Method for controlling a gas injector for an internal combustion engine

Abstract

The invention relates to a method for controlling a gas injector for an internal combustion engine, wherein an injector valve needle (1) is moved into an open position by means of electromagnetic actuation in order to adjust the gas flow introduced into the internal combustion engine, characterised in that, during the return of the injector valve needle (1) into the closed position with the current supply switched off, the triggering time (to) for generating a braking current pulse (23) to electromagnetically decelerate the injector valve needle (1) is determined by comparing the electromagnetically generated current (21), measured at each time point and corrected for electromagnetic self-induction, with a predetermined comparative current value (Io).

Description

[0001] Method for controlling a gas injector for an internal combustion engine

[0002] The invention relates to a method for controlling a gas injector for an internal combustion engine according to the type defined in more detail in the preamble of claim 1.

[0003] From GB 2 552 516 A a method for controlling a fuel injection valve is known, wherein an actuator is provided for actuating a needle-controlled valve and an activation signal moves the needle away from a valve seat to open the valve, wherein the activation signal contains a subsequent braking pulse which is designed to slow down the needle during the subsequent closing of the valve when the needle returns to the valve closing position.

[0004] DE 10 2014 203 538 A1 teaches a method for controlling switchable valves of an internal combustion engine, wherein a braking pulse for the valve movement is generated depending on the voltage supply of the valve.

[0005] DE 102014202 106 B3 shows a method for operating an injection valve with a closing speed control which uses as a controlled variable the actual closing speed of the valve needle derived from an instant between a braking time and an induction signal.

[0006] DE 10 2009 000 132 A1 discloses a method for operating an injection valve, in which a closing delay time of the valve is determined and the braking pulse is adjusted accordingly.

[0007] WO 2016 / 062494 A1 discloses a method for valve control in which the length and timing of the braking pulse are adjusted based on a specific event, such as a discontinuity in the second derivative of the voltage or current curve or a zero-line section in their first derivatives. DE 10 2011 005 672 A1 describes a method for operating an actuator, in which stop positions are determined in advance and the time for determining an armature stop is based on the temporal course of the current intensity.

[0008] Finally, DE 10 2010 063 009 A1 proposes to derive a braking pulse for a fuel injector from the comparison of a magnetic hysteresis with a predetermined hysteresis.

[0009] The invention is based on the object of proposing a method of the aforementioned type in which the wear of the gas injector during operation is reduced and the operational reliability is increased.

[0010] The problem is solved by the features of claim 1. Further advantageous and claimed embodiments emerge from the respective subclaims, the description, and the drawings.

[0011] Thus, a method for controlling a gas injector for an internal combustion engine is proposed, in which an injector valve needle is moved to an open position by electromagnetic actuation to adjust the gas flow introduced into the internal combustion engine. During the return of the injector valve needle to the closed position with the power supply switched off, the triggering time for generating a braking current pulse for electromagnetically braking the injector valve needle is determined by comparing the electromagnetically generated current measured at the respective time and corrected for electromagnetic self-induction with a predetermined reference current value.

[0012] In this way, it is possible to ensure targeted, safe electromagnetic braking of the injector valve needle in an electromagnetically actuated gas injector, reliably preventing mechanical wear or damage to the injector valve needle and / or the valve seat when the injector valve needle hits the valve seat. Since the total current measured during resetting is corrected for the self-induced current caused by the magnetic field decaying when the current supply is switched off, the corrected current can be linearly assigned to a specific speed of the injector valve needle being moved during resetting, and the triggering time for braking can be easily and precisely determined by comparison with a predetermined reference current value.This reliably prevents triggering too late and touching down at high speed, but also triggering too early and reversing the movement of the injector valve needle and touching down at even higher speed and with an extended closing time.

[0013] In a preferred embodiment of the invention, the current generated by electromagnetic self-induction at the respective point in time is stored as a predetermined current value assigned to the respective point in time. Thus, by subtracting this stored current value assigned to the respective point in time from the electromagnetically generated electrical current measured during the reset at the respective point in time, the current corrected for self-induction at the respective point in time can be calculated. In this way, the triggering point in time for braking can be determined very quickly after the start of the reset of the injector valve needle, since the proposed method requires only a fast computational operation in the form of a subtraction to determine the generated corrected current.

[0014] Preferably, the stored current value is predetermined by experiments and corresponds to the measured electrical current generated by electromagnetic self-induction at the respective time when the current supply is switched off.

[0015] The current generated by electromagnetic self-induction at any given time is preferably determined simply and experimentally for each type and stored as a temporal current profile. Other effects, particularly eddy current effects, can also be taken into account.

[0016] The test can be carried out, for example, with the current supply to the electromagnetic actuator switched off and with the electromagnetic actuator, in particular the magnet armature of an electromagnet, held in place and the self-induced current can be measured as a time course.

[0017] Accordingly, the proposed method can be implemented using a programmable control unit already present in the internal combustion engine, which, in particular, includes a current measurement and a programmable field-programmable gate array (FPGA) that allows the implementation of digital circuits. Consequently, the proposed method can be implemented in an internal combustion engine as a pure software application without additional hardware.

[0018] In a further preferred embodiment of the invention, the reference current value determining the triggering time for the braking current pulse is optimized through testing, particularly with regard to minimizing the impact speed of the injector valve needle and minimizing the closing time. In this way, the proposed method enables the braking current pulse for electromagnetically braking the injector valve needle to be implemented very precisely with regard to minimizing the closing time and the impact speed of the injector valve needle. This high level of accuracy allows the braking to be carried out with particularly high intensity and a short duration, thus enabling very short closing times with very high dosing accuracy.

[0019] In a further development of the invention, a freewheeling diode is switched on when the power supply is switched off during the reset of the injector valve needle. In this way, the electrical current generated electromagnetically during the reset is dissipated only by the existing electrical resistance, for example, a magnetic coil of an electromagnet, so that the current flow is not subject to any further influences, in particular a current regulator. This facilitates the continuous measurement of the current generated electromagnetically during the reset.

[0020] In a further development of the invention, a capacitor is connected to electromagnetically decelerate the injector valve needle, and the braking current pulse is amplified using the capacitor's current. Connecting the capacitor achieves a strong and brief deceleration of the injector valve needle, ensuring rapid resetting without delaying the closing process and high dosing accuracy of the gas injector.

[0021] It is also possible to initially brake only with the capacitor current and then, for a gentle touchdown, to brake with a current just below the holding current from the internal combustion engine's electrical system.

[0022] Preferably, the capacitor is switched on before the injector valve needle resets with the power off and reversed electrical polarity to clear the residual current. This accelerates the closing process.

[0023] Preferably, the same conditions are always created by a predetermined fixed electrical voltage of the capacitor and a predetermined fixed duration of the extinguishing phase at the end of this phase and at the beginning of the reset in each injection cycle.

[0024] Preferably, at the end of the holding phase, the current for holding the injector valve needle in the open position is adjusted to a predetermined fixed value. This ensures that the same conditions are always established in each injection cycle before the start of the previously described extinguishing phase.

[0025] It is also advantageous if, preferably during the electromagnetic actuation of the injector valve needle to move into the open position, the capacitor is switched on to increase the electrical voltage and to accelerate the opening process.

[0026] Preferably, the braking current pulse for electromagnetically braking the injector valve needle occurs within a time period of less than or equal to 0.3 milliseconds after the injector valve needle begins to retract. This achieves particularly rapid closing of the injector valve needle with particularly high dosing accuracy.

[0027] In a further advantageous manner, the injector valve needle is decelerated by the electromagnetic braking during return to a speed of less than or equal to 0.5 meters per second. In this way, wear on the injector valve needle and the valve seat during closing can be minimized and damage can be reliably avoided. Further claimed features of the invention will become apparent from the following description and the drawings, which further explain the present invention. They show:

[0028] Figure 1 shows in a diagram the course of the electric current, the electric voltage for electromagnetic actuation as well as the stroke and the speed of the injector valve needle as a function of time during an injection cycle of a gas injector for an internal combustion engine,

[0029] Figure 2 shows a partial sectional view of a gas injector for an internal combustion engine

[0030] Figure 3 shows the time course of the electric current electromagnetically generated during the resetting of the injector valve needle in correlation with the speed of the injector valve needle,

[0031] Figure 4 shows the time course of the electric current generated by self-induction as determined by experiments when the injector valve needle is held still and the current supply is switched off,

[0032] Figure 5 shows the time course of the calculated adjusted electrical current electromagnetically generated during the resetting of the injector valve needle in correlation with the speed of the injector valve needle.

[0033] Figure 1 illustrates, by way of example, the method according to the invention for controlling a gas injector for an internal combustion engine. Starting from the left edge, the diagram shows the temporal progression of an injection cycle from the opening of the gas injector to introduce the gas, preferably hydrogen, into the combustion chamber of the internal combustion engine to the closing and shutting off of the gas supply to the combustion chamber.

[0034] The gas injector illustrated by way of example in Figure 2 has a gas connection 22 and an injector valve needle 1 for metering the gas introduced into the combustion chamber of the internal combustion engine. The injector valve needle 1 is arranged so as to be longitudinally displaceable along a displacement axis 2 and is directly actuated by an electromagnet integrated into the gas injector. By energizing the magnetic coil 3 of the electromagnet, the injector valve needle 1 can be axially displaced from a closed position shown in Figure 2 into an open position (not shown) for introducing the gas into the combustion chamber, to the right in the image plane of Figure 2, by an actuating element arranged so as to be displaceable coaxially to the injector valve needle 1, in this case a magnet armature 4 of the electromagnet. To actuate the injector valve needle 1, the magnet armature 4 can be permanently connected to it. It is also conceivable for the magnet armature 4 to be arranged so as to be decoupled from the injector valve needle 1.

[0035] According to Figure 2, the injector valve needle 1 is mounted for longitudinal displacement in a multi-part housing 5 of the gas injector. At its valve-side axial end, it has a valve body 6, which is arranged in a valve seat 7 formed on the housing 5 and serves to adjust the gas flow introduced into the combustion chamber (not shown) of the internal combustion engine. Figure 2 shows the gas injector in the closed position, in which the valve body 6 is in gas-tight contact with the valve seat 7 of the housing 5.

[0036] By energizing the solenoid coil 3 of the electromagnet, the injector valve needle 1 can be moved into the open position (not shown) by the solenoid armature 4 of the electromagnet, which is arranged coaxially to the injector valve needle 1. In this case, return spring means 8, which are arranged between the injector valve needle and the housing 5 and act coaxially to the injector valve needle 1, are preloaded. In the open position, a flow gap is formed between the valve body 6 and the valve seat 7, through which the gas can flow into the combustion chamber of the internal combustion engine.

[0037] The injector valve needle 1 is returned to the closed position after the current supply to the solenoid coil 3 of the electromagnet is switched off by the spring force of the pre-tensioned return spring means 8. When the injector valve needle 1 is returned to the closed position, it strikes the valve seat 7.

[0038] To prevent wear and damage to the injector valve needle 1 and the valve seat 7, a braking current pulse 23 from the solenoid coil 3 (Figure 1) of the electromagnet is used to electromagnetically brake the injector valve needle 1 through the magnet armature 4 during the closing process, allowing it to gently strike the valve seat 7. The braking current pulse 23 exerts a force on the magnet armature 4 in the opening direction, thereby braking its movement.

[0039] The magnetic coil 3 of the electromagnet is supplied with electrical current from an electrical battery of the internal combustion engine (not shown).

[0040] In the diagram according to Figure 1, the course of the electrical current in the magnetic coil 3 is shown in curve 9, the course of the electrical voltage in the magnetic coil 3 in curve 10, the course of the axial stroke of the magnetic armature 4 and the injector valve needle 1 in curve 11 and the speed of the injector valve needle 1 and the magnetic armature 4 in curve 12, each as a function of time t.

[0041] To open the gas injector, a capacitor (not shown) is connected in the start phase 13, which is marked by a double arrow running parallel to the time axis, to increase the electrical voltage (curve 10) of the solenoid coil 3 relative to the battery voltage and accelerate the opening process. The electrical current (curve 9) in the solenoid coil 3 increases sharply, and the injector valve needle 1 moves with the axial stroke (curve 11) toward the opening position in the image plane of Figure 2 to the right, with the speed (curve 12) of the injector valve needle 1 increasing sharply.

[0042] In the opening and holding phase 14 indicated by another double arrow, the injector valve needle 1 moves with a further axial stroke (curve 11) and with a further increasing speed (curve 12) into the open position, in which the injector valve needle 1 comes to a standstill and the speed (curve 12) is zero. The injector valve needle 1 is held in the open position with a constant stroke (curve 11). The electrical current (curve 9) and the electrical voltage (curve 10) drop and, compared to the start phase 13, are regulated at a lower level with a slightly rippled curve with an on-off control to hold the injector valve needle 1 in the open position. During holding, there is a rapid change between “holding” and “freewheeling” in order to allow a certain holding current IH to flow on average.Before the injector valve needle 1 is returned to the closed position, the current supply (curve 9) to the solenoid coil 3 is switched off in a clearing phase 15 indicated by another double arrow, and the capacitor is switched on with reversed electrical polarity, thus extinguishing the residual current. A predetermined fixed electrical voltage of the capacitor and a predetermined fixed duration of the clearing phase 15 ensure that the same conditions are always maintained at the end of the clearing phase and at the beginning of the detection phase 16 during the reset in each injection cycle. This also applies to the holding current IH for holding the injector valve needle 1 in the open position at the end of the opening and holding phase 14 and at the beginning of the clearing phase 15.

[0043] Simultaneously with the capacitor's shutdown, a current regulator disconnects the battery power supply. The current can continue to flow through the solenoid coil 3 via a freewheeling diode. A subsequent detection phase 16, marked by another double arrow, is initiated during the return of the injector valve needle 1 to the closed position. The return is achieved by the spring force of the return spring means 8, with the axial stroke (curve 11) of the solenoid armature 4 and the injector valve needle 1 returning toward the closed position at an increasing speed (curve 12).The electric current (curve 9) generated by self-induction, the decaying magnetic field in the solenoid coil 3, and the movement of the armature 4 in the solenoid coil 3 when the current supply is switched off is dissipated only by the electrical resistance of the solenoid coil 3, so that the electric current and voltage curves (curves 9 and 10) are not subject to any further influences, e.g., by a current regulator. The electric current generated during the retraction of the armature 4 (curve 9) is measured, which predominantly contains a current component generated by self-induction.

[0044] The time course of the total electrical current in the magnetic coil (curve 9) measured in the detection phase 16 during the reset, unadjusted for the current component generated by self-induction, and the speed measured (curve 12) of the injector valve needle 1 and the magnetic armature 4 are shown in a separate diagram in Figure 3.

[0045] To determine the triggering time t0 for triggering the braking current pulse 23 for braking the injector valve needle 1, a corrected current value (curve 21, Figure 5) is calculated during the resetting of the same and the magnet armature 4 in the detection phase 16 (Figure 1) by subtracting a predetermined stored current value (curve 17 in Figure 4) assigned to the respective time from the total current value measured at the respective time (curve 9).

[0046] The stored current value assigned to the respective time (curve 17 in Figure 4) corresponds to the current generated by the electromagnetic self-induction of the magnetic coil 3 when the current supply is switched off due to the decaying magnetic field at the respective time. The temporal progression of the stored current value is shown in the separate diagram as curve 17 in Figure 4.

[0047] The current value calculated at the respective point in time, adjusted for the current component generated by self-induction, is shown as a time profile, for example, in curve 21 in a separate diagram in Figure 5. Accordingly, the calculated adjusted current value corresponds to the electrical current generated by the movement of the magnet armature 4 during resetting at the respective point in time, which, over time, is largely proportional to the speed of the magnet armature 4 or the injector valve needle 1 (Figure 5). Each adjusted current value (curve 21, Figure 5) can thus be assigned to a specific speed (curve 12, Figure 5) of the magnet armature 4 and the injector valve needle 1 at the respective point in time.

[0048] The adjusted current value (curve 21, Figure 5) calculated at the respective time during the resetting of the magnet armature 4 in the detection phase 16 (Figure 1) is compared with a predetermined further stored current value Io which corresponds to a predetermined speed (curve 12, Figure 5) of the magnet armature 4 or the injector valve needle 1. As soon as the predetermined comparison current value Io is recognized as an adjusted current value (curve 21, Figure 5), the triggering time t0 for braking is reached and a braking current pulse 23 is generated for the electromagnetic braking of the injector valve needle 1 in a braking phase 19 (Figure 1) marked in the diagram in Figure 1 by a further double arrow.

[0049] In this way, the calculated adjusted current value curve 21 in Figure 5 and the predetermined stored comparison current value Io determine the triggering time t0 for the braking current pulse 23. The comparison current value Io is preferably determined through tests, particularly with regard to minimized impact speed vi and minimized closing time. In this way, the proposed method makes it possible to execute the braking current pulse 23 for electromagnetically braking the injector valve needle 1 with an accuracy of + / - 0.05 milliseconds based on the triggering time t0, which is optimal with regard to minimized closing duration and minimized impact speed vi of the injector valve needle 1 on the valve seat 7. The high accuracy allows the braking of the injector valve needle 1 to be carried out with particularly great intensity and a particularly short duration, so that very short closing times with very high dosing accuracy can be achieved.

[0050] The braking current pulse 23 occurs within a time period of 0.3 milliseconds after the start of the reset of the injector valve needle 1 .

[0051] At the beginning of the braking phase 19, the capacitor is switched on in an amplification phase 18 and the braking current pulse 23, curve 9, is amplified with current from this. By switching on the capacitor, a strong and brief deceleration of the injector valve needle 1 is achieved. Consequently, at the closing time ti, with the stroke reduced to zero (curve 11), the injector valve needle 1 strikes the valve seat 7 with a greatly reduced impact speed vi of less than or equal to 0.5 meters per second and is once again in the closed position shown in Figure 2. This concludes an injection cycle of the gas injector. The current generated by the electromagnetic self-induction of the magnetic coil 3 by the decaying magnetic field at any given time when the current supply is switched off is determined once by tests depending on the type and stored as a time curve. The time curve is shown as an example in the so-called silent curve 17 in Figure 4.The speed 18 of the held magnet armature 4 or the held injector valve needle 1 is shown as zero.

[0052] To do this, the solenoid armature 4 is simply mechanically locked by, for example, fixing the injector valve needle 1 in the open position and running the usual closing sequence. The temporal current curve can thus be determined once for the same type and stored in a control device. The curve then takes into account all complex effects, such as self-induction and eddy current effects.

[0053] This adjusted current value, determined by subtraction at the respective time during reset, is shown as an example as a time curve in the adjusted curve 21 in another diagram in Figure 5 in correlation with the speed (curve 12) of the injector valve needle or the magnet armature. The speed (curve 12) behaves largely proportionally to the course of the adjusted current value (curve 21) over time up to the closing time ti.

[0054] Accordingly, figuratively speaking, at any time the adjusted current value (curve 21 in Figure 5) can be determined by subtracting the silent curve 17 from Figure 4 from the unadjusted raw curve 9 in Figure 3 measured at the respective time during the detection phase 16 (Figure 1).

[0055] The proposed method can be implemented using a programmable control unit already present in the internal combustion engine. This control unit is programmable, particularly in multiple phases, and includes a current measurement and a programmable field-programmable gate array (FPGA) that allows the implementation of digital circuits. This allows the calculation of the braking trigger point to be carried out simply and quickly using standard computing power. Accordingly, the proposed method can be implemented in an internal combustion engine as a pure software application without additional hardware.

[0056] List of reference symbols

[0057] 1 injector valve needle

[0058] 2 sliding axis

[0059] 3 Solenoid coil

[0060] 4 magnet armatures

[0061] 5 housings

[0062] 6 valve bodies

[0063] 7 Valve seat

[0064] 8 Return spring means, helical compression spring

[0065] 9 Curve, course of the electric current of the magnetic coil

[0066] 10 Curve, course of the electrical voltage of the magnetic coil

[0067] 11 Curve, course of the axial stroke of the injector valve needle / magnetic armature

[0068] 12 Curve, progression of the speed of the injector valve needle / magnetic armature

[0069] 13 Start phase

[0070] 14 Opening and holding phase

[0071] 15 Extinguishing phase

[0072] 16 Detection phase

[0073] 17 stored silent curve, measured temporal course of the electric current

[0074] 18 calculated adjusted curve, time course of the calculated

[0075] differential current value

[0076] 19 Braking phase

[0077] 20 Reinforcement phase

[0078] 21 Curve, time course of the differential current value

[0079] 22 Gas connection

[0080] 23 Braking current pulse t Time to Trigger time

[0081] Io predetermined reference current value for triggering the braking current pulse

[0082] IH holding current ti closing time

[0083] V1 Impact velocity of the injector valve needle

Claims

Patent claims 1. A method for controlling a gas injector for an internal combustion engine, wherein an injector valve needle (1) is moved into an open position by electromagnetic actuation to adjust the gas flow introduced into the internal combustion engine, characterized in that during the return of the injector valve needle (1) to the closed position with the current supply switched off, the triggering time (to) for generating a braking current pulse (23) for electromagnetically braking the injector valve needle (1) is determined by comparing the electromagnetically generated current (21) measured at the respective time and corrected for electromagnetic self-induction with a predetermined reference current value (Io).

2. Method according to claim 1, characterized in that the current (17) generated by electromagnetic self-induction at the respective time is stored as a predetermined current value assigned to the respective time, the adjusted current (21) electromagnetically generated at the respective time being calculated by subtracting this current value (17) from the electromagnetically generated current (9) measured during the reset at the respective time.

3. Method according to one of claims 1 or 2, characterized in that the comparison current value (Io) for triggering the braking current pulse (23) is predetermined in an optimized manner by tests with regard to minimized impact speed (vi) of the injector valve needle and minimized closing duration thereof.

4. Method according to one of claims 1 to 3, characterized in that when the current supply is switched off during the resetting of the injector valve needle (1), a freewheeling diode is switched on and the electrical current (9) electromagnetically generated by the resetting is measured.

5. Method according to one of claims 1 to 4, characterized in that for the electromagnetic braking of the injector valve needle (1) a capacitor is connected and the braking current pulse (23) is amplified with current from this.

6. Method according to one of claims 1 to 5, characterized in that a capacitor is switched on with the power supply switched off before the injector valve needle (1) is reset with reversed electrical polarity to extinguish the residual current with a predetermined fixed electrical voltage and with a predetermined fixed time duration.

7. Method according to one of claims 1 to 6, characterized in that at the end of the holding phase (14) the current (IH) for holding the injector valve needle (1) in the open position is adjusted to a predetermined fixed value.

8. Method according to one of claims 1 to 7, characterized in that during the electromagnetic actuation of the injector valve needle (1) to move into the open position, a capacitor is switched on to increase the electrical voltage and the opening process is accelerated.

9. Method according to one of claims 1 to 8, characterized in that the braking current pulse (23) for electromagnetically braking the injector valve needle (1) occurs within 0.3 milliseconds after the start of the resetting of the injector valve needle (1).

10. Method according to one of claims 1 to 9, characterized in that the injector valve needle (1) is braked by the electromagnetic braking to a speed of less than or equal to 0.5 meters per second.

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