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JP2017225013

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DESCRIPTION JP2017225013
Abstract: In an ultrasonic handset having a thick portion in which a piezoelectric vibrating
element is fixed to the bottom of a case and a thin portion, the impact resistance to stepping
stones is increased without significantly deteriorating the directivity characteristic. In the present
invention, by providing an intermediate thickness portion 9 between a thick portion 10 and a
thin portion 8, the shapes of the thin portion 8 and the intermediate thickness portion 9 are
mainly given the role of directivity control. The shape of the thick portion 10 has a main role in
controlling the impact resistance, and both the improvement of the impact resistance and the
narrow directivity can be easily realized. [Selected figure] Figure 2
Ultrasonic transducer
[0001]
The present invention relates to an ultrasonic transducer for detecting the distance to an obstacle
existing around a vehicle and the presence or absence thereof in a corner sensor or back sensor
of an automobile, an automatic parking system or the like.
[0002]
The ultrasonic transducer transmits and receives ultrasonic waves using ultrasonic waves having
a frequency of 20 kHz or more.
The transmission of the ultrasonic wave is performed by inputting a voltage pulse signal to the
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ultrasonic transducer, converting the ultrasonic pulse signal into an ultrasonic pulse signal by a
piezoelectric vibration element provided in the ultrasonic transducer. When the transmitted
ultrasonic pulse signal is reflected by a surrounding obstacle and received by the ultrasonic
transducer, the received ultrasonic pulse signal is converted again into a voltage pulse signal by
the above-mentioned piezoelectric vibration element. It is converted. By measuring the time from
transmission to reception, it is possible to sense the distance to surrounding obstacles. As a
conventional vehicle-mounted ultrasonic transducer, an ultrasonic transducer as shown in FIG. 1
is known. In many cases, the inner bottom surface of the bottomed cylindrical case 2 used for the
ultrasonic transducer has an elliptical shape or a rectangular shape. Here, in the case where the
inner bottom surface described above has an elliptical or rectangular shape, the longitudinal
direction of the inner bottom surface is taken as the X direction, and the short direction is taken
as the Y direction. In the case where the inner bottom surface described above is a perfect circle,
the entire direction of the inner bottom surface is the X direction. Generally, in the longitudinal
direction with a large vibration area, the directivity of the transmitted ultrasonic wave becomes
narrower than that in the lateral direction. The shape of the inner bottom is deeply related to the
directivity of this transmitted ultrasonic wave, and when it is attached to the bumper of a car, the
ultrasonic wave transmitted from the ultrasonic transducer is reflected from the road surface and
becomes noise In order to control the road surface, the narrow X direction of directivity is used
in the direction perpendicular to the road surface, and the Y direction of wide directivity is used
in the direction horizontal to the road surface in order to widen the detection range. A
piezoelectric vibrating element 7 having an electrode 7 a and a folded electrode 7 b is fixed to
the inner bottom surface of the bottomed cylindrical case 2. The electrode 7 a and the return
electrode 7 b are electrically connected to the lead wire 5 connected to the harness 6 by
soldering. In the figure, reference numeral 3 is a sound absorbing material made of foam such as
silicone foam covering the inner bottom surface of the bottomed cylindrical case 2, and
ultrasonic waves emitted inward from the bottom surface of the case 2 are multiply reflected
internally The effect of suppressing becoming noise, and the effect of preventing the blocking of
ultrasonic vibration by the sealing material such as silicone rubber or urethane rubber used for
the sealing material 4 of the ultrasonic transducer being attached to the inner bottom surface
Have.
[0003]
Conventional applications detect obstacles at a low speed of about 20 km / h or less in
automobiles, so the obstacle detectable distance required for an ultrasonic transducer is at most
5 meters. In recent years, obstacle detection at a speed of 20 km / h or more is also required for
applications such as automatic driving, and 10 meters are required as a detectable distance. In
order to improve the detectable distance, raising the transmission sound pressure and reception
sensitivity of the ultrasonic wave in the ultrasonic transducer, narrowing the directivity of the
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transmitted ultrasonic wave, and focusing the ultrasonic energy, transmission The attenuation of
ultrasonic waves in air can be reduced by lowering the frequency of ultrasonic waves.
[0004]
As a method for narrowing the directivity of ultrasonic waves, for example, in the ultrasonic
transducer described in Patent Document 1, a thick portion is provided at the center of the inner
bottom surface of the bottomed cylindrical case, and the inner bottom surface in the X direction.
Thin-walled portions are provided in the vicinity of both ends of As a result, the rigidity in the
vicinity of both ends in the X direction of the inner bottom surface is reduced, the vibration
transmission effectiveness to the vicinity of both ends in the X direction is increased, and the
directivity can be narrowed.
[0005]
In the ultrasonic transducer described in Patent Document 2, the thickness of the inner bottom
surface of the bottomed cylindrical case is linearly reduced from the thick portion at the center
of the inner bottom surface toward both ends in the X direction. As a result, the rigidity gradually
decreases toward both ends of the inner bottom surface in the X direction, the vibration
transmission effectiveness to the vicinity of both ends of the inner bottom surface X is increased,
and the directivity can be narrowed.
[0006]
The ultrasonic transducer described in Patent Document 3 has a structure in which the width in
the Y direction is expanded on a dumbbell near both ends in the X direction of the inner bottom
surface of the bottomed cylindrical case. Thereby, the rigidity in the vicinity of both ends in the X
direction is reduced as compared with the rigidity of the r central portion of the inner bottom
surface described above, and directivity can be narrowed by enhancing the vibration
transmission efficacy to the vicinity of both ends in the X direction.
[0007]
JP 2000-32594 JP 2006-174003 JP 2010-154059 JP 2000-152387
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[0008]
In the conventional ultrasonic transducer (for example, Patent Document 1 and Patent Document
2), the thickness of the thick portion to which the piezoelectric vibration element is fixed is
limited in order to achieve the directivity and reverberation characteristics of the aim.
In particular, when the thickness of the thick portion is less than 0.8 mm, there is a large risk
that the piezoelectric vibrating element may crack and cause malfunction when the stepping
stone collides with the outer bottom surface of case 2 which is a design surface during traveling
of an automobile. Become.
[0009]
Also, in the conventional ultrasonic transducer comprising only the thick part and thin part, if the
dimension of the thick part is increased to improve the shock resistance, the rigidity of the case
becomes high, and the resonance frequency is the size of the other part of the case. Designing an
ultrasonic transducer that combines the required directivity and drive frequency, requiring a
major structural change to match the resonant frequency to the required drive frequency, as it
rises significantly compared to the change. Is difficult.
[0010]
Furthermore, when an adhesive is used to fix the piezoelectric vibrating element and the case 2,
the adhesive may flow to the thin portion of the bottom of the case 2.
When the flowed adhesive is cured in a thin rigid portion with low rigidity, the vibration of the
thin portion is inhibited to impair directivity and reverberation characteristics. In the ultrasonic
transducer described in Patent Document 3, since the rigidity of the side wall of the case 2 in
contact with both ends of the inner bottom surface X is also reduced, vibration of the
aforementioned side wall of the case 2 occurs when the ultrasonic transducer is driven. If the
ultrasonic transducer is held at a location including the above-mentioned side wall of the case 2
as well as it becomes large and causes noise, the reverberation time and reception sensitivity of
the ultrasonic transducer depending on the holding position and holding power Etc.
characteristic variation becomes large.
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[0011]
The main object of the present invention is to make the resistance to impact by stepping stones
high with a small change of the resonance frequency, while the directivity of the transmitted
ultrasonic waves in at least one of the vertical direction and horizontal direction to the road
surface is relatively narrow, In addition, it is an object of the present invention to provide an
ultrasonic transducer which can be easily adjusted in directivity and which is less affected by the
characteristic variation due to the adhesive of the piezoelectric vibrating element or the side wall
vibration of the case 2.
[0012]
According to the first aspect of the present invention, the piezoelectric vibrating element, the
silver electrode formed by sintering the conductive paste provided on both sides of the
piezoelectric vibrating element, and the metal or resin in which the piezoelectric ceramic having
the silver electrode is fixed to the bottom In an ultrasonic transducer including a bottom
cylindrical case and a lead wire joined to the aforementioned silver electrode, the inner bottom
surface of the bottomed cylindrical case is a thick portion to which the piezoelectric vibrating
element is fixed, and the directivity on the inner bottom surface A thin-walled portion and one or
more middle-thickness portions between the thick-walled portion and the thin-walled portion are
provided in the vicinity of both ends in the direction in which the rigidity is to be narrowed.
Assuming that the thickness of the middle-thickened portion is t [middle] and the thickness of the
thin-walled portion is t [min], it is formed such that t [max]> t [middle]> t [min]. It is an ultrasonic
transducer.
[0013]
In the ultrasonic transducer according to the present invention, by providing the medium
thickness portion between the thick portion to which the piezoelectric vibration element is fixed
and the thin portion, the vicinity of the fixing surface of the piezoelectric vibration element is
limited to increase the thickness. As a result, the impact resistance is improved by a small
amount of change of the resonance frequency, and it is possible to easily obtain the directivity
required by the presence of the above-mentioned medium thickness portion.
[0014]
In addition, when the adhesive used for fixation spreads more than necessary by providing a flat
middle-thickness portion, capillary phenomenon occurs at the corner of the step shape existing
between the thick-walled portion and the middle-thickness portion. Since the adhesive flows
along the corners, it is possible to hold the adhesive depending on the step shape.
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[0015]
In the invention according to claim 2, the fillet is provided at the corner of the stepped portion
formed by the thin portion, the medium thickness portion, and the thin portion, so that the
corner of the stepped portion is driven when the ultrasonic transducer is driven. While
suppressing that stress concentration arises and a crack generate ¦ occur ¦ produces, it
suppresses that foreign substances, such as a burr ¦ flash, generate ¦ occur ¦ produce at the time
of processing of a level ¦ step-difference part.
In addition, when the piezoelectric vibration element is fixed, the adhesive spread at the thick
portion is promptly flowed to the middle thickness portion, the adhesive stays at the thick
portion and the adhesive creeps up on the non-fixed surface of the piezoelectric vibration
element. It can be suppressed.
[0016]
In the invention according to claim 3, by making the shape of the inner bottom surface of the
bottomed cylindrical case asymmetric with respect to the axis of the bottomed cylindrical case,
the rigidity of the inner bottom surface of the bottomed cylindrical case is also obtained. The
ultrasonic wave transmission and reception described in Patent Document 4 can be made
asymmetric with respect to the axis of the bottomed cylindrical case, and a thick portion is
provided on one of the inner bottom surfaces of the case and the thickness becomes thinner
toward the other. It is possible to decenter the directivity as well as the
[0017]
As described above, according to the present invention, since the thick-walled portion, the thinwalled portion, and one or more middle-thickness portions are provided on the bottom surface of
the bottomed cylindrical case, even if the thick-walled portion is thickened As a result, it is
possible to enhance the vibration transmission efficiency, and to obtain an ultrasonic transducer
that is resistant to external impacts such as stepping stones and can detect narrow directional
and long distance obstacles.
[0018]
Further, by providing the middle-thickness portion, the spread of the adhesive used for fixing the
piezoelectric vibration element can be controlled, and adhesion of the adhesive to the thin-walled
portion can be suppressed to stabilize the acoustic characteristics.
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[0019]
It is the schematic of the conventional ultrasonic transducer.
A schematic view of a bottomed cylindrical case and a piezoelectric vibrating element in an
ultrasonic transducer according to a first embodiment of the present invention. A schematic view
of how an adhesive spreads in the present invention and a conventional ultrasonic transducer. A
schematic view of a bottomed cylindrical case and a piezoelectric vibrating element in an
ultrasonic transducer according to a second embodiment of the invention A bottomed cylindrical
case in an ultrasonic transducer according to a third embodiment of the present invention And a
schematic view of a piezoelectric vibrating element A schematic view of a bottomed cylindrical
case and a piezoelectric vibrating element in an ultrasonic transducer according to a fourth
embodiment of the present invention
[0020]
FIG. 2 is a schematic view of a bottomed cylindrical case and a piezoelectric element fixedly
attached to an ultrasonic transducer according to the first embodiment of the present invention.
This ultrasonic transducer has an outer diameter of φ14 with a rectangular bottom shape, a
height of 9 mm and a bottomed cylindrical case 2 and an outer diameter of 6 mm fixed to the
thick portion 10 of the bottom of the case 2 A thin-walled portion 8 is formed in an arc shape
including the piezoelectric vibrating element 7 at each end in the longitudinal direction on the
bottom surface of the case 2 and the thickness of the bottom is the smallest, and a thickness
between the thick portion and the thin portion It is characterized by having a middle thickness
portion 9 which takes a thickness between the thickness portion and the thin portion.
[0021]
A sound absorbing material made of foamed silicone is disposed on the bottom of the case 2, and
lead wires are respectively joined to the electrode 7 a and the folded electrode 7 b provided on
the surface of the piezoelectric vibrating element 7. Each end is connected to a pin terminal for
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connection to an external drive substrate.
In the inside of the case 2, the space above the sound absorbing material is filled with resin.
[0022]
The case 2 is an aluminum case manufactured by press molding of an aluminum alloy.
Other possible materials for Case 2 are metal materials such as magnesium alloy, stainless steel
and titanium alloy, and resin materials with excellent heat resistance and high rigidity such as
engineering plastics and epoxy resin highly filled with metal filler or glass filler. Can be
mentioned.
Other processing methods for the case 2 include cutting and injection molding.
[0023]
The electrode 7a and the folded electrode 7b are mainly formed using silver as a conductive
material.
[0024]
The internal shape of the case 2 is 8 mm in width in the short direction and 0.5 mm in thickness
in the longitudinal direction.
The bottom shape of the case 2 is provided with a thick portion 10 of 0.8 mm in thickness at the
center, and a thin portion 8 and a medium thickness portion 9 of 0.6 mm at a thickness of 0.3
mm on both sides in the longitudinal direction. It is provided to be symmetrical on the left and
right of the longitudinal direction.
[0025]
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Table 1 below shows ultrasonic transmission / reception when the thickness of the thin portion
is 0.3 mm and the thickness of the middle portion is 0.6 mm, and the value of the thick portion is
changed from 0.6 mm to 0.9 mm. The resonance frequency of the resonance frequency of the
unit and the vibration distribution of the bottom surface of the case are indicated by contour
lines.
As a case of the present invention, the shape of FIG. 2 was used, and as a comparison, a case of a
conventional shape consisting of only a thick portion and a thin portion in which the middle
thickness portion 9 in FIG. The resonance frequency and the vibration distribution of the case
outer bottom were evaluated using ANSYS of the finite element method CAE.
[0026]
[0027]
According to Table 1, when the thick portion is changed from 0.6 mm to 0.9 mm, the resonance
frequency is increased by 13.2 kHz in the conventional case, but is suppressed to 7.9 kHz in the
shape of the present invention. did it.
Furthermore, in the case of the present invention in which the medium thickness portion is
provided, the vibration distribution near the center of the case outer bottom surface corresponds
to the longitudinal direction of the inner bottom surface as compared to the case where the thick
portion has the same thickness as the conventional case. It spreads in the left and right direction.
This means that the vibration transmission efficacy is improved and the directivity in the
longitudinal direction is narrowed, and it was found that there is an effect of narrowing the
directivity more than expected.
[0028]
The schematic diagram of the mode of the expansion of the adhesive material 12 by the presence
or absence of the middle meat part 9 is shown in FIG. Comparing the case of providing the
medium thickness portion 9 shown in FIG. 2 with the case of the conventional thick portion 10
and the thin portion 8 only, in which the thickness of the middle thickness portion shown in FIG.
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The adhesive flows from the thick part 10 directly to the thin part 8 in the conventional case,
whereas the case of the invention shown in FIG. 2 has the thick part 10 from the thick part 10 to
the middle part 9. In order to move along the boundary of the medium thickness portion 9, the
adhesive is less likely to adhere to the thin portion 8 than in the conventional case.
[0029]
FIG. 4 is a schematic view of a bottomed cylindrical case and a piezoelectric element fixed to an
ultrasonic transducer according to a second embodiment of the present invention. The ultrasonic
transducer shown in FIG. 4 has a structure in which the entire circumference of the thick portion
10 in the ultrasonic transducer shown in the first embodiment is surrounded by the medium
thickness portion 9. As a result, the adhesive spread around the piezoelectric vibrating element
when the piezoelectric vibrating element is fixed can be easily retained at the boundary between
the thick portion 10 and the middle thick portion 9, and the spreading of the adhesive can be
controlled in all directions. Become.
[0030]
FIG. 5 is a schematic view of a bottomed cylindrical case and a piezoelectric element fixed to an
ultrasonic transducer according to a third embodiment of the present invention. The ultrasonic
transducer shown in FIG. 5 has a structure in which the entire circumference of the medium
thickness portion 10 in the ultrasonic transducer shown in the second embodiment is
surrounded by the thin portion 8. As a result, the vibration transmission efficiency can be
enhanced up to the vicinity of the entire circumference of the bottom surface of the case 2, so
that it is possible to narrow the directivity in all directions while having high impact resistance.
[0031]
FIG. 6 is a schematic view of a bottomed cylindrical case and a piezoelectric element fixed to an
ultrasonic transducer according to a fourth embodiment of the present invention. The ultrasonic
transducer shown in FIG. 6 is the ultrasonic transducer shown in the first embodiment, in which
two medium thickness portions are provided at one side in the longitudinal direction on the
bottom surface of the case 2 and one medium thickness portion is provided at the other. It has a
structure with a place. As a result, the rigidity on the side provided with the two medium
thickness portions is enhanced, so that the vibration transmission effectiveness is asymmetrical
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on the left and right in the longitudinal direction of the bottom surface of the case 2 and the
directivity of the ultrasonic wave transmitted from the outer bottom surface is eccentric. It is
possible to
[0032]
The present invention can be applied not only to back sensors and corner sensors of vehicles,
and automatic parking systems, but also to various fields where drip-proof ultrasonic transducers
are used.
[0033]
DESCRIPTION OF SYMBOLS 1 Ultrasonic transducer 2 Bottomed cylindrical case 3 Sound
absorbing material 4 Sealing material 5 Lead wire 6 Harness 7 Piezoelectric vibration element 7a
Electrode 7b Folded electrode 8 Thin part 9 Medium thickness part 10 Thick part 11 Step
difference part 12 Adhesive
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