DE102011087288A1 - Exhaust gas aftertreatment system and method for introducing a reducing agent into an exhaust passage of an internal combustion engine - Google Patents

Abstract

The invention relates to an exhaust aftertreatment system 10 and a method for introducing a reducing agent 42 into an exhaust passage 20 of an internal combustion engine 5. The exhaust aftertreatment system 10 comprises a reservoir 40, a metering pump 55, a mixing chamber 70 and a compressed gas supply 30. The metering pump 55 brings the reducing agent 42 from the storage tank 40 in the mixing chamber 70, wherein the compressed gas supply 30, a gas 33 so introduces into the mixing chamber 70, that the reducing agent 42 is atomized. The mixing chamber 70 is spaced from the metering pump 55, wherein the metering pump (55) supplies the mixing chamber (70) via a reducing agent line (60) with reducing agent (42). The mixing chamber 70 is arranged directly on an exhaust-carrying region of the exhaust gas duct 20. The metering of the reducing agent 42 to the exhaust duct 20 is effected by the metering pump 55.

Description

State of the art

The invention relates to an exhaust aftertreatment system and a method for introducing a reducing agent into an exhaust passage of an internal combustion engine according to the preamble of the independent claims.

For the aftertreatment of the exhaust gases of internal combustion engines, in particular for the aftertreatment of nitrogen oxides in the exhaust gas, exhaust aftertreatment systems are known in which a reducing agent, usually aqueous urea solution is metered into the exhaust duct of the internal combustion engine, wherein ammonia is formed from the aqueous urea solution by hydrolysis in the exhaust duct. By selective catalytic reduction, the nitrogen oxides are converted by the ammonia to environmentally harmless substances such as nitrogen and water. From the DE 19856366 an exhaust aftertreatment system is known in which aqueous urea solution and compressed air are supplied via a pump to a mixing chamber, the urea solution is atomized by means of the compressed air in the mixing chamber and the aerosol is metered by means of an injection valve in the exhaust passage.

epiphany

The exhaust aftertreatment system according to the invention and the method for introducing a reducing agent into an exhaust passage of an internal combustion engine with the features of the independent claims have the advantage that the pump are designed as a metering pump, wherein the promotion and a demand-based metering of the reducing agent to the mixing chamber or to the exhaust passage through the Metering pump takes place. In this case, according to the invention, the metering pump is valve-free connected via a reducing agent line to the exhaust passage of an internal combustion engine. The combination of delivery and metering functions by means of a metering pump can reduce the complexity and thus the costs for the exhaust gas aftertreatment system, since an additional metering unit can be dispensed with. By virtue of the valve-free connection of the metering pump to the exhaust passage, the system is "ice-pressure-proof", that is, if reducing agent in the reducing agent line freezes, it is possible for this reducing agent to expand without damaging components of the exhaust aftertreatment system. This can be realized by an elastic reducing agent line as well as by a volume compensation, since the reducing agent can optionally extend over the end of the reducing agent line in the direction of the mixing chamber or the exhaust gas passage. Due to the spatial separation of the mixing chamber and metering pump, this is not exposed to the high thermal load through the exhaust passage, while the mixing chamber is heated in an advantageous manner by the exhaust passage. Due to the distance-free arrangement of the mixing chamber on the exhaust duct can be dispensed with an additional line which connects the mixing chamber and the exhaust duct. Furthermore, the mixing chamber can be heated by the exhaust gas channel, for example to promote evaporation of the reducing agent or to melt deposits of the reducing agent in the mixing chamber.

The measures listed in the dependent claims advantageous refinements and improvements of the specified exhaust aftertreatment system and the specified method are possible.

An advantageous development is that the reducing agent line, at least in an opening into the mixing chamber section, is designed as a capillary. Due to the high adhesion forces between the liquid reducing agent and the wall of the capillary, an uncontrolled entry of the reducing agent from the reducing agent line into the mixing chamber is avoided. Thus, only reducing agent enters the mixing chamber, if the reducing agent in the capillary is additionally set under a, compared to the pressure in the mixing chamber, increased pressure. Furthermore, the free surface of the reducing agent with respect to the interface to the outlet opening in the mixing chamber is small, so that there is only a slight evaporation of the reducing agent.

It is particularly advantageous if a throttle is arranged in the reducing agent line between the metering pump and the mixing chamber. Through the throttle pressure fluctuations in the reducing agent line can be damped, so that no unwanted metering of reducing agent into the mixing chamber.

A further advantageous development is that heating means, in particular an exhaust gas are provided in the exhaust passage, which heat the mixing chamber to a temperature above a melting temperature of crystallization of the reducing agent. By the heating means, such as an electrical resistance heater, the mixing chamber can also be heated to a temperature above the melting temperature of crystallization of the reducing agent in operating points of the internal combustion engine in which the heat supplied by the exhaust gas of the internal combustion engine alone is insufficient. Thus, a malfunction of the exhaust aftertreatment system by crystal formation in the mixing chamber in all Operating points of the internal combustion engine safely prevented.

A further advantageous development is that conveying means are provided, which convey the reducing agent, in particular in a shutdown request for the internal combustion engine, from the reducing agent line in the reservoir. By the funding, in particular of the metering pump different funding, the reducing agent from the reducing agent line can be promoted back into the reservoir, which can be dispensed with a freeze-resistant design of the system and the components of the system of inexpensive materials, such as simple polymer materials, can be produced ,

A further advantageous development is that the mixing chamber is connected via a spray tube with an exhaust passage of an internal combustion engine. Via a spray tube, the atomized reducing agent can be supplied to the exhaust passage such that the exiting reducing agent does not deposit on the walls of the exhaust passage. By a targeted supply of the reducing agent on the spray tube also a good uniform distribution of the reducing agent is achieved over the cross section of the exhaust passage, whereby the conversion rate can be improved in a downstream catalyst.

Furthermore, it is advantageously provided that in a compressed gas line, which connects the compressed gas supply and the mixing chamber, a valve, in particular a check valve, is arranged. About the valve, the compressed gas supply to the mixing chamber can be interrupted or opened as needed, whereby the demand for compressed gas, compared to a continuous supply of the mixing chamber with compressed gas, is reduced. Particularly advantageous in this case is the use of a check valve, which additionally prevents backflow of the reducing agent from the mixing chamber into the pressurized gas supply.

It is particularly advantageous if the valve in the compressed gas supply and the metering pump are controlled by a common control unit, as can be the amount of supplied compressed gas ideally adapted to the supplied by the metering amount of the reducing agent.

drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. In the 1 and 2 the same components or components with the same function with the same reference numerals.

1 shows a first embodiment of an exhaust aftertreatment system according to the invention.

In 2 an alternative embodiment of an exhaust aftertreatment system according to the invention is shown.

3 shows a further alternative embodiment of an exhaust aftertreatment system according to the invention.

4 shows a further alternative embodiment of an exhaust aftertreatment system according to the invention.

Embodiments of the invention

In the 1 is an exhaust aftertreatment system according to the invention 10 shown. A storage container 40 for a reducing agent 42 is over a line 43 . 45 with a delivery unit 50 connected. In the line 43 . 45 is a filter 44 arranged. The delivery unit 50 includes a metering pump 55 as well as a pre-filter 52 , The delivery unit 50 is via a reducing agent line 60 with a first entrance 71 a mixing chamber 70 connected. Here is the delivery unit 50 spatially from the mixing chamber 70 separated. The mixing chamber 70 has a second entrance 72 on, over which a pressurized gas supply 30 to the mixing chamber 70 connected. The compressed gas supply 30 includes a pressurized gas source 32 from which a gas under pressure 33 via a supply line 34 . 36 the mixing chamber 70 can be supplied. In the supply line 34 . 36 is a valve 35 arranged, with which the compressed gas source 32 from the mixing chamber 70 can be separated. The mixing chamber 70 has a mixing room 75 in which the supply line 34 . 36 and the reducing agent line 60 lead. Between the first entrance 71 the mixing chamber 70 and the mixing room 75 are in the reductant line 60 a filter 74 and a throttle 73 arranged. From the mixing room 75 leads a spray pipe 77 in an exhaust duct 20 an internal combustion engine 5 , where the mixing chamber 70 or the mixing room 75 directly on an exhaust-carrying region of the exhaust gas passage 20 are arranged. In the exhaust gas flow direction downstream of the spray tube 77 is a device 25 for exhaust aftertreatment in the exhaust duct 20 arranged. A control unit 80 is via a signal line 82 with the dosing pump 55 of the delivery unit 50 connected. The control unit 80 is over another signal line 84 with the valve 35 connected. The dosing pump 55 of the delivery unit 50 is valve-free with the exhaust duct 20 connected, ie between the Output of the dosing pump 55 and the exhaust duct no valve is arranged, the metering pump 55 however, even a known pressure-side valve may terminate a compression space in the metering pump 55 exhibit.

The exhaust gas of the internal combustion engine 5 flows through the exhaust duct 20 to the device 25 for exhaust gas aftertreatment. To the effectiveness of the device 25 to increase the exhaust aftertreatment, can over the spray tube 77 a reducing agent 42 in the exhaust duct 20 exhaust duct 20 be metered. The activation of the exhaust aftertreatment system 10 done by the controller 80 , via which the metering pump 55 of the delivery unit 50 is controlled. In this case, the reducing agent 42 from the reservoir 40 over the line 43 to a first filter 44 promoted, are filtered out of the reducing agent particles and impurities. About the line 45 becomes the reducing agent 42 continue to the delivery unit 50 promoted. In the delivery unit 50 flows through the reducing agent 42 another filter 52 , in which again impurities and particles from the reducing agent 42 be filtered out, and reaches the metering pump 55 , The dosing pump 55 measures in dependence of the signal of the control unit 80 an amount of the reducing agent 42 and promotes this amount of reducing agent 42 via the reducing agent line 60 to the first entrance 71 the mixing chamber 70 , In the mixing chamber 70 flows through the reducing agent 42 another filter 74 and a throttle 73 before putting it in the mixing room 75 entry. In the mixing room 75 becomes the reducing agent 42 by means of a gas 33 atomized, with the supply of gas 33 over a line 36 which is done with a second input 72 the mixing chamber 70 connected is. To the second entrance 72 the mixing chamber 70 is the compressed gas supply 30 connected, the gas 33 from the compressed gas source 32 , For example, a compressed air reservoir, via the line 34 . 36 to the mixing room 75 the mixing chamber 70 flows. This is the gas 33 , preferably compressed air, at a pressure greater than that in the exhaust passage 20 or in the mixing room 75 increased pressure, for example, a pressure between 5 and 20 bar. To the compressed gas source 32 from the mixing chamber 70 to disconnect, the line can 34 . 36 through a valve 35 which is via the control unit 80 is controlled, the connection between the compressed gas source 32 and mixing chamber 70 close. In particular, via the common control of the valve 35 and the dosing pump 55 via the control unit 80 also the need of the gas 33 for atomizing the reducing agent 42 to the through the metering pump 55 to the mixing chamber 70 or to the mixing room 75 supplied amount of the reducing agent 42 be adjusted. The atomized reducing agent 42 , in particular an aerosol of the reducing agent 42 , gets out of the mixing room 75 over the spray tube 77 the exhaust duct 20 supplied there and supports the exhaust aftertreatment in the device 25 for exhaust aftertreatment. As a reducing agent 42 find, for example, aqueous urea solution or fuel, especially diesel fuel, for the reduction of nitrogen oxides use. The control of the valve 35 , For example, a solenoid valve is carried out electrically, but can also be done mechanically, pneumatically or hydraulically. The activation of the dosing pump 55 is also preferably electrically, but is not limited to electrical drive sources.

In a particularly simple embodiment, the filters 44 . 52 . 74 , especially the filters 52 and 74 , at least partially omitted. Instead of the throttle 73 in the reducing agent line 60 can also use the entire reducing agent line 60 or at least the one in the mixing room 75 opening part of the reducing agent line 60 be designed as a capillary. In a very simplified embodiment, the throttle 73 completely eliminated.

In 2 is another embodiment of an exhaust aftertreatment system according to the invention 10 disclosed. One directly on the exhaust duct 20 arranged mixing chamber 70 has 2 entrances 71 . 72 on, with the mixing chamber above the first entrance 71 through the reducing agent line 60 with the delivery unit 50 connected is. In addition, the second entrance 72 the mixing chamber 70 in this embodiment via a second line 34 for the gas 33 with the delivery unit 50 connected. The delivery unit 50 includes the dosing pump 55 with which the reducing agent 42 from the reservoir 40 the mixing chamber 70 can be supplied. Furthermore, the delivery unit has 50 a compressed gas supply 30 with another pump 90 on, with the other pump 90 over a line 92 connected to the environment. At the other pump 90 is a drive unit 91 , For example, an electric motor arranged. In the line 92 is an air filter 29 arranged. The administration 34 which the further pump 30 with the mixing room 75 the mixing chamber 70 connects, includes a storage volume 37 as well as another filter 38 to remove impurities from the compressed gas 33 filter out. The delivery unit 50 is over a line 43 . 45 with the reservoir 40 for the reducing agent 42 connected, wherein from the reducing agent line 60 which the metering pump 55 of the delivery unit 50 with the mixing room 75 the mixing chamber 70 connects, a return line 57 . 59 branches, which for the return of the reducing agent 42 into the pipe 45 in front of the dosing pump 55 empties. In the return line 57 . 59 is a first, preferably electrically switchable, valve 53 and a check valve 54 arranged. A control unit 80 is via a first signal line 82 with the metering 55 and via a second signal line 84 with the other pump 90 or the drive unit 91 the other pump 90 connected.

For dosing the reducing agent 42 becomes the metering pump 55 via the control unit 80 controlled, which the reducing agent 42 to the mixing room 75 the mixing chamber 70 promotes. At the same time, the control unit 80 the other pump 90 directly or by means of the drive unit 91 controlled, causing the mixing chamber 75 according to the amount of reducing agent supplied 42 an appropriate amount of gas 33 , in particular compressed air, is supplied, with which the reducing agent 42 in the mixing room 75 is atomized. In this first, hereinafter referred to as normal operation, operating state is the valve 53 closed, reducing the return line 57 . 59 is interrupted and a return flow of the reducing agent 42 via the return line 57 . 59 is prevented. Furthermore, the return line 57 . 59 also through the check valve 54 interrupted, so as not to bypass the metering pump 55 produce, so no reducing agent 42 , For example, by a pressure increase in the reservoir 40 at the dosing pump 55 over into the mixing chamber 70 can flow. By the demand-based supply of reducing agent 42 and from that for atomizing the reducing agent 42 required gas 33 an unnecessary delivery of fluids is avoided, thereby improving the exhaust aftertreatment system 10 is particularly energy efficient. Exists during normal operation of the exhaust aftertreatment system 10 a shutdown request for the internal combustion engine 5 , so become parts of the exhaust aftertreatment system 10 , in particular the mixing chamber 70 and the reducing agent line 60 emptied. This is the valve 53 open. About the further pump 90 or the storage volume 37 becomes the mixing room 75 pressurized gas 33 supplied, which is the reducing agent 42 in the mixing chamber 70 and in the reducing agent line 60 pushes back. By the gas 33 becomes the reducing agent 42 via the return line 57 . 59 and the wires 45 . 43 back to the reservoir 40 promoted. The check valve opens 54 by the pressure of the gas 33 or of the backflowing reducing agent 33 , whereby the connection over the return line 57 . 59 is released.

In 3 is another, alternative embodiment of an exhaust aftertreatment system according to the invention 10 shown. The structure largely corresponds to the structure according to 1 , so that in the following only the differences will be discussed. The storage tank 40 for the reducing agent 42 is via lines 43 . 45 with the delivery unit 50 connected, which in turn via the reducing agent line 60 with the first entrance 71 the mixing chamber 70 are connected. The mixing chamber 70 has a mixing room 75 which is within an exhaust gas leading portion of the exhaust passage 20 is arranged. A continuation of the reducing agent line 60 in the mixing chamber 70 has a filter 74 and a throttle 73 , preferably a supercritical throttle, which is located between the first input 71 the mixing chamber 70 and the mixing room 75 are arranged. The mixing room 75 is via a pressurized gas supply 30 , which are connected to the second entrance 72 the mixing chamber 70 connected to a pressurized gas 33 acted upon, between the second input 72 and the mixing chamber a filter 38 , a throttle 79 and a check valve 39 are arranged. At the mixing room 75 are heating means 78 arranged in the form of an electrical heating resistor with which the mixing chamber 75 can be heated additionally. The delivery unit 50 points next to the dosing pump 55 a return line 57 . 59 on, in which a Rücksaugpumpe 58 is arranged. The return line 57 . 59 sets a bypass to the dosing pump 55 wherein the reducing agent 42 from the reducing agent line 60 through the suction pump 58 via the return line 57 . 59 and the wires 45 . 43 with the reservoir 40 connected is. The control unit 80 is via a first signal line 82 with the dosing pump 55 connected. Via a second signal line 84 is the control unit 80 with the valve 35 in the pipe 34 . 36 which the compressed gas source 32 with the mixing room 75 the mixing chamber 70 connects, connected. A third signal line 86 leads from the controller 80 to the suction pump 58 ,

The metering of the reducing agent 42 is analogous to the comments on 1 and 2 , Since, when using reducing agents which contain soluble substances, for example aqueous urea solution, crystallization of these substances may occur, the reducing agent may cause 42 leading areas of the exhaust aftertreatment system, for example in the mixing chamber 70 , especially in the mixing room 75 in the spray tube 77 , Deposits and / or crystallizations forming the fluidic connection from the reservoir 40 to the exhaust duct 20 reduce in cross-section or clog completely, resulting in a functional impairment up to the failure of the exhaust aftertreatment system 10 can lead. By the arrangement of the mixing room 75 the mixing chamber 70 in the exhaust gas leading portion of the exhaust passage 20 the exhaust gas can be the mixing chamber 70 , especially the mixing room 75 the mixing chamber 70 , in certain operating states of the internal combustion engine 5 heat so far that such crystallizations melt and release the original cross-section of the fluidic connection again. This effect may be due to additional heating means 78 as an electrical resistance heater reinforced or on Operating conditions of the internal combustion engine 5 be extended, in which the over the exhaust of the internal combustion engine 5 supplied heat alone is not sufficient to melt the crystallization or decomposition of the deposits. Corresponding additional heating means 78 can also in the embodiments too 1 . 2 and 4 according to the embodiment 3 be integrated. In a simple embodiment eliminates the additional heating means 78 and the mixing chamber 70 or the mixing chamber 75 as well as the spray tube 77 be alone by the heat of the exhaust gas in the exhaust duct 20 heated so that it comes to melting the crystallization or decomposition of the deposits.

In normal operation, the return line 57 . 59 through the suction pump 58 closed, so that no bypass of the metering pump 55 is possible. At a shutdown request of the internal combustion engine 5 becomes the reducing agent 42 from the reducing agent line 60 through the suction pump 58 back to the reservoir 40 promoted.

Alternatively, the suction pump 58 or a Rücksaugfunktion also in the metering pump 55 be integrated, reducing the return line 57 . 59 can be omitted.

4 shows a further embodiment of an exhaust aftertreatment system according to the invention. The embodiment according to 4 differs from the embodiment according to 2 only in so far as that the further pump 90 not in the delivery unit 50 integrated, but the other pump 90 , as well as with the other pump 90 in a directly functional context air filter 29 and / or the optional storage volume 37 as well as the further filter 38 outside the delivery unit, in particular spatially separated from the delivery unit, is arranged. The further pump 90 is from a drive unit 91 driven, which is for example an electric motor. The function largely corresponds to the exemplary embodiment 2 , however, is the delivery unit 50 In manufacturing and assembly due to the smaller number of components less complex and the other pump 90 can at any point, in particular away from the exhaust duct 20 and or the reducing agent 42 be arranged.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely 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.

Cited patent literature

• DE 19856366 [0002]

Claims (10)

Exhaust aftertreatment system ( 10 ) for introducing a reducing agent ( 42 ) in an exhaust duct ( 20 ) an internal combustion engine ( 5 ), comprising a reservoir ( 40 ), a metering pump ( 55 ), a mixing chamber ( 70 ) and a pressurized gas supply ( 30 ), whereby the metering pump ( 55 ) the reducing agent ( 42 ) from the reservoir ( 40 ) into the mixing chamber ( 70 ), and wherein the pressurized gas supply ( 30 ) a gas ( 33 ) into the mixing chamber ( 70 ) that the reducing agent ( 42 ) is atomized, characterized in that the mixing chamber ( 70 ) from the dosing pump ( 55 ), wherein the metering pump ( 55 ) the mixing chamber ( 70 ) via a reducing agent line ( 60 ) with reducing agent ( 42 ) that the mixing chamber ( 70 ) directly on an exhaust-carrying region of the exhaust gas duct ( 20 ), wherein a metering of the exhaust gas channel ( 20 ) supplied reducing agent ( 42 ) through the metering pump ( 55 ) he follows. Exhaust aftertreatment system ( 10 ) according to claim 1, characterized in that the metering pump ( 55 ) valve-free with the exhaust duct ( 20 ) of the internal combustion engine ( 5 ) connected is. Exhaust aftertreatment system ( 10 ) according to claim 1 or 2, characterized in that the reducing agent line ( 60 ), at least in one in the mixing chamber ( 70 ) opening section, designed as a capillary. Exhaust aftertreatment system ( 10 ) according to one of claims 1 to 3, characterized in that in the reducing agent line ( 60 ) between the dosing pump ( 55 ) and the mixing chamber ( 70 ) a throttle ( 62 ) is arranged. Exhaust aftertreatment system ( 10 ) according to one of claims 1 to 4, characterized in that heating means ( 78 ), in particular of an exhaust gas in the exhaust gas channel ( 20 ) different heating means ( 78 ), which are the mixing chamber ( 70 ) to a temperature above the melting temperature of crystallization of the reducing agent ( 42 ) heat. Exhaust aftertreatment system ( 10 ) according to one of claims 1 to 5, characterized in that conveying means ( 55 . 58 ), in particular a Rücksaugpumpe ( 58 ), which are the reducing agent ( 42 ), in particular in a shutdown request for the internal combustion engine ( 5 ), from the reducing agent line ( 60 ) in the reservoir ( 40 ). Exhaust aftertreatment system ( 10 ) according to one of claims 1 to 6, characterized in that to the mixing chamber ( 70 ) a spray tube ( 77 ) is connected, wherein the spray tube and at least the mixing chamber ( 75 ) of the mixing chamber ( 70 ) in the exhaust duct ( 20 ) of the internal combustion engine ( 5 ) protrudes. Exhaust aftertreatment system ( 10 ) according to one of claims 1 to 7, characterized in that the pressurized gas supply ( 30 ) a compressed gas line ( 34 . 36 ) comprising a compressed gas source ( 32 ) and the mixing chamber ( 70 ), wherein in the compressed gas line ( 34 . 36 ) a valve ( 35 ), in particular a check valve, is arranged. Exhaust aftertreatment system ( 10 ) according to claim 8, characterized in that the valve ( 35 ) and the dosing pump ( 55 ) by a common control device ( 80 ). Method for introducing a reducing agent ( 42 ) in an exhaust duct ( 20 ) an internal combustion engine ( 5 ), wherein the reducing agent ( 42 ) from a storage container ( 40 ) in a mixing chamber ( 70 ), and wherein the reducing agent ( 42 ) in the mixing chamber ( 70 ) by a gas ( 33 ) is atomized, characterized in that the of the metering pump ( 55 ) spaced mixing chamber ( 70 ) via a reducing agent line ( 60 ) with reducing agent ( 42 ), that the mixing chamber ( 70 ) directly on an exhaust-carrying region of the exhaust gas duct ( 20 ), wherein the exhaust duct ( 20 ) supplied reducing agents ( 42 ) through the metering pump ( 55 ) is metered.

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