Emission control apparatus and method of internal combustion...

Details Emission control apparatus and method of internal combustion... Emission control apparatus and method of internal combustion...

1999-12-03

2002-06-04

Denion, Thomas (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

C060S285000, C060S291000

Reexamination Certificate

active

06397586

ABSTRACT:

INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-364670 filed on Dec. 22, 1998 including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an emission control apparatus and method for purifying exhaust gas emitted from an internal combustion engine.
2. Description of Related Art
Many internal combustion engines of, for example, motor vehicles, have in the exhaust system thereof a catalyst device in which precious metals, such as platinum, palladium and the like, are supported as catalysts in order to eliminate or lessen harmful exhaust gas components, for example carbon monoxide (CO), oxides of nitrogen (NOx), hydrocarbons (HC) and the like, before letting out the components into the atmosphere.
A typical catalyst device causes HC and CO present in exhaust gas to react with O
2
present in exhaust gas thereby oxidizing HC and CO into H
2
O and CO
2
, and causes NOx present in exhaust gas to react with HC and CO present in exhaust gas thereby reducing NOx into H
2
O, CO
2
and N
2
.
At the time of start of an internal combustion engine, relatively large amounts of unburned gas components, such as unburned hydrocarbons (HC) and the like, are emitted because unstable combustion is caused by relatively low engine temperature and, at the same time, the engine air-fuel ratio is set lower than the theoretical air-fuel ratio (shifted to the fuel-rich side) in order to facilitate the starting of the engine.
The catalyst device of an internal combustion engine becomes able to significantly lessen the harmful exhaust gas components when the temperature of the device reaches or exceeds a predetermined activation temperature. Therefore, when the activation temperature has not been reached, for example, at the time of cold start of the engine, the catalyst device cannot significantly lessen unburned gas components, which are emitted in large amounts in such a situation.
A known measure against the aforementioned problem is an engine exhaust gas removing apparatus described in Japanese Patent Application Laid-Open No. HEI 4-194309. The engine exhaust gas removing apparatus includes a catalytic converter disposed in an exhaust passage, a bypass passage connected to the exhaust passage and bypassing the catalytic converter, a filter chamber disposed in the bypass passage, a recovery passage connected between a portion of the bypass passage extending downstream of the filter chamber and a portion of the exhaust passage extending upstream of the catalytic converter. In addition, a first open-close valve opens and closes the exhaust passage portion upstream of the catalytic converter, a second open-close valve opens and closes the recovery passage, a third open-close valve opens and closes a portion of the bypass passage extending downstream of the connecting portion between the bypass passage and the recovery passage, and a flow adjusting valve adjusts the amount of exhaust gas flowing into the filter chamber provided in the bypass passage.
The filter chamber adsorbs unburned exhaust gas components when a predetermined temperature has not been reached, and the filter chamber desorbs the adsorbed unburned gas components when the predetermined temperature has been reached or exceeded. When the catalytic converter is not activated, the engine exhaust gas removing apparatus constructed as described above completely closes the first and second open-close valves and fully opens the third open-close valve and the flow adjusting valve in order to prevent exhaust gas from flowing into the catalytic converter. Therefore, the entire amount of exhaust gas is led to the exhaust passage portion downstream of the catalytic converter, via the bypass passage, so that unburned gas components in the exhaust gas are collected in the filter chamber.
When the catalytic converter is activated, the engine exhaust gas removing apparatus fully opens the first and second open-close valves and completely closes the third open-close valve and adjusts the flow adjusting valve to a desired opening, so that a major portion of exhaust gas flows into the catalytic converter and a small portion of exhaust gas flows into the filter chamber, and so that exhaust gas let out of (desorbed from) the filter chamber is led to the exhaust passage portion upstream of the catalytic converter via the recovery passage. In this situation, unburned gas components desorbed from the filter chamber are led to the exhaust passage portion upstream of the catalytic converter via the recovery passage, so that the unburned gas components, together with exhaust gas flowing from an upstream portion of the exhaust passage, flows into the catalytic converter and is subjected to the converting processes in the catalytic converter.
The catalytic converters that are disposed in the exhaust systems of internal combustion engines are represented by three-way catalyst devices, NOx-lessening catalyst devices and the like. The catalytic converters represented by these devices are able to eliminate or lessen unburned gas components and harmful gas components present in exhaust gas provided that the air-fuel ratio of inflowing exhaust gas is within a predetermined range. Therefore, when unburned gas components desorbed from the filter chamber are to be converted by a catalytic converter as mentioned above, it is necessary to set the air-fuel ratio of exhaust gas containing the unburned gas components to a predetermined air-fuel ratio.
In a technology proposed in conjunction with the aforementioned need in internal combustion engines, generally termed air-fuel ratio feedback control is performed in which the air-fuel ratio of exhaust gas flowing into the catalytic converter is detected, and the amount of fuel injected is adjusted so as to bring the actual air-fuel ratio of exhaust gas flowing into the catalytic converter to a desired air-fuel ratio.
It is also known that the catalytic converter has a certain oxygen storing capacity (OSC) and therefore is able to significantly lessen harmful gas components by utilizing the oxygen storing capacity even if the exhaust air-fuel ratio temporarily changes.
The engine exhaust gas removing apparatus described in Japanese Patent Application Laid-Open No. HEI 4-194309 opens the recovery passage so that the filter chamber releases the unburned gas components at the same time when the catalytic converter is activated. In some cases, therefore, the air-fuel ratio of exhaust gas flowing into the catalytic converter becomes an excessively rich ratio, so that harmful gas components and unburned gas components in exhaust gas are not processed by the catalytic converter. Thus, there is a problem of deterioration of emissions.
It may be conceivable to achieve a lean air-fuel ratio of exhaust gas in accordance with the amount of desorbed unburned gas components in the aforementioned case by reducing the fuel injection amount through utilization of the oxygen storing capacity of the catalytic converter and execution of the air-fuel ratio feedback control, so that the exhaust air-fuel ratio resulting from addition of the desorbed unburned gas components to exhaust gas becomes a predetermined air-fuel ratio. However, if large amounts of unburned gas components become desorbed from the filter chamber in unison, the amount of oxygen pre-stored in the catalytic converter due to the oxygen storing capacity is instantly consumed, so that it may become impossible to process the unburned gas components in the catalytic converter before the air-fuel ratio feedback control is reflected in the actual exhaust air-fuel ratio. Furthermore, the engine air-fuel ratio temporarily becomes an excessively lean air-fuel ratio, so that the operating condition of the internal combustion engine may become unstable.
Still further, in order to realize the air-fuel ratio feedback control, it is necessary to provide an air-fuel ratio sensor or the like in a portion of the exhaust passage extending upstrea

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