JP2009509493A - Assemblies with piezo actuators and methods of making assemblies with piezo actuators - Google Patents

Abstract

  The present invention is an assembly having a piezo actuator, for example a piezo injector, for example for operating a mechanical component, and is provided with a multilayer structure comprising a plurality of piezo layers (26). The layer (26) is held as a piezo element (3; 21) in the holding body (2; 29, 30), and the piezo element (3; 21) has an internal electrode (22, 23) and a contact element (24). , 25) and the electrical lines (34, 25) which are guided towards the contact elements (24, 25) through the head part (30) of the holding body (29). 35). According to the invention, the electrical line is connected to the contact element (24, 25) through the head part (30) of the holding body (29) via the connection element (50, 51, 52) whose length can be adapted. The connecting element consists of an electrically conductive sleeve (50) of a configurable length, on one side in the sleeve (50) The end portion (51) of the line can be inserted into the end portion (52) of the line as an extension of the contact element (24, 25) on the other side.

Description

TECHNICAL FIELD The present invention relates to an assembly with a piezo actuator, for example a piezo injector, for operating a mechanical component such as a valve or the like of the type described in the superordinate conception of the main claim. An assembly including a piezo actuator, which is provided with a multilayer structure composed of a plurality of piezo layers, and these piezo layers are held as a piezo element in a holding body, and the piezo element includes an internal electrode and a contact element. And an electric line that is guided toward the contact element through the head portion of the holding body. The invention further relates to a method of manufacturing an assembly with a piezo actuator.

Such an assembly can be used, for example, in a motor vehicle, preferably for controlling the stroke of a needle for fuel injection, and strictly for a control with a single stage conversion, a two-stage conversion. It can also be used for the control to perform. It is known per se that a piezo element can be used to implement a needle stroke control of a valve or the like under the use of the so-called piezoelectric effect in order to constitute the piezo actuator. The piezo element is configured such that a mechanical reaction of the piezo element occurs from a material having an appropriate crystal structure when an external voltage is applied. This mechanical reaction realizes push-pull in a settable direction (push or pull) depending on the crystal structure and the voltage application range. This type of piezo actuator is suitable, for example, for applications in which the stroke movement proceeds with a high operating force and a high clock frequency.

  For example, such a piezo actuator is known from DE 10026005. This known piezo actuator can be used to activate and control a nozzle needle with an injector for injecting fuel into a combustion chamber of an internal combustion engine. In this piezoelectric actuator, the piezoelectric element is configured as a stack of a plurality of piezoelectric ceramic layers electrically connected to each other as described above. The stack is held between two stoppers in a preloaded state. Each piezoelectric ceramic layer is sandwiched between two internal electrodes as a piezo layer, and a voltage can be applied from the outside via the internal electrodes. Based on this voltage, each piezoelectric ceramic layer performs a small stroke movement in the direction of potential drop. These stroke movements are summed to form the entire stroke of the piezo actuator. This total stroke can be changed via the height of the applied voltage and can be transmitted to the mechanical actuating member.

  In the piezo actuator, in order to introduce different potentials, contacts are formed on alternate sides of the internal electrode via the outer electrode. In the outer electrode, the conductive surface is attached to one side surface of the piezo element, and is in contact with each inner electrode. In contrast, in the piezo actuators known from DE 103 35 015 A1, the internal electrodes and the intrinsic contact between the contact elements located in the respective inner notch of the piezo element. Contact formation is performed.

  EP 1174615 also describes a piezo actuator in which a piezo element is present as an actuator for direct needle stroke control of an injection injector of an internal combustion engine. Between the piezo element as the actuator and the needle, there is only a coupler provided with a hydraulic conversion device for expansion compensation. In this case, the operation of the piezo element causes the needle held for closing the injection nozzle under preload to be separated from the nozzle opening. This is because the needle is directly converted and follows the motion of the actuator.

  In the published German Patent Application No. 10026005 as background art mentioned at the beginning, the electrical connection of the piezo element to an external voltage source is made through the base part of the piezo actuator by means of an extension of the outer electrode. Done. This extension can be further guided to the connector. As a result, the extension is contacted in an area that is not mechanically critical. The extension can then be electrically insulated and guided through an actuator base made of steel, for example. A piezo element is in contact with or fixed to the actuator base. Furthermore, it is known from this background art that the extension is held in the casting material in order to fix the external electrode and relieve the tensile load. The casting material is placed in a notch in the actuator base, possibly surrounded by a molded part made of steel or polymer.

  Often, in the piezo actuator, the structural length must be adapted to the application. This changes the length of the supply line between the actuator base and the connector part, particularly in the region of the head part of the holding body for the piezoelectric actuator. In known piezo actuators, a contact element for supplying a voltage to the piezo element is guided to the connector part by a consistent or continuous line.

  Known and consistent lines are connected to a dense glass seal against high pressure and must be adapted to the lengths of piezo actuators, eg injection injectors, which vary from customer to customer. . The wire is generally made of a material with a small thermal expansion, for example NiFe, has low electrical conductivity and is relatively thin, so in this case it is very difficult to achieve an electrical connection at the end of the wire. .

DISCLOSURE OF THE INVENTION The present invention starts from an assembly with a piezo actuator of the type described at the outset. The assembly has a multilayer structure composed of a plurality of piezoelectric layers in the piezoelectric element. The piezo layer is held in the holding body. At that time, there are alternating contact forming portions between the internal electrodes and the contact elements in the piezoelectric element. Furthermore, a power supply line as an electrical line is guided toward the contact element through the head portion of the holding body. According to the invention, the electrical line is advantageously guided towards the contact element through the head part of the holding body via a connection element whose length can be adapted. The connecting element then consists of an electrically conductive sleeve of a configurable length, in which the end of the electrical line of the connector part on one side contacts the other side. The end of the track as an extension of the element can be inserted.

  Advantageously, the line leading to the contact element provided in the piezo element or along the piezo element is embedded in the glass sealing part in the direction of the piezo element, close to the high pressure of the liquid Has been. In that case, the glass sealing part is preferably embedded in the region of the head part of the holding body. Glass sealing can be performed relatively easily according to the present invention. This is because there are no long line ends. This simplifies handling, transport and assembly.

  By dividing the line according to the invention on the upper side of the glass seal, the disadvantages of consistent thin connections with NiFe wires can therefore be eliminated by additional plug connections. A simple length adaptation of the line to the length of the piezo actuator and expansion compensation can be implemented. Furthermore, the upper end of the line on the connector part side can be made of a freely selectable material. In this case, the line leading to the connector portion may be formed as a flat pin outside the sleeve.

  The electrically conductive sleeve can be insulated from the head portion by an insulating sleeve. Further, an additional insulating tube can be disposed between the glass sealing portion and the conductive sleeve, and the outer diameter of the insulating tube is smaller than the outer diameter of the glass sealing portion. The sleeve can be made of a greater thickness from a material that is more conductive than NiFe wire, such as copper or brass.

  In an advantageous manufacturing method, the first method step carries out the polarization and signal inspection of the piezo element and the high-pressure seal, and in the second method step between the connector part and the contact element in the connection element. Can be connected.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the assembly according to the present invention will be described with reference to the drawings.
FIG. 1 is a longitudinal sectional view of a piezo injector with a piezo actuator having a basic geometric structure according to the background art,
FIG. 2 shows the invention according to the invention of a piezo actuator with an internal contact forming part of the internal electrode of a piezo element, in which an electrical line is guided from the outer connector through the head part of the holding body together with the glass sealing part. It is a partial longitudinal cross-sectional view of one embodiment,
3a and 3b are schematic views showing different length heads of the holding body for the piezo element and correspondingly adapted sleeves for the track, and FIGS. FIG. 5 is a detail view showing sleeves for the ends of the lines leading to the connectors and contact elements, respectively.

FIG. 1 shows the basic structure of a known single-stage piezo injector with a piezo actuator. Based on its proposed application, the piezo injector 1 is also referred to hereinafter as an injector, and can be used for direct needle stroke control in an injection system for fuel, for example in an internal combustion engine. The holding body 2 exists in the upper part. The holding body 2 can be adapted to a substantially specific use location in terms of its geometric dimensions. The holding body 2 has a connector portion not shown here. A voltage for controlling the activation of the piezo element 3 can be connected by a connector portion having a connector configuration adapted to a specific use case.

  From the connector portion, here, feeder lines as the electrical lines 4 and 5 are guided toward the external electrodes 6 and 7 provided on the piezoelectric element 3. In operation, the piezo element 3 acts on the nozzle needle 9 via a mechanical assembly with a coupler 8, which here is present vertically downward, where the nozzle opening 10 can be opened. Thereby, the fuel guided through the inner chamber of the holding body 2 inside the piezo actuator 1 can be injected into a combustion chamber of an internal combustion engine (not shown).

  According to FIG. 1, the piezo element 3 comes into contact with a spherical seal seat provided in the inner chamber of the holding body 2 on the upper side via the actuator base 11. At that time, the piezo element 3 is pressed by the spring 12 in order to form a good sealing seat. In particular, in the case of the common rail system described at the beginning, a high-pressure seal for the electrical connection chamber 13 is required here. Two electrical lines 4 and 5 are guided toward the piezo element 3 through the electrical connection chamber 13.

In the holding member 2 is particularly head unit shown in FIG. 1, must generally with respect to its length L _o, application-specific circumstances, such as to be adapted to the circumstances of the fuel injector in an internal combustion engine. As a result, when the electrical line is guided inside, a unique characteristic is generated with respect to contact formation.

  FIG. 2 shows a part of the piezo actuator 20 according to the invention in the assembled state. Here, the piezoelectric element 21 exists. Here, only the internal electrodes 22 and 23 are indicated by reference numerals. Voltage is supplied to the internal electrodes 22 and 23 alternately via the inner contact elements 24 and 25 in the stack structure of the piezo elements 21. Due to the potential drop at the time of applying the voltage, the mechanical reaction described at the beginning occurs in the piezoelectric layer 26 made of the ceramic sheet between the internal electrode 22 and the internal electrode 23.

  The piezo element 21 further abuts on a holding body 29 of the piezo actuator 20 via a cover plate 27 made of ceramic and an actuator base 28 made of steel. At that time, the holding body 29 has a head portion 30. The head unit 30 includes a fuel supply unit 31 and an electrical connection unit 32. The piezo element 21 is sealed against the fuel inside the holding body 29 by an outer insulating layer 33.

  Inside the head portion 30, feed lines as the lines 34 and 35 are insulated and fitted. The lines 34, 35 are tightly connected to the high pressure for connection to the piezo element 21, preferably press-fitted by a glass seal 36, and are connected to the contact elements 24 and 25. For this purpose, a contact connection 37 or 38 is present. The contact connecting portions 37 and 38 are respectively located in the insulating sleeve or the centering sleeve 39.

In FIG. 2, the lines 34 and 35 are guided in a conventional manner after the contact connections 37 and 38 as a continuous line to a connector part 32 not shown in detail here. At that time, line length is must be adapted to the required length L _o of the head portion 30 of the holding member 29. For example, the lines 34 and 35 made of NiFe are relatively thin and have low conductivity, so that it is relatively difficult to realize pin connection at the ends of the lines 34 and 35.

In accordance with the present invention, application specific length adaptations of lines 34 and 35 can be recognized in FIGS. 3a and 3b and FIGS. In this case, description will be made mainly with reference to FIG. The reference numerals of the members are almost the same. In Figure 3a, in addition to the fixed length _{L 1} and _{L 2,} where it is seen that a relatively short length _{L variabel} exists. In contrast, FIG. 3b shows a long head portion 29 having a relatively long length L _variable . There is one electrically conductive sleeve 50 in each assembly. The sleeve 50 is made of, for example, copper, bronze, or brass, and can form a flexible connector-like connection portion when inserted from both sides of the wire.

  Such connector-like connections can be seen from FIGS. 4 and 5, respectively. In this case, the supply lines 34 and 35 are replaced by lines or pins 51 and 52, respectively. Lines or pins 51, 52 are inserted into the sleeve 50 on both sides, thereby forming a flexible connector-like connection. In this case, the lower pin 52 connected to the contact element 24 or 25 is located in the head part 29 via the glass sealing part 53. Above the glass seal 53, the pin 52 is guided in the insulating sleeve 54 until it opens into the sleeve 50. The pin 51 may then be formed as a connector pin 55, for example a flat pin, at the other end.

  In the variant shown in FIG. 5, an additional insulating tube 56, for example made of polymer or formed as a shrink tube, is attached. The outer diameter of the insulating tube 56 is smaller than that of the glass sealing portion 53. Accordingly, it is possible to attach the glass sealing portion 53 together with the sleeve 50 fixedly attached to the pin 52 by, for example, brazing, welding, pressure bonding, or adhesion using a conductive adhesive. At that time, the outer diameter of the sleeve 50 is still smaller than the diameter of the glass sealing portion 53.

  In the assembly described here, the glass sealing portion 53 serves as a high-pressure seal against the external hydraulic pressure when the piezoelectric element 21 or the welding seam 41 (see FIG. 2) leaks to the outside.

INDUSTRIAL APPLICABILITY The present invention can be used for controlling the stroke of a needle for fuel injection in an automobile. Strictly speaking, the control for performing single-stage conversion or control for performing two-stage conversion is possible. Is available.

1 is a longitudinal sectional view of a piezo injector equipped with a piezo actuator having a basic geometric structure according to the background art. An embodiment according to the invention of a piezo actuator with an internal contact formation of an internal electrode of a piezo element in which an electrical track is guided from the outer connector through the head of the holding body together with a glass seal. It is a partial longitudinal cross-sectional view. Fig. 3b is a schematic view of a holding body for a piezo element with different length heads in Figs. 3a and 3b and a correspondingly adapted sleeve for the track. FIG. 5 is a detail view showing a sleeve for the end of the line leading to the connector and contact element. FIG. 5 is a detail view showing a sleeve for the end of the line leading to the connector and contact element.

Claims (9)

An assembly with a piezo actuator,
A multilayer structure composed of a plurality of piezo layers (26) is provided, and these piezo layers (26) are held in the holding body (2; 29, 30) as piezo elements (3; 21). The element (3; 21) has alternating contact forming portions between the internal electrodes (22, 23) and the contact elements (24, 25), and contacts through the head portion (30) of the holding body (29). In the type in which electrical lines (34, 35) guided towards the elements (24, 25) are provided,
The electrical lines are guided towards the contact elements (24, 25) through the head part (30) of the holding body (29) via connecting elements (50, 51, 52) whose length can be adapted. And
The connecting element comprises an electrically conductive sleeve (50) of a configurable length, into the sleeve (50), on one side, the end (51) of the electrical line of the connector part However, on the other side, the end (52) of the line as an extension of the contact elements (24, 25) can be inserted, and the assembly with a piezo actuator is provided.   On the lower side of the connection element in the direction of the piezo element (21), a line leading to the contact element (24, 25) provided in the piezo element (21) or along the piezo element (21) is a glass sealing portion. The assembly according to claim 1, wherein the assembly is densely embedded in the liquid within a high pressure.   The assembly according to claim 2, wherein the glass sealing part (53) is embedded in the area of the head part (30) of the holding body (29).   The assembly according to any one of the preceding claims, wherein the electrically conductive sleeve (50) is insulated from the head portion (30) by an insulating sleeve (54).   An additional insulating tube (54) is disposed between the glass sealing portion (53) and the conductive sleeve (50), and the outer diameter of the insulating tube (54) is such that the glass sealing portion ( The assembly according to any one of claims 2 to 4, which is smaller than the outer diameter of 53).   6. An assembly according to claim 1, wherein the end of the electrical line is formed as a metal pin (51, 52) in the sleeve.   The assembly according to claim 6, wherein the metal pins (51, 52) have a constant length.   The assembly according to claim 1, wherein the line leading to the connector part is formed as a flat pin (55) outside the sleeve (50). A method for manufacturing an assembly comprising a piezo actuator according to any one of claims 1 to 8,
In the first method step, the polarization and signal inspection of the piezo element (21) and the high-pressure seal are inspected, and in the second method step the connector part and contacts in the connection element (50, 51, 52) A method for producing an assembly with a piezoelectric actuator, characterized in that the connection of the lines (24, 25; 51, 52) to the elements (34, 35) is carried out.

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