5, wherein the sensor element further comprises: a reference electrode in contact with a reference gas; a first vacant-chamber sensor cell comprising the adjusting electrode, the reference electrode, and the solid electrolyte present between the adjusting electrode and the reference electrode, wherein an electromotive force V0 corresponding to the oxygen concentration in the first vacant-chamber is generated between the adjusting electrode and the reference electrode; a second vacant-chamber sensor cell comprising the first measurement electrode, the reference electrode, and the solid electrolyte present between the first measurement electrode and the reference electrode, wherein an electromotive force V1 corresponding to the oxygen concentration in the second vacant-chamber is generated between the first measurement electrode and the reference electrode; and a third vacant-chamber sensor cell comprising the second measurement electrode, the reference electrode, and the solid electrolyte present between the second measurement electrode and the reference electrode, wherein an electromotive force V2 corresponding to the oxygen concentration in the third vacant-chamber is generated between the second measurement electrode and the reference electrode; and the controller a regulating pump cell control means for controlling a voltage applied between the regulating electrode and the pump electrode outside the cavity in the regulating pump cell so that an electromotive force V0 in the first vacant-chamber sensor cell is maintained at a predetermined target value within a range of 1000 mV to 1500 mV during the first pumping operation and at a predetermined target value within a range of 400 mV to 700 mV during the second pumping operation; a first measurement pump cell control means for controlling a voltage applied between the first measurement electrode and the pump electrode outside the cavity in the first measurement pump cell so that an electromotive force V1 in the second vacant-chamber sensor cell is maintained at a predetermined target value within a range of 250 mV to 450 mV; and a second measurement pump cell control means for controlling a voltage applied between the second measurement electrode and the pump electrode outside the cavity in the second measurement pump cell so that an electromotive force V2 in the third vacant-chamber sensor cell is maintained at a predetermined target value within a range of 100 mV to 300 mV.

7. A method for measuring the concentrations of a plurality of target gas components contained in a measurement gas containing at least water vapor and carbon dioxide using a gas sensor, the gas sensor comprising a sensor element having a structure made of an oxygen ion conductive solid electrolyte, the sensor element comprising: a gas inlet into which the measurement gas is introduced; a plurality of chambers sequentially communicating with the gas inlet via different diffusion rate-limiting sections; and a heater for heating the sensor element, wherein two of the plurality of chambers are a first measurement chamber and a second measurement chamber, the second measurement chamber being the innermost chamber from the gas inlet among the plurality of chambers, and the first measurement chamber being the chamber immediately preceding the second measurement chamber; and the sensor element comprising: oxygen pumping means capable of performing a first pumping operation for pumping oxygen contained in the measurement gas so that substantially all of the water vapor and carbon dioxide contained in the measurement gas are reduced before the measurement gas introduced from the gas inlet reaches the first measurement chamber. a first measurement pump cell including a first measurement electrode formed facing the first measurement chamber, an outside-void pump electrode provided at a location other than the plurality of chambers, and the solid electrolyte present between the first measurement electrode and the outside-void pump electrode; and a second measurement pump cell including a second measurement electrode formed facing the second measurement chamber, the outside-void pump electrode, and the solid electrolyte present between the second measurement electrode and the outside-void pump electrode, and the measurement apparatus further includes: a) a step in which the oxygen pumping means performs the first pumping operation; and b) a step in which the first measurement pump cell pumps oxygen into the first measurement chamber, thereby selectively oxidizing hydrogen in the first measurement chamber, the hydrogen being produced by reduction of water vapor accompanying the first pumping operation and being contained in the measurement gas introduced into the first measurement chamber. c) pumping oxygen into the second measuring chamber by the second measuring pump cell, thereby oxidizing, in the second measuring chamber, carbon monoxide produced by reduction of carbon dioxide during the first pumping operation, which is contained in the measurement gas introduced into the second measuring chamber;d) determining the concentration of water vapor contained in the measurement gas based on the magnitude of the current flowing between the first measurement electrode and the pump electrode outside the cavity when the first measurement pump cell pumps oxygen into the first measurement chamber; and e) determining the concentration of carbon dioxide contained in the measurement gas based on the magnitude of the current flowing between the second measurement electrode and the pump electrode outside the cavity when the second measurement pump cell pumps oxygen into the second measurement chamber, wherein during step a), the oxygen pumping means performs a second pumping operation for a predetermined time to pump oxygen contained in the measurement gas to an extent that water vapor and carbon dioxide contained in the measurement gas until it reaches the first measurement chamber are not reduced, thereby interrupting the reduction of water vapor and carbon dioxide by the oxygen pumping means, thereby discharging water vapor generated in the first measurement chamber and carbon dioxide generated in the second measurement chamber to the outside of the sensor element.

8. A concentration measurement method using a gas sensor as set forth in claim 7, wherein the plurality of chambers are a first chamber, a second chamber which is the first measurement chamber, and a third chamber which is the second measurement chamber, and the sensor element further comprises an adjusting pump cell which is the oxygen pumping means and which is composed of an adjusting electrode formed facing the first chamber, the pump electrode outside the cavity, and the solid electrolyte present between the adjusting electrode and the pump electrode outside the cavity, and in step a), the adjusting pump cell performs, as the first pumping operation, an operation of pumping oxygen from the first chamber so that substantially all of the water vapor and carbon dioxide contained in the measurement gas introduced into the first chamber are reduced, and, as the second pumping operation, an operation of pumping oxygen from the first chamber to an extent that the water vapor and carbon dioxide contained in the measurement gas introduced into the first chamber are not reduced, for a predetermined time during the first pumping operation, thereby interrupting the reduction of the water vapor and carbon dioxide in the first chamber, thereby discharging the water vapor generated in the second chamber and the carbon dioxide generated in the third chamber to the outside of the sensor element via the first chamber.

9. A method for measuring concentration using a gas sensor as defined in claim 8, characterized in that in step a), the adjusting pump cell alternately and periodically performs the first pumping operation and the second pumping operation, and in step b), the first measuring pump cell pumps oxygen into the second chamber, and in step c), the second measuring pump cell pumps oxygen into the third chamber, each periodically performed in accordance with the first pumping operation and the second pumping operation by the adjusting pump cell in step a).

10. A method for measuring concentration using a gas sensor as described in claim 9, characterized in that the pumping of oxygen into the second chamber by the first measuring pump cell in step b) and the pumping of oxygen into the third chamber by the second measuring pump cell in step c) are performed in synchronization with the second pumping operation by the regulating pump cell in step a).

11. A method for measuring concentration using a gas sensor as described in claim 9, characterized in that the pumping of oxygen into the second chamber by the first measuring pump cell in step b) and the pumping of oxygen into the third chamber by the second measuring pump cell in step c) are carried out from the middle of the first pumping operation by the adjusting pump cell in step a) to the middle of the second pumping operation.

12. A concentration measurement method using a gas sensor according to any one of claims 8 to 11, wherein the sensor element further comprises a reference electrode in contact with a reference gas, and in step a), a voltage applied between the adjusting electrode and the pump electrode outside the cavity in the adjusting pump cell is controlled so that an electromotive force V0 generated between the adjusting electrode and the reference electrode in response to the oxygen concentration in the first chamber is maintained at a predetermined target value within a range of 1000 mV to 1500 mV during the first pumping operation, and at a predetermined target value within a range of 400 mV to 700 mV during the second pumping operation; and in step b), a voltage applied between the first measuring electrode and the pump electrode outside the cavity in the first measuring pump cell is controlled so that an electromotive force V1 generated between the first measuring electrode and the reference electrode in response to the oxygen concentration in the second chamber is maintained at a predetermined target value within a range of 250 mV to 450 mV. In the step c), a voltage applied between the second measurement electrode and the pump electrode outside the cavity in the second measurement pump cell is controlled so that an electromotive force V2 generated between the second measurement electrode and the reference electrode in accordance with the oxygen concentration in the third cavity is maintained at a predetermined target value within a range of 100 mV to 300 mV.

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