gas sensor

Abstract

To detect specific gas concentration and water concentration in gas to be measured.SOLUTION: A gas sensor 100 comprises a sensor element 101 and a controller. The sensor element 101 includes an element body, a measuring pump cell 41 containing a measuring electrode 44, an auxiliary pump cell 50 containing an auxiliary pump electrode 51, and a reference electrode 42. The controller performs adjusting pump control processing of controlling the auxiliary pump cell 50 so that voltage V1 between the reference electrode 42 and the auxiliary pump electrode 51 is a target value V1*. The controller performs measuring pump control processing of controlling the measuring pump cell 41 so that voltage V2 between the reference electrode 42 and the measuring electrode 44 is a target value V2*. The controller detects the specific gas concentration on the basis of a pump current Ip2. The controller performs water concentration detection processing of detecting the water concentration in gas to be measured on the basis of a change of the pump current Ip2 when at least one of the target value V1* and the target value V2* has been changed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas sensor.

Background Art

[0002] Conventionally, gas sensors for detecting the concentration of specific gases such as NOx in a measured gas such as exhaust gas of an automobile have been known. For example, Patent Document 1 describes a gas sensor including an element body provided therein with a measured gas flow section for introducing and flowing a measured gas containing an oxygen ion conductive solid electrolyte layer, and a plurality of electrodes disposed on the element body. When detecting the concentration of NOx with this gas sensor, first, oxygen is pumped out or pumped in between an oxygen concentration adjustment chamber in the measured gas flow section and the outside of the sensor element, and the oxygen concentration in the oxygen concentration adjustment chamber is adjusted. The measured gas after the oxygen concentration is adjusted reaches a measurement chamber provided on the downstream side of the oxygen concentration adjustment chamber in the measured gas flow section. In the measurement chamber, NOx in the measured gas is reduced around a measurement electrode disposed in the measurement chamber. Then, the measurement pump cell is feedback-controlled so that the voltage V2 generated between the measurement electrode and the reference electrode becomes a predetermined target value, and oxygen around the measurement electrode is pumped out. Based on the pump current Ip2 flowing at this time, the concentration of NOx in the measured gas is detected.

[0003] Furthermore, gas sensors that detect water in a gas being measured are also known. For example, the gas sensor described in Patent Document 2 detects a first current flowing between a pair of second electrodes when a first voltage, set within a range in which the water in the gas being measured does not substantially dissociate, is generated between a pair of first electrodes. This gas sensor also detects a second current flowing between a pair of second electrodes when a second voltage, set within a range in which the water in the gas being measured does dissociate, is generated between a pair of first electrodes. Based on the first and second currents, the humidity of the gas being measured is detected. The gas sensor described in Patent Document 3 adjusts the oxygen partial pressure in the first internal cavity of the sensor element so that substantially all of the water vapor and carbon dioxide components in the gas being measured are decomposed in the first internal cavity. Then, oxygen is supplied to the second internal cavity by a first measuring electrochemical pumping cell so that the hydrogen generated by the decomposition of the water vapor component selectively burns in the second internal cavity, and the concentration of the water vapor component present in the gas being measured is determined based on the magnitude of the current that flows at this time. Furthermore, this gas sensor supplies oxygen to the surface of the second measuring inner electrode via a second measuring electrochemical pumping cell so that carbon monoxide produced by the decomposition of carbon dioxide components is selectively combusted, and determines the concentration of carbon dioxide components present in the gas being measured based on the magnitude of the current that flows at this time. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-091669 [Patent Document 2] Patent No. 5021697 [Patent Document 3] Patent No. 5918177 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Incidentally, even with the gas sensor described in Patent Document 1, there was a demand to detect not only the concentration of a specific gas but also the concentration of water. However, the sensor element of the gas sensor in Patent Document 2 does not have the oxygen concentration adjustment chamber and measurement chamber described in Patent Document 1, and the structure of the sensor element differs between Patent Document 1 and Patent Document 2. Furthermore, the gas sensor in Patent Document 3 detects the concentration of water vapor and carbon dioxide components based on the current when oxygen is drawn into the sensor element, and does not describe detecting the concentration of a specific gas based on the current when oxygen is drawn out of the measurement chamber, as in Patent Document 1, and the method of detecting the concentration of a specific gas differs between Patent Document 1 and Patent Document 3. For this reason, in a gas sensor that has an oxygen concentration adjustment chamber and a measurement chamber and detects the concentration of a specific gas based on the pump current when oxygen is drawn out of the measurement chamber, as in Patent Document 1, a method for further detecting the concentration of water in the gas being measured was not known.

[0006] This invention was made to solve these problems, and its main purpose is to detect the concentration of a specific gas and the concentration of water in a gas being measured. [Means for solving the problem]

[0007] To achieve the main objectives described above, the present invention employs the following means.

[0008] [1] The gas sensor of the present invention is The element body has an oxygen ion conductive solid electrolyte layer and an internal gas flow section for introducing and circulating the gas to be measured, The system comprises an internal measuring electrode disposed in the measuring chamber of the gas flow section to be measured, and a measuring pump cell that pumps oxygen from the measuring chamber to the outside of the element body, The system includes an internal adjustment electrode located in an oxygen concentration adjustment chamber situated upstream of the measurement chamber within the gas flow section to be measured, and comprises an adjustment pump cell for adjusting the oxygen concentration in the oxygen concentration adjustment chamber, A reference electrode is disposed inside the element body so as to be in contact with a reference gas that serves as a reference for detecting the specific gas concentration, which is the concentration of a specific gas in the gas being measured. A sensor element having, A control device that performs: an adjustment pump control process to adjust the oxygen concentration in the oxygen concentration adjustment chamber by controlling the adjustment pump cell so that the adjustment voltage, which is the voltage between the reference electrode and the inner adjustment electrode, becomes the adjustment voltage target value; and a measurement pump control process to pump oxygen from the measurement chamber by controlling the measurement pump cell so that the measurement voltage, which is the voltage between the reference electrode and the inner measurement electrode, becomes the measurement voltage target value. Equipped with, The control device detects the concentration of the specific gas in the gas to be measured based on the measuring pump current flowing through the measuring pump cell by the measuring pump control process, The control device performs a water concentration detection process to detect the water concentration in the gas to be measured based on the change in the measuring pump current that flows during the execution of the adjustment pump control process and the measuring pump control process when at least one of the adjustment voltage target value and the measuring voltage target value is changed. It is.

[0009] In this gas sensor, the control device performs adjustment pump control processing to adjust the oxygen concentration in the oxygen concentration adjustment chamber by controlling the adjustment pump cell so that the adjustment voltage, which is the voltage between the reference electrode and the inner adjustment electrode, becomes the adjustment voltage target value. The control device also performs measurement pump control processing to pump oxygen from the measurement chamber by controlling the measurement pump cell so that the measurement voltage, which is the voltage between the reference electrode and the inner measurement electrode, becomes the measurement voltage target value. The control device then detects the concentration of a specific gas in the gas being measured based on the measurement pump current flowing through the measurement pump cell as a result of the measurement pump control processing. Furthermore, the control device performs water concentration detection processing to detect the water concentration in the gas being measured based on the change in the measurement pump current flowing during the execution of the adjustment pump control processing and the measurement pump control processing when at least one of the adjustment voltage target value and the measurement voltage target value is changed. Here, the inventors have found that the change in the measurement pump current when at least one of the adjustment voltage target value and the measurement voltage target value is changed correlates with the water concentration in the gas being measured. Therefore, the water concentration in the gas being measured can be detected based on this change in measurement pump current. Based on the above, the gas sensor of the present invention can detect the concentration of a specific gas and the concentration of water in the gas being measured.

[0010] [2] In the gas sensor described above (the gas sensor described in [1] above), the control device may, in the water concentration detection process, change the absolute value of the adjustment voltage target value to a small value and change the absolute value of the measurement voltage target value to a large value, or change the absolute value of the adjustment voltage target value to a large value and change the absolute value of the measurement voltage target value to a small value. In this way, even if the amount of change in each of the adjustment voltage target value and the measurement voltage target value is small, the change in the measurement pump current due to water in the gas being measured will be relatively large, making it easier to detect the water concentration.

[0011] [3] In the gas sensor described above (the gas sensor described in [1] or [2] above), the oxygen concentration adjustment chamber has a first internal cavity and a second internal cavity provided downstream of the first internal cavity and upstream of the measurement chamber, the adjustment pump cell has a main pump cell that adjusts the oxygen concentration in the first internal cavity and an auxiliary pump cell that adjusts the oxygen concentration in the second internal cavity, the internal adjustment electrode is an internal auxiliary pump electrode disposed in the second internal cavity and constituting a part of the auxiliary pump cell, and the adjustment pump control process may include a main pump control process that controls the main pump cell to adjust the oxygen concentration in the first internal cavity and an auxiliary pump control process that controls the auxiliary pump cell so that the adjustment voltage becomes the adjustment voltage target value.

[0012] [4] In the gas sensor described above (the gas sensor described in any of [1] to [3] above), the control device may correct the specific gas concentration in the gas to be measured based on the water concentration in the gas to be measured detected in the water concentration detection process. Here, even if the specific gas concentration in the gas to be measured is the same, the current of the measuring pump may change depending on the water concentration in the gas to be measured. Therefore, by correcting the specific gas concentration based on the detected water concentration, the detection accuracy of the specific gas concentration is improved.

[0013] [5] In the gas sensor described above (the gas sensor described in any of [1] to [4] above), the control device may perform a gas temperature detection process to detect the gas temperature of the gas to be measured based on the change in the measuring pump current that flows during the execution of the adjustment pump control process and the measuring pump control process when the adjustment voltage target value is changed, and the change in the measuring pump current that flows during the execution of the adjustment pump control process and the measuring pump control process when the measuring voltage target value is changed. Here, the inventors have found that when comparing the change in the measuring pump current when the adjustment voltage target value is changed and the change in the measuring pump current when the measuring voltage target value is changed, the former is less affected by the gas temperature of the gas to be measured. Therefore, the gas temperature of the gas to be measured can be detected based on the former and the latter by utilizing this fact. In this case, it is preferable that the control device detects the water concentration in the gas to be measured based on the change in the measuring pump current when the adjustment voltage target value is changed in the water concentration detection process.

[0014] [6] In the gas sensor described above (the gas sensor described in [5] above), the control device may correct the specific gas concentration in the gas to be measured based on the water concentration detected in the water concentration detection process and the gas temperature detected in the gas temperature detection process. Here, even if the specific gas concentration in the gas to be measured is the same, the measuring pump current may change depending on the water concentration and gas temperature in the gas to be measured. Therefore, the detection accuracy of the specific gas concentration is improved by correcting the specific gas concentration based on the measuring pump current based on the detected water concentration and the detected gas temperature. [Brief explanation of the drawing]

[0015] [Figure 1] A schematic cross-sectional diagram illustrating an example of the configuration of the gas sensor 100. [Figure 2] A block diagram showing the electrical connection relationships between the control device 95 and each cell and heater 72. [Figure 3] A graph showing the relationship between the target value V1*, water concentration, and pump current Ip2. [Figure 4] Graph showing the relationship between the change in the offset current Ip2offset and the changes in the water concentration and the target value V1*. [Figure 5] Graph showing the relationship between the target value V2*, the water concentration, and the pump current Ip2. [Figure 6] Graph showing the relationship between the change in the offset current Ip2offset and the changes in the water concentration and the target value V2*. [Figure 7] Flowchart showing an example of a control routine. [Figure 8] Conceptual diagram showing the relationship between the slope of the change in the offset current Ip2offset with respect to the changes in the water concentration and the target value V2*, and the gas temperature. [Figure 9] Conceptual diagram showing the relationship between the water concentration, the gas temperature, and the offset current Ip2offset. [Figure 10] Schematic cross-sectional view of the sensor element 201 of a modification.

Embodiments for Carrying Out the Invention

[0016] Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view schematically showing an example of the configuration of a gas sensor 100 according to an embodiment of the present invention. FIG. 2 is a block diagram showing the electrical connection relationship between the control device 95, each cell, and the heater 72. This gas sensor 100 is attached to a pipe such as an exhaust gas pipe of an internal combustion engine, for example. The gas sensor 100 detects the concentration of specific gases such as NOx and ammonia in the measured gas, with the exhaust gas of the internal combustion engine as the measured gas. In the present embodiment, the gas sensor 100 is configured to measure the NOx concentration as the specific gas concentration. The gas sensor 100 includes a sensor element 101 having a long rectangular parallelepiped shape, cells 21, 41, 50, 80 to 83 provided in the sensor element 101, a heater section 70 provided inside the sensor element 101, variable power supplies 24, 46, 52, and a heater power supply 76, and a control device 95 that controls the entire gas sensor 100.

[0017] The sensor element 101 is a laminated element having six layers stacked in this order from the bottom as seen in the drawing: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, each consisting of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO2). Furthermore, the solid electrolytes forming these six layers are dense and airtight. Such a sensor element 101 is manufactured, for example, by performing predetermined processing and printing circuit patterns on ceramic green sheets corresponding to each layer, stacking them, and then firing them to integrate them.

[0018] On the tip side of the sensor element 101 (the left end side in Figure 1), a gas inlet 10, a first diffusion rate-limiting section 11, a buffer space 12, a second diffusion rate-limiting section 13, a first internal cavity 20, a third diffusion rate-limiting section 30, a second internal cavity 40, a fourth diffusion rate-limiting section 60, and a third internal cavity 61 are formed adjacent to each other in this order, communicating with each other.

[0019] The gas inlet 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are spaces inside the sensor element 101, provided in a manner in which the spacer layer 5 has been hollowed out, with the upper part partitioned by the lower surface of the second solid electrolyte layer 6, the lower part partitioned by the upper surface of the first solid electrolyte layer 4, and the sides partitioned by the side surface of the spacer layer 5.

[0020] The first diffusion rate-limiting section 11, the second diffusion rate-limiting section 13, and the third diffusion rate-limiting section 30 are all provided as two horizontally elongated slits (with their longitudinal openings perpendicular to the drawing). The fourth diffusion rate-limiting section 60 is provided as a single horizontally elongated slit (with its longitudinal openings perpendicular to the drawing) formed as a gap with the lower surface of the second solid electrolyte layer 6. The section from the gas inlet 10 to the third internal cavity 61 is also referred to as the gas flow section under measurement.

[0021] Furthermore, a reference gas introduction space 43 is provided at a position further from the tip side than the gas flow section to be measured, between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, with its sides partitioned by the side surface of the first solid electrolyte layer 4. For example, air is introduced into the reference gas introduction space 43 as the reference gas when measuring the NOx concentration.

[0022] The reference gas introduction layer 48 is a layer made of porous ceramics, and the reference gas is introduced into the reference gas introduction layer 48 through the reference gas introduction space 43. The reference gas introduction layer 48 is also formed to cover the reference electrode 42.

[0023] The reference electrode 42 is formed in such a manner that it is 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 will be described later, it is possible to measure the oxygen concentration (partial pressure of oxygen) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 using the reference electrode 42. The reference electrode 42 is formed as a porous cermet electrode (for example, a cermet electrode made of Pt and ZrO2).

[0024] In the gas flow section, the gas inlet 10 is a part that opens to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas inlet 10. The first diffusion rate-limiting section 11 is a part that imparts a predetermined diffusion resistance to the gas to be measured taken in from the gas inlet 10. The buffer space 12 is a space provided to guide the gas to be measured introduced from the first diffusion rate-limiting section 11 to the second diffusion rate-limiting section 13. The second diffusion rate-limiting section 13 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal space 20. When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, the gas to be measured, which is rapidly drawn into the sensor element 101 from the gas inlet 10 due to pressure fluctuations of the gas to be measured in the external space (pulsations of exhaust pressure if the gas to be measured is automobile exhaust gas), is not directly introduced into the first internal cavity 20. Instead, the pressure fluctuations of the gas to be measured are canceled out through the first diffusion rate-limiting unit 11, the buffer space 12, and the second diffusion rate-limiting unit 13 before being introduced into the first internal cavity 20. As a result, the pressure fluctuations of the gas to be measured introduced into the first internal cavity 20 become almost negligible. The first internal cavity 20 is provided as a space for adjusting the partial pressure of oxygen in the gas to be measured introduced through the second diffusion rate-limiting unit 13. This partial pressure of oxygen is adjusted by the operation of the main pump cell 21.

[0025] The main pump cell 21 is an electrochemical pump cell comprising an inner pump electrode 22 having a ceiling electrode portion 22a provided over almost the entire lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, an outer pump electrode 23 provided in a manner exposed to the external space in a region corresponding to the ceiling electrode portion 22a on the upper surface of the second solid electrolyte layer 6, and the second solid electrolyte layer 6 sandwiched between these electrodes.

[0026] The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that partition the first internal cavity 20, and the spacer layer 5 that provides the side walls. Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling 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 provides the bottom surface. A side electrode portion (not shown) is formed on the side wall surface (inner surface) of the spacer layer 5 that constitutes both side walls of the first internal cavity 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b, and is arranged in a tunnel-shaped structure at the location where the side electrode portion is installed.

[0027] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (for example, cermet electrodes made of Pt containing 1% Au and ZrO2). The inner pump electrode 22, which comes into contact with the gas to be measured, is formed using a material with reduced reducing ability to NOx components in the gas to be measured.

[0028] In the main pump cell 21, by applying a desired voltage Vp0 between the inner pump electrode 22 and the outer pump electrode 23, and flowing a pump current Ip0 in the positive or negative direction between the inner pump electrode 22 and the outer pump electrode 23, it is possible to pump oxygen from the first internal cavity 20 to the external space, or pump oxygen from the external space into the first internal cavity 20.

[0029] Furthermore, in order to detect the oxygen concentration (partial pressure of oxygen) in the atmosphere in the first internal cavity 20, an electrochemical sensor cell, i.e., a main pump control oxygen partial pressure detection sensor cell 80, is constructed using an inner pump electrode 22, a second solid electrolyte layer 6, a spacer layer 5, a first solid electrolyte layer 4, a third substrate layer 3, and a reference electrode 42.

[0030] The oxygen concentration (oxygen partial pressure) in the first internal cavity 20 can be determined by measuring the electromotive force (voltage V0) in the oxygen partial pressure detection sensor cell 80 for main pump control. Furthermore, the pump current Ip0 is controlled by feedback control of the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes a target value. As a result, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value.

[0031] The third diffusion rate-limiting section 30 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (partial oxygen pressure) is controlled by the operation of the main pump cell 21 in the first internal cavity 20, and guides the gas to be measured to the second internal cavity 40.

[0032] The second internal cavity 40 is provided as a space for further adjustment of the oxygen partial pressure by the auxiliary pump cell 50 for the gas to be measured, which is introduced through the third diffusion rate-limiting unit 30 after the oxygen concentration (oxygen partial pressure) has been adjusted in the first internal cavity 20. As a result, the oxygen concentration in the second internal cavity 40 can be kept constant with high precision, enabling highly accurate NOx concentration measurement in the gas sensor 100.

[0033] The auxiliary pump cell 50 is an auxiliary electrochemical pump cell composed of an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided over substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40, an outer pump electrode 23 (not limited to the outer pump electrode 23, any suitable electrode on the outside of the sensor element 101 is sufficient), and the second solid electrolyte layer 6.

[0034] The auxiliary pump electrode 51 is disposed within the second internal cavity 40 in a tunnel-shaped structure similar to that of the inner pump electrode 22 provided within the first internal cavity 20. Specifically, a ceiling electrode portion 51a is formed on the second solid electrolyte layer 6 which forms the ceiling surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 which forms the bottom surface of the second internal cavity 40. Side electrode portions (not shown) connecting the ceiling electrode portion 51a and the bottom electrode portion 51b are formed on both walls of the spacer layer 5 which forms the side walls of the second internal cavity 40, creating a tunnel-shaped structure. The auxiliary pump electrode 51 is also formed using a material with weakened reduction ability for NOx components in the gas being measured, similar to the inner pump electrode 22.

[0035] In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, it is possible to pump oxygen from the atmosphere in the second internal cavity 40 to the outside space, or pump oxygen from the outside space into the second internal cavity 40.

[0036] Furthermore, in order to control the partial pressure of oxygen in the atmosphere within the second internal cavity 40, an electrochemical sensor cell, namely an oxygen partial pressure detection sensor cell 81 for auxiliary pump control, is constructed using an auxiliary pump electrode 51, a reference electrode 42, a second solid electrolyte layer 6, a spacer layer 5, a first solid electrolyte layer 4, and a third substrate layer 3.

[0037] Furthermore, the auxiliary pump cell 50 is pumped by a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the oxygen partial pressure detection sensor cell 81 for auxiliary pump control. As a result, the oxygen partial pressure in the atmosphere inside the second internal cavity 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

[0038] Furthermore, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input to the oxygen partial pressure detection sensor cell 80 for main pump control as a control signal, and the aforementioned target value of its voltage V0 is controlled so that the gradient of the oxygen partial pressure in the gas to be measured, introduced from the third diffusion rate-limiting unit 30 into the second internal cavity 40, remains constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of approximately 0.001 ppm through the action of the main pump cell 21 and the auxiliary pump cell 50.

[0039] The fourth diffusion rate-limiting section 60 is the part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (partial pressure of oxygen) is controlled by the operation of the auxiliary pump cell 50 in the second internal cavity 40, and guides the gas to be measured to the third internal cavity 61. The fourth diffusion rate-limiting section 60 plays a role in limiting the amount of NOx flowing into the third internal cavity 61.

[0040] The third internal cavity 61 is provided as a space for performing processing related to the measurement of nitrogen oxide (NOx) concentration in the gas to be measured, which is introduced through the fourth diffusion rate-limiting unit 60 after the oxygen concentration (partial pressure of oxygen) has been adjusted in advance in the second internal cavity 40. The NOx concentration is measured mainly in the third internal cavity 61 by the operation of the measuring pump cell 41.

[0041] The measuring pump cell 41 measures the NOx concentration in the gas to be measured within the third internal cavity 61. The measuring pump cell 41 is an electrochemical pump cell composed of a measuring electrode 44 provided on the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 61, an outer pump electrode 23, a second solid electrolyte layer 6, a spacer layer 5, and the first solid electrolyte layer 4. The measuring electrode 44 is a porous cermet electrode made of a material that has a higher reduction capacity for NOx components in the gas to be measured than the inner pump electrode 22. The measuring electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere within the third internal cavity 61.

[0042] In the measuring pump cell 41, oxygen generated by the decomposition of nitrogen oxides in the atmosphere surrounding the measuring electrode 44 can be pumped out, and its amount can be detected as the pump current Ip2.

[0043] Furthermore, in order to detect the partial oxygen pressure around the measuring electrode 44, an electrochemical sensor cell, namely an oxygen partial pressure detection sensor cell 82 for controlling the measuring pump, is formed by the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the oxygen partial pressure detection sensor cell 82 for controlling the measuring pump.

[0044] The gas to be measured, introduced into the second internal cavity 40, reaches the measuring electrode 44 in the third internal cavity 61 via the fourth diffusion rate-limiting section 60 under controlled conditions of oxygen partial pressure. Nitrogen oxides in the gas to be measured surrounding the measuring electrode 44 are reduced (2NO → N2 + O2) to generate oxygen. This generated oxygen is then pumped by the measuring pump cell 41, and at this time, the voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the oxygen partial pressure detection sensor cell 82 for measuring pump control remains constant (target value). Since the amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, the nitrogen oxide concentration in the gas to be measured is calculated using the pump current Ip2 in the measuring pump cell 41.

[0045] Furthermore, by combining the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 to constitute an oxygen partial pressure detection means as an electrochemical sensor cell, it is possible to detect an electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of NOx components in the atmosphere around the measuring electrode 44 and the amount of oxygen contained in the reference atmosphere, thereby making it possible to determine the concentration of NOx components in the gas to be measured.

[0046] Furthermore, an electrochemical sensor cell 83 is constructed from a second solid electrolyte layer 6, a spacer layer 5, a first solid electrolyte layer 4, a third substrate layer 3, an outer pump electrode 23, and a reference electrode 42. The electromotive force (voltage Vref) obtained by this sensor cell 83 makes it possible to detect the partial pressure of oxygen in the gas being measured outside the sensor.

[0047] In a gas sensor 100 having such a configuration, the gas to be measured, whose oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect the measurement of NOx) by operating the main pump cell 21 and the auxiliary pump cell 50, is supplied to the measuring pump cell 41. Therefore, the NOx concentration in the gas to be measured can be determined based on the pump current Ip2 that flows as oxygen generated by the reduction of NOx is pumped out from the measuring pump cell 41, which is approximately proportional to the NOx concentration in the gas to be measured.

[0048] Furthermore, the sensor element 101 is equipped with a heater section 70 that plays a role in temperature control by heating and maintaining the sensor element 101 to enhance the oxygen ion conductivity of the solid electrolyte. The heater section 70 comprises a heater connector electrode 71, a heater 72, a through-hole 73, a heater insulating layer 74, and a pressure relief hole 75.

[0049] The heater connector electrode 71 is an electrode formed in such a manner that it is in contact with the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to an external power supply, power can be supplied to the heater unit 70 from an external source.

[0050] The heater 72 is an electrical resistor formed sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 is connected to the heater connector electrode 71 via a through-hole 73, and generates heat when power is supplied from the heater power supply 76 (see Figure 2) through the heater connector electrode 71, thereby heating and maintaining the temperature of the solid electrolyte forming the sensor element 101.

[0051] Furthermore, the heater 72 is embedded throughout the entire area from the first internal cavity 20 to the third internal cavity 61, making it possible to adjust the entire sensor element 101 to a temperature at which the solid electrolyte is activated.

[0052] The heater insulating layer 74 is an insulating layer formed on the upper and lower surfaces of the heater 72 using an insulator such as alumina. The heater insulating layer 74 is formed to provide electrical insulation between the second substrate layer 2 and the heater 72, and between the third substrate layer 3 and the heater 72.

[0053] The pressure relief hole 75 is a portion that penetrates the third substrate layer 3 and the reference gas introduction layer 48 and communicates with the reference gas introduction space 43, and is formed for the purpose of mitigating the rise in internal pressure due to the rise in temperature within the heater insulating layer 74.

[0054] As shown in Figure 2, the control device 95 comprises the variable power supplies 24, 46, and 52 described above, the heater power supply 76 described above, and the control unit 96. The control unit 96 is a microprocessor equipped with a CPU 97 and a memory unit 98. The memory unit 98 is a non-volatile memory that can be rewritten and can store various programs and various data, for example. The control unit 96 receives the voltage V0 detected by the oxygen partial pressure detection sensor cell 80 for main pump control, the voltage V1 detected by the oxygen partial pressure detection sensor cell 81 for auxiliary pump control, the voltage V2 detected by the oxygen partial pressure detection sensor cell 82 for measuring pump control, the voltage Vref detected by the sensor cell 83, the pump current Ip0 detected by the main pump cell 21, the pump current Ip1 detected by the auxiliary pump cell 50, and the pump current Ip2 detected by the measuring pump cell 41. Furthermore, the control unit 96 controls the voltages Vp0, Vp1, and Vp2 output by the variable power supplies 24, 46, and 52 by outputting control signals to them, thereby controlling the main pump cell 21, the measuring pump cell 41, and the auxiliary pump cell 50. The control unit 96 controls the power supplied by the heater power supply 76 to the heater 72 by outputting control signals to the heater power supply 76. The memory unit 98 also stores target values ​​V0*, V1*, V2*, which will be described later. The CPU 97 of the control unit 96 controls each of the cells 21, 41, and 50 by referring to these target values ​​V0*, V1*, V2*.

[0055] The control unit 96 performs auxiliary pump control processing to control the auxiliary pump cell 50 so that the oxygen concentration in the second internal cavity 40 reaches a target concentration. Specifically, the control unit 96 controls the auxiliary pump cell 50 by feedback control of the voltage Vp1 of the variable power supply 52 so that the voltage V1 becomes a constant value (referred to as the target value V1*). The target value V1* is defined as a value such that the oxygen concentration in the second internal cavity 40 becomes a predetermined low concentration that does not substantially affect the measurement of NOx.

[0056] The control unit 96 performs main pump control processing to control the main pump cell 21 so that the pump current Ip1 flowing when the auxiliary pump cell 50 adjusts the oxygen concentration in the second internal cavity 40 by the auxiliary pump control processing becomes a target current (referred to as target value Ip1*). Specifically, the control unit 96 sets a target value of voltage V0 (referred to as target value V0*) based on the pump current Ip1 so that the pump current Ip1 flowing due to voltage Vp1 becomes a constant target value Ip1* (feedback control). Then, the control unit 96 feedback controls the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0* (i.e., so that the oxygen concentration in the first internal cavity 20 becomes the target concentration). This main pump control processing ensures that the gradient of the oxygen partial pressure in the gas to be measured introduced into the second internal cavity 40 from the third diffusion rate-limiting unit 30 is always constant. The target value V0* is set to a value such that the oxygen concentration in the first internal cavity 20 is higher than 0% but lower than 0%. Furthermore, the pump current Ip0 that flows during this main pump control process changes according to the oxygen concentration of the gas to be measured (i.e., the gas to be measured around the sensor element 101) flowing into the gas flow section from the gas inlet 10. Therefore, the control unit 96 can also detect the oxygen concentration in the gas to be measured based on the pump current Ip0.

[0057] The main pump control process and auxiliary pump control process described above are collectively referred to as the adjustment pump control process. The first internal cavity 20 and the second internal cavity 40 are collectively referred to as the oxygen concentration adjustment chamber. The main pump cell 21 and the auxiliary pump cell 50 are collectively referred to as the adjustment pump cell. The control unit 96 performs the adjustment pump control process, causing the adjustment pump cell to adjust the oxygen concentration in the oxygen concentration adjustment chamber.

[0058] Furthermore, the control unit 96 performs a measurement pump control process to control the measurement pump cell 41 so that the voltage V2 becomes a constant value (referred to as the target value V2*) (i.e., so that the oxygen concentration in the third internal cavity 61 becomes a predetermined low concentration). Specifically, the control unit 96 controls the measurement pump cell 41 by feedback control of the voltage Vp2 of the variable power supply 46 so that the voltage V2 becomes the target value V2*. Through this measurement pump control process, oxygen is pumped out from the third internal cavity 61.

[0059] The measurement pump control process is performed so that oxygen is pumped out of the third internal cavity 61 so that the oxygen generated by the reduction of NOx in the gas being measured in the third internal cavity 61 becomes virtually zero. The control unit 96 then acquires the pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal cavity 61 originating from the specific gas (in this case, NOx), and calculates the NOx concentration in the gas being measured based on this pump current Ip2.

[0060] The memory unit 98 stores relationships between the pump current Ip2 and NOx concentration, such as relational equations (e.g., linear or quadratic functions) or maps. Such relational equations or maps can be determined in advance through experiments.

[0061] The control unit 96 outputs a control signal to the heater power supply 76 to perform heater control processing so that the temperature of the heater 72 reaches a target temperature (for example, 800°C). Here, the temperature of the heater 72 can be expressed as a linear function of the resistance value of the heater 72. Therefore, in the heater control processing, the control unit 96 calculates the resistance value of the heater 72 as a value that can be considered as the temperature of the heater 72 (a value that can be converted to temperature), and feedback controls the heater power supply 76 so that the calculated resistance value becomes the target resistance value (the resistance value corresponding to the target temperature). The control unit 96 can, for example, acquire 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 acquired voltage and current. The control unit 96 may also calculate the resistance value of the heater 72 using, for example, the three-terminal method or the four-terminal method. When energizing the heater 72, the heater power supply 76 adjusts the power supplied to the heater 72 by changing the value of the voltage applied to the heater 72 based on, for example, the control signal from the control unit 96.

[0062] The inventors investigated the relationship between the target value V1* of the gas sensor 100, the water concentration in the gas to be measured, and the pump current Ip2. First, three types of gases were prepared as the gas to be measured: a first gas with nitrogen as the base gas, an oxygen concentration of 0%, a water concentration of 3%, and an NO concentration of 0 ppm; a second gas with the same composition as the first gas except that the water concentration was set to 9%; and a third gas with the same composition as the first gas except that the water concentration was set to 15%. Next, with a target value V2* set to 400 mV and a target value V1* set to 300 mV, the pump current Ip2 was measured when the control unit 96 performed the adjustment pump control process and the measurement pump control process described above for the first gas. The control unit 96 started the adjustment pump control process and the measurement pump control process after the heater 72 temperature reached near the target temperature following the start of the heater control process described above, and then measured the value of the pump current Ip2 when the pump current Ip2 was stable. Furthermore, the pump current Ip2 corresponding to each target value V1* was measured in the same manner as above, except that the target value V1* was changed to 350mV, 400mV, and 450mV. For the second and third gases, the pump current Ip2 corresponding to each target value V1* was measured in the same manner as above. The results are shown in Figure 3. Figure 3 is a graph showing the relationship between the target value V1*, the water concentration in the gas being measured, and the pump current Ip2. The pump current Ip2 on the vertical axis of Figure 3 is shown as the value (unit: ppm) obtained by converting the pump current Ip2 to NO concentration using the correspondence between the pump current Ip2 and NOx concentration stored in the memory unit 98. Since the NO concentration is 0 ppm for all of the first to third gases, theoretically the pump current Ip2 should be 0 μA in all cases, but in reality a small amount of pump current Ip2 flows. Pump current Ip2 that flows due to factors other than the specific gas (NOx in this case) is called the offset current Ip2 offset. Therefore, Figure 3 shows the relationship between the target value V1*, the water concentration in the gas being measured, and the offset current Ip2offset. The offset current Ip2offset is also included in the pump current Ip2 when the NOx concentration is not 0 ppm.

[0063] As shown in Figure 3, there is a linear correlation between the target value V1* and the offset current Ip2offset, and it was confirmed that the higher the target value V1*, the smaller the offset current Ip2offset tends to be. Furthermore, regarding the slope of the change in the offset current Ip2offset in response to the change in the target value V1*, it was confirmed that the absolute value of the slope tends to increase as the water concentration in the gas being measured increases. Figure 4 is a graph showing the relationship between the water concentration in the gas being measured and the slope of the change in the offset current Ip2offset in response to the change in the target value V1*, calculated from the data shown in Figure 3. As shown in Figure 4, there is a linear correlation between the water concentration and the slope of the offset current Ip2offset, and it was confirmed that the higher the water concentration, the smaller the slope of the offset current Ip2offset tends to be (the negative absolute value increases). From these results, it can be seen that the water concentration in the gas being measured can be detected based on the change in the pump current Ip2 when the target value V1* is changed (for example, the slope of the change in the offset current Ip2offset when the target value V1* is changed). This point is a new finding discovered by the present inventors.

[0064] The inventors investigated the relationship between the target value V2* of the gas sensor 100, the water concentration in the gas being measured, and the pump current Ip2, similar to the relationship shown in Figure 3. Specifically, using the same first to third gases as described above, the target value V1* was set to 385mV, and the target value V2* was changed to four different values: 300mV, 350mV, 400mV, and 450mV. The pump current Ip2 corresponding to each target value V2* was measured, similar to the measurement of the data in Figure 3. The results are shown in Figure 5. Figure 5 is a graph showing the relationship between the target value V2*, the water concentration in the gas being measured, and the pump current Ip2. Figure 6 is a graph showing the relationship between the water concentration in the gas being measured and the slope of the change in the offset current Ip2 offset with respect to the change in the target value V2*, calculated from the data shown in Figure 5.

[0065] As shown in Figure 5, there is a linear correlation between the target value V2* and the offset current Ip2offset, and it was confirmed that the offset current Ip2offset tends to increase as the target value V2* increases. Furthermore, regarding the slope of the change in the offset current Ip2offset in response to the change in the target value V2*, it was confirmed that the absolute value of the slope tends to increase as the water concentration in the gas being measured increases. As shown in Figure 6, there is a linear correlation between the water concentration and the slope of the offset current Ip2offset, and it was confirmed that the slope of the offset current Ip2offset tends to increase (the positive absolute value increases) as the water concentration increases. From these results, it can be seen that the water concentration in the gas being measured can be detected based on the change in the pump current Ip2 when the target value V2* is changed (for example, the slope of the change in the offset current Ip2offset when the target value V2* is changed). This is a new finding discovered by the inventors in this study.

[0066] From the above, it can be seen that the change in the pump current Ip2 that flows during the execution of the adjustment pump control process and the measurement pump control process when at least one of the target value V1* and target value V2* is changed is correlated with the water concentration in the gas being measured, and therefore the water concentration can be detected based on this change in pump current Ip2. In this embodiment, a linear function equation or map representing the linear relationship between the slope of the change in pump current Ip2 when the target value V1* is changed and the water concentration in the gas being measured, as shown in Figure 4, is stored in the storage unit 98.

[0067] The reason for the relationship between the target values ​​V1* and V2*, the water concentration in the gas being measured, and the pump current Ip2 (especially the offset current Ip2offset) as shown in Figures 3 to 6 is thought to be as follows.

[0068] First, let's explain the relationship between water in the gas being measured and the offset current Ip2 offset. When water is present in the gas being measured and the adjustment pump control process (in this case, the main pump control process and the auxiliary pump control process) is performed, at least a portion of the water around the auxiliary pump electrode 51 is decomposed by the voltage Vp1 of the variable power supply 52, producing hydrogen (H2) and oxygen (O2). The resulting oxygen is pumped out by the auxiliary pump cell 50 from around the auxiliary pump electrode 51, i.e., from the second internal cavity 40, but at least a portion of the resulting hydrogen reaches the third internal cavity 61. Then, the hydrogen that reaches the third internal cavity 61 reacts with the oxygen in the third internal cavity 61 to form water, so the amount of oxygen pumped out of the third internal cavity 61 by the measurement pump control process decreases, i.e., the pump current Ip2 decreases. On the other hand, when the measurement pump control process is performed while water is present in the gas being measured, the voltage Vp2 of the variable power supply 46 causes at least a portion of the water around the measurement electrode 44 in the third internal cavity 61 to decompose, producing hydrogen (H2) and oxygen (O2). As a result, the amount of oxygen pumped out of the third internal cavity 61 by the measurement pump control process increases, i.e., the pump current Ip2 increases. Thus, the pump current Ip2 decreases due to the hydrogen produced from water around the auxiliary pump electrode 51, and the pump current Ip2 increases due to the oxygen produced from water around the measurement electrode 44. Therefore, the sum of these decreases and increases in pump current Ip2, which are not caused by NOx in the gas being measured, appears as the offset current Ip2offset.

[0069] Furthermore, the higher the target value V1*, that is, the lower the target value of the oxygen concentration in the second internal cavity 40, the more likely the voltage Vp1 is to become high due to the auxiliary pump control process. As a result, more hydrogen is produced by the decomposition of water around the auxiliary pump electrode 51 due to the voltage Vp1, and the decrease in pump current Ip2 also increases. In addition, the higher the water concentration in the gas being measured, the more hydrogen is produced by the decomposition of water around the auxiliary pump electrode 51. Therefore, the decrease in pump current Ip2 in response to the change in target value V1*, that is, the slope of the change in pump current Ip2 with respect to the change in target value V1* becomes steeper. In other words, the absolute value of the slope becomes larger. For these reasons, it is thought that the relationships shown in Figures 3 and 4 appear.

[0070] Similarly, the higher the target value V2*, that is, the lower the target value of the oxygen concentration in the third internal cavity 61, the more likely the voltage Vp2 will be to become high due to the measurement pump control process. As a result, more oxygen is produced by the decomposition of water around the measurement electrode 44 due to the voltage Vp2, and the amount of increase in the pump current Ip2 also increases. Furthermore, the higher the water concentration in the gas being measured, the more oxygen is produced by the decomposition of water around the measurement electrode 44. Therefore, the amount of increase in the pump current Ip2 in response to the change in the target value V2*, that is, the slope of the change in pump current Ip2 with respect to the change in the target value V2*, becomes steeper. In other words, the absolute value of the slope becomes larger. For these reasons, it is thought that the relationships shown in Figures 5 and 6 appear.

[0071] Next, an example of the process by which the control unit 96 of the gas sensor 100 measures water concentration and NOx concentration will be described. Figure 7 is a flowchart showing an example of a control routine executed by the control unit 96. The control unit 96 stores this routine in, for example, the memory unit 98. When the control unit 96 receives a start command from, for example, an engine ECU (not shown), it starts this control routine.

[0072] When the control routine is started, the CPU 97 of the control unit 96 first starts the heater control process described above (step S100). Next, the CPU 97 starts the adjustment pump control process and the measurement pump control process described above (step S110). At this time, the target values ​​V1* and V2* are the values ​​that have been stored in the storage unit 98 in advance as the values ​​used when measuring the NOx concentration. Next, the CPU 97 determines whether or not it is the concentration derivation timing to derive the water concentration and NOx concentration (step S120). The CPU 97 determines that it is the concentration derivation timing, for example, after a predetermined time has elapsed or when a concentration derivation command is input from the engine ECU.

[0073] If it is determined in step S120 that it is time to derive the concentration, the CPU 97 first performs a water concentration detection process to detect the water concentration in the gas to be measured based on the change in the pump current Ip2 that flows during the execution of the adjustment pump control process and the measurement pump control process when at least one of the target value V1* and target value V2* is changed (steps S130, S140). In this embodiment, the CPU 97 changes the target value V1* in the water concentration detection process but does not change the target value V2*. In the water concentration detection process, the CPU 97 first calculates the slope G of the change in pump current Ip2 when the target value V1* is changed (step S130). Specifically, the CPU 97 first measures the current pump current Ip2 and obtains it as the value of the pump current Ip2 before the change in the target value V1*. Next, the CPU 97 changes the target value V1*, waits until the value of the pump current Ip2 stabilizes, measures the pump current Ip2 after it has stabilized, and obtains it as the value of the pump current Ip2 after the change. Then, the slope G is derived by dividing the difference in the pump current Ip2 value before and after the change by the difference in the target value V1* before and after the change. Note that the time from when the target value V1* is changed until the pump current Ip2 stabilizes is very short (a few msec to a dozen msec, etc.), and normally there is almost no change in the NOx concentration in the exhaust gas of the internal combustion engine during this time. Therefore, the difference in the pump current Ip2 value before and after the change in the target value V1* can be considered as the amount of change in the offset current Ip2offset before and after the change in the target value V1*. Thus, the slope G derived in step S130 corresponds to the slope of the straight line shown in Figure 3 and the value on the vertical axis in Figure 4. Then, the CPU 97 calculates the water concentration in the gas to be measured based on the derived slope G and the correspondence stored in the memory unit 98 (the correspondence between the slope of the change in pump current Ip2 when the target value V1* is changed and the water concentration in the gas to be measured, as described above) (step S140). The CPU 97 outputs the derived water concentration value to the engine ECU or stores it in the memory unit 98. In step S130, the absolute value of the target value V1* may be changed to increase it or decrease it. However, it is preferable that the values ​​before and after the change are both less than or equal to the absolute value of the target value V1* determined for measuring NOx concentration.For example, if the target value V1* before the change was the same as the target value V1* set for measuring NOx concentration, it is preferable to change the target value V1* in a direction that decreases its absolute value. This prevents the voltage Vp1 from becoming too high and causing NOx decomposition around the auxiliary pump electrode 51, thereby suppressing a decrease in the accuracy of NOx concentration measurement.

[0074] In step S140, when the water concentration is derived, the CPU 97 returns the target value V1* to its original value. That is, it returns the target value V1* to the value specified for measuring NOx concentration (step S150). Next, the CPU 97 obtains the pump current Ip2 that flows due to the measurement pump control process (step S160), and derives the NOx concentration in the gas to be measured based on the correspondence between the obtained pump current Ip2 and the storage unit 98 (the correspondence between pump current Ip2 and NOx concentration as described above) (step S170). Then, the CPU 97 corrects the NOx concentration derived in step S170 based on the water concentration derived in step S140, and derives the corrected NOx concentration (step S180). The CPU 97 outputs the derived corrected NOx concentration value to the engine ECU or stores it in the storage unit 98. As shown in Figure 3, the offset current Ip2offset of the pump current Ip2 changes depending on the water concentration in the gas to be measured. Therefore, even if the NOx concentration in the gas being measured is the same, the pump current Ip2 may change depending on the water concentration in the gas being measured, which may result in an error in the derived NOx concentration. In this embodiment, the CPU 97 corrects the NOx concentration based on the pump current Ip2 based on the detected water concentration. For example, in Figure 3, when the target value V1* is 350mV, the offset current Ip2 offset when the water concentration is 15% is 3ppm larger in NOx concentration terms compared to the offset current Ip2 offset when the water concentration is 3%. Therefore, for example, if the relationship between the pump current Ip2 and NOx concentration pre-stored in the memory unit 98 is calculated using a gas being measured with a water concentration of 3%, then when the actual water concentration of the gas being measured is 15%, the derived NOx concentration will be calculated to be 3ppm larger than the actual concentration. Therefore, if the water concentration derived in step S140 is 15%, the CPU97 derives a corrected NOx concentration by subtracting 3 ppm as a correction amount from the NOx concentration [ppm] derived in step S170. In this way, the change in the offset current Ip2offset due to the difference in water concentration can be canceled out, and the corrected NOx concentration will be a value closer to the actual concentration.The correspondence between the water concentration and the correction amount for NOx concentration can be determined in advance through experiments or other means and stored in the memory unit 98. In step S180, the CPU 97 derives the correction amount based on the water concentration and this correspondence, and calculates the corrected NOx concentration. Alternatively, instead of deriving the correction amount, the memory unit 98 may store the correspondence between the water concentration, the NOx concentration based on the pump current Ip2, and the corrected NOx concentration, and derive the corrected NOx concentration based on this correspondence. In addition, the CPU 97 may correct the pump current Ip2 derived in step S170 based on the water concentration, and derive the NOx concentration based on the corrected pump current Ip2. These methods also constitute correction of NOx concentration based on water concentration.

[0075] If it is not the concentration derivation timing after step S180, or in step S120, the CPU 97 executes the processing from S120 onward. As described above, the CPU 97 executes the control routine, and the water concentration and NOx concentration in the gas being measured are repeatedly measured.

[0076] Here, the correspondence between the components of this embodiment and the components of the present invention will be clarified. The laminate formed by stacking the six layers of this embodiment—the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6—in this order corresponds to the element body of the present invention. The third internal cavity 61 corresponds to the measurement chamber, the measurement electrode 44 corresponds to the internal measurement electrode, the first internal cavity 20 and the second internal cavity 40 correspond to the oxygen concentration adjustment chamber, the auxiliary pump electrode 51 corresponds to the internal adjustment electrode, the main pump cell 21 and the auxiliary pump cell 50 correspond to the adjustment pump cell, the reference electrode 42 corresponds to the reference electrode, the voltage V1 corresponds to the adjustment voltage, the target value V1* corresponds to the adjustment voltage target value, the voltage V2 corresponds to the measurement voltage, the target value V2* corresponds to the measurement voltage target value, the control device 95 corresponds to the control device, and the pump current Ip2 corresponds to the measurement pump current. Furthermore, the auxiliary pump electrode 51 corresponds to the inner auxiliary pump electrode.

[0077] As described in detail above, the gas sensor 100 of this embodiment detects the NOx concentration in the gas to be measured based on the pump current Ip2 flowing through the measuring pump cell 41 by the measuring pump control process. The control device 95 also performs a water concentration detection process to detect the water concentration in the gas to be measured based on the change in the pump current Ip2 flowing during the execution of the adjustment pump control process and the measuring pump control process when at least one of the target value V1* and target value V2* is changed. Therefore, the gas sensor 100 of this embodiment can detect both the NOx concentration and the water concentration in the gas to be measured.

[0078] Furthermore, the control device 95 corrects the NOx concentration in the gas being measured based on the water concentration detected in the water concentration detection process, thereby improving the detection accuracy of specific gas concentrations.

[0079] It goes without saying that the present invention is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of the present invention.

[0080] For example, in the embodiment described above, in step S130 of the control routine in Figure 7, the CPU 97 derived the water concentration based on the slope G of the change in pump current Ip2 when the target value V1* was changed. However, the water concentration can be derived based on the change in pump current Ip2 when the target value V1* is changed, not limited to the slope G. For example, the water concentration can be derived based on the amount or rate of change of pump current Ip2 before and after the change in target value V1*. In this case, the correspondence between the amount or rate of change of pump current Ip2 and the water concentration can be stored in the storage unit 98 in advance.

[0081] In the embodiment described above, in step S130 of the control routine in Figure 7, the CPU 97 derived the water concentration based on the slope G of the change in pump current Ip2 when the target value V1* was changed. However, the water concentration may also be derived based on the change in pump current Ip2 when the target value V2* is changed. For example, the CPU 97 may derive the slope of the change in pump current Ip2 when the target value V2* is changed without changing the target value V1* (corresponding to the slope of the straight line shown in Figure 5 and the value on the vertical axis in Figure 6), and derive the water concentration based on the derived slope. In this case, the correspondence between the slope of the change in pump current Ip2 when the target value V2* is changed and the water concentration (corresponding to the correspondence of the straight line shown in Figure 6) should be stored in the storage unit 98 in advance. When changing the target value V2*, the absolute value of the target value V2* may be changed in the direction of increasing it, or in the direction of decreasing it. However, it is preferable that the values ​​before and after the change are both greater than or equal to the target value V2* set for measuring NOx concentration. For example, if the target value V2* before the change was the same as the target value V2* set for measuring NOx concentration, it is preferable to change it in a direction that increases the absolute value of the target value V2*. This prevents the voltage Vp2 from becoming too low, which would cause the pump current Ip2 to not reach the limit current, and thus prevents a decrease in the accuracy of NOx concentration measurement.

[0082] The CPU97 may derive the water concentration based on the pump current Ip2 when both target value V1* and target value V2* are changed during the water concentration detection process. In this case, it is preferable that the direction of the change in pump current Ip2 due to the change in target value V1* and the direction of the change in pump current Ip2 due to the change in target value V2* are the same. For example, if the absolute value of target value V1* is changed to a small value and the absolute value of target value V2* is changed to a large value, both of these changes will work in the direction of increasing the pump current Ip2. Alternatively, if the absolute value of target value V1* is changed to a large value and the absolute value of target value V2* is changed to a small value, both of these changes will work in the direction of decreasing the pump current Ip2. If target value V1* and target value V2* are changed in either of these ways, even if the amount of change in each of target value V1* and target value V2* is small, the change in pump current Ip2 due to water in the gas being measured will be relatively large. Therefore, it is easy to detect the water concentration based on the change in pump current Ip2. Furthermore, when both target value V1* and target value V2* are changed, instead of calculating the slope of the pump current Ip2, one can calculate, for example, the amount or rate of change of the pump current Ip2 and derive the water concentration based on this amount or rate of change.

[0083] In the embodiment described above, the CPU 97 corrected the NOx concentration using the water concentration, but this correction is not required. Alternatively, the CPU 97 may determine whether the derived water concentration is within a predetermined tolerance range that does not affect the measurement accuracy of the NOx concentration, and correct the NOx concentration if it is not within the tolerance range.

[0084] In the embodiment described above, the gas sensor 100 may also be configured to detect the gas temperature of the gas being measured. The inventors found that when the change in pump current Ip2 when the target value V1* is changed is less affected by the gas temperature of the gas being measured, and when the change in pump current Ip2 when the target value V2* is changed, the former is less affected by the gas temperature of the gas being measured. That is, the latter is more susceptible to the gas temperature than the former, and the inventors found that the gas temperature in the gas being measured can be detected by comparing the former and the latter. Figure 8 is a conceptual diagram showing the relationship between the slope of the change in offset current Ip2offset with respect to the change in water concentration and target value V2* and the gas temperature. While Figure 6 is a graph when the gas temperatures of the first to third gases are all the same, Figure 8 conceptually shows how the slope of the offset current Ip2offset changes in accordance with the gas temperature when the gas temperatures of the first to third gases are changed. As shown in Figure 8, the slope of the change in the offset current Ip2offset with respect to the change in the target value V2* changes when the gas temperature changes, even if the water concentration is the same, and it was confirmed that the slope tends to increase as the gas temperature increases. On the other hand, the slope of the change in the offset current Ip2offset with respect to the change in the target value V1* did not change much even when the gas temperature changed, as long as the water concentration was the same. This difference is thought to be due to the difference in temperature between the auxiliary pump electrode 51 and the measuring electrode 44. In the embodiment described above, it was omitted from the explanation, but the gas sensor 100 is configured such that the temperature Tm of the measuring electrode 44 is lower than the temperature Tq of the auxiliary pump electrode 51 when the heater 72 generates heat to at least one of the temperatures in the range of 700°C to 900°C. For example, when the target temperature of the heater 72 is 800°C, the temperature Tq of the auxiliary pump electrode 51 is approximately 750°C, while the temperature Tm of the measuring electrode 44 is a value in the range of 650°C to 700°C. Since the auxiliary pump cell 50 needs to pump out a larger amount of oxygen than the measuring pump cell 41, the temperature Tq > temperature Tm is set to further enhance the pumping capacity of the auxiliary pump cell 50.Furthermore, for the same reason, it is preferable to increase the pumping capacity of the main pump cell 21 compared to the auxiliary pump cell 50. Therefore, if the temperature of the inner pump electrode 22 is denoted as temperature Tp, it is preferable to configure the gas sensor 100 such that temperature Tp > temperature Tq > temperature Tm when the heater 72 is controlled to the target temperature. Temperatures Tp, Tq, and Tm can be adjusted, for example, by adjusting the shape and arrangement of the heater 72. With temperature Tq > temperature Tm, the temperature Tq of the auxiliary pump electrode 51 is relatively close to the gas temperature of the gas being measured (e.g., 700°C to 800°C), and temperature Tq does not change easily even if the gas temperature changes. In contrast, the temperature Tm of the measuring electrode 44 has a large difference from the gas temperature of the gas being measured, so temperature Tm changes easily when the gas temperature changes. Furthermore, even if the water concentration is the same, as temperature Tm increases, the amount of water decomposition around the measuring electrode 44 increases, so the change in the offset current Ip2offset with respect to the change in the target value V2* becomes larger, that is, the slope of the offset current Ip2offset becomes larger. As a result, it is thought that the trend shown in Figure 8 will appear depending on the gas temperature. By utilizing these findings, a gas temperature detection process can be performed to detect the gas temperature of the gas being measured based on the change in pump current Ip2 when the target value V1* is changed, and the change in pump current Ip2 when the target value V2* is changed.

[0085] Let's explain a specific example of gas temperature detection. First, the relationship between the water concentration, the slope of the change in the offset current Ip2offset, and the gas temperature, as shown in Figure 8, is determined experimentally beforehand and stored in the memory unit 98. The CPU 97 of the control device 95 performs steps S100 to S140 of the control routine in Figure 7 to derive the water concentration based on the slope G of the change in the pump current Ip2 when the target value V1* is changed. Since this water concentration is derived by changing the target value V1*, it is less affected by the gas temperature. Next, the CPU 97 returns the target value V1* to its value before the change and derives the slope of the change in the pump current Ip2 when the target value V2* is changed. Then, the CPU 97 derives the gas temperature in the gas being measured based on the derived water concentration, the slope of the change in the pump current Ip2 when the target value V2* is changed, and the correspondence stored in the memory unit 98. For example, if the relationship shown in Figure 8 is stored in the memory unit 98, and the derived water concentration is 15%, and the slope of the change in pump current Ip2 when the target value V2* is changed is value a, then value b is derived as the gas temperature. This allows the gas sensor 100 to detect the gas temperature in addition to the NOx concentration and water concentration of the gas being measured. Note that the water concentration in Figure 8 corresponds to the water concentration based on the slope G of the change in pump current Ip2 when the target value V1* is changed, so the relationship between the slope G of the change in pump current Ip2 with respect to the change in target value V1*, the slope of the change in pump current Ip2 with respect to the change in target value V2*, and the gas temperature is the same as in Figure 8. Therefore, instead of using the derived water concentration, the gas temperature can also be derived based on the slope G of the change in pump current Ip2 with respect to the change in target value V1*, the slope of the change in pump current Ip2 with respect to the change in target value V2*, and the correspondence relationship previously stored in the memory unit 98. Alternatively, the difference or ratio between the slope G of the change in pump current Ip2 with respect to the change in target value V1* and the slope of the change in pump current Ip2 with respect to the change in target value V2* can be derived, and the gas temperature can be derived based on the derived difference or ratio. In this case, the correspondence between this difference or ratio and the gas temperature can be stored in the memory unit 98 in advance. Also, as mentioned above, instead of using the slope, the amount or rate of change of pump current Ip2 can be used.

[0086] Furthermore, the control device 95 may correct the NOx concentration in the gas being measured based on the derived water concentration and gas temperature. As the gas temperature of the gas being measured increases, the amount of water decomposition around the measuring electrode 44 increases, so the offset current Ip2 offset increases as the gas temperature rises. Also, as mentioned above, the offset current Ip2 offset changes depending on the water concentration. Therefore, even if the actual NOx concentration in the gas being measured is the same, the pump current Ip2 changes depending on the gas temperature and water concentration of the gas being measured, which may cause errors in the derived NOx concentration. By correcting the NOx concentration in the gas being measured based on the derived water concentration and gas temperature, the control device 95 can suppress such errors and improve the detection accuracy of the NOx concentration. When performing such a correction, for example, the correspondence between the water concentration, gas temperature and the offset current Ip2 offset is investigated in advance and stored in the storage unit 98. Figure 9 is a conceptual diagram showing an example of such a correspondence. The control device 95 derives the offset current Ip2offset based on the derived water concentration, the derived gas temperature, and the correspondence shown in Figure 9. Then, it corrects the NOx concentration in the gas being measured based on the derived offset current Ip2offset. For example, with respect to the correspondence between pump current Ip2 and NOx concentration that is pre-stored in the memory unit 98, the value of the offset current Ip2offset used when calculating that correspondence is examined and stored in the memory unit 98 as a reference value. More specifically, the pump current Ip2 can be measured under the same conditions as when calculating the correspondence, except that the NOx concentration in the gas being measured is set to 0 ppm, and that value can be used as the reference value. The control device 95 derives the difference between the derived offset current Ip2offset and the reference value stored in the memory unit 98 and uses it as the correction amount for pump current Ip2. Then, the control device 95 derives the corrected pump current Ip2 by subtracting the correction amount from the pump current Ip2 obtained in step S160. Subsequently, the control unit 96 derives the NOx concentration based on the corrected pump current Ip2 and the correspondence between the pump current Ip2 and the NOx concentration stored in the memory unit 98.The NOx concentration derived in this way is the corrected NOx concentration, which compensates for the changes in the offset current Ip2 offset due to the water concentration and gas temperature. Therefore, it is closer to the actual NOx concentration compared to the case without correction. Alternatively, instead of the correspondence shown in Figure 9, the correspondence between the water concentration and gas temperature and the correction amount of the pump current Ip2 may be used. Or, the correspondence between the water concentration and gas temperature and the correction amount of the NOx concentration may be used.

[0087] The correspondence shown in Figure 9 indicates that, when the gas temperature is the same, the offset current Ip2offset tends to increase as the water concentration increases. However, this is not the only case; there are also cases where, when the gas temperature is the same, the offset current Ip2offset tends to decrease as the water concentration increases. For example, as can be seen from Figures 3 and 5, when the target value V1* is 400mV or less and the target value V2* is 350mV or more, the offset current Ip2offset tends to increase as the water concentration increases. Conversely, when the target value V1* exceeds 400mV, or when the target value V2* is less than 350mV, the offset current Ip2offset tends to decrease as the water concentration increases. Therefore, it is preferable to investigate in advance the appropriate correspondence (correspondence between water concentration and gas temperature and the offset current Ip2offset) according to the target values ​​V1* and V2* when acquiring the pump current Ip2 for NOx concentration measurement, and store it in the storage unit 98.

[0088] As mentioned above, the change in pump current Ip2 when the target value V2* is changed is easily affected by the gas temperature; therefore, it is preferable to detect the water concentration based on the change in pump current Ip2 when the target value V1* is changed. However, if the effect of gas temperature on the accuracy of water concentration detection is small, or if the range of change in the gas temperature of the gas being measured is small, then detecting the water concentration based on the change in pump current Ip2 when the target value V2* is changed is unlikely to cause problems.

[0089] Although not described in the embodiments described above, the target values ​​V0*, V1*, and V2* may each be 900mV or less, or 800mV or less. This prevents the voltages Vp0, Vp1, and Vp2 from becoming too high, and consequently prevents the blackening of the sensor element 101. The target value V1* may be a value within the range of 300mV to 450mV. The target value V2* may be a value within the range of 300mV to 450mV. Even when the control device 95 changes the values ​​of each of the target values ​​V0*, V1*, and V2* while controlling the sensor element 101, it is preferable to change them within the various ranges described above.

[0090] In the embodiment described above, the adjustment pump control process and the measurement pump control process were executed continuously from step S110 onward. However, the embodiment is not limited to this, and at least one of the adjustment pump control process and the measurement pump control process may be temporarily suspended. For example, in step S130, the adjustment pump control process and the measurement pump control process may be temporarily suspended, and then the target value V1* may be changed and the adjustment pump control process and the measurement pump control process may be resumed.

[0091] In the embodiment described above, the oxygen concentration adjustment chamber had a first internal cavity 20 and a second internal cavity 40, but it is not limited to this, for example, the oxygen concentration adjustment chamber may have another internal cavity, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the embodiment described above, the adjustment pump cell had a main pump cell 21 and an auxiliary pump cell 50, but it is not limited to this, for example, the adjustment pump cell may have another pump cell, or one of the main pump cell 21 and the auxiliary pump cell 50 may be omitted. For example, if the oxygen concentration of the gas to be measured can be sufficiently lowered with only the main pump cell 21, the auxiliary pump cell 50 may be omitted. If the auxiliary pump cell 50 is omitted, the control unit 96 only needs to perform the main pump control process as the adjustment pump control process. Also, in the main pump control process, the setting of the target value V0* based on the pump current Ip1 described above may be omitted. Specifically, a predetermined target value V0* is stored in the memory unit 98 beforehand, and the control unit 96 controls the main pump cell 21 by feedback-controlling the voltage Vp0 of the variable power supply 24 so that the voltage V0 becomes the target value V0*. If the auxiliary pump cell 50 is omitted, the inner pump electrode 22 corresponds to the inner adjustment electrode, the voltage V0 corresponds to the adjustment voltage, and the target value V0* corresponds to the adjustment voltage target value. If the oxygen concentration adjustment chamber has another internal cavity in addition to the first internal cavity 20 and the second internal cavity 40, and the adjustment pump cell has three or more pump cells, the target value of the voltage in the control processing of the downstream pump cell among the three or more pump cells, i.e., the pump cell located closest to the measurement chamber, corresponds to the adjustment voltage target value.

[0092] In the embodiment described above, the sensor element 101 of the gas sensor 100 is provided with a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61, but is not limited to this. For example, as shown in the sensor element 201 of Figure 10, the third internal cavity 61 may not be provided. In the modified sensor element 201 shown in Figure 10, a gas inlet 10, a first diffusion rate-limiting section 11, a buffer space 12, a second diffusion rate-limiting section 13, a first internal cavity 20, a third diffusion rate-limiting section 30, and a second internal cavity 40 are formed adjacent to each other in this order, communicating between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 within the second internal cavity 40. The measuring electrode 44 is covered by a fourth diffusion rate-limiting section 45. The fourth diffusion rate-limiting section 45 is a film made of a porous ceramic material such as alumina (Al2O3). Similar to the fourth diffusion rate-limiting section 60 in the embodiment described above, the fourth diffusion rate-limiting section 45 plays a role in limiting the amount of NOx flowing into the measuring electrode 44. The fourth diffusion rate-limiting section 45 also functions as a protective film for the measuring electrode 44. The ceiling electrode portion 51a of the auxiliary pump electrode 51 is formed up to directly above the measuring electrode 44. Even with a sensor element 201 configured in this way, the NOx concentration can be detected, for example, based on the pump current Ip2, similar to the embodiment described above. In this case, the area around the measuring electrode 44 functions as a measurement chamber.

[0093] In the embodiment described above, the outer pump electrode 23 served as an electrode paired with the inner pump electrode 22 in the main pump cell 21 (also referred to as the outer main pump electrode), an electrode paired with the auxiliary pump electrode 51 in the auxiliary pump cell 50 (also referred to as the outer auxiliary pump electrode), and an electrode paired with the measuring electrode 44 in the measuring pump cell 41 (also referred to as the outer measuring electrode), but is not limited to this. One or more of the outer main pump electrode, outer auxiliary pump electrode, and outer measuring electrode may be provided separately from the outer pump electrode 23 on the outside of the element body so as to be in contact with the gas to be measured.

[0094] In the embodiments described above, the inner pump electrode 22 is a cermet electrode made of Pt and ZrO2 containing 1% Au, but it is not limited to this. The inner pump electrode 22 may contain a catalytically active noble metal. Examples of catalytically active noble metals include at least one of Pt, Rh, Ir, Ru, and Pd. However, as in the embodiments described above, it is preferable that the inner pump electrode 22 contains Pt as the catalytically active noble metal. It is preferable that the inner pump electrode 22 contains a catalytically active noble metal and Au. The auxiliary pump electrode 51 may also contain a catalytically active noble metal, similar to the inner pump electrode 22, and it is even preferable that it contains Au. By containing Au in the inner pump electrode 22 and the auxiliary pump electrode 51, the catalytic activity against NOx is suppressed, thereby preventing the reduction of NOx in the first internal cavity 20 and the second internal cavity 40. The outer pump electrode 23, the reference electrode 42, and the measuring electrode 44 may each contain the catalytically active noble metals described above. Each electrode 22, 23, 42, 44, and 51 is preferably a cermet containing a noble metal and an oxide having oxygen ion conductivity (e.g., ZrO2), but one or more of these electrodes may not be cermets. Each electrode 22, 23, 42, 44, and 51 is preferably a porous material, but one or more of these electrodes may not be porous.

[0095] In the embodiment described above, the sensor element 101 is used to detect the NOx concentration in the gas to be measured, but it is not limited to this, as long as it detects the concentration of a specific gas in the gas to be measured. For example, the specific gas concentration may be other oxide concentrations, not just NOx. If the specific gas is an oxide, oxygen is generated when the specific gas itself is reduced in the third internal cavity 61, as in the embodiment described above, so the measuring pump cell 41 can detect the specific gas concentration by obtaining a detection value (e.g., pump current Ip2) corresponding to this oxygen. Alternatively, the specific gas may be a non-oxide such as ammonia. If the specific gas is a non-oxide, oxygen is generated when the converted gas is reduced in the third internal cavity 61 by converting the specific gas to an oxide (e.g., converting ammonia to NO), so the measuring pump cell 41 can detect the specific gas concentration by obtaining a detection value (e.g., pump current Ip2) corresponding to this oxygen. For example, the inner pump electrode 22 of the first internal cavity 20 functions as a catalyst, allowing ammonia to be converted to NO in the first internal cavity 20. The specific gas may be a predetermined gas other than oxygen. The specific gas may be a predetermined gas other than oxygen and carbon dioxide. The specified gas may be either NOx or ammonia.

[0096] In the embodiment described above, the element body of the sensor element 101 is a laminate having a plurality of solid electrolyte layers (layers 1 to 6), but it is not limited to this. The element body of the sensor element 101 only needs to include at least one solid electrolyte layer that conducts oxygen ions. For example, in Figure 1, layers 1 to 5 other than the second solid electrolyte layer 6 may be layers made of a material other than a solid electrolyte layer (for example, a layer made of alumina). In this case, each electrode of the sensor element 101 should be arranged in the second solid electrolyte layer 6. For example, the measuring electrode 44 in Figure 1 should be arranged on the lower surface of the second solid electrolyte layer 6. Also, the reference gas introduction space 43 may be provided in the spacer layer 5 instead of the first solid electrolyte layer 4, the reference gas introduction layer 48 may be provided between the second solid electrolyte layer 6 and the spacer layer 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3, and the reference electrode 42 may be provided behind the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6.

[0097] In the embodiment described above, the control unit 96 sets a target value V0* for the voltage V0 based on the pump current Ip1 so that the pump current Ip1 becomes the target value Ip1* (feedback control), and then feedback controls the voltage Vp0 so that the voltage V0 becomes the target value V0*. However, other control methods may be used. For example, the control unit 96 may feedback control the voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 becomes the target value Ip1*. In other words, the control unit 96 may omit the acquisition of the voltage V0 from the oxygen partial pressure detection sensor cell 80 for main pump control and the setting of the target value V0*, and instead directly control the voltage Vp0 (and consequently the pump current Ip0) based on the pump current Ip1. [Industrial applicability]

[0098] This invention can be used in gas sensors that detect the concentration of specific gases, such as NOx, in a gas to be measured, such as automobile exhaust gas. [Explanation of symbols]

[0099] 1 First substrate layer, 2 Second substrate layer, 3 Third substrate layer, 4 First solid electrolyte layer, 5 Spacer layer, 6 Second solid electrolyte layer, 10 Gas inlet, 11 First diffusion-controlled section, 12 Buffer space, 13 Second diffusion-controlled section, 20 First internal cavity, 21 Main pump cell, 22 Inner pump electrode, 22a Ceiling electrode section, 22b Bottom electrode section, 23 Outer pump electrode, 24 Variable power supply, 30 Third diffusion-controlled section, 40 Second internal cavity, 41 Measurement pump cell, 42 Reference electrode, 43 Reference gas introduction space, 44 Measurement electrode, 45 Fourth diffusion-controlled section, 46 Variable power supply, 48 Reference gas introduction layer, 50 Auxiliary pump cell, 51 Auxiliary pump electrode, 51a Ceiling electrode section, 51b Bottom electrode section, 52 Variable power supply, 60 Fourth diffusion-controlled section, 61 Third internal cavity, 70 Heater section, 71 Heater connector electrode, 72 Heater, 73 Through hole, 74 Heater insulating layer, 75 Pressure relief hole, 76 Heater power supply, 80 Oxygen partial pressure detection sensor cell for main pump control, 81 Oxygen partial pressure detection sensor cell for auxiliary pump control, 82 Oxygen partial pressure detection sensor cell for measuring pump control, 83 Sensor cell, 95 Control device, 96 Control unit, 97 CPU, 98 Memory unit, 100 Gas sensor, 101, 201 Sensor elements.

Claims

1. The element body has an oxygen ion conductive solid electrolyte layer and an internal gas flow section for introducing and circulating the gas to be measured, The system comprises an internal measuring electrode disposed in the measuring chamber of the gas flow section to be measured, and a measuring pump cell that pumps oxygen from the measuring chamber to the outside of the element body, The system includes an internal adjustment electrode located in an oxygen concentration adjustment chamber situated upstream of the measurement chamber within the gas flow section to be measured, and comprises an adjustment pump cell for adjusting the oxygen concentration in the oxygen concentration adjustment chamber, A reference electrode is disposed inside the element body so as to be in contact with a reference gas that serves as a reference for detecting the specific gas concentration, which is the concentration of a specific gas in the gas being measured. A sensor element having, A control device that performs: an adjustment pump control process to adjust the oxygen concentration in the oxygen concentration adjustment chamber by controlling the adjustment pump cell so that the adjustment voltage, which is the voltage between the reference electrode and the inner adjustment electrode, becomes the adjustment voltage target value; and a measurement pump control process to pump oxygen from the measurement chamber by controlling the measurement pump cell so that the measurement voltage, which is the voltage between the reference electrode and the inner measurement electrode, becomes the measurement voltage target value. Equipped with, The control device detects the concentration of the specific gas in the gas to be measured based on the measuring pump current flowing through the measuring pump cell by the measuring pump control process, The control device performs a water concentration detection process to detect the water concentration in the gas to be measured based on the change in the measuring pump current that flows during the execution of the adjustment pump control process and the measuring pump control process when at least one of the adjustment voltage target value and the measuring voltage target value is changed. Gas sensor.

2. The control device, in the water concentration detection process, changes the absolute value of the adjustment voltage target value to a smaller value and the absolute value of the measurement voltage target value to a larger value, or changes the absolute value of the adjustment voltage target value to a larger value and the absolute value of the measurement voltage target value to a smaller value. The gas sensor according to claim 1.

3. The oxygen concentration adjustment chamber has a first internal cavity and a second internal cavity located downstream of the first internal cavity and upstream of the measurement chamber. The adjustment pump cell comprises a main pump cell that adjusts the oxygen concentration in the first internal cavity and an auxiliary pump cell that adjusts the oxygen concentration in the second internal cavity. The inner adjustment electrode is an inner auxiliary pump electrode disposed in the second internal cavity and constituting a part of the auxiliary pump cell, The adjustment pump control process includes a main pump control process that controls the main pump cell to adjust the oxygen concentration in the first internal cavity, and an auxiliary pump control process that controls the auxiliary pump cell so that the adjustment voltage reaches the adjustment voltage target value. The gas sensor according to claim 1 or 2.

4. The control device corrects the concentration of the specific gas in the gas to be measured based on the water concentration in the gas to be measured detected in the water concentration detection process. The gas sensor according to claim 1 or 2.

5. The control device performs a gas temperature detection process to detect the gas temperature of the gas to be measured based on the change in the measuring pump current that flows during the execution of the adjustment pump control process and the measuring pump control process when the adjustment voltage target value is changed, and the change in the measuring pump current that flows during the execution of the adjustment pump control process and the measuring pump control process when the measuring voltage target value is changed. The gas sensor according to claim 1 or 2.

6. The control device corrects the specific gas concentration in the gas to be measured based on the water concentration detected in the water concentration detection process and the gas temperature detected in the gas temperature detection process. The gas sensor according to claim 5.

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