CN119222026A

CN119222026A - Method for operating an SCR system

Info

Publication number: CN119222026A
Application number: CN202410855448.5A
Authority: CN
Inventors: K·法尔卡斯; A·Z·阿梅德
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2023-06-29
Filing date: 2024-06-28
Publication date: 2024-12-31
Also published as: DE102023206139A1

Abstract

The invention relates to a method for operating an SCR system with an intake and return line of an internal combustion engine, in which at least one dosing valve doses a reagent upstream of at least one SCR catalytic converter, wherein the reagent is delivered to the dosing valve from a tank at a constant pressure by means of a controllable pump, characterized by the following steps: - determining a stiffness for the SCR system; - determining a performance factor for a pump for the SCR system; - determining a first consumption deviation; - determining a correction function as a function of the temperature of the urea liquid, the stiffness and the performance factor; - determining a corrected consumption deviation as a function of the first consumption deviation and the correction function; - wherein the corrected consumption deviation is compared with a second, predeterminable consumption deviation, - and from the comparison it is determined whether the urea liquid for the SCR system is overdosed or underdosed.

Description

Method for operating an SCR system

Technical Field

The invention relates to a method for detecting a blockage of one or more injection openings of a dosing valve of an SCR system 25. The invention also relates to a computer program which, when run on a computer, performs all the steps of the method according to the invention. The invention also relates to a computer program product with a program code stored on a machine-readable carrier for performing the method when the program is implemented on a computer or a controller.

Background

In order to comply with increasingly stringent emission regulations, it is necessary to reduce nitrogen oxides (NO _x) in the exhaust gases of internal combustion engines, in particular diesel engines. For this purpose, it is known to arrange an SCR (Selective Catalytic Reduction) catalyst in the exhaust gas region of the internal combustion engine. In the SCR catalyst, nitrogen oxides contained in exhaust gas of an internal combustion engine are reduced to nitrogen gas in the presence of a reducing agent. The proportion of nitrogen oxides in the exhaust gas can thus be significantly reduced. Ammonia (NH ₃) is required in the reduction process, which is mixed into the exhaust gas. Thus, NH ₃ or a reagent that releases NH ₃ is used as a reducing agent. Generally, an aqueous urea solution (urea aqueous solution; HWL) is used for this purpose, which is injected downstream of the SCR catalyst in the exhaust gas system. Ammonia is formed from this solution, which acts as a reducing agent. A32% aqueous urea solution is commercially available under the trade nameObtained.

A dosing system for an SCR-catalyst according to the prior art comprises a reductant tank, a delivery module and a dosing valve. The reductant solution is delivered from the reductant tank to the dosing valve via the delivery module. The delivery module comprises a pump which is connected by means of a line to the dosing valve and, if necessary, to the reducing agent return. Such a pipeline system is called a hydraulic system.

The california air resources committee (California Air Resources Board, CARB) requires the identification of dosing deviations in the catalyst system that result in exceeding defined nitrogen oxide emission limits for the exhaust system of the diesel engine. This may occur, inter alia, due to blockage of one or more injection openings of the dosing valve of the SCR system 25. Therefore, a reducing medium must be carried outIs provided for the identification between the required and the actual metered dispensing quality. In particular, due to the presence of a return flow of reducing agent in the delivery module of the SCR system 25, and due to the metering of a certain quantity of reducing agentThe influence of the air volume contained in the system on the pressure profile is such that the detection of a deviation in the metering by evaluating the gradient of the pressure profile in the hydraulic system or by a deviation in the pump speed is not possible.

Therefore, in order to identify deviations in the dosing amount of the urea aqueous solution due to blockage of one or more injection openings of the dosing valve, an additional mass flow sensor has to be used in the hydraulic system of the SCR-system 25.

Disclosure of Invention

According to the invention, the operation of an SCR system with a suction and return line of an internal combustion engine, as well as a computing unit and a computer program for its execution are proposed with the features of the independent patent claims. The subject matter described in the dependent claims is advantageous.

In a first aspect, the invention relates to a method according to the invention for operating an SCR system with a suction and return line of an internal combustion engine, wherein at least one dosing valve doses reagent upstream of at least one SCR catalyst, wherein the reagent is fed from a tank to the dosing valve by means of a controllable pump under constant pressure, characterized by the following steps:

-determining a stiffness for the SCR-system;

-determining a performance factor of a pump for the SCR-system;

-determining a first consumption deviation;

-determining a correction function based on the temperature, the stiffness and the performance factor of the urea liquid;

-determining a corrected consumption deviation from the first consumption deviation and the correction function;

wherein the corrected consumption deviation is compared with a predefinable second consumption deviation,

And from the comparison it follows whether the urea liquid for the SCR-system is over-or under-dosed.

A particular advantage of the invention is that an overdosing or underdosing of the reagent can be derived from a comparison of the corrected consumption deviation with a predefinable second consumption deviation. The influence of the temperature of the urea liquid, the rigidity of the SCR system and the performance factor of the pump are taken into account by means of a correction function for the first consumption deviation. Thus a more accurate consumption deviation of the SCR system is obtained. This can further improve the dosing accuracy of the urea liquid of the SCR system and lead to an improved exhaust gas aftertreatment. It is thus also possible to prevent an overdosing of urea liquid in the exhaust system, so that no ammonia leaks or reduced ammonia leaks. In an advantageous development, it can therefore also be concluded that the dosing valve and/or the SCR system is blocked or bleedover.

In a further embodiment, if the corrected consumption deviation exceeds a predefinable second consumption deviation, an overdosing of urea liquid is detected.

It is particularly advantageous to identify an overdose of reagent, since an adaptation of the dosage can thus be performed. The dosing strategy can thus be modified, for example, so that an overdosing situation of Adblue, for example, does not occur.

In a special embodiment, if the first consumption deviation is lower than a predefinable consumption deviation, an insufficient dosing of urea liquid is detected.

It is particularly advantageous to identify an under-dosing of the reagent, since an adaptation of the dosing amount can thus be performed. The allocation strategy can thus be modified, for example, so that an under-allocation situation of Adblue, for example, does not occur. Thereby emissions regulations may be complied with and undesirable pollutant emissions may be prevented.

In an advantageous embodiment, the method is activated when a constant system pressure for the SCR system is present, in particular within a predefinable time period.

In a further embodiment, the performance factor is determined as a function of the current pump frequency.

In an advantageous embodiment, the correction function is determined as a function of the rigidity of the SCR system, the temperature of the urea liquid and the current performance factor.

By taking into account the rigidity of the SCR system, the temperature of the urea liquid and the performance factor, a more accurate consumption deviation can be determined. By means of the further addition, a correction function can be determined, with which a known consumption deviation of the SCR system can be corrected.

In a special embodiment, the first consumption deviation for an SCR system with suction and return lines is determined by means of the following equation:

Wherein c represents the rigidity of the SCR system (25), p (t ₃) represents a third pressure value at a third point in time (t ₃), p (t ₄) represents a fourth pressure value at a fourth point in time (t ₄), and Represents the average between the third and fourth pressure values (p (t ₃);p(t₄)).

In an advantageous embodiment, the rigidity for an SCR system with suction and return lines is determined by means of the following formula:

Wherein a _b,eff represents the cross-sectional area of the throttle valve 320 and ρ represents the density of the urea liquid (105), p (t ₁) represents a first pressure value at a first point in time (t ₁), p (t ₂) represents a second pressure value at a second point in time (t ₂), and p _sys represents a predefinable system pressure of the SCR system (25).

In an alternative embodiment, the rigidity for an SCR system with suction and return lines is determined by means of the following formula:

Wherein the parameters a, b, x and y are:

Wherein A _b,eff represents the effective cross section of the return line (103), p _sys represents a predefinable system pressure, p ₀ represents a fourth pressure of the SCR system (25) at a fourth point in time (t ₀), p _tf represents a fifth pressure of the SCR system (25) at a fifth point in time (t _f), p _p represents the pump factor of the pump (120) and ρ represents the density of the dosing medium (105).

The computer program according to the invention can carry out all the steps of the method according to the invention when it runs on a computer. This enables the method according to the invention to be carried out in existing SCR catalytic converter systems without structural changes being made to the same. For this purpose, the computer program product according to the invention has a program code stored on a machine-readable carrier and for carrying out the method according to the invention, when the program is implemented on a controller or a computer.

Drawings

Embodiments of the invention are illustrated in the accompanying drawings and described further in the following description.

Figure 1 shows an SCR-system,

Figure 2 schematically shows an SCR-system with suction-and return lines for an internal combustion engine,

Figure 3 shows an example of measurement of the pressure profile for an SCR system with suction and return lines,

Fig. 4 shows a first embodiment of a method according to the invention for an SCR system with suction and return lines according to a combined flow/block diagram.

Detailed Description

Fig. 1 shows an SCR system 25 having a return line 103 of an internal combustion engine (not shown), only the elements of such a reduction system being shown here that are essential to the invention.

Tank 100 stores a reductant solution, such as aqueous urea solution 105, which is also sold under the product name "AdBlue". The aqueous urea solution 105 is fed by means of a pump 120 via a suction line 101 to a dosing medium unit 300 (pump mass flow rate)) By means of which the urea aqueous solution is injected into the exhaust gas channel 400 before the catalyst K (dosing mass flow rate))。

The pressure in the SCR-system 25 is detected by a pressure sensor 130 arranged in the suction line 101. This signal is converted in the pressure-voltage converter 132 and fed to a control device 200, for example a motor controller. The controller 200 also enables the pump 120 to be actuated, specifically to maintain a constant pressure in the SCR system 25. For this purpose, a system pressure p _sys is predefined for the SCR system 25, which is in particular between 4 and 12 bar. Thus, when, for example, the reducing agent flows out via the dosing medium unit 300 and from there into the exhaust gas, the pump 120 is actuated, as a result of which the reducing agent is transported out of the tank 100 and thus the pressure in the SCR system 25 remains virtually unchanged. In particular for the method according to the invention, the pump frequency f _p of the pump 120 remains constant. The dosing medium unit 300 has an own dosing valve 310, which can be actuated by the control device 200 via an electromagnet 312 arranged in the housing 309 together with the dosing valve 310, and a throttle valve 320, which is arranged in the return line 103, which leads to the tank 100 and which effects a return flow of the return medium to the tank 100 (return mass flow rate). The return line 103 serves to cool a distribution valve 310, which is arranged directly in front of the catalyst K in the hot exhaust gas.

Fig. 2 shows the course of the pressure p in the SCR system 25, the actuation PM of the pump 120 in the delivery module of the SCR system 25, and the actuation DV of the dispensing valve 310 of the SCR system 25, each for an embodiment of the invention, based on the time t. Pump 120 is constantly operated during the period of t ₀ to t ₁. Depending on the requirements of the SCR catalyst, the dosing valve is actuated more or less strongly in order to dose the aqueous urea solution 105 into the SCR catalyst. The pressure in the SCR-system 25 of the SCR-system 25 fluctuates similarly to the manipulation of the dosing valve 310. At time t ₁, the internal combustion engine connected to the SCR catalytic converter system is shut down and the urea aqueous solution 105 is no longer required. Thus, neither the pump 120 nor the dispensing valve 310 is operated. The pressure p in the SCR-system 25 gradually drops via the throttle 320. At time t ₂, the method according to the present invention now begins for identifying a blockage of one or more injection openings of dispensing valve 310. For this purpose, a sudden change in rotational speed is caused by the actuation, which causes the pressure p in the SCR system 25 to suddenly increase to its system pressure p _sys. Where the dispensing valve 310 remains closed. From the first pressure profile, a stiffness c of the SCR system 25 is modeled according to equation 1 based on a first pressure p (t ₁) at a first point in time t ₁ and a second pressure p (t ₂) at a second point in time t ₂:

here, a _b,eff represents the cross-sectional area of the throttle valve 320, and ρ represents the density of the urea aqueous solution.

At a third point in time t ₃, the pump 120 is closed and the dispensing valve 310 is opened. The pressure p in the SCR system 25 drops as a result via the metering valve 310 and via the throttle valve 320. Next, the dispensing valve 310 is closed again at the fourth time point t ₄. From this second pressure profile and the calculated stiffness c, it is determined on a modeling basis according to equation 2 based on a third pressure p (t ₃) at a third point in time t ₃ and a fourth pressure p (t ₄) at a fourth point in time t ₄ whether a blockage of one or more injection openings of the dispensing valve 310 is present:

Here, a _d,eff represents the cross-sectional area of the dispensing valve 310. By comparing the cross-sectional area A _d,eff thus determined with the cross-sectional area of the permeable dispensing valve 310, it can be concluded whether there is a blockage of one or more of the injection openings of the dispensing valve 310.

Next, the pump 120 of the pump 120 is constantly controlled. Once the pressure p is again set to a constant value, the SCR-catalyst system is ready for re-dosing the urea aqueous solution 105.

Fig. 3 shows a flow path for an SCR system 25 with suction and return lines 101;103 as a function of the measurement. Starting from the system pressure p _sys, the pressure profile p of the SCR system 25 is shown, wherein at a third point in time t _inj the urea liquid is dosed into the exhaust gas channel 400 by means of the dosing valve 310, preferably a test injection. During the entire time period, the pump 120 of the SCR system 25 is continuously operated at a constant pump frequency f _p and urea liquid is fed via the suction and return lines 101; 103. From the fifth time point t _inj, the pressure p decreases until a sixth time point t ₀. That is, at a fifth point in time t _inj, the dispensing valve 310 is opened and at a sixth point in time t ₀ is closed again. From the sixth time point p ₀, the pressure p increases again.

The pump factor P _p is read from the characteristic field P _p,map as a function of the pressure difference P _sys- P. In this case, the characteristic field P _p,map is determined in the application phase of the SCR system 25 used as a function of the different system pressures (in particular between 0 and 12 bar). Here, the pump factor p _p describes the power of the pump 120 at different system pressures, and thus forms a measure for the power of the pump 120. In particular, the system pressure P _sys and the determined pressure P _avg＝(p₀+p_tf)/2 can be used to determine the pump factor P _p as input variables for the characteristic field P _p,map.

The effective cross section a _b,eff of the return line 103 and the density ρ of the urea liquid 105 are present in the controller 200 as predetermined values. They are already stored in the controller 200, in particular during the application phase.

In a further embodiment, the rigidity c of the SCR system 25 with the suction and return lines 101;103 can alternatively be determined by means of the following equation:

Dosing of the fluid, in particular a test injection, particularly occurs before the period from the fifth point in time t ₀ to the sixth point in time t _f. That is, the dispensing valve 310 is opened and the closing time point of the dispensing valve 310 corresponds to the fifth time point t ₀. In the control unit 200, a predefinable time t _app, in particular between 0.3ms and 2s, is stored. For SCR system 25 with return line 103, this predefinable time t _app characterizes the evaluation period after the previously occurring dosing.

Thus, the sixth time point t _f is defined as t _f＝t₀+t_app.

The parameters a, b, x and y are defined as follows:

Where p _sys denotes the predefined system pressure, p ₀ denotes the pressure at the fifth point in time t ₀, p _tf denotes the pressure at the sixth point in time t _f, and p _p denotes the pump factor at the current pressure p. In particular, the system pressure P _sys and the determined pressure P _avg＝(p₀+p_tf)/2 can be used to determine the pump factor pp as input variable for the characteristic field P _p,map.

The first consumption bias CDM _cal for the SCR-system 25 is calculated according to the following equation:

Wherein A _d,eff represents the effective cross section of the distribution valve 310 of the SCR system 25, A _b,eff represents the effective cross section of the return line 130 or the throttle valve 320 of the SCR system 25, c represents the rigidity, p (t ₃) represents the third pressure value at the third point in time t ₃, p (t ₄) represents the fourth pressure value at the fourth point in time t ₃, and The average of the third and fourth pressure values p (t ₃);p(t₄) is shown.

In addition, the temperature of the urea aqueous solution 105 is measured continuously, in particular by a temperature sensor (not further shown) placed in the urea liquid 105, and received and stored by the controller 200.

The correction function f (c, T, d _p) is also stored on the controller 200, wherein the correction factor f of the regulating deviation CDM is determined during the run-time by means of the correction function. The calculation is determined from the determined stiffness c, the current temperature T of the urea liquid 105 and a performance factor dp that depends on the current pressure p.

By means of the polynomial method, the correction function f (c, T, d _p) can be described as follows:

f(c,T,d_p)＝D₀(T)+D₁(T)·c+D₂(T)·c²+D₃(T)·c³+d_p(T) (9)

Where D ₀、D₁、D₂ and D ₃ represent temperature-dependent coefficients, T represents the current temperature of the urea liquid 105, c represents stiffness, and D _p (T) represents the performance factor of the pump 120 as a function of the current temperature T of the urea liquid 105.

In this case, the temperature-dependent coefficients D ₀、D₁、D₂ and D ₃ are determined during the application phase from the temperature T of the urea liquid 105, the rigidity c determined for the SCR system 25 and the temperature-dependent performance factor D _p and are then stored in the controller 200, in particular in the property field. The advantage of this polynomial method of the function f is that the influence of the stiffness c, the current temperature T of the urea liquid 105 and the performance factor d _p can be taken into account for calculating the current consumption deviation in order to determine the consumption deviation even more accurately.

The first consumption bias CDM _cal is corrected according to the following equation and the corrected consumption bias CDM _Cor for SCR-system 25 is obtained:

An exemplary flow of a method according to the invention for an SCR system 25 with a suction line 101 is shown in fig. 4.

In a first step 500, the activation condition of the method is monitored in the controller 200. The method is enabled when the controller 200 for the SCR-system 25 detects a pressure stable system condition. When the pressure is successfully established at a stable system pressure psys (preferably between 6 and 12 bar), a pressure stable system state exists. In particular, a stable system state can exist when an reached system pressure psys is detected by the controller 200 within a predefinable time. For this purpose, the controller 200 can monitor the pressure p and perform the activation when a predefined system pressure psys is applied for a predefinable time.

The method may also continue in step 540 if the stiffness c for the SCR-system 25 has been calculated and stored in the controller 200.

If there is no stiffness c in the controller 200 for the SCR-system 25, the method continues in step 510.

In step 510, a stiffness c for the SCR-system 25 is determined. This can be performed during the depressurization phase by means of equation 1. To this end, the pump 120 is deactivated at a first point in time t ₁. As depicted in fig. 2, the pressure p slowly drops via the throttle valve 320. At a second point in time t ₂, pump 120 is again activated, so that a sudden increase in pressure p in SCR system 25 to its system pressure p _sys occurs. The dispensing valve 310 remains closed during this period. The stiffness c of the SCR system 25 is determined from the first pressure profile on the basis of a modeling from equation 1 based on the first pressure p (t ₁) at the first point in time t ₁ and the second pressure p (t ₂) at the second point in time t ₂.

Alternatively, the rigidity c may also be determined according to equation 3. At dosing point in time t _inj, dispensing valve 310 is opened, and at a later fourth point in time t ₀, dispensing valve 310 is closed again. During this dosing, the pressure p in the SCR system 25 drops. Here, the pressure is continuously received and stored by the controller 200. During this dosing, the pump frequency f _p remains constant.

With the dosing valve 310 closed at a fourth point in time t ₀, a fourth pressure p ₀ of the SCR-system 25 is determined. With the dosing valve 310 closed, the pressure p of the SCR system 25 increases again. The controller 200 then waits a predefinable time Δt until a fifth time t _f is reached and determines a fifth pressure p _tf of the SCR system 25. Further, the performance factor d _p is map-determined from the characteristic field d _p according to the pump frequency f _p. The stiffness c for the SCR-system 25 is then determined by the controller 200 according to equation 3.

The method then continues at step 520.

In step 520, a third pressure value pi at a third point in time t ₃ and a fourth pressure value pf at a fourth point in time t ₄ are determined in the pump stroke determined in step 510. In this case, the fourth pressure value p _f at the fourth time t ₄ is determined at a later time point than at the third time point t ₃. Preferably, a predefinable time t _app of at least 10ms is present between the third and fourth time points t ₃、t₄.

The method then continues in step 530.

In step 530, the method continues when the pressure of the SCR-system 25 again reaches the system pressure psys. The pump frequency f _p remains constant and dosing of the urea liquid 105 is performed. For this purpose, the dispensing valve 320 is opened at a third point in time t ₃ and a third pressure value p is determined (t ₃). At a fourth point in time t ₄, the dispensing valve 320 is again closed and a fourth pressure value p is determined (t ₄). Further, an average value is determined from the third and fourth pressure values p (t ₃);p(t₄)

According to the following equation 8,

A first consumption bias CDM _cal for the SCR-system 25 may be determined.

The method then continues at step 540.

In step 540, the current temperature T of the urea liquid 105 is determined by the controller 200. Based on the determined stiffness c, the current temperature T of the urea liquid 105 and the determined performance factor d _p, a correction function is determined according to equation 9:

f(c,T,d_p)＝D₀(T)+D₁(T)·c+D₂(T)·c²+D₃(T)·c³+d_p(T)

The method then continues in step 550.

The corrected consumption bias CDM _cor is determined in step 560 according to equation 10:

Wherein the correction function is f (c, T, d _p) and the first consumption bias is CDM _cal.

The method then continues in step 550.

In step 550, the corrected consumption deviation CDM _cor is compared with a predefinable consumption deviation CDM _app for SCR system 25. The consumption deviation, i.e., the parameter CDM _app, which can be predefined here corresponds to the parameter stored in the control unit 200 during the application phase, which corresponds to the quotient of the effective cross section a _d,eff for the dispensing valve 310 and the effective cross section a _b,eff for the throttle valve 320.

If the corrected consumption deviation CDM _cor is below the predefinable consumption deviation CDM _app, an underdosing of urea liquid 105 for the SCR system 25 is identified.

If the corrected consumption deviation CDM _cor exceeds the consumption deviation CDM _app, an overdose of urea liquid 105 for the SCR system 25 is identified.

In a special embodiment, a threshold band may be defined around the value of the predefinable consumption deviation CDM _app, for example a threshold band around ±10% of the value of the predefinable consumption deviation CDM _app. If the corrected consumption deviation CDM _cor is within the threshold band, dosing of the urea liquid 105 of the SCR-system 25 is normal. The result of the comparison can preferably be used to correct or adapt the metering quantity m _dos or the metering mass flow m _D determined by the metering strategy. For this purpose, a corrected metering quantity m _dos,corr or a corrected metering mass flow is determined by the control unit 200And subsequently dosed via the dosing valve 310.

The method may then end or begin from scratch.

Claims

1. Method for operating an SCR system (25) with a suction and return line (101; 103) of an internal combustion engine, in which at least one dosing valve (310) doses reagent upstream of at least one SCR catalyst, wherein the reagent (105) is fed from a tank (100) to the dosing valve (310) by means of a controllable pump (120) at a constant pressure, characterized by the following steps:

-determining a stiffness (c) for the SCR-system (25);

-determining a performance factor (d _p) of a pump (120) for the SCR-system (25);

-determining a first consumption bias (CDM _cal);

-determining a correction function (f (c, T, d _p)) from the temperature (T) of the urea liquid (105), the stiffness (c) and the performance factor (d _p);

-determining a corrected consumption deviation (CDN _cor) from the first consumption deviation (CDN _cal) and the correction function (f (c, T, d _p));

Wherein the corrected consumption deviation (CDM _cor) is compared with a predefinable second consumption deviation (CDM _app),

-And deriving from said comparison, whether the urea liquid (105) for said SCR-system (25) is over-or under-dosed.

2. The method according to claim 1, characterized in that an overdosing of urea liquid (105) is identified when the corrected consumption deviation (CDM _cor) exceeds the predefinable second consumption deviation (CDM _app).

3. The method according to claim 1, characterized in that an under-dosing of urea liquid (105) is identified when the first consumption deviation (CDM _cal) is below a predefinable consumption deviation (CDM _app).

4. Method according to claim 1, characterized in that the method is activated when a constant system pressure (p _sys) for the SCR system (25) is present, in particular within a predefinable period of time.

5. The method according to claim 1, characterized in that the performance factor (d _p) is determined from the current pump frequency (f _p).

6. Method according to claim 1, characterized in that the correction function (f (c, T, d _p)) is determined from the stiffness (c) of the SCR-system (25), the temperature (T) of the urea liquid (105) and the current performance factor (d _p).

7. Method according to claim 1, characterized in that the first consumption deviation for an SCR system (25) with suction and return lines (101; 103) is determined by means of the following formula:

8. Method according to claim 1, characterized in that the rigidity (c) for an SCR-system (25) with suction-and return lines (101; 103) is determined by means of the following formula:

9. Method according to claim 1, characterized in that the rigidity (c) for an SCR-system (25) with suction-and return lines (101; 103) is determined by means of the following formula:

Wherein the parameters a, b, x and y are:

10. Computer program arranged to perform the method according to any of claims 1 to 9.

11. An electronic storage medium having a computer program according to claim 10.

12. Device, in particular controller (200), arranged to implement the method according to any of claims 1 to 9.