System for controlling engine

Details System for controlling engine System for controlling engine

2000-08-15

2002-07-23

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...

C060S286000, C060S295000, C060S301000, C060S303000

Reexamination Certificate

active

06422004

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to system for controlling an engine equipped with a fuel injector through which fuel in injected directly into an engine.
2. Description of the Related Art
Typically, three-way catalysts are known as a catalytic operative to simultaneously and quite effectively lowers emission levels of HC, CO and NOx in exhaust gas from an internal combustion engine so as thereby to purify the exhaust gas at an approximately stoichiometric air-to-fuel ratio. However, a diesel engine is operated with an air-to-fuel ratio in an extremely lean state (for example, A/F≧18), so the three-way catalyst can not reduce NOx in exhaust gas. Furthermore, when the air-to-fuel ratio is in the extremely lean state, the oxygen concentration of exhaust gas becomes extremely high, so that it is difficult to reduce NOx sufficiently in such an atmosphere even through a NOx purifying catalyst. In this regards, the same thing can be said of a gasoline engine with air-to-fuel ratios in a lean range. To the contrary, there has been known a technology in which utilization is made of a so-called NOx trapping substance that absorbs NOx in an excess oxygen exhaust gas with an oxygen concentration higher than a predetermined oxygen concentration of, for example, 4%, and releases the absorbed NOx as the oxygen concentration drops. However, it is necessary for the NOx trapping substance to carry out so-called refreshing that is referred to releasing the absorbed NOx before the absorption capacity declines, since the NOx trapping substance encounters a decline in absorption capacity with an increase in the amount of NOx absorption.
A fuel injection system such as disclosed in, for example, Japanese Unexamined Patent Publication No. 6-200045, performs primary fuel injection ordinarily at a point of time near a top dead center of a compression stroke and, however, performs post fuel injection at a point of time between an expansion and an exhaust stroke in addition to the primary fuel injection at the point of time near a top dead center of a compression stroke so as thereby to enrich an exhaust gas or decreasing an air-to-fuel ratio of the exhaust gas (which is referred to as an exhaust gas air-to-fuel ratio) in order to release NOx from the NOx trapping substance disposed in an exhaust passage. NOx released from the NOx trapping substance reacts to HC and/or CO in the exhaust gas to be deoxidized. The fuel injection control means further discloses that, in order to prevent a large amount of unburned fuel from being admitted into an intake air stream, an exhaust gas recirculation passage is shut off when the fuel injection control for refreshing the NOx trapping substance in an engine operating region of moderate and lower engine loads where an increase in the amount of exhaust gas is required.
Japanese Unexamined Patent Publication No. 10-252543 discloses improving the NOx conversion efficiency of a NOx deoxidization catalyst disposed in an exhaust passage by changing a post-fuel injection timing so as to reform highly fuel that is sprayed through post-fuel injection according to in-cylinder temperatures that are estimated on the basis of a temperature of then exhaust gas.
When the post-fuel injection is implemented, a large amount of NOx is released abruptly at the beginning of a change in exhaust gas air-to-fuel ratio from a lean state to a rich state (including an exhaust gas air-to-fuel ratio represented by an excess air ratio (&lgr;) of approximately 1 (one), so that there occurs a lack of HC for NOx deoxidization, as a result of which the NOx trapping substance encounters aggravation of NOx conversion efficiency. In order to provide an amount of HC sufficient to deoxidize the temporarily increased amount of NOx released from the NOx trapping substance, though it can be acceptable to increase the amount of post-fuel injection so as to provide highly reformed fuel by advancing a post-fuel injection timing, nevertheless, it causes aggravation of fuel consumption.
Diesel engines are operated with significantly low air-to-fuel ratios and, in consequence, and, in consequence, often generate exhaust gases at low temperatures below than 200° C. When the exhaust gas is at a low temperature like this, even though the post-fuel injection is implemented to raise the air-to-fuel ratio so as thereby to produce an atmosphere suitable for the NOx deoxidization catalyst to deoxidize NOx or to cause the NOx trapping substance to release NOx, it is difficult to deoxidize NOx and purify the exhaust gas because of low activity of the catalyst itself. When the NOx trapping substance is at lower temperatures, it is hard to release NOx as expected even when an exhaust gas air-to-fuel ratio is raised. Further, though an exhaust gas temperature raises due to an advance in post-fuel injection timing, nevertheless, the fuel sprayed through the post-fuel injection becomes apt to burn in the cylinder, so as to cause a less increase in the amount of HC in the exhaust gag. In this regard, it is unfavorable for the NOx trapping substance to advance the post-fuel injection timing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a control system for controlling an engine which prevents aggravation of NOx conversion efficiency of an NOx trapping substance at the beginning of a change in exhaust gas air-to-fuel ratio from a lean state to a rich state due to post-fuel injection that is implemented to release NOx from a NOx trapping substance.
It is another object of the present invention to provide a control system for controlling an engine which activates early a catalyst while post-fuel injection is implemented.
The foregoing objects of the present invention have been accomplished by an engine control system devised on the basis of the fact, which has been revealed by the inventors of the present application, that a relatively large increase in the amount of HC is caused in an exhaust gas by changing a post-fuel injection timing without increasing the amount of post-fuel injection,
According to an aspect of the present invention, a control system for an engine equipped with a fuel injector through which fuel is sprayed directly into a combustion chamber of the engine and a catalyst containing a NOx trapping substance which is operative to absorb NOx in an excess oxygen exhaust gas and release NOx into the exhaust gas when there is a drop in oxygen concentration and, as a result of which, a reaction of HC to NOx released from the NOx trapping substance so as thereby to purify the exhaust gas, comprises fuel injection control means for performing fuel injection through primary fuel injection which is made at a primary fuel injection timing near a dead top center of a compression stroke and post-fuel injection which is made at a post-fuel injection timing between an expansion stroke and an exhaust stroke after the primary fuel injection when causing a drop in oxygen concentration so as to release NOx from the NOx trapping substance, wherein the control means controls a retardation of the post-fuel injection timing so as to be large for a specified period of time from commencement of the post-fuel injection and to be small after a lapse of the specified period of time.
The term “excess oxygen atmosphere” or “excess oxygen exhaust gas” as used herein shall mean and refer to atmosphere or exhaust gas in a state where oxygen exists sufficiently around a NOx trapping substance so much as to cause the NOx trapping substance to absorb NOx in an exhaust gas and prevent the NOx trapping substance from releasing NOx into the exhaust gas. Specifically, the excess oxygen atmosphere or excess oxygen exhaust gas has an oxygen concentration higher than a specific value of, for example, 4% and an exhaust gas air-to-fuel ratio is higher than a stoichiometric air-to-fuel ratio, for example equal to or greater than 18. The exhaust gas air-to-fuel ratio is consistent with an air-to-fuel ratio of an air-fuel mixture in a combustion chamber (which is referred to a

Affiliated with

Also associated with

Rating

System for controlling engine does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with System for controlling engine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System for controlling engine will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2876716