CROSS-REFERENCE TO RELATED
This is a division of U.S. application Ser. No. 09/499,853, filed Feb. 7, 2000, U.S. Pat. No. 6,681,462 which was a continuation of copending International Application No. PCT/DE98/02061, filed Jul. 22, 1998, which designated the United States.
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a piezoelectric assembly including a piezoelectric actuator prestressed and inserted into an elastic hollow body in an extension direction between a top and a bottom cover plate connected to the hollow body.
Piezoelectric actuators are used, for example, in motorvehicle technology to control an injection valve of an internal combustion engine. German Published, Non-Prosecuted Patent Application DE 196 53 555 Al describes a piezoelectric actuator which is preloaded by a spring device against a cover plate of a housing. The cover plate is screwed through the use of a screw joint to the housing, in which the spring device and the piezoelectric actuator are situated.
German Patent DE 38 44 134 C2 has disclosed an injection valve which has a piezoelectric actuator as a final control element. The actuator is inserted into a hollowcylindrical spring and is preloaded against a housing of the injection valve by the spring. The injection valve has a complex construction and, moreover, the preloading of the actuator is dependent on manufacturing tolerances of the housing.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a piezoelectric assembly, which overcomes the hereinaforementioned disadvantages of the heretofore-known devices and methods of this general type, in which the assembly has a simple construction and is optimized in terms of installation space.
With the foregoing and other objects in view there is provided, in accordance with the invention, a piezoelectric assembly, comprising an elastic hollow body; a top cover plate connected to the hollow body by one of welding and flanging, and a bottom cover plate connected to the hollow body; and a piezoelectric actuator having an extension direction, the actuator inserted into the hollow body in the extension direction between the cover plates for prestressing the actuator.
In accordance with another feature of the invention, the hollow body has a given length, two butting edges and at least one connecting seam connecting the two butting edges to one another and extending entirely over the given length.
In accordance with a further feature of the invention, the hollow body has a longitudinal direction and two butting edges associated with one another and disposed in the longitudinal direction, the butting edges not being connected to one another.
In accordance with an added feature of the invention, the hollow body has apertures at least partially determining an elasticity of the hollow body.
In accordance with an additional feature of the invention, the hollow body is made of at least one plate formed into the hollow body and then fixed by at least one connecting seam.
With the objects of the invention in view, there is also provided a method for producing a piezoelectric structural unit, which comprises inserting a front end of a piezoelectric actuator into a hollow body; force-lockingly or form-lock
5 ingly connecting the inserted front end of the actuator to the hollow body; pressing the actuator into the hollow body with a defined force establishing a prestress of the actuator; and force-lockingly or form-lockingly connecting the actuator to the hollow body in the vicinity of a rear end of the actuator,
10 for fixing the prestress of the actuator.
In accordance with another mode of the invention, there is provided a method which comprises force-lockingly or form-lockingly connecting an open end of the hollow body to a first cover plate for closing the open end, before the step
15 of inserting the actuator; placing a second top plate on the inserted actuator and pressing the second top plate into the hollow body with a given force; and force-lockingly or form-lockingly connecting the second cover plate to the hollow body while maintaining the given force, for perma
20 nently prestressing the actuator with the hollow body.
In accordance with a further mode of the invention, there is provided a method which comprises elastically elongating the hollow body during the prestressing of the actuator with the given force.
25 With the objects of the invention in view, there is additionally provided a method for the production of a hollow body, which comprises producing a plate with a defined area; forming apertures in the plate for affecting an elasticity of the plate; forming the plate into a hollow body to be used
30 to prestress a piezoelectric actuator; and fixing a shape of the formed plate.
In accordance with a concomitant mode of the invention, there is provided a method which comprises at least partially compacting an edge bounding at least one of the apertures.
35 A significant advantage of the invention is that the piezoelectric actuator is surrounded by a hollow body, and the hollow body forms a single structural unit with the prestressed piezoelectric actuator. The prestress of the actuator is permanently fixed during the production of the structural
40 unit. The actuator thus does not need to be prestressed again every time it is removed and installed. The structural unit is therefore easy to install, requires little maintenance and is economical in terms of cost. Other features which are considered as characteristic for the invention are set forth in
45 the appended claims.
Although the invention is illustrated and described herein as embodied in a piezoelectric assembly, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein
50 without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following
55 description of specific embodiments when read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
60 FIG. 1 is a diagrammatic, sectional view of a first embodiment of a prestressed piezoelectric actuator;
FIG. 2 is a sectional view of a second embodiment of the piezoelectric actuator;
FIG. 3 is an elevational view of a sleeve with transverse 65 slots;
FIG. 4 is an elevational view of a sleeve with oblique slots;