WO2008148634A1

WO2008148634A1 - Filter and catalyst element

Info

Publication number: WO2008148634A1
Application number: PCT/EP2008/056100
Authority: WO
Inventors: Harald Bressler; Teruo Komori; Hans-Peter Frisse
Original assignee: Robert Bosch Gmbh
Priority date: 2007-06-05
Filing date: 2008-05-19
Publication date: 2008-12-11
Also published as: EP2165054A1; DE102007026108A1

Abstract

The invention relates to a prismatic filter element (8) for an internal combustion engine, which deviates in cross section from the ideal circular shape in such a way that the filter element (18) is connected positively to the surrounding housing (16).

Description

description

title

Filter and catalyst element

State of the art

The invention relates to a filter element for cleaning the exhaust gases of an internal combustion engine according to the preamble of claim 1 and a filter with a filter element according to the independent claim 5. Such filter elements are used for example as a soot filter for diesel internal combustion engines. But they can also be used as catalyst elements.

The filter elements often consist of a ceramic material and have a plurality of mutually parallel inlet channels and outlet channels.

Filter elements made of ceramic materials are produced by extrusion. This means that the blank of the filter element is a prismatic body with a plurality of mutually parallel channels. The channels of a blank are initially open at both ends. Such a blank may be completed to a catalyst element if its surface is provided with a catalytically active coating.

When the blank is to become a filter element, a part of the channels at the rear end of the filter element is closed, while another part of the channels are closed at the front end of the filter element. As a result, two groups of channels are formed, namely the so-called inlet channels, which are closed at the end, and the so-called outlet channels, which are closed at the beginning of the filter element.

Then there is only the porous between the inlet channels and the outlet channels Walls of the filter element (hereinafter filter walls) a flow connection, so that the exhaust gas can only flow through the filter element by flowing from the inlet channels through the walls of the filter element into the outlet channels. In this case, the soot contained in the exhaust gas deposits in the filter walls.

During the regeneration of the filter elements, these soot deposits are oxidized, whereby heat is released. This results in a temperature increase in the filter element. If the temperatures occurring during regeneration become too great, the filter element will be damaged. This risk is present especially in filter elements made of cordierite, since cordierite has a relatively low specific heat capacity and therefore in the oxidation of

Soot deposits locally very high temperatures can occur. As a result, such high temperatures and so large temperature differences within the filter element can occur during regeneration in critical engine operating points that the filter element gets cracks and thus unusable.

Due to the manufacturing process, these filter elements are manufactured as prismatic bodies. Usually, these filter elements have a circular cross section and are pressed together with a sealing mat in a housing of a filter device. It is essential for the function of the filter device that the sealing mat gas-tightly closes the gap between the housing and filter element, otherwise a bypass to the

Filter element would arise and thus flow parts of the exhaust gas to be cleaned unfiltered through the filter device.

Due to the large thermal and mechanical stresses, in particular by vibrations of the internal combustion engine, there is a risk that the filter element in the

Sealing mat loosens and twisted relative to the housing. This relative movement between the sealing mat and filter element causes an increasingly larger gap between the sealing mat and the filter element is formed, which forms a bypass for the exhaust gas.

Disclosure of the invention The invention has for its object to provide a filter and catalyst element and filter devices whose Filtration- or conversion rate over the entire life remains at the highest possible level and their life is still increased.

This object is achieved with a filter element, in particular for filtering or catalytic cleaning of exhaust gases of an internal combustion engine, with a parallel to the main flow direction of the exhaust gas longitudinal axis, with a plurality of inlet channels, with a plurality of outlet channels, wherein the inlet channels and / or the Outlet passages are limited by filter walls, wherein the filter element is circular in cross-section, achieved in that the circular cross-section over the circumference of the filter element distributed deviations are superimposed.

These deviations in the radial direction result in a positive connection between the sealing mat and the filter element, and thus a rotation of the filter element about its longitudinal axis within the housing of the filter device is effectively prevented.

As a result, the connection, the seal between the filter element and housing remains effective through the sealing mat over the entire life, so that even at the end of the life of the filter element, the entire exhaust gas to be cleaned flows through the filter element and thus the filter rate of a erfinduingsgemäßen filter device and the conversion rate a catalyst element remains at a high level throughout its lifetime.

A further advantage of the filter element according to the invention is that it does not cause any additional costs, since the costs for the production of an extrusion unit for producing a conventional filter element and an extrusion unit for producing the filter element according to the invention are the same.

It has proven to be sufficient if a radius of the filter element in the range of the deviations deviates by at least 0.2 mm in the radial direction from the circular shape. Deviations from larger diameters or towards smaller diameters are possible. Particularly advantageous is a combination of these deviations, so that in total an at least partially "wavy" outer contour of the Filter element results.

It has also proven to be advantageous for filter elements whose filter walls are perpendicular to each other in cross section that a radius to the deviations cuts the filter walls at an angle between 20 ° and 70 °, preferably at an angle between 30 ° and 60 ° ,

Thereby, the advantage according to the invention is achieved that the filter walls, which cut a radius at an angle of about 45 °, are exposed to a higher pressure load, as the other filter walls, the pressure load is substantially parallel to its extension. Namely, when the filter walls are acted upon at an angle of about 45 ° with a radially inwardly acting compressive stress, this compressive stress can be better introduced into the filter element, so that a higher pressure load is possible. This higher pressure supports the internal strength of the filter element against so-called "ring off cracks" and "face cracks". Thus, it is also ensured at the same time that the inventive

Filter elements greater temperatures or larger resulting from temperature differences internal stresses withstand without cracks.

The aforementioned object is also achieved in a filter device with a filter element, with a housing and with an exhaust pipe, achieved in that the filter element is a filter element according to one of the preceding claims.

In these filter elements, the housing usually has an annular cross-section. Due to the different circumferential compressive stresses between the filter element and the housing, which are transmitted through the sealing mat, the housing deforms locally, especially where the radius of the filter element is greater than that of a filter element with an ideal circular shape. As a result, the positive connection between the filter element and the housing and the sealing mat arranged therebetween is further improved and the safety against rotation of the filter element relative to the housing is further improved.

Alternatively, it is also possible that the housing has deviations from the circular shape in cross section, which correspond to the deviations of the filter element. Then results even without elastic or plastic deformation of the housing during insertion of the filter element a positive connection between housing and filter element.

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable. All mentioned in the drawing, the description and the claims advantages may be essential to the invention both individually and in any combination.

Brief description of the drawings

Show it:

Figure 1 is a schematic representation of an internal combustion engine with an exhaust aftertreatment device according to the invention and

Figure 2 shows an embodiment of a filter element according to the invention in a longitudinal section and Figures 3 and 4 further embodiments of inventive filter elements in cross section.

Embodiments of the invention

In Figure 1, an internal combustion engine carries the reference numeral 10. The exhaust gases are discharged via an exhaust pipe 12, in which a filter device 14 is arranged. With this soot particles are filtered out of the exhaust gas flowing in the exhaust pipe 12 to comply with legal requirements.

In the exemplary embodiment illustrated in FIG. 1, the filter device 14 comprises a cylindrical housing 16, in which a filter element 18, which is also rotationally symmetrical in the present exemplary embodiment, is also arranged. Of course, the invention is not limited to these geometries.

FIG. 2 shows a cross section through a first exemplary embodiment of a filter element 18 according to the invention. The filter element 18 is manufactured as an extruded shaped body from a ceramic material, such as cordierite. The filter element 18 is in Direction of the arrows 20 flows through not shown exhaust gas. An entrance surface has the reference numeral 22 in FIG. 2, while an exit surface in FIG. 2 has the reference numeral 24.

Parallel to a longitudinal axis 26 of the filter element 18 extend a plurality of inlet channels 28 in alternation with outlet channels 30. The inlet channels 28 are closed at the second end face 24. The sealing plugs are shown in FIG. 2 without reference numerals. In contrast, the outlet channels 30 are open at the second end face 24 and closed in the region of the first end face 22.

The flow path of the unpurified exhaust gas thus leads into one of the inlet channels 28 and from there through a filter wall 34 into one of the outlet channels 30. This is illustrated by the arrows 32 by way of example.

It can be clearly seen in FIG. 2 that the filter element 18 is surrounded on the outside by a sealing mat 36. This sealing mat 36 is in turn located within a wall 38 of the housing 16th

FIG. 3 shows a cross section through an exemplary embodiment of a filter element 18 according to the invention along the line A-A. Only two filter walls 34 are provided with reference numerals by way of example. For reasons of clarity, the inlet channels 28 and the outlet channels 30 are not provided with reference numerals.

A dashed line 40 is exactly circular, thus illustrating a cross section of a conventional filter element with a circular cross section.

As can be seen from FIG. 3, the cross section of the filter element 18 according to the invention has deviations 42 and 44 from the circular shape (see line 40) over an angular range of αi ~ 20 ° to 01 ₂ ~ 70 °. The X-axis and the Y-axis of the Korrdinatensystems are placed so that they are parallel to the filter walls 34. The filter walls 34 are arranged at right angles to each other in the illustrated embodiment.

The deviations 42 and 44 of the outer contour of the filter element 18 relative to a circular cross-section are shown greatly enlarged in FIG. It has become practical It has been found that in the radial direction an amount of about 0.2 mm is sufficient for the deviations 42 and 44 from the ideal circular shape in order to achieve the desired security against twisting of the filter element in the housing 16 (see FIG. 4).

If the deviations 42 and 44 are within the specified angle range between 20 ° and 70 °, particularly preferably between 30 ° and 60 °, an increased compressive force in the radial direction is introduced into the filter element 18, in particular in the region of the deviations 42. Since this force acts on the filter walls 34 essentially in an angle range between 35 ° and 55 °, this force can be very well dissipated into the interior of the filter element, without resulting in mechanical overloading and as a result to cracks in the filter element 18. These radial stresses caused by these deviations 42 and 44 increase the internal strength of the filter element against "ring off cracks" and "face catches".

4 shows an inventive filter element 18 is shown in the installed state. By clearly visible in Figure 4 positive connection between the sealing mat 36 and filter element 18 on the other hand, a rotation, indicated by the reference numeral 46, the filter element 18 is excluded relative to the sealing mat 36. The radial forces F _{R, which} are increased in particular in the region of the deviations 42, are shown by way of example in FIG. 4 in the region of the first quadrant.

The embodiment shown in Figure 4, the wall 38 of the housing 16 has a circular cross-sectional point. Alternatively, however, it is also possible to provide the wall 38, for example in the region of the deviations 44, with corresponding indentations 48, as indicated in the region of the second and fourth quadrants.

Claims

claims

A filter element, in particular for filtering exhaust gases of an internal combustion engine, having a longitudinal axis (26) running parallel to the main flow direction of the exhaust gas, having a multiplicity of inlet channels (28), and having a multiplicity of outlet channels (30), the inlet channels (28) being and / or the outlet channels (30) are bounded by filter walls (34), wherein the filter element (18) is circular in cross-section, characterized in that the circular cross-section deviations (42, 44) are superimposed.

2. Filter element according to claim 1, characterized in that a radius of the filter element (18) in the region of the deviations (42, 44) deviates by at least 0.2 mm from the circular shape (40).

3. Filter element according to claim 1 or 2, characterized in that the filter walls (34) in cross section perpendicular to each other, and that a radius to the deviations (42, 44) the filter walls (34) at an angle (α) between 20 ° and 70 °, preferably at an angle (α) between 30 ° and 60 °.

4. Filter element according to one of the preceding claims, characterized in that the filter walls (34) made of aluminum-magnesium silicate, preferably cordierite, titanium dioxide (TiC ^), silicon carbide (SiC) and / or aluminum titanate exist.

5. Filter device with a filter element (18), with a housing (16) and with an exhaust pipe (12), characterized in that the filter element is a filter element (18) according to one of the preceding claims.

6. Filter device according to claim 5, characterized in that the housing (16) in cross-section deviations (48) of the circular shape, which correspond to the deviations (42) of the filter element (18).

7. Filter device according to claim 5 or 6, characterized in that between Housing (16) and filter element (18) is a mat (36) is provided, and that the mat (36) closes the gap between the housing (16) and filter element (18) gas-tight.