EP1537303A1

EP1537303A1 - Exhaust gas cleaning system and method for the cleaning of exhaust gases

Info

Publication number: EP1537303A1
Application number: EP03794765A
Authority: EP
Inventors: Joerg Lange; Peter Khatchikian
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2002-09-06
Filing date: 2003-06-24
Publication date: 2005-06-08
Also published as: DE10241898A1; WO2004025090A1

Abstract

The invention relates to an exhaust gas cleaning system which is used to clean the exhaust gases of an internal combustion engine, comprising an exhaust gas post-treatment unit and a feeder device for supplying an active substance to an input side of the exhaust gas post-treatment unit for the regeneration thereof. According to the invention, at least one adjustable flow divider (8) is arranged on the input side of the exhaust gas post-treatment unit (6) for variably dividing the flow (61) of exhaust gas into at least two partial flows (81, 82) and which is coupled to the feeder device (10) such that the active substance (101) which is fed to the exhaust gas flow (61) can be incorporated essentially in only one of the at least two or three partial flows (81, 82). The invention also relates to a corresponding method for cleaning exhaust gases.

Description

Exhaust gas cleaning system and method for cleaning exhaust gases

The invention relates to an / exhaust gas purification system with a regenerable / exhaust gas aftertreatment unit. The invention further relates to a method for purifying exhaust gases in which a ^'Abgasstrpm is passed through a standardized regenerable Abgasnachbehandlungsein-.

State of the art

The known design measures such as, for example, a favorable combustion chamber design are no longer sufficient to comply with future exhaust gas limit values of internal combustion engines. In particular, internal combustion engines whose exhaust gas has a high proportion of oxygen, for example diesel engines or gasoline engines with direct fuel injection, require more effort to reduce pollutants, with the diesel engine also having to reduce its particle emissions.

The particles contained in the exhaust gas consist largely of soot, which can be collected in a filter. Such a filter must, however, be reached after a certain particle load regenerated, ie usually burned free. One possibility for regeneration is to heat the exhaust gases to temperatures of approximately 450 to 650 ° C., which can be done, for example, by adding hydrocarbons, in particular vaporized or atomized fuel, into the exhaust system upstream of an oxidation catalytic converter. The exothermic conversion to CO, C0 ₂ and H ₂ 0 releases the heat required for free burning.

DE 197 31 865 C2 describes an exhaust gas catalytic converter which is used primarily to reduce nitrogen oxides (NO _x ) in the exhaust gas of internal combustion engines with self-ignition (diesel engines). In an oxidation catalytic converter of the catalytic converter arrangement, the NO present in the exhaust gas is first converted into N0. The nitrogen oxides are then stored in a downstream storage unit, for example as barium nitrate. These storage catalytic converters are able to store the nitrogen oxides from the exhaust gas stream over a period of several seconds to minutes. The loaded storage catalysts must be regenerated at regular intervals, the nitrogen oxides being reduced to nitrogen and being released into the exhaust gas. A reducing environment (rich mixture) with a prevailing air ratio of λ <1 is necessary for this emptying or regeneration process.

An air ratio of λ <1 can be generated internally in the engine directly by controlling the combustion or externally by metering a reducing agent (eg diesel fuel, HC) into the exhaust system become. The ratio of fuel to combustion air is regulated internally in the engine, producing a rich mixture (λ <1) with insufficient air. With this type of control, low-soot combustion is only possible in a lower speed / load range. In known internal combustion engines, regeneration of the storage catalytic converter in the entire engine map is associated with increased particle emissions or with a burst of smoke.

The high oxygen content in the exhaust gas of diesel engines or direct-injection gasoline engines is generally problematic. If the entire exhaust gas flow has to be enriched, a large amount of the reducing agent is only required to bring the oxygen content in the exhaust gas to zero, ie to set a λ value of one (λ = 1). Comparatively little reducing agent is used for the subsequent conversion of the nitrogen oxides.

DE 100 62 957 describes an exhaust gas purification system with a catalytic converter arrangement which comprises a storage catalytic converter for the reduction of nitrogen oxides and a supply device for supplying a reducing agent to the input side of the storage catalytic converter during a regeneration phase. The catalytic converter arrangement has an orifice arrangement which partially covers the cross-sectional area of the storage catalytic converter.

Another possibility for reducing the proportions of N0 _X in the exhaust gas is their reduction in a special catalyst with the addition of ammonia

(NH ₃ ) to molecular nitrogen (N ₂ ). For practical See use is particularly suitable for a urea-water solution or solid urea, which is converted to NH ₃ in a further catalyst.

An exhaust gas cleaning system with a regenerable exhaust gas aftertreatment unit is further described in the older German patent application with the file number 101 42 804.9. Here, i t _ß an adjustable flow divider provided with- means of which a partial exhaust gas stream is generated in a regeneration position, flow through which an exhaust gas aftertreatment unit. A remaining second partial flow flows through at least one further exhaust gas aftertreatment unit. Due to the adjustable flow divider, a partial flow can be generated, which ensures regeneration of the exhaust gas aftertreatment unit. At the same time, the main exhaust gas stream flows through a further exhaust gas aftertreatment unit, so that the continuity of the exhaust gas purification is also ensured during the regeneration phase of the exhaust gas aftertreatment unit.

Advantages of the invention

In the case of a generic exhaust gas cleaning system for cleaning the exhaust gas of an internal combustion engine, the invention proposes an arrangement in which, on the input side of an exhaust gas aftertreatment unit e; Ln, an adjustable flow divider is provided for the variable division of the exhaust gas flow into at least two partial flows. This adjustable flow divider is according to the invention with a feed device for feeding an active substance to the cyclic and / or permanent regeneration of the exhaust gas aftertreatment unit in such a way that the active substance supplied to the exhaust gas stream can be introduced almost completely into one of the at least two partial streams. The arrangement with the flow divider is particularly suitable for the use of an external regeneration principle, in which no throttle valve is required on the engine side during the regeneration phase and no direct intervention in the engine control system and thus no rich operation of the engine is required. The arrangement according to the invention enables a compact, space-saving and simply constructed quasi-continuously operating exhaust gas cleaning system, which in its simplest embodiment only requires a storage catalytic converter. At the same time, with the arrangement according to the invention, an additional consumption of fuel can be minimized by the fact that no stoichiometric air-fuel ratio of the entire engine exhaust gas is required for the regeneration of the exhaust gas aftertreatment unit or the storage catalytic converter.

An advantageous embodiment of the invention provides that the adjustable flow divider comprises a pivotable flap which is arranged in the exhaust gas flow upstream of the exhaust gas aftertreatment unit. The exhaust gas flow is divided into two or three partial flows with the aid of the swiveling flap, which are produced by the exhaust gas aftertreatment unit in the form of a catalyst, particle filter or the like. stream. In the so-called loading phase of the exhaust gas aftertreatment unit, two partial flows of approximately the same extent are formed, which can be achieved by a central position of the flap. For the regeneration of the exhaust gas aftertreatment unit, the pivotable flap can be adjusted so that the path to be regenerated is flowed through with a smaller partial flow (for example 10% of the total flow). A stoichiometric air ratio (λ = 1) only has to be established in this smaller exhaust gas flow, for which purpose, in a first approximation, only 10% of the amount of regeneration agent that would be required to enrich the entire exhaust gas flow. This drastically reduces the consumption of regeneration agent. A higher dwell time of the active substance in the catalyst also improves the conversion, which is why the volume of the catalyst unit can possibly be kept smaller than in a single-flow system.

In an upper and lower stop position of the flap, two unequal partial flows are formed. The active substance is preferably fed to the smaller substream, so that a small amount of active substance is consumed during a short regeneration cycle. Since the exhaust gas aftertreatment unit i.d-R- has an axial flow through the channel structure, the part of the channels to be regenerated can be precisely defined with the position of the flap.

With the help of the adjustable flap, it is possible to enable short regeneration phases for the two parts and overall quasi-continuous operation. If the active substance is to be supplied to the entire exhaust gas flow, the flap can be periodically pivoted back and forth (or up and down) in order to meter the active substance evenly. This can take place between the two stop positions or in a smaller angular range of, for example, +/- 10 ° around the central position. If these vibrations occur quickly enough, for example at 1 Hz, an approximately even distribution of the active substance between the two partial flows is achieved. The enrichment of the full flow can make sense, for example, when some of the exhaust gas aftertreatment components are operated in full flow.

Some exhaust gas treatment concepts require the exhaust gas to be heated up temporarily. A considerably lower energy is required to heat only a partial stream.

According to an embodiment of the invention, the feed device for feeding the active substance is integrated in a hollow shaft of the flow divider which can be pivoted about a pivot axis of the flap. The pivotable hollow shaft of the flap preferably has an opening for feeding the active substance into the exhaust gas stream. Furthermore, the opening in the pivotable hollow shaft is preferably connected to a metering device. In known arrangements for dividing an exhaust gas flow into two structurally separate paths and for metering the two paths, at least two flaps and two separate metering units are generally necessary. In contrast, the arrangement of the system in a common housing brings only a flap and only one dosing unit offers considerable advantages in terms of construction costs and space requirements. In addition, the compact dimensions of the system ensure a lower total heat emission. The device is suitable, for example, for regenerating a NO _x store and a particle filter and for desulfurizing both.

The pivotable flap of the flow divider preferably has at least two guide plates fastened to the hollow shaft, the surfaces of which have an increasing distance in the direction of flow. These baffles ensure a reliable deflection of the exhaust gas flow and, in the regeneration position, prevent active substance from flowing into an unaffected partial flow. of the exhaust gas can get. This reduces the consumption of active substance during the regeneration phase.

According to a further embodiment of the invention, a flow baffle can be arranged behind the pivotable flap and in front of the exhaust gas aftertreatment unit. This flow baffle can comprise, for example, a single sheet metal plate, which is parallel to the flow direction of the exhaust gas and its

Surface is arranged parallel to the pivot axis of the flap. Alternatively, the flow guide plate can comprise at least two V-shaped plate disks, the spaced free ends of which connect approximately flush with the free ends of the guide plates of the pivotable flap in its central position. Such a flow baffle ensures reliable division and separation of the two or three exhaust gas partial flows and prevents this Entry of active substance in the partial flow not to be regenerated.

A particularly compact exhaust gas aftertreatment system can be realized by integrating the exhaust gas aftertreatment unit together with the adjustable flow divider and the feed device in a common housing. For example, in the area in front of the exhaust gas aftertreatment unit, the housing can have a conically widening contour, starting from an exhaust gas duct of smaller diameter. This configuration leads to a very compact structural unit, which is characterized by low heat losses and a high degree of freedom with regard to the placement of the system in the vehicle.

The flap of the flow divider can be controlled pneumatically, in particular electro-pneumatically, for example. In particular, there is the possibility of using existing pneumatic devices in a motor vehicle to control the exhaust gas cleaning system. Alternatively, other controls are also possible, for example by means of an electromagnet or an electric servomotor or the like.

An embodiment according to the invention provides that the exhaust gas aftertreatment unit comprises at least one storage catalytic converter, which is accommodated with the flow divider and the feed device in a common housing. In particular, the exhaust gas aftertreatment unit can have one or more NO _x storage catalytic converters, one or more par- include particle filter and / or at least one oxidation catalyst.

Furthermore, one embodiment can consist in that a system for selective catalytic reduction (so-called SCR system) for reducing the NO _x components in the exhaust gas is integrated in the exhaust gas aftertreatment unit. In this case, aqueous urea solution is typically added to the exhaust gas, so that the actual reducing agent ammonia (NH ₃ ) is released by thermolysis and subsequent catalyzed hydrolysis of the urea. Such a device can advantageously be combined with the exhaust gas purification system according to the invention and leads to an extensive minimization of the undesirable and harmful exhaust gas components.

A further advantageous embodiment of the inventions may fertil in a coating of the particulate contained in the exhaust gas aftertreatment unit having a storing N0 _X and / or are made with an oxidising type catalytic substance. With this configuration, a particularly effective and compact exhaust gas cleaning system can be realized.

In one embodiment of the invention, the active substance can comprise a reducing agent or a desulfating agent. Such a reducing agent can be vaporized or atomized fuel, for example. Means for desulfating (desulfurization) the exhaust gas are known and used to further improve the cleaning effect of the exhaust gas.

To further improve the effectiveness of the exhaust gas purification system, it may be advantageous to provide an additional heating element or an additional burner in the exhaust gas stream or in the exhaust gas aftertreatment system. The heating element can, for example, be electrically operated and possibly have a catalytic coating. With such a heating element or a burner, the exhaust gas flow can be heated to temperatures at which the cleaning effect is optimized or takes place at all. For example, the catalytic cleaning effect only begins at elevated exhaust gas temperatures that are not reached immediately after the internal combustion engine is started. A catalytic coating of the heating element can serve to initiate the catalytic cleaning process even before the exhaust gas aftertreatment unit.

The use of an electrically heatable catalyst is particularly advantageous, since • it only has to heat up a small part of the stream. The electricity requirement for this is considerably lower than that for heating the full exhaust gas flow. The electrical system is thus less burdened.

A method according to the invention for cleaning exhaust gases of an internal combustion engine, in which an exhaust gas stream is passed through an exhaust gas aftertreatment unit and in which an active substance is supplied to the exhaust gas aftertreatment unit on the inlet side during a regeneration phase, provides that the exhaust gas stream in the Regeneration position on the input side of the exhaust gas aftertreatment unit is divided into two or three partial flows by means of an adjustable flow divider, one of the partial flows being acted upon by an active substance for regeneration of the exhaust gas aftertreatment unit. In the case of this method according to the invention, only a very small amount of active substance is required for regeneration of the exhaust gas aftertreatment unit compared to known systems, since only a smaller partial flow is acted upon by the active substance and in this way an almost continuous regeneration of the exhaust gas aftertreatment unit due to the variably adjustable flow divider is possible while driving. In this way, no phases are necessary during which the entire exhaust gas aftertreatment unit is cleaned at once and during which a relatively large amount of active substance has to be added.

One embodiment of the method provides that the flow divider takes the position of regeneration when the exhaust gas aftertreatment unit is activated for regeneration. Due to the variable adjustability of the flow divider, a variable proportion of the exhaust gas aftertreatment unit can be regenerated. Because the active substance is supplied to only one of the two or the three partial flows, preferably the smaller one, only a slight enrichment of the exhaust gas is necessary, as a result of which the fuel consumption is increased only insignificantly. In the process according to the invention, the exhaust gas stream can flow through at least one storage catalytic converter, at least one particle filter and / or one or more oxidation catalytic converters. One or more of these parts can be electrically heated. The cleaning effect can be very effective in this way with a particularly compact exhaust gas cleaning system.

The supply of the active substance can serve to regenerate the at least one particle filter and / or the at least one N0 _X store. Alternatively or additionally, the active substance of the particulate filter and / or the N0 _x storage can be desulfurized by means of feed.

drawings

The invention is explained in more detail below in preferred exemplary embodiments with reference to the associated drawings. It shows:

FIG. 1 shows a schematic illustration of an exhaust gas aftertreatment unit in the exhaust gas stream of an internal combustion engine;

FIG. 2 shows a schematic longitudinal section of an exhaust gas aftertreatment unit according to the invention with a pivotable flow divider;

FIG. 3 shows the exhaust gas aftertreatment unit according to FIG. 2 with a swiveled flow divider; FIG. 4 shows a schematic longitudinal section of an alternative embodiment of the exhaust gas aftertreatment unit;

FIG. 5 the exhaust gas aftertreatment unit according to FIG. 4 with the flow divider pivoted;

FIG. 6 shows a schematic detailed section of the pivotable flow divider of the exhaust gas aftertreatment unit;

Figure 7 is a schematic cross section of the flow divider;

Figure 8 is a plan view of the swiveling flow divider and

Figure 9 is another view of the flow divider.

Description of the embodiments

Preferred exemplary embodiments of the invention are described below with reference to FIGS. 1 to 9. The same parts are basically provided with the same reference numerals and are therefore sometimes not explained several times.

FIG. 1 illustrates in a schematic representation the arrangement of an exhaust gas aftertreatment unit 6 in the exhaust gas duct 24 of an internal combustion engine 2. This has an inlet duct 21 on the input side for the supply of fresh gas 23 and optionally an adjustable throttle valve 22 arranged therein for regulating. the fresh gas supply. However, the throttle valve is only optional on internal combustion engines. An exhaust gas cleaning system, which is accommodated in a housing 67 and is provided for cleaning / soot filtering of the exhaust gas of the internal combustion engine 2 and / or for the catalytic conversion of harmful combustion products, is arranged in an exhaust gas duct 24. The exhaust gas purification system can comprise, for example, one or more particle filters, one or more oxidation catalysts, one or more storage catalysts and / or a so-called SCR system (system for selective catalytic reduction). The modules mentioned can optionally be arranged one behind the other in any order and / or at least partially in an integrated design.

An adjustable flow divider 8 is provided on the input side of the unit characterized as exhaust gas aftertreatment unit 6, comprising one or more catalysts or particle filters 68, 69, which according to the invention has a feed device 10 for variable metering of an active substance by means of an adjustable metering device 103. The active substance is preferably a means for regeneration of the particulate filter or of the N0 _X - storage and / or desulfurization of the above components.

A central control unit 4 of the internal combustion engine 2 has inputs for sensor signals 41 and outputs for control signals 42. The values of a speed sensor, an air mass sensor, temperature sensors or the like can be used as sensor signals. are processed. A differential pressure Δp is preferably also measured between an input side and an output side of the exhaust gas aftertreatment unit 6. Some of the control signals are indicated as examples. For example, an actuating signal 43 controls an actuator 44 for adjusting the throttle valve 22 as a function of the corresponding input signals 41. Furthermore, an actuating signal 45 controls an actuator 46 of the flow divider 8, which can be adjusted, for example, by pneumatic, electromagnetic or electromotive means. Furthermore, a control signal 47 is provided for controlling an actuator 48 for the metering device 103, by means of which a variable amount of active substance can be fed into the exhaust gas stream 61 upstream of the exhaust gas aftertreatment unit. The exhaust gas stream 62 after the exhaust gas aftertreatment unit 6 is either passed through further exhaust gas aftertreatment units, for example further catalytic converters, or to an outlet which leads to the outside.

FIGS. 2 and 3 each show a schematic longitudinal section of the exhaust gas aftertreatment unit 6 according to the invention which, in the exemplary embodiment shown, has a first catalytic converter or particle filter 68 and a second catalytic converter or particle filter 69 in a common housing 67. The catalysts or particle filters 68, 69 each have axially extending flow channels 70 through which the exhaust gas stream 61 flows. An adjustable flow divider 8 is arranged in the exhaust gas duct 24 in front of the first catalytic converter 68 and can divide the exhaust gas flow 61 into two or three partial flows. In a loading In the charging position (FIG. 2) of the exhaust gas aftertreatment unit 6, the flow divider 8, which is designed as a pivotable flap 83, is in a central position, so that an upper and lower portion of the catalysts or particle filters 68, 69 are each subjected to approximately the same exhaust gas mass flow. No active substance is added in this position.

For regeneration, the flap 83 is pivoted up or down in a direction about a pivot axis 84 (see FIG. 3) and is in a regeneration position. In this position, a larger part of the exhaust gas flow 61 flows below the pivotable flap 83, is partly guided through a fixed flow baffle 63 and flows into a lower part of the catalysts or particle filters 68, 69. A smaller part of the exhaust gas flows through a passage 89 in a hollow shaft 85 of the pivotable flap 83. In this regeneration position, an active substance, for example evaporated fuel in the case of the NO _x accumulator, is metered in via the hollow shaft 85 and its passage 89 of the flap 83 and flows between them in the direction of flow opens

Baffles 86 (cf. FIG. 6) into a smaller upper part of the catalysts or particle filters 68, 69. Backmixing within the components is largely ruled out since all common components such as catalysts, particle filters etc. have a channel structure with flow channels 70, which only allow flow in the axial direction. If the upper side is regenerated, as shown in FIG. 3, the flap 83 set so that the lower part of the exhaust gas aftertreatment unit 6 can be regenerated.

If the partial flow ratio is to be varied, the flap 83 can easily be pivoted from one of the two stop positions towards the middle position. Exhaust gas then flows through the gap opening formed above the upper baffle 86 or below the lower baffle into the upper or lower part of the catalytic converters or particle filters and the partial flow ratio becomes smaller. Tests have shown that the metering flow then only reaches the path to be regenerated almost up to the middle position of the flap 83 (loading position). It can make sense to operate only the first exhaust gas aftertreatment component 68 in the partial flow and the second component 69 in the full flow. In this case, a distance between the components 68, 69 is chosen so large that the partial flows 81 and 82 reunite in it and the component 69 is flowed through homogeneously. On the other hand, if component 69 is also to be operated in the partial flow, the distance must be chosen to be very small. The distance is ideally zero.

The size of the distance between the two components 68, 69 is of important importance. If it is not available or is very small, component 69 is also operated in the partial flow. However, if the distance is greater than approx. 0.5 ... 1 mm, the partial flows 81, 82 are mixed in the gap, which is caused by the pressure drop. The component 69 is then flowed homogeneously and uniformly over its entire cross section. You can thus be found in full flow and behaves sφ as if it were installed in a separate housing at position 62.

FIGS. 4 and 5 show corresponding representations of an alternative exhaust gas aftertreatment unit 6, in which the flow guide plate 63 arranged downstream of the flap 83 consists of a single plate disk arranged parallel to the flow direction. The shape of the fixed flow guide plate 63 slightly favors the flow control in the regeneration position (FIG. 5). In the loading position (FIG. 4), however, the flow guidance is not as favorable as in the embodiment according to FIGS. 2 and 3 with the V-shaped flow guide plate 63, which consists of a first and second plate disk 64, 65.

FIG. 6 illustrates a detailed view of the front area of the exhaust gas aftertreatment unit 6 with the pivotable flap 83 and the V-shaped flow baffle 63. In a region in front of the flap 83 up to approximately its pivot axis 84 there is in each case above and below the hollow shaft 85 Flap wing 88 arranged. These flap vanes 88, which are arranged symmetrically to a central axis of the exhaust gas duct 24, direct the exhaust gas flow 61 from the internal combustion engine onto the hollow shaft 85 and ensure that the metered-in current is directed exclusively into the path to be regenerated. Numerous tests with the pivotable flap have shown, however, that the flap vanes 88 are not absolutely necessary for the system to operate properly. In the detailed view of FIG. 6, the hollow shaft 85 is drawn in a section through the passage 89. The hollow shaft 85 has an opening 102 of the feed device 10, which enables an active substance to be metered in (cf. FIG. 8). The two baffles 86 of the flap 83 direct the main part of the exhaust gas flow 61 (second partial flow 82) into the lower part of the catalysts or particle filter 68, 69 for exhaust gas aftertreatment. The smaller part of the exhaust gas flow (first partial flow 81) enters the cutout of the hollow shaft 85 on the left and out again between the guide plates 86 on the right. This exhaust gas flow entrains the metering flow, which is introduced from below in the axial direction into the center of the hollow shaft 85, into the upper part of the arrangement.

The mixing of the exhaust gas with the dosing substance (active substance 101) is particularly advantageous with this flap. The high flow velocity and the small size of the opening in the hollow shaft 85 produce vortices that promote mixing. If the eddies do not occur, they can be artificially induced by suitable measures when designing the window. The introduction of the mixture in the middle between the flap blades is very cheap in that the dosing agent has little contact with the relatively cold housing walls. With evaporated diesel fuel as a reducing agent, the liquid dosing agent could otherwise condense out. The part of the housing in which the flap 83 is installed can be cylindrical or - as shown - slightly conical.

FIG. 7 again shows a cross section through the flap 83, which can be rotated about the pivot axis 84 by means of the pivotable hollow shaft 85. An opening 102 is provided in the middle of the hollow shaft, which is illustrated with reference to FIG. 8. A feed line 104 serves to feed the active substance 101 to the opening 102 between the two baffles 86, which at the same time forms the passage 89 for the exhaust gas flow.

FIG. 9 again shows a top view of the flap 83 of the flow divider 8 and illustrates the elongated contour of the opening 102 on the rear side of the hollow shaft 85 facing away from the guide plates 86.

Claims

claims

1. Exhaust gas cleaning system for cleaning the exhaust gas of an internal combustion engine with an exhaust gas aftertreatment unit and a feed device for supplying an active substance to an input side of the exhaust gas aftertreatment unit for its regeneration, characterized in that at least one adjustable flow divider (8) for the variable division of the exhaust gas aftertreatment unit (6) on the input side Exhaust gas stream (61) is provided in at least two partial streams (81, 82), which is coupled to the feed device (10) in such a way that the active substance (101) supplied to the exhaust gas stream (61) can be either in both or largely in only one of which at least two partial flows (81, 82) can be introduced.

2. Exhaust gas cleaning system according to claim 1, characterized in that the adjustable flow divider (8) comprises a pivotable flap (83) which is arranged in the exhaust gas stream (61) upstream of the exhaust gas aftertreatment unit (6).

3. Exhaust gas purification system according to claim 1 or 2, characterized in that the feed device (10) is integrated in a hollow shaft (85) of the flow divider (8) which can be pivoted about a pivot axis (84) of the flap (83).

4. Emission control system according to claim 3, characterized in that the pivotable hollow shaft

(85) of the flap (83) has an opening (102) for feeding the active substance (101) into the exhaust gas stream (61 or 81).

5. Exhaust gas cleaning system according to claim 4, characterized in that the opening (102) in the pivotable hollow shaft (85) is connected to a metering device (103).

6. Exhaust gas purification system according to one of claims 2 to 5, characterized in that the pivotable flap (83) of the flow divider (8) has at least two guide plates (86) fastened to the hollow shaft (85), the surfaces of which have an increasing distance in the flow direction exhibit.

7. Exhaust gas cleaning system according to one of claims 2 to 5, characterized in that a flow guide plate (63) is arranged behind the pivotable flap (83) and in front of the exhaust gas aftertreatment unit (6).

8. Exhaust gas cleaning system according to claim 7, characterized in that the flow baffle

(63) comprises a single sheet metal disk (64) which is arranged parallel to the direction of flow of the exhaust gas and whose surface is parallel to the pivot axis (84) of the flap (83).

9. Emission control system according to claim 7, characterized in that the flow baffle (63) comprises at least two V-shaped sheet metal disks (64, 65), the spaced free ends (66) of which are approximately flush with the free ends (87) of the guide plates (86) of the pivotable flap (83) in their central position.

10. Exhaust gas purification system according to one of the preceding claims, characterized in that the exhaust gas aftertreatment unit (6) is integrated together with the adjustable flow divider (8) and the feed device (10) in a common housing (67).

11. The exhaust gas purification system according to claim 10, characterized in that the housing (67) in the area in front of the exhaust gas aftertreatment unit (6) has a conically widening contour starting from an exhaust gas duct (24) of smaller diameter.

12. Exhaust gas purification system according to one of the preceding claims, characterized in that the exhaust gas aftertreatment unit (6) comprises at least one storage catalytic converter which is housed with the flow divider (8) and the feed device (10) in a common housing (67).

13. Exhaust gas cleaning system ^' according to one of the preceding claims, characterized in that the exhaust gas aftertreatment unit (6) comprises a system for selective catalytic reduction to reduce the NO _x components in the exhaust gas.

14 exhaust gas purification system according to any one of the preceding claims, characterized in _/ that the exhaust gas aftertreatment unit (6) comprises a par ^~ - comprises particle filter.

15. Exhaust gas purification system according to one of the preceding claims, characterized in that the exhaust gas aftertreatment unit (6) comprises an oxidation catalytic converter, which can optionally be heated electrically.

16. Exhaust gas cleaning system according to one of claims 12 to 15, characterized in that the components (68, 69) of the exhaust gas aftertreatment unit (6) are arranged in a common housing (67).

17. Exhaust gas purification system according to claim 16, characterized in that the components, n (68, 69) of the exhaust gas aftertreatment unit (6) are arranged one behind the other at a distance of less than approximately 0.5 mm.

18. Emission control system according to claim 16, characterized in that the components

(68, 69) of the exhaust gas aftertreatment unit (6) are arranged one behind the other at a distance of more than about 0.5 to 1 mm.

19. Emission control system according to one of the preceding claims, characterized in that the active substance (101) comprises a reducing agent.

20. A method for cleaning exhaust gases of an internal combustion engine, in which an exhaust gas stream is passed through an exhaust gas aftertreatment unit, and in which an active substance is supplied to the exhaust gas aftertreatment unit on the input side during a regeneration phase, characterized in that the exhaust gas stream (61) in the Regeneration position on the inlet side of the exhaust gas aftertreatment unit (6) is divided into at least two partial flows (81, 82) by means of at least one adjustable flow divider (8), with either only one of the partial flows (81, 82) or both partial flows (81, 82) with one active substance for the regeneration of the exhaust gas aftertreatment unit (6).

21. The method according to claim 20, characterized in that the flow divider (8) assumes the position of regeneration when the exhaust gas aftertreatment unit (6) is activated for regeneration.

22. The method according to claim 20 or 21, characterized in that the partial streams (81, 82) are variable.

23. The method according to any one of claims 22 to 22, characterized in that the active substance (101) is supplied to only one of the at least two partial streams (81, 82).

24. The method according to any one of claims 20 to 23, characterized in that in a medium ren position of the flap (83) two equal partial streams (81, 82) are formed.

25. The method according to claim 24, characterized in that the active substance (101) in the middle position of the flap (83) is fed to two partial flows (81, 82).

26. The method according to claim 24 or 25, characterized in that the active substance (101) is alternately supplied to two partial flows (81, 82) during a periodic pivoting of the flap (83) via the central position.

27. The method according to claim 26, characterized in that the flap (83) is pivoted back and forth between the two stop positions.

28. The method according to claim 26, characterized in that the flap (83) is pivoted back and forth in a limited angular range between the two stop positions.

29. The method according to any one of claims 20 to 28, characterized in that two different sized partial flows (81, 82) are formed in a lower or an upper stop position of the flap (83).

30. The method according to any one of claims 20 to 29, characterized in that a particle filter and / or a NO _x store is regenerated by supplying the active substance (101).

31. The method according to any one of claims 20 to 30, characterized in that the particle filter and / or the NO _x store is desulfated by supplying the active substance (101).