EP1972778B1 - Cable duct for a piezo actuator module - Google Patents

Description

State of the art

The invention relates to cable bushings for the electrical contacting in a piezoelectric actuator according to the preamble of the main claim, which can be used, for example, in a piezo injector for timely and quantitative metering of fuel in an internal combustion engine.

Such a piezo injector essentially consists of a holding body and the piezoelectric actuator arranged in the holding body, which has arranged between an actuator head and an actuator base, stacked piezoelectric elements, each consisting of enclosed with internal electrodes piezoelectric layers. The piezoelectric elements are constructed using a material with a suitable crystal structure (piezoceramic) for the piezoelectric layers so that upon application of an external voltage to the internal electrodes, a mechanical reaction of the piezoelectric elements takes place, which in dependence on the crystal structure and the contact areas of the electrical voltage, a pressure or train in a predeterminable direction. The piezoelectric actuator is connected to a nozzle injector with a nozzle needle, so that by applying a voltage to the piezoelectric elements, a nozzle opening is released or closed.

From the DE 101 39 871 A1 a piezo injector with a via a hydraulic pressure booster acting on a valve member piezoelectric actuator is known in which the piezoelectric elements of the piezoelectric actuator are arranged in a sleeve-membrane combination. In this case, the piezoelectric actuator is positioned within a sleeve and the open ends of the sleeve are closed by welds and there are arranged at one end (actuator head) a steel component and a metal diaphragm, wherein the diaphragm adapts to the stroke of the piezoelectric actuator. Located at the other end Also a steel component (actuator foot), through the isolated leads, the electrical contacting of the piezoelectric elements of the piezoelectric actuator is made possible.

In this case, wires may be routed via plug parts as electrical leads to external electrodes on the piezo elements of the piezoelectric actuator. Particularly in the case of piezo injectors in so-called common-rail (CR) systems, a high-pressure seal to an electrical connection space arranged above the piezoelectric actuator is necessary here, through which the electrical lines for electrical contacting of the piezo injector are led to the outside, for example via a high-pressure-tight, for Example, against pressures of about 2000 bar, glass-melted sealing bush in the actuator base of the piezoelectric actuator can be done. The Glaseinschmelzung is either pressed as a separate component in a support member made of metal or the glass is melted directly into the metal part.

The disadvantage of this arrangement is mainly because the press connection can not be made completely tight and in the direct fusion, the metal part is soft, ie. it can not be remunerated.

Another possibility, which is to use conventional ceramic components, is disadvantageous in that in the production of the necessary complex components high surface and tolerance requirements must be met and they are very expensive, since the post-processing of such ceramics requires a very high effort, In addition, the connection of conventional ceramic components to the metallic components (actuator foot) is difficult. Furthermore, a finishing and remuneration of the metallic support member is not possible in all variants.

From the later published document EP 1849991 A a piezoelectric actuator is known in which ceramic bushes are fixed by means of brazed joint on the actuator housing.

Disclosure of the invention

The invention is based on the above-described cable bushings for a piezoelectric actuator with a piezoelectric actuator having arranged between an actuator head and an actuator base arranged piezoelectric elements, wherein in the metallic Aktorfuß isolated running cables for the electrical contacting of the piezoelectric elements are present. According to the invention advantageously have the cable bushings sockets, each consisting of a solderable or weldable non-conductive material and the outside with the metallic actuator foot and / or inside the metallic conductor of the cable with the leads to the piezo elements are soldered or welded.

Preferably, the sockets are made of a solderable ceramic material, for example, alumina.

Such a piezoactuator module may advantageously be part of a piezo injector for an injection system for fuel in an internal combustion engine, as this eliminates the need for the use of expensive special components and the risk of leakage to the environment, d. H. in particular, a discharge of fuel is reduced. Furthermore, simple ceramic mass parts can be used favorably, since the guarantee of absolute tightness and a compensation of surface tolerances by soldering can be achieved; In addition, the metal components (actuator foot) can also be tempered.

The jacks can be made individually or advantageously be sheared from a long round material for cost reasons. According to a first embodiment of the cable bushing according to the invention, the bushes are cylindrical and can be inserted into a corresponding stepped bore in the metallic Aktorfuß, wherein advantageously a solder ring can be introduced into the stepped bore before introducing the respective socket, which facilitates the soldering during the soldering process.

According to another also very advantageous embodiment, the bushings are tapered and then inserted into a likewise conical bore in the metallic Aktorfuß. Both variants improve the supporting action of the cable glands against the high pressure of a liquid in the surrounding space.

Brief description of the drawings

• Figur 1 eine schematische Darstellung eines Piezoinjektors mit einem Piezoaktormodul mit Kabeldurchführungen im Längsschnitt und
• Figur 2 eine separate Darstellung des Aktorfußes des Piezoaktormoduls nach der Figur 1 mit einer gelöteten konischen Buchse als Bestandteil der Kabeldurchführungen.

The invention will be explained below with reference to the embodiment shown in the drawings. Showing:

• FIG. 1 a schematic representation of a piezo injector with a piezoelectric actuator with cable glands in longitudinal section and
• FIG. 2 a separate view of the actuator base of the piezoelectric actuator according to the FIG. 1 with a soldered conical socket as part of the cable glands.

Embodiment of the invention

In FIG. 1 an arrangement 1 is shown with a piezoelectric actuator 2, which can be used for example for Nadelhubsteuerung in the injection system for fuel in an internal combustion engine. Not shown here in detail, but known from the aforementioned prior art piezoelectric elements 3 are part of the piezoelectric actuator 2, which still has an actuator base 4 and an actuator head 5 as a metallic tether of steel. There are electrical leads 6 and 7 passed through the actuator base 4, which are contacted via external electrodes 8 and 9 at here also not shown internal electrodes of the piezoelectric elements 3. Upon actuation of the piezoelectric actuator 2 by applying voltage to the internal electrodes, a mechanical arrangement located vertically below the actuator head 5 can be actuated such that, for example, a release of a nozzle opening of the injection system can take place.

The arrangement 1 with the piezoelectric actuator 2 is installed in an injector body, not shown here, wherein the fuel is guided past the arrangement 1 through the interior of the injector body. This fuel can then be injected for example in a so-called common rail system under the rail pressure mentioned in the introduction or another predetermined pressure in the combustion chamber of an internal combustion engine, not shown here.

The leads 6 and 7 are guided by means of cable bushings 10 and 11 through the actuator base 4, wherein here only schematically ceramic bushings 12 and 13 and in each case an electrical coupling 14 and 15 to the not visible here lead wires in the outwardly guided cable 16 can be seen.

In FIG. 2 the cable ducts 10 and 11 can be seen more clearly in detail. The leads 6 and 7 are here in the jacks 12 and 13 made of a non-conductive but solderable ceramic material, such as alumina, and at the end of the sockets 12 and 13 with the leads of the outer cable 16 preferably also by soldering to the here exemplary meadow executed electrical couplings 14 and 15 conductively connected. In particular, at the cable duct 10 after the FIG. 2 It can be seen that the bush 12 made of the nonconductive but solderable ceramic material is connected via a solder 17 to the actuator base 4 and via a solder 18 the supply line 6 to the corresponding connecting wire of the outer cable 16.

According to another embodiment, not shown here, the bushings are cylindrical and inserted into a corresponding stepped bore in the metallic actuator base 4, in which case a solder ring can be introduced into the stepped bore before the introduction of the respective bush, which facilitates the soldering in the soldering process.

With the invention, in the embodiments shown, the actuator foot 4 as a metallic support member, the piezoelectric actuator 2 after the FIG. 1 Connect with a holding body, not shown here, thereby ensuring the electrical connection of the piezoelectric actuator 2 and seals it at the same time against the hydraulic fuel pressure of about 2000 bar, in the actuator chamber of the piezoelectric actuator to the arrangement 1 after the FIG. 1 prevails against the environment.

The actuator foot 4 as a metallic support member must be quenched before the surface treatment, usually grinding, which is achieved with the inventive introduction of the ceramic jacks 12 and 13, wherein the leads 6 and 7 as control of the piezoelectric elements 3 of the ceramic piezoelectric actuator 2 positionally accurate can be clamped and the seal between the sockets 12 and 13 and between the sockets 12 and 13 and the actuator base 4 via a standard brazing process.

Claims (7)

1. Cable ducts (10, 11) for a piezo actuator module with a piezo actuator (2), which has piezo elements (3) arranged between an actuator head (4) and an actuator base (5), with cables (16) and leads (6, 7) for the electrical contacting of the piezo elements (3) running in an insulated manner in the metallic actuator head (4), characterized in that the cable ducts (10, 11) also have bushes (12, 13), which each consist of a solderable or weldable nonconducting material and the metallic conductors of the cable (16) and the leads (6, 7) are soldered or welded to one another on the outside with the metallic actuator head (4) and on the inside in the bushes (12, 13).
2. Cable ducts according to Claim 1, characterized in that the bushes (12, 13) consist of a solderable ceramic material.
3. Cable ducts according to Claim 2, characterized in that the bushes (12, 13) consist of aluminium oxide.
4. Cable ducts according to Claim 1, 2 or 3, characterized in that the bushes (12, 13) are cylindrically formed and can be inserted into a corresponding stepped bore in the metallic actuator head (4).
5. Cable ducts according to Claim 1, 2 or 3, characterized in that the bushes (12, 13) are conically formed and can be inserted into a corresponding conical bore in the metallic actuator head (4).
6. Method for producing the cable ducts according to Claim 4, characterized in that a solder ring is introduced into the stepped bore before the introduction of the respective bush (12, 13).
7. Use of a piezo actuator module with a cable duct (10, 11) according to one of the preceding claims, characterized in that the piezo actuator module is a component part of a piezo injector for a fuel injection system in an internal combustion engine.

Images