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JPS60252284

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DESCRIPTION JPS60252284
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic sensor used to detect an object distance and the like by transmitting and receiving
ultrasonic signals, and more particularly to an improvement of a transmission / introduction
horn of the transmission / reception waves. (Background of the Invention) As an ultrasonic
sensor used to detect an object distance by using an ultrasonic signal, for example, as disclosed
in Japanese Patent Application Laid-Open No. 57-182544, “Road Condition Check IB Dressing
Cheek” Those applied to automobiles have been proposed. Some ultrasonic transmitters /
receivers constituting such an ultrasonic sensor have a horn 1.2 attached as shown in FIG. 5321958)). However, as described above, even if the directivity is enhanced by the horn, the
transmitter 8 is transmitted to the receiver 4 when the ultrasonic transmitters / receivers 3 and 4
are installed close to each other. In addition to the reflected wave s2 of the ultrasonic signal S1, a
signal wave (hereinafter, referred to as a "looping wave") S8 which is incident from the side of
the direct transmission D8 without being reflected to the object is received. In particular, when
detecting a short deviation as in the case of the vehicle height of the above-mentioned vehicle,
this wraparound wave S8 partially overlaps the reflected wave S2 to cause interference, or
detects the reflected wave Sg, etc. It is easy for phenomena that cause errors. (Object of the
Invention) An object of the present invention is to provide an ultrasonic sensor in which
detection performance is improved by effectively attenuating the above-mentioned wraparound
wave by improving the pawn shape. In order to achieve the above object, according to the
present invention, at least one of an ultrasonic wave transmitter and a wave receiver is provided
with a horn comprising a straight cylinder and a conical cylinder, and a length of the straight
cylinder Is set to be approximately 1.5 × (radius of transmitting or receiving wave) ”/
(wavelength of M3 sound wave signal). DESCRIPTION OF THE PREFERRED EMBODIMENT The
construction of one embodiment of the present invention is shown in cross section in FIG. The
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case 10 is made of a synthetic resin molding such as plastic, and the ultrasonic wave transmitter
3 and the ultrasonic wave receiver 4 are accommodated in two juxtaposed accommodation
chambers. An insulator 11.12 made of a material having a soundproof effect such as soft rubber
is interposed in a portion between the case 10 and the sending and receiving devices 3, 4 except
the transmitting surface 3a and the receiving surface 4a. Further, in the case 10, horns 18.14,
which are formed to communicate respectively with the transmitting surface 8a and the receiving
surface 4a from the lower surface, are stepped. The horns 1.8 and 14 are formed from a straight
cylindrical portion 13a # 14a cylindrically formed downward from the transmitting / receiving
wavefronts 8a and 4a (7) LtJ, and the lower surface of the case 10 from the lower end of the
straight cylindrical portion 18a + 14a. It comprises cone-shaped conical barrel parts 18b and
14b which are spread toward the end.
The length X of the straight cylindrical portions 18a and 14a is set to satisfy the relationship X =
1.57 / λ (1). Here, l is the transmitting wave front 8a and the radius of the receiving wave front
4a, and λ is the wavelength of the ultrasonic wave signal generated from the transmitter 8.
Further, the opening diameter y of the ton 18, 14 is set to be y = 2λ (2). By forming the above
relationship (111 (2) fi-satisfying horn), 3.degree. 14, it is possible to significantly attenuate the
wraparound wave and to avoid the influence thereof. Hereinafter, the results of experiments
conducted by the present inventors to derive the above relationship (1, 11 (2) will be shown. The
ultrasonic transmitters and receivers 3 and 4 used in the experiment had a center frequency of
40 KH2 (wavelength λ = 8.5 m + ++) and a radius r of the transmitting / receiving wavefront 8 a
e 4 a of 5.4 r, a ( However, since the vibration mode of normal ultrasonic wave transmission and
reception is the bending mode, it is considered here as an effective radius of 5.0 振動 of the
vibration surface). The experimental results shown in FIG. 8 show the S / N when the aperture
diameter y of the horns 18 and 141 is changed (The intensity of the reflected wave and the
wraparound wave when the aluminum plate is placed at a distance of 80 cm from the aperture
surface Change in the ratio of From the figure, it can be seen that the S / N is largest when the
aperture diameter y is 1.8.5 ms (this is about twice the wavelength λ). The experimental results
shown in FIG. 4 are S when the length X of the straight cylinder portion is changed in the horns
xa 14 having an aperture diameter y = 18.5 mm which is found to be optimum from the
experimental results in FIG. Indicates / N. From the figure, it can be seen that the S / N becomes
maximum when the length X of the straight cylinder portion is about 4.5. Next, as parameters
relating to the optimum value of the length X of the straight cylinder portion, the radius r of the
transmission / reception wavefront and the wavelength λ of the ultrasonic wave signal can be
considered. = F, (x 2) ... (3) In FIG. 5, assuming that the wavelength λ is constant (8, 5 + ++ m),
the length of the straight cylinder where the s / N becomes maximum when the radius r of the
transmission / reception is changed is made the optimum straight both lengths. ) Shows the
results of experiments with X. Further, FIG. 6 shows an experimental result obtained by setting
the radius r to be constant (5 酌) and the optimum straight portion length X when the
wavelength λ is changed. From both figures, it was found that the optimum straight part length
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X is proportional to the square of the radius and inversely proportional to the wavelength λ.
Therefore, the functional equation (3) is x = one 7 / λ (4) (k is a constant).
Here, the optimum straight part lengths x = 4 and 5 (-1 and λ = 8.5 (-) and y = 5 (sm)
determined from the experimental results shown in FIG. Substituting the constant k gives k = 1..5.
Thus, the relational expression (1) for making the length X of the straight cylinder parts 111a
and 14a the optimum length is obtained. Furthermore, the results of experimenting on the
attenuation effect of the wraparound wave that the above-mentioned horn shape brings about
are shown in FIGS. 7 and 8. FIG. However, Fig. 7 shows the transmitter 80 directivity
characteristics, and Fig. 8 the received wave! The directional characteristic of a4 is shown, P in
the figure is the characteristic in the present embodiment, and Q in the figure is the
characteristic when the horn is not used. From the two figures, it can be seen that in the case of
the present embodiment, the amount of attenuation on the side of the horn is large, that is, the
attenuation of the wraparound wave is sufficiently performed. In the above embodiment, the
straight cylinder portion 18a. 14a includes the insulator 1111 and the case 11 in that the
soundproof effect by the insulator 11.12 is added to the attenuation effect of the wraparound
wave of the horns 18 and 14, and the transmission / reception Wa, 4 In the housing step, the
positioning error due to the elasticity of the insulator 11 ° 12 is suppressed by the case 11. In
addition, the present invention sends as shown in FIG. It is apparent that the present invention
can be applied to one in which the wave receivers 8 and 4 are housed in separate cases and
juxtaposed. (Effects of the Invention) As described above in detail, in the present invention, the
wraparound wave can be greatly attenuated by the improvement of the horn shape, and it is
possible to prevent the hindrance to the detection of the reflected wave. In addition, since the
wraparound wave attenuation efficiency of the horn is high, the transmitter and receiver can be
disposed close to each other, and the ultrasonic sensor itself can be miniaturized.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a cross-sectional view showing a conventional ultrasonic sensor, FIG. 2 is a crosssectional view showing the configuration of an embodiment of the present invention, and FIG. 8
shows the relationship between the horn opening diameter and S / N obtained by experiment.
Figure 4 shows the relationship between the length of the straight cylinder section and S / H
obtained by experiment Figure 9 Figure 5 shows the relationship between the radius of the
transmitting / receiving surface and the optimum straight section length obtained by experiment
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6 shows the relationship between the wavelength of the ultrasonic signal and the optimum
straight part length by experiment, and FIG. 7 shows the directivity characteristic of the
transmitter in the embodiment shown in FIG. 2, and FIG. It is a directional characteristic view of a
wave receiver similarly.
8 ... ultrasonic wave transmitter 4 ... ultrasonic wave receiver lO ... case 11. , T2 ... insulator 18.14
... horn 3a ... transmitting wave front 4a ... receiving wave front 18a, 14a ... straight cylinder part
1! 3b, 14b ... spindle portion. Patent applicant Nissan Motor Co., Ltd. Fig. 5 on 1 and Fig. 6 (1)
and Fig. 6 ヲ length (rnm) Fig. 7 Fig. 8 One item-J □-N-1 θ θ
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