Electrical resistors – Resistance value responsive to a condition – Gas – vapor – or moisture absorbing or collecting
Patent
1980-03-14
1982-06-15
Albritton, C. L.
Electrical resistors
Resistance value responsive to a condition
Gas, vapor, or moisture absorbing or collecting
338229, 338271, H01L 700
Patent
active
043353690
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an oxygen sensor for detecting oxygen content in a waste gas from automobiles or the like which has superior mechanical toughness and sensitivity and comprises a ceramic base which is provided with a porous thick membrane of transition-metal oxide and thick membranes of electrode metal and these thick membranes are coated with a protective ceramic layer.
BACKGROUND OF THE INVENTION
In a tertiary catalyst system empolyed as one of measures for public nuisance of automobile waste gas, an air/fuel ratio is controlled within a very narrow range of the equivalence point and an oxygen content after combustion is detected as an oxygen partial pressure by means of an oxygen sensor and then the detected signal is fed back to a control system of a fuel supplying unit. Therefore, the oxygen sensor is required to respond quickly to the oxygen partial pressure in the waste gas emitted from a heat engine of automobiles or the like. Namely, the oxygen sensor is required to exhibit a quick response time at least in the same degree as that shown by transmission property between a heat engine and a fluid medium with an efficient contact of the waste gas with an oxide. In the oxygen sensor detecting a change in the oxygen partial pressure of the ambient atmosphere as a change in the electric resistance, a transition-metal oxide is conventionally used for the material. The change in the electric resistance of the transition-metal oxide is caused due to variation in the stoichiometry of the oxide crystal and this change in the stoichiometry is induced through a possible contact with an oxygen in the waste gas. The response characteristic of the oxygen sensor is nothing but the response characteristic of the change in the electric resistance and the speed of the response of the stoichiometry or that of the change in the electric resistance of the oxide crystal is directly influenced by the contact efficiency between the waste gas and the oxide crystal, or the diffusion rate of the waste gas into the crystal. In general, the sensor element consisting essentially of such transition-metal oxide is formed into a disc shape by mixing an oxide with an organic binder solution, forming the mixture into green sheets by a doctor blade and then holding electrodes between the sheets for firing. Since, however, the element alone is mechanically weak, it must be assembled into a ceramic or metal support for practical use. Further, there is another disadvantage that the speed of the response of the oxygen sensor through the change in resistance of the transition-metal oxide is inferior to the conventional sensor wherein a change in the electromotive force of the zirconium oxide is utilized.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an oxygen sensor in which an element per se comprising an oxide and a connecting lead wire has a mechanically strong structure with superior response characteristic. This object may be performed by an oxygen sensor in which a porous thick membrane of transition-metal oxide having a thickness of 50 to 100 .mu.m and electrode metal thick membranes divided into two parts in contact with the porous thick membrane are arranged on a ceramic base and all free surfaces of the thick membrane of transition-metal oxide and at least a part of free surfaces of electrode metal thick membranes are covered with a ceramic protective layer. By this arrangement, there may be brought such the advantages that the waste gas from automobiles or the like is diffused well rapidly into the oxide crystal, that the mechanical stress due to vibration in the heat engine is minimized since the oxide in the form of the membrane reduced the mass and weight and that generation of heat shock or heat cycle through start, stop, acceleration or deceleration of the operation produce a low thermal gradient because of the oxide in the form of membrane, resulting in increase of resistance to the spalling.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings illustrate several
REFERENCES:
patent: 4007435 (1977-02-01), Tien
patent: 4033169 (1977-07-01), Fujishiro et al.
patent: 4130797 (1978-12-01), Hattori et al.
patent: 4206173 (1980-06-01), Yamaguchi et al.
Hara Kenichi
Shiraishi Hideo
Taniguchi Harutaka
Albritton C. L.
Fuji Electric & Co., Ltd.
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