Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2002-10-11
2004-10-05
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
06799420
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of evaluating a deteriorated state of a hydrocarbon adsorbent which is disposed in the exhaust passage of an internal combustion engine for adsorbing hydrocarbons in an exhaust gas emitted from the internal combustion engine.
2. Description of the Related Art
Some known systems for purifying exhaust gases emitted from 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 adsorbing 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, such as when the internal combustion engine starts to operate at a low temperature. The hydrocarbon adsorbent functions 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.
One conventional technique for evaluating a deteriorated state of such a hydrocarbon adsorbent is disclosed in Japanese laid-open patent publication No. 10-159543, for example. According to the disclosed technique, temperature sensors are positioned respectively upstream and downstream of an exhaust gas purifier which has the hydrocarbon adsorbent. On the assumption that the hydrocarbon adsorbent is not deteriorated but brand-new, the temperature downstream of the exhaust gas purifier is estimated from the temperature detected by the temperature sensor that is positioned upstream of the exhaust gas purifier. A deteriorated state of the hydrocarbon adsorbent is then evaluated on the basis of the difference between the estimated temperature and the temperature detected by the temperature sensor that is positioned downstream of the exhaust gas purifier.
However, it is difficult for the above conventional evaluating system to evaluate a deteriorated state of the hydrocarbon adsorbent with accuracy because the temperatures detected by the respective temperature sensors positioned upstream and downstream of the exhaust gas purifier are susceptible to various factors including the ambient temperature, etc. The conventional evaluating system is disadvantageous as to its cost because it requires two temperature sensors positioned respectively upstream and downstream of the exhaust gas purifier.
According to another known technique, a hydrocarbon sensor (HC sensor) is positioned downstream of a hydrocarbon adsorbent, and an adsorbed state of HC adsorbed by the hydrocarbon adsorbent, e.g., an adsorbed amount of HC, is directly recognized on the basis of a detected output signal from the HC sensor, so that a deteriorated state of the hydrocarbon adsorbent can be evaluated from the recognized adsorbed state of HC.
Generally, however, an HC sensor reacts with not all kinds of hydrocarbons that can be adsorbed by a hydrocarbon adsorbent. Consequently, the adsorbed state of HC adsorbed by the hydrocarbon adsorbent, as recognized by the HC sensor, may not sufficiently represent the actually adsorbed state of HC adsorbed by the hydrocarbon adsorbent. Accordingly, it often is difficult to accurately evaluate a deteriorated state of the hydrocarbon adsorbent. In addition, the HC sensor poses a cost problem as it is relatively expensive.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of accurately evaluating, with a relatively inexpensive arrangement, a deteriorated state of a hydrocarbon adsorbent disposed in the exhaust passage of an internal combustion engine.
According to the findings of the inventor of the present invention, a hydrocarbon adsorbent disposed in the exhaust passage of an internal combustion engine is capable of adsorbing not only hydrocarbons contained in the exhaust gas emitted from the internal combustion engine, but also moisture in the exhaust gas. The ability of the hydrocarbon adsorbent to adsorb moisture is highly related to its ability to adsorb hydrocarbons (a maximum amount of hydrocarbons that can be adsorbed). The ability to adsorb moisture and the ability to adsorb hydrocarbons drop in the same manner as each other when the hydrocarbon adsorbent is progressively deteriorated. Therefore, the ability to adsorb hydrocarbons can be evaluated by evaluating the ability of the hydrocarbon adsorbent to adsorb moisture.
As described in detail later on, the findings of the inventors of the present invention indicate that the humidity (relative humidity) in the exhaust passage near the hydrocarbon adsorbent 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 (relative humidity) near the hydrocarbon adsorbent increases, as indicated by the left end portions of curves shown in an upper section of
FIG. 4
of the accompanying drawings, immediately after the internal combustion engine is shut off (generally for a period of time of several tens minutes from the termination of the operation of the internal combustion engine) because the saturated water vapor pressure drops due to a temperature reduction caused by the radiation of heat from the hydrocarbon adsorbent. After the temperature of the hydrocarbon adsorbent falls to a temperature capable of adsorbing moisture, the hydrocarbon adsorbent starts adsorbing moisture in the exhaust gas that remains around the hydrocarbon adsorbent. Therefore, the humidity (relative humidity) of the exhaust gas near (around) the hydrocarbon adsorbent increases to a maximum value and thereafter decreases. The humidity increases and decreases near the hydrocarbon adsorbent, i.e., the humidity increases before the maximum value and decreases after the maximum value, not instantaneously, but within a period of time ranging from several tens minutes to several hours. When the hydrocarbon adsorbent continuously adsorbs moisture until it is saturated, the humidity near (around) the hydrocarbon adsorbent becomes substantially constant, or more specifically, its time-dependent changes are extremely small.
As the hydrocarbon adsorbent further deteriorates, it is harder for the hydrocarbon adsorbent to adsorb moisture. Therefore, as the hydrocarbon adsorbent further deteriorates, the hydrocarbon adsorbent adsorbs moisture at a lower rate after its temperature has dropped to a temperature capable of adsorbing moisture. As a result, the maximum value or an increase in the humidity from the time when the internal combustion engine is shut off to the maximum value becomes larger. Furthermore, as the hydrocarbon adsorbent further deteriorates, the amount of moisture absorbed by the hydrocarbon adsorbent until it is saturated becomes smaller. Therefore, when the humidity near the hydrocarbon adsorbent is substantially constant, the humidity is basically higher as the hydrocarbon adsorbent is deteriorated more. 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. Therefore, the humidity (relative humidity) in the exhaust passage near the hydrocarbon adsorbent after the internal combustion engine is shut off changes in a manner highly correlated to the deteriorated state of the hydrocarbon adsorbent within a period before the humidity is converted to a humidity equal to the humidity in the exhaust passage.
According to the present invention, a method of evaluating a deteriorated state of a hydrocarbon adsorbent which is disposed in an exhaust passage of an internal combustion engine fo
Endo Tetsuo
Machida Kei
Miyahara Yasuyuki
Sato Tadashi
Takakura Shiro
Armstrong Kratz Quintos Hanson & Brooks, LLP
Honda Giken Kogyo Kabushiki Kaisha
Nguyen Tu M.
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