JPH10198385A - Sound absorbing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the sound absorbing ability by prolonging an orifice so that sound in a low frequency band can be effectively absorbed. SOLUTION: First and second base boards 1A, 1B are bent in a mountain shape and are superposed together by means of a first hinge 1a so that casing halves 11A, 11B formed respectively in the first and second base boards 1A, 1B are mated with each other, and as well, semicylinders 13A, 13B which are extended toward a boundary between the first and second base boards 1A, 1B are mated together, thereby making it possible to obtain a sound absorbing element 10 composed of a casing 11 and a cylindrical orifice 13 which is extended from the casing 11 and opened to the sound source side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound absorbing material which is used as a countermeasure for noise of a vehicle or the like and which resonates and absorbs sound using a Helmholtz resonator.

[0002]

2. Description of the Related Art As a soundproof means for an engine room or the like of a vehicle, for example, a sound absorbing structure in which a number of cases are arranged on the upper surface (engine side) of a sound insulating plate (under cover) provided below an engine as a sound source. Is adopted. That is, as shown in FIG. 10, a part of the sound absorbing structure is provided with a sound absorbing material 102 attached to and fixed to a sound source side of a sound insulating plate 101. The sound absorbing material 102 has a large number of cases having different internal volumes. The orifice 102a is formed as a ridge, and the orifice hole 102b is formed at the top thereof. The resonance cavities in each case 102a have different resonance frequencies. The sound is taken in and absorbed by resonance.

[0003]

In this type of sound absorbing structure, the volume of the resonance cavity in the case 102a is V, the area of the orifice hole 102b is S, the length of the orifice hole 102b is L, and the sound speed is c. , The resonance frequency f of the case 102a is given by the following equation:

(Equation 1) Required by Assuming that the spring constant of the air spring due to the resonance cavity volume V in the case 102a is k and the density of the air is ρ, the resonance frequency f of the case 102a is expressed by the following equation:

(Equation 2) It is represented by Therefore, to set the resonance frequency f low, the length L of the orifice hole 102b can be calculated from the above equation.
It can be seen that it is effective to increase the mass SLρ of the air mass on the inner periphery of the orifice hole 102b and to increase the resonance sinusoidal volume V by increasing the diameter of the orifice hole 102b.

However, according to the conventional structure, the length L of the orifice hole 102b is short corresponding to the thickness of the case 102a. In addition, typically, a vacuum forming method using only a female mold is employed for forming the sound absorbing material 102 having a large number of cases 102a. In this case, the case 102 must be raised to increase the resonance cavity volume V. The wall thickness becomes thin in the raised portion. Therefore, in the conventional structure in which the length L of the orifice hole 102b depends on the thickness of the case 102, it has been difficult to set the resonance frequency f of the case 102 low and enhance the sound absorbing effect in a low frequency band.

SUMMARY OF THE INVENTION The present invention has been made under the above circumstances, and it is a technical object of the present invention to make it possible to effectively absorb noise in a low frequency band and to improve sound absorption. It is in.

[0006]

Means for Solving the Problems As a means for effectively solving the above-mentioned technical problems, a sound absorbing material according to the present invention is provided on a substrate provided on a sound source side surface of a sound insulating plate. A required number of sound absorbing elements including a case defining a sinus and a cylindrical orifice extending from the case in a direction substantially perpendicular to the sound insulating plate and opening the resonance sinus to the space on the sound source side are formed. It is a thing. That is, according to the present invention, since the orifice is formed in a cylindrical shape from each case, the length can be made sufficiently long regardless of the thickness of the case. The possible sound range can be extended to a low frequency range. Further, since the cylindrical orifice faces the sound source side, the vibration displacement direction of the incident sound from the sound source and the vibration displacement direction of the air mass in the cylindrical orifice are substantially the same direction, and the mass of the air mass increases. Therefore, an excellent sound absorbing effect in a low frequency band (low sound range) can be obtained.

[0007] In this case, preferably, a pair of sound absorbing material substrates are connected to each other via a first hinge and a pair of first substrates are connected to each other via a second hinge opposite to the first hinge. The first substrate includes a pair of second substrates, and the first substrates each have a required number of case halves and half cylinders extending from each of the case halves toward a boundary between the first substrates. It is formed symmetrically, and by mountain folding at the first hinge and valley folding at the second hinge,
The first substrate is self-standing with respect to the second substrate attached to the sound source side surface of the sound insulating plate, and the case halves and half cylinders of the two first substrates abut against each other. And a sound absorbing element comprising a cylindrical orifice extended from the case. In this case, the volume of the resonance cavity of the case and the length of the cylindrical orifice are made sufficiently large, so that the resonance frequency can be easily reduced.

In the above structure, the angle between the first substrate folded and folded in a mountain and the second substrate folded in a valley with respect to the first substrate by the second hinge is substantially equal to the angle of the second hinge. If the second substrate is fixed to the second substrate via an orthogonal third hinge by engagement with the support plate, the first substrate carrying the sound absorbing element including the case and the cylindrical orifice is stabilized with respect to the second substrate. be able to.

[0009]

FIG. 1 shows a first embodiment of a sound absorbing material according to the present invention. That is, the sound absorbing material is attached to and fixed to the surface of the sound insulating plate 2 on the sound source side.
A case 11 defining a resonance cavity 12 between the sound insulation plate 2 and the resonance cavity 12 extending from a top end wall 11a of each case 11 in a direction substantially perpendicular to the sound insulation plate 2 (substrate 1); 1
A required number of sound absorbing elements 10 are formed of cylindrical orifices 13 that open toward the external space on the sound source side.
The sound absorbing elements 10 adjacent to each other are formed by the volume of the case 11 (resonance sinus 12) or the length L of the cylindrical orifice 13.
And those having different resonance areas are arranged.

This sound absorbing material is typically made of a synthetic resin material such as polypropylene, and when used as soundproofing means such as an engine room of a vehicle, an under sound provided below the engine as a sound source. The cover is disposed on the upper surface (on the engine side) as the sound insulating plate 2 and is fixed by joining means such as ultrasonic welding.

According to Helmholtz's resonance theory, the resonance frequency of each sound absorbing element 10 decreases as the length L of the orifice increases, as determined by the above-described equation. According to the sound absorbing material of the embodiment shown in FIG.
The length L of the cylindrical orifice 13 protruding from
1 (usually about 1 mm), so that the resonance frequency for effectively absorbing the sound from the sound source is sufficiently higher than that of the conventional structure shown in FIG. For example, it can be set to 400 Hz or lower.

Further, since the cylindrical orifice 13 extends toward the sound source, when a sound wave of a specific frequency from the sound source is incident, the air mass on the inner periphery of the cylindrical orifice 13 is in the direction of incidence of the sound wave. Vibrates in almost the same direction. In addition, since the length of the cylindrical orifice 13 is long, the mass SLρ (ρ is the air density) of the air mass on the inner periphery thereof is large, so that the cylindrical orifice 13 has an excellent resonance absorbing function for the sound incident from the sound source side.

In the above embodiment, the cylindrical orifice 13 has a shape protruding from the top end wall 11a of each case 11, but as shown in FIG. 2, a second embodiment of the present invention is shown in FIG. The cylindrical orifice 13 may have a shape extending from the top end wall 11 a of the case 11 into the resonance cavity 12.

FIGS. 3 to 6 show a third embodiment of the sound absorbing material according to the present invention. In the sound absorbing material according to this embodiment, as shown in FIGS. 3 and 4, the substrate 1 has a first hinge 1a and second hinges 1b and 1c formed on both sides thereof in parallel with each other. First hinge 1a
The first substrates 1A, 1B connected to each other via the first hinges 1b, and the first substrates 1 via the respective second hinges 1b, 1c.
A pair of second substrates 1C and 1D continuous with A and 1B. The first hinge 1a is formed at both ends of a narrow slit 1d along the boundary between the first substrates 1A and 1B.

In the following description, for convenience, the direction in which the second substrates 1C and 1D are arranged on a plane, that is, the first hinge 1a
A direction perpendicular to the second hinges 1b and 1c is defined as X, and a direction parallel to the first hinge 1a and the second hinges 1b and 1c is defined as Y.

On one first substrate 1A, a required number of case halves 11A having different sizes from each other, and extending from each of these case halves 11A in the X direction toward the boundary between the first substrates 1A and 1B, respectively. A half cylindrical body 13A reaching the slit 1d is formed. In addition, the other first substrate 1B has a required number of case halves 11B corresponding to each case half 11A in the first substrate 1A, and from each of these case halves 11B to the boundary between the first substrates 1A and 1B, respectively. A half cylinder 13B extending in the X direction toward the slit 1d and facing each half cylinder 13A of the first substrate 1A is formed. That is, the case half body 11A and the half-cylinder body 13A on the first board 1A and the case half body 11B and the half-cylinder body 13B on the first board 1B are mutually symmetric with respect to the boundary (slit 1d) between the first boards 1A and 1B. It is formed symmetrically.

On the second substrates 1C and 1D, a plurality of cases 21 having different capacities are formed so as to be adjacent to each other, and an orifice hole 22 is formed at the top of each case 21. Each of these cases 21 is formed by folding the first hinge 1a in a mountain shape as described later, and by folding the second hinges 1b, 1b.
When the first substrates 1A and 1B are erected against the second substrates 1C and 1D by valley-folding the c, they may interfere with the case halves 11A and 11B on the first substrates 1A and 1B. It is formed at a position appropriately separated from the second hinges 1b and 1c so as not to be present.

That is, as shown in FIGS. 5 and 6, the sound absorbing material according to the third embodiment has a substrate 1
3 and FIG. 4, the lower surfaces of the first substrates 1A and 1B in FIG. 3 and FIG. 4 are folded in a mating manner, and the second hinges 1b and 1c are used to valley-fold the second substrate. The first substrates 1A and 1B are made independent on the substrates 1C and 1D. Then, in this state, the second substrates 1C and 1D are attached to a sound insulating plate 2 such as an under cover provided below the engine, for example, and joined by an appropriate welding means such as ultrasonic welding or a fastener. In addition, the folded first substrates 1A and 1B also
Join together as needed.

The substrate 1 is folded as described above and the sound insulating plate 2
To the case half 11A of the first substrate 1A and the case half 11B of the other first substrate 1B.
Abuts each other to form the case 11, and the half-cylindrical body 13A of the first substrate 1A and the other first substrate 1B
Of the cylindrical orifice 13
That is, a case 11 and a cylindrical orifice extending from the case 11 along the first substrates 1A and 1B in a direction (upward) substantially perpendicular to the sound insulating plate 2 and having a tip open to the sound source (engine) side. Thus, a sound absorbing element 10 made up of 13 is formed. In addition, each case 21 in the second substrates 1C and 1D
By attaching and fixing the second substrates 1C and 1D on the sound insulating plate 2, a sound absorbing element 20 having the same structure as the conventional structure of FIG. These sound absorbing elements 20 also have orifice holes 22 open to the sound source (engine) side.

The cylindrical orifices 13 arranged along the first substrates 1A and 1B have substantially the same length and cross-sectional area, respectively, but have the same size as the case 11 (the volume V of the resonance cavity 12). ) Are different from each other, whereby each sound absorbing element 10 is given a different resonance frequency. Since the volume V of the resonance cavity 12 in the sound absorbing element 10 is equivalent to the sum of the volumes of the two case halves 11A and 11B, the volume of each of the case halves 11A and 11B is, for example, in the second substrates 1C and 1D. Even if the volume is about the same as or slightly smaller than the volume of the sound absorbing element 20, the volume V of the resonance cavity 12 including the case halves 11A and 11B is combined.
Is sufficiently larger than the resonance sinus volume of the sound absorbing element 20, and the resonance frequency f given by the above equation can be set sufficiently low.

That is, according to this embodiment, the first substrates 1A and 1B absorb low-frequency sounds.
Each sound absorbing element 20 on the second substrates 1C and 1D absorbs sound in a high frequency range.

According to this embodiment, even if the substrate 1 is formed into the shape shown in FIG. 3 by an inexpensive vacuum forming method or the like, the length of the half-cylinders 1A and 13B depends on the length of the half-cylinders 13A and 13B.
The thickness of 3A and 13B does not decrease or cracks do not occur. For this reason, the length L of the cylindrical orifice 13 in the sound absorbing element 10 can be made sufficiently long, so that excellent sound absorbing performance with respect to sound in a low frequency range can be provided.
It can be manufactured at low cost.

According to the third embodiment,
The first substrates 1A and 1B folded by being mountain-folded by the first hinge 1a stand on the second substrates 1C and 1D via the second hinges 1b and 1c which are easily folded. Therefore, when used as a soundproofing means in an engine room of a vehicle, for example, there is a concern that the vehicle may be tilted or fluttered by the wind pressure during traveling of the vehicle. FIG.
The fourth embodiment shown in FIG. 9 to FIG. 9 eliminates such a risk of tilting and fluttering.

In the fourth embodiment, engaging plates 31, 32 are integrally formed at both ends in the Y direction of each of the first substrates 1A, 1B, and the engaging plates 31, 32 are respectively mounted on the first hinge 1a. It is folded so as to be folded together with the first substrates 1A and 1B. A pair of support plates 33 connected to the second substrate 1C on both sides in the Y direction of one second substrate 1C via third hinges 1e and 1f extending in the X direction orthogonal to the second hinge 1b. , 34 are formed on both sides of the other second substrate 1D in the Y direction, and are connected to the second substrate 1D via third hinges 1g, 1h extending in the X direction orthogonal to the second hinge 1c, respectively. A pair of support plates 35 and 36 are formed symmetrically with the support plates 33 and 34 with the boundary as the axis of symmetry.

The first boards 1A, 1
Hook groove 31 which becomes downward by folding with B
a, 32a are formed. On the other hand, the support plates 33 to 36
Has hook grooves 33a to 36a, and as shown in FIG. 8, in a state where the first substrates 1A and 1B are folded in a mountain by the first hinge 1a, opposing ends of the support plates 33 and 35 are connected to each other. The hook grooves 33a and 35a overlap with each other, and the opposite ends of the support plates 34 and 36 also overlap with each other, and the hook grooves 34a and 36a also overlap with each other. Further, from the state shown in FIG.
C, 1D, and the third hinge 1f,
1h is folded in a valley, and the support plates 34 and 36 are
When it stands perpendicular to D, as shown in FIG. 9, the mutually overlapping hook grooves 33a, 35a of the support plates 33, 35 are engaged with the hook grooves 31a of one of the engagement plates 31 of the first substrates 1A, 1B. And the hook grooves 3 of the support plates 34, 36 which overlap each other.
4a and 36a are one of the engagement plates 32 of the first substrates 1A and 1B.
Is engaged with the hook groove 32a.

The configuration of the other parts is almost the same as that of the third embodiment described above.

That is, according to the fourth embodiment,
By assembling as shown in FIG. 9 through the state shown in FIG. 8, the first substrates 1A and 1B self-standing on the second substrates 1C and 1D are supported by the support plates 33 to 32 via the engagement plates 31 and 32.
36, and is supported from both sides in the X direction.
The assembly state shown in FIG. 9 is maintained by the engagement between the support plates 1 and 32 and the support plates 33 to 36. For this reason, the second substrates 1C, 1
D can be easily joined to the sound insulating plate by ultrasonic welding or a suitable joining means such as a fastener.
Further, the first substrates 1A, 1A receive the wind pressure during traveling of the vehicle.
B can be reliably prevented from tilting or fluttering through the fourth second hinges 1b, 1c.

[0028]

According to the sound absorbing material of the present invention, the following effects are realized. (1) By making the orifice long in a cylindrical shape, the resonance frequency of the sound absorbing element can be set lower than in the conventional structure, and the sound in the low frequency range can be absorbed. (2) The mass of the air mass at the cylindrical orifice increases,
Moreover, since the vibration displacement direction of the air mass in the cylindrical orifice is substantially coaxial with the sound wave incident direction, excellent sound absorbing performance in a low frequency band can be obtained. (3) The length of the cylindrical orifice can be increased without causing difficulty in forming the sound absorbing element by forming the sound absorbing element by abutting the case half and the half cylinder which are arranged symmetrically to each other. In addition, it is possible to increase the sound absorbing performance in a low frequency band by increasing the resonance sinus volume.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a first embodiment of a sound absorbing material according to the present invention.

FIG. 2 is a partial sectional view showing a second embodiment of the sound absorbing material according to the present invention.

FIG. 3 is a perspective view of a sound absorbing material according to a third embodiment of the present invention in a state before assembly.

FIG. 4 is a partial cross-sectional view taken along line IV-IV in FIG.

FIG. 5 is a perspective view of an assembled state showing the third embodiment.

FIG. 6 is a partial sectional view taken on line VI-VI in FIG. 5;

FIG. 7 is a perspective view of a sound absorbing material according to a fourth embodiment of the present invention before being assembled.

FIG. 8 is a perspective view of the assembling process showing the fourth embodiment.

FIG. 9 is a perspective view of the assembled state showing the fourth embodiment.

FIG. 10 is a partial cross-sectional view showing a typical conventional example of a sound absorbing material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 board | substrate 1A, 1B 1st board | substrate 1C, 1D 2nd board | substrate 1a 1st hinge 1b, 1c 2nd hinge 1d Slit 1e-1h 3rd hinge 2 Sound insulation board 10,20 Sound absorption element 11,21 Case 11A, 11B Case half 11a Top end wall 12 Resonant cavity 13 Cylindrical orifice 13A, 13B Half cylindrical body 22 Orifice hole 31, 32 Engagement plate 31a-36a Hook groove 33-36 Support plate

Claims (3)

[Claims] A required number of cases (1) defining a resonance cavity (12) inside a substrate (1) attached to a sound source side surface of a sound insulating plate (2).
1) and a cylindrical orifice (13) extending from each of these cases (11) in a direction substantially perpendicular to the sound insulating plate (2) and opening the resonance cavity (12) to the space on the sound source side. A sound absorbing material, wherein a number of sound absorbing elements (10) are formed. 2. The first hinge according to claim 1, wherein the substrate (1) comprises a first hinge (1a) and a pair of second hinges (1b, 1c) formed parallel to each other on both sides thereof. A pair of first substrates (1A, 1B) continuous with each other via (1a) and the respective second hinges (1b, 1b).
1c) and a pair of second substrates (1C, 1D) connected to the first substrates (1A, 1B) via the first substrates (1A, 1B). 11A, 11B) and each case half (11A, 11B).
11B), semi-cylindrical bodies (13A, 13B) extending toward a boundary between the first substrates (1A, 1B) are formed symmetrically with respect to the boundary as the axis of symmetry, and a mountain is formed by the first hinge (1a). By folding and valley folding with the second hinges (1b, 1c), the second substrate (1C, 1) attached to the sound-insulating plate (2) sound source side surface
D), the first substrate (1A, 1B) becomes independent, and the case halves (1
1A and 11B) and the semi-cylindrical bodies (13A and 13B) abut against each other to form a case (11) and this case (1).
A sound absorbing material characterized by forming a sound absorbing element (10) comprising a cylindrical orifice (13) extended from 1). 3. The first substrate (1A, 1B) according to claim 2, wherein the first substrate is folded and folded.
By the second hinge (1b, 1c), the first substrate (1A,
An angle between the second substrate (1C, 1D) and the second substrate (1C, 1D), which is valley-folded with respect to the second hinge (1b, 1c), is substantially perpendicular to the second hinge (1b, 1c). 1C,
1D) The sound absorbing material is fixed to each other by engagement with a support plate (33 to 36) continuous with the sound absorbing material.