Gas sensor

Abstract

A gas sensor detects a specific gas concentration and a water concentration in a measured gas. The gas sensor includes a sensor element and a control device. The sensor element includes an element main body, a measurement pump unit including a measurement electrode, an auxiliary pump unit including an auxiliary pump electrode, and a reference electrode. The control device controls an adjustment pump control process of the auxiliary pump unit in such a manner that a voltage between the reference electrode and the auxiliary pump electrode reaches a target value (V1*). The control device controls a measurement pump control process of the measurement pump unit in such a manner that a voltage between the reference electrode and the measurement electrode reaches a target value (V2*). The control device detects the specific gas concentration based on a pump current. The control device performs a water concentration detection process of detecting the water concentration in the measured gas based on a change in the pump current when at least one of the target value (V1*) and the target value (V2*) is changed.

Description

Technical Field

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

[0002] Previously, gas sensors were known for detecting the concentration of specific gases such as NOx in measured gases, such as automobile exhaust. For example, Patent Document 1 describes a gas sensor comprising: an element body including a solid electrolyte layer with oxygen ion conductivity and an internal gas flow section for introducing and circulating the measured gas; and multiple electrodes disposed on the element body. When using this gas sensor to detect NOx concentration, firstly, oxygen is drawn in or out between the oxygen concentration adjustment chamber in the gas flow section and the outside of the sensor element to adjust the oxygen concentration in the adjustment chamber. The measured gas, with its oxygen concentration adjusted, reaches a measuring chamber disposed downstream of the oxygen concentration adjustment chamber in the gas flow section. In the measuring chamber, NOx in the measured gas is reduced around the measuring electrode disposed in the measuring chamber. Then, a measuring pump unit is feedback-controlled to draw out oxygen from around the measuring electrode in such a way that the voltage V2 generated between the measuring electrode and the reference electrode reaches a predetermined target value. The concentration of NOx in the gas being measured is detected based on the pump current Ip2 flowing at this time.

[0003] In addition, gas sensors for detecting water in a measured gas 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 is generated between a pair of first electrodes, within a range set such that the water in the measured gas does not substantially dissociate. Furthermore, this gas sensor detects a second current flowing between a pair of second electrodes when a second voltage is generated between the pair of first electrodes, within a range set such that the water in the measured gas dissociates. Then, based on the first and second currents, the humidity of the measured gas is detected. The gas sensor described in Patent Document 3 adjusts the oxygen partial pressure in the first internal cavity of the measured gas in a manner that substantially all water vapor and carbon dioxide components in the first internal cavity of the sensor element are decomposed. Then, oxygen is supplied to the second internal cavity via a first electrochemical pumping unit in a manner that selectively combusts hydrogen generated from the decomposition of water vapor components within the second internal cavity, and the concentration of water vapor components present in the measured gas is determined based on the magnitude of the current flowing at this time. In addition, the gas sensor supplies oxygen to the surface of the inner electrode of the second measuring device through the second measuring electrochemical pumping unit in such a way that carbon monoxide generated from the decomposition of carbon dioxide is selectively burned, and determines the concentration of carbon dioxide present in the measured gas based on the magnitude of the current flowing at this time.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2022-091669

[0007] Patent Document 2: Japanese Patent No. 5021697

[0008] Patent Document 3: Japanese Patent No. 5918177 Summary of the Invention

[0009] However, regarding the gas sensor described in Patent Document 1, it is desirable to detect not only the concentration of a specific gas but also the concentration of water. However, the gas sensor in Patent Document 2 lacks the oxygen concentration adjustment chamber and measuring chamber described in Patent Document 1; the structures of the sensor elements in Patent Documents 1 and 2 are different. Furthermore, the gas sensor in Patent Document 3 detects the concentrations of water vapor and carbon dioxide based on the current when oxygen is drawn into the sensor element, but does not describe detecting the concentration of a specific gas based on the current when oxygen is drawn out of the measuring chamber, as in Patent Document 1; the methods for detecting the concentration of a specific gas differ between Patent Documents 1 and 3. Therefore, for a gas sensor like Patent Document 1, which has an oxygen concentration adjustment chamber and a measuring chamber and detects the concentration of a specific gas based on the pump current when oxygen is drawn out of the measuring chamber, a method for further detecting the water concentration in the gas being measured is unknown.

[0010] This invention was implemented to solve the above-mentioned problems, and its main purpose is to detect the concentration of a specific gas and the concentration of water in the gas to be measured.

[0011] The present invention employs the following means to achieve the aforementioned main objectives.

[0012] [1] The gas sensor of the present invention includes a sensor element and a control device.

[0013] The sensor element has:

[0014] The main body of the element has a solid electrolyte layer with oxygen ion conductivity, and is provided with a gas flow section inside for introducing and circulating the gas to be measured.

[0015] A measuring pump unit is configured to include an inner measuring electrode disposed in a measuring chamber within the gas flow section being measured, which draws oxygen from the measuring chamber to the outside of the element body.

[0016] An adjustment pump unit, configured to include an inner adjustment electrode disposed in an oxygen concentration adjustment chamber located upstream of the measuring chamber in the gas flow section, for adjusting the oxygen concentration in the oxygen concentration adjustment chamber; and

[0017] A reference electrode is disposed inside the element body in such a way that it is in contact with a reference gas, which serves as the detection reference for the concentration of a specific gas in the gas being measured, i.e., the concentration of the specific gas.

[0018] The control device performs adjustment pump control processing and measurement pump control processing. In the adjustment pump control processing, the adjustment pump unit is controlled to adjust the oxygen concentration in the oxygen concentration adjustment chamber by ensuring that the voltage between the reference electrode and the inner adjustment electrode, i.e., the adjustment voltage, reaches the target value of the adjustment voltage. In the measurement pump control processing, the measurement pump unit is controlled to draw oxygen out of the measurement chamber by ensuring that the voltage between the reference electrode and the inner measurement electrode, i.e., the measurement voltage, reaches the target value of the measurement voltage.

[0019] The control device detects the concentration of the specific gas in the gas being measured based on the measuring pump current flowing through the measuring pump unit due to the measuring pump control processing.

[0020] The control device performs water concentration detection processing. In this water concentration detection processing, the water concentration in the gas to be measured is detected based on the change in the current of the measuring pump flowing during the execution of the adjusting pump control processing and the measuring pump control processing when at least one of the adjusting voltage target value and the measuring voltage target value changes.

[0021] 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 unit to achieve a target adjustment voltage value between the reference electrode and the inner adjustment electrode. Additionally, the control device performs measurement pump control processing to extract oxygen from the measurement chamber by controlling the measurement pump unit to achieve a target measurement voltage value between the reference electrode and the inner measurement electrode. Furthermore, the control device detects the concentration of a specific gas in the gas being measured based on the measurement pump current flowing through the measurement pump unit due to 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 adjustment pump control processing when at least one of the target adjustment voltage value and the target measurement voltage value changes, and the change in the measurement pump current flowing during the execution of the measurement pump control processing. Here, the inventors of this invention have discovered that the change in the measurement pump current when at least one of the target adjustment voltage value and the target measurement voltage value changes is correlated with the water concentration in the gas being measured. Therefore, the water concentration in the gas being measured can be detected based on changes in the pump current used for measurement. Thus, it can be seen that the gas sensor of the present invention can detect the concentrations of specific gases and water in the gas being measured.

[0022] [2] Based on the gas sensor described above (the gas sensor described in [1] above), the control device can be configured such that, during the water concentration detection process, the absolute value of the adjustment voltage target value becomes smaller and the absolute value of the measurement voltage target value becomes larger, or the absolute value of the adjustment voltage target value becomes larger and the absolute value of the measurement voltage target value becomes smaller. Accordingly, even if the changes in the adjustment voltage target value and the measurement voltage target value are small, the change in the measurement pump current caused by the water in the gas being measured is relatively large, so the water concentration can be easily detected.

[0023] [3] Based on the gas sensor described above (the gas sensor described in [1] or [2] above), the oxygen concentration adjustment chamber may have: a first internal cavity and a second internal cavity configured to be downstream of the first internal cavity and upstream of the measuring chamber; the adjustment pump unit may have: a main pump unit for adjusting the oxygen concentration of the first internal cavity and an auxiliary pump unit for adjusting the oxygen concentration of the second internal cavity; the inner adjustment electrode may be an inner auxiliary pump electrode disposed in the second internal cavity and constituting part of the auxiliary pump unit; the adjustment pump control process may include: a main pump control process for controlling the main pump unit to adjust the oxygen concentration of the first internal cavity, and an auxiliary pump control process for controlling the auxiliary pump unit in such a way that the adjustment voltage reaches the target value of the adjustment voltage.

[0024] [4] Based on the gas sensor described above (the gas sensor described in any one of [1] to [3] above), the control device may calibrate the concentration of the specific gas in the gas being measured based on the water concentration detected in the water concentration detection process. Here, even if the concentration of the specific gas in the gas being measured is the same, the pump current used for measurement may sometimes change accordingly with the water concentration in the gas being measured. Therefore, by calibrating the concentration of the specific gas based on the detected water concentration, the detection accuracy of the specific gas concentration is improved.

[0025] [5] Based on the gas sensor described above (the gas sensor described in any one of [1] to [4] above), the control device can perform a gas temperature detection process, in which the gas temperature of the gas to be measured is detected based on the change in the current of the measuring pump flowing during the execution of the adjustment pump control process and the measuring pump control process when the adjustment voltage target value changes, and the change in the current of the measuring pump flowing during the execution of the adjustment pump control process and the measuring pump control process when the measuring voltage target value changes. Here, the inventors of the present invention have found that if the change in the current of the measuring pump when the adjustment voltage target value changes is compared with the change in the current of the measuring pump when the measuring voltage target value changes, the former is less affected by the gas temperature of the gas to be measured. Therefore, based on this discovery, the gas temperature of the gas to be measured can be detected based on the former and the latter. In this case, the control device preferably detects the water concentration in the gas to be measured based on the change in the current of the measuring pump when the adjustment voltage target value changes in the water concentration detection process.

[0026] [6] Based on the gas sensor described above (the gas sensor described in [5] above), the control device can correct the concentration of the specific gas in the gas being 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 concentration of the specific gas in the gas being measured is the same, the pump current used for measurement may sometimes change accordingly with the water concentration and gas temperature in the gas being measured. Therefore, by correcting the specific gas concentration obtained based on the pump current used for measurement based on the detected water concentration and the detected gas temperature, the detection accuracy of the specific gas concentration is improved. Attached Figure Description

[0027] Figure 1 This is a schematic cross-sectional view illustrating an example of the structure of the gas sensor 100.

[0028] Figure 2 This is a block diagram showing the electrical connections between the control device 95 and each unit and heater 72.

[0029] Figure 3 It is a graph showing the relationship between the target value V1*, water concentration, and pump current Ip2.

[0030] Figure 4 This is a graph showing the relationship between the change in water concentration and the slope of the change in bias current Ip2offset relative to the change in target value V1*.

[0031] Figure 5 It is a graph showing the relationship between the target value V2*, water concentration, and pump current Ip2.

[0032] Figure 6 This is a graph showing the relationship between the change in water concentration and the slope of the change in bias current Ip2offset relative to the change in target value V2*.

[0033] Figure 7 This is a flowchart illustrating an example of a control routine.

[0034] Figure 8 This is a conceptual diagram showing the relationship between the changes in water concentration, the slope of the change in bias current Ip2offset relative to the change in target value V2*, and gas temperature.

[0035] Figure 9 This is a conceptual diagram illustrating the relationship between water concentration, gas temperature, and bias current Ip2offset.

[0036] Figure 10 This is a cross-sectional schematic diagram of the sensor element 201 in a modified example.

[0037] Symbol Explanation

[0038] 1…First substrate layer, 2…Second substrate layer, 3…Third substrate layer, 4…First solid electrolyte layer, 5…Isolation layer, 6…Second solid electrolyte layer, 10…Gas inlet, 11…First diffusion rate control unit, 12…Buffer space, 13…Second diffusion rate control unit, 20…First internal cavity, 21…Main pump unit, 22…Inner pump electrode, 22a…Top electrode, 22b…Bottom electrode, 23…Outer pump electrode, 24…Variable power supply, 30…Third diffusion rate control unit, 40…Second internal cavity, 41…Measurement pump unit, 42…Reference electrode, 43…Reference gas inlet space, 44…Measurement electrode, 45…Fourth diffusion rate control unit, 46…Variable power supply, 48…Reference gas inlet layer 50…Auxiliary pump unit, 51…Auxiliary pump electrode, 51a…Top electrode section, 51b…Bottom electrode section, 52…Variable power supply, 60…Fourth diffusion rate control section, 61…Third internal cavity, 70…Heater section, 71…Heater connector electrode, 72…Heater, 73…Through hole, 74…Heater insulation layer, 75…Pressure relief hole, 76…Heater power supply, 80…Oxygen partial pressure detection sensor unit for main pump control, 81…Oxygen partial pressure detection sensor unit for auxiliary pump control, 82…Oxygen partial pressure detection sensor unit for measuring pump control, 83…Sensor unit, 95…Control device, 96…Control section, 97…CPU, 98…Storage section, 100…Gas sensor, 101, 201…Sensor element. Detailed Implementation

[0039] The embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 This is a schematic cross-sectional view showing an example of the structure of a gas sensor 100 as one embodiment of the present invention. Figure 2 This is a block diagram showing the electrical connections between the control device 95, each unit, and the heater 72. The gas sensor 100 is installed in piping such as the exhaust pipe of an internal combustion engine. The gas sensor 100 detects the concentration of specific gases such as NOx and ammonia in the exhaust gas of the internal combustion engine. In this embodiment, the gas sensor 100 measures the NOx concentration as the concentration of the specific gas. The gas sensor 100 includes: a sensor element 101, which is a long rectangular parallelepiped; units 21, 41, 50, and 80-83 included in the sensor element 101; a heater section 70 disposed inside the sensor element 101; and a control device 95, which has variable power supplies 24, 46, and 52 and a heater power supply 76 and controls the entire gas sensor 100.

[0040] The sensor element 101 is a stacked element comprising six layers stacked in the following order from bottom to top in the accompanying drawings: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, an insulating layer 5, and a second solid electrolyte layer 6, each containing an oxygen ion-conducting solid electrolyte such as zirconium oxide (ZrO2). Furthermore, the solid electrolyte forming these six layers is a dense and gas-tight solid electrolyte. For example, the sensor element 101 is manufactured by performing a prescribed processing and circuit pattern printing on ceramic green sheets corresponding to each layer, then stacking them, and finally firing them to achieve integration.

[0041] At the front end side of sensor element 101 ( Figure 1 The gas inlet 10, the first diffusion rate control unit 11, the buffer space 12, the second diffusion rate control unit 13, the first internal cavity 20, the third diffusion rate control unit 30, the second internal cavity 40, the fourth diffusion rate control unit 60, and the third internal cavity 61 are formed adjacently in a connected manner in this order between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4.

[0042] The gas inlet 10, buffer space 12, first internal cavity 20, second internal cavity 40 and third internal cavity 61 are spaces inside the sensor element 101 provided by cutting through the isolation layer 5. The upper part of the space is formed by the lower surface of the second solid electrolyte layer 6, the lower part of the space is formed by the upper surface of the first solid electrolyte layer 4, and the side part of the space is formed by the side of the isolation layer 5.

[0043] The first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 are all configured as two horizontally elongated slits (the length direction of the opening is perpendicular to the drawing). Furthermore, the fourth diffusion rate control unit 60 is configured as a single horizontally elongated slit (the length direction of the opening is perpendicular to the drawing) formed as a gap between itself and the lower surface of the second solid electrolyte layer 6. Additionally, the portion from the gas inlet 10 to the third internal cavity 61 is referred to as the measured gas flow section.

[0044] Furthermore, a reference gas introduction space 43 is provided at a position further away from the front end of the gas flow section, between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and at a position where the side is divided by the side of the first solid electrolyte layer 4. For example, atmospheric air is introduced into the reference gas introduction space 43 as a reference gas for NOx concentration measurement.

[0045] The reference gas introduction layer 48 is a layer made of porous ceramic, and the reference gas is introduced into the reference gas introduction layer 48 through the reference gas introduction space 43. In addition, the reference gas introduction layer 48 is formed to cover the reference electrode 42.

[0046] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, a reference gas introduction layer 48 communicating with the reference gas introduction space 43 is provided around it. Furthermore, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) within the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61. The reference electrode 42 is formed as a porous metal-ceramic electrode (e.g., a Pt and ZrO2 metal-ceramic electrode).

[0047] Regarding the gas flow section, the gas inlet 10 is an opening relative to the external space through which the gas to be measured enters the sensor element 101 from the external space. The first diffusion rate control unit 11 is a section that applies a predetermined diffusion resistance to the gas to be measured entering from the gas inlet 10. The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13. The second diffusion rate control unit 13 is a section that applies a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal cavity 20. When the gas to be measured is introduced from outside the sensor element 101 into the first internal cavity 20, the gas that rapidly enters the sensor element 101 from the gas inlet 10 due to pressure fluctuations in the external space (in the case of automobile exhaust, the pulsation of exhaust pressure) is not directly introduced into the first internal cavity 20. Instead, it is introduced into the first internal cavity 20 only after the pressure fluctuations of the gas to be measured have been eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. Therefore, the pressure fluctuations of the gas to be measured introduced into the first internal cavity 20 are almost negligible. The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured introduced through the second diffusion rate control unit 13. The main pump unit 21 operates to adjust this oxygen partial pressure.

[0048] The main pump unit 21 is an electrochemical pump unit consisting of an inner pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 sandwiched between these electrodes. The inner pump electrode 22 has a top electrode portion 22a disposed on the lower surface of the second solid electrolyte layer 6, facing the first internal cavity 20. The outer pump electrode 23 is disposed such that the area on the upper surface of the second solid electrolyte layer 6 corresponding to the top electrode portion 22a is exposed to the external space.

[0049] The inner pump electrode 22 is formed as follows: a solid electrolyte layer (a second solid electrolyte layer 6 and a first solid electrolyte layer 4) spanning the upper and lower sections of the first internal cavity 20, and an isolation layer 5 forming the sidewalls. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 forming the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 forming the bottom surface. Furthermore, side electrode portions (not shown) are formed on the sidewall surfaces (inner surfaces) of the isolation layers 5 forming the two sidewall portions of the first internal cavity 20. The top electrode portion 22a and the bottom electrode portion 22b are connected, and the side electrode portions are arranged in a tunnel-like structure at their respective locations.

[0050] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous metal-ceramic electrodes (e.g., metal-ceramic electrodes of Pt and ZrO2 containing 1% Au). It should be noted that the inner pump electrode 22, which is in contact with the gas being measured, is formed using a material that reduces the reducing power of NOx components in the gas being measured.

[0051] Regarding the main pump unit 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, causing the pump current Ip0 to flow between the inner pump electrode 22 and the outer pump electrode 23 in either a positive or negative direction. This allows oxygen in the first internal cavity 20 to be drawn out to the external space, or oxygen in the external space to be drawn into the first internal cavity 20.

[0052] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an electrochemical sensor unit, namely the main pump control oxygen partial pressure detection sensor unit 80, is composed of the inner pump electrode 22, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42.

[0053] The oxygen concentration (oxygen partial pressure) within the first internal cavity 20 is determined by measuring the electromotive force (voltage V0) of the oxygen partial pressure detection sensor unit 80 for main pump control. Furthermore, the voltage Vp0 of the variable power supply 24 is controlled by feedback to ensure that the voltage V0 reaches a target value, thereby controlling the pump current Ip0. Thus, the oxygen concentration within the first internal cavity 20 can be maintained at a predetermined constant value.

[0054] The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20, thereby guiding the gas to be measured into the second internal cavity 40.

[0055] The second internal cavity 40 is configured as a space for performing the following process: for the gas to be measured, which has had its oxygen concentration (oxygen partial pressure) pre-adjusted in the first internal cavity 20 and then introduced through the third diffusion rate control unit 30, the oxygen partial pressure is further adjusted using the auxiliary pump unit 50. As a result, the oxygen concentration within the second internal cavity 40 can be kept constant with high precision, thus enabling the gas sensor 100 to achieve high-precision NOx concentration measurement.

[0056] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit consisting of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any suitable electrode outside the sensor element 101), and a second solid electrolyte layer 6. The auxiliary pump electrode 51 has a top electrode portion 51a disposed on the lower surface of the second solid electrolyte layer 6 and facing the second internal cavity 40.

[0057] The auxiliary pump electrode 51 is disposed in the second internal cavity 40 with the same tunnel-shaped structure as the inner pump electrode 22 previously disposed in the first internal cavity 20. Specifically, a top electrode portion 51a is formed relative to the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40. Side electrode portions (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b are formed on the two wall surfaces of the isolation layer 5 constituting the sidewall of the second internal cavity 40, thereby forming a tunnel-shaped structure. Furthermore, similar to the inner pump electrode 22, the auxiliary pump electrode 51 is also formed using a material that reduces the reducing power of NOx components in the measured gas.

[0058] Regarding the auxiliary pump unit 50, a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23, thereby enabling oxygen in the atmosphere within the second internal cavity 40 to be drawn out to the external space, or oxygen to be drawn in from the external space into the second internal cavity 40.

[0059] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely the oxygen partial pressure detection sensor unit 81 for auxiliary pump control, is constructed from the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, and the third substrate layer 3.

[0060] Furthermore, the auxiliary pump unit 50 utilizes a variable power supply 52 for pumping, and the voltage of this variable power supply 52 is controlled based on the electromotive force (voltage V1) detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control. As a result, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a low partial pressure that substantially has no impact on NOx measurement.

[0061] In addition, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor unit 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor unit 80 for main pump control and the aforementioned target value of its voltage V0 is controlled, thereby keeping the gradient of oxygen partial pressure in the gas to be measured introduced from the third diffusion rate control unit 30 into the second internal cavity 40 constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump unit 21 and the auxiliary pump unit 50.

[0062] The fourth diffusion rate control unit 60 is configured to apply a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) has been controlled in the second internal cavity 40 by the operation of the auxiliary pump unit 50, and to guide the gas to be measured into the third internal cavity 61. The fourth diffusion rate control unit 60 is responsible for limiting the amount of NOx flowing into the third internal cavity 61.

[0063] The third internal cavity 61 is configured as a space for performing the following process: measuring the concentration of nitrogen oxides (NOx) in a gas to be measured, which has had its oxygen concentration (oxygen partial pressure) pre-adjusted in the second internal cavity 40 and then introduced through the fourth diffusion rate control unit 60. The NOx concentration is primarily measured in the third internal cavity 61 by the operation of the measuring pump unit 41.

[0064] The measuring pump unit 41 measures the NOx concentration in the gas to be measured within the third internal cavity 61. The measuring pump unit 41 is an electrochemical pump unit composed of a measuring electrode 44, an outer pump electrode 23, a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. The measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4, facing the third internal cavity 61. The measuring electrode 44 is a porous metal-ceramic electrode made of a material with improved reduction capability for NOx components in the gas to be measured compared to the inner pump electrode 22. The measuring electrode 44 also functions as a NOx reduction catalyst for reducing NOx present in the atmosphere within the third internal cavity 61.

[0065] Regarding the measuring pump unit 41, oxygen generated by the decomposition of nitrogen oxides in the atmosphere surrounding the measuring electrode 44 can be drawn out and its generation amount can be detected as pump current Ip2.

[0066] In addition, to detect the oxygen partial pressure around the measuring electrode 44, an electrochemical sensor unit, namely the oxygen partial pressure detection sensor unit 82 for measuring pump control, is constructed from 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 unit 82 for measuring pump control.

[0067] The gas to be measured, introduced into the second internal cavity 40, reaches the measuring electrode 44 in the third internal cavity 61 through the fourth diffusion rate control unit 60 under controlled oxygen partial pressure. Nitrogen oxides in the gas to be measured around the measuring electrode 44 are reduced (2NO→N2+O2) to generate oxygen. This generated oxygen is pumped by the measuring pump unit 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled to keep the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control constant (target value). The amount of oxygen generated around the measuring electrode 44 is directly proportional to the concentration of nitrogen oxides in the gas to be measured; therefore, the concentration of nitrogen oxides in the gas to be measured is calculated using the pump current Ip2 in the measuring pump unit 41.

[0068] Furthermore, if the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form an oxygen partial pressure detection mechanism as an electrochemical sensor unit, the electromotive force corresponding to the difference between the amount of oxygen produced by the reduction of NOx components in the atmosphere surrounding the measuring electrode 44 and the amount of oxygen contained in the reference atmosphere can be detected, thereby also determining the concentration of NOx components in the measured gas.

[0069] In addition, the electrochemical sensor unit 83 is composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23 and the reference electrode 42. The oxygen partial pressure in the gas to be measured outside the sensor can be detected based on the electromotive force (voltage Vref) obtained by the sensor unit 83.

[0070] Regarding the gas sensor 100 with such a structure, the gas to be measured, which operates the main pump unit 21 and the auxiliary pump unit 50 to keep the oxygen partial pressure at a constant low value (a value that has no substantial impact on the determination of NOx), is supplied to the measuring pump unit 41. Therefore, the NOx concentration in the gas to be measured can be determined based on the pump current Ip2, which is approximately proportional to the NOx concentration in the gas to be measured and flows due to the absorption of oxygen generated by the reduction of NOx by the measuring pump unit 41.

[0071] In addition, the sensor element 101 includes a heater section 70, which performs temperature regulation functions to heat and maintain the sensor element 101, thereby improving the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes a heater connector electrode 71, a heater 72, a through hole 73, a heater insulation layer 74, and a pressure relief hole 75.

[0072] The heater connector electrode 71 is formed in a manner that contacts the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to an external power source, power can be supplied to the heater section 70 from the outside.

[0073] The heater 72 is a resistive element formed by being sandwiched between the second substrate layer 2 and the third substrate layer 3 from the top and bottom. The heater 72 is connected to the heater connector electrode 71 via a through-hole 73, and receives power from the heater power supply 76 (see reference 76) through this heater connector electrode 71. Figure 2 The power supply generates heat, thereby heating and keeping the solid electrolyte forming the sensor element 101 warm.

[0074] In addition, the heater 72 is embedded in the entire area from the first internal cavity 20 to the third internal cavity 61, which can adjust the entire sensor element 101 to the temperature that activates the solid electrolyte.

[0075] The heater insulation layer 74 is an insulation layer formed on the upper and lower surfaces of the heater 72 by an insulator such as alumina. The purpose of forming the heater insulation layer 74 is to achieve electrical insulation between the second substrate layer 2 and the heater 72, and electrical insulation between the third substrate layer 3 and the heater 72.

[0076] The pressure relief hole 75 is a portion that is configured to penetrate the third substrate layer 3 and the reference gas introduction layer 48 and communicate with the reference gas introduction space 43. The purpose of forming the pressure relief hole 75 is to mitigate the increase in internal pressure that accompanies the temperature rise in the heater insulation layer 74.

[0077] like Figure 2As shown, the control device 95 includes: the aforementioned variable power supplies 24, 46, and 52, the aforementioned heater power supply 76, and a control unit 96. The control unit 96 is a microprocessor equipped with a CPU 97 and a storage unit 98. The storage unit 98 is a non-volatile memory capable of rewriting information, such as storing various programs and various data. The control unit 96 is input to the voltage V0 detected by the oxygen partial pressure detection sensor unit 80 for main pump control, the voltage V1 detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control, the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control, the voltage Vref detected by the sensor unit 83, the pump current Ip0 detected by the main pump unit 21, the pump current Ip1 detected by the auxiliary pump unit 50, and the pump current Ip2 detected by the measuring pump unit 41. In addition, the control unit 96 outputs control signals to the variable power supplies 24, 46, and 52, thereby controlling the voltages Vp0, Vp1, and Vp2 output by the variable power supplies 24, 46, and 52, and thus controlling the main pump unit 21, the measuring pump unit 41, and the auxiliary pump unit 50. The control unit 96 also outputs control signals to the heater power supply 76, thereby controlling the power supplied by the heater power supply 76 to the heater 72. The storage unit 98 also stores target values ​​V0*, V1*, V2*, etc., which will be described later. The CPU 97 of the control unit 96 refers to these target values ​​V0*, V1*, and V2* to control each unit 21, 41, and 50.

[0078] The control unit 96 performs auxiliary pump control processing on the auxiliary pump unit 50 to ensure that the oxygen concentration in the second internal cavity 40 reaches a target concentration. Specifically, the control unit 96 performs feedback control on the voltage Vp1 of the variable power supply 52 to ensure that the voltage V1 reaches a constant value (referred to as the target value V1*), thereby controlling the auxiliary pump unit 50. The target value V1* is defined as a value in which the oxygen concentration in the second internal cavity 40 reaches a specified low concentration that has no substantial impact on the measurement of NOx.

[0079] The control unit 96 performs main pump control processing on the main pump unit 21 to ensure that the pump current Ip1 flowing through the auxiliary pump unit 50 adjusts the oxygen concentration in the second internal cavity 40 using auxiliary pump control processing reaches a target current (referred to as target value Ip1*). Specifically, the control unit 96 sets a target value (referred to as target value V0*) of voltage V0 based on the pump current Ip1 to ensure that the pump current Ip1 flowing due to voltage Vp1 reaches a constant target value Ip1* (feedback control). Furthermore, the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 to ensure that voltage V0 reaches the target value V0* (that is, to ensure that the oxygen concentration in the first internal cavity 20 reaches a target concentration). Through this main pump control processing, the gradient of oxygen partial pressure in the measured gas introduced from the third diffusion rate control unit 30 into the second internal cavity 40 remains constant. The target value V0* is set to a value where the oxygen concentration in the first internal cavity 20 is higher than 0% and is a low concentration. Furthermore, the pump current Ip0 flowing in the main pump control process changes accordingly with 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 to be measured 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.

[0080] The aforementioned main pump control processing and auxiliary pump control processing are collectively referred to as adjustment pump control processing. Furthermore, the first internal cavity 20 and the second internal cavity 40 are collectively referred to as oxygen concentration adjustment chambers. The main pump unit 21 and the auxiliary pump unit 50 are collectively referred to as adjustment pump units. The adjustment pump control processing is performed by the control unit 96, causing the adjustment pump units to adjust the oxygen concentration in the oxygen concentration adjustment chambers.

[0081] Furthermore, the control unit 96 performs pump control processing on the measuring pump unit 41 to ensure that the voltage V2 reaches a constant value (referred to as the target value V2*) (that is, to ensure that the oxygen concentration in the third internal cavity 61 reaches a predetermined low concentration). Specifically, the control unit 96 performs feedback control on the voltage Vp2 of the variable power supply 46 to ensure that the voltage V2 reaches the target value V2*, thereby controlling the measuring pump unit 41. Through this pump control processing, oxygen is drawn out from the third internal cavity 61.

[0082] Oxygen is drawn out of the third internal cavity 61 by performing a pump control process to reduce the oxygen generated from the reduction of NOx in the gas being measured to practically zero. Furthermore, the control unit 96 acquires a pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal cavity 61 from a specific gas (here, NOx), and calculates the NOx concentration in the gas being measured based on this pump current Ip2.

[0083] The memory 98 stores formulas (e.g., linear or quadratic functions) and mappings that represent the correspondence between pump current Ip2 and NOx concentration. These formulas or mappings can be determined experimentally beforehand.

[0084] The control unit 96 performs heater control processing by outputting a control signal to the heater power supply 76 to control the heater 72 so that its temperature reaches a target temperature (e.g., 800°C). Here, the 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 considered as the temperature of the heater 72 (which can be converted to a temperature value), and performs feedback control on the heater power supply 76 to ensure that the calculated resistance value reaches the target resistance value (the resistance value corresponding to the target temperature). The control unit 96 can acquire, for example, the voltage of the heater 72 and the current flowing through the heater 72, and calculate the resistance value of the heater 72 based on the acquired voltage and current. The control unit 96 can calculate the resistance value of the heater 72 using, for example, a 3-terminal method or a 4-terminal method. When the heater power supply 76 powers on the heater 72, it adjusts the power supplied to the heater 72 by changing the value of the voltage applied to the heater 72, for example, based on a control signal from the control unit 96.

[0085] The inventors of this invention investigated the relationship between the target value V1* of the gas sensor 100, the water concentration in the measured gas, and the pump current Ip2. First, as the measured gas, three gases were prepared: a first gas with a base gas of nitrogen, an oxygen concentration of 0%, a water concentration of 3%, and a 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, the target value V2* was set to 400 mV, and the target value V1* was set to 300 mV. For the first gas, the control unit 96 measured the pump current Ip2 during the aforementioned adjustment pump control processing and measurement pump control processing. It should be noted that the control unit 96 starts the aforementioned heater control processing, and after the temperature of the heater 72 reaches near the target temperature, it starts the adjustment pump control processing and measurement pump control processing. Then, the pump current Ip2 is measured when it is stable. Furthermore, the target value V1* was changed to 350mV, 400mV, and 450mV. In addition, the pump current Ip2 corresponding to each target value V1* was measured, similar to the measurements described above. For the second and third gases, the pump current Ip2 corresponding to each target value V1* was also measured, similar to the measurements described above. The results are shown below. Figure 3 . Figure 3It is a graph showing the relationship between the target value V1*, the water concentration in the measured gas, and the pump current Ip2. Figure 3 The pump current Ip2 on the vertical axis is expressed as the value of pump current Ip2 converted to NO concentration (unit: ppm) using the correspondence between pump current Ip2 and NOx concentration stored in storage unit 98. The NO concentration of the first to third gases is 0 ppm; therefore, theoretically, the pump current Ip2 is 0 μA. However, in reality, a small amount of pump current Ip2 flows. This pump current Ip2 flowing due to a primary cause other than a specific gas (in this case, NOx) is called the bias current Ip2offset. Therefore, Figure 3 The relationship between the target value V1*, the water concentration in the measured gas, and the bias current Ip2offset is shown. The bias current Ip2offset is also included in the pump current Ip2 when the NOx concentration is not 0 ppm.

[0086] like Figure 3 As shown, a linear correlation exists between the target value V1* and the bias current Ip2offset, confirming a trend that the higher the target value V1*, the smaller the bias current Ip2offset. Furthermore, regarding the slope of the change in bias current Ip2offset relative to the change in target value V1*, a trend was confirmed where the higher the water concentration in the measured gas, the larger the absolute value of the slope. Figure 4 It shows the basis Figure 3 The graph shown illustrates the relationship between the slope of the change in water concentration in the measured gas and the change in bias current Ip2offset relative to the target value V1*, calculated from the data. Figure 4 As shown, a linear correlation exists between water concentration and the slope of the bias current Ip2offset, confirming a trend that the higher the water concentration, the smaller the slope of the bias current Ip2offset (the larger the absolute value of the negative value). These results indicate that the water concentration in the measured gas can be detected based on the change in pump current Ip2 (e.g., the slope of the change in bias current Ip2offset when the target value V1* changes). This is a new insight discovered by the inventors of this invention.

[0087] The inventor of this invention and Figure 3 Similarly, the relationship between the target value V2* of the gas sensor 100, the water concentration in the measured gas, and the pump current Ip2 was investigated. Specifically, the same first to third gases as described above were used, and the target value V1* was set to 385mV, and the target value V2* was set to 300mV, 350mV, 400mV, and 450mV. Figure 3 Similarly, the pump current Ip2 corresponding to each target value V2* was measured. The results are shown below. Figure 5 . Figure 5 It is a graph showing the relationship between the target value V2*, the water concentration in the measured gas, and the pump current Ip2. Figure 6 It shows the basis Figure 5 The graph shown shows the relationship between the slope of the change in water concentration in the measured gas and the change in bias current Ip2offset relative to the change in target value V2*, calculated from the data.

[0088] like Figure 5 As shown, a linear correlation exists between the target value V2* and the bias current Ip2offset, confirming a trend that the higher the target value V2*, the larger the bias current Ip2offset. Furthermore, regarding the slope of the change in bias current Ip2offset relative to the change in target value V2*, a trend was confirmed where the higher the water concentration in the measured gas, the larger the absolute value of the slope. Figure 6 As shown, a linear correlation exists between water concentration and the slope of the bias current Ip2offset, confirming a trend that the higher the water concentration, the greater the slope of the bias current Ip2offset (the larger the absolute value of the positive value). These results indicate that the water concentration in the measured gas can be detected based on the change in pump current Ip2 (e.g., the slope of the change in bias current Ip2offset when the target value V2* is changed). This is a new insight discovered by the inventors of this invention.

[0089] As can be seen from the above, the change in pump current Ip2 flowing during the execution of the adjustment pump control process and the measurement pump control process when at least one of the target values ​​V1* and V2* changes is correlated with the water concentration in the gas being measured. Therefore, water concentration can be detected based on the change in this pump current Ip2. In this embodiment, the relationship between the slope of the change in pump current Ip2 when the target value V1* changes and the water concentration in the gas being measured is expressed as... Figure 4 The linear relationship shown is represented by a linear function or mapping and stored in storage unit 98.

[0090] It should be noted that there is a relationship between the target values ​​V1* and V2*, the water concentration in the measured gas, and the pump current Ip2 (especially the bias current Ip2offset). Figures 3-6 The reasoning behind the relationship shown is as follows.

[0091] First, the relationship between water in the gas being measured and the bias current Ip2offset will be explained. When water is present in the gas being measured, during the adjustment pump control process (here, main pump control and auxiliary pump control), the voltage Vp1 of the variable power supply 52 causes at least a portion of the water to decompose into hydrogen (H2) and oxygen (O2) around the auxiliary pump electrode 51. The generated oxygen is drawn out from the periphery of the auxiliary pump electrode 51, i.e., the second internal cavity 40, through the auxiliary pump unit 50. However, at least a portion of the generated hydrogen reaches the third internal cavity 61. Then, the hydrogen reaching the third internal cavity 61 reacts with the oxygen within the third internal cavity 61 to become water. Therefore, the amount of oxygen drawn out from the third internal cavity 61 is reduced by the measurement pump control process, i.e., the pump current Ip2 is reduced. On the other hand, when water is present in the gas being measured, during the measurement pump control process, the voltage Vp2 of the variable power supply 46 causes at least a portion of the water to decompose into hydrogen (H2) and oxygen (O2) around the measuring electrode 44 within the third internal cavity 61. Therefore, the amount of oxygen drawn out of the third internal cavity 61 by the measurement pump control process increases, i.e., the pump current Ip2 increases. In this way, the pump current Ip2 decreases due to the hydrogen generated from water around the auxiliary pump electrode 51, and increases due to the oxygen generated from water around the measuring electrode 44. Therefore, the sum of the decrease and increase in these pump currents Ip2, which do not originate from NOx in the gas being measured, is represented by the bias current Ip2offset.

[0092] Furthermore, the higher the target value V1*, i.e., the lower the target oxygen concentration in the second internal cavity 40, the easier it is to control the voltage Vp1 through the auxiliary pump, thus increasing the amount of hydrogen generated by the decomposition of water around the auxiliary pump electrode 51 through the voltage Vp1, and consequently, the greater the decrease in pump current Ip2. Additionally, the higher the water concentration in the measured gas, the more hydrogen is generated by the decomposition of water around the auxiliary pump electrode 51. Therefore, the decrease in pump current Ip2 corresponding to the change in target value V1*, i.e., the slope of the change in pump current Ip2 relative to the change in target value V1*, becomes steeper. That is, the absolute value of the slope increases. Based on these reasons, it is believed that... Figure 3 and Figure 4 The relationship shown.

[0093] Similarly, the higher the target value V2*, i.e., the lower the target oxygen concentration in the third internal cavity 61, the easier it is to make the voltage Vp2 a higher value through the pump control process. Therefore, the more oxygen is generated by the decomposition of water around the measuring electrode 44 due to the voltage Vp2, and the greater the increase in pump current Ip2. Furthermore, the higher the water concentration in the measured gas, the more oxygen is generated by the decomposition of water around the measuring electrode 44. Therefore, the increase in pump current Ip2 corresponding to the change in target value V2*, i.e., the slope of the change in pump current Ip2 relative to the change in target value V2*, becomes steeper. That is, the absolute value of the slope becomes larger. Based on these reasons, it is believed that... Figure 5 and Figure 6 The relationship shown.

[0094] Next, an example of the processing of water concentration and NOx concentration measurement by the control unit 96 of the gas sensor 100 will be described. Figure 7 This is a flowchart illustrating an example of a control routine executed by the control unit 96. The control unit 96 stores this routine in, for example, a storage unit 98. For example, when a start command is input to an engine ECU (not shown), the control unit 96 begins this control routine.

[0095] When the CPU 97 of the control unit 96 starts the control routine, it first begins the heater control process described above (step S100). Next, the CPU 97 begins the adjustment pump control process and the measurement pump control process described above (step S110). The target values ​​V1* and V2* at this time are values ​​that have been pre-stored in the storage unit 98 as values ​​used when measuring NOx concentration. Next, the CPU 97 determines whether it is an opportune time to export water concentration and NOx concentration (step S120). The CPU 97 determines the concentration export opportunity, for example, when a predetermined time has elapsed or when a concentration export command is input from the engine ECU.

[0096] If it is determined in step S120 that it is time to derive concentration, the CPU 97 first performs a water concentration detection process (steps S130 and S140) to detect the water concentration in the gas being measured, based on the change in pump current Ip2 during the execution of the adjustment pump control process and the measurement pump control process when at least one of the target values ​​V1* and V2* changes. In this embodiment, the CPU 97 changes the target value V1* but not the target value V2* during the water concentration detection process. During 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* changes (step S130). Specifically, the CPU 97 first measures the current pump current Ip2 and obtains the value of the pump current Ip2 as the state before the change in the target value V1*. Next, the CPU 97 changes the target value V1* until the value of the pump current Ip2 stabilizes, measures the stabilized pump current Ip2, and obtains the value of the pump current Ip2 as the state after the change. Then, the difference between the pump current Ip2 before and after the change is divided by the difference between the target value V1* before and after the change, thereby deriving the slope G. It should be noted that the time for the target value V1* to change until the pump current Ip2 stabilizes is an extremely short time (a few msec to tens of msec, etc.), during which time almost no change occurs in the NOx concentration in the exhaust gas of the internal combustion engine. Therefore, the difference between the pump current Ip2 before and after the change in the target value V1* can be considered as the change in the bias current Ip2offset before and after the change in the target value V1*. Therefore, the slope G derived in step S130 is equivalent to... Figure 3 The slope of the line shown and Figure 4 The value of the vertical axis is then calculated. The CPU 97 calculates the water concentration in the gas being measured based on the derived slope G and the correspondence stored in the storage unit 98 (the correspondence between the slope of the change in pump current Ip2 when the target value V1* changes and the water concentration in the gas being measured, as described above). The CPU 97 outputs the derived water concentration value to the engine ECU or stores it in the storage unit 98. In step S130, the value can be changed in the direction of increasing the absolute value of the target value V1*, or it can be changed in the direction of decreasing the absolute value. However, it is preferable that the values ​​before and after the change are both below the absolute value of the target value V1* specified for measuring NOx concentration. For example, if the target value V1* before the change is the same as the target value V1* specified for measuring NOx concentration, it is preferable to change it in the direction of decreasing the absolute value of the target value V1*. Accordingly, it is possible to suppress the decomposition of NOx around the auxiliary pump electrode 51 due to excessively high voltage Vp1, thus suppressing the decrease in the accuracy of NOx concentration measurement.

[0097] After deriving the water concentration in step S140, the CPU 97 returns the target value V1* to its original value. That is, the target value V1* is returned to the value specified for measuring the NOx concentration (step S150). Next, the CPU 97 acquires the pump current Ip2 flowing due to the pump control processing for measurement (step S160), and based on the correspondence between the acquired pump current Ip2 and the data stored in the storage unit 98 (the aforementioned correspondence between pump current Ip2 and NOx concentration), derives the NOx concentration in the gas being measured (step S170). Then, the CPU 97 corrects the NOx concentration derived in step S170 based on the water concentration derived in step S140, thereby deriving 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. Figure 3 As shown, the bias current Ip2offset of the pump current Ip2 changes due to the water concentration in the gas being measured. Therefore, even if the NOx concentration in the gas being measured is the same, the pump current Ip2 may sometimes change accordingly with the water concentration in the gas being measured, sometimes resulting in an error in the derived NOx concentration. Therefore, in this embodiment, the CPU97 corrects the NOx concentration obtained based on the pump current Ip2 based on the detected water concentration. For example, Figure 3In the case where the target value V1* is 350mV, the bias current Ip2offset at a water concentration of 15% is 3ppm higher than the bias current Ip2offset at a water concentration of 3%. Therefore, if the relationship between the pump current Ip2 and NOx concentration pre-stored in the storage unit 98 is calculated using the measured gas with a water concentration of 3%, and the actual water concentration of the measured gas is 15%, the calculated NOx concentration is 3ppm higher than the actual concentration. Thus, when the water concentration derived in step S140 is 15%, the CPU 97 subtracts the 3ppm correction amount from the NOx concentration [ppm] derived in step S170 to obtain the corrected NOx concentration. This offsets the change in bias current Ip2offset caused by different water concentrations, resulting in a corrected NOx concentration closer to the actual concentration. This relationship between the water concentration and NOx concentration correction amount can be pre-determined through experiments and stored in the storage unit 98. In step S180, CPU97 derives a correction value based on the water concentration and the corresponding relationship, and calculates the corrected NOx concentration. It should be noted that instead of deriving the correction value, the corresponding relationship between the water concentration, the NOx concentration obtained based on the pump current Ip2, and the corrected NOx concentration can be stored in the storage unit 98 beforehand, and the corrected NOx concentration can be derived based on this relationship. Alternatively, CPU97 can 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 fall under the category of NOx concentration correction based on water concentration.

[0098] After step S180, or if it is not a concentration derivation opportunity in step S120, CPU97 executes the processing after S120. By executing the control routine as described above, CPU97 repeatedly measures the water concentration and NOx concentration in the gas being measured.

[0099] Here, the correspondence between the constituent elements of this embodiment and the constituent elements of the present invention is clarified. The laminate obtained by sequentially stacking the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5, and the second solid electrolyte layer 6 in this embodiment corresponds to the main body of the component of the present invention. The third internal cavity 61 corresponds to the measuring chamber, the measuring electrode 44 corresponds to the inner measuring 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 inner adjustment electrode, the main pump unit 21 and the auxiliary pump unit 50 correspond to the adjustment pump unit, the reference electrode 42 corresponds to the reference electrode, the voltage V1 corresponds to the adjustment voltage, the target value V1* corresponds to the target value of the adjustment voltage, the voltage V2 corresponds to the measuring voltage, the target value V2* corresponds to the target value of the measuring voltage, the control device 95 corresponds to the control device, and the pump current Ip2 corresponds to the measuring pump current. Furthermore, the auxiliary pump electrode 51 corresponds to the inner auxiliary pump electrode.

[0100] According to the gas sensor 100 of this embodiment described in detail above, the control device 95 detects the NOx concentration in the gas to be measured based on the pump current Ip2 flowing through the measuring pump unit 41 due to the measuring pump control processing. Furthermore, the control device 95 performs a water concentration detection process to detect the water concentration in the gas to be measured based on changes in the pump current Ip2 flowing during the execution of the adjustment pump control processing and the measuring pump control processing when at least one of the target values ​​V1* and V2* changes. Therefore, the gas sensor 100 of this embodiment can detect both the NOx concentration and the water concentration in the gas to be measured.

[0101] In addition, 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, thus improving the detection accuracy of a specific gas concentration.

[0102] It should be noted that the present invention is not limited to any of the above embodiments. Of course, as long as it falls within the technical scope of the present invention, it can be implemented in various ways.

[0103] For example, in the above embodiments, in Figure 7 In step S130 of the control routine, the CPU 97 derives the water concentration based on the slope G of the change in pump current Ip2 when the target value V1* changes. However, it is not limited to the slope G; the water concentration can be derived based on the change in pump current Ip2 when the target value V1* changes. 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 the 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 pre-stored in the storage unit 98.

[0104] In the above embodiments, in Figure 7 In step S130 of the control routine, CPU97 derives the water concentration based on the slope G of the change in pump current Ip2 when the target value V1* changes. However, the water concentration can also be derived based on the change in pump current Ip2 when the target value V2* changes. For example, CPU97 can derive the slope G of the change in pump current Ip2 when the target value V2* changes instead of V1* (equivalent to...). Figure 5 The slope of the line shown and Figure 6 The value of the vertical axis), based on the derived slope, yields the water concentration. In this case, the relationship between the slope of the change in pump current Ip2 as the target value V2* changes and the water concentration is (equivalent to...). Figure 6 The correspondence of the straight lines shown can be pre-stored in the storage unit 98. It should be noted that when changing the target value V2*, it can be changed in the direction of increasing the absolute value of the target value V2*, or it can be changed in the direction of decreasing the absolute value. However, it is preferable that both the value before and after the change are at or above the target value V2* specified for measuring NOx concentration. For example, if the target value V2* before the change is the same as the target value V2* specified for measuring NOx concentration, it is preferable to change it in the direction of increasing the absolute value of the target value V2*. Accordingly, it is possible to suppress the voltage Vp2 from being too low, causing the pump current Ip2 to not reach the limiting current, and therefore, it is possible to suppress the decrease in the accuracy of NOx concentration measurement.

[0105] The CPU97 can also derive water concentration in water concentration detection processing based on the pump current Ip2 when both target values ​​V1* and V2* change. In this case, it is preferable that the direction of change of pump current Ip2 caused by the change in target value V1* is the same as the direction of change of pump current Ip2 caused by the change in target value V2*. For example, if the absolute value of target value V1* is made smaller and the absolute value of target value V2* is made larger, these changes will both act in the direction of increasing pump current Ip2. Alternatively, if the absolute value of target value V1* is made larger and the absolute value of target value V2* is made smaller, these changes will both act in the direction of decreasing pump current Ip2. If the target values ​​V1* and V2* are changed using either of the above methods, even if the changes in target values ​​V1* and V2* are small, the change in pump current Ip2 caused by water in the measured gas will be relatively large. Therefore, water concentration can be easily detected based on the change in pump current Ip2. It should be noted that when both the target values ​​V1* and V2* are changed, the water concentration can be derived by calculating, for example, the amount or rate of change of the pump current Ip2, rather than the slope of the pump current Ip2.

[0106] In the above embodiment, the CPU97 corrected the NOx concentration using water concentration; however, this correction may not be necessary. Furthermore, the CPU97 can determine whether the derived water concentration is within a specified permissible range that is considered not to affect the accuracy of the NOx concentration measurement. If it is not within the permissible range, the CPU97 corrects the NOx concentration.

[0107] In the above embodiments, the gas sensor 100 can also be configured to detect the gas temperature of the gas being measured. The inventors of this invention compared the change in pump current Ip2 when the target value V1* changes with the change in pump current Ip2 when the target value V2* changes, and found that the former is less affected by the gas temperature of the gas being measured. That is, it was found that the latter is more easily affected by gas temperature compared to the former; therefore, by comparing the former and the latter, the gas temperature of the gas being measured can be detected. Figure 8 This is a conceptual diagram showing the relationship between water concentration, the slope of the change in bias current Ip2offset relative to the change in target value V2*, and gas temperature. Figure 6 This is a graph where the temperatures of the first to third gases are set to the same value. In contrast, Figure 8 This schematically illustrates how the slope of the bias current Ip2offset changes in relation to the gas temperature when the temperatures of the first to third gases are varied. Figure 8As shown, even with the same water concentration, the slope of the change in bias current Ip2offset relative to the change in target value V2* changes with the gas temperature, confirming a trend that the slope increases with higher gas temperature. On the other hand, even with changes in gas temperature, if the water concentration remains the same, the slope of the change in bias current Ip2offset relative to the change in target value V1* is unlikely to change. This difference is believed to be due to the temperature difference between the auxiliary pump electrode 51 and the measuring electrode 44. While the above embodiment omits further explanation, the gas sensor 100 is configured such that when the heater 72 is heated to at least one temperature within the range of 700°C to 900°C, the temperature Tm of the measuring electrode 44 is lower than the temperature Tq of the auxiliary pump electrode 51. 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, for example, a value within the range of 650°C to 700°C. Compared to the measuring pump unit 41, the auxiliary pump unit 50 handles a larger amount of oxygen. Therefore, to further improve the pumping capacity of the auxiliary pump unit 50, it is designed to satisfy temperature Tq > temperature Tm. It should be noted that, for the same reason, it is preferable that the pumping capacity of the main pump unit 21 is higher than that of the auxiliary pump unit 50. Therefore, when the temperature of the inner pump electrode 22 is set to temperature Tp, the gas sensor 100 is preferably configured such that temperature Tp > temperature Tq > temperature Tm when the heater 72 is controlled to the target temperature. For example, by adjusting the shape and arrangement of the heater 72, temperature Tp, temperature Tq, and temperature Tm can be adjusted. Furthermore, because temperature Tq > temperature Tm, the temperature Tq of the auxiliary pump electrode 51 is closer to the gas temperature of the measured gas (e.g., 700°C to 800°C), and even if the gas temperature changes, temperature Tq is less likely to change. In contrast, the temperature Tm of the measuring electrode 44 differs significantly from the gas temperature of the measured gas; therefore, if the gas temperature changes, temperature Tm is more likely to change. Furthermore, it is believed that even with the same water concentration, if the temperature Tm increases, the amount of water decomposition around the measuring electrode 44 increases. Therefore, the slope of the change in bias current Ip2offset relative to the change in the target value V2* becomes larger, i.e., the slope of bias current Ip2offset becomes larger. Based on this, it is believed that a change occurs corresponding to the gas temperature. Figure 8 The trends shown. Using these findings, a gas temperature detection process can be performed to detect the gas temperature of the gas being measured based on the changes in pump current Ip2 when the target value V1* changes and the changes in pump current Ip2 when the target value V2* changes.

[0108] A specific example of gas temperature detection will be explained. First, the temperature is determined experimentally beforehand. Figure 8The relationship, or mapping, between the slope of the change in water concentration, bias current Ip2offset, and gas temperature is shown and stored in the storage unit 98. The CPU 97 of the control device 95 performs... Figure 7 In control routines S100 to S140, the water concentration is derived based on the slope G of the change in pump current Ip2 when the target value V1* changes. Since this water concentration is derived by changing the target value V1*, it is less susceptible to influence by gas temperature. Next, the CPU 97 returns the target value V1* to its original value and derives the slope of the change in pump current Ip2 when the target value V2* changes. Then, based on the derived water concentration, the slope of the change in pump current Ip2 when the target value V2* changes, and the corresponding relationship stored in the storage unit 98, the CPU 97 derives the gas temperature of the gas being measured. For example, Figure 8 When the relationship is stored in the storage unit 98, if the derived water concentration is 15% and the slope of the change in pump current Ip2 when the target value V2* changes is value a, then value b is derived as the gas temperature. Therefore, in addition to detecting the NOx concentration and water concentration of the gas being measured, the gas sensor 100 can also detect the gas temperature. It should be noted that... Figure 8 The water concentration corresponds to the water concentration obtained based on the slope G of the change in pump current Ip2 when the target value V1* changes. Therefore, the relationship between the slope G of the change in pump current Ip2 relative to the change in target value V1*, the slope of the change in pump current Ip2 relative to the change in target value V2*, and the gas temperature is also related to... Figure 8 The same applies. Therefore, instead of using the derived water concentration, the gas temperature can be derived based on the slope G of the change in pump current Ip2 relative to the target value V1*, the slope of the change in pump current Ip2 relative to the target value V2*, and the correspondence pre-stored in the storage unit 98. Alternatively, the difference or ratio between the slope G of the change in pump current Ip2 relative to the target value V1* and the slope of the change in pump current Ip2 relative to the 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 the difference or ratio and the gas temperature can be pre-stored in the storage unit 98. In addition, as mentioned above, instead of using the slope, the amount or rate of change of pump current Ip2 can be used.

[0109] Furthermore, the control device 95 can also correct the NOx concentration in the gas being measured based on the derived water concentration and gas temperature. If the gas temperature of the gas being measured increases, the amount of water decomposition around the measuring electrode 44 increases; therefore, the higher the gas temperature, the larger the bias current Ip2offset. Additionally, as mentioned above, the bias current Ip2offset also varies depending on the water concentration. Therefore, even if the actual NOx concentration in the gas being measured is the same, the pump current Ip2 will change accordingly with the gas temperature and water concentration, sometimes resulting in errors in the derived NOx concentration. The control device 95 corrects the NOx concentration in the gas being measured based on the derived water concentration and gas temperature, thereby suppressing such errors and improving the detection accuracy of the NOx concentration. When performing such correction, for example, the correspondence between water concentration and gas temperature and the bias current Ip2offset can be investigated in advance and stored in the storage unit 98. Figure 9 This is a conceptual diagram illustrating one example of such a correspondence. Control device 95 is based on the derived water concentration, the derived gas temperature, and... Figure 9 The bias current Ip2offset is derived from the shown correspondence. Then, the NOx concentration in the gas being measured is corrected based on the derived bias current Ip2offset. For example, regarding the correspondence between the pump current Ip2 and the NOx concentration pre-stored in the storage unit 98, the value of the bias current Ip2offset when calculating this correspondence is investigated in advance and stored in the storage unit 98 as a reference value. More specifically, except that the NOx concentration in the gas being measured is set to 0 ppm, the pump current Ip2 under the same conditions as when the correspondence was calculated can be measured and its value used as the reference value. The control device 95 derives the difference between the derived bias current Ip2offset and the reference value stored in the storage unit 98 and sets it as the correction amount for the pump current Ip2. Then, the control device 95 derives the value obtained in step S160 by subtracting the correction amount from the pump current Ip2 as the corrected pump current Ip2. Subsequently, the control unit 96 derives the NOx concentration based on the corrected pump current Ip2, the pump current Ip2 stored in the storage unit 98, and the corresponding NOx concentration. This derived NOx concentration is a corrected NOx concentration where the change in bias current Ip2 offset caused by water concentration and gas temperature is offset, thus becoming a value closer to the actual NOx concentration compared to the uncorrected case. It should be noted that this can also be replaced with... Figure 9 The correspondence can be determined by using the relationship between water concentration and gas temperature and the correction value of pump current Ip2. Alternatively, the correspondence between water concentration and gas temperature and the correction value of NOx concentration can also be used.

[0110] Figure 9The relationships shown exhibit the following trend: for the same gas temperature, the higher the water concentration, the larger the bias current Ip2offset. However, this is not limited to this; sometimes the following trend also holds true: for the same gas temperature, the higher the water concentration, the smaller the bias current Ip2offset. For example, from... Figure 3 and Figure 5 It is known that when the target value V1* is below 400mV and the target value V2* is above 350mV, there is a trend that the higher the water concentration, the larger the bias current Ip2offset. Conversely, when the target value V1* exceeds 400mV or the target value V2* is less than 350mV, there is a trend that the higher the water concentration, the smaller the bias current Ip2offset. Therefore, it is preferable to investigate in advance the appropriate correspondence (the correspondence between water concentration and gas temperature and bias current Ip2offset) corresponding to the target values ​​V1* and V2* when obtaining the pump current Ip2 used for NOx concentration measurement, and store it in the storage unit 98.

[0111] As mentioned above, the change in pump current Ip2 when the target value V2* changes is easily affected by gas temperature. Therefore, water concentration detection is preferably based on the change in pump current Ip2 when the target value V1* changes. However, if the gas temperature has little impact on the accuracy of water concentration detection, or if the temperature variation of the gas being measured is small, then even if water concentration is detected based on the change in pump current Ip2 when the target value V2* changes, it is unlikely to cause problems.

[0112] While not described in the above embodiments, the target values ​​V0*, V1*, and V2* can each be 900mV or less, or 800mV or less. This prevents voltages Vp0, Vp1, and Vp2 from becoming excessively high, thereby suppressing blackening of the sensor element 101. The target value V1* can be a value in the range of 300mV or more and 450mV or less. The target value V2* can also be a value in the range of 300mV or more and 450mV or less. Even if the control device 95 changes the values ​​of the target values ​​V0*, V1*, and V2* during the control of the sensor element 101, it is preferable that these values ​​change within the aforementioned ranges.

[0113] In the above embodiment, the adjustment pump control process and the measurement pump control process continue to be executed after step S110, but this is not particularly limited to this. Sometimes, at least one of the adjustment pump control process and the measurement pump control process may be temporarily stopped. For example, in step S130, after temporarily stopping the adjustment pump control process and the measurement pump control process, the target value V1* is changed to the new value, and the adjustment pump control process and the measurement pump control process are restarted.

[0114] In the above embodiment, the oxygen concentration adjustment chamber has a first internal cavity 20 and a second internal cavity 40, but is not limited thereto. For example, the oxygen concentration adjustment chamber may further include another internal cavity, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the above embodiment, the adjustment pump unit has a main pump unit 21 and an auxiliary pump unit 50, but is not limited thereto. For example, the adjustment pump unit may further include another pump unit, or one of the main pump unit 21 and the auxiliary pump unit 50 may be omitted. For example, if the oxygen concentration of the gas to be measured can be sufficiently low using only the main pump unit 21, the auxiliary pump unit 50 may be omitted. If the auxiliary pump unit 50 is omitted, the control unit 96 only needs to be configured to perform only the main pump control processing as the adjustment pump control processing. In addition, for the main pump control processing, the setting of the target value V0* based on the pump current Ip1 mentioned above can be omitted. Specifically, by pre-storing the predetermined target value V0* in the storage unit 98, the control unit 96 can control the voltage Vp0 of the variable power supply 24 in a manner that makes the voltage V0 reach the target value V0*, thereby controlling the main pump unit 21. When the auxiliary pump unit 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 target value of the adjustment voltage. When the oxygen concentration adjustment chamber has another internal cavity besides the first internal cavity 20 and the second internal cavity 40, resulting in three or more adjustment pump units, the target value of the voltage in the control processing of the pump unit located furthest downstream of the three or more pump units—that is, the pump unit closest to the measuring chamber—corresponds to the target value of the adjustment voltage.

[0115] In the above embodiments, the sensor element 101 of the gas sensor 100 includes a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61, but is not limited thereto. For example, it can also be like... Figure 10 The sensor element 201 does not have a third internal cavity 61. Figure 10In the modified sensor element 201 shown, the gas inlet 10, the first diffusion rate control unit 11, the buffer space 12, the second diffusion rate control unit 13, the first internal cavity 20, the third diffusion rate control unit 30, and the second internal cavity 40 are connected in this order between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. Furthermore, 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 control unit 45. The fourth diffusion rate control unit 45 is a membrane composed of a porous ceramic material such as alumina (Al2O3). Similar to the fourth diffusion rate control unit 60 in the above embodiment, the fourth diffusion rate control unit 45 serves to limit the amount of NOx flowing into the measuring electrode 44. Additionally, the fourth diffusion rate control unit 45 also functions as a protective film for the measuring electrode 44. The top electrode portion 51a of the auxiliary pump electrode 51 is formed directly above the measuring electrode 44. Even with this sensor element 201, it is possible to detect NOx concentration based on, for example, the pump current Ip2, in the same manner as in the embodiments described above. In this case, the area around the measuring electrode 44 functions as a measuring chamber.

[0116] In the above embodiment, the outer pump electrode 23 serves as an electrode paired with the inner pump electrode 22 in the main pump unit 21 (also called the outer main pump electrode), an electrode paired with the auxiliary pump electrode 51 in the auxiliary pump unit 50 (also called the outer auxiliary pump electrode), and an electrode paired with the measuring electrode 44 in the measuring pump unit 41 (also called the outer measuring electrode), but is not limited thereto. Any one or more of the outer main pump electrode, outer auxiliary pump electrode, and outer measuring electrode may be disposed separately from the outer pump electrode 23 and in contact with the gas being measured on the outside of the element body.

[0117] In the above embodiment, the inner pump electrode 22 is a cermet electrode containing 1% Au in Pt and ZrO2, but is not limited thereto. The inner pump electrode 22 may contain any 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 above embodiment, it is preferable that the inner pump electrode 22 contains Pt as a catalytically active noble metal. The inner pump electrode 22 preferably contains both a catalytically active noble metal and Au. Similarly, the auxiliary pump electrode 51 may contain any catalytically active noble metal, and preferably further contains Au. By containing Au in the inner pump electrode 22 and the auxiliary pump electrode 51, the catalytic activity against NOx is suppressed, thus inhibiting 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 any of the aforementioned catalytically active noble metals. Each of the electrodes 22, 23, 42, 44, and 51 is preferably a cermet containing a noble metal and an oxide (e.g., ZrO2) with oxygen ion conductivity; however, one or more of these electrodes may not be a cermet. Each of the electrodes 22, 23, 42, 44, and 51 is preferably a porous material; however, one or more of these electrodes may not be a porous material.

[0118] In the above embodiment, the sensor element 101 detects the NOx concentration in the gas to be measured. However, it is not limited to detecting the concentration of a specific gas in the gas to be measured. For example, it is not limited to NOx; the concentration of other oxides can be set as the concentration of the specific gas. When the specific gas is an oxide, similar to the above embodiment, oxygen is generated when the specific gas itself is reduced in the third internal cavity 61. Therefore, the measuring pump unit 41 can obtain a detection value (e.g., pump current Ip2) corresponding to this oxygen and detect the concentration of the specific gas. Alternatively, the specific gas can also be a non-oxide such as ammonia. When the specific gas is a non-oxide, the specific gas is converted into an oxide (e.g., NO if it is ammonia). As a result, oxygen is generated when the converted gas is reduced in the third internal cavity 61. Therefore, the measuring pump unit 41 can obtain a detection value (e.g., pump current Ip2) corresponding to this oxygen and detect the concentration of the specific gas. For example, the inner pump electrode 22 of the first internal cavity 20 acts as a catalyst, thereby enabling the conversion of ammonia into NO in the first internal cavity 20. The specific gas can also be a specified gas other than oxygen. The specified gas may also be any of the specified gases other than oxygen and carbon dioxide. The specified gas may also be either NOx or ammonia.

[0119] In the above embodiments, the main body of the sensor element 101 is configured as a laminate having multiple solid electrolyte layers (layers 1 to 6), but is not limited thereto. The main body of the sensor element 101 only needs to include at least one oxygen ion-conducting solid electrolyte layer. For example, Figure 1 Layers 1 to 5, other than the second solid electrolyte layer 6, can also be layers formed of a material other than the solid electrolyte layer (e.g., layers formed of aluminum oxide). In this case, each electrode of the sensor element 101 only needs to be disposed on the second solid electrolyte layer 6. For example, Figure 1 The measuring electrode 44 can be disposed on the lower surface of the second solid electrolyte layer 6. Alternatively, it can be formed as follows: the reference gas introduction space 43 is disposed in the isolation layer 5 instead of the first solid electrolyte layer 4; the reference gas introduction layer 48 is disposed between the second solid electrolyte layer 6 and the isolation layer 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3; and the reference electrode 42 is disposed behind the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6.

[0120] In the above embodiment, the control unit 96 sets the target value V0* of the voltage V0 based on the pump current Ip1 in a manner that makes the pump current Ip1 reach the target value Ip1* (feedback control), and performs feedback control on the voltage Vp0 in a manner that makes the voltage V0 reach the target value V0*. However, other control methods are also possible. For example, the control unit 96 may also perform feedback control on the voltage Vp0 based on the pump current Ip1 in a manner that makes the pump current Ip1 reach the target value Ip1*. That is, the control unit 96 may omit obtaining the voltage V0 from the oxygen partial pressure detection sensor unit 80 for main pump control, or omit setting the target value V0*, and directly control the voltage Vp0 based on the pump current Ip1 (and thus control the pump current Ip0).

[0121] Industrial availability

[0122] This invention relates to a gas sensor capable of detecting the concentration of specific gases such as NOx in measured gases such as automobile exhaust.

Claims

1. A gas sensor comprising a sensor element and a control device, The sensor element has: The main body of the element has a solid electrolyte layer with oxygen ion conductivity, and is provided with a gas flow section inside for introducing and circulating the gas to be measured. A measuring pump unit is configured to include an inner measuring electrode disposed in a measuring chamber within the gas flow section being measured, which draws oxygen from the measuring chamber to the outside of the element body. An adjustment pump unit is configured to include an inner adjustment electrode disposed in an oxygen concentration adjustment chamber located upstream of the measuring chamber in the gas flow section, for adjusting the oxygen concentration of the oxygen concentration adjustment chamber. as well as A reference electrode is disposed inside the element body in such a way that it is in contact with a reference gas, which serves as the detection reference for the concentration of a specific gas in the gas being measured, i.e., the concentration of the specific gas. The control device performs adjustment pump control processing and measurement pump control processing. In the adjustment pump control processing, the adjustment pump unit is controlled to adjust the oxygen concentration in the oxygen concentration adjustment chamber by ensuring that the voltage between the reference electrode and the inner adjustment electrode, i.e., the adjustment voltage, reaches the target value of the adjustment voltage. In the measurement pump control processing, the measurement pump unit is controlled to draw oxygen out of the measurement chamber by ensuring that the voltage between the reference electrode and the inner measurement electrode, i.e., the measurement voltage, reaches the target value of the measurement voltage. The control device detects the concentration of the specific gas in the gas being measured based on the measuring pump current flowing through the measuring pump unit due to the measuring pump control processing. The control device performs water concentration detection processing. In this water concentration detection processing, the water concentration in the gas to be measured is detected based on the change in the current of the measuring pump flowing during the execution of the adjusting pump control processing and the measuring pump control processing when at least one of the adjusting voltage target value and the measuring voltage target value changes.

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

3. The gas sensor according to claim 1 or 2, characterized in that, The oxygen concentration adjustment chamber has: a first internal cavity, and a second internal cavity configured to be downstream of the first internal cavity and upstream of the measuring chamber. The adjustment pump unit includes: a main pump unit for adjusting the oxygen concentration of the first internal cavity, and an auxiliary pump unit for adjusting the oxygen concentration of the second internal cavity. The inner adjustment electrode is an inner auxiliary pump electrode disposed in the second internal cavity and forming part of the auxiliary pump unit. The adjustment pump control process includes: main pump control process that controls the main pump unit to adjust the oxygen concentration in the first internal cavity, and auxiliary pump control process that controls the auxiliary pump unit in such a way that the adjustment voltage reaches the target value of the adjustment voltage.

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

5. The gas sensor according to claim 1 or 2, characterized in that, The control device performs gas temperature detection processing. In this gas temperature detection processing, the gas temperature of the gas to be measured is detected based on the change in the current of the measuring pump flowing during the execution of the adjustment pump control processing and the measuring pump control processing when the target value of the adjustment voltage changes, and the change in the current of the measuring pump flowing during the execution of the adjustment pump control processing and the measuring pump control processing when the target value of the measuring voltage changes.

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

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