Apparatus and method for engine exhaust purification

Details Apparatus and method for engine exhaust purification Apparatus and method for engine exhaust purification

2002-03-27

2003-10-28

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...

C060S274000, C060S276000, C060S277000, C701S109000

Reexamination Certificate

active

06637195

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to technique of purifying exhaust gases of engine, and more specifically to apparatus and method of exhaust emission control for an engine equipped with a catalyst.
For maximizing the conversion efficiency of NOx, CO, and HC in three-way catalyst, the control of oxygen storage amount in the catalyst is effective. In this case, a catalyst system can control the atmosphere of the catalyst around stoichiometry to maximize the conversion efficiency, by controlling the oxygen storage amount at a constant level so that oxygen in exhaust gases is stored in the catalyst in the case of deviation of the exhaust gases flowing into the catalyst to the lean side, and that oxygen is released from the catalyst in the case of deviation to the rich side.
SUMMARY OF THE INVENTION
An object of the present invention is to further reduce exhaust emissions in technique of computing an oxygen storage amount in a catalyst.
According to one aspect of the present invention, an engine exhaust purifying apparatus comprises: an air flow sensor, a catalyst, an upstream exhaust sensor, a downstream exhaust sensor and a controller. The air flow sensor is arranged to sense an engine intake air amount. The catalyst is disposed in an engine exhaust passage. The upstream exhaust sensor is disposed in the engine exhaust passage on an upstream side of the catalyst, and arranged to sense an upstream exhaust condition representing an air-fuel ratio of an inflowing exhaust gas mixture flowing into the catalyst. The downstream exhaust sensor is disposed on a downstream side of the catalyst and arranged to sense a downstream exhaust condition representing an air-fuel ratio of an outflowing exhaust gas mixture flowing out of the catalyst. The controller is configured; to compute an estimated oxygen storage amount of the catalyst in accordance with the air-fuel ratio of the inflowing exhaust gas mixture and the engine intake air amount; to control an air-fuel ratio of the engine in accordance with the estimated oxygen storage amount so as to bring an actual oxygen storage amount of the catalyst to a desired value; to correct the estimated oxygen storage amount to reduce an error in computing the estimated oxygen storage amount when the downstream exhaust condition sensed by the downstream exhaust sensor becomes equal to a predetermined threshold; and to modify the threshold in accordance with the intake air amount.
According to another aspect of the present invention, an engine exhaust purifying process for an engine equipped with a catalyst disposed in an engine exhaust passage, comprises: computing an estimated oxygen storage amount of the catalyst in accordance with a sensed upstream exhaust condition representing an air-fuel ratio of an inflowing exhaust gas mixture flowing into the catalyst and a sensed engine intake air amount; controlling an air-fuel ratio of the engine in accordance with the estimated oxygen storage amount; correcting the estimated oxygen storage amount to reduce an error in computing the estimated oxygen storage amount when a downstream exhaust condition representing an air-fuel ratio of an outflowing exhaust gas mixture flowing out of the catalyst becomes equal to a predetermined threshold; and modifying the threshold in accordance with the sensed engine intake air amount.
According to still another aspect of the present invention, an engine exhaust purifying apparatus for an engine equipped with a catalyst, comprises: means for sensing an engine intake air amount; means for sensing an upstream exhaust condition representing an air-fuel ratio of an inflowing exhaust gas mixture flowing into the catalyst; means for sensing an downstream exhaust condition representing an air-fuel ratio of an outflowing exhaust gas mixture flowing out of the catalyst; and means for computing an estimated oxygen storage amount of the catalyst in accordance with the upstream exhaust condition of the inflowing exhaust gas mixture and the engine intake air amount; means for controlling an air fuel ratio of the engine in accordance with the oxygen storage amount; means for correcting the estimated oxygen storage amount to reduce an error in computing the estimated oxygen storage amount when the downstream exhaust condition sensed by said means for sensing the downstream exhaust condition becomes equal a predetermined threshold; and means for modifying the threshold in accordance with the intake air amount.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.


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