Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
1999-03-26
2001-07-03
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S177000, C422S179000
Reexamination Certificate
active
06254837
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention concerns a honeycomb body, in particular for an exhaust gas catalytic converter, through which a fluid can flow and which has an intake region and an outlet region. The intake region and the outlet region are connected together by passages through which the fluid can flow.
Published, International Patent Application WO 90/03220 discloses honeycomb bodies through which a fluid can flow and which can be of the most widely varying cross-sectional shapes. To reduce the polluting components in the exhaust gas flow of an exhaust gas system it is necessary for the honeycomb body to be at a temperature which is sufficiently high for the catalytic reaction of the pollutants. In order to endow the catalytic converter with a performance such that it starts operating as quickly as possible, it has already been proposed in Published, International Patent Application Wo 89/10471 that the honeycomb body is to be electrically heated. Electrical heating of such a honeycomb body reduces the emission of exhaust gas pollutants that are produced in the cold-start phase of an internal combustion engine. The internal combustion engine and the entire exhaust gas system cools down when a motor vehicle is operated in a short-distance mode with interruptions of greater or lesser lengths between the individual travel cycles. Cooling of the exhaust gas system and in particular the honeycomb body in that way has the result that the honeycomb body has to be repeatedly electrically heated. Under some circumstances the consequence of this is that the power source, a battery in a motor vehicle, is severely loaded. When the vehicle is used to cover short distances therefore it is not possible to guarantee that the battery is always sufficiently charged up again.
In order to reduce the amount of power necessary to heat the honeycomb body it has therefore already been proposed that the honeycomb body should be provided with thermal insulation. Thus for example Published International Patent Application WO 90/04087 discloses a honeycomb body with a thermal insulation which is in the form of a double casing system. That double casing system includes an inner tubular casing which is disposed in an outer tubular casing at a spacing relative thereto. The intermediate space between the inner and the outer tubular casings acts as a thermal insulation. That affords a reduction in the emission of heat by the peripheral surface of the honeycomb body.
For the purposes of reducing thermal conductivity U.S. Pat. No. 5,549,873 already discloses a honeycomb body having an intermediate region with a considerably reduced level of thermal conduction. That intermediate region is produced by openings or stamped-out portions provided in the metal sheets of the honeycomb body. The region upstream of the openings serves in practice as a pre-catalyst, that is to say that partial region of the honeycomb body forms a mass which can rapidly heat up immediately after a cold start of the engine, while in the region of the main catalyst the carrier body forms a substantially larger number of flow paths so that there too a shorter active catalytic surface area is made available.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a honeycomb body of reduced thermal conductivity in the intake and outlet regions that overcome the above-mentioned disadvantages of the prior art devices of this general type, in which the heat losses of the honeycomb body are further reduced.
With the foregoing and other objects in view there is provided, in accordance with the invention, a honeycomb body, including: an intake region; an outlet region; and passages connected between the intake region and the outlet region for conducting a fluid flow, the passages in a proximity of the intake region having an intake portion of reduced thermal conductivity and the passages in a proximity of the outlet region having an outlet portion of reduced thermal conductivity.
The honeycomb body according to the invention is distinguished in that it has a portion of reduced thermal conductivity at least in the proximity of the intake and the outlet region. It has surprisingly been found that, in the case of honeycomb bodies, in particular for an exhaust gas catalytic converter, the heat losses at the ends, due to the conduction of heat to the components of an exhaust gas system which are connected to the honeycomb body, and due to convection of the exhaust gas in the exhaust gas system, make a considerable contribution to the overall heat losses. The honeycomb body according to the invention is proposed to avoid those heat losses, in particular at the ends. The fact that a respective portion of reduced thermal conductivity is provided in the proximity of each of the intake and the outlet regions provides for substantial thermal decoupling of the honeycomb body from adjacent components of an exhaust gas system. The portion that is of a reduced thermal conductivity extends at least partially into the honeycomb body.
Because the honeycomb body has a portion of reduced thermal conductivity in the proximity of each of the intake and outlet regions, the thermal losses of the central portion are reduced, whereby the portion of the honeycomb body which is between the intake and outlet regions is at a higher temperature over a longer period of time than is the case with the known honeycomb bodies. This provides for an improved cleaning action for an exhaust gas after re-starting as the honeycomb body between the intake and the outlet regions is at a higher temperature level. Consequently the portion between the intake and the outlet regions heats up substantially more quickly, whereby the temperature required for catalytic reaction is also reached more rapidly.
A preferred configuration of the honeycomb body is one in which the portion of the reduced thermal conductivity extends over the entire cross-section of the honeycomb body. A reduction in the level of thermal conductivity of the honeycomb body can be achieved by the wall of at least one of the passages thereof being at least partially of reduced wall thickness or gauge. That reduces the cross-section in the heat transportation direction.
In accordance with a further advantageous configuration of the honeycomb body it is proposed that the portion of reduced thermal conductivity is formed by the wall of at least one of the passages having at least one opening. With such a configuration for the honeycomb body the cross-section of the honeycomb body which is available for heat transport is reduced. It is to be noted however that the strength of the honeycomb body can be adversely affected by the provision of the openings in the wall. Such an adverse effect in terms of the strength of the honeycomb body does not occur if however the portion, without openings, includes a heat-insulating material.
The provision of openings in a honeycomb body can be effected prior to, during or after the procedure for producing the honeycomb body. If the honeycomb body is formed by wound and/or stratified or stacked layers of at least partially structured metal sheets the operation of producing the openings is to be effected prior to the step of winding or stratifying the layers of the sheets.
A honeycomb body through which a fluid can flow and which has a respective portion of reduced thermal conductivity in the proximity of the intake and outlet regions is suitable in particular as a honeycomb body for an exhaust gas catalytic converter, and preferably is disposed in a tubular casing.
Ideally, the tubular casing has a portion of reduced thermal conductivity in the proximity of the intake and outlet regions. For this purpose it is proposed that the portion is formed by openings in the tubular casing. The openings in the tubular casing or in the honeycomb body, may involve perforations. The portion of reduced thermal conductivity is preferably disposed in aligned relationship. The interrelationship already referred to above between the physical configuration of
Bruck Rolf
Diewald Robert
Emitec Gesellschaft fuer Emissions-technologie mbH
Greenberg Laurence A.
Lerner Herbert L.
Stemer Werner H.
Tran Hien
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