Emission control apparatus of internal combustion engine

Details Emission control apparatus of internal combustion engine Emission control apparatus of internal combustion engine

2001-12-03

2004-03-02

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...

C060S295000, C060S301000, C060S276000

Reexamination Certificate

active

06698188

ABSTRACT:

INCORPORATION BY REFERENCE
The disclosures of Japanese Patent Applications Nos. 2000-374482 filed on Dec. 8, 2000, 2000-388978 filed on Dec. 21, 2000 and 2001-9306 filed on Jan. 17, 2001, each including the specification, drawings and abstract, are incorporated herein by reference in their entireties.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an emission control apparatus of an internal combustion engine.
2. Description of the Related Art
In a known internal combustion engine, a NOx occluding member that occludes NOx when the air-fuel ratio of an inflow exhaust gas is on a fuel-lean side of a stoichiometric fuel-air ratio and that releases occluded NOx and reduces NOx by a reducing agent contained in exhaust gas when the inflow exhaust gas air-fuel ratio changes to the fuel-rich side of the stoichiometric fuel-air ratio is disposed within an engine exhaust passage. During a combustion mode under a fuel-lean air-fuel ratio condition, NOx in exhaust gas is occluded into the NOx occluding member. When NOx is to be released from the NOx occluding member, the air-fuel ratio of exhaust gas that flows into the NOx occluding member is changed toward the rich side.
In order to change the air-fuel ratio of exhaust gas flowing into the NOx occluding member from the fuel-rich side to the fuel-lean side when the release of NOx from the NOx occluding member is completed in an internal combustion engine as described above, there has been proposed an internal combustion engine (Japanese Patent Application Laid-Open No. 2000-104533) in which a NOx sensor capable of detecting the concentration of NOx in exhaust gas is disposed in an engine exhaust passage downstream of the NOx occluding member, and in which when the NOx concentration detected by the NOx sensor decreases to or below a predetermined concentration, the release of NOx from the NOx occluding member is considered to have been completed, and the air-fuel ratio of exhaust gas flowing into the NOx occluding member is changed from the rich side to the lean side.
However, while NOx is being released from the NOx occluding member, the released NOx is reduced by the reducing agent, and therefore is not released in the form of NOx. Therefore, during the release of NOx from the NOx occluding member, the NOx concentration detected by the NOx sensor remains substantially at zero. Therefore, it is not possible to determine whether the release of NOx from the NOx occluding member has been completed, through the use of the NOx sensor.
If the air-fuel ratio of exhaust gas flowing into the NOx occluding member is shifted to the rich side in the aforementioned internal combustion engine, the air-fuel ratio of exhaust gas flowing out of the NOx occluding member is normally a slightly lean air-fuel ratio during the NOx releasing operation of the NOx occluding member. After the release of NOx from the NOx occluding member is completed, the air-fuel ratio of exhaust gas flowing out of the NOx occluding member shifts to the rich side.
In order to change the air-fuel ratio of exhaust gas flowing into the NOx occluding member at the time of completion of the release of NOx from the NOx occluding member in an internal combustion engine as described above, there has been proposed an internal combustion engine (see Japanese Patent Application Laid-Open No. 8-232646) in which an air-fuel ratio sensor that produces an output whose level is proportional to the air-fuel ratio of exhaust gas is disposed in an exhaust passage downstream of a NOx occluding member, and in which after the air-fuel ratio of exhaust gas flowing into the NOx occluding member is changed from the lean side to the rich side so as to release NOx from the NOx occluding member, it is determined that the release of NOx from the NOx occluding member is completed when the rate of change in the output level of the air-fuel ratio sensor when the air-fuel ratio of exhaust gas flowing out of the NOx occluding member changes from the lean side to the rich side exceeds a predetermined rate of change.
The output level of the air-fuel ratio sensor changes in a good response to completion of the release of NOx from the NOx occluding member. Therefore, by determining whether the NOx releasing operation is completed based on a change in the output level of the air-fuel ratio sensor as mentioned above, it becomes possible to change the air-fuel ratio of exhaust gas flowing into the NOx occluding member from the rich side to the lean side in a good response to completion of the NOx releasing operation. However, at the time of completion of the release of NOx, the output level of the air-fuel ratio sensor changes in various fashions, depending on performance variations among air-fuel ratio sensors and NOx occluding members, or time-depending changes thereof. Therefore, the rate of change in the output level exceeding the predetermined rate of change does not necessarily mean that the NOx releasing operation has been completed. Therefore, there is a drawback in the conventional art. That is, it is difficult to change the air-fuel ratio from the fuel-rich side to the fuel-lean side at the time of completion of the release of NOx.
SUMMARY OF THE INVENTION
Through experiments and researches on NOx occluding members carried out by the present inventors and the like, it has been found that if an NOx occluding member is supplied with a reducing agent in an amount that is greater than the amount needed to reduce the amount of NOx occluded in the NOx occluding member when the air-fuel ratio flowing into the NOx occluding member is changed to the fuel-rich side, that is, if the air-fuel ratio of exhaust gas flowing into the NOx occluding member continues to be on the rich side even after completion of the release of NOx from the NOx occluding member, a surplus amount of reducing agent that has not been used to release NOx from the NOx occluding member and reduce NOx is discharged from the NOx occluding member in the form of ammonia.
Therefore, if the amount of ammonia discharged from the NOx occluding member is determined, the surplus amount of the reducing agent is determined, which in turn makes it possible to determine the amount of the reducing agent needed to reduce the amount of NOx occluded in the NOx occluding member. If the amount of the reducing agent needed to reduce the NOx occluded in the NOx occluding member is determined, it become possible to change the air-fuel ratio of exhaust gas flowing into the NOx occluding member at the time of completion of the release of NOx from the NOx occluding member by setting a degree of fuel-richness and a duration of rich-side shift of the air-fuel ratio of exhaust gas flowing into the NOx occluding member so as to supply the needed amount of the reducing agent. Furthermore, if the amount of the reducing agent needed to reduce the NOx is determined, the amount of NOx occludable by the NOx occluding member can be determined, which in turn makes it possible to determine the degree of deterioration of the NOx occluding member.
Thus, given a surplus amount of the reducing agent is determined, the state of the NOx occluding member can be recognized, and the release of NOx from the NOx occluding member can be appropriately controlled.
Furthermore, if the discharge of ammonia from the NOx occluding member is monitored when the air-fuel ratio of exhaust gas flowing into the NOx occluding member is shifted to the rich side so as to release NOx from the NOx occluding member, it is possible to determine whether the release of NOx from the NOx occluding member has been completed.
It is an object of the invention to provide an emission control apparatus of an internal combustion engine capable of appropriately controlling the release of NOx from a NOx occluding member.
A first aspect of the invention is an emission control apparatus of an internal combustion engine in which a NOx occluding member that occludes a NOx when an air-fuel ratio of an inflow exhaust gas is on a fuel-lean side, and that, when the air-fuel ratio of the inflow exhaust gas c

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