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JP2004040614

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DESCRIPTION JP2004040614
The object of the present invention is to provide an inexpensive ultrasonic sensor that is easy to
manufacture, has less variation in characteristics, and has improved directivity characteristics,
without the need for complicated machining such as steps on the bottom surface of a metal case.
A sound absorbing material provided with a recess is joined on a vibrating plate so as to engage
with a piezoelectric vibrating element in a noncontact manner, thereby avoiding vibration
inhibition of the piezoelectric vibrator due to contact of the sound absorbing material or inflow of
elastic material. As a result, it is possible to stabilize the resonance frequency and the impedance
characteristic of the piezoelectric vibrator, and as a result, it is possible to provide an ultrasonic
sensor in which the half angle of the ultrasonic sensor is small and the directivity characteristic is
improved. [Selected figure] Figure 1
Ultrasonic sensor
[0001] The present invention relates to an ultrasonic sensor that transmits ultrasonic signals and
receives reflected waves from obstacles to detect the presence of obstacles, and more particularly
to a motor vehicle. The present invention relates to a drip-proof ultrasonic sensor suitable for
back sonars and corner sonars. [0002] A conventional ultrasonic sensor of this type is shown in
FIG. 6 (a). FIG. 6 (b) is a plan view of the EE cross section of FIG. 6 (a) viewed from above in the
drawing. In the ultrasonic sensor, the bottom surface of a bottomed cylindrical case 61 made of
metal such as aluminum is an oval diaphragm 62, and a piezoelectric vibrator 63 is joined to the
inside of the diaphragm 62. It has a structure. The front and back surfaces of the piezoelectric
vibrator 63 are metallized, and electrical connection is made by lead wires 64 and 65. One lead
wire 64 is soldered to the surface electrode of the piezoelectric vibrator. The other lead wire 65
is joined to the bottomed cylindrical case 61, and is electrically connected to the surface
electrode through the vibrating plate 62 at the joint surface with the piezoelectric vibrator. A
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sound absorbing material layer 66 formed of a sponge or the like not in contact with the
piezoelectric vibrator 63 is formed inside the bottomed cylindrical case 61, and inside the
bottomed cylindrical case 61 outside the sound absorbing material layer 66. In order to prevent
the ingress of raindrops and moisture, an elastic body 67 such as silicone resin is filled. The lead
wires 64 and 65 and the signal wires 68 and 69 are connected by soldering inside the elastic
body 67. The aforementioned ultrasonic sensor operates as follows. When a drive AC voltage is
intermittently applied to the piezoelectric vibrator 63 from the signal lines 68 and 69, the
piezoelectric vibrator 63 vibrates due to the piezoelectric effect and the vibration of the
bottomed cylindrical case joined to the piezoelectric vibrator 63 accordingly. The plate 62
vibrates, and ultrasonic waves are emitted from the vibrating plate 62 into the air. The driving of
the piezoelectric vibrator 63 is performed intermittently, and during the time when the driving is
stopped, the ultrasonic wave reflected from the object to be detected reaches the piezoelectric
vibrator 63 through the diaphragm 62, The voltage is converted into a voltage signal by the
piezoelectric effect of the piezoelectric vibrator 63 and output from the signal lines 68 and 69.
Here, since the time from the emission of the ultrasonic wave to the return of the reflected wave
and the distance to the object to be detected have a proportional relationship, by observing the
elapsed time from the transmission to the reception The distance to the object to be detected can
be measured. In particular, ultrasonic sensors used for back sonars and corner sonars of motor
vehicles have a wide detection area in the lateral direction (horizontal direction) to detect the
presence of obstacles, and a road surface that does not need to be detected. Since it is required to
narrow the detection area in the vertical direction (vertical direction) in order to avoid detection
of curbs etc., the ultrasonic sensor used has a wide directivity in the horizontal direction and a
narrow directivity characteristic in the vertical direction. Desired.
It is known that the directivity characteristics of the ultrasonic sensor become narrower as the
vibration area is increased and become wider as the vibration area is reduced. Therefore, in the
conventional ultrasonic sensor, as shown in FIG. 6, in order to change the directivity
characteristics in the longitudinal direction and the lateral direction, the diaphragm is oblong,
and the major axis direction of the oblong is short in the vertical direction. A method is adopted
in which the ultrasonic sensor is installed so that the axial direction is horizontal. Meanwhile, on
the other hand, the ultrasonic sensor is required to be downsized because of the appearance and
the mounting space, and as described above, the directivity characteristic of the ultrasonic sensor
and the vibration area, ie, the outer shape, contradict each other. Due to the relationship, there is
a problem that it is difficult to narrow the directivity characteristics in the vertical direction while
keeping the outer size small. Japanese Patent Application Laid-Open No. 2000-32594 is an
example of a solution to this problem. In this publication, as shown in FIG. 7 (a), an oblong
diaphragm 72 is provided on the bottom of a bottomed cylindrical case 71, and a thin portion 74
and a thick portion 73 are formed on the diaphragm 72. An attempt is made to control the
directivity characteristics in the horizontal direction and the vertical direction by providing the
piezoelectric vibrator 75 on the thick portion 73. FIG. 7 (b) shows a GG cross-sectional plan view
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of FIG. 7 (a) viewed from above in the drawing. An example of another solution is shown in FIG.
In FIG. 8, the bottom of the bottomed cylindrical case 81 is used as the diaphragm 82, and the
sound absorbing material 84 is disposed on the piezoelectric vibrator 83 joined to the inner
surface of the diaphragm 82. There is a device in which the constraining force of the vibrating
surface is partially changed to control directivity characteristics by a structure in which the
inside is filled with an elastic body 85. However, in the structure shown in FIG. 7A, the thickness
is different between the minor axis direction (horizontal direction in the figure) and the major
axis direction (vertical direction in the figure) of the vibrating surface. The vibration mode has
two resonant frequencies close to each other. However, since the frequency of the drive circuit is
constant, driving is performed at one of the resonant frequencies, and the directivity
characteristic becomes unstable due to the influence of the vibration mode of another nearby
resonant frequency. There is a point. Further, although the bottomed cylindrical case 71 shown
in FIG. 7A is manufactured by mechanical machining, the diaphragm 72 of the bottom surface of
the bottomed cylindrical case 71 has a thin portion 74 and Machining with the thick part 73 is
expensive, and dimensional variations are likely to occur in each part, and the dimensional
variations greatly affect various characteristics such as the resonance frequency, sensitivity,
reverberation characteristics, etc. of the ultrasonic sensor. Therefore, there is also a problem that
it is difficult to produce an ultrasonic sensor with uniform characteristics.
Further, in the case of the structure as shown in FIG. 8, the sound absorbing material 84 on the
piezoelectric vibrator 83 restrains the vibration of the piezoelectric vibrator 83 and the pressure
or elastic body 85 when the sound absorbing material 84 is arranged. Since the restraint force
varies depending on the contact pressure, the resonance frequency and impedance
characteristics of the ultrasonic sensor vary, and as a result, various characteristics such as
sensor sensitivity, directivity characteristics, and reverberation characteristics vary. An object of
the present invention is to provide an inexpensive ultrasonic sensor which is easy to
manufacture, has less variation in characteristics, and has improved directivity characteristics.
According to the present invention, there is provided a bottomed cylindrical case in which the
bottom portion is an oblong vibrating plate, and a piezoelectric member joined to the inside of
the bottom portion of the bottomed cylindrical case. A vibrator, a sound-absorbing material
joined to the bottom of the bottomed cylindrical case having a recess engaged with the
piezoelectric vibrator in a noncontact manner, and an elastic body filled inside the cylindrical
case An ultrasonic sensor characterized in that [0015] In the ultrasonic sensor, half of the inner
dimension of the recess of the sound absorbing material in the long axis direction of the
diaphragm is r1, and half of the length in the long axis direction of the diaphragm is R. The value
r1 / R is in the range of 0.3 ≦ r1 / R <1 to obtain an ultrasonic sensor. In the ultrasonic sensor,
when the half of the inner dimension in the long axis direction of the concave portion of the
sound absorbing material in the long axis direction of the diaphragm is r1 and the half of the
outer dimension is r2, r1 / l An ultrasonic sensor characterized in that the value of r2 is in the
range of 0.4 ≦ r1 / r2 <1 is obtained. In the present invention, the sound absorbing material
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provided with the recess is joined on the vibrating surface so as to engage with the piezoelectric
vibrating element in a noncontact manner, so that the vibration of the piezoelectric vibrator due
to the contact of the sound absorbing material or the inflow of the elastic material. It is possible
to avoid interference and stabilize the resonance frequency and impedance characteristics of the
piezoelectric vibrator, and as a result, the characteristics of the ultrasonic sensor, such as
sensitivity, directivity angle, and reverberation characteristics, become less dispersed and
stabilized. It is possible. In addition, the inside of the case of the sound absorbing material is filled
with an elastic material to restrain the vibrating surface and to control the displacement form at
the time of vibration, thereby narrowing the directivity characteristics of the ultrasonic sensor. It
is possible to realize EXAMPLES The present invention will be described in detail by way of the
following examples. FIG. 1 (a) is a cross-sectional view showing the structure of an ultrasonic
sensor according to an embodiment of the present invention, and FIG. 1 (b) shows AA of FIG. 1
(a) seen from above in the figure. The cross section top view is shown.
On the bottom of a bottomed cylindrical case 11 with an outer diameter of 20 mm and a height
of 10 mm made by machining aluminum, an oval-shaped diaphragm 1 with a thickness of 1 mm
for emitting and receiving ultrasonic vibration is integrally provided. It is done. Next, a diskshaped piezoelectric vibrator 13 with an outer diameter of 6 mm and a thickness of 1 mm, which
has electrodes formed on the front and back surfaces and is polarized in the thickness direction,
is bonded to the center of the inner surface of the diaphragm 12 with an epoxy adhesive. One
end of a lead 14 was connected to the electrode. Furthermore, a cylindrical recess 21 having a
depth of 1.5 mm, which is larger than the outer diameter of the piezoelectric vibrator 13 and
deeper than the thickness, is molded on the sound absorbing material 16 made of a foamed
polyurethane material as shown in FIG. The sound absorbing material 16 was bonded to the
diaphragm 2 with a heat-resistant adhesive so as to be engaged on the piezoelectric vibrator 13
without contact. The sound absorbing material 16 is disposed in order to prevent an ultrasonic
wave generated by the vibration of the diaphragm 12 from being reflected inside the case and
affecting the sensitivity and directivity. Further, as shown in FIG. 2, the sound absorbing material
16 is provided with a hole 22 for passing the lead wire 14, and after passing through the lead
wire 14 in the hole 22, it was adhered to the diaphragm 12. Thereafter, in order to narrow the
directivity of the ultrasonic sensor, a silicone resin 17 for restraining the vibration surface was
filled in the inside of the bottomed cylindrical case 11 to manufacture an ultrasonic sensor. The
directivity characteristics when the dimensions of the sound absorbing material were changed
were investigated using the prototype ultrasonic sensor. FIG. 3A is a cross-sectional view showing
the dimensions of the prototype ultrasonic sensor. Moreover, in FIG.3 (b), CC sectional top view
of FIG. 3 (a) seen from the top in the figure is shown. An object at a distance of 60 cm from the
ultrasonic sensor, with half of the length in the major axis direction of the vibrating surface as R
and half of the dimension on the major axis side of the recess of the sound absorbing material as
r1 and the ratio of r1 to R as a parameter On the other hand, the angle (half value angle) at which
the reflected wave of the ultrasonic wave in the vertical direction is halved was measured. The
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results are shown in FIG. As shown in FIG. 4, in the case of r1 / R = 1, the sound absorbing
material is not adhered to the vibrating surface, so that the same structure as the conventional
example shown in FIG. 6 is obtained, and the half value angle is 40 °. On the other hand, it was
confirmed that the half value angle was reduced to 30 ° when the sound absorbing material was
configured such that r1 / R = 0.3. Then, since the half value angle gradually decreases from r1 /
R = 1 to r1 / R = 0.3, it is pointed that the value of r1 / R is in the range of 0.3 ≦ r1 / R <1. It is
necessary to improve gender. Also, assuming that half of the inner dimension of the sound
absorbing material is r1 and the half of the outer dimension of the sound absorbing material in
the major axis direction is r2, the ratio of r1 to r2, ie, the bonding area of the sound absorbing
material The measurement results of the half angle in the vertical direction with respect to are
shown in FIG.
It can be confirmed from FIG. 8 that the half angle is about 30 ° when r1 / r2 = 0.9 and the r1 /
r2 decreases, that is, r2 increases and the bonding area of the sound absorbing material
increases, the half angle increases. The Therefore, it is necessary to improve the directivity of the
ultrasonic sensor that the value of r1 / r2 is in the range of 0.4 ≦ r1 / r2 <1. From this result,
the sound absorbing material provided with the recess is joined on the vibrating surface so as to
engage with the piezoelectric vibrator in a noncontact manner, and the space inside the sound
absorbing material is in a range that does not restrict the vibration of the piezoelectric vibrator.
By reducing the size and reducing the bonding area of the sound absorbing material, the half
angle becomes narrow. This indicates that the larger the restriction range of the silicone resin
from the inside, the narrower the directional characteristics. As a result of measuring the
displacement shape of the vibration surface, it is confirmed that the displacement surface shape
of the vibration surface becomes flat as the range of restraint of the silicone resin increases.
Therefore, the directivity angle can be narrowed by the shape of the sound absorbing material. It
is possible. As described above, according to the present invention, the vibration characteristic is
controlled by non-contacting the sound absorbing material provided with the recess with the
piezoelectric vibrator and bonding it to the vibrating surface. It is possible to improve the
directional characteristics. In addition, there is no need for complicated machining such as steps
on the bottom surface of the metal case, and it becomes possible to obtain an inexpensive
ultrasonic sensor with less variation in characteristics. BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the structure of an ultrasonic sensor according to the present invention. Fig.1 (a) is
sectional drawing, FIG.1 (b) is a top view of AA cross section of Fig.1 (a). FIG. 2 shows a sound
absorbing material of an ultrasonic sensor according to the present invention. FIG. 3 shows the
structure of the present invention. Fig.3 (a) is sectional drawing, FIG.3 (b) is a top view of CC
cross section of Fig.3 (a). FIG. 4 is a graph showing the relationship between the ratio of the inner
radius of the sound absorbing material to the major axis radius of the diaphragm and the halfvalue angle. FIG. 5 is a view showing a relationship between a ratio of a sound absorbing material
inner radius to a sound absorbing material outer radius and a half value angle. FIG. 6 is a view
showing the structure of a conventional ultrasonic sensor. 6 (a) is a cross-sectional view, and FIG.
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6 (b) is a plan view of an EE cross-section of FIG. 6 (a). 7 is a view showing the structure of an
ultrasonic sensor according to JP-A-2000-32594, FIG. 7 (a) is a cross-sectional view, and FIG. 7
(b) is a plan view of a GG cross-section of FIG. 7 (a). FIG. 8 is a cross-sectional view of an
ultrasonic sensor as an example of directional characteristic control. [Description of the code] 11
bottomed cylindrical case 12 diaphragm 13 piezoelectric vibrator 14, 15 lead wire 16 sound
absorbing material 17 silicone resin 18, 19 signal wire 21 recess formed in sound absorbing
material 22 hole 61 bottomed cylindrical case 62 Diaphragm 63 Piezoelectric vibrator 64, 65
Lead wire 66 Sound absorbing material layer 67 Elastic body 68, 69 Signal line 71 Bottomed
cylindrical case 72 Diaphragm 73 Thick portion 74 Thin portion 75 Piezoelectric vibrator 81
Bottomed cylindrical case 82 Vibrating plate 83 Piezoelectric vibrator 84 Sound absorbing
material 85 Elastic body
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