Electrical resistors – Resistance value responsive to a condition – Gas – vapor – or moisture absorbing or collecting
Patent
1980-03-18
1982-03-16
Albritton, C. L.
Electrical resistors
Resistance value responsive to a condition
Gas, vapor, or moisture absorbing or collecting
73 27R, 338229, 338271, 422 98, H01L 700
Patent
active
043203787
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 metal tube having vent holes and a ceramic round rod inserted therein and including a thick membrane of transition-metal oxide, electrode thick membranes divided into two parts and a protective layer covering the membranes wherein one electrode thick membrane is connected to the metal tube whereas the opposite thick membrane is connected to a connecting lead wire electrically insulated from the tube.
BACKGROUND OF THE INVENTION
As one convenient measure for public nuisance of the waste gas exhausted from a heat engine such as an automobile internal engine, a tertiary catalyst system has been suitably employed to clear up at once the desired regulations of nitrogen oxides (NO.sub.x), carbon monooxide (CO) and hydrocarbons. In the tertiary catalyst system, the characteristics of the tertiary catalyst may not have effective function unless an air/fuel ratio (A/F ratio) is controlled in a very narrow range of equivalent ratio or a theoretical air/fuel ratio. The A/F ratio is conveniently controlled in such a way that the oxygen content after combustion is measured by the oxygen sensor as a change in the oxygen partial pressure and the measured signal is fed back to the control system of the electronic fuel injection pump for example. To measure the change in the oxygen partial pressure, various types of oxygen sensors have been developed employing the transition-metal oxide in which the electric resistance is varied depending on the oxygen concentration.
The oxygen sensor of this type may be prepared by mixing for example titanium dioxide material powder with suitable solvent, binder, plasticizer, dispersant and the like forming a green sheet by the doctor blade technique for subsequent lamination with a platinum electrode and a heater under the pressure with dryness and then sintering the resultant product to form a porous disc. This process is disclosed in the opened Japanese Patent application No. 50-56292. In order to actually mount this element for an exhaust tube of the automobile, a platinum lead wire is lead out through a passage provided in a ceramic body fixed to a metal housing with a possible seal preventing the gas leakage from the sensor element to the atmosphere. The actual layout of such the element is technically disclosed in the opened Japanese Utility Model Applications No. 52-46781 and No. 52-4792.
However, the structure of the known element is relatively inferior in strength with such the disadvantage that a boundary part of the lead wire prolonged from the element becomes weak against oscillation and impact. Further, the prolonged platinum wire necessitates a passage to be formed as a groove or hole in the ceramic with relatively the high cost in production and difficulty in sealing for the gas leakage.
DISCLOSURE OF THE INVENTION
An object of the invention is to solve the problems of the disc type oxygen sensor by inserting into a metal tube a ceramic round rod comprising a thick membrane of transition-metal oxide, electrode thick membranes and a protective layer therefor and also to provide an oxygen sensor which is superior in the mechanical strength, durability and economy. This object may be achieved in accordance with the invention in such a way that into a metal tube having a closed end and vent holes in its side wall is inserted a ceramic round rod which includes on its surface a thick membrane of transition-metal oxide, electrode thick membranes made into contact with the thick membrane and divided into two parts and a protective layer covering whole the thick membrane of transition-metal oxide and at least part of electrode thick membranes and one of the electrode thick membranes divided into two parts is connected to a bottom of the tube whereas the opposite electrode thick membrane is connected to a connecting lead wire extended from an open end of the tube in insulatio
REFERENCES:
patent: 4007435 (1977-02-01), Tien
patent: 4130797 (1978-12-01), Hattori et al.
patent: 4206173 (1980-06-01), Yamaguchi et al.
Hara Kenichi
Kiyofuji Shinji
Shiraishi Hideo
Taniguchi Harutaka
Albritton C. L.
Fuji Electric & Co., Ltd.
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