Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-07-26
2003-03-04
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S408000, C204S427000, C204S428000
Reexamination Certificate
active
06527928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for assembling a heater-equipped air-fuel ratio sensor, which is preferably installed on an exhaust gas emission system of an internal combustion engine for automotive vehicles and others.
2. Related Art
In general, to improve the exhaust gas purification efficiency, an air-fuel ratio of exhaust gas is sensed by an air-fuel ratio sensor, such as an oxygen (O
2
) sensor. An air-fuel ratio sensor usually comprises a cylindrical or cup-shaped sensor element having an open end and an opposed closed end with an inside chamber. A stick-like heater is inserted in the inside chamber of this sensor element.
The heater is necessary to warm up the sensor element quickly to its active temperature during an engine start-up condition where the engine is operated at a low temperature.
More specifically, a portion sensing an air-fuel ratio of exhaust gas is a particular portion of the sensor element which is subjected to the exhaust gas (i.e. gas to be sensed), normally the front end of the sensor element. Accordingly, in the detection of the air-fuel ratio, it is definitely necessary to heat up the sensitive portion of the air-fuel ratio sensor to its active temperature. Without this warmup operation, the sensor element cannot operate accurately nor its characteristics is stabilized.
For example, Japanese Patent No. 5-46498, published in 1993, discloses this kind of air-fuel ratio sensor. According to this prior art, a heater is united with a fixing metal by soldering and the fixing metal is fixed to the open end of an inside chamber by means of a coil spring.
Furthermore, Japanese Patent No. 6-3430, published in 1994, discloses another air-fuel ratio sensor. According to this prior art, a heater is fixed to an inside chamber by utilizing a fixing metal, although the heater and the fixing metal are not united.
Meanwhile, to satisfy the exhaust gas emission requirements strictly regulated year by year, it is required to detect an air-fuel ratio within a short time period even immediately after an engine is just started up. One measure for solving this requirement is to dispose a heater as close as possible to the sensitive edge of the sensor element. By doing so, heat generated from the heater is effectively used to warm up the sensitive edge of the sensor element. More specifically, it is most preferable to bring the tip end of the heater into contact with the bottom surface of the inside chamber and to keep the contact between the heater and the bottom surface.
However, there are following problems in assembling the heater in the sensor element.
There is a necessity of checking or confirming during the assembling operation that the tip end of the heater is surely brought into contact with the bottom surface of the inside chamber.
Both of the sensor element and the heater are fragile and weak against shock. Hence, if the heater is forcibly inserted into the inside chamber of the sensor element by applying an excessively large force, there will be a possibility that either the sensor element or the heater is damaged.
SUMMARY OF THE INVENTION
Accordingly, in view of above-described problems encountered in the related art, a principal object of the present invention is to provide an improved method for assembling a heater-equipped air-fuel sensor which is capable of surely bringing the tip end of a heater into contact with the bottom surface of an inside chamber of a sensor element without damaging the heater and the sensor element.
In order to accomplish this and other related objects, the present invention provides a novel and excellent assembling method for a heater-equipped air-fuel ratio sensor having various aspects as described hereinafter.
A first aspect of the present invention provides an method for assembling a heater-equipped air-fuel ratio sensor which comprises a cylindrical sensor element having an open end and an opposed closed end with an inside chamber defined therein and a stick-like heater inserted in the inside chamber of the sensor element so that a tip end of the heater is brought into contact with a bottom surface of the inside chamber, and the heater is supported to the sensor element by a metallic holder.
More specifically, the first aspect assembling method comprises the steps of inserting the heater into the inside chamber of the sensor element until the tip end of the heater is brought into contact with the bottom surface of the inside chamber, and sliding the metallic holder along an outside surface of the heater toward the bottom surface of the inside chamber until the metallic holder is engaged with the sensor element.
A function of the above-described first aspect assembling method will be explained hereinafter.
According to the first aspect assembling method, the stick-like heater is inserted into the inside chamber of the sensor element so that the tip end of the heater can be brought into contact with the bottom surface of the inside chamber. Then, the metallic holder is fixed to the sensor element.
Accordingly, it becomes possible to prevent the heater from interfering with other components of this air-fuel ratio sensor, and therefore it becomes possible to bring the tip end of the heater safely into contact with the bottom surface of the inside chamber. In other words, the heater can be smoothly installed to a predetermined position in the sensor element.
Then, the metallic holder is elastically installed on the heater under the condition where the heater keeps contact with the bottom surface of the inside chamber.
Next, the metallic holder slides along the outer surface of the heater and shifts toward the bottom surface of the sensor element. When the metallic holder is slid along the outer surface of the heater, a sliding frictional force is caused between a heater holding portion (described later) and the outer surface of the heater. With this sliding frictional force, the heater can be firmly pressed to the bottom surface of the inside chamber. The contact between the tip end of the heater and the bottom surface of the inside chamber is maintained until the metallic holder is fixed to the open end of the sensor element. Accordingly, the tip end of the heater is surely fixed while keeping contact with the bottom surface of the inside chamber.
As described above, a force acting on the bottom surface of the sensor element is substantially equivalent to a pressing force acting in the axial direction by the above-described sliding frictional force. Thus, the heater can be fixed in the inside chamber with its tip end kept in firm contact with bottom surface of the inside chamber without adding an excessive force to the sensor element. Furthermore, the sensor element and the heater can be surely prevented from being damaged during their assembly.
According to the above-described first aspect of the invention, it becomes possible to provide an assembling method for a heater-equipped air-fuel ratio sensor which is capable of surely bringing the tip end of the heater into contact with the bottom surface of the inside chamber of the sensor element, without damaging the sensor element and the heater during their assembly.
Next, it is possible to install the metallic holder to the sensor element at an intermediate portion of the wall of the inside chamber between the bottom surface and a open end (described below).
Furthermore, it is possible to fix the metallic holder to the open end region of the sensor element. In this case, the open end region the sensor element includes both of inside and outside surfaces of the sensor element as well as the opened top surface of the sensor element.
Even further, it is preferable to provide a tapered portion or a shoulder portion somewhere in the open end region or on the wall of the inside chamber of the sensor element for supporting the metallic holder.
According to preferred embodiments of the present invention, it is preferable that the above-described first aspect assembling method further comprise a step of installing the meta
Fukutani Masanori
Watanabe Isao
Yamakawa Michihiro
Denso Corporation
Nixon & Vanderhye PC
Tung T.
LandOfFree
Heater-equipped air-fuel ratio 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 Heater-equipped air-fuel ratio sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heater-equipped air-fuel ratio sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3008919