Note: Descriptions are shown in the official language in which they were submitted.
The presellt invention relates to filters for fluid
supplles of vehicle occupant restraint systems employing
combustible gas generators.
Multilayer filter assemblies for vehicle occupant
restraint systems employing combustible gas generators are
known in the prior art. "Exemplary of this art are filters
shown in applicant's U.S. Patent number 4,012,211, issued
March 15, 197~, and entitled Filter For Occupant Restraint
System Fluid Supply."
Certain disadvantages have been noted, however,
in the use of such filter assemblies.
One of these is the tendency of solid contaminants
to concentrate in certain areas of the filter and there-
after to burn through the filter layers. This tendency
is commonly referred to as "pinholding".
Another disadvantage is the tendency of such
filters to permit "channelling", that is, bypassing of one
or more filter layers by a portion of the flowing gas
due to inadequate support of one or more of the layers
when intermediate support members are not used or are
ineffective.
Still another disadvantage lies in the fact that
the prior art filters tend to have high heat capacity,
necessitating the use of large amounts of combustible
material to effect inflation of the confinement.
SUMMARY OF THE INVENTION
It is an object of the present invention to
provide an improved filter assembly for vehicle occupant
restraint systems employing combustible gas generators
which minimizes the concentration of contaminants passing
through the filter.
It is another object to provide a filter which
minimizes the tendency of combustion aases to bypass the
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filter.
It is yet another object to provide a filter
whose heat capacity tends to permit the use of a minimum
amount of combustion material fox effecting inflation.
According to the present invention there is
provided a filter for filtration of contaminants produced
in the gas flow of a gas generator of the type used for
inflation in vehicle occupant restraint systems. The
filter includes a plurality of layers of a first filter
material, the first filter material being fibrous and
porous, each of the layers of the first filter material
defining a plenum zone for dispersing and filtering con-
taminants contained in the gas flow throughout the plenum
zone. The filter further includes a plurality of layers of
second filter material, the second filter material being
fibrous and having a porosity substantially less than the
first filter material, the plurality of first and second
filter material layers being disposed in alternating
arrangement such that each layer of the second filter
material is bounded on either side thereof by a layer of
the first filtex material.
The above objects and features, as well as
others, will be apparent to those skilled in the art of
filters for occupant restraint systems employing combustible
gas generators upon reading the accompanying detailed
description with reference to the drawlngs in which:
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Figure 1 is a fragmentary cross sectional view of
a fluid supply incorporating the invention filter;
Figure 2 is an exploded fragmentary cross sectional
view of the filter assembly of the present invention; and
Figure 3 is a cross sectional view of the invention
filter assembly taken along line 3-3 of Figure 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
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Referring now to Figure 1, a fluid supply 10 is
illustrated as including a cylindrical housing assembly 12,
an igniter assembly 14, means 16 for generating gas for
inflation through combustion, and a filter assembly 18 dis-
posed between the gas generating means 16 and the housing 12.
It should be understood, however, that the illustration of
the filter assembly 18 as employed in the cylindrically housed
fluid supply of the drawings is not intended to be limiting.
The applicability of the invention filter to other fluid
supplied (See, e.g.-, the flat pack fluid supply disclosed by
applicat-~on U.S. Patent No. 4,017,100, issued April 12, 1977
and assigned to the assignee of the present invention.) will
be apparent as the description continues.
The housing assembly 12 includes a base portion 20,
a fluid directing portion 22, and an end cap 24. Base portion
20 is preferably secured to one end of the fluid directing
portion 22 by welding or the like as illustrated at 26 and
carries one end of the igniter assembly 14 in a centrally --
located bore 28 closed by a plug 30.
; Fluid directing portion 22 defines a generally
cylindrical shell through which a multiplicity o axially
and circumferentially spaced ports 32 are formed.
The end of fluid directing portion 22 opposite
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the base portion 20 is illustrated as being internally
threaded at 36 to receive the end cap 24 which is externally
threaded.
The igniter assembly 14 is threadedly received
in a centrally located internally threaded bore 38 in the
end cap 24, The igniter assembly 14 may be of any known
design but is illustrated in Figure 1 as being of the type
including electrical leads 140 for receiving a signal from
a crash sensor (not shown) upon the occurrence of a collision.
The gas generating means 16 comprises suitable
combustible material filling the space between the igniter
assembly 14 and the filter assembly 18. While other com-
bustible materials may be chosen, that having a granular
solid form and composition as disclosed by applicant in
Canadian Patent ~pplication Serial No. 240,246, filed
November 24, 1975 and assigned to the assignee of the present
invention is preferred. The particular arrangement of the
gas generating material is preferably as set forth in the
above referenced concurrent application of Applicant G. W.
Goetz.
The filter assembly 18 is formed in a substantially
cylindrical configuration as may best be seen in the Figures
1 and 3 and is illustrated as including a relatively thin
perforated plate 40 having formed through it a plurality
of axially and radially spaced holes 42, an inner support
screen 44, first and second outer support screens 46 and
48, respectively, and a plurality of layers of deformable
- fibrous filter material 50.
. The components of the filter assembly 18 are
arranged generally in the order of their decreasing porosity
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in the flow direction as taught in the U.S. Patent No.
4,017,100 and assigned to the assignee of the present
invention. Inner support screen 44 is adjacent the
perforated plate 40 and has a relatively high porosity and
National Bureau of Standards mesh number, U.S. Standard
testing sieve, market grade or equivalent such as No. 24.
First outer support screen 46 is also highly porous with a
National Bureau of Standards mesh number such as #24.
Second outer support screen 48 is formed from a still more
porous screen fabric such as No. 8 mesh.
The layers 50 of filter material are illustrated
here as being arranged to effect filtration of the products
of combustion of the gas generating means 16 while preventing
clogging, channelling, or pin holing. Specifically, the
layers 50 of deformable fibrous filter material, whi~h are
supported by the screens 44, 46 and 48, are arranged as
two sets of layers. The layers 52 and 54 may be formed of
fibers having diameters in the range of about 1 to about
20 microns. In the preferred~embodiment one set comprises
layers 52, 54 of high temperature washed fiberglas having
fiber diameters in the range of two to ten microns such as
is manufactured and sold under the trade mark "Lo Con" by
Carborundum Corp., P.O. Box 339, Niagra Falls, New York
14302.
It will be clear to those skilled in the art,
however, that other fibrous filter materials including those
employing metallic fibers, could be used providing the layers
are arranged to effect generally finer filtration in the
downstream flow direction.
The other set comprises layers 51, 53, 55 of steel
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wool, preferably but not necessarily no. 0000 steel wool,
which is substantially more porous than the washed fiberglas.
The layers 51, 53 and 55 may consist of fibers having
diameters in the range of about 50 to about 150 microns.
As can best be seen in Fig. 2, the steel wool layers 51,
53, 55 are interdigitated with respect to the fiberglas layers
52,~54, with layer 51 being placed adjacent the inner support
screen 44 and layer 55 being placed adjacent first outer
support screen 46.
It is this arrangement of the layers that the
present invention departs from the teaching of previously
- referenced U.S. Patent No. 4,017,100. The layer arrangement
described presents a filter assembly of alternating porosity
to the gas flowing from the gas generating means 16 outward
through the fluid directing portion 22. The steel wool
layers 51, 53, 55 serve as,intermediate plenums, provide
- additional support for the adjacent filter layers, and
redistribute contaminants. The redistribution tends to
elminate "pinholding". The additional support tends to --prevent channelling; and the provision of intermediate plenum
space tends to reduce the overall heat capacity of the filter
through increased filter efficiency which is defined as
~log particulates passed~heat capacity). This last effect
in the preferred embodiment creates a warmer gas flow and
- consequently a greater volume flow per mass of propellant,
allowing use of less propellant material for inflation.
It should be clear, however, that improved filter efficiency
might also be utilized to remove more solid product.s of
combustion with a lower resulting gas temperature.
Many modifications of the array of filter layers
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are possible without departing from the spirit of invention.
For example, more layers of filter and plenum material may
be used, more than one plenum layer may be positioned
adjacent the inner support screen 44 or different filter or
plenum materials may be utilized. One specific substitution
that has been successfully made is a layer of approximately
1.5 micron fiber high filtration paper such as is sold by
Carborundum Corporation under the Registered Trade Mark
HI-FI 660-FH PAPER.
FABRICATION AND INSTALLATION OF THE FILTER ASSEMBLY
To form the filter assembly 18 in the embodiment
illustrated, the support screens 44, 46, and 48, and the
layers 50 of deformable fibrous filter material are first
fabricated substantially rectangular sheets of equal length
denoted by reference letter -L- in Figure 2 and having
widths increasing proportionally with their distance from
the central axis of the housing assembly 12, as viewed in
Figure 1.
The sheet forming second outer support screen 48
includes an inwardly extending flange portion 58 at one end
to facilitate insertion into the housing assembly 12.
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'I'he she~t forming the first outer support screen 46
includcs inwardly extending flange portions 60 on each
longitudinal edge to effect closure of the filter assembly.
' After fabrication the sheets are arranged in a rlat
5l pack shown in Figure 2 and placed in a press wherein a
high compressive force is applied.
Referring now to Figure 3, the resulting compressed
I rectangular filter pack is subsequently formed by rolling or
I like process into a resilient cylinder having a transverse
10' dimension, in its radially compressed condition, less than .he
mer diameter 68 of the housing assembly 12. The barrier
effect of the flange portions 60 tosether with the main-
~! taining of a uniform thickness in the fabrication of the
¦, filter back insures uniform distribution of the compressed
15~I filter material.
'I ~ The perforated plate 40, which may be fabricatedfirst as a rectangular sheet, is rolled or otherwise processed
to form a cylinder (as may best be seen in Figure 4) whose
- , longitudinal seam 64 is closed by fixïng a thin plate 66 to
the inner diameter 70 of the perforated plate 40 at the seam
64 by weldments 72 or the like and whose inner diameter 70
is sized to receive th~ gas generating means 16.
- To prepare the filter assembly 18 for installatior. in
~ !, the typical radial flow generator housing 12 the perforated
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25ll plate 40 is first placed within the resilient cylinder 61.
The cylinder 61 is then radially loaded by means of a
fixture (not snown) which is configured to allow sliding
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movemcllt of the cylinder 61 with respect thereto. The
longitudinal axis of cylinder 61 is then aligned with the
~ longitudinal aY.is of the housing 12. An axial load is then
; ~ applied to the filter assembly 18 to slide it out of the
5,~ fixture into the housing 12, with inwardly extending flange
portion 58 of second outer screen 48 providing a relatively
, smooth leading edge to facilitate insertion. In order to
~~ further aid insertion, the housing 12 may be vibrated to
,' effectively reduce the frictional forces acting between the
10; filter assembly 18 and the inner surface of housing 12.
i When installed as described in Figure 1 the filter
'" assembly 18 effects filtration of the products of combustion
il of the gas generating means 16 which are released to flow
,' outward through fluid directing passages 32 in the housing 12
5;¦ when the gas generating means 16 is actuated by the igniter
assembly 14 upon the occurrence of a collision. Gaseous
products flow outward from the gas generating means 16 through
holes 42 in the perforated plate 40, bypassing being prevented
1, by the plate 66. Filtration of the solid products of the
combustion is effected during passage through the screen 44,
and the layers of filter material 50. Bypassing of these
" portions of the filter assembly 18 is prevented through the
',j positioning of the seam 62.
, Although the filter assembly of the present invention has
25~ been described in only certain embodiments, o.her embodiments
and modifications may be constructed without departing from
the spirit of the invention as presently claimed.
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