JPH0634683Y2 - Oxygen sensor for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention detects the air-fuel ratio of an engine intake air-fuel mixture, which is attached to the exhaust system of an internal combustion engine and is closely related to the oxygen concentration in the exhaust gas. The present invention relates to an oxygen sensor, and particularly to the structure of its protective layer.

<Prior Art> Conventional oxygen sensors include various types using an oxygen ion conductive solid electrolyte (see Japanese Utility Model Publication No. 61-89160 and Japanese Utility Model Publication No. 60-163354).

FIG. 4 shows an example of a conventional oxygen sensor, which includes a substrate 1 made of alumina (Al ₂ O ₃ ), an alumina frame plate 2 having a reference air introduction hole 3, and a plate-shaped platinum plate on each side. Oxygen ion conductive solid electrolytes 4 for concentration cells represented by zirconia (ZrO ₂ ) on which electrodes 5A and 5B are formed are sequentially laminated and fired in a green sheet state, and thereafter, the outside of the laminated fired body, that is, the solid body. A protective layer 6 is formed by spraying a ceramic powder such as magnesia spinel on the exhaust side (electrode 5A side) of the electrolyte 4. Then, this is exposed to the exhaust gas of the engine, an electromotive force is generated by the ratio of the oxygen concentrations of the reference air and the exhaust gas, and it is used as a feedback signal in air-fuel ratio feedback control.

<Problems to be solved by the invention> However, in such a conventional oxygen sensor, since the protective layer is formed by spraying ceramic powder or the like on the surface of the laminated fired body, The adhesion strength with the surface is very weak and peeling may occur as indicated by X in FIG. 4. Also, since the laminated fired body is formed by laminating and cutting green sheets, there are corners and The strength of the thermal spray protection layer also decreases, causing peeling and cracking,
As a result, there are problems that the electromotive force characteristics vary and the durability is poor.

In view of such conventional problems, the present invention aims to increase the strength of the protective layer to improve durability and obtain stable detection accuracy.

<Means for Solving the Problems> In order to achieve the above object, the present invention provides a protective layer, which is integrally and simultaneously at about 1500 ° C. when firing the solid electrolyte,
And a thermal sprayed protective layer formed by thermal spraying on the print protective layer.

<Operation> According to the above configuration, since the print protection layer is integrally and simultaneously fired with the solid electrolyte, the adhesion strength with the solid electrolyte is increased, and the thermal spray protection layer is formed due to the roughness of the surface of the print protection layer. It is possible to improve the adhesiveness of, improve durability, and obtain stable detection accuracy. The print protection layer cannot have a sufficient thickness due to its manufacturing method and cannot serve as the protection layer by itself. Therefore, the thermal spray protection layer is also provided to secure the thickness of the protection layer.

<Example> An example of the present invention will be described below.

1 and 2 show a first embodiment. Alumina substrate 1, an alumina frame plate 2 having a reference air introduction hole 3, and plate-shaped platinum electrodes 5A and 5B each having an oxidation catalyst function on both sides are formed of oxygen ion conductive material typified by zirconia. Solid electrolyte for concentration cell 4
Are sequentially laminated in a green sheet state. Then, a paste-like ceramic is screen-printed on the exhaust side surface of the solid electrolyte 4 to form a print protection layer 7, and in this state
Bake at about 1500 ° C. Then, the surface of the print protection layer 7, the outer surface of the substrate 1 and the frame plate 2 is sprayed with magnesia spinel or the like to form the spray protection layer 8.

According to this, since the print protection layer 7 is integrally fired with the solid electrolyte 4, the adhesion strength between the print protection layer 7 and the solid electrolyte 4 is increased, and the thermal spray protection layer 8 is adhered due to the roughness of the surface of the print protection layer 7. In addition, it is possible to improve durability, improve durability, and obtain stable detection accuracy.

Further, platinum (oxidation catalyst), rhodium (reduction catalyst), etc. can be easily mixed in the paste of the print protection layer 7, and platinum or rhodium evaporates during printing unlike the case of thermal spraying performed at high temperature. There is no possibility, which also makes it possible to add functionality to the protective layer.

The second embodiment shown in FIG. 3 is a case in which the print protection layer 7 and the thermal spray protection layer 8 are coated only on the exhaust side surface of the solid electrolyte 4, and this alone provides a sufficient function.

<Effects of the Invention> As described above, according to the present invention, the protective layer is composed of the printing protective layer and the thermal spraying protective layer which are integrally and simultaneously fired when the solid electrolyte is fired. The strength is increased, and it is possible to achieve improvement in durability and stabilization of electromotive force characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view of an oxygen sensor showing a first embodiment of the present invention, FIG. 2 is an exploded perspective view of the oxygen sensor, and FIG. 3 is a sectional view of an oxygen sensor showing a second embodiment of the present invention. FIG. 4 is a sectional view of a conventional oxygen sensor. 1 ... Substrate, 2 ... Frame plate, 3 ... Reference air introduction hole, 4
...... Solid electrolyte, 5A, 5B ...... Platinum electrode, 7 ...... Printing protection layer, 8 ...... Spraying protection layer

Claims (1)

[Scope of utility model registration request] 1. Exhaust of an engine in which electrodes are formed on both surfaces of a plate-type solid electrolyte for concentration cells having oxygen ion conductivity, and one surface is brought into contact with reference air and the other surface is covered with a protective layer. In the oxygen sensor of the internal combustion engine, which detects the air-fuel ratio of the air-fuel mixture sucked into the engine through the oxygen concentration in the exhaust gas, the protective layer is integrated with the solid electrolyte and at the same time at about 1500 ° C. An oxygen sensor for an internal combustion engine, comprising: a print protective layer that is fired; and a thermal spray protective layer that is formed by thermal spraying on the print protective layer.