DE102018115231A1 - Exhaust gas mixer and exhaust gas treatment system with such an exhaust gas mixer - Google Patents

Abstract

The invention relates to an exhaust gas mixer (24) for an exhaust gas system of an internal combustion engine (10). The exhaust gas mixer (24) has an adjustment actuator (22), via which the position of the segments (38, 42, 46) of the exhaust gas mixer (24) can be adjusted. It is provided that the segments (38, 42, 46) of the exhaust gas mixer (24) are connected to one another via joints (42) such that the segments (38, 42, 46) of the exhaust gas mixer (24 The exhaust gas aftertreatment system (12) for an internal combustion engine (10) with a metering element (20) for metering a reducing agent into the exhaust gas duct (14) of the internal combustion engine (10) and such an exhaust gas mixer (24).

Description

The invention relates to an exhaust gas mixer for mixing a reducing agent for the selective catalytic reduction of nitrogen oxides with the exhaust gas of an internal combustion engine and an exhaust gas aftertreatment system for exhaust gas aftertreatment of the exhaust gases of an internal combustion engine.

The current exhaust gas legislation, which will become increasingly stringent in the future, places high demands on raw engine emissions and exhaust gas aftertreatment of internal combustion engines. The demands for a further decrease in consumption and the further tightening of the exhaust gas standards with regard to the permissible nitrogen oxide emissions represent a challenge for the engine developers. In gasoline engines, exhaust gas cleaning is carried out in a known manner using a three-way catalytic converter and the three-way Catalyst upstream and downstream further catalysts. Exhaust gas aftertreatment systems are currently used in diesel engines, which have an oxidation catalytic converter, a catalytic converter for the selective catalytic reduction of nitrogen oxides (SCR catalytic converter) and a particle filter for the separation of soot particles and, if appropriate, further catalytic converters. Ammonia is preferably used as the reducing agent. Because the use of pure ammonia is complex, a synthetic, aqueous urea solution is usually used in vehicles, which is mixed with the hot exhaust gas stream in a mixing device upstream of the SCR catalytic converter. This mixing heats the aqueous urea solution, the aqueous urea solution releasing ammonia in the exhaust gas duct. A commercially available, aqueous urea solution generally consists of 32.5% urea and 67.5% water.

In order to achieve sufficient mixing between the reducing agent and the exhaust gas of the internal combustion engine before entering the SCR catalytic converter, an adequate mixing section must be provided in the exhaust system. Therefore, in addition to a particle filter close to the engine with an SCR coating, one or more further SCR catalysts are optionally arranged in an underbody layer of a motor vehicle remote from the engine.

A disadvantage of such a position, however, is that the necessary temperatures can only be reached with difficulty in such a position remote from the motor.

Mixing elements arranged in the exhaust system are also known from the prior art, which lead to turbulent flow conditions and thus to good mixing of exhaust gas and reducing agent. The mixing section can be shortened by the mixing elements or better mixing of exhaust gas and reducing agent can be achieved before entering the SCR catalytic converter with the same mixing section length.

From the DE 10 2010 045 156 A1 An exhaust gas aftertreatment system for an internal combustion engine is known in which an aqueous urea solution is metered into the exhaust gas duct upstream of an SCR catalytic converter. In order to achieve an improved mixing of exhaust gas and urea solution and to promote the evaporation of the urea solution, a mixing element is provided. The mixing element has guide vanes, which can be rotated via a shaft, so that the flow angle of the guide vanes is adjustable.

The DE 10 2015 011 410 A1 discloses an exhaust system for an internal combustion engine, wherein an exhaust gas mixer with an adjustable geometry is arranged in the exhaust system to mix a reducing agent with the exhaust gas of the internal combustion engine. A pneumatic actuator for adjusting the exhaust gas mixer is provided, the pneumatic actuator having an actuating element which is acted upon by an exhaust gas pressure, in particular upstream of the exhaust gas mixer.

In addition, the DE 10 2015 201 378 A1 an exhaust gas mixer and an exhaust gas system with such an exhaust gas mixer for an internal combustion engine, wherein a mixing element with flexible mixing blades is provided, which deform depending on the flow rate of the exhaust gas or the exhaust gas temperature, so that the mixer is adjusted from a mixing position to a passage position.

A disadvantage of such a solution is that the rotation of the guide vanes leads to a relatively strong blockage of the cross section of the exhaust gas duct and the exhaust gas back pressure rises accordingly.

The object of the invention is to improve the mixing of exhaust gas and reducing agent and to reduce the flow resistance in operating situations in which no reducing agent is metered in.

According to the invention, this object is achieved by an exhaust gas mixer for an exhaust gas aftertreatment system of an internal combustion engine, the exhaust gas mixer comprising an adjustment actuator with which the segments of the exhaust gas mixer can be adjusted from a mixing position to a passage position. According to the invention it is provided that at least two segments of the exhaust gas mixer at least one joint are connected. As a result, the flow cross section can be varied in a simple manner between a turbulence-optimized mixing position, in which the best possible mixing of exhaust gas and reducing agent is achieved, and a passage position, in which a flow-favorable passage is achieved. In particular, the exhaust gas back pressure can be reduced if no reducing agent is metered in.

The features listed in the dependent claims allow advantageous further developments and improvements of the exhaust gas aftertreatment assembly specified in the independent claim.

In a preferred embodiment of the invention, it is provided that the exhaust gas mixer has a first end segment, a middle segment and a second end segment, the middle segment being connected to one of the end segments via a joint. The flow cross section can be varied in a variety of ways by three-part or multi-part segments of the exhaust gas mixer, so that more and different functional positions can be set compared to the known mixers with rotatable guide vanes. This allows the number of possible flow cross sections to be increased, which extends the functionality of the exhaust gas mixer.

An advantageous further development of the exhaust gas mixer provides that opening the joint angle of the second joint results in simultaneous opening of the joint angle of the first joint. A functional connection of the joints can simplify the opening and closing of the segments, as a result of which the exhaust gas mixer can be easily adjusted from the mixing position to the open position.

It is particularly preferred if the adjustment actuator is connected to one of the joints via at least one adjustment means. A shaft or a slide is preferably provided as the adjustment means, which can be adjusted from a first position to a second position via the adjustment actuator, in particular an electric motor. For this purpose, actuating the adjustment actuator means that the joint angle between the segments is increased or decreased.

In a preferred embodiment of the exhaust gas mixer, it is provided that the exhaust gas mixer has a plurality of mixing elements arranged parallel to one another, the mixing elements each having a first end segment, a middle segment and a second end segment. In order to achieve the mixing effect over the entire flow cross section of the exhaust gas duct, it is provided that the exhaust gas mixer has a plurality of mixing elements arranged parallel to one another.

In a further improvement of the invention, it is provided that the segments of the exhaust gas mixer are provided with a structure that minimizes deposits or a coating that minimizes deposits. A deposit-minimizing structure, for example a nub structure or a sharkskin-like structure, can prevent or at least reduce deposits by crystallizing urea. This reduces the risk that the exhaust gas channel becomes clogged with deposits in the area of the exhaust gas mixer and thus the flow cross section is reduced, which would lead to an increase in the exhaust gas back pressure and thus to an increase in consumption.

In a preferred embodiment of the exhaust gas mixer, it is provided that the end segments are connected to one another via a cable pull. In this case, a guide channel for the cable pull is preferably provided on the joints in order to fix the position of the cable pull and to avoid damaging the segments of the exhaust gas mixer. A cable pull can be used in a simple and inexpensive manner to open the end segments of the exhaust gas mixer so that the exhaust gas mixer can be adjusted in a simple manner.

According to the invention, an exhaust gas aftertreatment system for an internal combustion engine with an exhaust gas mixer according to the invention and with a metering element arranged in the flow direction of an exhaust gas of the internal combustion engine upstream of the exhaust gas mixer for metering a reducing agent into an exhaust gas duct of the exhaust gas aftertreatment system and an SCR catalyst or particle filter with a coating for selective purposes Catalytic reduction of nitrogen oxides proposed. An exhaust gas aftertreatment system according to the invention can both achieve excellent mixing of exhaust gas and reducing agent and also reduce the flow resistance, so that the exhaust gas emissions and the consumption of the internal combustion engine can be reduced.

In a preferred embodiment of the exhaust gas aftertreatment system, it is provided that the opening angles of the joints in a first operating state of the metering element, in which no reducing agent is metered into the exhaust gas duct, are increased compared to the opening angles of the joints in a second operating state, in which reducing agent is metered in.

In a preferred embodiment of the invention, it is provided that the adjustment actuator is connected to a control unit of the internal combustion engine via a signal line. As a result, the position of the exhaust gas mixer can be adjusted in a simple manner depending on the operating situation of the internal combustion engine, without the need for an additional control unit.

Unless otherwise stated in the individual case, the various embodiments of the invention mentioned in this application can advantageously be combined with one another.

• 1 einen Verbrennungsmotor mit einer Abgasanlage und einem erfindungsgemäßen Abgasnachbehandlungssystem; und
• 2 ein Ausführungsbeispiel eines erfindungsgemäßen Abgasmischers mit einem Verstellaktuator und einem Verstellmittel, welches mit den Gelenken des Abgasmischers verbunden ist.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Show it:

• 1 an internal combustion engine with an exhaust system and an exhaust gas aftertreatment system according to the invention; and
• 2 an embodiment of an exhaust gas mixer according to the invention with an adjustment actuator and an adjustment means which is connected to the joints of the exhaust gas mixer.

1 shows schematically an internal combustion engine 10 , which is designed as a self-igniting diesel engine. The internal combustion engine 10 is with its outlet with an exhaust duct 14 of an exhaust gas aftertreatment system 12 connected. In the exhaust duct 14 are in the flow direction of the exhaust gas of the internal combustion engine 10 a turbine 16 of an exhaust gas turbocharger, downstream of the turbine 16 a catalyst 18 , in particular an oxidation catalyst or a NOx storage catalyst, and downstream of the catalyst 18 an SCR catalyst 28 or a particle filter 36 arranged with an SCR coating.

Downstream of the catalyst 18 and upstream of the SCR catalyst 28 or the particle filter 36 with SCR coating are a dosing element 20 for metering in a preferably liquid reducing agent 34 and downstream of the metering element 20 an exhaust mixer 24 arranged with which the reducing agent 34 with an exhaust gas flow 32 of the internal combustion engine 10 is mixed. From the dosing element 20 until entering the SCR catalytic converter 28 or the particle filter 36 with the SCR coating is a mixing section 30 educated.

The exhaust mixer 24 includes an adjustment actuator 22 and a plurality of mixing elements, the adjustment actuator 22 via an adjusting device 26 , in particular a shaft or a rod, are connected to the mixing elements of the exhaust gas mixer. The mixing elements comprise a middle segment 42 which has a first joint 40 with a first end segment 38 and a second joint 44 with a second end segment 46 of the mixing element are connected. The adjustment actuator 22 is over a signal line 48 with a control unit 50 of the internal combustion engine 10 connected.

In 2 The exhaust gas mixer is shown in a first operating position I, which is referred to below as the mixing position and in a second operating position II, which is referred to below as the open position. In the first operating position I is through the metering element 20 a liquid reducing agent 34 , especially aqueous urea solution, in the exhaust duct 14 of the exhaust gas aftertreatment system 12 metered. The exhaust mixer 24 is in a mixed position in which the end segments 38 . 46 of the mixing elements in relation to the middle segment 42 are tilted such that a flow through the exhaust gas mixer 24 is not possible without redirecting the exhaust gas flow. This leads to a corresponding turbulence in the exhaust gas flow 32 , which ensures thorough mixing of the reducing agent 34 with the exhaust gas flow 32 of the internal combustion engine 10 is achieved.

The adjustment element 22 is about the adjustment 26 with the second joints 44 the mixing elements connected. By shifting or rotating the adjusting means 26 becomes the joint angle β of the second joint 44 increases or decreases, causing the joint angle a of the first joint 40 also changed in the same direction.

In the open position II, the metering of reducing agent is reduced or completely stopped. Here are the joints 40 . 44 of the mixing elements so far that the end segments 38 . 46 in the direction of flow essentially in continuation of the respective middle segment 42 run. Here, a joint angle a, β in the joints 40 . 44 of at least 150 °, preferably at least 160 °, so that the exhaust gas flow 32 of the internal combustion engine 10 the exhaust mixer 24 can flow through essentially without diversions. In addition, opening or closing the exhaust mixer can be supported by the selection of appropriate materials. For example, the end segments 38 . 46 in the form of a bimetallic body or a shape memory material, so that the mixing element opens with increasing temperatures and / or with higher exhaust gas flows, if due to the higher flow velocity and the higher exhaust gas temperature, better mixing of the exhaust gas flow 32 and reducing agents 34 is to be expected.

LIST OF REFERENCE NUMBERS

10

internal combustion engine

12

aftertreatment system

14

exhaust duct

16

turbine

18

oxidation catalyst

20

metering

22

adjustment actuator

24

exhaust mixer

26

adjustment

28

SCR catalyst

30

mixing section

32

exhaust gas flow

34

reducing agent

36

Particle filter with SCR coating

38

first end segment

40

first joint

42

middle segment

44

second joint

46

second end segment

48

signal line

50

control unit

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102010045156 A1 [0006]
• DE 102015011410 A1 [0007]
• DE 102015201378 A1 [0008]

Claims (10)

Exhaust gas mixer (24) for an exhaust gas aftertreatment system (12) of an internal combustion engine (10), the exhaust gas mixer (24) comprising an adjustment actuator (22) with which the segments (38, 42, 46) of the exhaust gas mixer (24) move from a mixing position into one Passage position are adjustable, characterized in that at least two segments (38, 42, 46) of the exhaust gas mixer (24) are connected to one another via at least one joint (40, 44). Exhaust mixer (24) after Claim 1 , characterized in that the exhaust gas mixer (24) has a first end segment (38), a middle segment (42) and a second end segment (46), the middle segment (42) each having a joint (40, 44) with one of the end segments (38, 46) is connected. Exhaust mixer (24) after Claim 1 or 2 , characterized in that opening the joint angle (a) of the second joint (44) causes simultaneous opening of the joint angle (β) of the first joint (40). Exhaust mixer (24) according to one of the Claims 1 to 3 , characterized in that the adjustment actuator (22) is connected to at least one adjustment means (28) with one of the joints (40, 44). Exhaust mixer (24) according to one of the Claims 1 to 4 , characterized in that the exhaust gas mixer (24) has a plurality of mixing elements arranged parallel to one another, the mixing elements each having a first end segment (38), a middle segment (42) and a second end segment (46). Exhaust mixer (24) according to one of the Claims 1 to 5 , characterized in that the segments (38, 42, 46) of the exhaust gas mixer (24) are provided with a deposit-minimizing structure or deposit-minimizing coating. Exhaust mixer (24) according to one of the Claims 1 to 6 , characterized in that the end segments (38, 46) are connected to one another via a cable pull. Exhaust gas aftertreatment system (12) for an internal combustion engine (10) with an exhaust gas mixer (24) according to one of the Claims 1 to 7 and with a metering element (20) arranged in the flow direction of an exhaust gas of the internal combustion engine (10) upstream of the exhaust gas mixer (24) for metering a reducing agent (34) into an exhaust gas duct (14) of the exhaust gas aftertreatment system (12) and one downstream of the exhaust gas mixer (24) SCR catalyst (28) or particle filter (36) with a coating for the selective catalytic reduction of nitrogen oxides. Exhaust aftertreatment system (12) Claim 8 , characterized in that the opening angle (a, β) of the joints (40, 44) in a first operating state of the metering element (20), in which no reducing agent (34) is metered into the exhaust gas duct (14), compared to the opening angle (a , β) of the joints (40, 44) are enlarged in a second operating state in which reducing agent (34) is metered in. Exhaust aftertreatment system (12) according to one of the Claims 1 to 9 , characterized in that the adjustment actuator (22) is connected to a control unit (50) of the internal combustion engine (10) via a signal line (48).

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