Exhaust emission control device

Details Exhaust emission control device Exhaust emission control device

1999-06-08

2001-10-16

Tran, Hien (Department: 1764)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

Waste gas purifier

C422S171000, C422S180000

Reexamination Certificate

active

06303084

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
BACKGROUND OF THE INVENTION
Tokkcai Hei 9-228828 published by the Japanese Patent Office in 1997 discloses the reduction of hydrocarbons (hereafter HC) emissions immediately after engine start-up by the provision in the exhaust pipe of an HC absorbent catalytic converter, which is comprised of an HC absorbent material and a three-way catalyst The HC absorbent material absorbs HC when the catalyst temperature is lower than a fixed temperature and emits HC at temperatures higher than the fixed temperature.
In such a way, HC emitted from the engine is temporarily absorbed by the HC absorbent material in the HC absorbent catalytic converter. When the temperature of exhaust gases in the HC absorbent catalytic converter reaches a fixed temperature, the air-fuel ratio is varied to a lean air-fuel ratio, that is to say, the air-fuel ratio is varied upwardly. This results in a super-oxygenated mixture in the exhaust gases and HC which is emitted from the HC absorbent material is oxidized by the three-way catalyst.
SUMMARY OF THE INVENTION
In this way, it is necessary to control an air-fuel ratio towards a lean air-fuel ratio from a stoichiometric air-fuel ratio and supply sufficient oxygen to react with emitted HC in the exhaust gas in order to improve the reduction of HC emissions. However the more an air-fuel ratio is varied towards a lean air-fuel ratio, the greater the amount of emitted nitrogen oxides (NO
x
) becomes.
It is therefore an object of the present invention to remove HC while suppressing amounts of emitted NO
x
when HC is emitted from an HC absorbent catalytic converter.
In order to achieve the above object, this invention provides an exhaust emission control device for an engine which is provided with an exhaust pipe. The emission control device comprises a first catalytic converter which contains the element Rhodium (Rh), and a second catalytic converter which contains Rh and a hydrocarbon (HC) absorbent material which absorbs HC. The first catalytic converter and the second catalytic converter are provided in series in the exhaust pipe and the Rh content by percentage in the second catalytic converter is higher than the Rh content by percentage in the first catalytic converter.


REFERENCES:
patent: 5935530 (1999-08-01), Langer et al.
patent: 196 17 563-C1 (1997-06-01), None
patent: 9-228828 (1997-09-01), None

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