Electricity: measuring and testing – Using ionization effects – For analysis of gas – vapor – or particles of matter
Reexamination Certificate
1998-11-20
2001-04-24
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Using ionization effects
For analysis of gas, vapor, or particles of matter
C204S424000
Reexamination Certificate
active
06222372
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an improvement on a gas sensor which may be employed in an oxygen measuring device of an air-fuel ratio control system measuring an oxygen content in exhaust gasses of an internal combustion engine of automotive vehicles.
2. Background of Related Art
For burning control of fuel in internal combustion engines of automotive vehicles, an air-fuel ratio sensor is installed in an exhaust system to measure an air-fuel ratio. Such an air-fuel ratio sensor is usually implemented with an oxygen sensor which has a pair of electrodes one of which is exposed to a gas to be measured and the other is exposed to a reference gas introduced into a reference gas chamber from the outside of the oxygen sensor.
In recent years, in order to improve installation of the oxygen sensor in the vehicle and decrease manufacturing costs thereof, the size of the oxygen sensor is required to be decreased. To this end, there has been proposed an improved structure in which the length of the oxygen sensor is shortened, and an outer cover or other parts are joined by crimping. The crimping, however, leads to a problem of reducing an area of a gas passage introducing the reference gas into the reference gas chamber, which will cause the flow of the reference gas to be lowered, resulting in a decrease in measuring accuracy.
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 compact structure of a gas sensor capable of measuring a given component content in gasses with desired accuracy.
According to one aspect of the present invention, there is provided a gas sensor measuring a given component content in a gas which comprises: (a) a housing; (b) a sensing unit having a given length, disposed in the housing, the sensing unit having defined in one end portion thereof a reference gas chamber to be filled with a reference gas and also having installed in the one end portion a measuring electrode to be exposed to the gas to be measured and a reference electrode to be exposed to the reference gas in the reference gas chamber, the measuring electrode and the reference electrode being disposed adjacent each other through a solid electrolyte body and providing through signal pickup leads sensor signals which are used in determining the given component content in the gas; (c) a first metallic cover installed on the housing to cover the other end portion of the sensing unit; (d) a second metallic cover installed on a periphery of the first metallic cover through a water-repellent filter, the second metallic cover being crimped to be joined to the first metallic cover through the water-repellent filter; (e) a first vent formed in the first metallic cover; (f) a second vent formed in the second metallic cover which communicates with the first vent through the water-repellent filter to introduce the reference gas into the reference gas chamber through a reference gas passage extending from the second vent to the reference gas chamber; and (g) an insulator mounted within the first metallic cover, having formed therein holes through which the signal pickup leads pass, the insulator having an outer wall different in geometry from an inner wall of the first metallic cover to define a portion of the reference gas passage between the outer wall of the insulator and the inner wall of the first metallic cover.
In the preferred mode of the invention, the portion of the reference gas passage faces the first vent of the first metallic cover.
The insulator is made of a cylindrical member. The portion of the reference gas passage defined between the outer wall of the insulator and the inner wall of the first metallic cover is determined in sectional area as a function of a maximum and minimum diameter of the insulator. A ratio of the minimum diameter to the maximum diameter is within a range of 0.8 to 0.95.
The outer wall of the insulator is of a polygonal shape which has either of flat surfaces and recessed surfaces each lying between adjacent two of vertexes so that the portion of the reference gas passage may include clearances between either of the flat surfaces and the recessed surfaces and the inner wall of the first metallic cover.
The outer wall of the insulator holder is of an octagonal shape.
The outer wall of the insulator has curved surfaces and either of flat surfaces and recessed surfaces each lying between adjacent two of the curved surfaces. The curved surfaces are opposed to each other so that the portion of the reference gas passages may include clearances between either of the flat surfaces and the recessed surfaces and the inner wall of the first metallic cover.
The outer wall of the insulator may be oval.
The second metallic cover has an opening through which the signal pickup leads extend to the outside of the second metallic cover. A sealing member is disposed in the second metallic cover to seal the opening and lies above the insulator with a clearance therebetween communicating with the portion of the reference gas passage between the outer wall of the insulator and the inner wall of the first metallic cover.
A spacer member may be disposed between the sealing member and the insulator to define the clearance communicating with the portion of the reference gas passage.
The sealing member may have a flange which is supported by ends of the first and second metallic covers.
The insulator may have a vent which defines a second portion of the reference gas passage.
The first metallic cover includes an outer cover member and an inner cover member. The outer cover member is so crimped to be joined to the inner cover member. The inner cover member has an end caulked to the housing.
According to the second aspect of the invention, there is provided a gas sensor measuring a given component content in a gas which comprises: (a) a housing; (b) a sensing unit having a given length, disposed in the housing, the sensing unit having defined in one end portion thereof a reference gas chamber to be filled with a reference gas and also having installed in the one end portion a measuring electrode to be exposed to the gas to be measured and a reference electrode to be exposed to the reference gas in the reference gas chamber, the measuring electrode and the reference electrode being disposed adjacent each other through a solid electrolyte body and providing through signal pickup leads sensor signals which are used in determining the given component content in the gas; (c) a first metallic cover having first and second ends, the first metallic cover being installed at the first end on the housing to cover the other end portion of the sensing unit and defining an opening in the second end; (d) a second metallic cover installed on a peripheral portion of the first metallic cover through a water-repellent filter, the second metallic cover being crimped to be joined to the first metallic cover through the water-repellent filter; (e) a first vent formed in the first metallic cover; (fl a second vent formed in the second metallic cover which communicates with the first vent through the water-repellent filter to introduce the reference gas into the reference gas chamber through a reference gas passage extending from the second vent to the reference gas chamber; (g) an insulator mounted within the first metallic cover, having formed therein holes through which the signal pickup leads pass; and (h) a sealing member sealing the opening defined in the second end of the first metallic cover, the sealing member having formed thereon a protrusion in contact with the insulator to define a gap between the sealing member and the insulator which occupies a portion of the reference gas passage.
In the preferred mode of the invention, the sealing member is disposed within the second end of the first metallic cover.
According to the third aspect of the invention, there is provided a gas sensor measuring a given comp
Fukaya Kenji
Kojima Takashi
Watanabe Isao
Yamada Hirokazu
Yamauchi Masanobu
Denso Corporation
Kerveros James C
Metjahic Safet
Pillsbury & Winthrop LLP
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