JP4283686B2 - Gas sensor element and control method and manufacturing method of gas sensor element. - Google Patents

Description

  The present invention relates to a gas sensor element used for an exhaust system of an internal combustion engine for automobiles and the like and used for detecting a nitrogen oxide (NOx) concentration in a gas to be measured, and a control method and a manufacturing method of the gas sensor element.

Air pollution caused by exhaust gas discharged from an internal combustion engine for automobiles has become a big problem in modern society, and purification standards and regulations for harmful substances in exhaust gas are becoming stricter year by year. Examples of means for reducing harmful components in exhaust gas include a system that suppresses the generation of harmful components by engine combustion control and a system that purifies harmful components using a catalytic converter. If a certain nitrogen oxide (NOx) density | concentration is detected and a detection result is fed back to these systems, it will be thought that exhaust gas purification can be performed more efficiently. From such a background, a gas sensor element capable of accurately detecting the NOx concentration in exhaust gas has been demanded, and various configurations have been proposed so far (for example, Patent Document 1).
Japanese Patent No. 2885336

  By the way, as a well-known gas sensor element, there is a laminated type gas sensor element using an oxygen ion conductive solid electrolyte. As shown in FIG. 12, the gas sensor element 1 has an internal space 7 formed between the solid electrolyte body 51 and the solid electrolyte body 52, and the porous protective layer 12 and the pinhole 11 are passed through the internal space 7. An exhaust gas that is a gas to be measured is introduced. The internal space 7 is partitioned into a first internal space 7a and a second internal space 7b. On the first internal space 7a side, an oxygen pump cell 2 comprising a solid electrolyte body 52 and electrodes 2b and 2a on the upper and lower surfaces thereof is provided. Has been placed. By applying a voltage to the oxygen pump cell 2, oxygen in the first internal space 7a can be pumped outside the element, or oxygen outside the element can be pumped into the first internal space 7a.

  On the first internal space 7a side, there is also provided an oxygen monitor cell 3 comprising a solid electrolyte body 51 and electrodes 3a and 3b on the upper and lower surfaces thereof and capable of detecting the oxygen concentration in the first internal space 7a. The oxygen pump cell 2 is feedback-controlled so that the oxygen concentration in the first internal space 7a detected by the oxygen monitor cell 3 is constant. On the other hand, on the second internal space 7b side, a sensor cell 4 including a solid electrolyte body 51 and electrodes 4a and 4b on the upper and lower surfaces thereof is provided, and configured to measure oxygen ions generated by decomposition of NOx. ing.

  As described above, since the oxygen concentration in the first internal space 7a is controlled to be constant, the oxygen concentration in the second internal space 7b is also constant. Therefore, the amount of oxygen ions moving through the sensor cell 4, that is, the magnitude of the oxygen ion current in the sensor cell 4 corresponds to the NOx concentration. Thereby, it is possible to measure the exact NOx concentration regardless of the increase or decrease of the oxygen concentration in the exhaust gas. In the figure, 61 and 62 are spacers, 81 is a reference gas space, and 9 is a heater.

  Here, in the gas sensor element 1 configured as described above, rhodium (Rh) is used as a metal component in the electrode 4a on the second internal space 7b side of the sensor cell 4 that detects the NOx concentration in order to promote reduction and decomposition of NOx. The containing cermet electrode is preferably used.

  However, when the present inventors conducted an endurance test of the gas sensor element 1 having the above-described configuration, it has been found that the NOx decomposition activity of the electrode 4a of the sensor cell 4 gradually decreases during long-term operation. For this reason, the oxygen ion current in the sensor cell 4 does not accurately reflect the NOx concentration, and there is a problem that the detection accuracy deteriorates.

  The present invention has been made in view of such conventional problems, and can maintain the NOx decomposition activity of the electrode 4a of the sensor cell 4 and accurately detect the concentration of a specific gas component such as NOx over a long period of time. Is to provide.

The gas sensor element according to claim 1 of the present invention includes an internal space into which a measurement gas is introduced under a predetermined diffusion resistance,
On the surface of an oxygen ion conductive solid electrolyte body, the electrode has a pair of electrodes provided so that one electrode faces the internal space, and oxygen is introduced into the internal space by energizing the pair of electrodes or An oxygen pump cell that discharges and adjusts the oxygen concentration in the internal space;
On the surface of an oxygen ion conductive solid electrolyte body, there is a sensor cell having a pair of electrodes provided so that one electrode faces the internal space and detecting the concentration of a specific gas component in the gas to be measured . Also,
During the measurement of the specific gas component concentration, the oxygen concentration in the internal space is maintained at a low concentration, and oxygen is introduced into the internal space at a specific timing except during the measurement of the specific gas component concentration, and the internal space of the sensor cell is introduced. Control means is provided for performing control to restore the activity of the electrode facing the internal space of the sensor cell by exposing the facing electrode to an oxidizing atmosphere.
Specifically, when the gas to be measured is exhaust gas of an internal combustion engine, the control means stops the operation of at least one of the oxygen pump cell and the sensor cell when the exhaust gas is in a lean state. Control is performed such that oxygen is introduced into the internal space, and the electrode facing the internal space of the sensor cell is exposed to an oxidizing atmosphere.
In the invention of claim 2, the gas sensor element has a heater for heating the element. Specifically, the control means uses the gas to be measured as an exhaust gas of the internal combustion engine and stops the internal combustion engine when the internal combustion engine is stopped. Control of introducing oxygen into the internal space and exposing the electrode facing the internal space of the sensor cell to an oxidizing atmosphere by stopping the operation of at least one of the oxygen pump cell and the sensor cell while the heater is energized I do.

  The decrease in the activity of the sensor cell electrode is considered to be due to a decrease in surface area due to aggregation of metal components contained in the electrode. The control means of the present invention performs control to expose the sensor cell electrode to an oxidizing atmosphere, and oxidizes a part of the metal component. It is considered that the activity of the sensor cell electrode is recovered because the volume expansion due to oxidation eliminates aggregation of metal components and increases the surface area. Therefore, high detection accuracy can be maintained over a long period of time.

In the invention of claim 3, the internal space into which the gas to be measured is introduced under a predetermined diffusion resistance;
On the surface of an oxygen ion conductive solid electrolyte body, the electrode has a pair of electrodes provided so that one electrode faces the internal space, and oxygen is introduced into the internal space by energizing the pair of electrodes or An oxygen pump cell that discharges and adjusts the oxygen concentration in the internal space;
On the surface of an oxygen ion conductive solid electrolyte body, there is a sensor cell having a pair of electrodes provided so that one electrode faces the internal space and detecting the concentration of a specific gas component in the gas to be measured For gas sensor element,
During the measurement of the specific gas component concentration, the oxygen concentration in the internal space is maintained at a low concentration, and oxygen is introduced into the internal space at a specific timing except during the measurement of the specific gas component concentration, and the internal space of the sensor cell is introduced. Control means is provided for performing control to restore the activity of the electrode facing the internal space of the sensor cell by exposing the facing electrode to an oxidizing atmosphere.
The control means introduces oxygen into the internal space by flowing a direct current through at least one of the oxygen pump cell and the sensor cell so that oxygen is pumped to the internal space side, and Control is performed to expose the electrode facing the space to an oxidizing atmosphere.

By controlling the direction of voltage application to the oxygen pump cell or the sensor cell, oxygen can be introduced into the internal space. Therefore, the same effect of recovering the activity by exposing the sensor cell electrode to an oxidizing atmosphere can be obtained.

In the invention of claim 4, the electrode facing the internal space of the sensor cell is a cermet electrode containing rhodium.

The decrease in the activity of the electrode facing the internal space of the sensor cell is particularly likely to occur, for example, in an electrode containing rhodium used for detecting NOx or the like. Therefore, it is effective to provide the control means of the present invention in the gas sensor element in which the sensor cell electrode is a cermet electrode containing rhodium, and a high-performance and highly durable gas sensor element can be realized.

According to a fifth aspect of the present invention, in the structure of any one of the first to fourth aspects, a pair of electrodes provided on the surface of the oxygen ion conductive solid electrolyte body so that one electrode faces the internal space is provided. a, Ru provided an oxygen monitor cell for detecting the oxygen concentration in the internal space. 3. The oxygen pump cell according to claim 1, wherein the gas to be measured is exhaust gas of the internal combustion engine, wherein the control means is in a heater energized state when the exhaust gas is in a lean state or when the internal combustion engine is stopped. By stopping the operation of at least one of the sensor cell and the oxygen monitor cell, oxygen can be introduced into the internal space. Therefore, the same effect of recovering the activity by exposing the sensor cell electrode to an oxidizing atmosphere can be obtained.

Also in the configuration of claim 3 , at this time, the control means operates at least one of the oxygen pump cell, the sensor cell, and the oxygen monitor cell so as to introduce oxygen into the internal space. There line control exposing the electrode facing the interior space to an oxidizing atmosphere, similar effects to restore activity.

  In the configuration having the oxygen monitor cell, oxygen can be introduced into the internal space using any one of the oxygen pump cell, sensor cell, and oxygen monitor cell, and the sensor cell electrode is exposed to an oxidizing atmosphere to restore activity. Similar effects can be obtained.

According to a sixth aspect of the present invention, the control means performs the control of exposing the electrode facing the internal space of the sensor cell to an oxidizing atmosphere in a state where the temperature of the gas sensor element is 400 ° C. or higher. When the treatment for restoring the activity of the sensor cell electrode is performed in a state where the temperature of the gas sensor element is high, the oxidation of the metal component is promoted, which is more effective.

In the invention of claim 7, the specific gas component is nitrogen oxide. The present invention is suitably applied to a gas sensor element for detecting a nitrogen oxide concentration. In particular, when the electrode facing the internal space of the sensor cell is an electrode containing rhodium, by providing the control means, the nitrogen oxide concentration in the measured gas such as exhaust gas can be accurately determined over a long period of time. Can be detected.

Claim 8 of the present invention is an invention of a gas sensor element control method, wherein an internal space into which a gas to be measured is introduced under a predetermined diffusion resistance,
On the surface of an oxygen ion conductive solid electrolyte body, the electrode has a pair of electrodes provided so that one electrode faces the internal space, and oxygen is introduced into the internal space by energizing the pair of electrodes or An oxygen pump cell that discharges and adjusts the oxygen concentration in the internal space;
On the surface of an oxygen ion conductive solid electrolyte body, there is a sensor cell having a pair of electrodes provided so that one electrode faces the internal space and detecting the concentration of a specific gas component in the gas to be measured Using gas sensor element,
At the time of measuring the specific gas component concentration, the oxygen concentration in the internal space is maintained at a low concentration, and the exhaust gas of the internal combustion engine as the measured gas is in a lean state at a specific timing except at the time of measuring the specific gas component concentration. Sometimes , by stopping the operation of at least one of the oxygen pump cell and the sensor cell, oxygen is introduced into the internal space, and the electrode facing the internal space of the sensor cell is exposed to an oxidizing atmosphere, thereby the sensor cell The control of recovering the activity of the electrode facing the internal space is performed.
In the invention of claim 9, the gas sensor element has a heater for heating the element, and the exhaust gas of the internal combustion engine is used as the gas to be measured.
When the specific gas component concentration is measured, the oxygen concentration of the internal space is maintained at a low concentration, and the oxygen pump cell is in a state where the heater is energized when the internal combustion engine is stopped as a specific timing excluding the specific gas component concentration measurement. And by stopping the operation of at least one of the sensor cells, oxygen is introduced into the internal space, and an electrode facing the internal space of the sensor cell is exposed to an oxidizing atmosphere, so that the internal space of the sensor cell is exposed to the internal space. Control to restore the activity of the facing electrode.
In the control method of claim 10, the gas sensor element is used,
At the time of the specific gas component concentration measurement, the oxygen concentration in the internal space is maintained at a low concentration, and at a specific timing excluding the specific gas component concentration measurement, at least one of the oxygen pump cell and the sensor cell is connected to the internal space side. By introducing a direct current so that oxygen is pumped into the internal space, oxygen is introduced into the internal space, and an electrode facing the internal space of the sensor cell is exposed to an oxidizing atmosphere, whereby the internal space of the sensor cell is exposed to the internal space. Control to restore the activity of the facing electrode.

The decrease in the activity of the sensor cell electrode is considered to be due to a decrease in surface area due to aggregation of metal components contained in the electrode. Therefore, for the gas sensor element having such a configuration, the sensor cell electrode is exposed to an oxidizing atmosphere by a control method according to claims 8 and 9 to oxidize a part of the metal component. It is considered that the activity is restored because the aggregation of the metal component is eliminated by the volume expansion due to oxidation and the surface area is increased. With this control method, high detection accuracy can be maintained over a long period of time.
In the control method of claim 10 , oxygen can be introduced into the internal space by controlling the direction of voltage application to the oxygen pump cell or the sensor cell. Therefore, the same effect of recovering the activity by exposing the sensor cell electrode to an oxidizing atmosphere can be obtained.

In an eleventh aspect of the invention, the electrode facing the internal space of the sensor cell is a cermet electrode containing rhodium.

  The decrease in the activity of the electrode facing the internal space of the sensor cell is particularly likely to occur, for example, in an electrode containing rhodium used for detecting NOx or the like. Therefore, when the control method of the present invention is applied to a gas sensor element in which the sensor cell electrode is a cermet electrode containing rhodium, performance can be effectively improved and durability can be increased.

The control method according to claim 12 , wherein the gas sensor element has a pair of electrodes provided on the surface of an oxygen ion conductive solid electrolyte body so that one electrode faces the internal space, and the internal space. It is assumed that an oxygen monitor cell for detecting the oxygen concentration is provided.

  If the gas sensor element has an oxygen monitor cell, the applied voltage of the oxygen pump cell can be controlled by the signal of the oxygen monitor cell, and the oxygen concentration in the internal space can be controlled to be constant. Even in the configuration having this oxygen monitor cell, by applying oxygen to the internal space and applying a control method in which the sensor cell electrode is exposed to an oxidizing atmosphere, aggregation of metal components in the sensor cell electrode is eliminated, and activity is increased. A similar effect can be obtained.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of the distal end portion of the gas sensor element 1 of the present invention, and FIG. 2 is a schematic exploded view of the distal end portion of the gas sensor element 1 of the present invention. In FIG. 1, the upper half shows a sectional view in the axial direction of the element, and the lower half shows a sectional view taken along line AA. The gas sensor element 1 of the present invention is disposed in the measurement gas existence space and is used for detecting a specific gas component in the measurement gas, here, a nitrogen oxide (NOx) concentration in the exhaust gas. When measuring, the entire element is housed in a cylindrical case (not shown), fixed to the exhaust pipe wall of the internal combustion engine, which is the gas-existing space, and inside the exhaust pipe with the tip shown in the figure protected by a cover body. To be inserted. The rear end portion of the gas sensor element 1 is protected by a cover body and disposed in the atmosphere serving as a reference oxygen concentration gas.

  1 and 2, the gas sensor element 1 includes a sheet-like solid electrolyte body 51 for constituting the oxygen pump cell 2, an oxygen monitor cell 3, a solid electrolyte body 52 for constituting the sensor cell 4, and an internal space 7. A spacer 61 for forming, a sheet-like spacer 62, 63, 64 for forming the reference gas spaces 81, 82, and a heater 9 for heating them are provided. Above the heater 9, the spacer 62, the solid electrolyte body 51, the spacer 61, the solid electrolyte body 52, and the spacers 63 and 64 are laminated in this order.

  The internal space 7 is a chamber into which the measurement gas is introduced from the measurement gas existence space in which the tip of the gas sensor element 1 is arranged, and as shown in FIG. 2, a spacer located between the solid electrolyte bodies 51 and 52 It is formed by punch holes 61 a and 61 b provided in 61. The punched hole 61a and the punched hole 61b are connected by a throttle 61c, and the internal space 7 is pulled out in order from the distal end side (the left side in FIGS. 1 and 2) of the gas sensor element 1 with the throttle 61c as a boundary. A first internal space 7a composed of a hole 61a and a second internal space 7b composed of a punched hole 62b are defined.

  The first internal space 7 a communicates with the measurement gas existing space via the pinhole 11 that penetrates the tip of the solid electrolyte body 52. The pinhole 11 functions as a diffusion resistance means. The size of the pinhole 11 is determined by the diffusion rate of the gas to be measured that passes through the pinhole 11 and is introduced into the first internal space 7a and the second internal space 7b. It sets suitably so that it may become this speed.

  Further, a porous protective layer 12 made of porous alumina or the like is formed on the solid electrolyte body 52 so as to cover the pinhole 11 from the measured gas existence space side, and an electrode located in the internal space 7 Poisoning and clogging of the pinhole 11 are prevented.

  The reference gas spaces 81 and 82 are chambers into which air as a reference oxygen concentration gas having a constant oxygen concentration is introduced. The reference gas space 81 is provided in the spacer 62 stacked above the solid electrolyte body 52, and the reference gas space 82 is provided in the spacer 63 stacked above the solid electrolyte body 52. The hole 63a is formed. The through holes 62a and 63a communicate with the external space where the atmosphere exists through groove-like passage portions 62b and 63b extending in the longitudinal direction of the gas sensor element 1, respectively, and the reference gas space 81 and the like through the passage portions 62b and 63b. Atmosphere is introduced to 82.

  The spacers 61, 62, 63, 64 constituting the internal space 7 and the reference gas spaces 81, 82 are made of an insulating material such as alumina. The solid electrolyte bodies 51 and 52 for constituting the oxygen pump cell 2, the oxygen monitor cell 3 and the sensor cell 4 are made of a solid electrolyte having oxygen ion conductivity such as zirconia and ceria.

  As shown in FIG. 1, the oxygen pump cell 2 includes a solid electrolyte body 51 and a pair of electrodes 2 a and 2 b arranged so as to sandwich the solid electrolyte body 51, and oxygen is introduced into the internal space 7 or the internal space. Oxygen is discharged from 7 to adjust the oxygen concentration in the internal space 7. Of the pair of electrodes 2a and 2b, one electrode 2a is provided in contact with the upper surface of the solid electrolyte body 51 so as to face the first internal space 7a located on the upstream side of the gas flow in the internal space 7. The other electrode 2 b is provided in contact with the lower surface of the solid electrolyte body 51 so as to face the reference gas space 81.

  The sensor cell 4 includes a solid electrolyte body 52 and a pair of electrodes 4a and 4b disposed so as to sandwich the solid electrolyte body 52, and detects a specific gas component concentration, for example, a NOx concentration in the gas to be measured. Of the pair of electrodes 4a and 4b, one electrode 4a is provided in contact with the lower surface of the solid electrolyte body 52 so as to face the second internal space 7b located on the downstream side of the gas flow in the internal space 7. The other electrode 4 b is provided in contact with the upper surface of the solid electrolyte body 52 so as to face the reference gas space 82.

  The oxygen monitor cell 3 includes a solid electrolyte body 52 and a pair of electrodes 3 a and 3 b arranged so as to sandwich the solid electrolyte body 52, and detects the oxygen concentration in the internal space 7. Of the pair of electrodes 3a and 3b, one electrode 3a is provided in contact with the lower surface of the solid electrolyte body 52 so as to face the second internal space 7b, and the other electrode 3b faces the reference gas space 82. Thus, it is provided in contact with the upper surface of the solid electrolyte body 52. Further, when the electrodes 3a and 3b of the oxygen monitor cell 3 and the electrodes 4a and 4b of the sensor cell 4 are substantially in the same position with respect to the introduction direction of the gas to be measured, the electrodes 3a and 4a facing the second internal space 7b This is preferable because the oxygen concentration is almost equal.

  Here, as one of the electrodes 2a and 3a of the oxygen pump cell 2 and the oxygen monitor cell 3, an electrode having a low NOx decomposition activity may be used in order to suppress decomposition of NOx in the gas to be measured. Specifically, a porous cermet electrode containing platinum (Pt) and gold (Au) as main metal components is preferably used. At this time, the content of Au in the metal component is usually preferably about 1 to 10% by weight. The porous cermet electrode is obtained by pasting and firing a metal alloy powder and ceramics such as zirconia and alumina.

  Moreover, in order to decompose | disassemble NOx in to-be-measured gas, it is good to use an electrode with high decomposition activity of NOx for one electrode 4a of the sensor cell 4. Specifically, a porous cermet electrode containing platinum (Pt) and rhodium (Rh) as main metal components is preferably used. At this time, the content of Rh in the metal component is preferably about 10 to 50% by weight. For example, a Pt porous cermet electrode is suitably used for the other electrodes 2b, 3b, and 4b of the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4.

  As shown in FIG. 2, the electrodes of the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4 include leads 2c, 2d, 3c, and the like for taking out electrical signals from these electrodes 2a, 2b, 3a, 3b, 4a, and 4b. 3d, 4c, and 4d are integrally formed. Here, on the upper and lower surfaces of the solid electrolyte bodies 51 and 52, the leads 2c, 2d, 3c, 3d, It is preferable to form an insulating layer (not shown) such as alumina between 4c and 4d.

  The heater 9 is formed by patterning a heater electrode 14 that generates heat by energization on the upper surface of a heater sheet 13 made of an insulating material such as alumina, and alumina for insulation is formed on the upper surface of the heater electrode 14 (the surface on the spacer 62 side). A layer 15 is formed. As the heater electrode 14, a cermet electrode of Pt and ceramics such as alumina is usually used. The heater 9 generates heat by supplying power from the outside to the heater electrode 14, and heats the cells 2, 3, and 4 to the activation temperature.

  As shown in FIG. 2, the heater electrode 14 and the electrodes 2a, 2b, 3a, 3b, 4a, and 4b of the cells 2, 3, and 4 are respectively connected to the leads 2c, 2d, 3c, 3d, 4c, and 4d. And through the through holes SH formed in the solid electrolyte bodies 51 and 52, the spacers 61, 62, 63 and 64, the alumina layer 15 and the heater sheet 13, to the terminal (pad electrode) P of the sensor base. A lead wire is connected to the terminal P through a connector (not shown) by crimping, brazing, or the like, so that signals can be exchanged between the external circuit and each of the cells 2, 3, 4 and the heater 9. .

  A method for manufacturing the gas sensor element 1 having the above configuration will be described. First, a raw sheet made of zirconia or the like for the solid electrolyte bodies 51 and 52 and an alumina raw sheet to be the spacers 61, 62, 63 and 64, the heater sheet 13 and the alumina layer 15 are prepared. These raw sheets can be formed into a sheet shape by a doctor blade method, an extrusion method or the like. Next, electrodes 2 a, 2 b, 3 a, 3 b, 4 a, 4 b, heater electrode 14 are placed at predetermined positions on the raw sheets for the solid electrolyte bodies 51, 52, the raw sheet for the spacer 64, and the raw sheet for the heater sheet 13. The lead portions 2c, 2d, 3c, 3d, 4c, 4d, and terminals P are formed by screen printing or the like. The sheets are laminated in the order shown in FIG. 1 and fired in the air to integrate the elements.

  Next, the operation principle of the gas sensor element 1 having the above configuration will be described. In FIG. 1, the exhaust gas that is the gas to be measured passes through the porous protective layer 12 and the pinhole 11 and is introduced into the first internal space 7a. The amount of gas introduced is determined by the diffusion resistance of the porous protective layer 12 and the pinhole 11. Furthermore, the introduced gas is introduced into the second internal space 7b that communicates with the first internal space 7a via the throttle portion 61c.

  When a voltage is applied to the pair of electrodes 2a and 2b of the oxygen pump cell 2 so that the electrode 2b on the reference gas space 81 side becomes a positive electrode, oxygen in the gas to be measured is formed on the electrode 2a on the first internal space 7a side. It is reduced to oxygen ions and discharged to the electrode 2b side by the pumping action. On the other hand, when a voltage is applied so that the electrode 2a on the first internal space 7a side becomes a positive electrode, oxygen is reduced on the electrode 2b on the reference gas space 81 side to become oxygen ions, and is pumped to the electrode 2a side. be introduced. The oxygen concentration in the internal space 7 can be controlled by this oxygen pump action.

  On the other hand, when a predetermined voltage (for example, 0.40 V) is applied to the pair of electrodes 3a and 3b of the oxygen monitor cell 3 so that the electrode 3b on the reference gas space 82 side becomes a positive electrode, Oxygen in the gas to be measured is reduced on the electrode 3a to become oxygen ions, and is discharged to the electrode 3b side by a pumping action. Here, since the electrode 3a is a Pt—Au cermet electrode that is inactive in decomposing NOx, which is a specific gas component, the oxygen ion current flowing between the electrodes 3a and 3b is caused by the porous protective layer 12, the pinhole 11, It depends on the amount of oxygen that passes through the internal space 7a and the like and reaches the electrode 3a in the second internal space 7b, and does not depend on the amount of NOx. Therefore, if the applied voltage between the electrodes 2a and 2b of the oxygen pump cell 2 is controlled so that the value of the current flowing between the electrodes 3a and 3b becomes a predetermined constant value (for example, 0.2 μA), the second internal space 7b. The oxygen concentration can be controlled to be constant.

  A predetermined voltage (for example, 0.40 V) is applied to the pair of electrodes 4 a and 4 b of the sensor cell 4 so that the electrode 4 b on the reference gas space 82 side becomes a positive electrode. Here, since the electrode 4a is a Pt—Rh cermet electrode that is active in decomposing NOx, which is a specific gas component, oxygen and NOx in the gas to be measured are reduced on the electrode 4a on the second internal space 7b side to reduce oxygen. It becomes ions and is discharged to the electrode 4b side by the pumping action. At this time, as described above, in the present embodiment, the oxygen pump cell 2 is controlled so that the current value between the pair of electrodes 3a and 3b of the oxygen monitor cell 3 becomes a predetermined constant value (for example, 0.2 μA). Therefore, if NOx does not exist in the gas to be measured, the current value between the electrodes 4a and 4b of the sensor cell 4 is also controlled to a constant value (for example, 0.2 μA). On the other hand, if NOx is present in the gas to be measured, the current value increases in accordance with the NOx concentration, so that the NOx concentration in the gas to be measured can be detected.

  FIG. 3A shows the current-voltage characteristics of the sensor cell 4. This is because, under the conditions of NO: 1000 ppm and 500 ppm, O2: 100 ppm, N2: balance gas, the applied voltage of the oxygen pump cell 2 is 0.3 V so that the electrode 2b becomes a positive electrode, and the oxygen monitor cell 3 is stopped (oxygen). Monitor cell 3 current was measured as 0). As shown in FIG. 3A, an oxygen ion current generated by decomposition of NO flows through the sensor cell 4, and the current-voltage characteristics indicate a limit current (state in which the current value is saturated) corresponding to the NOx concentration. Therefore, the operating voltage of the sensor cell 4 is set to a voltage at which the sensor cell current becomes the limit current (0.4 V in this embodiment), and the NOx concentration is measured by measuring the sensor cell current value (limit current value) at this time. Can do.

  However, when the gas sensor element 1 was installed in the engine exhaust pipe and an endurance test was performed for a travel distance of 100,000 km, it was found that the current-voltage characteristics of the sensor cell 4 changed. FIG. 3B shows the sensor cell current-voltage characteristics after durability. Compared to FIG. 3A before durability, it is found that the resistance value in the current increase region (region on the lower voltage side than the limit current region) is increased, and the NOx decomposition activity of the electrode 4a of the sensor cell 4 is decreased. It was. For this reason, the applied voltage that reaches the limit current increases, and the sensor cell 4 deviates from the limit current region at the operating voltage of 0.4 V. As a result, as shown in FIG. 4 showing the relationship between the NOx concentration and the sensor output, the NOx sensitivity after the endurance is smaller than that before the endurance, and the detection accuracy is deteriorated. In addition, the measurement of FIG. 4 was measured on the conditions of NO: 0-1000 ppm, O2: 5%, N2: balance gas.

  On the other hand, when the operation of the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4 is stopped (the current of each cell is 0), and only the heater 9 is energized and the endured gas sensor element 1 is exposed to the air, the sensor cell 4 It was found that the NOx decomposition activity of the electrode 4a was restored. FIG. 3C shows the sensor cell current-voltage characteristics after the gas sensor element 1 after the endurance of 100,000 km is exposed to the air for 10 minutes. Moreover, the sensor output characteristic (after in-air oxidation treatment) of the gas sensor element 1 exposed to the air is shown in FIG. As can be seen from FIG. 3, the current-voltage characteristic in FIG. 3C is almost the same as that in FIG. 3A before the endurance, and the sensor output in FIG. 4 also recovers to the same extent as before the endurance.

  The above phenomenon is considered to be due to a decrease in surface area due to aggregation of metal components constituting the electrode 4a of the sensor cell 4 and an increase in surface area due to oxidation. That is, during durability, the second internal space 7b is in a low oxygen concentration atmosphere, and the metal components of the electrode 4a gradually aggregate. Along with this, the electrode surface area decreases, so the NOx decomposition activity of the electrode 4a decreases. On the other hand, when the electrode 4a of the sensor cell 4 having reduced decomposition activity is exposed to a high oxygen concentration atmosphere (desirably an oxygen concentration of 1% or more in the vicinity of the electrode 4a), Rh contained in the electrode 4a of the sensor cell 4 is oxidized. It becomes rhodium (Rh2 O3) and expands in volume. Thereby, the aggregation of the metal component is eliminated, the surface area is increased, and it is considered that the NOx decomposition activity of the electrode 4a is recovered. In order to obtain the above effect, it is usually desirable that 1% or more of all Rh atoms contained in the electrode 4a of the sensor cell 4 are oxidized. However, since the NOx decomposition activity by the electrode 4a decreases when the amount of Rh2O3 increases, it is preferable that the Rh atoms contained in the electrode 4a are present as Rh2O3 at 5% or less.

  Therefore, in the present invention, a control means for controlling the operation of the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4 is provided, and at the time of measuring the NOx concentration, as described above, the control for maintaining the oxygen concentration in the internal space 7 at a low concentration. Then, oxygen is introduced into the internal space 7 at a specific timing except when measuring the NOx concentration, and control is performed to recover the NOx decomposition activity of the electrode 4a of the sensor cell 4. Specifically, the NOx decomposition activity of the electrode 4a is performed by performing a recovery process at a timing that does not hinder the measurement of NOx concentration at a timing immediately after the engine is stopped or at regular intervals (every time or every mileage), for example. Can be maintained.

  More specifically, as a first method for recovering the NOx decomposition activity of the electrode 4a of the sensor cell 4, at least one of the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4 when oxygen is in the exhaust pipe of the internal combustion engine. Stop one operation. For example, when the above control is performed when the engine is stopped or the exhaust gas of the internal combustion engine, which is the gas to be measured, is in a lean state, the exhaust gas having a high oxygen concentration is introduced into the internal space 7, so that the electrode 4a of the sensor cell 4 Can be exposed to an oxidizing atmosphere. Preferably, the oxygen pump cell 2, the oxygen monitor cell 3 and the sensor cell 4 are all stopped, but oxygen remains in the internal space 7 even when any of the oxygen pump cell 2, the oxygen monitor cell 3 and the sensor cell 4 is operating. The effect described above can be obtained by controlling to be in the state of being. Further, since the Rh is not sufficiently oxidized when the element temperature is low, it is preferable to perform the recovery control while the heater 9 is energized. Preferably, the element temperature (the temperature of the electrode 4a of the sensor cell 4) is 400 ° C. or higher and 1000 ° C. or lower. Preferably, the element temperature is 600 ° C. or higher and 800 ° C. or lower.

  According to the first method, the engine is stopped every 10 hours, and even after the engine is stopped, only the heater 9 is energized for 5 minutes to perform recovery control of the electrode 4a of the sensor cell 4 (the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4). The operation was stopped), and then the engine was restarted, and a durability test for running a total of 100,000 km was conducted. As a result, as shown in FIG. 5, it was found that the NOx sensitivity did not change even after endurance, and high detection accuracy could be maintained. This is considered to be because NOx decomposition activity of the electrode 4a is maintained for the above-described reason by energizing only the heater 9 in a state where the gas sensor element 1 is exposed to a high oxygen concentration atmosphere after the engine is stopped. Here, the recovery process is performed for 5 minutes every 10 hours, but the interval and the processing time of the recovery process can be arbitrarily set.

  As the control means, for example, an NOx sensor element ECU (not shown) using a microcomputer is used. An example of a control flowchart by the ECU is shown in FIG. The ECU first determines in step 101 whether or not the ignition switch of the vehicle is ON. If the ignition switch is OFF, the ECU proceeds to step 102. In step 102, it is determined whether or not the ignition switch has just been turned from ON to OFF. If the determination in step 102 is affirmative, the routine proceeds to step 103, where a timer for 5 minutes is started.

  In step 104, it is determined whether or not 5 minutes have elapsed since the timer was started. If 5 minutes have not elapsed, the process proceeds to step 105, and the oxygen pump cell 2 and oxygen monitor cell 3 are maintained while the heater 9 is kept energized. The voltage applied to the sensor cell 4 is cut off. Thereafter, the process returns to step 101 and the following steps are repeated. When it is confirmed in step 104 that five minutes have elapsed after the timer is started, the process proceeds to step 106. In step 106, in addition to the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4, the heater 9 is also turned off, and the recovery process is terminated. When the ignition switch of the vehicle is turned on in step 101, the routine proceeds to step 107, where the heater 9, the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4 are normally operated to perform an operation of detecting the NOx concentration.

  As a second method for recovering the NOx decomposition activity of the electrode 4a of the sensor cell, at least one of the oxygen pump cell 2, the oxygen monitor cell 3, and the sensor cell 4 may be operated so that oxygen is introduced into the internal space 7. it can. For example, when a voltage is applied to the oxygen pump cell 2 so that the electrode 2a on the first internal space 7a side becomes a positive electrode, oxygen is pumped to the first internal space 7a side, so that the electrode 4a of the sensor cell 4 is brought into an oxidizing atmosphere. Can be exposed. Also in this case, it is preferable to perform the recovery process while the heater 9 is energized.

  In order to confirm the effect of the second method, the following test was performed. In the 100,000 km endurance test, the gas sensor element 1 was continuously operated, and an electric current was passed through the oxygen pump cell 2 so as to send oxygen into the first internal space 7a every hour. (In this example, a voltage of 0.5 V was applied so that the electrode 2a on the first internal space 7a side becomes a positive electrode. As a result, the same effect as in the case of the first method can be obtained. confirmed.

  FIG. 7 shows a timing chart of the voltage applied to the oxygen pump cell 2 when this control is performed. An event timer may be provided in the NOx sensor element ECU serving as the control means, and as shown in the drawing, control may be performed to invert the applied voltage of the oxygen pump cell 2 for one minute every hour.

  As another example for confirming the effect of the second method, the following test was performed. In the 100,000 km endurance test, the gas sensor element 1 was continuously operated, and an electric current was passed through the sensor cell 4 so as to send oxygen into the second internal space 7b every hour for one minute. (In this embodiment, a voltage of 0.5 V was applied so that the electrode 4a on the second internal space 7b side becomes a positive electrode. Thus, instead of the oxygen pump cell 2, the sensor cell 4 is used to replace the internal space 7 It was confirmed that even when oxygen was introduced into the inside, the same effect as in the case of the first method was obtained.

  FIG. 8 shows a timing chart of the applied voltage of the sensor cell 4 when performing this control. An event timer may be provided in the NOx sensor element ECU serving as the control means, and control may be performed to invert the applied voltage of the sensor cell 4 for one minute every time one hour elapses as shown in the figure.

  FIGS. 9A and 9B are diagrams showing another operation principle, and will be described as a second embodiment of the gas sensor element 1 to which the method of the present invention is applied. The configuration of the gas sensor element 1 is the same as that of the first embodiment. In the first embodiment, the applied voltage between the electrodes 2a and 2b of the oxygen pump cell 2 is controlled so that the current value between the electrodes 3a and 3b of the oxygen monitor cell 3 is constant. From the relationship between the oxygen pump cell applied voltage and the oxygen pump cell current, by applying a voltage according to the oxygen concentration so that the oxygen pump cell current becomes the limiting current, the oxygen concentration in the first internal space 7a is reduced to a predetermined low oxygen concentration. Control to concentration.

  However, when the oxygen concentration in the internal space 7 is controlled by this method, the oxygen concentration in the second internal space 7b is smaller than in the control based on the detection value of the oxygen monitor cell 3 as in the first embodiment. Therefore, if the current flowing between the electrodes 4a and 4b of the sensor cell 4 is directly used as a sensor signal, the detection accuracy of NOx deteriorates. Therefore, in the present embodiment, a current difference detection circuit is provided, and the difference between the current flowing between the electrodes 3a and 3b of the oxygen monitor cell 3 and the current flowing between the electrodes 4a and 4b of the sensor cell 4 is used as a sensor signal. In this way, the influence of the oxygen concentration fluctuation in the second internal space 7b can be eliminated, a sensor output independent of the oxygen concentration in the gas to be measured can be obtained, and the NOx concentration can be detected with high accuracy.

  Also in the gas sensor element 1 having this configuration, as described above, high NOx detection accuracy can be maintained for a long period of time by performing the process of restoring the NOx decomposition activity of the electrode 4a of the sensor cell 4 at a specific timing.

  In each of the above-described embodiments, the oxygen concentration in the second internal space 7b is detected by the value of the current flowing through the oxygen monitor cell 3, but it can also be detected by the electromotive force generated in the oxygen monitor cell 3. This will be described as a third embodiment with reference to FIG. In the present embodiment, the basic configuration including the oxygen monitor cell 3 and the sensor cell 4 is the same as that of the first embodiment, but the arrangement is different, and the second oxygen pump cell 20 is further installed. . Further, the reference gas space 82 is not provided, and only the reference gas space 81 is provided.

  In FIG. 10, the oxygen pump cell 2 has electrodes 2 a and 2 b provided on the upper and lower surfaces of the solid electrolyte body 52, and one electrode 2 a facing the first internal space 7 a The electrode 2b is provided on the upper surface of the solid electrolyte body 52 so as to face the measurement gas existence space. The oxygen monitor cell 3 is provided so that one electrode 3 a faces the first internal space 7 a on the upper surface of the solid electrolyte body 51, and the other electrode 3 b opens on the lower surface of the solid electrolyte body 51 and in the reference gas space 81. It is provided facing. In the sensor cell 4, one electrode 4 a facing the second internal space 7 b is provided on the upper surface of the solid electrolyte body 51, and the other electrode 4 b is provided on the lower surface of the solid electrolyte body 51 so as to face the reference gas space 81. The electrode 4b is a common electrode with the electrode 3b of the oxygen monitor cell 3.

  The second oxygen pump cell 20 includes a solid electrolyte body 52 and a pair of electrodes 20a and 2b provided on the surface thereof. One electrode 20 a is provided on the lower surface of the solid electrolyte body 52 so as to face the second internal space 7 b, and the other electrode 2 b is a common electrode with the oxygen pump cell 2. The second oxygen pump cell 20 has a function of discharging residual oxygen in the measurement gas introduced into the second internal space 7b without being discharged by the oxygen pump cell 2 into the measurement gas existence space.

  The operation in this case will be described with reference to FIG. In the above configuration, the electrode 3a of the oxygen monitor cell 3 faces the first internal space 7a, and the electrode 3b faces the reference gas space 81 into which the atmosphere is introduced. An electromotive force based on the Nernst equation is generated between the electrodes 3a and 3b due to a difference in oxygen concentration between the first internal space 7a and the reference gas space 81 in contact with both electrodes. Since the oxygen concentration in the reference gas space 81 is constant, the electromotive force generated between the electrodes 3a and 3b reflects the oxygen concentration in the first internal space 7a. Therefore, if the applied voltage between the electrodes 2a and 2b of the oxygen pump cell 2 is controlled so that the electromotive force generated between the electrodes 3a and 3b becomes a predetermined constant value (for example, 0.20 V), the second internal space The oxygen concentration flowing into 7b can be controlled to be constant. Further, in the present embodiment, the second oxygen pump cell 20 is formed by the solid electrolyte body 52 and the electrodes 20a and 2b, and oxygen that has not been discharged by the oxygen pump cell 2 but has flowed into the second internal space 7b is exposed to the outside. Exhaust. As a result, the oxygen concentration in the second internal space 7b becomes substantially zero, and the sensor cell 4 enables highly accurate NOx concentration measurement.

  Also in the gas sensor element 1 having this configuration, the NOx concentration can be detected with high accuracy over a long period of time by performing the process of restoring the NOx decomposition activity of the electrode 4a of the sensor cell 4 at a specific timing according to the present invention.

  In each of the above-described embodiments, the control method for recovering the gas sensor element 1 manufactured by a normal method when the detection accuracy decreases due to long-term use has been described. However, the detection accuracy can be improved by changing the manufacturing method. Reduction can be suppressed and recovery control can be made unnecessary. In this manufacturing method, a raw sheet made of zirconia or the like for a solid electrolyte body and an alumina raw sheet to be a spacer, a heater sheet, and an alumina layer are formed, and the electrodes, heater electrodes, lead portions, and terminals are printed and then laminated. The process up to baking in the atmosphere is performed in the same manner as described above, and thereafter, an oxidation treatment is performed in which the integrated element is exposed to a high-temperature oxidizing atmosphere. The oxidation treatment temperature is preferably 400 to 1000 ° C, more preferably 600 to 900 ° C. Since the metal Rh is more stable than Rh2 O3 at 1000 ° C. or higher, the above-described precipitation phenomenon cannot be expected, and at 400 ° C. or lower, the precipitation rate becomes slow and the effect cannot be obtained. The oxidizing atmosphere is usually preferably an oxygen concentration of 1% or more and an oxidation treatment time of 1 hour or more.

  The effect by this manufacturing method is demonstrated. Rh becomes Rh2 O3 in a high temperature oxidizing atmosphere. The electrode 4a on the inner space side of the sensor cell 4 is a Pt-Rh electrode, and when exposed to an oxidizing atmosphere, the inner Rh gradually precipitates as Rh2O3 on the surface, and the surface Rh concentration increases. The electrode surface concentration of Rh, which is a NOx decomposition active component, increases. Further, since the deposited Rh is not poisoned by the inert substance (Au) scattered from the electrode 2a of the oxygen pump cell 2, the NOx decomposition activity of the sensor cell 4 is remarkably improved.

  FIG. 11 shows a result of performing an endurance test with a traveling distance of 100,000 km by installing the gas sensor element 1 that has been treated in air at 900 ° C. for 10 hours after the firing step on the engine exhaust pipe. As is apparent from the figure, there is almost no change in sensitivity before and after endurance. As described above, the gas sensor element 1 manufactured by performing the oxidation treatment after the firing step can maintain a high NOx decomposition activity for a long period of time, and therefore does not require recovery control. Therefore, a recovery control device is not required, and a high effect can be obtained with a simple configuration.

  In the above manufacturing method, when the Pt-Rh electrode 4a on the inner space side of the sensor cell 4 is exposed to an oxidizing atmosphere, the inner Rh gradually deposits as Rh2O3 on the surface, and the Rh concentration on the surface increases. However, the deposition rate of Rh decreases as the surface is covered with Rh2 O3. Therefore, it may be alternately exposed to an oxidizing atmosphere and a reducing atmosphere. That is, after the oxidation treatment, it is once exposed to a reducing atmosphere to reduce Rh2O3 on the surface to metal Rh. Thereafter, by re-exposure to an oxidizing atmosphere, the precipitation of Rh can be further promoted. In this method, as a specific method for reducing Rh2 O3 to metal Rh, a reducing atmosphere may be formed by introducing a flammable gas such as H2, or an internal space side electrode is provided in the sensor cell 4. You may electrically reduce by applying a voltage so that 4a may become a negative electrode.

  This manufacturing method can be suitably applied to any of the gas sensor element 1 configurations of the above-described embodiments.

It is a typical sectional view of a gas sensor element in a 1st embodiment of the present invention. It is an exploded development view of the gas sensor element in a 1st embodiment. It is a diagram which shows the electric current-voltage characteristic of a sensor cell, (a) is before durability, (b) is after durability, (c) is a characteristic diagram after an in-air oxidation process. It is a diagram which shows the relationship between NOx density | concentration and sensor output for demonstrating the effect of this invention. It is a diagram which shows the relationship between NOx density | concentration and sensor output for demonstrating the effect of this invention. It is a figure which shows the flowchart of recovery control of NOx decomposition | disassembly activity by this invention. It is a figure which shows the time chart of recovery | restoration control of NOx decomposition | disassembly activity by this invention. It is a figure which shows the time chart of recovery | restoration control of NOx decomposition | disassembly activity by this invention. It is a typical sectional view of a gas sensor element in a 2nd embodiment of the present invention. It is a typical sectional view of a gas sensor element in a 3rd embodiment of the present invention. It is a diagram which shows the relationship between NOx density | concentration and sensor output for demonstrating the effect of this invention. It is typical sectional drawing of the conventional gas sensor element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas sensor element 11 Pinhole 12 Porous protective layer 2 Oxygen pump cell 21, 22 A pair of electrodes 3 Oxygen monitor cell (monitor cell)
4 sensor cell 41, 42 pair of electrodes 51, 52 solid electrolyte body 61, 62, 63, 64 spacer 7 internal space 7a first internal space 7b second internal space 81, 82 reference gas space 9 heater P terminal

Claims (12)

An internal space into which the gas to be measured is introduced under a predetermined diffusion resistance;
On the surface of an oxygen ion conductive solid electrolyte body, the electrode has a pair of electrodes provided so that one electrode faces the internal space, and oxygen is introduced into the internal space by energizing the pair of electrodes or An oxygen pump cell that discharges and adjusts the oxygen concentration in the internal space;
On the surface of an oxygen ion conductive solid electrolyte body, there is a sensor cell having a pair of electrodes provided so that one electrode faces the internal space and detecting the concentration of a specific gas component in the gas to be measured A gas sensor element,
During the measurement of the specific gas component concentration, the oxygen concentration in the internal space is maintained at a low concentration, and oxygen is introduced into the internal space at a specific timing except during the measurement of the specific gas component concentration, and the internal space of the sensor cell is introduced. Providing a control means for performing control to recover the activity of the electrode facing the internal space of the sensor cell by exposing the facing electrode to an oxidizing atmosphere;
Using the gas to be measured as exhaust gas of the internal combustion engine, the control means introduces oxygen into the internal space by stopping the operation of at least one of the oxygen pump cell and the sensor cell when the exhaust gas is in a lean state. A gas sensor element characterized by comprising: An internal space into which the gas to be measured is introduced under a predetermined diffusion resistance;
On the surface of an oxygen ion conductive solid electrolyte body, the electrode has a pair of electrodes provided so that one electrode faces the internal space, and oxygen is introduced into the internal space by energizing the pair of electrodes or An oxygen pump cell that discharges and adjusts the oxygen concentration in the internal space;
A sensor cell that has a pair of electrodes provided on the surface of the oxygen ion conductive solid electrolyte body so that one electrode faces the internal space, and detects a specific gas component concentration in the gas to be measured ;
A gas sensor element having a heater for heating the element,
During the measurement of the specific gas component concentration, the oxygen concentration in the internal space is maintained at a low concentration, and oxygen is introduced into the internal space at a specific timing except during the measurement of the specific gas component concentration, and the internal space of the sensor cell is introduced. Providing a control means for performing control to recover the activity of the electrode facing the internal space of the sensor cell by exposing the facing electrode to an oxidizing atmosphere;
By using the gas to be measured as exhaust gas of the internal combustion engine, the control means stops the operation of at least one of the oxygen pump cell and the sensor cell while energizing the heater when the internal combustion engine is stopped. A gas sensor element, wherein oxygen is introduced into a space. An internal space into which the gas to be measured is introduced under a predetermined diffusion resistance;
On the surface of an oxygen ion conductive solid electrolyte body, the electrode has a pair of electrodes provided so that one electrode faces the internal space, and oxygen is introduced into the internal space by energizing the pair of electrodes or An oxygen pump cell that discharges and adjusts the oxygen concentration in the internal space;
On the surface of an oxygen ion conductive solid electrolyte body, there is a sensor cell having a pair of electrodes provided so that one electrode faces the internal space and detecting the concentration of a specific gas component in the gas to be measured A gas sensor element,
During the measurement of the specific gas component concentration, the oxygen concentration in the internal space is maintained at a low concentration, and oxygen is introduced into the internal space at a specific timing except during the measurement of the specific gas component concentration, and the internal space of the sensor cell is introduced. Providing a control means for performing control to recover the activity of the electrode facing the internal space of the sensor cell by exposing the facing electrode to an oxidizing atmosphere;
The control means introduces oxygen into the internal space by flowing a direct current through at least one of the oxygen pump cell and the sensor cell so that oxygen is pumped to the internal space side. element. The gas sensor element according to any one of claims 1 to 3, wherein the electrode facing the internal space of the sensor cell is a cermet electrode containing rhodium . It has a pair of electrodes provided on the surface of an oxygen ion conductive solid electrolyte body so that one electrode faces the internal space, and an oxygen monitor cell for detecting the oxygen concentration in the internal space. The gas sensor element according to any one of claims 1 to 4 .   The gas sensor element according to any one of claims 1 to 5, wherein the control means performs control of exposing the electrode facing the internal space of the sensor cell to an oxidizing atmosphere in a state where the temperature of the gas sensor element is 400 ° C or higher.   The gas sensor element according to claim 1, wherein the specific gas component is nitrogen oxide. An internal space into which the gas to be measured is introduced under a predetermined diffusion resistance;
On the surface of an oxygen ion conductive solid electrolyte body, the electrode has a pair of electrodes provided so that one electrode faces the internal space, and oxygen is introduced into the internal space by energizing the pair of electrodes or An oxygen pump cell that discharges and adjusts the oxygen concentration in the internal space;
On the surface of an oxygen ion conductive solid electrolyte body, there is a sensor cell having a pair of electrodes provided so that one electrode faces the internal space and detecting the concentration of a specific gas component in the gas to be measured Using gas sensor element,
At the time of measuring the specific gas component concentration, the oxygen concentration in the internal space is maintained at a low concentration, and the exhaust gas of the internal combustion engine as the measured gas is in a lean state at a specific timing except at the time of measuring the specific gas component concentration. Sometimes , by stopping the operation of at least one of the oxygen pump cell and the sensor cell, oxygen is introduced into the internal space, and the electrode facing the internal space of the sensor cell is exposed to an oxidizing atmosphere, thereby the sensor cell A method for controlling a gas sensor element, comprising: recovering the activity of an electrode facing the internal space. An internal space into which the gas to be measured is introduced under a predetermined diffusion resistance;
On the surface of an oxygen ion conductive solid electrolyte body, the electrode has a pair of electrodes provided so that one electrode faces the internal space, and oxygen is introduced into the internal space by energizing the pair of electrodes or An oxygen pump cell that discharges and adjusts the oxygen concentration in the internal space;
A sensor cell that has a pair of electrodes provided on the surface of the oxygen ion conductive solid electrolyte body so that one electrode faces the internal space, and detects a specific gas component concentration in the gas to be measured ;
Using a gas sensor element having a heater for heating the element, and using the exhaust gas of the internal combustion engine as the measured gas,
When the specific gas component concentration is measured, the oxygen concentration of the internal space is maintained at a low concentration, and the oxygen pump cell is in a state where the heater is energized when the internal combustion engine is stopped as a specific timing excluding the specific gas component concentration measurement. And by stopping the operation of at least one of the sensor cells, oxygen is introduced into the internal space, and an electrode facing the internal space of the sensor cell is exposed to an oxidizing atmosphere, so that the internal space of the sensor cell is exposed to the internal space. A method for controlling a gas sensor element, wherein the activity of the facing electrode is restored. An internal space into which the gas to be measured is introduced under a predetermined diffusion resistance;
On the surface of an oxygen ion conductive solid electrolyte body, the electrode has a pair of electrodes provided so that one electrode faces the internal space, and oxygen is introduced into the internal space by energizing the pair of electrodes or An oxygen pump cell that discharges and adjusts the oxygen concentration in the internal space;
On the surface of an oxygen ion conductive solid electrolyte body, there is a sensor cell having a pair of electrodes provided so that one electrode faces the internal space and detecting the concentration of a specific gas component in the gas to be measured Using gas sensor element,
At the time of the specific gas component concentration measurement, the oxygen concentration in the internal space is maintained at a low concentration, and at a specific timing excluding the specific gas component concentration measurement, at least one of the oxygen pump cell and the sensor cell is connected to the internal space side. By introducing a direct current so that oxygen is pumped into the internal space, oxygen is introduced into the internal space, and an electrode facing the internal space of the sensor cell is exposed to an oxidizing atmosphere, whereby the internal space of the sensor cell is A method for controlling a gas sensor element, wherein the activity of the facing electrode is restored . The method for controlling a gas sensor element according to any one of claims 8 to 10, wherein the electrode facing the internal space of the sensor cell is a cermet electrode containing rhodium . An oxygen monitor cell in which the gas sensor element has a pair of electrodes provided on the surface of an oxygen ion conductive solid electrolyte body so that one electrode faces the internal space, and detects the oxygen concentration in the internal space The method for controlling a gas sensor element according to claim 8, wherein:

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