WO2017092839A1

WO2017092839A1 - Exhaust gas aftertreatment method and exhaust gas system

Info

Publication number: WO2017092839A1
Application number: PCT/EP2016/001673
Authority: WO
Inventors: Ortwin Balthes; Thomas Beckmann; Berthold Keppeler; Uwe KRONMÜLLER; Siegfried Mueller; Thorsten Woog
Original assignee: Daimler Ag
Priority date: 2015-12-02
Filing date: 2016-10-10
Publication date: 2017-06-08
Also published as: DE102015015634A1

Abstract

The invention relates to a method for the aftertreatment of exhaust gas of a vehicle, wherein the exhaust gas of an internal combustion engine of the vehicle is treated by means of a particle filter (18) and by means of an exhaust gas aftertreatment device (20) which is arranged downstream of the particle filter (18) and which is designed to selectively catalytically reduce nitrogen oxides. A quantity of a reductant provided for the selective catalytic reduction is temporarily increased following a regeneration of the particle filter (18), said reductant being introduced into the exhaust gas upstream of the particle filter (18). The invention further relates to an exhaust gas system (10) for a vehicle.

Description

Process for exhaust aftertreatment and exhaust system

The invention relates to a method for exhaust gas aftertreatment of a vehicle. Here, the exhaust gas of an internal combustion engine of the vehicle by means of a

Particulate filter and by means of a downstream of the particulate filter, designed for the selective catalytic reduction of nitrogen oxides

Treated exhaust treatment device. Furthermore, the invention relates to a trained for carrying out the method exhaust system for a vehicle.

Current and future emission guidelines provide for a significant limitation of emissions from internal combustion engines of vehicles, especially with regard to hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NO _x ) and the emissions of particulates (PM). At the same time due to the increasingly lower fuel consumption of the vehicles, the exhaust gas temperatures for the catalytic

Exhaust gas aftertreatment continues from. Exhaust gas aftertreatment concepts in which one designed for the selective catalytic reduction of nitrogen oxides

Exhaust after-treatment device and a particulate filter are arranged comparatively close to the engine in the exhaust system, therefore, play an important role in order to meet these increased requirements can. In this case, a particulate filter with an integrated SCR coating (SCR = selective catalytic reduction, selective catalytic reduction) can be used as particulate filter. Also, the future review of exhaust emissions in real driving by means of a PEMS measurement technology (PEMS = portable emission measurement system, mobile emission measurement) in this context represent a major challenge.

In the SCR treatment of nitrogen oxides, the nitrogen oxides in the corresponding exhaust aftertreatment device are converted into nitrogen and water in a selective catalytic reduction reaction with ammonia. The ammonia is often formed from urea, which in the form of an aqueous urea solution in the hot Exhaust gas is introduced. In the hot exhaust gas, the ammonia is formed from the urea.

A particle filter with integrated SCR coating (SDPF) must be thermally regenerated at regular intervals analogous to a conventional particle filter. During this regeneration, the soot stored on and in the filter wall is completely burned off. However, following regeneration, the filter does not show its full filtration efficiency. To achieve the full filtration performance, it is in fact necessary for a certain amount of soot to form on the filter wall first.

In this context, WO 20/144273 A1 describes a method for

Operating an internal combustion engine, in which a particulate filter only partially

is regenerated. During this partial regeneration, the soot is not completely burned off. Rather, the regeneration is carried out so that the soot layer on the surface of the filter wall is at least partially retained.

A disadvantage here is the fact that such a particulate filter always has an increased flow resistance, so that the higher pressure loss of the filter to a reduction of the internal combustion engine for driving the

Vehicle provides achievable power. Moreover, such is one

Operating procedure not suitable for brand new, so still completely unused particulate filter. For such particle filters inevitably no soot layer is present, which could improve the filter effect of the filter.

Object of the present invention is therefore to provide an improved method of the type mentioned above and a corresponding exhaust system.

This object is achieved by a method having the features of patent claim 1 and by an exhaust system having the features of patent claim 10. Advantageous embodiments with expedient developments of the invention are in the

specified dependent claims.

In the inventive method for exhaust aftertreatment of a vehicle, the exhaust gas of an internal combustion engine of the vehicle is treated by means of a particulate filter. Furthermore, the exhaust gas of the vehicle by means of a

Treated exhaust treatment device, which is connected downstream of the particulate filter and which is designed for the selective catalytic reduction of nitrogen oxides. Here, following regeneration of the particulate filter, an amount of a selective catalytic reduction reducing agent temporarily introduced into the exhaust gas upstream of the particulate filter is temporarily increased.

Surprisingly, it has been found that, in the case of an active metering of the reducing agent, which may in particular be a urea-water solution, the particle emission of the exhaust system is lower than without introduction of the reducing agent into the exhaust gas. In other words, the introduction of the reducing agent into the exhaust gas upstream of the particulate filter actively contributes to the reduction of the particle mass output. Accordingly, an improved method is provided.

This makes it possible, in particular, to use particulate filters with a pore size which, without the temporary introduction of the increased amount of the reducing agent immediately after complete regeneration of the particulate filter, would not meet the requirements of certain exhaust gas tests with regard to particle emission. These requirements are met, however, by using the particle filter used with the larger pore size following the complete regeneration of the

Particle filter for a while, the amount of introduced into the exhaust gas upstream of the particulate filter reducing agent is increased. Furthermore, each time the particle filter is regenerated, the particle filter can be completely regenerated, ie the soot

completely burned off. This reduces the back pressure of the

Exhaust system compared to a not fully regenerated particulate filter. This is advantageous in view of the power available from the internal combustion engine of the vehicle for driving the vehicle.

In particular, it has surprisingly been observed that by this measure the particle emission during the first driving kilometers after regeneration can be reduced.

The amount of upstream of the particulate filter introduced into the exhaust gas

Reducing agent is in particular based on an introduced during normal operation of the exhaust system amount, for example, based on the average before the

Regenerate introduced amount of reducing agent increases.

The invention is based on the finding that directly following a

complete particulate filter regeneration of the particulate filter is not yet its full

Filtration efficiency shows. This is because initially only a depth filtration takes place, during which the particles are deposited there as they flow through the pores in the walls of the filter matrix in the filter matrix. Only with increasing loading of the particulate filter is formed on one of the surfaces of the channels, a filter cake. In the then onset surface filtration is a significant increase in

To observe filtration efficiency. Especially in the phase in which only the depth filtration takes place, by increasing the amount introduced into the exhaust gas

Reducing agent, in particular by increasing the dosage of urea-water solution, the effect of such a dosage on the emissions of particles are used. Thus, the temporarily lower filtration efficiency of the

Particulate filter will be balanced and yet will be a lower overall

Particle emission achieved.

The excess consumption of reducing agent caused by temporarily increasing the amount of the reducing agent introduced into the exhaust gas is negligible. On the one hand, this is due to the fact that regeneration of the particulate filter is usually carried out only every 500 kilometers to 1000 kilometers of the vehicle's travel distance. Also, the temporary increase in the amount of gas introduced into the exhaust

Reducing agent in a new car with brand new or brand new particulate filter (or after replacement of the particulate filter) is not significant in view of the anyway to reduce the nitrogen oxides in the exhaust gas to be introduced amount of reducing agent.

So that no permanently increased consumption of reducing agent is present, it has proven to be advantageous to terminate the introduction of the increased amount of the reducing agent into the exhaust gas when at least one termination criterion is met. Different termination criteria can be considered here.

Thus, the introduction of the increased amount of the reducing agent into the exhaust gas may be stopped when a pressure loss between a first measuring point upstream of the particulate filter and a second measuring point downstream of the particulate filter reaches a predetermined value. So it can be about the counterpressure behavior of the

Particle filter, which changes with increasing Rußbeladung, the time are detected, at which the depth filtration passes into the surface filtration. Additionally or alternatively, the time profile of the pressure loss can be monitored and the introduction of the increased amount can be terminated if the time course of the pressure loss corresponds to at least one predetermined criterion. Namely, the pressure loss is detected as a function of time and thus the time course of the Determined pressure loss, it is noted at the transition from the depth filtration to surface filtration kinking in a curve indicating the course of the pressure loss. Accordingly, it can be determined by monitoring the pressure loss or the differential pressure between the two measuring points in a particularly simple and reliable manner, when the particulate filter its full

Filtration efficiency has reached. With this full filtration performance then no increased amount of reducing agent needs to be introduced into the exhaust gas, but only the usual amount.

Additionally or alternatively, the increase in the dosage can also be withdrawn time-controlled or fuel mass controlled. Accordingly, the introduction of the increased amount of the reducing agent in the exhaust gas can then be stopped as soon as a mass to after the regeneration of the particulate filter in the

Combustion engine introduced fuel has reached a predetermined value. Additionally or alternatively, the introduction of the increased amount of

Reducing agent are terminated in the exhaust gas after a predetermined period of time. Such methods can be particularly simple to implement control technology or control technology.

Additionally or alternatively, the introduction of the increased amount of

Reducing agent are terminated in the exhaust gas, as soon as by means of a storage of soot into the particulate filter descriptive model, a predetermined state of

Particle filter was determined. It is therefore possible to model the condition of the particle filter by means of a soot emission model or filtration model. Such a method is particularly easy to carry out. Several of the abovementioned termination criteria can also be taken into account in order to determine particularly reliably the achievement of the full filtration efficiency of the particulate filter.

Preferably, a stoichiometric ratio, which relates the amount of reducing agent introduced into the exhaust gas to the emission of nitrogen oxides, is temporarily increased to a value of more than 1 following the regeneration. In particular, this value a, which indicates the ratio of the metered NH ₃ amount based on the NO _x emissions, can be increased immediately after the regeneration of the particulate filter to a value between α = 1, 5 and α = 3. By increasing the amount of reducing agent introduced into the exhaust gas in such orders of magnitude, a particularly effective reduction of the particle emission during the increase of the metering can be achieved. Increasing the metered amount of, for example, the urea-water solution increases the amount of reductant provided for the SCR reaction, even though that amount at the appropriate time does not even increase the NO _x conversion in the

Exhaust after-treatment device is needed.

Accordingly, it has been found to be advantageous if, after temporarily increasing the amount of reducing agent introduced into the exhaust gas, the amount is reduced to a substoichiometric ratio, the ratio relating the amount of reducing agent introduced into the exhaust gas to the emission of nitrogen oxides. So it can be the extra amount about the storage capacity of the selective

catalytic reduction trained exhaust aftertreatment device to be buffered. About a model, which the ammonia loading of the

Thus, it can be determined how long the reducing agent can be added in the substoichiometric ratio to compensate for the temporary increase in the amount of exhaust gas aftertreatment device. As a result, a temporary excess consumption of reducing agent can be at least largely eliminated,

especially completely, compensate.

Additionally or alternatively, reducing agent leaving the exhaust gas aftertreatment device can be converted by means of a downstream catalytic converter. Thus, downstream of the exhaust gas aftertreatment device designed for the selective catalytic reduction of nitrogen oxides, a so-called ammonia blocking catalyst can be provided, which converts or converts the ammonia into N ₂ and H ₂ O. By providing such an ammonia blocking catalyst or ammonia slip catalyst, leakage of ammonia into the environment is avoided.

Alternatively, in one embodiment of the method according to the invention during the temporary increase in the amount of introduced into the exhaust gas

Reducing agent and the NOx raw emissions of the internal combustion engine can be increased, for example, by lowering an exhaust gas recirculation rate in the

Internal combustion engine, which in addition to preventing an ammonia breakthrough has a reduction in C0 ₂ emissions result.

Furthermore, in one embodiment of the method according to the invention during the temporary increase in the amount of introduced into the exhaust gas Reducing agent are increased particulate emissions of the internal combustion engine, for example by increasing an exhaust gas recirculation rate in the

Internal combustion engine, and so a faster construction of a soot cake in the

Particle filter, which leads to an improved separation efficiency of the particulate filter, can be achieved without the Partikelemssion after the particulate filter thereby deteriorates. A period of time until a regenerated particulate filter reaches a maximum

Particle filter efficiency achieved, can thus be significantly shortened, resulting in an overall low particle emission of the vehicle.

As further advantageous, it has been shown that with increasing operating time of the particulate filter in response to at least one parameter, the amount of

Reducing agent is reduced, which after each regeneration of the

Particulate filter is introduced upstream of the particulate filter in the exhaust gas. Thus, the operating strategy can be adapted with increasing transit time of the particulate filter.

This is based on the finding that with increasing transit time of the particulate filter, the increasing ash deposition in the filter wall compensates for the poorer filtration efficiency during depth filtration. The ash, so the unburned residues of retained in the particulate filter soot, namely only partially discharged with the exhaust gas from the particulate filter. The increase in the dosage of the urea-water solution or such a reducing agent after the complete particle filter regeneration can therefore gradually with increasing ash load of the particulate filter

be withdrawn. As a result, an excess consumption of reducing agent over the runtime of the particulate filter can be reduced.

As a parameter or reference variable, in particular the number of so far

carried out regeneration of the particulate filter and / or aging of the

Particle filter descriptive factor and / or be used based on a model of the particulate filter ash charge of the filter. Additionally or alternatively, the operation of the internal combustion engine of the vehicle or the exhaust system can be used as a parameter, the duration of the

Internal combustion engine or the vehicle and / or covered by the vehicle route can be considered. Also, more of these quantities or parameters may be used for determining the decrease in the amount of the reducing agent introduced into the exhaust gas to increase the reliability. The appropriate sizes or parameters will be Usually determined at different locations of a control device such as an engine control unit and are thus available for the evaluation.

It is also advantageous if there is a defect in the particle filter

is temporarily increased, the amount of the reducing agent, which is introduced upstream of the particulate filter in the exhaust gas. If, for example due to a defect of the particulate filter increased particulate emissions is to be feared, up to a repair of the vehicle or until replacement of the defective particulate filter by the temporary introduction of the increased amount

Reducing agent of particle emissions can be reduced. The presence of the defect of the particulate filter can in particular by a user of a vehicle

corresponding engine indicator light will be displayed.

If the exhaust system has an exhaust gas recirculation, so exhaust into one

Is the intake manifold of the internal combustion engine is recycled, so in the presence of the defect of the particulate filter additionally or alternatively, the amount of in the

Internal combustion engine recirculated exhaust gas can be reduced. In particular, the amount can be reduced to zero. The exhaust gas recirculation can therefore be reduced or completely switched off. On the one hand, this leads to a reduction of the particle raw emissions. On the other hand, this increases the NO _x raw emissions. This results in an increase in the amount of reducing agent introduced into the exhaust gas during operation of the exhaust system. This, in turn, has a positive effect on reducing particulate emissions.

Also in this case of the defect of the particulate filter, the dosage of the

Reductant about in the form of the urea-water solution superstoichiometrically, where typically a value of α = 3 can be provided. Theoretically, however, this value is limited only by the maximum metering amount, which depends on the structural conditions, in particular of a metering valve of the metering device.

Preferably, for the exhaust aftertreatment for selective catalytic

Reduction of nitrogen oxides formed particulate filter used, so a particulate filter with integrated SCR coating (SDPF). Here is the introduction of the

Reducing agent upstream of the particulate filter particularly useful because so the

Reducing agent already in the SCR-coated particulate filter for the reduction of the nitrogen oxide content in the exhaust gas can provide. Preference is given to using a particle filter designed for the selective catalytic reduction of nitrogen oxides, which has a copper-containing zeolite as the catalytically active material.

The exhaust system according to the invention for a vehicle comprises a particle filter for treating exhaust gas of an internal combustion engine of the vehicle. Downstream of the particulate filter, an exhaust gas aftertreatment device is arranged, which is designed for the selective catalytic reduction of nitrogen oxides. A

Control device is used to control a metering device, by means of which a reductant, which is provided for the selective catalytic reduction, can be introduced into the exhaust gas upstream of the particle filter. The control device is designed to temporarily introduce an amount of the upstream of the particulate filter into the exhaust gas after a regeneration of the particulate filter

Increase reducing agent. By means of such an exhaust system it can also be ensured immediately after the regeneration of the particulate filter that reduced particulate emissions occur. Accordingly, an improved

Exhaust system provided.

The advantages and preferred embodiments described for the method according to the invention also apply to the exhaust system according to the invention and vice versa.

The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures are not only in the respectively indicated combination but also in other combinations or in

Used alone, without departing from the scope of the invention. Thus, embodiments are also included and disclosed by the invention, which are not explicitly shown or explained in the figures, but by separated

Feature combinations emerge from the described embodiments and can be generated. Thus, embodiments and combinations of features are also to be regarded as disclosed which do not have all the features of an originally formulated independent claim.

Further advantages, features and details of the invention will become apparent from the

Claims, the following description of preferred embodiments and with reference to the drawings. Showing: exemplary and schematically an exhaust system of a vehicle with close-coupled SCR system, in which by metering in an increased amount of a urea-water solution following the regeneration of a particulate filter, a reduced particulate emission can be achieved;

Fig. 2 shows a variant of the exhaust system according to Fig. 1, in which additionally a

Ammonia blocking catalyst is provided;

Column diagrams illustrating the particle emissions for two driving cycles, showing the influence of metering a urea-water solution on the particle emission;

Fig. 4 is a graph showing the course of the pressure loss of the SCR-coated

Particulate filter as a function of the soot loading, wherein in the

Graphs is an area in which an elevated area is illustrated

Metering of the urea-water solution takes place;

5 shows in another graph the increase in the filtration efficiency of the SCR-coated particulate filter with increasing soot loading, wherein in the further graph, a range of increasing the metered amount of the

Urea-water solution illustrates; and in another graph, the retraction of the increase in the metered amount of the urea-water solution with increasing ash charge of the SCR-coated particulate filter.

Fig. 1 shows schematically an exhaust system 10 of a vehicle, in particular a motor vehicle. The exhaust gas from an internal combustion engine (not shown) of the vehicle is first supplied to an oxidation catalytic converter 12. Of the

Oxidation catalyst 12 may be formed in particular as a diesel oxidation catalyst (DOC). Optionally, the oxidation catalyst 12 may be an electrical

Have heater to the oxidation catalyst 12 quickly to his To bring light-off, such as a cold start of the vehicle. Instead of the oxidation catalyst 12 may also be provided a nitrogen oxide storage catalyst.

In an exhaust pipe 14 of the exhaust system 10, the oxidation catalyst 12, an SCR system 16 is connected downstream. The SCR system 16 includes a particulate filter 18, which in the present case is designed as a particulate filter with an SCR coating. If the SCR-coated particulate filter 18 is designed as a diesel particulate filter, this is also referred to as SDPF for short. The SCR system 16 further includes an SCR catalyst 20 disposed downstream of the particulate filter 18. Upstream of the particulate filter 18, a pressure sensor 22 is arranged in the exhaust pipe 14 and downstream of the particulate filter 18, a second pressure sensor 24. By means of this

Pressure sensors 22, 24, which detect the pressure at different measuring points, the pressure loss AP _S DPF or differential pressure of the particulate filter 18 can be determined. Between the oxidation catalytic converter 12 and the particle filter 18 there is provided an inlet 26 of a metering device 26 shown only partially here, via which a reducing agent for selective catalytic reduction (SCR = selective catalytic reduction) can be introduced into the exhaust gas, which is supplied to the SCR system 16 becomes.

The construction of the exhaust system 10 according to FIG. 2 essentially corresponds to the design of the exhaust system 10 shown in FIG. 1. However, in this case additionally an ammonia blocking catalytic converter 28 is a component of the SCR system 16. The ammonia blocking catalytic converter 28 is downstream of the SCR catalytic converter 20 arranged. Optionally, furthermore, an exhaust gas recirculation system can be provided, in which a high-pressure exhaust gas recirculation and / or a low-pressure exhaust gas recirculation can be realized. Accordingly, the exhaust gas upstream of the compressor of an exhaust gas turbocharger can be introduced into an intake tract of the internal combustion engine (low-pressure exhaust gas recirculation) or downstream of the compressor (high-pressure exhaust gas recirculation).

In the case of the exhaust system 10 shown here, the position close to the engine of the SCR system 16 is utilized, in which the metering device 26 for the

Introducing the urea-water solution in the exhaust gas immediately downstream of the oxidation catalyst 12 is located. In particular, a reducing agent obtainable under the brand name AdBlue® can be used as the urea solution. In the case of the exhaust systems 10 shown in FIGS. 1 and 2, the position of the metering device 26 for the urea-water solution results upstream of the particle filter 18 shows a relationship between the emission of particulate matter (PM) and the dosing amount. This will be illustrated with reference to FIG. 3.

In a graph 30 shown in FIG. 3, the ordinate 32 indicates the particle mass emitted by the vehicle into the environment in milligrams per kilometer. Two columns 34, 36 illustrate the particulate mass emissions detected at an exhaust system 10 outlet during a first drive cycle. The driving cycle illustrated by pillars 34, 36 are the results of three extra Urban Driving Cycles (EUDCs), three of the extra-urban driving cycles used to pre-condition the new European Driving Cycle (NEDC). Here, the first column 34 illustrates the particulate mass emission without metering the urea-water solution upstream of the particulate filter 18 and the second column 36 the particulate emission at a dosage of urea-water solution. Accordingly, it can be seen that by introducing the urea-water solution upstream of the particulate filter 18, the particulate emissions can be reduced.

The same applies to the particulate emissions as measured during a driving cycle in the form of the Federal Highway Test (BAB) of the ADAC (General German Automobile Club). The results of this BAB test are illustrated in FIG. 3 by two further columns 38, 40. Here, the column 38 illustrates the particle emission without a dosage of urea-water solution and the column 40, the particle emission with the dosage of the urea-water solution.

Following a complete regeneration of the particulate filter 18 shows the

Particulate filter 18 does not yet have its full filtration efficiency. First, namely, only a depth filtration takes place in the particulate filter 18, in which the particles in the

Flow through pores in walls of a filter matrix of the particulate filter 8 are embedded in the pores. With increasing loading of the particulate filter 18, a filter cake of soot is also formed on the surface of the channels. Accordingly, then a surface filtration takes place, which leads to a significant increase in the filtration efficiency of the particulate filter 18.

During the period in which only the depth filtration takes place, the amount of urea-water solution introduced into the exhaust gas by means of the metering device 26 is increased in the present case. Thus, the effect of dosing the urea-water solution on particle mass emission is utilized to compensate for the transiently lower filtration efficiency of the particulate filter 18. So can be very low Particle emissions in all operating conditions of the exhaust system 10 and the internal combustion engine of the vehicle can be achieved.

To control the metering device 26, a control device 42 is presently provided (compare FIGS. 1 and 2). The control unit 42 can immediately after the regeneration of the particulate filter 18, a ratio α of the metered amount of ammonia based on the NO _x emission to a value of α = 1, 5 to α = 3 increase. This caused by the controller 42 temporary lifting the metered amount of urea-water solution can be withdrawn taking into account different termination criteria.

For example, in a graph 44 in FIG. 4, the ordinate 46 indicates the differential pressure or pressure drop AP _S DPF of the particle filter 18 in millibars. In the graph 44, the soot load of the particulate filter 18 in grams per liter is indicated on an abscissa 48. A line 50 in the graph 44 illustrates that through the

Filter material of the particulate filter 18 caused pressure loss. A curve 52 describes the increase of the pressure loss AP _S DPF- In a first section 54 of the curve 52, a depth filtration takes place, during which the soot is retained in the substrate. Here, the increase in pressure loss is comparatively steep. A second section 56 illustrates a transition region, ie a transition of the curve 52 from

Section 54, which illustrates the depth filtration, to a section 58, which illustrates the surface filtration, so the filtration through a filter cake or soot cake. At the transition from section 54 to section 56, the curve 52 kinks, the curve 52 is thus flatter. At the transition from section 56 to

Section 58 again bends curve 52, so curve 52 becomes even flatter.

Based on the bending of the curve 52, the time can be detected in which the depth filtration passes into the surface filtration.

Accordingly, in the present case during one of the duration of the depth filtration

corresponding period of time 60, which in Fig. 4 by a rectangular

Surface area is illustrated, introduced the increased amount of urea-water solution by means of the metering device 26 in the exhaust gas.

In another graph 62 shown in FIG. 5, on an ordinate 64 is the

Filtration efficiency of the particulate filter 18 in percent and on an abscissa 66 again the soot load of the particulate filter 18 in grams per liter. Again, a rectangular area illustrates the period 60 during which the increased Amount of urea-water solution is introduced into the exhaust gas and, accordingly, the depth filtration continues. A curve 68, in contrast, gives the increasing

Filtration efficiency of the particulate filter 18 on. Accordingly, the temporary increase in the amount of the reducing agent introduced into the exhaust gas may be stopped or stopped when the filtration efficiency has reached a predetermined threshold. The corresponding defined or predetermined time can be determined via a model which incorporates soot in the

Particle filter 18 describes, and which can be based on the first steeply rising and then increasingly flatter curve 68 shown in Fig. 5.

This is due to the increase in HWL (urea-water solution) dosage in the

Excess reducing agent can be present in the SCR catalyst 20 and in the

Particle filter 18 are stored. Accordingly, following the increase, that is, after the completion of the elevation, the urea-water solution need not even be added in a stoichiometric ratio of α = 1. Rather, then the urea-water solution can be introduced over a certain period of time in a reduced amount in the exhaust gas. In addition, ammonia, which can not be stored in the SCR system 16, via the optionally downstream

Ammonia blocking catalyst 28 are converted to N ₂ .

Preferably, the operating strategy of the exhaust system 10 is adjusted with increasing transit time of the particulate filter 18. Because with increasing duration of use of the particulate filter 18, the ash storage in the filter wall of the particulate filter 18 increases. Dies

compensates for the initially poorer filtration efficiency during depth filtration. Increasing the dosage of urea-water solution after each

complete regeneration of the particulate filter 18 can therefore with increasing

Ash charge of the particulate filter 8 are gradually withdrawn. This will be illustrated with reference to FIG. 6.

In a graph 70 shown in FIG. 6, the ordinate 72 plots the ratio α of the metered amount of ammonia relative to the NO _x emission. On an abscissa 74 in the graph 70, a number of the total performed

Regeneration of the particulate filter 18, an ash charge of the particulate filter 18 in grams per liter, an aging factor of the particulate filter 18 or a running time or a traveled distance to be applied. By way of example, as shown in FIG. 6, an initial increase in the ratio α to α = 3 is assumed.

In contrast, a line 76 in Fig. 6 illustrates the ratio of α = 1, that is For the complete, stoichiometric nitrogen oxide conversion required HWL dosing. Another line 78 in FIG. 6 illustrates the reduced amount of the excessively added urea-water solution, which is introduced into the exhaust gas after each regeneration of the particulate filter 18, as the particle filter 18 is operated longer. In particular, in this case a gradual withdrawal of the introduced into the exhaust gas amount of urea-water solution may be provided. However, the ratio α can also be reduced continuously down to the value α = 1.

Even in the case of a reported as defective particulate filter, which is displayed to a user of the vehicle by lighting a motor control light, increased particulate emissions can be limited to a repair of the vehicle or until replacement of the defective particulate filter 18 by increasing the HWL dosing. In addition, reducing the particulate emissions of the defective particulate filter 18 may be assisted by shutting off exhaust gas recirculation or decreasing the recirculated amount of exhaust gas, respectively.

LIST OF REFERENCE NUMBERS

10 exhaust system

12 oxidation catalyst

14 exhaust pipe

16 SCR system

18 particle filters

20 SCR catalyst

22 pressure sensor

24 pressure sensor

26 metering device

28 ammonia blocking catalyst

30 graph

32 ordinates

34 pillar

36 pillar

38 pillar

40 column

42 control unit

44 graph

46 ordinates

48 abscissa

50 line

52 curve

54 section

56 section

58 section

60 time span

62 graph

64 ordinates

66 abscissa 68 curve

70 graph

72 ordinates

74 abscissa

76 line

78 line

Claims

claims

1. A method for exhaust aftertreatment of a vehicle, wherein the exhaust gas of an internal combustion engine of the vehicle by means of a particulate filter (18) and by means of a particulate filter (18) downstream, for selective

catalytic reduction of nitrogen oxides formed

Exhaust gas aftertreatment device (20) is treated,

characterized in that

temporarily, upon regeneration of the particulate filter (18), an amount of one for selective catalytic reduction

Reducing agent is added, which is introduced upstream of the particulate filter (18) in the exhaust gas.

2. The method according to claim 1,

characterized in that

introducing the increased amount of the reducing agent into the exhaust gas is stopped when a pressure drop between a first measuring point (22) upstream of the particulate filter (18) and a second measuring point (24) downstream of the particulate filter (18) reaches and / or a predetermined value Time course of the pressure loss corresponds to at least one predetermined criterion.

3. The method according to claim 1 or 2,

characterized in that

introducing the increased amount of the reducing agent into the exhaust gas - is terminated as soon as a mass of fuel introduced into the internal combustion engine after regeneration of the particulate filter (18) reaches a predetermined value and / or

- Is terminated after a predetermined period of time.

Method according to one of claims 1 to 3,

characterized in that

the introduction of the increased amount of the reducing agent is terminated in the exhaust gas, as soon as a predetermined state of the particulate filter (18) is determined by means of a model describing the incorporation of soot in the particulate filter (18).

Method according to one of claims 1 to 4,

characterized in that

a stoichiometric ratio, which relates the amount of reducing agent introduced into the exhaust gas to the emission of nitrogen oxides, is temporarily increased to a value of more than 1 following the regeneration.

Method according to one of claims 1 to 5,

characterized in that

after temporarily increasing the amount of the reducing agent introduced into the exhaust gas, the amount is reduced to a substoichiometric ratio, which relates the amount of the reducing agent introduced into the exhaust gas to the emission of nitrogen oxides, and / or from

Exhaust gas aftertreatment device (20) exiting reducing agent is converted by means of a downstream catalyst (28).

Method according to one of claims 1 to 6,

characterized in that

with increasing operating time of the particulate filter (18) in dependence on at least one parameter, the amount of the reducing agent is reduced, which is introduced into the exhaust gas after each regeneration of the particulate filter (18) upstream of the particulate filter (18).

8. The method according to any one of claims 1 to 7,

characterized in that

in the event of a defect of the particulate filter (18), temporarily increasing the amount of the reducing agent introduced into the exhaust gas upstream of the particulate filter (18) and / or an amount thereof

Internal combustion engine recirculated exhaust gas is reduced.

9. The method according to any one of claims 1 to 8,

characterized in that

for the exhaust aftertreatment, a particulate filter (18) designed for the selective catalytic reduction of nitrogen oxides is used, which has a copper-containing zeolite as the catalytically active material.

10. Exhaust system for a vehicle, with a particulate filter (18) for treating exhaust gas of an internal combustion engine of the vehicle, wherein downstream of the particulate filter (18) an exhaust aftertreatment device (20) is arranged, which is designed for the selective catalytic reduction of nitrogen oxides, and with a Control means (42) for controlling a metering device (26), by means of which provided for the selective catalytic reduction

Reducing agent upstream of the particulate filter (18) can be introduced into the exhaust gas, characterized in that

the control device (42) is designed to be connected to a

Regenerating the particulate filter (18) temporarily to increase an amount of the upstream of the particulate filter (18) to be introduced into the exhaust reducing agent.