Exhaust-gas mixer

1. An exhaust-gas mixing pipe for admixing at least one additive into an exhaust-gas stream of an internal combustion engine, comprising: a housing wall of longitudinal axis L and of round cross section, and a closed end wall on which can be placed an injection nozzle, for said additive wherein the housing wall has multiple rows arranged over a circumference U, of openings, through which exhaust gas can flow from an outer side of the exhaust-gas mixing pipe into an interior of the exhaust-gas mixing pipe, wherein several openings of a row form in each case one stage M and wherein the respective stage M is characterized according to its size by an average opening cross section Q of its openings, wherein a sum of all the opening cross sections Q of all the openings of all the rows of the exhaust-gas mixing pipe is equal to SQ, wherein at least one first-order stage, stage M 1 , is provided, wherein the stage M 1 has openings having an average opening cross section Q 1 , and an, in addition, at least one second-order stage, stage M 2 , is provided, wherein a stage M 2 has openings having an average opening cross section Q 2 , where Q 2 ≥f Q 1 , where 5≤f≤25, and there is provided a first sector S 1 which is designed as a flushing sector and consists of at least the one stage M 1 , and a second sector S 2 which is designed as a mixing sector and consists of at least the one stage M 2 , wherein, in the direction of the longitudinal axis L toward the end wall, the first sector S 1 is positioned first and the second sector S 2 is positioned thereafter.

2. The exhaust-gas mixing pipe according to claim 1 , wherein the stage M or a sector S has at least predominantly openings which are each designed as a recess of the housing wall, and/or the stage M or the sector S has at least predominantly openings which are designed as a formation of the housing wall, wherein the formed part of the housing wall at least partially forms a blade.

3. The exhaust-gas mixing pipe according to claim 2 , wherein the blade has a straight blade axis which extends parallel to the longitudinal axis L or which extends tangentially to the circumference U or which is arranged in a joint plane E with the longitudinal axis L.

4. The exhaust-gas mixing pipe according to claim 2 , wherein at least one additional sector S 3 is provided with at least one third-order stage, stage M 3 , having an average opening cross section Q 3 and having a sum SQ 3 of the opening cross sections Q 3 , where SQ 3 ≤x 2 SQ, where 0.05≤x 2 ≤0.35.

5. The exhaust-gas mixing pipe according to claim 4 , wherein the openings of the stage M 3 are an average distance r 3 from the longitudinal axis L and the openings of the stage M 2 are an average distance r 2 from the longitudinal axis L, where r 3 ≤1.05 r 2 .

6. The exhaust-gas mixing pipe according to claim 5 , wherein the openings and/or the blades of the respective stage M 1 , M 2 , M 3 are arranged offset to one another with respect to the direction of the longitudinal axis L.

7. The exhaust-gas mixing pipe according to claim 4 , wherein at least one additional sector S 4 is provided with at least one stage M 1 , M 2 and/or M 3 , wherein the sector S 4 is arranged between the sector S 2 and the sector S 3 .

8. The exhaust-gas mixing pipe according to claim 4 , wherein the opening cross section Q 2 or Q 3 has a value qa over a first partial circumference Ua of 100° to 180° which can be turned toward the stream and has a value qb over an opposite partial circumference Ub of 100° to 180° with respect to the longitudinal axis L, where 1.1 qa≤=qb.

9. The exhaust-gas mixing pipe according to claim 1 , wherein the sector S 1 has a sum SQ 1 of the opening cross sections Q 1 , where SQ 1 <=x 1 SQ, where 0.05<=x 1 <=0.25.

10. The exhaust-gas mixing pipe according to claim 1 , wherein the sector S 1 consists of a maximum of three to five stages M 1 and/or the sector S 2 consists of a maximum of 2 to 10 stages M 2 .

11. The exhaust-gas mixing pipe according to claim 1 , wherein the exhaust-gas mixing pipe has an average diameter DS 1 in the region of the sector S 1 and the sector S 1 is a maximum distance AS 1 from the end wall, where AS 1 ≤y 1 DS 1 , and where 0≤y 1 ≤0.3.

12. The exhaust-gas mixing pipe according to claim 1 , wherein the exhaust-gas mixing pipe is calibrated at least in a region of a start of a pipe and/or of the end of a pipe with respect to the diameter and/or cross-sectional form.

13. The exhaust-gas mixing pipe according to claim 1 , wherein the exhaust-gas mixing pipe has an average diameter DS 1 in the region of the sector S 1 and an average diameter DS 2 in a region of the sector S 2 , wherein DS 1 =DS 2 or the diameter DS 1 deviates by a maximum of 5%-10% from the diameter DS 2 .

14. An exhaust-gas mixer consisting of an exhaust-gas mixing pipe according to claim 1 and a mixer housing, wherein the mixer housing has an inlet opening and an outlet opening for exhaust gas and the exhaust-gas mixing pipe is positioned with an end of a pipe opposite the end wall at an outlet opening.

15. The exhaust-gas mixer according to claim 14 , wherein the inlet opening has an inflow cross section T, where 0.8 SQ≤T≤4SQ.

16. The exhaust-gas mixer according to claim 14 between the end of the pipe of the exhaust-gas mixing pipe and the outlet opening there is provided an annular gap having an opening cross section QR, where QR≤x 3 SQ, and where 0.05≤x 3 ≤0.35.

17. The exhaust-gas mixer according to claim 14 , wherein the exhaust-gas mixing pipe has a conical widened portion at the start of the pipe and/or at the end of the pipe.

18. The exhaust-gas mixer according to claim 14 , wherein a nozzle is provided with a discharge opening for introducing the additive, wherein the exhaust-gas mixing pipe has the average diameter DS 1 in a region of the sector S 1 and the discharge opening is a maximum distance ADA from the end wall, where ADA≤y 2 DS 1 , and where 0.4≤y 2 ≤0.8.

19. An exhaust system for an internal combustion engine having an exhaust-gas mixer according to claim 14 and an exhaust-gas aftertreatment device such as a DPF and/or a SCR arranged downstream in the direction of flow of the exhaust gas.