Method for determining an individual target boost duration of a fuel injector

Abstract

The invention relates to a method for determining an individual target boost duration of a boost phase (307) for driving a fuel injector (130), comprising: providing (502) at least one boost duration value for the fuel injector (130), which boost duration value has been used during a corresponding boost phase (307) of the fuel injector; providing (504) in each case one extinction duration value following the respective boost phase (307) of the fuel injector (130); determining (506) an extinction duration / boost duration correlation (601a, 601b, 601c) between the at least one boost duration value and the respective extinction duration value; and determining (508) the individual target boost duration of the fuel injector (130) on the basis of the extinction duration / boost duration correlation (601a, 601b, 601c).

Description

[0001] R.414520

[0002] - 1 -

[0003] Description

[0004] title

[0005] Method for determining an individual target boost duration for a fuel injector!

[0006] The present invention relates to a method for determining an individual target boost duration of a boost phase for controlling a fuel injector, as well as a computing unit and a computer program for carrying it out.

[0007] Background of the invention

[0008] Fuel injection systems for internal combustion engines deliver fuel from the tank to the combustion chambers of the engine. Fuel injectors supply fuel from a high-pressure storage tank to a combustion chamber of the engine. These fuel injectors can have a solenoid valve in which a magnetic coil is energized to lift a magnetic armature, thereby opening a passage for fuel. Due to manufacturing tolerances, each solenoid valve can exhibit unique opening and / or closing characteristics. The fuel can be a gaseous fuel, particularly hydrogen.

[0009] Disclosure of the invention

[0010] According to the invention, a method for determining an individual target boost duration for controlling a fuel injector, as well as a computing unit and a computer program for carrying it out, with the features R.414520

[0011] - 2 - of the independent patent claim is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0012] The invention relates to a method for determining an individual target boost duration of a boost phase for controlling a fuel injector.

[0013] The fuel injector can include a solenoid valve, which in particular has a solenoid coil and a magnetic armature that can be lifted by energizing the solenoid coil, thus opening a fuel flow orifice. To introduce or inject fuel, the flow orifice can be opened for a predetermined duration corresponding to the amount of fuel to be injected. This can be achieved by actuating the solenoid valve by applying a voltage to the solenoid coil for a specific injection or actuation time. This injection or actuation time can differ from the opening duration in that a certain amount of time is required for the flow orifice to be fully opened after the start of the actuation (opening delay), and a similar amount of time may elapse for the flow orifice to close again after the end of the actuation (closing delay).The actuation time of the solenoid valve is calculated by adding the opening delay to the opening time and subtracting the closing delay.

[0014] The fuel can be hydrogen, which is introduced or injected into a combustion engine via a direct injection system using a fuel injector. The fuel injector is specifically an H2 or HIDI injector. However, the proposed procedure also works with other fuels, generally with fuel injectors.

[0015] As part of the fuel injector control, the solenoid coil for lifting the magnetic armature can be energized with a boost current at the beginning of the control phase during a boost phase. For this purpose, a boost voltage can be applied to the solenoid coil or the solenoid valve. Such a boost duration R.414520

[0016] - 3 - can be used to shorten switching times. In particular, a particularly high current is applied to the magnetic coil. The boost phase thus primarily characterizes the beginning of an armature movement with a strong initial acceleration of the magnetic armature.

[0017] After the boost phase, the magnetic coil can, at least when necessary, preferably be energized in a pull-in phase with a pull-in current that is lower than the boost current. The pull-in phase primarily ensures the magnetic force is maintained until approximately the maximum armature stroke is reliably reached. Typically, a holding phase follows the pull-in phase, at least when necessary. During this phase, the magnetic coil can be energized with a further current, the holding current, which is smaller than the currents in the first two phases. The holding phase primarily ensures that the magnetic armature remains at approximately a constant stroke.

[0018] The proposed method now includes providing at least one boost duration value for the fuel injector, which was used during a corresponding boost phase of the fuel injector. In particular, several boost phases, each with different boost duration values, can be provided, which were used when controlling the fuel injector. These boost duration values ​​can, for example, be or be specified by the control unit. Furthermore, a reset duration value for the fuel injector is provided following each boost phase, whereby the reset duration value can be recorded during the fuel injector control. The reset duration value is, in particular, the duration until a current flowing through the fuel injector or a corresponding solenoid valve during the boost phase is dissipated by a rapid reset.A correlation between the extinguishing and boosting duration values ​​is determined, which is specifically an extinguishing duration characteristic curve. Based on this correlation, an individual target boosting duration for the fuel injector is determined and can then be adjusted accordingly. R.414520.

[0019] - 4 - Within the scope of the present invention, a method is proposed that allows an individual target boost duration to be determined for each fuel injector. This makes it particularly advantageous to take into account individual opening delays of the respective fuel injector, which can occur, for example, due to manufacturing tolerances. These tolerances can occur in gap dimensions, the needle stroke of the solenoid valve, or spring and magnetic forces. By determining and setting an individual target boost duration, a predetermined opening time of the fuel injector or the solenoid valve can be advantageously ensured.

[0020] After the boost phase, particularly during rapid extinguishing or transition phases, a corresponding extinguishing duration or extinguishing duration value can be determined. The corresponding current in the solenoid coil of the solenoid valve decreases. The extinguishing duration can be measured using a voltage signal that correlates with the extinguishing duration.

[0021] The extinguishing duration value can be recorded, particularly during regular operation of a corresponding engine or internal combustion engine, and a reference extinguishing duration value can be determined. To determine the reference extinguishing duration value, the boost duration of the fuel injector is selected so that the fuel injector is fully open (full-stroke control). Subsequently, the boost duration can be shortened, starting from the boost duration at which the fuel injector is fully open, e.g., incrementally. A corresponding boost duration value and a corresponding extinguishing duration value are recorded for each step. This results in several boost duration values ​​and a corresponding extinguishing duration value, depending on the respective boost duration value.

[0022] The deletion duration value can be determined particularly during a control gap or a transition phase after the boost phase.

[0023] The correlation between boost duration and deletion duration can be determined. The deletion duration-boost duration R.414520

[0024] - 5 -

[0025] Correlation can vary for different fuel injectors. In particular, the extinguishing time-boosting time correlation can be non-linear, with the extinguishing time increasing with increasing boosting time up to a maximum extinguishing time value, decreasing with further increasing boosting time up to a reference extinguishing time value, and then exhibiting essentially a constant reference extinguishing time value with further increasing boosting time.

[0026] The individual target boost duration refers specifically to a boost duration at which the fuel injector's open time is optimized, ensuring that the combustion engine is supplied with fuel as intended. This allows the engine to receive an optimal amount of fuel, thereby achieving the desired combustion characteristics.

[0027] Furthermore, an advantageous boost duration can reduce the mechanical stress on fuel injector components, thereby extending the maximum operating life of the fuel injector. Additionally, the control gap or transition phase, which occurs particularly after the boost phase and before the start of the next phase, can be optimally positioned to ensure reliable operation, especially opening, of the fuel injector. This ensures reliable operation of the internal combustion engine.

[0028] The proposed method can be particularly advantageously carried out during the operation of the fuel injector or a corresponding internal combustion engine. This allows the effects of any wear or aging of the fuel injector or solenoid valve to be taken into account by individually setting the target boost duration.

[0029] Determining the individual target boost duration can be performed continuously or repeated after a predefined period. Alternatively, the target boost duration can be determined based on a signal (e.g., as a trigger), which is particularly related to the aging or wear of the fuel injector. R.414520

[0030] - 6 - In one embodiment, an individual opening delay of the fuel injector is determined based on the individual target boost duration using a boost duration-opening delay correlation between the boost duration values ​​and the respective opening delay.

[0031] The boost duration-opening delay correlation can be fuel injector-specific, meaning that a corresponding boost duration-opening delay correlation is provided for each different fuel injector. This correlation can be non-linear. Furthermore, it can depend on the fuel injector type and be stored on a processing unit or control unit. If the boost duration corresponds to the individual target boost duration, the boost duration-opening delay correlation is generally and essentially independent of the fuel injector.

[0032] In a further embodiment, an individual control duration of the fuel injector is determined, in particular taking into account its individual opening delay, and the fuel injector is controlled based on the individual control duration.

[0033] Depending on the individual opening delay, the fuel injector can be controlled with a correspondingly adjusted individual control duration, so that the fuel injector can be operated as optimally as possible and an internal combustion engine, whose fuel supply is controlled by the fuel injector, is advantageously supplied with a predetermined amount of fuel.

[0034] Furthermore, the extinguishing time is proportional to the opening delay, which can be specific to each fuel injector. The individual opening delay can be determined for each fuel injector such that the extinguishing time is essentially the same for each injector. This allows for particularly efficient operation of an internal combustion engine with multiple fuel injectors. R.414520

[0035] - 7 - In a further embodiment, an individual target boost duration is set for or during the control of the fuel injector by means of a ramp or a controller approach.

[0036] A ramp allows the boost duration to be adjusted or modified, particularly with a predefined boost duration increment, so that the boost duration essentially matches the target boost duration or is sufficiently close to it. A ramp provides a particularly simple way to set or adjust the target boost duration.

[0037] The controller approach can utilize a PID controller, which is particularly easy to implement, an adaptive controller, especially one based on a Model-Reference Adaptive Control (MRAC) approach, or a fuzzy logic controller. Using a controller approach, the target boost duration can be set very precisely and quickly, ensuring that an optimal amount of fuel is delivered by each fuel injector.

[0038] In a further embodiment, a reference extinguishing duration value is determined, in particular from the extinguishing duration value at which the fuel injector is fully open. Furthermore, according to this embodiment, an inflection point in the extinguishing duration-boost duration correlation is determined at which, with a decrease in the boost duration value, an increase in the extinguishing duration value occurs, starting from the reference extinguishing duration value.

[0039] In another embodiment, the individual target boost duration corresponds to the boost duration value of the inflection point of the ejection duration-boost duration correlation.

[0040] The critical point in the extinguishing time-boosting time correlation is, in particular, the minimum boosting time at which the reference extinguishing time value occurs. This ensures reliable opening of the fuel injector and thus its intended operation. Simultaneously, the boosting time is kept as short as possible to minimize stress, especially mechanical stress, on the fuel injector components. R.414520

[0041] - 8 - In another embodiment, the individual target boost duration corresponds to a boost duration value where the corresponding extinguishing duration value is higher than the reference extinguishing duration value.

[0042] The individual target boost duration is set specifically so that the corresponding extinguishing duration value lies within a range of the extinguishing duration-boost duration correlation, in which the extinguishing duration value increases essentially monotonically when the boost duration is reduced from the reference extinguishing duration value. Within this extinguishing duration range, reliable opening of the fuel injector can be assumed. Simultaneously, the target boost duration, and thus the corresponding extinguishing duration value, can be set within this extinguishing duration range so that the corresponding extinguishing duration value is essentially the same for multiple fuel injectors.

[0043] In another embodiment, the boost phase consists of a first boost phase and a second boost phase. Based on the first boost phase, the individual target boost duration is then determined, whereby the boost duration of the second boost phase is adjusted for or during the control of the fuel injector so that the sum of the first and second boost phases is constant.

[0044] Even if the first boost phase briefly falls below a minimum duration (during which the fuel injector is not fully opened), the second boost phase or the combined duration of both boost phases ensures that the fuel injector opens. This allows the fuel injector to be fully opened, thus enabling the intended operation of the corresponding internal combustion engine.

[0045] A target extinguishing duration or target boost duration can be determined and set based on the first boost phase, whereby the first boost phase can be so short that the fuel injector is not fully open. R.414520

[0046] - 9 -

[0047] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0048] Implementing a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this incurs particularly low costs, especially if an executing control unit is already available for other tasks. Suitable data carriers for providing the computer program are, in particular, magnetic, optical, and electrical storage media, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0049] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0050] The invention is schematically illustrated in the drawing using an exemplary embodiment and is described below with reference to the drawing.

[0051] Brief description of the drawings

[0052] Figure 1 schematically shows an internal combustion engine with fuel injectors in which a proposed method is feasible.

[0053] Figure 2 schematically shows a fuel injector in which a proposed method is feasible.

[0054] Figure 3 shows the voltage and current profile of a method in one embodiment.

[0055] Figures 4a and 4b show the current, voltage, and valve stroke profiles for a method in one embodiment. R.414520

[0056] - 10 -

[0057] Figure 5 schematically shows a flowchart of a process in one embodiment.

[0058] Figure 6 schematically shows a deletion duration-boost duration correlation.

[0059] embodiment(s) of the invention

[0060] Figure 1 schematically shows an internal combustion engine 100, in particular a gas engine, with fuel injectors 130, in which a proposed method can be implemented. Three fuel injectors 130 for the internal combustion engine 100 and a high-pressure accumulator 120 are shown as examples. A low-pressure accumulator 122 is supplied with fuel from the high-pressure accumulator 120 via a pressure regulator 121. The fuel injectors 130 are supplied with fuel, in particular gaseous fuel, via the low-pressure accumulator 121, which can then be introduced into combustion chambers 105 of the internal combustion engine 100. A pressure sensor 190 is also provided, by means of which the pressure in the low-pressure accumulator 122 can be detected. Furthermore, a control unit 180, designed as an engine control unit, is provided, by means of which not only the pressure sensor 190 can be read, but also the fuel injectors 130 can be controlled.By means of the pressure regulator 121, the pressure in the gas system of the high-pressure storage tank 120, which can be as high as 700 bar, can be reduced to a pressure of, for example, 40 bar.

[0061] Figure 2 schematically depicts a fuel injector 130 in which a proposed method can be implemented. The fuel injector 130 can be one of the fuel injectors shown in Figure 1. The fuel injector 130 has an inlet 132 for fuel, optionally with a filter, a spring 134, a solenoid coil 136 with a magnetic armature movably mounted therein, and a valve needle 140 guided in a housing 138 and bearing against the magnetic armature. In the unactivated state of the solenoid coil 136, the valve needle 140 closes a passage or valve outlet 144 in a valve seat 142. The solenoid coil 136 and the magnetic armature form part of a solenoid valve, so the fuel injector 130 can also be referred to as R.414520.

[0062] - 11 -

[0063] This can be referred to as a solenoid injector. Furthermore, a connection 148 of the fuel injector 130 is shown, via which a voltage can be applied to the solenoid coil 136. For this purpose, the connection 148 can be connected to a power stage in an engine control unit (see Figure 1). In a fuel injector 130 designed for the injection of hydrogen (or general gaseous fuel), the valve needle 140 can, unlike the one shown here, also be openable to the outside.

[0064] Figure 3 shows a voltage curve (upper diagram) and a current curve (lower diagram) for a method in one embodiment. For this purpose, a voltage II applied to the fuel injector or the solenoid valve and a current I flowing through the fuel injector or the solenoid valve are plotted over a time t.

[0065] At the start of the control process, a boost voltage 301, particularly a positive one, is applied to the fuel injector, thereby initiating the boost phase 307. At the beginning of the boost phase 307, the current I increases up to a certain maximum current value. The boost voltage 301 is pulsed or clocked, especially when the maximum current value has been reached, so that the corresponding current through the fuel injector fluctuates between two current values, resulting in an effective boost current 315.

[0066] The boost phase 307 is followed by a transition phase 308, in which a negative boost voltage 303 is applied for a specific extinguishing duration 304. During the transition phase, the current I flowing through the fuel injector decreases.

[0067] After the extinguishing period 304, the magnitude of the voltage U is reduced, in particular non-linearly, and a holding voltage 302, in particular a positive one, is applied during a holding phase 309. This holding voltage 302 is applied until the current I reaches a predetermined current value. Subsequently, the fuel injector is pulsed with the holding voltage 302, so that an effective holding current 306 is established. R.414520

[0068] - 12 -

[0069] During a rapid quenching phase 310, the negative boost voltage 315 is applied, causing the current I to decrease. After the rapid quenching phase 310, the voltage U drops, in particular non-linearly or exponentially.

[0070] The duration of the boost phase, i.e., the boost duration 311, is variable or adjustable, as indicated by the double arrow 313. Similarly, the control duration 312 can also be changed by the amount of any change in the boost duration 311, as illustrated by the double arrow 314.

[0071] Figures 4a and 4b show a current waveform (upper diagram), a valve lift waveform (lower diagram, positive vertical axis segment), and a voltage waveform (lower diagram, negative vertical axis segment) for a proposed method in a preferred embodiment. For this purpose, a voltage II applied to the fuel injector, a current I flowing through the fuel injector, and a lift H of the valve needle 140 of the fuel injector are plotted over a time t.

[0072] The current profile in Figure 4a, with which the fuel injector is controlled, corresponds to the current I curve shown in Figure 3. During a boost phase, the current I increases with a boost duration of 307 and fluctuates around an effective boost current of 315 due to the pulsed control.

[0073] In the subsequent transition phase 308, the current decreases until it rises again in the following holding phase 309 and fluctuates around an effective holding current 306. The control duration 312 comprises the boost duration 307, the duration of the transition phase 308, and the duration of the holding phase 309.

[0074] The stroke H of the fuel injector's valve needle 140 increases during boost phase 307, thus opening the fuel injector and allowing fuel flow. This increase in stroke H is delayed from the start of boost phase 307. Specifically, the stroke H during boost phase 307 exhibits a left-handed, monotonically increasing curve. R.414520

[0075] - 13 -

[0076] During the transition phase 308, which can also be referred to as the control gap, the stroke H continues to increase. The slope of the stroke H decreases, particularly over time. During the extinguishing period 304, the stroke H increases linearly with time.

[0077] During holding phase 309, the stroke H of the valve needle reaches its maximum value. In this phase, the fuel injector is fully open.

[0078] During the rapid extinguishing phase 310, the stroke H decreases, with the stroke H decreasing more rapidly over time. Subsequently, the stroke H decreases linearly over time, particularly until the fuel injector is completely closed.

[0079] The control profile shown in Figure 4b has a first and a second boost phase. The first boost phase 307, with a boost duration of 311, corresponds to boost phase 307, which is shown schematically in Figures 3 and 4a. The transition phase 308 following the first boost phase 307 also corresponds to transition phase 308, which is shown in Figures 3 and 4a.

[0080] Following the transition phase 308, the second boost phase 407 begins. The total duration 411 of the first and second boost phases 307 and 407 is fixed at a predetermined value. The boost duration 311 of the first boost phase 307 can be modified according to the proposed procedure, allowing it to be adapted to an individual target boost duration. The modifiability of the boost duration 311 of the first boost phase 307 is represented by the double arrow 313. The variable boost duration 311 of the first boost phase 307 does not affect the predetermined total duration 411 of the first and second boost phases 307.

[0081] Following the second boost phase 407, a second transition phase 408 occurs, in which the current I through the fuel injector decreases. Unlike the transition phase 307 after the first boost phase 307, the current I drops to a specific, predetermined value, which is particularly higher than R.414520.

[0082] - 14 - minimum current value reached in the transition phase 307 after the first boost phase 307.

[0083] The second transition phase 408 is followed by the holding phase 309 and the rapid extinguishing phase 310, which correspond to the respective phases in Figures 3 and 4a.

[0084] Figure 5 schematically shows a flowchart of the procedure in one embodiment for determining an individual target boost duration.

[0085] In step 502, at least one boost duration value (preferably several) is provided for controlling the fuel injector. In step 504, a reset duration value is provided following each boost phase, depending on the respective boost duration value. In step 506, a reset duration-boost duration correlation between the at least one boost duration value and the respective reset duration value is determined. This reset duration-boost duration correlation is, in particular, a reset duration characteristic curve. In step 508, the individual target boost duration of the fuel injector solenoid valve is determined based on the reset duration-boost duration correlation. In step 510, an individual opening delay of the fuel injector is determined based on the individual target boost duration using a boost duration-opening delay correlation between the boost duration values ​​and the respective reset duration values.In step 512, the fuel injector is controlled taking into account the individual opening delay.

[0086] Figure 6 schematically illustrates several extinguishing-boosting time correlations 601a, 601b, 601c, in particular in the form of extinguishing time characteristic curves, as may be the case, for example, for different examples of fuel injectors. The boosting time 311 is plotted on the horizontal axis, and the extinguishing time 304 on the vertical axis.

[0087] The erase duration-boost duration correlations 601a, 601b, 601c each comprise several boost duration values, each of which has a corresponding erase duration value R.414520.

[0088] - 15 - is assigned. In the representation shown in Figure 6, the individual boost duration and delete duration values ​​of the respective delete duration-boost duration correlation 601a, 601b, 601c are connected by means of an interpolated line.

[0089] The extinguishing duration-boost duration correlation 601a, 601b, 601c is non-linear. As the boost duration 311 increases, the extinguishing duration 304 increases up to a maximum extinguishing duration value of 602. As the boost duration 311 continues to increase, the extinguishing duration 304 decreases down to a reference extinguishing duration value of 603. With a further increase in the boost duration 311, the corresponding extinguishing duration 304 remains essentially constant and assumes a value that is essentially equal to the reference extinguishing duration value of 603. The reference extinguishing duration value 603 for each extinguishing duration-boost duration correlation 601a, 601b, 601c is essentially the same for each of the different fuel injectors.

[0090] The extinguishing duration-boost duration correlation 601a, 601b, 601c each exhibits a specific inflection point 604. At this inflection point 604, with decreasing boost duration 311, the region 605 of the extinguishing duration-boost duration correlation 601, in which the extinguishing duration 304 corresponds to the reference extinguishing duration value 603, transitions into a region that is essentially monotonically increasing. The inflection point 604 of the respective extinguishing duration-boost duration correlation 601a, 601b, 601c is specific to each of the different fuel injectors.

[0091] In the range 605 of the extinguishing duration-boost duration correlation 601a, 601b, 601c, where the extinguishing duration 304 corresponds to the reference extinguishing duration value 603, reliable opening of the fuel injector can be ensured. At a lower boost duration 311, which lies particularly in the range 606 shown in Figure 6, reliable opening of the fuel injector cannot be ensured. In this range 606, the fuel injector can, particularly in an unintended manner, enter a closed state.

[0092] The individual target boost duration can be determined or set using the erase duration-boost duration correlation 601a, 601b, 601c so that it corresponds to the boost duration 311 at the inflection point 604. The individual target boost duration R.414520

[0093] - 16 - can alternatively be in an extinguishing duration range 607, in which the extinguishing duration 304 increases essentially monotonically when the boost duration 311 is reduced, starting from the reference extinguishing duration value 603.

Claims

R.414520 - 17 - Claims 1. Method for determining an individual target boost duration of a boost phase (307) for the control of a fuel injector (130), comprising: Providing (502) at least one boost duration value for the fuel injector (130) that has been used during a corresponding boost phase (307) of the fuel injector, Providing (504) a quenching duration value following each boost phase (307) of the fuel injector (130), Determine (506) a deletion duration-boost duration correlation (601a, 601b, 601c) between the at least one boost duration value and the respective deletion duration value, and Determine (508) the individual target boost duration of the fuel injector (130) based on the extinguishing duration-boost duration correlation (601a, 601b, 601c).

2. The method according to claim 1, further comprising: Determine (510) an individual fuel injector opening delay (130) based on the individual target boost duration using a boost duration-opening delay correlation (601).

3. The method of claim 2, further comprising: Determining an individual actuation duration of the fuel injector, taking into account the individual opening delay of the fuel injector (130), for the introduction of fuel, and Control (512) of the fuel injector based on the individual control duration.

4. A method according to any of the foregoing claims, further comprising: R.414520 - 18 - Setting the individual target boost duration for or during the control of the fuel injector using a ramp or a controller approach.

5. Method according to any of the foregoing claims, further comprising: Determining a reference extinguishing duration value (603), in particular from the extinguishing duration value at which the fuel injector is fully open, and Determining a kink point (604) of the deletion duration-boost duration correlation (601a, 601b, 601c) at which, when the boost duration is reduced, the deletion duration increases from the reference deletion duration value (603).

6. Method according to claim 5, wherein the individual target boost duration corresponds to the boost duration value of the inflection point (604) of the quenching duration-boost duration correlation (601a, 601b, 601c).

7. Method according to claim 5, wherein the individual target boost duration corresponds to a boost duration value where the corresponding extinguishing duration value is higher than the reference extinguishing duration value (603).

8. Method according to one of the preceding claims, wherein the boost phase (307) is a first boost phase and wherein a second boost phase (407) is provided, wherein the determination of the individual target boost duration of the fuel injector (130) is based on the first boost phase (307), and wherein the boost duration of the second boost phase (407) is adjusted for or during the control of the fuel injector such that the sum (411) of the boost duration (311) of the first boost phase (307) and the second boost phase (407) is constant.

9. Computing unit (180) configured to perform all process steps of a process according to any of the preceding claims. R.414520 - 19 - 10. A computer program that causes a computing unit (180) to perform all the steps of a method according to any one of claims 1 to 8 when executed on the computing unit (180).

11. A machine-readable storage medium with a computer program according to claim 10 stored thereon.

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