Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/50—Piezoelectric or electrostrictive devices having a stacked or multilayer structure

Definitions

• the invention relates to a piezo actuator, for example for actuating a mechanical component, according to the generic features of the main claim.
• a piezo element for controlling the needle stroke of a valve or the like can be constructed from a material with a suitable crystal structure.
• an external electrical voltage is applied, there is a mechanical reaction of the piezo element which, depending on the crystal structure and the contact areas of the electrical voltage, represents a push or pull in a predeterminable direction.
• piezo actuators can be provided for the construction of actuators, for example for driving switching valves in fuel injection systems in motor vehicles.
• the voltage or charge control te deflection of the piezo actuator is used to position a control valve, which in turn controls the stroke of a nozzle needle.
• this piezo actuator is constructed here in several layers from stacked metallized piezo ceramics to a so-called multilayer Actuator.
• there are internal electrodes between the layers which e.g. applied with a printing process, and there are external electrodes through which the electrical voltage is applied.
• a typical method for producing such layers is in the film casting technique. The individual layers are metallized and stacked one above the other to produce the inner electrodes, the piezo effect then acting between two layers with inner electrodes of different polarity.
• the inner electrodes are usually missing at the head and foot area, because on the one hand a certain insulation distance to the end faces is necessary to avoid short circuits to the outside and on the other hand passive zones are used for the electrical connection of the outer electrodes. Passive areas can also be present in the middle of the piezo actuator. However, there is the problem here that these passive layers, as cover packs, represent parasitic or interference capacities with respect to the electrical ground, which can lead to electromagnetic radiation in motor vehicles or other applications.
• the passive layers consist of the same ceramic material as the active area, but with outer electrodes that are not electrically contacted on one side or not at all, so that the inactive areas are also interspersed with the inner electrode metal layers.
• the respective inactive area can also be a complete, electrically insulated metal or ceramic block, which, for example, can simply be glued onto the piezoelectrically active area.
• the piezo actuator described at the outset is constructed with a multilayer structure of piezo layers and in a piezoelectrically active region with internal electrodes arranged between the layers, and is provided with contacting of the internal electrodes which changes from layer to layer and is subjected to an electrical voltage.
• the dielectric constant of at least the head or foot part as inactive areas is lower than the dielectric constant of the active area.
• the inactive regions and the active region are preferably produced from the same basic ceramic substance, additional dopants in the inactive regions are inserted in such a way that there is a minimum dielectric constant.
• the basic substance is, for example, lead zirconate titanate (PZT) and the dopant is silver.
• the layer thicknesses of the inactive areas on the head and / or foot part are the same.
• the inactive regions are formed from an electrically polarized ceramic with an electrical field applied in such a way that there is a minimal dielectric constant.
• the advantage of the invention is in particular that initially the active area of the piezo actuator remains untouched with a predetermined piezoceramic, that is to say that parameters such as idle stroke, blocking force etc. of the active actuating element remain unchanged.
• the parasitic capacitance C para on the head and / or foot part can then be minimized by the choice of material according to the invention, the geometry or the polarity of the cover packs on the head and / or foot part.
• FIG. 1 shows a section through a piezo actuator with a multilayer structure of layers made of piezoceramic and active and inactive areas
• FIG. 2 shows an electrical equivalent circuit diagram of the capacities occurring at the piezo actuator when a connection formation of the inactive areas on inner electrodes of the active area with the same polarity
• FIG. 2 shows an electrical equivalent circuit diagram of the capacitances occurring at the piezo actuator when the inactive regions are connected to the internal electrodes of the active region with an unequal polarity
• FIG. 3 shows a course of the parasitic capacitances at certain ratios of the layer thicknesses of the inactive areas.
• a piezo actuator 1 is shown, which is made in a manner known per se from piezo layers 2 of a ceramic material, e.g. So-called green foils, is constructed with a suitable crystal structure, so that a mechanical reaction of the piezo actuator 1 takes place using the so-called piezo effect when an external electrical direct voltage is applied to internal electrodes 3 and 4 via externally contacted electrodes 5 and 6.
• a ceramic material e.g. So-called green foils
• the piezo actuator 1 is divided into a piezoelectrically active area A and two inactive or passive areas B and C attached to the head and foot ends as cover packs.
• an area is actively referred to, which is penetrated by the internal electrodes 3 and 4 of alternating polarity and thus ultimately contributes to the overall longitudinal expansion of the piezo actuator 1 that is desired for operation.
• the multilayer piezo actuator 1 is constructed in such a way that the Material compositions of the ceramic layers in the active area A and in the passive areas B and C differ.
• two types of ceramics are necessary for green film production. These can be, for example, differently prepared types of ceramic, for example based on lead zirconate titanate (PZT).
• PZT lead zirconate titanate
• These or other ceramics on a jointly based base substance can be changed and adapted accordingly by adding suitable dopants, for example silver.
• the ceramic in the active area A has a dielectric constant of 8 33 .
• the dielectric constant ⁇ '33 of the region B or C is chosen such that the relationship ⁇ ' 33 « ⁇ 33 applies.
• the ceramic of the areas B and C according to FIG. 1 is then selected or modified in such a way that the dielectric constant ⁇ '33 is minimized in any case.
• the parasitic capacitances C B and C c of the areas B or C are accordingly determined as a function of the layer thicknesses d B and d c
• A represents the active area
• the exemplary embodiment according to the invention includes the possibilities that the last connected inner electrode layer 3 or 4 can be selected with the same or different polarity towards the head part B and towards the foot part C at the foot side.
• the invention presented here thus explicitly includes a piezo actuator 1 with symmetrical cover packs B and C on the head and foot part.
• the minimization due to this geometric effect also works in particular when the cover packs B and C are made of the same ceramic material as the active area A.
• a further, not shown in the figures aspect relates to the adjustment of the parasitic capacitance C para by an at least partially polarity of the covering assemblies B and C. If one wants to for a particular electrical vote a certain capacitance value C para to the deck packages B and C set, so this can be done by adjusting the
• Dielectric constant ⁇ '33 and in particular take place via the polarity of the cover packs B and C. Since unpolarized ceramic has a dielectric constant that is only half as large as that of a polarized ceramic, the parasitic capacitance C para quasi can be tuned by installing a suitable electric field.

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• General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)
• Fuel-Injection Apparatus (AREA)

Applications Claiming Priority (2)

Publications (1)

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Country Status (7)

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Family Cites Families (14)

• 2003
  • 2003-11-14 DE DE10353171A patent/DE10353171A1/de not_active Withdrawn
• 2004
  • 2004-09-07 WO PCT/DE2004/001980 patent/WO2005053046A1/de not_active Application Discontinuation
  • 2004-09-07 JP JP2006515701A patent/JP2006527486A/ja active Pending
  • 2004-09-07 CN CNA2004800334030A patent/CN1879231A/zh active Pending
  • 2004-09-07 US US10/578,902 patent/US7402937B2/en not_active Expired - Fee Related
  • 2004-09-07 KR KR1020067009232A patent/KR20060125750A/ko not_active Application Discontinuation
  • 2004-09-07 EP EP04786708A patent/EP1687854A1/de not_active Withdrawn

Non-Patent Citations (1)

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