WO2016043133A1

WO2016043133A1 - Gas sensor

Info

Publication number: WO2016043133A1
Application number: PCT/JP2015/075824
Authority: WO
Inventors: 啓杉浦; 安藤　芳康
Original assignee: 株式会社デンソー
Priority date: 2014-09-16
Filing date: 2015-09-11
Publication date: 2016-03-24

Abstract

　A gas sensor in which exhaust gas is introduced into a chamber 2 provided to a gas sensor element 1, the oxygen concentration in an upstream pump cell 3 is reduced, and NOx is detected in exhaust gas in a downstream sensor cell 4, wherein the surface of a shielding sheet 13 and/or a solid electrolyte sheet 11 constituting a wall face of the chamber 2 is configured so as to have a curved shape convex toward the inside of the chamber at the position where the pump cell 3 is formed, the amount of curvature is set to a range of 0.10% to 1.38%, and the height Hp of a diffusion layer 21 in the layering direction thereof is configured so as to be less than the average height Have of the chamber in the layering direction at the position where the pump cell is formed.

Description

Gas sensor

The present invention relates to a gas sensor for detecting a specific gas component such as nitrogen oxide (NOx) contained in exhaust gas of an internal combustion engine, and more particularly to a chamber formed in a stacked sensor element.

A gas sensor used in an exhaust gas purification system of an internal combustion engine to detect NOx concentration is generally a chamber into which exhaust gas containing NOx is introduced, and a pump cell that is arranged upstream of the chamber and pumps oxygen in the exhaust gas. And a sensor cell that is disposed downstream of the chamber and detects the NOx concentration in the exhaust gas with a reduced oxygen concentration. The pump cell and the sensor cell of the gas sensor are formed by forming a pair of electrodes on an oxygen ion conductive solid electrolyte sheet constituting the chamber wall, and further stacking a heater sheet and an insulating sheet on the solid electrolyte sheet to form a sensor element. In addition to this two-cell gas sensor, a three-cell gas sensor is known in which a sensor cell and a monitor cell are arranged in parallel on the downstream side of the chamber to monitor the oxygen concentration in the chamber (for example, Patent Document 1). .

The principle of NOx detection by a gas sensor is described in Patent Document 1 and the like. First, exhaust gas is taken into a chamber, which is an internal space of a stacked sensor element, and detection is prevented while passing through an upstream pump cell. The oxygen which becomes becomes exhausted out of the chamber. At this time, if the voltage applied to the pump cell is set so that the value of the current flowing by the oxygen in the chamber does not depend on the voltage value, it operates as a limiting current type oxygen sensor. Thereafter, in the downstream sensor cell, NOx in the exhaust gas having a reduced oxygen concentration can be decomposed, and the NOx concentration can be detected from the generated current value. In addition, a monitor cell can be provided to detect the residual oxygen concentration in the exhaust gas that has reached the sensor cell, and to feedback control the voltage applied to the pump cell.

A gas sensor having a two- or three-cell structure in which solid electrolyte sheets are laminated is generally known as an oxygen sensor (for example, Patent Document 2).

Japanese Patent Laid-Open No. 11-83793 JP 2013-117428 A

Here, the required characteristics of the gas sensor include NOx detection accuracy and responsiveness. Among these, in order to improve the accuracy of NOx detection, the gas in which the oxygen concentration is sufficiently reduced by increasing the chance of contact between the exhaust gas passing through the pump cell and the electrode of the pump cell in the chamber and exhausting sufficient oxygen gas. Is preferably sent to the sensor cell. Further, in order to improve the responsiveness of NOx detection, it is necessary to cause the exhaust gas to reach the sensor cell promptly due to the good diffusibility of the gas taken into the chamber.

However, these two required characteristics are contradictory conditions, and it has been difficult to achieve both at present. That is, for sufficient oxygen gas discharge, for example, it is preferable that the exhaust gas stays on the electrode of the pump cell, but on the other hand, the time for the exhaust gas to pass through the pump cell becomes long and the gas is good. Diffusivity is inhibited.
The present invention has been made in view of the above problems, and efficiently diffuses exhaust gas into the chamber while efficiently exhausting oxygen in the exhaust gas, thereby improving both NOx detection accuracy and responsiveness. It is intended to provide a high performance gas sensor.

One aspect of the present invention is a gas sensor for detecting a specific gas component in a gas to be measured,
A chamber into which a gas to be measured is introduced from the outside through a porous diffusion layer provided in a gas sensor element in which a flat ceramic sheet is laminated, and provided at an end in a longitudinal direction of the gas sensor element;
A pump cell that has a pump electrode disposed upstream of the gas flow in the chamber and pumps out oxygen in the gas to be measured;
A sensor cell that has a sensor electrode disposed on the downstream side of the gas flow in the chamber, and that detects a specific gas component concentration in the gas to be measured with a reduced oxygen concentration;
The gas sensor element includes a second ceramic sheet having an opening serving as the chamber, a first ceramic sheet on which the pump electrode and the sensor electrode are disposed on a surface facing the chamber, and the opening covering the opening. Having a structure in which the third ceramic sheets defining the chamber are sequentially laminated;
The chamber has a warped shape in which at least one surface of the first ceramic sheet and the third ceramic sheet constituting the chamber wall is convex inward of the chamber at the position where the pump cell is formed, and The amount of warpage of the surface is set in the range of 0.10% to 1.38%,
In the diffusion layer and the chamber, the height Hp in the stacking direction of the diffusion layer and the average height Have in the stacking direction of the chamber at the position where the pump cell is formed satisfy the relationship of Hp <Have. , In the gas sensor.

The gas sensor faces the chamber provided in the stacked gas sensor element, and at least one surface of the two ceramic sheets constituting the inner wall surface thereof has a warped shape. At the pump cell position located on the upstream side, the space is narrower than the inlet side. For this reason, a gas flow from the side end toward the center of the pump cell is generated due to the difference in flow velocity, and an agitation effect of the gas flow is obtained. Further, since the height Hp of the porous diffusion layer into which gas is introduced from the outside is made lower than the chamber average height Have at the pump cell position, the amount of gas introduced into the chamber space is suppressed, and the space becomes wider. Gas diffusibility at the inlet of the chamber is improved. As a result, the oxygen pump capacity is improved toward the outlet side while a sufficient amount of gas to be measured is taken in on the inlet side of the pump cell.

As a result, the chance of the gas to be measured coming into contact with the pump electrode is greatly increased, and oxygen discharge by the pump electrode is promoted, whereby the gas to be measured is further drawn into the pump cell from the space at the side end. Thereby, oxygen can be efficiently removed, and the oxygen concentration of the measurement gas introduced into the sensor cell can be sufficiently reduced. At this time, since the amount of warpage of the surface serving as the chamber wall is in the range of 0.10% or more and 1.38% or less, the occurrence of cracks in the firing and degreasing process and the sheet laminating and pressing process is prevented while exhibiting the above effects. Can improve reliability.
Therefore, according to the said aspect, favorable gas discharge property and gas diffusibility can be made compatible, the detection accuracy of the specific gas by a sensor cell is improved, responsiveness is ensured, and a high-performance gas sensor is implement | achieved.

FIG. 2 is a diagram showing a tip structure of a gas sensor element constituting the gas sensor according to the first embodiment, and is a cross-sectional view taken along line IA-IA in FIG. 1B. BRIEF DESCRIPTION OF THE DRAWINGS It is 1st Embodiment of this invention, and the whole schematic block diagram of the gas sensor element which comprises a gas sensor. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1, showing a planar structure of a tip portion of the gas sensor element. The longitudinal section showing the chamber structure which is the principal part of a gas sensor element typically. The sectional view of the transversal direction which shows typically the chamber structure which is the principal part of a gas sensor element. Sectional drawing of the longitudinal direction which is 2nd Embodiment and shows typically the chamber structure which is the principal part of a gas sensor element. Sectional drawing of the transversal direction which is 2nd Embodiment and shows typically the chamber structure which is the principal part of a gas sensor element. The typical sectional view of the transversal direction for explaining the gas flow in a chamber. FIG. 5 is a schematic cross-sectional view in the longitudinal direction for explaining the gas flow in the chamber by comparing the chamber height with the chamber height. The figure which shows the relationship between the amount of chamber deformation and sensor characteristics for demonstrating an effect. The typical sectional view for explaining the relation between a sensor characteristic and a chamber shape. The typical sectional view of the longitudinal direction and the transversal direction which show the example of a chamber shape. Process drawing for demonstrating the chamber formation method of a gas sensor element. Process drawing for demonstrating the chamber formation method of a gas sensor element. Process drawing for demonstrating the chamber formation method of a gas sensor element. The typical sectional view for explaining the method of adjusting the chamber shape of a gas sensor element. The typical sectional view for explaining other methods of adjusting the chamber shape of a gas sensor element. Sectional drawing which is 3rd Embodiment and shows the planar structure of the front-end | tip part of a gas sensor element. The longitudinal section showing the chamber structure which is the principal part of a gas sensor element typically. The sectional view of the transversal direction which shows typically the chamber structure which is the principal part of a gas sensor element. The top view which shows the example of a shape of the gas sensor element in an Example. Typical sectional drawing for demonstrating the evaluation method of the curvature amount in an Example. The typical sectional view for explaining the method of prescribing the position of the end of a chamber in evaluation of the amount of curvature. The typical sectional view for explaining the calculation method of the chamber average height in an example. The figure which shows the relationship between the curvature amount in an Example, and oxygen exhaust capability. Typical sectional drawing for demonstrating the crack suppression effect by the curvature amount in an Example. The typical sectional view showing the relation between the amount of curvature and the occurrence of a crack in a comparative example.

(First embodiment)
Hereinafter, a first embodiment of a gas sensor will be described in detail with reference to the drawings. The gas sensor of this embodiment is installed in an exhaust passage of an internal combustion engine as a NOx sensor, for example, and detects nitrogen oxide (that is, NOx) gas as a specific gas component contained in exhaust gas that is a gas to be measured. FIG. 1B shows a gas sensor element 1 constituting a gas sensor, and FIG. 1A shows a cross section of the tip of the element (that is, the left end part in the figure). The main part of the gas sensor element 1 is a space provided in the element. The exhaust gas is introduced through the porous diffusion layer 21. As shown in FIG. 2, in the chamber 2, the pump cell 3 is disposed on the distal end side (that is, the left end side in the drawing) that is the upstream side of the gas flow, and the proximal end side that is the downstream side of the gas flow (that is, The sensor cell 4 and the monitor cell 5 are arranged in parallel on the right end side in the figure.

The gas sensor element 1 has a chamber structure in which the inside of the chamber 2 is not partitioned, and the diffusion layer 21 is positioned so as to close the opening on the upstream side of the chamber 2 at the distal end in the element longitudinal direction. The chamber 2 changes the height of the chamber from the upstream side to the downstream side of the gas flow by changing the height of the chamber with a part of the inner surface constituting the chamber wall being warped, so that the oxygen (ie, O ₂ ) of the pump cell 3 is changed. The pump function is promoted, and the gas diffusion property to the sensor cell 4 is improved. Each of the cells 3 to 5 is connected to an unillustrated electrode terminal formed at the proximal end by a lead wire (not shown). Details of cross-sectional shape examples of the chamber 2 in the longitudinal direction and the lateral direction schematically shown in FIGS. 3 and 4 will be described later.

In FIG. 1A, the gas sensor element 1 is composed of a laminate in which a plurality of elongated flat plate-like ceramic sheets are stacked in the thickness direction. Specifically, a basic structure in which a chamber forming sheet 12 serving as a second ceramic sheet and a shielding sheet 13 serving as a third ceramic sheet are sequentially laminated on the upper surface of the solid electrolyte sheet 11 serving as a first ceramic sheet. In the chamber forming sheet 12, a rectangular opening 22 that becomes the chamber 2 is formed by punching. The heater layer 6 is laminated on the lower surface of the solid electrolyte sheet 11 via a duct forming sheet 14 that is a fourth ceramic sheet. The duct forming sheet 14 is formed with a duct 33 having an opening reaching a base end (not shown), and the atmosphere as a reference gas is introduced from the outside. The heater layer 6 has a configuration in which a heater electrode 61 is embedded in a heater sheet 62 which is a fifth ceramic sheet. The first to fifth ceramic sheets are made of insulating sheets that are not permeable to the gas to be measured.

The gas sensor element 1 is covered with a porous layer whose entire outer surface becomes the trap layer 15. The trap layer 15 captures moisture, poisoning components, and the like contained in the exhaust gas, prevents entry into the chamber 2, and protects the gas sensor element 1. Each

cell

3, 4, 5 and heater layer 6 in the gas sensor element 1 is connected to a terminal portion 7 (see, for example, FIG. 1B) at the element base end via a lead wire (not shown), and gas detection means or It is connected to an external drive control unit having energization means and the like. The heater layer 6 generates heat by energization and heats the

cells

3, 4, and 5 to a temperature suitable for gas detection.

The pump cell 3 includes a solid electrolyte sheet 11, a pump electrode 31 as a pair of electrodes formed at opposite positions on both sides thereof, and a reference electrode 32. The solid electrolyte sheet 11 is a sheet made of a solid electrolyte body having oxygen ion conductivity such as partially stabilized zirconia. For the pump electrode 31 and the reference electrode 32, a porous cermet electrode mainly composed of a noble metal is used. Preferably, the pump electrode 31 is an electrode having a low NOx decomposition activity, for example, a porous cermet electrode containing Pt (ie, platinum) and Au (ie, gold) to suppress decomposition of NOx in the exhaust gas. It is good to do. At this time, by applying a predetermined voltage between the pair of electrodes, the O ₂ gas in the exhaust gas that has reached the pump electrode 31 is decomposed and permeates through the solid electrolyte sheet 11 to the reference electrode 32 side. Discharged. By this pumping action, O ₂ gas is discharged from the pump electrode 31 side facing the chamber 2 to the reference electrode 32 side facing the duct 33, and the O ₂ concentration in the exhaust gas passing through the pump cell 3 can be reduced. it can.

The sensor cell 4 includes a solid electrolyte sheet 11, a sensor electrode 41 as a pair of electrodes formed at opposite positions on both sides thereof, and a reference electrode 32. The monitor cell 5 includes a solid electrolyte sheet 11, a monitor electrode 51 as a pair of electrodes formed at opposite positions on both sides thereof, and a reference electrode 32. As the sensor electrode 41 and the monitor electrode 51, a porous cermet electrode mainly composed of a noble metal is preferably used. Preferably, the sensor electrode 41 is an electrode having a high decomposition activity for NOx gas in the exhaust gas, for example, a porous cermet electrode containing Pt and Rh (ie, rhodium), and the monitor electrode 51 is an NOx decomposition activity. Low electrode, for example, a porous cermet electrode containing Pt and Au. The reference electrode 32 is a common electrode for the pump cell 3, sensor cell 4, and monitor cell 5, on the surface of the solid electrolyte sheet 11 opposite to the surface defining the chamber 2, and on all of the pump electrode 31, sensor electrode 41, and monitor electrode 51. For example, a porous cermet electrode mainly composed of Pt is used.

At this time, the NOx gas in the exhaust gas reaching the sensor cell 4 is decomposed on the sensor electrode 41, and the generated oxygen ions pass through the solid electrolyte sheet 11 and are discharged to the reference electrode 32 side. The current flowing at that time is detected as the concentration of NOx contained in the exhaust gas. On the other hand, in the monitor cell 5, the O ₂ gas that has reached the monitor electrode 51 is decomposed and discharged to the reference electrode 32 side, and the current flowing at that time is detected as the residual oxygen concentration in the exhaust gas. Since the monitor cell 5 is in the same position in the gas flow direction as the sensor cell 4 in the chamber 2, the pump cell 3 can be effectively feedback controlled by monitoring the residual oxygen concentration.

2, the chamber 2 has a rectangular shape in which the length in the longitudinal direction of the gas sensor element 1 (that is, the chamber length) is longer than the length in the short direction (that is, the chamber width). A diffusion layer 21 made of a porous material having the same width as the chamber width is disposed at the inlet portion of the chamber 2 with a predetermined thickness in the longitudinal direction so as to partition the outer space across the inlet portion. Exhaust gas is introduced into the interior by the diffusion resistance. In the chamber 2, the pump electrode 31 positioned on the upstream side of the gas flow has a substantially rectangular shape having a width slightly smaller than the chamber width between the sensor electrode 41, the monitor electrode 51 and the diffusion layer 21 positioned at the downstream end. It is formed in a shape. The sensor electrode 41 and the monitor electrode 51 have substantially the same shape and are formed in a substantially rectangular shape having a width slightly smaller than ½ of the chamber width.

The pump electrode 3 has a sufficiently large area with respect to the sensor electrode 41 and the monitor electrode 51, and effectively discharges O ₂ gas in the introduced exhaust gas. Preferably, the length of the pump electrode 31 in the gas flow direction is 2 to 4 times, for example, about 3 times that of the sensor electrode 41 and the monitor electrode 51, thereby enabling sufficient contact with the exhaust gas. To do. Here, in order to reliably discharge the O ₂ gas in the exhaust gas introduced through the diffusion layer 21, the larger the pump electrode 31, the better. On the other hand, it takes time to pass through the pump cell 31 and the sensor cell. 4 responsiveness decreases. Further, the O ₂ gas in the exhaust gas may pass through without being discharged along the side end portion of the chamber 2 where the pump electrode 31 is not formed.

Therefore, as shown in FIG. 1A, a part of the wall surface of the chamber 2 in the stacking direction of the gas sensor element 1 is deformed so that the gas flow in the chamber 2 can be controlled and disposed at the inlet of the chamber 2. The height of the diffusion layer 21 is made lower than the wall surface height of the chamber 2 to limit the amount of exhaust gas introduced. Specifically, at least one surface of the shielding sheet 13 and the solid electrolyte sheet 11 facing each other with the chamber 2 interposed therebetween is a warped surface having a warped shape that protrudes inward of the chamber 2 at the position where the pump cell 3 is formed. Thereby, in the longitudinal direction and the short direction of the gas sensor element 1, the height in the stacking direction of the chamber 2 is changed, and the introduced gas is stirred with a flow rate difference to form a flow toward the pump cell (for example, (See FIG. 2).

This warp surface is usually set to a predetermined warp amount range of 0.10% or more and 1.38% or less. The amount of warpage represents the deformation ratio of the warped surface with respect to the reference surface without warpage, and is defined here based on the maximum amount of deformation in the cross section of the gas sensor element 1 in the longitudinal direction and the short direction. If the amount of warpage is less than 0.10%, the effect of the warped surface cannot be obtained, and cracks may occur in the process of firing and degreasing in the manufacturing process of the gas sensor element 1. As the amount of warpage increases, the flow velocity difference increases, but if it exceeds 1.38%, cracking may occur in the sheet lamination pressing step.

Further, when the diffusion layer 21 and the chamber 2 have a height in the stacking direction of the diffusion layer 21 as Hp and an average height in the stacking direction of the chamber 2 at the position where the pump cell 3 is formed as Have, Hp <Have, Satisfy the relationship. As a result, the exhaust gas that has passed through the porous diffusion layer 21 is quickly diffused into the wider internal space of the chamber 2 to improve responsiveness. The average height Have of the chamber 2 is calculated based on, for example, the average value of the chamber height at a plurality of locations from the inlet side to the outlet side of the pump cell 3 in the longitudinal section of the gas sensor element 1.

The diffusion layer 21 is formed, for example, by embedding a porous sheet on the front end side of the chamber forming sheet 12 forming the chamber 2, and the height Hp of the diffusion layer 21 is the height of the chamber forming sheet 12 (ie, Sheet thickness). At this time, the arrangement of the diffusion layer 21 with respect to the chamber forming sheet 12 may be any of a position in contact with the solid electrolyte sheet 11, a position in contact with the shielding sheet 13, or an intermediate position in the stacking direction as illustrated.

Preferably, as schematically shown in FIGS. 3 and 4, in the longitudinal direction of the gas sensor element 1 in the gas flow direction, the downstream end with respect to the upstream end (that is, the gas inlet) of the pump electrode 31. The cross-sectional area of the portion (that is, the gas outlet portion) becomes smaller, and in the short direction, the intermediate portion where the pump cell 3 is formed, particularly the pump electrode 31 with respect to the height of at least one wall surface of the side end portion. It is set as the shape where the height of the center part position becomes low. In this embodiment, the shielding sheet 13 constituting the wall of the chamber 2 located on the opposite side to the pump electrode 31 is deformed among the wall surfaces to be the chamber 2, and in the longitudinal section (for example, see FIG. 3), The surface of the shielding sheet 13 exposed to the chamber 2 (that is, the lower surface in FIG. 3) has a warped shape that protrudes inward of the chamber 2.

This warped shape is preferably formed on a curved surface of a mountain-shaped curved surface that is curved smoothly so that the deformation is maximized, that is, the height of the chamber 2 is lowered, at the downstream side of the central portion of the pump electrode 31. In the present embodiment, the height of the chamber 2 is gradually decreased from the inlet portion a on the inlet side of the pump electrode 31 toward the outlet portion d on the outlet side, and the sectional area is gradually reduced. Between the inlet part a and the outlet part d, the height of the chamber 2 is lower at the intermediate part c downstream from the central part of the pump electrode 31 than at the intermediate part b upstream. The height of the outlet part d and the intermediate part c upstream thereof is substantially the same, and the relationship between the heights of the parts in the longitudinal direction is preferably, for example, the inlet height Ha> Hb> Hc ≧ the outlet height Hd. . The downstream side e of the pump electrode 31 (that is, the position where the sensor electrode 41 and the monitor electrode 51 are formed) is slightly higher than the outlet part d, and the height of the chamber 2 gradually increases from the outlet part d which is the minimum height. It is formed to be higher. Specifically, the height between the inlet portion a and the downstream intermediate portion c, for example, the same level as the upstream intermediate portion b can be set.

4 shows specific cross-sectional shapes corresponding to the respective parts a to e in FIG. 3. In the inlet part a of the pump electrode 31, the chamber 2 has a substantially rectangular cross-sectional shape. . There is almost no deformation | transformation of the shielding sheet 13 used as the wall of the chamber 2 on the opposite side to the pump electrode 31, and a sufficient amount of exhaust gas is introduced into the inlet part a through the diffusion layer 21. In each of the downstream portions b to e, the surface of the shielding sheet 13 exposed to the chamber 2 is warped so as to be convex inward of the chamber 2, and in this case, the surface is curved so that the deformation is maximized at the central portion. A mountain-shaped curved surface is formed, and the central space in the chamber 2 is narrowed. The amount of deformation is gradually increased toward the outlet portion d of the pump electrode 31, and the cross-sectional area is gradually decreased. The amount of deformation of the downstream portion e of the pump electrode 31 is slightly smaller than that of the outlet portion d, and the sectional area is slightly larger.

The cross-sectional shape of each part b to e is such that the side wall end has a constant wall height and the space remains wide, and the intermediate part has a chamber 2 height that gradually decreases toward the center position of the pump electrode 31, The space becomes narrower toward the center. The cross-sectional area is, for example, in the relationship of the inlet part a>b> c ≧ the outlet part d, and the downstream side E is between the inlet part a and the downstream intermediate part c, for example, the upstream intermediate part b. It has the same cross-sectional area. At this time, since the intermediate portion is narrowed, the O ₂ pump capability is enhanced, and gas diffusibility is ensured at the wide side end portions. In addition, since the difference in flow velocity between the side end portions and the central portion is increased, the gas flow is agitated, and efficient O ₂ discharge becomes possible.

(Second Embodiment)
As shown in FIGS. 5 and 6 as the second embodiment, both the wall surfaces of the chamber 2 facing the stacking direction of the gas sensor elements 1 can be deformed. In the present embodiment, the shape and arrangement of the diffusion layer 21 (not shown), the relationship between the height Hp of the diffusion layer 21 and the average height Have of the chamber 2 at the position where the pump cell 3 is formed are the same as in the first embodiment. The difference will be mainly described. Specifically, in the longitudinal section (see, for example, FIG. 5), the surface of the solid electrolyte sheet 11 on which the shielding sheet 13 and the pump electrode 31 are formed is exposed to the inside of the chamber 2. The chamber 2 is gradually lowered from the inlet portion a to the outlet portion d of the pump electrode 31 and is formed in a chevron-shaped warped surface in which the amount of warpage is maximized at the gas outlet portion. The As in the first embodiment, the relationship between the height of the outlet portion d and the upstream portion thereof may be, for example, the inlet height Ha>Hb> Hc ≧ the outlet height Hd, and the gas inlet portion of the pump electrode 31. The cross-sectional area is maximized at the gas outlet, and the cross-sectional area is minimized at the gas outlet. The downstream E (the position where the sensor electrode 41 and the monitor electrode 51 are formed) can be approximately the same as the height between the inlet portion a and the downstream intermediate portion c, for example, the upstream intermediate portion b.

The cross section in the short direction of FIG. 6 corresponds to the cross section of each part ae of FIG. As in the first embodiment, at the inlet a of the pump electrode 31, the chamber 2 has a substantially rectangular cross-sectional shape, and there is almost no deformation of the shielding sheet 13 and the solid electrolyte sheet 11 that become the walls of the chamber 2. . In the downstream portions b to e, the surfaces of the shielding sheet 13 and the solid electrolyte sheet 11 that are exposed to the chamber 2 are warped so as to protrude inward of the chamber 2, and in this case, the warping amount at the center is maximum. It has a mountain shape. The amount of deformation gradually increases toward the outlet portion d of the pump electrode 31, and the amount of deformation on the downstream side e of the pump electrode 31 is slightly smaller than that on the outlet side d. The side ends of each part b to e are less deformed than the middle part, the wall surface is high and the space remains wide, the middle part is narrow, and the height of the chamber 2 gradually decreases toward the center part. It has a cross-sectional shape. The cross-sectional area is, for example, the relationship of the inlet part a> b> c ≧ the outlet part d, and the downstream side e has a cross-sectional area similar to that of the upstream part b, for example, between the inlet part a and the upstream part c. ing.

The shielding sheet 13 and the solid electrolyte sheet 11 both set the amount of warpage of the surface exposed to the chamber 2 within a range of 0.10% to 1.38%. The warpage shape and the amount of warpage of the shielding sheet 13 and the solid electrolyte sheet 11 satisfy the height Hp in the stacking direction of the diffusion layer 21 <the average height Have in the stacking direction of the chamber 2 at the position where the pump cell 3 is formed. Can be set as appropriate so that

Thus, the shape of the chamber 2 of the first and second embodiments is such that the average height Have at the position where the pump cell 3 is formed is appropriately set with respect to the height Hp of the diffusion layer 21, and one of the surfaces facing the stacking direction or Both are warped and the cross-sectional area of the inlet side end of the pump electrode 31 is ensured, thereby enabling the same gas intake as before. Furthermore, the deformation of the wall surface increases from the inlet side to the outlet side end and the cross-sectional area decreases, thereby promoting O ₂ discharge of the pump electrode 31 shown in FIG. 1 and increasing the pump capacity. Further, the downstream side of the inlet side end portion has a narrow cross section at the middle portion and both side end portions, and as shown in FIG. 2, a difference in flow velocity occurs in the gas flow introduced from the inlet side. In the part, the gas flow is agitated by the flow rate difference from the central part while improving the gas diffusibility. As a result, O ₂ discharge by the pump electrode 31 can be further promoted while ensuring responsiveness. The function and effect of the present invention will be described with reference to FIGS.

FIG. 7A schematically shows a representative shape in the short direction of the chamber 2 of the second embodiment. The volume of the central portion where the distance between the opposing walls in the chamber 2 is minimum is V1, and the distance is maximum. Let V2 be the volume of the side end. When the differential pressure between the central portion and the side end portion is Δp, the gas flow rate Q is represented by the following general formula.
General formula of gas flow rate Q Q = C × Δp
In the formula, C is a coefficient representing the ease of gas flow.
here,
From the equation of state of gas PV = nRT,
Differential pressure Δp = P1-P2
= NRT x (1 / V1-1 / V2)
= NRT × {(V2−V1) / V1 · V2}
In the formula, P1: pressure at the center, P2: pressure at the side end, R: gas constant, T: temperature.
Therefore, the gas flow rate Q increases in proportion to the differential pressure Δp, and the gas volume Q becomes easier to flow as the volume difference between the side end portion and the central portion increases.

FIG. 7B schematically shows the relationship between the height in the longitudinal direction of the chamber 2 and the gas flow, comparing the case where the chamber height is high (ie, the left figure) and the case where the chamber height is low (ie, the right figure). ing. When the chamber height is constant in the longitudinal direction, when exhaust gas is introduced into the chamber 2 from the left inlet side in the figure, gas molecules including O _{2 and the} like collide with the wall surface of the chamber 2. Head downstream. As is clear from the figure, the lower the chamber height (ie, the right figure), the higher the collision frequency of the gas molecules, the O ₂ molecules in the exhaust gas collide with the surface of the pump electrode 31 and decompose. It is easily removed and the O ₂ discharge capacity is improved. However, if the height on the inlet side is lowered, the amount of gas taken into the chamber 2 is reduced and the detection accuracy of NOx is lowered. On the other hand, when the chamber height is high (that is, the left figure), although the O ₂ exhaust capability is low, the detection accuracy is expected to be improved by increasing the gas inflow amount.

For this reason, in the present invention, as shown in FIGS. 4 and 6, on the inlet side of the pump electrode 31, the chamber height (that is, the cross-sectional area) is sufficiently increased to secure the gas inflow amount, and the chamber gradually The height (that is, the cross-sectional area) is reduced so that the O ₂ discharge capacity becomes higher toward the outlet side. Also, in the short direction, the chamber height of the intermediate part where the pump electrode 31 is formed, especially the central part, is lowered, and a wide space is secured on both sides, thereby improving gas diffusibility and improving responsiveness. Let At this time, the deformed wall surface has a smooth curved surface shape and does not obstruct the gas flow, and the flow rate difference between the central portion and the side end portion where the flow velocity is slow becomes large, and the gas flow is agitated, so that the pump electrode The frequency of collision with 31 increases, and the surrounding gas is further drawn by the O ₂ discharge, thereby enabling efficient O ₂ removal. Preferably, in the longitudinal direction, the chamber height is the lowest at the downstream side of the central portion of the pump electrode 31, more preferably at the gas outlet portion of the pump electrode 31, particularly at or near the outlet side edge. When the chamber 2 is formed, the space gradually becomes narrower in the gas flow direction and the O ₂ pump capacity is increased, so that the O ₂ concentration can be made substantially zero while passing through the pump cell 3. Downstream from the outlet side of the pump electrode 31, the chamber height (that is, the cross-sectional area) is increased again to improve the gas diffusibility, and the exhaust gas from which O ₂ has been exhausted is quickly introduced into the sensor cell 4. Thus, accurate detection with high responsiveness can be realized.

Thus, in the present invention, the relationship between the shape of the surface of the ceramic sheet serving as the inner wall surface of the chamber 2 and the height Hp of the diffusion layer 21 and the average height Have of the chamber 2 is determined as the position where the pump electrode 31 of the pump cell 3 is formed. It is possible to achieve both responsiveness and detection accuracy by prescribing them in correspondence with. FIG. 8 shows the relationship between the sensor characteristics of the gas sensor element 1 of the present invention and the amount of deformation of the wall surface of the chamber 2 (that is, the amount of warpage). The amount of gas discharged in proportion to the amount of deformation increases. On the other hand, the gas responsiveness is almost constant. Here, for example, the deformation amount represents the size of the surface warpage shape of both wall surfaces that deform so as to approach the opposing direction with respect to the shape of the chamber 2 of the second embodiment shown in FIG. This corresponds to the warped surface height Hm at the center where the height H2 is minimized. From the relationship of FIG. 8, the larger the amount of deformation of the chamber 2, the better the gas discharge efficiency. However, if the deformation of the chamber 2 is increased, problems are likely to occur during molding. Therefore, preferably, in FIG. 8, by appropriately setting the warp shape and the deformation amount so that good gas discharge efficiency and gas responsiveness can be obtained within a predetermined warp amount range that can ensure good moldability. Good characteristics can be obtained.

For example, for the shape of the chamber 2 in FIG. 9, the sensor characteristics are defined by the height of the chamber 2 (that is, the height H1 at both ends and the height H2 at both ends). Therefore, the gas discharge efficiency can be optimized by setting the height H1 at both ends that can ensure the desired gas responsiveness, and setting the center height H2 from the upper limit value of the warp amount. Alternatively, the height difference ΔH (that is, the difference between the height H1 at both ends and the height H2 at the both ends) is calculated from the center height H2 for obtaining a desired gas discharge efficiency, and the warpage of the two opposing wall surfaces is calculated. The surface height Hm can also be set. At this time, the warpage amount of the two wall surfaces may be the same, but if the warpage amount of the wall surface on which the pump electrode 31 is formed is made smaller, the deformation of the pump electrode 31 can be suppressed. Further, when the wall surface on which the pump electrode 31 is formed is a flat surface and only the opposing wall surface is warped, as in the shape of the chamber 2 of the first embodiment shown in FIG. And the chamber 2 can be easily formed.

FIGS. 10B to 10G are other examples of the shape of the chamber 2. In the present invention, if the average height of the chamber and the amount of warpage are within the specified ranges, the shape of the warped surface is the shape of the above embodiment. It is not limited to. Preferably, if the cross-sectional area of the outlet side is smaller than the inlet side of the pump electrode 31 in the longitudinal direction and the height of the intermediate portion where the pump electrode 31 is formed is lower than the side end portion in the short direction, The above effect is enhanced. Moreover, if the deformation | transformation shape of the wall surface of the chamber 2 is the curvature shape in which one surface is convex inward of the chamber 2, and the said prescription | regulation is satisfied, the other surface will not be restricted to this, FIG.10 (b) The wall surface on which the pump electrode 31 is formed may be shaped to warp outward of the chamber 2 as shown in the longitudinal and lateral views. In this case, following the deformation of the wall surface facing the pump electrode 31, it is slightly deformed in the longitudinal direction or the short direction. As shown in FIG. 10C, the wall surface of the chamber 2 may have a corrugated warped shape with irregularities in the longitudinal direction or the short direction.

Further, the deformed wall surface of the chamber 2 is not limited to a smooth curved surface, and may be a warped surface having a substantially V-shaped cross section as shown in FIGS. At this time, the position having the minimum height in the longitudinal direction (that is, the vertex position of the V-shape) is the outlet side edge of the pump electrode 31 (FIG. 10 (e)) or the outlet side end (FIG. 10 (d) )), And also in the short direction, the position having the minimum height may be at the center of the pump electrode 31 (FIG. 10E) or the central portion in the vicinity thereof (FIG. 10D). Further, as shown in the longitudinal view of FIG. 10 (f), the height of the chamber 2 may be constant downstream from the outlet position of the pump electrode 31. Here, the upstream warp shape is a smooth curved surface, but it may be an inclined surface as shown in FIGS. Similarly, in the lateral view of FIG. 10 (f), the chamber 2 only needs to have a height of at least one side end sufficiently higher than the intermediate portion where the pump electrode 31 is formed, and the other side end. The height of the part may be approximately the same as the height of the intermediate part. FIG. 10G is an example in which both the wall surfaces of the chamber 2 are warped, as in the second embodiment, and the amount of warpage is changed. Here, the amount of warpage of the wall surface on which the pump electrode 31 is formed is made smaller. In these FIGS. 10A to 10G, the longitudinal and short chamber shapes can be arbitrarily combined.

FIG. 11 shows an example of the manufacturing process of the gas sensor element 1 having the shape of the chamber 2 of the present invention. 11A, first, in the step (1), unfired ceramic sheets to be the solid electrolyte sheet 11, the chamber forming sheet 12, and the shielding sheet 13 are respectively molded. Next, in the step (2), a paste that becomes the diffusion layer 21, the pump electrode 31, the sensor electrode 41, and the monitor electrode 51 is printed at a predetermined position on the surface of the solid electrolyte sheet 11. In addition, a paste (not shown) that is a lead wire for connecting each electrode to an electrode terminal (not shown) is printed. In the step (3), a predetermined position of the chamber forming sheet 12 is punched to form an opening 22 that becomes the chamber 2. Furthermore, the burnt material sheet 16 is inserted into the opening 22 of the chamber forming sheet 12 in the step (4).

The solid electrolyte sheet 11 is, for example, a mixed sheet of zirconia and an organic substance, and the chamber forming sheet 12 and the shielding sheet 13 are, for example, a mixed sheet of alumina and an organic substance. The burnt-out material sheet 16 is a single sheet or mixed sheet made of an organic material having a decomposition temperature of 1000 ° C. or lower, and includes, for example, a burned-out material such as acrylic resin, PVB, fluorine-based resin, carbon, etc. It is formed to become. By adjusting the composition, thickness, shape, etc. of the burnt-out material sheet 16, the shape of the chamber 2 can be adjusted.

In FIG. 11B, the step (4) -1 shows a specific example of the method of inserting the burnt material sheet 16. The burnt material sheet 16 is laminated on the chamber forming sheet 12, and a punching shape corresponding to the chamber 2 is punched out. The die is used to punch out the burnt material sheet 16 from above, and at the same time, the punched burnt material sheet 16 is inserted into the punched hole of the chamber forming sheet 12. Alternatively, as in the step (4) -2, the chamber forming sheet 12 punched into a predetermined shape may be placed on the suction plate, and the burned material sheet 16 having a corresponding shape may be transported and inserted. it can. Thereafter, in the step (5) -1, the chamber forming sheet 12 and the shielding sheet 13 are stacked in this order on the upper surface of the solid electrolyte sheet 11, and the release film 17 is stacked on the top and bottom, and placed in a molding die.

· A load (for example, 15-50 MPa) is applied to the laminated body from above and below, and crimped at a temperature (for example, 60-80 ° C). As shown in the step (4) -3 in FIG. 11C, a chamber-forming sheet 12 and a shielding sheet obtained by printing or applying a paste made of a burned material at a predetermined position on the upper surface of the solid electrolyte sheet 11 and punching it into a predetermined shape in advance. 13 may be stacked in the order of 13 and placed in the molding die, and the burning material can be embedded and crimped simultaneously. Thereafter, in the step (5) -2, the pressure-bonded body of the duct forming sheet 14 and the heater layer 6 manufactured by a known method is laminated and bonded, and fired to obtain the gas sensor element 1.

The shape of the chamber 2 of the obtained gas sensor element 1 can be controlled by the sheet thickness of the burned material placed in the chamber 2 prior to the step (5). For example, the left figure of FIG. 12A schematically shows a case in which one wall surface (that is, the upper surface in the figure) side of the chamber 2 is warped, and as a burnt out material whose thickness is adjusted in advance according to the warpage amount, An organic sheet mainly composed of resin or carbon is used. Here, when the mold is pressed, the burnt material is accommodated with the upper end portion of the chamber 2 left, and the wall surface facing the space portion of the chamber 2 is bent and deformed by applying a load from above. At this time, since the deformation amount is small in the vicinity of the corner portion of the chamber 2, the warped shape as in the first embodiment is relatively easy by appropriately adjusting the thickness of the burned material with respect to the distance A between both ends. After being formed and fired, it can be formed into a hollow chamber 2 shape having a desired deformation amount B as shown in the right figure of FIG. 12A.

When deforming so that only one wall surface is convex inward as in the shape of the chamber 2 in FIG. 12A, in the step (5), 1: between the sheet to be deformed and the release film 17, Insert the rubber film 2: Thicken the release film 17 on the sheet side to be deformed and thin the release film 17 on the opposite side 3: Make the release film 17 on the opposite side of the sheet to be deformed by pre-pressing Means such as hardening can also be employed. Further, by having a space part on both sides of the burned material accommodated in the chamber 2 and pressing from both sides, the warped chamber 2 shape in which both opposing wall surfaces protrude inward as in the second embodiment, can do.

Alternatively, prior to the step (5) -1, a desired warp shape can be imparted to the surface of the burnt-out material sheet 16, as shown in FIG. 12B. In the figure, an unfired ceramic sheet 13 to be a shielding sheet 13 is disposed above the surface of the solid electrolyte sheet 11 to which the electrode paste is applied (that is, the upper surface in the figure). A chamber forming sheet 12 containing a burnt-out material sheet 16 which is an organic material sheet as a component is disposed. At this time, for example, the upper and lower surfaces of the burnt-out material sheet 16 are recessed in a mortar shape, and the surfaces of the shielding sheet 13 and the solid electrolyte sheet 11 that are in contact with these surfaces are deformed at the time of laminating and pressing the sheets, A predetermined warpage shape corresponding to the shape of the burned-out material sheet 16 can be obtained. Of course, only one side of the burnt-out material sheet 16 may be recessed and only one corresponding surface may be deformed.

(Third embodiment)
As shown in FIGS. 13 to 15 as a third embodiment, in addition to the wall surface of the chamber 2 facing the stacking direction of the gas sensor elements 1, a chamber that constitutes the wall surface of the chamber 2 facing the short direction of the gas sensor elements At least one of the inner surfaces of the opening 22 of the forming sheet 12 may be warped. In the present embodiment, the relationship between the warp shape of the shielding sheet 13 serving as the chamber wall, the shape and arrangement of the diffusion layer 21, the height Hp of the diffusion layer 21 and the average height Have of the chamber 2 at the position where the pump cell 3 is formed is as follows. This is the same as the embodiment, and the following description will be focused on the differences.

Specifically, as shown in FIGS. 13 and 14, in the longitudinal section, the chamber forming sheet 12 is formed with a substantially rectangular opening 22 that becomes the chamber 2, and the inner surface exposed to the chamber 2 is exposed. Among them, both the pair of inner surfaces extending in the longitudinal direction are angled warpage surfaces that protrude inward of the chamber 2. The warped surface gradually reduces the width of the chamber 2 from the inlet portion a of the pump electrode 31 toward the outlet portion d at the position where the pump cell 3 is formed, and is preferably downstream of the central portion of the pump electrode 31. Thus, it is preferable that the amount of warpage is maximized. At this time, the relationship between the chamber widths Wa to We in the respective parts a to e in the chamber 2 is preferably, for example, the inlet width Wa> Wb> Wc ≧ the outlet width Wd. The relationship between the chamber heights Ha to He due to the warped surface of the shielding sheet 13 is, for example, the inlet height Ha> Hb> Hc ≧ the outlet height Hd, as in the first embodiment.

As shown in FIG. 15, the cross-sectional area of the chamber 2 in the short direction is the smallest on the downstream side of the central portion of the pump electrode 31. The chamber 2 has a warped shape in which the surface of the shielding sheet 13 serving as the upper wall and the pair of surfaces of the chamber forming sheet 12 serving as the side walls are convex inward of the chamber 2, both of which are warped at the center. It has a mountain shape with a maximum. In the inlet portion a (not shown), the chamber 2 has a substantially rectangular cross-sectional shape as in the first embodiment, and the cross-sectional area becomes smaller as the amount of warpage gradually increases toward the downstream side.

At this time, the gas introduced into the chamber 2 travels toward the center of the pump cell 3 along the warped shape of the pair of surfaces of the chamber forming sheet 12 protruding into the chamber 2 as indicated by arrows in FIG. It becomes a flow. Also, along the warped shape of the surface of the shielding sheet 13 becomes a flow directed to the pumping electrodes 31 on the solid electrolyte sheet 11, it is possible to increase the O ₂ discharge capacity in the pump electrode 31. Since the chamber 2 has spaces at the four corners in the cross section in the short direction, gas diffusibility is ensured.

The amount of warpage of the surface of the chamber forming sheet 12 can be arbitrarily set. Normally, if the amount of warpage is 0.10% or more, the gas flow stirring effect can be obtained. Preferably, the maximum amount of warpage may be set so that the warped surface does not protrude inward of the chamber 2 from the outer peripheral edge of the pump electrode 31. The maximum amount of warpage varies depending on the shape of the chamber 2 and the arrangement of the pump electrode 31. For example, when the length of the chamber 2 is 14 mm and the gap between the side wall of the chamber 2 and the outer peripheral edge of the pump electrode 31 is 160 μm, The maximum amount of warpage is 1.2%.

As described above, according to the shape of the chamber 2 of the third embodiment, it is possible to further increase O ₂ discharge by the pump electrode 31 by increasing the difference in flow velocity of the gas flow while ensuring responsiveness. Further, the warped shape of the surface of the chamber forming sheet 12 can be combined with the shape of the chamber 2 of the second embodiment.

Next, in order to confirm the effect of the present invention, the height Hp of the diffusion layer 21, the shape of the chamber 2, and the shape of the pump cell 3 are shown in Table 1 for the gas sensor element 1 having the shape shown in FIGS. The test element having a predetermined chamber warp shape was fabricated by the method described above, and the relationship with the sensor characteristics was examined (Examples 1 to 6). Test elements outside the scope of the invention were produced (Comparative Examples 1 to 5). As shown in the table in FIG. 16, the short direction length A of the sensor electrode 41 of the sensor cell 4 is 1 mm, the long direction length B is 2 mm, the short length C of the chamber 2 is 2.4 mm, and the pump electrode of the pump cell 3 31 in the short direction E: 2.1 mm is common to all the examples and all the comparative examples. Examples 1 to 6 and Comparative Examples 1 and 3 to 5 are the longitudinal length D of the chamber 2: 9 mm, The longitudinal length B of the pump electrode 31 was 6.5 mm. Further, the length in the longitudinal direction D of the chamber 2 was 14 mm, and the length in the longitudinal direction F of the pump electrode 31 of the pump cell 3 was 11 mm.

As shown in FIGS. 17A and 17B, the test elements of Examples 1 to 6 and Comparative Examples 3 to 5 are externally arranged so as to bend and deform the solid electrolyte sheet 11 serving as the lower wall surface of the chamber 2. The warped shape is recessed by applying a load, and the surface on which the pump electrode 31 and the sensor electrode 41 are formed is a warped surface that curves so as to protrude inward of the chamber 2, that is, toward the shielding sheet 13. In Comparative Examples 1 and 2, the solid electrolyte sheet 11 has a warped shape that swells to the outside of the chamber 2. Table 1 shows the results of measuring the amount of warpage in each of these Examples and Comparative Examples.

In addition, evaluation of the amount of curvature was performed as follows. As shown in FIG. 17A, the obtained element sintered body was cut or polished perpendicularly to the longitudinal direction and the lateral direction to produce a chamber cross section. By observing images of the cross section of the chamber, the end portions of the chamber were connected with a straight line, and the maximum amount of deformation in the vertical direction was measured. Furthermore, the amount of deformation in the longitudinal direction and the short direction of the chamber 2 was converted into the amount of warpage (%), respectively, and both were compared and the larger value was taken as the amount of warpage.
Warpage (%) = 100 × [chamber deformation (μm) / chamber end distance (μm)] The position of the end of the chamber is defined by FIG. 17B. That is, three points are arbitrarily drawn in the vertical direction of the chamber, and approximate lines (dotted lines) are drawn on both sides of the chamber 2. Three points are arbitrarily drawn within a range of 0.5 mm in the vertical direction from this approximate line, and an approximate line (dotted line) is drawn, and the intersection of these approximate lines is defined as the chamber end.

For each example and comparative example, the height Hp of the diffusion layer 21 in the stacking direction and the average height Have of the chamber 2 at the position where the pump cell 3 is formed are measured and shown in Table 1. As shown in FIG. 18, the average height Have is obtained by measuring the height between the solid electrolyte sheet 11 and the shielding sheet 13 for the inlet portion, the center portion, and the outlet portion of the pump electrode 31 in the gas flow direction. The value is obtained.
Average height Have = (pump cell inlet height Hi + center height Hc + outlet height Ho) / 3
In each of Examples 1 to 6, the height Hp of the diffusion layer 21 is lower than the average height Have of the chamber 2, and the height of the chamber 2 is equal to the central height Hc and the inlet height Hi of the pump cell 3. The exit height Ho is low. Among these, in Examples 1 and 2, the height gradually decreases from the inlet to the outlet of the pump cell 3, or the heights of the center and the outlet are the same. Examples 3 to 6 are the heights of the center and the outlet. Are almost equal or slightly higher in the middle. In Comparative Example 5, the height Hp of the diffusion layer 21 is higher than the average height Have of the chamber 2.

Table 1 shows the results of examining the O ₂ discharge capacity and gas responsiveness of Examples 1 to 6 and Comparative Examples 1 to 5. O ₂ discharge capacity, large oxygen current monitor cell 5 (background is large), × what difference current value of the sensor cell 4 and the monitor cell 5 is not measured NOx current value because it does not stabilize, the monitor cell 5 The case where the oxygen current value was small (background was small) and the differential current value between the sensor cell 4 and the monitor cell 5 was stable and the NOx current value was measurable was evaluated as ◯. The gas responsiveness can be measured because the response to NOx gas concentration fluctuation is poor and the NOx current value is not stable and cannot be measured, and the response to NOx gas concentration fluctuation is good and the NOx current value is stable. The thing was made into (circle). Further, FIG. 19A shows the relationship between the amount of chamber warpage and the O ₂ discharge capacity in Examples and Comparative Examples in which the chamber is recessed.

As is apparent from FIG. 19A, the O ₂ discharge capacity is improved as the chamber warp amount increases. However, in Comparative Example 4 in which the chamber warpage amount was 1.40%, a crack occurred in the sheet lamination pressure bonding step. Further, it can be seen that in Comparative Example 3 in which the chamber warpage amount is 0.05%, cracks are generated in the baking and degreasing process, and good results cannot be obtained if the chamber warpage amount is too large or too small. FIG. 19B and FIG. 19C show the behavior in the firing and degreasing process when the chamber warpage amount exceeds 0.05% and when it is 0.05% or less. Due to this variation, if degreasing shrinkage occurs only on the upper surface first, there is no room for elongation, so tensile stress is generated and cracks are likely to occur (see, for example, FIG. 19C). On the other hand, it is considered that the solid electrolyte sheet 11 on the lower surface side is warped and stretched and deformed, so that the tensile strain during degreasing can be relaxed and cracks can be prevented (see, for example, FIG. 19B).

On the other hand, no cracks occurred in Example 3 of 0.10% and Example 4 of 1.38%. Therefore, in the present invention, the amount of warpage of the chamber should be in the range of 0.10% to 1.38%, and as is apparent from the results of Table 1, Examples 1 to 6 are O ₂ Good results were obtained for both discharge capacity and gas responsiveness. On the other hand, in Comparative Example 1 in which the chamber 2 is expanded outward and deformed, and in Comparative Example 5 in which the height Hp of the diffusion layer 21 is higher than the average height Have, sufficient O ₂ discharge capability is not obtained. In the comparative example 2 in which the chamber 2 is expanded outward and deformed, the O ₂ discharge capacity is improved by increasing the longitudinal lengths of the chamber 2 and the pump cell 3, but the gas responsiveness is lowered.

In this invention, the gas sensor element 1 should just be the structure which has arrange | positioned the pump cell 3 and the sensor cell 4 from the upstream at least in a chamber, and is not restricted to the laminated body structure of the said embodiment, The chamber 2 shape of this invention is applied. Therefore, the same effect can be expected. Further, the wall surface shape of the chamber 2 may be a shape other than the above-described shape, and the manufacturing method of the gas sensor element 1 is not limited to the method described in the above embodiment, and the chamber 2 shape of the present invention is formed. Various methods can be employed.

As described above, according to the present invention, a gas sensor having both detection accuracy and responsiveness can be realized. This gas sensor is suitable as a NOx sensor installed in an exhaust system of an internal combustion engine, and contributes to an improvement in exhaust purification performance. The specific gas component detected by the gas sensor of the present invention is not limited to NOx, but may be SOx or the like. The gas to be measured is not limited to the exhaust gas from the internal combustion engine, but includes specific gas components in various gases. Used for detection, good sensor characteristics can be emitted.

1 Gas Sensor Element 11 Solid Electrolyte Sheet (First Ceramic Sheet)
12 Chamber forming sheet (second ceramic sheet)
13 Shielding sheet (third ceramic sheet)
2 Chamber 21 Diffusion layer 3 Pump cell 31 Pump electrode 4 Sensor cell 41 Sensor electrode

Claims

A gas sensor for detecting a specific gas component in a gas to be measured,
A gas to be measured is provided from outside through a diffusion layer (21) provided in a gas sensor element (1) in which flat ceramic sheets (11 to 13) are laminated and provided at an end portion in the longitudinal direction of the gas sensor element. A chamber (2) to be introduced;
A pump cell (3) having a pump electrode (31) disposed upstream of the gas flow in the chamber, and pumping out oxygen in the gas to be measured;
A sensor cell (4) having a sensor electrode (41) disposed on the downstream side of the gas flow in the chamber and detecting a specific gas component concentration in the gas under measurement having a reduced oxygen concentration;
The gas sensor element includes a second ceramic sheet (12) having an opening (22) serving as the chamber in a first ceramic sheet (11) on which the pump electrode and the sensor electrode are disposed on a surface facing the chamber. And a third ceramic sheet (13) covering the opening and defining the chamber in order,
The chamber has a warped shape in which at least one surface of the first ceramic sheet and the third ceramic sheet constituting the chamber wall is convex inward of the chamber at the position where the pump cell is formed, and The amount of warpage of the surface is set in the range of 0.10% to 1.38%,
In the diffusion layer and the chamber, the height Hp in the stacking direction of the diffusion layer and the average height Have in the stacking direction of the chamber at the position where the pump cell is formed satisfy the relationship of Hp <Have. , Gas sensor.
The gas sensor according to claim 1, wherein the amount of warpage of the surface is calculated based on a maximum deformation amount in a longitudinal direction and a short direction of the gas sensor element.
The chamber has a gas flow direction in a longitudinal direction of the gas sensor element, a cross-sectional area at the gas outlet portion is smaller than a cross-sectional area at the gas inlet portion of the pump electrode, and the short direction of the gas sensor element The height at the central portion of the pump electrode is lower than the height of at least one wall surface of the chamber end, and the diffusion layer is disposed along the gas inlet of the pump electrode. The gas sensor according to 1.
In the longitudinal direction of the gas sensor element, the chamber gradually decreases in cross-sectional area from the gas inlet portion to the gas outlet portion of the pump electrode, and has a minimum cross-sectional area downstream from the central portion in the gas flow direction. The gas sensor according to claim 1, which has a shape.
2. The chamber according to claim 1, wherein the chamber has a shape that gradually decreases in height from one or both ends of the chamber toward a central portion of the pump electrode in a short direction of the gas sensor element. Gas sensor.
In the chamber, at least one of the inner surfaces of the opening of the second ceramic sheet constituting the chamber wall facing the short direction of the gas sensor element protrudes inward of the chamber at the position where the pump cell is formed. The gas sensor according to claim 1, which has a warped shape.
The first ceramic sheet is an oxygen ion conductive solid electrolyte sheet, and has a reference electrode (32) corresponding to the pump electrode or the sensor electrode on a surface opposite to the chamber, and the pump cell. Or the gas sensor of Claim 1 which comprises the said sensor cell.
2. The gas sensor according to claim 1, wherein the second ceramic sheet and the third ceramic sheet are insulating sheets that are not permeable to the gas to be measured.
The gas sensor according to claim 1, wherein the gas to be measured is an exhaust gas of the internal combustion engine, and the specific gas component is a nitrogen oxide gas.