Gas sensor

Abstract

A gas sensor (100) is provided with a sensor element (101) and a control device (95). When a predetermined condition is satisfied, the control device (95) executes a first regeneration process for controlling the main pump unit (21) so as to suck oxygen from the periphery of the outer pump electrode (23) to the periphery of the inner pump electrode (22). And a second regeneration process for controlling the first measurement pump unit (50) so as to suck more oxygen from the periphery of the outer pump electrode (23) to the periphery of the first measurement electrode (51) than the first measurement pump control process. And at least one of third regeneration treatments for controlling the second measurement pump unit (41) so as to suck more oxygen from the periphery of the outer pump electrode (23) to the periphery of the second measurement electrode (44) than the second measurement pump control treatment is used as the regeneration treatment.

Description

Technical Field

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

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

[0003] Existing technical documents

[0004] Patent documents

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

[0006] In the aforementioned gas sensors, during or after use, gas may be adsorbed onto at least one of the main inner pump electrode, the first inner pump electrode for measurement, and the second inner pump electrode for measurement, resulting in a decrease in reducing or oxidizing capacity, thereby reducing the accuracy of the measurement of water concentration and / or carbon dioxide concentration.

[0007] The main objective of the gas sensor of the present invention is to suppress the decrease in the measurement accuracy of water concentration and / or carbon dioxide concentration in the gas being measured.

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

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

[0010] The sensor element includes:

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

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

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

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

[0015] The control device performs:

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

[0017] The second pump unit is controlled to draw oxygen from the area around the second outer electrode to the area around the second inner electrode, so that the hydrogen generated by the reduction of water in the first chamber is oxidized in the second chamber.

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

[0019] The process includes water concentration measurement and / or carbon dioxide concentration measurement. In the water concentration measurement process, the water concentration in the gas to be measured is measured based on a second pump current flowing through the second pump unit due to the control process of the second pump unit. In the carbon dioxide concentration measurement process, the carbon dioxide concentration in the gas to be measured is measured based on a third pump current flowing through the third pump unit due to the control process of the third pump unit.

[0020] When specified conditions are met, the control device performs at least one of the following three processes as a regeneration process:

[0021] The first regeneration process controls the first pump unit to draw oxygen from the vicinity of the first outer electrode to the vicinity of the first inner electrode.

[0022] The second regeneration process involves controlling the second pump unit to draw in more oxygen from around the second outer electrode to around the second inner electrode than the second pump unit control process.

[0023] The third regeneration process involves controlling the third pump unit to draw in more oxygen from around the third outer electrode to around the third inner electrode than the third pump unit control process.

[0024] In the gas sensor of the present invention, when predetermined conditions are met, at least one of the following regeneration processes is performed: a first regeneration process that controls the first pump unit to draw in oxygen from around the first outer electrode to around the first inner electrode; a second regeneration process that controls the second pump unit to draw in more oxygen from around the second outer electrode to around the second inner electrode than the second pump unit control process; and a third regeneration process that controls the third pump unit to draw in more oxygen from around the third outer electrode to around the third inner electrode than the third pump unit control process. By performing the first regeneration process, the gas adsorbed on the first inner electrode can be oxidized and detached from the first inner electrode, thereby restoring the reducing capacity of the first inner electrode. By performing the second regeneration process, the gas adsorbed on the second inner electrode can be oxidized and detached from the second inner electrode, thereby restoring the oxidizing capacity of the second inner electrode. By performing the third regeneration process, the gas adsorbed on the third inner electrode can be oxidized and detached from the third inner electrode, thereby restoring the oxidizing capacity of the third inner electrode. As a result, the accuracy of measuring the water concentration and / or carbon dioxide concentration in the measured gas can be suppressed. It should be noted that when the gas sensor of the present invention is installed in the exhaust pipe of an internal combustion engine, the gas adsorbed on at least one of the first inner electrode, second inner electrode, and third inner electrode takes into account components contained in the exhaust gas of the internal combustion engine, i.e., exhaust gas components or source components originating from exhaust gas components. Source components can be considered, for example, reduced components obtained from the reduction of exhaust gas components, oxidized components obtained from the oxidation of reduced components, etc.

[0025] [2] In the gas sensor of the present invention (the gas sensor described in [1] above), the control device may perform at least the first regeneration process as the regeneration process.

[0026] [3] In the gas sensor of the present invention (the gas sensor described in [1] or [2] above), the specified conditions may include the condition that the solid electrolyte layer has been activated.

[0027] [4] In the gas sensor of the present invention (the gas sensor described in any of [1] to [3] above), the specified conditions may include the condition that the first pump unit control processing, the second pump unit control processing, and the third pump unit control processing are continuously executed for a specified time.

[0028] [5] In the gas sensor of the present invention (the gas sensor described in any of [1] to [4] above), at least two of the first outer electrode, the second outer electrode, and the third outer electrode may be universal electrodes. Attached Figure Description

[0029] Figure 1 This is a simplified cross-sectional view illustrating an example of the configuration of the gas sensor 100.

[0030] Figure 2 This is a block diagram showing the electrical connections between the control device 95 and various units, etc.

[0031] Figure 3 This is a flowchart illustrating an example of a processing routine.

[0032] Figure 4 This is an explanatory diagram showing the experimental results for the gas sensor 100.

[0033] Figure 5 This is a flowchart illustrating one example of the processing routine for a variant example.

[0034] Figure 6 This is a simplified cross-sectional view of the sensor element 201 in the modified example. Detailed Implementation

[0035] 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 This is a block diagram showing the electrical connections between the control device 95, each unit, and the heater 72. The gas sensor 100 is installed in piping such as the exhaust pipe of an internal combustion engine. The gas sensor 100 uses the exhaust gas of the internal combustion engine as the measured gas and measures the concentration of a specific gas in the measured gas, i.e., the specific gas concentration. In this embodiment, the gas sensor 100 measures water concentration and carbon dioxide concentration as the specific gas concentration. The gas sensor 100 includes: a sensor element 101 having a rectangular cuboid-shaped element body 102; units 21, 41, 50, 80-83 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 24, 46, 52 and a heater power supply 76, and controlling the entire gas sensor 100. It should be noted that the length direction of the sensor element 101 (…) Figure 1 The left and right directions in the image are set as the front and back directions, and the thickness direction of the sensor element 101 is set as the front and back directions. Figure 1 The vertical direction is set as the vertical direction, and the width direction of the sensor element 101 (the direction perpendicular to the front-back direction and the vertical direction) is set as the left-right direction.

[0036] The component body 102 is a laminate obtained by stacking six layers in sequence from bottom to top in the attached drawing: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, an isolation layer 5, and a second solid electrolyte layer 6, each composed of an oxygen ion conductive solid electrolyte layer such as zirconium oxide (ZrO2). Furthermore, the solid electrolyte forming these six layers is a dense, gas-tight solid electrolyte. The component body 102 is manufactured as follows: for example, the ceramic green sheets corresponding to each layer are subjected to prescribed processing and circuit pattern printing, then they are stacked, and subsequently fired to achieve integration.

[0037] On the front end side of the sensor element 101 (element body 102), between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, a gas inlet 10, a first diffusion rate control unit 11, a buffer space 12, a second diffusion rate control unit 13, a first internal cavity 20, a third diffusion rate control unit 30, a second internal cavity 40, a fourth diffusion rate control unit 60, and a third internal cavity 61 are formed adjacently in a sequentially connected manner.

[0038] The gas inlet 10, buffer space 12, first internal cavity 20, second internal cavity 40 and third internal cavity 61 are spaces inside the sensor element 101 provided by hollowing out the isolation layer 5, wherein their upper parts are separated by the lower surface of the second solid electrolyte layer 6, their lower parts are separated by the upper surface of the first solid electrolyte layer 4, and their sides are separated by the side of the isolation layer 5.

[0039] The first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 are each configured as two horizontally elongated slits (forming an opening along the length direction perpendicular to the drawing). Additionally, the fourth diffusion rate control unit 60 is configured as a single horizontally elongated slit (forming an opening along the length direction perpendicular to the drawing) formed as a gap between itself and the lower surface of the second solid electrolyte layer 6. Furthermore, the portion from the gas inlet 10 to the third internal cavity 61 is referred to as the measured gas flow section.

[0040] The sensor element 101 (element body 102) includes a reference gas inlet 49 that allows a reference gas for measuring a specific gas concentration to flow from the outside of the sensor element 101 to a reference electrode 42. The reference gas inlet 49 has a reference gas inlet space 43 and a reference gas inlet layer 48. The reference gas inlet space 43 is a space provided from the rear end face of the sensor element 101 toward the inward direction. The reference gas inlet space 43 is provided between the upper surface of the third substrate layer 3 and the lower surface of the insulating layer 5, and is positioned to separate the side portion from the side of the first solid electrolyte layer 4. The reference gas inlet space 43 is open at the rear end face of the sensor element 101, and this opening functions as an inlet 49a of the reference gas inlet 49. The reference gas is introduced into the reference gas inlet space 43 from the inlet 49a. The reference gas inlet 49 applies a predetermined diffusion resistance to the reference gas introduced from the inlet 49a and introduces the reference gas toward the reference electrode 42. In this embodiment, the reference gas is atmospheric gas.

[0041] 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.

[0042] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around it. Furthermore, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) within the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61. The reference electrode 42 is formed as a porous metal-ceramic electrode (e.g., a Pt and ZrO2 metal-ceramic electrode).

[0043] In the gas flow section, the gas inlet 10 is an opening relative to the external space, through which the gas to be measured enters the sensor element 101 from the external space. The first diffusion rate control unit 11 applies a predetermined diffusion resistance to the gas to be measured entering through the gas inlet 10. The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13. The second diffusion rate control unit 13 applies a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal cavity 20. When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, the gas that rapidly enters the sensor element 101 from the gas inlet 10 due to pressure fluctuations in the external space (in the case of automobile exhaust, pulsations in exhaust pressure) is not directly introduced into the first internal cavity 20. Instead, it is introduced into the first internal cavity 20 after the pressure fluctuations are eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. Therefore, the pressure fluctuations of the gas to be measured introduced into the first internal cavity 20 are negligible. The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured introduced through the second diffusion rate control unit 13. This oxygen partial pressure is adjusted by the operation of the main pump unit 21.

[0044] The main pump unit 21 is an electrochemical pump unit consisting of an inner pump electrode 22, an outer pump electrode 23, a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4 that form the current path between these electrodes. The inner pump electrode 22 has a top electrode portion 22a disposed on the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, which is generally the entire surface. The outer pump electrode 23 is disposed on the upper surface of the second solid electrolyte layer 6 in a region corresponding to the top electrode portion 22a, in a manner that exposes it to the outside of the sensor element 101.

[0045] The inner pump electrode 22 spans the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that define the first internal cavity 20, as well as the isolation layer 5 that forms the sidewalls. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that forms the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that forms the bottom surface of the first internal cavity 20. Furthermore, side electrode portions (not shown) are formed on the sidewall surfaces (inner surfaces) of the isolation layer 5 that forms the two sidewall portions of the first internal cavity 20 in a manner that connects the top electrode portion 22a and the bottom electrode portion 22b. Thus, the side electrode portions are arranged in a tunnel-shaped structure.

[0046] In the main pump unit 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, so that the pump current Ip0 flows between the inner pump electrode 22 and the outer pump electrode 23 in either the positive or negative direction. As a result, oxygen in the first internal cavity 20 can be drawn out to the external space, or oxygen in the external space can be drawn into the first internal cavity 20.

[0047] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an electrochemical sensor unit, namely the main pump control oxygen partial pressure detection sensor unit 80, is composed of the inner pump electrode 22, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42.

[0048] By measuring the electromotive force (voltage V0) of the oxygen partial pressure detection sensor unit 80 for main pump control, the oxygen concentration (oxygen partial pressure) within the first internal cavity 20 can be determined. Furthermore, by feedback control of the voltage Vp0 of the variable power supply 24 to achieve a target voltage V0, the pump current Ip0 is controlled. This adjusts the oxygen concentration within the first internal cavity 20.

[0049] The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20, and guides the gas to be measured into the second internal cavity 40.

[0050] The second internal cavity 40 is configured as a space for performing the following process: adjusting the oxygen partial pressure using the first measuring pump unit 50 for the gas to be measured introduced through the third diffusion rate control unit 30, thereby performing a process related to the measurement of the water concentration in the gas to be measured.

[0051] The first measuring pump unit 50 is an electrochemical pump unit composed of a first measuring electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any appropriate electrode disposed on the outer surface of the sensor element 101), a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. The first measuring electrode 51 has a top electrode portion 51a disposed substantially integrally on the lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40.

[0052] The first measuring electrode 51 is disposed in the second internal cavity 40 with the same tunnel-shaped structure as the inner pump electrode 22 disposed in the previous first internal cavity 20. That is, it is configured with the following tunnel shape: a top electrode portion 51a is formed on the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40. Furthermore, side electrode portions (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b are respectively formed on the two wall surfaces of the isolation layer 5 constituting the side wall of the second internal cavity 40.

[0053] In the first measuring pump unit 50, a desired voltage Vp1 is applied between the first measuring electrode 51 and the outer pump electrode 23, thereby enabling oxygen in the atmosphere inside the second internal cavity 40 to be drawn out to the external space, or oxygen to be drawn in from the external space into the second internal cavity 40.

[0054] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely the first measuring electrode 51, a reference electrode 42, a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, and a third substrate layer 3 are constructed.

[0055] Furthermore, the first measuring pump unit 50 utilizes a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the oxygen partial pressure detection sensor unit 81 for controlling the first measuring pump. Thus, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is adjusted by the pump current Ip1 flowing through the first measuring pump unit 50.

[0056] The fourth diffusion rate control unit 60 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the first measuring pump unit 50 in the second internal cavity 40, and introduces the gas to be measured into the third internal cavity 61.

[0057] The third internal cavity 61 is configured as a space for performing the following process: adjusting the oxygen partial pressure using the second measuring pump unit 41 for the gas to be measured introduced through the fourth diffusion rate control unit 60, thereby performing a process related to the measurement of the carbon dioxide concentration in the gas to be measured.

[0058] The second measuring pump unit 41 is an electrochemical pump unit composed of a second measuring electrode 44, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any appropriate electrode disposed on the outer surface of the sensor element 101), a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. The second measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 at a position facing the third internal cavity 61.

[0059] In the second measuring pump unit 41, by applying the desired voltage Vp2 between the second measuring electrode 44 and the outer pump electrode 23, oxygen in the atmosphere of the third internal cavity 61 can be drawn out to the external space, or drawn from the external space into the second internal cavity 40.

[0060] In addition, in order to detect the oxygen partial pressure around the second measuring electrode 44, an electrochemical sensor unit, namely the second measuring pump control oxygen partial pressure detection sensor unit 82, is formed by the first solid electrolyte layer 4, the third substrate layer 3, the second measuring electrode 44, and the reference electrode 42.

[0061] It should be noted that, based on the electromotive force (voltage V2) detected by the oxygen partial pressure detection sensor unit 82 for controlling the second measuring pump, the variable power supply 46 is controlled, and the voltage Vp2 of the variable power supply 46 is applied to the second measuring pump unit 41. Thus, the oxygen partial pressure in the atmosphere within the third internal cavity 61 is adjusted by the pump current Ip2 flowing through the second measuring pump unit 41.

[0062] Furthermore, the electrochemical sensor unit 83 is composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42, which can detect the oxygen partial pressure in the gas to be measured outside the sensor using the electromotive force (voltage Vref) obtained through the sensor unit 83.

[0063] Here, the electrodes 22, 23, 42, 44, and 51 are described. The inner pump electrode 22, the first measuring electrode 51, and the second measuring electrode 44 each contain a first noble metal with catalytic activity. Examples of the first noble metal include at least one of Pt, Rh, Ir, Ru, and Pd. The outer pump electrode 23 and the reference electrode 42 also contain the first noble metal. The first measuring electrode 51 preferably contains a second noble metal that suppresses the catalytic activity of the first noble metal against carbon monoxide. By including the second noble metal in the first measuring electrode 51, the oxidation ability of the first measuring electrode 51 against carbon monoxide is weakened. Examples of the second noble metal include Au. The inner pump electrode 22 and the second measuring electrode 44 do not contain the second noble metal. The outer pump electrode 23 and the reference electrode 42 also preferably do not contain the second noble metal. Each electrode 22, 23, 42, 44, and 51 is preferably a cermet containing a noble metal and an oxide (e.g., ZrO2) with oxygen ion conductivity. Each of the electrodes 22, 23, 42, 44, and 51 is preferably a porous material. In this embodiment, the first measuring electrode 51 is a porous metal-ceramic electrode containing 1% Au and Pt and ZrO2. In addition, the inner pump electrode 22, the outer pump electrode 23, the reference electrode 42, and the second measuring electrode 44 are all porous metal-ceramic electrodes containing Pt and ZrO2.

[0064] 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.

[0065] The heater connector electrode 71 is an electrode formed in contact with the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to the heater power supply 76 (see reference...) Figure 2 The connection allows power to be supplied from the heater power supply 76 to the heater section 70.

[0066] The heater 72 is a resistive element formed by being sandwiched between the second substrate layer 2 and the third substrate layer 3 from the top and bottom. The heater 72 is connected to the heater connector electrode 71 via the through hole 73, and heats up by being powered by the heater power supply 76 through the heater connector electrode 71, thereby heating and maintaining the temperature of the solid electrolyte forming the sensor element 101.

[0067] In addition, the heater 72 is embedded in the entire area from the first internal cavity 20 to the third internal cavity 61, which can adjust the sensor element 101 as a whole to the temperature at which the solid electrolyte is activated.

[0068] The heater insulation layer 74 is an insulation layer formed from an insulator such as aluminum oxide on the upper and lower surfaces of the heater 72. The heater insulation layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72, and electrical insulation between the third substrate layer 3 and the heater 72.

[0069] The pressure relief hole 75 is a portion that passes through the third substrate layer 3 and the reference gas introduction layer 48 and communicates with the reference gas introduction space 43, and is formed to mitigate the internal pressure rise that accompanies the temperature rise in the heater insulation layer 74.

[0070] like Figure 2 As shown, the control device 95 includes: the aforementioned variable power supplies 24, 46, and 52, the aforementioned heater power supply 76, and a control unit 96. The control unit 96 is a microprocessor having a CPU 97 and a storage unit 98, etc. The storage unit 98 is a non-volatile memory capable of rewriting information, such as capable of storing various programs and various data. The control unit 96 is input with voltage V0 of the main pump control oxygen partial pressure detection sensor unit 80, voltage V1 of the first measuring pump control oxygen partial pressure detection sensor unit 81, voltage V2 of the second measuring pump control oxygen partial pressure detection sensor unit 82, voltage Vref of the sensor unit 83, pump current Ip0 flowing through the main pump unit 21, pump current Ip1 flowing through the first measuring pump unit 50, and pump current Ip2 flowing through the second measuring pump unit 41. In addition, the control unit 96 outputs control signals to the variable power supplies 24, 52, and 46, thereby controlling the voltages Vp0, Vp1, and Vp2 output by the variable power supplies 24, 52, and 46, and thus controlling the main pump unit 21, the first measuring pump unit 50, and the second measuring pump unit 41. The control unit 96 also outputs control signals to the heater power supply 76, thereby controlling the power supplied by the heater power supply 76 to the heater 72. The storage unit 98 also stores target values ​​V0*, V1*, V2*, etc., which will be described later. The CPU 97 of the control unit 96 refers to these target values ​​V0*, V1*, and V2* to control each unit 21, 50, and 41.

[0071] The control unit 96 performs the following main pump control process (an example of the first pump unit control process): it controls the main pump unit 21 to draw oxygen from around the inner pump electrode 22 to around the outer pump electrode 23. Specifically, the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 to achieve a target value V0*, thereby controlling the main pump unit 21. The target value V0* is defined as a low concentration in the first internal cavity 20 such that the oxygen concentration is sufficiently low to substantially completely reduce the water and carbon dioxide in the gas to be measured. By performing this main pump control process, water in the gas to be measured is reduced to produce hydrogen and oxygen within the first internal cavity 20, and carbon dioxide in the gas to be measured is reduced to produce carbon monoxide and oxygen. The generated oxygen is drawn from around the inner pump electrode 22 to around the outer pump electrode 23 by the pump current Ip0 flowing through the main pump unit 21.

[0072] The control unit 96 performs a first measuring pump control process (an example of a second pump unit control process) to control the first measuring pump unit 50 by drawing oxygen from around the outer pump electrode 23 to around the first measuring electrode 51. Specifically, the control unit 96 performs feedback control on the voltage Vp1 of the variable power supply 52 to bring the voltage V1 to a target value V1*, thereby controlling the first measuring pump unit 50. The target value V1* is defined as a concentration in the second internal cavity 40 such that the oxygen concentration reaches a level that substantially oxidizes all the hydrogen within the second internal cavity 40. By performing this first measuring pump control process, hydrogen generated in the second internal cavity 40 due to the reduction of water in the first internal cavity 20 is oxidized and water is generated again. At this time, the pump current Ip1 flowing through the first measuring pump unit 50 is correlated with the amount of oxygen drawn into the second internal cavity 40 to generate hydrogen in the second internal cavity 40, and further correlated with the amount of water in the measured gas in the first internal cavity 20 used to generate hydrogen in the second internal cavity 40. Therefore, the pump current Ip1 is correlated with the water concentration in the measured gas, and the water concentration in the measured gas can be measured based on the pump current Ip1. Hereinafter, this process of measuring the water concentration in the measured gas based on the pump current Ip1 will be referred to as the water concentration measurement process.

[0073] The control unit 96 performs a second measurement pump control process (an example of a third pump unit control process) to control the second measurement pump unit 41 by drawing oxygen from the area around the outer pump electrode 23 to the area around the second measurement electrode 44. Specifically, the control unit 96 performs feedback control on the voltage Vp2 of the variable power supply 46 to bring the voltage V2 to a target value V2*, thereby controlling the second measurement pump unit 41. The target value V2* is defined as a concentration in the third internal cavity 61 such that the oxygen concentration reaches a predetermined level that substantially all carbon monoxide in the third internal cavity 61 is oxidized. By performing this second measurement pump control process, carbon monoxide generated in the third internal cavity 61 due to the reduction of carbon dioxide in the first internal cavity 20 is oxidized and carbon dioxide is generated again. At this time, the pump current Ip2 flowing through the second measuring pump unit 41 is correlated with the amount of oxygen drawn into the third internal cavity 61 to oxidize the carbon monoxide in the third internal cavity 61, and further correlated with the amount of carbon dioxide in the measured gas in the first internal cavity 20 used to generate carbon monoxide in the third internal cavity 61. Therefore, the pump current Ip2 is correlated with the carbon dioxide concentration in the measured gas, and the carbon dioxide concentration in the measured gas can be measured based on the pump current Ip2. Hereinafter, this process of measuring the carbon dioxide concentration in the measured gas based on the pump current Ip2 will be referred to as the carbon dioxide concentration measurement process.

[0074] It should be noted that both hydrogen and carbon monoxide generated in the first internal cavity 20 reach the second internal cavity 40. However, hydrogen diffuses faster than carbon monoxide, and it readily bonds with oxygen. Therefore, in the second internal cavity 40, hydrogen in the hydrogen and carbon monoxide can be selectively oxidized by the first measuring pump control process. Furthermore, hydrogen hardly reaches the third internal cavity 61, which is downstream of the second internal cavity 40; therefore, carbon monoxide can be oxidized in the second measuring pump control process. In addition, in this embodiment, as described above, the first measuring electrode 51 contains a second noble metal, thereby reducing its oxidation ability against carbon monoxide. Therefore, in the periphery of the first measuring electrode 51, i.e., in the second internal cavity 40, hydrogen in the hydrogen and carbon monoxide can be further selectively oxidized by the first measuring pump control process.

[0075] The control unit 96 performs heater control processing by outputting a control signal to the heater power supply 76 to control the heater 72 so that its temperature reaches a target temperature (e.g., 800°C). Here, the target temperature of the heater 72 is defined as the temperature obtained by adding a margin to the activation temperature of the solid electrolyte. The temperature of the heater 72 can be expressed as a linear function of its resistance value. Therefore, in the heater control processing, the control unit 96 calculates the resistance value of the heater 72 in the form of a value that can be considered as the temperature of the heater 72 (convertible to a temperature value), and performs feedback control on the heater power supply 76 to ensure that the calculated resistance value reaches the target resistance value (the resistance value corresponding to the target temperature). The control unit 96 can obtain, for example, the voltage of the heater 72 and the current flowing through the heater 72, and calculate the resistance value of the heater 72 based on the obtained voltage and current. The control unit 96 can calculate the resistance value of the heater 72 using, for example, a 3-terminal method or a 4-terminal method. When the heater power supply 76 supplies power to the heater 72, for example, the value of the voltage applied to the heater 72 changes based on a control signal from the control unit 96, thereby adjusting the power supplied to the heater 72.

[0076] In addition, including Figure 2 The control device 95, including the variable power supplies 24, 46, 52 and heater power supply 76 shown, utilizes leads (not shown) actually formed within the sensor element 101 and connector electrodes (not shown) formed on the rear end side of the sensor element 101 (only the heater connector electrode 71 is shown). Figure 1 It is connected to each electrode inside the sensor element 101.

[0077] Next, an example of the processing of the control unit 96 of the gas sensor 100 will be described. Figure 3 This is a flowchart illustrating an example of a processing routine executed by the CPU 97 of the control unit 96. This routine is stored in, for example, a storage unit 98 of the control unit 96 and is repeatedly executed by the CPU 97. It should be noted that when using the gas sensor 100, the CPU 97 uses heater control processing to control the temperature of the heater 72 to a target temperature (e.g., 800°C). In this embodiment, the period from the start to the end of the heater control processing is defined as one use of the gas sensor 100.

[0078] When execution Figure 3 During the processing routine, the CPU97 first determines whether the solid electrolyte of the sensor element 101 has been activated (step S100). This processing can be performed, for example, by determining whether the resistance value of the heater 72 is below a predetermined resistance value. The predetermined resistance value is a resistance value corresponding to the activation temperature of the solid electrolyte (a value higher than the aforementioned target resistance value). If the CPU97 determines that the solid electrolyte of the sensor element 101 has not been activated, the routine ends.

[0079] If the CPU97 determines in step S100 that the solid electrolyte of the sensor element 101 has been activated, it determines whether a regeneration process has been performed or not during this use of the gas sensor 100 (step S110). If the CPU97 determines that a regeneration process has not been performed during this use of the gas sensor 100, it performs a regeneration process for a predetermined time T1 (step S120) and ends the current routine.

[0080] Here, the specified time T1 is, for example, several seconds to several minutes. During the regeneration process, the CPU97 executes the first, second, and third regeneration processes. The first regeneration process is a process that controls the main pump unit 21 to draw oxygen from around the outer pump electrode 23 to around the inner pump electrode 22. The second regeneration process is a process that controls the first measuring pump unit 50 to draw more oxygen from around the outer pump electrode 23 to around the first measuring electrode 51 than the first measuring pump control process. The third regeneration process is a process that controls the second measuring pump unit 41 to draw more oxygen from around the outer pump electrode 23 to around the second measuring electrode 44 than the second measuring pump control process.

[0081] Specifically, in the first regeneration process, the CPU 97 performs feedback control on the voltage Vp0 of the variable power supply 24 to make the voltage V0 reach a target value V0r* whose absolute value is smaller than the target value V0*, thereby controlling the main pump unit 21. The target value V0r* is defined as a value where the oxygen concentration in the first internal cavity 20 is higher than when the main pump control process is performed. During the first regeneration process, the direction of the pump current Ip0 is opposite to that during the main pump control process. In the second regeneration process, the control unit 96 performs feedback control on the voltage Vp1 of the variable power supply 52 to make the voltage V1 reach a target value V1r* whose absolute value is smaller than the target value V1*, thereby controlling the first measurement pump unit 50. The target value V1r* is defined as a value where the oxygen concentration in the second internal cavity 40 is higher than (close to the reference gas) when the first measurement pump control process is performed. In the third regeneration process, the control unit 96 performs feedback control on the voltage Vp2 of the variable power supply 46 to make the voltage V2 reach a target value V2r* whose absolute value is smaller than the target value V2*, thereby controlling the second measuring pump unit 41. The target value V2r* is defined as a value in which the oxygen concentration in the third internal cavity 61 is higher than that when the second measuring pump control process is performed (close to the reference gas).

[0082] In the gas sensor 100, during use or when not in use, gas may adhere to at least one of the inner pump electrode 22, the first measuring electrode 51, and the second measuring electrode 44, resulting in a decrease in reducing or oxidizing capacity, thereby reducing the accuracy of the measurement of water concentration and carbon dioxide concentration. To address this, in this embodiment, by performing a first regeneration process, the gas adsorbed on the inner pump electrode 22 can be oxidized and detached from the inner pump electrode 22, thereby restoring the reducing capacity of the inner pump electrode 22. By performing a second regeneration process, the gas adsorbed on the first measuring electrode 51 can be oxidized and detached from the first measuring electrode 51, thereby restoring the oxidizing capacity of the first measuring electrode 51. By performing a third regeneration process, the gas adsorbed on the second measuring electrode 44 can be oxidized and detached from the second measuring electrode 44, thereby restoring the oxidizing capacity of the second measuring electrode 44. As a result, the decrease in the accuracy of the measurement of water concentration and carbon dioxide concentration in the measured gas can be suppressed. It should be noted that in this embodiment, the gas sensor 100 is installed in the exhaust pipe of an internal combustion engine. In this case, the gas adsorbed on at least one of the inner pump electrode 22, the first measuring electrode 51, and the second measuring electrode 44 takes into account the components contained in the exhaust gas of the internal combustion engine, such as exhaust gas components and source components derived from exhaust gas components. Source components, for example, include reduced components obtained from the reduction of exhaust gas components and oxidized components obtained from the oxidation of reduced components.

[0083] If, in step S110, the CPU97 determines that regeneration processing has been performed during this use of the gas sensor 100, it executes the normal processing (step S130) and terminates the current routine. Here, in the normal processing, the CPU97 executes the main pump control processing, the first measuring pump control processing, the second measuring pump control processing, the water concentration measurement processing, and the carbon dioxide concentration measurement processing.

[0084] Figure 4This is an explanatory diagram showing the experimental results regarding the gas sensor 100. In the diagram, the horizontal axis represents the carbon dioxide concentration, and the vertical axis represents the absolute value of the pump current Ip2. As an experiment regarding the gas sensor 100, the inventors of this invention performed the following in sequence: preparation process, first experimental process, preparation process, second experimental process, preparation process, third experimental process, preparation process, fourth experimental process, preparation process, and fifth experimental process. In each of the five preparation processes, the gas sensor 100, equipped with a sensor element 101, was installed in the exhaust pipe of an internal combustion engine with the front end of the sensor element 101 protruding into the exhaust pipe. The internal combustion engine was run for several hours to tens of hours, and heater control processing, main pump control processing, first measuring pump control processing, second measuring pump control processing, water concentration measurement processing, and carbon dioxide concentration measurement processing were performed on the gas sensor 100. After the internal combustion engine finished running, the gas sensor 100 was removed. First, second, and fourth experimental processes ( Figure 4 In the third and fifth experimental processes (without regeneration treatments 1, 2, and 3), the gas sensor 100 is installed in the piping with the front end of the sensor element 101 protruding into the piping. The solid electrolyte of the sensor element 101 is activated using a heater-controlled process without regeneration. The pump current Ip2 is detected at each concentration while the carbon dioxide concentration is gradually increased (step S130). Afterward, the heater-controlled process is ended, and the gas sensor 100 is removed from the piping. Figure 4 In the regeneration processes 1 and 2, the gas sensor 100 is installed in the piping with the front end of the sensor element 101 protruding into the piping. The solid electrolyte of the sensor element 101 is activated using a heater-controlled process to perform regeneration (step S120). Then, the pump current Ip2 is detected at each concentration while the carbon dioxide concentration is gradually increased (step S130). Afterward, the heater-controlled process is terminated, and the gas sensor 100 is removed from the piping. In the first to fifth experimental processes, a gas obtained by gradually changing the carbon dioxide concentration using nitrogen as the base gas is used as the model gas.

[0085] Depend on Figure 4It can be seen that for the third and fifth experimental treatments, the deviation in the relationship between carbon dioxide concentration and the absolute value of pump current Ip2 is relatively small. On the other hand, it can be seen that for the first, second, and fourth experimental treatments, compared with the third and fifth experimental treatments, the deviation in the relationship between carbon dioxide concentration and the absolute value of pump current Ip2 is relatively large, and the absolute value of pump current Ip2 for the same carbon dioxide concentration is relatively small. Therefore, in the first, second, and fourth experimental treatments, compared with the third and fifth experimental treatments, it can be assumed that the measurement accuracy of carbon dioxide concentration in the measured gas is reduced. In other words, in the third and fifth experimental treatments, by performing regeneration treatment, compared with the first, second, and fourth experimental treatments, the reduction in measurement accuracy of carbon dioxide concentration in the measured gas can be suppressed. Similarly, it can be considered that, with regeneration treatment, compared with the case without regeneration treatment, the reduction in measurement accuracy of water concentration in the measured gas can also be suppressed.

[0086] Here, the correspondence between the constituent elements of this embodiment and the constituent elements of the present invention is clarified. The sensor element 101 of this embodiment corresponds to the sensor element of the present invention, and the control device 95 corresponds to the control device. The element body 102 corresponds to the element body, the first internal cavity 20 corresponds to the first chamber, the inner pump electrode 22 corresponds to the first inner electrode, the main pump unit 21 corresponds to the first pump unit, the second internal cavity 40 corresponds to the second chamber, the first measuring electrode 51 corresponds to the second inner electrode, the first measuring pump unit 50 corresponds to the second pump unit, the third internal cavity 61 corresponds to the third chamber, the second measuring electrode 44 corresponds to the third inner electrode, the second measuring pump unit 41 corresponds to the third pump unit, and the outer pump electrode 23 corresponds to the first outer electrode, the second outer electrode, and the third outer electrode. The main pump control processing corresponds to the first pump unit control processing, the first measuring pump control processing corresponds to the second pump unit control processing, and the second measuring pump control processing corresponds to the third pump unit control processing.

[0087] According to the gas sensor 100 of this embodiment described in detail above, the control device 95 performs a regeneration process when the solid electrolyte of the sensor element 101 has been activated; specifically, it performs the first to third regeneration processes. This restores the reducing or oxidizing capabilities of the inner pump electrode 22, the first measuring electrode 51, and the second measuring electrode 44. Consequently, it suppresses the decrease in the measurement accuracy of water concentration and carbon dioxide concentration in the measured gas.

[0088] It should be noted that the present invention is not limited to any of the above embodiments. Of course, any method that falls within the technical scope of the present invention can be implemented in various ways.

[0089] For example, in the above implementation, CPU97 executes... Figure 3However, it can also be replaced by executing the processing routine. Figure 5 The processing routine. Regarding Figure 5 The processing routine, besides adding steps S125 and S140, is similar to... Figure 3 The processing routines are the same. Therefore, regarding Figure 5 The processing routine and Figure 3 For processes with the same processing routine, the same step number is marked, and detailed descriptions are omitted.

[0090] Figure 5 In the processing routine, if the CPU 97 determines in step S110 that a regeneration process has been performed during this use of the gas sensor 100, it determines whether the normal processing has been continuously executed for a predetermined time ΔT (a predetermined time ΔT has elapsed since the last regeneration process) (step S125). Here, "the normal processing has been continuously executed for a predetermined time ΔT" means that in this routine, the normal processing is repeatedly executed for the predetermined time ΔT without performing a regeneration process (step S130). The predetermined time ΔT is approximately several seconds to several minutes. If the CPU 97 determines that the normal processing has not been continuously executed for the predetermined time ΔT, it executes the normal processing (step S130) and terminates the routine.

[0091] In step S125, if the CPU97 determines that the normal processing has been continuously executed for a specified time ΔT, it performs a regeneration process for a specified time T2 (step S140) and terminates the current routine. Here, the specified time T2 is defined as a time less than or equal to the specified time T1, for example, a few milliseconds to a few seconds. This allows the regeneration process to be performed periodically (without interrupting the specified time ΔT). As a result, the frequency of the regeneration process is ensured, suppressing any decrease in the accuracy of the measurement of water concentration and carbon dioxide concentration in the gas being measured.

[0092] Figure 5 In the processing routine, the CPU97 performs a regeneration process for a predetermined time T1 (step S120) when the solid electrolyte of the sensor element 101 has been activated. After that, whenever the normal process has been performed for a predetermined time ΔT, a regeneration process for a predetermined time T2 is performed (step S140). However, the CPU97 may also choose not to perform the regeneration process for the predetermined time T1.

[0093] In the above embodiment, the CPU97 determines whether the solid electrolyte of the sensor element 101 has been activated by determining whether the resistance value of the heater 72 is below a predetermined resistance value, but it is not limited to this. For example, the CPU97 may also determine whether the solid electrolyte has been activated by determining whether the execution time of the heater control process is above a predetermined time.

[0094] In the above embodiment, the CPU97 is configured to perform feedback control on the voltage Vp0 of the variable power supply 24 as a first regeneration process, so that the voltage V0 reaches a target value V0r* whose absolute value is smaller than the target value V0*, thereby controlling the main pump unit 21, but is not limited thereto. For example, the CPU97 may also be configured to perform feedback control on the voltage Vp0 of the variable power supply 24 as a first regeneration process, so that the pump current Ip0 reaches a target value Ip0r*, thereby controlling the main pump unit 21. The target value Ip0r* is a value in the direction of oxygen intake into the first internal cavity 20, and is defined as a value with the opposite sign to that when the main pump control process is performed.

[0095] In the above embodiment, the CPU97 is configured to perform feedback control on the voltage Vp1 of the variable power supply 52 as a second regeneration process, so that the voltage V1 reaches a target value V1r* whose absolute value is smaller than the target value V1*, thereby controlling the first measuring pump unit 50, but is not limited thereto. For example, the CPU97 may also be configured to perform feedback control on the voltage Vp1 of the variable power supply 52 as a second regeneration process, so that the pump current Ip1 reaches a target value Ip1r*, thereby controlling the first measuring pump unit 50. The target value Ip1r* is defined as a value whose absolute value is larger than the pump current Ip1 normally flowing when the first measuring pump control process is performed.

[0096] In the above embodiment, the CPU97 is configured to perform feedback control on the voltage Vp2 of the variable power supply 46 as a third regeneration process, so that the voltage V2 reaches a target value V2r* whose absolute value is smaller than the target value V2*, thereby controlling the second measuring pump unit 41, but is not limited thereto. For example, the CPU97 may also be configured to perform feedback control on the voltage Vp2 of the variable power supply 46 as a third regeneration process, so that the pump current Ip2 reaches a target value Ip2r*, thereby controlling the second measuring pump unit 41. The target value Ip2r* is defined as a value whose absolute value is larger than the pump current Ip2 normally flowing when the second measuring pump control process is performed.

[0097] In the above embodiments, the CPU97 is configured to perform the first, second, and third regeneration processes as a regeneration process. However, it is also possible to perform only a portion of the first, second, and third regeneration processes as a regeneration process. The inventors of the present invention have discovered through experiments or analysis that during or after use of the gas sensor 100, gas tends to adhere to the inner pump electrode 22, the first measuring electrode 51, and the second measuring electrode 44, particularly the inner pump electrode 22, resulting in a decrease in reduction capacity. Therefore, when only a portion of the first, second, and third regeneration processes is performed as a regeneration process, it is preferable to perform at least the first regeneration process.

[0098] In the above-described embodiment, the CPU 97 measures the water concentration and carbon dioxide concentration in the gas to be measured by performing a water concentration measurement process and a carbon dioxide concentration measurement process. However, the control device 95 may also measure only one of the water concentration and carbon dioxide concentration in the gas to be measured by performing only one of the water concentration measurement process and the carbon dioxide concentration measurement process.

[0099] In the above embodiments, the outer pump electrode 23 serves as a first outer electrode paired with the inner pump electrode 22 in the main pump unit 21, a second outer electrode paired with the first measuring electrode 51 in the first measuring pump unit 50, and a third outer electrode paired with the second measuring electrode 44 in the second measuring pump unit 41. That is, the first to third outer electrodes are configured as a universal outer pump electrode 23. However, this is not a limitation. For example, two of the first to third outer electrodes may be configured as universal outer pump electrodes 23, and the remaining one may be configured as an electrode independent of the outer pump electrode 23, and disposed on the outer surface of the element body 102 in a manner that contacts the gas to be measured. Alternatively, the first to third outer electrodes may be configured as separate electrodes and disposed on the outer surface of the element body 102 in a manner that contacts the gas to be measured.

[0100] In the above embodiments, the sensor element 101 of the gas sensor 100 includes a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61, but is not limited thereto. For example, it can be as follows: Figure 6 The modified sensor element 201 shown does not have a third internal cavity 61. Figure 6In the modified sensor element 201, a gas inlet 10, a first diffusion rate control unit 11, a buffer space 12, a second diffusion rate control unit 13, a first internal cavity 20, a third diffusion rate control unit 30, and a second internal cavity 40 are sequentially connected and adjacent to each other between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. Furthermore, a second measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 within the second internal cavity 40. The second measuring electrode 44 is covered by a fourth diffusion rate control unit 45. The fourth diffusion rate control unit 45 is a membrane composed of a porous ceramic material such as alumina (Al2O3). Like the fourth diffusion rate control unit 60 in the above embodiment, the fourth diffusion rate control unit 45 applies a predetermined diffusion resistance to the gas to be measured in the second internal cavity 40 and guides it towards the second measuring electrode 44. Additionally, the fourth diffusion rate control unit 45 also functions as a protective film for the second measuring electrode 44. The top electrode portion 51a of the first measuring electrode 51 is formed directly above the second measuring electrode 44. Even with this configuration, the sensor element 201 can measure the carbon dioxide concentration based on the pump current Ip2 flowing through the second measuring pump unit 41, just like in the embodiment described above. Figure 6 In the sensor element 201, the area surrounding the second measuring electrode 44 functions as a third chamber. That is, the area surrounding the second measuring electrode 44 performs the same function as the third internal cavity 61.

[0101] In the above embodiments, the main body 102 of the sensor element 101 is configured as a laminate having multiple solid electrolyte layers (layers 1 to 6), but is not limited thereto. The main body of the sensor element 101 only needs to include at least one oxygen ion-conductive solid electrolyte layer and have an internal passage for the gas to be measured. For example, Figure 1 Alternatively, layers 1 to 5, other than the second solid electrolyte layer 6, can be structural layers formed of a material other than a solid electrolyte (e.g., layers formed of aluminum oxide). In this case, it is sufficient that the electrodes of the sensor element 101 are disposed on the second solid electrolyte layer 6. For example, as long as... Figure 1 The second measuring electrode 44 can be disposed on the lower surface of the second solid electrolyte layer 6. Alternatively, the reference gas introduction space 43 can be disposed in the isolation layer 5 instead of the first solid electrolyte layer 4, and the reference gas introduction layer 48 can be disposed between the second solid electrolyte layer 6 and the isolation layer 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3. The reference electrode 42 can be disposed behind the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6.

[0102] In the above embodiments, the first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 are all configured as two horizontally elongated slits, but are not limited thereto. Alternatively, for example, one or more of the first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 may be configured as a single horizontally elongated slit.

[0103] This application claims priority based on Japanese Patent Application No. 2023-109464, filed on July 3, 2023, the entire contents of which are incorporated herein by reference.

[0104] Industrial availability

[0105] This invention can be used as a gas sensor to measure the water concentration and / or carbon dioxide concentration in gases such as automobile exhaust.

[0106] Explanation of reference numerals in the attached figures

[0107] 1 First substrate layer, 2 Second substrate layer, 3 Third substrate layer, 4 First solid electrolyte layer, 5 Isolation layer, 6 Second solid electrolyte layer, 10 Gas inlet, 11 First diffusion rate control unit, 12 Buffer space, 13 Second diffusion rate control unit, 20 First internal cavity, 21 Main pump unit, 22 Inner pump electrode, 22a Top electrode, 22b Bottom electrode, 23 Outer pump electrode, 24 Variable power supply, 30 Third diffusion rate control unit, 40 Second internal cavity, 41 Second measuring pump unit, 42 Reference electrode, 43 Reference gas inlet space, 44 Second measuring electrode, 45 Fourth diffusion rate control unit, 46 Variable power supply, 48 Reference gas inlet layer, 49 Reference gas inlet, 49a Inlet, 50 First measuring pump unit, 51 First measuring electrode, 51a Top electrode, 51b Bottom electrode, 52 Variable power supply, 60 Fourth diffusion rate control unit, 61 Third internal cavity, 70 heater section, 71 heater connector electrode, 72 heater, 73 through hole, 74 heater insulation layer, 75 pressure relief hole, 76 heater power supply, 80 oxygen partial pressure detection sensor unit for main pump control, 81 oxygen partial pressure detection sensor unit for first measuring pump control, 82 oxygen partial pressure detection sensor unit for second measuring pump control, 83 sensor unit, 95 control device, 96 control unit, 97 CPU, 98 storage unit, 100 gas sensor, 101, 201 sensor elements, 102 element body.

Claims

1. A gas sensor comprising a sensor element and a control device, for measuring the water concentration and / or carbon dioxide concentration in a gas to be measured. The sensor element includes: The main body of the element has a solid electrolyte layer with oxygen ion conductivity, and is provided with a gas flow section inside for introducing and circulating the gas to be measured. The first pump unit is configured to include a first inner electrode disposed in a first chamber in the gas flow section to be measured and a first outer electrode disposed on the outer surface of the element body. The second pump unit is configured to include a second inner electrode disposed in a second chamber located downstream of the first chamber in the gas flow section to be measured, and a second outer electrode disposed on the outer surface of the element body. as well as The third pump unit is configured to include a third inner electrode disposed in a third chamber located downstream of the second chamber in the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body. The control device performs: The first pump unit is controlled to reduce the water and carbon dioxide in the gas being measured in the first chamber by drawing oxygen from the area around the first inner electrode to the area around the first outer electrode. The second pump unit is controlled to draw oxygen from the area around the second outer electrode to the area around the second inner electrode, thereby oxidizing the hydrogen generated by the reduction of water in the first chamber in the second chamber. The third pump unit is controlled to draw oxygen from the vicinity of the third outer electrode to the vicinity of the third inner electrode, thereby oxidizing carbon monoxide generated by the reduction of carbon dioxide in the first chamber in the third chamber; and The process includes water concentration measurement and / or carbon dioxide concentration measurement. In the water concentration measurement process, the water concentration in the gas to be measured is measured based on a second pump current flowing through the second pump unit due to the control process of the second pump unit. In the carbon dioxide concentration measurement process, the carbon dioxide concentration in the gas to be measured is measured based on a third pump current flowing through the third pump unit due to the control process of the third pump unit. When specified conditions are met, the control device performs at least one of the following three processes as a regeneration process: The first regeneration process controls the first pump unit to draw oxygen from the vicinity of the first outer electrode to the vicinity of the first inner electrode. The second regeneration process involves controlling the second pump unit to draw in more oxygen from around the second outer electrode to around the second inner electrode than the second pump unit control process. The third regeneration process involves controlling the third pump unit to draw in more oxygen from around the third outer electrode to around the third inner electrode than the third pump unit control process.

2. The gas sensor according to claim 1, characterized in that, As part of the regeneration process, the control device performs at least the first regeneration process.

3. The gas sensor according to claim 1 or 2, characterized in that, The specified conditions include the condition that the solid electrolyte layer has been activated.

4. The gas sensor according to claim 1 or 2, characterized in that, The specified conditions include the condition that the control processing of the first pump unit, the control processing of the second pump unit, and the control processing of the third pump unit have been continuously executed for a specified time.

5. The gas sensor according to claim 1 or 2, characterized in that, At least two of the first outer electrode, the second outer electrode, and the third outer electrode are universal electrodes.

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