Exhaust purification device of internal combustion engine

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

1993-06-14

1995-12-05

Hart, Douglas

Power plants

Internal combustion engine with treatment or handling of...

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

60285, 60286, 422169, 423212, F01N 300

Patent

active

054718368

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a exhaust purification device of an internal combustion engine.


BACKGROUND ART

A diesel engine in which an engine exhaust passage is branched to a pair of exhaust branch passages for purifying NO.sub.x, a switching valve is disposed at the branched portion of these exhaust branch passages to alternately guide the exhaust gas to one of the exhaust branch passages by a switching function of the switching valve, and a catalyst which can oxidize and absorb the NO.sub.x is disposed in each of the exhaust branch passages is well known (refer to Japanese Unexamined Patent Publication No. 62-106826). In this diesel engine, NO.sub.x in the exhaust gas introduced into one exhaust branch passage is oxidized and absorbed by the catalyst disposed in that exhaust branch passage. During this time, the inflow of the exhaust gas to the other exhaust branch passage is stopped and, at the same time, a gaseous reducing agent is fed into this exhaust branch passage. The NO.sub.x accumulated in the catalyst disposed in this exhaust branch passage is reduced by this reducing agent. Subsequently, after a short time, the introduction of the exhaust gas to the exhaust branch passage to which the exhaust gas had been introduced heretofore is stopped by the switching function of the switching valve, and the introduction of the exhaust gas to the exhaust branch passage to which the introduction of the exhaust gas had been stopped heretofore is started again.
However, when the temperature of the catalyst becomes low, the oxidation and absorption of NO.sub.x can no longer be carried out. Therefore, in this diesel engine, when the temperature of the exhaust gas becomes low and therefore the temperature of the catalyst is low, the NO.sub.x is not oxidized and absorbed and therefore there is the problem that NO.sub.x is discharged to the atmosphere.


DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an exhaust purification device which can efficiently absorb NO.sub.x even when the temperature of the exhaust gas is low.
According to the present invention, there is provided an exhaust purification device of an internal combustion engine wherein an NO.sub.x absorbent which absorbs the NO.sub.x when an air-fuel ratio of an inflowing exhaust gas is lean, while releasing the absorbed NO.sub.x when the concentration of oxygen in the inflowing exhaust gas is lowered is disposed in an engine exhaust passage, an NO.sub.x oxidizing agent which can oxidize NO.sub.x is disposed in the engine exhaust passage upstream of the NO.sub.x absorbent, and the NO.sub.x absorbed in the NO.sub.x absorbent when the exhaust gas flowing into the NO.sub.x absorbent is lean, is released from the absorbent when the oxygen concentration in the exhaust gas flowing into the NO.sub.x absorbent is lowered.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall view of an internal combustion engine; FIG. 2 is a diagram showing a map of a basic fuel injection time; FIG. 3 is a diagram showing a change of a correction coefficient K; FIG. 4 is a graph schematically showing the concentration of unburnt HC and CO in the exhaust gas and oxygen discharged from the engine; FIG. 5 is a diagram for explaining an absorption and releasing operation of the NO.sub.x ; FIG. 6 is a diagram showing an absorption rate of NO.sub.x ; FIG. 7 is a diagram showing a control of the air-fuel ratio; FIG. 8 is a flow chart showing an interruption routine; FIG. 9 is a flow chart for calculating a fuel injection time TAU; FIG. 10 is an overall view showing another embodiment of the internal combustion engine; FIG. 11 is an overall view showing still another embodiment of the internal combustion engine; FIG. 12 is a flow chart for performing the NO.sub.x releasing processing.


BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows a case where the present invention is applied to a gasoline engine.
Referring to FIG. 1, 1 denotes an engine body; 2 a piston; 3 a combustion chamber; 4 a spark plug; 5 an intake valve; 6 an in

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