Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD OF FORMING
VARIABLE DENSITY SEATING MATERIALS
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention generally relates to a system and method of
forming
seating materials having a variable density gradient and more specifically to
forming foam
materials for vehicle seats having a variable density gradient that allow
greater comfort
across a wider range of occupant weights, and the use of single foam
formulations across a
wide range of types of vehicle seats having significantly different desired
performance
characteristics.
[0004] 2. Related Art
[0005] Vehicle manufacturers must make their vehicle seats comfortable to a
wide
range of vehicle occupants having significantly different weights and sizes.
The
manufacturer of a vehicle seat must consider a weight range from that of a
small child who
no longer needs a booster seat through the upper weight and size range of
adults. A lighter
occupant and a heavier occupant would find the same vehicle seat to perform
significantly
different, and each occupant would prefer very different hardness and more
specifically the
amount of deflection of seating materials. For example, the static comfort of
a seating
foam, such as a polyurethane seating foam, depends greatly on the hardness and
density of
the foam, especially at high deflection. Although vehicle manufacturers
attempt to select
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the hardness of the foam to provide desired static comfort for a wide range of
occupant
weights, it is difficult to please every occupant due to the variation between
occupant
weights and thereby the amount of deflection which is related to the
occupant's penetration
into the foam while sitting upon the seat. More specifically, a soft foam
material is likely to
provide a comfortable seat for a light occupant, while most heavy occupants
would feel
bottomed out, feel frame components, or feel uncomfortable in the same seat.
Conversely, a
harder foam generally ensures a comfortable seating material for a heavy
occupant, but also
results in less deflection, which causes lighter occupants to find the seat
not comfortable,
such as the seat being too hard, causing them to sit on top of the foam, and
not sink, at least
partially, into the foam. While manufacturers may adjust the hardness of the
foam to that
preferred by an average user, the more displaced the vehicle occupant is in
weight from the
average user, the less comfortable they find the vehicle seat. Therefore, in a
single material,
a single piece of foam construction seat, to date manufactures are limited in
their ability to
provide a comfortable seating surface for a wide range of occupant weights.
[0006] The variance in comfort of seating materials or desired
performance of
seating materials may also vary depending on the desired application, vehicle
type, target
consumer, and vehicle manufacturer preferences. For example, in many sport or
performance cars, it is desirable to have a firmer seat than in luxury cars.
[0007] Originally, to address the desire for different seating
characteristics, and in
particular the hardness of the foam, most manufacturers created a wide variety
of foam
formulations. While these different foam formulations allowed variations in
the properties
of the particular seat to be addressed, it did not solve any of the above
described problems
related to the differences between occupants of the vehicle seats. In
addition, the demand
for increased comfort and increased durability, as well as an expanded range
of required
properties, limit the ability of manufacturers to address all desired
properties with only
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changing the foam formulation. Furthermore, as the range of required
properties increase
and the desire of high hardness foam for some individuals and low hardness
foam for
comfort for other individuals, these competing dynamic comfort issues caused
the foam
formulations used to not be as well-balanced chemical mixes as traditional
foam
formulations and therefore caused difficulty during the manufacturing process.
Also, many
of these unique foam formulations required specialty chemicals which increased
raw
material costs and at times required additional manufacturing equipment and
processes
which increased the cost of the vehicle seat.
[0008] To address the above shortcomings and a wider weight range of
vehicle
occupants, some manufacturers have created a two-part foam assembly for the
seating
material, which requires time consuming and expensive manufacturing processes.
Therefore, due to the cost of assembly of multiple slabs of foam having
different densities,
its application across a wide range of vehicle seats is currently limited. The
two-part seat
material may be formed by two methods. The first is to generally apply a
separately soft
layer of foam to a harder molded foam wherein the soft slab of foam is closest
to the A
surface or seating surface of the seat material. In such a method of forming a
two-part foam
seating material, first the harder foam seat material is molded and then a
second softer seat
material is molded or cut from slabstock foam with the desired shape. Then the
two parts
are glued together with an adhesive, which increases production costs
significantly due to
the extra labor, equipment, materials and space needed. As manufactures also
strive to
improve the environmental aspects of the manufacturing process as well as the
recyclability
of the materials, the use of an adhesive to glue the soft die cut slabstock
foam or separately
molded piece to the harder molded foam is generally not desirable. For
example, in using
the two-part seating material, the adhesive may make it more difficult to
recycle the seat at
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the end of the life cycle and it is difficult to find environmentally friendly
adhesives with
desired performance characteristics over the life cycle of the seat.
[0009] The second method some seating manufacturers have also developed
is a
mold-in process to form a two-part seating material that eliminates the need
for the
adhesive. Even though the need for the adhesive is eliminated, significant
disadvantages
also occur in the molding process that significantly slow the line speed and
processing time
for each seating material. More specifically, many manufacturers use a method
of foam
production that pours multiple formulations within one mold, typically in
layers to achieve
high hardness bolsters while maintaining a softer insert near the A surface.
The additional
formulations and processing steps require additional space to store the
different components
that are used in the mold, additional equipment space, and additional demands
are placed on
the operators of the manufacturing process. Furthermore, no suitable
technology has been
found to date to prevent contamination of the mold-in slab from the liquid
polyurethane
chemical blends mixing during foaming process. More specifically, many times
the
different layers of foam would have uncontrollable or undesirable blending or
be outside of
their desired layer boundaries such as a hard foam formulation intruding upon
an area where
a soft foam formulation is desired and even worse, at times intruding only
partially, causing
an uneven feeling of hardness or hard spots in the vehicle seat. Though many
manufacturers adjusted the pour processes to attempt to prevent such quality
issues, this
often added complexity, and cost in the manufacturing process and also limited
at times the
types of formulations that may be used with each other. This contamination or
mixing of
formulations typically negates the comfort benefit found in providing a slab-
molded two-
part material seating slab.
[0010] In vehicle seats that used a backing material such as placing a
precut cloth-
like material in the mold and then directly molding foam to the material other
problems may
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occur. These methods are typically used to produce a strong B surface bond for
increased
durability as well as other performance characteristics but are difficult to
use with multiple
foam formulations as well as the above described two-part mold in process.
More
specifically, molding to a backing material in the mold may create a number of
issues
during the foam molding process, such as movement of the backing material as
multiple
layers are injected, as well as the undesirable mixing of various types of
materials.
SUMMARY
[0011] The present invention generally relates to a system and method of
forming
seating materials having variable density gradient for high hardness ratio of
high-to-low
deflection. More specifically to forming foam materials for vehicle seats
having variable
density gradient that allow greater comfort across a wider range of occupant
weights.
[0012] The present invention uses a method to create a variable hardness
seating
material with only minimal tooling changes and limited to no reduction in
manufacturing
efficiency. First, the material is placed in a mold and then expanded to fill
the mold.
Unlike prior molds, the present invention uses molds that have larger cavity
areas in which
moveable plates or mold sections rest. With the mold cavities filled with the
expanded
foam and approaching the cured state, the moveable plate compresses the seat
to the final
size, such that the areas closest to the moveable plate are compressed to have
greater
densities. This creates a variable density seat with greater differential in
hardness between
low and high deflections. The seat foam is more comfortable to a wide range of
occupant
weights, deflecting as desired for the lighter weight occupants while
providing sufficient
support for heavier occupants in order to prevent the sensation known as
"bottoming out."
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BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Various exemplary embodiments of the systems and methods
according to
the present disclosure will be described in detail, with reference to the
following figures,
wherein:
[0014] FIG. 1 illustrates an exemplary seating mold with an A surface
being on the
bottom side and the initial location of the mold materials after the mold of
the present
invention is closed;
[0015] FIG. 2 illustrates the mold in FIG. 1 with the foam seating
material expanded
to completely fill the mold cavity and a moveable plate in a first position;
[0016] FIG. 3 illustrates the mold of FIG. 2 wherein the moveable plate
has moved
from the first position to a second position, which compresses the seating
material providing
the illustrated increased density gradient on the backside of the seating
material;
[0017] FIG. 4 illustrates an exemplary graph of strain in millimeters
relative to an
applied force to the seating material of the present invention compared to
that of a
conventional seating material;
[0018] FIG. 5 illustrates an exemplary graph of frequency versus
transmissibility
using the same formulation, density and thickness wherein transmissibility has
the same
formulation density and thickness;
[0019] FIG. 6 illustrates deflection versus hardness with the same
formulation,
thickness and weight; and
[0020] FIG. 7 illustrates an exemplary graph of a load deflection curve
with the
deflector percentage versus force and more specifically illustrating that a
similar load
deflection curve may be obtained using a foam that is only 70 mm and 1,096 g
versus
conventional foam that is 96 mm and 1,220 g.
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DETAILED DESCRIPTION
[0021] The present invention generally relates to a system and method of
forming a
seat (not illustrated). The seat generally includes a seating material that
provides support to
the vehicle occupant, such as the illustrated foam base 10. The foam base 10
includes an A
surface 12, a back surface 13 and bolsters 18. As further illustrated in FIG.
3, the cross
sectional view shows a density gradient area 14, having a higher density area
15 and a lower
density area 16 in the final foam base 10 configuration.
[0022] The seat, specifically the foam base 10, is generally formed in a
mold. While
the seat material, in particular the foam base 10, may be formed in any style,
size, or
configuration, the Figures show an exemplary seat and the present invention is
applicable to
other styles and configurations. In addition, the mold 20 would vary in style,
shape, size,
and configuration as desired to form the particular desired seating material
and in addition
to the illustrated foam base 10. The mold 20 generally includes a base 24 and
sidewalls 26
into which the foam material is placed for the mold process to begin. The
illustrated mold
20 generally includes bolster cavities 28 and a main cavity 30 which are
confined by the
sidewalls 26, base 24, and an upper plate 32. As illustrated in FIG. 2, the
upper plate 32
may have a first or retracted position 34, and as further illustrated in FIG.
3, a second or
extended position 36. The illustrated mold 20 is for forming a base 10 of a
seat and
different molds may be used for different styles, shapes, sizes and
configurations, as well as
different molds to be required for the seating materials for the upper back of
a seat, or for
example, a rear seat of a vehicle. In addition, even though not illustrated,
other portions of
the mold may include additional moveable plates to vary the density of other
portions of the
seat such as a moveable plate in the bolster area (not illustrated) to provide
different
densities in the bolster area.
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[0023] The present invention, and in particular the process of forming
the seat, starts
similar to other seat forming processes in that the mold is open and a mold
material such as
a polyurethane seating foam initial material is placed or inserted in the mold
in desired
quantities and then the mold is closed. The mold, depending upon the type of
material used,
may be preheated to a desired temperature before the material is placed into
the mold. The
material 11 may be any type of material commonly used or desirable for use in
forming the
seating structure. The present invention as illustrated in FIG. 4 compares a
conventional
polyurethane foam seat base to a polyurethane foam seat base that incorporates
the present
invention. With the polyurethane foam material 11 being placed in the mold in
the desired
quantities, the process of expanding the foam to fill the mold starts as
illustrated in FIG. 2.
More specifically, the material in FIG. 2 has filled the mold and has reached
a state of semi-
cure and normally would be allowed to stay in the mold without change for some
additional
specified time period. The mold 20 of the present invention includes an
enlarged cavity
area such as the illustrated main cavity 30 wherein in the initial position as
illustrated in
FIG. 2 the foam fills a greater area than desired for the final seat base 10
as illustrated in
FIG. 3. Once the mold material has completely filled the mold cavity 30 for
the desired
time, the inner plate 32 is moved from the first position 34 as illustrated in
FIG. 2 to the
second position 36 as illustrated in FIG. 3. Upon the movement of the upper
plate 32 to the
second position 36, the mold cavity forms the final desired shape and size of
the seat base
10. As illustrated in FIG. 3, by moving the upper plate 32 from the first
position 34 to the
second position 36, the area closest to the upper plate 32 of the foam base 10
has the highest
density area 15. In comparison, the lowest density area 16 is furthest away
from the upper
plate 32 and is approximately the A surface 12 which is engaged against the A
mold surface
24. The density of the foam in the main cavity 30 may vary on a gradual even
density
gradient but is expected that the increase in density is more of an
exponential nature than a
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linear nature. More specifically, the lower density area 16 extends further
into the foam
base 10 and as it approaches the back surface 13, the density substantially
increases quickly
to the high density area 15. As the graph illustrates in FIG. 4, the present
invention allows
for low hardness at low deflection and then increased hardness at a higher
rate than a
conventional seat foam as the deflection increases. The present invention as
illustrated in
FIG. 4 provides a better static comfort for a wider range of occupant weights
while
eliminating expensive two-part foam seating materials. Furthermore, the
present invention
may use less material and have less overall mass by providing high density in
only the
sections where needed.
[0024] The mold 20 is only one style of a particular foam base 10, and
other styles
may be used which in addition include other areas that include moveable plates
in addition
to the illustrated upper plate or in place of the upper plate, such that the
density gradient
could have greater adjustment to particular seat styles, shapes or
configurations allowing for
the complete tailoring of a particular seat for the most comfortable possible
position. For
example, the cavity of the bolster cavity 28 could be intentionally enlarged
and include a
moveable bolster plate (not illustrated) that increases the density on the
outer boundaries of
the bolsters to provide more support when needed.
[0025] In addition, for molds such as those that form the upper back of
the seating
material to provide comfort along the complete upper back, the moveable plate
may not
have uniform compression along the length of the upper back (not illustrated).
Therefore, it
is possible through using multiple plates across a surface to create various
density gradients
where desired to increase seating comfort. Another example, though not
illustrated for a
seating base such as the illustrated foam base 10, would be to provide a
larger cavity near
the rear surface of the seat than the front edge of the seat and then
compresses such that the
density gradient also varies between the rear of the foam base to the front of
the foam base.
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The front, where less weight is placed by the legs, would have a softer, more
comfortable
seating position, while the seat would allow greater support in the foam base
where the most
weight is placed by a particular user. This would increase seating comfort and
reduce
fatigue of the vehicle operator.
[0026] It is important to note in FIG. 7 that both the mass and
thickness provide a
reduction in vehicle weight and also provides increased cabin space.
[0027] The foregoing invention has been described in accordance with the
relevant
legal standards, thus the description is exemplary rather than limiting in
nature. Variations
and modifications to the disclosed embodiment may become apparent to those
skilled in the
art and fall within the scope of the invention.
