JPH0436139Y2 - - 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. A piezoelectric actuator used in such a fuel injection valve is shown in FIG. This piezoelectric actuator includes a metal piston 52 slidably supported by a metal actuator body 51, and a convex portion 54a in a small diameter hole 52a formed at one end of the piston 52.
a ceramic lower insulating member 54 fitted with a piezoelectric element 56 having one end glued to the lower insulating member 54;
An upper insulating member 58 made of ceramic to which the other end of the piezoelectric element 56 is bonded, a small diameter hole 60a that fits into a convex portion 58a provided on the upper insulating member 58, and is attached to the actuator body 51 with bolts 62. Metal outer cover 60, metal outer cover 60
Two electrodes 66a and 66b are attached to the electrodes through a hermetic seal 64.

The piezoelectric element 56 is a laminated structure in which a large number of lead zirconate titanate piezoelectric units (specific gravity 5.3 g/cm ³ ) are laminated. On the outer periphery of the piezoelectric element 56, two types of three electrodes 56 are provided to connect the individual piezoelectric elements.
Each of the electrodes 56a, 56b is also provided.
6b is connected to the electrodes 66a and 66b.

The lower insulating member 54 and the upper insulating member 58 bonded to both ends of the piezoelectric element 56 electrically insulate the piezoelectric element 56 from the actuator main body 1 and the outer cover 60, respectively.

Furthermore, an O-ring 70 that is prevented from being deformed by a back-up spring 68 is attached to the sliding portion 52b of the piston 52. On the other hand, a disc spring 7 is provided between the piston 52 and the actuator body 51 to bias the piston 52 in a direction that compresses the piezoelectric element 56.
2. Ring-shaped preload adjustment spacer 7 provided between the disc spring 72 and the actuator body 51
There are 4. Further, an insulating sleeve 76 is fitted into the actuator body 51 to insulate the actuator body 51 and the piezoelectric element 56.

In this piezoelectric actuator, when a positive voltage is applied to the piezoelectric element 56 via the electrode 66 from the state shown in FIG. At the same time, the piston 52 is slid downward in the figure. Furthermore, when a negative voltage is applied to the piezoelectric element 56, the piezoelectric element 56 contracts, and the spring force of the disc spring 72 causes the piston 52 to slide upward in the figure.

[Problems to be solved by the invention] However, such conventional piezoelectric actuators have the following problems. (1) Conventional piezoelectric actuators have had the problem of increasing the overall length of the piezoelectric actuator because it is necessary to provide an insulating member to accommodate the piezoelectric element within the metal actuator body.

(2) Also, when a piezoelectric actuator is driven, a large force is applied to the piezoelectric element itself, and if the piezoelectric element is not assembled with appropriate flatness and parallelism on both end faces of the piezoelectric element to which the insulating material is bonded, the piezoelectric element will be damaged. There was also the problem that stress concentration and bending stress occurred, causing cracks and cracks in the piezoelectric element.

(3) The amount of expansion and contraction of a piezoelectric element is usually around 0.1 mm, so when using a piezoelectric actuator as a hydraulic source for hydraulic oil, such as when using a fuel injection valve, it is important to manage the assembly dimensions of the hydraulic chamber. becomes. Therefore, when a piezoelectric actuator has a large number of component parts as in the past, it is difficult to assemble the piezoelectric actuator in the expansion and contraction direction due to variations in the processing dimensions of each component. Therefore, when assembling, insulating members of various thicknesses are manufactured in advance, and an insulating member of an appropriate thickness is selected and assembled, which poses a problem in that assembly takes time.

(4) On the other hand, the speed at which the piezoelectric element expands and contracts is
It is extremely fast, less than 100μsec. Therefore, the weight of the piston that moves in conjunction with the piezoelectric element has a large effect on the high-speed response of the piezoelectric actuator. Furthermore, the spring force of the spring that biases the piston in the contraction direction is determined by making the piston follow the piezoelectric element when it contracts, so if the weight of the piston is large, the spring force must be increased. If this spring force is increased, it is necessary to use a piezoelectric element with a large driving force, and there is also a problem that a large piezoelectric element is required.

Therefore, the present invention has been made with the aim of solving the above-mentioned problems and providing a piezoelectric actuator having a simple configuration.

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, in a piezoelectric actuator comprising a piezoelectric element, a piston that is slidably supported by an actuator body and moves as the piezoelectric element expands and contracts, the piston is formed of ceramic having electrical insulation properties, and One end of the piezoelectric element is fitted into a fitting hole formed in the piston so that one end of the piezoelectric element can be fitted coaxially with the sliding direction of the piston, and an electrically insulating outer cover is attached to the actuator main body. The other end of the piezoelectric element is fitted into a fitting hole formed in the outer cover so that the other end of the piezoelectric element can be fitted coaxially with the sliding direction, together with a shim adjusted to a predetermined thickness. Further, the structure of the piezoelectric actuator is characterized in that an electrode having one end connected to the piezoelectric element is inserted through the outer cover.

The piezoelectric element may be made of any material as long as it generates displacement or force when a voltage is applied, and is not limited to lead zirconate titanate-based materials, such as barium titanate-based materials, etc.
Composite perovskite/lead zirconate titanate may also be used. Moreover, the property may be such that it is displaced in the direction of the applied electric field, or it may be displaced in a direction perpendicular to the applied electric field. 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.

[Operation] In the piezoelectric actuator of the present invention having the above configuration, the end of the piezoelectric element is fitted into the fitting hole between the piston and the outer cover together with a shim adjusted to a predetermined thickness, and the tip position of the piston is corrected. . Further, the piston and the outer cover electrically insulate the piezoelectric element, and the outer cover supports the electrode connected to the piezoelectric element in an electrically insulated state.

[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 showing an embodiment of the present invention. In FIG. 1, parts that are the same as those of the conventional piezoelectric actuator shown in FIG. 4 described above are given the same reference numerals and detailed explanations will be omitted.

The piezoelectric actuator of this embodiment described above includes a piston 2 made of ceramic and slidably supported by an actuator body 51.

This piston 2 is made of electrically insulating ceramic with a specific gravity of 3 g/cm ³ and whose main component is alumina, and a fitting hole 2 c having a diameter slightly larger than the outer diameter of the piezoelectric element 56 is bored at one end. ing.
Moreover, six grooves 2d are also formed in the fitting hole 2c at the same intervals as the six electrodes 56a of the piezoelectric element 56 (see FIG. 2). One end of the piezoelectric element 56 is fitted into the fitting hole 2c, aligning the position of the groove 2d with the position of the electrode 56a.

Further, an outer cover 4 is provided on the upper part of the actuator main body 51 and is attached with bolts 62. The outer cover 4 is made of electrically insulating ceramic mainly composed of alumina, and has a fitting hole 4a and six grooves 4b having the same shape as the fitting hole 2c and six grooves 2d of the piston 2.
is provided. The position of this groove 4b and the electrode 56
The other end of the piezoelectric element 56 is fitted into the fitting hole 4a together with the disk-shaped shim 6, aligning with the positions of the piezoelectric element 56a and 56b. On the other hand, two rod-shaped electrodes 8a and 8b are inserted through the outer cover 4. One end of these two electrodes 8a, 8b is the electrode 56 of the piezoelectric element 56.
a and 56b, respectively. The shim 6 is used to correct the position of the tip of the piston 2 by adjusting its thickness during assembly. Since the shim 6 has a simple shape, it is easy to manufacture, and its thickness can be easily adjusted.

As described above, the piezoelectric actuator of this embodiment connects the piezoelectric element 56 via the two electrodes 8a and 8b.
When a positive voltage is applied to the piezoelectric element 56, the piezoelectric element 56 rapidly expands, and the piston 2 moves at high speed downward in the figure against the spring force of the disc spring 72. Furthermore, when the voltage applied to the piezoelectric element 56 is removed, the piezoelectric element 56 rapidly contracts, and following this contraction, the piston 2 is moved upward in the figure at high speed by the spring force of the disc spring 72.

Next, a fuel injection valve that suitably uses the piezoelectric actuator of this embodiment will be described. As shown in FIG. 3, this fuel injection valve includes a fuel injection valve body 10 into which an actuator body 51 of the piezoelectric actuator is screwed, a nozzle hole 12 in which a nozzle hole 11 is formed, a spacer 14, a nozzle 12, and a spacer. The nozzle holder 16 fixes the fuel injection valve 14 to the fuel injection valve body 10, and the connecting member 20 is screwed into the fuel injection valve body 10 and has a fuel inlet 18 formed therein.

A control rod 22 is provided inside the fuel injection valve body 10 so as to be slidable in the axial direction, and a pressure pin 24 and a pressure pin 24 are also provided inside the nozzle 12 and the spacer 14 so as to be slidable in the axial direction. needle 2
5 are arranged in series. Further, within the fuel injection valve body 10, a fuel chamber 26 is formed at the rear end of the control rod 22 and communicates with the fuel inlet 18, and pressurized fuel is supplied to this fuel chamber 26 by a fuel pump (not shown). Ru. Therefore, the fuel pressure in the fuel chamber 26 acts on the rear end of the control rod 22.

Further, the control rod 22 has a conical pressure receiving surface 22a at its intermediate portion, and a control rod pressurizing chamber 28 is formed in the fuel injection valve body 10 around the pressure receiving surface 22a. This control rod pressurization chamber 2
8 is the actuator body 5 of the piezoelectric actuator
1, it communicates with a pressure chamber 30 formed by the piston 2 and the fuel injection valve body 10.

On the other hand, a spring 32 is inserted into the fuel injection valve body 10 to urge the pressure pin 24 downward in the figure, and the needle 25 is pressed downward by the spring 32 via the pressure pin 24. This needle 25 has a conical pressure receiving surface 34 formed in its middle portion, and a needle pressurizing chamber 36 is provided in the nozzle 12 around this pressure receiving surface 34 . The needle pressurizing chamber 36 includes the fuel injection valve main body 10 and the spacer 1.
4. Fuel passages 3 each bored in the nozzle 12
8 , 40 , and 42 communicate with the fuel chamber 26 , and communicate with the nozzle hole 11 via an annular fuel passage 44 formed around the needle 28 .

The present fuel injection valve described above, when fuel at a predetermined pressure is supplied to the fuel chamber 26 through the fuel inlet 18,
The fuel pressure in the fuel chamber 26 presses the control rod 22 downward in the figure, and together with the spring force of the spring 32, the needle 25 is pressed downward in the figure via the pressure pin 24.
This blocks communication between the fuel passage 44 and the nozzle hole 11 (the state shown in FIG. 3). Therefore, no fuel is injected from the nozzle hole 11.

Next, from this state, when a positive voltage is applied to the piezoelectric element 56 of the piezoelectric actuator and the piston 2 is moved, the pressure in the pressure chamber 30 increases. Along with this, the pressure in the control rod pressurizing chamber 28 increases, pushing the control rod 22 upward in the figure. On the other hand, since the fuel pressure from the fuel pump is always applied to the needle pressurizing chamber 36, which communicates with the fuel chamber 26 through the fuel passages 38, 40, and 42, this pressure causes the needle 25 to be moved by the spring force of the spring 32. Push it upwards in the figure. Therefore, the fuel passage 44 and the nozzle hole 11 are communicated with each other, and fuel is injected from the nozzle hole 11.

Furthermore, when the voltage applied to the piezoelectric element 56 is removed, the piston 2 moves to the right in the figure, and the fuel chamber 26
The fuel pressure and the spring force of the spring 32 push the needle 25 downward in the figure via the control rod 22 and the pressure pin 24. Therefore, communication between the fuel passage 44 and the nozzle hole 11 is cut off, and fuel injection is stopped.

As described above, according to the piezoelectric actuator of this embodiment, by making the piston 2 and the outer cover 4 from ceramic having electrical insulation properties,
It is no longer necessary to provide an insulating member at both ends of the piezoelectric element 56, the total length of the piezoelectric actuator can be shortened, and the hermetic seal 64 is also no longer necessary, simplifying the electrical configuration and facilitating assembly. Furthermore, since the ends of the piezoelectric element 56 are fitted into the fitting holes 2c and 4a between the piston 2 and the outer cover 4, assembly is not only facilitated, but also the piezoelectric element 56 is prevented from shifting in the radial direction during assembly. There is no. Therefore, there is less possibility that the piezoelectric element 56 will crack or crack due to assembly defects.

Moreover, since it has electrical insulating properties, there is no risk of shortening compared to the case where the fitting hole is formed of a metal member.

Furthermore, since the number of parts is reduced, it becomes easy to assemble both end faces of the piezoelectric element 56 with appropriate flatness and parallelism, and there is no fear that the piezoelectric element 56 will crack or break when driven. Furthermore,
By reducing the number of parts, assembly becomes easier, and assembly errors in the expansion/contraction direction due to variations in processing dimensions of each part are reduced. On the other hand, since the shape of the shim 6 is simple, the thickness can be easily adjusted. In some cases, the shim 6 is not necessary.

Furthermore, by making the piston 2 made of ceramic having a specific gravity smaller than that of the piezoelectric element 56 to reduce its weight, the spring force of the disc spring 72 can be weakened, and furthermore, the driving force of the piezoelectric element 56 can be reduced. It becomes possible. Therefore, the electric power applied to the piezoelectric element 56 can be reduced, or the piezoelectric element 56 can be made smaller.

Further, by using the piezoelectric actuator of this embodiment in a fuel injection valve, the fuel injection valve becomes smaller and the occurrence of cracks and cracks in the piezoelectric element 56 is reduced, so that the failure rate of the fuel injection valve is improved.
Furthermore, since the piezoelectric actuator has better responsiveness, it is also possible to perform more suitable fuel injection.

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, the piezoelectric actuator of the present invention has excellent effects in that the number of components can be reduced and the overall length can also be shortened. In addition, the reduction in the number of parts makes assembly easier, and it also becomes easier to assemble the piezoelectric element with appropriate flatness and parallelism on both end faces, which can prevent problems such as cracks and cracks in the piezoelectric element. It also has the effect of not being there. Furthermore, since the end of the piezoelectric element is fitted into the fitting hole between the piston and the outer cover, not only is assembly easy, but there is no possibility of displacement in the radial direction during assembly. Moreover, since it has electrical insulation properties, there is no risk of shot.

In addition, the electrode can be inserted directly into the outer cover, and there is no need to rotate the hermetic seal, simplifying the electrode structure.

On the other hand, since the number of parts is reduced, variations in dimensions during assembly are reduced, and the position of the tip of the piston can be easily corrected by adjusting the thickness of the shim. Furthermore, since the weight of the piston can be reduced, the electric power applied to the piezoelectric element can be reduced, or the piezoelectric element can be made smaller.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a piezoelectric actuator showing an embodiment of the present invention, Fig. 2 is a sectional view taken along line AA in Fig. 1, and Fig. 3 is a sectional view of a fuel injection valve using the piezoelectric actuator of the embodiment. , FIG. 4 is a sectional view of a conventional piezoelectric actuator. 2, 52... Piston, 4, 60... Outer cover, 56... Piezoelectric element.

Claims (1)

[Claims for Utility Model Registration] A piezoelectric actuator comprising a piezoelectric element and a piston that is slidably supported on an actuator body and moves as the piezoelectric element expands and contracts, wherein the piston is made of ceramic having electrical insulation properties. one end of the piezoelectric element is fitted into a fitting hole that is formed so that one end of the piezoelectric element can be fitted into the piston coaxially with the sliding direction; the piezoelectric element together with a shim adjusted to a predetermined thickness into a fitting hole formed in the outer cover so that the other end of the piezoelectric element can be fitted coaxially with the sliding direction; A piezoelectric actuator characterized in that the other end of the piezoelectric actuator is inserted into the outer cover, and an electrode having one end connected to the piezoelectric element is inserted through the outer cover.