Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2003-01-21
2004-07-06
Olsen, Kaj K. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S427000
Reexamination Certificate
active
06758952
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas sensor having a detecting element having a pair of electrodes formed on a surface of a solid electrolytic body of an oxygen ion conductive property, and measuring the concentration of a measured gas.
2. Description of the Related Art
Various kinds of gas sensors such as an HC sensor, a NOx sensor, etc. are conventionally known as a gas sensor for detecting a concentration of a specific gas component from a mixing gas. An oxygen sensor having a detecting element made by a solid electrolytic body of an oxygen ion conductive property is known as one of these gas sensors.
As shown in
FIG. 10
, a detecting element
102
of a general oxygen sensor
101
is made such that an inside electrode
102
a
and an outside electrode
102
b
are formed on an inner and outer surfaces of a cylindrical body having a bottom. A tip side of the cylindrical body is covered by the solid electrolytic body. A rear end side of the cylindrical body is opened by the solid electrolytic body.
The oxygen sensor
101
detects an oxygen concentration of a measured gas by electromotive force caused between electrodes by a concentration difference between the measured gas outside the detecting element
102
and an atmosphere as a reference gas filling an internal space
102
c
of the cylindrical body.
In the oxygen sensor
101
for detecting the oxygen concentration of the measured gas by such a principle, the detecting element
102
is held by a metal shell
111
such that the tip portion of the detecting element
102
is exposed to the measured gas from the tip side of a through hole
112
formed in the axial direction of the metal shell
The detecting element is covered with an outer sleeve
113
so as to protect the detecting element from dust, water, oil, flied stones, etc. therearound.
In the oxygen sensor
101
, a rear end opening portion of the outer sleeve
113
is covered by an outer sleeve cover
130
as a seal member manufactured by rubber.
However, in a perfect covering state, no sufficient atmosphere (reference gas) can be sent into the internal space
102
c
of the detecting element
102
stored into the oxygen sensor
101
. Accordingly, it is known that a vent hole
131
is arranged in the outer sleeve cover
130
of the oxygen sensor
101
of this kind.
A filter
153
has a permeable property and a water repellent property to selectively introduce the atmosphere into the outer sleeve
113
while preventing the invasion of water into the outer sleeve
113
. The filter
153
is arranged in this vent hole
131
so as to block the vent hole
131
(e.g., see patent literatures 1 and 2).
[Patent Literature 1]
JP-A-2000-193632 (see
FIG. 3
)
[Patent Literature 2]
JP-A-2001-208724 (see
FIG. 1
)
In the oxygen sensors described in the above patent literatures, a vent hole is covered by a filter by fixing the filter using another member such that the filter comes in contact with an entire inner face of the vent hole. Therefore, there are cases in which manufacture cost of the sensor is raised and the filter is damaged in a manufacture process of the sensor.
Namely, in the oxygen sensors described in the above patent literatures, as shown in
FIG. 11
, a sleeve-shaped insertion member
151
is covered with a sheet-shaped filter
153
, and this filter
153
is pushed into the vent hole
131
from forward (the side of a metal shell).
Thus, the vent hole
131
is covered by the filter
153
while the filter
153
comes in contact with the inner face of the vent hole
131
. Therefore, in the pushing process of the insertion member
151
into the vent hole
131
, there is a case in which the filter
153
is pulled in the direction opposed to the insertion direction so that the filter
153
is broken.
When the vent hole
131
is covered by the filter
153
in such a method, the filter
153
is arranged outside the insertion member
151
, and is fixedly nipped and supported between the inner face of the vent hole
131
and the outer circumferential face of the insertion member
151
in design. Accordingly, the filter
153
of a size sufficiently greater than the diameter of the vent hole
131
must be prepared. Therefore, manufacture cost is raised and there are many useless portions.
SUMMARY OF THE INVENTION
It is an object of the present invention is to provide a gas sensor capable of attaching a filter to a vent hole simply and with a low cost.
To achieve such an object, a gas sensor comprising a detecting element having a pair of electrodes formed on the surface of a solid electrolytic body of an oxygen ion conductive property; a metal shell having a through hole formed in the axial direction and holding the detecting element within the through hole so as to expose the tip portion of the detecting element to a measured gas from the tip side of this through hole; an outer sleeve arranged on the rear end side of the metal shell and internally accommodating the detecting element; and an outer sleeve cover fitted and inserted in a rear end opening portion of this outer sleeve and extended from its own rear end face to the tip face, and having a vent hole as a circulating path of a gas of the interior and the exterior of the outer sleeve. A filter unit formed by a body separated from a gas sensor main body is arranged in the gas sensor.
The filter unit has a tubular member fitted and inserted into the vent hole of the outer sleeve cover, and a filter arranged inside this tubular member and fixed on the inside of this tubular member and having a permeable property and a water repellent property. The filter unit has such that the filter unit is fitted and inserted in the vent hole of the outer sleeve cover and the vent hole is covered by the filter.
In the gas sensor made in this way, the filter unit for fixing the filter inside (interior) the tubular member is used. Accordingly, if this filter unit is fitted and inserted into the vent hole of the outer sleeve cover, the vent hole can be simply covered by the filter. In other words, in the present invention, the gas sensor can be simply made by attaching the filter unit to the vent hole such that a gas can be circulated in the interior and the exterior of the outer sleeve while the invasion of a waterdrop, dust, etc. into the outer sleeve from the vent hole is prevented by the function of the filter. The productivity of a product can be improved in the gas sensor of the present invention.
The conventional gas sensor adopts the method for mounting the filter to the outer sleeve cover so as to set the filter to the exterior of an insertion member and directly push the filter into the vent hole. Therefore, there is a case in which the filter is damaged during the insertion. However, in the present invention, since the filter is mounted to the inside of the tubular member in advance, no filter is damaged when the filter unit is fitted and inserted. Accordingly, in the gas sensor of the present invention, manufacture cost of the product can be restrained and reliability of the filter, therefore, reliability of the gas sensor can be improved.
When the filter unit includes a separate body in this way and the filter unit is simply fitted, inserted and attached to the outer sleeve cover, there is a possibility that the filter unit gets out of the vent hole by vibrating the gas sensor after the attachment. Accordingly, for example, the filter unit is preferably fixed to the outer sleeve cover by an adhesive, etc. so as to prevent the filter unit from getting out of the outer sleeve cover.
However, performance of the adhesive is reduced when time has passed. Therefore, there is a possibility that no filter unit can be firmly fixed to the outer sleeve cover for a long period.
Therefore, in the gas sensor, a first engaging portion engaged with the tip portion (metal shell side) of the outer sleeve cover, and a second engaging portion engaged with the rear end portion (the side opposed to the metal shell) of the outer sleeve cover are preferably arranged in the tubular
NGK Spark Plug Co. Ltd.
Olsen Kaj K.
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