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DESCRIPTION JP2001326987

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DESCRIPTION JP2001326987
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transducer used as, for example, a clearance sensor or a back sensor of a car.
[0002]
2. Description of the Related Art Heretofore, an ultrasonic transducer has been known in which a
piezoelectric vibrating element is fixed to the inner bottom surface of a bottomed cylindrical case,
and the outer bottom surface of the case is made an ultrasonic wave transmitting / receiving
surface. When such an ultrasonic transducer is used as a sensor for an automobile, if the
transmission / reception range in the vertical direction is too wide relative to the ground, the
reflected wave from the ground becomes noise and the transmission / reception range in the
horizontal direction is narrow. If it is too large, a blind spot will occur in the detection range,
which is not preferable. Therefore, the hollow portion of the case is formed to be long in the
vertical direction and short in the horizontal direction, and by forming the thick portion and the
thin portion at the bottom of the case, the transmission / reception range in the vertical direction
is narrow. An ultrasonic transducer with a wide transmission / reception range was devised. In
such an ultrasonic transducer, for example, a thick portion with a thickness of 0.75 mm and a
thin portion with a thickness of 0.3 mm are formed at the bottom of a case having a diameter of
18 mm, and the thin portions are arranged in the vertical direction. Thus, it is possible to obtain
an ultrasonic transducer having a transmission / reception range of 40 ░ in the vertical
direction.
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[0003]
The example which provided such an ultrasonic transducer 1 as a back sensor of a motor vehicle
is shown in FIG. The transmission / reception range is represented by the half-width of ultrasonic
waves. The half-full angle is an angle between directions which are 20 log 0.5 dB (about 6 dB)
lower than the transmission / reception sensitivity of the direction opposite to the bottom surface
(direction of 0 ░).
[0004]
However, in such a conventional ultrasonic transducer, since the reverberation characteristic is
unstable and the reverberation time is long, the ultrasonic wave reflected from the object close to
the ultrasonic transducer is long. In some cases, the reverberation and the reverberation buffer,
making it impossible to detect the presence of a close object or to measure the distance to a close
object. In particular, since reverberation time tends to be long when water droplets are attached
to the transmission / reception wavefront, there is a practical problem as a sensor for an
automobile exposed to wind and rain.
[0005]
Therefore, a main object of the present invention is to provide an ultrasonic transducer having a
relatively narrow transmission / reception range in at least one direction and a stable
reverberation characteristic.
[0006]
SUMMARY OF THE INVENTION An ultrasonic transducer according to the present invention is an
ultra-sound transducer in which a piezoelectric vibrator is fixed to the inner bottom surface of
the bottom of a bottomed cylindrical case and the outer bottom surface is an ultrasonic wave
transmitting / receiving surface. In the sound wave transmitter-receiver, the bottom of the case
includes a thick portion to which the piezoelectric vibrator is fixed and a thin portion thinner
than the thick portion. Assuming that the thickness is t1, the thickness of the thin portion is t2,
the thickness of the side portion continuously provided to the thin portion is A, and x = t2 / t1,
0.50 ? x ? 0.640. It is an ultrasonic transducer formed so that it may become the range of 75
<= y <= 1.75y <-(50/7) x + 163/28 y ?- (50/7) y + 135/28.
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[0007]
The above-described objects, other objects, features and advantages of the present invention will
become more apparent from the detailed description of the embodiments of the present
invention given below with reference to the drawings.
[0008]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic crosssectional view showing an embodiment of an ultrasonic transducer according to the present
invention.
The ultrasonic transducer 10 includes a substantially cylindrical case 12.
Case 12 is made of, for example, aluminum.
A thick portion 14 and a thin portion 16 are formed at the bottom of the case 12. The
piezoelectric vibrating element 18 is fixed on the thick portion 14 of the inner bottom surface of
the case 12. One electrode of the piezoelectric vibrating element 18 is grounded to the case. A
sound absorbing material 20 is disposed on the opposite side of the inner bottom surface of the
case 12 of the piezoelectric vibrating element 18.
[0009]
A capacitor 22 is disposed on the opposite side of the sound absorbing agent 20 to the
piezoelectric vibrating element 18. Fixing members 24 made of silicone rubber or the like are
fitted to both ends of the capacitor 22. One electrode of the capacitor 22 and the other electrode
of the piezoelectric vibrating element 18 are electrically connected by a lead wire 26. Further, an
external terminal 28 is connected to one electrode of the capacitor 22. The other electrode of the
capacitor 22 is grounded to the case 12 by a lead (not shown). Furthermore, the case 12 is
provided with an external terminal (not shown).
[0010]
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The inner bottom surface of the case 12 is filled with a first adhesive 30 such as a silicone
adhesive having a relatively high viscosity while covering the sound absorbing material 20 and
the piezoelectric vibrating element 18. The use of a high viscosity adhesive is to minimize the
possibility of the adhesive impregnating the sound absorbing material 20 and affecting the
acoustic characteristics. After curing the first adhesive 30, the fixing members 24 at both ends of
the capacitor 22 are placed thereon. And further, a second adhesive 32 such as a silicone
adhesive having a relatively low viscosity is filled thereon. The use of a second adhesive 32
having a relatively low viscosity is in consideration of the ease of filling operation.
[0011]
2 (a) is a cross-sectional view showing a state in which an example of the case 12 of the
ultrasonic transducer 10 shown in FIG. 1 is cut along a plane parallel to the bottom, and FIG. ) Is
a longitudinal sectional view taken along the line b-b. As shown in FIG. 2, the hollow portion of
the case 12 is formed, for example, in a substantially oval shape in plan view. Then, thin-walled
portions 16 thinner than the thick-walled portions 14 are formed on both sides of the thickwalled portions 14 in the direction in which the major axis of the oval extends. On the other
hand, the thick portion 14 of the case 12 is formed to extend in the minor axis direction of the
oval. The ultrasonic transducer 10 shown in FIG. 1 is used in the direction in which the long axis
direction of the cross-sectional shape of the case 12 extends perpendicularly to the ground, and
the short axis direction is provided in the direction extending horizontally to the ground Be done.
In the ultrasonic transducer 10, the outer bottom surface of the case 12 serves as an ultrasonic
wave transmitting / receiving wave surface. The cross section of the case 12 is not limited to the
substantially oval shape, but may be formed into a substantially rectangular shape, a
substantially elliptical shape, a substantially circular shape, or the like.
[0012]
The ultrasonic wave using the case 12 is changed by changing the thickness of the thick portion
14, the thin portion 16, and the side portion 12a continuously provided to the thin portion 16 of
the case 12 shown in FIG. The half-full angle and reverberation time of the transducer 10 were
measured. The results are shown in Tables 1 to 10 below and in Figures 3 to 6 below. The case
12 used in this embodiment is all made of aluminum and has a diameter of 18 mm.
[0013]
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Further, in Table 11 and FIG. 10, when the ultrasonic transducer 10 is used as a back sensor for
an automatic person as shown in FIG. The relationship between full-width and detection distance
is shown.
[0014]
As apparent from Table 11 and FIG. 10, the narrower the half full angle, the longer the detection
distance.
In particular, when the half angle is 40 ░, the detection distance is 1.5 times that of the 60 ░
one. However, since this ultrasonic transducer 10 combines transmission and reception of
ultrasonic waves with one transmission / reception wave front, if the vibration when transmitting
ultrasonic waves is not damped in as short a time as possible, the reflected wave is transmitted. It
is buried in the vibration of time and can not be detected. Therefore, in addition to the fact that
the half-full angle is narrow, it is practically required that the reverberation time is 1.5
milliseconds or less in a state where water droplets are attached to the transmission / reception
wavefront. If the reverberation time is 1.5 milliseconds or less in the state in which the water
droplets are attached, the reverberation time becomes shorter in the dry state.
[0015]
From the above results, Table 12 shows that the half-full angle is 40 ░ or less and the
reverberation time is 1.5 milliseconds or less at the same time.
[0016]
As is apparent from Table 12, in order to obtain the operation and effect aimed by the present
invention, the ratio of the thickness t1 of the thick portion 14 to the thickness t2 of the thin
portion 16 is 0.57. Preferably, the ratio of the thickness A of the side portion 12a to the
thickness t2 of the thin portion 16 is 0.75 to 1.75.
When the ratio of the thickness t1 of the thick portion 14 to the thickness t2 of the thin portion
16 is 0.50, the ratio of the thickness A of the side portion 12a to the thickness t2 of the thin
portion 16 is 1.25 to It is preferable to set it as 1.75. Furthermore, when the ratio of the
thickness t1 of the thick portion 14 to the thickness t2 of the thin portion 16 is 0.64, the ratio of
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the thickness A of the side portion 12a to the thickness t2 of the thin portion 16 is 0.75 to It is
preferable to set it as 1.25.
[0017]
From these results, the relationship shown in FIG. 7 is derived. That is, assuming that x = t2 / t1
and y = A / t2, 0.50 ? x ? 0.64 иии Expression 0.75 ? y ? 1.75 иии Formula y ? ? (50 / 7) и x +
163/28 и и и Formula y ?-(50/7) и y + 135/28 и и и и и и thickness t1 of the thin portion 16 and
thickness of the thick portion 14 so as to be within the range enclosed by the equation By setting
t2 and the thickness A of the side portion 12a, the intended effect of the present invention can be
obtained.
[0018]
In FIG. 8, the diameter 18 mm, the thickness t1 of the thick portion 14 is 0.70 mm, the thickness
t2 of the thin portion 16 is 0.40 mm, and the thickness A of the side portion 12a connected to
the thin portion is 0.4 mm. The directivity characteristics in the vertical direction and the
horizontal direction of the ultrasonic transducer 10 of the embodiment using the case are shown
by solid lines. Further, in FIG. 8, the diameter 18 mm, the thickness t1 of the thin portion is 0.30
mm, the thickness t2 of the thick portion is 0.70 mm, and the thickness A of the side portion 12a
connected to the thin portion is 0.4 mm. The directivity characteristic in the vertical direction of
the ultrasonic transducer 10 of the comparative example using the case is shown by a broken
line. As apparent from FIG. 8, the half-full angle (about 30 ░) of the ultrasonic transducer 10
according to the embodiment of the present invention has directivity characteristics in the
vertical direction compared to the half-full angle (about 60 ░) of the conventional product.
narrow.
[0019]
As described above, according to the ultrasonic transducer 10 of this embodiment, since the half
angle in the vertical direction is 40 ░ or less, the detection distance can be made longer. In
addition, it is not easily affected by the reflected waves from the ground. Furthermore, according
to the ultrasonic transducer 10 of this embodiment, since the reverberation time in the case
where a water drop is attached to the transmission / reception wavefront is within 1.5
milliseconds, the influence of the transmission wave on the reflected wave can be minimized. it
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can.
[0020]
According to the present invention, it is possible to obtain an ultrasonic transducer having a
relatively narrow transmission / reception range in at least one direction and a stable
reverberation characteristic. This ultrasonic transducer has a long detection distance and can be
used as a high performance back sensor or the like.
[0021]
Brief description of the drawings
[0022]
1 is a cross-sectional schematic view showing an embodiment of the ultrasonic transducer
according to the present invention.
[0023]
Fig.2 (a) is a cross-sectional view which shows the state which cut | disconnected an example of
the case of the ultrasonic transducer shown in FIG. 1 in a plane parallel to a bottom face, (b) is
line bb of (a). It is a longitudinal cross-sectional view in.
[0024]
It is a graph which shows the relationship of t2 / t1 and half-full angle at the time of changing
FIG. 3A / t2.
[0025]
It is a graph which shows the relationship between t2 / t1 and reverberation time at the time of
changing FIG. 4A / t2.
[0026]
FIG. 5 is a graph showing the relationship between A / t 2 and the half-full angle when t 2 / t 1 is
changed.
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[0027]
FIG. 6 is a graph showing the relationship between A / t2 and reverberation time when t2 / t1 is
changed.
[0028]
FIG. 7 is a graph showing a preferable numerical range when x = t2 / t1 and y = A / t2.
[0029]
8 is a diagram showing the transmission and reception sensitivity of the ultrasonic transducer.
[0030]
9 is an illustrative view showing a detection range of the back sensor of the vehicle.
[0031]
10 is a graph showing the relationship between the half-full angle and the detection distance.
[0032]
Explanation of sign
[0033]
DESCRIPTION OF SYMBOLS 10 Ultrasonic transducer 12 Case 14 Thick-walled part 16 Thinwalled part 18 Piezoelectric vibration element 20 Sound absorbing material 22 Condenser 24
Fixing member 26 Lead wire 28 Input-output terminal 30 1st adhesive 32 2nd adhesive 34
Hollow part
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