Piezoelectric actuator

Details Piezoelectric actuator Piezoelectric actuator

2000-12-29

2001-12-04

Budd, Mark (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

Reexamination Certificate

active

06326717

ABSTRACT:

PRIOR ART
The invention relates to a piezoelectric actuator, in particular for actuating control valves or injection valves in motor vehicles, having an actuator body in the form of a multilayered laminate made up of stacked layers of piezoelectric material with intervening metallic or electrically conductive layers that function as electrodes. The actuator body, on its end faces between a bottom plate oriented toward the valve and a top plate on the opposite end, is elastically prestressed by means of two spring bands that are disposed in the longitudinal direction on opposite sides of the actuator body in which the prestressing force can be adjusted by adjusting means.
A piezoelectric actuator of this kind has been disclosed, for example, by DE 196 50 900 A1 from Robert Bosch GmbH. A multilayered piezoelectric actuator of this kind, embodied in the form of a laminated stack of piezoelectric layers with intervening electrode layers, must be installed under an initial stress since otherwise, it would tear apart when actuated. The order of magnitude of this initial stress depends on the triggering speed and the dimensions of the actuator body. Depending on the embodiment of the piezoelectric actuator body, the initial stress force is 500-1000 N.
The accompanying
FIG. 1
shows a piezoelectric actuator known from the above-mentioned reference, which has a multilayered actuator body
3
. During the manufacture of the known piezoelectric actuator, the end faces of the actuator body
3
are respectively glued to a bottom plate
7
and a covering plate
8
. The required initial stress is exerted by spring bands
4
a
and
4
b,
which are disposed in the longitudinal direction in relation to the two sides of the actuator body
3
. In order to compensate for the tolerances occurring due to manufacturing imprecisions in the production of the actuator body, high precision compensation disks
1
,
2
, &
5
are required. Maintaining a supply of compensation disks and the installation of the disks increases the manufacturing costs of the piezoelectric actuator.
OBJECT AND ADVANTAGES OF THE INVENTION
An object of the invention is to produce a cheaper-to-manufacture piezoelectric multilayered actuator with improved adjusting and compensating elements, which can be used to arbitrarily adjust or readjust the prestressing force exerted on the actuator body by the spring bands.
As in the known embodiment, the actuator body is elastically prestressed by means of spring bands lying laterally across the actuator body. In contrast to the known embodiment, however, the spring force is adjusted by turning an adjusting nut.
A compensation rocker, which engages centrally on a concave recess of the adjusting nut, serves to prevent a unilateral introduction of force as a result of tolerance-encumbered spring bands and has an axially protruding centering bolt whose spherical contour can move on the concave recess of the adjusting nut. As a result, when the adjusting nut is turned, the initial stress is uniformly exerted, i.e. in a centered fashion. Tolerances in the spring rigidities are compensated for by a tilting of the compensation rocker. In this way, arbitrary prestressing forces in a desired force range can be smoothly adjusted or readjusted during the service life of the piezoelectric actuator or the valve that is equipped with the prestressing force. Simultaneously, the assembly is simplified and is made less expensive since a correction with the adjusting nut only has to be carried out at one location.
With the embodiment according to the invention of a piezoelectric actuator, the following advantages in particular are achieved:
A unilateral introduction of force is prevented through the use of the compensation rocker. This means that the piezoelectric actuator has a longer service life because the probability of fracture formations is reduced.
Through the use of prefabricated parts and the force adjustment at a single location, i.e. at the adjusting nut, the assembly of the piezoelectric actuator is simplified and therefore less expensive.
The prestressing force can be readjusted during the service life of the piezoelectric actuator. This advantageously takes into account a fatigue of the spring bands producing the prestressing force.
The above features and advantages of the piezoelectric actuator according to the invention will be clarified further by the following description of two exemplary embodiments when taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 5359252 (1994-10-01), Swift et al.
patent: 19650900 (1998-06-01), None
patent: 19653555 (1998-06-01), None

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