JP6971939B2 - Ultrasonic sensor - Google Patents

Description

The present disclosure relates to an ultrasonic sensor.

Currently, ultrasonic sensors are used in clearance sonar for parking assistance. In addition, in automatic driving systems and automatic parking systems that are expected to become widespread in the future, complex systems including cameras, millimeter-wave radars, and ultrasonic sensors (clearance sonar) will be used. As such an ultrasonic sensor, a bottomed tubular case having a bottom and a tubular portion connected to the outer periphery of the bottom, a piezoelectric element attached to the inner surface of the bottom, and an opening of the case are fixed. A base (lid portion) that closes the opening is known (see, for example, Patent Document 1 and Patent Document 2).

Japanese Unexamined Patent Publication No. 5-244692 Japanese Unexamined Patent Publication No. 2007-282058

When the ultrasonic sensor emits ultrasonic waves, the bottom portion of the diaphragm vibrates by receiving the force from the piezoelectric element. At this time, a force that deforms the tubular portion located on the side surface of the case is also applied. Here, since the base (cover) is fixed to the opening of the case, the deformation of the tubular portion is suppressed, but the amplitude of the bottom of the case is also reduced, and the sound pressure and sensitivity may decrease. be.

In addition, ultrasonic sensors are required to be able to measure obstacles at a longer distance.

The present disclosure has been made in view of the above circumstances, and an object of the present invention is to provide an ultrasonic sensor having excellent sound pressure and sensitivity and capable of detecting a long distance.

The ultrasonic sensor of the present disclosure is fixed to a bottomed tubular case having a tubular portion connected to the bottom and the outer periphery of the bottom, a piezoelectric element attached to the inner surface of the bottom, and an opening of the case. It is equipped with a base that closes the opening. The tubular portion has a first region having a relatively large inner dimension and a thin thickness located on the upper side, and a second region having a relatively small inner dimension and a thick thickness located on the lower side. From the inner surface of one region to the inner surface of the second region, there is a stepped inner surface. The base has a protrusion that protrudes outward in a part of the outer peripheral portion when viewed in a plan view, and the outer dimension of the outer peripheral portion excluding the protrusion when viewed in a plan view is the first. It is smaller than the inner dimension of the area. The first region has a notch portion corresponding to the protrusion so that the protrusion is fitted when viewed in a plan view. The base is fixed to the upper end of the second region so as to have a gap between the side surface of the base and the inner surface of the first region, and the protrusion of the base and the second region The portion of the upper end facing the protrusion is bonded with the first adhesive, and the outer peripheral portion of the base excluding the protrusion and the protrusion of the upper end of the second region are joined. The non-faced portion is bonded with the second adhesive, and the young ratio of the first adhesive is larger than the young ratio of the second adhesive.

According to the ultrasonic sensor of the present disclosure, it is possible to increase the sound pressure and sensitivity and detect an object over a longer distance.

It is a partial transmission schematic plan view which shows an example of an ultrasonic sensor. It is a schematic cross-sectional view cut along line II-II shown in FIG. It is a partial transmission schematic plan view which shows another example of an ultrasonic sensor. FIG. 3 is a schematic cross-sectional view taken along the line IV-IV shown in FIG. It is a partial transmission schematic plan view which shows another example of an ultrasonic sensor. FIG. 5 is a schematic cross-sectional view cut along the VI-VI line shown in FIG.

Hereinafter, embodiments of the ultrasonic sensor will be described with reference to the accompanying drawings.

The ultrasonic sensors shown in FIGS. 1 and 2 include a bottomed tubular case 1 having a bottom portion 11 and a tubular portion 12 connected to the outer periphery of the bottom portion 11, and a piezoelectric element 2 attached to the inner surface of the bottom portion 11. It is provided with a base 3 (cover portion) that is fixed to the opening of the case 1 and closes the opening. The opening of the case 1 means a state before being closed by the base 3.

The case 1 in the present embodiment has a circular shape when viewed in a plan view, and the outer peripheral portion of the base 3 excluding the protrusion 31 has a circular shape, but the shape is particularly limited to this shape. is not it.

The tubular portion 12 constituting the case 1 has, for example, a cylindrical shape, and functions as a support for supporting the outer periphery of the bottom portion 11. The height (length) of the tubular portion 12 is, for example, 2 mm to 15 mm. Further, the inner diameter of the tubular portion 12 (the inner diameter of the second region 122 described later) is, for example, 5 mm to 30 mm, and the thickness of the tubular portion 12 (the thickness of the second region 122 described later) is, for example, 0.5 mm to 3. It is 0 mm. The tubular portion 12 is made of, for example, a metal material such as aluminum, titanium, or magnesium, or a resin material such as ABS resin, PBT resin, or PPS resin.

A piezoelectric element 2 is attached to the inner surface of the bottom portion 11, and the bottom portion 11 functions as a diaphragm vibrating due to the vibration of the piezoelectric element 2. Further, the bottom portion 11 functions as an acoustic matching layer that matches the acoustic impedance between the piezoelectric element 2 and the space when the piezoelectric element 2 emits ultrasonic waves. Here, in FIG. 2, the bottom portion 11 and the tubular portion 12 are integrally represented, but they do not have to be integrally formed. For example, the bottom portion 11 may be inserted into the opening of the tubular portion 12. The bottom portion 11 has a thickness of, for example, 0.5 mm to 5 mm in the direction perpendicular to the surface to which the piezoelectric element 2 is attached. As the material of the bottom portion 11, for example, in addition to the above-mentioned synthetic resin, a rubber-like elastic body, a carbon material, or the like can be used. Examples of the fixing method when the bottom portion 11 is inserted into the tubular portion 12 include fixing by a compressive force and a frictional force by pushing the bottom portion 11 into the opening, and fixing by an adhesive.

The base 3 is made of, for example, the same material as the tubular portion 12. For example, two terminals 4 are inserted through the base 3, and the surface electrodes of the piezoelectric element 2 and an external circuit are electrically connected via the terminals 4 and wiring. The terminal 4 is, for example, a metal rod-shaped body having a diameter of 0.2 mm to 3.0 mm and a length of 5.0 mm to 15.0 mm.

The piezoelectric element 2 is attached to the bottom portion 11 via, for example, an adhesive. The piezoelectric element 2 is, for example, a plate-shaped body having a rectangular shape, a square shape, a circular shape, or the like in a plan view. For example, when viewed in a plan view, it has a square shape with a side of 4.0 mm to 6.0 mm and a thickness of 0.1 mm to 3.0 mm.
Can be used.

The piezoelectric element 2 includes a single-plate piezoelectric body made of piezoelectric ceramics such as lead zirconate titanate, and a surface electrode made of a metal such as silver provided on the upper and lower surfaces of the piezoelectric body. good. Further, the piezoelectric element 2 may include, for example, a laminate in which a piezoelectric layer and an internal electrode layer are laminated, and surface electrodes provided on the upper and lower surfaces of the laminate. As the adhesive, for example, an epoxy-based adhesive or an acrylic-based adhesive can be used.

The tubular portion 12 has a first region 121 having a relatively large inner dimension and a thin thickness located on the upper side, and a second region 122 having a relatively small inner dimension and a thick thickness located on the lower side. There is. Then, from the inner surface of the first region 121 to the inner surface of the second region 122, there is a stepped inner surface. Here, the difference from the radial width of the upper end of the second region 122 ((inner diameter of the first region 121 − inner diameter of the second region 122) / 2) is, for example, 0.25 mm to 2.0 mm.

The outer surface of the first region 121 and the outer surface of the second region 122 are usually flush with each other, but are not particularly limited. Further, the thickness t1 of the first region 121 is set in the range of, for example, 30 to 70% of the thickness t2 of the second region 122, and the difference between the thickness t2 of the second region 122 and the thickness t1 of the first region 121 (t2). -T1) is set to, for example, 0.15 to 2.1 mm.

The base 3 has a protrusion 31 that protrudes outward in a part of the outer peripheral portion when viewed in a plan view, and the outer dimension of the outer peripheral portion excluding the protrusion 31 when viewed in a plan view is the first. It is smaller than the inner dimension of the region 121. Further, the first region 121 has a notch portion 1210 notched corresponding to the protrusion 31 so that the protrusion 31 is fitted when viewed in a plan view. Further, the base 3 is fixed to the upper end of the second region 122 so as to have a gap between the side surface of the base 3 and the inner surface of the first region 121. The width of the protrusion 31 along the circumferential direction of the base 3 is, for example, 2.0 mm to 4.0 mm, and the protrusion distance is, for example, 0.5 mm to 3.0 mm.

Here, since the base 3 is fixed to the upper end of the second region 122, the outer diameter of the outer peripheral portion of the base 3 excluding the protrusion 31 is shorter than the inner diameter of the first region 121, and the second region 122 It is longer than the inner diameter of. The gap formed between the side surface of the base 3 and the inner surface of the first region 121 is, for example, a width of 5 to 50% of the difference between the thickness of the second region 122 and the thickness of the first region 121.

Then, the protrusion 31 of the base 3 and the portion of the upper end of the second region 122 facing the protrusion 31 are joined with the first adhesive 51. Further, the outer peripheral portion of the base 3 excluding the protrusion 31 and the portion of the upper end of the second region 122 that does not face the protrusion 31 are bonded with the second adhesive 52. Further, the Young's modulus of the first adhesive 51 is larger than the Young's modulus of the second adhesive 52.

Conventionally, there is no gap between the side surface of the base 3 (cover portion) and the inner surface of the first region 121, and in the conventional ultrasonic sensor having a structure in which the base 3 is pressed from the side surface, deformation of the case is hindered. It was a structure like this.

On the other hand, an ultrasonic sensor having a gap between the side surface of the base 3 and the inner surface of the first region 121 and having a structure in which the outer peripheral portion of the base 3 and the upper end of the second region 122 are bonded with an adhesive. Has a structure that does not hinder the deformation of the case. However, in a structure in which a gap is provided between the side surface of the base 3 and the inner surface of the first region 121, and the outer peripheral portion of the base 3 and the upper end of the second region 122 are joined with an adhesive, the joining strength is high. There is also the problem that it is low and easy to come off.

Therefore, a part of the outer peripheral portion of the base 3 has a protrusion 31 protruding outward, and the protrusion 31 and the notch 1210 are joined in correspondence with each other, and only that portion is younger than the other parts. By joining with a high-ratio (hard) adhesive, it is possible to make a partially strong bond and increase the joint strength, and at the same time, it is possible to easily deform other parts.

As the first adhesive 51 that is hard after curing with a relatively large Young's modulus, for example, an epoxy adhesive, an acrylic adhesive, or the like can be used. As the first adhesive 51, for example, one having a Young's modulus of 1 GPa or more may be used.

On the other hand, as the second adhesive 52 that is soft after curing with a relatively small Young's modulus, for example, a butyl rubber adhesive, an acrylic adhesive, a modified silicone adhesive, or the like can be used. As the second adhesive 52, for example, one having a Young's modulus of 100 MPa or less may be used.

Here, as shown in FIGS. 3 and 4, the upper end of the second region 122 has a first groove 1221 along the circumferential direction at a portion not facing the protrusion 31, and a second bond is formed. The agent 52 may be provided so as to be embedded in the first groove 1221. At this time, it is preferable that the second adhesive 52 is embedded in the first groove 1221 and is provided around the first groove 1221 along the first groove 1221. The opening width (diameter width) of the first groove 1221 is, for example, 0.1 mm to 1.8 mm. The depth of the first groove 1221 is, for example, 0.1 mm to 1.5 mm.

By providing the second adhesive 52 so as to be embedded in the first groove 1221, more soft second adhesive 52 can be provided after curing with a small Young's modulus, and the case 1 can be easily deformed. can do.

Further, as shown in FIGS. 5 and 6, the portion facing the protrusion 31 is also separated from the first groove 1221 provided along the circumferential direction in the portion not facing the protrusion 31. The groove 1222 of 2 is provided, and the first adhesive 51 is provided in the second groove 1222 provided in the portion facing the protrusion 31, and is provided in the portion not facing the protrusion 31. The second adhesive 52 may be provided in the first groove 1221. The opening width (diameter width) of the second groove 1222 is, for example, 0.1 mm to 2.5 mm. The depth of the second groove 1222 is, for example, 0.1 mm to 1.5 mm.

With this configuration, the region where the first adhesive 51 is provided and the region where the second adhesive 52 is provided can be partitioned, and the hard adhesive having a large Young's modulus and the soft adhesive having a small Young's modulus are mixed. It is possible to realize a highly accurate ultrasonic sensor with less deformation variation.

1 Case 11 Bottom 12 Cylindrical part 121 First area 122 Second area 1221 First groove 1222 Second groove 2 Piezoelectric element 3 Base 31 Projection part 4 Terminal 51 First adhesive 52 Second adhesive

Claims (4)

A bottomed tubular case having a bottom and a tubular portion connected to the outer periphery of the bottom, a piezoelectric element attached to the inner surface of the bottom, and a piezoelectric element attached to the inner surface of the bottom are fixed to the opening of the case to close the opening. The cylindrical portion is provided with a first region having a relatively large inner size and a thin thickness located on the upper side, and a second region having a relatively small inner size and a thick thickness located on the lower side. The base has a stepped inner surface from the inner surface of the first region to the inner surface of the second region, and the base protrudes outward in a part of the outer peripheral portion when viewed in a plan view. In addition to having a protrusion, the outer dimension of the outer peripheral portion excluding the protrusion when viewed in a plan view is smaller than the inner dimension of the first region, and the first region is when viewed in a plan view. It has a notch corresponding to the protrusion so that the protrusion can be fitted, and the base has a gap between the side surface of the base and the inner surface of the first region. Is fixed to the upper end of the second region, and the protrusion of the base and the portion of the upper end of the second region facing the protrusion are bonded with the first adhesive. At the same time, the outer peripheral portion of the base excluding the protrusion and the portion of the upper end of the second region that does not face the protrusion are joined with the second adhesive, and the first adhesive is used. The ultrasonic sensor is characterized in that the young ratio of the second adhesive is larger than the young ratio of the second adhesive. The upper end of the second region has a groove along the circumferential direction in a portion not facing the protrusion, and the second adhesive is provided so as to be embedded in the groove. The ultrasonic sensor according to claim 1. The groove is separated from the groove provided along the circumferential direction in the portion not facing the protrusion, and the groove is also provided in the portion facing the protrusion, and is provided in the portion facing the protrusion. The second aspect of claim 2, wherein the first adhesive is provided in the groove, and the second adhesive is provided in the groove provided in a portion not facing the protrusion. Ultrasonic sensor. Any of claims 1 to 3, wherein the case has a circular shape when viewed in a plan view, and the outer peripheral portion of the base excluding the protrusion is circular. Ultrasonic sensor described in Crab.

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