Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-09-19
2001-09-04
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06285116
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric element for use in a piezoelectric injector.
2. Description of the Related Art
The piezoelectric element utilizes the piezoelectric effect of a piezoelectric material, and since it has a high response speed and uses no mechanical components, the piezoelectric element is used as an actuator in various fields. For instance, an injector utilizing the piezoelectric element has been developed for use, instead of a solenoid which utilizes an electromagnetic force, in driving a fuel injector to open or close in an internal combustion engine of an automotive vehicle.
FIG. 12
shows a piezoelectric element connected to a driving circuit. The piezoelectric element
91
has a laminated body
91
a
in which piezoelectric layers
911
and internal electrodes
912
are alternately laminated, whereby the piezoelectric element
91
is constructed so as to be displaced by applying a voltage between the internal electrodes
912
. The application of the voltage to the piezoelectric element
91
is implemented from a current source
921
for the driving circuit
92
which is constituted by a capacitor or the like via external electrodes
914
formed on side surfaces of the laminated body
91
a
.
Over-charging the piezoelectric layers
91
may cause, immediately the piezoelectric layers
911
are charged, an elongation thereof which is greater than required, leading a failure of the piezoelectric layer
911
. To cope with this, an inductor
922
is provided in series with the piezoelectric element
91
at an intermediate position along the length of a line
93
for suppressing the over-charging of the piezoelectric layers. However, it is necessary to avoid the interference, by the inductor utilizing electromagnetic induction, with other coil components or the like, and this imposes a limitation to the layout of components in the driving circuit, thus there is no way to prevent the enlargement of the driving circuit. Moreover, especially in the event that the number of inductors increases as the number of piezoelectric elements does, as seen in a case where a plurality of piezoelectric elements of different specifications are driven, the driving circuit
92
becomes larger.
The present invention was made in view of the aforesaid situation, and an object thereof is to provide a piezoelectric element which can be driven with a small and simple driving circuit.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a piezoelectric element wherein an inductor is provided at an intermediate position along a line connecting an external electrode of one polarity with an internal electrode of the one polarity, and, via the inductor, a voltage is applied across internal electrodes formed between piezoelectric layers.
According to this construction, no inductor is required to be provided in a driving circuit for the piezoelectric element. Alternatively, there has to be provided in the driving circuit only one inductor which is connected in series with inductors provided in the piezoelectric elements and is common to the respective piezoelectric elements, thereby making it possible to make the driving circuit small and simple.
According to a second aspect of the present invention, there is provided a piezoelectric element as set forth in the first aspect, wherein the inductor comprises a plurality of insulating layers for incorporation with the laminated body of piezoelectric layers, and wherein a conductor pattern is formed, of a conductive material, into a spiral or a loop and is provided between the respective insulating layers.
Since the conductive pattern is formed between the respective insulating layers, space can be saved. Additionally, a method like the green sheet method which is common in the production of piezoelectric elements, can also be used for producing the inductor portion.
According to a third aspect of the present invention, there is provided a piezoelectric element as set forth in the second aspect, wherein the inductor comprises the conductive patterns and the insulating layers which are laminated alternately, the laminated conductive patterns being electrically connected in series with each other by means of a contact portion which penetrates the respective insulating layers.
According to this construction, the inductance of the inductor can be adjusted in response to the number of insulating layers and conductor patterns.
According to a fourth aspect of the present invention, there is provided a piezoelectric element as set forth in the second or third aspect, wherein a magnetic member is provided close to the conductor pattern between the insulating layers.
The magnetic permeability can be increased by provision of the magnetic member so as to increase the inductance while substantially maintaining the configuration of the inductor.
According to a fifth aspect of the present invention, there is provided an piezoelectric element as set forth in the fourth aspect, wherein the magnetic member is a magnetic material pattern formed between the insulating layers.
The magnetic material pattern can easily be formed using screen printing or the like.
According to a sixth aspect of the present invention, there is provided a piezoelectric element as set forth in the fourth aspect, wherein the magnetic member is a magnetic material core which penetrates the insulating layers.
According to this construction, a high magnetic permeability can be obtained.
According to a seventh aspect of the present invention, there is provided a piezoelectric element as set forth in the first aspect, wherein the inductor comprises three or more insulating layers that are laminated on one another so as to be incorporated with the laminated body of the piezoelectric layers, wherein a plurality of conductor patterns of a first kind, which are formed linearly of a conductive material, are provided in parallel between a first inter-layer portions of the insulating layers, while a plurality of conductor patterns, of a second kind which are formed linearly and diagonally relative to the conductor patterns of the first kind, are provided between second inter-layer portions in such a manner that each of the conductor patterns of the second kind extends from one end of one of two adjacent conductor patterns of the first kind to an opposite end of the other, whereby the respective conductor patterns of the first kind and the respective conductor patterns of the second kind are caused to electrically connect to each other at ends thereof by means of contact portions which penetrate the insulating layer.
Since the conductor patterns are formed between the insulating layers, the inductance of the inductor can freely be controlled in response to the number of conductor patterns while the number of laminated insulating layers and conductor patterns can remain as they are, whereby the space can advantageously be saved. Additionally, a method like the green sheet method which is common in production of piezoelectric elements can also be used.
According to an eighth aspect of the present invention, there is provided a piezoelectric element as set forth in any of the second to seventh aspects, wherein the insulating layers are constituted of the same material as the piezoelectric layers.
According to this construction, it is possible to reduce the production cost by reducing the number of kinds of materials used.
According to a ninth aspect of the present invention, there is provided a piezoelectric element as set forth in the second, third or seventh aspect, wherein the insulating layers are each constituted by a magnetic member.
According to this construction, it is possible to increase the inductance with the configuration of the inductor being maintained substantially as it is. Moreover, there is no need to provide a separate magnetic member, this eliminating a complicated production process which would otherwise be required.
According to a tenth aspect of the present invention, there
Kobayashi Masayuki
Murai Atsushi
Denso Corporation
Enad Elvin
Medley Peter
Pillsbury & Winthrop LLP
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