Measuring and testing – Gas analysis – Detector detail
Reexamination Certificate
1999-02-25
2001-12-11
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Detector detail
C073S023310, C073S866500, C204S424000
Reexamination Certificate
active
06327891
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas sensor for detecting a component of a gas to be measured (hereinafter referred to as a measurement gas), such as an oxygen sensor, an HC sensor, an NO
x
sensor, or a like sensor.
2. Description of Related Art
Conventionally, there has been known a gas sensor is having a structure in which an insulator is disposed inside a metallic shell; a sensor element is disposed inside the insulator; and a sealing layer is formed between the inner surface of the insulator and the outer surface of the sensor element from a sealing material such as glass. The sealing layer is formed through charging of the sealing material into a cavity that is formed in the insulator around the sensor element.
In gas sensors having the above-described structure, the sensor element is frequently formed into a ceramic layered element. In such a case, as shown in
FIG. 14
, there is generally used a sensor element
102
having a rectangular cross section. However, a cavity portion
131
(i.e., a sealing material layer
132
) formed in an insulator
104
conventionally has a circular cross section. This results in a structure in which the sealing material layer
132
having a circular cross section encloses the sensor element
102
having a rectangular cross section. Therefore, the thickness of the sealing material layer naturally becomes uneven such that the thickness is greater at portions corresponding to the longer sides of the cross section of the sensor element
102
, and smaller at portions corresponding to the shorter sides of the cross section of the sensor element
102
. For example, an oxygen sensor for automobile use is often mounted at a location, such as an exhaust manifold or an exhaust pipe located near a suspension system and tires, where the sensor may be exposed to high temperature or subjected to a strong thermal shock. When the sealing material layer
132
has an uneven thickness as described above, thermal stresses tend to concentrate at thin wall portions, resulting in the problem of shortening the life of the sealing material layer
132
.
An object of the present invention is to provide a gas sensor in which the effect of thermal stress on a sealing-material layer is mitigated and which therefore has excellent durability.
SUMMARY OF THE INVENTION
A gas sensor of the present invention has the following structure. An insulator is disposed inside a metallic shell, and a sensor element for detecting a component of a gas to be measured is disposed inside the insulator. A cavity is formed in the insulator to surround the sensor element and a sealing material mainly made of glass is charged into the cavity in order to establish sealing between the inner surface of the insulator and the outer surface of the sensor element. In order to achieve the above described object, in accordance with a first aspect of the present invention, an inner surface of the insulator that defines the cavity (hereinafter referred to as a “cavity defining inner surface”) has a sectional profile that conforms to that of the sensor element, when the sectional profile of the sensor element is square, rectangular, or elliptical.
In the case where the sensor element has a square, rectangular or elliptical cross section, a sealing material layer of uniform thickness can be formed around the sensor element if the cavity defining inner surface; i.e., the outer circumference of the sealing material layer charged into the cavity, has a sectional profile that conforms to that of the sensor element. By virtue of this structure, there can be prevented concentration of stresses at a thin wall portion, which has arisen in conventional gas sensors in which a sealing material layer of a circular cross section is formed around a sensor element of, for example, a rectangular cross section. Thus, the durability of the sealing-material layer can be improved.
In accordance with a second aspect of the present invention, the gas sensor has the following features (see FIGS.
3
(
a
) and
3
(
c
) for the following description). That is, the sensor element (
2
) has a rectangular cross section along a plane Q perpendicular to the axis of the sensor element (
2
). On the plane Q, a line L
1
is drawn such that the line L
1
passes through the centroid G of the cross section of the sensor element (
2
) and perpendicularly intersects the shorter sides of the cross section of the sensor element (
2
). The intersections between the line L
1
and the inner surface defining the cavity (
31
) are taken as P
1
and P
2
, respectively. Similarly, a line L
2
is drawn such that the line L
2
passes through the centroid G of the cross section of the sensor element (
2
) and perpendicularly intersects the longer sides of the cross section of the sensor element (
2
). The intersections between the line L
2
and the inner surface defining the cavity (
31
) are taken as P
3
and P
4
, respectively. Further, while the longer of the distances GP1 and GP2 (or either one when GP1=GP2) is used as a radius, a circle C centered at the centroid G is drawn. The sectional profile of the inner surface defining the cavity (
31
) is determined such that both the points P
3
and P
4
fall within the circle C.
When the sensor element has a rectangular cross section and, as shown in
FIG. 14
, the cavity defining inner surface—i.e., the outer circumference of the sealing material layer charged in the cavity—has a circular profile, thick wall portions are formed in regions along the longer sides of the cross section of the sensor element, which causes stress concentration at thin wall portions formed along the shorter sides of the cross section. In order to solve this problem, in accordance with the second aspect of the present invention, the sectional profile of the cavity defining inner surface of the insulator (or the sectional outer profile of the sealing material layer) is set such that both the points P
3
and P
4
fall within the circle C. In this case, since the sealing material layer has a reduced wall thickness in regions along the longer sides of the cross section of the sensor element, the above-described problem can be avoided.
Preferably, the average wall thickness of the sealing material layer formed around the sensor element is adjusted within the range of 0.2 to 5 mm. When the thickness of the sealing material layer becomes less than 0.2 mm, the air tightness between the sensor element and the insulator is impaired. Further, since the size and weight of gas sensors mounted on automobiles and like have recently been reduced drastically, it has became difficult to secure space for allowing use of a sealing material layer having a thickness of 5 mm or greater. Further, when the thickness of the sealing material layer exceeds 5 mm, the absolute amount of thermal contraction of the sealing material layer increases, thereby increasing the thermal stress acting on the sensor element disposed inside the sealing material layer, possibly shortening the life of the sensor element. More preferably, the average wall thickness of the sealing material layer is adjusted within the range of 0.3 to 3 mm.
Further, when the sensor element has a rectangular cross section, the maximum thickness of the sealing material layer in regions along the shorter sides is preferably set substantially equal to the maximum thickness of the sealing material layer in regions along the longer sides. Specifically, the cavity defining inner surface preferably has a rectangular sectional profile such that the centroid of the sectional profile of the cavity defining inner surface substantially coincides with the centroid of the cross section of the sensor element and such that the sectional profile of the cavity defining inner surface corresponds to that of the cross section of the sensor element. In this case, each of the four corners of the sectional profile of the cavity defining inner surface preferably has a rounded or chamfered shape. Alternatively, the cavity defining inner surface has an ellipt
Nishio Hisaharu
Noda Keiichi
Taguchi Kazuo
Yabuta Katsuhisa
Brinks Hofer Gilson & Lione
Cygan Michael
NGK Spark Plug Co., Ltd
Williams Hezron
LandOfFree
Gas sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gas sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gas sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2601397