EP0472008B1 - Particle filter regenerable by combustion for exhaust gases of internal combustion engine - Google Patents

Abstract

The invention discloses a particle filter regenerable by combustion for cleaning the exhaust gas of internal combustion engines, the filter comprising filter plugs (11) which are arranged in a housing (1) with an external heat supply (10) and are covered with different lengths of filter material (13) in accordance with the flow profile of the exhaust gas in the housing (1). <IMAGE>

Description

The invention relates to a particle filter for cleaning the exhaust gas of internal combustion engines with filter cartridges, which are arranged in a housing provided with an inlet chamber and an outlet funnel between holding plates and are formed from a support tube provided with exhaust gas passage openings and covered with filter material, and which also provide heat from a heat source is supplied for regeneration by free burning.

Particle filters of this type are required for cleaning exhaust gases from internal combustion engines, in particular in vehicles which are operated with diesel fuel, in order to filter out the soot particles which are harmful to health and represent a high and dangerous environmental impact. Several versions of these particle filters are known. In one embodiment, the exhaust gas is filtered as it flows through a ceramic block (monolith), which has a large number of through-channels, of which one channel is closed like a chessboard and one channel is closed on the outlet side, so that the exhaust gas flows into one channel, then through the surrounding monolith section acting as a filter flows into the adjacent channel and leaves it, freed of soot particles. Such a soot filter describes e.g. DE-OS 32 17 357.

Another embodiment uses filter cartridges for particle filtering. These filter cartridges are preferably designed as a wound filter. Here, a support tube provided with exhaust gas passage openings wrapped in multiple layers with filter material threads, so that an element comparable to a textile yarn spool is created. Such an arrangement shows, for example, DE-OS 38 15 148 with a special representation of the storage of the filter candles in holding plates. The filter candles can also be formed by a hose cover made of filter material via a support tube according to DE-OS 38 23 205. The filter candles are flowed through from the outside in, the exhaust gas to be cleaned enters the support pipes through the filter material, which are closed on the inlet side, the soot particles are retained when the wound filter material flows through, and the cleaned exhaust gas flows through the support pipes into the outlet funnel and is released by dissipated there. The filter cartridges are arranged on concentric circles in the filter housing and are of a uniform design. Instead of the inlet-side holding plate provided with exhaust gas passage openings, a holding grille can also be arranged.

During operation of the internal combustion engine, sooting occurs when it flows through the particle filter, ie the filter material becomes increasingly clogged with soot particles and the soot has to be removed after a relatively short period of operation. Mechanical removal is practically out of the question, since the entire filter would have to be removed and the soot would have to be disposed of. It is therefore necessary to burn off the enriched soot. For this purpose, oxidizing agents are added to the exhaust gas from a storage container as additives, so that the collected soot comes into contact with these reducing the soot ignition temperature and increasing the combustion rate and can be burned off at relatively low exhaust gas temperatures. However, this type of burning the accumulated soot has the disadvantage that the additives are chemical compounds that are easily flammable and enrich the exhaust gas with undesirable components, the environmental compatibility of which has not yet been proven. Attempts have therefore already been made to connect a diesel burner as an external heat source, but the known arrangement has not been able to regenerate the filters while the vehicle is in operation. Therefore one is on this solution very large filters instructed to obtain a storage capacity that allows longer driving between the regeneration phases. This regeneration regeneration is possible for vehicles that work in intervals, for example buses in inner-city operation. For other vehicles, the regeneration must take place while driving. For this purpose, two filters have been arranged parallel to each other and one of the two filters has been regenerated.

In the case of arrangements of only one particle filter with several filter cartridges, it is also known to "drive regeneration" as soon as there is a higher occupancy with soot particles, e.g. can be determined via the exhaust gas back pressure, switch on an external heat source that heats the exhaust gas to be cleaned to such an extent (> 600 ° C) that the free-burning process can take place. It has been shown, however, that the filter candles are not burned free along their entire length, especially in load conditions with a low exhaust gas mass flow. The reason for this is that already burning free the approximately front half of the filter candles ensures a sufficiently low flow resistance and thus the rear part or the outermost filter candles are not sufficiently flowed through. This imperfect regeneration results in shorter and shorter re-infiltration times, which in the worst case can lead to failure of the filter. Experiments have shown that the infusion time of e.g. 135 minutes at the first infusion decreased to 15 to 20 minutes.

In order to achieve a substantial improvement in the free-burning regeneration, according to the unpublished German patent application P 40 04 861.6, an improvement in the free-burning has already been achieved in that so-called overflow pipes are arranged in the space between the filter candles, via which the exhaust gas to be cleaned passes the filter candles is fed in such a way that a uniform application is achieved over the entire length of the filter candles.

It is also known from DE 38 36 697 A1 a generic device in which the holding plates together with the filter candles form a rotating drum, so that a segment of this drum can always be guided into an area in which the free burning takes place. Such a device is very complex, especially with regard to the storage of the rotatable drum and the seal against the flow of uncleaned exhaust gas. These problems are solved in this document. However, such devices with segmental free firing are not suitable for series installation.

Based on this prior art, the invention has for its object to show a particle filter that enables regeneration while driving and in which a high degree of free burning is achieved over the entire length of the filter, so that the re-infusion time is approximately constant and corresponds to the first infusion time.

In solving this task, it is assumed that the exhaust gas flows through the filter in a certain flow profile and that the sooting of the filter corresponds to this flow profile.

The solution to this problem is a generic particle filter in which filter candles of different active lengths are arranged equidistantly distributed over the cross section of the housing. "Active length" is understood to mean the section of the filter candle covered with filter material. A different active length can be formed in that the filter material occupancy is different over the length of the filter candle, for example, is stronger at the front when viewed in the direction of flow than in the following area. This different occupancy can be different for the individual filter cartridges, so a different occupancy can be selected in the edge area of the filter than in the central (middle) area. The strength of the occupancy can be selected according to the flow profile of the exhaust gas to be cleaned.

A particularly expedient continuation is characterized in that the length of the support tubes is covered with filter material to different degrees. With this arrangement it is achieved that the filter candles designed as a wound filter can be produced in a simple and proven method in the same way and the filter candles can be inserted into flat holding plates in the filter housing due to the identical length of the support tubes. According to a further embodiment, the filter candles are arranged according to the flow profile of the exhaust gas flowing through, i.e. that the filter cartridges with the shorter active length are arranged radially on the outside in the housing. In a preferred arrangement according to claim 2 with a differently occupied support tube, the support tubes with a short filter material occupancy are arranged in the outer, radially more distant area of the housing. This achieves an adaptation of the internal filter geometry to the actually existing streamline field in the filter and that the regeneration of the exhaust gas by burning off the particles accumulated in the filter takes place uniformly over the filter area mentioned, with a reduced expenditure of filter material. To burn off the particles, externally generated heat is at least temporarily supplied, e.g. via a burner arranged on the filter housing, e.g. is known from so-called vehicle parking or additional heaters.

These advantageous and expedient further refinements of the invention shown in the subclaims have, at least in part, independent or inventive features.

Fig. 1

einen Längsschnitt durch einen Partikelfilter mit in der oberen und der unteren Hälfte dargestellten unterschiedlichen Möglichkeiten der Abgasführung,

Fig. 2

einen Querschnitt an der mit A-A angegebenen Stelle

Fig. 3

eine Filterkerze mit einer Filtermaterialbelegungsvarianten.

In the figures, an embodiment is simplified and shown schematically. In this example, the arrangement is described below, including extensions. It shows:

Fig. 1

2 shows a longitudinal section through a particle filter with different exhaust gas routing options shown in the upper and lower half,

Fig. 2

a cross section at the point indicated by AA

Fig. 3

a filter candle with a filter material allocation variants.

In the particulate filter example shown in FIG. 1, two variants are shown. In the upper half of FIG. 1, an arrangement is shown in which the exhaust gas to be cleaned is fed to the filter material above the filter space, in the illustration in the lower half the exhaust gas is supplied via the support tubes of the filter candles. The version shown in the upper half represents a preferred arrangement.

1 shows a housing 1 with thermal insulation 4, which is required in order to maintain the free-burning temperature with the lowest possible energy supply and to protect the components surrounding the filter. The housing 1 is subdivided into three chambers by an upstream holding base 3a which is fixedly arranged in the housing 1 and a downstream holding base 3b which is preferably arranged with a sliding seat. The upstream inlet chamber 4, which is designed as a mixing chamber, is followed downstream by the filter chamber 5 between the holding plates 3a, 3b and the downstream outlet chamber 6, which is provided with an outlet funnel 7 and to which an exhaust gas outlet connection 8 is connected. The radial or tangential supply of the exhaust gas to be cleaned takes place via at least one exhaust gas inlet connection 9 in the inlet chamber 4. In this inlet chamber 4, the required external heat supply also takes place via the connection 10, which in this exemplary embodiment also represents a suitable burner as it is is known for example from DE-OS 34 10 716.9. A DE-OS 35 45 437.7 shows an example of an external heat supply at 10. The filter candles 11 are arranged between the holding bases 3a, 3b. These consist of a support tube 12 which is provided with filter material 13 in the form of, for example, a ceramic ring winding. The support tubes 12 have a perforation 14 for the passage of the exhaust gas, at least in the area covered by filter material 13. The support tubes 12 are fixedly mounted in the holding plate 3a. The other end of the support tubes 12 is also fixedly mounted in the holding plate 3b if the holding plate 3b is arranged with a sliding seat in the housing 1 or is mounted in the holding plate 3b with a sliding seat if the holding plate 3b is also arranged firmly in the housing 1. This one-sided movable storage is required to accommodate the thermal change in length of the support tubes 12 during the free burning process.

The exhaust gas to be cleaned is supplied via the exhaust gas inlet connection 9 into the inlet chamber 4, into which additional heating is also carried out via the external heat supply at 10. There are two possibilities for supplying the exhaust gas to the filter chamber 5. In the upper part of FIG. 1, the preferred "flow from outside to inside" of the filter candles 11 is shown. Here, the exhaust gas to be cleaned, loaded with soot particles, enters the filter chamber 5 from the inlet chamber 4 via inlet openings 15 arranged in the holding plate 3a. This is closed downstream by the holding plate 3b, so that the exhaust gas through filter material 13 enters through the perforation 14 in the support tube 12 and leaves this downstream open support tube 12 cleaned in the outlet chamber 6 and is discharged via the exhaust outlet port 8.

In the lower half of FIG. 1, the "flow from the inside out" of the filter candles 11 is shown as a variant. With otherwise the same arrangement, according to this configuration, the holding base 3a on the downstream side is designed to be closed, while the holding base 3b on the downstream side has outflow openings 16 and the support tubes 12 which are open on the outlet side are closed in the other embodiment, so that the exhaust gas flowing into the support tubes 12 which are open on the inlet side is closed flows out through the filter material 13 into the filter chamber 5 and is discharged via the outflow openings 16. The support tubes 12, which are open on the inlet side, can have an integrally formed inlet tulip 17 in order to improve the inflow of the exhaust gas.

A variant of a filter candle 11 is shown in FIG. 3. In these variants, the different active length of the filter candle 11 is achieved in that on the support tube 12, in the example with an integrally formed inlet tulip 17, an occupancy of filter material 13 of different lengths over the length of the support tube 12 is made. In this example, the support tube 12 is provided with the largest filter material occupancy in the downstream first section, in the second section there is a harmonious transition to a low filter material occupancy in the last section. Such filter cartridges 11 are preferably used for particle filters for vehicles with load conditions with a low exhaust gas mass flow or with a strongly changing mass flow.

Claims (5)

1. Particle filter for cleaning the exhaust gas of internal combustion engines having filter plugs (11) which are distributed in equidistant manner over the cross-section of the housing (1) and which are arranged in a housing (1), which is provided with an inlet chamber (4) and an outlet funnel (7), between holding plates (3a, 3b) and are formed from a bearing tube (12) which is provided with openings (14) for exhaust gas to pass through and is covered with filter material (13), and having a heat source (10) for regeneration by burning away, characterized in that filter plugs (11) of different active length are arranged.
2. Particle filter according to Claim 1, characterized in that the bearing tubes (12) are covered in their longitudinal extent with filter material (13) to different extents.
3. Particle filter according to Claim 1 or 2, characterized in that the arrangement of the filter plugs (11) in the housing (1) is effected in accordance with the flow profile of the exhaust gas flowing through.
4. Particle filter according to Claim 1, 2 or 3, characterized in that the bearing tubes (12) having a shorter covering of filter material are arranged in the outer region of the housing (1).
5. Particle filter according to one of Claims 1 to 4, characterized in that the bearing tubes (12) are free of perforations in their section which is not covered with filter material.

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