EP2524122A1

EP2524122A1 - Device and method for warming a reductant in an scr system for a motor vehicle

Info

Publication number: EP2524122A1
Application number: EP11733145A
Authority: EP
Inventors: Per Bremberg; Erik Gustafsson; Andreas Liljestrand; Lars Eriksson; Thomas ÅKERBLOM; Ulf Carlsson
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2010-01-14
Filing date: 2011-01-10
Publication date: 2012-11-21
Also published as: EP2524122A4; CN102713183B; CN102713183A; SE1050024A1; RU2012134615A; RU2524158C2; WO2011087430A1; SE535338C2

Abstract

The invention relates to a method for warming a reductant in an SCR system which comprises a container (205) for said reductant and a dosing unit (250). The method comprises the step of extracting at least part of said reductant from said container (205) and warming said at least part by means of at least one warming element (261; 262; 263; 264; 265) outside said container (205). The method further comprises the step of returning the warmed part of said reductant to the container (205) before dosing of said warmed part via the dosing unit (250) commences in the SCR system. The invention relates also to a computer programme product comprising programme code (P) for a computer (200; 210) for implementing a method according to the invention. The invention relates also to a device and to a motor vehicle which is equipped with the device.

Description

Device and method for warming a reductant in an SCR system for a motor vehicle

5 TECHNICAL FIELD

The present invention relates to a method for warming a reductant in an SCR system. The invention relates also to a computer programme product comprising programme code for a computer for implementing a method 10 according to the invention. The invention relates also to a device for warming a reductant in a SCR system and to a motor vehicle which is equipped with the device.

BACKGROUND

15

Today's vehicles use, for example, urea as reductant in SCR systems which comprise an SCR catalyst in which said reductant and NOx gas can react with the reductant and be converted to nitrogen gas and water. Various types of reductants may be used in SCR systems. These reductants have 20 different freezing points. AdBlue is an example of a commonly used reductant.

One type of SCR system incorporates a container which holds a reductant. The SCR system has also a pump adapted to drawing said reductant from

25 the container via a suction hose and supplying it via a pressurised hose to a dosing unit situated adjacent to an exhaust pipe of the vehicle. The dosing unit is adapted to injecting a necessary amount of reductant into the exhaust pipe upstream of the SCR catalyst according to operating routines which are stored in a control unit of the vehicle. To make it easier to regulate the

30 pressure with respect to small dosage amounts, the system comprises also a return hose which runs back from a pressure side of the system to the container. This configuration also makes it possible to use the reductant for cooling the dosing unit.

To be able to use the aforesaid SCR system at low temperatures, the system is equipped with warming elements associated with appropriate components of the SCR system, e.g. in or adjacent to the container and adjacent to hoses, pump unit and dosing unit. These warming elements are currently used to ensure that any "plugs" of frozen reductant can be thawed. A disadvantage of this system is that the reductant in the container thaws too slowly when the vehicle is started up at low temperatures at which the reductant is totally or partly frozen. AdBlue has a freezing point of -11 degrees Celsius. In a case where AdBlue is at least partly frozen in the SCR system and the system is started up too early during operation of the vehicle, there is risk that all of the available AdBlue (in liquid form) might be injected via the dosing unit. This may entail risk of the suction hose in the container drawing air instead of thawed AdBlue, a situation which is undesirable for several different reasons. Specification WO 00/21881 describes an SCR system for reducing NOx emissions from a combustion engine, which system uses urea in liquid form. In the SCR system described, the urea dosing is shut off when the system, and consequently the reductant, is frozen. After a certain thawing of the system, both pumping of urea from a container to a dosing unit and dosing of urea are initiated at the same point in time. A disadvantage of this solution is that the amount of thawed urea in the container is not sufficient for continuous dosing, so the container becomes empty of liquid urea, with consequent adverse affects on the operation of the system. In the SCR system described, only one warming element is used for the urea container. A disadvantage of this is that thawing of frozen urea in the container takes a relatively long time. SUMMARY OF THE INVENTION

An object of the present invention is to propose a novel and advantageous method for warming a reductant in an SCR system.

Another object of the invention is to propose a novel and advantageous device and a novel and advantageous computer programme for warming a reductant in an SCR system.

A further object of the invention is to propose a method, a device and a computer programme for achieving quicker starting of an SCR system for a motor vehicle. A further object of the invention is to propose a method, a device and a computer programme for achieving more robust starting of an SCR system for a motor vehicle.

A further object of the invention is to propose a method, a device and a computer programme for improving the performance of a motor vehicle.

An object of the invention is to achieve an SCR system such that dosing of a reductant, e.g. urea in the form of AdBlue, can be commenced more quickly in a situation where said reductant is initially in an at least partly frozen state.

These objects are achieved with a method for warming a reductant in an SCR system which comprises a container for holding said reductant and a dosing unit according to claim 1. An aspect of the invention provides a method for warming a reductant in an SCR system which comprises a container for holding said reductant and a dosing unit, which method comprises the step of extracting at least part of said reductant from said container and warming said at least part by means of at least one warming element outside said container. The method comprises also the step of returning the warmed part of said reductant to the container before dosing of said warmed part via the dosing unit commences in the SCR system.

The method may further comprise the step of:

- the extraction of at least part of said reductant being preceded by warming of at least one of the following components: the container, a first line, a second line, a third line, a pump means and said dosing unit.

The method may further comprise the step of:

- determining whether a first liquid state is fulfilled, and

- initiating said step of extracting said at least part of said reductant from said container and warming it if the first liquid state is fulfilled.

The method may further comprise the step of:

- warming the extracted part of said reductant by means of a plurality of warming elements outside said container.

The method may further comprise the step of:

- determining whether a first liquid state is fulfilled, and

- initiating dosing of the reductant via the dosing unit if the second liquid state is fulfilled.

An advantage of the innovative method is that a quicker process of thawing at least partly frozen reductant which is in the container is achieved by using at least one warming element which is external to the container. Beginning as early as possible to pump round a sufficient amount of thawed reductant which is in the container before dosing it to exhaust gases of the vehicle makes it possible for warming effects of other parts of the SCR system than the container only to be used for thawing the reductant in the container.

An advantageous synergy effect of using warming elements external to the container in conjunction with a warming element of the container is quicker thawing of the reductant in the container on the basis of increased stirring in the container. This is achieved by a flow of the reductant during a phase when it is being circulated within the SCR system, and particularly in the container, without being dosed into the exhaust flow.

According to a version, a plurality of warming elements external to the container are used in the process of thawing the reductant which is in the container. The quicker commencement of normal operation of the SCR system achieved by the innovative method may result in a reduction in a total amount of undesirable emissions.

Providing a number of different warming elements to warm the reductant which is in various lines and components of the vehicle's SCR system is an effective solution to the problem of quickly initiating normal operation of that system. This distributed configuration makes it possible to implement a warming element of reduced size and/or performance for warming the reductant in the container. Such a warming element may be less expensive than a warming element of superior performance. If a smaller warming element can be used to warm the reductant in the container, the container may itself also be made smaller, since according to an aspect of the invention the warming element is situated in the container. Alternatively, a container of undiminished size may contain a larger amount of the reductant if the warming element is made smaller. The result is a cost-effective solution to the problems indicated above. A more versatile solution to the problems indicated above is thus achieved. The method is easy to implement in existing motor vehicles. Software for warming a reductant in an SCR system according to the invention may be installed in a control unit of the vehicle during the manufacture of the vehicle. A purchaser of the vehicle may alternatively have the possibility of selecting the function of the method as an option. Alternatively, software comprising programme code for effecting the innovative method for warming a reductant in an SCR system may be installed in a control unit of the vehicle on the occasion of upgrading at a service station, in which case the software may be loaded into a memory in the control unit. Implementing the innovative method is therefore cost-effective, particularly as no further sensors, e.g. temperature sensors, or other units, e.g. warming elements for warming the reductant in or outside the container, need be installed in the vehicle's fuel tank. Necessary hardware is currently already provided in the vehicle. The invention therefore represents a cost-effective solution to the problems indicated above.

Software which comprises programme code for warming a reductant in an SCR system is easy to update or replace. Moreover, various portions of the software which comprise programme code for warming a reductant in an SCR system may be replaced independently of one another. This modular configuration is advantageous from a maintenance perspective.

An aspect of the invention pertains to a device according to claim 6.

An aspect of the invention pertains to a device for warming a reductant in an SCR system which comprises a container for said reductant and a dosing unit, comprising:

- means for extracting at least part of said reductant from said container, and means for warming said at least part of said reductant outside said container. The device comprises also means for returning the warmed part of said reductant to the container before dosing of said warmed part via the dosing unit commences in the SCR system.

The device may further comprise means for warming at least one of the following before said at least one part of said reductant is extracted: the container, a first line, a second line, a third line, a pump means and said dosing unit.

The device may further comprise means for determining whether a first liquid state is fulfilled, and means for initiating extraction of said at least part of said reductant from said container and warming of said at least part if the first liquid state is fulfilled.

Said at least one warming element may be a plurality of warming elements all situated outside said container.

The device may further comprise means for determining whether a second liquid state is fulfilled, and means for initiating dosing of the reductant via the dosing unit if the second liquid state is fulfilled.

The reductant in all of the components, e.g. in the first, second and third lines as well as the container, can be thawed relatively quickly, since the amount of reductant in them is limited. The above objects are also achieved with a motor vehicle which comprises the aforesaid device for warming a reductant in an SCR system. The vehicle may be a truck, bus or passenger car.

An aspect of the invention pertains to a device for warming a reductant in an SCR system which comprises a container for said reductant and a dosing unit for a marine engine. An aspect of the invention pertains to a device for warming a reductant in an SCR system which comprises a container for said reductant and a dosing unit for an industrial engine. It should be noted that the innovative method herein described for warming a reductant in an SCR system which comprises a container for said reductant and a dosing unit for a motor vehicle may also be used in a similar way to warm a reductant in an SCR system for other systems or products, e.g. a marine engine or an industrial engine. The industrial engine may be used to drive a generator. The marine engine may be situated on a watercraft, e.g. a road ferry.

An aspect of the invention pertains to a computer programme for warming a reductant in an SCR system which comprises a container for holding said reductant and a dosing unit, which computer programme comprises programme code stored on a computer-readable medium for causing an electronic control unit or another computer connected to the electronic control unit to perform steps according to any of claims 1-5. An aspect of the invention pertains to a computer programme product comprising a programme code stored on a computer-readable medium for performing method steps according to any of claims 1-5 when said computer programme is run on an electronic control unit or another computer connected to the electronic control unit.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas the invention is described below, it should be noted that it is not confined to the specific details described. Specialists having access to the teachings herein will recognise further applications, modifications and incorporations in other fields, which are within the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

For fuller understanding of the present invention and other objects and advantages thereof, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which:

Figure 1 illustrates schematically a vehicle according to an embodiment of the invention;

Figure 2 illustrates schematically a subsystem for the vehicle depicted in Figure 1 , according to an embodiment of the invention;

Figure 3 illustrates schematically a subsystem for the vehicle depicted in Figure 1 , according to an embodiment of the invention;

Figure 4a is a schematic flowchart of a method according to an embodiment of the invention;

Figure 4b is a more detailed schematic flowchart of a method according to an embodiment of the invention; and

Figure 5 illustrates schematically a computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 depicts a side view of a vehicle 100. The exemplified vehicle 100 comprises a tractor unit 110 and a trailer 112. The vehicle may be a heavy vehicle, e.g. a truck or a bus. The vehicle may alternatively be a passenger car.

The term "link" refers herein to a communication link which may be a physical connection such as an opto-electronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link. The term "line" refers herein to a passage for holding and transferring a fluid, e.g. a reductant in liquid form. The line may be a pipe of any desired size. The line may be made of any suitable material, e.g. plastic, rubber or metal. The term "reductant" refers herein to an agent used for reacting with certain emissions in an SCR system. These emissions may for example be NOx gas. According to a version, said reductant is one known as AdBlue. Other kinds of reductants may of course be used. AdBlue is cited herein as an example of a reductant, but specialists will appreciate that the innovative method and the innovative device are feasible with other types of reductants, subject to necessary adaptations, e.g. adaptations to appropriate freezing points for chosen reductants, in control algorithms for executing software code in accordance with the innovative method. The term "warming element" refers herein to a device adapted to warming an adjacent component, e.g. a line, pump or dosing valve containing said reductant. The warming elements herein indicated are therefore adapted to warming the reductant at various locations in the vehicle 100. A warming element may be an electrical warming element powered by, for example, one or more batteries (not depicted). Alternatively, a warming element may be a cooling medium-based warming element which utilises coolant from an engine of the vehicle to warm an adjacent component, e.g. a line, pump or dosing valve containing said reductant, in which case the reductant is also warmed.

Figure 2 depicts a subsystem 299 of the vehicle 100. The subsystem 299 is situated in the tractor unit 110. The subsystem 299 may form part of an SCR system. The subsystem 299 comprises in this example a container 205 adapted to holding a reductant. The container 205 is adapted to containing a suitable amount of reductant and also to being replenishable as necessary. A first line 271 is adapted to leading the reductant to a pump 230 from the container 205. The pump 230 is adapted to drawing the reductant from the container 205 via the first line 271 and to supplying said reductant via a second line 272 to a dosing valve 250. The pump 230 is adapted to pressurising the reductant in the second line 272.

The dosing valve 250 is adapted to supplying said reductant to an exhaust system of the vehicle 100. More specifically, the dosing valve 250 is adapted to supplying a suitable amount of reductant in a controlled way to an exhaust system of the vehicle 100. In this version, an SCR catalyst (not depicted) is situated downstream of a location where supply of the reductant takes place. The amount of reductant supplied in the exhaust system is intended to be used in a conventional way in the SCR catalyst in order to reduce in a known way the amount of undesirable emissions.

A third line 273 runs between the dosing valve 250 and the container 205. The third line 273 is adapted to leading back to the container 205 a certain amount of the reductant which has been fed to the dosing valve 250. This configuration achieves advantageous cooling of the dosing valve 250 and warming of the reductant.

A first coolant line 281 is adapted to holding and transferring coolant for an engine of the vehicle 100. The first coolant line 281 is partly situated in the container 205 in order to warm the reductant therein. In this example, the first coolant line 281 is adapted to leading radiator liquid which has been warmed by the engine of the vehicle 100 back to the engine in a closed circuit through the container 205, via the pump 230 and a second radiator liquid line 282. According to a version, the first coolant line 281 is configured with a substantially U-shaped portion situated in the container 205, as schematically depicted in Figure 2. This configuration achieves improved warming of the reductant in the container 205. According to an alternative, an electrical warming element is provided in or adjacent to the container 205 to warm the reductant therein. According to an embodiment, any suitable warming element is provided to warm the reductant in the container 205.

A first warming element 261 is situated adjacent to the second line 272 to warm as necessary the reductant therein. A second warming element 262 is provided adjacent to the dosing valve 250 to warm as necessary both the dosing valve 250 and the reductant therein. A third warming element 263 is provided adjacent to the third line 273 to warm as necessary the reductant therein.

It should be noted that according to the invention it is possible for a warming element to be situated at any suitable location in the subsystem 299. Various configurations are feasible, inter alia the alternative configuration described in more detail below with reference to Figure 3.

A first control unit 200 is arranged for communication with a temperature sensor 220 via a link 293. The temperature sensor 220 is adapted to detecting a prevailing temperature of the reductant where the sensor is fitted. In this version, the temperature sensor 220 is situated at a bottom of the substantially U-shaped configuration of the first coolant line 281. The temperature sensor 220 is adapted to sending continuously to the first control unit 200 signals which contain information about a prevailing temperature of the reductant.

The first control unit 200 is arranged for communication with the pump 230 via a link 292. The first control unit 200 is adapted to controlling operation of the pump 230 in order, for example, to regulate the flow of the reductant within the subsystem 299. The first control unit 200 is arranged for communication with the dosing valve 250 via a link 291. The first control unit 200 is adapted to controlling operation of the dosing valve 250 in order, for example, to regulate supply of the reductant to the exhaust system of the vehicle 100.

In one version, the first control unit 200 is adapted to controlling the pump 230 and the dosing valve 250 in accordance with the innovative method on the basis of the signals received which contain a prevailing temperature of the reductant in the region of the temperature sensor 220.

A second control unit 210 is arranged for communication with the first control unit 200 via a link 290. The second control unit 210 may be releasably connected to the first control unit 200. The second control unit 210 may be a control unit external to the vehicle 100. The second control unit 210 may be adapted to effecting the innovative method steps according to the invention. The second control unit 210 may be used to cross-load software to the first control unit 200, particularly software for applying the innovative method. The second control unit 210 may alternatively be arranged for communication with the first control unit 200 via an internal network in the vehicle. The second control unit 210 may be adapted to performing functions substantially similar to the first control unit 200, e.g. on the basis of the signals received which contain temperatures of a part-amount of the reductant in the container 205. In the embodiment schematically illustrated in Figure 2, the first control unit 200 is adapted to controlling the pump 230 in such a way that, where appropriate, at least part of said reductant is extracted from the container 205 to make it possible for it to be warmed by at least warming elements 261 , 262 and 263 outside the container 205. The first control unit 200 is further adapted to controlling the pump 230 in such a way that the warmed part of said reductant is returned to the container 205 prior to its dosing via the dosing unit 250 commences in the SCR system. Figure 3 illustrates schematically an alternative configuration of the subsystem 299 described with reference to Figure 2. Some of the components described with reference to Figure 2 are omitted in Figure 3. These omitted components and further components may therefore be part of the schematic configuration illustrated in Figure 3.

A basic difference in this alternative configuration of the subsystem 299 is that in this case the third pipe 273 runs between the pump 230 and the container 205 instead of between the dosing valve 250 and the container 205.

In this alternative configuration of the subsystem 299, the third warming element 263 is adjacent to the second line 272. There are also a fourth warming element 264 adjacent to the first line 271 , and a fifth warming element 265 adjacent to the pump 230.

In this embodiment, the pump 230 in a first example is adapted to extracting at least part of said reductant from the container 205 and warming it by means of at least the warming element 264 and the warming element 265 outside said container 205 before it is returned to the container 205 prior to its dosing via the dosing unit 250 commences in the SCR system.

In this embodiment, the pump 230 in a second example is adapted to extracting at least part of said reductant from the container 205 and warming it by means of at least the warming element 264 and the warming element 265 outside said container 205. In addition, the pump 230 in this second example is adapted to feeding the reductant towards the dosing valve 250 in the second line 272 to allow the reductant to be warmed by the third warming element 263 and thereafter be returned to the container 205 before its dosing via the dosing unit 250 in the SCR system. It should be noted that any desired combination of the components described with reference to Figure 2 and Figure 3 is feasible. For example, the second warming element 262 might be situated adjacent to the dosing valve in Figure 3.

Figure 4a is a schematic flowchart of a method for warming a reductant in an SCR system which comprises a container for said reductant and a dosing unit, according to an embodiment of the invention. The method comprises a first step s401 of extracting at least part of said reductant from said container and warming said at least part by means of at least one warming element outside said container. Step s401 comprises also returning the warmed part of said reductant to the container before dosing of said warmed part via the dosing unit commences in the SCR system. The method ends after step s401.

Figure 4b is a schematic flowchart of a method for warming a reductant in an SCR system which comprises a container for holding said reductant and a dosing unit, according to an embodiment of the invention. The method comprises a first step s410 of, where appropriate, commencing warming of the SCR system which comprises the container 205, the first line 271 , the second line 272, the third line 273, the pump 230 and the dosing unit 250. This takes place, for example, when it is established that the reductant in at least the container 205 is at least partly frozen and therefore not in a completely liquid phase. Step s410 is followed by a step s420.

Method step s420 comprises determining a liquid state of the reductant which is in the container 205. This may be done in various different ways. One way is to detect a temperature of the reductant in the container 205 by means of the temperature sensor 220 and to estimate on that basis how large a volume of the reductant is in a liquid phase. In another example, the temperature of the reductant in the container 205 is detected by the temperature sensor 220 and on that basis the volume of the reductant which is in a liquid phase is calculated by using a physical model stored in the first control unit 200. Step s420 is followed by a step s430. Method step s430 comprises determining whether a first liquid state prevails in the container 205. This may comprise determining whether a volume of liquid reductant in the container 205 exceeds a first threshold value. If a volume of liquid reductant determined in the container 205 exceeds a first threshold value, it is established that the first liquid state is fulfilled. The threshold value is any suitable threshold value representing a volume of thawed reductant which is necessary for it to be transferable within the SCR system without the first line 271 drawing dry in the container. If the first liquid state is fulfilled, a subsequent step s440 is performed. If the first liquid state is not fulfilled, step s420 is performed again. It should be noted that warming of the SCR system as described with reference to step s410 takes place throughout the method or until it is established that all of the reductant has reached a desired temperature.

Method step s440 comprises running the pump 230. By running the pump 230 it is possible for at least part of the thawed reductant to be extracted from the container 205 and be warmed by at least one warming element outside said container. Running the pump 230 also returns the warmed part of said reductant to the container 205 before dosing of said warmed part via the dosing unit commences in the SCR system. Step s440 is followed by a step s445.

Method step s445 comprises determining a liquid state of the reductant which is in the container 205. This may be done in various different ways. One way is to detect a temperature of the reductant in the container 205 by means of the temperature sensor 220 and to estimate on that basis how large a volume of the reductant is in a liquid phase. In another example, the temperature of the reductant in the container 205 is detected by the temperature sensor 220 and on that basis the volume of the reductant which is in a liquid phase is calculated by using a physical model stored in the first control unit 200. Step s445 is followed by a step s450. Method step s450 comprises determining whether a second liquid state prevails in the container 205. This may comprise determining whether a volume of liquid reductant in the container 205 exceeds a second threshold value. If a volume of liquid reductant determined in the container 205 exceeds a second threshold value, it is established that the second liquid state is fulfilled. The second threshold value is any suitable threshold value representing a volume of thawed reductant which is necessary for it to be possible to reliably commence dosing of the reductant within the SCR system. If the second liquid state is fulfilled, a subsequent step is performed. If the second liquid state is not fulfilled, step s445 is performed again. It should be noted that warming of the SCR system as described with reference to step s410 takes place throughout the method or until it is established that all of the reductant has reached a desired temperature.

Method step s460 comprises running the dosing valve according to operating routines stored in the first control unit 200. The method ends after step s460.

Figure 5 is a diagram of a version of a device 500. The control units 200 and 210 described with reference to Figure 2 may in a version comprise the device 500. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer programme, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540. A computer programme P is provided which comprises routines for warming a reductant in an SCR system according to the innovative method. The programme P comprises routines for determining whether a first liquid state is fulfilled and for initiating operation of the pump 230 in order to effect extraction of at least part of the reductant from the container 205 and warm it if the first liquid state is fulfilled. The programme P also comprises routines for returning the warmed part of said reductant to the container 205 before dosing of said warmed part via the dosing unit 250 commences in the SCR system. The programme P comprises routines for determining whether a second liquid state is fulfilled and for initiating dosing of the reductant via the dosing unit 250 if the second liquid state is fulfilled, in accordance with the innovative method. The programme P may be stored in an executable form or in compressed form in a memory 560 and/or in a read/write memory 550. Where it is stated that the data processing unit 510 performs a certain function, it means that the data processing unit 510 effects a certain part of the programme which is stored in the memory 560 or a certain part of the programme which is stored in the read/write memory 550. The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read/write memory 550 is intended to communicate with the data processing unit 510 via a data bus 514. The links 290, 291 , 292 and 293, for example, may be connected to the data port 599 (see Figure 2).

When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 will be ready to effect code execution in a manner described above. In one version, signals received on the data port 599 contain information about a prevailing temperature of part of the reductant in the container 205. The signals received on the data port 599 may be used by the device 500 to determine a liquid state in the container 205. The device 500 is adapted to determining whether a first liquid state prevails in the container 205 on the basis of the liquid state determined. The device 500 is adapted to determining whether a second liquid state prevails in the container 205 on the basis of the liquid state determined. The device 500 in one example is adapted to determining the first and second liquid states by means of a stored physical model. Parts of the methods herein described may be applied by the device 500 by means of the data processing unit 510 which runs the programme stored in the memory 560 or the read/write memory 550. When the device 500 runs the programme, methods herein described are executed. The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive, nor to limit the invention to the variants described. Many modifications and variants will obviously suggest themselves to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and the practical applications thereof and hence to make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims

1. A method for warming a reductant in an SCR system which comprises a container (205) for said reductant and a dosing unit (250), which method is characterised by the steps of:

- warming the container (205);

- determining whether a first liquid state in the container (205) is fulfilled, and

- if the first liquid state is fulfilled, extracting at least part of said reductant from said container (205) and warming said at least part by means of at least one warming element (261 ; 262; 263; 264; 265) outside said container (205);

- returning the warmed part of said reductant to the container (205) before dosing of said warmed part via the dosing unit (250) commences in the SCR system;

- determining whether a second liquid state in the container (205) is fulfilled, and,

- if the second liquid state is fulfilled, initiating dosing of reductant via the dosing unit (250).

2. A method according to claim 1 , further comprising the step of:

- warming at least one of the following components before the step of extracting at least part of said reductant: a first line (271), a second line (272), a third line (273), a pump (230) and said dosing unit (250).

3. A method according to any one of the foregoing claims, further comprising the step of:

- warming the extracted part of said reductant by means of a plurality of warming elements (261 ; 262; 263; 264; 265) situated outside said container (205).

4. A device for warming a reductant in an SCR system which comprises a container (205) for said reductant and a dosing unit (250), which device comprises: - means (271 ; 230) for extracting at least part of said reductant from said container (205); and

- means (261 ; 262; 263; 264; 265) for warming said at least part of said reductant outside said container (205);

- means (273; 230) for returning the warmed part of said reductant to the container (205) before dosing of said warmed part via the dosing unit (250) commences in the SCR system;

characterised by

- means (261 ; 262; 263; 264; 265) for warming the container (205) before said at least part of said reductant is extracted;

- means (200; 210; 500) for determining whether a first liquid state in the container (205) is fulfilled, and

- means (200; 210; 500) for initiating extraction of said at least part of said reductant from said container (205) and warming of said at least part if the first liquid state is fulfilled;

- means (200; 210; 500) for determining whether a second liquid state is fulfilled in the container (205), and,

- means (200; 210; 500) for initiating dosing of the reductant via the dosing unit (250) if the second liquid state is fulfilled.

5. A device according to claim 4, further comprising:

- means (261 ; 262; 263; 264; 265) for warming at least one of the following components before said at least part of said reductant is extracted: a first line (271), a second line (272), a third line (273), a pump (230) and said dosing unit (250).

6. A device according to either of claims 4 and 5, whereby said at least one warming element is a plurality of warming elements (261 ; 262; 263; 264; 265) all situated outside said container (205).

7. A motor vehicle (100; 110) comprising a device according to any one of claims 4-6.

8. A motor vehicle (100; 110) according to claim 7, which vehicle is any from among truck, bus or passenger car.

9. A computer programme (P) for warming a reductant in an SCR system, which computer programme (P) comprises programme code stored on a computer-readable medium for causing an electronic control unit (200; 500) or another computer (210; 500) connected to the electronic control unit (200; 500) to perform steps according to any one of claims 1-3.

10. A computer programme product comprising a programme code stored on a computer-readable medium for performing method steps according to any one of claims 1-3, which computer programme is run on an electronic control unit (200; 500) or another computer (210; 500) connected to the electronic control unit (200; 500).