Heat source for airbag inflation gas generation via a dissociating material

An apparatus and method for inflating an inflatable device which involve a heat source composed of a load of fuel material and an initiator is actuatable to be in heat transmitting communication such as to initiate dissociation of a gas source material to form at least one gaseous dissociation product used to inflate the inflatable device.

BACKGROUND OF THE INVENTION
 This invention relates generally to inflatable restraint systems and, more
 particularly, to an apparatus and method for inflating an inflatable
 device such as an inflatable vehicle occupant restraint for use in such
 systems.
 It is well known to protect a vehicle occupant using a cushion or bag,
 e.g., an "airbag cushion," that is inflated or expanded with gas such as
 when the vehicle encounters sudden deceleration, such as in a collision.
 In such systems, the airbag cushion is normally housed in an uninflated
 and folded condition to minimize space requirements. Upon actuation of the
 system, the cushion begins to be inflated, in a matter of no more than a
 few milliseconds, with gas produced or supplied by a device commonly
 referred to as "an inflator."
 Many types of inflator devices have been disclosed in the art for the
 inflating of one or more inflatable restraint system airbag cushions.
 Prior art inflator devices include compressed stored gas inflators,
 pyrotechnic inflators and hybrid inflators. Unfortunately, each of these
 types of inflator devices has been subject to certain disadvantages such
 as greater than desired weight and space requirements, production of
 undesired or non-preferred combustion products in greater than desired
 amounts, and production or emission of gases at a greater than desired
 temperature, for example.
 In view of these and other related or similar problems and shortcomings, a
 new type of inflator, called a "fluid fueled inflator," has been
 developed. Such inflators are the subject of commonly assigned Smith et
 al., U.S. Pat. No. 5,470,104, issued Nov. 28, 1995; Rink, U.S. Pat. No.
 5,494,312, issued Feb. 27, 1996; and Rink et al., U.S. Pat. No. 5,531,473,
 issued Jul. 2, 1996, the disclosures of which are fully incorporated
 herein by reference.
 Such inflator devices typically utilize a fuel material in the form of a
 fluid, e.g., in the form of a gas, liquid, finely divided solid, or one or
 more combinations thereof, in the formation of an inflation gas for an
 airbag. In one such inflator device, the fluid fuel material is burned to
 produce gas which contacts a quantity of stored pressurized gas to produce
 inflation gas for use in inflating a respective inflatable device.
 While such an inflator can successfully overcome, at least in part, some of
 the problems commonly associated with the above-identified prior types of
 inflator devices, there is a continuing need and demand for further
 improvements in safety, simplicity, effectiveness, economy and reliability
 in the apparatus and techniques used for inflating an inflatable device
 such as an airbag cushion.
 To that end, the above-identified Rink, U.S. Pat. No. 5,669,629 discloses a
 new type of inflator wherein a gas source material undergoes decomposition
 or dissociation to form products including at least one gaseous product
 used to inflate an inflatable device. As disclosed in Rink, U.S. Pat. No.
 5,669,629, a pyrotechnic load-containing initiator device can be actuated
 to commence dissociation or decomposition of the gas source material.
 Such an inflator can be helpful in one or more of the following respects:
 reduction or minimization of concerns regarding the handling of content
 materials; production of relatively low temperature, non-harmful inflation
 gases; reduction or minimization of size and space requirements and
 avoidance or minimization of the risks or dangers of the gas producing or
 forming materials undergoing degradation (thermal or otherwise) over time
 as the inflator awaits activation.
 "Rise rate," i.e., the rate at which the gas output from an inflator
 increases pressure as measured when such gas output is directed into a
 closed volume, is a common vehicular airbag inflator performance parameter
 used in the design, selection and evaluation of an inflator for particular
 airbag restraint system installations. In general, the rise rate produced
 by each of the above-identified types or kinds of inflator devices is
 controlled, selected or otherwise predetermined by the area provided by or
 in the particular inflator device for inflation output flow.
 While the rise rate produced or resulting from an inflator, such as
 described above and which inflator contains a gas source material which
 undergoes decomposition or dissociation to form products including at
 least one gaseous product used to inflate an inflatable device, can be
 controlled or selected based on the inflation output flow through area
 provided by the inflator, such reliance can in practice be problematic.
 For example, restrictions in the inflation output flow through area
 provided by an inflator can result in dramatic increases in pressure
 within the inflator upon the actuation thereof. As will be appreciated,
 proper inflator design will generally necessitate that the inflator design
 account for such pressure increases, such as by inflator fabrication using
 materials of higher strength or through the use of increased inflator wall
 thicknesses.
 Further, the inflation output flow through areas of such inflators are
 commonly normally covered or obstructed such as by means of one or more
 burst discs or the like, until such time flow therethrough is actuated.
 Thus, inflators with increased inflation output flow through areas
 commonly require burst discs or the like of increased strength or
 thickness. As will be appreciated, such uses of materials of higher
 strength or of greater thickness generally have associated therewith
 increased costs.
 In view of the above, there is a need and a demand for an apparatus and a
 method for inflating an inflatable device such as an inflatable vehicle
 occupant restraint for use in an inflatable restraint system which permits
 either or both the design and control of the rise rate resulting from an
 inflator device such as an inflator device which contains a gas source
 material which undergoes decomposition or dissociation to form products,
 including at least one gaseous product used to inflate an inflatable
 device, without altering the inflation output flow through area of the
 inflator device.
 Further, there is a continuing need and demand for further improvements in
 safety, simplicity, effectiveness, economy and reliability in the
 apparatus and techniques used for inflating an inflatable device such as
 an airbag cushion. More specifically, there is a need and a demand for an
 inflator device which can provide at least some of the benefits provided
 by the inflator of the above-identified Rink, U.S. Pat. No. 5,669,629,
 wherein a gas source material undergoes decompositional or
 dissociative-type reaction to form products including at least one gaseous
 product used to inflate an inflatable device while permitting either or
 both the design and control of the rise rate resulting from such an
 inflator device without altering the inflation output flow through area of
 the inflator.
 SUMMARY OF THE INVENTION
 A general object of the invention is to provide an improved apparatus for
 inflating an inflatable device and methods of operating such an inflation
 apparatus.
 A more specific objective of the invention is to overcome one or more of
 the problems described above.
 The general object of the invention can be attained, at least in part,
 through an apparatus for inflating an inflatable device which apparatus
 includes a heat source and a first chamber. The first chamber contains at
 least one gas source material which undergoes dissociation to form at cast
 one gaseous dissociation product used to inflate the inflatable device.
 The heat source includes a load of pyrotechnic and an initiator to
 initiate reaction of at least a portion of the pyrotechnic load to produce
 heat. The heat source is actuatable to be in heat transmitting
 communication with the contents of the first chamber to initiate
 dissociation of the at least one gas source material.
 The prior art fails to provide an apparatus and a method for inflating an
 inflatable device such as an inflatable vehicle occupant restraint for use
 in an inflatable restraint system which permits either or both the design
 and control of the rise rate resulting from an inflator device such as an
 inflator device which contains a gas source material which undergoes
 decomposition or dissociation to form products, including at least one
 gaseous product used to inflate an inflatable device, without altering the
 inflation output flow through area of the inflator device.
 The invention further comprehends an apparatus for inflating an inflatable
 device, which apparatus includes a heat source and a first chamber
 containing nitrous oxide. The heat source includes a load of pyrotechnic
 and an initiator to initiate reaction of at least a portion of the
 pyrotechnic load to produce heat. The heat source is actuatable to be in
 heat transmitting communication with the contents of the first chamber to
 initiate dissociation of at least a portion of the nitrous oxide to form
 at least one gaseous dissociation product used to inflate the inflatable
 device. The pyrotechnic is selected to provide at least about 95% of the
 total heat liberated by the reaction of the pyrotechnic prior to
 dissociation and release from the first chamber of associated dissociation
 product of more than about 90% of the gas source material originally
 contained within the first chamber.
 The invention also comprehends methods for inflating an inflatable safety
 device in a vehicle.
 One such method involves the step actuating an initiator to initiate
 reaction of at least a portion of a load of pyrotechnic to produce heat.
 At least a portion of the so produced heat is then transmitted to at least
 one gas source material in a first chamber of the apparatus to initiate
 dissociation of the at least one gas source material. The dissociation
 thereof forms dissociation products including at least one gaseous
 dissociation product. Inflation gas comprising at least a portion of the
 at least one gaseous dissociation product is then released from the
 apparatus to inflate the inflatable device.
 As used herein, references to "dissociation," "dissociation reactions" and
 the like are to be understood to refer to the dissociation, splitting,
 decomposition or fragmentation of a single molecular species into two) or
 more entities.
 "Thermal dissociation" is a dissociation controlled primarily by
 temperature. It will be appreciated that while pressure may, in a complex
 manner, also influence a thermal dissociation such as perhaps by changing
 the threshold temperature required for the dissociation reaction to
 initiate or, for example, at a higher operating pressure change the energy
 which may be required for the dissociation reaction to be completed, such
 dissociation reactions remain primarily temperature controlled.
 An "exothermic thermal dissociation" is a thermal dissociation which
 liberates heat.
 "Equivalence ratio" (100) is an expression commonly used in reference to
 combustion and combustion-related processes. Equivalence ratio is defined
 as the ratio of the actual fuel to oxidant ratio (F/O).sub.A divided by
 the stoichiometric fuel to oxidant ratio (F/O).sub.S :
EQU .phi.=(F/O).sub.A /(F/O).sub.S (1)
 (A stoichiometric reaction is a unique reaction defined as one in which all
 the reactants are consumed and converted to products in their most stable
 form. For example, in the combustion of a hydrocarbon fuel with oxygen, a
 stoichiometric reaction is one in which the reactants are entirely
 consumed and converted to products entirely constituting carbon dioxide
 (CO.sub.2) and water vapor (H.sub.2 O). Conversely, a reaction involving
 identical reactants is not stoichiometric if any carbon monoxide (CO) is
 present in the products because CO may react with O.sub.2 to form
 CO.sub.2, which is considered a more stable product than CO.)
 For given temperature and pressure conditions, fuel and oxidant mixtures
 are flammable over only a specific range of equivalence ratios. Mixtures
 with an equivalence ratio of less than 0.25 are herein considered
 nonflammable, with the associated reaction being a decomposition reaction
 or, more specifically, a dissociative reaction, as opposed to a combustion
 reaction.
 A "pyrotechnic" material, in its simplest form, consists of an oxidizing
 agent and a fuel that produce an exothermic, self-sustaining reaction when
 heated to the ignition temperature thereof.
 Other objects and advantages will be apparent to those skilled in the art
 from the following detailed description taken in conjunction with the
 appended claims and drawings.

DETAILED DESCRIPTION OF THE INVENTION
 The present invention may be embodied in a variety of different structures.
 Referring initially to FIG. 1, there is illustrated an airbag inflator
 assembly, generally designated by the reference numeral 10, in accordance
 with one preferred embodiment of the invention and such as may be used to
 inflate an inflatable vehicle occupant restraint, e.g., an inflatable
 airbag cushion, (not shown). As is known and upon proper actuation, such
 inflatable vehicle occupant restraints are typically inflated by a flow of
 an inflation fluid, e.g., gas, from an inflator assembly to restrain
 movement of an occupant of the vehicle. In practice, it is common that the
 inflatable vehicle occupant restraints be designed to inflate into a
 location within the vehicle between the occupant and certain parts of the
 vehicle interior, such as the doors, steering wheel, instrument panel or
 the like, to prevent or avoid the occupant from forcibly striking such
 parts of the vehicle interior.
 The invention is described hereinafter with particular reference to an
 inflator for use in various automotive vehicles including vans, pick-up
 trucks, and particularly automobiles. As will be appreciated by those
 skilled in the art, the invention has applicability to various types or
 kinds of airbag installations for automotive vehicles including driver
 side, passenger side and side impact airbag assemblies, for example.
 Moreover, the invention has applicability with other types of vehicles as
 well, including airplanes, for example.
 The inflator assembly 10 comprises a pressure vessel 12 including a chamber
 14 that contains a fluid load including a gas source material. As
 disclosed in above-identified Rink, U.S. Pat. No. 5,669,629, there are
 various gas source materials which, under specified conditions, undergo
 reaction variously termed decomposition or dissociation reaction to form
 products including at least one gaseous product such as may be used to
 inflate an associated vehicle occupant restraint. Thus, the chamber 14 is
 sometimes referred to herein as a "dissociation chamber."
 As disclosed in Rink, U.S. Pat. No. 5,669,629, a wide variety of gas source
 materials which undergo dissociative or decompositional reactions,
 preferably an exothermic such reaction, to form gaseous products are
 available. Such gas source materials include:
 acetylene(s) and acetylene-based materials such as acetylene and methyl
 acetylene, as well as mixtures of such acetylene(s) and acetylene-based
 materials with inert gas(es);
 hydrazines such as hydrazine (N.sub.2 H.sub.4), mixtures of hydrazine(s)
 and water, methyl derivatives of hydrazine, as well is mixtures of such
 hydrazine materials with inert gas(es);
 peroxides and peroxide derivatives such as methyl hyperoxide (CH.sub.3 OOH)
 and mixtures of methyl hyperoxide and methanol, hydrogen peroxide, alkyl
 hydroperoxides, propionyl and butyryl peroxides, as well as mixtures of
 such peroxides and peroxide derivatives with inert gas(es); and
 nitrous oxide (N.sub.2 O) and mixtures of nitrous oxide with inert gas(es),
 for example.
 Generally, dissociative gas source materials used in the practice of the
 invention are preferably:
 a.) non-toxic and non-corrosive both in the pre- and post-dissociation
 states;
 b.) relatively stable at atmospheric conditions thus permitting and
 facilitating storage in a liquid phase, where a liquid, as compared to a
 gas, permits the storage of a greater amount of material in the same
 volume at a given pressure;
 c.) do not require the presence of catalyst(s) to trigger the dissociation
 reaction, and which catalysts may be difficult to remove or handle; and
 d.) form products of dissociation which do not contain undesirable levels
 of undesirable species, such as carbonaceous material (e.g., soot),
 CO.sub.x and NO.sub.x (where x=1 or 2), and NH.sub.3, for example.
 A currently preferred dissociative gas source material for use in the
 practice of the invention is nitrous oxide (N.sub.2 O). Nitrous oxide is
 advantageously generally non-toxic and non-corrosive. Further, nitrous
 oxide, as compared to gases such as air, nitrogen and argon, liquefies
 relatively easily at ambient temperatures. Additionally, nitrous oxide is
 relatively inert up to temperatures of about 200.degree. C. or more. As a
 result, nitrous oxide is desirably relatively safe to handle, thermally
 stable, facilitates storage, and alleviates manufacturing concerns.
 Further, in accordance with the chemical reaction (2) identified below,
 upon the dissociation of nitrous oxide, the dissociation products ideally
 are nitrogen and oxygen:
EQU 2N.sub.2 O=2N.sub.2 +O.sub.2 (2)
 Thus, not only does such reaction form products which are generally
 non-toxic and non-corrosive but also results in the production or
 formation of molecular oxygen, such as may be desired with certain
 inflator designs.
 It is to be understood that such nitrous oxide can be, for example, stored
 in a gaseous, liquid or multi-phase form (i.e., partially gaseous and
 partially liquid mixture), as may be desired. The common premium in modern
 vehicle design placed on minimizing the size requirements for vehicular
 components such as inflatable restraint systems generally results in a
 preference for smaller sized airbag inflators. In view thereof and the
 fact that the density of nitrous oxide is significantly greater when in
 liquid, rather than gaseous form, one preferred embodiment of the
 invention involves storage of nitrous oxide primarily in a liquid form.
 It is also to be understood that while such nitrous oxide dissociative gas
 source material can be contained within the dissociative chamber in a pure
 form (e.g., such that the chamber contents include no more than minor
 levels of other materials, such as air as may be present in the
 dissociative chamber prior to being filled with the dissociative gas
 source material), it may be preferred for the fluid load contained within
 the chamber to also include an inert gas therewith. For example, an inert
 gas such as helium can be included with nitrous oxide to facilitate leak
 checking of the inflator apparatus or, more specifically, of the
 dissociative chamber thereof. Alternatively or in addition, an inert gas,
 such as argon and helium, for example, or mixture of such inert gases, can
 be included to supplement the gas produced or formed upon the dissociation
 of the nitrous oxide.
 Further, additionally or alternatively and as disclosed in the
 above-identified U.S. patent application Ser. No. 08/935,016, the fluid
 load within the dissociation chamber 14 may include a quantity of at least
 one radioactive isotope leak trace material whereby fluid leakage from the
 chamber can be detected as disclosed therein.
 In addition, if desired, the fluid load within the dissociation chamber 14
 may additionally include a quantity of oxygen gas such as in molecular
 form and such as may beneficially and desirably supplement such molecular
 oxygen as may be formed upon the dissociation of stored or included
 nitrous oxide.
 Still further, the fluid load within such a dissociation chamber can, if
 and as desired, also include a sensitizer material to promote or
 accelerate the rate of such dissociative reaction. Various sensitizer
 materials are disclosed and identified in above-identified Rink, U.S. Pat.
 No. 5,669,629. As disclosed therein, sensitizer materials are typically
 hydrogen-bearing materials and are generally added to the dissociative gas
 source material in relatively small amounts. Specifically, the sensitizer
 material is preferably added to the dissociative gas source material in an
 amount below the flammability limits for the content mix, such that the
 contents of the dissociative chamber are generally at an equivalence ratio
 of less than 0.25, preferably less than 0.15. At such low relative
 amounts, the chamber contents are essentially non-flammable and thus
 combustion and the formation of combustion products are practically
 avoided.
 Hydrogen-bearing sensitizer materials useable in the practice of the
 invention are typically gaseous, liquid, solid, or multi-phase
 combinations thereof including hydrogen, hydrocarbons, hydrocarbon
 derivatives and cellulosic materials. Preferred hydrocarbon
 hydrogen-bearing sensitizer materials useable in the practice of the
 invention include paraffins, olefins, cycloparaflins and alcohols.
 Molecular hydrogen (H.sub.2), which does not result in the formation of
 carbon oxides such as carbon monoxide or carbon dioxide, has been found to
 be quite effective as a sensitizer and is an especially preferred
 hydrogen-bearing sensitizer material for use in the practice of the
 invention.
 Returning to the FIG. 1, the chamber 14 is defined in part by an elongated
 generally cylindrical sleeve 16. The sleeve 6 may include a fill port (not
 shown), as is known in the art, wherethrough materials can be passed into
 the chamber 14.
 In practice, in such an inflator design that uses about 10% to about 30%
 (by volume) nitrous oxide in an inert gas such as argon, such a
 dissociation chamber 14 is typically filled to a pressure in the range of
 about 3500 psia (24.1 MPa) to about 4500 psia (31.0 MPa). On the other
 hand, such inflator designs that contain nitrous oxide in a pure or nearly
 pure state (e.g., contain about 90% up to 100% by volume nitrous oxide),
 may typically be filled to pressures of about 500 psia (3.4 MPa) to about
 2500 psia (17.2 MPa).
 The sleeve 16 has a first end 20 and a second end 22. The first end 20 is
 closed by means of a diffuser assembly 26. Such a diffuser assembly can be
 integral (i.e., formed continuous with and in one piece) with the sleeve
 16 or, if desired or preferred, joined or attached thereto in an
 appropriate manner, such as by an inertial weld.
 The contents of the chamber 14 are normally kept separated from the
 diffuser assembly 26 and contained within the chamber 14 through the
 inclusion of a selected sealing means, e.g., by means of a burst disc 30
 in sealing relationship therebetween. The diffuser assembly 26 includes i
 plurality of openings 32, wherethrough the inflation gas from the inflator
 assembly 10 is properly dispensed into the associated occupant restraint.
 Thus, the diffuser assembly 26 can serve to facilitate direction of the
 inflation fluid from the inflator assembly 10 into the associated
 inflatable vehicle occupant restraint.
 The sleeve second end 22 is partially closed by a base wall 34. The base
 wall 34 includes an opening 36 therein, wherethrough a heat source 40,
 such as described in greater detail below, is attached in sealing relation
 within the dissociation chamber 14. As will be appreciated, such
 attachment can be effected by various appropriate means such as with a
 weld, crimp or other suitable hermetic seal, for example.
 In accordance with one preferred embodiment of the invention, the heat
 source 40 is actuatable to be in heat transmitting communication with the
 contents of the dissociation chamber 14 to initiate dissociation of the at
 least one gas source material stored therewithin. The heat source 40
 includes an initiator device 42 and a cup 44 containing a load of a
 selected fuel material, such as a pyrotechnic material. As described in
 greater detail below, such a fuel material may as desired take the form of
 a pyrotechnic material, such as defined above, or a fuel such as contains
 insufficient oxygen to produce a self-sustaining exothermnic reactions
 when heated to the ignition temperature thereof.
 A representative portion of the heat source pyrotechnic load, designated by
 the reference numeral 46, is shown. The pyrotechnic load 46 is generally
 adjacent the discharge end 42a of the initiator device 42 such as in
 reaction initiation communication with the initiator device 42.
 The heat source cup 44 is shown as including a burst disc 50 about the open
 end 44a thereof. It is to be appreciated that the inclusion of such a
 burst disc may be desired or needed to ensure hermeticity such as where
 the heat source may be incapable of withstanding the elevated pressures
 normally associated with the storage of material within the dissociation
 chamber for the extended periods of time that such inflator devices are
 normally placed in vehicular occupant inflatable restraint systems. It
 will also be appreciated that other forms or means of separation can, if
 desired, be utilized including, for example, a retainer in the form of an
 appropriate foil.
 Further, it will be appreciated that the inclusion of such a burst disc 50
 or other suitable closure at the open end 44a of the heat source cup 44
 will better ensure that the pyrotechnic load 46 of the heat source 44 will
 remain desirably positioned relative to the initiator discharge end 42a
 throughout the lifetime of the unactuated inflator assembly.
 The initiator device 42 can be of any suitable type of initiator means
 including: bridgewire, spark-discharge, heated or exploding wire or foil,
 through bulkhead (e.g., an initiator which discharges through a bulkhead
 such as in the form of a metal hermetic seal), for example, and may, if
 desired, optionally contain a desired load of an ignition pyrotechnic
 charge.
 Such ignition charge pyrotechnic can be variously formulated, as is known
 in the art. In general, such an ignition charge pyrotechnic desirably has
 a calorific content of about 5 to about 75 calories and, more preferably,
 about 15 to about 40 calories, per gram of inflator assembly fluid load.
 In practice, pyrotechnic formulations for initiators are often designed to
 be over-oxidized to better ensure complete combustion of the fuel. For
 example, typical initiators containing a pyrotechnic formulation of
 zirconium potassium perchlorate (commonly referred to as "ZPP") have a
 formulation equivalence ratio in a range of 0.7 to 1.0. Generally
 speaking, initiator formulations having an equivalence ratio of greater
 than one have been sought to be avoided as such formulations generally
 contain insufficient oxidant to fully oxidize the available fuel and thus
 such fuel will not contribute to the sought reaction.
 As disclosed in parent patent application, U.S. Ser. No. 09/027,020 filed
 on Feb. 20, 1998, it may be desirable that the initiator device include a
 desired load of an enhanced fuel pyrotechnic charge. More specifically,
 such an initiator device contains a pyrotechnic formulation, such that
 upon actuation of the initiator device, the discharge serves to form
 particles to interact with one or more of at least a portion of the
 remaining quantity of the gas source material contained within the
 inflator and dissociation products to form additional inflation products
 for inflating the inflatable device. In accordance with one preferred
 embodiment of such invention, such an enhanced pyrotechnic formulation
 discharges hot particles into contact with the dissociating gas source
 material contained within the inflator assembly. In such formulations it
 is generally desirable to maintain the hot radiant metal fuel particles in
 a relative amount to the quantity of nitrous oxide within the dissociation
 chamber to result in an equivalence ratio of less than 0.15.
 In one embodiment, such an enhanced fuel pyrotechnic formulation
 constitutes a metal-based pyrotechnic composition, such as ZPP, which is
 oxidized to a lesser extent, e.g., often near stoichiometric or at least
 sightly fuel-rich, than normally associated for a composition of such a
 pyrotechnic material. However, various handling concerns may arise with
 the production and use of relatively large loads of ZPP such as may be
 needed to better ensure proper operation of such inflator devices. In view
 thereof, U.S. Ser. No. 09/027,020 has proposed the use of metal hydride
 pyrotechnic materials such as zirconium hydride potassium perchlorate
 (ZHPP) and titanium hydride potassium perchlorate (THPP) which are
 generally significantly safer to handle than metal perchlorates (such as
 ZPP).
 Many different reactive materials are available and useful as heat source
 fuel or pyrotechnic materials. Suitable materials are suitable for use in
 the practice of the invention may include, for example, polyolefins, waxes
 and internally partially oxidized compounds such as polyesters,
 polyethers, acrylic polymers, phenols, polysaccharides (such as cellulose
 or starch), cellulose ethers, cellulose esters, nitrate salts of amines,
 nitramines, nitrocompounds and mixtures of two or more such listed
 materials. More specifically, suitable solid fuel materials for use in the
 practice of the invention may be exemplified by ethyl cellulose, cellulose
 acetate, cellulose acetate butyrate, cellulose propionate, polyacetal,
 polyethylene, polypropylene, polystyrene, hydroxy-terminated
 polybutadiene, polymethylacrylate, naphthalene, and nitrocellulose, as
 well as combinations thereof.
 In general, these heat source reactive materials can be classified into two
 general categories or types: those that are fully- or self-oxidized (i.e.,
 they do not generally require an additionally provided oxidant) and those
 that are under-oxidized (i.e., they generally require an additionally
 provided oxidant). Operation with an under-oxidized heat source reactive
 material, however, will typically require some oxidant contribution from
 either or both the stored nitrous oxide or the balance of the fluid load
 of the inflator in order to properly bum and thus result in the lose of
 some of the independence of operation normally possible with a similar
 inflator containing a fully- or self-oxidized heat source pyrotechnic
 material. While such under-oxidized materials may ignite, they generally
 are incapable of burning to completion without such an oxidant
 contribution. In general, with such an under-oxidized material which
 ignites with the functioning of the initiator device 42 and discharges or
 interacts with the nitrous oxide-including mixture contained within the
 dissociation chamber 14, heat produced from the reaction of the reactive
 material is transferred to the nitrous oxide and dissociation thereof
 commences, resulting in the formation of gaseous oxygen which interacts
 with under-oxidized reactive material to permit the combustion thereof
 As will be appreciated, self-oxidized pyrotechnic materials can simplify
 the operational dynamics of the inflator as such materials generally do
 not require direct interaction with the stored nitrous oxide, or the
 dissociation products thereof, in order to properly burn. In general, such
 self-oxidized materials will ignite with the functioning of the initiator
 42 and discharge or interact with the nitrous oxide-including mixture
 contained within the dissociation chamber 14. Heat, resulting from the
 reaction of the heat source reictive material, is transferred to the
 nitrous oxide and dissociation thereof commences.
 Such heat source pyrotechnic or other reactive material can be variously
 formulated, as is known in the art. In general, such heat source reactive
 fiel materials desirably have generally higher energy contents than
 ignition charge pyrotechnics, if such ignition charge pyrotechnics are
 used. More specifically, such heat source pyrotechnic or other reactive
 fuel material generally desirably has a calorific content of about 75 to
 about 300 calories and, more preferably, about 100 to about 175 calories
 per gram of inflator assembly fluid load.
 In operation, such as upon the sensing of a collision, an electrical signal
 is sent to the initiator device 42. The initiator device 42 functions to
 initiate reaction of at least a portion of the pyrotechnic load 46 such as
 to result in the rupture or otherwise opening of the burst disc 50 sealing
 the heat source cup 44. As will be appreciated such rupture or otherwise
 opening of the burst disc 50 may result in particularly designed
 assemblies from either or both an increase of pressure within the cup 44,
 such as due to the formation of gaseous products upon reaction of
 pyrotechnic material, and the direction or discharge of hot particles at
 the burst disc 50.
 With the opening of the cup 44, high temperature combustion products are
 discharged therefrom into the dissociation chamber 14 to initiate
 dissociation of at least a portion of the quantity of gas source material
 contained therewithin, which in a preferred embodiment includes primarily
 liquid-phase N.sub.2 O. The large heat addition from the heat source 40
 desirably results in commencement of the exothermic thermal dissociation
 of the N.sub.2 O. In this thermal dissociation, the N.sub.2 O begins to
 breakdown into smaller molecular fragments. As the N.sub.2 O molecules
 fragment, the associated release of energy results in further heating of
 the remaining chamber contents. The increase both in temperature and the
 relative amount of gaseous products within the dissociation chamber 14
 results in a rapid pressure rise within the dissociation chamber.
 When the gas pressure within the dissociation chamber 14 exceeds the
 structural capability of the burst disc 30, the disc ruptures or otherwise
 permits the passage of the inflation gas into the diffuser assembly 26 and
 subsequently through the openings 32 therein into an associated airbag
 assembly.
 As described in greater detail below, the geometry of a fuel material or
 pyrotechnic formulation can, for example, impact either or both the rate
 at which a gas source material dissociates and the amount (i.e., extent)
 of such dissociation. Thus, in accordance with the invention, the geometry
 of a fuel material or pyrotechnic formulation and, in particular, various
 parameters and characteristics thereof can be selected to provide or
 result in particular or desired operation of a corresponding inflator
 device. For example, fuel material or pyrotechnic formulation parameters
 and characteristics such as quantity, size and shape, may each be
 selected, as described in greater detail below, in order to assist in
 providing desired operation of an associated inflator device.
 With respect to size, it is generally desirable to maintain the particle
 diameter in pyrotechnic or other such fuel formulations in a range of
 about 1 to about 20 microns and, more particularly, in a range of about 1
 to about 10 microns. In accordance with the invention, however, the
 inclusion of some larger particles of fuel in such formulations is
 generally desired. In practice. such larger particles can be distributed
 in a range of from about 25 to about 10,000 microns, preferably particles
 of a diameter of up to about 1000 microns and, more specifically,
 particles of a diameter of up to about 500 microns.
 It will be appreciated that while such larger particles may constitute up
 to about 100% of the fuel content of such pyrotechnic or fuel formulations
 in accordance with the invention, in general it is believed desirable to
 limit inclusion of such larger particles to no more than about 50% by
 mass, and, more preferably, no more than about 25% by mass of the total
 fuel load.
 Shape, in conjunction with size, may also play a significant role in the
 practice of the invention. As will be appreciated, if the particles are
 relatively fine and the pyrotechnic or fuel formulation features a
 relatively high surface area, the formulation will generally burn very
 rapidly and may result in high internal pressures within the inflator and
 less or incomplete dissociation of the nitrous oxide. On the other hand,
 if the particles are too large, they can be relatively difficult to ignite
 and thus may not ultimately be utilized or at least fully utilized in the
 invention.
 FIG. 2 illustrates an airbag inflator assembly 210 in accordance with an
 alternative embodiment of the invention. The inflator assembly 210 is
 generally similar to the inflator assembly 10 illustrated in FIG. 1 and
 described above. The inflator assembly 210, similar to the inflator
 assembly 10, includes a pressure vessel 212 including a chamber 214 that
 contains a gas source material, such as described above. The chamber 214
 may, if desired and as described above, additionally contain quantities of
 one or more inert gases, radioactive isotope leak trace material, oxygen
 gas, or rate of dissociative reaction sensitizer materials.
 The chamber 214 is defined in part by an elongated generally cylindrical
 sleeve 216 having a first end 220 and a second end 222. The first end 220
 is closed by means of a diffuser assembly 226, such as generally similar
 to the diffuser assembly 26 described above. The diffuser assembly 226
 includes a plurality of openings 232, wherethrough the inflation gas from
 the inflator assembly 210 is properly dispensed into the associated
 occupant restraint (not shown).
 The contents of the chamber 214 are normally kept separated from the
 diffuser assembly 226 and contained within the chamber 214 through the
 inclusion of a selected sealing means, e.g., by means of a burst disc 230
 in sealing relationship therebetween.
 The sleeve second end 222 is partially closed by a base wall 234. The base
 wall 234 includes an opening 236 therein, wherethrough a heat source 240
 such as described in greater detail below, is attached in sealing relation
 within the dissociation chamber 214. As will be appreciated, such
 attachment can be effected by various appropriate means such as with a
 weld, crimp or other suitable hermetic seal, for example.
 The heat source 240, similar to the heat source 40 described above,
 includes an initiator device 242 and a cup 244 containing a load of
 pyrotechnic or other selected fuel material such as described above,
 designated by the reference numeral 246 adjacent the discharge end 242a of
 the initiator device 242 such as in reaction initiation communication with
 the initiator device 242. The heat source 240, however, stores or contains
 the pyrotechnic load 246 under the influence of the contents of the
 dissociation chamber 214. More specifically, the cup 244 is composed of
 perforated or the like, such as screen, for example, steel or other
 selected metal to permit contact by and between the contents of the
 dissociation chamber 214 and the stored pyrotechnic material 246. Such
 inflator assemblies in which such heat source load of pyrotechnic material
 246 is stored under the conditions within the dissociation chamber 214 may
 be less subject to internal pressure extremes upon actuation and thus
 preferred for at least certain particular inflator installations.
 In addition, as such inflator assemblies may more easily permit interaction
 and communication by and between the pyrotechnic material 246 and the
 contents of the dissociation chamber 214, such assemblies may facilitate
 the use of under-oxidized heat source pyrotechnic materials such as
 described above. For example, with such assemblies, oxidizer such as
 available or produced by or in the dissociation chamber may be in reaction
 communication with the stored pyrotechnic material and thus facilitate or
 permit reaction therewith.
 The operation of the inflator assembly 210 is generally similar to that
 described above relative to the inflator assembly 10. For example, in the
 event of the sensing of a collision, an electrical signal is sent to the
 initiator device 242. The initiator device 242 fuinctions to initiate
 reaction of at least a portion of the pyrotechnic load 246 such as may
 result in the discharge of products of such reaction from the cup 244 and
 into communication with the gas source material contained within the
 chamber 214.
 As will be appreciated, high temperature combustion products are discharged
 from the cup 244 into the dissociation chamber 214 to initiate
 dissociation of at least a portion of the quantity of gas source material
 contained therewithin, which in a preferred embodiment includes primarily
 liquid-phase N.sub.2 O. The large heat addition from the heat source 240
 desirably results in comlmencement of the exothermic thermal dissociation
 of the N.sub.2 O. In this thermal dissociation, the N.sub.2 O begins to
 breakdown into smaller molecular fragments. As the N.sub.2 O molecules
 fragment, the associated release of energy results in further heating of
 the remaining chamber contents. The increase both in temperature and the
 relative amount of gaseous products within the dissociation chamber 214
 results in a rapid pressure rise within the dissociation chamber.
 Consequently and similar to the above-described embodiment, when the gas
 pressure within the dissociation chamber 214 exceeds the structural
 capability of the burst disc 230, the disc ruptures or otherwise permits
 the passage of the inflation gas into the diffuser assembly 226 and
 subsequently through the openings 232 therein into an associated airbag
 assembly.
 The present invention is described in further detail in connection with the
 following examples which either or both illustrate or simulate various
 aspects involved in the practice of the invention. It is to be understood
 that all changes that come within the spirit of the invention are desired
 to be protected and thus the invention is not to be construed as limited
 by these examples.
 EXAMPLES
 The following examples illustrate the effect of the surface area of the
 respective heat source fuel material. As described in greater detail
 below, test inflator devices were used containing a selected fuel material
 in the form of:
 1) a single continuous pyrotechnic grain of selected size and dimensions
 (Examples 1-6),
 2) a plurality of extrudlets of pyrotechnic material, e.g., where each
 extrudlet has the shape or form of a tubular segment having or including a
 generally cylindrical bore (Examples 7-11), and
 3) a fiel/oxidizer pyrotechnic material composed of a fuel having a
 selected particle size (Examples 12-14), respectively.
 In each of these examples, a test inflator containing the corresponding
 pyrotechnic material and a specified dissociating gas load was fired into
 a closed (constant volume) vessel, also referred to as a "test tank." The
 portion of the inflator which vents gas was wholly contained within the
 tank so that the volume of the tank was completely closed off from the
 outside atmosphere. For each example, the pressure within the inflator and
 within the test tank were continuously monitored and recorded via
 respectively mounted pressure transducers.
 Examples 1-6
 In these Examples, test inflators each containing a specific one of the six
 (6) below identified grain configurations of a PVC-based pyrotechnic
 formulation were fired using a 100 liter-closed tank as the test tank.
 More specifically, the PVC-based pyrotechnic formulation was composed of
 (on a mass basis):
 about 45% 90 micron particle size potassium perchlorate;
 about 30% 10 micron particle size potassium perchlorate;
 about 9% dioctyl abipate;
 about 8% sodium oxalate;
 about 7.5% PVC; and
 the balance being minor amounts of various additives.
 This formulation was prepared in the six (6) different initial grain
 configurations (individually designated A-F) shown in FIGS. 3A-3F,
 respectively. The grain configurations A-F had the initial surface areas
 (A.sub.I) respectively shown in the TABLE 1, below.
 TABLE 1
 Example Grain Configuration A.sub.I (in.sup.2)
 1 A 10.485
 2 B 8.5
 3 C 7.5
 4 D 5.1
 5 E 4.89
 6 F 8.92
 While each of the grain configurations, as indicated, provided a different
 respective initial surface area, the inflators of each of Examples 1-6
 utilized 20 grams of the respectively configured pyrotechnic material.
 Each such 20 gram load had an energy content of 25000 calories (104.7
 kilojoules). In each of these examples, the specified pyrotechnic grain
 configuration was used as the heat source material relative to a
 dissociation chamber containing a 162 gram fluid load of 20% nitrous
 oxide, 70% argon and 10% helium (on a molar basis).
 DISCUSSION OF RESULTS
 The tank pressure traces obtained for the inflators in Examples 1-6 are
 shown in FIG. 4 which shows gas output measured in terms of tank pressure
 versus time. The pressure traces obtained within the inflators
 ("combustion pressures") of Examples 1-6 (as measured by a pressure
 transducer mounted in a dissociating chamber wall of the inflator) are
 shown in FIG. 5.
 As shown by FIG. 4, the rate of pressure increase in the test tank for
 Examples 1-6 (as evidenced in FIG. 4 by the initially increasing slopes of
 the curves), e.g., the rise rate, was directly related to the initial
 pyrotechnic grain surface area. More specifically, the rate of pressure
 increase in the test tank was greater for those examples featuring higher
 surface area pyrotechnic configurations.
 As shown by FIG. 5, both the maximum internal pressure and the rate of
 initial increase of internal pressure for Examples 1-6 correlated well
 with the initial pyrotechnic grain surface area. More specifically, the
 maximum internal pressure (as evidenced in FIG. 5 by the respective curve
 peaks) and the rate at which the internal pressure initially increased (as
 evidenced in FIG. 5 by the initial curve slopes, e.g., the slopes of the
 curves within the first 0.01 seconds after actuation) both generally
 increased with the use of pyrotechnic of increased initial surface area.
 Thus, the rate of combustion of the pyrotechnic appears to be directly
 proportional to the surface area of the pyrotechnic grain.
 Examples 7-11
 In these Examples, test inflators each containing a specific one of the
 five (5) below identified extrudlet sizes of a pyrotechnic formulation
 composed of a transition metal amine nitrate with oxidizer and binder were
 fired using a 100 liter-closed tank as the test tank.
 More specifically, the extrudlets utilized in each of Examples 7-11 were
 generally of the shape or form of tubular segments having or including a
 generally cylindrical bore, such as shown in FIG. 6. For each of Examples
 7-11: the initial extrudlet outside diameter (d.sub.o), the initial
 extrudlet inside diameter (d.sub.j), initial extrudlet length (1) are
 identified in TABLE 2, below. TABLE 2 also identifies the initial surface
 area of the respective individual extrudlets (A.sub.e), the quantity or
 number of extrudlets (Q), as well as the total initial extrudlet surface
 area (A.sub.t, where A.sub.t =QA.sub.e), for each of Examples 7-11.
 TABLE 2
 Example d.sub.0 (in) d.sub.1 (in) 1 (in) A.sub.e (in.sup.2) Q
 A.sub.t (in.sup.2)
 7 0.250 0.062 0.250 0.3371 57 19.21
 8 0.187 0.042 0.187 0.1868 132 24.65
 9 0.150 0.042 0.150 0.1230 279 34.32
 10 0.128 0.042 0.125 0.0897 459 41.17
 11 0.090 0.035 0.090 0.0461 1139 52.51
 While each of the extrudlet forms provided a different respective initial
 surface area, as indicated, in each of Examples 7-11, the same mass of the
 pyrotechnic formulation (16 grams) was used. As will be appreciated, as
 the size of the extrudlets used in each of Examples 7-11 was different,
 the number of extrudlets required to achieve 16 grams of material also
 differed for each of these examples.
 In each of Examples 7-11, the 16 grams of the pyrotechnic formulation was
 used as the heat source material relative to a dissociation chamber
 containing a 163 gram fluid load of 20% nitrous oxide, 70% argon and 10%
 helium (on a molar basis).
 DISCUSSION OF RESULTS
 The tank pressure traces obtained for the inflators in Examples 7-11 are
 shown in FIG. 7 which shows gas output measured in terms of tank pressure
 versus time. The pressure traces obtained within the inflators of Examples
 7-11 (as measured by a pressure transducer mounted in a dissociating
 chamnber wall of the inflator) are shown in FIG. 8.
 As shown in FIG. 7, the maximum tank pressure clearly decreased as the
 total surface area of the extudlets decreased. This is attributable to a
 larger fraction of the stored gas load passing into the test tank without
 having been heated by the combustion products since the rate of combustion
 decreased as the total surface area of extrudlets decreased.
 As shown in FIG. 8, the maximum internal pressure within the pressure
 vessel generally increased as the total extrudlet area increased. This is
 indicative of more heat being added to the stored gas as the total surface
 area in increased.
 Examples 12-14
 In these Examples, test inflators each containing a 1.0 gram load of
 fuel/oxidizer pyrotechnic material composed of 23% titanium (Ti) and 77%
 cupric oxide (CuO), percents on a mass basis, were fired using a 60
 liter-closed tank as the test tank. In each of Examples 12-14, the
 particle size of the fuel constituent (Ti) was varied as shown in TABLE 3,
 below, using Ti particles of a particle size of 75 .mu.m and 150 .mu.m.
 TABLE 3
 Ti Mass Fraction
 Example 75 .mu.m 150 .mu.m
 12 1.0 0
 13 0.5 0.5
 14 0 1.0
 In each of Examples 12-14, the 1.0 gram load of the pyrotechnic formulation
 was used as the heat source material relative to a dissociation chamber
 containing a 54.4 grams of a fluid load composed of 40% nitrous oxide, 50%
 argon and 10% helium (on a molar basis).
 DISCUSSION OF RESULTS
 FIGS. 9 and 10 illustrate the pressure versus time traces obtained in the
 associated test tank and within the inflator pressure vessel itself,
 respectively.
 It is clear that as the fuel particle size is decreased, the maximum tank
 pressure increased. (See FIG. 9) Analysis of the effluent gases from these
 tests also indicates that the amount of nitrous oxide dissociation
 increased as particle size decreased. Analysis of the gas mixture obtained
 from the large particle (150 microns) test indicated about 6% nitrous
 dissociation. The percentage nitrous oxide dissociation increased to about
 26% for the blended mixture test, and increased further to about 31% for
 the small particle test. Although the effiect of particle size on the rise
 rate was unclear, it appears that the smaller fuel particles participated
 more fully in the reaction, thereby releasing more heat and resulting in
 higher maximum tank pressures. This conclusion is further supported by the
 internal pressure characteristics, as shown in FIG. 10. In FIG. 10, the
 smallest particle size pyrotechnic clearly produced the highest internal
 pressure, while the largest particle size produced the lowest internal
 pressure.
 It is interesting to note that in FIG. 10 the particle size does not seem
 to affect the rate of internal pressure increase. To more closely examine
 this effect, FIG. 11, which is merely a portion of the plot of FIG. 10
 plotted on an enlarged scale, is presented. It is seen in FIG. 11 that
 while there is a slight reduction in the rate of pressure increase as the
 particle size is increased, the effect is relatively minor. There are at
 least two reasons why the change in pyrotechnic particle size did not
 appear to affect the rate of nitrous oxide dissociation and the pressure
 rise rate in the test tank. Firstly, the particle sizes of both the fule
 and oxidant components of the pyrotechnic formulation were not varied
 through a wide range. Thus, although particle size would be expected to
 have a strong effect on the amount and rate of dissociation, it was
 perhaps not noticed in these tests given the limited amount of particle
 size variation. Secondly, effects of the pyrotechnic constituents of the
 initiator itself may have been such that they effectively concealed the
 combustion properties of the additional titanium cupric oxide pyrotechnic.
 This is often the case for relatively large loads of very high temperature
 and rapid burning pyrotechnics like zirconium potassium perchlorate (ZPP).
 The results shown clearly demonstrate that the physical characteristics of
 the beat source used to induce dissociation of nitrous oxide-bearing
 mixtures can be used to modify the performance characteristics of these
 systems. As pyrotechnic or other fuel materials with different physical
 characteristics burn, heat is transferred to the nitrous oxide-bearing
 mixtures at different rates. Thus, the amount (or degree) of dissociation
 of the nitrous oxide is affected by the rate at which the gas is heated to
 dissociation temperature of nitrous oxide. Understanding this effect is
 important because important inflation parameters--like rate of pressure
 rise--can then be changed through physical modifications of the
 dissociation heat source.
 As described above, the invention relates the physical characteristics of
 the heat source pyrotechnic material or formulation to either or both the
 rate at which the gas source material dissociates and the amount (i.e.,
 extent) of such dissociation. Thus, the invention yields a method by which
 important inflator performance parameters such as rise rate can be
 tailored for specific inflatable restraint system installations while
 minimizing or avoiding apparatus hardware changes or alterations. As will
 be appreciated, through the alteration of the physical characteristics of
 the heat source pyrotechnic material or formulation, the same or similar
 inflator device hardware can be used with heat source pyrotechnic
 materials of particularly selected physical characteristics to provide
 inflator devices having particularly desired, and possibly distinct,
 performance parameters. The ability to use the same hardware to provide
 inflators having selected and varied performance parameters can
 dramatically simply one or more of the manufacture, production and supply
 of corresponding inflatable restraint system assemblies and components and
 thus, for example, reduce or minimize the costs associated therewith. In
 view of the above, significant benefits can be realized through the
 practice of the above-described invention.
 The invention illustratively disclosed herein suitably may be practiced in
 the absence of any element, part, step, component, or ingredient which is
 not specifically disclosed herein.
 While in the foregoing detailed description this invention has been
 described in relation to certain preferred embodiments thereof, and many
 details have been set forth for purposes of illustration, it will be
 apparent to those skilled in the art that the invention is susceptible to
 additional embodiments and that certain of the details described herein
 can be varied considerably without departing from the basic principles of
 the invention.