Measuring and testing – Gas analysis
Reexamination Certificate
1999-09-27
2001-08-28
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
C073S023320, C073S031070
Reexamination Certificate
active
06279376
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and claims priority from Japanese Patent Application Nos. 10-272952 filed on Sep. 28, 1998 and 11-219862 filed on Aug. 3, 1999, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas sensor which is suitably used for measuring a concentration of oxygen in exhaust gas, an air-fuel mixture ratio or the like of a vehicle engine.
2. Related Art
Conventionally, in a vehicle engine, a concentration of oxygen in exhaust gas, an air-fuel mixture ratio or the like are detected. Fuel combustion of the engine is controlled according to the detected values so that energy is more saved, exhaust gas is more efficiently purified and so on. As a gas sensor for detecting a concentration of oxygen or the like in exhaust gas (sample gas), a gas sensor having a gas sensing element made of solid electrolyte such as zirconia is known.
There are various kinds of the gas sensing elements including a cup-shaped gas sensing element having one end closed and a rectangular-shaped layered type gas sensing element formed by layering sheet members. Each of the gas sensing element has a gas contact portion to directly contact the sample gas. The gas contact portion is exposed in the sample gas for air-fuel mixture ratio detection. Since the gas sensing element is made of solid electrolyte, the gas sensing element is relatively fragile, and it may be difficult to continuously use the gas sensing element in the sample gas. Therefore, the gas sensing element is generally covered by an element cover for protection. The element cover needs to have an opening through which the sample gas flows toward the gas contact portion. However, depending on a position or a shape of the opening, condensed water contained in the sample gas may directly adhere to the gas sensing element and break the gas sensing element.
To cope with this problem, various gas sensors in which an element cover prevents condensed water from adhering to the gas sensing element while maintaining flow characteristics of the sample gas to the gas contact portion are developed. JP-Y2-2-33167 discloses such a gas sensor having a single-pipe structure element cover for protecting a gas sensing element. JP-U-59-194059 and JP-A-9-222416 also disclose such gas sensors having a double-pipe structure element cover for protecting a gas sensing element. The double-pipe element cover is made of an outer pipe and an inner pipe both having plural openings.
In JP-A-9-222416, as shown in
FIG. 23
, a gas sensor
9
includes a gas sensing element
10
having a gas contact portion
11
, a housing
4
for holding the gas sensing element
10
and an element cover
90
secured to the housing
4
for covering the gas contact portion
11
. The element cover
90
has a double pipe structure formed by layering an outer pipe
91
and an inner pipe
92
. The outer pipe
91
has a side portion having plural outer side holes
911
and a bottom portion having an outer bottom hole
912
. The inner pipe
92
also has a side portion having plural inner side holes
921
and a bottom portion having an inner bottom hole
922
. The outer side holes
911
and the inner side holes
921
are disposed not to overlap each other. The element cover
90
is designed to protect the gas sensing element
10
, prevent condensed water from adhering to the gas sensing element
10
and improve flow characteristics of the sample gas within the element cover
90
so that response of the gas sensor
9
is improved.
However, although the gas sensing element
10
is sufficiently protected by the element cover
90
and condensed water is prevented from adhering to the gas sensing element
10
, flow characteristics of the sample gas within the element cover
90
is not sufficiently improved. That is, a speed of introduction of the sample gas to the gas sensing element
10
is relatively small, thereby worsening response of the gas sensor
9
.
SUMMARY OF THE INVENTION
In view of the foregoing problems, it is an object of the present invention to provide a gas sensor having an element cover which protects a gas sensing element, prevents condensed water from entering inside of the gas sensor and improves response of the gas sensor.
According to the present invention, a gas sensor has a gas sensing element having a gas contact portion to contact sample gas, a housing for holding the gas sensing element and an element cover connected to the housing and covering the gas contact portion. The element cover has a double pipe structure formed by layering an inner pipe and an outer pipe. Each of the inner pipe and the outer pipe is formed into a cylindrical shape with a bottom. The inner pipe has a side portion including a first side portion having a side hole through which the sample gas flows and a second side portion which prevents the sample gas from flowing therethrough, and a bottom portion having a bottom hole through which the sample gas flows. The outer pipe also has a side portion having a side hole through which the sample gas flows and a bottom portion having a bottom hole through which the sample gas flows. The second side portion of the inner pipe is exposed through the side hole of the outer pipe, and a spacing of 0.2-1.0 mm is formed between the bottom portion of the inner pipe and the bottom portion of the outer pipe. Therefore, the sample gas introduced into the element cover through the side hole of the outer pipe does not directly contact the gas contact portion, but first contacts the inner pipe and then flows through the side hole of the inner pipe toward the gas contact portion. As a result, condensed water in the sample gas is prevented from directly contacting and damaging the gas sensing element. Further, since the spacing between the bottom portion of the inner pipe and the bottom portion of the outer pipe is as small as 0.2-1.0 mm, flow resistance of the sample gas in the spacing is relatively large. Therefore, the sample gas entering between the outer pipe and inner pipe tends to flow into the inner side hole rather than into the spacing. As a result, the sample gas is sufficiently and more smoothly introduced to the gas contact portion, thereby improving response of the gas sensor.
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patent: 4033170 (1977-07-01), Kawamura et al.
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patent: 4199424 (1980-04-01), Jeitelbaum
patent: 4222026 (1980-09-01), Heiney, III et al.
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patent: 4535316 (1985-08-01), Wertheimer et al.
patent: 4756885 (1988-07-01), Raff et al.
patent: 4883643 (1989-11-01), Nishio et al.
patent: 5238552 (1993-08-01), Kato et al.
patent: 5880353 (1999-03-01), Graser et al.
patent: 5948963 (1999-09-01), Kato et al.
patent: 6164120 (2000-12-01), Friese et al.
patent: 6202469 (2001-03-01), Nakamura et al.
patent: 6214186 (2001-04-01), Watanabe et al.
patent: 59-194059 (1984-12-01), None
patent: 2-33167 (1990-09-01), None
patent: 2653831 (1997-05-01), None
patent: 9-222416 (1997-08-01), None
Hayashi Hidetaka
Imamura Hiroo
Makino Daisuke
Nakamura Satoshi
Toguchi Kengo
Denso Corporation
Pillsbury & Winthrop LLP
Wiggins David J.
Williams Hezron
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