Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-11-27
2004-03-02
Tung, T. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S425000, C204S426000, C204S427000, C204S428000
Reexamination Certificate
active
06699376
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensing element and a gas sensor used for controlling the combustion of an internal combustion engine.
Conventionally, a gas sensor is equipped in an exhaust gas system of an automotive vehicle to control an air-fuel ratio of gas mixture introduced into an internal combustion engine.
A gas sensing element, disposed in the gas sensor, usually comprises a solid electrolytic substrate having oxygen ion conductivity, a measured gas side electrode provided on the solid electrolytic substrate so as to be exposed to a measured gas, and a reference gas side electrode provided on the solid electrolytic substrate so as to be exposed to a reference gas.
The gas sensing element obtains a sensing value (e.g., limit current value) representing the concentration of oxygen involved in exhaust gas. The sensing value of the gas sensing element reflects the air-fuel ratio in a combustion chamber of an internal combustion engine.
The internal combustion engine is often left in an inoperative condition for a long time (e.g., several hours and several days). It is conventionally known that the gas sensing element produces an extraordinary output at a moment the engine is operated again after such a long interruption.
This kind of extraordinary sensor output continues for several seconds to several tens seconds after a cold starting up of the engine. During this period, the sensor output shifts with a great extent to the rich side (refer to a later-described characteristic curve (c) shown in FIG.
4
).
In response to such an abnormal sensor output (i.e., an extraordinary rich signal), an engine control system adjusts an air-fuel ratio of the gas mixture introduced into the combustion chamber to a lean side.
However, the detected extraordinary rich signal does not reflect an actual air-fuel condition in the combustion chamber. Continuously generating a lean signal during a significant period will result in an excessive increase of oxygen in the combustion chamber. The fuel amount reduces contrarily and will stop the engine due to the shortage of fuel.
The occurrence of such an extraordinary sensor output is generally limited to a first startup operation when the engine is driven after a long-term interruption. Such a problem is no longer found in the second or succeeding startup operations.
SUMMARY OF THE INVENTION
To solve the above-described problems, an object of the present invention is to provide a gas sensing element and a gas sensor capable of accurately detecting the oxygen concentration as well as the air-fuel ratio even after the engine is left in an inoperative condition for a long time.
In order to accomplish the above and other related objects, the present invention provides a first gas sensing element comprising a solid electrolytic substrate. A measured gas side electrode is provided on one surface of the solid electrolytic substrate so as to be exposed to a measured gas. A reference gas side electrode is provided on an opposite surface of the solid electrolytic substrate so as to be exposed to a reference gas stored in a reference gas chamber. And, a water-vapor absorbing member is provided in the reference gas chamber.
The first gas sensing element of this invention is characterized in that the water-vapor absorbing member is provided in the reference gas chamber.
The water-vapor absorbing member is any substance capable of trapping water components and is not limited to a specific material. Details of the water-vapor absorbing member will be explained later.
The first gas sensing element of this invention operates in the following manner.
First of all, it is believed that the abnormal sensor output is produced according to the following mechanism.
The gas sensing element, after being left for a long time (several hours or several days), produces an abnormal sensor output. The magnitude of the abnormal sensor output is dependent on the humidity of an atmosphere in which the gas sensing element is left.
The inventor of the present invention has heated a gas sensing element being left for a long term to check the component of a gas leaving out of this gas sensing element and detected a great amount of H
2
O adhering on the gas sensing element.
Namely, when a gas sensing element is left in an atmosphere including moisture, water molecules adhere or settle on a reference gas side electrode. The largeness of an abnormal sensor output shows the presence of a great amount of water molecules. It is believed that a large surface roughness of the reference gas electrode allows the water molecules to easily adhere or settle on the surface of the reference gas side electrode. Once the water molecules adhere or settle on the electrode surface, another water molecules easily accumulate thereon through hydrogen bridge.
The gas sensing element in such condition is subjected to heat upon starting the operation of the engine.
As shown in
FIG. 2
, the supply of heat and the catalytic function of a reference gas side electrode
112
cooperatively activate the water molecules adhering on the surface of a solid electrolytic substrate
12
and decompose them into oxygen atoms and hydrogen atoms. Oxygen atoms, when ionized, move toward a measured gas side electrode
111
across the solid electrolytic substrate
12
as an oxygen ion current. The oxygen ion current thus produced is believed to cause an abnormal sensor output.
Once all of the water molecules have decomposed, no abnormal sensor output is produced. Hence, no problem occurs in the second and succeeding startup operations of the engine as long as no water molecules remain on the surface of the reference gas side electrode.
In view of the above, the present invention provides the water-vapor absorbing member in the reference gas chamber to prevent the water molecules from adhering on the surface of the reference gas side electrode. Thus, it becomes possible to obtain an accurate sensor output reflecting an actual oxygen concentration in the measured gas.
As apparent from the foregoing description, the present invention provides an excellent gas sensing element capable of accurately detecting the oxygen concentration as well as the air-fuel ratio even after the engine is left in an inoperative condition for a long time.
According to a preferable embodiment of the present invention, the water-vapor absorbing member is provided so as to close an inside space of the reference gas chamber.
This arrangement makes it possible to prevent the water vapor from entering into the reference gas chamber.
The water-vapor absorbing member can be provided at an opening end of the reference gas chamber so as to close the opening end entirely as shown in FIG.
1
. In general, the opening end of the reference gas chamber is a place where the temperature is not so increased. Thus, a member not strong against heat can be used as the water-vapor absorbing member.
Furthermore, as shown in
FIG. 3
, it is possible to provide the water-vapor absorbing member at an intermediate position so as to close a middle part of the reference gas chamber. This arrangement is advantageous in that the water-vapor absorbing member is free from damage when the gas sensing element is installed in a gas sensor.
In any case, it is preferable to the water-vapor absorbing member is disposed entirely along the inside wall of the reference gas chamber so as to prevent the water vapor from reaching the reference gas side electrode.
According to the preferable embodiment of the present invention, the water-vapor absorbing member is provided so as to cover the reference gas side electrode provided in the reference gas chamber (refer to FIG.
5
).
This arrangement surely prevents the water molecules from reaching the reference gas side electrode.
According to the preferable embodiment of the present invention, the water-vapor absorbing member is porous.
When the water vapor passes through the porous member, the water vapor collides with a wall surface of a labyrinth formed in this porous member. The wall surface absorbs (i.e., traps
Denso Corporation
Nixon & Vanderhye PC
Tung T.
LandOfFree
Gas sensing element and gas 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 Gas sensing element and gas sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gas sensing element and gas sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3235568