Measuring and testing – Gas analysis – Gas of combustion
Reexamination Certificate
1998-11-20
2002-03-12
Dombroske, George (Department: 2855)
Measuring and testing
Gas analysis
Gas of combustion
C060S276000
Reexamination Certificate
active
06354134
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a heater-equipped oxygen sensing element which is preferably installed in an internal combustion engine to detect the concentration of oxygen gas involved in the exhaust gas and control an air-fuel ratio of the internal combustion engine.
To control the air-fuel ratio, internal combustion engines have oxygen sensing elements provided in their exhaust passages.
For example, a conventional oxygen sensing element comprises a cup-shaped solid electrolytic body having an inside space serving as a reference chamber, a sensing electrode provided on an outer surface of the solid electrolytic body so as to be exposed to measuring gas, and a reference electrode provided on an inner surface of the solid electrolytic body. The sensing electrode and the reference electrode may extend entirely or partly on the inner and outer surfaces of the solid electrolytic body (refer to Unexamined Japanese Patent Application No. SHO 58-73857).
Furthermore, an electric heater is disposed in the reference chamber. This kind of oxygen sensing elements do not operate properly until their temperature reaches a predetermined temperature level. Thus, the heater is usually equipped to quickly increase the temperature of the oxygen sensing element when the ambient temperature is low, thereby reducing a deactivated duration and correctly measuring the oxygen concentration.
However, this kind of conventional oxygen sensing elements have the following problems.
The outer surface of the oxygen sensing element has a gas receiving surface region extending from a distal end of the sensing element to a position spaced by a distance L away from the distal end of the sensing element. The gas receiving surface region is exposed to the measuring gas whose temperature increases to a higher temperature level during the operation of this sensing element.
When the sensing electrode and the reference electrode are formed entirely on the outside and inside surfaces of the solid electrolytic body, the oxygen sensing element produces a sensor signal equivalent to a composite output from a plurality of electric circuits sequentially arranged from a high-temperature section to a low-temperature section along an entire surface of the solid electrolytic body. When the oxygen sensing element has a low-temperature portion, its sensor output and response will deteriorate due to insufficient activation at the low-temperature portion.
Furthermore, similar problems may arise even when the sensing electrode and the reference electrode are formed partly on the outer and inner surfaces of the solid electrolytic body. For example, when these electrodes are located in the low-temperature region, the sensor will produce an inaccurate sensor output due to insufficient activation at the low-temperature portion.
The oxygen sensing elements, when installed in the exhaust passage of an internal combustion engine, need to produce an accurate sensor output within a short period of time after the internal combustion engine starts its operation. To satisfy this requirement, the oxygen sensing elements must operate properly with a short dead time which is required for the heater to increase the temperature of the solid electrolytic body to a predetermined active level. These requirements were difficult goals to attain for the conventional oxygen sensing elements.
SUMMARY OF THE INVENTION
In view of the conventional problems, the present invention has an object to provide an oxygen sensing element that is rapid in activation and excellent in response.
To accomplish this and other related objects, one aspect of the present invention provides an oxygen sensing element comprising a cup-shaped solid electrolytic body with one end closed and an inside space serving as a reference gas chamber, a sensing electrode provided on an outer surface of the solid electrolytic body so as to be exposed to measuring gas, a reference electrode provided on an inner surface of the solid electrolytic body, and a heater disposed in the inside space of the reference gas chamber. A contact portion comprises a region where the heater is brought into contact with the inner surface of the solid electrolytic body and an opposing region on the outer surface of the solid electrolytic body. The sensing electrode includes at least part of the contact portion. A gas receiving surface region, exposed to the measuring gas when the oxygen sensing element is operated, is provided on the outer surface of the oxygen sensing element so as to extend from a distal end of the oxygen sensing element to a position spaced by a distance L away from the distal end of the oxygen sensing element. At least part of the contact portion is located in a region extending from the distal end of the oxygen sensing element to a position spaced by a distance 0.4L away from the distal end of the oxygen sensing element. And, the sensing electrode is entirely located in a region extending from the distal end of the oxygen sensing element to a position spaced by a distance 0.8L away from the distal end of the oxygen sensing element.
With this arrangement, the inner surface is brought into contact with the heater at the contact portion. The sensing electrode includes at least part of the contact portion.
FIG. 5
shows the contact portion including an inner point “Pi” where the heater is brought into contact with the inner surface of the solid electrolytic body and an outer point “Po” opposing the inner point “Pi” via the solid electrolytic body, together with a neighboring region including the vicinity of these points “Pi” and “Po.”
The contact portion on the inner surface may be a point (or points), a line (or lines), or a surface (or surfaces) which depends on the contact condition between the heater and the inner surface. The heater may be brought into contact with the inner surface at a single portion or a plurality of portions.
The gas receiving surface region is directly exposed to the measuring gas when the oxygen sensing element is operated. The gas receiving surface region has a neighbored surface region that is not exposed to the measuring gas. A clearance between the gas receiving surface region and the neighbored surface region is sealed by a packing, such as a metallic spring, which is capable of preventing gas leakage.
At least part of the contact portion is located in the region extending from the distal end of the oxygen sensing element to the position spaced by the distance 0.4L away from the distal end of the oxygen sensing element. If the contact portion is located at an altitudinal level higher than this region, heat leakage toward the upper low-temperature region of the oxygen sensing element will increase. This will result in insufficient temperature increase at the contact portion. Activation of the oxygen sensing element will be delayed.
The sensing electrode is entirely located in the region extending from the distal end of the oxygen sensing element to the position spaced by the distance 0.8L away from the distal end of the oxygen sensing element. If the sensing electrode is not completely located in this region, the sensing electrode temperature may decrease locally. Such a local temperature reduction will result in deteriorated response in the sensor performance.
The heater includes a resistor element generating heat in response to supplied electric power. It is preferable that the heat-generating resistor element opposes the measuring electrode. With this arrangement, it becomes possible to effectively heat the sensing electrode, enhancing the activity of the oxygen sensing element.
The oxygen sensor of the present invention operates in the following manner. The inner surface of the oxygen sensing element is brought into contact with the heater at the contact portion. The sensing electrode includes at least part of the contact portion.
Heat generated from the heater is directly transmitted to the sensing electrode via the inner surface and the solid electrolytic body. Thus, the sensing electrode is directly heated by the heater. Ac
Fujii Namitsugu
Katafuchi Tooru
Kobayashi Kiyomi
Sano Hiromi
Denso Corporation
Dombroske George
Pillsbury Madison & Sutro LLP
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