Method and control unit for operating an injection valve

In a method for operating an injection valve, in particular a fuel injector of an internal combustion engine of a motor vehicle, one component of the injection valve, particularly a valve needle, is disposed in a manner allowing movement relative to other components of the injection valve, and preferably is able to be driven at least partially by an actuator. A structure-borne-noise signal is detected by a structure-borne-noise sensor, and the structure-borne-noise signal is evaluated in order to infer an operating state of the movably disposed component.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Application No. 10 2008 042 556.7, filed in the Federal Republic of Germany on Oct. 2, 2008, which is expressly incorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention relates to a method for operating an injection valve, in particular a fuel injector of an internal combustion engine of a motor vehicle, in which one component of the injection valve, particularly a valve needle, is disposed in a manner allowing movement relative to other components of the injection valve, and preferably is able to be driven at least partially by an actuator.

The present invention further relates to a control unit for such an injection valve.

SUMMARY

Example embodiments of the present invention provide a method and a control unit of the kind indicated at the outset to the effect that a more precise operation of the injection valve is possible, especially in the case of changing operating parameters such as temperature, fuel pressure and the appearance of signs of wear, as well.

According to example embodiments of the present invention, a structure-borne-noise signal is detected by a structure-borne-noise sensor, and the structure-borne-noise signal is evaluated in order to infer an operating state of the movably disposed component.

The evaluation of the structure-borne-noise signal makes it possible to draw particularly precise conclusions about the operational performance or the state of individual components of the injection valve. In particular, compared to conventional methods which, for example, provide for an analysis of the control variables (control current, voltage) of the injection valve, it is also possible to determine when one or more movable components of the injection valve such as, for example, the valve needle, strike against a stop delimiting their travel. That is, using the method described herein, it is also possible to obtain information about changes in the state of internal components of the injection valve.

The evaluation of the structure-borne-noise signal may be simplified when the structure-borne-noise signal is detected in a specifiable detection time range during an operating cycle of the injection valve which is selected as a function of at least one control variable of the actuator. Since usually those operating states or changes in the state of the injection valve or of its movably disposed components are of special interest which occur as a result of the actuator being activated, the time range of the structure-borne-noise signal to be evaluated may be limited particularly advantageously to the time ranges of interest, as a function of the control variable known as a rule.

Alternatively or additionally, the method also allows the evaluation of structure-borne-noise signals which do not develop directly as a result of an activation of the actuator, but rather, for example, due to a change in pressure conditions of a fluid located in the injection valve or other processes generating structure-borne noise. In this instance, the detection time range considered is to be selected accordingly. Furthermore, a continuous acquisition and evaluation of a structure-borne-noise signal is considered, so that upon the occurrence of relevant ranges of the structure-borne-noise signal, for example, a range to be analyzed more precisely may first be determined later.

The method may include selecting the detection time range such that it includes an estimated instant of impact at which the movably disposed component strikes a further component of the injection valve, especially a valve seat and/or a lift stop. With knowledge of the mechanical or hydraulic configuration of the injection valve, the estimated instant of impact may be ascertained, for example, with the aid of a suitable model. Advantageously, the detection time range around the estimated instant of impact may also include tolerance ranges, which take into account the limited exactitude in estimating the instant of the occurrence of the event generating structure-borne noise.

The structure-borne-noise signal may be evaluated particularly advantageously to the effect that an actual instant the movably disposed component strikes a further component of the injection valve, for example, the instant the valve needle strikes the valve seat, is ascertained. In this manner, it is possible in particular to determine the position in time of the actual hydraulic opening or closing of the injection valve, which may occasionally deviate considerably from corresponding changes in the state of a control signal.

Alternatively or additionally, it is possible to monitor further events generating structure-borne noise characteristic for the operation of the injection valve, for example, the lifting of a valve needle from its seat or the striking of a magnet armature on a lift stop assigned to it.

In principle, the operational method is suitable for any injection valve which has at least one movable component and therefore is able to generate structure-borne-noise signals. In particular, the operational method may be used advantageously with high-pressure injection valves, where the valve needle is driven via an electromagnetic actuator. The use of the operational method described herein for injection valves having valve needles driven piezoelectrically or hydraulically is possible.

DETAILED DESCRIPTION

InFIG. 1, an internal combustion engine is designated overall by reference numeral10. It includes a plurality of cylinders, of which only one having reference numeral12is shown inFIG. 1. Cylinder12is disposed in an engine block14, and includes a combustion chamber16which is bounded by a piston18. Piston18sets a crankshaft20into rotation, whose rotational speed and position are sensed by a crankshaft sensor22.

Intake air arrives in combustion chamber16via an intake port24and an intake valve26. The combustion emissions are conducted via an exhaust valve28into an exhaust duct30. Fuel44is injected directly into combustion chamber16by an injection valve100. A fuel-pressure accumulator34, taking the form of a common rail, for instance, is connected to injection valve100via a pressure line.

The operation of internal combustion engine10and especially of injection valve100, as well, is controlled and regulated by control unit46. Control unit46receives signals from crankshaft sensor22, for instance, as well as from a structure-borne-noise sensor48that is connected to engine block14. Control unit46has an electronic memory element on which a computer program is stored that is designed to execute the method according to example embodiments of the present invention described in greater detail in the following.

FIG. 2shows injection valve100fromFIG. 1in a detailed view. Injection valve100has an electromagnetic actuator for driving a valve needle110, the actuator being formed by a magnet coil102and a magnet armature104cooperating with magnet coil102, as apparent fromFIG. 2. Magnet armature104is joined to valve needle110in a manner familiar to one skilled in the art in order to move the valve needle out of its closed position, shown inFIG. 2, in the area of spray holes108against the spring force of valve spring106, so that fuel44may be injected into combustion chamber16(FIG. 1).

In order to attain a fuel injection, magnet coil102of injection valve100is acted upon, e.g., in a conventional manner, by a control signal, preferably by a control current. Current-carrying magnet coil102exerts a magnetic force on magnet armature104and moves it up inFIG. 2. During this movement, magnet armature104takes along valve needle110and thus lifts it out of its closed position against the spring force of valve spring106, so that fuel may be injected through spray holes108.

After the current application, magnetic force no longer acts on magnet armature104, and it, together with valve needle110, is moved downward inFIG. 2by valve spring106, so that valve needle110ultimately assumes its closed position again, shown inFIG. 2, and the fuel injection is ended.

According to example embodiments of the present invention, a structure-borne-noise signal S, which emanates from injection valve100, is detected by structure-borne-noise sensor48(FIG. 1). An evaluation is carried out as a function of structure-borne-noise signal S, in order to infer an operating state of injection valve100, particularly of its valve needle110and/or of magnet armature104.

FIG. 3shows a simplified flow chart of a method according to an example embodiment of the present invention. In a first method step200, structure-borne-noise signal S is detected with the aid of structure-borne-noise sensor48. In following method step210, acquired structure-borne-noise signal S is evaluated in order to deduce an operating state of injection valve100.

As a function of the findings about the operating state of injection valve100obtained in step210, in a further method step220, control parameters may advantageously be formed or modified for injection valve100. In doing this, it is advantageously possible to adapt the control parameters like, for example, a control current for magnet coil102(FIG. 2) of injection valve100in such a manner to the actual operating state of injection valve100that as precise a fuel injection as possible is permitted.

The evaluation in step210may include a filtering of structure-borne-noise signal S (FIG. 1), a band-pass filtering being considered in particular. In this manner, it is advantageously possible to select for the evaluation, those signal portions contained in structure-borne-noise signal S which are of special interest. Given a suitable selection of the mid-frequency and the limit frequencies of the band-pass filter used, advantageously, those frequency portions of structure-borne-noise signal S which, for example, are attributable to components other than injection valve100may therefore be excluded from the evaluation, and are to be considered as disturbance variable for the evaluation.

As an alternative to the band-pass filtering, preferably a high-pass filtering of structure-borne-noise signal S may also be carried out.

In the course of evaluation210, after the band-pass filtering has been performed, for example, the filtered structure-borne-noise signal may be compared to a specifiable threshold value. If the band-pass-filtered structure-borne-noise signal exceeds the specifiable threshold value, it may be inferred that a movable component of injection valve100has struck a further component of injection valve100, whereby a structure-borne-noise signal S with correspondingly great amplitude has been generated.

In the case of injection valve100illustrated inFIG. 2, under evaluation210of structure-borne-noise signal S, it is possible to particularly reliably recognize the following operating states, in response to which evaluable structure-borne-noise signals are obtained:

a) Striking of valve needle110on a valve seat in the area of spray holes108,

b) Striking of magnet armature104on a bottom stop inFIG. 2,

c) Striking of magnet armature104on an upper stop inFIG. 2in the area of magnet coil102,

d) Onset of the carrying-along of valve needle110by magnet armature104.

In response to each of the events or operating states indicated above, a structure-borne-noise signal S of a particular signal form, i.e., especially having a characteristic frequency and amplitude, is generated, which is evaluable using the method described herein.

The principles described herein may also be applied to other types of injection valves, for instance, to injection valves which have an electromagnetically driven servo valve. Moreover, the principles described herein are also transferable to those injection valves in which a movable component of the injection valve is driven by a piezoelectric actuator.

Alternatively or in addition to the band-pass filtering described above, acquired structure-borne-noise signal S may also be rectified and integrated over a specifiable period of time, thereby obtaining a measure for the signal energy of structure-borne-noise signal S.

Instead of the rectification, which corresponds mathematically to an absolute-value generation, the individual sampling values of structure-borne-noise signal S may also be squared before the integration is carried out.

Alternatively or additionally, one or more spectral components of a power density spectrum of structure-borne-noise signal S may also be analyzed, particularly again with implementation of a threshold-value comparison. The power density spectrum of structure-borne-noise signal S may be obtained, e.g., in a conventional manner, for instance, with the aid of a fast Fourier transform (FFT) or a discrete Fourier transform (DFT).

The variables derived from structure-borne-noise signal S and obtained using the evaluation methods described above, may be checked as to whether they exceed a corresponding threshold value to infer from that, for example, one of the above-indicated events a), b), c), d) producing structure-borne noise.

The threshold values used during evaluation210(FIG. 3) may be established in the application, for example, or may also be modified dynamically. In this context, consideration is given in particular to altering an existing threshold value as a function of one or more previous evaluations210of structure-borne-noise signal S. For example, the method may be carried out over a plurality of similar working cycles of injection valve100, and suitable threshold values may be obtained in self-learning fashion directly from structure-borne-noise signals S obtained in so doing, or from the variables derived from them.

According to example embodiments of the present invention, an evaluation of structure-borne-noise signal S which is particularly robust with respect to interference signals is provided by normalizing structure-borne-noise signal S to be evaluated and/or a signal derived from it, to a reference signal. For example, a structure-borne-noise signal S which is acquired over a comparable period of time and which is ascertained in an operating phase of injection valve100in which no structure-borne-noise events produced by movable components104,110are to be expected may be used as reference signal. Accordingly, the reference signal contains solely those structure-borne-noise-signal components which are produced by other processes in injection valve100and, in particular, in internal combustion engine10, that are not to be evaluated.

The detection time range within which structure-borne-noise signal S is to be acquired is advantageously selected as a function of at least one control variable of injection valve100. In particular, to precisely limit the detection time range, a control current of magnet coil102may be evaluated. The detection time range is advantageously selected so that it includes at least one estimated instant of impact at which movably disposed component104,110strikes another component of injection valve100, especially the valve seat or a lift stop.

In step210, acquired structure-borne-noise signal S may also be correlated with a reference signal that has been ascertained in connection with a reference system, for example, and has been stored in non-volatile manner in a memory of control unit46.

The correlation may be carried out, e.g., in a conventional manner, in that a temporal shift, at which the correlation result is at its maximum, is sought between the reference signal and acquired structure-borne-noise signal S. This temporal shift corresponds to the temporal shift between an actual instant of impact of the movable component of injection valve100considered, with respect to the instant of impact of the reference system.

An example embodiment of the present invention is described in the following with reference to the flow chart according toFIG. 4. This method provides for implementing a plurality of test activations of actuator102,104, during which in each instance, actuator102,104receives different control signals, a plurality of structure-borne-noise signals corresponding in each case to the different test activations being obtained, and the operating state of injection valve100, particularly of its movably disposed components104,110, being inferred from the plurality of structure-borne-noise signals.

That is to say, in contrast to the method variants described with reference to the flow chart according toFIG. 3, the method variant according toFIG. 4provides for an evaluation of such structure-borne-noise signals S as are obtained under separate test activations of actuator102,104carried out especially for that purpose, and not such structure-borne-noise signals S as occur during a conventional operation of injection valve100.

Assuming the type of injection valve illustrated inFIG. 2, a control current is again considered as control signal. In each instance, an activation period may be modified for the plurality of test activations. That is, each of the test activations is carried out with an activation period assigned to it, which is different from the activation periods for the other test activations.

In a first step300of the method illustrated inFIG. 4, initially a starting value, in the present case, particularly a minimum value, is predefined for the activation period, and a first test activation is subsequently carried out using the minimum value for the activation period.

In the following step310, a structure-borne-noise signal yielded during the first test activation is recorded.

To evaluate the recorded structure-borne-noise signal, in method step320, a variable characterizing the energy of the recorded structure-borne-noise signal is ascertained in one of the procedures already described above, for example, by squaring the individual sampling values of the structure-borne-noise signal and subsequent integration. That is, after carrying out step320of the operational method, a variable is available characterizing the energy of the recorded structure-borne-noise signal.

In the present case, this variable represents a structure-borne-noise interference-signal energy, since for first step300of the method, a minimal activation period has been selected which, with certainty, would not already lead to a movement of valve needle110(FIG. 2), under actuation by actuator102,104. In particular, the minimal activation period may also be selected at zero for this purpose, so that actuator102,104is actually not driven at all for the first test activation. Accordingly, no structure-borne-noise signal corresponding to a movement of components104,110results based on the activation during method step300, so that the structure-borne-noise signal evaluated in step320corresponds merely to an interference-signal energy.

In method step330, it is thereupon checked whether preceding activation310is the first test activation. If this is the case, the method branches to step340, in which the interference-signal energy, ascertained as described herein, of the structure-borne-noise signal recorded during the first test activation is stored for subsequent utilization. Thereupon, in step350, the activation period for the following test activation is increased by a specifiable value.

Preferably, the increase in the activation period may follow a predefined test scheme that, for example, provides for a constant increment for the activation period, that is, with each further test activation, an activation period increased by a constant increment is used. Alternatively, the increment may also be selected not to be constant, in particular, it may be selected as a function of the number of test activations already implemented, or perhaps as a function of the activation period itself, and so forth.

After the activation period has been increased in step350, a further test activation is carried out. To that end, the method again branches to step310, as evident fromFIG. 4. In step320, a structure-borne-noise-signal energy is subsequently ascertained for the second test activation. Since the instantaneous test activation is no longer the first test activation for ascertaining the interference-signal energy, after the query in step330, the method does not branch to step340, but rather to step360, which has as its object a special evaluation of the previously ascertained structure-borne-noise-signal energy.

In the present case, the evaluation of the structure-borne-noise-signal energy includes a division of the instantaneously ascertained structure-borne-noise-signal energy, that is, the structure-borne-noise-signal energy of the second test activation, by the interference-signal energy stored in step340, by which a relative measure is obtained for the structure-borne-noise-signal energy.

Finally, in query370, a threshold-value comparison is carried out, in which the relative measure for the structure-borne-noise-signal energy is checked with respect to the exceeding of a specifiable threshold value. If this is not the case, the method branches to step380which, just like method step350, provides for a further increase in the activation period according to the predefined test scheme. Thereupon, the method again branches to step310, which leads to the implementation of a third test activation, etc.

If the query in method step370reveals that the relative structure-borne-noise-signal energy mass from step360exceeds the specifiable threshold value, the method branches to step390in which, based on the exceeding of the threshold value, it is inferred that in response to the instantaneous test activation, an event has occurred in injection valve100causing a sufficiently strong structure-borne-noise signal S, e.g., the striking of valve needle110in its valve seat. Such an impact of valve needle110is only obtained after a sufficiently great activation period for electromagnetic actuator102,104, during which actuator102,104initially lifts valve needle110from its valve seat, so that after the activation period, it is moved back into its valve seat under the effect of the spring force of valve spring106.

Given suitable selection of the test scheme for the increase of the activation period, the method described above with reference toFIG. 4permits a very precise ascertainment of the minimal activation period necessary for a fuel injection. Namely, only when the activation period is selected to be so great that valve needle110is actually moved out of its valve seat, is it possible for fuel44(FIG. 1) to be injected by injection valve100. However, due to the above-described backward movement of valve needle110into its closed position in the area of the valve seat, the structure-borne-noise signal results in this case, as well.

FIG. 5shows the variable E, ascertained during the execution of step360(FIG. 4) and representing an energy of the structure-borne-noise signal, plotted over the parameter activation period ti. The diagram ofFIG. 5is obtained during an implementation of the method according toFIG. 4using a constant increment for activation period ti.

As soon as signal E illustrated inFIG. 5exceeds specifiable threshold value E1for the first time—starting from the minimal value for activation period ti—in it is inferred in step370of the method according toFIG. 4that activation period ticorresponding to it has been selected to be great enough to bring about a fuel injection.

That is, the activation periods where ti≦ti1are interpreted as not already resulting in a fuel injection. All activation periods where ti≦ti1are regarded by the evaluation as great enough to reliably bring about a fuel injection100.

Accordingly, the operational method described above advantageously makes it possible to very precisely ascertain an actual minimal activation period ti1, also denoted as pickup time, for a real injection valve100. Consequently, in particular, especially small quantities of fuel may be injected far more precisely than when using conventional systems which utilize a predefined standard injection period that possibly does not take into account the particular properties of injection valve100considered, especially its wear, etc.

FIGS. 6a,6b, and6cshow the time characteristic of structure-borne-noise signals as ascertained during three test activations310(FIG. 4) using different activation periods ti=0, ti<ti1, ti>=ti1. It is apparent from the signal amplitudes in diagrams6a,6bthat the structure-borne-noise signals in question exhibit no relatively great signal energy. In contrast, the structure-borne-noise signal portrayed inFIG. 6cexhibits markedly greater amplitude values, so that it may be inferred that in the case of this test activation, activation period tihas been great enough to bring about a lifting of valve needle110off of its valve seat and a subsequent striking of valve needle110on its valve seat, consequently, a fuel injection.

The scenarios shown inFIGS. 6a,6b, and6ceach correspond to one measured value of the diagram illustrated inFIG. 5.

To further increase the precision of the method, in each case, a plurality of test activations310may also be carried out using the same activation period ti, so that the results of the evaluation may be supported on averaged data, and are therefore correspondingly more precise.

Alternatively or in addition to a pure threshold-value comparison (see step370fromFIG. 4) of variable E representing the energy of the structure-borne-noise signal, the characteristic shown inFIG. 5, as obtained during several cycles of the method according toFIG. 4, may also be evaluated to deduce the presence of a relevant event generating structure-borne noise. In particular, characteristic (variable) E may be analyzed for local extrema, for a deviation from a specifiable reference characteristic, etc. Specifiable threshold value E1may also be determined particularly advantageously relative to other values of the curve shown inFIG. 5, for example, to such values for variable E which are obtained for ti=0 or a maximum considered activation period ti.

As already described, as a test scheme for specifying respective activation period tifor a corresponding test activation, in particular, an intelligent search function may also be used as a basis, in which, for example, the step size or the increment for increasing activation period tiis altered logarithmically. For instance, a vanishing activation period or a non-vanishing, minimally specifiable activation period may be selected as activation period for the first test activation. Accordingly, for a second test activation, an activation period may be selected, for example, that corresponds to half the maximum activation period which is predefined for implementing the method. Correspondingly, as activation period for a further test activation, a value may be selected which corresponds to 150% of the previous value, and so forth.

Based on the minimal activation period, i.e., the pickup time, ascertained as described above, it is possible to calibrate an injection characteristic curve stored in control unit46(FIG. 1) for injection valve100. This may be accomplished, for instance, by shifting the characteristic curve, stored at the beginning in control unit46, in accordance with the minimal activation period ascertained.

In the case of an internal combustion engine10having a plurality of cylinders12, preferably the calibration of the injection characteristic curve may be carried out simultaneously for injection valves100of all cylinders12. It is possible to apply the method to different injection valves100of internal combustion engine10in succession.

In addition to recognizing the striking of valve needle110in its valve seat, using the operational method, it is also possible to recognize the striking of magnet armature104on its upper stop inFIG. 2in the area of magnet coil102. A suitable method variant is illustrated by the flow chart indicated inFIG. 7.

In a first step400, the activation period for the first test activation is already selected to be great enough that magnet armature104(FIG. 2) executes a lift which is as close as possible to its maximum possible full lift, in which magnet armature104actually strikes the upper lift stop. This activation period may be ascertained especially advantageously as a function of a pickup time obtained beforehand.

Subsequently in step410, the first test activation is carried out, and a structure-borne-noise signal S resulting in so doing is recorded. In step420, a variable is calculated which characterizes the energy of structure-borne-noise signal S, and which advantageously may in turn be related to an interference-signal energy ascertained beforehand.

A threshold-value comparison comparable to step370(FIG. 4) is carried out according toFIG. 7in step430. In this step430, it is analyzed whether structure-borne-noise signal S obtained during previous test activation410already has sufficiently great energy so that it is possible to infer the striking of magnet armature104on its upper lift stop.

If this is not the case, the activation period is increased—see step440—and a new method cycle410,420is performed.

Otherwise, the method branches directly from step430to step450, which corresponds to the reaching of a full lift by magnet armature104.

A particularly simple and precise evaluation for recognizing the striking of magnet armature104on its upper lift stop may be carried out by selecting the detection time range for structure-borne-noise signal S to be evaluated, so that the detection time range does not include the actual instant valve needle110strikes its valve seat. This ensures that the structure-borne-noise signals arising in this connection are not mistakenly interpreted as structure-borne-noise signals such as occur when magnet armature104strikes its upper lift stop.

Moreover, it is also possible to apply separation algorithms to acquired structure-borne-noise signal S, which detect, for example, whether just one closing noise (striking of valve needle110on valve seat) or two noise events (full lift of magnet armature104and striking of valve needle110on valve seat) are occurring, and which permit a separation of the corresponding signal components.

The minimal activation period actually necessary for reaching the upper lift stop of magnet armature104may be used, just like the pickup time ascertained, for calibrating the injection characteristic curve of injection valve100.

The operational method is carried out exceedingly advantageously at different operating points, e.g., at different fuel-pressure values, so that a precise operation of injection valve100is possible over a large operating range using the injection characteristic curve.

On one hand, the operational method may be carried out particularly advantageously during a regular operation of injection valve100, in order to evaluate structure-borne-noise signals occurring in this context.

The implementation of the operational method using separate test activations is possible—see the variants of described with reference toFIGS. 4,7.

In general, it is advantageous to position the test activations in time such that the structure-borne-noise signals to be evaluated are as free as possible from interference signals. For example, the test activations and the suitably selected detection time ranges for sensing structure-borne-noise signals S resulting in this context may be selected such that structure-borne-noise signals generated by a valve operation of internal combustion engine10or by other components do not fall in the detection time ranges considered.

Furthermore, it is especially advantageous to carry out the method at relatively low speeds of internal combustion engine10, particularly at speeds below one half the maximum speed of internal combustion engine10, optimally at approximately 500 to 1500 revolutions per minute, because the signal to noise ratio for the evaluation of the structure-borne-noise signals is particularly great in the low speed range.

The calibration, that is, the formation or modification of control variables for future activations as a function of the evaluation of structure-borne-noise signal S may advantageously be carried out during the entire operating time of injection valve100.

Alternatively or additionally, the calibration may also be carried out during special calibration phases, for example, at the end of a manufacturing process of injection valve100and/or of an internal combustion engine10containing injection valves100considered or during an inspection or servicing. This variant offers the advantage that, in contrast to a normal operation of internal combustion engine10, particularly favorable operating parameters (e.g., speed, reduction of other interference signals) exist or may be set for the evaluation of structure-borne-noise signals S. In particular, a test activation may also be carried out in an after run or even during a standstill of internal combustion engine10, provided, for example, a sufficient fuel pressure is still present in this case to ensure the transferability of the knowledge obtained to the normal operation.

At the end of the manufacturing process of injection valve100, the method may be carried out both within the framework of a wet test, i.e., with injection valve100already filled, and within the framework of a dry test, i.e., in an unfilled state of injection valve100, the possibility of the dry test in particular representing a less costly test method.

To ensure a torque-neutral implementation of the test activations during a normal operation of internal combustion engine10, corresponding fuel quantities of the test activations may be subtracted from a remaining main injection.

Structure-borne-noise signals S may be detected by a plurality of structure-borne-noise sensors48. The structure-borne-noise signals coming from individual structure-borne-noise sensors48may advantageously be evaluated together, in order to make it possible, for instance, to determine the plausibility of the acquired signals. Moreover, based on the customarily known mounting locations of structure-borne-noise sensors48in internal combustion engine10, particularly also in relation to the mounting locations of injection valves100, by comparing the structure-borne-noise signals of different structure-borne-noise sensors48, it is even possible to make observations concerning propagation time, where from a corresponding phase shift between the structure-borne-noise signals, it is possible to infer their distance to a corresponding structure-borne-noise-signal source, that is, for example, an injection valve100.

Injection valve100may be assigned its own structure-borne-noise sensor, which preferably is disposed directly in the area of injection valve100or even on injection valve100. In this configuration, only a minor influence of interference signals results on the evaluation of the structure-borne-noise signals.

In addition to being used to calibrate individual injection valves100, the method described herein may also be used advantageously for the equalization of a plurality of injection valves100of an internal combustion engine10.

In general, the method permits a precise sensing of the actual operating state of an injection valve100, and with that, advantageously, an adjustment of the driving of injection valve100in order to compensate for aging-induced effects (wear, coking, etc.) as well as inexactness in a control path for the control current, etc.