DE102005014766A1 - Piezoelectric actuator for use in, e.g., automotive engineering for controlling injection valves has piezo-stack, which is electrically connected with contact pins by contact wires according to polarity at opposite longitudinal sides - Google Patents

Abstract

The piezoelectric actuator has piezo-stack (1), which is electrically connected with contact pins (2), running parallel to piezo stack, by contact wires (3) according to the polarity at opposite longitudinal sides and is positioned in longitudinally stretched housing (5) with nearly equal length of piezo-stack. A gap is present between the contacting piezo-stack and the housing, which is approximately completely filled with the sealing compound (4).

Description

The The invention relates to a piezoelectric actuator whose piezo stack via wires and Pins to the outside contacted and in a housing is housed.

piezoelectric Actuators are used, for example, in automotive technology to control Injectors used. The core of the actor is usually composed of a plurality of piezoelectric layers. The electrical contacting of the piezo stack is caused by a variety of thin copper wires made, which at one end on the piezoelectric element and with the other end depending on polarity soldered to one of two pins.

The state of the art is in 5 illustrated and shows a cross section through a piezoelectric actuator with piezo stack 1 , Contact pins 2 , Contact wires 3 , casting compound 4 and housing 5 , The pins each represent the negative and the positive pole and are usually positioned opposite to the piezo stack and parallel to this. The contact pins have, for example, a diameter of 1.0 or 1.2 mm. For manufacturing reasons, the contact pins are rigid. At the same time, their surface for the production of electrical connections must be solderable, for example.

To the Protection against, for example, contained in diesel fuel aggressive Components is the actual piezo element of a silicone encapsulation surround. This silicone coating surrounds both the contact wires as also the contact pins. To simplify the casting of the actuator, forms an outer plastic tube the mold for the actor. The casting mold is retained after casting as an outer shell. When used of piezoelectric actuators are recorded failures to a large part on detachments attributed by Kontaktierdrähten. there decreases first the operating range of the actuator, until finally the total failure follows. For the There is currently no solution to the cause of the error.

Of the Invention is based on the object, a piezoelectric actuator to provide, which has a required creep rupture strength.

The solution This task is done by the combination of features accordingly Claim 1. Advantageous embodiment can be taken from the dependent claims become.

Based of simulations, especially by finite element simulation is the a designed according to the prior art piezoelectric actuator impressed System of vibration elements analyzable. It was recognized that in the frequency range of 50-100 kHz special vibrational eigenmodes pronounced are where the pins individually or in combination the represent oscillating mass and thus, for example, detachment from bonding wires cause. The between the housing the piezoelectric actuator and the piezo stack existing gap is filled with a mass, for example silicone compound, so that in the vibration system, this between contact pin and housing or Mass fractions existing between the contact pin and the piezo stack the function take over a spring.

vibrations the contact pins with high amplitudes lead directly to strong mechanical loads, in particular of contacting stations. The vibration behavior The contact pins offers a very diverse picture, with both three as well as two-dimensional vibrations occur and essential Bending vibrations can be present.

to Remedy of the hitherto existing problem is only that with considered directly related to the Kontaktierstift system. This is composed of the Kontak animal pin, the swinging Measures that approximately at opposite Pages connected with springs, extending between Kontaktierstift and housing on the one hand and between Kontaktierstift and piezo stack on the other are located. To damage in this area, it makes sense to the natural vibration conditions to change that way that no or few natural modes of this system in the area between 50 and 100 kHz occur. This can be done through change the mass of Kontaktierstifte done only to a limited extent. changeable Sizes are however the length and the stiffness of the spring present in the system.

Consequently On the one hand, by changing the Properties of the potting compound to higher viscosities and on the other hand by changing the Expansion of the potting compound the characteristic of the simulation model existing springs are affected. Thus, overall, the frequency spectrum the excitable vibrations of the contact pins to significantly higher values postponed. The extension of the spring is so shortened that the distances be minimized between contact pin and surrounding elements, so for the casting compound remains only a small distance.

in the The following are the basis of schematic figures, the variants represent the invention, embodiments described.

The Figures invariably show a cross section through a finished mounted piezoelectric actuator.

1 shows a section through an actuator with vibration-reducing housing;

2 shows a further embodiment of a vibration-reducing housing, wherein the contact pins are partially enclosed by the housing material;

3 shows a variant in which the contact pins are almost completely enclosed by the housing;

4 shows a variant accordingly 1 , wherein not directly adjacent to the contact pins bulges of the housing are adapted to the described vibration behavior;

5 shows a piezoelectric actuator according to the prior art with a hollow cylindrical housing 5 ,

activities for reducing the vibrations on the contact pins can be various be. For example, you can also the bushings the contact pins by a subsequent to the piezoelectric actuator metal housing, for example be provided with glass beads or a glass-ceramic transition, so that the contact pins are fixed. However, such solutions are rules in terms of ease of assembly, in particular, let certain bends or pressing the pins in such solutions do not continue.

1 shows a shape of the housing 5 on the one hand, the frequency spectrum of the excitable vibrations, which can have a negative effect on the contact pins, shifted to significantly higher values. Furthermore, the amplitudes of the vibrations compared to the prior art can be reduced. This is achieved by the fact that the housing 5 in the area of the contact pins 2 is not formed in the form of a hollow cylinder of constant thickness, but that this inward approaches 6 has, in the form of bulges or bulges, the contact pins partially or almost completely enclose. For the potting compound introduced in between 4 For example, a material with very high stiffness or viscosity is used in relation to the prior art.

The in 1 represented cross section through a piezoelectric actuator does not vary over the entire length, inasmuch as the housing is still produced by extrusion and appropriate cutting to length. Preferably, the housing 5 made of polyamide, which is not a problem for the assembly.

In the 2 to 4 Embodiments are shown that indicate vibration-reduced housing.

2 shows an embodiment in which the contact pins 2 in a range of slightly more than 90 ° from the approaches 6 of the housing 5 are surrounded. The distances are minimized accordingly, so that there are dimensions necessary for the assembly, but the potting compound does not occupy an unnecessarily large volume.

3 shows an embodiment in which the contact pins almost completely from lugs of the lugs 6 are enclosed. There are only openings for the passage of Kontaktierdrähte 3 free.

In 4 an embodiment is shown, wherein additionally in the region of the sides of the piezo stack 1 , where there are no contact pins 2 are located, approaches 6 located inside the housing wall. Accordingly, the entire vibration pattern of the potting compound can be additionally influenced. For the selection of an optimal embodiment with regard to a maximum relief of the contact zone between the contact pin and contacting wire, a simulation can be used. The expansions of the bulges or bulges shown in cross-section in the figures are usually sufficient.

The Advantages of the solution according to the invention are in the oppression the unwanted replacement of wires from the pins. Still is a simple production or assembly of the housing by extrusion, cutting to length and joining together possible. There is no need for changes in the course of the manufacturing process of the piezoelectric actuator.

It is particularly advantageous to use a highly viscous potting compound, in particular, a curable Material represents, so for the preparation of the potting compound is easy to insert and subsequently hardened to the manufacturing process. If the potting compound is designed as an insulator, further results Advantages with regard to the encapsulation of the electrically operated piezo stack.

Claims (8)

Piezoelectric actuator with a piezo stack ( 1 ), which according to the polarity on opposite longitudinal sides by Kontaktierdrähte ( 3 ) with parallel to the piezo stack extending contact pins ( 2 ) in an elongated housing ( 5 ) is positioned with approximately the same length of piezo stack and housing and between the contacted piezo stack and the housing existing space is with a potting compound ( 4 ) filled almost completely with high viscosity. Piezoelectric actuator according to Claim 1, in which the housing ( 5 ) at its inner periphery longitudinally directed approaches ( 6 ), which the contact pins ( 2 ) partially. Piezoelectric actuator according to Claim 2, in which the lugs ( 6 ) have longitudinally directed grooves to the contact pins ( 2 ) to enclose at least over half its circumference. Piezoelectric actuator according to Claim 3, in which the longitudinal projections are nose-shaped in order to form a contact pin ( 2 ) except for a passage for Kontaktierdrähte ( 3 ) to enclose. Piezoelectric actuator according to one of Claims 1 to 4, in which the housing ( 5 ) consists of polyamide. Piezoelectric actuator according to one of Claims 1 to 5, in which the casting compound ( 4 ) is a posthardenable material. Piezoelectric actuator according to one of Claims 1 to 6, in which the casting compound ( 4 ) is a silicone. Piezoelectric actuator according to one of Claims 1 to 7, in which the casting compound ( 4 ) is an insulator.