DE102015217193A1 - Detection method for detecting a gap size of a gap between an injector valve assembly and a piezo stack and driving method for driving an actuator in a piezo stack. - Google Patents

Abstract

Detection method for detecting a gap size of a gap between an injector valve assembly and a piezo stack and driving method for driving an actuator in a piezo stack. The invention relates to a detection method for detecting a gap size (34) of a gap (32) between an injector valve assembly (12) of an internal combustion engine and a piezo stack (14), which is designed to actuate the injector valve assembly (12), wherein a period of time (.DELTA.t) detected is, which is necessary until it comes to a frictional connection between the Injektorventilbaugruppe (12) and the piezo stack (14), and from this period (.DELTA.t) then the gap size (34) of the gap (32) is determined. Furthermore, the invention relates to a driving method for driving an actuator unit (22) in the piezo stack (14), in which the detection method is performed.

Description

Detection method for detecting a gap size of a gap between an injector valve assembly and a piezo stack and driving method for driving an actuator in a piezo stack.

The invention relates to a detection method for detecting a gap size of a gap between an injector valve assembly and a piezo stack, which is intended to actuate the injector valve assembly. Furthermore, the invention relates to a driving method for driving an actuator unit in the piezo stack, which is used for actuating the Injektorventilbaugruppe.

An actuator unit in a piezo stack used to actuate an injector valve assembly in an internal combustion engine typically includes a stacked device having a plurality of electrode layers and a plurality of material layers responsive to application of an electric field. Each material layer is arranged between two of the electrode layers. When an electric field is applied to the actuator unit via the electrode layers, the material layers react by expanding, so that the actuator unit as a whole extends along an actuator unit longitudinal axis. This deflection can then be transferred to other components, such as an injector valve assembly of an internal combustion engine to lift an injector needle from a needle seat and thereby inject fuel into the combustion chambers of the internal combustion engine.

The injector needle assembly is opened and closed in the injector valve assembly by direct or indirect transmission of the actuator member longitudinal extent to the injector valve assembly, where force transfer occurs at any point between the piezo stack comprising the actuator assembly and the injector valve assembly.

Out DE 10 2013 206 933 A1 It is known to construct a piezo stack modular, so that the piezo stack in addition to the described actuator unit also has a sensor unit which is non-positively coupled to the actuator unit. The sensor unit has at least one ceramic material layer, each with two electrode layers. As a result, force changes that are transmitted to the piezo stack by the opening or closing of the injector needle can be detected, so that opening and closing times of the injector needle can be detected.

In the installed state, a gap exists between the piezo stack and the injector valve assembly, which changes over the life of the two elements due to, for example, wear or abrasion on the two elements or depolarization of the actuator unit.

As emission and fuel consumption requirements increase, fuel injection requirements increase in the combustion chambers, with higher pressures, higher temperatures, and multiple injections requiring greater accuracy in metering the injected fuel. In order to achieve the required accuracies, it is not sufficient to drive an injector into actuating mode, but regulation is unavoidable. Among other things, it is also important in this scheme to be able to compensate for the gap between Injektorventilbaugruppe and piezo stack, to which the knowledge of the gap size, especially the over life changing gap size, is necessary.

The object of the invention is therefore to propose a detection method for detecting this gap size.

This object is achieved by a detection method having the features of claim 1.

Another object is to propose a driving method for driving the actuator unit, with which the gap size can be compensated.

A driving method for driving an actuator unit in a piezo stack is the subject of the independent claim.

Advantageous embodiments of the invention are the subject of the dependent claims.

• – Bereitstellen eines Piezostapels mit einer Aktoreinheit und einer Sensoreinheit, die kraftschlüssig miteinander gekoppelt sind, wobei die Sensoreinheit zum Erfassen von an der Aktoreinheit wirkenden Kräftegradienten ausgebildet ist;
• – Bereitstellen einer Injektorventilbaugruppe, die im Betrieb über die Aktoreinheit betätigt wird, wobei die Injektorventilbaugruppe und der Piezostapel über einen Spalt mit unbekannter Spaltgröße voneinander beabstandet angeordnet sind;
• – Erfassen eines Spannungssignals der Sensoreinheit;
• – Beaufschlagen der Aktoreinheit mit einem definierten Spannungspuls, sodass sich die Aktoreinheit unter Verringerung des Spaltes entlang einer Aktoreinheitlängsachse auslenkt;
• – Erfassen einer Zeitdauer der Spannungspulsbeaufschlagung der Aktoreinheit ausgehend von einem ersten Zeitpunkt, in dem die Spannungspulsbeaufschlagung beginnt, bis zu einem zweiten Zeitpunkt, in dem in dem erfassten Spannungssignal der Sensoreinheit ein Spannungsgradient auftritt;
• – Ermitteln der Spaltgröße des Spaltes aus der erfassten Zeitdauer und dem definierten Spannungspuls.

A detection method for detecting a gap size of a gap between an injector valve assembly of an internal combustion engine and a piezo stack for actuating the injector valve assembly comprises the following steps:

• - Providing a piezo stack with an actuator and a sensor unit, which are non-positively coupled to each other, wherein the sensor unit is designed to detect force acting on the actuator unit gradients;
• - Providing an Injektorventilbaugruppe which is actuated in operation via the actuator unit, wherein the Injektorventilbaugruppe and the piezo stack are arranged spaced apart from each other via a gap of unknown gap size;
• - detecting a voltage signal of the sensor unit;
• - Actuating the actuator with a defined voltage pulse, so that the actuator unit deflects while reducing the gap along a Aktoreinheitlängsachse;
• Detecting a time duration of the voltage pulse application of the actuator unit from a first point in time when the voltage pulse application starts, to a second point in time in which a voltage gradient occurs in the detected voltage signal of the sensor unit;
• - Determining the gap size of the gap from the detected time duration and the defined voltage pulse.

In the detection method, the knowledge is used that a frictional connection between the piezo stack and the injector valve assembly leads to a force surge in the piezo stack. The power surge corresponds to a force gradient that generates a charge in the, so that, for example, a voltage can be tapped from the outside. The frictional connection and thus the force gradient occur in the moment in which the gap between the piezo stack and Injektorventilbaugruppe is overcome. Since the voltage with which the actuator unit is subjected to expansion is known, the gap size of the gap can be deduced over a measured period of time until the sensor unit detects the frictional connection with the injector valve assembly.

For this purpose, a previously determined characteristic field is advantageously stored which, for predefined voltage pulses, sets a gap size of the gap as a function of a time duration of the voltage pulse application.

In order later to be able to compensate the gap size of the gap, for example via a control, it is necessary to determine defined measured variables from the system, in order to calculate the corresponding control variables therefrom. In the present case, the modular construction of the piezo stack consisting of an actuator unit and a sensor unit is advantageously used in order to determine the gap size. Therefore, it is not necessary to provide further sensors, via which the gap size is to be determined, since already the existing sensor unit is used. The sensor unit detects an increase in force in the second time point in which the piezo stack reaches a force fit to the injector valve assembly.

Preferably, the gap size of the gap between the piezo stack and the injector valve assembly is detected at each actuation cycle of the injector valve assembly. Thus, it is possible to record further data on the aging phenomena of the elements, for example a depolarization of the actuator unit or wear or abrasion phenomena of the elements, which are reflected in the life span of the gap.

In an advantageous embodiment, a positive voltage gradient in the voltage signal of the sensor unit is detected at the second time. Accordingly, if the signal of the sensor unit representing the voltage gradient is positive, it can be immediately recognized that the second time is present.

Preferably, in a third time, in which an injector needle of the injector valve assembly lifts off a needle seat, a second voltage gradient is detected in the voltage signal of the sensor unit. This can advantageously be detected exactly the time in which opens an injector for injecting fuel.

In particular, a negative voltage gradient is detected in the voltage signal of the sensor unit. Accordingly, the signs can be used to detect whether a force gradient in the piezo stack was caused by a force connection between the piezo stack and injector valve assembly, or in that the injector needle has lifted off the needle seat.

In particular, in the case of injector units with a direct transmission of the longitudinal extent from the actuator unit to the injector valve assembly, a third voltage gradient is detected in the voltage signal of the sensor unit at a fourth time, in which the injector needle comes into frictional connection with the needle seat, wherein between the fourth time and the second Time is the third time. In the fourth time, a negative voltage gradient is advantageously detected. Also, by closing the injector and thus terminating the fuel injection, a force gradient occurs in the piezo stack, which can be detected by the sensor unit by a voltage gradient. Therefore, it can now be accurately detected via the sensor unit when there is a force fit with the injector valve assembly, when the injector needle opens, and also when the injector needle closes again. Thus, the injected fuel can be metered exactly to the respective combustion chamber. From the measured data, it is also possible to provide a control that can compensate for aging phenomena, so that an exact injection of the fuel into the respective combustion chamber remains possible.

In a driving method for driving an actuator unit in a piezo stack for actuating an injector valve assembly in an internal combustion engine, the actuator unit is provided with a predetermined opening voltage pulse for lifting an injector needle of the injector valve assembly acted upon by a needle seat. Before the actuation of the actuator with the

• – Durchführen des oben beschriebenen Erfassungsverfahrens, um eine Spaltgröße eines Spaltes zwischen dem Piezostapel und der Injektorventilbaugruppe zu erfassen;
• – Beaufschlagen der Aktoreinheit mit einem Prä-Spannungspuls zum Schließen des Spaltes zwischen dem Piezostapel und der Injektorventilbaugruppe.

Opening voltage pulse, the following steps are performed:

• Performing the above-described detection method to detect a gap size of a gap between the piezo stack and the injector valve assembly;
• - Actuating the actuator unit with a pre-voltage pulse for closing the gap between the piezo stack and the Injektorventilbaugruppe.

Because the gap size is now known, it is possible to compensate for the gap by readjusting the actuator unit by applying a pre-voltage pulse to the actuator unit so that it deflects and overcomes the gap.

For this purpose, it is advantageous if a further characteristic field is deposited, from which a size of the pre-voltage pulse necessary for closing the gap can be read out.

The actuator unit can therefore be operated based on the highly accurate measurement in the detection method with said pre-voltage pulse, so that at the respective time at which the injection is to start, a reproducible gap-free state between the piezo stack and injector valve assembly is reached. The injection control can thus be completely independent of an absolute length of the piezo stack, of closure phenomena, etc. As a result, negative disturbance variables such as the absolute change in the length of the piezo stack and signs of wear, in particular at the needle seat, can be eliminated, and a reproducible opening and closing behavior of the injector needle results.

At the same time, it can also be detected by the required pre-voltage pulse when the gap can no longer be compensated by being subjected to the pre-voltage pulse, so that maintenance is necessary. In this case, a signal can be output as a wear indicator to the outside.

Preferably, the pre-voltage pulse is determined from the gap size determined by the detection method, wherein the pre-voltage pulse is redetermined, in particular during each actuation cycle of the injector valve assembly. As a result, the gap size which changes over the service life can also be continuously compensated over the life of the arrangement.

Preferably, the detection method is carried out in a first actuation cycle of the injector valve assembly, wherein the actuation of the actuator unit with the pre-voltage pulse is performed at a second actuation cycle of the injector valve assembly that is temporally downstream of the first actuation cycle. Therefore, it is advantageously first detected with the detection method how large the gap size currently is, so that the necessary pre-voltage pulse can be determined. Only in the next cycle of operation, this pre-voltage pulse is used to compensate for the gap.

It is advantageous if the pre-voltage pulse is given to the actuator unit so early that a voltage pulse for opening the injector needle can be output as intended to the actuator unit without any time delay. For example, the pre-voltage pulse can also be given immediately after the detection process has been carried out, even if the actual subsequent injection should take place much later in time.

It is advantageous if the first actuation cycle and the second actuation cycle follow one another directly in time.

Overall, a total injector comprises an actuator, a valve assembly with a valve seat and a valve piston, and a nozzle with a nozzle seat and a needle.

An injector unit for injecting fuel into a combustion chamber of an internal combustion engine has an injector valve assembly with an injector needle, wherein the injector needle forms an injector valve with a needle seat. Furthermore, the injector unit has a piezo stack with an actuator unit and a sensor unit, which are coupled to one another in a force-locking manner. The sensor unit is designed to detect force gradients acting on the actuator unit, and the actuator unit is designed to actuate the injector valve assembly. Between the piezo stack and the Injektorventilbaugruppe a gap with an unknown gap size is formed. Furthermore, a control unit is provided, which is designed to detect a voltage signal of the sensor unit and to act on the actuator unit with a voltage pulse. The control unit is designed to carry out the detection method described above or to carry out the drive method described above.

For this purpose, the control unit has, for example, the two named maps, as well as means for detecting voltage gradients of the voltage signal of the sensor unit. Furthermore, the control unit advantageously has elements with which the gap size of the gap and the required size of the pre-voltage pulse for closing the gap can be determined from various parameters. In addition, the control unit advantageously has an output device in order to output voltage pulses to the actuator unit so that they can vary in their length along the actuator unit longitudinal axis.

Advantageous embodiments of the invention will be explained in more detail with reference to the accompanying drawings. It shows:

1 a schematic representation of a first embodiment of an injector with a piezo stack and an injector valve assembly, the injector operates according to the directly operated operating principle;

2 a schematic representation of a second embodiment of an injector with a piezo stack and an injector valve assembly, the injector operates according to the operating principle of the servo operation;

3 a schematic longitudinal section through the piezo stack 1 and 2 in greater detail;

4 a flowchart illustrating a detection method for detecting a gap size of a gap between the piezo stack and the Injektorventilbaugruppe in 1 and 2 represents;

5 a flowchart illustrating a driving method of an actuator in the piezo stack of the 1 - 3 to overcome the according to 4 recorded gap, and

6 a schematic representation of a control unit, the embodiments of the detection method according to 4 or the driving method according to 5 is trained.

1 and 2 each show schematic representations of an injector unit 10 , which is used for injecting fuel into a combustion chamber of an internal combustion engine. The injector unit 10 has an injector valve assembly 12 and a piezo stack 14 on, with which the injector valve assembly 12 can be operated. In the injector valve assembly 12 is an injector needle 16 arranged with a needle seat 18 so interacts that an injector valve 20 forms. The injector needle lifts 16 from the needle seat 18 off, the injector valve 20 open, and it can inject fuel into the respective combustion chamber, which is connected to the injector unit 10 is injected. Comes the injector needle 16 but again in force with the needle seat 18 , is the injector valve 20 closed, and the injection of fuel is finished.

The piezostack 14 points, as later with reference to 3 is explained in more detail, an actuator 22 and a sensor unit 24 on. These are along an actuator unit longitudinal axis 26 one above the other in the piezo stack 14 arranged, wherein the sensor unit 24 above the actuator unit 22 (see. 3 ) or under the actuator unit 22 can be arranged.

The piezostack 14 is with a control unit 28 connected, on the one hand voltage signals from the sensor unit 24 can capture, on the other hand, but also voltage pulses to the actuator 22 can spend so that they along the Aktoreinheit longitudinal axis 26 expands.

Such expansion along the actuator unit's length 25 causes the piezostack 14 , for example via a pin attached thereto 30 , on the injector valve assembly 12 too moved. This is a gap 32 overcome in the installed state of injector valve assembly 12 or the piezo stack 14 always exists, and also over the life of each element in its gap size 34 changed. Is the gap 32 overcome, and distracts the actuator unit 22 further along the Aktoreinheitlängsachse 26 out, is about an operating unit 36 through the from the piezostack 14 on the operating unit 36 acting force the injector needle 16 from the needle seat 18 lifted. Is the voltage applied to the actuator unit 22 finished, this moves again along the Aktoreinheitlängsachse 26 together so the contact between injector valve assembly 12 and Piezo stacks 14 is finished, and the Injektornadel 16 back in the needle seat 18 can return.

In 1 In this case, a directly operated functional system is shown in which the operating unit 36 the injector needle 16 at a force application of the piezo stack 14 over lever 38 from the needle seat 18 lifts.

2 shows an alternative embodiment in which the injector unit 10 via a servo operation works, with the operating unit 36 a liquid filled control chamber 40 having a closing force by the in the control chamber 40 existing fluid pressure on the Injektornadel 16 exercises, and so in the needle seat 18 holds. Upon contact of the piezo stack 14 over the pin 30 with a valve element 42 the operating unit 36 becomes a fluid pressure in the control chamber 40 degraded, so that the Injektornadel 16 from the needle seat 18 can lift.

3 shows a schematic longitudinal sectional view of the piezo stack 14 out 1 and 2 in greater detail.

The piezostack 14 indicates the actuator unit 22 and the sensor unit 24 on, along the Aktoreinheitlängsachse 26 in the 3 shown embodiment are arranged one above the other, in such a way that the sensor unit 24 on the side of the actuator unit 22 is arranged, that of the injector valve assembly 12 turned away. However, it is also a reverse arrangement of actuator unit 22 and sensor unit 24 possible.

The actuator unit 22 comprises a plurality of electrode layers and a plurality of material layers responsive to application of an electric field along the actuator unit longitudinal axis 26 are arranged alternately stacked. The electrode layers and the material layers are in 3 not shown for reasons of clarity. The electrical contacting of the electrode layers takes place via external electrodes 44 which via electrical conductors 46 mi are electrically connected to the electrode layers. A contacting of the outer electrode 44 but can also be done differently. The outer electrodes 44 are with the control unit 28 connected via the outer electrodes 44 Voltage pulses to the actuator unit 22 can leave so that they along the Aktoreinheitlängsachse 26 expands. The actuator unit 22 is non-positive with the sensor unit 24 connected. Also the sensor unit 24 advantageously has a sensor body 48 on, for example, from the same material, which also includes the material layers of the actuator 22 forms, is formed. On the sensor body 48 are electrode layers 50 arranged, in particular on two opposite side surfaces 52 along the actuator unit longitudinal axis 26 are arranged. The electrode layers 50 are with a voltage measuring device 54 connected, which is a voltage signal of the sensor unit 24 to the control unit 28 forwards.

In that the control unit 28 Voltage signals of the sensor unit 24 , mediated via the voltage measuring device 54 , can capture all forces gradients that are within the piezo stack 14 occur from the control unit 28 be recorded.

This makes it possible with the control unit 28 also perform a detection method with which the gap size 34 of the gap 32 between the injector valve assembly 12 and the piezostack 14 can be detected reliably.

A flowchart for detecting this gap size 34 is in to 4 shown.

First, a first time t _{1 is} detected, to which the actuation of the actuator unit 22 with a voltage pulse from the control unit 24 he follows. Thereafter, it is detected when at a second time t ₂ in a voltage signal from the sensor unit 24 to the control unit 28 is reported, a voltage gradient dU occurs. From the two times t ₁ , t ₂ , the time duration .DELTA.t can be detected, which has elapsed until the occurrence of the voltage gradient dU. Using a first map K ₁ , the gap size 34 depending on the time duration .DELTA.t sets, then the existing present time gap size 34 be determined. At the same time, the voltage signal of the sensor unit 24 further from the control unit 28 detected, so that a third time t ₃ can be determined, to which a further voltage gradient dU occurs, namely, when the Injektornadel 16 from the needle seat 18 takes off. In order to distinguish the second time t ₂ from the third time t ₃ , the sign of the voltage gradient is used, which is positive at time t ₂ and negative at time t ₃ . In the further course, especially in the case of directly driven injector units, a further voltage gradient dU, which has a positive sign, can also be detected at a fourth time t4, which indicates a closing of the injector needle 16 is due.

In 5 FIG. 3 is a flow chart schematically showing a driving method by which the actuator unit 22 via the control unit 28 can be controlled. At first, as with reference to 4 described the gap size 34 of the gap 32 between the injector valve assembly 12 and the piezostack 14 determined. From a second map K ₂ , which is a size of a necessary pre-voltage pulse to close the gap 32 depending on the determined gap size 34 is set, then the size of the pre-voltage pulse is determined, which is necessary to the gap 32 close.

In a subsequent step then becomes the actuator unit 22 subjected to this pre-voltage pulse. Subsequently, the actuator unit 22 with an opening pulse applied to the Injektornadel 16 from the needle seat 18 withdraw.

The control unit 28 is educated, both in 4 presented preliminary investigation as well as in 5 to perform illustrated driving method. For this purpose, the control unit 28 , as in 6 is shown schematically, the maps K ₁ and K ₂ on. Next is a detection device 56 for detecting a voltage gradient dU in the voltage signal from the sensor unit 24 intended. In addition, the control unit includes 28 a time measuring device 58 and an output device 60 which includes an opening pulse output device 62 comprises, from which an opening pulse to the actuator unit 22 for opening the injector needle 16 is issued. The Opening pulse output device 62 gives a signal to the time measuring device 58 when it sends an opening pulse to the actuator unit 22 spent. The detection device 56 gives a signal to the time measuring device 58 if over the sensor unit 24 a voltage gradient dU has been determined. From this, the time measuring device 58 determine the duration Δt.

In the control unit 28 is still an investigative unit 64 provided the gap size 34 can determine. You will be from the time measuring device 58 supplied the detected time period .DELTA.t and the map K ₁ and the size of the opening pulse. From this data it is possible to determine the gap size 34 to determine, since the map K _1, the gap size 34 depending on the time duration .DELTA.t and the size of the opening pulse.

Next is in the control unit 28 a determination unit 66 provided to determine the size of the pre-voltage pulse, based on the determined gap size 34 and the second map K ₂ , the necessary pre-voltage pulse to close the gap 32 depending on the determined gap size 34 , The output device 60 includes in addition to the opening pulse output device 62 also a pre-voltage pulse output device 68 , which is the definite pre-voltage pulse from the determination unit 66 is supplied. The pre-voltage pulse output device 68 then sends a signal to the actuator unit 22 which corresponds to the predetermined pre-voltage pulse, so that the actuator unit 22 so along the Aktoreinheitlängsachse 26 can stretch that gap 32 disappears.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102013206933 A1 [0005]

Claims (10)

A detection method for detecting a gap size of a gap between an injector valve assembly ( 12 ) an internal combustion engine and a piezo stack ( 14 ) for actuating the injector valve assembly ( 12 ), comprising the steps of: - providing a piezo stack ( 14 ) with an actuator unit ( 22 ) and a sensor unit ( 24 ), which are non-positively coupled to each other, wherein the sensor unit ( 24 ) for detecting at the actuator unit ( 22 ) acting force gradient is formed; Providing an injector valve assembly ( 12 ), which in operation via the actuator unit ( 22 ), the injector valve assembly ( 12 ) and the piezo stack ( 14 ) over a gap ( 32 ) with unknown gap size ( 34 ) are spaced from each other; Detecting a voltage signal of the sensor unit ( 24 ); - applying the actuator unit ( 22 ) with a defined voltage pulse so that the actuator unit ( 22 ) while reducing the gap ( 32 ) along an actuator unit longitudinal axis ( 26 ) deflects; Detecting a time duration (Δt) of the voltage pulse application of the actuator unit from a first time point (t ₁ ) in which the voltage pulse application starts, to a second time point (t ₂ ) in which the detected voltage signal of the sensor unit ( 24 ) a voltage gradient (dU) occurs; Determining the gap size ( 34 ) of the gap ( 32 ) from the detected time duration (Δt) and the defined voltage pulse. Detection method according to claim 1, characterized in that the gap size ( 34 ) of the gap ( 32 ) between the piezo stack ( 14 ) and the injector valve assembly ( 12 ) at each actuation cycle of the injector valve assembly ( 12 ) is detected. Detection method according to one of claims 1 or 2, characterized in that in the second time (t ₂ ) a positive voltage gradient (dU) in the voltage signal of the sensor unit ( 24 ) is detected. Detection method according to one of claims 1 to 3, characterized in that in a third time (t ₃ ), in which an injector needle ( 16 ) of the injector valve assembly ( 12 ) from a needle seat ( 18 ), a second voltage gradient (dU) in the voltage signal of the sensor unit ( 24 ), wherein in particular a negative voltage gradient (dU) in the voltage signal of the sensor unit ( 24 ) is detected. Detection method according to claim 4, characterized in that at a fourth point in time (t ₄ ) in which the injector needle ( 16 ) in frictional engagement with the needle seat ( 18 ), a third voltage gradient (dU) in the voltage signal of the sensor unit ( 24 ) is detected, wherein between the fourth time (t ₄ ) and the second time (t ₂ ), the third time (t ₃ ), wherein in the fourth time (t ₄ ) in particular a positive voltage gradient (dU) in the voltage signal of Sensor unit ( 24 ) is detected. Driving method for driving an actuator unit ( 22 ) in a piezo stack ( 14 ) for actuating an injector valve assembly ( 12 ) in an internal combustion engine, wherein the actuator unit ( 22 ) with a predetermined opening voltage pulse for lifting an injector needle ( 16 ) of the injector valve assembly ( 12 ) from a needle seat ( 18 ) is acted upon, wherein prior to the actuation of the actuator unit ( 22 ) the following steps are carried out with the opening voltage pulse: - performing the detection method according to one of claims 1 to 5 for detecting a gap size ( 34 ) of a gap ( 32 ) between the piezo stack ( 14 ) and the injector valve assembly ( 12 ); - applying the actuator unit ( 22 ) with a pre-voltage pulse for closing the gap ( 32 ) between the actuator unit ( 22 ) and the injector valve assembly ( 12 ). A driving method according to claim 6, characterized in that the pre-voltage pulse is determined from the gap size determined by the detection method ( 34 In particular, the pre-voltage pulse is determined during each actuation cycle of the injector valve assembly (FIG. 12 ) is redetermined. Drive method according to one of Claims 6 or 7, characterized in that the detection method is used in a first actuation cycle of the injector valve assembly ( 12 ) and that the actuation of the actuator unit ( 22 ) with the pre-voltage pulse at a second actuation cycle of the injector valve assembly (11) after the first actuation cycle ( 12 ) is carried out. Control method according to claim 8, characterized in that the first actuation cycle and the second actuation cycle follow one another directly in time. Injector unit ( 10 ) for injecting fuel into a combustion chamber of an internal combustion engine, comprising: - an injector valve assembly ( 12 ) with an injector needle ( 16 ), whereby the injector needle ( 16 ) with a needle seat ( 18 ) an injector valve ( 20 ) forms; - a piezo stack ( 14 ) with an actuator unit ( 22 ) and a sensor unit ( 24 ), which are non-positively coupled to each other, wherein the sensor unit ( 24 ) for detecting at the actuator unit ( 22 ) acting force gradient is formed, and wherein the actuator unit ( 22 ) for actuating the injector valve assembly ( 12 ) is trained; between the piezo stack ( 14 ) and the injector valve assembly ( 12 ) A gap ( 32 ) with an unknown gap size ( 34 ) is trained; A control unit ( 28 ), for detecting a voltage signal of the sensor unit ( 24 ) and for acting on the actuator unit ( 22 ) is formed with a voltage pulse, wherein the control unit ( 28 ) for carrying out the detection method according to one of claims 1 to 5 and / or for carrying out the drive method according to any one of claims 9 is formed.

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