Gas sensor and sensor element

Abstract

Provided is a gas sensor and a sensor element that suppress a decrease in measurement accuracy of a specific gas concentration in a measured gas. The gas sensor includes a sensor element and a control device. The sensor element has an element main body in which first to third internal cavities that are not in communication with each other and to which a measured gas can reach from the outside of the sensor element, respectively, are provided. The control device measures at least two of first to fourth concentrations as specific gas concentrations by performing at least two processes selected using a combination of pump currents Ipl to Ip3, among a first concentration measurement process of measuring a first concentration based on pump currents Ipl and Ip2, a second concentration measurement process of measuring a second concentration based on pump currents Ip2 and Ip3, a third concentration measurement process of measuring a third concentration based on a pump current Ip3, and a fourth concentration measurement process of measuring a fourth concentration based on pump currents Ipl and Ip3.

Description

Technical Field

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

[0002] Previously, gas sensors were known for measuring the concentration of carbon dioxide in gases such as automobile exhaust. For example, Patent Document 1 describes a gas sensor that includes a sensor element composed of a solid electrolyte layer with oxygen ion conductivity, which determines the concentrations of water vapor and carbon dioxide in the gas being measured. In this gas sensor, the oxygen partial pressure in the first internal cavity of the gas being measured is adjusted so that the water vapor and carbon dioxide components in the gas being measured are substantially completely decomposed within the first internal cavity of the sensor element. Furthermore, oxygen is supplied to the second internal cavity via a first measuring electrochemical pumping unit in a manner that allows the hydrogen generated from the decomposition of water vapor to selectively combust within the second internal cavity, which is connected to the first internal cavity. The concentration of water vapor present in the gas being measured is determined based on the magnitude of the current flowing at this time. In addition, the gas sensor supplies oxygen to the surface of the inner electrode of the second measurement via a second measurement electrochemical pumping unit by selectively burning carbon monoxide generated from the decomposition of carbon dioxide in a third internal cavity that is connected to the second internal cavity. Based on the magnitude of the current flowing at this time, the concentration of carbon dioxide present in the measured gas is determined.

[0003] Existing technical documents

[0004] Patent documents

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

[0006] In the gas sensor of Patent Document 1, as described above, the first, second, and third internal cavities of the sensor element are interconnected. In this case, water (water vapor) produced by the combustion of hydrogen in the second internal cavity and carbon dioxide produced by the combustion of carbon monoxide in the third internal cavity sometimes reach the first internal cavity due to back diffusion (countercurrent). Furthermore, the water and carbon dioxide that reach the first internal cavity due to back diffusion are decomposed (reduced) again to produce hydrogen and carbon monoxide, which sometimes reach the second and third internal cavities respectively and are burned again. This indicates that the accuracy of measuring the water concentration (concentration of water vapor component) and carbon dioxide concentration in the measured gas sometimes decreases. Therefore, it is desirable to suppress the decrease in the accuracy of measuring specific gas concentrations in the measured gas caused by such back diffusion.

[0007] This invention was implemented to solve such a problem, and its main objective is to suppress the decrease in the accuracy of measuring the concentration of a specific gas in the gas being measured.

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

[0009] [1] The first gas sensor of the present invention includes a sensor element and a control device, and measures the concentration of a specific gas in the gas to be measured, wherein...

[0010] The sensor element has:

[0011] The main body of the element has a solid electrolyte layer with oxygen ion conductivity, and is provided with a first chamber, a second chamber and a third chamber that are not interconnected and can be reached from the outside of the sensor element by the gas to be measured.

[0012] The first pump unit is configured to include a first inner electrode disposed in the first chamber and a first outer electrode disposed on the outer surface of the component body.

[0013] A second pump unit, configured to include a second inner electrode disposed in the second chamber, and a second outer electrode disposed on the outer surface of the component body; and

[0014] The third pump unit is configured to include a third inner electrode disposed in the third chamber and a third outer electrode disposed on the outer surface of the component 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 two or more oxide gases, i.e., the gases to be reduced, in the gas to be measured in the first chamber.

[0017] The second pump unit control process suppresses the reduction of a portion of the oxide gas (i.e., the first gas) in the target gas of the measured gas in the second chamber, and draws oxygen from the vicinity of the second inner electrode to the vicinity of the second outer electrode, compared to the first pump unit control process; and controls the second pump unit in such a way that oxygen is drawn from the vicinity of the second inner electrode to the vicinity of the second outer electrode.

[0018] The third pump unit is controlled in a manner that, compared to the second pump unit control process, suppresses the reduction of one or more oxide gases (i.e., the second gas) other than the first gas in the target gas being reduced in the measured gas in the third chamber, and draws oxygen from around the third inner electrode to around the third outer electrode.

[0019] The control device determines at least two of the first to fourth concentrations as the specific gas concentration by performing at least two processes selected using a combination of the first to third pump currents.

[0020] The first concentration measurement process measures the concentration of the first gas in the gas to be measured, i.e., the first concentration, based on the first pump current flowing through the first pump unit due to the first pump unit control process and the second pump current flowing through the second pump unit due to the second pump unit control process.

[0021] The second concentration measurement process measures the concentration of the second gas in the gas to be measured, i.e., the second concentration, based on the second pump current and the third pump current flowing through the third pump unit due to the control process of the third pump unit; and

[0022] The third concentration measurement process involves measuring the total concentration of the first gas, the target gas for reduction (other than the second gas), and oxygen in the gas being measured, based on the third pump current.

[0023] The fourth concentration measurement process involves measuring the total concentration of the first gas and the second gas in the gas being measured, i.e., the fourth concentration, based on the first pump current and the third pump current.

[0024] In this first gas sensor, the control device performs at least two processes selected using a combination of first and third pump currents in a first to fourth concentration measurement process, and measures at least two of the first to fourth concentrations based on the first and third pump currents. Here, the first pump current flowing through the first pump unit due to the first pump unit control process is correlated with the total concentration of the reducing target gas and oxygen in the measured gas. The second pump current flowing through the second pump unit due to the second pump unit control process is correlated with the total concentration of the reducing target gas other than the first gas and oxygen in the measured gas. The third pump current flowing through the third pump unit due to the third pump unit control process is correlated with the total concentration of the reducing target gas other than the first and second gases and oxygen in the measured gas. Therefore, based on the first and second pump currents, the concentration of the first gas in the measured gas, i.e., the first concentration, can be measured. Furthermore, based on the second and third pump currents, the concentration of the second gas in the measured gas, i.e., the second concentration, can be measured. Based on the third pump current, the combined concentration of the first gas, the reducing target gas (other than the second gas), and oxygen in the gas being measured—the third concentration—can be measured. Based on the first and third pump currents, the combined concentration of the first and second gases in the gas being measured—the fourth concentration—can be measured. Furthermore, the first, second, and third chambers are not interconnected, and the gas being measured reaches each chamber from outside the sensor element via independent paths. Therefore, mutual influence between the gases in the first, second, and third chambers can be suppressed, and the aforementioned reduction in measurement accuracy due to back diffusion is less likely to occur. Therefore, this gas sensor can suppress the reduction in measurement accuracy of specific gas concentrations in the gas being measured.

[0025] It should be noted that when the first gas is two or more oxide gases among the target gases for reduction, the first concentration is the total concentration of those two or more oxide gases. Furthermore, if the second gas is one or more oxide gases other than the first gas among the target gases for reduction, it is also possible to have a scheme where the second gas is all types of oxide gases other than the first gas among the target gases for reduction. In this scheme, since there is no "target gas for reduction other than the first gas and the second gas in the gas being measured," the oxygen concentration in the gas being measured is the third concentration. The first gas can be one or more oxide gases selected sequentially, starting with the oxide gas least likely to be reduced among the target gases for reduction. The second gas can be one or more oxide gases selected sequentially, starting with the oxide gas least likely to be reduced among the target gases for reduction other than the first gas.

[0026] [2] The first gas sensor (the gas sensor mentioned in [1] above) can be: the gas to be reduced is water and carbon dioxide, the first gas is carbon dioxide and the second gas is water.

[0027] [3] In the first gas sensor described above (the gas sensor described in [2] above), the second inner electrode may contain a first noble metal with catalytic activity and a second noble metal that inhibits carbon dioxide reduction. By containing both the first and second noble metals in the second inner electrode, the second pump current is less susceptible to the influence of the carbon dioxide concentration in the gas being measured. Therefore, the measurement accuracy of the first concentration measurement process, i.e., the measurement accuracy of carbon dioxide concentration based on the first and second pump currents, is improved. In this case, the first inner electrode may contain the first noble metal.

[0028] [4] The first gas sensor (the gas sensor described in [3] above) can be: the first noble metal is at least one of Pt, Rh, Ir, Ru, and Pd, and the second noble metal is Au.

[0029] [5] In the first gas sensor described above (the gas sensor described in [3] or [4] above), the ratio R2 of the second inner electrode calculated by the following formula (1) can be 2% or more. By having the ratio R2 of the second inner electrode be 2% or more, the reduction ability of the second inner electrode against carbon dioxide can be reduced more reliably.

[0030] R2=S2 / (S1+S2)×100 (1)

[0031] in,

[0032] S1: Mass percentage of the first precious metal [wt%]

[0033] S2: Mass percentage of the second precious metal [wt%]

[0034] [6] The first gas sensor described above (the gas sensor described in any one of [1] to [5] above) may be: the sensor element has a reference electrode, which is disposed inside the element body in a manner that contacts a reference gas; the control device is configured such that: in the first pump unit control process, the first pump unit is controlled in such a manner that the voltage between the reference electrode and the first inner electrode, i.e., the first voltage, reaches a first voltage target value; in the second pump unit control process, the second pump unit is controlled in such a manner that the voltage between the reference electrode and the second inner electrode, i.e., the second voltage, reaches a second voltage target value whose absolute value is smaller than the first voltage target value; and in the third pump unit control process, the third pump unit is controlled in such a manner that the voltage between the reference electrode and the third inner electrode, i.e., the third voltage, reaches a third voltage target value whose absolute value is smaller than the second voltage target value.

[0035] [7] In the first gas sensor described above (the gas sensor described in any one of [1] to [6] above), the first concentration measurement process may be: a process of measuring the first concentration based on the difference between the first pump current and the second pump current, or a process of measuring the first concentration based on the difference between the total concentration of the reducing target gas and oxygen in the measured gas derived from the first pump current and the total concentration of the reducing target gas other than the first gas and oxygen in the measured gas derived from the second pump current. The second concentration measurement process may be: a process of measuring the second concentration based on the difference between the second pump current and the third pump current, or a process of measuring the second concentration based on the difference between the total concentration of the reducing target gas other than the first gas and oxygen in the measured gas derived from the second pump current and the total concentration of the reducing target gas other than the first gas and oxygen in the measured gas derived from the third pump current. The fourth concentration measurement process can be: a process of measuring the fourth concentration based on the difference between the first pump current and the third pump current, or a process of measuring the fourth concentration based on the difference between the total concentration of the reducing target gas and oxygen in the measured gas derived from the first pump current and the total concentration of the reducing target gas other than the first gas and the second gas and oxygen in the measured gas derived from the third pump current. It should be noted that the "process of measuring the first concentration based on the difference between the first pump current and the second pump current" further includes: "deriving the difference after correcting for at least one of the first pump current and the second pump current, and measuring the first concentration based on this difference." The "process of measuring the second concentration based on the difference between the second pump current and the third pump current" further includes: "deriving the difference after correcting for at least one of the second pump current and the third pump current, and measuring the second concentration based on this difference." The "process for measuring the fourth concentration based on the difference between the first pump current and the third pump current" further includes: "deriving the difference after correcting at least one of the first pump current and the third pump current, and measuring the fourth concentration based on the difference."

[0036] [8] The first gas sensor described above (the gas sensor described in any one of [1] to [7] above) may be: the element body is a cuboid shape having a first to a sixth surface as its outer surface, and the element body has: a first inlet for the gas to be measured from the outside toward the first chamber; a second inlet for the gas to be measured from the outside toward the second chamber; and a third inlet for the gas to be measured from the outside toward the third chamber, wherein the first, second, and third inlets are open on different surfaces of the first to sixth surfaces. Accordingly, it is possible to further suppress the mutual influence of the gases in the first, second, and third chambers.

[0037] [9] The first gas sensor described above (the gas sensor described in any one of [1] to [7] above) may be: the element body is a cuboid shape having a first to a sixth surface as its outer surface, and the element body has: a first inlet, which is an inlet for the gas to be measured from the outside toward the first chamber; a second inlet, which is an inlet for the gas to be measured from the outside toward the second chamber; and a third inlet, which is an inlet for the gas to be measured from the outside toward the third chamber, wherein the first inlet, the second inlet, and the third inlet are open on the same surface among the first to sixth surfaces. Accordingly, even if the concentration of a specific gas in the gas to be measured changes in a short time, the gas to be measured reaching each of the first to third chambers is likely to have the same specific gas concentration. Therefore, the measurement accuracy of the concentration (first concentration, second concentration, and fourth concentration) measured based on two of the first to third pump currents is improved.

[0038]

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

[0039] The sensor element has:

[0040] The main body of the element has a solid electrolyte layer with oxygen ion conductivity, and is provided with a first chamber and a second chamber that are not interconnected and can be reached from the outside of the sensor element by the gas being measured.

[0041] A first pump unit, configured to include a first inner electrode disposed in the first chamber and a first outer electrode disposed on the outer surface of the component body; and

[0042] The second pump unit is configured to include a second inner electrode disposed in the second chamber and a second outer electrode disposed on the outer surface of the component body.

[0043] The control device performs the following processing:

[0044] 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 target gas containing water and at least water in the measured gas in the first chamber.

[0045] The second pump unit control process controls the second pump unit in a manner that, compared to the first pump unit control process, suppresses the reduction of one or more gases (i.e., the first gas) in the target gas being reduced in the measured gas in the second chamber and draws oxygen from the vicinity of the second inner electrode to the vicinity of the second outer electrode; and

[0046] The concentration measurement process determines the concentration of the first gas in the gas to be measured, i.e., the first concentration, as the specific gas concentration, based on the first pump current flowing through the first pump unit due to the control processing of the first pump unit and the second pump current flowing through the second pump unit due to the control processing of the second pump unit.

[0047] The first gas is water when the gas to be reduced is water, and is one or more gases in the gas to be reduced that contain at least carbon dioxide when the gas to be reduced is both water and carbon dioxide.

[0048] In this second gas sensor, the control device measures the concentration of a first gas in the gas to be measured, i.e., a first concentration, based on a first pump current and a second pump current. Here, the first pump current flowing through the first pump unit due to the control processing of the first pump unit is correlated with the combined concentration of the reducing target gas and oxygen in the gas to be measured. The second pump current flowing through the second pump unit due to the control processing of the second pump unit is correlated with the combined concentration of the reducing target gas other than the first gas and oxygen in the gas to be measured. Therefore, based on the first pump current and the second pump current, the concentration of the first gas in the gas to be measured, i.e., the first concentration, can be measured as the specific gas concentration. Furthermore, the first chamber and the second chamber are not interconnected, and the gas to be measured reaches the first chamber and the second chamber from the outside of the sensor element via separate independent paths. Therefore, it is possible to suppress the mutual influence between the gases in the first chamber and the second chamber, and the reduction in measurement accuracy caused by the aforementioned back diffusion is less likely to occur. Therefore, in this gas sensor, it is possible to suppress the reduction in measurement accuracy of the specific gas concentration in the gas to be measured. The reducing target gas includes at least water from water and carbon dioxide. That is, the reducing target gas is water, or water and carbon dioxide. Furthermore, when the target gas for reduction is water, the first gas is water. When the target gas for reduction is both water and carbon dioxide, the first gas is at least one gas in the target gas that contains carbon dioxide. That is, when the target gas for reduction is both water and carbon dioxide, the first gas is carbon dioxide, or water and carbon dioxide. When the first gas is both water and carbon dioxide, the first concentration is the total concentration of water and carbon dioxide in the gas being measured. The second gas sensor can be the same as the various schemes of the first gas sensor described above, or it can have the same configuration as the first gas sensor described above.

[0049]

[11] The sensor element of the present invention is used to measure the concentration of a specific gas in the gas to be measured, and has the following characteristics:

[0050] The main body of the element has a solid electrolyte layer with oxygen ion conductivity, and is provided with a first chamber, a second chamber and a third chamber that are not interconnected and can be reached from the outside by the gas to be measured.

[0051] The first pump unit is configured to include a first inner electrode disposed in the first chamber and a first outer electrode disposed on the outer surface of the component body.

[0052] A second pump unit, configured to include a second inner electrode disposed in the second chamber, and a second outer electrode disposed on the outer surface of the component body; and

[0053] The third pump unit is configured to include a third inner electrode disposed in the third chamber and a third outer electrode disposed on the outer surface of the component body.

[0054] Similar to the sensor element of the first gas sensor described above, the first, second, and third chambers of this sensor element are not interconnected. The gas to be measured reaches the first, second, and third chambers from the outside of the sensor element via separate, independent paths. Therefore, mutual interference between the gases in the first, second, and third chambers can be suppressed, and the reduction in measurement accuracy caused by back diffusion is less likely to occur. Therefore, the sensor element of the present invention is suitable for use in the first gas sensor described above. It should be noted that the sensor element of the present invention can employ the same design as the various designs of the sensor element in the first gas sensor described above, or additionally incorporate the same configuration. Attached Figure Description

[0055] Figure 1 This is a simplified cross-sectional view illustrating an example of the configuration of the gas sensor 100.

[0056] Figure 2 yes Figure 1 A partial cross-sectional view of the isolation layer 5.

[0057] Figure 3 This is a block diagram showing the electrical connections between the control device 95 and each unit and heater 72.

[0058] Figure 4 This is an explanatory diagram showing an example of the V-I characteristics of a pump unit (first to third measuring pump units 15, 25, 35).

[0059] Figure 5 This is an explanatory diagram showing an example of the V-I characteristics when the inner electrodes (first to third measuring electrodes 16, 26, 36) contain a second noble metal.

[0060] Figure 6 This is a partial cross-sectional view of the main body 102 of the modified example.

[0061] Figure 7 This is a simplified cross-sectional view of the main body 102 of the modified example.

[0062] Explanation of reference numerals in the attached figures

[0063] 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, 7 Third solid electrolyte layer, 8 Fourth solid electrolyte layer, 11, 21, 31 First to third gas inlets, 12, 22, 32 First to third buffer spaces, 13, 23, 33 First to third diffusion rate control units, 14, 24, 34 First to third internal cavities, 15, 25, 35 First to third measuring pump units, 16, 26, 36 First to third measuring electrodes, 17, 27, 37 Variable power supply, 18, 28, 38 First to third sensor units, 40 Outer pump electrode, 42 Reference electrode, 43 Reference gas inlet space, 48 Reference gas inlet layer, 49 Reference gas inlet section, 49a Inlet section, 70 Heater section, 71 Heater connector electrode, 72 Heater, 73 Through hole, 74 Heater insulating layer, 75 Pressure relief port, 76 heater power supply, 95 control device, 96 control unit, 97 CPU, 98 storage unit, 100 gas sensor, 101 sensor element, 102 element body, 102a~102f first to sixth surfaces. Detailed Implementation

[0064] 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 2 yes Figure 1 A partial cross-sectional view of the isolation layer 5. Figure 3 This is a block diagram showing the electrical connections between the control device 95 and each unit and heater 72. It should be noted that... Figure 2 This is a partial cross-sectional view of the periphery of the first to third internal cavities 14, 24, and 34, taken from above, along the front-back and left-right directions of the isolation layer 5. Additionally, Figure 2 In the diagram, for reference, the first to third diffusion rate control units 13, 23, and 33 are indicated by dashed lines. 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 from the internal combustion engine as the measured gas and detects the concentration of a specific gas within the measured gas, i.e., the specific gas concentration. In this embodiment, the gas sensor 100 measures the concentrations of carbon dioxide, water, oxygen, and the combined concentration of carbon dioxide and water as the specific gas concentration.

[0065] The gas sensor 100 includes: a sensor element 101 having a main body 102 in the shape of a long rectangular parallelepiped; units 15, 25, 35, 18, 28, and 38 included in the sensor element 101; a heater section 70 disposed inside the sensor element 101; and a control device 95 having variable power supplies 17, 27, and 37 and a heater power supply 76, and controlling the gas sensor 100 as a whole. 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 vertical direction. Figure 2 The vertical direction is set as the horizontal direction. The main body 102 is a cuboid; therefore, as... Figure 1 and Figure 2 As shown, the outer surface of the component body 102 has six surfaces: a first surface 102a (upper surface), a second surface 102b (lower surface), a third surface 102c (left side surface), a fourth surface 102d (right side surface), a fifth surface 102e (front end surface), and a sixth surface 102f (rear end surface).

[0066] The component body 102 is a laminate formed by stacking six layers in the following order from bottom to top, as shown 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 containing an oxygen ion conductive solid electrolyte layer such as zirconium dioxide (ZrO2). Furthermore, the solid electrolyte forming these six layers is a dense and airtight solid electrolyte. The component body 102 is manufactured as follows: for example, after performing prescribed processing and printing circuit patterns on the ceramic green sheets corresponding to each layer, they are stacked, and then fired to achieve integration.

[0067] On the front end side of the sensor element 101 (element body 102), and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the first gas inlet 11, the first buffer space 12, the first diffusion rate control unit 13, and the first internal cavity 14 are formed adjacently in this order, connected from front to back. Similarly, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the second gas inlet 21, the second buffer space 22, the second diffusion rate control unit 23, and the second internal cavity 24 are formed adjacently in this order, connected from left to right. Furthermore, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the third gas inlet 31, the third buffer space 32, the third diffusion rate control unit 33, and the third internal cavity 34 are formed adjacently in this order, connected from right to left.

[0068] The first gas inlet 11 is the inlet for the gas to be measured from the outside of the sensor element 101 toward the first internal cavity 14, and in this embodiment, it is open on the fifth surface 102e. The second gas inlet 21 is the inlet for the gas to be measured from the outside of the sensor element 101 toward the second internal cavity 24, and in this embodiment, it is open on the third surface 102c. The third gas inlet 31 is the inlet for the gas to be measured from the outside of the sensor element 101 toward the third internal cavity 34, and in this embodiment, it is open on the fourth surface 102d. Therefore, in this embodiment, the first gas inlet 11, the second gas inlet 21, and the third gas inlet 31 are open on different surfaces among the first to sixth surfaces 102a to 102f.

[0069] The first to third gas inlets 11, 21, 31, the first to third buffer spaces 12, 22, 32, and the first to third internal cavities 14, 24, 34 are spaces inside the sensor element 101, which is formed by hollowing out the isolation layer 5. The upper part of the space is separated by the lower surface of the second solid electrolyte layer 6, the lower part is separated by the upper surface of the first solid electrolyte layer 4, and the side part is separated by the side of the isolation layer 5.

[0070] The first diffusion velocity control unit 13 is configured with two horizontally elongated slits (and... Figure 1 The vertical direction of the attached diagram constitutes the length direction of the opening. (For example...) Figure 1 As shown, the two slits of the first diffusion rate control unit 13 are configured as the gap between the lower surface of the second solid electrolyte layer 6 and the upper surface of the isolation layer 5, and the gap between the upper surface of the first solid electrolyte layer 4 and the lower surface of the isolation layer 5. Regarding the second diffusion rate control unit 23 and the third diffusion rate control unit 33, although not shown in the figures, they are similarly configured with two horizontally elongated slits (and...) Figure 1 The vertical direction of the attached diagram constitutes the length direction of the opening.

[0071] The first buffer space 12 is a space provided for guiding the gas to be measured, introduced from the first gas inlet 11, to the first diffusion rate control unit 13. In this embodiment, the first buffer space 12 is open on the fifth surface 102e, which becomes the first gas inlet 11. The first diffusion rate control unit 13 is a portion that applies a predetermined diffusion resistance to the gas to be measured introduced from the first buffer space 12 into the first internal cavity 14. The second buffer space 22 is a space provided for guiding the gas to be measured, introduced from the second gas inlet 21, to the second diffusion rate control unit 23. In this embodiment, the second buffer space 22 is open on the third surface 102c, which becomes the second gas inlet 21. The second diffusion rate control unit 23 is a portion that applies a predetermined diffusion resistance to the gas to be measured introduced from the second buffer space 22 into the second internal cavity 24. The third buffer space 32 is a space provided for guiding the gas to be measured, introduced from the third gas inlet 31, to the third diffusion rate control unit 33. In this embodiment, the third buffer space 32 is open on the fourth surface 102d, and this opening becomes the third gas inlet 31. The third diffusion rate control unit 33 is a part that applies a predetermined diffusion resistance to the gas to be measured that is introduced from the third buffer space 32 into the third internal cavity 34.

[0072] When the gas to be measured is introduced from the outside of the sensor element 101 into the first internal cavity 14, it rapidly enters the interior of the sensor element 101 from the first gas inlet 11 due to pressure fluctuations in the external space (in the case of exhaust gas from a car, the pressure fluctuations). This gas is not directly introduced into the first internal cavity 14, but rather its pressure fluctuations are eliminated by the first buffer space 12 and the first diffusion rate control unit 13 before it is introduced into the first internal cavity 14. Therefore, the pressure fluctuations of the gas introduced into the first internal cavity 14 are almost negligible. Similarly, the gas to be measured introduced into the sensor element 101 from the second gas inlet 21 is introduced into the second internal cavity 24 after its pressure fluctuations are eliminated by the second buffer space 22 and the second diffusion rate control unit 23. The gas to be measured, introduced into the sensor element 101 from the third gas inlet 31, is introduced into the third internal cavity 34 after pressure fluctuations are eliminated by passing through the third buffer space 32 and the third diffusion rate control unit 33.

[0073] The portion extending from the outside of sensor element 101 to the first internal cavity 14 (here, the first gas inlet 11, the first buffer space 12, and the first diffusion rate control unit 13) is also referred to as the first measured gas flow section. The portion extending from the outside of sensor element 101 to the second internal cavity 24 (here, the second gas inlet 21, the second buffer space 22, and the second diffusion rate control unit 23) is also referred to as the second measured gas flow section. The portion extending from the outside of sensor element 101 to the third internal cavity 34 (here, the third gas inlet 31, the third buffer space 32, and the third diffusion rate control unit 33) is also referred to as the third measured gas flow section. The measured gas can travel from the outside of sensor element 101 through the first measured gas flow section to the first internal cavity 14. The measured gas can travel from the outside of sensor element 101 through the second measured gas flow section to the second internal cavity 24. The measured gas can travel from the outside of sensor element 101 through the third measured gas flow section to the third internal cavity 34. like Figure 1 and Figure 2 As shown, the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 are independently disposed inside the element body 102 without being interconnected. More specifically, the first gas to be measured flow section, the second gas to be measured flow section, and the third gas to be measured flow section are not interconnected, and there is no gas flow path allowing the gas to be measured to flow between at least two of the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 inside the element body 102. Therefore, the gas to be measured reaches the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 from outside the sensor element 101 via separate independent paths (the first to third gas to be measured flow sections).

[0074] 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 disposed from the sixth surface 102f of the sensor element 101 toward the inward side. The reference gas inlet space 43 is disposed between the upper surface of the third substrate layer 3 and the lower surface of the insulating layer 5, and is located at a position separated by the side of the first solid electrolyte layer 4. The reference gas inlet space 43 is open at the sixth surface 102f 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 it to the reference electrode 42. In this embodiment, the reference gas is atmospheric gas.

[0075] 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.

[0076] 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. In addition, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 14, the second internal cavity 24 and the third internal cavity 34.

[0077] The first internal cavity 14 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured, which is introduced through the first diffusion rate control unit 13. This oxygen partial pressure is adjusted by operating the first measuring pump unit 15. The second internal cavity 24 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured, which is introduced through the second diffusion rate control unit 23. This oxygen partial pressure is adjusted by operating the second measuring pump unit 25. The third internal cavity 34 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured, which is introduced through the third diffusion rate control unit 33. This oxygen partial pressure is adjusted by operating the third measuring pump unit 35.

[0078] The first measuring pump unit 15 is an electrochemical pump unit consisting of a first measuring electrode 16, an outer pump electrode 40, a second solid electrolyte layer 6 forming the current path between these electrodes, an isolation layer 5, and the first solid electrolyte layer 4. The first measuring electrode 16 is disposed in the first internal cavity 14 and is arranged such that it covers most of the area of ​​the upper surface of the first solid electrolyte layer 4 facing the first internal cavity 14 (i.e., the area constituting the bottom surface of the first internal cavity 14). The outer pump electrode 40 is an electrode disposed on the first surface 102a of the outer surface of the element body 102. The outer pump electrode 40 is disposed in a form that exposes to the outside of the sensor element 101; however, it can be covered by a porous material, i.e., a protective layer, through which the measured gas can pass.

[0079] In the first measuring pump unit 15, a desired voltage Vp1 is applied between the first measuring electrode 16 and the outer pump electrode 40, so that the pump current Ip1 flows between the first measuring electrode 16 and the outer pump electrode 40 in a positive or negative direction, thereby enabling oxygen in the first internal cavity 14 to be drawn out to the external space or oxygen in the external space to be drawn into the first internal cavity 14.

[0080] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 14, an electrochemical sensor unit, namely the first sensor unit 18, is constructed by the first measuring electrode 16, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42.

[0081] The oxygen concentration (oxygen partial pressure) within the first internal cavity 14 is determined by measuring the electromotive force (voltage V1) between the first measuring electrode 16 and the reference electrode 42 in the first sensor unit 18. Furthermore, the voltage Vp1 of the variable power supply 17 is controlled by feedback to bring the voltage V1 to a target value, thereby controlling the pump current Ip1. This adjusts the oxygen concentration within the first internal cavity 14.

[0082] The second measuring pump unit 25 is an electrochemical pump unit consisting of a second measuring electrode 26, an outer pump electrode 40, a second solid electrolyte layer 6 that forms the current path between these electrodes, an isolation layer 5, and a first solid electrolyte layer 4. The second measuring electrode 26 is disposed in the second internal cavity 24 and is disposed in such a way that it covers most of the area of ​​the upper surface of the first solid electrolyte layer 4 facing the second internal cavity 24 (i.e., the area constituting the bottom surface of the second internal cavity 24).

[0083] In the second measuring pump unit 25, a desired voltage Vp2 is applied between the second measuring electrode 26 and the outer pump electrode 40, so that the pump current Ip2 flows between the second measuring electrode 26 and the outer pump electrode 40 in either the positive or negative direction, which can draw oxygen out of the second internal cavity 24 to the external space or draw oxygen from the external space into the second internal cavity 24.

[0084] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the second internal cavity 24, an electrochemical sensor unit, namely the second sensor unit 28, is formed by the second measuring electrode 26, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42.

[0085] The oxygen concentration (oxygen partial pressure) within the second internal cavity 24 is determined by measuring the electromotive force (voltage V2) between the second measuring electrode 26 and the reference electrode 42 in the second sensor unit 28. Furthermore, the voltage Vp2 of the variable power supply 27 is controlled by feedback to bring the voltage V2 to a target value, thereby controlling the pump current Ip2. This adjusts the oxygen concentration within the second internal cavity 24.

[0086] The third measuring pump unit 35 is an electrochemical pump unit consisting of a third measuring electrode 36, an outer pump electrode 40, a second solid electrolyte layer 6 that forms the current path between these electrodes, an isolation layer 5, and a first solid electrolyte layer 4. The third measuring electrode 36 is disposed in the third internal cavity 34 and is disposed in such a way that it covers most of the area of ​​the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 34 (i.e., the area constituting the bottom surface of the third internal cavity 34).

[0087] In the third measuring pump unit 35, a desired voltage Vp3 is applied between the third measuring electrode 36 and the outer pump electrode 40, so that the pump current Ip3 flows between the third measuring electrode 36 and the outer pump electrode 40 in either the positive or negative direction, which can draw oxygen out of the third internal cavity 34 to the external space or draw oxygen from the external space into the third internal cavity 34.

[0088] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the third internal cavity 34, an electrochemical sensor unit, namely the third sensor unit 38, is formed by the third measuring electrode 36, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42.

[0089] The oxygen concentration (oxygen partial pressure) within the third internal cavity 34 is determined by measuring the electromotive force (voltage V3) between the third measuring electrode 36 and the reference electrode 42 in the third sensor unit 38. Furthermore, the voltage Vp3 of the variable power supply 37 is controlled by feedback to bring the voltage V3 to a target value, thereby controlling the pump current Ip3. This adjusts the oxygen concentration within the third internal cavity 34.

[0090] Here, the electrodes 16, 26, 36, 40, and 42 will be described. The first measuring electrode 16, the second measuring electrode 26, and the third measuring electrode 36 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 40 and the reference electrode 42 also contain the first noble metal. The second measuring electrode 26 preferably contains, in addition to the first noble metal, a second noble metal that inhibits the catalytic activity of the first noble metal against carbon dioxide. By containing the second noble metal, the reducing ability of the second measuring electrode 26 against carbon dioxide can be weakened. Examples of the second noble metal include Au. Each electrode 16, 26, 36, 40, and 42 is preferably a cermet containing a noble metal and an oxide (e.g., ZrO2) with oxygen ion conductivity. Each electrode 16, 26, 36, 40, and 42 is preferably a porous body. In this embodiment, each electrode 16, 26, 36, 40, and 42 is a porous metal-ceramic electrode made of Pt and ZrO2 without the second noble metal.

[0091] When the second measuring electrode 26 contains a second noble metal, the proportion R2 of the second measuring electrode 26 calculated by the following formula (1) is preferably 2% or more. If the proportion R2 of the second measuring electrode 26 is 2% or more, the reducing ability of the second measuring electrode 26 to carbon dioxide can be reduced more reliably. The proportion R2 of the second measuring electrode 26 can be 5% or more. The proportion R2 of the second measuring electrode 26 can be 10% or less, or 5% or less. Similar to the proportion R2, the proportion of the second noble metal contained in the first measuring electrode 16 is set as proportion R1, and the proportion of the second noble metal contained in the third measuring electrode 36 is set as proportion R3. Proportions R1 and R3 are calculated in the same way as the following formula (1). Proportions R1 to R3 are values ​​obtained by measuring using an electron probe microanalyzer (EPMA).

[0092] R2=S2 / (S1+S2)×100 (1)

[0093] in,

[0094] S1: Mass percentage of the first precious metal [wt%]

[0095] S2: Mass percentage of the second precious metal [wt%]

[0096] 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.

[0097] The heater connector electrode 71 is an electrode formed in contact with the lower surface of the first substrate layer 1. This is achieved by connecting the heater connector electrode 71 to the heater power supply 76 (see reference 76). Figure 3 The connection allows power to be supplied from the heater power supply 76 to the heater section 70.

[0098] The heater 72 is a resistive element formed by being sandwiched between the second substrate layer 2 and the third substrate layer 3. The heater 72 is connected to the heater connector electrode 71 via the through hole 73, and is heated by the heater power supply 76 through the heater connector electrode 71 to heat and maintain the temperature of the solid electrolyte forming the sensor element 101.

[0099] In addition, the heater 72 is embedded in the entire region containing the first internal cavity 14, the second internal cavity 24 and the third internal cavity 34, which can adjust the sensor element 101 as a whole to the temperature of the above-mentioned solid electrolyte activation.

[0100] The heater insulation layer 74 is an insulation layer formed on the upper and lower surfaces of the heater 72 by means of an insulator such as alumina. 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 between the third substrate layer 3 and the heater 72.

[0101] The pressure relief hole 75 is configured to penetrate the third substrate layer 3 and the reference gas inlet layer 48 and communicate with the reference gas inlet space 43. It is formed for the purpose of mitigating the increase in internal pressure that accompanies the temperature rise in the heater insulation layer 74.

[0102] like Figure 3As shown, the control device 95 includes: the aforementioned variable power supplies 17, 27, and 37, the aforementioned heater power supply 76, and a control unit 96. The control unit 96 is a microprocessor equipped with a CPU 97 and a storage unit 98. The storage unit 98 is a non-volatile memory capable of information rewriting, for example, capable of storing various programs and various data. The control unit 96 is input with voltage V1 of the first sensor unit 18, voltage V2 of the second sensor unit 28, voltage V3 of the third sensor unit 38, pump current Ip1 flowing through the first measuring pump unit 15, pump current Ip2 flowing through the second measuring pump unit 25, and pump current Ip3 flowing through the third measuring pump unit 35. Furthermore, the control unit 96 controls the voltages Vp1, Vp2, and Vp3 output by the variable power supplies 17, 27, and 37 by outputting control signals to them, thereby controlling the first measuring pump unit 15, the second measuring pump unit 25, and the third measuring pump unit 35. The control unit 96 controls the power supplied by the heater power supply 76 to the heater 72 by outputting a control signal to the heater power supply 76. The storage unit 98 also stores target values ​​V1*, V2*, V3*, etc., which will be described later. The CPU 97 of the control unit 96 controls each pump unit 15, 25, 35 with reference to these target values ​​V1*, V2*, V3*.

[0103] The control unit 96 performs a first measuring pump control process, that is, it controls the first measuring pump unit 15 to draw oxygen from the area around the first measuring electrode 16 to the area around the outer pump electrode 40. Specifically, the control unit 96 performs feedback control on the voltage Vp1 of the variable power supply 17 to make the voltage V1 reach a target value V1*, thereby controlling the first measuring pump unit 15. The target value V1* is defined as a value in which the oxygen concentration in the first internal cavity 14 reaches a sufficiently low level that substantially all of the two or more oxide gases in the gas to be measured, i.e., the reduction target gases, are water and carbon dioxide. By performing this first measuring pump control process, in the first internal cavity 14, water in the gas to be measured is reduced to produce hydrogen and oxygen, and carbon dioxide in the gas to be measured is reduced to produce carbon monoxide and oxygen. Furthermore, the oxygen generated during reduction, along with the oxygen already present in the gas being measured before reduction, is drawn from around the first measuring electrode 16 to around the outer pump electrode 40 due to the pump current Ip1 flowing through the first measuring pump unit 15. Therefore, the pump current Ip1 flowing through the first measuring pump unit 15 due to the first measuring pump control process is correlated with the total concentration of the target gas for reduction and oxygen in the gas being measured.

[0104] The control unit 96 performs a second measurement pump control process, that is, it controls the second measurement pump unit 25 to draw oxygen from the area around the second measurement electrode 26 to the area around the outer pump electrode 40. Specifically, the control unit 96 performs feedback control on the voltage Vp2 of the variable power supply 27 to make the voltage V2 reach a target value V2*, thereby controlling the second measurement pump unit 25. The target value V2* is defined as a value in which the oxygen concentration in the second internal cavity 24 reaches a predetermined low concentration that suppresses the reduction of a portion of the oxide gas, i.e., the first gas (here, carbon dioxide), in the gas being measured compared to the first measurement pump control process. By performing this second measurement pump control process, in the second internal cavity 24, the reduction target gas (here, water) other than the first gas in the gas being measured is reduced to produce hydrogen and oxygen, while the reduction of the first gas (here, carbon dioxide) in the gas being measured is suppressed. Furthermore, the oxygen produced by water reduction and the oxygen already present in the gas being measured before reduction are drawn from around the second measuring electrode 26 to around the outer pump electrode 40 due to the pump current Ip2 flowing through the second measuring pump unit 25. Therefore, the pump current Ip2 flowing through the second measuring pump unit 25 due to the second measuring pump control process is correlated with the total concentration of water (i.e., the gas to be reduced other than the first gas) and oxygen in the gas being measured.

[0105] The control unit 96 performs a third measuring pump control process, that is, it controls the third measuring pump unit 35 to draw oxygen from the area around the third measuring electrode 36 to the area around the outer pump electrode 40. Specifically, the control unit 96 performs feedback control on the voltage Vp3 of the variable power supply 37 to make the voltage V3 reach a target value V3*, thereby controlling the third measuring pump unit 35. The target value V3* is defined as: the oxygen concentration in the third internal cavity 34 reaches a predetermined low concentration that, compared with the second measuring pump control process, suppresses the reduction of one or more oxide gases other than the first gas in the target gas of the measured gas, namely the second gas (here, water). By performing this third measuring pump control process, the reduction of the first gas (here, carbon dioxide) and the second gas (here, water) in the target gas of the measured gas is suppressed in the third internal cavity 34. If there are oxide gases other than the first gas and the second gas in the target gas, the oxide gases are reduced to produce oxygen. Furthermore, the oxygen generated by the reduction and the oxygen already present in the measured gas before reduction are drawn from around the third measuring electrode 36 to around the outer pump electrode 40 by the pump current Ip3 flowing through the third measuring pump unit 35. Therefore, the pump current Ip3 flowing through the third measuring pump unit 35 due to the third measuring pump control process is correlated with the total concentration of the reduction target gas other than the first and second gases and oxygen in the measured gas. It should be noted that in this embodiment, as described above, the reduction target gases are water (the second gas) and carbon dioxide (the first gas), therefore, there is no "reduction target gas other than the first and second gases in the measured gas". Therefore, in this embodiment, the pump current Ip3 flowing through the third measuring pump unit 35 due to the third measuring pump control process is correlated with the oxygen concentration in the measured gas.

[0106] Furthermore, the control unit 96 performs a first concentration measurement process, namely, based on the pump current Ip1 flowing through the first measuring pump unit 15 due to the first measuring pump control process and the pump current Ip2 flowing through the second measuring pump unit 25 due to the second measuring pump control process, the concentration of the first gas (here, carbon dioxide) in the gas to be measured, i.e., the first concentration (here, carbon dioxide concentration), is measured. As described above, the pump current Ip1 flowing through the first measuring pump unit 15 due to the first measuring pump control process is correlated with the total concentration of the reducing target gas and oxygen in the gas to be measured. Additionally, the pump current Ip2 flowing through the second measuring pump unit 25 due to the second measuring pump control process is correlated with the total concentration of water (i.e., the reducing target gas other than the first gas) and oxygen in the gas to be measured. Therefore, based on these pump currents Ip1 and Ip2, the concentration of the first gas (here, carbon dioxide), i.e., the first concentration (here, carbon dioxide concentration), in the gas to be measured can be measured. For example, the control unit 96 can measure the carbon dioxide concentration based on the difference between the pump current Ip1 and the pump current Ip2. In this case, a first correspondence between the difference between the pump current Ip1 and the pump current Ip2 and the carbon dioxide concentration can be pre-stored in the storage unit 98. The first correspondence can be, for example, a linear function, a mapping, etc. This first correspondence can be pre-solved using experiments, analysis, etc. Furthermore, the control unit 96 can derive the difference between the pump current Ip1 and the pump current Ip2, and based on the derived value and the first correspondence stored in the storage unit 98, derive (measure) the carbon dioxide concentration.

[0107] The control unit 96 performs a second concentration measurement process, namely, based on the pump current Ip2 flowing through the second measuring pump unit 25 due to the second measuring pump control process and the pump current Ip3 flowing through the third measuring pump unit 35 due to the third measuring pump control process, the concentration of the second gas (here, water) in the gas to be measured, i.e., the second concentration (here, water concentration), is measured. As described above, the pump current Ip2 flowing through the second measuring pump unit 25 due to the second measuring pump control process is correlated with the total concentration of water (i.e., the reducing gas other than the first gas) and oxygen in the gas to be measured. In addition, the pump current Ip3 flowing through the third measuring pump unit 35 due to the third measuring pump control process is correlated with the total concentration of the first gas and the reducing gas other than the second gas, and oxygen in the gas to be measured (here, the oxygen concentration in the gas to be measured). Therefore, based on these pump currents Ip2 and Ip3, the concentration of the second gas (here, water) in the gas to be measured, i.e., the second concentration (here, water concentration), can be measured. For example, the control unit 96 can measure the water concentration based on the difference between the pump current Ip2 and the pump current Ip3. In this case, a second correspondence between the difference between the pump current Ip2 and the pump current Ip3 and the water concentration can be pre-stored in the storage unit 98. The second correspondence can be, for example, a linear function, a mapping, etc. This second correspondence can be solved in advance using experiments, analysis, etc. Furthermore, the control unit 96 can derive the difference between the pump current Ip2 and the pump current Ip3, and based on the derived value and the second correspondence stored in the storage unit 98, derive (measure) the water concentration.

[0108] The control unit 96 performs a third concentration measurement process, which involves measuring the total concentration of the target gas (excluding the first and second gases) and oxygen in the gas being measured, based on the pump current Ip3 flowing through the third measurement pump unit 35 due to the third measurement pump control process. As described above, in this embodiment, the target gas contains only the first gas (carbon dioxide) and the second gas (water), and no other oxide gases are present. Therefore, the oxygen concentration in the gas being measured is the third concentration. Furthermore, as described above, the pump current Ip3 flowing through the third measurement pump unit 35 due to the third measurement pump control process is correlated with the oxygen concentration in the gas being measured. Therefore, based on this pump current Ip3, the third concentration (here, the oxygen concentration) in the gas being measured can be measured. In this case, the third correspondence between the pump current Ip3 and the oxygen concentration can be pre-stored in the storage unit 98. The third correspondence can be, for example, a linear function, a mapping, etc. This third correspondence can be pre-solved using experiments, analysis, etc. Furthermore, the control unit 96 can derive (measure) the oxygen concentration based on the pump current Ip3 and the third correspondence stored in the storage unit 98.

[0109] The control unit 96 performs a fourth concentration measurement process, namely, based on the pump current Ip1 flowing through the first measuring pump unit 15 due to the first measuring pump control process and the pump current Ip3 flowing through the third measuring pump unit 35 due to the third measuring pump control process, the combined concentration of the first gas and the second gas in the gas to be measured, i.e., the fourth concentration (here, the combined concentration of carbon dioxide and water), is measured. As described above, the pump current Ip1 flowing through the first measuring pump unit 15 due to the first measuring pump control process is correlated with the combined concentration of the reducing target gas and oxygen in the gas to be measured. In addition, the pump current Ip3 flowing through the third measuring pump unit 35 due to the third measuring pump control process is correlated with the combined concentration of the reducing target gas other than the first and second gases and oxygen in the gas to be measured (here, the oxygen concentration in the gas to be measured). Therefore, based on these pump currents Ip1 and Ip3, the combined concentration of the first gas (here, carbon dioxide) and the second gas (here, water) in the gas to be measured, i.e., the fourth concentration, can be measured. For example, the control unit 96 can measure the fourth concentration based on the difference between pump current Ip1 and pump current Ip3. In this case, the fourth correspondence between the difference between pump current Ip1 and pump current Ip3 and the fourth concentration can be pre-stored in the storage unit 98. The fourth correspondence can be, for example, a linear function, a mapping, etc. This fourth correspondence can be solved in advance using experiments, analysis, etc. Furthermore, the control unit 96 can derive the difference between pump current Ip1 and pump current Ip3, and based on the derived value and the fourth correspondence stored in the storage unit 98, derive (measure) the water concentration.

[0110] 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 temperature of the heater 72 can be expressed as a linear function of the resistance value of the heater 72. Therefore, in the heater control processing, the control unit 96 calculates the resistance value of the heater 72 in the form that can be considered as the temperature of the heater 72 (a value that can be converted into temperature), and performs feedback control on the heater power supply 76 so 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 powers on the heater 72, it changes the value of the voltage applied to the heater 72 based on, for example, a control signal from the control unit 96, thereby adjusting the power supplied to the heater 72.

[0111] It should be explained, including Figure 2The control device 95, including the variable power supplies 17, 27, 37 and heater power supply 76 shown, is actually controlled by leads (not shown) 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.

[0112] Here, an example of the aforementioned target values ​​V1*, V2*, and V3* will be explained. Figure 4 This is an explanatory diagram showing an example of the relationship (V-I characteristic) between the target voltage values ​​(V1*, V2*, V3*) and the pump currents (Ip1, Ip2, Ip3) in the pump units (first to third measuring pump units 15, 25, 35). Figure 4 Curve A, a thick solid line, represents the relationship between the target voltage and pump current in the pump unit when the base gas is nitrogen and a model gas containing oxygen, water, and carbon dioxide is used as the measured gas. Curve B, a thick dashed line, represents the relationship between the target voltage and pump current in the pump unit when the base gas is nitrogen and a model gas containing oxygen but not water or carbon dioxide is used as the measured gas. Curve C, a thin solid line, represents the relationship between the target voltage and pump current in the pump unit when the base gas is nitrogen and a model gas containing water but not oxygen or carbon dioxide is used as the measured gas. Curve D, a thin dashed line, represents the relationship between the target voltage and pump current in the pump unit when the base gas is nitrogen and a model gas containing carbon dioxide but not oxygen or water is used as the measured gas. Figure 4 The diagram shows the curves for a gas sensor 100, for example, by making the diffusion resistance of the first to third gas flow sections of the gas being measured the same, and by making the first to third measuring electrodes 16, 26, and 36 all electrodes of the same material, so that the V-I characteristics of the first to third measuring pump units 15, 25, and 35 are the same. Therefore, Figure 4 And then Figure 5 In the description, sometimes the first to third measuring pump units 15, 25, and 35 are not distinguished, and are simply recorded as "pump unit"; the target values ​​V1*, V2*, and V3* are not distinguished, and are simply recorded as "voltage target value"; the pump currents Ip1, Ip2, and Ip3 are not distinguished, and are simply recorded as "pump current"; the first to third internal cavities 14, 24, and 34 are not distinguished, and are simply recorded as "internal cavity"; the first to third measuring electrodes 16, 26, and 36 are not distinguished, and are simply recorded as "inner electrode"; the proportional electrodes R1, R2, and R3 are not distinguished, and are simply recorded as "proportional R". Additionally, Figure 4 The V-I characteristics are shown when the inner electrode does not contain a second noble metal.

[0113] like Figure 4As shown, the following trend is confirmed in curves A through D: the larger the absolute value of the target voltage, the larger the pump current. It should be noted that the pump unit is controlled in a way that the target value of the target voltage is larger, so that the target value of the oxygen concentration in the internal cavity is lower than the oxygen concentration of the reference gas around the reference electrode 42 (i.e., the way that more oxygen is drawn out of the internal cavity).

[0114] Figure 4 In curve D, in the region where the target voltage is above 200mV and below 700mV, the pump current is a roughly constant value close to 0. In the region where the target voltage exceeds 700mV, the pump current increases with the increase of the target voltage. Furthermore, in the region where the target voltage is above 1250mV and below 1400mV, the pump current is a roughly constant value. That is, the pump current reaches its limiting current. This region is called the flat region. From curve D, it can be seen that in the region where the target voltage exceeds 700mV, carbon dioxide is reduced, and the oxygen produced by the reduction is drawn out by the pump current. Regarding carbon dioxide, the region where the target voltage is above 1250mV and below 1400mV is a flat region, where the pump current becomes a value correlated with the carbon dioxide concentration in the internal cavity. Similarly, from curve C, it can be seen that regarding water, the region where the target voltage is above 1000mV and below 1400mV is a flat region, where the pump current becomes a value correlated with the water concentration in the internal cavity. Furthermore, curve B shows that for oxygen, the region with a target voltage above 200mV and below 1400mV is considered a flat region. In this region, the pump current becomes a value correlated with the oxygen concentration in the internal cavity. Curves B through D show that the lower limits of the target voltage values ​​for the flat regions of carbon dioxide, water, and oxygen are different. Regarding the lower limits of the target voltage values, oxygen has the lowest (200mV), water the second lowest (1000mV), and carbon dioxide the highest (1250mV). Moreover, compared to water, carbon dioxide has a higher lower limit of the target voltage value for the flat region of its appearance, indicating that carbon dioxide is less easily reduced than water.

[0115] Furthermore, it can be seen that: the V-I characteristics shown are obtained using a measured gas containing oxygen, water, and carbon dioxide. Figure 4In curve A, three flat regions appear corresponding to the flat regions of curves B through D. In this embodiment, the target voltage values ​​(V1*, V2*, V3*) are made different from each other, and the absolute value relationship is set as |V3*| < |V2*| < |V1*|, so that the target values ​​V1*, V2*, and V3* respectively reach the voltage target values ​​corresponding to the three flat regions of curve A. This allows the pump currents Ip1 through Ip3 to correspond to different gas concentrations. Specifically, the target value V1* is set as a specified value of 1250mV or more and 1400mV or less, corresponding to the region with the highest voltage target value among the three flat regions of curve A. In this region, as can be seen from curves B through D, carbon dioxide, water, and oxygen all reach flat regions, allowing for the absorption of oxygen and the reduction of water and carbon dioxide from the measured gas. Therefore, by performing the first measurement pump control process based on the target value V1* set in this way, the pump current Ip1 is made to reach a relatively large value, and the pump current Ip1 becomes a value correlated with the total concentration of water, carbon dioxide, and oxygen in the measured gas. The target value V2* is set as a specified value of 1000mV or more and 1200mV or less, corresponding to the second highest voltage target value among the three flat regions of curve A. As can be seen from curves B to D, this region is a flat region for water and oxygen, but it deviates from the flat region for carbon dioxide (the voltage target value is lower than that of the flat region for carbon dioxide). In this region, oxygen is absorbed and water is reduced in the measured gas, but the reduction of carbon dioxide is suppressed. Therefore, by performing the second measurement pump control process based on the target value V2* set in this way, the pump current Ip2 is made to reach a value that is smaller than the pump current Ip1 by an amount corresponding to the amount of carbon dioxide reduction suppressed, and the pump current Ip2 becomes a value correlated with the total concentration of water and oxygen in the measured gas. The target value V3* is set as a specified value between 200mV and 700mV, corresponding to the region with the lowest voltage target value among the three flat regions of curve A. As can be seen from curves B to D, this region is a flat region for oxygen, but it deviates from the flat regions for water and carbon dioxide (regions where the voltage target value is lower than that for water and carbon dioxide). Oxygen is extracted from the gas being measured in this region; however, the reduction of water and carbon dioxide is suppressed. Therefore, by performing third-stage pump control based on the target value V3* set in this way, the pump current Ip3 is made to be a value that is smaller than the pump current Ip2 by an amount corresponding to the amount of water and carbon dioxide reduction suppressed. Thus, the pump current Ip3 becomes a value correlated with the oxygen concentration in the gas being measured.

[0116] As mentioned above, even when the gas being measured contains oxygen, water, and carbon dioxide simultaneously ( Figure 4Curve A shows that by varying the target voltage values, partial or complete reduction of the target gases (here, water and carbon dioxide) can be selectively suppressed. More specifically, as the absolute value of the target voltage decreases, reduction is sequentially suppressed, starting with gases in the target gases (here, water and carbon dioxide) that are less easily reduced (here, carbon dioxide reduction is suppressed first, followed by water reduction). Utilizing this phenomenon, the relationship between pump current and gas concentration can be adjusted according to the target voltage value. Furthermore, in this embodiment, by setting the target values ​​V1*, V2*, and V3* to the aforementioned values, as described above, the pump current Ip1 corresponds to the total concentration of water, carbon dioxide, and oxygen, the pump current Ip2 corresponds to the total concentration of water and oxygen, and the pump current Ip3 corresponds to the oxygen concentration, thereby enabling the measurement of the first to fourth concentrations.

[0117] Next, the V-I characteristics when the inner electrode contains a second noble metal will be explained. Figure 5 The V-I characteristics of the pump unit are shown when the inner electrode contains a second noble metal in a manner where the proportion R is 2% or more and less than 10%. Figure 5 The measured gas and curves A to D are... Figure 4 The measured gases in curves A through D are the same. Figure 4 curve D and Figure 5 Comparing curve D and curve D, the similarity is that if the target voltage value is above 700mV, the pump current increases as the target voltage value increases (pump current rises). However, Figure 5 curve D and Figure 4 Compared to curve D, in the region where the target voltage is above 900mV and below 1100mV, the pump current does not rise significantly. However, when the target voltage exceeds 1100mV, the pump current begins to increase. Furthermore, Figure 5 curve D and Figure 4 Similarly, curve D shows a flat region where the voltage target value is above 1250mV and below 1400mV. However, the rise in pump current before reaching this flat region is greater than... Figure 4 The curve D is small. These results confirm that by including a second noble metal in the inner electrode, the reduction of carbon dioxide around the inner electrode is suppressed. In contrast, Figure 5 Curves B and C relative to Figure 4 For curves B and C, there was almost no change. That is, it was confirmed that even when the inner electrode contained a second noble metal, the reduction of water around the inner electrode was hardly inhibited, and the oxygen extraction by the pump unit was hardly affected. From the above... Figure 4 and Figure 5 The comparison results confirmed that by including a second noble metal in the inner electrode, the reduction of carbon dioxide was selectively suppressed.

[0118] And even Figure 4 curve A and Figure 5 A comparison with curve A also confirms that this is due to the selective inhibition of the reduction of carbon dioxide mentioned above. Figure 4 curve D and Figure 5 The trend resulting from the difference in curve D. Specifically, Figure 4 The pump current of curve A is not only affected by the voltage target value in the region above 1000mV and below 1200mV, but also... Figure 4 The flat region of curve C is also affected by... Figure 4 The curve D is affected by the increase in pump current (i.e., the reduction of carbon dioxide), and therefore rises slightly to the right. In contrast, Figure 5 The pump current of curve A is as described above in the region where the voltage target value is above 1000mV and below 1100mV. Figure 5 The rise in pump current on curve D is suppressed, therefore, the phenomenon appears more strongly. Figure 5 The shapes of the flat regions of curves B and C, and Figure 4 Compared to curve A, the pump current curve is flatter. That is, Figure 5 The pump current of curve A is in the region where the voltage target value is above 1000mV and below 1100mV. Figure 4 The influence of the pump current originating from carbon dioxide reduction is suppressed compared to curve A. Therefore, when the second measuring electrode 26 contains a second noble metal, as long as the target value V2* is equal to... Figure 5 The value corresponding to the second highest voltage target value in the three flat regions of curve A is set to a specified value of 1000mV or higher and 1100mV or lower. Accordingly, the pump current Ip2 is less affected by the carbon dioxide concentration in the gas being measured, and therefore, the pump current Ip2 corresponds more accurately to the combined concentration of water and oxygen. Thus, when the carbon dioxide concentration is measured based on the difference between pump current Ip1 and pump current Ip2, this difference corresponds well to the carbon dioxide concentration. In this way, by including a second noble metal in the second measuring electrode 26, the measurement accuracy of the first concentration measurement process, i.e., the measurement accuracy of carbon dioxide concentration based on pump current Ip1 and pump current Ip2, is improved. The second measuring electrode 26 preferably contains a second noble metal for the reasons stated above.

[0119] It should be noted that, regarding the first measuring electrode 16, as mentioned above, it only needs to contain the first noble metal; it may or may not contain a second noble metal. If the first measuring electrode 16 contains a second noble metal, according to... Figure 4 curve D and Figure 5Comparison of curve D shows that in the region where the target voltage value is above 1250mV and below 1400mV, although there is a trend of decreasing pump current value due to carbon dioxide reduction, a flat region for carbon dioxide also appears. Therefore, if the target voltage value V1* is set to a specified value of above 1250mV and below 1400mV, the pump current Ip1 reaches a value that is correlated with the combined concentration of water, carbon dioxide, and oxygen in the measured gas. Therefore, even if the first measuring electrode 16 contains a second noble metal, the carbon dioxide concentration can be measured based on the pump current Ip1 and the pump current Ip2. It should be noted that when the first measuring electrode 16 contains a second noble metal, the proportion R1 of the second noble metal in the first measuring electrode 16 can be 2% or more, or 5% or more. The proportion R1 can be 10% or less, or 5% or less. The proportion R1 can be a value less than or equal to the proportion R2.

[0120] Regarding the third measuring electrode 36, a voltage target value (V3*) is used such that carbon dioxide is almost not reduced. Therefore, as mentioned above, it is sufficient to contain only the first noble metal; a second noble metal may or may not be present. Even if the third measuring electrode 36 contains a second noble metal, the target value V3* is also set to... Figure 5 The value corresponding to the region with the lowest voltage target value among the three flat regions of curve A, and... Figure 4 Similarly, a specified value of 200mV or higher and 700mV or lower is sufficient. It should be noted that if the third measuring electrode 36 contains a second noble metal, the proportion R3 of the third measuring electrode 36 can be 2% or higher, or 5% or higher. The proportion R3 can be 10% or lower, or 5% or lower. The proportion R3 can be a value lower than or equal to the proportion R2.

[0121] Figure 4 and Figure 5 Taking the V-I characteristics and target values ​​V1*, V2*, and V3* as an example, when, for example, the diffusion resistance values ​​of the first to third measured gas flow sections change... Figure 4 The target voltage values ​​appearing in the three flat regions of curve A sometimes vary. In this case, similarly, the target values ​​V1*, V2*, and V3* can be determined based on the V-I characteristics of the first to third measuring pump units 15, 25, and 35. However, the diffusion resistance values ​​of the first to third measured gas flow sections are preferably close to each other or the same. For example, Figure 2In this configuration, the first buffer space 12 is shorter along the gas flow direction than the second buffer space 22 and the third buffer space 32, and its length (i.e., width) perpendicular to the gas flow direction is larger. Therefore, the diffusion resistance of the first buffer space 12 is smaller than that of the second buffer space 22 and the third buffer space 32. Even so, by, for example, making the diffusion resistance of the first diffusion rate control unit 13 higher than that of the second diffusion rate control unit 23 and the third diffusion rate control unit 33 (for example, by reducing the cross-sectional area of ​​the slit in the first diffusion rate control unit 13), it is possible to make the diffusion resistance values ​​of the first to third gas flow sections being measured close to or the same.

[0122] It should be explained that, for example Figure 2 As shown, in this embodiment, the top-view areas of the first to third measuring electrodes 16, 26, and 36 are different from each other, with the first measuring electrode 16 having the largest area, the second measuring electrode 26 having the second largest area, and the third measuring electrode 36 having the smallest area. This corresponds to the fact that, as described above, the magnitudes of the pump currents flowing due to the first to third measuring pump control processing satisfy Ip1 > Ip2 > Ip3. Since a larger inner electrode area results in a higher oxygen extraction capacity of the pump unit, it is preferable to have a pump unit with a larger pump current flowing through it, thereby increasing the area of ​​the inner electrode.

[0123] The following describes an example of using the gas sensor 100 configured in this way. When the gas sensor 100 is installed in a pipe or similar conduit through which the gas to be measured flows, the control unit 96 first performs the aforementioned heater control process 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 is near the target temperature), the control unit 96 begins the aforementioned first to third measuring pump control processes. While continuously performing the first to third measuring pump control processes, the control unit 96 obtains (measures) the pump currents Ip1 to Ip3, and based on the obtained values, performs the first to fourth concentration measurement processes to measure the concentration of a specific gas in the gas being measured (here, the first to fourth concentrations, i.e., carbon dioxide concentration, water concentration, oxygen concentration, and the combined concentration of carbon dioxide and water).

[0124] 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, the element body 102 corresponds to the element body, the first internal cavity 14 corresponds to the first chamber, the second internal cavity 24 corresponds to the second chamber, the third internal cavity 34 corresponds to the third chamber, the first measuring electrode 16 corresponds to the first inner electrode, the first measuring pump unit 15 corresponds to the first pump unit, the second measuring electrode 26 corresponds to the second inner electrode, the second measuring pump unit 25 corresponds to the second pump unit, the third measuring electrode 36 corresponds to the third inner electrode, the third measuring pump unit 35 corresponds to the third pump unit, the outer pump electrode 40 corresponds to the first outer electrode, the second outer electrode, and the third outer electrode, the control device 95 corresponds to the control device, the first measuring pump control processing corresponds to the first pump unit control processing, the second measuring pump control processing corresponds to the second pump unit control processing, the third measuring pump control processing corresponds to the third pump unit control processing, the pump current Ip1 corresponds to the first pump current, the pump current Ip2 corresponds to the second pump current, and the pump current Ip3 corresponds to the third pump current. Additionally, voltage V1 is equivalent to the first voltage, and target value V1* is equivalent to the target value of the first voltage; voltage V2 is equivalent to the second voltage, and target value V2* is equivalent to the target value of the second voltage; voltage V3 is equivalent to the third voltage, and target value V3* is equivalent to the target value of the third voltage. First gas inlet 11 is equivalent to the first inlet, second gas inlet 21 is equivalent to the second inlet, and third gas inlet 31 is equivalent to the third inlet.

[0125] According to the gas sensor 100 of this embodiment described in detail above, the control device 95 measures the first to fourth concentrations as specific gas concentrations based on pump currents Ip1 to Ip3. Here, the pump current Ip1 flowing through the first measuring pump unit 15 due to the first measuring pump control process is correlated with the total concentration of the reducing target gas and oxygen in the measured gas. The pump current Ip2 flowing through the second measuring pump unit 25 due to the second measuring pump control process is correlated with the total concentration of water (i.e., the reducing target gas other than the first gas) and oxygen in the measured gas. The pump current Ip3 flowing through the third measuring pump unit 35 due to the third measuring pump control process is correlated with the oxygen concentration in the measured gas. Therefore, based on the pump currents Ip1 and Ip2, the concentration of the first gas (here, carbon dioxide) in the measured gas, i.e., the first concentration (here, carbon dioxide concentration), can be measured. Furthermore, based on pump currents Ip2 and Ip3, the concentration of the second gas (here, water) in the gas being measured, i.e., the second concentration (here, water concentration), can be measured. Based on pump current Ip3, the third concentration (here, oxygen concentration) in the gas being measured can be measured. Based on pump currents Ip1 and Ip3, the combined concentration of the first gas (here, carbon dioxide) and the second gas (here, water) in the gas being measured, i.e., the fourth concentration, can be measured. Moreover, in the gas sensor 100, the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 are not interconnected; the gas being measured reaches the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 from the outside of the sensor element 101 via independent paths. Therefore, mutual influence between the gases in the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 can be suppressed, and the reduction in measurement accuracy caused by the aforementioned back diffusion is less likely to occur. For example, if the first internal cavity 14 and the second internal cavity 24 are interconnected inside the sensor element 101, the measurement accuracy of the first concentration and / or the second concentration based on the pump current Ip2 may sometimes decrease because the hydrogen and carbon monoxide produced by the reduction of water and carbon dioxide in the first internal cavity 14 reach the second internal cavity 24. However, such a problem is unlikely to occur in the gas sensor 100 of this embodiment. Therefore, in this gas sensor 100, the decrease in the measurement accuracy of a specific gas concentration in the gas being measured can be suppressed.

[0126] Furthermore, since the second measuring electrode 26 contains both the first and second precious metals, the pump current Ip2 is less susceptible to the influence of the carbon dioxide concentration in the gas being measured. Therefore, the measurement accuracy of the first concentration measurement process, i.e., the measurement accuracy of carbon dioxide concentration based on pump currents Ip1 and Ip2, is improved. Additionally, since the ratio R2 of the second measuring electrode 26 is 2% or more, the reducing ability of the second measuring electrode 26 for carbon dioxide can be more reliably reduced.

[0127] Furthermore, the first gas inlet 11, the second gas inlet 21, and the third gas inlet 31 are open on different surfaces in the first to sixth surfaces 102a to 102f, thus further suppressing the mutual influence of the gases between the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34.

[0128] It should be noted that the present invention is not limited to any of the above embodiments. Of course, any solution that falls within the technical scope of the present invention can be implemented in various ways.

[0129] For example, in the above embodiment, the control device 95 performs first to fourth concentration measurement processes to measure the first to fourth concentrations. However, it is sufficient to perform at least two of the first to fourth concentration measurement processes. In this case, at least two of the first to fourth concentration measurement processes can be performed in a combination that utilizes pump currents Ip1 to Ip3. For example, a combination of performing only the second and third concentration measurement processes does not utilize pump current Ip1, and is therefore not preferred. Similarly, a combination of performing only the third and fourth concentration measurement processes does not utilize pump current Ip2, and is therefore not preferred. Furthermore, the control device 95 may omit the fourth concentration measurement process. That is, the control device 95 can perform the first to third concentration measurement processes to measure the first to third concentrations.

[0130] In the above embodiment, the control device 95 measures the first concentration based on the difference between pump current Ip1 and pump current Ip2 in the first concentration measurement process. However, it is not limited to this; the first concentration can be measured based on pump current Ip1 and pump current Ip2. For example, the control device 95 can derive the total concentration of the reducing target gas and oxygen in the measured gas (also called the first total concentration) based on pump current Ip1, and derive the total concentration of the reducing target gas other than the first gas and oxygen in the measured gas (also called the second total concentration) based on pump current Ip2. Then, the difference between the first total concentration and the second total concentration is derived (measured) as the first concentration. In this case, the correspondence between pump current Ip1 and the first total concentration, and the correspondence between pump current Ip2 and the second total concentration are pre-stored in the storage unit 98. The control device 95 can use pump current Ip1, pump current Ip2, and their correspondence to measure the first total concentration, the second total concentration, and the first concentration. The same consideration can be given to the measurement of the second concentration and the fourth concentration. For example, in the second concentration measurement process, the control device 95 can derive a second total concentration based on the pump current Ip2, and derive the total concentration (also called the third total concentration) of the first gas, the reducing target gas other than the second gas, and oxygen in the measured gas based on the pump current Ip3. Then, the difference between the second total concentration and the third total concentration is derived (measured) as the second concentration. In the fourth concentration measurement process, the control device 95 can derive a first total concentration based on the pump current Ip1, derive a third total concentration based on the pump current Ip3, and then derive (measure) the difference between the first total concentration and the third total concentration as the fourth concentration.

[0131] In the above embodiment, the correspondence between the difference between pump current Ip1 and pump current Ip2 and the carbon dioxide concentration is stored in the storage unit 98 as a first correspondence. However, the correspondence between pump current Ip1, pump current Ip2, and the first concentration can also be stored in the storage unit 98 as a first correspondence. In this case, the control device 95 may not derive the difference between pump current Ip1 and pump current Ip2, but instead derive the first concentration based on the first correspondence. The determination of the second and fourth concentrations can be considered in the same way.

[0132] In the above embodiments, the control device 95 measures the first concentration based on the difference between pump current Ip1 and pump current Ip2 in the first concentration measurement process. However, it is also possible to derive the difference after correcting at least one of the pump currents Ip1 and Ip2, and then measure the first concentration based on this difference. That is, the control device 95 can measure the first concentration based on the difference between the corrected pump current Ip1 (i.e., pump current Ip1') and pump current Ip2 in the first concentration measurement process, or it can measure the first concentration based on the difference between pump current Ip1 and the corrected pump current Ip2 (i.e., pump current Ip2'), or it can measure the first concentration based on the difference between pump current Ip1' and pump current Ip2'. These methods are also included in the method of "measuring the first concentration based on the difference between pump current Ip1 and pump current Ip2". The correction of at least one of the pump currents Ip1 and Ip2 is preferably performed in a manner that minimizes the difference between the sensitivity of pump current Ip1 to the gas and the sensitivity of pump current Ip2 to the gas. Basically, calibration only needs to be performed on either the pump current Ip1 or the pump current Ip2; however, both can also be calibrated as described above. Here, if, for example, the ratio R1 of the second noble metal in the first measuring electrode 16 is different from the ratio R2 of the second noble metal in the second measuring electrode 26, then as follows... Figure 4 and Figure 5As shown, the V-I characteristics of the first measuring pump unit 15 and the second measuring pump unit 25 are sometimes different. Furthermore, as described above, if the diffusion resistance values ​​of the first and second measured gas flow sections are different, the V-I characteristics of the first measuring pump unit 15 and the second measuring pump unit 25 are sometimes different. Moreover, when the V-I characteristics of the first measuring pump unit 15 and the second measuring pump unit 25 are different, the sensitivity of the pump current Ip1 to the gas and the sensitivity of the pump current Ip2 to the gas may sometimes differ. For example, when the composition of the measured gas in the first internal cavity 14 and the second internal cavity 24 is the same and the carbon dioxide concentration is 0%, if the sensitivity of the first measuring pump unit 15 and the second measuring pump unit 25 to the gas is the same, the pump current Ip1 flowing due to the first measuring pump control processing and the pump current Ip2 flowing due to the second measuring pump control processing become substantially the same value. In contrast, if there is a difference in gas sensitivity between the first measuring pump unit 15 and the second measuring pump unit 25, even if the composition of the gas to be measured in the first internal cavity 14 and the second internal cavity 24 is the same and the carbon dioxide concentration is 0%, the values ​​of the pump current Ip1 flowing due to the control processing of the first measuring pump and the pump current Ip2 flowing due to the control processing of the second measuring pump may sometimes deviate. Thus, when there is a difference in gas sensitivity between the first measuring pump unit 15 and the second measuring pump unit 25, the difference between the pump current Ip1 and the pump current Ip2 includes not only the carbon dioxide concentration but also the aforementioned deviation. Therefore, by correcting at least one of the pump currents Ip1 and Ip2 in a way that reduces this deviation, the corrected difference can better correspond to the carbon dioxide concentration. For example, the pump current Ip1 can be corrected by multiplying it by a predetermined correction factor. For example, when the composition of the gas to be measured in the first internal cavity 14 and the second internal cavity 24 is the same and the carbon dioxide concentration is 0%, the value of the pump current Ip2 is 0.9 times the value of the pump current Ip1. The value obtained by multiplying the pump current Ip1 by the correction factor 0.9 can be set as the corrected pump current Ip1'. The pump current Ip1' can be derived by using the correspondence between the pump current Ip1 and the corrected pump current Ip1', thereby correcting the pump current Ip1. Such correction factor and correspondence can be calculated in advance by experiment or analysis and stored in the storage unit 98. The correction of the pump current Ip2 can also be performed in the same way. The determination of the second concentration and the fourth concentration can also be considered in the same way. For example, the control device 95 can correct at least one of the pump currents Ip2 and Ip3 in the second concentration determination process, and then derive the difference and determine the second concentration based on the difference. This scheme is also included in the scheme of "determining the second concentration based on the difference between the pump currents Ip2 and Ip3".The control device 95 can correct at least one of the pump current Ip1 and pump current Ip3 in the fourth concentration determination process, and then derive the difference, based on which the fourth concentration is determined. This scheme is also included in the scheme of "determining the fourth concentration based on the difference between pump current Ip1 and pump current Ip3".

[0133] In the above embodiments, the gases to be reduced are water and carbon dioxide, the first gas is carbon dioxide, and the second gas is water, but the embodiments are not limited to these. The gases to be reduced are not limited to water and carbon dioxide; they can be two or more oxide gases from the gas being measured. A subset of the oxide gases in the gases to be reduced can be the first gas. One or more oxide gases other than the first gas in the gases to be reduced can be the second gas. It should be noted that the first gas is one or more oxide gases selected sequentially from the two or more oxide gases included in the gases to be reduced, starting with the oxide gas least difficult to reduce. Similarly, the second gas is one or more oxide gases selected sequentially from the oxide gases other than the first gas in the gases to be reduced, starting with the oxide gas least difficult to reduce. For example, consider the case where the gases to be reduced are gas a, gas b, gas c, and gas d, and these gases are oxide gases least difficult to reduce in this order. In this case, the first gas could be, for example, gas a, or gas a and gas b, etc., selected sequentially from the least difficult-to-reduce oxide gases in the gases to be reduced. Furthermore, if the first gas is gas a, the second gas may be, for example, gas b, or a combination of gas b and gas c, and the selection will proceed sequentially from the oxide gases other than the first gas in the target gas, starting with oxide gases that are not easily reduced. In the above embodiment, since the target gases are water and carbon dioxide, carbon dioxide, which is not easily reduced, is designated as the first gas, and the other oxide gases, i.e., water, are designated as the second gas. Two or more gases containing carbon dioxide may be designated as the first gas. Two or more gases containing water may also be designated as the second gas. It should be noted that even if the measured gas contains oxide gases, oxide gases that are not reduced in the processing performed by the control device 95 (at least two processing steps performed in the first to fourth pump unit control processing using a combination of pump currents Ip1 to Ip3) are not the target gases for reduction.

[0134] In the above embodiments, the first gas inlet 11, the second gas inlet 21, and the third gas inlet 31 are open on different surfaces of the first to sixth surfaces 102a to 102f, but this is not limited to this. Alternatively, two of the first gas inlet 11, the second gas inlet 21, and the third gas inlet 31 may be open on the same surface of the first to sixth surfaces 102a to 102f. Furthermore, it may be like... Figure 6As shown in the modified example of the component body 102, the first gas inlet 11, the second gas inlet 21 and the third gas inlet 31 are open on the same surface of the first to sixth surfaces 102a to 102f. Figure 6 In a modified example, the first gas inlet 11, the second gas inlet 21, and the third gas inlet 31 are all open on the third surface 102c. Therefore, even if the concentration of a specific gas in the gas being measured changes within a short period, the gas reaching the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 will easily reach the same specific gas concentration. Thus, the accuracy of the concentration (first, second, and fourth concentrations) measured based on two of the first to third pump currents is improved.

[0135] In the above embodiments, the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 are all spaces formed by hollowing out the isolation layer 5, but are not limited thereto. Two or more of the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 may also be formed in different layers among the multiple layers of the component body 102. For example, they can be like... Figure 7 As with the component body 102 in the modified example shown, the first internal cavity 14, the second internal cavity 24 and the third internal cavity 34 are formed in different layers. Figure 7 In a modified example, the element body 102, in addition to having layers 1 to 6 as described in the above embodiment, also includes a third solid electrolyte layer 7 and a fourth solid electrolyte layer 8. Furthermore, the first internal cavity 14 is formed by hollowing out the insulating layer 5, the second measuring pump unit 25 is formed by hollowing out the second solid electrolyte layer 6, and the third measuring pump unit 35 is formed by hollowing out the third solid electrolyte layer 7. Additionally, the outer pump electrode 40 is disposed on the upper surface of the first surface 102a of the element body 102, i.e., the upper surface of the fourth solid electrolyte layer 8.

[0136] In the above embodiments, any one of the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 provided in the element body 102 of the sensor element 101 can be omitted. In this case, the two internal cavities that are not omitted from the first internal cavity 14, the second internal cavity 24, and the third internal cavity 34 are equivalent to the first chamber and the second chamber of the second gas sensor of the present invention. Even in this case, the control device 95 only needs to perform the processing corresponding to the two internal cavities that are not omitted in the first to third measuring pump control processing of the above embodiments, so that two pump currents Ip1 to Ip3 flow, and measure the concentration of a specific gas based on these two pump currents. For example, if the third internal cavity 34 is omitted, the control unit 96 can measure the concentration of the first gas (e.g., carbon dioxide concentration) in the gas to be measured as the concentration of the specific gas based on the pump current Ip1 flowing in the first measuring pump unit 15 due to the first measuring pump control processing and the pump current Ip2 flowing in the second measuring pump unit 25 due to the second measuring pump control processing. The same applies to cases where the first internal cavity 14 or the second internal cavity 24 is omitted.

[0137] In the above embodiments, the outer pump electrode 40 serves as: a first outer electrode paired with the first measuring electrode 16 in the first measuring pump unit 15; a second outer electrode paired with the second measuring electrode 26 in the second measuring pump unit 25; and a third outer electrode paired with the third measuring electrode 36 in the third measuring pump unit 35. That is, the first to third outer electrodes constitute a universal outer pump electrode 40. However, this is not a limitation. For example, two of the first to third outer electrodes may be universal electrodes, and the remaining one may be an electrode independent of the outer pump electrode 40, and disposed on the outer surface of the element body 102. Alternatively, the first to third outer electrodes may each be an independent electrode and disposed on the outer surface of the element body 102.

[0138] Industrial availability

[0139] This invention relates to a gas sensor that can be used to detect the concentrations of specific gases such as carbon dioxide, water, and oxygen in gases such as automobile exhaust.

Claims

1. A gas sensor comprising a sensor element and a control device, for measuring the concentration of a specific gas in a gas to be measured. The sensor element has: The main body of the element has a solid electrolyte layer with oxygen ion conductivity, and is provided with a first chamber, a second chamber and a third chamber that are not interconnected and can be reached from the outside of the sensor element by the gas to be measured. The first pump unit is configured to include a first inner electrode disposed in the first chamber and a first outer electrode disposed on the outer surface of the component body. A second pump unit, configured to include a second inner electrode disposed in the second chamber, and a second outer electrode disposed on the outer surface of the component body; and The third pump unit is configured to include a third inner electrode disposed in the third chamber and a third outer electrode disposed on the outer surface of the component 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 two or more oxide gases, i.e., the gases to be reduced, in the gas to be measured in the first chamber. The second pump unit control process is to suppress the reduction of a portion of the oxide gas, i.e. the first gas, in the gas to be measured in the second chamber, and to draw oxygen from the area around the second inner electrode to the area around the second outer electrode, compared to the first pump unit control process. as well as The third pump unit is controlled in a manner that, compared to the second pump unit control process, suppresses the reduction of one or more oxide gases (i.e., the second gas) other than the first gas in the target gas being reduced in the measured gas in the third chamber, and draws oxygen from around the third inner electrode to around the third outer electrode. The control device determines at least two of the first to fourth concentrations as the specific gas concentration by performing at least two processes selected using a combination of the first to third pump currents. The first concentration measurement process measures the concentration of the first gas in the gas to be measured, i.e., the first concentration, based on the first pump current flowing through the first pump unit due to the first pump unit control process and the second pump current flowing through the second pump unit due to the second pump unit control process. The second concentration measurement process measures the concentration of the second gas in the gas to be measured, i.e., the second concentration, based on the second pump current and the third pump current flowing through the third pump unit due to the control process of the third pump unit. as well as The third concentration measurement process involves measuring the total concentration of the first gas, the target gas for reduction (other than the second gas), and oxygen in the gas being measured, based on the third pump current. The fourth concentration measurement process involves measuring the total concentration of the first gas and the second gas in the gas being measured, i.e., the fourth concentration, based on the first pump current and the third pump current.

2. The gas sensor according to claim 1, characterized in that, The gases to be reduced are water and carbon dioxide. The first gas is carbon dioxide. The second gas is water.

3. The gas sensor according to claim 2, characterized in that, The second inner electrode contains a first noble metal with catalytic activity and a second noble metal that inhibits carbon dioxide reduction.

4. The gas sensor according to claim 3, characterized in that, The first precious metal is at least one of Pt, Rh, Ir, Ru, and Pd. The second precious metal is Au.

5. The gas sensor according to claim 3 or 4, characterized in that, The proportion R2 of the second inner electrode, calculated by the following formula (1), is 2% or more. R2=S2 / (S1+S2)×100 (1) in, S1: The mass percentage of the first precious metal [wt%] S2: The mass percentage of the second precious metal [wt%].

6. The gas sensor according to any one of claims 1 to 4, characterized in that, The sensor element has a reference electrode disposed inside the element body in a manner that allows it to contact a reference gas. In the control process of the first pump unit, the control device controls the first pump unit in a manner that the voltage between the reference electrode and the first inner electrode, i.e., the first voltage, reaches a first voltage target value. In the control process of the second pump unit, the control device controls the second pump unit in a manner that makes the voltage between the reference electrode and the second inner electrode, i.e., the second voltage, reach a second voltage target value whose absolute value is smaller than the first voltage target value. In the control process of the third pump unit, the control device controls the third pump unit in such a way that the voltage between the reference electrode and the third inner electrode, i.e., the third voltage, reaches a third voltage target value whose absolute value is smaller than the second voltage target value.

7. The gas sensor according to any one of claims 1 to 4, characterized in that, The first concentration measurement process can be either a process that measures the first concentration based on the difference between the first pump current and the second pump current, or a process that measures the first concentration based on the difference between the total concentration of the target gas and oxygen in the measured gas derived from the first pump current and the total concentration of the target gas other than the first gas and oxygen in the measured gas derived from the second pump current. The second concentration measurement process can be either a process that measures the second concentration based on the difference between the second pump current and the third pump current, or a process that measures the second concentration based on the difference between the total concentration of the reducing target gas (excluding the first gas) and oxygen in the measured gas derived from the second pump current and the total concentration of the reducing target gas (excluding the first gas and the second gas) and oxygen in the measured gas derived from the third pump current. The fourth concentration measurement process is either a process of measuring the fourth concentration based on the difference between the first pump current and the third pump current, or a process of measuring the fourth concentration based on the difference between the total concentration of the target gas and oxygen in the measured gas derived from the first pump current and the total concentration of the target gas and oxygen other than the first and second gases in the measured gas derived from the third pump current.

8. The gas sensor according to any one of claims 1 to 4, characterized in that, The main body of the component is a cuboid shape having a first to a sixth surface as its outer surface. The main body of the component has: A first inlet, which is an inlet for the gas to be measured from the outside toward the first chamber; The second inlet is an inlet for the gas to be measured from the outside toward the second chamber; as well as The third inlet is an inlet for the gas to be measured, which flows from the outside toward the third chamber. The first inlet, the second inlet, and the third inlet are open on different surfaces of the first to sixth surfaces.

9. The gas sensor according to any one of claims 1 to 4, characterized in that, The main body of the component is a cuboid shape having a first to a sixth surface as its outer surface. The main body of the component has: A first inlet, which is an inlet for the gas to be measured from the outside toward the first chamber; The second inlet is an inlet for the gas to be measured from the outside toward the second chamber; as well as The third inlet is an inlet for the gas to be measured, which flows from the outside toward the third chamber. The first inlet, the second inlet, and the third inlet are open on the same surface of the first to sixth surfaces.

10. A gas sensor comprising a sensor element and a control device, for measuring the concentration of a specific gas in a gas to be measured. The sensor element has: The main body of the element has a solid electrolyte layer with oxygen ion conductivity, and is provided with a first chamber and a second chamber that are not interconnected and can be reached from the outside of the sensor element by the gas being measured. The first pump unit is configured to include a first inner electrode disposed in the first chamber and a first outer electrode disposed on the outer surface of the component body. as well as The second pump unit is configured to include a second inner electrode disposed in the second chamber and a second outer electrode disposed on the outer surface of the component 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 target gas containing water and at least water in the measured gas in the first chamber. The second pump unit control process controls the second pump unit in a manner that, compared to the first pump unit control process, suppresses the reduction of one or more gases (i.e., the first gas) in the target gas being reduced in the measured gas in the second chamber and draws oxygen from the vicinity of the second inner electrode to the vicinity of the second outer electrode; and The concentration measurement process determines the concentration of the first gas in the gas to be measured, i.e., the first concentration, as the specific gas concentration, based on the first pump current flowing through the first pump unit due to the control processing of the first pump unit and the second pump current flowing through the second pump unit due to the control processing of the second pump unit. The first gas is water when the gas to be reduced is water, and is one or more gases in the gas to be reduced that contain at least carbon dioxide when the gas to be reduced is both water and carbon dioxide.

11. A sensor element for measuring the concentration of a specific gas in a gas to be measured. have: The main body of the element has a solid electrolyte layer with oxygen ion conductivity, and is provided with a first chamber, a second chamber and a third chamber that are not interconnected and can be reached from the outside by the gas to be measured. The first pump unit is configured to include a first inner electrode disposed in the first chamber and a first outer electrode disposed on the outer surface of the component body. The second pump unit is configured to include a second inner electrode disposed in the second chamber and a second outer electrode disposed on the outer surface of the component body. as well as The third pump unit is configured to include a third inner electrode disposed in the third chamber and a third outer electrode disposed on the outer surface of the component body.

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