Ultrasonic sensor

Abstract

To realize an ultrasonic sensor capable of suppressing clogging of foreign matter in a waveguide while protecting an ultrasonic element.SOLUTION: An ultrasonic element 2 is housed in a housing space 46 of a case member 4 and communicates with a branch waveguide 43 provided in a base material 41 of the case member 4. The base material 41 of the case member 4 has a penetrating waveguide 42 that is a through hole formed in a portion that does not communicate with the housing space 46. The branch waveguide 43 is branched and extended from the penetrating waveguide 42 toward the ultrasonic element 2 side.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an ultrasonic sensor.

Background Art

[0002] Conventionally, an ultrasonic sensor that includes at least one ultrasonic element for transmission (hereinafter referred to as a "transmission element") and a plurality of ultrasonic elements for reception (hereinafter referred to as "reception elements") and is capable of detecting the distance and direction to an obstacle is known (for example, Patent Document 1). The ultrasonic sensor described in Patent Document 1 includes a base material, a transmission element, a plurality of reception elements arranged at a predetermined interval within the base material, and a waveguide provided on the base material for guiding ultrasonic waves between the outside and the outer surface of the reception element. In this ultrasonic sensor, the ultrasonic elements are protected by the base material, and while achieving both good appearance and impact resistance, the waveguide guides the ultrasonic waves reflected outside to the reception elements, thereby constituting an object detection device capable of detecting the distance and azimuth to an obstacle or the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In this ultrasonic sensor, only one end of the waveguide on the side opposite to the ultrasonic element communicates with the outside. When foreign matter enters the waveguide from the outside, the structure makes it difficult to discharge the foreign matter. For example, when applied to in-vehicle use in an automobile or the like, if foreign matter caused by the in-vehicle environment such as water, mud, or wax enters the waveguide, there is a risk of clogging in the waveguide of the ultrasonic sensor. In this case, not only does the propagation of ultrasonic waves in the waveguide be inhibited, resulting in a decrease in the accuracy of object detection, but also the reliability of the ultrasonic sensor decreases.

[0005] In view of the above points, an object of the present invention is to provide an ultrasonic sensor that can suppress clogging of foreign matter in a waveguide while protecting an ultrasonic element and has improved reliability.

Means for Solving the Problems

[0006] To achieve the above object, the ultrasonic sensor according to claim 1, 5 comprises an ultrasonic element (2) having a plurality of vibrating parts (25), a base material (41), a storage space (46) in which the ultrasonic element is stored, a through waveguide (42) which is a through hole provided in a part of the base material that does not communicate with the storage space, and a case material (4) having a plurality of branch waveguides (43) that branch from the wall surface of the through waveguide and extend toward the ultrasonic element and communicate with the vibrating parts. The ultrasonic sensor according to claim 1 further includes a protective film (5) made of a porous body that transmits sound waves. The protective film is disposed in the branch waveguide. The direction along which the branch waveguide extends from the wall surface of the through waveguide is defined as the branch direction (DR1). With the vertical direction as the downward direction and the direction opposite to the vertical direction as the upward direction, the state in which the branch directions are aligned upward is defined as the installation state. The through waveguide has two openings (42a, 42b) facing the external space. Taking the opening (42a) into which the reflected wave of the transmitted wave transmitted to the outside enters among the two openings as the inlet, the opening of the branch waveguide on the side of the through waveguide is located downward of the lower end of the inlet in the installation state. Also, the ultrasonic sensor according to claim 5 defines the direction along which the branch waveguide extends from the wall surface of the through waveguide as the branch direction (DR1). With the vertical direction as the downward direction and the direction opposite to the vertical direction as the upward direction, the state in which the branch directions are aligned upward is defined as the installation state. The through waveguide has two openings (42a, 42b) facing the external space. The width of one opening is larger than the width of the other opening. The bottom surface (42c) in the installation state is inclined with respect to the plane with the upward direction as the normal. Taking the opening (42a) into which the reflected wave of the transmitted wave transmitted to the outside enters among the two openings as the inlet and the other opening (42b) as the outlet, the bottom surface of the through waveguide is inclined such that the side of the outlet is located upward of the side of the inlet.

[0007] As a result, an ultrasonic sensor is obtained in which the ultrasonic element is housed in a case material provided with a waveguide, and transmission and reception waves are propagated through the through waveguide and the branch waveguides branched therefrom. In this ultrasonic sensor, the through waveguide faces the external space, and even when foreign matter enters the through waveguide from one opening, the foreign matter can be discharged from the one opening or the other opening. Further, since the branch waveguide through which the transmission wave generated by the ultrasonic element is directly propagated first is provided in the middle of the through waveguide, even if foreign matter enters the through waveguide, clogging due to the foreign matter does not occur. Therefore, this ultrasonic sensor has a structure that can suppress clogging of foreign matter in the waveguide while protecting the ultrasonic element, and has improved reliability.

[0008] The reference numerals in parentheses attached to each component etc. show an example of the correspondence relationship between the component etc. and the specific components etc. described in the embodiments described later.

Brief Description of the Drawings

[0009]

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Best Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.

[0011] (First Embodiment) The ultrasonic sensor 1 of the first embodiment will be described with reference to FIGS. 1 to 3. The ultrasonic sensor 1 is preferably used, for example, as an object detection device mounted on a vehicle such as an automobile to detect an object such as an external obstacle. Of course, it can also be applied to other uses.

[0012] In FIG. 1, a part of the outer contour in a different cross section of the ultrasonic element 2, the mounting substrate 3, and the base material 41, which will be described later, is shown by a broken line. In FIG. 2, the region corresponding to the outer contour of the ultrasonic element 2 on one surface 3a of the mounting substrate 3 and the outer contour of the diaphragm 25, which will be described later and cannot be seen at the angle shown in FIG. 2 of the ultrasonic element 2 are shown by broken lines, respectively. In FIG. 2, the auxiliary lines indicating the corresponding positions of the ultrasonic element 2 and the mounting substrate 3 are shown by a two-dot chain line.

[0013] The ultrasonic sensor 1 of the present embodiment includes, for example, as shown in FIG. 1, an ultrasonic element 2, a mounting substrate 3, and a case material 4, and the ultrasonic element 2 and the mounting substrate 3 are housed in the housing space 46 of the case material 4. The ultrasonic sensor 1 has a through waveguide 42 and a branched waveguide 43 branched therefrom formed in the case material 4, and a diaphragm 25 that functions as a vibrating portion of the ultrasonic element 2 communicates with the external space through the branched waveguide 43 and the through waveguide 42.

[0014] The ultrasonic element 2 is, for example, as shown in FIG. 2, formed in a rectangular plate shape, has a plurality of diaphragms 25 that can vibrate at a predetermined frequency, and is fixed to the mounting substrate 3 with an adhesive or the like (not shown). The ultrasonic element 2 is configured, for example, as shown in FIG. 3, using an SOI (Silicon on Insulator) substrate in which a support substrate 21, a buried insulating film 22, and a semiconductor layer 23 are laminated in this order. The ultrasonic element 2 is provided, for example, with a recess 24 that penetrates the support substrate 21 and the buried insulating film 22 and exposes the semiconductor layer 23, and the portion of the semiconductor layer 23 corresponding to the recess 24 serves as the diaphragm 25. The ultrasonic element 2 has, for example, a piezoelectric film 26 formed on the surface of the diaphragm 25 on the side opposite to the buried insulating film 22. The piezoelectric film 26 is sandwiched between electrodes (not shown) in which a predetermined piezoelectric material such as scandium aluminum nitride (ScAlN) is paired, and is configured to contract or expand in a predetermined direction by the application of an electric field. The diaphragm 25 serves as a vibrating portion that can vibrate at a predetermined driving frequency (for example, but not limited to, 30 kHz to 100 kHz for in-vehicle applications) by the driving of the piezoelectric film 26. For example, as shown in FIG. 3, the ultrasonic element 2 has four diaphragms 25 (driving portions) and is an array element arranged in two rows and two columns at a predetermined pitch interval P1. The ultrasonic element 2 is, for example, of the MEMS (Micro Electro Mechanical Systems) type having a plurality of driving portions. The ultrasonic element 2 functions, for example, as a transmitting element that transmits ultrasonic waves to the outside with the diaphragm 25 serving as a vibrating portion, and as a receiving element that receives sound waves from the outside.

[0015] Hereinafter, for the sake of simplicity of explanation, the diaphragm 25 that functions as a driving portion may be referred to as a "cell", the diameter of the cell may be referred to as the "cell diameter", and an element having a plurality of cells and arranged in α rows and β columns (α, β: natural numbers) may be referred to as an "α×β array element", respectively. In the above example, the ultrasonic element 2 is a 2×2 array element having four cells. Also, the transmitted wave transmitted from the ultrasonic element 2 to the outside and the received wave incident on the through waveguide 42 from the outside may be collectively referred to as the "transmitted / received wave".

[0016] The ultrasonic element 2 has, for example, a thickness t1 of the SOI substrate of 0.5 mm, a thickness t2 of the cell of 17 μm, and a cell diameter of 2.6 mm. The ultrasonic element 2 is arranged, for example, at a position where, taking the wavelength conversion value of the driving frequency as λ (unit: mm) and the straight-line distance from the opening on the through waveguide 42 side to the cell in the branch waveguide 43 as L1 (unit: mm), L1 is nλ / 4 (n is an odd number).

[0017] Note that various designs such as the thickness of the SOI substrate constituting the ultrasonic element 2, the number of cells, thickness, diameter, and pitch interval are not limited to the above examples and can be appropriately changed. For example, the ultrasonic element 2 may have two cells, or three or five or more cells, and the arrangement of the cells is not limited to a 2×2 array arrangement and may be appropriately changed according to the number of cells.

[0018] The mounting substrate 3 is, for example, a circuit board on which wirings and circuits (not shown) are formed on a substrate made of an arbitrary insulating material such as glass epoxy resin or ceramic, and various electronic components and the like can be mounted. The mounting substrate 3 is fixed to the base material 41 of the case material 4 by an adhesive (not shown). The mounting substrate 3 is electrically connected to the ultrasonic element 2 by a wire or the like in a region located outside the outer contour of the ultrasonic element 2 and is also connected to a control unit, a power supply, etc. (not shown), enabling driving control of the ultrasonic element 2 and the exchange of electrical signals. As shown in FIG. 1, for example, a plurality of through holes 31 are formed in the mounting substrate 3 at positions corresponding to the diaphragm 25. The plurality of through holes 31 are propagation paths for transmitting and receiving waves independent of each other. For example, when the cells of the ultrasonic element 2 are circular, they have the same diameter, but it is not limited to this, and they can be of any shape such as an elliptical shape or a polygonal shape according to the shape of the cells. Also, the plurality of through holes 31 have, for example, the same shape and dimensions as the communicating branch waveguides 43.

[0019] As shown in FIG. 1 for example, the case member 4 includes a base material 41, a through waveguide 42, a plurality of branch waveguides 43, a frame portion 44, a lid portion 45, and a storage space 46 for housing the ultrasonic element 2 and the mounting substrate 3. The case member 4 is made of, for example, resin, metal, ceramic, or a composite material formed by combining some or all of these materials.

[0020] The base material 41 includes, for example, a through waveguide 42 and a branch waveguide 43 that branches from the through waveguide 42 toward the ultrasonic element 2. Taking the surface of the base material 41 where one opening of the through waveguide 42 (corresponding to the "entrance 42a" described later) is formed as one surface 41a, the base material 41 has the one surface 41a arranged on the surface of a bumper or a vehicle body.

[0021] Hereinafter, for convenience of explanation, the vertical direction, that is, the direction of gravity, is referred to as the "downward direction", and the direction opposite to the vertical direction is referred to as the "upward direction". Also, as shown in FIG. 1, the direction along the direction in which the branch waveguide 43 extends and from the through waveguide 42 toward the ultrasonic element 2 is referred to as the "branch direction DR1". Further, the arrangement state of the ultrasonic sensor 1 when the branch direction DR1 is aligned upward is referred to as the "installation state". In this specification, the arrangement of the through waveguide 42 and the branch waveguide 43 in the installation state will be mainly described.

[0022] Note that, for convenience of explanation, the installation state is used as a reference, but the ultrasonic sensor 1 does not necessarily need to be used in the installation state, and it may be used in a state where clogging in the branch waveguide 43 is less likely to occur, and its application form is not limited to the installation state. For example, taking the state where the branch direction DR1 is horizontal with respect to the plane whose normal is the upward direction (that is, the ground plane) as the reference (0°), the case where it faces upward from the ground plane is regarded as positive, and the case where it faces downward from the ground plane is regarded as negative. In this case, when the ultrasonic sensor 1 is used in the installation state (the branch direction DR1 is 90°), the occurrence of clogging in the branch waveguide 43 is most suppressed, but it is not limited to this, and as long as the branch direction DR1 is in a state of 0° or more, the occurrence of clogging is suppressed.

[0023] The through waveguide 42 is a through hole provided in a part of the base material 41 different from the storage space 46, and is a waveguide that does not communicate with the storage space 46. The through waveguide 42 is a propagation path of sound waves that propagates the transmitted wave from the branch waveguide 43 to the outside and propagates the received wave incident from the outside to the branch waveguide 43. The through waveguide 42 has, for example, a width in a direction orthogonal to the extending direction larger than that of the branch waveguide 43, and has dimensions such that even if foreign matter enters from the outside, the foreign matter is easily discharged. When the through waveguide 42 is, for example, a cylindrical through hole, from the viewpoint of the discharge property of foreign matter, the diameter is preferably 9 mm or more, but is not limited thereto.

[0024] Note that examples of foreign matter from the outside include, for in-vehicle applications, solid matter such as sand, stones, and plastic fragments that have fallen on the road, liquid matter such as water and mud, and paste-like matter such as wax applied to the vehicle body, but are not limited thereto.

[0025] The through waveguide 42 has, for example, two openings and is a circular through hole extending linearly. The opening that mainly functions as an entrance for sound waves from the outside among the two openings is defined as the "entrance 42a", and the other opening is defined as the "exit 42b". In the installed state, the entrance 42a and the exit 42b are at the same height. In other words, the bottom surface 42c is the portion of the wall surface of the through waveguide 42 that becomes the downward bottom surface in the installed state, and the through waveguide 42 is parallel to the plane with the branching direction DR1 as the normal line, that is, the ground plane.

[0026] For example, as shown in FIG. 1, the through waveguide 42 has a distance L2 from the central position located at the center of the two branch waveguides 43 to the entrance 42a, and a distance L3 from the central position to the exit 42b, and L2 and L3 are substantially the same. Thereby, even if foreign matter enters from either the entrance 42a or the exit 42b of the through waveguide 42, it is difficult for the foreign matter to reach the branch waveguide 43, and clogging in the branch waveguide 43 can be suppressed.

[0027] The plurality of branch waveguides 43 are through holes extending from the wall surface of the through waveguide 42 toward the storage space 46 side. The plurality of branch waveguides 43 are provided in the same number as the number of cells of the ultrasonic element 2, communicate with the external space through the through waveguide 42, and are arranged such that their openings do not directly face the outside. Thus, foreign matter from the outside does not directly enter the plurality of branch waveguides 43. The plurality of branch waveguides 43 are, for example, independently arranged in parallel and communicate with different cells of the ultrasonic element 2 through the through holes 31 of the mounting substrate 3. The plurality of branch waveguides 43 are, for example, cylindrical through holes similar to the through waveguide 42, and their diameter is 2.5 mm. Preferably, the pitch interval P1 between the openings on the through waveguide 42 side of the plurality of branch waveguides 43 is λ / 2 or less. Here, the "pitch interval P1" means the distance between the centers of adjacent branch waveguides 43 when the branch waveguides 43 are circular in top view.

[0028] Note that the through waveguide 42 and the branch waveguides 43 are, for example, cylindrical through holes extending linearly, but are not limited to this shape and may be other shapes such as elliptical columnar or polygonal columnar. Also, the through waveguide 42 and the branch waveguides 43 may be appropriately changed according to the driving frequency and acoustic mode of the ultrasonic element 2, etc. The plurality of branch waveguides 43 may extend linearly from the through waveguide 42 toward the ultrasonic element 2, or may have a shape that bends or curves on the way toward the ultrasonic element 2.

[0029] The frame portion 44 is a portion of the case material 4 that surrounds the ultrasonic element 2 and the mounting substrate 3, and has, for example, an inner contour shape along the outer shape of the mounting substrate 3.

[0030] The lid portion 45 is arranged at the end of the frame portion 44 opposite to the base material 41 and is a member that closes the frame portion 44.

[0031] In the above description, an example in which the base material 41, the frame portion 44, and the lid portion 45 constituting the case material 4 are separate bodies has been described. However, the present invention is not limited to this, and the base material 41 and the frame portion 44, or the frame portion 44 and the lid portion 45 may be integrated, and the configuration can be appropriately changed. Further, the outer shapes of the frame portion 44 and the lid portion 45 can be appropriately changed according to the outer shapes of the ultrasonic element 2 and the mounting substrate 3.

[0032] The storage space 46 is a space in which the ultrasonic element 2 and the mounting substrate 3 are stored. For example, it is formed by being surrounded by the frame portion 44 and the lid portion 45. The storage space 46 only needs to be able to store the ultrasonic element 2 and the mounting substrate 3, and the shape, dimensions, etc. can be appropriately changed.

[0033] The above is the basic configuration of the ultrasonic sensor 1 of the present embodiment. In this ultrasonic sensor 1, the through waveguide 42 communicates directly with the external space, and a plurality of branch waveguides 43 branched from the middle of the through waveguide 42 communicate with different cells of the ultrasonic element 2 respectively. Therefore, the ultrasonic sensor 1 can suppress foreign matter from the outside from entering the branch waveguide 43 and causing blockage, and the effect of improving reliability can be obtained.

[0034] 〔Foreign matter discharge property of through waveguide〕 Next, from the viewpoint of foreign matter discharge, the preferable diameter of the through waveguide 42 will be described with reference to FIGS. 4 to 10.

[0035] First, the evaluation of the water discharge property in the through waveguide 42 will be described with reference to FIGS. 4 to 7.

[0036] For example, as shown in FIG. 4, a plurality of simulated samples S in the shape of a cube having a cylindrical through-hole S1 formed therein are prepared. The through-hole S1 of the simulated sample S is different for each simulated sample S, for example, with diameters of 6 mm, 7 mm, 8 mm, 9 mm, 15 mm, 20 mm, etc., and corresponds to the through waveguide 42. The simulated sample S has, for example, a width, depth, and height of 23 mm, and the length of the through-hole S1 is 23 mm. Note that the simulated sample S may be, for example, a rectangular parallelepiped having a plurality of through-holes S1, S2, S3, S4 with different diameters, as shown in FIG. 5. The simulated sample S is made of, for example, a transparent resin such as acrylic in order to facilitate viewing the inside of the through-hole S1.

[0037] Next, the simulated samples S with different diameters of the through-hole S1 are immersed in water so that the inside of the through-hole S1 is completely filled with water. Then, the simulated sample S with the through-hole S1 filled with water is tilted at an inclination angle θ1, and it is confirmed how much water is discharged from the opening S1b that becomes the lower side when tilted, out of the two openings S1a and S1b of the through-hole S1. Here, the "inclination angle θ1" refers to the angle formed between the ground plane and the direction in which the through-hole S1 extends. The opening S1a corresponds to the inlet 42a, and the opening S1b corresponds to the outlet 42b.

[0038] When the remaining state of water in the through-hole S1 was confirmed when the inclination angle θ1 was changed within the range of 0° to 60° in the case where the diameter of the through-hole S1 was φ6 mm, 9 mm, or 20 mm, the results shown in FIG. 6 were obtained.

[0039] In the case of the through-hole S1 with a diameter of φ6 mm, although the amount of water discharged to the outside increased as the inclination angle θ1 was increased from 0° to 60°, the entire area of the opening S1b was in a state where water was blocked.

[0040] In the case of the through-hole S1 with a diameter of φ9 mm, when the inclination angle θ1 was 0°, similar to the case of φ6 mm, the water inside was not discharged much, and more than half of the opening S1b was in a state where water was blocked. However, in the case of the through-hole S1 with a diameter of φ9 mm when the inclination angle θ1 was 10° or more, almost all of the water inside was discharged, and more than half of the opening S1b became a void.

[0041] The through-hole S1 with a diameter of φ20 mm discharged more than half of the internal water and more than half of the opening S1b became voids even when the inclination angle θ1 was 0°. When the inclination angle θ1 of the through-hole S1 with a diameter of φ20 mm was 10° or more, almost all of the internal water was discharged, and there was a state where a little water remained in the opening S1b.

[0042] Also, as shown in FIG. 4, regarding the water dischargeability in the through-hole S1, the ratio of the area of the region where water remains in the opening S1b to the total cross-sectional area of the opening S1b was conveniently defined as the "residual water ratio" (%), and an evaluation using the residual water ratio as an index was also performed. A residual water ratio of 0% means that no water remains in the opening S1b, a residual water ratio of 100% means that the opening S1b is completely blocked by water, and the smaller the residual water ratio, the more water is discharged from the through-hole S1 to the outside.

[0043] As a result, for example, as shown in FIG. 7, in the simulated sample S with a diameter of the through-hole S1 of φ6 mm to φ8 mm, the residual water ratio was 100% in the entire range of the inclination angle θ1 from 0° to 60°.

[0044] In the simulated sample S with a diameter of the through-hole S1 of φ9 mm, although the residual water ratio was 100% when the inclination angle θ1 was 0°, it decreased to about 40% when the inclination angle θ1 was 10° and 20°, and decreased to about 30% when the inclination angle θ1 was 30°. Also, when the inclination angle θ1 of this simulated sample S was 45° and 60°, the residual water ratio was 20% or less.

[0045] In the simulated sample S with a diameter of the through-hole S1 of φ20 mm, the residual water ratio was about 20% when the inclination angle θ1 was 0°, about 10% when the inclination angle θ1 was 10° and 20°, and about 5% when the inclination angle θ1 was 30° or more.

[0046] This result shows that when the diameter of the through-hole S1 is 8 mm or less, the water drainage in the through-hole S1 is poor. In contrast, when the diameter is 9 mm, the water drainage is significantly improved by inclining. When the diameter reaches 20 mm, most of the water is drained without inclining. Therefore, when the foreign matter is water, from the perspective of clogging prevention, the through waveguide 42 preferably has a diameter of 9 mm or more.

[0047] Next, the evaluation of the mud drainage in the through waveguide 42 will be described with reference to FIGS. 8 and 9.

[0048] For example, as shown in FIG. 8, the mud drainage was evaluated by visually checking the remaining degree of mud in the through-hole S1 by preparing a simulation sample S with the same configuration as the water drainage evaluation and immersing the simulation sample S in mud.

[0049] Specifically, for the evaluation of mud drainage, five simulation samples S with through-hole S1 diameters of 2.2 mm, 3 mm, 6 mm, 9 mm, and 20 mm were prepared, immersed in mud, taken out and dried, and then evaluated from the perspective of whether the mud in the through-hole S1 can be discharged by washing with water.

[0050] As shown in FIG. 9, after the through-hole S1 with a diameter of 2.2 mm was immersed in mud and dried, the inside was filled with mud, and even after washing with water, the inside was still filled, and the opening S1b was completely blocked.

[0051] As shown in FIG. 9, after the through-holes S1 with diameters of 3 mm, 6 mm, 9 mm, and 20 mm were immersed in mud and dried, although the inside was filled with mud, all the mud inside was discharged when washed with water.

[0052] This result shows that for the through-hole S1 to discharge mud by washing with water, it is preferably 3 mm or more in diameter.

[0053] Next, the evaluation of the wax drainage in the through waveguide 42 will be described with reference to FIG. 10.

[0054] The wax drainage property was evaluated by visually checking the remaining degree of the wax that had entered the opening S1b after applying wax to one side of the simulation sample S having the same configuration as the water drainage property evaluation, as shown in FIG. 10 for example. Further, the wax drainage property evaluation was performed from two viewpoints: drainage by water washing and drainage by wiping after water washing, using four simulation samples S with through-hole S1 diameters of φ3 mm, 6 mm, 9 mm, and 20 mm.

[0055] Immediately after applying the wax, the wax almost completely blocked the opening S1b of the through-hole S1 with a diameter of φ3 mm. Also, for the through-hole S1 with a diameter of φ3 mm, the wax in the opening S1b remained in almost the same state as immediately after application, regardless of whether it was washed with water or wiped afterwards.

[0056] Immediately after applying the wax, the wax almost completely blocked the opening S1b of the through-hole S1 with a diameter of φ6 mm. Also, for the through-hole S1 with a diameter of φ6 mm, the wax in the opening S1b remained in almost the same state as immediately after application, similar to the case of φ3 mm, regardless of whether it was washed with water or wiped afterwards.

[0057] Immediately after applying the wax, the wax blocked approximately 30% of the area of the opening S1b of the through-hole S1 with a diameter of φ9 mm, and the state of the wax was the same as immediately after application when washed with water. Also, for the through-hole S1 with a diameter of φ9 mm, almost all of the wax in the opening S1b was removed by wiping.

[0058] Immediately after applying the wax, the wax blocked approximately 20% of the area of the opening S1b of the through-hole S1 with a diameter of φ20 mm, and the state of the wax was the same as immediately after application when washed with water. Also, for the through-hole S1 with a diameter of φ20 mm, all of the wax in the opening S1b was removed by wiping.

[0059] This result indicates that the through-hole S1 preferably has a diameter of φ9 mm or more in order to remove the wax by wiping it off.

[0060] 〔Azimuth Detection〕 Next, the azimuth detection in the ultrasonic sensor 1 of this embodiment will be described with reference to FIGS. 11 and 12.

[0061] First, the reception angle and phase difference of the reflected wave will be described with reference to FIG. 11.

[0062] For example, as shown in FIG. 11, when two waveguides extending linearly are arranged with a pitch d and a reflected wave with a wavelength λ (unit: mm) from the outside is incident at a reception angle θ2, it is assumed that a phase difference Δx (unit: deg) occurs in the reflected waves incident on the two waveguides. In this case, the reception angle θ2 is represented by the following equation (1).

[0063] θ2 = sin -1 (Δx × λ / (2π × d)) ··· (1) The "reception angle θ2" here means the angle (unit: deg) formed between the direction along the extending direction of the waveguide at the opening of the waveguide where the reflected wave is incident and the incident direction of the reflected wave (hereinafter simply referred to as the "incident direction") as shown in FIG. 11. Also, the reception angle θ2 is 0° when, for example, the extending direction of the waveguide and the incident direction overlap. As shown in FIG. 11, it is positive when the reflected wave is incident from the upper direction on the paper surface with respect to the extending direction, and negative when the reflected wave is incident from the lower direction on the paper surface with respect to the extending direction. Also, the two waveguides shown in FIG. 11 correspond to the branch waveguides 43 in the ultrasonic sensor 1.

[0064] When the cell of the ultrasonic element is arranged on the extension line of two waveguide tubes extending linearly, the pitch d of the waveguide tubes is substantially the same as the pitch of the receiving elements. The wavelength λ of the incident reflected wave depends on the wavelength of the transmitted wave transmitted from the ultrasonic element 2, that is, the driving frequency of the cell. Also, as shown in FIG. 11, the pitch d is determined by the arrangement of the outer ends on the receiving surface with the plane facing the outer ends of the waveguide tubes as the receiving surface. And when the pitch d and the wavelength λ of the reflected wave are fixed at a certain value, according to equation (1), the phase difference Δx depends on the reception angle θ2.

[0065] That is, the relationship between the reception angle θ2 and the phase difference Δx is basically uniquely determined by the interval of the pitch d on the receiving surface and the driving frequency. In other words, by utilizing the fact that the phase difference Δx of each reflected wave received by a plurality of receiving elements changes according to the reception angle θ2 of the reflected wave, the reception direction of the reflected wave, that is, the orientation of an external obstacle or the like can be calculated.

[0066] Subsequently, the simulation results of the relationship between the reception angle θ2 and the phase difference Δx in the ultrasonic sensor 1 of the present embodiment will be described with reference to FIG. 12.

[0067] For example, the change in the phase difference Δx at the reception angle θ2 shown in FIG. 12 can be calculated by, for example, simulation calculation using acoustic analysis software using the finite element method. In the simulation calculation shown in FIG. 12, L2 and L3 of the through waveguide tube 42 were set to 5 mm, the diameter of the branch waveguide tube 43 was set to φ2.5 mm, and the driving frequency of the ultrasonic element 2 was set to 46.4 kHz (the wavelength conversion value was 7.4 mm).

[0068] When the diameter of the through waveguide 42 is φ10 mm, as shown in Fig. 12, the phase difference Δx gradually increased within the range of 0° to 100° as the reception angle θ2 increased within the range of 0° to 30°. Also, the phase difference Δx gradually decreased within the range of 0° to -100° as the reception angle θ2 decreased within the range of -30° to 0°. On the other hand, within the ranges of the reception angle θ2 being -40° to -70° and 40° to 60°, the phase difference Δx was almost 0° and hardly changed. This result indicates that when the diameter of the through waveguide 42 is φ10 mm, the ultrasonic sensor 1 can detect the azimuth within the range of the reception angle θ2 being -30° to 30°.

[0069] When the diameter of the through waveguide 42 is φ15 mm, the phase difference Δx gradually increased within the range of 0° to 300° as the reception angle θ2 increased within the range of 0° to 70°. Also, the phase difference Δx gradually decreased within the range of 0° to -300° as the reception angle θ2 decreased within the range of -70° to 0°. This result indicates that when the diameter of the through waveguide 42 is φ15 mm, the ultrasonic sensor 1 can detect the azimuth within the range of the reception angle θ2 being -70° to 70°.

[0070] As described above, the ultrasonic sensor 1 has a structure in which the through waveguide 42 communicates directly with the external space and includes a plurality of branch waveguides 43 that branch from the through waveguide 42 toward the ultrasonic element 2, and azimuth detection is possible. Note that the results shown in Fig. 12 are merely examples, and the length and diameter of the through waveguide 42, the number of branch waveguides 43, the diameter, pitch, etc. can be appropriately changed according to the drive frequency of the ultrasonic element 2, etc.

[0071] According to this embodiment, since the ultrasonic element 2 is housed in the case material 4 and not exposed to the outside, the ultrasonic sensor 1 is formed with the ultrasonic element 2 being protected. Further, the ultrasonic sensor 1 includes a through waveguide 42 which is a through hole provided in the base material 41 of the case material 4, and a plurality of branch waveguides 43 that branch from the through waveguide 42 toward the ultrasonic element 2, and has a structure that enables the discharge of foreign matter even when foreign matter enters the through waveguide 42. Therefore, the ultrasonic sensor 1 can detect the presence or absence of an object and its orientation while achieving both the protection of the ultrasonic element 2 and the suppression of clogging of foreign matter in the waveguide.

[0072] (Modification of the First Embodiment) Next, a modification of the ultrasonic sensor 1 of the first embodiment will be described with reference to FIGS. 13 to 15. In FIGS. 13 to 15, similar to FIG. 1, a part of the outer contour in a different cross-section of the ultrasonic element 2, the mounting substrate 3, and the base material 41 is shown by a broken line.

[0073] The ultrasonic sensor 1 may be configured such that, for example, as shown in FIG. 13, in the installed state, the bottom surface 42c of the through waveguide 42 is inclined at a predetermined angle θ3 with respect to the ground plane, and the inlet 42a is located above the outlet 42b. In this case, even if foreign matter enters the through waveguide 42, since the foreign matter is discharged from the outlet 42b by gravity, the structure is such that clogging by foreign matter is further suppressed compared to the first embodiment.

[0074] The ultrasonic sensor 1 may be configured such that, for example, as shown in FIG. 14, in the installed state, the bottom surface 42c is inclined with respect to the ground plane so that the outlet 42b of the through waveguide 42 is located above the inlet 42a. In this case, even if foreign matter enters the through waveguide 42, due to the action of gravity, the foreign matter is discharged from the inlet 42a.

[0075] As shown in FIG. 15 for example, in the installed state, the ultrasonic sensor 1 may have a configuration in which the bottom surface 42c of the through waveguide 42 is inclined at a predetermined angle θ3 with respect to the ground plane, and the vicinity of the outlet 42b located downward from the inlet 42a is a curved surface 42ca. In this case, the through waveguide 42 has a configuration that makes it easier to exclude the intruding foreign matter, and the occurrence of clogging is further suppressed.

[0076] Note that FIG. 15 shows the case where the inlet 42a is located upward from the outlet 42b, but it is not limited to this example. For example, in the installed state of the through waveguide 42, when the outlet 42b is located upward from the inlet 42a, a curved surface 42ca may be formed on the side of the bottom surface 42c where the inlet 42a is located. Further, the through waveguide 42 may have a configuration in which a curved surface 42ca is also formed on the side of the opening located upward, and the shape may be such that foreign matter is less likely to intrude due to the action of gravity. Furthermore, the angle θ3 corresponds to the above-described inclination angle θ1 and can be appropriately changed within a range of 60° or less, for example, although not limited.

[0077] With each of the above-described modifications, the ultrasonic sensor 1 that can obtain the effects of the first embodiment is obtained. Also, in the installed state, since the bottom surface 42c of the through waveguide 42 is extended so as to be inclined with respect to the ground plane, even if external foreign matter intrudes into the through waveguide 42, the foreign matter easily falls by gravity toward one of the inlet 42a and the outlet 42b that is located downward. Therefore, compared with the first embodiment, an effect that the foreign matter that has intruded into the through waveguide 42 is more easily discharged is also obtained.

[0078] (Second Embodiment) The ultrasonic sensor 1 of the second embodiment will be described with reference to FIG. 16.

[0079] In FIG. 16, as in FIG. 1, a part of the outer contour in a different cross section of the ultrasonic element 2, the mounting substrate 3, and the base material 41 is shown by a broken line. This is the same for FIGS. 17 to 19 described later.

[0080] The ultrasonic sensor 1 of this embodiment is different from the first embodiment in that, as shown in FIG. 16 for example, the through waveguide 42 has a configuration in which the diameters of its inlet 42a and outlet 42b are different. In this embodiment, this difference will be mainly described.

[0081] In this embodiment, as shown in FIG. 16 for example, in the installed state, the through waveguide 42 has a configuration in which the bottom surface 42c and the top surface 42d are inclined in different directions with respect to the ground plane, with the topmost surface of its wall surface being defined as the top surface 42d. Specifically, the through waveguide 42 is inclined such that the bottom surface 42c is higher on the inlet 42a side than on the outlet 42b side, while the top surface 42d is inclined in the opposite direction. That is, the through waveguide 42 has an increasing distance, i.e., diameter, between the bottom surface 42c and the top surface 42d from the inlet 42a toward the outlet 42b. In other words, the through waveguide 42 is configured such that it is difficult for foreign matter to enter from the inlet 42a, and even if foreign matter does enter, it is easily discharged from the outlet 42b due to the action of gravity.

[0082] Also according to this embodiment, the ultrasonic sensor 1 achieves the same effects as the first embodiment. Further, this ultrasonic sensor 1 has a configuration in which the through waveguide 42 has a larger diameter at the outlet 42b than at the inlet 42a, and the bottom surface 42c is inclined with respect to the ground plane. Therefore, while suppressing the intrusion of foreign matter from the inlet 42a, an effect of improving the foreign matter dischargeability from the outlet 42b is also obtained even if foreign matter does enter.

[0083] (Modification of the Second Embodiment) The ultrasonic sensor 1 of the second embodiment may have a configuration in which, as shown in FIG. 17 for example, the width of the inlet 42a of the through waveguide 42 is larger than the width of the outlet 42b, and the bottom surface 42c is inclined with respect to the ground plane. In this case, even if foreign matter enters from the inlet 42a of the through waveguide 42, the ultrasonic sensor 1 is configured such that the foreign matter is easily discharged from the inlet 42a due to the action of gravity. Here, the width refers to the dimension of the maximum width, and when the inlet 42a and the outlet 42b are circular, it is the diameter.

[0084] As shown in, for example, FIG. 18, the ultrasonic sensor 1 may have a configuration in which the diameter of the outlet 42b of the through waveguide 42 is larger than that of the inlet 42a, the bottom surface 42c is inclined with respect to the ground plane, while the upper surface 42d is horizontal with respect to the ground plane. In this case, the through waveguide 42 has improved foreign matter discharge property at the outlet 42b.

[0085] As shown in, for example, FIG. 19, the ultrasonic sensor 1 may have a configuration in which the diameter of the inlet 42a of the through waveguide 42 is larger than that of the outlet 42b, the bottom surface 42c is inclined with respect to the ground plane, while the upper surface 42d is horizontal with respect to the ground plane. In this case, the through waveguide 42 has improved foreign matter discharge property at the inlet 42a.

[0086] Also according to this modification example, the ultrasonic sensor 1 can obtain the same effects as those of the second embodiment.

[0087] (Third Embodiment) The ultrasonic sensor 1 of the third embodiment will be described with reference to FIG. 20.

[0088] In FIG. 20, as in FIG. 1, a part of the outer contour in a different cross-section of the ultrasonic element 2, the mounting substrate 3, and the base material 41 is shown by a broken line.

[0089] The ultrasonic sensor 1 of the present embodiment is different from the first embodiment in that, for example, as shown in FIG. 20, a protective film 5 is attached to the branch waveguide 43. In the present embodiment, this difference will be mainly described.

[0090] In the present embodiment, a plurality of branch waveguides 43 are each covered by a protective film 5 attached to the opening on the side of the through waveguide 42. Thereby, even if foreign matter enters the through waveguide 42, the foreign matter does not enter the branch waveguide 43.

[0091] The protective film 5 is a member that transmits at least the sound waves of the frequency emitted by the ultrasonic element 2 and prevents foreign matter from entering the branch waveguide 43, and is attached to the branch waveguide 43 by, for example, an adhesive (not shown). The protective film 5 is, for example, a porous body having a large number of fine gaps connecting the branch waveguide 43 and the through waveguide 42, and is composed of an arbitrary material such as resin, metal, ceramic, or a composite thereof. The protective film 5 only needs to be configured to prevent the intrusion of solids and liquids and transmit the transmitted and received waves, and is not limited to a porous body, and arbitrary treatments such as water repellent treatment may be performed.

[0092] That is, the branch waveguide 43 to which the protective film 5 is attached has a structure that allows the transmitted and received waves to propagate while preventing foreign matter that has entered the through waveguide 42 from entering.

[0093] According to the present embodiment, the ultrasonic sensor 1 can obtain the same effects as those of the first embodiment. In addition, by attaching a protective film 5 that transmits sound waves and blocks solids and liquids to each of the plurality of branch waveguides 43, it is possible to prevent clogging of foreign matter in the branch waveguides 43, and an effect of further improving reliability can be obtained.

[0094] (Other Embodiments) The present invention has been described based on the embodiments, but it is understood that the present invention is not limited to the embodiments and structures. The present invention includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and further, other combinations and forms including only one element thereof, more, or less, fall within the scope and spirit of the present invention.

[0095] (1) For example, the protective film 5 of the third embodiment may be attached to the branched waveguide 43 in the first and second embodiments and their modified examples. Further, the protective film 5 may be attached, for example, at a position spaced apart from the opening on the through waveguide 42 side of the branched waveguide 43 as shown in FIG. 21. In this case, compared with the third embodiment, the ultrasonic sensor 1 has a structure in which foreign matter that has entered the through waveguide 42 from the outside is less likely to contact the protective film 5, and the protective film 5 is less likely to be damaged, resulting in an effect of further improving reliability. In particular, as shown in FIG. 21, in the case of a structure in which the opening on the through waveguide 42 side of the branched waveguide 43 is located below the lower end of the inlet 42a (the position of the bottom surface 42c), the foreign matter that has entered does not contact the protective film 5, so the effect of improving reliability can be further enhanced. That is, by arranging the protective film 5 at a position where it cannot be seen when looking at the through waveguide 42 from the inlet 42a side, the possibility of contact with foreign matter is further reduced, and the reliability of the ultrasonic sensor 1 is further enhanced.

[0096] (2) In each of the above embodiments, the ultrasonic sensor 1 having a structure in which the ultrasonic element 2 is attached to the mounting substrate 3 and the cell and the branched waveguide 43 are connected via the mounting substrate 3 has been described, but the present invention is not limited thereto. For example, the ultrasonic sensor 1 may have a structure in which the ultrasonic element 2 is directly attached to the base material 41, arranged at another position in the storage space 46, and connected to the mounting substrate 3 having no through hole 31 by a wire or the like.

[0097] (3) In the second embodiment and its modified example, the through waveguide 42 has an internal structure in which at least the bottom surface 42c is inclined with respect to the ground plane in the installed state. However, for example, as shown in FIG. 22, only the upper surface 42d may be inclined with respect to the ground plane. In this case, since one of the widths of the inlet 42a or the outlet 42b is larger than the other, even when foreign matter enters the through waveguide 42, the ultrasonic sensor 1 has a structure in which the foreign matter can be easily discharged from the inlet 42a or the outlet 42b.

[0098] (4) In each of the above embodiments, an example in which a plurality of branch waveguides 43 are provided in the case member 4 has been described. However, the ultrasonic sensor 1 may have a configuration having only one branch waveguide 43, for example, as shown in FIG. 23. Even in this case, the ultrasonic sensor 1 can protect the ultrasonic element 2 and suppress the occurrence of foreign matter clogging in the through waveguide 42. Thus, the number and arrangement of the branch waveguides 43 can be changed as appropriate.

Explanation of Signs

[0099] 2... Ultrasonic element, 25... Vibration part, 4... Case member, 41... Base material, 42... Through waveguide, 42a, 42b... Openings, 42c... (Bottom surface of the through waveguide), 43... Branch waveguide, 46... Storage space, 5... Protective film, DR1... Branch direction

Claims

1. An ultrasonic sensor, comprising: an ultrasonic element (2) having a vibrating portion (25); a base material (41), a storage space (46) for housing the ultrasonic element, a through waveguide tube (42) which is a through hole provided in a portion of the base material that does not communicate with the storage space, and a branch waveguide tube (43) which branches from the wall surface of the through waveguide tube and extends toward the ultrasonic element and communicates with the vibrating portion, and a case material (4) having the same; a protective film (5) made of a porous body that transmits sound waves; the protective film is disposed in the branch waveguide tube; with the direction along which the branch waveguide tube extends from the wall surface of the through waveguide tube being defined as the branch direction (DR1), the vertical direction being the downward direction, and the direction opposite to the vertical direction being the upward direction, the state in which the branch direction is aligned with the upward direction is defined as the installation state; the through waveguide tube has two openings (42a, 42b) facing the external space, and using the opening (42a) into which the reflected wave of the transmitted wave transmitted to the outside among the two openings enters as the inlet; an ultrasonic sensor, wherein the opening on the side of the through waveguide tube of the branch waveguide tube is located in the downward direction from the lower end of the inlet in the installation state.

2. The ultrasonic sensor according to claim 1, wherein with the opening (42a) into which the reflected wave of the transmitted wave transmitted to the outside among the two openings enters as the inlet and the other opening (42b) as the outlet, the width of the outlet of the through waveguide tube is larger than the width of the inlet.

3. The ultrasonic sensor according to claim 1, wherein with the opening (42a) into which the reflected wave of the transmitted wave transmitted to the outside among the two openings enters as the inlet and the other opening (42b) as the outlet, the bottom surface (42c) of the through waveguide tube in the installation state is inclined such that the side of the inlet is located in the upward direction from the side of the outlet.

4. The ultrasonic sensor according to any one of claims 1 to 3, wherein the protective film is disposed at a position spaced apart from the opening on the side of the through waveguide tube of the branch waveguide tube.

5. An ultrasonic sensor, comprising: an ultrasonic element (2) having a vibrating portion (25); A case member (4) comprising a base material (41), a storage space (46) for housing the ultrasonic element, a through waveguide (42) which is a through hole provided in a portion of the base material that does not communicate with the storage space, and a branch waveguide (43) which branches and extends from the wall surface of the through waveguide towards the ultrasonic element and communicates with the vibration part. With the direction along which the branch waveguide extends from the wall surface of the through waveguide as the branch direction (DR1), the vertical direction as the downward direction, and the direction opposite to the vertical direction as the upward direction, the state in which the branch direction is aligned with the upward direction is defined as the installation state. The through waveguide has two openings (42a, 42b) facing the external space, the width of one of the openings is larger than the width of the other opening, and the bottom surface (42c) in the installation state is inclined with respect to the plane having the upward direction as the normal. An ultrasonic sensor in which, with the opening (42a) into which the reflected wave of the transmitted wave transmitted to the outside among the two openings as the inlet and the other opening (42b) as the outlet, the bottom surface of the through waveguide is inclined such that the side of the outlet is positioned more in the upward direction than the side of the inlet.

6. The ultrasonic element has a plurality of the vibration parts. A plurality of the branch waveguides are provided. The ultrasonic sensor according to any one of claims 1 to 5, wherein the plurality of branch waveguides are independent of each other and communicate with different vibration parts.

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