How to Activate a Gas Injector

Abstract

The present invention relates to a method for operating a gas injector (1) of an internal combustion engine so as to avoid a closing collision reaction during the closing process of an armature (2) of the magnetic actuator, the method comprising the following steps: at a switching time t0, de-energizing the magnetic actuator in order to start the closing process of the gas injector, and defining a switching time t3 at which the voltage U of the magnetic actuator is reduced to zero after a period Z has elapsed after the switching time t0.

Description

[Technical Field]

[0001] Background technology The present invention relates to a method for operating a gas injector of an internal combustion engine so as to avoid a closing crash reaction during the closing movement of an armature of a magnetic actuator.

[0002] Gas injectors are known in various configurations in the prior art. Depending on the gaseous medium to be injected, such as hydrogen or methane, improved regulation of the opening and closing processes of the gas injector is required to maintain a precise injection quantity. During the closing process, the lack of hydraulic damping compared to injectors for liquid fuels makes a so-called closing reaction more likely to occur. During this closing reaction, the gas injector reopens, thereby injecting an additional amount of gas, which can significantly increase the defined amount of gas to be injected. This also increases wear on the sealing seat and generates loud noise, especially if several closing reactions occur in succession.

[0003] Disclosure of the Invention The method for operating a gas injector for an internal combustion engine so as to avoid a closing reaction during the closing of the magnetic actuator armature, as described in claim 1, has the advantage that a closing reaction can be reliably avoided. This reduces the mismetering of the injected gas and significantly improves the noise characteristics of the gas injector during operation. The method is highly reliable and repeatable with high accuracy. This is achieved by de-energizing the magnetic actuator of the gas injector at switching time t0 to close the open gas injector, so that the current I becomes zero at a second switching time t1. After a period Z has elapsed after the first switching time t0, a zero voltage U is then applied to the coil of the magnetic actuator of the gas injector. This measure prevents the voltage from rising according to an e function after switching time t0, when the current I becomes zero, as in the prior art, and achieving a level of U equal to zero only after the decay of eddy currents in the magnetic actuator, with a significant delay. In the method according to the present invention, the termination phase of the conventional e function is terminated early, and zero voltage U is applied to the coil of the magnetic actuator. After the switching process to zero voltage, the magnetic force then decreases significantly more slowly than in the prior art. As a result of the slower magnetic force decrease, the resulting force does not increase very rapidly over time. This results in a slower closing of the gas injector, which also reduces the speed at which the armature contacts the armature stop. This prevents the gas injector from reopening due to a closing impact reaction, and significantly improves the noise characteristics of the gas injector.

[0004] The dependent claims describe preferred further configurations of the invention.

[0005] Preferably, the zero voltage switching time t3 after the magnetic actuator is deenergized for the closing process of the gas injector is not always set at a constant value after the magnetic actuator is deenergized, but the switching time t3 at which U equals 0 varies depending on the closing behavior of the gas injector, thereby achieving the best possible braking effect when the armature is returned.

[0006] In this case, the switching time t3 at which the voltage is reduced to zero must be determined very precisely. If the voltage U is switched to zero too late, the braking action for the armature is small, so that the armature still abuts against the armature stop at high speed, which may lead to further closing collision recoil. If the voltage U is switched to zero too early, too strong a braking action for the armature occurs, which results in a significant deterioration in the metering accuracy of the gaseous fuel to be injected.

[0007] In order to determine the correct switching time for the voltage to zero as accurately as possible after the start of the closing process, the position of the armature of the magnetic actuator is preferably detected, so that the zero switching time t3 can be determined very accurately.

[0008] Furthermore, it is preferred to define a starting point L at the switch point t2 of the armature, and to set the switch point t3 of the voltage to zero so that it occurs only after the starting point L in order to avoid a closing collision reaction.

[0009] Furthermore, preferably, a voltage U equal to zero is applied only when, after the start of the closing process, the current I in the magnetic actuator has reached the value zero.

[0010] Alternatively, after the start of the closing process of the gas injector, the zero voltage is applied already before the current I in the magnetic actuator reaches the value zero, which allows for earlier braking of the armature.

[0011] According to another preferred embodiment of the invention, the period Z between the start of closing of the gas injector and the switch-over time t3 of the voltage U to zero is determined as a function of the start time L of the armature and / or as a function of the armature closing speed and / or as a function of the actual closing time of the gas injector. In this case, the period Z can be determined by a learning system, preferably arranged in the control device of the gas combustion engine. This allows an adaptation of the period Z for the operation of the gas combustion engine to be carried out individually for the gas combustion engine if, for example, the armature closing speed changes due to external influences, for example, due to changed friction.

[0012] Preferably, the starting time L of the armature during the closing movement is determined based on the current and voltage values ​​of the magnetic actuator. Preferably, the measurement of the current I and voltage of the magnetic actuator is performed in a pressure-free state of the gas injector, and a first Psi(t) curve is calculated in the pressure-free state. In this case, the Psi(t) curve is the integral of the voltage induced over the control curve of the magnetic actuator. In this case, in a further step, the measurement of the current I and voltage of the magnetic actuator is repeated in a pressure-free state of the gas injector. This calculates a second Psi(t) curve for this pressure state, and a comparison is then made between the first and second Psi(t) curves to determine the starting time of the armature. In this case, the starting time L is the point at which the two Psi(t) curves begin to deviate from each other.

[0013] Preferably, the switching point for valve closure, i.e., when the closing element of the gas injector seals again on the sealing seat, is determined by a local maximum of the current I. This is preferably determined by observing the current profile of the magnetic actuator. When the armature is at rest, the current I first rises to its initial level after the voltage is switched to zero. The current I in the coil then slowly decreases with a constant time constant. However, when the armature moves, the inductance is not constant. Therefore, when the armature moves during the closing process, the current I decreases significantly more slowly than when the armature is at rest. If the closing movement is fast, the current I may even increase. At the moment of valve closure (when the armature speed is equal to zero), the armature speed changes, and thus the initial decrease in the current I is also very fast. Therefore, the current profile over time has a strong downward curve characteristic of this moment, which can be detected as the armature closing time.

[0014] The switching point of the voltage U to zero is preferably carried out by adjustment in the same cycle, so that the switching point t3 is adapted simultaneously for each injection, or alternatively, the switching point can be determined, for example, averaged, from several measurement cycles.

[0015] Furthermore, the invention relates to a control device configured to implement the steps of the method according to the invention, particularly preferably the control device implementing a closed-loop control cycle in order to improve the injection accuracy of the gas injector by optimizing the closing process.

[0016] Furthermore, a computer program is proposed which has a program code for implementing the steps of the method according to the invention when it is executed on a computer or a corresponding computing unit, for example in a control device according to the invention.

[0017] Furthermore, a computer program product is proposed, comprising a computer program according to the invention stored on a machine-readable data carrier or storage medium.

[0018] Furthermore, the invention relates to a gas injector for a gas internal combustion engine, adapted to carry out the method according to the invention.

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram of four graphs arranged one above the other, showing the current I, voltage U, magnetic force F and valve stroke H of a gas injector over time, for illustrating the method according to the invention according to a first embodiment; FIG. [Figure 2] 3 is a schematic diagram of two graphs showing the current I and the voltage U over time t to explain the method according to the invention according to a second embodiment of the invention; FIG. [Figure 3] 3 is a schematic diagram of three graphs showing the current I, the voltage U and the valve stroke H over time to explain the method according to the invention according to a third embodiment; FIG. [Figure 4] 1 is a longitudinal cross-sectional view of a gas injector configured to perform a method according to the invention;

[0021] Preferred embodiments of the invention A first embodiment of the present invention will be described in detail below with reference to FIGS.

[0022] Figure 4 shows an exemplary 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 contact a closing element 4, in particular a valve needle, in order to release the injection cross section at a sealing seat 5. Reference number 8 denotes a return element of the gas injector. The closing element 4 is held in the closed position shown in Figure 4 by a valve spring 7.

[0023] When the magnetic coil 3 is energized, a magnetic field is generated, the magnetic force of which moves the armature 2 in the direction of the closing element 4 (arrow 11). At this time, the armature pin 9 connected to the armature 2 abuts against the closing element 4, which opens the closing element 4 at the sealing seat 5 against the spring force of the valve spring 7. The armature 2 is then moved up to the armature's travel stop 6, which is the fully open state of the gas injector.

[0024] To close the gas injector 1, the magnetic coil 3 is de-energized, so that the return element 8 returns the armature 2 to the starting position shown in Figure 4. At the same time, the valve spring 7 also returns the closing element 4 to the closed position shown in Figure 4.

[0025] 1 shows a schematic representation of a method according to a first embodiment of the invention, in which four graphs are shown one above the other to clarify the invention for improved progression and understanding of the invention.

[0026] The top graph of FIG. 1 shows the current I supplied to the magnetic actuator as curve A over time t over one injection cycle. Starting from point zero (I=0), which represents the closed state of the de-energized gas injector, the current I rises rapidly after an opening command for the magnetic actuator. Subsequently, over time t, the current I remains substantially constant, which represents the open state of the gas injector and subsequent injection of gaseous fuel. At switching time t0, the magnetic actuator is de-energized, thereby initiating the closing process of the gas injector. At switching time t1, the current I becomes zero again. Without the method according to the invention, the current I remains at level zero, which is indicated by A1 in FIG. 1.

[0027] The second graph in Figure 1 shows the voltage U over time t (curve B). At switching time t0, which indicates the beginning of the closing time, the voltage becomes negative. At switching time t1, when the current I is equal to 0, the voltage U again begins to approximate the value zero as a function of e. This is shown in Figure 1 as the prior art curve B1.

[0028] The third graph in Figure 1 shows the magnetic force F versus time t (curve C). During the closing process, the magnetic force decreases substantially linearly starting from the switching time t0, and in the prior art shown by curve C1, the magnetic force is zero at the switching time t4 when the armature abuts against the armature stop.

[0029] The bottom graph in Figure 1 shows the valve stroke H over time t (curve D). In this case, the bottom graph shows the starting point L at the switching time t2. Due to inertia, the closing element of the gas injector does not immediately begin its return movement to the closed state at switching time t0, but only at switching time t2. When the closing element reaches the closed state at switching time t4 (curve D1 in Figure 1), the high closing speed results in two closing collision reactions P1 and P2. These closing collision reactions are avoided by the concept of the present invention, as will be explained below.

[0030] According to the present invention, a switching point is defined after the period Z (see the second graph in FIG. 1 ) at which the voltage U is set to zero. This is the switching point t3 in FIG. 1 . As can be seen from the graph of voltage U versus time t, this results in the voltage curve B2, shown by the dashed line. The voltage U remains zero (on curve B2) after switching point t3. Compared to the prior art, where the voltage curve follows the path B1, in the present invention, the voltage is set to zero at switching point t3. This allows the termination phase present in the prior art to be terminated early, and a voltage U=0 can be applied to the coil of the magnetic actuator. As a result, the final stage of the magnetic actuator can operate in a so-called "freewheeling" mode. As can be seen from the third graph in FIG. 1 , which shows the magnetic force F versus time t, the magnetic force decay is significantly slower at switching point t3, at which the voltage U is set to zero. This is indicated by the dashed line C2 in FIG. 1 . As a result of the slower magnetic force decay, the resulting force does not increase too rapidly over time. This results in slower closing of the gas injector, less wear and less noise.

[0031] As shown in the bottom graph of Figure 1, the curve D of the valve stroke H also changes, which is marked with a dashed line in Figure 1 and is designated D2. In this case, the closing time is shifted from t4 to t4' by the measures according to the invention. In this case, the closing element remains closed for the remaining time (curve D2=0).

[0032] The present invention is preferably used in gas injectors with a two-part closing element, where the closing element includes a valve needle for sealing against a sealing seat and an armature pin, with an armature attached to the armature pin. In prior art two-part closing elements like this, two types of closing collision reactions often occur during the closing process: needle collision reaction of the valve needle against the sealing seat and armature collision reaction of the armature against the armature stop. In needle collision reaction, only the valve needle collides with the sealing seat, while the armature pin separates and continues to move. Therefore, the collision reaction height of the valve needle itself is rather small. Armature collision reaction occurs during the subsequent return oscillation of the armature, which can push the valve needle open again, which can lead to undesired re-injection.

[0033] As can be seen from Figure 1, the switching time t3, at which the voltage is set to zero, occurs after the switching time t2, at which the closing element starts to move from the open position towards the closed position, which is designated as the starting time L in Figure 1. In this case, the starting time L at the switching time t2 occurs after the switching time t1, at which the current I is equal to zero.

[0034] The starting point L of the armature is preferably determined based on the current I and voltage U of the armature.

[0035] Switching the voltage U to zero at the switching instant t3 also causes a slight sudden increase in the current I, which is shown in dashed line by the curve A2 in Figure 1. This occurs in particular because the armature is still moving at the switching instant t3.

[0036] Preferably, the period Z to the switching time t3 is not constant but depends on the closing behavior of the gas injector. To obtain the best possible braking effect for braking the armature, it is desirable to define the switching time t3 very precisely. In a first embodiment, the switching time t3 is immediately after the starting time L (time t2). Preferably, the switching time t3 is always defined depending on the starting time L.

[0037] The concept of the invention therefore makes it possible to avoid the occurrence of closing recoils and, accordingly, inaccuracies and undesirable noise during metering.

[0038] FIG. 2 shows a method according to a second embodiment of the present invention. This second embodiment substantially corresponds to the first embodiment, except that the switching time t3 for switching the voltage to zero is selected differently. For simplicity's sake, only the current I and voltage are shown superimposed on each other in the graph of FIG. 2. The switching time t3 here occurs before the current I reaches zero. As can be seen from FIG. 2, the current I still has the value I1 at the switching time t3. This allows for earlier braking of the rotor. In this case, the period Z can be determined for each injection cycle, or, for example, an average value from several cycles can be used.

[0039] Figure 3 shows a graph of a method according to a third embodiment of the invention, in which only three graphs are shown for the current I, the voltage U and the valve stroke H over time t.

[0040] In a third embodiment, a variable switching time t3, which zeros the voltage U, is combined with the braking current G. This allows for a further optimization of the braking action for the armature. Due to the braking action achieved by switching the voltage to zero at switching time t3, the armature moves more slowly when the braking current G is applied to the magnetic actuator after switching time t3. This is the case at switching time t5 in FIG. 3. Therefore, a significantly lower closing speed occurs at the switching time when the braking current is released. However, this allows for greater flexibility in the subsequent application of the braking current. In particular, the requirements for the exact switching time of the braking current can be relaxed, or the application range for the braking current can be significantly expanded. This results in a significantly more reliable method for applying the braking current. Therefore, even in the event of incorrect application of the braking current, the impact on the injector function, especially on possible closing shock reactions or incorrect injection quantities, is reduced.

[0041] As shown in the lower graph of the valve travel H over time t in Figure 3, the braking current G further shifts the actual closing time to a significantly later switching time t4', which is indicated in Figure 3 by the very flat dash-dot line D2.

[0042] It should be noted that for all the described embodiments, the method according to the invention may be configured as a learning system that can be applied to a current switching instant t3 based on previously defined switching instants t3.

Claims

1. A method for operating a gas injector (1) of an internal combustion engine so as to avoid a closing collision reaction during the closing process of an armature (2) of a magnetic actuator, comprising: - de-energizing the magnetic actuator at a switching time t0 to initiate the closing process of the gas injector; defining a switching time t3 at which the voltage U of the magnetic actuator is set to zero after a period Z has elapsed after the switching time t0; A method comprising:

2. 2. The method according to claim 1, further comprising the step of: defining a starting time L at a switching time t2 of the armature after the termination of the energization of the magnetic actuator; and setting the switching time t3 for the voltage U so that it occurs only after the starting time L.

3. 3. The method according to claim 1, wherein the switching time t3 at which the voltage U is set to zero always occurs after the switching time t1 at which the current I reaches the value zero during the closing process.

4. 3. The method according to claim 1, wherein the switching time t3 at which the voltage U is forced to zero always precedes the switching time t1 at which the current I reaches the value zero.

5. 5. The method according to claim 1, wherein the switching time t3 is determined as a function of the starting time L of the armature and / or as a function of the closing speed of the armature and / or as a function of the actual closing time t4 at which the closing element of the gas injector abuts against the sealing seat.

6. 6. The method of claim 5, wherein the starting point L is determined based on the current I and the voltage U of the magnetic actuator.

7. 7. The method according to claim 5, wherein the closing time t4 of the closing element of the gas injector is determined based on a local maximum of the current I.

8. 8. The method according to claim 1, further comprising applying a braking current G for reducing the closing speed of the armature after the switching time t3 at which the voltage U is set to zero.

9. 9. The method of claim 8, wherein the duration of the braking current G is determined as a function of the closing speed of the armature.

10. A control device configured to carry out the steps of the method according to any one of claims 1 to 9.

11. 11. Computer program having a program code for implementing the steps of the method according to any one of claims 1 to 10 when the computer program is executed on a computer or a corresponding computing unit, for example in a control device.

12. A computer program product comprising a computer program according to claim 11 stored on a machine-readable data carrier or storage medium.

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