Catalyst – solid sorbent – or support therefor: product or process – Miscellaneous
Reexamination Certificate
2000-05-08
2003-03-04
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Miscellaneous
C502S527230, C502S527240
Reexamination Certificate
active
06528454
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a catalyst carrier body for an exhaust system of an internal combustion engine, in particular of a vehicle, including a matrix having an inflow surface, an outflow surface and a multiplicity of catalytic surfaces which form flow-through passages and around which exhaust gas can flow.
The known catalyst carrier bodies are generally wound or wrapped into cylindrical bodies or are laid or stacked so as to form bodies which have different shapes. The actual honeycomb-like matrix structure is formed as a result of substantially smooth sheet-metal layers and wavy sheet-metal layers or wires or wire meshes being wound, wrapped or stacked alternately on top of one another. The substantially cylindrical bodies which are formed when the sheet-metal layers are wrapped or wound over one another have a multiplicity of through-flow passages. A substance which realizes a catalytic reaction is applied to inner surface of the passages. The catalytic reaction proceeds exothermically, so that energy which is released in individual passages is transmitted to adjoining passages. Consequently, the passages which are situated in the interior of the matrix body are heated to a greater extent than the passages located immediately at the periphery or at an exit side, from which heat is radiated to the environment or to the exhaust system in which the catalyst carrier body is embedded.
European Patent 0 121 175 B1 describes a catalyst carrier body which is composed of sheet-metal strips that are wound helically in the shape of a cone. A ratio of a width of the sheet-metal strips to a pitch of a helix or a diameter of the matrix of the catalyst carrier body is selected in such a way that no cross section through the winding intersects all of the layers of sheet-metal strips. That means that the axial extent of the hollow conical carrier body being formed in that way is greater than twice the width of the sheet-metal strips. The matrix which has been formed in that way is fitted in the catalytic converter in such a way that the gas flows in through an outside point of the conical matrix body. The matrix body which is constructed in that way has a high flexibility in terms of its freedom to expand. A drawback is that the energy which is released as a result of the exothermic reaction that takes place in the matrix body remains in the individual layers of the catalyst carrier body for a long time. That is because each section of a layer, on the side remote from the flow, emits the energy substantially in its entirety to an adjacent layer. Therefore, the matrix body is locally exposed to relatively high temperatures, which ultimately may lead to at least local overheating of the carrier body or bed.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a catalyst carrier body with exposed heat-radiating surfaces, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which exhibits an improved heat dissipation behavior from individual layers of a matrix.
With the foregoing and other objects in view there is provided, in accordance with the invention, a catalyst carrier body for an exhaust system of an internal combustion engine, in particular of a vehicle, comprising a matrix having an inflow surface, an outflow surface with an inner region, a periphery, and a multiplicity of catalytic surfaces around which exhaust gas can flow, the catalytic surfaces having front regions and the catalytic surfaces forming flow-through passages with a given length; the outflow surface having a shape, at least in the inner region, causing the front regions to be exposed and not covered outwardly, toward the periphery, by others of the catalytic surfaces; and the exposed front regions having lengths, at least in a partial region of the outflow surface, amounting to from 55% to 90% of the given length, for increasing an outward dissipation of heat.
According to the invention, the catalyst carrier body, which is intended for an exhaust system of an internal combustion engine, in particular of a vehicle, includes a matrix which has layers of an at least partially structured thin material. These layers are wound, wrapped or stacked to form an assembly, so that the interior of the matrix contains a multiplicity of catalytic surfaces around which exhaust gas can flow. The matrix, which is preferably disposed in a casing, has an inflow surface and an outflow surface, as is seen in the direction of flow. According to the invention, at least in the inner region of its outflow surface, the matrix has a projecting shape which is formed as a result of end regions of individual catalytic surfaces being offset with respect to one another. Consequently, at least in its inner region, the matrix has exposed exit-side front regions of the catalytic surfaces. Those front regions are not covered on the outside toward the periphery of the catalyst carrier body, by other catalytic surfaces. According to the invention, these exposed front regions of the catalytic surfaces face toward the periphery of the catalyst carrier body, i.e. they are directed outward. In this context, “directed outward” is understood to mean a direction from an imaginary axis of the catalyst carrier body running in the direction of flow toward the outer periphery or, if present, the casing. In order to improve the dissipation of heat, front regions which are as large as possible are advantageous at least in the inner region of the outflow surface.
A significant advantage of a matrix constructed in this way is that, over the outwardly-facing exposed front regions of the catalytic surfaces, the energy which is released as a result of the exothermic reaction inside the catalyst carrier body is emitted directly to the environment, i.e. to areas of the exhaust system which do not form part of the catalyst carrier body. This prevents the energy which is absorbed by the catalytic surfaces as a result of the exothermic reaction from being transmitted entirely to adjoining catalytic surfaces. The proportion of energy which is not transmitted to adjacent catalytic surfaces, i.e. the proportion of energy which is dissipated directly to the environment, becomes greater the more the front regions of the catalytic surfaces of adjacent layers are offset with respect to one another, i.e. the larger the exposed front regions of the catalytic surfaces are made.
In accordance with another feature of the invention, the matrix is wound, wrapped or stacked in honeycomb form from at least partially structured thin sheet-metal layers, so that a multiplicity of passages through which exhaust gas can flow are formed, and the walls of the passages are the catalytic surfaces.
In accordance with a further feature of the invention, the projecting shape of the outflow surface has a concave curvature running substantially from the periphery of the matrix toward the axis, i.e. inward, at least in sections, so that a finger-like projection is formed in a central region in the area of the axis of the catalyst carrier body. The advantage of a projecting shape configured in this way is that the extent to which the front regions of the passage walls are offset with respect to one another increases the closer they are to the axis of the catalyst carrier body. This is because these walls are exposed to the greatest amount of energy uptake due to the catalytic reaction proceeding in the catalyst carrier body, and they consequently ensure improved dissipation of heat in conjunction with larger front regions.
In accordance with an added feature of the invention, the projecting shape is formed by a convex curvature running inward substantially from the periphery of the matrix toward the axis of the catalyst carrier body, at least in sections.
This convex curvature, if it is provided substantially continuously, results in a domed bulge in the outflow surface of the catalyst carrier body.
In accordance with an additional feature of the invention, the projecting
Brück Rolf
Diewald Robert
Emitec Gesellschaft für Emissionstechnologie mbH
Johnson Edward M.
Mayback Gregory L.
Silverman Stanley S.
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