Emission control device for internal combustion engine

Details Emission control device for internal combustion engine Emission control device for internal combustion engine

1999-06-01

2001-05-15

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...

C060S297000, C060S301000, C422S171000, C422S177000

Reexamination Certificate

active

06230489

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an emission control device for an internal combustion engine and in particular a device which removes toxic components from exhaust gas by a catalyst which has a hydrocarbon (hereafter HC) absorbent layer.
BACKGROUND OF THE INVENTION
Devices are well known in the art which control exhaust emissions by the oxidization of HC and CO and reduction of NO
x
components present in exhaust gas emitted from an internal combustion engine by use of a catalyst. However emission control performance is relatively low when a catalyst is not sufficiently activated as, for example, in a low temperature gas environment produced immediately after cold-starting an engine.
Attempts have been made to absorb HC components from low temperature exhaust gas emissions by using an HC absorbent material which absorbs HC from the exhaust gases thus preventing such components from being emitted into the atmosphere. However such HC absorbent materials release bound HC when the temperature exceeds a certain level and thus can only be used in a low temperature exhaust gas environment. Furthermore the temperature at which HC release is initiated is generally lower than the activation temperature of the catalyst and so when the temperature of the exhaust gas exceeds the temperature at which HC release is initiated but is lower than the activation temperature of the catalyst, HC is released into the atmosphere.
Tokkai-Hei-8-224449 discloses a catalyst converter which comprises a lower layer comprised an HC absorbent material and an upper layer formed from a catalyst which are formed on a honeycomb-shaped catalyst carrier. In this way, HC permeating the catalyst layer at low temperatures is absorbed by the HC absorbent material on the lower layer. When such bound HC is released from the HC absorbent material due to rises in temperature, the HC is oxidized by the action of the catalyst when passing through the upper catalyst layer.
However even in this case, the HC absorbent material releases bound HC at temperatures lower than the catalyst activation temperature for example at 150-200° C. As a result, if the catalyst is not activated, released HC is not oxidized and unavoidably released directly into the atmosphere.
SUMMARY OF THE INVENTION
The present invention is proposed to solve the above-mentioned problems and has the object of synchronizing as closely as possible, at low operating temperatures, the period at which HC begins to be released from the HC absorbent material with the period at which the catalyst is activated and thus radically minimize emission of HC into the atmosphere.
In order to achieve above the objects the present invention provides an emission control device for an internal combustion engine.
The emission control device comprises an upstream catalyst disposed in an exhaust passage of said engine, a downstream catalytic converter disposed downstream of the upstream catalytic converter, which contains a multi-layered catalyst, the surface of a catalyst carrier of the multi-layered catalyst being covered with an outer catalyst layer and an underlying HC absorbent layer, a catalyst temperature control mechanism is provided which establishes a large temperature gradient between the surface catalyst layer and the inner underlying HC absorbent layer;and
The details as well as other features and advantages of the invention are set forth in the remainder of the specification and are shown in the accompanying drawings.


REFERENCES:
patent: 4253992 (1981-03-01), Soejima et al.
patent: 5125231 (1992-06-01), Patil et al.
patent: 5538697 (1996-07-01), Abe et al.
patent: 5795840 (1998-08-01), Takami et al.
patent: 6029441 (2000-02-01), Mizuno et al.
patent: 6047544 (2000-04-01), Yamamoto et al.
patent: 8-224449 (1996-09-01), None

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