JPH0436141Y2 - - Google Patents

Description

[Detailed Description of the Invention] Purpose of the Invention [Industrial Application Field] The present invention relates to a piezoelectric actuator, and more particularly to a piezoelectric actuator that obtains mechanical displacement in response to expansion and contraction of a piezoelectric element.

[Prior Art] In recent years, piezoelectric elements have been widely used as actuators in fields that require high-speed response, with attention paid to the high responsiveness of their extension action. An example of such a field is a fuel injection device that injects fuel with good responsiveness in response to the high-speed rotation of an internal combustion engine, and proposals have already been made to apply piezoelectric elements to fuel injection valves (for example, in Japanese Patent Application Laid-Open No. 1972-
``Hydraulic Fuel Bubble Assembly'' of Publication No. 4823). In one type of piezoelectric actuator used in such a fuel injection device, one end of the piezoelectric element is fixed to a cover provided at one opening of a metal cylindrical case, and the other end is fixed to the other end of the piezoelectric element. There is a device in which a piezoelectric element is installed in a cylindrical case so as to be attached to a moving member provided in an opening of the cylindrical case. A voltage of several hundred volts is applied to this piezoelectric element, and the moving member is moved in accordance with the expansion and contraction of the piezoelectric element. In such a piezoelectric actuator, in order to ensure the operation of the piezoelectric element, it is necessary to ensure sufficient electrical insulation between the piezoelectric element and the cylindrical case. Therefore, conventionally, an electrically insulating liquid is sealed in the cylindrical case (for example, ``Method for preventing separation of piezoelectric device'' in Japanese Patent Publication No. 10153/1983), or heat shrinkage is applied to the piezoelectric element. Countermeasures were taken, such as covering the tube with covering material.

[Problems to be Solved by the Invention] However, the above-mentioned conventional techniques have the following problems and are still not satisfactory. That is, (1) In the conventional technology in which an electrically insulating liquid is sealed in a cylindrical case, rust etc. develop in the cylindrical case over time, and impurities become mixed in the liquid. As a result, there was a problem in that the electrical insulation between the piezoelectric element and the cylindrical case was impaired.

(2) In the conventional technology in which a piezoelectric element is covered with a covering material such as a heat shrink tube, the piezoelectric element is covered with the covering material in contact with the piezoelectric element. There was a problem that could be suppressed and reduced. In fact, since the displacement of the piezoelectric element is about 1/1000 of the total length of the piezoelectric element, the amount of reduction described above becomes a big problem.

The present invention has been developed in view of the above problems, and is designed to prevent impurities from intervening between the cylindrical case and the piezoelectric element, and to prevent the displacement and force generated by the expansion and contraction of the piezoelectric element from being reduced. The purpose is to provide a piezoelectric actuator.

Structure of the invention [Means for solving the problems] In order to achieve the above object, the present invention has the following structure as a means for solving the problems. That is, the present invention includes: a cylindrical case made of ceramic having electrical insulation properties; and a cylindrical case disposed within the cylindrical case with a space between the cylindrical case and the cylindrical case, which expands and contracts in response to applied voltage. The piezoelectric element is housed in each of the openings of the cylindrical case via a sealing member to liquid-tightly close each of the openings, and is located at each end of the piezoelectric element to accommodate expansion and contraction of the piezoelectric element. two cylindrical members that are movable according to the conditions; a cooling liquid having electrical insulation sealed between the cylindrical case and the piezoelectric element; and a cooling liquid embedded in at least one of the two cylindrical members. and passing through the cylindrical member, one end of which is located within the cylindrical case and electrically connected to the piezoelectric element;
A piezoelectric actuator comprising: a pair of electrodes with the other end located outside the cylindrical case; and the cylindrical member in which the electrodes are embedded is made of electrically insulating ceramic.

Here, the piezoelectric element may be of any type as long as it generates mechanical strain and displacement or force by applying a voltage, such as piezoelectric ceramics such as ceramics made of laminated PZT, polymers, etc. This includes piezoelectric materials, crystal, etc.
Furthermore, the structure may be, for example, one in which a large number of thin piezoelectric elements are laminated, or one in which several thick piezoelectric elements are laminated.

Examples of ceramics having electrical insulating properties include alumina, beryllia, magnesium, and nitride.

[Function] The piezoelectric actuator of the present invention configured as described above includes a cylindrical case that covers the piezoelectric element with a space between the cylindrical case and the piezoelectric element. It has excellent corrosion resistance. Therefore, the cylindrical case will not corrode, and impurities such as rust will not be present between the cylindrical case and the piezoelectric element. Furthermore, since the cylindrical case is spaced from the piezoelectric element, it does not affect the expansion and contraction drive of the piezoelectric element, and does not suppress the displacement and generated force of the piezoelectric element.

Furthermore, since a cooling liquid is sealed between the cylindrical case and the piezoelectric element, heat generated from the piezoelectric element when voltage is applied to the piezoelectric element is dissipated through the cooling liquid.

In addition, since two cylindrical members are housed in both openings of the cylindrical case via seal members, both cylindrical members can be moved relative to the cylindrical case.

In addition, since the cylindrical member in which the electrode is embedded is made of electrically insulating ceramic, it is easy to ensure sealing and electrical insulation of the electrode-embedded portion.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway view of a piezoelectric actuator as an embodiment of the present invention.

As shown in the figure, the piezoelectric actuator 1 has an outer shape formed by a cylindrical case 3 having a cylindrical shape. This cylindrical case 3 is molded from a material made of phosphorous nitride, which has an electrically insulating property and a thermal conductivity comparable to that of steel, and an annular groove 5b is provided in the inner circumferential wall 5a of the opening 5 on the left side of the figure. It is being A sealing member 7, which is an O-ring, is attached to the annular groove 5b, and a cylindrical member 9 is inserted through the sealing member 7.
is stored. The columnar member 9 is made of ceramic whose main component is alumina.
Its peripheral edge is tapered, and a fitting hole 11 is provided on the right side in the figure. Furthermore, two electrodes 13 are fitted into the cylindrical member 9 to which a voltage is applied from a drive circuit (not shown).

A piezoelectric element 15 is provided inside the cylindrical case 3 so that one end thereof is fitted and fixed into the fitting hole 11 of the cylindrical member 9 and is spaced from the cylindrical case 3 by a predetermined distance. The piezoelectric element 15 is constructed by laminating PZT, and expands and contracts in the horizontal direction in the figure when a voltage is applied from the electrode 13 through the conductor 17.

On the other hand, the inner peripheral wall 105a of the opening 105 on the right side of the figure in the cylindrical case 3 is provided with an annular groove 105b, similar to the opening 5 on the left side in the figure.
A sealing member 107 is attached to the piston 107, and a piston 109 is slidably housed through the sealing member 107. Like the columnar member 9, the piston 109 is made of ceramic mainly composed of alumina, has a tapered peripheral edge, and is provided with a fitting hole 111 on the left side of the figure. The end of the piezoelectric element 15 in the opposite direction from the cylindrical member 9 is adapted to fit into and abut the fitting hole 111 . As is clear from FIG. 1, the cylindrical member 9 and the piston 109 are housed and fixed in both openings of the cylindrical case 3 via seal members 7 and 107, respectively. Therefore, piezoelectric element 15
When expanded, the cylindrical member 9 and the piston 109
move relative to the cylindrical case 3, respectively.
For example, as a general usage mode, the cylindrical member 9 is attached to a fixed member such as a wall (not shown) together with the cylindrical case 3.
When fixed, when the piezoelectric element 15 expands, the piston 109 moves in the right direction in the figure. Further, when the piezoelectric element 15 shortens, the piston 109 moves to the left in the figure due to a restoring force such as a spring (not shown) applied to the surface 115 of the piston 109 on the opposite side to the piezoelectric element 15.

Note that silicone oil 120 is filled between the cylindrical case 3 and the piezoelectric element 15.

When the piezoelectric actuator 1 of this embodiment configured as described above is used, for example, in a fuel injection valve, the surface 115 of the piston 109 opposite to the piezoelectric element 15
The plunger is configured to abut against the piezoelectric element 15, and the voltage applied to the piezoelectric element 15 is controlled to drive the plunger. Furthermore, instead of bringing the plunger into direct contact with the piston 109, the plunger may be driven by amplifying the displacement of the piezoelectric element 15 via a pressure chamber.

In the piezoelectric actuator 1 of this embodiment that has been described in detail above, the cylindrical case 3 that the piezoelectric element 15 covers is made of phosphorus nitride. For this,
The cylindrical case 3 will not corrode over time, and no impurities will be mixed into the silicone oil 120. As a result, the electrical insulation between the piezoelectric element 15 and the cylindrical case 3 is not impaired. Furthermore, the cylindrical case 3 can be made lighter, and the piezoelectric actuator 1 can also be made lighter.

Further, since the cylindrical case 3 is configured to have a predetermined distance from the piezoelectric element 15,
This does not affect the expansion/contraction drive of the piezoelectric element 15, and does not reduce the displacement and generated force of the piezoelectric element 15.

Furthermore, since the piezoelectric actuator 1 of this embodiment is configured to fill the inside of the cylindrical case 3 with a cooling liquid having electrical insulation properties such as silicone oil 120, the amount of heat generated by the piezoelectric element 15 can be further reduced. It can emit a lot. Therefore, the capacitance of the piezoelectric element 15 does not change due to the temperature rise of the piezoelectric element 15, and the displacement of the piezoelectric element 15 and the characteristics of the generated force do not deteriorate, and the drive performance of the piezoelectric actuator 1 is improved. It can be stabilized. Note that in this embodiment, the cylindrical case 3
Since it is made of phosphoric nitride, which has good thermal conductivity, the heat dissipation property described above is even higher, making the above-mentioned effects even more excellent.

In addition, the cylindrical member 9 and the piston 109, which contact both ends of the piezoelectric element 15, are housed and fixed in both openings of the cylindrical case 3 via the seal members 7 and 107, respectively. Each of them is movable relative to the cylindrical case 3 by expansion of the piezoelectric element 15. Therefore, depending on the manner in which the piezoelectric actuator 1 is used, for example, the cylindrical member 9 or the piston 109
By fixing a convenient one of them together with the cylindrical case 3, the other can be made movable according to the expansion and contraction of the piezoelectric element 15. Therefore, the cylindrical member 9 can be used on either the fixed side or the movable side, whichever is easier to connect the electrical wiring to, thereby simplifying the electrical wiring between the electrode 13 embedded in the cylindrical member 9 and the power source. Is possible.

Further, as described above, the cylindrical member 9 and the piston 1
09 are movable relative to the cylindrical case 3 according to the expansion and contraction of the piezoelectric element 15. For example, by fixing only the cylindrical case 3 and making the cylindrical member 9 and the piston 109 movable together, the cylindrical member 9 can be moved. The distance between the two members connected to each of the outer surface and the outer surface of the piston 109 can also be changed according to the expansion and contraction of the piezoelectric element 15.

Moreover, since both the columnar member 9 and the piston 109 can be removed from the cylindrical case 3, it is easy to take out the piezoelectric element 15 from the cylindrical case 3 and perform repairs.

Furthermore, since the electrode 13 is embedded in the cylindrical member 9 made of electrically insulating ceramic, it is possible to easily achieve sealing and electrical insulation between the electrode 13 and the cylindrical member 9.

Further, in the piezoelectric actuator 1, a seal member 7 is installed between the cylindrical case 3 and the cylindrical member 9, and a seal member 107 is installed between the cylindrical case 3 and the piston 109. For this, silicone oil 1
20 has a high sealing performance, the silicone oil 120 does not leak out of the cylindrical case 3, and external air etc. do not enter into the cylindrical case 3.

Furthermore, the piezoelectric actuator 1 is configured such that the cylindrical member 9 and the piston 109 have tapered peripheral edges. Therefore, the seal members 7 and 107 are not damaged during assembly of the piezoelectric actuator 1.

Although the above embodiment is configured to fill the inside of the cylindrical case 3 with silicone oil,
Instead of silicone oil 120, light oil, oil,
Alternatively, the cooling liquid may be filled with another electrically insulating cooling liquid such as pure water, and this cooling liquid also has the same effect as the silicone oil 120.

Further, in order to improve heat dissipation of the cylindrical case 3, the outer peripheral wall or the inner peripheral wall of the cylindrical case 3 may be configured to have a fin shape, and the piezoelectric element 15
can dissipate more of the heat generated.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-mentioned embodiments, and may be modified in various ways without departing from the gist of the present invention.

Effects of the Invention In the piezoelectric actuator of the present invention described in detail above, the cylindrical case that covers the piezoelectric element with a space between the piezoelectric element and the piezoelectric element is formed of ceramic having electrical insulation properties. Therefore, the cylindrical case does not corrode over time, and the electrical insulation between the piezoelectric element and the cylindrical case is not impaired. Further, the displacement and generated force of the piezoelectric element are not reduced. Furthermore, as a secondary effect, it is possible to reduce the weight of the cylindrical case, which in turn contributes to reducing the weight of the piezoelectric actuator as a whole.

In addition, the heat generated from the piezoelectric element is easily dissipated by the cooling liquid sealed between the cylindrical case and the piezoelectric element, so the temperature rise of the piezoelectric element is suppressed and the piezoelectric element becomes stable. Operation can be ensured.

Further, since the two cylindrical members housed in both openings of the cylindrical case via the seal members can be moved relative to the cylindrical case, the two cylindrical members can be moved depending on the mode of using the present invention. Any one of them can be fixed together with the cylindrical case, and the other can be made movable according to the expansion and contraction of the piezoelectric element.

Furthermore, it is also possible to fix only the cylindrical case and make the two cylindrical members movable together so that each of the two cylindrical members can move together in accordance with the expansion and contraction of the piezoelectric element.

In addition, since both of the two cylindrical members are housed so that they can move relative to the cylindrical case, it is easy to remove the cylindrical members from the cylindrical case, take out the piezoelectric element, and repair the piezoelectric element. .

In addition, since the electrodes are embedded in a cylindrical member made of electrically insulating ceramic, it is possible to easily secure the sealing of the electrode portion without using a complicated sealing structure such as a hermetic seal. Furthermore, electrical insulation can also be ensured.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of a piezoelectric actuator as an embodiment of the present invention. 1...Piezoelectric actuator, 3...Cylindrical case, 7,107...Sealing material, 9...Cylindrical member,
15... Piezoelectric element, 109... Piston, 120
……silicon oil.

Claims (1)

[Scope of Claim for Utility Model Registration] A cylindrical case formed of ceramic having electrical insulation properties; a piezoelectric element that expands and contracts; and a piezoelectric element that is housed in each of the openings of the cylindrical case via a sealing member to liquid-tightly close each of the openings, and that is located at both ends of the piezoelectric element and two cylindrical members movable according to expansion and contraction; a cooling liquid having electrical insulation sealed between the cylindrical case and the piezoelectric element; and at least one of the two cylindrical members. embedded in the cylindrical member, passing through the cylindrical member, and having one end located within the cylindrical case and electrically connected to the piezoelectric element;
A piezoelectric actuator comprising: a pair of electrodes whose other ends are located outside the cylindrical case; and the cylindrical member in which the electrodes are embedded is made of electrically insulating ceramic.