DE19714610A1 - Charging and discharging piezoelectric element, e.g for fuel injector of IC engine - Google Patents

Abstract

The procedure for charging and discharging a piezoelectric element (11) has at least the charging or the discharging taking place at least partly by displacement of charges between the element to be charged or discharged and one or more elements not to be charged or discharged. The displacement of the charges takes place by intermediate storage of their energy in an element (5) working as an inductance. This element is a coil, actually a transformer. The charging and discharging of the piezoelectric element take place through the same element working as an inductance. During the running of the device for executing the procedure, or after the charging and discharging, a preliminary or subsequent charging is executed in which the existing piezoelectric energy is charged up to a voltage that is less than a threshold, from which thereafter the elements can work as actuators or control elements.

Description

The present invention relates to a method according to the Preamble of claim 1 and a device according to the preamble of claim 11, d. H. a procedure and a device for loading and unloading a piezo electrical element.

In the case of the piezoelectric elements considered in more detail here elements are particularly, but not exclusively Lich around piezoelek used as actuators or actuators trical elements. Piezoelectric elements can be used for use such purposes because they are known to Have property depending on one of them contracting or expanding applied voltage.

The practical realization of actuators by piezo electrical elements prove particularly then from before part if the actuator in question quickly and / or frequently has to make cautious movements.

The use of piezoelectric elements as an actuator proves itself among other things with fuel injectors for Internal combustion engines as advantageous. The applicability of  piezoelectric elements in fuel injectors for example EP 0 371 469 B1 and EP 0 379 182 B1 referred.

Piezoelectric elements are capacitive consumers, which itself, as has already been partially indicated above speaking of the respective state of charge or of it contracting or applying voltage and expand.

For loading and unloading a piezoelectric element known two basic principles, namely charging and Discharging through an ohmic resistor or charging and Discharge via a coil, with both the ohmic resistance as well as serving the coil, among other things, when charging occurring charging current and that occurring during discharging Limit discharge current.

The first variant, that is to say charging and discharging via an ohmic resistor, is illustrated in FIG. 5.

The piezoelectric element to be charged or discharged, which is designated in FIG. 5 with the reference number 101 , is connected to a charge transistor 102 and a discharge transistor 103 .

The charging transistor 102 is driven by a charging amplifier 104 and connects the piezoelectric element 101 with a positive supply voltage in the on state; The discharge transistor 103 is controlled by a discharge amplifier 105 and connects the piezoelectric element 101 to ground in the switched-on state.

In the switched-on state of the charging transistor 102 , a charging current flows through it, through which the piezoelectric element 101 is charged. With increasing charge of the piezoelectric element 101 , the voltage at this setting increases, and accordingly its outer dimensions also change. A blocking of the charging transistor 102 , that is, an interruption or termination of the charging process, causes the charge stored in the piezoelectric element 101 or the voltage resulting therefrom and therefore also the current external dimensions of the piezoelectric element 101 to be retained essentially unchanged .

In the switched-on state of the discharge transistor 103 , a discharge current flows through it, through which the piezoelectric element 101 is discharged. With increasing discharge of the piezoelectric element 101 , the voltage which is established thereon decreases, and accordingly its external dimensions also change. Disabling of the Ent charge transistor 103, causing thus interrupting or stopping of the discharge, that the 101 still stored charge element in the piezoelectric Ele and which thereby adjusting voltage and hence the current external dimensions of the piezoelectric element to be kept at 101 thereto.

The charging transistor 102 and the discharging transistor 103 act like controllable ohmic resistors for the charging current and for the discharging current. The controllability of the charging current and the discharging current which this gives enables the charging process and the discharging process to be carried out exactly as desired. However, the charging current flowing through the charging transistor 102 and the discharging current flowing through the discharging transistor 103 generate not inconsiderable power losses there. The loss of energy consumed in the transistors per charging / discharging cycle is at least twice as high as the energy stored in the piezoelectric element 101 . This high loss energy causes the charging transistor 102 and the discharging transistor 103 to heat up very strongly, which is clearly a disadvantage.

The loading and unloading procedure under consideration is therefore in particular especially when frequent and / or extensive loading and Unloading operations are to be carried out, either completely usable or only usable to a limited extent.

Not least because of this, the above-mentioned second variant for loading and unloading the piezoelectric element, ie loading and unloading via a coil, is often used; a practical implementation of this two-th variant is illustrated in Fig. 6.

The piezoelectric element to be charged or discharged, which is designated in FIG. 6 with the reference number 201 , is part of a charging circuit which can be closed via a charging switch 202 and a discharging circuit which can be closed via a discharging switch 206 , the charging circuit comprising a series circuit of the charging switch 202 , a diode 203 , a charging coil 204 , the piezoelectric element's 201 , and a voltage source 205 , and wherein the discharge circuit consists of a series circuit of the discharge switch 206 , a diode 207 , a discharge coil 208 and the piezoelectric element 201 .

The diode 203 of the charging circuit prevents a current that discharges the piezoelectric element from flowing in the charging circuit. The diode 203 and the charge switch 202 can be realized together as a semiconductor switch.

The diode 207 of the discharge circuit prevents the piezoelectric element charging current from flowing in the discharge circuit. The diode 207 and the discharge switch 206 , like the diode 203 and the charge switch 202, can be implemented together as a semiconductor switch.

If the normally open charging switch 202 is closed, a charging current flows through the charging circuit, through which the piezoelectric element 201 is charged; the electrical charge stored in the piezoelectric element 201 or at this thereby adjusting voltage and thus also the ak tual external dimensions of piezoelectric element 201 are substantially changed unverän after loading thereof maintained.

If the normally open discharge switch 206 is closed, a discharge current flows through the discharge circuit through which the piezoelectric element 201 is charged; the state of charge of the piezoelectric element 201, which at this voltage by adjusting the current and thus also the external dimensions of the piezoelectric element 201 are after unloading thereof maintained substantially unchanged.

Since circuits according circle of FIG. 6, both the charging current and the discharging circuit are free from appreciable ohmic resistances is generated by loading and unloading load of the piezoelectric element (which stands by the flow of the charging current and the discharge current through ohmic Wider) Thermal energy extremely low.

On the other hand, rela tively a lot of space is required for the practical implementation of the like circuits, in particular because of the not inconsiderable size of the charging coil 204 and the discharge coil 208 , as a result of which the charging and discharging of piezoelectric elements via coils in certain cases is not, or at least not readily is possible.

Circuits of the type shown in FIG. 6 and methods for charging and discharging piezoelectric elements using such circuits are known from the publications EP 0 371 469 B1 and EP 0 379 182 B1 already mentioned at the beginning.

The piezoelectric with reference to FIGS. 5 and 6, the more basic the principle according to described methods and apparatus for loading and unloading elements are Ver drive according to the preamble of claim 1 and Prior devices according to the preamble of patent claim 11.

The known methods and devices have in common that especially when the load and unload Piezoelectric elements can be quickly charged and discharged should, for at least briefly, very high loading and unloading currents must be designed. One consequence of this is that the Supply voltage sources are appropriately large have to be. This can be especially true if there are a variety of the known devices is to be provided to a variety of being able to charge or discharge piezoelectric elements NEN, a not inconsiderable size of the arrangement to have. Because of this, the use of piezo electrical elements as actuators or actuators under cramped conditions as difficult or completely impossible prove. This is clearly a disadvantage that it has to be eliminated applies.

The present invention is therefore based on the object the method according to the preamble of claim 1 or the device according to the preamble of the patent entit 11 to develop such that thereby also under cramped conditions for efficient loading and unloading piezoelectric elements is made possible.  

According to the invention, this object is characterized by the the part of claim 1 (method) and by the in characterizing part of claim 11 (device) claimed features solved.

Accordingly, it is provided

• - That at least either loading or unloading at least partly by moving loads between them charging or discharging piezoelectric element and one or several piezoelek not to be loaded or unloaded trical element (s) (characteristic part of the Pa claim 1) or
• - That means are provided which enable that at least either loading or unloading at least partially moving cargo between the charging or discharging piezoelectric element and one or several piezoelek not to be loaded or unloaded tric element (s) can take place (characteristic part of the Claim 11).

The piezoelectric elements are therefore not only as Actuators or actuators, but also as charge stores used.

Exploiting the charge storage function of the piezoelectric elements makes it possible to load a load Piezoelectric element no longer or at least not more completely directly via the supply voltage source, but at least partially by fetching in Piezoelectric elements not to be loaded To carry out loads, of which not to be loaded Piezoelectric elements brought charges on Ent load the piezoelectric element to be charged back there  can be restored.

The use of the piezoelectric elements as a charge memory causes no fluctuations in their dimensions, when the piezoelectric elements are mechanically biased are; on a mechanical preload can be whole or in part be wisely waived if the use of the Piezoelectric elements occurring as charge storage Dimensional changes are not sufficient to the piezoelek trical elements act as actuators or actuators to let.

Ideally, that is when there is no energy in the reloading process would be lost and if the piezoelectric elements in there would be a number that is sufficient to "only" before charged state to store so many charges that these, when reloaded into a piezoelectric element to be charged will be sufficient to complete this or at least would load the supply voltage as desired source only needed to add the piezoelectric elements preload the commissioning of the arrangement; the later (sequential or simultaneous) loading and unloading any ger single or several of the existing piezoelectric Elements could then only be replaced by a corresponding one Reloading or moving the existing loads. Initial precharging of the piezoelectric elements the supply voltage source can, since the piezoelek trical elements at this point not yet as actuators or actuators must act relatively slowly go, causing the supply voltage source not even must be designed for short-term high performance and that can be made correspondingly small.

This also applies in the event that the aforementioned ideal conditions do not exist, the supply  voltage source during the operation of the arrangement for a more or less extensive reloading of the piezoelek trical elements must worry; even then the utility voltage source by far not for the performances be interpreted, which would have to be provided if the loading and discharging the piezoelectric elements without charge ver shift between the existing piezoelectric elements would take place.

The supply voltage source can therefore be of a size be reduced to a minimum. In addition, a buffer condensers connected to the supply voltage source sator can be reduced or omitted.

A method and a device have therefore been found through which it is easily possible, even under be efficient loading and unloading perform.

Advantageous developments of the invention are the subject of subclaims.

The invention is described below with reference to exemplary embodiments len explained with reference to the drawing. It demonstrate

Fig. 1 shows a first embodiment of a loading and unloading of piezoelectric elements by the novel process according to Inventive suitable circuit,

Fig. 2 shows the time course of in operation of the circuit of FIG. 1-adjusting voltage and current profiles,

Fig. 3 shows a second embodiment of a loading and unloading of piezoelectric elements by the novel process according to Inventive suitable circuit,

Fig. 4 shows the time course of in operation of the circuit of FIG. 3-adjusting voltage and current profiles,

Fig. 5 is a conventional circuit for charging and discharging a piezoelectric element via acting for the charging and discharging current as ohmic resistances elements, and

Fig. 6 shows a conventional circuit for charging and discharging a piezoelectric element via acting for the charging and discharging current as coil elements.

The piezoelectric elements, their loading and unloading in the the following is described in more detail, for example as Actuators in fuel injectors (especially in so-called common rail injectors) of internal combustion engines applicable. On such use of the piezoelectric However, there are no restrictions to elements; the piezoelectric elements can basically be used in any Devices can be used for any purpose.

It is assumed that what is to be loaded in each case resp. discharging piezoelectric element in response the loading expands and in response to the unloading pulls together. The invention is of course also applicable when this is the other way round.

If before or later from a "to be charged" piezoelectric  element is usually mentioned understand that the piezoelectric element in question is to charge heavily that it as a result of the caused Expansion of the same can act as an actuator or actuator. Although, as described in detail below will be, also in this sense, not "to be loaded" piezo electrical elements are charged, but one must any expansion caused the same so lead ben that the relevant piezoelectric elements still cannot act as an actuator or actuator.

Conversely, unloading "to be unloaded" piezoelectric elements usually understand that piezoelectric elements that are so strongly charged that they can act as an actuator or actuator, from their active State to be inactive, in which chem they can no longer act as an actuator or actuator. Although, as described in detail below will also discharge inactive piezoelectric elements , but this does not cause the transition from active in the inactive state.

The piezoelectric elements by the following described devices and methods loaded and ent are more or less mechanical biased. As a result, they do not stretch during a pre-loading and / or reloading described in more detail out; before they expand and as an actuator or actuator they must be able to work (naturally without changing their Dimensions) overcome the preload.

Additionally or alternatively, the piezoelectric rule elements be arranged so that one during Size change occurring before or after loading no or in any case no significant impact on the  system containing piezoelectric elements that Piezoelectric elements not yet as an actuator or Actuator can act.

A first exemplary embodiment of the circuit according to the invention for carrying out the method according to the invention for charging and discharging a piezoelectric element will now be described with reference to FIG. 1.

The piezoelectric element that it is in the example considered To be loaded or unloaded in each case is one from one Variety of piezoelectric elements that successively load and unload.

The piezoelectric elements, from which the piezoelectric element to be charged and discharged is selected in each case, are arranged in parallel piezo branches 11 , 12 ,. . . 1 n contain and with the reference numerals 11 ₁ , 12 ₁ . . . 1 n ₁ denotes net.

Of the piezoelectric elements 11 ₁ , 12 ₁ . . . 1 n ₁ may the piezoelectric element 11 ₁ for controlling an injection nozzle assigned to a first cylinder of an internal combustion engine, the piezoelectric element 12 ₁ for controlling an injection nozzle assigned to a second cylinder of an internal combustion engine, and the piezoelectric element 1 n ₁ for controlling a one Serve n-th cylinder of an internal combustion engine-associated injection nozzle. The piezoelectric elements are therefore successively charged and discharged in a predetermined order.

Each of the piezo branches 11 , 12 ,. . . 1 n contains in series with the respective piezoelectric element 11 ₁ , 12 ₁ . . . 1 n ₁ a selection switch 11 ₂ , 12 ₂ ,. . . 1 n ₂ with diode 11 ₃ , 12 ₃ , connected in parallel. . . 1 n ₃ . Via the selector switches 11 ₂ , 12 ₂ ,. . . 1 n _{2 it} can be determined whether the piezoelectric element 11 ₁ , 12 ₁ contained in the respective piezo branch 11 , 12 , 1 n. . . 1 n ₁ should be charged during a charging process (assigned selector switch closed) or not (assigned selector switch open).

The selection switches 11 ₂ , 12 ₂ ,. . . 1 n ₂ and the diodes 11 ₃ , 12 ₃ , arranged in parallel thereto. . . 1 n ₃ can each be implemented as an electronic switch with parasitic diodes such as MOS-FETs.

In addition to the piezo branches 11 , 12 ,. . . 1 n contains the circuit shown in FIG. 1, a supply voltage source consisting of a battery 2 and a DC voltage converter 3 , a capacitor 4 , an element acting as an inductance in the form of a coil 5 , a precharge switch 6 a with a diode 6 b connected in parallel , a first main charge and discharge switch 7 , a second main charge and discharge switch 8 and diodes 9 and 10 .

The precharge switch 6 a and the diode 6 b arranged in parallel thereto can be implemented by an electronic switch with a parasitic diode, such as a MOS-FET.

By said supply voltage source (battery 2 with a downstream DC converter 3 ), the voltage of the battery (for example the 12 V of a motor vehicle battery) is converted into an essentially any other DC voltage and is provided as a supply voltage.

The further structure of the circuit shown in FIG. 1 can be most easily written and understood based on its function and mode of operation during loading and unloading of one of the piezoelectric elements.

The function and operation of the circuit of FIG. 1 will now be described with reference to the charging and discharging of the piezoelectric element 11 _1.

The starting point of the considerations is a state in which all Liche switch opened and the piezoelectric elements and the capacitor are essentially discharged.

The charging of the piezoelectric element 11 ₁ takes place in two stages, more precisely in a precharging stage and a main charging stage that follows immediately or at any time thereafter.

The precharge stage is by closing the precharge switch 6 a and the selector switch 11 ₂ , 12 ₂ ,. . . 1 n ₂ initiated. Closing said switch causes the condenser 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ connected in parallel and connected to the DC-DC converter 3 . As a result, the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ charged to a first (low) voltage.

Said first voltage is dimensioned such that on the one hand the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ do not yet act as actuators or actuators, and that on the other hand the thereby in the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ stored energy is sufficient to charge one of the piezoelectric elements completely (as desired).

After this precharging of the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ , the precharge switch 6 a and the selection switches 11 ₂ , 12 ₂ ,. . . 1 n ₂ opened again. Since the capacitor 4 and the piezoelectric elements 11 , 12 ₁ ,. . . 1 n ₁ separated from each other and from the DC converter 3 .

The in the capacitor 4 and in the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ stored charges remain essentially unchanged there.

Starting from this state, the complete charging of the piezoelectric element 11 ₁ (or any other of the piezoelectric elements) can now be carried out at any time. This takes place in the main charging stage already mentioned above.

The main charging stage consists of two steps; it, more precisely ge says the first sub-step of the same is initiated by closing the first main charge and discharge switch 7 and the second main charge and discharge switch 8 . The closing of said switch causes the formation of a first and a second closed Umladestromkreises, wherein the he ste Umladestromkreis of a series circuit of Kondensa gate 4, the diode 6 is b and the coil 5, and wherein the second Umladestromkreis of a parallel circuit pa rallelen the Piezo branches 11 , 12 ,. . . 1 n and the coil 5 there .

In the recharging circuits, a (reloading) current flow is established by closing the same, through which the capacitor 4 and in the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ stored charges (stored electrical energy) flow to the coil 5 and are stored there in the form of magnetic energy. The coil 5 is preferably dimensioned so that the total electrical energy of the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ . . . 1 n ₁ can be stored in this. If the total elec trical energy or a lot of energy from the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ , as desired. . . 1 n _{1 is transferred} into the coil 5 , the first main charge and discharge switch 7 and the second main charge and discharge switch 8 are opened again.

When the first main charging and discharging switch 7 and the second main charging and discharging switch 8 open, the first main charging stage sub-step ends and the second main charging stage sub-step begins.

Simultaneously with the opening of the first main charging and discharging switch 7 and the second main charging and discharging switch 8 or before, the selection switch of the piezoelectric element to be charged, in the example considered the piezoelectric element 11 ₁ associated with selector switch 112 is closed; thereby a closing of the piezoelectric element 11 ₁ , the diode 9 , the coil 5 and the diode 10 containing charging circuit will be effective.

In this charging circuit, the opening of the main charging and discharging switch 7 and the second main charging and discharging switch 8 is a (charging) current flow through which the energy stored in the coil 5 into the piezoelectric element 11 to be loaded _{1 is} reloaded.

The piezoelectric element closes due to the charge current flow increasingly loaded, which means that the Tension and its external dimensions increase. As at the beginning has already been hinted at is the piezoelectric element mechanically biased or arranged so that it is only now (in the second main charging step) as an actuator or Actuator can act; in the initial precharge stage the dimensions of the piezoelectric element remained constant  constant (if it is mechanically preloaded) or changes the dimensions without affecting the to be operated or element to be adjusted (if the piezoelectric element is so it is ordered that a certain minimum extent of the same must be reached before actuating or adjusting the to be actuated or adjusting element).

When the energy stored in the coil 5 has been completely or, as desired, largely stored in the piezoelectric element to be charged, the selection switch 11 ₂ and thus also the charging circuit are opened again. This completes the second main charging step and the entire charging process.

In this state, the piezoelectric element 11 ₁ (or another of the piezoelectric elements) is substantially fully charged (as desired, far), while the other piezoelectric elements and the capacitor 4 are essentially completely discharged.

The charges stored in the piezoelectric element 11 ₁ , the voltage resulting from this at the piezoelectric element and the dimensions of the piezoelectric element remain essentially unchanged at this stage (until they are discharged).

The discharge of the piezoelectric element takes place like the main charging stage in two steps; it, more precisely ge says the first partial discharge step is initiated by closing the first main charge and discharge switch 7 and the second main charge and discharge switch 8 . Closing these switches causes the first and second recharging circuits to be closed again.

As a result, a (charge) current flow is established in the charge-reversal circuits, through which the charges (stored electrical energy) stored in the charged piezoelectric element 11 ₁ flow via the diode 11 ₃ to the coil 5 and are stored there in the form of magnetic energy. The coil 5 is preferably dimensioned so that the entire electrical cal energy of the charged piezoelectric element 11 ₁ can be stored in this.

By reloading, the voltage setting on the piezoelectric element 11 ₁ and the external dimensions decrease.

When all of the electrical energy of the piezoelectric element 11 _{1 is transferred} into the coil 5 , the first main charge and discharge switch 7 and the second main charge and discharge switch 8 are opened again.

When the first main charge and discharge switch 7 and the second main charge and discharge switch 8 open, the first partial discharge step ends and the second partial discharge step begins.

Simultaneously with the opening of the first main charging and discharging switch 7 and the second main charging and discharging switch 8 or before, the precharging switch 6 a and all selection switches 11 ₂ , 12 ₂ ,. . . 1 n ₂ closed; thereby the energy stored in the coil 5 in the condenser 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n _{1 can be} reloaded.

When the energy stored in the coil 5 is recharged, the discharge process is ended.

The precharge switch 6 a and the selection switch 11 ₂ , 12 ₂ ,. . . 1 n ₂ , however, remain open for a short time so that the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ can be charged to the first voltage as in the precharge stage. This reloading, which is similar to precharging, is necessary because loading and unloading the piezoelectric elements can be done with little loss, but not entirely without loss.

If the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ are charged to the first voltage, who the precharge switch 6 a and the selector switch 11 ₂ , 12 ₂ ,. . . 1 n ₂ opened again. The arrangement is thus prepared for a next main charging stage for charging the same or a different one of the piezoelectric elements.

If you operate the circuit shown in FIG. 1, more precisely the charging and discharging of one of the existing piezoelectric elements as described above, the current and voltage curves shown in FIG. 2 are established. The current and voltage curves shown are the result of a simulation in which the piezoelectric elements were modeled as pure capacities.

The curves shown at the top and in the middle of FIG. 2 are provided with symbols representing their measured variables. Represent from the symbols used

the voltage U _{p1 occurring} at the piezoelectric element 11 ₁ ,
◊ the voltage U _p2 established at the piezoelectric element 12 ₁ ,
∇ the voltage U _pn occurring at the piezoelectric element 1 n ₁ ,
○ the (recharging) current flowing through the coil 5 .

The respective switch positions are illustrated in the diagram shown in FIG. 2 below.

The current and voltage profiles shown in FIG. 2 illustrate the charging process (more precisely, the first main charging stage sub-step in the range from approximately 75 μs to 250 μs on the time scale, the second main charging stage sub-step in the range from approximately 250 μs to 350 μs) the time scale, and the precharge or reload level in the range of approximately 600 µs to 775 µs on the time scale) and the discharge process (more precisely the first partial discharge step in the range of approximately 500 µs to 600 µs), and the (with the - or reloading step (coinciding) second partial discharge step in the range from about 600 µs to 775 µs) of a piezoelectric element; the current and voltage curves shown are readily understandable given the knowledge of the structure, function and mode of operation of the circuit shown in FIG. 1 and do not require any further explanation.

As can be seen from FIG. 2, the voltage which arises at the piezoelectric element to be charged and discharged has an extremely homogeneous course.

At the same time, the circuit by which the loading and unloading is effected, more precisely the circuit according to FIG. 1 is extremely simple and optimal in efficiency. Four factors in particular contribute to this, namely

• 1) that the loading and unloading of the piezoelectric elements essentially done by reloading,
• 2) that a large number of piezoelectric elements can be charged and discharged via a single output stage (circuit according to FIG. 1),
• 3) that the loading and unloading takes place via one and the same coil (namely coil 5 ), and
• 4) negligible heat generation in ohmic resistors bar is low.

The first point makes it possible to keep the energy to be given off by the supply voltage source low, and high loads can also be avoided for a short time. Since the supply voltage source, more precisely the battery 2 and the DC-DC converter 3 can be designed for only relatively small powers and can therefore be made relatively small in construction. Due to the fact that the reloading takes place at least partially between the existing piezoelectric elements, the capacitor 4 can also be made very small or even completely eliminated. This is advantageous insofar as power capacitors in the automotive sector are critical components (low shaking capacity, short service life at high temperatures).

The second and third of the above points are possible Chen it, the number of components, especially the number to keep the inherently relatively large coils to a minimum where recognizable further minimization of the circuit can achieve size.

The fourth of the above points can on the one hand energy consumption kept low and on the other hand on Cooling measures are dispensed with, which can also be seen advantageous to the size of the arrangement under consideration works.

All of the points mentioned - be it alone or in a combination nation - enable or at least contribute to the  for charging and discharging piezoelectric elements to accommodate the circuit in the smallest space and the To keep costs for their production and operation to a minimum.

The circuit of FIG. 1 is modifiable while maintaining their we key functions, and mode of operation in several respects. One of the possible modifications is illustrated in FIG. 3.

Fig. 3 shows a second embodiment of an inventive circuit for performing the inventive method.

The circuit shown in FIG. 3 corresponds in part to the circuit shown in FIG. 1 and already described in detail above; Corresponding elements are identified by the same reference symbols.

The difference between the circuits according to FIGS. 1 and 3 consists essentially in that the loading and unloading of a piezoelectric element Ver shifting of charge carriers to be charged or to be loaded from the piezoelectric element ent in the circuit according to FIG. 1st via the coil 5 , and in the circuit according to FIG. 3 via a transformer 15 .

The piezoelectric element to be charged or discharged is in turn a piezoelectric element selectable from a plurality of piezoelectric elements, the many piezoelectric elements as in the circuit according to FIG. 1 in parallel piezo branches 11 , 12 ,. . . 1 n contain and with the reference numerals 11 ₁ , 12 ₁ ,. . . 1 n _{1 are} designated.

Each of the piezo branches 11 , 12 ,. . . 1 n also contains off selector switch 11 ₂ , 12 ₂ ,. . . 1 n ₂ with diodes 11 ₃ , 12 ₃ , arranged in parallel. . . 1 n ₃ .

The supply voltage source is in turn formed by a battery 2 (for example a motor vehicle battery) and a downstream DC / DC converter 3 , where the DC / DC converter 3 converts the battery voltage (for example 12V) into any other DC voltage.

The circuit according to FIG. 3, in accordance with the circuit according to FIG. 1, also has the known capacitor 4 , the precharge switch 6 a and the diode 6 b.

Up to this point, the circuits according to FIGS. 1 and 3 are identical.

In contrast to the circuit according to FIG. 1, the circuit according to FIG. 3 has, in addition to the elements mentioned, the transformer 15 already mentioned above, a main charge and discharge switch 16 and diodes 17 and 18 , which are connected as shown in FIG. 3 are.

The structure of the circuit according to FIG. 3 can be described and understood most simply based on its function and mode of operation during charging and discharging of one of the piezoelectric elements.

The function and the mode of operation of the circuit according to FIG. 3 will now be described with reference to the charging and discharging of the piezoelectric element 11 ₁ .

The starting point of the considerations is a state in which all Liche switch opened and the piezoelectric elements and the capacitor are essentially discharged.

The loading of the piezoelectric element 11 ₁ takes place in two stages, more precisely in a precharging stage and a main charging stage which follows immediately or at any time thereafter.

The precharge stage is by closing the precharge switch 6 a and the selector switch 11 ₂ , 12 ₂ ,. . . 1 n ₂ initiated. Closing said switch causes the condenser 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ connected in parallel and connected to the DC-DC converter 3 . As a result, the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ charged to a first (low) voltage.

Said first voltage is dimensioned such that on the one hand the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ do not yet act as actuators or actuators, and that on the other hand the thereby in the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ stored energy is sufficient to fully charge one of the piezoelectric elements (as desired).

After charging the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ to the first voltage, the precharge switch 6 a and the selection switches 11 ₂ , 12 ₂ ,. . . 1 n ₂ opened again. As a result, the capacitor 4 and the piezoelectric elements 11 , 12 ₁ ,. . . 1 n ₁ separated from each other and from the DC converter 3 .

The in the capacitor 4 and in the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1n ₁ stored charges remain essentially unchanged there.

Starting from this state, the complete charging of the piezoelectric element 11 ₁ (or any other of the piezoelectric elements) can now be carried out at any time. This takes place in the main charging stage already mentioned above.

The main charging stage consists of two steps; it, more precisely ge says the first part of the same step is initiated by closing the main charge and discharge switch 16 . The closing of this switch causes the formation of a he sten and a second closed Umladestromkreises, where in the first Umladestromkreis of a series circuit of the capacitor 4, the diode 6 b, the diode 17 and a first winding of the transformer 15, and wherein the second Umladestromkreis from a series connection of the parallel piezo branches 11 , 12 ,. . . 1 n, the diode 17 and the first winding of the transformer 15 .

In the recharging circuits, a (reloading) current flow is established by closing the same, through which the capacitor 4 and in the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1n ₁ stored charges (stored electrical energy) flow to the transmitter 15 and are stored there in the form of magnetic energy. The transformer is preferably dimensioned so that the total electrical energy of the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1n ₁ can be stored in this. If all or a desired amount of electrical energy from the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1n _{1 is transferred} into the transformer 15 , the main charge and discharge switch 16 is opened again.

When the main charging and discharging switch 16 opens, the first main charging stage sub-step ends and the second main charging stage sub-step begins.

Simultaneously with the opening of the main charging and discharging switch 16 or previously, the selection switch of the piezoelectric element to be loaded, in the example considered the piezoelectric element 11 ₁ associated with the selection switch 11 _{2 is} closed; thereby a closing of the piezoelectric element 11 ₁ , the diode 18 and a second winding of the transformer 15 containing charging circuit is effected.

In this charging circuit, when the main charging and discharging switch 16 opens, a (charging) current flows, through which the energy stored in the transformer 15 is transferred to the piezoelectric element 11 _{1 to be} charged.

The piezoelectric element closes due to the charge current flow increasingly loaded, which means that the Tension and its external dimensions increase. As at the beginning has already been hinted at is the piezoelectric element mechanically biased or arranged so that it is only now (in the second main charging step) as an actuator or Actuator can act; in the initial precharge stage the dimensions of the piezoelectric element remained constant constant (if it is mechanically preloaded) or changes the dimensions without affecting the to be operated or element to be adjusted (if the piezoelectric element is so it is ordered that a certain minimum extent of the same must be reached before actuating or adjusting the to be actuated or adjusting element).  

If the energy stored in the transformer 15 is completely or as desired largely stored in the piezoelectric element to be charged, the selection switch 112 and there with the charging circuit is opened again. This completes the second main charging step and therefore the entire charging process.

In this state, the piezoelectric element 11 ₁ (or another of the piezoelectric elements) is substantially fully charged (as desired, far), while the other piezoelectric elements and the capacitor 4 are essentially completely discharged.

The charges stored in the piezoelectric element 11 ₁ , the voltage resulting from this at the piezoelectric element and the dimensions of the piezoelectric element remain essentially unchanged at this stage (until they are discharged).

The discharge of the piezoelectric element takes place like the main charging stage in two steps; it, more precisely ge says the first discharge sub-step is initiated by closing the main charge and discharge switch 16 . Closing this switch causes the first and second recharging circuits to be closed again.

As a result, a (charge) current flow is established in the charge-reversal circuits, through which the charges (stored electrical energy) stored in the charged piezoelectric element 11 ₁ flow via the diode 11 ₃ to the transformer 15 and are stored there in the form of magnetic energy.

By reloading, the voltage setting on the piezoelectric element 11 ₁ and the external dimensions decrease.

When all the electrical energy of the piezoelectric element 11 _{1 has been transferred} into the transformer 15 , the main charging and discharging switch 16 is opened again.

When the main discharge and discharge switch 16 is opened , the first partial discharge step ends and the second partial discharge step begins.

Simultaneously with the opening of the main charging and discharging switch 16 or before, the pre-charging switch 6 a and all selection switches 11 ₂ , 12 ₂ ,. . . 1 n ₂ closed; thereby the stored energy in the transformer 15 in the condenser 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n _{1 can be} reloaded.

When the energy stored in the transformer 15 has been transferred, the discharge process is ended.

The precharge switch 6 a and the selection switch 11 ₂ , 12 ₂ ,. . . 1 n ₂ , however, remain open for a short time so that the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ can be charged to the first voltage as in the precharge stage. This reloading, which is similar to precharging, is necessary because loading and unloading the piezoelectric elements can be done with little loss, but not entirely without loss.

If the capacitor 4 and the piezoelectric elements 11 ₁ , 12 ₁ ,. .. 1 n ₁ are charged to the first voltage, who the precharge switch 6 a and the selector switch 11 ₂ , 12 ₂ ,. . . 1 n ₂ opened again. The arrangement is thus prepared for a next main charging stage for charging the same or another of the piezoelectric elements.

If one operates the circuit shown in FIG. 3 to the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ consecutively to carry out a pre-injection and a subsequent main injection and to discharge, the current and voltage profiles shown in FIG. 4 are set. The current and voltage curves shown are the result of a simulation in which the piezoelectric elements were modeled as pure capacitances.

The curves shown in Fig. 4 are provided with their measurement variables representing symbols. Represent from the symbols used

in the upper diagram according to FIG. 4
the (recharging) current flowing through the diode 18 , and
◊ the (recharging) current flowing through the diode 17 , and

in the lower diagram according to FIG. 4

the voltage U _{p1 occurring} at the piezoelectric element 11 ₁ ,
◊ the voltage U _p2 established at the piezoelectric element 12 ₁ , and
∇ the voltage U _pn occurring at the piezoelectric element 1 n ₁ ,

Designate in the lower representation according to FIG. 4

If the voltage occurring at the respective piezoelectric elements if they are fully (as desired) charged,
U1 the above-mentioned first voltage to which the piezoelectric elements and the capacitor are charged during precharging and reloading, and
U2 a second voltage to which the uncharged piezoelectric elements and the capacitor are charged by discharging (recharging) a charged piezoelectric element.

The current and voltage profiles shown in FIG. 4 illustrate the charging process and the discharging process of the piezoelectric elements 11 ₁ , 12 ₁ ,. . . 1 n ₁ , wherein first the piezoelectric element 11 ₁ , then the piezoelectric element 12 ₁ , and then the piezoelectric element 1 n ₁ are successively charged and discharged two times in succession (in order to carry out a pre-injection and a subsequent main injection).

As can be seen from FIG. 4, the voltage which arises at the piezoelectric element to be charged and discharged has an extremely homogeneous and easily controllable course.

At the same time, the circuit by which the charging and discharging is effected, more precisely the circuit according to FIG. 3 is extremely simple and optimal in efficiency. In this regard, there is agreement with the corresponding embodiment for the circuit according to FIG. 1 (if what has been said about the coil 5 is transferred to the transformer 15 ); To avoid repetition, reference is therefore made to the explanations given there.

In summary, it can be said that it is both off leadership examples of the device according to the invention and the The inventive method in a simple and elegant way  and enable way, even under cramped conditions efficient charging and discharging of piezoelectric elements perform.

Claims (11)

1. A method for loading and unloading a piezoelectric element ( 11 ₁ , 12 ₁ ,... 1 n ₁ ), characterized in that we least at least either loading or unloading at least partially by shifting charges between those to be loaded or unloaded piezoelectric element and one or more non-charging or discharging piezoelectric element (s). 2. The method according to claim 1, characterized in that the shifting of the charges while temporarily storing their energy in an element acting as an inductance ( 5 ; 15 ) it follows. 3. The method according to claim 2, characterized in that a coil ( 5 ) is used as the element acting as inductance ( 5 ; 15 ). 4. The method according to claim 2, characterized in that a transformer ( 15 ) is used as the element acting as inductance ( 5 ; 15 ). 5. The method according to any one of claims 2 to 4, characterized in that the loading and unloading of the piezoelectric element ( 11 ₁ , 12 ₁ ,... 1 n ₁ ) via the same element acting as inductance ( 5 ; 15th ) respectively. 6. The method according to any one of the preceding claims, characterized in that at least when commissioning the device for performing the method or after loading and unloading a piezoelectric element ( 11 ₁ , 12 ₁ , ... 1 n ₁ ) a pre or recharging is carried out, in which at least the existing piezoelectric elements are charged to a first voltage (U1) which is less than a threshold voltage, from which the piezoelectric elements can act as actuators or actuators. 7. The method according to claim 6, characterized in that the piezoelectric elements ( 11 ₁ , 12 ₁ , ... 1 n ₁ ) are mechanically biased such that their dimensions are not changed by the precharging. 8. The method according to claim 6 or 7, characterized in that the piezoelectric elements ( 11 ₁ , 12 ₁ ,... 1 n ₁ ) are used in such a way that during the precharging on occurring dimensional changes are not sufficient to a in desired actuated state of the relevant piezoelectric element to be actuated or adjusted element to actuate or to adjust. 9. The method according to any one of claims 6 to 8, characterized in that the loading of a piezoelectric element ( 11 ₁ , 12 ₁ ,... 1 n ₁ ) is carried out in two substeps, the first part being at least the precharged one Piezoelectric elements stored energy is supplied to an energy storage element and stored there, and in the second part step the energy stored in the energy storage element is supplied to the piezoelectric element to be charged. 10. The method according to any one of the preceding claims, characterized in that the discharge of a piezoelectric's rule ( 11 ₁ , 12 ₁ ,... 1 n ₁ ) it follows in two substeps, in the first substep at least the loaded piezoelectric Element stored energy is supplied to an energy storage element and stored there, and in the second sub-step the energy stored in the energy storage element is distributed at least to the existing piezoelectric elements. 11. Device for loading and unloading a piezoelectric element's ( 11 ₁ , 12 ₁ ,... 1 n ₁ ), characterized by means which make it possible for at least either the loading or the unloading to be carried out at least partially by shifting charges between the piezoelectric element to be charged or discharged and one or more piezoelectric element (s) not to be charged or discharged.