JP2006170888A - Gas sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor element capable of preventing an unsintered break from being generated in an unsintered solid electrolyte sheet, capable of preventing a crack of a solid electrolyte from being generated caused by the unsintered break, and capable of enhancing reliability compared with the prior art. <P>SOLUTION: An electrode 11 constituting an oxygen partial pressure detecting cell 3 is arranged in the first measuring chamber 5, and formed into a rectangular shape. Both side ends of the electrode 11 are wrapped with an insulating ceramic 15 forming a side wall part of the first measuring chamber 5. That is, a protrusion 151 is formed in an inner end of the insulating ceramic 15 to be interposed between the electrode 11 and the solid electrolyte 19, and an end 111 of the electrode 11 is arranged on the protrusion 151, and one part of the end part 111 is arranged to be embedded into the insulating ceramic 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas sensor element for detecting a predetermined gas concentration in a gas to be measured, such as an oxygen concentration, NOx concentration, air-fuel ratio, etc., in an automobile exhaust gas, for example.

  2. Description of the Related Art Conventionally, various gas sensor elements for detecting the concentration of a predetermined gas in a gas to be measured such as oxygen concentration, NOx concentration, air-fuel ratio, etc. in an automobile exhaust gas are known.

For example, the following gas sensor elements are known as NOx sensor elements for measuring NOx concentration. That is, this NOx sensor element has a first measurement chamber into which a gas to be measured is introduced via a first diffusion resistor, and a second measurement chamber that communicates with the first measurement chamber via a second diffusion resistor. ing. Further, a first oxygen pump cell and an oxygen concentration detection cell are formed so as to face the first measurement chamber, and a second oxygen pump cell is formed so as to face the second measurement chamber. Each of the measurement chambers described above is formed by two plate-shaped solid electrolyte bodies that are stacked and spaced apart, and a side wall portion that is sandwiched between these solid electrolyte bodies and that is made of an insulating member that forms the side wall of the measurement chamber. Yes. And the electrode which comprises an oxygen pump cell etc. is formed in the solid electrolyte body so that it may be located in these measurement chambers (for example, refer patent document 1).
Japanese Patent Laid-Open No. 2004-151018

  In such a gas sensor element, a crack may occur in the solid electrolyte body and the function of the gas sensor element may be impaired. As a result of detailed investigations by the inventors regarding the occurrence of such cracks, it has been found that cracks may occur due to the following reasons.

  That is, an unsintered electrode serving as an electrode, an unsintered sidewall sheet serving as a sidewall of a measurement chamber, and the like are printed and laminated on an unsintered solid electrolyte sheet serving as a solid electrolyte body to form a laminate, and then heated in a degreasing process. In some cases, the unfired solid electrolyte sheet constituting the laminate is broken. And when a piece of raw material occurs in this way, the part where the piece of raw material has occurred becomes a crack starting point under thermal shock, and a crack is generated in the solid electrolyte body after firing. Note that, as shown in FIG. 5 to be described later, such a piece 30 is generated around the contact portion with the insulating member (side wall portion), particularly in the peripheral portion of the measurement chamber.

  The present invention has been made to solve the above problems. The present invention prevents the occurrence of burnout in the unfired solid electrolyte sheet, can prevent the occurrence of cracks in the solid electrolyte body due to the burnout, and improves the reliability as compared with the prior art. An object of the present invention is to provide a gas sensor element that can handle the above.

(Claim 1)
In order to achieve the above object, the gas sensor element of the present invention introduces a gas to be measured between two solid electrolyte bodies by interposing an insulator forming a side wall between the two solid electrolyte bodies. A gas sensor element in which a measurement chamber is formed and an electrode is formed on the surface of at least one of the two solid electrolyte bodies so as to face the measurement chamber, At least a part of the end portion is disposed so as to overlap the insulator.

  If the end of the electrode does not overlap with the insulator that constitutes the side wall, the unfired electrode can be freely shrunk when the laminated body serving as the gas sensor element is heated, while the unfired solid electrolyte sheet is shrunk by the side wall. Is suppressed. For this reason, the unsintered solid electrolyte sheet is pulled by the shrinkage of the unsintered electrode, and the raw material is cut. In the gas sensor element of the present invention, when the unsintered solid electrolyte sheet to be the solid electrolyte body is heated in the degreasing process, the unsintered solid electrolyte sheet and the unsintered electrode to be the electrode are separated by the side wall (insulator). In both cases, shrinkage is suppressed, and it is possible to prevent the unfired solid electrolyte sheet from being burned out.

(Claim 2)
The gas sensor element of the present invention is characterized in that the electrode is formed in a quadrangular shape and two opposing sides overlap with the insulator. In this way, by suppressing shrinkage during heating on the two opposing sides of the rectangular electrode, it is possible to more reliably prevent the unfired solid electrolyte sheet from being burned out.

(Claim 3)
In addition, the gas sensor element of the present invention is configured such that at least a part of the electrode disposed so as to overlap the insulator is sandwiched between both sides in its thickness direction by the insulator. It is characterized by. By setting it as such a structure, the adhesion margin of an insulator and a solid electrolyte body is securable.

(Claim 4)
In the gas sensor element of the present invention, a protruding portion that protrudes toward the inside of the measurement chamber is formed in a part of the insulator so as to be interposed between the one solid electrolyte body and the electrode. It is characterized by that. By adopting such a configuration, it is possible to secure a bonding allowance between the insulator and the solid electrolyte body while suppressing a decrease in the volume of the measurement chamber.

(Claims 5 and 6)
The gas sensor element of the present invention includes a first measurement chamber that introduces a gas to be measured through a first diffusion resistor, and pumps out oxygen in the gas to be measured from the first measurement chamber to the outside. A first oxygen pump cell for pumping oxygen into the first measurement chamber, an oxygen partial pressure detection cell for detecting the oxygen concentration in the gas under measurement in the first measurement chamber, and a second diffusion resistance in the first measurement chamber A second measurement chamber connected through the body, and a second oxygen pump cell for detecting NOx concentration by detecting movement of oxygen generated by decomposition of nitrogen oxides in the gas to be measured in the second measurement chamber; It is characterized by comprising. Further, in such a gas sensor element, the electrode is arranged in the first measurement chamber in order to constitute the oxygen partial pressure detection cell. The gas sensor element of the present invention can be applied to the NOx sensor element having such a configuration, prevents the unfired solid electrolyte sheet from being burned out, and prevents the occurrence of cracks in the solid electrolyte body due to the burnout. Can be prevented.

  According to the present invention, it is possible to prevent the unfired solid electrolyte sheet from being burned out, and to prevent the occurrence of cracks in the solid electrolyte body due to the burned out, improving the reliability compared to the conventional case. A gas sensor element capable of achieving the above can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a main part of a NOx sensor element according to an embodiment of the present invention. As shown in FIG. 1, the NOx sensor element includes a first oxygen pump cell 1, a second oxygen pump cell 2, and an oxygen partial pressure detection cell 3 that are stacked on each other. Further, a heater 4 for heating the NOx sensor element to a predetermined operating temperature is provided adjacent to the NOx sensor element.

  A first measurement chamber 5 is formed between the first oxygen pump cell 1 and the oxygen partial pressure detection cell 3. A gas to be measured is introduced into the first measurement chamber 5 through the first diffusion hole 7. The first measurement chamber 5 communicates with the second measurement chamber 6 through the second diffusion hole 8.

  The first oxygen pump cell 1 includes a plate-like solid electrolyte body 17 having oxygen ion conductivity such as zirconia, and a pair of electrodes 9 and 10 formed on the solid electrolyte body 17. The electrode 10 is disposed so as to be located in the first measurement chamber 5, and the electrode 9 is disposed so as to be located outside the first measurement chamber 5. In the first oxygen pump cell 1, oxygen ions generated by dissociating oxygen or the like in the first measurement chamber 5 on the electrode 10 are pumped to the electrode 9 side through the solid electrolyte body 17. At this time, the current flowing through the solid electrolyte body 17 is the first oxygen pump current Ip1.

  The second oxygen pump cell 2 includes a plate-like solid electrolyte body 18 having oxygen ion conductivity such as zirconia, and a pair of electrodes 13 and 14 formed on the solid electrolyte body 18. The electrode 13 is disposed so as to be located in the second measurement chamber 6. The electrode 14 is disposed outside the second measurement chamber 6 and exposed to an atmosphere having a stable oxygen concentration. Oxygen ions generated by dissociating NOx and the like in the second measurement chamber 6 on the electrode 13 are pumped to the electrode 14 side through the solid electrolyte body 18. At this time, the current flowing through the solid electrolyte body 18 is the second oxygen pump current Ip2.

  The oxygen partial pressure detection cell 3 includes a plate-shaped solid electrolyte body 19 having oxygen ion conductivity such as zirconia, and a pair of electrodes 11 and 12 formed on the solid electrolyte body 19. The electrode 11 is disposed so as to be located in the first measurement chamber 5. By supplying a constant controlled current Icp between the electrodes 11 and 12 through the oxygen partial pressure detection cell 3, the amount of oxygen ions pumped to the electrode 12 side through the oxygen partial pressure detection cell 3 becomes constant. As a result, the electrode 12 is exposed to an atmosphere having a stable oxygen concentration. Accordingly, based on the potential difference generated between the electrode 11 and the electrode 12, the oxygen concentration in the first measurement chamber 5, that is, the oxygen concentration in the gas to be measured can be detected.

  In FIG. 1, 20 is a first oxygen pump cell control means, 21 is an oxygen partial pressure detection cell control means, and 22 is a second oxygen pump cell control means. The oxygen partial pressure cell control means 21 detects the oxygen concentration in the first measurement chamber 5 appearing in the oxygen partial pressure detection cell 3 and controls the oxygen concentration on the electrode 12 provided outside the first measurement chamber 5. . The first oxygen pump cell control means 20 controls the first oxygen pump current Ip1 based on the detection output of the oxygen partial pressure detection cell 3, thereby controlling the oxygen concentration in the first measurement chamber 5 as constant as possible. To do. The second oxygen pump cell control means 22 applies a predetermined voltage as constant as possible to the second oxygen pump cell 2 so that the second oxygen pump current Ip2 corresponding to the NOx concentration flows. To control. The first oxygen pump current Ip1 can be extracted from the resistor 120, and the second oxygen pump current Ip2 can be extracted from the resistor 122.

  In the NOx sensor element having the above configuration, the electrode 11 constituting the oxygen partial pressure detection cell 3 is formed in a rectangular shape in the first measurement chamber 5 as shown in FIG. Then, both end portions (vertical end portions in the figure) 111 of the electrode 11 extend to a portion of the insulating ceramic 15 made of alumina or the like that forms the side wall portion of the first measurement chamber 5. It is arranged so as to overlap (wrap). In FIG. 2, 16 is a columnar porous body serving as a column for maintaining the inside of the first measurement chamber 5 at a predetermined interval, and 112 is a base end side of the NOx sensor element from the electrode 11 ( This is the lead portion derived on the right side in the figure.

  FIG. 3 shows an enlarged configuration of the AA cross section of FIG. As shown in the figure, at the inner end of the insulating ceramic 15 forming the side wall of the first measurement chamber 5, the inside of the first measurement chamber 5 is interposed between the electrode 11 and the solid electrolyte body 19. A projecting portion 151 projecting toward the surface is formed. The end portion 111 of the electrode 11 is disposed on the protruding portion 151, and a part of the end portion 111 is embedded in the insulating ceramic 15, that is, both surfaces thereof are formed by the insulating ceramic 15. It is arranged to be sandwiched. With such a configuration, the area (wrap amount) of the overlapping portion of the electrode 11 and the insulating ceramic 15 when viewed from the stacking direction of the NOx sensor element can be increased, and the insulating ceramic 15 The allowance for bonding with the solid electrolyte body 19 and the volume of the first measurement chamber 5 can be ensured.

  That is, simply extending the end portion of the electrode 11 between the solid electrolyte body 19 and the insulating ceramic 15 reduces the bonding allowance between the solid electrolyte body 19 and the insulating ceramic 15, thereby improving the adhesion. Problems can arise. Further, if the insulating ceramic 15 side is simply extended so as to overlap the end portion of the electrode 11, the volume of the first measurement chamber 5 is reduced. The structure shown in FIG. 3 is adopted in order to increase the lap amount while solving such a problem.

  With the above-described configuration, when heated in a degreasing process or the like in an unfired stage, the unfired solid electrolyte sheet that becomes the solid electrolyte body 19 and the unfired electrode that becomes the electrode 11 are held together by the side wall portion. Shrinkage is suppressed, and it is possible to prevent the burned solid electrolyte sheet from being burned out.

  That is, for example, as shown in FIG. 5, in the case where the end of the electrode 11 is not overlapped with the insulating ceramic 15 constituting the side wall, when the laminated body that becomes the gas sensor element is heated in the degreasing step, the electrode 11 can be freely shrunk, while the unfired solid electrolyte sheet to be the solid electrolyte body 19 is suppressed from being shrunk by the side wall. For this reason, the unfired solid electrolyte sheet is pulled by the shrinkage of the unfired electrode, and there is a possibility that the raw material 30 is generated. The possibility that such a raw piece 30 is generated is particularly high when the end portion of the electrode 11 extends to the vicinity of the side wall portion. Generation | occurrence | production of the raw material 30 of such an unbaking solid electrolyte sheet can be prevented by setting it as the structure shown in FIG.

  Actually, the NOx sensor element (500 samples) manufactured with the configuration shown in FIGS. 2 and 3 was heated for about 4 hours at a holding temperature of about 400 ° C. in the degreasing process, and then the green solid electrolyte sheet was formed. When the occurrence of cutting was observed, the occurrence rate of raw cutting was 0%. On the other hand, when the NOx sensor element (sample number: 500) manufactured with the electrode 11 having the configuration shown in FIG. 5 was heated by the same degreasing process, the unburned solid electrolyte sheet was about 70% out of life. Met. As is clear from this result, according to the present embodiment, it is possible to reliably prevent the unburned solid electrolyte sheet from being burned out. Therefore, it is possible to prevent the occurrence of cracks in the solid electrolyte body due to the cutting and improve the reliability.

  In the present embodiment, as shown in FIG. 4, the electrode 12 formed on the solid electrolyte body 19 and the electrode 14 formed on the solid electrolyte body 18 have the same configuration as the electrode 11 described above. Yes. Further, the electrode 10 formed on the solid electrolyte body 17 and the electrode 13 formed on the solid electrolyte body 18 shown in FIG.

  In the above embodiment, the case has been described in which the both ends in one direction of the rectangular electrode 11 of the NOx sensor element are wrapped with the insulating ceramic constituting the side wall, but the present invention is such an embodiment. It is not limited to. For example, with respect to an electrode in which all four sides are arranged close to the side wall portion, a configuration may be adopted in which all four sides are wrapped with the side wall portion. Further, in the case where only one side of the electrode is disposed close to the side wall portion, only one side may be wrapped with the side wall portion. Further, the present invention is not limited to the NOx sensor element, and can be similarly applied to other gas sensor elements such as an air-fuel ratio sensor element.

The figure which shows the cross-sectional schematic structure of the whole NOx sensor element which concerns on one Embodiment of this invention. The figure which shows the internal cross-sectional structure of the 1st measurement chamber of the NOx sensor element of FIG. The figure which expands and shows the AA cross-section structure of FIG. The figure which shows the principal part cross-section structure of the NOx sensor element of FIG. The figure which expands and shows the cross-sectional structure of the conventional NOx sensor element.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... 1st oxygen pump cell, 2 ... 2nd oxygen pump cell, 3 ... Oxygen partial pressure detection cell, 4 ... Heater, 5 ... 1st measurement chamber, 6 ... 2nd measurement chamber, 7 ... 1st 1 diffusion hole, 8 ... second diffusion hole, 9-14 ... electrode, 15 ... insulating ceramic, 16 ... porous body, 17-19 ... solid electrolyte body, 20 ... first oxygen pump cell control Means 21... Oxygen partial pressure detection cell control means 22... Second oxygen pump cell control means.

Claims (6)

A measurement chamber for introducing a gas to be measured is formed between the two solid electrolyte bodies by interposing an insulator forming a side wall between the two solid electrolyte bodies, and the two solid electrolyte bodies A gas sensor element in which an electrode is formed on the surface of at least one of the solid electrolyte bodies so as to face the measurement chamber,
A gas sensor element, wherein at least a part of an end portion of the electrode is disposed so as to overlap the insulator. The gas sensor element according to claim 1,
The gas sensor element, wherein the electrodes are formed in a quadrangular shape, and two opposing sides overlap with the insulator. The gas sensor element according to claim 1 or 2,
A gas sensor element characterized in that at least a part of a portion of the electrode arranged so as to overlap the insulator is configured such that both surfaces in the thickness direction of the electrode are sandwiched by the insulator. . The gas sensor element according to any one of claims 1 to 3,
A gas sensor element, wherein a protruding portion that protrudes toward the inside of the measurement chamber is formed in a part of the insulator so as to be interposed between the one solid electrolyte body and the electrode. The gas sensor element according to any one of claims 1 to 4,
The gas sensor element is
A first measurement chamber for introducing a gas to be measured through a first diffusion resistor;
A first oxygen pump cell that pumps oxygen in the gas to be measured from the first measurement chamber to the outside, or pumps oxygen from the outside into the first measurement chamber;
An oxygen partial pressure detection cell for detecting the oxygen concentration in the gas under measurement in the first measurement chamber;
A second measurement chamber connected to the first measurement chamber via a second diffusion resistor;
A second oxygen pump cell for detecting NOx concentration by detecting the movement of oxygen generated by decomposition of nitrogen oxides in the gas to be measured in the second measurement chamber;
A gas sensor element comprising: The gas sensor element according to claim 5,
The gas sensor element, wherein the electrode is disposed in the first measurement chamber to constitute the oxygen partial pressure detection cell.

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