Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-08-12
2001-11-20
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S421000, C204S428000
Reexamination Certificate
active
06319378
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a gas sensor which may be employed in an air-fuel ratio control system for automotive vehicles for measuring the concentration of gas such O
2
, NO
x
, or CO, and more particularly to an improved structure of such a gas sensor which is designed to provide an air-tight seal for avoiding mixing of the air and a gas to be measured.
2. Background Art
Gas sensors constructed of a sensing element for measuring the concentration of a given gas component and a housing having disposed therein the sensing element hermetically are known. In such gas sensors, an upper portion of the gas sensing element is exposed to an air chamber filled with the air that is a reference gas, while a lower portion of the sensing element is exposed to a gas chamber filled with a gas to be measured.
The above gas sensors, however, have the following disadvantages in manufacturing processes.
The sensing element is usually made of a solid electrolyte ceramic to which electrodes and signal output wires are attached and which has a great strength, but is fragile.
The sensing element is in air-tight engagement with the housing to define the air chamber and the gas chamber so that the gas to be measured may be insulated from the air.
In order to increase the degree of air-tightness between the sensing element and the housing, the sensing element may be press-fitted into the housing, but it may cause the sensing element to be broken. Conversely, the press-fit of the sensing element in the housing is loosened in order to avoid such broken, it may cause the air to be mixed with the gas to be measured, thus resulting in a decrease in measurement accuracy.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide an improved structure of a gas sensor which is designed to provide an air-tight seal between an air chamber and a gas chamber without causing damage to a sensing element during manufacturing.
According to one aspect of the invention, there is provided a gas sensor which may be used in measuring the concentration of a gas. The gas sensor includes: (a) a hollow housing having a first and a second inner wall and a first and a second step projecting inward between the first and second inner walls; (b) a sensing element having a given length, disposed within the housing, the sensing element having a first end portion exposed to an air chamber filled with air and a second end portion exposed to a gas chamber filled with a gas to be measured and having a flange formed between the first and second end portions, the flange being in engagement with the second step of the housing; and (c) an insulating powder packed in a chamber defined by the first step and the first inner wall of the housing and an outer wall of the first end portion of the sensing element to provide an air-tight seal between the air chamber and the gas chamber. If a difference between an inner diameter h of the first inner wall of the housing and an outer diameter S
1
of the outer wall of the first end portion of the sensing element (h−S
1
) is defined as a, and a difference between the outer diameter S
1
and an outer diameter S
2
of the flange of the sensing element (S
2
−S
1
) is defined as b, a relation of 0.2≦b/a≦0.5 is met.
In the preferred mode of the invention, a seal ring is disposed between the second step of the housing and the flange of the sensing element.
A cylindrical insulating seal member is further provided which has a tapered outer end portion. The tapered outer end portion is in contact with the insulating powder so as to compress the insulating powder.
An air cover and a gas cover are further provided. The air cover is installed on an end of the housing to define the air chamber. The gas cover is installed on the other end of the housing to define the gas chamber.
According to another aspect of the invention, there is provided a gas sensor which comprises: (a) a hollow housing having a first and a second inner wall; (b) a hollow insulator fitted in the housing, the insulator having a first and a second inner wall and a first and a second step, the first step continuing from the first inner wall, the second step being formed between the first and second inner walls: (c) a sensing element having a given length, disposed within the insulator, the sensing element having a first end portion exposed to an air chamber filled with air and a second end portion exposed to a gas chamber filled with a gas to be measured and having a flange formed between the first and second end portions, the flange being in engagement with the second step of the insulator; and (d) an insulating powder packed in a chamber defined by the second step of the insulator, the first inner wall of the housing, and an outer wall of the first end portion of the sensing element to provide an air-tight seal between the air chamber and the gas chamber. If a difference between an inner diameter h of the first inner wall of the housing and an outer diameter S
1
of the outer wall of the first end portion of the sensing element (h−S
1
) is defined as a, and a difference between the outer diameter S
1
and an outer diameter S
2
of the flange of the sensing element (S
2
−S
1
) is defined as b, a relation of 0.2≦b/a≦0.5 is met.
In the preferred mode of the invention, a seal ring is disposed between the second step of the insulator and the flange of the sensing element.
A cylindrical insulating seal member is disposed in the housing so as to compress the insulating powder.
An air cover and a gas cover are provided. The air cover is installed on an end of the housing to define the air chamber. The gas cover is installed on the other end of the housing to define the gas chamber.
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patent: 4883643 (1989-11-01), Nishio et al.
patent: 5271821 (1993-12-01), Ogasawara et al.
patent: 5695625 (1997-12-01), Yamada et al.
patent: 5759365 (1998-06-01), Yamada et al.
patent: 5804050 (1998-09-01), Hayakawa et al.
patent: 2-147817 (1990-06-01), None
patent: 8-160002 (1996-06-01), None
Kojima Takashi
Watanabe Isao
Yamada Hirokazu
Denso Corporation
Pillsbury & Winthrop LLP
Tung T.
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