Method for operating a gas injector

Abstract

The invention relates to a method for operating a gas injector of an internal combustion engine, which gas injector injects a gaseous fuel and has a magnetic actuator for operating the gas injector, wherein, in the case of an outlet function in which the gaseous fuel is discharged from the gas injector before the internal combustion engine is shut down in order to still be burnt in the internal combustion engine before the internal combustion engine is finally shut down, the following steps are executed: driving the magnetic actuator in a boost phase (A') comprising continuously increasing a current (I) until the end of the boost phase (A') for the magnetic actuator, and keeping the current (I) constant in an attraction phase (B') of the magnetic actuator at a level which corresponds to a maximum current intensity in the boost phase (A') in order to compensate for a gas pressure, which was reduced during the outlet function of the gas injector, within the gas injector owing to an increased actuator force of the magnetic actuator.

Description

[0001] Description

[0002] title

[0003] Method for operating a gas injector

[0004] State of the art

[0005] The present invention relates to a method for operating a gas injector of an internal combustion engine during a discharge function of the gas injector before the internal combustion engine is switched off.

[0006] Gas injectors are known in various designs from the prior art. One problem with gas injectors that inject a gaseous fuel is that when the internal combustion engine is switched off, leaks of the gaseous fuel, which is still under high pressure, can occur in the gas injector even though the gas injector is closed. However, this must be avoided for environmental reasons. Therefore, before the internal combustion engine is finally switched off, the gas injector is operated in a venting function (so-called "purge function"). This function releases gas that is still under high pressure from the gas injector into a combustion chamber of the internal combustion engine and is burned there after the internal combustion engine is finally switched off. In this case, the connection between the gas injector and a gas reservoir is already interrupted by additional closing elements.Since the pressure in the gas injector drops during this release function, the gas injector must be designed to open even at low system pressure. To date, the magnetic circuit of a gas injector's magnetic actuator has been dimensioned to ensure sufficient magnetic force even at the minimum achievable system pressure. However, this results in large magnetic actuators, which require a large installation space—larger than the space required for actual injector operation.

[0007] Disclosure of the Invention The inventive method for operating a gas injector of an internal combustion engine during a venting function before shutting down the internal combustion engine, with the features of claim 1, has the advantage that a magnetic actuator for the gas injector can be designed to be significantly smaller. This saves installation space on the gas injector, which is particularly advantageous for direct-injection gas injectors, since little installation space is available for the gas injector near a combustion chamber of the internal combustion engine. Furthermore, the gas injector can be manufactured more cost-effectively using a smaller magnetic actuator.This is achieved according to the invention in that, during the venting function, in which gaseous fuel is vented from the gas injector into the combustion chamber before the internal combustion engine is finally shut down in order to be combusted while still in the internal combustion engine, the magnetic actuator is first controlled in a boost phase in such a way that the current for the magnetic actuator is continuously increased until the end of the boost phase. In a further step, the current for the magnetic actuator is kept constant in a pull-in phase that follows the boost phase. The current is kept constant at a level that corresponds to a maximum current intensity in the boost phase.This allows the gas injector to open and remain open during the discharge function despite the reduced gas pressure in the gas injector, since an increased actuator force compensates for the reduced gas pressure during the discharge function of the gas injector.

[0008] Thus, during the pull-in phase, a current level can be increased during the release function in order to compensate for the continuously decreasing gas pressure during the release function.

[0009] The subclaims show preferred developments of the invention.

[0010] Preferably, the increased current requirement in the pull-in phase is provided by a DC / DC converter and / or a boost capacitor. In this case, control in the pull-in current phase preferably occurs with boost voltage. The boost capacitor was charged during normal operation of the internal combustion engine and can thus provide the increased current requirement during the venting function. Further preferably, the length of the pull-in phase is reduced compared to normal operation of the gas injector, i.e., normal injection operation. The reason for the longer boost current phase is a higher boost current level. Preferably, a switchover time from pull-in current to holding current is stored in the control unit as a constant value. Thus, a longer boost current phase results in a shorter pull-in current phase.

[0011] Further preferably, the current level is increased during the boost phase compared to the normal operation of the gas injector. Thus, at the end of the boost phase, a higher current level is achieved than during the normal operation of the gas injector, which makes it easy to maintain the current level during the pull-in phase at a higher level than during normal operation.

[0012] Alternatively, the current level during the boost phase is kept the same as during normal operation of the gas injector. In this case, the higher current level during the pull-in phase is provided, for example, by using the boost capacitor.

[0013] Further preferably, the boost phase during the discharge function is extended compared to normal operation of the gas injector. This provides more time to achieve a higher absolute current level during the boost phase compared to normal operation.

[0014] In order to be able to inject as much gaseous fuel as possible into the combustion chamber during the discharge function of the gas injector, a holding phase of the gas injector, in which the gas injector is kept open, is preferably extended compared to the normal operation of the gas injector.

[0015] Furthermore, the present invention relates to a control unit configured to execute the steps of the method according to the invention. The control unit preferably executes the method until a gas pressure in the gas injector corresponds to the ambient pressure. This allows the gas injector to be held in the closed position without leakage when the internal combustion engine is shut off. Furthermore, the invention relates to a computer program with program code that executes steps of the method according to the invention when the computer program is executed on a computer or a corresponding processing unit, for example, on a control unit according to the invention.

[0016] Furthermore, a computer program product is proposed with a computer program according to the invention which is stored on a machine-readable data carrier or storage medium.

[0017] Short description of the drawing

[0018] The present invention will be described in detail below with reference to the accompanying drawings. In the drawing:

[0019] Figure 1 is a schematic diagram showing the voltage and

[0020] Current of a magnetic actuator according to the invention and a force curve and a stroke of an armature of the magnetic actuator over time during normal operation of an internal combustion engine,

[0021] Figure 2 is a schematic diagram showing the voltage and

[0022] Current of a magnetic actuator according to the invention and a force curve and a stroke of an armature of the magnetic actuator over time during a discharge function of an internal combustion engine, and

[0023] Figure 3 shows a longitudinal section through a gas injector used for

[0024] Carrying out the method according to the invention.

[0025] Preferred embodiment of the invention

[0026] A preferred embodiment of the invention is described in detail below with reference to Figures 1 to 3. Figure 3 shows an example of a gas injector 1 with a magnetic actuator. The magnetic actuator comprises a magnetic coil 3 for acting on an axially movable armature 2. The armature 2 can be brought into contact with a closing element 4, in particular a valve needle, in order to release an injection cross-section at a sealing seat 5. Reference numeral 8 denotes a return element of the gas injector. The closing element 4 is held in the closed position shown in Figure 3 by means of a valve spring 7.

[0027] When the solenoid coil 3 is energized, a magnetic field is created, the magnetic force of which moves the armature 2 toward the closing element 4 (arrow 11). An armature bolt 9 connected to the armature 2 comes into contact with the closing element 4, so that the closing element 4 is opened against the spring force of the valve spring 7 at the sealing seat 5. The armature 2 is moved up to a stroke stop 6 for the armature, which represents the fully open state of the gas injector.

[0028] To close the gas injector 1, the current supply to the solenoid coil 3 is stopped, so that the return element 8 returns the armature 2 to the initial position shown in Figure 3. At the same time, the valve spring 7 also returns the closing element 4 to the closed position shown in Figure 1.

[0029] The gas injector 1 is an outward opening injector.

[0030] Hydrogen, methane, or the like is preferably used as gaseous fuel.

[0031] The diagram in Figure 1 shows normal operation of the gas injector 1 for injecting gaseous fuel, in particular hydrogen, directly into the combustion chamber of an internal combustion engine. The gas injector and the magnetic actuator generally go through four phases: a boost phase A, a pull-in phase B, a hold phase C, and a closing phase D.

[0032] Figures 1 and 2 show four curves plotted against time t in the four phases. K1 shows the current curve for the magnetic actuator over time. K2 shows the average voltage of the magnetic actuator over time. K3 shows the force curve of the armature over time, and K4 shows the stroke of the armature over time t. Figures 1 and 2 also show a closing force K5, which represents the subtraction of the pressure force of the system pressure in the gas injector from the spring force of the valve spring. This is at F1 in normal operation in Figure 1 and increased by F' to F2 in the discharge operation shown in Figure 2, since the supporting opening pressure is missing during discharge operation due to the pressure level of the gaseous fuel being injected.

[0033] Furthermore, Figures 1 and 2 show a battery voltage K6, which is constant both in normal operation and in discharge operation.

[0034] As can be seen from Figure 1, in normal operation of the internal combustion engine, the boost phase A ends after the time t1, the pull-in phase B ends after the time t2, the hold phase C ends after the time t3 and the closing phase D ends after the time t4.

[0035] Furthermore, in normal operation in Figure 1, the current curve K1 is such that at the end of the boost phase, the current level drops and is then maintained at a constant level 11 in the pull-in phase. As can be seen from Figure 1, the opening process, ie, the lifting of the closing element from the sealing seat, begins at the transition between the boost phase A and the pull-in phase B. The maximum opening stroke is reached in the pull-in phase B (stroke curve K4).

[0036] In the gas injector's venting function shown in Figure 2 before the final shutdown of the internal combustion engine, the current profile K1 is such that a continuous increase in current up to point IT is achieved in the boost phase A'. This current value I is maintained throughout the entire pull-in phase B' in the venting function. As a comparison between Figures 1 and 2 shows, the current level in the boost phase A' or pull-in phase B' in the venting function is significantly higher than in the boost phase A or pull-in phase B of Figure 1 during normal operation.

[0037] In particular, the current level is not reduced during the pull-in phase B' of the gas injector's purge function. Furthermore, the absolute value IT is greater than the value 11 in normal operation at the end of the boost phase. This can be achieved by dimensioning a DC / DC converter and / or a boost capacitor. The DC / DC converter and the boost capacitor are dimensioned such that all relevant operating points of the gas injector can be served during normal operation (Figure 1). In the event of the engine shutting down and the subsequent purge function, power reserves are available that are sufficient for the few necessary injections in the purge function, usually at a lower speed than in normal operation.

[0038] Thus, the energy reserves from the DC / DC converter and / or the boost capacitor are used for the control shown in Figure 2 to increase the current level (curve K1 in Figure 2 in the pull-in phase B').

[0039] As can also be seen from the comparison between Figure 1 and Figure 2, the pull-in phase B' in drain operation (t2'-tT) is shorter than the pull-in phase B in normal operation (t2-t1). In contrast, the boost phase A' in drain operation is longer than in normal operation due to the higher boost current level, which is shown in Figure 2 by the time tT compared to the time t1 in normal operation.

[0040] The higher current level IT in discharge mode also provides an increased opening force of the solenoid actuator, which can be seen by comparing the force curves K3 in Figure 1 and Figure 2. This compensates for the missing gas pressure force component for opening the gas injector due to the decreasing gas pressure in the gas injector. In the holding phase C, C' and the closing phase D, D' in discharge mode and in normal operation, all four curves K1, K2, K3, and K4 are again identical.

[0041] Thus, by using the boost voltage for the pull-in current control in pull-in phase B, a higher average voltage and thus also a higher pull-in current IT can be achieved. This allows for higher magnetic forces from the magnetic actuator, which compensate for the reduced opening pressure forces of the gaseous fuel being injected.

[0042] The described embodiment shows a control variant with increased boost current at the end of boost phase A'. However, control variants are also conceivable in which the current curve in boost phase A' during discharge operation is the same as in normal operation, and then the compensation by the magnetic force is only realized in the pull-in phase B' with increased current.

Claims

Claims 1. A method for operating a gas injector of an internal combustion engine, which injects a gaseous fuel and has a magnetic actuator for actuating the gas injector, wherein in a venting function in which the gaseous fuel is released from the gas injector before the internal combustion engine is switched off in order to be burned in the internal combustion engine before the internal combustion engine is finally switched off, the following steps are carried out: Controlling the magnetic actuator in a boost phase (A') with a continuous increase of a current (I) until the end of the boost phase (A') for the magnetic actuator, and Keeping the current (I) constant in a pull-in phase (B') of the magnetic actuator at a level corresponding to a maximum current in the boost phase (A') in order to compensate for a reduced gas pressure within the gas injector during the discharge function of the gas injector by an increased actuator force of the magnetic actuator.

2. The method according to claim 1, wherein the increased current requirement in the pull-in phase (B') is provided by a boost capacitor and / or a DC / DC converter.

3. Method according to one of the preceding claims, wherein a length of the pull-in phase (B') is reduced compared to a normal operation of the gas injector.

4. Method according to one of the preceding claims, wherein the current level in the boost phase (A') is increased compared to the normal operation of the gas injector.

5. Method according to one of claims 1 to 3, wherein the current level in the boost phase (A') remains the same compared to the normal operation of the gas injector.

6. Method according to one of the preceding claims, wherein a length of the boost phase (A') is extended compared to the normal operation of the gas injector.

7. Method according to one of the preceding claims, wherein a holding phase (C') of the gas injector, in which the gas injector is kept open, is extended in comparison with the normal operation of the gas injector.

8. Control device configured to carry out steps of a method according to one of the preceding claims.

9. Computer program with a program code which executes steps of a method according to one of claims 1 to 7 when the computer program runs on a computer or a corresponding computing unit, for example on a control unit.

10. A computer program product comprising a computer program according to claim 9, which is stored on a machine-readable data carrier or storage medium.

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