piezoelectric actuator

Abstract

The piezoelectric actuator of the present disclosure is provided with: a piezoelectric element; a housing that houses the piezoelectric element inside, deforms following the expansion and contraction of the piezoelectric element, the housing includes a cylindrical body with a first end portion being open and a first cover, the first cover has a first bottom plate portion in a circular plate shape and a first protruding portion in a ring shape located at a first surface of the first bottom plate portion and protruding in a direction perpendicular to the first surface. The first protruding portion of the first cover is inserted into the first end portion of the cylindrical body, the inner peripheral surface of the first end portion is engaged with the outer peripheral surface of the first protruding portion, and in the axial direction of the cylindrical body, the front end of the first end portion is located at a position closer to the front end of the first protruding portion than the first surface of the first bottom plate portion.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a piezoelectric actuator. BACKGROUND

[0002] As a piezoelectric actuator, for example, a housing-sealed type laminated piezoelectric actuator configured by housing a laminated piezoelectric element in the inside of a metal housing having a stretchability, wherein the laminated piezoelectric element has a laminated body formed by alternately laminating a piezoelectric ceramic layer and an internal electrode layer, is known. The metal housing has a hollow member that communicates the inside and the outside, and the hollow member is sealed by an upper cover body and a lower cover body, thereby cutting off the inside and the outside of the metal housing (for example, refer to Patent Literature 1).

[0003] In the existing piezoelectric actuator, since the upper cover body and the lower cover body are joined with the hollow member having a stretchability, if the piezoelectric element is elongated, the hollow member is also elongated. Therefore, stress is easily concentrated at the joint surface of the upper cover body and the lower cover body and the hollow member, and sometimes the sealing of the hollow member is degraded. In this way, the existing piezoelectric actuator has room for improvement in terms of durability.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: JP Patent Application Laid-Open No. 2010-192832 SUMMARY

[0007] The piezoelectric actuator of the present disclosure has a piezoelectric element, and a housing that houses the piezoelectric element in the inside and deforms following the stretchability of the piezoelectric element. The housing includes a cylindrical body having a first end portion that is open, and a first cover body having a first bottom plate portion that is a circular plate, and a first protruding portion that is a ring shape located on a first surface of the first bottom plate portion and protruding in a direction perpendicular to the first surface. The first end portion of the cylindrical body is inserted into the first protruding portion of the first cover body. An inner peripheral surface of the first end portion and an outer peripheral surface of the first protruding portion are joined. In the axial direction of the cylindrical body, a front end of the first end portion is located at a position closer to a front end of the first protruding portion than the first surface of the first bottom plate portion. BRIEF DESCRIPTION OF DRAWINGS

[0008] The objects, features, and advantages of the present application will become more apparent from the following detailed description and accompanying drawings.

[0009] Figure 1 is a perspective view showing the schematic structure of an example of the piezoelectric actuator of the first embodiment of the present disclosure.

[0010] Figure 2 is a longitudinal sectional view showing the schematic structure of an example of the piezoelectric actuator cut along the A-A line shown in Figure 1 is a longitudinal sectional view showing the schematic structure of an example of the piezoelectric actuator cut along the A-A line shown in

[0011] Figure 3 is an enlarged longitudinal sectional view of the first cap in the first embodiment of the piezoelectric actuator of the present disclosure.

[0012] Figure 4 is an enlarged longitudinal sectional view showing a state in which the first cap in the first embodiment of the piezoelectric actuator of the present disclosure is inserted into the cylinder.

[0013] Figure 5 is an enlarged longitudinal sectional view showing a state in which the first cap in the second embodiment of the piezoelectric actuator of the present disclosure is inserted into the cylinder.

[0014] Figure 6 is an enlarged longitudinal sectional view showing a state in which the first cap in the third embodiment of the piezoelectric actuator of the present disclosure is inserted into the cylinder.

[0015] Figure 7 is an enlarged longitudinal sectional view showing a state in which the first cap in the second embodiment of the piezoelectric actuator of the present disclosure is inserted into the cylinder in the third embodiment.

[0016] Figure 8 is an enlarged longitudinal sectional view showing a state in which the first cap in the fourth embodiment of the piezoelectric actuator of the present disclosure is inserted into the cylinder.

[0017] Figure 9 is an enlarged longitudinal sectional view showing Figure 8 is an enlarged longitudinal sectional view showing a modification of the piezoelectric actuator shown in DETAILED DESCRIPTION

[0018] Hereinafter, a first embodiment of a piezoelectric actuator of the present disclosure will be described with reference to the drawings. Figure 1 is a perspective view showing an outline of the structure in the first embodiment of the piezoelectric actuator 10. Figure 2 is a longitudinal sectional view showing an outline of the structure of the piezoelectric actuator 10 cut along the A-A line shown in Figure 1 Figure 3 is an enlarged longitudinal sectional view of the first cap 30 of the piezoelectric actuator 10. Figure 4 is an enlarged longitudinal sectional view showing a state in which the first cap 30 of the piezoelectric actuator 10 is inserted into the cylinder 20. Note that the present application is not limited by the following embodiment.

[0019] Figures 1 to 4 The piezoelectric actuator 10 shown in

[0020] The piezoelectric element 1 constituting the piezoelectric actuator 10 is, for example, a laminated piezoelectric element. The piezoelectric element 1 is​Figure 2 The piezoelectric element 1 is, for example, a laminate having an active portion in which a piezoelectric layer and an internal electrode layer are alternately laminated a plurality of times, and a non-active portion including a piezoelectric layer laminated at both ends in the lamination direction of the active portion. Here, the active portion is a portion in which the piezoelectric layer is elongated or contracted in the lamination direction at the time of driving. The non-active portion is a portion in which the piezoelectric layer is not elongated or contracted in the lamination direction at the time of driving.

[0021] The laminate constituting the piezoelectric element 1 is, for example, formed in a rectangular parallelepiped shape having a length of 4 mm to 7 mm, a width of 4 mm to 7 mm, and a height of 20 mm to 50 mm. In addition, the shape of the laminate can be, for example, a hexagonal column shape, an octagonal column shape, or the like.

[0022] The piezoelectric layer constituting the laminate includes a piezoelectric ceramic having a piezoelectric property. The piezoelectric ceramic can be a ceramic using a powder having an average particle diameter of, for example, 1.6 μm to 2.8 μm as a material. As the piezoelectric ceramic, for example, a perovskite-type oxide having lead zirconate titanate (PbZr03-PbTi03), lithium niobate (LiNb03), lithium tantalate (LiTa03), or the like can be used.

[0023] In addition, the internal electrode layer constituting the laminate can be, for example, a metal layer using silver, silver-palladium, silver-platinum, copper, or the like as a main component. The internal electrode layer is, for example, alternately arranged in the lamination direction with a positive electrode and a negative electrode respectively. The positive electrode is led out to one side surface of the laminate. The negative electrode is led out to the other side surface of the laminate. With this structure, in the active portion, it is possible to apply a driving voltage to the piezoelectric layer sandwiched between the internal electrode layers adjacent to each other in the lamination direction. In addition, the laminate can include a layer for relaxing stress, that is, a metal layer that does not function as an internal electrode layer, or the like.

[0024] Further, on the pair of side surfaces of the laminate opposite to the positive electrode or the negative electrode (or the ground electrode) of the internal electrode layer from which the electrodes are led out, external electrodes are respectively provided. The external electrodes are electrically connected to the internal electrode layer from which the electrodes are led out. The external electrodes can be, for example, a metallized layer having silver and glass.

[0025] On the other pair of side surfaces of the laminate opposite to each other, both of the positive electrode and the negative electrode (or the ground electrode) of the internal electrode layer are exposed, and a coating layer having an insulator is provided on the side surfaces as needed. By providing the coating layer, it is possible to suppress the surface discharge between the two electrodes generated at the time of applying a high voltage at the time of driving. As the insulator of the coating layer, a ceramic material is exemplified. As the ceramic material, a material that can be deformed according to stress heat can be used in particular, so that it is possible to follow the driving deformation of the laminate at the time of driving the piezoelectric actuator, and it is not worried that the coating layer is peeled off to generate surface discharge.

[0026] As a material used in the coating layer, for example, a partially stabilized zirconia which locally phase changes and changes in volume to be able to deform when stress is generated, Ln 1-x Si x AlO 3+0.5x (Ln represents any at least one selected from Sn, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb. x = 0.01 to 0.3), or a piezoelectric material such as barium titanate, lead zirconate titanate, or the like, in which the interionic distance within the crystal lattice changes so that the generated stress is relaxed. The coating layer is formed, for example, by forming the above-described ceramic material or piezoelectric material in an ink form, coating the side surface of the laminate by dipping or screen printing, and performing sintering.

[0027] The housing 2 constituting the piezoelectric actuator 10 houses the piezoelectric element 1 inside. The lower end surface of the piezoelectric element 1 is in contact with the upper surface of the first cover 30. The upper end surface of the piezoelectric element 1 is in contact with the lower surface of the second cover 40.

[0028] The cylinder 20 is a cylindrical body which is open at both ends extending upward and downward. The cylinder 20 is formed in a corrugated shape or a bellows shape, for example, after being made into a seamless pipe in a prescribed shape, by rolling processing or hydrostatic pressure stamping, or the like. The cylinder 20 has a prescribed spring constant so as to be able to follow the expansion and contraction of the piezoelectric element 1 when a voltage is applied to the piezoelectric element 1. The spring constant of the cylinder 20 can be adjusted according to the thickness of the cylinder 20, the groove shape, and the number of grooves. The thickness of the cylinder 20 can be, for example, 0.1 to 0.5 mm.

[0029] As shown in FIG. 1, the first cover 30 has a first bottom plate portion 31 which is a circular plate, and a first protruding portion 32 which is a ring. The first protruding portion 32 is positioned on a first surface 311 of the first bottom plate portion 31, and protrudes in a direction perpendicular to the first surface 311. Figure 3

[0030] As shown in FIG. 1, the first cover 30 has an outer diameter which is formed to be the same degree as the inner diameter of the first end portion 21 side of the cylinder 20. The first cover 30 is inserted from the first end portion 21 side of the cylinder 20, and the first protruding portion 32 of the first cover 30 is inserted into the first end portion 21 of the cylinder 20. The inner peripheral surface 213 of the first end portion 21 of the cylinder 20 and the outer peripheral surface 321 of the first protruding portion 32 of the first cover 30 are joined. In the axial direction of the cylinder 20, the front end (also referred to as the open end) 211 of the first end portion 21 is positioned at a position closer to the front end side of the first protruding portion 32 than the first surface 311 of the first bottom plate portion 31. The inner peripheral surface 213 of the first end portion 21 and the outer peripheral surface 321 of the first protruding portion 32 can be joined by welding, such as laser welding, resistance welding, or the like. Figure 4

[0031] ​​The front end 211 of the first end 21 is located closer to the front end of the first protrusion 32 than the first surface 311 of the first base plate portion 31. As a result, when the piezoelectric element 1 is extended, stress concentration in the groove portion between the cylinder 20 and the first cover 30 can be suppressed. Consequently, the deflection of the outer periphery of the first cover can be reduced, and the seal is less likely to be damaged.

[0032] The first cover 30 may also have a corner portion 313 that connects the outer peripheral surface 312 of the first base plate portion 31 to the first surface 311. In addition, the first cover 30 may have a corner portion 322 that connects the outer peripheral surface 321 of the first protrusion 32 to the first surface 311 of the first base plate portion 31.

[0033] The first cover 30 generates stress at each corner by having corner portions 313 and 322. As a result, the stress in the stress-concentrated areas of the prior art can be dispersed and mitigated.

[0034] Furthermore, the outer peripheral surface 212 of the first end 21 can be a curved surface covering the entire circumference, as in this embodiment. This structure helps to suppress stress concentration at the junction of the cylinder 20 and the first protrusion 32. Moreover, if stress is applied by elongating the piezoelectric element 1, the curvature change of the curved surface can disperse the stress.

[0035] like Figure 2 As shown, the second cover 40 has a circular second bottom plate portion 41 and an annular second protrusion 42. The second protrusion 42 is located on the third surface 411 of the second bottom plate portion 41. The cylinder 20 has an open second end portion 22 on the side opposite to the first end portion 21. The second protrusion 42 of the second cover 40 is inserted into the second end portion 22 of the cylinder 20, and the inner peripheral surface 224 of the second end portion 22 is joined to the outer peripheral surface 421 of the second protrusion 42. Furthermore, the end face 222 of the second end portion 22 is separated from the third surface 411 of the second bottom plate portion 41. The inner peripheral surface 224 of the second end portion 22 and the outer peripheral surface 421 of the second protrusion 42 can be joined, for example, by welding methods such as laser welding or resistance welding.

[0036] With this structure, in the piezoelectric actuator 10 of this embodiment, stress concentration at the junction of the inner peripheral surface 224 of the second end 22 and the outer peripheral surface 421 of the second protrusion 42 can be suppressed. Furthermore, even if the piezoelectric element 1 elongates and generates stress, the stress can be more effectively dispersed compared to the case where the housing 2 only has the first cover 30.

[0037] The cylinder 20, the first cover 30, and the second cover 40 are, for example, made of metal such as SUS304 or SUS316L.

[0038] The first bottom plate portion 31 can have a through hole 315 that penetrates from the first face 311 to the second face 314 on the opposite side of the first face 311. A pin 50 that is electrically connected to the piezoelectric element 1 can be inserted into the through hole 315.

[0039] Next, a second embodiment of the piezoelectric actuator of the present disclosure will be described with reference to the drawings. Figure 5 is an enlarged longitudinal sectional view that shows a state in which the first protrusion 32 of the first cover 30 in the piezoelectric actuator 10 of the present embodiment is inserted into the first end portion 21 of the cylinder 20.

[0040] The first protrusion 32 has a first annular region 323 and a second annular region 324. The second region 324 is located on the first bottom plate portion 31 side than the first region 323. The outer diameter of the second region 324 is larger than that of the first region 323. The inner peripheral surface 214 of the first end portion 21 is joined to the outer peripheral surface 321 of the first region 323. As in the present embodiment, by separating the front end 211 of the first end portion 21 from the upper surface 325 of the second region 324 of the first protrusion 32, even for the stress of the torsion that occurs due to a slight deviation in the direction of expansion of the piezoelectric element 1 from the direction of expansion of the housing 2, the stress that occurs at the boundary of the second region 324, which has a relatively thick wall thickness, with respect to the first region 323 can be dispersed around the entire circumference. As a result, even if the piezoelectric actuator 10 is repeatedly driven for a long period of time, the seal is less likely to be damaged.

[0041] With this structure, in the piezoelectric actuator 10 of the present embodiment, stress concentration at the joint between the inner peripheral surface 214 of the first end portion 21 of the cylinder 20 and the outer peripheral surface 321 of the first region 323 of the first protrusion 32 can be suppressed. Furthermore, even if stress is generated by the elongation of the piezoelectric element 1, the stress can be dispersed, and the concern that a crack will occur at the joint can be reduced.

[0042] Next, a third embodiment of the piezoelectric actuator of the present disclosure will be described with reference to the drawings. Figure 6 is an enlarged longitudinal sectional view that shows a state in which the first protrusion 32 of the first cover 30 in the piezoelectric actuator 10 of the present embodiment is inserted into the first end portion 21 of the cylinder 20.

[0043] The first end portion 21 of the cylinder 20 has a first portion 215 that includes the front end 211 and a second portion 216. The second portion 216 is located on the inner side in the axial direction of the cylinder 20 than the first portion 215, and has a larger inner diameter than the first portion 215. The inner peripheral surface 214 of the first portion 215 is joined to the outer peripheral surface 321 of the first protrusion 32. In addition, in the radial direction of the cylinder 20, the inner peripheral surface 214 of the second portion 216 is separated from the outer peripheral surface 321 of the first protrusion 32.

[0044] With this structure, stress concentration at the junction of the inner peripheral surface 214 of the first portion 215 and the outer peripheral surface 321 of the first protrusion 32 can be suppressed in the piezoelectric actuator 10 of this embodiment. Furthermore, even if stress is generated due to the elongation of the piezoelectric element 1, the stress can be dispersed. In addition to the effect of dispersing stress, axial misalignment of the piezoelectric element 1 can also be suppressed.

[0045] Furthermore, the first end 21 of the piezoelectric actuator 10 in the second embodiment of this disclosure can also have the structure of the first end 21 in this embodiment. In this case, as Figure 7 As shown, the inner peripheral surface 214 of the first part 215 is joined to the outer peripheral surface 321 of the first region 323.

[0046] With this structure, stress concentration at the junction of the inner peripheral surface 214 of the second portion 216 and the outer peripheral surface 321 of the first region 323 can be suppressed in the piezoelectric actuator 10 of this embodiment. Furthermore, even if stress is applied by elongation of the piezoelectric element 1, the stress can be dispersed. In addition to the effect of dispersing stress, axial misalignment of the piezoelectric element 1 can also be suppressed.

[0047] Next, a fourth embodiment of the piezoelectric actuator of this disclosure will be described with reference to the accompanying drawings. Figure 8 This is an enlarged longitudinal sectional view showing the state in which the first protrusion 32 of the first cover 30 of the piezoelectric actuator 10 of this embodiment is inserted into the first end 21 of the cylinder 20. Figure 9 It means Figure 8 An enlarged longitudinal sectional view of a modified example of the piezoelectric actuator 10 shown.

[0048] like Figure 8 As shown, the piezoelectric actuator 10 can be a structure in which the housing 2 has a metal joint 217 located between the inner peripheral surface 213 of the first end 21 and the outer peripheral surface 321 of the first protrusion 32. Because the housing 2 has the metal joint 217, when stress is concentrated at the joint between the first end 21 and the first protrusion 32 due to the elongation of the piezoelectric element 1, the stress can be dispersed on the outer peripheral surface of the metal joint 217. As a result, even if stress is concentrated at the front end 211 of the first end 21, the development of microcracks into a straight line can be suppressed, and the seal is less likely to be damaged. The outer peripheral surface 212 of the first end 21 can also be curved along its entire circumference. This further mitigates stress.

[0049] The metal joint 217 is a portion whose crystalline structure differs from that of the first cover 30 and the cylinder 20. The metal joint 217 may, for example, be a cross-diffusion portion formed by the inter-diffusion of the components of the first cover 30 and the cylinder 20. The metal joint 217 may be a portion where the metal constituting the first cover 30 diffuses into the cylinder 20, or a portion where the metal constituting the cylinder 20 diffuses into the first cover 30. The metal joint 217 may, for example, be a portion formed by melting the inner peripheral surface 213 of the first end 21 and the outer peripheral surface 321 of the first protrusion 32 through laser irradiation used for laser welding of the first cover 30 and the cylinder 20. The metal joint 217 may contain, for example, the components of the first cover 30 and the cylinder 20.

[0050] The cross-sectional shape of the metal joint 217 can be, for example, circular, elliptical, racetrack-shaped, or other shapes. The metal joint 217 may exist throughout the entire circumference of the inner circumferential surface 212 of the first end 21, or it may exist only in a portion of the circumferential direction of the inner circumferential surface 212. The presence or absence of the metal joint 217, and its shape, can be confirmed, for example, by structural analysis using an electron probe microanalyzer (EPMA) or similar instrument.

[0051] Metal joint 217 can be as follows Figure 9 As shown, it extends to the front end 211 of the first end 21. Therefore, even if stress is concentrated at the front end 211 of the first end 21, the front end 211 is unlikely to become the starting point of a microcrack. Thus, stress can be mitigated more effectively, and the seal is less likely to be damaged. Additionally, the metal joint 217 can also be located on the outer peripheral surface of the first end 21.

[0052] The example described above illustrates a housing 2 having a metal joint 217 located between the first end 21 and the first protrusion 32. However, the housing 2 may also have a metal joint 217 located between the inner peripheral surface 224 of the second end 22 and the outer peripheral surface 421 of the second protrusion 42. Furthermore, the housing 2 may have both a metal joint 217 located between the first end 21 and the first protrusion 32, and a metal joint 217 located between the second end 22 and the second protrusion 42. Even if stress is generated between at least one of the first cover 30 and the second cover 40 and the cylinder 20 due to the elongation of the piezoelectric element 1, the piezoelectric actuator 10 of this embodiment can effectively disperse the stress. As a result, since the development of microcracks at the joint between at least one of the first cover 30 and the second cover 40 and the cylinder 20 can be suppressed, the seal is less likely to be damaged.

[0053] In the above, the piezoelectric actuator in which the laminated piezoelectric element is housed is described, but the piezoelectric actuator of the present disclosure is not limited thereto, and can be applied to any piezoelectric element to which the piezoelectric actuator of the present disclosure can be applied.

[0054] Symbol explanation

[0055] 1 piezoelectric element

[0056] 2 housing

[0057] 10 piezoelectric actuator

[0058] 20 barrel

[0059] 21 first end portion

[0060] 211 front end

[0061] 22 second end portion

[0062] 222 end surface

[0063] 224 inner peripheral surface

[0064] 212, 312, 321 outer peripheral surface

[0065] 213, 214 inner peripheral surface

[0066] 215 first portion

[0067] 216 second portion

[0068] 217 metal joint portion

[0069] 30 first cover

[0070] 31 first bottom plate portion

[0071] 32 first protrusion

[0072] 311 first surface

[0073] 312 outer peripheral surface

[0074] 313 corner portion

[0075] 314 second surface

[0076] 315 through hole

[0077] 321 outer peripheral surface

[0078] 322 corner portion

[0079] 323 first region

[0080] 324 second region

[0081] 325 upper surface

[0082] 40 second cover body

[0083] 41 second bottom plate portion

[0084] 42 second protruding portion

[0085] 411 third surface

[0086] 421 outer peripheral surface

[0087] 50 pin

Claims

1. A piezoelectric actuator, comprising: piezoelectric elements; and A housing that encloses the piezoelectric element and deforms in accordance with the expansion and contraction of the piezoelectric element; the housing includes a cylindrical body with a first open end and a first cover; the first cover has a first plate-shaped bottom plate portion and an annular first protrusion located on a first surface of the first bottom plate portion and protruding in a direction perpendicular to the first surface. The first protrusion of the first cover is inserted into the first end of the cylinder, the inner circumferential surface of the first end is engaged with the outer circumferential surface of the first protrusion, and in the axial direction of the cylinder, the front end of the first end is located closer to the front end of the first protrusion than the first surface of the first bottom plate. The first protrusion has: an annular first region and an annular second region located further from the first base plate portion than the first region and having an outer diameter larger than the first region. The inner peripheral surface of the first end is engaged with the outer peripheral surface of the first region.

2. A piezoelectric actuator, comprising: piezoelectric elements; and A housing that encloses the piezoelectric element and deforms in accordance with the expansion and contraction of the piezoelectric element; the housing includes a cylindrical body with a first open end and a first cover; the first cover has a first plate-shaped bottom plate portion and an annular first protrusion located on a first surface of the first bottom plate portion and protruding in a direction perpendicular to the first surface. The first protrusion of the first cover is inserted into the first end of the cylinder, the inner circumferential surface of the first end is engaged with the outer circumferential surface of the first protrusion, and in the axial direction of the cylinder, the front end of the first end is located closer to the front end of the first protrusion than the first surface of the first bottom plate. The first cover has a corner portion that connects the outer peripheral surface of the first base plate portion to the first surface.

3. A piezoelectric actuator, comprising: piezoelectric elements; and A housing that encloses the piezoelectric element and deforms in accordance with the expansion and contraction of the piezoelectric element; the housing includes a cylindrical body with a first open end and a first cover; the first cover has a first plate-shaped bottom plate portion and an annular first protrusion located on a first surface of the first bottom plate portion and protruding in a direction perpendicular to the first surface. The first protrusion of the first cover is inserted into the first end of the cylinder, the inner circumferential surface of the first end is engaged with the outer circumferential surface of the first protrusion, and in the axial direction of the cylinder, the front end of the first end is located closer to the front end of the first protrusion than the first surface of the first bottom plate. The first cover has a corner portion that connects the outer peripheral surface of the first protrusion to the first surface.

4. The piezoelectric actuator according to any one of claims 1 to 3, wherein, The outer peripheral surface of the first end is a curved surface.

5. The piezoelectric actuator according to any one of claims 1 to 3, wherein, The housing further includes a metal joint located between the inner peripheral surface of the first end portion and the outer peripheral surface of the first protrusion.

6. The piezoelectric actuator according to claim 2 or 3, wherein, The first protrusion has: an annular first region and an annular second region located further from the first base plate portion than the first region and having an outer diameter larger than the first region. The inner peripheral surface of the first end is engaged with the outer peripheral surface of the first region.

7. The piezoelectric actuator according to claim 1, wherein, The end face of the first end is separated from the upper surface of the second region of the first protrusion.

8. The piezoelectric actuator according to any one of claims 1 to 3, wherein, The first end of the cylinder has: a first portion including an end face of the first end, and a second portion located inside the cylinder along the axial direction, which is closer to the first portion than the first portion and has an inner diameter larger than the first portion. The inner peripheral surface of the first portion is joined to the outer peripheral surface of the first protrusion. In the radial direction of the cylinder, the inner circumferential surface of the second portion is separated from the outer circumferential surface of the first protrusion.

9. The piezoelectric actuator according to claim 1, wherein, The first end of the cylinder has: a first portion including an end face of the first end, and a second portion located inside the cylinder along the axial direction, which is closer to the first portion than the first portion and has an inner diameter larger than the first portion. The inner peripheral surface of the first portion is joined to the outer peripheral surface of the first protrusion. In the radial direction of the cylinder, the inner circumferential surface of the second portion is separated from the outer circumferential surface of the first protrusion. The inner peripheral surface of the second part is engaged with the outer peripheral surface of the first region.

10. The piezoelectric actuator according to any one of claims 1 to 3, wherein, The first base plate has a through hole extending from the first surface to a second surface on the opposite side of the first surface, through which a pin electrically connected to the piezoelectric element is inserted.

11. The piezoelectric actuator according to any one of claims 1 to 3, wherein, The housing further includes: a second cover having a circular second bottom plate portion and an annular second protrusion located on a third surface of the second bottom plate portion. The second end of the cylinder, on the side opposite to the first end, is open. The second protrusion of the second cover is inserted into the second end of the cylinder, the inner circumferential surface of the second end is engaged with the outer circumferential surface of the second protrusion, and the end face of the second end is separated from the third surface of the second bottom plate.

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