DE102005033400A1 - Piezoelectric valve actuator electrically contacts spring surfaces and the metallized recess to screw contact elements in to recess - Google Patents

Abstract

The actuator has inner electrode (12) contact elements formed of spiral springs (13). The contact elements have a conductive surface and by electrically contacting the surfaces and the metallized recesses (11) of the actuator, the contact elements are screwed in to the recesses.

Description

The Invention relates to a piezoelectric actuator with internal contact, for example, for operation a mechanical component such as a valve or the like, according to the generic features of the main claim.

It is known per se that for the construction of the aforementioned piezoelectric actuator a piezoelectric element can be used so that under utilization the so-called piezo effect, a control of the needle stroke of a Valve or the like can be made, wherein the piezoelectric element made of a material with a suitable crystal structure is. When applying an external electrical voltage there is a mechanical reaction of the piezoelectric element, depending on from the crystal structure and the contact areas of the electric voltage represents a pressure or train in a predeterminable direction. such Piezo actuators are suitable, for example, for applications in which lifting movements under high operating forces and run high clock frequencies.

From the DE 103 35 019 A1 is such a piezoelectric actuator is known, which has a multi-layer structure of piezoelectric layers with interposed in the direction of effect internal electrodes which are mutually acted upon by a positive and a negative electric charge. The mutual contacting of the internal electrodes with contact elements takes place here in such a way that these contact elements each lie in an inner recess of the piezoelectric element and are then contacted with the respective internal electrodes in a suitable manner. For example, this can be done by a corresponding design of the respective internal electrodes, which each have a different design pattern depending on the respective polarity, and are thereby alternately introduced to the inner recesses and thus to the contact elements.

by virtue of the over the internal electrodes to each piezoceramic layer as a piezoelectric layer applied electrical voltage lead the piezoceramic layers then each small strokes in the direction of the potential gradient, which add up to the total stroke of the piezoelectric actuator. This total stroke is over the height the applied voltage changeable and can be transferred to a mechanical actuator.

For an external connection contact the inner pins are perpendicular to the layer structure outward guided. In the piezoelectric actuator according to the prior art, the contact elements doing electrically conductive pins with a conductive material, e.g. a polymer, so shed that the respective contact the internal electrodes with the positive and the negative connection a voltage source via the respective associated pins is feasible. The interior walls of the Holes as inner recesses can also be used with a base metallization be provided.

Farther is in the generic piezoelectric actuators to note that by the stroke of the piezoelectric actuator a desired Elongation of the piezoelectric element takes place in the longitudinal direction. Continue to arise through the mutual recesses in the internal electrode design to the contact elements, which should not be contacted, mechanical stresses caused by the relatively low occurring here Elongation caused. In general, also arise in the Application of the previously described piezoactuators by high temperatures or strong temperature fluctuations thermal expansion due to different Materials, in particular in the area of the contacts of the contact elements, so that stretching forces which also vary in size in the area extent may have the internal electrodes and can not always be included in ceramics. It can thus cracks arise as interruptions in the conductor guide, which are safely bridged have to.

Out WO 00/79608 A1 discloses a piezoactuator in which conductive surfaces on each side surface of the piezoelectric element as external contact elements are attached, which contacts with the respective internal electrodes are and each case a net, screen, fabric or corrugated outer electrode on the respective conductive surface is arranged. This outer electrode is at least intermittently contacted with the conductive surface, wherein between the Contact stretches stretchable areas come to absorb the tensile forces can.

Advantages of invention

Of the The piezoelectric actuator described above has a multilayer structure of Piezo layers with a mutual contacting of internal electrodes with Contact elements in the inner metallized recess of the Piezoactors lie. According to the invention are in an advantageous manner the contact elements formed from spiral or coil springs, the have at least one electrically conductive surface and under production an electrically conductive connection between the surface of the Spring wire of the respective spiral or coil springs and the respective metallized Ausneh tion of the piezoelectric actuator in the recesses, or holes of the piezoelectric actuator can be screwed.

In general, this is the inside electrical connection of the internal electrodes, in particular when used in injection systems for fuel, for example diesel, in a motor vehicle advantageous since a better high-pressure seal against the voltage applied externally to the piezoelectric actuator is made possible here. In itself, it is also known that conductive contacting in holes, for example as plated-through holes of printed circuit boards (epoxy or ceramic multilayer technology), are made for electronic circuits. With the invention, such contacting in the particularly deep holes of the piezoelectric element with inner guide surfaces is proposed, which at the same time allow a bridging of interruptions or cracks by a suitable elastic medium.

The Holes according to the invention are advantageously initially with a base metallizations provided and then possibly additionally coated conductive, so that it contacts the internal electrodes brought to the holes mutually are. When the piezo actuator is in operation then in its longitudinal axis expands, it may happen that the contacting tracks interrupted become. Furthermore a relatively high current must be conducted in thin layers, so that a safe cooling the contacting tracks is advantageous.

The Spiral according to the invention or coil springs act as inserted in the respective bore Wire webs or bridges, since they are conductively connected to the conductive wall of the respective bore. It only needs to be ensured that the stretching of the Spiral or coil springs with little or no effort can be done. A spiral or coil springs made of suitable material and more conductive surface is capable of doing so because the strain on the circumference of the bore and the slope of the spring is stretched, it arises here predominantly torsional instead of stretching.

With a suitable production tool, the spiral or coil springs, preferably in the relaxed state larger diameter as the bore has, by turning in the sense in which when friction reduces the diameter, be introduced. This can be either by holding at the inner end or a guide at the outer end happen. The end of the spring can then be designed that with the insertion tool the rotation can be easily initiated and thus screwed. This is also a bending of the end of the spring wire transverse to Center axis advantageous.

Of the Wire of the spiral or coil springs is thus supported in many places on the wall of the bore, leaving a conductive contact with many points the bore is made and at the same time is a good power line in the wire along the bore ensured.

The Spiral according to the invention or coil springs can with the other end in the screwing direction after screwing in protrude a predetermined area from the recess or bore, so that by slight supernatant the spiral or coil springs from the outside a contact with a connection can be produced.

multiplied can be the contact points in the respective bore also by a screwing together of several spiral or coil springs, two- or multi-speed. Of the electrical contact can also be reinforced by the fact that the spiral or coil spring received a mechanical bias or a solid galvanic connection with the wall of the bore by soldering or gluing, For example, with a conductive adhesive is produced.

drawing

embodiments the piezoelectric actuator according to the invention will be explained with reference to the drawing. Show it:

1 a longitudinal section through a piezoelectric actuator according to the prior art with internal contacting of the internal electrodes,

2 a partial longitudinal section through an inventive embodiment of a piezoelectric actuator with internal contact, in which the contacting is performed by means of a coil spring and

3 a partial longitudinal section through an inventive embodiment of a piezoelectric actuator with internal contact, in which two coil springs are present.

description the embodiments

In 1 is a piezoelectric actuator constructed as a so-called multilayer 1 According to the state of the art DE 103 35 019 A1 shown, which is composed of piezofilms of a quartz material with a suitable crystal structure, so that taking advantage of the so-called piezoelectric effect, when applying an external electrical voltage to here only by way of example provided with reference numerals internal electrodes 2 and 3 , a mechanical reaction of the piezoelectric actuator 1 in the direction of action 4 he follows. Inside the piezo actuator 1 There are two longitudinal extensions ments or bores 5 and 6 , wherein the internal electrodes 2 and 3 with a corresponding surface design depending on the polarity to the left hole 5 or to the right hole 6 are introduced.

In the holes 5 and 6 are contact elements, here round pins as the core electrode 7 and 8th present in a conductive but flexible fabric 9 , eg a polymer, are firmly embedded by casting. The core electrodes 7 and 8th and the conductive substance 9 Contact the respective internal electrodes 2 or 3 to the outside, so that with the installation of an electrical voltage to contact areas (in the 1 located below) of the core electrodes 7 and 8th the effect described above can be produced. An attachment of the usually metallic core electrodes 7 and 8th is necessary in the prior art as well as in the embodiments according to the invention, since the electrical conductivity of the flexible material is usually not large enough to the total current for driving the internal electrodes 2 and 3 to lead.

In 2 is a partial longitudinal section through a piezoelectric actuator according to the invention 10 shown as the first embodiment, in which here schematically the area of a bore 11 is shown for the inner contact element. internal electrodes 12 are indicated here only schematically. The inner walls of the hole 11 are here provided with a base metallization and the contact element for the inner contacts of the internal electrodes 12 each consists of a spiral spring 13 or a coil spring. According to the embodiment 3 is additionally a second coil spring 14 in the spiral spring 13 has been screwed, which can be formed by the screwing together of springs a two or more common spring arrangement.

The holes 11 can not only be provided with a base metallization here but also additionally conductive coated, so that the mutually to the holes 11 brought inner electrodes 12 be contacted well. As mentioned above, the piezoelectric actuator expands 10 during operation in its longitudinal axis, so that there may be interruptions in the contact between the base metallization or the conductive layer. It should also be noted that a relatively high current in the thin layers of the internal electrodes 12 must be conducted, which also requires a reliable cooling of the conductor track.

The spiral or coil springs according to the invention 13 . 14 act as several in the hole 11 inserted wire webs and thus as conductive bridges. The spiral springs 13 . 14 can also with a bias in the hole 11 be introduced and also galvanically with the conductive wall of the bore 11 be electrically connected, for example by soldering or gluing by means of a conductive adhesive.

With a suitable tools, the coil spring 13 . 14 in the production of the piezoelectric actuator 10 into the hole 11 be introduced. In this case, the coil spring 13 . 14 in the relaxed state a larger diameter than the bore 11 exhibit and by turning in the sense in which in the friction on the wall of the bore 11 the diameter is reduced, introduced; either by holding at the inner end or guided at the outer end. The end of the spiral spring 13 . 14 should then be designed so that easily with the insertion tool rotation can be initiated and thus screwed, for example by bending the end of the spring wire transverse to the central axis.

After screwing in the spiral spring 13 . 14 The spring wire is supported at many points on the wall of the bore 11 off, leaving a contact with many bodies of the bore 11 is produced and thus a good power line along the bore 11 is ensured. By a slight projection of the coil springs 13 . 14 In addition, a contact with an external terminal contact or a terminal contact surface can be made.

Claims (12)

Piezoactuator, with - a multilayer structure of piezoelectric layers with internal electrodes interposed in the direction of action ( 2 . 3 ; 12 ), which can be acted upon alternately with a positive and a negative electric charge, and with - a mutual contacting of the internal electrodes ( 2 . 3 ; 12 ), which takes place with contact elements, in the inner metallized recess ( 5 . 6 ; 11 ) of the piezo actuator ( 1 ; 10 ) are guided perpendicular to the layer structure to the outside, characterized in that - the contact elements of spiral or coil springs ( 13 . 14 ) are formed, which have at least one electrically conductive surface and to produce an electrically conductive connection between the surface of the spring wire of the respective spiral or coil springs ( 13 . 14 ) and the respective metallized recess ( 11 ) of the piezo actuator ( 10 ) into the recesses ( 11 ) of the piezo actuator ( 10 ) are screwed. Piezoelectric actuator according to claim 1, characterized in that - the spiral or coil springs ( 13 . 14 ) before screwing into the holes ( 11 ) As recesses have a larger diameter by a predetermined amount than the inner diameter the holes ( 11 ). Piezoelectric actuator according to claim 1 or 2, characterized in that - a single spiral or helical spring ( 13 ) is screwed. Piezoelectric actuator according to claim 1 or 2, characterized in that - in addition to a first spiral or helical spring ( 13 ) at least one further spiral or coil springs ( 14 ) for producing a two or more screw arrangement in the first spiral or coil spring ( 13 ) is screwed. Piezoelectric actuator according to one of the preceding claims, characterized in that - the spiral or coil springs ( 13 ) are made of a metal wire. Piezoelectric actuator according to one of claims 1 to 4, characterized in that - the spiral or coil springs ( 13 ) are made of a resilient material with an electrically conductive coating. Piezoelectric actuator according to one of the preceding claims, characterized marked that - one electrically conductive coating by means of a galvanic connection, preferably with solder, can be produced. Piezoelectric actuator according to one of claims 1 to 6, characterized in that - along the spiral or coil springs ( 13 ) a Leitpolymer for contact surface enlargement is attached. Piezoelectric actuator according to one of the preceding claims, characterized in that - the spiral or coil springs ( 13 ) are angled towards the central axis at the end lying in the screwing direction. Piezoelectric actuator according to one of the preceding claims, characterized in that - the recesses ( 11 ) are provided with a conductive layer in addition to a base metallization. Piezoelectric actuator according to one of the preceding claims, characterized in that - the spiral or coil springs ( 13 ) with the other end in Einschraubrichtung after screwing a predetermined area of the recess ( 11 protrude and are electrically contacted there. Piezoelectric actuator according to one of the preceding claims, characterized in that - the piezoelectric actuator ( 10 ) can be used for Nadelhubsteuerung for fuel injection in a motor vehicle.