SE538382C2 - Method of heating a reducing agent in an SCR system and determining suitability for circulation of said reducing agent in said SCR system - Google Patents

Description

Process for heating a reducing agent in an SCR system and determination of suitability for circulation of said reducing agents in said SCR system TECHNICAL FIELD The present invention relates to a method of an SCR system. The invention also relates to a computer program product comprising program code for a computer for implementing a method according to the invention. The invention also relates to an SCR system and a motor vehicle equipped with the SCR system.

BACKGROUND In today's vehicles, e.g. urea as a reductant in SCR systems comprising an SCR catalyst, in which catalyst said reductant and NCvgas can react with each other and be converted to nitrogen gas and water. Different types of reductants can be used in SCR systems. These reductants have different freezing points. A common reductant is e.g. AdBlue.

One type of SCR system includes a container holding a reductant. The SCR system also has a pump which is arranged to inflate said reductant from the container via a suction hose and supply it via a pressurized hose to a dosing unit which is arranged at an exhaust system of the vehicle. The dosing unit is arranged to inject a required amount of reductant into the exhaust system upstream of the SCR catalyst according to drivers stored in a control unit of the vehicle.

Said reductant may have a freezing point in a range of -10 to -15 degrees Celsius. Different reductants have unique freezing points depending on, among other things, their substance composition. For example, AdBlue has a freezing point at about -12 degrees Celsius. In this case, said reductant in the container and other parts of the SCR system will freeze if an ambient temperature for a certain time falls below said freezing point.

According to current regulations regarding emissions, certain vehicles equipped with an SCR system must be operated in a normal manner after a certain predetermined time after the start-up of the vehicle. Said predetermined time may, according to an example, be 70 minutes. Thus, frozen reducing agent must be at least partially melted in order to be able to circulate in the SCR system before dosing is started within said time period.

According to a known method of assessing whether the start-up of a circulation pump and the reducing agent dosing are suitable, a temperature sensor presently arranged in the container is used to measure a prevailing temperature of said reducing agent. In this case, it can be determined with a certain degree of probability whether the said reducing agent in the container has been thawed or not. A disadvantage of said method is that temperature measurements as a basis do not always give a correct assessment, depending on, for example, where the sensor is mounted, the configuration of, for example, suction hose and the configuration and size of the container. In this case, rather large safety margins are required to avoid starting a circulation pump of the SCR system too early. If the circulation pump is started up too early, when an insufficient amount of reducing agent has thawed, there is a risk that the pump "sucks dry", which can lead to a number of undesirable effects. An example of such an undesirable effect is that air enters the SCR system, which can significantly impair the performance of the system. Furthermore, effective continued thawing of frozen reducing agent is prevented.

In some cases, where frozen reducing agent in the tank, for example, is thawed by means of a circulating heating medium, and where the circulation pump sucks dry, a situation may arise where frozen reducing agent in the container can not be further thawed by said circulating heating medium. This can have extremely serious consequences, where current legal requirements regarding emissions of the vehicle cannot be met within the required time. Furthermore, the pump may be at risk of permanent damage or suffer from high wear if it is started up prematurely.

US 8011176 describes a method for thawing frozen urea in an SCR system by means of a heater. It is further described that said heater is switched off after a certain time when it is judged that the heater has been in operation long enough for said urea to melt. A disadvantage of this method is that rather large safety margins are required, which means that operation of a pump and reducing agent dosing can only be started at a relatively late time.

US 20100095653 describes a method for thawing frozen urea in which the dosing system is activated when said urea has reached a certain temperature.

SUMMARY OF THE INVENTION Thus, there is a need to reliably assess whether a circulation pump of the SCR system where reducing agents have been frozen can be started up, without using excessive safety margins to avoid said undesirable effects when the pump is forced to suck dry.

An object of the present invention is to provide a new and advantageous method in an SCR system.

Another object of the invention is to provide a new and advantageous SCR system and a new and advantageous computer program in an SCR system.

A further object of the invention is to provide a method of an SCR system, an SCR system and a computer program for effecting a faster start-up of an SCR system of a motor vehicle in which a reducing agent for exhaust gas purification is at least partially frozen.

A further object of the invention is to provide a method of an SCR system, an SCR system and a computer program for achieving a reliable commissioning of an SCR system of a motor vehicle.

A further object of the invention is to provide a method of an SCR system, an SCR system and a computer program for improving the performance of a motor vehicle.

An object of the invention is to provide an SCR system in which dosing of a reductant, e.g. urea in the form of AdBlue, can be started more quickly in a situation where said reductant is initially, at least partially, in a frozen state.

An object of the invention is to provide an SCR system in which circulation of a reductant, e.g. urea in the form of AdBlue, can be started more quickly in a situation where said reductant is initially, at least partially, in a frozen state.

These objects are achieved by a method in an SCR system according to claim 1.

According to one aspect of the invention, a method is provided in an SCR system comprising a circulation pump and a dosing unit for assessing the need to heat reducing agent arranged in a container for exhaust gas purification by means of a heating medium circulating through said container and assessing a start-up of circulation of said reducing agent in said SCR system is suitable for such heating. The method comprises the steps of: - determining whether a reducing agent present in the container is at least partially frozen, and if so, - continuously determining a temperature of said reducing agent in said container; - continuously determining a difference between a temperature of said heating medium and the temperature of said reducing agent in said container, or - continuously determining a difference between the temperature of said heating medium upstream of said container and a temperature of said heating medium downstream of said container; and - continuously determining an accumulated amount of molten reducing agent based on said temperature difference as a basis for determining suitability for said start-up.

According to one embodiment, an estimated heat transfer from said circulating heating medium to said reducing agent is continuously integrated over time to determine a molten amount of reducing agent in the container. In this case, the circulation pump can be started when a first sufficient amount of reducing agent has thawed instead of having to wait until a temperature of said reducing agent in the tank has exceeded a certain limit value. In this case, dosing of reducing agent can be started when a sufficient second amount of reducing agent has thawed instead of having to wait until a temperature of said reducing agent in the tank has exceeded a certain limit value.

The procedure may further comprise the step of: - continuously determining an accumulated amount of energy transferred to said reducing agent based on said temperature difference during said heating. In this case, an improved method is achieved in an SCR system where an adequate estimate of the amount of energy transferred is the basis for determining as soon as possible whether the SCR system can be started up in a safe and component-friendly manner.

The procedure may further comprise the step of: determining said accumulated amount of molten reducing agent based on said accumulated amount of energy transferred and the melting enthalpy of the reducing agent. In this case, a simple and non-calculation-heavy method is provided for accurately calculating said accumulated amount of molten reducing agent. Melting talpin for the reducing agent provided is known in advance. By accurately modeling the amount of thawed reducing agent present in the container according to the invention, an earlier start-up of the circulation pump and dosing of reducing agent can be achieved compared to technology where pump is started up after a predetermined time or at a predetermined temperature of said reducing agent.

According to the present invention there is provided a method where circulation of reducing agent and subsequent dosing thereof can be performed even when not all reducing agent in the container is thawed. According to the invention, it is only necessary to thaw a predetermined first and second amount of reducing agent, respectively, in order to activate said pump in a reliable manner and dosing of reducing agent by means of the dosing unit.

Start-up of said circulation pump can be considered suitable for a certain determined accumulated amount of molten reducing agent. Said accumulated amount of molten reducing agent may be an appropriate amount. Said suitable amount can be determined on the basis of, for example, the size of the container, the amount of remaining reducing agent and the configuration of the SCR system. Said suitable amount may be, for example, 5 liters.

The procedure may further comprise the step of: start dosing said reducing agent at a certain accumulated amount of molten reducing agent. Said accumulated amount of molten reducing agent may be an appropriate amount. Said suitable amount can be determined on the basis of, for example, the size of the container, the amount of remaining reducing agent and the configuration of the SCR system. Said suitable amount may be, for example, 15 liters.

An advantage of the innovative method is that a faster thawing process of at least partially frozen reductant present in the container is achieved because the circulation pump can be started at a relatively early stage. By using heating elements in the circulation of said reducing agent in the SCR system, a faster thawing process can be provided. According to an alternative embodiment, a circulating heating medium can be used to heat the reductant of different portions of the SCR system outside the container.

By starting to circulate a sufficient amount of molten reductant present in the tank of the SRC system as early as possible without dosing it to the exhaust gases of the vehicle, a heating effect of other vehicle components, such as a muffler, in the SCR system can be used to melt the reductant in the tank .

As an advantageous synergy effect of using external heating elements for the container together with a said heating medium of the container, a faster thawing of the reductant in the container is achieved on the basis of an increased stirring in the container. This is accomplished due to a flow of the reductant during a phase when it is circulating within the SCR system, and in particular in the container, without being metered into the exhaust stream.

According to one embodiment, a plurality of heating elements external to the container are used in the thawing process of the reductant present in the container.

Since a faster start-up of normal operation of the SCR system is achieved with the innovative procedure, a reduction of a total amount of unwanted emissions can be realized.

According to one aspect of the invention, there are a number of different heating elements of the SCR system, which are arranged to heat the reductant present in different lines and components of the SCR system of the vehicle. The procedure is easy to implement in existing motor vehicles. Software in an SCR system according to the invention can be installed in a control unit of the vehicle in the manufacture thereof. A buyer of the vehicle may alternatively be given the opportunity to choose the function of the procedure as an option. Alternatively, software including program code for performing the innovative procedure of an SCR system may be installed in a control unit of the vehicle when upgrading at a service station. In this case, the software can be loaded into a memory in the control unit.

According to one aspect of the invention, there is provided a device according to claim 6.

According to one aspect of the invention, there is provided an SCR system comprising: - a circulation pump; - a dosage unit, means adapted to assess the need to heat reducing agent arranged in a container for exhaust gas purification by means of a heating medium circulating through said container and to assess whether a start-up of circulation of said reducing agent in said SCR system is suitable for such heating; means adapted to determine whether reducing agents are present in the container (205) is at least partially frozen, - means adapted to continuously determine a temperature of said reducing agent in said container; means adapted to continuously determine a difference between a temperature of said heating medium and the temperature of said reducing agent in said container, or - means adapted to continuously determine a difference between the temperature of said heating medium upstream of said container and a temperature of said heating medium downstream said container; and - means adapted to continuously determine an accumulated amount of molten reducing agent based on said temperature difference as a basis for determining suitability for said start-up.

The SCR system may further comprise: means adapted to continuously determine an accumulated amount of energy transferred to said reducing agent based on said temperature difference during said heating.

The SCR system may further comprise: means adapted to determine said accumulated amount of molten reducing agent based on said accumulated amount of energy transferred and the melting enthalpy of the reducing agent.

The SCR system may further include means adapted to judge that the start-up of said circulation pump is suitable for a certain determined accumulated amount of molten reducing agent.

The SCR system may further comprise: means adapted to initiate dosing of said reducing agent at a certain accumulated amount of molten reducing agent.

The above objects are also achieved with a motor vehicle which includes the above-mentioned SCR system. The motor vehicle can be a truck, bus or car.

According to one aspect of the invention, there is provided an SCR system, which SCR system comprises a container for said reductant and a dosing unit of an exhaust system of a marine engine.

According to one aspect of the invention, there is provided an SCR system, which SCR system comprises a container for said reductant and a dosing unit of an exhaust system of an industrial engine.

According to one aspect of the present invention, there is provided a computer program in an SCR system, said computer program comprising program code stored on a computer readable medium for causing an electronic controller or another computer connected to the electronic controller to perform the steps of any of claims 1-5.

According to one aspect of the present invention, there is provided a computer program in an SCR system, said computer program comprising program code for causing an electronic controller or another computer connected to the electronic controller to perform the steps of any of claims 1-5.

According to one aspect of the present invention, there is provided a computer program product comprising a program code stored on a computer readable medium for performing the method steps of any of claims 1-5, when said computer program is run on an electronic control unit or another computer connected to the electronic the control unit.

Additional objects, advantages, and novel features of the present invention will become apparent to those skilled in the art from the following details, as well as through practice of the invention. While the invention is described below, it should be understood that the invention is not limited to the specific details described. Those skilled in the art having access to the teachings herein will recognize additional applications, modifications, and incorporations within other fields which are within the scope of the invention. SUMMARY DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and further objects and advantages thereof, reference is now made to the following detailed description which is to be read in conjunction with the accompanying drawings in which like reference numerals refer to like parts in the various figures, and in which: Figure 1 schematically illustrates a vehicles, according to an embodiment of the invention; Figure 2 schematically illustrates a subsystem of the vehicle shown in Figure 1, according to an embodiment of the invention; Figure 3 schematically illustrates a subsystem of the vehicle shown in Figure 1, according to an embodiment of the invention; Figure 4a schematically illustrates a flow chart of a method, according to an embodiment of the invention; Figure 4b schematically illustrates in further detail a flow chart of a method, according to an embodiment of the invention; and Figure 5 schematically illustrates a computer, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE FIGURES Referring to Figure 1, a side view of a vehicle 100 is shown. The exemplary vehicle 100 consists of a tractor 110 and a trailer 112. The vehicle may be a heavy vehicle, such as a truck or a bus. The vehicle can alternatively be a car.

Here, the term "link" refers to a communication link which may be a physical line, such as an optoelectronic communication line, or a non-physical line, such as a wireless connection, for example a radio or microwave link.

Here, the term "reductant" refers to an agent used to react with certain emissions in an SCR system. These emissions can e.g. be NOx gas. Said reductant is according to an embodiment so-called AdBlue. Of course, other types of reductants can be used. Here, AdBlue is mentioned as an example of a reductant, but a person skilled in the art realizes that the innovative method and the innovative device can be realized for other types of reductants, with necessary adaptations, such as e.g. adjustments to adequate freezing point for selected reductants, in control algorithms for executing software code in accordance with the innovative procedure.

Here, the term "heating element" refers to a device which is arranged to heat an adjacent component, such as e.g. a line, pump or dosage unit containing said reductant. The heating elements specified herein are arranged to heat the reductant at different positions in the vehicle 100. A heating element can be an electric heating element which is energized by e.g. one or more batteries (not shown).

Alternatively, a heating element may be a coolant-based heating element which uses coolant from an engine of the vehicle to heat said reductant in a reducing agent container of the SCR system.

It should be noted that the invention is suitable for application to any SCR system and is not limited to SCR systems of motor vehicles. The innovative method and the innovative liquid supply system according to an aspect of the invention are well suited for platforms other than an SCR system other than motor vehicles, such as e.g. watercraft. The watercraft can be of any kind, such as e.g. motorboats, ships, ferries or ships.

The innovative method and the innovative SCR system according to an aspect of the invention are also well suited for e.g. systems including tractors, dumpers, power tools, industrial engines and / or powered industrial robots.

The innovative method and the innovative SCR system according to an aspect of the invention are also well suited for different types of power plants, such as e.g. an electric power plant comprising a diesel generator.

The innovative procedure and the innovative SCR system are well suited for an arbitrary engine system that includes an engine and an SCR system, such as e.g. at a locomotive or other platform.

The innovative procedure and the innovative SCR system are well suited for a system that includes an NCv generator, such as a diesel engine, whose exhaust gases are to be purified.

Herein, the term "conduit" refers to a passageway for holding and transporting a fluid, such as e.g. a reductant in liquid form. The pipe can be a pipe of any dimension. The conduit may consist of any suitable material, such as e.g. plastic, rubber or metal.

With reference to Figure 2, a subsystem 299 of the vehicle 100 is shown. The subsystem 299 may be arranged in the tractor 110. The subsystem 299 may form part of an SCR system. According to this example, the subsystem 299 consists of a container 205 which is arranged to hold a reductant. The container 205 is arranged to contain a suitable amount of reductant and is further arranged to be able to be refilled if necessary.

A first line 271 is arranged to direct the reductant to a pump 230 from the container 205. Said pump is 230 arranged to pump up the reductant from the container 205 via the first line 271 and via a second line 272 supply said reductant to a dosing unit 250. The pump 230 is arranged to pressurize the reductant in the second line 272.

The dosing unit 250 is arranged to supply said reductant to an exhaust system of the vehicle 100. More specifically, the dosing unit 250 is arranged to supply in a controlled manner an appropriate amount of reductant to an exhaust system of the vehicle 100. According to this embodiment, an SCR catalyst (not shown) arranged downstream of a position where supply of the reductant is effected. The amount of reductant supplied to the exhaust system is intended to be used in a conventional manner in the SCR catalyst to reduce the amount of unwanted emissions.

A third conduit 273 is presently disposed between the metering device 250 and the container 205. The third conduit 273 is arranged to return a certain amount of the reductant fed to the metering unit 250 to the container 205.

A first fluid conduit 281 is arranged to hold and transport a fluid. Said fluid is a heating medium. Said fluid may be coolant for an engine (not shown) of the vehicle 100. The first fluid conduit 281 is partially disposed in the container 205 to heat the reductant present therein. The first fluid conduit 281 is partially disposed in the container 205 to, where applicable, melt the reductant present therein by energy transfer. According to this example, the first fluid line 281 is arranged to direct coolant heated by the vehicle engine in a closed loop through the container 205, via the pump 230 and a second fluid line 282 back to the engine of the vehicle 100.

According to one embodiment, a separate pump, for example a pump for the engine coolant, is presently provided. According to this exemplary embodiment, the fluid does not have to be circulated by means of the pump 230. Said pump 230 can also be referred to as a supply means or circulation pump. Said pump 230 may be of any suitable type. Said pump 230 may be a diaphragm pump. Said pump 230 can according to one embodiment be heated with a circulating heating medium. According to an example, for example, the first line 271 may be arranged to heat the pump 230 downstream of said container 205. According to an alternative, the pump may be heated with a circulating medium provided by equipment intended therefor.

According to one embodiment, the first fluid conduit 281 is partially configured as a coil, which coil is arranged around said first conduit 271 and said third conduit 273 present in the container 205, as schematically shown in Figure 2. With this configuration an efficient heating or melting is achieved of the reductant in the container 205. The first fluid line 281 may alternatively have another suitable shape, for example a U-shape.

A first heating element 261 is provided at the second conduit 272 to heat, if necessary, the reductant present therein. A second heating element 262 is provided at the metering valve 250 to heat, if necessary, both the metering valve 250 and the reductant present therein. A third heating element 263 is provided at the third conduit 273 to heat the reductant present therein if necessary.

It should be pointed out that according to the invention it is possible to place a heating element in any suitable place in the subsystem 299. Different configurations are possible to realize.

A first control unit 200 is arranged to control operation of said first heating element 261, said second heating element 262 and said third heating element 263 in a suitable manner. Said first control unit 200 may be arranged to control operation of said first heating element 261, said second heating element 262 and said third heating element 263 independently of each other. According to an embodiment, the first control unit is arranged to activate and drive said heating element when circulation of said reducing agent in the SCR system is judged to be suitable.

Said first control unit 200 is arranged for communication with a first temperature sensor 221 via a link L221. Said first temperature sensor 221 is arranged to detect a prevailing temperature of the reductant where the sensor is mounted. According to one embodiment, the first temperature sensor 221 is arranged in the immediate vicinity of the first and / or third line in the container 205. According to one embodiment, the first temperature sensor 221 is arranged in the immediate vicinity of the first and / or third line at the bottom of the container 205. According to one embodiment, the first temperature sensor 221 is arranged in a lower part of the container 205. The temperature sensor 221 is arranged to continuously send signals to the first control unit 200 including information about a prevailing temperature of the reductant via the link L221.

The first control unit 200 is arranged for communication with the pump 230 via a link 292. The first control unit 200 is arranged to control operation of the pump 230 in order to e.g. regulating flows of the reductant within the subsystem 299. The first control unit 200 is arranged to activate circulation of said reducing agent when it is deemed appropriate, according to an embodiment of the present invention.

The first control unit 200 is arranged for communication with the dosing unit 250 via a link L250. The first control unit 200 is arranged to control the operation of the dosing unit 250 in order to e.g. controlling supply of the reductant to the exhaust system of the vehicle 100. The first control unit 200 is arranged to activate dosing of said reducing agent when it is deemed appropriate, according to an embodiment of the present invention.

A second control unit 210 is arranged for communication with the first control unit 200 via a link L210. 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 arranged to perform the innovative method steps according to the invention. The second control unit 210 can be used to upload software to the first control unit 200, in particular software for performing 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 arranged to perform substantially similar functions as the first control unit 200.

According to the embodiment schematically illustrated with reference to Figure 2, the first control unit 200 is arranged to control the pump 230 in such a way that, where applicable, at least a part of said molten reductant is extracted from the container 205 to enable heating thereof by at least any of the heating elements 261, 262 and 263 outside the container 205. The first control unit 200 is further arranged to control the pump 230 in such a way that the molten part of said reductant is returned to the container 205 before dosing thereof by the dosing unit 250 is started in the SCR system. .

Figure 3 schematically illustrates a part of the subsystem 299 which is described with reference to Figure 2. In Figure 3 a part of the components described with reference to Figure 2 is omitted.

Said first control unit 200 is arranged for communication with a second temperature sensor 222 via a link L222. Said second temperature sensor 222 is arranged to continuously measure a prevailing temperature T2 of said fluid upstream of said container 205. Said second temperature sensor 222 is arranged to continuously send signals including current temperature information of the fluid to the first control unit 200 via said link L222. Said second temperature sensor 222 may be provided in the immediate vicinity of the container 205 at an upstream side thereof or at the vehicle engine or at a suitable location between said engine and said container 205.

Said first control unit 200 is arranged for communication with a third temperature sensor 223 via a link L223. Said third temperature sensor 223 is arranged to continuously measure a prevailing temperature T3 of said fluid downstream of said container 205. Said third temperature sensor 223 is arranged to continuously send signals including current temperature information of the fluid to the first control unit 200 via said link L223. Said third temperature sensor 223 may be provided in close proximity to the container 205 at a downstream side thereof or at the vehicle engine or at a suitable location between said engine and said container 205. According to an example, said third temperature sensor 223 may be provided at the pump 230.

According to one embodiment, said first control unit 200 is arranged to communicate with said temperature sensors via said second control unit 210. which may be signal connected to said temperature sensors.

Said first conduit 281 is arranged to conduct a heating fluid to effect melting of frozen reducing agent in the container 205. According to one example, said first conduit is arranged to cool an engine of the vehicle. During said cooling of the engine, thermal energy is transferred from said engine to said fluid. According to one example, said fluid is a coolant of an engine cooling system. According to one example, said pump 230 is arranged to circulate said fluid from the motor to the container and back to the motor via the line 282 in a closed loop. It should be noted that said reducing agent and said heating fluid are never mixed but are physically separated by said conduits.

According to an alternative embodiment, a vehicle external heating medium can be used. According to this embodiment, a separate container with a heating medium can be used, whereby the container can be connected to a circulation line present in the vehicle. In this case, either a vehicle external feeding device or a dedicated feeding device of the vehicle can be used for circulation of said heating fluid.

The first control unit 200 is according to an embodiment arranged to control on the basis of the received signals comprising a prevailing temperature T1 of the reductant at the area of the temperature sensor 221 and a prevailing temperature T2 of the fluid upstream of said container 205 operation of the pump 230 and dosing unit 250 according to the innovative procedure.

According to an embodiment, the first control unit 200 is arranged to determine on the basis of the received signals comprising a prevailing temperature T1 of the reductant at the area of the temperature sensor 221 and a prevailing temperature T2 of the fluid upstream of said container 205 according to an aspect of the innovative procedure.

According to one embodiment, the first control unit 200 is arranged to determine on the basis of the received signals comprising a prevailing temperature T3 of the fluid downstream of said container 205 and a prevailing temperature T2 of the fluid upstream of said container 205 a temperature difference thereof in accordance with an aspect of the innovative procedure.

Figure 4a schematically illustrates a flow chart of a method of an SCR system comprising a circulation pump 230 and a dosing unit 250 for assessing the need for heating in a container arranged reducing agent for exhaust gas purification by means of a heating medium circulating through said container 205 and assessing whether a start-up of circulation of said reducing agent in said SCR system is suitable for such heating, according to an embodiment of the invention. The method comprises a first method step s401. Step s401 includes the steps of: - determining whether reducing agent present in the container 205 is at least partially frozen, and if so, - continuously determining a temperature of said reducing agent in said container 205, - continuously determining a difference between a temperature of said heating medium and the temperature of said reducing agent in said container, or - continuously determining a difference between the temperature of said heating medium upstream of said container and a temperature of said heating medium downstream of said container; and - continuously determining an accumulated amount of molten reducing agent based on said temperature difference as a basis for determining suitability for said start-up.

After the procedure step s401, the procedure is terminated.

Figure 4b schematically illustrates a flow chart of a method in an SCR system comprising a circulation pump 230 and a dosing unit 250 for assessing the need to heat reducing agent arranged in a container 205 by means of a heating medium circulating through said container 205 and if a start-up of circulation of said reducing agent in said SCR system is suitable for such heating, according to an embodiment of the invention.

The method includes a first method step s410. Process step s410 may include the step of determining if reducing agent present in the container 205 is at least partially frozen. This can be achieved by measuring the temperature of the reducing agent by means of the first temperature sensor 221. This can alternatively be achieved by considering an ambient temperature determined when the vehicle is switched off and / or an ambient temperature when starting the vehicle. Method step s410 includes the step of continuously determining a temperature T1 of said reducing agent in said container. After the process step s410, a subsequent process step s420 is performed.

The process step s420 comprises the step of continuously determining a difference between a temperature T2 of said heating medium and the temperature T1 of said reducing agent in said container 205, or continuously determining a difference between the temperature of said heating medium upstream of said container and a temperature of said heating medium downstream of said container. After the process step s420, a subsequent process step s430 is performed.

Method step s430 includes the step of continuously determining an accumulated amount of energy transferred to said reducing agent based on any of said temperature differences during said heating. This can be done by a continuous integration of the estimated amount of transferred energy from said heating medium to said reducing agent in the container 205. Said estimated amount of transferred energy can be based on said determined difference in temperature (T1-T2, T3-T2) multiplied by a suitable heat transfer constant . Said heat transfer constant can be empirically determined. Said heat transfer constant may be an appropriate value and is based on the characteristics of said reducing agent. After the process step s430, a subsequent process step s440 is performed.

Method step s440 includes the step of continuously determining an accumulated amount of molten reducing agent based on said temperature difference as a basis for determining suitability for said start-up. Method step s440 may include the step of determining said accumulated amount of molten reducing agent based on said accumulated amount of energy transferred and the melting enthalpy of the reducing agent. Process steps s420, s430 and s440 are performed until it is determined that start-up of pump 230 is appropriate. After the process step s440, a subsequent step s450 is performed.

The process step s450 may include the step of, when it is deemed appropriate to start the pump 230 for circulating said reducing agent, starting the pump 230 for circulating said reducing agent. According to one embodiment, it is considered appropriate to start the pump 230 when a predetermined first amount of reducing agent has been thawed. Said first amount of reducing agent may be any suitable amount of reducing agent, for example 2, 5 or 10 liters. The process step s450 may include the step of heating reducing agent by means of the heating elements 261, 262 and / or 263. After the process step s450, a process step s460 is performed.

The process step s460 may comprise the step of, after it is deemed appropriate, starting the dosing of reducing agent according to drivers stored in the first control unit by means of said dosing unit 250. According to an exemplary embodiment, it is considered suitable to start dosing unit 250 when a predetermined second amount of reducing agent has been thawed. Said second amount of reducing agent may be any suitable amount of reducing agent, for example 12, 15 or 20 liters.

After the procedure step s460, the procedure is terminated.

Referring to Figure 5, a diagram of an embodiment of a device 500 is shown. The controllers 200 and 210 described with reference to Figure 2 may in one embodiment 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 part 530 in which a computer program, such as a operating system, is stored to control the operation of the device 500. Furthermore, the device 500 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 interrupt controller (not shown). The non-volatile memory 520 also has a second memory portion 540.

A computer program P is provided which comprises routines for assessing the need to heat reducing agent arranged in a container for exhaust gas cleaning by means of a heating medium circulating through said container and assessing whether a start-up of circulation of said reducing agent in said SCR system is suitable for such heating. The computer program P includes routines for continuously determining a temperature of said reducing agent in said container. The computer program P includes routines for continuously determining a difference between a temperature of said heating medium and the temperature of said reducing agent in said container. Alternatively, the computer program P comprises routines for continuously determining a difference between the temperature of said heating medium upstream of said container 205 and a temperature of said heating medium downstream of said container 205. The computer program P comprises routines for continuously determining an accumulated amount of molten reducing agent based on as a basis for determining suitability for said start-up. The computer program P includes routines for continuously determining an accumulated amount of energy transferred to said reducing agent based on said temperature difference during said heating. The computer program P includes routines for determining said accumulated amount of molten reducing agent based on said accumulated amount of energy transferred and the melting enthalpy of the reducing agent. The computer program P comprises routines for judging that the start-up of said circulation pump is suitable for a certain determined accumulated amount of molten reducing agent. The computer program P comprises routines for starting dosing of said reducing agent at a certain accumulated amount of molten reducing agent.

The program P can be stored in an executable manner or in a compressed manner in a memory 560 and / or in a read / write memory 550.

When it is described that the data processing unit 510 performs a certain function, it is to be understood that the data processing unit 510 performs a certain part of the program which is stored in the memory 560, or a certain part of the program 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. Read / write memory 550 is arranged to communicate with the data processing unit 510 via a data bus 514. To the data port 599, e.g. the links L210, L221, L222 and L223 are connected (see Figure 2 and Figure 3).

When data is received on the data port 599, it is temporarily stored in the second memory part 540. Once the received input data has been temporarily stored, the data processing unit 510 is arranged to perform code execution in a manner described above. According to one embodiment, signals received at the data port 599 include information about a prevailing temperature T1 of the reducing agent in the container 205. According to one embodiment, signals received at the data port 599 include information about a prevailing temperature T2 of said heating medium upstream of the container 205. According to one embodiment, signals received include on the data port 599 information about a prevailing temperature T2 of said heating medium downstream of the container 205.

Parts of the methods described herein may be performed by the device 500 by means of the data processing unit 510 running the program stored in the memory 560 or the read / write memory 550. When the device 500 runs the program, the methods described herein are executed.

The foregoing description of the preferred embodiments of the present invention has been provided for the purpose of illustrating and describing the invention. It is not intended to be exhaustive or to limit the invention to the variations described. Obviously, many modifications and variations will occur to those skilled in the art. The embodiments were selected and described to best explain the principles of the invention and its practical applications, thereby enabling those skilled in the art to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims (14)

A method of an SCR system comprising a circulation pump (230) and a dosing unit (250) for assessing, on the one hand, the need for heating in a container (205) arranged for exhaust gas purification by means of a heating medium circulating through said container (205) and secondly, assessing whether a start-up of circulation of said reducing agent in said SCR system is appropriate for such heating, including the steps of: - determining whether reducing agent present in the container (205) is at least partially frozen, and if so, - continuously determining ( s410) a temperature (T1) of said reducing agent in said container (205), characterized by the steps of: - continuously determining (s420) a difference between a temperature (T2) of said heating medium and the temperature (T1) of said reducing agent in said container (205), or - continuously determining (s420) a difference between the temperature (T2) of said heating medium upstream of said container (205) and a temperature (T3) of n said heating medium downstream of said container (205); and - continuously determining (s440) an accumulated amount of molten reducing agent based on said temperature difference as a basis for determining suitability for said start-up. The method of claim 1, further comprising the step of: - continuously determining (s430) an accumulated amount of energy transferred to said reducing agent based on said temperature difference during said heating. The method of claim 2, further comprising the step of: - determining (s430) said accumulated amount of molten reducing agent based on said accumulated amount of energy transferred and the melting enthalpy of the reducing agent. A method according to any one of the preceding claims, wherein start-up (s450) of said circulation pump is judged suitable for a certain determined accumulated amount of molten reducing agent. A method according to any one of the preceding claims, further comprising the step of: - starting dosing (s460) of said reducing agent at a certain accumulated amount of molten reducing agent. An SCR system comprising: - a circulation pump (230); - a dosage unit (250); means (200; 210; 500) adapted to assess the need to heat reducing agent arranged in a container (205) for exhaust gas purification by means of a heating medium circulating through said container (205) and to assess whether a start-up of circulation of said reducing agent in said SCR system is suitable for such heating; means adapted to determine whether reducing agent present in the container (205) is at least partially frozen, - means (221) adapted to continuously determine a temperature (T1) of said reducing agent in said container (205), characterized by: - means (200; 210; 500) adapted to continuously determine a difference between a temperature (T2) of said heating medium and the temperature (T1) of said reducing agent in said container (205), or means (200; 210; 500) adapted to continuously determine a difference between the temperature (T2) of said heating medium upstream of said container (205) and a temperature (T3) of said heating medium downstream of said container (205); and - means (200; 210; 500) adapted to continuously determine an accumulated amount of molten reducing agent based on said temperature difference as a basis for determining suitability for said start-up. The SCR system of claim 6, further comprising: - means (200; 210; 500) adapted to continuously determine an accumulated amount of energy transferred to said reducing agent based on said temperature difference during said heating. The SCR system of claim 7, further comprising: - means (200; 210; 500) adapted to determine said accumulated amount of molten reducing agent based on said accumulated amount of energy transferred and the melting enthalpy of the reducing agent. An SCR system according to any one of claims 6-8, comprising - means (200; 210; 500) adapted to judge that start-up of said circulation pump (230) is suitable for a certain determined accumulated amount of molten reducing agent. The SCR system of any of claims 6-9, further comprising: - means (200; 210; 500) adapted to initiate dosing of said reducing agent at a certain accumulated amount of molten reducing agent. A motor vehicle (100; 110) comprising an SCR system according to any one of claims 6-10. A motor vehicle (100; 110) according to claim 11, wherein the motor vehicle is something of a truck, bus or passenger car. Computer program (P) in an SCR system, wherein said computer program (P) comprises program code for causing an electronic control unit (200; 500) or another computer (210; 500) connected to the electronic control unit (200; 500) to perform the steps according to any one of claims 1-5. A computer program product comprising a computer program stored on a computer readable medium for performing the method steps according to any one of claims 1-5, when said computer program is run on an electronic control unit (200; 500) or another computer (210; 500) connected to the electronic control unit (200; 500).