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DESCRIPTION JPS6194496

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DESCRIPTION JPS6194496
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
ultrasonic microphones, and more particularly to an ultrasonic microphone having a closed
structure. (Prior Art) An ultrasonic microphone is an object detection by an ultrasonic wave. It
can be used for distance detection and the like, and is therefore used outdoors for vehicle
detection of a parking meter and obstacle detection behind a vehicle. And when it is used
outdoors as such, since the microphone itself is directly exposed to wind and rain, a drip-proof
type is used. In this type of ultrasonic microphone, in order to prevent the deposition of water
droplets and dust on an ultrasonic transducer that transmits and receives ultrasonic waves, the
ultrasonic transducer is housed in a closed microphone case, and the closed case itself is an
ultrasonic wave. It is structured to vibrate efficiently as a transformer. In addition, in order to
improve the sealing performance and the weather resistance performance of the terminal portion
of the ultrasonic microphone, a structure in which elastic sealing is performed by silicon rubber
is conventionally used. This silicone rubber has gas permeability, so even if the air inside the
microphone expands or contracts due to temperature change, the air flows to the outside
through this silicone rubber, so Changes due to air expansion and contraction of the case are
prevented. (Problems of the prior art) However, in the conventional ultrasonic microphone of this
type, since the molecular density of the silicone rubber is low and the air flowability is high, for
example, the vehicle body for detecting the vehicle height, road surface condition, etc. When
attached to the lower surface, corrosive gas contained in surrounding exhaust gas and the like is
likely to be introduced into the inside of the microphone, resulting in the problem that the
durability and performance of the microphone deteriorate. SUMMARY OF THE INVENTION The
present invention has been made in view of the above-described conventional problems, and it is
an object of the present invention to provide an ultrasonic microphone of this type with high
weather resistance that can maintain stable performance over a long period of time. is there.
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1
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is
characterized in that the end portion of the microphone case in which the ultrasonic transducer
is accommodated is sealed with a urethane-based elastic material having low gas permeability. .
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the
ultrasonic microphone according to the present invention will be described below based on the
drawings. FIG. 1 shows a first preferred embodiment of the ultrasonic microphone according to
the present invention, which is attached to the underside of the vehicle body of the vehicle and
detects road surface distance to thereby make unevenness of the road surface such as side
grooves. It is used to detect the situation. Reference numeral 10 in FIG. 1 denotes a piezoelectric
element, and the piezoelectric element 10 constitutes an ultrasonic transducer for transmitting
and receiving ultrasonic waves for the detection.
The piezoelectric element 10 is of ceramic type. It is housed in the vibration case 12. As can be
understood from FIG. 1, the vibration case 12 is formed in a cap-like shape on the upper side in a
truncated cone shape, and the lower side is formed in a cylindrical shape. The upper portion is a
vibrating portion 14, and the piezoelectric element 10 is attached to the bottom thereof. In
addition, as a material of the vibration case 12, aluminum whose surface is coated with a
corrosion resistant coating is used. Further, a metal inner ring 16 is inserted into the lower
cylindrical portion of the vibration case 12, and the lead wire 18 of the piezoelectric element 10
is inserted into the inner side and connected to the terminal bin 20. The terminal bins 20 are
press-fit into the terminal plate 22 by heating, and their ends projecting from the vibration case
12 are connected to a road surface distance detecting device mounted on a vehicle. Here, the
terminal plate 22 is inserted into the vibration case 12 after the insertion of the spacer 24 made
of urethane rubber, and a urethane rubber adhesive is formed in the space formed between the
terminal plate 22 and the vibration case 12. 26 have been injected. The present embodiment is
configured as described above, and the operation thereof will be described below. When
detecting the distance between the vehicle and the road surface, transmission and reception 7 of
ultrasonic waves are performed by the piezoelectric element 10, and its lead wire 18. The
detection operation is performed by the detection device connected via the terminal bin 20.
Further, since the upper side of the photographing case 12, that is, the vibrating portion 14 is
formed into a truncated cone as shown in FIG. 1, sub resonance is suppressed in the resonance
characteristic in terms of photographing efficiency, and the output sound at the resonance
frequency The pressure is increased and the bandwidth is also expanded. Since this shape can be
obtained by drawing of an aluminum plate, this can be mass-produced inexpensively.
Furthermore, since aluminum whose surface is coated with a corrosion resistant coating is used
as the material, corrosion resistance and Q at resonance can be improved. Further, since the
metal inner ring 16 is fitted inside the cylindrical portion of the vibration case 16, the side
vibration thereof is prevented, whereby the change of the output sound pressure and the
resonance frequency is prevented. In order to optimize the output sound pressure and the
sensitivity, it is preferable to make the neutral surface of the vibration coincide with the bonding
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2
surface of the vibration case 12 and the piezoelectric element 10 when the vibration portion 14
bends and vibrates. Further, it is preferable to set the ratio of the diameter of the vibrating
portion 14 to the diameter of the piezoelectric element 10 to a predetermined value. Here, since
the end portion of the ultrasonic microphone is sealed by the spacer 24 and the urethane rubber
adhesive 26, characteristic change due to imaging buffer with the vibration case 16 is prevented
and the sealing property is maintained. Weatherability is obtained.
As the urethane rubber has a low gas permeability as understood from Table 1 below, the
amount of corrosive gas sucked into the microphone through the spacer 24 and the urethane
rubber adhesive 26 is greatly reduced. Therefore, good microphone performance is stably
maintained over a long period of time even when used by being attached to the lower surface of
the vehicle, and the weather resistance is significantly improved. According to the freezing test,
the high temperature and the high humidity test conducted on the weather resistance, extremely
good test results have been confirmed. Regarding the temperature change, when the so-called
thermal shock test was repeated in which the ultrasonic microphone was left in an environment
of 40 ° C. for 30 minutes and left in an environment of 85 ° C. for 30 minutes, the microphone
characteristics changed. It was confirmed that even if the air inside the microphone expands or
contracts due to temperature change, sufficient air flow is maintained between the inside and the
outside of the microphone. Urethane-based rubbers are considered to be optimal in terms of cost,
workability, stability to use environment, and the like. Next, the second preferred embodiment of
the ultrasonic microphone according to the present invention. A third embodiment will be
described. FIGS. 2 and 3 respectively show those embodiments, and in both drawings, the same
members as those in FIG. In the second embodiment of FIG. 2, the urethane sealant 28 is
embedded in the base of the terminal bin 20 projecting from the terminal plate 22 so that the
urethane sealant 28 is injected into the gap between the two. Therefore, according to the present
embodiment, water, water vapor and corrosive gas which enter the inside of the microphone
from the gap between the terminal bottle 20 and the terminal plate 26 are blocked, so the
weather resistance is further improved as compared with the embodiment of FIG. Is possible.
Further, in the third embodiment of FIG. 3, after the terminal plate 22 is inserted into the
vibration case 12, the urethane rubber sealing material 30 is injected into the vibration case 12
and the outer surface of the terminal plate 22 is this urethane rubber. It is covered by the sealing
material 30. According to the present embodiment, the microphone structure and the process
thereof are simplified, so that the manufacturing cost can be reduced. Further, since the terminal
bin 20 protrudes from the terminal plate 22 through the urethane rubber sealing material 30,
the sealing property is assured as in the second embodiment of FIG. 2, and therefore the weather
resistance is improved. Ru. (Effects of the Invention) As described above, according to the present
invention, since an elastic material having a low gas permeability is used for sealing, entry of
corrosive gas into the interior of the mold is prevented, and thus severeness is caused. Even in
the use environment, it is possible to stably maintain good microphone characteristics over a
long period of time.
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[0002]
Brief description of the drawings
[0003]
1, 2 and 3 are sectional views respectively showing the internal structure of a third preferred
embodiment of the ultrasonic microphone according to the present invention.
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