Exhaust emission control apparatus for combustion engine

Details Exhaust emission control apparatus for combustion engine Exhaust emission control apparatus for combustion engine

1998-09-11

2001-01-09

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, C060S284000, C060S295000

Reexamination Certificate

active

06170260

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to an exhaust emission control apparatus for a combustion engine, including a hydrocarbon adsorbent for adsorbing hydrocarbons at a lower temperature, and a catalytic converter being activated at a higher temperature.
In Japanese Patent Application Laid-open No.10178/93, a hydrocarbon adsorbent and a three-way catalytic converter are disposed in series from an upstream side in an exhaust pipe connected to a combustion engine. This hydrocarbon adsorbent adsorbs hydrocarbons in the exhaust gas at a lower temperature such as the start-up period of the engine, and desorbs it at a higher temperature. The three-way catalytic converter disposed downstream of the hydrocarbon adsorbent purifies hydrocarbons desorbed from the hydrocarbon adsorbent.
During the start-up period of the engine at a lower temperature, fuel is not effectively mixed with intake air. Therefore, to warm up the engine, the air fuel mixture is controlled to be rich relative to stoichiometric.
Then the temperature of the engine rises, the hydrocarbon adsorbent begins desorbing hydrocarbons. At this time, the air fuel mixture is controlled to be lean relative to stoichiometric so that the air fuel mixture entering the catalytic converter does not get too rich. Therefore, even if the hydrocarbon adsorbent desorbs hydrocarbons, the three-way catalytic converter performs oxidation of hydrocarbons (HC) and carbon monoxide (CO), and reduction of nitrogen oxides (NOx).
After desorbing hydrocarbons from the hydrocarbon adsorbent, the air fuel mixture is controlled to be stoichiometric.
According to this disclosure, during the start-up period of the engine at a lower temperature, the engine may maintain steady state by controlling the air fuel mixture to be rich.
However, as the inventors of the present invention have discovered, even if the air fuel mixture is controlled to be rich, a sufficient rise of the exhaust gas temperature is not obtained, and activation of the three-way catalytic converter is not expected. Therefore, it is necessary to install a second air supply device separately so that the exhaust temperature may be raised. This increases cost.
On the other hand, when the hydrocarbon adsorbent desorbs hydrocarbon, the air fuel mixture is controlled to be lean relative to stoichiometric. Therefore, the rapid rise of the exhaust gas temperature is not obtained in this period, and early activation of the three-way catalytic converter is not expected either.
Generally, the desorbing temperature of the hydrocarbon adsorbent is lower than the activation temperature of the three-way catalytic converter.
Therefore, the period after reaching the desorbing temperature of the hydrocarbon adsorbent until reaching the activation temperature of the three-way catalytic converter becomes a matter of concern. In this period, the three-way catalytic converter might not purify the hydrocarbon desorbed from the hydrocarbon adsorbent. In other words, the amount of hydrocarbons discharged to atmosphere might increase until the three-way catalytic converter activates.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an exhaust emission control system for a combustion engine having a new method of operation, which can decrease hydrocarbons discharged to atmosphere from the start of the engine to the activation of the catalytic converter.
In order to achieve the above object, this invention provides an exhaust emission control apparatus for a combustion engine, comprising a hydrocarbon adsorbent for adsorbing hydrocarbons at a lower temperature, and desorbing hydrocarbons at a higher temperature, disposed in an exhaust passage of an engine, a catalytic converter for purifying hydrocarbons desorbed from the hydrocarbon adsorbent, disposed in the exhaust passage of the engine, a sensor to detect an engine low load region, and an exhaust temperature control device to raise exhaust temperature when the adsorbent begins to desorb hydrocarbons in a low load region.
It is preferable that the exhaust temperature control device to raise exhaust temperature when the adsorbent begins to desorb hydrocarbons in an idling region.
The invention also provides an exhaust emission control apparatus for a combustion engine, comprising a hydrocarbon adsorbent for adsorbing hydrocarbons at a lower temperature, and desorbing hydrocarbons at a higher temperature, disposed in an exhaust passage of an engine, a catalytic converter for purifying hydrocarbons desorbed from the hydrocarbon adsorbent, disposed in the exhaust passage of the engine, a sensor to detect an engine low load region, a processor to determine whether or not the adsorbent desorbs hydrocarbons, and an exhaust temperature control device to raise an exhaust temperature when the adsorbent desorbs hydrocarbons in a low load region.
It is preferable that the processor determines whether or not the adsorbent begins desorbing hydrocarbons based on an adsorbent temperature. Alternatively, the processor can presume the adsorbent temperature based on a fuel injection amount and/or intake air amount.
It is also preferable that the exhaust temperature control device raises exhaust temperature when the adsorbent desorbs hydrocarbons before the catalytic converter has activated in the low load region.
It is also preferable that the processor presumes whether or not the hydrocarbon adsorbent has finished desorbing hydrocarbons, and the exhaust temperature control device raises exhaust temperature when the hydrocarbon adsorbent begins desorbing hydrocarbons until the hydrocarbon adsorbent finishes desorbing hydrocarbons.
It is also preferable that the processor determines whether or not the catalytic converter has activated based on a temperature of engine coolant.
In one embodiment, the exhaust temperature control device retards ignition timing of the engine.
In another embodiment, the exhaust temperature control device increases engine rotation.
It is also preferable that the exhaust temperature control device retards ignition timing of the engine corresponding to a temperature of engine coolant.
It is further preferable that an intake air control valve for making a flow in a combustion chamber be closed, when the ignition timing is retarded.
In one embodiment, the hydrocarbon adsorbent and the catalytic converter are combined as a combined catalytic-hydrocarbon adsorbent.
In another embodiment, the catalytic converter be disposed downstream of the hydrocarbon adsorbent.
The invention also provides an exhaust emission control apparatus for a combustion engine, comprising, means for adsorbing hydrocarbons at a lower temperature, and desorbing hydrocarbons at a higher temperature, disposed in an exhaust passage of an engine, means for purifying hydrocarbons desorbed from the hydrocarbon adsorbent, disposed in the exhaust passage of the engine, means for detecting an low engine load region, and means for raising an exhaust temperature when the adsorbent begins to desorb hydrocarbons in a low load region.
These and other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawing.


REFERENCES:
patent: 5315824 (1994-05-01), Takeshima et al.
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patent: 5538697 (1996-07-01), Abe et al.
patent: 5551231 (1996-09-01), Tanaka et al.
patent: 5713198 (1998-02-01), Aoki et al.
patent: 5804148 (1998-09-01), Kanesaka et al.
patent: 5979157 (1999-11-01), Kinugasa et al.
patent: 5-10178 (1993-01-01), None

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