Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing gas sample
Reexamination Certificate
1998-07-09
2001-04-03
Snay, Jeffrey (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing gas sample
C422S098000, C060S276000, C060S285000, C123S696000
Reexamination Certificate
active
06210641
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air-fuel control system for a gas fueled engine applicable to motor vehicles, generation of electricity, and other fields employing a natural gas as a principal component. Further, this invention relates to an O
2
sensor for air-fuel ratio control for use in an internal combustion engine or the like, which is used as an air-fuel ratio sensor or the like for detecting an air-fuel ratio over a wider area, and more particularly to a gas sensor suitable for a natural-gas-fueled engine.
2. Description of the Prior Art
Recently, a requirement for the suppression or inhibition of exhaust emissions (HC, CO, NO
x
, CO
2
) from an internal combustion engine has increased from the viewpoint of the improvement of atmospheric conditions. For meeting this suppression requirement, much attention has been focused on a natural-gas-used motor vehicle, or a motor vehicle with an engine for cogeneration, substituted for the conventional oil-used motor vehicle. A natural-gas-fueled engine for use in the natural-gas-used motor vehicle permits the reduction of the emission quantity of CO
2
, for example, as compared with a gasoline engine so that a clean exhaust emission characteristic is expectable. As a fuel supply system therefor, there has hitherto been known a system (gas mixer system) based upon a carburetor system for a LPG (Liquefied Pertroleum Gas)-used motor vehicle. Moreover, for further improvement of the exhaust emission characteristic to create a very-low-pollution motor vehicle equivalent to an electric motor vehicle, a high-accuracy air-fuel ratio control superior to the gas mixer system is essential, and from this point of view, for instance, the development of a natural-gas-used motor vehicle with an injection system providing less air-fuel ratio fluctuation and excellent in response characteristic has been in progress.
As well as such a natural-gas-fueled engine, a gasoline engine or the like is also desired to accomplish a clean exhaust emission, and therefore, in addition to the aforesaid high-accuracy air-fuel ratio control, a gas sensor for the control is required to more quickly operate after the engine start.
FIG. 58
is an illustration of an activation time of a sensor device and an exhaust emission in a traveling pattern in the case of an example of NO
x
emission quantity. From this illustration, it is found that shortening the activation time of the sensor device causes the exhaust emission to be significantly improvable.
The air-fuel ratio is under the feedback control based upon the output of an O
2
sensor installed in an exhaust pipe of an engine. For this reason, the promotion of the air-fuel ratio control accuracy significantly relies upon the enhancement of the detection accuracy of the O
2
sensor. However, if an O
2
sensor for a gasoline engine is used directly for detecting the air-fuel ratio in a natural-gas-fueled engine, a slippage or discrepancy occurs in the output characteristic of the O
2
sensor. This is because a natural gas contains methane as a principal component and the H/C ratio larger than that of a gasoline increases the quantity of hydrogen (H
2
) of an exhaust gas. This phenomenon takes place remarkably in an injection system.
That is, as compared with the gas mixer system which evenly mixes gases in an upstream portion of an intake passage and introduces it into a combustion chamber, the injection system made to directly inject a gas to the vicinity of a combustion chamber of the engine in order to ensure the response characteristic in the fuel control tends to create lack of uniformity of the mixture within the combustion chamber. Whereupon, a large amount of H
2
develops in an area where the air-fuel ratio is on the rich side within the combustion chamber, and the H
2
concentration of an exhaust gas becomes higher as compared with the gas mixer system, which adds to the slippage or deviation of the sensor output. For this reason, in the case of the O
2
sensor for a natural-gas-fueled engine, the elimination of the influence of H
2
on the sensor output leading to the slippage of the sensor output is inevitable for a high air-fuel ratio control accuracy.
In addition, the O
2
sensor or an air-fuel ratio sensor for detecting an air-fuel ratio over a wider area uses a detecting device made of an oxygen ion conductive solid electrolyte. This device does not work until its temperature rises to some extent. For example, the temperature is approximately 300° C. in the case of the O
2
sensor, whereas approximately 700° C. in the case of the air-fuel ratio sensor. That is, an important factor to operate the sensor more quickly is raising the device temperature more quickly, and particularly, a great problem lies in the case of the air-fuel ratio sensor requiring a high activation temperature.
Moreover, a natural-gas-fueled engine creates a problem in that, since a point where an electromotive force of an O
2
sensor (rich/lean sensor) rapidly varies shifts into a leaner zone with respect to a stoichiometric value (theoretical air-fuel ratio), the air-fuel ratio (A/F) goes into a lean condition to be output of a window of a three-way catalytic converter, thereby increasing the emission of NO
x
.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an air-fuel ratio control system for a gas-fueled engine which is capable of achieving the combustion in the target air-fuel ratio to certainly purify exhaust gases through the use of an exhaust emission purifying catalyst.
Another object of this invention is to provide an gas sensor which is capable of preventing the sensor output slippage caused by H
2
of an exhaust gas to greatly enhance the detection accuracy, thus allowing a high-accuracy air-fuel ratio control to improve the exhaust emission even if a large amount of H
2
exists in an exhaust gas, for example, like a natural-gas-fueled engine with an injection system does.
A further object of this invention is to provide a gas sensor whose temperature rises quickly so that the sensor operates more quickly.
As exemplified by “SAE 872165” or “Internal Combustion Engine” Vol. 28 No. 12, H
2
of the exhaust emitted from a natural-gas-fueled engine reaches approximately twice that of a gasoline engine. Thus, the present inventors consider that the reason why the air-fuel ratio is on a lean side is that, since H
2
of the exhaust gas shows a higher diffusion velocity or rate than that of O
2
, its component concentration differs from the component concentration of the actual exhaust gas on a reactive interface of a sensor.
Accordingly, in accordance with an aspect of the present invention, an air-fuel ratio control system for gas-fueled engine is equipped with a hydrogen invasion preventing means for preventing the invasion of hydrogen of an exhaust gas to a surface of an exhaust gas side electrode of an air-fuel ratio sensor.
This hydrogen invasion preventing means prevents the invasion of hydrogen to the surface of the exhaust gas side electrode to remove H
2
, causing a sensor output slippage or discrepancy, from a reactive interface (exhaust gas side electrode surface) of the sensor, so that the sensor output slippage is preventable and a suitable air-fuel ratio control is feasible.
Another aspect of an air-fuel ratio control system for a gas fueled engine according to this invention is that an exhaust gas side electrode of an air-fuel ratio sensor is coated with a catalyst layer which removes hydrogen through a catalytic reaction.
Coating the exhaust gas side electrode of the air-fuel ratio sensor with the catalyst layer can eliminate the problem of H
2
owing to the catalytic reaction, which removes H
2
, causing a sensor output slippage, from a reactive interface (exhaust gas side electrode surface) of the sensor, so that the sensor output slippage is preventable to ensure an adequate air-fuel ratio control.
A further aspect of an air-fuel ratio control system for a gas fueled engine according to this invention is that
Hayashi Hidetaka
Iizuka Motomasa
Kanehara Kenji
Kuroda Takahiko
Mizobuchi Takeshi
Denso Corporation
Pillsbury & Winthrop LLP
Snay Jeffrey
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