EP2678538A1

EP2678538A1 - Method for heating a delivery system

Info

Publication number: EP2678538A1
Application number: EP12704073.1A
Authority: EP
Inventors: Jan Hodgson; Sven Schepers
Original assignee: Emitec Gesellschaft fuer Emissionstechnologie mbH
Current assignee: Continental Automotive GmbH
Priority date: 2011-02-25
Filing date: 2012-02-13
Publication date: 2014-01-01
Also published as: DE102011012441A1; WO2012113669A1; US9032712B2; JP2014507596A; US20130340409A1

Abstract

The invention relates to a method for heating a delivery system (1) for providing reducing agents in an exhaust gas treatment device (2) of an internal combustion machine (3) having a plurality of electrically driven components (6, 7, 8, 9, 10, 11). The method comprises at least the following steps: a) determining at least one temperature in the delivery system (1), b) determining a heat energy required for error-free operation of the delivery system (1) in a time interval (4), and c) introducing the required heat energy into the delivery system (1) by operating the electrically operated components (6, 7, 8, 9, 10, 11) within the time interval. The electrically operated components (6, 7, 8, 9, 10, 11) are activated at a time offset of at least 30 seconds in each case. The required energy is determined so that at least four times the quantity of reducing agent to be delivered per hour is provided in liquid form after the time interval (4). The method according to the invention effectively prevents overloading a vehicle electrical system of a motor vehicle (19) when heating the delivery system (1). In addition, ice cavity formation in the reducing agent in the tank (16) is prevented.

Description

Method for heating a conveyor system

The present invention relates to a method for heating a delivery system for providing reducing agent in an exhaust gas treatment device of an internal combustion engine with a plurality of electrically operated components. With the added reducing agent, the selective catalytic reduction (SCR) process can be carried out.

In the selective catalytic reduction, nitrogen compounds in the exhaust gas are reduced with the reducing agent to harmless components such as carbon dioxide, water and nitrogen. Ammonia is often used as the reducing agent. Ammonia is regularly not directly stored in motor vehicles, but in the form of a reducing agent precursor, which is then converted in the exhaust system and / or in an intermediate evaporator unit and / or hydrolysis unit to the actual reducing agent. A particularly frequently used reducing agent precursor solution is urea-water solution. A 32.5% urea-water solution for this purpose is for example available under the trade name AdBlue ^®. In the following, the terms reducing agent and reducing agent precursor are used synonymously for each other. In particular, reducing agent precursor is also referred to as a reducing agent.

For the provision of the reducing agent, a conveyor system in the motor vehicle is regularly provided. Such conveyor systems include a tank for storing the reducing agent, lines for fluidic connection of the tank with the Abgasbehandlungsvorrich- device, a pump for conveying the reducing agent, filters for cleaning the reducing agent and sensors for monitoring the operation of the conveyor system and the properties of the reducing agent. At temperatures below -11 ° C, the reducing agent solidifies so that it can not be promoted. Nevertheless, at such low temperatures the To ensure smooth operation of the conveyor system and in particular thaw the reducing agent after prolonged service life of the vehicle, it is known to provide heating elements that melt or heat the solidified reducing agent. For this purpose, it is known in particular to use heating elements and to use the heat of electrically operated components of the conveyor system for thawing the reducing agent. As heating elements in particular PTC heating elements (PTC: Positive Temperature Coefficient) have prevailed. In these heating elements, the electrical resistance is proportional to the temperature of the heating element. In general, the dependence of the resistance on the temperature is not linear, so that such heating elements can be used self-regulating for predetermined temperature ranges.

During thawing of the reducing agent and immediate removal of the thawed reducing agent, an ice chamber can form in the reducing agent, whereby effective heat conduction from the heating to the frozen reducing agent is prevented.

In this context, it is desired that reductant delivery systems be operational 20 minutes after starting at an outside temperature greater than -20 ° C. For even lower temperatures, the time after which the conveyor system should be operational, larger. For example, if the outside temperature is between -20 ^° C and -30 ^° C, the conveyor system should be operational after 30 minutes. It is therefore known to turn on all the heating components of a conveyor system in order to achieve the fastest possible thawing of the reducing agent. When switching on the motor vehicle but other electrical loads are turned on, so that it can easily lead to an overload of the electrical system.

The invention is therefore based on the object to provide a method for heating a conveyor system, which at least partially solves the technical problems described with reference to the prior art. In particular, a method should be specified, which is an overload prevents the on-board network and still allows a proper operation of the conveyor system.

These objects are achieved by a method according to the features of claim 1. Further embodiments of the invention are specified in the dependent formulated claims. It should be noted that the features listed individually in the dependent formulated claims can be combined with each other in any technologically meaningful manner and show further embodiments of the invention. The description, in particular in conjunction with the figures, further explains the invention and provides additional embodiments.

The objects are achieved by a method for heating or thawing a delivery system for providing reducing agent in an exhaust gas treatment device of an internal combustion engine with a plurality of electrically operated components, comprising at least the following steps:

a) determining at least one temperature in the conveyor system, b) determining a heat energy required for (trouble-free) operation of the conveyor system in a time interval,

c) feeding the required heat energy into the conveyor system

Operating the electrically operated components within the

Time interval,

wherein the activation of the electrically operated components takes place in each case with a time offset.

The conveyor system usually comprises a tank for storing the reducing agent and a dosing module for conveying the reducing agent to an injector, through which the reducing agent is introduced into the exhaust gas treatment device. The dosing module is preferably arranged in the bottom or in a sump region of the tank and comprises a housing in which a distributor block is arranged. In particular, the remaining components of the dosing module are assigned to the distributor block. net, so that the distribution block preferably forms a base or a holder for all other components and / or the housing. In particular, a line, a filter element arranged in the line with a filter heater, a pump and a return line with a solenoid valve for selectively returning the reducing agent into the tank are integrated in the distributor block and / or associated therewith. Furthermore, the dosing module comprises at least one sensor for detecting at least one state variable of the conveyor system or of the reducing agent. For example, a temperature sensor for detecting the temperature in the dosing module can be provided and / or at least one pressure sensor for detecting the pressure in the line. Also, an ultrasonic sensor for detecting the level of the tank can be provided in the dosing. The conveyor system also preferably comprises at least one electric heater, which is optionally thermally conductively connected by heat-conducting elements with other components of the conveyor system.

In method step a), a temperature of a component of the delivery system and / or of the reducing agent is determined at at least one point in the delivery system. Preferably, both the temperature of the reducing agent and the temperature of a großvo lumigen component of the conveyor system is determined. Furthermore, temperature information from other locations in the motor vehicle can be used by the method according to the invention in which, for example, via a bus system (CAN) access remote temperature sensors of the motor vehicle and their measurement results are processed. After a long service life of the conveyor system, the temperature should be almost the same at all points of the conveyor system and the reducing agent. From the determined temperature and / or an average of the determined temperatures, the state of matter of the reducing agent can be determined. Moreover, the determined temperature is characteristic of the heat energy stored in the conveyor system.

The (currently) stored in the conveyor system heat energy from the known for the conveyor system heat capacity in combination with the (current) temperature of the conveyor system and derived from the last known amount of reducing agent and their specific heat capacity (ie, for example, estimated and / or calculated). Furthermore, the heat energy introduced in a previous operating cycle can be taken into account. In this case, it is preferable to take into account both the quantity of reducing agent stored in the lines and the amount of reducing agent present in the tank. The heat capacity is a measure of the energy required to be delivered (to be delivered) for inducing a temperature difference of the conveyor system components (without reducing agent). The heat capacity of the conveyor system itself is temperature-dependent and can be determined experimentally and / or by a simulation. The determination of an absolute heat energy stored in the conveyor system in method step a) serves above all as a reference for the thermal energy to be determined in method step b) and does not have to be arbitrarily accurate.

In method step b), the required thermal energy (and / or optionally the location of the heat input) is determined in particular taking into account at least one of the following system parameters: the (current) ambient temperature, the specific heat capacity of the reducing agent, the heat of fusion of the reducing agent, the heat capacity of the conveyor system , the thermal conductivity of the reducing agent and the delivery system, the amount of reducing agent in the pipes and the tank. The required heat energy is chosen so that after the time interval, a predeterminable amount of reducing agent in the liquid state in the delivery line and in the tank is present.

The specific heat capacity of the reducing agent also takes into account, in particular, that the specific heat capacity for the reducing agent in the liquid and solidified state is different. Thus, the specific heat capacity of liquid AdBlue ^® ranges in the relevant temperature range of -11 ° C to 60 ° C of 3.4 J / gK [Joule per gram per Kelvin] to 3.6 J / gK, and the specific heat capacity of solidified AdBlue ^® from 1.4 J / gK to 1.7 J / gK in the temperature range of - To -11 ^° C. In order to increase 50 ^° C for example, the temperature of 100 g of liquid AdBlue ^® by 5 ^° C, are thus 1.75 kj [kilojoules] necessary. The heat of fusion of AdBlue ^®, which is necessary for melting AdBlue ^® in -HC without temperature increase amounts to 270 J / g [Joules / gram]. So to 100 g solidified Adblue ^® to melt, thereby increasing the temperature of -12 ^° C to -10 ^° C for about 27.5 kj are therefore necessary. The thermal conductivity of liquid Adblue ^® at 25 ^° C is 0.5 W / mK [watts per meter per Kelvin]. The heat capacity and the thermal conductivity vary greatly for different conveyor systems. For a specific conveyor system, however, the heat capacity and the thermal conductivity in the relevant temperature range of -50 ^° C to 60 ^° C can be determined experimentally and / or by computer simulation and thus also be assumed to be known. As a system parameter in step b), the total heat capacity of the reducing agent in the tank and / or the total stored in the reducing agent in the tank (or currently present) amount of heat can be considered. The total heat capacity of the reducing agent in the tank is in particular the product of the specific heat capacity of the reducing agent and the filling quantity of the reducing agent in the tank in kilograms. The filling quantity can be determined with a level sensor. In particular, in the case when frozen reducing agent is present in the tank, a level sensor can not measure the level in the tank or insufficiently accurate. Therefore, it is possible to determine the level during an operating phase of the delivery system, in which the reducing agent in the tank is completely liquefied and to store this measured value in a memory of a control unit. This level can then be used for the determination or calculation of the total heat capacity for process step b). The total amount of heat stored in the reducing agent can be determined based on the total heat capacity of the reducing agent and at least one temperature of the reducing agent in the tank. It is possible that only one temperature of the reducing agent is measured, and this temperature of a mean temperature of the reduction by means of the tank. Furthermore, it is also possible to determine a plurality of temperatures of the reducing agent at different locations in the tank and / or in the line system. This can be done by a plurality of temperature sensors in the tank. In a further process variant, a temperature distribution in the reducing agent tank can be determined.

According to a simple calculation method, the stored heat quantity can be calculated or calculated from the product of the mean temperature of the reducing agent and the total heat capacity. However, this simple calculation method can be in particular due to the phase transition of the reducing agent from liquid to solid, or from solid to liquid to inaccurate. For the phase transition, a relatively large amount of heat energy is necessary without a temperature increase occurs. In addition, the specific heat capacity of reducing agent, as explained above, is not constant at all temperatures. Therefore, in a more accurate calculation method of the stored heat quantity, the amount of heat energy necessary to reach a certain temperature of the reducing agent in the tank can be added together / integrated together starting from a predetermined reference temperature. If several temperatures in the tank or even a temperature distribution in the tank are known, the amount of heat energy stored in the tank can also be accurately determined locally and added / integrated over the entire tank volume. Thus, an even more accurate determination of the stored amount of heat energy in the reducing agent in the tank is possible.

The system parameters and the determined temperatures are supplied in step b) in particular an energy model of the conveyor system, on the one hand taken into account by the energy model, the heat energy from the electrically operated components and on the other hand flowing from the environment or flowing into the environment heat energy. The energy model is preferably a three-dimensional model of the conveyor system, which locally resolves the system template. taken into account, so that the dissolved and discharged heat energies can be considered locally resolved and thus predicted and / or can be determined by the heat conduction resulting temperature distribution in the conveyor system. The energy model is thus able to determine the heat energy required by the individual electrically driven components.

Taking into account the heat energies which can be provided by the various electrically operated components, in step c) the electrically operated components are switched on within the time interval. The electrically operated components are not switched on at the same time, but with a temporal offset from one another. But it is easily possible that different components are operated at the same time after the staggered switching. By the time-delayed activation of the electrically operated components overloading of the electrical system is effectively prevented in particular when turning on the motor vehicle after a longer life. If the supply of heat energy in step c) is interrupted, the thermal energy introduced into the conveyor system during the restart (step b) is taken into account, in particular the influence of the ambient temperature during the service life on the heat energy balance of the conveyor system - is considered. In this case, it is particularly considered that the temperature measured at one point in the conveyor system need not be characteristic of the entire conveyor system. In particular, a comparison of the temperature measured in the conveyor system and the temperature predicted by the energy model (locally resolved or locally determined) can be used for this purpose. It is thus possible to continue supplying the heat energy determined during the previous operation, the supply of which has been interrupted, or to re-adjust the required heat energy after the determination in method step b). Thus, in particular, a kind of pre-test is possible after which before or with the initiation of step a) it is checked whether a currently measured temperature is also characteristic for the conveyor system. If a (temporally or spatially offset) correction temperature measurement shows that the conveyor system is not "in equilibrium", but a heat point is locally formed (eg due to a previous, possibly aborted, heating process), the energy model can take this into account Likewise, in addition or alternatively, important parameters of the last heating process can be stored so that the residual thermal energy can be calculated and subsequently taken into account.

Due to the time-delayed switching on of the electrically operated component, it is preferable to first thaw the reducing agent stored in the lines of the metering module and the reducing agent adjacent to the metering module in the tank. The electrically operated components are switched on in particular in such a way that heat is first introduced into the reducing agent along the lines via its inner surfaces. The degree of the introduced thermal energy and / or the location of the heat input is particularly chosen so that even when removing a relatively large amount of reducing agent with respect to the amount of reducing agent normally used no ice cavity is formed in the reducing agent.

The time delay of activating the electrically operated components is preferably at least 30 seconds, more preferably at least 60 seconds, most preferably at least 120 seconds. By the time offset is meant in particular the time period between the activation of a first electrically operated component and a second electrically operated component. It is particularly preferred that the majority or even all energy-consuming components of the delivery system with such time offset are switched on or activated. The temporal offset is particularly adapted to the power consumption characteristics of the PTC heating elements used. It is also advantageous that (in method step b)) the energy required is determined such that at least three times, preferably six times, the amount of reducing agent to be delivered per hour is provided after the time interval in liquid form. Both the average delivery rate determined over a predetermined observation time interval and the maximum delivery rate of the reducing agent can be used as the basis for determining the required energy. At an average delivery rate of 150 ml / h [milliliters per hour] for a passenger car in a passenger vehicle, at least 400 ml of reducing agent should be thawed after 20 minutes. In this way, it is effectively prevented that an ice cavity forms in the reducing agent tank, thereby preventing the deterioration of the thermal conductivity and hence the further thawing of the reducing agent. It is also particularly advantageous if at least for step a) or step b) an ambient temperature is determined and taken into account. In particular, in step b), the heat energy flowing into the environment or flowing in from the environment can thus be taken into account so that the heat energy provided by the electrically operated components in step c) is adjusted.

According to one embodiment of the invention, the conveyor system has at least two of the following electrically operated components, which are switched on in step c) in the following order: electric heater, pump, filter heater, solenoid valve, sensor. As a result of the initial activation of the electric heater (s), at least part of the reducing agent present in the metering module and the reducing agent adjacent to the metering module are first at least partially thawed in the tank. At least a part of the reducing agent is preferably After the time interval in an eligible state, so that with the staggered switching on the pump, the filter heater, the solenoid valve and / or the sensor, the reducing agent is further heated in the dosing. For example, a suitable for the purpose of this pump provides a heat output of 30 W [watt] to 50 W and a solenoid valve, a heat output of 5 W to 20 W the conveyor system available. An effective heating without forming an ice cave and without overloading the electrical system is thus given. In a further advantageous embodiment of the invention, the conveyor system on several PTC heating elements, which are activated offset in time for supplying the required heat energy. The PTC heaters will require a maximum current within the first minute of being turned on, which will later drop below 70% of the maximum. In addition, since the required power of the particular PTC heating elements is not constant in time, high demands are placed on the electrical system of a motor vehicle at the same time switching all required for heating components. Especially with the use of PTC heating elements, overloading of the on-board network is prevented by the time-delayed activation, since these have an increasing power consumption after activation, which after a certain time decays again to a lower, relatively constant value. Particularly preferably, the time interval has a value of 10 minutes to 20 minutes, preferably 15 minutes to 20 minutes.

According to a further expedient embodiment, for step a) at least one temperature of the conveyor system is determined with at least one temperature sensor arranged at at least one of the following positions:

in an opening of a heat-conducting carrier plate of the conveyor system, on a board for control electronics, which within a

Housing of the conveyor system is arranged,

on a pump of the conveyor system,

at a distribution block of the conveyor system.

At all these positions, a temperature characteristic of the conveyor system is present, so that in step a) the heat energy stored in the conveyor system can be accurately determined. In this case, an average value of temperatures measured at two positions is particularly preferred for determining the heat energy stored in the conveyor system. Furthermore, it is preferred that the ambient temperature is taken into account in the determination of the characteristic temperature. In order to allow safe Betereiben the pump and prevent possible malfunction of the pump of the delivery system, the pump is initially operated in step c) with reduced driving force to determine whether there is still frozen reducing agent in lines of the conveyor system. If it should be found that frozen reducing agent is still present in lines of the delivery system, the heat energy to be introduced can be purposefully increased, so that this reducing agent thaws.

According to a further aspect of the invention, a motor vehicle is proposed, which has an internal combustion engine and an exhaust gas treatment device for cleaning the exhaust gases of the internal combustion engine, as well as a delivery system for delivering reducing agent into the exhaust gas treatment device and a control device connected to the delivery system, which is used to operate the delivery system is set up according to the inventive method. For this purpose, z. B. a control software may be provided which controls the operation or activation of the components by appropriately provided signal lines and pretending. The invention and the technical environment will be explained by way of example with reference to the figures. It should be noted that the figures show particularly preferred embodiments of the invention, but this is not limited thereto. They show schematically:

1: a motor vehicle with a conveyor system for reducing agent,

Fig. 2: a conveyor system for reducing agent, and Fig. 3: a diagram for illustrating the method according to the invention.

1 schematically shows a motor vehicle 19 with an internal combustion engine 3 and an exhaust gas treatment device 2, comprising a catalytic converter 22 for cleaning the exhaust gases of the internal combustion engine 3. The motor vehicle 19 further comprises a conveyor system 1 for feeding a reducing agent into the exhaust gas treatment device 2 through an injector 21. The conveyor system 1 has a tank 16 for storing reducing agent and a pump 7 for removing the reducing agent via a line 18. In line 18, a filter 23 is further arranged for purifying the reducing agent. The pump 7 is followed by a sensor 10 in the line 18, which is adapted to detect operating parameters of the reducing agent in the conduit 18. Here, for example, the pressure or the temperature of the reducing agent can be monitored. For ventilation of the line 18, a solenoid valve 9 is provided which allows a return of the reducing agent via a return line 27 into the tank 16. For monitoring and control of the conveyor system 1, the motor vehicle 19 comprises a control unit 20 which is connected to the pump 7, the sensor 10 and the solenoid valve 9. In principle, it is also possible that these components are arranged as a module in / on the tank 16.

2, a further embodiment of a conveyor system 1 is shown schematically. The conveyor system 1 comprises a tank 16, to whose Floor 28 a housing 15 is embedded with other components of the conveyor system 1. The housing 15 is thus in direct contact with the reducing agent in the tank 16. In the housing 15 is a manifold block 17, in which a line 18, a filter 23 with a Filterhei- tion 8, a pump 7, a sensor 10, a plurality of PTC heating elements 11 and a solenoid valve 9 are integrated. In addition, an electric heater 6 and a circuit board 14 with a temperature sensor 12 are arranged in the housing 15. On the board 14, an electronic control unit or control unit is integrated, which is connected via signal lines, not shown, with the electrically operated components 6, 7, 8, 9, 10, 11. The housing 15 and the distributor block 17 are arranged on a thermally conductive carrier plate 13.

Via the line 18, reducing agent is removed from the tank 16 on the left side with the aid of the pump 7, and is first cleaned in the filter 23. The sensor 10 monitors the parameters of the reducing agent present in the line 18, so that, if necessary, by switching the solenoid valve 9 reducing agent can be fed back into the tank 16. In normal operation, however, the reducing agent is passed to an injector 21.

At temperatures below -H C, the reducing agent freezes. The present invention therefore proposes a method for heating the conveyor system 1, in particular after a prolonged service life of the motor vehicle 19. Accordingly, a heat energy stored in the conveyor system 1 is to be determined, in order subsequently to determine a heat energy required for trouble-free operation. This so determined heat energy is to be introduced via the waste heat of the electrically operated components 6 to 11 in the conveyor system 1, wherein the electrically operated components 6 to 11 are activated in each case with a time offset 5.

To illustrate the method according to the invention, FIG. 3 shows a diagram with the temporal current profile 26 of the method. dersystem 1, wherein on the abscissa axis, the time 24 and on the or- dinatenachse the current 25 is plotted. The operating times of the electrically operated components 6 to 11 are shown schematically as black blocks. The dashed line shows the current profile 26 in a representation of current 25 over time 24. Within a time interval 4, all electrically operated components 6 to 11 are to be activated. The electrically operated components electric heater 6, pump 7, filter heater 8, solenoid valve 9, sensor 10 and PTC heating elements 11 are each activated with a temporal offset 5 zueinan-. The resulting required current of the conveyor system 1 is shown by way of example with the dashed line of the current waveform 26. The time offset is at least 30 seconds. Due to the time offset 5 of activating the electronic components 6 to 11, the required current in the time interval 4 is limited to a predetermined size. An overload of the electrical system is thus avoided.

The inventive method, an overload of a vehicle electrical system of a motor vehicle 19 during the heating of the conveyor system 1 is effectively prevented. In addition, ice formation in the reducing agent in the tank 16 is avoided.

LIST OF REFERENCE NUMBERS

1 conveyor system

2 exhaust treatment device

3 internal combustion engine

4 time interval

5 Time offset

6 electric heating

7 pump

8 filter heating

9 solenoid valve

10 sensor

11 PTC heating element

12 temperature sensor

13 carrier plate

14 board

15 housing

16 tank

17 distribution block

18 line

19 motor vehicle

20 control unit

21 injector

22 catalyst

23 filters

24 time

25 electricity

26 current course

27 return line

28 floor

Claims

claims

Method for heating a delivery system (1) for providing reducing agent to an exhaust treatment device (2) of an internal combustion engine (3) having a multiplicity of electrically operated components (6, 7, 8, 9, 10, 11), comprising at least the following steps:

a) determining at least one temperature in the conveyor system (1),

b) determining a heat energy required for an operation of the conveyor system (3) in a time interval (4),

c) supplying the required heat energy into the conveyor system (1) by operating the electrically operated components (6, 7, 8, 9, 10, 11) within the time interval,

wherein the activation of the electrically operated components (6, 7, 8, 9, 10, 11) takes place in each case with a time offset.

Method according to claim 1, wherein the time offset (5) of activating the electrically operated components (6, 7, 8, 9, 10, 11) is at least 30 seconds in each case.

A method according to claim 1 or 2, wherein the required energy is determined so as to provide at least three times the amount of reducing agent to be delivered per hour after the time interval (4) in liquid form.

Method according to one of the preceding claims, wherein at least for step a) or step b) an ambient temperature is determined and taken into account.

Method according to one of the preceding claims, wherein the conveyor system (1) at least two of the following electrically operated components (6, 7, 8, 9, 10, 11) and in step c) be switched on in the following order: electric heater (6), pump (7), filter heater (8), solenoid valve (9), sensor (10).

Method according to one of the preceding claims, wherein the conveyor system (1) comprises a plurality of PTC heating elements (11) which are activated in time to supply the required heat energy.

Method according to one of the preceding claims, wherein the time interval has a value of 10 minutes to 20 minutes.

Method according to one of the preceding claims, wherein for step a) at least one temperature of the conveyor system (1) with at least one temperature sensor (12) is arranged, which is arranged at at least one of the following positions:

in an opening of a heat-conducting carrier plate (13) of the

Conveyor system (1),

on a board (14) for a control electronics, which is arranged within a housing (15) of the conveyor system,

on a pump (7) of the conveyor system (1),

on a distributor block (17) of the conveyor system (1).

Method according to one of the preceding claims, wherein the pump (7) of the conveyor system (1) in step c) is first operated with reduced driving force to determine whether there is still frozen reducing agent in lines (18) of the conveyor system (1).

A motor vehicle (19) comprising an internal combustion engine (3) and an exhaust treatment device (2) for cleaning the exhaust gases of the internal combustion engine (3), and a conveyor system (1) for conveying reducing agent into the exhaust gas treatment device (2) and to the conveyor system (1) connected Ssen controller (20) which is adapted to operate the conveyor system (1) by a method according to one of the preceding claims.