Exhaust gas purification device of internal combustion engine

Details Exhaust gas purification device of internal combustion engine Exhaust gas purification device of internal combustion engine

2002-09-30

2004-03-23

Tran, Binh (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

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

C060S286000, C060S292000, C060S287000, C060S295000, C060S303000, C060S324000, C055SDIG003

Reexamination Certificate

active

06708486

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purification device of an internal combustion engine.
2. Description of the Related Art
A particulate filter which carries an active oxygen release agent for releasing active oxygen and an NO
x
catalyst for purifying NO
x
has already been filed (Japanese Patent Application No. 2000-122409). An active oxygen release agent oxidizes and removes the particulate trapped on a particulate filter by active oxygen continuously in a short time. On the other hand, when the air-fuel ratio of the inflowing exhaust gas is lean, the catalyst absorbs the NO
x
in the exhaust gas, while when the air-fuel ratio of the inflowing exhaust gas becomes rich, it releases the absorbed NO
x
and reduces and purifies the NO
x
by the hydrocarbons in the exhaust gas.
Now, the particulate filter described in the above patent application continuously oxidizes a greater amount of particulate per unit time the higher the temperature (hereinafter referred to as “the filter temperature”). That is, the amount of the particulate which can be oxidized and removed continuously by the particulate filter described in the above patent application (hereinafter referred to as “the unit amount of continuous oxidation of particulate”) becomes greater the higher the filter temperature. Therefore, there is a temperature at which the particulate in the inflowing exhaust gas can be continuously removed by oxidation in accordance with the unit amount of inflowing particulate for the particulate filter described in the above patent application (hereinafter referred to as “the continuous oxidation temperature of the particulate”).
Therefore, the above patent application calls for the filter temperature to be controlled so that the filter temperature becomes higher than the particulate continuous oxidation temperature so that the unit amount of continuous oxidation of particulate becomes greater than the amount of particulate flowing into the particulate filter per unit time (hereinafter referred to as “the unit amount of inflowing particulate”).
On the other hand, the NO
x
catalyst described in the above patent application absorbs the NO
x
once in advance while the air-fuel ratio of the inflowing exhaust gas is lean and releases, reduces, and purifies the absorbed NO
x
when the air-fuel ratio of the inflowing exhaust gas becomes rich. Therefore, to maintain the NO
x
purification rate of the NO
x
catalyst high as a whole, it is necessary to maintain the NO
x
absorption rate of the NO
x
catalyst high. Here, the NO
x
catalyst can absorb the NO
x
at a high absorption rate when its temperature is within a certain temperature range (hereinafter referred to as the “NO
x
absorption temperature range”). Therefore, to maintain the NO
x
purification rate of the NO
x
catalyst high, it is necessary to maintain the filter temperature in the NO
x
absorption temperature range.
Therefore, the above patent application calls for the filter temperature to be controlled so that the temperature of the NO
x
catalyst is kept within the above NO
x
absorption temperature range when controlling the filter temperature so that the unit amount of continuous oxidation of the particulate becomes greater than the unit amount of inflowing particulate.
That is, the above patent application calls for the filter temperature to be controlled so that the filter temperature becomes higher than the particulate continuous oxidation temperature in the NO
x
absorption temperature range so as to maintain the particulate oxidation removal level and NO
x
purification level of the particulate filter at high levels.
Further, the above patent application calls for the temperature of the exhaust gas emitted from the internal combustion engine to be raised and the particulate filter to be heated by that high temperature exhaust gas so that the filter temperature becomes higher than the particulate continuous oxidation temperature in the NO
x
absorption temperature range when the filter temperature becomes lower than the low temperature of the NO
x
absorption temperature range or becomes lower than the particulate continuous oxidation temperature.
In the above patent application, however, when the NO
x
absorbed in the NO
x
catalyst should be reduced and purified, rich air-fuel ratio exhaust gas is supplied to the particulate filter, whereby NO
x
is made to be released from the NO
x
catalyst and the released NO
x
is reduced and purified by the hydrocarbons (HC) in the exhaust gas. The NO
x
catalyst described in the above patent application, however, can reduce and purify the NO
x
when its temperature is within a certain temperature range (hereinafter referred to as the “NO
x
reduction temperature range”).
Therefore, to reduce the NO
x
with a high reduction rate, when supplying rich air-fuel ratio exhaust gas to the particulate filter, it is necessary that the filter temperature be kept in this NO
x
reduction temperature range. Further, even while reducing and purifying the NO
x
, a continuous oxidation and removal action of the particulate trapped on the particulate filter is preferable for maintaining the particulate oxidation removal level high.
In the particulate filter described in the above patent application, however, nothing at all is described regarding the point of control of the filter temperature during NO
x
reduction and purification. Therefore, there is room left for raising the particulate oxidation removal level and NO
x
purification level further even for the particulate filter described in the above patent application.
Therefore, an object of the present invention is to provide an exhaust gas purification device provided with particulate filters which can continuously oxidize and remove particulate and purify NO
x
where the particulate oxidation removal level and the NO
x
purification level are improved.
SUMMARY OF THE INVENTION
A first aspect of the invention for solving the above problems provides an exhaust gas purification device of an internal combustion engine provided with a pair of particulate filters arranged in parallel in an engine exhaust passage, an exhaust flow switching means for switching almost all of the engine exhaust gas emitted from an engine to cause it to flow into one of the particulate filters, and a combustion device for feeding to a particulate filter an exhaust gas having a higher temperature elevation capability than a temperature elevation capability of an engine exhaust gas able to cause the temperature of the particulate filters to rise, an NO
x
catalyst able to absorb NO
x
in the exhaust gas when an air-fuel ratio of the inflowing exhaust gas is lean and to release the absorbed NO
x
when the air-fuel ratio of the inflowing exhaust gas becomes rich so as to enable the NO
x
to be reduced and purified by hydrocarbons in the exhaust gas and an oxidizing substance able to continuously oxidize and remove particulate being carried in the particulate filters, said NO
x
catalyst being able to release and reduce NO
x
when its temperature is in an NO
x
reduction temperature range, and said oxidizing substance being able to continuously oxidize and remove almost all inflowing particulate when the temperature of said oxidizing substance is higher than a particulate continuous oxidation temperature, characterized by being provided with a reduction judging means for judging if the NO
x
absorbed in the NO
x
catalyst should be reduced, suppressing by said exhaust flow switching means the inflow of engine exhaust gas to the one of the particulate filters carrying the NO
x
catalyst for which it is judged the NO
x
absorbed in the NO
x
catalyst should be reduced when it is judged by said reduction judging means that the NO
x
absorbed in the NC should be reduced, and feeding rich air-fuel ratio exhaust gas to said particulate filter from a combustion device so that the temperature of said particulate filter is maintained higher the particulate continuous oxidation temperature in a NO
x
reduction temperat

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