JP2004132960A - Gas sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance measuring precision for a specified gas. <P>SOLUTION: A gas introducing passage 10 is provided to introduce the gas to be measured from the outside to a chamber of gas to be measured, and the gas chamber comprises cell arranging chambers 121, 122 for arranging electrochemical cells, and a diffusion rate-determining passage 103 for connecting a space between the cell arranging chambers 121, 122 to rate-determine the gas to be measured moving between the cell arranging chambers 121, 122. (Sn/Ln)/(S0/L0)≪0.4 is satisfied, where L0 is a route length of the gas introducing passage 10, S0 is a cross-sectional area in a direction orthogonally crossing the route length of the gas introducing passage 10, Ln represents a route length of the diffusion rate-determining passage 103, and where Sn represents a cross-sectional area in a direction orthogonally crossing the route length of the diffusion rate-determining passage 103. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a stacked gas sensor element which is installed in an exhaust system of an internal combustion engine and used for combustion control and the like.

Many elements are known as gas sensor elements incorporated in gas sensors used for controlling combustion of an automobile engine.
For example, a plurality of electrochemical cells including a solid electrolyte plate and a pair of electrodes provided on the solid electrolyte plate and a plurality of the electrochemical cells, and a measured gas chamber having a gas introduction passage for introducing a gas to be measured from the outside. 2. Description of the Related Art There is known a stacked gas sensor element including a solid electrolyte and a spacer for forming a gas to be measured.
In the gas sensor element, the measured gas chamber is a cell arrangement chamber in which an electrochemical cell is arranged, and a diffusion-controlled passage that connects the cell arrangement chambers and diffusion-controls the measured gas moving between the cell arrangement chambers. And

This gas sensor element introduces a gas to be measured into a gas chamber to be measured from a gas introduction path, and measures the concentration of the gas to be measured in an electrochemical cell installed in the gas chamber to be measured. In the gas sensor element, a plurality of types of electrochemical cells are arranged, one is a pump cell for adjusting the oxygen concentration of the gas chamber to be measured, and the other is a sensor cell for measuring the specific gas concentration in the gas chamber to be measured. is there. The specific gas whose concentration is to be measured is decomposed on the electrode of the sensor cell, and the specific gas concentration is detected by measuring the oxygen ion current obtained from the generated oxygen ions.
JP-A-2000-275215 (page 5, FIG. 1)

By the way, when oxygen exists near the electrode of the sensor cell, the oxygen ion current flowing through the sensor cell is the sum of the current derived from the specific gas and the current derived from oxygen.
Therefore, when the oxygen concentration fluctuates in the vicinity of the sensor cell of the gas chamber to be measured, the oxygen ion current changes with the oxygen concentration even if the specific gas concentration does not fluctuate. Becomes difficult, and the measurement accuracy decreases.

The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a gas sensor element having high measurement accuracy for a specific gas.

According to a first aspect of the present invention, the solid electrolyte plate includes an electrochemical cell including a solid electrolyte plate, a pair of electrodes provided on the solid electrolyte plate, and a measured gas chamber configured to introduce a measured gas from outside. In the gas sensor element of a stacked type configured by stacking spacers for forming the gas chamber to be measured,
The gas sensor element has a plurality of electrochemical cells,
At least one electrochemical cell is a pump cell that pumps oxygen from the measured gas chamber and adjusts the oxygen concentration in the measured gas chamber.
At least one electrochemical cell is a sensor cell that decomposes a specific gas in the gas chamber to be measured and measures a specific gas concentration in the gas chamber to be measured using oxygen ions generated by the decomposition.
For the measured gas chamber, has a gas introduction path configured to introduce a measured gas from outside,
The measured gas chamber includes a cell arrangement chamber in which the electrochemical cell is arranged, and a diffusion-controlled passage connecting the cell arrangement chambers and diffusion-controlling the measured gas moving between the cell arrangement chambers. ,
The path length of the gas introduction path is L0, the cross-sectional area in the direction orthogonal to the path length of the gas introduction path is S0, the path length of the diffusion-controlled path is Ln, and the cross-sectional area in the direction perpendicular to the path length of the diffusion-controlled path is L0. If Sn
(Sn / Ln) / (S0 / L0) ≦ 0.4
The gas sensor element according to claim 1 (claim 1).

The gas sensor element according to the first aspect of the present invention has a value (Sn / Ln) between the path length L0 of the gas introduction path, the cross-sectional area S0 of the gas introduction path, the path length Ln of the diffusion control path, and the cross-sectional area Sn of the diffusion control path. The relationship of /(S0/L0)≦0.4 is established.
By the way, in the gas sensor, the gas to be measured enters the gas chamber to be measured from the gas introduction passage, and in the cell arrangement chamber where the pump cell of the gas chamber to be measured is installed, the concentration of oxygen in the gas to be measured is substantially reduced by pumping of the pump cell. It is constant (small time fluctuation) and low in density.
If the gas to be measured moves to the cell placement room with the sensor cell before sufficient pumping is performed, the oxygen concentration may increase or the oxygen concentration may fluctuate over time in the cell placement room with the sensor cell. There is.
Further, as will be described later, the pumping ability of the pump cell may temporarily decrease depending on the usage environment of the gas sensor element. In this case, there is a possibility that the gas to be measured having a high oxygen concentration or the gas to be measured whose oxygen concentration fluctuates with time moves to the cell arrangement chamber provided with the sensor cells.

Therefore, by controlling the diffusion of the gas from the cell arrangement chamber provided with the pump cell to the cell arrangement chamber provided with the sensor cell to an appropriate state, oxygen contained in the gas to be measured diffuses into the cell arrangement chamber provided with the sensor cell. Before the measurement, the oxygen can be sufficiently removed from the gas chamber to be measured by using the pump cell, the oxygen concentration in the cell arrangement chamber in which the sensor cell is provided is thinner, and the oxygen concentration hardly fluctuates over time. Therefore, the output fluctuation of the sensor cell caused by the high oxygen concentration and the time fluctuation can be extremely reduced.

Further, even when the specific gas concentration is zero, an output is generated from the sensor cell, and a current flowing through the sensor cell causing the output is called an offset current.
In the configuration according to the first aspect of the present invention, the diffusion of oxygen into the cell arrangement chamber in which the sensor cell is provided can be limited, so that the offset current is low, time variation is difficult, and the measurement accuracy of the gas sensor element for a specific gas is increased. be able to.
Further, when the offset current is so large as to be not negligible as compared with the current value derived from the specific gas flowing through the sensor cell, the resolution of the gas sensor element with respect to the concentration change of the specific gas may be reduced.
If (Sn / Ln) / (S0 / L0) is larger than 0.4, the offset current becomes large, and the detection accuracy of the specific gas concentration may be deteriorated.

In addition, when the gas sensor element is installed and used in the exhaust system of a vehicle engine such as an automobile, the oxygen concentration and temperature in the exhaust gas fluctuate due to fluctuations in engine operating conditions and the like, and the oxygen pumping ability of the pump cell varies. Sometimes. When the oxygen pumping capability of the pump cell varies, the value of the offset current increases or decreases according to the amount of oxygen pumping.
The gas sensor element according to the first aspect of the invention can detect the specific gas concentration with excellent accuracy in an environment where the oxygen pumping ability of the pump cell varies because the value of the offset current is small and the fluctuation of the offset current is small.

According to a second aspect of the present invention, there is provided an electrochemical cell including a solid electrolyte plate, a pair of electrodes provided on the solid electrolyte plate, and a measured gas chamber configured to introduce a measured gas from the outside. In the gas sensor element of a stacked type configured by stacking spacers for forming the gas chamber to be measured,
The gas sensor element has a plurality of electrochemical cells,
At least one electrochemical cell is a pump cell that pumps oxygen from the measured gas chamber and adjusts the oxygen concentration in the measured gas chamber.
At least one electrochemical cell is a sensor cell that decomposes a specific gas in the gas chamber to be measured and measures a specific gas concentration in the gas chamber to be measured using oxygen ions generated by the decomposition.
For the measured gas chamber, has a gas introduction path configured to introduce a measured gas from outside,
The measured gas chamber includes a cell arrangement chamber in which the electrochemical cell is arranged, and a diffusion-controlled passage connecting the cell arrangement chambers and diffusion-controlling the measured gas moving between the cell arrangement chambers. ,
At the oxygen concentration of 20%, between the pump limit current value Ip flowing between the electrodes of the pump cell and the sensor limit current value Is flowing between the electrodes of the sensor cell (provided that only the sensor cell is operated without operating the pump cell) The gas sensor element is characterized in that a relationship of Is / Ip ≦ 0.3 is satisfied.

In the gas sensor element, the voltage applied to the pump cell fluctuates, but the pump current flowing through the pump cell hardly changes, and the current-voltage characteristic diagram may be flat. A substantially constant current value in such a voltage range is called a limit current value. The limit current value in the pump cell is referred to herein as a pump limit current value. If the pumping ability of the pump cell for oxygen is high, the pump limit current value increases even if the oxygen concentration contained in the gas to be measured is equal.
The limit current value in the sensor cell is referred to as a sensor limit current value here.
The magnitude of the sensor current flowing through the sensor cell without operating the pump cell corresponds to the amount of oxygen ions obtained from oxygen in the gas to be measured and the specific gas to be measured in the gas to be measured. If the diffusion of the gas to be measured into the vicinity of the sensor cell is restricted, Is decreases.

In the second invention, the gas sensor element is configured so as to satisfy Is / Ip ≦ 0.3, and the pumping capacity of the pump cell for oxygen is increased, and the gas sensor element is moved from the cell placement chamber provided with the pump cell to the cell placement chamber provided with the sensor cell. , The oxygen concentration in the vicinity of the sensor cell can be made thinner, and the time variation of the oxygen concentration in the vicinity of the sensor cell can be reduced.
As a result, the offset current flowing through the sensor cell when the specific gas concentration is zero can be made small and hardly fluctuate with time, and the measurement accuracy of the gas sensor element for the specific gas concentration can be increased.

If Is / Ip is greater than 0.3, the offset current is so large that it cannot be ignored compared to the current value derived from the specific gas flowing through the sensor cell. There is a possibility that.
In particular, when the specific gas concentration is detected by the fluctuation of the sensor current flowing through the sensor cell, if the fluctuation of the offset current becomes dominant with respect to the fluctuation of the sensor current, there is a possibility that the measurement accuracy may be significantly deteriorated.

A third invention provides an electrochemical cell comprising a solid electrolyte plate, a pair of electrodes provided on the solid electrolyte plate, and a measured gas chamber configured to introduce a measured gas from the outside. In the gas sensor element of a stacked type configured by stacking spacers for forming the gas chamber to be measured,
The gas sensor element has a plurality of electrochemical cells,
At least one electrochemical cell is a pump cell that pumps oxygen from the measured gas chamber and adjusts the oxygen concentration in the measured gas chamber.
At least one electrochemical cell is a sensor cell that decomposes a specific gas in the gas chamber to be measured and measures a specific gas concentration in the gas chamber to be measured using oxygen ions generated by the decomposition.
For the measured gas chamber, has a gas introduction path configured to introduce a measured gas from outside,
The measured gas chamber includes a cell arrangement chamber in which the electrochemical cell is arranged, and a diffusion-controlled passage connecting the cell arrangement chambers and diffusion-controlling the measured gas moving between the cell arrangement chambers. ,
The sensor limit current value Is flowing between the electrodes of the sensor cell at an oxygen concentration of 20% (where only the sensor cell is operated without operating the pump cell) and the electrode area of the pump cell exposed in the cell arrangement chamber are Sp. And the following relationship is satisfied: Is / Sp ≦ 0.06 mA / mm ² (Claim 3).

Increasing the electrode area of the pump cell increases the oxygen pumping capability of the pump cell. By setting Is / Sp ≦ 0.06 mA / mm ² , the oxygen pumping capacity of the pump cell becomes larger than the diffusion amount of gas diffusion from the cell arrangement chamber provided with the pump cell to the cell arrangement chamber provided with the sensor cell. In addition, the oxygen concentration in the vicinity of the sensor cell can be made thinner, and the time variation of the oxygen concentration in the vicinity of the sensor cell can be reduced.
As a result, the offset current flowing through the sensor cell when the specific gas concentration is zero can be made small and hardly fluctuate with time, and the measurement accuracy of the gas sensor element for the specific gas concentration can be increased.

If Is / Sp is larger than 0.06 mA / mm ² , the offset current is so large that it cannot be ignored compared to the current value derived from the specific gas flowing through the sensor cell. Resolution may decrease.
In particular, when the specific gas concentration is detected by the fluctuation of the sensor current flowing through the sensor cell, if the fluctuation of the offset current becomes dominant with respect to the fluctuation of the sensor current, there is a possibility that the measurement accuracy may be significantly deteriorated.
It is more preferable that Is / Sp ≦ 0.05 or less.

As described above, according to the first to third aspects, a gas sensor element having high measurement accuracy for a specific gas can be provided.

In the first invention (claim 1), (Sn / Ln) / (S0 / L0) is more preferably not more than 0.04.
As a result, the offset current can be further reduced, and when the gas sensor element is used in an exhaust system of a vehicle engine such as an automobile, when the operating condition of the engine fluctuates and the offset current changes, the specific gas can be reduced. Of the detection accuracy can be made ± 1% or less.

In the exhaust system of a vehicle engine such as an automobile, the gas sensor element according to the first to third aspects of the present invention is mounted after the air pollutant purification catalyst in the exhaust gas (that is, the gas sensor element is exhausted from the purification catalyst). By installing the catalyst downstream of the gas flow), the detection of catalyst deterioration can be monitored more accurately. If the purification catalyst deteriorates, more air pollutants are detected downstream of the purification catalyst, and the gas sensor elements according to the first to third inventions can be used for detecting the concentration of NOx, one of the air pollutants. That's why.
Further, when the catalyst is deteriorated, it is detected by the gas sensor element, and the purging rate can be maintained at a high level by performing the rich purge and the regeneration processing.
By using the gas sensor element according to the first to third inventions having high detection accuracy, the purification rate of the purification catalyst can be maintained at a high level.

下限 The lower limit of the value of (Sn / Ln) / (S0 / L0) is preferably set to 0.01. If it is smaller than this, the amount of gas to be measured becomes very small, and accordingly, the amount of oxygen ion current flowing through the sensor cell also becomes small. Therefore, it becomes difficult to detect the oxygen ion current in the sensor cell, and the measurement accuracy may be reduced.

Examples of the electrochemical cell include the above-described pump cell and sensor cell, a monitor cell for monitoring the oxygen concentration in the gas chamber to be measured, an oxygen sensor cell for measuring the oxygen concentration outside the element, and the like.
In the case where the gas sensor element according to the first to third aspects of the present invention is used by being built in a gas sensor particularly installed in an exhaust system of an engine, the electrochemical cell is used as the electrochemical cell based on the oxygen concentration detected in the oxygen sensor cell. There is an air-fuel ratio cell for detecting the air-fuel ratio, a λ cell for detecting the stoichiometric air-fuel ratio, and the like.

The oxygen sensor cell includes electrodes facing the measured gas chamber and the reference gas chamber, and measures the oxygen concentration from the electromotive force generated by both electrodes. There is a cell that includes electrodes facing each other and measures the oxygen concentration from a limit current generated by applying a voltage to both electrodes.

In the first to third inventions, the gas introduction path for introducing the gas to be measured from the outside can be constituted by a through hole such as a pinhole. Alternatively, the gas introduction path can be constituted by a through hole such as a pinhole whose entrance side is covered with a porous body (see FIGS. 1 and 3).
Particularly in the first invention, in the latter case, the path length L0 of the gas introduction path is the shortest distance of the through hole such as a pinhole and the porous body covering the entrance side. The cross-sectional area S0 in the direction orthogonal to the path length of the gas introduction path is a cross-sectional area in a through hole such as a pinhole.
Further, the gas introduction path may be configured such that a porous body is filled in a through hole such as a pinhole. Only a part of the inside may be filled, or the entire inside may be filled.

In the first to third inventions, the gas chamber to be measured includes the cell arrangement chamber and the diffusion-controlled passage as described above.
The gas chamber to be measured may be provided with a diffusion-controlled passage between the cell arrangement chambers. Alternatively, a configuration may be adopted in which some of the cell arrangement chambers are directly adjacently connected to each other, and no diffusion-controlling passage is provided therebetween.
The diffusion-controlling passage may be constituted by a narrowed portion narrower than the cell arrangement chamber, but may be constituted so as to have the same width as the cell arrangement chamber (see FIG. 6 described later).

The path length of the gas introduction path is L0, and the cross-sectional area in the direction orthogonal to the path length of the gas introduction path is S0.
In the case of a configuration having a plurality of gas introduction paths, the path length L0 employs the shortest of the plurality of gas introduction paths. Also, the cross-sectional area S0 employs the total cross-sectional area of a plurality of gas introduction paths.
The path length L0 of the gas introduction path is determined by the center and the exit side (facing the measured gas chamber) of the gas introduction path on the gas inlet side (facing the outside of the gas sensor element and entering the gas to be measured). This is a line segment connecting the center of the measurement gas (where the measurement gas enters the measurement gas chamber) and the shortest length when the measurement gas passes through the gas introduction path. The cross-sectional area on a plane orthogonal to the path length is S0.

The simplest configuration of the gas chamber to be measured is a configuration including two cell disposition chambers and a diffusion-controlling passage provided between the two cell disposition chambers, as described in Example 1 described later. Further, if there are three cell arrangement chambers, which are assumed to be A, B, and C, there is no diffusion-controlling path between the cell arrangement chambers for A and B, and there is no diffusion control between the cell arrangement chambers for B and C. Some configurations have a rate-limiting passage.
Further, there may be a case where a plurality of diffusion control paths are provided. For example, there are three cell arrangement chambers, and the respective cell arrangement chambers are connected by a diffusion-controlled passage.
As for Sn / Ln in the case where there are a plurality of diffusion control paths, Sn / Ln having the smallest value as a result of calculating the value of Sn / Ln in each diffusion control path is adopted in the equation of the first invention.

The gas sensor element according to the first to third aspects of the present invention includes a solid electrolyte plate forming an electrochemical cell, a spacer forming a gas chamber to be measured, a spacer for a reference gas chamber, and a gas sensor element having a predetermined shape. And a plate-shaped ceramic heater or the like for heating to the activation temperature.
Further, the specific gas in the gas sensor element according to the first to third inventions is a gas such as NOx, CO, and HC.

In the second and third inventions, the pump cell is an electrochemical cell having the ability to pump oxygen, and the electrochemical cell for detecting the oxygen concentration in the measured gas chamber is a pump cell according to the present invention. May be included. This is because oxygen ionized at the time of detecting the oxygen concentration flows between the electrodes, and may exhibit oxygen pumping ability. Electrochemical cells having other functions may also exhibit oxygen pumping capability, and may be included in the pump cell of the present invention.

Further, the width Wn of the diffusion-controlling passage in the width direction orthogonal to the longitudinal direction of the gas sensor element is preferably 0.8 mm or less (claim 4).
Thereby, the offset current can be reduced. If the width is larger than 0.8 mm, the offset current may increase.

More preferably, the width Wn is 0.4 mm or less.
This makes it possible to further reduce the offset current, and when the gas sensor element according to the first invention is installed and used in the exhaust system of an automobile engine as described above, the operating conditions of the engine fluctuate, and so on. Can be reduced to ± 1% or less in the detection accuracy of the specific gas.
The lower limit of the width Wn can be set to 0.1 mm. If it is smaller than this, manufacturing may be difficult. Further, the response of the gas sensor element may be reduced. When there are a plurality of diffusion-controlled paths, it is preferable that the above-mentioned requirements are satisfied for all the diffusion-controlled paths.

Further, it is preferable that the path length Ln of the diffusion control path is 0.4 mm or more.
Thus, the offset current can be reduced.
If the length is shorter than 0.4 mm, the offset current may increase and the measurement accuracy of the gas sensor element may deteriorate.
Further, the path length Ln is more preferably set to 0.6 mm or more.

The upper limit of the path length Ln is preferably set to 3 mm. If the length is longer than this, the time required for the gas to be measured to enter from the introduction path and reach each cell arrangement chamber becomes longer, and the response of the gas sensor element may be reduced.
When there are a plurality of diffusion-controlled paths, it is preferable that the above-mentioned requirements be satisfied for all of them.

In addition, the pump cell is arranged in a cell arrangement chamber closest to the gas introduction path, and the sensor cell is arranged in a cell arrangement chamber farthest from the gas introduction path,
Assuming that the volume of the cell arrangement chamber in which the sensor cells are arranged is v and the total volume of the cell arrangement chamber is V, v / V ≦ 0.5 is preferred (claim 6).
Since the gas to be measured after the adjustment of the oxygen concentration by the pump cell needs to be supplied to the sensor cell, it is necessary to provide the sensor cell downstream of the flow of the gas to be measured. In addition, by setting v / V ≦ 0.5, it is possible to reduce the offset current, improve the accuracy, and obtain good responsiveness. If it becomes larger than 0.5, the offset current may increase.

Further, v / V is more preferably set to 0.25 or less.
Thus, when the gas sensor element according to the first invention is installed and used in the exhaust system of an automobile engine as described above, even when the offset current changes due to a change in the operating conditions of the engine, etc. Variation in detection accuracy can be made ± 1% or less.
The lower limit of v / V is preferably set to 0.1. If this is the case, the output sensitivity may be reduced.

Further, it is preferable that the thickness t of the cell arrangement chamber along the stacking direction of the gas sensor elements is 0.16 mm or less.
Thereby, the offset current can be reduced. If it is thicker than 0.16 mm, the offset current may increase.

Further, it is more preferable that the thickness t of the cell arrangement chamber is 0.1 mm or less. More preferably, it is 0.05 mm or less.
Thus, when the gas sensor element according to the first invention is installed and used in the exhaust system of an automobile engine as described above, even when the offset current changes due to a change in the operating conditions of the engine, etc. Variation in detection accuracy can be made ± 1% or less.
The lower limit of the thickness t of the cell arrangement chamber is preferably set to 0.01 mm. If the thickness t is smaller than this, the output current may be smaller. In addition, responsiveness may be reduced.
In addition, when there are a plurality of cell arrangement chambers or when the thickness t is different in one cell arrangement chamber, the above-mentioned requirement is satisfied for the minimum thickness.

Further, it is preferable that the total volume of the cell arrangement chamber is 4.1 mm ³ or less (claim 8).
Thereby, the offset current can be reduced.
If the total volume is larger than 4.1 mm ³ , the offset current may increase.

Further, the total volume of the cell arrangement chamber is more preferably not more than 3.6 mm ³ .
Thus, when the gas sensor element according to the first invention is installed and used in the exhaust system of an automobile engine as described above, even when the offset current changes due to a change in the operating conditions of the engine, etc. Variation in detection accuracy can be made ± 1% or less. When the total volume of the cell arrangement chamber is 0.1 mm ³ , the output current is too small.

In addition, it is preferable that a porous body is disposed in any part of the gas introduction path, the cell arrangement chamber, and the diffusion control path (claim 9).
Thereby, the offset current can be reduced.
The porosity of the porous body is preferably 10 to 50%.
Thereby, the offset current can be reduced, and the response performance of the gas sensor element can be set to an appropriate state.
If it is less than 10%, the diffusion of the gas to be measured is hindered, and the response performance of the gas sensor element may be reduced. If it is more than 50%, the effect of reducing the offset current may be reduced.
Further, the porous material is preferably an alumina and / or zirconia-containing material.

Further, it is preferable that the electrode exposed in the cell arrangement chamber of the pump cell has a region where the surface temperature becomes 800 ° C. or more when the gas sensor element is used (claim 11).
The higher the temperature of the electrode, the higher the pumping ability of the pump cell. Therefore, the higher the temperature, which does not exceed the heat resistance limit of the gas sensor element, is preferable to reduce the offset current.

(Example 1)
As shown in FIGS. 1 to 3, the gas sensor element 1 according to the first invention has a pair of electrodes 31 and 32, 41 and 42, 51 and 52 provided on the solid electrolyte plate 11, and a pair of electrodes provided on the solid electrolyte plate 13. An electrochemical cell comprising electrodes 21 and 22 and a gas chamber to be measured configured to introduce a gas to be measured from the outside, and a spacer 12 for forming the gas chamber to be measured with respect to the solid electrolyte plates 11 and 13. Is a laminated gas sensor element 1 configured by laminating.

The gas sensor element 1 has a plurality of electrochemical cells.
One electrochemical cell is a pump cell 2 for pumping oxygen from the gas chamber to be measured and adjusting the oxygen concentration in the gas chamber to be measured.
One electrochemical cell is a sensor cell 4 that decomposes NOx in the measured gas chamber and measures the NOx concentration in the measured gas chamber using oxygen ions generated by the decomposition.
In addition, it has a monitor cell 3 and a λ cell 5 as electrochemical cells.

Further, a gas introduction path 10 configured to introduce a gas to be measured from the outside to the gas chamber to be measured is provided, and the gas chamber to be measured is a third chamber in which the electrochemical cells 2, 3, and 4 are arranged. The first and second cell placement chambers 121 and 122 are connected to each other, and the diffusion control passage 103 is connected between the cell placement chambers 121 and 122 and controls the diffusion of the gas to be measured moving between the cell placement chambers 121 and 122.

As shown in FIG. 3, the path length of the gas introduction path 10 is L0, the cross-sectional area in the direction perpendicular to the path length of the gas introduction path 10 is S0, the path length of the diffusion control path 103 is Ln, and the diffusion control path 103 is (Sn / Ln) / (S0 / L0) ≦ 0.4, where Sn is the cross-sectional area in the direction orthogonal to the path length of

The details will be described below.
The gas sensor element 1 of this embodiment is installed in an exhaust system of an automobile engine and is used by being incorporated in a gas sensor used for controlling combustion of the engine. Then, the NOx concentration in the exhaust gas is measured, the oxygen concentration is measured, and the λ point (the stoichiometric air-fuel ratio point) in the engine is detected.

The gas sensor element 1 includes first and second cell placement chambers 121 and 122 and first and second reference gas chambers 140 and 160, and a pump cell 2 and a second cell that pump oxygen to the first cell placement chamber 121. A monitor cell 3 for monitoring the oxygen concentration in the placement chamber 122, a sensor cell 4 for detecting the NOx concentration in the second cell placement chamber 122, and a λ for detecting the λ point of the engine based on the oxygen concentration in the gas to be measured outside the gas sensor element 1. It has a cell 5.

As shown in FIG. 1, in this example, the heater unit 6, the spacer 14 for the first reference gas chamber 140, the solid electrolytic plate 13 for the pump cell, the first and second cell placement chambers 121 and 122, and the diffusion-controlling passage are arranged in this order from the bottom of the drawing. The gas sensor element 1 is formed by sequentially stacking a spacer 12 for forming a measured gas chamber 103, a solid electrolyte plate 11, a spacer 16 for forming a second reference gas chamber 160, and a porous body 17.
Exhaust gas is introduced into the first and second cell arrangement chambers 121 and 122 from the outside through the gas introduction passage 10, and air is introduced into the first and second reference gas chambers 140 and 160.

The first cell placement chamber 121 communicates directly with the gas introduction passage 10 and is a place where the pump cell 2 is placed. The second cell placement chamber 122 communicates with the first cell placement chamber 121 through the diffusion resistance passage 103, and is a place where the monitor cell 3 and the sensor cell 4 are placed. As shown in FIG. 2, the monitor cell 3 and the sensor cell 4 are arranged side by side in the width direction of the gas sensor element 1.

First and second cell placement chambers 121 and 122 are formed between the solid electrolyte plate 11, the pump cell solid electrolyte plate 13, and the spacer 12.
Further, the gas sensor element 1 of the present example has a porous body 17 that covers the gas introduction passage 10 of the solid electrolyte plate 11, and a spacer that forms a second reference gas chamber 160 adjacent to the porous body 17. 16 is arranged.
Further, a first reference gas chamber 140 is formed by the spacer 14 between the solid electrolyte plate 13 for the pump cell, the spacer 14, and the heater 6.

The heater section 6 has a heater substrate 15 and a heating element 61 provided on the heater substrate 15. The solid electrolyte plate 11 and the pump cell solid electrolyte plate 13 are made of zirconia ceramic, and the heater substrate 15, the spacers 14, 12, 16 and the porous body 17 are made of insulating alumina ceramic.

As shown in FIGS. 1 and 2, the pump cell 2 includes a first pump electrode 21 facing a first cell placement chamber 121 provided on a solid electrolyte plate 13 for a pump cell, and a second pump electrode facing a first reference gas chamber 140. 22. Both electrodes 21 and 22 are connected to a pump circuit 25 having a variable power supply 251 and an ammeter 252.

The monitor cell 3 includes a measured gas side electrode 32 serving as a second cell placement chamber 122 provided on the solid electrolyte plate 11, and a reference electrode 31 facing the second reference gas chamber 160. The electrodes 31 and 32 are connected to a monitor circuit 35 having a power supply 351 and an ammeter 352.
In order to control the operation of the pump cell 2 by the monitor cell 3, a feedback circuit 255 from the ammeter 352 to the power supply 251 is provided.
Although the feedback circuit 255 is divided and shown in FIG. 1 and FIG. 2, the position of z shown in both drawings is a division point.

The sensor cell 4 includes the measured gas side electrode 42 facing the second cell placement chamber 122 provided on the solid electrolyte plate 11, and the reference electrode 41 facing the second reference gas chamber 160. Both electrodes 41 and 42 are connected to a sensor circuit 45 having a power supply 451 and an ammeter 452.

As shown in FIG. 1, the λ cell 5 is provided between the solid electrolyte plate 11 and the porous body 17, and the measured gas side electrode 52 in contact with the measured gas outside the element through the porous body 17, the second reference gas It comprises a chamber 160 and a reference electrode 51 facing the chamber. Both electrodes 51 and 52 are connected to a λ cell circuit 55 having a voltmeter 552.
The heating element 61 of the heater 6 is connected to a heater circuit 65 having a power supply 651 through heater leads and terminals (not shown).
The reference electrodes 31, 41, and 51 of the monitor cell 3, the sensor cell 4, and the λ cell 5 are formed of a common electrode integrally formed as shown in FIGS.

Further, as shown in FIGS. 1 and 3A, the gas introduction path 10 of the present embodiment is composed of a pinhole 102 whose entrance side is covered with a porous body 101. Therefore, the path length L0 of the gas introduction path 10 is the shortest distance including the pinhole 102 and the porous body 101 covering the entrance side. The cross-sectional area S0 of the gas introduction path 10 in the direction orthogonal to the path length L0 is determined from the cross-sectional area of the pinhole 102.
Then, as shown in FIGS. 3A and 3B, the path length L0 of the gas introduction path 10 of the gas sensor element 1 according to the present example is 0.28 mm, the sectional area S0 of the gas introduction path 10 is 0.13 mm ² , The path length Ln of the diffusion control passage 103 is 1.6 mm, and the cross-sectional area Sn of the diffusion control passage 103 is 0.04 mm ² . Therefore, (Sn / Ln) / (S0 / L0) is 0.05, which is 0.4 or less.

The width Wn of the diffusion-controlling passage in the width direction orthogonal to the longitudinal direction of the gas sensor element 1 is 0.32 mm, which is 0.8 mm or less.
The volume v of the second cell placement chamber 122 in which the sensor cells 4 are placed is 0.94 mm ³ , the volume of the first cell placement chamber 121 with which the gas introduction path 10 directly communicates is 1.54 mm ³ , and the total volume V is 2.48 mm ³ And becomes 0.5 or less when v / V = 0.38.

In addition, the thickness t of the first and second cell placement chambers 121 and 122 along the stacking direction of the gas sensor element 1 is different from the surface of the electrode 21 provided on the solid electrolyte plate 13 and the solid electrolyte plate 11 facing the electrode 21. , Or the distance between the electrode 32 or 42 provided on the solid electrolyte plate 11 facing the surface of the solid electrolyte plate 13, whichever is smaller.
In the gas sensor element 1 according to this example, t shown in FIG. 3A is the thickness of the cell arrangement chamber, and is 0.12 mm or less and 0.16 mm or less.
Further, in the gas sensor element 1 of this embodiment, the total volume of the first and second cell placement chamber 121 is 2.48 mm ^3, is 4.1 mm ³ or less.

Further, as shown in FIG. 3B, in the spacer 12, the minimum distance K1 between the side surfaces 191 and 192 of the gas sensor element 1 and the inner side surfaces 195 and 196 of the first cell placement chamber 121, and the side surfaces 191 and 192 of the gas sensor element 1. The minimum distance K2 between the inner surface 193 and the inner side surface 193 of the second cell placement chamber 122 is as shown in the figure, and both the distances K1 and K2 are preferably 0.5 mm or more. This makes it difficult for the gas to be measured to leak from the first and second cell arrangement chambers 121 and 122 to the side surface of the gas sensor element 1. More preferably, the distances K1 and K2 are set to 0.8 mm or more.

Further, a method for manufacturing the gas sensor element 1 of the present example will be described.
Green sheets of the heater substrate 15, the spacer 14, the solid electrolyte plate 13, the solid electrolyte plate 11, and the porous body 17 are formed.
A printed portion serving as a heating element or the like is formed on the heater substrate 15 by printing a paste containing a conductive material. Further, on the solid electrolyte plate 13, a printed portion serving as each electrode is formed by printing a paste containing an electrode material, and a portion serving as the spacer 12 is printed using a paste containing a ceramic material.
In addition, a printed portion serving as each electrode is also formed on the solid electrolyte plate 11 by using a paste, and a portion serving as the spacer 16 is formed by printing using a paste containing a ceramic material.
Thereafter, the green sheets are laminated, pressed and integrated, and fired.

The operation and effect of this example will be described.
The gas sensor element 1 of the present example has a value (Sn / Sn) between the path length L0 of the gas introduction path 10, the cross-sectional area S0 of the gas introduction path 10, the path length Ln of the diffusion control path 103, and the cross-sectional area Sn of the diffusion control path 103. Ln) / (S0 / L0) ≦ 0.4.
Therefore, before the oxygen in the gas to be measured diffused from the gas introduction path 10 diffuses into the second cell arrangement chamber 122 provided with the sensor cell 4 for detecting NOx, oxygen is removed from the gas to be measured by the pump cell 2. Can be. Therefore, the oxygen concentration in the measured gas chamber can be made thinner, and the time variation of the oxygen concentration can be made extremely small.
As a result, when the NOx concentration is zero, the offset current flowing through the sensor cell 4 is small and hardly fluctuates over time (see Embodiment 2), and the measurement accuracy of the gas sensor element 1 for NOx can be increased.

As described above, according to the present embodiment, it is possible to provide a gas sensor element having high measurement accuracy for a specific gas.

(Example 2)
In this example, the performance of the gas sensor element 1 according to Example 1 was evaluated.
Several gas sensor elements having different (Sn / Ln) / (S0 / L0) are prepared, and the current (offset current) flowing through the sensor cell when the NO concentration in the gas to be measured is zero is prepared for these gas sensor elements. It was measured. The configuration of the gas sensor element is the same as that shown in the first embodiment, and the offset current can be measured by the ammeter 452 in FIG.

Further, several gas sensor elements having different (Sn / Ln) / (S0 / L0) are prepared, and these gas sensor elements are exposed to a gas to be measured in which the NO concentration is switched from 300 ppm to 100 ppm, and the gas sensor elements are exposed to the sensor cells. The flowing current was measured by the ammeter 452 in FIG.
The time at which the NO concentration was switched is T0, the value of the ammeter 452 corresponding to the NO concentration of 300 ppm before the time T0 is I0, and the value of the ammeter 452 is 0.6I0 (a value reduced by 60%) after the time T0. The value of T1−T0 was measured with T1 being the time at which the change occurred. The smaller the value of T1-T0, the better the response of the gas sensor element.
Then, the measurement results are shown in a diagram in which the offset current is plotted on the left vertical axis, the value of T1−T0 is the response, the unit is ms, and the right vertical axis is (Sn / Ln) / (S0 / L0) on the horizontal axis. And this is shown in FIG.

As shown in the figure, it was found that when (Sn / Ln) / (S0 / L0) was larger than 0.4, the offset current exceeded 0.1 μA. In addition, it was found that the offset current increases as (Sn / Ln) / (S0 / L0) increases.
At this time, when the offset current exceeds 0.1 μA, the accuracy when the oxygen concentration is changed exceeds 10% as shown in FIG.
When (Sn / Ln) / (S0 / L0) is 0.2 or more, the response becomes smaller than 2000 ms, and after that, even if (Sn / Ln) / (S0 / L0) increases, the response becomes smaller. Gender was found to hardly change.
Therefore, it can be seen from FIG. 3 that by setting (Sn / Ln) / (S0 / L0) to 0.4 or less, a gas sensor element having high measurement accuracy and excellent responsiveness can be obtained.

In addition, several gas sensor elements according to the first embodiment having different (Sn / Ln) / (S0 / L0) were prepared, the NO concentration in the gas to be measured was constant at 0 ppm, and the oxygen concentration was 0 to 20. %, The current flowing through the sensor cell was measured by the ammeter 452 in FIG.
The change rate of the current value was determined from the current value when the oxygen concentration was shifted to 20% with respect to the current value at the oxygen concentration of 0%.
Further, a value obtained by subtracting the current value at the same oxygen concentration and the NO concentration of 0 ppm from the current position when the oxygen concentration is 0% and the NO concentration is set to 100 ppm is defined as the NO sensitivity. Asked.
Ideally, the value of the ammeter 452 should not change, so the rate of change should be zero. However, in practice, the rate of change is not zero because of the contribution from the oxygen ion current generated by the decomposition of oxygen.
FIG. 5 shows a diagram in which this change rate is adopted as accuracy as the ordinate and the abscissa is (Sn / Ln) / (S0 / L0).

As shown in the figure, when (Sn / Ln) / (S0 / L0) exceeds 0.4, the sensor current greatly increases with the change in oxygen concentration, and the accuracy exceeds 10%.
That is, it was found that by setting (Sn / Ln) / (S0 / L0) ≦ 0.4, a sensor current that hardly depends on the oxygen concentration was obtained, and a gas sensor element with excellent measurement accuracy was obtained.
If the accuracy of the gas sensor element exceeds 10%, erroneous detection of catalyst deterioration may occur, and the frequency of regeneration processing for maintaining a high purification rate of the catalyst becomes excessive, and consequently fuel efficiency deteriorates. Resulting in.
On the other hand, if the response exceeds 2 seconds, it is impossible to follow the fluctuation in exhaust gas concentration during running of the vehicle, and real-time measurement becomes difficult.

(Example 3)
In this example, a gas sensor element 1 including a gas chamber 7 to be measured as shown in FIG. 6 will be described.
As shown in FIG. 6A, in the gas sensor element 1 of the present example, a gas chamber 7 to be measured is formed between the solid electrolyte plate 11, the solid electrolyte plate 13 for the pump cell, and the spacer 12. Further, a porous body 17 that covers the gas introduction passage 10 of the solid electrolyte plate 11 is provided, and a spacer 16 that forms a second reference gas chamber 160 is disposed adjacent to the porous body 17.
Further, a first reference gas chamber 140 is formed by the spacer 14 between the solid electrolyte plate 13 for the pump cell, the spacer 14, and the heater 6.

The gas chamber 7 to be measured in this example includes first, second, and third cell arrangement chambers 71, 72, and 74, and a diffusion resistance passage 73 between the second cell arrangement chamber 72 and the third cell arrangement chamber 74. Consisting of
The pump cell 2 includes a pair of electrodes 21 and 22 provided on the solid electrolyte plate 13, and both electrodes 21 and 22 are formed so as to straddle the first to third cell arrangement chambers 71 to 74. The monitor cell 3 is placed in the second cell placement chamber 72, and the sensor cell 4 is placed in the third cell placement chamber 74.
The diffusion resistance passage 73 and the first to third cell arrangement chambers 71 to 74 have the same width.

In the gas sensor element 1 according to this example, the path length L0 of the gas introduction path 10 is 0.28 mm, and the cross-sectional area S0 of the gas introduction path 10 is 0.126 mm ² . The path length Ln of the diffusion control passage 73 is 1.6 mm, and the cross-sectional area Sn of the diffusion control passage 73 is 0.038 mm ² . Therefore, (Sn / Ln) / (S0 / L0) = 0.05, which is 0.4 or less. Other details are the same as in the first embodiment. Further, the gas sensor element 1 according to the present embodiment also has the same operation and effect as the first embodiment.

(Example 4)
The present embodiment is a gas sensor element having the same configuration as that of the first embodiment, however, as shown in FIG. 7, the second cell placement chamber 122 is filled with a porous material.
This porous material is made of alumina ceramic having the same composition as the spacer 12 forming the second cell placement chamber 122 and the like, and has a porosity of 25%.
The other details are the same as those of the first embodiment. The pump cell can sufficiently discharge oxygen and have the same functions and effects as those of the first embodiment.

(Example 5)
The present embodiment is a gas sensor element 1 having the same configuration as that of the first embodiment, but as shown in FIG. 8, three cell arrangement chambers 81, 83, and 85, and a diffusion chamber communicating between the cell arrangement chambers 81, 83, and 85. The measured gas chamber 8 has two resistance passages 82 and 84 and two gas introduction passages 801 and 802.
As shown in FIG. 8B, in the gas sensor element 1, a gas chamber 8 to be measured is formed between the solid electrolyte plate 11, the pump cell solid electrolyte plate 13, and the spacer 12. In addition, the spacer 16 forming the second reference gas chamber 160 is disposed on the solid electrolyte plate 11.
Further, a first reference gas chamber 140 is formed by the spacer 14 between the solid electrolyte plate 13 for the pump cell, the spacer 14, and the heater 6.

The measured gas chamber 8 of the present example includes first, second, and third cell disposition chambers 81, 83, and 85, and a diffusion resistance passage 82 between the first cell disposition chamber 81 and the second cell disposition chamber 83. A diffusion resistance passage 84 is provided between the two-cell arrangement chamber 83 and the third cell arrangement chamber 85.
The pump cell 2 is placed in the first cell placement chamber 81, the monitor cell 3 is placed in the second cell placement chamber 83, and the sensor cell 4 is placed in the third cell placement chamber 85.
Further, gas introduction passages 801 and 802 communicating with the first cell arrangement chamber 81 are also provided in the spacer 12, so that the gas to be measured is introduced from the side surface 805 of the gas sensor element.

In the gas sensor element 1 according to the present example, the gas introduction paths 801 and 802 have the same path length L0 and 0.28 mm. The cross-sectional area S0 of the combined gas introduction paths 801 and 802 is 0.13 mm ² .
The path lengths Ln of the diffusion control passages 82 and 84 are also equal to 0.8 mm, and the cross-sectional areas Sn of the diffusion control passages 82 and 84 are also equal to 0.038 mm ² .
Therefore, (Sn / Ln) / (S0 / L0) = 0.05, which is 0.4 or less.
Other details are the same as in the first embodiment.
Further, the gas sensor element 1 according to the present embodiment also has the same operation and effect as the first embodiment.

(Example 6)
The gas sensor element 1 according to the present example is the gas sensor element 1 as shown in FIGS.
That is, in the gas sensor element 2 having the pump cell 2, the monitor cell 3, and the sensor cell 4, the first pump electrode 21 facing the first cell arrangement chamber of the pump cell 2 is, as shown in FIG. , The diffusion controlling passage 103 and the second cell placement chamber 122 are formed. At this time, the area of the first pump electrode 21 of the pump cell is 20 mm ² .
The second pump electrode 22 facing the first reference gas chamber 140 of the pump cell 2 may be smaller than the first cell arrangement chamber 121 as shown in FIG.
By increasing the area of the first pump electrode 21 over the pump cell 2 to 20 mm ² , it is possible to more effectively discharge oxygen, which is an interfering gas in the gas to be measured.

The pump cell 2 of this example is connected to a pump circuit 25 having a variable power supply 251 and an ammeter 252. The voltage applied to the pump cell 2 from the variable power supply 251 is fed back according to the value of the ammeter 252, that is, the value of the pump current. Under control, a voltage is applied to the pump cell 2 so that the value of the ammeter 252 becomes approximately constant.
As shown in FIG. 10, the measured gas-side electrode 32 of the monitor cell 3 and the measured gas-side electrode 42 of the sensor cell 4 face the second cell placement chamber 122, and their areas are equal and 3.6 mm ² . is there.
The respective dimensions D1 to D5 of the first cell placement chamber 121, the diffusion control passage 103, and the second cell placement chamber 122 of this example are D1 = 5 mm, D2 = 1.6 mm, D3 = 2.7 mm, D4 = 14 mm, D5 = 0.24 mm.

With respect to the gas sensor element 1 according to this example, the pump limit current value Ip flowing between the electrodes 21 and 22 of the pump cell 2 and the sensor current value Is flowing between the electrodes 41 and 42 of the sensor cell 4 (when the pump cell 2 is not operated) And the offset current were measured as shown below.
That is, a gas sensor element serving as a sample is prepared, a nitrogen-diluted mixed gas having an oxygen concentration of 20% is supplied as a gas to be measured, and air having an oxygen concentration of 21% is supplied to the first and second reference gas chambers 140 and 160. did. With the variable power supply 251 of the pump circuit 25 turned off, the value of the ammeter 452 connected to the sensor circuit 45 is Is. The value of the ammeter 252 when a voltage of 0.45 V is supplied from the variable power supply 251 is Ip.

To the same gas sensor element 1 as described above, a nitrogen-diluted mixed gas containing no NOx and having an oxygen concentration of 0 to 20% is supplied as a gas to be measured, and a voltage of 0 to 0.45 V is supplied from the variable power supply 251 to supply current. The value of the ammeter 452 was measured when the total 252 reached the pump cell limit current value corresponding to each oxygen concentration, and this was defined as the offset current.
Such a measurement was performed on the gas sensor elements 1 having different widths K5 of the seven diffusion-controlled passages 103, and the measurement results are shown in FIG.
As is clear from the figure, it was found that the offset current can be suppressed to as low as 0.1 μA or less by setting Is / Ip ≦ 0.3.

Further, the response of the gas sensor element was measured in the same manner as in Example 2.
As a result, even when Is / Ip is very small, the response is 2000 ms. In addition to the above measurement results, if Is / Ip ≦ 0.3, the offset current is small and the element has excellent response. Was obtained.

(Example 7)
The gas sensor element 1 according to the present example has a configuration having five electrochemical cells as shown in FIGS.
That is, as shown in FIG. 14, the gas sensor element 1 of this example is formed by laminating a porous body 921, a solid electrolyte plate 922, a spacer 923, a solid electrolyte plate 924, a spacer 925, and a substrate 926. The heating element 61 is sandwiched between two insulating plates 927 and 928 made of alumina and generates heat when energized.

Between the solid electrolyte plate 922, the spacer 923, and the solid electrolyte plate 924, there are a gas introduction passage 97, a first cell arrangement chamber 121, a diffusion control passage 103, and a second cell arrangement chamber 122. There is a reference gas chamber 9240 between the solid electrolyte plate 924 and the spacer 925.
An electrode 911 is provided between the solid electrolyte plate 922 and the porous body 921, an electrode 912 is provided on a surface of the solid electrolyte plate 922 facing the first cell placement chamber 121, and a first cell placement chamber is provided by the solid electrolyte plate 924. On the side facing 121, there is an electrode 913.

Electrodes 914 and 916 are provided on the surface of the solid electrolyte plate 924 facing the second cell placement chamber 122. The surface of the electrode 916 is covered with a porous body 9230. Further, the electrode 914 is located at a position closer to the diffusion control passage 103.
There is an electrode 915 between the solid electrolyte plate 924 and the spacer 925. Part of the electrode 915 faces the reference gas chamber 9240.

Five electrochemical cells of the gas sensor element 1 of the present example will be described.
The five electrochemical cells are a pump cell 93, a λ cell 94, a monitor cell 945, a sub-pump cell 95, and a sensor cell 96, respectively.
A cell that discharges oxygen from the first cell placement chamber 121 of the pump cell 93 to the outside of the element. The pump cell 930 includes an electrode 911, an electrode 912, an electrode 913, and a solid electrolyte plate 922, and has a variable power supply 931 and an ammeter 932. Connected.
The λ cell 94 is a cell that detects the λ point by measuring the oxygen concentration in the gas to be measured. This is an electromotive force type cell including an electrode 911, an electrode 915, and solid electrolyte plates 922 and 924, and using the electrode 915 as a reference electrode. The λ cell 94 is connected to a λ circuit 940 having a voltmeter 942.

The monitor cell 945 is provided for monitoring the oxygen concentration in the first cell placement chamber 121 and controlling the operation of the pump cell 93. The monitor cell 945 includes an electrode 913, an electrode 915, and a solid electrolyte plate 924, and uses the electrode 915 as a reference electrode. It is an electromotive force type cell. The monitor cell 945 is connected to a monitor circuit 9450 having a voltmeter 946, and is provided with a control circuit 947 so that the variable power supply 931 of the pump circuit 930 can be controlled based on the output of the voltmeter 946.
The sub-pump cell 95 is a cell for discharging oxygen remaining in the second cell placement chamber 122, and includes an electrode 914, an electrode 915, and a solid electrolyte plate 924. The sub-pump cell 95 is connected to a sub-pump circuit 950 having a power supply 951 and an ammeter 952.

The sensor cell 96 is a cell for measuring a specific gas concentration (NOx or the like) in the second cell placement chamber 122, and includes an electrode 916, an electrode 915, and a solid electrolyte plate 924. The difference from the sub-pump cell 95 is that the electrode 915 is configured on the side exposed to the reference gas chamber 9240, and the surface of the electrode 916 is not directly exposed to the second cell placement chamber 122, and has a gas-permeable porous structure. It is covered with the body 9230 and indirectly exposed. The sensor cell 96 is connected to a sensor circuit 960 having a power supply 961 and an ammeter 962.

With respect to the gas sensor element 1 having the configuration according to this example, the pump limit current value Ip flowing through the pump cell 93 and the sub-pump cell 95 and the sensor current value Is flowing through the sensor cell 96 (provided that the pump cell 93 and the sub-pump cell 95 are not operated) When the relationship of Is / Ip ≦ 0.3 is established between the two, the offset current can be suppressed small, and a gas sensor element capable of performing highly accurate measurement can be obtained. Other details are the same as in the sixth embodiment.

(Example 8)
In this example, the relationship between the length of the width Wn of the diffusion controlled passage, the offset current, and the response was evaluated.
A plurality of gas sensor elements described in Example 1 having different diffusion-controlled passage widths Wn were prepared, and the offset current and the responsiveness were measured in the manner described in Example 2, and the results were shown in the diagram of FIG. Was described.
From the figure, it was found that by setting Wn to 0.8 mm or less, a gas sensor element having a small offset current and excellent responsiveness can be obtained.

(Example 9)
In this example, the relationship between the length Ln of the diffusion-controlled path, the offset current, and the response was evaluated.
A plurality of gas sensor elements described in Example 1 having different lengths Ln of diffusion-controlled paths were prepared, and the offset current and the responsiveness were measured in the manner described in Example 2; The results are described.
From the figure, it was found that by setting Ln to 0.4 mm or less, a gas sensor element having a small offset current and excellent responsiveness can be obtained.

(Example 10)
In the present example, the relationship between the thickness t of the cell placement chamber, the offset current, and the response was evaluated.
A plurality of gas sensor elements having different cell arrangement chamber thicknesses t were prepared in the first embodiment, and the offset current and the response were measured in the manner described in the second embodiment. Was described.
From the figure, it was found that by setting t to 0.4 mm or less, a gas sensor element having a small offset current and excellent responsiveness can be obtained.

FIG. 2 is an explanatory cross-sectional view of the gas sensor element in the longitudinal direction according to the first embodiment. FIG. 2 is a sectional view taken along the line AA according to FIG. 1. FIG. 2A is an explanatory cross-sectional view of a main part of a measured gas chamber, and FIG. 2B is a plan view of a spacer for the measured gas chamber in the first embodiment. FIG. 9 is a diagram showing a relationship between (Sn / Ln) / (S0 / L0) and an offset current and a response in a sensor cell in the second embodiment. FIG. 9 is a diagram showing a relationship between (Sn / Ln) / (S0 / L0) and accuracy in the second embodiment. FIG. 9A is a cross-sectional view of a main part of a gas sensor element having a gas chamber to be measured in which the width of a cell arrangement chamber is equal to the width of a diffusion resistance passage, and FIG. FIG. 15 is a plan view of a spacer of a gas sensor element in which a second cell placement chamber is filled with a porous material in a fourth embodiment. FIG. 15A is a plan view of a spacer of a gas sensor element having a gas chamber to be measured provided with three cell arrangement chambers and two gas introduction paths, and FIG. FIG. 13 is an explanatory cross-sectional view of a gas sensor element in a longitudinal direction according to a sixth embodiment. FIG. 14 is an explanatory view showing a measured gas side electrode of a sensor cell and a monitor cell in a sixth embodiment. FIG. 19 is an explanatory diagram illustrating a first pump electrode according to the sixth embodiment. FIG. 19 is an explanatory view showing a second pump electrode in the sixth embodiment. FIG. 4 is an explanatory diagram showing a relationship between Is / Ip and an offset current. FIG. 13 is an explanatory cross-sectional view in a longitudinal direction of a gas sensor element having five electrochemical cells according to a seventh embodiment. FIG. 18 is an explanatory view showing a first cell placement chamber and a second cell placement chamber in the seventh embodiment. FIG. 19 is a diagram showing a relationship between the width Wn of the diffusion-controlling passage, the offset current in the sensor cell, and the response in the eighth embodiment. FIG. 19 is a diagram showing a relationship between a path length Ln of a diffusion-controlled path and an offset current and a response in a sensor cell in a ninth embodiment. FIG. 19 is a diagram illustrating a relationship between a cell placement chamber t, an offset current in a sensor cell, and responsiveness in the tenth embodiment.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Gas sensor element 10 Gas introduction path 11, 13 Solid electrolyte plate 12, 14 Spacer 121 1st cell arrangement room 122 2nd cell arrangement room 103 Diffusion resistance passage 2 Pump cell 3 Monitor cell 4 Sensor cell 5 λ cell

Claims (11)

An electrochemical cell including a solid electrolyte plate and a pair of electrodes provided on the solid electrolyte plate, and a measured gas chamber configured to introduce a measured gas from the outside, wherein the measured gas is applied to the solid electrolyte plate. In a laminated gas sensor element configured by laminating chamber forming spacers,
The gas sensor element has a plurality of electrochemical cells,
At least one electrochemical cell is a pump cell that pumps oxygen from the measured gas chamber and adjusts the oxygen concentration in the measured gas chamber.
At least one electrochemical cell is a sensor cell that decomposes a specific gas in the gas chamber to be measured and measures a specific gas concentration in the gas chamber to be measured using oxygen ions generated by the decomposition.
For the measured gas chamber, has a gas introduction path configured to introduce a measured gas from outside,
The measured gas chamber includes a cell arrangement chamber in which the electrochemical cell is arranged, and a diffusion-controlled passage connecting the cell arrangement chambers and diffusion-controlling the measured gas moving between the cell arrangement chambers. ,
The path length of the gas introduction path is L0, the cross-sectional area in the direction orthogonal to the path length of the gas introduction path is S0, the path length of the diffusion-controlled path is Ln, and the cross-sectional area in the direction perpendicular to the path length of the diffusion-controlled path is L0. If Sn
(Sn / Ln) / (S0 / L0) ≦ 0.4
A gas sensor element, characterized in that: An electrochemical cell including a solid electrolyte plate and a pair of electrodes provided on the solid electrolyte plate, and a measured gas chamber configured to introduce a measured gas from the outside, wherein the measured gas is applied to the solid electrolyte plate. In a laminated gas sensor element configured by laminating chamber forming spacers,
The gas sensor element has a plurality of electrochemical cells,
At least one electrochemical cell is a pump cell that pumps oxygen from the measured gas chamber and adjusts the oxygen concentration in the measured gas chamber.
At least one electrochemical cell is a sensor cell that decomposes a specific gas in the gas chamber to be measured and measures a specific gas concentration in the gas chamber to be measured using oxygen ions generated by the decomposition.
For the measured gas chamber, has a gas introduction path configured to introduce a measured gas from outside,
The measured gas chamber includes a cell arrangement chamber in which the electrochemical cell is arranged, and a diffusion-controlled passage connecting the cell arrangement chambers and diffusion-controlling the measured gas moving between the cell arrangement chambers. ,
At the oxygen concentration of 20%, between the pump limit current value Ip flowing between the electrodes of the pump cell and the sensor limit current value Is flowing between the electrodes of the sensor cell (provided that only the sensor cell is operated without operating the pump cell) Wherein a relationship of Is / Ip ≦ 0.3 is satisfied. An electrochemical cell including a solid electrolyte plate and a pair of electrodes provided on the solid electrolyte plate, and a measured gas chamber configured to introduce a measured gas from the outside, wherein the measured gas is applied to the solid electrolyte plate. In a laminated gas sensor element configured by laminating chamber forming spacers,
The gas sensor element has a plurality of electrochemical cells,
At least one electrochemical cell is a pump cell that pumps oxygen from the measured gas chamber and adjusts the oxygen concentration in the measured gas chamber.
At least one electrochemical cell is a sensor cell that decomposes a specific gas in the gas chamber to be measured and measures a specific gas concentration in the gas chamber to be measured using oxygen ions generated by the decomposition.
For the measured gas chamber, has a gas introduction path configured to introduce a measured gas from outside,
The measured gas chamber includes a cell arrangement chamber in which the electrochemical cell is arranged, and a diffusion-controlled passage connecting the cell arrangement chambers and diffusion-controlling the measured gas moving between the cell arrangement chambers. ,
The sensor limit current value Is flowing between the electrodes of the sensor cell at an oxygen concentration of 20% (where only the sensor cell is operated without operating the pump cell) and the electrode area of the pump cell exposed in the cell arrangement chamber are Sp. And a relationship of Is / Sp ≦ 0.06 mA / mm ² is established. The gas sensor element according to claim 1, wherein the width Wn of the diffusion-controlling passage in the width direction orthogonal to the longitudinal direction of the gas sensor element is 0.8 mm or less. The gas sensor element according to any one of claims 1 to 4, wherein a path length Ln of the diffusion-controlling path is 0.4 mm or more. The pump cell according to any one of claims 1 to 5, wherein the pump cell is arranged in a cell arrangement chamber closest to the gas introduction path, and the sensor cell is arranged in a cell arrangement chamber farthest from the gas introduction path.
A gas sensor element, wherein v / V ≦ 0.5, where v is the volume of the cell arrangement chamber in which the sensor cells are arranged, and V is the total volume of the cell arrangement chamber. (7) The gas sensor element according to any one of (1) to (6), wherein the thickness t of the cell arrangement chamber along the stacking direction of the gas sensor element is 0.16 mm or less. The gas sensor element according to claim 1, wherein a total volume of the cell arrangement chamber is 4.1 mm ³ or less. A gas sensor element according to any one of claims 1 to 8, wherein a porous body is arranged in any part of the gas introduction path, the cell arrangement chamber, and the diffusion control path. The gas sensor element according to claim 9, wherein the porosity of the porous body is 10 to 50%. The gas sensor element according to any one of claims 1 to 10, wherein the electrode of the pump cell, which is exposed in the cell arrangement chamber, has a region where the surface temperature is 800 ° C or higher when the gas sensor element is used.

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