SCR exhaust aftertreatment device

Abstract

An SCR exhaust aftertreatment device of an internal combustion engine, containing an injector for injecting a reductant, a mixing unit and an SCR catalytic converter disposed immediately downstream in the direction of exhaust flow, wherein the mixing unit exhibits a swirl element and an impact element positioned upstream of the swirl element in the direction of exhaust flow, whereby the swirl element is configured of two guide elements disposed inside one another and swirl vanes for creating a swirling motion are disposed in an inner guide element and swirl vanes, which create a counterswirling motion, are disposed between the inner guide element and the outer guide element.

Claims

1. An SCR exhaust aftertreatment device of an internal combustion engine, containing an injector for injecting a reductant, a mixing unit and an SCR catalytic converter disposed immediately downstream in the direction of exhaust flow, wherein the mixing unit contains a swirl element and an impact element positioned upstream of the swirl element in the direction of exhaust flow, whereby the swirl element is configured of two guide elements disposed inside one another and swirl vanes for creating a swirling motion are disposed in an inner guide element and swirl vanes, which create a counterswirling motion, are disposed between the inner guide element and the outer guide element; and wherein the impact element has at least two baffles, is directly connected to and firmly bonded to the swirl element, and the baffles are arranged to face one another in a radial direction and angled in the direction of exhaust flow.

2. The SCR exhaust aftertreatment device according to claim 1, wherein the guide elements are configured as an inner bushing and an outer bushing.

3. The SCR exhaust aftertreatment device according to claim 1, wherein the swirl vanes for creating the swirling motion and the swirl vanes for creating the counterswirling motion are arranged at the same height and/or next to one another with respect to the direction of exhaust flow.

4. The SCR exhaust aftertreatment device according to claim 1, wherein the swirl element is configured to be opaque in the direction of exhaust flow and/or that the swirl element is configured in one piece and in a material uniform manner.

5. The SCR exhaust aftertreatment device according to claim 1, wherein the entirety of the exhaust flowing through the exhaust aftertreatment device flows through the swirl element.

6. The SCR exhaust aftertreatment device according to claim 1, wherein the impact element is configured as a sheet metal component, in particular a sheet metal formed part.

7. The SCR exhaust aftertreatment device according to claim 1, wherein the injector is positioned upstream of the impact element in axial direction of the swirl element, so that an injection jet is oriented and hits the impact element in an axial direction of the swirl element.

8. The SCR exhaust aftertreatment device according to claim 1, wherein the outer bushing of the swirl element is used as a connecting element of an SCR catalytic converter with an exhaust pipe duct positioned upstream of the SCR catalytic converter; the swirl element is inserted into it.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional advantages, features, characteristics and aspects of the present invention are the subject matter of the following description. Preferred design variants are depicted in the schematic figures. They provide easy comprehension of the invention. The figures show:

(2) FIG. 1 is a perspective view of an SCR exhaust aftertreatment device;

(3) FIG. 2 consists of FIGS. 2A, 2B and 2C showing a mixing unit according to the invention;

(4) FIG. 3 is an exploded view of a mixing unit according to the invention; and

(5) FIG. 4 is a sectional view of the SCR exhaust aftertreatment device of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(6) The same reference signs are used for the same or similar components in the figures, even if the description is not repeated for the sake of simplicity. The guide elements are described as bushings, but can have other geometric designs as well.

(7) FIG. 1 shows a perspective view of an SCR exhaust aftertreatment device 1. For this purpose a first component 2, for example an oxidation catalyst, is shown, which is followed in the direction of exhaust flow S by a connecting element 3, through which the exhaust flow passes. The connecting element 3 is followed by an SCR catalytic converter 4.

(8) On the connecting element 3 there is an injector 5, which injects injection jets 7 of a reductant into the interior space 6 of the connecting element 3. A mixing unit 8, which is described in more detail in FIG. 2A to C and FIG. 3, is disposed in a passage from the connecting element 3 to the SCR catalytic converter 4.

(9) The mixing unit 8 exhibits a swirl element 9 and an impact element 10. With respect to the direction of exhaust flow S, the impact element 10 is positioned upstream of the swirl element 9. The swirl element 9 exhibits an outer bushing 11 and an inner bushing 12 disposed therein. Swirl vanes 13, which create a counterswirling motion GD upon passage of one part of the exhaust stream 19, are arranged between the inner bushing 12 and the outer bushing 11. The counterswirling motion GD is opposite a swirling motion D created by the swirl vanes 14 disposed within the inner bushing 12. The swirling motion D is created upon passage of the other part of the exhaust stream through the inner bushing 12. The direction of the swirling motion D and the counterswirling motion GD can also be opposite to those shown in FIG. 2A.

(10) The entire exhaust stream is thus fed through the mixing unit 8, because part of the exhaust stream 19 passes through the inner bushing 12 and the remaining part of the exhaust stream passes though the space between the inner bushing 12 and the outer bushing 11. In doing so, the part that passes through the inner bushing 12 is set into a swirling motion D by the swirl elements 14 in the inner bushing 12 and the other part, which passes through the outer bushing 11 at the same time, is set into an opposite counterswirling motion GD.

(11) To improve the initial dispersion of the droplets of the respective injection jet 7, and with it also their vaporization in the exhaust stream, however, an impact element 10 is disposed upstream of the swirl element 9 in the direction of exhaust flow S. The impact element 10 has baffles 15; three baffles 15 are shown in the drawing. They correspond to the three depicted injection jets 7 of FIG. 1. Therefore, each injection jet 7 hits one baffle 15. The injection jets 7, which are not shown in more detail, proceed at a small angle, in particular oriented parallel to an axial direction 16 of the swirl element 9. The baffles 15 of the impact element 10 are oriented to face one another in radial direction R, as shown in FIG. 2A, and arranged at an angle with respect to the direction of exhaust flow S, as shown in FIG. 2B. The reductant droplets that form upon impact are thus deflected in radial direction R and picked up by the exhaust flow in the cross-flow principle.

(12) The angle can be individually optimized for every baffle 15. FIG. 3 shows particularly well that the impact element 10 is manufactured as a sheet metal forming part in one piece and in a material uniform manner. This sheet metal forming part can exhibit insertion slots 17, for example, via which it can be set onto fins 18 disposed in the swirl element 9. The baffles 10 are, in particular integrally and in a material uniform manner, coupled to one another by a partially circumferential clip 21. The snapped on impact element 10 is shown in FIG. 2C. It can additionally be coupled to the swirl element 9 in a firmly bonded manner. There is, however, a functional separation of the initial breakup of the injection jet 7 on the impact element 10 and the subsequent mixing and vaporization in and after the swirl element 9, in each case with respect to the direction of exhaust flow S.

(13) FIG. 2B again shows a time axis t or a reference sign h for the height. One part of the exhaust flowing through the swirl element 9 in the direction of exhaust flow S is thus set in swirling motion D, and the other part is set in counterswirling motion GD. This takes place at substantially the same time or at the same height h with respect to the direction of exhaust flow S. A small offset with respect to time and/or height h upstream or downstream is shown as , and represents the concept of the invention. It is again evident here that not at least one part, in particular the entire exhaust stream, is first set in a swirling motion D and then in a counterswirling motion GD, but rather that both take place at the same time.

(14) This is also shown again in FIG. 4. FIG. 4 shows a cross-sectional view through the SCR exhaust aftertreatment device 1 according to the invention, in which one part of the exhaust stream 19 flows through the inner bushing 12 of the swirl element 9 and the other part 20 flows between the inner bushing 12 and the outer bushing 11 through the mixing unit 8. Therefore, with respect to the direction of exhaust flow S, the entire exhaust stream 19, 20 is set simultaneously in swirling motion D and in counterswirling motion GD, which results in increased turbulence with respect to the direction of exhaust flow S downstream of the mixing unit 8, and thus in improved mixing and vaporization of the exhaust stream and the reductant.

REFERENCE SYMBOLS

(15) 1SCR exhaust aftertreatment device 2First component 3Connecting element 4SCR catalytic converter 5Injector 6Interior space of 3 7Injection jets 8Mixing unit 9Swirl element 10Impact element 11Outer bushing 12Inner bushing 13Swirl vanes in 11 14Swirl vanes in 12 15Baffle 16Axial direction to 9 17Insertion slot 18Fins 19Part of the exhaust stream 20Other part of the exhaust stream 21Clip DSwirling motion GDCounterswirling motion RRadial direction SDirection of exhaust flow tTime axis hHeight Offset