JPS61108957A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To decrease the internal resistance of an oxygen sensor and to prevent the exfoliation thereof by increasing the area of a reference electrode embedded into the base body of a sensor and to increase the strength of the sensor by decreasing the width of a gap for introduction of a reference material. CONSTITUTION:The plane shape of the reference electrode 6 of the sensor element 1 constituted of a sensor part 20 and a heater part 30, etc. is made into a recessed shape by a notch 6a coinciding approximately with the peripheral edge shape of the gap 7 provided so as to be sandwiched approximately thoroughly between middle and lower solid electrolyte plates 3 and 4. A measuring electrode 5 has the plane shape formed approximately the same as the plane shape of the electrode 6 and is so disposed as to face thoroughly the electrode 6 via the upper and middle solid electrolytes 2 and 3. The width of the gap 7 is decreased by embedding the electrode 6 into said gap, by which the strength of the element 1 is increased and the exfoliation of the electrode 6 is prevented. The area of the electrode 6 is increased so that measuring electrode 5 and the electrode 6 face each other at the area expanded to the same size. The decrease in the internal resistance is thus made possible.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an oxygen sensor used for measuring the oxygen concentration in exhaust gas of a car, for example, and particularly relates to an oxygen sensor in which a sensor element is formed in the shape of a long flat plate. This paper relates to improvements to oxygen sensors.

(Prior art) In recent years, from the viewpoint of ease of manufacturing and compactness, oxygen sensor elements using long flat plate-shaped oxygen sensors have been introduced, replacing the existing low-profile cylindrical oxygen sensors. A sensor has been proposed.

An example of the conventional structure of such a long flat oxygen sensor element is shown in an exploded view in FIG.

This oxygen sensor element 40 is an oxygen sensor element equipped with a heater, and is roughly composed of a sensor section 50 and a heater section 60.

The sensor section 50 includes a long flat solid electrolyte plate 5 made of an oxygen ion conductive solid electrolyte containing zirconia as a main component.
1 and a solid electrolyte plate 56 made of the same material and having a groove 57 from one end to the vicinity of the other end are overlapped to form an outer shell.

A porous measuring electrode 52 made of platinum or the like is printed on one end of the surface of the flat solid electrolyte plate 51, and a measuring electrode 52 is attached on the back side with the solid electrolyte plate 51 sandwiched between them. A reference electrode 55 made of the same material is applied so as to face each other.

Further, on both sides of the solid electrolyte plate 51, each of the above-mentioned electrodes 52,
Leads 58 and 59 made of the same material as 55 are coated in a strip shape from both electrodes 52.55 to the other end of the solid electrolyte 51, and the ends serve as a reference electrode terminal 53 and a measurement electrode terminal 54. ing.

The entire surface of the reference electrode 55 is exposed within the groove 57,
It is exposed to the outside air flowing in from the open end of the groove 57.

The heater section 60 has two long flat plate-shaped insulating ceramic layers 61 and 62 stacked on top of each other, a resistive heating element 65 is sandwiched between one end of the insulating ceramic layers 61 and 62, and the insulating ceramic layers 61 and 62 are formed from both poles of the resistive heating element 65. Two strip-shaped conductive leads 66 and 67 are similarly sandwiched between the insulating ceramic layers 61 and 62 to the other end.

Since the length of one insulating ceramic layer 62 is shorter than the other 61, the ends of the leads 66 and 67 are exposed and serve as connection terminals 63 and 64 for connecting to an external power source.

This heater section 60 is laminated and fixed on one side of the sensor section to form an oxygen sensor element 40 with a heater.

As shown in FIG.
．． Cement, talc, and glass are housed in a cylindrical metal protection tube 71 with the ends where 54, 63, and 64 are formed supported by the connector insulator 74, and filled on the insulator 72. A large number of through holes 75 are formed in the tip portion 71A of the protective tube 71, which is fixed by a filler 73 such as the like and a filler 78 such as talc filled under the insulator 72. The measuring electrode 52 at the tip of the oxygen sensor element 40 exposed inside comes into contact with the substance to be measured, such as engine exhaust gas. Further, a lead wire is inserted into the rear end portion 71B of the protection tube 71 through the rubber stopper 76. ? The earth lead wire connected to a to 77c and the protective tube 77? 7d are the connection terminals 63 and 64 of the heater section 60 provided in the oxygen sensor element 40, the reference electrode terminal 53, and the measurement electrode terminal 54.
are connected correspondingly to each other.

The oxygen sensor 70 having such a configuration includes, for example, the protective tube 7
By inserting the tip end 71A of No. 1 into the exhaust pipe of an automobile, it is used for detecting the oxygen concentration in exhaust gas. At this time, the resistance heating element 65 of the heater section 60 is energized to heat and activate the electrodes 52 and 55 of the sensor section 50.

And the tip with high temperature exhaust gas and heater heating like this? Since LA becomes high temperature, lead wires 77a to 77d
Because of the need to prevent contact failure due to high-temperature oxidation of the connector portion, the long oxygen sensor 70 as described above is advantageous in that the connector portion can be kept at a low temperature.

(Problems to be Solved by the Invention) However, as is clear from the cross-sectional view shown in FIG.
A groove 57 in the center is covered with a solid electrolyte plate 51 to form a gap in which a reference substance exists, and a reference electrode 5
The width of the groove 57 is relatively wide due to the need to expose the entire surface of the groove 57 to the reference substance, such as air, in the gap.

Therefore, as shown in Fig. 8, the force F applied in the vertical direction
In addition, since the width of the bonded portion between the solid electrolyte plates 56 and 51 is narrow, leaks are likely to occur at the bonded portion.

Therefore, the width of the groove 57 is limited,
Along with this, the width of the reference electrode 55 is also limited, so the opposing area between the measurement electrode 52 and the reference electrode 55 becomes smaller, resulting in an increase in internal resistance.

Further, the reference electrode 55 is mainly formed of a metal component such as platinum. Therefore, since the adhesive strength with the solid electrolyte plate 51 is relatively weak, there is a possibility that peeling may occur during repeated heating and cooling, which also causes an increase in the internal resistance value.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention consists of a long flat plate made mainly of an oxygen ion conductive solid electrolyte, and one end of which is closed in the longitudinal direction. a sensor base having a tubular gap; one or more measurement electrodes in contact with the analyte formed in a planar shape on a part of the outer surface of the sensor base; one or more reference electrodes that are buried and are provided so that the reference material in the void and the unburied portion are in direct contact with each other, or are provided so that they are in contact with each other through a porous body that can transmit the reference material; It is characterized by being prepared.

By allowing a small part (mostly buried) of the reference electrode, or the edge of the reference electrode, to be in contact with the reference material in the cavity, such as air, directly or through a porous body, The present inventors have experimentally discovered that this oxygen sensor can generate a nearly accurate signal output, leading to the present invention.

It is presumed that the reason why this oxygen sensor is able to generate a nearly accurate signal output is that the reference substance diffuses into the reference electrode through the boundary layer of material particles forming the reference electrode or small pores within the reference electrode. . Therefore, the reference electrode is preferably a polycrystalline material with many grain boundaries, and more preferably a porous electrode with many pores. Further, if there is a porous layer in contact with, for example, one large surface of the reference electrode, the reference substance can diffuse more easily, which is a preferable form. In addition, platinum group metals are usually used as electrode materials in the buried part of the reference electrode, but since the adhesion between these metal components and solid electrolytes is weak, at least the buried part of the reference electrode is made of oxygen ion conductive solid electrolytes. A mixed layer with a platinum group metal is preferable.

(Function) Since the reference electrode is substantially buried within the sensor base, both sides thereof are held between them, and peeling can be prevented.

Furthermore, since the reference electrode can come into contact with the reference substance, such as air, in the gap either directly or through the porous body, the reference electrode can fully perform its function even if it is embedded within the sensor base.

Therefore, it is possible to reduce the width of the gap and increase the area of the reference electrode.

(Example) The configuration of a first embodiment of the present invention is shown in an exploded view in FIG.

The oxygen sensor element 1 shown in the figure is housed in a protective tube 71 similar to that shown in FIG. And the eighth
Similar to the oxygen sensor element 40 shown in the figure, the sensor section 20
and a heater section 30.

The sensor unit 20 includes a sensor base 10 formed by laminating and fixing three oxygen ion conductive solid electrolyte plates 2, 3, and 4 containing zirconia as a main component, and printed on the left end of the upper surface of the upper solid electrolyte plate 2. A measuring electrode 5 coated in a flat shape by
A reference electrode 6 is provided on the left end of the upper surface of the lower solid electrolyte plate 4, which is also applied in a flat manner by printing.

A slit is formed in the middle solid electrolyte plate 3 in the longitudinal direction and at the center of the width direction.
A long rectangular gap 7 whose left end is closed is formed inside the space 0 in the longitudinal direction.

The reference electrode 6 is a conductive film formed by mixing a mixture of one or more platinum group metals and an oxygen ion conductive solid electrolyte mainly composed of zirconia, etc., printing and coating the mixture, and then firing the mixture. be. The planar shape of the reference electrode 6 has a concave shape with a notch 6a that almost matches the peripheral shape of the gap 7 so that it is almost completely sandwiched between the middle and lower solid electrolyte plates 3 and 4. The situation is as follows. Further, the outer peripheral edge of the planar shape of the reference electrode 6 is extended to the vicinity of the left end peripheral edge of the sensor base 10, and occupies two or more areas of the upper surface of the left end of the lower solid electrolyte plate 4.

Further, the measurement electrode 5 is formed so that its planar shape is almost the same as that of the reference electrode 6, and is completely opposed to the reference electrode 6 via the solid electrolytes 2 and 3 in the upper and middle stages. It is located in In addition, the material of the reference electrode 6
The material is the same as that of

Leads 8 and 9 for external circuit connection are formed in a band shape from the right ends of the measurement electrode 5 and the reference electrode 6 to the right end of the sensor base 10.

Furthermore, the upper surface of the measuring electrode 5 is covered with a protective layer 17 made of porous insulating ceramics made of spinel or the like and having a larger area than the measuring electrode 5. Contact with test substance.

Next, in the heater section 30, a resistive heating element 14 is sandwiched between the left end portion between two elongated flat plate-shaped insulating ceramic layers 12.13. Leads 15 and 16 for connecting an external power source to the right end of the ceramic layer 12 and 13 are formed in the shape of two bands.

The heater section 30 configured in this manner is integrally joined to the lower surface of the sensor section 20 via the insulating ceramic layer 11, and heats the reference electrode 6 by the heat generated by the resistance heating element 14. I do.

FIG. 2 is a diagram showing a cross section (cross section taken along line nn in FIG. 1) of the electrode portion of the oxygen sensor element 1 described above.

As shown in the figure, the upper and lower surfaces of the reference electrode 6 are almost completely sandwiched between the two solid electrolyte plates 3.4, and only the inner peripheral end surface 6b faces the gap 7. Therefore, the reference substance (for example, the atmosphere) in the cavity 7 is
It is estimated that the reference electrode 6 diffuses into the reference electrode 6 and spreads over almost the entire surface, generating a highly accurate signal output.

Further, by embedding the reference electrode 6, the width of the gap 7 can be reduced, the strength of the oxygen sensor element 1 can be improved, and peeling of the reference electrode 6 can be prevented.

This makes it possible to increase the area of the reference electrode 6, and by enlarging the measurement electrode 5 to the same shape as the reference electrode 6 and facing each other, the internal resistance can be reduced.

Next, as a second embodiment of the present invention, the reference electrode 6 which was in contact with the gap 7 at its inner peripheral end surface 6b in the first embodiment is replaced with a porous material as shown in FIG. 21
An example of a structure that communicates with the air gap 7 via the air gap 7 is mentioned below.

The inner periphery of the reference electrode 6 is slightly retracted deeper into the solid electrolyte plates 3 and 4 than the boundary with the gap 7, and the inner periphery of the reference electrode 6
A porous body 21 is provided so as to be in contact with the inner peripheral end surface of the porous body 21 . This porous body 21 is mainly made of porous ceramics using spinel, alumina, zirconia, etc.

In this embodiment, by providing the porous body 21 in this way, the solid electrolyte plates 4 and 3 at the inner peripheral end face of the reference electrode 6 are
(The porous body 21 is mainly made of ceramics and bonds well with the solid electrolyte plate).Also, since the porous body 21 has strong adhesiveness with the solid electrolyte plate, the third As can be seen in the figure, since it can bulge into the cavity 7, the area of contact with the reference substance within the cavity 7 can be increased.

Note that the other components are the same as in the first embodiment,
The same reference numerals are used to omit the explanation.

Further, as shown in FIG. 4 as a third embodiment of the present invention,
If the porous body 21 used in the second embodiment is laid over the entire lower surface of the reference electrode 6 to form the porous body layer 31, the efficiency with which the reference substance is distributed over the entire surface of the reference electrode 6 is further increased.

Further, as shown in FIG. 5 as a fourth embodiment of the present invention,
The reference electrode 6 is arranged so as to be in contact with the solid electrolyte plate 2, and the plane 6C of the central part of the reference electrode (most of the electrode is buried between the solid electrolyte plates 2 and 3) is placed in the reference material in the gap 7. It is also possible to make them touch each other.

The central portion 6C of the reference electrode forms a continuous layer with the temporarily buried solid electrolyte portion, and is therefore supported by the buried portion, so it hardly peels off and allows the reference material to be distributed throughout the electrode more stably. It can be spread widely. Furthermore, as shown in this embodiment, since the area facing the measurement electrode is increased, the internal resistance of the oxygen sensor can be further reduced.

Furthermore, as shown in FIGS. 6 and 7, the planar shape of the reference electrode 6 is made into a multi-lobed shape with cuts 22 provided on the outer periphery,
If the shape increases the contact area between the upper and lower solid electrolyte plates 3 and 4, such as a net shape with a large number of round holes 23 or a grid shape (not shown), the bonding at the reference electrode 6 can be achieved. The strength can be further increased. in this case,
If the total area of the reference electrode 6 is increased by the area of the notch 22, round hole 23, etc., the performance will not deteriorate.

In addition, although the above embodiment shows an example in which the present invention is applied to a general oxygen sensor equipped with a heater, the present invention can be similarly applied to other types of oxygen sensors, such as oxygen sensors equipped with an oxygen pump. It is clear that there are some applicable methods.

(Effects of the Invention) As explained in detail above, the present invention can prevent the reference electrode from peeling off by embedding the reference electrode in the sensor base, and the width of the gap for introducing the reference substance can be reduced. It becomes possible to increase the strength of the element by narrowing the width.

In addition, it is possible to expand the area of the reference electrode,
An oxygen sensor with low internal resistance can be provided.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing the configuration of an oxygen sensor element according to a first embodiment of the present invention, FIG. 2 is a sectional view taken along nn in FIG. 1, and FIG. 3 is an electrode according to a second embodiment of the present invention. FIG. 4 is a cross-sectional view of the electrode portion in the third embodiment of the present invention; FIG. 5 is a cross-sectional view of the electrode portion in the fourth embodiment of the present invention; FIGS. 6 and 7 8 is an exploded perspective view showing the configuration of a conventional example, FIG. 9 is a cross-sectional view of the electrode portion, and FIG. FIG. 2 is a longitudinal cross-sectional view showing the overall configuration of an oxygen sensor. 1... Oxygen sensor element 2.3.4... Solid electrolyte plate 5... Measuring electrode 6... Reference electrode 7.
...Gap 10...Sensor base 21...
・Porous body 31... Porous body layer Fig. 1 ■ Fig. 2 f Fig. 3 Fig. 4 Fig. 5

Claims (1)

[Scope of Claims] 1. A sensor base formed into a long flat plate mainly made of an oxygen ion conductive solid electrolyte, and having a tubular void with one end closed inside the sensor base in the longitudinal direction; and an outside of the sensor base. one or more measurement electrodes formed in a planar shape on a part of the surface and in contact with the test substance, and substantially buried in a part of the sensor base, and the reference substance in the gap and the unburied part. 1 provided in direct contact or provided in contact via a porous body that allows the reference substance to pass through.
An oxygen sensor comprising the above reference electrode. 2. The oxygen sensor according to claim 1, wherein a part of the edge of the reference electrode faces the gap. 3. The oxygen sensor according to claim 1, wherein the porous body is made of porous ceramics. 4. The oxygen sensor according to any one of claims 1 to 3, wherein the reference electrode is porous. 5. The porous body is laminated on one side of the reference electrode,
The oxygen sensor according to claim 1, 3, or 4, wherein a portion of the oxygen sensor is exposed to the void. 6. The oxygen sensor according to any one of claims 1 to 5, wherein the measurement electrode and the reference electrode are disposed at positions substantially facing each other. 7. The oxygen sensor according to any one of claims 1 to 6, wherein the reference electrode contains one or more platinum group metals as a main component. 8. Claims 1 to 7 in which the reference electrode comprises a mixture of a platinum group metal and an oxygen ion conductive solid electrolyte.
The oxygen sensor according to any of paragraphs.