Method for operating gas injector

Abstract

The invention relates to a method for operating a gas injector (1) of an internal combustion engine for avoiding a closing rebound during a closing process of an armature (2) of an electromagnetic actuator, comprising the following steps: ending an energization of the electromagnetic actuator at a switching time t0 in order to initiate the closing process of the gas injector; and determining a switching time point t3 after a time period Z elapses after the switching time point t0, at which time point t3 the voltage U of the electromagnetic actuator is set to zero.

Description

Technical Field

[0001] The invention relates to a method for operating a gas injector of an internal combustion engine in order to avoid a closing rebound during the closing movement of an armature of an electromagnetic actuator. Background Art

[0002] Gas injectors are known from the prior art in various configurations. Due to the gaseous media to be injected, such as hydrogen, methane or the like, it is necessary to improve the regulation of the opening and closing process of the gas injector in order to comply with the exact injection quantity. During the closing process, compared with injectors for liquid fuels, a so-called closing rebound can easily occur due to the lack of hydraulic damping. In the event of such a closing rebound, the gas injector opens again, thereby injecting an additional gas quantity, which significantly increases the defined injection quantity. This also leads to increased wear on the sealing seat and the generation of loud noises, especially in the event of multiple closing rebounds occurring in succession. Summary of the invention

[0003] The method according to the invention for operating a gas injector of an internal combustion engine to avoid closing rebound during the closing process of the armature of the electromagnetic actuator, having the features of claim 1, has the following advantages: Closing rebound can be reliably avoided. As a result, the erroneous amount of gas to be blown in is reduced and the noise performance of the gas injector during operation is significantly improved. The method according to the invention is very robust and can be repeated with high accuracy. According to the invention, this is achieved in the following way: at the switching time t0, the energization of the electromagnetic actuator of the gas injector is ended to close the open gas injector so that the current I becomes zero at the second switching time t1. Then, after a time period Z has passed after the first switching time t0, a zero voltage U is applied to the coil of the electromagnetic actuator of the gas injector. This measure prevents: after the switching time t0 (at which the current I becomes zero), the voltage rises according to an exponential function as in the prior art and reaches the U level (voltage level) equal to zero with a significant delay after the eddy current in the electromagnetic actuator decays. In the method according to the invention, the conventional arc extinguishing phase in the form of an exponential function The switching process ends early and a zero voltage U is applied to the coil of the electromagnetic actuator. Then, after the switching process in which the voltage is set to zero, the magnetic force drops significantly slower than in the prior art. The slower rate of magnetic force drop results in that the resultant force does not rise rapidly over time. As a result, the closing of the gas injector slows down, which also reduces the impact speed of the armature hitting the armature stop. Therefore, it is possible to avoid the gas injector from opening again due to closing rebound, and significantly improve the noise characteristics of the gas injector.

[0004] The dependent claims reveal preferred developments of the invention.

[0005] Preferably, after the electromagnetic actuator is energized for the closing process of the gas injector, the switching time t3 at which the voltage is set to zero is not always implemented as a constant setting value after the electromagnetic actuator is energized, but the switching time t3 at which the voltage U is equal to zero is changed according to the closing characteristics of the gas injector. As a result, the best possible braking effect can be achieved when the armature is reset.

[0006] The switching time t3 at which the voltage is set to zero should be determined very accurately. If the voltage U is switched to zero too late, the braking effect on the armature is so low that the armature still strikes the armature stop at a high speed, which can then lead to a closing rebound. If the voltage U is switched to zero too early, the braking effect of the armature is too strong, which leads to a significant deterioration in the metering accuracy of the gaseous fuel to be injected.

[0007] In order to determine the correct switching time at which the voltage is set to zero as accurately as possible after the closing process begins, the position of the armature of the electromagnetic actuator is preferably detected. As a result, the switching time t3 at which the voltage is set to zero can be determined very accurately.

[0008] It is further preferred that, in order to avoid closing rebound, a start of movement time L is determined at a switching time t2 of the armature and that a switching time t3 at which the voltage is set to zero is arranged only after the start of movement time L.

[0009] It is further preferred that the voltage U equal to zero is applied only when the current I of the electromagnetic actuator reaches a zero value after the closing process has started.

[0010] Alternatively, after the closing process of the gas injector has begun, a voltage of zero is already applied before the current I of the electromagnetic actuator has reached a value of zero, thereby enabling the armature to be braked earlier.

[0011] According to another preferred embodiment of the present invention, the time period Z between the start of closing of the gas injector and the switching time point t3 at which the voltage U is switched to zero is determined based on the armature start movement time point L and / or the armature closing speed and / or the actual closing time point of the gas injector. Here, the time period Z can be determined by means of a learning system, which is preferably arranged in a controller of the gas internal combustion engine. Thus, when the armature closing speed changes, for example due to external influences, for example due to changes in friction, the time period Z can be adapted to the operation of the gas internal combustion engine in an individualized manner for the gas internal combustion engine.

[0012] Preferably, the time L at which the armature starts moving in the closing movement is determined based on the current value and the voltage value of the electromagnetic actuator.

[0013] Here, preferably, the current I and the voltage of the electromagnetic actuator are measured in the pressure-free state of the gas injector, and the first Ψ(t) variation curve is calculated in the pressure-free state. Here, the Ψ(t) variation curve is the integral of the induced voltage within the control process of the electromagnetic actuator. In a further step, the current I and the voltage of the electromagnetic actuator are measured again in the (pressurized) state of the gas injector. From this, a second Ψ(t) variation curve for the pressure state is calculated, and then a comparison between the first and second Ψ(t) variation curves is performed, and the start movement time point of the armature is determined. Here, the start movement time point L is the point at which the two Ψ(t) variation curves begin to deviate from each other.

[0014] Preferably, the switching time point of valve closure, i.e. when the closing element of the gas injector seals again at the sealing seat, is determined by means of the local maximum of the current I. This is preferably determined by monitoring the current variation curve of the electromagnetic actuator. When the armature is stationary, after the voltage is switched to zero, the current I first rises to the initial level. Then, the current I of the coil decays slowly with a time constant. However, in the case of armature movement, the inductance is not constant. Therefore, in the case of armature movement during the closing process, the speed at which the current I drops is significantly slower than in the case of armature stationary. In a fast closing movement, the current I may even rise. At the moment of valve closing (armature speed is zero), the armature speed changes, and therefore the first-order derivative of the current I also changes very quickly. Therefore, the current variation curve over time has a strong downward curvature that is typical for this moment, which can be detected as the closing time point of the armature.

[0015] The switching time at which the voltage U switches to zero is preferably implemented in the same cycle by regulation, so that the switching time t3 is adapted simultaneously during each injection, or alternatively a switching time can be determined which is obtained from a plurality of measuring cycles, for example averaged.

[0016] Furthermore, the invention relates to a control device which is configured to carry out the steps of the method according to the invention. Particularly preferably, the control device implements a control loop in order to improve the blowing accuracy of the gas injector by optimizing the closing process.

[0017] Furthermore, a computer program is proposed which has a program code and which executes the steps of the method according to the invention when it is run on a computer or a corresponding processing unit, for example a control unit according to the invention.

[0018] Furthermore, a computer program product is proposed which comprises a computer program according to the invention, which is stored on a machine-readable data carrier or storage medium.

[0019] Furthermore, the invention relates to a gas injector for a gas internal combustion engine, which is configured to carry out the method according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the accompanying drawings:

[0021] Figure 1 A schematic diagram is shown, which shows four graphs of the current I, the voltage U, the magnetic force F and the valve stroke H of a gas injector as a function of time t, in order to explain the method according to the first embodiment of the invention,

[0022] Figure 2 A schematic diagram is shown which shows two graphs of current I and voltage U as a function of time t in order to explain the method according to a second embodiment of the invention,

[0023] Figure 3 A schematic diagram is shown, which shows three graphs of current I, voltage U and valve travel H as a function of time t, in order to explain the method according to the third embodiment of the present invention,

[0024] Figure 4 Shown is a longitudinal section through a gas injector which is provided for carrying out the method according to the invention. DETAILED DESCRIPTION

[0025] Below, refer to Figure 1 and Figure 4 A first embodiment according to the present invention is described in detail.

[0026] Figure 4 A gas injector 1 with an electromagnetic actuator is shown by way of example. The electromagnetic actuator comprises an electromagnetic coil 3 for acting on an axially movable armature 2. The armature 2 can come into contact with a closing element 4, in particular a valve needle, in order to release the blowing cross section at a sealing seat 5. Reference numeral 8 denotes a reset element of the gas injector. The closing element 4 is held in place by means of a valve spring 7. Figure 4 in the closed position shown in .

[0027] When the electromagnetic 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). Here, the armature pin 9 connected to the armature 2 abuts against the closing element 4, so that the closing element 4 opens at the sealing seat 5 against the spring force of the valve spring 7. Here, the armature 2 moves until the travel stop 6 for the armature, which represents the fully opened state of the gas injector.

[0028] In order to close the gas injector 1, the current supply to the electromagnetic coil 3 is terminated, so that the reset element 8 resets the armature 2 to the position again. Figure 4At the same time, the valve spring 7 also resets the closing element 4 to the initial position shown in FIG. Figure 4 in the closed position shown in .

[0029] Figure 1 The method according to the first embodiment of the present invention is schematically shown. Here, in order to explain the present invention more clearly, four graphs arranged one above the other are shown to improve the process of the present invention and the understanding of the present invention.

[0030] Figure 1 The topmost graph in the diagram shows, as curve A, the current I supplied to the electromagnetic actuator as a function of time t within a blowing cycle. Starting from the zero point representing the closed state of the gas injector when not energized (I=0), the current I rises rapidly in accordance with the opening command for the electromagnetic actuator. Subsequently, the current I remains essentially constant over time t, which indicates the open state of the gas injector, in which the gaseous fuel is then blown in. At the switching time t0, the energization of the electromagnetic actuator is terminated to start the closing process of the gas injector. Then, at the switching time t1, the current I is zero again. Without carrying out the method according to the invention, the current I remains at zero level, which is Figure 1 A1 is used to represent it.

[0031] Figure 1 The second graph in FIG. 1 shows the voltage U (curve B) as a function of time t. At the switching time t0, which represents the start of the switch-off time, the voltage becomes negative. At the switching time t1, when the current I becomes equal to zero, the voltage U begins to approach the value zero again in an exponential function, which is Figure 1 The variation curve in the prior art is represented by B1.

[0032] Figure 1 The third graph shows the magnetic force F (curve C) over time t. During the closing process, the magnetic force decreases essentially linearly from the switching time t0, wherein in the prior art according to curve C1, the magnetic force is zero at the switching time t4 when the armature strikes the armature stop.

[0033] Figure 1 The bottom graph in the figure shows the valve stroke H (curve D) as a function of time t. Here, the bottom graph shows the start of movement time L at the switching time t2. Due to inertia reasons, the closing element of the gas injector does not immediately start the return movement to the closed state at the switching time t0, but only starts the return movement at the switching time t2. When the closing element reaches the closed state at the switching time t4 ( Figure 1When the curve D1 in FIG. 2 is used, due to the high closing speed, two closing rebounds P1 and P2 are generated. This closing rebound can be avoided by the concept according to the present invention, which will be described below.

[0034] According to the present invention, during a period of time Z (see Figure 1 , second curve), a switching time point is defined at which the voltage U is set to zero. Figure 1 , which is the switching time point t3. As can be seen from the graph of the voltage U varying with time t, a voltage curve B2 is obtained, which is drawn with a dotted line. From the switching time point t3 onwards, the voltage U remains at zero (on curve B2). Compared to the prior art in which the voltage curve has a variation curve B1, in the present invention, the voltage is set to zero at the switching time point t3. As a result, the arc extinguishing phase existing in the prior art can be terminated prematurely, and a voltage U=0 can be applied to the coil of the electromagnetic actuator. The final stage of the electromagnetic actuator can therefore be operated in a so-called "free action (Freilauf)". From Figure 1 It can be seen from the third graph of (which shows the magnetic force F as a function of time t) that at the switching time t3 when the voltage U is set to zero, the magnetic force drops significantly more slowly. Figure 1 The slow magnetic force drop results in the resultant force not rising too quickly over time. As a result, the gas injector closes more slowly, wears less, and noise is reduced.

[0035] like Figure 1 As shown in the bottom graph, the curve D of the valve travel H also changes. Figure 1 In the figure, the closing element is shown with a dashed line and marked with D2. Here, the closing time is shifted from t4 to t4' by the measures according to the invention. The closing element then remains closed for the remaining time (curve D2=0).

[0036] The invention is preferably used in a gas injector with a two-part closing element, in which the closing element comprises a valve needle for sealing at a sealing seat and an armature column, wherein the armature is fastened to the armature column. In the prior art, in the case of such a two-part closing element, two types of closing rebounds often occur during the closing process, namely needle rebound of the valve needle on the sealing seat and armature rebound of the armature on the armature stop. In the case of needle rebound, only the valve needle strikes the sealing seat, while the armature column is decoupled and continues to move. As a result, the rebound height of the valve needle itself is relatively low. The armature rebound occurs when the armature swings back later, as a result of which the valve needle can be pressed up again, which can lead to undesired re-blowing.

[0037] from Figure 1It can be further seen that the switching time point t3 at which the voltage is set to zero is after the switching time point t2 (at which the closing element begins to move from the open position to the closed position). Figure 1 It is called the starting movement time point L. Here, the starting movement time point L at the switching time point t2 is after the switching time point t1 in terms of time (at the switching time point t1, the current I is equal to zero).

[0038] The time L at which the armature starts moving is preferably determined on the basis of the current I and the voltage U of the armature.

[0039] By switching the voltage U to zero at the switching time t3, a small sudden increase in the current I also occurs, which Figure 1 This is indicated by the dashed curve A2 in FIG.

[0040] Preferably, the time period Z until the switching time t3 is not constant, but is dependent on the closing behavior of the gas injector. In order to achieve the most optimized braking effect for the brake armature, the switching time t3 should be determined very accurately. In the first embodiment, the switching time t3 is shortly after the start of the movement time L (time t2). Preferably, the switching time t3 is always determined according to the start of the movement time L.

[0041] Thus, by means of the concept according to the invention, the occurrence of closing rebounds and correspondingly inaccuracies and undesired noise in the metered quantity can be avoided.

[0042] Figure 2 The method according to a second exemplary embodiment of the invention is shown. The second exemplary embodiment corresponds substantially to the first exemplary embodiment, wherein the difference from the first exemplary embodiment is that the switching time t3 for setting the voltage to zero is selected differently. Figure 2 The curve diagram of FIG. 1 shows only the current I and the voltage. Here, the switching time point t3 is a switching time point before the current I is equal to zero. Figure 2 As shown, at the switching time t3, the current I still has the value I1. As a result, the armature can be braked earlier. Here, the time period Z can be determined for each cycle of the injection, or an average value, for example, obtained from a plurality of cycles can also be used.

[0043] Figure 3 A graph showing a method according to a third embodiment of the present invention is shown. Figure 3 In FIG. 1 , only three graphs of current I, voltage U and valve travel H varying with time t are shown.

[0044] In the third embodiment, a variable switching time t3, at which the voltage U is set to zero, is combined with a braking current G. This allows the braking effect on the armature to be further optimized. The braking effect achieved by switching the voltage to zero at the switching time t3 means that the armature has already moved more slowly when the braking current G is applied to the electromagnetic actuator after the switching time t3. Figure 3 This is the case at the switching time t5 in the example. Therefore, at the switching time when the braking current is switched on, there is a significantly lower closing speed. However, this results in greater flexibility in the subsequent application of the braking current. In particular, the requirements for the exact switching time for the braking current can be reduced or the application range for the braking current can be significantly increased. As a result, the method is significantly more robust when using the braking current. Even in the case of incorrect application of the braking current, the influence on the injector function is thus smaller, and in particular the influence on a possible closing rebound or an incorrect injection amount is also smaller.

[0045] As in Figure 3 As shown in the graph of the valve stroke H at the bottom of FIG. 1 as a function of time t, the actual closing time is further shifted to the switching time t4 'by the braking current G. This Figure 3 This is indicated by the very gentle dotted line D2.

[0046] For all described embodiments, it should be noted that the methods according to the invention can also be performed as learning systems which can be applied to current switching times t3 based on previously determined switching times t3.

Claims

1. A method for operating a gas injector (1) of an internal combustion engine, the method being used to avoid closing rebound during the closing process of an armature (2) of an electromagnetic actuator, the method comprising the following steps: At the switching time point t0, the energization of the electromagnetic actuator is terminated to start the closing process of the gas injector; and A switching time t3 is determined after a time period Z has elapsed after the switching time t0, at which the voltage U of the electromagnetic actuator is set to zero.

2. The method according to claim 1, wherein: After the energization of the electromagnetic actuator has ended, the start of movement time L is determined at the switching time t2 of the armature, and the switching time t3 for the voltage U is placed only after the start of movement time L.

3. The method according to any one of the preceding claims, wherein: The switching time t3 at which the voltage U is set to zero is always located after the switching time t1 at which the current I reaches the value zero during the shutdown process.

4. The method according to claim 1 or 2, wherein: The switching time t3 at which the voltage U is set to zero is always before the switching time t1 at which the current I reaches the value zero.

5. The method according to any one of the preceding claims, wherein: The switching time t3 is determined as a function of the start of movement time L of the armature and / or the closing speed of the armature and / or the actual closing time t4 at which the closing element of the gas injector abuts against the sealing seat.

6. The method according to claim 5, wherein: The movement start time point L is determined based on the current I or voltage U of the electromagnetic actuator.

7. The method according to claim 5 or 6, wherein: The closing time t4 of the closing element of the gas injector is determined based on the local maximum of the current I.

8. The method according to any one of the preceding claims, wherein: After the switching time t3 , at which the voltage U is set to zero, a braking current G is applied in order to reduce the closing speed of the armature.

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

10. A controller configured to perform the steps of the method according to one of the preceding claims. 11 . A computer program having a program code which executes the steps of the method according to claim 1 , when the computer program is run on a computer or a corresponding processing unit, such as a control unit. 12 . A computer program product having a computer program according to claim 11 , which is stored on a machine-readable data carrier or storage medium.

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