JP6596535B2 - Gas sensor - Google Patents

Description

  The present invention relates to a gas sensor that detects the concentration of a specific gas component in a gas to be measured.

A gas sensor element that detects the concentration of a specific gas component is disposed at a site for exhausting exhaust gas such as an engine exhaust pipe, and includes nitrogen oxide (NOx) and hydrocarbon (HC) contained in exhaust gas as a measurement gas. Etc. are detected.
For example, in the gas sensor element of Patent Document 1, a pair of electrodes is provided on a solid electrolyte body to form an oxygen pump cell, an oxygen monitor cell, and a sensor cell, and the concentration of a specific gas component in the gas to be measured introduced into the internal space is determined. Detected. Further, in the gas sensor element of Patent Document 1, in order to detect the concentration of a specific gas component without being affected by the oxygen concentration in the internal space, an oxygen monitor cell is introduced from a gas inlet for introducing the gas to be measured into the internal space. The distances between the electrodes of the sensor cell and the electrodes of the sensor cell are equal to the upstream end position of the gas flow.

JP 2002-310987 A

The current flowing between the pair of electrodes constituting the oxygen pump cell, the oxygen monitor cell, and the sensor cell is affected by the electron conduction by the heater that heats the gas sensor element. The current flowing between the pair of electrodes due to this electron conduction tends to increase as the operating temperature of the gas sensor element heated by the heater increases.
The heating amount of the heater is controlled so as to keep the operating temperature of the gas sensor element constant based on the magnitude of the resistance value between the pair of electrodes in the oxygen pump cell. However, the electrode in contact with the gas to be measured deteriorates with time. Due to the deterioration of the electrodes, the resistance value between the pair of electrodes increases, and the amount of heating by the heater increases. Therefore, the longer the gas sensor element is used, the higher the operating temperature of the gas sensor element, and the current flowing between the pair of electrodes tends to increase due to electron conduction.

  The oxygen monitor cell disclosed in Patent Document 1 and the like simultaneously detects both an oxygen ion current due to residual oxygen in a gas to be measured and a current due to electronic conduction. Therefore, the oxygen monitor cell cannot detect the current due to electron conduction separately from the oxygen ion current due to residual oxygen. Therefore, depending on the oxygen monitor cell, it is difficult to improve the detection accuracy of the specific gas component concentration by the sensor cell when the operating temperature of the gas sensor element changes.

  The present invention has been made in view of such a background, and has been obtained by providing a gas sensor capable of improving the detection accuracy of a specific gas component concentration by a sensor cell, reflecting changes in the operating temperature of the gas sensor element. It is.

One aspect of the present invention is a solid electrolyte body (2) having oxygen ion conductivity,
A measurement gas space (101) formed on one surface side of the solid electrolyte body and into which a measurement gas (G) that has passed through the diffusion resistor (3) is introduced;
A sensor electrode (23) provided on the surface of the solid electrolyte body on the measured gas space side;
An electron conduction electrode (24) provided on a surface of the solid electrolyte body on the gas space to be measured side;
A reference electrode (25) provided on the other surface of the solid electrolyte body;
A heater (6) for heating the sensor electrode,
A sensor cell for detecting a concentration of a specific gas component in the measured gas space based on an oxygen ion current flowing between the sensor electrode and the reference electrode by the solid electrolyte body, the sensor electrode, and the reference electrode ( 43),
An electron conduction detection cell (44) for detecting the current flowing between the electron conduction electrode and the reference electrode upon receiving the electron conduction of the heater by the solid electrolyte body, the electron conduction electrode and the reference electrode. A gas sensor comprising:
The distance from the sensor electrode to the heating center of the heater is shorter than the distance from the electron conduction electrode to the heating center of the heater,
The gas sensor is calibrated so that a difference value obtained by subtracting the current value in the electron conduction detection cell from the current value in the sensor cell becomes zero under the condition that the specific gas component concentration is 0 ppm .

The gas sensor element of the gas sensor has an electron conduction detection cell that detects the strength of electron conduction generated by the heater. Therefore, it is possible to detect the heating amount by the heater and further the operating temperature of the gas sensor element by detecting the current due to the electron conduction in the electron conduction detection cell. Further, according to the electron conduction detection cell, it is possible to detect a current due to electron conduction which increases when the gas sensor element changes with time.
Thus, by subtracting the current in the electron conduction detection cell from the detection current in the sensor cell, the change in the operating temperature of the gas sensor element can be reflected to detect the specific gas component concentration by the sensor cell. The value of the detection current in the sensor cell is a value obtained by adding a current due to electron conduction to the oxygen ion current for detecting the specific gas component concentration.

  Therefore, according to the gas sensor, it is possible to improve the detection accuracy of the specific gas component concentration by the sensor cell, reflecting the change in the operating temperature of the gas sensor element.

1 is a cross-sectional view showing a gas sensor element according to Example 1. FIG. FIG. 2 is a cross-sectional view taken along the line II of FIG. The graph which shows the relationship between working temperature and an electric current value concerning Example 1 by taking the operating temperature of a gas sensor element on a horizontal axis, and taking the electric current which flows into a sensor cell and an electric conduction detection cell on a vertical axis | shaft. Sectional drawing which shows the gas sensor element concerning Example 2. FIG. II-II sectional drawing of FIG. The graph which shows the relationship between operating temperature and an electric current value which takes the operating temperature of a gas sensor element concerning Example 2, and takes the electric current which flows into the sensor cell and the electronic conduction detection cell on the vertical axis | shaft. FIG. 11 is a cross-sectional view of the other gas sensor element according to the second embodiment, taken along the line II-II in FIG. 4. FIG. 4 is a cross-sectional view corresponding to the II-II section of FIG. The magnitude | sizes of the electric current value which flows into a sensor cell, a monitor cell, and an electronic conduction detection cell concerning Example 3 are shown about (a) the initial state before a gas sensor element deteriorates, (b) the durable state after a gas sensor element deteriorates. Graph.

A preferred embodiment of the gas sensor described above will be described.
In the gas sensor, at least a surface of the electron conducting electrode that is exposed to the gas to be measured may be made of an electrode material that is inert to oxygen decomposition in the gas to be measured.
In this case, an electron conduction detection cell can be easily formed by devising an electrode material used for the electron conduction electrode. The entire electron conductive electrode may be formed or the surface layer of the electron conductive electrode may be formed of an electrode material that is inert to oxygen decomposition in the measurement gas.
Examples of the electrode material include a gold material, a silver material, a copper material, and a lead material.

Further, the surface of the electron conducting electrode on the measured gas space side may be covered with a coating layer that does not allow oxygen components in the measured gas to pass therethrough.
In this case, the electron conduction detection cell can be easily formed by providing a coating layer while keeping the electrode material used for the electron conduction electrode as a normal material.

In addition, the pump electrode may be located in a longer direction of the surface of the solid electrolyte body on which the sensor electrode and the electron conducting electrode are provided than the position where the sensor electrode and the electron conducting electrode are arranged. It is provided in the upstream position of the flow of the gas to be measured, and the sensor electrode and the electron conduction electrode may be arranged at an equal distance from the arrangement position of the pump electrode in the longitudinal direction.
In this case, by providing the pump electrode on the solid electrolyte body provided with the sensor electrode and the electron conduction electrode, it becomes easy to heat the pump electrode with the heater. Further, the distances from the heating center in the heater to the sensor electrode and the electron conduction electrode can be made equal, and the currents flowing in the sensor electrode and the electron conduction electrode by the electron conduction from the heater can be made equivalent. Therefore, the detection accuracy of the specific gas component concentration by the sensor cell can be further improved.

  The gas sensor includes a monitor cell having a monitor electrode provided on a surface of the solid electrolyte body provided with the sensor electrode and the electron conduction electrode on the gas gas side to be measured, and the sensor electrode, The electron conductive electrode and the monitor electrode are arranged at an equal distance from the arrangement position of the pump electrode in the longitudinal direction, and the monitor cell is based on an oxygen ion current flowing between the monitor electrode and the reference electrode. Thus, the oxygen concentration in the gas space to be measured may be detected.

  In this case, the distances from the heating center in the heater to the sensor electrode, the electron conduction electrode, and the monitor electrode are made equal, and the currents flowing in the sensor electrode, the electron conduction electrode, and the monitor electrode are made equal by the electron conduction from the heater. be able to. Therefore, the detection accuracy of the specific gas component concentration by the sensor cell can be further improved.

The sensor electrode is made of an electrode material that is active in decomposing a specific gas component in the gas to be measured, and the monitor electrode is an electrode that is inactive in decomposing the specific gas component (NOx, etc.) in the gas to be measured. Consists of materials. In the sensor cell, the oxygen ion current is detected depending on the oxygen concentration and the specific gas component concentration, while in the monitor cell, the oxygen ion current is detected depending on the oxygen concentration. In the gas sensor, the concentration of the specific gas component in the gas to be measured is detected by subtracting the current detected by the monitor cell from the current detected by the sensor cell. Thus, by using the monitor cell, it is possible to correct the influence of the oxygen ion current due to the residual oxygen in the gas to be measured on the detection of the specific gas component concentration by the sensor cell when the gas sensor element changes with time.
Each of the current value detected by the sensor cell and the current value detected by the monitor cell is a value obtained by adding a current due to electron conduction to the oxygen ion current for detecting the specific gas component concentration.

Further, the influence of the electron conduction by the heater on the sensor cell and the monitor cell can be corrected by the electron conduction detection cell. Specifically, when the gas sensor element changes over time due to deterioration, the sensor cell can detect the specific gas component concentration in consideration of the influence of electronic conduction when the amount of heating by the heater increases.
When detecting the specific gas component concentration, the oxygen ion current due to residual oxygen and the current due to electron conduction can be detected separately.

The heater includes a conductor layer that generates heat when energized, and an insulating layer that sandwiches the conductor layer, and the conductor layer so that a current value detected by the electron conduction detection cell is constant. May be configured to energize.
The value of current flowing through the electron conduction detection cell due to electron conduction has a correlation with the operating temperature of the gas sensor element. In addition, the electron conduction detection cell does not detect oxygen ion current generated by oxygen decomposition in the measurement gas, and the electron conduction electrode of the electron conduction detection cell deteriorates over time due to decomposition of the oxygen component in the measurement gas. Hardly occurs. Therefore, the operating temperature of the gas sensor element can be accurately controlled by energizing the conductor layer so that the current value detected by the electron conduction detection cell is constant.

Below, the example concerning a gas sensor is described with reference to drawings.
Example 1
As shown in FIGS. 1 and 2, the gas sensor element 1 of the gas sensor of this example includes a solid electrolyte body 2, a measured gas space 101, a reference gas space 102, a heater 6, a pump cell 41, a sensor cell 43, and an electron conduction detection cell 44. It has.
The solid electrolyte body 2 is made of a material having oxygen ion conductivity. The measured gas space 101 is formed on one surface side of the solid electrolyte body 2 and is configured such that the measured gas G that has passed through the diffusion resistor 3 is introduced. The reference gas space 102 is formed on the other surface side of the solid electrolyte body 2 and is configured such that the reference gas A is introduced. A reference electrode 25 that is exposed to the reference gas A is provided on the surface 202 of the solid electrolyte body 2 on the reference gas space 102 side.

  As shown in FIGS. 1 and 2, the heater 6 is stacked on the solid electrolyte body 2 through a reference gas space 102. The pump cell 41 is provided on the surface 201 of the solid electrolyte body 2 on the measured gas space 101 side, and has a pump electrode 21 that is exposed to the measured gas G. The pump cell 41 is configured to adjust the oxygen concentration in the measured gas space 101 by applying a voltage between the pump electrode 21 and the reference electrode 25. The reference electrode 25 in this example also serves as one of the pump electrodes 21. The sensor cell 43 is provided on the surface 201 of the solid electrolyte body 2 on the measured gas space 101 side and has a sensor electrode 23 that is exposed to the measured gas G. The sensor cell 43 is used for detecting a specific gas component concentration in the measured gas space 101 based on an oxygen ion current flowing between the sensor electrode 23 and the reference electrode 25. The electron conduction detection cell 44 has an electron conduction electrode 24 provided on the surface 201 of the solid electrolyte body 2 on the measured gas space 101 side so as not to be exposed to the measured gas G. The electron conduction detection cell 44 is configured to detect a current flowing between the electron conduction electrode 24 and the reference electrode 25 by the electron conduction of the heater 6.

Hereinafter, the gas sensor element 1 of the gas sensor of this example will be described in detail with reference to FIGS.
The gas sensor element 1 of this example is used by being placed in an exhaust pipe of an automobile while being placed in a cover. The gas G to be measured is exhaust gas that passes through the exhaust pipe, and the gas sensor element 1 is used to detect the concentration of NOx (nitrogen oxide) as a specific gas component in the exhaust gas.
As shown in FIG. 1, the solid electrolyte body 2 is a zirconia substrate having oxygen ion conductivity. The pump electrode 21, the sensor electrode 23, and the electron conduction electrode 24 are provided with a certain thickness on the surface 201 of the solid electrolyte body 2 on the side exposed to the gas G to be measured. The reference electrode 25 is provided with a certain thickness on the surface 202 of the solid electrolyte body 2 on the side exposed to the reference gas A. The reference electrode 25 of this example is provided at a position on the back side of the entire region where the pump electrode 21, the sensor electrode 23, and the electron conduction electrode 24 are located in the solid electrolyte body 2. In addition to providing one reference electrode 25 for the entire pump electrode 21, sensor electrode 23, and electron conduction electrode 24, the reference electrode 25 is separated into positions on the back side of the pump electrode 21, sensor electrode 23, and electron conduction electrode 24. It is also possible to provide three.

  As shown in FIGS. 1 and 2, a diffusion resistor 3 and a first insulator 51, which is a flat substrate made of alumina, are laminated on the surface 201 of the solid electrolyte body 2 on the measured gas G side. ing. On the surfaces of the diffusion resistor 3 and the first insulator 51, a second insulator 52, which is a flat substrate made of alumina, is laminated. The diffusion resistor 3 is arranged at one end of the gas sensor element 1 on the side where the measurement gas G is introduced in the longitudinal direction L. The measurement gas G is introduced into the measurement gas space 101 through the diffusion resistor 3 and flows in the measurement gas space 101 in the longitudinal direction L. The first insulator 51 includes the other end in the longitudinal direction L and both sides in the width direction W so as to surround the pump electrode 21 and the sensor electrode 23 from three sides on the surface 201 of the solid electrolyte body 2 on the measured gas G side. Is provided at the end.

  The measured gas space 101 is located between the solid electrolyte body 2 and the second insulator 52 on the surface 201 of the solid electrolyte body 2 on the measured gas G side by the diffusion resistor 3 and the first insulator 51. The four sides are surrounded. The measured gas space 101 has a constant space height in the thickness direction T perpendicular to the longitudinal direction L and the width direction W at the position where the pump electrode 21 and the sensor electrode 23 are provided.

  As shown in FIGS. 1 and 2, a third insulator 53, which is a flat substrate made of alumina, is laminated on the surface 202 of the solid electrolyte body 2 on the reference gas A side. The third insulator 53 is provided at one end in the longitudinal direction L and at both ends in the width direction W so as to surround the reference electrode 25 from three sides on the surface 202 of the solid electrolyte body 2 on the reference gas A side. ing. The reference gas space 102 is formed between the solid electrolyte body 2 and the fourth insulator 61 by one end of the surface 202 on the reference gas A side of the solid electrolyte body 2 and the width direction W by the third insulator 53. The three sides of both ends of the are surrounded.

The third insulator 53 is laminated with a heater 6 for heating the pump electrode 21 and the sensor electrode 23. The heater 6 includes a fourth insulator 61 as an insulating layer laminated on the surface of the third insulator 53, and a conductor layer 62 provided on the fourth insulator 61 and energized. Yes. The fourth insulator 61 sandwiches the conductor layer 62 between two insulating plates 611. The conductor layer 62 includes a pair of electrode portions to which an external energization means is connected, and a heat generating portion that connects the pair of electrode portions and generates heat when energized by a voltage applied to the pair of electrode portions. .
Further, the fourth insulator 61 and the conductor layer 62 of the heater 6 are arranged in parallel to the solid electrolyte body 2, and the conductor layer 62 is connected to the pump electrode 21, the sensor electrode 23 and the electron conduction electrode 24. Are arranged in parallel.

  As shown in FIGS. 1 and 2, the pump electrode 21 has a sensor electrode 23 in the longitudinal direction L of the surface 201 of the solid electrolyte body 2 provided with the sensor electrode 23 and the electron conducting electrode 24 on the gas space 101 side to be measured. Is provided at a position upstream of the flow of the gas G to be measured. The pump cell 41 adjusts the oxygen concentration in the measured gas space 101 to be constant by applying a voltage between the pump electrode 21 and the reference electrode 25. The pump electrode 21 can also be provided on another solid electrolyte body laminated on the solid electrolyte body 2 via an insulator.

The sensor electrode 23 is made of an electrode material that is active in decomposing NOx as a specific gas component in the gas G to be measured. The sensor cell 43 detects the NOx concentration in the measurement gas G according to the magnitude of the oxygen ion current value flowing between the sensor electrode 23 and the reference electrode 25 when decomposing NOx.
The electron conductive electrode 24 is located on the other end side in the longitudinal direction L with respect to the sensor electrode 23 and is covered with a first insulator 51 as a coating layer that does not allow oxygen components in the measurement gas G to pass therethrough. The electron conductive electrode 24 of this example is embedded in the first insulator 51.

Next, the effect of the gas sensor element 1 of this example is demonstrated.
The gas sensor element 1 of this example includes an electron conduction detection cell 44 that detects the strength of electron conduction generated by the heater 6. Therefore, it is possible to detect the heating amount by the heater 6 and further the operating temperature of the gas sensor element 1 by detecting the current due to the electron conduction in the electron conduction detection cell 44. Further, according to the electron conduction detection cell 44, it is possible to detect a current due to electron conduction which increases when the gas sensor element 1 changes with time.
Thereby, by subtracting the current in the electron conduction detection cell 44 from the detection current in the sensor cell 43, the change in the operating temperature of the gas sensor element 1 can be reflected and the specific gas component concentration can be detected by the sensor cell 43. The value of the detection current in the sensor cell 43 is a value obtained by adding a current due to electron conduction to the oxygen ion current for detecting the specific gas component concentration.

  Therefore, according to the gas sensor element 1 of this example, the detection accuracy of the specific gas component concentration by the sensor cell 43 can be improved by reflecting the change in the operating temperature of the gas sensor element 1.

  FIG. 3 shows the relationship between the operating temperature and the current value, with the operating temperature of the gas sensor element 1 on the horizontal axis and the current I1 flowing through the sensor cell 43 and the current I3 flowing through the electron conduction detecting cell 44 on the vertical axis. In this case, the concentration of NOx as the specific gas component is 0 ppm. As shown in the figure, in both the sensor cell 43 and the electron conduction detection cell 44, it can be seen that the current values I1 and I3 increase as the operating temperature of the gas sensor element 1 increases. Most of the current values I1 and I3 having a correlation with the operating temperature are based on electron conduction by the heater 6. Therefore, by subtracting the current value I3 in the electron conduction detection cell 44 from the current value I1 in the sensor cell 43, the sensor cell 43 can detect the oxygen ion current generated when decomposing NOx as the specific gas component as accurately as possible. it can.

  In the longitudinal direction L of the gas sensor element 1, there exists a temperature distribution corresponding to the distance from the heating center of the heater 6. The distance from the sensor electrode 23 to the heating center of the heater 6 is shorter than the distance from the electron conductive electrode 24 to the heating center of the heater 6. Therefore, the difference value obtained by subtracting the current value I3 in the electron conduction detection cell 44 from the current value I1 in the sensor cell 43 does not become zero. The difference value tends to increase as the operating temperature of the gas sensor element 1 increases. Therefore, when using the gas sensor element 1, it calibrates so that this difference value may become zero.

(Example 2)
This example is an example in which the arrangement location of the electron conduction detection cell 44 is changed in the gas sensor element 1 shown in the first embodiment.
As shown in FIGS. 4 and 5, the electron conduction electrode 24 </ b> A of the electron conduction detection cell 44 of this example is in the width direction W orthogonal to the longitudinal direction L of the surface 201 on the gas G to be measured side of the solid electrolyte body 2. It is formed adjacent to the sensor electrode 23 of the sensor cell 43. The pump electrode 21, the sensor electrode 23, and the electron conduction electrode 24 </ b> A are disposed in the measured gas space 101. The sensor electrode 23 and the electron conductive electrode 24A are arranged at an equal distance from the arrangement position of the pump electrode 21 in the longitudinal direction L of the surface 201 of the solid electrolyte body 2 on the measurement gas space 101 side. The electron conductive electrode 24A is made of a gold material as an electrode material that is inactive against oxygen decomposition in the gas G to be measured. A surface layer made of a gold material may be provided on the surface of the electron conducting electrode 24A that is exposed to the gas G to be measured.

In this example, the distances from the heating center in the heater 6 to the sensor electrode 23 and the electron conduction electrode 24A are made equal, and the currents flowing in the sensor electrode 23 and the electron conduction electrode 24A by the electron conduction from the heater 6 are made equivalent. be able to. Therefore, the detection accuracy of the specific gas component concentration by the sensor cell 43 can be further improved.
Also in this example, the other configurations and the reference numerals in the drawings are the same as those in the first embodiment, and the same effects as those in the first embodiment can be obtained.

  FIG. 6 shows the relationship between the operating temperature of the gas sensor element 1 and the current I1 flowing through the sensor cell 43 and the current I3 flowing through the electron conduction detection cell 44 in the same manner as in FIG. As shown in FIG. 6, in both the sensor cell 43 and the electron conduction detection cell 44, it can be seen that the current values I1 and I3 increase as the operating temperature of the gas sensor element 1 increases based on the electron conduction by the heater 6. In this example, since the distance from the heating center in the heater 6 to the sensor electrode 23 and the electron conduction electrode 24A is equal, the current value I3 in the electron conduction detection cell 44 is subtracted from the current value I1 in the sensor cell 43. It can be seen that there is almost no difference. This indicates that the oxygen ion current in the sensor cell 43 can be detected more accurately.

  Further, as shown in FIG. 7, the electron conduction electrode 24 may be covered with a coating layer 55 that does not allow oxygen components in the measurement gas G to pass therethrough. The electron conducting electrode 24 is arranged in the measured gas space 101 along with the sensor cell 43 in the width direction W, and is covered with a coating layer 55 so as not to be exposed to the measured gas G. In this case, the electrode material used for the electron conduction electrode 24 can obtain the same effect as the above as a platinum material used normally. In addition, the thickness of the coating layer 55 can be made as thin as possible within a range in which the oxygen component in the measurement gas G is not transmitted.

(Example 3)
In this example, the gas sensor element 1 includes a monitor cell 42 in addition to the sensor cell 43 and the electron conduction detection cell 44.
As shown in FIG. 8, the monitor cell 42 has the monitor electrode 22 provided on the surface 201 on the measured gas space 101 side of the solid electrolyte body 2 provided with the sensor electrode 23 and the electron conducting electrode 24. The monitor electrode 22 is formed side by side with the sensor electrode 23 and the electron conduction detection cell 44 in the width direction W orthogonal to the longitudinal direction L of the surface 201 of the solid electrolyte body 2 on the measured gas G side. The sensor electrode 23, the electron conduction electrode 24, and the monitor electrode 22 are disposed in the measured gas space 101. The sensor electrode 23, the electron conduction electrode 24, and the monitor electrode 22 are arranged at equal distances from the arrangement position of the pump electrode 21 in the longitudinal direction L of the surface 201 of the solid electrolyte body 2 on the measurement gas space 101 side. The electron conducting electrode 24 is covered with a coating layer 55 that does not allow the oxygen component in the measurement gas G to pass through, as in the case shown in FIG. In addition, FIG. 8 shows the site | part corresponded to the II-II cross section of FIG.

The monitor cell 42 is configured to detect the oxygen concentration in the measured gas space 101 based on the oxygen ion current flowing between the monitor electrode 22 and the reference electrode 25.
The sensor electrode 23 is made of an electrode material that is active in decomposing NOx as a specific gas component in the measurement gas G, and the monitor electrode 22 is inactive in decomposing NOx in the measurement gas G. It is comprised with the electrode material. The sensor cell 43 detects the oxygen ion current depending on the oxygen concentration and the specific gas component concentration, while the monitor cell 42 detects the oxygen ion current depending on the oxygen concentration. In the gas sensor element 1, the concentration of the specific gas component in the measurement gas G is detected by subtracting the current detected by the monitor cell 42 from the current detected by the sensor cell 43. Thus, by using the monitor cell 42, when the gas sensor element 1 changes with time, the influence of the oxygen ion current due to residual oxygen in the gas G to be measured on the detection of the NOx concentration by the sensor cell 43 can be corrected.
Each of the current value detected by the sensor cell 43 and the current value detected by the monitor cell 42 is a value obtained by adding a current due to electron conduction to an oxygen ion current for detecting a specific gas component concentration. Become.

In addition, the influence of the electron conduction by the heater 6 on the sensor cell 43 and the monitor cell 42 can be corrected by the electron conduction detection cell 44. Specifically, when the gas sensor element 1 changes over time due to long-term use, the residual oxygen amount in the measurement gas G after the oxygen amount is adjusted by the pump cell 41 tends to increase. This is because the oxygen amount adjustment capability of the pump cell 41 is reduced due to the deterioration of the pump electrode 21 in contact with the gas G to be measured.
Moreover, when the gas sensor element 1 changes with time due to long-term use and the pump electrode 21 deteriorates, the resistance value between the pump electrode 21 and the reference electrode 25 increases. This resistance value tends to decrease as the temperature increases. Therefore, when the resistance value increases due to deterioration, the heating amount of the heater 6 increases in an attempt to increase the temperature of the gas sensor element 1. And in each cell 42, 43, 44, the electric current by the electron conduction from the heater 6 increases.

FIG. 9 shows the magnitudes of the currents I1, I2, and I3 flowing through the sensor cell 43, the monitor cell 42, and the electron conduction detection cell 44 in (a) the initial state before the gas sensor element 1 is deteriorated, and (b) the gas sensor element 1 It shows about the durable state after deterioration. In this case, the concentration of NOx as the specific gas component is 0 ppm.
In both of the initial state and the endurance state, the sensor cell 43 and the monitor cell 42 flow a current I3 due to electron conduction and oxygen ion currents I1 ′ and I2 ′, and the electron conduction detection cell 44 has a current I3 due to electron conduction. Only flows. Since the current I3 due to electron conduction is equal to the distance from the heating center of the heater 6 to the sensor electrode 23, the monitor electrode 22, and the electron conduction electrode 24 in both the initial state and the durable state, each cell 42 , 43 and 44 are the same. The material used for the sensor electrode 23 is more likely to cause oxygen decomposition than the material used for the monitor electrode 22. Therefore, even if the NOx concentration is 0 ppm, the oxygen ion current I1 ′ flowing through the sensor cell 43 is larger than the oxygen ion current I2 ′ flowing through the monitor cell 42.

Further, it can be seen that in the sensor cell 43 and the monitor cell 42 in the durable state, the oxygen ion currents I1 ′ and I2 ′ are increased due to the influence of the increase in the residual oxygen amount. The increase in the oxygen ion currents I1 ′ and I2 ′ can be dealt with by subtracting the value of the current I2 ′ in the monitor cell 42 from the value of the current I1 ′ in the sensor cell 43.
In the endurance state, the current I3 due to electron conduction in each of the cells 42, 43, and 44 increases as compared with the initial state as the heating amount of the heater 6 increases due to deterioration of the pump electrode 21. Recognize. This increase in current I3 due to electron conduction can be detected by the amount of increase in current value I3 in the electron conduction cell.

In the sensor cell 43 and the monitor cell 42 in the durable state, the oxygen ion currents I1 ′ and I2 ′ are changed due to the decrease in the oxygen amount adjusting ability of the pump cell 41, and the heating amount of the heater 6 is increased due to the deterioration of the pump electrode 21. The change in the current I3 due to the electron conduction caused by can be separated. In particular, by monitoring the amount of increase in the current I3 due to electron conduction, it is possible to know the degree of increase in the operating temperature of the gas sensor element 1 and the degree of deterioration of the pump electrode 21, and these are the NOx by the sensor cell 43 and the monitor cell 42. It is possible to detect the influence of concentration on detection accuracy. Therefore, according to the gas sensor element 1 of this example, it is possible to accurately detect the NOx concentration by learning the change in the operating temperature.
Also in this example, the other configurations and the reference numerals in the drawing are the same as those in the first and second embodiments, and the same effects as those in the first and second embodiments can be obtained.

Further, by monitoring the amount of change of the current I3 in the electron conduction detection cell 44, failure diagnosis (temperature abnormality, pump cell capacity abnormality, etc.) of the gas sensor element 1 can be performed.
Note that the amount of current I3 due to electron conduction cannot be known only by using the sensor cell 43 and the monitor cell 42 without using the electron conduction detection cell 44. Therefore, in order to know the amount of the current I3 due to electron conduction, it is necessary to use the electron conduction detection cell 44.

Example 4
In this example, the conductor layer 62 of the heater 6 is energized so that the current value detected by the electron conduction detection cell 44 is constant.
The value of the current flowing through the electron conduction detection cell 44 due to electron conduction has a correlation with the operating temperature of the gas sensor element 1. Further, the electron conduction detection cell 44 does not detect an oxygen ion current generated by oxygen decomposition in the measurement gas G, and the electron conduction electrode 24 of the electron conduction detection cell 44 decomposes the oxygen component in the measurement gas G. Almost no deterioration over time due to Therefore, the operating temperature of the gas sensor element 1 can be accurately controlled by energizing the conductor layer 62 so that the current value detected by the electron conduction detection cell 44 is constant.
Also in this example, other configurations and the reference numerals in the drawings are the same as those in the first to third embodiments, and the same effects as those in the first to third embodiments can be obtained.

DESCRIPTION OF SYMBOLS 1 Gas sensor element 101 Gas space to be measured 2 Solid electrolyte body 21 Pump electrode 22 Monitor electrode 23 Sensor electrode 24 Electron conduction electrode 25 Reference electrode 3 Diffusion resistor 41 Pump cell 42 Monitor cell 43 Sensor cell 44 Electron conduction detection cell 6 Heater G Gas to be measured

Claims (5)

A solid electrolyte body (2) having oxygen ion conductivity;
A measurement gas space (101) formed on one surface side of the solid electrolyte body and into which a measurement gas (G) that has passed through the diffusion resistor (3) is introduced;
A sensor electrode (23) provided on the surface of the solid electrolyte body on the measured gas space side;
An electron conduction electrode (24) provided on a surface of the solid electrolyte body on the gas space to be measured side;
A reference electrode (25) provided on the other surface of the solid electrolyte body;
A heater (6) for heating the sensor electrode,
A sensor cell for detecting a concentration of a specific gas component in the measured gas space based on an oxygen ion current flowing between the sensor electrode and the reference electrode by the solid electrolyte body, the sensor electrode, and the reference electrode ( 43),
An electron conduction detection cell (44) for detecting the current flowing between the electron conduction electrode and the reference electrode upon receiving the electron conduction of the heater by the solid electrolyte body, the electron conduction electrode and the reference electrode. A gas sensor comprising:
The distance from the sensor electrode to the heating center of the heater is shorter than the distance from the electron conduction electrode to the heating center of the heater,
A gas sensor calibrated so that a difference value obtained by subtracting a current value in the electron conduction detection cell from a current value in the sensor cell becomes zero under a condition where the specific gas component concentration is 0 ppm . The diffusion resistor is disposed on one end side, which is the side to introduce the gas to be measured, in the longitudinal direction (L) of the gas sensor,
The gas sensor according to claim 1, wherein the electron conducting electrode is located on the other end side in the longitudinal direction with respect to the sensor electrode. The gas sensor further includes a pair of pump electrodes (21, 25) provided on both surfaces of the solid electrolyte body or another solid electrolyte body laminated on the solid electrolyte body,
A pump cell (41) configured to adjust the oxygen concentration in the measured gas space by applying a voltage between the pair of pump electrodes by the solid electrolyte body or the other solid electrolyte body and the pair of pump electrodes. The gas sensor according to claim 1 or 2.   4. The gas sensor according to claim 3, wherein the pump electrode is located on one end side, which is the side where the gas to be measured is introduced, in the longitudinal direction (L) of the gas sensor with respect to the sensor electrode.   The gas sensor according to any one of claims 1 to 4, wherein the electron conducting electrode is provided on a surface of the solid electrolyte body on the gas gas space side in a state where the gas to be measured is not in contact.

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