EP2100020B1 - Method for operating an injection valve - Google Patents

Description

State of the art

The invention relates to a method for operating an injection valve, in particular a fuel injection valve of an internal combustion engine of a motor vehicle, wherein the injection valve has a piezoelectric actuator for driving a with the actuator, preferably hydraulically coupled valve needle.

From the WO 2005/026516 is a method for operating an injection valve, in particular a fuel injection valve of an internal combustion engine, known. This piezoelectric actuator has a switching valve, via which the movement of the valve needle is controlled. In a first phase of the injection process, the actuator voltage increases and the piezoelectric actuator changes its length. If the voltage reaches the value Uab, the charging process of the piezo actuator is terminated. Due to electrical effects, the voltage at the piezoelectric actuator still slightly increases to the value Umax. After reaching the value U _max , the voltage drops to an undefined value. This waste is due to hydraulic effects. Subsequently, the piezoelectric actuator slowly discharges until it has reached the voltage U _rule . The difference in voltage between the end of the charging process and the end of the injection process is regulated.

Injectors and methods of this type are known and usually include presetting an actuator voltage to which the piezoelectric actuator is to be loaded or reloaded to move the valve needle of the injector to a desired position or to put the injector in a desired operating condition , Due to aging effects, in particular of the piezoelectric actuator itself and the mechanical and hydraulic components contained in the injection valve, however, changes in the corresponding electrical or mechanical parameters of the injection valve result, so that, for example, the precise metering of an amount of fuel to be injected using the known methods in the long run is not possible. In addition to these aging effects, in particular, temperature fluctuations in the region of the injection valve cause a change in the electrical capacity of the piezoelectric actuator, which leads to further inaccuracies in the metering of fuel or other fluids through the injection valve or generally in the positioning of the actuator. In addition, lead piece scatters between different injectors, which are assigned, for example, all the different cylinders of a particular internal combustion engine, to cylinder-individual deviations in the fuel injection, which are also undesirable.

Disclosure of the invention

Accordingly, it is an object of the present invention to improve a method of the type mentioned in that increased precision in the metering of a fluid to be injected over a longer period of time and at least a partial compensation of aging-related changes of the injection valve is given.

This object is achieved in a method of the type mentioned in the present invention that the actuator, starting from a first operating state of the injector corresponding output voltage by a predetermined voltage swing reloaded to a second operating state of the injector corresponding target voltage, d. H. charged or discharged, will. It was recognized that the valve needle during the opening of the injection valve and before reaching a Nadelhubanschlags corresponding to a fully open state of the injection valve, a reaction on the actuator exerts, which increases the actuator voltage by a reaction voltage. It is advantageously provided that the voltage swing is selected so that there is a desired feedback voltage.

The reaction of the valve needle to the actuator is caused by the fact that the valve needle, after one end of the energization of the actuator, initially moves toward the actuator and exerts a corresponding force on the actuator, which is essentially at rest after the end of the energization piezoelectric effect corresponding to the feedback voltage leads. The specification according to the invention of the voltage lift used to open the injection valve allows a conclusion on the voltage stroke corresponding Aktorhub and thus also on the traversed by the valve needle path during the opening process of the injector or during the energization of the actuator. With a relatively large voltage swing used for discharging the actuator or for opening the injection valve, the valve needle has already covered a corresponding, relatively large path away from its valve seat on its Nadelhubanschlag during actuation of the actuator, so that they subsequently only a relatively small way must travel back to their Nadelhubanschlag and this causes a correspondingly relatively low feedback voltage. With a comparatively small selected voltage stroke for the opening process of the injection valve, the valve needle accordingly has a longer path up to its needle stroke stop after the end of the energization, so that a comparatively large reaction voltage also occurs. Due to the corresponding choice of the voltage stroke according to the invention, it is therefore advantageously possible to determine the remaining after the Bestromungsende path of the valve needle to her Nadelhubanschlag and thus the timing of impact of the valve needle on the Nadelhubanschlag, which, for example, over several operating cycles of the injector away or. even over the entire operating time a precise injection of fuel is feasible. The inventive method can also be advantageously used to equalize the time of reaching the respective Nadelhubanschlags by the valve needles of a plurality of injectors to adjust their injection behavior or the injected through them fluid quantities to each other.

By appropriate selection of the feedback voltage and the specification of a corresponding voltage stroke, it is advantageously possible, for example, to specify a predeterminable time for the entire opening process of the injection valve.

In contrast to the conventional activation of piezoelectric actuators of injection valves, in which an absolute voltage value to be set is fixed, the inventive consideration of the voltage swing, ie the voltage difference between an output voltage and the target voltage for the actuator a particularly precise adjustment of a desired operating state of the injector, in particular with changing properties of the injector or its components. According to the invention, it has been recognized that an actuator stroke caused by the piezoelectric actuator is approximately proportional to a corresponding voltage swing of the actuator voltage, regardless of aging effects of the piezoelectric actuator or, for example, a temperature-related change in the electrical capacitance of the piezoelectric actuator. By a corresponding regulation of the voltage level corresponding to a desired operating state, accordingly, a particularly precise control of the piezoelectric actuator and thus a precise achievement of the desired operating state for the injection valve can take place.

Particularly advantageously, according to a further embodiment of the method according to the invention, the actuator can be reloaded in a predefinable recharging time with a charge-dependent charging current. This ensures that the same predefinable recharging time is required for each transshipment, while the Umladestrom required for reloading the actuator can be selected accordingly. By varying the recharging current during the reloading operation, a multiplicity of possible movement profiles of the valve needle during the transfer from a first operating state to a second operating state can be advantageously set. For example, hereby also characteristic working or lifting positions of the valve needle can be regulated or even equalized among several injection valves.

In a further embodiment of the method according to the invention, in which the valve needle rests on a valve seat in the first operating state, that the injection valve is closed, and in which the actuator at the output voltage has a first length, it is provided that the actuator to the predeterminable Voltage stroke is discharged to the target voltage, wherein it is shortened to a second length which is smaller than the first length, to convert the injection valve from its closed state to its open state.

In a further, particularly advantageous embodiment of the method according to the invention, it is provided that the voltage stroke is selected such that the valve needle reaches the valve seat and / or a needle stroke stop, when the current supply to the actuator is terminated. According to the invention, it has been recognized that in such a configuration, there is no significant reaction of the valve needle to the actuator, so that, for example, the above-described effects of the feedback voltage need not be considered advantageous, resulting in a further increase in the precision in the control of the actuator. In particular, when the feedback voltage disappears, a larger voltage range which can be used to control the actuator, ie a larger effective voltage swing, also results.

If the voltage swing for driving the actuator is selected so that an amount of the first time derivative of the actuator voltage is minimal between one end of the current supply of the actuator and a first change of sign of the first time derivative of the actuator voltage since the end of the energization of the actuator, the above described configuration in which the achievement of a valve seat or the Nadelhubanschlags takes place simultaneously with the end of the energization of the actuator, particularly precisely realized.

In a further advantageous embodiment of the method according to the invention, a recharging time, which is required for the transfer of the injection valve from its open state to its closed state, regulated, thereby ensuring a precise adherence to the recharging even with changing properties of the injection valve and the piezoelectric actuator is.

Particularly advantageously, the recharging time of a further variant of the invention can be selected as a function of a desired closing time, within which the valve needle moves from an initial position to its valve seat.

The regulation of the voltage stroke according to the invention is preferably carried out for each operating cycle of the injection valve, so that a particularly high accuracy in the control is achieved. Also, the above-mentioned recharging time can be controlled according to the invention advantageously for each operating cycle of the injector.

The regulation of the feedback voltage and / or the regulation of the first time derivative of the actuator voltage between one end of the current supply of the actuator and a first change of sign of the first time derivative of the actuator voltage since the end of energization of the actuator and / or the control of the closing time is carried out according to the invention advantageously in every n-th operating cycle of the injector, where n> 1, so that corresponding steps of the respective control method not in each Operating cycle of the injector must be performed, which in particular resources of the control method exporting processing unit can be spared, which is integrated, for example, in a control valve controlling the injection valve.

Of particular importance is the realization of the method according to the invention in the form of a computer program executable on a computer or a computer unit of a control unit and suitable for carrying out the method. The computer program may be stored, for example, on an electronic storage medium, wherein the storage medium in turn may be contained for example in the control unit.

Further advantages, features and details will become apparent from the following description in which, with reference to the drawings, various embodiments of the invention are shown. The features mentioned in the claims and in the description may each be essential to the invention individually or in any desired combination.

Short description of the drawing

Figur 1

eine schematische Schnittdarstellung eines Ausführungsbeispiels eines Kraftstoffeinspritzventils zur Ausführung des erfindungsgemäßen Verfahrens,

Figur 2a

schematisch einen zeitlichen Verlauf einer Aktorspannung eines piezoelektrischen Aktors des Kraftstoffeinspritzventils aus Figur 1,

Figur 2b

einen zeitlichen Verlauf der Aktorspannung des piezoelektrischen Aktors zusammen mit einem zeitlichen Verlauf des Ansteuerstroms des piezoelektrischen Aktors und eines entsprechenden Aktorhubs,

Figur 3a

eine Detaildarstellung des zeitlichen Verlaufs der ersten zeitlichen Ableitung der Aktorspannung des piezoelektrischen Aktors,

Figur 3b

eine Detaildarstellung des zeitlichen Verlaufs der zweiten zeitlichen Ableitung der Aktorspannung des piezoelektrischen Aktors,

Figur 4a

schematisch ein Funktionsdiagramm einer Reglerstruktur zur Implementierung einer ersten Ausführungsform des erfindungsgemäßen Verfahrens,

Figur 4b

schematisch ein Funktionsdiagramm einer Reglerstruktur zur Implementierung einer weiteren Ausführungsform des erfindungsgemäßen Verfahrens,

Figur 5a bis 5c

jeweils weitere Beispiele für einen zeitlichen Verlauf der Aktorspannung des piezoelektrischen Aktors, und

Figur 6

schematisch ein Funktionsdiagramm einer weiteren Reglerstruktur einer dritten Ausführungsform des erfindungsgemäßen Verfahrens.

In the drawing shows:

FIG. 1

FIG. 2 is a schematic sectional view of an exemplary embodiment of a fuel injection valve for carrying out the method according to the invention, FIG.

FIG. 2a

schematically a time course of an actuator voltage of a piezoelectric actuator of the fuel injection valve FIG. 1 .

FIG. 2b

a time profile of the actuator voltage of the piezoelectric actuator together with a time profile of the drive current of the piezoelectric actuator and a corresponding actuator stroke,

FIG. 3a

a detailed representation of the time profile of the first time derivative of the actuator voltage of the piezoelectric actuator,

FIG. 3b

a detailed representation of the time profile of the second time derivative of the actuator voltage of the piezoelectric actuator,

FIG. 4a

1 schematically a functional diagram of a controller structure for implementing a first embodiment of the method according to the invention;

FIG. 4b

1 schematically a functional diagram of a controller structure for implementing a further embodiment of the method according to the invention,

FIGS. 5a to 5c

in each case further examples of a time profile of the actuator voltage of the piezoelectric actuator, and

FIG. 6

schematically a functional diagram of another controller structure of a third embodiment of the method according to the invention.

Embodiment (s) of the invention

In the FIG. 1 a fuel injection valve 10 designed as an injection valve of an internal combustion engine of a motor vehicle is shown, which is provided with a piezoelectric actuator 12. The piezoelectric actuator 12 is as in FIG. 1 indicated by the arrow driven by a control unit 20. Furthermore, the fuel injection valve 10 has a valve needle 13, which can sit on a valve seat 14 a in the interior of the housing of the fuel injection valve 10.

When the valve needle 13 is lifted from the valve seat 14a, the fuel injection valve 10 is opened and fuel is injected. This condition is in the FIG. 1 shown. A fully opened state of the fuel injection valve 10 is characterized in that the valve needle 13 is arranged on a needle stroke stop arranged in the region 14b and not shown, which prevents further movement of the valve needle 13 away from its valve seat 14a, ie towards the actuator 12 , If the valve needle 13 is seated on the valve seat 14a, the fuel injection valve 10 is closed. That is, the whole, according to the picture FIG. 1 vertically extending stroke, which the valve needle 13 can travel, is limited on the one hand by the valve seat 14a (closed position) and on the other hand by the Nadelhubanschlag in the area 14b (opening position).

The transition from the closed to the open state is effected by means of the piezoelectric actuator 12. For this purpose, a voltage referred to below as the actuator voltage U is applied to the actuator 12, which causes a change in length of a arranged in the actuator 12 piezo stack, which in turn is used to open or close the fuel injection valve 10.

The fuel injection valve 10 further includes a hydraulic coupler 15. The hydraulic coupler 15 is disposed within the fuel injection valve 10 and has a coupler housing 16 in which two pistons 17, 18 are guided. The piston 17 is connected to the actuator 12 and the piston 18 is connected to the valve needle 13. Between the two pistons 17, 18, a volume 19 is included, which accomplishes the transmission of the force exerted by the actuator 12 on the valve needle 13.

The coupler 15 is surrounded by pressurized fuel 11. The volume 19 is also filled with fuel. Via the guide gaps between the two pistons 17, 18 and the coupler housing 16, the volume 19 can be adapted over a longer period of time to the respectively existing length of the actuator 12. For short-term changes in the length of the actuator 12, however, the volume 19 remains virtually unchanged and the change in the length of the actuator 12 is transmitted to the valve needle 13.

FIG. 2a schematically shows the time course of the actuator voltage U for driving the piezoelectric actuator 12 of the injection valve 10 from FIG. 1 again. How out FIG. 2a can be seen, the actuator voltage U is lowered from the time t ₀ in the context of the inventive method, starting from an output voltage U ₀ by a symbolized by the double arrow ΔU voltage swing to a corresponding target voltage U ₁ , as well as from FIG. 2a can be seen at the time t ₁ on the piezoelectric actuator 12 (FIG. FIG. 1 ) is present. At the time t ₁ is also not one FIG. 2a apparent energization of the actuator 12, that is, an actuation of the actuator 12 with a voltage swing ΔU corresponding discharge current set. However, at this point in time t _1, the valve needle 13 continues to move towards its needle stroke stop 14 b located in the region of the coupler housing 16 and in this case exerts a corresponding force on the piezoelectric actuator 12. This force is metrologically detected by the hereinafter also referred to as feedback voltage voltage .DELTA.U _R , which is superimposed on the actual actuator voltage U of the actuator 12 and this changed. To the in FIG. 2a shown time t ₂ , the valve needle 13 has reached its Nadelhubanschlag 14 b and thus assumed its rest position corresponding to a fully open state of the injection valve 10. Accordingly, the valve needle 13 now exerts no further pressure on the actuator 12, and it turns from the time t ₂ which is also referred to as the plateau voltage substantially time constant voltage U _p .

From a subsequent time t ₃ , the piezoelectric actuator 12 is driven again, in particular charged by a corresponding charging current, so that up to the time t _5, the actuator voltage U increases again to the value of the output voltage U ₀ . During charging, the actuator 12 undergoes the length change already described above, which moves the valve needle 13 from its rest position on the Nadelhubanschlag 14b again to its valve seat 14a, whereby the closed position of the injector 10 and its closed operating state is characterized. After charging, ie from time t ₅ , the injection valve is ready for a new operating cycle.

FIG. 2b additionally shows a metrologically recorded, to the schematic representation FIG. 2a Comparable, time course of the actuator voltage U of the actuator 12 together with a time course of the charge / discharge current I, with which the actuator 12 during the intervals (t ₀ ; t ₁ ) or (t ₃ ; t ₅ ) ( FIG. 1 ) is applied. A Hubverlauf h, ie the actually traversed by the valve needle 13 way is off FIG. 2b also visible.

The reloading of the actuator 12 according to the invention by triggering with a predefinable voltage swing .DELTA.U ( FIG. 2a ) or a corresponding charge-reversal l allows a particularly precise control of the valve needle 13 and thus, for example, a particularly precise metering of fuel through the injection valve 10. According to the invention, a control method is used to implement the voltage to be applied during the discharge of the actuator 12 voltage ΔU, in which a Discharge current I _E as a function of the voltage _{to be} set ΔU _{should be} set. A corresponding controller structure is shown schematically in FIG FIG. 4a played.

The first part of R1 in FIG. 4a illustrated regulator receives as a target size to be set voltage deviation .DELTA.U _soll , which is processed in a subtractor not specified in detail together with the actually occurring voltage swing .DELTA.U _is to a corresponding control difference. This control difference is fed to a function block 30, which may for example be formed as a characteristic curve and a transformation of the control difference in a discharge current I _E , with which the piezoelectric actuator 12 is to be controlled in a subsequent control cycle to the control difference ΔU _soll -ΔU _is to minimize. The discharge current I _E is supplied to a function block representing the injection valve 10, and the quantities actuator voltage U and actuator current I resulting from the triggering with the discharge current I _E , which are measured, for example, by the control unit 20 (FIG. FIG. 1 ), are supplied to an evaluation unit 25, which is preferably also implemented in the control unit 20.

The evaluation unit 25 determines, on the one hand, the actual voltage swing .DELTA.U from the measured quantities U, I supplied to _it , for example by subtracting the instantaneous actuator voltage U from the output voltage U ₀ . On the other hand, the evaluation unit 25 determines from the quantities U, I supplied to it also an actual quantity ΔU _Rist to be described later.

By the above-described control circuit R1, an efficient control of the desired voltage swing .DELTA.U during a discharging operation of the actuator 12 for opening the injection valve 10 is indicated. A comparable voltage swing .DELTA.U can also be used, for example, to charge the actuator 12, in particular in order to shift the injection valve 10 from an open state to a closed state. In this case too, the regulator R1 described above can be used. The regulation according to the invention of the voltage swing .DELTA.U always ensures that a desired actuator stroke h is established, independently of aging effects of the piezoelectric actuator 12 and / or of the further components of the injection valve 10.

Since the time at which the valve needle 13 of the injection valve 10 actually has its Nadelhubanschlag 14b ( FIG. 1 ), and the in FIG. 2a designated by the reference numeral t ₂ , for a precise control of the operation of the injection valve 10 is particularly interested, the operating method according to the invention in addition to the above-described control of the voltage .DELTA.U also provides a regulation of the feedback voltage .DELTA.U _R before.

The inventive specification of the voltage ΔU is - in addition to the defined reloading of the actuator 12 - advantageously determines which way the valve needle 13, starting from its closed position on the valve seat 14a during the intended for discharging Bestromungszeit t ₀ to t ₁ ( FIG. 2a ) covers. At the same time, this also defines the remaining path of the valve needle 13 as far as its needle stroke stop 14b, which it covers in the time t ₁ to t ₂ .

Since the energizing or recharging time t ₁ -t _{0 is} known and predetermined, for example, by the control unit 20, can be selected in this way by selecting the Spannungshubs .DELTA.U also the total opening time t ₂ -t _{0 are} set, ie the time between the start of the control at t = t ₀ and the impact of the valve needle on the Nadelhubanschlag 14b at t = t ₂ .

A regulation of the opening time t ₂ -t ₀ is by the invention, also in FIG. 4a illustrated additional loop R2 allows. In accordance with a desired opening time t ₂ -t ₀ , a set value ΔU _{Rsoll is} set, which determines the desired feedback voltage ΔU _R and, accordingly, also influences the time difference t ₂ -t ₁ and thus also t ₂ itself. Together with the actual quantity ΔU _Rist obtained as already described above by the evaluation unit 25, a corresponding control difference ΔU _Rsoll -ΔU _Rist for the feedback _voltage is again formed, which is fed to a function _block 31 and thereby transformed into a corresponding desired value for the voltage deviation ΔU to be set according to the invention.

That is, the combination of in FIG. 4a imaged inventive control circuits R1, R2 allows by their interaction the specification of the opening time t ₂ -t ₀ corresponding feedback voltage corresponding to the manner described above with a corresponding voltage swing .DELTA.U for the discharge of the actuator 12.

The detailed view FIG. 3a gives a timing of the actuator voltage U for the actuator 12 in the time range between about t ₁ and t ₂ FIG. 2a again. The in FIG. 3a The time designated by the reference symbol t _BE indicates the end of a current supply of the actuator 12 and thus corresponds to the in FIG. 2a with the reference numeral t ₁ designated time. According to the invention, the first change in sign of the first time derivative U̇ of the actuator voltage U occurring after the lighting end t _{BE is} evaluated and interpreted as a characteristic for the reaching of the needle stroke stop 14b by the valve needle 13, so that the time t ₂ according to FIG FIG. 2a can be determined. This first sign change of the first time derivative U̇ occurs in the scenario according to FIG. 3a at the time t _VZW on. At this time t _VZW (= t ₂ according to FIG. 2a ) According to the invention the actual size for the feedback voltage ΔU _Rist , cf. FIG. 4a , determined and used for the described scheme. Since the evaluation of the first time derivative U̇ ( FIG. 3a ) of the actuator voltage U is more computationally intensive than the mere monitoring of the actuator voltage U by the regulator R1, that in the controller R2 (FIG. FIG. 4a ) implemented method preferably only every n-th operating cycle of the injection valve 10, where n> 1, that is, for example, for n = 4 at every fourth discharge.

Investigations by the Applicant have shown that this gives a sufficiently high accuracy in the regulation of the desired feedback voltage ΔU _R , without requiring an unnecessarily high computing power of a computing unit provided in the control unit 20 on which the control methods of the controllers R1, R2 are implemented ,

In addition to an evaluation of the first time derivative U̇ of the actuator voltage U of the actuator 12, an equivalent detection of reaching the Nadelhubanschlags 14b, for example, under analysis of the second time derivative U̇ of the actuator voltage U or by equivalent, known in the art process.

In a further very advantageous embodiment of the method according to the invention, it is provided that a recharging time, which is required for the transfer of the injection valve 10 from its open state into its closed state, is regulated.

The reloading time is out FIG. 2a as a time difference between the times t ₃ and t ₅ visible.

The inventive regulation of the recharging time allows a particularly precise closing of the injection valve 10 and can be advantageous by the in FIG. 4b imaged controller structure can be implemented.

The Umladezeit to be set, within which the injection valve 10 is to be transferred from its open state (time t ₃ ) to its fully closed state (time t ₅ ), is in FIG. 2a symbolized by the double arrow Δt _35soll .

A corresponding setpoint Δt _35soll for this reloading time is the in FIG. 4b shown controller R3 and processed together with a corresponding, determined by the evaluation unit 25 actual size .DELTA.t _{35ist processed} in a _conventional manner to a corresponding control difference, which is supplied to a downstream function _block 32. The function block 32 transforms the control difference into a charging current I _L , with which the actuator 12 is to be charged during the recharging time t ₅ -t _{3 in} order to maintain the desired recharging time Δt _35soll . As already mentioned with reference to the regulator R1 FIG. 4a described, also works in FIG. 4b Charging current I _{L shown} on the injection valve symbolizing function block 10, which actually adjusting variables U, I can be detected in the manner already described by metrology by the evaluation unit 25 and processed. In order to improve the control quality of the control loop R3, a correction _value K which _is dependent on the control difference ΔU _soll -ΔU and can be taken into account, for example, by the controller R1 ( _FIG . FIG. 4a ). The correction value K advantageously takes into account that the charging time for the reloading of the actuator 12 changes accordingly in the event of an enlarged voltage swing ΔU, for example.

At the end t ₅ ( FIG. 2a ) of the recharging time, the actuator 12 is charged again to its output voltage U ₀ and ready for a renewed operating cycle, ie for a subsequent discharge.

Usually, however, the valve needle 13 reaches its valve seat 14a during the transfer time t ₅ -t ₃ already at an earlier time t ₄ (FIG. FIG. 1 ), ie the fully closed operating state of the injection valve 10 is already reached after a time subsequently referred to as the closing time t ₄ - t ₃ . When the valve seat 14a is reached, the valve needle 13 likewise exerts an already above in connection with the opening operation or reaching the stroke stop 14b described feedback effect on the actuator 12, which is detected as a change of the first time derivative U̇, ie as a kink, the actuator voltage U.

A precise regulation of the actual closing time t ₄ -t ₃ is _achieved according to the invention by _{presetting a} value corresponding to the desired closing time Δt _34soll for the reloading time Δt _35soll . This is done by the likewise in FIG. 4b illustrated regulator R4, the corresponding control _deviation .DELTA.t _34soll - .DELTA.t _{34 is transformed} in a function _block 33 in the corresponding setpoint .DELTA.t _35soll for the Umladezeit.

Analogous to the controllers R1, R2 ( FIG. 4a ) may also be the controller R3 preferably in each operating cycle of the injector 10, that is to be active during each charging of the actuator 12, while the controller R4 is preferably active only in each nth charging of the actuator 12. This is particularly advantageous because the detection according to the invention of the time t ₄ , to which the valve needle 13 meets its valve seat 14 a based on an evaluation of the second time derivative Ü of the actuator voltage U of the actuator 12 and accordingly requires a greater amount of computation than the processing of Sizes U, I used in controller R3.

Insofar as the time derivatives of the actuator voltage U are determined by the evaluation unit 25 indicated within the controllers R1, R3, such a determination takes place correspondingly only every n operating cycles, although the calculation of further variables required for the operation of the controllers R1, R3 is preferably as described takes place in each operating cycle.

FIG. 3b shows a detailed view of the time course of the second time derivative Ü of the actuator voltage U of the actuator 12. According to the invention, a local maximum of the second time derivative Ü is interpreted as a feature that _closes the closing time t (= t ₄ according to _FIG FIG. 2a ) indicates. FIG. 3b shows the corresponding local maximum of the second time derivative Ü at t = t _closing .

The evaluation unit 25 of in FIG. 4b The controller structure shown accordingly evaluates the second time derivative Ü, determines the closing time _tclose ( FIG. 3b ) and forms from this as in FIG. 4b represented the size At _{34 is} .

By using the control method according to the invention for the transfer time t ₅ -t ₃ during a closing operation of the injection valve 10, a particularly precise adjustment of the actual closing time t ₄ -t _{3 is} possible.

The evaluation of the actual closing time t _closes according to FIG. 3b Alternatively, an analysis of the first time derivation of the actuator voltage U or equivalent measures known to the person skilled in the art can also be carried out.

The FIGS. 5a and 5b represent further time courses of the actuator voltage U, as they can occur during operation of the injection valve 10.

From both FIGS. 5a, 5b It can be seen that during the discharge of the actuator 12 in the context of an opening operation of the injection valve 10 at a time t ₇ , in particular directly after the time t ₇ , fluctuations of the actuator voltage U occur, as well as the described feedback voltage due to a reaction of components of the hydraulic system or the valve needle 13 on the actuator 12 arise. These fluctuations of the actuator voltage U are undesirable and are effectively avoided in a further very advantageous embodiment of the operating method according to the invention.

According to the invention, it has been recognized that the above-described fluctuations of the actuator voltage U fail to occur when the actuation of the actuator 12 takes place such that the valve needle 13 reaches the valve seat 14a and / or the needle stroke stop 14b when the energization of the actuator 12 is terminated. In order to achieve such a control of the actuator 12, a particularly advantageous variant of the operating method according to the invention provides that the voltage swing .DELTA.U is selected such that the first time derivative U.sub.A of the actuator voltage U or the magnitude thereof becomes minimal between an end t _BE (FIG. FIG. 3a ) of the energization of the actuator 12th and a first sign change t _VZW ( FIG. 3a ) of the first time derivative U̇ of the actuator voltage U since the end t _{BE of} the energization of the actuator 12th

D. h., The inventive method analyzes the first time derivative U̇ of the actuator voltage U of the actuator 12 and minimizes them in the time range in question t _VZW - t _BE , to which the valve needle 13 hits the valve seat 14a and the Nadelhubanschlag 14b. Starting from a fixed charge or discharge time, for example, at the end of the charge / discharge time, the first time derivative of the actuator voltage U is determined, cf. the size U̇ _is the regulator R5, R6 off FIG. 6 , In order to minimize the first time derivative U̇ of the actuator voltage U, the value zero is set as desired value U̇ soll, and a corresponding control difference is supplied to the function block 26 of the regulator R6. The function block 26 forms according to the invention a mean value of the control difference of the last example, three past cycles of operation of the injection valve 10. This average value is transformed by the downstream function block 35 in a target value for an inventively adjusted voltage swing .DELTA.U _to which the minimization according to the invention of the first time derivative of U of Actuator voltage U causes the end of each reload.

In this way, it is advantageously ensured that within the fixed predefined recharging time, in each case at its end, cf. the time t ₇ from the FIGS. 5a, 5b . 5c on the one hand both the energization of the actuator 12 is terminated and on the other hand, the valve needle 13, the respective, their stroke limiting element 14a, 14b contacted.

When using the control method according to the invention according to FIG. 6 is a consideration of any occurring feedback voltages (cf. FIG. 2a ) is no longer necessary, so the controller R2 off FIG. 4a easily by the regulator R6 FIG. 6 can be replaced. The function block 34 in the controller R5 corresponds with regard to its function with the function block 30 from the controller R1 (FIG. FIG. 4a ).

Advantageously, instead of the actuator voltage U, a corresponding filtered variable can also be used in the method according to the invention.

Analogous to the averaging of the control difference by the function block 26 of the controller R6 (FIG. FIG. 6 ) can also be used with the controllers R2 ( FIG. 4a ), R4 ( FIG. 4b ) an averaging of the respective control difference may be provided in order to increase the stability of the respective controller.

Since the controller R2 ( FIG. 4a ) or R4 ( FIG. 4b ) changes or forms the setpoint for the subordinate controller R1 or R3, the downstream controllers R1, R3 are preferably designed so that they operate faster than the higher-level controller R2, R4. As already described above, this can be achieved, for example, by a corresponding design of the cycle time for the higher-level controllers R2, R4, which are preferably activated only every nth operating cycle. In the sense of a particularly rapid control by the downstream controllers R1, R3, no averaging of the respective control difference is preferably provided here.

In general, the regulators R1, .., R4 can have any suitable characteristic for the above operating purposes, wherein in particular a P (proportional) behavior and / or an I (integral) behavior is considered.

The inventive method allows by controlling the voltage .DELTA.U advantageously advantageous, for example, a precise constant holding the voltage .DELTA.U, so that the effects of temperature-induced changes in the properties of the actuator 12, resulting for example during operation, reduced to a fuel quantity actually injected or completely compensated , That is, by the inventive control of the voltage .DELTA.U to a predetermined, preferably constant, value can be achieved in conjunction with a certain corresponding discharge advantageously a temperature compensation of Einspritzzeigenschaften the fuel injection valve 10 and thus the injected fuel quantity.

Temperature-related changes of the actuator 12 such as a change in its electrical capacity also affect the Umladezeit .DELTA.t _35soll . Again, the inventive control of the recharge time .DELTA.t _35soll for realizing a temperature compensation, ie, for example, to keep constant a predetermined _recharge time .DELTA.t _35soll can be used.

The use according to the invention of the voltage swing and the recharging time as a control variable also advantageously avoids the need for direct regulation of the corresponding currents I _E , I _L , which is disadvantageous due to a usually relatively low accuracy in the metrological detection of the currents. The quantities required for the control according to the invention actuator voltage U and time t can be detected very precisely contrast and allow a correspondingly precise control.

Claims (11)

1. Method for operating an injection valve (10), in particular a fuel injection valve of an internal combustion engine of a motor vehicle, wherein the injection valve (10) has a piezoelectric actuator (12) for driving a valve needle (13) which is coupled, preferably hydraulically, to the actuator 12, the actuator being recharged, i.e. charged or discharged, by a predefinable voltage swing (ΔU) starting from an output voltage (U₀) corresponding to a first operating state of the injection valve (10) to a target voltage (U₁) corresponding to a second operating state of the injection valve (10), characterized in that in the first operating state the valve needle (13) rests on a valve seat (14a) in such a way that the injection valve (10) is closed, and at the output voltage (U₀) the actuator (12) has a first length, and in that the actuator (12) is discharged by the predefinable voltage swing (ΔU) to the target voltage (U₁), wherein said actuator (12) shortens to a second length which is shorter than the first length in order to change the injection valve (10) from its closed state into its open state, in that during the opening of the injection valve (10) and before a needle/stop (14b) which corresponds to a completely open state of the injection valve (10) is reached the valve needle (13) applies a reaction to the actuator (12) which increases the actuator voltage (U) by a reaction voltage (ΔU_R), and in that the voltage swing (ΔU) is selected such that a desired reaction voltage (ΔU_R) is produced, wherein the reaction of the valve needle (13) applied to the actuator (12) is caused in that the valve needle (13) also firstly moves further onto the actuator (12) after the end of the energization of the actuator and the valve needle (13) applies a corresponding force to the actuator (12), which is essentially stationary after the end of energization, which force controls the piezoelectric effect in accordance with the reaction voltage (ΔU_R).
2. Method according to Claim 1, characterized in that the actuator (12) is recharged in a predefinable recharging time with a recharging current which is dependent on the voltage swing (ΔU).
3. Method according to Claim 1, characterized in that the reaction voltage (ΔU_R) is selected for the opening process of the injection valve (10) as a function of a predefinable time.
4. Method according to one of the preceding claims, characterized in that the voltage swing (ΔU) is selected such that the valve needle (13) reaches the valve seat (14a) and/or a/the needle/stop (14b) when the energization of the actuator (12) is ended.
5. Method according to Claim 4, characterized in that the voltage swing (ΔU) is selected such that an absolute value of the first time derivative of the actuator voltage (U) becomes minimal between an end of the energization of the actuator (12) and a first change of sign of the first time derivative of the actuator voltage (U) since the end of the energization of the actuator (12).
6. Method according to one of the preceding claims, characterized in that a recharging time, which is necessary for changing the injection valve (10) from its opened state into its closed state, is regulated.
7. Method according to Claim 6, characterized in that the recharging time is selected as a function of a desired closing time within which the valve needle (13) moves from an initial position onto its valve seat (14a).
8. Method according to one of the preceding claims, characterized in that the voltage swing (ΔU) is preferably regulated for each operating cycle of the injection valve (10).
9. Method according to one of Claims 1 to 8, characterized in that a) the regulation of the reaction voltage (ΔU_R) and/or b) the regulation of the first time derivative (U̇) of the actuator voltage (U) takes place between the end of the energization of the actuator (12) and a first change of sign of the first time derivative (U̇) of the actuator voltage (U) since the end of the energization of the actuator (12) and/or c) the regulation of the closing time takes place in every n-th operating cycle of the injection valve (10), wherein n > 1.
10. Computer program, characterized in that it is programmed to carry out the method according to one of Claims 1 to 9.
11. Control device (20) for a fuel injection valve (10), in particular of an internal combustion engine of a motor vehicle, characterized in that it is designed to carry out the method according to one of Claims 1 to 9.

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