Exhaust gas purifying apparatus of internal combustion engine

Details Exhaust gas purifying apparatus of internal combustion engine Exhaust gas purifying apparatus of internal combustion engine

1999-09-07

2001-03-06

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...

C060S278000

Reexamination Certificate

active

06195987

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purifying apparatus of an internal combustion engine for cleaning up noxious matter in exhaust gas emitted from the internal combustion engine.
2. Related Background Art
Examples of known emission cleaning apparatus having an NO
x
absorption-reduction catalyst include those as described in International Laying-open Publication WO93/25806. The NO
x
absorption-reduction catalyst is a catalyst that temporarily absorbs nitrogen oxides NO
x
included in the exhaust gas when the internal combustion engine burns fuel at an air/fuel ratio leaner than the stoichiometric ratio (the leaner ratio than the stoichiometric ratio being called a lean air/fuel ratio) and that reduces the absorbed NO
x
into harmless matter when the engine burns fuel at the stoichiometric ratio or at an air/fuel ratio richer than the stoichiometric ratio (the richer ratio than the stoichiometric ratio being called a rich air/fuel ratio). This NO
x
absorption-reduction catalyst also has the function of a three way catalyst to reduce the absorbed NO
x
, using hydrocarbons HC and carbon monoxide CO included in the exhaust gas after combustion at the stoichiometric ratio or at a rich air/fuel ratio, as reductant. (On this occasion, HC and CO are oxidized.)
SUMMARY OF THE INVENTION
An object of the present invention is to provide an exhaust gas purifying apparatus of an internal combustion engine capable of maintaining the cleanness of exhaust gas by accurately reducing NO
x
absorbed in the NO
x
absorption-reduction catalyst.
The NO
x
absorption-reduction catalyst has a limit of NO
x
-absorbing capacity. Therefore, the amount of NO
x
absorbed in the NO
x
absorption-reduction catalyst is estimated and a so-called “rich spike” is executed when the estimated amount of NO
x
exceeds a certain permissible reference value. The rich spike is an engine operation method for cleaning up NO
x
, HC, and CO in the exhaust gas by actively turning the air/fuel ratio of the engine into a rich air/fuel ratio so as to reduce NO
x
absorbed in the NO
x
absorption-reduction catalyst with HC and CO in the exhaust gas while oxidizing HC and CO per se.
The amount of NO
x
absorbed in the NO
x
absorption-reduction catalyst is estimated based on an engine load and an engine speed. Then the reduction cleanup with the NO
x
absorption-reduction catalyst is carried out based on the estimated NO
x
amount. The inventors, however, found out the following fact; intake air flows vary with variations in the atmospheric pressure and such variations of intake air flows affect the engine load and engine speed, so as to fail in accurate reduction cleanup with the NO
x
absorption-reduction catalyst and deteriorate purifying performance.
Many exhaust gas recirculation systems for recirculating the emitted exhaust gas to an inlet system to reduce the NO
x
amount in the exhaust gas make use of the depression at engine manifold (intake vacuum). Therefore, in cases where the exhaust gas recirculation system is adopted, emitted NO
x
amounts also vary with variations in the intake vacuum due to the variations in the atmospheric pressure.
Namely, in the cases where the exhaust gas recirculation system is adopted, when the atmospheric pressure is lowered during a run on the highlands or the like, recirculation amounts of the exhaust gas by the exhaust gas recirculation system decrease, so that NO
x
amounts in the exhaust gas become greater than an estimated value. The inventors also found out the following; as a consequence of the deviation, the reduction cleanup with the NO
x
absorption-reduction catalyst is not effected accurately, and purifying performance could be deteriorated, particularly, where the exhaust gas recirculation system is adopted.
An exhaust gas purifying apparatus of an internal combustion engine according to the present invention comprises an NO
x
absorption-reduction catalyst placed in an exhaust path of the internal combustion engine, acting to absorb nitrogen oxides NO
x
included in exhaust when an air/fuel ratio of the exhaust flowing thereinto is lean, and acting to reduce the absorbed NO
x
when the air/fuel ratio of the exhaust flowing thereinto is a stoichiometric ratio or rich; NO
x
amount estimating means for estimating an amount of NO
x
absorbed in said NO
x
absorption-reduction catalyst, from an operating condition of said internal combustion engine; atmospheric pressure detecting means for detecting atmospheric pressure; and NO
x
amount correction means for correcting the amount of NO
x
estimated by said NO
x
amount estimating means, based on the atmospheric pressure detected by said atmospheric pressure detecting means.
Since the amount of NO
x
absorbed in the NO
x
absorption-reduction catalyst, which was estimated by the NO
x
amount estimating means, is corrected according to the atmospheric pressure detected by the atmospheric pressure detecting means, the present invention permits the amount of NO
x
absorbed in the NO
x
absorption-reduction catalyst to be estimated accurately, also taking increase/decrease of the NO
x
amount in the exhaust gas due to the influence of the atmospheric pressure into consideration. Therefore, the NO
x
absorbed in the NO
x
absorption-reduction catalyst can be reduced with accuracy to be cleaned up, based on the absorption amount of NO
x
estimated accurately, whereby the deterioration of purifying performance can be suppressed.
Another exhaust gas purifying apparatus of an internal combustion engine according to the present invention comprises an NO
x
absorption-reduction catalyst placed in an exhaust path of the internal combustion engine, acting to absorb nitrogen oxides NO
x
included in exhaust when an air/fuel ratio of the exhaust flowing thereinto is lean, and acting to reduce the absorbed NO
x
when the air/fuel ratio of the exhaust flowing thereinto is a stoichiometric ratio or rich; atmospheric pressure detecting means for detecting atmospheric pressure; rich spike executing means for executing a rich spike while switching the air/fuel ratio of the internal combustion engine to the stoichiometric ratio or a rich air/fuel ratio according to a rich spike execution condition defined in connection with an operating condition of the engine; and execution condition modifying means for modifying said rich spike execution condition according to the atmospheric pressure detected by said atmospheric pressure detecting means.
Since the NO
x
absorbed is cleaned up by the rich spike executing means while the rich spike execution condition is modified according to the atmospheric pressure detected by the atmospheric pressure detecting means, the present invention permits NO
x
in the exhaust gas to be cleaned up more efficiently and also permits the NO
x
absorbed in the NO
x
absorption-reduction catalyst to be reduced with accuracy, whereby the deterioration of purifying performance can be suppressed.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.


REFERENCES:
patent: 5201173 (1993-04-01), Fujimoto et al.
patent: 5448887 (1995-09-01), Takeshima
patent: 5482020 (1996-01-01), Shimizu et al.
patent: 5595060 (1997-01-01), Togai et al.
patent: 5894725 (1999-04-01), Cullen et al.
patent: 7305644 (1995-11-01), None
patent: 7310534 (1995-11-01), None
patent: 1047121 (1998-02-01), None
patent: 5825806 (1993-12-01

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