Measuring and testing – Instrument casing
Reexamination Certificate
2003-03-25
2004-09-28
Cygan, Michael (Department: 2855)
Measuring and testing
Instrument casing
C073S023320, C073S031050, C073S023200
Reexamination Certificate
active
06796175
ABSTRACT:
This application claims the benefit of Japanese Application 2002-095842, filed Mar. 29, 2002, the entirety of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas sensor, a gas sensor installation structure, and a method for installing gas sensor. More particularly, the present invention relates to a gas sensor which is rarely dislodged from an installation section, even if the gas sensor is installed in a vehicle or the like and is used under high temperature conditions, a gas sensor installation structure equipped with such a gas sensor, and a method for installing a gas sensor in such a manner.
2. Description of Related Art
Various types of gas sensors are installed in the exhaust pipe (pipe) of a vehicle in order to detect a specific gas component (NO
x
, for example) contained in exhaust gas. These types of gas sensors are generally installed in a specific pipe, such as the pipe
6
of the present invention shown in FIG.
1
.
In the context of the present invention, a gas sensor
10
includes a sensor element
1
having a function of detecting NO
x
or the like, and a housing
5
which contains the sensor element
1
therein and includes a thread section
2
outside the housing and a sealing surface
4
which can form a sealing section
3
by coming in contact with a specific area of an installation section (boss
7
). The boss
7
having a thread groove which can be screwed together with the thread section
2
of the housing
5
is secured to the pipe
6
in which the gas sensor
10
is installed. The gas sensor
10
is installed in the pipe
6
by screwing the housing
5
into the boss
7
. As shown in
FIG. 2
, the sealing section
3
may be formed in a state in which a gasket
8
is disposed on the sealing surface
4
when installing the gas sensor
10
.
As shown in
FIG. 3
, there may be a case where a rotating member (rotational hexagon
15
), which can be rotated concentrically with the central axis of the housing
5
, is disposed outside the housing
5
, and the gas sensor
10
is installed so that the sealing surface
4
is pressed against the boss
7
by screwing the rotating member without rotating the housing
5
. In the case of using the rotational hexagon is, the sealing section
3
may also be formed in a state in which the gasket
8
is disposed on the sealing surface
4
in the same manner as shown in
FIG. 2
(see FIG.
4
).
Conventionally, in the case where the gas sensor is installed in the installation section by screwing the housing at an appropriate tightening torque, the installation area of the gas sensor may be subjected to high temperature when the temperature of the pipe is increased. For example, in the case where the gas sensor is installed in the exhaust pipe of a vehicle, the installation area of the gas sensor is subjected to a high temperature of 800-900° C. In this case, depending on the combination of the material for the boss and the material for the housing or gasket, a gap is easily formed at the sealing section under high temperature conditions due to the difference in coefficient of thermal expansion between the materials.
If a gap is formed at the sealing section, the tightening force of the screw is gradually decreased as the gap is increased. If the gas sensor is continuously used in a state in which the tightening force of the screw is decreased, the gas sensor may be dislodged from the pipe. In particular, since the possibility of dislodgement of the gas sensor is increased when used in an installation environment in which vibration is applied either continuously or intermittently, measures for eliminating such problems have been demanded.
The present invention has been achieved in view of the above-described problems in the conventional art. Accordingly, an object of the present invention is to provide a gas sensor which rarely allows the tightening force of the screw to be decreased even if the gas sensor is used under high temperature conditions when installed in a vehicle or the like, and is rarely dislodged from the pipe or the like in which the gas sensor is installed even if vibration is applied, a gas sensor installation structure equipped with the gas sensor, and a method for installing gas sensor.
SUMMARY OF THE INVENTION
According to the present invention, a gas sensor is provided, comprising a sensor element, which functions to detect a specific gas component, a housing containing the sensor element therein and having a sealing surface, a thread section which is adapted to be screwed into a specific installation section, and a sealing section formed between the sealing surface of the housing and a sealing surface of the installation section a t a position deeper than the thread section in a direction in which the sensor element is inserted. When the housing is screwed into the installation section, the release torque of the housing at 850° C. (1123 K) is 9 N·m or more, and an estimated value X
1
of a gap formed between the sealing surface of the housing and the sealing surface of the installation section at 850° C. (1123 K), that is calculated according to the following equation (1), is 31 &mgr;m or less:
X
1
(&mgr;m)={(
L
1
×&agr;
1
)−(
L
2
×&agr;
2
)}×1123 (1);
wherein X
1
represents an estimated value (&mgr;m) of the gap, L
1
represents a length (&mgr;m) from the sealing surface of the installation section to a top end of the installation section, L
2
represents a length (&mgr;m) from the sealing surface of the housing to a top end of the thread section, &agr;
1
represents a coefficient of thermal expansion (×10
−6
/° C.) of the installation section, and &agr;
2
represents a coefficient of thermal expansion (×10
−6
/° C.) of the housing.
In the present invention, it is preferable that a gasket is provided in contact with the sealing surface of the housing and that an estimated value X
2
of the gap, that is calculated according to equation (2), is 31 &mgr;m or less:
X
2
(&mgr;m)={(L
1
×&agr;
1
)−(
L
2
×&agr;
2
)−(L
3
×&agr;
3
)}×1123 (2);
wherein X
2
represents an estimated value (&mgr;m) of the gap, L
1
represents a length (&mgr;m) from the sealing surface of the installation section to a top end of the installation section, L
2
represents a length (&mgr;m) from the sealing surface of the housing to a top end of the thread section, L
3
represents a thickness (&mgr;m) of the gasket, &agr;
1
represents a coefficient of thermal expansion (×10
−6
/° C.) of the installation section, &agr;
2
represents a coefficient of thermal expansion (×10
−6
/° C.) of the housing, and &agr;
3
represents a coefficient of thermal expansion (×10
−6
/° C.) of the gasket.
In the present invention, the material for the gasket is preferably at least one material selected from the group consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS.
According to another aspect of the present invention, a gas sensor is provided, comprising a sensor element, which functions to detect a specific gas component, a housing containing the sensor element therein and having a sealing surface that forms a sealing section together with a sealing surface of an installation section at the front in the direction in which the sensor element is inserted, and a rotating member having a thread section formed on an outer surface thereof that is adapted to be screwed into the installation section and that can be rotated concentrically with respect to a central axis of the housing. When the gas sensor is installed in the installation section by screwing the rotating member into the installation section, the release torque of the rotating member at 850° C. (1123 K) is 9 N·m or more, and an estimated value X
3
of a gap formed between the sealing surface of the housing and the sealing surface of the installation section at 850° C. (1123 K), that is calculated according to the following equat
Ikoma Nobukazu
Kurachi Hiroshi
Lee Sang Jae
Burr & Brown
Cygan Michael
NGK Insulators Ltd.
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