U.S. patent application number 11/034173 was filed with the patent office on 2005-07-14 for automotive dash insulators containing viscoelastic foams.
This patent application is currently assigned to Dow Global Technologies Inc.. Invention is credited to Korchnak, Greg, Siavoshai, Saeed J., Tao, Xiaodong, Tudor, Jay.
Application Number | 20050150720 11/034173 |
Document ID | / |
Family ID | 34794374 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050150720 |
Kind Code |
A1 |
Tudor, Jay ; et al. |
July 14, 2005 |
Automotive dash insulators containing viscoelastic foams
Abstract
Sound insulating systems including viscoelastic foams are
described. The sound insulating system includes a sound-absorbing
layer. The sound-absorbing layer can include viscoelastic foams. An
optional barrier layer is adjacent to the sound-absorbing layer.
Additionally, an optional substrate layer is adjacent to the
sound-absorbing layer, and is spaced and opposed from the optional
barrier layer. The sound insulating system is particularly well
adapted to be employed as vehicle dashmats.
Inventors: |
Tudor, Jay; (Grand Blanc,
MI) ; Tao, Xiaodong; (Troy, MI) ; Siavoshai,
Saeed J.; (Bloomfield Hills, MI) ; Korchnak,
Greg; (Howell, MI) |
Correspondence
Address: |
Richard W. Hoffmann
PO Box 70098
Rochester Hills
MI
48307
US
|
Assignee: |
Dow Global Technologies
Inc.
Midland
MI
|
Family ID: |
34794374 |
Appl. No.: |
11/034173 |
Filed: |
January 12, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60535933 |
Jan 12, 2004 |
|
|
|
Current U.S.
Class: |
181/286 ;
181/204 |
Current CPC
Class: |
G10K 11/162
20130101 |
Class at
Publication: |
181/286 ;
181/204 |
International
Class: |
E04B 002/02; E04B
001/82; F01N 001/00 |
Claims
What is claimed is:
1. A sound insulating system, comprising: a sound-absorbing layer
including an absorption coefficient in the range of about 0.2 to
about 1.0, and a damping loss factor in the range of about 0.3 to
about 2.0.
2. A sound insulating system as set forth in claim 1 wherein said
sound-absorbing layer comprises viscoelastic foam.
3. A sound insulating system as set forth in claim 2 wherein said
viscoelastic foam has a damping loss factor in the range of about
0.4 to 1.6.
4. A sound insulating system as set forth in claim 3 wherein said
viscoelastic foam has an elastic modulus in the range of about
4.times.10.sup.3 Pa to about 1.times.10.sup.6 Pa.
5. A sound insulating system as set forth in claim 4 further
comprising a barrier layer secured to said viscoelastic foam, said
barrier layer substantially impermeable to fluid flow
therethrough.
6. A sound insulating system as set forth in claim 5 wherein said
absorption coefficient of said viscoelastic foam is preferably in
the range of about 0.7 to about 1 at frequencies in the range of
about 1000 Hz to about 6000 Hz.
7. A sound insulating system as set forth in claim 6 further
comprising a substrate, said viscoelastic foam secured to said
substrate.
8. A sound insulating system as set forth in claim 7 wherein said
substrate is a metal structure on a vehicle.
9. A sound insulating system, comprising: a sound-absorbing layer
including an absorption coefficient in the range of about 0.2 to
about 1.0, and a damping loss factor in the range of about 0.3 to
about 2.0; and a barrier layer substantially impermeable to fluid
flow therethrough connected to said sound-absorbing layer.
10. A sound insulating system as set forth in claim 1 wherein said
sound-absorbing layer comprises viscoelastic foam.
11. A sound insulating system as set forth in claim 10 wherein said
viscoelastic foam has a damping loss factor in the range of about
0.4 to 1.6.
12. A sound insulating system as set forth in claim 11 wherein said
viscoelastic foam has an elastic modulus in the range of about
4.times.10.sup.3 Pa to about 1.times.10.sup.6 Pa.
13. A sound insulating system as set forth in claim 12 wherein said
absorption coefficient of said viscoelastic foam is preferably in
the range of about 0.7 to about 1 at frequencies in the range of
about 1000 Hz to about 6000 Hz.
14. A sound insulating system as set forth in claim 13 further
comprising a substrate, said viscoelastic foam secured to said
substrate.
15. A sound insulating system as set forth in claim 14 wherein said
substrate is a metal structure on a vehicle.
16. A sound insulating system, comprising: a sound-absorbing layer
comprising a viscoelastic foam including an absorption coefficient
in the range of about 0.7 to about 1 at frequencies in the range of
about 1000 Hz to about 6000 Hz, and a damping loss factor in the
range of about 0.4 to 1.6; and a barrier layer substantially
impermeable to fluid flow therethrough connected to said
viscoelastic foam.
17. A sound insulating system as set forth in claim 16 wherein said
viscoelastic foam has an elastic modulus in the range of about
4.times.10.sup.3 Pa to about 1.times.10.sup.6 Pa.
18. A sound insulating system as set forth in claim 17 further
comprising a substrate, said viscoelastic foam secured to said
substrate.
19. A sound insulating system as set forth in claim 18 wherein said
substrate is a metal structure on a vehicle.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/535,933, filed Jan. 12, 2004. The disclosure of
the above application is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to a sound
insulating system. More particularly, the present invention relates
to sound insulator systems containing viscoelastic foams.
BACKGROUND OF THE INVENTION
[0003] Automotive makers have endeavored to reduce the overall
noise and vibration in vehicles. Limiting noise, vibration, and
harshness (i.e., "NVH") has become an important consideration in
vehicle designs. Previously, engine noise typically dominated the
overall vehicle noise. Other noise sources, such as from tires,
wind and exhaust have also become as important to reduce as engine
noise. More recently, interior vehicle noise constriction has been
a direct result of consumer demands to reduce the noise in the
vehicle.
[0004] Accordingly, significant efforts have been directed to
reduction of interior vehicle noise. One of these efforts has been
to use a barrier concept, also referred to as a dashmat or dash
insulator system. These dashmats are used to reduce noise from the
engine to the interior of the vehicle. Typically such dashmats are
placed on or adjacent a substrate, such as a firewall to reduce the
amount of noise passing from the engine through the firewall to the
vehicle interior. A general description of dashmat technology can
be found in U.S. Patent Application Publication No. 2003/0180500
A1, the entire specification of which is expressly incorporated
herein by reference.
[0005] Prior dashmats are typically made of a decoupler, usually
made of foam (slab or cast foam) and a barrier, typically made of
thermoplastic polyolefin (TPO) or ethylene vinyl acetate sheet
(EVA). These dashmats are all intended to reduce overall engine
compartment noise. Such barrier type dashmats have typically been
relatively heavy, in order to produce the desired noise reduction
results.
[0006] It is believed that a significant portion of a dashmat's
performance relies on the properties of the foam. Foam performance
is generally considered to be a function of the foam's transmission
loss, absorption, modulus, and damping characteristics.
[0007] More recently, lightweight dashmats have been used. The
lightweight concept utilizes absorptive material, such as shoddy
cotton. Rather than blocking the engine noise, the goal of this
type of dashmat is to absorb and dissipate the engine noise as it
travels from the engine compartment to the vehicle interior. These
lightweight dashmat systems also decrease the overall weight of the
vehicle. A general description of these types of lightweight
dashmat systems can be found in U.S. Pat. Nos. 6,145,617 and
6,296,075, the entire specifications of which are expressly
incorporated herein by reference.
[0008] The primary function of either type of dashmat is to reduce
noise levels in the vehicle's interior. Traditionally, it was
believed that blocking the noise in accordance with the mass law
provides the best noise transmission loss and noise reduction.
Transmission loss and noise reduction are typical measurement
parameters used to quantify the performance of the dashmat
system.
[0009] Although conventional dashmats have been somewhat successful
in reducing noise levels in the vehicle's interior, they have not
been completely satisfactory. More specifically, the insulation
foam (i.e., the decoupler) has been relatively ineffective in that
it does not possess suitable absorptive acoustic properties. Thus,
the noise, regardless of origin, is either not blocked, dissipated
or otherwise reduced enough as it travels through the dashmat and
into the vehicle's interior. Further, earlier insulation foams are
less effective at preventing noise due to vibration of the
substrate or barrier layer.
[0010] Accordingly, it would be desirable to provide dashmats that
have enhanced transmission loss performance characteristics so as
to be operable to reduce both engine compartment noise coming
through the firewall and noise that comes into the passenger
compartment from other sources during vehicle operation.
SUMMARY OF THE INVENTION
[0011] According to a first embodiment of the present invention,
there is provided a sound insulating system, comprising a
sound-absorbing layer including an absorption coefficient in the
range of about 0.2 to about 1.0, and a damping loss factor in the
range of about 0.3 to about 2.0.
[0012] According to an alternate embodiment of the present
invention, there is provided a sound insulating system, comprising
a sound-absorbing layer including an absorption coefficient in the
range of about 0.2 to about 1.0, and a damping loss factor in the
range of about 0.3 to about 2.0. The system further comprises a
barrier layer substantially impermeable to fluid flow therethrough
connected to said sound-absorbing layer.
[0013] According to an alternate embodiment of the present
invention there is provided a sound insulating system, comprising a
sound-absorbing layer comprising a viscoelastic foam. The
viscoelastic foam includes an absorption coefficient in the range
of about 0.7 to about 1 at frequencies in the range of about 1000
Hz to about 6000 Hz, and a damping loss factor in the range of
about 0.4 to 1.6. The system further comprises a barrier layer
substantially impermeable to fluid flow therethrough connected to
said viscoelastic foam.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0015] FIG. 1 is a sectional view of an illustrative sound
insulating system, in accordance with the general teachings of the
present invention;
[0016] FIG. 1A is a sectional view of the sound insulating system
depicted in FIG. 1 attached to a substrate, in accordance with one
embodiment of the present invention;
[0017] FIG. 2 is a graphical illustration comparing the normal
incidence absorption coefficient characteristics of the
illustrative sound-absorbing layers, in accordance with one
embodiment of the present invention;
[0018] FIG. 3 is a schematic illustration of an illustrative test
setup to determine elastic modulus and damping of the illustrative
sound-absorbing layers, in accordance with one embodiment of the
present invention;
[0019] FIG. 4 is a graphical illustration comparing the
transmission loss characteristics of the sound insulating systems
in accordance with the present invention and conventional sound
insulting systems;
[0020] FIG. 5 is a graphical illustration comparing the surface
weight characteristics of the sound insulating systems in
accordance with the present invention and conventional sound
insulting systems;
[0021] FIG. 6 is a graphical illustration comparing the
transmission loss characteristics of a sound insulating system in
accordance with the present invention and a conventional sound
insulting system in relationship to a pre-determined target
profile, in accordance with one embodiment of the present
invention;
[0022] FIG. 7 is a graphical illustration comparing the decibel
improvement in average noise reduction characteristics of a sound
insulating system of the present invention and conventional sound
insulting systems, in accordance with one embodiment of the present
invention;
[0023] FIG. 8 is a graph showing damping test results;
[0024] FIG. 9 is a graph showing damping test results;
[0025] FIG. 10 is a graph showing insertion loss test results;
and
[0026] FIG. 11 is a graph showing damping test results.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The following description of the preferred embodiment(s) is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0028] FIG. 1 is a cross-sectional view of one embodiment of the
present invention. As shown in FIG. 1, there is a sound insulating
system, generally shown at 10. The sound insulating system 10
preferably comprises a multilayer system. The sound insulating
system 10 preferably comprises a sound-absorbing layer generally
indicated at 12. An optional barrier layer generally indicated at
14 is preferably adjacent to the sound-absorbing layer 12. It
should be appreciated that system 10 is preferably operable to be
fastened or otherwise attached, either removably or permanently, to
an optional substrate generally indicated at 14, such as a
firewall, as shown in FIG. 1A. The substrate 16 is preferably
adjacent to the sound-absorbing layer 12 and spaced and opposed
from the barrier layer 14.
[0029] The system 10 preferably provides a multilayer dashmat that
is preferably used to reduce noise transmission to the interior of
the vehicle through the front-of-dash panel. In addition to the
noise-blocking feature, the system 10 preferably reduces noise
levels within the vehicle interior through sound absorption.
Additionally, the system 10 preferably can be used in the engine
compartment to reduce noise exiting the engine compartment to the
exterior of the vehicle. The system 10 also preferably enhances the
sound quality perception for interior and/or exterior environments.
The system 10 can also be incorporated into other automotive
components such as, but not limited to, liners for wheel wells,
fenders, engine compartments, door panels, roofs (e.g.,
headliners), floor body treatments (e.g., carpet backing), trunks
and packaging shelves (e.g., package tray liners). Furthermore, the
system 10 can be incorporated into non-automotive applications.
[0030] The sound-absorbing layer 12 preferably comprises a foam
material 18. The foam material 18 preferably comprises viscoelastic
foam, more preferably viscoelastic flexible foam, and still more
preferably viscoelastic flexible polyurethane foam. Viscoelastic
foam, also referred to as memory or temper foam, is substantially
open-celled and is generally characterized by its slow recovery
after compression.
[0031] The use of viscoelastic foam in accordance with the present
invention in a dashmat system can also possibly be used as a
replacement for vibration damping materials, commonly referred to
as mastic.
[0032] Although viscoelastic foams are preferred in the practice of
the present invention, other foams can be used, either alone or in
combination, that have the requisite properties to be described
herein. Accordingly, the foam material 18 can comprise any natural
or synthetic foam, both slab and molded. The foam material 18 can
be open or closed cell or combinations thereof. The foam material
18 can comprise latex foam polyolefin, polyurethane, polystyrene,
polyester, and combinations thereof. The foam material 18 can also
comprise recycled foam, foam impregnated fiber mats or
micro-cellular elastomer foam. Additionally, the foam material 18
can include organic and/or inorganic fillers. Furthermore,
additional additives may be incorporated into the foam material 18,
such as, but not limited to, flame retardants, anti-fogging agents,
ultraviolet absorbers, thermal stabilizers, pigments, colorants,
odor control agents, and the like.
[0033] In accordance with a preferred embodiment of the present
invention, the foam material 18 has a relatively high absorption
coefficient. Without being bound to a particular theory of the
operation of the present invention, it is believed that a
relatively high absorption coefficient will increase the overall
transmission loss through dissipation of the sound within the foam
material 18.
[0034] FIG. 2 shows sound absorption of various foams. VE refers to
viscoelastic foam. PCF is a density measure referring to
lb/ft.sup.3. The specific VE foam used was FOAMEX H300-10N. The
slab foam was Melamine and the cast foam was polyurethane foam. In
accordance with a preferred embodiment of the present invention,
the foam material 18 has an absorption coefficient of about 0.2 or
greater, more preferably about 0.4 or greater, still more
preferably about 0.7 or greater, and most preferably about 1.0. In
the most preferred embodiment, the absorption coefficient is in the
range of between about 0.7 and 1 at frequencies in the range about
1000 Hz to about 6000 Hz.
[0035] In accordance with a preferred embodiment of the present
invention, the foam material 18 has a relatively low elastic
modulus. Without being bound to a particular theory of the
operation of the present invention, it is believed that a
relatively low elastic modulus will allow the foam material 18 to
contact the substrate 16 (e.g., the firewall or the vehicle's steel
structure) more uniformly and prevent flanking noise from entering
the vehicle's interior. Thus, it is preferred to have a relatively
lower modulus. A lower modulus allows the foam layer 18 to conform
more readily to a substrate. If the modulus is too high, the foam
18 will be too stiff and not easily conform to the substrate.
However, the modulus should not be so low as to not have structural
integrity.
[0036] In general, the minimum modulus would be sufficient for the
foam cells to retain their structure. In accordance with a
preferred embodiment of the present invention, the foam material 18
has an elastic modulus in the range of about 4.times.10.sup.3 Pa to
about 1.times.10.sup.6 Pa.
[0037] In another preferred embodiment, the modulus is in the range
of about 1.times.10.sup.4 to about 1.times.10.sup.5. These ranges
are measured according to test setup shown in FIG. 3.
[0038] In accordance with a preferred embodiment of the present
invention, the foam material 18 has a relatively high damping loss
factor (tan delta). Without being bound to a particular theory of
the operation of the present invention, it is believed that a
relatively high damping loss factor helps reduce vibration in the
vehicle's steel structure which will increase the overall
transmission loss of the dashmat. In accordance with a preferred
embodiment of the present invention, the foam material 18 has a
damping loss factor (tan delta) of about 0.3 or greater, more
preferably about 0.4 or greater, still more preferably about 1.0 or
greater.
[0039] In accordance with another preferred embodiment of the
present invention, the foam material 18 has a damping loss factor
(tan delta) in the range of about 0.3 to about 2.0, more preferably
in the range of about 0.4 to about 2.0, and still more preferably
in the range of about 0.4 to about 1.6. These values are measured
according to test setup shown in FIG. 3.
[0040] By way of a non-limiting example, foam materials that
satisfy the above requirements include Dow experimental
viscoelastic polyurethane foams #76-16-06 HW, #76-16-08HW,
#76-16-10HW, #056-53-01HW, and #056-53-29HW; Foamex 2 pound per
cubic foot (pcf) and Foamex H300-10N 3 pcf viscoelastic foams
(readily commercially available); Carpenter 2.5 pcf viscoelastic
foam (readily commercially available); and Leggett and Platt
viscoelastic foams 25010MF and 30010MF (readily commercially
available).
[0041] The thickness of the sound-absorbing layer 12 can vary
depending on the particular application. While it is preferred that
the thickness be between about 6 mm to about 100 mm, more
preferably about 12 mm to about 50 mm, and still more preferably
about 12 mm to about 25 mm, it will be appreciated that the
thickness can vary, even outside these ranges depending on the
particular application. The thickness has a bearing on the
stiffness of the sound-absorbing layer 12. It will also be
appreciated that the thickness of the sound-absorbing layer 12 can
vary and can be non-uniform.
[0042] Further, it is to be understood that the sound-absorbing
layer 12 can comprise combinations of materials adjacent one
another. That is, the sound-absorbing layer 12 can comprise more
than one sublayer of either a similar or dissimilar material.
[0043] The normal incidence absorption coefficient of the
sound-absorbing layers of the present invention was measured
according to ASTM E1050. Referring to FIG. 2, there is shown the
normal incidence absorption coefficient profiles of the three of
the sample foams, Dow #76-16-10HW and #76-16-08HW, and Leggett
& Platt 30010MF. It should be noted that these three sample
foams fall into a preferred range of absorption coefficient, i.e.,
around the 1000 to 8000 Hz range.
[0044] The elastic modulus and damping of the sound-absorbing
layers of the present invention were measured using a plate,
shaker, and two accelerometers. Referring to FIG. 3, there is shown
a schematic illustration of an illustrative test setup. The
transmissibility was measured between accelerometer 1 and
accelerometer 2 and the first resonant frequency of the system is
determined. The elastic modulus was then be determined by: 1 E = 2
mt WL
[0045] wherein:
[0046] E=elastic modulus (Pa)
[0047] .omega.=angular frequency (rad/s)
[0048] m=plate mass (kg)
[0049] t=foam thickness (m)
[0050] W=plate width (m)
[0051] L=plate length (m)
[0052] The damping was measured from the transmissibility using the
half power bandwidth technique.
[0053] The barrier layer 14 preferably comprises a relatively thin
substantially impermeable layer. The barrier layer 14 is
substantially impermeable to fluid flow therethrough. In accordance
with a preferred embodiment of the present invention, the barrier
layer 14 comprises a thermoplastic olefin. By way of a non-limiting
example, the barrier layer 14 preferably comprises sheets of
acrylonitrile-butadiene-styrene, high-impact polystyrene,
polyethylene teraphthalate, polyethylene, polypropylene (e.g.,
filled polypropylene), polyurethane (e.g., molded polyurethane),
ethylene vinyl acetate, and the like. The barrier layer 14 can also
include natural or synthetic fibers for imparting strength. The
barrier layer 14 is also preferably shape formable and retainable
to conform to the sound-absorbing layer 12 and/or the substrate 16
for any particular application. Additionally, the barrier layer 14
may include organic and/or inorganic fillers. Furthermore,
additional additives may be incorporated into the barrier layer 14
composition, such as but not limited to flame retardants,
anti-fogging agents, ultraviolet absorbers, thermal stabilizers,
pigments, colorants, odor control agents, and the like.
[0054] In accordance with a preferred embodiment of the present
invention, the barrier layer 14 is preferably comprised of about 15
wt. % polypropylene, about 25 wt. % thermoplastic elastomer (e.g.,
Kraton.RTM., commercially available), about 55 wt. % calcium
carbonate filler, and about 5 wt. % additives (e.g., processing
aids, colorants, and the like).
[0055] In accordance with a preferred embodiment of the present
invention, the barrier layer 14 preferably has a specific gravity
of about 0.9 or greater, more preferably about 1.4 or more, and
still more preferably about 1.6 or greater. It is also preferable
that the barrier layer 14 have a surface weight of about 0.1
kg/m.sup.2 or greater. It is more preferred that the barrier layer
14 have a surface weight of greater than 0.4 kg/m.sup.2.
[0056] As with the absorbing layer 12, the barrier layer 14 can
have varying thickness. It is preferred that the thickness of the
barrier layer be between 0.1 and 50 mm. Again, it is to be
understood that the thickness can be varied, even outside the
preferred range, depending on the particular application and the
thickness can also be non-uniform.
[0057] While a single barrier layer 14 is shown, it is to be
understood that multiple barrier layers 14 of varying thickness may
be used. Thus, each barrier layer 14 may comprise more than one
sublayer of either a similar or dissimilar material.
[0058] As noted, the barrier layer 14 is preferably shape formable
and retainable in order to conform the shape of the system 10 to
the substrate 16 for any application. In order to combine the
sound-absorbing layer 12 with the barrier layer 14, any suitable
fabrication technique may be used. Some such examples include
connecting the various layers by heat laminating, or by applying
adhesives between the various layers. Such adhesives may be heat
activated. The various layers may also be adhered during the
process of shape forming by heating the layers and then applying
pressure in the forming tool, or by applying adhesive to the layers
and then applying pressure in the forming tool.
[0059] The system 10 could also be constructed in a cast foam tool
by inserting the barrier layer 14 material, such as a polymer film,
into the center section of a mold and then injecting foam, such as
viscoelastic polyurethane foam into both sides of the tool. The
system 10 can also be formed by creating the sound-absorbing layer
12 and barrier layer 14 jointly and/or independently and then
securing them by conventional methods, for example, using
mechanical fasteners, heat fusing, sonic fusing, and/or adhesives
(e.g., glues, tapes, and the like).
[0060] The substrate 16 can be comprised of any number of suitable
materials. By way of a non-limiting example, the substrate 16 can
be comprised of metals, natural fiber mats, synthetic fiber mats,
shoddy pads, flexible polyurethane foam, rigid polyurethane foam,
and combinations thereof.
[0061] With respect to fastening or otherwise attaching the
sound-absorbing layer 12 to the substrate 16, any number of
suitable methods can be employed. By way of a non-limiting example,
mechanical fasteners, heat fusing, sonic fusing, and/or adhesives
(e.g., glues, tapes, and the like) may be used.
[0062] Analysis was conducted in order to demonstrate the
performance benefit of using the viscoelastic foam of the present
invention in a dashmat over the traditional lightweight slab foam
construction. The dashmat performance was determined by examining
the transmission loss of a 0.8 mm steel panel and dashmat system
(i.e., viscoelastic foam sound-absorbing layer and a thermoplastic
olefin barrier layer). The transmission loss was computed using a
simulation method called statistical energy analysis. This analysis
utilized the material properties of the foam and other materials in
order to compute the transmission loss and other quantities within
the frequency range of 100 to 10,000 Hz.
[0063] The design variables in the analysis were: (1) Foam types:
(a) traditional lightweight slab foam; (b) Dow viscoelastic foam
(formulation #76-16-10HW); and (c) Foamex 2 pcf viscoelastic foam;
(2) Barrier layer (e.g., thermoplastic olefin) specific gravity:
1.2, 1.4, and 1.6; and (3) Foam thickness: 13 mm and 18 mm. It
should be noted that the barrier layer thickness was held constant
at 2.4 mm.
[0064] The dashmat construction was simulated according to the
typical sound-absorber/barrier layer system, as generally shown in
FIG. 1A. The transmission loss was computed for each combination of
the design variables.
[0065] Referring to FIG. 4, there is shown a comparison between
configurations using various foam types and various specific
gravity barrier layers at 18 mm foam thickness. The test procedure
is described below. As shown in FIG. 4, changing the foam type to
either of the viscoelastic foams improves the transmission loss of
the dashmat system, especially in the region of 1000 to 10,000 Hz.
Furthermore, changing the foam type to either of the viscoelastic
foams increases the transmission loss greater than increasing the
specific gravity of the barrier layer while using slab foam.
[0066] In order to compare the performance of the design variables
more effectively, a target configuration was chosen. The target
configuration was chosen to be that of 18 mm traditional slab foam
with a barrier layer having a 1.4 specific gravity. All other
viscoelastic configurations were compared to the performance of
this target configuration.
[0067] The samples were placed over a 0.8 mm thick steel plate, and
the assembly was inserted into the wall between the reverberation
chamber and the semi-anechoic chamber. Noise was generated in the
reverberation room using a speaker, and the sound pressure level
was measured using four microphones placed at a distance of 1.17 m
from the steel plate. An array of twelve microphones was placed in
the semi-anechoic chamber at a distance of 0.76 m from the outer
foam side of the sample. Noise reduction was calculated using
Equation 1, in accordance with the general protocol of SAE J1400.
The result of the noise reduction test is shown in FIG. 4.
NR=(average SPL.sub.1)-(average SPL.sub.2) Equation 1
[0068] Where:
[0069] SPL.sub.2=Anechoic Sound Pressure level (dB)
[0070] SPL.sub.1=Reverberation Sound Pressure Level (dB)
[0071] Referring to FIG. 5, there is shown the surface weight of
all the viscoelastic foam configurations in comparison to the
target surface weight. The surface weight (i.e., the mass of the
dashmat construction divided by the area of the panel) was used to
compare the relative weight of each configuration. Lower weight in
the dashmat configuration is desirable for improved vehicle fuel
economy, engine performance, and the like. Three of viscoelastic
foam configurations had a lower surface weight than the target.
These are: (1) 13 mm Dow viscoelastic foam (formulation
#76-16-10HW) with 1.2 specific gravity; (2) 18 mm Foamex 2 pcf
viscoelastic foam; and (3) 13 mm Foamex 2 pcf viscoelastic
foam.
[0072] Referring to FIG. 6, there is shown two of the viscoelastic
foam configurations in comparison to the target configuration.
These two configurations demonstrate the viscoelastic foam's
ability to increase the dashmat transmission loss with similar or
lower weight.
[0073] Testing was also completed on a GM truck vehicle dash
section to determine the noise reduction capability of the
viscoelastic foam in comparison to traditional slab foam dashmats.
Because transmission loss is difficult to measure for a vehicle
section, noise reduction was used instead of transmission loss. The
vehicle section was placed in a wall between a reverberation room
and an anechoic chamber. Sound pressure level measurements were
made in both rooms to compute the noise reduction.
[0074] Referring to FIG. 7, there is shown the results from the
vehicle dash section testing with three different dashmats. The
three dashmats tested can be described by: (1) Optimized 1.4
specific gravity dashmat, i.e., a dashmat with traditional slab
foam with a 1.4 specific gravity barrier layer (e.g., TPO); (2)
Optimized 1.8 specific gravity dashmat, i.e., a dashmat with
traditional slab foam with a 1.8 specific gravity barrier layer
(e.g., TPO); and (3) Optimized 1.4 specific gravity dashmat, i.e.,
a dashmat with Foamex 2 pcf viscoelastic foam with a 1.4 specific
gravity barrier layer (e.g., TPO). It is noted that a seal wear
issue was identified in 630 Hz for some tests (particularly those
showing negative dB improvements).
[0075] FIG. 7 illustrates that the dashmat with the viscoelastic
foam in accordance with the present invention performs better up to
2000 Hz as compared to traditional slab foam and similar to the
traditional slab foam above 2000 Hz.
[0076] The use of viscoelastic foam as the sound-absorbing layer 12
increases the damping of vibration on the steel sheet metal to
which the system 10 is applied. This reduces the noise radiation
into the interior of the vehicle. The viscoelastic foam also
reduces the vibration motion of the barrier layer 14 through
damping. That is, the absorbing layer dampens vibrations to the
barrier layer to reduce vibration of said barrier layer. In this
manner, the absorbing layer also acts as a vibration-damping layer.
This may result in an increase in transmission loss of the system
10. Further viscoelastic foams have good sound absorption
properties due to the foam's cell structure and viscoelasticity. It
will be appreciated that the viscoelastic foam layer is adapted to
be placed against a substrate, such as the component of the
vehicle.
[0077] FIG. 8 shows a damping comparison of various samples of foam
of equal thickness. The first foam listed in the legend is a
viscoelastic foam as set forth above but is 2 pcf foam. The second
foam listed is a slab foam that is 1.2 pcf. The weight of the foam
sample is also shown. The slab foam used comprises Melamine. The
damping test was performed in a manner known in the art. The sample
was excited with vibration. The transfer function is calculated by
dividing the acceleration of the plate with the force applied. In
this manner, the effect of the force magnitude on the results is
eliminated. As can be seen in FIG. 8, the viscoelastic foam results
in lower vibration levels by means of higher damping. Thus, when
used in a system 10 as the sound-absorbing layer 12, the
viscoelastic foam reduces the vibration motion of the barrier layer
14 through damping. This can increase the transmission loss of the
overall system.
[0078] FIG. 9 shows a damping comparison of samples having equal
mass. The test was performed in the same manner as set forth above
in connection with FIG. 8.
[0079] FIG. 10 shows the effect on insertion loss by placing the
viscoelastic layer against the steel. More specifically, one sample
of a system 10 was prepared. The sample consisted of a viscoelastic
foam absorbing layer 12, a HIPS barrier layer 14 and a shoddy
absorbing layer 12. The tests were performed by first placing the
shoddy absorber layer adjacent the steel and determining the
insertion loss in the same manner as set forth above. Subsequently,
the same sample was tested by placing the viscoelastic absorber
layer against the steel and determining the insertion loss. The
results are shown in FIG. 10. As can be seen, an increase in
insertion loss is achieved when the viscoelastic foam is place
against the steel. Thus, it is preferred that the viscoelastic foam
layer be placed against the substrate, such as the vehicle
component when the system 10 is installed.
[0080] FIG. 11 shows the effect of the damping of the viscoelastic
foam on the barrier layer. In order to test the effect of damping
by a viscoelastic-absorbing layer on the barrier, two samples were
tested. In each case the absorbing layer was a viscoelastic foam.
In the first sample, the viscoelastic foam is the FOAMEX foam
identified above. In the second sample, the viscoelastic foam
comprises Qylite, also available from FOAMEX. The barrier layer in
each case was HIPS. Frequency response as shown in FIG. 11 means
the same thing as the transfer function as shown in FIG. 8. The
test to determine the frequency response was the same as set forth
above in connection with FIG. 8. As can be seen from the results
shown in FIG. 11, a viscoelastic foam absorber layer reduces the
motion or vibration of the barrier layer. This results in less
noise being transmitted to the interior of the vehicle.
[0081] It will also be appreciated that, while particularly well
suited for automotive applications, the system 10 can also be used
in other applications. Such other applications include
construction, industrial, appliance, aerospace, truck/bus/rail,
entertainment, marine and military applications.
[0082] Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood
that such detail is solely for that purpose and that variations can
be made therein by those skilled in the art without departing from
the spirit and scope of the invention except as it may be limited
by the claims.
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