Fluid sprinkling – spraying – and diffusing – With means to vibrate or jiggle discharge
Reexamination Certificate
2001-06-05
2003-12-16
Hwu, Davis (Department: 3752)
Fluid sprinkling, spraying, and diffusing
With means to vibrate or jiggle discharge
C239S102200, C239S533200, C239S585100, C239S533100
Reexamination Certificate
active
06663015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stack-type piezoelectric device used as a drive source of an injector.
2. Description of the Related Art
The injector (fuel injector) of the internal combustion engine of an automotive vehicle is configured, for example, in such a manner that, by moving the valve body of a three-way valve or a two-way valve connected to a common rail having stored therein a high-pressure fuel, a fuel path is switched between open and closed states thereby to change the pressure applied to the nozzle needle and, by thus opening the nozzle needle, the fuel is injected.
A solenoid valve or the like is generally used as a drive source for activating the valve body. On the other hand, for the purpose of controlling the fuel injection accurately by controlling the drive source in finely detailed fashion, and as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 11-229993, for example, an attempt has been made to use a stack-type piezoelectric device as a drive source for the injector.
Nevertheless, an injector using the piezoelectric device as a drive source, though proposed as described above, has yet to be practically implemented.
Depending on the type of the injector, fuel must be injected under a pressure as high as more than 100 MPa. Thus, the piezoelectric device for the injector is required to have high reliability in a harsh operating environment.
Further, the piezoelectric device for the injector which opens/closes the valve at high speed requires a very quick response. The piezoelectric device for the injector charges and discharge in a short time, and a large current flows therein. With the conventionally known piezoelectric device, therefore, the energy consumption is so large that a large burden is imposed on the control circuit and the circuit configuration becomes undesirably bulky.
A typical configuration of the piezoelectric device for the injector is described below.
Specifically, the piezoelectric device for the injector comprises a plurality of piezoelectric layers which expand or contract in accordance with the applied voltage and a plurality of internal electrode layers for supplying the applied voltage, the piezoelectric layers and the inner electrode layers being stacked alternately with each other, and a pair of side electrode layers formed on the outer peripheral sides, respectively, of the piezoelectric device for the injector which are alternately electrically energized in such a manner that adjacent ones, with a piezoelectric layer therebetween, of the internal electrode layers alternately assume different polarities, wherein a pair of the outer electrode layers each include a terminal for supplying the applied voltage from an external power supply.
In a harsh operating environment, the outer electrode layers are liable to a crack or become disconnected, and it becomes impossible to supply the applied voltage to the internal electrode layers, with the result that the performance and the function, of the piezoelectric device for the injector, are liable to be adversely affected.
Japanese Unexamined Patent No. 10-229227 proposes, in addition to a single outer electrode layer, a three-dimensional structure of electrodes formed through partial contact points of the single outer electrode layer.
With this configuration, even in the case that the outer electrode layer develops a crack or is disconnected, the three-dimensionally structured electrodes can secure the electric conduction of the outer electrode layer.
In view of the very harsh operating environment of the injector, however, the partial contact points are liable to become disconnected and also have an insufficient practical durability.
Further, in the case where a plurality of cracks develop in the outer electrode layer between adjacent partial contact points, current fails to flow between the cracks, resulting in an electrical disconnection.
On the other hand, Japanese unexamined Patent Publication No. 59-204288 proposes a piezoelectric device of a different configuration.
In this piezoelectric device, a material like a conductive rubber is continuously coated on the side thereof, and the piezoelectric device has a configuration including a plurality of piezoelectric short plates each 0.5 mm thick stacked one on another. The inner layer electrode extends to the side surfaces of the short plates.
With the piezoelectric device described above, however, the piezoelectric layer has a thickness of only about 100 &mgr;m and therefore it is difficult to extend the inner layer electrode to the side surfaces thereof. Thus, it is difficult to positively secure the electrical connection between the first outer electrode and the inner layer electrode with a conductive rubber-like material and an ordinary method of baking metal is required.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the problems in the prior art described above, and an object thereof is to provide a piezoelectric device most suitably used as a drive source for the injector in a harsh environment or, in particular, to a piezoelectric device for the injector which consumes less energy and has a faster response.
According to a first aspect of the invention, there is provided a piezoelectric device, built in an injector for generating the driving force for the injector, comprising:
a plurality of piezoelectric layers adapted to expand or contract in accordance with an applied voltage and a plurality of inner electrode layers for supplying the applied voltage, the piezoelectric layers and the inner electrode layers being stacked alternately with each other;
a pair of first outer electrode layers formed on the outer peripheral sides, respectively, of the piezoelectric device for the injector, which outer electrode layers are adapted to be alternately electrically energized so that adjacent ones of the inner electrode layers, with a piezoelectric layer therebetween, assume different polarities; and
second outer electrode layers are formed on the first outer electrode layers, respectively, and are made of a conductive material having a larger breaking elongation than the first outer electrode layers.
One aspect of the invention is that a second outer electrode layer made of a conductive material having a larger breaking elongation than a first outer electrode layer is formed on each of a pair of the first outer electrode layers.
The operation of this aspect of the invention will be explained below.
Each of the second side electrode layers has so large a breaking elongation that it is not easily cracked or disconnected even in a harsh operating environment. The cracking or disconnection of the electrode layer is caused by the expansion of the piezoelectric device which generates the stress in the piezoelectric device for the injector or the electrode layers.
In the configuration according to this aspect of the invention, even in the case where the first outer electrode layers are cracked and disconnected, the electrical conduction between the first outer electrode layers and the inner electrode layers is secured through the second outer electrode layers which have a large breaking elongation and are not easily cracked or disconnected. As a result, a piezoelectric device for the injector can be produced which is usable even in a harsh operating environment.
Also, the reliability can be improved by providing substantially two outer electrode layers including a first outer electrode layer and a second outer electrode layer. With the first outer electrode alone, a slight cracking or disconnection would grossly deteriorate the reliability of the piezoelectric device for the injector. With the configuration according to this aspect of the invention, however, the provision of two outer electrode layers including the second outer electrode layer permits either the first or second outer electrode layer to apply a voltage to the inner electrode layers.
The breaking elongation is determined by the value based on the dumbbell elongation measuring m
Kawazoe Naoyuki
Kobayashi Masayuki
Yamada Yutaka
Hwu Davis
Nixon & Vanderhye P.C.
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