Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-06-09
2003-12-09
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S408000, C204S427000, C204S428000, C205S785000
Reexamination Certificate
active
06660143
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 in the oxygen detection element 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.
In an oxygen sensor of this type, when the temperature of exhaust gas is low, as is the case upon startup of an engine, an oxygen detection element formed of a solid electrolyte member is not sufficiently active, consuming a considerably long time before providing an electromotive force which is sufficiently large to be measurable. In order to cope with this problem, a rodlike heating member having a heating portion is inserted into a hollow portion of the oxygen detection element so as to activate the oxygen detection element through application of heat at the time of startup of the engine, thereby promptly rendering output (electromotive force) available for measurement at the time of startup of the engine, when exhaust gas contains a relatively large amount of harmful components.
In order to efficiently transmit to the oxygen detection element heat generated by the heating member, for improved activity of the oxygen detection element at the time of startup, the oxygen sensor may assume a structure such that the heating portion of the heating member is brought into contact with the inner wall surface of the hollow portion of the oxygen detection element. In such an oxygen sensor, a metallic terminal member—which is inserted into the hollow portion of the oxygen detection element and is electrically conductive with an internal electrode layer formed on the inner surface of the oxygen detection element—as a single or a plurality of holder portions (holder means), each having a substantially C-shaped cross section, so as to hold the heating member. Being held by means of the holder portion(s), the heating member is disposed within the oxygen detection element such that a front end portion of the heating member is in contact with the inner wall surface of the hollow portion of the oxygen detection element. In order to hold the heating member firmly and to maintain the end portion of the heating member in contact with the inner wall surface of the hollow portion of the oxygen detection element, the metallic terminal member including the holder portion(s) assumes a complicated form which requires bending in the course of manufacture thereof. Further, assembly of the oxygen sensor requires a jig for preliminarily attaching the heating member to the metallic terminal member. These features increase the cost of manufacture of the oxygen sensor.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a sensor structure which does not require attachment of special heating-member holder means to a metallic terminal member and which allows for simple assembly.
To achieve the above object, an oxygen sensor according to a first aspect of the invention is characterized by comprising:
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 of a hollow portion thereof;
a rodlike heating member disposed within the hollow portion of the oxygen detection element and adapted to heat the oxygen detection element; and
a metallic terminal member formed so as to circumferentially surround the heating member and having an attachment portion, which is fixedly attached to the inner surface of the oxygen detection element, directly or indirectly via another member.
The metallic terminal member includes at least one press portion for pressing the heating member in a direction intersecting the center axis of the hollow portion of the oxygen detection element.
The heating member is held by holding means formed separately from the metallic terminal member, and the press portion causes at least a portion of the heating member to be in contact with the inner wall surface of the hollow portion of the oxygen detection element.
According to the first aspect of the invention, the metallic terminal member includes a press portion for pressing the heating member in a direction intersecting the center axis of the hollow portion of the oxygen detection element. Also, the holding means for holding the heating member is formed separately from the metallic terminal member (i.e., the holding means is formed independently of the metallic terminal member). Thus, at least a portion of the heating member can be in contact with the inner wall surface of the hollow portion of the oxygen detection element without the metallic terminal member having special heating-member holder means. Further, assembly of the oxygen sensor does not require a jig for preliminarily attaching the heating member to the metallic terminal member, thereby reducing cost.
The term “contact” typically implies one of the following three kinds of so-called laterally-abutting structure, in which the surface of a heating portion formed at a front end portion of the heating member is laterally pressed against the inner wall surface of the hollow portion of the oxygen detection element.
(1) First it is conceivable that only a front-end portion of the surface of the heating member is in contact with the inner wall surface of the hollow portion (so-called point contact state or near point-contact state). This state of contact arises, for example, when the center axis of the heating member and that of the hollow portion intersect. In the vicinity of the heating portion of the heating member, the center axis of the heating member is laterally biased (offset) from the center axis of the hollow portion of the oxygen detection element.
(2) Next it is conceivable that the surface of the heating portion of the heating member is in contact with the inner wall surface of the hollow portion over a relatively long distance (so-called line contact state or near line-contact state). This state of contact arises, for example, when the center axis of the heating member is substantially in parallel with the center axis of the hollow portion of the oxygen detection element. The center axis of the heating member is laterally biased (offset) from the center axis of the hollow portion of the oxygen detection element.
(3) Further it is conceivable that the surface of the heating member is in contact with the inner wall surface of the hollow portion of the oxygen detection element over substantially the entire length of the heating member (so-called overall contact state or near overall-contact state). This state of contact arises, for example, when the center axis of the heating member approaches that of the hollow portion of the oxygen detection element such that the distance therebetween decreases toward the front-end side. The center axis of the heating member is laterally biased (offset) from the center axis of the hollow portion of the oxygen detection element.
Point contact, line contact, and overall contact are all applicable to the first aspect of the invention.
In the first aspect of the invention, the holding means for holding the heatin
Akatsuka Shoji
Ishikawa Satoshi
NGK Spark Plug Co. Ltd.
Tung T.
LandOfFree
Oxygen 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 Oxygen sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Oxygen sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3117984