Patent Application
20110173956
The invention relates to a particle trap disposed in a junction region between an exhaust gas line and an exhaust gas recirculation line. Such particle traps are used, in particular, in exhaust systems of (mobile) internal combustion engines. The invention also relates to an automobile having a particle trap.
With respect to the treatment of exhaust gasses of mobile internal combustion engines, such as for example spark ignition engines and diesel engines, efforts are made today to condition exhaust gasses in such a way that they can be output into the environment in a virtually completely purified form. Such post-treatment can be carried out, for example, by purifying the exhaust gasses in a catalytic converter and/or in a filter. It is also known to recirculate a portion of the produced exhaust gas back into the internal combustion engine. That means that a portion of the exhaust gasses is removed from the exhaust gas line and transported back to the intake side of the internal combustion engine through an exhaust gas recirculation line, in order to be introduced, together with the intake air, into the combustion chamber of the internal combustion engine. The purification of exhaust gasses of a diesel engine, which have a relatively large amount of non-combusted carbon particles, frequently also referred to as soot particles, represents a particular demand. An important objective of exhaust gas purification is to remove those carbon particles or soot particles from the exhaust gas of a diesel engine. Soot particles can also have an adverse effect during the recirculation of exhaust gas into the internal combustion engine. The objective of a particle trap between the exhaust gas line and the exhaust gas recirculation line is therefore to prevent the recirculation of carbon particles or soot particles and, if appropriate, also to hold back other solid bodies. Furthermore, the exhaust gas recirculation also influences the production and/or conversion of nitrogen oxides.
So-called soot burn-off filters are also used to a certain extent in exhaust gas lines in order to remove soot particles from the exhaust gas. Those soot burn-off filters are frequently fabricated from ceramic materials. Porous, sintered ceramic filters (“wall flow filters”) are frequently used. Ceramic filters are, in any case, already distinguished by a high degree of brittleness. That behavior is further reinforced by the different temperatures when used by an exhaust gas line. Small particles can easily become detached from a ceramic filter or a mounting mat surrounding the ceramic filter. If such solid bodies are fed back into the combustion chamber of an internal combustion engine through an exhaust gas recirculation line, they can cause considerable damage there. The ceramic particles behave there as abrasive bodies and can bring about considerable wear on engine components.
A filter device which is disposed in the exhaust gas recirculation line is capable of removing particles from the recirculated exhaust gas. However, a disadvantage of such a filter device is that it can become blocked by the particles. Once particles have been trapped by such a filter device, they continue to be held in the filter device by the continually flowing exhaust gas. As a result, the properties of the filter device change considerably. The permeability of the filter is reduced with the effect that, for example, an undesired drop in pressure can occur across the filter. Drops in pressure and permeability in turn influence the quantity of recirculated exhaust gas. Therefore, regular cleaning of the filter device is necessary in order to maintain filter properties which are constant over time.
In order to avoid regular cleaning of the filter device, it is known from Published German Application DE 38 33 957 A1, corresponding to U.S. Pat. No. 4,924,668, to place an exhaust gas filter insertion unit directly at the branching point between an exhaust gas line and the exhaust gas recirculation line. The exhaust gas filter insertion unit is disposed in that case in such a way that the surface runs parallel to the flow direction of the main exhaust gas stream. It is also stated that the exhaust gas filter insertion unit is to be manufactured from a porous sintering ceramic or from a sintering metal. A typical porosity value for such a filter device can be between 0.1 and 10 micrometers.
Published German Application DE 10 2006 013 709 A1, corresponding to U.S. Patent Application Publication No. US 2009/0071151, also discloses providing a cross-sectional widened portion in an exhaust gas recirculation line and providing a sieve layer in that cross-sectional widened portion. In that way, the pressure loss in the exhaust gas stream as a result of the filtering can be kept small.
It is accordingly an object of the invention to provide a particle trap for an exhaust gas recirculation line and an automobile having a particle trap, which overcome the hereinafore-mentioned disadvantages and further alleviate the highlighted technical problems of the heretofore-known devices of this general type. In particular, an especially cost-effective device for trapping particles upstream of an exhaust gas recirculation line is to be presented.
With the foregoing and other objects in view there is provided, in accordance with the invention, a particle trap disposed between an exhaust gas line and an exhaust gas recirculation line. The particle trap comprises at least one partially permeable hollow body separating the exhaust gas recirculation line from the exhaust gas line. The at least one partially permeable hollow body includes a wall defining a primary shape having an inner space with at least one open side. The wall is gas-permeable and has a secondary structure with elevations and depressions.
Such exhaust gas systems are usually embodied in such a way that they have a line section in which the exhaust gas recirculation line is connected by a flange or flanges to the exhaust gas line or is connected through the use of a welding seam there. To this extent, this device can, for example, also include a type of T element of the exhaust system.
The at least partially permeable hollow body is generally embodied in such a way that it has a wall through which exhaust gas can flow (preferably completely). This wall represents in this case in particular the fluidic boundary between the exhaust gas flow of the exhaust gas line and the exhaust gas flow which is recirculated by the exhaust gas recirculation line. The wall of the partially permeable hollow body accordingly includes a permeable material which gives the hollow body its permeability. The hollow body is quite particularly preferably configured in the manner of a radial sieve. It is also advantageous in this case if the wall of the hollow body is dimensionally stable, that is to say maintains its primary shape itself. In this context, it is considered advantageous that the wall is embodied with at least one entangled configuration, a fabric or mesh configuration or a sintered material, in particular metallic, temperature-resistant materials. The use of at least one nonwoven with wire filaments which are woven (asymmetrically), with the wire filaments being sintered to one another, is very particularly preferred.
The “primary shape” of the permeable hollow body is meant herein to refer to a geometric shape which substantially determines the shape of the hollow body. The primary shape therefore forms the shape of the hollow body, with the result that in particular at least 80% or even 95% of the volume of the hollow body is included in this primary shape. Pipe-shaped primary shapes are preferably used. In this context, a pipe-shaped hollow body with a circular cross section is preferred but, if appropriate, oval, triangular, square, rectangular or polygonal cross sections are also possible as a primary shape of the at least one partially permeable hollow body.
In most cases, there is an axial flow against the hollow body from at least one side, with the result that in particular an open side has to be provided so that the exhaust gas can be introduced into the inner space which is defined by the wall. Depending on the primary shape of the hollow body and/or the configuration of the hollow body in the exhaust system, the second side (which is fluidically opposite) can also be open, but it is also possible for that side to be closed off (fluidically), with the result that all of the exhaust gas entering the inner space then generally leaves the inner space again through the wall.
In addition to the primary shape, the hollow body also has a smaller secondary structure which is superimposed on the primary shape. A “secondary structure” means in this case in particular a (periodic and/or regular) deviation from the cross section of the primary shape in the transverse direction with respect to the profile of the wall (circumferential direction), for example radially outward, which is also referred to as elevated portions, and/or radially inward and is also referred to as depressions. It is possible, for example, to provide corrugated, folded, bent and/or meandering deviations. Elevated portions and/or depressions particularly preferably run over the entire axial extent of the primary shape of the partially permeable hollow body or of the wall, with the result that (linearly) elongate elevated portions and/or depressions are formed in the axial direction.
The secondary structure of the at least one partially permeable hollow body increases the strength of the particle trap. The particle trap proposed herein with a secondary structure can cope with significantly greater drops in pressure while having a significantly smaller thickness. Furthermore, the surface for the deposition of the particles is enlarged. In addition, it is also to be borne in mind that with the secondary structure it is possible to selectively generate microflows at the surface or into the wall. Such microflows can implement (for example as a function of the flow of the exhaust gas (speed, mass throughput rate, etc.)) a predetermined quantity of the exhaust gas mass flow which is to be recirculated and/or a predetermined embedding characteristic of the particles and/or a predetermined purification characteristic for the particle trap (or the wall). As a result, with this device, which is of simple construction, further significant advantages can be obtained in addition to the enduring protection of the components of the exhaust gas recirculation system and the purification of exhaust gasses.
In accordance with another feature of the invention, the exhaust gas line has a first central cross section and a first enlarged cross section which is widened as compared to the first central cross section. The at least one partially permeable hollow body is disposed in this case in the first enlarged cross section. It is thus possible to ensure, in particular, that there is not a direct flow against the hollow body or its wall but rather the hollow body or its wall is positioned, for example, in a flow shadow which is formed by the first enlarged cross section. In this way, it is possible, if appropriate, also to ensure an indirect setting of the exhaust gas recirculation rate by virtue of the fact that as the pressure in the exhaust gas line rises an increased flow into this “flow shadow” and therefore also through the hollow body to the exhaust gas recirculation line is established.
In accordance with a further feature of the invention, in this context, it is considered advantageous for the at least one partially permeable hollow body to be attached in the region of the first enlarged cross section to the exhaust gas line through the use of push-in ring connections. It is particularly advantageous if push-in ring connections, into which the (open) sides of the permeable hollow body can engage directly in a form-locking fashion, are provided in the exhaust gas line or in the widened portion of the exhaust gas line, in the region of the particle traps. A form-locking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements. Such push-in connections can, for example, be provided directly during the manufacture of a branching off component by punching or deep drawing. Fluidic advantages for the main exhaust gas stream (smaller drop in pressure) and less contamination are also achieved by the configuration of the push-in ring attachments in the flow shadow, so that changing the hollow body is unproblematical.
In accordance with an added feature of the invention, in the same way as the exhaust gas line, the exhaust gas recirculation line can likewise have a second central cross section and a second enlarged cross section, wherein the at least one partially permeable hollow body is disposed in the second enlarged cross section. With respect to the advantages of this construction, reference is made to the remarks given above, in which case it is to be noted in this case that due to the relatively small exhaust gas flows in this case it is possible, under certain circumstances, for flow losses and/or blocking to play a significantly greater role.
A combined configuration in which a permeable hollow body is disposed in the first enlarged cross section of the exhaust gas line and (respectively) in the second enlarged cross section of the exhaust gas recirculation line is basically possible, wherein then, if appropriate, different refinements of the hollow bodies should be present (for example in terms of permeability, stability, etc.).
In accordance with an additional feature of the invention, under certain circumstances, it is also appropriate for an open side of the at least one partially permeable hollow body to be closed off by a cap. As a result, it is possible, under certain circumstances, to simplify the manufacture by virtue of the fact that a tube-like hollow body with two open sides is made available, with a separate cap, through which there cannot be a flow, being attached (e.g. welded) to the wall thereof on one side. Furthermore, it is also possible for the cap (in particular a metal cap) to have a selective bypass, that is to say, for example, a small hole. It is then possible, under certain circumstances, for the cap also to be attached on both sides, wherein one cap is provided with a bypass function and one without a bypass function. In addition to the passage of the flow, the stability of the primary shape can also be set with the cap.
In accordance with yet another feature of the invention, it has proven particularly advantageous for the elevated portions and depressions of the secondary structure to run parallel to a first main direction of the exhaust gas line or to a second main direction of the exhaust gas recirculation line. As a result, the exhaust gas stream can flow (as a function of the load) through the depressions in the secondary structure without a large flow resistance and therefore clean the latter of deposited carbon particles or soot particles or ceramic particles.
In accordance with yet a further feature of the invention, the wall of the at least one partially permeable hollow body is preferably formed from at least one layer with elevated portions and depressions, wherein the at least one layer forms a region which overlaps with itself and in which the elevated portions and the depressions engage in one another in a form-locking fashion. A layer is understood in this case to be, for example, a planar filter material or sieve material, wherein basically also a plurality of materials (and, if appropriate, different materials) can be provided for embodying the wall. This layer can be positioned to form a primary shape with two open sides, with the result that it forms a region which overlaps with itself. The elevated portions and depressions of the layer can thus engage in one another in a form-locking fashion if the layer is rolled up so as to form an inner space. In this way, a stable, tube-shaped hollow body is formed without materially joined connections having to be formed in the overlapping region. The stability is provided in particular if such a hollow body is secured in a materially joined fashion at the edges of its open sides to an exhaust gas line or an exhaust gas recirculation line.
In accordance with yet an added feature of the invention, the stiffness of such a hollow body can additionally be increased by virtue of the fact that at least one support layer is provided which has a shape that corresponds to the secondary structure of the at least one hollow body. Although it would in principle be possible for the hollow body and the supporting layer which at least partially surrounds it to only bear against one another superficially, a (materially joined) connection of the two elements is preferred. The surface structures of the hollow body and of the supporting layer, for example with elevated portions and depressions, can then engage in one another in a form-locking fashion. Basically, the at least one supporting layer can support the hollow body from the inside and/or outside, and if appropriate integration into a plurality of layers of filter material and/or sieve material is also possible. Whether support from the inside or outside is preferred depends on the direction of action of a possible drop in pressure. The supporting layer should be provided in such a way that the drop in pressure presses the layer against the supporting layer.
In accordance with yet an additional feature of the invention, in the particle trap, a wall with meshes or openings of up to 0.3 mm is preferably used. The width of the meshes is preferably in the range of less than 0.2 mm and quite particularly preferably in the range from 0.05 mm to 0.15 mm.
With the objects of the invention in view, there is also provided an automobile, comprising an internal combustion engine, an exhaust system having at least one particle trap according to the invention, and an exhaust gas recirculation line defining a first flow direction leading to the internal combustion engine. The particle trap is disposed in such a way that the first flow direction in the exhaust gas recirculation line directly downstream of the particle trap runs counter to the force of gravity.
This means, in other words, in particular that the exhaust gas recirculation line or the junction region with the hollow body is subjected to the force of gravity in such a way that particles or the like fall out again from there automatically, specifically in particular back into the exhaust gas line again and from there further into the exhaust gas purification components of the exhaust gas line which are disposed downstream. It is quite particularly preferred in this case for the hollow body itself to have a center axis which is oriented substantially parallel to the force of gravity. In this way, the force of gravity can additionally counteract the deposition of soot particles and/or ceramic particles on the trap.
With the objects of the invention in view, there is concomitantly provided an automobile, comprising an internal combustion engine, an exhaust system having at least one particle trap according to the invention and at least one ceramic filter, and
an exhaust gas line defining a second flow direction leading away from the internal combustion engine. The at least one ceramic filter is disposed upstream of the particle trap in the second flow direction.
Furthermore, the exhaust gas recirculation line is preferably part of a low-pressure EGR (exhaust gas recirculation) system in which the exhaust system is therefore embodied with at least one turbocharger, and the exhaust gas recirculation line is disposed downstream of the turbocharger as viewed in the second flow direction.
If appropriate, the hollow body described herein can also, as an exhaust gas purification unit, advantageously be independent of the specific configuration in the exhaust system or in the exhaust gas recirculation line. A nonwoven for treating exhaust gasses in an exhaust gas recirculation line will be presented briefly herein, in which case it can also advantageously be used independently of the configuration, such as is described herein, for example also in an embodiment such as is specified in Published German Application DE 10 2006 013 709 A1, corresponding to U.S. Patent Application Publication No. US 2009/0071151, to which reference is additionally also made in this case with respect to the description of the configuration.
Accordingly, the nonwoven is a fabric in the manner of a 3-shed twill or 5-shed twill fabric (referred to as “Atlas fabric”, TELA fabric or fabric with a 5-shed Atlas binding). Such a nonwoven has warp filaments and weft filaments which are woven with one another at an angle of approximately 90°. In the nonwoven, the direction along the warp filaments is subsequently referred to as the warp direction and the direction along the weft filaments as the weft direction. The weaving of warp filaments and weft filaments is carried out in such a fabric so that the weft filaments run in each case above four warp filaments lying one on top of the other and subsequently below an individual warp filament. This profile repeats for each weft filament over the entire nonwoven. Two weft filaments lying one next to the other run in each case below different warp filaments. It is preferred in this case that a weft filament runs in each case below the warp filament after the next, below which the directly adjacent weft filament runs. This configuration results in a regularly repeated pattern which runs obliquely with respect to the weft direction and obliquely with respect to the warp direction in the nonwoven. The nonwoven, which may also be referred to as a fleece or mat and is woven in this way, is particularly robust and has a relatively smooth surface.
As a result of this type of fabric, a high throughflow with simultaneous stability can be achieved. In this context wire filaments (used as warp and weft filaments) of a different configuration can be used, specifically relatively thick warp filaments (for example 160 μm filament diameter) and relatively thin weft filaments (for example 150 μm filament diameter). In each case a tolerance of +/−4 μm is appropriate for the filament diameters, with the result that warp filaments have a diameter of at least 156 μm and at maximum 164 μm, and weft filaments have a diameter of at least 146 μm and at maximum 154 μm. In the finished fabric, the relatively thin weft filaments bend to a greater extent than the relatively thick warp filaments. This influences the shape of the available meshes.
Such a nonwoven has rectangular meshes which have a greater mesh width in the weft direction than in the warp direction. The mesh width in the warp direction should preferably on average be approximately 77 μm. In this context, a tolerance of +/−6 μm is appropriate. According to the invention, an average mesh width in the warp direction is thus at least 71 μm and at maximum 83 μm. In the weft direction, the mesh width should preferably be on average 149 μm. In this context, a tolerance of +/−10 μm is appropriate. According to the invention, an average mesh width in the weft direction is thus at least 139 μm and at maximum 159 μm.
The preferred mesh width and preferred filament diameter result in a mesh number of 107 meshes/inch or approximately 41 meshes/mm in the warp direction and a mesh number of 85 meshes/inch or approximately 33 meshes/mm in the weft direction.
Furthermore, it is appropriate to define a maximum mesh width in both the warp and weft directions in order to ensure that particles above a certain size generally cannot pass through the nonwoven. The largest permissible mesh width in the warp direction of 58 μm is proposed as a tolerance. A mesh must therefore have at maximum a mesh width of 135 μm in the warp direction. The maximum permissible mesh width in the weft direction of 84 μm is proposed as a tolerance. A mesh must therefore have at maximum a mesh width of 233 μm in the weft direction.
The properties of such a nonwoven can be checked, for example, by using a microscope. The number of filaments per length unit in the warp direction or weft direction can be determined by counting the filaments per length unit. The average mesh width can then be determined by subtracting the filament wire diameter from the pitch (distance between two filaments in the nonwoven).
The maximum permissible mesh width at least partially predefines the filter permeability. This can be determined by using a ball passage test. The greatest opening of the meshes in a fabric (nonwoven) is referred to as the ball passage. A precisely round ball can still pass through the fabric and a relatively large one is held back. From the definition it is apparent that given a genuinely polygonal mesh, the smaller of the two mesh widths (mesh width in the warp direction) substantially determines the ball passage. The permissible ball diameter in the case of a test with the nonwoven proposed in this case should be between 140 μm and 180 μm, preferably between 150 μm and 170 μm, and in particular between 155 μm and 160 μm. The permissible ball passage is therefore greater than the above-stated mesh width in the warp direction. This is the case because due to the fabric structure of the nonwoven and to the filament wire diameters in relation to the mesh widths, slightly enlarged passage openings compared to the defined mesh widths result obliquely with respect to the plane of the nonwoven (in particular not orthogonally with respect to the plane of the nonwoven spanned between the warp direction and the weft direction) for a predefined mesh width.
The thickness of the nonwoven should be between 0.4 and 0.5 mm and preferably be approximately 0.44 mm. The nonwoven should have an air permeability of between at minimum 4000 l/m2s and at maximum 8000 l/m2s, preferably between at minimum 5000 l/m2s and at maximum 7000 l/m2s and in particular between at minimum 5500 l/m2s and at maximum 6000 l/m2s, if the difference in pressure present across the nonwoven is 2 mbar.
For the further processing, the nonwoven should be free of oil films, auxiliary materials and other impurities.
It may, under certain circumstances, also be advantageous to integrate such a fabric, which is present as described above, differently into an exhaust gas recirculation line so that this combination can also separately form an unexpected further development of the prior art.
The wire filaments are preferably sintered to one another in this case in the form being used, that is to say in particular are not welded to one another.
If the nonwoven is used as the wall of a hollow body in the manner of a sieve, it may at least be characterized by one of the following parameters:
sieve area of at least 50 cm2 per 1.0 liter displacement of the internal combustion engine;
construction with (only) 2 different types of metallic wire filaments with different thicknesses, which are connected in a nonwoven with different orientation through the use of a sintered connection;
the degree of separation of the sieve of at least 0.05 mm, in particular 0.1 mm or even 0.25 mm (particles with a relatively small diameter generally flow through the sieve);
shape of the hollow body in the manner of a (flattened) cone;
hollow body (having at least one cap and) having a bypass;
wall thickness between 0.3 mm and 1 mm, in particular between 0.4 mm and 0.5 mm; and
material of the wall (wire, wire filaments, etc.) with the material no. 14841 according to the German Steel Key.
The mesh width of the sieve (and/or of the nonwoven described above) is preferably in the region of less than 0.3 mm, in particular of less than 0.2 mm and quite particularly preferably of less than 0.15 mm. In this context, the mesh width should equally preferably be at least 0.05 mm (millimeters).
Other features which are considered as characteristic for the invention are set forth in the appended claims, noting that the features which are disclosed individually in the claims can be combined with one another in any desired technically appropriate way and can be supplemented by explanatory data from the description, in which context further embodiment variants of the invention are disclosed.
Although the invention is illustrated and described herein as embodied in a particle trap for an exhaust gas recirculation line and an automobile having a particle trap, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now in detail to the figures of the drawing for explaining the invention and the technical field in more detail by showing particularly preferred structural variants to which the invention is not restricted, and first, particularly, to
The radially permeable hollow body 3 has a wall 27 which defines an inner space or chamber 5. The inner space 5 has two open sides 28. In
Furthermore,
Within the scope of the invention, a refinement of the particle trap 6 is also possible in which both a partially permeable hollow body 3 is provided in the exhaust gas line 2 and a second partially permeable hollow body 3 is provided in the exhaust gas recirculation line 1. All of the other improvements and developments, explained separately for the refinements of the invention illustrated in
Reference is made, merely for the sake of completeness, to the fact that the device described herein can be changed in many ways without departing from the inventive concept. In particular, the types of exhaust gas purification systems, heat exchangers, sensors, turbochargers etc., can be correspondingly constructed in accordance with the conditions of the internal combustion engine.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 038 983.8 | Aug 2008 | DE | national |
This is a continuation, under 35 U.S.C. §120, of copending International Application No. PCT/EP2009/060401, filed Aug. 12, 2009, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2008 038 983.8, filed Aug. 13, 2008; the prior applications are herewith incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2009/060401 | Aug 2009 | US |
| Child | 13026829 | US |
