Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-02-25
2004-03-02
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S366000
Reexamination Certificate
active
06700306
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laminated piezo-electric device. More specifically, the invention relates to a laminated piezo-electric device that can be particularly desirably used for the fuel injection devices for automobiles, for the positioning devices used for precision equipment such as optical devices, and as a drive device for preventing vibration.
2. Description of the Related Art
Laminated piezo-electric devices are provided with a pole-like laminate formed by alternately laminating piezo-electric layers and electrode layers (inner electrodes), and can be classified into two types, i.e., those of the co-fired type and those of the stacked type. From the standpoint of lowering the voltage, lowering the cost of production and decreasing the thickness of the layers, the laminated piezo-electric device of the co-fired type is advantageous and is finding gradually spreading applications.
FIG. 10
is a diagram schematically illustrating the structure of a conventional laminated piezo-electric device having a pole-like laminate
53
formed by alternately laminating piezo-electric layers
51
and internal electrode layers
52
in the direction of height. Inert ceramic layers
55
and
55
are laminated on the upper end and on the lower end of the pole-like laminate
53
. The inner electrode layer
52
is covered at its one end (side surface) with an insulator
61
. As is obvious from
FIG. 10
, the two inner electrode layers
52
and
52
neighboring each other with the piezo-electric layer
51
sandwiched therebetween have their different ends (side surfaces) covered with the insulators
61
. For example, the inner electrode layer
52
laminated on the upper surface of the piezo-electric layer
51
has its right side surface covered with the insulator
61
, whereas the inner electrode layer
52
laminated on the lower surface of the piezo-electric layer
51
has its left side surface covered with the insulator
61
.
Thus, the insulators
61
are provided on the different side surfaces of the pole-like laminate
53
so as to cover the side surfaces of the inner electrode layers
52
in an alternate manner. As shown in
FIG. 10
, further, belt-like outer electrodes
70
and
70
are formed on the side surfaces, and lead wires
76
are attached by a solder
77
to the belt-like outer electrodes
70
(one of the belt-like outer electrodes
70
,
70
is a positive electrode, and the other one is a negative electrode).
Therefore, the inner electrode layers
52
are connected to the belt-like outer electrode
70
at their side surfaces that have not been covered with the insulators
61
. Each of the belt-like outer electrodes
70
and
70
is conductive to every other inner electrode layer
52
. Among the inner electrode layers
52
,
52
which are neighbored with each other, one of the inner electrode layers
52
,
52
is conductive to the belt-like outer electrode
70
of the positive polarity and another of the inner electrode layers
52
,
52
is conductive to the belt-like outer electrode
70
of the negative polarity.
Concerning the laminated piezo-electric device having the above-mentioned structure, Japanese Unexamined Patent Publication (Kokai) No. 237172/1992 discloses the one wherein every other end (side surface) of the inner electrode layer exposed to the side surface of the pole-like laminate is covered with a glass (insulator) layer, and the inner electrode layer
52
and the neighboring upper and lower piezo-electric layers (
51
) are firmly joined together with the glass layer, the glass layer being held in a recessed portion of the outer electrode
70
.
In recent years, however, it is a trend to apply a higher electric field and to continuously drive the device for extended periods of time in order to obtain a large amount of displacement under a large pressure by using a small piezoelectric device.
When the above-mentioned conventional laminated piezo-electric device is continuously driven for extended periods of time under the conditions of a high electric field and a large pressure, however, the inner electrode layers
52
formed among the piezo-electric layers
51
peel off the outer electrodes
70
of the positive polarity and of the negative polarity, whereby no voltage is supplied to some of the piezo-electric layers
51
causing a change in the displacement characteristics during the operation. Even the piezo-electric device disclosed in the above-mentioned prior art permits the glass layer (insulating layer) to be cracked when it is continuously driven for extended periods of time under the conditions of a high electric field and a large pressure. Due to the cracking, a short-circuit occurs between the inner electrode layers and the outer electrodes, whereby the voltage is not applied to some of the piezo-electric layers still causing a change in the displacement characteristics during the operation.
That is, the pole-like laminate which is the main body of the laminated piezo-electric device undergoes the stretching and contraction in a direction in which the piezo-electric layers and the inner electrode layers are laminated (in the direction of height). Therefore, the glass layer of a high Young's modulus covering the ends of the inner electrode layers (also covering the ends of the piezo-electric layers neighboring the inner electrode layers) becomes no longer capable of withstanding the stretching/contraction operation due to the continuous drive for extended periods of time and is destroyed, and a short-circuit occurs between the inner electrode layers and the outer electrodes via the destroyed portions.
Japanese Unexamined Patent Publications (Kokai) Nos. 283451/1995 and 51240/1996 disclose laminated piezo-electric devices having electrically conducting protuberances formed by plating on the ends (side surfaces) of the inner electrode layers
52
. With the above piezo-electric devices, however, the junction strength is weak between the electrically conducting protuberances and the pole-like laminate, and the ends of the inner electrode layers peel off the electrically conducting protuberances while the piezo-electric device is in operation. Accordingly, no voltage is supplied to some of the piezo-electric layers like in the above-mentioned case still unable to avoid the problem in that the displacement characteristics undergo a change while the piezo-electric device is in operation.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a laminated piezo-electric device which maintains stable displacement characteristics and excellent durability without permitting the wires to be broken between the outer electrodes and the inner electrodes even after continuously driven for extended periods of time under the conditions of a high electric field and a large pressure.
Another object of the present invention is to provide an injection device by using the above laminated piezo-electric device.
According to the present invention, there is provided a laminated piezo-electric device comprising a pole-like laminate formed by alternately laminating the piezo-electric layers and the inner electrode layers in the direction of height, and a pair of outer electrode plates formed on the different side surfaces of the pole-like laminate, the two inner electrode layers neighboring each other with the piezo-electric layer sandwiched therebetween being electrically connected at their side surfaces to the outer electrode plates which are different from each other, wherein flexible protruded electrically conducting terminals are provided on the side surfaces of the pole-like laminate on where the outer electrodes are arranged, the flexible protruded electrically conducting terminals extending along the side surfaces of the inner electrode layers and being capable of following the stretching and contraction of the pole-like laminate in the direction of height thereof, and the inner electrode layers are joined to the outer electrode plates via the protruded electrically condu
Ashida Koki
Nakamura Shigenobu
Dougherty Thomas M.
Hogan & Hartson
Kyocera Corporation
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