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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric sounding device using a piezoelectric element, which is used, for example, as an
alarm sound generating device for automobiles. [Technical background of the invention] In order
to be used as a generator of alarm sound for a car, a sound generator configuration that
resonates in the vicinity of 300 to 600) -1z which is the basic frequency of the alarm sound to be
generated You need to FIG. 1 shows the configuration of a conventionally-known sounding
device for setting the resonance frequency as described above. First, the sounding body 11 is a
plate of about O, 2 to Q, 3 mm with respect to the diaphragm 12 A thin disk-shaped piezoelectric
element 13 is bonded to each other. The sounding body 11 configured in this manner has its
outer peripheral portion fixed to the inside of the housing 14 and set so that the primary
resonance frequency thereof is set so as to fall within the necessary range. It is a thing. However,
in the sounding device configured as described above, since the outer peripheral portion of the
sounding body 11 is fixed in a state of being pressed against the housing 14, the vibration of the
sounding body 11 inevitably occurs. In this state, the resonance sound pressure is small. In
addition, since the vibration of the sound producing body 11 is directly transmitted to the
housing 14, when the housing 14 is thin, the housing 14 vibrates in accordance with the
vibration of the sound producing body 11. As a result, a so-called cracked sound is generated,
and the function as the sound generation device can not be effectively exhibited. SUMMARY OF
THE INVENTION The present invention has been made in consideration of the above-described
points, and enables effective increase in sound pressure due to the primary resonance frequency,
and, for example, the housing is configured in a thin state. However, it is an object of the present
invention to provide a piezoelectric sounding device which can generate a good alarm sound with
a sufficient sound pressure without generating unnecessary noise from the housing portion.
[Summary of the invention] That is, the piezoelectric sounding device according to the present
invention fixes and sets a sounding body formed by joining a diaphragm and a piezoelectric
element to an opening surface of a box formed by opening one side. That is, the box body to
which the sounding body is attached is supported and set inside the housing via a support
member made of an elastic body. Hereinafter, an embodiment of the present invention will be
described with reference to the drawings. FIG. 2 shows the cross-sectional structure thereof. The
sounding body 21 is a piezoelectric element 22 made of PZT-based ceramic having a diameter Q
of 42 mm and a thickness Q of 3 mm, Kovar (trade name; It is integrally joined to the diaphragm
23 of a high-nickel alloy (manufactured by Nippon Mining Co., Ltd.).
The piezoelectric sounding body 21 configured in this manner is set to be attached to the box 24,
and the box 24 is configured in a shallow box that is open at one side by a synthetic resin, and
the opening thereof is The outer peripheral portion of the piezoelectric sounding body 21 is set
in a pair with respect to the surface, and adhered and fixed. That is, the opening is sealed by the
sounding body 21, and the sounding member 26 in which the air layer 25 is formed is
configured. Here, the lead wire taken out from the diaphragm 22 and the piezoelectric element
23 of the sounding body 21 is taken out via a groove (not shown) which is appropriately
provided on the opening joint surface of the box 24. The sounding member 26 configured in this
manner is set so as to be housed inside the housing 27. The housing 27 is composed of a main
body 27a1 and a lid 27b each made of a synthetic resin having a thickness of 1.5 n + n +, and a
large number of lids 27b serving as the front of the housing 27 are provided. The openings 28a,
28b,... For sound emission are formed. Here, the sounding member 26 is provided on the inner
peripheral surface of the C housing 27 by a plurality of, for example, four support members 29a,
29b,... Set at equal intervals with respect to the outer peripheral portion of the box 24. The
support members 29a, 29b,... Are each made of an elastic member such as a sponge so that the
sounding member 26 is elastically supported in the housing 27. A sound generation drive circuit
30 is set at the bottom of the housing 27. The circuit 30 is constituted by an oscillator generating
a frequency signal corresponding to the sound generation basic frequency, and a means for
amplifying a signal from the oscillator. The frequency signal is supplied as a drive signal to the
sound generator 21 through the lead wire. In the sounding device configured as described above,
the primary resonance mode of the piezoelectric sounding body 21 is generated when the outer
peripheral portion is an antinode as shown in FIG. 3, and the box 24 is also vibrated integrally. It
will be in the state of The sound is also emitted from the bottom 24 a of the box 24. In this case,
the air layer 25 inside the box 24 exerts a role of giving a repulsive force to the sounding body
21 and increasing its vibration. Since the box 24 is supported by the support members 29a
129b,... Made of an elastic material with respect to the housing 27 in a state in which such
vibration is generated, the vibration of the sound-producing member 26 is restrained. Thus, the
box 24 and the sounding body 21 can be integrally vibrated.
In this case, in the housing 27, since the vibration from the sounding member 26 is blocked by
the support members 29a, 29b, ..., for example, the plate thickness of the housing 27 is as thin as
i, 5 mm Even in this case, noise such as chattering noise is not generated in the housing 27. FIG.
4 shows the sound pressure characteristics versus frequency of the sounding device shown in the
above embodiment and the conventional sounding device shown in FIG. 1, for example. The state
of the response sound pressure with respect to each frequency is shown. The solid line shows the
characteristic of the embodiment device, and the broken line shows the characteristic of the
conventional device. That is, the resonance sound pressure in the fundamental frequency range
of the sound generation device shown in the embodiment is in a larger state as compared with
the prior art, and thus the voltage of the period equal to the resonance frequency (for example,
about 400 Hz) in the above device. By applying a signal (a rectangular wave signal of 400 Hz or
the like), it is possible to generate an effective warning sound with a soft feeling, with the basic
sound in a sufficiently large state. In the piezoelectric sounding apparatus configured as
described above, there are various conceivable means for supporting and setting the sounding
member 26 in the housing 27. As shown in FIG. 2, molding is performed in a state in which the
side of the box 24 is sandwiched. It is not limited to the use of the support members 29a, 29b,.
That is, the sounding member 26 may be supported and set in a state in which a space is set in
the front direction and the rear direction and further in the surrounding portion in the housing
27, and may be elastically supported and set. . FIG. 5 shows an example of the support means for
the sounding member 26. The support member 31 for supporting the sounding member 26 is
made of an elastic material such as rubber, and one end portion of the support member 31 is of
the box 24. The other end portion is engaged with and set in a recess formed in the main body
portion 27 a of the housing 27 so as to elastically support and set the sound producing member
26. In this case, by making the central portion of the support member 31 thin, it is possible to
more reliably prevent the vibration in the sound emitting member 26 from being transmitted to
the housing 27. Further, as shown in FIG. 6, a projecting portion 32 flanged to the outer
peripheral portion of the box 24 is provided, and a supporting member 33 made of rubber is
provided on the inner peripheral portion of the housing 27 opposed to the projecting portion 32.
Set to hold. Then, the projecting portion 32 may be held by the tip end portion of the supporting
member 33 so that the sound emitting member 26 is elastically supported and set.
In addition, such a support member is not limited to one using an elastic material such as sponge
or rubber as described above, but the same effect can be exhibited even with a support structure
using, for example, a coil spring. . [Effects of the Invention] As described above, according to the
present invention, the sound pressure at the primary resonance frequency of the sounding body
using the piezoelectric element can be effectively increased and set, and the sound of sufficient
volume can be easily made. For example, it can be effectively applied as an alarm sound
generator for automobiles. In addition, even in the state where such a large sound pressure is set,
generation of unnecessary noise and vibration in the housing is surely prevented, and even in
terms of the timbre of the generated sound, etc. It can be put into a sufficiently effective state.
Brief description of the drawings
FIG. 1 is a cross-sectional view of a conventional sound producing apparatus, FIG. 2 is a crosssectional view of a piezoelectric sound producing apparatus according to an embodiment of the
present invention, and FIG. 3 is a resonance mode of the sound producing body of the above
embodiment. FIG. 4 is a graph showing the sound pressure characteristics with respect to the
frequency of the apparatus shown in the above embodiment in comparison with the conventional
example, and FIG. 5 (A> shows other than the support structure of the sounding member FIG. 6B
is a cross-sectional view corresponding to the line b-b in FIG. 6A, and FIG. 6 is a cross-sectional
view showing still another example of the support structure.
21 ... sounding body, 22 ... diaphragm, 23 ... piezoelectric element, 24 ... box, 25 ... sounding
member, 26 ... internal air layer, 27 ... housing, 29a , 29b,... 31.33 ・ ・ ・ Supporting members.
Applicant Agent Patent Attorney Suzue Takehiko Figure 1 Figure 2 Figure 3 Figure 4a Figure 4
Figure 5
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