WO2013072189A1

WO2013072189A1 - Method for stopping the operation of a metering device

Info

Publication number: WO2013072189A1
Application number: PCT/EP2012/071516
Authority: WO
Inventors: Peter Bauer
Original assignee: Emitec Gesellschaft Für Emissionstechnologie Mbh
Priority date: 2011-11-16
Filing date: 2012-10-30
Publication date: 2013-05-23
Also published as: DE102011118626A1

Abstract

The invention relates to a method for stopping the operation of a metering device (1) for metering a liquid additive in an exhaust gas treatment system (2) for cleaning the emissions of an internal combustion engine (3), comprising at least one line system (4), which interconnects a reservoir (5) for storing the additive and a feeding device (6) for feeding the additive to the exhaust gas treatment system (2). The additive can be conveyed through the line system (4) from the reservoir (5) to the feeding device (6) by way of a conveyor unit (7). Initially, in a step a) of the method, the internal combustion engine (3) is stopped. Subsequently, in a step b), at least one time interval is waited out. Next, in a step c), at least a partial emptying of the line system (4) toward the conveyor unit (7) is carried out after the first time interval. For step c), a penetrable flow path (13) from the exhaust gas treatment system (2) into the line system (4) is thereby opened up, and the line system (4) is ventilated via the flow path (13) during step c).

Description

Method for stopping the operation of a metering device

The invention relates to a method for stopping the operation of a metering device, with which a liquid additive can be supplied to an exhaust gas treatment device.

Exhaust treatment devices, in which a liquid additive is supplied, are also known in the automotive field. An exhaust gas purification process which is particularly frequently carried out in such exhaust gas treatment devices is the selective catalytic reduction (SCR) process, in which nitrogen oxide compounds in the exhaust gas are reduced with the aid of a reducing agent. The reducing agent used is preferably ammonia, which is not fed directly to the exhaust gas treatment device, but in the form of a reducing agent precursor. A particularly frequently used reducing agent precursor is urea-water solution. A 32.5 sodium urea -water solution is available as an additive for exhaust gas treatment devices under the trade name AdBlue ^®.

A problem in the provision of a liquid additive (in particular when it comes to reducing agents) is that this may optionally freeze. Liquid urea-water solution freezes, for example at temperatures of -H C. Such temperatures can occur in motor vehicles, especially during long periods of inactivity. By freezing the additive in a metering device, the metering device can be damaged because during freezing (especially with water-based additives) regularly an increase in volume occurs.

For this reason, it is known to heat metering devices for liquid additive when needed. Due to the high energy consumption is a heating during long breaks (for example, when a motor vehicle for several days or weeks) but not possible. One approach to avoid heating a metering device is to empty the metering device during operation stop. In this way it can be prevented that there is additive in the metering device which can freeze. However, a problem with emptying the metering device is that for this purpose a more complex technical design of the metering device is necessary on a regular basis. In addition, when emptying a metering device regularly occurs a loss of reducing agent, especially when the metering device is emptied into an exhaust treatment device through an injector. Based on this prior art, it is an object of the present invention to solve the technical problems described or at least alleviate. In particular, a particularly advantageous method for stopping the operation of a metering device should be presented.

These objects are achieved by a method according to the features of patent claims 1 and 8 and with a metering device according to the features of claim 9. Further advantageous embodiments of the invention are specified in the dependent formulated claims. The features listed individually in the claims are combinable with each other in any technologically meaningful manner and can be supplemented by explanatory facts from the description, wherein further embodiments of the invention are shown.

The invention relates to a method for stopping the operation of a metering device for metering a liquid additive into an exhaust gas treatment device for cleaning the exhaust gases of an internal combustion engine with at least one line system, which connects a tank for storing the additive and a supply device for feeding the additive into the exhaust gas treatment device, wherein the additive is conveyable through the conduit system from the tank to the delivery device with a conveying direction and the method comprises at least the following steps:

a) stopping the internal combustion engine;

b) waiting at least a first time interval; and

c) at least partial emptying of the line system against the conveying direction after the first time interval,

wherein for step c) a permeable flow path is released from the exhaust treatment device into the conduit system and during step c) the conduit system is vented via the flow path.

The liquid additive is preferably reducing agent and more preferably liquid urea-water solution. The metering device is suitable for conveying quantities of the liquid additive predetermined by a control unit into the exhaust gas treatment device. For this purpose, the metering device has at least one metering agent for the exact definition of the quantity supplied. A dosing agent may be a metering pump and / or a metering valve. In a metering valve, the amount supplied is determined over an opening time of the metering valve. With a dosing pump, the quantity supplied is determined by a pump movement of the dosing pump.

The piping system of the metering device is preferably divided into a suction section which extends from the tank to the pump and into a pressure section which extends from the pump to the supply device. The exhaust treatment device preferably includes an SCR catalyst in which the selective catalytic reduction process may be carried out together with the liquid additive (in this case preferably reducing agent and in particular urea-water solution). The described method is preferably carried out at each stop of operation of an internal combustion engine. The process steps a) to c) preferably proceed in the order specified by the letters a), b) and c).

When stopping an internal combustion engine in step a), the exhaust gas treatment in a connected

Exhaust treatment device and the metering device and the dosage of additive in the exhaust treatment device stopped. The stopping of the internal combustion engine and thus also the method according to the invention, normally takes place when a motor vehicle is parked. The stop of the internal combustion engine is characterized in particular by the completion of the combustion processes, at the same time the motor vehicle is at rest.

In step c), the line system is preferably completely emptied. By "emptying" is meant, in particular, that the additive is removed from the piping system or conveyed out. This happens contrary to the conveying direction. The additive flows during emptying at least in a portion of the conduit system opposite to the direction of promotion in regular operation. The emptying is preferably carried out in the tank in which the additive is stored and from which the conveying device had taken the additive for the addition. The additive is conveyed from the piping system into the tank during emptying. In this case, it is preferred that the amount of the additive (especially completely) located in the line system immediately before the stop of operation is reduced. It is particularly preferred that at least the region of the line system in the conveying direction following the pump (in particular up to the metering device) is emptied, so that a significant pressure drop takes place starting from the operating pressure of the additive. During emptying, another medium (for example air) is conveyed or sucked into the line system. The other medium replaces the additive (at least regionally) in the piping system. The other medium preferably does not freeze (in the case of the temperatures usually occurring during operation of the motor vehicle) and / or at least does not expand during freezing. The metering device or the pipe system can therefore no longer be damaged. When emptying against the conveying direction, the liquid additive present in the line system is preferably conveyed back into a tank for storing the additive, so that no loss of additive occurs by the method.

In order for the other medium to enter the piping system and replace the liquid additive, there exists a flow path into the piping system through which the other medium can be sucked / introduced into the piping system.

If a metering device is operated in such a way that the described method is used for the stop of operation, it is also expedient to first fill the metering device again with liquid additive at the start of operation of the metering device. The metering device with which the method described is carried out is therefore preferably designed to be filled with liquid additive at the start of operation.

By waiting for the first time interval in step b), it can be avoided that harmful substances are sucked into the pipeline system during the emptying in step c) for the pipeline system. Harmful substances are, for example, exhaust gases and / or other gases and / or vapors which occur during the operation or stoppage of operation of a motor vehicle and in particular during the operation or stoppage of an internal combustion engine. Harmful substances can produce deposits in the piping system which affect the metering accuracy and / or the performance of the system Affect conveyor. It would thus even be possible for such substances to at least partially block the line system.

A permeable flow path is in particular a path which is passable for a fluid (for example for the liquid additive or another medium which is sucked into the line system during emptying). The permeable flow path preferably extends from the exhaust treatment device into the conduit system through the delivery device. The permeable flow path is a fluid-communicable connection between the exhaust treatment device and the conduit system. In step c), the liquid additive in the line section is replaced by a medium which enters the line section via the permeable flow path. The medium is preferably gaseous and particularly preferably air or exhaust gas from the exhaust gas treatment device. Air in the exhaust treatment device differs from normal "ambient air" in that it has a reduced oxygen content and an increased carbon dioxide content. In addition, air in an exhaust treatment device or exhaust gas may also contain pollutants, such as carbon monoxide, nitrogen oxide compounds and / or soot particles.

By waiting for the first time interval (time delay), it is possible for certain pollutants in the exhaust gas treatment device to settle there, so that they are not sucked in when emptying the piping system. This can prevent these pollutants from entering the pipeline system. In particular, the occurrence of soot particles in the piping system can be prevented.

In addition, the method is advantageous if the supply device has a supply valve, which is opened before step c) and thus releases the permeable flow path. The feed valve is in particular opened only immediately before or at the beginning of step c), after step b) has expired and the first time interval has elapsed. Thus it can be avoided that during the first time interval, contrary to expectations, pollutant components from the

Be exhausted exhaust treatment device in the piping system.

The feed device for the additive regularly has a switchable valve (in particular a metering valve). By opening this valve, the described flow path can be released into the line system. For the method according to the invention, it may be important that the flow path is released only after the end of step b) immediately before or during the beginning of step c). When the valve is closed, the described flow path does not exist or is blocked. When the valve is opened, the described flow path is formed.

It is also possible that in addition to the valve in the supply device, an additional valve is provided, via which a flow path can be released from the exhaust treatment device in the piping system and this is used to establish the flow path from the exhaust treatment device in the piping system.

By such a structure, a vent valve for connecting the piping to the environment can be avoided. Via the flow path from the exhaust gas treatment device into the line system, air or medium present in the exhaust gas treatment device (in particular exhaust gas) is sucked into the line system.

At first glance, problematic in such a structure or such an approach is that then exhaust gas components (including soot particles) are sucked into the pipe system by the exhaust treatment device. However, it has been found that this is achieved by the method according to the invention and in particular by the wait of the first time interval in step b). can be avoided, even if the other medium is sucked through the exhaust gas treatment device. During the first time interval, pollutant components in the exhaust gas are removed remotely from the intake point in the exhaust treatment device. In particular, soot particles in the exhaust gas are deposited. These particles are particularly harmful to the piping system because they can lead to blockages. In particular, soot particles no longer float freely in the exhaust gas treatment device. It has been found that during operation stop or when sucking in exhaust gas by the supply device and in particular by the supply valve in the line system can regularly occur very high temperatures. These temperatures can z. B. damage the supply valve. Therefore, it is advantageous to open the supply valve when sucked back or when emptying clocked and close. Thus, overheating of the supply valve can be avoided. The amount of sucked exhaust gas is thus reduced and / or the contact with the hot exhaust gas is temporally reduced / interrupted. In addition, an additional heat input is avoided by a long-lasting operation of the electric drive coil for opening and closing the supply valve.

Since possibly also the valve or venting valve can be exposed in the Abstellfall the metering an increased thermal load, a clocked opening and closing is also proposed here preferably.

A clocked operation is understood in particular to mean that an intermittent power supply takes place at least temporarily in the first time interval. Preferably, this pulsed operation thus takes place with several pauses in which the valve can cool. In particular, in this case the temperature of the valve due to the power supply is not increased above a predetermined limit temperature and / or the temperature before the operation stop. The method is particularly advantageous when the first time interval is at least 1 second. The first time interval which is waited for in step b) is preferably even more than 10 seconds, particularly preferably more than 20 seconds and particularly preferably more than 1 minute. In addition, the first time interval is preferably a maximum of 2 minutes. This time interval is sufficient for particles (in particular particles in the exhaust gas treatment device) to settle and can no longer be sucked into the pipeline system. At the same time, the time interval is short enough to ensure that the additive does not freeze in the piping system. In addition, the time interval should be sufficiently short so that a motor stop phase of a motor vehicle does not become too long. The phase of the operation stop is the time interval which elapses from stopping the motor vehicle until the standstill of all components of the motor vehicle (including cooling, ventilation and the metering device).

The method is particularly advantageous if at least one pump with reversible conveying direction is arranged in the line system, which is designed to convey the additive both in the conveying direction and counter to the conveying direction.

Preferred for the method is the use of a positive displacement pump. In displacement pumps, the medium is conveyed by self-contained volumes. Prevention of backflow is achieved by a valve and / or a flap, other media or by gravity. Apart from design-related leaks, the medium can not flow in the reverse direction through the pump even when the pump is at a standstill. Such a pump can be switched for example by means of valves, so that the conveying direction of the pump is changed. With such a pump, a Metering device, with which the described method can be performed, be particularly simple. Such a pump may also be a flow pump (or a centrifugal pump), which may be constructed in the manner of an axial pump or a radial pump. In such pumps, a blade assembly drives the additive to be delivered. By reversing a direction of rotation of the blade arrangement, a reversal of the conveying direction can be achieved regularly in such pumps. In one embodiment, the pump with reversible conveying direction is a vane pump. A vane pump is also called a rotary vane pump. In a preferred embodiment, this type of pump has a stator and a rotor arranged eccentrically in the stator. In the stator open a pump inlet and a pump outlet. The rotor has one or more, preferably radially arranged guides, in which rotary valve sit. These rotary valves divide the space between stator and rotor into several chambers. During the rotation of the rotor occur for each rotary valve pitch changes between the rotor and stator. By at least one arranged in the guides spring, the rotary valve are pressed against the inner wall of the stator. During the rotation of the rotor, the additive to be delivered is conveyed from the pump inlet to the pump outlet or vice versa, depending on the direction of rotation of the rotor.

Furthermore, the method is advantageous if at least one pump is arranged in the line system, which has two separate pump chambers, wherein one pump chamber is designed for conveying the additive in the conveying direction and the additive in step c) is conveyed against the conveying direction with the other pump chamber , In such a pump can be dispensed with valve arrangements to change the conveying direction. The change in the conveying direction is achieved by a suitable control and flow to the pump. Also advantageous is the method, if at least one pump for conveying the additive in the conveying direction and at least one drain pump are provided in the line system, wherein in step c) the additive with the drain pump is conveyed against the conveying direction.

In such a construction, particularly cost-effective and simple pumps can be provided because the pump for their task to promote in the conveying direction and the drain pump can be adapted for their task for emptying. The pump and drain pump may optionally be arranged in two parallel flow paths of the conduit system or in series in a flow path of the conduit system. When the pumps are arranged in parallel, the emptying takes place partly via a different flow path than the conveying in the conveying direction. The pump and the drain pump are then preferably both constructed such that they can not be flowed through in the switched-off state for the additive counter to their respective conveying direction.

If the pumps are arranged in series, the feed pump and the drain pump can each be switched so that they are passable for the liquid additive. If the pump is active for pumping, the drain pump for the liquid additive must be passable in the opposite direction to the discharge direction. If the drainage pump is active during emptying in step c), the pump must be passable for delivery against the direction of conveyance for the liquid additive. An arrangement of the pump and the drain pump in series makes it possible to dispense with branching in the piping system largely.

Moreover, the method described is advantageous if an internal pressure in the line system during step b) is at least maintained. The operating pressure in the line system is used in particular for the promotion and / or the appropriate dosage of the reducing agent during operation. The dosing quantity of the reducing agent is predetermined for dosing devices with a dosing valve as dosing agent over the opening time of the dosing agent. The internal pressure is during operation of the internal combustion engine and the metering device in particular in a range of 5 to 10 bar, preferably in a range of 7 to 9 bar. Preferably, this internal pressure is maintained throughout the step b).

It has been found that, especially immediately after the shutdown of an internal combustion engine, the temperature in an exhaust gas treatment device for a longer period of time is still relatively high. However, the heat is no longer dissipated with the exhaust stream and / or active cooling systems, as happens during operation of the internal combustion engine. This creates a temperature accumulation, which can greatly increase the temperature in the vicinity of the exhaust gas treatment device. This is particularly true in a near-motor arrangement of the metering device, because the engine compartment here forms a partially closed space in which the heat from the engine or the exhaust gas treatment device can be accumulated there. The additive present in the line system can thereby evaporate. If the additive is a reducing agent, an at least partial thermal / chemical conversion of the additive into ammonia may even take place. This at least partial thermal / chemical conversion is usually not reversible at decreasing temperatures again. Ammonia is then present in the gas system in gaseous form, regardless of the temperature.

By maintaining the internal pressure with the dosing agent is at least the temperature for evaporation of the additive and / or the temperature at which a chemical reaction of the additive takes place, raised. By maintaining the internal pressure so the evaporation and / or chemical reaction of the additive can be at least partially prevented. In a further preferred embodiment, the internal pressure during step b) is even increased. Preferably, the internal pressure is increased to at least 15 bar and more preferably to at least 19 bar. Preferably, the internal pressure is increased to a maximum of 25 bar. Preferably, the pressure increase takes place already during and / or immediately after step a). The internal pressure is then preferably maintained at the set level during the entire step b). By a further pressure increase, the temperatures for evaporation and / or chemical reaction of the additive can be further increased. The chemical reaction and / or evaporation of the valve can be prevented even better. The described increase of the operating pressure can be carried out with the pump of the metering device.

The pressure maintenance or the pressure increase preferably takes place for the entire first time interval of step b). The pressure maintenance can also take place independently of the first time interval for a second time interval, which is in particular more than 30 seconds, preferably more than 5 minutes and particularly preferably more than 30 minutes. This is particularly advantageous if the first time interval is very long.

For the process step of pressure maintenance / pressure increase can also be provided that the pump is at least temporarily activated again. This is done z. B. still in step a) and / or in step b).

Furthermore, a method for stopping the operation of a metering device for metering a liquid additive into an exhaust gas treatment device for cleaning the exhaust gases of a Combustion engine proposed, wherein the metering device with at least one conduit system which connects a tank for storing the additive and a supply device for supplying the additive into the exhaust gas treatment device, wherein the additive is conveyed through the conduit system from the tank to the supply device with a conveying direction. The method has at least the following steps:

x) stopping the internal combustion engine;

y) determining if there is a start-stop situation; and

z) carrying out an operating stop of the metering device, if it was determined in step y) that there is no start-stop situation. The method characterized by method steps x), y) and z) can also be used independently of the other features described. The method steps a), b) and c) described above are not necessary for this purpose. Nevertheless, the method steps b) and c) can then advantageously be carried out as processes in the context of step z).

A start-stop situation (of an internal combustion engine and / or of a motor vehicle) means, in particular, a situation in which the motor vehicle or the internal combustion engine is not switched off for a longer time interval but only has a short break in operation, in which case it is clear and / or known in that after the brief break in operation (for example less than five minutes, less than two minutes or even less than one minute), the internal combustion engine should be reactivated. Such a start-stop situation can for example be characterized in a motor vehicle in that the stop signal (which triggers a deactivation of the internal combustion engine) is triggered by an engine control unit in order to save fuel. In particular, the stop signal is not triggered by an ignition (or an ignition lock), via which a user pretends that the internal combustion engine is to be activated (started or started) or deactivated (stopped). If it is recognized in step z) that there is a start-stop situation, no stop of operation of the metering device should be initiated, but the "operating state" should be maintained (unchanged) over this period of time The functionality of the dosing device can (again) be ensured immediately after the start-stop situation has been completed Deactivation of the dosing device should only take place when the internal combustion engine is stopped and there is no start-stop situation.

The method characterized by the method steps x), y) and z) can be supplemented by all disclosed features without the need for implementing the method steps a), b) and c) for this purpose. For example, it is possible to perform an operation stop of a metering device in step z), without a suck back according to step c) is carried out and / or without a first time interval is waited according to step b). However, it is also particularly preferred that in step z) an operation stop with the described method steps a), b) and c) is performed. For the function or mode of action of the addressed components and / or processes of the dosing device, reference may be made in full to the explanations concerning the "operation stop method." If an operation stop is carried out without the method steps b) and c) in step z), it is preferred to In the context of the invention, a metering device is also proposed for metering a liquid additive into an exhaust gas treatment device for cleaning the exhaust gases of an internal combustion engine with at least one line system a tank for storing the additive and at least one supply device for Supply of the additive into the exhaust gas treatment apparatus connects, wherein the additive is conveyed through the conduit system from the tank to the feed device with a conveying direction, and the conduit system against the conveying direction is at least partially emptied, the conduit system via at least one permeable flow path with the exhaust gas treatment device and at least one permeable flow path can be connected to the tank and, moreover, no further permeable flow path can be produced in the line system.

Permeable flow paths are for a fluid (in particular for liquid additive or for other media such as air or exhaust gas) passable ways into the piping system. In that, apart from the tank and the exhaust gas treatment device, there are no further flow paths, it is particularly meant that the line system does not have an additional venting or venting connection which, for example, can be associated with the (external) environment. It is quite possible that several permeable flow paths can be produced in the tank. For example, this can be when the metering device has a return line through which the present in the metering liquid additive can be emptied back into the tank. It is also possible for a plurality of flow paths to be provided in the tank in order to be able to convey a residual amount of liquid additive from the tank even when the tank is inclined, wherein it is also possible for a plurality of permeable flow paths to be present in the exhaust gas treatment apparatus. This may be the case, for example, if several injection points for the additive are provided in the exhaust gas treatment device.

The metering device described is particularly suitable for stopping operation according to the described method. The advantages and special design features explained for the method described can be transferred to the dosing device in an analogous manner. The same applies to the particular design features and advantages described below for metering devices, which are transferable in an analogous manner to the described method. The metering device is particularly advantageous if one of the following pump arrangements is provided in the line system: at least one pump with reversible conveying direction;

at least one pump, which has two separate pump chambers, wherein one pump chamber for conveying the additive in the conveying direction and the other pump chamber for conveying the

Additive are counter to the direction of conveying proceed; and

at least one pump for conveying the additive in the conveying direction and at least one drain pump for conveying the additive counter to the conveying direction.

The various specified pump arrangements have already been described above for the method. These explanations are hereby incorporated by reference. In the context of the invention, a motor vehicle with an internal combustion engine, an exhaust gas treatment device for cleaning the exhaust gases of the internal combustion engine, a metering device for metering a liquid additive into the exhaust gas treatment device, and a control unit is specified, the latter being designed and set up, according to the operation of the metering device to stop the described method. The motor vehicle preferably has a metering device, as described above. The invention and the technical environment will be explained in more detail with reference to FIGS. The figures show particularly preferred embodiments, to which the invention is not limited. In particular, it should be noted that the figures and in particular the illustrated proportions are only schematic. Show it: 1 shows a first embodiment of a metering device;

2 shows a second embodiment of a metering device;

3 shows a third variant of a dosing device;

4 shows a fourth embodiment variant of a metering device; Fig. 5: a pump for a metering device; and

Fig. 6: a motor vehicle, comprising a metering device whose

Operation can be stopped by the method according to the invention.

The common features of the various embodiments of metering devices according to FIGS. 1 to 4 will be explained together below. The metering devices 1 each have a tank 5 for storing the additive and a supply device 6 for supplying the additive into an exhaust gas flow 16 in an exhaust gas treatment device 2. The tank 5 and the supply device 6 are connected to one another via a line system 4. In the line system 4 there is at least one pump 9 with which the additive can be conveyed from the tank 5 along a conveying direction 7 through the line system 4 to the feed device 6. In the supply device 6, a supply valve 8 is optionally provided, with which the supply of additive via the supply device 6 in the exhaust gas treatment device 2 can be controlled. From the tank 5 into the conduit system 4 there is a flow path 13, which is passable for the additive. From the line system 4 into the exhaust gas treatment device 2, there is a flow path 13 through the supply device 6, which can be passed from the exhaust gas treatment device 2 into the line system 4 for the additive and optionally against the conveying direction for another medium. In Fig. 1, a pump 9 is provided with reversible conveying direction in the metering device 1 to perform the method described.

In Fig. 2, a pump 9 is provided in the metering device 1, which also has a reversible conveying direction, wherein the reversible conveying direction is realized here with two separate pump chambers 11 to perform the method described.

In Fig. 3, a metering device with a pump 9 for conveying in the conveying direction 7 and an additional drain pump 10 is shown. The evacuation pump 10 is located (in a parallel arrangement) in a bypass path 18 around the pump 9 to assist in discharging the liquid additive around the pump 9 against the direction of conveyance 7. In the embodiment according to FIG. 3, the pump 9 and the emptying pump 10 are preferably both constructed in such a way that, when conveying with the pump 9 in the conveying direction 7, the emptying pump 10 for the liquid additive is not permeable. When emptying with the drain pump 10 counter to the conveying direction 7, the pump 9 is again not permeable to the liquid additive.

4, a pump 9 for conveying in the conveying direction and an emptying pump 10 for emptying in step c) are provided in the embodiment variant of the metering device according to FIG. The pump 9 and the drain pump 10 are here in series (ie in the conveying direction 7 behind each other) arranged. The pump 9 is preferably constructed so that it can be passed against the conveying direction 7 during the emptying in step c) for the liquid additive. The drain pump 10 is preferably constructed so that it is passable during the conveying of the liquid additive in the conveying direction 7 with the pump 9 for the liquid additive. In Fig. 5, a pump 9 is shown, which has two pump chambers 11, wherein the upper pump chamber 11 is arranged for conveying in the conveying direction 7. This is ensured by pump valves 12 which predetermine the conveying direction 7. The lower pump chamber 11 is provided for conveying against the conveying direction 7. Also, the promotion against the conveying direction 7 is predetermined by pump valves 12.

FIG. 6 shows a motor vehicle 14 having an internal combustion engine 3 and an exhaust gas treatment device 2 for cleaning the exhaust gases of the internal combustion engine 3. In the exhaust gas treatment device 2 with a metering device 1 liquid additive via a supply device 6 can be fed. The metering device 1 can be controlled during operation stop of the internal combustion engine 3 via the control unit 15 according to the described method.

In the exhaust treatment device 2, an SCR catalyst 17 is preferably provided. In order to be able to carry out the process of the selective catalytic reduction in the SCR catalytic converter 17, it is preferable to add reducing agent to the supply device 6 as a liquid additive which passes from the supply device 6 with the exhaust gas flow 16 to the SCR catalytic converter 17. The described method makes possible a particularly cost-effective metering device which can be emptied counter to the conveying direction. Dirt on the piping system of the metering be effectively avoided by the process. LIST OF REFERENCE NUMBERS

1 dosing device

2 exhaust treatment device

3 internal combustion engine

4 pipe system

5 tank

6 feeder

7 conveying direction

8 supply valve

9 pump

10 drain pump

11 pump chamber

12 pump valve

13 flow path

14 motor vehicle

15 control unit

16 exhaust gas flow

17 SCR catalyst

18 Bypass path

Claims

claims

Method for stopping the operation of a metering device (1) for metering a liquid additive into an exhaust gas treatment device (2) for cleaning the exhaust gases of an internal combustion engine (3) with at least one line system (4) comprising a tank (5) for storing the additive and a supply device ( 6) for supplying the additive into the exhaust treatment device (2), wherein the additive is conveyable through the piping system (4) from the tank (5) to the supply device (6) with a conveying direction (7) and the method comprises at least the following steps having:

a) stopping the internal combustion engine (3);

b) waiting at least a first time interval; and

c) at least partial emptying of the conduit system (4) against the conveying direction (7) after the first time interval, wherein for step c) a permeable flow path (13) of the exhaust treatment device (2) in the conduit system (4) is released and during step c ) the conduit system (4) via the flow path (13) is vented.

Method according to claim 1, wherein the supply device (6) comprises a supply valve (8) which is opened before step c) and thus releases the permeable flow path (13).

Method according to one of the preceding claims, wherein the first time interval is at least 1 second.

Method according to one of claims 1 to 3, wherein in the line system (4) at least one pump (9) is arranged with reversible conveying direction, which is adapted to the additive both in the conveying direction (7) and against the conveying direction (7) promote.

5. The method according to any one of claims 1 to 3, wherein in the conduit system (4) at least one pump (9) is arranged, which has two separate pump chambers (11), wherein the one pump chamber (11) for conveying the additive in the conveying direction ( 7) is formed and with the other pump chamber (11)

Additive in step c) is conveyed against the conveying direction (7).

6. The method according to any one of claims 1 to 3, wherein in the line system (4) at least one pump (9) for conveying the additive in the conveying direction (7) and at least one

Emptying pump (10) are provided, wherein in step c) the additive with the drain pump (10) is conveyed against the conveying direction (7).

7. The method according to any one of the preceding claims, wherein an internal pressure in the conduit system (4) during step b) is at least maintained.

8. A method for stopping operation of a dosing device (1) for dosing a liquid additive in a

Exhaust treatment device (2) for cleaning the exhaust gases of an internal combustion engine (3) with at least one line system (4), which connects a tank (5) for storing the additive and a supply device (6) for supplying the additive into the exhaust gas treatment device (2) the additive is conveyable through the conduit system (4) from the tank (5) to the supply device (6) with a conveying direction (7) and the method comprises at least the following steps:

x) stopping the internal combustion engine (3);

y) determining if there is a start-stop situation; and

z) deactivating the dosing device (1) if it was determined in step b) that there is no start-stop situation. Dosing device (1) for dosing a liquid additive in an exhaust gas treatment device (2) for cleaning the exhaust gases of an internal combustion engine (3) with at least one line system (4) having a tank (5) for storing the additive and at least one supply device (6) Supply of the additive into the exhaust gas treatment device (2) connects, wherein the additive through the conduit system (4) from the tank (5) to the supply device (6) with a conveying direction (7) is conveyed, and the conduit system (4) against the conveying direction (7) is at least partially emptied, wherein the conduit system (4) via at least one permeable flow path (13) with the exhaust gas treatment device (2) and at least one permeable flow path (13) with the tank (5) is connectable and beyond no further permeable flow path (13) in the line system (4) can be produced.

Dosing device (1) according to claim 9, wherein one of the following pump arrangements is provided in the line system (4):

- At least one pump (9) with reversible conveying direction;

- At least one pump (9) having two separate pump chambers (11), wherein the one pump chamber (11) for conveying the additive in the conveying direction (7) and the other pump chamber (11) for conveying the additive against the conveying direction (7) proceed; and

- At least one pump (9) for conveying the additive in the conveying direction (7) and at least one emptying pump (10) for conveying the additive against the conveying direction (7)

Motor vehicle (14) having an internal combustion engine (3), an exhaust gas treatment device (2) for cleaning the exhaust gases of the internal combustion engine (3), a metering device (1) for metering a liquid additive into the exhaust gas treatment device (2) and a control unit (15), which is designed and arranged to stop the operation of the dosing device (1) according to a method according to one of the claims 1 to 8.