DE102021206351A1 - Process for exhaust aftertreatment of an internal combustion engine and exhaust aftertreatment system - Google Patents

Abstract

The invention relates to a method for the aftertreatment of exhaust gas from an internal combustion engine (10) of a motor vehicle, with at least one reducing agent being used to reduce NOx in the exhaust gas, with the reducing agent being stored in at least one storage tank (12), with the reducing agent being used in a circuit (14) conveyed at least out of the storage container (12) and into the storage container (12) and in which the storage container (12) can be heated by means of a heating device (16).In a method in which the reducing agent is kept in the liquid state for longer and in an energy-optimal manner can be stored without damage in the storage tank (12) without an electric heater, it is provided that the reducing agent is pumped into the storage tank (12) after the internal combustion engine (10) has been switched off and that the heating device (16) is heated by means of waste heat from at least one element of the motor vehicle is heated.

Description

The invention relates to a method for the aftertreatment of exhaust gas from an internal combustion engine of a motor vehicle, in which at least one reducing agent is used to reduce NO _x in the exhaust gas, in which case the reducing agent is stored in at least one storage tank, the reducing agent being circulated at least out of the storage tank and into the Reservoir is funded into it and the reservoir can be heated by a heater.

In addition, the invention relates to an exhaust aftertreatment system for an internal combustion engine, with at least one reservoir for storing a reducing agent for reducing NO _x in the exhaust gas of the internal combustion engine, with at least one injection system, with at least one circulation pump with at least one ventilation device, with at least one circuit for conveying the reducing agent at least from the reservoir and into the reservoir and with at least one heating device for heating the reservoir.

Due to the development of exhaust gas legislation, vehicle manufacturers are faced with the challenge of reducing engine raw emissions and purifying the exhaust gas that is still produced by means of appropriate exhaust gas aftertreatment. The level of legislation requires a reduction in nitrogen oxide emissions to a certain level, particularly for diesel vehicles. The reduction of nitrogen oxides is often achieved with Selective Catalytic Reduction (SCR) technology. In the process, NO _x is reduced to nitrogen and water vapour. Ammonia (NH3), ammonia in aqueous solution or urea in aqueous solution are generally used as the reducing agent. The reducing agent is injected into the exhaust system as part of the exhaust aftertreatment system by means of an injection system in order to reduce the nitrogen oxides there in the catalytic converter.

In modern diesel vehicles, the so-called AdBlue liquid has established itself as a reducing agent for reducing the NO _x concentration in the exhaust gas. The disadvantage of AdBlue liquid is that it freezes at -11 degrees Celsius. Since the AdBlue fluid contains > 60% water, there is a risk of volume expansion in the event of frost. In order to prevent damage caused by this volume expansion, the liquid must be heated by the vehicle electrical system battery when there is frost, as is customary in the prior art. The heating time is limited and depends on the battery charge.

the DE 10 2005 002 318 A1 tries to circumvent this problem by pumping the reducing agent in a circuit, even after dosing has already been completed, so that the reducing agent is prevented from freezing.

The invention is based on the object of specifying a method for exhaust gas aftertreatment of an internal combustion engine and an exhaust gas aftertreatment system in which the reducing agent can be kept in the liquid state for longer and in an energy-optimal manner or can be stored in the storage tank without damage without electrical heating.

This object is achieved in the present invention by the features of the characterizing part of claim 1 in that the reducing agent is pumped into the reservoir after the internal combustion engine is switched off and that the heating device is heated by waste heat from at least one element of the motor vehicle.

Ammonia (NH3), ammonia in an aqueous solution and/or urea in an aqueous solution can be used as the reducing agent. The reducing agent is preferably an AdBlue liquid. AdBlue liquids are known from the prior art. Ad-Blue consists of a mixture of demineralized water and around 32% urea.

The reservoir is a container that is suitable for accommodating the reducing agent. The reservoir is dimensioned in such a way that all of the reducing agent in the circuit can be stored in it. The circuit is to be understood as meaning a fluidic connection, in particular pipelines, through which the reducing agent can be conveyed out of the reservoir. In the circuit, the reducing agent can be conveyed to other units or elements of the vehicle. In particular, the reducing agent is conveyed via an injection system to the catalytic converter for the reduction of NO _x before it is at least partially conveyed back into the reservoir.

The reservoir can be heated by means of a heating device. The heating device is not, as is usual in the prior art, an electric heater, but in particular a heat exchanger which is designed to absorb waste heat from at least one element of the motor vehicle. An element of the motor vehicle is understood to mean any device of the vehicle that warms up during the course of the vehicle's operation, and more advantageously wise can be used to transfer the heat to the reservoir. Preferably, the elements are located in the vicinity of the reservoir, for example elements within or in the vicinity of the engine compartment.

This heat integration means that the storage container and, above all, the reducing agent are heated to a certain extent and freezing can thus be prevented. It is provided according to the invention that the circuit, ie the pipelines and other fluidic connections, are flushed completely so that there is no longer any reducing agent in the circuit. The reducing agent is then completely in the reservoir. In this way, there is no longer a risk that the reducing agent will freeze within the circuit. Flushing can be understood, for example, as ventilation of the circuit, in which the reducing agent in the circuit is conveyed into the reservoir by means of air.

The reservoir is preferably insulated so that the heat loss within the reservoir to the environment is as small as possible.

Further preferred configurations of the invention result from the remaining features mentioned in the dependent claims.

In a first embodiment of the method according to the invention, the reducing agent is initially circulated after the internal combustion engine has been switched off until the temperature of the reducing agent is in equilibrium with the engine temperature or with the temperature of the engine compartment. The reducing agent is consequently conveyed further past the warmer sections of the engine compartment, so that heat transfer can take place. With this additional thermal energy, the reducing agent can remain in the liquid state in the insulated storage tank for longer.

In order to be able to heat the reducing agent within the reservoir to a certain extent, it is provided in a further embodiment of the method according to the invention that the heating device is heated using waste heat from an engine cooling system of the motor vehicle. The heating device, for example in the form of a heat exchanger, can use the waste heat from the engine cooling system to heat the reservoir for the reducing agent or to keep it at a specific temperature level. It can be provided that a heating heat exchanger, as an element of the engine cooling system, is supplemented by an additional set of fins including a continuous spiral. Heat from the engine then travels through a line to the reservoir. The reservoir is expanded accordingly with a water-carrying heating coil, which can be immersed in the reservoir. A circulation pump can ensure demand-oriented circulation.

Additionally or alternatively, in a further embodiment of the method according to the invention, it is provided that the heating device is heated by means of waste heat from an oil cooler and/or from a transmission oil cooler of the motor vehicle. Analogously to the above embodiment, the waste heat from the oil cooler and/or the transmission oil cooler can also be used. In this case, it can be provided that the oil cooler and/or the transmission oil cooler of the internal combustion engine are supplemented by an additional disk pack including a continuous spiral. The waste heat then reaches the storage tank via a line, the storage tank being supplemented by a water-carrying heating coil as part of the heating device, with the heating coil being immersed in the tank. Only heat is transferred. There is no material transport between the line and the reservoir. A circulation pump ensures demand-oriented circulation.

In a further alternative or a further supplement, it is provided that the heating device is heated using waste heat from an exhaust system of the motor vehicle. In the same way as the options mentioned above, the heat is taken from the exhaust system of the internal combustion engine. The mufflers can be expanded with a water-carrying spiral inside the pot. Exhaust heat then reaches the storage tank via a line. The reservoir is correspondingly expanded to include a water-carrying heating coil that can be immersed in the reservoir. A circulation pump ensures demand-oriented circulation. This variant can be combined with the run-on time of the vehicle as part of a regeneration of the prescribed diesel particulate filter. Here, the thermal energy that has to be reduced when the motor vehicle is switched off shortly after regeneration of the soot particle filter can be released directly via the circuit to the reservoir.

The aforementioned object is also achieved by an aforementioned exhaust gas aftertreatment system for an internal combustion engine, with at least one reservoir for storing a reducing agent for reducing NO _x in the exhaust gas of the internal combustion engine, with at least one injection system, with at least one circulation pump, with at least one ventilation device, with at least a cycle to the För those of the reducing agent at least from the reservoir and into the reservoir and with at least one heating device for heating the reservoir. Provision is made for the exhaust gas aftertreatment system to be designed to carry out a method according to one of Claims 1 to 5. The above statements on the method according to the invention also apply correspondingly to the exhaust gas aftertreatment system according to the invention.

The injection system is designed to inject the reducing agent into the exhaust system as part of the exhaust aftertreatment system in order to reduce nitrogen oxides that have formed there in the catalytic converter. The circulation pump is used to pump the reducing agent in the circuit mentioned above. The venting device is designed to convey the reducing agent completely into the reservoir, the lines of the circuit being vented through the venting device, for example by means of air.

In a first embodiment of the exhaust gas aftertreatment system according to the invention, it is provided that the heating device is arranged inside the reservoir and that the heating device comprises a heat exchanger for absorbing waste heat from at least one element of the motor vehicle. The heating device can be designed, for example, as a liquid-carrying heating coil that can be immersed in the reservoir. Only heat is transferred through the heating device. A mass transport between the heat exchanger and the storage tank does not take place.

In order to accelerate possible thawing of the reducing agent, a further embodiment of the exhaust gas aftertreatment system according to the invention provides that the reservoir comprises a first reservoir and a second reservoir and that the first reservoir has a smaller volume than the second reservoir. Depending on the volume of the reservoir, a possible thawing process for the reducing agent can take more or less time. Defrosting time can be significantly reduced by using a first reservoir and a second reservoir. The first reservoir has a smaller volume than the second reservoir, so there is a main tank and a small auxiliary tank. The first, smaller reservoir is used to quickly thaw the reducing agent that is required immediately when the engine is started. The first reservoir can also be heated with an electric heater, since the amount of energy required is comparatively small. The thawing process takes a little longer in the larger second storage container. The second reservoir is not dependent on an electrical heating device, but can be heated with the available engine waste heat.

In order to further improve the flexibility of the exhaust gas aftertreatment system, a further embodiment of the exhaust gas aftertreatment system according to the invention provides that the reservoir is designed to be elastic, so that volume expansion is made possible. The reservoir is consequently designed to be stretchable. The reservoir can preferably withstand an expansion in volume of >10% in order to be able to compensate for the volume expansion of a possibly frozen reducing agent. This solution has the advantage that after the reducing agent has been conveyed into the reservoir, there is no risk of frost or damage and no electrical energy is required to heat the reducing agent.

In addition, in a further embodiment of the invention, it can be provided that the reservoir is designed spherically. The spherical configuration minimizes the surface area of the reservoir, so heat loss across the surface of the reservoir is also minimized.

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

• 1 eine schematische Darstellung eines Abgasnachbehandlungssystems mit der Nutzung der Abwärme eines Motorkühlsystems,
• 2 eine schematische Darstellung eines Abgasnachbehandlungssystems mit der Nutzung der Abwärme eines Ölkühlers,
• 3 eine schematische Darstellung eines Abgasnachbehandlungssystems mit der Nutzung der Abwärme eines Getriebeölkühlers und
• 4 eine schematische Darstellung eines Abgasnachbehandlungssystems mit der Nutzung der Abwärme eines Abgassystems.

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

• 1 a schematic representation of an exhaust aftertreatment system using the waste heat of an engine cooling system,
• 2 a schematic representation of an exhaust aftertreatment system using the waste heat of an oil cooler,
• 3 a schematic representation of an exhaust aftertreatment system using the waste heat of a transmission oil cooler and
• 4 a schematic representation of an exhaust aftertreatment system using the waste heat of an exhaust system.

1 shows the implementation of a method for exhaust gas aftertreatment of an internal combustion engine 10 of a motor vehicle, not shown here. A reducing agent is used to reduce NO _x in the exhaust gas. The reducing agent is stored in a storage tank 12 and can be discharged via a circuit 14 be conveyed out of the reservoir 12 and into the reservoir 12 . The storage container can be heated by means of a heating device 16 . In the present exemplary embodiment, the heating device works with the waste heat of an engine cooling system 18. In addition to the engine cooling system 18, in the area of the internal combustion engine 10, oil cooling systems in particular, such as an oil cooler 20 and a transmission oil cooler 22, but also the exhaust system 24 itself should be mentioned as heat sources.

For an exhaust gas aftertreatment system 26, an injection system 28 is also required, which is arranged in the circuit 14 of the reducing agent. The reducing agent is injected into the exhaust system 24 by means of the injection system 26 in order to reduce the nitrogen oxides there in the catalytic converter. The exhaust aftertreatment system also includes a circulation pump 30 and a ventilation system 32.

In the exemplary embodiment shown, after the internal combustion engine 10 has been switched off, the reducing agent in the existing circuit 14 is flushed, so that the liquid reducing agent is heated by the residual heat of the environment. The thermal energy is stored in the reducing agent. The flushing takes place in such a way that the reducing agent circulates in the circuit 14 , the circulation being driven by the circulation pump 30 or the ventilation system 32 . The circulation is continued until the temperature of the reducing agent is in equilibrium with the engine temperature or in equilibrium with the area around the engine.

As soon as equilibrium is reached, the circuit 14 is aerated, that is to say the circulation pump 30 conveys all of the reducing agent into the reservoir 12 and flushes the lines of the circuit 14 with air, for example. The lines and the injection system 28 are thus frost-proof since they are free of liquid reducing agent. If AdBlue is used as a reducing agent, for example, the freezing point is around -11 degrees Celsius.

Only the reservoir still contains liquid reducing agent after flushing. The reservoir 12 is thermally insulated in order to conserve the thermal energy for as long as possible. In addition, the heating device 16 is arranged inside the storage container 12 . The heating device 16 can be controlled by the vehicle electrical system as needed. The comparatively higher residual heat increases the initial temperature of the reducing agent, so that there is no risk of the reducing agent freezing if it is left standing overnight, for example.

The heating device 16 is heated by means of waste heat from the engine cooling system 18 of the motor vehicle. The heating device 16 includes a heat exchanger 34, which can use the waste heat from the engine cooling system 18 to heat the reservoir 12 of the reducing agent or to keep it at a specific temperature level. In this case, a heating heat exchanger, not shown here, as an element of the engine cooling system 18, is supplemented by an additional set of fins including a continuous spiral. Heat from the engine then passes through a line to the reservoir 12. The reservoir 12 is correspondingly expanded to include a water-carrying heating coil as part of the heat exchanger 34, which is immersed in the reservoir 12.

2 shows the embodiment analogous to 1 , whereby the waste heat for heating up the reservoir 12 is not taken from the engine cooling system 18, but from the oil cooler 20.

3 shows the embodiment analogous to the 1 and 2 , wherein the waste heat for heating up the reservoir 12 is not taken from the engine cooling system 18 or the oil cooler 20, but from the transmission oil cooler 22.

4 shows the embodiment analogous to the 1 , 2 and 3 , wherein the waste heat for heating the reservoir 12 is removed from the exhaust system 24. In addition, the storage container 12 is divided into a first storage container 36 and a second storage container 38 . The first reservoir 36 has a smaller volume than the second reservoir 38. In this way, a possible thawing of the reducing agent can be accelerated. Depending on the volume of the reservoir 12, a possible thawing process for the reducing agent can take more or less time. Defrosting time is reduced by dividing the reservoir 12 into two reservoirs 36,38. The first reservoir 36 has a smaller volume than the second reservoir 38 so that there is a main tank and a small auxiliary tank. The first, smaller reservoir 36 is used to quickly thaw the reducing agent that is required immediately when the engine is started. The first reservoir 36 can also be heated with an electric heater since the amount of energy required is comparatively small. In the larger, second storage container 38, the thawing process takes a little longer. The second reservoir 38 is not dependent on an electrical heating device, but can be heated by the heating device 16 with the available waste heat from the exhaust system 24 .

In this embodiment, the first reservoir 36 is designed to be elastic. In this way, a volume expansion of the first reservoir 36 is possible. The first reservoir 36 is thus designed to be stretchable. The first reservoir 36 can withstand an expansion in volume of >10% in order to be able to compensate for the volume expansion of a possibly frozen reducing agent. This solution has the advantage that after the reducing agent has been conveyed into the first reservoir 36 there is no risk of frost or damage and no permanent electrical energy is required to heat the reducing agent.

In addition, the first reservoir 36 is spherical in shape. The spherical configuration minimizes the surface area of the first reservoir 36 such that heat loss across the surface of the first reservoir 36 is also minimized.

Reference List

10

combustion engine

12

reservoir

14

cycle

16

heating device

18

engine cooling system

20

oil cooler

22

transmission oil cooler

24

exhaust system

26

exhaust aftertreatment system

28

injection system

30

circulation pump

32

ventilation system

34

heat exchanger

36

first reservoir

38

second reservoir

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was 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.

Patent Literature Cited

• DE 102005002318 A1 [0005]

Claims (10)

Method for exhaust gas aftertreatment of an internal combustion engine (10) of a motor vehicle, wherein at least one reducing agent is used to reduce NOx in the exhaust gas, wherein the reducing agent is stored in at least one storage tank (12), the reducing agent in a circuit (14) at least from the storage tank (12) is conveyed out and into the storage container (12) and in which the storage container (12) can be heated by means of a heating device (16), characterized in that the reducing agent is fed into the storage container (12) after the internal combustion engine (10) has been switched off. is promoted and that the heating device (16) is heated by means of waste heat of at least one element of the motor vehicle. procedure after claim 1 , characterized in that the reducing agent after switching off the internal combustion engine (10) is first promoted in the circuit (14) until the temperature of the reducing agent is in equilibrium with the engine temperature. procedure after claim 1 or 2 , characterized in that the heating device (16) by means of waste heat from an engine cooling system (18) of the motor vehicle is heated. Procedure according to one of Claims 1 until 3 , characterized in that the heating device (16) by means of waste heat from an oil cooler (20) and / or from a transmission oil cooler (22) of the motor vehicle is heated. Procedure according to one of Claims 1 until 4 , characterized in that the heating device (16) by means of waste heat from an exhaust system (24) of the motor vehicle is heated. Exhaust aftertreatment system (26) for an internal combustion engine (10), with at least one reservoir (12) for storing a reducing agent for reducing NOx in the exhaust gas of the internal combustion engine (10), with at least one injection system (28), with at least one circulation pump (30). at least one ventilation device (32), with at least one circuit (14) for conveying the reducing agent at least out of the storage container (12) and into the storage container (12) and with at least one heating device (16) for heating the storage container (12), characterized That the exhaust aftertreatment system (26) is designed to use a method according to one of Claims 1 until 5 to execute. Exhaust aftertreatment system (26) after claim 6 , characterized in that the heating device (16) is arranged within the reservoir (12) and that the heating device (16) comprises a heat exchanger (34) for absorbing waste heat of at least one element of the motor vehicle. Exhaust aftertreatment system (26) after claim 6 or 7 , characterized in that the reservoir (12) comprises a first reservoir (36) and a second reservoir (38) and that the first reservoir (36) has a smaller volume than the second reservoir (38). Exhaust aftertreatment system (26) according to one of Claims 6 until 8th , characterized in that the reservoir (12) is designed to be elastic, so that an expansion in volume is made possible. Exhaust aftertreatment system (26) according to one of Claims 6 until 9 , characterized in that the reservoir (12) is designed spherical.

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