Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2000-05-26
2002-11-26
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S276000, C060S285000
Reexamination Certificate
active
06484493
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust emission control device for an internal combustion engine, and in particular relates to an exhaust emission control device for an internal combustion engine for reducing and purifying nitrogen oxides contained in the exhaust gas.
2. Description of the Related Art
Conventionally, the air-fuel ratio of the mixture supplied to an internal combustion engine is set leaner than the stoichiometric air-fuel ratio, however when a so-called lean-burn control is performed there is a tendency for the discharge amount of nitrogen oxides (NO
X
) to increase. To address this there is known a technique for carrying out exhaust gas purification, by providing an exhaust emission control device incorporating a NO
X
absorbent for absorbing, or adsorbing, and removing NO
X
from the exhaust gas in the exhaust system of an internal combustion engine.
This NO
X
absorbent absorbs NO
X
in a condition where the air-fuel ratio of the exhaust gas is set to leaner than the stoichiometric air-fuel ratio so that the oxygen concentration in the exhaust gas is relatively high, and conversely reduces and purifies the absorbed NO
X
and expels it in the form of nitrogen gas (N
2
) in a condition where the air-fuel ratio is set to richer than the stoichiometric air-fuel ratio so that the oxygen concentration in the exhaust gas is low and there is an abundance of hydrocarbons and carbon monoxide and the like.
However, when NO
X
accumulates in the NO
X
absorbent the NO
X
absorption capacity thereof is reduced so that the purifying efficiency with respect to the exhaust gas is reduced. Therefore, it is necessary to desorb the NO
X
absorbed by the NO
X
absorbent at an appropriate timing. In this case there is known a technique for carrying out regeneration of the NO
X
absorbent by performing so-called rich-spiking which involves; temporarily setting the airfuel ratio of the exhaust gas flowing into the NO
X
absorbent richer than the stoichiometric air-fuel ratio to thereby desorb the NO
X
which has been absorbed in the NO
X
absorbent, and to reduce and purify the desorbed NO
X
by means of the hydrocarbons and carbon monoxide and the like contained in the rich atmosphere of the exhaust gas.
Here, it is known that in the case where the air-fuel ratio of the exhaust gas flowing into the NO
X
absorbent is set to richer than the stoichiometric air-fuel ratio, then while the NO
X
is being desorbed from the NO
X
absorbent, the air-fuel ratio of the exhaust gas discharged from the NO
X
absorbent becomes, if only slightly, leaner than the stoichiometric air-fuel ratio, and after this when the desorption of the NO
X
from the NO
X
absorbent is completed, the air-fuel ratio of the exhaust gas becomes richer than the stoichiometric air-fuel ratio. In this case, the smaller the amount of NO
X
absorbed in the NO
X
absorbent, the shorter the time taken after implementation of rich-spiking for the air-fuel ratio of the exhaust gas discharged from the NO
X
absorbent to change to richer than the stoichiometric air-fuel ratio . Therefore, for example as disclosed for example in PCT International Publication WO 94/17291, there is known an exhaust emission control device for an internal combustion engine which judges the degree of deterioration of the NO
X
absorbent, from the time taken after the implementation of rich-spiking for the exhaust gas discharged from the NO
X
absorbent to change to a rich atmosphere.
Furthermore, because sulfur is contained in fuel and lubricants for internal combustion engines, sulfur compounds such as sulfur oxides (SOx) are present in the exhaust gases. NO
X
absorbents such as those mentioned above also absorb sulfur compounds in addition to NO
X
. Here, the sulfur compounds absorbed by NO
X
absorbents have the propensity to accumulate more easily compared to NO
X
, and with an increase in the accumulated amount of sulfur compounds the absorption of NO
X
is hindered. Hence the purifying efficiency of NO
X
is gradually reduced and a deterioration of the NO
X
absorbent occurs due to so-called poisoning.
In the case where poisoning of the NO
X
absorbent occurs in this way, there is known a method for recovering such poisoning by removing sulfur compounds absorbed by the NO
X
absorbent by heating the NO
X
absorbent to an appropriate high temperature and setting the air-fuel ratio of the exhaust gas to richer than the stoichiometric air-fuel ratio and maintaining these condition for an appropriate period of time. As such an exhaust emission control device for an internal combustion engine, there is known an exhaust emission control device for an internal combustion engine as disclosed in Japan Unexamined Patent Application, First Publication No. Hei 7-186785, which performs the reduction and removal of sulfur compounds absorbed by the NO
X
absorbent when an estimated amount of sulfur compounds absorbed by the NO
X
absorbent exceeds a predetermined value, by controlling the temperature of the exhaust gas by controlling the transmission stage of an automatic transmission connected to the internal combustion engine, and setting the air-fuel ratio of the internal combustion engine to richer than the stoichiometric air-fuel ratio.
However, with the exhaust emission control device for an internal combustion engine according to the above-mentioned conventional technology, the amount of sulfur compounds absorbed by the NO
X
absorbents is estimated on the basis of the operating conditions of the internal combustion engine.
However, for the data considered necessary at the time of estimating the amount of these sulfur compounds, it is impossible to accurately know the amount of sulfur already contained in the fuel supplied to an internal combustion engine. Hence the problem arises in that the sulfur concentration within the NO
X
absorbent cannot be specified.
Moreover, even if the amount of sulfur compounds within the NO
X
absorbent are constant, since due to the temperature and the like of the NO
X
absorbent, the amount of sulfur compounds actually absorbed changes, there is a problem in that it is not possible to accurately judge the degree of deterioration of the NO
X
absorbent due to sulfur poisoning.
SUMMARY OF THE INVENTION
The present invention takes into consideration the above-mentioned situations with the object of providing an exhaust emission control device for an internal combustion engine which is able to accurately judge, by employing a simple method, whether the NO
X
absorption capacity of the NO
X
absorbent has deteriorated or not due to sulfur poisoning of the NO
X
absorbent.
In order to attain the object related to solving the above problem, the exhaust emission control device for an internal combustion engine according to the present invention which includes a nitrogen oxides purification device (the NO
X
absorbent
26
in the later described embodiment) provided in an exhaust system of an internal combustion engine for absorbing nitrogen oxides when an air-fuel ratio of exhaust gas is leaner than a stoichiometric air-fuel ratio, and reducing the nitrogen oxides when richer, comprising: an oxygen concentration measurement device (the second O
2
sensor
24
in the later described embodiment) provided downstream from said nitrogen oxides purification device for measuring oxygen concentration in said exhaust gas; a time measurement device (the step S
7
and step S
8
in the later described embodiment) for measuring the time taken for an output signal from said oxygen concentration measurement device to change from lean to rich, when the air-fuel ratio of the mixture supplied to said internal combustion engine changes from a condition leaner than the stoichiometric air-fuel ratio to a richer condition; a threshold value setting device (the step S
17
in the later described embodiment) for setting in relation to said time, a predetermined first threshold value (the sulfur poisoning stoichiometric conversion time threshold value tm: LMT-S deterioration, in the later
Arent Fox Kintner Plotkin & Kahn
Denion Thomas
Honda Giken Kogyo Kabushiki Kaisha
Nguyen Tu M.
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