Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2002-02-28
2004-08-31
Tran, Binh Q. (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S274000, C060S286000, C060S295000, C060S297000, C060S300000
Reexamination Certificate
active
06782694
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control system of an engine and, more particularly, to a method and an apparatus for controlling exhaust emission of a lean burn engine, which enables combustion to be carried out in a wide range of air-fuel ratios.
Recently, a low fuel consumption type engine has been requested even for an automobile along the lines of worldwide efforts for energy conservation.
Various types have been presented for low fuel consumption engines. The lean burn engine using a so-called wide range of air-fuel ratios is representative one of such engines, which is designed to improve fuel economy by burning a lean mixture having a larger ratio of air compared to a ratio of fuel. Generally, a low fuel consumption engine is achieved by modifying an intake port injection engine.
In addition, as another lean burn engine using a wide range of air-fuel ratios, there has been developed an engine, which has an overall air-fuel ratio increased to about 40 by directly injecting fuel into cylinders of the engine so as to generate a stratified charged mixture in the cylinder.
On the other hand, different from the above-described viewpoint of fuel economy, because of environmental problems such as global warming, a strong request has similarly made of achievement of a low exhaust emission engine designed to reduce harmful components in exhaust gas emitted from the engine. In the individual countries of the world, own exhaust gas emission control regulations have been in practice.
To pass such an exhaust gas emission control regulation, it is important to reduce carbon monoxide (CO), nitrogen oxide (NO
x
) and unburned hydrocarbon (HC). At present, such harmful exhaust components are controlled by a catalyst called a three-way catalyst.
However, to pass a strict exhaust gas emission control regulation by further reducing the harmful exhaust components, a reduction in harmful exhaust components generated before the three-way catalyst is activated at the time of starting is a big problem, especially a reduction in HC.
As one of effective means for reducing HC before the activation of the three-way catalyst, there has been available a system of using an HC adsorbing catalyst. For the HC adsorbing catalyst, a system filled with a catalyst having an HC adsorbing function and a three-way purifying function provided on the same catalyst bed, or a system using both a catalyst bed having an HC adsorbing function and a separate catalyst bed having a three-way purifying function may be employed.
The former catalyst having the HC adsorbing function and the three-way purifying function includes precious metals having an HC adsorbing function and a three-way purifying function carried by the same carrier. In this case, HC discharged from the engine at a low temperature is physically or electrically adsorbed, and the HC eliminated following an increase in a temperature of the catalyst is subjected to oxidation control by using the precious metal having the three-way purifying function carried in the same catalyst.
However, to efficiently control the eliminated HC, sufficient oxygen must be supplied to oxidize the eliminated HC.
On the other hand, in the case of the latter HC adsorbing catalyst, heat resistance of an adsorption material is low. Accordingly, disposition of the catalyst directly below the engine increased to a high temperature by exhaust gas is not preferable, and the three-way catalyst is activated early by using heat of high-temperature exhaust gas. For such reasons, the three-way catalyst is often disposed in a position, where a high temperature of exhaust gas on the upstream side of the HC adsorbing catalyst.
However, in the case of disposing the three-way catalyst on the upstream side of the HC adsorbing catalyst, as shown in
FIG. 5
, oxygen much contained at an engine outlet is consumed by HC and CO oxidation reaction of the three-way catalyst. Consequently, concentration of oxygen at an inlet of the HC adsorbing catalyst tends to be lowered as indicated by an arrow.
Thus, to efficiently control the HC eliminated from the HC adsorbing catalyst, it is necessary to feed sufficient oxygen into the HC adsorbing catalyst by greatly shifting an air-fuel ratio of the engine to a lean side (lean mixture side).
However, if the air-fuel ratio is shifted to the lean side, another problem occurs. That is, as shown in
FIG. 6
, NO
x
control efficiency of the three-way catalyst is suddenly decreased from a point C, making it impossible to efficiently control NO
x
.
Against such a background, several methods haven now been presented to efficiently control HC adsorbed by the HC adsorbing catalyst.
For example, according to a technology described in JP-A-4-230561, eliminated HC is efficiently controlled with a three-way catalyst by controlling an air-fuel ratio to a lean side by fuel control with time from a start of elimination in HC elimination.
However, in the above-described technology, because of the adjustment of the air-fuel ratio by the fuel control, there are problems inherent, including deterioration of drivability by great shifting to the lean side, deterioration of NO
x
control performance by impossibility of NO
x
control with the three-way catalyst caused by shifting to the lean side, and the like.
In addition, JP-A-5-79319 discloses a technology for controlling air necessary for controlling HC by a catalyst.
However, if air enough for controlling HC is supplied to a three-way catalyst, oxidizing atmosphere in the catalyst is increased, possibility causing a reduction in NO
x
control efficiency.
SUMMARY OF THE INVENTION
Objects of the present invention are to provide a method and an apparatus for controlling an engine, capable of efficiently controlling HC at a time of starting without losing NO
x
control efficiency and driving stability of the engine.
A first aspect of the present invention is directed to a control method of an engine. This control method of the engine comprises at least an HC adsorbing catalyst having an HC adsorbing function for adsorbing HC in an exhaust gas pipe of the engine at a low temperature and for emitting the adsorbed HC at a high temperature, and a three-way purifying function on the same carrier; and an NO
x
adsorbing (occluding) catalyst having an NO
x
adsorbing (occluding) function for adsorbing or occluding NO
x
in oxidizing atmosphere and for emitting NO
x
in reducing atmosphere, and a three-way purifying function. In this case, the method comprises a step of driving the engine by using an air-fuel ratio as a stoichiometric air-fuel ratio or a rich air-fuel ratio when a temperature of the HC adsorbing catalyst and/or a temperature of the NO
x
adsorbing (occluding) catalyst is equal to/lower than a predetermined value, or alternatively driving the engine by the air-fuel ratio as a lean air-fuel ratio when the temperature of the HC adsorbing catalyst and/or a temperature of the NO
x
adsorbing (occluding) catalyst is equal to/higher than the predetermined value.
A second aspect of the present invention is directed to a control device of an engine. That is, a lean burn engine capable of combustion by a lean air-fuel ratio comprises at least: an HC adsorbing catalyst having an HC adsorbing function for adsorbing HC to an exhaust gas pipe of the engine at a low temperature, and emitting adsorbed HC at a high temperature, and a three-way purifying function on the same carrier; an NO
x
adsorbing (occluding) catalyst having an NO
x
adsorbing (occluding) function for adsorbing or occluding NO
x
in oxidizing atmosphere, and emitting NO
x
in reducing atmosphere; and means for directly or indirectly detecting a temperature of the HC adsorbing catalyst and/or a temperature of the NO
x
adsorbing (occluding) catalyst. In this case, an engine driving state is controlled based on the temperature of the HC adsorbing catalyst and/or the temperature of the NO
x
adsorbing (occluding) catalyst.
Thus, according to the invention having the foregoing aspects, HC discharged from the engine at a starting
Nagano Masami
Nakagawa Shinji
Ohsuga Minoru
Hitachi , Ltd.
Tran Binh Q.
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