JP2008120216A - Noise reducing structure of automobile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a sound absorbing material arranged on the back side of an inner plate effectively work for reducing noise in a vehicular cabin of a required frequency. <P>SOLUTION: The sound absorbing material 4 is provided between a roof trim 2 and a roof panel 3, and the roof trim 2 is divided into a plurality of 1×1 vibration mode natural frequency areas by a vibration regulating element 9. On the sound absorbing material 4, a large number of high density portions 8 is disposed so as to exist around the maximum amplitude portions 6 which are centers of the areas. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

    The present invention relates to an automobile noise reduction structure.

    Various kinds of noise are generated in a running car, and road noise and wind noise are known as one of particularly disturbing for passengers. This road noise is generated by a vehicle tire as a vibration source and vibrations are transmitted to the vehicle body to become vehicle interior noise, and is usually a low / medium frequency sound of 100 to 1000 Hz. On the other hand, wind noise is sound in a high frequency range of 1001 Hz to 10 kHz. As a countermeasure against such noise, a sound absorbing material is disposed between the roof trim and the roof panel or between the door trim and the door inner panel.

In addition, as a sound absorbing material, a material obtained by laminating a plurality of fiber layers having different sound absorbing characteristics (sound absorbing frequency characteristics) is also known (see Patent Document 1). For example, a sound absorbing material formed by laminating a fiber layer having a sound absorption characteristic set to 100 to 500 Hz and a fiber layer having a sound absorption characteristic set to 100 to 300 Hz can be applied to a roof panel portion, a floor carpet, a dash panel portion, etc. of an automobile. It is to arrange.
JP 2001-306080 A

    As a result of previous research on the noise problem in automobiles, the present inventor has found that low and medium frequency sound propagated from the road surface of the vehicle into the passenger compartment, for example, two plates such as a gap between the roof trim and the roof panel. When the sound enters the flat space formed by the above, the direction in which the sound wave travels changes to the direction along the plate surface, and the low and medium frequencies are provided by the sound absorbing material provided along the plate surface in the flat space. We found that sound was absorbed efficiently.

    By the way, the sound absorbing material and the low / medium frequency sound have the following relationship. That is, in order to make low / medium frequency sound easy to enter the sound absorbing material, it is preferable to increase the air permeability of the sound absorbing material. On the other hand, it is preferable to reduce the air permeability of the sound absorbing material in order to reduce the absorption of the sound incident inside the sound absorbing material. When sound waves are incident on the sound absorbing material, the air in the sound absorbing material vibrates, and the vibration of the air is converted into thermal energy by friction with the fibers. However, the lower the air permeability, the greater the friction and the higher the sound absorption rate. Because.

    Therefore, it is not possible to increase both the incident efficiency and the sound absorption rate of low / medium frequency sound only by adjusting the air permeability of the sound absorbing material.

    In the present invention, “breathability” refers to the length of travel distance required for air particles to pass through the interior of the sound absorbing material. That is, the low air permeability means that the distance that the air particles move when traveling through the sound absorbing material for a unit length is long. For example, when the fiber density is high and the fibers are intertwined in a complicated manner, the air particles move in a zigzag so as to sew the gaps between the fibers, so that the moving distance becomes long. In that case, since the frequency | count of friction with an air particle and a fiber increases, it becomes easy to absorb a sound (The sound-absorbing property is so high that air permeability is low).

    On the other hand, in order to improve sound absorption, it is effective to dispose the sound absorbing material on the antinode portion of the particle velocity (velocity of air molecules by sound waves) where the amount of movement of air particles is large. For this reason, it is conceivable to arrange a sound-absorbing material with low air permeability in the abdomen of the particle velocity in the flat space, and arrange a sound-absorbing material with high air permeability in other parts. However, since the resonance of various directions is mixed in the flat space and the sound propagation direction is not constant, the sound absorption with low air permeability is high so that the sound absorption is high for the particle velocity distribution in any direction. It is difficult to arrange the material.

    Therefore, an object of the present invention is to make it possible for the sound absorbing material disposed on the back side of the inner plate to effectively work to reduce vehicle interior noise at a desired frequency.

    In order to solve such problems, the present invention divides an inner plate that forms a passenger compartment space into a region that vibrates at an appropriate natural frequency, and the vehicle interior noise is detected from the maximum amplitude portion of the vibration region to the inner plate. And the sound propagates radially between the two plates from the maximum amplitude part, and the particle velocity between the inner and outer plates (air molecules by sound waves) In addition, the noise in the vehicle cabin can be efficiently reduced by controlling the distribution of the velocity and arranging the sound absorbing material in correspondence with the particle velocity distribution.

In the invention according to claim 1, the sound absorbing material spreads along at least one of the inner plate and the outer plate between the inner plate forming the passenger compartment space and the outer plate provided outside the inner plate. In the automobile noise reduction structure arranged as follows:
The inner plate is partitioned into a plurality of natural vibration regions by a vibration restricting element that locally restricts the membrane vibration of the inner plate,
The sound absorbing material is characterized in that a high density portion having a locally increased density is disposed around a maximum amplitude portion of each natural vibration region of the inner plate.

    That is, when no vibration restricting element is provided on the inner plate, the inner plate does not always vibrate with a specific position at the maximum amplitude portion. On the other hand, according to the present invention, by providing the vibration restricting element and dividing the inner plate into a plurality of natural vibration regions, each natural vibration region of the inner plate vibrates due to the vehicle interior noise. Propagates between the outer plates. The noise propagates radially along the plate surface around the maximum amplitude portion of each natural vibration region. That is, between the inner and outer plates, sound always propagates in a certain direction (in this case, the radial direction centered on the maximum amplitude part), and the particle velocity distribution ripples around the maximum amplitude part. It becomes the form which spread like. For this reason, in the sound absorbing material between the inner plate and the outer plate, not only the noise entry site works to absorb and reduce the noise, but also the sound absorbing material extending along the inner plate or the outer plate is widely used for noise absorption. It will work for absorption and reduction.

    Thus, if the sound absorbing material is the same fiber material, the higher the density, the higher the sound absorption rate. Therefore, the high density portion (the portion with low air permeability) is located in the abdominal portion of the particle speed with the highest energy. It is desirable to arrange them. On the other hand, in the present invention, as described above, since sound always propagates radially around the maximum amplitude portion, the sound always passes through the high density portion arranged around the maximum amplitude portion. The high-density part works efficiently for sound absorption.

    In addition, since the sound absorbing material is partially dense and the other parts are low density (air permeability is high), the sound incident efficiency is high as a whole. Therefore, sound can be efficiently incident on the sound absorbing material to reduce absorption.

    As the vibration restricting element, a support member that supports the inner plate to the outer plate can be used, or when the sound absorbing material is in close contact with the outer plate, a harder protrusion that protrudes from the sound absorbing material and contacts the inner plate. The part can be a vibration regulating element. That is, by arranging such support members and protrusions at appropriate intervals and partially restricting the membrane vibration of the inner plate (suppressing vibration), the inner plate can be divided into a plurality of natural vibration regions (for example, each 1 × 1 mode vibration region that produces a belly at the center).

    The sound absorbing material is preferably formed of a porous material, in particular, natural fibers such as wool and cotton, synthetic fibers such as polyethylene terephthalate, inorganic fibers such as glass wool, and other fibrous materials. The sound-absorbing material is not limited to a single layer, and sound-absorbing materials having different sound-absorbing characteristics (for example, different densities and materials) can be laminated and used in two or more layers.

    The high-density portion and the protruding portion as the vibration regulating element can be formed by partially compression-molding the sound-absorbing material, or formed by embedding the high-density material in the sound-absorbing material body at appropriate intervals. be able to. In the latter case, the high-density material may be the same material as the sound-absorbing material body or a different material. The high density part may be arranged in a dotted line around the maximum amplitude part, or may be arranged in a form that forms a continuous line.

The invention according to claim 2 is the invention according to claim 1,
The inner plate is divided into a natural vibration region having a natural frequency of 1000 Hz or less.

    That is, road noise that is particularly problematic as vehicle interior noise is usually a sound of 100 to 1000 Hz, and the natural frequency of each natural vibration region is set to 1000 Hz or less in order to reduce the noise. In addition, in each natural vibration region, not all of them are adjusted to the same natural frequency, but by providing a plurality of natural vibration regions having different natural frequencies, it is possible to reduce vehicle interior noise in a wide frequency range. .

The invention according to claim 3 is the invention according to claim 1 or claim 2,
The high-density portion is arranged so as to form a multiple ring around the maximum amplitude portion.

    That is, even when a high density is randomly arranged around the maximum amplitude portion, the sound absorption rate of the sound that propagates radially from the maximum amplitude portion can be increased. However, in the random arrangement, the high density portion does not always work effectively for absorbing sound propagating from the maximum amplitude portion in all directions. Further, when sound propagates radially from the maximum amplitude portion, the particle velocity is distributed like a ripple. Therefore, in a random arrangement, a high density portion that does not contribute to sound absorption appears.

    Therefore, in the present invention, the high-density portion is arranged so as to form a multiple ring around the maximum amplitude portion, and thereby, sound absorption of the sound propagating radially from the maximum amplitude portion, particularly the target frequency. It is advantageous for sound absorption.

The invention according to claim 4 is the invention according to claim 3,
The high-density part is arranged so as to be a multiple concentric ring centered on the maximum amplitude part.

    This is further advantageous in efficiently absorbing the sound of the target frequency.

The invention according to claim 5 is the invention according to claim 4,
The high-density part is arranged so as to be a multiple concentric circles centered on the maximum amplitude part, thereby further advantageous in efficiently absorbing the sound of the target frequency. become.

The invention according to claim 6 is any one of claims 2 to 5,
The pitch of the high-density part arranged in the radial direction centering on the maximum amplitude part is 17 cm or less.

    That is, the pitch of 17 cm corresponds to 1/2 of the wavelength of the sound wave of 1000 Hz. Therefore, when the pitch is 17 cm, the high-density portion can be disposed on each abdominal portion of the particle velocity of the sound wave of 1000 Hz, and the sound at the frequency can be efficiently reduced. Thus, the pitch being 17 cm or less means that each high-density portion is likely to be positioned at the abdomen of the particle velocity of sound waves of various frequencies, and ranges from a low frequency to a high frequency. This is advantageous for reducing sound in a wide frequency range.

The invention according to claim 7 is the invention according to any one of claims 1 to 6,
The sound absorbing material is stacked on one of the inner plate and the outer plate, and a gap is formed between the sound absorbing material and the other plate,
The high density portion protrudes into the gap from the sound absorbing material.

    Therefore, the sound that has entered the back of the inner plate from the maximum amplitude portion collides with the high density portion protruding into the gap in the process of propagating through the gap, and vibrates the high density portion. Since the space between the inner plate and the outer plate is agitated by the vibration of the high density portion, the particle velocity in the space is increased, and the sound absorbing performance can be improved.

The invention according to claim 8 is any one of claims 1 to 7,
The inner plate is a roof trim that forms a ceiling surface of the vehicle compartment,
The outer plate is a roof panel forming an outer wall of the vehicle body.

    Therefore, the vehicle interior noise can be efficiently absorbed and reduced in the roof portion where it is easy to ensure a wide sound absorption area.

    In each of the above inventions, the inner plate is provided with a flexible portion whose rigidity is adjusted so as to vibrate with a low / medium frequency sound of 100 Hz to 1000 Hz, and the natural vibration region is disposed in the flexible portion. Is preferred. The vibration between the inner plate and the outer plate is agitated by the vibration of the flexible part of the inner plate, and this agitation increases the particle velocity of low and medium frequency sound that propagates radially from the maximum amplitude part of each natural vibration region. The low / medium frequency sound is efficiently absorbed by the sound absorbing material at the back of the inner plate, which is advantageous for noise reduction.

    As described above, according to the present invention, the inner plate is divided into a plurality of natural vibration regions, and the sound-absorbing material between the inner plate and the outer plate exists around the maximum amplitude portion of each natural vibration region. Since the high-density portion is disposed in the vehicle interior noise, the vehicle interior noise enters between the inner plate and the outer plate from the maximum amplitude portion and propagates radially around the maximum amplitude portion. The high-density part around the maximum amplitude part works efficiently for sound absorption, and the sound-absorbing material spreading along the inner plate or outer plate can be widely used for absorbing and reducing noise, and the low-density sound-absorbing material The main body portion and the high density portion can efficiently absorb sound in a wide frequency range.

    Hereinafter, embodiments of the present invention will be described with reference to the drawings.

    FIG. 1 is a diagram illustrating the principle of the present invention. In the figure, reference numeral 1 denotes a vehicle interior space, 2 denotes an inner plate (for example, a trim) that forms the vehicle interior space 1, and 3 denotes an outer plate (for example, a vehicle body panel) provided outside the inner plate 2. A gap is formed between the outer plate 3 and the outer plate 3, and a porous sound absorbing material 4 formed of a fiber material or the like is disposed in the gap so as to spread along at least one of the inner plate 2 and the outer plate 3. ing. The rigidity of the inner plate 2 is adjusted so as to vibrate with a low / medium frequency sound of, for example, 100 Hz to 1000 Hz.

    In the illustrated example, the sound absorbing material 4 is stacked on the outer plate 3, and a gap 5 is formed between the sound absorbing material 4 and the inner plate 2. However, the sound absorbing material 4 may overlap the inner plate 2 and form a gap between the outer plate 3 or overlap both the inner plate 2 and the outer plate 3, that is, between the inner plate 2 and the outer plate 3. The gap may be filled with a sound absorbing material, or a gap may be formed between the inner plate 2 and the outer plate 3.

    The sound-absorbing material 4 is provided with a large number of high-density portions 8 with locally increased density (lower air permeability) and a plurality of vibration restricting protrusions (vibration restricting elements) 9. As shown in FIG. 2, the high-density portion 8 in the illustrated example is formed by a velor that compresses the fiber material of the sound absorbing material from the outer plate 3 side toward the passenger compartment side by a punch and protrudes into the gap 5. Yes. Similarly to the high-density portion, the vibration restricting projection 9 is also formed by a velor that is compressed by a punch from the outer plate 3 side toward the passenger compartment side by a punch and protrudes into the gap 5. However, the density is higher than that of the high-density portion 8 and is formed harder, and the tip contacts the inner plate 2. The high density portion 8 does not hit the inner plate 2.

    The vibration restricting projection 9 is a stick rod of the inner plate 2 with respect to the outer plate 3, so that the inner plate 2 can suppress membrane vibration at the portion where the tip of the vibration restricting projection 9 is in contact. . FIG. 3 shows an arrangement example of the vibration restricting protrusions 9. In this arrangement example, the plurality of vibration restricting protrusions 9 are arranged at regular intervals (an interval of 140 cm or less corresponding to a half wavelength of a 125 Hz sound wave) in the front-rear and left-right directions. Thereby, the inner plate 2 is partitioned into a plurality of square natural vibration regions A. That is, the four vibration restricting protrusions 9 are arranged at the respective vertices of the square natural vibration region A. Therefore, in each natural vibration region A, 1 × 1 that produces a belly at the center of the square. Mode membrane vibration is likely to occur.

    Therefore, each natural vibration region A is arranged so that the center thereof is the maximum amplitude portion 6 and the high-density portion 8 exists around the maximum amplitude portion 6. In the example of FIG. 3, a large number of high-density portions 8 are arranged in multiple concentric circles centered on the maximum amplitude portion 6.

    With the above configuration, as indicated by an arrow in FIG. 1, each natural vibration region A vibrates in resonance with the vehicle interior noise, whereby the vehicle interior noise propagates between the inner plate 2 and the outer plate 3. To do. Since the inner plate 2 and the outer plate 3 are narrow, the noise propagates radially around the maximum amplitude portion 6 along the plate surface. That is, a particle velocity distribution spreading in a ripple pattern around the maximum amplitude portion 6 is obtained. For this reason, the sound-absorbing material 4 spreading along the inner plate 2 or the outer plate 3 works widely in absorbing and reducing noise.

    And the high density part 8 may adjust a density suitably according to the frequency of the sound to absorb. For example, when it is desired to actively reduce low / medium frequency sound of 100 Hz to 1000 Hz in the passenger compartment space, the density of the high density portion 8 may be set so as to absorb the low / medium frequency sound. When it is desired to actively reduce high frequency sound from 1000 Hz to about 10 kHz, the density of the high density portion 8 may be set so as to absorb the high frequency sound. At this time, since the density of the sound-absorbing material body (portion other than the high-density portion 8) is lower than that of the high-density portion 8, the sound incident efficiency is increased, and relatively high frequency sound is absorbed by the high-density portion 8. Noise in the passenger compartment is reduced.

    Further, when a plurality of high-density parts 8 are provided, even if the same density is set, a high-density part that absorbs low / medium frequency sound and a high-density part that absorbs high frequency sound are mixed. It may be arranged. If they are mixed and disposed as described above, the sound in a wider frequency range is absorbed as a whole.

    According to the arrangement example of the high-density part in FIG. 3, since the high-density part 8 is arranged so as to have multiple concentric circles with the maximum amplitude part 6 as the center, all of the radial propagation from the maximum amplitude part 6 is performed. Directional sound waves are affected by the high density portion 8, which is advantageous for sound absorption. Further, as in this example, when the high-density portions 8 are arranged concentrically and arranged at regular intervals in the radial direction, that is, when the pitch P arranged in the radial direction of the high-density portions 8 is constant, The sound of the frequency located in each high-density part 8 in which the antinodes of the particle velocity are arranged in the radial direction is efficiently absorbed by these high-density parts 8. Therefore, it is advantageous for efficiently absorbing sound of a specific frequency.

    The pitch P is preferably 17 cm or less, which corresponds to a half wavelength of a 1000 Hz sound wave having the shortest wavelength in the frequency range where sound absorption is desired. This increases the possibility that each high-density portion 8 is positioned at the abdomen of the particle velocity of sound waves having various frequencies, which is advantageous for reducing sound in a wide frequency range from low frequencies to high frequencies. The diameter of the high density portion 8 is preferably 4.3 cm or more and 8.5 cm or less. 4.3 cm corresponds to 1/8 wavelength of a 1000 Hz sound wave, and 8.5 cm also corresponds to 1/4 wavelength.

    4 to 6 show other arrangement examples of the high density portion 8 in the sound absorbing material 4. In FIG. 4, the high-density portion 8 is arranged so as to be a multiple concentric square centered on the maximum amplitude portion 6. According to this example, as in the example of FIG. 3, sound waves in all directions propagating radially from the maximum amplitude portion 6 are affected by the high-density portion 8, which is advantageous for sound absorption. Further, in this example, the high-density portion 8 arranged in the direction orthogonal to each side of the square has a smaller arrangement pitch than the high-density portion 8 arranged in the diagonal direction of the square, so that a higher frequency sound can be obtained. Is absorbed. Further, when resonance occurs in the gap between the inner plate 2 and the outer plate 3 in the direction orthogonal to each side of the square, it is advantageous in absorbing sound at the resonance frequency. Note that the high-density portion 8 may be arranged in a multiple rectangular shape centered on the maximum amplitude portion 6.

    In FIG. 5, the high-density portion 8 is arranged so as to be a multiple concentric ellipse centered on the maximum amplitude portion 6. According to this example, as in the example of FIG. 3, sound waves in all directions propagating radially from the maximum amplitude portion 6 are affected by the high-density portion 8, which is advantageous for sound absorption. Further, in this example, the arrangement pitch is smaller in the high-density portions 8 arranged in the minor axis direction of the ellipse than in the high-density portions 8 arranged in the major axis direction, so that higher frequency sound is absorbed. . In the case of this ellipse, it is preferable that the arrangement pitch in the major axis direction be equal to or less than a half wavelength (17 cm) of 1000 Hz.

    In each of the examples shown in FIGS. 3 to 5, a large number of velor-shaped high-density portions 8 are interspersed so as to form a predetermined figure, but in FIG. 6, the high-density portions 8 are formed to be linear. In addition, they are arranged so as to have multiple concentric circles centered on the maximum amplitude portion 6. Also in this example, the same effect as the example of FIG. 3 is obtained.

    4 and 5 also, the high density portion 8 can be linearly connected as shown in FIG.

    Further, in each example of FIGS. 3 to 6, the high-density portion 8 is arranged so as to draw a multiple figure around the high acoustic transmittance portion 6, but it is a single circle, ellipse, or rectangle. You may arrange | position so that it may become a shape, circular arc shape, etc.

    FIG. 7 shows experimental data for confirming the effect of the rigidity (flexibility) of the inner plate 2 on the sound absorption. In the experiment, four types of inner plates with different stiffnesses were prepared, the inner plate was installed in a model simulating the passenger compartment, and the model inner space was defined as a space between the simulated passenger compartment space and the inner and outer plates. And a sound absorbing material disposed in the sound absorbing space (noise reduction structure similar to FIG. 1). Then, a sound of 100 to 1000 Hz is generated in the simulated passenger compartment space, and the amplitude of the vibrating inner plate is measured with a laser vibrometer, and the sound pressure in the sound absorbing space is measured with an SPL (sound pressure level) microphone. did.

    When the relationship between the vibration amount (amplitude) of the inner plate and the sound pressure reduction allowance is examined, as shown in FIG. 7, the sound pressure reduction allowance increases as the vibration amount of the inner plate increases. This is because the vibration of the inner plate increases the particle velocity of the sound that is agitated by the air between the inner plate and the outer plate and propagates radially from the maximum amplitude portion, and the particle velocity increases as the vibration amount of the inner plate increases. This is because the amount of increase increases and the sound is efficiently absorbed by the sound absorbing material on the back of the inner plate.

    8 and 9 show specific examples in which the present invention is applied to a roof portion of an automobile. FIG. 8 is a view showing the arrangement of the high density portion 8 and the vibration restricting projection 9. In the figure, reference numeral 3 denotes a roof panel (outer plate). A small circle indicates the high density portion 8, a large single circle indicates the vibration restricting projection 9, and a large double circle indicates the trim (inner plate) support portion 10. The trim support portion 10 is a rod-shaped member that supports the roof trim to the roof panel 3, and the membrane vibration of the portion of the roof trim supported by the trim support portion 10 is suppressed by the trim support portion 10. The trim support portion 10 is a vibration restricting element. In FIG. 8, the sound absorbing material itself and the roof trim itself are not drawn. A plurality of reinforcements (hereinafter referred to as roof rain) 12 extending in the vehicle width direction are provided on the inner surface side of the roof panel 3 at intervals in the longitudinal direction of the vehicle body. Reference numeral 13 denotes a ceiling lamp mounting portion, and reference numeral 14 denotes an assist grip mounting portion.

    FIG. 9 is a sectional view of the roof portion, and the roof trim 2 is in contact with the lower surface of the roof rain 12. Therefore, since the roof trim 2 is suppressed from membrane vibration by the roof rain 12, the roof rain 12 is a vibration restricting element. Further, the roof trim 2 is supported at its peripheral edge by the roof panel 3 or the like, so that vibration is restricted. In the case of this example, the vibration of the roof trim is not restricted by the ceiling light attaching part 13 and the assist grip attaching part 14, and they are not vibration restricting elements.

    Thus, a sound absorbing material 4 having a high density portion 8 is provided in the gap between the roof trim 2 and the roof panel 3. Unlike the example of FIG. 1, the sound absorbing material 4 is stacked on the inner plate side, that is, on the roof trim 2, and a gap 5 is formed between the sound absorbing material 4 and the roof panel 3. The high density portion 8 and the vibration restricting projection 9 protrude from the sound absorbing material main body into the gap 5, and the tip of the vibration restricting protrusion 9 is in contact with the roof panel 3. The tip of the high density portion 8 is separated from the roof panel 3.

    As described above, since the vibration restricting protrusion 9, the trim support portion 10, and the roof rain 12 work as vibration restricting elements, the roof trim 2 is separated from the natural vibration regions (1 × 1 mode) by the vibration restricting elements. Vibration region).

    For example, between the roof rains 12, a portion sandwiched between the roof rain 12 adjacent to the front and rear and the vibration restricting protrusions 9 adjacent to the left and right becomes one natural vibration region, or the roof rain 12 adjacent to the front and rear A portion sandwiched between the vibration restricting protrusion 9 and the trim support portion 10 adjacent to each other is one natural vibration region.

    On the front side of the front roof rain 12, one natural vibration region is defined by the four vibration restricting projections 9 existing in the center thereof, and adjacent to the rear side of the natural vibration region, A natural vibration region is formed by the front roof rain 12. In addition, at both ends, the natural vibration region is defined by the vibration restricting protrusion 9, the trim support portion 10, and the roof rain 12.

    Even on the rear side of the rear roof rain 12, the natural vibration region is defined by the vibration restricting protrusion 9 and the rear roof rain 12, or by the vibration restricting protrusion 9 and the support portion at the periphery of the roof trim.

    Each of the natural vibration regions is a flexible part whose rigidity is adjusted so as to vibrate with a low / medium frequency sound of 100 Hz to 1000 Hz. The rigidity can be adjusted by compression molding so that each natural vibration region is thinner than a portion where vibration is restricted. That is, by reducing the plate thickness, the rigidity is lowered and vibration is likely to occur. Alternatively, when the roof trim 2 has a structure in which glass fiber layers are laminated on both sides of the urethane base layer, the rigidity is lowered by partially reducing the fiber density of the glass fiber layer. Good. Alternatively, the rigidity may be lowered by partially lowering the strength of the urethane constituting the base material layer (using partially soft urethane).

    Thus, the high-density portion 8 is disposed around the center portion of each natural vibration region, that is, around the maximum amplitude portion 6 so as to have a plurality of concentric circles around the maximum amplitude portion 6. . Further, between the roof rains 12, a large number of high density portions 6 are arranged in a straight line in the vehicle longitudinal direction and the vehicle width direction between the center natural vibration region and the left and right natural vibration regions. Yes.

    Therefore, as shown in FIG. 10, in the portion where the high density portion 8 is arranged so as to have a plurality of concentric circles, the sound incident on the back portion of the roof trim 2 from the passenger compartment through the maximum amplitude portion 6 is an arrow. As shown in FIG. 6, the sound propagates radially from the maximum amplitude portion 6, but the high-density portion 8 is provided in a shape that blocks the radial propagation, so that the sound is efficiently absorbed by the high-density portion 8. Furthermore, since the high density portion 8 vibrates in response to a collision of sound propagating in the space between the inner plate 2 and the outer plate 3, the space between the inner plate 2 and the outer plate 3 is agitated. Therefore, the particle velocity in the space is increased and the sound absorption performance is improved.

    A space between adjacent roof rains 12 shown in FIG. 8 is a space surrounded by a roof rain 12 and a roof side in a rectangular shape. For this reason, as shown in FIGS. 11 and 12, resonance between the roof rains 12 is likely to occur in which the vibration propagation direction is the vehicle width direction or the vehicle body front-rear direction, as indicated by the wavy line. Then, as shown in FIG. 8, in the portion where the high density portion 8 is arranged so as to be linearly arranged in the vehicle longitudinal direction and the vehicle width direction, the resonance in the vehicle width direction and the vehicle longitudinal direction is concerned. It is blocked by the high density portion 8 and has good sound absorption. 11 and 12, the arrangement state of the high-density portions 8 is different from that in FIG. 8, and the high-density portions 8 are alternately arranged in rows in the vehicle longitudinal direction. is doing. Even with such an arrangement, resonance in the vehicle width direction and the vehicle body longitudinal direction can be efficiently suppressed. As for the periphery of the maximum amplitude portion 6, the high-density portion 8 is provided around the maximum amplitude portion 6 for the purpose of absorbing / reducing the radially propagating sound and suppressing the resonance in the vehicle width direction and the vehicle body longitudinal direction. May be arranged in multiple squares or rectangles as shown in FIG.

    Furthermore, the high density part 8 may adjust the density of the high density part 8 so as to be effective in absorbing high frequency sound from about 1000 Hz to about 10 kHz. That is, the main high-frequency sound is wind noise, and one of the wind noises is due to air eddy currents generated outside the vehicle. This air eddy current is likely to occur at a portion where the shape of the vehicle body has changed, particularly at a portion where the shape has changed from the roof to the vehicle body side. In addition, although it is not wind noise, a sucking sound is generated when air is sucked out of the vehicle interior due to a pressure difference between the vehicle interior and the exterior during traveling. This is likely to occur at the door seal portion, particularly the seal portion at the upper edge of the door. Such high-frequency sound generated in the vicinity of the roof portion is absorbed by the high-density portion of the sound absorbing material and is prevented from propagating into the vehicle interior, which is advantageous for reducing vehicle interior noise.

    FIG. 13 shows an example in which the noise reduction structure according to the present invention is employed on the floor of an automobile. In the figure, 15 is a floor panel, 16 is a floor tunnel extending in the vehicle longitudinal direction at the center position of the vehicle width, 17 is a front seat arrangement portion arranged on both sides of the floor tunnel 16, 18 is a rear seat arrangement portion, and 19 is a spare. It is a trunk board arrangement part provided on the tire accommodating part 20, and the noise reduction structure is adopted in the areas on the front and rear sides of the front seat arrangement part 17 and the area around the trunk board arrangement part 19.

    That is, in the above region, the sound absorbing material (not shown) having the above-described high density portion is disposed in the gap between the floor panel 15 and the floor mat (not shown). A circle in the region indicates the position of the vibration restricting element 9. The floor mat in the area is divided into a plurality of natural vibration areas by the fixed portion of the periphery of the floor mat laid in the area and the vibration regulating element 9.

It is sectional drawing which shows typically the noise reduction structure of the motor vehicle based on this invention. It is sectional drawing which shows the high-density part of a sound-absorbing material. It is a front view which shows the example of arrangement | positioning of the vibration control element in a sound-absorbing material, and a high-density part. It is a front view which shows another example of arrangement | positioning of the vibration control element in a sound-absorbing material, and a high-density part. It is a front view which shows the example of arrangement | positioning of the high-density part in the natural vibration area | region of a sound-absorbing material. It is a front view which shows another example of arrangement | positioning of the high-density part in the natural vibration area | region of a sound-absorbing material. It is a graph which shows the relationship between an inner-plate vibration amount and a sound pressure reduction allowance. It is a top view which shows the example which applied the noise reduction structure of the motor vehicle based on this invention to the roof part. It is a center longitudinal cross-sectional view of the example. It is a top view which shows the propagation direction of the sound in the part which has arrange | positioned the high density part of the example in multiple concentric form. It is a top view which shows the resonance of the vehicle width direction in the part arrange | positioned so that the high-density part of the example may be located in a line with front and rear, and right and left. It is a top view which shows the resonance of the vehicle body front-back direction in the part arrange | positioned so that the high-density part of the example may be located in a line with front and rear, and right and left. It is a top view which shows the example which applied the noise reduction structure of the motor vehicle based on this invention to the floor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Car interior space 2 Inner plate, trim 3 Outer plate, body panel 4 Sound absorbing material 5 Air gap 6 Maximum amplitude part 8 High density part 9 Vibration restricting projection (vibration restricting element)
10 Trim support (vibration restricting element)
12 Roof rain (vibration control element)
15 Floor panel A Natural vibration area

Claims (8)

An automobile in which a sound absorbing material is disposed between an inner plate that forms a passenger compartment space and an outer plate provided outside the inner plate so as to spread along at least one of the inner plate and the outer plate. In the noise reduction structure,
The inner plate is partitioned into a plurality of natural vibration regions by a vibration restricting element that locally restricts the membrane vibration of the inner plate,
Noise reduction of an automobile characterized in that the sound absorbing material is arranged such that a high density portion having a locally increased density exists around the maximum amplitude portion of each natural vibration region of the inner plate. Construction. In claim 1,
A noise reduction structure for an automobile, wherein the natural frequency of each natural vibration region is 1000 Hz or less. In claim 1 or claim 2,
The automobile noise reduction structure, wherein the high-density portion is arranged in a multiple ring around the maximum amplitude portion. In claim 3,
The automobile noise reduction structure according to claim 1, wherein the high-density portion is arranged so as to be a multiple concentric ring centered on the maximum amplitude portion. In claim 4,
The noise reduction structure for an automobile, wherein the high-density portion is arranged in a multiple concentric shape centering on the maximum amplitude portion. In any one of Claims 2 thru | or 5,
A noise reduction structure for an automobile, wherein a pitch of the high density portions arranged in a radial direction centering on the maximum amplitude portion is 17 cm or less. In any one of Claims 1 thru | or 6,
The sound absorbing material is overlaid on the outer plate, and a gap is formed between the sound absorbing material and the inner plate,
As the vibration regulating element, provided with a contact body protruding from the sound absorbing material and contacting the inner plate,
The automobile noise reduction structure, wherein the high density portion protrudes into the gap from the sound absorbing material. In any one of Claims 1 thru | or 7,
The inner plate is a roof trim that forms a ceiling surface of the vehicle compartment,
A structure for reducing noise in an automobile, wherein the outer plate is a roof panel forming an outer wall of a vehicle body.

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