WO2007028743A1

WO2007028743A1 - Method for producing a filter element and a support structure for a catalyst with improved heat resistance

Info

Publication number: WO2007028743A1
Application number: PCT/EP2006/065824
Authority: WO
Inventors: Bernd Schumann; Joerg Jockel; Matthias Kruse
Original assignee: Robert Bosch Gmbh
Priority date: 2005-09-06
Filing date: 2006-08-30
Publication date: 2007-03-15
Also published as: DE102005042209A1

Abstract

A method for producing a filter element and a filter element for an exhaust treatment device of an internal combustion engine with increased heat resistance and mechanical endurance under thermal stress in comparison with conventional ceramic bodies are proposed. The filter element consists of magnesium aluminium silicate and contains fibres (42), with preference coated fibres.

Description

A method of manufacturing a filter element and a support structure for a catalyst having improved temperature resistance.

State of the art

The invention relates to processes for the production of ceramic bodies with improved temperature resistance and ceramic bodies, in particular filter elements and support structures for exhaust aftertreatment devices of an internal combustion engine.

Filter elements for particulate filters of diesel engines and the support structures of catalysts for internal combustion engines are often made of cordierite. Pure cordierite has a very small thermal expansion coefficient and thus has a good resistance to sudden temperature changes (thermal shocks).

In the continuous or cyclic regeneration of the filter elements temperatures of over 1,000 ° Celsius can occur because the regeneration of soot is exothermic. Since the soot distribution within the filter element is not homogeneous and also the possibilities of heat dissipation locally are different, caused during regeneration local temperature differences in the filter element.

The local temperature differences in the filter element result in thermal stresses that can lead to the destruction of the filter element by cracks.

One possible starting point for reducing these thermal stresses is to design the engine control of the internal combustion engine so that impermissibly high temperature gradients in the filter element are reliably avoided. However, this leads to considerable restrictions in the control of the internal combustion engine and is therefore not advantageous.

The invention has for its object to provide a method for producing a filter element and a filter element, which is more robust in terms of thermal stresses than conventional ceramic body made of cordierite.

This object is achieved in a method for producing bodies of magnesium-aluminum-silicate, preferably cordierite, or a body of another ceramic material, wherein the starting materials of magnesium-aluminum-silicate or other ceramic material to a moldable mass be mixed, the moldable mass fibers are added. From this fiberized moldable mass, a body is then formed and subjected to a heat treatment.

Advantages of the invention

The ceramic body produced by the process according to the invention has a fiber-reinforced structure, which is mechanically very resilient and has a good internal damping. As a result, naturally increases the temperature resistance of the body produced by the process according to the invention.

An advantage of the method according to the invention is that, with the exception of the addition of the fibers to the moldable mass, no further process-related expense is required compared to the production of a cordierite ceramic body according to the prior art. Thus, the inventive method is very inexpensive and effective.

The mechanical strength of the body produced by the method of the invention can be further increased by coating the fibers before adding them to the moldable mass. Preferably, the fibers are coated with iron, cobalt, nickel, palladium, platinum and / or titanium. It has been shown in practical experiments that by the coating of the fibers in the finished ceramic body a direct

Contact between the actual ceramic material and the fibers is avoided, and that between the originally coated fibers and the ceramic material, an air cushion is formed. The increase in the thermo-mechanical stability of the ceramic body produced by the method according to the invention is based on an improved vibration damping by the fibers. This vibration damping is particularly effective when there is a cavity around the fibers that can absorb and dampen vibration present in the ceramic body.

The coatings of the invention act as a release agent between the fibers and the ceramic material. It has proven to be advantageous if the body is formed by extrusion, since in this method, in particular prismatic body with honeycomb-shaped cross-section can be made quickly and inexpensively.

The advantages of the invention are also achieved in a ceramic body of magnesium-aluminum-silicate, preferably cordierite, in particular a filter element or a support structure of a catalyst for an exhaust aftertreatment device of an internal combustion engine, if it is manufactured according to one of the preceding methods.

A particularly advantageous variant of the invention provides that the fibers of a temperature-resistant

Material exist. It has proved particularly advantageous if the fibers consist of magnesium-aluminum-silicate, preferably cordierite, or a material with similar properties, and that the material of the fibers is doped with a material which suppresses the sintering. This doping suppresses the sintering in the calcination process, so that the fibers remain as such after the calcination process.

Zirconium, lanthanum and / or cerium have proven to be suitable materials for doping the fibers.

Alternatively, it is also possible that the fibers consist of other ceramic materials. With regard to the dimensions of the fibers, a thickness of 3 .mu.m-6 .mu.m, more preferably of 3 .mu.m-5 .mu.m, has proven. For the length of the fibers have dimensions of 10 .mu.m - 100 .mu.m, more preferably from 10 .mu.m - 20 .mu.m, proved.

Further advantages and advantageous embodiments of Invention are the following drawings, the description and the claims removable. All features described in the drawing, the description and the claims 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,

FIG. 2 shows a longitudinal section of a filter element according to the invention,

FIG. 3 shows a flow diagram of an exemplary embodiment of the method according to the invention and

Figure 4 shows the structure of a body according to the invention.

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 particularly necessary in diesel engines to comply with legal requirements.

The filter device 14 comprises a cylindrical housing 16, in which one in the present embodiment rotationally symmetrical, also a total cylindrical filter element 18 is arranged.

FIG. 2 shows a cross-section of 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 at the

Exit surface 24 closed. 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 numeral) into one of the outlet channels 30. This is illustrated by the arrows 32 by way of example.

FIG. 3 is a flow chart of a

Embodiment of a method according to the invention shown.

In a first step 34, the materials required for producing a ceramic body are mixed together in the desired composition. Thereafter, temperature-resistant ceramic fibers are added to this mixture. Subsequently, in a third Step 38 of the mass given the desired shape in a molding process. Preferably, the shaping can be effected by extrusion.

The body resulting from the shaping process 38 is subjected to a heat treatment, in particular a sintering process, in a further step 40. The fibers retain their shape and structure and increase the mechanical strength of the ceramic material. Ideally, a small air cushion forms between the ceramic material and the fibers, which further increases the internal damping of the ceramic body produced by the process according to the invention.

FIG. 4 schematically shows the structure of a ceramic body produced by the method according to the invention. The ceramic workpiece is shown in Figure 4 by hatching. Fibers 42 are incorporated in this matrix. This structure is interrupted by various pores 44, which ensure the required for a filter element porosity of the ceramic body. As can be seen in FIG. 4, some of the fibers 42 protrude into the pores 44. This effect is desirable because it increases the storage capacity of the filter element, in particular for soot. If the fibers 42 have been provided with a suitable coating, the ends of the fibers 42 which protrude into the pores 44 may also have a catalytic effect.

In the right-hand part of FIG. 4, a dashed line 46 indicates by way of example that an air cushion 48 forms between the hatched ceramic body and the fibers 42 due to the coating of the fibers 42 before the sintering process. This air cushion 48 increases the internal damping of ceramic material and is therefore advantageous.

Claims

claims

1. A process for producing bodies of magnesium-aluminum-silicate, preferably cordierite, or a body of another ceramic material, characterized by the following process steps:

Mixing the starting materials of magnesium aluminum silicate or another ceramic material into a moldable mass,

Adding fibers (42) to the moldable mass,

Forms a body from the malleable mass and

Calcining and / or sintering the body.

A method according to claim 1, characterized in that the fibers (42) are coated prior to being added to the moldable mass.

3. The method according to claim 2, characterized in that the fibers (42) with iron (Fe), cobalt (Co), nickel

(Ni), palladium (Pd), platinum (Pt) and / or titanium (Ti) are coated.

4. The method according to any one of the preceding claims, characterized in that the body (18) is formed by extrusion.

5. Ceramic body made of magnesium-aluminum-silicate, preferably cordierite, in particular filter element (18) or support structure of a catalyst for an exhaust aftertreatment device of an internal combustion engine, characterized in that it is manufactured according to one of the preceding methods.

6. Ceramic body according to claim 5, characterized in that the fibers (42) consist of a temperature-resistant material.

A ceramic body according to claim 5 or 6, characterized in that the fibers (42) consist of magnesium-aluminum silicate, preferably cordierite, or a material having similar properties, and in that the material of the fibers (42) is doped with a material is, which suppresses the sintering.

A ceramic body according to claim 7, characterized in that the material of the fibers (42) is doped with zirconium (Zr), lanthanum (La) and / or cerium (Ce).

9. Ceramic body according to claim 5 or 6, characterized in that the fibers of a ceramic

Material, in particular of alumina and / or aluminosilicate exist.

10. Ceramic body according to one of claims 5 to 7, characterized in that the fibers (42) preferably have a thickness of 3 microns to 6 microns, more preferably from 3 microns to 5 microns.

11. Ceramic body according to one of claims 5 to 8, characterized in that the fibers (42) preferably have a length of 10 .mu.m to 100 .mu.m, particularly preferably from 10 .mu.m to 20 .mu.m.