EP2616181B1 - Device for producing an electric field in an exhaust gas system - Google Patents

Description

The present invention relates to a device for generating an electric field in an exhaust system, in particular in the exhaust system of a motor vehicle. In particular, the invention relates to a device for the treatment of soot particles containing exhaust gas, which can be used in particular with a so-called electrostatic filter or electrostatic precipitator. In this respect, the invention is preferably used in the treatment of exhaust gases of mobile internal combustion engines in the automotive sector.

A large number of different concepts for removing soot particles from exhaust gases of mobile internal combustion engines have already been discussed. In addition to mutually closed wall-flow filters, open bypass filters, gravity separators, etc., systems have also been proposed in which the particles are electrically charged in the exhaust gas and then deposited by means of electrostatic attraction forces. These systems are known in particular under the name "electrostatic filter" or "electrostatic precipitator".

Thus, for such electrostatic filters regularly (multiple) spray electrodes and collector electrodes are proposed, which are positioned in the exhaust pipe. In this case, for example, a central spray electrode, which extends approximately centrally through the exhaust pipe, and a surrounding jacket surface of the exhaust pipe as a collector electrode used to form a capacitor. With this arrangement of the spray electrode and the collector electrode, an electric field is formed transversely to the flow direction of the exhaust gas, wherein the spray electrode, for example, can be operated with a high voltage which is in the range of about 15 kV. As a result, in particular corona discharges can be formed by which the particles flowing with the exhaust gas through the electric field are charged in a unipolar manner. Due to this charge, the particles migrate to the collector electrode due to the electrostatic Coulomb forces.

In addition to systems in which the exhaust pipe is designed as a collector electrode, systems are also known in which the collector electrode, for example, is designed as a wire grid. In this case, the addition of particles takes place on the wire grid for the purpose of possibly combining the particles with other particles, so as to achieve an agglomeration. The exhaust gas flowing through the grid then tears the larger particle agglomerates again and leads them to classical filter systems.

Although the systems described above have been found to be suitable for the treatment of soot particles, at least in tests, the implementation of this concept for series production in motor vehicles still represents a major technical challenge. This applies in particular with regard to the highly fluctuating, temporally very high Soot load in the exhaust gas. Likewise, the desired retrofittability of such a system for currently existing exhaust systems is still a major problem. In particular, occur in the exhaust system of motor vehicles regularly abruptly increasing amounts of exhaust gas, for example, in stationary internal combustion engines, which are used to generate electricity, not occur. Furthermore, exhaust systems, eg. Due to uneven floors, exposed to mechanical stress. In addition, it should be noted that with the increased performance or effectiveness of such exhaust systems with respect to the removal of soot particles also a (periodic and / or continuous) regeneration of the filter systems is required, in which the soot is converted into gaseous components.

In the regeneration of filter systems is in addition to the intermittent regeneration by brief heating, ie burning of the soot (catalytically motivated, oxidative reaction), also known to convert carbon black by means of nitrogen dioxide (NO ₂ ). The advantage of continuous regeneration with nitrogen dioxide is that the conversion of soot can already take place at significantly lower temperatures (in particular less than 250 ° C.). For this reason, continuous regeneration is preferred in many applications. But that leads to that Problem is that it must be ensured that the nitrogen dioxide in the exhaust gas comes into contact with the deposited soot particles to a sufficient extent.

Also in this context, there are technical difficulties in the realization of a permanent operation of such exhaust systems in motor vehicles, the different loads of the internal combustion engines lead to different exhaust gas streams, exhaust gas compositions and / or temperatures.

In addition, it should be noted that in the provision of such components for such a soot deposition system as simple as possible components should be used, especially those that can be produced inexpensively in the context of mass production. In addition, especially in the design of the electrodes to take into account that they may need to be positioned aligned in the exhaust pipe, in particular so that an undesirably high dynamic pressure or an undesirable turbulence of the exhaust gas in the region of the electrode does not occur.

The EP-A2-0 862 949 describes an exhaust treatment device that can be ionized by generating an electric field soot particles and disposed in an exhaust pipe of a diesel engine. The device comprises a plurality of tip electrodes connected to a tip electrode holder, wherein a row of tip electrode holders are each formed from a sheet metal. Several, each formed from a sheet of rows of tip electrode holders are arranged side by side and electrically connected to each other via connecting elements.

From the WO-A1-2010 / 021128 a device for the electrostatic cleaning of air is known. It comprises an ionization section and a separating section, through which air flows successively. The ionization device comprises a discharge electrode plate and ground electrode plate, which are arranged alternately transversely to the flow direction.

The DE 23 63 149 discloses an electrostatic precipitator for collecting dust from industrial exhaust gases comprising a plurality of discharge electrode plates juxtaposed in a gas flow and collecting electrode plates arranged substantially parallel to the gas flow. At the upstream edge of the discharge electrode plate and at the downstream edge of the collecting electrode plate, respectively, needle tips are attached via hollow profiles as discharge electrodes.

From the WO-A1-2009 / 15717 For example, a fan is known which has an air treatment device in which fresh air and room air are mixed together and treated by an ionization unit.

On this basis, it is an object of the present invention, at least partially solve the problems described with reference to the prior art. In particular, a device for generating an electric field in an exhaust system is to be proposed, which can be provided by simple means and known technologies as part of a series production. In addition, the device should be easy to integrate into an exhaust pipe, in particular so that a targeted alignment of the electrodes is made possible towards the desired electric field or the associated particle trap.

These objects are achieved with a device according to the features of claim 1. Further advantageous embodiments of the invention are specified in the dependent formulated claims. It should be noted that the features listed individually in the claims in any, technologically meaningful manner with each other can be combined and show further embodiments of the invention.

The inventive device for generating an electric field in an exhaust system of a mobile internal combustion engine has an exhaust pipe, in which at least one electrode is arranged, which is contacted with a power supply. In this case, the at least one electrode is formed with at least one metal sheet, the at least one electrode extends in the flow direction of the exhaust gas and all electrodes have in the flow direction of the exhaust gas a plurality of projections, which were generated by removing material of at least one metal sheet near the front edge, wherein the at least one electrode is integrated in a honeycomb copper.

This device is in particular a pole of an electrostatic filter. It is preferred that the electric field (possibly a pulsed) DC field is. In particular, voltages in the range of 10 kV to 30 kV [kilo-volts] can be generated. The exhaust system is in particular that of a mobile internal combustion engine, in particular that of a diesel engine of a motor vehicle. The region of the exhaust pipe, which is performed with a corresponding electric field, may optionally be electrically isolated, which may be realized in the axial direction of the exhaust pipe, as well as radially outward. The at least one electrode is positioned in the interior of the exhaust pipe, ie in the space through which the exhaust gas flows. The at least one electrode is electrically contacted with a power supply, for example by means of appropriate electrical conductors, connectors, solder joints, etc. Here, in particular, an electrically encapsulated implementation of the power supply through the exhaust pipe is preferred.

For an improved alignment of the electrode in the interior of the exhaust pipe and a simplified production and contacting of the electrode, it is now proposed that the electrode is formed with at least one metal sheet. A "metal sheet" is understood in particular to mean a (flat) strip of metallic flat material. The metal sheet can be made substantially smooth or flat, but it is also possible that the metal sheet is structured, so for example. has a corrugation. Especially with regard to the production of metallic honeycomb bodies as catalyst support in exhaust systems, the series production is already very advanced, so that here a precise design of similarly shaped metal sheets has already been implemented. This manufacturing knowledge can now be used to perform such metal sheets as electrodes and to use for generating a corresponding electric field. For this purpose, the metal sheet with corresponding contact conductors, electrical conductors, soldering points and the like is executed, so that possibly even with the use of insulating coatings or deposits for the metal sheet, a predetermined current path can be formed by the metal sheet itself. Of course, correspondingly electrically conductive materials come into consideration here.

Preferably, a flat side of the metal sheet is arranged parallel to the flow direction of the exhaust gas. Thus, the metal sheet represents the smallest possible flow resistance for the flowing exhaust gas.

The metal sheet is in particular of a material with a low ohmic resistance, which cumulatively or alternatively has only a low oxidation capacity. The metal sheet should preferably consist of a homogeneous material, so that a uniform field with a good ionizing ability is formed on the projections. The metal sheet preferably has a thickness of less than 0.1 mm, more preferably less than 0.065 mm, most preferably less than 0.035 mm. In this context, it is considered to be particularly preferred that the at least one electrode extends in the flow direction of the exhaust gas. In other words, that means that the metal sheet is arranged to the flow direction of the exhaust gas, that it represents the smallest possible flow resistance. In this respect, the flat side of the metal sheet is arranged in particular parallel to the flow direction of the exhaust gas. As a result of this arrangement and design of the electrode strong turbulence of the exhaust gas upon contact with the electrode and / or an increased pressure loss when passing the exhaust gas can be avoided.

In addition, the at least one electrode has a plurality of projections in the flow direction of the exhaust gas. A corresponding projection can be generated, for example, by the material of the metal sheets being removed near an end edge, for example being punched out. The remaining projections, which are directed in particular in the direction of the electric field, are suitable for forming local centers for the electric field. Possibly. It may also be useful that only these projections are contacted with corresponding electrical conductors, while remaining parts of the metal sheet are electrically insulated. So the power line can be targeted to these projections. Especially in this context, it is considered advantageous that the metal sheet or, the projections are arranged or aligned with respect to the exhaust pipe so that they have a uniform electric field towards a collector electrode, in particular a downstream particle trap result. It is particularly preferred that only one (single) metal sheet is provided, but which has a plurality of projections, each forming electrode tips. In particular, it is preferred that the at least one projection has a length of 15 mm [millimeter] to 20 mm [millimeter] in the flow direction, so that oscillation of the projections during operation is avoided.

Furthermore, it is proposed that at least three projections are each formed at a distance from at least two adjacent projections, wherein the distances are substantially equal. This means in particular that the distances differ by no more than 10%. Preferably, the distances are at least 10 mm, more preferably at least 30 mm, most preferably at least 50 mm. In this way, a very uniform electric field is formed which has local field strength maxima uniformly distributed over a cross section in the region of the projections. For this purpose, the projections on the metal sheet with a winding corresponding distance must be arranged to each other. In particular, the relatively large distances also prevent an (undesired) electric field from forming between the projections.

Preferably, the at least one projection forms a tapered electrode, wherein the tip of the projection has an angle of at most 30 °, preferably of at most 20 °, particularly preferably of at most 10 °. In addition, it is proposed that the at least one tip of the projection is oriented transversely to the flow direction, wherein tips of different projections can be aligned in different directions.

According to a development of the device, it is proposed that the at least one electrode is integrated in a honeycomb body. For example, it is known to provide metallic honeycomb bodies in which at least partially structured layers of metal foils are stacked, wound and / or wound to form substantially parallel channels. Although these metal foils of the honeycomb body may possibly be designed with a thinner material thickness, the honeycomb structure as a whole must be considered relatively stiff, so that the electrode can be securely fixed to the metal sheet with these metal foils or the honeycomb body. As a result, it is possible that the honeycomb body is a kind of support structure for the electrode or the metal sheet. It is obvious that the electrode may need to be electrically insulated from the honeycomb body. If, for example, electrically insulating coatings are provided here, they can also serve as a basis for electrical conductors to the electrode, which are simply applied to this electrical insulating coating.

According to a particularly preferred field of application of the present invention, it is finally proposed that the at least one electrode is arranged downstream of a particle trap in the flow direction of the exhaust gas. It is very particularly preferred that the here (directly) downstream particle trap serves as a kind of collector electrode. In this way, the soot particles which flow through the region between the at least one electrode and the particle trap are charged in the electric field positioned there and finally deflected toward the filter material of the particle trap. Of course, this can be done at the same time an agglomeration take place. The particulate trap is in particular a so-called open bypass filter in which there are no completely closed flow channels. The particle trap is rather formed with a metallic fleece and metallic corrugated layers in which openings, conductive structures, etc. are provided. The guide structures form flow bottlenecks in the flow passages, so that the residence time or impact probability for soot particles in the interior of the particle trap is increased. In this connection reference is made to the applicant's well-known patent publications which can be used to further characterize the particle trap and / or to regenerate it: WO-A-01/80978 ; WO-A-02/00326 ; WO-A-2005/099867 ; WO-A-2005/066469 ; WO 2006/136431 ; WO 2007/140932 ,

The regeneration of such a particle trap is preferably carried out continuously based on the CRT method. For this purpose, the device z. B. upstream of an oxidation catalyst in which (also) nitric oxide is oxidized to nitrogen dioxide, which then reacts with the soot in the particulate trap. In addition, it is also possible that such an oxidatively acting coating is realized in the particle trap itself, either in a zone thereof or in all areas of the particle trap.

Fig. 1:

eine erste Ausführungsvariante der erfindungsgemäßen Vorrichtung im Querschnitt, und

Fig. 2:

ein Detail einer weiteren Ausführungsvariante der Vorrichtung betreffend eine mit einer Wabenstruktur gebildeten Elektrode,

Fig. 3

eine Aufsicht in Strömungsrichtung auf eine Ausführungsvariante der Vorrichtung.

The present invention will be explained in more detail with reference to FIGS. It should be noted that the figures show particularly preferred embodiments, to which the invention is not limited. They show schematically:

Fig. 1:

a first embodiment of the device according to the invention in cross section, and

Fig. 2:

a detail of a further embodiment of the device relating to an electrode formed with a honeycomb structure,

Fig. 3

a view in the flow direction of a variant of the device.

Fig. 1 shows a first embodiment of the device 1 according to the invention for generating an electric field 2 in an exhaust system 3. The device 1 also includes a region of an exhaust pipe 4, in which at least one electrode 5 is arranged. In the embodiment variant shown here, a plurality of electrodes 5 are integrated into a (single) honeycomb body 10. For the corresponding electrical contacting a power supply 6 is provided, which is electrically isolated from the exhaust pipe 4 is passed through the electrical contact 12. The electrodes 5 are in this case formed with a (optionally separate) metal sheet 7, which extends substantially parallel in the flow direction 8 of the exhaust gas and the front side has a plurality of projections 9. In this case, the desired electric field 2 is formed between the electrodes 5 and the particle trap 11 following in the flow direction 8, in which the soot particles can agglomerate or be charged. The electrically charged particles then strike the particle trap 11, where they are preferably stored in or on the filter material and converted into gaseous constituents as part of a regeneration. Likewise, here are the protrusions 9 illustrated by their length 16 to the top 18, wherein the tip 18 forms an angle 17.

Fig. 2 now illustrates a variant of the device 1, wherein the electrodes 5 are again integrated in a honeycomb body 10. Shown here is a perspective view of a cylindrical housing 13, in which a plurality of at least partially structured (electrically inactive) metal foils (shown in white) and (electrically at least partially active) metal sheets (indicated in black) is arranged. Between the structures of the metal foils or metal sheets, passages are provided which are longitudinally passable and run essentially parallel to one another. By an appropriate power supply 6 through the housing 13 through an electrical contact can be realized towards the desired metal sheet 7, so that thus a power supply is guaranteed to the electrodes 5. In this case, the electrodes 5 extend beyond an end face, wherein preferably a uniform distribution over the cross section of the honeycomb body 10 is preferred.

Fig. 3 schematically shows a plan view in or against the flow direction of the exhaust gas to an embodiment of the device according to the invention 1. A honeycomb body 10 is arranged in a housing 13. The honeycomb body 10 contains at least one metal sheet 7, which forms projections 9, which serve as an electrode 5. Via an electrical contact 12, the electrodes can be subjected to a voltage. Each projection 9 has at least a first distance 14 and a second distance 15 to adjacent electrodes 5. The first distance 14 and the second distance 15 are substantially equal, the projections 9 being distributed uniformly over an end face of the honeycomb body 10.

Thus, the problems described at the beginning with reference to the prior art were at least partially solved. In particular, an apparatus has been provided for generating an electric field in an exhaust system, which can be provided by simple means and known technologies as part of a series production. In addition, the device can be easily integrated into an exhaust pipe, in particular so that a targeted alignment of the electrodes is made possible towards the desired electric field or the associated particle trap.

LIST OF REFERENCE NUMBERS

1

contraption

2

electric field

3

exhaust system

4

exhaust pipe

5

electrode

6

power supply

7

metal sheet

8th

flow direction

9

head Start

10

honeycombs

11

particulate trap

12

electric contact

13

casing

14

first distance

15

second distance

16

length

17

angle

18

top

Claims (4)

1. Device (1) for producing an electrical field (2) in an exhaust gas system (3) of a mobile internal combustion engine, having an exhaust gas line (4), by which a flow direction (8) of the exhaust gas is established, and in which at least one electrode (5), which is placed in contact with a power supply (6), is arranged, and a honeycomb body (10), wherein the at least one electrode (5) is formed with at least one metal plate (7), wherein the at least one electrode (5) extends in the flow direction (8) of the exhaust gas, wherein the at least one electrode (5) is integrated into the honeycomb body (10) and wherein all the electrodes (5) have a plurality of projections (9) in the flow direction (8) of the exhaust gas, characterized in that the projections (9) are generated by removing material of the at least one metal plate (7) close to a front-side edge.
2. Device (1) according to Patent Claim 1, wherein at most three electrodes (5) are provided.
3. Device (1) according to Patent Claim 1 or 2, wherein at least three projections (9) are formed with, in each case, a distance (14, 15) from at least two adjacent projections (9), wherein the distances (14, 15) are equal.
4. Device (1) according to one of the preceding patent claims, wherein a particle trap (11) is arranged downstream of the at least one electrode (5) in the flow direction (8) of the exhaust gas.

Images