Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-06-22
2002-05-07
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S427000, C204S428000
Reexamination Certificate
active
06383353
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oxygen sensor for detecting oxygen in a gas to be measured, such as exhaust gas from an internal combustion engine.
2. Description of the Related Art
A known oxygen sensor includes an oxygen detection element assuming the form of a hollow rod which is closed at a front end, and having electrode layers formed on the inner and outer surfaces thereof. In an oxygen sensor of this type, while the atmosphere serving as a reference gas is introduced into an oxygen detection element such that the inner surface (internal electrode layer) of the element is exposed to the reference gas, the outer surface (external electrode layer) of the oxygen detection element is exposed to exhaust gas. As a result, an electromotive force is induced by the oxygen concentration cell effect, according to the difference in oxygen concentration between the inner and outer surfaces. This electromotive force induced by the oxygen concentration cell effect is led out from the internal and external electrode layers through lead wires and serves as a detection signal indicative of oxygen concentration in the exhaust gas.
FIG. 12
of the accompanying drawings shows a conventional metallic internal-electrode connection member (metallic terminal member)
23
′ to be installed into a hollow portion
2
a
of such an oxygen detection element
2
so as to establish electrical connection with an internal electrode layer formed on the inner wall surface of the hollow portion
2
a
. The conventional metallic internal-electrode connection member
23
′ includes the following integrally formed portions: a connector
23
a
′ to be connected to a lead wire; a main body portion
23
c
′ to come into contact with the inner wall surface of the hollow portion
2
a
of the oxygen detection element
2
; a lead portion
23
b
′ for connecting the connector
23
a
′ and the main body portion
23
c
′; and a heating member holder portion
23
d
′ for firmly holding a heating member which is disposed within the hollow portion
2
a
for heating the oxygen detection element
2
.
The main body portion
23
c
′ of the conventional metallic internal-electrode connection member
23
′ is formed by bending into a cylindrical form a sheet member which has a plurality of contact portions
23
e
′ formed into a saw-toothed form and arranged at opposite side edges thereof in a staggered manner. Substantially the entire outer circumferential surface of the main body portion
23
c
′ is brought into contact with the inner wall surface (internal electrode layer) of the hollow portion
2
a
of the oxygen detection element
2
, whereby electrical continuity is established and the main body portion
23
c
′ is axially positioned relative to the hollow portion
2
a.
In order to reliably position the metallic internal-electrode connection member
23
′ in the axial direction relative to the hollow portion
2
a
and to establish reliable contact and electrical connection between the metallic internal-electrode connection member
23
′ and the internal electrode layer, the outside diameter of the cylindrical main body portion
23
c
′ is rendered greater than the inside diameter of the hollow portion
2
a
of the oxygen detection element
2
a
. Thus, as shown in
FIG. 12
, when the metallic internal-electrode connection member
23
′ is to be installed in the oxygen detection element
2
, the main body portion
23
c
′ is inserted under pressure into the hollow portion
2
a
while substantially the entire outer circumferential surface of the main body portion
23
c
′ is squeezed radially. As a result, the resistance of insertion tends to increase, potentially raising a problem in assembly. Particularly, since a plurality of contact portions
23
e
′ formed into a saw-toothed form are arranged at opposite sides in a staggered manner, the resistance of insertion tends to occur intermittently. As a result, in some cases, an upper portion (the base-end side relative to the insertion direction) of the metallic internal-electrode connection member
23
′ suffers plastic deformation, such as crushing, bending, or buckling. In order to prevent such plastic deformation, a relevant jig may be employed; however, this involves additional work and causes an increase in cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a sensor structure which reduces the resistance of insertion in the course of insertion of a metallic terminal member into the hollow portion of an oxygen detection element so as to enable smooth assembly, and such that portions of the metallic terminal member become less susceptible to plastic deformation.
Accordingly, an oxygen sensor of the present invention comprises an oxygen detection element assuming the form of a hollow rod which is closed at one end, and having an electrode layer formed on at least the inner surface thereof; and a metallic terminal member connected electrically to the electrode layer. The oxygen sensor is characterized in that:
the metallic terminal member includes an attachment portion having a substantially circular cross section, which is disposed within a hollow portion of the oxygen detection element; and
the attachment portion is disposed such that, as observed in cross section, the attachment portion is in contact with the inner wall surface of the hollow portion of the oxygen detection element at opposite sides thereof located along a predetermined direction (hereinafter called the direction of contact), and a gap is formed between the attachment portion and the inner wall surface of the hollow portion of the oxygen detection element at opposite sides thereof located along a direction intersecting the direction of contact (hereinafter called the direction of gap formation).
As described above, according to the present invention, the attachment portion of the metallic terminal member is in contact with the inner wall surface of the hollow portion of the oxygen detection element, directly or indirectly via another member, at opposite sides thereof located along the direction of contact. Also, a gap is formed between the attachment portion and the inner wall surface at opposite sides of the attachment portion located along the direction of gap formation. Thus, only a portion of the outer circumferential surface of the attachment portion is in contact with the inner wall surface of the hollow portion to thereby establish electrical continuity therebetween. Specifically, the attachment portion is in contact with the inner wall surface of the hollow portion at two or more contact points to thereby establish electrical continuity therebetween. Thus, in the course of insertion of the metallic terminal member into the hollow portion of the oxygen detection element, the resistance of insertion decreases, whereby assembly can be performed smoothly, and portions of the metallic terminal member become less susceptible to plastic deformation, such as crushing, bending, or buckling.
Preferably, the attachment portion of the present invention, as observed in cross section, has an opening formed at a portion of the circumference thereof and includes a direction change portion, which is located opposite the opening with respect to the center axis of the hollow portion of the oxygen detection element; and
edge portions located at opposite sides of the opening and the direction change portion are in contact with the inner wall surface of the hollow portion of the oxygen detection element, directly or indirectly via another member, and a direction extending between the direction change portion and one of the edge portions located at opposite sides of the opening is the direction of contact. Thus, the attachment portion can be manufactured through bending of a sheet member. Also, the attachment portion can be designed and machined with high accuracy so as to establish the above-mentioned state of contact and gap fo
Akatsuka Shoji
Asai Masahiro
Ishikawa Satoshi
NGK Spark Plug Co. Ltd.
Tung T.
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