Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-02-05
2001-01-09
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06172445
ABSTRACT:
PRIOR ART
The invention is based on a piezoelectric actuator, having a piezoelectric body, in particular in the form of a multilayer laminate with layers of piezoelectric or piezoceramic material layered on one another and intervening metal or electrically conductive layers acting as electrodes, in which the body, upon pulsating electrical action on its electrodes, executes analogously pulsating strokes, changing the distance between two face ends, facing away from one another, of the body.
Piezoelectric actuators are widely known and in the case of motor vehicles may be used for instance for injection valves of the engine and in brake systems that have anti-locking (ABS) and traction controls (ASR). Such injection valves have an injection nozzle controlled by a tappetlike closure device. An operative surface on the nozzle side is disposed on the tappet and acted upon by the pressure of the fuel supplied to the nozzle; the pressure forces seek to force the tappet in the opening direction of the closure device. The tappet, with a plungerlike end whose cross section is larger than the aforementioned operative surface, protrudes into a control chamber. The pressure prevailing there seeks to urge the tappet in the closing direction of the closure device. The control chamber communicates with the fuel delivery, which is at high pressure, via an inlet throttle and with a fuel return line that has only slight pressure via what as a rule is a throttled outlet valve, or an outlet valve combined with an outlet throttle. When the outlet valve is closed, a high pressure prevails in the control chamber, by which the tappet is moved in the closing direction of the closure device or is held in the closing position, counter to the pressure at its operative surface toward the nozzle. When the outlet valve opens, the pressure in the control chamber drops; the magnitude of the pressure drop is determined by the size of the inlet throttle and the magnitude of the throttle resistance of the opened outlet valve, or the outlet throttle combined with it. The outcome is that the pressure in the control chamber decreases when the outlet valve is opened, such that the tappet is moved in the opening direction of the closure device, or is retained in the opening position, by the pressure forces operative at its operative face toward the nozzle.
The aforementioned outlet valve can be actuated by means of a piezoelectric actuator; in comparison with the reciprocating motion of the closure device of the injection nozzle, short strokes suffice.
ADVANTAGES OF THE INVENTION
Piezoelectric actuators have proven to be reliable adjusting and drive devices. However, when the piezoelectric actuators are used or disposed care must be taken that the piezoelectric bodies which are embodied as multilayer laminates by multilayer technology must not be loaded by tensile stress, or can be so loaded only slightly. This can make the construction of piezoelectrically actuated assemblies more difficult.
According to the invention, the piezoelectric actuators are also suitable for loads in the tensile direction, because it is provided that the piezoelectric body has an elastic chucking means that braces the end faces against one another, with precompression of the piezoelectric body.
The invention is based on the general concept of elastically precompressing the piezoelectric body of the actuator by means of prestressing elements disposed or retained on it, counter to the direction of the desired tensile stress, and thus of loading them constantly with pressure; upon imposition of pulsating or alternating electrical fields, the piezoelectric body forces the aforementioned face ends apart, thereby exerting pressure on the piezoelectric material and elastically stretching the chucking means, and then these face ends are subsequently urged toward one another, utilizing the energy elastically stored in the chucking means, thereby exerting pressure on the piezoelectric body, and work that is operative toward the outside can then be accomplished in both directions of motion.
In the invention, the fact that the face ends, which vary their spacing during work strokes of the piezoelectric body, are meant to be covered with stable coupling elements or end plates in order to transmit force to abutments or to elements that are to be driven, which coupling elements or end plates can be structurally simply connected by elastic tensioning elements, can advantageously be exploited in order to constant assure the desired impingement of pressure on the piezoelectric body.
In a first embodiment of the invention, the tensioning elements may be embodied as one or more resilient clips, which seek to force the aforementioned coupling elements or end plates toward one another, exerting pressure on the piezoelectric body.
Instead of this, it is also possible to connect the coupling elements or end plates to one another by means of resiliently embodied tensioning bands.
The tensioning bands may comprise round or flat material. Finally, the possibility exists of connecting the coupling elements or end plates to one another via a tubular bellows embodied in the manner of a tension spring, so that the chucking means of the piezoelectric body also forms a housing that protects the piezoelectric body.
The tensioning elements are preferably embodied with only slight stiffness, such that their tensioning forces vary only relatively little upon pulsating motions of the piezoelectric body; in particular, the magnitude of the change in force should be slight in comparison with the operative force.
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Boecking Friedrich
Heinz Rudolf
Kienzler Dieter
Potschin Roger
Schmoll Klaus-Peter
Budd Mark O.
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
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