Title: Gas sensor, gas sensor installation structure, and method for installing gas sensor
Abstract: A gas sensor includes a sensor element having a specific function, and a housing containing the sensor element therein and including a thread section, and a sealing surface which forms a sealing section together with an installation section at 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.degree. C. (1123 K) is 9 N.multidot.m or more, and an estimated value of a gap formed between the sealing surface and the installation section at 850.degree. C. (1123 K) that is calculated according to a specific equation is 31 .mu.m or less.
Patent Number: 6,857,316 Issued on 02/22/2005 to Kurachi, et al.
| Inventors:
|
Kurachi; Hiroshi (Nagakute-Gun, JP);
Ikoma; Nobukazu (Nagoya, JP);
Lee; Sang Jae (Ama-Gun, JP)
|
| Assignee:
|
NGK Insulators, Ltd. (Nagoya, JP)
|
| Appl. No.:
|
854728 |
| Filed:
|
May 26, 2004 |
Foreign Application Priority Data
| Mar 29, 2002[JP] | 2002-095842 |
| Current U.S. Class: |
73/431; 73/23.2; 73/31.05 |
| Intern'l Class: |
G01N 007//00; G01D 011//24 |
| Field of Search: |
73/31.05,23.2,23.32,431
|
References Cited [Referenced By]
U.S. Patent Documents
| 4096752 | Jun., 1978 | Tonnelli.
| |
| 5401962 | Mar., 1995 | Ferran.
| |
| 5571947 | Nov., 1996 | Senn et al.
| |
| 6302402 | Oct., 2001 | Rynders et al.
| |
| 6673224 | Jan., 2004 | Shirai.
| |
| 6796175 | Sep., 2004 | Kurachi et al. | 73/431.
|
| Foreign Patent Documents |
| 05-232062 | Sep., 1993 | JP.
| |
| 06-331596 | Dec., 1994 | JP.
| |
| 08-278280 | Oct., 1996 | JP.
| |
Primary Examiner: Cygan; Michael
Attorney, Agent or Firm: Burr & Brown
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a division of U.S. application Ser. No. 10/396,633,
filed Mar. 25, 2003, now U.S. Pat. No. 6,796,175 the entirety of which is
incorporated herein by reference.
This application also claims the benefit of Japanese Application No.
2002-095842, filed Mar. 29, 2002, the entirety of which is incorporated
herein by reference.
Claims
What is claimed:
1. A gas sensor comprising a sensor element for detecting a specific gas
component, a housing which contains said sensor element therein and has a
sealing surface which forms a sealing section together with an
installation section at the front in a direction in which said sensor
element in inserted, and a rotating member which has a thread section
which is formed outside said rotating member and is to be screwed into the
installation section and can be rotated concentrically with respect to a
central axis of said housing;
wherein when said gas sensor is installed in the installation section by
screwing said rotating member into the installation section, a release
torque of said rotating member at 850.degree. C. (1123 K) is 9
N.multidot.m or more; and
wherein an estimated value X.sub.3 of a gap formed between said sealing
surface of said housing and a sealing surface of the installation section
at 850.degree. C. (1123 K), that is calculated according to the following
equation, is 31 .mu.m or less:
X.sub.3
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.4.times..alpha..sub.4)-(L.
sub.5.times..alpha..sub.5)}.times.1123;
wherein X.sub.3 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.4 represents a
length (.mu.m) from a bottom end to a top end of said thread section,
L.sub.5 represents a length (.mu.m) from said sealing surface of said
housing to the bottom end of said thread section, .alpha..sub.1 represents
a coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of the
installation section, .alpha..sub.4 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of said rotating member, and
.alpha..sub.5 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of said housing.
2. The gas sensor according to claim 1, wherein a gasket is provided in
contact with said sealing surface of said housing and an estimated value
X.sub.4 of the gap, that is calculated according to the following
equation, is 31 .mu.m or less:
X.sub.4 (.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.3
.times..alpha..sub.3)-(L.sub.4.times..alpha..sub.4)-(L.sub.
5.times..alpha..sub.5)}.times.1123;
wherein X.sub.4 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.3 represents a
thickness (.mu.m) of said gasket, L.sub.4 represents a length (.mu.m) from
a bottom end to a top end of said thread section, L.sub.5 represents a
length (.mu.m) from said sealing surface of said housing to the bottom end
of said thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section,
.alpha..sub.3 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of said gasket, .alpha..sub.4 represents a
coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of said
rotating member, and .alpha..sub.5 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of said housing.
3. The gas sensor according to claim 2, wherein said gasket comprises at
least one material selected from the group consisting of 430 SS, 304 SS,
310 SS, 316 SS, and 321 SS.
4. The gas sensor according to claim 1, wherein said rotating member
comprises at least one material selected from the group consisting of 430
SS, 304 SS, 310 SS, 316 SS, and 321 SS.
5. A gas sensor installation structure comprising:
an installation section; and
a gas sensor comprising a sensor element for detecting a specific gas
component, a housing which contains said sensor element therein and has a
sealing surface which forms a sealing section together with said
installation section at the front in a direction in which said sensor
element is inserted, and a rotating member which has a thread section
which is formed outside said rotating member and is screwed into said
installation section and can be rotated concentrically with respect to a
central axis of said housing;
wherein said gas sensor is installed in said installation section by
screwing said rotating member into said installation section;
wherein a release torque of said rotating member at 850.degree. C. (1123 K)
is 9 N.multidot.m or more; and
wherein an estimated value X.sub.7 of a gap formed between said sealing
surface of said housing and a sealing surface of said installation section
at 850.degree. C. (1123 K), that is calculated according to the following
equation, is 31 .mu.m or less:
X.sub.7
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.4.times..alpha..sub.4)-(L.
sub.5.times..alpha..sub.5)}.times.1123;
wherein X.sub.7 represents an estimated value (.mu.m) of said gap, L.sub.1
represents a length (.mu.m) from said sealing surface of said installation
section to a top end of said installation section, L.sub.4 represents a
length (.mu.m) from a bottom end to a top end of said thread section,
L.sub.5 represents a length (.mu.m) from said sealing surface of said
housing to the bottom end of said thread section, .alpha..sub.1 represents
a coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of said
installation section, .alpha..sub.4 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of said rotating member, and
.alpha..sub.5 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of said housing.
6. The gas sensor installation structure according to claim 5, wherein said
sealing section is formed through a gasket and an estimated value X.sub.8
of said gap, that is calculated according to the following equation, 31
.mu.m or less:
X.sub.8
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.3.times..alpha..sub.3)-(L.
sub.4.times..alpha..sub.4)-(L.sub.5.times..alpha..sub.5)}.times.1123;
wherein X.sub.8 represents an estimated value (.mu.m) of said gap, L.sub.1
represents a length (.mu.m) from said sealing surface of said installation
section to a top end of said installation section, L.sub.3 represents a
thickness (.mu.m) of said gasket, L.sub.4 represents a length (.mu.m) from
a bottom end to a top end of said thread section, L.sub.5 represents a
length (.mu.m) from said sealing surface of said housing to the bottom end
of said thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of said installation section,
.alpha..sub.3 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of said gasket, .alpha..sub.4 represents a
coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of said
rotating member, and .alpha..sub.5 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of said housing.
7. The gas sensor installation structure according to claim 6, wherein said
gasket comprises at least one material selected from the group consisting
of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS.
8. The gas sensor installation structure according to claim 5, wherein said
rotating member comprises at least one material selected from the group
consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS.
9. A method for installing a gas sensor comprising the steps of:
providing an installation section having a sealing surface;
providing a gas sensor comprising a sensor element for detecting a specific
gas component, a housing which contains said sensor element therein and
has a sealing surface which forms a sealing section together with said
installation section at the front in a direction in which said sensor
element in inserted, and a rotating member which has a thread section
which is formed outside said rotating member and is screwed into said
installation section and can be rotated concentrically with respect to a
central axis of said housing; and
installing said gas sensor in said installation section by screwing said
rotating member;
wherein a release torque of said rotating member at 850.degree. C. (1123 K)
is 9 N.multidot.m or more; and
wherein an estimated value X.sub.11 of a gap formed between said sealing
surface of said housing and a sealing surface of said installation section
at 850.degree. C. (1123 K), that is calculated according to the following
equation, is 31 .mu.m or less:
X.sub.11
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.4.times..alpha..sub.4)-(L.
sub.5.times..alpha..sub.5)}.times.1123;
wherein X.sub.11 represents an estimated value (.mu.m) of said gap, L.sub.1
represents a length (.mu.m) from said sealing surface of said installation
section to a top end of said installation section, L.sub.4 represents a
length (.mu.m) from a bottom end to a top end of said thread section,
L.sub.5 represents a length (.mu.m) from said sealing surface of said
housing to the bottom end of said thread section, .alpha..sub.1 represents
a coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of said
installation section, .alpha..sub.4 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of said rotating member, and
.alpha..sub.5 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of said housing.
10. The method for installing a gas sensor according to claim 9, wherein
said sealing section is formed through a gasket and said rotating member
is screwed in said installation step so that an estimated value X.sub.12
of the gap, that is calculated according to the following equation, is 31
.mu.m or less:
X.sub.12
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.3.times..alpha..sub.3)-(L.
sub.4.times..alpha..sub.4)-(L.sub.5.times..alpha..sub.5)}.times.1123;
wherein X.sub.12 represents an estimated value (.mu.m) of said gap, L.sub.1
represents a length (.mu.m) from said sealing surface of said installation
section to a top end of said installation section, L.sub.3 represents a
thickness (.mu.m) of said gasket, L.sub.4 represents a length (.mu.m) from
a bottom end to a top end of said thread section, L.sub.5 represents a
length (.mu.m) from said sealing surface of said housing to the bottom end
of said thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of said installation section,
.alpha..sub.3 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the gasket, .alpha..sub.4 represents a
coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of said
rotating member, and .alpha..sub.5 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of said housing.
Description
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.
BACKGROUND OF THE INVENTION
Various types of gas sensors are installed in the exhaust pipe (pipe) of a
vehicle in order to detect a specific gas component (NO.sub.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.sub.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 15, 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.degree. 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
at 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.degree. C.
(1123 K) is 9 N.multidot.m or more, and an estimated value X.sub.1 of a
gap formed between the sealing surface of the housing and the sealing
surface of the installation section at 850.degree. C. (1123 K), that is
calculated according to the following equation (1), is 31 .mu.m or less:
X.sub.1
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.
2)}.times.1123 (1);
wherein X.sub.1 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section, and
.alpha..sub.2 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. 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.sub.2 of the gap, that is calculated according to equation (2), is
31 .mu.m or less:
X.sub.2
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.2)-(L.
sub.3.times..alpha..sub.3)}.times.1123 (2);
wherein X.sub.2 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, L.sub.3 represents a thickness (.mu.m) of the gasket,
.sub..alpha.1 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the installation section, .alpha..sub.2
represents a coefficient of thermal expansion (.times.10.sup.-6 /.degree.
C.) of the housing, and .alpha..sub.3 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. 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.degree. C. (1123 K) is 9 N.multidot.m or more, and an
estimated value X.sub.3 of a gap formed between the sealing surface of the
housing and the sealing surface of the installation section at 850.degree.
C. (1123 K), that is calculated according to the following equation (3),
is 31 .mu.m or less:
X.sub.3
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.4.times..alpha..sub.4)-(L.
sub.5.times..alpha..sub.5)}.times.1123 (3);
wherein X.sub.3 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.4 represents a
length (.mu.m) from a bottom end to a top end of the thread section,
L.sub.5 represents a length (.mu.m) from the sealing surface of the
housing to the bottom end of the thread section, .alpha..sub.1 represents
a coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of the
installation section, .alpha..sub.4 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the rotating member, and
.alpha..sub.5 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. 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.sub.4 of the gap, that is calculated according to equation (4), is
31 .mu.m or less:
X.sub.4
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.3.times..alpha..sub.3)-(L.
sub.4.times..alpha..sub.4)-(L.sub.5.times..alpha..sub.5)}.times.1123 (4);
wherein X.sub.4 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.3 represents a
thickness (.mu.m) of the gasket, L.sub.4 represents a length (.mu.m) from
a bottom end to a top end of the thread section, L.sub.5 represents a
length (.mu.m) from the sealing surface of the housing to the bottom end
of the thread section, .alpha..sub.1, represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section,
.alpha..sub.3 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the gasket, .alpha..sub.4 represents a
coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of the
rotating member, and .alpha..sub.5 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the housing.
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. In the present invention, the material for the
rotating member is preferably at least one material selected from the
group consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS. The
material for the housing 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
installation structure is provided, including an installation section
having a sealing surface and a gas sensor. The gas sensor comprises 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 the
installation section, and a sealing section formed between the sealing
surface of the housing and a sealing surface of the installation section
at a position deeper than the thread section in a direction in which the
sensor element is inserted. The gas sensor is installed by screwing the
housing into the installation section. The release torque of the housing
at 850.degree. C. (1123 K) is 9 N.multidot.m or more, and an estimated
value X.sub.5 of a gap formed between the sealing surface of the housing
and the sealing surface of the installation section at 850.degree. C.
(1123 K), that is calculated according to the following equation (5), is
31 .mu.m or less:
X.sub.5
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.
2)}.times.1123 (5);
wherein X.sub.2 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section, and
.alpha..sub.2 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the housing.
In the present invention, it is preferable that the sealing section is
formed through a gasket and that the estimated value X.sub.6 of the gap,
that is preferably calculated according to equation (6), is 31 .mu.m or
less:
X.sub.6
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.2)-(L.
sub.3.times..alpha..sub.3)}.times.1123 (6);
wherein X.sub.6 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, L.sub.3 represents a thickness (.mu.m) of the gasket,
.alpha..sub.1 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the installation section, .alpha..sub.2
represents a coefficient of thermal expansion (.times.10.sup.-6 /.degree.
C.) of the housing, and .alpha..sub.3 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. 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
installation structure is provided, including an installation section
having a sealing surface and a gas sensor. The gas sensor comprises a
sensor element, which functions to detect a specific gas component, a
housing containing the sensor element therein and having a sealing surface
which forms a sealing section together with the sealing surface of the
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. 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.degree. C. (1123
K) is 9 N.multidot.m or more, and an estimated value X.sub.7 of a gap
formed between the sealing surface of the housing and the sealing surface
of the installation section at 850.degree. C. (1123 K), that is calculated
according to the following equation (7), is 31 .mu.m or less:
X.sub.7
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.4.times..alpha..sub.4)-(L.
sub.5.times..alpha..sub.5) }.times.1123 (7);
wherein X.sub.7 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.4 represents a
length (.mu.m) from a bottom end to a top end of the thread section,
L.sub.5 represents a length (.mu.m) from the sealing surface of the
housing to the bottom end of the thread section, .alpha..sub.1 represents
a coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of the
installation section, .alpha..sub.4 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the rotating member, and
.alpha..sub.5 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the housing.
In the present invention, it is preferable that the sealing section is
formed through a gasket and an estimated value X.sub.8 of the gap, that is
calculated according to the following equation (8), is 31 .mu.m or less:
X.sub.8
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.3.times..alpha..sub.3)-(L.
sub.4.times..alpha..sub.4)-(L.sub.5.times..alpha..sub.5)}.times.1123 (8);
wherein X.sub.8 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.3 represents a
thickness (.mu.m) of the gasket, L.sub.4 represents a length (.mu.m) from
a bottom end to a top end of the thread section, L.sub.5 represents a
length (.mu.m) from the sealing surface of the housing to the bottom end
of the thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section,
.alpha..sub.3 represents a coefficient of thermal expansion (x 10.sup.-6
/.degree. C.) of the gasket, .alpha..sub.4 represents a coefficient of
thermal expansion (.times.10.sup.-6 /.degree. C.) of the rotating member,
and .alpha..sub.5 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the housing.
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. In the present invention, the material for the
rotating member is preferably at least one material selected from the
group consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS. The
material for the housing 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 method for
installing a gas sensor is provided comprising the steps of providing an
installation section having a sealing surface and providing a gas sensor
which comprises 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 the
installation section, and a sealing section formed between the sealing
surface of the housing and the sealing surface of the installation section
at a position deeper than the thread section in a direction in which the
sensor element is inserted. The gas sensor is installed in the
installation section by screwing the housing so that release torque of the
housing at 850.degree. C. (1123 K) is 9 N.multidot.m or more and an
estimated value X.sub.9 of a gap formed between the sealing surface of the
housing and the sealing surface of the installation section at 850.degree.
C. (1123 K), that is calculated according to the following equation (9),
is 31 .mu.m or less:
X.sub.9
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.
2)}.times.1123 (9);
wherein X.sub.9 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section, and
.alpha..sub.2 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the housing.
In the present invention, it is preferable that the sealing section is
formed through a gasket and the housing is screwed so that an estimated
value X.sub.10 of the gap, that is calculated according to the following
equation (10), is 31 .mu.m or less:
X.sub.10
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.2)-(L.
sub.3.times..alpha..sub.3)}.times.1123 (10);
wherein X.sub.10 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, L.sub.3 represents a thickness (.mu.m) of the gasket,
.alpha..sub.1, represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the installation section, .alpha..sub.2
represents a coefficient of thermal expansion (.times.10.sup.-6 /.degree.
C.) of the housing, and .alpha..sub.3 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the gasket.
According to another aspect of the present invention, a method for
installing a gas sensor is provided, comprising the steps of providing an
installation section having a sealing surface and providing a gas sensor,
which comprises a sensor element which functions to detect a specific gas
component, a housing containing the sensor element therein and having a
sealing surface which forms a sealing section together with the sealing
surface of the installation section at the front in a 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 can be rotated concentrically with
respect to a central axis of the housing. The gas sensor is installed in
the installation section by screwing the rotating member so that release
torque of the rotating member at 850.degree. C. (1123 K) is 9 N.multidot.m
or more and an estimated value X.sub.11 of a gap formed between the
sealing surface of the housing and the sealing surface of the installation
section at 850.degree. C. (1123 K), that is calculated according to the
following equation (11), is 31 .mu.m or less:
X.sub.11
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.4.times..alpha..sub.4)-(L.
sub.5.times..alpha..sub.5)}.times.1123 (11);
wherein X.sub.11 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.4 represents a
length (.mu.m) from a bottom end to a top end of the thread section,
L.sub.5 represents a length (.mu.m) from the sealing surface of the
housing to the bottom end of the thread section, .alpha..sub.1 represents
a coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of the
installation section, .alpha..sub.4 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the rotating member, and
.alpha..sub.5 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the housing.
In the present invention, it is preferable that the sealing section is
formed through a gasket and that the rotating member is screwed so that an
estimated value X.sub.12 of the gap, that is calculated according to the
following equation (12), is 31 .mu.m or less:
X.sub.12
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.3.times..alpha..sub.3)-(L.
sub.4.times..alpha..sub.4)-(L.sub.5.times..alpha..sub.5)}.times.1123 (12)
wherein X.sub.12 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.3 represents a
thickness (.mu.m) of the gasket, L.sub.4 represents a length (.mu.m) from
a bottom end to a top end of the thread section, L.sub.5 represents a
length (.mu.m) from the sealing surface of the housing to the bottom end
of the thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section,
.alpha..sub.3 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the gasket, .alpha..sub.4 represents a
coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of the
rotating member, and .alpha..sub.5 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the housing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross-sectional view showing an embodiment of a gas
sensor installation structure of the present invention.
FIG. 2 is a partial cross-sectional view showing another embodiment of the
gas sensor installation structure of the present invention.
FIG. 3 is a partial cross-sectional view showing still another embodiment
of the gas sensor installation structure of the present invention.
FIG. 4 is a partial cross-sectional view showing yet another embodiment of
the gas sensor installation structure of the present invention.
FIG. 5 is a graph showing the relation between dislodgement of a gas sensor
and release torque (N.multidot.m) and an estimated value (.mu.m) of a gap.
FIG. 6 is a graph in which release torque (N.multidot.m) at 850.degree. C.
is plotted with respect to an estimated value of a gap for each gas sensor
installation structure obtained in examples.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention are described below. However, the
present invention is not limited to these embodiments. Various
modifications, improvements, and the like are possible within the scope of
the present invention based on the knowledge of a person skilled in the
art.
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
and a thread section which is adapted to be screwed into a specific
installation section. The sensor element also includes a sealing section
formed between the sealing surface of the housing and a sealing surface of
the installation section at 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.degree. C. (1123 K) is 9 N.multidot.m or more, and an estimated
value X.sub.1 of a gap formed between the sealing surface of the housing
and the sealing surface of the installation section at 850.degree. C.
(1123 K), that is calculated according to the following equation (1), is
31 .mu.m or less:
X.sub.1
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.
2)}.times.1123 (1);
wherein X.sub.1 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section, and
.alpha..sub.2 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the housing.
The gas sensor of the present invention is described below in detail taking
the gas sensor installation structure shown in FIG. 1 as an example. FIG.
1 illustrates a state in which the gas sensor 10 is installed in the pipe
6 by screwing the housing 5 into the boss 7 as described above. In the
case where the relationship between the coefficient of thermal expansion
(.alpha..sub.1) of the boss 7, which is the installation section, and the
coefficient of thermal expansion (.alpha..sub.2) of the housing 5 is
.alpha..sub.1 >.alpha..sub.2, a gap is formed between the sealing
surface 4 of the housing 5 and the installation section (boss 7) at the
sealing section 3 when the temperature of the pipe 6 is increased, whereby
the tightening force of the screw is decreased. However, in the gas sensor
of the present embodiment, since the release torque at 850.degree. C.
(1123 K) when the housing 5 is screwed into the installation section (boss
7) and the estimated value X.sub.1 of the gap calculated according to the
above equation (1) are specific values in the relationship between the
coefficient of thermal expansion (.alpha..sub.1) of the installation
section and the length (L.sub.1) between the sealing surface of the
installation section and the top end of the installation section, the
tightening force of the thread section 2 is maintained moderately.
Therefore, the gas sensor of the present embodiment is rarely dislodged
from the installation section (boss 7), even if the gas sensor is used in
an installation environment in which vibration is applied either
continuously or intermittently under high temperature conditions.
The term "release torque" used in the present invention means the torque
necessary for dislodging the tightened product (gas sensor) from the
installation section, or the torque necessary to cause the tightening
force between the tightened product and the installation section to be
lost, and is a measured value which is actually measured using a torque
gauge.
In order to further reduce the possibility of dislodgement, it is
preferable that the release torque at 850.degree. C. (1123 K) when the
housing is screwed into the installation section is 15 N.multidot.m or
more, and that the estimated value X.sub.1 of the gap calculated according
to the above equation (1) is 20 .mu.m or less. It is still more preferable
that the release torque at 850.degree. C. (1123 K) is 20 N.multidot.m or
more and that the estimated value X.sub.1 of the gap that is calculated
according to the above equation (1) is 15 .mu.m or less.
The upper limit of the release torque is not limited in the present
invention. It is sufficient that the release torque is equal to or less
than the torque during tightening from the viewpoint of preventing
deformation of the thread section, seizing of the screw, and the like. The
lower limit of the estimated value X.sub.1 of the gap in the present
invention is not limited. There may be a case where the estimated value
X.sub.1 of the gap is a negative value, since the estimated value X.sub.1
is a theoretical value, and it is sufficient that the estimated value
X.sub.1 is about -10 .mu.m or more.
The gas sensor of the present invention may have a configuration in which
the gasket 8 is provided in contact with the sealing surface 4, as shown
in FIG. 2. In this case, an estimated value X.sub.2 of the gap can be
calculated according to the following equation (2):
X.sub.2
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.2)-(L.
sub.3.times..alpha..sub.3)}.times.1123 (2);
wherein X.sub.2 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, L.sub.3 represents a thickness (.mu.m) of the gasket,
.alpha..sub.1 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the installation section, .alpha..sub.2
represents a coefficient of thermal expansion (.times.10.sup.-6 /.degree.
C.) of the housing, and .alpha..sub.3 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the gasket.
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 which forms a sealing section together with a
sealing surface of an installation section at the front in a 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.degree. C. (1123 K) is 9 N.multidot.m or more, and an
estimated value X.sub.3 of a gap formed between the sealing surface of the
housing and the sealing surface of the installation section at 850.degree.
C. (1123 K), that is calculated according to the following equation (3),
is 31 .mu.m or less:
X.sub.3
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.4.times..alpha..sub.4)-(L.
sub.5.times..alpha..sub.5)}.times.1123 (3);
wherein X.sub.3 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.4 represents a
length (.mu.m) from a bottom end to a top end of the thread section,
L.sub.5 represents a length from the sealing surface of the housing to the
bottom end of the thread section (.mu.m), .alpha..sub.1 represents a
coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of the
installation section, .alpha..sub.4 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the rotating member, and
.alpha..sub.5 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the housing.
The gas sensor of the present invention is described below taking the gas
sensor installation structure shown in FIG. 3 as an example.
As described above, FIG. 3 illustrates a state in which the rotating member
(rotational hexagon 15) which can be rotated concentrically with respect
to the central axis of the housing 5 is disposed outside the housing 5,
and the gas sensor 10 is installed by screwing the rotating member so that
the sealing surface 4 of the housing 5 is pressed against a sealing
surface of the installation section (boss 7) without rotating the housing
5. In the case where the relationship between the coefficient of thermal
expansion (.alpha..sub.1) of the boss 7, which is the installation
section, and the coefficients of thermal expansion (.alpha..sub.4 and
.alpha..sub.5) of the housing 5 and the rotating member (rotational
hexagon 15) is .alpha..sub.1 >.alpha..sub.4 and .alpha..sub.1
>.alpha..sub.5, a gap is formed between the sealing surface 4 of the
housing 5 and the installation section (boss 7) at the sealing section 3
when the temperature of the pipe 6 is increased, whereby the tightening
force of the screw is decreased. However, in the gas sensor of the present
embodiment, since the value of the release torque at 850.degree. C. (1123
K), when the rotational hexagon 15 (which is the rotating member) is
screwed into the installation section (boss 7), and the estimated value
X.sub.3 of the gap that is calculated according to the above equation (3),
are specific values in the relationship between the coefficient of thermal
expansion (.alpha..sub.1) of the installation section and the length
(L.sub.1) between the sealing surface of the installation section and the
top end of the installation section, the tightening force of the thread
section 2 is maintained moderately. Therefore, the gas sensor of the
present embodiment is rarely dislodged from the installation section (boss
7) even if the gas sensor is used in an installation environment in which
vibration is applied either continuously or intermittently under high
temperature conditions.
In order to further reduce the possibility of dislodgement, it is
preferable that the release torque at 850.degree. C. (1123 K), when the
rotating member is screwed into the installation section, is 15
N.multidot.m or more and that the estimated value X.sub.3 of the gap that
is calculated according to the above equation (3) is 20 .mu.m or less. It
is still more preferable that the release torque at 850.degree. C. (1123
K) is 20 N.multidot.m or more and the estimated value X.sub.3 of the gap
that is calculated according to the above equation (3) is 15 .mu.m or
less.
In the present invention, the upper limit of the release torque is not
limited. It is sufficient that the release torque is equal to or less than
the torque during tightening from the viewpoint of preventing deformation
of the thread section, seizing of the screw, and the like. The lower limit
of the estimated value X.sub.1 of the gap in the present invention is not
limited. There may be a case where the estimated value X.sub.3 of the gap
is a negative value since the estimated value X.sub.3 is a theoretical
value, and it is sufficient that the estimated value X.sub.3 is about -10
.mu.m or more.
In the present invention, a configuration in which the gasket 8 is provided
in contact with the sealing surface 4, as shown in FIG. 4, may be
employed. In this case, an estimated value X.sub.4 of the gap can be
calculated according to the following equation (4):
X.sub.4
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.3.times..alpha..sub.3)-(L.
sub.4.times..alpha..sub.4)-(L.sub.5.times..alpha..sub.5)}.times.1123 (4);
wherein X.sub.4 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.3 represents a
thickness (.mu.m) of the gasket, L.sub.4 represents a length (.mu.m) from
a bottom end to a top end of the thread section, L.sub.5 represents a
length (.mu.m) from the sealing surface of the housing to the bottom end
of the thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section,
.alpha..sub.3 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the gasket, .alpha..sub.4 represents a
coefficient of thermal expansion (.times.10.sup.-6 /.degree. C.) of the
rotating member, and .alpha..sub.5 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the housing.
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. These materials can exhibit superior sealing
properties at the sealing section and have excellent workability.
In the present invention, general-purpose materials are suitably used as
the materials that make up the rotating member and the housing. As
specific examples of the material for the rotating member, at least one
material selected from the group consisting of 430 SS, 304 SS, 310 SS, 316
SS, and 321 SS is preferably used. As specific examples of the material
for the housing, at least one material selected from the group consisting
of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS is preferably used.
According to another aspect of the present invention, a gas sensor
installation structure is provided, including an installation section
having a sealing surface and a gas sensor. The gas sensor comprises 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 the
installation section, and a sealing section formed between the sealing
surface of the housing and the sealing surface of the installation section
at a position deeper than the thread section in a direction in which the
sensor element is inserted. The gas sensor is installed by screwing the
housing into the installation section. The release torque of the housing
at 850.degree. C. (1123 K) of the housing is 9 N.multidot.m or more, and
an estimated value X.sub.5 of a gap formed between the sealing surface of
the housing and the sealing surface of the installation section at
850.degree. C. (1123 K), that is calculated according to the following
equation (5), is 31 .mu.m or less:
X.sub.5
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.
2)}.times.1123 (5);
wherein X.sub.2 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, .alpha..sub.1 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. C.) of the installation section, and
.alpha..sub.2 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the housing.
The gas sensor installation structure of the present invention is described
below taking the gas sensor installation structure shown in FIG. 1 as an
example.
As described above, a gap is formed between the sealing surface 4 of the
housing 5 and the installation section 7 at the sealing section 3 when the
temperature of the pipe 6 is increased, whereby the tightening force of
the screw is decreased. However, in the gas sensor installation structure
of the present embodiment, since the release torque at 850.degree. C.
(1123 K) and the estimated value X.sub.5 of the gap calculated according
to the above equation (5) are specific values, the tightening force of the
thread section 3 is maintained moderately. Therefore, even if the gas
sensor installation structure of the present embodiment is used in an
installation environment in which vibration is applied either continuously
or intermittently under high temperature conditions, the gas sensor 10 is
significantly rarely dislodged from the installation section (boss 7).
In order to further reduce the possibility of dislodgement, it is
preferable that the release torque of the housing at 850.degree. C. (1123
K) is 15 N.multidot.m or more and that the estimated value X.sub.5 of the
gap that is calculated according to the above equation (5) is 20 .mu.m or
less. It is still more preferable that the release torque at 850.degree.
C. (1123 K) is 20 N.multidot.m or more and that the estimated value
X.sub.5 of the gap that is calculated according to the above equation (5)
is 15 .mu.m or less.
In the present invention, the upper limit of the release torque is not
limited. It is sufficient that the release torque is equal to or less than
the torque during tightening from the viewpoint of preventing deformation
of the thread section, seizing of the screw, and the like. The lower limit
of the estimated value X.sub.1 of the gap in the present invention is not
limited. There may be a case where the estimated value X.sub.5 of the gap
is a negative value since the estimated value X.sub.5 is a theoretical
value, and it is sufficient that the estimated value X.sub.5 is about -10
.mu.m or more.
The gas sensor installation structure of the present invention may have a
configuration in which the sealing section 3 is formed through the gasket
8, as shown in FIG. 2. In this case, an estimated value X.sub.6 of the gap
can be calculated according to the following equation (6):
X.sub.6
(.mu.m)={(L.sub.1.times..alpha..sub.1)-(L.sub.2.times..alpha..sub.2)-(L.
sub.3.times..alpha..sub.3)}.times.1123 (6);
wherein X.sub.6 represents an estimated value (.mu.m) of the gap, L.sub.1
represents a length (.mu.m) from the sealing surface of the installation
section to a top end of the installation section, L.sub.2 represents a
length (.mu.m) from the sealing surface of the housing to a top end of the
thread section, L.sub.3 represents a thickness (.mu.m) of the gasket,
.alpha..sub.1 represents a coefficient of thermal expansion
(.times.10.sup.-6 /.degree. C.) of the installation section, .alpha..sub.2
represents a coefficient of thermal expansion (.times.10.sup.-6 /.degree.
C.) of the housing, and .alpha..sub.3 represents a coefficient of thermal
expansion (.times.10.sup.-6 /.degree. 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. These materials can exhibit superior sealing
properties at the sealing section and have excellent workability.
According to another aspect of the present invention, a gas sensor
installation structure is provided, including an installation section
having a sealing surface and a gas sensor. The gas sensor comprises a
sensor element, which functions to detect a specific gas component, a
housing containing the sensor element therein and having a sealing surface
which forms a sealing section together with the sealing surface of the
installation section at the front in a direction in which the sensor
element is inserted, and a rotating member having a thread section formed
on an outer surface thereof that is ada
