The present invention pertains to a method for selection of maximum reducing agent dosage at an SCR system for exhaust purification. The invention also relates to a computer program product, comprising program code for a computer, to implement a method according to the invention. The invention also pertains to a device for the selection of maximum reducing agent dosage at an SCR system for exhaust purification and a motor vehicle which is equipped with this device. BACKGROUND

In vehicles today e.g. urea is used as a reducing agent in SCR systems (Selective Catalytic Reduction) comprising an SCR catalyst, in the catalyst of which the said reducing agent and NO _x gas may react and transform into nitrogen and water. Different types of reducing agents may be used in SCR systems. A commonly occurring reducing agent is e.g. AdBlue.

In one type of SCR system a container holding a reducing agent is included. The SCR system also has a pump which is arranged to pump the said reducing agent from the container via a suction hose and add it via a pressurised hose to a dosage device which is arranged at an exhaust system of e.g. a vehicle, such as at an exhaust pipe of the exhaust system. The dosage device is arranged to inject a required amount of reducing agent into an exhaust system upstream of the SCR catalyst, according to operational procedures in a control device of the vehicle. There is a constant need to reduce the amount of emissions from engines of motor vehicles. This applies not least to heavy goods vehicles such as trucks and buses, since legislative requirements for smaller emissions are continuously being sharpened.

The possibility of evaporating reducing agent comprising urea may constitute a strict limitation for how large an amount of NO _x gas an exhaust after treatment system based on SCR may reduce. It is important to be able to determine limits to the quantities of reducing agent that may be evaporated under certain given operating conditions. Today there are known problems associated with reducing agent dosage, which are attributable to the formation of reducing agent crystals in exhaust systems.

In order to prevent the formation of reducing agent crystals, there is, according to prior art, a map-based model for reducing agent dosage stored in a control device of the vehicle, the model of which depends on the parameters exhaust mass flow and exhaust temperature. However, even when this model is used to determine a limit for maximum dosage of reducing agent under certain operating conditions, the said problem with formation of reducing agent crystals may arise.

In cases where the said map-based model for reducing agent dosage is set too conservatively, this will result in an undesirably high fuel consumption by the said engine.

US 61 19448 describes a method for dosage of urea.

US 20090199540 describes a method for control of a dosage valve for dosage of urea.

SUMMARY OF THE INVENTION There is a need to improve the control and selection of maximum reducing agent dosage in an SCR system, where a reduced risk of formation of reducing agent crystals as well as a possibility of not causing unnecessarily high fuel consumption of the vehicle is achieved.

One objective of the present invention is to provide a new and advantageous method for the selection of maximum reducing agent dosage at an SCR system for exhaust purification. Another objective of the invention is to provide a novel and advantageous device and a novel and advantageous computer program for the selection of maximum reducing agent dosage at an SCR system for exhaust purification.

Another objective of the invention is to provide a method, a device and a computer program to achieve a reliable and user-friendly selection of maximum reducing agent dosage at an SCR system for exhaust purification.

Yet another objective of the invention is to provide an alternative method, an alternative device and an alternative computer program for the selection of maximum reducing agent dosage at an SCR system for exhaust purification.

These objectives are achieved with a method for the selection of maximum reducing agent dosage at an SCR system for exhaust purification according to patent claim 1 .

According to one aspect of the invention, a method is provided for the selection of maximum reducing agent dosage at an SCR system for exhaust purification, where evaporation of a dosed amount of reducing agent is required. The method may comprise the step to:

- select the said maximum reducing agent dosage based on an exhaust mass flow, an effective evaporation temperature and a reducing agent temperature. By also taking into account external circumstances in the environment of the said SCR system, and thus implementing the method according to the invention for the selection of maximum reducing agent dosage by introducing reducing agent temperature, the above-mentioned disadvantages with e.g. formation of crystals in doses of reducing agent may be avoided. The temperature of the surrounding air impacts the temperature of the said reducing agent. According to one aspect of the invention, a method is provided for the selection of maximum reducing agent dosage at an SCR system for exhaust purification, where evaporation of a dosed amount of reducing agent is required. The method may comprise the step of:

- select the said maximum reducing agent dosage based on an exhaust mass flow, a temperature for exhausts from an engine and a reducing agent temperature.

Thus an existing model for the selection of maximum reducing agent dosage may in an advantageous manner be extended to comprise the parameter reducing agent temperature. Thus an improved method for the selection of reducing agent dosage is achieved.

According to one embodiment, an existing map model, which is based on the parameters exhaust mass flow, and an effective evaporation temperature may in an advantageous manner be extended to comprise both the effective evaporation temperature and the temperature of the said reducing agent.

The actual dosage of the reducing agent may be lower than the said maximum reducing agent dosage.

According to one embodiment, an existing map model, which is based on the parameters exhaust mass flow, and an exhaust temperature may in an advantageous manner be extended to comprise both the exhaust temperature and the temperature of the said reducing agent.

Thus an automated selection of maximum reducing agent dosage may be achieved. The temperature sensors to measure a temperature of the said reducing agent are relatively cheap and reliable, which advantageously entails that the method according to the invention is cost-efficient.

Thus, over time, a relatively low fuel consumption of an engine in the vehicle may be achieved. Further, the formation of solid reducing agent crystals in an exhaust system may be prevented to a higher degree than according to prior art technology.

The said maximum reducing agent dosage may be selected based on a determined matrix showing maximum reducing agent dosage for evaporation depending on exhaust mass flow and a reference parameter depending on effective evaporation temperature as well as reducing agent temperature.

The said maximum reducing agent dosage may be selected based on an empirically determined matrix showing maximum reducing agent dosage for evaporation depending on exhaust mass flow and a reference parameter depending on effective evaporation temperature as well as reducing agent temperature. The said maximum reducing agent dosage may be selected based on a predetermined matrix showing maximum reducing agent dosage for evaporation depending on exhaust mass flow and a reference parameter depending on effective evaporation temperature as well as reducing agent temperature.

Information about maximum reducing agent dosage depending on exhaust mass flow and a reference parameter depending on effective evaporation temperature as well as reducing agent temperature may be stored in a memory of a control device in suitable manner.

The said reference parameter may be defined as a suitable function which depends on the effective evaporation temperature as well as the reducing agent temperature.

The said reference parameter may, alternatively, be defined as a suitable function which depends on the exhaust temperature as well as the reducing agent temperature.

The said reference parameter may be determined according to a connection which is defined by: Tref=Tv-K1 ^* Tu+K2 where:

Tv is the effective evaporation temperature;

Tu is the reducing agent temperature; and

K1 and K2 are predetermined constants.

K1 and K2 may be empirically determined. K1 and K2 may be determined in a suitable manner. K1 and K2 may be predetermined constants. The effective evaporation temperature may be set as the exhaust temperature or a temperature for a component in a configuration of an exhaust pipe and an SCR catalyst of the said SCR system.

The effective evaporation temperature is, according to one embodiment, the temperature of the exhaust mass flow which is needed to evaporate the reducing agent at a normalised reducing agent temperature which depends on e.g. the engine's ambient temperature. The new evaporation temperature (Tref) then becomes a function of the effective evaporation temperature (at normalised reducing agent temperatures) and the actual reducing agent temperature at the time. The method according to the invention may be carried out during operation when the vehicle is at a standstill, e.g. when an engine in the vehicle is running at idle.

The method according to the invention may be carried out during operation, e.g. when the vehicle is driven on a suitable road section. The method according to the invention may be carried out when the vehicle is driven under circumstances where advantageous operating cases may be achieved; operating cases which may comprise that a minimum temperature in the vehicle's SCR catalyst is achieved and that an exhaust flow which is advantageous for the method is achieved.

The extension according to the invention of an existing model may increase the accuracy in the model and thus facilitates that quality problems caused by crystals of reducing agent forming may be avoided without having to provide an excessively high safety margin in the event of many driving cases.

The method is easy to implement in existing motor vehicles. Software for selection of maximum reducing agent dosage at an SCR system for exhaust purification may, according to the invention, be installed in a control device of the vehicle when the said vehicle is manufactured. A purchaser of the vehicle may thus be afforded the opportunity to select the performance function as an extra option. Alternatively, software comprising program code to perform the innovative method for the selection of maximum reducing agent dosage at an SCR system for exhaust purification is installed in a control device of the vehicle, when upgraded at a service station. In this case, the software may be uploaded into a memory in the control device. Program code comprising program code for selection of maximum reducing agent dosage at an SCR system for exhaust purification, where evaporation of a dosed amount of reducing agent is required, may easily be updated or replaced. Further, different parts of the program code for the selection of maximum reducing agent dosage at an SCR system for exhaust purification may be replaced independently of each other. This modular configuration is advantageous from a maintenance perspective.

According to one aspect of the invention, a device is provided for the selection of maximum reducing agent dosage at an SCR system for exhaust purification, where evaporation of a dosed amount of reducing agent is required. The device may comprise elements adapted to select the said maximum reducing agent dose based on an exhaust mass flow, an effective evaporation temperature and a reducing agent temperature.

In the device, the said maximum reducing agent dosage may be selected based on an empirically determined matrix for evaporation of a maximum reducing agent dosage depending on exhaust mass flow and a reference parameter depending on effective evaporation temperature as well as reducing agent temperature.

In the device, the said reference parameter may be determined according to a connection which is defined by: Tref=Tv-K1 ^* Tu+K2 where:

Tv is the effective evaporation temperature;

Tu is the reducing agent temperature; and

K1 and K2 are predetermined constants. K1 and K2 may be empirically determined. K1 and K2 may be determined in a suitable manner. K1 and K2 may be predetermined constants.

In the device, the said maximum reducing agent dosage may be selected based on an empirically determined matrix showing the maximum reducing agent dosage for evaporation depending on exhaust mass flow and a reference parameter depending on exhaust temperature as well as reducing agent temperature. In the device, the effective evaporation temperature may be set as the exhaust temperature or a temperature of a component in a configuration of an exhaust channel and an SCR catalyst of the said SCR system.

According to one aspect of the present invention, a motor vehicle is provided comprising a device according to any of the claims 5-8.

According to one aspect of the present invention, a motor vehicle is provided comprising a device for the selection of maximum reducing agent dosage at an SCR system for exhaust purification.

The motor vehicle may be a truck, a bus or a car.

According to one aspect of the invention, a computer program is provided for selection of maximum reducing agent dosage at an SCR system for exhaust purification, wherein said computer program comprises program code stored in a computer-readable medium in order to cause an electronic control device or another computer connected to the electronic control device to perform the steps according to any one of the patent claims 1 -4. According to one aspect of the invention, a computer program is provided for the selection of maximum reducing agent dosage at an SCR system for exhaust purification, wherein said computer program comprises program code to cause an electronic control device or another computer connected to the electronic control device to perform the steps according to any one of the patent claims 1 -4. According to one aspect of the invention, a computer program product comprising program code stored in a computer-readable medium is provided to perform the method steps according to any one of the patent claims 1 -4, when said computer program is run in an electronic control device or in another computer connected to the electronic control device.

Additional objectives, advantages and novel features of the present invention will be apparent to one skilled in the art from the following details, and through exercising the invention. While the invention is described below, it should be apparent that the invention is not limited to the specifically described details. One skilled in the art, having access to the teachings herein, will recognise additional applications, modifications and incorporations in other areas, which are within the scope of the invention.

GENERAL DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the additional objects and advantages thereof, reference is now made to the following detailed description, which is to be read together with the accompanying drawings, in which the same reference designations pertain to identical parts in the various figures, and in which:

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

Figure 2 schematically illustrates a device for the selection of maximum reducing agent dosage at an SCR system for exhaust purification, according to one embodiment of the invention; Figure 3a schematically illustrates a diagram, according to one aspect of the invention;

Figure 3b schematically illustrates a diagram, according to one aspect of the invention;

Figure 4a schematically illustrates a flow chart of a method, according to one embodiment of the invention;

Figure 4b schematically illustrates in more detail a flow chart of a method, according to one embodiment of the invention;

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

DETAILED DESCRIPTION OF THE FIGURES

A side view of a vehicle 100 is shown with reference to Figure 1 . The exemplary vehicle 100 consists of a tractor 1 10 and a trailer 1 12. The vehicle may be a heavy goods vehicle, such as a truck or a bus. The vehicle may, alternatively, be a car.

It should be pointed out that the invention is suitable for application in a suitable SCR system and is therefore not limited to SCR systems of motor vehicles. The method according to the invention and the device according to the invention in an SCR system, according to one aspect of the invention, are well suited to platforms other than motor vehicles comprising an SCR system, such as watercraft. The watercraft may be of any suitable type, such as motor boats, ships, ferries or vessels.

The method according to the invention and the device according to the invention in an SCR system, according to one aspect of the invention, are also suitable for e.g. systems comprising a stone crusher or similar.

The method according to the invention and the device according to the invention in an SCR system, according to one aspect of the invention, are also suitable for e.g. systems comprising industrial engines and/or motor driven industrial robots.

The method according to the invention and the device according to the invention in an SCR system, according to one aspect of the invention, are also suitable for power plants, e.g. electricity production comprising a diesel generator.

The method according to the invention and the device according to the invention in an SCR system are well suited for any suitable motor system comprising an engine and an SCR system, such as in a locomotive or another platform.

The method according to the invention and the device according to the invention in an SCR system are well suited for any system comprising a NO _x generator and an SCR system.

The term "link" herein refers to a communications link, which may be a physical line, such as an opto-electronic communication line, or a non- physical line such as a wireless connection, e.g. a radio or microwave link.

The term "pipe" as used herein means a passage to hold and transport a fluid, such as a reducing agent in liquid form. The pipe may be a pipe of any dimension. The pipe may consist of any suitable material, such as plastic, rubber or metal.

The terms "reducing agent", or "reductant" as used herein, means a substance used to react with certain emissions in an SCR system. These emissions may be e.g. NO _x gas. The terms "reductant" and "reducing agent" are used synonymously herein. The said reductant is, according to one embodiment, also known as AdBlue. Obviously other types of reductants may be used. AdBlue is given as an example of a reducing agent, however, one skilled in the art will realise that the method according to the invention and the device according to the invention may be realised for other types of reducing agent. According to one example embodiment, the said reducing agent comprises a urea solution. The said urea solution comprises a suitable urea concentration.

With reference to Figure 2, a device 299 in the vehicle 100 is shown. The device 299 may be arranged in the tractor 1 10. The device 299 may constitute a part of an SCR system or comprise an SCR system. The device 299 comprises, according to this example, a container 205 which is arranged to hold a reducing agent. The container 205 is arranged to comprise a suitable amount of reducing agent and is also arranged to be filled as needed. A first pipe 271 is arranged to lead the reducing agent to a pump 230 from the container 205. The pump 230 may be any suitable pump. The pump 230 may be a membrane pump comprising at least one filter. The pump 230 may be arranged to be driven with an electric motor (not shown). The pump 230 may be arranged to pump the reducing agent from the container 205 via the first pipe 271 and via a second pipe 272 to add the said reducing agent to a dosage device 250. The dosage device 250 may comprise an electrically controlled dosage device, through which a flow of reducing agent added to the exhaust system may be controlled. The pump 230 is arranged to pressurise the reducing agent in the second pipe 272. The dosage device 250 is arranged with a throttle device, which may also be called a throttle valve, against which the said pressure in the reducing agent may be built up in the device 299.

The dosage device 250 is arranged to add the said reducing agent to an exhaust channel 290 in the vehicle 100. More precisely, the dosage device 250 is arranged to, in a controlled manner, add a suitable amount of reducing agent to an exhaust channel 290 in the vehicle 100, according to one aspect of the method according to the invention. According to this embodiment, an SCR catalyst 270 is arranged downstream of a location in the exhaust system where the reducing agent is added. The amount of reducing agent which is added in the exhaust system is intended to be used in the SCR catalyst in order to reduce the amount of undesired emissions.

The dosage device 250 may be arranged at the said exhaust channel 290 which is arranged to lead exhausts from a combustion engine (not shown) in the vehicle 100 to the SCR catalyst and further to an environment of the vehicle.

A third pipe 273 is arranged between the dosage device 250 and the container 205. The third pipe 273 is arranged to lead back a certain amount of the reducing agent which has been fed to the dosage valve 250 to the container 205.

The first control device 200 is arranged for communication with the pump 230 via a link L230. The first control device 200 is arranged to control the operation of the pump 230. According to one example, the first control device 200 is arranged to control the pump 230 with an electric motor (not shown). The first control device 200 is arranged to impact a working pressure in the second pipe 272. This may take place in different suitable ways. According to one example, the first control device 200 is arranged to change a prevailing engine speed RPM in the pump 230. Here, the pressure may be altered in a desirable manner. By increasing the engine speed RPM of the pump 230, the working pressure may be increased. By reducing the engine speed RPM of the pump 230, the working pressure may be reduced.

The first control device 200 is arranged for communication with a first temperature sensor 240 via a link L240. The temperature sensor 240 is arranged to detect a prevailing temperature T1 of an exhaust flow from the vehicle's engine. According to one example, the first temperature sensor 240 is arranged in the said exhaust channel 290 directly downstream of the vehicle's engine and upstream of a dosage device 250. The temperature sensor 240 may be arranged in a suitable manner in the said exhaust channel 290. The first temperature sensor 240 is arranged to continuously detect a prevailing temperature T1 of the exhaust stream and to send signals comprising information about the said prevailing temperature T1 via the link L240 to the first control device 200.

The first control device 200 is arranged for communication with a second temperature sensor 260 via a link L260. The second temperature sensor 260 may be arranged to detect a prevailing temperature T2 in a surface of the exhaust system where the reducing agent is evaporated. The second temperature sensor 260 may be arranged to detect a prevailing temperature T2 in the exhaust pipe 290 at a suitable location. The second temperature sensor 260 may be arranged to detect a prevailing temperature T2 in a suitable surface or component of the exhaust channel 290. According to one example, the second temperature sensor 260 is arranged in the exhaust channel 290 upstream of the dosage device 250. According to another example, the second temperature sensor 260 is arranged in an evaporation device (not shown) or in the SCR catalyst 270 downstream of the dosage device 250. The second temperature sensor 260 is arranged to continuously detect a prevailing temperature T2 of a surface or a component of the exhaust channel 290 and to send signals comprising information about the said prevailing temperature T2 via the link L260 to the first control device 200.

According to one embodiment, the first control device 200 and/or the second control device 210 is arranged to calculate the said first temperature T1 . This may occur through a stored calculation model. The first control device 200 and/or the second control device 210 may be arranged to calculate the said first temperature T1 based on e.g. a prevailing exhaust mass flow MF, prevailing engine speed RPM of the engine and prevailing load of the engine. According to one embodiment, the first control device 200 and/or the second control device 210 is arranged to calculate the said second temperature T2. This may occur through a stored calculation model. The first control device 200 and/or the second control device 210 may be arranged to calculate the said second temperature T2 based on e.g. a prevailing exhaust mass flow MF, prevailing engine speed RPM of the engine and prevailing load of the engine.

Herein the said first temperature T1 and the said second temperature T2 are called effective evaporation temperature. Thus the effective evaporation temperature Tv may be set as the exhaust temperature T1 or a temperature T2 of a component in a configuration of the exhaust channel 290 and an SCR catalyst 270 of the said SCR system. The said effective evaporation temperature Tv may be a prevailing temperature at a position where the said reducing agent is evaporated. The said effective evaporation temperature Tv may correspond to and/or be a representation of a prevailing temperature in at least one position where the said reducing agent is evaporated.

An exhaust mass flow sensor 255 is arranged for communication with the first control unit 200 via a link L255. The exhaust mass flow sensor 255 is arranged to continuously determine a prevailing exhaust mass flow MF in the exhaust flow upstream of the said SCR catalyst 270. According to one example, the exhaust mass flow sensor 255 is arranged in the exhaust channel 290 upstream of the said dosage device 250. The exhaust mass flow sensor 255 is arranged to continuously send signals comprising information about a prevailing exhaust mass flow MF upstream of the said SCR catalyst 270 to the first control device 200.

According to one embodiment, the first control device 200 and/or the second control device 210 is arranged to determine the said exhaust mass flow MF. This may occur through a stored calculation model. The first control device 200 and/or the second control device 210 may be arranged to calculate the said exhaust mass flow MF based on e.g. a prevailing, prevailing engine speed RPM of the engine and a charge air pressure or cylinder pressure in the engine.

The first control device 200 may be arranged to calculate an exhaust mass flow MF in the exhausts from the vehicle's engine. The first control device 200 is arranged to continuously determine an exhaust mass flow MF in the exhausts from the vehicle's engine. This may occur in any suitable manner.

A ΝΟχ sensor 265 is arranged for communication with the first control device 200 via a link L265. The NO _x sensor 265 is arranged to continuously determine a prevailing NO _x level in the exhaust flow downstream of the said SCR catalyst 270. The NO _x sensor 265 is arranged to continuously send signals comprising information about a prevailing NO _x level downstream of the said SCR catalyst 270 to the first control device 200.

According to one embodiment, the first control device 200 and/or the second control device 210 is arranged to calculate the said one NO _x level upstream of the said SCR catalyst 270. This may occur through a stored calculation model. The first control device 200 and/or the second control device 210 may be arranged to calculate the said NO _x level upstream of the said SCR catalyst 270 based on e.g. a prevailing exhaust mass flow MF, a prevailing engine speed RPM of the engine and a prevailing load of the engine.

The first control device 200 maybe arranged to control the operation of the engine in the vehicle 100 based on the said determined NO _x level upstream of the said SCR catalyst 270 and/or the said determined NO _x level downstream of the said SCR catalyst 270. The first control device 200 is arranged for communication with a third temperature sensor 275 via a link L275. The temperature sensor 275 is arranged to detect a prevailing temperature Tu in the said reducing agent. According to one example, the third temperature sensor 275 is arranged in the said second pipe 272 upstream of the said dosage device 250. The temperature sensor 275 may be arranged in a suitable location in the device 299. According to one embodiment, the said third temperature sensor is arranged in the container 205. According to one embodiment, the third temperature sensor 275 is arranged in the pump 230. According to one embodiment, the third temperature sensor 275 is arranged in a third pipe 273. The second temperature sensor 275 is arranged to continuously detect a prevailing temperature Tu of the reducing agent and to send signals comprising information about the said prevailing temperature Tu via the link L240 to the first control device 200.

According to one embodiment, the first control device 200 and/or the second control device 210 is arranged to calculate the said temperature Tu of the reducing agent. This may occur through a stored calculation model. The first control device 200 and/or the second control device 210 may be arranged to continuously calculate the temperature Tu of the reducing agent based on e.g. a temperature measure of the reducing agent in the container at the upstart of the device 299 and an energy amount which is added to the said reducing agent through heating. The said heating may e.g. occur through elements suitable for this purpose. The said elements may comprise a number of electrical heating elements, which are placed in suitable places, such as in the container 205 or at any of the first pipe 271 , the second pipe 272 and the third pipe 273.

The said first control device 200 may be arranged to continuously select a suitable reducing agent dosage in the dosage device 250 based on a determined exhaust mass flow MF, a determined effective evaporation temperature T1 or T2 and a reducing agent temperature Tu. The said first control device 200 may be arranged to continuously select a suitable reducing agent dosage in the dosage device 250 based on a determined exhaust mass flow MF, a determined temperature T1 of the exhausts and a reducing agent temperature Tu.

The said first control device 200 may be arranged to continuously select a suitable reducing agent dosage in the dosage device 250 based on a determined exhaust mass flow MF, a determined temperature T2 of a section of the exhaust channel 290 and a reducing agent temperature Tu.

The said first control device 200 may be arranged to continuously select a suitable reducing agent dosage in the dosage device 250 based on a determined exhaust mass flow MF, a determined temperature T2 of the SCR catalyst 270 and a reducing agent temperature Tu. The said suitable reducing agent dosage may be lower than the said maximum reducing agent dosage.

The said first control device 200 may be arranged to continuously select a suitable maximum reducing agent dosage in the dosage device 250 based on a determined exhaust mass flow MF, a determined temperature T2 of a section of the exhaust channel 290 and a reducing agent temperature Tu. The said suitable reducing agent dosage may be lower than the said maximum reducing agent dosage.

The said first control device 200 may be arranged to continuously select a suitable maximum reducing agent dosage in the dosage device 250 based on a determined exhaust mass flow MF, a determined temperature T2 of the SCR catalyst 270 and a reducing agent temperature Tu.

In the first control device 200 is an empirically determined matrix stored showing maximum reducing agent dosage for evaporation depending on exhaust mass flow and a reference parameter depending on effective evaporation temperature T1 or T2 as well as reducing agent temperature Tu.

The first control device 200 is arranged for communication with the presentation means 280 via a link L280. The said presentation means 280 may be arranged in a driver's cabin in the vehicle 100. The said presentation means may comprise a so-called touch screen. The said presentation element 280 may be fixed in the vehicle 100. The said presentation element 280 may be a mobile electronic device. The said presentation element 280 may comprise e.g. a display screen. The first control device 200 is arranged to present an error code or other relevant information concerning the innovative method. The first control device 200 may be arranged through the said presentation means 280 continuously, intermittently or as needed to present information about the said stored matrix. An operator may with the said display elements change stored information as required.

The first control device 200 is arranged for communication with the dosage device 250 via a link L250. The first control device 200 is arranged to control the operation of the dosage device 250 in order to e.g. control the supply of reducing agent to the exhaust system of the vehicle 100.

A second control device 210 is arranged for communication with the first control unit 200 via a link L210. The second control device 210 may be detachably connected to the first control device 200. The second control device 210 may be a control unit external to the vehicle 100. The second control device 210 may be arranged to carry out the innovative steps of the method according to the invention. The second control device 210 may be used to transfer software to the first control device 200, in particular software to perform the innovative method. Alternatively, the second control device 210 may be arranged for communication with the first control device 200 via an internal network in the vehicle. The second control device 210 may be arranged to carry out substantially similar functions as the first control device 200, such as to select maximum reducing agent dosage in an SCR system for exhaust purification, according to one aspect of the present invention.

Figure 3a illustrates schematically an empirically determined matrix showing maximum reducing agent dosage for evaporation depending on exhaust mass flow MF and a reference parameter Tref depending on effective evaporation temperature Tv as well as reducing agent temperature Tu.

The said exhaust mass flow MF is specified in kg/minute. The said reference parameter Tref is specified in degrees Kelvin. The matrix comprises a number of values Mu1 1 -Mu44 which specify values for maximum reducing agent dosage for a given exhaust mass flow MF and a given reference temperature Tref. The said values Mu1 1 -Mu44 are predetermined and stored in a memory of the said first control device 200. The said values Mu1 1 -Mu44 are empirically determined and stored in a memory of the said first control device 200. The said values Mu1 1 -Mu44 may be used according to one aspect of the method according to the invention for selection of maximum reducing agent dosage. The first control device is arranged to control the reducing agent dosage based on information from the said matrix and prevailing operation conditions, comprising the said exhaust mass flow MF and the reference temperature Tref. According to one embodiment of the present invention, a model-based function is provided to determine the maximum reducing agent dosage for evaporation depending on the exhaust mass flow MF and a reference parameter Tref depending on effective evaporation temperature Tv as well as the reducing agent temperature Tu. The said function may be any suitable function. The said function may be any suitable function. According to one aspect, a model-based function is provided to determine the maximum reducing agent dosage for evaporation in real time depending on the exhaust mass flow MF and a reference parameter Tref depending on effective evaporation temperature Tv as well as the reducing agent temperature Tu.

According to one example embodiment, the effective evaporation temperature Tv may be set as the exhaust temperature T1 or a temperature T2 of a component in a configuration of an exhaust channel or an SCR catalyst of the said SCR system.

Figure 3b schematically illustrates a diagram where a graph for a reference temperature reference Tu for the said reducing agent is shown.

A temperature Tu relating to a temperature of the said reducing agent is specified in degrees Kelvin. A reference temperature Tref is specified in degrees Kelvin, the reference temperature of which depends on the temperatures T1 and T2. The said reference temperature reference Tu is specified in degrees Kelvin. The matrix comprises a number of values Mu1 1 - Mu44 which specify values for maximum reducing agent dosage for a given exhaust mass flow MF and a given reference temperature Tref. Here, a reference temperature reference Tu may be applied, e.g. 330 Kelvin. The said reference temperature reference Tu may also be called working temperature of the said reducing agent and is a desired suitable working temperature of the said SCR system relating to the reducing agent temperature. Thus the said constants K1 and K2 may be selected so that the condition Tv=Tu is met at the applied reference temperature. Thus an advantageous connection is achieved Tref=Tv-K1 ^* Tu+K2.

In the event the reducing agent temperature Tu is below the reference temperature reference Tu, the risk of crystal formation of doses of reducing agent is reduced, however, the fuel consumption of the vehicle's engine increases. In the event the reducing agent temperature Tu exceeds the reference temperature reference Tu, the fuel consumption of the vehicle's engine is reduced, but the risk of crystal formation of dosed reducing agent is increased.

Figure 4a illustrates schematically a flow chart of a method for the selection of maximum reducing agent dosage at an SCR system for exhaust purification, where evaporation of a dosed amount of reducing agent is required, according to one embodiment of the invention. The method comprises an initial method step of the procedure s401 . Step s401 comprises the step to:

- select maximum reducing agent dosage based on an exhaust mass flow, an effective evaporation temperature and a reducing agent temperature. The method is completed after step s401 .

Figure 4b illustrates schematically a flow chart of a method for the selection of maximum reducing agent dosage at an SCR system for exhaust purification, where evaporation of a dosed amount of reducing agent is required, according to one embodiment of the invention.

The method comprises an initial method step of the procedure s410. The method step s410 may comprise the step to continuously determine a prevailing exhaust mass flow MF. This may occur through the exhaust mass flow sensor 255. Alternatively, a prevailing exhaust mass flow MF may be calculated in a suitable manner with the said first control device 200 or the said second control device 210. Following the method step s410, a subsequent method step s420 is completed.

Method step s420 comprises the step to continuously determine a prevailing effective evaporation temperature. This may occur through the first temperature sensor 240, which is arranged to determine an exhaust temperature upstream of the SCR catalyst 270. Alternatively, this may occur through the second temperature sensor 260, which is arranged to determine an exhaust temperature upstream of the SCR catalyst 270. Alternatively, a prevailing effective evaporation temperature may be calculated in a suitable manner with the said first control device 200 or the said second control device 210. Following the method step s420, a subsequent method step s430 is completed.

The method step s430 comprises the step to continuously determine a prevailing temperature Tu of the said reducing agent. This may occur with the third temperature sensor 275. Alternatively, a prevailing temperature Tu of the said reducing agent may be calculated in a suitable manner with the said first control device 200 or the said second control device 210. Following the method step s430, a subsequent method step s440 is completed.

The method step s440 comprises the step to select a maximum reducing agent dosage based on the said exhaust mass flow MF, effective evaporation temperature and a reducing agent temperature Tu. The step s440 may comprise the step to continuously, intermittently and/or where applicable select the maximum reducing agent dosage based on an exhaust mass flow, an effective evaporation temperature and a reducing agent temperature. The step s440 may comprise the step to continuously, intermittently and/or where applicable select the maximum reducing agent dosage based on an exhaust mass flow, an exhaust temperature T1 and a reducing agent temperature Tu.

The said selection of the maximum reducing agent dosage may suitably occur based on at least the said reducing agent temperature Tu.

The said maximum reducing agent dosage may be selected based on an empirically determined matrix showing maximum reducing agent dosage for evaporation depending on exhaust mass flow MF and a reference parameter Tref depending on effective evaporation temperature Tv as well as reducing agent temperature Tu. Following the method step s440, a subsequent method step s450 is completed.

The method step s450 comprises the step to control the said reducing agent dosage based on the said selection. This may be carried out by the said first control device 200 with the said dosage device 250. Following the method step s450, the method is completed.

With reference to Figure 5, a diagram of an embodiment of system 500 is shown. The control units 200 and 210, which are described with reference to Figure 2, may in one embodiment comprise the system 500. The unit 500 includes 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 wherein a computer program, such as an operative system, is stored to control the function of the unit 500. Further, the unit 500 includes a bus controller, a serial communications port, an I/O device, an A D converter, a date-time input and transmission unit, an event counter and an interrupt controller (not shown). The non-volatile memory 520 also has a second memory part 540.

A computer program P is provided which may comprise procedures for selection of maximum reducing agent dosage at an SCR system for exhaust purification, where evaporation of a dosed amount of reducing agent is required. The computer program P may comprise procedures to continuously determine a prevailing exhaust mass flow MF. The computer program P may comprise procedures to continuously determine a prevailing effective evaporation temperature. According to one embodiment, the said effective evaporation temperature may be set at the prevailing temperature T1 of the exhausts from the said engine. According to one embodiment, the said effective evaporation temperature may be set at the prevailing temperature T2 in a component in a configuration of the said exhaust channel 290 and the said SCR catalyst 270 of the said SCR system. The computer program P may comprise procedures to continuously determine a prevailing temperature Tu of the said reducing agent. The computer program P may comprise procedures to select the maximum reducing agent dosage based on the said prevailing exhaust mass flow MF, the said effective evaporation temperature T1 or T2 and the said reducing agent temperature Tu. The computer program P may comprise procedures to control the reducing agent dosage through the said dosage device 250 based on the said selection of maximum reducing agent dosage. The program P may be stored in an executable manner or in a compressed manner in a memory 560 and/or a read/write memory 550.

A statement that the data processing unit 510 performs a certain function means 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 stored in the read/write memory 550.

The data processing unit 510 may 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 for communication with the data processing unit 510 via a data bus 51 1 . The read/write memory 550 is arranged for communication with the data processing unit 510 via a data bus 514. The links L210, L230, L240, L250, L255, L260, L265, L275 and L280 may be connected to the data port 599 (see Figure 2).

When data is received in the data port 599, it is temporarily stored in the second memory part 540. When in-data received is temporarily stored, the data processing unit 510 is ready to carry out execution of code in the manner described above. According to one embodiment, signals received in the data port 599 comprise information about the prevailing temperature T1 in the exhausts. According to one embodiment, signals received in the data port 599 comprise information about temperature T2 in a component in a configuration of an exhaust channel and an SCR catalyst of the said SCR system. According to one embodiment, signals received in the data port 599 comprise information about the prevailing exhaust mass flow MF. According to one embodiment, signals received in the data port 599 comprise information about the prevailing temperature Tu of the said reducing agent. The signals received in the data port 599 may be used by the device 500 to select the said reducing agent dosage based on an exhaust mass flow MF, an effective evaporation temperature Tv and a reducing agent temperature Tu. The signals received in the data port 599 may be used by the device 500 to control the said reducing agent dosage based on an exhaust mass flow MF, an effective evaporation temperature Tv and a reducing agent temperature Tu. The signals received in the data port 599 may be used by the device 500 to control the said reducing agent dosage based on the said selected reducing agent dosage. Parts of the methods described herein may be carried out by the device 500 with the help of the data processing unit 510, which runs the program stored in the memory 560 or the read/write memory 550. When the unit 500 runs the program, the procedures described herein are executed.

The foregoing description of the preferred embodiments of the present invention has been furnished for illustrative and descriptive purposes. It is not intended to be exhaustive, or to limit the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order to best explicate the principles of the invention and its practical applications, and to thereby enable one skilled in the art to understand the invention in terms of its various embodiments and with the various modifications that are applicable to its intended use.