TECHNICAL FIELD

The present invention relates to a method for controlling operation of a dosing unit of a fluid dosing system. The invention relates also to a computer program product comprising program code for a computer for implementing a method according to the invention. It relates also to a system for controlling operation of a dosing unit of a fluid dosing system and a motor vehicle equipped with the system.

BACKGROUND ART

Today many different fluid dosing systems are known. One such fluid dosing system is a reducing agent dosing system being installed in vehicles for purposes of emission control.

According to one variant a reducing agent dosing unit a valve unit is electrically controlled and a sealing member position is alternated for setting the valve unit in an open state and a closed state, alternately. Hereby a pressurized reducing agent is dosed into an exhaust gas stream of a combustion engine for emission control.

In a case where an inductive member is used for controlling the position of the sealing member it is common to initially apply a peak voltage followed by a hold voltage during a dosing cycle. Hereby an excessive amount of electrical energy may be contained in the inductive member. This is resulting in an unpredictable behaviour of the operation of the valve unit.

W02006032098 relates to a method wherein a duration of applied peak voltage is selected for optimizing the amount of energy contained in an inductive member of an injector. SUMMARY OF THE INVENTION

An object of the present invention is to propose a novel and advantageous method for controlling operation of a dosing unit of a fluid dosing system.

Another object of the invention is to propose a novel and advantageous system and a novel and advantageous computer program for controlling operation of a dosing unit of a fluid dosing system.

Another object of the present invention is to propose a novel and advantageous method providing a cost effective and reliable operation control of a dosing unit of a fluid dosing system.

Another object of the invention is to propose a novel and advantageous system and a novel and advantageous computer program providing a cost effective and reliable operation control of a dosing unit of a fluid dosing system.

Yet another object of the invention is to propose a method, a system and a computer program achieving a robust, accurate and automated controlling operation of a dosing unit of a fluid dosing system.

Yet another object of the invention is to propose an alternative method, an alternative system and an alternative computer program for controlling operation of a dosing unit of a fluid dosing system.

Some of these objects are achieved with a method according to claim 1. Other objects are achieved with a system in accordance with what is depicted herein. Advantageous embodiments are depicted in the dependent claims. Substantially the same advantages of method steps of the proposed method hold true for corresponding means of the proposed system. According to an aspect of the invention there is provided a method for controlling a dosing unit of a fluid dosing system comprising an electrically controlled valve unit having a coil arranged for shifting the valve unit between an open state and a closed state by moving a sealing member between a first position and a second position, the method comprising the steps of:

- applying a peak voltage over the coil;

- continuously determining a first energy state of the coil;

- comparing the first energy state with a second energy state of the coil corresponding to a hold voltage; and - shifting the applied peak voltage to the hold voltage at a point of time at which the first energy state has reached the second energy state.

Hereby an improved dosing procedure is achieved. The proposed method is energy efficient because of a shortened time period for applying the hold voltage. Hereby a smooth peak/hold voltage shifting procedure of the dosing unit is achieved. The coil may also be referred to as solenoid.

Hereby a total operational time period of the solenoid (coil) is increased due to that it is not overcharged during application of the peak voltage. This further leads to effective use of power as the total amount of consumed energy is reduced during each dosing cycle the proposed method is applied. Advantageously the behaviour of the solenoid hereby becomes more predictable.

The method may comprise the step of:

- determining that the valve unit is in an open state prior to shifting the applied peak voltage to the hold voltage. This may be performed after the step of applying the peak voltage over the coil but prior to shifting the applied peak voltage to the hold voltage.

Hereby a reliable and robust method for controlling operation of the dosing unit is provided. It may be determined that the valve unit is in an open state by at least one of the procedures of:

- detecting a significant dip in a coil current course during application of the peak voltage;

- detecting a significant dip in a fluid supply pressure; and - detecting a sealing member position corresponding to the open state.

Hereby a versatile and accurate way of determining whether the valve unit is in an open state is provided.

The significant dip of the coil current course is a temporary dip. The significant dip is occurring due to magnetic force phenomena. The significant dip of the coil current course presents a typical/characteristic/unique/representative form. The significant dip of the coil current course presents a temporary decrease before presenting an increase again.

The significant dip in the fluid supply pressure is a temporary dip. The significant dip in the fluid supply pressure presents a typical/characteristic/unique/representative form. The significant dip in the fluid supply pressure presents a temporary decrease before presenting an increase again.

The method may comprise the steps of:

- determining the point of time at which the first energy state has reached the second energy state on the basis of the peak voltage over the coil and electrical characteristics of the coil; and - shifting the applied peak voltage to the hold voltage at the determined point of time.

Hereby an improved operation control of the dosing unit is achieved. The electrical characteristics of the coil may comprise impedance, which is an inherent characteristics of the coil. Hereby the electrical characteristics of the coil may be predetermined resulting in a reliable determination of point of time at which the first energy state has reached the second energy state.

The method may comprise the steps of: - continuously determining a first energy state of the coil on the basis of a prevailing current I in the coil; and

- determining the second energy state as an energy state appearing during steady state conditions corresponding to hold voltage application over the coil.

According to an aspect of the invention there is provided a system for controlling a dosing unit of a fluid dosing system comprising an electrically controlled valve unit having a coil arranged for shifting the valve unit between an open state and a closed state by moving a sealing member between a first position and a second position, the system comprising: - means being arranged for applying a peak voltage over the coil;

- means being arranged for continuously determining a first energy state of the coil;

- means being arranged for comparing the first energy state with a second energy state of the coil corresponding to a hold voltage; and

- means being arranged for shifting the applied peak voltage to the hold voltage at a point of time at which the first energy state has reached the second energy state.

The system may comprise:

- means being arranged for determining that the valve unit is in an open state prior to shifting the applied peak voltage to the hold voltage.

The system may comprise means being arranged for determining that the valve unit is in an open state, the means for determining comprising at least one of the following:

- means being arranged for detecting a significant dip in a coil current course during application of the peak voltage;

- means being arranged for detecting a significant dip in a fluid supply pressure; and

- means being arranged for detecting a sealing member position corresponding to the open state. The system may comprise:

- means being arranged for determining the point of time at which the first energy state has reached the second energy state on the basis of the peak voltage over the coil and electrical characteristics of the coil; and - means being arranged for shifting the applied peak voltage to the hold voltage at the determined point of time.

The system may comprise:

- means being arranged for continuously determining a first energy state of the coil on the basis of a prevailing current I in the coil; and - means being arranged for determining the second energy state as an energy state appearing during steady state conditions corresponding to hold voltage application over the coil.

According to an aspect of the invention there is provided a vehicle comprising a system according to what is presented herein. The vehicle may be any from among a truck, bus or passenger car. According to an embodiment the system is provided for a marine application or industrial application.

According to an aspect of the invention there is provided a computer program for controlling operation of a dosing unit of a fluid dosing system comprising an electrically controlled valve unit having a coil arranged for shifting the valve unit between an open state and a closed state by moving a sealing member between a first position and a second position, wherein the computer program comprises program code for causing an electronic control unit or a computer connected to the electronic control unit to perform anyone of the method steps depicted herein, when run on the electronic control unit or the computer. According to an aspect of the invention there is provided a computer program for controlling operation of a dosing unit of a fluid dosing system comprising an electrically controlled valve unit having a coil arranged for shifting the valve unit between an open state and a closed state by moving a sealing member between a first position and a second position, wherein the computer program comprises program code stored on a computer-readable medium for causing an electronic control unit or a computer connected to the electronic control unit to perform anyone of the method steps depicted herein.

According to an aspect of the invention there is provided a computer program for controlling operation of a dosing unit of a fluid dosing system comprising an electrically controlled valve unit having a coil arranged for shifting the valve unit between an open state and a closed state by moving a sealing member between a first position and a second position, wherein the computer program comprises program code stored on a computer-readable medium for causing an electronic control unit or a computer connected to the electronic control unit to perform anyone of the method steps depicted herein, when run on the electronic control unit or the computer.

According to an aspect of the invention there is provided a computer program product containing a program code stored on a computer-readable medium for performing any one of the method steps depicted herein, when the computer program is run on an electronic control unit or a computer connected to the electronic control unit.

According to an aspect of the invention there is provided a computer program product containing a program code stored non-volatile on a computer-readable medium for performing any one of the method steps depicted herein, when the computer program is run on an electronic control unit or a computer connected to the electronic control unit.

According to an aspect of the invention there is provided a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out any of the steps of the method depicted herein.

According to an aspect of the invention there is provided a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out any of the steps of the method depicted herein. Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas the invention is described below, it should be noted that it is not confined to the specific details described. One skilled in the art having access to the teachings herein will recognise further applications, modifications and incorporations in other fields, which are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 schematically illustrates a vehicle according to an embodiment of the invention; Figure 2a schematically illustrates a system according to an embodiment of the invention; Figure 2b schematically illustrates a system according to an embodiment of the invention; Figure 2c schematically illustrates a system according to an embodiment of the invention;

Figure 3a schematically illustrates a diagram according to an embodiment of the invention;

Figure 3b schematically illustrates a diagram according to an embodiment of the invention;

Figure 3c schematically illustrates a diagram according to an embodiment of the invention;

Figure 3d schematically illustrates a diagram according to an embodiment of the invention; Figure 4a is a schematic flowchart of a method according to an embodiment of the invention;

Figure 4b is a schematic function diagram 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

Figure 1 depicts a side view of a vehicle 100. The exemplified vehicle 100 comprises a tractor unit 110 and a trailer 112. The vehicle 100 may be a heavy vehicle, e.g. a truck or a bus. It may alternatively be a car. The proposed method and system are applicable to various vehicles, such as e.g. a mining machine, tractor, dumper, wheel-loader, platform comprising an industrial robot, forest machine, earth mover, road construction vehicle, road planner, emergency vehicle or a tracked vehicle.

The proposed method and system are applicable to various dosing units of fluid dosing systems, such as reducing agent dosing systems or fuel dosing systems for regenerating emission control systems. The proposed method and system are applicable to any suitable dosing unit of a fluid dosing system, which dosing unit comprising an electrically controlled valve unit having a coil arranged for shifting the valve unit between an open state and a closed state by moving a sealing member between a first position and a second position.

The invention is suitable for application in various systems comprising a combustion engine and an associated emission control arrangement comprising a reducing agent dosing system. The invention is suitable for application in various systems comprising a combustion engine and a catalytic configuration. The catalytic configuration may comprise at least one reducing agent dosing unit, each dosing unit being arranged for providing a reducing agent upstream of a corresponding SCR unit. The catalytic configuration may comprise one or more DOC units. The catalytic configuration may comprise one or more DPF units. It should be noted that the invention is applicable to various catalytic configurations and is therefore not confined to catalytic configurations for motor vehicles. The proposed method and the proposed system according to one aspect of the invention are well suited to other platforms which comprise a combustion engine and a catalytic configuration, e.g. watercraft. The watercraft may be of any kind, e.g. motorboats, steamers, ferries or ships.

The proposed method and the proposed system according to one aspect of the invention are also well suited to, for example, systems which comprise industrial combustion engines and/or combustion engine-powered industrial robots and an associated emission control arrangement comprising at least one SCR unit and at least one reducing agent dosing unit.

The proposed method and the proposed system according to one aspect of the invention are also well suited to various kinds of power plants, e.g. an electric power plant which comprises a combustion engine-powered generator and an associated emission control arrangement comprising at least one reducing agent dosing unit for catalytic operation of an SCR unit.

The proposed method and the proposed system are also well suited to various combustion engine systems comprising an associated emission control arrangement having at least one reducing agent dosing unit for catalytic operation of an SCR unit.

The proposed method and the proposed arrangement are well suited to any engine system which comprises an engine, e.g. on a locomotive or some other platform, and an associated emission control arrangement having at least one SCR unit.

The proposed method and the proposed system are well suited to any system which comprises a NO _x -generator an associated emission control arrangement having at least one SCR units.

The proposed method and the proposed system are well suited to various fluid dosing systems having an electrically controlled valve unit, whereby the fluid may be any suitable liquid or gas.

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

The term "line" refers herein to a passage for holding and conveying a fluid, e.g. a reducing agent in liquid form or fuel. The line may be a pipe of any size and be made of any suitable material, e.g. plastic, rubber or metal.

The term "reductant" or "reducing agent" refers herein to an agent used for reacting with certain emissions in an SCR system. These emissions may for example be NO _x -gas. The terms "reductant" and "reducing agent" are herein used synonymously. In one version, the reductant is so-called AdBlue. Other kinds of reductants may of course be used. AdBlue is herein cited as an example of a reductant, but one skilled in the art will appreciate that the proposed method and the proposed system are feasible with other types of reductants.

The terms "SCR unit" and "SCR configuration" are herein used synonymously. The SCR unit/SCR configuration may also be referred to as "reduction catalyst device". The SCR units of the emission control arrangement may be any suitable SCR units. According to one example the SCR unit may comprise an SCRF unit, comprising a coated filter. The SCR unit may according to other examples provide a combination of SCR functionality and at least one additional functionality (other than NO _x conversion), such as SCR functionality and DOC functionality, SCR functionality and ammonia slip catalyst functionality, etc. The SCR unit may comprise ceramic materials used as a carrier, such as titanium oxide, and active catalytic components which usually are oxides of base metals, such as vanadium, molybdenum and tungsten.

Figure 2a schematically illustrates a system 289 according to an example embodiment of the invention. The system 289 is situated in the tractor unit 110 and may be part of a catalytic configuration, also denoted exhaust gas processing configuration. It comprises in this example a container 205 arranged to hold a reductant. The container 205 is adapted to holding a suitable amount of reductant and also to being replenishable as necessary. The container may be adapted to hold e.g. 75 or 50 litres of reductant.

A first line 271 is provided to lead the reductant to a pump 230 from the container 205. The pump 230 may be any suitable pump. The pump 230 may be arranged to be driven by an electric motor (not depicted). The pump 230 may be adapted to drawing the reductant from the container 205 via the first line 271 and supplying it via a second line 272 to a dosing unit 237. The dosing unit 237 may also be referred to as a reducing agent dosing unit. The dosing unit 237 comprises an electrically controlled dosing valve by means of which a flow of reductant added to the exhaust system can be controlled. The pump 230 is adapted to pressurising the reductant in the second line 272. A third line 273 is provided with a throttle unit (not shown), against which the pressure of the reductant may build up in the system 289. Alternatively the throttle unit is provided within the dosing unit 237. A first control unit 200 is arranged for communication with the pump 230 via a link L230. The first control unit 200 is arranged to send control signals S230 via the link L230. The first control unit 200 is arranged to control operation of the pump 230 so as to for example adjust flows of the reducing agent within the system 289. The first control unit 200 is arranged to control an operation power of the pump 230 e.g. by controlling the electric motor.

The dosing unit 237 is adapted to supplying the reductant to an exhaust gas system (see Fig. 2b) of the vehicle 100. More specifically, it is adapted to supplying a suitable amount of reductant in a controlled way to an exhaust system of the vehicle 100. In this version, one SCR unit (see Fig. 2b) is situated downstream of the location in the exhaust system where the supply of reductant takes place. The dosing unit 237 is depicted in greater detail with reference to Figure 2c.

The third line 273 running between the dosing unit 237 and the container 205 is adapted to leading back to the container 205 a certain amount of the reductant fed to the dosing unit 237. This configuration results in advantageous cooling of the dosing unit 237. The dosing unit 237 is thus cooled by a flow of the reductant when it is pumped through it from the pump 230 to the container 205.

The first control unit 200 is arranged for communication with the dosing unit 237 via a link L237. The first control unit 200 is arranged to send control signals S237 via the link L237. The first control unit 200 is arranged to control operation of the dosing unit 237 so as to for example control dosing of the reducing agent to the exhaust gas system of the vehicle 100. The first control unit 200 is arranged to control operation of the dosing unit 237 so as to for example adjust return flow of the reducing agent to the container 205.

A second control unit 210 is arranged for communication with the first control unit 200 via a link L210. It may be releasably connected to the first control unit 200. It may be a control unit external to the vehicle 100. It may be adapted to performing the proposed steps according to the invention. It may be used to cross-load software to the first control unit 200, particularly software for applying the proposed method. It may alternatively be arranged for communication with the first control unit 200 via an internal network on board the vehicle. It may be adapted to performing functions corresponding to those of the first control unit 200, such as e.g. controlling operation of a dosing unit of a fluid dosing system comprising an electrically controlled valve unit having a coil arranged for shifting the valve unit between an open state and a closed state by moving a sealing member between a first position and a second position.

Figure 2b schematically illustrates a system 290 of the vehicle shown in Figure 1 according to an embodiment of the invention. The system 290 may constitute a part of the proposed system comprising the dosing unit 237.

The first control unit 200 is arranged for communication with the combustion engine 231 via a link L231. The first control unit is arranged to control operation of the combustion engine 231 by means of control signals S231.

The combustion engine 231 is during operation causing an exhaust gas flow which is lead via a first passage 255 to an SCR-unit 260. A second passage 265 is arranged to convey the exhaust gas flow from the SCR-unit 260 to an environment of the vehicle.

The emission control system provided downstream the engine 231 may comprise a DOC-unit (not shown) and/or a DPF-unit (not shown). The emission control system may comprise a number of SCR units and at least one reducing agent dosing unit.

The dosing unit 237 is arranged to provide the reductant to the first passage 255 upstream of the SCR-unit 260. The first control unit 200 is arranged to control operation of the dosing unit 237 so as to, where applicable, dose reducing agent into the first passage 255.

The SCR-unit 260 may comprise a vaporizing module (not shown) which is arranged to vaporize the dosed reducing agent so as to achieve a mixture of exhaust gas and reducing agent for treatment by means of an SCR-portion of the SCR-unit 260. The vaporizing module may comprise a mixer (not shown) for mixing the vaporized reducing agent with the exhaust gas. The vaporizing module may be formed in any suitable way. The vaporizing module is configured to achieve a most effective vaporizing of provided reducing agent as possible. Herein the vaporizing module is providing large surfaces where vaporizing of provided reducing agent may be performed in an effective way. The vaporizing module may consist of a metal or a metal alloy.

The SCR-unit 260 may according to one possible configuration comprise an ammonia slip catalyst ASC, not illustrated.

The first control unit 200 is arranged to perform the process steps depicted herein, comprising the process steps which are detailed with reference to Figure 4b.

Figure 2c schematically illustrates the closing unit 237 in greater detail. Hereby the second line 272 is arranged to provide pressurized reducing agent to an opening O of the dosing unit 237. The third line 273 is arranged to lead reducing agent which has not been dosed via the opening O back to the tank 205.

The first control unit 200 is arranged to control dosing by means of an electrically controlled valve unit. The valve unit comprises a number of parts of the dosing unit 237. The valve unit is according to this example comprising a sealing member 291. The sealing member 291 is according to this example pin like. The valve unit is spring biased by means of a spring 293. The first control unit 200 is arranged to control a position of the sealing member 291 by means of an electrical wiring 292 comprising a coil surrounding the sealing member 291. The coil is arranged for shifting the valve unit between an open state OS and a closed state CS by moving the sealing member 291 between a first position PI and a second position P2.

The movement of the sealing member 291 between the first position PI and the second position P2 is performed by means of an electromagnetic force. By applying a voltage U by means of the first control unit 200 a current I is generated. Hereby an electromagnetic force is overcoming the force applied by the spring 293 and the sealing member 291 is moved from the second position P2 to the first position PI. Hereby dosing of reducing agent is controlled. Dosing of the pressurized reducing agent is performed when the valve unit is in the open state OS. When the applied voltage U is shut off, the spring 293 will affect the valve unit to change from the open state OS to the closed state CS. The first control unit 200 is arranged to continuously determine the prevailing current I in the electrical wiring 292. The current I is presenting variations over time due to the electromagnetic force.

A position sensor 238 is arranged to determine a prevailing position of the sealing member 291. The position sensor 238 is arranged to determine if the sealing member 291 is in a first position PI or in a second position P2. The position sensor 238 is arranged for

communication with the first control unit 200 via a link L238. The position sensor 238 is arranged to continuously determine if the sealing member 291 is in a first position PI or in a second position P2 and send signals S238 comprising this information to the first control unit 200 via the link L238.

A pressure sensor 239 is arranged to determine a prevailing pressure Pr of the fluid

(reducing agent) in the second line 272 or in the third line 273 upstream of a valve unit of the third line 273 and downstream of the pump 230, i.e. in a pressurized portion of the system 289. The pressure sensor 239 is arranged for communication with the first control unit 200 via a link L239. The pressure sensor 239 is arranged to continuously determine the pressure Pr and send signals S239 comprising this information to the first control unit 200 via the link L239.

Figure 3a is illustrating a diagram wherein a voltage U being applied over the coil 292 is given as a function of time t. The voltage U is given in Volt (V) and the time t is given in

milliseconds (ms).

At a point of time tl a peak voltage Ul is applied over the coil 292. The peak voltage Ul may be any suitable voltage sufficient for achieving the sealing member 291 to move from the second position P2 to the first position PI, i.e. to set the valve unit of the dosing unit 237 in the open state OS. The peak voltage Ul is according to one example a predetermined voltage, e.g. 24V. According to one embodiment the peak voltage Ul is 12V. This value may be relevant in case the vehicle 100 is a car. According to one embodiment the peak voltage Ul is 60V.

The prevailing current I in the coil is hereby initially increasing and at a time point when the sealing member 291 is actually moved a temporarily dip is observed. The current I is increasing to a top level before a point of time tx. This is illustrated in Figure 3b.

The peak voltage Ul is applied during a time period tl-tx. At a certain point of time the peak voltage Ul is shifted to a hold voltage U2. The hold voltage U2 may be any suitable voltage sufficient for maintaining the sealing member 291 in the first position PI, i.e. to keep the valve unit in the open state OS. The hold voltage U2 is lower than the peak voltage Ul. The hold voltage U2 is according to one example a predetermined voltage, e.g. 18V (e.g. in a case where the peak voltage Ul is 24V). According to one example the hold voltage U2 is any suitable voltage being lower than the peak voltage Ul and higher than 0V. The hold voltage U2 is applied until a point of time t2. During this time period the prevailing current in the coil 291 is stabilized at a certain level.

A prevailing energy state of the coil 292 is based upon the prevailing current I in the coil 292. Thus the level of the energy state is increasingly building up after the point of time tl when the peak voltage Ul is applied. When the force which is induced by the coil 292 is exceeding the force of the spring 293 the sealing member 291 is moved from the second position P2 to the first position PI, whereby dosing is commenced.

The level of the energy state may be determined continuously. This energy state is referred to as a first energy state El, i.e. it is a prevailing energy state under influence of the applied peak voltage Ul. A second energy state E2 is associated with the hold voltage U2. The second energy state E2 may be a predetermined energy state. The second energy state E2 may be corresponding to a steady state condition when the hold voltage U2 is applied. According to an embodiment the applied peak voltage Ul is shifted to the hold voltage U2 at a point of time tx at which the first energy state El has reached the second energy state E2.

For comparison reasons it is illustrated with a broken line a case where the peak voltage Ul is shifted to the hold voltage U2 at a point of time t2. Hereby, at the point of time t2, the first energy state El is at a higher level compared to the energy level at the point of time tx. Advantageously an improved voltage shift may be performed when the first energy state El is substantially equal to the expected second energy state E2.

Figure 3b is illustrating a diagram wherein a prevailing current in the coil 292 is given as a function of time t. The prevailing current I is given in milliampere (mA) and the time t is given in milliseconds (ms).

It is illustrated that the current I in the coil 292 is increasing over time when the peak voltage Ul is applied. However, at the moment when the sealing member 291 is shifting position from the second position P2 to the first position PI, a temporary dip is presented due to magnetic force phenomena. This temporary dip may be taken as evidence that the valve unit of the dosing unit 237 is shifted to the open state OS.

When the hold voltage U2 is shifted to zero voltage at the point of time t3 the prevailing current I is decreasing to zero mA.

Figure 3c schematically illustrates a diagram according to an embodiment of the invention. An upper graph is referring to the voltage U being applied over the coil 292 given as a function of time t. The voltage U is given in Volt (V) and the time t is given in milliseconds (ms). A lower graph is referring to a prevailing current in the coil 292 given as a function of time t. The prevailing current I is given in milliampere (mA) and the time t is given in milliseconds (ms). For reasons of clarity two different and corresponding cases are illustrated in the upper graph and the lower graph.

In a first case (continuous line) the peak voltage Ul is applied at the point of time tl. The prevailing current I is then increasing and is eventually presenting the characteristic temporary dip. At the point of time tx the hold voltage Ul is shifted to the hold voltage U2. After this point of time the prevailing current I will hereafter be substantially constant, as well as the energy level of the coil 292. At the point of time t3 the hold voltage U2 is shifted to 0 voltage and the prevailing current I will decrease to a level of 0 mA.

In a second case (broken line) the peak voltage Ul is applied at the point of time tl. The prevailing current I is then increasing and is eventually presenting the characteristic temporary dip. At the point of time t2 the hold voltage Ul is shifted to the hold voltage U2. The prevailing current I is then decreased to a steady state level corresponding to the hold voltage U2. At the point of time t3 the hold voltage U2 is shifted to 0 voltage and the prevailing current I will decrease to a level of 0 mA.

Figure 3d is illustrating a diagram wherein a prevailing pressure Pr of the reducing agent in the pressurized portion of the system 289 is presented as a function of time t. The pressure Pr is given in bar and the time t is given in milliseconds ms.

It is illustrated that a pressure dip is provided as the valve unit is shifted from the closed state CS to the open state OS. This dip is explained by that the pressure drops to some extent as the dosing is performed, but recovers as a response to that pressure once again is built up by means of the pump 230. This temporarily pressure dip may be taken as evidence that the valve unit of the dosing unit 237 is shifted to the open state OS.

Figure 4a schematically illustrates a flow chart of a method for controlling operation of a dosing unit 237 of a fluid dosing system comprising an electrically controlled valve unit having a coil 292 arranged for shifting the valve unit between an open state OS and a closed state CS by moving a sealing member 291 between a first position PI and a second position P2.

The method comprises a first method step s401. The method step s401 comprises the steps of: - applying a peak voltage Ul over the coil;

- continuously determining a first energy state El of the coil;

- comparing the first energy state El with a second energy state E2 of the coil corresponding to a hold voltage U2; and - shifting the applied peak voltage Ul to the hold voltage U2 at a point of time tx at which the first energy state El has reached the second energy state E2.

The method may comprise the step of determining that the valve unit is in an open state OS prior to shifting the applied peak voltage Ul to the hold voltage U2.

After the method step s401 the method ends/is returned.

Figure 4b schematically illustrates a method for controlling operation of a dosing unit of a fluid dosing system comprising an electrically controlled valve unit having a coil 292 arranged for shifting the valve unit between an open state OS and a closed state CS by moving a sealing member 291 between a first position PI and a second position P2.

The method comprises a first method step s410. The method step s410 comprises the step of applying a peak voltage Ul over the coil 292. This is performed by means of the first control unit 200. Hereby the applied voltage U is increased from zero voltage to the peak voltage Ul. The peak voltage Ul may be a predetermined voltage, such as e.g. 24V. The peak voltage Ul is sufficient to eventually achieve the sealing member 291 to move from the second position P2 to the first position PI, whereby the valve unit of the dosing unit 237 is set to the open state OS.

After the method step s410 a subsequent method step s420 is performed.

The method step s420 comprises the step of continuously determining a first energy state El of the coil 292. This is performed by means of the first control unit 200. The first energy state El may be continuously determined on the basis of a prevailing current I in the coil 292. The first energy state El may be determined on the basis of the detected current I in the coil 292. This process may comprise the step of continuously determining an integral value of the prevailing current and use the result to determine the prevailing energy state of the coil 292. After the method step s420 a subsequent method step s430 is performed.

The method step s430 comprises the step of comparing the first energy state El with a second energy state E2 of the coil corresponding to a hold voltage U2. This is performed by means of the first control unit 200. The second energy state E2 may be a predetermined energy state. The second energy state E2 may be empirically determined. The second energy state E2 may be determined paying regard to electrical characteristics of the coil 292 and an accumulated provided current I given a specific applied hold voltage. The second energy state E2 may be determined by means of a predetermined calculation model. The second energy state E2 may be determined as an energy state appearing during steady state conditions corresponding to hold voltage application over the coil 292.

A relevant value of the second energy state E2 may be stored in a memory of the first control unit 200.

After the method step s430 a subsequent method step s440 is performed.

The method step s440 comprises the step of determining if the valve unit is in an open state OS or not. This is performed by means of the first control unit 200. This may be performed in a number of different ways. The method step s440 may be performed at any suitable point of time before the method step s450. The method step s440 may be performed before any of the method steps s420 or s430. According to one embodiment the method step s440 is performed at substantially the same time as the method step s410. According to one embodiment the method step s440 is performed directly after the method step s410 and before the method step s420. According to a first example it is determined that the valve unit is in an open state OS by detecting a significant dip in a coil current course during application of the peak voltage Ul. This is performed by means of the first control unit 200. This is depicted in greater detail with reference to Figure 3b. According to a second example it is determined that the valve unit is in an open state OS by detecting a significant dip in a fluid supply pressure Pr. This is performed by means of the first control unit 200 and the pressure sensor 239. This is depicted in greater detail with reference to Figure 3c.

According to a third example it is determined that the valve unit is in an open state OS by detecting a sealing member position corresponding to the open state OS, namely the first position PI. This is performed by means of the first control unit 200 and the position sensor 238. This is depicted in greater detail with reference to Figure 2c.

If it is determined that the valve unit is in an open state OS the applied peak voltage Ul is shifted to the hold voltage U2, which is depicted with reference to the method step s450. If it is determined that valve unit is not in an open state OS the applied peak voltage Ul is not shifted to the hold voltage U2 and the method is returned to the method step s430.

The method step s450 comprises the step of shifting the applied peak voltage Ul to the hold voltage U2 at a point of time tx at which the first energy state El has reached the second energy state E2.

The method step s450 may comprise the steps of:

- determining the point of time tx at which the first energy state El has reached the second energy state E2 on the basis of the peak voltage Ul over the coil and electrical characteristics of the coil; and - shifting the applied peak voltage Ul to the hold voltage U2 at the determined point of time tx.

The point of time tx is determined by means of the first control unit 200. After the method step s450 the method ends/is returned.

The proposed method may be applied to any sequence of dosing cycles. According to one embodiment the proposed method is applied to each consecutive dosing cycle of the dosing unit 237. According to one embodiment the proposed method is applied to every second, fifth or tenth dosing cycle of the dosing unit 237.

Figure 5 is a diagram of one version of a device 500. The control units 200 and 210 described with reference to Figure 2a and Figure 2b may in one version comprise the device 500. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer program, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

The computer program P comprises routines for controlling operation of a dosing unit 237 of a fluid dosing system comprising an electrically controlled valve unit having a coil 292 arranged for shifting the valve unit between an open state OS and a closed state CS by moving a sealing member 291 between a first position PI and a second position P2.

The computer program P comprises routines for applying a peak voltage Ul over the coil 292.

The computer program P comprises routines for continuously determining a first energy state El of the coil 292.

The computer program P comprises routines for comparing the first energy state El with a second energy state E2 of the coil 292 corresponding to a hold voltage U2. The computer program P comprises routines for shifting the applied peak voltage Ul to the hold voltage U2 at a point of time tx at which the first energy state El has reached the second energy state E2.

The computer program P may comprise routines for determining that the valve unit is in an open state OS prior to shifting the applied peak voltage Ul to the hold voltage U2.

The computer program P may comprise routines for determining that the valve unit is in an open state OS by at least one of the procedures of:

- detecting a significant dip in a coil current course during application of the peak voltage Ul;

- detecting a significant dip in a fluid supply pressure Pr; and - detecting a sealing member position corresponding to the open state OS.

The computer program P may comprise routines for:

- determining the point of time tx at which the first energy state El has reached the second energy state E2 on the basis of the peak voltage Ul over the coil and electrical characteristics of the coil; and - shifting the applied peak voltage Ul to the hold voltage U2 at the determined point of time tx.

The computer program P may comprise routines for:

- continuously determining a first energy state El of the coil 292 on the basis of a prevailing current I in the coil 292; and - determining the second energy state E2 as an energy state appearing during steady state conditions corresponding to hold voltage application over the coil 292.

The computer program P may comprise routines for performing any of the process steps detailed with reference to Figure 4a and Figure 4b.

The program P may be stored in an executable form or in compressed form in a memory 560 and/or in a read/write memory 550. Where it is stated that the data processing unit 510 performs a certain function, it means that it conducts 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 via a data bus 511. The read/write memory 550 is arranged to communicate with the data processing unit 510 via a data bus 514. The links L210, L230, L231, L237, L238 and L239, for example, may be connected to the data port 599 (see Fig. 2a, 2b and 2c).

When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 will be prepared to conduct code execution as described above.

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

The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive, nor to limit the invention to the variants described. Many modifications and variations will obviously suggest themselves to one skilled in the art. The embodiments have been chosen and described in order to best explain the principles of the invention and their practical applications and thereby make it possible for one skilled in the art to understand the invention for different embodiments and with the various modifications appropriate to the intended use.