Mixing arrangement for an exhaust system of an internal combustion engine

Abstract

Mixing arrangement (10) for an exhaust system (12) of an internal combustion engine for mixing exhaust gas emitted by the internal combustion engine with a reactant, comprising: - a case (14), - a component carried in the housing (14), extending in the direction of an outer tube longitudinal axis (L) A ) elongated mixing section outer pipe (20), wherein the mixing section outer pipe (20) is open in an upstream end region (24) to an exhaust gas supply volume (26) and in a downstream end region (30) to an exhaust gas discharge volume (32), - a mixing section insert (38), wherein the mixing section insert (38) comprises an insert carrier (40) to be fixed to the housing (14), a support mounted on the insert carrier (40) in the direction of an inner tube longitudinal axis (L) I ) elongated mixing section inner tube (50) and a heating arrangement (72) with a heating area (74) arranged on an outside of the mixing section inner tube (50).

Description

[0001] The present invention relates to a mixing arrangement for an exhaust system of an internal combustion engine.

[0002] By means of such a mixing arrangement, the exhaust gas emitted by an internal combustion engine is mixed with a reactant, for example a urea / water solution, in order to reduce the pollutant content, for example the nitrogen oxide content, in the exhaust gas, for example by means of selective catalytic reduction.

[0003] In a mixing arrangement known from DE 10 2017 124 276 A1, an outer mixing section pipe, elongated in the direction of an outer pipe's longitudinal axis, is open in its upstream end region to receive exhaust gas from an exhaust gas supply volume, and an SCR catalyst is arranged in a downstream end region of the outer mixing section pipe. An inner mixing section pipe, elongated in the direction of an inner pipe's longitudinal axis, is arranged within the outer mixing section pipe and includes a heating element on its outer surface. A reagent can be injected into the inner mixing section pipe through the upstream end region of the outer mixing section pipe via a reagent delivery unit.

[0004] From KR 10 2 338 746 B1, a mixing arrangement with two mixing pipes arranged successively in the direction of exhaust gas flow is known. A downstream end section of the upstream mixing pipe is inserted into an upstream end section of the downstream mixing pipe. A projection for receiving a reaction agent discharge unit is provided on the upstream mixing pipe.

[0005] RU 2 612 306 C1 discloses a mixing arrangement in which an inner mixing section pipe, elongated in the direction of an inner pipe's longitudinal axis, is arranged in a mixing section outer pipe which is elongated in the direction of an outer pipe's longitudinal axis. An upstream end region of the mixing section outer pipe is open to receive exhaust gas, which flows through the mixing section inner pipe and a volume formed between it and the mixing section outer pipe. A reactant can be introduced into the exhaust gas flowing in the mixing section inner pipe via an injection nozzle of a reactant delivery unit positioned in the mixing section inner pipe.

[0006] The object of the present invention is to provide a mixing arrangement for an exhaust system of an internal combustion engine, by means of which a reliable mixing of exhaust gas and reaction agent is ensured.

[0007] According to the invention, this problem is solved by a mixing arrangement for an exhaust system of an internal combustion engine for mixing exhaust gas emitted by the internal combustion engine with a reactant, comprising: - a case, - a mixing section outer pipe carried in the housing, elongated in the direction of an outer pipe longitudinal axis, wherein the mixing section outer pipe is open to an exhaust gas supply volume in an upstream end region and to an exhaust gas discharge volume in a downstream end region, - a mixing section insert, wherein the mixing section insert comprises an insert carrier to be fixed to the housing, a mixing section inner tube elongated in the direction of an inner tube longitudinal axis and a heating arrangement with a heating area arranged on an outside of the mixing section inner tube.

[0008] By integrating the heating element with the inner tube of the mixing section, the evaporation of the reagent, which is generally injected into the exhaust gas in liquid form or as a spray mist, is supported, and the risk of reagent deposits forming on the surface areas of the mixing element is significantly reduced. Since the inner tube of the mixing section, the heating element, and the insert carrier are combined into a modular unit that can be mounted on or removed from the housing as a pre-assembled assembly, maintenance work can be carried out easily, or, if necessary, a malfunctioning or partially functional mixing section insert can be replaced with a new one, thus ensuring reliable operation of the mixing section even over a long service life.

[0009] In order to enable the mixing section outer pipe to interact with the mixing section inner pipe when fixing the mixing section insert to the housing, it is proposed that an insert receiving opening be provided in the housing on a housing wall opposite the upstream end region of the mixing section outer pipe in the direction of the outer pipe longitudinal axis, wherein, when the insert carrier is fixed to the housing, the insert carrier is arranged to cover the insert receiving opening and the mixing section inner pipe is positioned engaging in the mixing section outer pipe.

[0010] In order to achieve a compact design on the one hand and to operate the heating arrangement efficiently on the other, it may be provided that, with the insert carrier fixed to the housing, the mixing section outer pipe and the mixing section inner pipe are arranged essentially coaxially or with essentially parallel longitudinal axes to each other, and / or that, with the insert carrier fixed to the housing, the heating area is arranged at a distance from an inner side of the mixing section outer pipe.

[0011] To ensure a defined positioning of the mixing section inner pipe within the mixing section outer pipe, it is proposed that a support arrangement be provided on the mixing section outer pipe to support the mixing section inner pipe relative to the mixing section outer pipe.

[0012] For example, the support structure can be fixed to the inside of the mixing section's outer pipe, and / or the outer pipe's longitudinal axis can be formed in a ring-like manner, and / or it can be constructed of wire. This ensures a flow of exhaust gas between the mixing section's outer and inner pipes, and thus efficient heat dissipation from the heating element. Overheating of the heating area can therefore be reliably prevented.

[0013] For efficient mixing of exhaust gas and reactant, the mixing section insert can include a mixer between the insert carrier and the inner pipe of the mixing section.

[0014] In order to bring the exhaust gas emitted by an internal combustion engine into interaction with a reactant, the mixer can comprise a mixing body that expands radially in the direction of the inner tube longitudinal axis in the direction from the insert carrier to the mixing section inner tube and defines a mixing volume, with a plurality of exhaust gas inlet openings.

[0015] To provide the mixing section insert with its various associated components as a pre-assembled unit, it is proposed that the mixer body connects to the insert carrier at an upstream end and to an upstream end of the mixing section inner tube at a downstream end. Specifically, the mixer body can be fixed to the insert carrier at its upstream end, for example, by a material connection such as soldering or welding, and to the upstream end of the mixing section inner tube at its downstream end, for example, by a material connection such as soldering or welding.

[0016] For the purpose of dispensing reagent into the mixing section, the deployment carrier can be designed to accommodate a reagent dispensing unit.

[0017] To achieve a stable connection of the mixing section insert to the housing, a housing mounting assembly can be provided on the housing, and an insert carrier mounting assembly can be provided on the insert carrier, which can be detachably connected to the housing mounting assembly by means of a plurality of fastening elements in order to fix the insert carrier to the housing.

[0018] The stable arrangement can be supported by the housing mounting assembly being designed to surround the insert receiving opening in a ring-like manner. In particular, the housing mounting assembly can include a mounting ring fixed to the housing and surrounding the insert receiving opening.

[0019] In order to enable the fastening elements to interact with the two mounting formations, the housing mounting formation and / or the insert carrier mounting formation can include a plurality of fastening element engagement openings.

[0020] For efficient heat transfer to the mixing section inner pipe, it is proposed that the heating area be arranged on the outside of the mixing section inner pipe with a winding path.

[0021] For this purpose, the heating area can, for example, have a meandering shape, at least in some sections. Alternatively or additionally, the heating area can have a helical shape surrounding the longitudinal axis of the inner pipe, at least in some sections.

[0022] In order to integrate the heating arrangement stably into the mixing section insert, it is proposed that the heating area on the outside of the mixing section inner tube is preferably fixed by material connection, for example by welding or soldering.

[0023] The heating arrangement can, at least in the heating area, comprise a heating conductor with at least one electrically insulated heating wire arranged in a sheath, the sheath being fixed to the outside of the inner pipe of the mixing section. In such a heating area, designed as a so-called sheath heater, the sheath is generally made of a metal material, which allows for particularly simple attachment to the inner pipe of the mixing section by means of a material connection.

[0024] For connection to a voltage source, the heating arrangement can have a connection section that penetrates the insert carrier.

[0025] For a stable integration of the mixing section outer pipe into the housing, it can be provided that the mixing section outer pipe is fixed in its upstream end region by a wall on the housing that limits the exhaust gas supply volume, for example by material connection, such as welding or brazing, and / or that the mixing section outer pipe is fixed in its downstream end region by a wall on the housing that limits the exhaust gas discharge volume, for example by material connection, such as welding or brazing.

[0026] The invention further relates to an exhaust system for an internal combustion engine with a mixing arrangement constructed according to the invention.

[0027] The present invention is described below with reference to the accompanying documents. Fig.Figure 1 describes in detail. This figure shows a schematic representation of a longitudinal section of a mixing arrangement 10 for an exhaust system of an internal combustion engine in a vehicle, generally designated by 12. The mixing arrangement 10 comprises a housing 14, for example, constructed from several parts, in which a mixing section outer pipe 20 of a mixing section, generally designated by 22, is supported by means of two walls 16, 18. The mixing section outer pipe 20 is supported by an upstream end region 24 on the wall 16, which delimits an exhaust gas supply volume 26, such that an upstream opening 28 of the mixing section outer pipe to the exhaust gas supply volume 26 is open. In a downstream end region 30, the mixing section outer pipe 20 is supported on the wall 18 which limits an exhaust gas discharge volume 32 in such a way that an opening 34 of the mixing section outer pipe 20 formed at the downstream end region 30 is open to the exhaust gas discharge volume 32.The direction of an outer tube longitudinal axis L. A The elongated, for example essentially cylindrical, outer pipe of the mixing section can be firmly connected to the two walls 16, 18, for example by material joining, such as welding or soldering, and thus firmly integrated into the housing 14.

[0028] A wall region of the housing 14 opposite the upstream end region 24 or the opening 28 formed there of the mixing section outer pipe 20 is formed by an insert receiving opening 36. A mixing section insert 38 comprises a plate-like insert carrier 40, which can be fixed to the housing 14 such that it completely covers the insert receiving opening 36. For example, the insert receiving opening 36 and the insert carrier 40 can have a rounded, for example circular, outer circumferential contour.

[0029] To secure the insert carrier 40 to the housing 14, a housing mounting assembly 42 can be provided on the housing 14, for example, surrounding the insert receiving opening in a ring-like manner. For example, the housing mounting assembly 42 can comprise a mounting ring 44 that is fixed to the housing 14 around the insert receiving opening.

[0030] In association with the housing mounting assembly 42, an insert carrier mounting assembly 46 is provided on the insert carrier 40. This can, for example, encompass a radially outer circumferential region or edge region of the plate-like insert carrier 40.

[0031] To secure the insert carrier to the housing 14, a plurality of bolt-like fastening elements 48, indicated in principle, can be used. For example, the insert carrier mounting assembly 46 can comprise a plurality of fastening element engagement openings through which the fastening elements, designed, for example, as screw bolts, can be screwed into fastening element engagement openings designed as internal thread openings of the housing mounting assembly 42 or the mounting ring 44. In an alternative embodiment, bolt-like fastening elements projecting outwards and arranged successively in a ring-like formation can be permanently mounted on the housing mounting assembly 42, over which the insert carrier with its fastening element engagement openings, also arranged successively in a ring-like formation, can be slid.Subsequently, nuts can be screwed onto the fastening elements to secure the insert carrier 40 to the housing 14. To achieve a gas-tight seal between the insert carrier 40 and the housing 14 or the housing mounting assembly 42 provided thereon, a ring-shaped sealing element or the like can be provided. The interaction of the housing mounting assembly 42 with the insert carrier mounting assembly 46 enables a detachable connection of the mixing section insert 38 to the housing 14.

[0032] The mixing section insert 38 further comprises a mixing section inner pipe 50. This can be supported directly on the insert carrier 40 or via a mixer generally designated 52. For this purpose, an upstream end 54 of a mixer body 56, for example, a frustoconical shape, can be fixed to the insert carrier, for example, by material connection such as welding or brazing. A downstream end 58 of the mixer body 56 can be attached to an upstream end 60 of the inner pipe, which extends in the direction of a longitudinal axis L. I The elongated, for example essentially cylindrical, inner pipe 50 of the mixing section can be fixed in place by welding or brazing, i.e., by material bonding. Thus, a solid connection between the insert carrier 40, the mixer 52, and the inner pipe 50 of the mixing section is achieved, with this connection providing a pre-assembled unit.

[0033] A reaction agent delivery unit 62, generally referred to as an injector, is mounted on the insert carrier 40 via an interface 64 and is positioned such that it delivers a liquid reaction agent in the form of a spray cone into a mixing volume 66 enclosed by the mixer body 56. Exhaust gas supplied via the exhaust gas supply volume 26 can flow into the mixing volume 66 through a plurality of openings 68, generating a swirl flow, and can enter the inner pipe 50 of the mixing section together with the reaction agent delivered by the reaction agent delivery unit 62. The exhaust gas flows along the inner pipe 50 of the mixing section together with the reaction agent and mixes with it.At a downstream end 70 of the mixing section inner pipe 50, the mixture of exhaust gas and reactant exits, for example, via the downstream end region 30 of the mixing section outer pipe 20 towards the exhaust gas discharge volume 32 and can flow from there, for example, to one or more SCR catalyst units. A urea / water mixture can be used as the reactant to achieve the desired selective catalytic reduction there.

[0034] The mixing section insert 38 further comprises a heating arrangement generally designated 72. The heating arrangement 72 includes a heating zone 74 which, in the illustrated example, surrounds the inner tube 50 of the mixing section on its outer surface in a helical fashion, and a connection section 76 extending from the upstream end 60 towards or through the insert carrier 40. This connection section is electrically insulated and passes through the insert carrier 40, and its portion located outside the housing can be connected to a voltage source.

[0035] The heating arrangement 72 is designed, at least in the heating area 74, as a so-called sheathed heating conductor and comprises at least one heating wire 80 electrically insulated within a sheath 78 constructed of metal material, preferably fixed to the inner tube 50 of the mixing section by material connection, i.e., for example, by welding or soldering. When a voltage is applied to the heating arrangement 72, the at least one heating wire 80 is heated, and the heat emitted by it is transferred via the sheath 78 to the inner tube 50 of the mixing section.

[0036] The heating section 74 of the heating arrangement 72 can comprise one or more sections independently guided on the outside of the mixing section inner tube 50 in order to efficiently cover the surface of the mixing section inner tube 50 and thus achieve a uniform heat input. Other heating section profiles than the helical profile shown are possible. For example, meandering profiles, spiral profiles, or the like can be provided for one or more of the sections of the heating section 74.

[0037] To achieve a stable connection of the heating arrangement 72 to the mixing section insert, the heating arrangement 72 can, for example, be firmly bonded to the inner pipe 50 of the mixing section by means of a material bond. The heating arrangement 72, together with the inner pipe 50 of the mixing section, the mixer 52, and the insert carrier 40, thus forms the essential components of the mixing section insert 38. To position this insert stably in its state mounted to the housing 14, it is advantageous not only to connect the mixing section insert 38 to the housing 14 in the area of ​​the insert carrier 40 by means of the fastening elements 48 described above, but it is also advantageous to radially support the inner pipe 50 of the mixing section with respect to the outer pipe 20 of the mixing section by means of a support arrangement 82.The support arrangement 82 can comprise a support ring 84 constructed with wire mesh, wire fabric or other wire material, which can be fixed, for example, on the inside of the mixing section outer pipe in or near the downstream end region 30 of the same.

[0038] When installing the mixing section insert 38 on the housing 14, it is inserted, with the mixing section inner tube 50 leading, through the insert receiving opening 36 into the mixing section outer tube 20 until the downstream end 70 of the mixing section inner tube 50 is guided through the support ring 84 and the insert carrier 40 rests against the housing 14. Subsequently, the fastening elements 48 are inserted or used to fasten the insert carrier 40 to the housing 14. No further measures are then required to integrate the mixing section insert 38 into the housing 14.

[0039] The inventive design makes it possible to heat the reactant discharged from the reactant discharge unit 62 when it comes into contact with the inner surface of the mixing section inner tube 50, in order to promote its evaporation and prevent the formation of deposits. Since the heating element 74 of the heating arrangement 72 is in direct contact with the mixing section inner tube 50, efficient heat transfer is possible. Furthermore, because the annular space between the mixing section outer tube 20 and the mixing section inner tube 50 is open to allow the inflow of exhaust gas, and exhaust gas can also flow through the nozzle 84 towards the exhaust gas discharge volume 32, the formation of a heat build-up in the space between the mixing section outer tube 20 and the mixing section inner tube 50 is prevented, thus avoiding overheating and any associated damage to the heating element 74.This makes it possible to operate the heating arrangement 72 even with a comparatively high heating output. Due to the ability to release heat essentially uniformly towards the inner pipe 50 of the mixing section, lower maximum temperatures and smaller temperature gradients across the cross-section of the heating area 74 also occur, which has a positive effect on its service life.

[0040] The input of heat not only supports the evaporation of reactant, but also allows heat to be transferred to the exhaust gas, which is particularly advantageous at the start of operation of an internal combustion engine, since the heat introduced into the heating arrangement 72 by means of the exhaust gas can thus be transferred to subsequent system areas in the exhaust gas stream, such as catalysts or the like, and these can therefore be brought more quickly to the temperature required for carrying out a catalytic reaction.

[0041] By providing the mixing section insert with the aforementioned system components as a pre-assembled unit, it becomes possible to remove the entire assembly from the housing for maintenance and, if necessary, repair it or replace it with a new mixing section insert. This extends the overall service life of such a mixing arrangement because, in the event of a defect in a component located internally and attributable to the mixing section insert, only that insert needs to be removed or replaced, and not the entire mixing arrangement. Furthermore, no special tools are required for such a replacement. 10 Mixing arrangement 12 Exhaust system 14 cases 16 wall 18 wall 20 Mixing section outer pipe 22 Mixed section 24 upstream end section 26 Exhaust gas supply volume 28 upstream opening 30 downstream end area 32 Exhaust gas discharge volume 34 Opening 36 Insert opening 38 Mixed track deployment 40 deployment personnel 42 Housing assembly diagram 44 Mounting ring 46 Deployment Carrier Assembly Formation 48 Fastening element 50 Mixing section inner pipe 52 mixers 54 upstream end 56 mixer bodies 58 downstream end 60 upstream end 62 Reaction agent delivery unit 64 interface 66 mixing volumes 68 Opening 70 upstream end 72 Heating arrangement 74 Heating area 76 Connection section 78 Coat 80 heating wire 82 Support arrangement 84 Support ring L AOuter tube longitudinal axis L I Inner tube longitudinal axis

Claims

[1] Mixing arrangement (10) for an exhaust system (12) of an internal combustion engine for mixing exhaust gas emitted by the internal combustion engine with a reactant, comprising: - a case (14), - a component carried in the housing (14), extending in the direction of an outer tube longitudinal axis (L) A ) elongated mixing section outer pipe (20), wherein the mixing section outer pipe (20) is open in an upstream end region (24) to an exhaust gas supply volume (26) and in a downstream end region (30) to an exhaust gas discharge volume (32), - a mixing section insert (38), wherein the mixing section insert (38) comprises an insert carrier (40) to be fixed to the housing (14), a support mounted on the insert carrier (40) in the direction of an inner tube longitudinal axis (L) I ) elongated mixing section inner tube (50) and a heating arrangement (72) with a heating area (74) arranged on an outside of the mixing section inner tube (50). [2] Mixing arrangement (10) according to claim 1, characterized by , that in the housing (14) at a longitudinal axis (L) in the direction of the outer tube A ) an insert receiving opening (36) is provided in the housing wall opposite the upstream end region (24) of the mixing section outer pipe (20), wherein, with the insert carrier (40) fixed to the housing (14), the insert carrier (40) is arranged to cover the insert receiving opening (36) and the mixing section inner pipe (50) is positioned engaging in the mixing section outer pipe (20). [3] Mixing arrangement (10) according to claim 2, characterized by , that with the insert carrier (40) fixed to the housing (14), the mixing section outer tube (20) and the mixing section inner tube (50) are essentially coaxial to each other or have essentially parallel longitudinal axes (L) A , L I) are arranged, or / and that, with the insert carrier (40) fixed to the housing (14), the heating area (74) is arranged at a distance from an inner side of the mixing section outer tube (20). [4] Mixing arrangement (10) according to one of claims 1-3, characterized by , that a support arrangement (82) is provided on the outer pipe (20) of the mixing section for supporting the inner pipe (50) of the mixing section with respect to the outer pipe (20) of the mixing section. [5] Mixing arrangement (10) according to claim 4, characterized by , that the support arrangement (82) is fixed on an inside of the mixing section outer pipe (20) and / or the outer pipe longitudinal axis (L A ) is formed in a ring-like surrounding shape and / or is constructed with wire material. [6] Mixing arrangement (10) according to any one of claims 1-5, characterized by , that the mixing section insert (38) comprises a mixer (52) between the insert carrier (40) and the mixing section inner pipe (50). [7] Mixing arrangement (10) according to claim 6, characterized by , that the mixer (52) has a direction in the direction of the inner pipe longitudinal axis (L I ) in the direction of the insert carrier (40) to the mixing section inner tube (50) comprising a mixing body (56) which extends radially and encloses a mixing volume (66) and has a plurality of exhaust gas inlet openings (68). [8] Mixing arrangement (10) according to claim 7, characterized by , that the mixer body (56) connects with an upstream end (54) to the insert carrier (40) and with a downstream end (58) to an upstream end (60) of the mixing section inner pipe (50). [9] Mixing arrangement (10) according to claim 8, characterized by , that the mixer body (56) is fixed at its upstream end (54) to the insert carrier (40) and at its downstream end (58) is fixed to the upstream end (60) of the mixing section inner tube (50). [10] Mixing arrangement (10) according to any one of claims 1-9, characterized by , that the deployment carrier (40) is designed to attach a reaction agent delivery unit (62) to the deployment carrier (40). [11] Mixing arrangement (10) according to any one of claims 1-10, characterized by , that a housing mounting assembly (42) is provided on the housing (14), and that an insert carrier mounting assembly (46) is provided on the insert carrier (40) for fixing the insert carrier (40) to the housing (14) by means of a plurality of fastening elements (48) which can be detachably connected to the housing mounting assembly (42). [12] Mixing arrangement (10) according to claim 11, characterized by , that the housing mounting formation (42) is designed to surround the insert receiving opening (36) in a ring-like manner. [13] Mixing arrangement (10) according to claim 12, characterized by , that the housing assembly (42) comprises a mounting ring (44) fixed to the housing (14) surrounding the insert receiving opening (36). [14] Mixing arrangement (10) according to one of claims 11-13, characterized by , that the housing mounting assembly (42) and / or the insert carrier mounting assembly (46) comprises a plurality of fastening element engagement openings. [15] Mixing arrangement (10) according to any one of claims 1-14, characterized by , that the heating area (74) is arranged on the outside of the mixing section inner pipe (50) with a winding course. [16] Mixing arrangement (10) according to claim 15, wherein the heating area (74) has at least a meandering course in some areas, and / or wherein the heating area (74) has at least a meandering course in some areas along the inner tube longitudinal axis (L) I ) has a spiral-like surrounding shape. [17] Mixing arrangement (10) according to any one of claims 1-16, characterized by , that the heating area (74) is fixed on the outside of the mixing section inner pipe (50). [18] Mixing arrangement (10) according to claim 17, characterized by, that the heating arrangement (72) comprises at least in the heating area (74) a heating conductor with at least one heating wire (80) electrically insulated in a sheath (78), wherein the sheath (78) is fixed on the outside of the mixing section inner tube (50). [19] Mixing arrangement (10) according to any one of claims 1-18, characterized by that the heating arrangement (72) has a connection section (76) penetrating the insert carrier (40). [20] Mixing arrangement (10) according to any one of claims 1-19, characterized by , that the mixing section outer pipe (20) is fixed in its upstream end region (24) by a wall (16) limiting the exhaust gas supply volume (26) on the housing (14), or / and that the mixing section outer pipe (20) is fixed in its downstream end region (30) by a wall (18) limiting the exhaust gas discharge volume (32) on the housing (14). [21] Exhaust system (12) for an internal combustion engine, comprising a mixing arrangement (10) according to one of the preceding claims.

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