DE102009027986A1 - Piezoelectric actuator with a multi-layer structure and a method for its production - Google Patents

Abstract

A piezo actuator with a multilayer structure of piezo layers is proposed, each of which is enclosed between internal electrodes (4, 5) of alternating polarity and each of which has a different polarity of an electrical voltage applied to the internal electrodes via external electrodes (6, 7) in that one external electrode each (6, 7) is in contact with the inner electrodes (4, 5) of one polarity and are separated from the inner electrodes (4, 5) of the other polarity by means of an insulation zone. In at least one insulation zone (10, 11) there is a section (13) running parallel to the direction in which the piezo layers extend.

Description

State of the art

The The invention relates to a piezoelectric actuator with a multi-layer structure of Piezo layers and an alternating internal electrode design as well a method for its preparation according to the generic Features of the main claim and the independent method claim.

Such a piezoelectric actuator is for example from the DE 102 36 986 A1 known, which can be used to actuate a mechanical component in fuel injection systems in motor vehicles. From this it is known that by utilizing the so-called piezoelectric effect, a multilayer structure of piezoelectric layers can be arranged in each case of a material having a suitable crystal structure so that when a voltage is applied, a mechanical reaction of the piezoelectric layer takes place, which depends on the crystal structure and the contact areas of electrical voltage represents a pressure, or a mechanical elongation in a predetermined direction.

Of the Multi-layer construction has an alternating (interdigital) Internal electrode design, in which each piezoceramic layer between is bordered by two internal electrodes, via which an electrical Voltage can be applied and thus each a piezoelectric element forms. Due to the electrical voltage lead the piezo elements each small strokes in the direction of the potential gradient off, which add up to the total stroke of the piezoelectric actuator.

The Internal electrodes are mutually connected with external electrodes connected to the supply of electrical voltage, wherein the internal electrodes, which are connected to the positive electrical pole the outer electrode are contacted, from the negative pole of the outer electrodes are separated by a so-called isolation zone. Another Isolation zone then separates the internal electrodes, which with the negative pole are connected by the positive pole of the external electrodes.

Both Isolation zones form a relatively rigid corset, which mechanically obstructed the piezoelectric actuator during its stroke movement. consequently it may be in the electrical Poland of the piezoelectric actuator for the formation of so-called Polungsrissen come. These poling cracks usually go Cracks through the isolation zone, causing the clamping effect of the multilayer structure possibly can be reduced. If no further action can be provided to control such Polungsrisse the polarity cracks statistically spread in the piezoelectric actuator, possibly with an uncontrolled crack over the whole Length of the piezo actuator. Due to the uncontrolled crack growth branching poling cracks often occur which reduce the insulation between two internal electrodes sensitive can. The probability of an electrical failure of the piezoelectric actuator during operation increases considerably, the branching poling cracks are also a reject criterion can represent the production.

From the WO 2007/104301 A2 It is known, for example, that deliberate weaknesses are built into the multilayer construction, which control the formation and growth of such poling cracks. This is achieved in the prior art, in particular by a modified material structure, which lowers the mechanical tensile strength of the internal electrodes below that of the piezoceramic. For this purpose, piezoelectric layers with lower strength are introduced into the multi-layer structure. However, the incorporation of such vulnerabilities generally has the disadvantage that the piezo actuators are already very vulnerable during the process steps of production in terms of damage, for example, by a breakage of the piezoelectric actuator at the introduced vulnerability. This is especially true when grinding the piezoelectric actuators after sintering, in which they are particularly exposed to high shear stress.

Disclosure of the invention

The Invention is based on a piezoelectric actuator with a multi-layer structure Piezo layers, each alternating between internal electrodes Polarity are bordered. The internal electrodes are via external electrodes each having a different polarity of an electrical Stress thereby applied, that in each case an outer electrode each contacted with the internal electrodes of a polarity and of the inner electrodes of the other polarity, respectively separated by an isolation zone. According to the Invention is advantageously in at least one isolation zone a parallel to the extension direction of the piezoelectric layers extending Bleed available.

The According to the invention sections are here preferably under a base metallization and the overlying Outside electrode, so that with the invention it in an advantageous Way succeeds, predetermined breaking points for poling cracks in the Piezo actuator with a suitable mechanical removal method, without resulting disadvantages in the subsequent process steps the production of the piezoelectric actuator result. Is particularly advantageous it here, if the cuts over the entire multi-layer structure are distributed.

A particularly advantageous method for Production of the piezoelectric actuator described above thus results when the gates are introduced during the process steps in the production after grinding and before applying a base metallization on the side surfaces of the piezoelectric actuator.

The Strength of brittle materials, including the piezoceramic depends on the piezo layers depends essentially on the condition of the surface. damage the surface, such. As cracks, reduce the strength the piezoceramic drastically. With the invention, it is thus in a simple manner possible, predetermined breaking points on the surface of the Piezoactors by manipulation of the ceramic surface in Form of gates. The surface of the piezoceramic can, for example, at the points where Polungsrisse train are targeted, weakened by a cut of the isolation zone become. Enough to weaken the piezoceramic is enough even small cutting depths (for example 100 to 200 μm) out.

Around to introduce thin and defined cuts, laser cutting, precision cutting, such as B. wire saw, and water jet cutting. The introduction of such predetermined breaking points is after the final grinding process the piezo actuators and before the application of the base metallization particularly favorable, since the piezoelectric actuator in this state is no longer exposed to strong mechanical loads. While the Polungsprozedur and the operation of the piezoelectric actuator can thus the poling cracks only defined at the predetermined breaking points arise and the risk of cracking and uncontrolled Crack growth is significantly reduced.

Short description of the drawing

One Embodiment of the invention will be described below the figures of the drawing described in more detail. Show it:

1 a schematic representation of a known piezoelectric actuator with inner and outer electrodes.

2 a detailed representation of two internal electrodes and isolation zones to external electrodes.

3 a view of a piezoelectric actuator with gates according to the invention in the isolation zones.

Way to execution the invention

An in 1 schematically illustrated piezoelectric actuator known per se 1 comprises a plurality of multi-layer structure stacked piezoelectric elements, each of piezoelectric layers 3 made of piezoceramic and these enclosing internal electrodes 4 and 5 consist. The piezo actuator 1 may for example be part of a piezo injector for controlling the fuel injection in an internal combustion engine. The internal electrodes 4 and 5 the piezo elements are with external electrodes 6 and 7 alternately to a voltage source 8th connected, so taking advantage of the piezo effect when voltage is applied to the respective internal electrodes 4 and 5 over the intermediate piezolayers 3 a mechanical reaction of the piezoelectric actuator 1 can be effected in the stacking direction of the multilayer structure.

Out 2 it can be seen that the respective inner electrode 5 to the positive outer electrode 7 is connected and from the minus outer electrode 6 by means of an insulation zone not printed with an inner electrode layer 10 the piezo layer which is not completely visible here is separated. On the other hand, the respective inner electrode 6 to the minus outer electrode 6 connected and from the plus outer electrode 7 likewise by means of an insulation zone not printed with an inner electrode layer 11 separated.

In 3 is shown as in a piezoelectric actuator according to the invention 12 visible here in the isolation zones 11 (see. 2 ) of the piezo layers indicated by dashed lines gates 13 present under a base metallization and the outer electrodes 6 or 7 are attached.

The gates 13 after 3 form predetermined breaking points for poling cracks in the piezoelectric actuator 12 and are introduced with a suitable removal method. This can preferably after grinding and before applying the base metallization on the side surfaces of the piezoelectric actuator 12 be performed. As Abtragverfahren in particular laser beam cutting, precision separation process such. As wire saw, and water jet cutting in question.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10236986 A1 [0002]
• WO 2007/104301 A2 [0006]

Claims (10)

Piezoelectric actuator with a multilayer structure of piezoelectric layers, each between internal electrodes ( 4 . 5 ) of alternating polarity and the internal electrodes via external electrodes ( 6 . 7 ) are each acted upon by a different polarity of an electrical voltage, that in each case an outer electrode ( 6 . 7 ) with in each case the internal electrodes ( 4 . 5 ) of a polarity and of the internal electrodes ( 4 . 5 ) of the other polarity are each separated by means of an isolation zone, characterized in that in at least one isolation zone ( 10 . 11 ) a parallel to the direction of extension of the piezoelectric layers running gate ( 13 ) is available. Piezoelectric actuator according to claim 1, characterized in that the respective gate ( 13 ) under a base metallization and the overlying outer electrode ( 6 . 7 ) is located. Piezoelectric actuator according to claim 1 or 2, characterized in that the gates ( 13 ) over the entire multilayer structure of the piezoelectric actuator ( 12 ) are distributed. Piezoelectric actuator according to one of claims 1 to 3, characterized in that the gates ( 13 ) in the isolation of piezoceramic isolation zone ( 10 . 11 ) are mounted. Piezoelectric actuator according to one of claims 1 to 4, characterized in that the gates ( 13 ) are formed by a mechanical removal. Method for producing a piezoactuator according to one of the preceding claims, characterized in that the gates ( 13 ) during the process steps in the production after grinding and before applying a base metallization on the side surfaces of the piezoelectric actuator ( 12 ) are introduced. Method according to claim 6, characterized in that the gates ( 13 ) are introduced by means of a laser beam cutting method. Method according to claim 6, characterized in that the gates ( 13 ) are introduced by means of a Präzionstrennverfahrens, in particular with a wire saw. Method according to claim 6, characterized in that the gates ( 13 ) are introduced by means of a water jet cutting process. Use of a piezoelectric actuator according to one of the preceding claims, characterized in that the piezoelectric actuator ( 12 ) Part of a piezo injector for controlling the fuel injection in an internal combustion engine is.

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