DE102006053804B4 - flange - Google Patents

Abstract

An exhaust aftertreatment device for the aftertreatment of exhaust gases in an exhaust system of an internal combustion engine, comprising a device for introducing a reducing agent into an exhaust pipe (22, 24) of the exhaust system, the device comprising a metering module (15) and a direct heat input into the metering module (15) is minimized in which a connection of a flange (10, 28) for receiving the metering module (15) is thermally insulated from a line carrying exhaust gas, characterized in that a pipe socket in a two-shell structure (23) comprises an inner pipe section and an outer pipe section, - a joint ( 28) of the flange (10) is formed on the outer pipe section of the pipe socket in two-shell structure (23), - the inner pipe section and the outer pipe section of the pipe socket due to the two-shell structure (23) by an air gap (25) are thermally insulated from each other and the air gap (25) in the region of the joint (28) below the flange ( 10) to an inner tube (24) of the exhaust pipe (22, 24) is open, wherein the inner tube is the exhaust gas leading line.

Description

State of the art

In the course of the further tightening of exhaust emission limits for internal combustion engines, the chemical exhaust aftertreatment becomes more important. As a promising method, which for example, the reduction of nitrogen oxides NO _{x is used} in oxygen-rich exhaust gases, represents the selective catalytic reduction (SCR) using NH ₃ or NH ₃ -ausspenden reagents. In development, there are currently systems that as Reducing agent Use urea-water solution (HWL) as NH ₃ -separating reagent. As a reducing agent used urea water solution is generally introduced via a metering valve in the exhaust stream. The metering valve is arranged in a metering module, which takes over the connection of hydraulic components as well as the cooling of the unit either by air or by means of a cooling medium. A significant problem of the connection of the dosing to the exhaust system is that the metering valve has a permissible limit temperature of about 150 ° C. In the exhaust system of internal combustion engines, however, maximum temperatures of 700 ° C can be achieved, so that the previously commonly used execution of a connection of the dosing to the exhaust system of the internal combustion engine inevitably to a high heat input into the dosing and thus to temperatures well above 200 ° C at the metering valve leads. This represents a high thermal load of the metering valve and can lead to the destruction of the metering valve in extreme cases and thus make the exhaust gas purification system useless. In previously commonly used Flanschanbindungen that flange which receives the dosing, directly via a cohesive connection, such as a welded joint, connected to the exhaust pipe. This cohesive connection, in addition to the radiant heat of the exhaust pipe, conducts further heat into the metering module. The heat flow entered into the metering module must be removed from the metering module and thus from the metering valve by cooling measures, for example by air or liquid cooling. However, these additional active measures to be taken cooling are associated with a large technical and a large cost.

From the DE 10 2004 056 791 A1 is known an exhaust system with an injection nozzle for injecting fuel, which is arranged via a flange and a thermal insulator on the exhaust line.

The DE 198 56 366 C1 describes a metering device with a double-walled valve receiving body.

Presentation of the invention

According to the invention, it is proposed to form a flange connection of the metering module or the metering valve received therein to the exhaust pipe in such a way that the flange is insulated from the exhaust pipe via an air gap. By such an air gap-insulated flange connection a significant reduction of the heat input is achieved in the metering and thus in the metering valve contained in this. This means that less heat has to dissipate by reducing the heat input into the metering module and the metering module can also be dimensioned smaller with reduced heat input. The inventively proposed solution of the flange connection to the exhaust pipe reduces the heat input into the metering or the metering valve contained in this via the flange due to heat conduction as well as the introduction of radiant heat of the exhaust pipe in the dosing. Furthermore, the heat shields previously used for thermal insulation can be completely eliminated, allowing a more compact design of the entire unit.

The inventively proposed flange connection as an air gap-insulated pipe, comprising an inner and an outer tube, offers the possibility not to fix the flange on the inner tube, which is exposed to the hot exhaust gases, but on the outer tube, which from the peripheral surface of the inner tube by an annular trained air gap is isolated. Between the inner tube and the outer tube, an annular gap can be formed in a width of 2 to 4 mm, so that a direct heat transfer from the inner tube to the flange no longer takes place.

In principle, exhaust gas can be conducted through the resulting air gap between the inner tube and the outer tube. A flow of the exhaust gas through the air gap does not take place, since the outer tube is closed against the atmosphere and from the air gap between the inner and outer tube no exhaust gas reaches the atmosphere. The width of the inner tube of the outer tube insulating air gap is chosen so that form no deposits by urea in the annular gap.

In comparison to previously known flange connections, temperatures of around 100 K are measured at the flange, which significantly reduces the heat input into the dosing module. The peak temperatures at the flange, ie at the point where the metering module together with the metering valve received therein with the Exhaust pipe is mounted, can be lowered from about 420 ° C to about 320 ° C. Due to the insulation of the inner tube by the air gap-insulated design against the outer tube also results in isolation of the Flanschinnenrohres against low outside temperatures, so that at the entry point of the medium at the metering simultaneously higher temperatures compared to the previous version can be achieved, what the education counteracts urea deposits at the injection point and thus is to be emphasized as a further advantageous effect of the proposed solution according to the invention.

An improvement of the heat output can additionally be achieved in that the surface of the outer tube surrounding the inner tube is enlarged, for example, with a number of cooling fins extending substantially in the radial direction and running in the axial direction of the tube; In addition, other design geometries of the cooling fins are possible.

In a further advantageous embodiment variant of the solution proposed according to the invention, the inner tube and the outer tube, which are insulated from one another by the annular air gap, can be designed as a welded construction. A cost-saving variant is to produce an inner flange tube from the inner tube by means of the deep-drawing process. Alternatively, it is also conceivable to weld the inner tube and to press the outer tube pressed by means of two deep-drawn sheet metal halves and to fasten the flange cohesively thereto. This embodiment has some cost advantages over a completely executed weldment.

list of figures

• 1 eine Darstellung einer Eindüsestelle in ein Abgasrohr einer Verbrennungskraftmaschine gemäß des Standes der Technik,
• 2 eine erfindungsgemäß gestaltete Flanschanbindung mit einem Luftspaltisolierten Abgasrohr mit Außenrohr und Innenrohr und
• 3 eine weitere Ausführungsvariante der in 2 dargestellten, erfindungsgemäß ausgebildeten Flanschverbindung mit an einem Außenrohr verlaufenden Kühlrippen.

With reference to the drawing, the invention will be described below in more detail. Show it:

• 1 a representation of a injection point in an exhaust pipe of an internal combustion engine according to the prior art,
• 2 an inventively designed flange with an air gap insulated exhaust pipe with outer tube and inner tube and
• 3 a further embodiment of in 2 illustrated, inventively designed flange with running on an outer tube cooling fins.

variants

The representation according to 1 is a flange connection according to the prior art can be seen.

1 shows an exhaust pipe 14 , which is flowed through by an exhaust gas flow in the direction of flow B. The exhaust stream comes from an in 1 Internal combustion engine, not shown, on the outlet side, the exhaust pipe 14 is arranged. This is symmetrical to its axis 16 built up. At the exhaust pipe 14 is along an example cohesively executed compound 13 , which is designed for example as a welded joint, a pipe socket 12 appropriate. Instead of a cohesive connection 13 can also be a screw with a fine thread or the like may be provided. Both the exhaust pipe 14 as well as the pipe socket 12 are single-walled. The angle of inclination of the pipe socket 12 in relation to the axis 16 of the exhaust pipe 14 is chosen so that a best possible mixing of the exhaust stream, in the flow direction B through the exhaust pipe 14 flows, with a injected within the spray cone A reagent, such as urea, is achieved.

A flange 10 a dosing module 15 , in which a metering valve is received, via which the reagent is introduced in the spray cone A in the exhaust gas stream, for example by means of a welded connection 11 on the pipe socket 12 attached. Alternative to the welded connection 11 can also be used a screw connection. The exhaust gas temperature of the exhaust gas stream flowing in the direction B reaches at this point a temperature of up to 700 ° C. As a result, the exhaust pipe is 14 heated by the flowing in the direction of flow B exhaust stream accordingly. This heating heat is transferred both by way of heat radiation from the exhaust pipe 14 on the dosing module 15 as well as in the way of heat conduction from the exhaust pipe 14 by the example cohesively executed connection 13 to the pipe socket 12 and from this over the welded joint 11 on the flange 10 where the dosing module 15 is included. The flange 10 reaches peak temperatures of up to 420 ° C during operation.

For this reason, considerable additional measures are required to prevent the permissible temperature of 150 ° C for the metering valve, which in Dosiermodul 15 is exceeded. In general, the dosing module contains 15 Devices for cooling by flowing around with air or by flowing around with another cooling medium for cooling for the required Wärmeaustrag from the dosing 15 , The exhaust pipe 14 includes one with reference numerals 17 designated peripheral surface.

2 shows a first embodiment of the inventively proposed flange connection in a two-shell configuration.

2 shows a clam-shell design of the exhaust pipe and the pipe socket. This in the illustration according to 1 integrally formed exhaust pipe 14 comprises in the proposed solution according to the invention as shown in FIG 2 an outer tube 22 and an inner tube 24 which are separated from one another by a circumferential air gap (annular gap) 25 , are separated. Direct exhaust gas (arrow B) is the inner tube 24 while the outer tube 22 with an air gap 25 in an air gap width 27 in the order of 2 to 4 mm, the inner tube 24 completely wrapped. The pipe socket is also in a two-shell structure 23 educated. It is the inner tube of the pipe socket 23 over the welded joint 13 or a screw connection with the exhaust-carrying inner tube 24 while the outer tube of the pipe socket in two-shell structure 23 which the flange 10 carries, with the outer tube 22 is connected, that of the exhaust-carrying inner tube 24 through the air gap 25 is isolated. The air gap 25 in the area of a joint 28 from flange 10 with the outer tube of the pipe socket in two-shell structure 23 is connected, is below the surface of the flange 10 to the exhaust-carrying inner tube 24 open. The air gap 25 in the area of the flange 10 can not be flowed through by hot exhaust gas, since the outer tube 22 is sealed to the outside. The outer tube 22 Can also be used together with the outer tube of the pipe socket in two-shell structure 23 be formed as a metal stamping, for example, composed of two half-shells. The air gap 25 in an air gap 27 is formed, and between the outer tube 22 and the exhaust-carrying inner tube 24 runs, prevents the heat transfer from the inner tube 24 in the radial direction outwards, so that the outer tube 22 and the outer shell of the pipe socket in a two-shell structure 23 stay much cooler. The exhaust gas itself cools on this route by the insulating effect of the air gap-insulated pipe and reaches at higher temperatures subsequent reaction zones. As a result, the following effects can advantageously be achieved with the solution proposed according to the invention:

First, the heat radiation from the two-part exhaust pipe, the inner tube 24 and the outer tube 22 comprising, on the dosing module 15 significantly reduced. Furthermore, the flange 10 with the cooler outer tube 22 connected, which through the exhaust gas flow leading inner tube 24 through the air gap 25 is disconnected. This leads to a considerable decrease in temperature at the flange 10 , Temperature drops of the order of 100 K could be detected experimentally compared to the prior art solutions. Furthermore, the higher achievable exhaust gas temperatures favor the chemical reactions in the subsequent reaction zones and counteract, for example, when metering in an aqueous urea solution within the spray cone A, a urea deposit.

As a consequence of the embodiment of the metering point of an aqueous urea solution proposed according to the invention, to give an example, a significant reduction of the heat emission of the exhaust pipe and associated therewith, a significant reduction of the heat input into the dosing 15 achieved with metering valve. This can be omitted in particular costly Wärmeabschirmbleche in the environment of the exhaust pipe; Furthermore, extensive Wärmeableitmaßnahmen, given by Ableitbleche, heatsink, liquid cooling and the like, to dosing 15 and metering valve no longer required. The unit dosing module 15 thus builds considerably more compact compared to previous solutions of the prior art, which contained a complex Kühlungsmimik.

For the sake of completeness, it should be mentioned that the flow cross-section which the exhaust gas originating from the internal combustion engine is in the inner tube 24 flows through, with reference numerals 26 is identified. The diameter of the pipe socket in a two-shell structure 23 - as in 2 shown - is chosen so that the spray cone A is formed so that an optimal mixing of the exhaust gas mass flow can be achieved with the injected at the injection point reagent.

3 Finally, a design variant of the in 2 illustrated solution proposed according to the invention with a likewise double-shell exhaust pipe, on whose outer peripheral surface a number of cooling fins is formed.

The representation according to 3 is removable, that in this embodiment, the inner tube 24 Exhaust gas flows through in the direction of flow B. The flow cross section of the inner tube 24 is in 3 by reference numerals 26 indicated. The inner tube 24 is from the outer tube 22 through the annular air gap 25 separated. Also in this embodiment is the air gap width 27 between the outer circumference of the inner tube 24 and the inner circumference of the outer tube 22 on the order of, for example, between 2 to 4 mm. Depending on the installation situation can also be a larger or smaller air gap width 27 to get voted.

At the exhaust pipe, which is the exhaust pipe leading inner tube 24 and this surrounding outer tube 22 includes, the pipe socket is in a two-shell structure 23 attached to the outer tube at the joint 28 the flange 10 is connected cohesively, so preferably by way of a welded joint. The flange 10 in turn carries the dosing 15 comprising the metering valve.

Unlike in 2 illustrated embodiment run on the outer circumference of the outer tube 22 a number of cooling fins 31 , The cooling fin surface of the cooling fins 31 on the outer circumference of the outer tube 22 are by reference numbers 32 denotes and extend in this embodiment in the axial direction 33 , as in 3 indicated; In individual cases, this depends on the installation situation.

From the illustration according to 3 also shows that a division 34 of cooling fins 31 can be done on the circumference of the outer tube, wherein the individual, in the axial direction 33 extending cooling fins 31 For example, at an angle of 45 ° to each other can be arranged. Of course, any other angular pitch with respect to the arrangement of the cooling fins 31 on the outer circumference 17 of the outer tube 22 conceivable. With reference number 16 is in 3 the axis of the double-shell exhaust pipe, the exhaust pipe leading inner tube 24 and that of this over the air gap 25 separate outer tube 22 full.

By the additional application of the axial direction 33 extending cooling fins 31 on the outer tube 22 can the temperature of the outer tube 22 and thus the temperature of the attached to this flange 10 for receiving the dosing module 15 be lowered further. With the in 3 The measure shown can be the safety margin against the achievement of critical temperatures on dosing 15 , in particular in relation to the metering valve accommodated in this further increase.

Because the inner tube 24 through the in the 2 and 3 shown air gap insulated design is insulated against low outside temperatures, higher temperatures are achieved at the injection point, for example, for an aqueous urea solution within the spray cone A in the exhaust stream compared to previous versions, which counteracts the formation of urea deposits.

Claims (8)

An exhaust aftertreatment device for the aftertreatment of exhaust gases in an exhaust system of an internal combustion engine, comprising a device for introducing a reducing agent into an exhaust pipe (22, 24) of the exhaust system, the device comprising a metering module (15) and a direct heat input into the metering module (15) is minimized in which a connection of a flange (10, 28) for receiving the dosing module (15) is thermally insulated from a line carrying exhaust gas, characterized in that - a pipe socket in a two-shell structure (23) comprises an inner pipe section and an outer pipe section, - a joint ( 28) of the flange (10) is formed on the outer pipe section of the pipe socket in two-shell structure (23), - the inner pipe section and the outer pipe section of the pipe socket as a result of the two-shell structure (23) by an air gap (25) are thermally insulated from each other and - the air gap (25) in the area of the joint (28) below the Flansc hes (10) to an inner tube (24) of the exhaust pipe (22, 24) is open, wherein the inner tube is the exhaust gas leading line. Exhaust after-treatment device according to Claim 1 , characterized in that the exhaust pipe (22, 24) in the region of the metering module (15) is double-shelled. Exhaust after-treatment device according to Claim 1 , characterized in that the inner tube (24) is thermally insulated from an outer tube (22) of the exhaust pipe by an air gap (25). Exhaust after-treatment device according to Claim 1 , characterized in that the thermally insulating air gap (25) has an air gap width (27) in the order of a few millimeters. Exhaust after-treatment device according to Claim 3 , characterized in that at least one in the axial direction (33) extending cooling rib (31) extends on a peripheral surface (17) of the outer tube (22). Exhaust after-treatment device according to Claim 3 or 5 , characterized in that the outer tube (22) comprises two halves produced by means of the deep-drawing process, which are pressed together and to which the pipe socket in two-shell structure (23) is integrally formed. Exhaust after-treatment device according to one or more of the preceding claims, characterized in that in the exhaust system, a catalyst for reducing NOx components of the internal combustion engine is arranged. Exhaust after-treatment device according to Claim 7 , characterized in that the device is arranged for introducing the reducing agent into the catalyst.

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