Gas sensor and sensor element

Abstract

Provided is a gas sensor and a sensor element that improve the measurement responsiveness of water concentration and / or carbon dioxide concentration. A gas sensor (100) includes a sensor element (101) and a control device. The control device measures water concentration based on a pump current Ip1, and the ratio Ih / Ir of the limiting current Ih to the limiting current Ir in the sensor element (101) is 0.44 or less; and / or the control device measures carbon dioxide concentration based on a pump current Ip2, and the ratio Ic / Ir of the limiting current Ic to the limiting current Ir in the sensor element (101) is 0.24 or less. The limiting current Ir [mA] is the limiting current when oxygen is drawn from the periphery of the inner pump electrode (22) to the periphery of the outer pump electrode (23). The limiting current Ih [mA] is the limiting current when oxygen is drawn from the periphery of the first measurement electrode (51) to the periphery of the outer pump electrode (23). The limiting current Ic [mA] is the limiting current when oxygen is drawn from the periphery of the second measurement electrode (44) to the periphery of the outer pump electrode (23).

Description

Technical Field

[0001] This invention relates to gas sensors and sensor elements. Background Technology

[0002] Previously, gas sensors were known for measuring the concentrations of water and carbon dioxide in gases such as automobile exhaust. For example, Patent Document 1 describes a gas sensor comprising a sensor element that measures the concentrations of water vapor and carbon dioxide in a gas being measured. This sensor element has a solid electrolyte layer with oxygen ion conductivity and includes a gas flow section inside. The gas flow section comprises a gas inlet, a first diffusion rate control section, a first internal cavity, a second diffusion rate control section, and a second internal cavity, connected sequentially in the following order: A main pump unit is formed by a main inner pump electrode disposed in the first internal cavity and an outer pump electrode disposed on the outer surface of the sensor element. A first measuring pump unit is formed by a first measuring inner pump electrode and an outer pump electrode disposed in the second internal cavity. A second measuring pump unit is formed by a second measuring inner pump electrode and an outer pump electrode disposed on the side opposite to the second diffusion rate control section, relative to the first measuring inner pump electrode. In this gas sensor, the oxygen partial pressure in the first internal cavity is adjusted by a main pump unit in such a way that the water vapor and carbon dioxide components in the gas being measured are substantially completely decomposed. Furthermore, oxygen is supplied to the second internal cavity by a first measuring pump unit in such a way that hydrogen generated from the decomposition of water vapor is selectively combusted (oxidized) in the second internal cavity. The concentration of water vapor in the gas being measured is measured based on the magnitude of the current flowing at this time. Conversely, oxygen is supplied to the vicinity of the surface of the second measuring inner pump electrode by a second measuring pump unit in such a way that carbon monoxide generated from the decomposition of carbon dioxide is selectively combusted (oxidized) near the surface of the second measuring inner pump electrode. The concentration of carbon dioxide in the gas being measured is measured based on the magnitude of the current flowing at this time.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 5918177 Summary of the Invention

[0006] In the aforementioned gas sensor, it is desirable to shorten the time required for the current flowing through the first measuring pump unit to reach a value corresponding to the changed water concentration when the water concentration in the measured gas changes, i.e., to improve the gas sensor's responsiveness to water concentration. Similarly, it is desirable to improve the gas sensor's responsiveness to carbon dioxide concentration.

[0007] This invention was implemented to solve such problems, and its main objective is to improve the responsiveness of water concentration and / or carbon dioxide concentration determination.

[0008] The present invention employs the following means to achieve the aforementioned main objectives.

[0009] [1] The first gas sensor of the present invention comprises a sensor element and a control device, and measures the water concentration and / or carbon dioxide concentration in the gas to be measured, wherein...

[0010] The sensor element has:

[0011] The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated.

[0012] The first pump unit is configured to include a first inner electrode disposed in a first chamber in the gas flow section to be measured and a first outer electrode disposed on the outer surface of the element body.

[0013] A second pump unit, configured to include a second inner electrode disposed in a second chamber located downstream of the first chamber in the gas flow section being measured, and a second outer electrode disposed on the outer surface of the element body; and

[0014] The third pump unit is configured to include a third inner electrode disposed in a third chamber located downstream of the second chamber in the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body.

[0015] The control device performs the following processing:

[0016] The first pump unit is controlled to draw oxygen from the area around the first inner electrode to the area around the first outer electrode, thereby reducing water and carbon dioxide in the gas being measured in the first chamber.

[0017] The second pump unit is controlled to draw oxygen from the vicinity of the second outer electrode to the vicinity of the second inner electrode, thereby oxidizing the hydrogen generated by the reduction of water in the first chamber in the second chamber; and

[0018] The third pump unit is controlled to draw oxygen from the vicinity of the third outer electrode to the vicinity of the third inner electrode, thereby oxidizing carbon monoxide generated by the reduction of carbon dioxide in the first chamber within the third chamber.

[0019] With the inlet of the gas flow section being measured exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is defined as the limiting current Ir [mA], the limiting current when the second pump unit draws oxygen from around the second inner electrode to around the second outer electrode is defined as the limiting current Ih [mA], and the limiting current when the third pump unit draws oxygen from around the third inner electrode to around the third outer electrode is defined as the limiting current Ic [mA].

[0020] The control device performs a water concentration measurement process based on a second pump current flowing through the second pump unit due to the control processing of the second pump unit, and the ratio of the limiting current Ih to the limiting current Ir in the sensor element, Ih / Ir, is 0.44 or less; and / or, the control device performs a carbon dioxide concentration measurement process based on a third pump current flowing through the third pump unit due to the control processing of the third pump unit, and the ratio of the limiting current Ic to the limiting current Ir in the sensor element, Ic / Ir, is 0.24 or less.

[0021] In this first gas sensor, a water concentration measurement process is performed based on the second pump current flowing through the second pump unit due to the control processing of the second pump unit, and / or a carbon dioxide concentration measurement process is performed based on the third pump current flowing through the third pump unit due to the control processing of the third pump unit, to measure the carbon dioxide concentration in the gas to be measured. Thus, the gas sensor measures the water concentration and / or carbon dioxide concentration in the gas to be measured. Furthermore, when the gas sensor is used for water concentration measurement, it is configured such that the ratio of the limiting current Ih to the limiting current Ir in the sensor element, Ih / Ir, is 0.44 or less. This improves the responsiveness of water concentration measurement. Similarly, when the gas sensor is used for carbon dioxide concentration measurement, it is configured such that the ratio of the limiting current Ic to the limiting current Ir in the sensor element, Ic / Ir, is 0.24 or less. This improves the responsiveness of carbon dioxide concentration measurement. The inventors of this invention have confirmed these effects through experiments and analysis. The reason why a water concentration measurement responsiveness of Ih / Ir ratio below 0.44 can be considered improved is as follows: First, the limiting current Ir is negatively correlated with the diffusion resistance from the outside of the sensor element to the first chamber of the gas being measured. Furthermore, the limiting current Ih is negatively correlated with the diffusion resistance from the outside of the sensor element to the second chamber of the gas being measured. Therefore, the larger the Ih / Ir ratio, the less water flows into the first chamber from the outside, and the more water diffuses back into the first chamber from the second chamber. Consequently, the amount of hydrogen produced by the reduction of water in the first chamber under the control of the first pump unit and the amount of water in the gas being measured outside the sensor element are prone to deviation. As a result, when the water concentration in the gas being measured outside the sensor element changes, the time required for the amount of hydrogen produced by the reduction of water in the first chamber to correspond to the changed water concentration becomes longer. Consequently, the time required for the second pump current flowing through the second pump unit under the control of the second pump unit to correspond to the changed water concentration also becomes longer. Based on this reasoning, it is believed that the higher the ratio of Ih / Ir, the lower the responsiveness of water concentration determination. Furthermore, it is argued that by setting the ratio of Ih / Ir to 0.44 or lower, the proportion of water in the gas being measured in the first chamber that has back-diffused from the second chamber to the first chamber can be sufficiently reduced, thus improving the responsiveness of water concentration determination. The same reasoning is used to argue that setting the ratio of Ic / Ir to 0.24 or lower can improve the responsiveness of carbon dioxide concentration determination.A larger Ic / Ir ratio results in a lower proportion of carbon dioxide flowing into the first chamber from the outside and a higher proportion of carbon dioxide backdiffused from the third chamber into the first chamber. Consequently, the amount of carbon monoxide generated by the reduction of carbon dioxide in the first chamber under the control of the first pump unit is prone to deviate from the amount of carbon dioxide in the measured gas outside the sensor element. As a result, when the concentration of carbon dioxide in the measured gas outside the sensor element changes, the time required for the amount of carbon monoxide generated by the reduction of carbon dioxide in the first chamber to correspond to the changed carbon dioxide concentration increases. Furthermore, the time required for the third pump current flowing through the third pump unit under the control of the third pump unit to correspond to the changed carbon dioxide concentration also increases. Based on this reasoning, it is believed that a larger Ic / Ir ratio leads to a lower response time for carbon dioxide concentration measurement. Moreover, it is believed that by setting the Ic / Ir ratio to 0.24 or lower, the proportion of carbon dioxide backdiffused from the third chamber into the first chamber in the measured gas can be sufficiently reduced, thus improving the response time for carbon dioxide concentration measurement. It should be noted that the difference in the upper limits for Ih / Ir and Ic / Ir used to improve responsiveness is believed to be due to the different diffusion rates of water (and hydrogen) and carbon dioxide (and carbon monoxide).

[0022] [2] In the above-mentioned gas sensor (the gas sensor described in [1] above), the control device may perform the water concentration measurement process, and the limiting current Ih is less than 0.3 mA; and / or, the control device may perform the carbon dioxide concentration measurement process, and the limiting current Ic is less than 0.3 mA. If the limiting current Ih is too large, that is, the diffusion resistance from the outside of the sensor element to the second chamber is too small, the flow rate of hydrogen into the second chamber may sometimes be too large, resulting in insufficient oxidation of hydrogen by the second pump unit control process. As a result, sometimes the second pump current and the water concentration cannot correspond well, and the accuracy of water concentration measurement decreases. If the limiting current Ih is less than 0.3 mA, such a decrease in the accuracy of water concentration measurement can be suppressed. Similarly, if the limiting current Ic is less than 0.3 mA, insufficient oxidation of carbon monoxide in the third chamber by the third pump unit control process can be suppressed, and the decrease in the accuracy of carbon dioxide concentration measurement can be suppressed.

[0023] [3] In the above-mentioned gas sensor (the gas sensor described in [1] or [2] above), the control device may perform the water concentration measurement process and the carbon dioxide concentration measurement process, wherein in the sensor element, the ratio Ih / Ir is 0.44 or less, and the ratio Ic / Ir is 0.24 or less. Accordingly, the water concentration measurement responsiveness and the carbon dioxide concentration measurement responsiveness can be improved simultaneously.

[0024] [4] The second gas sensor of the present invention includes a sensor element and a control device, and measures the water concentration in the gas to be measured, wherein...

[0025] The sensor element has:

[0026] The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated.

[0027] A first pump unit, configured to include a first inner electrode disposed in a first chamber of the gas flow section being measured, and a first outer electrode disposed on the outer surface of the component body; and

[0028] The second pump unit is configured to include a second inner electrode disposed in a second chamber located downstream of the first chamber in the gas flow section being measured, and a second outer electrode disposed on the outer surface of the element body.

[0029] The control device performs the following processing:

[0030] The first pump unit is controlled to draw oxygen from the area around the first inner electrode to the area around the first outer electrode, thereby reducing the water in the gas being measured in the first chamber.

[0031] The second pump unit is controlled to draw oxygen from the vicinity of the second outer electrode to the vicinity of the second inner electrode, thereby oxidizing the hydrogen generated by the reduction of water in the first chamber in the second chamber; and

[0032] The water concentration determination process measures the water concentration in the gas being measured based on the second pump current flowing through the second pump unit due to the control processing of the second pump unit.

[0033] The sensor element is configured such that, when the inlet of the gas flow section to be measured is exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is set as the limiting current Ir [mA], and the limiting current when the second pump unit draws oxygen from around the second inner electrode to around the second outer electrode is set as the limiting current Ih [mA], the ratio of the limiting current Ih to the limiting current Ir, Ih / Ir, is 0.44 or less.

[0034] In this second gas sensor, similar to the first gas sensor described above, the water concentration measurement responsiveness can be improved by having a ratio Ih / Ir of 0.44 or less.

[0035] [5] The third gas sensor of the present invention includes a sensor element and a control device, and measures the carbon dioxide concentration in the gas to be measured, wherein...

[0036] The sensor element has:

[0037] The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated.

[0038] A first pump unit, configured to include a first inner electrode disposed in a first chamber of the gas flow section being measured, and a first outer electrode disposed on the outer surface of the component body; and

[0039] The third pump unit is configured to include a third inner electrode disposed in a third chamber located downstream of the first chamber in the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body.

[0040] The control device performs the following processing:

[0041] The first pump unit is controlled to draw oxygen from the area around the first inner electrode to the area around the first outer electrode, thereby reducing carbon dioxide in the gas being measured in the first chamber.

[0042] The third pump unit is controlled to draw oxygen from the vicinity of the third outer electrode to the vicinity of the third inner electrode, thereby oxidizing carbon monoxide generated by the reduction of carbon dioxide in the first chamber within the third chamber; and

[0043] The carbon dioxide concentration measurement process measures the carbon dioxide concentration in the gas being measured based on the third pump current flowing through the third pump unit due to the control processing of the third pump unit.

[0044] The sensor element is configured such that, when the inlet of the gas flow section to be measured is exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is set as the limiting current Ir [mA], and the limiting current when the third pump unit draws oxygen from around the third inner electrode to around the third outer electrode is set as the limiting current Ic [mA], the ratio of the limiting current Ic to the limiting current Ir, Ic / Ir, is 0.24 or less.

[0045] In this third gas sensor, similar to the first gas sensor described above, the responsiveness for measuring carbon dioxide concentration can be improved by having a ratio Ic / Ir of 0.24 or less.

[0046] [6] The first sensor element of the present invention is used to measure the water concentration and / or carbon dioxide concentration in the gas to be measured, and has the following characteristics:

[0047] The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated.

[0048] The first pump unit is configured to include a first inner electrode disposed in a first chamber in the gas flow section to be measured and a first outer electrode disposed on the outer surface of the element body.

[0049] A second pump unit, configured to include a second inner electrode disposed in a second chamber located downstream of the first chamber in the gas flow section being measured, and a second outer electrode disposed on the outer surface of the element body; and

[0050] The third pump unit is configured to include a third inner electrode disposed in a third chamber located downstream of the second chamber in the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body.

[0051] With the inlet of the gas flow section being measured exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is set as the limiting current Ir [mA], the limiting current when the second pump unit draws oxygen from around the second inner electrode to around the second outer electrode is set as the limiting current Ih [mA], and the limiting current when the third pump unit draws oxygen from around the third inner electrode to around the third outer electrode is set as the limiting current Ic [mA], wherein the ratio of the limiting current Ih to the limiting current Ir, Ih / Ir, is 0.44 or less, and / or the ratio of the limiting current Ic to the limiting current Ir, Ic / Ir, is 0.24 or less.

[0052] In this sensor element, the ratio Ih / Ir is 0.44 or less, and / or the ratio Ic / Ir is 0.24 or less. Therefore, when the ratio Ih / Ir of this sensor element is 0.44 or less, it is suitable as a sensor element for measuring water concentration (e.g., the first gas sensor described above). When the ratio Ic / Ir is 0.24 or less, it is suitable as a sensor element for measuring carbon dioxide concentration (e.g., the first gas sensor described above).

[0053] [7] The second sensor element of the present invention is used to measure the water concentration in the gas to be measured, and has the following characteristics:

[0054] The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated.

[0055] A first pump unit, configured to include a first inner electrode disposed in a first chamber of the gas flow section being measured, and a first outer electrode disposed on the outer surface of the component body; and

[0056] The second pump unit is configured to include a second inner electrode disposed in a second chamber located downstream of the first chamber in the gas flow section being measured, and a second outer electrode disposed on the outer surface of the element body.

[0057] When the inlet of the gas flow section to be measured is exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is set as the limiting current Ir [mA], and the limiting current when the second pump unit draws oxygen from around the second inner electrode to around the second outer electrode is set as the limiting current Ih [mA], the ratio of the limiting current Ih to the limiting current Ir, Ih / Ir, is 0.44 or less.

[0058] In this sensor element, the ratio Ih / Ir is 0.44 or less, therefore, it is a suitable sensor element for gas sensors (such as the second gas sensor described above) for measuring water concentration.

[0059] [8] The third sensor element of the present invention is used to measure the carbon dioxide concentration in the gas to be measured, and has the following characteristics:

[0060] The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated.

[0061] A first pump unit, configured to include a first inner electrode disposed in a first chamber of the gas flow section being measured, and a first outer electrode disposed on the outer surface of the component body; and

[0062] The third pump unit is configured to include a third inner electrode disposed in a third chamber located downstream of the first chamber in the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body.

[0063] With the inlet of the gas flow section being tested exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is set as the limiting current Ir [mA], and the limiting current when the third pump unit draws oxygen from around the third inner electrode to around the third outer electrode is set as the limiting current Ic [mA], the ratio of the limiting current Ic to the limiting current Ir, Ic / Ir, is 0.24 or less.

[0064] In this sensor element, the ratio Ic / Ir is less than 0.24, therefore, it is a suitable sensor element for gas sensors (such as the third gas sensor described above) for measuring carbon dioxide concentration. Attached Figure Description

[0065] Figure 1 This is a simplified cross-sectional view illustrating an example of the configuration of the gas sensor 100.

[0066] Figure 2 This is a block diagram showing the electrical connections between the control device 95 and various units, etc.

[0067] Figure 3 The graph shows the relationship between the ratio Ih / Ir and the response time Th0 for each of Experimental Examples 1 to 10.

[0068] Figure 4 The graph shows the relationship between the ratio Ih / Ir and the response time Th1 for each of Experimental Examples 1 to 10.

[0069] Figure 5 The graph shows the relationship between the ratio Ic / Ir and the response time Tc0 for each of Experimental Examples 11-20.

[0070] Figure 6 The graph shows the relationship between the ratio Ic / Ir and the response time Tc2 for each of Experimental Examples 11-20.

[0071] Figure 7 This is a simplified cross-sectional view of the sensor element 201 in the modified example.

[0072] Figure 8 This is a simplified cross-sectional view illustrating one example of the configuration of a modified gas sensor 300.

[0073] Figure 9 This is a simplified cross-sectional view illustrating one example of the configuration of a modified gas sensor 400.

[0074] Explanation of reference numerals in the attached figures

[0075] 1…First substrate layer, 2…Second substrate layer, 3…Third substrate layer, 4…First solid electrolyte layer, 5…Isolation layer, 6…Second solid electrolyte layer, 10…Gas inlet, 11…First diffusion rate control unit, 12…Buffer space, 13…Second diffusion rate control unit, 20…First internal cavity, 21…Main pump unit, 22…Inner pump electrode, 22a…Top electrode, 22b…Bottom electrode, 23…Outer pump electrode, 24…Variable power supply, 30…Third diffusion rate control unit, 40…Second internal cavity, 41…Second measuring pump unit, 42…Reference electrode, 43…Reference gas inlet space, 44…Second measuring electrode, 45…Fourth diffusion rate control unit, 46…Variable power supply, 48…Reference gas inlet layer, 49…Reference gas inlet, 49a…Inlet, 50…First… Measurement pump unit, 51…first measuring electrode, 51a…top electrode section, 51b…bottom electrode section, 52…variable power supply, 60…fourth diffusion rate control section, 61…third internal cavity, 70…heater section, 71…heater connector electrode, 72…heater, 73…through hole, 74…heater insulation layer, 75…pressure relief hole, 76…heater power supply, 80…oxygen partial pressure detection sensor unit for main pump control, 81…oxygen partial pressure detection sensor unit for first measurement pump control, 82…oxygen partial pressure detection sensor unit for second measurement pump control, 83…sensor unit, 95…control device, 96…control section, 97…CPU, 98…storage section, 100, 300, 400…gas sensors, 101, 201, 301, 401…sensor elements, 102…element body. Detailed Implementation

[0076] The embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 This is a simplified cross-sectional view illustrating an example of the configuration of a gas sensor 100 as an embodiment of the present invention. Figure 2This is a block diagram showing the electrical connections between the control device 95, each unit, and the heater 72. The gas sensor 100 is installed in piping such as the exhaust pipe of an internal combustion engine. The gas sensor 100 uses the exhaust gas of the internal combustion engine as the measured gas and measures the concentration of a specific gas in the measured gas, i.e., the specific gas concentration. In this embodiment, the gas sensor 100 measures water concentration and carbon dioxide concentration as the specific gas concentration. The gas sensor 100 includes: a sensor element 101 having a rectangular cuboid-shaped element body 102; units 21, 41, 50, 80-83 of the sensor element 101; a heater 70 disposed inside the sensor element 101; a porous protective layer 90 of the sensor element 101; and a control device 95 having variable power supplies 24, 46, 52 and a heater power supply 76, and controlling the entire gas sensor 100. It should be noted that the length direction of the sensor element 101 (… Figure 1 The left and right directions are set as the front and back directions, and the thickness direction of the sensor element 101 is set as the front and back directions. Figure 1 The vertical direction is set as the vertical direction, and the width direction of the sensor element 101 (the direction perpendicular to the front-back direction and the vertical direction) is set as the left-right direction.

[0077] The component body 102 is a laminate obtained by stacking six layers in sequence from bottom to top in the attached drawing: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, an isolation layer 5, and a second solid electrolyte layer 6, each composed of an oxygen ion conductive solid electrolyte layer such as zirconium dioxide (ZrO2). Furthermore, the solid electrolyte forming these six layers is a dense, gas-tight solid electrolyte. The component body 102 is manufactured as follows: for example, the ceramic green sheets corresponding to each layer are subjected to prescribed processing and circuit pattern printing, then they are stacked, and subsequently fired to achieve integration.

[0078] On the front end side of the sensor element 101 (element body 102), between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, a gas inlet 10, a first diffusion rate control unit 11, a buffer space 12, a second diffusion rate control unit 13, a first internal cavity 20, a third diffusion rate control unit 30, a second internal cavity 40, a fourth diffusion rate control unit 60, and a third internal cavity 61 are formed adjacently in a sequentially connected manner.

[0079] The gas inlet 10, buffer space 12, first internal cavity 20, second internal cavity 40 and third internal cavity 61 are spaces inside the sensor element 101 provided by hollowing out the isolation layer 5, wherein their upper parts are separated by the lower surface of the second solid electrolyte layer 6, their lower parts are separated by the upper surface of the first solid electrolyte layer 4, and their sides are separated by the side of the isolation layer 5.

[0080] The first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 are each provided as two horizontally elongated slits (forming an opening along the length direction perpendicular to the drawing). Additionally, the fourth diffusion rate control unit 60 is provided as a single horizontally elongated slit (forming an opening along the length direction perpendicular to the drawing) formed as a gap between itself and the lower surface of the second solid electrolyte layer 6. Furthermore, the portion from the gas inlet 10 to the third internal cavity 61 is referred to as the measured gas flow section.

[0081] The sensor element 101 (element body 102) includes a reference gas inlet 49 that allows a reference gas for measuring a specific gas concentration to flow from the outside of the sensor element 101 to a reference electrode 42. The reference gas inlet 49 has a reference gas inlet space 43 and a reference gas inlet layer 48. The reference gas inlet space 43 is a space provided from the rear end face of the sensor element 101 toward the inward direction. The reference gas inlet space 43 is provided between the upper surface of the third substrate layer 3 and the lower surface of the insulating layer 5, and is positioned to separate the side portion from the side of the first solid electrolyte layer 4. The reference gas inlet space 43 is open at the rear end face of the sensor element 101, and this opening functions as an inlet 49a of the reference gas inlet 49. The reference gas is introduced into the reference gas inlet space 43 from the inlet 49a. The reference gas inlet 49 applies a predetermined diffusion resistance to the reference gas introduced from the inlet 49a and introduces the reference gas toward the reference electrode 42. In this embodiment, the reference gas is atmospheric gas.

[0082] A reference gas introduction layer 48 is disposed between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. The reference gas introduction layer 48 is a porous material made of ceramic, such as alumina. A portion of the upper surface of the reference gas introduction layer 48 is exposed within the reference gas introduction space 43. The reference gas introduction layer 48 is formed to cover the reference electrode 42. The reference gas introduction layer 48 allows reference gas to flow from the reference gas introduction space 43 to the reference electrode 42.

[0083] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around it. Furthermore, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) within the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61. The reference electrode 42 is formed as a porous metal-ceramic electrode (e.g., a Pt and ZrO2 metal-ceramic electrode).

[0084] In the gas flow section, the gas inlet 10 is an opening relative to the external space, through which the gas to be measured enters the sensor element 101 from the external space. The first diffusion rate control unit 11 applies a predetermined diffusion resistance to the gas to be measured entering through the gas inlet 10. The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13. The second diffusion rate control unit 13 applies a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal cavity 20. When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, the gas that rapidly enters the sensor element 101 from the gas inlet 10 due to pressure fluctuations in the external space (in the case of automobile exhaust, pulsations in exhaust pressure) is not directly introduced into the first internal cavity 20. Instead, it is introduced into the first internal cavity 20 after the pressure fluctuations are eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. Therefore, the pressure fluctuations of the gas to be measured introduced into the first internal cavity 20 are negligible. The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured introduced through the second diffusion rate control unit 13. This oxygen partial pressure is adjusted by the operation of the main pump unit 21.

[0085] The main pump unit 21 is an electrochemical pump unit consisting of an inner pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4 that form the current path between these electrodes. The inner pump electrode 22 has a top electrode portion 22a disposed on the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, which is generally the entire surface. The outer pump electrode 23 is disposed on the upper surface of the second solid electrolyte layer 6 in a region corresponding to the top electrode portion 22a, in a manner that exposes it to the outside of the sensor element 101.

[0086] The inner pump electrode 22 spans the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that define the first internal cavity 20, as well as the isolation layer 5 that forms the sidewalls. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that forms the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that forms the bottom surface of the first internal cavity 20. Furthermore, side electrode portions (not shown) are formed on the sidewall surfaces (inner surfaces) of the isolation layer 5 that forms the two sidewall portions of the first internal cavity 20 in a manner that connects the top electrode portion 22a and the bottom electrode portion 22b. Thus, the side electrode portions are arranged in a tunnel-shaped structure.

[0087] In the main pump unit 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, so that the pump current Ip0 flows between the inner pump electrode 22 and the outer pump electrode 23 in either the positive or negative direction. As a result, oxygen in the first internal cavity 20 can be drawn out to the external space, or oxygen in the external space can be drawn into the first internal cavity 20.

[0088] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an electrochemical sensor unit, namely the main pump control oxygen partial pressure detection sensor unit 80, is composed of the inner pump electrode 22, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42.

[0089] By measuring the electromotive force (voltage V0) of the oxygen partial pressure detection sensor unit 80 for main pump control, the oxygen concentration (oxygen partial pressure) within the first internal cavity 20 can be determined. Furthermore, by feedback control of the voltage Vp0 of the variable power supply 24 to achieve a target voltage V0, the pump current Ip0 is controlled. This adjusts the oxygen concentration within the first internal cavity 20.

[0090] The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20, and guides the gas to be measured into the second internal cavity 40.

[0091] The second internal cavity 40 is configured as a space for performing the following process: adjusting the oxygen partial pressure using the first measuring pump unit 50 for the gas to be measured introduced through the third diffusion rate control unit 30, and measuring the water concentration in the gas to be measured.

[0092] The first measuring pump unit 50 is an electrochemical pump unit composed of a first measuring electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any appropriate electrode disposed on the outer surface of the sensor element 101), a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. The first measuring electrode 51 has a top electrode portion 51a disposed on the lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40.

[0093] The first measuring electrode 51 is disposed in the second internal cavity 40 with the same tunnel-shaped structure as the inner pump electrode 22 disposed in the previous first internal cavity 20. That is, a top electrode portion 51a is formed relative to the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40. Furthermore, the side electrode portion (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b is formed with a tunnel-shaped structure on the two walls of the isolation layer 5 constituting the side wall of the second internal cavity 40.

[0094] In the first measuring pump unit 50, a desired voltage Vp1 is applied between the first measuring electrode 51 and the outer pump electrode 23, thereby enabling oxygen in the atmosphere inside the second internal cavity 40 to be drawn out to the external space, or oxygen to be drawn in from the external space into the second internal cavity 40.

[0095] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely the first measuring electrode 51, a reference electrode 42, a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, and a third substrate layer 3 are constructed.

[0096] Furthermore, the first measuring pump unit 50 utilizes a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the oxygen partial pressure detection sensor unit 81 for controlling the first measuring pump. Thus, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is adjusted by the pump current Ip1 flowing through the first measuring pump unit 50.

[0097] The fourth diffusion rate control unit 60 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the first measuring pump unit 50 in the second internal cavity 40, and introduces the gas to be measured into the third internal cavity 61.

[0098] The third internal cavity 61 is configured as a space for performing the following process: adjusting the oxygen partial pressure of the gas to be measured by means of the second measuring pump unit 41, and measuring the carbon dioxide concentration in the gas to be measured, for the gas to be measured introduced by the fourth diffusion rate control unit 60.

[0099] The second measuring pump unit 41 is an electrochemical pump unit composed of a second measuring electrode 44, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any appropriate electrode disposed on the outer surface of the sensor element 101), a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. The second measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 at a position facing the third internal cavity 61.

[0100] In the second measuring pump unit 41, by applying the desired voltage Vp2 between the second measuring electrode 44 and the outer pump electrode 23, oxygen in the atmosphere of the third internal cavity 61 can be drawn out to the external space, or drawn from the external space into the second internal cavity 40.

[0101] In addition, in order to detect the oxygen partial pressure around the second measuring electrode 44, an electrochemical sensor unit, namely the second measuring pump control oxygen partial pressure detection sensor unit 82, is formed by the first solid electrolyte layer 4, the third substrate layer 3, the second measuring electrode 44, and the reference electrode 42.

[0102] It should be noted that, based on the electromotive force (voltage V2) detected by the oxygen partial pressure detection sensor unit 82 for controlling the second measuring pump, the variable power supply 46 is controlled, and the voltage Vp2 of the variable power supply 46 is applied to the second measuring pump unit 41. Thus, the oxygen partial pressure in the atmosphere within the third internal cavity 61 is adjusted by the pump current Ip2 flowing through the second measuring pump unit 41.

[0103] Furthermore, the electrochemical sensor unit 83 is composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42, which can detect the oxygen partial pressure in the gas to be measured outside the sensor using the electromotive force (voltage Vref) obtained through the sensor unit 83.

[0104] Here, the electrodes 22, 23, 42, 44, and 51 are described. The inner pump electrode 22, the first measuring electrode 51, and the second measuring electrode 44 each contain a first noble metal with catalytic activity. Examples of the first noble metal include at least one of Pt, Rh, Ir, Ru, and Pd. The outer pump electrode 23 and the reference electrode 42 also contain the first noble metal. The first measuring electrode 51 preferably contains a second noble metal that inhibits the catalytic activity of the first noble metal against carbon monoxide. By including the second noble metal in the first measuring electrode 51, the oxidation capacity of the first measuring electrode 51 against carbon monoxide is weakened. Examples of the second noble metal include Au. The inner pump electrode 22 and the second measuring electrode 44 do not contain the second noble metal. The outer pump electrode 23 and the reference electrode 42 also preferably do not contain the second noble metal. Each electrode 22, 23, 42, 44, and 51 is preferably a cermet containing a noble metal and a solid electrolyte (e.g., ZrO2) with oxygen ion conductivity. Each of the electrodes 22, 23, 42, 44, and 51 is preferably a porous material. In this embodiment, the first measuring electrode 51 is a porous metal-ceramic electrode containing 1% Au and Pt and ZrO2. In addition, the inner pump electrode 22, the outer pump electrode 23, the reference electrode 42, and the second measuring electrode 44 are all porous metal-ceramic electrodes containing Pt and ZrO2.

[0105] The sensor element 101 includes a heater section 70, which performs temperature regulation functions to heat and maintain the sensor element 101, thereby improving the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes: a heater connector electrode 71, a heater 72, a through hole 73, a heater insulating layer 74, and a pressure relief hole 75.

[0106] The heater connector electrode 71 is an electrode formed in contact with the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to the heater power supply 76 (see reference...) Figure 2 The connection allows power to be supplied from the heater power supply 76 to the heater section 70.

[0107] The heater 72 is a resistive element formed by being sandwiched between the second substrate layer 2 and the third substrate layer 3 from the top and bottom. The heater 72 is connected to the heater connector electrode 71 via the through hole 73, and heats up by being powered by the heater power supply 76 through the heater connector electrode 71, thereby heating and maintaining the temperature of the solid electrolyte forming the sensor element 101.

[0108] In addition, the heater 72 is embedded in the entire area from the first internal cavity 20 to the third internal cavity 61, which can adjust the sensor element 101 as a whole to the temperature at which the solid electrolyte is activated.

[0109] The heater insulation layer 74 is an insulation layer formed from an insulator such as aluminum oxide on the upper and lower surfaces of the heater 72. The heater insulation layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72, and electrical insulation between the third substrate layer 3 and the heater 72.

[0110] The pressure relief hole 75 is a portion that passes through the third substrate layer 3 and the reference gas introduction layer 48 and communicates with the reference gas introduction space 43, and is formed to mitigate the internal pressure rise that accompanies the temperature rise in the heater insulation layer 74.

[0111] The porous protective layer 90 is a porous material that covers a defined area (a defined range extending from the front end to the rear end of the element body 102) on the outer surface of the element body 102. More specifically, the porous protective layer 90 covers a portion of each of the top, bottom, left, and right sides of the element body 102 and the entire front end surface. The porous protective layer 90 also covers the gas inlet 10 and the outer pump electrode 23. The rear end of the porous protective layer 90 is located further rearward than the rear end of the gas flow section. Accordingly, the porous protective layer 90 almost completely covers the portion of the element body 102 exposed to the gas being measured, thus protecting that portion. The porous protective layer 90 functions to inhibit the adhesion of substances such as moisture in the gas being measured, which could cause cracks in the element body 102. The porous protective layer 90 covers the gas inlet 10. However, since the porous protective layer 90 is a porous material, the gas to be measured can flow inside the porous protective layer 90 and reach the gas inlet 10.

[0112] The porous protective layer 90 is composed of a porous ceramic material such as alumina, zirconium dioxide, spinel, cordierite, titanium dioxide, or magnesium oxide. In this embodiment, the porous protective layer 90 is composed of alumina. The porosity of the porous protective layer 90 can be, for example, 10% or more and 70% or less. The thickness (length in the front-to-back direction) of the portion of the porous protective layer 90 covering the gas inlet 10 can be, for example, 850 μm or less.

[0113] like Figure 2As shown, the control device 95 includes: the aforementioned variable power supplies 24, 46, and 52, the aforementioned heater power supply 76, and a control unit 96. The control unit 96 is a microprocessor having a CPU 97 and a storage unit 98, etc. The storage unit 98 is a non-volatile memory capable of rewriting information, such as capable of storing various programs and various data. The control unit 96 is input with voltage V0 of the main pump control oxygen partial pressure detection sensor unit 80, voltage V1 of the first measuring pump control oxygen partial pressure detection sensor unit 81, voltage V2 of the second measuring pump control oxygen partial pressure detection sensor unit 82, voltage Vref of the sensor unit 83, pump current Ip0 flowing through the main pump unit 21, pump current Ip1 flowing through the first measuring pump unit 50, and pump current Ip2 flowing through the second measuring pump unit 41. In addition, the control unit 96 outputs control signals to the variable power supplies 24, 52, and 46, thereby controlling the voltages Vp0, Vp1, and Vp2 output by the variable power supplies 24, 52, and 46, and thus controlling the main pump unit 21, the first measuring pump unit 50, and the second measuring pump unit 41. The control unit 96 also outputs control signals to the heater power supply 76, thereby controlling the power supplied by the heater power supply 76 to the heater 72. The storage unit 98 also stores target values ​​V0*, V1*, V2*, etc., which will be described later. The CPU 97 of the control unit 96 refers to these target values ​​V0*, V1*, and V2* to control each unit 21, 50, and 41.

[0114] The control unit 96 performs main pump control processing (an example of first pump unit control processing), that is, it controls the main pump unit 21 to draw oxygen from the area around the inner pump electrode 22 to the area around the outer pump electrode 23. Specifically, the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 to make the voltage V0 reach a target value V0*, thereby controlling the main pump unit 21. The target value V0* is defined as a value where the oxygen concentration in the first internal cavity 20 is sufficiently low to substantially reduce all the water and carbon dioxide in the gas to be measured. By performing this main pump control processing, in the first internal cavity 20, the water in the gas to be measured is reduced to produce hydrogen and oxygen, and the carbon dioxide in the gas to be measured is reduced to produce carbon monoxide and oxygen. The generated oxygen is drawn from the area around the inner pump electrode 22 to the area around the outer pump electrode 23 by the pump current Ip0 flowing through the main pump unit 21.

[0115] The control unit 96 performs a first measurement pump control process (an example of a second pump unit control process), that is, it controls the first measurement pump unit 50 to draw oxygen from around the outer pump electrode 23 to around the first measurement electrode 51. Specifically, the control unit 96 performs feedback control on the voltage Vp1 of the variable power supply 52 to make the voltage V1 reach a target value V1*, thereby controlling the first measurement pump unit 50. The target value V1* is defined as a value such that the oxygen concentration in the second internal cavity 40 is a predetermined concentration that causes the hydrogen in the second internal cavity 40 to be substantially completely oxidized. By performing this first measurement pump control process, the hydrogen generated in the second internal cavity 40 due to the reduction of water in the first internal cavity 20 is oxidized and water is generated again in the second internal cavity 40. At this time, the pump current Ip1 flowing through the first measurement pump unit 50 is correlated with the amount of oxygen drawn into the second internal cavity 40 to generate hydrogen in the second internal cavity 40, and further correlated with the amount of water in the measured gas in the first internal cavity 20 where hydrogen is generated in the second internal cavity 40. Therefore, the pump current Ip1 is correlated with the water concentration in the gas being measured.

[0116] Therefore, the control unit 96 performs a water concentration measurement process, that is, it measures the water concentration in the gas to be measured based on the pump current Ip1 flowing through the first measuring pump unit 50 due to the first measuring pump control process. For example, the control unit 96 derives the water concentration using a water concentration derivation mapping. The water concentration derivation mapping is predetermined and stored in the storage unit 98 in the form of a correspondence between the absolute value of the pump current Ip1 and the water concentration through experiments, analysis, etc. In the water concentration measurement process, the control unit 96 applies the measured absolute value of the pump current Ip1 to the water concentration derivation mapping to derive the water concentration corresponding to the absolute value of the pump current Ip1. Thus, the water concentration in the gas to be measured is measured. Alternatively, instead of the water concentration derivation mapping, the relational expression (e.g., a linear or quadratic function formula) representing the correspondence between the pump current Ip1 and the water concentration can be stored in the storage unit 98.

[0117] The control unit 96 performs a second measuring pump control process (an example of a third pump unit control process), that is, it controls the second measuring pump unit 41 to draw oxygen from the area around the outer pump electrode 23 to the area around the second measuring electrode 44. Specifically, the control unit 96 performs feedback control on the voltage Vp2 of the variable power supply 46 to make the voltage V2 reach a target value V2*, thereby controlling the second measuring pump unit 41. The target value V2* is defined as a value in which the oxygen concentration in the third internal cavity 61 is a predetermined concentration that causes the carbon monoxide in the third internal cavity 61 to be substantially completely oxidized. By performing this second measuring pump control process, carbon monoxide generated in the third internal cavity 61 due to the reduction of carbon dioxide in the first internal cavity 20 is oxidized and carbon dioxide is generated again. At this time, the pump current Ip2 flowing through the second measuring pump unit 41 is correlated with the amount of oxygen drawn into the third internal cavity 61 to oxidize the carbon monoxide in the third internal cavity 61, and further correlated with the amount of carbon dioxide in the measured gas in the first internal cavity 20 where carbon monoxide is generated in the third internal cavity 61. Therefore, the pump current Ip2 is correlated with the carbon dioxide concentration in the measured gas.

[0118] Therefore, the control unit 96 performs carbon dioxide concentration measurement processing, that is, it measures the carbon dioxide concentration in the gas to be measured based on the pump current Ip2 flowing through the second measuring pump unit 41 due to the second measuring pump control processing. For example, the control unit 96 derives the carbon dioxide concentration using a carbon dioxide concentration derivation mapping. The carbon dioxide concentration derivation mapping is predetermined and stored in the storage unit 98 in the form of a correspondence between the absolute value of the pump current Ip2 and the carbon dioxide concentration through experiments, analysis, etc. In the carbon dioxide concentration measurement processing, the control unit 96 applies the measured absolute value of the pump current Ip2 to the carbon dioxide concentration derivation mapping to derive the carbon dioxide concentration corresponding to the absolute value of the pump current Ip2. Thus, the carbon dioxide concentration in the gas to be measured is measured. Alternatively, instead of the carbon dioxide concentration derivation mapping, the relational expression (e.g., a linear or quadratic function formula) representing the correspondence between the pump current Ip2 and the carbon dioxide concentration can be stored in the storage unit 98.

[0119] It should be noted that both hydrogen and carbon monoxide generated in the first internal cavity 20 reach the second internal cavity 40. However, regarding hydrogen and carbon monoxide, hydrogen diffuses faster and readily bonds with oxygen. Therefore, within the second internal cavity 40, hydrogen in both hydrogen and carbon monoxide can be selectively oxidized by the first measuring pump control process. Furthermore, since hydrogen hardly reaches the third internal cavity 61, which is downstream of the second internal cavity 40, carbon monoxide can be oxidized during the second measuring pump control process. In addition, in this embodiment, by including a second noble metal in the first measuring electrode 51 as described above, the oxidation ability against carbon monoxide is weakened. Therefore, around the first measuring electrode 51, i.e., within the second internal cavity 40, hydrogen in both hydrogen and carbon monoxide can be further selectively oxidized by the first measuring pump control process.

[0120] The control unit 96 performs heater control processing, that is, it outputs a control signal to the heater power supply 76 to control the heater 72 so that its temperature reaches a target temperature (e.g., 800°C). Here, the target temperature of the heater 72 is defined as the temperature at which the solid electrolyte is activated plus a margin. The temperature of the heater 72 can be expressed as a linear function of its resistance. Therefore, in the heater control processing, the control unit 96 calculates the resistance value of the heater 72 in the form of a value that can be considered as the temperature of the heater 72 (convertible to a temperature value), and performs feedback control on the heater power supply 76 to ensure that the calculated resistance value reaches the target resistance value (the resistance value corresponding to the target temperature). The control unit 96 can obtain, for example, the voltage of the heater 72 and the current flowing through the heater 72, and calculate the resistance value of the heater 72 based on the obtained voltage and current. The control unit 96 can calculate the resistance value of the heater 72 using, for example, a 3-terminal method or a 4-terminal method. When the heater power supply 76 supplies power to the heater 72, for example, the value of the voltage applied to the heater 72 changes based on a control signal from the control unit 96, thereby adjusting the power supplied to the heater 72.

[0121] In addition, including Figure 2 The control device 95, including the variable power supplies 24, 46, 52 and heater power supply 76 shown, utilizes leads (not shown) actually formed within the sensor element 101 and connector electrodes (not shown) formed on the rear end side of the sensor element 101 (only the heater connector electrode 71 is shown). Figure 1 It is connected to each electrode inside the sensor element 101.

[0122] Next, the manufacturing method of the gas sensor 100 will be described. In the manufacturing method of the gas sensor 100, firstly, the element body 102 is manufactured, and then a porous protective layer 90 is formed on the element body 102 to manufacture the sensor element 101.

[0123] First, the method for manufacturing the main body 102 of the component will be described. First, six unfired ceramic green sheets are prepared. Multiple sheet holes and necessary through holes for positioning during printing or lamination are pre-formed on these green sheets. Additionally, spaces for the flow of the gas to be measured are pre-formed on the green sheet constituting the isolation layer 5 through punching or other processes. Spaces for the reference gas introduction space 43 are pre-formed on the green sheet constituting the first solid electrolyte layer 4 through punching or other processes. Furthermore, pattern printing processes are performed on each ceramic green sheet to form various patterns, corresponding to the first substrate layer 1, second substrate layer 2, third substrate layer 3, first solid electrolyte layer 4, isolation layer 5, and second solid electrolyte layer 6, respectively. The patterns to be formed are specifically, for example, the patterns of each electrode such as the inner pump electrode 22, the leads connected to each electrode, the reference gas introduction layer 48, the heater connector electrode 71, and the heater section 70. Pattern printing is performed as follows: using a known screen printing technique, a pattern forming paste prepared according to the characteristics required for each object is applied to the green sheet. During pattern printing, a known drying mechanism is used for drying. After pattern printing and drying, an adhesive paste for bonding the corresponding green sheets is printed and dried. Then, a pressing process is performed: the green sheets with the adhesive paste are positioned using the sheet holes and stacked in a prescribed order, and pressed together under prescribed temperature and pressure conditions to form a laminate. It should be noted that the spaces in the laminate, such as the gas flow area, can be filled with a material that disappears during firing (e.g., organic materials such as theobromine). The resulting laminate contains multiple element bodies 102. The laminate is cut into the size of the element bodies 102. The cut laminate is then fired at a prescribed firing temperature to obtain the element bodies 102.

[0124] It should be noted that by pre-coating the aforementioned disappearing material onto the upper and lower surfaces of the green sheet constituting the isolation layer 5 during pattern printing, and then removing the disappearing material during firing, the first to third diffusion rate control sections 11, 13, and 30 can be formed. Similarly, by pre-coating the disappearing material onto the upper surface of the green sheet constituting the isolation layer 5 during pattern printing, and then removing the disappearing material during firing, the fourth diffusion rate control section 60 can be formed. Furthermore, by adjusting the thickness of the disappearing material, the diffusion resistance of each of the first to fourth diffusion rate control sections 11, 13, 30, and 60 can be adjusted.

[0125] Next, a porous protective layer 90 is formed on the component body 102 using plasma spraying. For example, using a plasma gun (not shown), the powder-sprayed material is heated and melted by plasma and accelerated, causing it to impact the surface of the component body 102, rapidly solidifying the powder-sprayed material to form the porous protective layer 90. The powder-sprayed material includes raw material powder that becomes the raw material for the porous protective layer 90; in this embodiment, the raw material powder is alumina powder. When forming the porous protective layer 90 using plasma spraying, plasma spraying can be performed separately on the multiple surfaces of the component body 102 where the porous protective layer 90 is formed (here, the upper surface, lower surface, left surface, right surface, and front end surface). It should be noted that the formation of the porous protective layer 90 is not limited to plasma spraying; it can also be performed using various methods such as die casting, screen printing, and dipping.

[0126] By forming a porous protective layer 90 on the element body 102 as described above, the sensor element 101 can be obtained. Then, a gas sensor 100 with the sensor element 101 embedded is manufactured. For example, the sensor element 101 is sealed and fixed by mounting an element sealing body, and a connector and leads are mounted on the rear end side of the sensor element 101. Additionally, a protective cover is mounted on the front end side of the sensor element 101 within the element sealing body. Furthermore, an outer cylinder is mounted on the rear end side of the sensor element 101 within the element sealing body, and leads are led out from the outer cylinder to the outside. Furthermore, by connecting the led-out leads to the control device 95, the electrodes of the sensor element 101 and the heater 72 are electrically connected to the control device 95. It should be noted that this process of embedding the sensor element 101 to assemble the gas sensor 100 is known, for example, as described in Japanese Patent Application Publication No. 2015-178988.

[0127] The following describes an example of the use of the gas sensor 100 configured in this way. The CPU 97 of the control unit 96 first performs the aforementioned heater control processing to control the temperature of the heater 72 in a manner that achieves the target temperature. When the temperature of the heater 72 reaches the target temperature (or near the target temperature), the CPU 97 begins control of the aforementioned pump units 21, 50, and 41 (main pump control processing, first measuring pump control processing, and second measuring pump control processing), and obtains voltages V0, V1, V2, and Vref from the aforementioned sensor units 80 to 83. The CPU 97 of the control unit 96 continues to perform these processes, and performs the aforementioned water concentration measurement processing and carbon dioxide concentration measurement processing to measure the water concentration and carbon dioxide concentration in the gas being measured.

[0128] The inventors of this invention investigated the relationship between the responsiveness of pump currents Ip0, Ip1, and Ip2 to changes in the gas concentration in the measured gas and the diffusion resistance of the gas flow section. It should be noted that directly measuring the diffusion resistance of the gas flow section in the actual sensor element 101 is difficult; therefore, limiting currents were used as values ​​correlated with diffusion resistance. Specifically, the limiting current Ir [mA] of pump current Ip0 was used as a value negatively correlated with the diffusion resistance from the outside of sensor element 101 to the first internal cavity 20 of the gas flow section. The limiting current Ih [mA] of pump current Ip1 was used as a value negatively correlated with the diffusion resistance from the outside of sensor element 101 to the second internal cavity 40 of the gas flow section. The limiting current Ic [mA] of pump current Ip2 was used as a value negatively correlated with the diffusion resistance from the outside of sensor element 101 to the third internal cavity 61 of the gas flow section.

[0129] The limiting current Ir is set to the value obtained from the following measurement. First, a model gas with nitrogen as the base gas and an oxygen concentration of 20% is prepared as the gas to be measured. The front end periphery of the sensor element 101, including the gas inlet 10, is exposed to the atmosphere of this model gas. Next, the control unit 96 performs the aforementioned heater control process, bringing the temperature of the heater 72 to near the target temperature. In this state, while gradually increasing the set value of the target value V0*, the control unit 96 performs the same process as the aforementioned main pump control process. As the target value V0* gradually increases, the pump current Ip0 increases accordingly; however, when the target value V0* is further increased, the pump current Ip0 does not increase even if the target value V0* changes. That is, the pump current Ip0 reaches the limiting current. This limiting current value of the pump current Ip0 is set as the limiting current Ir. That is, the limiting current Ir is the limiting current when the periphery of the front end of the sensor element 101 is exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, and the main pump unit 21 draws oxygen from around the inner pump electrode 22 to around the outer pump electrode 23. The limiting currents Ih and Ic are also measured using the same method. The limiting current Ih is the limiting current when the periphery of the front end of the sensor element 101 is exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, and the first measuring pump unit 50 draws oxygen from around the first measuring electrode 51 to around the outer pump electrode 23. The limiting current Ic is the limiting current when the periphery of the front end of the sensor element 101 is exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, and the second measuring pump unit 41 draws oxygen from around the second measuring electrode 44 to around the outer pump electrode 23. It should be noted that when measuring the limiting current Ir, the first measuring pump unit 50 and the second measuring pump unit 41 were not activated. When measuring the limiting current Ih, the main pump unit 21 and the second measuring pump unit 41 were not activated. When measuring the limiting current Ic, the main pump unit 21 and the first measuring pump unit 50 were not activated. The limiting currents Ir, Ih, and Ic are values ​​that have a negative correlation with the diffusion resistance of the gas flow section as described above. That is, the limiting currents Ir, Ih, and Ic are values ​​representing the structural characteristics of the gas flow section of the sensor element 101.

[0130] The inventors of this invention investigated the responsiveness of pump currents Ip0 and Ip1 to changes in water concentration in the measured gas and the relationship between the limiting current Ih and the limiting current Ir, which represents the diffusion resistance of the gas flow section, as follows. First, sensor elements 101 with the same structure were fabricated, except that the limiting currents Ih were made different by varying the diffusion resistance of the third diffusion rate control unit 30, as described in Experimental Examples 1 to 10. In the above-described method for manufacturing the sensor element 101, the thickness of the disappearing material coated on the upper and lower surfaces of the green sheet constituting the isolation layer 5 corresponding to the third diffusion rate control unit 30 was changed, thereby changing the height of the third diffusion rate control unit 30 (two slits), and thus adjusting the diffusion resistance of the third diffusion rate control unit 30. Next, as the measured gas, a model gas with nitrogen as the base gas and an oxygen concentration of 0%, a water concentration of 1%, and a carbon dioxide concentration of 0% was prepared, and the periphery of the front end of the sensor element 101 in Experimental Example 1 was exposed to the atmosphere of this model gas. Additionally, the control unit 96 executes the aforementioned heater control process to bring the temperature of the heater 72 to near the target temperature. In this state, the control device 95 executes the main pump control process, the first measuring pump control process, and the second measuring pump control process, waiting until the pump currents Ip0, Ip1, and Ip2 stabilize. Next, the water concentration of the model gas is abruptly changed from 1% to 5%, and the process waits until the pump currents Ip0 and Ip1 rise sharply and then stabilize again. It should be noted that the pump currents Ip0, Ip1, and Ip2 are considered stable when the change in their current values ​​over time reaches 0.2% / sec or less. Furthermore, the value of the pump current Ip0 before the abrupt change in water concentration is set to 0%, and the value of the pump current Ip0 after the abrupt change in water concentration (the average value over 10 seconds after stabilization) is set to 100%. The time until the pump current Ip0 reaches 90% of its value after the abrupt change in water concentration is measured as the response time Th0 [sec] of the pump current Ip0 to the change in water concentration. Similarly, the pump current Ip1 before the water concentration changes abruptly was set to 0%, and the value when the pump current Ip1 stabilizes again after the water concentration changes abruptly was set to 100%. The time until the pump current Ip1 reaches 90% of its value after the water concentration changes abruptly was measured as the response time Th1 [sec] of the pump current Ip1 to the change in water concentration. The response times Th0 and Th1 were also measured similarly for the sensor element 101 in Examples 2-10. A shorter response time Th0 indicates a higher responsiveness to changes in water concentration. A shorter response time Th1 indicates a higher responsiveness to changes in water concentration, and consequently, a higher responsiveness to the measurement of water concentration (the measured value of water concentration in the water concentration measurement process). The ratio Ih / Ir, response time Th0, and response time Th1 of Examples 1-10 are shown in Table 1 and... Figure 3 ,4 . Figure 3 , Figure 4 The dashed line in the middle represents the approximate straight line calculated based on the results of Experiments 1-10.

[0131] Table 1

[0132]

[0133] As shown in Table 1, Figure 3 and Figure 4 As shown, the following trend was confirmed: the smaller the ratio of Ih / Ir, the smaller the response times Th0 and Th1. In Experiments 5-10, the response time Th1 was less than 10 seconds, indicating a high responsiveness in water concentration determination. Furthermore, Figure 4 The approximate straight line shown is given by equation (1). Equation (1) confirms that if the ratio Ih / Ir is 0.44 or less, the response time Th1 is 10 seconds or less, thereby improving the responsiveness of water concentration measurement. Regarding the sensor element 101 of this embodiment, the flow path cross-sectional area or the length in the front-to-back direction of the first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 are adjusted in such a way that the ratio Ih / Ir reaches 0.44 or less, thereby increasing the responsiveness of water concentration measurement.

[0134] Th1=25.506*Ih / Ir-1.2527 (1)

[0135] The reason why the water concentration measurement responsiveness can be improved by having a ratio Ih / Ir of 0.44 or less is as follows. First, as mentioned above, the limiting current Ir is negatively correlated with the diffusion resistance from the outside of the sensor element 101 to the first internal cavity 20 of the gas being measured flow section. Furthermore, the limiting current Ih is negatively correlated with the diffusion resistance from the outside of the sensor element 101 to the second internal cavity 40 of the gas being measured flow section. Therefore, it can be considered that the larger the ratio Ih / Ir, the less water in the gas being measured flows into the first internal cavity 20 from the outside, and the more water back diffuses from the second internal cavity 40 back into the first internal cavity 20. The back diffusion of water from the second internal cavity 40 to the first internal cavity 20 will be explained. The water in the first internal cavity 20 is reduced by the main pump control process to produce hydrogen. This hydrogen reaches the second internal cavity 40, is oxidized by the first measurement pump control process, and becomes water again. This water then returns to the first internal cavity 20 due to back diffusion. Furthermore, since there is a tendency for the diffusion resistance from the second internal cavity 40 to the first internal cavity 20 to be smaller relative to the diffusion resistance from the outside of the sensor element 101 to the first internal cavity 20 of the gas flow section, there is a tendency for more water to reach the first internal cavity 20 due to back diffusion. Therefore, since the larger the Ih / Ir ratio, the less water flows into the first internal cavity 20 from the outside and the more water back diffuses from the second internal cavity 40 to the first internal cavity 20, the amount of hydrogen generated by the reduction of water in the first internal cavity 20 due to the main pump control process and the amount of water in the gas being measured outside the sensor element 101 are prone to deviation. As a result, it is believed that when the water concentration in the gas being measured outside the sensor element 101 changes, the time until the amount of hydrogen generated by the reduction of water in the first internal cavity 20 corresponds to the changed water concentration is longer. That is, it is believed that the larger the ratio of Ih / Ir, the lower the responsiveness of the pump current Ip0. In fact, although the limiting current Ir of the sensor element 101 in Experimental Examples 1-10 is the same for each other, i.e., the diffusion resistance from the outside of the sensor element 101 to the first internal cavity 20 is the same for each other, as shown in Table 1 and... Figure 3The results also confirm the trend that the larger the ratio of Ih / Ir, the longer the response time Th0, i.e., the decreasing responsiveness of the pump current Ip0. Therefore, in Experiments 1-10, the larger the ratio of Ih / Ir, i.e., the smaller the diffusion resistance between the first internal cavity 20 and the second internal cavity 40, the longer the response time Th0, which is considered to be due to the aforementioned reverse diffusion of water. Furthermore, if the responsiveness of the pump current Ip0 is low, the time until the pump current Ip1 corresponds to the changed water concentration becomes longer, i.e., the responsiveness of the pump current Ip1 also decreases. Therefore, it is believed that the larger the ratio of Ih / Ir, the longer the response time Th1, which is actually reflected in Table 1 and... Figure 4 This trend has also been confirmed. Furthermore, it is believed that by having a ratio of Ih / Ir of 0.44 or less, the proportion of water in the gas being measured in the first internal cavity 20 that has back-diffused from the second internal cavity 40 to the first internal cavity 20 can be sufficiently reduced, thereby improving the responsiveness of water concentration measurement.

[0136] The inventors of this invention investigated the responsiveness of pump currents Ip0 and Ip2 to changes in carbon dioxide concentration in the measured gas and the relationship between the limiting current Ic and the limiting current Ir, which represents the diffusion resistance of the gas flow section, as follows. First, sensor elements 101 with the same structure were fabricated, except that the limiting currents Ic were made different by varying the diffusion resistance of the fourth diffusion rate control unit 60, as described in Experimental Examples 11 to 20. In the above-described manufacturing method of the sensor element 101, the thickness of the disappearing material coated on the upper surface of the green sheet constituting the isolation layer 5 corresponding to the fourth diffusion rate control unit 60 was changed, thereby changing the height of the fourth diffusion rate control unit 60 (one slit), and thus adjusting the diffusion resistance of the fourth diffusion rate control unit 60. Next, as the measured gas, a model gas with nitrogen as the base gas and an oxygen concentration of 0%, a water concentration of 0%, and a carbon dioxide concentration of 1% was prepared, and the periphery of the front end of the sensor element 101 in Experimental Example 11 was exposed to the atmosphere of this model gas. Additionally, the control unit 96 executes the aforementioned heater control process to bring the temperature of the heater 72 to near the target temperature. In this state, the control device 95 executes the main pump control process, the first measuring pump control process, and the second measuring pump control process, waiting until the pump currents Ip0, Ip1, and Ip2 stabilize. Next, the carbon dioxide concentration of the model gas is abruptly changed from 1% to 5%, and the process waits until the pump currents Ip0 and Ip2 rise sharply and then stabilize again. It should be noted that the pump currents Ip0, Ip1, and Ip2 are considered stable when the change in their current values ​​over time reaches 0.2% / sec or less. Furthermore, the pump current Ip0 before the abrupt change in carbon dioxide concentration is set to 0%, and the value of the pump current Ip0 after the abrupt change in carbon dioxide concentration (the average value over 10 seconds after stabilization) is set to 100%. The time until the pump current Ip0 reaches 90% of its value after the abrupt change in carbon dioxide concentration is measured as the response time Tc0 [sec] of the pump current Ip0 to the change in carbon dioxide concentration. Similarly, the value of the pump current Ip2 before the carbon dioxide concentration changes abruptly is set to 0%, and the value when the pump current Ip2 stabilizes again after the sudden change in carbon dioxide concentration is set to 100%. The time until the pump current Ip2 reaches 90% of its value after the sudden change in carbon dioxide concentration is measured as the response time Tc2 [sec] of the pump current Ip2 to the change in carbon dioxide concentration. The response times Tc0 and Tc2 are also measured similarly for the sensor element 101 in Experimental Examples 12-20. A shorter response time Tc0 indicates a higher responsiveness to changes in carbon dioxide concentration in the pump current Ip0. A shorter response time Tc2 indicates a higher responsiveness to changes in carbon dioxide concentration in the pump current Ip2, and consequently, a higher responsiveness to the measurement of carbon dioxide concentration (the measured value of carbon dioxide concentration in the carbon dioxide concentration measurement process).The ratios Ic / Ir, response times Tc0, and response times Tc2 of Experimental Examples 11–20 are shown in Table 2. Figure 5 , 6 . Figure 5 , Figure 6 The dashed line in the middle represents the approximate straight line calculated based on the results of Experiments 11-20.

[0137] Table 2

[0138]

[0139] As shown in Table 2, Figure 5 and Figure 6 As shown, the following trend was confirmed: the smaller the ratio of Ic / Ir, the smaller the response times Tc0 and Tc2. In Experiments 19 and 20, the response time Tc2 was below 10 seconds, indicating a high responsiveness in the determination of carbon dioxide concentration. Furthermore, Figure 6 The approximate straight line shown is given by equation (2). Equation (2) confirms that if the ratio Ic / Ir is 0.24 or less, the response time Tc2 is 10 seconds or less, thereby improving the responsiveness of carbon dioxide concentration measurement. Regarding the sensor element 101 of this embodiment, by adjusting the flow path cross-sectional area or the length in the front-to-back direction of the first diffusion rate control unit 11, the second diffusion rate control unit 13, the third diffusion rate control unit 30, and the fourth diffusion rate control unit 60 so that the ratio Ic / Ir is 0.24 or less, the responsiveness of carbon dioxide concentration measurement is improved.

[0140] Tc2=71.195*Ic / Ir-7.5921 (2)

[0141] The reason why the responsiveness of carbon dioxide concentration measurement can be improved by having a ratio Ic / Ir of 0.24 or less is as follows. First, as mentioned above, the limiting current Ir is negatively correlated with the diffusion resistance from the outside of the sensor element 101 to the first internal cavity 20 of the gas being measured flow section. Furthermore, the limiting current Ic is negatively correlated with the diffusion resistance from the outside of the sensor element 101 to the third internal cavity 61 of the gas being measured flow section. Therefore, it is considered that the larger the ratio Ic / Ir, the less carbon dioxide in the gas being measured flows into the first internal cavity 20 from the outside, and the more carbon dioxide back diffuses from the third internal cavity 61 back into the first internal cavity 20. The back diffusion of carbon dioxide from the third internal cavity 61 to the first internal cavity 20 will be explained. The carbon dioxide in the first internal cavity 20 is reduced by the main pump control process to produce carbon monoxide, which reaches the third internal cavity 61 and is oxidized by the second measurement pump control process, becoming carbon dioxide again. The carbon dioxide re-enters the first internal cavity 20 due to back diffusion. Furthermore, since there is a tendency for the diffusion resistance from the third internal cavity 61 to the first internal cavity 20 to decrease relative to the diffusion resistance from the outside of the sensor element 101 to the first internal cavity 20 of the gas flow section, as Ic / Ir increases, there is a tendency for more carbon dioxide to reach the first internal cavity 20 due to back diffusion. Therefore, since the larger the Ic / Ir ratio, the less carbon dioxide flows into the first internal cavity 20 from the outside, and the more carbon dioxide back diffuses from the third internal cavity 61 to the first internal cavity 20, the more likely a discrepancy will occur between the amount of carbon monoxide generated by the reduction of carbon dioxide in the first internal cavity 20 due to the main pump control process and the amount of carbon dioxide in the measured gas outside the sensor element 101. As a result, it is considered that when the carbon dioxide concentration in the measured gas outside the sensor element 101 changes, the time until the amount of carbon monoxide generated by the reduction of carbon dioxide in the first internal cavity 20 corresponds to the changed carbon dioxide concentration becomes longer. That is, it is believed that the larger the ratio of Ic / Ir, the lower the responsiveness of the pump current Ip0. In fact, although the limiting current Ir of the sensor element 101 in Experimental Examples 11-20 is the same for each other, i.e., the diffusion resistance from the outside of the sensor element 101 to the first internal cavity 20 is the same for each other, as shown in Table 2 and... Figure 5The results also confirm the trend that the larger the ratio of Ic / Ir, the longer the response time Tc0, i.e., the decreasing responsiveness of the pump current Ip0. Therefore, in Experiments 11-20, the larger the ratio of Ic / Ir, i.e., the smaller the diffusion resistance between the first internal cavity 20 and the third internal cavity 61, the longer the response time Tc0, which is considered to be due to the aforementioned reverse diffusion of carbon dioxide. Furthermore, if the responsiveness of the pump current Ip0 is low, the time until the pump current Ip2 corresponds to the changed carbon dioxide concentration becomes longer, i.e., the responsiveness of the pump current Ip2 also decreases. Therefore, it is considered that the larger the ratio of Ic / Ir, the longer the response time Tc2. In fact, as shown in Table 2 and... Figure 6 This trend has also been confirmed. Furthermore, it is believed that by setting the Ic / Ir ratio to 0.24 or less, the proportion of carbon dioxide in the gas being measured in the first internal cavity 20 that has back-diffused from the third internal cavity 61 to the first internal cavity 20 can be sufficiently reduced, thereby improving the responsiveness of carbon dioxide concentration measurement.

[0142] It should be noted that the difference in the upper limits of Ih / Ir and Ic / Ir used to improve responsiveness is believed to be due to the different diffusion rates of water (and hydrogen) and carbon dioxide (and carbon monoxide).

[0143] Examples 5-10 and 19-20 correspond to embodiments of the present invention, and examples 1-4 and 11-18 correspond to comparative examples. However, the present invention is not limited to these embodiments.

[0144] The limiting current Ih is preferably 0.3 mA or less. If the limiting current Ih is too large, i.e., the diffusion resistance from the outside of the sensor element 101 to the second internal cavity 40 is too small, the flow rate of hydrogen into the second internal cavity 40 may sometimes be too large, resulting in insufficient oxidation of hydrogen by the first measuring pump control process. As a result, sometimes the pump current Ip1 and the water concentration cannot correspond accurately, and the accuracy of water concentration measurement decreases. If the limiting current Ih is 0.3 mA or less, such a decrease in the accuracy of water concentration measurement can be suppressed. Similarly, the limiting current Ic is preferably 0.3 mA or less. If the limiting current Ic is 0.3 mA or less, insufficient oxidation of carbon monoxide in the third internal cavity 61 by the second measuring pump control process can be suppressed, and the decrease in the accuracy of carbon dioxide concentration measurement can be suppressed.

[0145] The limiting current Ih can be above 0.05mA. The limiting current Ic can be above 0.05mA. The limiting current Ir can be above 0.1mA. The limiting current Ir can be below 1.5mA.

[0146] Here, the correspondence between the constituent elements of this embodiment and the constituent elements of the present invention is clarified. The sensor element 101 of this embodiment corresponds to the sensor element of the present invention, and the control device 95 corresponds to the control device. The element body 102 corresponds to the element body, the first internal cavity 20 corresponds to the first chamber, the inner pump electrode 22 corresponds to the first inner electrode, the main pump unit 21 corresponds to the first pump unit, the second internal cavity 40 corresponds to the second chamber, the first measuring electrode 51 corresponds to the second inner electrode, the first measuring pump unit 50 corresponds to the second pump unit, the third internal cavity 61 corresponds to the third chamber, the second measuring electrode 44 corresponds to the third inner electrode, the second measuring pump unit 41 corresponds to the third pump unit, the outer pump electrode 23 corresponds to the first outer electrode, the second outer electrode, and the third outer electrode, and the reference electrode 42 corresponds to the reference electrode. The main pump control processing corresponds to the first pump unit control processing, the first measuring pump control processing corresponds to the second pump unit control processing, and the second measuring pump control processing corresponds to the third pump unit control processing. The pump current Ip1 corresponds to the second pump current, and the pump current Ip2 corresponds to the third pump current.

[0147] The gas sensor 100 of this embodiment, as described in the above detailed description, has its sensor element 101 configured such that the ratio of limiting current Ih to limiting current Ir, Ih / Ir, is 0.44 or less, which improves the responsiveness for measuring water concentration. Furthermore, by configuring the sensor element 101 such that the ratio of limiting current Ic to limiting current Ir, Ic / Ir, is 0.24 or less, the responsiveness for measuring carbon dioxide concentration is improved.

[0148] Furthermore, by keeping the limiting current Ih below 0.3 mA, the accuracy of water concentration measurement can be reduced. Similarly, by keeping the limiting current Ic below 0.3 mA, the accuracy of carbon dioxide concentration measurement can be suppressed.

[0149] It should be noted that the present invention is not limited to any of the above embodiments. Of course, any method that falls within the technical scope of the present invention can be implemented in various ways.

[0150] For example, in the above embodiment, the ratio Ih / Ir is 0.44 or less, and the ratio Ic / Ir is 0.24 or less. However, it can be either Ih / Ir 0.44 or less, or Ic / Ir 0.24 or less. If the ratio Ih / Ir is 0.44 or less, the responsiveness of water concentration measurement can be improved. If the ratio Ic / Ir is 0.24 or less, the responsiveness of carbon dioxide concentration measurement can be improved.

[0151] In the above embodiments, the control device 95 performs both water concentration measurement and carbon dioxide concentration measurement. However, it is permissible to perform only one of these two processes. When the control device 95 performs only water concentration measurement, the ratio Ih / Ir only needs to be 0.44 or less, and the ratio Ic / Ir does not necessarily need to be 0.24 or less. When the control device 95 performs only carbon dioxide concentration measurement, the ratio Ic / Ir only needs to be 0.24 or less, and the ratio Ih / Ir does not necessarily need to be 0.44 or less. It should be noted that when the control device 95 does not perform water concentration measurement, it is also preferable to perform first measurement pump control. When the control device 95 does not perform carbon dioxide concentration measurement, it is also preferable to perform second measurement pump control.

[0152] In the above embodiment, the sensor element 101 includes a porous protective layer 90; however, it may not include a porous protective layer 90. It should be noted that the diffusion resistance of the porous protective layer 90 is smaller than the diffusion resistance of the gas flow section being measured (e.g., the diffusion resistance of each of the first to fourth diffusion rate control sections 11, 13, 30, and 60). Therefore, the presence or absence of the porous protective layer 90 has a relatively small impact on the values ​​of the limiting currents Ir, Ih, and Ic.

[0153] In the above embodiments, the outer pump electrode 23 serves as: a first outer electrode paired with the inner pump electrode 22 in the main pump unit 21; a second outer electrode paired with the first measuring electrode 51 in the first measuring pump unit 50; and a third outer electrode paired with the second measuring electrode 44 in the second measuring pump unit 41. That is, the first to third outer electrodes are configured as a universal outer pump electrode 23. However, this is not a limitation. For example, two of the first to third outer electrodes can be configured as universal outer pump electrodes 23, and the remaining one can be configured as an electrode independent of the outer pump electrode 23, and disposed on the outer surface of the element body 102 in a manner that contacts the gas to be measured. Alternatively, the first to third outer electrodes can be configured as separate electrodes, disposed on the outer surface of the element body 102 in a manner that contacts the gas to be measured.

[0154] In the above embodiments, the sensor element 101 of the gas sensor 100 includes a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61, but is not limited thereto. For example, such as Figure 7 As shown in the modified example of sensor element 201, it may not have a third internal cavity 61. Figure 7In the modified sensor element 201, a gas inlet 10, a first diffusion rate control unit 11, a buffer space 12, a second diffusion rate control unit 13, a first internal cavity 20, a third diffusion rate control unit 30, and a second internal cavity 40 are sequentially connected and adjacent to each other between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. Furthermore, a second measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 within the second internal cavity 40. The second measuring electrode 44 is covered by a fourth diffusion rate control unit 45. The fourth diffusion rate control unit 45 is a membrane composed of a porous ceramic material such as alumina (Al2O3). Like the fourth diffusion rate control unit 60 in the above embodiment, the fourth diffusion rate control unit 45 applies a predetermined diffusion resistance to the gas to be measured in the second internal cavity 40 and guides it to the second measuring electrode 44. Additionally, the fourth diffusion rate control unit 45 also functions as a protective film for the second measuring electrode 44. The top electrode portion 51a of the first measuring electrode 51 is formed directly above the second measuring electrode 44. Even with this configuration, the sensor element 201, as in the above embodiment, can measure the carbon dioxide concentration based on the pump current Ip2 flowing through the second measuring pump unit 41. Figure 7 In the sensor element 201, the area surrounding the second measuring electrode 44 functions as a third chamber. That is, the area surrounding the second measuring electrode 44 performs the same function as the third internal cavity 61.

[0155] In the above embodiments, the sensor element 101 includes a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61; however, for example, as... Figure 8As shown in the modified gas sensor 300, the third internal cavity 61 may not be included. The sensor element 301 of this gas sensor 300 does not include: the fourth diffusion rate control unit 60, the third internal cavity 61, the second measuring electrode 44, the second measuring pump unit 41, and the oxygen partial pressure detection sensor unit 82 for controlling the second measuring pump, as described in the above embodiment. Therefore, the control device for controlling this sensor element 301 differs from the control device 95 and does not include a variable power supply 46. In this gas sensor 300, the water concentration in the gas being measured can also be measured by performing main pump control processing, first measuring pump control processing, and water concentration measurement processing through the control device. Furthermore, if the ratio Ih / Ir of the limiting current Ir of pump current Ip0 to the limiting current Ih of pump current Ip1 is 0.44 or less, the responsiveness for water concentration measurement can be improved. It should be noted that in this gas sensor 300, the target value V0* for the main pump control processing is preferably set to a value such that water in the gas being measured is reduced, but carbon dioxide is suppressed from reduction. Since carbon dioxide is less easily reduced than water, by setting the target value V0* to a lower value than the target value V0* in the above embodiment (setting the oxygen concentration in the first internal cavity 20 to a predetermined concentration higher than the oxygen concentration in the first internal cavity 20 during the main pump control process in the above embodiment), the water in the first internal cavity 20 can be reduced, and the reduction of carbon dioxide can be suppressed. Alternatively, the gas sensor 300 can also be used to measure the water concentration in a gas to be measured that does not contain carbon dioxide.

[0156] In the above embodiments, the sensor element 101 includes a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61; however, for example, as... Figure 9As shown in the modified gas sensor 400, the second internal cavity 40 may be omitted. The sensor element 401 of this gas sensor 400 does not include: the third diffusion rate control unit 30, the second internal cavity 40, the first measuring electrode 51, the first measuring pump unit 50, and the oxygen partial pressure detection sensor unit 81 for controlling the first measuring pump, as described in the above embodiment. In the gas flow section of the sensor element 401, the first internal cavity 20, the fourth diffusion rate control unit 60, and the third internal cavity 61 are connected sequentially in this order. Therefore, the control device for controlling this sensor element 401 differs from the control device 95 and does not include a variable power supply 52. ​​In this gas sensor 400, the carbon dioxide concentration in the gas being measured can also be measured by performing main pump control processing, second measuring pump control processing, and carbon dioxide concentration measurement processing through the control device. Furthermore, if the ratio of the limiting current Ir of pump current Ip0 to the limiting current Ic of pump current Ip2, Ic / Ir, is 0.24 or less, the responsiveness for carbon dioxide concentration measurement can be improved. It should be noted that the gas sensor 400 is preferably used for measuring the concentration of carbon dioxide in a gas to be measured that does not contain water.

[0157] In the above embodiments, the element body 102 of the sensor element 101 is configured as a laminate having multiple solid electrolyte layers (layers 1 to 6), but is not limited thereto. It is sufficient as long as the element body of the sensor element 101 has at least one oxygen ion-conducting solid electrolyte layer and has an internal passage for the gas to be measured. For example, Figure 1 In this case, layers 1 to 5 other than the second solid electrolyte layer 6 can also be structural layers made of a material other than the solid electrolyte (e.g., layers made of aluminum oxide). In this case, it is sufficient that each electrode of the sensor element 101 is disposed on the second solid electrolyte layer 6. For example, as long as... Figure 1 The second measuring electrode 44 can be disposed on the lower surface of the second solid electrolyte layer 6. Alternatively, the reference gas introduction space 43 can be disposed in the isolation layer 5 instead of the first solid electrolyte layer 4, the reference gas introduction layer 48 can be disposed between the second solid electrolyte layer 6 and the isolation layer 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3, and the reference electrode 42 can be disposed at a position further back than the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6.

[0158] Industrial availability

[0159] This invention relates to a gas sensor that can be used to measure the concentration of water and / or carbon dioxide in gases such as automobile exhaust.

Claims

1. A gas sensor comprising a sensor element and a control device, for measuring the water concentration and / or carbon dioxide concentration in a gas to be measured. The sensor element has: The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated. The first pump unit is configured to include a first inner electrode disposed in a first chamber in the gas flow section to be measured and a first outer electrode disposed on the outer surface of the element body. The second pump unit is configured to include a second inner electrode disposed in a second chamber located downstream of the first chamber in the gas flow section to be measured, and a second outer electrode disposed on the outer surface of the element body. as well as The third pump unit is configured to include a third inner electrode disposed in a third chamber located downstream of the second chamber in the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body. The control device performs the following processing: The first pump unit is controlled to draw oxygen from the area around the first inner electrode to the area around the first outer electrode, thereby reducing water and carbon dioxide in the gas being measured in the first chamber. The second pump unit is controlled to draw oxygen from the vicinity of the second outer electrode to the vicinity of the second inner electrode, thereby oxidizing the hydrogen generated by the reduction of water in the first chamber in the second chamber; and The third pump unit is controlled to draw oxygen from the vicinity of the third outer electrode to the vicinity of the third inner electrode, thereby oxidizing carbon monoxide generated by the reduction of carbon dioxide in the first chamber within the third chamber. With the inlet of the gas flow section being measured exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is defined as the limiting current Ir; the limiting current when the second pump unit draws oxygen from around the second inner electrode to around the second outer electrode is defined as the limiting current Ih; and the limiting current when the third pump unit draws oxygen from around the third inner electrode to around the third outer electrode is defined as the limiting current Ic. The units of these limiting currents Ir, Ih, and Ic are all mA. The control device performs a water concentration measurement process based on a second pump current flowing through the second pump unit due to the control processing of the second pump unit, to measure the water concentration in the gas to be measured, and the ratio of the limiting current Ih to the limiting current Ir in the sensor element, Ih / Ir, is 0.44 or less; and / or, the control device performs a carbon dioxide concentration measurement process based on a third pump current flowing through the third pump unit due to the control processing of the third pump unit, to measure the carbon dioxide concentration in the gas to be measured, and the ratio of the limiting current Ic to the limiting current Ir in the sensor element, Ic / Ir, is 0.24 or less.

2. The gas sensor according to claim 1, characterized in that, The control device performs the water concentration measurement process, and the limiting current Ih is below 0.3mA; and / or, the control device performs the carbon dioxide concentration measurement process, and the limiting current Ic is below 0.3mA.

3. The gas sensor according to claim 1 or 2, characterized in that, The control device performs the water concentration measurement process and the carbon dioxide concentration measurement process. In the sensor element, the ratio Ih / Ir is 0.44 or less, and the ratio Ic / Ir is 0.24 or less.

4. A gas sensor comprising a sensor element and a control device, for measuring the water concentration in a gas to be measured. The sensor element has: The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated. The first pump unit is configured to include a first inner electrode disposed in a first chamber in the gas flow section to be measured and a first outer electrode disposed on the outer surface of the element body. as well as The second pump unit is configured to include a second inner electrode disposed in a second chamber located downstream of the first chamber in the gas flow section being measured, and a second outer electrode disposed on the outer surface of the element body. The control device performs the following processing: The first pump unit is controlled to draw oxygen from the area around the first inner electrode to the area around the first outer electrode, thereby reducing the water in the gas being measured in the first chamber. The second pump unit is controlled to draw oxygen from the vicinity of the second outer electrode to the vicinity of the second inner electrode, thereby oxidizing the hydrogen generated by the reduction of water in the first chamber in the second chamber; and The water concentration determination process measures the water concentration in the gas being measured based on the second pump current flowing through the second pump unit due to the control processing of the second pump unit. The sensor element is configured such that, when the inlet of the gas flow section to be measured is exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is set as the limiting current Ir, and the limiting current when the second pump unit draws oxygen from around the second inner electrode to around the second outer electrode is set as the limiting current Ih. When the units of the limiting currents Ir and Ih are both mA, the ratio of the limiting current Ih to the limiting current Ir, Ih / Ir, is 0.44 or less.

5. A gas sensor comprising a sensor element and a control device, for measuring the concentration of carbon dioxide in a gas to be measured. The sensor element has: The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated. The first pump unit is configured to include a first inner electrode disposed in a first chamber in the gas flow section to be measured and a first outer electrode disposed on the outer surface of the element body. as well as The third pump unit is configured to include a third inner electrode disposed in a third chamber located downstream of the first chamber in the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body. The control device performs the following processing: The first pump unit is controlled to draw oxygen from the area around the first inner electrode to the area around the first outer electrode, thereby reducing carbon dioxide in the gas being measured in the first chamber. The third pump unit is controlled to draw oxygen from the vicinity of the third outer electrode to the vicinity of the third inner electrode, thereby oxidizing carbon monoxide generated by the reduction of carbon dioxide in the first chamber within the third chamber; and The carbon dioxide concentration measurement process measures the carbon dioxide concentration in the gas being measured based on the third pump current flowing through the third pump unit due to the control processing of the third pump unit. When the sensor element is exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20% at the inlet of the gas flow section being measured, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is defined as the limiting current Ir, and the limiting current when the third pump unit draws oxygen from around the third inner electrode to around the third outer electrode is defined as the limiting current Ic. When the units of the limiting currents Ir and Ic are both mA, the ratio of the limiting current Ic to the limiting current Ir, Ic / Ir, is 0.24 or less.

6. A sensor element for measuring the concentration of water and / or carbon dioxide in a gas to be measured. have: The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated. The first pump unit is configured to include a first inner electrode disposed in a first chamber in the gas flow section to be measured and a first outer electrode disposed on the outer surface of the element body. The second pump unit is configured to include a second inner electrode disposed in a second chamber located downstream of the first chamber in the gas flow section to be measured, and a second outer electrode disposed on the outer surface of the element body. as well as The third pump unit is configured to include a third inner electrode disposed in a third chamber located downstream of the second chamber in the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body. With the inlet of the gas flow section being measured exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is defined as the limiting current Ir, the limiting current when the second pump unit draws oxygen from around the second inner electrode to around the second outer electrode is defined as the limiting current Ih, and the limiting current when the third pump unit draws oxygen from around the third inner electrode to around the third outer electrode is defined as the limiting current Ic. When the units of the limiting currents Ir, Ih, and Ic are all mA, the ratio of the limiting current Ih to the limiting current Ir, Ih / Ir, is 0.44 or less, and / or the ratio of the limiting current Ic to the limiting current Ir, Ic / Ir, is 0.24 or less.

7. A sensor element for measuring the water concentration in a gas to be measured. have: The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated. The first pump unit is configured to include a first inner electrode disposed in a first chamber in the gas flow section to be measured and a first outer electrode disposed on the outer surface of the element body. as well as The second pump unit is configured to include a second inner electrode disposed in a second chamber located downstream of the first chamber in the gas flow section to be measured, and a second outer electrode disposed on the outer surface of the element body. With the inlet of the gas flow section being measured exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is defined as the limiting current Ir, and the limiting current when the second pump unit draws oxygen from around the second inner electrode to around the second outer electrode is defined as the limiting current Ih. When the units of the limiting currents Ir and Ih are both mA, the ratio of the limiting current Ih to the limiting current Ir, Ih / Ir, is 0.44 or less.

8. A sensor element for measuring the concentration of carbon dioxide in a gas to be measured. have: The main body of the component has a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for the gas to be measured to be introduced and circulated. The first pump unit is configured to include a first inner electrode disposed in a first chamber in the gas flow section to be measured and a first outer electrode disposed on the outer surface of the element body. as well as The third pump unit is configured to include a third inner electrode disposed in a third chamber located downstream of the first chamber in the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body. With the inlet of the gas flow section being measured exposed to an atmosphere of a model gas with nitrogen as the base gas and an oxygen concentration of 20%, the limiting current when the first pump unit draws oxygen from around the first inner electrode to around the first outer electrode is defined as the limiting current Ir, and the limiting current when the third pump unit draws oxygen from around the third inner electrode to around the third outer electrode is defined as the limiting current Ic. When the units of the limiting currents Ir and Ic are both mA, the ratio of the limiting current Ic to the limiting current Ir, Ic / Ir, is 0.24 or less.

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