PERFORATED BOARD

Description

Technical Field

[0001] The present invention relates to a perforated plate.Background Art

[0002] For example, Patent Literature 1 discloses a technique about a perforated plate as a sound-insulating material for a vehicle or the like. In a perforated sound-absorbing structure disclosed in Patent Literature 1, reinforcement plate materials each having a large number of through-holes are attached to surfaces of an outer material and an inner material on the side of a hollow portion respectively so as to form an air layer between those surfaces. Sound absorbability can be imparted to the inside of the hollow portion due to the reinforcement plate materials having a large number of through-holes. In the perforated sound-absorbing structure, a frequency range of high sound-absorptivity can be widened easily without attaching a fibrous sound-absorbing material to a lower surface of the inner material.Citation ListPatent Literature

[0003] Patent Literature 1: JP-A-2014-48632

[0004] JP S52 88301 A discloses a perforated plate having through-holes in a cross-section of parabolic shape. The largest hole diameter portion of the through-holes is at the side of a first opening, and the smallest hole diameter portion of the through-holes is at the side of a second opening. Each of the through-holes is closely formed so that the adjacent through-holes contact each other on the largest hole diameter side.

[0005] US 2009 / 038883 A1 discloses a sound-absorbing panel having through-holes having a largest hole diameter portion on the upper side of the through-holes and a smallest hole diameter portion on the lower side of the through-holes. The portion on the upper side is tapered. The portion on the lower side is non-tapered.

[0006] JP S63 153592 A discloses cylindrical through-holes in many examples. In an example, the through-holes consist of two connected cylindrical through-holes of different diameters. In another example, the through-holes have a tapered shape.

[0007] DE 10 2004 040112 A1 discloses a sound-absorbing element having holes with a sectional area which is decreasing from a side of the largest hole diameter portion to a side of the smallest hole diameter portion. The holes shall have an increasing depth in spherical shape. DE 10 2004 040112 A1 discloses a perforated plate having the features of the preamble of claim 1.

[0008] JP H10 116084 A discloses a structure consisting of an upper shell and a lower shell with holes of tube shape which can be formed at one side as throat shed sections. The upper shell has a through-hole that swells inside a straight line connecting the largest hole diameter portion and the smallest hole diameter portion. The lower shell has a straight through-hole.Summary of the InventionTechnical Problems

[0009] In Patent Literature 1, there is no direct suggestion about specific detailed shapes of through-holes formed in each reinforcement plate material. As for a method for perforating the reinforcement plate material, punching is referred to in Paragraph 0054 of Patent Literature 1. A hole made by punching is formed as a hole having a columnar shape whose sectional area is same from the front surface to back surface of the plate material. That is, it can be said that Patent Literature 1 discloses a perforated plate having a large number of holes having columnar shapes each having the same sectional area from the front surface to back surface of the plate material.

[0010] When a perforated plate is used as a sound-insulating material for a vehicle or the like, it is preferable that the number of through-holes formed in the perforated plate is reduced regardless of whether the perforated plate is used as a reinforcement plate or not. When a large number of through-holes are made in the plate, strength of the plate deteriorates. On the other hand, when the number of through-holes is simply reduced, sound absorbability deteriorates. In addition, when the number of through-holes is increased, there arises another problem that the perforating cost is increased. Further, when the number of through-holes is increased excessively, there arises another problem that through-holes adjacent to each other interfere with each other.

[0011] The present invention has been made in consideration of the aforementioned situation. An object of the present invention is to provide a perforated plate capable of obtaining high sound absorbability with a smaller number of through-holes than that of the through-holes in conventional cases.Solution to Problems

[0012] The object is solved by a perforated plate having the features of claim 1. An alternative perforated plate is claimed in claim 2. Further developments are stated in the dependent claims.Advantageous Effects of the Invention

[0013] Each through-hole is formed into a shape swelling outside a straight line connecting a largest hole diameter portion and a smallest hole diameter portion. Thus, thickness in any part of the through-hole in a plate thickness direction (which is a direction in which sound waves pass) affecting propagation of the sound waves can be made smaller than the case where the sectional shape of each hole is formed by a straight line. That is, in the shape of the through-hole in the present invention, thickness in any part of the through-hole in the plate thickness direction is smaller than that in a through-hole whose sectional shape is formed by a straight line, when the two through-holes are compared with each other at the parts having the same hole diameter. It is therefore possible to obtain high sound absorbability in spite of a reduced number of through-holes. Further, there are additional effects of reducing the cost in machining the hole, avoiding interference between adjacent through-holes, and improving strength of the perforated plate. Further, there is the effect of improving the sound absorbing performance due to the hole shape of the through-hole swelling outside the straight line connecting the largest hole diameter portion and the smallest hole diameter portion.Brief Description of the Drawings

[0014] [FIG. 1] A sectional view showing a perforated sound-absorbing structure including a perforated plate in an embodiment of the present invention. [FIG. 2] An enlarged view of a part of a through-hole in the perforated plate shown in FIG. 1. [FIG. 3] A graph showing a relation between flow resistance of the perforated plate and a frequency of a sound wave. [FIG. 4] A sectional view showing two embodiments of through-holes in the perforated plate. [FIG. 5] A sectional view showing an embodiment of a through-hole in the perforated plate. [FIG. 6] A graph showing a comparison result as to sound absorbability between a through-hole 7 shown in FIG. 4 and a through-hole having no swelling in the comparative example. [FIG. 7] A graph showing a comparison result as to the number of holes having the same sound absorbability between each of the through-holes 6 and 7 shown in FIG. 4 and the through-hole having no swelling in the comparative example. Description of Embodiments

[0015] Embodiments of the present invention will be described below with reference to the drawings.(Sound-Absorbing Structure Using Perforated Plate)

[0016] As shown in FIG. 1, a perforated plate 1 in an embodiment of the present invention is placed at a predetermined distance from a plate-shaped or wall-shaped closing member 2 so that an air layer 3 is formed between the perforated plate 1 and the closing member 2. The air layer 3 communicates with the outside only through a large number of through-holes 4 of the perforated plate 1. That is, ends of the perforated plate 1 are, for example, connected to the closing member 2, and they are closed by plates having no through-holes or the like.

[0017] The closing member 2 is a member where no holes are made, that is, a front surface thereof does not communicate with a back surface thereof. In addition, the closing member 2 is placed on the opposite side to a noise source 5 across the perforated plate 1.

[0018] Examples of materials of the perforated plate 1 and the closing member 2 may include aluminum, aluminum alloys, stainless steel, iron, resin, etc.(Shape of Through-hole)

[0019] FIG. 2 is an enlarged view of a part of a through-hole 4 in the perforated plate 1 shown in FIG. 1. As shown in FIG. 2, the through-hole 4 has a largest hole diameter portion 11 formed in one surface S1 of the perforated plate 1, and a smallest hole diameter portion 12 formed in the other surface S2. That is, the through-hole 4 is a through-hole whose diameter is different between the front surface and the back surface of the perforated plate 1, and reaches a maximum (Dmax) and a minimum (Dmin) respectively in the front and back surfaces of the hole.

[0020] The Dmin (smallest hole diameter) is equal to or smaller than plate thickness t of the perforated plate 1. The smallest value of the Dmin is 0.01 mm. The hole diameter 0.01 mm is a diameter in which the sound absorbability cannot be improved more due to influence of overdamping. That is, the Dmin (smallest hole diameter) is 0.01 mm or more and equal to or smaller than the plate thickness t.

[0021] The Dmax (largest hole diameter) is a larger diameter than the Dmin (smallest hole diameter), and is smaller than 1 / 2 of a hole pitch. The hole pitch is a distance between centers of adjacent holes.

[0022] As shown in FIG. 2 which is a sectional view in the direction of the plate thickness t of the perforated plate 1, the wall surface of the through-hole 4 between the largest hole diameter portion 11 and the smallest hole diameter portion 12 is put on a radially outer side from a straight line L connecting the largest hole diameter portion 11 and the smallest hole diameter portion 12, that is, a straight line L connecting one edge part of the largest hole diameter portion 11 and one edge part of the smallest hole diameter portion 12 on the same side as the edge part of the largest hole diameter portion 11. That is, the through-hole 4 has a shape swelling on a radially outer side from the straight line L. In addition, the through-hole 4 has a sectional area which is fixed or reduced as approaching the other surface S2 of the perforated plate 1 where the smallest hole diameter portion 12 is formed, from the one surface S1 of the perforated plate 1 where the largest hole diameter portion 11 is formed. In the embodiment shown in FIG. 2, the sectional area is fixed (the largest sectional area is kept) between the largest hole diameter portion 11 and a wall surface position 13 under the largest hole diameter portion 11, and then reduced gradually and continuously toward the other surface S2.

[0023] In the sectional view in the direction of the plate thickness t of the perforated plate 1, it is the most essential that the through-hole 4 has a shape swelling outside the straight line L connecting the largest hole diameter portion 11 and the smallest hole diameter portion 12. In this configuration, plate thickness ta2 is smaller than plate thickness ta1 (ta2<ta1) as shown in FIG. 2, when ta1 designates a plate thickness at a middle point of a through-hole and ta2 designates a plate thickness where the hole diameter is the same as that at the middle point of the plate thickness ta1. In this manner, at any part of the through-hole 4 in the perforated plate 1, the thickness in the plate thickness direction is smaller than that in the hole shown by the straight line L, which does not swell outward, when the two parts of the through-hole are compared at the same hole diameter. To say other words, at any part excluding the both end parts of the hole in the direction of the plate thickness t, a position in the direction of the plate thickness t having the same hole diameter as that in the hole shown by the straight line L is disposed on the smallest diameter side.

[0024] In examples not forming part of the present invention, in the sectional view in the direction of the plate thickness t of the perforated plate 1, the wall surface of the hole may be formed by a curve at most parts of the through-hole 4. However, the wall surface of the hole may be formed by a combination of straight lines extending in an up / down direction, in an oblique direction and in a lateral direction (or the sectional area may be discontinuously reduced as going from the surface S1 toward the surface S2). That is, it will go well if the through-hole 4 has a sectional area being same or reduced as going from the surface S1 toward the surface S2. In the embodiments of the present invention, the sectional view in the direction of the plate thickness t of the perforated plate 1, the wall surface of the through-hole 4 is formed by a combination of only curves having different curvatures.

[0025] In examples not forming part of the present invention, in the sectional view in the direction of the plate thickness t of the perforated plate 1, the wall surface of the through-hole 4 may be formed by a combination of straight lines and curves, or may be formed by a combination of only straight lines.

[0026] As shown in FIG. 1, of the through-hole 4, a larger hole diameter (sectional area) side may be disposed on the noise source 5 side, or on the contrary, of the through-hole 4, a smaller hole diameter (sectional area) side may be disposed on the noise source 5 side. This reason will be described below. A sound absorbing effect is determined by a pressure loss generated when a sound wave passes through the hole. The pressure loss is determined by the smallest part of the hole. Therefore, a similar sound absorbing effect can be obtained regardless of whether the smaller hole diameter side or the larger hole diameter side is disposed on the noise source 5 side.(Reason why thickness in the plate thickness direction at any part of the through-hole 4 is smaller than that in the case of a through-hole having a sectional shape formed by a straight line when the two parts of the through-hole are taken to have the same hole diameter)

[0027] Flow resistance (front and back pressure loss / passing flow rate) in a perforated plate having a large number of through-holes having a columnar shape with the same sectional area from its front surface to its back surface is expressed by the following formula (1).

[0028] [Formula 1] R t = 32 η 0 βd 2 t 1 + d 2 ρ 0 ω 256 η 0 + d 2 8 t ρ 0 ω η 0

[0029] Rt: flow resistance η 0 : viscous resistance of air β: opening ratio of perforated plate d: hole diameter t: plate thickness of perforated plate ρ 0 : density of air ω: angular velocity of sound wave (= frequency)

[0030] FIG. 3 is a graph showing a relation between the flow resistance and the frequency. As shown in FIG. 3, when the plate thickness is large, the flow resistance Rt is larger than the case where the plate thickness is small. When the flow resistance Rt is large, it is necessary to increase the opening ratio β (number of holes) in the perforated plate to thereby reduce damping in order to obtain optimum damping. It is therefore necessary to increase the opening ratio β when the plate thickness is large.

[0031] As described above, when the through-hole 4 is formed into a hole shape swelling outside the straight line L connecting the largest hole diameter portion 11 and the smallest hole diameter portion 12, the thickness in the plate thickness direction at any part of the through-hole 4 is smaller than that in a through-hole having a sectional shape formed by a straight line, when the two parts of the through-hole are compared at parts having the same hole diameter as each other. Thus, the same effect as the case where the plate thickness of the perforated plate is reduced can be obtained. As a result, it is possible to reduce the number of through-holes 4 for obtaining the same sound absorbability. In this manner, it is possible to obtain high sound absorbability with a reduced number of through-holes. Further, there are additional effects of reducing the cost in machining the hole, avoiding interference between adjacent through-holes, and improving strength of the perforated plate.

[0032] A part having great contribution to obtaining the same effect as that when the plate thickness of the perforated plate is reduced is a hole lower part B of the through-hole 4, which is a peripheral part of the smallest hole diameter portion 12 in the through-hole 4. When the hole swells outside the straight line L at the hole lower part B (when the hole is formed into a curve like a concave (or may be formed by a straight line)), the plate thickness can be easily reduced at any part of the through-hole 4 from the surface S1 to the surface S2.

[0033] FIG. 4 shows two embodiments of through-holes. In the sectional view in the direction of the plate thickness t of the perforated plate 1, of a part swelling outside the straight line L connecting the largest hole diameter portion 11 and the smallest hole diameter portion 12 in the through-hole, a largest swelling position (a position of a largest swelling amount δa in a direction parallel to the surfaces S1 and S2 of the perforated plate 1) is a central position in the direction of the plate thickness t of the perforated plate 1, or a position on the smallest hole diameter portion 12 side from the central position.

[0034] As for a through-hole 6 of two through-holes 6 and 7 shown in FIG. 4, a largest swelling position 14 of the through-hole 6 is set at the central position in the direction of the plate thickness t of the perforated plate 1. As for the other through-hole 7, a largest swelling position 15 of the through-hole 7 (a position of a largest swelling amount δb in a direction parallel to the surfaces S1 and S2 of the perforated plate 1) is set on the smallest hole diameter portion 12 side from the central position in the direction of the plate thickness t and at a position of 1 / 4·t from the surface S2 on the smallest hole diameter portion 12 side.

[0035] As shown in FIG. 5, in order to ensure satisfactory strength near the smallest hole diameter portion 12, it is preferable to have a structure in which the smallest hole diameter portion 12 has a certain thickness. When the thickness of the smallest hole diameter portion 12 is larger than the hole diameter Dmin of the smallest hole diameter portion, the effect of improving the sound absorbing performance due to the hole shape of the through-hole swelling outside the straight line connecting the largest hole diameter portion and the smallest hole diameter portion is reduced. Therefore, the thickness td of the smallest hole diameter portion 12 is set at a predetermined thickness equal to or smaller than the hole diameter Dmin of the smallest hole diameter portion 12.

[0036] In this structure, it is possible to ensure satisfactory strength near the smallest hole diameter portion 12 as described above. In addition, there is another effect that the hole can be machined more easily than when the smallest hole diameter portion 12 has a sharp structure.(Validation Result)

[0037] FIG. 6 is a graph showing a comparison result of sound absorbability between the through-hole 7 shown in FIG. 4 and a through-hole having no swelling in the comparative example (a conical through-hole in which the largest hole diameter portion 11 and the smallest hole diameter portion 12 are connected by the straight line L in sectional view). In FIG. 6, a line indicated as "present invention" designates the through-hole 7 shown in FIG. 4 (an example of the embodiment). The opening ratio in the perforated plate having each through-hole was equally set at 0.5%. As is found from FIG. 6, the sound absorbability can be improved on a larger scale in the through-hole 7 (the perforated plate 1 having a large number of through-holes 7) in the present invention than the case in the through-hole (the perforated plate having through-holes having no swelling) in the comparative example.

[0038] FIG. 7 is a graph showing a comparison result as to the number of holes having the same sound absorbability between each through-holes 6 and 7 shown in FIG. 4 and the through-hole having no swelling in the comparative example (the conical through-hole in which the largest hole diameter portion 11 and the smallest hole diameter portion 12 are connected by the straight line L in sectional view).

[0039] The ordinate in the graph shown in FIG. 7 designates the ratio of the number of through-holes 6 and 7 in the present invention (the perforated plate 1 having a large number of through-holes 6 or 7) when the number of holes in the through-hole having no swelling in the comparative example (the perforated plate having through-holes having no swelling) is taken as 100%. The abscissa in the graph designates the swelling amount at the largest swelling positions 14 and 15 of each of the through-holes 6 and 7.

[0040] As is found from FIG. 7, the number of through-holes 6 and 7 in the present invention (the perforated plate 1 having a large number of through-holes 6 or 7) can be reduced in comparison with the number of through-holes having no swelling in the comparative example (the perforated plate having through-holes having no swelling), in order to attain the same sound absorbability.

[0041] When the case of the through-hole 6 (the largest swelling position is 1 / 2·t from the surface S2) is compared with the case of the through-hole 7 (the largest swelling position is 1 / 4·t from the surface S2), the number of holes can be reduced in the case of the through-hole 7 in order to attain the same sound absorbability. That is, as the largest swelling position is made closer to the smallest hole diameter portion 12, the number of holes can be reduced.(Operation / Effect)

[0042] Each through-hole in a perforated plate in the present invention includes a largest hole diameter portion that is formed in one surface of the perforated plate, and a smallest hole diameter portion that is formed in the other surface of the perforated plate. In the sectional view in the plate thickness direction of the perforated plate, the through-hole swells outside a straight line connecting the largest hole diameter portion and the smallest hole diameter portion.

[0043] In this configuration, the thickness in the plate thickness direction at any part of the through-hole in the perforated plate can be made smaller than that in a case where the sectional shape of a through-hole is formed by a straight line, when the two parts of the through-hole are compared at places with the same diameter. In this manner, the same effect as that when the plate thickness of the perforated plate is reduced can be obtained. Thus, it is possible to obtain high sound absorbability with a small number of through-holes.

[0044] In the sectional view in the plate thickness direction of the perforated plate in the present invention, of the part of the through-hole swelling outside the straight line connecting the largest hole diameter portion and the smallest hole diameter portion, a largest swelling position is a central position in the plate thickness direction of the perforated plate or a position on the smallest hole diameter portion side from the central position. In this configuration, it is possible to obtain high sound absorbability with a smaller number of through-holes.

[0045] In the sectional view in the plate thickness direction of the perforated plate, the wall surface of the through-hole is formed by a combination of only curves having different curvatures.

[0046] In addition, in the present invention, it is preferable that the smallest hole diameter portion has a thickness equal to or smaller than the hole diameter of the smallest hole diameter portion. In this configuration, it is possible to ensure satisfactory strength near the smallest hole diameter portion. In addition, it is also possible to obtain an effect of making it easier to machine the hole than the case where the smallest hole diameter portion is made to have a sharp structure.

[0047] The present application is based on a Japanese patent application No. 2015-101502 filed on May 19, 2015.Description of Reference Numerals and Signs

[0048] 1: Perforated plate 2: Closing member 3: Air layer 4: Through-hole 11: Largest hole diameter portion 12: Smallest hole diameter portion L: Straight line connecting the largest hole diameter portion 11 and the smallest hole diameter portion 12 S1: One surface S2: Other surface t: Plate thickness

Claims

1. A perforated plate (1) comprising a large number of through-holes (4); wherein: each through-hole (4) includes a largest hole diameter portion (11) that is formed on one surface (S1) of the perforated plate (1), said largest hole diameter portion (11) having the largest hole diameter (Dmax), and a smallest hole diameter portion (12) that is formed on the other surface (S2) of the perforated plate (1); and in a sectional view in a plate thickness (t) direction of the perforated plate (1), each through-hole (4) swells outside a straight line (L) connecting a point on the edge of the largest hole diameter portion (11) and a corresponding point on the edge of the smallest hole diameter portion (12); wherein in the sectional view in the plate thickness (t) direction of the perforated plate (1), of a part of each through-hole (4) swelling outside the straight line (L), a largest swelling position (14, 15) is a position on the wall surface of the through-hole (4) of a largest swelling amount (δa) in a direction parallel to the surfaces (S1 and S2) of the perforated plate (1), the largest swelling position (14, 15) being located on a central position in the plate thickness (t) direction of the perforated plate (1) or on the smallest hole diameter portion (12) side with respect to the central position, characterized in that in the sectional view in the plate thickness (t) direction of the perforated plate (1), the wall surface of the through-hole (4) is formed by a combination of only curves having different curvatures.

2. A perforated plate (1) comprising a large number of through-holes (4); wherein: each through-hole (4) includes a largest hole diameter portion (11) that is formed on one surface (S1) of the perforated plate (1), said largest hole diameter portion (11) having the largest hole diameter (Dmax), and a smallest hole diameter portion (12) that is formed on the other surface (S2) of the perforated plate (1); and in a sectional view in a plate thickness (t) direction of the perforated plate (1), each through-hole (4) swells outside a straight line (L) connecting a point on the edge of the largest hole diameter portion (11) and a corresponding point on the internal edge of the smallest hole diameter portion (12); wherein in the sectional view in the plate thickness (t) direction of the perforated plate (1), of a part of each through-hole (4) swelling outside the straight line (L), a largest swelling position (14, 15) is a position on the wall surface of the through-hole (4) of a largest swelling amount (δa) in a direction parallel to the surfaces (S1 and S2) of the perforated plate (1), the largest swelling position (14, 15) being located on a central position in the plate thickness (t) direction of the perforated plate (1) or on the smallest hole diameter portion (12) side with respect to the central position, characterized in that in the sectional view in the plate thickness (t) direction of the perforated plate (1), the wall surface of the through-hole (4) between said point on the edge of largest hole diameter portion (11) and the corresponding point on the internal edge of the smallest hole diameter portion (12) is formed by a combination of only curves having different curvatures.

3. The perforated plate (1) according to claim 2, wherein: the smallest hole diameter portion (12) of each through-hole (4) comprises a predetermined portion of constant diameter in the plate thickness (t) direction, the predetermined portion of constant diameter having a thickness (td) equal to or smaller than the smallest hole diameter (Dmin) of the smallest hole diameter portion (12).

4. The perforated plate (1) according to any of the claims 1 to 3, wherein: the through-holes (4) are disposed at a constant distance between the centers of adjacent through-holes (4); and each through-hole (4) has the largest hole diameter (Dmax) which is smaller than ½ of a hole pitch, the hole pitch being defined as the distance between the centers of adjacent through-holes (4).

5. A combination of a plate-shaped or wall-shaped closing member (2), an air layer (3) and the perforated plate (1) according to one of the claims 1 to 4, wherein: the perforated plate (1) is placed so that the air layer (3) is formed between the perforated plate (1) and the plate-shaped or wall-shaped closing member (2).