EP0286932B1 - Filtering arrangement for removing soot particles from the exhaust gases of a combustion engine - Google Patents

Abstract

A filter system for removing particulates from exhaust gases of an internal combustion engine, in particular a diesel engine, having at least one filter member formed by filter channels in the configuration of a honeycomb and made of a porous filter material, in which the region of the inlet openings of the filter channels open on the gas intake side, electrical resistance looped heating elements are arranged that are connected via a lead-in and a lead-out to a power supply. A secure positioning of the heating loops in the honeycomb is assured and contact errors are avoided. The loops of the resistance heating elements and/or the loop connections are received in grooves of the filter system in such a manner that they retain their pre-determined position despite vibrations, thermally-induced shape changes and the like. The grooves can be located in the filter member and/or in a cover plate overlying the inlet face of the filter member.

Description

The invention relates to a filter arrangement for removing soot particles from the exhaust gases of an internal combustion engine, in particular a diesel engine, with at least one filter body made of a porous filter material formed by honeycomb-arranged filter channels, wherein in the area of the inlet openings of the filter channels open on the gas inlet side, electrical resistance heating elements are arranged, which are arranged via a The supply line and a discharge line are connected to a power supply, and the electrical resistance heating elements, which are each assigned in the area of the inlet openings of the filter channels as several inlet openings and protrude in the form of loops into the filter channels.

Exhaust gas aftertreatment systems are known for reducing particle emissions, particularly in diesel engines. These usually consist of filter systems that retain and collect the particles present in the exhaust gas. The soot particles retained in the filter lead to an increase in the flow resistance in the exhaust system, so that the exhaust gas back pressure of the engine increases. This leads to an increase in fuel consumption and, in extreme cases, to engine shutdown. It is therefore necessary to remove the particles that have accumulated in the filter, for example by oxidation at high temperatures.

Honeycomb filters made of a porous ceramic material have proven to be useful as filter bodies for the retention of the soot particles. These honeycomb filters are formed by a large number of parallel filter channels, which are alternately on the gas inlet side and are closed on the gas outlet side so that the exhaust gases flow through the porous filter walls and the soot particles are deposited on the walls of the filter channels. The filter can be regenerated by burning off the collected particles.

The temperatures required to ignite the soot particles in the exhaust gas are often not reached frequently enough by diesel engines, so that regeneration is not ensured. Forced regeneration can be achieved by adding additional energy. A particularly energy-efficient regeneration can be achieved if the soot layer deposited on the filter body is ignited point by point in the inlet area of the filter channels by a brief supply of energy. The release of energy during the soot combustion that then begins leads to self-supporting soot combustion in the filter body. The soot layer can be ignited by loop-shaped resistance wires inserted into the opening of the filter channels, as described, for example, in US Pat. No. 4,373,330.

This document describes a filter arrangement for removing soot particles from exhaust gases of an internal combustion engine, in particular a diesel engine, with at least one filter body made of a porous filter material formed by honeycomb-arranged filter channels, whereby electrical resistance heating elements are arranged in the area of the inlet openings of the filter channels open on the gas inlet side The supply line and a discharge line are connected to a power supply, and the electrical resistance heating elements, which are each assigned in the area of the inlet openings of the filter channels as several inlet openings and protrude in the form of loops into the filter channels.

In filter arrangements of this type, however, there is the disadvantage that the loops do not remain in the channels due to vibrations and thermal effects, but migrate out of the channels after a more or less long operating time. Hence measures required to hold the heating conductor in the specified position, but the thermal effectiveness and the free mobility of the heating elements should be impaired as little as possible.

This requirement is not met by the arrangement described in US Pat. No. 4,512,786, since the heating elements are pushed into the outlet channel through the plug on the inlet side which is necessary for the function of the filter. By embedding the heating conductors in the plugs, both their thermal effectiveness and their mobility are significantly impaired.

A loop of the heating conductor must be inserted into as many filter channels of the honeycomb filter as possible for the regeneration to be as complete as possible. The number of filter channels that can be provided with loops of a heating conductor is limited by the electrical resistance of the heating conductor.

With a supply voltage of 12 V common in motor vehicles, the heating conductor length is approximately 15 to 25 cm, from which 10 to 15 loops can be bent. Ceramic honeycomb filters have around 1000 channels that need to be heated. A large number of individual heating wires bent into loops must therefore be used and connected in parallel for the filter to be heated as completely as possible. For the simultaneous regeneration of the entire filter, a high heating output is required, which cannot be applied by the vehicle's electrical system. The heating power can therefore only be applied by sequential regeneration of individual sections of the filter. This is e.g. known from US-A-4 427 418.

In order to be able to carry out sequential regeneration, the loop-shaped heating conductors have to be connected to small groups. The individual groups are electrically isolated from each other and connected to the vehicle's supply voltage so that they are switched on independently of one another can be. The distance between the individual connections, which must be electrically insulated from each other, is very narrow due to the small channel cross sections of approx. 2 x 2 mm. A mutual touch of the individual connections would lead to a short circuit during operation of the vehicle or to simultaneous switching on of several areas with high power consumption for the vehicle electrical system. When the wires migrate out, individual loops can also be bridged. As a result, the electrical resistance of the heating conductor drops, as a result of which the heating conductor temperature rises and the wire burns out.

Measures for the regeneration of exhaust gas filters are also described in US-A-4 456 457 for foam ceramic filters. Here, however, no loop-shaped heating elements are used, but rather more or less straight-line heating conductors which run in grooves to improve the heat transfer, the grooves being closed individually or overall by closing bodies to avoid heat radiation. The transfer of measures of this type to honeycomb filters therefore primarily encounters manufacturing problems.

The invention has for its object to provide a regeneration arrangement for diesel particulate filter of the type mentioned, that is, for honeycomb filters, in which a secure fixation of the heating loops in the honeycomb body is ensured in a thermally favorable and production-technically simple manner and short circuits are avoided.

This object is achieved in a filter arrangement of the type mentioned in the introduction in that the electrical connections of the loops of the resistance heating elements are inserted between the individual filter channels in grooves in the filter body or in a cover. The connections of the resistance heating elements are preferably accommodated in grooves, while the resistance heating elements are freely movable.

According to a further preferred embodiment it is provided that the grooves in the end face of the filter body are alternately formed in opposite directions, so that the resistance heating elements can be hooked in for fixing. Also, at least some of the grooves in the filter channels can be closed upwards after the resistance heating elements have been inserted, and it can be advantageous for the resistance heating elements to be covered with a material before the grooves are closed, which material burns or evaporates when the resistance heating elements are heated, so that there is no non-positive connection between the resistance heating elements and the filter.

In connection with the described task, it is advantageous that a gas-permeable cover plate is arranged in the flow direction of the exhaust gases in front of the resistance heating elements. The cover plate is preferably made of a material with low thermal conductivity and it can be formed by a lattice structure which forms flow channels, but it can also consist of open-pore ceramic foam.

The resistance heating elements and / or their connections can be accommodated in grooves of the filter body made of porous filter material, but they can also be accommodated in grooves in the cover plate or at the same time arranged in grooves in both the filter body and the cover plate.

It is advantageous that the resistance heating elements and / or their connections are guided over the end plugs of filter outlet channels, and the resistance heating elements and / or their connections can be arranged in a meandering shape on the input side of the filter body, whereby they can have a rectangular cross-section.

For a filter arrangement with the end face on the filter body arranged heating elements, in particular with heating elements arranged in individual heating zones, is provided in an advantageous embodiment of the invention that the free ends of the heating conductor are each connected via a connecting element to a supply line or discharge line which is guided at a distance from the end face. Such an embodiment has the advantage that a stable heating element is formed from each of a plurality of heating wires running parallel to one another with the inlets and outlets running transversely to the end region in each case, which enables reliable positioning of the heating wires, even if the filter arrangement, such as in a motor vehicle, is exposed to vibrations.

In an expedient embodiment, it is provided that the connecting element consists of a pipe made of electrically conductive material parallel to the direction of flow against the end face of the filter body, one end of which is firmly connected to the supply line or discharge line and the other end of which is firmly connected to the free heating wire end. This makes it possible to create a rigid component formed from the supply line or discharge line and connecting element, which can be brought up directly to the end face of the filter body and thus leads to an improvement in the fixation of the loop-shaped curved heating wire pieces in the filter channels. With the rigid connection piece created in this way, the connection of closely spaced heating conductors of different areas is made possible without the risk of a short circuit by bending the connection pieces when heated.

The connection between the connection piece and the pipe guided against the filter end face can be made in a simple embodiment by pressing in the heating conductor. A high thermal load at the clamping point during production, which is mechanically strongly stressed by vibrations, such as can occur when the heating conductor is welded on, is thus avoided. Soldering from the top of the filter is also possible.

In order to reliably prevent the heating loops from migrating between the connection points, the loops between the rigid connection pieces are additionally fixed at least at certain intervals. As a result of the different thermal expansion coefficients of the heating conductor material and the filter ceramic, there is a firm connection, e.g. would arise when gluing the heat conductor with ceramic glue, not possible. The heating conductor should also not be clamped firmly, as this could lead to material abrasion of the heating conductor in the long term due to the vibrations. In addition, a firm connection between the heating conductor and filter material leads to poorer heat transfer at this point, which would cause the wire to overheat locally.

In an embodiment of the invention it is therefore provided that the heating conductors on the filter end face are led at least in part through openings which are closed at the top. These openings are designed so that the heating conductor can move with a certain amount of play in it, so that mechanical stress due to the action of force is largely avoided. The heat transfer to the environment is not limited by the insulating effect of the ceramic, so that the heating conductor temperature in the opening does not rise.

The openings can be formed by grooves made in the filter face in the running direction or perpendicular to the running direction of the heating loops, in which grooves the heating conductors are inserted.

If several short grooves are inserted obliquely into the filter end face in the running direction of the heating conductor, the grooves are largely closed at the top in terms of production. A possible lateral migration is counteracted by the oblique groove prevented in the further course. If the groove is inserted vertically, it can be closed at the top after inserting the heating conductor. This can be done by the gas-permeable cover arranged on the filter face. The cover is drilled in the area of the connection ends of the heating conductors. It is therefore also possible to close only part of the groove length in the case of grooves in the direction of the heating conductor or part of the groove in the case of grooves transverse to the direction of the heating conductor approximately in the middle between the connection ends at the top. It is then sufficient to fix a few webs of gas-permeable plates on the filter end face transversely to the running direction of the heating conductors, for example by cementing them onto the plug of the honeycomb filter. It is then also possible to guide a few thin webs of ceramic gas-impermeable material, for example thin tubes, which do not substantially close the filter channels with their cross-section, on the plug of the honeycomb structure, so that the grooves are again partially closed are.

Fig. 1

zeigt einen Längsschnitt durch eine Filteranordnung.

Fig. 2

zeigt eine Teilaufsicht auf den Filterkörper in der Ausführungsform Gemäß Fig. 1

Fig. 3

zeigt einen Längsschnitt durch eine Filteranordnung mit Nuten in der Stirnfläche des Filterkörpers quer zur Laufrichtung der Heizleiter und poröser Abdeckung.

Fig. 4

zeigt eine Teilaufsicht auf den Filterkörper in der Ausführungsform gemäß Fig. 3

Fig. 5

zeigt einen Längsschnitt durch eine weitere Ausführungsform einer Filteranordnung mit Nuten in der Stirnfläche des Filterkörpers quer zur Laufrichtung der Heizleiter und elektrisch leitenden Schienen in den Nuten.

Fig. 6

zeigt eine Teilaufsicht auf den Filterkörper in der Ausführungsform gemäß Fig. 5.

Fig. 7

zeigt einen Längsschnitt durch eine Filteranordnung mit poröser Abdeckung auf der Stirnfläche des Filterkörpers und Nuten in der Abdeckung.

Fig. 8

zeigt einen ersten Längsschnitt durch eine Filteranordnung mit abwechselnd gegenläufig schräg angeordneten Nuten.

Fig. 9

zeigt einen weiteren Längsschnitt durch eine Filteranordnung mit abwechselnd gegenläufig schräg angeordneten Nuten entsprechend Fig. 8, wobei der Schnitt seitlich verschoben ist.

Fig. 10

zeigt einen Längsschnitt durch eine Filteranordnung mit Nuten in der porösen Abdeckung des Filterkörpers.

Fig. 11

zeigt eine Aufsicht auf den Filterkörper in der Ausführungsform gemäß Fig. 10.

Fig. 12

zeigt eine Teilaufsicht auf eine in mehrere Heizzonen unterteilte Filteranordnung.

However, the same configuration of the openings can also be produced by correspondingly arranged grooves in the cover plate or in the webs when the filter face is not machined. The invention is explained in more detail with reference to the drawings.

Fig. 1

shows a longitudinal section through a filter arrangement.

Fig. 2

shows a partial view of the filter body in the embodiment according to FIG. 1st

Fig. 3

shows a longitudinal section through a filter arrangement with grooves in the end face of the filter body transverse to the running direction of the heat conductor and porous cover.

Fig. 4

shows a partial top view of the filter body in the embodiment according to FIG. 3

Fig. 5

shows a longitudinal section through a further embodiment of a filter arrangement with grooves in the end face of the filter body transverse to the running direction of the heating conductor and electrically conductive rails in the grooves.

Fig. 6

shows a partial top view of the filter body in the embodiment according to FIG. 5.

Fig. 7

shows a longitudinal section through a filter arrangement with porous cover on the end face of the filter body and grooves in the cover.

Fig. 8

shows a first longitudinal section through a filter arrangement with alternating grooves arranged in opposite directions.

Fig. 9

shows a further longitudinal section through a filter arrangement with alternating oppositely inclined grooves corresponding to FIG. 8, the section being laterally displaced.

Fig. 10

shows a longitudinal section through a filter arrangement with grooves in the porous cover of the filter body.

Fig. 11

shows a plan view of the filter body in the embodiment according to FIG. 10.

Fig. 12

shows a partial view of a filter arrangement divided into several heating zones.

In Fig. 1, the placement and attachment of a resistance heating element in a filter arrangement is the beginning identified type recognizable. The resistance heating element essentially consists of a loop-shaped heating wire 1, the loops of which are inserted into the inlet openings of filter channels 2 of a filter body 3 designed as a honeycomb filter. It is also possible to design the heating wire in such a way that only the loops arranged in the channel consist of heating conductor material, while the connections between the individual heating conductors consist of material of lower electrical resistance. The exhaust gas flow flows through the filter channels 2 in the direction of arrow 18. The loops of the heating wire 1, as can be seen in FIG. 2, are inserted diagonally into the filter channels 2 having a square cross-section, so that a piece of heating wire, as also shown in FIG. 2, covers several filter channels 2 lying next to one another. To fix the heating wire 1 in the individual filter channels 2, it is bent so that it lies against the wall 4 of the filter channel 2 in question.

The ends 5 and 6 of the heating wire 1 are led out of the inlet opening of the respective filter channel and are connected above the end face 7 of the filter body 3 via connecting pieces 8, 9 to a feed line 17 or a corresponding discharge line (not shown here). The connectors 8, 9 are designed so that they fix the heating wire ends 5 and 6 in the filter channels. For this purpose, connecting lines 10 and 11 are made of a dimensionally stable, electrically conductive material, for example a thin-walled tube. The feed line 17 and correspondingly also the associated discharge line are then passed through the wall of the filter housing 12, in which the filter body 3 is fixed by means of a packing mat 13. In order to avoid electrical contact between the supply line 17 and the (grounded) filter housing 12, an insulation 14 made of ceramic material is used. Since the connecting pieces 8, 9 forming lines are thin-walled Pieces of pipe are into which the free ends 5 and 6 of the heating wire are inserted and connected to them, it is also ensured that contact with the adjacent connection 15 of a resistance heating element 16 forming another heating zone is avoided.

The length of the heating wire can not be chosen arbitrarily, but is determined by the specific resistance of the material, the cross section and by the surface power required to achieve the ignition temperature and by the electrical energy available. Thus, the number of filter channels 2 covered by a heating wire element is constant, so that, as shown in FIG. 2, the entire end face of the filter body is divided into several separate heating zones in view of the electrical power available.

2 shows the end face 20 of a ceramic honeycomb filter body with inlet channels 22 and the filter plug 23 closing off the filter outlet channels to the inlet side. In the embodiment shown, a heating wire 25 with its loops each covers nine inlet channels 22. Eight to ten heating wires 25 are in each case interconnected via power connection 28 and ground connections 27 to form a heating zone 26. The mass 27 is common to all heating zones 26, while the power supply for each heating zone 26 can be switched on individually (not shown). The individual resistance heating elements are designed such that the end face of the filter body 3 is divided into triangular and quadrangular, preferably rectangular, heating zones. Since the individual heating zones adjoin one another, all inlet channels 22 are connected to a heating element. The heating zones 26, each with eight to ten heating wires 25, cover almost all filter channels in the embodiment shown, so that the filter can be regenerated by sequential power supply to the individual heating zones.

In the embodiment shown in FIG. 3, the resistance heating wires 1 are arranged in grooves 51, which are formed perpendicular to the running direction of the heating wires 1 in the end face of the filter. The grooves 51 are so wide that the walls of the filter channels 2 are cut and the heating wires 1 can be inserted into the filter, as can be seen from FIG. 4. The advantage of guiding the grooves 51 perpendicular to the running direction of the heating wires 1 is that the mechanical processing of the filter end face takes place predominantly in the area of the filter plug. The grooves 51 are worked into the filter end face so deep that the heating wires 1 do not protrude beyond the end face. To fix the heating wires 1 in the grooves 51, a cover 52 made of a heat-resistant, gas-permeable, electrically non-conductive material, e.g. ceramic foam, attached to the filter face. The cover 52 need not cover the entire filter face. It is sufficient if the heating wires 1 are additionally held in the filter material at some points in order to avoid migration.

The grooves 53 made in the filter face perpendicular to the running direction of the heating wires, as shown in FIGS. 5 and 6, can also be closed at the top with electrically conductive rails 54, to which the individual heating loops 1 are attached. A low electrical resistance in the area of the transitions between the heating loops is particularly advantageous here, as a result of which the heat generated is particularly low here. The heating conductors are held in the filter material by the rails fixed in the ceramic material. The rails 54 do not need to cover the entire filter face. It is sufficient if the heating conductors 1 are additionally held in some places in the filter material with some rails in order to avoid migration.

A corresponding mounting of the heating conductors 1 on the filter end face is achieved if grooves 55, as shown in Fig. 7, in a cover 56 made of a heat-resistant, gas-permeable, electrically non-conductive material, e.g. ceramic foam. The main advantage of this embodiment lies in the easier production of the grooves 55, in particular when the cover 56 is produced by a casting process. The grooves 55 can then already be taken into account when casting the cover 56, so that subsequent processing is not necessary.

In the embodiment shown in FIGS. 8 and 9, the filter body 3 is provided on the end face 20 with grooves 47, 48 arranged alternately in opposite directions, which are expediently incorporated into the stopper 31 closing the outlet channels. FIG. 8 shows a first longitudinal section, while FIG. 9 is a second longitudinal section that is laterally displaced in the filter end face compared to FIG. 8. The advantage of this measure is that the resistance heating wire 1 is accommodated in alternately inclined grooves 47 and 48, so that it is, as it were, "hooked in" and requires no further fixation.

10 shows a further embodiment and arrangement of the resistance heating elements on the filter end face. For a better representation of the arrangement, the filter channels 32a, 32b are shown in an exaggerated size. In Fig. 10 and the associated front view in Fig. 11, only one heating zone is therefore shown schematically.

On the end face 33 of the ceramic filter body 30, which is designed as a honeycomb filter, a heating wire 34a, 34b, which is curved in a meandering manner in the plane of the end face 33, is arranged running across the filter plug 31. To a low flow resistance with large heat transfer To reach the surface, the heating wire 34a, 34b has a rectangular cross section, and it is arranged upright on the end face 33. Other cross-sectional shapes for the heating wire with a large heat transfer area are also possible. For example, resistance heating conductors with heat transfer fins can be provided. It is also possible to arrange several heating wires with a round cross section one above the other. In order to avoid heat losses from the heating wire 34a, 34b to the filter housing 37 and adjacent filter areas (not shown here) due to thermal radiation, a gas-permeable ceramic cover plate 35 is arranged above the heating wire 34 in a lattice structure defining flow channels, which radiates the radiation of the heating wire 34a directed against the exhaust gas flow. 34b absorbed and fed back to the heating area by convective heat transfer with the exhaust gas mass flow, represented by arrows 36 and 39. The cover plate 35 can, however, also be formed from another material with a different structure, for example from open-pore, that is to say gas-permeable, ceramic foam. However, it is essential that the material is radiation absorbing. The cover plate 35 and the filter body 30 are inserted into the filter housing 37 with a packing mat 38. The cover plate 35 can be designed so that it mechanically fixes the heating wire 34a, 34b on the end face 33 by pressing. In addition, the side of the cover plate 35 facing the heating wire 34a, 34b can be provided with a groove contour adapted to the meandering shape, which fixes the exact alignment of the heating wire 34a, 34b to the filter body 30.

The exhaust gas mass flow, represented by arrows 36 and 39, can flow past the heating wire 34a, 34b into the filter channels 32a in the arrangement shown with low flow resistance. For filter regeneration, the heating wire 34a, 34b is connected to a current source E via a switching device (not shown). This will remove the soot in the contact area ignited between the filter body 30 and the heating wire 34a, 34b, so that the soot deposit then burns off into the fitting channels 32a automatically.

In this embodiment, too, it is again necessary that the electrical energy required to generate the ignition temperature be matched to the electrical power available via the vehicle lighting system. Accordingly, here too, how the supervision acc. 12 shows a plurality of resistance heating elements 40 defining different heating zones arranged on the end face 41 of a filter body 42. The cover plate 35 shown in FIG. 11 has been removed. The heating zone in each case acted upon by a resistance heating element is larger in this embodiment because of the larger cross section of the heating wire and therefore comprises the arrangement of rectangular and triangular heating zones 45 and 46 shown in FIG. 12. The resistance heating elements are designed in such a way that the triangular heating zones 46 have half the size of the rectangular heating zones 45, so that two successive heating elements covering a triangular heating zone 46 have the same electrical resistance as a heating element covering a rectangular heating zone 45. In this arrangement, too, the individual heating elements can be switched on and off individually to the power supply via a switching device (not shown), so that the entire filter surface can be regenerated by successively switching the individual heating elements on and off.

The reference numerals used in the description, the claims and the summary at present or at a later point in time serve only to facilitate readability. Under no circumstances should they limit the scope of protection in any way.

Claims (18)

1. A filter arrangement for removing soot particles from exhaust gases of an internal combustion engine, especially a Diesel engine, having at least one filter body (3) of a porous filter material formed by filter passages (2) arranged in honeycomb form in relation to one another, where electric resistance heating elements (1) are arranged in the region of the entry openings (22) of the filter passages (2) open on the gas entry side, which resistance heating elements are connected by a supply lead (17) and a discharge lead with a current supply (SW) and are formed in each case in the region of the entry openings (22) of the filter passages (2) as electric resistance heating elements (1) allocated to several entry openings (22) and protruding in loop form into the filter passages (2), characterised in that the electric connections of the loops of the resistance heating elements (1) are inserted between the individual filter passages (2) into grooves (51, 53, 55, 47, 48) of the filter body (3) or of a gas-permeable covering (56).
2. A filter arrangement according to Claim 1, characterised in that the connections of the resistance heating elements (1) are firmly accommodated in grooves (51, 53, 55, 47, 48), while the resistance heating elements (1) are freely movable.
3. A filter arrangement according to Claim 1 or 2, characterised in that the grooves (47, 48) in the filter end face (20) are made alternately oppositely oblique so that the resistance heating elements (1) can be hooked in for fixing.
4. A filter arrangement according to any one of Claims 1 - 3, characterised in that at least a part of the grooves (47, 48) in the filter passages (2) is upwardly closed after the insertion of the resistance heating elements (1).
5. A filter arrangement according to Claim 4, characterised in that the resistance heating elements (1) are jacketed, before the closure of the grooves (47, 48), with a material which burns or evaporates away on heating of the resistance heating elements (1) so that there is no connection effective, due to force application, between the resistance heating elements (1) and the filter.
6. A filter arrangement according to any one of Claims 1 - 5, characterised in that a gas-permeable cover plate (35) is arranged before the resistance heating elements (1), in the direction (36, 39) of flow of the exhaust gases.
7. A filter arrangement according to Claim 6, characterised in that the cover plate (35) consists of a material having low thermal conductivity.
8. A filter arrangement according to either one of Claims 6 or 7, characterised in that the cover plate (35) is formed by a lattice structure defining flow passages.
9. A filter arrangement according to either one of Claims 6 or 7, characterised in that the cover plate (35) consists of open-pored ceramic foam.
10. A filter arrangement according to any one of Claims 1 - 9, characterised in that the resistance heating elements (1) and/or their connections are accommodated in grooves (51, 52, 55, 47, 48) of the filter body (3) of porous filter material.
11. A filter arrangement according to any one of Claims 1 - 10, characterised in that the resistance heating elements (1) and/or their connections are accommodated in grooves (55) of the cover plate (35).
12. A filter arrangement according to any one of Claims 1 - 11, characterised in that the resistance heating elements (1) and/or their connections are guided by way of the end stoppers (31) of filter outlet passages.
13. A filter arrangement according to any one of Claims 1 - 12, characterised in that the resistance heating elements (1) and/or their connections are bent in serpentine form on the entry side of the filter body (3).
14. A filter arrangement according to any one of Claims 1 - 13, characterised in that the resistance heating elements (1) and/or their connections have a rectangular cross-section.
15. A filter arrangement according to any one of Claims 1 - 14, characterised in that the grooves (51, 53, 55, 47, 48) extend transversely of the running direction of the resistance heating elements (1) and are filled out with electrically-conductive material so that the electric resistance of the resistance heating elements (1) in the region of the grooves (51, 53, 55, 47, 48) is lower compared with the region of the filter passages.
16. A filter arrangement according to any one of Claims 6 - 15, characterised in that,on the filter end face (7), the gas-permeable covering (35) covering at least some of the connections of the resistance heating elements (1) in the passages is provided with grooves (55) in such a way that the electrical connections between the loops of the resistance heating elements (1) lie between the individual passages (2) in the grooves (55) of the gas-permeable covering (35) on the end face (7) of the filter body (3).
17. A filter arrangement according to any one of Claims 1 to 16, characterised in that the free ends (5, 6) of the resistance heating elements (1) are each connected by way of an attachment element (8, 9, 10, 11) with a supply lead (17) or outlet lead guided with spacing over the end face (7) of the filter body (3).
18. A filter arrangement according to Claim 17, characterised in that the attachment element is formed by a tube (10, 11) of electrically-conductive material guided parallel to the flow direction (18) against the end face (7) of the filter body (3), one end of which tube is firmly connected with the supply lead (17) and/or discharge lead and the other end of which tube is firmly connected with the free heating wire end (5, 6) of the resistance heating element (1).

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