JP2011129736A - Piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric actuator that can be also used in a high-pressure fluid in which various impurities are mixed, and has a large degree of freedom of design for qualities of the high-pressure fluid and a piezo stack. <P>SOLUTION: A case 50 which houses the piezo stack 4 is formed using an elastically deformable metal material, and has a thin elastic portion 51a formed of an annular groove 51c extending to the overall periphery, and the thin elastic portion 51a is elastically deformed in response to expansion and contraction of the piezo stack 4 to axially extend and contract. Also, in the case 50, second metal members 52 made cylindrically of metals are arranged opposite each other. Consequently, portions which are exposed to the high-pressure fluid are made of the metals to form a structure which is not easily influenced by impurities, and the expansion and contraction of the piezo stack 4 can be coped with, by varying the thickness and width of the thin elastic portion 51a. Therefore, the thickness and width of the thin elastic portion 51 can be easily and precisely varied not to mention adaptation to various high-pressure fluids, thereby the degree of freedom of design is large. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a piezoelectric actuator used as a drive source for various functional components, and is particularly suitable as a drive source for a functional component used under a high-pressure fluid, such as an injector of a fuel injection device for an internal combustion engine mounted on a vehicle. The present invention relates to a piezoelectric actuator.

(Conventional technology)
Conventionally, a piezoelectric actuator using expansion and contraction of a piezo stack is known as a driving source that exhibits a powerful driving force. In recent years, in particular, in fuel injection devices for internal combustion engines, fuel injection pressure has been increased by injectors in order to further atomize the fuel spray injected from the injectors and increase combustion efficiency, enhancing injection response. Including this, a piezoelectric actuator has been adopted as a drive source for the injector (see, for example, Patent Document 1).

  However, since this type of piezoelectric actuator does not like the moisture and foreign matter entering from the outside, the place where the piezoelectric stack is accommodated must be devised such as a sealed structure. There are restrictions.

On the other hand, when a piezoelectric actuator is employed as the drive source of the above-described injector, as is apparent from Patent Document 1, the surroundings of the piezoelectric actuator are made of fuel from the physique, functional aspect, manufacturing aspect, and the like imposed on the injector itself. It is in a situation where the structure that is satisfied, in other words, the structure in which the piezoelectric actuator is exposed to the high-pressure fuel must be taken.
In addition, as fuel is apt to dissolve in water, as represented by gasoline, it is important to pay attention to the fuel to be used because foreign matter and impurities are easily mixed even with light oil.

Therefore, there is a strong demand for a versatile one that completes the sealing of the piezo stack by itself on the piezoelectric actuator side and can be mounted on various injectors.
Therefore, in the piezoelectric actuator, as a structure for sealing the piezo stack, it is considered that the entire piezo stack is surrounded by a resin such as a resin film or accommodated in a bellows-like metal case (for example, Patent Document 2, 3).

(Problems of conventional technology)
However, such a structure has the following problems.
First, the former resin surrounding structure (see Patent Document 2) has a protective function against moisture and foreign matters, but as represented by light oil, the fuel includes chemical substances such as cleaning agents and ionized substances (hereinafter referred to as impurities). In general, the impurities may cause deterioration of the resin due to the influence of the impurities, or may penetrate the resin film and adversely affect the piezo stack. In particular, recently, fuels contain various impurities in terms of production and handling, and fuels with various components tend to be developed and used as alternatives to fossil fuels. For example, it has poor versatility as a powerful drive source using piezoelectric actuators.

  Further, since the latter bellows structure (see Patent Document 3) is made of metal, the degree of freedom of fuel selection can be ensured, but the desired expansion / contraction appropriate for the pressure of the fuel used and the required characteristics of the piezo stack can be ensured. In order to ensure the action, it is necessary to form the bellows part, the peak part, and the valley part with a certain thickness and with a high accuracy in a curved surface, but it is difficult to manufacture such a curved part with high accuracy. Further, productivity is poor and design flexibility for obtaining a desired stretching action is lacking.

  The example of the injector has been described in detail above. This type of piezoelectric actuator is now used in various applications such as a drive source of a valve of a hydraulic device, and can be used for various high-pressure fluids. Therefore, a useful piezoelectric actuator having a design freedom corresponding to diversification of applications is desired.

JP 2008-255869 A Special table 2009-527117 German Patent Application Publication No. 102008003839

  An object of the present invention is to provide a piezoelectric actuator that can be used even under a high-pressure fluid in which various impurities are mixed, and that has a high degree of design freedom with respect to the characteristics of the high-pressure fluid and piezo stack according to the application.

[Means of claim 1]
According to the first aspect of the present invention, the case that forms a cylindrical body as a whole that divides the inside that accommodates the piezo stack and the outside that is exposed to the high-pressure fluid is formed of an elastically deformable metal material. , Having a thin thin elastic portion formed by a groove over the entire circumference, and this thin elastic portion is elastically deformed in response to expansion and contraction in the axial direction of the piezo stack (piezo element stacking direction). As a result, the case expands and contracts in the axial direction.

  As a result, the portion exposed to the high-pressure fluid has a structure made of metal and is not easily affected by impurities, so that it can handle high-pressure fluids of various properties, as well as the thickness and axial width of the thin elastic portion. Furthermore, the degree of axial elasticity (a kind of spring constant) in the case can be freely set by the combination of the number of the thin elastic portions arranged in the axial direction. Since it can be selected easily and accurately, the productivity is high, and the design flexibility for the characteristics of the high-pressure fluid and piezo stack according to the application is large.

  Further, a metal reinforcing member having a cylindrical body is provided inside the case with a predetermined clearance. Since this reinforcing member has its own rigidity due to its cylindrical shape, it can prevent problems (such as excessive local deformation that leads to plastic deformation of the thin elastic part) due to the provision of the thin elastic part, and by providing clearance. Since the contact area between the case and the reinforcing member can be reduced, inhibition of expansion and contraction due to contact can be minimized.

[Means of claim 2]
According to the invention described in claim 2, the case is combined with a part of the reinforcing member to partition the inside and the outside. Therefore, the reinforcing member can be effectively used as a part of the case component as well as the case reinforcement.

[Means of claim 3]
According to invention of Claim 3, all the reinforcement members are accommodated in the inside of a case. According to such a configuration, the reinforcing member is not involved in the inside and outside compartments of the case at all, and thus may not be a complete cylindrical body.

[Means of claim 4]
According to invention of Claim 4, a thin elastic part is provided by the groove | channel formed only in the outer peripheral surface of a case. According to such a configuration, the thin elastic portion is located on the inner peripheral surface side, and even if the influence of high-pressure fluid is applied when elastically deforming so as to swell inward (reinforcing member side), the base of the thin elastic portion is provided. The stress applied to the portion can be reduced.

[Means of claim 5]
According to invention of Claim 5, a thin elastic part is provided by the some annular groove formed only in the outer peripheral surface of a case.
[Means of claim 6]
According to the sixth aspect of the present invention, the thin elastic portion is provided by a spiral groove formed only on the outer peripheral surface of the case.
According to the configurations of both of the above claims, since the axial width of the thin elastic portion can be substantially divided into a plurality of portions, the degree of elasticity (a kind of spring constant) can be freely adjusted while maintaining the strength. be able to.

[Means of Claim 7]
According to the seventh aspect of the present invention, the coating made of a material having a low friction coefficient is provided on the inner peripheral surface of the case or the outer peripheral surface of the reinforcing member. Therefore, even if the inner peripheral surface of the case comes into contact with the outer peripheral surface of the reinforcing member due to the elastic deformation of the thin elastic portion, it smoothly slides and does not adversely affect the expansion / contraction action of the piezo stack. Further, the clearance can be set smaller, which is advantageous for downsizing.

[Means of Claim 8]
According to the eighth aspect of the invention, the coating made of a material having a low coefficient of friction is provided only on the surface of the thin elastic portion facing the reinforcing member, or only on the surface of the reinforcing member facing the thin elastic portion. According to this configuration, the same function as that of the invention of claim 7 can be obtained efficiently with a small amount of coating.

It is a longitudinal section showing typically the whole composition of the injector provided with the piezoelectric actuator concerning Example 1 of the present invention. It is a longitudinal cross-sectional view of the piezoelectric actuator shown in FIG. It is a longitudinal cross-sectional view of the piezoelectric actuator which concerns on Example 2 of this invention. (A), (b) It is typical sectional drawing of the effect verification model for demonstrating the characteristic of the piezoelectric actuator which concerns on this invention. It is a graph which shows the analysis result of the effect verification model shown in FIG.

  The best mode for carrying out the present invention can be used even under a high-pressure fluid mixed with various impurities, and increases the degree of design freedom with respect to the characteristics of the high-pressure fluid and piezo stack according to the application. The piezo stack housing case is devised, that is, a case made of an elastically deformable metal material, a thin elastic part is formed by a groove around the entire circumference, and this case is reinforced inside the case. This is realized by providing a cylindrical metal reinforcing member and elastically deforming the thin elastic portion in response to expansion and contraction of the piezo stack.

[Example 1]
FIG. 1 shows an injector provided with a piezoelectric actuator according to a first embodiment of the present invention as a drive source. First, the overall configuration and function of the injector 1 will be described.

The injector 1 is mounted on a direct injection type engine (not shown) such as a diesel engine, and injects and supplies high pressure fuel received from a common rail directly into the cylinder, and lifts the needle 2. The fuel is injected by opening the nozzle hole 3 by driving.
A piezoelectric actuator 5 having a built-in piezo stack 4 is incorporated as means for enhancing this driving force, and the extension force of the piezo stack 4 is used as the driving force for the needle 2. Details of the piezoelectric actuator 5 will be described later.

  The injector 1 includes a needle 2 that opens and closes a nozzle hole 3, a piezoelectric actuator 5 that expands and contracts in the axial direction, a piston 6 that moves forward and backward in the axial direction in accordance with the expansion and contraction of the piezoelectric actuator 5, and a needle 2 that is slidable. A first sleeve 7 for supporting, a second sleeve 8 for slidably supporting the piston 6, a flange 9 disposed between the first and second sleeves 7, 8, and the first and second sleeves 7, 8 and a body 10 into which the flange 9 is loosely inserted.

  The needle 2 forms a first shaft portion 13 that is supported by the first sleeve 7 at a portion on the rear end side in the axial direction. Further, the portion on the distal end side in the axial direction forms a second shaft portion 14 that is provided with a smaller diameter than the first shaft portion 13 and is slidably supported by the body 10. Furthermore, the portion on the tip side from the second shaft portion 14 (that is, the tip portion of the needle 2) is provided with a diameter smaller than that of the second shaft portion 14 and forms a valve portion 15 that opens and closes the nozzle hole 3. Therefore, the needle 2 opens and closes the nozzle hole 3 when the first and second shaft portions 13 and 14 are individually slidably supported and displaced in the axial direction.

Here, the body 10 includes a first inner chamber 17 having a large diameter that accommodates the first and second sleeves 7 and 8 and the flange 9, and a second inner portion having a smaller diameter than the first inner chamber 17 at the distal end thereof. The second shaft portion 14 is supported by the body 10 such that its outer peripheral surface 19 is in sliding contact with an inner peripheral surface 20 forming the second inner chamber 18.
The first and second sleeves 7 and 8 and the flange 9 are integrally arranged adjacent to each other in the axial direction in the order of the first sleeve 7, the flange 9, and the second sleeve 8 from the front end side. The body 21 is constituted.

  In the second inner chamber 18, the space formed by the inner peripheral surface 20 and the outer peripheral surface 22 of the valve portion 15 forms a nozzle chamber 23 into which fuel that exerts fuel pressure on the needle 2 in the valve opening direction flows in and out. In addition, a seat surface 24 to which the valve portion 15 is attached and detached is provided on the distal end side of the inner peripheral surface 20, and the injection hole 3 is opened at the distal end of the seat surface 24. Therefore, when the valve portion 15 is separated from the seat surface 24, the space between the nozzle hole 3 and the nozzle chamber 23 is opened, the fuel in the nozzle chamber 23 is injected from the nozzle hole 3, and the valve portion 15 is seated on the seat surface 24. Then, the space between the nozzle hole 3 and the nozzle chamber 23 is closed, and fuel injection is stopped.

  The piezoelectric actuator 5 has a rear end fixed to the body 10 and a front end in contact with the rear end surface of the piston 6. When a voltage is applied, the piezoelectric actuator 5 expands toward the distal end side and biases the piston 6 toward the distal end side. The first internal chamber 17 is filled with high-pressure fuel received from the common rail, and the piezoelectric actuator 5 is housed in the first internal chamber 17 and is therefore exposed to the high-pressure fuel.

  The piston 6 forms a cylindrical body having a flange portion 25 on the rear end side, and forms a pressure chamber 27 by the front end surface 26. The piston 6 is displaced to the front end side by an extension force received from the piezoelectric actuator 5, and the pressure chamber 27. Increase the fuel pressure. That is, the tip surface 26 forms a pressurizing surface that increases the fuel pressure in the pressure chamber 27. When the extension force of the piezoelectric actuator 5 is no longer generated, the piston 6 is biased by a first spring 28 described later and is displaced to the rear end side.

  The first sleeve 7 is urged toward the distal end side and is seated on the inner surface 30 forming the first inner chamber 17, thereby forming a control chamber 31 together with the needle 2 and the body 10. That is, the control chamber 31 is defined by the inner peripheral surface 32 of the first sleeve 7, the outer peripheral surface 19 of the second shaft portion 14, the tip surface 33 of the first shaft portion 13, and the inner surface 30.

  The front end surface 33 functions as a pressure receiving surface that receives the fuel pressure in the control chamber 31 toward the rear end, so that the needle 2 is urged in the valve opening direction by the fuel pressure in the control chamber 31. The sleeve body 21 is urged toward the distal end side by a first spring 28 described later, and the distal end surface of the first sleeve 7 is seated on the inner surface 30.

  The second sleeve 8 forms a pressure chamber 27 together with the piston 6 and the flange 9. That is, the pressure chamber 27 is defined by the inner peripheral surface 36 of the second sleeve 8, the front end surface 26 of the piston 6, and the rear end surface 37 of the flange 9. And the fuel pressure of the pressure chamber 27 is increased / decreased because the front end surface 26 functions as a pressurization surface as mentioned above. That is, as the piston 6 advances and retreats, the volume of the pressure chamber 27 is expanded and contracted, and the fuel pressure in the pressure chamber 27 is increased or decreased.

  Further, since the pressure chamber 27 communicates with the control chamber 31 through the communication passage 35, when the fuel pressure in the pressure chamber 27 is increased or decreased, the fuel pressure in the control chamber 31 is also increased or decreased. That is, the fuel pressure in the control chamber 31 is also increased or decreased according to the advance / retreat of the piston 6. Note that. The communication path 35 is isolated from the flange 9 filled with high-pressure fuel and the first inner chamber 17 on the outer peripheral side of the first sleeve 7, and penetrates the flange 9 and the first sleeve 7.

  A first spring 28 is mounted between the tip of the second sleeve 8 and the flange 25 of the piston 6. The first spring 28 urges the second sleeve 8 and the piston 6 in opposite directions in the axial direction, and urges the second sleeve 8 toward the distal end side so that the first sleeve 7 is moved toward the body 10. Seated on the inner surface 30. The first spring 28 functions as a restoring spring for the piston 6 by urging the piston 6 toward the rear end.

  The flange 9, together with the first sleeve 7 and the needle 2, forms a back pressure chamber 41 into which fuel that exerts fuel pressure on the needle 2 in the valve closing direction flows in and out. Therefore, the needle 2 receives the fuel pressure of the back pressure chamber 41 in the valve closing direction by the rear end face 42. The front end surface 43 of the flange 9 comes into contact with the rear end surface 42 of the needle 2 when the needle 2 is lift-driven and displaced toward the rear end side. That is, the flange 9 functions as a stopper that regulates the lift amount of the needle 2.

  Further, the back pressure chamber 41 communicates with the first internal chamber 17 through a communication passage 40 provided in the flange 9, and fuel flows into and out of the first internal chamber 17 through the communication passage 40. . Further, the back pressure chamber 41 communicates with the nozzle chamber 23 through a communication passage 46 provided in the second shaft portion 14. The back pressure chamber 41 accommodates a second spring 47 that biases the needle 2 in the valve closing direction.

  With the above configuration, when a voltage is applied to the piezoelectric actuator 5, the piston 6 is displaced to the tip side, and the fuel pressure in the pressure chamber 27 is increased. As a result, the fuel increased in pressure in the pressure chamber 27 flows into the control chamber 31 via the communication path 35, so that the fuel pressure in the control chamber 31 is also increased and the needle 2 is driven in the valve opening direction. For this reason, the nozzle hole 3 is opened and the fuel in the nozzle chamber 23 is injected.

  At this time, the fuel in the back pressure chamber 41 flows out to the first inner chamber 17 through the communication passage 40, and the lift amount of the needle 2 is regulated by the first shaft portion 13 coming into contact with the flange 9. Further, high-pressure fuel flows into the nozzle chamber 23 from the first inner chamber 17 through the communication passage 40, the back pressure chamber 41, and the communication passage 46.

  When the voltage application to the piezoelectric actuator 5 is stopped, the fuel pressure in the pressure chamber 27 is not increased, so the fuel pressure in the control chamber 31 is also reduced. As a result, the needle 2 is urged by the second spring 47 and driven in the valve closing direction, the nozzle hole 3 is closed, and fuel injection is stopped. Further, high pressure fuel flows from the first inner chamber 17 into the back pressure chamber 41 through the communication passage 40, and the piston 6 is urged by the first spring 28 to be displaced to the rear end side.

(Background of Example 1)
As described above, since the piezoelectric actuator 5 is efficiently incorporated in the injector 1, it is constantly exposed to high-pressure fuel. For this reason, when the piezo stack 4 is exposed and directly touches the fuel, problems such as malfunction occur due to the influence of components contained in the fuel. Therefore, it is important to seal the piezo stack 4.

(Characteristics of Example 1)
The above-mentioned piezo stack 4 itself is a well-known general one, and is configured by laminating a plurality of piezo elements, and has a function of expanding and contracting in the laminating direction by charge and discharge, and seals the piezo stack 4. Therefore, the piezoelectric actuator 5 according to the first embodiment employs the following technique and will be described in detail with reference to FIG.

  The piezoelectric actuator 5 is arranged so as to cover the outer periphery of the piezo stack 4, and includes a case 50 that divides an inside that accommodates the piezo stack 4 and an outside that is exposed to fuel (high pressure fluid) and seals the piezo stack 4. Yes. The case 50 has a cylindrical body (particularly a cylindrical body) as a whole, and is disposed inside the first metal member 51 and a first metal member 51 that forms an outer frame that is substantially exposed to fuel. A pair of metal members that support the second metal member 52 that reinforces the first metal member 51 and the both ends of the piezo stack 4 in the stacking direction and that covers the open ends of the first and second metal members 51 and 52. Support members 53 and 54.

  The first metal member 51 is made of an elastically deformable metal material. As this material, an amorphous metal such as metallic glass (for example, Zr—Al—Ni—Cu alloy) or a titanium alloy such as rubber metal (registered trademark) is preferable. These metals have characteristics such as being able to achieve both low Young's modulus and high tensile strength, exhibiting non-hysteretic elastic deformation behavior with superelastic properties, and a simplified shape as described below. Can be manufactured accurately and easily by known casting methods and cold working methods.

  Further, the first metal member 51 has a thin elastic portion 51a having a small thickness and a rigid portion 51b having a large thickness by changing the thickness only on the outer peripheral surface side. In other words, the thin elastic portion 51a and the rigid portion 51b are divided and formed by a plurality of annular grooves 51c over the entire circumference, and each has an annular shape with a rectangular cross section so as to surround the outer periphery of the first metal member 51. None and are alternately arranged in the axial direction. Therefore, the first metal member 51 expands and contracts in the axial direction due to the elastic deformation of the thin elastic portion 51a. Thus, the expansion / contraction function can be ensured with a simple shape of only the thin elastic portion 51a.

  On the other hand, the second metal member 52 is formed of a high-strength material such as stainless steel (for example, SUS304), and has a cylindrical body as a whole. A large-diameter portion 52a having an outer diameter substantially the same as the inner diameter of one metal member 51, and a lower-diameter portion having an outer diameter smaller than the inner diameter of the first metal member 51 toward the lower end side (tip side) in the figure below 52b. The outer peripheral surface of the small diameter portion 52b faces the inner peripheral surface of the first metal member 51 through a slight clearance 55 that allows elastic deformation of the thin elastic portion 51a.

  Of the pair of support members 53 and 54, one support member 53 located on the upper end side (rear end side) in the figure has a disk shape. Further, the other support member 54 located on the lower end side (tip side) in the figure has a disk shape as a whole, but the upper surface side in the figure has a stepped recess having a large diameter hole part 54a and a small diameter hole part 54b. The lower surface side in the figure is formed as a spherical convex portion 54d. The convex portion 54d acts on the piston 6 described above.

  And the inner peripheral surface of the large diameter part 52a of the 2nd metal member 52 is fitted to the outer peripheral surface of one supporting member 53, and it seal-joins by laser welding over the perimeter. Further, the outer peripheral surface of one end (the lower end side in the figure) of the first metal member 51 is fitted into the inner peripheral surface of the large-diameter hole portion 54a of the other support member 54, and is sealed and bonded by laser welding over the entire periphery. . Further, the inner peripheral surface of the other end (the upper end side in the drawing) of the first metal member 51 is fitted to the outer peripheral surface of the large-diameter portion 52a of the second metal member 52 and is sealed by laser welding over the entire periphery. . Therefore, the large diameter portion 52a forms a part of the case 50 that accommodates the piezo stack 4 and is exposed to the fuel.

  The small-diameter portion 52b of the second metal member 52 is free at the lower end in the figure, although it is inserted into the small-diameter hole portion 54b of the concave portion 54c with respect to the other support member 54. The space 56 between the small-diameter portion 52b and the concave portion 54c is adjusted to such a dimension that the lower end of the small-diameter portion 52b does not contact the bottom portion of the concave portion 54c even when the first metal member 51 contracts to the maximum.

Therefore, the conventionally known piezo stack 4 includes, for example, an integrally laminated element group 4a configured by laminating a plurality of piezo elements, an insulating substrate 4b for electrically insulating the support members 53 and 54, and an element. The insulating coating 4c that protects the group 4a is formed as a main component.
As described above, the piezo stack 4 expands when a voltage is applied, and the axial length of the first metal member 51 needs to be preset in order to be used as an actual machine.

  That is, the state shown in the figure shows a state when the piezo stack 4 is extended to the maximum extent (at the time of operation), and when the piezo stack 4 is not operating (at the time of the minimum shaft length), the first state is correspondingly generated. The metal member 51 itself must also have its axial length contracted. Therefore, in the process of assembling the first metal member 51, the above-described seal joining (the first metal member 51 and the support member 54) is performed in a state where the thin elastic portion 51a is elastically deformed (deformed so as to swell toward the inner peripheral surface). Is made). In addition, in order to ensure this contracted state smoothly, the above-described clearance 55 and separation space 56 are useful.

(Effect of Example 1)
In the above configuration, the first metal member 51 responsible for the axial expansion and contraction of the case 50 must respond to the expansion and contraction characteristics of the piezo stack 4. The expansion / contraction characteristics (a kind of spring constant) of the first metal member 51 can be uniquely determined by the degree of elasticity of the thin elastic portion 51a. In other words, in the thin elastic part 51a, the degree of elasticity can be freely selected according to the thickness, the axial width, and the number of installations (the number of divisions), and it also has a simple shape as a whole. As described above, the manufacture of the first metal member 51 can be accurately and easily achieved by a known manufacturing method. Thereby, the design freedom with respect to the fuel pressure according to the application and the characteristics of the piezo stack 4 can be largely secured.

The first metal member 51 is exposed to high-pressure fuel, and particularly has a thin elastic portion 51a. Therefore, the first metal member 51 is easily bent in the radial direction, and the thin elastic portion 51a locally undergoes excessive elastic deformation. This may cause problems such as malfunction of the piezo stack 4 and damage to the first metal member 51. On the other hand, the second metal member 52 disposed on the inner side has a cylindrical shape and has a rigidity itself, so that the first metal member 51 is reinforced from the inner side to prevent the above-described problems. Can do.
The second metal member 52 can be easily obtained by cutting a metal pipe like a stainless steel pipe, but a pair of halved cylindrical members may be joined to form a pipe.

Further, since the clearance 55 exists between the first metal member 51 and the second metal member 52, even if the thin elastic portion 51a is elastically deformed so as to swell toward the inner peripheral surface side, the second metal member Contact with 52 can be avoided.
In addition, this thin elastic part 51a is located in the inner peripheral surface side, and as a matter of course, the stress at the time of elastic deformation applied to the base portion can be reduced as compared with the case where it is positioned on the outer peripheral surface side. In this embodiment, the root portion is provided at a right angle, but the stress can be further relaxed by forming it at a curved surface.

[Example 2]
FIG. 3 shows the piezoelectric actuator 5 according to the second embodiment of the present invention. Compared to the first embodiment, the structure of the case 50 has the following characteristics.
In the present embodiment, one support member 53 located on the upper end side (rear end side) in the figure has a disk shape but has a large diameter portion 53a and a small diameter portion 53b. The upper end of the cylindrical first metal member 51 is directly fitted into the large-diameter portion 53a, and is sealed by laser welding.
On the other hand, the second metal member 52 has an outer diameter smaller than the inner diameter of the first metal member 51, but has the same outer diameter over the entire length, and an upper end that forms a fixed end inside the first metal member 51. Is fitted into the small-diameter portion 53b and sealed by laser welding.

  According to the said structure, since the 2nd metal member 52 is located inside the 1st metal member 51 over the full length and all are accommodated in the 1st metal member 51, it is not exposed to a high pressure fuel. Therefore, the 2nd metal member 52 should just be a form of the grade which achieves a reinforcement function, and does not need to be a perfect cylindrical body. For example, a pair of substantially halved members may be arranged to face each other with a gap therebetween to constitute a substantially cylindrical body. In this way, selection of a material for forming the second metal member 52 is advantageous.

Since the features of the present invention are summarized in the structure of the case 50, the verification results of characteristics obtained by the present invention will be described with reference to FIGS.
First, two types of models shown in FIGS. 4A and 4B were prepared as effect verification models for the case 50. 4A shows a plurality of types of thin elastic portions 51a of the first metal member 51, and FIG. 4B shows a single type of thin elastic portions 51a of the first metal member 51 that are extremely wide. Is schematically shown.

The outer tube A corresponds to the first metal member 51, which is made of metal glass as an elastically deformable metal material and formed into a predetermined shape by a casting method. Fixed and fully constrained.
The inner tube B corresponds to the second metal member 52, is made of a stainless steel tube, and is disposed on the inner side of the outer tube A via a clearance C (corresponding to the above-described clearance 55). The upper end is fixed to the support base X and is in a completely restrained state, but the lower end is separated from the support base Y and becomes a free end.

Here, the outer tube A had a Young's modulus of 100 GPa and a yield stress of 1650 MPa, and the dimensions of the main shape necessary as a model were determined as follows.
Inner diameter D of first metal member 51 = 7.5 mm, maximum effective length L = 20 mm contributing to elastic deformation, thickness Ta = 0.1 mm of thin elastic portion 51a, Tb = 0.114 mm, axis of thin elastic portion 51a Directional width Ha = 3, thickness Tc of rigid portion 51b = 0.2 mm, axial width Hb of rigid portion 51b = 1.25 mm, axial length K of both ends of first metal member 51 = 3 mm, first metal member The thickness Td of both ends of 51 is 1 mm.

When an external pressure corresponding to a high pressure fluid is applied from the outer periphery of the outer tube A (in this example, it is uniquely set to 20 MPa), the outer tube A is elastically deformed, and its inner peripheral surface is the outer peripheral surface of the inner tube B. To touch. The graph of FIG. 5 shows the result of measuring the total radial load R (kN) applied to the inner tube B at this time according to the size of the clearance C (μm). The solid line shown in FIG. 5 is the result of the model shown in FIG. 4A, and the broken line shown in FIG. 5 is the result of the model shown in FIG. 4B. As shown by the arrows, the solid line is about 20 (μm). It can be put to practical use up to the nearby clearance.
The frictional force generated when the inner peripheral surface of the outer tube A slides on the outer peripheral surface of the inner tube B due to elastic deformation of the outer tube A can be converted into a radial load applied to the inner tube B.

On the other hand, making the clearance C as small as possible is important for miniaturization of the piezoelectric actuator 5 and lowers the coefficient of friction during sliding contact between the inner peripheral surface of the outer tube A and the outer peripheral surface of the inner tube B. It is desirable to take measures. As such means, use of a coating made of a material having a low friction coefficient can be mentioned. As a material having a low coefficient of friction, a well-known Teflon (registered trademark) or molybdenum material having excellent lubricity can be used.
Next, this film will be described.

One is means for providing a coating made of a material having a low coefficient of friction on at least one of the inner peripheral surface of the first metal member 51 and the outer peripheral surface of the second metal member 52.
As another example, a coating made of a material having a low friction coefficient only on the surface of the thin elastic portion 51a facing the second metal member 52 or only on the surface of the second metal member 52 facing the thin elastic portion 51a. It is means to provide. According to this latter means, a coating is effectively provided only on the surface where friction is most likely to occur, and the same low friction function can be efficiently imparted with a small amount of coating.

[Modification]
In the above embodiment, the case 50 has a cylindrical shape as an example. However, it may be a polygonal cylinder such as a square. In short, it covers the outer periphery of the piezo stack 4 and houses the piezo stack 4 and the high pressure. Any shape may be used as long as it forms a cylindrical body that divides the outside exposed to the fluid and prevents the piezo stack 4 from touching the high-pressure fluid. It is also possible to integrate the first metal member 51 and the one support member 53.
The annular groove 51c forming the thin elastic portion 51a may be spiral. In this case, the thin elastic portion 51a also has a spiral shape, and the case 50 expands and contracts in the axial direction while rotating. This is useful for applications that allow such movement.
In any case, substantially dividing the axial width of the thin elastic portion 51a into a plurality of grooves by a plurality of grooves can freely adjust the degree of elasticity (a kind of spring constant) while maintaining the strength. Therefore, as is clear from the comparison shown in FIGS. 4 and 5, it is advantageous in design.

4 Piezo stack 5 Piezoelectric actuator 50 Case 51 First metal member 51a Thin elastic portion 51b Rigid portion 51c Annular groove 52 Second metal member (reinforcing member)
53 Support members
54 Support member 55 Clearance

Claims (8)

A piezo stack that is constructed by laminating a plurality of piezo elements, and expands and contracts in the laminating direction by charge and discharge,
A case that is arranged so as to cover the outer periphery of the piezo stack, and that forms a cylindrical body as a whole that divides the inside that houses the piezo stack and the outside that is exposed to the high-pressure fluid;
In the piezoelectric actuator in which the case expands and contracts in the stacking direction of the piezo stack as the piezo stack expands and contracts,
The case is formed of an elastically deformable metal material, and has a thin thin elastic portion formed by a groove over the entire circumference,
Provided inside the case is a metal reinforcing member that is disposed opposite to the case via a clearance that allows elastic deformation of the thin elastic portion and forms a cylindrical body that reinforces the case. Piezoelectric actuator characterized by being made. The piezoelectric actuator according to claim 1,
A portion of the reinforcing member is exposed to a high pressure fluid;
The other part of the reinforcing member is accommodated in the case,
The case is combined with a part of the reinforcing member, and divides an inside that houses the piezo stack and an outside that is exposed to a high-pressure fluid. The piezoelectric actuator according to claim 1,
All of the reinforcing members are accommodated in the case. The piezoelectric actuator according to any one of claims 1 to 3,
The piezoelectric actuator according to claim 1, wherein the thin elastic portion is provided by the groove formed only on the outer peripheral surface of the case. The piezoelectric actuator according to claim 4,
The piezoelectric actuator according to claim 1, wherein the thin elastic portion is provided by a plurality of annular grooves formed only on the outer peripheral surface of the case. The piezoelectric actuator according to claim 4,
The piezoelectric actuator according to claim 1, wherein the thin elastic portion is provided by a spiral groove formed only on the outer peripheral surface of the case. The piezoelectric actuator according to any one of claims 1 to 6,
A piezoelectric actuator characterized in that a coating made of a material having a low friction coefficient is provided on at least one of the opposing surfaces of the case and the reinforcing member. The piezoelectric actuator according to any one of claims 4 to 6,
A piezoelectric actuator characterized in that a coating made of a material having a low coefficient of friction is provided only on a surface of the thin elastic portion facing the reinforcing member or only on a surface of the reinforcing member facing the thin elastic portion.

Images