Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2001-01-16
2002-04-30
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...
C060S274000, C060S286000, C060S324000, C060S298000
Reexamination Certificate
active
06378298
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2000-026281 filed on Feb. 3, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an exhaust purifying apparatus and method for purifying exhaust gas discharged from an internal combustion engine through the use of a catalytic converter.
2. Description of Related Art
As a measure for reducing the amount of harmful components of exhaust gas discharged from an internal combustion engine into the atmosphere, an exhaust system is known which purifies the exhaust gas of the harmful components by using the oxidizing or reducing effect of a catalyst.
In general, this type of catalyst has an activation temperature range, and is not able to substantially remove harmful components in exhaust gas when the catalyst midbed temperature is outside the activation temperature range. This type of catalyst also has a temperature characteristic that its exhaust purifying capability considerably varies in accordance with the catalyst midbed temperature even within the activation temperature range.
The temperature of a catalyst disposed in an exhaust passage of the engine significantly depends on the temperature of exhaust gas flowing through the catalyst. Since the exhaust gas temperature changes considerably in accordance with the operating state of the internal combustion engine, the catalyst midbed temperature also changes depending on the operating state of the engine.
Therefore, if measures are not taken to control the catalyst midbed temperature, the exhaust purifying capability of the catalyst changes from moment to moment and does not stabilize, which may undesirably result in fluctuations in the concentrations of harmful components in exhaust gas escaping into the atmosphere.
In exhaust purifying systems using catalysts, it is particularly important to determine how to keep the catalyst midbed temperature within the activation temperature range and, furthermore, how to stabilize the catalyst midbed temperature within a temperature range in which the exhaust purifying capability is high, in order to improve exhaust purifying performance.
Furthermore, the catalyst is likely to undergo heat deterioration when exposed to high temperatures. It is therefore desirable to prevent inadvertent flow of high-temperature exhaust gas to the catalyst.
Typical fuels for internal combustion engines contain sulfur. When such a fuel is burned, sulfur contained in the fuel is caused to burn and produce oxides of sulfur (SOx), such as SO
2
and SO
3
, which become exhaust gas components. When the exhaust gas containing SOx reaches the catalyst, SOx is apt to be absorbed into the catalyst and form sulfates, and the like. Since the sulfates are stable, the sulfates are unlikely to be decomposed and released, and tend to be accumulated in the catalyst. If the amount of SOx accumulated in the catalyst increases, the ability of the catalyst to reduce other harmful components (HC, CO, NOx) in exhaust gas may deteriorate. This is generally called “S-poisoning”.
In order to maintain a high exhaust purifying capability of the catalyst for a long time, therefore, it is necessary to recover the catalyst from S-poisoning by decomposing SOx accumulated in the catalyst and releasing decomposed SOx from the catalyst. This S-poisoning recovery process requires the catalyst to be placed in a high-temperature atmosphere having a certain temperature or higher. In this case, too, appropriate control of the catalyst midbed temperature is very important in order to efficiently recover the catalyst from S-poisoning.
Japanese Patent Laid-Open Publication No. 8-105318 discloses a technology relating to catalyst temperature control performed at the time of the aforementioned S-poisoning recovery process. In an exhaust purifying apparatus disclosed in this publication, an exhaust manifold of an engine capable of operation in a lean-burn mode and a catalyst capable of substantially removing NOx in exhaust gas discharged from the engine (a generally termed lean-burn NOx catalyst) are connected by a first exhaust passage and by a second exhaust passage that are disposed in parallel with each other.
In this apparatus, the channel length of the first exhaust passage is set to be greater than the channel length of the second exhaust passage. With this arrangement, the temperature of exhaust gas flowing through the first exhaust passage decreases by a larger extent than that of exhaust gas flowing through the second exhaust passage. In other words, a greater exhaust gas cooling effect can be achieved by heat dissipation from the first exhaust passage than from the second exhaust passage.
Furthermore, a control valve is mounted in the second exhaust passage in such a manner that exhaust gas is caused to flow through the first exhaust passage while the control valve is closed, and that exhaust gas is caused to flow through the second exhaust passage while the control valve is opened.
When the S-poisoning recovery process is performed on the catalyst, the catalyst midbed temperature needs to be kept high. Therefore, the control valve is placed in an open position so that exhaust gas flows through the second exhaust passage, which has a shorter channel length, and is less likely to cool exhaust gas. When the S-poisoning recovery process is not performed, the control valve is placed in a closed position so that exhaust gas flows through the first exhaust passage, which has a greater channel length, and is more likely to cool exhaust gas.
In the above-described known catalyst temperature control system, however, the first exhaust passage and the second exhaust passage must be formed with largely different channel lengths in order to provide significantly different exhaust-gas cooling effects. As a result, the channel length of the first exhaust passage becomes very long, and a catalyst temperature control unit becomes large in size, thus causing a problem in installing the control system on the vehicle.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an exhaust purifying apparatus that is simple and compact in construction, wherein the catalyst midbed temperature can be suitably controlled.
To accomplish the above and/or other objects, one aspect of the invention provides an exhaust purifying apparatus for an internal combustion engine having a catalyst, a first passage, a second passage and a flow amount controller. The catalyst purifies exhaust gas emitted from the internal combustion engine. The first passage is disposed between the engine and the catalyst to allow exhaust gas to flow therethrough from the engine to the catalyst. The first passage includes an accelerated cooling portion whose cross section is designed so that a first quantity of heat is released from the exhaust gas in the first passage. The second passage is disposed between the engine and the catalyst to allow exhaust gas to flow therethrough from the engine to the catalyst. The second passage has a cross section that is designed so that a second quantity of heat that is smaller than the first quantity of heat is released from the exhaust gas in the second passage. The flow amount controller controls amounts of exhaust gas flowing through the first passage and the second passage, such that: (i) the amount of exhaust gas flowing through the first passage is made larger than that flowing through the second passage when the temperature of exhaust gas emitted from the engine is to be lowered by a relatively large degree before the exhaust gas flows into the catalyst; and (ii) the amount of exhaust gas flowing through the second passage is made larger than that flowing through the first passage when the temperature of exhaust gas emitted from the engine is to be lowered by a relatively small degree before the exhaust gas flows into the catalyst. By controlling the amounts of exhaust gas flowing through the first passage and through the second
Harima Kenji
Ichinose Hiroki
Itou Keiji
Itou Takaaki
Katoh Kenji
Denion Thomas
Nguyen Tu M.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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