JPS6031260B2 - oxygen sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen sensor used primarily to measure the oxygen concentration of automobile engine exhaust gas.

This type of oxygen sensor has conductive inner and outer electrodes on the inner and outer surfaces of a solid electrolyte container made of an oxygen ion conductive material.
There are many types in which an internal standard substance is filled in the solid electrolyte container, and the top is sealed with a glass layer with a ceramic layer interposed therebetween.

However, this type of oxygen sensor is installed in a car and is used under extremely harsh conditions, such as being exposed to high-temperature exhaust gas while being constantly vibrated while driving, and conventional oxygen sensors The degree of sealing gradually decreases, and the inside of the solid electrolyte container is exposed to exhaust gas, water, dust, etc., which denatures the internal standard substance and internal charge, making it difficult to accurately detect the oxygen concentration in the exhaust gas. The main cause of the decrease in the degree of sealing is poor contact between the solid electrolyte container and the internal electrodes. The solid electrolyte container is
The solid electrolyte container is mainly made of zirconia, and platinum-based thin films are formed on the inner and outer surfaces of the solid electrolyte container as internal electrodes, but such platinum-based thin films do not have good contact with the zirconia base material, so they are susceptible to vibrations and heat.・When the oxygen sensor is exposed to dust, moisture, etc., it is likely to peel off. In particular, if the internal electrodes in the sealed area are peeled off, a gap is created between the ceramic layer, glass layer, etc. and the solid electrolyte container, and the degree of sealing is naturally significantly reduced. An object of the present invention is to improve the sealing degree of an oxygen sensor and to maintain a high degree of sealing for a long period of time. change,
The main point is to use a conductive glass layer.

The present invention will be described with reference to an embodiment shown in the drawings. Reference numeral 1 denotes a solid electrolyte container, which is mainly made of zirconia as a base material, and preferably 8 to 10% of yttrium oxide is added to the zirconia as a stabilizer.

The inner and outer surfaces of the solid electrolyte container 1 are coated with platinum or platinum and gold,
A platinum-based thin film such as an alloy of palladium, rhodium, etc. is provided, and this is used as the inner and outer electrodes IA and IB. The platinum-based thin film is provided by chemical plating, electroplating, vapor deposition, or the like. In the sealed portion of the solid electrolyte container 1, the internal electrode IA is removed and a conductive glass layer IC is provided. The conductive glass layer IC is manufactured by applying a paste of platinum or platinum-based powder such as platinum and gold, palladium, rhodium, etc. mixed with high melting point glass to the removed portion of the internal electrode IA on the inner wall of the solid electrolyte container 1. established by Glasses used as high melting point glasses include general ones containing silica, soda lime, silicic acid, lead, borosilicate, aluminum silicic acid, etc., and preferably have a coefficient of thermal expansion approximately equal to that of the solid electrolyte container 1. Things can be selected. In the sealed area, instead of forming the internal electrode IA once and then removing it, it is possible to mask the sealed area on the inner wall of the solid electrolyte container 1 in advance and then form the internal electrode IA. A solid electrolyte container 1 is obtained which is omitted at the sealing point. As shown in FIG. 2, the solid electrolyte container 1 contains a metal-metal oxide such as Ni-Ni○, Cu-Cu○,
A mixed powder of Co-Coo and Fe-Fe○ is filled. A high melting point glass layer 4 is placed on top of the standard material 2 via a ceramic lower layer 3A. The material used for the ceramic layer is alumina, zircon, titanium, etc., and the material used for the high melting point glass layer 4 may be the same as that used for the conductive glass layer described above. Further, as shown in FIG. 3, the above-mentioned conductive glass may be used as the high melting point glass layer 4. In addition, the ceramic lower layer 3
A prevents direct contact between the high melting point glass layer 4 and the internal standard substance 2, and prevents a reaction between the high melting point glass and the internal standard substance from denaturing the internal standard substance. A ceramic upper layer 38 is further placed on top of the high melting point glass layer 4.

The ceramic upper layer 3B is also formed of the same material as the ceramic lower layer 3A. A similar conductive glass layer may preferably be provided on the surface of the ceramic upper layer 3B in order to improve adhesion and wettability with the conductive glass layer IC. When heating and softening the high melting point glass layer 4 to seal the oxygen sensor, the ceramic upper layer 3B is heated to soften the high melting point glass layer 4 by applying a pressing force in the direction of arrow A shown in FIG. Although this is intended to improve the throwing power and adhesion with the inner wall, the ceramic lower layers 3A, 3B, etc., it is not essential for the purpose of the present invention. In addition,
In order to improve the degree of sealing, it is desirable to increase the effective sealing thickness by making it larger than the vertical length of the ceramic upper layer 3B. To seal the oxygen sensor, the high melting point glass layer 4 is heated to a temperature higher than the softening point of the high melting point glass while being pressed in the direction of arrow A through the ceramic upper layer 3B.

Heating can be done by placing the entire oxygen sensor in a furnace, but this method heats the entire oxygen sensor, so
The solid electrolyte container 1 may be deformed or cracked. In order to prevent this, the heating rate must be sufficiently slowed down or two-stage heating must be performed, which is a cumbersome process. A preferred method is to heat only the high melting glass portion with a torch. Thus, the high melting point glass layer 4 is
The inner wall of the solid electrolyte container 1 and the upper and lower ceramic layers 3 are softened.
It flows into the gap between A and 3B and fills it. At this time, when the high melting point glass layer 4 is pressed through the ceramic upper layer 3B,
As described above, it has good throwability, and the penetration and diffusion of the high-melting point glass component into the ceramic upper and lower layers 3A, 3B is promoted, resulting in improved adhesion. High melting point glass layer 4
At the same time as softening, the conductive glass layer IC also softens,
Therefore, the two are almost integrally attached. In the present invention, as described above, a conductive glass layer is provided in place of the platinum-based thin film in the sealed portion of the solid electrolyte container, which has inner and outer electrodes made of platinum-based thin films on the inner and outer surfaces. It has extremely good adhesion to the high melting point glass as the vehicle for the layer, and there is little risk of peeling.

Furthermore, the conductive glass layer and the high melting point glass layer used as a sealing material are miscible and adhere almost integrally, and the adhesion between the ceramic upper and lower layers sandwiching the high melting point glass layer and the conductive glass layer is also high. Therefore, the degree of sealing of the oxygen sensor is maintained at a high level for a long period of time, and the internal standard substance within the solid electrolyte container is stably sealed.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a sectional view of a solid electrolyte container, FIG. 2 is a sectional view of the solid electrolyte container in a sealed state, and FIG. 3 is a sectional view of another embodiment. It is. In the figure, 1... solid electrolyte container, IA...
・Internal electrode, IB...External electrode, IC...
...Conductive glass layer, 2...Internal standard substance, 3A...Ceramic lower layer, 4...High melting point glass layer. Figure 1, Figure 2, Figure 3

Claims (1)

[Claims] 1 In a structure in which an internal standard substance is filled in a solid electrolyte container with inner and outer electrodes made of platinum-based thin films on the inner and outer surfaces, and the solid electrolyte container is sealed with a high melting point glass layer with a ceramic layer interposed thereon, the solid electrolyte container at the sealed part is An oxygen sensor characterized by using a conductive glass layer instead of a platinum-based thin film for the internal electrode.