The present invention relates to a dual stage inflator
capable of providing various levels of inflation for inflating an airbag.
Inflators provide inflation gas by burning a pyrotechnic
material, releasing stored gas, or by some combination thereof. Aggressive airbag
deployment has the advantage of deploying an inflated airbag in front of the vehicle
occupant as soon as possible. The problem associated with aggressive airbag deployment
is the possibility of a child, a small adult, or an out of position adult interacting
with the airbag while it is being inflated. Out of position is a term utilized in
the safety restraint industry that refers to a vehicle occupant that is not sitting
properly in his seat or sitting too close to the airbag module.
Dual stage inflators reduce the injury to small adults
or children by reducing the aggressiveness of airbag deployment. These inflators
provide varying output levels of inflation gas in accordance with the size and position
of the vehicle occupant. Dual stage inflators provide a full output of inflation
gas to protect a full size vehicle occupant who is not out of position. A dual stage
inflator is also able to provide a staged output of inflation gas for vehicle occupants
who are smaller in size or out of position. The staged output deployment first provides
inflation gas to partially inflate the airbag and after a period of time the inflator
provides more inflation gas to fill the airbag.
Dual stage inflators disclosed in
US 6 189 922 B1
US 6 168 200 B1
have two gas generant sources. Dual stage inflators having two separate
burst disks are disclosed in
US 5 022 674 A1
US 5 351 988 A1
US 5 016 914 A1
US 6 557 890 B1
discloses a hybrid inflator that has two charges for gas production arranged
outside on opposite sides of a gas chamber charged with compressed gas. The compressed
gas is completely separated from the ignitable gas charges. A similar construction
is disclosed in
entitled "Gas Generator for Air Bag".
US 6 557 890 B1
relies on a piston to separate the ignition gas from the compressed gas
which according to
is very difficult to move causing unusual pressure rises internal to the
inflator that may destroy the housing. To avoid this
discloses an inflator that employs a ball-like destructive means that
acts like a check valve that can normally seal the inert gas, but upon ignition
of a charge is unseated and moved into the gas chamber colliding with a burst disk.
Both of these inflators require extra components and increase the length of the
inflator accommodating the ignitable charges thereby reducing the amount of length
available for the compressed gas. To accommodate this loss of volume the compressed
gas chamber in each case typically has an enlarged diameter of 60 mm or greater.
Ideally a hybrid inflator should be small in size, but extremely reliable. Reliability
often requires a desire to simplify and eliminate unnecessary features or elements.
Figure 4 shows a prior art inflator 100 according to
US 6,769,714 B2
that has a housing 110 wherein a gas generator subassembly 122 is located
inside of a pressure vessel 112 and two separate igniters 121, 122 were used. One
igniter 122 would ignite an enhancer charge 130 and gas generant charge 140 in the
subassembly 120 while the second igniter 121 could be used to rupture a seal 150
to allow the compressed gas 111 to be released. The igniters 121, 122 could be used
sequentially or separately or simultaneously if so desired to achieve variations
in the airbag fill rate. The present invention provides some of the very reliable
aspects of this earlier inflator in combination with new elements to achieve the
extremely reliable dual stage inflator described herein. The present invention according
to Claim 1 provides a more efficient use of the space available for the inflator
while providing a variety of inflation fill rates and volumes.
- FIG. 1 is a cross sectional view of the dual stage inflator in the present invention.
- FIGS. 2A, 2B, 2C, and 2D show various burst disk configurations.
- FIG. 3 is a perspective view of the first gas generator subassembly.
- FIG. 4 shows a prior art inflator according to
US 6,769,714 B2
The present invention provides a dual stage inflator 10
with various output levels of inflation gas to gently inflate an airbag so as not
to injure an out of position child or small adult while still being capable of providing
crash protection to a full size adult. The dual stage inflator 10 comprises a cylindrical
elongated outer inflator housing 11 forming a pressure vessel 12 having a first
portion 10A that is filled with stored gas 13, which is released from the inflator
during a crash to inflate a vehicle airbag. The outer inflator housing 11 of the
dual stage inflator 10 has a generally cylindrical shape and may be formed of stainless
steel, low carbon steel, or any other suitable material, which has sufficient strength
and extremely low gas permeability.
Ideal characteristics for the stored gas 13 are that the
gas is inert, is not highly temperature sensitive, and is capable of inflating an
airbag at a high inflation rate. The stored gas 13 can include one or more gases,
which include but are not limited to argon, carbon dioxide, oxygen, helium, and
The pressure vessel 12 is filled with stored gas 13 through
the gas fill port 14, which is preferably located on a first end closure 20 of the
dual stage inflator 10. The gas fill port 14 is sealed by a plug 15 made from low
carbon steel to prevent gas from escaping after the dual stage inflator 10 has been
filled to the specified pressure. It is preferred that the plug 15 is secured to
the gas fill port 14 by a resistance weld, but one skilled in the art realizes that
other types of welding could be utilized to fuse the plug 15 to the outer inflator
In FIG. 1, the dual stage inflator 10 has a first end closure
20 and a central support column 21 holding a first gas generator subassembly 23.
The first gas generator subassembly 23 lies centrally disposed within the pressure
vessel and extends longitudinally along the longitudinal axis A of the outer inflator
housing 11 a distance extending nearly the entire length L of the internal chamber
of the pressure vessel 12, as shown about 85% of L.
In FIG. 1, the first gas generator subassembly 23 is situated
on the support column 21 of the inflator first end closure 20. The first gas generator
subassembly 23 has an igniter 40 for receiving an electrical signal from a controller
(not shown) via two or more electrodes 41 that in turn communicate with a sensor
means (not shown). The igniter 40 is an electrical device that initiates the activation
of the inflator when a suitable electric current is passed through a resistor element
embedded in one or more layers of pyrotechnic compositions. The igniter may be of
the standard direct fire design, receiving the firing current directly from the
controller, or the igniter 40 may be of an advanced design which communicates with
the controller by digital signals and which contains on board the igniter an application
specific integrated circuit, firing capacitor, and related components.
The pyrotechnic compositions and load weight contained
within the igniter 40 are designed to break through the gas tight sealing disk 46
and fully ignite the enhancer 47. An example of a suitable pyrotechnic composition
or ignition material for the present invention is zirconium potassium perchlorate,
however, one skilled in the art realizes that other ignition materials can be utilized
in the present invention. The igniter 40 is encased in an igniter housing opening
42 in the support column 21 of the end closure 20, which is attached to the outer
inflator housing 11.
The enhancer 47 may be any of a number of known compositions
that are readily ignited by the igniter 40 and burn at a high rate and temperature.
Examples of enhancers include boron potassium nitrate and non-azide formulations
containing a metal. The gases and hot burning particles from the ignited enhancer
47 exit through the pellet retainer 43 and ignite the gas generant 48. The first
gas generator subassembly 23 has a spring like cushion 44 located on the end furthest
away from the enhancer 47. The cushion 44 is a resilient member that biases the
gas generant 48 against the pellet retainer 43 to ensure the gas generant 48 pellets
occupy a predetermined volume without being able to rattle. The pellet retainer
43 is a porous wall that divides the enhancer 47 from the gas generant 48. An optional
sealing foil may be used to cover the openings of the pellet retainer 43. The hot
gases from the ignition of the enhancer 47 flow through the pellet retainer 43 but
neither the enhancer 47 material nor the gas generant 48 pellets can pass through
the pellet retainer 43.
Representative gas generant 48 compositions useful in the
dual stage inflator 10 include fuels such as aminotetrazoles, tetrazoles, bitetrazoles,
triazoles, the metal salts thereof, nitroguanidines, guanidine nitrate, amino guanidine
nitrate, and mixtures thereof; in combination with an oxidizer such as the alkali
and alkaline earth metal nitrates, chlorates, perchlorates, ammonium nitrate, and
mixtures thereof. The gas generant 48 can be formed into various shapes using various
techniques known to those skilled in the art.
The first gas generant subassembly 23 inside the pressure
vessel 12 has a housing 49 retains the gas generant 48 and is made from stainless
steel, low carbon steel, or other suitable material. The gas generant subassembly
housing 49 has a plurality of apertures 45, which can be seen in FIG. 3. The plurality
of apertures 45 are situated along the length of the gas generant subassembly housing
49, and an important facet about the size and number of apertures 45 is that the
first gas generator subassembly 23 remains thrust neutral during the burning of
the gas generant 48. Importantly, the apertures 45 directly expose the gas generant
48 in the first gas generator subassembly 23 to the stored gas 13 present in the
pressure vessel 12. The location of the apertures 45 allows the hot gases to be
discharged on the walls of the outer inflator housing 11 thus cooling and retaining
solid particulates preventing a portion of the particulates from entering the gas
diffuser 26. When the pressure vessel 12 is filled with stored gas 13, some of the
stored gas 13 is able to flow into the first gas generator subassembly 23 equalizing
the pressure in the pressure vessel 12 with the first gas generant subassembly 23.
A sealing disk 46 is utilized in the present invention to prevent the stored gas
13 from escaping from the dual stage inflator 10 through the first gas generator
subassembly 23. The sealing disk 46 is attached by laser welding over the igniter
housing opening 42 to an enhancer retaining washer 54 or optionally to the end of
the support column 21, but could be attached by other welding techniques. Preferably
the support column 21 includes an annular depression 51 for retaining the gas generant
subassembly housing 49 that includes an inwardly directed annular protrusion 52
that snaps into the depression 51 upon assembly. A crimped protrusion 53 extends
inwardly to provide a mechanical stop for the pellet retainer 43 that separates
the enhancer charge 47 from the gas generant pellets 48.
At a second end 70 of the pressure vessel 12 is a gas diffuser
26 located in an intermediate gas diffuser portion 10B of the cylindrical outer
inflator housing 11. This intermediate gas diffuser portion 10B has a first bulkhead
62 adjacent the first end portion 10A forming an internal second end 70 of the pressure
vessel 12. The first bulkhead 62 has one or more openings 28A sealed by a burst
disk 24A. A second bulkhead 63 is located adjacent the second end portion 10C and
an internal end 72 of the combustion chamber 90 of the second gas generator subassembly
80. The second bulkhead 63 has one or more openings 28B sealed by a burst disk 24B.
Interposed between said first and second bulkheads 62, 63 are a plurality of circumferentially
aligned exhaust openings 29. The exhaust openings 29 provide passages for the gas
to escape into the airbag for inflation when one or both igniters 30, 40 are activated.
Inside the intermediate gas diffuser portion 10B is a porous filtration means 74
situated between said first and second bulkheads 62, 63 covering the exhaust openings
29 as shown in Fig. 1. The exhaust openings 29 are preferably sized and oriented
in a radially opposed manner to create a thrust neutral condition as the gases leave
the inflator 10. As shown the intermediate gas diffuser portion 10B is cylindrically
shaped and is welded at end 70 that aligns with the second end of the first end
portion 10A of the pressure vessel 12.
At the opposite or second end of the intermediate gas diffuser
portion 10B, the second end portion 10C is shown similarly welded along the circumferential
ends 73 to the intermediate gas diffuser portion 10B thus forming a second gas generator
subassembly 80 with a combustion chamber 90. The second bulkhead 63 as shown has
a plurality of openings 28B sealed by a burst disk 24B on the gas diffuser facing
side of the bulkhead 63. A gas generant 88 is contained in a region spaced slightly
from the second bulkhead 63 by a porous generant retaining means 81 such as a filter
or screen that both cushions the gas generant pellets 88 and prevents most of the
ignited burning particles from spewing into the airbag upon ignition.
An end cap 33 is welded to the second end portion 10C.
A separator bulkhead 75 with a plurality of small holes 28C is sealed by a burst
disk 24C. The separator bulkhead 75 isolates the second generant charge of pellets
88 from an enhancer charge 86 that is held in a small cavity 34 in the end cap 33.
To activate the charges 86, 88 in the combustion chamber 90 of the second gas generator
subassembly 80 an opening device is employed.
The opening device comprises an electrically actuated igniter
30 and the end cap 33. The opening device is positioned so that the longitudinal
axis of the opening device is essentially parallel with a longitudinal axis A of
the dual stage inflator 10. The igniter 30 communicates with a controller (not shown)
via two or more electrodes 31, which in turn communicate with a sensor means (not
shown). The igniter 30 is an electrical device that initiates the activation of
the inflator when a suitable electric current is passed through a resistor element
embedded in one or more layers of pyrotechnic compositions. The igniter 30 may be
of the standard direct fire design, receiving the firing current directly from the
controller, or the igniter 30 may be of an advanced design which communicates with
the controller by digital signals and which contains on board the igniter an application
specific integrated circuit, firing capacitor, and related components. The pyrotechnic
compositions and load weight contained within the igniter are designed to generate
an output energy that will reliably ignite the enhancer charge 86 which will rupture
the burst disk or foil 24C. An example of a suitable pyrotechnic composition or
ignition material for the present invention is zirconium potassium perchlorate or
ZPP. A person skilled in the art will recognize that other ignition materials could
be used in the present invention.
The end cap 33 is a metal member that houses the igniter
30. The end cap 33 may be made of a plastic material using an injection molding
process. The end cap 33 as seen in FIG. 1 has threads, which are utilized for attachment
to an airbag module (not shown).
The opening device may also include reinforced walls 35
for directing an output of energy from the ignition of the ignition material towards
the burst disk 24C. The reinforced walls extend towards the burst disk 24C. Without
the reinforced walls 35, the igniter 30 would still rupture the burst disk 24C but
would need to be loaded with extra ignition material to provide consistent opening
at - 40° C. It is also possible to utilize an igniter 30 with a nozzle, which
would eliminate the need for reinforced walls 35. The reinforced walls 35 act in
a similar fashion to a nozzle by focusing the output energy in the direction of
the burst disk 24C.
The burst disk 24A is attached to the first bulkhead 62
of the intermediate gas diffuser portion 10B and seals the first bulkhead 62 so
that stored gas 13 cannot exit the dual stage inflator 10. The burst disk 24A shown
in FIG. 2A is made from stainless steel, inconel material, monel material, or any
other suitable material that allows the burst disk 24A to open reliably at -40°
C. The hardness of the burst disk 24A should be between "half hard" and "full hard"
to minimize the thickness of the burst disk 24A. Hardness is the degree to which
a metal will resist cutting, abrasion, penetration, bending and stretching. The
indicated hardness of metals will differ somewhat with the specific apparatus and
technique of measuring. The radially outer portion of the burst disk 24A is attached
to the bulkhead 62 by a laser weld 60 but could be attached by other welding techniques.
The radially inner portion of the burst disk 24A is not attached to any portion
of the gas diffuser 26 and bulges upon filling of the pressure vessel 12. The burst
disk 24A adopts a dome shape configuration due to the force of the stored gas 13
being applied to the burst disk 24A. Alternatively, the burst disk 24A can be bulged
in the direction of the opening device by a hydro-forming process after the burst
disk. 24A is attached to the bulkhead 62.
Upon actuation of the igniter 30, the enhancer 86 ignites
and ruptures the burst disk 24C, which ignites the gas generant charge 88, which
ruptures the burst disk 24B resulting in discharge openings 28B, which allows the
ignited gases to flow into the gas diffuser 26 and out of the dual stage inflator
10. The burst disks 24A, B or C can have one or more secondary discharge openings
61 to control the internal pressure and flow within the inflator 10. FIGS. 2B-2D
show various burst disk configurations having one discharge opening 28 and at least
one secondary discharge opening 61. The actuation of the igniters 30, 40 ruptures
the burst disks 24 A, B or C so there is one or more discharge flow paths through
the openings 28A, 28B, 28C and 61 allowing the ignited gases to flow out of the
inflator 10 through the exhaust openings 29. The actuation of the second gas generator
subassembly 80 can be accomplished without rupturing the burst disk 24A by sizing
the openings 28A, 28B, 28C and 61 such that the airbag can be more slowly and gently
filled to accommodate a small child or out of position occupant. More typically
the first gas generant subassembly 23 is actuated before or at the same time the
second gas generator subassembly 80 is activated. Typically in normal operation
the igniter 40 is fired bursting the disk 46 and igniting the enhancer 47 which
then ignites the generant pellets 48 which rapidly heats the inert gas 13 causing
the internal pressure of the pressure vessel 12 to increase and rupture the burst
disk 24A in such a way that one or more discharge opening(s) 28, 61 are created
allowing the gases to enter the intermediate gas diffuser portion 10B and exit out
the exhaust openings.
The cylindrical elongated shape of the inflator 10 provides
a compact device that can be made in a size more compact diametrically while still
providing various deployment scenarios. As shown the outer inflator housing 11 has
an outside diameter of 50 mm, and can be made even smaller. A 45 mm diameter is
feasible without necessarily increasing the length of the device. This ability to
reduce the size of the inflator 10 without sacrificing performance is valuable to
many vehicle manufacturers whose need to accommodate the airbag module takes space
away from other features such as the glove box on the instrument panel.
The inflator as shown can be deployed in many different
The normal deployment involves activating the first gas
generant subassembly 23, heating the inert gas 13 and rupturing the first disk 24A
to fill the airbag. This scenario arrives at maximum airbag inflation pressure the
The second deployment scenario would be to fire both gas
generant charges 48, 88 simultaneously; this fills the airbag the quickest to the
largest volume and also achieves maximum airbag inflation pressure the quickest.
A third deployment scenario is to employ the first deployment
scenario followed by a sequentially delayed activation of the second gas generator
subassembly 80 to prolong inflation of the airbag.
A fourth deployment scenario is to activate only the second
gas generator subassembly 80. This results in a lower output of gases to provide
a gentler airbag opening to accommodate a child or out of position occupant.
The primary advantage of the present invention is that
the time delays possible are greatly increased by the inflator having separate gas
generating sources. One gas generating source combined with pressurized charge of
inert gas the other gas generating source separate from and isolated from the pressure
vessel. A key advantage of the present invention is the ignition of one gas generator
subassembly 23, 80 will not cause the other gas generator subassembly 23, 80 to
ignite. The sizing of the discharge openings 28A, 28B, 28C and 61 and the large
exhaust openings 29 are designed to insure the internal pressures are quickly vented
to fill the airbag avoiding a secondary undesired ignition. Only by igniting both
igniters will both the charges ignite and thus ignition can be simultaneously timed
or sequentially triggered as desired.