Piezoelectric device and ultrasonic flowmeter

Abstract

To provide a piezoelectric device capable of suppressing propagation of vibrations to a housing by increasing the acoustic impedance difference.SOLUTION: A piezoelectric device 40 is provided in a case member 20a, 20b and includes a packing 45 for supporting a metal plate 41 having a piezoelectric element 42 mounted thereon in the inner periphery. The packing 45 has protrusions 53 to form hollow spaces S between the case member 20a, 20b and the metal plate 41.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to a piezoelectric device and an ultrasonic flowmeter.

Background Art

[0002] Patent Document 1 discloses a piezoelectric device having a piezoelectric element. The piezoelectric device disclosed in Patent Document 1 generates vibration by expanding and contracting the piezoelectric element. Further, in the piezoelectric device disclosed in Patent Document 1, a mounting plate to which the piezoelectric element is attached is fixed to a housing via a vibration damping member.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The piezoelectric device disclosed in Patent Document 1 is provided with protrusions on the outer peripheral portion of a vibration damping member formed of a resin material. These protrusions are in contact with the housing. Therefore, the piezoelectric device disclosed in Patent Document 1 attenuates the vibration of the piezoelectric element and the vibration of the mounting plate generated by receiving this vibration, and suppresses the transmission of vibration to the housing.

[0005] Here, considering from the viewpoint of acoustic impedance indicating the ease of sound transmission, between solids, there is almost no difference in the acoustic impedance between each other. Therefore, in the piezoelectric device disclosed in Patent Document 1, even if the protrusion of the vibration damping member and the housing are brought into contact with each other, since the difference in their acoustic impedance is small, the transmission of vibration from the vibration damping member to the housing cannot be sufficiently suppressed.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to provide a piezoelectric device capable of suppressing the transmission of vibration to a housing by increasing the difference in acoustic impedance.

Means for Solving the Problems

[0007] The piezoelectric device according to the present disclosure includes a packing that is provided in a housing and supports a mounting plate to which a piezoelectric element is attached at an inner peripheral portion, and the packing has a hollow forming portion that forms a hollow portion between the housing and the mounting plate.

Effects of the Invention

[0008] According to the present disclosure, by increasing the difference in acoustic impedance, the transmission of vibration to the housing can be suppressed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0011] Embodiment 1. The piezoelectric devices 40a and 40b according to Embodiment 1 will be described with reference to FIGS. 1 to 6.

[0012] First, the configuration of the ultrasonic flowmeter 100 according to Embodiment 1 will be described with reference to FIGS. 1 and 2. FIG. 1 is an external perspective view of the ultrasonic flowmeter 100 to which the piezoelectric devices 40a and 40b according to Embodiment 1 are applied, and FIG. 2 is a perspective view of the state in which the piezoelectric device 40b according to Embodiment 1 is attached to the case member 20b. In FIG. 1, the upstream wiring 44 and the downstream cap 30b are removed.

[0013] The ultrasonic flowmeter 100 shown in FIG. 1 measures the flow rate or flow velocity of a fluid using ultrasonic waves. The fluid to be measured is a gas such as air or gas, or a liquid such as water. The ultrasonic flowmeter 100 is mounted on, for example, a gas meter or a water meter. The arrow shown in FIG. 1 indicates the flow direction of the fluid passing through the inside of the ultrasonic flowmeter 100.

[0014] As shown in FIG. 1, the ultrasonic flowmeter 100 includes one measurement tube 10, a pair of case members 20a and 20b, a pair of caps 30a and 30b, and a pair of piezoelectric devices 40a and 40b. The measurement tube 10 and the case members 20a and 20b constitute the housing of the ultrasonic flowmeter 100.

[0015] The measurement tube 10 has a cylindrical shape. The measurement tube 10 has a measurement flow path 11, an inlet 12, and an outlet 13. The measurement tube 10 is formed of, for example, a resin material. The measurement flow path 11, the inlet 12, and the outlet 13 are integrally formed.

[0016] The measurement flow path 11 is constituted by the inner peripheral surface of the measurement tube 10 and is formed along the axial direction of the measurement tube 10. The fluid flows along the axial direction of the measurement flow path 11. The upstream opening end of the measurement flow path 11 constitutes an inlet 12 through which the fluid flows in. On the other hand, the downstream opening end of the measurement flow path 11 constitutes an outlet 13 through which the fluid flows out. That is, the measurement tube 10 supplies the fluid supplied into the measurement flow path 11 from the inlet 12, passes it through the measurement flow path 11, and then discharges it from the outlet 13. Although details will be described later, the ultrasonic flowmeter 100 measures the flow rate or flow velocity of the fluid when the fluid passes through the measurement flow path 11.

[0017] As shown in FIGS. 1 and 2, the case members 20a and 20b are members for attaching the piezoelectric devices 40a and 40b to the measurement tube 10. The case members 20a and 20b are provided along the axial direction (fluid flow direction) of the measurement flow path 11 on the upper surface that is the same surface of the measurement tube 10. One case member 20a is arranged on the upstream side of the measurement flow path 11. The other case member 20b is arranged on the downstream side of the measurement flow path 11.

[0018] The case members 20a and 20b are formed of, for example, a resin material. The case members 20a and 20b may be integrally formed with the measurement tube 10 or may be separate from the measurement tube 10.

[0019] The case members 20a and 20b have an annular bottom plate (not shown) and a vertical wall 22 provided on the outer peripheral portion of this bottom plate. In this way, the case members 20a and 20b are box-shaped with an open upper side. For this reason, the case members 20a and 20b can accommodate and attach the piezoelectric devices 40a and 40b inside them. The case members 20a and 20b are arranged such that their central axes are inclined with respect to the axial direction of the measurement flow path 11. Note that the vertical wall 22 has a cutout-shaped passage port 22a for wiring.

[0020] As shown in FIGS. 1 and 2, the caps 30a and 30b can be respectively attached to the respective vertical walls 22 of the case members 20a and 20b as covers for protecting the piezoelectric devices 40a and 40b. The caps 30a and 30b are formed of, for example, a resin material.

[0021] The piezoelectric devices 40a and 40b are, for example, ultrasonic sensors or ultrasonic vibration elements that generate ultrasonic waves. The piezoelectric devices 40a and 40b enable the transmission and reception of ultrasonic waves between each other. One of the piezoelectric devices 40a functions as an oscillator and receiver of ultrasonic waves. The other piezoelectric device 40b functions as a receiver and transmitter of ultrasonic waves.

[0022] The piezoelectric devices 40a and 40b are provided along the axial direction of the measurement flow path 11. The piezoelectric devices 40a and 40b are attached inside the case members 20a and 20b. That is, one of the piezoelectric devices 40a arranged on the upstream side of the measurement flow path 11 is attached inside the case member 20a. The other piezoelectric device 40b arranged on the downstream side of the measurement flow path 11 is attached inside the case member 20b.

[0023] In this way, the piezoelectric devices 40a and 40b are attached inside the case members 20a and 20b, so that their central axes are inclined with respect to the axial direction of the measurement flow path 11 and are arranged to face the measurement flow path 11. Specifically, the piezoelectric device 40a is arranged to be inclined so that its transmission / reception surface faces the downstream side. The piezoelectric device 40b is arranged to be inclined so that its transmission / reception surface faces the upstream side. Further, when the piezoelectric devices 40a and 40b are attached inside the case members 20a and 20b, their peripheries will be surrounded by the vertical walls 22, but they do not protrude above the upper ends of the vertical walls 22.

[0024] Here, the ultrasonic flowmeter 100 propagates the ultrasonic waves transmitted from the piezoelectric devices 40a and 40b into the fluid flowing through the measurement channel 11. Then, the ultrasonic flowmeter 100 measures the flow rate or flow velocity of the fluid flowing through the measurement channel 11 based on the propagation time difference of the ultrasonic waves between the piezoelectric devices 40a and 40b.

[0025] Specifically, the ultrasonic wave transmitted from the piezoelectric device 40a obliquely propagates from the upstream side to the downstream side in the fluid flowing through the measurement channel 11, reflects off the bottom surface of the measurement channel 11, and is then received by the piezoelectric device 40b. On the other hand, the ultrasonic wave transmitted from the piezoelectric device 40b obliquely propagates from the downstream side to the upstream side in the fluid flowing through the measurement channel 11, reflects off the bottom surface of the measurement channel 11, and is then received by the piezoelectric device 40a. That is, the propagation paths of both ultrasonic waves are each formed in a V shape. Then, the ultrasonic flowmeter 100 determines the propagation times of the two-direction ultrasonic waves respectively when the piezoelectric devices 40a and 40b transmit and receive ultrasonic waves, and then measures the flow rate or flow velocity of the fluid flowing through the measurement channel 11 based on the propagation time difference between them.

[0026] Next, the configurations of the piezoelectric devices 40a and 40b will be described with reference to FIGS. 3 to 6. FIG. 3 is an external perspective view of the piezoelectric device 40 according to Embodiment 1. FIG. 4 is an external perspective view of the packing 45 as seen from the front side. FIG. 5 is an external perspective view of the packing 45 as seen from the back side. FIG. 6 is a plan view of the state where the piezoelectric device 40 is attached to the case member 20a. FIG. 7 is a view partially showing the hollow portions 56A and 56B as a modified example. Since the piezoelectric devices 40a and 40b have the same configuration and the same functions, in the following description, the piezoelectric devices 40a and 40b are described as the piezoelectric device 40.

[0027] As shown in FIG. 3, the piezoelectric device 40 is circular as a whole. The piezoelectric device 40 has a metal plate 41, a piezoelectric element 42, an acoustic matching layer 43, a wiring 44, and a packing 45.

[0028] The metal plate 41 is flat and circular in shape. This metal plate 41 serves as a diaphragm. The metal plate 41 has an upper surface 41a and a lower surface 41b. The upper surface 41a and the lower surface 41b are arranged on opposite sides in the thickness direction of the metal plate 41. The metal plate 41 is formed of a metal material such as stainless steel, aluminum, or copper, for example.

[0029] When the piezoelectric device 40 is attached to the case members 20a, 20b, the upper surface 41a is arranged on the opening side of the case members 20a, 20b. This upper surface 41a is a surface for attaching the piezoelectric element 42. When the piezoelectric device 40 is attached to the case members 20a, 20b, the lower surface 41b faces the bottom plate of the case members 20a, 20b. This lower surface 41b is a surface for attaching the acoustic matching layer 43.

[0030] Note that the metal plate 41 constitutes a mounting plate. The upper surface 41a constitutes the first surface. The lower surface 41b constitutes the second surface.

[0031] The piezoelectric element 42 can mutually convert an ultrasonic signal, which is an electrical signal, and ultrasonic waves. Also, the piezoelectric element 42 can transmit and receive ultrasonic waves. Specifically, when a voltage is applied, the piezoelectric element 42 expands and contracts (vibrates) in the thickness direction of the metal plate 41 to generate ultrasonic waves. Also, when ultrasonic waves (vibrations) are applied from the outside, the piezoelectric element 42 generates a voltage. The piezoelectric element 42 is attached to the upper surface 41a of the metal plate 41 via an adhesive, for example.

[0032] The acoustic matching layer 43 improves the efficiency of ultrasonic wave transmission and reception in the piezoelectric element 42. This acoustic matching layer 43 matches the acoustic impedance of the piezoelectric element 42 and the acoustic impedance of the fluid to suppress reflection of ultrasonic waves therebetween. For this reason, the acoustic matching layer 43 is attached to the lower surface 41b facing the measurement flow path 11.

[0033] Therefore, the ultrasonic waves generated by the piezoelectric element 42 are emitted from the acoustic matching layer 43 into the measurement channel 11 through the metal plate 41. On the other hand, the ultrasonic waves incident on the acoustic matching layer 43 from the measurement channel 11 are propagated to the piezoelectric element 42 through the metal plate 41.

[0034] The two wirings 44 are respectively connected to the upper surface 41a of the metal plate 41 and the surface of the piezoelectric element 42. These wirings 44 are drawn out from the piezoelectric device 40 mounted inside the case members 20a and 20b through the through-hole 22a in the vertical wall 22 thereof to a control device (not shown) provided in the ultrasonic flowmeter 100.

[0035] Specifically, one end of one wiring 44 is connected to the upper surface 41a of the metal plate 41, and the other end of the wiring 44 is connected to a control device (not shown) provided in the ultrasonic flowmeter 100. Also, one end of the other wiring 44 is connected to the surface of the piezoelectric element 42, and the other end of the wiring 44 is connected to the control device.

[0036] The packing 45 is designed to achieve both the fixation of the piezoelectric device 40 to the case members 20a and 20b and the suppression of the attenuation of the ultrasonic vibrations generated by the piezoelectric element 42. In this way, the ultrasonic flowmeter 100 can suppress the vibration transmitted from the piezoelectric device 40 to the measurement pipe 10 through the case members 20a and 20b by fixing the piezoelectric device 40 to the case members 20a and 20b via the packing 45. Therefore, the ultrasonic flowmeter 100 can suppress the deterioration of the measurement accuracy.

[0037] As shown in FIGS. 4 and 5, the packing 45 has a main body 51, an outer peripheral wall portion 52, a protruding portion 53, a wiring holding portion 54, and an insertion groove 55. The packing 45 is formed of, for example, an elastic resin material. The main body 51, the outer peripheral wall portion 52, the protruding portion 53, the wiring holding portion 54, and the insertion groove 55 are integrally formed.

[0038] The main body 51 is annular. The outer peripheral wall portion 52 is provided along the circumferential direction at the outer peripheral portion of the upper surface of the main body 51.

[0039] The protruding portions 53 are provided in plurality along the circumferential direction on the outer peripheral surface of the outer peripheral wall portion 52. The protruding portions 53 are formed so as to protrude radially outward from the outer peripheral surface of the outer peripheral wall portion 52. For this reason, the protruding portions 53 are in point contact or line contact with the inner peripheral surfaces of the case members 20a and 20b while being elastically deformed as if crushed. FIGS. 4 and 5 show an example in which five protruding portions 53 are formed for one outer peripheral wall portion 52. Further, FIGS. 4 and 5 show an example in which the protruding portions 53 have a shape of line contact with the case members 20a and 20b.

[0040] The wiring holding portion 54 holds two wirings 44. A groove for holding the wiring 44 is formed in the wiring holding portion 54. The wiring holding portion 54 is formed so as to protrude radially outward from the main body 51. Further, the wiring holding portion 54 is formed so as to be continuous with the outer peripheral wall portions 52 on both sides in the radial direction.

[0041] The insertion groove 55 is a groove into which the outer peripheral portion of the metal plate 41 is inserted. A plurality of insertion grooves 55 are provided on the inner side in the radial direction of the outer peripheral wall portion 52. The insertion grooves 55 are arranged at a predetermined interval in the radial direction. FIGS. 4 and 5 show an example in which four insertion grooves 55 are formed. Note that the insertion grooves 55 constitute the inner peripheral portion of the packing 45.

[0042] Here, the protruding portion 53 constitutes a hollow forming portion. As shown in FIG. 6, when the piezoelectric device 40 is attached to the case members 20a and 20b, the protruding portion 53 forms a plurality of hollow portions S that become gaps between the case members 20a and 20b and the metal plate 41 inserted into the packing 45. By having a plurality of protruding portions 53, the packing 45 forms a plurality of hollow portions S along the circumferential direction of the packing 45.

[0043] Note that FIG. 6 shows only the state in which the piezoelectric device 40 is attached to one case member 20a, and the state in which the piezoelectric device 40 is attached to the other case member 20b is omitted. Also, in FIG. 6, the wiring 45 is omitted.

[0044] In this way, by forming a plurality of protruding portions 53 in the packing 45, the piezoelectric device 40 can provide a plurality of hollow portions S between the inner surface of the vertical wall 22 in the case members 20a and 20b and the outer peripheral surface of the outer peripheral wall portion 52 in the packing 45. For this reason, in the packing 45, the contact area where the outer peripheral wall portion 52 contacts the hollow portion S is much wider than the contact area where the protruding portions 53 contact the case members 20a and 20b. As a result, a large difference occurs between the acoustic impedance of the packing 45 and the impedance of the gas (for example, air) present in the hollow portion S. Therefore, the vibration transmitted to the packing 45 is reflected by the gas and is less likely to be transmitted to the case members 20a and 20b.

[0045] In the above-described Embodiment 1, the protruding portion 53 is given as an example of the hollow forming portion, but it is not limited thereto as long as it forms the hollow portion S. This point will be described with reference to FIG. 7.

[0046] As shown in FIG. 7A, the hollow forming portion 56A is provided in place of the protruding portion 53. The hollow forming portion 56A is provided along the circumferential direction on the outer peripheral surface of the outer peripheral wall portion 52. That is, the hollow forming portion 56A is an annular portion provided over the entire circumferential direction of the outer peripheral surface of the outer peripheral wall portion 52. A plurality of rectangular hollow portions S are provided in the hollow forming portion 56A. For this reason, a large difference occurs between the acoustic impedance of the hollow forming portion 56A and the impedance of the gas present in the hollow portion S. As a result, the vibration transmitted to the packing 45 is reflected by the gas and is less likely to be transmitted to the case members 20a and 20b.

[0047] As shown in Fig. 7B, the hollow forming portion 56B is provided in place of the protruding portion 53. The hollow forming portion 56B is provided along the circumferential direction on the outer peripheral surface of the outer peripheral wall portion 52. That is, the hollow forming portion 56B is an annular portion provided over the entire circumferential direction of the outer peripheral surface of the outer peripheral wall portion 52. A plurality of circular hollow portions S are provided in the hollow forming portion 56B. For this reason, a large difference occurs between the acoustic impedance of the hollow forming portion 56B and the impedance of the gas present in the hollow portion S. As a result, the vibration transmitted to the packing 45 is reflected by the gas and it becomes difficult to be transmitted to the case members 20a and 20b.

[0048] As described above, the piezoelectric device 40 according to the first embodiment can suppress the transmission of vibration to the housing by increasing the difference in acoustic impedance.

[0049] It should be noted that within the scope of the present disclosure, any component of the embodiment can be modified or any component of the embodiment can be omitted.

Description of Reference Numerals

[0050] 10 Measuring tube, 11 Measuring flow path, 12 Inlet, 13 Outlet, 20a, 20b Case members, 22 Vertical wall, 22a Through hole, 30a, 30b Caps, 40, 40a, 40b Piezoelectric devices, 41 Metal plate, 41a Upper surface, 41b Lower surface, 42 Piezoelectric element, 43 Acoustic matching layer, 44 Wiring, 45 Packing, 51 Main body, 52 Outer peripheral wall portion, 53 Protruding portion, 54 Wiring holding portion, 55 Insertion groove, 56A, 56B Hollow forming portions, 100 Ultrasonic flowmeter, S Hollow portion.

Claims

1. A piezoelectric device comprising a packing that is provided in a housing and supports, at an inner peripheral portion thereof, a mounting plate to which a piezoelectric element is attached, wherein the packing, has a hollow forming portion that forms a hollow portion between the housing and the mounting plate. The piezoelectric device is characterized by this.

2. A plurality of the hollow portions are formed along the circumferential direction of the packing. The piezoelectric device according to Claim 1, characterized by this.

3. The hollow forming portion, is a protruding portion that protrudes outward from an outer peripheral surface of the packing and contacts the housing. The piezoelectric device according to Claim 1, characterized by this.

4. The hollow forming portion makes point contact or line contact with the housing. The piezoelectric device according to Claim 1, characterized by this.

5. An ultrasonic flowmeter comprising a pair of piezoelectric devices according to any one of Claims 1 to 4. The ultrasonic flowmeter is characterized by this.

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