Gas sensor

Abstract

A gas sensor (100) is provided with a sensor element (101) and a control device (95). A sensor element (101) is provided with an element main body (102), a main pump unit (21), a first measurement pump unit (50), a second measurement pump unit (41), and a reference electrode (42). The first measurement pump unit (50) is configured to include a first measurement electrode (51) (second inner electrode). The second measurement pump unit (41) is configured so as to include a second measurement electrode (44). The control device (95) performs a first measurement electrode deterioration determination process, that is, on the basis of whether or not the absolute value of the voltage V2 between the second measurement electrode (44) and the reference electrode (42) during the execution of the main pump control process and the first measurement pump control process and during the stop of the second measurement pump control process is included in a predetermined high voltage region. Deterioration of the first measurement electrode (51) is determined.

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 a gas flow section inside, 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 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 the hydrogen generated from the decomposition of water vapor is selectively combusted (oxidized) in the second internal cavity. The concentration of water vapor in the gas being measured is measured based on the magnitude of the current flowing at this time. Conversely, oxygen is supplied to the vicinity of the surface of the second measuring inner pump electrode by a second measuring pump unit in a manner that the carbon monoxide generated from the decomposition of carbon dioxide is selectively combusted (oxidized) near the surface of the second measuring inner pump electrode. The concentration of carbon dioxide in the gas being measured is measured based on the magnitude of the current flowing at this time.

[0003] Furthermore, Patent Document 2 describes a gas sensor for measuring the concentration of water vapor in a gas being measured, wherein the metal component of the inner pump electrode used for measuring the concentration of water vapor is composed of gold and an alloy of gold and other precious metals (e.g., platinum). It further states that this inner pump electrode is inactive against carbon monoxide, and can selectively burn (oxidize) hydrogen, thus enabling accurate determination of the water vapor concentration even when the gas being measured contains carbon dioxide.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5918177

[0007] Patent Document 2: Japanese Patent No. 6469462 Summary of the Invention

[0008] In this gas sensor, the second inner electrode used to oxidize hydrogen (the first inner pump electrode for measurement in Patent Document 1) deteriorates with the use of the gas sensor, and the accuracy of water concentration (concentration of water vapor component) measurement sometimes decreases.

[0009] The present invention was implemented to solve the above-mentioned problems, and its main objective is to determine the deterioration of the second inner electrode.

[0010] The present invention employs the following means to achieve the aforementioned main objectives.

[0011] [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, wherein...

[0012] The sensor element includes:

[0013] The main body of the component 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.

[0014] 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.

[0015] 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.

[0016] A third pump unit, configured to include a third inner electrode disposed in a third chamber located downstream of the second chamber within the gas flow section being measured, and a third outer electrode disposed on the outer surface of the element body; and

[0017] A reference electrode is disposed inside the component body in a manner that allows it to contact a reference gas.

[0018] The control device performs:

[0019] 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.

[0020] 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.

[0021] 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 produced by the reduction of carbon dioxide in the first chamber in the third chamber; and

[0022] The process includes water concentration measurement and / or carbon dioxide concentration measurement, wherein the water concentration measurement is based on a second pump current flowing through the second pump unit due to the control processing of the second pump unit, to measure the water concentration in the gas to be measured; and the carbon dioxide concentration measurement is based on a third pump current flowing through the third pump unit due to the control processing of the third pump unit, to measure the carbon dioxide concentration in the gas to be measured.

[0023] The control device performs a second inner electrode degradation determination process, that is, it determines the degradation of the second inner electrode based on whether the absolute value of the third voltage during the execution of the first pump unit control process, the second pump unit control process, and the stop of the third pump unit control process is included in a specified high voltage region.

[0024] In this gas sensor, the control device performs a second inner electrode degradation determination process, which determines the degradation of the second inner electrode based on whether the absolute value of a third voltage during the execution of the first pump unit control process, the second pump unit control process, and the stoppage of the third pump unit control process is contained within a predetermined high-voltage region. Here, if the second inner electrode is degraded, its hydrogen oxidizing ability decreases, and therefore, some of the hydrogen reaching the second chamber arrives at the third chamber without being oxidized. The absolute value of the third voltage at this time is larger than in the case where almost no hydrogen reaches the third chamber. Therefore, based on whether the absolute value of the third voltage is contained within a predetermined high-voltage region, the degradation of the second inner electrode can be determined. The inventors of this invention have confirmed this effect through experiments, analysis, and other methods.

[0025] [2] In the gas sensor described above (the gas sensor described above [1]), the gas to be measured may be the exhaust gas of an internal combustion engine, and the control device may perform the second inner electrode degradation determination process during or after the fuel cut-off of the internal combustion engine. Compared with the exhaust gas during operation (excluding the fuel cut-off of the internal combustion engine), the carbon dioxide concentration is lower in the exhaust gas during fuel cut-off and the exhaust gas during shutdown of the internal combustion engine. Therefore, regarding the absolute value of the third voltage, the influence of carbon monoxide reaching the third chamber is smaller, and the influence of hydrogen is dominant. Therefore, the fuel cut-off and shutdown of the internal combustion engine are suitable times for performing the second inner electrode degradation determination process.

[0026] [3] The gas sensor described above (the gas sensor described in [1] or [2] above) may contain: a first noble metal with catalytic activity and a second noble metal that suppresses the catalytic activity of the first noble metal against carbon monoxide. Here, if the second inner electrode contains both the first and second noble metals, it is possible to suppress the oxidation of carbon monoxide generated from carbon dioxide in the first chamber before it reaches the third inner electrode, thus suppressing the decrease in the accuracy of carbon dioxide concentration measurement based on the third pump current flowing through the third inner electrode. In the case where the second inner electrode contains the second noble metal, as a form of degradation of the second inner electrode, the second noble metal evaporates from the second inner electrode with the use of the gas sensor, resulting in a decrease in the accuracy of water concentration and / or carbon dioxide concentration measurement. Therefore, in the case where the second inner electrode contains the second noble metal, it is of great significance to determine the degradation of the third inner electrode.

[0027] [4] In the above gas sensor (the gas sensor described in any of [1] to [3] above), two or more of the first outer electrode, the second outer electrode and the third outer electrode can be common electrodes. Attached Figure Description

[0028] Figure 1 This is a simplified cross-sectional view illustrating an example of the configuration of the gas sensor 100.

[0029] Figure 2 This is a block diagram showing the electrical connections between the control device 95 and various units, etc.

[0030] Figure 3 This is a flowchart illustrating an example of a processing routine.

[0031] Figure 4 It is a graph showing the change in voltage V2 caused by the presence or absence of degradation of the first measuring electrode 51.

[0032] Figure 5It is a graph showing the relationship between carbon monoxide concentration, hydrogen concentration and voltage V2.

[0033] Figure 6 This is a simplified cross-sectional view of the sensor element 201 in the modified example. Detailed Implementation

[0034] 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 from 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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).

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The first measuring electrode 51 is disposed in the second internal cavity 40 with the same tunnel-shaped structure as the inner pump electrode 22 disposed in the previous first internal cavity 20. That is, a top electrode portion 51a is formed relative to the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40. The side electrode portion (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b is formed in a tunnel-shaped structure on the two walls of the isolation layer 5 constituting the side wall of the second internal cavity 40.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Here, the electrodes 22, 23, 42, 44, and 51 are described. The inner pump electrode 22, the first measuring electrode 51, and the second measuring electrode 44 each contain a first noble metal with catalytic activity. Examples of the first noble metal include at least one of Pt, Rh, Ir, Ru, and Pd. The outer pump electrode 23 and the reference electrode 42 also contain the first noble metal. The first measuring electrode 51 preferably contains a second noble metal that inhibits the catalytic activity of the first noble metal against carbon monoxide. By including the second noble metal in the first measuring electrode 51, the oxidation 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 a solid electrolyte (e.g., ZrO2) with oxygen ion conductivity. Each of the electrodes 22, 23, 42, 44, and 51 is preferably a porous material. In this embodiment, the first measuring electrode 51 is a porous metal-ceramic electrode containing 1% Au and Pt and ZrO2. In addition, the inner pump electrode 22, the outer pump electrode 23, the reference electrode 42, and the second measuring electrode 44 are all porous metal-ceramic electrodes containing Pt and ZrO2.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] The control unit 96 performs a first measurement pump control process (an example of a second pump unit control process) to control the first measurement pump unit 50 by drawing oxygen from around the outer pump electrode 23 to around the first measurement electrode 51. Specifically, the control unit 96 performs feedback control on the voltage Vp1 of the variable power supply 52 to bring the voltage V1 to a target value V1*, thereby controlling the first measurement 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 in the second internal cavity 40. By performing this first measurement pump control process, the hydrogen generated from the reduction of water in the first internal cavity 20 is oxidized and water is generated again in the second internal cavity 40. At this time, the pump current Ip1 flowing through the first measurement pump unit 50 is correlated with the amount of oxygen drawn into the second internal cavity 40 to generate hydrogen in the second internal cavity 40, and further correlated with the amount of water in the measured gas in the first internal cavity 20 used to generate hydrogen in the second internal cavity 40. Therefore, the pump current Ip1 is correlated with the water concentration in the gas being measured, and the water concentration in the gas being measured can be measured based on the pump current Ip1. The control unit 96 uses, for example, the correspondence between the pump current Ip1 and the water concentration stored in the storage unit 98 to derive the water concentration in the gas being measured based on the pump current Ip1. The correspondence between the pump current Ip1 and the water concentration can be solved experimentally in advance in the form of a relational expression (e.g., a linear or quadratic function) or a mapping. Hereinafter, this process of measuring the water concentration in the gas being measured based on the pump current Ip1 will be referred to as the water concentration measurement process.

[0072] 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 within the third internal cavity 61 is oxidized. By performing this second measurement pump control process, carbon monoxide generated from the reduction of carbon dioxide in the first internal cavity 20 is oxidized again within the third internal cavity 61 to generate carbon dioxide 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 the 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. The control unit 96 uses, for example, the correspondence between the pump current Ip2 and the carbon dioxide concentration stored in the storage unit 98 to derive the carbon dioxide concentration in the measured gas based on the pump current Ip2. The correspondence between the pump current Ip2 and the carbon dioxide concentration can be solved experimentally in advance in the form of a relation (e.g., a linear or quadratic function) or a mapping. Hereinafter, the 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.

[0073] It should be noted that both hydrogen and carbon monoxide generated in the first internal cavity 20 reach the second internal cavity 40. However, among hydrogen and carbon monoxide, hydrogen diffuses faster and readily bonds with oxygen. Therefore, in the second internal cavity 40, hydrogen in both 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 both hydrogen and carbon monoxide can be more selectively oxidized by the first measuring pump control process.

[0074] 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. 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.

[0075] 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.

[0076] When using the gas sensor 100 configured in this way, the CPU 97 of the control unit 96 first performs the aforementioned heater control processing to control the temperature of the heater 72 in a manner that achieves the target temperature. When the temperature of the heater 72 reaches the target temperature (or near the target temperature), the CPU 97 begins the control of each of the aforementioned pump units 21, 41, and 50 (main pump control processing, first measuring pump control processing, and second measuring pump control processing) and obtains each of the voltages V0, V1, V2, and Vref from each of the aforementioned sensor units 80 to 83. The control unit 96 continues to perform these processes, while repeatedly executing the water concentration measurement processing and the carbon dioxide concentration measurement processing, or executing the degradation determination processing of the first measuring electrode 51 described later. In addition, 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. Regarding the control unit 96, for example, when a command is input from an engine ECU (not shown) at the start of internal combustion engine operation, the heater control processing begins; when a command is input from the engine ECU at the stop of internal combustion engine operation, the heater control processing ends.

[0077] Next, an example of the deterioration determination process of the first measuring electrode 51 will be described. Figure 3 This is a flowchart illustrating an example of a processing routine that includes a degradation determination process for the first measuring electrode 51. This routine is stored in, for example, storage unit 98 of the control unit 96 and is repeatedly executed by the CPU 97.

[0078] When execution Figure 3 In the processing routine, the CPU 97 first determines whether the internal combustion engine is either in a fuel cut-off state or stopped (step S100). For example, the CPU 97 obtains information from the engine ECU that can identify whether the internal combustion engine is in a fuel cut-off state or stopped, and performs the determination in step S100 based on the obtained information. Alternatively, the CPU 97 can detect the oxygen concentration in the gas to be measured around the sensor element 101 based on the voltage Vref of the sensor unit 83, and perform the determination in step S100 based on whether the detected oxygen concentration is contained in a high concentration region that can be considered as fuel cut-off or stopped. If the CPU 97 determines in step S100 that the internal combustion engine is neither in a fuel cut-off state nor stopped, the routine ends.

[0079] If, in step S100, the CPU97 determines that the internal combustion engine is either in the process of fuel cut-off or stopped, it stops the second measuring pump control process (step S110) and measures the voltage V2 in this state (step S120). That is, the CPU97 measures the voltage V2 when the main pump control process and the first measuring pump control process are being executed, but the second measuring pump control process is stopped. Then, the CPU97 performs a degradation determination process for the first measuring electrode 51 based on the measured voltage V2 (step S130). The CPU97 determines whether the first measuring electrode 51 has deteriorated based on whether the absolute value of the measured voltage V2 is within a predetermined high-voltage region. For example, the CPU97 determines that the first measuring electrode 51 is deteriorated if the absolute value of the measured voltage V2 is greater than a predetermined threshold V2ref1, and determines that the first measuring electrode 51 is not deteriorated if the absolute value of the measured voltage V2 is less than the threshold V2ref1. If the absolute value of voltage V2 is greater than the threshold V2ref1 in step S130, CPU97 turns on the first measuring electrode deterioration flag (step S140), starts (restarts) the second measuring pump control process (step S150), and ends the current routine. If the absolute value of voltage V2 is less than the threshold V2ref1 in step S130, CPU97 proceeds to step S150 without turning on the first measuring electrode deterioration flag and ends the current routine. It should be noted that if CPU97 determines that the first measuring electrode 51 is deteriorated in step S130, it is preferable to report the abnormality of gas sensor 100 to other devices such as the engine ECU or users such as the driver. In addition, if the first measuring electrode deterioration flag is turned on, CPU97 may not perform at least one of the water concentration measurement process and carbon dioxide concentration measurement process. If the deterioration of the first measuring electrode 51 is eliminated, for example, after replacing the deteriorated sensor element 101 of the first measuring electrode 51, CPU97 turns off the first measuring electrode deterioration flag based on the operation from the operator.

[0080] Figure 4 It is a graph showing the change in voltage V2 caused by the presence or absence of degradation of the first measuring electrode 51. Figure 5 This is a graph showing the relationship between carbon monoxide concentration, hydrogen concentration, and voltage V2. The inventors of this invention conducted the following experiments on the gas sensor 100 and obtained... Figure 4 , Figure 5The graph shows the curves. First, a gas sensor 100 with an unused (initial state) sensor element 101 and a gas sensor 100 with a degraded first measuring electrode 51 are prepared. The degraded sensor element 101 is a sensor element 101 whose first measuring electrode 51 is degraded by performing heater control processing and first measuring pump control processing for 1000 hours with the front end side of the sensor element 101 exposed to the exhaust gas of the internal combustion engine.

[0081] Next, the relationship between the water concentration in the measured gas and the voltage V2 was investigated for both the initial state sensor element 101 and the degraded sensor element 101. Figure 4 The curve is shown. Specifically, the gas sensor 100, with the sensor element 101 in its initial state, is installed in the piping such that the front end of the sensor element 101 protrudes into the piping. Next, the model gas, which is the gas to be measured, is circulated through the piping, and the control unit 96 performs heater control processing, main pump control processing, first measuring pump control processing, and second measuring pump control processing. The model gas is a gas obtained by gradually varying the concentration of water while using nitrogen as the base gas and carbon dioxide at 10%. The process is performed once at regular intervals. Figure 3 Steps S110 and S120 involve measuring voltage V2 while the main pump control process and the first measuring pump control process are in progress and the second measuring pump control process is stopped, obtaining multiple data points that correspond to the measured voltage V2 and the water concentration of the model gas at that time. Using the same method, multiple data points corresponding to voltage V2 and water concentration are also obtained for the degraded sensor element 101. A graph obtained by plotting these data points is shown below. Figure 4 .

[0082] Furthermore, for the sensor element 101 in its initial state, the relationship between carbon monoxide concentration, hydrogen concentration, and voltage V2 was investigated, and the results were obtained. Figure 5The curve is obtained. Specifically, similar to the experiment described above, the gas sensor 100 is installed in the piping, and the voltage V2 is measured while the model gas, which is the gas to be measured, is flowing through it. However, it is set that the control unit 96 performs heater control processing but does not perform main pump control processing, first measuring pump control processing, or second measuring pump control processing. The model gas used is a nitrogen-based gas containing carbon monoxide. While gradually changing the carbon monoxide concentration of the model gas, the voltage V2 is measured, and multiple data points corresponding to the voltage V2 and carbon monoxide concentration are obtained. Similarly, a nitrogen-based gas containing hydrogen is used as the model gas, and while gradually changing the hydrogen concentration of the model gas, the voltage V2 is measured, and multiple data points corresponding to the voltage V2 and hydrogen concentration are obtained. The curve obtained by plotting these data is as follows. Figure 5 .

[0083] Depend on Figure 4 It can be seen that in the initial state of sensor element 101, regardless of the water concentration, the voltage V2 is a roughly constant value (approximately 870mV), which is consistent with... Figure 5 The voltage V2 value is approximately equal when the carbon monoxide concentration is 10%. On the other hand, in the degraded sensor element 101, when the water concentration is below 5%, the voltage V2 is the same as the voltage V2 of the sensor element 101 in its initial state; however, when the water concentration is above 10%, the voltage V2 value is higher than that of the sensor element 101 in its initial state. Furthermore, the voltage V2 value of the degraded sensor element 101 at this time is... Figure 5 The voltage V2 (approximately 970 mV) is roughly equal when the hydrogen concentration is above 10%. This is believed to be because: due to the deterioration of the first measuring electrode 51, its hydrogen oxidation capacity decreases, and even with the first measuring pump control process, at least a portion of the hydrogen reaching the second measuring electrode 44 in the third internal cavity 61 is not oxidized before reaching it. Utilizing this phenomenon, in the above-mentioned… Figure 3 In step S130, the first measuring electrode 51 is determined to be degraded by judging whether the voltage V2 is contained within a predetermined high-voltage region. The predetermined high-voltage region can be determined in advance using experiments, etc., as a region where, even if carbon monoxide is present around the second measuring electrode 44, the absolute value of the voltage V2 does not reach this region in the absence of almost no hydrogen, and the absolute value of the voltage V2 reaches this region when hydrogen is present around the second measuring electrode 44. In this embodiment, as a method capable of... Figure 5 The voltage V2 and the highest carbon monoxide concentration in the atmosphere when the carbon monoxide concentration is 15% Figure 5The voltage V2 at which the hydrogen concentration is at its lowest (0.1%) is used to distinguish such values. The threshold V2ref1 is pre-defined as 920 mV, and the region exceeding this value is designated as a high-voltage region. It should be noted that the voltage V2 also varies depending on the structure of the sensor element 101 (e.g., the position of the second measuring electrode 44 and the reference electrode 42 relative to the heater 72). Figure 4 , Figure 5 The voltage V2 value and the threshold V2ref1 value shown are examples.

[0084] It should be noted that the second measuring pump control process is executed in a manner that makes the voltage V2 reach the target value V2*. Therefore, the voltage V2 does not reach the value corresponding to the hydrogen concentration and carbon monoxide concentration around the second measuring electrode 44. Consequently, it is impossible to determine the degradation of the first measuring electrode 51 based on the voltage V2. This is why the voltage V2 measurement in step S120 is performed in step S110 with the second measuring pump control process stopped. Furthermore, without the main pump control process, no hydrogen is generated from the water in the measured gas. Even with the main pump control process, hydrogen reaches the second measuring electrode 44 even if the first measuring electrode 51 is not degraded, even without the first measuring pump control process. Therefore, the voltage V2 measurement in step S120 is performed during the execution of both the main pump control process and the first measuring pump control process.

[0085] As mentioned above, Figure 4 Even in the case of a degraded sensor element 101 with a water concentration below 5%, the voltage V2 remains the same as that of the sensor element 101 in its initial state. This is believed to be because even in a degraded first measuring electrode 51, if less hydrogen reaches the second internal cavity 40, all the hydrogen can be oxidized, preventing it from reaching the second measuring electrode 44. Therefore, it is believed that if the first measuring electrode 51 deteriorates further, even with a water concentration below 5%, the voltage V2 will exceed the threshold V2ref1, allowing for detection of deterioration based on the voltage V2.

[0086] It should be noted that the specific form of deterioration of the first measuring electrode 51 is considered to be: due to the sintering development of the first noble metal contained in the electrode, the active sites acting as catalysts decrease, and the oxidation capacity of the electrode decreases. Furthermore, it is also considered that: when the first measuring electrode 51 contains a second noble metal, due to the evaporation of the second noble metal, the three-phase interface of the noble metal, solid electrolyte, and measured gas in the first measuring electrode 51 decreases, the resistance of the first measuring electrode 51 increases, and the pump current Ip1 becomes difficult to flow (i.e., the hydrogen oxidation capacity of the first measuring electrode 51 decreases).

[0087] Here, the correspondence between the constituent elements of this embodiment and the constituent elements of the present invention is clarified. The sensor element 101 of this embodiment corresponds to the sensor element of the present invention, and the control device 95 corresponds to the control device. The element body 102 corresponds to the element body, the first internal cavity 20 corresponds to the first chamber, the inner pump electrode 22 corresponds to the first inner electrode, the main pump unit 21 corresponds to the first pump unit, the second internal cavity 40 corresponds to the second chamber, the first measuring electrode 51 corresponds to the second inner electrode, the first measuring pump unit 50 corresponds to the second pump unit, the third internal cavity 61 corresponds to the third chamber, the second measuring electrode 44 corresponds to the third inner electrode, the second measuring pump unit 41 corresponds to the third pump unit, the outer pump electrode 23 corresponds to the first outer electrode, the second outer electrode, and the third outer electrode, and the reference electrode 42 corresponds to the reference electrode. The main pump control processing corresponds to the first pump unit control processing, the first measuring pump control processing corresponds to the second pump unit control processing, and the second measuring pump control processing corresponds to the third pump unit control processing. Pump current Ip1 is equivalent to the second pump current, pump current Ip2 is equivalent to the third pump current, voltage V2 is equivalent to the third voltage, and the corrected pump current Ip2ad is equivalent to the corrected third pump current. The degradation judgment process of the first measuring electrode 51 is equivalent to the degradation judgment process of the second inner electrode.

[0088] According to the gas sensor 100 of this embodiment described in detail above, the control device 95 performs a degradation determination process for the first measuring electrode 51 based on whether the absolute value of the voltage V2 during the execution of the main pump control process and the first measuring pump control process, and the cessation of the second measuring pump control process, is contained within a predetermined high-voltage region. As described above, if the first measuring electrode 51 deteriorates, hydrogen reaches the second measuring electrode 44, causing the absolute value of the voltage V2 to increase. Therefore, the degradation of the first measuring electrode 51 can be determined based on whether the absolute value of the voltage V2 is contained within a predetermined high-voltage region.

[0089] Furthermore, the gas being measured is exhaust gas from an internal combustion engine. The control device 95 performs a degradation determination process on the first measuring electrode 51 during or after the internal combustion engine's fuel cut-off. Here, the exhaust gas (gas inside the exhaust pipe) during or after the internal combustion engine's fuel cut-off has a lower carbon dioxide concentration compared to the exhaust gas during operation other than fuel cut-off. Therefore, regarding the absolute value of voltage V2, the influence of carbon monoxide reaching the third internal cavity 61 is smaller, and the influence of hydrogen is dominant. Therefore, the period during or after the internal combustion engine's fuel cut-off is a suitable time to perform the degradation determination process on the first measuring electrode 51.

[0090] Furthermore, the first measuring electrode 51 comprises a first noble metal with catalytic activity and a second noble metal that suppresses the catalytic activity of the first noble metal against carbon monoxide. As described above, if the first measuring electrode 51 comprises both the first and second noble metals, oxidation of carbon monoxide generated from carbon dioxide within the first internal cavity 20 before it reaches the second measuring electrode 44 can be suppressed around the first measuring electrode 51. Therefore, the decrease in the measurement accuracy of carbon dioxide concentration based on the pump current Ip2 flowing through the second measuring electrode 44 can be suppressed. However, when the first measuring electrode 51 comprises the second noble metal, as a form of degradation of the first measuring electrode 51, the second noble metal evaporates from the first measuring electrode 51 with the use of the gas sensor 100, resulting in a decrease in the measurement accuracy of water and carbon dioxide concentrations. Therefore, when the first measuring electrode 51 comprises the second noble metal, determining the degradation of the first measuring electrode 51 is of great significance.

[0091] 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.

[0092] For example, in the above embodiment, the CPU97 can perform step S120 after a predetermined waiting time Tw1 following the execution of step S110. The waiting time Tw1 can be predetermined based on the time required for the voltage V2 to reach a value corresponding to the hydrogen concentration in the third internal cavity 61 after the second measuring pump control process is stopped (the pump current Ip2 is stopped). The waiting time Tw1 can be set to, for example, a few milliseconds to tens of milliseconds.

[0093] In the above embodiment, the CPU97 performs a degradation determination process on the first measuring electrode 51 when the internal combustion engine is in a state of fuel cut-off or shutdown, but it is not limited to this. For example... Figure 5As shown, the voltage V2 caused by carbon monoxide around the second measuring electrode 44 and the voltage V2 caused by hydrogen are different. Therefore, even if carbon monoxide is present around the second measuring electrode 44, the presence of hydrogen around the second measuring electrode 44 can be determined based on, for example, the measured value of voltage V2 and the threshold V2ref1. Therefore, not limited to fuel cut-off (when the concentration of carbon dioxide in the measured gas is low), the CPU 97 can perform a degradation determination process for the first measuring electrode 51. For example, instead of step S100, the CPU 97 can determine whether the degradation determination process for the first measuring electrode 51 has not been performed or whether a predetermined time T1 has elapsed since the last performance during the current use of the gas sensor 100. If it has not been performed or the predetermined time T1 has elapsed since the last performance, the processing after step S110 is performed. The predetermined time T1 can be set to, for example, the time required for the first measuring electrode 51 to potentially deteriorate from the initial state or a shorter time, such as a few seconds to a few minutes, or 1000 hours to several thousand hours.

[0094] In the above embodiment, the CPU 97 measures the water concentration and carbon dioxide concentration in the gas to be measured by performing water concentration measurement processing and carbon dioxide concentration measurement processing. 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 processing and carbon dioxide concentration measurement processing.

[0095] In the above embodiments, the outer pump electrode 23 serves as a first outer electrode paired with the inner pump electrode 22 in the main pump unit 21, a second outer electrode paired with the first measuring electrode 51 in the first measuring pump unit 50, and a third outer electrode paired with the second measuring electrode 44 in the second measuring pump unit 41. That is, the first to third outer electrodes are configured as a universal outer pump electrode 23. However, this is not a limitation. For example, two of the first to third outer electrodes can be configured as universal outer pump electrodes 23, and the remaining one can be configured as an electrode independent of the outer pump electrode 23, and disposed on the outer surface of the element body 102 in a manner that contacts the gas to be measured. Alternatively, the first to third outer electrodes can be configured as separate electrodes and disposed on the outer surface of the element body 102 in a manner that contacts the gas to be measured.

[0096] 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 a sensor element 201 configured like this, the carbon dioxide concentration can be measured based on the pump current Ip2 flowing through the second measuring pump unit 41, just like in the above embodiment. 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.

[0097] 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 may 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 In this configuration, layers 1 to 5, excluding the second solid electrolyte layer 6, can be structural layers formed of a material other than the solid electrolyte (e.g., layers formed of aluminum oxide). In this case, the electrodes of the sensor element 101 can be disposed within the second solid electrolyte layer 6. For example, 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.

[0098] This application claims priority based on Japanese Patent Application No. 2023-109463, filed on July 3, 2023, the entire contents of which are incorporated herein by reference.

[0099] Industrial availability

[0100] 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.

[0101] Explanation of reference numerals in the attached figures

[0102] 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 gas sensor is characterized in that... The sensor element includes: The main body of the component 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. 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 to be measured, and a third outer electrode disposed on the outer surface of the element body. as well as A reference electrode is disposed inside the component body in a manner that allows it to contact a reference gas. The control device performs: The first pump unit is controlled to draw oxygen from the area around the first inner electrode to the area around the first outer electrode, thereby reducing water and carbon dioxide in the gas being measured in the first chamber. The second pump unit is controlled to draw oxygen from the 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. 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 produced 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, wherein the water concentration measurement is based on a second pump current flowing through the second pump unit due to the control processing of the second pump unit, to measure the water concentration in the gas to be measured; and the carbon dioxide concentration measurement is based on a third pump current flowing through the third pump unit due to the control processing of the third pump unit, to measure the carbon dioxide concentration in the gas to be measured. The control device performs a second inner electrode degradation determination process, that is, it determines the degradation of the second inner electrode based on whether the absolute value of the third voltage during the execution of the first pump unit control process, the second pump unit control process, and the stop of the third pump unit control process is included in a specified high voltage region.

2. The gas sensor according to claim 1, characterized in that, The gas being measured is the exhaust gas from an internal combustion engine. The control device performs the second inner electrode degradation determination process during fuel cut-off or shutdown of the internal combustion engine.

3. The gas sensor according to claim 1 or 2, characterized in that, The second inner electrode contains a first noble metal with catalytic activity and a second noble metal that inhibits the catalytic activity of the first noble metal against carbon monoxide.

4. The gas sensor according to claim 1 or 2, characterized in that, Two or more of the first outer electrode, the second outer electrode, and the third outer electrode are common electrodes.

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