JP2000029528A - Method and device for controlling piezoelectric element so as to extend as desired - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend a piezoelectric element as desired without disturbing other processes or components by using the piezoelectric element consisting of many individual elements which can be charged and discharged individually or every group as the piezoelectric element. SOLUTION: When a charging switch 3a is turned on, a charging current which charges individual elements charged in a charging current circuit, begins to flow. In this case, the level of the charging current and the elapsed time depend basically upon the individual elements which are charged and an LC series vibration circuit formed of a coil 2 and a capacitor 8. The charging current rises very rapidly up to a maximum value after the charging switch 3a is turned ON and then, falls very quickly. A diode 3b stops the inversion in the direction of the current flow which possibly discharges the individual elements. The piezoelectric element consisting of the individual elements 111, 121...1n can be extended optionally as desired in spite of the fact that the charging quantity is not controlled during the charging in the charging of the individual elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method and apparatus for controlling a piezoelectric element to elongate as desired.

[0002]

2. Description of the Related Art Piezoelectric elements discussed in detail here are, but not exclusively, those used as actuators or adjusting elements. Piezoelectric elements are used for such purposes. This is because these piezoelectric elements have a characteristic of contracting or expanding depending on an applied voltage, as is well known.

The practical realization of an adjusting element by means of a piezoelectric element is particularly advantageous when the adjusting element needs to carry out fast and / or frequent movements.

The use of piezoelectric elements as adjusting elements has proven to be particularly advantageous in fuel injection nozzles of internal combustion engines. See, for example, EP 0 371 469 B1 and EP 0 379 182 B1 for the availability of piezoelectric elements in fuel injection nozzles.

[0005] The piezoelectric element is a capacitive load which, as indicated above, contracts and expands in response to the respective state of charge or to the voltage generated or applied to the piezoelectric element. .

The charging and discharging of the piezoelectric element takes place, inter alia, through components having inductive properties, for example coils. This coil is used primarily to limit the charging current generated during charging and the discharging current generated during discharging. Such a device is shown in FIG.

The piezoelectric element to be charged or discharged is indicated by reference numeral 101 in FIG. This piezoelectric element is a component of a charging current circuit that can be turned on via a charging switch 102 and a discharging current circuit that can be turned on via a discharging switch 106.
Diode 103, charging coil 104, piezoelectric element 101
The discharge current circuit includes a series circuit of a discharge switch 106, a diode 107, a discharge coil 108, and a piezoelectric element 101.

The diode 103 of the charging current circuit prevents a current for discharging the piezoelectric element from flowing in the charging current circuit. The diode 107 of the discharge current circuit prevents a current for charging the piezoelectric element from flowing through the discharge current circuit.

When the normally off charge switch 102 is turned on, a charging current flows through the charging current circuit, and the piezoelectric element 101 is charged by the charging current. Piezoelectric element 1
The charge stored in 01 and thereby the voltage generated at the piezoelectric element, ie the instantaneous external dimensions of the piezoelectric element 101, remain essentially unchanged after the charging of the piezoelectric element 101.

Normally, the discharge switch 10 in the off state
When the switch 6 is turned on, a discharge current flows through the discharge current circuit, and the piezoelectric element 101 is discharged by the discharge current. The state of charge of the piezo element and the voltage thereby generated at the piezo element, ie the instantaneous external dimensions of the piezo element 101, remain essentially unchanged after this discharge of the piezo element 101.

Such charging and discharging of the piezoelectric element is advantageous. This is because such charging / discharging is performed with only a small amount of heat generation with little power loss since there is no ohmic resistance that is set up in both the charging current circuit and the discharging current circuit.

However, on the other hand, the amount of charge / discharge cannot be controlled during this charge / discharge. Charge coil 104 and piezoelectric element 101 through discharge coil 108 and piezoelectric element 10
1 forms an LC series oscillating circuit when charging or discharging the piezo element, which is charged or discharged only by the first half-wave of the first oscillating circuit oscillation.
(Subsequent oscillations of the oscillating circuit are prevented by the diodes 103 or 107 included in the charging and discharging current circuits.) This itself also results in: That is, the amount of charge and discharge is basically determined exclusively by the technical data (more precisely, the inductance of the charge or discharge coil and the capacitance of the piezoelectric element) of the vibrating circuit element (which cannot be changed during operation). Will be done.

However, for certain applications (for example, when the piezoelectric element is used as an actuator in a fuel injection nozzle of an internal combustion engine), the various and possibly variable elongations are produced in the piezoelectric element as accurately as possible. It is necessary to be able to do it.

This is possible if the charging and / or discharging of the piezoelectric element is performed as follows (by timing control) when using a charge / discharge circuit as shown in FIG. 2, for example. That is, the charging coil 104 and the discharging coil 1
08 no longer or no longer acts primarily as an oscillatory circuit element, but rather as an energy buffer, which is repeatedly and alternately (during charging) by a current source or (during discharging). The electrical energy supplied by the piezoelectric element (in the form of magnetic energy)
Accumulate and then deliver this stored energy in the form of electrical energy to the piezo element (during charging) or elsewhere (during discharging), It is somehow possible if the point in time and the duration (ie the amount) of the delivery are performed (timed) as determined by the operation of the corresponding switch.

As a result, the piezoelectric element is charged and discharged as desired in a desired number of steps, of an arbitrary size, and successively at an arbitrary time interval.

As a result, the amount and / or time of charging and / or discharging can be controlled as desired, and without being fully dependent on the technical data of the coil and the piezoelectric element.

However, the timing-controlled charging and / or
Or, discharge requires relatively high cost and can cause electromagnetic interference.

[0018]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved method and apparatus for controlling a piezoelectric element to elongate as desired, to provide an efficient and simple process in a simple manner. Or to configure the piezoelectric element to stretch as desired without disturbing the components.

[0019]

SUMMARY OF THE INVENTION The above object is achieved in a method by using as a piezoelectric element a piezoelectric element consisting of a large number of individual elements which can be charged and discharged individually or in groups. Is configured to charge a piezoelectric element, which is solved by comprising a large number of individual elements which can be charged and discharged individually or in groups.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The possibility of charging or discharging individual elements individually or in groups opens up the possibility of charging or discharging these individual elements independently of one another. As a result, an arbitrary number of individual elements can be selectively charged and discharged simultaneously or sequentially in any order, individually or in groups. The charging or discharging of these individual elements changes their elongation, and the change of one, several or all individual elements also changes the elongation of the piezoelectric elements containing these individual elements. The change in extension of the piezoelectric element corresponds in this case to the sum of the changes in extension occurring in the individual elements.

If the selection of the individual elements to be charged or discharged depends on the target elongation of the piezoelectric element or on the change in elongation of the piezoelectric element required for this target elongation, this element is charged or discharged. Arbitrarily expanded without changing the total number of individual elements.

This makes it possible to charge and discharge the individual elements in any manner. In particular, in this case, the individual elements are charged or discharged via a charging or discharging current circuit which acts or operates as an oscillating circuit, thereby minimizing electromagnetic interference caused by charging and discharging of the piezoelectric element. Can be reduced to

The piezoelectric element can be arbitrarily stretched as desired and in a simple manner and without interfering with other processes or other components.

The individual elements can be charged and discharged simultaneously or consecutively in any order, individually or in groups without any problems, and are also configured for different sizes of extension (various sizes). ) Or individual elements (having various numbers of layers), the time lapse of charging and discharging can be set as desired. In particular, even when using a charging current circuit or a discharging current circuit that acts or operates as an oscillation circuit, it is possible to perform stepwise charging or discharging (subsequent charging of the previously charged piezoelectric element).

Advantageous embodiments of the invention result from the dependent claims, which can be taken from the following description and the drawings.

[0026]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of the invention.

A piezoelectric element whose charge / discharge is described in detail below is used as an adjusting element in a fuel injection nozzle of an internal combustion engine (for example, a so-called common rail injector). However, there are no restrictions on such use of piezoelectric elements. This piezoelectric element can be used in basically any device and for any purpose.

The piezoelectric element in this embodiment consists of a number of individual elements, which are charged and discharged simultaneously or sequentially in any order, individually or in groups,
The individual elements are layered on top of one another such that the elongation changes of these individual elements caused by charging and discharging occur in essentially the same direction.

A change in the elongation of these individual elements caused by the charging or discharging of the individual elements necessarily entails a change in the elongation of a piezoelectric element containing these individual elements, and a change in the elongation of the piezoelectric element results in a change in the elongation of these individual elements. Corresponds to the sum of the changes in elongation.

It is assumed that the individual elements (and thus also the piezoelectric elements containing these individual elements) expand in response to charging and contract in response to discharging. However, the invention is of course applicable in the opposite case.

An apparatus for charging and discharging such a piezoelectric element will be described with reference to FIG.

The piezoelectric element to be charged or discharged is composed of n individual elements stacked one on top of the other. These individual elements reference numeral 11 in FIG. _{1 1, 12 1, ... 1n} 1
Indicated by

The discrete elements 11 _1, 12 _1, ... 1n ₁ are piezoelectric branch passage 11 and 12 connected in parallel, a component of ... 1n, each individual element 11 _1, 12 _1, .. .1n ₁ is provided in its own piezoelectric branch. Piezoelectric branch 11, 1
2,... 1n are respective individual elements 11 ₁ , 1
2 _1, ... in addition to the individual elements selected connected in series with the switch 11 of 1n _{1 2,} 12 _2, ... 1n ₂ and diode 11 in parallel thereto _3, 12 _3, ... 1n ₃ Contains.

Included in each piezoelectric branch 11, 12,... 1n
Individual elements 11₁, 12₁, ... 1n ₁Is charged or discharged
(The assigned selection switch is turned on).
Or not (if the assigned selection switch is turned off
The selection switch 11_Two, 12_Two, ... 1n_TwoThrough
Can be set.

The diodes 11 ₃ , 12 ₃ ,... 1n ₃ are protection diodes, which prevent the individual elements from discharging too much during the discharging of these individual elements and being negatively charged. Is done. This can damage these individual elements in some circumstances.

Instead of the diodes 11 ₃ , 12 ₃ ,..., 1 n ₃ , it is also possible to use only one diode connected in parallel to the piezoelectric branches 11, 12,.

As can be seen from FIG. 1, one end of each of the piezoelectric branches 11, 12,... 1n is always grounded (this ground is connected to the first terminal of the voltage source). , On the other hand, the piezoelectric branch paths 11, 1
The other end of 2,... 1n is used as a charging coil during charging, or as a discharging coil during discharging, and a charging switch 3a. And a parallel circuit consisting of a charge switch branch including a diode 3b and a discharge switch branch including a discharge switch 4a and a diode 4b.
Terminal.

The above voltage source is a battery 6 (for example, an automobile battery), a DC voltage converter 7 connected to the battery 6 and a DC voltage converter 7 connected to the DC voltage converter 7 and used as a buffer capacitor. It is composed of a capacitor 8. With this device, the battery voltage (for example, 1
2V) is basically converted to any other DC voltage and supplied as a supply voltage.

The charging switch 3a and the diode 3b can be realized as semiconductor switches. The same applies to the discharge switch 4a and the diode 4b.

The selector switch 11 _2, 12 _2, ... 1n 1 that can be selected by turning on ₂ one or more piezoelectric branch paths 11, 12, ... 1n, the coil 2, charge switch 3
a, the diode 3b and the capacitor 8 form a charging current circuit (which can be turned on and off via the charging switch 3a). A series circuit composed of capacitively (individual elements 11 ₁ , 12 ₁ ,... 1n ₁ ; capacitor 8) and inductively (coil 2) acting elements uses the charging current circuit as an LC series oscillation circuit. Enable.

The selector switch 11 _2, 12 _2, ... 1n 1 that can be selected by turning on ₂ one or more piezoelectric branch paths 11, 12, ... 1n, the coil 2, the discharge switch 4
a, the diode 4b and the capacitor 8 form a discharge current circuit (which can be turned on and off via the discharge switch 4a). A series circuit consisting of elements acting capacitively (individual elements 11 ₁ , 12 ₁ ,... 1n ₁ ; capacitor 8) and inductively (coil 2) uses the discharge current circuit as an LC series oscillation circuit. Enable.

The charging of the piezoelectric elements 11 ₁ , 12 ₁ ,... 1n ₁ is performed by the (charge) current flow of the charging current circuit, and the discharging is performed by the (discharge) current flow of the discharge current circuit. In this case, the charging current circuit and the discharging current circuit are operated as oscillation circuits.

The charge switch 3a and the discharge switch 4a are turned off when neither charging nor discharging of the individual element needs to be performed and as long as neither charging nor discharging of the individual element needs to be performed. In this state, the circuit shown in FIG. 1 is stopped. In other words, the individual elements _{11 1, 12 1, ... 1n} 1
Keep their state of charge essentially unchanged and no current flows.

The charging is started by turning on the charging switch 3a.

When the charge switch 3a is turned on, which of the individual elements 11 ₁ , 12 ₁ ,... 1n ₁ is charged is determined by the selection switch assigned to each individual element as described above. 11 _2, 12 _2, is determined by ... 1n _2. Selector switch 11 _2, 12 _2, ... all of each 1n ₂ is turned on during the charging process the individual elements 1
_{1 1, 12 1, ... 1n} 1 is charged.

The individual elements 11 ₁ , 12 ₁ ,..., 1 to be charged
The selection of n ₁ depends on the assigned selection switch 11 ₂ , 1
By turning on 2 ₂ ,... 1n ₂ , the selection is canceled by turning off the selection switch, advantageously (but not forcibly) during periods other than the charging process (charging switch 3a).
Before or after the charging switch 3a is turned off).

In this embodiment, the individual elements 11 ₁ , 1
2 _1, ... 1n ₁ are charged separately in a continuous charging process. However, as already mentioned, these individual elements can in principle be charged simultaneously individually or in groups or continuously in any order.

When the charging switch 3a is turned on, a charging current for charging the individual element charged in the charging current circuit starts to flow. In this case, the magnitude and the passage of time of the charging current basically depend on the LC series oscillation circuit formed by the individual element 1x ₁ , the coil 2 and the capacitor 8 to be charged. This charging current rises to the maximum value very quickly after the charging switch 3a is turned on and then falls again very quickly. The reversal of the direction of the current flow which could discharge the individual elements is prevented by the diode 3b.

The charging is thus started and terminated by the first half-wave of the first oscillation circuit oscillation. The charging switch 3a is turned off again after the automatic end of the charging process.

The charge transport caused by the charging current to the individual elements to be charged results in an increase in the charge stored in the individual elements, and thus an increase in the voltage developed in the individual elements and in the extension of the individual elements. With consequently. An increase in the extension of the individual elements in this case causes an increase in the extension of the entire piezoelectric element.

The charge stored in the individual element, the voltage generated in the individual element and the extension of the individual element remain essentially unchanged after the end of the charging process.

The degree to which the individual elements are charged by the charging performed as described herein is basically determined in this embodiment by the individual elements 1x ₁ , the coil 2
And the technical data of the capacitor 8.

The inductance of the coil 2 determines in this case the maximum charging current intensity and the charging time, and the capacitance of the individual element ₁ × ₁ and of the capacitor 8 determines the voltage generated at this individual element after charging of the individual element.

The results of the charging performed as described herein
As a result, the voltage U generated in this individual element_pxIs given by
Yes: U_px= 2２C_B/ (C_B+ C_px)｝ ・ U_B  Where U_pxIs the individual element 1x₁Voltage generated at the
C_pxIs the individual element 1x₁The capacitance of U_B Is conde
Voltage at the sensor 8, C_B Is the capacitor of capacitor 8
It is.

[0055] Despite the control of the charge amount during charging in the charging of the individual elements is performed as described herein is not performed, the individual elements 11 _1, 12 _1, piezoelectric consisting ... 1n ₁ The element can be optionally stretched as desired. For this purpose, the appropriate selection of the individual elements to be charged is "once only"
It only needs to be done so that the sum of the elongation changes resulting from the charging of the individual elements to be charged gives rise to the desired elongation change of the piezoelectric element.

The number and size of the steps in which the piezoelectric element approaches the desired elongation by successive charging of the selected individual element or individual element group depends, inter alia, on the size of the individual element or the layers contained in the individual element. Depends on the number of

In this case, the following should be considered in some cases. That is, the voltage across the capacitor 8 (previously the voltage indicated by U _B) is considerably reduced significantly by each of the charging of the individual elements in the short continuous charging process, as a result, brought to the individual elements by the charging of the individual elements It should also be taken into account that the applied voltage (and thus the change in the extension of this individual element caused thereby) becomes progressively smaller as the number of successive charging processes increases.

Nevertheless, in order to extend the piezoelectric elements as desired in steps of the same size, the individual elements are made up of different sizes or with a different number of layers, in which case the charging takes place later in time. The individual elements charged or charged are configured to have larger or more layers than the individual elements charged or charged earlier in time. For this purpose, to what extent the size of these individual elements or the number of layers must be different,
That depends on: That is, it depends on whether the voltage generated in the capacitor 8 changes for each charging process or how much the voltage changes. The change in the elongation of the individual element caused by the charging of the individual element is proportional to the number of layers of the individual element and also to the voltage applied to the individual element by charging the individual element.

Of course, it is not necessary to charge the piezoelectric element in steps of the same size. It is also advantageous to stretch the piezoelectric element in different sized steps as desired.
This allows the piezoelectric element to be extended as desired with a minimum number of steps. However, the following should be considered in this case as well. That is, charged by the change of the individual devices suffer elongation of the individual elements should be taken into account that depending on the voltage U _B of the instantaneous capacitor 8.

The division of the piezoelectric element into individual elements does not only make it possible to accurately determine the magnitude of the expansion of the piezoelectric element and the passage of time. This makes it possible to charge the piezoelectric element in a multi-stage manner irrespective of the charging method used (piezoelectric element which has been precharged to a first size and further subsequently charged to a second size). become. This has not been possible before, at least when charging a piezoelectric element that is not divided into individual elements via a charging current circuit that acts or operates as an oscillating circuit (i.e. such piezoelectric elements are already After the first charging phase, it has a voltage which is approximately twice as large as the voltage on the capacitor 8 representing the supply voltage, so that in some cases subsequent charging phases can no longer be charged.

The multistage charging of the piezo element is advantageous, for example, when the piezo element is used as an actuator for a fuel injection nozzle of an internal combustion engine and must cause an additional injection by a small actuator displacement.

Furthermore, a piezoelectric element consisting of the above-mentioned individual elements can be used (continuously) even if one or more individual elements have failed or been damaged. This piezoelectric element "just needs to have" more individual elements than are required for normal operation. In this case, one of a relatively large number of elements can be used instead of a failed individual element.

Piezoelectric element (individual element 1 of this piezoelectric element)
1 _1, 12 _1, discharge ... 1n ₁₎ is initiated by the on of the discharge switch 4a.

[0064] discharging the switch 4a is turned on, the discharge current which discharges the individual devices 1x ₁ is discharged in the discharge current circuit starts to flow.

This is basically the only difference between the charging and discharging of the individual elements. Otherwise, discharging is performed in the same manner as charging. In particular, the discharge current circuit is likewise operated as an oscillating circuit, so that the piezoelectric element can be arbitrarily extended during discharge, as desired, without causing electromagnetic interference.

Thus, by charging and discharging performed as described herein, the piezoelectric element can be made in a simple manner efficiently and without any number and size of any size and without interfering with other processes or other components. In the next step, it is optionally stretched as desired.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of an embodiment of an apparatus of the present invention for charging and discharging a piezoelectric element.

FIG. 2 is a block circuit diagram of a conventional device for charging and discharging a piezoelectric element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Piezoelectric element 2 Coil 3a Charge switch 3b Diode 4a Discharge switch 4b Diode 6 Battery 7 DC voltage converter 8 Capacitors 11, 12, ... 1n Piezoelectric branch path _{11 1, 12 1, ... 1n} 1 discrete elements _{11 2, 12 2, ... 1n} 2 selection switch _{11 3, 12 3, ... 1n} 3 diode 101 piezoelectric element 102 charging switch 103 diode 104 Charge coil 105 Voltage source 106 Discharge switch 107 Diode 108 Discharge coil

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Jörg Reineke Germany Stuttgart Kalestraße 6 (72) Inventor Alexander Hock Schuttgart Germany Knitlinger Strasse 1

Claims (13)

[Claims] 1. A method for controlling a piezoelectric element to extend as desired, comprising: a plurality of individual elements (11 ₁ , 12 ₁ ,. 1n ₁ ). A method for controlling a piezoelectric element to stretch as desired, characterized by using a piezoelectric element consisting of 1n ₁ ). 2. An individual element (11 ₁ , 1) of piezoelectric elements.
2 _1, ... 1n ₁₎ are stacked on top of each other, according to claim 1, characterized by using said piezoelectric element
The described method. 3. The individual elements (11 ₁ , 12 ₁ ,..., 1n ₁ ) are stacked one on top of the other as follows, ie, the individual elements of the individual elements triggered by charging or discharging of the individual elements. 3. The method according to claim 2, wherein the changes in elongation take place essentially in the same direction and are stacked one on top of the other so as to produce an observed change in elongation of the piezoelectric elements as a sum. 4. The method according to claim ₁ , wherein the individual elements (11 ₁ , 12 ₁ ,..., 1n ₁ ) are charged or discharged individually or continuously in groups. The described method. 5. When charging or discharging a piezoelectric element, only a part of the individual elements (11 ₁ , 12 ₁ ,... 1n ₁ ) of the piezoelectric element is charged or discharged. 1 to
The method according to one of the preceding claims. 6. An individual element to be charged or discharged (11 ₁ ,
The selection of 12 ₁ ,... 1n ₁ ) is made depending on the following: how much the piezoelectric element should be stretched by charging or discharging, or in this case how much change in stretching is applied to the piezoelectric element. 6. The method according to claim 5, wherein the method is performed depending on what should happen. 7. Each of the individual elements (11 ₁ , 1
2 _1, ... 1n ₁ charge) is performed via the charging current circuit including the coil (2) and the individual elements, each of said individual elements _{(11 1, 12 1, ...} 1n 1) of The discharge is performed through a discharge current circuit including the coil (2) and the individual element.
The method of claim 1. 8. The charging current circuit and the discharging current circuit are operated as an oscillating circuit during charging or discharging, and the charging or discharging is caused by the first current half-wave of the first oscillating circuit oscillation. 7. The method according to claim 7, wherein
The described method. 9. The coil (2) comprises all the individual elements (11 ₁ , 12 ₁ ,..., 1n ₁ ) for charging or discharging the piezoelectric element.
9. The method according to claim 1, wherein the method is used for charging or discharging a battery. 10. The assigned selection of one or more individual elements (11 ₁ , 12 ₁ ,... 1n ₁ ) which must be charged or discharged during each charging or discharging process. 10. The method according to claim 9, wherein the selection is made via a switch (11 ₂ , 12 ₂ ,... 1n ₂ ). 11. An apparatus for controlling a piezoelectric element to stretch as desired, wherein the apparatus is configured to charge the piezoelectric element, wherein the piezoelectric element comprises a plurality of individual or group-by-group elements. An apparatus for controlling a piezoelectric element so as to extend as desired, characterized in that it comprises individual elements (11 ₁ , 12 ₁ ,..., 1n ₁ ) which can be charged and discharged. 12. The device according to claim 1, wherein the device is configured to charge or discharge a freely configurable number of individual elements (11 ₁ , 12 ₁ ,... 1n ₁ ) of the piezoelectric elements. The apparatus according to claim 11, wherein: 13. The device is configured to charge or discharge the individual elements (11 ₁ , 12 ₁ ,... 1n ₁ ) to be charged or discharged in a freely settable order. The apparatus according to claim 11 or 12, wherein