Power plants – Internal combustion engine with treatment or handling of... – Divider – collector – valve means – or boundary layer device...
Reexamination Certificate
2000-04-27
2001-11-06
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Divider, collector, valve means, or boundary layer device...
C060S299000, C422S176000, C422S211000, C422S220000
Reexamination Certificate
active
06311485
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a gas exhaust system for an internal combustion engine, in particular for vehicles.
Gas exhaust systems for internal combustion engines comprise an exhaust manifold in which the connector pipes from the individual combustion chambers are united to form a gas exhaust pipe. Generally, the gas exhaust pipe is directed rearward below the floor subassembly of the vehicle. To clean the flue gas, a catalyst with one or several catalyst elements is arranged in the gas exhaust pipe under the floor subassembly of the vehicle.
The catalytic effect of a coating on a catalyst element becomes active only above a relatively high operating temperature. When the distance between the exhaust manifold and the catalyst is relatively great, the operating temperature of the catalyst is reached only some time after the starting of the internal combustion engine (e.g. after two minutes). Since many vehicles are primarily used for short distance trips, the catalyst has not reached its required operating temperature over a great part of its operating time.
In order to reduce the warm-up time of the catalyst, i.e. the time until it reaches the required operating temperature, additional heating means are used, for example inductive heating of the catalyst, or heating the flue gas flow with gas or gasoline burners or heat accumulators located a short distance in front of the catalyst. The implementation of additional heating means results in an increase in weight, space requirement and cost.
In order to reduce the warm-up time of the catalyst, the catalyst may be located as close as possible to the exhaust manifold. Such an arrangement of the catalyst allows the required operating temperature to be reached very soon after the starting of the internal combustion engine. With this arrangement of the catalyst close to the exhaust manifold unburnt combustion gas mixtures may deposit in the catalyst and be ignited there. The resulting high combustion temperatures, as well as the sudden increase in pressure may cause damage to the catalyst. Pressure variations in the flue gas flow that occur near the exhaust manifold and caused by the delays between the outlet strokes of the combustion chamber, result in a degradation of the efficiency of the catalyst. Further, the distribution of the flow over the cross section of the exhaust pipe is strongly inhomogeneous just behind the exhaust manifold, seen in the flow direction. Due to the inhomogeneity of the flow, local overloads occur in the catalyst that may damage or destroy it.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a gas exhaust system in which the catalyst may be arranged close to the exhaust manifold.
In the present gas exhaust system for an internal combustion engine, a mixer is provided between the exhaust manifold and. the catalyst, the mixer being made of porous temperature-resistant material. The mixer homogenizes the distribution of the flow across the cross section of the exhaust pipe so that resultant local overloads are excluded. Likewise, the mixer compensates for pressure variations caused by the different opening times of the outlet valves. Further, due to its porous structure, the mixer also serves as a filter in which the not combusted combustion mixture deposits. The deposits are burned in the mixer so that a resultant destruction of or damage to the catalyst is excluded. Due to the temperature resistance of the mixer, the mixer is not damaged by the burning of the deposits.
Preferably, the mixer is a ceramic foamed material member. Ceramic foamed material members are porous and further have a high temperature resistance.
To avoid a too great backdraft of the flue gas flow due to the mixer and to improve the homogeneity of the flow distribution over the cross section of the exhaust pipe, the mixer may comprise a number of first channels arranged under an angle to the flow direction. Preferably, the mixer also comprises a number of second channels extending under an angle to the first channels and to the flow direction.
The mixer may be provided at the outlet of the exhaust manifold and within the flue gas pipe between the exhaust manifold and the catalyst. Preferably, the mixer is arranged immediately before the catalyst or within the catalyst hosing.
For the production of porous, temperature-resistant mixers, one may use flexible foamed plastic material members wetted with wetting material. By wetting, the entire surface of the structure of the foamed plastic material member is covered with the wetting material, for example, ceramic slip. Thereafter, the wetting material is cured. For curing, the wetted foamed plastic material member is heated to a degree that the foamed plastic material is removed by burning.
For producing a mixer suited for use in the gas exhaust system, the following method is proposed as a particularly advantageous method of production, wherein
at least one foamed plastic material member with a top and a bottom surface is formed from a flexible foamed plastic material,
the foamed material member being sheared in a first direction about a shear angle by being subjected to a first shearing force,
from the top and/or the bottom surface, first channels are formed in the foamed plastic material member thus sheared, the channels being formed under an angle to the normal of the top and/or bottom surface, this angle being different from the first shear angle, and
the first shearing force is relaxed and the foamed plastic material member restores itself.
The essential idea this method is based on is to first provide the flexible foamed plastic material structure with channels extending therethrough. For an improved mixing of the fluid passing through the member, these channels extend obliquely to the axial extension of the member. One could form these oblique channels under an angle other than 90° to the top or bottom surface of the foamed material structure or the foamed material member. This, however, makes the production process more difficult, which is due in particular to the flexible structure of the foamed material member. Therefore, in a first variant, it is proposed to shear the foamed material member, i.e., to subject the foamed material member to shearing forces. Now, the channels may be formed under an angle of 90°, in particular, to the top or bottom surface of the sheared foamed material member. When the shearing force acting on the foamed material member is subsequently relaxed so that the foamed material member is in its relaxed state, the channels extending through the foamed material member are oblique.
In the manner described above, first channels extending in a first direction may be formed in a foamed plastic material member. When the foamed plastic material member is sheared in another direction after the forming of the first channels, which direction is preferably opposite to the active direction of the previously applied shearing force, second channels may be formed in the foamed material member extending through the foamed material member in a direction different from that of the first channels. Thus, two groups of channels run through the foamed plastic material member, having different orientations.
Depending on the magnitude of the shearing forces and their effective directions, channels with different degrees of inclination may be formed in a formed plastic material member. The orientation of the channels also depends on the angle under which they are formed in the sheared foamed member.
The process steps of shearing the foamed plastic material member and of forming channels can also be performed simultaneously. To this end, for example, a punching tool may be set on the top or the bottom surface of the undeformed foamed member which is not yet subjected to shearing forces. As soon as the punching tool contacts one side of the foamed member, it is displaced relative to the opposite side of the foamed plastic material member so that shearing forces act on the foamed member. The punching is performed either upon reaching the
Becker Manfred
Hoffschmidt Bernhard
Meurer Josef
Denion Thomas
Deutsches Zentrum fuer
Diller Ramik & Wight
Nguyen Tu M.
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