DE102009020238A1 - Piezo actuator with electrical contacting pins - Google Patents

Abstract

Piezoelectric actuator (10) in multilayer construction, in which piezoelectric layers and electrode layers (20) are arranged alternately one above the other to form a stack, wherein the electrode layers (20) on opposite sides of the stack lead out of this and via an outer electrode (18) electrically connected to a contact pin (20). 14), wherein an electrical connection between the outer electrode (18) and the contact pin (14) is made via a conductive intermediate element. Furthermore, a method for attaching an intermediate element to a piezo stack is provided in order to form a simple and stable connection between the outer electrode (18) and an external voltage source.

Description

It a piezoelectric actuator is described in multilayer construction, in which piezoelectric layers and electrode layers alternately to each other a stack are arranged, wherein the electrode layers on opposite Take sides of the pile out of this and over an outer electrode is electrically connected to a contact pin are. When applying an electrical voltage to the internal electrodes The stack expands perpendicular to that from the applied voltage resulting electric field.

through Such a piezoelectric actuator, for example, a valve piston of a Control valve operated, which as injection valve in a motor vehicle is used.

A piezoelectric actuator is for example in the WO 2005/035971 A1 , of the DE 196 48 545 A1 and the DE 199 45 933 C1 described.

It is a problem to be solved, to specify a piezoelectric actuator, which has a high reliability and with the simplest possible manufacturing process can be produced.

These Task is by the objects of the independent Claims solved.

advantageous Refinements and developments of the invention will become apparent the dependent claims.

It a piezoelectric actuator is specified in multilayer construction, in the piezoelectric Layers and electrode layers alternately over each other a stack are arranged, wherein the electrode layers on opposite Take sides of the pile out of this and over an outer electrode is electrically connected to a contact pin are, with an electrical connection between one of the outer electrodes and a contact pin via a conductive intermediate element is made. The second outer electrode can on the same way be connected to a contact pin.

It a piezoelectric actuator is specified, which is a variety thinner Sheets of piezoceramic, which are arranged in a stack has. These films are made, for example, from lead zirconate titanate. Between the layers of piezoceramic lie electrode layers. However, it is not absolutely necessary to have a piezoceramic film on each one Apply electrode layer. Depending on the desired voltage-dependent behavior of the piezo stack can, for example only every second layer of piezoceramic with an electrode layer be provided. To form these electrode layers, can by means of a screen printing process, a metal paste, for example a silver palladium paste or a copper-containing paste to which films are applied.

Of Furthermore, when manufacturing a piezo stack, it is important to that in a piezo stack, in which the electrode layers mutually lead out of the piezo stack, the electrode layers not over the entire surface of a film made of piezoceramic pass. The respective free surfaces on a slide off Piezoceramics in which adjacent electrode layers do not overlap in the stacking direction, are called inactive zones. The provided with an electrode layer Surfaces which overlap with in the stacking direction have adjacent electrode layers are called active zone designated.

A Construction of a Piezostack, in the active and inactive zones are formed, for example, allows a common Connection of all electrode layers with the same polarity.

One Disadvantage of a construction of a piezo stack, in the active and Inactive zones are formed that at the transition areas between active and inactive zones frequent tensions and Breakages occur.

After this from the films with the applied electrode layers a stack Shaped on two opposite outer surfaces the piezostack applied the outer electrodes. An outer electrode For example, by means of a stoving paste by a screen printing process applied to the outside of the stack. Then it is sintered with the piezo stack. Around these outer electrodes conductive with a contact pin and over To connect this with an external power source, for example a so-called Harhtharfe be used.

A such wire harp connects the electrode layers over the outer electrode with the contact pin by means of a thin Wire. This electrically conductive wire is in a Variety of turns wrapped around the piezostack and the pins. Subsequently, this with the outer electrode and soldered to the contact pins. In another process section become the existing wire connections between the two outer electrodes severed and removed the compound completely the two outer electrodes completely apart to isolate.

After the two outer electrodes are completely isolated from each other, a passivation can be carried out to protect against external influences be gene. In addition, a film may be applied to the edges of the piezo stack as edge protection. Subsequently, this body can be put in sleeves and shed with plastic such as silicone.

There This lengthy process is only partially automated, finds here instead of a wire harp use a conductive intermediate element, that from as few individual parts, preferably from a single Part, consists and at the same time is stable against tension, as they occur in a piezo stack described above.

Preferably the intermediate element extends over the entire length the outer electrode.

Thereby, that the outer electrode over the entire length of the piezo stack is extended, all electrode layers same polarity contacted together. In a following Step becomes the conductive intermediate element on the outer electrode appropriate. The intermediate element has the task of a possible stable connection between the outer electrode and a To ensure contact pin.

For example when using a cylindrical wire spiral as an intermediate element can every turn of the wire spiral at the outer electrode be soldered. Should during operation of the piezoelectric actuator For example, a contact point between the intermediate element and tear off the outer electrode, so the piezoelectric actuator remains continue to be operational as the power supply over the other turns can be maintained.

Preferably The conductive intermediate element has a cylindrical shape.

Preferably it can be provided that it is the conductive intermediate element is a wire spiral.

By Attachment of, for example, a cylindrical wire spiral as an intermediate element It is possible to have an electrical connection to a variety from locations on the outer electrode.

Preferably the used wire spiral is elastic. This wears helping to ensure that a transmission of vibrations to the Contact pin is reduced because the wire spiral due to their elastic properties of the strains and vibrations of the piezo stack can dampen. The contact pin can, for example, at this Wire spiral be soldered and thus remains firmly with the outer electrode, and thus the stack, connected and is held in this position.

One elastic intermediate element, which together with the piezo stack can expand and contract, is particularly beneficial if, for example an AC voltage is applied to the piezo stack and the Stack then expands each time the voltage changes contracts. Through this dynamic load can Cracks on the outside of the piezostack arise, the when using an inelastic intermediate element in places tear off individual contact points or the outer electrode to damage. In the worst case, this would be too cause a complete failure of the piezoelectric actuator. Should the piezoelectric actuator, for example, a valve piston of a control valve operate, which as an injection valve in a motor vehicle serves, then the piezoelectric actuator must be replaced immediately to a to ensure further operation of the injector and thus of the engine.

In a further advantageous embodiment, the number the turns per unit length of the spiral and the number the electrode layers per unit length of the piezo stack do not differ by more than 20%.

A Spiral has a certain number of turns. These turns the spiral are with the electrode layers over the outer electrode connected. Thus, the wire spiral in the expansion of the stack optimally adapted to its length, it must be between be stretchable to the contact points and about one of the necessary Resilience adapted spring constant have.

There the extent of the stack when applying a voltage proportional is the number of layers of piezoceramic, it is necessary adjust the spring constant of the wire spiral to this situation. This can be done, for example, by adjusting the turns per Unit of length, by using a different material for the spiral or by changing the Shape of the spiral can be achieved.

Should it now when using the piezoelectric actuator and the occurring during operation dynamic stress to cracks or to release a contact come on a turn, the electrical connection remains over a contact point exist on another turn. In this way a high life of such a piezoelectric actuator can be achieved as a permanent and reliable connection to one external electrical connection is made.

In a further advantageous embodiment is on the Intermediate element, a pin receptacle for receiving the contact pin intended.

through this pin receptacle, the contact pin fixed to the intermediate element, and thus connected to the piezo stack. Likewise, the contact pin connected to the piezo stack always conductive and is located in the same distance to the stack.

Usefully it can be provided that the pin holder comprises a plurality of elements.

Of the The advantage is that the arrangement of the contact pins with respect the piezo stack is more stable and the contact pins in the further Can not move history. The more jobs the contact pin is connected to the intermediate element, the less likely it is that due to the tension occurring in the piezo stack the electrical contact between the contact pin and the intermediate element is interrupted. Because the piezo stack with the attached intermediate element and contact pin preferably in the further course of production is still shed, it is important that the contact pins themselves are located at a fixed distance to the piezo stack and that this have a fixed orientation with respect to the piezo stack.

These Alignment with respect to the piezo stack can be achieved by using an intermediate element which is over has the necessary rigidity and strength to a rotation or displacement of the contact pins with respect to prevent the piezostack.

Preferably it is provided that the pin receptacle a plurality of rings includes.

The Rings of the pin holder can tightly enclose the pin, or they can also be soldered firmly to the contact pin be. It is also possible that the contact pin tightly enclosing rings be soldered with this. Thus, the contact pin mechanically held in the immediate vicinity of the intermediate element. The rings of the pin holder can both on the intermediate element, and be attached to the contact pins.

Farther can also be provided that the pin recording several elements includes, and these are spaced from each other.

Should the contact pin in one place or in several places, the be directly adjacent, be attached, then one could Torque applied to the contact pin for this Make sure that the contact pin is no longer the right one Having orientation with respect to the piezo stack, which for later connection to the voltage source is necessary. However, if the contact pin is in several places, which are spaced apart, fixed, so can a rotation of the contact pin with respect to the piezo stack are avoided.

Farther can be provided that the piezo stack, the intermediate element and the contact pin are arranged parallel to each other.

Especially it is preferred that a contact pin by means of an intermediate element is kept at a constant distance to the piezo stack.

The Arrangement in this position and at a certain distance advantageous for the subsequent electrical contacting. To use the finished piezoelectric actuator, it is advantageous if its pins in predetermined Connections fit. This can be achieved by the Contact pins are arranged at a fixed distance from each other and have a fixed orientation to each other and to the piezo stack. This can, for example, by means of a cylindrical wire spiral be achieved.

Around to contact a piezo stack, is in a first step Contact pin attached to an intermediate element. This intermediate element becomes then, with the contact pin attached to it, to the piezo stack introduced and there at the outer electrode of the Soldered piezostacks.

By a suitable intermediate element, it is possible, the contacting process to automate. The contact pins and the intermediate elements can be produced in advance and then only have to be attached to the outer electrode of the piezo stack.

The Invention will now be described with reference to the accompanying drawings particularly preferred embodiments explained by way of example.

It shows:

1a a piezoelectric actuator with contact pins connected to the electrode layers via an intermediate element,

1b a top view of a piezoelectric actuator with a via an intermediate element connected to the electrode layers pins,

2a a wire spiral with attached pin holder and a contact pin,

2 B a wire spiral with attached pin holder and a contact pin mounted in the pin holder,

2c like two wire spirals with pin mounted in the pin holder with one Piezo stack to be connected.

1a schematically shows a side view of a piezoelectric actuator 10 , The electrode layers are clear 20 to recognize which mutually from the piezo stack 12 lead out. On the right and left side of the piezostack 12 is the outer electrode 18 applied, wherein in the representation used here only the right outer electrode 18 is visible.

A cylindrical wire spiral 16 is conductive via several contact points with the outer electrode 18 connected, so that on this particular side of the piezostack 12 leading out electrode layers 20 electrically connected to the outside can be connected. Such a connection is made via the on the cylindrical wire spiral 16 attached contact pins 14 produced.

These pins 14 are each surrounded by two spaced-mounted rings which serve as a pin recording. By means of these contact pins 14 can apply a voltage to the piezo stack 12 be created. Because the rings do not match the contact pins 14 are soldered, but only close tightly with them, the entire construction is stable but still flexible.

In 1b is a top view of the in 1a described Piezostacks 12 to see. However, this is in addition of a potting compound 26 wrapped for stability serves as well as protection against contamination. In the middle of the drawing is the piezo stack 12 to see. On the side surfaces of the stack is the outer electrode 18 , from a stoving paste, which is screen printed on the piezo stack 12 was applied, shown.

Also are the cylindrical wire spirals 16 to see which ones with the contact pins 14 are connected. The diametrically opposite the contact pins part of the cylindrical wire spiral 16 is with the outer electrode 18 via different contact points 24 connected. The whole construction is with a potting compound 26 , such as silicone, surrounded.

2a shows a first step to a connection between an outer electrode 18 and an external applied electrical power source. This will be a cylindrical wire spiral 16 which has a pin holder 22 features, with a contact pin 14 connected.

2 B shows a cylindrical wire spiral 16 which is connected to a spring pin. The pin receptacle is designed in the illustrated case of two spaced-apart rings, which firmly surround the contact pin and hold it so stable. This cylindrical wire spiral 16 with the attached contact pin 14 It is very easy to produce, cheap to produce and can be prefabricated to be attached to the piezo stack in a single step.

2c then shows a piezo stack with mutually out of the piezo stack leading out electrode layers and applied on opposite sides outer electrodes 18 , To these outer electrodes 18 Now each is an already prefabricated cylindrical wire spiral 16 , which with a contact pin 14 connected, introduced. Subsequently, the contact pins 14 diametrically opposite part of the cylindrical wire spiral 16 over the entire length of the piezostack 12 and thus the outer electrode 18 by vapor phase soldering on the outer electrode 18 attached. This piezostack 12 with the two attached cylindrical wire spirals 16 and the contact pins 14 , then can still with a potting compound 26 , such as silicone, shed.

The in the above description, in the drawings and in the Claims disclosed features of the present invention can be used individually or in any combination be essential for the realization of the invention.

10

piezo actuator

12

piezostack

14

pin

16

cylindrical wire spiral

18

outer electrode

20

electrode layer

22

pin receptacle

24

contact points

26

sealing compound

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

• WO 2005/035971 A1 [0003]
• - DE 19648545 A1 [0003]
• - DE 19945933 C1 [0003]

Claims (13)

Piezoelectric actuator ( 10 ) in multilayer construction, in which piezoelectric layers and electrode layers ( 20 ) are arranged alternately one above the other to form a stack, wherein the electrode layers ( 20 ) on opposite sides of the stack lead out of this and via an outer electrode ( 18 ) electrically with a contact pin ( 14 ), wherein an electrical connection between the outer electrode ( 18 ) and the contact pin ( 14 ) is made via a conductive intermediate element. Piezoelectric actuator ( 10 ) according to claim 1, wherein the intermediate element extends over the entire length of the outer electrode ( 18 ). Piezoelectric actuator ( 10 ) according to claim 1 or 2, wherein the conductive intermediate member has a cylindrical shape. Piezoelectric actuator ( 10 ) according to one of the preceding claims, wherein the conductive intermediate element is a wire spiral ( 16 ). Piezoelectric actuator ( 10 ) according to claim 4, wherein the number of turns of the wire spiral ( 16 ) per unit length and the number of electrode layers ( 20 ) do not differ by more than 20% per unit length of the piezo stack. Piezoelectric actuator ( 10 ) according to one of the preceding claims, wherein on the intermediate element a pin receptacle ( 22 ) for the contact pin ( 14 ) is provided. Piezoelectric actuator ( 10 ) according to claim 6, wherein the pin receptacle ( 22 ) comprises several elements. Piezoelectric actuator ( 10 ) according to claim 7, wherein the pin receptacle ( 22 ) comprises a plurality of rings. Piezoelectric actuator ( 10 ) according to claim 7 or 8, wherein the pin receptacle ( 22 ) comprises a plurality of elements spaced from each other. Piezoelectric actuator ( 10 ) according to one of the preceding claims, wherein the piezo stack ( 12 ), the intermediate element and the contact pin ( 14 ) are arranged parallel to each other. Piezoelectric actuator ( 10 ) according to one of the preceding claims, wherein the contact pin ( 14 ) by means of an intermediate element at a constant distance to the piezo stack ( 12 ) is held. Method for contacting a piezoactuator ( 10 ) comprising the following steps: - fixing a contact pin ( 14 ) on an intermediate element - bringing the intermediate element with the contact pin attached thereto ( 14 ) to the piezo stack ( 12 ) - soldering the intermediate element including the contact pin ( 14 ) on the outer electrode ( 18 ) of the piezostack ( 12 ) The method of claim 11, wherein the soldering of the intermediate element to the outer electrode ( 18 ) by vapor phase soldering.