Exhaust Gas Treatment Device and Method for Operating an Exhaust Gas Treatment Device

Abstract

An exhaust gas treatment device for an internal combustion engine, with a first particle filter and a second particle filter arranged downstream of the first particle filter in the flow direction of the exhaust gas through the exhaust gas treatment device. The second particle filter includes a support device that can be flown through by the exhaust gas, on which a filter unit is disposed. A pore size of the filter unit is less than a pore size of the support device. A method for operating an exhaust gas treatment device for an internal combustion engine is also provided.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an exhaust treatment device for an internal combustion engine, with a first particle filter and a second particle filter arranged downstream of the first particle filter in the flow direction of the exhaust gas through the exhaust gas treatment device. The invention further relates to a method for operating an exhaust gas treatment device for an internal combustion engine.

PCT Publication No. WO 2008/043422 A1 describes an exhaust treatment device for an internal combustion engine in which a second particle filter is arranged downstream of a first particle filter. A volume of the second particle filter is preferably less than 30% of the first particle filter, so that the second particle filter has a lower particle reception capacity than the first particle. Additionally or alternatively, a lower porosity of the second particle filter compared to the first particle filter can lead to a reduced particle reception capacity of the second particle filter. Due to the relatively low particle reception capacity of the second particle filter, an increase of the loading of the second particle filter can be detected relatively quickly. A malfunction of the first particle filter or a reduced degree of separation of the particles at the first particle filter can thus be recognized so that measures can be made to restore the functioning of the first particle filter.

Exemplary embodiments of the present invention provide an exhaust gas treatment device or a method of the above-mentioned type, by means of which an impairment of the functioning of the first particle filter can be determined even quicker.

The exhaust gas treatment device for an internal combustion engine according to the invention has a first particle filter and a second particle filter arranged downstream of the first particle filter in the flow direction of the exhaust gas through the exhaust gas treatment device. The second particle filter includes at least one support device that can be flown through by the exhaust gas, on which a filter unit is arranged, wherein a pore size of the filter unit is smaller than a pore size of the at least one support device.

The invention is based on the knowledge that, with a second particle filter known from the state of the art, a reduction of its particle reception capacity has limitations by providing a particularly small volume thereof, which restricts its mechanical stability. Presently, the porous support device that can be flown through by the exhaust gas ensures the sufficient mechanical stability of the second particle filter. The second filter unit, which has a smaller pore size compared to the support device, can thereby be comparatively delicate, and can be designed optimally to the particularly effective separation of particles.

For example, the filter unit is formed as filter membrane applied to the support device. A loading of the filter membrane then increases very quickly due to a damage, such as a crack, of the first particle filter. A duration up to the determination of the impairment of the functionality of the first particle filter is then particularly low. This ensures a particularly high accuracy when determining a reduction of a separation degree of the first particle filter. Furthermore, by means of this formation of the second particle filter, its installation space requirement, weight and cost are particularly low. Moreover, the second particle filter only slightly increases the counter pressure of the exhaust gas treatment device.

In an advantageous arrangement of the invention, the pore size of the filter unit is at least half, in particular half to one-tenth of the pore size of at least one support device. The pore size of the filter unit can also, for example, be a fifth of the pore size of the at least one support device. This is particularly effective to ensure that the retention of particles in the exhaust gas flow takes place through the filter. Thus, an increase of the loading of the second particle filter can be sensed detected very quickly and accurately.

It has further been shown to be advantageous if the filter unit for retaining particles is formed by surface filtration. The filter unit can thus be passed through by the exhaust gas with a very low pressure loss. However, soot particles cannot penetrate into the filter unit, but are retained on the surface of the filter unit.

The filter unit can have micro-filtration properties so that soot particles with a diameter of less than 10 mμ, particularly soot particles with a diameter of 10 mμ to 0.1 mμ, can be retained very well by the filter unit.

In a further advantageous arrangement of the invention, a thickness of at least one support device is a multiple of the thickness of the filter unit. Because the filter unit is designed so as to be particularly thin compared to the support device, the filter unit has a good flow-through capacity for the exhaust gas. Alternatively, but preferably in addition, a porosity of at least one support device is a multiple of the porosity of the filter unit. The filter unit thus having few and comparatively fine pores compared to the support device, very quickly blocks particles passing due to damage of the first particle filter, such as when the latter has as a tear or a hole as a result of repeated temperature changes or due to a long operation period. A concomitant significant increase of the pressure drop across the second particle filter can also be sensed with less sensitive and therefore very robust pressure sensing means in a very simple and clear manner.

In another advantageous embodiment of the invention, a smallest extension dimension of the at least one support device is a multiple, especially at least five times, of a thickness of at least one support device transversely to the flow direction of the exhaust gas. For example, with a support device formed as a porous round disk, the diameter is thus a multiple, particularly the five fold or the ten fold of the thickness of the support device. By means of this flat design of the support device, its flow through resistance is particularly low.

It has further been shown to be advantageous if the at least one support device and the filter unit are formed at least partially from an identical material. Tensions between the support device and the filter unit due to a different expansion behavior with a temperature increase can thereby be avoided. This coincides with a very high durability of the second particle filter.

The material forming the support device and the filter unit forming material can be a metallic or ceramic material. For example, the support device can be formed as a metallic wire mesh, as a single layer or multilayer metal sieve or as a metal foam component. The filter unit formed, for example, as a filter membrane filter unit can be a dense metal fiber fleece. Such a fleece of metal fibers preferably has a felt-like structure. Fibers of the fleece can be connected to each other during the manufacture of the filter unit and/or of the second particle filter, for example by sintering. In particular, a connecting of the support device and filter unit can take place by sintering. If the filter unit is manufactured separately, it can be connected to the support device by soldering or welding. Instead of a separate production of the filter unit and a subsequent connection to the support device, the support device and the filter unit can alternatively be produced in the same production process.

If the support device is formed from a ceramic material, such as highly porous ceramic component, the filter unit is preferably also formed from a porous ceramic material.

Metallic and ceramic materials used for the support device and the filter unit are advantageously resistant to high temperatures, so that an arrangement in great proximity to the first particle can be provided. These high temperature-resistant materials withstand a temperature load of 900° C., particularly from 1200° C. to 1300° C. without damage. This is particularly beneficial if high temperatures occur in the exhaust gas treatment device during the regeneration of the particle filter, thus during the combustion of soot deposited on the particle filter.

The at least one support device can be arranged downstream and/or upstream of the filter unit. If the support device is arranged upstream and downstream of the filter unit, a material-fit connection of the filter unit to at least one of the support units can be omitted, as the filter unit can be fixed in its position by the support devices arranged on both sides.

If the at least one support device is arranged upstream of the filter unit, the support device can take on a separation function in addition to its support function. The second particle filter then also has properties of a depth filter, as a separation of particles takes place in channels and/or pores of the support device and on the surface of the filter unit.

If the filter unit is arranged between two support devices, the two support devices can differ with regard to their structure and/or their pore size with regard to the materials respectively used for them.

The second particle filter can at least substantially be arranged vertically or inclined to the flow direction of the exhaust gas in the exhaust gas treatment device. By an arrangement inclined to the flow direction off exhaust gas in the exhaust gas treatment device, an enlargement of the surface of the second particle filter effective for separating particles can be achieved. With an installation vertical to the flow direction, a particularly low space requirement is however given.

In order to fix the second particle filter to an inner wall of the exhaust gas treatment device, the support device can be connected to the inner wall connected by welding or soldering. Additionally or alternatively, a fiber mat or the like can be provided between the inner wall of the exhaust gas treatment device and the least one support device, wherein the support device is fixed in position in the exhaust gas treatment device by a clamping effect of the fiber mat. This clamping effect is enhanced in particular by extending the fiber mat at an increased temperature of the exhaust gas treatment device.

For increasing an effective filter surface of second particle filter, the second particle filter can have at least one elevation. The elevation is hereby preferably aligned against the flow direction of the exhaust gas to prevent an accumulation of particles in a narrow region of the second particle filter. In particular, a plurality of concentric elevations can be provided. Additionally or alternatively, the second particle filter can have a plurality of concentric elevations, so that the second particle filter has a corrugated profile in its longitudinal section.

It has further been shown to be advantageous, if the second particle filter is arranged in the exhaust gas to be regenerated by a heat transfer, wherein the heat transfer can be effected by a thermal regeneration of the first particle filter. This ensures that a combustion of soot, which was separated from the exhaust gas by means of the first particle filter, leads to a combustion of soot at the second particle filter. A separate regeneration of the second particle filter can thus be omitted.

In order to effect a particularly efficient heat transfer from the first particle filter to the second particle filter, the second particle filter can be arranged within a housing surrounding the first particle filter. A distance of a few centimeters between the first particle filter and the second particle filter can be provided hereby. Alternatively, the first particle filter and the second particle filter can contact each other, at least in some regions.

Alternatively, the second particle filter can be accommodated in a separate housing, which has an enlarged cross section compared to a region of the exhaust gas tract upstream of this separate housing. By arranging the second particle filter in the housing surrounding the first particle filter or in the separate housing, the second particle filter can therefore have a particularly large cross section that can be flown through, and, consequently, have a particularly low flow-through resistance.

In that the second particle filter is also regenerated when regenerating the first particle filter, a continuous increase of the loading of the second particle filter as a result of operating the intact first particle filter can be avoided. As long as the first particle filter is intact and has a sufficient particle reception capacity for maintaining legal requirements, no significant increase of the exhaust gas counter pressure will be observed at the second particle filter.

According to a further advantageous arrangement of the invention, the exhaust gas treatment device has pressure sensing means and an evaluation device, wherein a difference of the pressure between a location upstream of the second particle filter and a location downstream of the second particle filter with regard to a state of the first particle filter can be evaluated by means of the evaluation device. The difference can hereby be determined by means of a differential pressure sensor or by means of two absolute pressure sensors. If the value of the difference exceeds a threshold, it can be concluded that the first particle filter is damaged. In contrast, when falling below the threshold, it can be concluded that the first particle filter is not in a critical state.

Such an evaluation of the difference with regard to the state of the first particle filter is particularly safe and fast. An evaluation of a temperature increase on the second particle during the thermal regeneration thereof that can be provided additionally or alternatively would, however, only enable a detection of a damage of the first particle filter during the regeneration. As the thermal regeneration is carried out in differently sized time intervals, damage of the first particle filter can then not always be detected immediately. In contrast, when sensing the pressure drop across the second particle filter, an already existing measuring device for sensing the pressure drop across the first particle filter, particularly a measuring line, can also be used.

It has hereby been shown to be advantageous if a reference value of the difference characterizing the state of the first particle filter is stored in a memory. The memory can be arranged in the evaluation unit. The reference value of the difference preferably characterizes a new state of the first and the second particle filter with the initial operation of the exhaust gas treatment device. If a value of the difference that is larger than a threshold compared to the reference value for the new state of the first particle filter is detected, a faulty state of the first particle filter can be concluded by means of the evaluation unit. Such a faulty state of the first particle filter can be communicated via a communication device, in the form of an optical and/or acoustic alarm signal or a display or the like.

The reference value characterizing the state of the first particle filter is preferably variable in dependence on an aging of the first particle filter. The reference value can be stored in the memory in the form of a characteristic line, which considers an operation duration of the exhaust gas treatment device and/or an exhaust gas flow rate through the exhaust gas treatment device and/or a fuel flow rate of the internal combustion engine comprising the exhaust gas treatment device and/or with an exhaust gas treatment device arranged in a vehicle, a distance traveled of the vehicle. Additionally or alternatively, temperature profiles of the gas treatment device can be consulted for the characterization of the aging of the first particle filter.

In order to prevent a short-term exceeding of the threshold leading to recognition of damage of the first particle filter, the value of the difference formed from the measuring values can be damped and/or, particularly with the use of a low pass filter, processed in the evaluation unit in a filtered manner or passed to the evaluation device in a damped or filtered manner.

The pressure drop across the second particle filter can particularly be evaluated continuously. A standardisation preferably takes place hereby, in order to obtain a value independent of the interfused exhaust gas volume flow.

In a further advantageous arrangement of the invention, the exhaust gas treatment device has pressure sensing means for sensing the pressure upstream and downstream of the first particle filter. The loading state of the first particle filter can thereby be determined in dependence on a pressure drop at the first particle filter. A differential pressure sensor can be used here. An absolute pressure sensor can respectively be provided upstream and downstream of the first particle filter. In an alternative embodiment, only one absolute pressure sensor is present at a location upstream of the first particle filter, and the pressure downstream of the first particle filter is calculated using a model.

If the pressure drop at the first particle is also sensed, this size can be used for the plausibility of the state of the first particle filter determined via the measuring of the pressure drop at the second particle filter. Furthermore, the measuring location of the pressure sensing means arranged downstream of the first particle filter can be used for determining the pressure drop at the first particle filter and for determining the pressure drop at the second particle filter.

In a supplementary or alternative embodiment of the invention, where the exhaust gas treatment device has pressure sensing means and an evaluating device, the pressure sensing means can be used to determine a ratio of a difference in pressure between a location upstream of the second particle filter and a location downstream of the second particle filter to a difference of the pressure between a location upstream of the first particle filter and a location downstream of the first particle filter. A ratio determined by means of the pressure sensing means can be compared to a ratio deposited in a memory by means of the evaluating unit and can be evaluated with regard to a state of the first particle filter.

The ratio stored in the memory is usually the highest in the new state of the gas treatment device and decreases with increasing operating time of the exhaust gas treatment device. Damage of the first particle filter can be determined by means of evaluation device, if the ratio determined by means of the pressure sensing means increases again during operation.

In a further advantageous embodiment of the invention, the evaluation is designed to evaluate the ratio determined by means of the pressure sensing means in dependence on a thermal regeneration at least of the first particle filter. This is based on the knowledge that the ratio deposited in the memory characterizing the new state of the exhaust gas treatment device can, at best, be reached if the first particle filter and the second particle filter were just regenerated. It can thus be provided to always evaluate the ratio determined by means of the pressure sensing means if a thermal regeneration of the first particle filter has just taken place. An average value of the ratio within a predetermined time window can be determined hereby for example.

It has finally been shown to be advantageous if the exhaust gas treatment device comprises an exhaust gas return line branching off downstream of the second particle filter, particularly comprising a throttle device. Accordingly, the second particle filter serves for the retention of particles coming from the first particle filter, which are present there, possibly due to a damage or due to the production of the first particle filter.

In particular, when the exhaust gas recirculation line opens upstream of a compressor of an exhaust gas turbocharger in an intake tract of the internal combustion engine, the second particle filter serves as a protection of the compressor from damage due to such particles. In addition, the second particle filter arranged upstream of the branch of the exhaust gas return line does not contribute to an increase of the counter pressure of the exhaust gas return line, so that has the exhaust gas return line has an undiminished effective scavenging gradient. Arranging the second particle filter upstream of the branch of the exhaust gas return line further avoids an increasing loading of the second particle filter with the operation of the exhaust gas return line leading to an impairment of the functioning of the exhaust gas return with an intact first particle.

A further aspect of the invention provides a method for operating an exhaust treatment device for an internal combustion engine in which exhaust gas is filtered by means of a first particle filter and a second particle filter arranged downstream of the first particle filter in the flow direction of the exhaust gas through the exhaust gas treatment device. The exhaust gas filtered by means of the second particle filter flows through at least one support device and a filter unit arranged at the at least one support device, with a pore size of the filter unit being smaller than a pore size of the at least one support device. The preferred embodiments and advantages described for the exhaust gas treatment device according to the invention also apply to the method for operating an exhaust treatment device. according to the invention.

The characteristics and characteristic combinations mentioned above in the description and the characteristics and characteristic combinations mentioned in the following in the figure description and or shown alone in the figures cannot only be used in the respectively given combination, but also in other combination or on their own, without leaving the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Further advantages, characteristics and details of the invention result from the claims, the following description of preferred embodiments and from the drawings. It shows thereby:

FIG. 1 a schematic representation of an internal combustion engine of a vehicle with an air intake tract and exhaust gas tract, which comprises an exhaust gas treatment device with a first particle filter and a second particle filter arranged downstream of the first particle filter;

FIG. 2 sectional views of three alternative designs of the second particle filter;

FIG. 3 in a sectional view, a first type of the arrangement of the second particle filter in the exhaust gas tract;

FIG. 4 in a sectional view, an alternative type of the arrangement of the second particle filter in the exhaust gas tract, wherein the second particle filter has an alternative design;

FIG. 5 in a sectional view, a further design of the second particle filter arranged in the exhaust tract;

FIG. 6 a sectional view and a top view of a further design of the second particle filter in the flow direction of the exhaust gas;

FIG. 7 a sectional view and a top view of a design of the second particle filter alternative to the design in FIG. 6 in the flow direction of the exhaust gas;

FIG. 8 a section of the exhaust gas tract according to FIG. 1 with a first example of an arrangement of pressure sensing means;

FIG. 9 a section of the exhaust gas tract according to FIG. 1 with a second example of an arrangement of pressure sensing means;

FIG. 10 a section of the exhaust gas tract according to FIG. 1 with a third example of an arrangement of pressure sensing means;

FIG. 11 a section of the exhaust gas tract according to FIG. 1 with a fourth example of an arrangement of pressure sensing means;

FIG. 12 a section of the exhaust gas tract according to FIG. 1 with a fifth example of an arrangement of pressure sensing means;

FIG. 13 a section of the exhaust gas tract according to FIG. 1 with a sixth example of an arrangement of pressure sensing means;

FIG. 14 a section of the exhaust gas tract according to FIG. 1 with a seventh example of an arrangement of pressure sensing means; and

FIG. 15 a section of the exhaust gas tract according to FIG. 1 with an eighth example of an arrangement of pressure sensing means.

DETAILED DESCRIPTION

FIG. 1 schematically shows an internal combustion engine 1 of a vehicle with an air intake tract 11 and an exhaust gas tract 3. Exhaust gas leaving the internal combustion engine 1 flows over a turbine 2 of an exhaust gas turbocharger, which drives a compressor 12. In the exhaust tract 3 is arranged an exhaust gas treatment device 13, where presently a catalyst 4, a first particle filter 5 and a second particle 6 are arranged in a housing 14. In the flow direction of the exhaust gas, which is specified in the exhaust gas tract 3 by flow arrows 15, the first particle filter 5 is hereby arranged downstream of the catalyst 4 and the second particle filter 6 downstream of the first particle filter. The housing 14 surrounding the particle filters 5, 6 and the catalyst 4 has a widened cross section compared to a region of the exhaust gas tract 3 upstream and downstream of this housing 14.

Downstream of the housing 14 and the exhaust gas tract 3, a branch of an exhaust gas return line 8 is provided. An exhaust gas cooler 9 is arranged in the exhaust gas return line 8. The exhaust gas return line 8 serves for a low-pressure exhaust gas return, wherein the returned exhaust gas upstream of the compressor 12 is guided to the air intake tract 11 of the internal combustion engine 1. Before the entry of the exhaust gas return line 8 into the air intake tract 11 a throttling device 10 is arranged for throttling the exhaust gas flow through the exhaust gas return line 8. A further throttling device 7 is arranged downstream of the branch of the exhaust gas return line 8 in the exhaust gas tract 3.

The second particle filter 6 has, seen in the flow direction of the exhaust gas through the housing 14, a thickness which is lower by a multiple than the first particle filter 5. A particle reception capacity of the second particle filter 6 is therefore considerably smaller than a particle reception capacity of the first particle filter 5.

The second particle filter 6 presently has two different functions. On the one hand, the second particle filter 6 retains particles coming from the first particle filter 5 and/or the catalyst 4, such as production residues or particles dislodged from damage. These particles could otherwise enter the exhaust gas return line 8 and thus possibly damage the compressor 12 of the exhaust gas turbocharger.

In addition to this component protection, the second particle filter 6 monitors the functionality of the first particle filter 5. The second particle filter 6, which has the particularly low particle reception capacity compared to the first particle filter, reacts extremely sensitively to an increase of its load, possibly as a result of a damage of the first particle filter 5. Such damage may be a crack and/or a hole in the first particle filter 5. If the first particle filter 5 has such damage, and its functionality with regard to the effective retaining of particles is thus restricted, the loading of the second particle filter 6 increases abruptly. The increase of the load of the second particle filter 6 in the case of a damage of the first particle filter 5 takes place particularly fast and reliably due to the design of the second particle filter 6. The increase of the load can be detected via a pressure drop at the second particle filter 6 coinciding with the load.

Three different examples for specific designs of the second particle filter 6 are given in enlarged, schematic representations in FIG. 2. The second particle filter 6 accordingly comprises at least one support device 16 that can be flown through by the exhaust gas, which serves as a support for a filter membrane 17.

The support device 16 can be formed from a metallic wire mesh, on which the filter membrane 17, possibly in the form of a dense metal fiber fleece, is fixed. The support device 16 can also be a, in particular single-or multi-layer, screen or be formed as metal foam component. Alternatively, a highly porous ceramic can be provided as the support device 16. The filter membrane 17 is then also preferably formed as a ceramic filter membrane 17. A pore size of the filter membrane 17 is presently only a fraction of the pore size of the supporting device 16. For example, the pore size of the filter membrane 17 can be half, a fifth or even only one-tenth of the pore size of the support device 16.

A retention of particles through the filter membrane 17 takes place by surface filtration. Soot particles can thus not penetrate the filter membrane 17. The filter membrane 17 further has a porosity smaller, particularly by a multiple, compared to the support device 16. The thickness of the filter membrane 17 in the flow direction of the exhaust gas through the second particle filter 6 is also several times smaller than a thickness of the support device 16.

The thin filter membrane 17 supported by the support device 16 in the housing 14 thereby enables a particularly quick and exact detection of a soot entry into the second particle filter 6. Thus, an operation duration up to the recognition of a damage of the first particle filter 5 is particularly low. The filter membrane 17 nevertheless has a particularly good flow through capacity for exhaust gas due to its small thickness and thus increases the overall counter pressure of the exhaust treatment device 13 at most minimally, if the filter membrane 17 is not loaded largely due to damage of the first particle filter 5.

According to a first design of the second particle filter 6 shown in FIG. 2, the support device 16 is arranged downstream of the filter membrane 17. If alternatively, as also shown in FIG. 2, the support device 16 is arranged upstream of the filter membrane 17, the support device 16 also contributes to the separating of particles from the exhaust gas flow, wherein a retention of particles by means of depth filtration can then take place in the region of the support device 16. According to a third design of the second particle filter 6 shown in FIG. 2, the filter membrane 17 is arranged as an intermediate layer between two support devices 16.

FIG. 3 shows the second particle filter 6 in a sectional view, as it can be arranged in an exemplary manner in the housing 14. Here, the second particle filter 6 is arranged vertical to the flow direction of the exhaust gas in the housing 14. Presently, the housing 14 is formed round in its cross section in the region of the second particle filter. The second particle filter 6 in the design according to FIG. 3 is also formed round the top view.

FIG. 4 shows an alternative shape and orientation of the second particle filter 6 in the housing 14. Here, the second particle filter 6 is formed ovally and is arranged inclined to the flow direction of the exhaust gas in the housing 14. Thereby, an enlarged filter-effective surface of the second particle filter 6 is provided compared to the vertical arrangement according to FIG. 3.

In an alternative design of the second particle filter 6, which is shown in cross section in FIG. 5, the second particle filter 6 is designed in a cone-shaped manner. A tip 18 of the second particle filter 6 points into a direction against the flow directions of the exhaust gas. The tip 18 of the second particle filter 6 lies on a center axis A of the housing 14, which simultaneously is a center axis of the second particle filter 6.

In an alternative design of the second particle filter 6, which is shown in FIG. 6 in a top view in the flow direction of the exhaust gas and in a sectional view, the filter membrane 17 of the second particle filter 6 facing the exhaust gas flow forms a plurality of concentric elevations 19. The support device 16 also has the plurality of concentric elevations 19, so that the second particle filter 6 has a jagged profile in the longitudinal section.

With a further design of the second particle filter 6 shown in FIG. 7, it has a corrugated form in its longitudinal section. A plurality of parallel elevations 19 of the filter membrane 17 and the support device supporting this is formed.

FIG. 8 to FIG. 15 show different arrangements of pressure sensing means, by means of which a difference of the pressure between a location upstream of the second particle filter 6 and a location downstream of the second particle filter 6 can also be sensed as a loading of the first particle filter 5. Depending on installation space conditions, access to respective regions of the exhaust gas tract 3 and the type of the selected pressure sensors, the pressure drop across the particle filter 6 can be determined reliably and quickly, in order to conclude a damage of the first particle filter 5.

According to FIG. 8, the pressure sensing means comprise two differential pressure sensors 20, 21. The first differential pressure sensor 20 uses a first measurement line 22, which is arranged upstream of the first particle filter 5. A second measurement line 23 of the differential pressure sensor 20 arranged downstream of the first particle filter 5 can simultaneously be used by the differential pressure sensor 21 which senses the pressure drop across the second particle filter 6.

With the arrangement of the pressure sensing means shown in FIG. 9, the pressure sensing means 21 senses the pressure downstream of the second particle filter 6 is not like the arrangement of FIG. 8 in the region of the housing 14, but the second measuring line of the differential pressure sensor 21 extends into the exhaust gas tract in the region of the branch of the exhaust gas return line 8.

With the arrangements of the pressure sensing means shown in FIG. 8 and FIG. 9, an absolute pressure sensor can additionally be provided downstream of the second particle filter 6. This is particularly sensible if the absolute pressure is to be used downstream of the second particle filter 6 as the input variable for a regulation of the low-pressure exhaust gas return rate through the exhaust gas return line 8.

According to FIG. 10, the pressure sensing means comprise three absolute pressure sensors instead of the differential pressure sensors 20, 21. These absolute pressure sensors 24 respectively sense the pressure at a location upstream of the first particle filter 5, downstream of the first particle filter 5, and thus upstream of the second particle filter 6 and downstream of the second particle filter 6 respectively within the housing 14.

With the arrangement of the pressure sensing means shown in FIG. 11, only the third absolute pressure sensor 24 is not arranged in the region of the housing 14, but at the branch of the exhaust gas return line 8 in the exhaust gas tract 3.

The arrangement of the pressure sensing means shown in FIG. 12 is largely identical to the arrangement according to FIG. 11, however, an absolute pressure sensor 24 senses the absolute pressure upstream of the first particle filter 5 and the differential pressure sensor 20 the pressure drop across the first particle filter 5 via the measuring lines 22, 23. The absolute pressure sensor 24 and the differential pressure sensor 20 use the same measurement line 22.

The arrangement of the pressure sensing means according to FIG. 13 is largely analogous to the arrangement of FIG. 12, but the absolute pressure sensor 24 detects the absolute pressure downstream of the first particle filter 5 here and uses the measuring line 23 together with the differential pressure sensor 20, which line serves for the measuring of the pressure in the housing 14 at the location downstream of the first particle filter 5.

With the arrangement of the pressure sensing means according to FIG. 14, the pressure is also present downstream of the second particle filter 6 as a direct measurement variable, which is sensed by means of an absolute pressure sensor 24. However, in the arrangement of FIG. 14, the pressure drop across the second particle filter 6 is determined by means of the differential pressure sensor 21. This differential pressure sensor 21 uses a measuring line 25 together with the absolute pressure sensor 24, which line extends into the exhaust gas tract downstream of the second particle filter 6 at the height of the branch of the exhaust gas return line 8.

With the arrangement of the pressure sensing means shown in FIG. 15, the absolute pressure downstream of the second particle filter 6 is present as an indirect measuring variable, which, as with the arrangement according to FIG. 14, is sensed at the height of the branch of the exhaust gas return line 8. Hereby, the differential pressure sensor 21 using the measuring line 25, by means of which the pressure drop across the second particle filter 6 can be determined, uses a measuring line 26 together with the absolute pressure sensor 24, which is used to sense the absolute pressure between the first particle filter 5 and the second particle filter 6.

Provided that an absolute pressure sensor is arranged in the air intake tract 11 upstream of the compressor 12, the absolute pressure downstream of the second particle filter 6 and the pressure drop across the exhaust gas return line 8 can also be sensed by means of a differential pressure sensor. Its measuring lines are then positioned in the air intake tract 11 upstream of the compressor 12 and downstream of the second particle filter 6. In this case, a measurement of the absolute pressure downstream of the second particle filter 6 can be omitted with the arrangements depicted in FIG. 12 to FIG. 14. With the arrangement of the pressure sensing means according to FIG. 14, the sensing of the differential pressure at the second particle filter 6 by means of the differential pressure sensor 21 can however be omitted.

The pressure drop across the second particle filter 6 can be continuously evaluated by an evaluation device, which can be arranged in a control device (not shown here) for controlling the internal combustion engine 1. The pressure drop is compared to a comparison value which characterizes a new state of the first particle filter 5. If the measured pressure drop exceeds the comparison value by a predetermined threshold, an alarm is triggered in a monitoring device of the control device, which is also called OBD unit (on board diagnosis).

The threshold is presently deposited in the form of a characteristic line, which takes into account the aging of the first particle filter 5.

Additionally or alternatively, for monitoring first particle filter 5, the pressure drop across the second particle filter 6 can be set into a ratio to the pressure drop across the first particle filter 5. The measured ratio is hereby compared to a ratio characterizing the new state of the exhaust treatment device 13. The alarm is triggered if the large ratio in the new state increases instead of decreasing and/or exceeds the value of the new state. The ratio is preferably formed in connection to a thermal regeneration of the particle filters 5, 6 taking place together of the measuring values measured by means of the pressure sensing means.

Claims

1-18. (canceled)

19. An exhaust gas treatment device for an internal combustion engine, comprising: a first particle filter; anda second particle filter arranged downstream of and spaced from the first particle filter in a flow direction of exhaust gas through the exhaust gas treatment device, wherein the second particle filter comprises a support device configured such that the exhaust gas passes through the support device; anda filter unit arranged on the support device, wherein a pore size of the filter unit is smaller than a pore size of the support device.

20. The exhaust gas treatment device according to claim 19, wherein the filter unit is arranged to retain particles by surface filtration.

21. The exhaust gas treatment device according to claim 19, wherein a thickness or a porosity of the one support device is respectively a multiple of a thickness or a porosity of the filter unit.

22. The exhaust gas treatment device according to claim 19, wherein the support device is arranged downstream or upstream of the filter unit.

23. The exhaust gas treatment device according to claim 19, wherein the second particle filter is arranged regeneratably by a heat transfer in an exhaust gas tract within a housing surrounding the first particle filter, wherein the heat transfer is effected by a thermal regeneration of the first particle filter.

24. The exhaust gas treatment device according to claim 19, further comprising: pressure sensing means; andan evaluation device configured to determine a pressure drop across the first particle filter and a pressure drop across the second particle filter.

25. The exhaust gas treatment device according to claim 20, further comprising: pressure sensing means; andan evaluation device configured to determine a pressure drop across the first particle filter and a pressure drop across the second particle filter.

26. The exhaust gas treatment device according to claim 23, further comprising: pressure sensing means; andan evaluation device configured to determine a pressure drop across the first particle filter and a pressure drop across the second particle filter.

27. The exhaust gas treatment device according to claim 19, further comprising: an evaluation device configured to evaluate a difference of the pressure between a location upstream of the second particle filter and a location downstream of the second particle filter with regard to a state of the first particle filter.

28. The exhaust gas treatment device according to claim 27, further comprising: a memory storing a reference value, variably depending on an aging of the first particle filter, of the pressure difference.

29. The exhaust gas treatment device according to claim 19, further comprising: pressure sensing means;an evaluation device; anda memory storing a ratio of a difference in pressure between a location upstream of the second particle filter and a location downstream of the second particle filter to a difference of pressure between a location upstream of the first particle filter and a location downstream of the first particle filter, andwherein the evaluation device is configured to evaluate a ratio determined by the pressure sensing means with regard to a state of the first particle filter.

30. The exhaust gas treatment device according to claim 24, further comprising: pressure sensing means;an evaluation device; anda memory storing a ratio of a difference in pressure between a location upstream of the second particle filter and a location downstream of the second particle filter to a difference of pressure between a location upstream of the first particle filter and a location downstream of the first particle filter, and

31. The exhaust gas treatment device according to claim 27, further comprising: pressure sensing means;an evaluation device; anda memory storing a ratio of a difference in pressure between a location upstream of the second particle filter and a location downstream of the second particle filter to a difference of pressure between a location upstream of the first particle filter and a location downstream of the first particle filter, andwherein the evaluation device is configured to evaluate a ratio determined by the pressure sensing means with regard to a state of the first particle filter.

32. The exhaust gas treatment device according to claim 29, wherein the evaluation unit is configured to evaluate the ratio determined by the pressure sensing means depending on a thermal regeneration of at least the first particle filter.

33. The exhaust gas treatment device according to claim 30, wherein the evaluation unit is configured to evaluate the ratio determined by the pressure sensing means depending on a thermal regeneration of at least the first particle filter.

34. The exhaust gas treatment device according to claim 31, wherein the evaluation unit is configured to evaluate the ratio determined by the pressure sensing means depending on a thermal regeneration of at least the first particle filter.

35. The exhaust gas treatment device according to claim 19, further comprising: an exhaust gas return line comprising a throttle device, which branches off downstream of the second particle filter.

36. A method for operating an exhaust gas treatment device with a first particle filter and a second particle filter arranged downstream of and spaced from the first particle filter in a flow direction of exhaust gas passing through the exhaust gas treatment device, and comprising a support device configured such that the exhaust gas passes through by the support device and on which a filter unit is arranged, the filter unit having a pore size smaller than a pore size of the support device, the method comprising: determining a state of the first particle filter with regard to its functionality based on a state of the second particle filter.

37. The method according to claim 36, further comprising: determining a pressure drop across the second particle filter; andevaluating, based on the pressure drop across the second particle filter, whether the first particle filter is damaged.

38. The method according to claim 36, wherein during a thermal regeneration with combustion of soot from the first particle filter, the second particle filter is also regenerated.