Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2001-07-09
2004-06-29
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, C060S297000, C060S275000
Reexamination Certificate
active
06755017
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for purifying exhaust gas of an internal combustion engine featuring an improved NOx purifying efficiency even in a lean operating condition without deteriorating the fuel efficiency, as a result of using an electrochemical catalyst as a catalyst for purifying harmful gases (NOx).
2. Prior Art
The exhaust pipe of an internal combustion engine is usually provided with a device for purifying exhaust gas in order to purify harmful components (NOx, HC, CO, etc.) contained in the exhaust gas.
The three-way catalyst that has heretofore been extensively used works to react NOx (nitrogen oxides) generated in the stoichiometric air-fuel ratio mode operation, HC (hydrocarbons) which are the unburned fuel components, and CO (carbon monoxide) which is a component produced by the incomplete combustion, simultaneously, in order to decrease the amount of emission of NOx, HC and CO.
However, the three-way catalyst works when the engine is operating in the stoichiometric (air-fuel ratio feedback) mode but does not sufficiently work in the lean mode (excess of O
2
state) or in the rich mode (lack of O
2
state).
In recent years, in particular, the operation in the lean mode has been widely adopted from the standpoint of improving fuel efficiency, and it has been urged to efficiently purify the exhaust gas in the lean operation condition.
In order to purify the exhaust gases in the lean operation condition, therefore, it has been proposed to dispose a NOx occlusion-type catalyst (NOx occluding catalyst) on the down stream of the three-way catalyst in order to occlude NOx that was not all reduced by the three-way catalyst.
However, NOx occluded by the NOx occluding catalyst during the lean operating condition must be reduced with reducing agents (HC, CO). For this purpose, the engine operating condition after the occlusion of NOx must be forcibly controlled from the lean mode into the rich mode, resulting in a drop in the fuel efficiency.
In order to purify NOx in the lean mode, further, it has been proposed to use a selection-type NOx purifying catalyst (selectively reducing catalyst) in addition to using the three-way catalyst.
However, the selectively reducing catalyst works to purity NOx in the lean mode but its poor purifying efficiency is low, requiring much reducing agent for purifying NOx and without having a reducing agent-adsorbing function for adsorbing the reducing agent.
When the selectively reducing catalyst is installed on the downstream of the three-way catalyst, therefore, no NOx reducing agent flows to the downstream of the three-way catalyst in the lean mode. Due to the lack of the reducing agent, therefore, the selectively reducing catalyst fails to properly work, and it becomes difficult to reduce the amount of emission of NOx.
It further becomes necessary to provide a device (device for feeding atomized gas of fuel) for feeding a NOx reducing agent (HC) to the selectively reducing catalyst in the lean atmosphere. However, since the selectively reducing catalyst has no function for adsorbing the reducing agent, the NOx reducing agent must be continuously fed, requiring fuel in large amounts and deteriorating the fuel efficiency.
Besides, even if a reducing agent adsorbing member is added to the selectively reducing catalyst, most of the reducing agent that is adsorbed reacts with oxygen in the air. Accordingly, only the unreacted reducing agent is used for the purification of NOx; i.e., only a small proportion of the reducing agent is used.
When the selectively reducing catalyst is installed on the upstream of the three-way catalyst, on the other hand, the function for purifying the NOx is maintained by the selectively reducing catalyst in the lean mode. Immediately after the start of the engine (rich mode), however, an extended period of time is required until the three-way catalyst on the downstream side reaches an activating temperature. Thus, the three-way catalyst fails to work to a sufficient degree, and it becomes difficult to decrease the amounts of emission of HC and CO.
In order to pass the regulations on the exhaust gases that are becoming stringent in recent years, further, activation of the three-way catalyst must be promoted right after the start and, hence, the three-way catalyst must be placed just under the engine.
Therefore, the selectively reducing catalyst is inevitably installed on the downstream of the three-way catalyst, and the NOx reducing agents (HC, CO) necessary for the selectively reducing catalyst may not be sufficiently fed under the lean operating condition.
In the conventional device for purifying exhaust gas of an internal combustion engine as described above, use of the three-way catalyst only is not enough for purifying NOx to a sufficient degree in the lean operating condition. When the NOx occluding catalyst is used in combination, the rich operating condition must be repetitively established to reduce NOx that is occluded resulting in a decrease in the fuel efficiency.
When the selectively reducing catalyst is installed on the downstream of the three-way catalyst, on the other hand, it becomes necessary to use a device for feeding a reducing agent, since the selectively reducing catalyst has a poor purifying efficiency, resulting in a decrease in the fuel efficiency, too.
When the selectively reducing catalyst is installed on the upstream of the three-way catalyst, an extended period of time is required until the three-way catalyst reaches the activating temperature. At the start, therefore, the three-way catalyst cannot exhibit its function of purification.
SUMMARY OF THE INVENTION
The present invention was accomplished in order to solve the above-mentioned problems, and has an object of providing a device for purifying exhaust gas of an internal combustion engine which features an improved purifying efficiency even in a lean operating condition without deteriorating the fuel efficiency, as a result of installing an electrochemical catalyst on the downstream of the three-way catalyst.
A device for purifying exhaust gas of an internal combustion according to the present invention comprises an electrochemical catalyst installed in the exhaust system of the internal combustion engine, the electrochemical catalyst containing an electron conducting substance and an ion conducting substance, the oxidizing reaction and the reducing reaction being promoted by the conduction of ions and electrons, thereby to electrochemically purify the exhaust gas in the exhaust system.
In the device for purifying exhaust gas of an internal combustion engine according to the present invention, the electrochemical catalyst contains at least either a NOx occluding member or an HC adsorbing member.
In the device for purifying exhaust gas of an internal combustion engine according to the present invention, further, a reducing agent feeding device is installed in the exhaust system of the internal combustion engine just on the upstream of the electrochemical catalyst to feed a NOx reducing agent into the exhaust system.
In the device for purifying exhaust gas of an internal combustion engine according to the present invention, the reducing agent feeding device feeds an atomized gas of fuel from the fuel tank as the NOx reducing agent.
In the device for purifying exhaust gas of an internal combustion engine according to the present invention, the reducing agent feeding device includes:
a canister for adsorbing the atomized gas of fuel; and
a reducing agent feed control valve for feeding the atomized gas of fuel adsorbed by the canister to the exhaust system of the internal combustion engine as the NOx reducing agent; and wherein,
the time for opening the reducing agent feed control valve is controlled depending upon the amount of the NOx reducing agent required by the electrochemical catalyst.
In the device for purifying exhaust gas of an internal combustion engine according to the present invention, the reducing agent feeding device feeds the fuel in the fuel tank as th
Hamano Kouji
Katashiba Hideaki
Mitsuda Kenro
Wachi Satoshi
Denion Thomas
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Tu M.
Sughrue & Mion, PLLC
LandOfFree
Device for purifying exhaust gas of an internal combustion... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for purifying exhaust gas of an internal combustion..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for purifying exhaust gas of an internal combustion... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3334776