Gas sensor

Abstract

The present invention provides a gas sensor capable of maintaining the detection accuracy of a gas to be measured in a gas to be measured at a high level. A gas sensor (100) for detecting a gas to be measured among a gas to be measured, the gas sensor (100) comprising a sensor element (101) and a control device for controlling the sensor element (101), the control device comprising: a storage unit; the oxygen demand storage unit (43) is used for pre-storing the oxygen demand which should exist in the reference gas chamber (43) when the oxygen concentration in the reference gas in the reference gas chamber (43) is a specified concentration; and a processing unit that performs a regeneration process in which an electric current is passed between a pump electrode (23) disposed at a position different from that in the reference gas chamber (43) and a reference electrode (42) disposed in the reference gas chamber (43), oxygen present in the reference gas chamber (43) is sucked out from the reference gas chamber (43), and thereafter the reference gas chamber (43) is regenerated by the pump electrode (23) and the reference electrode (42). The required amount of oxygen stored in advance in the storage unit is sucked into the reference gas chamber (43).

Description

Technical Field

[0001] The present invention relates to a gas sensor for detecting a measurement target gas in a measured gas. This application claims priority based on Japanese Patent Application No. 2022-100113 filed in Japan on June 22, 2022, the contents of which are incorporated herein by reference. Background Art

[0002] Gas sensors are used to detect and measure the concentration of target gas components (oxygen O2, nitrogen oxides NOx, ammonia NH3, hydrocarbons HC, carbon dioxide CO2, etc.) in measured gases such as automobile exhaust. As such gas sensors, there are known gas sensors having sensor elements using oxygen ion conductive solid electrolytes such as zirconium dioxide (ZrO2) (for example, Japanese Patent Publication No. 2021-156647 and WO2020 / 004356).

[0003] For example, Japanese Patent Publication No. 2021-156647 discloses a sensor element, which includes: an element body, which is provided with a measured gas circulation portion for introducing and circulating the measured gas, and a reference gas chamber for pre-accumulating a reference gas (such as the atmosphere) as a detection reference for a specific gas concentration in the measured gas; and a reference electrode, which is arranged in the reference gas chamber. In addition, it is disclosed that: the reference gas chamber is independently arranged inside the element body.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2021-156647

[0007] Patent Document 2: WO2020 / 004356 Summary of the invention

[0008] In the above-mentioned gas sensor, if the oxygen concentration in the reference gas around the reference electrode changes due to some reason, the detection accuracy of the measurement target gas in the measurement gas may be reduced.

[0009] When the oxygen concentration in the measured gas is known, for example, as described in Japanese Patent Application Laid-Open No. 2021-156647, the oxygen concentration in the reference gas can be confirmed based on the potential difference between the reference electrode and the outer pump electrode disposed in the portion of the sensor element exposed to the measured gas, and adjusted as needed. For example, when the measured gas is exhaust gas from a car or the like, when the fuel is cut, the oxygen concentration is known because the measured gas is the atmospheric atmosphere.

[0010] However, the oxygen concentration in the measured gas usually changes all the time, so the oxygen concentration in the reference gas chamber cannot be confirmed by the above method except for a specific time when the oxygen concentration is known, such as when the fuel is cut off. Therefore, during a period when the oxygen concentration is not known, even if the oxygen concentration in the reference gas changes, the change cannot be monitored, and the detection accuracy of the measurement target gas in the measured gas may be reduced.

[0011] Therefore, an object of the present invention is to provide a gas sensor capable of suppressing a decrease in the detection accuracy of a measurement target gas in a measured gas and maintaining high detection accuracy.

[0012] The inventors of the present invention have studied that the use of the gas sensor is not limited to the case where the oxygen concentration in the measured gas is known, and that the deviation of the oxygen concentration in the reference gas is corrected at an arbitrary timing regardless of the oxygen concentration.

[0013] For example, the WO2020 / 004356 Gazette discloses: oxygen intake control is performed, that is, a current is caused to flow between a reference electrode and a measured gas side electrode disposed in a portion exposed to the measured gas, so that oxygen is absorbed into the vicinity of the reference electrode. Furthermore, it is disclosed that: in order to suppress the reduction in the detection accuracy of the measured object gas in the measured gas, the specific gas concentration of the measured gas is corrected based on the difference between the first reference voltage between the reference electrode and the measured gas side electrode when the oxygen intake control is not performed and the second reference voltage between the reference electrode and the measured gas side electrode when the oxygen intake control is performed. However, this correction is performed based on the change in resistance of the reference electrode caused by time degradation, rather than monitoring the change in oxygen concentration in the reference gas around the reference electrode.

[0014] The inventor of the present invention has conducted intensive research and found that the oxygen concentration in the reference gas can be made to be the specified concentration by performing a regeneration process, wherein the oxygen in the reference gas chamber is sucked out to make the oxygen in the reference gas chamber substantially zero, and then oxygen is sucked into the reference gas chamber in such a manner that the oxygen concentration in the reference gas in the reference gas chamber reaches the specified concentration. It was found that if the regeneration process is performed, the oxygen concentration in the reference gas around the reference electrode can be made to be (returned to) the specified concentration at any time during the use of the gas sensor.

[0015] The present invention includes the following inventions.

[0016] (1) A gas sensor for detecting a measurement target gas in a measured gas, comprising a sensor element and a control device for controlling the sensor element,

[0017] The sensor element comprises:

[0018] A long plate-shaped substrate portion including an oxygen ion conductive solid electrolyte layer;

[0019] a measured gas flow cavity, the measured gas flow cavity being formed from one end portion in the length direction of the base portion, for introducing and flowing the measured gas;

[0020] a reference gas chamber formed inside the base portion in a manner isolated from the measured gas flow cavity and sealed inside the base portion;

[0021] a reference electrode disposed in the reference gas chamber; and

[0022] a pump electrode disposed in a position different from that in the reference gas chamber,

[0023] The control device comprises:

[0024] a storage unit that stores in advance a required amount of oxygen that should exist in the reference gas chamber when the oxygen concentration in the reference gas in the reference gas chamber is a predetermined concentration; and

[0025] A processing unit performs a regeneration process, that is, causes an electric current to flow between the pump electrode and the reference electrode to absorb oxygen existing in the reference gas chamber from the reference gas chamber, and then absorbs the required amount of oxygen pre-stored in the storage unit into the reference gas chamber.

[0026] (2) In the gas sensor described in (1) above,

[0027] The storage unit stores in advance, as the required oxygen amount, a required current integral value of the current flowing between the pump electrode and the reference electrode when the current is caused to flow between the pump electrode and the reference electrode to transfer the required oxygen amount.

[0028] The processing unit absorbs oxygen present in the reference gas chamber from the reference gas chamber during the regeneration process, and then allows current to flow until the integral value of the current flowing between the pump electrode and the reference electrode reaches the required current integral value, thereby sucking the required amount of oxygen into the reference gas chamber.

[0029] (3) In the gas sensor described in (1) above,

[0030] The storage unit stores in advance, as the required oxygen amount, a time required for causing a predetermined current to flow between the pump electrode and the reference electrode to transfer the required oxygen amount.

[0031] The processing unit absorbs oxygen existing in the reference gas chamber from the reference gas chamber during the regeneration process, and then causes the specified current to flow between the pump electrode and the reference electrode for the required time to absorb the required amount of oxygen into the reference gas chamber.

[0032] (4) In the gas sensor described in (1) above,

[0033] The storage unit stores in advance, as the required oxygen amount, a required current value when a current is passed between the pump electrode and the reference electrode for a predetermined time to transfer the required oxygen amount.

[0034] The processing unit absorbs oxygen present in the reference gas chamber from the reference gas chamber during the regeneration process, and then causes the required current value to flow between the pump electrode and the reference electrode for the specified time to absorb the required amount of oxygen into the reference gas chamber.

[0035] (5) In the gas sensor described in any one of (1) to (4) above,

[0036] The processing unit applies a predetermined voltage between the pump electrode and the reference electrode to flow a current during the regeneration process, thereby sucking oxygen present in the reference gas chamber out of the reference gas chamber until the current becomes equal to or less than a predetermined value.

[0037] (6) In the gas sensor described in any one of (1) to (4) above,

[0038] The processing unit applies a predetermined voltage between the pump electrode and the reference electrode to flow current during the regeneration process, thereby sucking oxygen present in the reference gas chamber out of the reference gas chamber until a change in the current per unit time becomes equal to or less than a predetermined value.

[0039] (7) In the gas sensor described in any one of (1) to (6),

[0040] A cycle for performing the regeneration process is determined based on the volume of the reference gas chamber.

[0041] (8) A method for controlling a gas sensor for detecting a measurement target gas in a measured gas, the gas sensor comprising a sensor element and a control device for controlling the sensor element,

[0042] The sensor element comprises:

[0043] A long plate-shaped substrate portion including an oxygen ion conductive solid electrolyte layer;

[0044] a measured gas flow cavity, the measured gas flow cavity being formed from one end portion in the length direction of the base portion, for introducing and flowing the measured gas;

[0045] a reference gas chamber formed inside the base portion in a manner isolated from the measured gas flow cavity and sealed inside the base portion;

[0046] a reference electrode disposed in the reference gas chamber; and

[0047] a pump electrode disposed in a position different from that in the reference gas chamber,

[0048] The control device comprises:

[0049] a storage unit that stores in advance a required amount of oxygen that should exist in the reference gas chamber when the oxygen concentration in the reference gas in the reference gas chamber is a predetermined concentration; and

[0050] a processing unit that performs a regeneration process, i.e., causes a current to flow between the pump electrode and the reference electrode to absorb oxygen present in the reference gas chamber from the reference gas chamber, and then absorbs the required amount of oxygen pre-stored in the storage unit into the reference gas chamber,

[0051] The control method comprises a regeneration process step,

[0052] That is, the processing unit causes current to flow between the pump electrode and the reference electrode to absorb oxygen present in the reference gas chamber from the reference gas chamber, and then the processing unit absorbs the required amount of oxygen pre-stored in the storage unit into the reference gas chamber.

[0053] Effects of the Invention

[0054] When the gas sensor of the present invention is used, it is not limited to the case where the oxygen concentration in the measured gas is known. In addition, regardless of the oxygen concentration, the oxygen concentration in the reference gas around the reference electrode can be set to a predetermined concentration at any time during the use of the gas sensor. As a result, the detection accuracy of the measured gas can be suppressed from decreasing, thereby maintaining high detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 1 is a schematic longitudinal sectional view showing an example of a schematic configuration of the gas sensor 100 .

[0056] Figure 2 1 is a schematic vertical cross-sectional view in the longitudinal direction of the sensor element 101 , showing an example of the schematic configuration of the gas sensor 100 .

[0057] Figure 3 1 is a block diagram showing an example of the electrical connection relationship between the control device 90 and each of the pump units 21 , 50 , 41 , 84 and each of the sensor units 80 , 81 , 82 , 83 of the sensor element 101 .

[0058] Figure 4 1 is a schematic diagram showing an example of a temporal change in the pump current Ip3 when oxygen is sucked from the reference gas chamber 43 .

[0059] Figure 5 This is a flowchart showing an example of the regeneration process.

[0060] Figure 6 is a diagram showing the oxygen absorption process in the regeneration process ( Figure 5 Schematic diagram of an example of the time variation of the pump current Ip3 during step S11 in FIG.

[0061] Figure 7 It is a flowchart which shows a specific example of a regeneration process.

[0062] Figure 8 This is a flowchart showing another specific example of the regeneration process.

[0063] Fig. 9 1 is a schematic vertical cross-sectional view in the longitudinal direction of a sensor element 201 according to a modified example.

[0064] Fig.10 1 is a schematic vertical cross-sectional view in the longitudinal direction of a sensor element 301 according to a modified example.

[0065] Fig.11 This is a graph showing the results of investigating the stability of NOx outputs in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0066] A gas sensor of the present invention includes a sensor element and a control device for controlling the sensor element.

[0067] The sensor element included in the gas sensor of the present invention includes:

[0068] A long plate-shaped substrate portion including an oxygen ion conductive solid electrolyte layer;

[0069] a measured gas flow cavity, the measured gas flow cavity being formed from one end portion in the length direction of the base portion, for introducing and flowing the measured gas;

[0070] a reference gas chamber formed inside the base portion in a manner isolated from the measured gas flow cavity and sealed inside the base portion;

[0071] a reference electrode disposed in the reference gas chamber; and

[0072] A pump electrode is disposed at a position different from that in the reference gas chamber.

[0073] The control device included in the gas sensor of the present invention includes:

[0074] a storage unit that stores in advance a required amount of oxygen that should exist in the reference gas chamber when the oxygen concentration in the reference gas in the reference gas chamber is a predetermined concentration; and

[0075] A processing unit performs a regeneration process, that is, causes an electric current to flow between the pump electrode and the reference electrode to absorb oxygen existing in the reference gas chamber from the reference gas chamber, and then absorbs the required amount of oxygen pre-stored in the storage unit into the reference gas chamber.

[0076] [General structure of gas sensor]

[0077] Hereinafter, the gas sensor of the present invention will be described with reference to the drawings. Figure 1 1 is a schematic longitudinal sectional view showing an example of a schematic configuration of a gas sensor 100 as one embodiment of the present invention. Figure 2 1 is a schematic vertical cross-sectional view in the longitudinal direction of the sensor element 101 , showing an example of the schematic configuration of the gas sensor 100 . Figure 3 1 is a block diagram showing an example of the electrical connection relationship between the control device 90 and the sensor element 101. Figure 2 As a benchmark, the so-called up and down Figure 2 Set the upper side of the Figure 2 The left side of is set as the front end side, and the right side thereof is set as the rear end side. Figure 1 In, with Figure 2 correspond, Figure 1 The left side is up, the right side is down, the down side is the front end side, and the up side is the rear end side. Figure 1 The structure of the gas sensor shown is well known and is described in, for example, Japanese Patent Application Publication No. 2021-156647 and WO2020 / 004356.

[0078] like Figure 1As shown in the figure, the gas sensor 100 includes: a sensor element 101; a protective cover 130 that protects the front end side of the sensor element 101; and a sensor assembly 140 that includes a connector 150 that is conductive with the sensor element 101. As shown in the figure, the gas sensor 100 is installed in a pipe 190 such as an exhaust pipe of a vehicle, and is used to measure the concentration of the measurement target gas such as NOx, NH3, O2 contained in the exhaust gas as the measured gas. In this embodiment, the gas sensor 100 measures the concentration of NOx as the measurement target gas.

[0079] The protective cover 130 includes an inner protective cover 131 having a bottomed cylindrical shape, which covers the front end of the sensor element 101, and an outer protective cover 132 having a bottomed cylindrical shape, which covers the inner protective cover 131. A plurality of holes 134 for allowing the measured gas to flow in the protective cover 130 are formed in the inner protective cover 131 and the outer protective cover 132. 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 arranged in the sensor element chamber 133.

[0080] The sensor assembly 140 includes: an element sealing body 141 that seals and fixes the sensor element 101; a nut 147 and an outer cylinder 148 that are attached to the element sealing body 141; and a connector 150 that is connected to a connector electrode (not shown) formed on the surface (upper and lower surfaces) of the rear end of the sensor element 101 (only the heater connector electrode 71 described later is shown in the figure). Figure 2 in the middle) and are electrically connected to these electrodes.

[0081] The element enclosure 141 includes: a cylindrical main metal member 142; a cylindrical inner tube 143, which is welded and fixed coaxially with the main metal member 142; and ceramic supports 144a to 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 member 142 and the inner tube 143. The sensor element 101 is located on the central axis of the element enclosure 141 and penetrates the element enclosure 141 in the front-rear direction. The inner tube 143 is formed with: a reduced diameter portion 143a, which is used to press the pressed powder body 145b in the central axis direction of the inner tube 143; and a reduced diameter portion 143b, which is used to press the ceramic supports 144a to 144c and the pressed powder bodies 145a and 145b forward by means of the metal ring 146. The pressed powder bodies 145a and 145b are compressed between the main metal part 142 and the inner tube 143 and the sensor element 101 by the pressing force from the reduced diameter parts 143a and 143b, thereby sealing the space between the sensor element chamber 133 in the protective cover 130 and the space 149 in the outer tube 148 and fixing the sensor element 101.

[0082] The nut 147 is fixed coaxially with the main metal fitting 142 and has an external threaded portion formed on the outer peripheral surface. The external threaded portion of the nut 147 is inserted into the fixing member 191, which is welded to the pipe 190 and has an internal threaded portion provided on the inner peripheral surface. Thus, the gas sensor 100 is fixed to the pipe 190 in a state where the tip of the sensor element 101 in the gas sensor 100 and a portion of the protective cover 130 protrude into the pipe 190.

[0083] The outer cylinder 148 covers the inner cylinder 143, the sensor element 101, and the connector 150, and a plurality of lead wires 155 connected to the connector 150 are led out from the rear end to the outside. The lead 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 lead wires 155 is closed by a rubber stopper 157. The space 149 in the outer cylinder 148 is filled with air. The rear end of the sensor element 101 is arranged in the space 149.

[0084] (Sensor element)

[0085] like Figure 2 As shown, the sensor element 101 is a long strip-shaped element, which includes a substrate portion 102 having a structure in which a plurality of oxygen ion conductive solid electrolyte layers are stacked. The long strip-shaped is also called a long plate or a strip. The substrate portion 102 has a structure in which six layers, namely, a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, an isolation layer 5, and a second solid electrolyte layer 6, which are respectively composed of oxygen ion conductive solid electrolyte layers such as zirconium dioxide (ZrO2), are stacked in order from the bottom side in the accompanying drawings. The solid electrolyte forming these six layers is a dense gas-tight solid electrolyte. The six layers can be all of the same thickness, or they can be different thicknesses for each layer. The layers are bonded to each other by means of an adhesive layer composed of a solid electrolyte, and the adhesive layer is included in the substrate portion 102. Figure 2 Although the layer structure consisting of the above six layers is exemplified in FIG. 1 , the layer structure in the present invention is not limited thereto, and may have any number of layers and layer structure.

[0086] The sensor element 101 is manufactured by, for example, subjecting ceramic green sheets corresponding to the respective layers to predetermined processing and printing of circuit patterns, and then laminating them and further sintering them to integrate them.

[0087] A gas inlet 10 is formed at one end (hereinafter referred to as the front end) in the longitudinal direction of the sensor element 101 and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The measured gas flow cavity 15, that is, the measured gas flow portion is formed by sequentially connecting the first diffusion rate control portion 11, the buffer space 12, the second diffusion rate control portion 13, the first internal cavity 20, the third diffusion rate control portion 30, the second internal cavity 40, the fourth diffusion rate control portion 60, and the third internal cavity 61 in the longitudinal direction starting from the gas inlet 10.

[0088] The gas inlet 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40 and the third internal cavity 61 are spaces inside the sensor element 101 which are arranged by hollowing out the isolation layer 5, wherein their upper parts are separated by the lower surface of the second solid electrolyte layer 6, their lower parts are separated by the upper surface of the first solid electrolyte layer 4, and their sides are separated by the side surfaces of the isolation layer 5.

[0089] The first diffusion rate control unit 11, the second diffusion rate control unit 13 and the third diffusion rate control unit 30 are all arranged in two horizontally long lines (the length direction of the opening is in Figure 2 The first diffusion rate control unit 11, the second diffusion rate control unit 13, and the third diffusion rate control unit 30 may be in any form as long as they can provide a desired diffusion resistance, and their forms are not limited to the slits.

[0090] The fourth diffusion rate control section 60 has a horizontally long (the length direction of the opening is in Figure 2 The fourth diffusion rate control unit 60 is provided in the form of a slit (in a direction perpendicular to the drawing) between the separator 5 and the second solid electrolyte layer 6. The fourth diffusion rate control unit 60 may be in any form as long as it provides a desired diffusion resistance, and its form is not limited to the slit.

[0091] A reference gas chamber 43 is provided between the lower surface of the isolation layer 5 and the upper surface of the third substrate layer 3. The reference gas chamber 43 is a space inside the sensor element 101 provided by hollowing out the first solid electrolyte layer 4. The reference gas chamber 43 is formed inside the base portion 102 in a manner isolated from the measured gas flow cavity 15. The reference gas chamber 43 is a space enclosed inside the base portion 102. The reference gas chamber 43 is an area for storing a reference gas that serves as a reference when measuring the NOx concentration in advance. The reference gas is a gas of a specified oxygen concentration. In the present embodiment, the atmosphere or a gas having the same oxygen concentration as the atmosphere (for example, a gas containing oxygen and based on nitrogen). A reference electrode 42 is provided in the reference gas chamber 43.

[0092] The reference electrode 42 is an electrode disposed on the upper surface of the third substrate layer 3 in the reference gas chamber 43. In addition, as described later, the reference electrode 42 can be used to measure the oxygen concentration (oxygen partial pressure) in 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 (for example, a metal ceramic electrode of Pt and ZrO2).

[0093] The gas inlet port 10 is a portion of the measured gas flow cavity 15 that is open to the external space, and the measured gas enters the sensor element 101 from the external space through the gas inlet port 10 .

[0094] In this embodiment, the measured gas flow cavity 15 is a form in which the measured gas is introduced from the gas inlet 10 that is open at the front end surface of the sensor element 101, but the present invention is not limited to this form. For example, there may be no concave part of the gas inlet 10 in the measured gas flow cavity 15. In this case, the first diffusion rate control unit 11 is substantially a gas inlet.

[0095] In addition, for example, the measured gas flow cavity 15 may be in the form of an opening connected to the buffer space 12 or a position near the buffer space 12 of the first internal cavity 20 on the side surface along the length direction of the base 102. In this case, the measured gas is introduced from the side surface along the length direction of the base 102 through the opening.

[0096] In addition, for example, the measured gas flow cavity 15 may be configured so that the measured gas is introduced through a porous body.

[0097] The first diffusion rate control unit 11 is a portion that applies a predetermined diffusion resistance to the gas to be measured that enters from the gas introduction port 10 .

[0098] The buffer space 12 is a space provided to guide the gas to be measured introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13 .

[0099] The second diffusion rate control unit 13 is a portion that applies a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal cavity 20 .

[0100] As a result, the amount of the measured gas introduced into the first internal cavity 20 only needs to be within a predetermined range. In other words, a predetermined diffusion resistance is applied to the entire area from the tip of the sensor element 101 to the second diffusion rate control unit 13. For example, the first diffusion rate control unit 11 may be directly connected to the first internal cavity 20, that is, the buffer space 12 and the second diffusion rate control unit 13 may not exist.

[0101] The buffer space 12 is a space provided to mitigate the influence of the pressure fluctuation on the detection value when the pressure of the gas to be measured fluctuates.

[0102] When the measured gas is introduced from the outside of the sensor element 101 into the first internal cavity 20, the measured gas that rapidly enters the sensor element 101 from the gas introduction port 10 due to the pressure fluctuation of the measured gas in the external space (when the measured gas is automobile exhaust gas, it is the pulsation of exhaust pressure) is not directly introduced into the first internal cavity 20, but is introduced into the first internal cavity 20 after the pressure fluctuation of the measured gas is eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. As a result, the pressure fluctuation of the measured gas introduced into the first internal cavity 20 is almost negligible.

[0103] The first internal cavity 20 is provided as a space for adjusting the oxygen partial pressure in the gas to be measured introduced by the second diffusion rate control unit 13. Such oxygen partial pressure is adjusted by operating the main pump unit 21.

[0104] The main pump unit 21 is an electrochemical pump unit consisting of an inner main pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 sandwiched by these electrodes, wherein the inner main pump electrode 22 has a top electrode portion 22a arranged on substantially the entire surface of the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, and the outer pump electrode 23 is arranged in the external space ( Figure 1 The sensor element chamber 133 in the upper surface of the second solid electrolyte layer 6 is provided in a region corresponding to the top electrode portion 22a in a manner that the sensor element chamber 133 in the upper surface is exposed.

[0105] The inner main pump electrode 22 is arranged across the solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) formed on the upper and lower sides that partition the first internal cavity 20, and the isolation layer 5 constituting the side wall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 constituting 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 constituting the bottom surface, and a side electrode portion (not shown) is formed on the side wall surface (inner surface) of the isolation layer 5 constituting the two side wall portions of the first internal cavity 20 in a manner that connects the top electrode portion 22a and the bottom electrode portion 22b, thereby configuring the side electrode portion in a tunnel-shaped structure.

[0106] The inner main pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (e.g., cermet electrodes containing 1% Au, Pt and ZrO2). In addition, the inner main pump electrode 22 in contact with the measured gas is formed using a material that weakens the ability to reduce NOx components in the measured gas.

[0107] In the main pump unit 21, a variable power supply 24 is used to apply a desired pump voltage Vp0 between the inner main pump electrode 22 and the outer pump electrode 23, so that the pump current Ip0 flows between the inner main pump electrode 22 and the outer pump electrode 23 in a positive direction or a negative direction. Thus, the oxygen in the first internal cavity 20 can be absorbed into the external space, or the oxygen in the external space can be absorbed into the first internal cavity 20.

[0108] 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, i.e., an oxygen partial pressure detection sensor unit 80 for main pump control, is formed by the inner main 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.

[0109] 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) in the first internal cavity 20 can be known. In addition, the pump voltage Vp0 is feedback-controlled so that the voltage V0 is constant, thereby controlling the pump current Ip0. In this way, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value.

[0110] The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20 , and guides the gas to be measured to the second internal cavity 40 .

[0111] The second internal cavity 40 is provided as a space for more accurately adjusting the oxygen partial pressure in the gas to be measured introduced by the third diffusion rate control unit 30. The auxiliary pump unit 50 is operated to adjust the oxygen partial pressure.

[0112] In the second internal cavity 40, the oxygen partial pressure of the measured gas, which has been previously adjusted in the first internal cavity 20 and introduced through the third diffusion rate control unit 30, is further adjusted by the auxiliary pump unit 50. Thus, the oxygen concentration in the second internal cavity 40 can be kept constant with high accuracy, and thus, the NOx concentration can be measured with high accuracy in the gas sensor 100.

[0113] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit composed of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, as long as it is an appropriate electrode arranged at a position different from the measured gas flow cavity 15), and a second solid electrolyte layer 6. The auxiliary pump electrode 51 has a top electrode portion 51a that is roughly entirely arranged on the lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40.

[0114] The auxiliary pump electrode 51 is disposed on the inner surface of the measured gas flow cavity 15 at a position farther from the one end (front end) in the longitudinal direction of the base portion 102 (sensor element 101 ) than the inner main pump electrode 22 .

[0115] The auxiliary pump electrode 51 is arranged in the second internal cavity 40 in the same tunnel-shaped structure as the inner main pump electrode 22 previously arranged in the first internal cavity 20. That is, a top electrode portion 51a is formed with respect 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, and a side electrode portion (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b is formed in a tunnel-shaped structure formed on the two wall surfaces of the isolation layer 5 constituting the side wall of the second internal cavity 40.

[0116] In addition, the auxiliary pump electrode 51 is formed using a material having a weakened reducing ability for NOx components in the measured gas, similarly to the inner main pump electrode 22 .

[0117] In the auxiliary pump unit 50, the variable power supply 52 applies a desired pump voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, thereby absorbing oxygen in the atmosphere in the second internal cavity 40 to the external space, or absorbing oxygen from the external space into the second internal cavity 40.

[0118] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely, an auxiliary pump control oxygen partial pressure detection sensor unit 81, is formed by 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.

[0119] The auxiliary pump unit 50 performs pumping using a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the auxiliary pump control oxygen partial pressure detection sensor unit 81. Thus, the oxygen partial pressure in the atmosphere in the second internal cavity 40 is controlled to a relatively low partial pressure that has substantially no effect on the measurement of NOx.

[0120] At the same time, the pump current Ip1 is used to control the voltage V0 of the main pump control oxygen partial pressure detection sensor unit 80. Specifically, the pump current Ip1 is input as a control signal to the main pump control oxygen partial pressure detection sensor unit 80, and by controlling the voltage V0, the gradient of the oxygen partial pressure in the measured gas introduced from the third diffusion rate control unit 30 into the second internal cavity 40 is controlled to be constant at all times. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump unit 21 and the auxiliary pump unit 50.

[0121] 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 to a lower level 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 .

[0122] The third internal cavity 61 is provided as a space for measuring the concentration of nitrogen oxides (NOx) in the gas to be measured introduced through the fourth diffusion rate control unit 60. The NOx concentration is measured by the operation of the measurement pump unit 41.

[0123] The measuring pump unit 41 measures the NOx concentration in the measured gas in the third internal cavity 61. The measuring pump unit includes: an inner measuring electrode (in this embodiment, the measuring electrode 44) disposed in the measured gas circulation cavity 15 (inner surface of the measured gas circulation cavity 15), and an outer measuring electrode (in this embodiment, the outer pump electrode 23) corresponding to the inner measuring electrode and disposed at a position of the base part different from the measured gas circulation cavity 15.

[0124] That is, in this embodiment, the measuring pump unit 41 is an electrochemical pump unit composed of a measuring electrode 44, an outer pump electrode 23 (not limited to the outer pump electrode 23, as long as it is an appropriate electrode arranged at a position different from the measured gas flow cavity 15), a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4, and the measuring electrode 44 is arranged at a position on the upper surface of the first solid electrolyte layer 4 facing the third internal cavity 61.

[0125] The measuring electrode 44 is disposed on the inner surface of the measured gas flow cavity 15 at a position farther from the one end (front end) in the length direction of the base portion 102 (sensor element 101 ) than the inner main pump electrode 22 and the auxiliary pump electrode 51 .

[0126] The measuring electrode 44 is a porous metal ceramic electrode. The measuring electrode 44 also functions as a NOx reduction catalyst for reducing NOx present in the atmosphere in the third internal cavity 61. For example, in this embodiment, the measuring electrode 44 uses a porous metal ceramic electrode of Pt, Rh, and ZrO2.

[0127] The measuring pump cell 41 can absorb oxygen generated by decomposition of nitrogen oxides in the atmosphere around the measuring electrode 44 , and the generated amount can be detected as the pump current Ip2 .

[0128] In order to detect the oxygen partial pressure around the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42 constitute an electrochemical sensor unit, that is, a measuring pump control oxygen partial pressure detection sensor unit 82. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the measuring pump control oxygen partial pressure detection sensor unit 82.

[0129] The gas to be measured introduced into the second internal cavity 40 passes through the fourth diffusion rate control unit 60 under the condition that the oxygen partial pressure is controlled and reaches the measuring electrode 44 in the third internal cavity 61. The nitrogen oxides in the gas to be measured around the measuring electrode 44 are reduced (2NO→N2+O2) to generate oxygen. And the generated oxygen is pumped by the measuring pump unit 41. At this time, the pump voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control is constant. The amount of oxygen generated around the measuring electrode 44 is 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.

[0130] In addition, if the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42 are combined to form an oxygen partial pressure detection mechanism in the form of an electrochemical sensor unit, the electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around the measuring electrode 44 and the amount of oxygen contained in the reference atmosphere can be detected, thereby also being able to calculate the concentration of the NOx component in the measured gas.

[0131] In addition, the electrochemical sensor unit 83 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 can detect the oxygen partial pressure in the measured gas outside the sensor by using the electromotive force (voltage Vref) obtained by the sensor unit 83.

[0132] In addition, 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 constitute an electrochemical reference gas adjustment pump unit 84. With respect to the reference gas adjustment pump unit 84, a pump current Ip3 flows due to a pump voltage Vp3 applied by a power supply circuit 85 connected between the outer pump electrode 23 and the reference electrode 42, thereby pumping oxygen. Accordingly, the reference gas adjustment pump unit 84 can pump oxygen from the space ( Figure 1 Oxygen is absorbed into the space around the reference electrode 42, i.e., the reference gas chamber 43, or oxygen is absorbed from the reference gas chamber 43 to the space around the outer pump electrode 23.

[0133] In the gas sensor 100 having such a structure, the main pump unit 21 and the auxiliary pump unit 50 are operated to supply the measured gas whose oxygen partial pressure is always kept at a constant low value (a value that has substantially no effect on the measurement of NOx) to the measurement pump unit 41. Therefore, based on the pump current Ip2 that is approximately proportional to the NOx concentration in the measured gas and flows due to the oxygen generated by the reduction of NOx being sucked out from the measurement pump unit 41, the NOx concentration in the measured gas can be known.

[0134] In addition, the sensor element 101 includes a heater unit 70, which has a temperature adjustment function of heating and keeping the sensor element 101 warm so as to improve the oxygen ion conductivity of the solid electrolyte. The heater unit 70 includes a heater connector electrode 71, a heater 72, a heater lead 76, a through hole 73, and a heater insulating layer 74.

[0135] The heater connector electrode 71 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 1. By connecting the heater connector electrode 71 to a heater power source as an external power source, power can be supplied to the heater unit 70 from the outside.

[0136] The heater 72 is a resistor formed by being sandwiched from the upper and lower sides by the second substrate layer 2 and the third substrate layer 3. The heater 72 is connected to the heater connector electrode 71 by means of a heater lead 76 connected to the heater 72 and extending to the rear end side in the longitudinal direction of the sensor element 101, and a through hole 73, and is supplied with power from the outside through the heater connector electrode 71, thereby generating heat, thereby heating and keeping the solid electrolyte forming the sensor element 101 warm.

[0137] In addition, the heater 72 is buried in the entire area from the first internal cavity 20 to the third internal cavity 61, and the sensor element 101 can be adjusted to a temperature that activates the solid electrolyte. It is sufficient to adjust the temperature so that the main pump unit 21, the auxiliary pump unit 50, and the measurement pump unit 41 can work. It is not necessary to adjust all the above areas to the same temperature, and the sensor element 101 can have a temperature distribution.

[0138] The sensor element 101 of the present embodiment is a scheme in which the heater 72 is implanted in the base part 102, but it is not limited to this scheme. It is sufficient as long as the heater 72 is arranged in a manner to heat the base part 102. That is, the heater 72 can heat the sensor element 101 to a degree that the main pump unit 21, the auxiliary pump unit 50 and the measuring pump unit 41 mentioned above can work. For example, it can be implanted in the base part 102 as in the present embodiment. Alternatively, for example, it can also be that the heater part 70 is formed as a heater substrate different from the base part 102 and is arranged at an adjacent position of the base part 102. Alternatively, the sensor element 101 can also be heated by a high-temperature gas to be measured. In order to perform measurements with good accuracy, it is preferred to keep the temperature of the sensor element 101 constant regardless of the temperature of the gas to be measured. Considering this point, it is preferred that the sensor element 101 has a heater part 70 as in the present embodiment.

[0139] The heater insulating layer 74 is an insulating layer formed on the upper and lower surfaces of the heater 72 and the heater lead 76 using an insulator such as alumina. The heater insulating layer 74 is formed to obtain electrical insulation between the second substrate layer 2 and the heater 72 and the heater lead 76 and electrical insulation between the third substrate layer 3 and the heater 72 and the heater lead 76.

[0140] (Control device)

[0141] The gas sensor 100 of this embodiment includes the sensor element 101 described above and a control device 90 that controls the sensor element 101. In the gas sensor 100, the electrodes 22, 23, 51, 44, 42 of the sensor element 101 are electrically connected to the control device 90 via lead wires 155, respectively. Figure 3 1 is a block diagram showing the electrical connection relationship between the control device 90 and each pump unit 21, 50, 41, 84 and each sensor unit 80, 81, 82, 83 of the sensor element 101 in this embodiment. The control device 90 includes: the above-mentioned variable power supply 24, 46, 52 and power supply circuit 85, and a control unit 91. The control unit 91 includes: a drive control unit 92, a storage unit 93 and a processing unit 94.

[0142] The control unit 91 is implemented by a general-purpose or dedicated computer, and uses a CPU, memory, etc. mounted on the computer to implement the functions of the drive control unit 92, the storage unit 93, and the processing unit 94. In addition, when the gas sensor 100 uses NOx contained in the exhaust gas from the engine of an automobile as the measurement target gas and the sensor element 101 is installed in the exhaust path, part or all of the functions of the control device 90 (especially the control unit 91) can be implemented by using the ECU (Electronic Control Unit: electronic control device) mounted on the automobile.

[0143] The control unit 91 is configured to obtain the electromotive force (voltage V0, V1, V2, Vref) of each sensor unit 80, 81, 82, 83 of the sensor element 101 and the pump current (Ip0, Ip1, Ip2, Ip3) of each pump unit 21, 50, 41, 84. In addition, the control unit 91 is configured to output a control signal to the variable power supply 24, 52, 46 and the power supply circuit 85.

[0144] The drive control unit 92 is configured to control the operation of the main pump unit 21 , the auxiliary pump unit 50 , and the measurement pump unit 41 . In addition, the drive control unit 92 may be configured to control the operation of the reference gas adjustment pump unit 84 .

[0145] The drive control unit 92 performs normal control, that is, operates at least the measurement pump unit 41 including the inner measurement electrode (measurement electrode 44) disposed on the inner surface of the measured gas flow cavity 15 to detect the measurement target gas in the measured gas.

[0146] In the present embodiment, the drive control unit 92 operates the main pump unit 21, the auxiliary pump unit 50, and the measurement pump unit 41 in normal control. More specifically, in the present embodiment, normal control is performed as follows.

[0147] In normal control, the driving control unit 92 is configured to make the voltage V0 of the main pump control oxygen partial pressure detection sensor unit 80 a constant value (referred to as a set value V0). SET ) is used to feedback control the pump voltage Vp0 of the variable power supply 24 in the main pump unit 21. The voltage V0 represents the oxygen partial pressure near the inner main pump electrode 22, so making the voltage V0 constant means making the oxygen partial pressure near the inner main pump electrode 22 constant. As a result, the pump current Ip0 in the main pump unit 21 changes according to the oxygen concentration in the measured gas.

[0148] The oxygen partial pressure in the measured gas is higher than the set value V0 SETWhen the oxygen partial pressure is equal to the set value V0, oxygen is discharged from the first internal cavity 20 in the main pump unit 21. On the other hand, when the oxygen partial pressure in the measured gas is lower than the set value V0, SET When the oxygen partial pressure is considerable (for example, when hydrocarbons HC are contained), the main pump unit 21 draws oxygen from the space outside the sensor element 101 into the first internal cavity 20. Therefore, the pump current Ip0 can take any positive or negative value.

[0149] The driving control unit 92 is configured to make the voltage V1 of the assist pump control oxygen partial pressure detection sensor unit 81 a constant value (referred to as a set value V1). SET ) is feedback-controlled for the pump voltage Vp1 of the variable power supply 52 in the auxiliary pump unit 50. The voltage V1 represents the oxygen partial pressure near the auxiliary pump electrode 51, so making the voltage V1 constant means making the oxygen partial pressure near the auxiliary pump electrode 51 constant. As a result, the oxygen partial pressure in the atmosphere in the second internal cavity 40 is controlled to a relatively low partial pressure that has substantially no effect on the measurement of NOx.

[0150] At the same time, the pump current Ip1 in the auxiliary pump unit 50 is set to a constant value (referred to as a set value Ip1). SET ) is used to set the voltage V0 based on the pump current Ip1. SET Specifically, the pump current Ip1 is input as a control signal to the main pump control oxygen partial pressure detection sensor unit 80, and its voltage V0 is controlled to a set value V0 set based on the pump current Ip1. SET , thereby, 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 be constant at all times. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of about 0.001 ppm by the operation of the main pump unit 21 and the auxiliary pump unit 50. That is, it is considered that the oxygen concentration in the gas to be measured introduced from the fourth diffusion rate control unit 60 into the third internal cavity 61 is maintained at a constant value of about 0.001 ppm.

[0151] The driving control unit 92 is configured to set the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control to a constant value (referred to as a set value V2). SET ) is used to feedback control the pump voltage Vp2 of the variable power supply 46 in the measuring pump unit 41. At the measuring electrode 44, the nitrogen oxides in the measured gas are reduced (2NO→N2+O2) to generate oxygen. The voltage V2 is set to V2 SET The generated oxygen is pumped out by the measuring pump unit 41 in the manner of SETThe value V2 can be set to a value that substantially decomposes all NOx at the measuring electrode 44. SET The pump current Ip2 may be set to a value that allows the pump current Ip2 to become a limiting current.

[0152] The drive control unit 92 can further perform control to apply a pump voltage Vp3 to the reference gas adjustment pump unit 84 using the power supply circuit 85 so that the pump current Ip3 flows. By causing the pump current Ip3 to flow, oxygen can be inhaled into the reference gas chamber 43 (oxygen inhalation control) or oxygen can be sucked out of the reference gas chamber 43 (oxygen exhalation control). In normal control, for example, control to apply a specified pump voltage Vp3 can be performed, and control to cause a specified pump current Ip3 to flow can also be performed. When this control is performed in normal control, for example, the pump current Ip3 can be made to flow continuously, or the pump current Ip3 can be made to flow intermittently. The pump current Ip3 can be constant or can be made to vary. When the oxygen inhalation control or the oxygen exhalation control is performed in normal control, it should be noted that it is performed within a range that does not substantially affect the measurement accuracy.

[0153] As will be described later, when the processing unit 94 performs the regeneration process, the drive control unit 92 only needs to stop the above-mentioned normal control of each pump unit 21 , 50 , 41 , 84 .

[0154] The storage unit 93 stores in advance the required amount of oxygen that should exist in the reference gas chamber 43 when the oxygen concentration in the reference gas in the reference gas chamber 43 reaches a predetermined concentration. The predetermined concentration can be appropriately set by a person skilled in the art, and may be, for example, the same oxygen concentration as the atmosphere.

[0155] In the storage unit 93, for example, as a required oxygen amount, a required current integral value of the current flowing between the pump electrode and the reference electrode 42 when the current is caused to flow between the pump electrode and the reference electrode 42 to move the oxygen of the required oxygen amount can be pre-stored. The pump electrode is an electrode having an oxygen pump function that is arranged at a position different from the reference gas chamber 43. The pump electrode is arranged at a position that is usually exposed to the measured gas. For example, the pump electrode can be arranged on the outside of the base 102, or it can be arranged in the measured gas flow cavity 15 (inner surface). For example, the pump electrode can be the outer pump electrode 23, the inner pump electrode 22, the auxiliary pump electrode 51, or the measuring electrode 44. In this embodiment, the case where the current is caused to flow between the outer pump electrode 23 and the reference electrode 42 is explained as an example.

[0156] Here, the current behavior when oxygen is sucked out from the reference gas chamber 43 will be described. Figure 4 2 is a schematic diagram showing an example of the time change of the pump current Ip3 when oxygen is sucked out from the reference gas chamber 43. Figure 4In FIG. 5 , the horizontal axis represents time (seconds) and the vertical axis represents pump current Ip3 (μA).

[0157] Reference Figure 4 , the behavior of the pump current Ip3 when a prescribed pump voltage Vp3 is applied to the reference gas adjustment pump unit 84 (between the outer pump electrode 23 and the reference electrode 42) so that the pump current Ip3 flows and oxygen is sucked out from the reference gas chamber 43 is described. When the prescribed pump voltage Vp3 is applied to the reference gas adjustment pump unit 84, the pump current Ip3 flows and oxygen is sucked out from the reference gas chamber 43. As oxygen is sucked out from the reference gas chamber 43, the amount of oxygen present in the reference gas chamber 43 decreases. As the amount of oxygen in the reference gas chamber 43 decreases, the current value of the pump current Ip3 decreases. Furthermore, when the oxygen in the reference gas chamber 43 reaches an amount of zero or near zero (substantially zero), the pump current Ip3 becomes zero or substantially zero. Figure 4 The area S of the portion indicated by the diagonal lines in the figure is the value obtained by integrating the pump current Ip3 over time. This integral value is called the current integral value (current accumulation value). The pump current Ip3 is the amount of charge moved per unit time, so the current integral value ( Figure 4 The area S in FIG. 4 corresponds to the oxygen ions O moving from the reference electrode 42 to the outer pump electrode 23. 2－ The amount of charge. Oxygen ion O 2－ The charge amount corresponds to the amount of oxygen present in the reference gas chamber 43 before the pump current Ip3 starts to flow. That is, the current integral value ( Figure 4 The area S) in the reference gas chamber 43 can be an indicator of the amount of oxygen present in the reference gas chamber 43.

[0158] Therefore, when the oxygen concentration in the reference gas in the reference gas chamber 43 is a predetermined concentration, the current integral value of the pump current Ip3 corresponding to the required amount of oxygen that should exist in the reference gas chamber 43 can be obtained, and the storage unit 93 stores the current integral value (referred to as the required current integral value). The required current integral value is roughly determined by the predetermined concentration of oxygen in the reference gas and the volume of the reference gas chamber 43.

[0159] For example, the required current integral value can be solved as follows. First, by utilizing the oxygen concentration confirmation process during the manufacture of the gas sensor 100 described later, etc., it is confirmed that the oxygen concentration in the reference gas in the reference gas chamber 43 is a specified concentration. In addition, the confirmation of the oxygen concentration in the reference gas is performed in a state where the outer pump electrode 23 of the sensor element 101 is in contact with a gas of a known oxygen concentration (such as the atmosphere). Then, when the oxygen concentration in the reference gas in the reference gas chamber 43 is a specified concentration, a specified pump voltage Vp3 is applied to the reference gas adjustment pump unit 84 (between the outer pump electrode 23 and the reference electrode 42) by the power supply circuit 85, so that the pump current Ip3 flows, and the oxygen present in the reference gas chamber 43 is sucked out from the reference electrode 42 to the outer pump electrode 23. The circulating pump current Ip3 and time are obtained, and the specified pump voltage Vp3 is continuously applied until the pump current Ip3 is substantially zero. Then, the value related to the pump current Ip3 is calculated. Figure 4 The area S in φ corresponds to the time integral value of the pump current Ip3 (the required current integral value).

[0160] In addition, the storage unit 93 may store in advance, as the required oxygen amount, for example, the time required to transfer the required oxygen amount by flowing a predetermined current between the pump electrode (for example, the outer pump electrode 23) and the reference electrode 42. That is, the time required to flow the predetermined current until the current integral value reaches the required current integral value may be stored.

[0161] In addition, the storage unit 93 may store in advance, as the required amount of oxygen, for example, a required current value when the required amount of oxygen is transferred by flowing current for a predetermined time between the pump electrode (for example, the outer pump electrode 23) and the reference electrode 42. That is, the required current value required for the current integral value to reach the required current integral value when the current is flowing for a predetermined time may be stored.

[0162] The processing unit 94 performs a regeneration process, that is, it causes a current to flow between the pump electrode and the reference electrode 42, thereby sucking out the oxygen existing in the reference gas chamber 43 from the reference gas chamber 43, and after the oxygen existing in the reference gas chamber 43 is substantially zero, the required amount of oxygen pre-stored in the storage unit 93 is sucked into the reference gas chamber 43. As described above, the pump electrode is an electrode disposed at a position different from that in the reference gas chamber 43. For example, it may be the outer pump electrode 23, the inner pump electrode 22, the auxiliary pump electrode 51, or the measuring electrode 44. The details of the regeneration process are described below.

[0163] [Manufacturing of gas sensors]

[0164] Next, an example of a method for manufacturing the gas sensor 100 described above is described. After a plurality of unfired sheet-shaped molded products (so-called green sheets) containing an oxygen ion conductive solid electrolyte such as zirconium dioxide (ZrO2) as a ceramic component are subjected to predetermined processing and circuit pattern printing, the plurality of sheets are stacked, and the stacked body is cut and then fired, thereby manufacturing the sensor element 101. Thereafter, the gas sensor 100 in which the sensor element 101 is embedded is manufactured.

[0165] The following is made Figure 2 The case where the sensor element 101 is composed of six layers is described as an example.

[0166] First, prepare 6 green sheets containing an oxygen ion conductive solid electrolyte such as zirconium dioxide (ZrO2) as a ceramic component. The green sheets can be made using a known molding method. The 6 green sheets can all have the same thickness, or the thickness can be different depending on the layer to be formed. Sheet holes (blank sheets) used for positioning during printing and stacking are pre-formed on the 6 green sheets using a known method such as a punching process based on a punching device. Through-portions such as internal cavities are also formed on the blank sheet used for the isolation layer 5 using the same method. A through-portion for the reference gas chamber 43 is also formed on the blank sheet used for the first solid electrolyte layer 4 using the same method. Necessary through-portions are also pre-formed in other layers.

[0167] Various patterns required for each layer are printed and dried on blank sheets for the six layers of 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. The patterns can be printed using a known screen printing technique. For the drying process, known drying means can also be used.

[0168] The above steps are repeated, and after the printing and drying of various patterns on each of the six blank sheets are completed, a pressure bonding process is performed, that is, the six printed blank sheets are stacked in a specified order while being positioned using the sheet holes, etc., and pressure-bonded under specified temperature and pressure conditions to form a laminate. The pressure bonding process is performed by heating and pressurizing using a known laminating machine such as a hydraulic press. The temperature, pressure and time of heating and pressurizing depend on the laminating machine used, but can be appropriately determined in a manner that can achieve good lamination.

[0169] The obtained laminated body includes a plurality of sensor elements 101. The laminated body is cut and divided into units of the sensor element 101. The divided laminated body is fired at a predetermined firing temperature to obtain the sensor element 101. The firing temperature may be a temperature at which the solid electrolyte of the base body 102 constituting the sensor element 101 is sintered to form a dense body and the electrode and the like maintain a desired porosity. For example, the firing is performed at a firing temperature of about 1300 to 1500°C.

[0170] After that, the gas sensor 100 in which the sensor element 101 is embedded is manufactured. For example, the element enclosure 141 is installed on the sensor element 101 to be sealed and fixed, and the connector 150 and the lead 155 are installed on the rear end side of the sensor element 101 in a manner that is conductive with the connector electrode such as the heater connector electrode 71. In addition, the protective cover 130 is installed on the front end side of the sensor element 101 in the element enclosure 141. In addition, the outer cylinder 148 is installed on the rear end side of the sensor element 101 in the element enclosure 141, and the lead 155 is led out from the outer cylinder 148 to the outside. Then, the control device 90 and the sensor element 101 are connected by the lead 155. In this way, the gas sensor 100 is obtained.

[0171] In the manufacturing process of the gas sensor 100, it is preferable to carry out an oxygen concentration confirmation process of confirming the oxygen concentration of the reference gas chamber 43 and adjusting the oxygen concentration of the reference gas chamber 43 as needed after obtaining the sensor element 101 or after obtaining the gas sensor 100. For example, this process is carried out as follows. First, in a state where the outer pump electrode 23 of the sensor element 101 is in contact with a gas (e.g., the atmosphere) having a known oxygen concentration, the sensor element 101 is kept at a predetermined driving temperature (e.g., 800° C.), and the voltage Vref of the sensor cell 83 is measured. Then, based on the known oxygen concentration and the voltage Vref, the oxygen concentration in the reference gas chamber 43 is derived. In addition, it is confirmed that the oxygen concentration in the reference gas chamber 43 is within a predetermined oxygen concentration range that is considered to be the same as the oxygen concentration of the reference gas. When the oxygen concentration in the reference gas chamber 43 deviates from the predetermined oxygen concentration range, the pump voltage Vp3 is applied from the power supply circuit 85 to the reference gas adjustment pump cell 84 to flow the pump current Ip3, thereby sucking oxygen into the reference gas chamber 43 or sucking oxygen out of the reference gas chamber 43. Thus, the oxygen concentration in the reference gas chamber 43 is adjusted to be within a predetermined oxygen concentration range. The voltage Vref can be measured and the oxygen concentration in the reference gas chamber 43 can be adjusted by the control device 90 of the gas sensor 100 or by connecting another device different from the control device 90 to the sensor element 101.

[0172] When measuring the voltage Vref in the oxygen concentration confirmation process, the pump voltage Vp3 is not applied to the reference gas adjustment pump unit 84. In addition, when measuring the voltage Vref, in order to reduce the measurement error caused by the voltage drop of the outer pump electrode 23 and the reference electrode 42, it is preferable not to control the sensor element 101 so that the current flows through the outer pump electrode 23. Specifically, it is preferable to stop the operation of the main pump unit 21, the auxiliary pump unit 50, and the measurement pump unit 41 (so that the variable power supply 24, 52, 46 does not apply the pump voltage Vp0, Vp1, Vp2). In particular, the value of the pump current Ip0 flowing through the main pump unit 21 is relatively large compared with the pump currents Ip1 and Ip2, so the voltage drop of the outer pump electrode 23 is large. Therefore, it is preferable to stop the operation of at least the main pump unit 21 among the main pump unit 21, the auxiliary pump unit 50, and the measurement pump unit 41.

[0173] In the manufacturing process of the gas sensor 100, it is preferred to further perform a required oxygen amount storage process after performing the oxygen concentration confirmation process, that is, to pre-store the required oxygen amount that should exist in the reference gas chamber 43 when the oxygen concentration in the reference gas in the reference gas chamber 43 is a specified concentration in the storage unit 93. For example, the process is performed as follows. First, the sensor element 101 is maintained at a specified driving temperature (for example, 800°C), and the operation of the main pump unit 21, the auxiliary pump unit 50, the measurement pump unit 41 and the reference gas adjustment pump unit 84 in normal control is stopped. The power supply circuit 85 applies a specified pump voltage Vp3 to the reference gas adjustment pump unit 84 (between the outer pump electrode 23 and the reference electrode 42) to allow the pump current Ip3 to flow, thereby sucking the oxygen present in the reference gas chamber 43 from the reference electrode 42 to the outer pump electrode 23. The circulating pump current Ip3 and time are obtained, and the specified pump voltage Vp3 is continuously applied until the pump current Ip3 is approximately zero. Then, the calculated value is Figure 4 The area S in φ corresponds to the time integral value of the pump current Ip3 (the required current integral value).

[0174] In addition, unlike the above-mentioned oxygen concentration confirmation step, the acquisition of the required oxygen amount (e.g., the required current integral value) is not affected by the gas atmosphere in contact with the outer pump electrode 23. Therefore, it can be performed in the same gas atmosphere (e.g., air) as the above-mentioned oxygen concentration confirmation step, or in a gas atmosphere different therefrom.

[0175] For each gas sensor in the manufactured gas sensor 100, the required oxygen amount (e.g., required current integral value) can be obtained as described above and stored in the storage unit 93 of the gas sensor 100. Alternatively, a representative required oxygen amount (e.g., required current integral value) can be obtained in advance and stored in the storage unit 93 of a plurality of gas sensors 100. For example, the same required oxygen amount (e.g., required current integral value) can be stored in gas sensors 100 of the same structure and gas sensors 100 of the same manufacturing batch. For example, the relationship between the volume of the reference gas chamber 43 and the required current integral value can be obtained or calculated in advance, and the corresponding required current integral values ​​can be stored in the storage unit 93 according to the volume of the reference gas chamber 43 of each gas sensor 100. In this case, the required oxygen amount storage process can be performed before the oxygen concentration confirmation process.

[0176] The control device 90 can perform the above-mentioned oxygen concentration confirmation process in a state where the oxygen concentration of the measured gas is known during the use of the gas sensor 100. For example, in a case where the measured gas is the exhaust gas of an internal combustion engine of an automobile or the like, if the fuel of the internal combustion engine is cut off, the oxygen concentration of the measured gas is deemed to be the same as that of the atmosphere, and therefore, the same oxygen concentration confirmation process as described above can be performed. And, thereafter, the required oxygen amount (for example, the required current integral value) can be obtained as described above, and the required oxygen amount storage process can be performed. In the manufacturing process, that is, if the required oxygen amount storage process is performed in advance before shipment, the regeneration process described later can be performed at any time from the start of use of the gas sensor, which is more preferred.

[0177] [Regeneration Processing]

[0178] In the gas sensor 100, if the oxygen concentration in the reference gas changes due to some reason, the potential (reference potential) of the reference electrode 42 also changes in accordance with the change. As a result, the voltages V0, V1, V2, and Vref in the sensor cells 80, 81, 82, and 83 detected with reference to the reference electrode 42 change. As a result, the detection accuracy of the NOx concentration in the measured gas may be reduced.

[0179] For example, in the present embodiment, the reference gas chamber 43 is a space that is roughly enclosed inside the base portion 102. Therefore, the inflow of gas from the outside of the sensor element 101 into the reference gas chamber 43 and the outflow of gas from the reference gas chamber 43 are both suppressed. However, as described above, in normal control, the voltages V0, V1, V2, and Vref in each sensor unit 80, 81, 82, and 83 are detected. During this voltage measurement, a small current flows in each sensor unit 80, 81, 82, and 83 due to a voltage measurement circuit such as a potentiometer. It can be considered that these currents cause oxygen to be electrochemically sucked into the reference gas chamber 43, or oxygen to be sucked out of the reference gas chamber 43. As a result, the oxygen concentration in the reference gas in the reference gas chamber 43 may change.

[0180] Regarding the gas sensor of the present invention, even if the oxygen concentration in the reference gas changes as described above, the oxygen concentration in the reference gas can be made (returned) to a predetermined concentration by performing a regeneration process. Therefore, it is possible to suppress the reduction in the detection accuracy of the NOx concentration in the measured gas, thereby maintaining high measurement accuracy. The regeneration process performed by the gas sensor of the present invention is described in detail below.

[0181] In the gas sensor 100, the processing unit 94 performs a regeneration process to make (return) the oxygen concentration in the reference gas to a predetermined concentration. The oxygen concentration in the reference gas is maintained at a predetermined concentration by the regeneration process.

[0182] In the regeneration process, the processing unit 94 causes a current to flow between the pump electrode and the reference electrode 42, and oxygen existing in the reference gas chamber 43 is sucked out of the reference gas chamber 43, so that the oxygen existing in the reference gas chamber 43 is zero or substantially zero. Thereafter, the processing unit 94 sucks the required amount of oxygen pre-stored in the storage unit 93 into the reference gas chamber 43. Through this process, the oxygen concentration in the reference gas chamber 43, that is, the oxygen concentration in the reference gas, can be made (returned) to a predetermined concentration.

[0183] That is, during the regeneration process, an oxygen absorption process is performed to absorb the oxygen in the reference gas chamber 43 so that the oxygen present in the reference gas chamber 43 is zero or substantially zero, and then an oxygen absorption process is performed to absorb the required amount of oxygen into the reference gas chamber 43 so that the oxygen concentration in the reference gas chamber 43 returns to the specified concentration.

[0184] The oxygen present in the reference gas chamber 43 is substantially zero, which means, for example, that the oxygen concentration in the reference gas chamber 43 is 2% or less, 1% or less, 0.5% or less, or 0.1% or less of the predetermined concentration, which is close to zero. Alternatively, it means that the amount of oxygen present in the reference gas chamber 43 is 2% or less, 1% or less, 0.5% or less, or 0.1% or less of the required amount of oxygen, which is close to zero, which is based on the required amount of oxygen.

[0185] In the present embodiment, the pump current Ip3 is caused to flow through the reference gas adjustment pump unit 84 (between the outer pump electrode 23 and the reference electrode 42 ) to absorb oxygen from and into the reference gas chamber 43 . Figure 5 This is a flowchart showing an example of the regeneration process.

[0186] When the regeneration process starts, the drive control unit 92 stops the normal control (step S10). Specifically, the voltage V0 is set to the set value V0. SET The pump voltage Vp0 of the main pump unit 21 is feedback-controlled so that the voltage V1 becomes the set value V1 SET The pump voltage Vp1 of the auxiliary pump unit 50 is fed back and controlled so that the voltage V2 becomes the set value V2. SET All pump controls such as the control of feeding back the pump voltage Vp2 of the measurement pump unit 41 in a manner are stopped. That is, the temperature of the sensor element 101 is maintained at a predetermined temperature by the heater 72, and no other control is performed. Therefore, the measurement of the NOx concentration in the measured gas is interrupted during the execution of the regeneration process.

[0187] Next, the processing unit 94 sucks oxygen from the reference gas chamber 43 (step S11). Specifically, for example, the power supply circuit 84 applies a pump voltage Vp3 to the reference gas adjustment pump unit 84 (between the outer pump electrode 23 and the reference electrode 42) to flow the pump current Ip3. The applied pump voltage Vp3 may be constant or may be changed continuously or in stages.

[0188] Next, the processing unit 94 determines whether the oxygen concentration in the reference gas in the reference gas chamber 43 is below a threshold value (step S12). The threshold value can be appropriately determined by a person skilled in the art, and the threshold value of the oxygen concentration in the reference gas chamber 43 can be determined in such a way that the oxygen present in the reference gas chamber 43 is zero or substantially zero. Alternatively, a threshold value can be set for the amount of oxygen present in the reference gas chamber 43.

[0189] In step S12, when the oxygen concentration in the reference gas is higher than the threshold, step S11 is performed. That is, oxygen is then sucked out from the reference gas chamber 43. On the other hand, when the oxygen concentration in the reference gas is below the threshold, the oxygen suction from the reference gas chamber 43 is terminated, and oxygen is sucked into the reference gas chamber 43 (step S13). That is, the oxygen suction process is terminated and the oxygen suction process is started. Specifically, for example, a pump voltage Vp3 having a positive and negative opposite to that of the step S11 is applied to the reference gas adjustment pump unit 84 (between the outer pump electrode 23 and the reference electrode 42), so that the pump current Ip3 flows in a direction of sucking oxygen into the reference gas chamber 43. The pump voltage Vp3 applied in step S13 may be constant, or it may be changed continuously or in stages. In addition, the absolute value of the pump voltage Vp3 applied in step S13 may be the same as or different from the pump voltage Vp3 applied in step S11.

[0190] The processing unit 94 reads the required oxygen amount from the storage unit 93. Then, it is determined whether the oxygen amount inhaled in step S13 has reached the required oxygen amount (step S14). Here, the oxygen amount inhaled refers to the total amount (integrated amount, accumulated amount) of oxygen inhaled from the start of oxygen inhalation into the reference gas chamber 43 to the determination in step S14.

[0191] When the determination in step S14 is performed, if the amount of oxygen (total amount) sucked has not reached the required amount of oxygen, that is, is less than the required amount of oxygen, step S13 is performed. That is, the oxygen is continuously sucked into the reference gas chamber 43. On the other hand, if the amount of oxygen (total amount) sucked has reached the required amount of oxygen, the oxygen is sucked into the reference gas chamber 43 and the normal control is restarted (step S15). And the regeneration process is completed.

[0192] The oxygen absorption process in the regeneration process will be described in more detail. Figure 6 The oxygen absorption process ( Figure 5 Schematic diagram of an example of the time variation of the pump current Ip3 during step S11 in FIG. Figure 6 In the above, the horizontal axis is time (seconds; sec) and the vertical axis is pump current Ip3 (μA). Figure 4 As described above, as the amount of oxygen in the reference gas chamber 43 decreases, the current value of the pump current Ip3 decreases. Figure 6 2 shows that the pump current Ip3 decreases with time (Ip3a>Ip3b>Ip3c). When the oxygen in the reference gas chamber 43 reaches zero or a value close to zero (substantially zero), the pump current Ip3 reaches a sufficiently small value close to zero or zero.

[0193] The processing unit 94 may, for example, apply a predetermined voltage (in this embodiment, the pump voltage Vp3) between the pump electrode (in this embodiment, the outer pump electrode 23) and the reference electrode 42 to flow a current (in this embodiment, the pump current Ip3) to draw oxygen present in the reference gas chamber 43 from the reference gas chamber 43 until the current becomes less than a predetermined value. A person skilled in the art may appropriately set the predetermined value (threshold value A) of the current, for example, it may be set to zero or a value close to zero. If the predetermined value (threshold value A) is set in this way, oxygen can be drawn from the reference gas chamber 43 until the oxygen in the reference gas chamber 43 is substantially zero. As a result, the oxygen concentration in the reference gas in the reference gas chamber 43 can be made (returned to) a predetermined concentration with higher accuracy by the regeneration process. The predetermined value (threshold value A) may be, for example, less than 1.0 μA, less than 0.5 μA, less than 0.25 μA, or less than 0.1 μA.

[0194] In addition, if Figure 6 As shown, as time passes, the amount of change per unit time (time change amount) of the pump current Ip3 becomes smaller. Figure 6 The slope of the curve in becomes smaller. Figure 6 , ΔIp3a>ΔIp3b>ΔIp3c. Therefore, the processing unit 94 may, for example, apply a predetermined voltage (pump voltage Vp3 in the present embodiment) between the pump electrode (the outer pump electrode 23 in the present embodiment) and the reference electrode 42 to flow a current (pump current Ip3 in the present embodiment) to draw oxygen present in the reference gas chamber 43 from the reference gas chamber 43 until the amount of change per unit time of the current (time change) reaches a predetermined value. A person skilled in the art may appropriately set the predetermined value (threshold value B) of the time change of the current, for example, it may be set to zero or a value close to zero. If the predetermined value (threshold value B) is set in this way, oxygen can be drawn from the reference gas chamber 43 until the oxygen in the reference gas chamber 43 is substantially zero. As a result, the oxygen concentration in the reference gas in the reference gas chamber 43 can be made (returned to) a predetermined concentration with higher accuracy by the regeneration process. The predetermined value (threshold value B) of the time variation of the current may be, for example, 0.1 μA / s or less, 0.05 μA / s or less, 0.02 μA / s or less, or 0.01 μA / s or less.

[0195] Figure 7 1 is a flowchart showing a specific example of the oxygen absorption process and the regeneration process of the oxygen absorption process. Figure 7 In, with Figure 5 The same steps are denoted by the same reference numerals, and thus description thereof will be omitted. In addition, a specific example of the oxygen intake process (steps S14a and S14b) will be described below.

[0196] exist Figure 7 In the example, as the oxygen absorption process, the processing unit 94 applies a specified pump voltage Vp3 between the outer pump electrode 23 and the reference electrode 42 to allow the pump current Ip3 to flow, thereby absorbing the oxygen present in the reference gas chamber 43 from the reference gas chamber 43 until the pump current Ip3 becomes below a specified value (threshold A).

[0197] In this case, the processing unit 94 determines whether the current value of the pump current Ip3 for sucking oxygen from the reference gas chamber 43 is less than a predetermined value (threshold value A) (step S12a). In step S12a, if the current value of the pump current Ip3 is greater than the threshold value A, step S11 is performed. That is, oxygen is sucked from the reference gas chamber 43 next. On the other hand, if the current value of the pump current Ip3 is less than the threshold value A, the suction of oxygen from the reference gas chamber 43 is terminated, and oxygen is sucked into the reference gas chamber 43 (step S13).

[0198] in addition, Figure 8 The oxygen inhalation treatment is shown Figure 7 A flowchart of a specific example of the regeneration process for different situations. Figure 8 In, with Figure 7 The same steps are marked with the same symbols.

[0199] exist Figure 8 In the example, as the oxygen absorption processing, the processing unit 94 applies a specified pump voltage Vp3 between the outer pump electrode 23 and the reference electrode 42 to allow the pump current Ip3 to flow, thereby absorbing the oxygen present in the reference gas chamber 43 from the reference gas chamber 43 until the change in the pump current Ip3 per unit time (time change) reaches a specified value (threshold B).

[0200] In this case, the processing unit 94 determines whether the time variation of the current value of the pump current Ip3 for sucking oxygen from the reference gas chamber 43 is less than a predetermined value (threshold value B) (step S12b). In step S12b, if the time variation of the current value of the pump current Ip3 is greater than the threshold value B, step S11 is performed. That is, oxygen is continuously sucked from the reference gas chamber 43. On the other hand, if the time variation of the current value of the pump current Ip3 is less than the threshold value B, the suction of oxygen from the reference gas chamber 43 is terminated, and oxygen is sucked into the reference gas chamber 43 (step S13).

[0201] Next, Figure 7 and Figure 8The oxygen intake process in the example of is described. In this case, the storage unit 93 pre-stores the above-mentioned required current integral value. The required current integral value is, for example, the integral value of the pump current Ip3 flowing between the outer pump electrode 23 and the reference electrode 42 when the pump current Ip3 flows between the outer pump electrode 23 and the reference electrode 42 to move the required amount of oxygen. And, as the oxygen intake process, the processing unit 94 flows the current until the integral value of the pump current Ip3 flowing between the outer pump electrode 23 and the reference electrode 42 reaches the required current integral value, thereby taking the required amount of oxygen into the reference gas chamber 43.

[0202] In this case, the processing unit 94 counts the current value of the pump current Ip3 for sucking oxygen into the reference gas chamber 43 and the time thereof, and calculates the current integral value from when the pump current Ip3 starts to flow to the current moment (step S14a). For example, in the case where the pump current Ip3 is measured periodically, the values ​​obtained by multiplying the pump current Ip3 during the measurement by the measurement period T can be sequentially added to calculate the current integral value. The processing unit 94 reads the required current integral value from the storage unit 93. And, it is determined whether the calculated current integral value has reached the required current integral value (step S14b). When the determination of step S14b is performed, if the current integral value has not reached the required current integral value, that is, is less than the required current integral value, step S13 is performed. That is, oxygen continues to be sucked into the reference gas chamber 43. On the other hand, if the current integral value has reached the required current integral value, oxygen is sucked into the reference gas chamber 43 and the normal control is restarted (step S15).

[0203] As described above, in the regeneration process, first, an oxygen absorption process is performed to make the oxygen present in the reference gas chamber 43 zero or substantially zero. And, thereafter, the required amount of oxygen pre-stored in the storage unit 93 is absorbed into the reference gas chamber 43. For example, the pump current Ip3 is circulated until the required current integral value is reached. Such a regeneration process is not affected by the composition of the measured gas (oxygen concentration, NOx concentration, etc.). Therefore, it can be performed regardless of the oxygen concentration and NOx concentration in the measured gas. In addition, it is not necessary to know the oxygen concentration and NOx concentration in the measured gas.

[0204] The regeneration process can be performed at any time. For example, it can be performed at specified intervals (every 50 hours, every 100 hours, etc.). In addition, for example, it can be performed when the operator inputs a start instruction for the regeneration process. In addition, for example, it can be performed at a specified event such as when the gas sensor 100 is started.

[0205] In addition, the volume of the reference gas chamber 43 is equivalent to the volume of the reference gas that can exist in the reference gas chamber 43. Therefore, when the amount of oxygen in the reference gas chamber 43 changes during use of the gas sensor 100, the larger the volume of the reference gas chamber 43, the smaller the change in the oxygen concentration in the reference gas caused by the change in the amount of oxygen in the reference gas chamber 43. The smaller the volume of the reference gas chamber 43, the larger the change in the oxygen concentration in the reference gas caused by the change in the amount of oxygen in the reference gas chamber 43. Therefore, for example, the cycle of performing the regeneration process can be determined based on the volume of the reference gas chamber 43. The cycle of performing the regeneration process can be determined relative to the accumulation of the time (accumulated driving time) of driving the gas sensor 100. For example, when the volume of the reference gas chamber 43 is large, the cycle of performing the regeneration process can be lengthened (the interval of performing the regeneration process can be lengthened). When the volume of the reference gas chamber 43 is small, the cycle of performing the regeneration process can be shortened (the interval of performing the regeneration process can be shortened).

[0206] The cycle of the regeneration process may be appropriately determined according to the purpose of use of the gas sensor 100, the required accuracy, the structure of the sensor element 101, etc. For example, the cycle of the regeneration process may be set to a value that is substantially proportional to the volume of the reference gas chamber 43. For example, the cycle may be determined as follows.

[0207] The volume of the reference gas chamber 43 is 0.036 mm 3 In the case of , regeneration is performed every 100 hours of cumulative driving time;

[0208] The volume of the reference gas chamber 43 is 0.06 mm 3 In the case of , regeneration is performed every 200 hours of cumulative driving time;

[0209] The volume of the reference gas chamber 43 is 0.26 mm 3 In the case of , regeneration is performed every 800 hours of cumulative driving time;

[0210] The volume of the reference gas chamber 43 is 0.50 mm 3 In the case of , the regeneration process is performed every 1500 hours of cumulative driving time.

[0211] The gas sensor 100 of the present embodiment can be regenerated as described above, so that the oxygen concentration in the reference gas in the reference gas chamber 43 is (returned to) a specified concentration. The regeneration process is not affected by the composition of the measured gas (oxygen concentration, NOx concentration, etc.). Therefore, unlike the oxygen concentration confirmation process in the above-mentioned manufacturing process, it is not necessary to know the oxygen concentration in the measured gas. Therefore, it is not limited to the case where the oxygen concentration and NOx concentration in the measured gas are known. In addition, regardless of their concentrations, the oxygen concentration in the reference gas in the reference gas chamber 43 can be (returned to) a specified concentration at any time during the use of the gas sensor 100. As a result, it is possible to suppress the reduction in the detection accuracy of the NOx concentration in the measured gas, thereby suppressing high measurement accuracy.

[0212] As described above, as an example of an embodiment of the present invention, the gas sensor 100 for detecting the NOx concentration in the measured gas is shown, however, the present invention is not limited to this form. In the present invention, various forms of gas sensors may be included as long as the purpose of the present invention is achieved to suppress the decrease in the detection accuracy of the measured gas in the measured gas and maintain high detection accuracy.

[0213] In the above-mentioned embodiment, when the oxygen concentration in the reference gas in the reference gas chamber 43 is a predetermined concentration, the pump current Ip3 is caused to flow through the reference gas adjustment pump unit 84 (between the outer pump electrode 23 and the reference electrode 42) so that the oxygen in the reference gas chamber 43 is substantially zero, thereby obtaining the required current integral value, but the present invention is not limited thereto. When obtaining the required current integral value, it is sufficient to cause the current to flow between the pump electrode disposed at a position different from that in the reference gas chamber 43 and the reference electrode 43. For example, the required current integral value can be obtained by causing the current to flow between the inner main pump electrode 22 and the reference electrode 42. It can also be obtained by causing the current to flow between the auxiliary pump electrode 51 and the reference electrode 42. It can also be obtained by causing the current to flow between the measuring electrode 44 and the reference electrode 42. The required current integral value is equivalent to the amount of oxygen that should exist in the reference gas chamber 43, so the required current integral value obtained when any pump electrode is used is substantially the same.

[0214] In addition, the required current integral value can also be obtained, for example, as follows. First, a pump voltage is applied between the pump electrode (the outer pump electrode 23, the inner main pump electrode 22, the auxiliary pump electrode 51, or the measuring electrode 44) and the reference electrode 42 in the direction of sucking out the oxygen in the reference gas chamber 43, and a pump current is passed to suck out the oxygen in the reference gas chamber 43 until the pump current becomes zero or substantially zero. Thereafter, oxygen is sucked into the reference gas chamber 43 in a state where the outer pump electrode 23 of the sensor element 101 is in contact with a gas (e.g., the atmosphere) having a known oxygen concentration. That is, a predetermined pump voltage is applied between the pump electrode and the reference electrode 42 in the direction of sucking out the oxygen in the reference gas chamber 43, and a pump current is passed. The voltage Vref of the sensor unit 83 (between the outer pump electrode 23 and the reference electrode 42) is measured, and based on the known oxygen concentration and the voltage Vref, a pump current is passed to suck out oxygen into the reference gas chamber 43 until the oxygen concentration in the reference gas chamber 43 reaches a predetermined concentration. By calculating the integral value of the pump current at this time, the required current integral value can be obtained. When oxygen is taken into the reference gas chamber 43 while measuring the voltage Vref of the sensor cell 83 in this manner, it is preferable to use the inner main pump electrode 22 , the auxiliary pump electrode 51 , or the measuring electrode 44 as the pump electrode.

[0215] In the above embodiment, the outer pump electrode 23 is used as the pump electrode in each of the steps of obtaining the required current integral value, oxygen absorption process in the regeneration process, and oxygen absorption process in the regeneration process, but the present invention is not limited thereto. In any one or more of the above steps, the current may be passed between the pump electrode and the reference electrode 42 different from those in other steps. The electrode used as the pump electrode may be different in all the steps.

[0216] In the above-mentioned embodiment, in step S10 of the regeneration process, all pump controls are stopped, but the present invention is not limited thereto. The drive control unit 92 stops at least one or more pump units among the main pump unit 21, the auxiliary pump unit 50, and the measurement pump unit 41. In the regeneration process, there is a step of sucking oxygen from the reference gas chamber 43 in such a way that the oxygen in the reference gas chamber 43 is substantially zero, and therefore, it is preferable to stop the pump control of the reference potential of the reference electrode 42. It is preferable to stop all pump controls as in the above-mentioned embodiment.

[0217] In addition, in the above-mentioned embodiment, in step S11 or step S13 of the regeneration process, the pump voltage Vp3 is applied to the reference gas adjustment pump unit 84 to make the pump current Ip3 flow, but the present invention is not limited to this. For example, the processing unit 94 can make the pump current Ip3 flow by using a current source. In addition, in normal control, the pump voltage is applied to each pump unit 21, 50, 41 (, 84) to make the pump current flow, but the present invention is not limited to this. In one or more of the above-mentioned pump units 21, 50, 41 (, 84), the current can be controlled to flow using a current source.

[0218] In the above embodiment, the reference gas chamber 43 is a space enclosed inside the base 102, but the present invention is not limited thereto. For example, the reference gas chamber 43 may be entirely or partially filled with a porous body such as alumina.

[0219] Fig. 9 It is a schematic vertical cross-sectional view in the length direction of a sensor element 201 of a modified example in which the reference gas chamber is filled with a porous body. In the sensor element 201, a reference gas chamber 243 is provided between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4 in a manner that covers the reference electrode 42. The reference gas chamber 243 is enclosed inside the base portion 102 and is filled with a porous body. As described above, the volume of the reference gas chamber 43 refers to: the volume of the reference gas that can exist in the reference gas chamber 43. Therefore, in the case of such a reference gas chamber 243, the volume of the reference gas chamber 243 is a value obtained by taking into account the size of the reference gas chamber 243 and the porosity of the porous body filled inside. In the sensor element 201, the volume of the reference gas chamber 243 is approximately the total volume of the pores in the reference gas chamber 243. Fig. 9 The other components of the sensor element 201 are Figure 2 The sensor elements described in are substantially the same.

[0220] In addition, the sensor element may further include a pressure release hole. Fig.10 : is a schematic diagram of a vertical cross section in the longitudinal direction of a sensor element 301 of a modified example having a pressure release hole. In the sensor element 301, a pressure release space 75b is formed at a position of the first solid electrolyte layer 4 that is open on the rear end surface of the sensor element 301, which is rearward of the reference gas chamber 43. In addition, a pressure release hole 75a is formed in a manner that connects the upper surface of the heater insulating layer 74 with the pressure release space 75b. The pressure release hole 75a is formed as a hole that penetrates the third substrate layer 3. The pressure release hole 75a plays a role in alleviating the internal pressure increase that accompanies the temperature increase in the heater insulating layer 74. The pressure release space 75b and the pressure release hole 75a are not connected to the reference gas chamber 43. Fig.10The other components of the sensor element 301 are Figure 2 The sensor elements described in are substantially the same.

[0221] In the gas sensor 100 of the above embodiment, the sensor element 101 has the following structure: Figure 2 As shown in the figure, there are three internal cavities, namely, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61, and the inner main pump electrode 22, the auxiliary pump electrode 51, and the measuring electrode 44 are respectively arranged in each internal cavity, but it is not limited to this. For example, it can also have a structure as follows: there are two internal cavities, namely, the first internal cavity 20 and the second internal cavity 40, the inner main pump electrode 22 is arranged in the first internal cavity 20, and the auxiliary pump electrode 51 and the measuring electrode 44 are arranged in the second internal cavity 40. In this case, for example, as a diffusion rate control unit between the auxiliary pump electrode 51 and the measuring electrode 44, a porous body protection layer covering the measuring electrode 44 can be formed.

[0222] In the above embodiment, the gas sensor 100 detects the NOx concentration in the measured gas, but the measured gas is not limited to NOx. The sensor element of the gas sensor 100 only needs to be a structure using an oxygen ion conductive solid electrolyte. The measured gas can be, for example, other oxide gases (such as carbon dioxide CO2, water H2O, etc.) other than oxygen O2 or NOx. Alternatively, it can be a non-oxide gas such as ammonia NH3. In the case where the measured gas is a non-oxide gas, the non-oxide gas is converted into an oxide gas (for example, in the case of ammonia NH3, it is converted into NO), and the measured gas containing the converted oxide gas is introduced into the third internal cavity 61. At the measuring electrode 44, the converted oxide gas in the measured gas is reduced to generate oxygen. The generated oxygen can be obtained in the form of the pump current Ip2 in the measuring pump unit 41 to detect the measured gas. The conversion of the non-oxide gas to the oxide gas can be performed by at least one of the inner main pump electrode 22 and the auxiliary pump electrode 51 acting as a catalyst.

[0223] Example

[0224] Hereinafter, the present invention will be further described using examples. In addition, the present invention is not limited to the following examples.

[0225] [Example 1]

[0226] According to the manufacturing method of the gas sensor 100, the Figures 1 to 3 The gas sensor 100 shown in FIG. 1 is set as Example 1. In Example 1, it is set that the control device 90 follows Figure 8The regeneration process is performed according to the flowchart of . After the driving time of the gas sensor 100 has been 200 hours since the start of driving, the regeneration process is performed. In the regeneration process, the threshold value B of oxygen absorption is set to 0.05 μA / s. In addition, the required current integral value of oxygen absorption is 30 μA·s.

[0227] [Comparative Example 1]

[0228] The same method as in Example 1 was adopted except that the control device 90 was set not to perform the regeneration process.

[0229] [NOx output stability investigation]

[0230] For the gas sensors of Example 1 and Comparative Example 1 produced, the stability of NOx output was investigated as follows.

[0231] First, the gas sensors of Example 1 and Comparative Example 1 were installed in a gas chamber. Then, each gas sensor was driven while maintaining the model gas atmosphere in the gas chamber, and the NOx output was continuously measured for a long time. The gas atmosphere of the model gas was set to: NO = 0 ppm, O2 = 0%, H2O = 3%, N2 (balance). The units of concentration were all volume-based. The measurement lasted for 400 hours.

[0232] Fig.11 This is a graph showing the results of a study on the stability of NOx output. Fig.11 In the figure, the horizontal axis is the measurement time (hours; H), and the vertical axis is the NOx output change (ppm). The NOx output change represents the deviation of the NOx output from the value that should be output according to the NOx concentration. In addition, in the above-mentioned NOx output stability investigation, the NO concentration in the model gas is 0 ppm, so the value of the NOx output that should be output according to the NOx concentration is 0 ppm. Therefore, the value of the NOx output and the NOx output change result are the same numerical value.

[0233] like Fig.11 As shown, in both Example 1 and Comparative Example 1, the NOx output gradually changes over time. In Example 1, it can be confirmed that when the regeneration process is performed, the NOx output change amount is substantially zero. As a result, compared with Comparative Example 1, it can be confirmed that the NOx output change amount can be suppressed to a small level for a long time. In this way, the NOx output change amount can be returned to substantially zero every time the regeneration process is performed. As a result, it can be considered that the detection accuracy of the measured object gas can be suppressed from decreasing, thereby maintaining high detection accuracy.

[0234] As described above, according to the present invention, the oxygen concentration in the reference gas around the reference electrode can be made (returned) to a predetermined concentration at any time during the use of the gas sensor, regardless of the oxygen concentration, without being limited to the case where the oxygen concentration in the measured gas is known. As a result, the detection accuracy of the measured gas can be suppressed from being reduced, thereby maintaining high detection accuracy.

[0235] Explanation of symbols

[0236] 1. First substrate layer

[0237] 2 Second substrate layer

[0238] 3 Third substrate layer

[0239] 4 First solid electrolyte layer

[0240] 5 Isolation layer

[0241] 6 Second solid electrolyte layer

[0242] 10 Gas inlet

[0243] 11. First diffusion rate control unit

[0244] 12 Buffer Space

[0245] 13. Second diffusion rate control unit

[0246] 15 Cavity for the gas to be measured

[0247] 20 first inner cavity

[0248] 21 Main pump unit

[0249] 22 Inner main pump electrode

[0250] 22a Top electrode portion (of the inner main pump electrode)

[0251] 22b Bottom electrode portion (of the inner main pump electrode)

[0252] 23 Outer pump electrode

[0253] 24 Variable power supply (of main pump unit)

[0254] 30 Third diffusion rate control unit

[0255] 40 Second internal cavity

[0256] 41 Measurement pump unit

[0257] 42 Reference electrode

[0258] 43, 243 Reference gas chamber

[0259] 44 Measuring electrode

[0260] 46 Variable power supply (of the measuring pump unit)

[0261] 50 Auxiliary pump unit

[0262] 51 Auxiliary pump electrode

[0263] 51a Top electrode portion (of auxiliary pump electrode)

[0264] 51b Bottom electrode portion (auxiliary pump electrode)

[0265] 52 Variable power supply (for auxiliary pump unit)

[0266] 60 Fourth diffusion rate control unit

[0267] 61 Third internal cavity

[0268] 70 Heater section

[0269] 71 Heater connector electrode

[0270] 72 Heater

[0271] 73 Through Holes

[0272] 74 Heater Insulator

[0273] 75a Pressure relief hole

[0274] 75b Pressure relief space

[0275] 76 Heater lead

[0276] 80 Main pump control oxygen partial pressure detection sensor unit

[0277] 81 Auxiliary pump control oxygen partial pressure detection sensor unit

[0278] 82 Measurement pump control oxygen partial pressure detection sensor unit

[0279] 83 Sensor unit

[0280] 84 Reference gas adjustment pump unit

[0281] 85 Power Circuit

[0282] 90 Control Device

[0283] 91 Control Department

[0284] 92 Drive control unit

[0285] 93 Storage

[0286] 94 Processing Department

[0287] 100 Gas Sensors

[0288] 101, 201, 301 sensor elements

[0289] 102 Base part

Claims

1. A gas sensor for detecting a gas to be measured in a gas to be measured, comprising a sensor element and a control device for controlling the sensor element, The sensor element comprises: A long plate-shaped substrate portion including an oxygen ion conductive solid electrolyte layer; a measured gas flow cavity, the measured gas flow cavity being formed from one end portion in the length direction of the base portion, for introducing and flowing the measured gas; a reference gas chamber formed inside the base portion in a manner isolated from the measured gas flow cavity and sealed inside the base portion; A reference electrode, the reference electrode is disposed in the reference gas chamber; as well as a pump electrode disposed in a position different from that in the reference gas chamber, The control device comprises: a storage unit that stores in advance a required amount of oxygen that should exist in the reference gas chamber when the oxygen concentration in the reference gas in the reference gas chamber is a predetermined concentration; as well as A processing unit performs a regeneration process, that is, causes an electric current to flow between the pump electrode and the reference electrode to absorb oxygen existing in the reference gas chamber from the reference gas chamber, and then absorbs the required amount of oxygen pre-stored in the storage unit into the reference gas chamber.

2. The gas sensor according to claim 1, characterized in that The storage unit stores in advance, as the required oxygen amount, a required current integral value of the current flowing between the pump electrode and the reference electrode when the current is caused to flow between the pump electrode and the reference electrode to transfer the required oxygen amount. The processing unit absorbs oxygen present in the reference gas chamber from the reference gas chamber during the regeneration process, and then allows current to flow until the integral value of the current flowing between the pump electrode and the reference electrode reaches the required current integral value, thereby sucking the required amount of oxygen into the reference gas chamber.

3. The gas sensor according to claim 1, characterized in that: The storage unit stores in advance, as the required oxygen amount, a time required for causing a predetermined current to flow between the pump electrode and the reference electrode to transfer the required oxygen amount. The processing unit absorbs oxygen existing in the reference gas chamber from the reference gas chamber during the regeneration process, and then causes the specified current to flow between the pump electrode and the reference electrode for the required time to absorb the required amount of oxygen into the reference gas chamber.

4. The gas sensor according to claim 1, characterized in that: The storage unit stores in advance, as the required oxygen amount, a required current value when a current is passed between the pump electrode and the reference electrode for a predetermined time to transfer the required oxygen amount. The processing unit absorbs oxygen present in the reference gas chamber from the reference gas chamber during the regeneration process, and then causes the required current value to flow between the pump electrode and the reference electrode for the specified time to absorb the required amount of oxygen into the reference gas chamber.

5. The gas sensor according to claim 1, characterized in that: The processing unit applies a predetermined voltage between the pump electrode and the reference electrode to flow a current during the regeneration process, thereby sucking oxygen present in the reference gas chamber out of the reference gas chamber until the current becomes equal to or less than a predetermined value.

6. The gas sensor according to claim 1, characterized in that The processing unit applies a predetermined voltage between the pump electrode and the reference electrode to flow current during the regeneration process, thereby sucking oxygen present in the reference gas chamber out of the reference gas chamber until a change in the current per unit time becomes equal to or less than a predetermined value.

7. The gas sensor according to claim 1, characterized in that: A cycle for performing the regeneration process is determined based on the volume of the reference gas chamber.

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