WO2007033904A1

WO2007033904A1 - Filter element and filter for exhaust gas aftertreatment

Info

Publication number: WO2007033904A1
Application number: PCT/EP2006/066052
Authority: WO
Inventors: Bernd Reinsch; Hans-Peter Frisse; Teruo Komori; Lars Thuener
Original assignee: Robert Bosch Gmbh
Priority date: 2005-09-20
Filing date: 2006-09-06
Publication date: 2007-03-29
Also published as: DE102005044765A1

Abstract

The invention relates to a filter element for an exhaust gas aftertreatment device of an internal combustion engine. Said filter element consists of a ceramic material and is, due to its geometry, insensitive to local temperature differences and the resulting thermal stresses.

Description

Filter element and filter for exhaust aftertreatment

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 soot filter with a filter element according to the independent claim 12. Such filter elements are used for example as a soot filter for diesel internal combustion engines.

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.

In order for the exhaust gas to be cleaned to flow through the walls of the filter, a part of the channels at the rear end of the

Filter element closed while another part of the channels at the front end of the filter element closed

become. As a result, two groups of channels are formed, namely the so-called inlet channels, which at the rear End are closed and the so-called outlet channels, which are closed at the beginning of the filter element.

There is a flow connection between the inlet channels and the outlet channels only via the porous walls of the filter element, 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.

During the regeneration of the filter elements, the soot deposits are oxidized, whereby heat is released. Since more soot deposits in the interior of the filter element than at its periphery. In addition, because the heat dissipation at the periphery of the filter element is better than in the interior of the same, occur especially in the regeneration of the filter element local temperature differences, which lead to thermal stresses within the filter element.

If the thermal stresses become too great, cracks will be created in the filter element which will cause it to fail.

The invention has for its object to provide a filter element and a soot filter whose temperature resistance and resistance to thermal stresses is improved.

This object is achieved with a filter element, in particular for filtering exhaust gases of a diesel engine, with a parallel to the main flow direction of the exhaust gas longitudinal axis, with a plurality of parallel to the longitudinal axis inlet channels and a plurality of parallel to the longitudinal axis extending outlet channels, the inlet channels and the Outlet channels are limited by several filter walls, wherein a cross-sectional area of the filter element is coated with a network of a plurality of equally spaced grid lines and a plurality of spaced apart second grid lines, the filter walls along the first grid line and along the second grid lines, achieved in that extending in the direction of the first grid lines filter walls of two adjacent channels on different first grid lines.

Advantages of the invention

The fact that the filter walls of two adjacent channels in the direction of the first grid lines offset from each other, the structure of the filter element according to the invention in the direction of the first grid lines is softer and more flexible, so that from local

Temperature differences resulting thermal stresses are reduced and thus increases the load capacity of the filter element according to the invention over local temperature differences.

Furthermore, the filter element according to the invention allows different cross sections of the inlet channels and the outlet channels. This degree of freedom can be used to equalize the flow of the exhaust gas within the filter element and to optimize the soot loading of the filter element.

A particularly advantageous variant of the invention provides that the filter walls extending in the direction of the second grid lines of two adjacent channels also run on different second grid lines. As a result, the structure of the filter element according to the invention becomes softer and more flexible, also in the direction of the second raster lines that results in a still increased resistance to local temperature differences.

The invention is particularly preferably applicable when the grid lines enclose an angle of 90 °, corresponding to the two axes of a Cartesian coordinate system. Furthermore, however, the invention can also be used if the first grid lines with the second grid lines enclose an angle of less than 90 °, corresponding to the axes of a skewed coordinate system.

In the same way, it is also possible and advantageous if the first grid lines extend radially to the longitudinal axis of the filter element and the second grid lines form concentric circles about the longitudinal axis of the filter element. As a result, centrally symmetrical filter elements can be designed so that they have the advantages according to the invention.

It is possible that the cross-sectional area of the inlet channels in the interior of the filter element is geometrically similar to the cross-sectional area of the inlet channels arranged at the periphery of the filter element, and that the cross-sectional area of the inlet channels of the

Filter element are smaller than the cross-sectional area of the arranged at the periphery of the filter element inlet channels. It is thereby achieved that the flow resistance of the inlet channels at the periphery of the filter element which is related to the entry surface is lower than in the center of the filter element, so that the loading of the filter element over the entire cross-sectional area is made uniform. It should be noted that in the center of the filter element, the inlet channels are exposed directly to the back pressure of the exhaust gas from the exhaust pipe entering. As a result, the inlet channels in the interior of the filter element are exposed to a greater amount of exhaust gas than the inlet channels arranged at the periphery of the filter element. This tendency is counteracted by the geometry claimed according to the invention.

It has proved to be advantageous if the

Cross-sectional areas of the inlet channels has the shape of a square, a rectangle, a parallelogram or a cross.

The advantages mentioned are also with a

Soot filter with a filter element, with a housing, with a feed line and with a discharge, achieved in that a filter element according to the invention is used.

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.

drawings

Show it:

Figure 1 shows a soot filter with a filter element according to the invention in a side view and

Figures 2 to 4 cross sections of various embodiments of inventive filter elements.

Description of the embodiments

Figure 1 illustrates a soot filter 1 with a feed line 3, a diffuser 5, a housing 7 and a filter element 9 according to the invention in a partially sectioned side view.

The soot filter 1 flows through in the direction of the arrows 11.

To the housing 7 close a cone 13 and a derivative

15 on. The filter element 9 is connected in a gas-tight manner to the housing so that the exhaust gas (not shown) flowing in through the supply line 3 has to flow through the filter element 9.

The filter element 9 has an entry surface 17 and an exit surface 19. The filter element 19 is traversed by a plurality of channels extending from the

Entry surface 17 extend to the exit surface 19.

In order for the exhaust gas to flow through the walls (without reference numeral) of the filter element 9, the inlet channels 21 are open at the inlet surface 17 and closed at the outlet surface 19. The so-called outlet channels 23 are closed at the entry surface 17 and open at the exit surface 19. The closures of the inlet channels 21 and the outlet channels 23 are shown in Figure 1 as black areas without reference numerals.

The pattern illustrated in a partial section in FIG. 1, in each case of an inlet channel 21 which alternates with an outlet channel 23, is located over the entire length Cross-sectional area of the filter element continues in a conventional manner.

FIG. 2 shows a section through a first exemplary embodiment of a filter element 9 according to the invention. To describe the arrangement of the filter walls between the inlet channels 21 and the outlet channels 23, the cross-sectional area of the filter element 9 is conceptually divided by a network of first grid lines 27 and second grid lines 29.

The first raster lines 27.0, 27.1 to 27 n run in Figure 2 from top to bottom parallel to a non-drawn Y-axis of a conventional Cartesian coordinate system.

The second grid lines 29.0, 29.1 to 27n are parallel to an X-axis (not shown) of a conventional Cartesian coordinate system. This means that they are shown in Figure 2 as parallel horizontal lines.

For reasons of clarity, not all inlet channels 21 and all outlet channels 23 are provided with the corresponding reference symbols. The walls between the inlet channels 21 and the outlet channels 23 are shown in FIG. 2 as thick black lines without reference numerals.

For example, if you have the bottom row of

2, it is clear that these channels are delimited on their lower side in FIG. 2 by the second raster line 29.0. At the top, the inlet channels 21 and the outlet channels 23 of the lowermost row are replaced by the second Grid line 29.2 limited. The second grid line 29.2 is at the same time the underside of the channels 21 and 23 from the second row. This second row of channels 21 and 23 is again bounded above by the second grid line 29.4. This scheme continues throughout the cross-sectional area of the filter element.

The left-most inlet channel 21 of the lowermost row in FIG. 2 is bounded to the left by a filter wall which runs on the first grid line denoted by 27.1. To the right of this inlet channel 21 is bounded by a filter wall, which runs on the first grid line 27.3. The right adjacent thereto arranged outlet channel 23 is bounded on the one hand by the filter wall extending on the first grid line 27.3 and limited to the right by the filter wall extending on the first grid line 27.5.

Considering now the overlying series of inlet channels 21 and outlet channels 23 delimited upwardly and downwardly by the second grid lines 29.2 and 29.4, it is apparent that, for example, the leftmost inlet channel 21 to the left of the first grid line 27.0 and to Right is bounded by the first grid line 27.2. The exit channel to the right is to the left of the first grid line

27.2 limited and limited to the right of the first grid line 27.4.

If one looks at the course of the filter walls in the direction of the first grid lines 27, it is clear that the filter walls of two adjacently arranged channels 21 and 23 not aligned with each other, but each offset by a grid line are arranged to each other.

This repetitive offset is shown in Figure 2 by an arrow 31 hinted. From the

Illustration of the course of the filter walls by means of the arrow 29 is also clear that the filter walls, which extend in the direction of the first grid lines 27, in the example shown by a grid line between the first grid line 27 n and the first grid line 27. n + 1 change.

As a result, the filter element according to the invention is flexible and soft with respect to forces acting on the filter element in the direction of the first grid lines 27, so that the

Forces are reduced and no major internal tensions arise. This is particularly advantageous if the areas located in the interior of the filter element 9 are heated to a greater extent than the area arranged on the edge or the periphery of the filter element. The resulting thermal stresses can be significantly reduced by the inventive structure of the filter element 9.

FIG. 3 shows a greatly enlarged exemplary embodiment of a further filter element according to the invention, in which the filter walls of adjacent channels extend offset relative to one another not only in the direction of the first raster lines 27 but also in the direction of the second raster lines 29. The resulting pattern results in cross-shaped cross sections of the inlet channels 21 and square cross sections of the outlet channels 23. This structure is particularly flexible both in the direction of the first grid lines 27 and in the direction of the second grid lines 29. In addition, the cross-shaped cross-sectional area of the inlet channels 21 has the further advantage that its circumferential area is relatively large in relation to the cross-sectional area. This can - based on the cross-shaped

Cross-sectional area - relatively much soot deposited on the inner wall of the inlet channels before regeneration is required. In addition, a ratio of the cross-sectional areas of the inlet channels 21 to the cross-sectional areas of the outlet channels 23 greater than 1 (ÄEmtπttsfiache / A _Austr itt _S flat> 1) can be achieved by this structure.

The square cross-section of the outlet channels 23 is therefore particularly advantageous because with very small volume of space a very low flow resistance is achieved, so that the exhaust gases can flow through the outlet channels 23 with low pressure drop. When the distances of the first raster lines 27 from each other are different from the distances which the second raster lines 29 have from each other, exit channels 23 having a rectangular cross section can also be obtained. For then is a width b of the outlet channels unequal to a height a of the outlet channels 23. Accordingly, the geometry of the inlet channels 21 changes accordingly by this measure.

Of course, the inventive geometries described by way of example can also be transferred radially to centrally symmetrical arrangements.

With reference to FIG. 4 a, the exemplary embodiment according to FIG. 2 has been transferred, as it were, from the Cartesian coordinate system to a polar coordinate system. In this case, the first grid lines 27 are arranged in the form of radius beams, while the second grid lines 29 in the form of concentric circles around a center 33.

Also in this embodiment, the inventive offset between two extending in the direction of the first grid lines filter walls of adjacent inlet channels 21 and outlet channels 23 a.

In FIG. 4b, the exemplary embodiment according to FIG. 3 is transferred to a network of raster lines, in which the first raster lines 27 extend radially to the center 33 and the second raster lines 29 are arranged as concentric circles around the center 33.

It goes without saying that the inventive concept can also be applied to other filter elements in which the inlet channels 21 and / or the outlet channels 23 have other shapes than the squares, rectangles or crosses described by way of example.

Claims

claims

A filter element for filtering soot, in particular for filtering exhaust gases of a diesel internal combustion engine, with a parallel to the main flow direction of the exhaust gas longitudinal axis (25), with a plurality of parallel to the longitudinal axis (25) extending inlet channels (21), and a plurality of the outlet channels (21) and / or the outlet channels (23) are delimited by a plurality of filter walls, wherein a cross-sectional area of the filter element (9) with a network of a plurality of spaced apart first grid lines (23) 27. 0 to 27. n) and a plurality of spaced second grid lines (29. 0 to 29. n) is coated, wherein the filter walls along the first grid lines (27. 0 to 27. m) and along the second grid lines (29. 0 to 29. m), characterized in that two in the direction of the first grid lines (27. 0 to 27. n) extending filter walls of two adjacent channels (21, 23) on different first grid lines (27. n, 27.n + l).

2. Filter element according to claim 1, characterized in that two in the direction of the second raster lines (29.0 to

29. m) extending filter walls of two adjacent channels (23, 21) on different second grid lines (29 n, 29. n + l).

3. Filter element according to claim 1 or 2, characterized in that the first grid lines (27) with the second grid lines (29) enclose an angle of 90 °.

4. Filter element according to claim 1 or 2, characterized in that the first grid lines (27) with the second grid lines (29) enclose an angle smaller than 90 °.

5. Filter element according to claim 1 or 2, characterized in that the first grid lines (27) extend radially to the longitudinal axis (25) of the filter element (9).

6. Filter element according to claim 5, characterized in that the second raster lines (29) form concentric circles about the longitudinal axis (25) of the filter element (9).

7. Filter element according to claim 5 or 6, characterized in that the cross-sectional area of the inlet channels (21) in the interior of the filter element (9) is geometrically similar to the cross-sectional area of the at the periphery of the filter element (9) arranged inlet channels (21), and that the cross-sectional area of the inlet channels (21) in the interior of the filter element (9) is smaller than the cross-sectional area of the inlet channels (21) arranged at the periphery of the filter element (9).

8. Filter element according to one of the preceding claims, characterized in that the inlet channels (21) on an inlet surface (17) of the filter element (9) begin and at an outlet surface (19) of the filter element (9) are closed, and that the outlet channels ( 23) are closed at the entry surface (17) and terminate at the exit surface (19).

9. Filter element according to one of the preceding claims, characterized in that the cross-sectional area of the inlet channels (21) have the shape of a square, a rectangle or a parallelogram.

10. Filter element according to one of claims 1 to 5, characterized in that the cross-sectional area of the inlet channels (21) has the shape of a cross (Figures 3 and 4b).

11. Filter element according to one of the preceding claims, characterized in that the filter element (9) is rotationally symmetrical or centrally symmetrical with respect to its longitudinal axis (25).

12. Rußfilter with a filter element (9), with a housing (7), with a feed line (3) and with a derivative (15), characterized in that the

Filter element is a filter element (9) according to one of the preceding claims.