Power plants – Internal combustion engine with treatment or handling of... – Divider – collector – valve means – or boundary layer device...
Reexamination Certificate
2001-08-08
2002-12-03
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Divider, collector, valve means, or boundary layer device...
C060S302000, C060S305000, C060S323000
Reexamination Certificate
active
06487854
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to an exhaust gas system with a collector for joining exhaust gas flows from two or more cylinders of a combustion engine. The collector has an outlet cross-section behind which a tubular jacket is connected and a honeycomb body is disposed in the tubular jacket. The invention furthermore relates to a method for applying flows of exhaust gas to a honeycomb body.
Regulations require improvement in the cold starting behavior of combustion engines with respect to their exhaust gas emissions. For that purpose, it is known to provide a first catalytic converter close to the engine, for example closely behind a manifold. Due to the high temperatures behind the manifold, that leads to rapid heating up of the catalytic converter disposed behind it. However, that catalytic converter is also exposed to high degrees of thermal and mechanical shocks at that location, because of pulsating exhaust gas flows.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an exhaust gas system with at least one guide surface and a method for applying exhaust gas flows to a honeycomb body, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and which improve an emission behavior of a combustion engine, in particular in a cold starting phase, and especially improve a useful life of a honeycomb body installed close to an engine.
With the foregoing and other objects in view there is provided, in accordance with the invention, an exhaust gas system, comprising a collector for joining exhaust gas flows from at least two cylinders of a combustion engine. The collector has an outlet cross-section. A tubular jacket is disposed downstream of the outlet cross-section in exhaust gas flow direction. A honeycomb body is disposed in the tubular jacket and defines a space between the outlet cross-section and the honeycomb body for conducting a flow. At least one first guide surface of the tubular jacket is disposed in the space for diverting at least a part of the exhaust gas flows.
Such a first guide surface delays the incidence of the individual exhaust gas flows upon the end surface of the honeycomb body facing the flow. Making the exhaust gas flows turbulent leads to an improved mixing of a total gas flow supplied to the honeycomb body which, in particular, improves the subsequent catalytic reaction. The measurement precision of a lambda probe for measuring oxygen content, which is optionally disposed in the collecting space or to the rear thereof, is increased, since the somewhat uneven composition of the individual exhaust gas flows is at least partially compensated for. As the flows of exhaust gas flow in the form of a pulsating flow into the collector, the first guide surface absorbs a pressure gradient and reduces it. The downstream honeycomb body is relieved to the extent of these pressure gradients. In this way, damage caused by the pulsating flow which could occur over a long period of operation, is advantageously avoided.
It is also advantageous to configure the first guide surface in such a way that the exhaust flows are diverted in front of the honeycomb body. Diversion, which means a substantial change to the original direction of the flow of exhaust gas flows, again delays their incidence upon the honeycomb body, so that in particular, interaction with the next pulse of exhaust gas from another exhaust gas pipe takes place in order to even out the pressure. In particular, a low pressure occurs in an advantageous manner after the pressure pulse, even in the other cylinders. Furthermore, because of the turbulence occurring in this way, it again makes it possible to obtain a good mixing of the fluid flows. A further development of the first guide surface is that it is configured in such a way that the flows of exhaust gas at least partially flow in reverse. This means that the exhaust gas flows are at least partially diverted back in the direction from which they have flowed. The first guide surface is preferably disposed in such a way that it is partly opposite the exhaust gas flows flowing into the chamber. A further development is that the first guide surface is disposed in such a way that direct flowing of the exhaust gas flows onto the honeycomb body is at least partially obstructed.
On one hand, this leads to limiting and preferably completely eliminating linear exposure of the end surface of the honeycomb body. With at least partial obstruction of the flow path, the pressure gradient is at least reduced to the point where possible damage to the honeycomb body occurring over a prolonged period of operation is prevented. Additionally, there are mixing effects between the individual exhaust gas flows. Chemical reactions, as well as homogenization of temperatures, can be obtained through the use of this mixing. Periodic differences in pressure in the individual exhaust gas flows can be compensated for in such a way that after turbulence of the flows has been obtained, a blended total exhaust gas flow impinges upon the end surface of the honeycomb body.
The first guide surface may use a guide plate for this purpose. The guide plate must be capable of absorbing temperature differences and pressure differences which occur. In particular, the first guide surface is configured in such a way that it reduces the free cross-section behind the outlet cross-section, to which in turn the free cross-section of the tubular jacket is joined. The first guide surface is therefore preferably constructed as a type of deflector.
Alternative and/or cumulative configurations of a first guide surface have regular or irregular holes distributed over part or all thereof, and/or notches on a lateral external edge, and/or at least one opening on an edge, and/or at least one arch or curvature on at least one of its surfaces.
An eddy space is preferably provided between the outlet cross section and the first guide surface, as a reaction space. There is sufficient space in the eddy space to ensure, for example, a mixing of the individual exhaust gas flows. Furthermore, this eddy space serves, in a certain way, as a steadying space for the entire exhaust gas flow finally impinging upon the end surface of the honeycomb body. Through the use of suitable dimensioning of the eddy space, the way in which mixing takes place, after eddying caused by the guide surface, can be adjusted. The layout of the eddy space also determines what pressure gradients of the individual exhaust gas flows act against one another, and can finally be homogenized. The eddy space also serves in the formation of an even temperature distribution within the entire exhaust gas flow finally impinging upon the honeycomb body.
Preferably, the first guide surface is disposed closer to the outlet cross-section than to the honeycomb body. For one thing, the guide surface absorbs a pressure gradient much earlier in this way. For another, in this way, a total flow resulting from different coinciding exhaust gas flows behind the guide surface is distributed over the subsequent free cross-section of the tubular jacket in such a way that the entire end surface of the honeycomb body receives the flow, homogenously over its cross-section.
In particular, the formation of rear turbulence behind the guide surface can be avoided, in combination with an appropriate layout of the flow surface. The same applies for the avoidance of areas in which a detached flow and thus an area exists, in which parts of the exhaust gas flow pause for a certain amount of time as compared to the rest of the flow. To the extent that one guide surface is insufficient for obtaining the advantages described, it is proposed to place a second guide surface between the first guide surface and the honeycomb body, in the space through which a flow is to take place.
The collector according to the invention is distinguished in that at least a first guide surface is a component of the collector. If it is, for example, a cast piece, the f
Denion Thomas
Emitec Gesellschaft fuer Emissions-technologie mbH
Greenberg Laurence A.
Mayback Gregory L.
Stemer Werner H.
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