Method for controlling a fuel injector, fuel system, computing unit and computer program

Abstract

The present invention relates to a method for controlling a fuel injector (1) for an internal combustion engine, a fuel system, and a computer program for carrying out this method. The method comprises 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 acting on the valve element (4, 6) at the target control end of the magnetic actuator (10), and determining (104) a stroke of the valve element (4, 6) at the target control end as a function of the determined cylinder pressure.If the specified stroke of the valve element (4, 6) at the target control end corresponds to its maximum stroke, the magnetic actuator (10) is actuated with the specified target control duration and the specified target control start time, and if the specified stroke of the valve element (4, 6) at the target control end is less than the maximum stroke of the valve element (4, 6), the specified target control duration and / or the specified target control start time are adjusted and the magnetic actuator (10) is actuated with the adjusted target control duration or the adjusted target control start time.

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 range during a combustion 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 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, to determine a resulting fuel quantity deviation and to adjust the control parameters of the fuel injector in such a way that the required amount of fuel is nevertheless introduced into the respective cylinder of the internal combustion engine.

[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), the expected stroke of the valve element at the target actuation end is determined as a function of the specified anticipated cylinder pressure. In other words, it is determined whether the valve element will still have its maximum stroke at the specified cylinder pressure at the target actuation end or not.

[0015] According to one embodiment, the expected stroke can be determined as a function of at least one stored stroke, wherein the at least one stored stroke 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 stroke. The at least one stroke is expediently stored in the processing unit.

[0016] According to one embodiment, the at least one stored stroke can be determined as a function of, or from, the extinction time 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 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 extinction time is understood to be the duration required for the current in the solenoid coil to drop to zero after the end of the actuation. 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 magnetic coil decreases, thereby extending the extinguishing time. In this way, the size of the air gap at the desired actuation end can be determined from the extinguishing time.

[0017] Since the magnetic armature is operatively connected to the valve element, the stroke of the valve element at the target actuation point can be directly determined using the extinction duration of the current in the magnetic coil. For example, a relationship between the extinction duration and the stroke of the valve element at the target actuation point can be stored in the processing unit. In particular, this relationship can be individually stored for each fuel injector in the processing unit.

[0018] According to one embodiment, the at least one stored stroke comprises a plurality of stored strokes for different cylinder pressures acting on the valve element at the target actuation end.

[0019] Different cylinder pressures result in particular from different operating points of the internal combustion engine.

[0020] In particular, the extinguishing time can be continuously determined during operation of the combustion engine, so that the stored values ​​are constantly updated and the extinguishing time, or the resulting stroke, can be learned from the cylinder pressure. For example, a moving average can be calculated from the determined strokes for each cylinder pressure value.

[0021] According to one embodiment, the at least one stored stroke comprises a plurality of stored strokes for different cylinder pressures acting on the valve element at the target actuation point and different fuel pressures. In this case, strokes can be learned as described above depending on the cylinder pressure and the fuel pressure to improve the accuracy of the result.

[0022] While the cylinder pressure acting on the valve element from the outside opposes the opening magnetic force, the fuel pressure supports 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 a corresponding activation point in the compression stroke can be determined, from which a reduction in the stroke of the valve element is to be expected.

[0023] If the expected stroke of the valve element, determined in the manner described, corresponds to a maximum stroke at the target actuation end, then in step (d) the magnetic actuator is actuated with the determined target actuation duration and the determined target actuation start time. In this case, no premature closing of the valve element is expected, and the magnetic actuator of the fuel injector can be operated with the actuation parameters determined in step (a).

[0024] If, however, the expected stroke of the valve element at the target actuation end is less than the maximum stroke of the valve element, then in step (e) the specified target actuation duration and / or the specified target actuation start are adjusted, and the solenoid actuator is actuated with the adjusted target actuation duration or the adjusted target actuation start. In this case, it is expected that the valve element will move towards the valve seat before the target actuation end and thus no longer open the entire flow cross-section. Therefore, the actuation parameters determined in step (a) are adjusted to introduce the required amount of fuel into the corresponding cylinder of the internal combustion engine.

[0025] 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.

[0026] According to one embodiment, if a smaller stroke than the maximum stroke of the valve element is expected at the target control end, a deviation between an expected fuel quantity and the target fuel quantity can be determined based on the expected stroke of the valve element at the target control end, and the target control duration and / or the target control start can be adjusted based on the determined fuel quantity deviation.

[0027] In particular, based on the expected stroke of the valve element at the target actuation end, an expected stroke profile of the valve element can be modeled, and the deviation between the expected fuel quantity and the target fuel quantity can be determined based on a difference or ratio between the expected stroke profile and a target stroke profile of the valve element. The target stroke profile can, for example, correspond to a maximum stroke of the valve element. Alternatively, a desired target stroke profile can be stored in the processing unit.

[0028] The expected stroke profile can be approximated, for example, by the expected stroke of the valve element at the target actuation end and other known points of the stroke profile, such as the actuation end where no stroke deviation occurs.

[0029] It is also possible that the expected stroke profile of the valve element, e.g. by means of a displacement sensor, was measured for a large number of cylinder pressures at the end of the actuation period (especially on a test bench), and the measured stroke profiles are stored in the computing unit.

[0030] The fuel quantity deviation ΔQ can then be determined, for example, using the following formula. ΔQ=∫Qstat∗HVNISTHVNSOLLdt where H VNIST the expected stroke of the valve element, H VNSOLL the target stroke of the valve element and Q stat denotes the steady-state flow rate of the fuel injector (flow rate when fully open, depending on the fuel pressure).

[0031] The integral given in formula (1) can be formed, for example, from a time point after the start of the holding current phase until the end of the actuation of the magnetic actuator or the end of the closing of the valve element.

[0032] Alternatively, the fuel quantity deviation ΔQ can be determined based on the stored extinguishing duration curve as a function of cylinder pressure. For this purpose, an expected stroke curve of the valve element as a function of cylinder pressure can be determined from the extinguishing duration curve, the values ​​of which can be expressed, for example, as H. VNIST can be used in formula (1). A maximum stroke of the valve element can be used as the target stroke HV. VNSOLL can be used. The integration limits can be the actuation end, at which no stroke deviation occurs yet, and the target actuation end, at which the current stroke of the valve element has been determined.

[0033] According to one embodiment, the target control duration can be adjusted by shifting the target control start time to compensate for fuel quantity deviations. In particular, the target control start time can be set earlier, thus extending the target control duration, to provide the required fuel quantity in the event of premature valve closure.

[0034] Alternatively, the target start and end of the actuation can be shifted by the same amount. In particular, the entire actuation of the magnetic actuator to operate the valve element can then occur earlier in the compression stroke, so that the external pressure force acting on the valve element is still less than the opening magnetic force even at the end of the actuation, and the valve element is not prematurely forced into the valve seat. In this case, the target actuation duration can remain constant.

[0035] According to one embodiment, the specified target activation duration and / or the specified target activation start of each fuel injector can be individually adjusted if the expected stroke of the valve element at the target activation end is less than the maximum stroke of the valve element. In this case, for example, the fuel quantity deviation for each fuel injector can be determined and the activation duration of each fuel injector can be individually adjusted, for example by advancing the activation start.

[0036] Alternatively, the target activation duration and / or the target activation start time of all fuel injectors can be adjusted together. This might be the case, for example, if there are only minor differences in the extinguishing duration determined from the characteristic maps and thus in the stroke of the valve element at the end of activation.

[0037] 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.

[0038] 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.).

[0039] Further advantages and embodiments of the invention will become apparent from the description of the accompanying drawings.

[0040] The invention is schematically illustrated in the drawings with reference to exemplary embodiments and is described below with reference to the drawings. Identical or similar elements in the drawings are provided with the same reference numerals, so that a repetitive description is omitted unless necessary. 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. Figure 2 schematically and exemplarily shows a relationship between a stroke profile of a valve element of a fuel injector according to Fig. 1 and an extinguishing time of a current in its magnetic coil at different cylinder pressures at the end of the actuation. Fig. Figures 3a to 3c schematically show two different embodiments for determining a fuel quantity deviation due to a reduced valve element stroke in a fuel injector according to Fig. 1. Fig. Figure 4 schematically and exemplarily shows the extinguishing duration depending on the cylinder pressure at the end of the activation phase for several fuel injectors according to Fig. 1. Fig. Figure 5 shows a flowchart describing the process steps of a method according to an embodiment of the invention. Detailed description

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The embodiments of the invention described below make it possible to detect such premature valve closing, to determine a resulting fuel quantity deviation and to adjust the control parameters of one or more fuel injectors 1 in such a way that the required amount of fuel is introduced into the respective cylinder of the internal combustion engine.

[0053] Fig. Figure 2 schematically and exemplarily shows a relationship between the stroke profile of a valve needle 4 of a fuel injector 1 according to Fig. 1 and a quenching time of a current in its magnetic coil 3.

[0054] In particular, three stroke profiles H resulting from different cylinder pressures p0, p1, p2 at the end of the actuation process are shown. VN_p0 , H VN_p1 , H VN_p2 the valve needle 4 and associated current paths I MV_p0 , I MV_p1 , I MV_p2The curves in magnetic coil 3 are superimposed over time t. Corresponding stroke and current curves are indicated by the same line type. The cylinder pressure p0 is lower than the cylinder pressure p1, which in turn is lower than the cylinder pressure p2.

[0055] In each of the three cases shown, the magnetic coil 3 is activated at the start of the control process t. SOE (SOE: start of energizing) 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 safely reached, the current I MV on a holding current I MV_H reduced, which extends to the end of the approach t EOE(EOE: end of energizing) of 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).

[0056] It becomes clear that the two stroke profiles H VN_p1 , H VN_p2 the valve needle 4 from the stroke profile H VN_p0 They differ in that their stroke already changes 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 or p2, 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_Hmaintains its maximum stroke. Since the cylinder pressure p2 at the end of the actuation t EOE If the pressure is higher than the cylinder pressure p1, the valve needle stroke decreases in the stroke profile H VN_P2 earlier than in the stroke H VN_p1. In particular, the stroke profiles H VN_p1 , H VN_p2 at the time of the end of the approach t EOE each a stroke deviation ΔH VN_p1 , ΔH VN_p2 to the maximum stroke H VN_max of the stroke path H VN_p0 .

[0057] Since the valve needle 4 is operatively connected to the magnetic armature 2, the stroke deviations ΔH VN_p1 , ΔH VN_p2 at approach end t EOE This 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 respective stroke deviation ΔH. VN_p1 , ΔH VN_p2 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 , I MV_p2 It is evident that the current flow I MV_p0 the shortest extinguishing time t L0 and the current flow I MV_p2 the longest extinguishing time t L2 shows, while the current profile I MV_p1 a deletion duration t L1 exhibits a value that lies between the other two. Consequently, by determining the extinction duration t L a size of the air gap LS and thus a stroke deviation ΔH VN_p1 , ΔH VN_p2 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.

[0058] Fig. Figures 3a to 3c schematically show two different embodiments for determining a fuel quantity deviation ΔQ due to the in Fig. 2 shown reduced valve needle lift profile H VN_p1 .

[0059] This shows Fig. 3a a progression of the deletion duration t L and Fig. 3b a course of the valve needle stroke H VN_EOE above cylinder pressure p Zyl_EOE at the end of the approach.

[0060] In Fig. 3a are the pressure p0, which is in Fig. 2 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. 2 shown valve needle stroke profile H VN_p1 and the associated deletion period t L1 leads, shown. The one in Fig. 3b shown valve needle stroke profile H VN_EOE was from the in Fig. 3a shown extinguishing duration curve t L determined and can be used to determine the fuel quantity deviation ΔQ according to a first embodiment.

[0061] Out of Fig. 3a shows that the deletion time t Lup 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. Therefore, the valve needle 4 reaches its maximum stroke H up to pressure p0. VN_max on (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 IMV is increasing.

[0062] The in Fig. 3a shown extinguishing duration curve t L depending on the cylinder pressure p Zyl_EOE At the end of the control phase, learning can be performed during the operation of the internal combustion engine at a multitude of operating points or for a multitude of cylinder pressures, so that both the cylinder pressure p0, from which premature closing of the valve needle occurs, and the pressure in the cylinder pressure p0 can be determined. Fig. 3b shown valve needle stroke profile H VN_EOE can be determined very precisely. Therefore, the H derived from the reduced valve needle lift profile can also be used. VN_p1 Resulting fuel quantity deviation ΔQ based on the valve needle lift profile H VN_EOE above cylinder pressure p Zyl_EOE to be determined at the end of the approach.

[0063] The two pressures p0, p1 are also in Fig. 3b marks and limits the area of ​​the valve needle lift curve H relevant for determining the fuel quantity deviation ΔQ.VN_EOE .

[0064] To determine the fuel quantity deviation ΔQ, for example the deviation of the valve needle lift curve H can be used. VN_EOE from the maximum stroke of the valve needle H VN_max integrated in the area between p0 and p1 (hatched area) and with the static flow rate Q stat of fuel injector 1 for the current fuel pressure.

[0065] Alternatively, the values ​​of the valve needle lift curve H can be used. VN_EOE between p0 and p1 as actual hub H VNIST in formula (1), where the lower integration limits can be a control end corresponding to the cylinder pressure p0 and the upper integration limit can be a control end corresponding to the pressure p1. Target stroke H VNSOLL In this case, the maximum valve needle lift H VN_max be used.

[0066] In Fig. 3c are the valve needle lift profiles H VN_p0 , H VN_p1 out of Fig. 2 shown again, which can be used to determine the fuel quantity deviation ΔQ according to a second embodiment.

[0067] The valve needle stroke curve corresponds to H VN_p0 a target stroke profile in which the valve needle permanently has its maximum stroke, whereas in the valve needle stroke profile H VN_p1 a reduced stroke in the holding current phase I MV_H occurs, which leads to the stroke deviation ΔH VN_p1 at the end of the approach.

[0068] The fuel quantity deviation ΔQ due to the reduced valve needle lift profile H VN_p1 can be based on a difference or ratio between the reduced valve needle lift profile H VN_p1 and the maximum valve needle lift curve H VN_p0 to be determined (hatched area). For this purpose, these can be used, for example, in formula (1), where values ​​of the maximum valve needle lift profile H VN_p0 as target stroke H VNSOLLand values ​​of the reduced valve needle lift curve H VN_p1 as Ist-Hub H VNIST can be used. The integral given in formula (1) can, for example, be formed from a time point after the start of the holding current phase until the end of the actuation of the magnetic actuator or the end of the closing of the valve element.

[0069] Since the reduced valve needle lift profile is not usually measurable during the operation of the internal combustion engine, it must be modeled. The reduced valve needle lift profile H VN_p1 can be achieved, for example, through the specific stroke H VN_EOE1The valve element's stroke at the end of its actuation and other known points of the stroke profile, such as the end of actuation at cylinder pressure p0, where no stroke deviation occurs, are approximated. It is also possible to pre-measure a large number of reduced valve needle stroke profiles, e.g., using a displacement sensor, for a large number of cylinder pressures at the end of actuation on a test bench, and to store the measured valve needle stroke profiles in the processing unit.

[0070] Fig. Figure 4 schematically and exemplarily shows the progression of extinguishing times depending on the cylinder pressure p. Zyl_EOE at the control end for multiple fuel injectors 1a, 1b, 1c, 1d according to Fig. 1.

[0071] In particular, extinguishing duration profiles t L_1a are L_1d for four different fuel injectors 1a, 1b, 1c, 1d above the cylinder pressure p Zyl_EOEApplied at the control end. Additionally, the minimum extinguishing time t L0 and for each fuel injector 1a, 1b, 1c, 1d a cylinder pressure p0_1a to p0_1d is applied at the end of actuation, at which no stroke deviation occurs or from which the valve needle 4 begins to move towards the valve seat 5.

[0072] It becomes clear that the individual fuel injectors 1a to 1d respond completely differently to an increase in cylinder pressure p. Zyl_EOE React at the end of the control process. For example, the extinguishing time t increases. L_1a In the case of fuel injector 1a, the pressure rises significantly earlier than the extinguishing time t. L_1d in the case of fuel injector 1d. This manifests itself in different cylinder pressures p0_1a to p0_1d, at which the respective valve needle begins the closing process. Therefore, it is advisable to determine the extinguishing durations t. L_1a are L_1dThe values ​​of the individual fuel injectors 1a to 1d are determined individually during operation of the combustion engine and stored in separate maps. In particular, the extinguishing durations t L_1a are L_1d The values ​​in the individual characteristic fields are continuously determined and updated to learn the extinguishing durations depending on the cylinder pressure.

[0073] Fig. Figure 5 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 an insufficient amount of fuel from entering the respective cylinder of the internal combustion engine if the valve needle 4 of a fuel injector 1 closes prematurely.

[0074] 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.

[0075] 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.

[0076] Depending on the determined cylinder pressure acting on the closing element 6 at the target actuation end, a predicted or expected stroke of the valve needle 4 at the target actuation end is determined in a subsequent step 103, depending on the determined cylinder pressure expected to act on it. The stroke of the valve needle 4 can, for example, be stored in the processing unit depending on the cylinder pressure at the actuation end. The stored stroke values ​​can be previously determined in a block 200 from a control expiration duration for different cylinder pressures (e.g., in a multitude of operating points of the internal combustion engine).

[0077] If the specific stroke H VN_EOE the valve needle 4 at the target control end the maximum stroke H VN_maxIf (path 1) corresponds, then in step 104 the magnetic actuator 10 of the fuel injector 1 is controlled with the target control duration and the target control start determined in step 101.

[0078] If the specific stroke H VN_EOE However, the valve needle 4 at the target actuation end is smaller than the maximum stroke H. VN_max If (path 0), then in step 105 a fuel quantity deviation is first calculated based on the determined stroke H. VN_EOEThe position of the valve needle 4 at the target activation end is determined. Subsequently, in step 106, the target activation duration and / or the target activation start are adjusted, and the magnetic actuator 10 of the fuel injector 1 is activated with the adjusted target activation duration and / or the adjusted target activation start. The described steps are continuously repeated for each fuel injector 1 in each cylinder of the combustion engine during operation; therefore, after step 104 or step 106, the procedure returns to step 101.

[0079] 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.

[0080] In block 200, for example regularly during operation, a deletion duration t is set for at least one control process. L determined during which a current in the solenoid coil 3 of the fuel injector 1 is extinguished, e.g. by applying a negative voltage, and a cylinder pressure p Zyl_EOE at the end of the approach.

[0081] Furthermore, based on the specified deletion duration t L the air gap LS EOE The actuation point is determined between magnetic armature 2 and stroke stop 16. This can be done, for example, using a characteristic curve stored in the processing unit. Alternatively, the air gap LS can be determined. EOE based on the specified deletion duration t L calculated by the processing unit. Since the air gap LS EOE simultaneously a stroke deviation ΔH VN_EOE the valve needle 4 from its maximum stroke H VN_max At the control end, an additional hub H can be represented. VN_EOEthe valve needle 4 at the end of the actuation phase for the given cylinder pressure p Zyl_EOE The target end is determined and stored.

[0082] From this stored data, in step 103 the expected stroke of the valve needle 4 at the target actuation end can be determined as a function of the determined 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), 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); Determining (103) an expected hub (H VN_EOE ) of the valve element (4, 6) at the target control end depending on the determined cylinder pressure expected to act on it; if the expected hub (H VN_EOE) of the valve element (4, 6) at the target actuation end a maximum stroke (H VN_max ) corresponds to controlling (104) the magnetic actuator (10) with the specified target control duration and the specified target control start time, if the expected hub (H VN_EOE ) of the valve element (4, 6) at the target actuation end is smaller than the maximum stroke (H) VN_max ) of the valve element (4,6) is, adjusting (106) the specified target control duration and / or the specified target control start, and controlling the magnetic actuator (10) with the adjusted target control duration or the adjusted target control start. [2] Method according to claim 1, wherein the expected stroke (H VN_EOE ) depending on at least one stored stroke of the valve element (4, 6) during the holding current phase of the solenoid coil (103), wherein the at least one stored stroke was determined for a cylinder pressure acting on the valve element (4, 6) at the target actuation end (200). [3] Method according to claim 2, wherein the at least one stored stroke (H VN_EOE ) 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 stroke (H VN_EOE ) a large number of stored strokes (H VN_EOE ) 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 stroke (H VN_EOE ) a large number of stored strokes (H VN_EOE ) 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, when the valve element (4, 6) reaches an expected stroke (H) at the target actuation end VN_EOE) exhibits a stroke that is smaller than a maximum stroke (H VN_max ) is a deviation between an expected fuel quantity and the target fuel quantity based on the expected stroke (H VN_EOE ) of the valve element (4, 6) at the target control end and the target control duration and / or the target control start are adjusted based on the determined fuel quantity deviation (105). [7] Method according to claim 6, wherein based on the expected stroke (H VN_EOE ) of the valve element (4, 6) at the target control end an expected stroke profile (HVN_p1, H VN_IST_p2 ) of the valve element (4, 6) is modeled and the deviation between the expected fuel quantity and the target fuel quantity is based on a difference between the expected stroke profile (HVN_p1, H VN_IST_p2 ) and a target stroke profile (H VN_SOLL ) of the valve element (4, 6) is determined. [8] Method according to any of the preceding claims, wherein the target control duration is adjusted by shifting the target control start time. [9] Method according to claim 8, wherein the target control start and target control end are shifted by the same value. [10] Method according to any of the preceding claims, which is carried out for each fuel injector (1) of the internal combustion engine. [11] Method according to claim 10, wherein the specified target control duration and / or the specified target control start of each fuel injector (1) is individually adjusted, or wherein the specified target control duration and / or the specified target control start of all fuel injectors (1) is adjusted jointly. [12] Computing unit configured to perform all the process steps of a process according to any of the preceding claims. [13] 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 a computing unit according to claim 12. [14] 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 10 when executed on the computing unit. [15] Machine-readable storage medium with a computer program stored thereon according to claim 14.

Images