Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Of electrical article or electrical component
Reexamination Certificate
1998-08-26
2001-01-16
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Of electrical article or electrical component
C264S619000
Reexamination Certificate
active
06174489
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of The Invention
This invention relates to a method for manufacturing an oxygen sensor unit which is suitable for use in oxygen sensors of internal combustion engines for automotive vehicles.
2. Description of the Prior Art
For the control of an air-to-fuel ration in internal combustion engines of automotive vehicles, oxygen sensors have been usually used. A typical structure of such a sensor is, for example, shown in
FIG. 4
which will be described hereinafter. An oxygen sensor unit incorporated in the oxygen sensor is, for example, of the type which comprises a solid electrolyte body, and a pair of electrodes formed on inner and outer sides of the solid electrolyte, respectively. Moreover, a protective layer is provided to cover the outer electrode therewith at the outer surface thereof so as to protect the outer electrode from a poisonous contaminant in a gas to be measured as shown in FIG.
3
. This figure will also be referred to hereinafter.
The solid electrolyte of the oxygen sensor unit has been conventionally made, for example, of a sintered body of zirconia to which a stabilizer is added.
The sintered bodies of the zirconia known in the art can be broadly classified into two groups. One group includes a body made of fully stabilized zirconia which consists essentially of a cubic phase (C phase) alone. The other group includes a body made of partially stabilized zirconia which is constituted mainly of a cubic phase (C phase), a monoclinic phase (M phase) and/or a tetragonal phase (T phase) existing in mingling relation.
The fully stabilized zirconia is one which is stable over a wide temperature range of room temperature (20° C.) to a high temperature of 1000° C. and is unlikely to degrade as time passes. However, this type of zirconia is neither resistant to mechanical shocks such as vibrations, nor resistant to thermal shocks, thus being liable to break. Owing to this deficiency of the fully stabilized zirconia, partially stabilized zirconia sintered bodies have been usually employed as a solid electrolyte in this field of the art.
However, when partially stabilized zirconia is repeatedly subjected to heating and cooling cycles at temperatures between room temperature (20° C.) and a high temperature of 1000° C., phase transformation takes place, as is shown in
FIG. 5
, between the monoclinic phase (i.e. monoclinic zirconia in the figure) and the tetragonal phase (tetragonal zirconia in FIG.
5
).
As will be apparent from
FIG. 5
, the phase transformation involves a great variation in volume. When using partially stabilized zirconia in an oxygen sensor unit as a solid electrolyte body and subjecting the unit to heating and cooling cycles, this solid electrolyte body may undesirably be cracked or, in the worst case, broken.
In usual practice, a protective layer is formed to protect an outside electrode which is exposed to a gas to be measured as described before. In this condition, if phase transformation accompanying the volumetric variation occurs between the M and T phases of the partially stabilized zirconia sintered body serving as the solid electrolyte, some stress is caused to occur between the solid electrolyte body and the protective layer, with the great possibility that the protective layer suffers cracks and the protective layer separates from the solid electrolyte body or the outer electrode.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for manufacturing an oxygen sensor unit which overcomes the problems of the prior art and wherein a protective layer is prevented from cracking or separation when the unit is repeatedly employed under heating and cooling cycle conditions in internal combustion engines of automotive vehicles and is thus durable.
It is another object of the invention to provide a method for manufacturing an oxygen sensor unit wherein a solid electrolyte body is unlikely to suffer crack or breakage when the unit is placed under heating and cooling cycle conditions.
The above objects can be achieved, according to an embodiment of the invention, by a method for manufacturing an oxygen sensor unit of the type which comprises a shaped body of a solid electrolyte, an inside electrode provided on an inside surface of the shaped body and exposed to a reference gas, an outside electrode provided on an outside side of the shaped body and exposed to a gas to be measured, and a porous protective layer covering the outside electrode and a portion of the shaped body adjoining to the outside electrode wherein the solid electrolyte is made of a mixture of zirconia and a stabilizer therefor and is constituted of partially stabilized, sintered zirconia, the improvement characterized in that the partially stabilized, sintered zirconia is obtained according to a high temperature sintering procedure which comprises the step of sintering the mixture at a temperature of 1200° C. or over for a duration of 2 to 6 hours wherein a value obtained by integrating a variation in the sintering temperature with the duration in the sintering step is 300 to 1500° C.·hour.
REFERENCES:
patent: 4219359 (1980-08-01), Miwa et al.
patent: 4296148 (1981-10-01), Friese
patent: 4866014 (1989-09-01), Cassidy et al.
patent: 5169513 (1992-12-01), Mase et al.
patent: 5419827 (1995-05-01), Nanataki et al.
patent: 2087569 (1982-05-01), None
patent: 59-41952 (1984-10-01), None
patent: 60-5548 (1985-02-01), None
patent: 1-261267 (1989-10-01), None
patent: 9-124365 (1997-05-01), None
Fujii Namitsugu
Kobayashi Kiyomi
Miwa Naoto
Saito Toshitaka
Sano Hiromi
Denso Corporation
Fiorilla Christopher A.
Pillsbury Madison & Sutro
LandOfFree
Method for manufacturing a gas sensor unit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for manufacturing a gas sensor unit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for manufacturing a gas sensor unit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2554010