Method for controlling a fuel injector, fuel system, computing unit and computer program
The fuel system with a magnetic actuator and computing unit addresses fuel metering inaccuracies by adjusting current profiles and monitoring cylinder pressure to prevent premature valve closure, ensuring accurate fuel delivery and reduced engine knocking.
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-11-04
- Publication Date
- 2026-05-07
AI Technical Summary
High-flow injectors for gaseous fuels in internal combustion engines face inaccuracies in fuel metering during partial-load operation due to large flow cross-sections and valve needle lifts, leading to premature closure and fuel quantity deviations.
A fuel system with a magnetic actuator and a computing unit controls the fuel injector by adjusting the current profile to prevent premature valve closure, using a two-point current control and monitoring the cylinder pressure to adjust the holding current level, ensuring accurate fuel delivery.
The system accurately controls fuel injection timing and quantity, reducing knocking tendency and compression work by preventing premature valve closure, thereby maintaining consistent engine performance.
Smart Images
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Abstract
Description
[0001] The present invention relates to a method for controlling a fuel injector of an internal combustion engine, a computing unit and a computer program for carrying out the method, as well as a fuel system. Background of the invention
[0002] Since gaseous fuels for an internal combustion engine, especially hydrogen, have a low volumetric energy density, high-flow injectors are typically required to supply the amount of fuel needed for maximum power output within a permissible time frame during an engine cycle. However, the resulting large flow cross-sections or valve needle lifts of the injectors can lead to inaccuracies in fuel metering during partial-load operation of the internal combustion engine.
[0003] To avoid excessively high injector flow rates and the associated disadvantages, it is advantageous to increase the permissible time range during the combustion engine's operating cycle in which fuel can be injected, thus extending the injector activation time. This permissible time range is typically limited by an earliest possible start and a latest possible end to injection. The earliest possible start of injection results from the potential for premature ignition of the fuel-air mixture in the combustion engine's intake manifold. Therefore, injection usually begins shortly before or immediately after the intake valve closes.With a currently used injector design featuring an outwardly opening valve element (relative to the space enclosed by the valve element), the latest possible injection point is limited by a magnetic force required to hold the valve element open against increasing cylinder pressure during a compression stroke in a cylinder of the internal combustion engine. It can be advantageous to inject the fuel as late as possible in the compression stroke, as this leads to reduced knocking tendency and reduced compression work. Disclosure of the invention
[0004] According to the invention, a method for controlling a fuel injector of an internal combustion engine, a computing unit and a computer program for carrying out the method, as well as a fuel system with the features of the independent claims, are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.
[0005] A fuel system according to the invention comprises one or more fuel injectors, each with a magnetic actuator for actuating a valve element that opens outwards (relative to the space enclosed by the valve element). The fuel injectors can, in particular, be gas injectors configured to inject a gaseous fuel, especially hydrogen, directly into a cylinder of the internal combustion engine. Any other type of fuel injector with an outwards opening valve element is also possible.
[0006] The magnetic actuator of each fuel injector comprises a solenoid coil configured to be energized to open the valve element and a magnetic armature operatively connected to the valve element. The valve element, in turn, can interact with a valve seat in a fuel injector housing. For example, the valve element can be a needle valve with a closing element at one end, which may be designed as a valve disc and configured to open and close a flow cross-section at the valve seat. In the closed position of the fuel valve, the closing element can be held on the valve seat by a valve spring. Each fuel injector can also include a return element that holds the magnetic armature in a rest position. This return element can also be a spring, particularly a coil spring.
[0007] Furthermore, the fuel system contains a computing unit, which may in particular be an engine control unit for the internal combustion engine, and is designed to control the fuel injectors.
[0008] When the solenoid coil of a fuel injector is energized based on a corresponding control signal from the control unit, a magnetic field is generated. The magnetic force of this field moves the magnetic armature towards the closing element. In this process, the magnetic armature can come into contact with the valve element, allowing it to lift off the valve seat against the spring force of the valve spring and thus opening the flow cross-section. To fully open the fuel injector, the magnetic armature can be moved to a stroke stop.
[0009] The magnetic coil can be energized with a specific current profile, which can be controlled by the processing unit. For example, the processing unit can define a target activation start time, at which the magnetic coil is energized, a target activation duration, during which the magnetic coil is energized, and a target activation end time, at which the magnetic coil is energized, and output this information to the fuel injector or its magnetic actuator. At the target activation start time of the magnetic actuator, the magnetic coil is initially energized with a so-called boost current. After a delay, the magnetic armature moves towards the stroke stop, lifting the valve element from the valve seat. When the magnetic armature reaches the stroke stop, the valve element completes its maximum stroke, and the flow cross-section at the valve seat is fully open.At the point when the valve element has reached its maximum stroke, the boost current in the solenoid coil can be reduced to a holding current, which is maintained until the end of the magnetic actuator's activation phase (holding current phase). After the activation phase, the current in the solenoid coil can be extinguished, for example, by applying a negative voltage to the solenoid coil during an extinguishing period. This causes the magnetic field to drop, and the magnetic armature is returned to its rest position by the return element. Simultaneously, the valve element is also returned to its closed position by the valve spring.
[0010] With a long activation duration of a fuel injector with a late activation end in the compression stroke of a cylinder of the internal combustion engine, it can happen that the magnetic force of the magnetic field at the activation end is less than the pressure force acting on the valve element. In this case, the valve element is forced towards the valve seat even before the current is completely deactivated, and less fuel than required enters the cylinder of the internal combustion engine.
[0011] The method according to the invention makes it possible to detect such premature valve element closing and to initiate suitable measures to prevent a resulting fuel quantity deviation.
[0012] In a first step (a), a target activation end and target activation duration of the magnetic actuator of a fuel injector are determined based on a target activation start of the magnetic actuator and a target fuel quantity. The target activation start and target fuel quantity can be stored in a corresponding characteristic map in the processing unit for each operating point of the internal combustion engine. The target activation duration of the fuel injector, or rather its magnetic actuator, can be determined from the target fuel quantity in a known manner. For example, a characteristic curve of the fuel injector can be used, which shows the relationship between the fuel injector flow rate and its activation duration for a specific fuel pressure. The target activation end can then be calculated from the target activation start plus the target activation duration.
[0013] In a subsequent step (b), the cylinder pressure expected to act on the valve element at the target activation end is determined. This pressure opposes the magnetic force that lifts the valve element from the valve seat and can lead to premature closing of the fuel injector. This effect can occur particularly at cylinder pressures greater than 15 bar to 20 bar. The expected cylinder pressure at the target activation end can be calculated by the processing unit, for example, based on a measured pressure in the intake manifold of the combustion engine and a cylinder volume at the target activation end determined, for example, from the piston stroke function, using a polytropic process. Alternatively, the cylinder pressure at the target activation end can also be measured directly beforehand.
[0014] Then, in a further step (c), it is determined whether the expected closing start of the valve element for the specified cylinder pressure lies within a holding current phase of the solenoid coil or not. In other words, it is determined whether the valve is likely to begin closing prematurely. This means, in particular, that a deviation of the actual stroke from a maximum stroke will occur even within the holding current phase of the solenoid coil.
[0015] According to one embodiment, the expected closing start can be determined as a function of at least one stored closing start, wherein the at least one stored closing start was determined for a cylinder pressure acting on the valve element at the target actuation end. In other words, measurement data can be used to determine the expected closing start. The at least one closing start as a function of the cylinder pressure is expediently stored in the processing unit.
[0016] It should be noted that, within the scope of the invention, it is sufficient to use a digital value (1 / 0 or Yes / No) as the expected or stored closing start, i.e., whether the expected closing start falls within the holding current phase or not. A specific determination of a time as the closing start is not necessary (but possible).
[0017] According to one embodiment, the at least one stored closing start can be determined from a control frequency of a current control of the fuel injector's solenoid coil. The current flowing through the solenoid coil depends on the inductance, which in turn depends on an air gap between the magnetic armature and the stroke stop of the magnetic armature in the magnetic actuator, i.e., on the position of the valve element. The current control can, in particular, be a so-called two-point current control, in which a circuit to the solenoid coil is interrupted when a predetermined upper limit of the target current is reached and the circuit is closed again when a lower limit of the target current is reached. With such a two-point current control, a self-adjusting control frequency results as a switching frequency, by means of which a stroke of the valve element can be determined within the holding current phase of the solenoid coil.
[0018] If the magnetic armature moves away from the stroke stop due to movement of the valve element during the holding current phase, thus increasing the air gap between the magnetic armature and the solenoid coil, the inductance of the solenoid coil decreases, which in turn reduces the control frequency of the current regulation. In this way, the size of the air gap, and therefore the start or premature closing of the valve element, can be determined by adjusting the control frequency of the current regulation during the holding current phase.
[0019] According to one embodiment, the at least one stored closing start can be determined as a function of, or from, the extinction duration of a current in the solenoid coil of the fuel injector. The current flowing through the solenoid coil depends on the inductance, which in turn depends on the air gap between the magnetic armature and the stroke stop of the magnetic armature in the magnetic actuator, i.e., on the position of the valve element. The extinction duration is understood to be the time required for the current in the solenoid coil to drop to zero after the end of the actuation phase. To extinction the current in the solenoid coil, a negative voltage can, for example, be applied to it.If, at the end of the actuation phase, the magnetic armature no longer rests against the stroke stop (which acts as the magnetic pole) due to movement of the valve element, and thus an increased air gap exists between the magnetic armature and the magnetic pole, the inductance of the solenoid coil decreases, thereby extending the extinction time. In this way, the size of the air gap at the target actuation end can be determined from the extinction time. If this gap is not zero, premature valve closure occurs.
[0020] According to one embodiment, the at least one stored closing start comprises a plurality of stored closing starts for different cylinder pressures acting on the valve element at the target actuation end.
[0021] Different cylinder pressures result in particular from different operating points of the internal combustion engine.
[0022] In particular, the closing start time can be continuously determined during operation of the combustion engine, so that the stored values are constantly updated and the closing start time can be learned based on the cylinder pressure. For example, for each cylinder pressure value, the earliest measured closing start time can be stored as the closing start time.
[0023] According to one embodiment, the at least one stored closing start comprises a plurality of stored closing starts for different cylinder pressures acting on the valve element at the target actuation point and different fuel pressures. In this case, closing starts can be learned as described above, depending on the cylinder pressure and the fuel pressure, in order to improve the accuracy of the result.
[0024] While the cylinder pressure acting on the valve element from the outside opposes the opening magnetic force, the fuel pressure assists it and thus prevents premature closing of the fuel injector. By taking the fuel pressure into account, the stroke of the valve element can therefore be determined even more precisely. Furthermore, it is possible to determine at which cylinder pressure the valve element begins to close prematurely and, from this, to determine a corresponding activation point in the compression stroke at which premature closing is to be expected.
[0025] If it is determined that the expected closing start of the valve element lies within the holding current phase of the solenoid coil, i.e., if premature valve closure is expected, then in step (d) the current level of the solenoid coil during the holding current phase is increased to counteract the premature closing of the valve element. The holding current level can be increased by a predetermined value, which, for example, has been determined in advance based on investigations on a component or engine test bench. In particular, the predetermined value can be determined at different cylinder pressures at the end of the solenoid actuator's actuation and stored in the processing unit. Alternatively, if premature valve closure is detected, the holding current level can be increased stepwise to prevent the solenoid coil from overheating.In this case, it can be checked after each step whether the selected holding current level is sufficient to prevent premature valve closure. If no further premature valve closure is detected, the set holding current level is retained and can be saved as a new holding current level, e.g., depending on the cylinder pressure and / or fuel pressure and / or the temperature of the solenoid coil.
[0026] According to one embodiment, the temperature of the solenoid coil can be determined from the control frequency of the solenoid coil's current regulation during the boost current phase. Since the solenoid coil's resistance increases with rising temperature, the control frequency of the two-point current regulation decreases. This relationship can be determined in advance and stored in the processing unit, allowing the solenoid coil temperature to be deduced from the boost current by calculating the control frequency. For this purpose, the control frequency can be determined within a specific time interval of the boost current phase. Advantageously, this time interval can be determined within a range of the boost current phase in which the magnetic armature is securely in contact with the stroke stop, thus avoiding interference from armature movement. The current level of the solenoid coil during the holding current phase can then be increased as a function of the solenoid coil's temperature.In particular, the measured solenoid coil temperature can be used to check after each step increase in the holding current level whether the solenoid coil temperature is still below a permissible temperature level. This prevents the temperature from rising above the permissible level.
[0027] According to one embodiment, steps (a) to (e) described above can be performed for each individual fuel injector of the internal combustion engine, since the cylinder pressures differ in the individual cylinders and the individual fuel injectors may also exhibit differences in magnetic force and internal friction. Therefore, different strokes of the valve element can be determined in different fuel injectors for the same target actuation point.
[0028] According to one embodiment, if premature valve closure is expected at a fuel injector, the current level of the solenoid coil during the holding current phase can be increased only at the affected fuel injector. Alternatively, in this case, the holding current level of the solenoid coil can be increased at all fuel injectors to prevent them from also closing prematurely in the event of minor changes in cylinder pressure.
[0029] According to a further embodiment, if premature valve closure is anticipated in a fuel injector, the current level of the solenoid coil during the holding current phase can be increased a predetermined time before the expected closing start. This predetermined time can be in the range of 0 µs to 500 µs before the expected closing start. This time should be long enough to increase the current in time, but short enough to limit heating. In this way, premature closure of the valve element can be prevented.
[0030] A computing unit according to the invention, e.g., a control unit of a motor vehicle, which may preferably be an engine control unit of an internal combustion engine, is configured, particularly by means of programming, to carry out a method according to the invention. The computing unit may be part of the fuel system according to the invention.
[0031] 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. Finally, a machine-readable storage medium is provided with a computer program stored on it as described above. Suitable storage media or 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. Such a download can be wired or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).
[0032] Further advantages and embodiments of the invention will become apparent from the description of the accompanying drawings.
[0033] The invention is schematically illustrated with reference to exemplary embodiments in the drawings and is described below with reference to the drawings. Brief description of the drawings Fig. Figure 1 shows a schematic sectional view of a fuel injector for an internal combustion engine which can be controlled by the claimed method. Fig. Figures 2a to 2c show an embodiment for determining the start of closing of a valve element during a holding current phase on a fuel injector according to Fig. 1. Fig. Figures 3a to 3c schematically show a further embodiment for determining the start of closing of the valve element during the holding current phase on a fuel injector according to Fig. 1. Fig. Figure 4 shows a flowchart describing the process steps of a method according to an embodiment of the invention. Detailed description
[0034] Fig. Figure 1 shows a schematic sectional view of a fuel injector 1 for an internal combustion engine (not shown) which can be controlled by a method according to embodiments of the invention.
[0035] The fuel injector 1 includes a magnetic actuator 10 for actuating an outwardly opening (downward in the figure) valve element 4, 6, which opens and closes a flow cross-section 20 at a valve seat 5 of a valve body 21 of the fuel injector 1. The fuel injector 1 is shown here in a closed state, in which the flow cross-section 20 is closed by the valve element 4, 6. The fuel injector 1 shown can, in particular, be a gas injector 1, which can be supplied with a gaseous fuel, especially hydrogen, via a schematically indicated gas supply line 12. The arrows 15 indicate the direction of gas flow.
[0036] The magnetic actuator 10 comprises a magnetic coil 3 for acting on an axially movable magnetic armature 2, which is operatively connected to a valve needle 4 that has a closing element 6 at its downstream end (valve element 4, 6). The closing element 6 shown is designed as the valve disc of the valve needle 4 and is configured to open or close the flow cross-section 20 at the valve seat 5. The closing element 6 is held in the closed position at the valve seat 5 by means of a valve spring 7.
[0037] To guide the valve needle 4 in the valve body 21, the valve needle 4 has two guide elements 25 which are attached to a shaft 40 of the valve needle 4.
[0038] The fuel injector 1 also includes a return element 8 designed as a coil spring 8, which holds the magnetic armature 2 in a rest position when de-energized.
[0039] When the solenoid coil 3 is energized, a magnetic field is generated, the magnetic force of which moves the magnetic armature 2 against a spring force of the helical spring 8 in the direction of the closing element 6 (see arrow 11). In this process, a magnetic armature pin 9 connected to the magnetic armature 2 can come into contact with the valve needle 4, so that the closing element 6 can lift off the valve seat 5 against a spring force of the valve spring 7 and the flow cross-section 20 is opened.
[0040] To fully open the fuel injector 1, the magnetic armature 2 is moved to a stroke stop 16. As a result, an air gap LS, which has a maximum value in the closed state of the fuel injector 1 shown, assumes a minimum value.
[0041] To close the fuel injector 1, the current to the solenoid coil 3 is cut off and the coil spring 8 returns the solenoid armature 2 to its rest position shown. Simultaneously, the valve spring 7 also returns the closing element 6 to its closed position shown.
[0042] The magnetic coil 3 can be energized with a specific current profile, which can be controlled by a processing unit (not shown), which may in particular be an engine control unit of the internal combustion engine. The processing unit can, for example, determine a target activation start time, at which the energization of the magnetic coil 3 begins, a target activation duration, during which the energization of the magnetic coil is maintained, and a target activation end time, at which the energization of the magnetic coil 3 ends or a negative voltage is applied to it, and output this information to the fuel injector 1 or its magnetic actuator 10.
[0043] To reduce knocking tendency and compression work in the internal combustion engine, it can be advantageous to inject the fuel into a cylinder as late as possible in the compression stroke. Furthermore, in the full-load range of the internal combustion engine, a long opening duration of fuel injector 1 may be necessary to provide the required fuel quantity, which can also result in a late target activation time for fuel injector 1.
[0044] This can lead to the magnetic force of the magnetic field at the intended actuation end being less than the pressure force acting on the closing element 6, which results from the cylinder pressure prevailing at the end of the compression stroke in the range of 15 bar to 20 bar. In this case, the closing element 6 is pressed back into the valve seat 5 before the current is fully applied at the intended actuation end, and less fuel than required enters the corresponding cylinder of the internal combustion engine.
[0045] The embodiments of the invention described below make it possible to detect such premature valve closing and to initiate suitable measures to prevent a resulting fuel quantity deviation.
[0046] Fig. Figures 2a to 2c show an exemplary embodiment for determining a closing start time t. VNC the valve needle 4 during a holding current phase on a fuel injector according to Fig. 1 as well as a measure against premature closing of the valve needle 1.
[0047] In particular, it shows Fig. 2a two current paths I MV_h1 , I MV_h2 , which differ in their holding current, Fig. 2b shows the current paths I MV_h1 , I MV_h2 corresponding stroke profiles H VN_h1 , H VN_h2 and Fig. 2c shows stroke profiles H VN_h1 , H VN_h2 corresponding control frequency profiles F R_h1 , FR_h2 of the two-point current control. Corresponding stroke and frequency profiles are indicated by the same line types.
[0048] In both cases, the starting point for the approach is t. SOE (SOE: start of energizing) of the magnetic actuator 10, the magnetic coil 3 is initially energized with a boost current I MV_B energized, whereupon the magnetic armature 2 moves after a delay time t V from its rest position towards the stroke stop 16, causing the valve needle 4 with the closing element 6 to lift out of the valve seat 5 and open the flow cross-section 20 (see also Fig. 1) At a time t BH , at which the valve needle 4 reaches its maximum stroke H VN_max Once reached, the current I MV on a holding current I MV_H reduced.
[0049] In the current flow I MV_h1 The holding current level I will be MV_H until the end of the approach t EOE(EOE: end of energizing) of the magnetic actuator 10 is maintained.
[0050] After the approach end t EOE will the current I MV deleted, for example by applying a negative voltage to the magnetic coil 3 (not shown).
[0051] Since in the present case the cylinder pressure at the end of the actuation phase t EOE If this results in a pressure force that is higher than the magnetic force of the magnetic field of the solenoid coil 3, the valve needle 4 will be opened from time t VNC (Closing point of the valve needle 4) is pressed towards the valve seat. As a result, it no longer reaches its maximum stroke H. VN_max one, but shows from the start of the closure t VNC a downward sloping stroke profile H VN_h1 .
[0052] To counteract this, as in the case of the current flow I, MV_h2 , the holding current level at the start of closing t VNC the valve needle 4 to the value I MV_H_kThis increases the magnetic force of the magnetic field of the solenoid coil 3 to a value greater than the pressure force of the cylinder pressure, thus preventing premature closing of the valve needle 4.
[0053] If one considers the in Fig. 2c shown, relating to the stroke profiles H VN_h1 , H VN_h2 corresponding frequency responses F R_h1 , F R_h2L , thus it becomes clear that the frequency response F R_h1 from the start of the closure t VNC The valve needle 4 has the same characteristics as the stroke profile H VN_h1 , and the frequency response F R_h2 from this point onwards it exhibits the same characteristics as the stroke profile H VN_h2L In other words, there is a direct relationship between corresponding stroke and frequency responses H. VN_h1 , H VN_h2 , F R_h1 , F R_h2 recognizable, so that based on a control frequency F determined during the holding current phase RThe two-point current control very easily creates a stroke profile H VN The valve needle 4 can be determined. For this purpose, the control frequency F can be used. R For example, the control frequency can be determined from a predetermined point in time, once the holding current has stabilized, during the holding current phase. In particular, the control frequency can be continuously determined during operation of the internal combustion engine. From the determined control frequency F R can stroke profiles H VN the valve needle 4 is determined as a function of a cylinder pressure at the end of the actuation t EOE These values can be stored in the processing unit. They can be used to assess whether premature closing of valve needle 4 is to be expected at the target control end or not. Alternatively, only the information (yes / no) indicating whether the closing start is premature or not can be stored.
[0054] Fig. Figures 3a to 3c schematically show another embodiment for determining the closing start time t. VNC the valve needle 4 during the holding current phase on a fuel injector according to Fig. 1.
[0055] The Fig. 3a and Fig. Figure 3b schematically and exemplarily shows a relationship between a stroke profile H VN a valve needle 4 of a fuel injector 1 according to Fig. 1 and a deletion duration t L of a current in its magnetic coil 3.
[0056] In particular, two stroke profiles H resulting from different cylinder pressures p0 and p1 at the end of the actuation process are VN_p0 , H VN_p1 , the valve needle 4 and associated current paths I MV_p0 , I MV_p1 The curves in magnetic coil 3 are superimposed over a time t. Corresponding stroke and current curves are again indicated by the same line type. The cylinder pressure p0 is lower than the cylinder pressure p1.
[0057] In both cases, the magnetic coil 3 is activated at the start of the control process t. SOE of the magnetic actuator 10 initially with a boost current I MV_B energized, whereupon the magnetic armature 2 moves after a delay time t V from its rest position towards the stroke stop 16, causing the valve needle 4 with the closing element 6 to lift out of the valve seat 5 and open the flow cross-section 20. At time t BH , at which the valve needle 4 reaches its maximum stroke H VN_max Once reached, the current I MV on a holding current I MV_H reduced, which extends to the end of the approach t EOE The magnetic actuator 10 is maintained. After the end of the control phase t EOE will the current I MV deleted, for example by during the deletion period t L a negative voltage is applied to the magnetic coil 3 (not shown).
[0058] It becomes clear that the stroke profile H VN_p1the valve needle 4 from the stroke profile H VN_p0 differ in that its stroke already occurs during the holding current phase I. MV_H reduced. This is due to the fact that a pressure force resulting from the cylinder pressure p1, which is greater than the magnetic force of the magnetic field of the solenoid coil 3, acts externally on the closing element 6 and pushes the valve needle 4 towards the valve seat 5. The cylinder pressure p0, on the other hand, results in a pressure force that is smaller than the magnetic force, so that the valve needle 4 remains closed during the holding current phase I. MV_H maintains its maximum stroke. In particular, the stroke curve H shows VN_p1 at the time of the end of the approach t EOE a stroke deviation ΔH VN_p1 to the maximum stroke H VN_max of the stroke path H VN_p0 .
[0059] Since the valve needle 4 is operatively connected to the magnetic armature 2, the stroke deviations ΔH VN_p1 at approach end t EOEThis causes the magnetic armature 2 to move away from the stroke stop 16, which acts as a magnetic pole, and the air gap LS between the two elements to change by an amount equal to the stroke deviation ΔH. VN_p1 enlarged (see Fig. 1) This reduces the inductance of the magnetic coil 3, which in turn reduces the extinguishing time t. L extended. Along the course of the descending flank of the current profiles I MV_P0 , I MV_p1 It is evident that the current flow I MV_p0 a shorter extinguishing time than the current profile I MV_p1 shows. Consequently, by determining the expiration time t, it is possible to L a size of the air gap LS and thus a stroke deviation ΔH VN_p1 the valve needle 4 from its maximum stroke at the end of the actuation phase t EOE or a hub H VN_EOE The position of the valve needle at the end of the actuation phase can be determined.
[0060] By determining the extinguishing time t L in a multitude of operating points of the internal combustion engine with different cylinder pressures pZyl_EOE At the end of the control phase, a relationship can be found between the cylinder pressure p Zyl_EOE at the end of the approach and the extinguishing duration t L , as in Fig. 3c shown, can be determined.
[0061] In Fig. 3c are additionally the pressure p0, which is in Fig. 3b shown valve needle stroke profile H VN_p0 as well as the associated deletion duration t L0 which results in, and the pressure p1, which leads to the in Fig. 3b shown valve needle stroke profile H VN_p1 as well as the associated deletion period t L1 leads, shown.
[0062] Out of Fig. 3c shows that the deletion time t L up to a cylinder pressure p0 at the end of the control phase, their minimum value t remains constant. L0 The pressure rises continuously from cylinder pressure p0. Consequently, the valve needle 4 reaches its maximum stroke H up to pressure p0. VN_max from (see Fig. 3b) and the magnetic armature 2 rests against the stroke stop 16 at the end of the actuation phase, so that the air gap LS between the two elements is minimal. In other words, the pressure force resulting from the cylinder pressure p0 at the end of the actuation phase is just not yet sufficient to overcome the magnetic force of the magnetic field of the solenoid coil 3 and to move the valve needle 4 towards the valve seat 5. If the cylinder pressure p increases Zyl_EOE When the control signal exceeds the value p0, the force ratios and the valve needle lift H change. VN_EOE At the end of the activation phase, the voltage is reduced, thereby increasing the air gap LS. This reduces the inductance of the magnetic coil 3 and the extinguishing time t. L to extinguish the current I MV is increasing.
[0063] The in Fig. 3c shown extinguishing duration curve t L depending on the cylinder pressure p Zyl_EOEAt the end of the control phase, the system can learn from a multitude of operating points during the combustion engine's operation, allowing for very precise determination of the cylinder pressure p0 at which premature valve needle closing occurs and the corresponding point in time within the combustion engine's compression stroke (valve needle closing point). Only the information (yes / no) indicating whether the closing point is premature or not can be stored again as the closing start time.
[0064] Fig. Figure 4 shows a flowchart describing the process steps of a method according to an embodiment of the invention. The method serves to control one or more fuel injectors 1 according to Fig. 1 and prevents premature closing of the valve needle 4 of a fuel injector 1 by increasing the holding current level of the solenoid coil if necessary.
[0065] After the process is started in step 100, in step 101 a target activation end and target activation duration of the magnetic actuator 10 of a fuel injector 1 are determined based on a target activation start of the magnetic actuator 10 and a target fuel quantity. The target activation start and the target fuel quantity can be stored in a corresponding characteristic map in the processing unit for each operating point of the internal combustion engine. The target activation duration of the fuel injector 1, or rather its magnetic actuator 10, can be determined from the target fuel quantity in a known manner. For this purpose, for example, a characteristic curve of the fuel injector 1 can be used, which includes a relationship between the flow rate of the fuel injector 1 and its activation duration. The target activation end can then be calculated from the target activation start plus the target activation duration.
[0066] In a subsequent step 102, the cylinder pressure expected to act on the closing element 6 at the target control end is determined. The cylinder pressure at the target control end can be calculated by the processing unit, for example, based on a measured pressure in the intake manifold of the internal combustion engine and a cylinder volume at the target control end determined, for example, from the piston stroke function, using a polytropic process. Alternatively, the cylinder pressure at the target control end can also have been previously measured and stored in a characteristic map. The cylinder pressure opposes the magnetic force by which the valve needle 4 with the closing element 6 is lifted from the valve seat 5 and can lead to premature closing of the fuel injector 1.
[0067] Depending on the specific cylinder pressure acting on the closing element 6 at the target actuation end, a predicted or expected closing start of the valve needle 4 is determined in a subsequent step 103, or it is determined whether this closing start will fall within the holding current phase or not. The closing start can, for example, be stored in the processing unit depending on the cylinder pressure at the actuation end. Such a closing start can be determined previously, for example in block 200, from a control frequency of the current control of the solenoid coil 3 or from a reset duration, as described above, for different cylinder pressures (e.g., in a multitude of operating points of the internal combustion engine).
[0068] If no premature closing of the valve needle 4 is expected within the holding current phase of the solenoid coil 3 (path 1), then in step 104 the solenoid actuator 10 of the fuel injector 1 is controlled with the target control duration and the target control start determined in step 101.
[0069] However, if premature closing of the valve needle 4 is expected within the holding current phase of the solenoid coil 3 (path 0), then in step 105 the solenoid actuator 10 of the fuel injector 1 is controlled with the target control duration and the target control start determined in step 101, and in step 106 the holding current level I MV_h the magnetic coil 3 increased, as for example in Fig. 2a described.
[0070] The described steps are continuously repeated during operation of the internal combustion engine for each fuel injector 1 in each cylinder of the internal combustion engine; therefore, after step 104 or step 106, the procedure jumps back to step 101.
[0071] In this way it is possible to reliably detect the closure of a fuel injector 1 and to initiate appropriate measures to ensure that the required amount of fuel is introduced into the respective cylinder of the internal combustion engine at all times.
[0072] In block 200, for example, a control frequency profile of the two-point current control during the holding current phase or a quenching duration and a cylinder pressure at the end of the control process are regularly recorded for at least one control operation. EOE certainly.
[0073] Furthermore, based on the specific control frequency profile or the extinguishing duration, an expected closing start for the given cylinder pressure at the end of the actuation process is determined and stored. This can be done, for example, using a relationship stored in the processing unit.
[0074] From this stored data, the expected closing start can be determined in step 103 depending on the specific cylinder pressure expected to act on it.
Claims
[1] Method for controlling a fuel injector (1) of an internal combustion engine with a magnetic actuator (10) for actuating an outwardly opening valve element (4, 6), wherein the magnetic actuator (10) has a magnetic coil (3) and a magnetic armature (2) which is operatively connected to the valve element (4, 6), and the magnetic coil (3) is configured to be supplied with a current in order to open the valve element (4, 6), the method comprising the steps: Determining (101) a target control end and a target control duration of the magnetic actuator (10) based on a target control start of the magnetic actuator (10) and a target fuel quantity; Determining (102) a cylinder pressure expected to act on the valve element (4, 6) at the target control end of the magnetic actuator (10); Determine (103) whether an expected closing start (t VNC) of the valve element (4, 6) for the specific cylinder pressure acting on the valve element (4, 6) is within a holding current phase of the solenoid coil (3) or not; when it is determined that the expected closing time (t VNC ) of the valve element (4, 6) within the holding current phase of the solenoid coil (3), increasing (106) a current level of the solenoid coil (3) in the holding current phase. [2] Method according to claim 1, wherein the expected closing start (t VNC ) depending on at least one stored closing start (t VNC ) is determined (103), wherein the at least one stored closing start (t) VNC ) for a cylinder pressure acting on the valve element (4, 6) at the target control end (200). [3] Method according to claim 2, where at least one stored closing start (t VNC ) from a control frequency (F R) a current control of the magnetic coil (3) of the fuel injector (1) was determined (200), or where at least one stored closing start (t VNC ) from a deletion duration (t L ) of a current (I MV ) in the magnetic coil (3) of the fuel injector (1) was determined (200). [4] Method according to claim 2 or 3, wherein the at least one stored closing start (t VNC ) a large number of stored closing times (t VNC ) for different cylinder pressures acting on the valve element (4, 6) at the target control end. [5] Method according to claim 2 or 3, wherein the at least one stored closing start (t VNC ) a large number of stored closing times (t VNC ) for different cylinder pressures acting on the valve element (4, 6) at the target control end and different fuel pressures. [6] Method according to one of the preceding claims, wherein increasing (106) the current level of the magnet coil (3) during the holding current phase comprises: Increasing (106) the current level of the magnetic coil (3) during the holding current phase a predetermined time before the closing start (t VNC ). [7] Method according to the preceding claim, wherein the increase (106) of the current level of the magnetic coil (3) in the holding current phase occurs a predetermined time before the start of closing (t VNC ) includes: gradual increase (106) of the current level of the magnetic coil (3) during the holding current phase a predetermined time before the closing start (t VNC ). [8] Method according to any of the foregoing claims, further comprising: Determining the temperature of the magnetic coil (3) using a control frequency (F) R) a current control of the solenoid coil (3) during a boost current phase of the solenoid coil (3), comprising increasing (106) the current level of the solenoid coil (3) during the holding current phase: Increasing (106) the current level of the magnetic coil (3) during the holding current phase as a function of the temperature of the magnetic coil (3). [9] Method according to any of the preceding claims, which is carried out for each fuel injector (1) of the internal combustion engine. [10] Method according to claim 9, wherein increasing (106) the current level of the magnet coil (3) during the holding current phase comprises: Increasing (106) the current level of the solenoid coil (3) at the fuel injector (1) for which the expected closing start (t) is determined VNC ) of the valve element (4, 6) during a holding current phase of the solenoid coil (3), or Increasing (106) the current level of the solenoid coil (3) at all fuel injectors (1). [11] Computing unit which is equipped to perform all the process steps of a process according to any of the preceding claims. [12] having a fuel system at least one fuel injector (1) with a magnetic actuator (10) for actuating an outwardly opening valve element (4, 6), wherein the magnetic actuator (10) has a magnetic coil (3) and a magnetic armature (2) which is operatively connected to the valve element (4, 6), and the magnetic coil (3) is configured to supply a current (I MV ) to be actuated in order to open the valve element (4, 6); and a computing unit according to claim 11. [13] Computer program that causes the computing unit of the fuel system according to claim 12 to perform all the process steps of a method according to any one of claims 1 to 11 when executed on the computing unit. [14] Machine-readable storage medium with a computer program stored thereon according to claim 13.