Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-07-12
2001-04-10
Tung, T. (Department: 1743)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S427000
Reexamination Certificate
active
06214186
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a gas sensor which may be employed in an air-fuel ratio control system for automotive vehicles for measuring the concentration of gas such O
2
, NOx, or CO, and more particularly to an improved structure of such a gas sensor which provides for ease of installation of a protective cover on a cover mount, firm engagement of the protective cover with the cover mount, and ease of machining of the cover mount.
2. Background Art
Typical gas sensors employed in measuring the concentration of O
2
, NOx, or CO in exhaust gasses of an internal combustion engine include a gas sensitive element, a sensor mount, and a protective cover. The sensor mount is used in mounting the sensor in an exhaust pipe and also serves as a holder which retains therein the gas sensitive element. The protective cover is installed on the sensor mount so as to cover the gas sensitive element. The gas sensors usually undergo a temperature change from room temperature to approximately 1000° C. after the engine is started, thereby causing thermal stress to be produced between the sensor mount and the protective cover, which may result in dislodgment of the protective cover from the sensor mount.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a simple structure of a gas sensor which provides for ease of installation of a protective cover on a cover mount, firm engagement of the protective cover with the cover mount, and ease of machining of the cover mount.
According to one aspect of the invention, there is provided a gas concentration sensor. The gas concentration sensor comprises: (a) a gas concentration measuring element having a gas-exposed portion exposed to a gas to be measured; (b) a hollow cylindrical holder holding therein the gas concentration measuring element, the holder having an end surface on which an inner and an outer extension are formed to define a groove therebetween, the inner extension being is smaller in height than the outer extension; and (c) a protective cover covering the gas-exposed portion of the gas concentration measuring element, the protective cover having a flange which is retained within the groove of the holder by crimping the outer extension inward to install the protective cover on the end surface of the holder.
In the preferred mode of the invention, a ratio of the height of the inner extension and the height of the outer extension lies within a range of 0.2 to 0.85.
The groove in the end surface of the holder is defined by side walls of the outer and inner extensions, a bottom formed between the side walls of the outer and inner extensions, and a tapered wall extending from the bottom to the side wall of the inner extension.
The height of the inner extension is greater than a thickness of the flange of the protective cover.
The protective cover has a hollow body. The flange of the protective cover consists of a curved portion continuing from the hollow body and a flat portion extending from the curved portion. The flange of the protective cover is retained within the groove of the holder in elastic engagement of an end of the flat portion, the flat portion, and the curved portion with the side wall of the outer extension, the bottom, and the tapered wall, respectively.
At least one inner protective cover is further disposed inside the protective cover. The inner protective cover has a flange retained within the groove of the holder together with the flange of the protective cover by the crimped outer extension.
The inner protective cover may be attached directly to the flange of the protective cover.
The protective cover and the inner protective cover have formed therein gas holes through which the gas enters inside the protective cover and the inner cover. One of the gas holes of the inner protective cover closest to the holder is closer to the holder than one of the gas holes of the protective cover closest to the holder.
The flange of one of the protective cover and the inner protective cover may have a corrugated surface which is in contact with the flange of the other cover.
The holder is formed with a forged member.
The holder is made of material having a hardness lower than that of the protective cover.
According to the second aspect of the invention, there is provided a gas concentration sensor which comprises: (a) a gas concentration measuring element having a gas-exposed portion exposed to a gas to be measured; (b) a hollow cylindrical holder holding therein the gas concentration measuring element, the holder having an end surface on which an inner and an outer extension are formed; (c) a groove formed in the end surface of the holder, the groove being defined by side walls of the outer and inner extensions, a bottom formed between the side walls of the outer and inner extensions, and a tapered wall extending from the bottom to the side wall of the inner extension; and (d) a protective cover covering the gas-exposed portion of the gas concentration measuring element, the protective cover having a flange which is retained within the groove of the holder by crimping the outer extension inward to install the protective cover on the end surface of the holder. In the preferred mode of the invention, the geometry of the groove of the holder is so determined that the flange of the protective cover may be fitted in the groove with a clearance of 0.4 mm or less between the flange and the bottom before the outer extension is crimped.
Specifically, the size and inclination of the tapered wall of the groove may be so determined that the flange of the protective cover may be fitted in the groove with a clearance of 0.4 mm or less between the flange and the bottom before the outer extension is crimped.
According to the third aspect of the invention, there is provided a gas concentration sensor which comprises: (a) a gas concentration measuring element having a gas-exposed portion exposed to a gas to be measured; (b) a hollow cylindrical holder holding therein the gas concentration measuring element, the holder having an end surface on which an inner and an outer extension are formed to define a groove therebetween; (c) an outer protective cover covering the gas-exposed portion of the gas concentration measuring element, the outer protective cover having a flange which is retained within the groove of the holder by crimping the outer extension inward to install the outer protective cover on the end surface of the holder; and (d) an inner protective cover disposed inside the outer protective cover, the inner protective cover having a flange which is retained within the groove of the holder in engagement with the flange of the outer protective cover by crimping the outer extension inward to install the inner protective cover on the end surface of the holder. The flange of one of the outer and inner protective cover has formed thereon protrusions which engage the flange of the other.
In the preferred mode of the invention, a third protective cover is provided which has a flange retained within the groove of the holder in engagement with the flange of one of the outer and inner protective covers which has the protrusions.
The protrusions are formed with undulation of a surface of the flange of the one of the outer and inner protective covers.
The outer protective cover may have the protrusions formed on the flange thereof.
A clearance of 0.05 to 0.2 mm is developed between the inner extension and an inner wall of the inner protective cover.
The holder is made of material having a hardness lower than that of the outer and inner protective covers.
The groove in the end surface of the holder is defined by side walls of the outer and inner extensions, a bottom formed between the side walls of the outer and inner extensions, and a tapered wall extending from the bottom to the side wall of the inner extension. Each of the outer and inner protectiv
Kojima Takashi
Watanabe Isao
Yamada Hirokazu
Denso Corporation
Pillsbury & Winthrop LLP
Tung T.
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