EP2464841B1 - Decoupling element, in particular for exhaust gas systems - Google Patents

Description

The invention relates to a decoupling element, in particular for exhaust systems, for use with an injection device for injecting a reducing agent, such as urea, with a corrugated metal bellows and disposed within the bellows flow-guiding element whose outer diameter is smaller than the inner diameter of the bellows. Furthermore, the invention relates to a method for guiding exhaust gas of an internal combustion engine through a corrugated metal bellows.

Increasing demands on limits of exhaust gases, in particular automobile exhaust gases, by recent legislation make the injection of reducing agent into an exhaust system necessary. Such a reducing agent is for example urea, as from the DE 10 2008 010 071 A1 or from the DE 10 2004 020 138 A is known. Therein a device for the conversion of exhaust components of an internal combustion engine by means of at least one catalyst and / or a particulate filter is described. It is provided that the at least one catalyst for the conversion of exhaust gas components is arranged within a part of the exhaust tract, which is permanently connected to a compensator. Such a compensator or decoupling element usually has a - helically or annular wavy - bellows and a protective Agraffschlauch protecting it, which rests against the wall of the bellows. The Agraffschlauch serves primarily for protection the bellows in front of the hot exhaust gas and shows a helical winding, with a substantially S-shaped cross-sectional profile, wherein adjacent elements of the winding intermesh.

If possible close to the engine, a reducing agent is added to the hot exhaust gas. This is done primarily by an injection device which injects an aqueous urea solution into the hot exhaust gas. The metering takes place as a function of operating parameters of the internal combustion engine, controlled by an engine control unit, in such a way that the aqueous urea solution is sprayed into the exhaust gas stream via a nozzle directly in front of a hydrolysis catalytic converter.

By the Agraffschlauch having a diameter which is smaller than or equal to the inner diameter of the bellows, it is almost directly on the inner turns of the bellows on. Between outer turns of the bellows and the Agraffschlauch therefore gaps are formed, which can fill with exhaust gas. Although the windings of the Agraffschlauchs represent a significant flow resistance, but a Agraffschlauch is not gas-tight as such, for different reasons, a gas exchange between Agraffschlauch and bellows takes place. Thus, small gas flows can arise due to turbulence of the flowing exhaust gas and by diffusion. Furthermore, pressure changes in the exhaust system, for example by load changes on the engine are possible. The movements of the vehicle generate movements of the decoupling element and thus of the bellows, thereby changing the volume between bellows and Agraffschlauch with each compression or stretching of the bellows. This allows a negative pressure in the space between bellows and Agraffschlauch arise. This causes a volume flow through the Agraffschlauch therethrough. The result is that in the bellows or in the Balgwindungen urea enriched exhaust passes, the urea can condense on the cooler bellows wall and crystallize. As a result, accumulates more and more urea over time and dirty the inner wall of the bellows, resulting in a reduced mobility of the bellows. The various parts of the exhaust system are thus no longer vibration decoupled from each other.

The object of the invention is therefore to provide an apparatus and a method which prevent the aforementioned disadvantages, in particular, to avoid that a reducing agent, such. Urea can settle in the Balgwandung.

According to the invention the object is achieved by a decoupling element of the type mentioned, which is characterized in that the flow-guiding element separates the interior of the bellows in an inner core flow path for a core flow of the exhaust stream and in an outer sheath flow path for a sheath flow of the exhaust stream. Furthermore, the invention provides a method for using the decoupling element of the aforementioned type, wherein flows in an exhaust gas stream flowing exhaust gas divided by a finite radial distance within the bellows arranged flow guiding element into a core stream and a sheath stream.

In order to protect the bellows from the hot exhaust gas flow, it is preferably further provided that an outer Agraffschlauch is disposed within the bellows, wherein the outer diameter is less than or equal to the inner diameter of the bellows. It is further provided that the flow-guiding element is formed as an inner Agraffschlauch.

The flow-guiding element is particularly preferably held coaxially within the bellows, it being provided that the flow-guiding element is held on the input and / or output side by at least two supports which are distributed uniformly over the circumference of the flow-guiding element. The flow-guiding element is arranged with finite radial distance within the bellows, which results in that between the flow-guiding element and the bellows and / or outer Agraffschlauch a cross-sectionally annular space is formed, in which exhaust gas flows in a sheath stream. An outer Agraffschlauch can also be provided for guiding the exhaust stream, so that turbulence in the region of the bellows shafts are prevented.

A urea injection into the core stream takes place by means of an injection device, with particular preference provided that the injection device is arranged on the input side. The reducing agent is thus injected into the core stream upstream of the flow-guiding element by an injection device arranged on the input side. The injection takes place at a certain angle. Alternatively, the invention provides that the injection device is arranged on the input side centrally in front of the inner Agraffschlauch and that the injection device is secured by struts on the input side of the inner Agraffschlauchs. So that an injection takes place evenly, it is provided that urea by means of the injector is injected cone-shaped in the core stream. It can also be provided according to the invention that the injection device is arranged laterally on an elongated exhaust pipe in front of the flow-guiding element, wherein the injection device is formed at an angle between 45 ° and 90 ° at the exhaust pipe, wherein in an intermediate space between flow-guiding element and bellows and / or outer Agraffschlauch urea-free exhaust flows freely in a sheath flow, wherein a wall of the inner Agraffschlauchs penetrating urea is washed away. Here, a conical tube insert is inserted into the exhaust pipe at the appropriate angle and connected to a pipe section as a flow-guiding element. As a result, a direct injection of urea is ensured in the core stream.

The invention further provides that the length of the flow-guiding element is greater than or equal to the length of the bellows, so that the flow-guiding element protrudes over the length of the bellows. The length of the flow-guiding element can be varied in such a way that the length of the flow-guiding element is smaller than the length of the bellows, the speed of the exhaust gas being dimensioned such that on the output side both exhaust gas streams are not mixed immediately. The decoupling element itself is positively connected by widening and / or by means of clamps with a rigid exhaust pipe, wherein the individual components of the decoupling element are preferably also materially connected by welding with each other.

A particularly preferred embodiment of the invention provides that urea-enriched exhaust gas flows in a core stream within the flow-guiding element, and that in a space between the flow-guiding element and bellows or outer Agraffschlauch urea-free exhaust flows freely in a bypass flow. The flow-conducting element is thus surrounded by urea-free sheath flow and a wall of the flow-guiding element penetrating urea is washed away by the sheath flow.

The invention of view that the flow-leading element is connected on the output side to a flange of the bellows, so that a passage between the bellows and inner Agraffschlauch is locked. It can be provided as a flow-guiding element within the bellows only an inner Agraffschlauch, so that an outer Agraffschlauch deleted. The flow-guiding element may also have a flange which is connected to the flange of the bellows. The connection provides that the flow-guiding element is on the output side materially connected by means of welding and / or positive fit by means of widening and / or clamps with a flange of the bellows. Also, the invention provides that the current-carrying element is connected to a conically widening piece of pipe, which is fastened with its free end on the flange. As a result, a tearing of a possibly used Agraffschlauchs is avoided. On the input side, the intermediate space between the bellows and the flow-guiding element is open towards the exhaust gas flow.

In this case, the invention provides that in such an outlet-side blocked passage, an overpressure in the sheath flow is generated, whereby a penetration of the urea is prevented from the bellows. It flows a urea-free sheath flow between flow-leading element and bellows. Due to the closed end of a velocity of the exhaust gas stream is greatly reduced, whereby the static pressure increases in the sheath flow. In the core stream in the interior of the flow-guiding element, the flow velocity increases due to the reduced cross section of the flow-guiding element, whereby the static pressure within the core stream decreases. The result is a pressure gradient between the inner and the outer region of the flow-guiding element, whereby a penetration of the urea is prevented to the bellows. Instead, it is provided that, in the case of a passage which is blocked on the output side, an exhaust gas flows in the jacket flow over the wall of the flow-guiding element toward the core flow. In this case, it is preferably provided that flow resistances for increasing the speed of the exhaust gas within the core flow are arranged on the input-side inside of the flow-guiding element.

Furthermore, an intermediate solution with only a small part of the sheath current is conceivable, which flows on the output side. Here, the passage is not completely blocked, but the gap is continuously reduced to the output side.

The decisive advantage of the invention is the separation between urea-free exhaust gas and urea-enriched exhaust gas in the inside. As another conceivable application possibility, the use of the (sheath flow) air gap is provided with only a small gas exchange for the thermal insulation of the exhaust gas flow with chemically identical composition of core and sheath flow. Preferably, it can also be provided that a urea injection is not mounted directly in front of the decoupling element, but further forward in the exhaust system is provided, wherein a current split can be carried out in an exhaust pipe in front of the decoupling element, so that core and sheath current are fed to the decoupling element separately. Decisive in the decoupling element according to the invention is that two gas streams with different composition are present. For this purpose, a suitable feed can be provided according to the invention. Also conceivable is the additional installation of a turbulator or a mixer for better mixing after the injection at the entrance or within the decoupling element.

The invention includes dividing the exhaust gas flow of an internal combustion engine into a catalyst through a flow-guiding element within a decoupling element as a flexible conduit element into a core flow through the flow-guiding element and a bypass flow between the flow-guiding element and a bellows of the decoupling element. The flow guiding element is formed or held so as not to restrict the mobility of the decoupling element, i. itself is designed as a flexible element, such as a winding tube, or stored as a more or less rigid inner tube with at least one end relatively movable to the bellows.

The reducing agent is only injected into the core flow, so that it can not condense in the cooler outer region, namely on the inner wall of the bellows or a lining arranged directly inside it (likewise as a wound hose).

The two partial streams are recombined downstream of the flow-conducting element and upstream of a catalyst, so that the reducing agent in the subsequent catalyst acts on the entire exhaust gas flow. This can be done in that the outlets for sheath flow and core flow at the downstream end face of the flow-guiding part are open and the two partial streams can mix in such a way, or in that the flow-conducting element itself is permeable or porous, such as a winding tube, and Therefore, at least one of the two flows can pass through the jacket of the flow-guiding element in the other partial flow. The invention further includes a conduit part having a decoupling element designed according to the invention and tubes inflated to both end sides thereof, and an exhaust system with at least one catalytic converter arranged downstream of the decoupling element.

Fig. 1

einen Längsschnitt eines Teils einer Abgasanlage mit einem Entkopplungselement, das nicht Teil der Erfindung ist.

Fig. 2

einen Längsschnitt durch ein Entkopplungselement das nicht Teil der Erfindung ist.

Fig. 3

einen Längsschnitt durch eine alternative Ausgestaltung eines erfindungsgemäßen Entkopplungselements; und

Fig. 4

einen Längsschnitt durch ein erfindungsgemäßes Entkopplungselement mit einer alternativen Einspritzungseinrichtung.

Further advantages and features of the invention will become apparent from the claims and from the following description in which an embodiment of the invention with reference to the drawings is explained in detail. Showing:

Fig. 1

a longitudinal section of a portion of an exhaust system with a decoupling element, which is not part of the invention.

Fig. 2

a longitudinal section through a decoupling element which is not part of the invention.

Fig. 3

a longitudinal section through an alternative embodiment of a decoupling element according to the invention; and

Fig. 4

a longitudinal section through an inventive decoupling element with an alternative injection device.

The Fig. 1 shows a longitudinal section through a decoupling element 1 in the composite part of an exhaust system 2. The decoupling element 1 is in this case inserted between an input-side exhaust pipe 3 and an output-side exhaust pipe 4. Downstream of the latter is a catalyst 5 and a further exhaust pipe 6, wherein the catalyst 5 (not shown) within a flared exhaust pipe or a suitable housing is arranged. As catalyst 5, an SCR catalyst may be provided. The components are materially bonded, preferably by welding or positively connected by widening and clamps. The decoupling element 1 is detailed in FIG Fig. 2 shown, which shows a longitudinal section through a decoupling element 1. The decoupling element 1 comprises a ring-corrugated bellows 7, which is positively connected to the rigid exhaust pipe 3 of the exhaust system 2, as by widening and clamps, or cohesively by welding. Inside the bellows 7, an outer Agraffschlauch 8 is arranged, which protects the bellows from the hot exhaust gas stream. Furthermore, coaxially within the outer Agraffschlauchs 8, a flow-guiding element 9 is arranged. In this example, an inner Agraffschlauch is provided as the flow-guiding element 9. There are also other flow-leading elements possible. The inner Agraffschlauch 9 is spirally wound or has a plurality of ring segments, which has a wall 10 form. Such a flow-guiding element may be formed from partially gas-permeable tubular shaped materials or other metallic elements for current conduction. The inner Agraffschlauch 9 is supported by means of supports 11 centrally within the outer Agraffschlauchs 8 and held in this position. There are at least two, preferably four evenly distributed over the circumference supports 11 provided on the input and output sides. The supports 11 do not interfere with a flowing exhaust gas stream 12 (characterized by an arrow pointing to the left in the image). The flow direction of the exhaust gas is given by the arrow direction.

An outer diameter D1 of the inner Agraffschlauchs 9 is smaller than an inner diameter D2 of the bellows 7. The outer Agraffschlauch 8 has an outer diameter corresponding to the inner diameter D2 of the bellows 7. As a result, between the inner Agraffschlauch 9 and bellows 7 and outer Agraffschlauch 8, a gap 13 is formed with a finite radial distance d, in which a part of the exhaust gas can flow. The outer Agraffschlauch 8 has an outer diameter which is equal to or smaller than the inner diameter D2 of the bellows 7, so that the outer Agraffschlauch 8 rests against the inside of the flange of the bellows 7. The width of the intermediate space 13, that is, the distance d between inner Agraffschlauch 9 and bellows 7 corresponds to the distance between inner Agraffschlauch 9 and outer Agraffschlauch 8 minus the wall thickness of the outer Agraffschlauchs 8. With regard to the magnitude of the decoupling element 1 is the wall thickness of the outer Agraffschlauchs 8 with respect to the width of the gap 13 is not relevant. The distance d of the inner Agraffschlauchs 9 to the bellows 7 can also be much narrower be formed, as long as a flow of an exhaust gas flow through the gap 13 is ensured. If the intermediate space 13 is very narrow, that is, in the size range of the wall thickness of the agraff tubes, then an outer agraflate tube 8 can also be omitted.

On the input side of the decoupling element 1, an injection device 14 for injecting urea into the exhaust gas flow is provided centrally in front of the inner injection hose 9. Urea is sprayed conically in an exhaust gas flow (characterized by an injection cone 15) and thus evenly distributed in the inner Agraffschlauch 9. The inner Agraffschlauch 9 is formed longer than the surrounding him bellows 7 and thus protrudes on the input and output side on the bellows 7 out into the adjacent exhaust pipes 3, 4 inside. It is also possible for the inner Agraffschlauch 9 as a flow-guiding element shorter than the bellows 7 form.

The arrangement of the inner Agraffschlauchs 9, the exhaust stream 12 is divided within the decoupling element 1 into two parallel streams. Within the inner Agraffschlauchs 9 urea enriched exhaust gas flows in a core stream 16 (black arrows). By this arrangement, the inner Agraffschlauchs 9 is between this and the bellows 7 - as I said - an annular gap 13 is formed. Through this gap 13 flows parallel to the core stream 16, urea-free exhaust gas in a bypass flow 17 (white arrows). The inner Agraffschlauchs 9 is thus washed around by urea-free exhaust gas, whereby any wall 10 of the inner Agraffschlauchs 9 penetrating urea is washed away by the exhaust gas flowing in the sheath flow 17. The urea injection itself is centered in the core stream 16 within the inner Agraffschlauchs 9 conical, so that a uniform injection is given. The outer Agraffschlauch 8 serves primarily the protection of the bellows 7 before the hot exhaust gas within the bypass flow 17 and the same leadership. A merging of the exhaust gas flows takes place in a rigid part of the exhaust system behind the decoupling element 1. This is in Fig. 1 shown. The urea-rich core stream 16 is highlighted by a black and white puncture. Due to the uniform flow of the exhaust gases in the core and sheath flow turbulence of the exhaust gases on the output side of the decoupling element is avoided. The bellows 7 thus comes in no way in contact with urea-enriched exhaust gas.

In Fig. 3 an alternative embodiment of the decoupling element 1 according to the invention is shown, wherein within the bellows 7 only an inner Agraffschlauch 9 is provided. An external Agraffschlauch 8 can also be omitted. On the output side of the decoupling element 1 of the Agraffschlauch 9 is connected gas-tight to the bellows 7 at the flange 18 preferably by welding and / or positive engagement, wherein the diameter D1 of the inner Agraffschlauchs 9 widens conically in the output side area to the diameter D2 of the bellows 7. On the output side is thus a passage for the exhaust gas locked. On the input side, the intermediate space 13 between the bellows and the inner agrafling hose 9 is open toward the exhaust gas flow 12.

Due to the closed end of the intermediate space 13, the velocity of the exhaust gas within the bypass flow 17 is greatly reduced, whereby the static pressure in the intermediate space 13 increases. Inside the inner Agraffschlauchs 9 takes the flow rate of the exhaust gas in the core stream 16 due to the reduced cross-section, whereby the static pressure within the core stream 13 decreases. As a result, a flow gradient arises between the two exhaust gas streams, as a result of which urea-free exhaust gas flows out of the sheath flow 17 through the Agraff hose 9 to the core stream 16. This is in the Fig. 3 indicated by the arrows 19 (outflowing sheath flow), which show the path of the exhaust gas from the sheath flow 17 through the wall of the inner Agraffschlauchs 9. A penetration of the urea to the bellows 7 is thus also prevented.

This effect can be enhanced by the input side of the inner Agraffschlauchs 9, a flow resistance 20 is arranged. The flow resistance 20 shows in Fig. 3 a quarter-circular cross-section, wherein the rounded side is opposite to the exhaust gas stream 12. The flow resistance 20 may have an annular configuration or be present in a plurality of annular section-shaped pieces. The flowing exhaust gas strikes the flow resistors 20 and is compacted into the inner injection hose 9. The speed of the flowing exhaust gas is thereby increased again.

If in the embodiment of the Fig. 3 instead of a winding tube as a flow-guiding element, a more or less rigid tube is provided, it must be at least axially movably mounted at least at one end within the supports 11 by this example is connected to a surrounding such a tube ring in which the tube is guided , In this way, the mobility of the bellows and thus of the decoupling element is not impaired.

Fig. 4 shows a longitudinal section through an alternative embodiment of the injection device 14. The same parts are identified by the same reference numerals. Before the decoupling element 1, an elongated exhaust pipe 22 is disposed on the input side flange 21. Within the exhaust pipe 22, a pipe section 23 is arranged by means of supports 11 as a flow-guiding element. The parts are dimensioned such that they can be inserted into the input-side end of the decoupling element. For a gas-tight connection, the exhaust pipe 22 is preferably welded to the flange 21 and the pipe piece 23 to the input-side end of the inner Agraffschlauchs 9. The exhaust gas stream 12 is again separated by means of the pipe section 23 into a sheath flow 17 and core flow 16. The injection device 14 is formed laterally outside the exhaust pipe 22 and is arranged at an angle of 45 ° - 90 ° to the central axis of the device, whereby the reducing agent is injected at an angle 45 ° to 90 °. In order to achieve a direct injection into the core flow 16, an opening 24, 25 are respectively formed in the exhaust pipe 22 and the flow-guiding pipe section 23, through which a tube 26 which widens conically to the core stream 16 is pushed. This is gas-tightly connected to the exhaust pipe 22 and the pipe section 23 by welding. Urea is thus, without entering the sheath flow 17, injected directly into the core stream 16.

Above all, the separation between pure exhaust gas and enriched with reducing agent or chemically modified exhaust gas is particularly advantageous. With this decoupling element 1, it is possible by splitting the exhaust gas stream into a core stream 16 with injected urea and a urea-free Sheath flow 17 to keep the additive added to the exhaust gas from the bellows and thus to avoid a deposition of the same completely.

LIST OF REFERENCE NUMBERS

1

decoupling element

2

exhaust system

3

exhaust pipe

4

exhaust pipe

5

catalyst

6

exhaust pipe

7

bellows

8th

outer agraff hose

9

flow guiding element / inner Agraff hose

10

wall

11

Support

12

exhaust gas flow

13

gap

14

injection device

15

Injection cone

16

nuclear power

17

ducted

18

flange

19

outflowing sheath flow

20

flow resistance

21

input side flange

22

extended exhaust pipe

23

pipe section

24

opening

25

opening

D1

Outer diameter inner Agraffschlauch

D2

Inner diameter bellows

d

distance

Claims (24)

1. Decoupling element, in particular for exhaust gas systems, with a corrugated metal bellows (7) and a flow-guiding element (9, 23) which is arranged within the bellows (7) and the outside diameter (D1) of which is smaller than the inside diameter (D2) of the bellows (7), wherein the flow-guiding element (9) separates the interior of the bellows (7) into an inner core flow path for a core flow (16) of the exhaust gas flow and an outer jacket flow path for a jacket flow (17) of the exhaust gas flow, and with an injection device (14) for injecting a reducing agent, such as urea, into the core flow, characterized
   in that the flow-guiding element is designed as an inner strip wound hose (9), and
   in that the flow-guiding element (9) is connected on the output side to a flange (18) of the bellows (7) such that a passage between the bellows and the flow-guiding element (9) is blocked.
2. Decoupling element according to Claim 1, characterized in that the flow-guiding element (9) is arranged at a finite radial distance within the bellows (7).
3. Decoupling element according to Claim 1 or 2, characterized in that an outer strip wound hose (8) for protecting the bellows (7) from the hot exhaust gas flow is arranged within the bellows (7), wherein the outside diameter of said strip wound hose is smaller than or equal to the inside diameter (D2) of the bellows (7).
4. Decoupling element according to one of Claims 1 to 3, characterized in that a cross-sectionally annular intermediate space (13), into which exhaust gas flows in a jacket flow (17), is formed between the flow-guiding element (9) and the bellows (7) and/or the outer strip wound hose (8).
5. Decoupling element according to one of Claims 1 to 4, characterized in that the flow-guiding element (9) is held coaxially within the bellows (2) by means of supports (11).
6. Decoupling element according to Claim 5, characterized in that the flow-guiding element (9) is held on the input side and/or on the output side by in each case at least two supports (11) which are uniformly distributed over the circumference of the flow-guiding element (9).
7. Decoupling element according to one of Claims 1 to 6, characterized in that the length of the flow-guiding element (9) is greater than or equal to the length of the bellows (7), and therefore the flow-guiding element (9) projects beyond the length of the bellows (7).
8. Decoupling element according to one of Claims 1 to 6, characterized in that the length of the flow-guiding element (9) is smaller than the length of the bellows (7).
9. Decoupling element according to Claim 8, characterized in that the flow-guiding element (9) is connected on the output side to a flange (18) of the bellows (7) in an integrally bonded manner, in particular by means of welding, and/or in an interlocking manner by means of expanded portions and/or clips.
10. Decoupling element according to Claim 8, characterized in that the flow-guiding element (9) is connected on the output side to the flange (18) of the bellows (7) via a tubular section in an integrally bonded manner, in particular by means of welding, and/or in an interlocking manner by means of expanded portions and/or clips.
11. Decoupling element according to Claim 1, characterized in that an injection device (14) is arranged on the input side centrally upstream of the flow-guiding element (9).
12. Decoupling element according to Claim 11, characterized in that the injection device (14) is fastened on the input side within the flow-guiding element (9) by means of struts.
13. Decoupling element according to Claim 1, characterized in that the injection device (14) is arranged laterally on an extended exhaust pipe (22) upstream of the flow-guiding element (9), wherein the injection device (14) is formed on the exhaust pipe (22) at an angle of between 45° and 90°.
14. Decoupling element according to one of the preceding claims, characterized in that the decoupling element (1) is connected to at least one rigid exhaust pipe (3, 4) in an interlocking manner by means of expanded portions and/or clips.
15. Decoupling element according to Claim 13, characterized in that the decoupling element (1) is connected to the at least one exhaust pipe (3, 4) in an integrally bonded manner, in particular by means of welding.
16. Decoupling element according to one of the preceding claims, characterized in that the inner strip wound hose (9), as the flow-guiding element, and the outer strip wound hose (8) are coiled spirally or have a plurality of annular segments.
17. Decoupling element according to one of the preceding claims, characterized in that an injection device (14) for injecting a reducing agent into the core flow is arranged on the input side upstream of the flow-guiding element (9).
18. Method for guiding exhaust gas of an internal combustion engine through a corrugated metal bellows (7), wherein exhaust gas flowing in an exhaust gas flow flows through a flow-guiding element (9), which is arranged at a finite radial distance within the bellows (7), in a manner divided into a core flow and a jacket flow, and reducing agent, such as urea, is injected into the core flow by means of an injection device, characterized
    in that the exhaust gas flow is divided into the core flow (16) and the jacket flow (17) by means of a strip wound hose (9), and
    in that, when a passage is blocked on the output side, a positive pressure is produced in the jacket flow (17), thus preventing the urea from penetrating to the bellows (7).
19. Method according to Claim 18, characterized in that a reducing agent is injected into the core flow upstream of the flow-guiding element by an injection device arranged on the input side.
20. Method according to Claim 18 or 19, characterized in that urea-enriched exhaust gas flows in a core flow within the flow-guiding element.
21. Method according to Claim 18, characterized in that urea is injected conically into the core flow by means of the injection device.
22. Method according to Claim 18, characterized in that urea is injected laterally into the core flow at an angle of between 45° - 90° with respect to the centre axis by means of the injection device.
23. Method according to one of Claims 18 to 22, characterized in that urea-free exhaust gas flows freely in a jacket flow in an intermediate space between the flow-guiding element and the bellows and/or the outer strip wound hose, wherein urea penetrating a wall of the inner strip wound hose is flushed away.
24. Method according to Claim 18, characterized in that, when a passage is blocked on the output side, exhaust gas in the jacket flow flows towards the core flow via the wall of the flow-guiding element.

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