Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-05-30
2004-09-07
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S328000
Reexamination Certificate
active
06787975
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a laminate type piezoelectric device used as a driving source of an injector.
2. Description of the Related Art
An injector (fuel injection device) of an internal combustion engine of an automobile, or the like, is constituted in such a fashion that when a valve body of a three-way valve or two-way valve connected to a common rail storing a high-pressure fuel is operated, an open/close state of a fuel passage is changed over to thereby change a pressure condition applied to a nozzle needle, and the nozzle needle is brought into an open state so as to inject fuel.
A solenoid valve has been used ordinarily as a driving source for operating the valve body. Attempts have been made to employ a laminate type piezoelectric device as the driving source so as to finely control the driving source and to precisely control the fuel injection state as described, for example, in Japanese Unexamined Patent Publication (Kokai) No. 11-229993.
However, an injector using the piezoelectric device for the driving source has not yet been put into practical application though proposals have been made as described above.
In the injector, atomization of the fuel must be repeated at an extremely high speed. In cases, atomization is done more than 10,000 times per minute. Therefore, extremely severe conditions are imposed on the piezoelectric device as the driving source when it is used in practice. No piezoelectric device has yet been developed that can be sufficiently used under such severe conditions without inviting cracks, and so forth.
A practical injector must have not only a sufficient driving force but must be small enough to be accommodated in a small accommodation space.
Further, to accommodate the piezoelectric device in the injector, it is effective to accommodate the piezoelectric device into a cylindrical case. When accommodated in this cylindrical space, the piezoelectric device must exhibit excellent dynamic performance (large force generation). When the piezoelectric device is accommodated in the cylindrical accommodation space, the temperature rise resulting from self-exothermy of the piezoelectric device becomes a problem. Therefore, heat radiation performance must also be improved.
SUMMARY OF THE INVENTION
In view of the prior art technologies described above, it is therefore a first object of the present invention to provide a piezoelectric device, for an injector, usable for a long time and having excellent durability when applied to an injector.
It is a second object of the present invention to provide a piezoelectric device, for an injector, capable of providing a large force generation and having excellent heat radiation performance when accommodated in a cylindrical accommodation space.
According to the first aspect of the present invention, there is provided a piezoelectric device for an injector, built in an injector and generating a driving force of the injector, characterized in that the piezoelectric device is fabricated by alternately laminating a plurality of piezoelectric layers generating displacement in proportion to an applied voltage and a plurality of internal electrode layers for supplying the applied voltage and, in the piezoelectric device, a relation d(0.1 Ec)/d(1.2 Ec)≧0.43 is established, where Ec is coercive electric field which causes the changing of polarizing direction, between an apparent piezoelectric constant d(1.2 Ec) calculated from static elongation when an electric field of 1.2 Ec is applied to the piezoelectric device in the same direction as a polarizing direction while a preset load of 500 N is applied to the piezoelectric device and an apparent piezoelectric constant d(0.1 Ec) calculated from static elongation when an electric field of 0.1 Ec is applied to the piezoelectric device in the same direction as the polarizing direction.
One noteworthy point in the first aspect of the present invention is that the ratio d(0.1 Ec)/d(1.2 Ec) is at least 0.43. When the piezoelectric device generates displacement, there exist a piezoelectric displacement component that immediately starts displacement upon application of a voltage and a 90° rotation component that starts displacement with a delay after the application of the voltage, and they together constitute the overall displacement.
The inventors of the present invention have found that a displacement when an electric field 1.2 times the coercive electric field Ec (the details of which will be explained later) is applied is the sum of the piezoelectric displacement component and the 90° rotation component described above, and a displacement when an electric field 0.1 times the coercive electric field Ec is applied hardly contains the 90° rotation component but almost completely consists of the piezoelectric displacement component.
Therefore, when these apparent piezoelectric constants d are determined, respectively, and their ratio is calculated, the existing ratio of the piezoelectric displacement component contributing to displacement in the piezoelectric device can be determined. In other words, the ratio d(0.1 Ec)/d(1.2 Ec) is the value that replaces the existing ratio of the piezoelectric displacement component when the piezoelectric device undergoes displacement.
Here, the present invention sets the value d(0.1 Ec)/d(1.2 Ec) to at least 0.43. In this way, the present invention can provide a piezoelectric device in which the existing ratio of the piezoelectric displacement component is higher than the 90° rotation component. Since the ratio of the 90° rotation component is smaller in this case, exothermy of the piezoelectric device due to its repeated displacement can be reduced and, eventually, durability of the piezoelectric device can be improved.
Consequently, the present invention can provide a piezoelectric device that can be used for a long time and has excellent durability when applied to an injector.
According to the second aspect of the present invention, it is more preferable that a relation d(0.1 Ec)/d(1.2 Ec)≧0.5 is established between the piezoelectric constant d(1.2 Ec) and the piezoelectric constant d(0.1 Ec).
Next, according to the third aspect of the present invention, there is provided a piezoelectric device for an injector, built into an injector and generating a driving force of the injector, characterized in that the piezoelectric device is fabricated by alternately laminating a plurality of piezoelectric layers generating displacement in proportion to an applied voltage and a plurality of internal electrode layers for supplying the applied voltage; and the piezoelectric device has a change ratio of displacement of 9% or below when a frequency of the applied voltage is changed from 1 Hz to 200 Hz under the state where an AC voltage is applied so that an electric field intensity of 0 to 1.5 kV/mm is generated by a sine wave while a preset load of 500 N is applied to the piezoelectric device.
It is noteworthy in this third aspect that the change ratio of displacement under the condition described above is 9% or below. When the change ratio exceeds 9%, the driving speed of the piezoelectric device cannot be much increased. It is preferable that this change ratio is as small as possible, because, when the change ratio is small, driving can be done at a higher speed. Therefore, according to a fourth aspect of the present invention, it is more preferable that the change ratio is 7% or below.
The change ratio of displacement is expressed by 100×(Y
1
-Y
200
)/Y
1
where Y
1
is displacement when the frequency of the applied voltage is 1 Hz and Y
200
is displacement when the frequency is 200 Hz.
The value of displacement is calculated at 5 seconds after the voltage application.
Next, the function and effect of the third or fourth aspect will be explained.
In the piezoelectric device according to the third aspect of the present invention, the change ratio of displacement described above is 9% or below, or 7% or below. In other words, displacement does not much drop even when the frequency of
Hattori Hidekazu
Kobayashi Masayuki
Mitarai Shinya
Yamamoto Takashi
Aguirrechea J.
Denso Corporation
Mullins Burton S.
Nixon & Vanderhye P.C.
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