EP3421745A1 - Construction unit for an exhaust system - Google Patents

Abstract

The invention relates to an assembly for an exhaust system for guiding an exhaust gas flow, in particular an internal combustion engine, having a base body which at least partially comprises a first material having a first thermal conductivity, and with a coating which a second material with a relative to the first thermal conductivity lower second heat conductivity and which covers the base body, in particular in a region of the first material, at least partially on a side facing the exhaust gas stream.

Description

The present invention relates to a structural unit for an exhaust system for guiding an exhaust gas stream, in particular an internal combustion engine.

Such a structural unit is used, for example, in systems for reducing the nitrogen oxide emission of an internal combustion engine, in particular a diesel engine, by means of selective catalytic reduction (SCR). In general, ammonia is used as the reducing agent, which is obtained from a injected into the exhaust stream urea-water solution.

For a particularly efficient, stoichiometric reaction between the ammonia generated from the urea-water solution and the nitrogen oxides of the exhaust gas, it is favorable if the injected urea-water solution is evaporated and distributed as completely as possible before reaching the catalyst. In addition to the pure droplet evaporation in a fluidic phase, the evaporation of the urea-water droplets at a (hot in operation) surface of the assembly is becoming increasingly important, which is due to the fact that due to an ever more compact design of modern exhaust systems less and less free Distance for the evaporation of droplets is available.

One way to increase the rate of evaporation of the droplets of urea-water solution on a surface of the assembly, is to make the assembly of a material with high thermal conductivity, so that by a sufficiently high heat transfer always sufficient heat for evaporation the urea-water solution is available at the surface of the component. However, it proves to be disadvantageous that the typically used materials with high thermal conductivity, such as copper or a low alloy steel, easily corrode under the conditions prevailing in the exhaust stream conditions, whereby the life of the assembly is significantly reduced.

An object of the invention is to provide a more efficient and at the same time more resistant unit for an exhaust system of the type mentioned.

To solve the problem, a structural unit with the features of claim 1 is provided. The structural unit according to the invention for an exhaust gas system for guiding an exhaust gas stream comprises a main body which at least partially has a first material with a first thermal conductivity, and a coating which has a second material with a second thermal conductivity which is lower relative to the first thermal conductivity and which comprises the main body, in particular in a region of the first material, at least partially covered on a side facing the exhaust gas stream.

The invention is based on the general idea to increase the evaporation rate of a urea-water solution by a structural unit with a base body of at least partially a first material with increased thermal conductivity and at the same time the main body of the assembly by a coating with a second material, which lower thermal conductivity than the first material to protect against corrosion. In other words, it is achieved by the increased thermal conductivity of the first material that the amount of heat energy necessary for the evaporation optimally reaches the points of the structural unit at which the urea-water solution is to evaporate. By the coating of a reaction material in comparison to the first material second material corrosion of the main body of the assembly is effectively prevented.

Such a structural unit according to the invention offers the advantages of an improved efficiency of the selective catalytic reaction and an increased service life of the structural unit.

As a coating is here generally a coating with a layer to understand, which may be both a thin layer as well as a layer with layer thicknesses, as are customary for films or sheets. The coating may have a uniform or locally varying layer thickness.

Advantageous embodiments of the invention are described in the dependent claims, the description and the drawings.

In order to achieve a sufficiently high evaporation rate of the urea-water solution, the thermal conductivity of the first material is at least twice as high, preferably at least four times as high and particularly preferably at least ten times as high as the thermal conductivity of the second material. In particular, the first material may have a thermal conductivity of at least 80 W / (m · K), preferably of at least 150 W / (m · K), and more preferably of at least 400 W / (m · K).

Typically, the thermal conductivity of metals such as aluminum, copper, silver or zinc is particularly high, so it is advantageous if the first material consists of at least one of the aforementioned metals. In this context, consisting of metal means that the first material consists of a non-alloyed metal which may contain at most unavoidable impurities.

Alternatively, the first material may be an alloy comprising at least one of the aforementioned metals. The alloy is preferably one A copper alloy, such as a substantially zinc-containing copper alloy (brass), a substantially tin-containing copper alloy (bronze) or a copper alloy comprising tin, zinc and optionally lead (gunmetal). However, iron alloys can also be considered as the first material. For example, the first material may be a low alloy steel defined by the mass fraction of one of its alloying elements being less than 5%.

Surprisingly, it has been found that the second material has a particularly high resistance to the gases occurring in the exhaust stream and the urea-water solution or ammonia, if the second material is nickel, a nickel-containing alloy or a stainless steel. If the second material consists only of nickel, this is unalloyed nickel, which may contain at most unavoidable impurities. Instead of a stainless steel, another non-rusting or corrosion-resistant steel alloy can be used, in particular, which is characterized by a minimum content of 10.5% chromium. In principle, however, other materials used for corrosion protection, such as chromium or a corrosion protection varnish, may also be suitable as the second material, whereby due to the high temperatures prevailing in the exhaust gas stream, particular importance should be attached to a high heat resistance and / or a high melting temperature of the material.

Preferably, the base body is at least partially, in particular completely, formed as a sheet metal component with two opposing surfaces, wherein at least one of the surfaces, in particular the surface facing the exhaust stream, at least in sections, in particular substantially completely, is covered by the coating.

A particularly high protection against corrosion of the base body can be achieved if the base body is not only coated on one side, but if the coating substantially the two opposite surfaces at least partially, in particular completely covered. In this case, a boundary edge delimiting the sheet metal component can be exposed, i. have no coating. This may be the case, in particular, if the base body is a sheet metal component coated with the coating, which has been produced for example by means of a stamping method or a laser cutting process.

An even greater protection against corrosion of the body results when not only the surface or surfaces of the body are covered with the coating, but also at least partially the boundary edge of the configured as a sheet metal body. In other words, the coating extends at least in sections over a surface of the base body as well as at least in sections over its boundary edge. In this case, the coating covering the boundary edge can be produced in one piece from the coating covering the surface (s). Additionally or alternatively, the coating covering the boundary edge may be formed separately from the coating covering the surface at least in sections. In particular, the coating may comprise the body, i. also its boundary edge (s), completely surrounded. As a boundary edge is here to understand the narrow side of the sheet metal component.

The coating is preferably applied to the base body by means of at least one of the following methods: electrodeposition, vacuum-based coating method, plating, lacquer coating. Vacuum-based coating methods include, for example, chemical vapor deposition methods, in particular plasma assisted chemical vapor deposition, but also physical vapor deposition methods, such as vapor deposition or physical sputtering, which are also known as Sputtering method is known. If a film or a metal sheet forms the coating of the main body, then the coating can be applied to the basic body by means of plating, in particular roll cladding, and / or by means of a composite solder. As a composite solder, for example, a copper, nickel, or Eisenbasislot can be used. The paint coating can be done for example by dip coating, brushing, spraying or any other paint coating process. It is understood that the surface or the surfaces and / or the boundary edge or the boundary edges of the base body can be coated by the same method or else with different methods.

In order to ensure the highest possible stability of the adhesion of the coating on the base body as well as a good heat transfer from the base body to the coating, it is advantageous if the coating is attached to the basic body in a positive and / or non-positive and / or cohesive manner.

In principle, the term "structural unit" is to be understood broadly in the present context. An assembly for an exhaust system may be any component or component of the exhaust system, including a portion of the multiple component exhaust system. A pipe or pipe section or a functional unit (for example a silencer or an exhaust gas purification device) or a component thereof is likewise a structural unit in the sense of the present invention. Preferably, the assembly is used for vaporizing and distributing a fluid, in particular a urea-water solution, in the exhaust gas flow of the internal combustion engine and may in particular be a static mixer

Some of the materials that may be used for the body or coating are difficult or impossible to weld. In these cases, it is advantageous, a positive or non-positive connection between components of the assembly and / or between the assembly and other Bautei len of the exhaust system to choose, such as a screw connection, riveting, folding or crimping. A combination of different types of connection is conceivable.

Fig. 1

eine Schnitt durch eine erfindungsgemäße Baueinheit gemäß einer ersten Ausführungsform;

Fig. 2

eine Schnitt durch eine erfindungsgemäße Baueinheit gemäß einer zweiten Ausführungsform;

Fig. 3

eine Schnitt durch eine erfindungsgemäße Baueinheit gemäß einer dritten Ausführungsform;

Fig. 4

eine Schnitt durch eine erfindungsgemäße Baueinheit gemäß einer vierten Ausführungsform; und

Fig. 5

eine Schnitt durch eine erfindungsgemäße Baueinheit gemäß einer fünften Ausführungsform.

The invention will now be described purely by way of example with reference to possible embodiments with reference to the accompanying drawings. Show it:

Fig. 1

a section through an assembly according to the invention according to a first embodiment;

Fig. 2

a section through an assembly according to the invention according to a second embodiment;

Fig. 3

a section through an assembly according to the invention according to a third embodiment;

Fig. 4

a section through an assembly according to the invention according to a fourth embodiment; and

Fig. 5

a section through an assembly according to the invention according to a fifth embodiment.

The Fig. 1 to 5 each show sections through different embodiments of a structural unit for a not shown exhaust system for guiding an exhaust gas flow of an internal combustion engine. Specifically, the in Fig. 1 to 5 represented cross-sectional views in each case about a portion of a static mixer (unit), which for evaporating and distributing a fluid, in particular a urea-water solution, in the exhaust gas stream of the internal combustion engine serves. In principle, however, the concept according to the invention can also be used with other components of an exhaust system.

The assembly comprises a main body 10, which is formed in the illustrated embodiments as a sheet metal component and which at least partially comprises a first material having a first thermal conductivity. The sheet metal component has two opposite surfaces 12 and is bounded by a peripheral boundary edge 14, which forms the narrow side of the base body 10.

The main body 10 is further covered with a coating 16 on at least one side facing the exhaust gas stream. Specifically, the base body 10 is covered in the illustrated embodiments at least on the two opposite surfaces 12 with the coating 16. The coating 16 serves to protect the main body 10 against corrosion and comprises a second material having a second thermal conductivity, which is lower in comparison to the first thermal conductivity of the first material. The second thermal conductivity of the second material may be at least half less, preferably four times and more preferably ten times less than the first thermal conductivity of the first material, the first material having a thermal conductivity of at least 80 W / (m · K). , preferably of at least 150 W / (m · K), and more preferably of at least 400 W / (m · K).

The first material may for example consist of at least one of the following metals aluminum, copper, silver or zinc or be an alloy comprising at least one of these metals. On the other hand, the second material may be, for example, nickel, a nickel-containing alloy, or a stainless steel.

When coating the base body 10 with the coating 16, for example, at least one of the following methods may be used: galvanic deposition, vacuum-based coating, plating, paint coating, wherein for better heat transfer from the body 10 to the coating 16 and improved adhesion properties of the coating 16 on the base 10, the coating 16 positively and / or non-positively and / or materially bonded to the base body 10th is applied.

In the in Fig. 1 to 5 In the illustrated embodiments, the coating 16 covering the surfaces 12 is applied to the surfaces 12 by roll-laminating a foil or sheet. However, it is also conceivable that the coating 16 of at least one of the surfaces 12 is a thin film deposited by means of a vacuum-based coating method.

According to a in Fig. 1 The basic body 10 is covered with a coating 16 only on two opposite surfaces 12 of the main body 10, so that the boundary edges 14 of the main body 10 are uncovered or uncovered. It is understood that only one of the two surfaces 12 can be covered with the coating 16.

In order to achieve even better protection of the base body 10 against corrosion, not only the two opposite surfaces 12 of the main body 10 may be covered with a coating 16, but also the respective boundary edges 14, as shown in the in FIG Fig. 2 to 5 shown embodiments. In other words, the main body 10 is completely covered with the coating 16. It is understood, however, that at least one of the boundary edges 14 of the main body 10 may be uncoated.

According to a second embodiment of the structural unit ( Fig. 2 ), the base body 10 is coated on both surfaces 12 such that the coatings 16 project beyond the boundary edges 14. By bending or folding the projecting portions of one of the two coatings 16, here the upper coating 16, the bent portions of the upper coating 16 with the protruding portions of the other coating 16, here the lower coating 16, come to rest, whereby the boundary edges 14 also covered by the coating 16 or are protected.

As based on Fig. 2 can be seen, the lower coating 16 is less over the boundary edges 14, as the upper coating 16, so that the bent portions of the upper coating 16 with the protruding portions of the lower coating 16 are substantially flush, but not necessarily so must be provided.

In the Figure 3 illustrated third embodiment of the assembly differs from the second embodiment of the assembly in that the coatings 16 of the lower and upper surface 12 so far beyond the boundary edges 14 of the body 10 that each projecting portion is longer and to cover the boundary edge 14th serves and the other protruding portion is shorter and serves to support the bent, longer section.

According to a in Fig. 4 4, the coatings 16 of the upper and lower surfaces 12 are projected so far that the protruding portions of the coatings 16 form a common fold 18 by compression, which protects the boundary edges 14 of the body 10 from corrosion.

However, the coating 16 on the boundary edges 14 of the main body 10 can not only be produced in one piece from the coatings 12 covering the surfaces 12 ( Fig. 2 to 4 ), but also separately from the surfaces 12 covering coatings 16 may be formed. In particular, the coating can 16 of the boundary edges 14 may be applied to the boundary edges 14 of the body 10 by another method. For example, in the in Fig. 5 5, the surface 12 of the base body 10 is covered by means of a roll-coated coating 16, whereas the coating 16 of the boundary edges 14 comprises corrosion protection by means of classical corrosion inhibitors, for example lacquer-based or by nickel plating, by spraying, brushing, vapor deposition or the like can be applied.

LIST OF REFERENCE NUMBERS

10

body

12

surface

14

boundary edge

16

coating

18

fold

Claims (11)

Assembly for an exhaust system for guiding an exhaust gas stream, in particular an internal combustion engine, with a base body (10) which at least partially comprises a first material having a first thermal conductivity, and with a coating (16) which a second material with a relative to the first Thermal conductivity lower second thermal conductivity comprises and which covers the base body (10), in particular in a region of the first material, at least partially on a side facing the exhaust gas stream. Assembly according to claim 1,
characterized in that
the thermal conductivity of the first material is at least twice as high, preferably at least four times as high and particularly preferably at least ten times as high as the thermal conductivity of the second material. Assembly according to claim 1 or 2,
characterized in that
the first material has a thermal conductivity of at least 80 W / (m · K), preferably of at least 150 W / (m · K), and more preferably of at least 400 W / (m · K). Assembly according to at least one of the preceding claims,
characterized in that
the first material consists of at least one of the following metals aluminum, copper, silver or zinc or is an alloy comprising at least one of the above metals. Assembly according to at least one of the preceding claims,
characterized in that
the second material is nickel, a nickel-containing alloy, or a stainless steel. Assembly according to at least one of the preceding claims,
characterized in that
the base body (10) is formed at least in sections, in particular completely, as a sheet-metal component with two opposing surfaces (12), wherein at least one of the surfaces (12) is covered at least in sections, in particular substantially completely, by the coating (16). Assembly according to claim 6,
characterized in that
the coating (16) essentially covers the two opposite surfaces (12) at least in sections, in particular completely. Assembly according to claim 6 or 7,
characterized in that
the coating (16) further at least partially covers a boundary edge (14) of the sheet-metal component and the coating (16) covering the boundary edge (14) integrally from the surface (12) covering Coating (16) emerges and / or the boundary edge (14) covering the coating (16) to the surface (12) covering the coating (16) is at least partially formed separately. Assembly according to at least one of the preceding claims,
characterized in that
the coating (16) is applied to the base body (10) by means of at least one of the following methods: electrodeposition, vacuum-based coating method, plating, lacquer coating. Assembly according to at least one of the preceding claims,
characterized in that
the coating (16) is positively and / or positively and / or materially attached to the base body (10). Assembly according to at least one of the preceding claims,
characterized in that
the assembly for vaporizing and distributing a fluid, in particular a urea-water solution, is used in the exhaust stream of an internal combustion engine.

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