Gas separation: apparatus – Solid sorbent apparatus – With control means responsive to sensed condition
Reexamination Certificate
2000-06-12
2002-05-07
Spitzer, Robert H. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
With control means responsive to sensed condition
C096S117000, C096S143000, C055S385300, C055SDIG001, C055SDIG003
Reexamination Certificate
active
06383267
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas cleaning system for an engine.
There are technologies of improving fuel economy of an engine in which an air-fuel ratio is set to a value having an air concentration higher (hereinafter, referred to as “a lean air-fuel ratio”) than that in the theoretical air-fuel ratio (hereinafter, referred to as “the stoichiometric air-fuel ratio”), and fuel is burned under the lean air-fuel ratio.
For example, a method of injecting fuel from a position near an air-intake port in an intake pipe portion (a port injection method) which can perform lean burning under a condition of an air-fuel ratio from 20 to 25 and a method of injecting fuel directly into a cylinder (in-cylinder injection method) which can perform very lean burning under a condition of an air-fuel ratio from 40 to 50 comes into practical use. These technologies can reduce the pumping loss and the heat loss by performing lean burning, that is, by increasing an amount of intake air, and accordingly can improve fuel economy.
From the viewpoint of exhaust gas cleaning, in a case of burning under the stoichiometric air-fuel ratio condition, HC, CO and NO
x
in an exhaust gas can be cleaned by being oxidized and reduced at a time by a ternary catalyst. However, in the case of burning under the lean condition, it is difficult to reduce NO
x
because the exhaust gas is in a condition of excessive oxygen. Therefore, an exhaust gas cleaning system for an engine is proposed. In the exhaust gas cleaning system for an engine, an NO
x
absorbent is placed in an exhaust gas passage to absorb NO
x
in the exhaust gas when the air-fuel ratio of exhaust gas is lean and to release the absorbed NO
x
from the NO
x
absorbent and to reduce or contact-reduce the NO
x
when the air-fuel ratio is rich (a condition of excessive fuel). The air-fuel ratio temporally changed from the lean air-fuel ratio to the stoichiometric or rich air-fuel ratio with a predetermined cycle to release or reduce the NO
x
trapped by the NO
x
absorbent in order to recover the NO
x
trapping performance (hereinafter, generically referred to as “purge”).
In such an exhaust gas cleaning system, in order to improve the fuel economy and reduce the compositions in the exhaust gas such as HC and so on, it is preferable that the period of the temporary change of the air-fuel ratio to the stoichiometric or rich air-fuel ratio condition is limited to only a period corresponding to an amount of absorbed NO
x
.
A technology of judging completion of NO
x
purge at temporary changing of the air-fuel ratio to the stoichiometric or rich air-fuel ratio is proposed in U.S. Pat. No. 2,692,380 (WO94/17291). After changing of the air-fuel ratio from the lean air-fuel ratio to the stoichiometric or rich air-fuel ratio, it is judged completion of NO
x
purge at the time when the air-fuel ratio detected by an air-fuel ratio sensor placed in the downstream side of the NO
x
absorbent changes from the lean air-fuel ratio to the rich air-fuel ratio. This is based on that until the NO
x
absorbed by the NO
x
absorbent is purged even if the air-fuel ratio in the upstream side of the NO
x
absorbent changes to the stoichiometric or rich air-fuel ratio, the air-fuel ratio detected by the air-fuel ratio sensor placed in the downstream side of the NO
x
absorbent is in a slightly lean air-fuel ratio because HC and CO in the exhaust gas flowing from the upstream side are consumed to reduce NO
x
, and the air-fuel ratio detected by the air-fuel ratio sensor becomes in the rich air-fuel ratio condition after completion of purging of the NO
x
absorbed by the NO
x
absorbent.
Japanese Patent Application Laid-Open. No. 10-128058 (U.S. Pat. No. 5,743,084) discloses the similar technology in which performance of an NO
x
trapping unit is monitored by estimating an amount of absorbed NO
x
from a time difference between the time when the air-fuel ratio is changed from the lean air-fuel ratio to the stoichiometric or rich air-fuel ratio to the time when the air-fuel ratio detected by an air-fuel ratio sensor placed in the downstream side of the NO
x
absorbent changes from the lean air-fuel ratio to the rich air-fuel ratio.
However, a waveform of the air-fuel ratio sensor placed in the downstream side of the NO
x
absorbent or trap (hereinafter, generically referred to as “NO
x
trap”) is affected by an oxygen storage capacity (OSC) even if an amount of NO
x
trapped by the NO
x
trap is the same. The above-mentioned technologies do not take this fact into consideration.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an exhaust gas cleaning system for an engine which is capable of separately judging an amount of trapped NO
x
and an oxygen storage capacity of an NO
x
trap agent and capable of diagnosing deteroration of the NO
x
trap agent.
The above object can be attained by an exhaust gas cleaning system for an engine comprising an NO
x
trap for trapping by absorbing or adsorbing NO
x
in an exhaust gas when an air-fuel ratio of the exhaust gas is a lean air-fuel ratio and for releasing or reducing NO
x
, when the air-fuel ratio is a rich air-fuel ratio, the NO
x
trap being arranged in an exhaust gas passage; and an air-fuel ratio changing means for temporally changing the air-fuel ratio of the exhaust gas from a lean air-fuel ratio to the stoichiometric air-fuel ratio or a rich air-fuel ratio with a predetermined cycle, which comprises an oxygen concentration detecting means for detecting an oxygen concentration in the exhaust gas in the downstream side of the NO
x
trap in the exhaust gas passage; and an NO
x
trap amount judging means for judging an amount of trapped NO
x
of the NO
x
, trap from a detected result of said oxygen concentration detecting means in taking an oxygen storage capacity when the air-fuel ratio changing means temporally changes the air-fuel ratio of the exhaust gas to the stoichiometric air-fuel ratio or the rich air-fuel ratio.
REFERENCES:
patent: 4522027 (1985-06-01), Hasegawa et al.
patent: 4544388 (1985-10-01), Rao et al.
patent: 4733605 (1988-03-01), Holter et al.
patent: 5743084 (1998-04-01), Hepburn
patent: 5941066 (1999-08-01), Araki et al.
patent: 6010547 (2000-01-01), Jeong et al.
patent: 6090187 (2000-07-01), Kumagai
patent: 6212882 (2001-04-01), Greger et al.
patent: 6233927 (2001-05-01), Hirota et al.
patent: 6237326 (2001-05-01), Russell
patent: WO94/17291 (1995-02-01), None
Fujii Yoshihisa
Ishii Toshio
Kawamoto Shigeru
Nakagawa Shinji
Ohsuga Minoru
Crowell & Moring LLP
Spitzer Robert H.
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