JPH0436140Y2 - - Google Patents

Description

[Detailed Description of the Invention] Purpose of the Invention [Industrial Field of Application] The present invention relates to an actuator, and specifically relates to a piezoelectric actuator using a piezoelectric element.

[Prior Art] Since piezoelectric elements have good responsiveness, they have been widely applied to various actuators. For example, a fuel injection valve for an internal combustion engine (Japanese Patent Application Laid-Open No. 48-4823, etc.) that utilizes the high-speed response of a piezoelectric element is known. In a piezoelectric actuator used in such a fuel injection valve, one end of the piezoelectric element is fixed to a metal case, etc., and the other end is attached to a moving member such as a piston. A voltage of several hundred volts is applied to make it expand and contract.
Therefore, in such a piezoelectric actuator, an insulating member is bonded to the end surface of the piezoelectric element in the direction of expansion and contraction in order to ensure electrical insulation between the piezoelectric element and the case or moving member.

[Problems to be solved by the invention] However, such conventional piezoelectric actuators have the following problems. That is, (1) If the insulating member is misaligned and adhered to the end face of the piezoelectric element during assembly, the contact pressure will increase during driving, and bending stress will be applied to the piezoelectric element, which may damage the piezoelectric element. There was a problem.

(2) Also, although the amount of expansion and contraction of the piezoelectric element is small at around 0.1 mm, the acceleration is large because it moves in a time of 100 μsec or less. Therefore, during movement, a large force is applied between the piezoelectric element and the insulating member, and the bonded portion may peel off. This peeling causes the piezoelectric element and the insulating member to become misaligned, resulting in the problem that the same problem as described in (1) above occurs even during driving.

Therefore, the present invention was made with the aim of solving the above-mentioned problems and providing a highly reliable 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, a piezoelectric element is disposed between a piston slidably supported by the actuator body and an outer cover fixed to the actuator body, and the piezoelectric element and the piston or the outer cover are formed of at least a conductive member. In the piezoelectric actuator, the insulating member has a bottomed fitting hole on the piezoelectric element side that is deeper than the expansion and contraction amount of the piezoelectric element that fits into the piezoelectric element,
The outer cover or the piston side is provided with a convex portion that fits into a fitting hole provided in the outer cover or the piston, and the piezoelectric element is interposed between the actuator main body and the piston and connects the piston. This is the structure of a piezoelectric actuator characterized by having a spring biased in a direction of contraction.

[Function] In the piezoelectric actuator of the present invention having the above configuration, the fitting hole of the insulating member limits displacement of the piezoelectric element in the radial direction, and the fitting hole of the outer cover or piston limits displacement of the fitting portion of the insulating member. The piezoelectric element expands and contracts while restricting, and the piston moves due to the expansion and contraction. Further, the spring biases the piezoelectric element in the contraction direction via the insulating member, and holds the piezoelectric element between the outer cover and the piston.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a sectional view of a piezoelectric actuator that is an embodiment of the present invention. This piezoelectric actuator includes a metal piston 2 that is slidably supported on an actuator body 1. An O-ring 6 that is prevented from being deformed by a back-up spring 4 is attached to the sliding portion 2a of the piston 2, and
Upper end 2b of piston 2 and actuator body 1
A disc spring 8 and a ring-shaped preload adjustment spacer 10 for adjusting the urging force of the disc spring 8 are installed between the disc spring 8 and the disc spring 8.

A piezoelectric element 14 is disposed at the upper end of the piston 2 via a lower insulating member 12 which is electrically insulating and is mainly composed of alumina. A metal outer cover 18 is provided at the upper end of the piezoelectric element 14 via an upper insulating member 16 which is also made of alumina as a main component and has electrical insulation properties, and a disc spring 8 holds the piezoelectric element 14 in its contracting direction. the outer cover 1 through the lower and upper insulating members 12 and 14.
A piezoelectric element 14 is held between the piston 8 and the piston 2. This configuration will be described later.

Details of the piezoelectric element 14 are shown in FIG. 2. This piezoelectric element 14 is composed of a laminated structure 20 in which a large number of piezoelectric elements are laminated, and stainless steel electrodes 22 and 24 provided on both end faces of the laminated structure 20, respectively. Three connecting portions 22a extending from one electrode 22 are provided at equal intervals along the axial direction of the side surface of the laminated structure 20. In addition, three connecting portions 24a extending similarly from other electrodes 24 are connected to each of the connecting portions 24a.
2a are provided at regular intervals along the axial direction of the side surface of the laminated structure 20.

Further, a fitting hole 2c is formed at the upper end of the piston 2, and a convex portion 12a as a fitting portion protruding from the lower end of the lower insulating member 12 is fitted into the fitting hole 2c. Next, the configuration of the upper end of the lower insulating member 12 will be described with reference to FIG. 3, which is a sectional view taken along line AA in FIG. 1. As shown in the figure, a bottomed fitting hole 12b that is slightly larger than the outer diameter of the piezoelectric element 14 is bored at the upper end of the lower insulating member 12. The depth of the fitting hole 12b is sufficiently larger than the amount of expansion and contraction of the piezoelectric element 14. Moreover, six grooves 12c are also provided at equal intervals in the fitting hole 12b, and the position of the grooves 12c and the connection part 22a of the piezoelectric element 14,
One end of the piezoelectric element 14 is fitted into the fitting hole 12b, aligning with the position of the piezoelectric element 24a.

On the other hand, a fitting hole 16b and a groove 16c having the same shape as the fitting hole 12b and groove 12c of the lower insulating member 12 are also formed at the lower end of the upper insulating member 16 disposed at the upper end of the piezoelectric element 14. The other end of the piezoelectric element 14 is fitted into the fitting hole 16b by aligning the position of this groove 16c with the position of the connecting parts 22a, 24a of the piezoelectric element 14. On the other hand, a convex portion 16a serving as a fitting portion protruding from the upper end of the upper insulating member 16 is fitted into a fitting hole 18a formed in the outer cover 18.

This outer cover 18 is fixed to the actuator main body 1 with bolts 26 through a packing 25, and two electrodes 30 and 32 are inserted into the outer cover 18 through a hermetic seal 28. One electrode 30 is connected to the connection part 22a of one electrode 22 of the piezoelectric element 14 by a lead wire 34, and the other electrode 32 is connected to the connection part 22a of one electrode 22 of the piezoelectric element 14.
The connecting portion 24a of the other electrode 24 and the lead wire 36
connected by.

Furthermore, an insulating sleeve 38 is fitted into the actuator body 1 to insulate the inner wall of the actuator body 1 from the side surface of the piezoelectric element 14 .

The piezoelectric actuator of this embodiment having the above-mentioned configuration is configured such that when a positive voltage is applied from the state shown in FIG. , the piezoelectric element 14 expands. Due to this expansion, the lower insulating member 12 resists the spring force of the disc spring 8.
At the same time, the piston 2 is moved downward in the figure. At this time,
The fitting hole 12b of the lower insulating member 12 into which one end of the piezoelectric element 14 is fitted and the fitting hole 2 of the piston 2
The convex portion 12 of the lower insulating member 12 fitted with c
a, the piezoelectric element 14 is restricted in its radial movement. At the same time, the piezoelectric element 14 is caused by the fitting hole 16b of the upper insulating member 16 into which the other end of the piezoelectric element 14 is fitted and the convex portion 16a of the upper insulating member 16 into which the fitting hole 18a of the outer cover 18 is fitted. , radial movement is restricted.

Furthermore, when the positive voltage to the piezoelectric element 14 is removed from this state, the piezoelectric element 1 whose radial movement is restricted by the lower insulating member 12 and the upper insulating member 16
4 is reduced without shifting in the radial direction. With this contraction, the piston 2 moves upward in the drawing together with the lower insulating member 12 due to the extension force of the disc spring 8. At this time, even if the piston 2 and the lower insulating member 12 are unable to follow the shrinking movement of the piezoelectric element 14, the piezoelectric element 14 will not come out of the fitting hole 12b having a sufficient depth.

As described above, according to the piezoelectric actuator of this embodiment, the lower insulating member 12 and the upper insulating member 16 provided at both ends of the piezoelectric element 14
be well isolated from the surrounding environment. Moreover, the piezoelectric element 14
When expanding and contracting, the piezoelectric element 14 is also prevented from shifting in the radial direction by the protrusion 12a and fitting hole 12b provided on the lower insulating member 12 and the protrusion 16a and fitting hole 16b provided on the upper insulating member 16. . Then,
There is no occurrence of shoots due to displacement of the piezoelectric element 14. Furthermore, this piezoelectric actuator includes a piezoelectric element 14, a lower insulating member 12, and an upper insulating member 1.
There is no need for adhesion to the piezoelectric element 14, and accurate assembly without radial deviation of the piezoelectric element 14 can be easily performed by fitting.Moreover, since the flatness and parallelism are deteriorated by using the adhesive, There is no possibility that an unbalanced load will be applied to the piezoelectric element 14, causing cracks or cracks in the piezoelectric element 14.

Note that, as in the second embodiment shown in FIG. 4, the lower insulating member 12 has a structure in which the outer periphery of the lower insulating member 12 is fitted into a fitting hole 2d formed in the piston 2 to prevent displacement in the radial direction. Good too.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments in any way, and it goes without saying that the present invention can be implemented in various forms without departing from the gist of the present invention.

Effects of the Invention As detailed above, according to the piezoelectric actuator of the present invention, the piezoelectric element is well insulated from the surroundings by the insulating member, and radial misalignment can be avoided during assembly and driving without using adhesive. It has the excellent effect of preventing the occurrence of shoots. Further, by fitting the piston or outer cover and the piezoelectric element with the insulating member without using adhesive, accurate assembly can be easily performed. Furthermore, it is possible to prevent cracks and cracks from occurring in the piezoelectric element due to deterioration of flatness and parallelism due to the adhesive. Furthermore, it is possible to prevent damage to the piezoelectric element due to the insulating member being attached to the piezoelectric element in a shifted manner. Therefore, the failure rate of the piezoelectric actuator can be improved.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a piezoelectric actuator showing one embodiment of the present invention, Fig. 2 is a parts diagram of a piezoelectric element, Fig. 3 is a sectional view taken along line AA in Fig. 1, and Fig. 4 is another embodiment. FIG. 2... Piston, 12... Lower insulating member, 14
... Piezoelectric element, 16 ... Upper insulating member.

Claims (1)

[Claims for Utility Model Registration] A piezoelectric element is disposed between a piston slidably supported by an actuator body and an outer cover fixed to the actuator body, and at least one of the piezoelectric element and the piston or the outer cover is disposed. In a piezoelectric actuator in which an insulating member is provided between the side formed by the conductive member and the insulating member, the insulating member has a bottomed fitting on the piezoelectric element side that is deeper than the expansion and contraction amount of the piezoelectric element that is fitted with the piezoelectric element. has a hole,
The outer cover or the piston side is provided with a convex portion that fits into a fitting hole provided in the outer cover or the piston, and the piezoelectric element is interposed between the actuator main body and the piston and connects the piston. A piezoelectric actuator characterized by comprising a spring biased in a direction of contraction.