Exhaust gas purifying device for engine

Details Exhaust gas purifying device for engine Exhaust gas purifying device for engine

1998-10-19

2001-03-13

Chapman, Jeanette (Department: 3748)

Power plants

Internal combustion engine with treatment or handling of...

Having sensor or indicator of malfunction, unsafeness, or...

C060S285000, C060S301000

Reexamination Certificate

active

06199374

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purifying device for an engine.
2. Description of the Related Art
It is well known that an engine in which a lean air-fuel mixture is burned is provided with a catalyst having an oxidizing ability arranged in the exhaust passage of the engine. In the engine, the unburned hydrocarbon (HC) and carbon monoxide CO contained in the exhaust gas are oxidized in the catalyst in the oxidizing atmosphere and converted to H
2
O and CO
2
. However, the exhaust gas flowing into the catalyst also contains sulfur dioxide SO
2
and the SO
2
is converted, in the catalyst in the oxidizing atmosphere, to sulfur trioxide SO
3
. If the SO
3
reacts with H
2
O in the catalyst, H
2
SO
4
is synthesized.
It is undesirable that the H
2
SO
4
is discharged from the catalyst in the form of the mist of sulfuric acid. To solve this problem, Japanese Unexamined Patent Publication No. 53-100314 discloses an exhaust gas purifying device for an engine in which the reducing agent is fed to the catalyst to reduce SO
3
and H
2
SO
4
, i.e., sulfates, in the catalyst to SO
2
.
To reduce the sulfates in the catalyst sufficiently, it is required that the concentration of the reducing agent in the exhaust gas flowing into the catalyst is always made relatively high. However, in a case where the lean air-fuel mixture is burned in the engine, the large amount of the reducing agent is needed to make the concentration of the reducing agent in the inflowing exhaust gas high and, if such a feeding of the reducing agent is performed continuously, a large amount of the reducing agent is needed.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an exhaust gas purifying device capable of reducing the amount of the reducing agent required for reducing sulfate, while maintaining the amount of sulfate discharged from the catalyst small.
According to the present invention, there is provided an exhaust gas purifying device for an engine having an exhaust passage through which the exhaust gas including excess oxygen flows, comprising: a catalyst arranged in the exhaust passage for purifying the exhaust gas, the catalyst having an oxidizing ability; feeding means capable of feeding a reducing agent to the catalyst; and judging means for obtaining an amount of sulfate adsorbed in the catalyst and judging whether the adsorbed sulfate amount is larger than a predetermined amount; and control means for controlling the feeding means to feed the reducing agent to the catalyst temporarily to desorb the adsorbed sulfate from the catalyst and to reduce the sulfate when the adsorbed sulfate amount is judged to be larger than the predetermined amount.
The present invention may be more fully understood from the description of the preferred embodiments of the invention as set forth below, together with the accompanying drawings.


REFERENCES:
patent: 5479775 (1996-01-01), Kraemer et al.
patent: 5778666 (1998-07-01), Cullen et al.
patent: 53-100314 (1978-09-01), None
patent: 6-88518 (1994-03-01), None
patent: 6-66129 (1994-03-01), None
patent: 6-229231 (1994-08-01), None
patent: 7-217474 (1995-08-01), None

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