JPS6194496A - Ultrasonic microphone - Google Patents

Abstract

PURPOSE:To improve weatherability and to maintain stability for a long period by sealing the end part of a microphone case with an urethane type elastic material with low gas permeability. CONSTITUTION:When a distance between a vehicle and a road is detected, ultrasonic wave transmitting and receiving are executed by a piezo-electric element 10, and the detecting action is executed through the lead wire 18 and a terminal pin 20 by a road surface distance detecting device. In such a case, after a urethane rubber-made spacer 24 is inserted, a terminal plate 22 is fitted into a vibration case 12, and in the space between the terminal plate 22 and the case 12, urethane-rubber adhesives is poured. For such a reason, the quantity of corrosive gas adsorbed into a microphone through a spacer 24 and an adhesives 26 is decreased widely. A vibration part 14 is a conical trapezoid, auxiliary resonance is suppressed, further, a metallic ring 16 is fitted into the case 12 and the side surface vibration is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ultrasonic microphone, and more particularly to a sealed ultrasonic microphone.

(Conventional technology) Ultrasonic microphones detect objects using ultrasonic waves.

It can be used for distance detection, etc., and is therefore used outdoors to detect vehicles with parking meters and to detect obstacles behind the vehicle.

When used outdoors, the microphone itself is directly exposed to wind and rain, so a drip-proof type is used.

In this type of ultrasonic microphone, the ultrasonic transducer is housed in a sealed microphone case to prevent water droplets and dust from adhering to the ultrasonic transducer that transmits and receives ultrasonic waves. The structure is such that it vibrates efficiently as a transducer.

Furthermore, a structure in which the terminal portion of an ultrasonic microphone is elastically sealed with silicone rubber has been used in order to improve airtightness and weather resistance.

This silicone rubber has gas permeability, so even if the air inside the microphone expands or contracts due to temperature changes, the air will flow between it and the outside through this silicone rubber. Changes due to air expansion and contraction of the case are prevented.

(Problems with the prior art) However, in conventional ultrasonic microphones of this kind, the molecular density of the silicone rubber is low and its air permeability is high. When used by attaching it to the bottom surface, there is a problem that corrosive gases contained in surrounding exhaust gas etc. are easily introduced into the microphone, which deteriorates the durability and performance of the microphone.

(Object of the invention) The present invention has been made in view of the above-mentioned conventional problems, and
The purpose is to provide this type of ultrasonic microphone with high weather resistance that can maintain stable performance over a long period of time.

(Summary of the Invention) In order to achieve the above object, the present invention is characterized in that the end portion of a microphone case in which an ultrasonic transducer is housed is sealed with a urethane-based elastic material having low gas permeability. .

(Embodiments of the Invention) Preferred embodiments of the ultrasonic microphone according to the present invention will be described below based on the drawings.

FIG. 1 shows a preferred first embodiment of the ultrasonic microphone according to the present invention, and this microphone is attached to the underside of the vehicle body and detects the distance to the road surface to detect irregularities on the road surface such as side ditches. It is used to detect the situation.

10 in FIG. 1 is a piezoelectric element, and this piezoelectric element 10
This constitutes an ultrasonic transducer that transmits and receives ultrasonic waves for the above-mentioned detection.

The piezoelectric element 10 is a ceramic type.
．． It is housed in a vibration case 12.

As can be seen from FIG. 1, the vibration case 12 has a truncated conical cap shape on the upper side, and a cylindrical shape on the lower side.

The upper part serves as a vibrating part 14, and a piezoelectric element 10 is attached to the bottom part of the vibrating part 14. The vibration case 12 is made of aluminum whose surface is coated with anti-corrosion coating.

Furthermore, a metal inner ring 16 is fitted into the lower cylindrical portion of the vibration case 12, and the lead wire 1 of the piezoelectric element 10
8 is inserted through the inside thereof and connected to the terminal pin 20.

This terminal pin 20 is heated and press-fitted into the terminal plate 22,
The ends protruding from the vibration case 12 are connected to a road surface distance detection device mounted on the vehicle.

Here, the terminal board 22 is a spacer 2 made of urethane rubber.
4 is inserted into the vibration case 12, and a urethane rubber adhesive 26 is injected into the gap created between the terminal plate 22 and the vibration case 12.

The present embodiment has the above configuration, and its operation will be explained below.

When detecting the distance between the vehicle and the road surface, ultrasonic waves are transmitted and received by the piezoelectric element 10, and the lead wire 18. The detection operation is performed by the detection device connected via the terminal bin 20.

Further, the upper side of the photographing case 12, that is, the vibrating part 14 is the first
Since it is shaped like a truncated cone as shown in the figure, in terms of imaging efficiency, sub-resonance is suppressed in its resonance characteristics, the output sound pressure at the resonance frequency is increased, and the bandwidth is also expanded.

Since this shape is formed by drawing an aluminum plate, it is possible to mass-produce it at low cost.

Furthermore, since the material used is aluminum with a corrosion-resistant coating applied to the surface, corrosion resistance and Q during resonance are improved.

Further, since the metal inner ring 16 is fitted inside the cylindrical portion of the vibration case 16, side vibrations thereof are prevented, thereby preventing changes in the output sound pressure and resonance frequency.

Note that in order to optimize the output sound pressure and sensitivity, when the vibrating section 14 bends and vibrates, it is preferable that the neutral plane of the vibration coincides with the bonding surface of the vibrating case 12 and the piezoelectric element 10. Furthermore, it is preferable that the ratio between the diameter of the vibrating part 14 and the diameter of the piezoelectric element 10 is set to a predetermined value.

Here, since the ends of the ultrasonic microphone are sealed by the spacer 24 and the urethane rubber adhesive 26, changes in characteristics due to image pickup buffering with the vibration case 16 are prevented, and the airtightness is maintained. Weather resistance has been achieved.

As understood from Table 1 below, urethane rubber has a low gas permeability, so the amount of corrosive gas sucked into the microphone through the spacer 24 and the urethane rubber adhesive 26 is greatly reduced. Therefore, even when used by being attached to the underside of a vehicle, good microphone performance is stably maintained over a long period of time, and weather resistance is significantly improved.

According to freeze tests, high temperature, and high humidity tests conducted regarding this weather resistance, extremely good test results have been confirmed compared to conventional ones.

In addition, regarding temperature changes, the ultrasonic microphone
When we conducted a so-called thermal shock test in which the microphone was left in an environment of 30 minutes at ℃ and then left in an environment at 85℃ for 30 minutes, no changes were observed in the microphone characteristics due to temperature changes. It was confirmed that sufficient air flow was maintained between the inside and outside of the microphone even when the air expanded or contracted.

Urethane rubber is considered to be optimal from the viewpoints of cost, workability, and stability against usage environments.

Next, a second preferred ultrasonic microphone according to the present invention.
A third embodiment will be explained.

2 and 3 respectively show these embodiments, and in both figures, the same members as in FIG. 1 are given the same reference numerals, and their explanation will be omitted.

In the second embodiment shown in FIG. 2, the urethane sealant 28 is applied to the base of the terminal pin 20 protruding from the terminal plate 22, so that the urethane sealant 28 is filled in the gap between the two.
is injected.

Therefore, according to this embodiment, water, water vapor, and corrosive gas are prevented from entering the microphone through the gap between the terminal bin 20 and the terminal plate 26, so that weather resistance can be further improved than in the embodiment shown in FIG. becomes possible.

Further, in the third embodiment shown in FIG. 3, after the terminal plate 22 is fitted into the vibration case 12, a urethane rubber sealing material 30 is injected into the vibration case 12, and the outer surface of the terminal plate 22 is covered with this urethane rubber. It is covered with a sealing material 30.

According to this embodiment, since the microphone structure and its process are simplified, it is possible to reduce its manufacturing cost.

Furthermore, since the terminal pin 20 is protruded from the terminal plate 22 through the urethane rubber sealing material 30, its sealing performance is ensured as in the second embodiment shown in FIG. 2, and therefore its weather resistance is improved. Ru.

(Effects of the Invention) As explained above, according to the present invention, since an elastic material with low gas permeability is used for sealing, corrosive gases are prevented from penetrating into the interior of the mold. It becomes possible to stably maintain good microphone characteristics over a long period of time even under the usage environment.

[Brief explanation of drawings]

FIGS. 1, 2, and 3 are cross-sectional views showing the internal structure of a third preferred embodiment of the ultrasonic microphone according to the present invention.

Claims (1)

[Claims] (1) An ultrasonic microphone characterized in that the end of a microphone case in which an ultrasonic transducer is housed is sealed with a urethane-based elastic material having low gas permeability.