Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-04-22
2001-08-14
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06274967
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a piezoelectric actuator for a servo drive, a servo drive with a piezoelectric actuator and methods for producing a piezoelectric actuator.
Piezoelectric actuators are used, for example, in a servo drive for a fuel injection valve in order to control an injection needle and therefore for controlling an injection process for an internal combustion engine.
German Patent DE 38 44 134 C2 has already disclosed a servo drive having a piezoelectric actuator with a piezoelectric actuator stack which is contained in a drive housing and is surrounded by a hollow cylindrical spring element. The actuator stack and the spring element are clamped between an actuator cap and a displaceable actuator base.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a piezoelectric actuator for a servo drive, a servo drive with a piezoelectric actuator and a method of producing a piezoelectric actuator, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and which improve damping characteristics of the piezoelectric actuator and the servo drive.
With the foregoing and other objects in view there is provided, in accordance with the invention, a piezoelectric actuator for a servo drive, comprising an actuator stack; a hollow cylindrical spring element surrounding the actuator stack; an actuator cap and an actuator base between which the actuator stack and the spring element are clamped; an actuator casing disposed between the spring element and the actuator stack; electrical connections and connection elements disposed with the actuator stack in the actuator casing; and an elastic compound at least one of force-lockingly and form-lockingly connecting the spring element to the actuator casing.
In accordance with another feature of the invention, the spring element has cutouts formed therein at least partly containing the elastic compound. The spring element has a surface over which the cutouts are distributed.
In accordance with a further feature of the invention, the actuator casing has a surface with a structure in which the elastic compound is at least partially incorporated. The actuator casing may be made of the elastic compound and the elastic compound may be made of silicone.
With the objects of the invention in view, there is also provided a servo drive, comprising a drive housing; and a piezoelectric actuator disposed in the drive housing, the actuator including an actuator stack, a hollow cylindrical spring element surrounding the actuator stack, an actuator cap and an actuator base between which the hollow cylindrical spring element and the actuator stack are clamped, and an elastic compound at least one of force-lockingly and form-lockingly connecting the spring element to the drive housing.
In accordance with another feature of the invention, there is provided a diaphragm connected to the actuator base and having a central opening through which part of the actuator base protrudes outwardly, the drive housing having end openings closed off by the actuator cap and by the diaphragm. The drive housing has an inner surface with a structure in which the elastic compound is at least partially incorporated. As mentioned above, the spring element may have cutouts formed therein in which the elastic compound is at least partially incorporated and the spring element may have a surface over which the cutouts in the spring element are distributed.
In accordance with a further feature of the invention, there is provided an actuator casing disposed between the spring element and the actuator stack, the actuator casing having a surface with a structure in which the elastic compound is at least partially incorporated. The actuator casing may be made of the elastic compound. The elastic compound may be made of silicone and the drive housing may be made of INVAR.
With the objects of the invention in view, there is additionally provided a method of producing the piezoelectric actuator, which comprises placing the actuator stack, the electrical connections and the connection elements into a hollow profile of the actuator casing; filling the hollow profile with the elastic compound; placing the actuator casing into the spring element and defining an interspace therebetween; clamping end surfaces of the actuator stack disposed in the actuator casing between the actuator base and the actuator cap; connecting the actuator cap and the actuator base to the spring element; and at least partly filling the interspace between the spring element and the actuator casing with the elastic compound.
With the objects of the invention in view, there is furthermore provided a method of producing the piezoelectric actuator, which comprises placing the actuator stack, the electrical connections and the connection elements into the spring element; closing off ends of the spring element and of the actuator stack with the actuator base and the actuator cap; connecting the actuator cap and the actuator base to the spring element; and filling an interior of the hollow cylindrical spring element with the elastic compound.
In accordance with a concomitant mode of the invention, there is provided a method of producing the piezoelectric actuator, which comprises providing the actuator stack, the electrical connections and the connection elements with a passivation layer before placing them into the spring element.
One advantage of the invention is that the damping properties of the servo drive are improved and therefore the reliability and the accuracy of the servo drive are increased. A further advantage is that the components of the servo drive are electrically well insulated from one another and are satisfactorily protected from external environmental influences.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a piezoelectric actuator for a servo drive, a servo drive with a piezoelectric actuator and a method of producing a piezoelectric actuator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein 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 description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 4958101 (1990-09-01), Takahashi et al.
patent: 5004945 (1991-04-01), Tomita et al.
patent: 5113108 (1992-05-01), Yamashita et al.
patent: 5148077 (1992-09-01), Grawey et al.
patent: 5208506 (1993-05-01), Yamashita
patent: 5239223 (1993-08-01), Miyoshi
patent: 5250868 (1993-10-01), Shirasu
patent: 5271133 (1993-12-01), Dam et al.
patent: 5295288 (1994-03-01), Dam et al.
patent: 38 33 109 A1 (1990-04-01), None
patent: 38 44 134 C2 (1992-02-01), None
patent: 197 15 487 A1 (1998-10-01), None
patent: 0 319 038 A2 (1989-06-01), None
International Patent Application WO 98/47188 (Fitzner et al.), dated Oct. 22, 1998.
Daniel J. Jendritza et al,: “Piezopower”, TR Technische Rundschau, vol. 41, 1992, pp. 38-42.
Frank Wilhelm
Lewentz Gunter
Schuh Carsten
Voigt Andreas
Zumstrull Claus
Budd Mark O.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemeer Werner H.
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