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BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for generating gas for
inflating a vehicle occupant restraint which restrains movement of an
occupant of a vehicle in the event of a collision. More specifically, the
invention relates to an inflator assembly which generates gas to expand an
airbag which cushions movement of a vehicle occupant in the event of a
collision.
A known safety apparatus for restraining movement of an occupant of a
vehicle in the event of a collision includes an airbag which is expanded
by the flow of gas obtained from gas generating material in an inflator
assembly. In order to protect the occupant of a vehicle adequately during
a collision, the inflator assembly quickly generates a large quantity of
gas and directs the gas into the airbag. The vehicle may be involved in a
collision at a very high ambient temperature or at a very low ambient
temperature. Thus, the inflator assembly must be able to provide the
required quantity of gas to expand the airbag properly over a large range
of ambient temperatures.
In very cold weather, the inflator assembly builds pressure more slowly
than in warm weather so there is a tendency in cold weather for the airbag
to be inflated too slowly or insufficiently to perform its intended
purpose. Also, as the ambient temperature increases, the burn rate of the
gas generating material increases. Consequently, at higher ambient
temperatures, high pressures are created and the deployment velocity of
the airbag increases. It is desirable that the airbag function uniformly
at all ambient temperatures.
Also, the inflator assembly must be able to endure normal vibrations and
shock loads to which a vehicle is subjected while being driven over many
different types of roads. It is particularly important that the gas
generating material in the inflator assembly be able to withstand severe
vibrations and shock loads due to the vehicle encountering uneven roads
and deep chuck holes.
Although the operating and durability requirements of the inflator assembly
are very stringent, the safety apparatus must have a resonable cost in
order to obtain consumer acceptance. Thus, the components of the safety
apparatus must be easily assembled and installed in a vehicle. However,
once the inflator assembly has been installed in the vehicle, it must be
capable of withstanding forces to which it is subjected due to driving of
the vehicle for many miles for a relatively long period of time. If and
when the vehicle is involved in a collision, the inflator assembly must be
capable of quickly generating a volume of gas sufficient to inflate the
airbag.
SUMMARY OF THE PRESENT INVENTION
The present invention provides an improved inflator assembly which
generates gas to expand an airbag to restrain movement of an occupant of a
vehicle when the vehicle is involved in a collision. In order to provide a
relatively large volume of gas quickly to expand an airbag, the inflator
assembly includes grains of a material which generates gas upon
combustion.
The grains are cylindrical in shape and have passages extending axially
therethrough. The centers of the passages are located on concentric
circles, the centers of which are located on the central axes of the
grains. The axes of the passages are spaced equal distances apart about
the concentric circles and the axes of the passages on one of the
concentric circles are circumferentially spaced from the axes of the
passages on the adjacent concentric circle. This arrangement of the
passages provides for uniform burning of the grains.
The grains are located in the inflator assembly with their axial end
surfaces facing each other. As the surfaces defining the passages burn,
the gas generated by the burning flows through the passages to the axial
ends of the grain. To enable gas to flow from the passages radially
between the grains and into the airbag, the ends of the grains are axially
spaced apart. Specifically, the axial end surfaces of each grain have
projections which engage the adjacent grain and provide space through
which the gas can flow radially between the grains.
The grains of the gas generating material are located internally of a
structure which includes a filter assembly. The generated gas flows
through the filter assembly and into the airbag. The grains are supported
by resilient retainer tubes which engage the outside of the grains and
keep the passages in the grains axially aligned. In addition to
maintaining the grains in axial alignment, the retainer tubes are made of
a resiliently yieldable material to cushion the grains against forces
encountered during normal operation of the vehicle. Further, the retainer
tubes minimize contact between the grains and the surrounding structure,
which contact could damage the grains.
The inflator assembly has first passages for directing gas into the airbag
and second passages for directing gas away from the airbag. The first and
second passages are blocked prior to activation of the inflator assembly.
The first passages open to direct gas into the airbag when a sufficient
pressure builds up in the inflator assembly. Thus, the airbag is not
subjected to relatively low pressures which would cause the airbag to be
slowly or otherwise improperly inflated under cold weather conditions. If
the pressure in the inflator assembly is too high, as may occur when the
ambient temperature is high, the second passages open to direct gas away
from the airbag. Thus, the airbag is not subjected to excessive gas
pressures because of high ambient temperatures.
The first and second passages in the inflator open at different pressures.
This occurs because a rupturable foil covers the first and second passages
in the inflator and the first passages are larger in cross section than
the second passages. Thus, the foil covering the first passages ruptures
at a lower pressure than the foil covering the second passages.
DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and features of the present invention will
become more apparent upon a consideration of the following description
taken in connection with the accompanying drawings wherein:
FIG. 1 is a fragmentary sectional view of an inflatable restraint system
constructed in accordance with the present invention, the restraint system
being shown in an inactive condition prior to a vehicle being involved in
a collision;
FIG. 2 is a fragmentary schematic sectional view of the inflatable
restraint system of FIG. 1, the system being shown in an expanded
condition immediately after a collision;
FIG. 3 is a fragmentary pictorial view of an inflator assembly used in the
inflatable restraint system of FIGS. 1 and 2;
FIG. 4 is a sectional view of the inflator assembly of FIG. 3, illustrating
the relationship between a housing for the inflator assembly and a
plurality of grains of gas generating material disposed in a
longitudinally extending array in the housing;
FIG. 5 is an enlarged fragmentary sectional view of a portion of the
inflator assembly of FIG. 4;
FIG. 6 is plan view, taken generally along the line 6--6 of FIG. 5,
illustrating the configuration of a grain of gas generating material;
FIG. 7 is a plan view, taken generally along the line 7--7 of FIG. 5,
illustrating the configuration of another grain of gas generating
material;
FIG. 8 is a sectional view, taken generally along the line 8--8 of FIG. 7,
illustrating the manner in which passages extend through the grain of gas
generating material;
FIG. 9 is an illustration depicting the relationship between and
configuration of tubular retainers used to position and support the grains
of gas generating material;
FIG. 10 is a fragmentary schematic illustration depicting the progression
of combustion of a portion of a grain of gas generating material;
FIG. 11 is an enlarged fragmentary sectional view of a filter used in the
inflator assembly of FIGS. 3 and 4;
FIG. 12 is a schematic illustration depicting the manner in which a rigid
perforated tube is positioned relative to a piece of screen during the
making of the filter of FIG. 11;
FIG. 13 is a schematic illustration depicting how two layers of screen are
wound around the tube during the formation of the filter;
FIG. 14 is a schematic illustration depicting the manner in which a layer
of steel wool and an additional layer of screen is wound around the tube
during the formation of the filter;
FIG. 15 is a schematic illustration depicting the manner in which layers of
fiberglass and additional layers of steel wool and screen are wound around
the tube during the formation of the filter;
FIG. 16 is a fragmentary sectional view illustrating the relationship of a
housing of the inflator assembly to a sheet of foil which functions as a
pressure control for the gas conducted from the inflator assembly;
FIG. 17 is a sectional view, generally similar to FIG. 16, illustrating how
openings are formed in the foil to direct the flow of gas into the airbag
during expansion of the airbag;
FIG. 18 is an enlarged illustration depicting the relationship between the
layer of foil and a housing opening through which gas is directed from the
inflator assembly into the airbag;
FIG. 19 is a sectional view illustrating the relationship between the layer
of foil and the housing openings during the exhausting of excess gas from
the inflator assembly;
FIG. 20 is an enlarged illustration further depicting the relationship
between the foil and a housing opening through which excess gas is
directed from the inflator assembly;
FIG. 21 (on the second sheet of the drawings) is an enlarged schematic
sectional view illustrating the manner in which the airbag is attached to
a reaction canister; and
FIG. 22 (on the second sheet of the drawings) is an enlarged schematic
sectional view illustrating a second embodiment of the connection between
the airbag and reaction canister.
DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
General Description of Inflatable Restraint System
An inflatable restraint system 30 constructed in accordance with the
present invention is illustrated in FIG. 1 in an inactive condition prior
to the vehicle being involved in a collision. When the vehicle becomes
involved in a collision, an airbag 32 is expanded from a collapsed
condition, shown in FIG. 1, to an extended condition, shown in FIG. 2, by
a rapid flow of gas from an inflator assembly 34. When the airbag 32 is in
the extended condition, it is effective to restrain movement of an
occupant of a vehicle and it prevents the occupant from violently
contacting structural parts of the vehicle interior.
Although the inflatable restraint system 30 could be mounted on many
different parts of the vehicle, the restraint system is illustrated in
FIGS. 1 and 2 as being mounted on a dashboard 35 of the vehicle. The
restraint system includes a rigid metal reaction canister 38 which is
fixed to the dashboard 35. The inflator assembly 34 is mounted within the
reaction canister 38 in an orientation so that an initial flow of gas,
indicated by the arrows 42 in FIG. 2, causes the airbag to expand
rearwardly into the passenger compartment. At high termpatures while the
airbag 32 is expanding, excess gas from the inflator assembly 34 is
exhausted in a forward direction, as indicated by the arrows 44 in FIG. 2.
When the airbag is expanded, it engages the torso of an occupant of a
vehicle to restrain forward movement of the occupant of the vehicle toward
the dashboard 35 under the influence of collision-induced forces. The
airbag 32 quickly collapses so that the occupant is free to exit from the
vehicle. To effect collapsing of the airbag 32, the airbag is preferably
formed of a porous material which enables gas to flow out of the bag into
the vehicle passenger compartment.
Upon the occurrence of a collision, an inertia sensor (not shown) transmits
a signal over leads 50 (FIGS. 3 and 4) to effect actuation of an ignitor
assembly or squib 52 at the left end (as viewed in FIGS. 3, 4 and 5) of
the inflator assembly 34. Hot gases and flame from the ignitor assembly 52
cause ignition of gas generating material 60. The gas generating material
60 includes a plurality of cylindrically shaped grains 64, which encircle
the ignitor assembly 52 and a plurality of cylindrically shaped grains 66
which are spaced from the ignitor assembly 52. The actuation of the
ignitor assembly 52 and the ignition of the grains 64, 66 is extremely
rapid and combustion of the grains 64, 66 occurs quickly to generate a
relatively large volume of gas rapidly.
The gas generated by combustion of the grains 64, 66 flows through openings
in a rigid cylindrical tube 70 which surrounds the grains 64, 66. The gas
then flows through a filter assembly 72. The filter assembly 72 prevents
sparks and/or particles of hot material from entering the airbag 32. The
gas then encounters a layer 76 of foil which the gas ruptures upon
building up sufficient pressure. Lastly, the gas flows through rearwardly
facing openings 78 in cylindrical sidewall 80 in the inflator housing 84
into the reaction canister 38 and the airbag 32 (FIG. 1). In the event
that excess gas is generated by the inflator assembly, such excess gas is
exhausted. The excess gas is directed from the inflator assembly into the
passenger compartment of the vehicle through forwardly facing openings 86
in the housing 84.
Inflator Assembly--Ignitor
Upon the occurrence of a collision, the ignitor assembly 52 ignites the gas
generating material 60. The ignitor assembly 52 includes a housing 90
(FIG. 5) which screws into a circular end wall 92 of the housing 84. The
ignitor housing 90 contains an ignitable material 96 which is ignited by
electrical current conducted through the leads 50 upon the occurrence of a
collision. Ignition of the material 96 results in actuation of a
pyrotechnic material 98 (FIG. 5). Actuation of the material 98 ruptures a
circular end wall 102 of the ignitor housing 90. As this occurs, a stream
of hot gases is directed against the grains 64, 66 to ignite the grains.
The material 98 may be any one of a number of different materials, such as
titanium potassium chlorate or zirconium potassium chlorate. However, it
is important that destructive effects due to igniter firing be avoided.
Specifically, it is important to avoid high peak pressure which could
cause a grain or grains to shatter. The use of a boron potassium nitrate,
20 microns in particle size, as the material 98 can minimize the peak
pressure and thus the possibility of grain damage.
Inflator Assembly--Grains
Upon ignition by the ignitor assembly 52, combustion of the grains 64, 66
quickly occurs to generate a large volume of gas in a short time. The
grains 64 and 66 have an outer combustion enhancing coating which is
highly combustible and results in rapid ignition of all outer surface
areas of the grains 64 and 66.
The grains 64, 66 may be made of an alkali metal azide compound. Those
compounds are represented by the formula MN.sub.3 where M is an alkali
metal, preferably sodium or potassium and most preferably sodium. The
grains 64, 66 preferaly are made of a material which includes 61 to 68% by
weight of sodium azide, 0 to 5% by weight of sodium nitrate, 0 to 5% by
weight of bentonite, 23 to 28% by weight of iron oxide, 2 to 6% by weight
of graphite fibers and 1 to 2% of fumed silicon dioxide. Preferably, the
composition of the grain is 63% by weight of sodium azide, 2.5% by weight
of sodium nitrate, 2% by weight of bentonite, 26.5% by weight of iron
oxide, 4% by weight of graphite fiber and 2% by weight of fumed silicon
dioxide. The fumed silicon dioxide is sold under the trademark CAB-O-SIL
by Cabot Manufacturing Company with a product designation EH5. The
graphite fibers are 3-6 microns in diameter and 40 to 80 thousandths of an
inch in length.
The material of which the grains 64, 66 are made is essentially known
except for the inclusion of the graphite fibers. The graphite fibers
mechanically reinforce the grains. Specifically, the fibers minimize the
possibility of the grain cracking. Cracks in a grain would produce
unwanted additional grain surface area that acts to accelerate the grain
burn rate in an unpredicatable manner. The graphite fibers also provide
mechanical reinforcement so that when the grain burns it more readily
forms a strong structural sinter. The sinter controls the combustion
products of the grain. Also, the graphite fibers cause the grains to burn
at an increased rate and at a decreased temperature. Specifically, the
graphite fibers increase the burn rate of the grain by 40%. The grain
burns at a relatively low temperature in the neighborhood of 1800 degrees
F. Other fibers such as fiberglass and steel wool could be used.
The combustion enhancing coating on the grains 64, 66 includes 20 to 50% by
weight of an alkali metal azide, preferably sodium azide, 25 to 35% by
weight of an inorganic oxidizer, preferably sodium nitrate, 1 to 3% by
weight of fumed silicon dioxide, 10 to 15% by weight of a fluoroelastomer
such as Viton or Teflon, 15 to 25% by weight of magnesium, and 1 to 6% by
weight of graphite. Preferably, the coating mix includes 34% by weight of
sodium azide, 28% by weight of sodium nitrate, 2% by weight of fumed
silicon dioxide, 12% by weight of a fluoroelastomer, 19% by weight of
magnesium, and 5% by weight of graphite. Generally, the coating should
provide a weight gain of 2 to 3.5% of the total weight of the grain prior
to being coated.
The fumed silicon dioxide in the coating is sold by the Cabot Manufacturing
Company under the trademark CAB-O-SIL and has a product designation of
EH5. The fumed silicon dioxide has a particle size of 0.01 microns. The
magnesium preferably has a particle size of 45 microns, and the sodium
azide and sodium nitrate have a particle size of preferably 4 microns.
Each of the two cylindrical grains 64 (FIG. 6) has a circular central
passage 106 which receives the cylindrical ignitor housing 90 (FIG. 5).
The passage 106 extends through the end grain 64 between axially opposite
end faces 108 and 110 (FIG. 5) of the end grain. The central axis of the
passage 106 is coincident with the central axis of the cylindrical grain
64.
In order to maximize the rate of combustion of the two end grains 64 and
the amount of gas generated, a plurality of cylindrical passages 112
extend through the grains 64 between the axially opposite end faces 108
and 110. The axes of the passages 112 extend parallel to the central axes
of the grains 64 and parallel to the central passages 106. The central
axes of the passages 112 are disposed on inner and outer concentric
circles 116 and 118 (FIG. 6) having a common center on the central axis of
the grain 64. The ratio of the diameter of the circle 116 to the diameter
of the circle 118 of the grains 64 is 2.91 to 1.93.
The passages 112 on the inner circle 118 are circumferentially spaced
around the grain from the axes of the passages 112 on the outer concentric
circle 116. Thus, a radius extending from the center of the grains 64 to
the central axis of any one of the passages 112 disposed on the outer
concentric circle 116 is angularly offset from any radius extending from
the center of the grain 64 to the central axis of a passage 112 disposed
on the inner concentric circle 118. This results in the central axis of
each of the passages 112 being disposed in a radial plane which is
angularly offset from a radial plane containing the central axis of any of
the other passages.
For example, the angular offset between the central axis of passage 112a on
circle 118 and the central axis of passage 112b on circle 116 is five (5)
degrees. The angular offset between the central axis of passage 112a and
the central axis of passage 112c on circle 116 is fifteen (15) degrees.
These angular offsets are shown in FIG. 6 and are the same for the
corresponding passages around the grain. The end grains 64 have thirty
passages 112 disposed on concentric circles. Twelve passages 112 are
disposed on the inner concentric circle 118. Eighteen passages 112 are
disposed on the outer concentric circle 116.
The main grains 66 have the same general construction as the end grains 64.
Each of the main grains 66 (FIGS. 7 and 8) has a relatively small
cylindrical central passage 126 having an axis disposed on the central
axis of the grain. The passage 126 extends between opposite axial end
faces 128 and 130 of the main grain. In addition, each main grain 66 has a
plurality of cylindrical passages 134 which extend axially through the
grain 66 between the opposite end faces 128 and 130. The central axes of
the passages 134 extend parallel to the central axis of the passage 126
and parallel to the central axis of the grain 66. The cross sections of
the passages 126 and 134 are circular and identical in diameter and
uniform throughout their extent. The diameters of the passages 126 and 134
in the main grains 66 are equal to the diameters of the passages 112 in
the end grains 64.
The centers of the passages 134 are evenly spaced on concentric circles
138, 140, and 142, which have their centers on the central axis of the
grain 66. There are eighteen passages 134 on the outer concentric circle
138, twelve passages 134 on the intermediate concentric circle 140 and six
passages 134 on the inner concentric circle 142. Thus, the total number of
passages 134 extending between the opposite end faces 128 and 130 of each
grain 66 is thirty-seven, counting the one passage 126 at the center of
the grain 66.
To promote uniform combustion of the main grains 66, the passages 134 are
disposed on the concentric circles 138, 140 and 142 with the centers of
the passages spaced the same distance apart along the concentric circles.
The radial distance of the axis of the central passage 126 to the axis of
any one of the passages 134 disposed on the concentric circle 142 is equal
to the spacing of the axes of the passages 134 along the concentric circle
142. The diameters of the concentric circles 138, 140 and 142 are in the
ratio of 2.91 to 1.93 to 1.
The axes of the passages 134 on any one of the concentric circles 138, 140
or 142 are circumferentially spaced around the grain from the axes of
passages on the other concentric circles. Thus, a radius extending from
the center of the grains 66 to the axis of any one of the passages 134 is
angularly offset from the radius extending from the center of the grain to
the central axis of any other passage 134. The extent of the angular
offset between the central axis of a passage 134 on any one of the
concentric circles 138, 140, and 142 and the central axes of the adjacent
passages on the other concentric circles varies between 5 and 30 degrees
depending upon which of the passages 134 is being considered. The angular
offsets are shown in FIG. 7 for certain passages and are the same for the
corresponding passages around the grain. The spacing of the passages in
the grains 64, 66 promotes uniform burning of the grain, as will be
described.
The gas which is generated within the passages 112 and 134 must be able to
get out of the passages and flow through the filter assembly 72 and
housing 84 into the airbag 32 to inflate the airbag. To provide for such
flow, spaces 148 (FIGS. 4 and 5) are provided between axial end faces of
adjacent grains 64 and 66. The spaces 148 on opposite axial ends of the
end grains 64 extend radially outwardly from the central opening 106 on
the end faces 108 or 110 (FIG. 5) to the cylindrical outer side surfaces
150 (FIG. 6) of the end grains. Similarly, the spaces 148 at opposite ends
of the grains 66 extend radially outwardly from the central passage 126
along the opposite axial end faces 128 or 130 (FIGS. 5 and 8) to a
cylindrical outer side 154 of the grains 66. Since the spaces 148 are
provided between the ends of adjacent grains 64 and 66 throughout the
extent of the longitudinally extending array of grains in the inflator
assembly 34, an even flow of gas from the inflator assembly throughout its
length is promoted.
The spaces 148 between the ends of adjacent grains are provided by axially
projecting standoff pads or projections 158 and 160 (FIG. 8) at the
axially opposite end faces 128 and 130 of the grains. Each of the pads
158, 160 has a circular configuration which is centrally disposed within a
rectangular array of passages 134 (see FIG. 7). The rectangular arrays of
passages 134 around the pads 160 include spaced apart pairs of passages
disposed along the intermediate concentric circle 140 (FIG. 7) and the
outer concentric circle 138.
The pads 158, 160 are disposed midway between the outer and intermediate
concentric circles 138 and 140. Each of the pads 158, 160 has a central
axis which is equally spaced from the central axes of each of the passages
134 forming a rectangular array around the pad. If the pads 158, 160 were
moved inwardly to a location between the intermediate concentric circle
140 and inner concentric circle 142, only three pads could be provided at
one end of the main grain 66 rather than the six pads which are provided
between the outer and intermediate concentric circles 138 and 140.
Although only the pads 158 and 160 on the main grain 66 are illustrated in
FIGS. 7 and 8, it should be understood that each of the end grains 64 is
provided with standoff pads 164 and 166 (FIGS. 5 and 6) which are disposed
on opposite axial end faces 108 and 110, respectively, of the end grains
64. The standoff pads 164 and 166 for the end grains 64 are centrally
disposed within rectangular arrays of passages 112 in the same manner as
the standoff pads 158 and 160 for the main grains 66. The standoff pads
164 and 166 for the end grains 64 are disposed between the concentric
circles 116 and 118 in the same manner as the standoff pads 158 and 160
for the main grains 66 are disposed between the concentric circles 140 and
142.
The standoff pads for one grain engage the standoff pads on a next adjacent
grain to provide the equal size spaces 148 between the grains 64 and 66.
Thus, the end grain 64 which is fartherest to the left in FIG. 5 has six
rightwardly projecting standoff pads 166 which abuttingly engage six
leftwardly projecting standoff pads 164 on the next adjacent end grain 64.
This results in the formation of a space 148 between the end faces 108 and
110 of the end grains 64, and this space has an axial extent equal to the
combined axial extent of the standoff pads 164 and 166. The axial extent
of the space 148 is also approximately equal to the diameter of the
passages 112 through the grains 64.
Similarly, standoff pads 166 on the rightwardmost (as viewed in FIG. 5) end
grain 64 engage leftwardly projecting standoff pads 160 on the
leftwardmost main grain 66 to form a space 148 between the end grain 64
and main grain 66. The rightwardly (as viewed in FIG. 5) projecting pads
158 on the main grain 66 illustrated in FIG. 5 abuttingly engage
leftwardly projecting pads 160 on a next succeeding main grain (not shown
in FIG. 5) to form the space 148 between the two main grains. Since all of
the standoff pads 158, 160, 164 and 166 are of the same size and
configuration, the spaces 148 between the grains 64 are all of the same
size and configuration. Although the standoff pads 158, 160, 164 and 166
have been shown as projecting from opposite axial ends of the grains 64
and 66, the pads could project from only one end of each of the grains so
that the space 148 between the grains would be formed by single standoff
pads rather abutting engagement between a pair of standoff pads.
Inflator Assembly--Grain Retainer
The grains 64 and 66 are held in axial alignment with each other and are
cushioned against forces encountered during operation of a vehicle by a
plurality of retainer tubes 170, 172 and 174 (FIG. 9). The hollow
cylindrical retainer tubes 170, 172 and 174 engage V-shaped notches 178
(FIG. 6) on the outer sides 150 of the end grains 64 and V-shaped notches
180 (FIG. 7) on the outer sides 154 of the main grains 66. The hollow
cylindrical retainer tubes 170, 172 and 174 are formed of a resiliently
deflectable material, preferably silicone rubber.
The retainer tube 170 (FIG. 9) is bent to form a pair of parallel legs 188
and 190 interconnected by an intermediate section 192. The retainer tubes
172 and 174 are similarly bent to form parallel legs 194, 196, 198 and
200. The legs 188 and 190 of the retainer tube 170 engage diametrically
opposite notches 178 in the end grains 64 and diametrically opposite
notches 180 in the main grain 66 in the manner shown in FIG. 5. The legs
194, 196, 198 and 200 are similarly placed in notches in the end and main
grains 64 and 66. The connector sections between the legs 188, 190, 194,
196, 198 and 200 extend across the end face of the last main grain 66 in
the longitudinal array of grains, that is the rightwardmost grain 66 of
FIG. 4.
The tubular legs of the retainer tubes 170, 172, 174 hold the grains in
axial alignment with each other so that the passages 112 through the end
grains 64 and the passages 134 through the main grains 66 are all disposed
in axial alignment with each other. This results in the grains 64 and 66
being stacked in a longitudinally extending cylindrical array.
The end and main grains 64 and 66 are supported in a coaxial and spaced
apart relationship with the rigid perforated tube 70 by engagement of the
retainer tubes 170, 172 and 174 with the perforated tube 70. The outer
side surfaces of the legs 188, 190, 194, 196, 198 and 200 of the retainer
tubes 170, 172, 174 abuttingly engage the cylindrical inner side surface
of the perforated tube 70 to support the end and main grains 64 and 66 in
a coaxial relationship within the tube 70.
The space between the outer side surfaces 150 and 154 of the end and main
grains 64 and 66 and the inner side surface of the perforated tube 70
forms an inner plenum chamber 206 (FIG. 5) between the grains 64 and 66
and the tube 70. This plenum chamber extends throughout the length of the
inflator assembly 34 and is formed by an annular array of arcuate chamber
segments disposed between the legs 188, 190, 194, 196, 198 and 200 of the
retainer tubes 170, 172 and 174. All of the spaces 148 between the grains
64 and 66 are connected with the plenum chamber 206 to tend to equalize
the pressure along the axial extent of the tube 70 and filter assembly 72
before the gases flow through the filter assembly.
Since the retainer tubes 170, 172, 174 are hollow and are made of a
resiliently yieldable material, the retainer tubes attenuate vibration and
shock forces transmitted to the inflator assembly 34 before these forces
reach the grains 64 and 66. The legs 188, 190, 194, 196, 198 and 200 of
the retainer tubes 170, 172 and 174 can also be resiliently compressed
slightly to allow the grains to shift somewhat relative to the tube 70
without touching the tube 70. The opposite ends of the longitudinally
extending array of grains 64 and 66 are sealed and cushioned by engagement
with resilient circular bodies 210 and 212 (FIG. 4) of silicone rubber
sealant. Similar results can be obtained by using roll pins, i.e. split
resilient metal tubes.
Inflator Assembly--Grain Combustion
Upon actuation of the ignitor assembly 52, combustion of all exposed
surfaces of the grains 64, 66 occurs. This occurs in a few milli-seconds.
A supersonic combustion wave propogates through the aligned passages 112,
134 and spreads across the axial end surfaces 108, 110, 128, 130 and
across outer side surfaces 150, 154 of the grains 64, 66. The passages
112, 134 allow for high speed spreading of the flame. The combustion is
uniform throughout the grains 64 and 66 due to the uniform spacing of the
passages. The grains 64 and 66 rapidly burn from their exposed surfaces.
The manner in which a main grain 66 burns is illustrated schematically in
FIG. 10.
As a grain 66 combusts or burns inwardly from its cylindrical outer side
154, material of the grain burns radially inwardly along a circular front,
a portion of which is indicated at 216 in FIG. 10. At the same time, the
material of the grain 66 combusts from the side surfaces of the passages
134 along circular fronts indicated at 218 in FIG. 10.
In the schematic illustration of FIG. 10, the combustion of the grain
material from the inner side surfaces of the passages 134 has progressed
outwardly to a location at which the burning fronts 218 for most of the
passages intersect burning fronts from adjacent passages. Similarly, the
burning front 216 from the outer side surface 154 of the grain has
progressed to a location where it has intercepted the outwardly moving
burning fronts 218 from the radially outermost passages 134.
The radially innermost surface portions of the notches 180 are spaced from
the surfaces of the most closely adjacent passages 134 by a distance which
is the same as the shortest distance between the surfaces of adjacent
passages in the radially outermost circul | | |
