Gas sensors and their control methods

Abstract

This invention relates to a gas sensor and a control method for the gas sensor. The gas sensor (100) includes a sensor element (101) and a control unit. The sensor element (101) includes: an element body (layers (1-6)) having a gas flow section for measurement disposed inside; a measuring electrode (44) disposed in the gas flow section for measurement; an outer pump electrode (23) disposed in the element body in contact with the gas to be measured; a reference electrode (42) disposed inside the element body; a reference gas inlet (49) for allowing reference gas to flow from the outside of the element body to the reference electrode (42); and a reference gas adjustment pump unit (90) configured to include the outer pump electrode (23) and the reference electrode (42). The control unit performs a moisture concentration reduction process, that is, it controls the reference gas adjustment pump unit (90) to draw oxygen from the vicinity of the reference electrode (42) to the vicinity of the outer pump electrode (23), thereby reducing the moisture concentration around the reference electrode (42).

Description

Technical Field

[0001] This invention relates to a gas sensor and a control method for the gas sensor. Background Technology

[0002] Previously, sensor elements used in gas sensors for detecting the concentration of specific gases such as NOx in measured gases such as automobile exhaust are known. For example, Patent Document 1 describes a sensor element comprising: an element body having a solid electrolyte layer with oxygen ion conductivity and a measured gas flow section therein for introducing and flowing the measured gas; a measuring electrode disposed on the inner peripheral surface of the measured gas flow section; a reference electrode disposed inside the element body; and a reference gas introduction section for introducing and flowing a reference gas (e.g., atmosphere) that serves as a detection reference for the concentration of the specific gas in the measured gas to the reference electrode. The reference gas introduction section has a porous reference gas introduction layer. Based on the electromotive force generated between the reference electrode and the measuring electrode of this sensor element, the concentration of the specific gas in the measured gas can be detected.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2020-094899 Summary of the Invention

[0006] However, during periods when the sensor element is not being driven, the reference gas inlet may sometimes absorb external water. When driving begins, the water in the reference gas inlet turns into gas and is discharged from the reference gas inlet to the outside as the sensor element is heated. Because gaseous water was present before the water was discharged, the oxygen concentration around the reference electrode decreases. Consequently, the detection accuracy of a specific gas concentration may sometimes decrease during the period before the water is discharged.

[0007] The present invention was implemented to solve the above-mentioned problems, and its main purpose is to suppress the reduction in the detection accuracy of specific gas concentrations caused by moisture around the reference electrode.

[0008] To achieve the above-mentioned main objectives, the present invention employs the following method.

[0009] The first gas sensor of the present invention is a gas sensor that detects the concentration of a specific gas in the gas to be measured.

[0010] This gas sensor includes a sensor element and a control unit.

[0011] The sensor element has:

[0012] The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for introducing and allowing the gas to be measured to flow.

[0013] A measuring electrode is disposed in the gas flow section to be measured;

[0014] A gas-to-measure side electrode is disposed on the element body in a manner that contacts the gas to be measured.

[0015] A reference electrode is disposed inside the main body of the component;

[0016] A reference gas inlet section, which allows a reference gas, serving as a detection reference for the concentration of the specific gas in the gas being measured, to flow from outside the element body to the reference electrode; and

[0017] A reference gas adjustment pump unit, configured to include the measured gas-side electrode and the reference electrode.

[0018] The control unit performs a moisture concentration reduction process, that is, it controls the reference gas adjustment pump unit to draw oxygen from the vicinity of the reference electrode to the vicinity of the gas being measured side electrode, thereby reducing the moisture concentration around the reference electrode.

[0019] According to this first gas sensor, during the moisture concentration reduction process, oxygen is drawn from the vicinity of the reference electrode to the vicinity of the electrode containing the gas to be measured. Accordingly, not only is oxygen drawn from the vicinity of the reference electrode, but the moisture around the reference electrode is also decomposed, resulting in the extraction of oxygen generated during decomposition. Therefore, the moisture concentration around the reference electrode can be rapidly reduced, thus suppressing the decrease in detection accuracy of a specific gas concentration caused by moisture around the reference electrode.

[0020] In the first gas sensor of the present invention, the control unit can control the reference gas adjustment pump unit during the moisture concentration reduction process to alternately perform: oxygen extraction from around the reference electrode to around the gas to be measured side electrode, and oxygen intake from around the gas to be measured side electrode to around the reference electrode. Here, if oxygen is extracted from around the reference electrode, water is decomposed, and oxygen around the reference electrode is also extracted, thus temporarily reducing the oxygen concentration around the reference electrode. By alternating extraction and intake, the oxygen reduced due to extraction can be replenished in advance by means of intake.

[0021] The second gas sensor of the present invention is a gas sensor that detects the concentration of a specific gas in the gas being measured.

[0022] The gas sensor includes a sensor element and a control unit.

[0023] The sensor element has:

[0024] The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for introducing and circulating the gas to be measured.

[0025] A measuring electrode is disposed in the gas flow section to be measured;

[0026] A gas-to-measure side electrode is disposed on the element body in a manner that contacts the gas to be measured.

[0027] A reference electrode is disposed inside the main body of the component;

[0028] A reference gas inlet section, which allows a reference gas, serving as a detection reference for the concentration of the specific gas in the gas being measured, to flow from outside the element body to the reference electrode; and

[0029] A reference gas adjustment pump unit, configured to include the measured gas-side electrode and the reference electrode.

[0030] The control unit performs the following processes: a reference gas adjustment process, which controls the reference gas adjustment pump unit to draw oxygen from the vicinity of the measured gas side electrode to the vicinity of the reference electrode, thereby adjusting the oxygen concentration around the reference electrode; and a moisture concentration reduction process, which controls the reference gas adjustment pump unit to temporarily draw more oxygen to the vicinity of the reference electrode compared to the reference gas adjustment process, thereby reducing the moisture concentration around the reference electrode.

[0031] According to this second gas sensor, by using a reference gas adjustment process to draw oxygen into the vicinity of the reference electrode, the decrease in oxygen concentration around the reference electrode can be compensated. Furthermore, in the moisture concentration reduction process, more oxygen is temporarily drawn into the reference electrode compared to the reference gas adjustment process; therefore, this process can also compensate for the decrease in oxygen concentration caused by moisture around the reference electrode. Therefore, compared to, for example, performing a reference gas adjustment process but without a moisture concentration reduction process, it is more effective in suppressing the decrease in detection accuracy of specific gas concentrations caused by moisture around the reference electrode.

[0032] In the first or second gas sensor of the present invention, the control unit can apply a control voltage of 0.3V to 1.5V to the reference gas adjustment pump unit during the moisture concentration reduction process, thereby causing the reference gas adjustment pump unit to operate. If the control voltage is 0.3V or higher, the reference gas adjustment pump unit can operate more reliably. If the control voltage is 1.5V or lower, blackening of the sensor element can be suppressed.

[0033] In the first or second gas sensor of the present invention, the execution time of the moisture concentration reduction process can be 5 seconds or more and 300 seconds or less. If the execution time is 5 seconds or more, the moisture concentration around the reference electrode can be reduced more reliably. In addition, during the execution of the moisture concentration reduction process, the potential of the reference electrode changes because current flows through it; therefore, the execution time is preferably 300 seconds or less.

[0034] In the first or second gas sensor of the present invention, a heater may be included to heat the main body of the element. After the control unit energizes the heater and causes its temperature to reach a predetermined temperature or higher, the moisture concentration reduction process is performed. Thus, by performing the moisture concentration reduction process after the heater temperature rises, the oxygen ion conductivity is activated by the solid electrolyte layer, enabling the reference gas adjustment pump unit to operate. Therefore, the moisture concentration reduction process can be performed at an appropriate time.

[0035] In the first or second gas sensor of the present invention, the control unit can perform a moisture determination process. That is, it determines whether there is a lot of moisture around the reference electrode based on the pump current flowing through the reference gas adjustment pump unit when controlling the reference gas adjustment pump unit to draw oxygen from around the reference electrode to around the gas to be measured side electrode. If it is determined that there is a lot of moisture, the moisture concentration reduction process is performed. Here, the pump current flowing through the reference gas adjustment pump unit when drawing oxygen from around the reference electrode to around the gas to be measured side electrode changes according to the amount of moisture around the reference electrode. Therefore, it is possible to determine whether there is a lot of moisture around the reference electrode based on this pump current. Furthermore, if it is determined that there is a lot of moisture, the moisture concentration reduction process is performed, thus enabling appropriate moisture concentration reduction processing.

[0036] In the first or second gas sensor of the present invention, the control unit can determine, during the moisture determination process, whether there is a lot of moisture around the reference electrode based on the pump current when a predetermined control voltage higher than the voltage of the limiting current region of the reference gas adjustment pump unit is applied between the electrode of the gas being measured and the reference electrode. If a voltage higher than the voltage of the limiting current region is applied, the moisture around the reference electrode is easily decomposed; therefore, the amount of moisture around the reference electrode easily affects the pump current. Therefore, by determining the moisture level based on the pump current when the aforementioned voltage is applied, it is possible to more appropriately determine whether there is a lot of moisture around the reference electrode.

[0037] In the first or second gas sensor of the present invention, the control unit can determine whether there is a lot of moisture around the reference electrode during the moisture determination process, based on a comparison between the pump current and the limiting current of the reference gas adjustment pump unit. The more moisture around the reference electrode, the greater the difference between the pump current and the limiting current; therefore, by comparing them, it is possible to more appropriately determine whether there is a lot of moisture around the reference electrode. In this case, the control unit can make the determination based on the difference between the limiting current and the pump current, or the ratio of the limiting current to the pump current.

[0038] In the first or second gas sensor of the present invention, the control unit may include a storage unit that stores the value of the limiting current. During the moisture determination process, the control unit compares the pump current with the limiting current stored in the storage unit. Thus, it is not necessary to measure the limiting current during the moisture determination process.

[0039] In the first or second gas sensor of the present invention, the control unit can compare the pump current with the limiting current measured by applying the voltage of the limiting current region to the reference gas adjustment pump unit during the moisture determination process. In this way, both the pump current and the limiting current are measured during the moisture determination process, thus enabling more accurate determination.

[0040] In the first or second gas sensor of the present invention, the specified control voltage can be a voltage of 0.8V or higher and 1.5V or lower. If the control voltage is 0.8V or higher, the pump current applied at this voltage range will easily change depending on the amount of moisture around the reference electrode, thus making it suitable for moisture determination processing. If the control voltage is 1.5V or lower, blackening of the sensor element can be suppressed.

[0041] The control method of the first gas sensor of the present invention is a control method for a gas sensor that detects the concentration of a specific gas in the gas to be measured.

[0042] The gas sensor includes sensor elements.

[0043] The sensor element has:

[0044] The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for introducing and circulating the gas to be measured.

[0045] A measuring electrode is disposed in the gas flow section to be measured;

[0046] A gas-to-measure side electrode is disposed on the element body in a manner that contacts the gas to be measured.

[0047] A reference electrode is disposed inside the main body of the component;

[0048] A reference gas inlet section, which allows a reference gas, serving as a detection reference for the concentration of the specific gas in the gas being measured, to flow from outside the element body to the reference electrode; and

[0049] A reference gas adjustment pump unit, configured to include the measured gas-side electrode and the reference electrode.

[0050] The control method includes a moisture concentration reduction process, namely, controlling the reference gas adjustment pump unit to draw oxygen from the vicinity of the reference electrode to the vicinity of the gas being measured side electrode, thereby reducing the moisture concentration around the reference electrode.

[0051] In the control method of this first gas sensor, similar to the first gas sensor described above, the reduction in detection accuracy of a specific gas concentration caused by moisture around the reference electrode can be suppressed. It should be noted that in the control method of this first gas sensor, various schemes of the first or second gas sensor described above can be used, and additional processing can be added to achieve the functions of the first or second gas sensor described above.

[0052] The control method of the second gas sensor of the present invention is a control method for a gas sensor that detects the concentration of a specific gas in the gas to be measured.

[0053] The gas sensor includes sensor elements.

[0054] The sensor element has:

[0055] The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for introducing and circulating the gas to be measured.

[0056] A measuring electrode is disposed in the gas flow section to be measured;

[0057] A gas-to-measure side electrode is disposed on the element body in a manner that contacts the gas to be measured.

[0058] A reference electrode is disposed inside the main body of the component;

[0059] A reference gas inlet section, which allows a reference gas, serving as a detection reference for the concentration of the specific gas in the gas being measured, to flow from outside the element body to the reference electrode; and

[0060] A reference gas adjustment pump unit, configured to include the measured gas-side electrode and the reference electrode.

[0061] The control method includes: a reference gas adjustment process, namely, controlling the reference gas adjustment pump unit to draw oxygen from the vicinity of the measured gas side electrode to the vicinity of the reference electrode, thereby adjusting the oxygen concentration around the reference electrode; and

[0062] The moisture concentration reduction process involves controlling the reference gas adjustment pump unit to temporarily draw in more oxygen around the reference electrode compared to the reference gas adjustment process, thereby reducing the moisture concentration around the reference electrode.

[0063] In the control method of this second gas sensor, similar to the second gas sensor described above, the reduction in detection accuracy of a specific gas concentration caused by moisture around the reference electrode can be suppressed. It should be noted that in the control method of this second gas sensor, various schemes of the first or second gas sensor described above can be used, and additional processing can be added to achieve the functions of the first or second gas sensor described above. Attached Figure Description

[0064] Figure 1 This is a longitudinal sectional view of the gas sensor 100.

[0065] Figure 2 This is a schematic cross-sectional view showing an example of the configuration of sensor element 101.

[0066] Figure 3 This is a block diagram showing the electrical connections between the control device 95 and each unit.

[0067] Figure 4 It is a graph showing the relationship between the voltage Vp3 and the pump current Ip3 of the reference gas regulating pump unit 90.

[0068] Figure 5 This is a flowchart illustrating an example of a control routine.

[0069] Figure 6 It is a graph showing the relationship between time t and voltage V2open.

[0070] Figure 7 This is a cross-sectional schematic diagram showing the configuration around the reference gas inlet 249 in a modified example.

[0071] Figure 8 This is a cross-sectional schematic diagram of the sensor element 201 in a modified example. Detailed Implementation

[0072] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a longitudinal sectional view of a gas sensor 100 as one embodiment of the present invention. Figure 2 This is a schematic cross-sectional view showing an example of the configuration of the sensor element 101 included in the gas sensor 100. Figure 3 This is a block diagram showing the electrical connections between the control device 95 and each unit. It should be noted that the sensor element 101 is in the shape of a long rectangular parallelepiped, and the length direction of the sensor element 101 ( Figure 2 The left and right directions in the image are set as the front and back directions, and the thickness direction of the sensor element 101 is set as the front and back directions. Figure 2 The vertical direction is set as the vertical direction. In addition, the width direction of the sensor element 101 (the direction perpendicular to the front-back direction and the vertical direction) is set as the left-right direction.

[0073] like Figure 1 As shown, the gas sensor 100 includes: a sensor element 101; a protective cover 130 that protects the front end of the sensor element 101; and a sensor assembly 140 that includes a connector 150 that is conductive to the sensor element 101. As shown, the gas sensor 100 is installed in a pipe 190, such as the exhaust pipe of a vehicle, for measuring the concentration of specific gases such as NOx and O2 contained in exhaust gas, which is the gas to be measured. In this embodiment, the gas sensor 100 measures the NOx concentration as the concentration of the specific gas.

[0074] The protective cover 130 includes: a bottomed cylindrical inner protective cover 131 that covers the front end of the sensor element 101; and a bottomed cylindrical outer protective cover 132 that covers the inner protective cover 131. Multiple holes are formed in the inner protective cover 131 and the outer protective cover 132 to allow the gas to be measured to flow within the protective cover 130. The sensor element chamber 133 is formed as a space surrounded by the inner protective cover 131, and the front end of the sensor element 101 is disposed within the sensor element chamber 133.

[0075] The sensor assembly 140 includes: an element enclosure 141 for sealing and fixing the sensor element 101; bolts 147 and an outer cylinder 148, which are mounted on the element enclosure 141; and a connector 150, which connects to connector electrodes (not shown) formed on the rear surface (upper and lower surfaces) of the sensor element 101. Figure 2 Only the heater connector electrode 71 described later is shown in the diagram, which is in contact with and electrically connected to these electrodes.

[0076] The element enclosure 141 includes: a cylindrical main metal part 142; a cylindrical inner cylinder 143, which is coaxially welded and fixed to the main metal part 142; and ceramic support members 144a-144c, pressed powder bodies 145a and 145b, and a metal ring 146, which are sealed in through holes on the inner sides of the main metal part 142 and the inner cylinder 143. The sensor element 101 is located on the central axis of the element enclosure 141 and extends through the element enclosure 141 in the front-rear direction. The inner cylinder 143 has: a reduced diameter portion 143a for pressing the pressed powder body 145b toward the central axis of the inner cylinder 143; and a reduced diameter portion 143b for pressing the ceramic support members 144a-144c and the pressed powder bodies 145a and 145b forward by means of the metal ring 146. The compressed powder 145a and 145b are compressed between the main metal part 142 and the inner cylinder 143 and the sensor element 101 by the pressing pressure from the reduced diameter parts 143a and 143b. As a result, the compressed powder 145a and 145b seal the space 149 between the sensor element chamber 133 in the protective cover 130 and the space 149 in the outer cylinder 148, and fix the sensor element 101.

[0077] Bolt 147 is coaxially fixed to the main metal part 142, and an external thread is formed on the outer peripheral surface of bolt 147. The external thread of bolt 147 is inserted into fixing member 191, which is welded to pipe 190 and has an internal thread on its inner peripheral surface. Thus, gas sensor 100 is fixed to pipe 190 with the front end of sensor element 101 or part of protective cover 130 protruding into pipe 190.

[0078] The outer cylinder 148 covers the inner cylinder 143, the sensor element 101, and the connector 150. Multiple wires 155, connected to the connector 150, extend outwards from the rear end. These wires 155 are connected to the electrodes (described later) of the sensor element 101 via the connector 150. The gap between the outer cylinder 148 and the wires 155 is sealed by a rubber stopper 157. The space 149 inside the outer cylinder 148 is filled with a reference gas (atmosphere in this embodiment). The rear end of the sensor element 101 is disposed within this space 149.

[0079] like Figure 2 As shown, the sensor element 101 is a laminated element. In the accompanying drawings, starting from the bottom, six layers are stacked sequentially: 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 composed of an oxygen ion-conducting solid electrolyte layer such as zirconium oxide (ZrO2). Furthermore, the solid electrolyte forming these six layers is a dense, gas-tight solid electrolyte. The sensor element 101 is manufactured by, for example, performing prescribed processing and printing circuit patterns on ceramic green sheets corresponding to each layer, then stacking them, and finally firing them to achieve integration.

[0080] At one end of sensor element 101 ( Figure 2 (on the left side) and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, 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.

[0081] The gas inlet 10, buffer space 12, first internal cavity 20, second internal cavity 40 and third internal cavity 61 are spaces inside the sensor element 101 provided by hollowing out the isolation layer 5. Their upper parts are formed by the lower surface of the second solid electrolyte layer 6, their lower parts are formed by the upper surface of the first solid electrolyte layer 4, and their sides are formed by the side of the isolation layer 5.

[0082] The first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 are each provided as two horizontally elongated slits (the length direction of the opening is perpendicular to the drawing). Additionally, the fourth diffusion rate control unit 60 is provided as a single horizontally elongated slit (the length direction of the opening is perpendicular to the drawing), which forms a gap between itself and the lower surface of the second solid electrolyte layer 6. Furthermore, the portion from the gas inlet 10 to the third internal cavity 61 is referred to as the measured gas flow section.

[0083] The sensor element 101 includes a reference gas inlet 49 that allows reference gas for NOx concentration measurement to flow from the outside of the sensor element 101 to the reference electrode 42. The reference gas inlet 49 includes a reference gas inlet space 43 and a reference gas inlet layer 48. The reference gas inlet space 43 is a space disposed inward from the rear end face of the sensor element 101. The reference gas inlet space 43 is disposed between the upper surface of the third substrate layer 3 and the lower surface of the insulating layer 5, and is located at a position defined by the side portion of the first solid electrolyte layer 4. The reference gas inlet space 43 is open at the rear end face of the sensor element 101, and this opening functions as the inlet 49a of the reference gas inlet 49. The inlet 49a is exposed within the space 149 (see reference). Figure 1 The reference gas is introduced into the reference gas introduction space 43 from the inlet 49a. The reference gas introduction section 49 applies a predetermined diffusion resistance to the reference gas introduced from the inlet 49a and introduces the reference gas into the reference electrode 42. In this embodiment, the reference gas is set to the atmosphere. Figure 1 (The atmosphere within space 149).

[0084] A reference gas introduction layer 48 is disposed between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. The reference gas introduction layer 48 is a porous material formed of ceramic, such as alumina. A portion of the upper surface of the reference gas introduction layer 48 is exposed within the reference gas introduction space 43. The reference gas introduction layer 48 is formed to cover the reference electrode 42. The reference gas introduction layer 48 allows reference gas to flow from the reference gas introduction space 43 to the reference electrode 42.

[0085] The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around it. Furthermore, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) within the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61. The reference electrode 42 is formed as a porous metal-ceramic electrode (e.g., a Pt and ZrO2 metal-ceramic electrode).

[0086] In the gas flow section, the gas inlet 10 is an opening relative to the external space, through which the gas to be measured enters the sensor element 101 from the external space. The first diffusion rate control unit 11 applies a predetermined diffusion resistance to the gas to be measured entering 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 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 exhaust gas from a car, the fluctuations in exhaust pressure) is not directly introduced into the first internal cavity 20. Instead, it is introduced into the first internal cavity 20 after the pressure fluctuations are eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. Therefore, the pressure fluctuation of the gas introduced into the first internal cavity 20 is negligible. The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas introduced through the second diffusion rate control unit 13. This oxygen partial pressure is adjusted by operating the main pump unit 21.

[0087] 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, and the outer pump electrode 23 is disposed in the external space. Figure 1 The sensor element chamber 133 is exposed in a manner that is disposed on the upper surface of the second solid electrolyte layer 6 in the area corresponding to the top electrode portion 22a.

[0088] The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that define the first internal cavity 20, and the isolation layer 5 that forms the sidewall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that forms the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that forms the bottom surface. Furthermore, side electrode portions (not shown) are formed on the sidewall surface (inner surface) of the isolation layer 5 that forms the two sidewall portions of the first internal cavity 20 in a manner that connects the top electrode portion 22a and the bottom electrode portion 22b. Thus, the side electrode portions are arranged in a tunnel-shaped structure.

[0089] 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). Furthermore, the inner pump electrode 22, which is in contact with the gas being measured, is formed using a material whose reducing ability against NOx components in the gas being measured is weakened.

[0090] In the main pump unit 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, so that the pump current Ip0 flows between the inner pump electrode 22 and the outer pump electrode 23 in either the positive or negative direction. As a result, oxygen in the first internal cavity 20 can be drawn out to the external space, or oxygen in the external space can be drawn into the first internal cavity 20.

[0091] 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.

[0092] By measuring the electromotive force (voltage V0) of the oxygen partial pressure detection sensor unit 80 for main pump control, the oxygen concentration (oxygen partial pressure) within the first internal cavity 20 can be determined. Furthermore, 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. As a result, the oxygen concentration within the first internal cavity 20 can be maintained at a predetermined constant value.

[0093] The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20, and introduces the gas to be measured into the second internal cavity 40.

[0094] The second internal cavity 40 is configured as a space for performing the following process: after the oxygen concentration (oxygen partial pressure) is pre-adjusted in the first internal cavity 20, the oxygen partial pressure of the gas to be measured, which is introduced through the third diffusion rate control unit 30, is further adjusted using the auxiliary pump unit 50. As a result, the oxygen concentration within the second internal cavity 40 can be maintained at a constant level with high accuracy, thus enabling high-precision NOx concentration measurement in such a gas sensor 100.

[0095] 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 on the outside of the sensor element 101), and a second solid electrolyte layer 6. The auxiliary pump electrode 51 has a top electrode portion 51a that is generally disposed on the lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40.

[0096] 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. The side electrode portion (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b is formed as a tunnel-shaped structure on each of the two walls of the insulating layer 5 constituting the sidewall of the second internal cavity 40. Furthermore, the auxiliary pump electrode 51, like the inner pump electrode 22, is formed using a material that reduces the reducing power of NOx components in the measured gas.

[0097] In 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 inside the second internal cavity 40 to be drawn out to the external space, or oxygen to be drawn from the external space into the second internal cavity 40.

[0098] 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.

[0099] Furthermore, the auxiliary pump unit 50 utilizes a variable power supply 52 for pumping, which is controlled based on the electromotive force (voltage V1) detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control. Thus, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a low partial pressure that substantially has no effect on NOx measurement.

[0100] Additionally, 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 by controlling the aforementioned target value of its voltage V0, the gradient of the oxygen partial pressure in the gas to be measured, introduced from the third diffusion rate control unit 30 into the second internal cavity 40, is controlled to remain constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of approximately 0.001 ppm due to the action of the main pump unit 21 and the auxiliary pump unit 50.

[0101] The fourth diffusion rate control unit 60 applies a predetermined diffusion resistance to the gas to be measured, whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump unit 50 in the second internal cavity 40, and introduces 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.

[0102] The third internal cavity 61 is configured as a space for performing the following process: after the oxygen concentration (oxygen partial pressure) has been pre-adjusted in the second internal cavity 40, the gas to be measured, introduced through the fourth diffusion rate control unit 60, is subjected to processing related to the measurement of the nitrogen oxide (NOx) concentration in the gas to be measured. The NOx concentration is measured primarily within the third internal cavity 61 by the operation of the measuring pump unit 41.

[0103] 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 whose reducing power for NOx components in the gas to be measured is higher than that of 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.

[0104] In 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 the amount generated can be detected as pump current Ip2.

[0105] 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.

[0106] 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 produce 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 such that the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control remains 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.

[0107] 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 electrochemical sensor unit 83 can detect the oxygen partial pressure in the gas to be measured outside the sensor by using the electromotive force (voltage Vref) obtained through the sensor unit 83.

[0108] Furthermore, an electrochemical reference gas adjustment pump unit 90 is constituted by a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, a third substrate layer 3, an outer pump electrode 23, and a reference electrode 42. This reference gas adjustment pump unit 90 pumps oxygen by means of a control current (pump current Ip3) flowing through a control voltage (voltage Vp3) applied by a power supply circuit 92 connected between the outer pump electrode 23 and the reference electrode 42. Thus, the reference gas adjustment pump unit 90 can pump oxygen from the space surrounding the outer pump electrode 23. Figure 1 The sensor element chamber 133 in the middle draws in oxygen to the area around the reference electrode 42 and draws out oxygen from the area around the reference electrode 42 to the area around the pump electrode 23.

[0109] In 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 effect on the determination of NOx), is supplied to the measuring pump unit 41. Therefore, based on the pump current Ip2, which is approximately proportional to the concentration of NOx in the gas being measured and is drawn out of the measuring pump unit 41 by oxygen generated due to the reduction of NOx, the concentration of NOx in the gas being measured can be determined.

[0110] Furthermore, 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, a pressure relief hole 75, and a wire 76.

[0111] The heater connector electrode 71 is an electrode formed in contact with the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to an external power source, power can be supplied to the heater section 70 from the outside.

[0112] The heater 72 is a resistive element formed by being sandwiched between the second substrate layer 2 and the third substrate layer 3 from the top and bottom. The heater 72 is connected to the heater connector electrode 71 via the wire 76 and the through hole 73. Because the heater connector electrode 71 is powered from the outside and generates heat, it heats and keeps the solid electrolyte forming the sensor element 101 warm.

[0113] In addition, the heater 72 is embedded in the entire area from the first internal cavity 20 to the third internal cavity 61, which can adjust the sensor element 101 as a whole to the temperature at which the solid electrolyte is activated.

[0114] The heater insulation layer 74 is an insulating layer containing porous alumina formed from an insulator such as alumina on the upper and lower surfaces of the heater 72. The heater insulation layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72, and electrical insulation between the third substrate layer 3 and the heater 72.

[0115] The pressure relief hole 75 is a portion that allows the third substrate layer 3 and the reference gas introduction layer 48 to pass through, and is formed to mitigate the increase in internal pressure that accompanies the temperature rise within the heater insulation layer 74.

[0116] like Figure 3As shown, the control device 95 includes: the aforementioned variable power supplies 24, 46, and 52; the heater power supply 78; the aforementioned power supply circuit 92; and a control unit 96. The control unit 96 is a microprocessor equipped with a CPU 97, RAM (not shown), and a storage unit 98, etc. The storage unit 98 is a non-volatile memory, for example, a device for storing various programs and data. The control unit 96 receives inputs of voltages V0 to V2 and voltage Vref from each sensor unit 80 to 83. The control unit 96 also receives inputs of pump currents Ip0 to Ip2 and pump current Ip3 flowing through each pump unit 21, 50, 41, and 90. The control unit 96 outputs control signals to the variable power supplies 24, 46, and 52 and the power supply circuit 92 to control the voltages Vp0 to Vp3 output by the variable power supplies 24, 46, and 52 and the power supply circuit 92, thereby controlling each pump unit 21, 41, 50, and 90. The control unit 96 outputs a control signal to the heater power supply 78, thereby controlling the power supplied by the heater power supply 78 to the heater 72, and thus adjusting the temperature of the sensor element 101. The storage unit 98 stores target values ​​V0*, V1*, V2*, and target current Ip1*, which will be described later. The CPU 97 of the control unit 96 refers to these target values ​​V0*, V1*, V2*, and target current Ip1* to control each unit 21, 41, and 50.

[0117] The control unit 96 performs auxiliary pump control processing to control the auxiliary pump unit 50 in a manner that ensures 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 that ensures the oxygen concentration in the second internal cavity 40 reaches a predetermined low concentration that has no substantial impact on the NOx measurement.

[0118] The control unit 96 performs main pump control processing such that the pump current Ip1 flowing through the auxiliary pump unit 50, when adjusting the oxygen concentration in the second internal cavity 40 through auxiliary pump control processing, reaches a target current (referred to as target current Ip1*). Specifically, the control unit 96 sets a target value for voltage V0 (referred to as target value V0*) based on the pump current Ip1 (feedback control) so that the pump current Ip1 flowing due to voltage Vp1 reaches a constant target current Ip1*. Furthermore, the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 so that the voltage V0 reaches the target value V0* (i.e., so 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 is always constant. The target value V0* is set to a value that makes the oxygen concentration in the first internal cavity 20 higher than 0% and a low oxygen concentration. Furthermore, the pump current Ip0 flowing in the main pump control process changes according to the oxygen concentration of the gas to be measured (i.e., the gas 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.

[0119] 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 control unit 96 performs adjustment pump control processing, causing the adjustment pump units to adjust the oxygen concentration in the oxygen concentration adjustment chambers.

[0120] Furthermore, the control unit 96 performs a pump control process to control the measuring pump unit 41 so that the voltage V2 reaches a constant value (target value) (i.e., so 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 make the voltage V2 reach the target value V2*, thereby controlling the measuring pump unit 41. Oxygen is drawn from the third internal cavity 61 through this pump control process.

[0121] Oxygen is drawn from the third internal cavity 61 by performing a pump control process, so that the oxygen generated by the reduction of NOx in the measured gas in the third internal cavity 61 becomes substantially zero. Furthermore, the control unit 96 acquires the pump current Ip2 in the form of a detection value corresponding to the oxygen generated in the third internal cavity 61 from a specific gas (in this case, NOx), and calculates the NOx concentration in the measured gas based on the pump current Ip2.

[0122] The storage unit 98 stores: a relational expression (e.g., a linear or quadratic function) and a mapping that represents the correspondence between the pump current Ip2 and the NOx concentration. Such a relational expression and mapping can be obtained in advance through experiments.

[0123] The control unit 96 controls the power supply circuit 92 to apply voltage Vp3 to the reference gas adjusting pump unit 90, thereby causing pump current Ip3 to flow through the reference gas adjusting pump unit 90. The control unit 96 changes the magnitude and sign of voltage Vp3, thereby controlling the magnitude and flow direction of pump current Ip3. Accordingly, the control unit 96 can control the direction of oxygen movement between the reference electrode 42 and the outer pump electrode 23 (oxygen being drawn into or out of the vicinity of the reference electrode 42), or control the amount of oxygen movement. In this embodiment, voltage Vp3 is set to a DC voltage that causes pump current Ip3 to reach a predetermined value (a certain value of DC current).

[0124] The control unit 96 performs a reference gas adjustment process by controlling the reference gas adjustment pump unit 90 to draw oxygen from around the outer pump electrode 23 to around the reference electrode 42, thereby adjusting the oxygen concentration around the reference electrode 42. Here, the gas to be measured is drawn from... Figure 1 The gas flow section, such as the gas inlet 10, in the sensor element chamber 133 shown is introduced into the sensor element 101. On the other hand, Figure 1 The reference gas (atmosphere) in the space 149 is introduced into the reference gas inlet 49 in the sensor element 101. Furthermore, the sensor element chamber 133 and the space 149 are separated and sealed by the sensor assembly 140 (particularly the powder presses 145a and 145b) so that gases do not flow between them. However, in cases where the pressure of the gas being measured is high, a small amount of the gas being measured may sometimes intrude into the space 149, causing a decrease in the oxygen concentration within the space 149. If this decreases to the level around the reference electrode 42, the potential of the reference electrode 42, i.e., the reference potential, changes. By performing a reference gas adjustment process, this decrease in oxygen concentration around the reference electrode 42 can be compensated for.

[0125] In addition, including Figure 2 Including the variable power supplies 24, 46, 52 and power supply circuit 92 shown, the control device 95 utilizes wires (not shown) actually formed within the sensor element 101. Figure 1 The connector 150 and wire 155 are connected to the electrodes inside the sensor element 101.

[0126] However, when the sensor element 101 is not driven, the reference gas inlet 49 sometimes absorbs water from the outside of the sensor element 101 (here, inside space 149). Regarding this, the inventors of this invention investigated the relationship between the moisture absorption state of the reference gas inlet 49 and the pump current Ip3 flowing through the reference gas adjustment pump unit 90. First, the sensor element 101 was driven using the control device 95. Specifically, with the gas sensor 100 placed in an atmospheric atmosphere, power was supplied from the heater power supply 78 to the heater 72 to heat the sensor element 101, and the temperature of the sensor element 101 was maintained at 800°C. After waiting for 0.5 hours in this state, the gas sensor 100 was obtained with a low moisture absorption rate in the reference gas inlet 49. Next, with the gas sensor 100 placed in an atmospheric atmosphere, the voltage Vp3 applied by the power supply circuit 92 to the reference gas adjustment pump unit 90 was gradually varied from 0mV to 1000mV, and the value of the pump current Ip3 during this process was measured. A voltage Vp3 is applied to the pump unit 90, which is adjusted to draw oxygen from around the reference electrode 42 towards the outer pump electrode 23, using a reference gas as the reference. The relationship between the voltage Vp3 and the pump current Ip3 in the gas sensor 100, under conditions of low moisture absorption, is shown as a solid curve L1. Figure 4 Next, the gas sensor 100 was stored in a constant temperature and humidity bath at 40°C and 85% for one week, allowing water to be adsorbed onto the reference gas inlet 49, thus obtaining a gas sensor 100 with a high moisture absorption capacity. The gas sensor 100 was then placed in an atmospheric atmosphere, and the temperature of the sensor element 101 was maintained at 800°C using a heater 72. In this state, as described above, the voltage Vp3 was gradually varied from 0mV to 1000mV, and the value of the pump current Ip3 was measured. The relationship between the voltage Vp3 and the pump current Ip3 in the gas sensor 100 with the high moisture absorption capacity, as measured in this way, is shown as a dashed curve L2. Figure 4 .

[0127] like Figure 4 As shown, in either curve L1 or curve L2, within the region where voltage Vp3 is between 100mV and 700mV, the pump current Ip3 remains approximately constant even as voltage Vp3 increases. That is, the pump current Ip3 is the limiting current. For example, the value of the limiting current can be determined by factors such as the diffusion resistance of the reference gas inlet 49. This region, where the pump current Ip3 hardly changes even when voltage Vp3 changes (… Figure 4In this context, the region where the voltage Vp3 is, for example, between 100mV and 700mV, is called the limiting current region. Furthermore, the following trend was observed: in either curve L1 or curve L2, in the region where the voltage Vp3 is higher than the limiting current region, the pump current Ip3 increases with increasing voltage Vp3. This can be attributed to the fact that the higher the voltage Vp3, the more moisture in the reference gas inlet 49, especially around the reference electrode 42, is decomposed to produce oxygen, which is then drawn out from around the reference electrode 42. Additionally, in either the limiting current region or the region where the voltage Vp3 is higher than the limiting current region, the value of the pump current Ip3 for curve L2 is greater than that for curve L1. That is, a trend was confirmed where the pump current Ip3 of the gas sensor 100 increases when the reference gas inlet 49 absorbs more moisture. Therefore, it can be concluded that even when the voltage Vp3 of the limiting current region is applied, the moisture around the reference electrode 42 is decomposed. In particular, in regions where the voltage Vp3 is higher than the limiting current region (e.g., Figure 4 In the region where the voltage Vp3 is above 800mV, the difference in pump current Ip3 between curve L2 and curve L1 appears more significant. For example, the difference between the pump current Ip3 value B1 of curve L1 and the pump current Ip3 value B2 of curve L2 when the voltage Vp3 is 1000mV (=B2-B1) is greater than the difference between the pump current Ip3 value A1 of curve L1 and the pump current Ip3 value A2 of curve L2 when the voltage Vp3 is 400mV in the limiting current region (=A2-A1).

[0128] Thus, the pump current Ip3 flowing through the reference gas adjusting pump unit 90 when it draws oxygen from around the reference electrode 42 to around the outer pump electrode 23 varies depending on the amount of moisture around the reference electrode 42. Specifically, the more moisture around the reference electrode 42, the larger the pump current Ip3. Therefore, the control unit 96 of this embodiment performs a moisture absorption state diagnosis process, that is, it diagnoses the moisture absorption state around the reference electrode 42 based on the pump current Ip3. More specifically, the control unit 96 of this embodiment performs a moisture determination process as an example of the moisture absorption state diagnosis process, that is, it determines whether there is a lot of moisture around the reference electrode 42 based on the pump current Ip3. The details of the moisture determination process will be explained below.

[0129] Next, an example of the process of measuring NOx concentration in the control unit 96 of the gas sensor 100 will be described. Figure 5 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. When a start command is input from, for example, an engine ECU (not shown), the control unit 96 begins executing this control routine.

[0130] When the control routine begins, the CPU 97 of the control unit 96 first performs heater control processing, that is, it outputs a control signal to the heater power supply 78 to control the heater 72 so that its temperature reaches a target temperature (e.g., 800°C) (step S100). 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 of this embodiment, the CPU 97 calculates the resistance value of the heater 72 as a value considered as the temperature of the heater 72 (which can be converted into a temperature value), and performs feedback control on the heater power supply 78 so that the calculated resistance value reaches the target resistance value (the resistance value corresponding to the target temperature). The CPU 97 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 CPU 97 can also calculate the resistance value of the heater 72 using, for example, a 3-terminal method or a 4-terminal method. CPU97 outputs a control signal to heater power supply 78 to provide feedback control over the power supplied by heater power supply 78, so that the calculated resistance value of heater 72 reaches the target resistance value. When heater power supply 78 powers on heater 72, it changes, for example, the voltage applied to heater 72, thereby adjusting the power supplied to heater 72.

[0131] Next, the CPU 97 determines whether the heater temperature has reached or exceeded a predetermined temperature through heater control processing (step S110). This predetermined temperature is predetermined as a value below the target temperature of the aforementioned heater control processing and is stored in the storage unit 98. The predetermined temperature is defined as a temperature that activates the solid electrolyte of the sensor element 101, enabling oxygen pumping using the reference gas adjustment pump unit 90. The predetermined temperature can be set to a value lower than the target temperature. The predetermined temperature can be set to a value of 80% or more, or 90% or more, of the target temperature. In this embodiment, the predetermined temperature is set to 90% of the target temperature. In this embodiment, as described above, the CPU 97 uses the resistance value as a representation of the heater 72's temperature; therefore, the determination in step S110 also uses the resistance value of the heater 72.

[0132] If the determination in step S110 is negative, the CPU97 repeatedly executes step S110 and waits until the determination is positive. That is, it waits until the temperature of the heater 72 reaches a predetermined temperature or higher. If the determination in step S110 is positive, the CPU97 performs the following steps S120 and S130 as a moisture determination process.

[0133] In the moisture determination process, CPU97 first applies a voltage Vp3 to the reference gas adjustment pump unit 90 and obtains the pump current Ip3 flowing at this time (step S120). The value of the applied voltage Vp3 is recorded as voltage Vha, and the value of the obtained pump current Ip3 is recorded as pump current Iph. Voltage Vha is applied in the direction that the reference gas adjustment pump unit 90 draws oxygen from around the reference electrode 42 towards the surrounding area of ​​the outer pump electrode 23. The value of voltage Vha can be set to... Figure 4 The voltage Vha is set to a value within the range of the limiting current region described herein; however, it is preferable to set it to a voltage higher than the limiting current region. The voltage Vha is preferably set to, for example, 0.8V or higher. The voltage Vha can be set to 1.5V or lower. In this embodiment, the voltage Vha is set to 1.0V.

[0134] Next, the CPU97 determines the moisture absorption state around the reference electrode 42 based on the acquired pump current Iph, specifically determining whether there is a lot of moisture around the reference electrode 42 (step S130). In this embodiment, the CPU97 makes this determination based on a comparison between the pump current Iph and the limiting current Iplim of the reference gas adjustment pump unit 90. More specifically, the CPU97 determines whether there is a lot of moisture in the reference electrode 42 based on whether the difference ΔI between the pump current Iph and the limiting current Iplim is greater than a threshold Iref. The limiting current Iplim of the reference gas adjustment pump unit 90 and the limiting current Iplim are compared with... Figure 4 The limiting current described herein is the limiting current when a voltage Vp3 is applied, with the reference gas adjustment pump unit 90 drawing oxygen from the vicinity of the reference electrode 42 towards the vicinity of the outer pump electrode 23. In this embodiment, the value of the limiting current in the sensor element 101 under conditions where the moisture absorption of the reference gas inlet 49 is low, as determined in advance through experiments (e.g., ... Figure 4 The value A1) is stored in the storage unit 98 as the limiting current Iplim. Therefore, the CPU 97 calculates the difference ΔI between the pump current Iph obtained in step S120 and the limiting current Iplim stored in the storage unit 98, and determines whether the difference ΔI is above the threshold Iref. As mentioned above, the more moisture around the reference electrode 42, the larger the pump current Iph, and therefore, the larger the difference ΔI. Therefore, the threshold Iref is predetermined as, for example, the value of the difference ΔI when the amount of moisture around the reference electrode 42 reaches an upper limit that is considered to have no impact on the detection accuracy of NOx concentration. Figure 4 In the example, when there is a lot of moisture around the reference electrode 42, the difference ΔI = B2 - A1; when there is little moisture around the reference electrode 42, the difference ΔI = B1 - A1. Therefore, a threshold Iref is predetermined, which is a value between the two.

[0135] If the determination in step S130 is affirmative, the CPU 97 performs a moisture concentration reduction process, namely, controlling the reference gas adjustment pump unit 90 to reduce the moisture concentration around the reference electrode 42 (step S140). In the moisture concentration reduction process of this embodiment, the CPU 97 applies a voltage Vp3 in the direction of drawing oxygen from the area around the reference electrode 42 to the area around the outer pump electrode 23. The value of the voltage Vp3 at this time is recorded as voltage Vhc. As described above, by applying voltage Vp3 to the reference gas adjustment pump unit 90 to draw oxygen from the area around the reference electrode 42, the moisture around the reference electrode 42 can be decomposed, thereby reducing the moisture concentration around the reference electrode 42. The value of voltage Vhc can be set to a value within the range of the limiting current region, or it can be set to a voltage higher than the limiting current region. For example, voltage Vhc can be set to 0.3V or more and 1.5V or less. Voltage Vhc can be set to 0.8V or more and voltage Vhc can be set to 1.0V or less. The voltage Vhc can be set to the same value as the voltage Vha in the moisture determination process described above. In this embodiment, the voltage Vhc is set to 1.0V. The execution time of the moisture concentration reduction process is preferably set to 5 seconds to 300 seconds.

[0136] If the condition is negative in step S130, or after performing the moisture concentration reduction process in step S140, the CPU 97 begins: normal control processing, i.e., control processing during NOx concentration measurement, i.e., normal control processing (step S150). Specifically, the CPU 97 begins: the aforementioned main pump control processing, auxiliary pump control processing, measurement pump control processing, and reference gas adjustment processing, and then ends the routine. After starting the normal control processing, the CPU 97 acquires the value of the pump current Ip2 at, for example, every predetermined time interval, and derives the NOx concentration in the measured gas based on the obtained pump current Ip2 and the correspondence stored in the storage unit 98. The CPU 97 outputs the derived NOx concentration value to the engine ECU or stores it in the storage unit 98.

[0137] use Figure 6 An example of reducing the moisture concentration in step S140 of the atmospheric atmosphere will be explained. Figure 6 This is a graph showing the relationship between time t (when the temperature of heater 72 reaches the specified temperature in step S110, which is set as time t = 0 seconds) and voltage V2open. Voltage V2open is the value of voltage V2 in the open state, where there is no control to allow current to flow through measuring electrode 44 and reference electrode 42. Figure 6 The curve of the embodiment shown by the solid line is obtained as follows. First, with Figure 4Similarly, for the determination of curve L2, a gas sensor 100 with a high moisture absorption rate at the reference gas inlet 49 is prepared and placed in the atmospheric atmosphere. Furthermore, heater control processing begins, starting at the moment when the heater 72 reaches the predetermined temperature of step S110 (time t=0), and the moisture concentration reduction process is executed until... Figure 6 The time interval t = t1 is defined as follows: The period from t = 0 to t = t1, i.e., the execution time of the moisture concentration reduction treatment, is set to a specified time of 5 to 300 seconds. The voltage Vhc is set to 1.0V. After t = t1, the reference gas adjustment pump unit 90 is not activated; instead, the measuring electrode 44 and the reference electrode 42 are kept in an open state. Furthermore, starting from t = 0, the voltage V2open is measured every 0.1 seconds to obtain the result. Figure 6 The solid line represents the curve of the embodiment. During the period from time t=0 to time t=t1, the moisture concentration reduction process is momentarily stopped, and the voltage V2open is measured. Furthermore, the reference gas adjustment pump unit 90 is not activated at all; instead, the measuring electrode 44 and the reference electrode 42 remain in an open state. Otherwise, the same measurement as in the embodiment is performed, and the result is obtained. Figure 6 The dashed line represents the curve of the comparative example.

[0138] Depend on Figure 6It can be observed that in either the embodiment or the comparative example, the following trend was confirmed: starting from time t=0, the voltage V2open decreases over time, and then stabilizes. However, in the comparative example without moisture concentration reduction treatment, the voltage V2open stabilizes later compared to the embodiment. Furthermore, in the comparative example, the voltage V2open is temporarily negative. This can be attributed to the fact that the moisture around the reference electrode 42 is heated by the heater 72 and becomes gas, causing the oxygen concentration around the reference electrode 42 to be temporarily lower than the atmospheric oxygen concentration. Under these conditions, the potential (reference potential) of the reference electrode 42 is unstable; therefore, the values ​​of voltages V0, V1, and V2 measured based on the reference potential will have errors, thus reducing the detection accuracy of NOx concentration. In contrast, in the embodiment where moisture concentration reduction treatment was performed, the voltage V2open stabilizes earlier compared to the comparative example. This can be attributed to the fact that the moisture concentration reduction treatment from time t=0 to time t=t1 decomposes the moisture around the reference electrode 42, thereby suppressing the decrease in oxygen concentration around the reference electrode 42 caused by moisture vaporization. In this case, the reference potential stabilizes rapidly, thus suppressing the decrease in NOx concentration detection accuracy compared to the comparative example. It should be noted that in either the example or the comparative example, the voltage V2open decreases over time from time t=0 because it contains the thermoelectric potential between the reference electrode 42 and the measuring electrode 44, which decreases over time. If, for example, there is a temperature difference within each electrode of the reference electrode 42 and the measuring electrode 44, the thermoelectric potential between them will increase. If the temperature within each electrode becomes uniform over time, the thermoelectric potential will decrease.

[0139] Here, the correspondence between the constituent elements of this embodiment and the constituent elements of the present invention is clearly defined. In this embodiment, 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 correspond to the main body of the component in the present invention; the measuring electrode 44 corresponds to the measuring electrode; the outer pump electrode 23 corresponds to the electrode on the side of the gas being measured; the reference electrode 42 corresponds to the reference electrode; the reference gas inlet 49 corresponds to the reference gas inlet; the reference gas adjustment pump unit 90 corresponds to the reference gas adjustment unit; the sensor element 101 corresponds to the sensor element; and the control unit 96 corresponds to the control unit. Additionally, the heater 72 corresponds to the heater, and the storage unit 98 corresponds to the storage unit. It should be noted that in this embodiment, by explaining the operation of the control device 95, an example of the control method of the gas sensor of the present invention is also clarified.

[0140] According to the gas sensor 100 of this embodiment described in detail above, during the moisture concentration reduction process, oxygen is drawn out from around the reference electrode 42 to around the pump electrode 23. Accordingly, not only is oxygen drawn out from around the reference electrode 42, but the oxygen generated from the decomposition of moisture around the reference electrode 42 is also drawn out. Therefore, the moisture concentration around the reference electrode 42 can be rapidly reduced, thus suppressing the decrease in detection accuracy of a specific gas concentration caused by moisture around the reference electrode 42.

[0141] In addition, during the moisture concentration reduction process, the control device 95 applies a control voltage (voltage Vhc) of 0.3V to 1.5V to the reference gas adjustment pump unit 90 to activate the reference gas adjustment pump unit 90. If the voltage Vhc is 0.3V or higher, the reference gas adjustment pump unit 90 can operate more reliably. When the voltage Vhc is greater than 1.5V, oxygen ions are lacking in the solid electrolyte of the sensor element 101, resulting in electron conduction of the solid electrolyte. The sensor element 101 may blacken and become unusable. However, if the voltage Vhc is 1.5V or lower, blackening of the sensor element 101 can be suppressed.

[0142] Furthermore, by setting the execution time of the moisture concentration reduction process to 5 seconds or more, the moisture concentration around the reference electrode 42 can be reduced more reliably. Additionally, during the execution of the moisture concentration reduction process, the potential (reference potential) of the reference electrode 42 changes due to the flow of the pump current Ip3; therefore, the execution time is preferably 300 seconds or less.

[0143] Furthermore, after energizing the heater 72 and raising its temperature above a predetermined level, the control device 95 performs a moisture concentration reduction process. By performing this moisture concentration reduction process after the heater 72's temperature rises, the reference gas adjustment pump unit 90 can be activated by activating the solid electrolyte layer and allowing it to exhibit oxygen ion conductivity. Therefore, the moisture concentration reduction process can be performed at the appropriate time.

[0144] Furthermore, the control device 95 performs a moisture determination process. That is, it determines whether there is excessive moisture around the reference electrode 42 based on the pump current Iph flowing through the reference gas adjusting pump unit 90 when controlling the pump unit 90 to draw oxygen from around the reference electrode 42 to the area around the outer pump electrode 23. If the moisture content is determined to be excessive, a moisture concentration reduction process is performed. Therefore, by performing a moisture concentration reduction process when it is determined that there is excessive moisture around the reference electrode 42, a suitable moisture concentration reduction process can be performed.

[0145] Furthermore, in the moisture determination process, the control device 95 determines whether there is a lot of moisture around the reference electrode 42 based on the pump current Iph when a predetermined control voltage (voltage Vha) higher than the voltage of the limiting current region of the reference gas adjusting pump unit 90 is applied between the outer pump electrode 23 and the reference electrode 42. If a voltage Vha higher than the voltage of the limiting current region is applied to the reference gas adjusting pump unit 90, the moisture around the reference electrode 42 is easily decomposed. Therefore, the amount of moisture around the reference electrode 42 easily affects the pump current Iph. Therefore, by determining the moisture level based on the pump current Iph when the aforementioned voltage Vha is applied, it is possible to more appropriately determine whether there is a lot of moisture around the reference electrode 42.

[0146] Furthermore, in the moisture determination process, the control device 95 determines whether there is a lot of moisture around the reference electrode 42 based on a comparison between the pump current Iph and the limiting current Iplim of the reference gas adjustment pump unit 90. When a voltage Vha higher than the voltage of the limiting current region is applied to the reference gas adjustment pump unit 90, the more moisture around the reference electrode 42, the greater the difference between the pump current Iph and the limiting current Iplim. Therefore, by comparing them, it is possible to more appropriately determine whether there is a lot of moisture around the reference electrode 42.

[0147] Furthermore, during the moisture determination process, the control device 95 compares the pump current Iph with the limiting current Iplim stored in the storage unit 98. This eliminates the need to measure the limiting current Iplim during the moisture determination process.

[0148] Furthermore, if the voltage Vha is 0.8V or higher, the pump current Iph when a voltage in this range is applied is easily affected by the amount of moisture around the reference electrode 42, making it suitable for moisture determination processing. If the voltage Vha is 1.5V or lower, blackening of the sensor element 101 can be suppressed.

[0149] Furthermore, the present invention is not limited to the above-described embodiments; as long as it falls within the technical scope of the present invention, it can be implemented in various ways.

[0150] For example, in the above embodiment, the moisture determination process uses a limiting current Iplim pre-stored in the storage unit 98, but it is not limited to this. For example, the control device 95 can apply a voltage Vp3 of the limiting current region to the reference gas adjustment pump unit 90 during the moisture determination process, and measure the pump current Ip3 flowing at this time as the limiting current Iplim. The value of the voltage Vp3 applied at this time is recorded as voltage Vhb. Voltage Vhb can be predetermined as a value within the range of the limiting current region (for example, if...). Figure 4For example, the value would be in the range of 100mV to 700mV. Alternatively, the control device 95 can measure the value of the pump current Ip3 while gradually changing the value of the voltage Vhb during the moisture determination process, and measure the value at which the pump current Ip3 is considered to no longer change, as the limiting current Iplim. If not only the pump current Iph but also the limiting current Iplim is measured during the moisture determination process in this way, the determination can be made with greater accuracy.

[0151] In the above embodiment, the determination of whether there is a lot of water around the reference electrode 42 is based on the difference between the pump current Iph and the limiting current Iplim, but it is not limited to this. The determination can be made by comparing the pump current Iph and the limiting current Iplim; for example, the determination can be based on the ratio of the pump current Iph to the limiting current Iplim. Alternatively, the determination can be based solely on the pump current Iph, and the limiting current Iplim may not be used for the determination. For example, the pump current Iph can be compared with a predetermined threshold; if the pump current Iph exceeds the threshold, it is determined that there is a lot of water around the reference electrode 42.

[0152] In the above embodiments, the moisture determination process can be omitted. For example, if the temperature of heater 72 reaches or exceeds a predetermined temperature in step S110, then the moisture concentration reduction process in step S140 is performed. In this case, the moisture concentration reduction process can be performed immediately after the temperature of heater 72 reaches or exceeds the predetermined temperature, or it can be performed after a predetermined time has elapsed after the temperature of heater 72 reaches or exceeds the predetermined temperature. Alternatively, the moisture concentration reduction process can be performed after a predetermined time has elapsed after the power is supplied to heater 72.

[0153] In the moisture concentration reduction process of the above embodiment, the control device 95 controls the reference gas adjustment pump unit 90 to draw oxygen from the vicinity of the reference electrode 42. Conversely, the control device 95 can control the reference gas adjustment pump unit 90 to draw oxygen from the vicinity of the outer pump electrode 23 to the vicinity of the reference electrode 42. That is, in the moisture concentration reduction process, oxygen can be drawn into the vicinity of the reference electrode 42 to compensate for the decrease in oxygen concentration caused by the vaporization of water, rather than decomposing the water. In this case, the control device 95 controls the reference gas adjustment pump unit 90 in the moisture concentration reduction process to temporarily draw more oxygen into the vicinity of the reference electrode 42 compared to the reference gas adjustment process. For example, the control device 95 will... Figure 5In step S140, the voltage Vp3 applied to the reference gas adjustment pump unit 90 is set to a value higher than the voltage Vp3 applied to the reference gas adjustment pump unit 90 in the reference gas adjustment process starting in step S150. By performing a moisture concentration reduction process in this way, more oxygen can be drawn into the vicinity of the reference electrode 42 before the moisture around the reference electrode 42 is discharged to the outside from the reference gas inlet 49. Therefore, the decrease in oxygen concentration caused by the moisture around the reference electrode 42 can be compensated. So, compared with, for example, the case where a reference gas adjustment process is performed after step S110 but no moisture concentration reduction process is performed, the decrease in the detection accuracy of a specific gas concentration caused by the moisture around the reference electrode 42 can be suppressed. The voltage Vp3 in the moisture concentration reduction process can be set to 0.3V or more and 1.5V or less. In addition, the amount of oxygen drawn in the moisture concentration reduction process can be set to 2 times or more and 50 times the amount of oxygen drawn in the reference gas adjustment process. For example, by setting the value of the voltage Vp3 in the moisture concentration reduction process to 2 times the voltage Vp3 in the reference gas adjustment process, the amount of oxygen drawn in can be doubled. Furthermore, when the voltage Vp3, as described later, is a voltage that is repeatedly switched on and off, the inhalation volume can be adjusted by the ratio of the repetition period T to the on-time Ton, i.e., the duty cycle (Ton / T). For example, by setting the duty cycle to 2 times, the inhalation volume can be doubled.

[0154] In the moisture concentration reduction process of the above embodiment, the control device 95 can control the reference gas adjustment pump unit 90 to alternately perform: oxygen extraction from around the reference electrode 42 to around the outer pump electrode 23, and oxygen intake from around the outer pump electrode 23 to around the reference electrode 42. If oxygen is extracted from around the reference electrode 42, water is decomposed, and oxygen around the reference electrode 42 is also extracted, thus temporarily reducing the oxygen concentration around the reference electrode 42. By alternating extraction and intake, the oxygen lost due to extraction can be replenished in advance by intake. The number of times extraction and intake are alternated can be set to once, or multiple times. When the number of alternations is once, that is, when extraction and intake are each performed only once, extraction is preferred first. The voltage Vp3 during intake can be set to a value higher than the voltage Vp3 applied to the reference gas adjustment pump unit 90 in the reference gas adjustment process. When the voltage Vp3 is a DC voltage, extraction and intake can be alternated by switching the positive and negative of the voltage. Alternatively, the extraction and intake can be performed alternately by setting the voltage Vp3 to an AC voltage.

[0155] In the above embodiment, the control device 95 starts the normal control process of S150 after performing the moisture concentration reduction process of S140, but is not limited to this. The control device 95 can perform the moisture concentration reduction process after starting the normal control process. In this case, the normal control process can be temporarily stopped during the execution of the moisture concentration reduction process. When the normal control process is temporarily stopped, it is important to set the execution time of the moisture concentration reduction process to 300 seconds or less. In addition, even when the moisture concentration reduction process is performed after the start of the normal control process, the timing of the execution of the moisture concentration reduction process is preferably a short time elapsed since the start of the driving of the sensor element 101 (e.g., the start of the energization of the heater 72). When the driving of the sensor element 101 starts, the moisture turns into gas due to the heat of the heater 72 and is released to the outside of the sensor element 101. At this time, the oxygen concentration around the reference electrode 42 decreases. Therefore, it is preferable to perform the moisture concentration reduction process during the period when the moisture turns into gas. For example, it is preferable to start the moisture concentration reduction process within 1 hour of the start of the driving of the sensor element 101.

[0156] In the above embodiment, the voltage Vp3 is set to a DC voltage, but it is not limited to this; it can be a voltage that is repeatedly switched on and off, such as a pulse voltage. Even so, the control device 95 can still perform moisture absorption state diagnosis processing, moisture concentration reduction processing, and reference gas adjustment processing. When the voltage Vp3 is a voltage that is repeatedly switched on and off, the control device 95 can measure the voltages V0, V1, and V2 during the period when the voltage Vp3 is off (in other words, during the period when no pump current Ip3 flows) for normal control processing. By doing so, it is not necessary to temporarily stop the normal control processing during the execution of moisture concentration reduction processing, and the moisture concentration reduction processing and normal control processing can be performed simultaneously.

[0157] In the above embodiments, the control device 95 may not need to perform reference gas adjustment.

[0158] In the above embodiment, the reference gas inlet 49 includes a reference gas inlet space 43 and a reference gas inlet layer 48; however, it is sufficient to include at least one of the reference gas inlet space 43 and the reference gas inlet layer 48. The reference gas inlet layer 48 readily absorbs moisture; therefore, when the reference gas inlet 49 includes the reference gas inlet layer 48, the moisture concentration reduction treatment of the present invention is of great significance. For example, in the above embodiment, a method can be used... Figure 7 The reference gas inlet 249 shown replaces the reference gas inlet 49. The reference gas inlet 249 has a reference gas inlet layer 48 but no reference gas inlet space 43. Figure 7The reference gas inlet layer 48 is configured to extend from the periphery of the reference electrode 42 to the rear end face of the element body of the sensor element 101. Figure 7 The portion of the reference gas inlet layer 48 exposed at the rear end of the sensor element 101 serves as the inlet 49a of the reference gas inlet section 249. The inlet 49a is exposed within the space 149 outside the sensor element 101.

[0159] In the above embodiments, the sensor element 101 of the gas sensor 100 includes: a first internal cavity 20, a second internal cavity 40, and a third internal cavity 61, but is not limited thereto. For example, it can be as follows: Figure 8 The sensor element 201 in the modified example shown does not have a third internal cavity 61. Figure 8 In 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 formed adjacently in this sequential manner 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, as in the embodiment described above, the NOx concentration can be detected using the measuring pump unit 41. Figure 8 In the sensor element 201, the area around the measuring electrode 44 functions as a measuring chamber. That is, the area around the measuring electrode 44 performs the same function as the third internal cavity 61.

[0160] In the above embodiment, the surface of the front side of the sensor element 101 (the part exposed in the sensor element chamber 133), including the outer pump electrode 23, can be covered by a porous protective layer formed of ceramic such as alumina.

[0161] 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, as in 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. In addition, the specific gas can 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., if it is ammonia, it is converted into NO). When the converted gas is reduced in the third internal cavity 61, oxygen is generated. 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, by using the inner pump electrode 22 of the first internal cavity 20 as a catalyst, ammonia can be converted into NO in the first internal cavity 20.

[0162] In the above embodiments, the main body of the sensor element 101 is a laminate having multiple solid electrolyte layers (layers 1 to 6), but is not limited thereto. The main body of the sensor element 101 may include at least one oxygen ion-conducting solid electrolyte layer. For example, Figure 2 Layers 1 to 5, excluding the second solid electrolyte layer 6, can be structural layers formed of a material other than the solid electrolyte layer (e.g., layers formed of aluminum oxide). In this case, it is sufficient that each electrode of the sensor element 101 is disposed on the second solid electrolyte layer 6. For example, as long as... Figure 2 The measuring electrode 44 can be disposed on the lower surface of the second solid electrolyte layer 6. Alternatively, the following configuration can be made: 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 further back than the third internal cavity 61 and on the lower surface of the second solid electrolyte layer 6.

[0163] In the above embodiment, the outer pump electrode 23 also serves as the following electrodes: an outer main pump electrode, which is part of the main pump unit 21 and disposed on the outside of the sensor element 101 exposed to the gas to be measured; an outer auxiliary pump electrode, which is part of the auxiliary pump unit 50 and disposed on the outside of the sensor element 101 exposed to the gas to be measured; an outer measuring electrode, which is part of the measuring pump unit 41 and disposed on the outside of the sensor element 101 exposed to the gas to be measured; and a measuring gas side electrode, which is part of the reference gas adjustment pump unit 90 and disposed on the outside of the sensor element 101 exposed to the gas to be measured, but is not limited thereto. Any one or more of the outer main pump electrode, outer auxiliary pump electrode, outer measuring electrode, and measuring gas side electrode may be disposed separately from the outer pump electrode 23 and disposed on the outside of the sensor element 101. Furthermore, as long as the measured gas-side electrode of the reference gas adjustment pump unit 90 is disposed on the sensor element 101 in a manner that it is in contact with the measured gas, it can be disposed on the inner side of the sensor element 101, for example, not limited to the outer side of the sensor element 101. More specifically, it can be disposed on the measured gas flow section of the sensor element 101. For example, the inner pump electrode 22 can also serve as the electrode of the main pump unit 21 (inner main pump electrode) and the measured gas-side electrode of the reference gas adjustment pump unit 90, and the reference gas adjustment pump unit 90 can perform oxygen intake or exhaust between the area around the inner pump electrode 22 and the area around the reference electrode 42.

[0164] Example

[0165] The inventors of this invention investigated the relationship between the voltage Vhc and execution time of the moisture concentration reduction treatment and the time required for the reference potential to stabilize. First, they prepared a method using... Figures 1-3The sensor element 101 and gas sensor 100 of the above-described embodiment have been described. The gas sensor 100 was stored in a constant temperature and humidity bath at 40°C and 85% for one week to allow water to be adsorbed onto the reference gas inlet layer 48. Next, the gas sensor 100 was installed in the piping. A sample gas with a base gas concentration of 0% nitrogen, 0% oxygen, and 1500 ppm NO was prepared and circulated in the piping as the gas to be measured. In this state, the sensor element 101 was driven by the control device 95 to perform: heater control processing and moisture concentration reduction processing. From the moment the heater control processing started and the temperature of the heater 72 reached the specified temperature (time t = 0) to the moment t = t1, the moisture concentration reduction processing was performed. The moisture concentration reduction processing was performed by controlling the reference gas adjustment pump unit 90 to draw oxygen from the vicinity of the reference electrode 42. After the moisture concentration reduction treatment is completed, the control device 95 performs normal control processing, which continues to control each pump unit and acquire the states of each voltage V0, V1, V2, and Vref from each sensor unit. Then, until 60 minutes after the start of the drive of sensor element 101 (heating start), normal control processing continues, and the pump current Ip2 is measured during this period. The value of pump current Ip2 60 minutes after the start of the drive of sensor element 101 is set as a reference value (100%), and the rate of change of the value of pump current Ip2 10 minutes after the start of the drive of sensor element 101 relative to the reference value is calculated. As shown in Table 1, various changes were made to the voltage Vhc and execution time of the moisture concentration reduction treatment, and the rate of change was calculated in the above order, as experimental examples 1 to 14. The voltage Vhc was varied within the range of 0.3V to 1.5V. The execution time of the moisture concentration reduction treatment (the time from time t=0 to time t=t1) was varied within the range of 5 seconds to 300 seconds. In addition, Experiment 15 was conducted by performing normal control treatment starting from time t=0, without performing the moisture concentration reduction treatment. The rate of change of pump current Ip2 was calculated similarly to Experiments 1-14. It should be noted that in any of Experiments 1-15, the reference gas adjustment pump unit 90 was not activated during the normal control treatment; that is, the reference gas adjustment treatment was not performed. Here, as described above, if moisture exists around the reference electrode 42, the moisture is heated by the heater 72 and turns into gas, thus temporarily destabilizing the potential of the reference electrode 42. Therefore, even if the NOx concentration of the measured gas is constant, the pump current Ip2 is unstable until the potential of the reference electrode 42 stabilizes. Furthermore, it can be considered that the smaller the rate of change of pump current Ip2, the less moisture is around the reference electrode 42 after 10 minutes from the start of self-drive, and the more stable the potential of the reference electrode 42.Therefore, by measuring the rate of change of the pump current Ip2, the time required for the potential of the reference electrode 42 to stabilize after the start of driving the sensor element 101 can be evaluated, i.e., the stabilization time. A shorter stabilization time is ideal. Therefore, for Experimental Examples 1-15, when the calculated rate of change is less than 3%, the stabilization time is considered very short (“A”). When the calculated rate of change is more than 3% but less than 5%, the stabilization time is considered relatively short (“B”). When the calculated rate of change is more than 5%, the stabilization time is considered relatively long (“F”). Table 1 shows the evaluation results of the voltage Vhc, execution time, and stabilization time for Experimental Examples 1-15 respectively. As shown in Table 1, it can be confirmed that Experimental Examples 1-14, which underwent moisture concentration reduction treatment, had a shorter stabilization time compared to Experimental Example 15, which did not undergo moisture concentration reduction treatment. Furthermore, the results of Experimental Examples 1-14 confirm that a higher moisture concentration reduction treatment voltage Vhc and a longer execution time result in a shorter stabilization time.

[0166] Table 1

[0167]

[0168] Examples 1-14 correspond to embodiments of the first gas sensor of the present invention and embodiments of the control method for the first gas sensor of the present invention, and Example 15 corresponds to a comparative example. It should be noted that the present invention is not limited to these embodiments.

[0169] This specification also discloses the following technical ideas: changing "gas sensor according to any one of claims 1-3" to "gas sensor according to any one of claims 1-4" in claim 5 of the original application; changing "gas sensor according to any one of claims 1-3" to "gas sensor according to any one of claims 1-5" in claim 6 of the original application; changing "gas sensor according to any one of claims 1-3" to "gas sensor according to any one of claims 1-6" in claim 7 of the original application; changing "gas sensor according to claim 8" to "gas sensor according to any one of claims 8-11" in claim 12 of the original application; and changing "control method of gas sensor according to any one of claims 13-15" to "control method of gas sensor according to any one of claims 13-16" in claim 17 of the original application.

[0170] This application claims priority based on Japanese Patent Application No. 2021-203830, filed on December 16, 2021, and Japanese Patent Application No. 2022-191634, filed on November 30, 2022, the entire contents of which are incorporated herein by reference.

[0171] Industrial availability

[0172] 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 that detects the concentration of a specific gas in a gas to be measured. The gas sensor is characterized by having a sensor element and a control unit. The sensor element has: The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for introducing and circulating the gas to be measured. A measuring electrode is disposed in the gas flow section to be measured; A gas-to-measure side electrode is disposed on the element body in a manner that contacts the gas to be measured. A reference electrode is disposed inside the main body of the component; A reference gas inlet section allows a reference gas, which serves as a detection reference for the concentration of the specific gas in the gas being measured, to flow from the outside of the element body to the reference electrode; as well as A reference gas adjustment pump unit, configured to include the measured gas-side electrode and the reference electrode. The control unit performs a moisture concentration reduction process, that is, it controls the reference gas adjustment pump unit to draw oxygen from the vicinity of the reference electrode to the vicinity of the gas being measured side electrode, thereby reducing the moisture concentration around the reference electrode.

2. The gas sensor according to claim 1, characterized in that, The control unit controls the reference gas adjustment pump unit during the moisture concentration reduction process to alternately perform: oxygen extraction from the vicinity of the reference electrode to the vicinity of the gas being measured side electrode, and oxygen extraction from the vicinity of the gas being measured side electrode to the vicinity of the reference electrode.

3. A gas sensor that detects the concentration of a specific gas in a gas to be measured. The gas sensor is characterized by having a sensor element and a control unit. The sensor element has: The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for introducing and circulating the gas to be measured. A measuring electrode is disposed in the gas flow section to be measured; A gas-to-measure side electrode is disposed on the element body in a manner that contacts the gas to be measured. A reference electrode is disposed inside the main body of the component; A reference gas inlet section allows a reference gas, which serves as a detection reference for the concentration of the specific gas in the gas being measured, to flow from the outside of the element body to the reference electrode; as well as A reference gas adjustment pump unit, configured to include the measured gas-side electrode and the reference electrode. The control unit performs the following process: reference gas adjustment process, which controls the reference gas adjustment pump unit to draw oxygen from the vicinity of the measured gas side electrode to the vicinity of the reference electrode, thereby adjusting the oxygen concentration around the reference electrode. In addition to the moisture concentration reduction process, the reference gas adjustment pump unit is controlled to temporarily draw in more oxygen around the reference electrode compared to the reference gas adjustment process, thereby reducing the moisture concentration around the reference electrode. The control unit performs a moisture determination process, that is, it determines whether there is a lot of moisture around the reference electrode based on the pump current flowing through the reference gas adjustment pump unit when controlling the reference gas adjustment pump unit to draw oxygen from the area around the reference electrode to the area around the gas to be measured side electrode. If the moisture is determined to be high, the moisture concentration reduction process is performed.

4. The gas sensor according to any one of claims 1 to 3, characterized in that, The control unit applies a control voltage of 0.3V to 1.5V to the reference gas adjustment pump unit during the moisture concentration reduction process, thereby causing the reference gas adjustment pump unit to operate.

5. The gas sensor according to any one of claims 1 to 3, characterized in that, The execution time for the moisture concentration reduction process is between 5 seconds and 300 seconds.

6. The gas sensor according to any one of claims 1 to 3, characterized in that, The gas sensor includes a heater that heats the main body of the element. After the control unit powers the heater to bring its temperature above a predetermined temperature, it performs the moisture concentration reduction process.

7. The gas sensor according to claim 3, characterized in that, In the moisture determination process, the control unit determines whether there is a lot of moisture around the reference electrode based on the pump current when a predetermined control voltage higher than the voltage of the limit current region of the reference gas adjustment pump unit is applied between the measured gas side electrode and the reference electrode.

8. The gas sensor according to claim 7, characterized in that, In the moisture determination process, the control unit determines whether there is a lot of moisture around the reference electrode based on a comparison between the pump current and the limit current of the reference gas adjustment pump unit.

9. The gas sensor according to claim 8, characterized in that, The control unit includes a storage unit that stores the value of the limiting current. In the moisture determination process, the control unit compares the pump current with the limiting current stored in the storage unit.

10. The gas sensor according to claim 8, characterized in that, In the moisture determination process, the control unit compares the pump current with the limiting current measured by applying the voltage of the limiting current region to the reference gas adjustment pump unit.

11. The gas sensor according to claim 7, characterized in that, The specified control voltage is a voltage between 0.8V and 1.5V.

12. A control method for a gas sensor, wherein the gas sensor detects the concentration of a specific gas in a gas to be measured. The control method for the gas sensor is characterized in that... The gas sensor includes sensor elements. The sensor element has: The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for introducing and circulating the gas to be measured. A measuring electrode is disposed in the gas flow section to be measured; A gas-to-measure side electrode is disposed on the element body in a manner that contacts the gas to be measured. A reference electrode is disposed inside the main body of the component; A reference gas inlet section allows a reference gas, which serves as a detection reference for the concentration of the specific gas in the gas being measured, to flow from the outside of the element body to the reference electrode; as well as A reference gas adjustment pump unit, configured to include the measured gas-side electrode and the reference electrode. The control method includes a moisture concentration reduction process, namely: controlling the reference gas adjustment pump unit to draw oxygen from the vicinity of the reference electrode to the vicinity of the gas being measured side electrode, thereby reducing the moisture concentration around the reference electrode.

13. The control method for the gas sensor according to claim 12, characterized in that, In the moisture concentration reduction process, the reference gas adjustment pump unit is controlled to alternately perform: oxygen extraction from the vicinity of the reference electrode to the vicinity of the gas being measured side electrode, and oxygen extraction from the vicinity of the gas being measured side electrode to the vicinity of the reference electrode.

14. A control method for a gas sensor, wherein the gas sensor detects the concentration of a specific gas in a gas to be measured. The control method for the gas sensor is characterized in that... The gas sensor includes sensor elements. The sensor element has: The main body of the component includes a solid electrolyte layer with oxygen ion conductivity, and a gas flow section is provided inside for introducing and circulating the gas to be measured. A measuring electrode is disposed in the gas flow section to be measured; A gas-to-measure side electrode is disposed on the element body in a manner that contacts the gas to be measured. A reference electrode is disposed inside the main body of the component; A reference gas inlet section allows a reference gas, which serves as a detection reference for the concentration of the specific gas in the gas being measured, to flow from the outside of the element body to the reference electrode; as well as A reference gas adjustment pump unit, configured to include the measured gas-side electrode and the reference electrode. The control method includes: a reference gas adjustment process, that is, controlling the reference gas adjustment pump unit to draw oxygen from the vicinity of the measured gas side electrode to the vicinity of the reference electrode, thereby adjusting the oxygen concentration around the reference electrode. The moisture concentration reduction process involves controlling the reference gas adjustment pump unit to temporarily draw in more oxygen around the reference electrode compared to the reference gas adjustment process, thereby reducing the moisture concentration around the reference electrode; and The moisture determination process involves determining whether there is a high level of moisture around the reference electrode based on the pump current flowing through the reference gas adjustment pump unit when controlling the unit to draw oxygen from around the reference electrode to around the electrode of the gas being measured. If the moisture content is determined to be high during the moisture determination process, the moisture concentration reduction process is performed.

15. The control method for a gas sensor according to any one of claims 12 to 14, characterized in that, The gas sensor includes a heater that heats the main body of the element. After powering the heater to bring its temperature above a specified level, the moisture concentration reduction process is performed.

16. The control method for a gas sensor according to claim 14, characterized in that, In the moisture determination process, the amount of moisture around the reference electrode is determined based on the pump current when a predetermined control voltage higher than the voltage of the limit current region of the reference gas adjustment pump unit is applied between the measured gas side electrode and the reference electrode.

17. The control method for a gas sensor according to claim 16, characterized in that, In the moisture determination process, the amount of moisture around the reference electrode is determined by comparing the pump current with the limit current of the reference gas adjustment pump unit.

18. The control method for a gas sensor according to claim 17, characterized in that, The gas sensor includes a storage unit that stores the value of the limiting current. In the moisture determination process, the pump current is compared with the limiting current stored in the storage unit.

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