Piezoelectric valve

Abstract

To provide a piezoelectric valve that can ensure sufficient driving stability without depending on variations in the contact resistance value of the piezoelectric element. [Solution] The piezoelectric valve 1 is a piezoelectric valve driven by a DC component and comprises a plurality of piezoelectric elements 12A, 12B electrically connected in parallel via electrodes 14 made of a metal plating film, a conductive diaphragm 13 joined to the plurality of piezoelectric elements 12A, 12B via electrodes 14, and a resistor 22 electrically connected to the plurality of piezoelectric elements 12A, 12B, wherein the electrical resistance value R1 of the resistor 22 is less than the insulation resistance value R2 of the piezoelectric elements 12A, 12B.

Description

Technical Field

[0001] This disclosure relates to a piezoelectric valve.

Background Art

[0002] Piezoelectric elements have the property of deforming by the reverse voltage effect and are used as piezoelectric actuators that convert electrical signals into physical deformations (see, for example, Patent Document 1). Examples of applications of piezoelectric actuators include piezoelectric valves. Piezoelectric valves can be applied, for example, to regulators for compressed air. A regulator for compressed air is attached to a pipe for compressed air used in a factory or the like and has a function of keeping the pressure in the pipe constant.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In piezoelectric valves, generally, piezoelectric elements utilizing strain deformation are used. Such a piezoelectric valve is configured to include, for example, a piezoelectric element and a diaphragm electrically connected to the piezoelectric element. The electrodes of the piezoelectric element are formed by baked electrodes using electrode materials such as Ag or an AgPd alloy. However, there is a risk of ion migration in baked electrodes using Ag, an AgPd alloy, or the like as the electrode material, and in piezoelectric valves driven by a DC component, a decrease in reliability has been a problem.

[0005] To address these problems, conventional methods have included forming baked electrodes with stable metals such as Pt, and forming plated electrodes with stable metals such as Au by sputtering. However, the former method tends to result in thicker baked electrodes, which could hinder the deformation of the piezoelectric element. The latter method tends to cause variations in the contact resistance of the piezoelectric element, which could reduce the stability of the drive.

[0006] This disclosure was made to solve the above-mentioned problems and aims to provide a piezoelectric valve that can ensure sufficient driving stability without depending on variations in the contact resistance value of the piezoelectric element. [Means for solving the problem]

[0007] The gist of this disclosure is as follows:

[0008] [1] A piezoelectric valve driven by a DC component, wherein the piezoelectric valve comprises a plurality of piezoelectric elements electrically connected in parallel via electrodes made of a metal plating film, a conductive diaphragm joined to the plurality of piezoelectric elements via the electrodes, and a resistor electrically connected to the plurality of piezoelectric elements, wherein the electrical resistance of the resistor is less than the insulation resistance of the piezoelectric elements. In this piezoelectric valve, multiple piezoelectric elements are electrically connected in parallel via electrodes made of metal plating. When electrodes made of metal plating are used, the problem of ion migration can be avoided even when the piezoelectric valve is driven by a DC component. When electrodes made of metal plating are used, it is possible to join the electrodes of multiple piezoelectric elements or the piezoelectric elements to the diaphragm with adhesive, but variations in the thickness of the adhesive can lead to variations in the contact resistance between multiple piezoelectric elements or between piezoelectric elements and the diaphragm. In contrast, in this piezoelectric valve, resistors are electrically connected to multiple piezoelectric elements. The resistors function as protective resistors that suppress the flow of excessive current through multiple piezoelectric elements. Furthermore, because the electrical resistance value of the resistors is less than the insulation resistance value of the piezoelectric elements, the current flowing through multiple piezoelectric elements can be stabilized regardless of variations in the contact resistance value between multiple piezoelectric elements. Therefore, sufficient stability of the piezoelectric valve's operation can be ensured.

[0009] [2] The piezoelectric valve according to [1], wherein the electrical resistance of the resistor is greater than the contact resistance between the diaphragm and the electrode of the piezoelectric element. In this case, when considering the circuit as a whole, including the piezoelectric element, the diaphragm, and the resistor, the variation in the contact resistance between the diaphragm and the electrode of the piezoelectric element can be relatively reduced. Therefore, the driving stability of the piezoelectric valve can be sufficiently ensured.

[0010] [3] The piezoelectric valve according to [1] or [2], wherein the electrical resistance of the resistor is greater than the contact resistance between the electrodes of the plurality of piezoelectric elements. In this case, the variation in the contact resistance between the electrodes of the plurality of piezoelectric elements can be relatively reduced when considering the circuit as a whole, including the piezoelectric elements, the diaphragm, and the resistor. Therefore, the driving stability of the piezoelectric valve can be sufficiently ensured.

[0011] [4] The electrode is formed by a sputtered film or a vapor-deposited film, as described in any of [1] to [3]. In this case, even when the piezoelectric valve is driven by a DC component, the problem of ion migration can be more reliably avoided, and the reliability of the piezoelectric valve can be improved.

[0012] [5] The piezoelectric valve according to any one of [1] to [4], wherein the electrode is arranged in a region inside the contour of the piezoelectric element. In this case, the occurrence of a short circuit due to the electrode can be suppressed.

[0013] [6] A piezoelectric valve according to any one of [1] to [5], wherein the plurality of piezoelectric elements and one of the plurality of piezoelectric elements are joined to the diaphragm by an adhesive member that does not contain conductive components. By using an adhesive member that does not contain conductive components, the adhesive members between the plurality of piezoelectric elements and between the piezoelectric elements and the diaphragm can be made thin. Therefore, deterioration of characteristics due to the thickness of the adhesive member can be prevented. In addition, by using an adhesive member that does not contain conductive components, the occurrence of short circuits can be suppressed.

[0014] [7] The piezoelectric valve according to [5], wherein the adhesive member is arranged to protrude outside the contour of the piezoelectric element. This improves the bonding strength between multiple piezoelectric elements and the bonding strength between the piezoelectric element and the diaphragm.

[0015] [8] A piezoelectric valve according to any one of [1] to [7], wherein one longitudinal end of the diaphragm is a fixed end and the other longitudinal end is a free end. This ensures sufficient displacement of the free end of the diaphragm due to the strain deformation of the piezoelectric element. Therefore, the piezoelectric element and the diaphragm can be suitably applied as the valve body of the piezoelectric valve.

[0016] [9] A piezoelectric valve according to [8], comprising a wiring section electrically connected to the electrode and the diaphragm, wherein the electrode and the wiring section and the diaphragm and the wiring section are joined by an adhesive member that does not contain conductive components. With such a configuration, the occurrence of malfunctions such as solder corrosion can be avoided. In addition, by using an adhesive member that does not contain conductive components, the occurrence of short circuits can be suppressed.

[0017]

[10] The wiring part is located on the fixed end side of the piezoelectric element and the diaphragm, and is the piezoelectric valve according to [9]. By positioning the wiring part on the fixed end side, it is possible to suppress the influence of the stress due to the strain deformation of the piezoelectric element from reaching the wiring part. Thereby, it is possible to suitably prevent disconnection of the wiring part and the like.

Effect of the Invention

[0018] According to the present disclosure, it is possible to sufficiently ensure the driving stability without depending on the variation in the contact resistance value between the piezoelectric element and the diaphragm.

Brief Description of the Drawings

[0019] [Figure 1] It is a perspective view of a piezoelectric valve according to an embodiment of the present disclosure. [Figure 2] It is an exploded perspective view of the piezoelectric valve shown in FIG. 1. [Figure 3] It is a plan view of the piezoelectric valve shown in FIG. 1. [Figure 4] It is a cross-sectional view of the piezoelectric valve shown in FIG. 1, where (a) is a state where the inflow hole is closed and (b) is a state where the inflow hole is open. [Figure 5] It is a perspective view of the piezoelectric part. [Figure 6] It is a side view of the piezoelectric part shown in FIG. 5. [Figure 7] It is a diagram showing the circuit configuration of the piezoelectric part.

Modes for Carrying Out the Invention

[0020] Hereinafter, with reference to the drawings, a preferred embodiment of a piezoelectric valve according to one aspect of the present disclosure will be described in detail.

[0021] Hereinafter, with reference to the drawings, a preferred embodiment of a piezoelectric valve according to one aspect of the present disclosure will be described in detail.

[0022] Figure 1 is a perspective view of a piezoelectric valve according to one embodiment of the present disclosure. Figure 2 is an exploded perspective view of the piezoelectric valve. Figure 3 is a plan view of the piezoelectric valve, and Figure 4 is a cross-sectional view of the piezoelectric valve. In Figure 3, for the sake of explanation, a plan view is shown with the housing cover removed.

[0023] The piezoelectric valve 1 shown in Figures 1 to 4 is a device applied, for example, to a compressed air regulator. A compressed air regulator is installed in compressed air piping used in factories and other places, and has the function of maintaining a constant pressure in the piping. As shown in Figures 1 to 4, the piezoelectric valve 1 comprises a housing 2 and a valve body 3.

[0024] The housing 2 is made of resin, for example, and has a bottomed main body 4 with an opening on one side, and a lid 5 fixed to one side of the main body 4 so as to close the opening of the main body 4. The housing 2 is a roughly rectangular box shape with an airtight internal space S, achieved by fixing the lid 5 to the main body 4 via a sealing member (not shown). In the following description, the longitudinal direction of the housing 2 (the direction along the long side in a plan view) is the X direction, the short direction of the housing 2 (the direction along the short side in a plan view) is the Y direction, and the thickness direction of the housing 2 is the Z direction.

[0025] The housing 2 is provided with an air inlet P1 and an air outlet P2 (see Figure 3). Both the inlet P1 and the air outlet P2 have a circular cross-section and communicate with the internal space S of the housing 2. The inlet P1 is the part that allows primary air to flow into the housing 2. The inlet P1 is provided, for example, at one end in the X direction and in the center in the Y direction of the bottom 4a of the main body 4. A nozzle 6 is provided at the location of the inlet P1, which protrudes toward the lid 5 side in the internal space S.

[0026] The outlet hole P2 is the part that allows air inside the housing 2 to flow out to the secondary side. The outlet hole P2 is located, for example, at the bottom 4a of the main body 4, closer to one end in the X direction and at the center in the Y direction than the inlet hole P1. There are no particular restrictions on the inner diameter of the inlet hole P1 and the inner diameter of the outlet hole P2, but in this embodiment, the inner diameter of the outlet hole P2 is larger than the inner diameter of the inlet hole P1.

[0027] The valve body 3 is located inside the housing 2 and opens and closes the inlet hole P1. As shown in Figures 5 and 6, the valve body 3 is composed of a piezoelectric section 11 which includes a plate-shaped piezoelectric element 12 and a diaphragm 13 on which the piezoelectric elements 12 are stacked. The piezoelectric section 11 is DC driven by a voltage supplied from the power supply unit 21 (see Figure 7), which will be described later. The DC drive causes the piezoelectric elements 12 and the diaphragm 13 to deform towards the lid 5. This switches between a closed state in which the diaphragm 13 contacts the tip surface 6a of the nozzle 6 of the inlet hole P1 (see Figure 4(a)) and an open state in which the diaphragm 13 is separated from the tip surface 6a of the nozzle 6 of the inlet hole P1 (see Figure 4(b)), thereby opening and closing the inlet hole P1.

[0028] The diaphragm 13 has, for example, a rectangular shape in plan view. The diaphragm 13 is made of a conductive material such as metal. The constituent material of the diaphragm 13 may be carbon fiber reinforced plastic, 42 alloy, etc. The thickness of the diaphragm 13 may be about the same as the thickness of the piezoelectric element 12, or it may be slightly greater than the thickness of the piezoelectric element 12.

[0029] A notch may be provided at one of the corners of the diaphragm 13. The notch serves as a visual indicator for recognizing the front and back sides of the diaphragm 13 and contributes to improving the ease of installation when attaching the piezoelectric element 11 to the housing 2. The shape of the notch (the shape cut out by the notch) can be various shapes such as triangular, rectangular, or arc-shaped.

[0030] In this embodiment, the piezoelectric unit 11 has a plurality of plate-shaped piezoelectric elements 12 (piezoelectric elements 12A and piezoelectric elements 12B), as shown in Figures 5 and 6. Each piezoelectric element 12 has a base body 10 and a pair of electrodes 14. The base body 10 does not have internal electrodes and is composed of a single layer of piezoelectric material. The piezoelectric layer is formed of a piezoelectric material such as a piezoelectric ceramic. Examples of piezoelectric ceramic materials include PZT[Pb(Zr,Ti)O3], PT(PbTiO3), PLZT[(Pb,La)(Zr,Ti)O3], or barium titanate (BaTiO3).

[0031] Electrodes 14 are provided on both sides of the piezoelectric element 12. The electrodes 14 are made of a metal plating film formed by, for example, sputtering or vapor deposition. That is, the electrodes 14 are formed by a sputtered film or a vapor-deposited film. The electrodes 14 may also be made of a multilayer metal plating film. Examples of constituent materials for the electrodes 14 include stable metals such as chromium (Cr) / copper-nickel alloy (Ni-Cu) / gold (Au) / platinum (Pt). The planar shape of the electrodes 14 on both sides of the piezoelectric element 12 is a rectangle, for example, one size smaller than the planar shape of the base body 10. In a plan view of the piezoelectric element 12, the electrodes 14 are located in a region inside the contour of the piezoelectric element 12, and a frame-shaped electrode-free region is formed at the edge of the piezoelectric element 12.

[0032] The piezoelectric section 11 is constructed by stacking, for example, multiple piezoelectric elements 12 with different longitudinal dimensions on a diaphragm 13 in order of increasing size. In the example shown in Figures 5 and 6, piezoelectric elements 12A and 12B are stacked parallel to each other in this order on one surface of the diaphragm 13. The electrode 14 on one side of piezoelectric element 12A is in contact with the surface of the diaphragm 13, and the electrode 14 on the other side of piezoelectric element 12A is in contact with the electrode 14 on one side of piezoelectric element 12B. As a result, the diaphragm 13 and piezoelectric element 12A are electrically connected to each other, and piezoelectric elements 12A and 12B are electrically connected to each other. In this embodiment, the thickness of piezoelectric element 12A and the thickness of piezoelectric element 12B are equal. However, one of the thicknesses of piezoelectric element 12A and piezoelectric element 12B may be greater than the other.

[0033] The piezoelectric element 12A, which overlaps the diaphragm 13, is an element that primarily contributes to the displacement of the piezoelectric part 11. The dimension of the piezoelectric element 12A in the X direction is smaller than the dimension of the diaphragm 13 in the X direction. This allows the position of the piezoelectric element 12A relative to the diaphragm 13 to be arbitrarily adjusted in the X direction. In this embodiment, the piezoelectric element 12A is located on one surface of the diaphragm 13, closer to the other end in the X direction. The overhang length of the diaphragm 13 from one end of the piezoelectric element 12A in the X direction is greater than the overhang length of the diaphragm 13 from the other end of the piezoelectric element 12A in the X direction. Also, the dimension of the piezoelectric element 12A in the Y direction is slightly smaller than the dimension of the diaphragm 13 in the Y direction. Due to this dimensional difference, the area for forming the adhesive portion 15A, described later, is provided on one surface of the diaphragm 13.

[0034] The piezoelectric element 12B, which overlaps with the piezoelectric element 12A, is primarily an element that contributes to the power (torque) of the piezoelectric section 11. The X-direction dimension of piezoelectric element 12B is smaller than that of piezoelectric element 12A. Piezoelectric element 12B is biased towards one end of piezoelectric element 12A in the X-direction, to the extent that a small portion of the electrode-free region at one end of piezoelectric element 12A in the X-direction is exposed. Furthermore, the Y-direction dimension of piezoelectric element 12B is slightly smaller than that of piezoelectric element 12A in the Y-direction. Due to this dimensional difference, the area for forming the adhesive portion 15B, described later, is provided in the electrode-free region of piezoelectric element 12A.

[0035] Adhesive portions 15 are provided for joining the diaphragm 13 to the piezoelectric element 12A, and for joining the piezoelectric element 12A to the piezoelectric element 12B. From the viewpoint of preventing short circuits, the adhesive portions 15 are made of an adhesive material that does not contain conductive components such as conductive particles. Examples of adhesive materials that make up the adhesive portions 15 include thermosetting epoxy resin. The adhesive portions 15 are located in a region inside the contour of the piezoelectric element 12 when viewed from the Z direction. Alternatively, the adhesive portions 15 may be arranged to protrude outward from the contour of the piezoelectric element 12 when viewed from the Z direction.

[0036] In this embodiment, as shown in Figures 5 and 6, the adhesive portion 15A used to join the diaphragm 13 and the piezoelectric element 12A is arranged over the entire surface of one side of the piezoelectric element 12A so as to connect one side of the diaphragm 13 with the electrode 14 on one side of the piezoelectric element 12A. A portion of the adhesive portion 15A protrudes slightly outward from the contour of the piezoelectric element 12A and is arranged to wrap around the side surface of the piezoelectric element 12A. In the example of Figures 5 and 6, the adhesive portion 15A protrudes outward from all edges of the piezoelectric element 12A. The adhesive portion 15A may protrude outward from only a portion of the edges of the piezoelectric element 12A. In this case, the adhesive portion 15A may protrude outward from only both ends of the piezoelectric element 12A in the X direction, or from only both ends of the piezoelectric element 12A in the Y direction.

[0037] The adhesive portion 15B used to join the piezoelectric element 12B and the piezoelectric element 12A is arranged across the entire surface of one side of the piezoelectric element 12B so as to connect the electrode 14 on the other side of the piezoelectric element 12A with the electrode 14 on one side of the piezoelectric element 12B. A portion of the adhesive portion 15B protrudes slightly outward from the contour of the piezoelectric element 12B and is arranged to wrap around the side surface of the piezoelectric element 12B. In the examples of Figures 5 and 6, the adhesive portion 15B protrudes outward from all edges of the piezoelectric element 12B. The adhesive portion 15B may protrude outward from only some edges of the piezoelectric element 12B. In this case, the adhesive portion 15B may protrude outward from only both ends of the piezoelectric element 12B in the X direction, or from only both ends of the piezoelectric element 12B in the Y direction.

[0038] As described above, the adhesive portion 15 is made of an adhesive material that does not contain conductive components. The driving voltage of the piezoelectric portion 11 includes a high voltage of, for example, several hundred volts. Therefore, even with the adhesive portions 15A and 15B, which are made of an adhesive material that does not contain conductive components, interposed, the electrical connection between the diaphragm 13 and the piezoelectric element 12A, and the electrical connection between the piezoelectric element 12A and the piezoelectric element 12B are maintained, respectively.

[0039] As shown in Figure 5, the piezoelectric section 11 has a wiring section 16 used to drive the piezoelectric element 12. The wiring section 16 is electrically connected by a joint 17 to one surface of the diaphragm 13, the electrode 14 on the other surface of the piezoelectric element 12A, and the electrode 14 on the other surface of the piezoelectric element 12B. The joint 17, like the adhesive section 15, is made of an adhesive material that does not contain conductive components. The joint 17 may be made by, for example, soldering. In this case, an example of a solder material used for the joint 17 is Sn-Ag-Cu.

[0040] Figure 7 shows the circuit configuration of the piezoelectric section. As shown in Figure 7, the piezoelectric section 11 is electrically connected to the power supply unit 21 for driving. Piezoelectric elements 12A and 12B are electrically connected in parallel. The diaphragm 13 and piezoelectric elements 12A and 12B are electrically connected in series. A resistor 22 is electrically connected in series between the electrically parallel piezoelectric elements 12A and 12B and the power supply unit 21.

[0041] The resistor 22 functions as a protective resistor to suppress the flow of excessive current to the piezoelectric elements 12A and 12B. In this embodiment, the electrical resistance R1 of the resistor 22 is less than the insulation resistance R2 of the piezoelectric elements 12A and 12B. The electrical resistance R1 of the resistor 22 is greater than the contact resistance R3 between the diaphragm 13 and the electrode 14 of the piezoelectric element 12 (in this case, piezoelectric element 12A). Furthermore, the electrical resistance R1 of the resistor 22 is greater than the contact resistance R3 between the electrodes 14 of the multiple piezoelectric elements 12 (in this case, piezoelectric elements 12A and 12B).

[0042] The insulation resistance R2 of piezoelectric elements 12A and 12B corresponds to the electrical resistance of the insulating element 10. The contact resistance R3 between the diaphragm 13 and the electrode 14 of piezoelectric element 12A corresponds to the electrical resistance between one surface of the diaphragm 13 and the electrode 14 on one surface of the piezoelectric element 12A via the adhesive portion 15A. The contact resistance R3 between the electrodes 14 of piezoelectric elements 12A and 12B corresponds to the electrical resistance between the electrode 14 on the other surface of piezoelectric element 12A and the electrode 14 on one surface of piezoelectric element 12B via the adhesive portion 15B. As an example, if the insulation resistance R2 of piezoelectric elements 12A and 12B is 1 × 10⁻⁶ 9 Ω, the contact resistance R3 between the diaphragm 13 and the electrode 14 of piezoelectric element 12A, and the contact resistance R3 between the electrodes 14 of piezoelectric element 12A and piezoelectric element 12B are 1 × 10 2 If it is Ω, the electrical resistance R1 of resistor 22 is 1 × 10⁻⁶. 5 It is set to Ω.

[0043] In fixing the piezoelectric unit 11 described above inside the housing 2, a stepped portion 31 is provided in the main body portion 4 of the housing 2, as shown in Figures 4(a) and 4(b). The stepped portion 31 is provided on the other end in the X direction at the bottom portion 4a of the main body portion 4. The top surface 31a of the stepped portion 31 is a flat surface and has a rectangular shape in plan view. The height of the stepped portion 31 from the bottom portion 4a is approximately the same as the amount of protrusion of the nozzle 6 from the bottom portion 4a.

[0044] The piezoelectric section 11 is positioned on the stepped section 31 with adhesive sections 15A and 15B located on the stepped section 31, and with the protruding portion 13a of the diaphragm 13 from one end in the X direction of the piezoelectric element 12A facing the nozzle 6 side. The other end of the diaphragm 13 in the X direction is fixed to the top surface 31a of the stepped section 31 by a joining material such as adhesive or double-sided tape. As a result, the diaphragm 13 is cantilevered on the stepped section 31. The end of the diaphragm 13 on the side of the inlet hole P1 is a free end, and the end of the diaphragm 13 opposite to the inlet hole P1 is a fixed end. The wiring section 16 is located on the fixed end side of the diaphragm 13 because the joint 17 is located on the stepped section 31.

[0045] In this embodiment, as shown in Figures 4(a) and 4(b), the lid portion 5 of the housing 2 is provided with a projection 32 that protrudes toward the stepped portion 31, in order to reinforce the cantilever support of the diaphragm 13. The projection 32 is provided with a constant width so as to extend in the Y-axis direction, and the tip of the projection 32 is a flat surface. The projection 32 holds the fixed end side of the diaphragm 13 by sandwiching the diaphragm 13 and the piezoelectric element 12 (piezoelectric element 12A and piezoelectric element 12B described later) between itself and the stepped portion 31.

[0046] The inlet P1 is opened and closed by the free end of the diaphragm 13. In this embodiment, in the cantilevered diaphragm 13, the protruding portion 13a of the diaphragm 13 from one end of the piezoelectric element 12A in the X direction abuts against the tip surface 6a of the nozzle 6 that defines the inlet P1. As shown in Figure 3, when viewed from the stacking direction (Z direction) of the piezoelectric elements 12 in the piezoelectric section 11, the inlet P1 does not overlap with the piezoelectric elements 12, but only with the diaphragm 13. In the example in Figure 3, when viewed from the stacking direction (Z direction) of the piezoelectric elements 12 in the piezoelectric section 11, the tip surface 6a of the nozzle 6 does not overlap with either the piezoelectric elements 12A or 12B, but only with the diaphragm 13.

[0047] The portion of the nozzle 6 that does not contact the diaphragm 13, i.e., the portion of the nozzle 6 excluding the tip surface 6a, may, similar to the tip surface 6a, not overlap with either piezoelectric element 12A or piezoelectric element 12B when viewed from the stacking direction (Z direction) of the piezoelectric elements 12 in the piezoelectric section 11, but only with the diaphragm 13. Furthermore, a portion of the portion of the nozzle 6 excluding the tip surface 6a may overlap with piezoelectric element 12A or both piezoelectric elements 12A and 12B when viewed from the stacking direction (Z direction) of the piezoelectric elements 12 in the piezoelectric section 11.

[0048] In the example shown in Figure 3, a portion of the outlet hole P2 overlaps with the diaphragm 13 when viewed from the stacking direction (Z direction) of the piezoelectric elements 12 in the piezoelectric section 11, but there are no particular restrictions on the positional relationship between the outlet hole P2 and the piezoelectric section 11. The entire outlet hole P2 may overlap with the diaphragm 13 when viewed from the stacking direction (Z direction) of the piezoelectric elements 12 in the piezoelectric section 11. The outlet hole P2 may overlap with both the piezoelectric elements 12 and the diaphragm 13 when viewed from the stacking direction (Z direction) of the piezoelectric elements 12 in the piezoelectric section 11.

[0049] As shown in Figures 4(a) and 4(b), a biasing part 33 is positioned opposite the inlet hole P1 with the diaphragm 13 in between, biasing the diaphragm 13 toward the inlet hole P1. In this embodiment, the biasing part 33 is made of a spring member such as a coil spring. The biasing part 33 is positioned in the internal space S between the lid 5 and the protruding portion 13a of the diaphragm 13 so as to face the inlet hole P1 directly with the diaphragm 13 in between. The biasing part 33 presses the protruding portion 13a of the diaphragm 13 against the tip surface 6a of the nozzle 6, thereby maintaining the closed state of the inlet hole P1 when the piezoelectric element 12 is not distorted or deformed.

[0050] An elastic member 34 is positioned between the diaphragm 13 and the inlet hole P1. The elastic member 34 is formed in the shape of a disc with a diameter larger than the inner diameter of the inlet hole P1, for example, by an elastomer. In this embodiment, the elastic member 34 is fixed to the nozzle 6 side surface of the protruding portion 13a of the diaphragm 13 by a bonding member such as an adhesive or double-sided tape. The elastic member 34 functions as a sealing member that enhances airtightness when the inlet hole is closed. The elastic member 34 also functions as a vibration absorbing member that mitigates vibrations when the diaphragm 13 strikes the inlet hole P1 (the tip surface 6a of the nozzle 6).

[0051] As explained above, in the piezoelectric valve 1, the piezoelectric elements 12A and 12B are electrically connected in parallel via electrodes 14 made of a metal plating film. When electrodes 14 made of a metal plating film are used, the problem of ion migration can be avoided even when the piezoelectric valve 1 is driven by a DC component. When electrodes 14 made of a metal plating film are used, it is possible to join the electrodes 14 of the piezoelectric elements 12A and 12B to each other, or to the piezoelectric element 12A to the diaphragm 13 with an adhesive, but variations in the thickness of the adhesive may lead to variations in the contact resistance between the piezoelectric elements 12A and 12B, or between the piezoelectric element 12A and the diaphragm 13. In contrast, in the piezoelectric valve 1, a resistor 22 is electrically connected to the piezoelectric elements 12A and 12B. The resistor 22 functions as a protective resistor to suppress excessive current flow through the piezoelectric elements 12A and 12B. Furthermore, because the electrical resistance value R1 of the resistor 22 is less than the insulation resistance value R2 of the piezoelectric elements 12A and 12B, the current flowing through the piezoelectric elements 12A and 12B can be stabilized regardless of variations in the contact resistance value R3 between the piezoelectric elements 12A and 12B. Therefore, sufficient stability of the operation of the piezoelectric valve 1 can be ensured.

[0052] In this embodiment, the electrical resistance R1 of resistor 22 is greater than the contact resistance R3 between the diaphragm 13 and the electrode 14 of piezoelectric element 12A. Furthermore, in this embodiment, the electrical resistance R1 of resistor 22 is greater than the contact resistance R3 between the electrodes 14 of piezoelectric elements 12A and 12B. As a result, when considering the entire circuit including piezoelectric elements 12A and 12B, the diaphragm 13, and resistor 22, the variation in the contact resistance R3 between the diaphragm 13 and the electrode 14 of piezoelectric element 12A can be relatively reduced. Therefore, sufficient stability in the operation of the piezoelectric valve 1 can be ensured.

[0053] In this embodiment, the electrode 14 is formed by a sputtered film or a vapor-deposited film. This makes it possible to more reliably avoid ion migration problems even when the piezoelectric valve 1 is driven by a DC component, thereby improving the reliability of the piezoelectric valve 1.

[0054] In this embodiment, the electrode 14 is positioned in a region inside the contours of the piezoelectric elements 12A and 12B. This suppresses the occurrence of short circuits caused by the electrode 14.

[0055] In this embodiment, the piezoelectric elements 12A and 12B are joined to each other, and the piezoelectric element 12A is joined to the diaphragm 13 by an adhesive member that does not contain conductive components. By using an adhesive member that does not contain conductive components, the adhesive members between the piezoelectric elements 12A and 12B and between the piezoelectric element 12A and the diaphragm 13 can be made thin. Therefore, deterioration of characteristics due to the thickness of the adhesive member can be prevented. In addition, by using an adhesive member that does not contain conductive components, the occurrence of short circuits can be suppressed.

[0056] In this embodiment, the adhesive member is positioned to protrude outside the contours of the piezoelectric elements 12A and 12B. This improves the bonding strength between the piezoelectric elements 12A and 12B, and the bonding strength between the piezoelectric element 12A and the diaphragm 13.

[0057] In this embodiment, one longitudinal end of the diaphragm 13 is a fixed end, and the other longitudinal end is a free end. This ensures sufficient displacement of the free end of the diaphragm 13 due to the strain deformation of the piezoelectric elements 12A and 12B. Therefore, the piezoelectric elements 12A and 12B and the diaphragm 13 can be suitably applied as the valve body 3 of the piezoelectric valve 1.

[0058] In this embodiment, the electrode 14 and the diaphragm 13 are electrically connected to a wiring section 16, and the electrode 14 and the wiring section 16, as well as the diaphragm 13 and the wiring section 16, are joined by an adhesive member that does not contain conductive components. With this configuration, the occurrence of defects such as solder corrosion can be avoided. In addition, by using an adhesive member that does not contain conductive components, the occurrence of short circuits can be suppressed.

[0059] In this embodiment, the wiring section 16 is located on the fixed end side of the piezoelectric elements 12A and 12B and the diaphragm 13. By positioning the wiring section 16 on the fixed end side, the influence of stress caused by the strain deformation of the piezoelectric elements 12A and 12B on the wiring section 16 can be suppressed. This effectively prevents disconnections of the wiring section 16.

[0060] This disclosure is not limited to the embodiments described above. For example, in the embodiments described above, the piezoelectric section 11 is composed of a laminate formed by stacking piezoelectric elements 12A and 12B with different longitudinal dimensions, but the piezoelectric elements 12A and 12B may have equal longitudinal dimensions. Also, the number of layers of piezoelectric elements 12 stacked on the diaphragm 13 is not limited to two, but may be one layer or three or more layers.

[0061] Furthermore, in the above embodiment, for example, the diaphragm 13 and piezoelectric elements 12A and 12B, which are arranged on the stepped portion 31, are held in place by the projection 32 on the lid portion 5. However, instead of the projection 32, an elastic member such as a leaf spring may be placed in the internal space S between the stepped portion 31 and the lid portion 5, and the diaphragm 13 and piezoelectric elements 12 (piezoelectric elements 12A and 12B, described later) may be held in place by the elastic member. [Explanation of symbols]

[0062] 1...Piezoelectric valve, 12 (12A, 12B)...Piezoelectric element, 13...Diaphragm, 14...Electrode, 15 (15A, 15B)...Adhesive part (adhesive material), 16...Wiring part, 17...Joint part (adhesive material), 22...Resistor, R1...Electrical resistance value, R2...Insulation resistance value, R3...Contact resistance value.

Claims

1. A piezoelectric valve driven by a DC component, The piezoelectric valve is Multiple piezoelectric elements electrically connected in parallel via electrodes made of metal plating, A conductive diaphragm joined to the plurality of piezoelectric elements via the electrodes, The plurality of piezoelectric elements are electrically connected to resistors, A piezoelectric valve in which the electrical resistance of the resistor is less than the insulating resistance of the piezoelectric element.

2. The piezoelectric valve according to claim 1, wherein the electrical resistance value of the resistor is greater than the contact resistance value between the diaphragm and the electrode of the piezoelectric element.

3. The piezoelectric valve according to claim 1, wherein the electrical resistance value of the resistor is greater than the contact resistance value between the electrodes of the plurality of piezoelectric elements.

4. The piezoelectric valve according to claim 1, wherein the electrode is formed by a sputtered film or a vapor-deposited film.

5. The piezoelectric valve according to claim 1, wherein the electrode is arranged in a region inside the contour of the piezoelectric element.

6. The piezoelectric valve according to claim 1, wherein the plurality of piezoelectric elements and one of the plurality of piezoelectric elements and the diaphragm are joined together by an adhesive member that does not contain conductive components.

7. The piezoelectric valve according to claim 6, wherein the adhesive member is arranged to protrude outside the contour of the piezoelectric element.

8. The piezoelectric valve according to claim 1, wherein one end of the diaphragm in the longitudinal direction is a fixed end and the other end in the longitudinal direction is a free end.

9. The electrode and the diaphragm are electrically connected to a wiring section, The piezoelectric valve according to claim 8, wherein the electrode and the wiring portion and the diaphragm and the wiring portion are joined together by an adhesive member that does not contain conductive components.

10. The piezoelectric valve according to claim 9, wherein the wiring portion is located on the fixed end side of the piezoelectric element and the diaphragm.

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