U.S. patent application number 11/160456 was filed with the patent office on 2006-12-28 for acoustical insulation for motor vehicles.
Invention is credited to Terence Connelly, PaulG Deacon.
Application Number | 20060289230 11/160456 |
Document ID | / |
Family ID | 37565949 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060289230 |
Kind Code |
A1 |
Connelly; Terence ; et
al. |
December 28, 2006 |
ACOUSTICAL INSULATION FOR MOTOR VEHICLES
Abstract
Acoustical insulation for attenuating sound entering the
passenger compartment of motor vehicles. The acoustical insulator
comprises dual nonwoven layers in which one nonwoven layer is an
airflow control layer and the second nonwoven layer is a support
layer positioned between the cap layer and the sheet metal of the
firewall separating the passenger and engine compartments. The
areal density of the cap layer is less than the areal density of
the support layer and, preferably, comprises polyethylene
terephthalate (PET) fibers. The cap layer has a specific airflow
resistance ranging from about 200 mks Rayls to about 1200 mks
Rayls.
Inventors: |
Connelly; Terence;
(Plymouth, MI) ; Deacon; PaulG; (Saline,
MI) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP (LEAR)
2700 CAREW TOWER
441 VINE STREET
CINCINNATI
OH
45202
US
|
Family ID: |
37565949 |
Appl. No.: |
11/160456 |
Filed: |
June 24, 2005 |
Current U.S.
Class: |
181/290 ;
181/286 |
Current CPC
Class: |
B32B 2262/0284 20130101;
B32B 5/26 20130101; B32B 2605/00 20130101; B60R 13/08 20130101;
B32B 15/14 20130101; B32B 2307/718 20130101; B32B 2260/023
20130101; B32B 2260/046 20130101; B32B 2262/062 20130101; B32B
2307/102 20130101; B32B 27/36 20130101; B32B 2250/03 20130101 |
Class at
Publication: |
181/290 ;
181/286 |
International
Class: |
E04B 1/82 20060101
E04B001/82; E04B 2/02 20060101 E04B002/02 |
Claims
1. An acoustical insulator for application to an interior surface
of a motor vehicle, comprising: a first nonwoven layer having a
first areal density; and a second nonwoven layer coupled with said
first nonwoven layer to define a laminate, said second nonwoven
layer having a second areal density less than said first areal
density, said laminate adapted to be applied to the interior
surface of the motor vehicle with said first nonwoven layer being
positioned between said second nonwoven layer and the surface, and
said second nonwoven layer having a specific airflow resistance
between about 200 mks Rayls and about 1200 mks Rayls.
2. The acoustical insulator of claim 1 wherein the specific airflow
resistance of said second nonwoven layer is within a range from
about 200 mks Rayls to about 1200 mks Rayls.
3. The acoustical insulator of claim 1 wherein said second nonwoven
layer has a thickness less than 1.5 mm.
4. The acoustical insulator of claim 3 wherein said laminate has a
thickness ranging from about 4 mm to 37 mm.
5. The acoustical insulator of claim 1 wherein said second nonwoven
layer has an areal density ranging from about 5 gramsft.sup.-2to
about 25 gramsft.sup.-2.
6. The acoustical insulator of claim 1 wherein said first nonwoven
layer has an areal density ranging from about 80 gramsft.sup.-2 to
about 150 gramsft.sup.-2.
7. The acoustical insulator of claim 1 wherein said second nonwoven
layer is a lofted fibrous layer compressed to a thickness less than
1.5 mm before part molding.
8. The acoustical insulator of claim 1 wherein said second nonwoven
layer includes a plurality of first fibers each formed from
polyethylene terephthalate (PET) and a plurality of second fibers
each formed from a binder fiber.
9. The acoustical insulator of claim 1 wherein said second nonwoven
layer is bonded to the first non-woven layer by the pressure of a
molding process.
10. The acoustical insulator of claim 1 wherein said first nonwoven
layer contacts the interior surface when said acoustical insulator
is applied to the interior surface.
11. The acoustical insulator of claim 1 wherein said first nonwoven
layer comprises cross-lapped cotton fibers.
12. The acoustical insulator of claim 11 wherein said first
nonwoven layer further comprises polyester fibers blended with the
cotton fibers.
13. The acoustical insulator of claim 1 wherein said first nonwoven
layer comprises cross-lapped polyester fibers.
14. The acoustical insulator of claim 13 wherein said first
nonwoven layer further comprises binder fibers blended with said
polyester fibers.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to motor vehicles and, in
particular, to acoustical insulation for use on interior and
exterior surfaces of the passenger compartment of motor
vehicles.
BACKGROUND OF THE INVENTION
[0002] Sound attenuating materials are provided for acoustically
insulating motor vehicles to reduce the level of noise inside the
vehicle passenger compartment. External noises, such as road noise,
wind noise, engine noise, vibrations, etc. may be attenuated
through the use of various acoustical materials applied to the
internal and external surfaces of the passenger compartment. Noises
emanating from sources within the passenger compartment may be
attenuated through the use of various acoustical materials applied
to the internal surfaces of the passenger compartment.
[0003] The attenuation of airborne noise from external sources
transmitted through the body structure and components to the
passenger compartment is commonly referred to as sound transmission
loss. The attenuation of internal airborne noise incident on the
interior surfaces of the vehicle is commonly referred to as sound
absorption. The specific-airflow resistance, of a material is
defined as the air pressure difference across the thickness of the
material divided by the linear velocity of the airflow and defines
the resistance to air movement through a material. The specific
airflow resistance may be expressed in units of mks Rayls
(Pasecm.sup.-1). The airflow resistance of fibrous materials
depends among other parameters upon the areal density of the
fibrous material, fiber orientation, fiber blend, and fiber
diameter. The sound transmission loss and sound absorption of a
single layer of material are determined by the weight and airflow
resistance.
[0004] There are two types of sound attenuating material used in
vehicles. The first type of sound attenuating material or
acoustical insulation comprises a molded barrier mat located on the
interior surface of the firewall separating the passenger
compartment from the engine compartment. This barrier mat system
comprises a layer of fiber or foam which rests against the firewall
and is attached to a thermoplastic barrier which can be made from
ethyl vinyl acetate (EVA), polyvinyl chloride (PVC), or a
thermoplastic polyolefin (TPO). These molded barrier mats are
designed to have high transmission loss. Increasing the areal mass
of the barrier mat and the thickness of the fiber-foam layer
increases the transmission loss. Generally, these dual layer sound
insulating materials are designed to provide high sound
transmission loss at the expense of the sound absorption, which is
low because the barrier mat is impermeable.
[0005] The other type of sound attenuating material or acoustical
insulation comprises a molded mat located on the interior surface
of the firewall separating the passenger compartment from the
engine compartment. Resinated cotton and phenolic impregnated
polyester fibers are two common types of sound absorption
substrates. However, these materials rely on phenolic resin as a
strengthening and binder agent. Phenolic resins are undesirable due
to the presence of formaldehyde and odors, as well as the need to
utilize a high-tonnage press to manufacture a shaped product.
Generally, such single layer sound insulating materials are not
optimized for sound absorption and transmission loss. To optimize
these properties, three or more layers of fibrous material are
combined into a laminate in which the individual layers contribute
to sound absorption and acoustical transmission loss. However,
these are complex structures that require multiple process steps to
successfully form into a shaped component.
[0006] It would be desirable to provide an improved sound
attenuating material for vehicle passenger compartments in which
sound absorption dominates as a sound attenuation mechanism rather
than sound transmission loss.
SUMMARY OF THE INVENTION
[0007] In an embodiment of the present invention, an acoustical
insulator comprises a first nonwoven layer having a first areal
density and a second nonwoven layer coupled with the first nonwoven
layer to define a laminate. The laminate is adapted to be applied
to a surface of a motor vehicle with the first layer positioned
between said second nonwoven layer and the surface when applied to
an interior surface of a motor vehicle. The second nonwoven layer
has a second areal density less than the first areal density and
specific airflow resistance between about 200 mks Rayls and about
1200 mks Rayls.
[0008] The invention therefore provides a sound attenuating
material that includes a layer of nonwoven material and an
underlying layer supporting the single cap layer. This simple
two-layer structure provides acoustical attenuation effective to
significantly reduce the audibility of common externally-originated
noises, such as road noise and engine noise. In comparison with
conventional barrier type acoustical insulators, the layered
acoustical insulator of the present invention is realized with
substantial cost savings and a lightweight construction. The
acoustical insulator is biased toward providing sound absorption
rather than sound transmission loss as the mechanism for acoustical
attenuation because of the construction of the cap layer, which
represents a benefit in comparison with conventional acoustical
insulators used to sonically insulate the passenger cabin in motor
vehicles.
[0009] These and other benefits and advantages of the invention
shall become more apparent from the accompanying drawings and
description thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and, together with a general description of the
invention given above, and the detailed description given below,
serve to explain the principles of the invention.
[0011] FIG. 1 is a perspective view of a portion of a passenger
compartment partially covered by an acoustical insulator in
accordance with the present invention; and
[0012] FIG. 2 is a detailed cross-sectional view of the acoustical
insulator of FIG. 1 showing the individual layers of a laminated
structure.
DETAILED DESCRIPTION
[0013] With reference to FIG. 1, a portion of a passenger cabin 10
of a motor vehicle 11 is shown with the instrument panel (not
shown) removed to reveal the underlying firewall 12 separating the
passenger compartment from the engine compartment. The firewall 12
is almost completely covered by an acoustical insulator 14. The
acoustical insulator 14 may be attached to the firewall 12 with
mechanical fasteners or by other attachment methods, such as
adhesive, familiar to those skilled in the art. The acoustical
insulator 14 functions by absorbing the sound that is transmitted
though the firewall 12 and registered holes 16 and cutouts 17 and
then reflected from the surface of the instrument panel onto the
surface of the acoustical insulator 14.
[0014] There are various openings or cutouts 17 defined in the
sheet metal 12 and registered holes 16 in the insulator 14 for the
steering column, brake booster, pedals, cables, hoses, etc., which
are commonly referred to by a person of ordinary skill in the art
as pass-thru's. Despite variations in the size and number of these
registered holes 16 and cutouts 17 among vehicle types, the
registered holes 16 and cutouts 17 generally degrade the
transmission loss of the acoustical insulator 14 by defining
regions through which noise from the engine can pass unimpeded by
the acoustical insulator 14. The area occupied by the holes 16 may
be as much as 5% to 20% of the total surface area of the acoustical
insulator 14, contingent upon the vehicle type. Moreover, portions
of the acoustical insulator 14 immediately surrounding the holes 17
are typically thinner than other portions of the acoustical
insulator 14 more distant from the holes 17.
[0015] In addition to the interior surface of firewall 12, the
acoustical insulator 14 may find other applications for
acoustically insulating the passenger cabin 10 of motor vehicle 11.
For example, the acoustical insulator 14 may be used as a sound
insulator for the wheel houses located behind the vehicle rear
quarter panels in a sports utility vehicle, minivan, etc.
[0016] With reference to FIG. 2 in which like reference numerals
refer to like features in FIG. 1, the acoustical insulator 14 has a
laminated structure that includes a nonwoven support layer 20 and a
nonwoven cap layer 22 that provides stiffness and structural
integrity. The nonwoven cap layer 22 is supported structurally by
the support layer 20 and has a lower areal density (i.e., mass per
unit area) than the support layer 20. The cap layer 22 may be
formed from a lofted layer in which the constituent fibers are
bound together to supply structural integrity to the porous
structure and then calendered to thickness less than 1.5 mm to
provide a consolidated nonwoven layer. The support layer 20 and the
cap layer 22 have an at least partially contacting face-to-face
relationship and are bonded together as understood by persons
skilled in the art during the manufacturing process to form a
shaped construction suitable for use inside the passenger
compartment.
[0017] The support layer 20 is placed into contact with sheet metal
24 of the firewall 12 (FIG. 1) and the cap layer 22 is separated
from the sheet metal 24 by the support layer 20. The support layer
20 provides the structural integrity to the acoustical insulator 14
required for handling, installation, and function and may be
manufactured from various natural and synthetic fibers or a porous
foam material, such as a polyurethane (PUR). The support layer 20
makes a major contribution to the sound attenuation. The cap layer
22 contributes increases the airflow resistance of the acoustical
insulator 14 and significantly improves the sound absorption in a
frequency range from 250 Hz to 10 kHz. Typically, the support layer
20 has an areal density ranging from about 80 gramsft.sup.-2 to
about 150 gramsft.sup.-2 and the cap layer 22 has an areal density
from about 10 gramsft.sup.-2 to about 25 gramsft.sup.-2.
[0018] In one specific embodiment of the present invention that
provides particularly advantageous sound insulation properties, the
cap layer 22 is a composite synthetic matrix that includes a
mixture of high melt matrix or staple fibers each formed from a
homopolymer or copolymer of polyester, which is generally termed
polyester herein unless otherwise indicated, and preferably
polyethylene terephthalate (PET), and low melt binding fibers each
formed from polyester. The cap layer 22 is formed from a layer that
is initially about 30 mm to about 10 mm thick and constituted by a
mixture of stable and binding fibers. This initial layer is heated
to a temperature effective to soften the binding fibers and
compressed to less than 1.5 mm, which binds the collection of
stable and binding fibers together upon cooling to form cap layer
22. In alternative embodiments, the binding fibers may be replaced
with a thermoplastic powder binder that binds the stable fibers
upon heating and compression. The support layer 20 is an underpad
consisting of cotton fibers blended with polyester fibers and may
include recycled materials. Cap layer mats suitable for use in this
embodiment of the present invention are commercially available
from, for example, Owens Corning (Toledo, Ohio).
[0019] The cotton and polyester fibers in support layer 20 are
preferably cross-lapped to impart structural integrity and strength
during the molding process. Cross-lapped fiber mats suitable for
use as support layer 20 are commercially available from, for
example, Hobbs Fibers (Waco, Tex.).
[0020] To make the acoustical insulator 14, continuous lengths of
layers 20 and 22 are unrolled from individual rolls, paired in a
face-to-face arrangement, and cut into blanks. The blanks can be
heated using convection, infrared, microwaves, radio frequency,
conduction through heated plates, and other conventional methods
familiar to persons of ordinary skill in the art. The layers 20, 22
are preferably heated for about 40 seconds to about 90 seconds at
about 300.degree. F. to 360.degree. F. to consolidate the layers
20, 22 and, thereafter, are transferred to a mold of a form tool.
When the mold is closed, the layers 20, 22 are preferably
compressed for approximately 40 seconds to approximately 50 seconds
to form the acoustical insulator 14, which has a three dimensional
molded shape that is retained, due to the cooling, after ejection.
The mold may be optionally chilled to reduce the cycle time. The
formed acoustical insulator 14 is then ejected from the mold,
trimmed, and shipped to an assembly line. Alternatively, cold
blanks of layers 20 and 22 can be loaded directly into a heated
tool without any pre-heating. When the mold of the heated tool is
closed, the layers 20, 22 are heated to about 360.degree. F. to
450.degree. F. and compressed for approximately 25 seconds to 60
seconds to consolidate the layers 20, 22 to form the acoustical
insulator 14 with the three dimensional molded shape that is
retained, after cooling.
[0021] In the final product, the acoustical insulator 14 preferably
has a total thickness of in the range of about 4 millimeters (mm)
to about 37 mm, with the cap layer 22 contributing less than 1.5 mm
of the total thickness and the support layer 20 accounting for
about 2.5 millimeters to about 35.5 millimeters of the total
thickness. In this configuration, the cap layer 22 has a specific
airflow resistance between about 200 and about 1200 mks Rayls
(Pasecm.sup.-1), and preferably between about 400 and 700 mks
Rayls. In addition, the support layer 20 has a specific airflow
resistance less than about 10,000 mks Rayls, and preferably between
about 500 and 3500 mks Rayls. The acoustical insulator 14 may be
placed on the sheet metal 24 so that the support layer 20 is
coextensive with the sheet metal 24 and the cap layer 22 is spaced
from the sheet metal 24 by the support layer 20.
[0022] While the present invention has been illustrated by the
description of one or more embodiments thereof, and while the
embodiments have been described in considerable detail, they are
not intended to restrict or in any way limit the scope of the
appended claims to such detail. Additional advantages and
modifications will readily appear to those skilled in the art. The
invention in its broader aspects is therefore not limited to the
specific details, representative apparatus and methods and
illustrative examples shown and described. Accordingly, departures
may be made from such details without departing from the scope or
spirit of Applicants' general inventive concept.
* * * * *