JPS61200800A - Piezo-electric type acoustic generator - Google Patents

Abstract

PURPOSE:To prevent rupture of a pizo-electric element even when the element is designed with reduced thickness by so arranging that a metal plate affixed to each of a first piezo-electric element and a second piezo-electric element are vibrated unitary. CONSTITUTION:Piezo-electric vibration units 13, 14 are formed essentially by the first piezo-electric element 15 and the second piezo-electric element 16. The elements 15, 16 are formed by PZT in the form of of a plate concentric with the diaphragm 12. Electrodes 17a, 17b, 18a, 18b are formed by printing on both sides of the elements 15, 16. The sides of the electrodes 17a, 18a of the elements 15, 16 are adhered to the side of the diaphragm 12 by adhesives 19, 20. Metal plates 23, 24 are adhered and secured to the electrodes 17b, 18b on the opposite sides of the diaphragm 12. Lead wires are connected to the diaphragm 12 and the metal plates 23, 24 for connecting to input terminals 25, 26 so that piezo-electric signals for driving the piezo-electric elements are applied to the elements 15, 16.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is effectively used for an alarm sound generation device used as a car horn, for example, in which acoustic vibration is generated by a voltage signal. The present invention relates to a piezoelectric sound generator.

[Background Art] For example, it is known to use a piezoelectric sound generating device for a sounding device such as a horn for an automobile. Such a sounding device is equipped with a sounding body that vibrates acoustically by applying a voltage signal, and this sounding body is made of lead zirconate titanate-based piezoelectric ceramic (PZT) or the like with respect to a metal diaphragm. It is constructed by bonding plate-shaped piezoelectric elements.

A sounding body using piezoelectric vibration configured in this state is
The resonant frequency is 2KH2 or more, and the frequency of the generated sound is too high for the human ear, resulting in an undesirable tone. For this reason,
For example, attempts have been made to reduce the thickness of the piezoelectric element to lower the resonance frequency of the vibrating sounding body.

However, if the piezoelectric element is configured to be thinner in this way, the generated acoustic frequency will be lowered, but the generated sound pressure will also be lowered, which may cause the problem that it will not be possible to generate sound at a sufficient volume. become.

In order to cope with such a decrease in sound pressure, it is necessary to set a large drive voltage value to be applied to the piezoelectric element to cause the sounding body to vibrate more greatly. However, when the sounding body is driven by a signal with a large voltage value as described above to generate large vibrations, a large stress is applied to the piezoelectric element, and the thin piezoelectric element becomes damaged.

[Problems to be Solved by the Invention] This invention has been made in view of the above points, and it is possible to set the resonant frequency to a sufficiently low state and generate acoustic vibrations with a good tone. , especially piezoelectric sound generation that does not directly apply large stress to the piezoelectric element, prevents damage to the piezoelectric element, and obtains acoustic vibrations with sufficient sound pressure. The aim is to provide equipment.

[Means for Solving the Problems] That is, the piezoelectric sound generator according to the present invention includes first and second plate-shaped piezoelectric elements each having electrodes formed on both sides. The first and second piezoelectric elements are bonded to both sides of the diaphragm so that their polarization directions are aligned. And the above first
A metal plate is bonded and set on the opposite side of the diaphragm of each of the second piezoelectric elements, and the diaphragm, the first and second piezoelectric elements, and the pair of metal plates are vibrated integrally. This is what I try to do.

[Function] In the piezoelectric sound generator configured as described above, for example, a piezoelectric element drive voltage is applied between a pair of metal plates and a diaphragm corresponding to the first and second piezoelectric elements, respectively. By applying and setting the signal, the diaphragm and the pair of metal plates are driven to vibrate together with the first and second piezoelectric elements, and it is necessary to set the resonance frequency to a sufficiently low state. can. Also, the first and second
Since the two piezoelectric elements are driven in parallel, it is easy to set the sound pressure of the generated sound to a sufficient level, and it is possible to obtain sound vibrations with a good tone and sufficient sound pressure. It is something that you will be able to do.

[Example] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

1 and 2 show its cross-sectional and planar structure, and the sounding body 11 that generates this acoustic vibration is
Although not particularly shown in this figure, for example, it is supported and set by a support mechanism in a case that constitutes an alarm sound generating device.
Acoustic vibrations generated by the vibrations of the sounding body 11 are emitted to the outside from a sound emitting hole formed in the case.

That is, the sounding body 11 includes a diaphragm 12 in the form of a disk, for example, made of a metal plate such as aluminum, brass, or Kovar, and the peripheral portion of the diaphragm is set inside the case. By the support mechanism,
This diaphragm 12 is supported and set so that it can freely vibrate. First and second piezoelectric vibrators #113 and 14 are set on both sides of this diaphragm 12, respectively, and these piezoelectric vibrating mechanisms 13 and 1
4 are first and second piezoelectric elements 15 and 16, respectively.
It is mainly composed of. These piezoelectric elements 15 and 16
is composed of a plate-shaped PZT concentric with the diaphragm 12, and an electrode 1 is provided on both surfaces of each of the first and second piezoelectric elements 15 and 16.
7a, 17b, and 18a, 18b are formed by printing or the like. And the above first and second
The surfaces of electrodes 17a and 18a of piezoelectric elements 15 and 16 are bonded to the surface of diaphragm 12 with adhesives 19 and 20. In this case, the first and second piezoelectric elements 15 and 16 are set so that their polarization directions are aligned with respect to the diaphragm 12,
It is said to have a bimorph structure.

Further, the electrodes 17a and 18a and the diaphragm 12 are electrically connected. In this case, adhesive 1
9. Even if 20 is not conductive, the electrodes 17a and 18a
1 and the diaphragm 12 are electrically connected because their surfaces are not completely flat.

The electrodes 17b and 18b of the first and second piezoelectric elements 15 and 16 on the opposite side from the diaphragm 12 are attached to the metal plate 2 by adhesives 21 and 22, respectively.
3 and 24 are set to be bonded, respectively. The metal plates 23 and 24 may be made of the same material as the diaphragm, and the electrode 17b.

18b are electrically connected to metal plates 23 and 24, respectively. Then, lead wires are connected to the diaphragm 12 and the metal plates 23 and 24, respectively, and connected to input terminals 25 and 26 to drive the first and second piezoelectric elements 15 and 16. This allows the voltage signal for this purpose to be applied and supplied.

Next, an example of a specific configuration of the sounding body 11 will be explained. Assuming that the resonance frequency of the sounding body 11 is set to approximately 1°2 KHz, the thickness of the diaphragm 12 is 0.2--
It is composed of a Kovar plate with a diameter of 9Q+u. Moreover, the piezoelectric elements 15 and 16 each have a thickness of 0.1 g (
It is composed of a disk with a diameter of 4211 mm, and this first
As described above, the second piezoelectric elements 15 and 16 are bonded to both sides of the diaphragm 12 with their polarization directions aligned, and have a parallel bimorph structure, and have a thickness of 0.
．． Metal plates 23 and 24 made of 05S Kovar are bonded together.

Here, without creating a bimorph structure as described above,
Furthermore, in the case of a conventional structure in which a piezoelectric element without a metal plate is adhesively set on one side of a diaphragm, in order to set the resonance frequency to approximately 1.2KH2, the thickness of the piezoelectric element must be The value is set to 0.211.

FIG. 3 shows the state of the sound pressure with respect to the frequency of the conventional sounding body and the sounding body 11 shown in the above embodiment. In this figure, the characteristics of the sounding body 11 shown in the above embodiment are as shown by the solid line A, whereas in the case of the above conventional example, the characteristics are as shown by the chain line B.
It will be shown as follows.

That is, by adopting the bimorph structure as shown in the embodiment, the sound pressure in the low frequency region increases, and the timbre of the generated sound becomes favorable.

FIG. 4 shows the state of stress acting on the sounding body during vibration, and FIG. 4(A) shows the case of the conventional example as described above. In this figure, a is a diaphragm, and b is a piezoelectric element. That is, in the conventional sounding body, a considerable amount of stress is applied to the piezoelectric element, with the maximum stress being applied to the center portion thereof. The stress on this piezoelectric element is shown by the solid line in this figure, and the maximum stress is 6.
It becomes 2KiJ/sm2.

On the other hand, in the sounding body 11 shown in the above embodiment, as shown in FIG.
Alternatively, a large stress reaching 11.8 KO/■2 is applied to the piezoelectric element 15.
Alternatively, as shown by the solid line, the stress acting on 26 is at maximum 3.7 Ka/*2, which is sufficiently reduced compared to the conventional example. That is, metal plates 23 and 2
By setting 4, the stress acting on this metal plate increases, and the stress applied to the piezoelectric elements 15 and 16 is significantly relaxed.

Note that the metal plates 23 and 24 used to reinforce the piezoelectric elements in this manner may be configured to be at least thinner than the piezoelectric elements 15 and 16 so as not to inhibit the vibrations of the piezoelectric elements 15 and 16. desirable.

When we actually conducted an experiment in which blowing was repeated intermittently, it was found that with the conventional structure, the piezoelectric element was damaged after 10,000 times, but with the sounding body configured as shown in the above example, Even after 100,000 repeated blasts, the piezoelectric element was not damaged.

Note that the metal plates 23 and 24 may be insulatedly bonded to the electrodes 17b and 18b, and voltage signals may be directly applied to the electrodes 17b and 18b. In this case, a portion of the metal plates 23 and 24 is removed, and the lead wires connected to the electrodes 17b and 18b are taken out from this removed portion.

FIG. 5 shows an example of an alarm sound generating device configured using the sounding bodies configured as described above. In this example, the configuration is such that two sets of sounding bodies 11a and 11b are used. has been done. These two sounding bodies 11a and 11b
are set to have different resonance frequencies, are parallel to each other with a small interval, and are integrally connected at their outer peripheries by a ring 31. Then, the sounding bodies 11a and 1 surrounded by this ring 31
An air chamber 32 is formed between the air chamber 1b and the sound generating member 33. This sounding member 33 is mounted inside this case 30 by a plurality of support members 34, for example, three, set on the inner circumferential surface of the case 30. Air chambers 35 and 36 are formed on the back surface, respectively, and an acoustic passage 31 is formed on the outer periphery of the ring 31 to connect the air chambers 35 and 36. It is something that exists. A sound emitting hole 38 for emitting sound is formed on the surface of the case 30 corresponding to the front air chamber 35.

[Effects of the Invention] As described above, according to the piezoelectric sound generator according to the present invention, the stress acting on the piezoelectric element can be set to be sufficiently reduced, so that, for example, the resonance frequency can be set to a low state. Therefore, even if the thickness of the piezoelectric element is set thin, the piezoelectric element will not be damaged and can withstand sufficient repeated use. Moreover, in this case, as mentioned above, it is possible to make the thickness of the piezoelectric element sufficiently thin, making it possible to effectively increase the sound pressure especially in the low frequency region, improving the timbre of the generated sound. This device exhibits a great effect in order to make the alarm sound more effective, and can be effectively used, for example, as an alarm sound generating device for automobiles.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the cross-sectional structure of a piezoelectric sound generator according to an embodiment of the present invention, FIG. 2 is a plan configuration diagram of the above embodiment, and FIG. Figures 4 (A) and 4 (B), which compare and show the state of the sound pressure of the sound generated by the conventional sounding body, show the state of stress acting on the conventional sounding body and the sounding body of the above embodiment, respectively. FIG. 5 shows an example of an alarm sound generating device using a sounding body as described above. 11...Sounding body, 12...Diaphragm, 13.14...
- First and second piezoelectric vibration mechanisms, 15.16... first and second pressure elements, 17a, 17b,
18a, 18b・'Rm, 19-22...Adhesive material, 23.24...Metal plate. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 0.2 1 2 area Absorption, (in Hz)

Claims (3)

[Claims] (1) first and second piezoelectric elements configured in a plate shape that are displaced when a voltage is applied and supplied; electrodes formed on both surfaces of each of the first and second piezoelectric elements; A diaphragm supported and set in a vibrating state, and the first and second piezoelectric elements set facing each other with their polarization directions aligned on both sides of the diaphragm, and each of the first and second piezoelectric elements and a pair of metal plates adhesively set to the other electrode surfaces of the first and second piezoelectric elements that are not bonded to the diaphragm. The vibration plate, the first and second piezoelectric elements, and the metal plate bonded to each of the first and second piezoelectric elements are vibrated integrally. Piezoelectric sound generator. (2) An adhesive layer is provided between each of the electrodes set for the first and second piezoelectric elements, the diaphragm, and the metal plate, and the pair of metal For plates and diaphragms, first and second
2. The piezoelectric sound generator according to claim 1, wherein lead wires are connected to supply voltage signals to the piezoelectric elements. (3) The piezoelectric sound generating device according to claim 1, wherein the thickness of the pair of metal plates is set to be thinner than the thickness of the piezoelectric element to which the metal plates are bonded.