CN110792492A

CN110792492A - Method for exhaust gas treatment, control device, exhaust gas system, motor vehicle and computer program product

Info

Publication number: CN110792492A
Application number: CN201910710374.5A
Authority: CN
Inventors: E·斯米尔诺夫; R·乌克罗派克; J·哈姆森; M·巴莱诺维奇
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2018-08-02
Filing date: 2019-08-02
Publication date: 2020-02-14
Also published as: DE102018212956A1

Abstract

The invention relates to a method for exhaust gas treatment, a control device, an exhaust gas system, a motor vehicle and a computer program product. Details for treating internal combustion enginesMethod for exhaust gas flow 1 in an exhaust system 2 of a machine 3, having the steps of: determining a temperature T1 of the nitrogen oxide trap 4, conducting the exhaust gas flow 1 through the nitrogen oxide trap 4, determining a temperature T2 of an SCR catalytic converter 5 arranged downstream of the nitrogen oxide trap 4, conducting the exhaust gas flow 1 through the SCR catalytic converter 5, if the temperature T1 exceeds a maximum temperature T1_maxAnd the temperature T2 does not reach the lowest temperature T2_minThe air supply to the exhaust gas flow 1 upstream of the nitrogen oxide trap 4 is activated and if the temperature T1 does not reach the minimum temperature T1_minAnd/or temperature T2 reaching or exceeding minimum temperature T2_minThe air supply to the exhaust gas flow 1 upstream of the nox trap 4 is deactivated. Furthermore, a control device, an exhaust system, a motor vehicle and a computer program product are detailed.

Description

Method for exhaust gas treatment, control device, exhaust gas system, motor vehicle and computer program product

Technical Field

The invention relates to a method for treating an exhaust gas flow in an exhaust system of an internal combustion engine, a control device for controlling the treatment of an exhaust gas flow in an exhaust system of an internal combustion engine, an exhaust system, a motor vehicle and a computer program product.

Background

Taken as a whole, in an oxidizing environment, lean-burn engines (that is to say with an air/fuel equivalence ratio lambda)>1 lean air/fuel mixture operated internal combustion engine) of the exhaust gas flow of a diesel engine_x) The reduction in (b) represents a significant challenge under various operating conditions.

NOx traps constitute one of two main technologies for the aftertreatment of NOx contained in an exhaust gas stream. In addition to storing only nitrogen oxides, nitrogen oxide traps may also exhibit catalytic properties. In these cases, they are also identified as nitrogen oxide storage catalytic converters (NSR catalytic converters, NO)_xStorage and reduction catalyst) or LNT catalytic converter (lean NO)_xA trap). The alternative main technique is based on Selective Catalytic Reduction (SCR) of nitrogen oxides by means of ammonia, which can be obtained, for example, from a supplied urea solution.

The nox trap is capable of storing nox that has been at a low temperature. The storage efficiency first increases with increasing temperature. However, if a threshold value of the temperature is exceeded, desorption of the previously stored nitrogen oxides takes place and the exhaust gas stream is enriched again by nitrogen oxides. Therefore, the temperature of the nox trap for storing nox should be within a defined temperature range.

To ensure this, DE 4334763 a1 proposes that the fuel be injected at too low a temperature, the combustion of which leads to an increase in the temperature of the nitrogen oxide trap. On the other hand, if the temperature of the nitrogen oxide trap is too high, so that desorption of nitrogen oxides is feared, air for cooling is supplied to the housing of the nitrogen oxide trap or to the exhaust gas.

At low temperatures, SCR technology generally does not provide high nox reduction reaction rates unless the optimum NO: NO₂The ratio achieves and ensures the availability of ammonia in order to promote a rapid reaction. However, an SCR catalytic converter shows excellent performance in terms of nitrogen oxide conversion as soon as a threshold value of the temperature of, for example, 200 ℃ is reached or exceeded.

In response to emission guidelines becoming more stringent, the coupling of two main technologies, in particular the coupling of a nitrogen oxide trap in series with an SCR catalytic converter arranged downstream, has become attractive. In this way, nitrogen oxides may be effectively treated over a much larger temperature range. At low temperatures, storage is first effected in the nitrogen oxide trap. If in further development a threshold value of the temperature of the SCR catalytic converter is reached or exceeded (for example by increasing the temperature of the exhaust gas), the nitrogen oxides are catalytically reduced.

However, the result of this is a problem in that the threshold value for the temperature for desorbing nitrogen oxides from the nitrogen oxide trap is exceeded, but the threshold value for the temperature of the SCR catalytic converter for the effective reduction of the released nitrogen oxides has not yet been reached. This can lead to undesirable emissions of nitrogen oxides into the environment. Such a situation may arise, for example, after a cold start of the internal combustion engine or during low load operation of the internal combustion engine (e.g. during driving in city traffic). In addition to this, it is also conceivable that the temperature of the SCR catalytic converter is generally lower compared to the nitrogen oxide trap, since the catalytic converter is arranged further away from the internal combustion engine.

It is therefore an object of the present invention to reduce or eliminate the above disadvantages.

This object is achieved by the subject matter of the independent claims. Advantageous further developments of the invention are specified in the dependent claims.

Disclosure of Invention

The basic idea of the invention is to control the temperature of the nitrogen oxide trap in such a way that an undesired desorption of nitrogen oxides from the nitrogen oxide trap is avoided to the extent that the temperature of the SCR catalytic converter is not yet high enough for a subsequent catalytic reduction. For this purpose, provision is made for the temperature threshold of the nitrogen oxide trap to be exceeded (maximum temperature T1)_max) In this case, air for cooling the exhaust gas and thus also for cooling the nitrogen oxide trap is supplied to the exhaust gas flow upstream of the nitrogen oxide trap.

When a threshold value of the temperature of the SCR catalytic converter is reached or exceeded, at which sufficient reduction of nitrogen oxides can take place (minimum temperature T2)_min) The threshold value of the temperature of the SCR catalytic converter may be obtained simultaneously, for example by electrical heating of the SCR catalytic converter. In this way, nitrogen oxides contained in the exhaust gas stream of an internal combustion engine can be converted efficiently and the emission of air pollutants into the environment can be reduced. At the same time, carbon monoxide and/or hydrocarbon slip (slip) may also be monitored.

The method according to the invention for treating an exhaust gas flow in an exhaust system of an internal combustion engine has the following steps: the method includes determining a temperature T1 of the nitrogen oxide trap, directing the exhaust gas flow through the nitrogen oxide trap, determining a temperature T2 of an SCR catalytic converter disposed downstream of the nitrogen oxide trap, and directing the exhaust gas flow through the SCR catalytic converter.

An "internal combustion engine" is understood to be a machine for converting chemical energy contained in a fuel into mechanical work by combustion. During the combustion process required for this purpose, exhaust gases are formed. The internal combustion engine may take the form of, for example, a compression ignition internal combustion engine or a spark ignition internal combustion engine. For example, motor gasoline or diesel may be used as the fuel.

The exhaust gas formed by the internal combustion engine enters the exhaust system as an exhaust gas flow and is discharged to the environment after being treated in the exhaust system. For treating the exhaust gas flow, a nitrogen oxide trap and an SCR catalytic converter are arranged in the exhaust system as means for exhaust gas aftertreatment. Alternatively, there may be other devices for exhaust aftertreatment, such as particulate filters, oxidation catalytic converters, etc.

According to the invention, it is provided that the exhaust gas flow first flows through the nitrogen oxide trap and then through the SCR catalytic converter. The SCR catalytic converter is therefore arranged downstream of the nitrogen oxide trap with respect to the flow direction of the exhaust gas flow. The SCR catalytic converter may optionally take the form of an SDPF catalytic converter (that is, a particulate filter with an SCR coating).

The remaining steps of the method according to the invention can be carried out in the order described, but also simultaneously, in a temporally overlapping manner or in a bifurcated order, as desired. For example, a temperature T1 of the NOx trap may be determined during the directing of the exhaust flow through the NOx trap.

The determination of the temperatures T1 and T2 can be achieved directly by directly measuring the temperatures of the nitrogen oxide trap and the SCR catalytic converter, respectively. Alternatively, the temperatures T1 and T2 may be determined indirectly by measuring the temperature of the exhaust gas stream immediately upstream of the nitrogen oxide trap and immediately upstream of the SCR catalytic converter, respectively, and by estimating the temperature of the nitrogen oxide trap and the temperature of the SCR catalytic converter, respectively, based on the temperature of the exhaust gas stream. By "immediately adjacent" is meant that no other means for exhaust gas aftertreatment influencing the temperature are arranged between the temperature measuring point and the nitrogen oxide trap and the SCR catalytic converter, respectively.

According to the invention, the air supply to the exhaust gas stream is activated or deactivated as a function of the temperatures T1 and T2, in order to cool or not cool the exhaust gas stream and thus the nitrogen oxide trap. If the temperature T1 exceeds the maximum temperature T1_maxAnd the temperature T2 did not reach the minimum temperature T2_minThe air supply is activated. On the other hand, if the temperature T1 does not reach the minimum temperature T1_minAnd/or temperature T2 reaching or exceeding minimum temperature T2_minThe air supply is deactivated. In other words, the air is controlled or regulated in a manner according to the temperatures T1 and T2And (4) supplying gas.

Minimum temperature T1_minLower than the maximum temperature T1_maxOr corresponding to the maximum temperature T1_maxThat is, T1_min≤T1_max。

Activation or deactivation is performed as soon as the temperature conditions required in each case are met. Subsequently, the air supply is kept in an activated or deactivated state until a temperature condition for activation (in a previous deactivated state) or deactivation (in a previous activated state) is fulfilled. In other words, "enabled" also means in an enabled state, while "disabled" also means in a disabled state.

Maximum temperature T1 of NOx trap_maxIt may for example correspond to a temperature beyond which the adsorption/desorption equilibrium of the nitrogen oxide trap has shifted in the desorption direction, i.e. more nitrogen oxides are desorbed instead of adsorbed.

Minimum temperature T2 of SCR catalytic converter_minMay for example correspond to the light-off temperature of the SCR catalytic converter, at which a sufficient catalytic conversion of the nitrogen oxides is ensured since this temperature has been reached. Minimum temperature T1 of NOx trap_minMay for example correspond to the light-off temperature of the nitrogen oxide trap, which ensures adequate adsorption and storage of nitrogen oxides since it has been reached.

Preferably, the minimum temperature T1 of the NOx trap_minIt may be above the light-off temperature of the carbon monoxide and hydrocarbons, so that the temperature T1 of the nitrogen oxide trap also corresponds to, or exceeds, the light-off temperature of the carbon monoxide and hydrocarbons in the case of a supply of air. Accordingly, the highest temperature T1_maxOr may be above the light-off temperature of carbon monoxide and hydrocarbons.

For example, the lowest temperature T1_minMay be in the range between 150 ℃ and 250 ℃, preferably between 200 ℃ and 230 ℃, and/or a maximum temperature T1_maxMay be in the range between 150 ℃ and 300 ℃, preferably between 200 ℃ and 250 ℃, and/or the lowest temperature T2_minCan be in the range between 150 ℃ and 200 ℃Preferably in the range between 170 ℃ and 190 ℃.

For example, if the temperature T1 of the nitrogen oxide trap is so high that more nitrogen oxides are desorbed rather than adsorbed, or this is desired, the air supply may be activated and thus the nitrogen oxides enter the SCR catalytic converter. Now, if the minimum temperature T2 of the SCR catalytic converter is not reached_minThese nitrogen oxides are not sufficiently catalytically converted and there is a risk of undesirable nitrogen oxides being released into the environment. In order to prevent this, the temperature of the nitrogen oxide trap is reduced by means of the air supply, so that no nitrogen oxides (or at most very small amounts of nitrogen oxides) enter the SCR catalytic converter. Such a procedure may be necessary, for example, after a cold start of the internal combustion engine.

When the lowest temperature T1 is not reached_min(for any longer time) and, for example, sufficient storage of nitrogen oxides in the nitrogen oxide trap is no longer guaranteed, the air supply may be deactivated, with a corresponding interruption of the cooling of the nitrogen oxide trap. In addition, when the temperature T2 reaches or exceeds the minimum temperature T2_minAnd thus ensures sufficient catalytic conversion of nitrogen oxides in the SCR catalytic converter, the air supply can be deactivated.

By means of the method according to the invention, the treatment of the exhaust gas stream, in particular with regard to nitrogen oxides, can be optimized such that smaller amounts of nitrogen oxides enter the environment and emission guidelines can be observed. This relates in particular to the situation after a cold start of the internal combustion engine, in which the light-off temperature of the SCR catalytic converter has not yet been reached. Due to the avoidance of cooling the nitrogen oxide trap below the minimum temperature T1_minCan be used, undesirable slipping of carbon monoxide and hydrocarbons from the nitrogen oxide trap can thus be minimized, so that on the one hand release into the environment is avoided and on the other hand damage to the SCR catalytic converter due to carbon monoxide and hydrocarbons can be largely avoided.

According to various embodiment variations, the method may be characterized in that if the temperature T1 exceeds the maximum temperature T1_maxAnd the temperature T2 does not reach the lowest temperature T2_minThe heating device for heating the SCR catalytic converter is activated. The heating means may for example take the form of electrical heating means. The electrical heating process is characterized by a fast reaction time and a small installation space. Furthermore, no fuel is required.

Furthermore, the heating device can be used for directly or indirectly heating the SCR catalytic converter, in which connection indirect heating can be achieved by means of an exhaust-gas stream heated upstream of the SCR catalytic converter. The heating device can therefore be arranged upstream of the SCR catalytic converter and downstream of the nitrogen oxide trap. In this case, in view of the indirect determination of the temperature of the SCR catalytic converter, the measurement point of the temperature should be arranged downstream of the heating device and upstream of the SCR catalytic converter.

By heating the SCR catalytic converter, its minimum temperature T2 can advantageously be reached more quickly_minAnd effective treatment of nitrogen oxides in the SCR catalytic converter can take place at an earlier point in time, so that the emission of nitrogen oxides into the environment can be reduced. Specifically, when the temperature T1 exceeds the maximum temperature T1_maxAnd thus heating is an advantage when nitrogen oxides are desorbed from the nitrogen oxide trap and enter the SCR catalytic converter.

If the temperature T2 reaches or exceeds the minimum temperature T2_minThe heating device can be deactivated again, since from this point in time sufficient catalytic activity of the SCR catalytic converter is present. The deactivation of the heating device prevents damage to the SCR catalytic converter due to overheating. In addition, heating may be performed as needed so that the additional energy requirements associated with heating are as low as possible.

According to a further embodiment variant, the method is characterized in that if the temperature T2 reaches or exceeds the minimum temperature T2_minThat is to say, for example, a temperature is reached which is sufficient for an effective catalytic reduction of nitrogen oxides in the SCR catalytic converter (for which ammonia is required), the supply device is activated to supply ammonia-forming compounds into the SCR catalytic converter.

On the other hand, if the temperature T2 does not reach the minimum temperature T2_minThen, thenThe supply means may be deactivated. In this case, no ammonia is needed, otherwise there is a risk of unwanted ammonia being released into the environment. In other words, the supply of the ammonia-forming compound can likewise be controlled or regulated in a manner dependent on the temperatures T1 and T2.

The ammonia-forming compound may be, for example, an aqueous urea solution. The ammonia-forming compounds can be applied directly to the SCR catalytic converter or to the exhaust-gas stream upstream of the SCR catalytic converter.

According to a further embodiment variant, the method may be characterized in that if the temperature T2 exceeds the maximum temperature T2_maxThen the air supply to the exhaust stream upstream of the nox trap is enabled. Correspondingly, if the temperature T2 does not exceed the maximum temperature T2_max(for any longer time) the air supply may be deactivated. Maximum temperature T2_maxAbove the minimum temperature T2_min。

Maximum temperature T2_maxMay be, for example, the temperature of the SCR catalytic converter, whereby an increased oxidation of ammonia may be expected. This may result in only insufficient ammonia being available to reduce the nitrogen oxides. In addition, due to oxidation, ammonia may be converted to other undesirable nitrogen oxides, and thus the emission of nitrogen oxides may increase.

By supplying air, cooling of the exhaust stream may advantageously be obtained so that the maximum temperature T2 is not exceeded_maxAnd thus an increase in oxidation of ammonia can be avoided.

According to various embodiment variants, the nitrogen oxide trap may take the form of a passive nitrogen oxide adsorber, an LNT catalytic converter or an LNT lean catalytic converter.

Passive nox adsorbers adsorb nox, in particular after a cold start of the internal combustion engine, and discharge these again at elevated exhaust gas temperatures without active regeneration, for example by means of unburned fuel. Passive nox adsorbers provide the advantage of rapid removal of nox from the exhaust stream after a cold start. In addition, no technical devices and control systems for active regeneration are required, so that these passive nitrogen oxide adsorbers are inexpensive and require only little installation space.

The LNT compact catalytic converter is an LNT catalytic converter with a low nitrogen oxide storage capacity, which is also optimized for cold start conditions and is characterized by low requirements on installation space.

The use of said special nox trap, which has been optimized for cold start conditions, provides the advantage associated with the method according to the invention that the optimization of the nox after cold start does not have to be carefully controlled or adjusted and/or require a large space for arranging the required components. Furthermore, since no active regeneration is performed, the air supply to the exhaust stream (which involves a change in the air/fuel equivalence ratio λ) has no or only a slight effect.

A control device according to the invention has been designed and provided for controlling the treatment of the exhaust gas flow in the exhaust system of an internal combustion engine, to receive a sensor signal relating to a temperature sensor TS1 for determining the temperature T1 of a nitrogen oxide trap arranged in the exhaust system, and to receive a sensor signal relating to a temperature sensor TS2 for determining the temperature T2 of an SCR catalytic converter arranged in the exhaust system, and to output a control signal for supplying air to the exhaust gas flow upstream of the nitrogen oxide trap to an air supply device in dependence on the received sensor signal.

In other words, the control device may receive input data relating to the temperature sensors TS1 and TS2, process these input data, and trigger the air supply device as an actuator on the basis of instructions or on the basis of code programmed in the control device corresponding to one or more routines in correspondence with the processed input data.

The control means may have been implemented in hardware and/or software and may be physically formed in one or more parts. In particular, the control device may be part of the engine control unit or may already be integrated into the engine control unit. For example, an engine control unit of a motor vehicle may be used as the control device.

In various configurations, the control device can, in addition to this, be designed and arranged to output a control signal to the heating device for heating the SCR catalytic converter and/or to output a control signal to the supply device for supplying the SCR catalytic converter with ammonia-forming compounds, depending on the received sensor signal. In other words, the heating and supply devices of the actuator can likewise be triggered in response to the processed input data on the basis of instructions or on the basis of code programmed in the control device corresponding to one or more routines.

For example, the control device according to the invention may be used to carry out the method according to the invention as described above. The above description, which is intended to clarify the method according to the invention, is therefore also intended to describe the control device according to the invention. The advantages of the control device according to the invention correspond to the advantages of the method according to the invention and its corresponding embodiment variants.

The exhaust system according to the invention has a nitrogen oxide trap, an SCR catalytic converter arranged downstream of the nitrogen oxide trap, a temperature sensor TS1 for determining the temperature T1 of the nitrogen oxide trap, a temperature sensor TS2 for determining the temperature T2 of the SCR catalytic converter, an air supply device for supplying air to the exhaust gas flow upstream of the nitrogen oxide trap, and a control device according to the above description. Alternatively, the exhaust system may have a heating device for heating the SCR catalytic converter and/or a supply device for supplying ammonia-forming compounds to the SCR catalytic converter.

The nitrogen oxide trap may in particular take the form of a passive nitrogen oxide adsorber, an LNT catalytic converter or an LNT compact catalytic converter.

The exhaust system according to the invention may, for example, be adapted to carrying out the method according to the invention described above. The above description, which is intended to clarify the method according to the invention, is therefore also intended to describe the exhaust system according to the invention. The advantages of the exhaust system according to the invention correspond to the advantages of the method according to the invention and its corresponding embodiment variants.

The motor vehicle according to the invention has an internal combustion engine and an exhaust system according to the above description. By "motor vehicle" is understood a vehicle propelled by an engine, such as a land vehicle, an aircraft or a watercraft. Alternatively, the motor vehicle may take the form of a hybrid electric vehicle.

The advantages of the motor vehicle according to the invention therefore correspond to the advantages of the exhaust system according to the invention and its corresponding embodiment variants. Furthermore, the invention has a particularly advantageous effect in the case of motor vehicles, since it is capable of complying with strict legal requirements with regard to the permitted emission of air pollutants.

The computer program product according to the invention comprises instructions for causing the exhaust system according to the above description to carry out the method according to the invention.

In this respect, a "computer program product" is to be understood as a program code stored on and/or retrievable via a suitable medium. To store the program code, any medium suitable for storing software (e.g., DVD, USB stick, flash memory card, etc.) may find its application. For example, the retrieval of the program code may be effected via the internet or an intranet or via other suitable wireless or hardwired network.

Drawings

The invention will be elucidated in more detail below on the basis of an illustration and a related description. The figures show:

FIG. 1 is an exhaust system in an exemplary configuration; and

FIG. 2 is a flow chart of an exemplary method.

Detailed Description

Fig. 1 schematically shows an exhaust system 2 adjoining an internal combustion engine 3. The internal combustion engine 3 may take the form of a compression ignition engine and may for example be operated on diesel fuel. The internal combustion engine 3 generates an exhaust gas flow 1, which exhaust gas flow 1 is absorbed by the exhaust system 2. Describing in terms of the flow direction of the exhaust gas flow 1, the exhaust system 2 of the exemplary embodiment has a nitrogen oxide trap 4, a heating device 6, an SCR catalytic converter 5 and a further exhaust gas aftertreatment device 12, for example a particle filter. The particulate filter may also be arranged downstream of the nitrogen oxide trap 4 and upstream of the heating device 6, for example.

The nitrogen oxide trap 4 may take the form of a passive nitrogen oxide adsorber, an LNT catalytic converter or an LNT compact catalytic converter; the SCR catalytic converter 5 may optionally take the form of an SDPF catalytic converter. The heating means 6 take the form of electrical heating means.

Immediately upstream of the nox trap 4 and the SCR catalytic converter 5, two temperature sensors TS1, TS2 are arranged, respectively, which are designed to determine the temperature of the exhaust gas stream 1, so that the temperature T1 of the nox trap and the temperature T2 of the SCR catalytic converter 5 can be determined indirectly on the basis of the temperature of the exhaust gas stream 1.

Furthermore, the exhaust system 2 has an air supply device 11 for supplying air to the exhaust gas flow 1 upstream of the nox trap 4, which device is arranged upstream of the temperature sensor TS 1. In addition to this, there is a supply device 7 for supplying ammonia-forming compounds (in the example of embodiment aqueous urea solution) to the SCR catalytic converter 5. The supply of ammonia-forming compounds to the exhaust gas stream 1 takes place upstream of the SCR catalytic converter 5 and downstream of the temperature sensor TS 2.

The temperature sensors TS1, TS2 are in operative signal communication with the control device 8. The control device 8 has been designed and arranged to receive the sensor signals 9a, 9b associated with the temperature sensors TS1, TS2 and to process said signals in order to generate the control signals 10a, 10b, 10 c. The control signals 10a, 10b, 10c are output to the air supply 11, the heating 6 and the supply 7 for supplying the ammonia-forming compound, respectively, so that the air supply 11, the heating 6 and the supply 7 are likewise in effective signal communication with the control 8. Alternatively, the control device 8 may take the form of a controller of the internal combustion engine 3, so that the control process can be implemented additionally by means of the control device 8.

The treatment of the exhaust gas flow 1 of the exhaust gas system 2 according to fig. 1 may be carried out, for example, by means of the method described below with reference to fig. 2, which, however, may itself also be carried out together with other exhaust gas systems 2.

In a first method step S1, the temperatures T1 and T2 are determined, for which the temperature sensors TS1, TS2 may be used.

In step S2, it is checked whether the temperature T1 exceeds the maximum temperature T1_maxAnd whether temperature T2 has not reached minimum temperature T2_minThat is, whether or not the condition T1 is satisfied>T1_maxAnd T2<T2_min. If one or neither condition is satisfied, the method returns to step S1 and the temperatures T1 and T2 are again determined.

On the other hand, if both conditions are satisfied, the method proceeds to step S3. In this case, there is a fear that nitrogen oxides will be desorbed from the nitrogen oxide trap 4 and discharged into the exhaust gas flow 1, but an effective catalytic conversion by means of the SCR catalytic converter 5 is not possible.

In step S3, the air supply to the exhaust gas flow 1 upstream of the nox trap 4 is therefore activated in order to cool the exhaust gas flow 1 and thus the nox trap 4. For example, cooling may be achieved in such a way: the temperature T1 is only slightly lower than the maximum temperature T1_maxOr a maximum temperature T1 is reached_maxIn order to avoid excessive cooling of the nitrogen oxide trap 4 and any undesired cooling of the SCR catalytic converter 5 arranged downstream. In addition to this, the heating device 6 is activated so that the SCR catalytic converter 5 is heated.

In step S4, it is checked whether the temperature T2 reaches or exceeds the minimum temperature T2_minThat is, whether the condition T2 ≧ T2 is satisfied_min. If this is not the case, the supply device 7 for supplying the ammonia-forming compound is deactivated or remains deactivated (step S6).

If the temperature T2 reaches or exceeds the minimum temperature T2_minThen in step S5 the supply means 7 for supplying the SCR catalytic converter 5 with ammonia-forming compounds are activated so that catalytic reduction of nitrogen oxides can take place in the SCR catalytic converter 5. At the same time, since no further heating of the SCR catalytic converter 5 is required and since no further cooling of the nitrogen oxide trap 4 is required, the heating device 6 is deactivated again and the air supply is also deactivated again.

From step S5, the method returns again to step S1 and again determines the temperatures T1 and T2. Alternatively, it is also possible to repeat the process onlyOr the temperature T2 is determined continuously, since no changes occur with respect to the heating device 6, the air supply and the activation and deactivation of the supply device 7, as long as the temperature T2 reaches or exceeds the minimum temperature T2_min。

In order to improve the clarity of the layout, the minimum temperature T1 is not shown in the flowchart of fig. 2_minIs monitored. If the temperature T1 does not reach the minimum temperature T1_min(for any longer time), for example due to excessive cooling of the nitrogen oxide trap 4 by means of the air supply, the air supply is deactivated in order to be able to store nitrogen oxides in the nitrogen oxide trap 4.

List of reference symbols

1 exhaust stream

2 exhaust system

3 internal combustion engine

4 nitrogen oxide trap

5 SCR catalytic converter

6 heating device

7 supply device

8 control device

9a, 9b sensor signal

10a, 10b, 10c control signals

11 air supply device

12 other exhaust gas aftertreatment device

TS1 temperature sensor for determining temperature T1

TS2 temperature sensor for determining temperature T2

T1 Nitrogen oxide trap temperature

Temperature of T2 SCR catalytic converter

T1_maxMaximum temperature of nitrogen oxide trap

T1_minMinimum temperature of NOx trap

T2_maxMaximum temperature of SCR catalytic converter

T2_minMinimum temperature of SCR catalytic converter

Method steps S1-S6

Claims

1. A method for treating an exhaust gas flow (1) in an exhaust system (2) of an internal combustion engine (3), characterized by the steps of:

-determining the temperature T1 of the nitrogen oxide trap (4),

-leading the exhaust gas flow (1) through the nitrogen oxide trap (4),

-determining the temperature T2 of an SCR catalytic converter (5) arranged downstream of the nitrogen oxide trap (4),

-leading the exhaust gas flow (1) through the SCR catalytic converter (5),

if the temperature T1 exceeds the maximum temperature T1_maxAnd the temperature T2 does not reach the lowest temperature T2_minActivating the air supply to the exhaust gas flow (1) upstream of the nitrogen oxide trap (4) and

if the temperature T1 does not reach the minimum temperature T1_minAnd/or temperature T2 reaching or exceeding minimum temperature T2_min-deactivating the air supply to the exhaust gas flow (1) upstream of the nitrogen oxide trap (4).

2. The method of claim 1, wherein:

if the temperature T1 exceeds the maximum temperature T1_maxAnd the temperature T2 does not reach the lowest temperature T2_min-activating a heating device (6) for heating the SCR catalytic converter (5).

3. The method of claim 2, wherein:

if the temperature T2 reaches or exceeds the minimum temperature T2_min-deactivating said heating means (6).

4. The method according to any of the preceding claims, characterized in that:

if the temperature T2 reaches or exceeds the minimum temperature T2_minActivating a supply device (7) for supplying ammonia-forming compounds to the SCR catalytic converter (5), and

if the temperature T2 does not reach the minimum temperature T2_min-deactivating said supply means (7).

5. Method according to any one of the preceding claims, wherein the minimum temperature T1_minIn the range between 150 ℃ and 250 ℃, preferably between 200 ℃ and 230 ℃ and/or a maximum temperature T1_maxIn the range between 150 ℃ and 300 ℃, preferably in the range between 200 ℃ and 250 ℃, and/or a minimum temperature T2_minIn the range between 150 ℃ and 200 ℃, preferably in the range between 170 ℃ and 190 ℃.

6. The method according to any of the preceding claims, characterized in that:

if the temperature T2 exceeds the maximum temperature T2_maxActivating the air supply to the exhaust gas flow (1) upstream of the nitrogen oxide trap (4), and

if the temperature T2 does not exceed the maximum temperature T2_max-deactivating the air supply to the exhaust gas flow (1) upstream of the nitrogen oxide trap (4).

7. Method according to any one of the preceding claims, wherein the nitrogen oxide trap (4) takes the form of a passive nitrogen oxide adsorber, an LNT catalytic converter or an LNT lean catalytic converter.

8. A method according to any one of the foregoing claims, in which the temperature T1 of the nitrogen oxide trap (4) is determined on the basis of the temperature of the exhaust gas flow (1) immediately upstream of the nitrogen oxide trap (4), and/or in which the temperature T2 of the SCR catalytic converter (5) is determined on the basis of the temperature of the exhaust gas flow (1) immediately upstream of the SCR catalytic converter (5).

9. Method according to any of claims 2-8, wherein the heating device (6) has been designed for indirectly heating the SCR catalytic converter (5) by means of heating the exhaust gas flow (1) upstream of the SCR catalytic converter (5).

10. A control device (8) for controlling a treatment of an exhaust gas stream (1) in an exhaust system (2) of an internal combustion engine (3), which control device has been designed and provided to receive a sensor signal (9a) relating to a temperature sensor TS1 for determining a temperature T1 of a nitrogen oxide trap (4) arranged in the exhaust system (2), and a sensor signal (9b) relating to a temperature sensor TS2 for determining a temperature T2 of an SCR catalytic converter (5) arranged in the exhaust system (2), and to output a control signal (10a) to an air supply device (11) for supplying air to the exhaust gas stream (1) upstream of the nitrogen oxide trap (4) in dependence on the received sensor signals (9a, 9 b).

11. A control device (8) according to claim 10, which has been designed and arranged to output a control signal (10b) to a heating device (6) for heating the SCR catalytic converter (5) depending on the received sensor signals (9a, 9 b).

12. A control device (8) according to claim 10 or 11, which has been designed and arranged to output a control signal (10c) to a supply device (7) for supplying ammonia-forming compounds to the SCR catalytic converter (5) in dependence on the received sensor signals (9a, 9 b).

13. An exhaust system (2) for treating an exhaust gas flow (1) produced by an internal combustion engine (3), characterized by:

-a nitrogen oxide trap (4),

-an SCR catalytic converter (5) arranged downstream of the nitrogen oxide trap (4),

-a temperature sensor TS1 for determining a temperature T1 of the NOx trap (4),

-a temperature sensor TS2 for determining the temperature T2 of the SCR catalytic converter (5),

-an air supply device (11) for supplying air to the exhaust gas flow (1) upstream of the nitrogen oxide trap (4), and

-a control device (8) according to any of claims 10 to 12.

14. The exhaust system (2) of claim 13, wherein:

-a heating device (6) for heating the SCR catalytic converter (5).

15. The exhaust system (2) according to claim 13 or 14, characterized in that:

-supply means (7) for supplying ammonia-forming compounds to the SCR catalytic converter (5).

16. The exhaust system (2) according to any of claims 13 to 15, wherein the nitrogen oxide trap (4) takes the form of a passive nitrogen oxide adsorber, an LNT catalytic converter or an LNT knock-down catalytic converter.

17. A motor vehicle having an internal combustion engine (3) and an exhaust system (2) according to any one of claims 13 to 16.

18. A computer program product comprising instructions to cause an exhaust system (2) according to any of claims 13 to 16 or a motor vehicle according to claim 17 to perform a method according to any of claims 1 to 9.