Coating processes – Immersion or partial immersion
Reexamination Certificate
2002-04-24
2003-12-02
Barr, Michael (Department: 1762)
Coating processes
Immersion or partial immersion
C427S379000, C427S376100, C427S314000, C427S240000
Reexamination Certificate
active
06656534
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a gas sensing element of a sensor. The gas sensor is generally installed in an exhaust gas passage of an internal combustion engine for combustion control or emission control of the internal combustion engine.
A gas sensing element is necessary to control the combustion control of an internal combustion engine. The gas sensing element has a cup-shaped solid electrolytic body having a reference gas chamber formed therein. An inside electrode is provided on an inner surface of the solid electrolytic body. An outside electrode is provided on an outer surface of the solid electrolytic body.
However, according to a conventional gas sensing element, there is the possibility that the outside electrode may separate from the solid electrolytic body.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention has an object to provide a method for manufacturing a gas sensing element having an excellent bonding strength between an outside electrode and a solid electrolytic body.
In order to accomplish the above and other related objects, the present invention provides a method for manufacturing a gas sensing element which has a cup-shaped solid electrolytic body having a reference gas chamber formed therein, an inside electrode provided on an inner surface of the solid electrolytic body, and an outside electrode provided on an outer surface of the solid electrolytic body. The manufacturing method of this invention comprises a step of forming a non-sintered element body having a predetermined shape from powdery raw material of the solid electrolytic body, a step of temporarily sintering the non-sintered element body to obtain a partially-sintered element body as a semi-finished product of the solid electrolytic body, a step of dipping an outer surface of the partially-sintered element body into a slurry containing surface-roughing powder including large and small grains which are mutually differentiated in grain size, and a step of completely sintering the partially-sintered element body with a rough slurry film coated thereon into the solid electrolytic body.
According to this invention, the outer surface of the partially-sintered element body is dipped into the slurry containing the surface-roughing powder including large and small grains. The slurry film with the mixed large and small grains is formed on the outer surface of the partially-sintered element body. Then, the complete sintering treatment is performed. Accordingly, the outer surface of the completely sintered solid electrolytic body is finished into a rough surface whose roughness depends on the grain size and the mixing ratio of the large and small grains.
The outside electrode is fixed to the outer surface of the sintered solid electrolytic body, after the outer surface is finished into the rough surface. The rough surface brings anchor effect. In other words, the rough surface assures an excellent bonding strength required for firmly fixing other member thereon. Thus, according to the manufacturing method of the present invention, the outside electrode can be firmly fixed on the outer surface of the solid electrolytic body due to the anchor effect brought by the coated rough surface. In other words, this invention provides an excellent method for manufacturing a gas sensor which is capable of effectively preventing the outside electrode from peeling off the solid electrolytic body and is also capable of assuring excellent durability.
According to the manufacturing method of the present invention, the surface roughness of the solid electrolytic body can be easily changed or adjusted by adequately selecting the grain size of the large and small grains and their contents relative to the slurry. Thus, the manufacturing method of this invention is easily realized and brings the effect of cost reduction.
As understood from the foregoing, according to the present invention, it becomes possible to obtain a manufacturing method of a gas sensor which assures an excellent bonding force for the outside electrode bonded on the outer surface of the solid electrolytic body.
According to the present invention, for the purpose of preventing the outside electrode from being directly exposed to the measured gas, it is preferable to provide a trap layer and/or a protective layer so as to cover the outside electrode. The trap layer traps poisonous or harmful substances contained in the measured gas.
Furthermore, it is also preferable to provide a diffusion resistive layer so as to cover the outside electrode. The diffusion resistive layer controls the time required for the measured gas to reach the outside electrode. The diffusion resistive layer further controls the amount of the measured gas reaching the outside electrode.
In this case, according to the manufacturing method of the present invention, the outer surface of the solid electrolytic body is finished into a rough surface. The rough surface brings a strong bonding force required for firmly fixing the outside electrode on the outer surface of the solid electrolytic body. The rough surface also brings a sufficient bonding force required for firmly fixing the additional layers on the outside electrode. The additional layers provided on the outside electrode include the trap layer, the protective layer, and the diffusion resistive layer.
Accordingly, the present invention makes it possible to prevent the outside electrode from peeling off the outer surface of the solid electrolytic body. Furthermore, the present invention makes it possible to prevent each additional layer from peeling off the outside electrode or the outer surface of the solid electrolytic body.
Furthermore, the portion of the solid electrolytic body to be dipped into the slurry containing the surface roughing powder can be limited to a specific region where the outside electrode is provided.
It is preferable that a coating area of the rough surface is sufficiently wide to entirely cover the region where the outside electrode is provided. However, the effect of the present invention can be obtained even when the coating area of the rough surface is somewhat smaller than the entire area of the outside electrode.
Furthermore, when the trap layer, the protective layer, and the diffusion resistive layer are provided on the outside electrode or on the outer surface of the solid electrolytic body, it is preferable to dip the corresponding portion of the solid electrolytic body into the slurry containing the surface roughing powder.
With this arrangement, it becomes possible to assure a strong bonding force required for firmly fixing these additional layers together with the outside electrode on the outer surface of the solid electrolytic body.
Furthermore, the gas sensing element is generally equipped with electric leads and terminals connected to the inside and outside electrodes for outputting a sensing signal from the electrodes or applying a voltage to the electrodes. Thus, some of the leads and terminals are provided on the outer surface of the solid electrolytic body.
In this case, to increase the bonding strength for fixing the leads and terminals on the outer surface of the solid electrolytic body, it is preferable to dip the portion of the solid electrolytic body corresponding to the leads and the terminals into the slurry containing the surface roughing powder.
Furthermore, it is preferable that the material of the surface roughing powder is identical with that of the solid electrolytic body. It is also preferable that the surface roughing powder can be integrated with the solid electrolytic body through the sintering treatment.
This is effective to prevent the slurry film containing the surface roughing powder from peeling off the solid electrolytic body.
Furthermore, a binder is generally added with the grains to form the slurry containing the surface roughing powder. A preferable binder is PVA (polyvinyl alcohol).
According to the manufacturing method of this invention, it is preferable that a coating density of t
Barr Michael
Denso Corporation
Nixon & Vanderhye P.C.
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