Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2002-12-06
2004-08-10
Nguyen, Tu M. (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S274000, C060S276000, C060S297000
Reexamination Certificate
active
06772586
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of detecting a failure of a humidity sensor that is disposed in the vicinity of a hydrocarbon adsorbent in the exhaust system of an internal combustion engine.
2. Description of the Related Art
Some known exhaust systems of internal combustion engines have an exhaust gas purifier disposed in the exhaust passage, which may comprise a hydrocarbon adsorbent such as zeolite or a hydrocarbon adsorption catalyst comprising a composite combination of a hydrocarbon adsorbent and a three-way catalyst, for adsorbing hydrocarbons (HC) in the exhaust gas while the catalytic converter such as a three-way catalyst or the like is not functioning sufficiently, i.e., while the catalytic converter is not sufficiently high in temperature and not activated as when the internal combustion engine starts to operate at a low temperature. The hydrocarbon adsorbent has a function to adsorb hydrocarbons in the exhaust gas at relatively low temperatures below 100° C., for example, and operates to release the adsorbed hydrocarbons when heated to a certain temperature in the range from 100 to 250° C., for example.
The applicant of the present application has attempted to evaluate a deteriorated state of the hydrocarbon adsorbent based on the output of a humidity sensor, which is disposed in the vicinity of the hydrocarbon adsorbent, e.g., downstream of the hydrocarbon adsorbent, under a certain operating condition of the internal combustion engine such as when the internal combustion engine is idling immediately after it has been started (see, for example, Japanese laid-open patent publication No. 2001-323811). The above evaluating technique is based on the fact that the hydrocarbon adsorbent has a property of adsorbing not only HC but also water contained in the exhaust gases emitted from the internal combustion engine, and the HC adsorbing ability (the maximum amount of HC that can be adsorbed) and the water adsorbing ability (the maximum amount of water that can be adsorbed) of the hydrocarbon adsorbent are highly correlated to each other. According to this evaluating process, the amount of water adsorbed by the hydrocarbon adsorbent is recognized based on the output of the humidity sensor, and the deteriorated state of the hydrocarbon adsorbent is evaluated based on the recognized amount of water adsorbed by the hydrocarbon adsorbent.
However, the above evaluating process fails to evaluate the deteriorated state of the hydrocarbon adsorbent in the event that the humidity sensor fails to operate. Therefore, it is desirous to have a technique on hand for detected whether or not the humidity sensor has suffered a failure i.e., whether or not the humidity sensor is normal.
One proposal is to detect whether or not the humidity sensor has suffered a failure based on the output of the humidity sensor in a certain operating state of the internal combustion engine. However, the internal combustion engines on automobiles operate in various operating states which tend to fluctuate with time or vary under various conditions. The internal combustion engines may not necessarily operate reliably in a certain operating state in which it is possible to detect whether or not the humidity sensor has suffered a failure. As the operating states of the internal combustion engines are liable to fluctuate with time, the output of the humidity sensor is subject to variations in the responsiveness thereof. It is thus generally difficult to detect whether or not the humidity sensor has suffered a failure in a certain operating state of the internal combustion engine.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of detecting, stably and easily, a failure of a humidity sensor disposed in the vicinity of a hydrocarbon adsorbent in the exhaust system of an internal combustion engine.
According to the present invention, the humidity in the exhaust passage of an internal combustion engine near a hydrocarbon adsorbent disposed therein changes after the internal combustion engine is shut off, as follows: When the internal combustion engine is shut off after it has been normally operated continuously for a certain period of time, the humidity of the exhaust gas decreases as the hydrocarbon adsorbent adsorbs moisture in an exhaust gas remaining thereafter after the temperature of the hydrocarbon adsorbent has dropped to a temperature capable of adsorbing the moisture. When the adsorption of the moisture by the hydrocarbon adsorbent is saturated, the humidity near (around) the hydrocarbon adsorbent becomes substantially constant, or more specifically, its time-dependent changes are extremely small. The humidity which has become substantially constant near the hydrocarbon adsorbent changes depending on the deteriorated state of the hydrocarbon adsorbent, i.e., the humidity is higher as the deterioration of the hydrocarbon adsorbent progresses. If the humidity sensor is normal, however, the humidity falls in a certain range. Finally, because a gas exchange progresses between the exhaust passage and its exterior (generally, the gas exchange progresses very slowly), the humidity in the exhaust passage is converged to a humidity equivalent to the humidity outside of the exhaust passage.
A method of detecting a failure of a humidity sensor according to the present invention has been devised in view of the above phenomenon. According to the present invention, there is provided a method of detecting a failure of a humidity sensor in an exhaust system having a hydrocarbon adsorbent disposed in an exhaust passage of an internal combustion engine for adsorbing hydrocarbons contained in an exhaust gas emitted from the internal combustion engine, the humidity sensor being disposed in the exhaust passage for detecting a humidity in the exhaust passage near the hydrocarbon adsorbent, the method comprising the step of detecting whether or not the humidity sensor has failed based on an output signal of the humidity sensor within a predetermined period in which the output signal of the humidity sensor is substantially constant and a humidity represented by the output signal of the humidity sensor is not converged to a humidity outside of the exhaust passage, after the internal combustion engine is shut off.
The output signal from the humidity sensor in the predetermined period, which is used in detecting whether or not the humidity sensor has failed, corresponds to the humidity (detected humidity) near the hydrocarbon adsorbent when the humidity near (around) the hydrocarbon adsorbent is substantially constant and in a state before the humidity near (around) the hydrocarbon adsorbent is converted to the humidity outside of the exhaust passage after the internal combustion engine is shut off (such a state will hereafter be referred to occasionally as “steady humidity state”). Because the hydrocarbon adsorbent and the state of the exhaust gas around the humidity sensor near the hydrocarbon adsorbent are substantially static (steady) in the predetermined period as the internal combustion engine is shut off, the output signal from the humidity sensor in the predetermined period is highly stable. Because the output signal from the humidity sensor in the predetermined period depends on the steady humidity, it is not affected by variations in the responsiveness of the humidity sensor. Accordingly, it is possible to detect stably and easily whether or not the humidity sensor has failed based on the output signal from the humidity sensor within the predetermined period.
According to the present invention, the predetermined period comprises, for example, a period after a lapse of a predetermined time at least after the internal combustion engine is shut off. Specifically, until the hydrocarbon adsorbent adsorbs moisture therearound and is saturated, i.e., until the steady humidity state is initiated, after the internal combustion engine is shut off, a certain period of time (two to four hours for the exhaust system of an
Abe Kenji
Komine Masao
Miyahara Yasuyuki
Ohmori Kenichi
Watanabe Norihito
Armstrong Kratz Quintos Hanson & Brooks, LLP
Honda Giken Kogyo Kabushiki Kaisha
Nguyen Tu M.
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