EP1941133A1

EP1941133A1 - Filter element and filter for the aftertreatment of exhaust gases

Info

Publication number: EP1941133A1
Application number: EP06819064A
Authority: EP
Inventors: Bernd Reinsch; Teruo Komori; Lars Thuener; Dominik Huelsmeier; Christian Schiller
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-10-05
Filing date: 2006-09-29
Publication date: 2008-07-09
Also published as: US20080314008A1; JP2009511242A; DE102005047598A1; WO2007039579A1

Abstract

A filter element for an exhaust gas aftertreatment system in an internal combustion engine is made of a coated ceramic material and is therefore less sensitive to local overheating.

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 15. 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 is closed while another part of the channels is closed at the front end of the filter element become. As a result, two groups of channels are formed, namely the so-called inlet channels, which are closed at the rear end 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. This risk is especially in filter elements made of cordierite, since cordierite has a relatively low specific heat capacity and therefore can occur in the oxidation of soot deposits locally very high temperatures.

The invention has for its object to provide a filter element made of a ceramic material, preferably cordierite, which is relatively insensitive to the released during the oxidation of carbon deposits heat. This object is achieved with a filter element, in particular for filtering exhaust gases of a diesel internal combustion engine, with a parallel to the main flow direction of the exhaust gas extending 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, wherein the inlet channels and the outlet channels be limited by filter walls, achieved in that the filter walls are at least partially coated.

Advantages of the invention

The inventive coating of the filter walls increases their thermal inertia, so that the temperature rise resulting from the release of heat during soot oxidation is reduced. Thereby, the filter element according to the invention is more resistant to local differences in the loading of soot and to local differences in the heat dissipation of the heat generated during the oxidation of the deposited soot.

It is not necessary according to the invention that the entire filter element is coated. Rather, it is often sufficient if the areas of the filter element in which the highest operating temperatures occur are provided with a coating according to the invention.

It is particularly preferred if the filter walls are coated on the inside of the inlet channels. This ensures that exactly where the soot is mainly deposited, namely on the insides of the inlet channels, the thermal inertia of the filter walls is particularly high, so that the heat generated during the oxidation of the deposited soot is not too Inadmissibly high local temperatures within the filter element leads.

Basically, all coatings are conceivable as coating materials, which are chemically stable and inert to the filter material, in particular cordierite, and have a large volume and / or mass-specific heat capacity. In this case, any specific heat capacity that is greater than the specific heat capacity of the starting material of the filter element is to be regarded as large.

It has proved to be advantageous if the coating of the filter walls consists of oxides of the metals zirconium, cerium, lanthanum, titanium and / or aluminum. In all these oxides, the aforementioned boundary conditions, namely chemical resistance, inert behavior towards the filter material, in particular cordierite, temperature resistance and high specific heat capacity are met.

It has proven to be advantageous in practical experiments if the thickness of the coating is between 12 μm and 150 μm, preferably between 12 μm and 50 μm.

It goes without saying that in individual cases, the thickness of the coating can be chosen locally different. This makes it possible to protect the most thermally stressed areas with a thicker layer against inadmissibly high temperatures than the thermally less stressed areas of the filter element. In general, the areas around the longitudinal axis and seen in the flow direction rear end of the filter element are thermally stressed the most. Particular preference is given to those coating materials which, for example, in addition to the required properties, such as chemical stability, inert behavior towards the filter material, in particular cordierite, temperature resistance and high specific heat capacity have other properties, such as catalytic properties.

The filter element according to the invention preferably has filter walls with a porosity between 40% and 65%, particularly preferably between 45% and 55%.

It has also proved to be advantageous if the cell density of the filter elements is between 100 cpsi (cpsi = cells per square inch) and 300 cpsi, preferably between 180 cpsi and 240 cpsi.

Suitable materials for the filter walls of the filter element are alumina, magnesium silicate, preferably cordierite, titanium oxide, silicon carbide and / or aluminum titanate.

The performance of the filter element according to the invention is further increased if the cross-sectional areas of the inlet channels and the cross-sectional areas of

Exit channels in a ratio between 2.0 and 1.0, preferably between 1.7 and 1.1 form. For then the inside of the inlet channels is larger than the inner surface of the outlet channels. Since the storage capacity of the filter element for soot deposits essentially depends on the inlet surface of the inner surface of the inlet channels, the storage capacity of the filter element for soot is increased by the claimed geometry according to the invention. The advantages mentioned above are also achieved with a soot filter with a filter element, with a housing, with a feed line and with a discharge, 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 is a schematic representation of a

Internal combustion engine with an exhaust aftertreatment device according to the invention,

Figure 2 shows an embodiment of a filter element according to the invention in longitudinal section and

FIG. 3 shows an enlarged detail from FIG. 2,

Description of the embodiments

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. This is especially true for diesel Internal combustion engines required 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 filter element 18 according to the prior art. The filter element 18 is manufactured as an extruded shaped body from a ceramic material, such as cordierite. The filter element 18 is flowed through in the direction of the arrows 20 of 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 outlet surface 24. The sealing plugs are shown in FIG. 2 without reference numerals. In contrast, the outlet channels 30 are open at the outlet surface 24 and closed in the region of the inlet surface 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 (without reference numerals) in one of

Exit channels 30. This is exemplified by the arrows 32.

The outer diameter of the filter element 18 is denoted by D _{a in} FIG. In FIG. 3, a greatly enlarged section of the filter element 18 of FIG. 2 is not shown to scale. From the enlarged view of the filter element 18 it is clear that the inner walls of the inlet channels 28 are coated with a coating 36. Of course, like the filter walls 34, this coating 36 must be porous, so that the exhaust gases can pass from the inlet channels 28 into the outlet channels 30 both through the coating 36 and through filter walls 34. Since the heat load of the filter element in the region of the exit surface 24 is greater than in the region of the entry surface 22, the thickness D of the coating 36 increases in the direction of the exit surface 24.

Since, as already mentioned, the coating 36 has a higher specific heat capacity than the filter walls 34, the heat capacity of the filter element is adapted to the thermal load of the same by the locally different thickness D of the coating 36. As a result, it is achieved, on the one hand, that no impermissibly high temperatures occur in the region of the exit surface 24 and, on the other hand, that no unnecessarily thick coating 36 is present in the region of the entry surface 22.

The coating 36 may be applied by various conventional methods known in the art. One possible method is to dive onto the filter element 18 in a suspension which contains the substances forming the subsequent coating 36 and then to subject it to a further heat treatment. In this case, both sides of the filter walls 34 would be coated.

A one-sided coating, as shown in FIG. 3 is shown, and how it is advantageous for technical and economic reasons, for example, be achieved in that the filter element 18 is filled at the inlet surface 22 with a suspension, and then the filter element 18 is subjected to a heat treatment.

Because a connection is only possible via the porous filter walls between the inlet surface 22 and the outlet channels 30, it can be achieved in this way that only the inner surfaces of the inlet channels 28 are coated.

Alternatively, it is also possible to fill the suspension at the entry surface 22 and at the exit surface

24 apply a negative pressure, so that the suspension is sucked through the filter walls 34 therethrough. In this case, the size of the grains contained in the suspension is to be matched to the size of the pores of the filter element 18, that the grains are deposited on the inner surface of the inlet channels 28 and the liquid of the suspension is sucked through the filter walls 34.

Alternatively, it would also be conceivable to suck a powder in air by applying a pressure difference through the filter element 18. In this case, the pressure on the inlet surface 22 is greater than at the outlet surface 24 and the air mixed with powder is sucked into the filter element 18 at the inlet surface 22.

Furthermore, it is also possible to fill the filter element 18 from the inlet surface 22 ago with the suspension and then to put the filter element 18 in a rotational movement, so that the suspension is pressed against the filter walls 34 and in this way the in the Deposit suspension containing grains on the inner surface of the inlet channels 28.

Claims

claims

1. Filter element, in particular for filtering exhaust gases of a diesel internal combustion engine, with a parallel to the main flow direction of the exhaust gas extending longitudinal axis (26), with a plurality of parallel to the longitudinal axis (26) extending inlet channels (28), and with a plurality of parallel to the longitudinal axis ( 26) extending outlet channels (30), wherein the inlet channels (28) and / or the outlet channels (30) are bounded by filter walls (34), characterized in that the filter walls (34) are at least partially coated.

2. Filter element according to claim 1, characterized in that the filter walls (34) on the inside of the inlet channels (28) are coated.

3. Filter element according to claim 1 or 2, characterized in that a coating (36) of the filter walls

(34) consists of a chemically stable and compared to the filter material, in particular cordierite, inert material with high volume and / or mass-specific heat capacity.

4. Filter element according to claim 3, characterized in that the coating (36) of the filter walls (34) made of oxides the metals zirconium (Zr), cerium (Ce), lanthanum (La), titanium (Ti) and / or aluminum (Al).

5. Filter element according to one of the preceding claims, characterized in that the thickness of the coating (36) between 12 .mu.m and 150 .mu.m, preferably between 12 .mu.m and 50 .mu.m.

6. Filter element according to one of the preceding claims, characterized in that the thickness of the coating

(36) is locally different.

7. Filter element according to claim 6, characterized in that the thickness of the coating (36) in the region of an inlet surface (22) is minimal and in the region of an exit surface (24) is maximum.

8. Filter element according to claim 6 or 7, characterized in that the thickness of the coating (36) in

Range of the longitudinal axis (26) is maximum and in the range of the outer diameter is minimal.

9. Filter element according to one of the preceding claims, characterized in that the thickness of the filter walls (34) is between 12 mils (1 mil = 25.4 mm / 1000) and 25 mils, preferably between 17 mils and 22 mils.

10. Filter element according to one of the preceding claims, characterized in that the porosity of the filter walls

(34) is between 40% and 65%, preferably between 45% and 55%.

11. Filter element according to one of the preceding claims, characterized in that the cell density of the filter walls

(34) is between 100 cpsi and 300 cpsi, preferably between 180 cpsi and 240 cpsi.

12. Filter element according to one of the preceding claims, characterized in that the filter walls (34) made of aluminum-magnesium silicate, preferably cordierite, titanium oxide

(TiO ₂ ), silicon carbide (SiC) and / or aluminum titanate exist.

13. Filter element according to one of the preceding claims, characterized in that the inlet channels (28) on the inlet surface (22) of the filter element (18) begin and on an outlet surface (24) of the filter element (18) are closed, and that the outlet channels ( 30) are closed at the entry surface (22) and terminate at the exit surface (24).

14. Filter element according to one of the preceding claims, characterized in that the cross-sectional areas (A _e ) of the inlet channels (21) and the cross-sectional areas

(A _a ) of the outlet channels (23) form a ratio (A _e / A _a ) between 2.0 and 1.0, preferably between 1.7 and 1.1.

15. 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.