WO2017041923A1

WO2017041923A1 - Detection method for detecting a gap size of a gap between an injector valve assembly and piezo stack, and actuation method for actuating an actuator unit in a piezo stack

Info

Publication number: WO2017041923A1
Application number: PCT/EP2016/066021
Authority: WO
Inventors: Claus Zumstrull; Grit KRÜGER; Thomas Richter
Original assignee: Continental Automotive Gmbh
Priority date: 2015-09-09
Filing date: 2016-07-06
Publication date: 2017-03-16
Also published as: KR102027076B1; JP6667619B2; CN107923334A; EP3347584B8; KR20180037049A; EP3347584A1; JP2018527512A; EP3347584B1; DE102015217193A1; CN107923334B

Abstract

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 time period (∆t) which is necessary for frictional engagement to occur between the injector valve assembly (12) and the piezo stack (14) to occur is determined, and the gap size (34) of the gap (32) is then determined from this time period (∆t). Furthermore, the invention relates to an actuation method for actuating an actuator unit (22) in the piezo stack (14) actuator unit in which, the detection method is carried out.

Description

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 a

Injector valve assembly and a piezo stack, which is seen before ^¬ 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 layer of material is arranged between two of the electrode layers. When an electric field across the electrode layers to the

Actuator is applied, the material layers react by expanding, so that the actuator unit extends along a total Aktoreinheitlängsachse. From this ^¬ steering can be transferred to other components then, for example, a Injektorventilbaugruppe of an internal combustion engine ^¬, of a needle seat to annul an injector needle off and thereby inject fuel into combustion chambers of the internal combustion ^¬ machine.

Opening and closing the injector needle in the

Injector valve assembly is made by direct or indirect Transmission of the longitudinal extent of the actuator to the Injektorventilbaugruppe, wherein for transmitting the Längsaus ^¬ expansion at any point between the piezo stack, which has the actuator unit, and the injector valve assembly is a positive connection.

From DE 102013206933 AI 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, changes in force 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, the gap between Injektorventilbaugruppe and

To be able to compensate piezostack, what the knowledge of the Gap size, especially over the lifetime 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 provide a driving method for

To propose 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. A detection method for detecting a gap size of a gap between an injector valve assembly of a combustion ^¬ engine and a piezo stack for actuating the

Injector valve assembly includes the following steps:

- Providing a piezoelectric stack with an actuator and a sensor unit, which are positively coupled to each other GE ^¬ , wherein the sensor unit is designed to detect force acting on the actuator unit gradients;

- Providing an injector valve assembly, 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 unit with a defined voltage pulse, so that the actuator unit deflects Ver ^¬ reduction of 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

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 surge in the piezo stack. The force pulse corresponds to a force gradient, which generates a charge in the, so that, for example, a voltage can be tapped from the outside. The adhesion and thus the forces ^¬ 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 by means of a control, it is necessary to determine defined measured variables from the system, in order to determine from this the to calculate speaking control variables. In the present case, the modular structure of the piezo stack is advantageous from a

Actuator unit and a sensor unit used to the

Gap size to be determined. 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 a force increase in the second time point in which the piezoelectric stack reaches a frictional connection to the Inj ektorventilbaugruppe.

Preferably, the gap size of the gap between the piezo stack and the Injektorventilbaugruppe is detected at each cycle of actuation betae ^¬ Injektorventilbaugruppe. Thus, it is possible to record further data on 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 is detected in the voltage signal of the Sen ^¬ soreinheit in the second time point. 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. About the signs can be detected accordingly, whether a force gradient in the piezo stack was caused by the fact that a positive connection between the piezo stack and Injektorventilbaugruppe has taken place, or in that the Injektornadel has lifted from the needle seat.

In particular, in injectors with a direct transmission of the longitudinal extent of the actuator unit to the Injektorventilbaugruppe a third voltage gradient is detected in the voltage signal of the sensor ^¬ unit in a fourth time in which the injector needle is in frictional engagement 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 frictional connection 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 which 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 with a predetermined opening voltage pulse for lifting a

Injector needle assembly of the injector valve assembly is loaded by a needle seat. Before the actuation of the actuator with the Opening voltage pulse, the following steps are Runaway ^¬ leads:

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 with a pre-voltage pulse to close the gap between the piezo stack and the Inj ektorventilbaugruppe. Because the gap size is now known, it is possible to compensate 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 high-precision measurement in the detection method with said pre-voltage pulse, so that at the particular time at which the injection is to start, a reproducible gap-free state between the piezo stack and injector valve assembly he ^{¬ is} enough. The injection control can thus be completely independent of an absolute length of the piezo stack, of

Closing phenomena and so on. 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, resulting in a reproducible opening and closing behavior of the injector needle.

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 a 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 newly determined 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 performed in a first actuation cycle of the injector valve assembly, wherein the actuation of the actuator unit with the

Pre-voltage pulse to a second actuation cycle of the first actuation cycle after the second actuation cycle

Injector valve assembly is performed. Therefore, is recognized in the acquisition proceedings before ^¬ geous how big the gap size is currently 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 includes an actuator, a valve assembly having a valve seat and a valve piston, and a nozzle having a nozzle seat and a needle.

An injector unit for injecting fuel into a combustion chamber of an internal combustion engine has a

Injector valve assembly with an injector needle, wherein the Injektornadel forms a Injektorventil 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 for detecting force gradients acting on the actuator unit, and the actuator unit is for actuating the

Injector valve assembly formed. Between the piezo stack and the Injektorventilbaugruppe a gap is formed with a un ^¬ known gap size. 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 thereby forms ^¬ out for carrying out the detection method described above, or for executing the driving 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. Further advantageously, the control unit on elements with which the gap size of the gap and the required size of the pre-voltage pulse to close the gap can be ^¬ it averages out ver ^¬ different 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. 1 shows a schematic representation of a first embodiment of an injector unit with a piezo stack and an injector valve assembly, wherein the

Injector unit according to the directly operated radio ^¬ tion principle works;

Fig. 2 is a schematic representation of a second embodiment of an injector with a

Piezo stack and an injector valve assembly, the injector according to the operating principle of the servo operation works;

Fig. 3 is a schematic longitudinal sectional view through the

Piezo stack of Figure 1 and Figure 2 in greater detail. 4 is a flowchart illustrating a detection method for

Detecting a gap size of a gap between the piezo stack and the injector valve assembly in Figs. 1 and 2; 5 is a flow chart illustrating a driving method of an actuator unit in the piezo stack of FIGS. 1 to 3 for overcoming the gap detected in FIG. 4; and FIG. 6 is a schematic diagram of a control unit used for executing the detection method according to FIG Fig. 4 and the driving method according to FIG. 5 is formed. FIGS. 1 and 2 each show schematic representations of an injector unit 10 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 with which the injector valve assembly 12 can be actuated. In the injector valve assembly 12, an injector needle 16 is arranged, which cooperates with a needle seat 18 so that an injector valve 20 is formed. If the injector needle 16 lifts off from the needle seat 18, this becomes

Injector 20 is opened, and it can fuel in the respective combustion chamber, which is connected to the injector 10, injected. However, if the injector needle 16 again comes into frictional connection with the needle seat 18, this is

Injector 20 is closed, and the injection of fuel is finished.

As will be explained in greater detail below with reference to FIG. 3, the piezo stack 14 has an actuator unit 22 and a sensor unit 24. These are arranged one above the other in the piezo stack 14 along an actuator unit longitudinal axis 26, wherein the

Sensor unit 24 may be disposed above the actuator unit 22 (see Fig. 3) or under the actuator unit 22.

The piezo stack 14 is connected to a control unit 28, which on the one hand can detect voltage signals from the sensor unit 24, but on the other hand can also output voltage pulses to the actuator unit 22 so that they can travel along the

Aktoreinheitlängsachse 26 expands. Such an expansion along the Aktoreinheitlängsache 25 causes the piezo stack 14, for example via a pin 30 attached thereto, to the Injektorventilbaugruppe 12 moves. In this case, a gap 32 is overcome, which in the installed state of Injektorventilbaugruppe 12 and des Piezo stack 14 is always present, and also changed over the life of the individual elements in its gap size 34. Once the gap 32 has been overcome, and the actuator unit 22 continues to deflect along the actuator unit longitudinal axis 26, it is supplied via an operating unit 36 by the actuator unit 36

Piezo stack 14 acting on the operating unit 36 force the Injektornadel 16 lifted from the needle seat 18. Will the

Tensioning of the actuator unit 22 ends, this pulls together again along the Aktoreinheitlängsachse 26, so that the contact between Injektorventilbaugruppe 12 and

Piezo stack 14 is terminated, and the Injektornadel 16 can return to the needle seat 18 again.

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

Fig. 2 shows an alternative embodiment in which the injector 10 operates via a servo operation, wherein the operating unit 36 has a liquid-filled control chamber 40 which exerts a closing force by the present in the control chamber 40 fluid pressure on the Injektornadel 16, and so in the Needle seat 18 stops. At contact of

Piezo stack 14 via the pin 30 with a valve element 42 of the operating unit 36, a fluid pressure in the control chamber 40 is degraded, so that the Injektornadel 16 can lift out of the needle seat 18. FIG. 3 shows a schematic longitudinal sectional illustration of the piezo stack 14 from FIG. 1 and FIG. 2 in greater detail.

The piezo stack 14 has the actuator unit 22 and the sensor ^¬ unit 24, along the Aktoreinheitlängsachse 26 in the 3 are arranged one above the other in such a way that the sensor unit 24 is arranged on the side of the actuator unit 22, the

Injector valve assembly 12 faces away. However, it is also possible a reverse arrangement of actuator unit 22 and sensor unit 24.

The actuator unit 22 comprises a plurality of electrode layers and a plurality of material layers which react with application of an electric field and which are arranged along the

Aktoreinheitlängsachse 26 are arranged alternately stacked. The electrode layers and the material ^¬ layers are not shown in Fig. 3 for reasons of clarity. The electrical contacting of the electrode layers takes place via external electrodes 44, which are electrically connected to the electrode layers via electrical conductors 46. However, a contacting of the outer electrode 44 can also be done differently. The outer electrodes 44 are connected to the control unit 28, which can deliver voltage pulses to the actuator unit 22 via the outer electrodes 44, so that it expands along the Aktoreinheitlängsachse 26. The actuator unit 22 is non-positively connected to the sensor unit 24. The sensor unit 24 also advantageously has a sensor body 48 which is formed, for example, from the same material which also forms the material layers of the actuator unit 22. Electric ^¬ the layers 50 are arranged on the sensor body 48, in particular on two opposite side surfaces 52 along the

Aktoreinheitlängsachse 26 are arranged. The electrode layers 50 are connected to a voltage measuring device 54, which forwards a voltage signal of the sensor unit 24 to the control unit 28. Characterized in that the control unit 28 of the voltage signals Sen ^¬ soreinheit 24, mediated by the voltage measuring device 54 can detect all can Kräftegradienten that occur within the piezoelectric stack 14 are detected by the control unit 28th

This makes it possible to carry out with the control unit 28, a detection method with which the gap size 34 of the gap 32 between the Injektorventilbaugruppe 12 and the piezo stack 14 can be reliably detected.

A flow chart for detecting this gap size 34 is shown in FIG. 4. First, a first point in time ti is detected, to which the actuation of the actuator unit 22 takes place with a voltage pulse, starting from the control unit 24. Thereafter, it is detected when a voltage gradient dU occurs at a second time t ₂ in a voltage signal, which is reported by the sensor unit 24 to the control unit 28. From the two points of time tl, t ₂ can then be detected the time duration At that has elapsed until the occurrence of the voltage gradient dU. Using a first characteristic diagram Ki, which sets the gap size 34 as a function of the time duration Δt, the gap size 34 present at the present time can then be determined. At the same time, the voltage signal of the sensor unit 24 is further detected by the control unit 28, so that a third time t3 can be determined, to which another one

Voltage gradient dU occurs, namely, when the Injektornadel 16 lifts from the needle seat 18. In order to distinguish the second time t ₂ from the third time t3, 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 directly driven injector units, a further voltage gradient dU detected in a fourth time t4, which has a positive sign, which is due to a closing of the Injektornadel 16.

FIG. 5 shows a flow chart which schematically shows a control method with which the actuator unit 22 can be controlled via the control unit 28. Initially, as described with reference to FIG. 4, the gap size 34 of the gap 32 between the injector valve assembly 12 and the piezo stack 14 is determined. From a second map K ₂ , which sets a size of a necessary pre-voltage pulse for closing the gap 32 as a function of the determined gap size 34, then the size of the pre-voltage pulse is determined, which is necessary to close the gap 32.

In a subsequent step, the actuator unit 22 is then subjected to this pre-voltage pulse. Subsequently, the actuator unit 22 is then subjected to an opening pulse in order to lift the injector needle 16 from the needle seat 18.

The control unit 28 is configured to perform both the detection method illustrated in FIG. 4 and the drive method illustrated in FIG. 5. For this purpose, the control unit 28, as shown schematically in FIG. 6, displays the maps Ki and K ₂ . Further, detecting means 56 for detecting a voltage gradient dU in the voltage signal from the sensor unit 24 is provided. In addition, the control unit 28 comprises a time measuring device 58 and an output device 60, which comprises an opening pulse output device 62, from which an opening pulse is output to the actuator unit 22 for opening the injector needle 16. The opening pulse output device 62 gives a signal to the time measuring device 58 when it sends an opening pulse to the timer Actuator 22 has issued. The detection device 56 sends a signal to the time measuring device 58 when a voltage gradient dU has been determined via the sensor unit 24. From this, the time measuring device 58 can determine the period of time Δt.

In the control unit 28, a determination unit 64 is further provided, which can determine the gap size 34. For this purpose, it is supplied from the time measuring device 58, the detected time period At and the map Ki and the size of the opening pulse. From this data it is possible to determine the gap size 34, since the characteristic field Ki sets the gap size 34 as a function of the duration Δt and the size of the opening pulse. Further, in the control unit 28, a determination unit 66 is provided to determine the size of the pre-voltage pulse, namely on the basis of the determined gap size 34 and the second map K ₂ , which sets the necessary pre-voltage pulse for closing the gap 32 in dependence the determined gap size 34. The output device 60 includes in addition to the opening pulse output device 62 and a

Pre-voltage pulse output device 68, the particular pre-voltage pulse from the determining unit 66 is supplied. The pre-voltage pulse output device 68 then outputs a signal to the actuator unit 22, which corresponds to the specific pre-voltage pulse, so that the actuator unit 22 can extend along the Aktoreinheitlängsachse 26 such that the gap 32 disappears.

Claims

claims

A detection method for detecting a gap size of a gap between an injector valve assembly (12) of 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 a

Actuator (22) and a sensor unit (24), which are coupled to each other force ^¬ conclusively, wherein the sensor unit (24) for detecting acting on the actuator unit (22) is formed force gradients;

Providing an injector valve assembly (12) actuated via the actuator unit (22) in operation, the injector valve assembly (12) and the piezo stack (14) being spaced from each other by a gap (32) of unknown gap size (34);

Detecting a voltage signal of the sensor unit (24); Acting on the actuator unit (22) with a defined voltage pulse, so that the actuator unit (22) deflects while reducing the gap (32) along an actuator unit longitudinal axis (26);

Detecting a time duration (At) of the voltage pulse application of the actuator unit, starting from a first time (ti) in which the voltage pulse begins, until a second time (t ₂ ), in which in the detected clamping ^¬ 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 period (At) and the defined voltage pulse.

2. A 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) is detected at each actuation cycle of the injector valve assembly (12).

3. 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.

A detection method according to any one of claims 1 to 3, characterized in that at a third time point (t3), in which an injector needle (16) of the injector valve assembly (12) is lifted off a needle seat (18), a second voltage gradient (dU) in the Voltage signal of the sensor unit (24) is detected, in particular a negative voltage gradient (dU) in the voltage signal of the sensor unit (24) is detected.

5. detection method according to claim 4,

characterized in that in a fourth time point (t ₄ ), in which the injector needle (16) comes into frictional connection with the needle seat (18), a third voltage gradient (dU) is detected in the voltage signal of the sensor unit (24), between the fourth time (t ₄ ) and the second time (t ₂ ) is the third time (t3), wherein in the fourth time (t ₄ ) in particular a positive voltage gradient (dU) in the voltage signal of the sensor unit (24) is detected.

6. control method for driving an actuator unit (22) in a piezo stack (14) for actuating a

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

Injektorventilbaugruppe (12) of a needle seat (18) is beauf ^¬ strike, wherein prior to actuation of the actuator (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);

Actuating the actuator unit (22) with a

Pre-voltage pulse for closing the gap (32) between the actuator unit (22) and the Injektorventilbaugruppe (12).

7. A driving method according to claim 6,

characterized in that the pre-voltage pulse is determined from the gap size (34) determined by the detection method, wherein the pre-voltage pulse is redetermined, in particular during each actuation cycle of the injector valve assembly (12).

8. A driving method according to any one of claims 6 or 7, characterized in that the detection method is carried out in a first operating cycle of the Injektorventilbaugruppe (12), and that the energizing of the actuator unit (22) with the pre-voltage pulse to a first Actuate the ^¬ supply cycle is carried out after the second operating cycle of the injector valve assembly (12).

9. A driving method according to claim 8,

characterized in that the first actuation cycle and the second actuation cycle follow one another directly in time.

10. injector unit (10) for injecting fuel into a combustion chamber of an internal combustion engine, comprising: an injector valve assembly (12) having an injector needle (16), the injector needle (16) having a needle seat (18) forming an injector valve (20);

a piezo stack (14) having an actuator unit (22) and a sensor unit (24), which are coupled to one another in a force-locking manner, wherein the sensor unit (24) is designed to detect force gradients acting on the actuator unit (22), and wherein the actuator unit (22 ) for actuating the

Injector valve assembly (12) is formed;

between the piezo stack (14) and the

There is formed a gap (32) with a non ^¬ known gap size (34) Injektorventilbaugruppe (12);

a control unit (28) which is adapted to detect a clamping ^¬ voltage signal of the sensor unit (24) and for biasing the actuator (22) with a voltage pulse, wherein the control unit (28) for executing the detection ^¬ method according to one of claims 1 to 5 and / or for carrying out the driving method according to one of claims 9 is formed.