Gas sensor

Abstract

To provide a gas sensor for accurately measuring a gas to be measured in a gas to be measured.SOLUTION: The sensor includes a sensor element 101 and a control device for controlling the sensor element 101, and the sensor element 101 includes oxygen ion conductive solid electrolyte layers 4, 6 and a proton conductive solid electrolyte layer 7. And an insulator layer 62 interposed between the oxygen ion conductive solid electrolyte layers 4 and 6 and the proton conductive solid electrolyte layer 7, an oxygen pump cell 21 including an in-space oxygen pump electrode 22 disposed on the oxygen ion conductive solid electrolyte layers 4 and 6 in the internal space 25, and a hydrogen pump cell 31 including an in-space hydrogen pump electrode 32 disposed on the proton conductive solid electrolyte layer 7 in the internal space 25, 102, the control device includes a pump control unit that controls operations of the oxygen pump cell 21 and the hydrogen pump cell 31, and a concentration calculation unit that calculates a measurement target gas concentration in the measurement-object gas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas sensor including a sensor element using an ion-conductive solid electrolyte. [Background technology]

[0002] Gas sensors are used to detect and measure the concentration of target gas components (oxygen O2, nitrogen oxides NOx, ammonia NH3, hydrocarbons HC, carbon dioxide CO2, etc.) in gases to be measured, such as automobile exhaust gases. Known examples of such gas sensors include gas sensors equipped with a sensor element that uses an oxygen-ion conductive solid electrolyte such as zirconia (ZrO2).

[0003] Japanese Patent Application Laid-Open Publication No. 2020-067432 discloses a carbon dioxide detection device that uses an ion conductor that conducts oxygen ions and a proton conductor that conducts hydrogen protons to detect carbon dioxide concentration taking into account the air-fuel ratio and water concentration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-067432 Summary of the Invention [Problem to be solved by the invention]

[0005] Japanese Patent Application Laid-Open Publication No. 2020-067432 discloses a sensor element having an ion conductor that conducts oxygen ions, a proton conductor that conducts hydrogen protons, and a gas chamber formed between the ion conductor and the proton conductor. In addition to the gas chamber, this sensor element also includes a reference gas duct facing the ion conductor and a reference gas duct facing the proton conductor. Sensor elements with such a complex internal structure are susceptible to cracking due to thermal stress during heating and cooling. Another problem is the increased number of manufacturing steps required for the sensor element.

[0006] The present invention has been made in view of the above problems, and has as its object to provide a gas sensor that can accurately measure a measurement target gas such as oxygen, water vapor, or carbon dioxide in a measurement gas. [Means for solving the problem]

[0007] The present inventors have conducted extensive research and have arrived at the present invention. The present invention includes the following.

[0008] (1) A gas sensor that detects a target gas in a measurement gas, the gas sensor including a sensor element and a control device that controls the sensor element, The sensor element is a long, plate-like substrate including an oxygen ion-conductive solid electrolyte layer and a proton-conductive solid electrolyte layer, with an insulating layer interposed between the oxygen ion-conductive solid electrolyte layer and the proton-conductive solid electrolyte layer; a measurement gas flow space having a gas inlet opening on the surface of the base portion and an internal space communicating with the gas inlet through a first diffusion-controlling passage and having the oxygen ion-conductive solid electrolyte layer and the proton-conductive solid electrolyte layer present on the internal surface; an oxygen pump cell including an intra-void oxygen pump electrode disposed on the oxygen ion conductive solid electrolyte layer in the inner void of the measurement gas flow space, and an extra-void oxygen pump electrode disposed at a position different from that inside the measurement gas flow space of the base portion and in contact with the intra-void oxygen pump electrode via the oxygen ion conductive solid electrolyte layer; a hydrogen pump cell including an in-void hydrogen pump electrode disposed on the proton-conductive solid electrolyte layer in the inner void of the measurement gas flow space, and an out-void hydrogen pump electrode disposed at a position different from that inside the measurement gas flow space of the base portion and in contact with the in-void hydrogen pump electrode via the proton-conductive solid electrolyte layer; Including, The control device a pump control unit that controls operations of the oxygen pump cell and the hydrogen pump cell, and a concentration calculation unit that calculates a measurement target gas concentration in a measurement target gas, The pump control unit applying a predetermined voltage between the oxygen pump electrode inside the cavity and the oxygen pump electrode outside the cavity of the oxygen pump cell to pass an oxygen pump current through the oxygen pump cell; applying a predetermined voltage between the hydrogen pump electrode inside the void and the hydrogen pump electrode outside the void of the hydrogen pump cell to cause a hydrogen pump current to flow through the hydrogen pump cell; The concentration calculation unit The gas sensor calculates a concentration of a gas to be measured in a measurement gas based on at least one of the oxygen pump current and the hydrogen pump current.

[0009] (2) The gas sensor according to (1), wherein the extra-void oxygen pump electrode and / or the extra-void hydrogen pump electrode are disposed at a position where they come into contact with the gas to be measured.

[0010] (3) The internal space includes a first internal space having at least the oxygen ion conductive solid electrolyte layer on an inner surface thereof, and a second internal space communicating with the first internal space via a second diffusion-controlling pathway and having at least the proton conductive solid electrolyte layer on an inner surface thereof, The gas sensor according to (1) or (2) above, wherein the intra-void oxygen pump electrode is disposed in the first internal cavity, and the intra-void hydrogen pump electrode is disposed in the second internal cavity.

[0011] (4) The sensor element further comprises: an oxidation pump cell including: an in-space oxidation electrode disposed on the oxygen ion conductive solid electrolyte layer in the inner space of the measurement gas flow space, at a position farther from the first diffusion-controlling passage than the in-space oxygen pump electrode; and an outside-space oxidation electrode disposed at a position different from within the measurement gas flow space of the base portion and in contact with the in-space oxidation electrode via the oxygen ion conductive solid electrolyte layer; The pump control unit further applying a predetermined voltage between the oxidation electrode inside the cavity and the oxidation electrode outside the cavity of the oxidation pump cell to cause an oxidation pump current to flow through the oxidation pump cell; The concentration calculation unit The gas sensor according to any one of (1) to (3) above, wherein the concentration of the gas to be measured in the measurement gas is calculated based on at least one of the oxygen pump current, the hydrogen pump current, and the oxidation pump current.

[0012] (5) The gas sensor according to (4), wherein the intra-void oxidation electrode is disposed on the oxygen ion conductive solid electrolyte layer at a position farther from the first diffusion-controlling passage than the intra-void hydrogen pump electrode.

[0013] (6) The internal space includes at least a first internal space having the oxygen ion conductive solid electrolyte layer on an inner surface thereof, and a second internal space communicating with the first internal space via a second diffusion-controlling pathway and having the oxygen ion conductive solid electrolyte layer and the proton conductive solid electrolyte layer on an inner surface thereof, The gas sensor according to (4) or (5) above, wherein the intra-void oxygen pump electrode is disposed in the first internal cavity, the intra-void hydrogen pump electrode is disposed on the proton-conductive solid electrolyte layer in the second internal cavity, and the intra-void oxidation electrode is disposed on the oxygen ion-conductive solid electrolyte layer in the second internal cavity.

[0014] (7) The internal space comprises a first internal space having at least the oxygen ion conductive solid electrolyte layer present on its inner surface, a second internal space communicating with the first internal space via a second diffusion-controlling path and having at least the proton conductive solid electrolyte layer present on its inner surface, and a third internal space communicating with the second internal space via a third diffusion-controlling path and having at least the oxygen ion conductive solid electrolyte layer present on its inner surface, The gas sensor according to (4) or (5) above, wherein the intra-void oxygen pump electrode is disposed in the first internal cavity, the intra-void hydrogen pump electrode is disposed in the second internal cavity, and the intra-void oxidation electrode is disposed in the third internal cavity.

[0015] (8) The sensor element is a reference electrode disposed inside the base portion so as to be in contact with a reference gas; The pump control unit The gas sensor according to any one of (1) to (7) above, wherein a predetermined voltage is applied between the oxygen pump electrode in the cavity and the oxygen pump electrode outside the cavity of the oxygen pump cell based on the electromotive force between the reference electrode and the oxygen pump electrode in the cavity of the oxygen pump cell, thereby causing an oxygen pump current to flow through the oxygen pump cell.

[0016] The sensor element is a reference electrode disposed inside the base portion so as to be in contact with a reference gas; The pump control unit a predetermined voltage is applied between the oxygen pump electrode inside the cavity and the oxygen pump electrode outside the cavity of the oxygen pump cell based on an electromotive force between the reference electrode and the oxygen pump electrode inside the cavity of the oxygen pump cell, thereby causing an oxygen pump current to flow through the oxygen pump cell; The gas sensor according to any one of (4) to (7) above, wherein a predetermined voltage is applied between the intra-void oxidation electrode and the extra-void oxidation electrode of the oxidation pump cell based on an electromotive force between the reference electrode and the intra-void oxidation electrode of the oxidation pump cell, thereby causing an oxygen pump current to flow through the oxygen pump cell.

[0017] (9) The gas sensor according to any one of (1) to (8), wherein in a plane including a longitudinal direction of the base portion and a width direction perpendicular to the longitudinal direction, the proton-conducting solid electrolyte layer and the oxygen-ion-conducting solid electrolyte layer are present on the same plane, and the insulator layer is interposed between the oxygen-ion-conducting solid electrolyte layer and the proton-conducting solid electrolyte layer.

[0018] (10) The oxygen ion conductive solid electrolyte layer has through-holes, the proton-conducting solid electrolyte layer is parallel to the oxygen-ion-conducting solid electrolyte layer and covers the through-holes on a surface of the oxygen-ion-conducting solid electrolyte layer facing the internal space, and the insulator layer is interposed between the proton-conducting solid electrolyte layer and the oxygen-ion-conducting solid electrolyte layer; the in-void hydrogen pump electrode is disposed on a surface of the proton-conducting solid electrolyte layer facing the internal void; The gas sensor according to any one of (1) to (8) above, wherein the external hydrogen pump electrode is disposed at a position corresponding to the through-hole on the surface of the proton-conducting solid electrolyte layer opposite to the surface on which the internal hydrogen pump electrode is disposed.

[0019] (11) The gas sensor according to any one of (1) to (3) above, wherein the gas to be measured is at least one selected from the group consisting of oxygen and water vapor.

[0020] (12) The gas sensor according to any one of (4) to (10) above, wherein the gas to be measured is at least one selected from the group consisting of oxygen, water vapor, and carbon dioxide. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a gas sensor that can accurately measure a measurement target gas such as oxygen, water vapor, or carbon dioxide in a measurement gas. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic vertical cross-sectional view of a sensor element 101 in the longitudinal direction, showing an example of the schematic configuration of a gas sensor 100 according to a first embodiment. [Figure 2] 2 is a partial cross-sectional view taken along the same cross section as FIG. 1, showing the measurement gas flow space 14 and its surrounding structure in the sensor element 101. FIG. [Figure 3] 3 is a block diagram showing the electrical connection relationship between the control device 90 and each pump cell 21, 31 of the sensor element 101. FIG. [Figure 4] 1 is a schematic vertical cross-sectional view of a sensor element 111 in the longitudinal direction, showing an example of the schematic configuration of a gas sensor 110. FIG. [Figure 5] 1 is a schematic vertical cross-sectional view of a sensor element 201 in the longitudinal direction, showing an example of the schematic configuration of a gas sensor 200 according to a second embodiment. [Figure 6] 6 is a partial cross-sectional schematic view showing the measurement gas flow space 15 and its surrounding structure in the sensor element 201, taken along the same cross section as FIG. 5. FIG. [Figure 7] 10 is a block diagram showing the electrical connection relationship between a control device 290 and each of pump cells 21, 31, and 51 of a sensor element 201 in a gas sensor 200 according to a second embodiment. FIG. [Figure 8] 6 is a partial cross-sectional schematic view taken along the same cross section as FIG. 5, showing another example of the measurement gas flow space and its surrounding configuration. FIG. [Figure 9] 6 is a partial cross-sectional schematic view taken along the same cross section as FIG. 5, showing another example of the measurement gas flow space and its surrounding configuration. FIG. [Figure 10] 1 is a schematic vertical cross-sectional view of a sensor element 301 in the longitudinal direction, showing an example of the schematic configuration of a gas sensor 300 according to a third embodiment. [Figure 11]10 is a block diagram showing the electrical connection relationship between a control device 390, pump cells 21 and 31 of a sensor element 301, and an oxygen pump control sensor cell 80 in a gas sensor 300 of a third embodiment. FIG. [Figure 12] 1 is a schematic vertical cross-sectional view of a sensor element 401 in the longitudinal direction, showing an example of the schematic configuration of a gas sensor 400 according to a fourth embodiment. [Figure 13] 10 is a block diagram showing the electrical connection relationship between a control device 490 and each of pump cells 21, 31, 51 and each of sensor cells 80, 81 of a sensor element 401 in a gas sensor 400 of a fourth embodiment. FIG. [Figure 14] 6 is a partial cross-sectional schematic view taken along the same cross section as FIG. 5, showing another example of the measurement gas flow space and its surrounding configuration. FIG. [Figure 15] 1 is a graph showing the relationship between the oxygen concentration (O2 concentration) in the measurement gas and each pump current Ip0, Ip1, and Ip2. The horizontal axis of the graph represents the O2 concentration (%), and the vertical axis represents the current value (μA) of each pump current Ip0, Ip1, and Ip2. The first vertical axis represents the pump current Ip0, and the second vertical axis represents the pump currents Ip1 and Ip2. [Figure 16] 1 is a graph showing the relationship between the water vapor concentration (H2O concentration) in the gas under measurement and each pump current Ip0, Ip1, and Ip2. The horizontal axis of the graph represents the H2O concentration (%), and the vertical axis represents the current value (μA) of each pump current Ip0, Ip1, and Ip2. The first vertical axis represents the pump current Ip0, and the second vertical axis represents the pump currents Ip1 and Ip2. [Figure 17] 1 is a graph showing the relationship between the oxygen concentration (CO2 concentration) in the measurement gas and each pump current Ip0, Ip1, and Ip2. The horizontal axis of the graph represents the CO2 concentration (%), and the vertical axis represents the current value (μA) of each pump current Ip0, Ip1, and Ip2. The first vertical axis represents the pump current Ip0, and the second vertical axis represents the pump currents Ip1 and Ip2. DETAILED DESCRIPTION OF THE INVENTION

[0023] The gas sensor of the present invention includes a sensor element and a control device that controls the sensor element.

[0024] The sensor element included in the gas sensor of the present invention is a long, plate-like substrate including an oxygen ion-conductive solid electrolyte layer and a proton-conductive solid electrolyte layer, with an insulating layer interposed between the oxygen ion-conductive solid electrolyte layer and the proton-conductive solid electrolyte layer; a measurement gas flow space having a gas inlet opening on the surface of the base portion and an internal space communicating with the gas inlet through a first diffusion-controlling passage and having the oxygen ion-conductive solid electrolyte layer and the proton-conductive solid electrolyte layer present on the internal surface; an oxygen pump cell including an intra-void oxygen pump electrode disposed on the oxygen ion conductive solid electrolyte layer in the inner void of the measurement gas flow space, and an extra-void oxygen pump electrode disposed at a position different from that inside the measurement gas flow space of the base portion and in contact with the intra-void oxygen pump electrode via the oxygen ion conductive solid electrolyte layer; a hydrogen pump cell including an in-void hydrogen pump electrode disposed on the proton-conductive solid electrolyte layer in the inner void of the measurement gas flow space, and an out-void hydrogen pump electrode disposed at a position different from that inside the measurement gas flow space of the base portion and in contact with the in-void hydrogen pump electrode via the proton-conductive solid electrolyte layer; Includes:

[0025] The control device included in the gas sensor of the present invention includes: a pump control unit that controls operations of the oxygen pump cell and the hydrogen pump cell, and a concentration calculation unit that calculates a measurement target gas concentration in a measurement target gas, The pump control unit applying a predetermined voltage between the oxygen pump electrode inside the cavity and the oxygen pump electrode outside the cavity of the oxygen pump cell to pass an oxygen pump current through the oxygen pump cell; applying a predetermined voltage between the hydrogen pump electrode inside the void and the hydrogen pump electrode outside the void of the hydrogen pump cell to cause a hydrogen pump current to flow through the hydrogen pump cell; The concentration calculation unit The concentration of the gas to be measured in the measurement gas is calculated based on at least one of the oxygen pump current and the hydrogen pump current.

[0026] [Embodiment 1] An example of an embodiment of a gas sensor of the present invention will be described below with reference to the drawings. Fig. 1 is a vertical cross-sectional view in the longitudinal direction showing an example of the general configuration of a gas sensor 100 including a sensor element 101. In the following, with reference to Fig. 1, the upper side of Fig. 1 refers to the top and the lower side to the bottom, with the left side of Fig. 1 referring to the front end and the right side to the rear end. Fig. 2 is a partial cross-sectional view taken along the same cross section as Fig. 1, showing the measurement gas flow space 14 and its surrounding configuration in the sensor element 101.

[0027] In FIG. 1, a gas sensor 100 is shown as an example of a gas sensor that detects oxygen O2 and water vapor H2O in a measurement gas by a sensor element 101 and measures the concentrations of these two types of gases.

[0028] The gas sensor 100 also includes a control device 90 that controls the sensor element 101. Figure 3 is a block diagram showing the electrical connection between the control device 90 and the sensor element 101.

[0029] (sensor element) The sensor element 101 is a long plate-like element including a long plate-like base portion 102 that includes an oxygen ion-conductive solid electrolyte layer (the second oxygen ion conductor layer 6 in this embodiment) and a proton-conductive solid electrolyte layer (the proton conductor layer 7 in this embodiment). The long plate shape is also referred to as a long plate shape or a strip shape.

[0030] The oxygen ion conductive solid electrolyte layer is made of an oxygen ion conductive solid electrolyte (oxygen ion conductor) and is a layer extending in the longitudinal direction of the sensor element 101 (base portion 102). Examples of the oxygen ion conductive solid electrolyte (oxygen ion conductor) that can be used include stabilized zirconia and partially stabilized zirconia, which are zirconia to which a rare earth metal oxide or alkaline earth metal oxide is added as a stabilizer. Examples of stabilizers include yttria (YO), calcia (CaO), magnesia (MgO), ceria (CeO), and scandia (ScO). For example, yttria-stabilized zirconia may be used.

[0031] The proton-conductive solid electrolyte layer is made of a proton-conductive solid electrolyte (proton conductor) and is a layer extending in the longitudinal direction of the sensor element 101 (base portion 102). As the proton-conductive solid electrolyte (proton conductor), for example, perovskite oxides or the like can be used. As the proton-conductive solid electrolyte (proton conductor), for example, perovskite ceramics represented by the following composition formula can be used.

[0032] A(B 1-x C x )O 3-δ Here, A is, for example, a divalent metal selected from the group consisting of Ba, Ca, and Sr. B is, for example, a tetravalent metal selected from the group consisting of Ce and Zr. C is, for example, a trivalent metal selected from the group consisting of In, Y, Yb, Mn, and Sc, which is a so-called dopant. x may be 0 or more and 0.7 or less. Specifically, for example, CaZr 0.9 In 0.1 O 3-δ and SrZr 0.9 Y 0.1 O 3-δ etc.

[0033] The base 102 has a structure in which six layers—a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first oxygen ion conductor layer 4, a spacer layer 5, and a second oxygen ion conductor layer 6—each of which is an oxygen ion conductive solid electrolyte layer made of zirconia (ZrO) or the like, are stacked in this order from bottom to top in the drawing in approximately parallel rows. The solid electrolyte forming these six layers is dense and airtight. The six layers may all have the same thickness, or each layer may have a different thickness. The layers are bonded together via adhesive layers made of solid electrolyte, and the base 102 includes the adhesive layers. While FIG. 1 illustrates a layer structure consisting of six layers, the layer structure of the present invention is not limited to this, and any number of layers and layer structure may be used. Furthermore, some layers (e.g., the first substrate layer 1, the second substrate layer 2, and the third substrate layer 3) may be dense layers made of an insulator such as alumina.

[0034] The second oxygen ion conductor layer 6 has through-holes 61 formed therein. The through-holes 61 penetrate the second oxygen ion conductor layer 6 in the vertical direction in FIG. 1 , i.e., in the thickness direction of the second oxygen ion conductor layer 6. A proton conductor layer 7 is disposed on the lower surface of the second oxygen ion conductor layer 6 at the position where the through-holes 61 are present, with an insulator layer 62 interposed therebetween. The insulator layer 62 is a dense layer made of an insulator such as alumina. The insulator layer 62 is interposed between the second oxygen ion conductor layer 6 and the proton conductor layer 7, and ensures electrical insulation between the oxygen-ion-conductive second oxygen ion conductor layer 6 and the proton-conductive proton conductor layer 7.

[0035] The measurement gas flow space 14 has a gas inlet 10 opening on the surface of the base portion 102, and an internal space 25 that communicates with the gas inlet 10 via a first diffusion-controlling passage 11 (first diffusion-controlling portion) and has an oxygen ion-conductive solid electrolyte layer (the second oxygen ion conductor layer 6 and the first oxygen ion conductor layer 4) and a proton-conductive solid electrolyte layer (the proton conductor layer 7) on its inner surface. That is, the first embodiment shows an example of a configuration having one internal space.

[0036] A gas inlet 10 is formed at one longitudinal end (hereinafter referred to as the tip end) of the sensor element 101, between the lower surface of the second oxygen ion conductor layer 6 and the upper surface of the first oxygen ion conductor layer 4. The measurement gas flow space 14, i.e., the measurement gas flow section, is formed by adjacently forming a first diffusion-controlling passage 11, a buffer space 12, a fourth diffusion-controlling passage 13 (fourth diffusion-controlling section), and an internal space 25 in the longitudinal direction from the gas inlet 10, in such a manner that they communicate with each other in this order. The internal space 25 faces the first oxygen ion conductor layer 4, the second oxygen ion conductor layer 6, and the proton conductor layer 7.

[0037] The gas inlet 10, the buffer space 12, and the internal space 25 are spaces within the sensor element 101, which are defined by hollowing out the spacer layer 5, with an upper portion defined by the underside of the second oxygen ion conductor layer 6, a lower portion defined by the upper surface of the first oxygen ion conductor layer 4, and sides defined by the side surfaces of the spacer layer 5.

[0038] The first diffusion-controlled passage 11 and the fourth diffusion-controlled passage 13 are both provided as two horizontally elongated slits (their openings extend in the direction perpendicular to the plane of the drawing in FIG. 1). The first diffusion-controlled passage 11 and the fourth diffusion-controlled passage 13 may have any shape that provides a desired diffusion resistance, and the shape is not limited to the slits.

[0039] In the measurement gas flow space 14, the gas inlet 10 is a portion that opens to the outside space, and the measurement gas is taken into the sensor element 101 from the outside space through the gas inlet 10.

[0040] In this embodiment, the measurement gas is introduced into the measurement gas flow space 14 through the gas inlet 10 opening at the tip end surface of the sensor element 101, but the present invention is not limited to this. For example, the measurement gas flow space 14 may not have a recess for the gas inlet 10. In this case, the first diffusion-controlling passage 11 essentially serves as the gas inlet.

[0041] Furthermore, for example, the measurement gas flow space 14 may have an opening in a side surface along the longitudinal direction of the base part 102, the opening communicating with the buffer space 12 or a position near the tip of the internal space 25. In this case, the measurement gas is introduced from the side surface along the longitudinal direction of the base part 102 through the opening.

[0042] Furthermore, for example, the measurement gas flow space 14 may be configured so that the measurement gas is introduced through a porous body.

[0043] The first diffusion rate-controlling passage 11 is a portion that provides a predetermined diffusion resistance to the measurement gas taken in through the gas inlet 10.

[0044] The buffer space 12 is a space provided to mitigate the influence of pressure fluctuations on the detected value when the pressure of the gas to be measured fluctuates. The sensor element 101 may not have a structure including the buffer space 12.

[0045] The fourth diffusion-controlling passage 13 is a portion that provides a predetermined diffusion resistance to the measurement gas introduced from the buffer space 12 into the internal space 25. The fourth diffusion-controlling passage 13 is provided in association with the provision of the buffer space 12.

[0046] When the buffer space 12 and the fourth diffusion-controlling passage 13 are not provided, the first diffusion-controlling passage 11 directly communicates with the internal space 25 .

[0047] The internal space 25 is provided as a space for measuring the oxygen concentration and water vapor concentration in the measurement gas introduced through the fourth diffusion-controlled passage 13. These measurements are performed by operating the oxygen pump cell 21 and the hydrogen pump cell 31.

[0048] The oxygen pump cell 21 is an electrochemical pump cell including an intra-void oxygen pump electrode (inner oxygen pump electrode 22 in this embodiment) disposed on an oxygen ion conductive solid electrolyte layer (first oxygen ion conductor layer 4 and second oxygen ion conductor layer 6 in this embodiment) in the internal space 25 of the measurement gas flow space 14, and an extra-void oxygen pump electrode (outer oxygen pump electrode 23 in this embodiment) disposed at a position different from inside the measurement gas flow space 14 of the base part 102 and in contact with the inner oxygen pump electrode 22 via the second oxygen ion conductor layer 6.

[0049] That is, the oxygen pump cell 21 is an electrochemical pump cell comprising an inner oxygen pump electrode 22 having a ceiling electrode portion 22a provided on the lower surface of the second oxygen ion conductor layer 6 facing the internal space 25, an outer oxygen pump electrode 23 provided on the upper surface of the second oxygen ion conductor layer 6 in a region corresponding to the ceiling electrode portion 22a so as to be exposed to the external space, and the second oxygen ion conductor layer 6 sandwiched between these electrodes.

[0050] The inner oxygen pump electrode 22 is formed across the upper and lower solid electrolyte layers (the second oxygen ion conductor layer 6 and the first oxygen ion conductor layer 4) that define the internal space 25 and the spacer layer 5 that defines the sidewalls. Specifically, a ceiling electrode 22a is formed on the lower surface of the second oxygen ion conductor layer 6 that defines the ceiling surface of the internal space 25, and a bottom electrode 22b is formed on the upper surface of the first oxygen ion conductor layer 4 that defines the bottom surface. Side electrodes (not shown) are formed on the sidewall surfaces (inner surfaces) of the spacer layer 5 that define both sidewalls of the internal space 25 to connect the ceiling electrode 22a and the bottom electrode 22b, and are arranged in a tunnel-like structure at the locations where the side electrodes are located. The inner oxygen pump electrode 22 is located between the inner surface of the internal space 25 of the measurement gas flow space 14 and the space within the internal space 25. The inner oxygen pump electrode 22 may be disposed on either the ceiling surface or the bottom surface of the inner space 25 .

[0051] The inner oxygen pump electrode 22 and the outer oxygen pump electrode 23 are porous cermet electrodes (electrodes in which a metal component and a ceramic component are mixed). The ceramic component is not particularly limited, but it is preferable to use an oxygen ion conductive solid electrolyte, similar to the second oxygen ion conductor layer 6. For example, ZrO2 (stabilized ZrO2) can be used as the ceramic component.

[0052] The inner oxygen pump electrode 22 and the outer oxygen pump electrode 23 may contain a catalytically active noble metal (e.g., at least one of Pt, Rh, Ir, Ru, and Pd) as a metal component. For example, the inner oxygen pump electrode 22 and the outer oxygen pump electrode 23 may be porous cermet electrodes of Pt and ZrO2.

[0053] In the oxygen pump cell 21, a desired pump voltage Vp0 is applied between the inner oxygen pump electrode 22 and the outer oxygen pump electrode 23 by a variable power supply 24, and an oxygen pump current Ip0 is passed between the inner oxygen pump electrode 22 and the outer oxygen pump electrode 23, thereby making it possible to pump oxygen from the internal space 25 to the external space. At this time, water vapor in the measurement gas is decomposed, and the oxygen generated by the decomposition can also be pumped out.

[0054] The through-holes 61 are located in the second oxygen ion conductor layer 6 farther from the first diffusion-controlling passage 11 than the inner oxygen pump electrode 22. The size and shape of the through-holes 61 are not particularly limited, but they may be located in at least a portion of the ceiling surface of the internal space 25 where the inner oxygen pump electrode 22 is not present. The opening shape of the through-holes 61 in a plan view may be circular, elliptical, rectangular, or the like. As shown in FIG. 2 , the proton conductor layer 7 is generally parallel to the second oxygen ion conductor layer 6 and is located on the lower surface of the second oxygen ion conductor layer 6, i.e., the surface facing the internal space 25, at a position covering the through-holes 61. The proton conductor layer 7 and the second oxygen ion conductor layer 6 may be formed as separate layers and are usually disposed generally parallel to each other, but they do not have to be parallel to each other. An insulating layer 62 is interposed between the proton conductor layer 7 and the second oxygen ion conductor layer 6 to prevent direct contact between the two. As described above, the insulator layer 62 is a dense layer made of an insulator such as alumina. The insulator layer 62 is not formed in the position corresponding to the through-hole 61. Therefore, the upper surface of the proton conductor layer 7 in the position corresponding to the through-hole 61 faces the outside of the sensor element 101. The second oxygen ion conductor layer 6, the insulator layer 62, and the proton conductor layer 7 are all dense layers and are in close contact with each other. Therefore, the measurement gas is introduced into the internal space 25 through the gas inlet 10.

[0055] The hydrogen pump cell 31 is an electrochemical pump cell including an intra-void hydrogen pump electrode (inner hydrogen pump electrode 32 in this embodiment) disposed on the proton conductor layer 7 in the internal space 25 of the measurement gas flow space 14, and an extra-void hydrogen pump electrode (outer hydrogen pump electrode 33 in this embodiment) disposed at a position different from that inside the measurement gas flow space 14 of the base part 102 and in contact with the inner hydrogen pump electrode 32 via the proton conductor layer 7.

[0056] 1 and 2, the hydrogen pump cell 31 is an electrochemical pump cell comprising an inner hydrogen pump electrode 32 provided on the lower surface of the proton conductor layer 7 facing the internal cavity 25, an outer hydrogen pump electrode 33 provided on the upper surface of the proton conductor layer 7 at a position corresponding to the through-hole 61 so as to be exposed to the external space, and the proton conductor layer 7 sandwiched between these electrodes. The outer hydrogen pump electrode 33, like the outer oxygen pump electrode 23, is in contact with the gas to be measured.

[0057] 1 and 2 , the outer hydrogen pump electrode 33 is larger than the opening of the through-hole 61, and when the through-hole 61 is viewed from above, the outer hydrogen pump electrode 33 is exposed over the entire surface at the back of the through-hole 61. The planar shape of the outer hydrogen pump electrode 33 may be substantially the same as the opening of the through-hole 61. Furthermore, it may be larger or smaller than the opening of the through-hole 61. When the planar shape of the outer hydrogen pump electrode 33 is substantially the same as or larger than the opening of the through-hole 61, the outer hydrogen pump electrode 33 is exposed over the entire surface at the back of the through-hole 61 when viewed from above. When the planar shape of the outer hydrogen pump electrode 33 is smaller than the opening of the through-hole 61, the outer hydrogen pump electrode 33 and the proton conductor layer 7 are exposed over the back of the through-hole 61 when viewed from above. In either case, the outer hydrogen pump electrode 33 has a portion exposed to the external space via the through-hole 61.

[0058] The inner hydrogen pump electrode 32 and the outer hydrogen pump electrode 33 are porous cermet electrodes (electrodes in which a metal component and a ceramic component are mixed). The ceramic component is not particularly limited, but it is preferable to use a hydrogen ion (proton) conductive solid electrolyte, similar to the proton conductor layer 7. For example, the ceramic component may be CaZr 0.9 In 0.1 O 3-δ and SrZr 0.9 Y 0.1 O 3-δ etc. can be used.

[0059] The inner hydrogen pump electrode 32 and the outer hydrogen pump electrode 33 preferably contain catalytically active noble metals (e.g., at least one of Pt, Rh, Ir, Ru, and Pd) as metal components. For example, the inner hydrogen pump electrode 32 and the outer hydrogen pump electrode 33 may contain Pt and CaZr 0.9 In 0.1 O 3-δ and SrZr 0.9 Y 0.1 O 3-δ The electrode may be a porous cermet electrode made of a ceramic such as

[0060] In the hydrogen pump cell 31, a desired pump voltage Vp1 is applied between the inner hydrogen pump electrode 32 and the outer hydrogen pump electrode 33 by a variable power supply 34, and a hydrogen pump current Ip1 is passed between the inner hydrogen pump electrode 32 and the outer hydrogen pump electrode 33, thereby making it possible to pump hydrogen generated by the reduction of water vapor at the inner oxygen pump electrode 22 into the external space.

[0061] Furthermore, in order to enhance the oxygen ion conductivity and hydrogen ion conductivity of the solid electrolyte, the sensor element 101 includes a heater section 70 that adjusts the temperature by heating and maintaining the temperature of the sensor element 101. The heater section 70 includes a heater electrode 71, a heater 72, a through hole 73, a heater lead 76, and a heater insulating layer 74.

[0062] The heater electrode 71 is an electrode formed in a manner to contact the lower surface of the first substrate layer 1. By connecting the heater electrode 71 to an external power supply, it is possible to supply power to the heater section 70 from the outside.

[0063] The heater 72 is an electrical resistor sandwiched between the second substrate layer 2 and the third substrate layer 3. The heater 72 is connected to the heater electrode 71 via a through-hole 73 and a heater lead 76 that is connected to the heater 72 and extends to the rear end side of the sensor element 101 in the longitudinal direction. The heater 72 generates heat when power is supplied from a heater power supply 77 through the heater electrode 71, thereby heating and keeping warm the solid electrolyte that forms the sensor element 101.

[0064] The heater 72 is embedded throughout the entire internal space 25, making it possible to adjust the temperature of the sensor element 101 to a temperature at which the solid electrolytes (oxygen ion conductive solid electrolyte and hydrogen ion conductive solid electrolyte) are activated. The temperature needs to be adjusted so that the oxygen pump cell 21 and the hydrogen pump cell 31 can operate. It is not necessary for the entire area to be adjusted to the same temperature, and the sensor element 101 may have a temperature distribution. By maintaining the heater 72 at a desired temperature, the sensor element 101 can be maintained at an operating temperature (e.g., about 800°C) at which the solid electrolytes are activated and the oxygen concentration and HO concentration can be measured accurately.

[0065] In the sensor element 101 of this embodiment, the heater 72 is embedded in the base portion 102, but this is not a limitation. The heater 72 is only required to be disposed so as to heat the base portion 102. That is, the heater 72 is only required to be capable of heating the sensor element 101 to an extent that the sensor element 101 exhibits oxygen ion conductivity that allows the oxygen pump cell 21 to operate and hydrogen ion conductivity that allows the hydrogen pump cell 31 to operate. For example, the heater 72 may be embedded in the base portion 102 as in this embodiment. Alternatively, the heater portion 70 may be formed as a heater substrate separate from the base portion 102 and disposed adjacent to the base portion 102.

[0066] The heater insulating layer 74 is an insulating layer made of an insulator such as alumina and formed on the upper and lower surfaces of the heater 72 and heater lead 76. The heater insulating layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72 and heater lead 76, and between the third substrate layer 3 and the heater 72 and heater lead 76.

[0067] (Control device) The gas sensor 100 of this embodiment includes the above-described sensor element 101 and a control device 90 that controls the sensor element 101. In the gas sensor 100, the electrodes 22, 23, 32, and 33 of the sensor element 101 are electrically connected to the control device 90 via lead wires (not shown). FIG. 3 is a block diagram showing the electrical connection between the control device 90 and the pump cells 21 and 31 of the sensor element 101. The control device 90 includes the above-described variable power supplies 24 and 34 and a control unit 91. The control unit 91 includes a pump control unit 92 and a concentration calculation unit 93.

[0068] The control unit 91 is realized by a general-purpose or dedicated computer, and the functions of the pump control unit 92 and the concentration calculation unit 93 are realized by a CPU, memory, etc. mounted on the computer. Note that when the gas sensor 100 measures oxygen and water vapor contained in exhaust gas from an automobile engine and the sensor element 101 is attached to the exhaust path, some or all of the functions of the control device 90 (particularly the control unit 91) may be realized by an ECU (Electronic Control Unit) mounted on the automobile.

[0069] The control unit 91 is configured to acquire pump currents (Ip0, Ip1) in the pump cells 21, 31 of the sensor element 101. The control unit 91 is also configured to output control signals to the variable power supplies 24, .

[0070] The pump control unit 92 is configured to control the operations of the oxygen pump cell 21 and the hydrogen pump cell 31 so as to measure the concentration of the measurement target gas (oxygen and water vapor in this embodiment) in the measurement gas.

[0071] The pump control unit 92 A predetermined pump voltage Vp0 is applied between the oxygen pump electrode inside the cavity (inner oxygen pump electrode 22) and the oxygen pump electrode outside the cavity (outer oxygen pump electrode 23) of the oxygen pump cell 21, and an oxygen pump current Ip0 is passed through the oxygen pump cell 21. A predetermined pump voltage Vp1 is applied between the hydrogen pump electrode inside the void (inner hydrogen pump electrode 32) and the hydrogen pump electrode outside the void (outer hydrogen pump electrode 33) of the hydrogen pump cell 31, causing a hydrogen pump current Ip1 to flow through the hydrogen pump cell 31.

[0072] The pump control unit 92 applies a predetermined pump voltage Vp0 between the oxygen pump electrode inside the cavity (inner oxygen pump electrode 22) and the oxygen pump electrode outside the cavity (outer oxygen pump electrode 23) using the variable power supply 24 to pump oxygen in the measurement gas from the internal cavity 25. At this time, water vapor in the measurement gas is decomposed (reduced) at the internal oxygen pump electrode 22, and oxygen generated by the decomposition of water vapor and oxygen originally present in the measurement gas are pumped out from the internal cavity 25. At this time, an oxygen pump current Ip0 flowing through the oxygen pump cell 21 flows from the internal oxygen pump electrode 22 to the external oxygen pump electrode 23 outside the sensor element 101. The oxygen pump current Ip0 includes a current flowing due to oxygen gas originally present in the measurement gas and a current flowing due to oxygen generated by the decomposition of water vapor.

[0073] The pump voltage Vp0 applied to the oxygen pump cell 21 should be set to a value that will decompose all or substantially all of the water vapor in the measurement gas in the internal space 25 (particularly around the inner oxygen pump electrode 22). The pump voltage Vp0 may vary depending on the intended use of the gas sensor 100 and the configuration of the sensor element 101, but may be, for example, about 800 mV to 1500 mV, or about 1000 mV to 1500 mV.

[0074] When a pump voltage Vp1 is applied between the inner hydrogen pump electrode 32 and the outer hydrogen pump electrode 33 of the hydrogen pump cell 31 to pump hydrogen from the internal cavity 25 to the external space, the hydrogen pump current Ip1 increases as the pump voltage Vp1 increases while the pump voltage Vp1 is low. As the pump voltage Vp1 subsequently increases, the hydrogen pump current Ip1 no longer increases even with increasing pump voltage Vp1 and reaches saturation. The saturated current value at this time is called the limiting current value. The region where the hydrogen pump current Ip1 becomes the limiting current value for the pump voltage Vp1 is called the limiting current region. In the limiting current region, it is believed that substantially all of the hydrogen that reaches the inner hydrogen pump electrode 32 is pumped out by the hydrogen pump cell 31.

[0075] When the gas sensor 100 is in operation, the pump control unit 92 applies a predetermined pump voltage Vp1 between the hydrogen pump electrode inside the void (inner hydrogen pump electrode 32) and the hydrogen pump electrode outside the void (outer hydrogen pump electrode 33) of the hydrogen pump cell 31 using the variable power supply 34, thereby pumping out hydrogen generated by decomposition of water vapor at the inner oxygen pump electrode 22 from the internal void 25. At this time, the hydrogen pump current Ip1 flowing through the hydrogen pump cell 31 flows from the outer hydrogen pump electrode 33 toward the inner hydrogen pump electrode 32 outside the sensor element 101. In other words, the oxygen pump current Ip0 and the hydrogen pump current Ip1 flow in opposite directions.

[0076] The pump voltage Vp1 applied to the hydrogen pump cell 31 should be set to a value that will pump out all or substantially all of the hydrogen generated by decomposition of water vapor at the inner oxygen pump electrode 22 in the internal space 25 (particularly around the inner hydrogen pump electrode 32). The pump voltage Vp1 may vary depending on the intended use of the gas sensor 100, the configuration of the sensor element 101, etc., but may be, for example, approximately 100 mV or more and 500 mV or less.

[0077] The concentration calculation unit 93 is configured to calculate the measurement target gas concentrations (O2 concentration and H2O concentration in this embodiment) in the measurement target gas. The concentration calculation unit 93 calculates the measurement target gas concentrations based on at least one of the oxygen pump current Ip0 and the hydrogen pump current Ip1.

[0078] The concentration calculation unit 93 acquires the hydrogen pump current Ip1 in the hydrogen pump cell 31, calculates the HO concentration in the measurement gas based on a pre-stored conversion parameter (current-HO concentration conversion parameter) between the hydrogen pump current Ip1 and the HO concentration in the measurement gas, and outputs the calculated value as a measurement value of the gas sensor 100. The current-HO concentration conversion parameter is pre-stored in the memory of the control unit 91, which functions as the concentration calculation unit 93. The current-HO concentration conversion parameter can be appropriately determined for the gas sensor 100 in advance through experiments or the like by a person skilled in the art. The current-HO concentration conversion parameter may be, for example, a coefficient of an approximate expression (such as a linear function) obtained through experiments, or may be a map showing the correspondence between the hydrogen pump current Ip1 and the HO concentration in the measurement gas. The current-HO concentration conversion parameter may be a parameter unique to each gas sensor 100, or a parameter commonly used by multiple gas sensors.

[0079] The concentration calculation unit 93 acquires the oxygen pump current Ip0 in the oxygen pump cell 21 and the hydrogen pump current Ip1 in the hydrogen pump cell 31, calculates the O2 concentration in the measurement gas based on a pre-stored conversion parameter (current-O2 concentration conversion parameter) between these currents and the oxygen concentration (O2 concentration) in the measurement gas, and outputs the calculated value as a measurement value of the gas sensor 100. The current-O2 concentration conversion parameter is stored in advance in the memory of the control unit 91, which functions as the concentration calculation unit 93, as data representing the relationship between the pump currents Ip0, Ip1 and the O2 concentration in the measurement gas. The current-O2 concentration conversion parameter can be appropriately determined for the gas sensor 100 by a person skilled in the art through experiments or the like. The current-O2 concentration conversion parameter may be, for example, the coefficient of an approximate equation (such as a linear function) obtained through experiments, or may be a map showing the correspondence between the pump currents Ip0, Ip1 and the O2 concentration in the measurement gas. The current-O2 concentration conversion parameter may be a parameter specific to each gas sensor 100, or may be a parameter commonly used by a plurality of gas sensors.

[0080] The concentration calculation unit 93 calculates the O2 concentration and the H2O concentration simultaneously or in parallel. In this way, the gas sensor 100 is configured to be able to measure the concentrations of multiple measurement target gases (two types of concentrations, O2 concentration and H2O concentration, in this embodiment). Alternatively, the gas sensor 100 may be configured to measure only one of the O2 concentration or the H2O concentration.

[0081] (Measurement of oxygen concentration and water vapor concentration in the measured gas) Next, a method for measuring the concentrations of oxygen O2 and water vapor H2O in a gas to be measured using the gas sensor 100 having the above-described configuration will be described.

[0082] The gas to be measured is introduced through the gas inlet 10, passes through the first diffusion-controlled passage 11, the buffer space 12, and the fourth diffusion-controlled passage 13 in this order, where a predetermined diffusion resistance is applied, and reaches the internal space 25.

[0083] As a result of the pump control unit 92 operating the oxygen pump cell 21 as described above, all or substantially all of the water vapor in the measurement gas is decomposed (2H2O → 2H2 + O2) to produce hydrogen and oxygen in the internal cavity 25 (particularly near the surface of the inner main pump electrode 22). The oxygen produced by the decomposition of water vapor and the oxygen originally present in the measurement gas are all or substantially all pumped out of the internal cavity 25 by the oxygen pump cell 21.

[0084] The measurement gas, which contains hydrogen generated by decomposition of water vapor and does not substantially contain water vapor or oxygen, reaches the inner hydrogen pump electrode 32 of the hydrogen pump cell 31 .

[0085] By operating the hydrogen pump cell 31 as described above, the pump control unit 92 pumps all or substantially all of the hydrogen from the internal cavity 25. The hydrogen pump current Ip1 flowing through the hydrogen pump cell 31 is a current resulting from hydrogen H2 generated by decomposition of water vapor HO in the measurement gas. When substantially all of the water vapor HO in the measurement gas is decomposed at the inner oxygen pump electrode 22 of the oxygen pump cell 21, the amount of hydrogen H2 generated by decomposition of water vapor HO corresponds to the amount (concentration) of water vapor HO in the measurement gas. That is, the current value of the hydrogen pump current Ip1 is considered to correspond to the water vapor concentration in the measurement gas. The current value of the hydrogen pump current Ip1 is considered to be roughly proportional to the water vapor concentration in the measurement gas. Such a relationship between the water vapor concentration in the measurement gas and the hydrogen pump current Ip1 may be determined in advance, and the concentration calculation unit 93 may store this relationship as a current-HO concentration conversion parameter. The concentration calculation unit 93 can calculate the water vapor concentration in the measurement gas based on the hydrogen pump current Ip1 using the current-H2O concentration conversion parameter.

[0086] As described above, the oxygen pump current Ip0 flowing through the oxygen pump cell 21 includes a current resulting from oxygen gas O2 originally present in the measurement gas and a current resulting from oxygen O2 generated by the decomposition of water vapor H2O in the measurement gas. Meanwhile, the hydrogen pump current Ip1 flowing through the hydrogen pump cell 31 is a current resulting from hydrogen H2 generated by the decomposition of water vapor H2O in the measurement gas. The amount of oxygen O2 generated by the decomposition of water vapor H2O and the amount of hydrogen H2 generated by the decomposition of water vapor H2O both correspond to the amount (concentration) of water vapor H2O in the measurement gas. Therefore, the current resulting from oxygen O2 generated by the decomposition of water vapor H2O in the oxygen pump current Ip0 can be calculated from the value of the hydrogen pump current Ip1 or the water vapor concentration calculated from the hydrogen pump current Ip1. Therefore, the oxygen concentration in the measurement gas can be calculated based on the oxygen pump current Ip0 and the hydrogen pump current Ip1. For example, the relationship between the concentration of oxygen pumped by the oxygen pump cell 21 (oxygen in the measurement gas plus oxygen produced by decomposition of water vapor) and the oxygen pump current Ip0, and the relationship between the water vapor concentration in the measurement gas and the hydrogen pump current Ip1 may be determined in advance, and these may be stored in advance as current-O2 concentration conversion parameters in the concentration calculation unit 93. The concentration calculation unit 93 can calculate the oxygen concentration in the measurement gas based on the oxygen pump current Ip0 and the hydrogen pump current Ip1 using the current-O2 concentration conversion parameters.

[0087] In this way, the gas sensor 100 can measure the oxygen concentration and water vapor concentration in the measurement gas. Accurate measurement is possible both when oxygen and water vapor coexist in the measurement gas and when only one of them is present. Such a gas sensor 100 is useful, for example, for measuring exhaust gas from a hydrogen engine.

[0088] As described above, in the sensor element 101, the insulator layer 62 is interposed between the second oxygen ion conductor layer 6 and the proton conductor layer 7 (FIGS. 1 and 2). The second oxygen ion conductor layer 6 and the proton conductor layer 7 are not in direct contact with each other and are electrically insulated from each other. Therefore, when the pump control unit 92 operates the oxygen pump cell 21 and the hydrogen pump cell 31, there is no electrical interference between their electrode potentials or pump currents, which is thought to enable more accurate measurement of the oxygen concentration and water vapor concentration.

[0089] Furthermore, as will be described later, when the sensor element 101 is formed by integral firing (co-firing), the presence of the insulator layer 62 prevents the second oxygen ion conductor layer 6 and the proton conductor layer 7 from coming into contact with each other during firing. This prevents the components in each layer from migrating during firing, making it easier to obtain the second oxygen ion conductor layer 6 and the proton conductor layer 7 with the desired compositions after firing. In other words, the insulator layer 62 functions as a buffer layer that does not contain alkaline earth metals, thereby suppressing material transfer during co-firing. For example, components such as alkaline earth metals in the proton-conducting solid electrolyte that constitutes the proton conductor layer 7 do not migrate during firing and form solid solutions in the oxygen ion-conducting solid electrolyte that constitutes the second oxygen ion conductor layer 6. Therefore, the sensor element 101 can be manufactured so that the second oxygen ion conductor layer 6 and the proton conductor layer 7 have the desired compositions. As a result, the sensor element 101 can exhibit the desired oxygen ion conductivity and proton conductivity, which is believed to enable more accurate measurement of oxygen concentration and water vapor concentration.

[0090] As shown in FIGS. 1 and 2 , in the sensor element 101, the oxygen pump electrode (outer oxygen pump electrode 23) outside the cavity of the oxygen pump cell 21 and the hydrogen pump electrode (outer hydrogen pump electrode 33) outside the cavity of the hydrogen pump cell 31 are both disposed on the outer surface of the sensor element 101 at positions in contact with the measurement gas. The sensor element 101 does not have an oxygen reference electrode that contacts a reference gas (gas with a known oxygen concentration; for example, air) that serves as a reference for the oxygen concentration, or a hydrogen reference electrode that contacts a reference gas (gas with a known hydrogen concentration) that serves as a reference for the hydrogen concentration. Therefore, there is no need to form a space for introducing a reference gas inside the base portion 102. For example, the more complex the internal structure of the base portion 102, such as by having a large volume or a large number of spaces inside the sensor element 101, the more thermal stress is generated in the sensor element 101, which may increase the likelihood of cracks occurring in the internal structure of the sensor element 101. The sensor element 101 can simplify the internal structure of the base portion 102, which is thought to reduce thermal stress during temperature rise and fall of the sensor element 101, thereby preventing cracks from occurring in the internal structure of the sensor element 101. The temperature rise and fall of the sensor element 101 refers to, for example, a temperature rise due to heating when the gas sensor 100 is operated, or a temperature drop caused by the sensor element 101 being cooled by the flow rate or temperature of the gas to be measured.

[0091] 1 and 2, in the gas sensor of the present invention, the intra-void hydrogen pump electrode (inner hydrogen pump electrode 32) of the hydrogen pump cell 31 is preferably disposed at a position farther from the first diffusion-limiting passage 11 than the intra-void oxygen pump electrode (inner oxygen pump electrode 23) of the oxygen pump cell 21, i.e., behind the intra-void oxygen pump electrode (inner oxygen pump electrode 23). In this case, substantially all of the water vapor in the measurement gas is decomposed at the inner oxygen pump electrode 23, and the oxygen generated by the decomposition of the water vapor is pumped out by the oxygen pump cell 21. Thereafter, the measurement gas containing hydrogen generated by the decomposition of the water vapor reaches the inner hydrogen pump electrode 32. Therefore, the hydrogen generated by the decomposition of the water vapor can be more efficiently pumped out by the hydrogen pump cell 31.

[0092] More preferably, the internal cavity in which the inner oxygen pump electrode 22 is disposed and the internal cavity in which the inner hydrogen pump electrode 32 is disposed should be separate internal cavities that communicate with each other via a diffusion-controlling passage. That is, a configuration having two internal cavities is preferable. Fig. 4 is a vertical cross-sectional view in the longitudinal direction of a sensor element 111, showing an example of the general configuration of a gas sensor 110. In Fig. 4, the same components as those in Fig. 1 are denoted by the same reference numerals.

[0093] In the sensor element 111, the measurement gas flow space 15 includes a gas inlet 10 opening on the surface of the base portion 112, a first internal space 20 communicating with the gas inlet 10 via a first diffusion-controlling passage 11 and having at least a second oxygen ion conductor layer 6 on its inner surface, and a second internal space 40 communicating with the first internal space 20 via a second diffusion-controlling passage 30 (second diffusion-controlling portion) and having a first oxygen ion conductor layer 4 and a proton conductor layer 7 on its inner surface. The first internal space 20 is formed facing the first oxygen ion conductor layer 4 and the second oxygen ion conductor layer 6, and the second internal space 40 is formed facing the first oxygen ion conductor layer 4, the second oxygen ion conductor layer 6, and the proton conductor layer 7.

[0094] The first internal space 20 and the second internal space 40 are spaces inside the sensor element 111, similar to the internal space 25 of the sensor element 101 described above, which are provided by hollowing out the spacer layer 5 and are defined by an upper portion defined by the underside of the second oxygen ion conductor layer 6, a lower portion defined by the upper surface of the first oxygen ion conductor layer 4, and sides defined by the side surfaces of the spacer layer 5.

[0095] The through-hole 61 is formed at a position where the second internal space 40 is present in the second oxygen ion conductor layer 6. The proton conductor layer 7 is disposed generally parallel to the second oxygen ion conductor layer 6, and is formed on the lower surface of the second oxygen ion conductor layer 6, i.e., on the surface side facing the second internal space 40, so as to completely cover the through-hole 61 and to cover substantially the entire ceiling surface of the second internal space 40.

[0096] The second diffusion-controlled passage 30 is provided as two horizontally elongated slits (the openings have their longitudinal direction perpendicular to the plane of the drawing in FIG. 4 ) similar to the first diffusion-controlled passage 11. The second diffusion-controlled passage 30 may have any shape that provides a desired diffusion resistance, and the shape is not limited to the slits.

[0097] An intra-void oxygen pump electrode (inner oxygen pump electrode 23) is disposed in the first internal space 20, and an intra-void hydrogen pump electrode (inner hydrogen pump electrode 32) is disposed in the second internal space 40. In this way, the first internal space 20 is provided as a space for adjusting the oxygen partial pressure in the measurement gas and decomposing water vapor in the measurement gas, and the second internal space 40 is provided as a space for pumping out hydrogen produced by decomposition of water vapor and measuring the water vapor concentration.

[0098] In the gas sensor 110 having the sensor element 111, the pump control unit 92 operates the oxygen pump cell 21, whereby substantially all of the water vapor in the measured gas is decomposed in the first internal space 20, and the oxygen produced by the decomposition of the water vapor and the oxygen originally present in the measured gas are all or substantially all pumped out of the first internal space 20 by the oxygen pump cell 21.

[0099] The measurement gas, which contains hydrogen generated by the decomposition of water vapor but is substantially free of water vapor and oxygen, is introduced into the second internal space 40 through the second diffusion-limited passage 30 and reaches the inner hydrogen pump electrode 32. Hydrogen molecules are smaller than water vapor molecules and have a sufficiently large diffusion coefficient, so they smoothly reach the inner hydrogen pump electrode 32 and are pumped out by the hydrogen pump cell 31. This is thought to enable more accurate detection of the water vapor concentration.

[0100] [Embodiment 2] The gas sensor 200 of the second embodiment is an example of a gas sensor that detects oxygen O, water vapor H, and carbon dioxide CO in a measurement gas and measures the concentrations of these three gases. The gas sensor 200 is an example of a configuration including a sensor element 201 having two internal cavities.

[0101] Fig. 5 is a vertical cross-sectional view of a sensor element 201 in the longitudinal direction, showing an example of the general configuration of a gas sensor 200 of Embodiment 2. In Fig. 5, the same components as those in Fig. 4 are denoted by the same reference numerals. Fig. 6 is a partial cross-sectional view taken along the same cross section as Fig. 5, showing the measurement gas flow space 15 and its surrounding configuration in the sensor element 101. Fig. 7 is a block diagram showing the electrical connection between a control device 290 and the sensor element 201 in the gas sensor 200 of Embodiment 2.

[0102] (sensor element) In addition to the oxygen pump cell 21 and the hydrogen pump cell 31, the sensor element 201 further includes an oxidation pump cell 51 including an intra-space oxidation electrode (inner oxidation electrode 52 in the sensor element 201) disposed on an oxygen ion-conductive solid electrolyte layer (first oxygen ion conductor layer 4 in the sensor element 201) located in the inner space of the measurement gas flow space 15, farther from the first diffusion-controlling passage 11 than the intra-space oxygen pump electrode (inner oxygen pump electrode 23), and an extra-space oxidation electrode disposed at a position different from that in the measurement gas flow space 15 of the base portion 112 and in contact with the intra-space oxidation electrode via the oxygen ion-conductive solid electrolyte layer (first oxygen ion conductor layer 4, spacer layer 5, and second oxygen ion conductor layer 6). In the sensor element 201, the inner oxidation electrode 52 is disposed in the second internal space 40 at a position further rearward (i.e., farther from the first diffusion-controlling passage 11) than the first internal space 20 in which the inner oxygen pump electrode 23 is disposed. In addition, in the sensor element 201, the outer oxygen pump electrode 23 also functions as an outer-space oxidation electrode of the oxidation pump cell 51.

[0103] That is, the oxidation pump cell 51 is an electrochemical pump cell comprising an inner oxidation electrode 52 provided on the upper surface of the first oxygen ion conductor layer 4 which provides the bottom surface of the second internal space 40, an outer oxygen pump electrode 23 provided on the upper surface of the second oxygen ion conductor layer 6 in a manner that it is exposed to the external space, and the first oxygen ion conductor layer 4, the spacer layer 5, and the second oxygen ion conductor layer 6 sandwiched between these electrodes.

[0104] The inner oxidation electrode 52 is a porous cermet electrode (an electrode in which a metal component and a ceramic component are mixed) similar to the inner oxygen pump electrode 22. The ceramic component is not particularly limited, but it is preferable to use an oxygen ion conductive solid electrolyte similar to the second oxygen ion conductor layer 6 and the first oxygen ion conductor layer 4. For example, ZrO2 (stabilized ZrO2) can be used as the ceramic component.

[0105] The inner oxidation electrode 52 may contain a catalytically active noble metal (e.g., at least one of Pt, Rh, Ir, Ru, and Pd) as a metal component, similar to the inner oxygen pump electrode 22. For example, the inner oxidation electrode 52 may be a porous cermet electrode of Pt and ZrO2.

[0106] In the oxidation pump cell 51, a desired pump voltage Vp2 is applied between the inner oxidation electrode 52 and the outer oxygen pump electrode 23 by a variable power supply 54, and an oxidation pump current Ip2 is passed between the inner oxidation electrode 52 and the outer oxygen pump electrode 23, thereby making it possible to pump oxygen from the external space into the second internal space 40.

[0107] (Control device) 7 is a block diagram showing the electrical connection relationship between a control device 290 and each of the pump cells 21, 31, and 51 of the sensor element 201 in the gas sensor 200 of the second embodiment. The control device 290 includes variable power supplies 24, 34, and 54 and a control unit 291. The control unit 291 includes a pump control unit 292 and a concentration calculation unit 293.

[0108] The control unit 291 is configured to acquire pump currents (Ip0, Ip1, Ip2) in the pump cells 21, 31, 51 of the sensor element 201. The control unit 291 is also configured to output control signals to the variable power supplies 24, 34, 54.

[0109] In the gas sensor 200, the pump control unit 292 is configured to control the operation of the oxygen pump cell 21, the hydrogen pump cell 31, and the oxidation pump cell 51 so as to measure the concentration of the target gas (oxygen O2, water vapor H2O, and carbon dioxide CO2) in the measurement gas.

[0110] The pump control unit 292 A predetermined pump voltage Vp0 is applied between the oxygen pump electrode inside the cavity (inner oxygen pump electrode 22) and the oxygen pump electrode outside the cavity (outer oxygen pump electrode 23) of the oxygen pump cell 21, and an oxygen pump current Ip0 is passed through the oxygen pump cell 21. A predetermined pump voltage Vp1 is applied between the hydrogen pump electrode inside the void (inner hydrogen pump electrode 32) and the hydrogen pump electrode outside the void (outer hydrogen pump electrode 33) of the hydrogen pump cell 31, causing a hydrogen pump current Ip1 to flow through the hydrogen pump cell 31, and further A predetermined pump voltage Vp2 is applied between the oxidation electrode inside the void (inner oxidation electrode 52) of the oxidation pump cell 51 and the oxidation electrode outside the void (outer oxygen pump electrode 23), thereby controlling the flow of an oxidation pump current Ip2 through the oxidation pump cell 51.

[0111] The pump control unit 292 applies a predetermined pump voltage Vp0 between the oxygen pump electrode inside the cavity (the inner oxygen pump electrode 22) and the oxygen pump electrode outside the cavity (the outer oxygen pump electrode 23) using the variable power supply 24 to pump oxygen in the measurement gas from the first internal cavity 20. At this time, water vapor and carbon dioxide in the measurement gas are decomposed (reduced) at the inner oxygen pump electrode 22, and oxygen generated by the decomposition of water vapor, oxygen generated by the decomposition of carbon dioxide, and oxygen originally present in the measurement gas are pumped out from the first internal cavity 20. At this time, the oxygen pump current Ip0 flowing in the oxygen pump cell 21 flows from the inner oxygen pump electrode 22 to the outer oxygen pump electrode 23 outside the sensor element 101. The oxygen pump current Ip0 includes a current flowing due to oxygen gas originally present in the measurement gas, a current flowing due to oxygen generated by the decomposition of water vapor, and a current flowing due to oxygen generated by the decomposition of carbon dioxide. The hydrogen generated by the decomposition of water vapor and the carbon monoxide generated by the decomposition of carbon dioxide are guided to the second internal space 40 via the second diffusion-controlling passage 30 .

[0112] The pump voltage Vp0 applied to the oxygen pump cell 21 is preferably set to a value that will decompose all or substantially all of the water vapor and carbon dioxide in the measurement gas in the first internal space 20 (particularly around the inner oxygen pump electrode 22). The pump voltage Vp0 may vary depending on the intended use of the gas sensor 200 and the configuration of the sensor element 201, but may be, for example, about 800 mV to 1500 mV, or about 1000 mV to 1500 mV.

[0113] Similar to the pump control unit 92, the pump control unit 292 applies a predetermined pump voltage Vp1 between the hydrogen pump electrode inside the void (inner hydrogen pump electrode 32) and the hydrogen pump electrode outside the void (outer hydrogen pump electrode 33) of the hydrogen pump cell 31 using the variable power supply 34, thereby pumping out hydrogen generated by decomposition of water vapor in the first internal void 20 from the second internal void 40. At this time, the hydrogen pump current Ip1 flowing through the hydrogen pump cell 31 flows from the outer hydrogen pump electrode 33 toward the inner hydrogen pump electrode 32 outside the sensor element 201. In other words, the oxygen pump current Ip0 and the hydrogen pump current Ip1 flow in opposite directions.

[0114] The pump voltage Vp1 applied to the hydrogen pump cell 31 should be set to a value such that all or substantially all of the hydrogen in the measurement gas introduced into the second internal space 40 (particularly around the inner hydrogen pump electrode 32) is pumped out. The pump voltage Vp1 may vary depending on the intended use of the gas sensor 200 and the configuration of the sensor element 201, but may be, for example, approximately 100 mV to 500 mV.

[0115] Furthermore, the pump control unit 292 applies a predetermined pump voltage Vp2 between the intra-void oxidation electrode (inner oxidation electrode 52) and the extra-void oxidation electrode (outer oxygen pump electrode 23) of the oxidation pump cell 51 using the variable power supply 54 to pump oxygen into the second internal space 40 and oxidize (burn) carbon monoxide produced by decomposition of carbon dioxide in the first internal space 20. At this time, the oxidation pump current Ip2 flowing through the oxidation pump cell 51 flows from the outer oxygen pump electrode 23 toward the inner oxidation electrode 52 outside the sensor element 201. In other words, the oxygen pump current Ip0 and the oxidation pump current Ip2 flow in opposite directions. Referring to FIG. 5, in the gas sensor 200 of this embodiment, the oxygen pump current Ip0 is detected as a positive current, and the oxidation pump current Ip2 is detected as a negative current.

[0116] The pump voltage Vp2 applied to the oxidation pump cell 51 is preferably set to a value such that all or substantially all of the carbon monoxide in the measurement gas introduced into the second internal space 40 is oxidized in the second internal space 40 (particularly around the inner oxidation electrode 52). The pump voltage Vp2 may vary depending on the intended use of the gas sensor 200, the configuration of the sensor element 201, etc., but may be, for example, approximately 100 mV or more and 200 mV or less.

[0117] The concentration calculation unit 293 is configured to calculate the measurement target gas concentrations (O2 concentration, H2O concentration, and CO2 concentration in this embodiment) in the measurement target gas. The concentration calculation unit 293 calculates the measurement target gas concentrations in the measurement target gas based on at least one of the oxygen pump current Ip0, the hydrogen pump current Ip1, and the oxidation pump current Ip2.

[0118] Similar to the concentration calculation unit 93, the concentration calculation unit 293 acquires the hydrogen pump current Ip1 in the hydrogen pump cell 31, calculates the HO concentration in the measurement gas based on a pre-stored conversion parameter (current-HO concentration conversion parameter) between the hydrogen pump current Ip1 and the HO concentration in the measurement gas, and outputs the calculated value as a measurement value of the gas sensor 200. The current-HO concentration conversion parameter is pre-stored in the memory of the control unit 291, which functions as the concentration calculation unit 293. The current-HO concentration conversion parameter can be appropriately determined for the gas sensor 200 in advance through experiments or the like by a person skilled in the art. The current-HO concentration conversion parameter may be, for example, a coefficient of an approximate expression (such as a linear function) obtained through experiments, or may be a map showing the correspondence between the hydrogen pump current Ip1 and the HO concentration in the measurement gas. The current-HO concentration conversion parameter may be a parameter unique to each gas sensor 200, or a parameter commonly used by multiple gas sensors.

[0119] The concentration calculation unit 293 acquires the oxidation pump current Ip2 in the oxidation pump cell 51, calculates the CO2 concentration in the measurement gas based on a pre-stored conversion parameter (current-CO2 concentration conversion parameter) between the oxidation pump current Ip2 and the CO2 concentration in the measurement gas, and outputs the calculated value as a measurement value of the gas sensor 200. The current-CO2 concentration conversion parameter is pre-stored in the memory of the control unit 291, which functions as the concentration calculation unit 293. The current-CO2 concentration conversion parameter can be appropriately determined for the gas sensor 200 in advance through experiments or the like by a person skilled in the art. The current-CO2 concentration conversion parameter may be, for example, a coefficient of an approximate equation (such as a linear function) obtained through experiments, or may be a map showing the correspondence between the oxidation pump current Ip2 and the CO2 concentration in the measurement gas. The current-CO2 concentration conversion parameter may be a parameter unique to each gas sensor 200, or may be a parameter commonly used by multiple gas sensors.

[0120] The concentration calculation unit 293 acquires the oxygen pump current Ip0 in the oxygen pump cell 21, the hydrogen pump current Ip1 in the hydrogen pump cell 31, and the oxidation pump current Ip2 in the oxidation pump cell 51, and calculates the O2 concentration in the measurement gas based on pre-stored conversion parameters (current-O2 concentration conversion parameters) between these currents and the oxygen concentration (O2 concentration) in the measurement gas, and outputs the calculated O2 concentration as a measurement value of the gas sensor 200. The current-O2 concentration conversion parameters are stored in advance in the memory of the control unit 291, which functions as the concentration calculation unit 293, as data representing the relationship between the pump currents Ip0, Ip1, and Ip2 and the O2 concentration in the measurement gas. The current-O2 concentration conversion parameters can be appropriately determined for the gas sensor 200 by a person skilled in the art through experiments or the like. The current-O2 concentration conversion parameters may be, for example, coefficients of an approximate equation (such as a linear function) obtained through experiments, or may be a map showing the correspondence between the pump currents Ip0, Ip1, and Ip2 and the O2 concentration in the measurement gas. The current-O2 concentration conversion parameter may be a parameter specific to each gas sensor 200, or may be a parameter commonly used by a plurality of gas sensors.

[0121] The concentration calculation unit 293 calculates the O2 concentration, the H2O concentration, and the CO2 concentration simultaneously or in parallel. In this way, the gas sensor 200 is configured to be able to measure the concentrations of a plurality of measurement target gases (three types of concentrations: O2 concentration, H2O concentration, and CO2 concentration in this embodiment). Alternatively, the gas sensor 200 may be configured to measure one or two types of concentrations among the O2 concentration, the H2O concentration, and the CO2 concentration.

[0122] (Measurement of oxygen concentration, water vapor concentration, and carbon dioxide concentration in the gas to be measured) Next, a method for measuring the concentrations of oxygen O2, water vapor H2O, and carbon dioxide CO2 in a measurement gas using the gas sensor 200 having the above-described configuration will be described.

[0123] The gas to be measured is introduced through the gas inlet 10, passes through the first diffusion-controlled passage 11, the buffer space 12, and the fourth diffusion-controlled passage 13 in that order, where a predetermined diffusion resistance is applied, and reaches the first internal space 20.

[0124] By operating the oxygen pump cell 21 as described above, the pump control unit 292 causes all or substantially all of the water vapor in the measurement gas to be decomposed (2H2O → 2H2 + O2) in the first internal space 20 (particularly near the surface of the inner main pump electrode 22) to produce hydrogen and oxygen. Also, all or substantially all of the carbon dioxide in the measurement gas is decomposed (2CO2 → 2CO + O2) to produce carbon monoxide and oxygen. The oxygen produced by the decomposition of water vapor, the oxygen produced by the decomposition of carbon dioxide, and the oxygen originally present in the measurement gas are all or substantially all pumped out of the first internal space 20 by the oxygen pump cell 21.

[0125] The measurement gas, which contains hydrogen produced by the decomposition of water vapor and carbon monoxide produced by the decomposition of carbon dioxide but does not substantially contain water vapor, carbon dioxide, or oxygen, passes through the second diffusion-controlling passage 30, where a predetermined diffusion resistance is applied, and reaches the second internal space 40.

[0126] The pump control unit 293 operates the hydrogen pump cell 31 as described above, thereby pumping all or substantially all of the hydrogen from the second internal space 40. The hydrogen pump current Ip1 flowing through the hydrogen pump cell 31 is a current resulting from hydrogen H2 generated by decomposition of water vapor HO in the measurement gas. When substantially all of the water vapor HO in the measurement gas is decomposed at the inner oxygen pump electrode 22 of the oxygen pump cell 21, the amount of hydrogen H2 generated by decomposition of water vapor HO corresponds to the amount (concentration) of water vapor HO in the measurement gas. That is, the current value of the hydrogen pump current Ip1 is considered to correspond to the water vapor concentration in the measurement gas. The current value of the hydrogen pump current Ip1 is considered to be approximately proportional to the water vapor concentration in the measurement gas. Such a relationship between the water vapor concentration in the measurement gas and the hydrogen pump current Ip1 may be determined in advance, and the concentration calculation unit 293 may store this relationship as a current-HO concentration conversion parameter. The concentration calculation unit 293 can calculate the water vapor concentration in the measurement gas based on the hydrogen pump current Ip1 using the current-H2O concentration conversion parameter.

[0127] Furthermore, by operating the oxidation pump cell 51 as described above, the pump control unit 293 pumps oxygen into the second internal space 40, oxidizing all or substantially all of the carbon monoxide that reaches the second internal space 40. The oxidation pump current Ip2 flowing through the oxidation pump cell 51 is a current resulting from carbon monoxide CO produced by the decomposition of carbon dioxide CO2. When substantially all of the carbon dioxide CO2 in the measurement gas is decomposed at the inner oxygen pump electrode 22, the amount of carbon monoxide CO produced by the decomposition of carbon dioxide CO2 corresponds to the amount (concentration) of carbon dioxide CO2 in the measurement gas. Therefore, the amount of oxygen pumped by the oxidation pump cell 51 to oxidize carbon monoxide CO corresponds to the amount (concentration) of carbon dioxide CO2 in the measurement gas. In other words, the current value of the oxidation pump current Ip2 is considered to correspond to the carbon dioxide concentration in the measurement gas. Such a relationship between the carbon dioxide concentration in the measurement gas and the oxidation pump current Ip2 may be determined in advance, and the concentration calculation unit 293 may store this relationship as a current-CO2 concentration conversion parameter. The concentration calculation unit 293 can calculate the carbon dioxide concentration in the measurement gas based on the oxidation pump current Ip2 using the current-CO2 concentration conversion parameter.

[0128] As described above, the oxygen pump current Ip0 flowing through the oxygen pump cell 21 includes a current resulting from oxygen gas O2 originally present in the measurement gas, a current resulting from oxygen O2 produced by the decomposition of water vapor HO in the measurement gas, and a current resulting from oxygen O2 produced by the decomposition of carbon dioxide CO2 in the measurement gas. Meanwhile, the hydrogen pump current Ip1 flowing through the hydrogen pump cell 31 is a current resulting from hydrogen H2 produced by the decomposition of water vapor HO in the measurement gas. Furthermore, the oxidation pump current Ip2 flowing through the oxidation pump cell 51 is a current resulting from carbon monoxide CO produced by the decomposition of carbon dioxide CO2 in the measurement gas. Since the amount of oxygen O2 produced by the decomposition of water vapor HO and the amount of hydrogen H2 produced by the decomposition of water vapor HO both correspond to the amount (concentration) of water vapor HO in the measurement gas, it is believed that the current resulting from oxygen O2 produced by the decomposition of water vapor HO can be determined from the value of the hydrogen pump current Ip1 or the water vapor concentration calculated from the hydrogen pump current Ip1. Because the amount of oxygen O2 produced by the decomposition of carbon dioxide CO2 and the amount of carbon monoxide CO2 produced by the decomposition of carbon dioxide CO2 both correspond to the amount (concentration) of carbon dioxide CO2 in the measurement gas, it is possible to determine the current attributable to oxygen O2 produced by the decomposition of carbon dioxide CO2 in the oxygen pump current Ip0 from the current value of the oxidation pump current Ip2 or the carbon dioxide concentration calculated from the oxidation pump current Ip2. Therefore, the oxygen concentration in the measurement gas can be calculated based on the oxygen pump current Ip0, the hydrogen pump current Ip1, and the oxidation pump current Ip2. For example, the relationship between the concentration of oxygen pumped by the oxygen pump cell 21 (oxygen in the measurement gas + oxygen produced by the decomposition of water vapor + oxygen produced by the decomposition of carbon dioxide) and the oxygen pump current Ip0, the relationship between the water vapor concentration in the measurement gas and the hydrogen pump current Ip1, and the relationship between the carbon dioxide concentration in the measurement gas and the oxidation pump current Ip2 may be determined in advance, and the concentration calculation unit 293 may store these as current-O2 concentration conversion parameters. The concentration calculation unit 293 can calculate the oxygen concentration in the measurement gas based on the oxygen pump current Ip0, the hydrogen pump current Ip1, and the oxidation pump current Ip2 using the current-O2 concentration conversion parameter.

[0129] In this way, the gas sensor 200 can measure the oxygen concentration, water vapor concentration, and carbon dioxide concentration in the measurement gas. Accurate measurement is possible even when oxygen, water vapor, and carbon dioxide coexist in the measurement gas, or when only one or two of them are present. Such a gas sensor 200 is useful for measuring exhaust gas from gasoline engines and diesel engines, for example.

[0130] In the sensor element 201, the outer oxygen pump electrode 23 functions as both the oxygen pump electrode outside the void of the oxygen pump cell 21 and the oxidation electrode outside the void of the oxidation pump cell 51, but the oxidation electrode outside the void may be formed as an electrode separate from the outer oxygen pump electrode 23.

[0131] In the sensor element 201, the intra-void oxidation electrode (inner oxidation electrode 52) is disposed on the first oxygen ion conductor layer 4 on the bottom surface of the second internal space 40, but is not limited thereto. The intra-void oxidation electrode (inner oxidation electrode 52) may be disposed at a position farther from the first diffusion-controlling passage 11 than the intra-void oxygen pump electrode (inner oxygen pump electrode 23) of the oxygen pump cell 21, i.e., behind the intra-void oxygen pump electrode (inner oxygen pump electrode 23). For example, an area where the second oxygen ion conductor layer 6 is present may be provided on the ceiling surface of the second internal space 40, and the intra-void hydrogen pump electrode (inner hydrogen pump electrode 32) and the intra-void oxidation electrode (inner oxidation electrode 52) may be disposed in parallel or in series on the ceiling surface of the second internal space 40.

[0132] More preferably, the void oxidation electrode (inner oxidation electrode 52) is disposed on the oxygen ion conductive solid electrolyte layer at a position farther from the first diffusion-limited passage 11 than the void hydrogen pump electrode (inner hydrogen pump electrode 32). In this case, the measurement gas containing hydrogen produced by decomposition of water vapor and carbon monoxide produced by decomposition of carbon dioxide reaches the inner hydrogen pump electrode 32, and substantially all of the hydrogen is pumped out by the hydrogen pump cell 31. Thereafter, the measurement gas containing carbon monoxide produced by decomposition of carbon dioxide reaches the inner oxidation electrode 52. Therefore, carbon monoxide can be oxidized more accurately in the oxidation pump cell 51. As a result, it is believed that the carbon dioxide concentration in the measurement gas can be measured more accurately.

[0133] For example, the intra-void oxidation electrode (inner oxidation electrode 52) may be disposed on the first oxygen ion conductor layer 4 or the second oxygen ion conductor layer 6 in the second internal space 40 at a position farther from the second diffusion-controlling passage 30 in the longitudinal direction of the sensor element 201 (base portion 112) than the intra-void hydrogen pump electrode (inner hydrogen pump electrode 32).

[0134] For example, as shown in Fig. 8, the second diffusion-controlling passage may be provided only between the second oxygen ion conductor layer 6 and the spacer layer 5, so that the inner oxidation electrode 52 is located farther from the first diffusion-controlling passage 11 than the inner hydrogen pump electrode 32. Fig. 8 is a partial cross-sectional schematic view taken along the same cross section as Fig. 5, showing a sensor element 211 of another example of a measurement gas flow space and its surrounding configuration. In the measurement gas flow space 16 of the sensor element 211, the second diffusion-controlling passage 230 is provided between the second oxygen ion conductor layer 6 and the spacer layer 5 as a single horizontally elongated slit (the opening has its longitudinal direction perpendicular to the plane of the drawing in Fig. 8). Therefore, the gas diffusion distance between the second diffusion-controlling passage 230 and the inner oxidation electrode 52 is longer than the gas diffusion distance between the second diffusion-controlling passage 230 and the inner hydrogen pump electrode 32. Furthermore, for example, a porous protective layer covering the inner oxidation electrode 52 may be formed as a diffusion rate-controlling portion between the inner hydrogen pump electrode 32 and the inner oxidation electrode 52 .

[0135] 9, the sensor element may further include a third internal space 65, and the inner oxidation electrode 52 may be disposed in the third internal space 65. FIG. 9 is a partial cross-sectional schematic view taken along the same cross section as FIG. 5, showing a sensor element 221 of another example of the measurement gas flow space and its surrounding configuration. In the sensor element 221, the measurement gas flow space 17 includes a gas inlet 10 opening to the surface of the sensor element 221, a first internal space 20 communicating with the gas inlet 10 via a first diffusion-controlling passage 11 and having at least a second oxygen ion conductor layer 6 on its inner surface, a second internal space 40 communicating with the first internal space 20 via a second diffusion-controlling passage 30 and having at least a proton conductor layer 7 on its inner surface, and a third internal space 65 communicating with the second internal space 40 via a third diffusion-controlling passage 60 and having at least a second oxygen ion conductor layer 6 on its inner surface. That is, the sensor element 221 shows an example of a configuration having three internal spaces.

[0136] In the sensor element 221, the inner oxygen pump electrode 22 is disposed in the first internal space 20, the inner hydrogen pump electrode 32 is disposed in the second internal space 40, and the inner oxidation electrode 52 is disposed in the third internal space 65. In the first internal space 20, decomposition of water vapor and carbon dioxide and pumping of oxygen occur, in the second internal space 40, pumping of hydrogen produced by decomposition of water vapor occurs, and in the third internal space 65, oxidation of carbon monoxide produced by decomposition of carbon dioxide occurs. It is believed that by dividing the roles of each internal space in this way, it is possible to measure the oxygen concentration, water vapor concentration, and carbon dioxide concentration with even greater accuracy.

[0137] [Embodiment 3] In the present invention, the sensor element may include a reference electrode disposed inside the base portion so as to be in contact with the reference gas.

[0138] A gas sensor 300 according to a third embodiment includes a sensor element 301 having a reference electrode 42. The gas sensor 300 according to the third embodiment is an example of a gas sensor that detects oxygen O2 and water vapor H2O in a measurement gas and measures the concentrations of these two gases. The gas sensor 300 is an example of a configuration that includes a sensor element 301 having two internal cavities. FIG. 10 is a schematic vertical cross-sectional view of the sensor element 301 in the longitudinal direction, showing an example of the general configuration of the gas sensor 300 according to the third embodiment. In FIG. 10, the same components as those in FIG. 4 are denoted by the same reference numerals. FIG. 11 is a block diagram showing the electrical connection between a control device 390 and the sensor element 301 in the gas sensor 300 according to the third embodiment.

[0139] In the sensor element 301, the measurement gas flow space 15 has the same configuration as the sensor element 111 in the gas sensor 110 described above.

[0140] In the sensor element 301, a reference gas introduction space 43 is provided between the upper surface of the second substrate layer 2 and the lower surface of the first oxygen ion conductor layer 4, at a position farther from the tip side than the measurement gas flow space 15, and at a position defined at its lateral side by the side surface of the third substrate layer 3. The reference gas introduction space 43 has an opening at the other end (hereinafter referred to as the rear end) of the sensor element 301. For example, air is introduced into the reference gas introduction space 43 as a reference gas for measuring the oxygen concentration. The heater lead 76 may be disposed at a position where the reference gas introduction space 43 is present in the width direction of the sensor element 301 as shown in FIG. 10 , or may be disposed at a position where the reference gas introduction space 43 is not present, sandwiched between the third substrate layer 3 and the second substrate layer 2.

[0141] The air introduction layer 48 is a layer made of porous alumina, and a reference gas is introduced into the air introduction layer 48 through the reference gas introduction space 43. The air introduction layer 48 is also formed so as to cover the reference electrode 42.

[0142] The reference electrode 42 is an electrode disposed inside the base portion 302 so as to be in contact with the reference gas. Specifically, in the sensor element 301, the reference electrode 42 is an electrode formed in a manner sandwiched between the third substrate layer 3 and the lower surface of the first oxygen ion conductor layer 4, and as described above, the air introduction layer 48 connected to the reference gas introduction space 43 is provided around the reference electrode 42. That is, the reference electrode 42 is disposed so as to be in contact with the reference gas via the porous air introduction layer 48 and the reference gas introduction space 43. The reference electrode 42 may be formed as a porous cermet electrode (for example, a cermet electrode of Pt and ZrO2) that is rectangular in plan view.

[0143] In the sensor element 301, the reference electrode 42 is in electrochemical correspondence with the intra-void oxygen pump electrode (inner oxygen pump electrode 22). That is, the reference electrode 42 is disposed so as to be in contact with the intra-void oxygen pump electrode (inner oxygen pump electrode 22) via an oxygen ion conductive solid electrolyte.

[0144] Specifically, the inner oxygen pump electrode 22, the second oxygen ion conductor layer 6, the spacer layer 5, the first oxygen ion conductor layer 4, and the reference electrode 42 constitute an electrochemical sensor cell, i.e., an oxygen pump controlling sensor cell 80. By measuring the electromotive force V0 between the inner oxygen pump electrode 22 and the reference electrode 42 in the oxygen pump controlling sensor cell 80, the oxygen concentration (oxygen partial pressure) in the first internal space 20 can be determined.

[0145] Furthermore, control is performed to apply a pump voltage Vp0 to the oxygen pump cell 21 based on the electromotive force V0. More specifically, the oxygen pump current Ip0 is controlled by feedback-controlling the pump voltage Vp0 so that the electromotive force V0 is constant. This makes it possible to control the oxygen concentration in the first internal space 20 to a predetermined concentration, more reliably decomposing substantially all of the water vapor in the measurement gas and pumping out the oxygen from the first internal space 20. Therefore, the water vapor concentration and oxygen concentration in the measurement gas can be detected more accurately.

[0146] 11 is a block diagram showing the electrical connections between a control device 390, the pump cells 21 and 31 of a sensor element 301, and the oxygen pump control sensor cell 80 in a gas sensor 300 of the third embodiment. In FIG. 11, the same components as those in FIG. 3 are denoted by the same reference numerals. The control device 390 includes variable power supplies 24 and 34 and a control unit 391. The control unit 391 includes a pump control unit 392 and a concentration calculation unit 93.

[0147] The control unit 391 is configured to acquire the pump currents (Ip0, Ip1) in the pump cells 21, 31 of the sensor element 301 and the electromotive force V0 in the oxygen pump control sensor cell 80. The control unit 391 is also configured to output control signals to the variable power supplies 24, 34.

[0148] In the gas sensor 300, the pump control section 392 of the control section 391 is configured to control the operation of the oxygen pump cell 21 and the hydrogen pump cell 31 so as to measure the concentration of the target gas (oxygen O2 and water vapor H2O) in the measurement gas.

[0149] In the gas sensor 300, the pump control unit 392 Based on the electromotive force V0 between the reference electrode 42 and the oxygen pump electrode (inner oxygen pump electrode 22) in the cavity of the oxygen pump cell 21 (electromotive force V0 in the oxygen pump control sensor cell 80), a predetermined pump voltage Vp0 is applied between the oxygen pump electrode (inner oxygen pump electrode 22) in the cavity of the oxygen pump cell 21 and the oxygen pump electrode (outer oxygen pump electrode 23) outside the cavity, causing an oxygen pump current Ip0 to flow through the oxygen pump cell 21, A predetermined pump voltage Vp1 is applied between the hydrogen pump electrode inside the void (inner hydrogen pump electrode 32) and the hydrogen pump electrode outside the void (outer hydrogen pump electrode 33) of the hydrogen pump cell 31, causing a hydrogen pump current Ip1 to flow through the hydrogen pump cell 31.

[0150] In the gas sensor 300, the pump control unit 392 controls the electromotive force V0 in the oxygen pump control sensor cell 80 to a predetermined target value (target value V0 SETThe pump voltage Vp0 of the variable power supply 24 in the oxygen pump cell 21 is feedback-controlled so that the electromotive force Vp0 represents the oxygen partial pressure near the inner oxygen pump electrode 22. Therefore, maintaining the electromotive force Vp0 constant means maintaining the oxygen partial pressure near the inner oxygen pump electrode 22 constant. As a result, the oxygen pump current Ip0 in the oxygen pump cell 21 changes depending on the total amount (concentration) of oxygen produced by decomposition of oxygen gas and water vapor in the measurement gas.

[0151] Target value V0 SET The value of V0 may be appropriately set as a value that will decompose all or substantially all of the water vapor in the gas to be measured in the first internal space 20 (particularly around the inner oxygen pump electrode 22). SET The value of Vp0 may vary depending on the intended use of the gas sensor 300 and the configuration of the sensor element 301, but may be, for example, about 800 mV to 1500 mV, or about 1000 mV to 1500 mV. As a result of the feedback control, the value of the pump voltage Vp0 may be, for example, about 800 mV to 1500 mV, or about 1000 mV to 1500 mV.

[0152] In the gas sensor 300, the pump control unit 392, similar to the pump control unit 92, may apply a predetermined pump voltage Vp1 between the intra-void hydrogen pump electrode (inner hydrogen pump electrode 32) and the extra-void hydrogen pump electrode (outer hydrogen pump electrode 33) of the hydrogen pump cell 31 in the second internal space 40 (particularly around the inner hydrogen pump electrode 32) so as to pump out all or substantially all of the hydrogen in the measurement gas introduced into the second internal space 40. The pump voltage Vp1 may vary depending on the intended use of the gas sensor 300, the configuration of the sensor element 301, etc., but may be, for example, approximately 100 mV or more and 500 mV or less.

[0153] In this way, feedback control of the pump voltage Vp0 of the variable power supply 24 in the oxygen pump cell 21 can more reliably decompose all or substantially all of the water vapor in the measurement gas at the inner oxygen pump electrode 22 of the oxygen pump cell 21. The amount of hydrogen produced by decomposition corresponds more accurately to the water vapor concentration in the measurement gas, so the hydrogen pump current Ip1 flowing through the hydrogen pump cell 31 can more accurately correspond to the water vapor concentration in the measurement gas. Furthermore, because oxygen is pumped out more accurately in the oxygen pump cell 21, the oxygen pump current Ip0 can more accurately correspond to the total amount of oxygen produced by decomposition of oxygen gas and water vapor in the measurement gas. As a result, the water vapor concentration and oxygen concentration in the measurement gas can be measured with even greater accuracy.

[0154] [Embodiment 4] Also, an example of a gas sensor 400 according to a fourth embodiment is shown, which includes a sensor element 401 having a reference electrode 42. Like the gas sensor 200 according to the second embodiment, the gas sensor 400 according to the fourth embodiment is an example of a gas sensor that detects oxygen O2, water vapor H2O, and carbon dioxide CO2 in a measurement gas and measures the concentrations of these three gases. FIG. 12 is a vertical cross-sectional view of the sensor element 401 in the longitudinal direction, showing an example of the general configuration of the gas sensor 400 according to the fourth embodiment. In FIG. 12, the same components as those in FIGS. 5 and 10 are denoted by the same reference numerals. Furthermore, FIG. 13 is a block diagram showing the electrical connection between a control device 490 and the sensor element 401 in the gas sensor 400 according to the fourth embodiment.

[0155] In the sensor element 401, the measurement gas flow space 15 and the electrodes have the same configuration as the sensor element 201 in the gas sensor 200 of the second embodiment.

[0156] In the sensor element 401, similarly to the sensor element 301, a reference gas introduction space 43, an air introduction layer 48, and a reference electrode 42 are provided.

[0157] In the sensor element 401, the reference electrode 42 is in electrochemical correspondence with the intra-void oxygen pump electrode (inner oxygen pump electrode 22) as in the sensor element 301. That is, the reference electrode 42 is disposed so as to be in contact with the intra-void oxygen pump electrode (inner oxygen pump electrode 22) via the oxygen ion conductive solid electrolyte (here, the second oxygen ion conductor layer 6, the spacer layer 5, and the first oxygen ion conductor layer 4).

[0158] Specifically, the inner oxygen pump electrode 22, the second oxygen ion conductor layer 6, the spacer layer 5, the first oxygen ion conductor layer 4, and the reference electrode 42 constitute an electrochemical sensor cell, i.e., an oxygen pump controlling sensor cell 80. By measuring the electromotive force V0 between the inner oxygen pump electrode 22 and the reference electrode 42 in the oxygen pump controlling sensor cell 80, the oxygen concentration (oxygen partial pressure) in the first internal space 20 can be determined.

[0159] Furthermore, control is performed to apply a pump voltage Vp0 to the oxygen pump cell 21 based on the electromotive force V0. More specifically, the oxygen pump current Ip0 is controlled by feedback-controlling the pump voltage Vp0 so that the electromotive force V0 is constant. This makes it possible to control the oxygen concentration in the first internal space 20 to a predetermined concentration, more reliably decomposing substantially all of the water vapor and carbon dioxide in the measurement gas and pumping out the oxygen from the first internal space 20. Therefore, the water vapor concentration, carbon dioxide concentration, and oxygen concentration in the measurement gas can be detected more accurately.

[0160] In addition, in the sensor element 401, the reference electrode 42 is also in electrochemical correspondence with the void oxidation electrode (inner oxidation electrode 52). That is, the reference electrode 42 is disposed so as to be in contact with the void oxidation electrode (inner oxidation electrode 52) via the oxygen ion conductive solid electrolyte (here, the first oxygen ion conductor layer 4).

[0161] Specifically, the inner oxidation electrode 52, the first oxygen ion conductor layer 4, and the reference electrode 42 constitute an electrochemical sensor cell, i.e., an oxidation pump controlling sensor cell 81. By measuring the electromotive force V2 between the inner oxidation electrode 52 and the reference electrode 42 in the oxidation pump controlling sensor cell 81, the oxygen concentration (oxygen partial pressure) in the second internal space 40 (particularly in the vicinity of the inner oxidation electrode 52) can be determined.

[0162] Furthermore, control is performed to apply a pump voltage Vp2 to the oxidation pump cell 51 based on the electromotive force V2. More specifically, the oxidation pump current Ip2 is controlled by feedback-controlling the pump voltage Vp2 so that the electromotive force V2 is constant. This allows the oxygen concentration in the second internal space 40 to be controlled to a predetermined concentration, so that carbon monoxide produced by the decomposition of carbon dioxide in the first internal space 20 can be oxidized substantially entirely at the inner oxidation electrode 52 with greater accuracy. Therefore, the carbon dioxide concentration in the measurement gas can be detected with greater accuracy.

[0163] 13 is a block diagram showing the electrical connection relationship between a control device 490 and the pump cells 21, 31, and 51 and the sensor cells 80 and 81 of a sensor element 401 in a gas sensor 400 of embodiment 4. In FIG. 13, the same components as those in FIG. 7 are denoted by the same reference numerals. The control device 490 includes variable power supplies 24, 34, and 54 and a control unit 491. The control unit 491 includes a pump control unit 492 and a concentration calculation unit 293.

[0164] The control unit 491 is configured to acquire pump currents (Ip0, Ip1, Ip2) in the pump cells 21, 31, 51 of the sensor element 401 and electromotive forces (V0, V2) in the sensor cells 80, 81. The control unit 491 is also configured to output control signals to the variable power supplies 24, 34, 54.

[0165] In the gas sensor 400, the pump control section 492 of the control section 491 is configured to control the operation of the oxygen pump cell 21, the hydrogen pump cell 31, and the oxidation pump cell 51 so as to measure the concentrations of the target gases (oxygen O2, water vapor H2O, and carbon dioxide CO2) in the measurement gas.

[0166] The pump control unit 492 Based on the electromotive force V0 between the reference electrode 42 and the oxygen pump electrode (inner oxygen pump electrode 22) in the cavity of the oxygen pump cell 21 (electromotive force V0 in the oxygen pump control sensor cell 80), a predetermined pump voltage Vp0 is applied between the oxygen pump electrode (inner oxygen pump electrode 22) in the cavity of the oxygen pump cell 21 and the oxygen pump electrode (outer oxygen pump electrode 23) outside the cavity, causing an oxygen pump current Ip0 to flow through the oxygen pump cell 21, A predetermined pump voltage Vp1 is applied between the hydrogen pump electrode inside the void (inner hydrogen pump electrode 32) and the hydrogen pump electrode outside the void (outer hydrogen pump electrode 33) of the hydrogen pump cell 31, and a hydrogen pump current Ip1 is passed through the hydrogen pump cell 31. Based on the electromotive force V2 (electromotive force V2 in the oxidation pump control sensor cell 81) between the reference electrode 42 and the oxidation electrode (inner oxidation electrode 52) in the void of the oxidation pump cell 51, a predetermined pump voltage Vp2 is applied between the oxidation electrode (inner oxidation electrode 52) in the void of the oxidation pump cell 51 and the oxidation electrode outside the void (outer oxygen pump electrode 23), thereby controlling the flow of an oxidation pump current Ip2 through the oxidation pump cell 51.

[0167] In the gas sensor 400, the pump control unit 492 controls the electromotive force V0 in the oxygen pump control sensor cell 80 to a predetermined target value (target value V0 SETThe pump voltage Vp0 of the variable power supply 24 in the oxygen pump cell 21 is feedback-controlled so that the electromotive force Vp0 is equal to the oxygen partial pressure near the inner oxygen pump electrode 22. Since the electromotive force Vp0 indicates the oxygen partial pressure near the inner oxygen pump electrode 22, maintaining the electromotive force Vp0 constant means maintaining the oxygen partial pressure near the inner oxygen pump electrode 22 constant. As a result, the oxygen pump current Ip0 in the oxygen pump cell 21 changes depending on the total amount (concentration) of oxygen gas in the measurement gas, oxygen produced by decomposition of water vapor, and oxygen produced by decomposition of carbon dioxide.

[0168] Target value V0 SET The value of V0 may be appropriately set as a value that will decompose all or substantially all of the water vapor and carbon dioxide in the gas to be measured in the first internal space 20 (particularly around the inner oxygen pump electrode 22). SET The value of Vp0 may vary depending on the intended use of the gas sensor 400 and the configuration of the sensor element 401, but may be, for example, about 800 mV to 1500 mV, or about 1000 mV to 1500 mV. As a result of the feedback control, the value of the pump voltage Vp0 may be, for example, about 800 mV to 1500 mV, or about 1000 mV to 1500 mV.

[0169] In the gas sensor 400, the pump control unit 492, similar to the pump control unit 92, may apply a predetermined pump voltage Vp1 between the intra-void hydrogen pump electrode (inner hydrogen pump electrode 32) and the extra-void hydrogen pump electrode (outer hydrogen pump electrode 33) of the hydrogen pump cell 31 in the second internal space 40 (particularly around the inner hydrogen pump electrode 32) so as to pump out all or substantially all of the hydrogen in the measurement gas introduced into the second internal space 40. The pump voltage Vp1 may vary depending on the intended use of the gas sensor 400, the configuration of the sensor element 401, etc., but may be, for example, approximately 100 mV or more and 500 mV or less.

[0170] In the gas sensor 400, the pump control unit 492 controls the electromotive force V2 in the oxidation pump control sensor cell 81 to a predetermined target value (target value V2 SETThe pump voltage Vp2 of the variable power supply 54 in the oxidation pump cell 51 is feedback-controlled so that the oxygen partial pressure near the inner oxidation electrode 52 is constant (hereinafter referred to as "voltage Vp2"). Since the electromotive force V2 indicates the oxygen partial pressure near the inner oxidation electrode 52, maintaining the electromotive force V2 constant means maintaining the oxygen partial pressure near the inner oxidation electrode 52 constant. As a result, the oxidation pump current Ip2 in the oxidation pump cell 51 changes depending on the total amount (concentration) of carbon monoxide produced by the decomposition of carbon dioxide in the measurement gas.

[0171] Target value V2 SET The value of V0 may be appropriately set as a value that oxidizes all or substantially all of the carbon monoxide in the measurement gas introduced into the second internal space 40 (particularly around the inner oxidation electrode 52). SET The value of may vary depending on the intended use of the gas sensor 400 and the configuration of the sensor element 401, but may be, for example, about 100 mV or more and 200 mV or less. As a result of the feedback control, the value of the pump voltage Vp2 may be, for example, about 100 mV or more and 200 mV or less.

[0172] In this way, feedback control of the pump voltage Vp0 of the variable power supply 24 in the oxygen pump cell 21 can more reliably decompose all or substantially all of the water vapor and carbon dioxide in the measurement gas at the inner oxygen pump electrode 22 of the oxygen pump cell 21. Because the amount of hydrogen produced by the decomposition of water vapor corresponds more accurately to the water vapor concentration in the measurement gas, the hydrogen pump current Ip1 flowing through the hydrogen pump cell 31 can more accurately correspond to the water vapor concentration in the measurement gas. Because the amount of carbon monoxide produced by the decomposition of carbon dioxide corresponds more accurately to the carbon dioxide concentration in the measurement gas, the oxidation pump current Ip2 flowing through the oxidation pump cell 51 can more accurately correspond to the carbon dioxide concentration in the measurement gas. Furthermore, because oxygen is pumped more accurately in the oxygen pump cell 21, the oxygen pump current Ip0 can more accurately correspond to the total amount of oxygen gas in the measurement gas, oxygen produced by the decomposition of water vapor, and oxygen produced by the decomposition of carbon dioxide. As a result, the water vapor concentration, carbon dioxide concentration, and oxygen concentration in the measurement gas can be measured with even greater accuracy.

[0173] Although the first to fourth embodiments of the present invention have been described above as examples of the present invention, the present invention is not limited to these embodiments. The present invention may include gas sensors including various configurations of sensor elements and control devices, as long as the object of the present invention, that is, to provide a gas sensor capable of accurately measuring a target gas in a measurement gas, is achieved.

[0174] In the above-described first to fourth embodiments, the proton conductor layer 7 is disposed so as to cover the through-holes 61 formed in the second oxygen ion conductor layer 6, but the present invention is not limited to this. For example, the proton conductor layer may be embedded in a part of the second oxygen ion conductor layer 6. FIG. 14 is a partial cross-sectional view of a sensor element 501 showing an example of an embodiment in which the proton conductor layer is disposed differently. This is the same partial cross-section as FIG. 6. The same configuration can be adopted regardless of whether or not the inner oxidation electrode 52 and the reference electrode 42 are present.

[0175] In the sensor element 501, the proton electrolyte layer 507 is located on the same horizontal plane as the second oxygen ion conductor layer 6, i.e., in a plane including the longitudinal direction of the sensor element 501 and a width direction perpendicular to the longitudinal direction, i.e., a horizontal plane. In other words, the second oxygen ion conductor layer 6 and the proton electrolyte layer 507 have approximately the same thickness and are located on the same plane. The second oxygen ion conductor layer 6 has a hollowed-out shape that penetrates it in the thickness direction at a position facing the second internal space 40, and the proton conductor layer 507 is located in the hollowed-out portion. An insulator layer 562 is interposed between the second oxygen ion conductor layer 6 and the proton conductor layer 507, thereby providing electrical insulation. An inner hydrogen pump electrode 32 is disposed on the lower surface of the proton electrolyte layer 507 facing the second internal space 40, and an outer hydrogen pump electrode 33 is disposed on the upper surface of the proton electrolyte layer 507. The proton electrolyte layer 507 may occupy the entire width of the sensor element 501, or may occupy a part of the width of the sensor element 501. The planar shape of the proton electrolyte layer 507 may be circular, elliptical, rectangular, or the like.

[0176] As in the above-described first to fourth embodiments, it is preferable that both the oxygen ion conductor layer 6 and the proton conductor layer 7 are present on the ceiling surface of the internal space (i.e., one of the inner surfaces of the internal space). The proton conductor layer 7 only needs to be present in the area where the hydrogen pump cell 31 is to be formed, and the proton conductor layer 7 is not formed as a layer extending over the entire length of the sensor element in the longitudinal direction, which can simplify the manufacturing process of the sensor element.

[0177] [Gas sensor manufacturing method] Next, an example of a method for manufacturing the above-mentioned gas sensor will be described. After performing predetermined processing and printing a circuit pattern on a plurality of unfired sheet-shaped molded articles (so-called green sheets) containing an oxygen-ion conductive solid electrolyte such as zirconia (ZrO2) as a ceramic component, the plurality of sheets are stacked, cut, and then fired to produce a sensor element. The fabricated sensor elements can then be assembled into a gas sensor.

[0178] The following description will be given by way of example of fabricating a gas sensor 100 including a sensor element 101 made up of six layers as shown in Fig. 1. Note that the gas sensors 110, 200, 300, and 400 shown in Figs. 4, 5, 8, and 10 can also be fabricated in the same manner.

[0179] First, six green sheets containing an oxygen-ion conductive solid electrolyte such as zirconia (ZrO2) as a ceramic component are prepared. A known forming method can be used to fabricate the green sheets. All six green sheets may have the same thickness, or the thickness may vary depending on the layer being formed. Holes and other features used for positioning during printing and lamination are formed in each of the six green sheets in advance using a known method, such as punching with a punching device, to form blank sheets. A through hole, such as an internal void, is also formed in the blank sheet used for the spacer layer 5 using a similar method. A through hole, which will become the through hole 61, is also formed in the blank sheet used for the second oxygen-ion conductor layer 6 using a similar method. Necessary through holes are also formed in the other layers in advance.

[0180] Various patterns required for each layer are printed and dried on blank sheets used for the six layers: the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first oxygen ion conductor layer 4, the spacer layer 5, and the second oxygen ion conductor layer 6. A known screen printing technique can be used for printing the patterns. A known drying means can also be used for the drying process.

[0181] For example, the proton conductor layer 7 may be formed by screen printing. Since it is not necessary to form a green sheet of the proton conductor, the manufacturing process can be simplified. First, an insulator layer paste used to form the insulator layer 62, an electrode paste used to form the inner hydrogen pump electrode 32 and the outer hydrogen pump electrode 33, and a proton conductor paste used to form the proton conductor layer 7 are prepared. Each paste is made by mixing raw material powder made of the material to be formed with an organic binder, an organic solvent, etc.

[0182] Next, a paste for an insulating layer is printed in a desired pattern at the position where the insulating layer 62 of the second oxygen ion conductor layer 6 is to be formed. A paste for an electrode is printed in a desired pattern at the position where the outer hydrogen pump electrode 33 is to be formed. A paste for a proton conductor is printed in a desired pattern at the position where the proton conductor layer 7 is to be formed. Furthermore, a paste for an electrode is printed in a desired pattern at the position where the inner hydrogen pump electrode 32 is to be formed.

[0183] This process is repeated until various patterns have been printed and dried on each of the six blank sheets. The six printed blank sheets are then stacked in a predetermined order while being positioned using sheet holes, etc., and then pressed under predetermined temperature and pressure conditions to form a laminate. The pressing process is carried out by applying heat and pressure using a laminator such as a known hydraulic press. The temperature, pressure, and time for heating and pressing depend on the laminator used, but can be determined appropriately to achieve good lamination.

[0184] Furthermore, for example, the proton conductor layer 7 may be prepared as a green sheet, similar to the second oxygen ion conductor layer 6. In this case, in the above-mentioned pressure bonding process, the proton conductor layer 7 may be stacked at a desired position and pressure bonded.

[0185] The obtained laminate contains a plurality of sensor elements 101. The laminate is cut into individual sensor elements 101. The cut laminate is fired at a predetermined firing temperature to obtain the sensor elements 101. That is, the sensor elements 101 are obtained by integral firing (co-firing) of the solid electrolyte layer and the electrodes. The firing temperature may be any temperature at which the solid electrolyte constituting the base portion 102 of the sensor element 101 is sintered into a dense body and the electrodes and the like maintain a desired porosity. For example, firing is performed at a firing temperature of about 1200°C or higher and 1500°C or lower.

[0186] The obtained sensor element 101 is incorporated into the gas sensor 100 in such a manner that the front end of the sensor element 101 contacts the gas to be measured and the rear end of the sensor element 101 contacts the reference gas. [Example]

[0187] The present invention will be further explained below using examples, but it should be noted that the present invention is not limited to the following examples.

[0188] As Example 1, the gas sensor 400 of the fourth embodiment shown in FIG. 12 was fabricated according to the above-described method for manufacturing a gas sensor.

[0189] The manufactured gas sensor 400 was examined for changes in the pump currents Ip0, Ip1, and Ip2 when the oxygen concentration, water vapor concentration, and carbon dioxide concentration were changed. Specifically, the gas sensor 400 was attached to a measurement pipe and driven. That is, the sensor element 401 was heated by the heater 72 and kept at the driving temperature (approximately 800°C), and the pump current 492 was controlled as described above. The target value V0 SET 1300mV, pump voltage Vp1 400mV, target value V2 SET The control was performed by setting the voltage at 200 mV. A model gas with a predetermined gas composition was flowed through the measurement pipe, and the pump currents Ip0, Ip1, and Ip2 were measured.

[0190] The pump currents Ip0, Ip1, and Ip2 were measured when the oxygen concentration was changed. The composition of the model gas was as follows. "%" always means volume % (the same applies below).

[0191] Oxygen concentration: 0, 5, 10, and 20% Water vapor concentration: 3% Carbon dioxide concentration: 0% Other gases: Nitrogen (balance)

[0192] The pump currents Ip0, Ip1, and Ip2 were measured when the water vapor concentration was changed. The composition of the model gas was as follows:

[0193] Oxygen concentration: 10% Water vapor concentration: 3, 5, 10, and 20% Carbon dioxide concentration: 0% Other gases: Nitrogen (balance)

[0194] The pump currents Ip0, Ip1, and Ip2 were measured when the carbon dioxide concentration was changed. The composition of the model gas was as follows:

[0195] Oxygen concentration: 10% Water vapor concentration: 3% Carbon dioxide concentrations: 0, 2, 6, 10, 15, and 20% Other gases: Nitrogen (balance)

[0196] The measurement results are shown in Figures 15 to 17. Figure 15 is a graph showing the relationship (O2 sensitivity) between the oxygen concentration in the measurement gas (model gas) and each pump current Ip0, Ip1, and Ip2. Figure 16 is a graph showing the relationship (H2O sensitivity) between the water vapor concentration in the measurement gas (model gas) and each pump current Ip0, Ip1, and Ip2. Figure 17 is a graph showing the relationship (CO2 sensitivity) between the carbon dioxide concentration in the measurement gas (model gas) and each pump current Ip0, Ip1, and Ip2. In all of these graphs, the vertical axis represents the oxygen pump current Ip0 (μA) (first axis), the hydrogen pump current Ip1, and the oxidation pump current Ip2 (μA) (second axis), and the horizontal axis represents the oxygen concentration (%), oxygen concentration (%), and carbon dioxide concentration (%), respectively.

[0197] 15 to 17, it was confirmed that the hydrogen pump current Ip1 increases linearly with increasing water vapor concentration (FIG. 16), but does not change with increasing oxygen concentration or carbon dioxide concentration (FIGS. 15 and 17). Thus, it was confirmed that the gas sensor 400 of Example 1 can measure the water vapor concentration in the measurement gas based on the hydrogen pump current Ip1.

[0198] 15 to 17, it was confirmed that the oxidation pump current Ip2 linearly decreases (the absolute value of the current value linearly increases) with increasing carbon dioxide concentration (FIG. 17), but does not change with increasing oxygen concentration or water vapor concentration (FIGS. 15 and 16). Thus, it was confirmed that the gas sensor 400 of Example 1 can measure the carbon dioxide concentration in the measurement gas based on the oxidation pump current Ip2.

[0199] 15 to 17, it was confirmed that the oxygen pump current Ip0 changes in value in response to changes in the oxygen concentration, water vapor concentration, and carbon dioxide concentration. Therefore, as described above, it was confirmed that the oxygen concentration in the measurement gas can be measured based on the oxygen pump current Ip0, the hydrogen pump current Ip1, and the oxidation pump current Ip2.

[0200] As described above, according to the present invention, by providing a solid electrolyte layer containing a plurality of solid electrolytes, i.e., by combining an oxygen ion conductor layer and a proton conductor layer, it is possible to provide a gas sensor capable of accurately measuring a target gas in a measurement gas, such as an O2 / CO2 / H2O sensor. [Explanation of symbols]

[0201] 1 First board layer 2 Second board layer 3 Third board layer 4. First oxygen ion conductor layer 5 Spacer layer 6 Second oxygen ion conductor layer 7. Proton conductor layer 10 Gas inlet 11 First diffusion-controlled pathway 12 Buffer space 13 Fourth diffusion-controlled pathway 14, 15, 16, 17, 515 Measurement gas flow space 20 1st internal void 21 Oxygen pump cell 22 Inner oxygen pump electrode 22a (Inner oxygen pump electrode) ceiling electrode part 22b Bottom electrode part (of the inner oxygen pump electrode) 23 Outer oxygen pump electrode 24 Variable power supply (for oxygen pump cell) 25 Internal void 30 Second diffusion-controlled passage 31 Hydrogen pump cell 32 Inner hydrogen pump electrode 33 Outer hydrogen pump electrode 34 Variable power supply (for hydrogen pump cell) 40 Second internal void 42 Reference electrode 43 Reference gas introduction space 48 Atmospheric introduction layer 51 Oxidation pump cell 52 Inner oxidation electrode 54 Variable power supply (for oxidation pump cell) 60 Third diffusion-controlled passage 61 Through hole 62 Insulator layer 65 Third internal void 70 Heater section 71 Heater electrode 72 Heater 73 through holes 74 Heater insulation layer 76 Heater lead 80 Oxygen pump control sensor cell 81 Oxidation pump control sensor cell 90,290,390,490 Control device 91,291,391,491 Control Unit 92,292,392,492 Pump control section 93,293 Concentration calculation section 100,110,200,300,400 Gas Sensor 101,111,201,211,221,301,401,501 sensor elements 102,112,302 Base

Claims

1. A gas sensor for detecting a measurement target gas in a measurement target gas, comprising: a sensor element; and a control device for controlling the sensor element, The sensor element is a long, plate-like substrate including an oxygen ion-conductive solid electrolyte layer and a proton-conductive solid electrolyte layer, with an insulating layer interposed between the oxygen ion-conductive solid electrolyte layer and the proton-conductive solid electrolyte layer; a measurement gas flow space having a gas inlet opening on the surface of the base portion and an internal space communicating with the gas inlet through a first diffusion-controlling passage and having the oxygen ion-conductive solid electrolyte layer and the proton-conductive solid electrolyte layer present on the internal surface thereof; an oxygen pump cell including an intra-void oxygen pump electrode disposed on the oxygen ion conductive solid electrolyte layer in the inner void of the measurement gas flow space, and an extra-void oxygen pump electrode disposed at a position different from that inside the measurement gas flow space of the base portion and in contact with the intra-void oxygen pump electrode via the oxygen ion conductive solid electrolyte layer; a hydrogen pump cell including an in-void hydrogen pump electrode disposed on the proton-conductive solid electrolyte layer in the inner void of the measurement gas flow space, and an out-void hydrogen pump electrode disposed at a position different from that inside the measurement gas flow space of the base portion and in contact with the in-void hydrogen pump electrode via the proton-conductive solid electrolyte layer; Including, The control device a pump control unit that controls operations of the oxygen pump cell and the hydrogen pump cell, and a concentration calculation unit that calculates a measurement target gas concentration in a measurement target gas, The pump control unit applying a predetermined voltage between the oxygen pump electrode inside the cavity and the oxygen pump electrode outside the cavity of the oxygen pump cell to pass an oxygen pump current through the oxygen pump cell; applying a predetermined voltage between the hydrogen pump electrode inside the void and the hydrogen pump electrode outside the void of the hydrogen pump cell to cause a hydrogen pump current to flow through the hydrogen pump cell; The concentration calculation unit The gas sensor calculates a concentration of a gas to be measured in the measurement gas based on at least one of the oxygen pump current and the hydrogen pump current.

2. 2. The gas sensor according to claim 1, wherein the extra-void oxygen pump electrode and / or the extra-void hydrogen pump electrode is disposed at a position where it comes into contact with the gas to be measured.

3. the internal space includes a first internal space having at least the oxygen ion conductive solid electrolyte layer on an inner surface thereof, and a second internal space communicating with the first internal space via a second diffusion-controlling pathway and having at least the proton conductive solid electrolyte layer on an inner surface thereof; 2. The gas sensor according to claim 1, wherein the intra-void oxygen pump electrode is disposed in the first internal cavity, and the intra-void hydrogen pump electrode is disposed in the second internal cavity.

4. The sensor element further comprises: an oxidation pump cell including: an in-space oxidation electrode disposed on the oxygen ion conductive solid electrolyte layer in the inner space of the measurement gas flow space, at a position farther from the first diffusion-controlling passage than the in-space oxygen pump electrode; and an outside-space oxidation electrode disposed at a position different from within the measurement gas flow space of the base portion and in contact with the in-space oxidation electrode via the oxygen ion conductive solid electrolyte layer, The pump control unit further applying a predetermined voltage between the oxidation electrode inside the cavity and the oxidation electrode outside the cavity of the oxidation pump cell to cause an oxidation pump current to flow through the oxidation pump cell; The concentration calculation unit 2. The gas sensor according to claim 1, wherein the concentration of the target gas in the measurement gas is calculated based on at least one of the oxygen pump current, the hydrogen pump current, and the oxidation pump current.

5. 5. The gas sensor according to claim 4, wherein the intra-void oxidation electrode is disposed on the oxygen ion conductive solid electrolyte layer at a position farther from the first diffusion-limiting passage than the intra-void hydrogen pump electrode.

6. the internal space includes at least a first internal space having the oxygen ion conductive solid electrolyte layer on an inner surface thereof, and a second internal space communicating with the first internal space via a second diffusion-controlling pathway and having the oxygen ion conductive solid electrolyte layer and the proton conductive solid electrolyte layer on an inner surface thereof, 5. The gas sensor according to claim 4, wherein the intra-void oxygen pump electrode is disposed in the first internal cavity, the intra-void hydrogen pump electrode is disposed on the proton-conducting solid electrolyte layer in the second internal cavity, and the intra-void oxidation electrode is disposed on the oxygen-ion-conducting solid electrolyte layer in the second internal cavity.

7. the internal space comprises a first internal space having at least the oxygen ion conductive solid electrolyte layer present on its inner surface, a second internal space communicating with the first internal space via a second diffusion-controlling path and having at least the proton conductive solid electrolyte layer present on its inner surface, and a third internal space communicating with the second internal space via a third diffusion-controlling path and having at least the oxygen ion conductive solid electrolyte layer present on its inner surface, 5. The gas sensor according to claim 4, wherein the intra-void oxygen pump electrode is disposed in the first internal cavity, the intra-void hydrogen pump electrode is disposed in the second internal cavity, and the intra-void oxidation electrode is disposed in the third internal cavity.

8. The sensor element is a reference electrode disposed inside the base portion so as to be in contact with a reference gas; The pump control unit 2. The gas sensor according to claim 1, wherein a predetermined voltage is applied between the oxygen pump electrode inside the cavity and the oxygen pump electrode outside the cavity of the oxygen pump cell based on an electromotive force between the reference electrode and the oxygen pump electrode inside the cavity of the oxygen pump cell, thereby causing an oxygen pump current to flow through the oxygen pump cell.

9. 2. The gas sensor according to claim 1, wherein, in a plane including a longitudinal direction of the base portion and a width direction perpendicular to the longitudinal direction, the proton-conducting solid electrolyte layer and the oxygen-ion-conducting solid electrolyte layer are present on the same plane, and the insulator layer is interposed between the oxygen-ion-conducting solid electrolyte layer and the proton-conducting solid electrolyte layer.

10. the oxygen ion conductive solid electrolyte layer has through-holes, the proton-conducting solid electrolyte layer is parallel to the oxygen-ion-conducting solid electrolyte layer and covers the through-holes on a surface of the oxygen-ion-conducting solid electrolyte layer facing the internal space, and the insulator layer is interposed between the proton-conducting solid electrolyte layer and the oxygen-ion-conducting solid electrolyte layer; the in-void hydrogen pump electrode is disposed on a surface of the proton-conducting solid electrolyte layer facing the internal void; 2. The gas sensor according to claim 1, wherein the external hydrogen pump electrode is disposed at a position corresponding to the through hole on a surface of the proton-conducting solid electrolyte layer opposite to the surface on which the internal hydrogen pump electrode is disposed.

11. 2. The gas sensor according to claim 1, wherein the measurement target gas is at least one selected from the group consisting of oxygen and water vapor.

12. 5. The gas sensor according to claim 4, wherein the measurement target gas is at least one selected from the group consisting of oxygen, water vapor, and carbon dioxide.

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