EP1828582B1 - Method and device for offsetting bounce effects in a piezo-actuated injection system of an internal combustion engine - Google Patents

Description

The invention relates to a method and a device for compensating bouncing effects in a piezo-controlled injection system of an internal combustion engine according to patent claims 1 and 8.

Pump-nozzle units (PDE) with a control valve actuated by a piezoactuator as an actuator are used in particular in pressure-controlled injection systems in internal combustion engines. In this case, the control valve is used for controlling a fuel flow from a low-pressure fuel area into a pressure chamber of the pump-nozzle unit and for controlling a pressure curve within the pump-nozzle unit.

Investigations have found that bouncing effects within the control valve can have a negative impact on system parameters of the piezo-controlled injection systems. Affected system parameters may include, for example, a hydraulic delivery start, a pressure build-up behavior and scatters within the pump-nozzle unit. This can, inter alia, adversely affect an injection quantity accuracy of the fuel into the pressure chamber. Disadvantageous effects of the bounce may further include unstable pressure build-up behavior as well as undefined transitions between switching states of the control valve. Under certain circumstances it is possible by bouncing that unwanted pressure waves are introduced into the injection system.

By bouncing the control valve, an instability of a performance of the unit injector may be adversely increased, the larger the instability is an intensity of the bounce is pronounced. Furthermore, elementary requirements for controlling the piezo-controlled injection systems, such as equality between the individual cylinders of the internal combustion engine and / or compensation of aging phenomena and tolerances on injection elements, may disadvantageously be hindered by the bouncing of the control valve.

The DE 199 21 456 A1 describes a method and apparatus for avoiding overshoot and bounce of a high pressure injector equipped with a piezoelectric actuator. A circuit arrangement for driving the piezoelectric actuator is designed so that it initially reloads the actuator only over a partial stroke with a maximum slope and loads after a break with a different pitch to reach the final stroke. The residual charge phase is selected such that an aperiodic transition to the final value is approximated for the mechanical system consisting of actuator valve needle hydraulics.

The DE 103 11 269 A1 describes a method for driving a piezoelectric element, wherein a drive variable is variable and for determining the drive quantity is dependent on the control variable Gütemaß for the transient response of a controlled state variable of the piezoelectric element is minimized. The method is particularly suitable for driving a piezoelectric element which is used as an actuator in a fuel injection nozzle in an internal combustion engine.

It is therefore the object of the present invention to provide a method with which the described disadvantageous effects are reduced within the piezo-controlled injection systems. The object is achieved with a method according to claim 1 and with a device according to claim 8. Preferred developments of the method according to the invention are specified in the dependent claims.

• Erfassen eines Ist-Prellverhaltens des Steuerventils, und
• Ermitteln und Ausregeln einer Abweichung zwischen dem Ist-Prellverhalten und einem Soll-Prellverhalten des Steuerventils, wobei eine Ansteuerinformation für das Steuerventil generiert wird, durch die eine Geschwindigkeitscharakteristik einer Nadel des Steuerventils beeinflusst wird.

The method according to the invention is provided for compensating bouncing effects in a piezo-controlled injection system of an internal combustion engine, wherein the injection system comprises a control valve controlled by a piezoactuator. The method comprises the following method steps:

• Detecting an actual bounce behavior of the control valve, and
• Determining and compensating a deviation between the actual bounce behavior and a desired bounce behavior of the control valve, wherein a control information for the control valve is generated, by which a speed characteristic of a needle of the control valve is influenced.

The method according to the invention is characterized in that an actual bounce behavior of the control valve is detected and a deviation between the actual bounce behavior and a desired bounce behavior of the control valve is determined and corrected. For this purpose, a speed characteristic a needle of the control valve influenced. In this way, a speed of movement of the needle of the control valve can be minimized or largely eliminated according to a difference between the actual bounce behavior and the target bounce behavior. A timely detection and compensation of bounce images of the piezo-controlled injection system is thus advantageously supported, whereby changes in the bounce images, which are caused by long and short-term effects, can be compensated.

A preferred development of the method according to the invention provides that the speed characteristic of the needle is determined by an embodiment of a holding phase in a loading and / or unloading process of the piezoactuator. The holding phase divides the charging process of the piezoactuator into two phases, which is interrupted by the holding phase. An amplitude of the holding phase represents a controlled Vorhubparameter, by means of which the speed characteristics of the needle of the control valve can be influenced in an advantageous manner.

A further preferred embodiment of the method according to the invention provides that when compensating the deviation between the actual bounce behavior and the desired bounce behavior of the control valve, a minimization of areas between maxima in the capacitance curve of the piezoactuator and a reference line connecting the maxima is performed.

Due to the fact that the bouncing of the control valve is imaged by the piezoelectric effect in electrical signals of the piezoactuator, the bouncing in a capacity curve of the piezoactuator can be evaluated. The bouncing of the control valve is reflected in the capacity curve of the piezoactuator, and can thus be minimized by minimizing the areas between the reference line connecting the capacity maxima and the capacity maxima. This is done by an optimized control the piezo actuator in the charging process, whereby a speed profile of the needle of the piezoelectric actuator is designed such that the needle when closing the control valve at the optimum speed on the valve seat and thereby bouncing is minimized. The minimized bounce is shown in minimized areas between the reference line connecting the capacity maxima and the capacity maxima of the piezoactuator.

• Figur 1 zeitliche Verläufe von elektrischen Signalen und Kenngrößen eines Piezoaktuators,
• Figur 2 zwei Graphen, die einen Zusammenhang zwischen einem Krafteintrag in den Piezoaktuator und einem mechanischen Hub des Piezoaktuators bzw. einer vom Piezoaktuator angesteuerten Steuerventilnadel darstellen,
• Figur 3 zwei Graphen, die abgetastete elektrische Signale des Piezoaktuators und einen daraus ermittelten Kapazitätsverlauf des Piezoaktuators darstellen,
• Figur 4 eine vergrößerte Darstellung des Kapazitätsverlaufs der unteren Abbildung von Figur 3,
• Figur 5 ein Ausführungsbeispiel einer Vorrichtung, mit der das erfindungsgemäße Verfahren durchführbar ist,
• Figur 6A Verläufe der Piezospannung und der Piezokapazität eines Piezoaktuators beim Prellen gemäß Stand der Technik,
• Figur 6B Verläufe der Piezospannung und der Piezokapazität eines Piezoaktuators, bei dem das Prellen erfindungsgemäß minimiert ist, und
• Figur 7 eine prinzipielle Darstellung eines von einem Piezoaktuator als Stellantrieb angesteuerten Steuerventils.

An embodiment of the invention will be described in detail below with reference to several figures. Showing:

• FIG. 1 temporal courses of electrical signals and characteristics of a piezoactuator,
• FIG. 2 two graphs illustrating a relationship between a force input into the piezo actuator and a mechanical stroke of the piezo actuator or a control valve needle controlled by the piezo actuator,
• FIG. 3 two graphs representing sampled electrical signals of the piezo actuator and a capacity curve of the piezoactuator determined therefrom;
• FIG. 4 an enlarged view of the capacity curve of the lower figure of FIG. 3 .
• FIG. 5 An embodiment of a device with which the method according to the invention is feasible,
• FIG. 6A Characteristics of the piezoelectric voltage and the piezo capacity of a piezoactuator when bouncing according to the prior art,
• FIG. 6B Characteristics of the piezoelectric voltage and the piezoelectric capacity of a piezoelectric actuator, in which the bouncing is minimized according to the invention, and
• FIG. 7 a schematic representation of a controlled by a piezo actuator as an actuator control valve.

FIG. 1 shows in three figures temporal courses of electrical signals and characteristics of a piezo actuator for controlling a control valve in a pump-nozzle unit of an internal combustion engine. In the upper figure, 1a shows a curve of a piezoelectric voltage u _piezo and 1b a curve of a piezoelectric current i _piezo with which the piezoactuator is driven. In the middle figure, a time characteristic of the _piezo voltage u _piezo and the piezoelectric current i _piezo- computationally determined characteristics of the piezoactuator is plotted. In this case, 1c denotes a time course of a piezoelectric charge q _piezo and 1d a time profile of a piezoelectric capacitance C _piezo , which is determined from a division of the piezoelectric charge q _piezo by the piezoelectric voltage u _piezo .

In the lower picture of the FIG. 1 is in a course 1f a mechanical stroke of an external reference sensor, which is arranged for measurement purposes within the control valve is shown. It can be seen that the course of the mechanical stroke 1f has pronounced extrema with maxima and minima, resulting from a bouncing of the control valve, in particular a needle of the control valve. In a course 1e, a time profile of the capacitance C _{piezo of} the piezoactuator is shown. It can be seen that the course of the piezoelectric capacitance C _piezo essentially correlates with the course 1f of the mechanical stroke of the reference sensor.

This can be justified by the fact that the bouncing of the control valve is imaged on the piezoelectric effect in the capacity curve of the piezo actuator. At about 0.25 ms in the lower figure, a first striking of the reference sensor to a valve seat of the control valve can be seen that the waveform 1f at this time has a first maximum. In correspondence with this is in the upper figure of the FIG. 1 a change in a gradient of the piezoelectric voltage u _piezo due to the piezoelectric effect recognizable. Further maxima in the signal curve 1f of the external reference sensor are correspondingly reflected in the course of the _piezo voltage U _piezo , but are difficult to recognize due to the coarse resolution of the upper image. The changes in the gradient of the _piezo voltage u _piezo due to the piezoelectric effect correspond to changes in the current profile 1b.

$$s\left(t\right)=d*u_{\mathit{piezo}}\left(t\right)+\frac{S}{d}*\left(q_{\mathit{piezo}}\left(t\right)-C_0*u_{\mathit{piezo}}\left(t\right)\right)$$

A closing behavior of the piezo-controlled control valve can be determined by the in FIG. 1 describe described electrical signal waveforms. The relationship between the individual variables can be used for a qualitative assessment of a bump characteristic of the valve needle. A simplified mathematical reconstruction model of the piezoactuator can be represented in the following way: $$f\left(t\right)=\frac{1}{d}*\left(q_{\mathit{piezo}}\left(t\right)-{\mathrm{<figure-callout\; id="0"\; label="C"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">C</figure-callout>}}_0*u_{\mathit{piezo}}\left(t\right)\right)$$

$$s\left(t\right)=d*u_{\mathit{piezo}}\left(t\right)+\frac{S}{d}*\left(q_{\mathit{piezo}}\left(t\right)-{\mathrm{<figure-callout\; id="0"\; label="C"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">C</figure-callout>}}_0*u_{\mathit{piezo}}\left(t\right)\right)$$

f(t)

Kraft des Piezoaktuators

s(t)

mechanischer Hub des Piezoaktuators

S

Kleinsignalelastizität des Piezoaktuators

d

piezoelektrische Ladungskonstante

C₀

Kleinsignalkapazität des Piezoaktuators

q_piezo

Piezoladung

u_piezo

Piezospannung

The parameters have the following meanings:

f (t)

Force of the piezoactuator

s (t)

mechanical stroke of the piezoactuator

S

Low-signal elasticity of the piezoactuator

d

piezoelectric charge constant

C ₀

Small signal capacity of the piezo actuator

q _piezo

piezo charge

u _piezo

piezovoltage

It can be seen from the mathematical relationships that, when measuring the piezoelectric charge q _piezo , the _piezo voltage u _piezo and the small signal capacitance C _o taking into account the piezoelectric charge and elasticity conditions, the force and the mechanical stroke of the piezo actuator can be calculated.

FIG. 2 shows in two figures determined by a simulation waveforms of a force input F _piezo in the piezoelectric actuator and thereby caused mechanical strokes. In the upper figure, 2a denotes a time profile of the force input F _piezo in the piezoactuator. 2b shows a resulting time course of a mechanical stroke of the piezo actuator. Correspondingly, in the lower figure of the FIG. 2 2c plotted a time course of a mechanical stroke of a needle of the control valve. The differences in the courses 2b and 2c result from the fact that between the piezo actuator and the control valve needle a Übertragerstrecke is arranged, which dampens the mechanical stroke of the piezo actuator.

FIG. 3 shows in two figures by means of a sampling process time-sampled electrical variables of the piezoelectric actuator and a calculated therefrom over time the piezoelectric capacitance C _{piezo of} the piezoelectric actuator. In the upper figure, 3a shows a time profile of the sampled _piezo voltage u _piezo . 3b is a _piezo voltage corresponding to the _piezo voltage sampled course of the piezoelectric charge q _piezo referred to, which is determined from an integration of the piezoelectric current i _piezo . In the lower illustration of FIG. 3, a time profile of the piezoelectric capacitance C _{piezo of} the piezoactuator, which is determined from the sampled values of the piezoelectric voltage u _piezo and the piezoelectric charge q _{piezo, is} shown.

It can be clearly seen that the course of the piezocapacitance C _piezo has pronounced extremes due to the bouncing of the control valve, which is reflected by a feedback effect in electrical signals of the piezoactuator. The lower picture of the FIG. 3 represents the course le of the _piezo capacitance C _{piezo of} the lower figure of FIG. 1 in scanned form. By simultaneous sampling of the piezoelectric charge q _piezo and the piezoelectric voltage u _piezo can thus be approximated to qualitative progression forms of the piezo strobe s (t) and the piezocraft f (t), which according to the above formulas correspond to the _piezo charge q _piezo and the _piezo voltage u _piezo .

FIG. 4 shows an enlarged view of the lower figure of FIG. 3 , It is the sampled course of the piezoelectric capacitance C _piezo shown, 4a with a first maximum of the piezoelectric capacitance C _piezo is designated. This first maximum results from a first striking of the needle of the control valve to the valve seat upon closure of the control valve. By 4b is exemplified a sampled, discrete value from the course of the piezoelectric capacitance C _piezo . FIG. 4c illustrates a temporal detection window in which the course of the piezoelectric capacitance C _{piezo is} detected in the method according to the invention. Denoted at 4d is a reference line connecting individual maxima in the course of the piezocapacitance C _piezo within the detection window 4c and used to define areas between the reference line and the path of the piezocapacitance C _piezo . With A1, A2 and A3 areas are referred to, which are detected according to the invention between the reference line 4d and maxima in the course of the piezoelectric capacitance C _piezo . The reference line is formed between adjacent maxima of the course of the piezoelectric capacitance as a straight line. The areas A1 and A3 are located below the reference line and the area A2 above the reference line.

Of the FIG. 4 can be taken that the bouncing of the needle of the control valve in the course of the piezoelectric capacitance C _piezo reflects such that the areas A1, A2 and A3 are greater, the more pronounced the bouncing of the needle. The extent of the area A2, which may be caused by an overshoot of the needle after impact with the valve seat, is in the illustration of FIG. 4 essentially zero. The size of the areas between the course of the piezocapacitance and the reference line between maximum values, ie local maxima The piezocapacity within a fixed time acquisition window is used as a controlled variable to reduce bouncing of the needle. In this case, the control valve is controlled in such a way that the areas between the reference line and the course of the piezoelectric capacitance are minimized within the temporal detection window. The smaller the area, the lower the bouncing behavior of the needle of the control valve. The detection window starts and ends preferably at a local maximum of the piezo capacitance.

FIG. 5 shows a schematic block diagram of an apparatus with which the inventive method is performed. By means of a detection device 13, the in FIG. 4 shown areas between the reference line 4d and the maxima in the course of the piezoelectric capacitance C detected _piezo summarily and fed to an absolute value of the total area a summation point 15 with a negative sign. A setpoint presetting device 12 is used to establish a minimized extent of the detected areas, wherein a value of substantially zero is desired. The output value of the setpoint input device 12 therefore essentially corresponds to a nominal value of the total area which is likewise fed to the summation point 15. The output value of the summation point 15 is thus a difference value between the area sum detected by the detection device 13 and a setpoint of the total area in the course of the piezoelectric capacitance C _piezo . The output value at the summation point 15 thus essentially corresponds to a control difference which is fed to a control device 11.

The control device 11 regulates the supplied control difference and generates for this purpose a timing control information for the piezoelectric actuator. The timing control information may include, for example, a number of charging steps in a charging of the piezo actuator. In this case, the generated control information is supplied to a limiter 14, which essentially performs a plausibility check represents. The control information generated by the control device 11 and limited by means of the limiter 14 control information is then supplied to an adder 16.

A pilot control device 10 is supplied with a first operating parameter 17 of the internal combustion engine, a second operating parameter 18 of the internal combustion engine and a third operating parameter 19 of the internal combustion engine. The first operating parameter 17, the second operating parameter 18 and the third operating parameter 19 model a system state of the internal combustion engine by means of characteristic map data. For example, the first operating parameter 17 may comprise a closing time of the control valve, the second operating parameter 18 a rotational speed of the internal combustion engine, and the third operating parameter 19 various physical environmental variables of the internal combustion engine. By means of the pilot control device 10, a pilot value or initial value for the time control information of the piezoactuator is generated and likewise fed to the adder 16 via an output of the pilot control device 10.

The control information generated by the pilot control device 10 can represent, for example, a rough estimate for the design of the holding phase during the charging process of the piezoactuator. By means of a pre-control algorithm implemented in the pre-controller 10, a time information for the first load time until the hold phase can thus be generated. This must always be smaller than the closing time of the control valve.

By means of the adder 16, the time control information generated by the pilot control device 10 and the control device 11 are added and are available at the output of the adder 16 as the fourth operating parameter 20 of the internal combustion engine for controlling the piezoelectric actuator available. The fourth operating parameter 20 thus represents an end value of a number of loading steps in the first phase during the charging process of the piezo actuator until the holding phase.

With the fourth operating parameter 20, it is possible to variably form the length of the holding phase and / or the partial lift level of the holding phase and thereby to influence a speed characteristic of the needle of the control valve. The design of the holding phase within the charging process of the piezoelectric actuator can, in addition to the aforementioned amplitude, also comprise a time duration of the holding phase. A speed profile of the needle of the control valve can be optimized in this way insofar as an impact of the needle in the valve seat on the one hand well defined and on the other hand designed substantially bounce-free. In its basic structure, the device represents the FIG. 5 Thus, a control loop that influences a speed of the needle of the control valve in response to the described surface difference in such a way that the bouncing of the needle is reflected as low as possible in the course of the piezoelectric capacitance C _piezo of Piezoaktuators.

The inventive device of FIG. 5 thus implements a strategy for designing the holding phase. The control algorithm implemented by the control unit 11 determines a residual error value from the supplied area information and adds this to the precontrol value.

FIG. 6A shows principal time courses of the piezoelectric voltage u _piezo and the piezoelectric capacitance C _piezo in a closing operation of the control valve according to the prior art. 6d denotes a curve of the _piezo voltage u _piezo , which undergoes a change of the gradient at a point 6a of a closing of the control valve as a result of the piezoelectric effect. It can be clearly seen that, starting from this point in time, the _piezo voltage u _{piezo is} steeper than before the time when the control valve closed. With 6e, a curve of the piezoelectric capacitance C _piezo is designated, based on the basis of FIG. 3 explained Way is determined. It can be seen that at the time of closing the control valve due to the bouncing of the control valve, a pronounced nonlinearity in the course of the piezoelectric capacitance C _{piezo is} generated. The charging of the piezo actuator is terminated at a time designated 6b. 6c designates the temporal detection window used to carry out the method according to the invention. The reference line 6f connects maxima in the course of the _piezo capacitance C _piezo between time end points of the detection window 6c. Significantly, the expression of the area between the reference line 6f and the course of the piezoelectric capacitance C _piezo within the detection window 6c due to the bouncing of the control valve can be seen.
In FIG. 6B is inserted according to the invention within the charging of the piezo actuator after a first charging phase, a holding phase. This can be recognized by the fact that a curve of the _piezo voltage u _piezo during the holding phase is essentially constant. The amplitude of the holding phase is variable according to the invention and is denoted by 6g. It can be seen that due to the insertion of the holding phase in the charging process of the piezo actuator from the time 6 a of the closing of the control valve, the gradient of the piezoelectric voltage u _piezo is substantially continuous. Furthermore, it can be seen in the course of the piezo capacitance C _piezor that the areas between the reference line 6f and the extremes in the course of the piezoelectric capacitance C _piezo in the detection window 6c are minimized or reduced.

It is considered to be particularly advantageous in the present invention that by varying the amplitude of the holding phase, the charging phase for the piezoactuator is influenced such that a speed profile of the control valve is achieved, with which the bouncing of the control valve is compensated. This can be done, for example, in that no energization of the piezoelectric actuator is performed during the holding phase, whereby a decrease in the speed of the needle of the control valve is achieved. This results a prevention of further acceleration of the needle of the control valve, so that at the time of impact of the control valve needle in the valve seat bouncing or Nachprellen is largely eliminated.

Furthermore, it is considered advantageous that by a timely detection of the electrical signals and characteristics of the piezoelectric actuator and their evaluation during a Steuerventilschließ- / opening phase, the bounce of each individual unit injector unit is individually observable and via a control or regulating device such for example, in Fig. 5 shown is timely compensated. Changing bounce images in the control valve of the pump-nozzle unit can be compensated adaptively with the method according to the invention during operation of the internal combustion engine.

By means of the inherent sensory properties of the piezoactuator by utilizing the piezoelectric effect, it is advantageously possible to save a complex and cost-intensive sensor system for detecting the electrical signals and parameters. It goes without saying that for compensating the bounce according to the invention, the holding phase can also be inserted into a discharge process of the piezoactuator.

In an alternative embodiment of the invention, it is also conceivable that, instead of the surface difference used as a control variable, the force determined via the piezoelectric effect and / or the mechanical stroke of the piezoactuator are used.

FIG. 7 shows a schematic representation of a control valve 22, with which the invention can be performed. In this case, the control valve 22 is controlled by means of a piezo actuator 21, which acts on a needle 23 in terms of power.
As a result of the force input of the piezoactuator 21 into the needle 23, the needle 23 is pressed into a valve seat 24, according to the invention bouncing of the needle 23 is minimized as a result of being impacted in the valve seat 24.

The features of the invention disclosed in the specification, the claims and the drawings may be essential to the practice of the invention both individually and in any combination.

• Erfassen eines Ist-Prellverhaltens des Steuerventils; und
• Ermitteln und Ausregeln einer Abweichung zwischen dem Ist-Prellverhalten und einem Soll-Prellverhalten des Steuerventils, wobei für das Steuerventil in der Weise angesteuert wird, dass die Geschwindigkeit der Nadel des Steuerventils beeinflusst wird, wobei beim Ausregeln der Abweichung zwischen dem Ist-Prellverhalten und dem Soll-Prellverhalten der Nadel Flächen zwischen einem Kapazitätsverlauf des Piezoaktuators und einer Maxima des Kapazitätsverlaufs verbindenden Bezugslinie minimiert werden.

In a further development, the invention relates to a method for compensating bouncing effects in a piezo-controlled injection system of an internal combustion engine, having a control valve actuated by a piezoactuator, with the following method steps:

• Detecting an actual bounce behavior of the control valve; and
• Determining and compensating for a deviation between the actual bounce behavior and a desired bouncing behavior of the control valve, wherein the control valve is controlled in such a way that the speed of the needle of the control valve is influenced, wherein when compensating the deviation between the actual bounce and the Target bounce behavior of the needle surfaces between a capacitance curve of the piezo actuator and a maximum capacity curve connecting the reference line are minimized.

In a further embodiment, the invention relates to a device for compensating for bounce effects in a piezo-controlled injection system of an internal combustion engine, wherein the injection system comprises a controlled by a piezo actuator 21 control valve 22, wherein the device comprises a detection device 13 for detecting an actual bounce of the control valve 22 and a Deviation between the actual bounce and the target bounce of the control valve 22 includes, wherein the device further comprises a control device 11 for compensating the deviation between the actual bounce and the target bounce behavior, wherein a control information for the control valve 22 is generated, when adjusting the deviation between the actual bounce behavior and the desired bounce behavior of the control valve are minimized in a time acquisition window areas between a capacity curve of the piezoelectric actuator and a reference line, wherein the reference line is formed between local maxima of the capacitance curve as a straight line.

Claims (7)

1. Method for compensating bounce effects in a piezo-controlled injection system of an internal combustion engine, having a control value which is actuated by a piezo actuator, having the following method steps:

   - detecting an actual bounce behaviour of the control value, and

   - determining and compensating a deviation between the actual bounce behaviour and a setpoint bounce behaviour of the control valve,

   wherein actuation information for the control valve, by which a speed characteristic of a needle of the control valve is influenced, is generated, wherein the speed characteristic of the needle is defined by a configuration of a holding phase in a charging and/or discharging process of the piezo actuator.
2. Method according to Claim 1, where charge values and voltage values of the piezo actuator are sampled, and a capacitant profile of the piezo actuator is determined on the basis of the charge values and voltage values.
3. Method according to Claim 2, wherein the configuration of the holding phase in the charging process of the piezo actuator is determined by means of the following method steps:

   - determining a pilot-control value of the holding phase; and

   - adding the generated actuation information to the pilot-control value.
4. Method according to Claim 3, wherein the holding phase is defined by a corresponding number of charging steps of the piezo actuator.
5. Method according to one of Claims 1 to 4, wherein during the compensation of the deviation between the actual bounce behaviour and the setpoint bounce behaviour of the control valve an extent of areas between the maximum values in the capacitance profile of the piezo actuator and a reference line connecting the maximum values is minimized.
6. Method according to one of Claims 1 to 5, wherein the method is carried out adaptively during operation of the internal combustion engine.
7. Device for compensating bounce effects in a piezo-controlled injection system of an internal combustion engine, wherein the injection system comprises a control valve (22) which is actuated by a piezo actuator (21) wherein the device comprises a detection apparatus (13) for detecting an actual bounce behaviour of the control valve (22) on the basis of a capitance profile of the piezo actuator and for determining a deviation between the actual bounce behaviour and the setpoint bounce behaviour of the control valve (22), wherein the device also comprises a regulating apparatus (11) for compensating the deviation between the actual bounce behaviour and the setpoint bounce behaviour, wherein actuation information for the control valve (22) is generated, wherein the device can be used for carrying out the method according to one of Claims 1 to 6.

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