WO2008135332A1 - Device for the metered injection of an exhaust gas aftertreatment medium/air mixture in an exhaust gas installation - Google Patents

Abstract

The invention relates to a device for the metered injection of an exhaust gas aftertreatment medium/air mixture into an exhaust gas installation of an internal combustion engine, especially for a motor vehicle. Said device comprises a mixing chamber into which the air is fed via a compressed-air line and the exhaust gas aftertreatment medium via a feed line. The invention is characterized in that the compressed-air line (10) is connected to the mixing chamber (5) via a connecting element (15) which is produced of a material having low surface tension.

Description

 description

title

Device for the metered injection of an exhaust gas aftertreatment agent-air mixture in an exhaust system

The invention relates to a device for the metered injection of an exhaust aftertreatment agent-air mixture into an exhaust system of an internal combustion engine, in particular for a motor vehicle, with a mixing chamber, are introduced into the air via a compressed air line and exhaust aftertreatment agent via a feed.

State of the art

Such a device for the metered injection of an exhaust gas aftertreatment agent-air mixture is known, for example, in the exhaust aftertreatment for reducing the nitrogen oxide emissions of a diesel engine by means of SCR catalyst (SCR: Selective Catalytic Reduction). The exhaust aftertreatment agent of the exhaust aftertreatment agent-air mixture is an aqueous urea solution (trade name: AdBlue). The aqueous urea solution is stored in a storage vessel and fed to a mixing chamber via a feed. In the mixing chamber, the aqueous urea solution is mixed with air, which is introduced via a compressed air line, and then injected by means of a spray or atomizer tube in front of the SCR catalyst in the exhaust system. Under the influence of the heat of the exhaust gas forms ammonia, which converts the nitrogen oxides (NO _x ) in the exhaust gas into nitrogen and water vapor in the SCR catalyst.

Upon introduction of the aqueous urea solution into the mixing chamber, crystallization of residues of the introduced urea solution occurs. The crystallization causes various feedback. Emerging crystals "migrate" into the compressed air line and block it in extreme cases.The crystallization also causes a pressure increase in the feed of the aqueous urea solution, for example between a delivery module and a dosing module. Due to the crystallization occurs in the worst case, a decrease in flow in the compressed air line and thus to increase the Dosiermenge, ie a misdosing, which leads to a nitrogen oxide or ammonia slip in the exhaust gas.

Disclosure of the invention

To avoid crystallization in the mixing chamber is provided that the compressed air line is connected via a connection element made of a material having a low surface tension to the mixing chamber. In this case, the connection element consists entirely of this material or has at least on the parts of its surface, which may come into contact with the air from the compressed air line and / or the exhaust aftertreatment agent, a material having a low surface tension. The material of the connection element has in particular a lower one

Surface tension on, as the material of the compressed air line and / or the walls of the mixing chamber. Due to the low surface tension of the material, the crystals formed during the crystallization can not adhere to the surface of the connection element. The crystals are flushed with the exhaust aftertreatment agent-air mixture from the mixing chamber toward an injection member for injecting the exhaust aftertreatment agent-air mixture into the exhaust system, such as a spray tube.

According to a development of the invention it is provided that the connection element has a smooth inner surface. The inner surface is a part or the part of the surface of the connection element, which can come into contact with the air from the compressed air line and / or the exhaust aftertreatment agent. A smooth inner surface provides nuclei on which crystals form, no stopping. Under a smooth inner surface is an inner surface with a low roughness to understand. The roughness is in particular less than the roughness of the inner surface of the compressed air line and or the walls of the mixing chamber.

In an advantageous embodiment of the invention, it is provided that the material of the connection element is plastic. This plastic is a Plastic with low surface tension. In particular, the smooth inner surface is made of this plastic.

In particular, it is provided that the material of the connecting element is polytetrafluoroethylene (PTFE), in particular Teflon. Polytetrafluoroethylene, sometimes called polytetrafluoroethene, is a fully fluorinated polymer. Colloquially, this plastic is referred to by the trade name Teflon. Polytetrafluoroethylene has an extremely low surface tension, so there is virtually no material adhering to the polymer tetrafluoroethylene. Furthermore, polytetrafluoroethylene has a very low coefficient of friction and a temperature range which is higher than other plastics, is very inert and resistant to aggressive substances such as acids, bases, alcohols, ketones, gasolines and oils. A connecting element of polytetrafluoroethylene, or with a surface made of polytetrafluoroethylene, has a smooth surface in the order of magnitude of crystallization nuclei.

It is advantageously provided that the exhaust aftertreatment agent is an aqueous urea solution, in particular AdBlue. An aqueous urea solution is an exhaust aftertreatment agent whose residues form crystals upon evaporation.

According to a development of the invention, it is provided that the connection element projects with a section into the mixing chamber. By protruding in the section this remains moist for a long time after dosing the aqueous urea solution, so that crystals formed on the surface, in particular by a sub-purge of the crystals, are dissolved. The section projects into the mixing chamber in such a way that an axis of symmetry of the supply of the exhaust gas aftertreatment agent into the mixing chamber is not surmounted. An exhaust gas aftertreatment agent spray from the feed, in particular a metering valve of the feed, thus does not strike the section of the connection element directly.

In an advantageous embodiment of the invention it is provided that the connection element is a hose, in particular a hose nozzle. Of the Hose is preferably a tube made of polytetrafluoroethylene (Teflon hose).

In particular, it is provided that the inner diameter of the connecting element 0.5 to 2 mm, in particular 2 mm in size. The

Connecting element is preferably a hose nozzle made of PTFE with an outer diameter of 4 mm and an inner diameter of 2 mm.

Finally, it is advantageously provided that the connection element runs upstream to a check valve. Preferably, the connection element and the upstream non-return valve (approximately 0.15 bar) are installed in a, the mixing chamber having, preferably made of plastic holding body. The spray of the feed and an axis of symmetry, which dictates the direction of flow of the compressed air in the connecting element, in particular form an angle of 45 °.

Brief description of the drawings

The drawings illustrate the invention with reference to an embodiment. It shows:

Figure 1 is a simplified functional diagram of a device for the metered injection of an exhaust gas aftertreatment agent-air mixture in an exhaust system and

FIG. 2 shows a mixing chamber of the device shown in FIG.

Embodiment (s) of the invention

1 shows a functional diagram of a device 1 for the metered injection of an exhaust aftertreatment agent-air mixture an exhaust system 2 of an internal combustion engine, not shown, of a motor vehicle. The device 1 has a dosing module 3 with a holding body 4, in which a mixing chamber 5 is formed. In the mixing chamber 5 is an exhaust gas aftertreatment agent-air mixture, which via a spray tube 6 a the metering module 3 downstream injection device 7 injected into the exhaust stream (arrow 8) of the exhaust system 2. The injection takes place in the direction of the exhaust gas flow (arrow 8) in front of an SCR catalyst 9 of the exhaust system 2. The two components of the exhaust aftertreatment agent-air mixture are the metering module 3 on two different paths, a compressed air line 10 for the air and a supply 11 for the exhaust aftertreatment agent, introduced by means of a conveyor module 11 'in the mixing chamber 4. The path of the air leads from a pressurized air reservoir 12 via the compressed air line 10 and arranged in the compressed air line 10 air control valve 13 to a arranged in the holding body 4 check valve 14, to which directly a connecting element 15 for connecting the compressed air line 10 to the mixing chamber. 5 followed. In the path of the exhaust aftertreatment agent, the exhaust gas aftertreatment agent, driven by a feed pump 17 configured as a membrane pump 16, is sucked from a storage container 19 via a suction line 18 and via a

Pressure line 20 a metering valve 21 of the dosing 3 feeds that metered the exhaust aftertreatment agent in the downstream mixing chamber 5. For venting the pressure line 20 is connected via a vent line 22 to the reservoir 19 for the exhaust aftertreatment agent. In the vent line 22, a vent valve 22 'is arranged. The

Air control valve 13, the feed pump 17 and the metering valve 21 are driven by a control unit 23. For this purpose, the air control valve 13 is connected via a first control line 24, the feed pump 17 via its second control line 25 and the metering valve 21 via a third control line 26 to the control unit 23.

This results in the following function of the device 1 for the metered injection of exhaust aftertreatment agent-air mixture into the exhaust system 2 of the internal combustion engine: For the metered injection of a mixture of air and an aqueous urea solution as exhaust aftertreatment agent-air mixture in the exhaust system 2 is air via the compressed air line 10 from the air reservoir 12 and aqueous urea solution as

Exhaust gas aftertreatment agent introduced from the reservoir 19 via the feed 11 into the mixing chamber 5 of the metering module 3. There, both components are mixed together and then on the spray tube. 6 the injection device 7 injected into the exhaust gas flow (arrow 8) of the exhaust system 2. In order to avoid or at least reduce crystallization of the urea in the mixing chamber 4 and the compressed air line 10, the Duckluftleitung 10 is connected to the check valve 14 via a connection element 15 made of a material having a low surface tension to the mixing chamber 5. The connection element 15 acts as insurmountable barrier for the crystals on their way from the mixing chamber 5 into the compressed air line 10.

FIG. 2 shows the dosing module 3 in the region of the holding body 4 made of plastic with the mixing chamber 5 formed in the holding body 4 in detail. In the path of the air, the compressed air line 10 is not shown connected via a connection device 27 to the built-in holding body 4 check valve 14. The check valve 14 is designed either as a poppet valve with spring preload or Ventsil. Between the check valve 14 and the mixing chamber 5 formed as a hose nozzle 28 connecting element 15 is arranged. The hose nozzle 28 is made of polytetrafluoroethylene. It has an inner diameter of 2 mm with an outer diameter of 4 mm. The hose nozzle 28 protrudes with its portion 29 into the mixing chamber 5. In this case, the portion 29 protrudes into the mixing chamber 5 only so far that it does not project beyond an axis of symmetry 30 of the outlet channel of the metering valve 21. The discharge channel runs along the symmetry axis 30. The result is an approximately straight spray along the axis of symmetry 30. The axis of symmetry 30 and an axis 31 of the hose nozzle 28 are arranged at an angle of 45 ° to each other, both axes 30, 31 in one central area of the mixing chamber 5 meet. On a side of the holding body 4 opposite to the outlet of the metering valve 21, the latter is connected via a connecting device 32 to the injection device 7, not shown.

By means of the arrangement with the connection element 15 shown in FIG. 2, a crystal formation of the exhaust gas aftertreatment agent formed in the region of the mixing chamber 5 of the urea solution is avoided. In particular, a "hiking" and setting of crystals or crystal nuclei from the mixing chamber 5 in the compressed air line 10 is avoided because the crystals or crystal nuclei due to the low Surface tension and a smooth inner surface 33 of the hose nozzle 28 can not fix on this inner surface 33 of polytetrafluoroethylene.

Alternatively to the formation of the connecting element 15 as a hose nozzle 28 made of PTFE, the connecting element 15 on its inner surface 33, a material with low surface tension, such as polytetrafluoroethylene, have or be coated with such a material. By projecting the connecting element 15 with its portion 29 into the mixing chamber 5, a sub-rinsing, and thus a rinsing, the crystals in the region of the connecting element 15 allows. The metering valve 21 is in particular a DNOX1 metering valve with a straight spray jet. The check valve 14 secures the path of the compressed air, in particular the pressure line 10, before setbacks of the exhaust aftertreatment agent. Furthermore, the check valve 14 in case of field failures also serves as a transport protection (for example, during transport to the service department).

Since polytetrafluoroethylene forms a very smooth surface, has a low surface tension, is insensitive to aggressive substances and has a very high temperature range for plastics, it is particularly well suited for use in a device 1 for metered injection of an exhaust aftertreatment agent-air mixture.

Claims

claims 1. A device for metered injection of an exhaust aftertreatment agent-air mixture in an exhaust system of an internal combustion engine, in particular for a motor vehicle, with a Mixing chamber are introduced into the air via a compressed air line and exhaust aftertreatment agent via a feed, characterized in that the compressed air line (10) via a connection element (15) made of a material having a low surface tension to the mixing chamber (5) is connected. 2. Device according to claim 1, characterized in that the connection element (15) has a smooth inner surface (33). 3. Device according to one of the preceding claims, characterized in that the material of the connecting element (15) is plastic. 4. Device according to one of the preceding claims, characterized in that the material of the connecting element (15) Polytetrafluoroethylene, in particular Teflon, is. 5. Device according to one of the preceding claims, characterized in that the exhaust gas aftertreatment agent is an aqueous urea solution, in particular AdBlue. 6. Device according to one of the preceding claims, characterized in that the connection element (15) projects with a portion (29) in the mixing chamber (5). 7. Device according to one of the preceding claims, characterized in that the connecting element (15) is a hose, in particular a hose nozzle (28). 8. Device according to one of the preceding claims, characterized in that the inner diameter (D) of the connecting element (15) is 0.5 to 2 mm, in particular 2 mm in size. 9. Device according to one of the preceding claims, characterized in that the connection element (15) upstream to a check valve (14).