Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-09-01
2002-04-09
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S276000, C060S278000, C060S292000, C060S297000
Reexamination Certificate
active
06367245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of evaluating a deteriorated state of an exhaust gas adsorbent for adsorbing an exhaust gas emitted from an internal combustion engine.
2. Description of the Related Art
Exhaust gas purifying systems for internal combustion engines generally have a three-way catalytic converter disposed in the exhaust passage of an internal combustion engine for removing unburned components including HC (hydrocarbon), NOx (nitrogen oxides), and CO (carbon oxide) from the exhaust gas emitted from the internal combustion engine.
Generally, the catalytic converters are not activated unless their temperature reaches a certain level, and do not perform an intended exhaust gas purifying function while they are being inactivated at low temperatures. Therefore, the exhaust gas purifying systems for internal combustion engines are required to increase its exhaust gas purifying capability at temperatures where the exhaust gas purifying function of the catalytic converter is not fully performed, e.g., immediately after the internal combustion engine has started up when the internal combustion engine and the catalytic converter are cold.
To meet the above requirement, there has been proposed an exhaust gas purifying systems having a catalytic converter and also an exhaust gas adsorbent for adsorbing a particular gas component, e.g., HC, of the exhaust gas, disposed in the exhaust passage of an internal combustion engine, as disclosed in Japanese laid-open patent publications Nos. 8-93458 and 8-218850, for example.
In the proposed exhaust gas purifying system, an exhaust passage downstream of the catalytic converter is divided into two exhaust passages, one of which (hereinafter referred to as “auxiliary exhaust passage”) houses the exhaust gas adsorbent for adsorbing HC therein. The auxiliary exhaust passage with the auxiliary exhaust passage housed therein is joined to the other exhaust passage (hereinafter referred to as “main exhaust passage”) downstream of the exhaust gas adsorbent. The joint between the auxiliary and main exhaust passages is associated with a switching valve which selectively vents one of the auxiliary and main exhaust passages to the atmosphere and closes the other exhaust passage from the atmosphere. The auxiliary exhaust passage is connected to an exhaust passage upstream of the catalytic converter via a recirculation path with an on/off valve from a location downstream of the exhaust gas adsorbent and upstream of the switching valve.
The exhaust gas adsorbent comprises zeolite or the like, and has such characteristics that it adsorbs HC when its temperature is relatively low and desorbs the adsorbed HC when its temperature rises.
The exhaust gas purifying system operates as follows: In a period (hereinafter referred to as “absorption period”) after the internal combustion engine has started up until the temperature of the exhaust gas adsorbent and the temperature of the exhaust gas or the time elapsed after the internal combustion engine has started up exceeds a predetermined value, the on/off valve in the recirculation path is closed and the auxiliary exhaust passage is vented to the atmosphere and the main exhaust passage is shut off from the atmosphere by the switching valve, so that the exhaust gas emitted from the internal combustion engine is discharged through the catalytic converter and the exhaust gas adsorbent, i.e., HC adsorbent, into the atmosphere. Immediately after the internal combustion engine has started up, the catalytic converter is unable to sufficiently remove HC from the exhaust gas because the catalytic converter is cold. However, since the exhaust gas adsorbent that adsorbs HC at a relatively low temperature is also cold, while the exhaust gas having passed through the catalytic converter is passing through the auxiliary exhaust passage, the exhaust gas adsorbent absorbs HC in the exhaust gas and hence removes HC from the exhaust gas.
In a subsequent period (hereinafter referred to as “desorption period”) after the adsorption period is ended until the temperature of the exhaust gas adsorbent and the temperature of the exhaust gas or the time elapsed after the internal combustion engine has started up exceeds a predetermined value, the main exhaust passage is vented to the atmosphere and the auxiliary exhaust passage is shut off from the atmosphere by the switching valve, and the on/off valve in the recirculation path is opened, so that a portion of the exhaust gas emitted from the internal combustion engine is recirculated via the auxiliary exhaust passage and the recirculation path to the exhaust passage upstream of the catalytic converter, and the exhaust gas is discharged through the catalytic converter into the atmosphere. As the exhaust gas supplied to the auxiliary exhaust passage is recirculated to the exhaust passage upstream of the catalytic converter, the HC adsorbed by the exhaust gas adsorbent in the adsorption period is desorbed from the exhaust gas adsorbent and supplied to the catalytic converter. The HC supplied to the catalytic converter is removed by the catalytic converter which has been increased in temperature and activated in the adsorption period.
The exhaust gas purifying system is thus capable of purifying the exhaust gas while the catalytic converter is being inactivated.
The exhaust gas adsorbent for adsorbing a particular gas component, e.g., HC, of the exhaust gas is deteriorated due to aging, and will not be able to sufficiently adsorb the particular gas component if it is deteriorated to a certain degree. The exhaust gas adsorbent thus deteriorated is unable to perform the desired exhaust gas purifying capability. It is therefore desirable evaluate a deteriorated state of the exhaust gas adsorbent according to some process so that the exhaust gas adsorbent can be replaced when it is deteriorated to some extent.
One proposal for evaluating a deteriorated state of the exhaust gas adsorbent is disclosed in Japanese laid-open patent publication No. 8-218850, for example.
According to the disclosed proposal, exhaust gas sensors for generating an output depending on the concentration of HC adsorbed by the exhaust gas adsorbent, e.g., an O
2
sensor (oxygen concentration sensor), an air-fuel ratio sensor, an HC sensor, etc., are disposed upstream and downstream of the exhaust gas adsorbent. A time required until the output from the downstream exhaust gas sensor becomes equal to the output from the upstream exhaust gas sensor is measured in the desorption period after the adsorption period. While the HC is being desorbed from the exhaust gas adsorbent, since the HC concentration downstream of the exhaust gas adsorbent is higher than the HC concentration upstream of the exhaust gas adsorbent, the output from the downstream exhaust gas sensor is greater than the output from the upstream exhaust gas sensor.
If the measured time does not fall in a predetermined range, then it is determined that the exhaust gas adsorbing system suffers a failure, e.g., the exhaust gas adsorbent is deteriorated, the exhaust gas leaks from the switching valve, etc.
In order to evaluate a deteriorated state of the exhaust gas adsorbent, however, the above proposed process is based on the assumption that the time measured in the desorption period remains substantially constant insofar as the exhaust gas adsorbent is not deteriorated. The assumption means that insofar as the exhaust gas adsorbent is not deteriorated, the total amount of HC adsorbed by the exhaust gas adsorbent in the adsorption period remains substantially the same, and the absorbed HC is desorbed from the exhaust gas adsorbent at substantially the same rate in the desorption period.
The amount of HC adsorbed by the exhaust gas adsorbent in the adsorption period and the rate at which the absorbed HC is desorbed from the exhaust gas adsorbent in the desorption period are affected by the rate of the exhaust gas supplied to the auxiliary exhaust passage with the auxiliary exhaust passage housed therei
Endo Tetsuo
Sato Tadashi
Takakura Shiro
Yasui Yuji
Denion Thomas
Honda Giken Kogyo Kabushiki Kaisha
Tran Binh
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