DE102010033689A1 - Exhaust gas aftertreatment system for internal combustion engine has flow-through monolith with storage capacity designed such that breakthrough signal downstream of flow-through monolith has highest gradient of concentration curve - Google Patents

Abstract

A flow-through monolith (2), which is arranged downstream of wall-flow filter (1), and wall-flow filter have storage function for same compound selected from sulfur oxide, nitrogen oxide, liquid ammonia, oxygen, hydrocarbon, and hydrogen sulfide present in exhaust gas. The storage capacity in flow-through monolith is designed such that breakthrough signal downstream of flow-through monolith has highest gradient of concentration curve resulting at respective termination criterion taken into consideration for exhaust-gas compound while using as little storage material as possible.

Description

The present invention relates to an exhaust aftertreatment system, which consists of a catalytically active particle filter (wall-flow filter), which in turn is followed by a flow-through monolith provided with a catalytically active function. The catalytically active material used in both units has the same storage functions for the gaseous substances SOx and NOx occurring in the exhaust gas of internal combustion engines. The system is particularly suitable for the simultaneous removal of particulates and pollutants from the exhaust gas of combustion engines operated with predominantly lean air / fuel mixture. Also described is the use of such a system for exhaust aftertreatment.

The emissions contained in the exhaust of a motor vehicle can be divided into three groups. For example, the term primary emission refers to noxious gases which are produced directly by the combustion process of the fuel in the engine and are present in the so-called raw exhaust gas at the cylinder outlet. In addition to the usual primary emissions carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO _x ), the raw exhaust gas of lean-burn engines contains a relatively high oxygen content of up to 15% by volume. In addition, particulate emissions can be added, which consist mainly of soot residues and possibly organic agglomerates and result from a partially incomplete fuel combustion in the cylinder. As a secondary emission noxious gases are referred to, which can be produced as by-products in the emission control system. A third group includes those exhaust components which are actively admixed to the exhaust gases, e.g. B. to be able to accomplish a reaction with certain primary gases or secondary emissions over catalyst surfaces (DeNOx, SCR).

Exhaust gases from combustion engines operated with predominantly stoichiometric air / fuel mixture are purified in conventional processes with the aid of three-way catalysts. These are able to simultaneously convert the three major gaseous pollutants of the engine, namely hydrocarbons, carbon monoxide and nitrogen oxides to harmless components. In addition to the gaseous pollutants hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ), the exhaust gas from gasoline engines also contains the finest particulates (PM) resulting from incomplete combustion of the fuel and consisting essentially of soot.

Due to the health hazard potential arising from respirable micro particles ("particulate matter"), the introduction of the EU-5 emission standard in Europe will limit the permitted particulate emissions for gasoline engines from 2009 onwards. In addition to the existing particle mass limit for diesel engines, an extension of the limit value by a more critical particle number limit for diesel engines has already been decided. For gasoline engines, this limit is still being discussed. Adherence to future regulatory emission limits for vehicles in Europe, and probably also North America and Japan, will require not only the removal of noxious gases, especially nitrogen oxides from the exhaust gas ("denitrification"), but also effective particle removal. The noxious gases carbon monoxide and hydrocarbons can from lean exhaust gas by oxidation to a suitable oxidation catalyst rel. easily rendered harmless. Particle filters with and without additional catalytically active coating are suitable aggregates for removing particulate matter. The reduction of nitrogen oxides to nitrogen is more difficult because of the high oxygen content in the exhaust gas of lean-burn engines. Known methods are based either on the use of nitrogen storage catalysts (NOx Storage Catalyst, NSC) or selective catalytic reduction (SCR), usually using ammonia as a reducing agent, on a suitable catalyst, short SCR catalyst. Combinations of these processes are also known, in which, for example, ammonia is produced as a secondary emission at an upstream nitrogen oxide storage catalyst, which is first stored in a downstream SCR catalyst and used in a subsequent lean phase of operation to reduce nitrogen oxides passing through the nitrogen oxide storage catalyst. The DE 102007060623 describes a number of existing in the prior art variants of exhaust gas purification systems with denitrification.

In the field of exhaust gas aftertreatment of motor vehicles, so-called wall-flow filters are used for reducing the soot particles, preferably in diesel vehicles. Such filters can be applied uncoated or with catalytic coating. Common are catalytic coatings in the form of oxidation catalysts, which cause oxidation of hydrocarbons and CO and optionally oxidize nitric oxide (NO) to nitrogen dioxide (NO ₂ ).

However, as said, future legislation requires that as many harmful emissions as possible, such as particulate matter, HC and CO, and NOx be reduced. In order to make optimum use of the space available for the aftertreatment systems in the vehicle, the wall-flow filters used must be provided with additional catalytic functions. Accordingly, in addition to a large number of patent applications which have particle filters with oxidation-catalytically active coating and / or Rußzündtemperaturabsenkender coating the subject ( Catalytically Activated Diesel Particular Traps, Engler et al., 1985, SAE850007 ). However, the coating of particle filters with other catalytically active materials is increasingly being considered ( EP1309775 for oxidation-catalyzed coated filters; EP2042225 . EP2042226 . US2009093796 for filters coated with TWC materials; EP1837497 or EP1398069 for filters coated with NOx storage catalysts; WO08106523 and EP1663458 for filters coated with SCR catalysts). In some applications, such as US 2006/0057046, the exhaust backpressure problem of filter substrates is also addressed. In this case, a particularly uniform flow of the exhaust gas through the filter walls over the entire length of the component is generated by special spatial arrangements of the catalytic coating.

The EP1300193 the applicant describes a method for the catalytic conversion of pollutants in the exhaust gas of internal combustion engines, wherein the exhaust gas passes through an optionally catalytically coated on both sides porous carrier body wall with open pore structure. In this case, the support body itself consist of catalytically active material. A particular embodiment of the method is suitable for cleaning the exhaust gases of stoichiometrically operated internal combustion engines. In this case, a substrate is provided with an unspecified three-way catalyst coating, which can simultaneously implement nitrogen oxides, hydrocarbons and carbon monoxide.

The WO 00/29726 describes a device for purifying diesel exhaust gas, in which a catalytically active filter is included. The filter comprises a first catalyst containing a first platinum group metal and a first cerium compound. The apparatus also includes a second catalyst containing a second cerium compound. Embodiments are described in which both catalysts are arranged on the filter substrate. The system is characterized in that, with the aid of the cerium compound contained in the second catalyst, the proportion of volatile organic components ("volatile organic fraction" VOF) adhering to the soot particles can be removed by oxidation in the diesel particle mass. Therefore, in the particularly preferred embodiments, the second catalyst is placed in front of the catalytically active diesel particulate filter.

In the catalytic coatings used in addition to the usual catalytically active precious metals more and more materials also play a role that can filter certain components from the exhaust or adsorb. These exhaust gas components may be, for example: hydrocarbons, nitrogen oxides, ammonia, sulfur components and oxygen. Modern lean-burn engines (such as the diesel engine) will in future increasingly be equipped with NOx aftertreatment systems, with SCR catalysts or NOx storage catalysts being used in this case. SCR catalysts often have a storage function for ammonia and NOx storage catalysts have a storage function for nitrogen oxides. In some applications, so-called sulfur traps are needed, which can filter or adsorb the sulfur from the exhaust gas, thus avoiding deactivation of downstream catalysts. For very strict emission regulations, it may also be necessary to use so-called hydrocarbon storage. At low exhaust temperatures, such as during cold start, these reservoirs may filter out the unburned hydrocarbons from the exhaust gas and desorb at higher temperature. In the exhaust aftertreatment of Otto engine exhaust gas three-way catalysts are used, which may have a storage function for oxygen.

In addition to the described catalytically coated particle traps, systems are also known which have a catalytically active particle trap and a subsequent further catalyst. The advantage of these arrangements is the fact that several catalytically active functionalities and the necessary particle removal can be accommodated in a space-saving manner on only two units. In the majority of the known devices are again oxidized and / or provided with a Rußzündbeschichtung particle traps, which are followed by an aggregate, which has a different catalytic function than the coating of the particulate filter. So there are z. B. many references in the literature to catalytically active. Diesel particulate filters downstream of a nitrogen oxide storage catalyst (NSC) ( WO08121167 . EP1606498 . EP1559879 etc.).

In all applications of storage systems, it is necessary to accommodate the respective storage function in the exhaust system that the storage medium can be used as fully as possible, whereby the catalyst volume can be kept low, resulting in a reduction in the cost, the back pressure of the exhaust system and improved Heating the catalysts leads. The addressed storage materials are embedded in the actual catalytically active functionality following the usual concepts. The operation of these storage materials is often carried out so that in a first phase, the storage of a component takes place from the exhaust gas of the internal combustion engine, such as in the storage of oxygen, nitrogen oxides or sulfur components, and upon reaching the storage capacity, a different composition of the exhaust gas is initiated ( especially fat-lean change). Then the stored components are released and implemented by the catalytically active functionality in their environment to harmless emissions. Furthermore - as already indicated - the memory also used to enrich a certain exhaust gas component in the catalyst and react with another exhaust gas component, such. B. ammonia is stored in order to react with nitrogen oxides. Some memory also serve only to retain an exhaust gas component until the catalysts arranged downstream have reached their working temperature to release the cached at low temperatures components back to the exhaust gas, so that they can then be implemented by the following catalysts, such as in the Trap of hydrocarbons and nitrogen oxides is often the case.

According to their respective functionality, certain storage media (eg NSC, nitrogen oxide storage catalysts) must therefore be emptied again from time to time, so that their functioning is not hindered. Other storage media must be topped up so that a catalytic function of the exhaust system can still be successfully carried out (eg NH ₃ storage in the SCR catalytic converter). For this purpose, different control systems are used, which detect whether a storage medium is filled or empty. The detection of the level of a storage medium can be done by suitable sensors or model calculations. In order to enable the most accurate control possible, however, the breakthrough of an exhaust gas component to be stored by the medium to be stored should ideally only take place when the memory is almost filled up. Thus, upon detecting a breakthrough of the component to be stored by the memory, the correspondingly necessary step can be initiated immediately.

An important criterion for the operation of an exhaust system in the vehicle is the ability to continuously monitor such a system in the field for the functionality of the catalysts. This legislator-mandated on-board diagnostic (OBD) states that the vehicle has its own self-monitoring electronic systems. The latest regulations are about monitoring surveillance. The basis is the fear that the diagnoses over the lifetime are not carried out regularly. Therefore, it must be recorded how often the diagnoses are performed and certain monitoring rates are given.

To diagnose the efficiency of catalytic converters, sensors in the exhaust line are positioned after the catalytic converters to check whether a memory function is still sufficiently good. To monitor three-way catalysts, for example, so-called lambda sensors are used, which measure the oxygen content in the exhaust gas. A decrease in the oxygen storage efficiency of the three-way catalyst can be detected via the sensors and the engine control, which can lead to a display in the driver's display and possibly to change the engine in the emergency when exceeding a stored in the engine control threshold. Clean catalyst diagnostics will become more important in the future as OBD thresholds are set lower and lower. A key feature of good monitorability is a clean, steeply rising or falling signal from the catalyst-breaching substances when the corresponding storage in the catalyst is depleted. In the case of a three-way catalyst with oxygen storage materials applied to a wall-flow filter, the oxygen breakthrough is relatively early and not very steep ( 2 ), which makes the diagnosability considerably more difficult. In addition, the accuracy of the previously used lambda and NOx sensors over the life of the vehicle is subject to drift, which in such a system, the diagnosis of the diagnosis (monitoring the function of the sensors) even more difficult.

As materials which exert a specific storage function in the catalytically active coatings, those are particularly interesting which contain the primary or secondary components nitrogen oxides (NO _x ), ammonia (NH ₃ ), sulfur components (such as hydrogen sulphide (H ₂ S) and sulfur oxides (SO _x ), oxygen (O ₂ ) and hydrocarbons (HC) are able to store.

All in all, the use of such storage materials in modern emission control systems for internal combustion engines is inconceivable. With regard to the use of such materials in the combination filter followed by the catalyst, wherein both the filter substrate and on the subsequent catalyst possibly the same reactions are catalyzed and the same storage materials are used on both aggregates, reference is made to two applications of Toyota ( EP1843016 . EP1959120 ). In these applications, a particulate filter is mentioned in each case, which is mounted in the exhaust system of an internal combustion engine. The exhaust gases of the internal combustion engine are passed through the particle filter. The particulate filter is configured with a nitrogen oxide storage function and a nitrogen oxide reduction function. According to this disclosure, such a prepared filter is followed by another flow-through catalyst, which is also designed with a nitrogen oxide storage function and a nitrogen oxide reduction function. Therefore, this arrangement is obviously proposed in order to be able to reduce the proportion of fuel required for the regeneration of the individual catalysts together with the proportion of fuel required for the combustion. However, nothing is reported about the effective utilization of the storage materials.

Object of the present invention was therefore to provide an exhaust aftertreatment system for exhaust gases of an internal combustion engine, which is from the economic and / or ecological point of view, superior to the systems of the prior art. In particular, it is desirable that certain compounds present in the exhaust gas are stored in the used storage material with optimum utilization of the storage capacity, so as to be available for the later necessary implementation. At the same time, the structural conditions in the automobile should be taken into account. With regard to OBD capability and controllability, signal discrimination that is as clear as possible is desirable.

These and other objects resulting from the prior art are achieved by a system having the features of claim 1. Preferred embodiments are to be taken from the dependent claims on claim 1. Claims 5-7 are directed to a preferred use.

By providing an exhaust aftertreatment system for internal combustion engines having a wall-flow filter as component (1) and downstream of a flow-through monolith as component (2) available, in which both components (1) and (2) at least a memory function for the same compound present in the exhaust gas selected from the group consisting of NOx and SOx, wherein the storage capacity of the memory function of the component (2) interpreted so that the breakdown signal after the component (2) has the largest slope, one arrives extremely simple, but not less advantageous to solve the task. By both the filter used as a component (1) is provided with appropriate storage material, on the one hand the size of the overall system can be limited, since different functionalities (filtering of the particles and storage of designated and present in the exhaust gas connections) are optimally combined. On the other hand, the utilization of the storage materials used is best supported by the system layout according to the invention. This was not obvious to the person skilled in the art in light of the known state of the art.

It has been observed that coated wall-flow filters containing a storage material such as e.g. B. oxygen storage material (OSC), have a different storage behavior than coated flow-through monoliths. In dynamic memory tests, it was found that the storage material on the wall-flow filter can not be fully exploited, since the gas to be stored obviously passes too fast through the filter, without being fully adsorbed. This means that there is a faster breakthrough of the gas to be stored, as in a flow-through monolith coated with the same storage material, where there is a breakthrough of the medium to be stored only when the storage medium is largely filled ( 2 ). The maximum available storage capacity of a wall-flow filter contained storage material is therefore often only about 30-70% utilized - depending on the design of the filter (eg volume, geometry, porosity, wall thickness, average pore diameter and pore diameter distribution) and the adsorption dynamics of the storage medium. If the same amount of storage material is applied to a coated flow-through monolith, then 70-95% of the maximum storage capacity can be used in a real application.

In addition, the control of an exhaust aftertreatment system with a storage material coated wall-flow filter is much more difficult compared to a storage material-coated flow-through monolith. It comes in a coated filter much faster to breakthroughs of the component to be stored. Thus, any necessary emptying / filling of the storage medium must be initiated very early on the control strategy. This may require additional fuel and / or increase other pollutant emissions. Furthermore, the course of the breakdown signal of the component to be stored is designed according to a filter containing a storage material different that the increase in the concentration of the component to be adsorbed after the filter increases less steeply than in the case of a monolith containing storage material. However, a slowly rising signal is difficult to detect by sensors, which makes the control of such a system even more difficult.

However, the respective storage material on a wall-flow filter can be fully exploited if the filter on the downstream side z. B. honeycomb flow-through monolith is followed, which also has a storage function for the same gas to be adsorbed. The fact that the downstream monolith intercepts the breakthrough of the gas to be adsorbed by the coated filter prevents the gas to be adsorbed from entering the atmosphere unhindered. Furthermore, the storage medium in the filter is further filled up by the extended adsorption phase and thus exploited in the best case up to 100% until it comes to the breakthrough of the gas to be adsorbed at the downstream flow-through monoliths.

The dimensioning of the storage capacity of the memory function on the component (2) can be freely selected by the skilled person according to the respective requirements of the system in the claimed invention. He will be guided by the fact that for cost reasons, of course, as little as possible of the expensive storage material to be used. On the other hand, however, the best possible storage utilization of the storage materials on the component (1) is desired.

Depending on the application, the wall-flow filter can be made of different materials and have different volumes, wall thicknesses, porosities and pore radius distributions. The possible amounts of catalytically active material and the storage components, which can be accommodated on the filter additionally vary accordingly from application to application. Since with increasing proportion of catalytically active material, the dynamic pressure over the filter can rise sharply, it is often useful to keep the amount of memory materials on the filter lower to keep performance degradation of the engine by a high back pressure of the exhaust system as low as possible.

According to the present invention, it is proposed as an optimal solution to accommodate just as much storage capacity in the form of a corresponding material on the flow-through monolith (2) that the breakdown signal after the monolith has the highest slope. That is, the storage capacity of the component (2) is designed so that the breakdown signal after the component (2) has the highest slope that can be achieved with the corresponding monolith with the respective storage material. If the storage capacity on the monolith (2) is further increased, then no more steep rise in the breakdown signal is achieved. In this context, the term "highest gradient" is understood as meaning the gradient of the pressure-ruptured signal which is averaged over the entire range of the capacitance of the storage material and which should assume the greatest possible value. This is not to be understood as an absolute point value, but may vary downwards by up to 5%, preferably by up to 3% and particularly preferably by up to 2% of the value of the highest achievable slope (fault tolerance). In 4 For example, it is shown how the memory capacity of the component (2) has to be designed in order to utilize the entire memory of the component (1). Here, the total breakdown signal to component (2) (solid line) is steeper than after component (1) (dotted line) and has the highest slope, which can be achieved with component (2) and the given storage material. Further increasing the storage capacity would shift the breakthrough curve further to the right approximately component parallel to the breakthrough curve shown for component (2), but without further increasing the slope.

In one embodiment of the present invention, it is very particularly preferred to design the storage capacity in the monolith (2) in such a way that the highest possible slope of the concentration curve results at the respective termination criterion for the exhaust gas component. For this interpretation, a rel. small amount of storage capacity and thus possibly storage material on the component (2), since in the gases under consideration (NOx and SOx) exceeded even after extremely low breakthroughs (eg concentrations in the exhaust gas of 10-100 ppm) a target value could be. Only up to this point, the storage capacity of the component (2) must then prevent the breakthrough of these gases and thus ensures the presence of a very steep and thus easily detectable signal in contrast to the wall-flow filter (1) alone. In this case, the focus of the invention is not so much on the optimal utilization of the existing storage materials, but on the better controllability of the system due to the steep signal, which contributes to the more secure compliance with the envisaged limit values. Such a design of the memory material of component (2) would be in the 4 shown breakthrough signal to component (2) (solid line) further in the direction of the breakdown signal to component (1) (dotted line) move. For example, if the target value were a concentration, which would correspond to 20% of the input concentration, then the storage capacity of the component 2 would be such that the O2 / O2in value of 0.2 results in the maximum slope of the curve after component (2), already with a very small amount of storage capacity Component 2 would be achieved. Correspondingly, beyond the value of O 2 / O 2 in of 0.2, the break-through signal would again be less steep, since the break-through by component (1) would also be followed directly by the breakdown by component (2), since the storage capacity of component (2) will already be exhausted.

• • höher die Menge an Speichermaterial auf dem Filter ist
• • langsamer die Einspeicherkinetik der einzuspeichernden Komponente ist
• • höher die Porosität, je geringer die Wandstärke und je breiter die Porenradienverteilung des Filtermaterials ist (erhöhte Wahrscheinlichkeit der Bypass-Bildung – siehe weiter hinten)
• • je kleiner bei asymmetrischen Ein- und Auslasskanälen das Verhältnis der Querschnittsflächen zwischen Auslasskanal (A_aus) und Einlasskanal (A_ein) ist (A_aus/A_ein).

The storage capacity, z. B. expressed as the amount of memory material on the monolith, which is necessary to convert the flat rising breakthrough signal through the filter completely in a steeply rising or falling signal to the monolith, it is difficult to predict. Depending on the design of the filter and the memory material on the filter, the breakdown signal after filter can vary widely. In general, it can be said that the breakdown signal of the medium to be adsorbed runs flatter according to component (1), depending:

• • the amount of storage material on the filter is higher
• • slower the Einspeicherkinetik the einzzubichernden component
• • the higher the porosity, the smaller the wall thickness and the wider the pore radius distribution of the filter material (increased probability of bypass formation - see further below)
• • the smaller at asymmetric inlet and outlet channels the ratio of the cross-sectional areas between the exhaust port (A _out), and inlet duct (A _a) is (A _out / A _a).

Correspondingly, the storage capacity in the monolith (2) must be adjusted by selecting the quantity, the type of embedding in the washcoat and the type of storage material.

Thus, it has proved to be advantageous if the memory function on component (2) is maximally dimensioned so that a ≥70%, more preferably ≥80%, and most preferably a ≥90% utilization of the memory function on the Component (1) is achieved. Depending on the requirement is therefore z. B. the amount of material on the component (2), which is capable of storing the corresponding exhaust gas components selected.

Depending on the application, the wall-flow filter as component (1) may consist of different materials and have different volumes, wall thicknesses, porosities and pore radius distributions. The possible amounts of catalytically active material and the storage components, which can be accommodated on the filter additionally vary accordingly from application to application. Since with increasing proportion of catalytically active material, the dynamic pressure over the filter can rise sharply, it is often useful to keep the amount of memory materials on the filter lower to keep performance degradation of the engine by a high back pressure of the exhaust system as low as possible.

In an extremely preferred embodiment, the storage materials used are identical compounds. Both the component (1) and the component (2) accordingly have the same storage material. It has proven to be advantageous in this case that the amount of storage material or the corresponding storage capacity in the component (2) is less than the corresponding amount of storage material of the component (1). Particularly preferred is an arrangement in which the storage capacity of the component (2) is only about 20-70% compared to the component (1). It is highly preferred if the storage capacity of component (2) is 30-50%. This embodiment of the system according to the invention is particularly preferred against the background that the distance between the two components (1) and (2) to each other is less than 50 cm. Possibly. The two components (1) and (2) can also sit on impact.

However, if between the two components (1) and (2) a greater spatial distance of 70 and more cm, preferably 60 and more and more preferably 50 and more cm or more catalysts are installed between the two components, it may also be advantageous when the storage materials for the same compound of component (1) and (2) are different from each other. Thus, it may be useful due to possibly different temperature requirement in component (1) and (2) to use storage materials that have different thermal stabilities or different temperature-dependent Einspeichercharakteristika.

As a further alternative to setting the two above-mentioned ratios, the person skilled in the art can select different measures from the group consisting of different carrier materials, differently prepared washcoats, different amounts and / or ratios of noble metals, different types of storage materials for the production of the components (1) and (2) use.

Regardless of the storage materials used, it is also desirable in a preferred embodiment for both components to catalyze the same chemical reactions. Of particular interest are applications in which exactly the same storage materials and the same catalytically active material are present on component (1) and on component (2).

• a) die Abgase über die Komponente (1) geleitet werden und anschließend über die Komponente (2);
• b) die Messung oder Modellierung der Konzentration einer der im Abgas vorhandenen Verbindung ausgewählt aus der Gruppe bestehend aus NOx und SOx nach der Komponente (2) erfolgt; und
• c) die Initiierung einer Maßnahme durch die ECU (elektronische Steuereinheit im Fahrzeug) erfolgt, sobald ein hinterlegter Zielwert erreicht ist.

Likewise provided by the present invention is the use of such an exhaust gas treatment system in a method for purifying exhaust gases of an internal combustion engine. Particularly advantageous is the application of the system according to the invention in the form that

• a) the exhaust gases are passed through the component (1) and then via the component (2);
• b) measuring or modeling the concentration of one of the compounds present in the exhaust gas selected from the group consisting of NOx and SOx after component (2); and
• c) the initiation of a measure by the ECU (electronic control unit in the vehicle) takes place as soon as a stored target value has been reached.

The measurement of the concentration of nitrogen oxides can be done by nitrogen oxide sensors in the exhaust system. Modeling is usually carried out via the calculation of the NOx loading of the nitrogen oxide storage material via the stored in the engine map NOx mass flow, the calculated level of the NOx storage material with the theoretical memory, which is stored in the NOx storage material map is adjusted. A measure is initiated here, for example, if the memory is filled up so far that a breakthrough of NOx is imminent. Analogously, the modeling of SOx would take place.

It is preferred if the stored target value is a value selected from the group consisting of concentration, mass flow and cumulative slip.

As already indicated, the achievement of a steeply increasing breakdown signal is one of the essential tasks of the present invention. A steeply rising breakdown signal is manifested by the greatest possible increase in concentration or attenuation per unit of time (slope of the concentration curve 2 ). As soon as a target value determined as a function of the present system characteristics, as described above, is registered or calculated (modeled) behind the component (2), a specific measure for changing the exhaust gas flow is initiated via the ECU. The measure is naturally dependent on which compound is to be stored from the exhaust.

The measure initiated by the ECU may preferably be one or more selected from the group consisting of: temperature change, mass flow change and / or concentration change of the exhaust gas.

For example, with the use of NO x storage materials, exceeding the target value beyond component (2) could initiate a change in the air / fuel ratio in the exhaust gas, thereby emptying the storage material. It is usually switched from a lean exhaust gas mixture, in which the storage of nitrogen oxides in the storage material, to a stoichiometric or rich exhaust gas mixture, in which the desorption and reduction of nitrogen oxides occurs.

The measurement of the air / fuel ratio can be done via known lambda sensors or oxygen sensors. Depending on the lambda sensor we output the signal in mV or as lambda value. As a definition of the value lambda (λ), according to the invention a number is to be regarded with which the mixture composition consisting of air and fuel is described. From the number conclusions can be drawn on the course of combustion, temperatures, pollutant formation and efficiency. Other terms are air ratio, air ratio, air ratio, excess air and excess air ratio.

The combustion air ratio sets the actual air mass m _{L, tats} available for combustion in relation to the minimum necessary stoichiometric air mass m _{L, st} required for complete combustion:

If λ = 1, then the ratio is considered to be a stoichiometric combustion air ratio with m _{L, tats} = m _{L, st} ; this is the case if all fuel molecules theoretically react completely with atmospheric oxygen, without any oxygen missing or unburned oxygen left over.

For internal combustion engines:
λ <1 (eg 0.9) means "lack of air": rich or rich mixture
λ> 1 (eg 1.1) means "excess air": lean or poor mixture
Statement: λ = 1.1 means that 10% more air is involved in the combustion than would be necessary for the stoichiometric reaction. This is also the excess of air.

When using a storage material for sulfur oxides, a temperature increase in the exhaust gas could be initiated upon reaching a target value first and then be switched to a rich air / fuel ratio to remove the sulfur components from the storage material. Of course, if appropriate, the filled-in storage material itself or the component contained in the storage material could also be exchanged in the exhaust gas line and replaced by a new component with a non-filled-up storage material.

As embodiments of the particle filter used according to the invention comprising a storage component described above, it is possible to use all filter bodies made of metal and / or ceramic materials customary in the prior art. These include, for example, metallic woven and knitted filter bodies, sintered metal bodies and foam structures made of ceramic materials. Porous wall flow filter substrates of cordierite, silicon carbide or aluminum titanate are preferably used. These wall flow filter substrates have inflow and outflow channels, with the outflow-side ends of the inflow channels and the inflow-side ends of the outflow channels being closed relative to one another with gas-tight "plugs".

Here, the exhaust gas to be cleaned, which flows through the filter substrate, forced to pass through the porous wall between the inlet and outlet, which causes an excellent particle filter effect. Due to the porosity, pore / radius distribution, and thickness of the wall, the filtration property can be designed for particles. The storage material and possibly the catalyst material may be present in the form of coatings in and / or on the porous walls between inlet and outlet channels. It is also possible to use filters which have been extruded directly or with the aid of binders from the corresponding storage and / or catalyst materials, that is to say that the porous walls consist directly of the catalyst material, as is the case, for example, in the case of vanadium-based SCR catalysts the case may be.

Preferably to be used filter substrates, the EP1309775 . EP2042225 . US2009093796 or EP1663458 be removed.

Flow-through monoliths are conventional catalyst carriers in the art that can be made of metal or ceramic materials. Preference is given to using refractory ceramics such as cordierite. The ceramic flow-through monoliths usually have a honeycomb structure consisting of continuous channels, which is why flow-through monoliths are also referred to as channel flow monoliths. The exhaust gas can flow through the channels and comes into contact with the channel walls, which are coated with a catalytically active substance and possibly a storage material. The number of channels per area is characterized by the cell density, which is usually between 300 and 900 cells per square inch (cpsi). The wall thickness of the channel walls is between 0.5-0.05 mm for ceramics.

By definition, nitrogen oxides in the exhaust gas are composed of nitrogen monoxide and nitrogen dioxide, with the nitrogen oxides being present in the exhaust gas of a lean-burn engine as nitrogen oxide, depending on the operating state of the engine, to about 50 to 90%. Owing to the high oxygen content in the exhaust gas of lean-burn engines, the nitrogen oxides (NOx) produced during the combustion can not be continuously reduced with the simultaneous oxidation of hydrocarbons and carbon monoxide to nitrogen, as in stoichiometric gasoline engines with the aid of three-way catalysts. Their catalytic reduction succeeds only in a stoichiometric to rich exhaust gas mixture. In order to reduce nitrogen oxides in the lean exhaust gas continuously, special catalysts are used, such as HC-DeNOx catalysts or SCR catalysts. Another possibility for the reduction of nitrogen oxides in lean exhaust gases is given by the use of nitrogen oxide storage catalysts.

In the lean, that is oxygen-rich, atmosphere in addition to the HC and CO component, the nitrogen oxides are oxidized under the catalytic effect of the existing noble metal in the NOx storage catalyst, absorbing nitrates such as barium nitrate in the catalyst and thus removed from the exhaust stream. If the absorption capacity of the NOx storage catalytic converter is exhausted, the engine electronics briefly set a rich, reducing exhaust gas mixture (rich operation) usually about ten seconds). Due to the regular short-term "enrichment", the reactions proceed in the opposite direction, whereby the stored nitrogen oxides are released back into the exhaust gas stream and through the present in the rich atmosphere, reducing components such as HC - incompletely burned hydrocarbons - or CO preferably to nitrogen (N ₂ ) can be reduced. The storage catalyst operates during this phase of operation as a three-way catalyst. This regenerates the catalyst for the next storage cycle. By doing so, it is also possible to minimize the pollutant emissions of economical lean-burn engines and to comply with the legally prescribed emission limit values. The absorption capacity of the nitrogen oxide storage catalytic converter can be monitored by a NOx sensor. The operation of nitrogen oxide storage catalysts is described in detail in the SAE script SAE 950809 described. Corresponding NOx sensors can be found in the font of car exhaust catalysts, Basics - Production - Development - Recycling - Ecology, 2005, Expert Verlag, 2nd edition be removed.

NOx storage catalytic converters consist of materials that can remove nitrogen oxides from the exhaust gas stream under lean exhaust gas conditions and, under lambda = 1 or rich exhaust gas conditions, can desorb and convert the nitrogen oxides.

The person skilled in the nitrogen oxide storage catalysts to be used here are well known [ EP0982066 . EP1317953 . WO2005 / 092481 ]. Concerning. The construction and composition of nitric oxide storage (NSC) catalysts will continue to be discussed in detail in EP1911506 such as EP1101528 and referenced there literature. The corresponding catalyst materials are applied together or separately from one another by the method known to the person skilled in the art to monolithic inert 4 or 6-cornered honeycomb bodies made of ceramic (for example cordierite) or metal in the form of a coating. The honeycomb bodies have in a narrow grid over their cross-section arranged, lying parallel to the longitudinal axis of the honeycomb body flow channels for the exhaust gas to be cleaned. The catalytically active coating is deposited on the wall surfaces of the partition walls bounding the flow channels in concentrations of 50 to 450 grams per liter (g / l) volume of the honeycomb body, preferably 200-400 g / l and most preferably 250-350 g / l. The catalyst material contains the nitrogen oxide storage material and a catalytically active component. The nitrogen oxide storage material in turn consists of the actual nitrogen oxide storage component which is deposited on a carrier material in highly dispersed form. The storage components used are predominantly the basic oxides of the alkali metals, the alkaline earth metals, but especially barium oxide, and the rare earth metals, in particular cerium oxide, which react with nitrogen dioxide to give the corresponding nitrates. Preferred storage materials are compounds containing Mg, Ba, Sr, La, Ce, Mn and K. The catalytically active components used are usually the noble metals of the platinum group (eg Pt, Pd, Rh), which are usually together with the storage component be deposited on the substrate. The support material used is predominantly active, high surface area alumina.

In the case of a wall-flow filter coated with NOx storage materials, both the injection and the desorption / conversion function are insufficiently utilized in comparison with the coated monolith. As a result, the lean running times are considerably shortened in real driving, which can lead to increased fuel consumption and adversely affect the drivability of the vehicle. Furthermore, there is likely to be an increased breakthrough of NOx through the filter during the lean phase, which significantly reduces the overall NOx conversion across the filter. The modeling or measurement of the NOx storage level and the resulting abortion of the lean phase is usually done by calculation or downstream of the filter NOx sensors. The termination of the initiated for the regeneration of the NOx storage material rich phase is usually via lambda sensors after the filter. Since, in the case of a filter coated with NOx storage materials, both the rich and lean phases are controlled by sensors, an insufficiently sharp breakthrough signal results in significantly reduced NOx conversion rates.

Usually, nitrogen oxide storage catalysts of sulfur compounds in the exhaust gas are deactivated. If the sulfur compounds generated in the combustion chamber of the engine meet the surface of the nitrogen oxide storage catalyst, it first becomes sulfur dioxide (SO ₂ ) or sulfur trioxide (SO ₃ ) in a lean atmosphere. The adsorption of the sulfur oxides can be carried out directly on the nitrogen oxide storage component or on the oxidative component. Since the corresponding sulfate compounds forming in the nitrogen oxide storage catalyst are very stable thermally and, in contrast to the corresponding nitrates, are difficult to destroy, it is attempted to minimize the SO _x in the exhaust gas before it deactivates the nitrogen oxide storage catalyst. This is done on the one hand by minimizing the proportion of sulfur compounds in the fuel used and on the other by the upstream of special sulfur trap before the actual nitrogen oxide storage catalysts (NSC).

There are known in the exhaust aftertreatment sulfur storage, which can remove both hydrogen sulfide and sulfur oxides from the exhaust gas. These are - as mentioned - preferably arranged in the flow direction in front of NOx storage catalytic converters and are intended to prevent the sulfur components from entering the NOx storage catalytic converter and chemically deactivating the NOx storage centers. So-called sulfur traps have a high storage capacity for sulfur and must be able to adsorb the sulfur almost quantitatively in order to avoid the deactivation of the subsequent catalysts.

For example, describes the EP1959120 and EP1843016 In which an appropriate SO _x trap positioned in front of a particulate filter, the latter being a nitrogen oxide storage catalyst (NSC) comprises (s emission control systems. Also EP1904721 ). Another strategy will be in the EP1911506 which is considered to be included in this application with respect to its disclosure with regard to the teaching of the aforementioned sulfur storage. Proposed herein is the reduction of the basicity of the nitrogen oxide storage material used by, inter alia, addition of cerium oxide. In principle, however, the storage material for sulfur storage is the same structure as that of the nitrogen oxide storage catalysts. Overviews of specific sulfur storage materials can be found in the following list: EP1843016 . EP1959120 . EP0945165 ,

The term coating refers to the application of catalytically active materials and / or storage components to a largely inert support body. The coating performs the actual catalytic function and contains storage materials and catalytically active metals, which are usually deposited in highly dispersed form on temperature-stable high surface area metal oxides. The coating is usually carried out by applying an aqueous suspension of the storage materials and catalytically active components - also called washcoat - on or in the wall of the inert support body. After application of the suspension, the support is dried and optionally calcined at elevated temperature. The coating may consist of a layer or be composed of several layers, which are applied one above the other (multi-layered) and / or staggered (zoned) to a support body.

It should be noted that the downstream-side component (2) with a memory function does not have to be arranged directly behind the component (1). Other devices found in exhaust aftertreatment systems may also be selected from the group consisting of sensors, injectors, further catalysts, between component (1) and component (2). Furthermore, the monolith (2) arranged downstream can also be arranged close to the engine in the underbody area of the vehicle and the filter (1). Close to the engine means at a distance of less than about one meter from the engine and the underbody position is over one meter from the engine. Furthermore, other catalysts with other functions may also be located between the two storage media. Thus, it may be useful to have a filter, which has a storage capability for nitrogen oxides, to follow an SCR catalyst with ammonia storage and NOx reduction function, which in turn is followed downstream of a monolith with NOx storage function. Such applications are known to the person skilled in the art ( DE69804371 . US2004076565 ).

Likewise, such additional catalytic function as the SCR function could be applied on the outlet side of the filter or the input side of the following flow monolith as a coating. Such zoned supporting bodies are familiar to the person skilled in the art ( US7375056 ).

Several systems are known in the prior art in which a reverse layout is chosen as compared to the inventive system described herein. This means that a flow-through monolith equipped with a corresponding memory function is located in front of the wall-flow filter provided with the same memory function [z. B. US20090193796A1 ]. In this layout, however, there is no improved utilization of the storage material on the coated filter. Although it also increases the storage capacity of the entire system, the storage capacity of the coated wall-flow filter is not fully utilized. Furthermore, z. For example, Toyota incorporated such systems into its commercially available DPNR system, in which a NOx flow-rate coated wall flow filter was preceded by a flow-through monolith coated with NOx storage material.

As already mentioned above, a coated filter results in a significantly premature breakthrough of the medium to be stored and thus in an insufficient utilization of the storage material ( 2 ). The problem is solved by disposing the coated filter on the downstream side of a catalyst which has a storage function for the same medium as the filter. As a result, more of the component to be stored can be stored per storage process. This can then be more advantageously available for subsequent reactions.

In the example part it is shown by means of model calculations that a system consisting of a wall-flow filter coated with storage material and correspondingly coated flow-through monoliths arranged downstream thereof, both having the same volume and being coated with the same amount of oxygen storage material, The memory material can exploit more effectively than an analogous system consisting of coated monoliths with filter arranged downstream. Furthermore, the breakthrough of the medium to be stored-in this example oxygen storage-is much steeper, making it easier to apply a corresponding control strategy and monitoring strategy. It should also be noted that both the volume and the amount of storage material on the filter (1) downstream monoliths (2) should be designed so that the storage material is used optimally on the coated filter. As in the example section ( 4 ), an approximately 60% smaller catalyst volume or a correspondingly smaller amount of storage on the downstream monolith would be sufficient to exploit the storage material on the upstream filter accordingly. In applications that have a shallower breakdown signal through the coated filter, the downstream monolith must be sized accordingly.

Another described advantage of the system layout according to the invention is the fact that a significantly steeper breakthrough signal results behind the flow-through monolith. Due to the steeper breakthrough signal of the medium to be stored by connecting the coated monolith, a control of the system is of course much easier ( 2 ). Theories suggest that in a coated wall-flow filter, the existing storage material can not be fully utilized because there are large pores in the wall of wall-flow filters that have increased permeability to the exhaust gas than other sites in the Wall. At these locations, the exhaust gas will be able to pass through the wall faster, and the adjacently located storage material will accordingly fill up faster than storage material located at locations of low permeability on the support wall. A further explanation for this could be that, in a wall-flow filter, the storage material, which is located in the inlet channel on the side facing the exhaust gas, is filled up more quickly than the storage material, which is located further back in the channels. As a result, a breakthrough of gases to be stored near the inlet of the filter will already occur if the storage material lying deeper in the channels is not yet completely filled up. This eventually leads to the blurring in the breakthrough signal. This blurring is manifested by a smaller slope of the concentration curve for the component to be stored ( 2 ).

Another achieved goal for the arrangement of a flow-through monolith with memory function after filter with the same memory function is thus the easier diagnosability of the catalysts due to the steeper running through signal of the component to be adsorbed after the monolith. A steeper breakthrough signal is achieved when the flow-through monolith downstream of the filter contains so much memory material or has a corresponding storage capacity such that the component that breaks through the filter and is stored is completely stored on the monolith until the memory component on the monolith Filter is completely filled. In this case, the total breakdown signal is steeper after the monolith than after the filter. However, it may also be desirable that the breakdown signal after the monolith is steeper only at the beginning of the breakthrough of the component to be stored than after the filter, because often a measure for emptying the memory material is already initiated early, z. B. if already a small breakthrough of the component to be stored is detected. In this case, a small amount of storage capacity on the following monolith is already sufficient to allow the breakthrough signal to increase more steeply at least at the beginning of the breakthrough and at the time of termination of the respective operating phase. Depending on the application, the skilled person will design the storage capacities of the filter and the subsequent monoliths accordingly.

All in all, it should be noted that in addition to the ease of diagnosability of the system it is possible by the use of the system layout of the invention advantageously exploit the exhaust aftertreatment system that with the same amount of storage materials used better storage performance or vice versa with comparable storage performance saving on storage material or the use of more favorable storage materials, which may be worse in storage performance. Such advantageous effects were by no means apparent to those skilled in the art based on the information in the prior art at the time of the invention.

Normally, it is more appropriate for the skilled person to arrange the coated monolith in the flow direction in front of the filter, since z. B. the heating of a coated monolith usually takes place faster than that of a coated filter, which usually by the thicker wall thickness has slower heating behavior and thus the cleaning function of the exhaust system after the cold start is more available. This arrangement is used for example in US2009193796 described.

Depending on the amount and degree of utilization of the storage medium on the filter can follow a certain amount of storage material on the downstream monolith in order to use the storage medium on the filter as completely as possible. That a smaller amount of memory material on the downstream flow-through monolith sufficient to achieve optimum utilization of the storage material on the wall-flow monolith, was not apparent to those skilled in the art. Also associated with the system and method according to the invention is to be able to achieve an advantageous controllability of exhaust systems, which is due to the resulting steeper signal waveforms, possibly in the termination point. The attendant advantages for the exhaust gas purification system according to the invention are evident and could not readily be expected by the person skilled in the art on the basis of the teachings of the prior art.

Characters:

1 shows by way of example a system layout according to the invention with filter (1) in front of a monolith (2)

2 shows by way of example how the storage of oxygen (this also applies analogously to all gases to be stored) takes place on a wall-flow filter coated with oxygen storage material or a flow-through monolith contained in an oxygen storage material. Shown in each case is the breakthrough signal of oxygen behind the respective component as an amount of oxygen after catalyst (O ₂ ) divided by the measured amount of oxygen before the catalyst (O ₂ in). In the present calculation, the same amount of oxygen storage material is present on the filter and on the monolith. The total amount of oxygen to be stored, that is, the storage capacity on both components is the same. The oxygen slip through the filter, however, is faster (dashed line) than through the monolith (solid line) and the breakthrough curve after the monolith runs much steeper than after the filter. In a real-time exhaust aftertreatment system, the storage phase would then be aborted if a minimum slip of the component to be stored is registered after the catalyst. It can clearly be seen that the storage over the monolith takes longer - about 2.7 sec. Until breakthrough compared to about 2 sec. Until the detection of the oxygen breakthrough after the filter. The oxygen storage material on the monolith is thus better utilized than the oxygen storage material on the filter.

In 3 an example is shown in which the Einspeicherverhalten of oxygen (O ₂ ) takes place at an oxygen storage. In each case, the same amount of oxygen storage material was applied to a wall-flow filter as well as to a flow-through monolith. The storage behavior of the two components was calculated when the filter is located downstream of the monolith (dashed lines) and when the monolith is located downstream of the filter (solid lines). It can be seen that the breakdown signal after the filter is always less sharp compared to the breakdown signal of the monolith. In the monolith, 92.1% of the storage material is utilized before breakthrough of the component to be stored, while only 72.7% of the storage medium is used in the filter until breakthrough. This means that in the preferred application (filter + monolith) the back monolith utilizes 19.4% more memory material than the filter in the monolith + filter arrangement. Based on the total amount of storage in the system be used in the embodiment according to the invention therefore 9.7% more storage material and the slip of the compound to be stored (here oxygen) is done by a much sharper signal, which a system control, for example, by a downstream oxygen sensor considerably simplified.

In 4 is schematically shown the signal of oxygen contained after an oxygen storage material filter (dashed line). Optimum utilization of the entire storage material on the filter takes place when a subsequent monolith contains just enough memory material that the break-through of the component to be stored takes place behind it when the storage capacity of the storage material on the filter is 100% exhausted, such as in the solid line in 4 shown. After 4 seconds, the oxygen breaks through 100% through the filter while the slip after the monolith just begins. In this example, the monolith contains only about 40% of the filter's memory, making it easier to exploit about 33% of the memory material in the filter. The time until the breakthrough of oxygen from 2 s to about 4 s is almost doubled. The sooner the breakthrough of a component to be stored by the filter takes place and the less the storage medium on the filter can be utilized, the higher should be the amount of memory on the subsequent monolith. For reasons of cost, it makes sense to use at least 70% of the storage medium on the filter before the breakthrough by a subsequent monolith. As mentioned earlier can be used for the better diagnosability, however, already sufficient a small amount of storage capacity on the subsequent monoliths to intercept only the beginning of the breakthrough through the filter in the monolith and at least let the breakthrough signal rise at least to Begin steeper. Thus, it will be apparent to those skilled in the art that it is sufficient to design the storage capacity on component (2) such that the breakthrough signal has a higher slope only up to the predetermined target value initiating a measure because a higher storage capacity on the component (2 ), the slope of the breakdown signal at the point of the target value will not increase further, but only the utilization of the storage material on the filter or the total storage capacity of filter + monolith will be increased.

Description of the model for calculating the breakthrough curves of 2 and 3 :

The simulation model used solves the balance equation for the concentrations in a representative section consisting of an inlet and outlet channel and the wall between the two channels. Such a model is described in detail in: Votsmeier, M .; Gieshoff, J .; Kögel, M .; Pfeifer, M .; Knoth, JF; Drochner, A .; Vogel, H. Wall-flow filters with wall-integrated oxidation catalyst: A simulation study. Appl Catal B 2007, 70, 233 ,

In the given reference catalytic reactions are treated without memory effects. To map memory effects in the wall (eg, oxygen storage), an additional balance equation for the component stored in the wall is solved. Because neither diffusion nor convection need be considered for the stored components, this balance equation is simplified to:

Where r represents the reaction rate of the corresponding storage reaction. The same reaction rate also appears in the balance equation for the gaseous components in the filter wall: 0 = -∇ · (cu) + ∇ · (D∇c) - r (2)

For an explanation of the remaining symbols in Equation 2, see the above reference. The reaction rate is calculated in the examples given as:

Where c _{g is} the dimensioned to the inlet concentration dimensionless gas phase concentration z. B. of oxygen in the gas phase, C represents _stored the concentration of the stored component in the wall, C _{max is} the maximum storage capacity of the wall. _Stored C and C _MAX are also dimensionless and indeed stated relative to the inlet concentration of the gas phase component.

The modeling of the flow-through monolith is also analogous to the above publication. Again, the catalytic gas phase reaction treated in the publication is replaced by a storage reaction (corresponding to Equations 1-2). The speed of the storage reaction is again calculated by Equation 3.

The relevant parameters for the given example are:
Space velocity: 37500 h - 1
Temperature: 400 ° C.

For the wall flow filter:

• Cell density: 300 cpsi
• Wall thickness: 0.33 mm
• Diffusion coefficient in the wall: 1E - 5 m ² / s
• k: 100
• C _M : 111

For the flow-through monoliths:

• Cell density: 400 cpsi
• Wall thickness: 0.1 mm
• Layer thickness Washcoat: 60 μm
• Diffusion coefficient in washcoat: 3E - 6 m ² / s
• k: 100s ^-1
• C _MAX : 182

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007060623 [0004]
• EP 1309775 [0006, 0048]
• EP 2042225 [0006, 0048]
• EP 2042226 [0006]
• US 2009093796 [0006, 0048]
• EP 1837497 [0006]
• EP 1398069 [0006]
• WO 08106523 [0006]
• EP 1663458 [0006, 0048]
• EP 1300193 [0007]
• WO 00/29726 [0008]
• WO08121167 [0010]
• EP 1606498 [0010]
• EP 1559879 [0010]
• EP 1843016 [0016, 0057, 0057]
• EP 1959120 [0016, 0057, 0057]
• EP 0982066 [0053]
• EP 1317953 [0053]
• WO 2005/092481 [0053]
• EP 1911506 [0053, 0057]
• EP 1101528 [0053]
• EP 1904721 [0057]
• EP 0945165 [0057]
• DE 69804371 [0059]
• US 2004076565 [0059]
• US 7375056 [0060]
• US 20090193796 A1 [0061]
• US 2009193796 [0067]

Cited non-patent literature

• Catalytically Activated Diesel Particular Traps, Engler et al., 1985, SAE850007 [0006]
• SAE 950809 [0051]
• Basics - Production - Development - Recycling - Ecology, 2005, Expert Verlag, 2nd edition [0051]
• Votsmeier, M .; Gieshoff, J .; Kögel, M .; Pfeifer, M .; Knoth, JF; Drochner, A .; Vogel, H. Wall-flow filters with wall-integrated oxidation catalyst: A simulation study. Appl Catal B 2007, 70, 233 [0074]

Claims (7)

Exhaust after-treatment system for internal combustion engines comprising a wall-flow filter as component (1) and downstream of a flow-through monoliths as component (2), both components (1) and (2) at least one storage function for the same existing in the exhaust gas connection selected from the group consisting of NOx and SOx, characterized in that the storage capacity of the component (2) is designed so that the breakdown signal after the component (2) has the highest slope. System according to claim 1, characterized in that the storage capacity of the memory function on the component (2) is dimensioned so that a ≥70% memory utilization of the memory function on the component (1) results in a memory operation. System according to one of the preceding claims, characterized in that both the component (1) and the component (2) have the same storage material. System according to one of the preceding claims, characterized in that component (1) as well as component (2) catalyses the same reactions. Use of a system according to one or more of claims 1-4 in a method for purifying exhaust gases of an internal combustion engine. Use according to claim 5, wherein: a) the exhaust gases are passed through the component (1) and then via the component (2); b) measuring or modeling the concentration of one of the compounds present in the exhaust gas selected from the group consisting of NOx and SOx after component (2); and (c) the initiation of a measure by the ECU shall take place as soon as a given target value has been reached. Use according to claim 6, characterized in that the stored target value is a value selected from the group consisting of concentration, mass flow and cumulative slip.

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