JP2006352829A - Ultrasonic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an ultrasonic sensor of a structure where a foaming resin is filled uniformly in a housing to achieve a good characteristic. <P>SOLUTION: The ultrasonic sensor 10 includes the cylindrical case 12 with a bottom 12a. A piezo-electric element 18 is adhered to the bottom 12a in the case 12. Further, a felt 22 is adhered on the piezo-electric element 18. A lid member 24 constituted by a holding part 26 and a substrate 28 harder than the holding part 26 are fit into the opening of the case 12. Wires 38a and 38b are connected to terminals 36a and 36b press-fitted in the substrate 28, and the terminals 36a and 36b are electrically connected to the piezo-electric element 18. As an excessive foaming resin 42 is extruded outside from a through-hole 40 formed in the holding part 26 by pouring the resin before foaming from the through-hole 40 to foam it, the foaming resin 42 fills up the case 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic sensor, and more particularly to an ultrasonic sensor used for, for example, a back sonar of an automobile.

  FIG. 6 is an illustrative view showing an example of a conventional ultrasonic sensor. The ultrasonic sensor 1 includes a bottomed cylindrical case 2 made of aluminum or the like. One surface of the piezoelectric element 3 is joined to the bottom surface inside the case 2. A foamable resin 4 such as foamable silicon is filled in almost the entire interior of the case 2 so as to cover the piezoelectric element 3. Further, a substrate 6 having terminals 5 a and 5 b is attached to the opening of the case 2 so as to cover the foamable resin 4. Electrodes 7a and 7b connected to the terminals 5a and 5b are formed on both surfaces of the substrate 6, respectively. One terminal 5 a is connected to the other surface of the piezoelectric element 3 by an electrode 7 a and a wire 8 formed inside the substrate 6. The other terminal 5 b is connected to one surface of the piezoelectric element 2 via the case 2 by an electrode 7 b and solder 9 formed outside the substrate 6.

  When measuring the distance to the object to be detected using the ultrasonic sensor 1, the piezoelectric element 3 is excited by applying a driving voltage to the terminals 5a and 5b. Due to the vibration of the piezoelectric element 3, the bottom surface of the case 2 also vibrates, and ultrasonic waves are emitted in a direction perpendicular to the bottom surface as shown by arrows in FIG. When the ultrasonic wave emitted from the ultrasonic sensor 1 is reflected by the object to be detected and reaches the ultrasonic sensor 1, the piezoelectric element 3 vibrates and is converted into an electric signal, and the electric signal is output from the terminals 5a and 5b. . Therefore, the distance from the ultrasonic sensor 1 to the object to be detected can be measured by measuring the time from when the drive voltage is applied until the electrical signal is output.

  In the ultrasonic sensor 1, vibration of the entire case 2 can be suppressed by filling the case 2 with the foamable resin 4. In addition, ultrasonic waves generated inside the case 2 are scattered and absorbed by a large number of foam holes present in the foamable resin 4. Thereby, both the vibration of case 2 itself and the ultrasonic wave which remains inside case 2 can be suppressed efficiently, and a reverberation characteristic can be improved (refer patent document 1).

JP-A-11-266498

  When the foamable resin is filled in the case, if the resin is put into the case and foamed before attaching the substrate to the case, the foamable resin comes out to the opening side of the case and hardly any internal pressure is applied. Therefore, the foamable resin may not be uniformly filled up to the corner of the case. When the filling unevenness of the foamable resin in the case is large, the reverberation characteristics are deteriorated. Also, if the resin is put into the case and foamed after attaching the substrate to the case, the internal pressure will increase and the foaming resin will push the substrate from the inside of the case, causing the substrate to deform and the foaming resin to be uniformly filled There is.

  Therefore, a main object of the present invention is to provide an ultrasonic sensor having a structure in which a foamable resin can be uniformly filled in a case and good characteristics can be obtained.

The present invention includes a bottomed cylindrical case, a piezoelectric element formed on a bottom surface inside the case, a foamable resin filled in the case so as to cover the piezoelectric element, and a lid attached to the opening of the case The ultrasonic sensor includes a member, a terminal attached to the lid member so as to be electrically connected to the piezoelectric element, and a through hole formed in the lid member.
By forming the through hole in the lid member, the resin can be injected from the through hole into the case after the lid member is attached to the case in which the piezoelectric element is formed. Then, by foaming the resin in the case, the case is filled with the foamable resin, and the excess foamable resin is pushed out from the through hole formed in the lid member. As a result, the foamable resin is applied with an appropriate internal pressure and spreads into the case, and the foamable resin can be uniformly filled in the case.

In such an ultrasonic sensor, when the sectional area of the opening of the case is Sc and the sectional area of the through hole formed in the lid member is Sh, Sh ≦ 5 (mm ² ) and 0.02 ≦ Sh / Sc ≦ It is desirable to be in the range of 0.3.
By setting it as such a range, a moderate internal pressure is applied when foaming resin, and a foamable resin can be filled uniformly in a case. If the cross-sectional area of the through-hole is too large, when the resin injected into the case is foamed, the foamable resin is easily pushed out of the through-hole, reducing the pressure in the case and expanding to the corner of the case. The resin cannot be filled uniformly. Also, if the cross-sectional area of the through hole is too small, when the resin injected into the case is foamed, the foaming resin is not extruded from the through hole, the internal pressure increases, the lid member is deformed, May not be uniformly filled.

Further, the lid member may be composed of a soft fixing portion fixed to the case and a substrate harder than the fixing portion formed in the fixing portion, and a terminal may be attached to the substrate.
If a hard material is used as the lid member, the fixing strength of the terminal can be increased. However, even if the fixing part to be fixed to the case is made of a relatively soft material, the substrate to which the terminal is attached is made of a hard material. By doing so, the fixing strength of the terminal can be increased.

When the lid member is configured by the fixing portion and the substrate, the case and the fixing portion can be fixed by fitting, and the fixing portion and the substrate can be fixed by fitting.
By fixing the case and the fixing part by fitting, and fixing the fixing part and the substrate by fitting, these can be fixed easily. Moreover, the position of the board | substrate with respect to a case can be decided by fixation by fitting, and the positional accuracy of a terminal can be made accurate.

Moreover, when a cover member is comprised with a fixing | fixed part and a board | substrate, it is preferable that the opening part of a case, a fixing | fixed part, and a board | substrate are formed circularly, and the opening part of a case, a fixing | fixed part, and a board | substrate are arrange | positioned concentrically.
By making the opening of the case, the fixing part and the substrate circular and arranging them concentrically, a uniform stress is applied from the fixing part to the substrate. Therefore, the substrate is not displaced with respect to the case and the fixed portion, the positional accuracy of the terminal attached to the substrate is increased, and the terminal can be arranged at the designed position.

  According to this invention, the foamable resin is injected into the case with an appropriate internal pressure while extruding excess foamable resin from the through-hole formed in the lid member by injecting the resin into the case and making it foam. Can be spread out. Therefore, the foamable resin can be uniformly filled in the case, and the reverberation characteristics of the ultrasonic sensor can be improved.

  The above object, other objects, features, and advantages of the present invention will become more apparent from the following description of the best mode for carrying out the invention with reference to the drawings.

  FIG. 1 is a plan view showing an example of the ultrasonic sensor of the present invention, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB in FIG. The ultrasonic sensor 10 includes a bottomed cylindrical case 12, for example. Therefore, the case 12 is composed of the bottom surface portion 12a and the side wall 12b. Case 12 is formed of a metal material such as aluminum, for example. As shown in FIG. 4, the cavity portion 14 inside the case 12 is formed so that, for example, both ends are arcuate and a straight and elongated cross-sectional shape is formed therebetween. Therefore, the wall thickness at one of the facing portions of the side wall 12b of the case 12 is thin, and the wall thickness at the facing portion in the direction orthogonal thereto is thick. Note that the shape of the cavity 14 is designed according to desired characteristics because the way in which the ultrasonic wave emitted from the ultrasonic sensor 10 spreads is determined by the shape of the cavity 14.

  A concave portion 16 is formed on the outside of the side wall 12b of the case 12 in the thick portion of the case 12. The recess 16 is formed from the opening side end of the case 12 toward the bottom surface 12a. The concave portion 16 is formed shallow on the opening side of the case 12 and deeply formed on the bottom surface portion 12a side. Therefore, a step 16 a that is substantially parallel to the opening side end of the case 12 is formed in the recess 16. The recess 16 is for fixing a lid member described later.

  Inside the case 12, the piezoelectric element 18 is attached to the inner surface of the bottom surface portion 12a. The piezoelectric element 18 is formed by forming electrodes on both surfaces of a piezoelectric substrate such as a disk shape or a square plate shape. Then, the electrode on one surface side of the piezoelectric element 18 is bonded to the bottom surface portion 12a with a conductive adhesive or the like. Further, the felt 22 is bonded onto the electrode on the other surface side of the piezoelectric element 18 via the adhesive layer 20. The felt 22 is used to absorb ultrasonic waves from the piezoelectric element 18 toward the inside of the case 12 and also serves to prevent the vibration of the piezoelectric element 18 from being hindered by a foamable resin described later.

  A lid member 24 is attached to the opening of the case 12. The lid member 24 includes a fixing portion 26 for fixing to the case 12 and a substrate 28 formed at an intermediate portion of the fixing portion 26. The fixing portion 26 is formed of a relatively soft resin material such as silicon rubber. The fixing portion 26 is formed in a disk shape having an outer diameter substantially the same as the outer diameter of the case 12. And the convex part 30 is formed so that it may extend in the thickness direction of the fixing | fixed part 26 in the part which the disk-shaped fixing | fixed part 26 opposes. The convex part 30 is formed thin on the fixed part 26 side, and a part away from the fixed part 26 is formed thick. Therefore, a step portion 30 a is formed in the middle portion of the convex portion 30.

  The fixing portion 26 is attached to the opening of the case 12. At this time, the convex portion 30 of the fixing portion 26 is fitted into the concave portion 16 of the case 12 by pressing the fixing portion 26 toward the opening of the case 12. Here, the fixing portion 26 is fixed to the case 12 by the step portion 16 a of the concave portion 16 and the step portion 30 a of the convex portion 30 engaging with each other. At this time, by forming the fixing portion 26 with a relatively soft resin material such as silicon rubber, the fitting between the convex portion 30 of the fixing portion 26 and the concave portion 16 of the case 12 is facilitated.

  For example, a rectangular hole 32 is formed in the intermediate portion of the fixing portion 26. A convex strip 26 a is formed on the inner wall of the hole 32 at an intermediate portion in the thickness direction of the fixed portion 26. The protruding portion 26 a is formed so as to go around the hole 32. The board 28 is fitted into the hole 32. The substrate 28 is formed of a material harder than silicon rubber such as PPS (polyphenylene sulfide). The substrate 28 is formed in a square shape corresponding to the shape of the hole 32 of the fixing portion 26. Then, a concave strip portion 28a is formed around the substrate 28 corresponding to the convex strip portion 26a. Therefore, when the substrate 28 is pushed into the hole 32 of the fixing portion 26, the protruding portion 26 a of the fixing portion 26 and the recessed portion 28 a of the substrate 28 are fitted together, and the substrate 28 is fixed to the fixing portion 26. Such fitting between the substrate 28 and the fixing portion 26 can be easily performed by forming the fixing portion 26 with a relatively soft resin material.

  Two terminal holes 34 are formed in the substrate 28, and terminals 36 a and 36 b are press-fitted into these terminal holes 34. The terminals 36 a and 36 b are made of a conductive material such as metal and are bent in a crank shape outside the lid member 24. The bent portions of the terminals 36a and 36b prevent the terminals 36a and 36b from falling into the through holes formed in the printed board when the ultrasonic sensor 10 is mounted on the printed board or the like, and the case 12 portion is separated from the printed board. This is to make it float.

  Inside the case 12, one terminal 36 a is connected to the case 12 via a wire 38 a and is electrically connected to an electrode on one surface side of the piezoelectric element 18 via the case 12. The other terminal 36b is electrically connected to the electrode on the other surface side of the piezoelectric element 18 through the wire 38b. The case 12, the piezoelectric element 18, the terminals 36a and 36b, and the wires 38a and 38b are connected, for example, by soldering.

In addition, in the fixing portion 26, for example, two circular through holes 40 are formed on both sides of the substrate 28. Here, when the sectional area of the opening of the case 12 is Sc and the sectional area of the through hole 40 formed in the fixing portion 26 of the lid member 24 is Sh, Sh ≦ 5 (mm ² ) and 0.02 ≦ Sh /Sc≦0.3.

  The inside of the case 12 and the inside of the through hole 40 formed in the fixing portion 26 are filled with a foamable resin 42 such as foamable silicon. The foamable resin 42 is filled by injecting resin before foaming from one of the through holes 40 and heating and curing it. At this time, by forming the cross-sectional area of the through hole 40 so as to be in the above-described range, the excess foamable resin 42 is pushed out from the through hole 40, and in the case 12, an appropriate amount is obtained. The foamable resin 42 is expanded by the internal pressure. Therefore, the foamable resin 42 can be filled up to the corner inside the case 12, and the foamable resin 42 can be filled uniformly in the case 12.

  If the cross-sectional area of the through hole 40 is too large, the foamable resin 42 is easily pushed out of the through hole 42 when the resin injected into the case 12 is foamed, and an appropriate internal pressure is not applied. The foamable resin 42 may not be filled up to the corners in the case 12. On the other hand, if the cross-sectional area of the through hole 42 is too small, when the resin injected into the case 12 is foamed, excess foamable resin 42 is not pushed out of the through hole 40, and the lid member 24 is lifted or deformed. In some cases, the foamable resin 42 may not be uniformly filled.

  When the ultrasonic sensor 10 is used as an automobile back sonar or the like, the piezoelectric element 18 is excited by applying a driving voltage to the terminals 36a and 36b. At this time, even if the periphery of the piezoelectric element 18 is covered with the foaming resin 42, the vibration region of the piezoelectric element 18 is secured by the felt 22 bonded to the piezoelectric element 18. Due to the vibration of the piezoelectric element 18, the bottom surface portion 12 a of the case 12 also vibrates, and ultrasonic waves are emitted in a direction orthogonal to the bottom surface portion 12 a. When the ultrasonic wave emitted from the ultrasonic sensor 10 is reflected by the object to be detected and reaches the ultrasonic sensor 10, the piezoelectric element 18 vibrates and is converted into an electric signal, and the electric signal is output from the terminals 36a and 36b. The Therefore, the distance from the ultrasonic sensor 10 to the object to be detected can be measured by measuring the time from when the drive voltage is applied until the electrical signal is output.

  In the ultrasonic sensor 10, vibration of the entire case 12 can be suppressed because the foamable resin 42 is uniformly filled in the case 12. In addition, ultrasonic waves from the piezoelectric element 18 toward the inside of the case 12 are absorbed by the felt 22, but ultrasonic waves that have passed through the felt 22 are scattered and absorbed by a large number of foam holes present in the foamable resin 42. . Thereby, both the vibration of case 12 itself and the ultrasonic wave which stays inside case 12 can be suppressed efficiently, and a reverberation characteristic can be improved.

  In such an ultrasonic sensor 10, as shown in FIGS. 5A, 5B, and 5C, the case 12 has a circular opening, and a relatively soft fixing portion 26 is fitted into the opening. The lid member 24 may be attached. The fixing portion 26 is formed in a disc shape, and concentric fitting convex portions 26b and 26c are formed on the peripheral portion and the inner peripheral side thereof. By forming the fitting convex portions 26b and 26c concentrically, a circular groove is formed between the fitting convex portions 26b and 26c. The fixing portion 26 is attached to the case 12 by fitting the opening side end portion of the side wall 12b of the case 12 into the groove. When the cavity 14 inside the case 12 has a shape other than a circle, the side wall of the case 12 is formed by forming the cavity 14 in a portion that enters the inside from the opening side end of the side wall 12b of the circular case 12. The shape of the opening side end of 12b can be made circular. Therefore, regardless of the shape of the cavity portion 14, the circular fixing portion 26 can be attached to the case 12.

  Further, the hole 32 of the fixing portion 26 and the substrate 28 attached to the fixing portion 26 are also formed in a circular shape. Moreover, in the ultrasonic sensor 10 shown in FIG. 5, the through-hole 40 is formed in the center part of a board | substrate. And the opening part of case 12, the fixing | fixed part 26, and the board | substrate 28 are arrange | positioned concentrically.

  As described above, by forming the opening portion of the case 12, the fixing portion 26, and the substrate 28 in a circular shape and arranging them concentrically, the stress applied to the substrate 28 from the fixing portion 26 becomes uniform. Therefore, the substrate 28 is not displaced with respect to the case 12 and the fixed portion 26, and the positional accuracy of the terminals 36a and 36b attached to the substrate 28 is improved. Therefore, the ultrasonic sensor 10 having the terminals 36a and 36b at the designed positions can be obtained, and the ultrasonic sensor 10 can be automatically mounted.

  In the above-described example, the lid member 24 is formed by combining the relatively soft fixing portion 26 and the substrate 28 that is harder than the fixing portion 26. However, the lid member 24 may be formed of one type of material. Good. In this case, in order to increase the fixing strength of the terminals 36a and 36b, it is desirable to form the lid member 24 from a relatively hard material.

  An ultrasonic sensor having the structure shown in FIGS. 1 to 4 was produced. First, the piezoelectric element 18 was attached to the inner bottom surface of the aluminum case 12. Then, one ends of the wires 38 a and 38 b were soldered to the piezoelectric element 18 and the side wall of the case 12. A felt 22 is bonded to the piezoelectric element 18. On the other hand, the terminals 36a and 36b were press-fitted into the terminal holes 34 formed in the substrate 28 made of PPS, and the substrate 28 was fitted into the fixing portion 26 made of silicon rubber. The other ends of the wires 38 a and 38 b were soldered to the terminals 36 a and 36 b press-fitted into the substrate 28, and the fixing portion 26 was fitted into the case 12. Then, foamable silicon was injected into the case 12 from the through hole 40 formed in the fixed portion 26, and was heated and foamed and cured at 60 ° C. At this time, the foamable silicon extruded from the through hole 40 was removed, and an ultrasonic sensor was produced. For such an ultrasonic sensor, the cross-sectional area of the through-hole 40 formed in the fixing portion 26 of the lid member 24 was changed, and the filling state of the foamable silicon in the case 12 was observed to determine whether it was good or bad. The results are shown in Table 1.

As can be seen from the sample numbers 3, 6, and 7 in Table 1, the cross-sectional area Sh of the through-hole 40 exceeds 5 (mm ² ), or the cross-sectional area Sh of the through-hole 40 and the cross-sectional area Sc of the opening of the case 12 When the ratio Sh / Sc exceeds 0.3, when foaming silicon is foamed, the foaming silicon is easily pushed out from the through hole 40, and the internal pressure in the case 12 cannot be sufficiently obtained. The foamable silicon could not be uniformly filled inside. Further, as can be seen from the sample number 1 in Table 1, when Sh / Sc is smaller than 0.02, excess foamable silicon is not pushed out from the through hole 40, and the internal pressure in the case 12 is increased, and foamability is increased. The filling of silicon became uneven, and the fixing portion 26 of the lid member 24 was deformed. On the other hand, in the range of Sh ≦ 5 (mm ² ) and 0.02 ≦ Sh / Sc ≦ 0.3, the foamable silicon was uniformly filled in the case 12.

  An ultrasonic sensor having the structure shown in FIG. 5 was produced. An ultrasonic sensor was manufactured in the same manner as in Example 1 except that the opening of the case 12, the fixing portion 26, and the substrate 28 were formed in a circular shape and these were arranged concentrically. As a comparative example, an ultrasonic sensor in which the shape of the substrate 28 was an ellipse and the terminals 36 a and 36 b were arranged in the longitudinal direction of the substrate 28 was manufactured. About these ultrasonic sensors, it measured about the positional accuracy of terminal 36a, 36b. Regarding the positional accuracy of the terminals 36a and 36b, the center of the case 12 was used as a reference, and the amount of deviation from the design position of the terminals 36a and 36b from this reference was measured. The measurement of the amount of deviation was performed in two directions (X direction and Y direction) in which the terminals 36a and 36b are arranged side by side and in the direction orthogonal thereto. The number of measurement samples was 10 for both the ultrasonic sensor of the present invention and the comparative example, and the average value and standard deviation (σn−1) were calculated and shown in Table 2.

  As can be seen from Table 2, in the ultrasonic sensor according to the present invention, the terminal has a very high positional accuracy even though it is a simple assembly method in which the substrate 28 is simply fitted into the fixing portion 26 formed of silicon rubber. 36a and 36b could be arranged.

It is a top view which shows an example of the ultrasonic sensor of this invention. It is AA sectional drawing of the ultrasonic sensor shown in FIG. It is BB sectional drawing of the ultrasonic sensor shown in FIG. It is a disassembled perspective view of the ultrasonic sensor shown in FIG. (A) is sectional drawing which shows the other example of the ultrasonic sensor of this invention, (B) is a top view of the fixing | fixed part used for it, (C) is a top view of the board | substrate used for it. It is an illustration figure which shows an example of the conventional ultrasonic sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ultrasonic sensor 12 Case 14 Cavity part 16 Concave part 18 Piezoelectric element 24 Lid member 26 Fixing part 28 Substrate 30 Protrusion part 36a, 36b Terminal 40 Through-hole 42 Foamable resin

Claims (5)

Bottomed cylindrical case,
A piezoelectric element formed on the bottom surface inside the case,
A foamable resin filled in the case so as to cover the piezoelectric element;
A lid member attached to the opening of the case;
An ultrasonic sensor comprising: a terminal attached to the lid member so as to be electrically connected to the piezoelectric element; and a through-hole formed in the lid member. The range of Sh ≦ 5 (mm ² ) and 0.02 ≦ Sh / Sc ≦ 0.3, where Sc is the sectional area of the opening of the case and Sh is the sectional area of the through hole formed in the lid member. The ultrasonic sensor according to claim 1, wherein The lid member includes a soft fixing portion fixed to the case, and a substrate harder than the fixing portion formed in the fixing portion,
The ultrasonic sensor according to claim 1, wherein the terminal is attached to the substrate.   The ultrasonic sensor according to claim 3, wherein the case and the fixing portion are fixed by fitting, and the fixing portion and the substrate are fixed by fitting.   The ultrasonic wave according to claim 3 or 4, wherein the opening portion of the case, the fixing portion, and the substrate are formed in a circular shape, and the opening portion, the fixing portion, and the substrate of the case are arranged concentrically. Sensor.

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