Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-12-05
2002-12-31
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S428000
Reexamination Certificate
active
06500322
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas sensor for mounting in a pipe defining a flow path in which a gas-to-be-measured such as an exhaust gas flows, and functions by introducing air as a reference gas from the outside.
2. Description of the Related Art
In the related art, various kinds of sensors such as an HC sensor or an NOx sensor are known as gas sensors for detecting the density of a specific gas component in a mixed gas. For example, as shown in
FIG. 12
, an oxygen sensor
501
comprising a detecting element
502
formed of an oxygen ion conductive solid-state electrolyte is known.
The detecting element
502
described above comprises an internal electrode
503
and an external electrode
504
formed respectively on the inner and outer surfaces of the element body of a cylindrical shape with a bottom wherein one end is closed by a solid-state electrolyte and the other end is left open. Between the internal electrode
503
and the external electrode
504
, an electromotive force is generated depending on the difference in the concentration or partial pressure of oxygen between the internal space in the detecting element
502
formed in a cylindrical shape and the outside. For example, the concentration of oxygen in a gas-to-be-measured can be detected by inserting the closed end of the detecting element
502
into the interior of the pipe defining a flow path of a gas-to-be measured via a cylindrical main fitting
505
to allow the external electrode
504
to come into contact with a gas-to-be-measured and the internal electrode
503
with the air, and then detecting an electromotive force generated between the internal electrode
503
and the external electrode
504
.
Introduction of air into the oxygen sensor may be carried out via a clearance formed in twisted core wires of a lead
507
. However, in order to introduce a large amount of air, a method of forming an air hole
509
on the side surface of a cylindrical cover
506
and plugging it by a water repellant filter
508
having gas permeability formed, for example, of a fluorine resin in order to prevent water or the like from entering therein has been employed.
When such an oxygen sensor is used for detecting the density of oxygen contained in an exhaust gas at an elevated temperature, the water repellant filter
508
may be deteriorated in gas permeability by heat due to exposure to an elevated temperature after long term use.
In order to solve this problem, as stated in Japanese Patent Laid-Open No.54063/97, a method of forming an air hole on the sealing member provided on the side of the opened end of the cylindrical cover facing toward the outside of the pipe defining a flow path for a gas-to-be-measured, and inserting a bar-shaped filter through the air hole is considered. By disposing the filter in the sealing member, the sealing member is positioned at a distance from the flow path and thus heat is not easily transferred from the pipe defining a flow path. Consequently, the possibility that the filter is exposed to an elevated temperature may be reduced. However, such a bar-shaped filter has a problem in that high resistance is generated when a gas is passed through and thus introduction of the air may be insufficient.
Such a problem occurs not only in an oxygen sensor, but also in gas sensors such as the NOx sensor or the HC sensor that require introduction of air.
SUMMARY OF THE INVENTION
In view of the above, it is therefore an object of the present invention to provide a gas sensor which functions by introducing air from the outside, wherein the property of introducing air may be maintained even when used at an elevated temperature.
Accordingly, a gas sensor according to a general aspect of the present invention comprises a cover including a gas permeable sealing member having an air hole and a gas permeable water repellant filter for closing said air hole, wherein said water repellant filter is formed in a sheet-shape and mounted in said air hole via a cylindrical inserting member that can be inserted into said air hole.
A gas sensor according to a first aspect of the present invention comprises a detecting element having electrodes on first and the second surfaces of an oxygen ion conductive solid-state electrolyte, a main fitting having a fitting portion to be fitted into a mounting hole formed on a wall of a pipe defining a flow path for a gas-to-be-measured for holding said detecting element in such manner that said first surface is disposed via said mounting hole at an inner position of said pipe with respect to said fitting portion, a cylindrical cover of which one end is connected to an outer position of said pipe with respect to the fitting portion of said main fitting and the other end is provided with a cylindrical sealing member having an air hole for introducing air to said second surface on one end and a through hole through which a lead connected to both electrodes of said detecting element passes on the other end, and a water repellant filter having gas permeability for closing said air hole, characterized in that said water repellant filter is formed in a sheet shape and mounted on said air hole by means of a cylindrical inserting member that can be inserted in said air hole.
In the gas sensor according to the first aspect of the present invention, since the water repellant filter is formed in a sheet shape, preferably gas permeability can be obtained. In addition, since the water repellant filter is mounted on the sealing member and thus it is hardly affected by heat, the gas permeability can be maintained even when said gas sensor is exposed to heat from the outside.
According to a second aspect of the invention, in order to fix the water repellant filter described above to the air hole, the water repellant filter is preferably interposed between the outer peripheral surface of the cylindrical inserting member and the inner peripheral surface of said air hole so as to close the opened end of the cylindrical inserting member.
In the gas sensor in this arrangement according to the second aspect of the invention, the water repellant filter can be mounted to the air hole easily by pressing the water repellant filter into the air hole by means of a cylindrical inserting member. It is also possible to cover the opening of the cylindrical inserting member in advance, and then insert the cylindrical inserting member into the air hole.
In the structure according to the second aspect, the water repellant filter is interposed or directly brought into intimate contact between the inner peripheral surface of the air hole and the outer peripheral surface of the cylindrical inserting member so that the sealing property between them is establised. Since the opened end of at least one cylindrical inserting member is closed by the water repellant filter, it can prevent passage of water drops through the inside of the cylindrical inserting member, thereby realizing waterproof at the air hole of the sealing member.
Though it is preferable to interpose the water repellant filter between the outer peripheral surface of the cylindrical inserting member and the inner peripheral surface of the air hole because the effects as described above may be obtained as described thus far, there is a possibility that the water repellant filter is displaced. As a consequence, there is a possibility that sufficient waterproof property may not be established at the air hole.
According to a third aspect of the invention, the cylindrical inserting member is preferably provided on its outer peripheral surface at the portion that comes into contact with the water repellant filter with an engaging portion with which the water repellant filter engages when the water repellant filter is interposed between the portion of the outer peripheral surface of the cylindrical inserting member being in contact with the water repellant filter and the inner peripheral surface of the air hole.
In the gas sensor in this arrangement according to the third aspect of the invention, since th
Akatsuka Shoji
Asai Masahiro
Ishikawa Satoshi
Matsuo Kouji
NGK Spark Plug Co. Ltd.
Tung T.
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-2992934