DE102011009216A1 - Reductant supply system for an SCR exhaust system - Google Patents

Abstract

A reducing agent storage system (34) for receiving a liquid reducing agent or a reducing agent solution (38) for an SCR exhaust system is disclosed, which has a reducing agent container (36) for receiving a liquid reducing agent or its solution (38), a filling line (50), whose first end (52) opens into the reducing agent container (36) and the second end (54) of which ends above a maximum filling level of the reducing agent container (36) and can be closed with a tank cap (56), a first vent line (60), which from an upper Section of the reducing agent tank (35) branches off and which opens into the filling line (50) above the maximum fill level of the reducing agent tank (36), and comprises a second vent line (64) whose first end (66) enters the reducing agent tank (36) with a certain Length protrudes and the second end (68) above a maximum filling level of the reducing agent container ters (36) opens into the filler line (50). For reliable functioning and refueling, the invention provides that a switching valve (62) is provided in the region of the opening of the first vent line (60) into the filler line (50), which is set up when the filler line (50) is closed with the tank cap (56) ) to open the first vent line (60) and to close the first vent line (60) with the filling line (50) open.

Description

The invention relates to a reducing agent supply system for receiving a liquid reducing agent, in particular an aqueous urea solution, for a working according to the principle of selective catalytic reduction (SCR for selective catalytic reduction) SCR exhaust system. The invention further relates to an SCR exhaust system having the reducing agent supply system and to a vehicle which is equipped with such an SCR exhaust system.

Internal combustion engines that are operated intermittently or predominantly with a lean air-fuel mixture produce nitrogen oxides NO _x (mainly NO ₂ and NO), which require NO _x -reducing measures. A motor measure for reducing the NO _x raw emission in the exhaust gas is the exhaust gas recirculation, in which part of the exhaust gas of the internal combustion engine is recirculated into the combustion air, whereby the combustion temperatures are lowered and thus the NO _x formation is reduced. However, the exhaust gas recirculation is not always sufficient to comply with legal NO _x limits, so in addition an active exhaust aftertreatment is required, which reduces the NO _x -Edemission. A known NO _x -Abgasnachbehandlung provides for the use of discontinuously operated NO _x storage catalytic converters, which store in lean operation (at λ> 1) nitrogen oxides in the form of nitrates and at short intervals with a rich exhaust gas atmosphere (λ <1) the stored nitrogen oxides Desorb and in the presence of existing in the rich exhaust reducing agent HC and H ₂ to nitrogen N ₂ reduce.

As a further approach to the conversion of nitrogen oxides in exhaust gases mlauflauffähiger internal combustion engines, the use of catalyst systems is known which operate on the principle of selective catalytic reduction (SCR). These systems comprise at least one SCR catalyst (also referred to as DeNOx catalyst), which converts the nitrogen oxides of the exhaust gas into nitrogen and water in the presence of a reducing agent continuously supplied to the exhaust gas, usually ammonia NH ₃ . In this case, the ammonia can be added in gaseous form or as aqueous ammonia solution to the exhaust gas stream. Alternatively, a NH ₃ -release precursor compound is often used, is obtained from the ammonia by way of thermolysis and hydrolysis. The currently most common precursor compound for ammonia is urea, which is used in the form of solid urea pellets or an aqueous urea solution. Often, a 32.5% by weight aqueous urea solution having a relatively low freezing point at about -11 ° C.

Regardless of the type of reducing agent used, it must be stored in the vehicle and carried along. In the case of liquid reducing agents or reducing agent solutions reducing agent containers are provided for this purpose, which are refueled via a filling line. If, after refueling with reducing agent, part of the amount of fluid filled remains in the filling line, freezing of the reducing agent in the filling line may occur at cold ambient temperatures. The frozen reducing agent can clog the filling line, which hinders further refilling, or possibly even damage the filling line by ice pressure.

From the DE 102 14 556 A1 a fuel system for a motor vehicle is known, which has, in addition to a fuel tank, a further tank for a reducing agent. Here, a simultaneous refueling is provided with both the fuel and with the reducing agent. The system includes an automatic stop means for refueling which stops receiving the fuel when the fuel tank is filled to a certain level and stops receiving the reducing agent when the reducing agent tank is filled to a certain level. The automatic shut-off device is realized by two combination vent valves, each having a float valve to interrupt the refueling. Depending on the arrangement of the float valves on the respective tank and depending on the position of the mouth of the respective filling lines to the tank, it may come after refueling to an at least partial retention of the tank liquid in the respective filling line.

The invention is based on the object of providing a concept for a reducing agent supply system for receiving liquid reducing agents or reducing agent solutions for SCR exhaust systems, in which the problems described above are overcome due to the reducing agent frozen in the filling line.

This object is achieved by a reducing agent supply system for receiving a liquid reducing agent or a reducing agent solution for an SCR exhaust system.

In the context of the present invention, the term "reducing agent" also means a precursor compound which releases the actual reducing agent (in particular ammonia NH ₃ ) through further process steps. In particular, in the context of the present invention, the liquid reducing agent or the liquid reducing agent solution also includes solutions of Urea or ammonia in a suitable solvent, especially water.

The reducing agent supply system according to the invention comprises a reducing agent container for receiving a liquid reducing agent or its solution, a filling line whose first end opens into the reducing agent container and whose second end ends above a maximum filling level of the reducing agent container and can be closed with a tank closure, a first venting line, the one from branches off the upper portion of the reducing agent container and which opens above the maximum level of the reducing agent container in the filling line, and a second vent line, the first end of which projects into the reducing agent container with a certain length and the second end opens above a maximum filling level of the reducing agent container in the filling line.

The reducing agent supply system according to the present invention is characterized in that a switching valve is provided in the region of the mouth of the first vent line in the filling line, which is adapted to open the first vent line with closed with the tank cap filling line and with open filling line to the first vent line close.

The essence of the invention is that on the switching valve, which is mechanically actuated by the fuel cap, a distinction between the modes refueling and driving and switching is.

According to an advantageous embodiment of the reducing agent supply system, this has at least one ventilation valve and / or ventilation valve, which can be arranged in particular in the tank cap and / or in the region of the second end of the filling line above the mouths of the first and the second vent line. The venting function of the valve ensures that there is no unduly high negative pressure in the system as a result of removal of the reducing agent, which could damage the system and in particular the reducing agent tank. If the valve is also equipped with a venting function, this ensures that no inadmissible overpressure in the system arises, for example as a result of a rise in temperature and / or due to a drop in the atmospheric air pressure outside the reducing agent tank.

For a purely mechanical and reliable function, a valve piston is provided in a preferred embodiment of the reducing agent supply system according to the invention in the switching valve, which is movable between an open position and a closed position.

Advantageously, a spring is arranged in the reducing agent supply system according to the invention in the switching valve, which presses the valve piston in the closed position. This ensures that the first breather line for the fueling mode is closed.

So that in the operating mode the ventilation can take place via the first vent line, in a preferred embodiment of the reducing agent supply system according to the invention the tank closure brings the valve piston against the spring force of the spring into the open position after closing the filling line.

For a structurally relatively simple construction of the reducing agent supply system according to the invention, the valve piston is arranged and displaceable substantially parallel to the longitudinal direction of the filling line. Alternatively, the valve piston may be arranged in its closed position substantially orthogonal to the longitudinal direction of the filling line and be tiltable from this position into its open position.

Another aspect of the present invention relates to an SCR catalyst system having at least one SCR catalyst and a reductant storage and delivery system having a reductant supply system according to the present invention.

The invention further relates to a vehicle with such an SCR catalyst system.

Further advantageous embodiments are the subject of the remaining dependent claims.

The invention will be explained in more detail in embodiments with reference to the accompanying drawings. Show it:

1 a schematic representation of an exhaust system with an inventive SCR catalyst system,

2 a schematic representation of a reducing agent supply system according to the invention,

3 an enlarged sectional view of a switching valve according to the invention according to a first embodiment of the invention in its open position,

4 an enlarged sectional view of the switching valve according to the invention 3 in its closed position,

5 an enlarged sectional view of a switching valve according to the invention according to a second embodiment of the invention in its open position,

6 an enlarged sectional view of the switching valve according to the invention 5 in its closed position.

1 shows a total of 10 designated motor vehicle, of which here only an internal combustion engine 12 with a connected exhaust system 14 is shown. In the internal combustion engine 12 it is an at least temporarily or permanently lean internal combustion engine, such as a diesel engine. He has in the example shown an injection system 16 that inject fuel directly into cylinders 18 of the internal combustion engine 12 injects. Likewise, the internal combustion engine 12 but work with a premixing. The combustion air is the internal combustion engine 12 via a suction channel 20 fed and optionally via a throttle device 22 For example, a throttle valve, be regulated.

An exhaust gas of the internal combustion engine 12 gets into an exhaust duct 24 the exhaust system 14 initiated, in which at a position close to the engine, a first catalyst 26 may be arranged, for example, an oxidation or 3-way catalyst.

The exhaust system 14 further comprises an SCR catalyst system operating on the selective catalytic reduction principle 28 that is an SCR catalyst 30 namely, a NO _x reduction catalyst, and a reductant storage and delivery system 32 having. The reductant storage and delivery system 32 includes a reductant supply system 34 containing a reducing agent tank 36 in which a liquid reducing agent or a liquid reducing agent solution (hereinafter only reducing agent 38 called) is stored. The reducing agent 38 is via a promotion line 40 by means of a pump 42 a metering device 44 supplied, which is designed in particular as a metering valve. The metering device 44 leads the reducing agent 34 the exhaust stream upstream of the SCR catalyst 30 to which nitrogen oxides NO _x by means of the reducing agent 38 catalytically converted to N ₂ and H ₂ O.

In the case of the SCR catalyst 30 supplied reducing agent is in particular ammonia NH ₃ , which is stored and metered in the form of a NH ₃ -splitting or releasing precursor compound. In particular, an aqueous ammonia solution or an aqueous urea solution is suitable as such a precursor compound. To cause the elimination or release of NH ₃ from the precursor compound is downstream of the metering device 44 a heatable hydrolysis device 46 in the exhaust duct 24 arranged. In the following it is assumed for the sake of simplicity that the reducing agent 38 is an aqueous urea solution without limiting the invention to these.

In operation of the vehicle 10 receives an engine control unit 48 via an indicated signal line operating data of the internal combustion engine 12 For example, engine speed, engine load, engine temperature, and the like. Depending on this data, the engine control unit controls 48 by means of stored maps various operating parameters of the internal combustion engine 12 , In particular, the injection system 16 so controlled that a predetermined amount of fuel per stroke in the cylinder 18 is injected. Optionally, the amount of combustion air supplied under the control of the throttle device 22 varied. In addition, a NO _x concentration of the exhaust gas by means of a not shown, in the exhaust duct 24 arranged NO _x sensor detected or characteristic map in dependence of the operating data of the internal combustion engine 12 determined. The engine control unit 48 determines based on the NO _x concentration a required, to be supplied to the exhaust stream reducing agent quantity and controls the pump 42 as needed so that the predetermined amount of reducing agent in the exhaust duct 24 is metered. Notwithstanding the illustrated embodiment, in which the control of the SCR exhaust system by the engine control unit 48 takes place, a separate control device may be provided for this purpose. Furthermore, the metered amount of reducing agent can also control the appropriately designed metering device 44 respectively.

In 1 For reasons of clarity, they are not elements of the reducing agent supply system 34 shown, which are required for refueling. Hereinafter, the reducing agent storage system of the present invention will be described 34 a little more detailed on the basis of 2 explained in more detail, in which, however, is dispensed with the presentation of the delivery line, pump and metering. The reductant storage system 34 with the reducing agent tank 36 for the reducing agent 38 has a filling line 50 on, their first end 52 into the reducing agent tank 36 at least partially protruding and its second end 54 above the maximum filling level of the reducing agent tank 36 ends. The second end 54 may in particular be arranged at a location accessible to a user of the vehicle.

At the second end 54 can the filling line 50 by means of a tank cap 56 be closed, as for example in the presentation of the 2 will be shown. To during the operation of the internal combustion engine 12 a ventilation of the reducing agent tank 36 to allow that due to the removal of reducing agent 38 is required is preferred in the tank cap 56 a ventilation valve 58 or a combined venting valve provided, which is known per se and therefore will not be further described here.

A first vent line 60 branches from a top of the reducing agent tank 36 and discharges above the maximum level of the reducing agent tank 36 in the filling line 50 , for example, near its second end 54 and the fuel cap 56 , In the area of the mouth of the first vent line 60 in the filling line 50 is a switching valve according to the invention 62 arranged in the representation of the 2 is indicated only schematically. Based on 3 to 6 below are two embodiments of the switching valve according to the invention 62 described in more detail.

A second vent line 64 is provided such that a first end 66 into the reducing agent tank 36 protrudes with a certain length. The first end 66 the second vent line 64 thus serves as a dip tube so that it can dip into the filled reducing agent. A second end 68 the second vent line 64 also opens above the maximum filling level of the reducing agent tank 36 in the filling line 50 , for example, slightly lower than the mouth of the first vent line 60 ,

The diameters of the first and the second vent line 60 . 64 For example, they are smaller than the diameter of the filling pipe 50 , Although in the 2 can not be shown at the separation points between reducing agent tank 36 and the filling line 50 and the two vent lines 60 . 64 suitable hose clamp connection and / or quick coupling systems may be provided for assembly reasons.

When refueling the reducing agent tank 36 is the fuel cap 56 removed and the filling line 50 is open. According to the invention is the tank cap 56 with the switching valve 62 such in mechanical operative connection that when removing the tank cap 56 the switching valve 62 the first vent line 60 closes. Thus, via the first vent line 60 no venting of the reducing agent tank 36 take place and the first vent line 60 forms a dead volume.

When refueling the reducing agent is running 38 over the filling line 50 into the reducing agent tank 36 , in which in the sequence the level of the reducing agent 38 increases. The venting of the reducing agent tank 36 takes over the second vent line 64 instead, through which the from the reducing agent tank 36 pushed out air to the mouth in the filling line 50 flows and from there via the filling line 50 from the reductant supply system 34 can escape.

If the level is the lower end of the first end serving as a dip tube 66 the second vent line 64 reached, closes the reducing agent 38 this vent path. With another refueling, the level now rises mainly in the filling line 50 and in the second vent line 64 which form a system of communicating tubes. The air above the reducing agent 38 in the reducing agent tank 36 is indeed compressible, so that the level of the reducing agent 38 in the reducing agent tank 36 increases slightly, but this increase is significantly lower than the increase in fill level in the fill line 50 and the second vent line 64 ,

The fueling process can now continue until the level of the reducing agent 38 at the top, the second end 54 the filling line 50 arrives. Further refueling can then no longer take place without danger of overflowing or running out. Once the fuel cap 56 again on the end of the filling line 50 is mounted, due to the mechanical operative connection between the tank cap 56 and the switching valve 62 the first vent line 60 opened again. The in the first vent line 60 and above the reducing agent 38 in the reducing agent tank 36 Existing and compressed air can now enter the filling line 50 flow out, causing the in the filling line 50 and the second vent line 64 existing reducing agents 38 also in the reducing agent tank 36 can run until the levels of the reducing agent 38 in the reducing agent tank 36 , the fill line 50 and the second vent line 64 have the same filling level. The filling line 50 and the second vent line 64 are now outside the reducing agent tank 36 no longer with reducing agent 38 filled, which could freeze depending on a cold environment.

Based on 3 and 4 is a first embodiment of the switching valve according to the invention 62 shown and described in more detail. The switching valve 62 is located in the area of the mouth of the first vent line 60 in the second, upper end 54 the filling line 50 that - as in 3 is shown - by means of the tank cap 56 is closed. The fuel cap 56 can by means of a suitable threaded connection 70 with the filling line 50 connected and sealed fluid-tight.

The switching valve 62 has a valve piston 72 on, which is substantially parallel to the longitudinal direction of the filling line 50 is arranged and displaceable. The fuel cap 56 pushes the valve piston 72 against a suitable spring 74 attached to a housing wall of the switching valve 62 is supported, so that one in the valve piston 72 located opening 76 the first vent line 60 opens and with the filling line 50 combines. The feather 74 may be as shown in the illustration a coil spring or other suitable spring. The vent is in the 3 through the arrow 78 indicated.

4 shows the switching valve 62 without the fuel cap 56 So with open filling line 50 , In this state ready for refueling, the spring pushes 74 the valve piston 72 to the outside, leaving the opening 76 in the valve piston 72 the area of the first vent line 60 leaves and this through the valve piston 72 is closed. The valve piston 72 is opposite the first vent line 60 with suitable seals 80 , For example, O-rings, sealed.

In contrast to the first embodiment, in the second embodiment of the switching valve according to the invention 62 ' that in the 5 and 6 shown is a valve piston 72 ' substantially orthogonal to the longitudinal direction of the switching valve 62 ' arranged. In the state with through the fuel cap 56 closed second end 54 the filling line 50 - like in the 5 is shown, is the valve piston 72 ' by means of the tank cap 56 tilted out of the vertical position and gives in the area of the head of the valve piston 72 ' a flow path for venting via the first vent line 60 free. This is on the tank cap 56 a lead 82 provided in the interior of the second end 54 the filling line 50 protrudes to push or tilt the valve piston in the open position. The possible vent is by the arrow 76 in the 5 indicated.

6 shows the switching valve 62 ' in the state ready for refueling, ie the fuel cap 56 is removed. By means of the spring 74 ' becomes the valve piston 74 ' against a housing wall of the switching valve 62 ' pressed and closes an opening provided there and the flow path for the vent.

LIST OF REFERENCE NUMBERS

10

vehicle

12

internal combustion engine

14

exhaust system

16

injection

18

cylinder

20

intake port

22

throttling device

24

exhaust duct

26

first catalyst

28

SCR-catalyst system

30

SCR catalyst

32

Reductant storage and delivery system

34

Reducing agent storage system

36

Reductant tank

38

reducing agent

40

delivery line

42

pump

44

metering

46

hydrolysis device

48

Engine control unit

50

filling line

52

first end of 50

54

second end of 50

56

filler cap

58

vent valve

60

first vent line

62, 62 '

switching valve

64

second vent line

66

first end of 64

68

second end of 64

70

threaded connection

72, 72 '

plunger

74, 74 '

feather

76

opening

78

Arrow (venting)

80

seals

82

head Start

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 10214556 A1 [0005]

Claims (9)

Reducing agent storage system ( 34 ) for receiving a liquid reducing agent or a reducing agent solution ( 38 ) for an SCR exhaust system comprising - a reducing agent tank ( 36 ) for receiving a liquid reducing agent or its solution ( 38 ), - a filling line ( 50 ), whose first end ( 52 ) into the reducing agent tank ( 36 ) and its second end ( 54 ) above a maximum filling level of the reducing agent tank ( 36 ) and with a fuel cap ( 56 ) is closable, - a first vent line ( 60 ) from an upper portion of the reducing agent tank ( 35 ) and the above the maximum level of the reducing agent container ( 36 ) in the filling line ( 50 ), and - a second vent line ( 64 ), whose first end ( 66 ) into the reducing agent tank ( 36 ) protrudes with a certain length and the second end ( 68 ) above a maximum filling level of the reducing agent tank ( 36 ) in the filling line ( 50 ), characterized in that a switching valve ( 62 . 62 ' ) in the region of the mouth of the first vent line ( 60 ) in the filling line ( 50 ) is provided, which is set up with the tank cap ( 56 ) closed filling line ( 50 ) the first vent line ( 60 ) and with the filling line open ( 50 ) the first vent line ( 60 ) to close. Reducing agent storage system ( 34 ) according to claim 1, characterized in that in the tank cap ( 56 ) and / or in the region of the second end ( 54 ) of the filling line ( 50 ) above the mouths of the first and second vent line ( 60 . 64 ) a ventilation valve and / or a ventilation valve ( 58 ) is arranged. Reducing agent storage system ( 34 ) according to claim 1 or 2, characterized in that the switching valve ( 62 . 62 ' ) a valve piston ( 72 . 72 ' ) which is movable between an open position and a closed position. Reducing agent storage system ( 34 ) according to claim 3, characterized in that in the switching valve ( 62 . 62 ' ) a feather ( 74 . 74 ' ) is arranged, which the valve piston ( 72 . 72 ' ) presses in the closed position. Reducing agent storage system ( 34 ) according to claim 4, characterized in that the tank closure ( 56 ) after closing the filling line ( 50 ) the valve piston ( 72 . 72 ' ) against the spring force of the spring ( 74 . 74 ' ) brings into the open position. Reducing agent storage system ( 34 ) according to one of the preceding claims 3 to 5, characterized in that the valve piston ( 72 ) substantially parallel to the longitudinal direction of the filling line ( 50 ) is arranged and displaceable. Reducing agent storage system ( 34 ) according to one of the preceding claims 3 to 5, characterized in that the valve piston ( 72 ' ) in the closed position substantially orthogonal to the longitudinal direction of the filling line ( 50 ) is arranged and tilted from this position in its open position. SCR catalyst system ( 28 ) with at least one SCR catalyst ( 30 ) and a reductant storage and delivery system ( 32 ) containing a reducing agent supply system ( 34 ) according to one of claims 1 to 7. Vehicle ( 10 ) with an SCR catalyst system ( 28 ) according to claim 8.

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