DE102004001717A1 - Filter device, in particular for an exhaust system of an internal combustion engine - Google Patents

Abstract

A filter device is arranged in an exhaust system of an internal combustion engine. It filters out particles from a gas stream (32) and comprises a housing and at least one filter structure with filter pockets (22) arranged in the housing. These are limited by gas-permeable filter walls (24). It is proposed that at least one filter pocket (22) has a support element (34) made of a gas-permeable ceramic material.

Description

The The invention relates to a filter device, in particular for an exhaust system an internal combustion engine, which filters out particles from a gas stream and a housing and at least one in the housing arranged filter structure with filter pockets, which is limited by gas-permeable filter walls are.

A filter device of the type mentioned is from the DE 101 28 936 A1 known. The filter device shown there is a particle filter for an exhaust system of a diesel internal combustion engine. The filter walls in the known filter device are made of sintered metal and arranged so that wedge-shaped filter bags are formed. The tapered wedge edges of the filter pockets show against the flow direction of the exhaust gas, seen in the flow direction rear narrow side of a filter side is open. The filter bags are usually arranged side by side in such a way that an overall rotationally symmetrical annular filter structure is formed. In operation, the exhaust gas passes through the side walls of the filter bags, retaining particles. In the known filter device, the filter walls are formed by flexible sintered metal or sintered metal foils, which are assigned to separate support structures, such as perforated plates, fabric, or the like.

The The present invention has the object, a filter device of educate the aforementioned type so that they during a as long as possible Life has good filter properties.

These Task is in a filter device of the aforementioned Kind solved by that at least one filter pocket a support member made of a gas-permeable ceramic material having.

Advantages of invention

The Use of a ceramic material for the support element has the advantage that the support element even at a high temperature retains its shape, the Filter bag so even at high temperatures does not "coincide". High operating temperatures can but especially in filter devices of internal combustion engines occur again and again to those accumulated in the filter device soot to burn. Since the filter bags and thus the entire filter structure their Maintaining shape even at high operating temperatures, neither change the flow conditions in the filter device over their life is still significantly the filter effect of the filter walls with the time affected by appropriate deformations.

Furthermore allows the use of a gas-permeable ceramic material for the support element a uniform distribution the filter effect over the filter wall, it will be so by the support element not "covered" by the support element of the filter wall created at which then only a limited filter effect would. The filter device according to the invention therefore has a high efficiency.

advantageous Further developments of the invention are specified in subclaims.

First, will suggested that the overall outer shape of the support element at least approximately corresponds to the inner shape of the filter bag and the support element is arranged snugly in the filter bag. This facilitates the production and allows the shape preservation not only one Filter wall but the entire filter bag by means of the support element.

The Production is facilitated if the support element as a whole resilient Has properties and introduced into the filter bag under tension.

Especially it is also advantageous if the material of the support element has a greater porosity as the material of the filter wall. As a result, the flow resistance kept small. Ultimately, this comes for example in an internal combustion engine benefit both fuel consumption and emissions.

One particularly preferred material for the support element is SiC ceramic, and here in particular recrystallized silicon carbide. in this connection it is a wear-resistant, chemically resistant Material with adjustable porosity and pore size respectively Pore size distribution, which can also be very thermally stressed. Because SiC ceramic a high thermal conductivity has it too over a good thermal shock resistance.

In a further development, it is proposed that the support element is formed from an initially unfired SiC film, in particular folded, and then sintered. An unfired SiC film is flexible and can therefore be processed very easily. SiC-containing films which can be folded like paper are known. hereby can be created in a simple and inexpensive way filter devices whose filter structure has a large specific surface area.

A further preferred embodiment of the filter device records characterized by the fact that the support element longitudinal the filter bag seen at least partially meandering, Z-shaped, or is wavy. The support element can thereby easily with the necessary rigidity, but also be provided with a certain spring elasticity, which for a slight Applicability to or in a filter bag is helpful. Furthermore can such a support element be made from a single blank, without any connection work are required, which further simplifies the production and reduces the manufacturing costs.

the support element can also have a secondary function be assigned, the same those, for that to take care of the gas flow in the area of the filter wall is optimal. For this purpose, the support element designed so that flow channels formed be passed through which the gas stream.

there can achieve a mixed channel and wall flow become.

A particularly advantageous embodiment of the filter device according to the invention provides that the support element at least partially a layer of a catalytic material having. This creates a large catalytically active surface, which, for example, during nitrogen oxide reduction or when burning deposited soot particles ensures a high catalytic efficiency. This is especially true then, although the filter structure at least partially with a catalytic material is provided.

It It is understood that when using the catalytic coating the soot oxidation promoted to be, the support element to the upstream arranged wrapping element becomes. In this case, the catalytic material on the supporting or wrapping element be particularly easily applied, for example, that the support or wrapping element into the catalytic material when it is liquid, soaked.

In Further development is proposed that the support or wrapping element projects beyond the filter bag. This causes an increase in the catalytically active surface, which further improves the catalytic efficiency.

In many applications might the supporting one Effect of the support element be easiest to implement, if the support element at least partially is arranged inside the filter bag. As already indicated above, but is basically also conceivable that the support element at least is arranged around an area of the filter bag and so on armoring member forms. This is particularly recommended if the support or armoring member is provided with a catalytic coating which reduces soot oxidation promote should.

In Further development can be provided that the filter bag cuneiform is and that the support respectively armoring member has on the axial narrow side a rounding, which is an upstream Edge of the filter bag streamlined covered. This comes above all the efficiency of the filter device according to the invention benefit, since such a rounding turbulence can be avoided, which an uneven flow through the Filter structure would result.

Further It is proposed that the filter structure as a whole is rotationally symmetric is with a radially outside and / or flow space located within the filter pockets, that the support respectively armoring member at least partially disposed around a filter bag, and that the support or wrapping element in the flow space having projecting guide sections through which the gas stream at least partially from the flow space is led to the filter bags. This again increases the efficiency the filter device according to the invention.

drawing

following become particularly preferred embodiments the present invention with reference to the accompanying Drawing explained in detail. In the drawing show:

1 a schematic representation of an internal combustion engine with an exhaust system with a filter device in which a filter structure is arranged;

2 a perspective view of the filter structure of 1 ;

3 a partially exploded view of two filter pockets of the filter structure of 2 and a support member;

4 a view along the arrow IV of 3 ;

5 a representation similar 4 an alternative embodiment of a support member;

6 a representation similar 4 a still alternative embodiment of a support member;

7 a perspective view of the support element of 6 ;

8th a section across a filter bag with a support element arranged in this, which is constructed similar to that of the 6 and 7 ;

9 a simplified representation of a filter device with a filter structure with again modified support elements;

10 a representation similar 4 a still alternative embodiment of a support member; and

11 a perspective view of a filter bag with a serving as wrapping element support element.

description the embodiments

In 1 is an area of an internal combustion engine 10 shown. It includes an engine 12 with aggregates and optionally a diesel oxidation catalyst. The exhaust gases are via exhaust system 13 with an exhaust pipe 14 derived. In the latter is a filter device 16 arranged, which soot particles from the exhaust pipe 14 filter out flowing exhaust gas. This is particularly necessary in diesel engines or will be required to comply with legal requirements.

The filter device 16 includes a cylindrical housing 18 , in which in the present embodiment, a rotationally symmetrical, overall also cylindrical filter structure 20 is arranged. This includes a variety of wedge-shaped filter bags, of which in 2 only two with the reference number 22a respectively 22b are provided. These filter bags 22a and 22b are in 3 shown enlarged again.

Each of the wedge-shaped filter bags 22 has two lateral filter walls, of which in the 2 and 3 for reasons of clarity, only one with the reference numeral 24a respectively 24b is provided. The one inlet 26 of the housing 18 facing and in the 2 and 3 left or front edges of the filter walls 24a and 24b a filter bag 22 are connected, whereas the one outlet 28 of the housing 18 facing and in the 2 and 3 right or rear edges of a filter bag 22 spaced apart from each other. This results in the wedge shape of the filter bags 22 , The filter pockets are radially inward and radially outward 22 through a total of triangular filter wall sections 24c and 24d ( 3 ) locked.

The filter bags 22 are in the present embodiment annular around a central channel-like flow space 30 arranged and sealed to each other. This one is at his in 2 rear and invisible end closed by a sealing plate. Opposite the case 18 is the filter structure 20 also in the area of their in 2 at the back through in 1 sealed sealing devices not shown in detail. The filter bags 22 and finally the filter structure 20 forming filter walls 24 are made of sintered metal. It is an open-pore and gas-permeable structure, which filters out soot particles from the gas stream, if this through the filter walls 24 passes. A corresponding gas stream is in 3 through an arrow 32 indicated. The purified gas stream leaves the filter bags 22 about their in the 2 and 3 right or rear and open end.

The filter walls 24 the filter bags 22 are extremely thin. Into the inside of each filter bag 22 is therefore a wedge-shaped support element 34 used, which in 3 only for the filter bag 22b shown and there before the introduction into the filter bag 22b along the arrows 36 is shown. The support element 34 has an overall outer shape, which is approximately the inner shape of the associated filter bag 22b equivalent. It is sized to fit after insertion into the filter bag 22b in this is established in the fit.

The support element 34 has a comparatively high rigidity. This prevents that during operation of the internal combustion engine 10 the side filter walls 24a and 24b by the gas flow acting on it from outside 32 compressed inwardly, resulting in an undesirable increase in resistance of the filter device 18 would result. Through the support element 34 So it is ensured that the two filter walls 24a and 24b a filter bag 22 also have a distance from each other during operation. The support element 34 is therefore also referred to as a "spacer".

The support element 34 is made of a silicon carbide film. It has two corrugated side walls 38a and 38b and a roughly triangular upper wall 38c on. For this purpose, the silicon carbide film in the green ("green") state at the edges 40a and 40b folded. Before or after that, in the longitudinal direction of the support element 34 extending Shafts (without reference numeral) in the two side walls 38a and 38b brought in.

Then, the silicon carbide film is sintered, thereby maintaining its predetermined shape by the folding or waves. The underside (reference numeral 42 ) of the support element 34 is as well as his back 44 open.

Will the support element 34 now along the arrows 36 in the filter bag 22b inserted, the side walls spring 38a and 38b together, causing the support element 34 in the filter bag 22a is braced under a certain bias and is set in the sequence in this reliable.

The sintered silicon carbide ceramic, from which the support element 34 is made, has an open-pore structure through which the exhaust stream 32 can pass through. In this case, the porosity of the silicon carbide ceramic of the support element 34 larger than that of the sintered metal from which the filter structure 20 or the filter walls 24 the filter bags 22 are made. As a result, the flow resistance is reduced.

That in the 2 to 4 shown support element 34 is itself wedge-shaped overall with two side walls 38a and 38b and a wall in between 38c , But it is also possible, the support element 34 in cross-section with a so-called "Z-fold" to provide, as in 5 is shown. Also possible is a meander folding according to the 6 to 8th , It should be noted that here as below applies that such elements and areas that have equivalent functions to previously described elements and areas, the same reference numerals and normally are not explained again in detail.

Due to the meandering fold lies the support element 34 partially flat on the filter walls 24a to 24c the filter bag 22 at. This causes the exhaust gas not only between the support member 34 and the filter walls 24 the filter bag 22 flows, but also through areas of the wall 38 of the support element 34 passes through, as by the arrow 50 is indicated. This is for an additional function of the support element 34 exploited: This is namely with a catalytic coating 46 provided, which thereby on the support element 34 is applied by immersing it in the previously liquefied catalytic material. This results in a catalytic coating 46 not just on the outside of the walls 38 of the support element 34 like this in 8th is shown, but also inside the open-pore structure of the support element 34 , which results in a very large catalytically active surface.

Also the filter walls 24a to d the filter bag 22 are on their inside with a catalytic coating 48 Mistake. Both catalytic coatings 46 and 48 So lie downstream of the filter walls 24 and are flowed around by the already freed from the soot particles gas flow. The catalytic coatings 46 and 48 serve to promote the reduction of nitrogen oxides contained in the exhaust gas of the internal combustion engine or for the oxidation of CO and HC. Due to the meandering design of the support element 34 becomes the catalytically active surface on the support element 34 extraordinary big.

In 9 is a further modified embodiment of support elements 34 in a filter device 16 shown schematically. In the 9 shown support elements 34 correspond in cross section and with respect to the catalytic coating in the 6 to 8th shown support element 34 , To increase the catalytically active surface, those in the filter device 16 in 9 used supporting elements 34 but each one supernatant 50 on, with which they are axial over one to the outlet 28 pointing edge of the filter structure 20 survive.

Another possible cross section of a support element 34 is in 10 shown: Also this support element 34 has been made by folding it from a single silicon carbide foil and then sintering it. By folding accordingly 10 become flow channels 52a to d created by the channel flow of the purified exhaust gas within the support element 34 is enforced. In addition, by the "channel folding" at the in 10 shown support element 34 increases its catalytically active surface.

A further modified embodiment of a support element 34 shows 11 : Here is the support element 34 not inside, but outside the filter bag 22 arranged around this. It is therefore also referred to as a wrapping element. Although this in 11 is not visible, here is the support or wrapping element 34 provided with a catalytic coating. However, this does support the oxidation of upstream of the filter walls 24 the filter bag 22 deposited soot particles or of carbon monoxide and hydrocarbon.

In the area of the upstream narrow side of the filter bag 22 has the support or wrapping element 34 a protruding, folded-over tab of the silicon carbide film surrounding the comparatively sharp edge of the filter pocket 22 is pulled around and thereby a streamlined curve 54 forms. Over there has the support or wrapping element 34 in the area of its narrow longitudinal side several in the centric flow space 30 (see 2 ) projecting guide sections 56 on, through which the gas flow in the centric flow space 30 from this to the filter bags 22 directed.

Claims (13)

Filter device ( 16 ), in particular for an exhaust system ( 13 ) an internal combustion engine ( 10 ), which particles from a gas stream ( 32 ) and a housing ( 18 ) and at least one in the housing ( 18 ) arranged filter structure ( 20 ) with filter bags ( 22 ), of gas-permeable filter walls ( 24 ) are limited, characterized in that at least one filter bag ( 22 ) a support element ( 34 ) comprises a gas-permeable ceramic material. Filter device ( 16 ) according to claim 1, characterized in that the overall external shape of the support element ( 34 ) at least approximately the inner shape of the filter bag ( 22 ) and the support element ( 34 ) in the fit in the filter bag ( 22 ) is arranged. Filter device ( 16 ) according to one of claims 1 or 2, characterized in that the supporting element ( 34 ) has overall elastic properties and in the filter bag ( 22 ) is inserted under tension. Filter device ( 16 ) according to one of the preceding claims, characterized in that the material of the support element ( 34 ) has a greater porosity than the material of the filter wall ( 24 ). Filter device ( 16 ) according to one of the preceding claims, characterized in that the supporting element ( 34 ) is made of SiC ceramic. Filter device ( 16 ) according to claim 5, characterized in that the supporting element ( 34 ) formed from an initially unfired SiC film, in particular folded, and is then sintered. Filter device ( 16 ) according to one of the preceding claims, characterized in that the supporting element ( 34 ) in the longitudinal direction of the filter bag ( 22 ) seen at least partially meandering, Z-shaped, or wavy. Filter device ( 16 ) according to one of the preceding claims, characterized in that the supporting element ( 34 ) is designed so that flow channels ( 52 ) are formed, through which the gas stream ( 32 ). Filter device ( 16 ) according to one of the preceding claims, characterized in that the supporting element ( 34 ) at least partially a layer ( 46 ) of a catalytic material. Filter device ( 16 ) according to claim 9, characterized in that the support element ( 34 ) over the filter bag ( 22 ) survives. Filter device ( 16 ) according to one of the preceding claims, characterized in that the supporting element ( 34 ) at least around an area of the filter bag ( 22 ) is arranged around. Filter device ( 16 ) according to claim 11, characterized in that the filter bag ( 22 ) is wedge-shaped and the support element ( 34 ) on an axial narrow side of an upstream edge of the filter bag ( 22 ) streamlined covering rounding ( 54 ) having. Filter device ( 16 ) according to one of the preceding claims, characterized in that the filter structure ( 20 ) is rotationally symmetrical with a radially outside / and / or within the filter pockets ( 22 ) flow space ( 30 ) that the support element ( 34 ) at least partially around a filter bag ( 22 ) is arranged around, and that the support element ( 34 ) in the flow space ( 30 ) leading sections ( 56 ), through which the gas stream ( 32 ) at least partially from the flow space ( 30 ) to the filter bags ( 22 ).