WO2010128001A1

WO2010128001A1 - Piezo-actuator comprising electrical contacting pins

Info

Publication number: WO2010128001A1
Application number: PCT/EP2010/055929
Authority: WO
Inventors: Herbert J. Thanner
Original assignee: Epcos Ag
Priority date: 2009-05-07
Filing date: 2010-04-30
Publication date: 2010-11-11
Also published as: DE102009020238A1; DE102009020238B4

Abstract

Piezo-actuator (10) having a multi-layer design, in which piezo-electrical layers and electrode layers (20) are alternately arranged on top of each other to form a stack, wherein the electrode layers (2) lead out of said stack at opposing sides of the stack and are electrically connected to a contact pin (14) by way of an outside electrode (18), wherein an electrical connection between the outside electrode (18) and the contact pin (14) is established by way of a conductive intermediate element. Furthermore, a method for attaching an intermediate element to a piezo-stack is provided in order to establish a simple and stable connection between the outside electrode (18) and an external voltage source.

Description

description

Piezo actuator with electrical contacting pins

A piezoelectric actuator in multilayer construction is described, in which piezoelectric layers and electrode layers are arranged alternately one above the other to form a stack, the electrode layers leading out of the stack on opposite sides of the stack and electrically connected to a contact pin via an outer electrode. When an electrical voltage is applied to the internal electrodes, the stack expands perpendicular to the electric field resulting from the applied voltage.

By means of such a piezoelectric actuator, for example, a valve piston of a control valve is actuated, which serves as an injection valve in a motor vehicle.

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

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

This object is solved by the subject matters of the independent claims.

Advantageous embodiments and modifications of the invention will become apparent from the dependent claims. It is a piezoelectric actuator in multilayer construction specified, in which piezoelectric layers and electrode layers are arranged alternately stacked, the electrode layers on opposite sides of the stack lead out of this and electrically connected via an outer electrode to a contact pin, wherein an electrical connection between a the outer electrodes and a contact pin is made via a conductive intermediate element. The second outer electrode can be connected to a contact pin in the same way.

It is a piezoelectric actuator specified, which has a plurality of thin films of piezoceramic, which are arranged to form a stack. 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 apply an electrode layer to each film of piezoceramic. Depending on the desired voltage-dependent behavior of the piezo stack, for example, only every second layer of piezoceramic can be provided with an electrode layer. In order to form these electrode layers, a metal paste, for example, a silver palladium paste or a copper-containing paste may be applied to the films by a screen printing method.

Furthermore, it must be ensured in the production of a piezo stack that the electrode layers do not extend over the entire surface of a film of piezoceramic in a piezo stack in which the electrode layers alternately lead out of the piezo stack. The respective free surfaces on a film of piezoceramics, in which adjacent electrode layers do not overlap in the stacking direction, are called inactive zones. Those with an electrode Layered surfaces which have an overlap with electrode layers adjacent in the stacking direction are referred to as the active zone.

A construction of a piezo stack, in which active and inactive zones are formed, allows, for example, a common connection of all electrode layers with the same polarity.

A disadvantage of a piezo stack construction, in which active and inactive zones are formed, is that tensions and breakages often occur at the transitional areas between active and inactive zones.

After a stack has been formed from the films with the applied electrode layers, the outer electrodes are applied to two opposite outer surfaces of the piezo stack. An outer electrode is made, for example, by means of a stoving paste applied to the outside of the stack by a screen printing process. Then it is sintered with the piezo stack. In order to conductively connect these external electrodes to a contact pin and via this to an external voltage source, it is possible, for example, to use what is known as a wire harp.

Such a wire harp connects the electrode layers via the outer electrode to the contact pin by means of a thin wire. This electrically conductive wire is wound in a plurality of turns around the piezo stack and the terminal pins. Subsequently, this is soldered to the outer electrode and the contact pins. In a further process section, the existing wire connections between the two outer electrodes cut and completely removed the connection to completely isolate the two outer electrodes from each other.

After the two outer electrodes are completely isolated from each other, a passivation can be applied to protect against external influences. 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.

Since this lengthy process can only be automated to a limited extent, instead of a wire harp, a conductive intermediate element is used which consists of as few individual parts as possible, preferably of a single part, and at the same time is stable against stresses such as occur in a piezo stack described above.

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

The fact that the outer electrode is extended over the entire length of the piezo stack, all electrode layers of the same polarity are contacted together. In a subsequent step, the conductive intermediate element is attached to the outer electrode. The intermediate element has the task of ensuring a stable connection between the outer electrode and a contact pin.

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

Preferably, the conductive intermediate element has a cylindrical shape.

Preferably, the intermediate element, for example, a cylindrical intermediate element, arranged laterally from the piezo stack. Preferably, the piezoelectric actuator is free of intermediate elements which enclose the piezoelectric stack. In this case, the intermediate element can be arranged and fixed in a particularly simple manner on the piezo stack. For example, the intermediate element is in front of the attachment to the piezo stack in its final outer shape, is introduced in this form to the piezo stack and attached to an outside of the piezo stack. For example, the piezo stack is in a cylindrical intermediate element outside the interior of the cylindrical shape.

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

By attaching an example, cylindrical wire spiral as an intermediate element, it is possible to produce an electrical connection at a plurality of locations on the outer electrode.

Preferably, the wire spiral used is elastic. This contributes to a transmission of vibrations is reduced to the contact pin, because the wire spiral due to their elastic properties can dampen the strains and vibrations of the piezo stack. The contact pin For example, it can be soldered to this wire spiral and thus remains firmly connected to the outer electrode, and thus the stack, and is thus held in its position.

An elastic intermediate element, which can expand and contract together with the piezo stack, is particularly advantageous if, for example, an AC voltage is applied to the piezo stack and the stack then expands or contracts with each change of voltage. As a result of this dynamic load, cracks may form on the outside of the piezo stack, which, if an inelastic intermediate element is used, may in places tear off individual contact points or damage the outer electrode. In the worst case, this would lead to a complete failure of the piezoelectric actuator. For example, if the piezoactuator actuates a valve piston of a control valve which serves as an injection valve in a motor vehicle, then the piezoactuator must be exchanged immediately in order to ensure further operation of the injection valve and thus of the engine.

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

A spiral has a certain number of turns. These turns of the spiral are connected to the electrode layers via the outer electrode. So that the wire spiral can optimally adapt to the length of the stack, it must be stretchable between the contact points and have a spring constant adapted to the required load capacity. Since the expansion of the stack when applying a voltage is proportional to the number of layers of piezoceramic, it is necessary to adapt the spring constant of the wire spiral to this situation. This can be achieved, for example, by adjusting the turns per unit length, by using another material for the spiral, or by changing the shape of the spiral.

Should it happen when using the piezoelectric actuator and the dynamic load occurring during operation to cracks or to release a contact on a winding, the electrical connection still exists over a contact point on another turn. In this way, a long life of such a piezoelectric actuator can be achieved because a durable and reliable connection to an external electrical connection is made.

In a further advantageous embodiment, a pin receptacle for receiving the contact pin is provided on the intermediate element. The pin receptacle can form an integral part of the intermediate element.

By means of this pin holder, the contact pin can be firmly connected to the intermediate element, and thus to the piezo stack. Likewise, the contact pin is always conductively connected to the piezo stack and is located at the same distance from the stack.

Usefully, it may be provided that the pin receptacle comprises a plurality of elements.

The advantage is that the arrangement of the contact pins with respect to the piezo stack is more stable and the Contact pins in the course can not move. The more points the contact pin is connected to the intermediate element, the less likely it is that the electrical contact between the contact pin and the intermediate element is interrupted by the stresses occurring in the piezoelectric stack. Since the piezo stack with the attached intermediate element and contact pin is preferably potted in the course of production, it is important that the contact pins are located at a fixed distance from the piezo stack and that they have a fixed alignment with respect to the piezo stack.

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

For example, the pin holder has at least one ring. It is preferably provided that the pin receptacle comprises a plurality of rings. The at least one ring of the pin receptacle can be formed by a wire section.

The rings of the pin receptacle can tightly enclose the contact pin, or they can also be firmly soldered to the contact pin. It is also possible that the contact pin closely enclosing rings are soldered to this. Thus, the contact pin is mechanically held in the immediate vicinity of the intermediate element. The rings of the pin holder can be attached to both the intermediate element, as well as to the contact pins. Furthermore, it can also be provided that the pin receptacle comprises a plurality of elements, and these are arranged at a distance from each other.

Should the contact pin be attached to one or more locations that are directly adjacent, then a torque applied to the contact pin could cause the contact pin in question to no longer have the proper orientation with respect to the piezostack used for later connection to the voltage source is necessary. If, however, the contact pin is fastened at several points which are spaced apart from each other, a rotation of the contact pin with respect to the piezo stack can be avoided.

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

It is particularly preferred that a contact pin is held by means of an intermediate element at a constant distance from the piezo stack.

The arrangement in this position and at a certain distance is advantageous for the subsequent electrical contact. In order to use the finished piezoelectric actuator, it is advantageous if the pins fit into predetermined connections. 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 be achieved for example by means of a cylindrical wire spiral. In order to contact a piezo stack, a contact pin is attached to an intermediate element in a first step. This intermediate element is then brought, with the contact pin attached thereto, to the piezo stack and soldered there to the outer electrode of the piezo stack.

By means of a suitable intermediate element, it is possible to automate the contacting process. 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 explained by way of example with reference to the accompanying drawings by means of particularly preferred embodiments.

It shows:

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

FIG. 1 b shows a top view of a piezoactuator with a contact pins connected to the electrode layers via an intermediate element,

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

FIG. 2b shows a wire spiral with attached pin holder and a contact pin mounted in the pin holder, Figure 2c as two wire spirals are connected with mounted in the pin holder contact pin with a piezo stack.

FIG. 1a schematically shows a side view of a piezoelectric actuator 10. The electrode layers 20 can be seen clearly, which lead out of the piezoelectric stack 12 alternately. On the right and left side of the piezo stack 12, the outer electrode 18 is applied, wherein in the representation used here, only the right outer electrode 18 is visible.

A cylindrical wire spiral 16 is conductively connected to the outer electrode 18 via a plurality of contact points, so that the electrode layers 20 leading out of the piezoelectric stack 12 on the respective side can be electrically conductively connected to the outside via this connection. Such a connection is made via the attached to the cylindrical wire spiral 16 pins 14.

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

FIG. 1 b shows a plan view of the piezo stack 12 described in FIG. 1 a. However, this is additionally enveloped by a potting compound 26 which serves for stability, as well as protection against contamination. In the middle of the drawing, the piezo stack 12 can be seen. On the side surfaces of the stack, the outer electrode 18, from a Baking paste, which was applied by screen printing on the piezo stack 12, shown.

Also visible are the cylindrical wire spirals 16 which are connected to the contact pins 14. The diametrically opposite the contact pins part of the cylindrical wire spiral 16 is connected to the outer electrode 18 via different contact points 24. The whole structure is surrounded by a potting compound 26, such as silicone. The cylindrical wire spirals 16 are arranged laterally from the piezo stack 12. The piezo stack 12 is not enclosed by turns of the wire spirals 16.

Figure 2a shows a first step to establish a connection between an outer electrode 18 and an external applied electrical voltage source. In this case, a cylindrical wire spiral 16, which has a pin receptacle 22, connected to a contact pin 14.

Figure 2b 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 is very easy to produce, inexpensive to manufacture and can be prefabricated to be attached to the piezo stack in a single step.

FIG. 2c then shows a piezo stack with electrode layers leading out of the piezoelectric stack and external electrodes 18 applied on opposite sides. An already prefabricated cylindrical wire spiral 16, which is connected to a contact pin 14, is now brought to each of these external electrodes 18. Subsequently, the contact pins 14 diametrically opposite part of the cylindrical wire spiral 16 over the entire length of the piezo stack 12 and thus the outer electrode 18 by means of vapor phase soldering to the outer electrode 18 is attached. This piezo stack 12 with the two attached cylindrical wire spirals 16 and the contact pins 14, can then be potted with a potting compound 26, such as silicone.

The features of the present invention disclosed in the foregoing description, in the drawings and in the claims may be essential to the realization of the invention both individually and in any combination.

List of reference numbers:

10 piezo actuator

12 piezo stack

14 contact pin

16 cylindrical wire spiral

18 outer electrode

20 electrode layer

22 pin holder

24 contact points

26 potting compound

Claims

claims

1 piezoelectric actuator (10) in multilayer construction, in which piezoelectric layers and electrode layers (20) are arranged alternately stacked to one another, wherein the electrode layers (20) on opposite sides of the stack out of this and via an outer electrode (18) electrically with a Contact pin (14) are connected, wherein an electrical connection between the outer electrode (18) and the contact pin (14) is made via a conductive intermediate element.

2. Piezoelectric actuator (10) according to claim 1, wherein the intermediate element extends over the entire length of the outer electrode (18).

3. Piezoelectric actuator (10) according to claim 1 or 2, wherein the conductive intermediate element has a cylindrical shape.

4. Piezoelectric actuator (10) according to one of the preceding claims, wherein the conductive intermediate element is a wire spiral (16).

5. 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) per unit length of the piezo stack do not differ from each other by more than 20%.

6. piezoelectric actuator (10) according to any one of the preceding claims, wherein on the intermediate element a pin receptacle (22) for the contact pin (14) is provided.

7. piezoelectric actuator (10) according to claim 6, wherein the pin receptacle (22) comprises a plurality of elements.

8. The piezoelectric actuator (10) according to claim 7, wherein the pin receptacle (22) comprises a plurality of rings.

9. piezoelectric actuator (10) according to claim 7 or 8, wherein the pin receptacle (22) comprises a plurality of elements which are arranged spaced from each other.

10. Piezoelectric actuator (10) according to one of the preceding claims, wherein the piezoelectric stack (12), the intermediate element and the contact pin (14) are arranged parallel to each other.

11. Piezoelectric actuator (10) according to one of the preceding claims, wherein the contact pin (14) is held by means of an intermediate element at a constant distance from the piezoelectric stack (12).

12. Piezoelectric actuator (10) according to one of claims 3 to 11, wherein the piezoelectric stack is arranged outside the interior of the cylindrical mold.

13. A method for contacting a piezoelectric actuator (10), comprising the following steps:

- Attaching a contact pin (14) to an intermediate element

- bringing the intermediate element with the contact pin (14) attached thereto to the piezo stack (12)

- Soldering of the intermediate element including the contact pin (14) on the outer electrode (18) of the piezo stack (12)

14. The method of claim 13, wherein the soldering of the intermediate member to the outer electrode (18) is carried out by vapor phase soldering.