JP3978875B2 - Ultrasonic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic sensor. In particular, the present invention relates to a drip-proof ultrasonic sensor used for automobile back sonar and corner sonar.
[0002]
[Prior art]
An ultrasonic sensor performs sensing using ultrasonic waves, intermittently transmits an ultrasonic pulse signal from the piezoelectric vibration element, and receives a reflected wave from an object to be detected in the vicinity by the piezoelectric vibration element. By doing so, an object is detected. As this type of ultrasonic sensor, one having a structure shown in FIG. 1 has been conventionally used. That is, in this ultrasonic sensor 1, the bottom surface of the bottomed cylindrical sensor case 2 made of metal is the diaphragm 3, and the element electrodes 4 a and 4 b are formed on both main surfaces inside the diaphragm 3. The piezoelectric vibration element 5 is attached. Electrical extraction from the element electrodes 4a and 4b formed on the piezoelectric vibration element 5 to the outside of the sensor case 2 is performed by lead wires 6 and 6 serving as input / output terminals. One lead wire 6 is connected to the element electrode 4a of the piezoelectric vibration element 5 on the side not in contact with the diaphragm 3 by soldering. The other lead wire 6 is soldered to a predetermined position of the metal sensor case 2, and the other electrode electrode 4 b (on the side in contact with the vibration plate 3) of the piezoelectric vibration element 5 through the metal sensor case 2. Is conducting.
[0003]
However, in the ultrasonic sensor 1 using such an integral sensor case having a bottomed cylindrical shape, the piezoelectric vibration element 5 is housed in the ultrasonic sensor 1 and the piezoelectric vibration element 5 is bonded to the inner surface of the vibration plate 3. The work of soldering the ends of the lead wires 6 and 6 to the piezoelectric vibration element 5 is difficult to perform, and the workability in the manufacturing process is poor.
[0004]
[Problems to be solved by the invention]
For this reason, the applicant of the present invention has applied for the ultrasonic sensor 11 having the structure shown in FIG. 2 (1998 Patent Application No. 4882). The ultrasonic sensor 11 mainly includes a case 12 having a bottomed cylindrical shape and a piezoelectric vibration element 15, and the case 12 has a diaphragm in a hollow portion 19 provided at one end of a substantially cylindrical case body 13. 14 is attached. The piezoelectric vibration element 15 is disposed on the surface of the vibration plate 14 corresponding to the inner bottom surface of the case 12. Two input / output terminals 16 and 17 are insert-molded in the side wall of the case body 13. One end of the input / output terminal 16 is electrically connected to an element electrode formed on one main surface of the piezoelectric vibration element 15 via a conductive adhesive 18. The other end of the input / output terminal 16 is pulled out of the case 12 for connection with an external circuit. One end of the input / output terminal 17 is crimped (adhered) to the diaphragm 14 made of a conductive member and is in electrical contact with the other main surface of the piezoelectric vibrating element 15 via the diaphragm 14. It is electrically connected to the formed device electrode. The other end of the input / output terminal 17 is drawn out of the case 12 like the input / output terminal 16.
[0005]
In the ultrasonic sensor 11 in which the vibration plate 14 to which the piezoelectric vibration element 15 is bonded is bonded to the case body 13, the outer peripheral portion of the vibration plate 14 vibrates when the central portion of the vibration plate 14 is excited by the piezoelectric vibration element 15. In order to be fixed to the case main body 13 and still, it is necessary that the surface bonding area (adhesion interface) between the diaphragm 14 and the case main body 13 is sufficiently adhered and firmly adhered. However, in such an ultrasonic sensor 11, no special surface treatment is applied to the bonding portion between the case body 13 and the diaphragm 14, and until now, the bonding surfaces of the case body 13 and the diaphragm 14 are degreased. After the treatment, the case main body 13 and the vibration plate 14 were simply bonded with an adhesive, so that the adhesive force between the vibration plate 14 and the case main body 13 was weak, and the variation in the bonding strength was large.
[0006]
If the adhesive force between the diaphragm 14 and the case body 13 is weak or the adhesive strength varies greatly, the pressure contact force (or adhesive force) between the input / output terminal 17 and the diaphragm 14 becomes non-uniform. Even if 11 is driven at a constant voltage, the contact resistance between the input / output terminal 17 and the diaphragm 14 varies, and the voltage drop at that portion varies. In addition, if the adhesive force of the diaphragm 14 is weak or the adhesive strength varies greatly, the displacement of the diaphragm 14 during vibration is not stable. As a result, there is a problem that the transmission and reception characteristics of the ultrasonic sensor 11 are not stabilized.
[0007]
Further, since there is a relationship as shown in FIG. 3 between the frequency and sensitivity (transmission / reception sensitivity) of the ultrasonic sensor 11, if there is a variation in the bonding strength between the case body 13 and the diaphragm 14, the ultrasonic sensor The resonance frequency of the ultrasonic sensor 11 varies, and the transmission / reception sensitivity of the ultrasonic sensor 11 varies due to the variation of the resonance frequency.
[0008]
The present invention has been made in view of the above technical background, and an object of the present invention is to join a case body and a diaphragm in an ultrasonic sensor in which a case is formed by joining a diaphragm to a case body. Is to improve the transmission / reception characteristics of the ultrasonic sensor.
[0009]
DISCLOSURE OF THE INVENTION
The ultrasonic sensor according to claim 1, wherein a piezoelectric vibration element is bonded to an inner surface of the diaphragm, and an outer peripheral portion of the diaphragm is bonded to one end opening of the case body, The case main body is characterized in that an adhesive surface with the diaphragm is a rough surface.
[0010]
In this ultrasonic sensor, since the adhesive surface of the case body is roughened, the adhesive applied between the case body and the diaphragm bites into the irregularities or grooves on the rough surface of the case body, and the case body And the diaphragm are firmly bonded without variation. For this reason, variation in the resonance frequency of the ultrasonic sensor is reduced and stabilized, and transmission characteristics such as transmission and reception sensitivity and reception characteristics of the ultrasonic sensor are stabilized without variation.
[0011]
The ultrasonic sensor according to claim 2 is an ultrasonic sensor in which a piezoelectric vibration element is bonded to an inner surface of a vibration plate, and an outer peripheral portion of the vibration plate is bonded to one end opening of a case body. The bonding surface with the case body is a rough surface.
[0012]
In this ultrasonic sensor, the adhesive surface of the diaphragm is roughened, so the adhesive applied between the case body and the diaphragm bites into the irregularities and grooves on the rough surface of the case body, and the case body And the diaphragm are firmly bonded without variation. For this reason, variation in the resonance frequency of the ultrasonic sensor is reduced and stabilized, and transmission characteristics such as transmission and reception sensitivity and reception characteristics of the ultrasonic sensor are stabilized without variation.
[0013]
In these ultrasonic sensors, in order to form a rough surface on the bonding surface, for example, at least one processing means among chemical etching, sandblasting, hairline, sandpaper, and buffing may be used. By using these methods, a fine rough surface can be formed efficiently. Alternatively, when the case body is molded of synthetic resin or the like, the rough surface provided on the mold for molding the case body is transferred to the case body to form a rough surface on the bonding surface of the case body. Can do. Similarly, when the diaphragm is die cast molded, the rough surface provided on the mold for molding the diaphragm can be transferred to the diaphragm to form a rough surface on the adhesive surface of the diaphragm. it can.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 4 is a sectional view showing the structure of the ultrasonic sensor 21 according to the embodiment of the present invention. The ultrasonic sensor 21 includes a case 22 having a bottomed cylindrical shape and a piezoelectric vibration element 25 having a thin plate shape. The case 22 is configured by adhering a diaphragm 24 made of aluminum to a front end surface 23a of a case main body 23 formed of a synthetic resin. The material of the case body 23 is preferably an engineering resin such as an insulating resin such as polyphenylene sulfide (PPS) or a liquid crystal polymer. The piezoelectric vibration element 25 has element electrodes formed on both main surfaces of a piezoelectric ceramic plate, and one element electrode of the piezoelectric vibration element 25 is bonded to the inner surface of the vibration plate 24 by a conductive adhesive 29a.
[0015]
More specifically, two input / output terminals 26 and 27 are insert-molded in advance in a side wall portion of the case main body 23 formed of a synthetic resin such as engineer plastic. One end of the input / output terminal 26 protrudes from the front inner peripheral surface of the case body 23, and the other end is drawn out to the rear end surface of the case body 23 for connection to an external circuit. Further, one end of the input / output terminal 27 is exposed on the front end face 23 a of the case body 23, and the other end is drawn out to the rear end face of the case body 23, similarly to the input / output terminal 26.
[0016]
The inner surface of the diaphragm 24 made of aluminum is roughened by chemical etching, sandblasting, hairline, sandpaper, buffing, etc., resulting in a rough surface 30 whose surface is uniformly roughened. One element electrode of the piezoelectric vibration element 25 is bonded to the inner surface of the vibration plate 24 by a conductive adhesive 29a.
[0017]
The vibration plate 24 to which the piezoelectric vibration element 25 is bonded is bonded to the front end surface of the case body 23 with an adhesive 29b. At this time, the adhesive 29b bites into the fine irregularities or grooves that are roughened on the surface of the diaphragm 24, and the adhesive force between the diaphragm 24 and the case body 23 is increased, and the diaphragm 24 is attached to the case body 23. It will adhere | attach firmly and the dispersion | variation in adhesive strength will also be reduced.
[0018]
The end portion of the input / output terminal 27 that has been insert-molded in the case body 23 is in pressure contact with the diaphragm 24 and is electrically connected to the element electrode of the piezoelectric vibration element 25 via the diaphragm 24. At this time, the diaphragm 24 is securely and firmly bonded to the case body 23, so that the variation in contact resistance between the input / output terminal 27 and the diaphragm 24 is reduced, and the variation in voltage drop at this location is also reduced. Transmission and reception characteristics are stabilized. Next, the other input / output terminal 26 is bonded to the other element electrode of the piezoelectric vibration element 25 by the conductive adhesive 28.
[0019]
A sound absorbing material (not shown) covers the vicinity of the piezoelectric vibration element 25 inside the case 22. Furthermore, an elastic insulating resin (not shown) is filled on the sound absorbing material.
[0020]
In such an ultrasonic sensor 21, an alternating voltage is applied to the piezoelectric vibration element 25 to spread the diaphragm 24 to excite vibration, thereby generating a sound wave, or conversely, a sound pressure of the sound wave. As a result of the vibration of the diaphragm 24, a voltage is generated in the piezoelectric vibration element 25, and the distance to the detected object can be detected based on the time from the emission of the sound wave to the reception.
[0021]
(Measurement example)
In FIG. 5, the inner surface of the diaphragm 24 is roughened to roughen the surface (surface roughness # 240) and the ultrasonic sensor of the present invention is not roughened (that is, the surface is not roughened). The resonance frequency Fr of the ultrasonic sensor is shown. As can be seen from this figure, the ultrasonic sensor of the present invention subjected to the rough surface treatment has a smaller variation in the resonance frequency Fr than the ultrasonic sensor not subjected to the rough surface treatment.
[0022]
As described above, the variation in the resonance frequency of the ultrasonic sensor can be reduced by subjecting the vibration plate 24 to the rough surface treatment to reduce the variation in the bonding strength between the case body 23 and the vibration plate 24. According to this, variation in transmission / reception sensitivity of the ultrasonic sensor can be reduced (see FIG. 3).
[0023]
Further, since the surface of the diaphragm 24 is roughened to roughen the surface, the diaphragm 24 and the case main body 23 can be firmly bonded without variation, and the contact resistance between the input / output terminal 27 and the diaphragm 24 is improved. And the displacement of the diaphragm 24 during vibration can be stabilized. As a result, the resonance frequency can be stabilized, and the transmission and reception characteristics of the ultrasonic sensor can be stabilized.
[0024]
(Second Embodiment)
FIG. 6 is a sectional view showing an ultrasonic sensor 31 according to another embodiment of the present invention. In the ultrasonic sensor 21 according to the first embodiment, the inner surface of the diaphragm 24 is roughened. However, in the ultrasonic sensor 31, the front end surface 23a of the case body 23 to which the diaphragm 24 is bonded is roughened. The rough surface 30 is formed by performing surface treatment. This rough surface treatment is also preferably performed by chemical etching, sand blasting, hairline, sand paper, buffing or the like.
[0025]
Even in this ultrasonic sensor 31, the front end surface of the case body 23 is roughened to uniformly roughen the surface, so that the adhesive 29 b bites into the fine irregularities or grooves formed by the roughening and vibrates. The plate 24 and the case body 23 are bonded uniformly. As a result, this ultrasonic sensor 31 can also be stabilized by reducing variations in resonance frequency, and the transmission / reception characteristics of the ultrasonic sensor 31 can also be stabilized by reducing variations.
[0026]
Further, if the case main body 23 made of synthetic resin is roughened, when the diaphragm 24 and the front end surface 23a of the case main body 23 are pressed through the adhesive 29b, the case main body 23 will be the diaphragm 24. Compared to the above, since it is made of a soft material, fine irregularities and the like of the case body 23 are crushed, and as a result, the adhesion between the diaphragm 24 and the case body 23 is increased. Therefore, it is possible to increase the adhesive strength by forming the rough surface treatment on the case body 23 rather than providing it on the diaphragm 24.
[0027]
(Third embodiment)
7A and 7B are a plan view and a sectional view showing an ultrasonic sensor 32 according to still another embodiment of the present invention. In this ultrasonic sensor 32, a shallow recess 34 and a deep recess 33 are provided on the front end surface 23a and the rear end surface of the case body 23 made of synthetic resin, respectively. The end of the input / output terminal 27 is exposed in the deep depression 33, and the roughened diaphragm 24 is placed in the shallow depression 34 and bonded.
[0028]
(Fourth embodiment)
FIG. 8 is a cross-sectional view showing an ultrasonic sensor 35 according to still another embodiment of the present invention. In this ultrasonic sensor 35, the inner surface of the shallow recess 34 of the case body 23 is roughened to form a rough surface 30, and the diaphragm 24 is placed in and bonded to the shallow recess 34.
[0029]
(Fifth embodiment)
FIG. 9 is a cross-sectional view showing an ultrasonic sensor 36 according to still another embodiment of the present invention. In this ultrasonic sensor 36, the roughening process is performed only on the bonding margin of the diaphragm 24, that is, on the outer peripheral portion of the inner surface. And the diaphragm 24 is stored in the shallow hollow part 34, and the rough surface 30 is adhere | attached on the case main body 23 with the adhesive agent 29b. On the other hand, the piezoelectric vibration element 25 is bonded to a smooth portion at the center of the vibration plate 24.
[0030]
(Sixth embodiment)
FIG. 10 illustrates another method for subjecting the case body 23 to a rough surface treatment. Reference numeral 41 denotes a mold for resin-molding the case body, and input / output terminals 26 and 27 are set in the mold 41. A rough surface 43 having a rough surface is formed on a surface of the inner surface of the cavity 42 of the mold 41 on which the front end surface 23a of the case body 23 is formed. Accordingly, when the case main body 23 is molded by injecting resin into the cavity 42, the input / output terminals 26 and 27 are inserted into the case main body 23, and the front end surface 23 a of the case main body 23 is formed on the inner surface of the cavity 42. The rough surface 43 is transferred to form the rough surface 30.
[0031]
Although not shown, even when the diaphragm 24 is molded by aluminum die casting, if a rough surface with fine irregularities is formed on the inner surface of the die casting mold, the rough surface of the mold is formed during molding. It can be transferred to the diaphragm 24.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a conventional ultrasonic sensor.
FIG. 2 is a cross-sectional view showing an ultrasonic sensor according to a previous application.
FIG. 3 is a diagram showing the relationship between frequency and sensitivity in an ultrasonic sensor.
FIG. 4 is a cross-sectional view showing an ultrasonic sensor according to an embodiment of the present invention.
FIG. 5 is a diagram showing resonance frequencies of the ultrasonic sensor of the present invention that has been subjected to roughening treatment and the ultrasonic sensor that has not been subjected to roughening treatment.
FIG. 6 is a cross-sectional view showing an ultrasonic sensor according to another embodiment of the present invention.
7A and 7B are a plan view and a cross-sectional view showing an ultrasonic sensor according to another embodiment of the present invention.
FIG. 8 is a cross-sectional view showing an ultrasonic sensor according to another embodiment of the present invention.
FIG. 9 is a cross-sectional view showing an ultrasonic sensor according to another embodiment of the present invention.
FIG. 10 is a diagram illustrating another method for performing a rough surface treatment on a case body.
[Explanation of symbols]
22 Case 23 Case body 24 Diaphragm 25 Piezoelectric vibration element 29b Adhesive 30 Rough surface

Claims (4)

An ultrasonic sensor in which a piezoelectric vibration element is bonded to the inner surface of the diaphragm, and an outer peripheral portion of the diaphragm is bonded to one end opening of the case body,
The ultrasonic sensor according to claim 1, wherein a bonding surface of the case body with the diaphragm is a rough surface. An ultrasonic sensor in which a piezoelectric vibration element is bonded to the inner surface of the diaphragm, and an outer peripheral portion of the diaphragm is bonded to one end opening of the case body,
An ultrasonic sensor, wherein an adhesive surface of the diaphragm with the case body is a rough surface. The rough surface formed on the adhesive surface is formed by at least one processing means among chemical etching, sandblasting, hairline, sandpaper, and buffing, according to claim 1 or 2. Ultrasonic sensor. The rough surface provided on the bonding surface of the case body or the vibration plate is a transfer of a rough surface provided on a mold for forming the case main body or the vibration plate. The ultrasonic sensor according to 1 or 2.

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