U.S. patent application number 10/475290 was filed with the patent office on 2004-09-02 for acoustic tile and its use in vehicle sound proofing.
Invention is credited to De Alwis, Marilyn, Gunasekera, Darren Aster.
Application Number | 20040168853 10/475290 |
Document ID | / |
Family ID | 19749507 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040168853 |
Kind Code |
A1 |
Gunasekera, Darren Aster ;
et al. |
September 2, 2004 |
Acoustic tile and its use in vehicle sound proofing
Abstract
An acoustic tile for damping vibration in a vehicle body panel,
comprises a base layer (11) comprising a closed cell synthetic
elastomeric foam bonded on one surface to a dense, stiff,
non-cellular constraining layer (12). The base layer (11)
preferably comprises nitryl rubber foam and the constraining layer
preferable comprises an elastomeric/plastomeric polymer-bitumen
blend.
Inventors: |
Gunasekera, Darren Aster;
(Selangor, MY) ; De Alwis, Marilyn; (Pebble Bay,
SG) |
Correspondence
Address: |
LOWE HAUPTMAN GILMAN AND BERNER, LLP
1700 DIAGONAL ROAD
SUITE 300 /310
ALEXANDRIA
VA
22314
US
|
Family ID: |
19749507 |
Appl. No.: |
10/475290 |
Filed: |
April 12, 2004 |
PCT Filed: |
April 2, 2002 |
PCT NO: |
PCT/IB02/01022 |
Current U.S.
Class: |
181/290 ;
181/291 |
Current CPC
Class: |
G10K 11/168
20130101 |
Class at
Publication: |
181/290 ;
181/291 |
International
Class: |
E04B 001/82; E04B
002/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 2001 |
MY |
PI20011553 |
Claims
1 An acoustic tile for damping vibration in a vehicle body panel,
comprising a base layer (11) comprising a closed cell synthetic
elastomeric foam bonded on one surface to a dense, stiff,
non-cellular constraining layer (12).
2 An acoustic tile according to claim 1 wherein foam of the base
layer (11) has a density between 10 kg/m.sup.3 and 140 kg/m.sup.3
and a modulus of elasticity between 4.times.10.sup.7 and 8'10.sup.7
N/m.sup.2.
3 An acoustic tile according claim 1 or claim 2, wherein the
thickness of the base layer (11) is between 3 mm and 15 mm.
4 An acoustic tile according to claim 3, wherein the thickness of
the base layer (11) is about 6 mm.
5 An acoustic tile according to any one of claims 1 to 4, wherein
the base layer (11) comprises closed cell polyurethane foam, closed
cell polyethylene foam or closed cell nitrile rubber foam.
6 An acoustic tile according to any one of claims 1 to 5, wherein
the thickness of the constraining layer (12) is between 1 and 5
mm.
7 An acoustic tile according to claim 6, wherein the thickness of
the constraining layer (13) is about 3 mm.
8 An acoustic tile according to any one of claims 1 to 7, wherein
the material of the constraining layer (13) has a density between
200 kg/m.sup.3 and 400 kg/m.sup.3,
9 An acoustic tile according to claim 8, wherein the material of
the constraining layer (13) has a density between 300 kg/m.sup.3
and 375 kg/m.sup.3
10 An acoustic tile according to any one of claims 1 to 9, wherein
the constraining layer (12) comprises bitumen.
11 An acoustic tile according to claim 10, wherein the constraining
layer (12) comprises a bitumen-polymer blend.
12 An acoustic tile according to any one of claims 1 to 11, wherein
the constraining layer (12) includes a protective layer (13).
13 An acoustic tile according to claim 12, wherein the protective
layer (13) comprises embossed polyethylene film.
14 An acoustic tile according to any one of claims 1 to 13, wherein
constraining layer (12) includes a reinforcing layer (14).
15 An acoustic tile according to claim 14, wherein the
reinforcement layer (14) comprises non-woven polyester fibre.
16 An acoustic tile according to any one of claims 12 to 15,
wherein the constraining layer (12), the protective layer (13)
and/or the reinforcing layer (14) form an integral structure.
17 An acoustic tile according to any one of claims 1 to 16, wherein
the tile is formed in two parts (2,3) with interlocking fingers
(4,5) so that the area of coverage of the tile can be increased by
drawing the two parts apart while retaining contact between at
least the ends of the fingers.
18 A method of damping vibration in a body panel of a motor
vehicle, which comprises applying to the surface of the panel at
least one acoustic tile according to any one of claims 1 to 17.
Description
[0001] The present invention relates to an acoustic tile,
especially to an acoustic tile for use in vehicle sound proofing by
damping vibration in a vehicle body panel.
BACKGROUND TO THE INVENTION
[0002] Noise inside a motor vehicle arises from various sources.
External sources include rain and wind impacting on the vehicle
body panels and internal sources include the engine of the vehicle.
Vibration of the body panels, such as the bonnet and the roof and
door panels, is the source of considerable noise inside the
vehicle.
[0003] Attempts have been made to damp vibration of the body panels
and hence reduce the noise inside the vehicle, by attaching layers
of damping material to the surfaces of the panels.
[0004] One traditional method has been to attach press-formed
fibrous composite sheets. However, the press-formed fibrous
composite sheets are prone to rotting when damp, as the material is
not water resistant. They are very difficult to clean, being
especially prone to trapping dirt, and abrasive handling will cause
a measure of material disintegration.
[0005] More recently synthetic materials, and especially
visco-elastic materials, have been used. One such material is a
co-polymer comprising ethylene, vinyl acetate and acrylic and/or
methacrylic acid.
[0006] Another proposal has been to apply a visco-elastic adhesive
composition comprising a polyepoxide, a polyether amine, a
hetrocrylic amine and a phenol, which is said to be useful as a
damping material over a temperature range of -25.degree. C. to
+60.degree. C.
[0007] A yet further proposal has been to use composite sheets
comprising an elastomeric butyl polymer sheet bonded to a thin
layer of non-elastomeric material on the surface that is to be
positioned away from the panel.
[0008] The various materials hitherto proposed as damping
materials, while providing a degree of damping are not particularly
effective and do not provide the required light weight, high
performance systems that are desired in this technological age.
They add considerably to the effective weight of the panel and thus
detract from the overall performance of the vehicle. Furthermore
they are not particularly useful in preventing transmission of
noise from other sources.
[0009] Improved materials that will not only effectively damp the
vibration of the body panels but will also reduce sound
transmission through the body panels would be a great advance in
the art of vehicle sound proofing.
SUMMARY OF THE INVENTION
[0010] According to the invention an acoustic tile for damping
vibration in a vehicle body panel, comprises a base layer
comprising a closed cell synthetic elastomeric foam bonded on one
surface to a dense, stiff, non-cellular constraining layer.
[0011] The acoustic tile of the invention is a multi-layer sound
and vibration-reducing overlay that can be applied to the doors,
mudguards, roof, engine compartment bulkhead and other body panels
of a vehicle.
[0012] The acoustic tile of the invention can be attached to the
body panels by any desired means but for greatest efficiency the
tiles should be held tight against the panel. Thus they are
preferably adhesively adhered to the panels. Preferably the tiles
have a layer of pressure sensitive adhesive on the surface opposite
the constraining layer.
[0013] The surface of the constraining layer may be patterned or
textured or the constraining layer may include a covering or
protecting layer, which may be patterned or textured. The
constraining layer may include a reinforcing layer between the
constraining layer and any covering or protecting layer. Preferably
the constraining layer and any covering or protecting layer and any
reinforcing layer form a single composite structure.
[0014] Unlike most currently used methods of noise and vibration
reducing techniques employed in motor vehicles, the acoustic tile
of the invention uses noise and vibration cancellation principles.
The constraining layer may be compared to a weight on a spring
attached to the body panel. The vibrations in the panel are
transmitted to the foam layer, which tries to transmit them to the
constraining layer. Since the constraining layer is stiffer and
more massive than the foam layer it does not move so readily and
hence the energy of the vibration is converted from kinetic energy
to potential energy and heat and hence the vibration is damped and
its frequency reduced to more tolerable levels.
[0015] The elastomeric foam layer should be sufficiently flexible
that it can readily conform to the contours of the body panels and
is preferably a polyurethane foam, a polyethylene foam or a nitrile
rubber foam. The thickness of the foam layer is preferably between
3 mm and 15 mm but is more preferably about 6 mm.
[0016] The foam preferably has a density between 10 and 140
kg/m.sup.3 more preferably between 60 kg/m.sup.3 and 140 kg/m.sup.3
and a modulus of elasticity between 4.times.10.sup.7 N/m.sup.2 and
8.times.10.sup.7 N/m.sup.2. It should also have reasonable tear
strength and be fire retardant or self-extinguishing. In addition
it should be resistant to UV, ozone, mildew and fungus normal motor
vehicle fluids.
[0017] Preferably a 6 mm layer having an area of 200 mm.times.120
mm has a compliance between 1.times.10.sup.-9 and
10.times.10.sup.-9 m/N, preferably between 2.times.10.sup.-9 and
6.times.10.sup.-9 m/N.
[0018] The constraining layer simply adds mass to the system and
may be a layer of any material that ensures that the moment of
inertia of the layer is such it will not move readily when the foam
layer is vibrated by the vibrations in the panel to which the tile
is attached. The constraining layer although stiffer than the foam
layer must not be so stiff that the tile cannot be conformed to the
contours of the body panels. It should also have high tear and
puncture resistance.
[0019] The thickness of the constraining layer is preferably
between 1 mm and 15 mm and will usually be about 3 mm.
[0020] The material of the constraining layer preferably has a
density between 200 kg/m.sup.3 and 500 kg/m.sup.3, more preferably
between 300 kg/m.sup.3 and 375 kg/m.sup.3
[0021] The mass ratio of the constraining layer to the foam layer
is preferably from 2:1 to 10:1, more preferably from 5:1 to
7:1.
[0022] Because of the manner in which the acoustic tile of the
invention operates, it only requires a few small pieces of tile on
any given body panel to make a dramatic difference to the vibration
characteristics of the panel.
[0023] Thus, by simply attaching conveniently sized pieces of the
acoustic tile onto at least some of the body panels in a vehicle,
noise from panel vibration and other sources can be reduced
significantly. With the acoustic tile installed, the noise inside a
vehicle can be reduced to levels that greatly enhance driving
comfort and enjoyment.
[0024] Since the entire surface of a body panel does not have to be
covered with tile, it is preferred that the individual tiles are
produced such that each tile is in two parts with interlocking
fingers so that the area of coverage of the tile can be increased
by drawing the two parts apart while retaining contact between at
least the ends of the fingers. By forming the tiles in this way a
big saving in packaging size can also be obtained.
[0025] Because of the closed cell structure of the foam layer, in
addition to the vibration noise being reduced or having its
frequency altered, the tiles also effectively suppress structural,
engine and road noise transmitted through the body panels to which
they are attached. Heat transfer through the body panels is also
reduced.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] The invention will now be described in greater detail, by
way of example, with reference to the accompanying drawings in
which:
[0027] FIG. 1 is a section through an acoustic tile according to
one embodiment of the invention;
[0028] FIG. 2 is a plan view of a preferred form of the tile shown
in FIG. 1
[0029] FIG. 3 shows one way in which the acoustic tiles can be
applied to vehicle body panels.
[0030] FIG. 4 is a graph showing typical performance
characteristics of a vehicle body panel fitted with the acoustic
tile.
[0031] Referring now to FIG. 1, the acoustic tile 1 comprises a
base layer 11 of closed cell fire retardant nitryl rubber and a
constraining layer 12 of a phase inverted distilled bitumen
compound, the continuous phase of which is formed of elastomeric
and plastomeric polymers in which the bitumen is dispersed, a
reinforcing layer 13 of a composite, high weight, rot-proof,
non-woven polyester fabric, stabilized with fiberglass mat and a
protective layer 14 of embossed polyethylene. Although the layers
12, 13 and 14 are shown in the drawing as separate layers the three
layers, in practice is a composite structure. apart until 30 mm of
the fingers 4, 5 remained overlapping giving a coverage area of 397
mm.times.200 mm. The plate thus has an area approximately 9 times
the area covered by the tile.
[0032] The metal panel was mounted onto the open end of a medium
density fiberboard box 45.7 cm.times.48.3 cm.times.50.8 cm with a
thickness of 12 mm and was securely attached on all four edges to
the box. An audio source generating a 50 Hz sinusoidal signal is
placed inside the box to generate an audio signal to cause the
metal panel to vibrate. The resulting panel vibrations cover the
full spectrum (20 Hz to 20,000 Hz) audible to the human ear.
[0033] A calibrated microphone was centrally positioned 3 cm above
the metal plate to record near field sound pressure levels. The
acoustic signature and reverberation strength of the panel with and
without the expanded acoustic tile attached were captured by
measuring the frequency spectrum from 20 Hz to 4,000 Hz. The
resulting data recorded are an average figure obtained from 100
sampling runs. The results are depicted graphically in FIG. 4.
[0034] From the results obtained, the acoustic tile has
significantly suppressed manifested panel frequencies from 50 Hz
onwards with the region between 80 Hz to 3150 Hz registering the
most impressive suppression. In this region, reductions in excess
of 40 dB are registered in some areas; this represents an energy
level drop of more than 10000 times between a panel without an
acoustic tile and one that has the acoustic tile attached. Since
the decibel scale is logarithmic a 40 dB reduction therefore
corresponds to a reduction in perceived volume of sixteen times the
reference audible volume.
* * * * *