Abstract:
A gas generator ( 10 ) is provided including a housing ( 12 ). A gas generating composition ( 16 ) produces expanded gases upon activation of the inflator ( 10 ), thereby increasing the internal pressure and compressing the spring ( 50 ) operably coupled to the gas release member ( 40 ). As the spring ( 50 ) is compressed, a gas exit aperture ( 27 ), sealed prior to gas generator ( 10 ) activation, is opened as the gas release member ( 40 ) is unseated from gas exit aperture ( 27 ). After gas generator ( 10 ) activation, the spring energy of the spring ( 50 ) gradually equalizes and then counters the gas pressure of the system gases, thereby once again attenuating the gas exit opening ( 27 ) to maintain an optimum average system pressure as the gas is released from the housing ( 12 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of U.S. Provisional Application Ser. No. 60/657,498 having a filing date of Mar. 1, 2005. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to inflators for vehicle airbags and, more particularly, to an inflator incorporating a mechanism for maintaining an average combustion pressure within a predetermined range. 
   Many solid propellants have an optimum pressure range for combustion. It can be difficult to maintain the inflator internal pressure within the optimum pressure range during the majority of the combustion reaction. In addition, low-pressure combustion of the propellant outside of the optimum pressure range may increase the generation of undesirable effluents. Furthermore, operating outside of the optimum combustion range may adversely affect the combustion, thereby abbreviating or shortening the burn of the propellant, or inhibiting sustained combustion of the propellant. It is therefore desirable to maintain the inflator internal pressure within the optimum range for combustion of the propellant for as much of the combustion reaction as possible. 
   SUMMARY OF THE INVENTION 
   The above-referenced concerns are resolved by a gas generator containing a spring-biased gas release member to provide a sustained optimum combustion pressure. A gas generating composition contained within the gas generator produces expanded gases upon activation of the gas generator, thereby increasing the inflator internal pressure. A perforate housing of the gas generator is formed by an outer wall, and has a first end and a second end. A combustion chamber formed by an inner wall within the housing, has a first end and an open second end, each chamber end corresponding to the respective ends of the housing. A spring-biased gas release member is seated within the open second end prior to gas generator activation. A spring is biased against the gas release member to provide a seal prior to gas generator activation, and yet also provide a controlled opening of the second end upon gas generator activation. After gas generator activation, as the gas pressure gradually decreases, the spring energy of the spring gradually equalizes and then counters the gas pressure of the system gases, thereby once again attenuating the gas exit opening to maintain an optimum average system pressure as the gas is released from the combustion chamber and routed out through the perforated housing wall. Accordingly, the spring-biased gas release member regulates pressure thereby affecting a resilient seal and at least partially sealing the gas exit aperture of the second end as combustion pressure dissipates. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings illustrating embodiments of the present invention: 
       FIG. 1  is a cross-sectional side view of an inflator in accordance with the present invention prior to inflator activation; and 
       FIG. 2  is a cross-sectional side view of the inflator of  FIG. 1  after inflator activation. 
       FIG. 3  exemplifies a combustion pressure regulation mechanism contained within a vehicle occupant protection system, in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a cross-sectional view of one embodiment of an inflator  10  in accordance with the present invention. Inflator  10  is contemplated for use primarily in passenger-side inflatable restraint systems in motor vehicles, such as are known in the art; however, it is not limited thereto. The components of inflator  10  may be manufactured from known materials and by known processes. 
   Inflator  10  includes an elongate, generally cylindrical inflator body  12  defining an enclosure and having a first end  12 - 1 , a second end  12 - 2 , and a longitudinal axis  100 . A plurality of inflation gas exit apertures  42  are formed along inflator body  12  to enable fluid communication between an interior of the inflator body and associated inflatable element of the vehicle occupant protection system (for example, an airbag.) Inflator body  12  may be cast, stamped, extruded, or otherwise metal-formed. Apertures  42  may be formed along the inflator body by punching, piercing, or other methods known in the art. 
   Endcaps  26  and  28  are secured at opposite ends of inflator body  12  using one or more known methods, to close the ends of the inflator body. In  FIG. 1 , ends of inflator body  12  are crimped over portions of first and second caps  26 ,  28  to secure the caps within the inflator body. Endcaps  26  and  28  may be cast, stamped, extruded, or otherwise metal-formed. Alternatively, endcaps  26  and  28  may be molded from a suitable high-temperature resistant polymer. 
   In one embodiment, the combustion chamber  14  is defined by an inner wall  20  positioned and secured concentrically within housing  12 , preferably centered about housing longitudinal axis  100 . Combustion chamber  14  forms, in conjunction with housing  12 , an annular passage or plenum  25  through which combustion gases propagate to discharge apertures  42  from combustion chamber  14 . As such, passage  25  is designed to cool the combustion products and to reduce or eliminate flaming of the combustion products prior to the products exiting the inflator through apertures  42 . Combustion chamber  14  may be cast, stamped, extruded, or otherwise metal-formed. 
   An aperture  27  is formed in an end portion of combustion chamber  14  for receiving a plug  40  therein. Plug  40  acts to seal combustion chamber  14  during combustion of a gas generant  16  until a predetermined pressure is achieved in chamber  14 , after which plug  40  is partially expelled from aperture  27  in a controlled manner, as described in greater detail below. Chamber  14  is sized such that a cavity  23  is formed between chamber  14  and endcap  27  to provide for positioning of plug  40 , a spring member  50 , and a buffer  52  therein, as described below. The use of the spring-biased gas release member  40  seals the combustion chamber thereby obviating the need to seal the perforations or gas exit orifices in the housing  12 , unless otherwise desired. 
   A quantity of a propellant or gas generant composition  16  is positioned in combustion chamber  14 . Any suitable propellant might be used and exemplary compounds are disclosed in U.S. Pat. Nos. 5,872,329, 6,074,502, and 6,210,505, incorporated herein by reference. The compositions described in these patents exemplify, but do not limit, gas generant compositions useful in the application described herein. 
   Referring again to  FIG. 1 , end cap  26  supports an igniter  62  operably associated with combustion chamber  14  such that upon receipt of a signal generated in a known manner, gas generant composition  16  is ignited in a conventional manner. Depending on spatial and manufacturing requirements, the position and orientation of igniter  62  might be varied without departing from the scope of the present invention. For example, igniter  62  need not be positioned within inflator body  12 . One example of an igniter suitable for the application described herein is disclosed in U.S. Pat. No. 6,009,809, incorporated herein by reference. Other igniters mountable so as to be in operable communication with chamber  14  may also be used. 
   A filter or buffer  52  is incorporated into the inflator design for filtering particulates from gases generated by combustion of gas generant  16 . The filter also acts as a heat sink to reduce the temperature of the hot inflation gas. In general, filter  52  is positioned in cavity  23  intermediate of the combustion chamber aperture  27  and annular passage  25 , thereby ensuring that inflation gas passes through the buffer before entering passage  26 . In a first embodiment, buffer  52  is formed from one or more layers of a compressed knitted metal wire, commercially available from vendors such as Metex Corp. of Edison, N.J. Other, suitable materials may also be employed. 
   A plug  40  is movably positioned within combustion chamber aperture  27  to seal the combustion chamber during combustion of gas generant  16  until a predetermined pressure is achieved in chamber  14 , after which plug  40  is partially expelled from aperture  27  in a controlled manner, as described in greater detail below. 
   Plug  40  may be cast, stamped, extruded, or otherwise metal-formed. Alternatively, plug  40  may be molded from a suitable high-temperature resistant polymer. In the embodiment shown in  FIGS. 1 and 2 , it is preferable that the design of plug  40  and the material from which the plug is formed be selected to minimize the mass of the plug. Reduction of the mass of the plug  40  reduces the static and dynamic inertia of the plug during actuation, thereby enhancing the responsiveness of the pressure regulation mechanism described herein. 
   A spring member  50  is operably coupled to endcap  28  and to plug  40  for exerting a biasing force on plug  40  acting in the direction indicated by arrow “B”. Spring member  50  may have any one of several configurations, such as a coil spring, a spiral spring, a leaf spring, or any other configuration suitable for providing the required biasing force while being enclosable in inflator body  12 . Spring member  50  is configured to have a spring constant that enables plug  40  to move in direction “A” in a predetermined manner in response to pressure variations within the inflator body, as described in greater detail below. It will be appreciated that “operably coupled” simply means that the spring  50  be positioned between the end cap  28  of housing  12  and the spring-biased gas release member  40 . Accordingly, the spring  50  may be fixed to either or both components  28  and/or  40 . Or, alternatively, the spring  40  may simply be positioned freely between the endcap  28  and the gas release member  40 . 
   Spring member  50  may be formed from a metal, metal alloy, or a polymer material. In the embodiment shown in  FIGS. 1 and 2 , it is preferable that the configuration of spring member  50  and the material from which the spring member is formed combine to minimize the mass of the spring member. This reduces the static and dynamic inertia of the spring member during actuation of plug  40 , thereby enhancing the responsiveness of the pressure regulation mechanism described herein. 
   It will further be appreciated that design considerations such as the type of propellant, and the burn characteristics thereof, and the pressure tolerances of the vessel  10 , combined with the spring energy of a given spring member  50  and the total area of the gas exit aperture  27  may be iteratively harmonized to result in a desired average pressure within the pressured vessel  10 . As such, when properly informed with the data typically developed in gas generant manufacture, such as the pressure and temperature characteristics required for an optimized combustion of the propellant, other design criteria such as the number and size of gas exit orifices in the housing  12 , and the type and strength of the spring member may be appropriately and iteratively selected to result in a pressure vessel that essentially maintains an optimized average pressure. In sum, the selection of spring  50 , and the total gas exit aperture area sealed by the plug  40  may be either singularly or jointly evaluated on a trial and error basis depending on the propellant composition desired, and further depending on other design variables as known in the art. 
   In an alternative embodiment, spring member  50  is not coupled to plug  40 , but is rather positioned to contact and exert force on plug  40  after the plug has traveled a predetermined amount along inflator housing  12 , in direction “A”. 
   In operation, the pressure regulation mechanism incorporated in inflator  10  is designed to maintain the inflator internal pressure within a specified range determined to be an optimum pressure range for combustion of gas generant  16 . It is desirable to maintain the internal inflator pressure within this pressure range for the majority of the combustion process. 
   Prior to activation of the inflator  10 , plug  40  rests in the position shown in  FIG. 1 . In this position, plug  40  prevents inflation gases from entering annular passage  25  until the predetermined pressure is achieved in chamber  14 . In operation, when deployment of the vehicle inflatable restraint system is desired, an activation signal is sent to igniter  62  operably associated with combustion chamber  14  of the inflator. Gas generant  16  is consequently ignited, directly or via a booster propellant such as is known in the art. Ignition of the gas generant  16  causes a rapid production of hot inflation gases in chamber  14 , and therefore a corresponding increase in gaseous pressure. 
   In order for inflation gas to exit combustion chamber  14  into annular passage  25 , plug  40  must be at least partially removed from combustion chamber aperture  27 . In addition, plug  40  must be removed from aperture  27  enough to provide an opening size sufficient to permit at least a minimum predetermined flow rate of inflation gas through aperture  27  and around plug  40 , in order to properly inflate the airbag. The required opening size for any given application may be determined in accordance with design requirements of a particular system. Referring to  FIG. 2 , the required minimum opening size may be achieved by moving plug  40  a distance X in direction “A”, against the biasing force exerted by spring member  50  on the plug. Plug  40  is preferably maintained in this position during combustion, to allow the inflation gas to exit combustion chamber  14 . As plug  40  is moved in direction “A”, spring member  50  compresses, thereby increasing the spring force f S  exerted on plug  40  in direction “B”. To maintain plug  40  in the desired open position when the plug has moved distance X, a substantially constant inflation gas pressure force f G  must be exerted on plug  40  in direction “A” to balance spring force f S . Gas pressure force f G  is a function of the inflator combustion pressure and the area on plug  40  over which the inflator pressure acts. As stated previously, it is desirable that the inflator internal pressure during gas generant combustion be maintained within a specified range. Thus, the spring constant of spring member  50  is preferably specified such that plug  40  is movable a distance X from its rest position to a new position (to provide the required minimum opening size) and maintainable in the new position by an inflator internal pressure within the specified pressure range. In cases where it is desirable to avoid internal pressures outside the specified range on the low end of the range, the spring constant of spring member  50  may be specified such that plug  40  is movable a distance X from its rest position (to provide the required minimum opening size) and maintainable in the new position by an inflator internal pressure residing between a median of the specified or design pressure range and an upper limit of the specified pressure range. Inflation gas exiting aperture  27  flows through buffer  52  into annular passage  25 , exiting the inflator through apertures  42 . 
   Inflator housings having configurations other than the cylindrical shape shown herein may be used, provided they are suitable for incorporating an embodiment of the pressure regulation mechanism described herein. 
   Accordingly, the present invention maintains the inflator combustion pressure within an optimum range during the majority of the combustion event by automatically and continually controlling the inflation gas exit aperture area. The pressure regulation mechanism disclosed herein greatly improves the ballistic performance of the inflator, while minimizing the generation of undesirable effluents due to low-pressure combustion. 
   Referring to  FIG. 3 , a gas generating system including a gas generator or inflator  10  described above is incorporated into an airbag system  200 . Airbag system  200  includes at least one airbag  202  and a gas generator  10  as described herein coupled to the airbag so as to enable fluid communication with an interior of the airbag upon activation of the gas generating system. Airbag system  200  may also be in communication with a known crash event sensor  210  that is in operative communication with a crash sensor algorithm (not shown) which signals actuation of airbag system  200  via, for example, activation igniter  62  (not shown in  FIG. 3 ) in the event of a collision. 
   Referring again to  FIG. 3 , an embodiment of the gas generating system or an airbag system including an inflator of the present invention may be incorporated into a broader, more comprehensive vehicle occupant protection system  180  including additional elements such as a safety belt assembly. Safety belt assembly  150  includes a safety belt housing  152  and a safety belt  160  extending from housing  152 . A safety belt retractor mechanism  154  (for example, a spring-loaded mechanism) may be coupled to an end portion of the belt. In addition, a safety belt pretensioner  156  may be coupled to belt retractor mechanism  154  to actuate the retractor mechanism in the event of a collision. Typical seat belt retractor mechanisms which may be used in conjunction with safety belt  100  are described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546, incorporated herein by reference. Illustrative examples of typical pretensioners with which safety belt  160  may be combined are described in U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference. 
   Exemplifying yet another gas generating system containing an inflator of the present invention, safety belt assembly  150  may be in communication with a known crash event sensor  158  (for example, an inertia sensor or an accelerometer) that is in operative communication with a known crash sensor algorithm (not shown) which signals actuation of belt pretensioner  156  via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner. 
   In yet another aspect of the invention, a method of controlling the combustion within a gas generator includes the following steps:
     1) providing a gas generant composition within a combustion chamber for production of gases upon combustion thereof;   2) resiliently sealing a gas exit aperture of the combustion chamber, thereby permitting egress of gases produced upon combustion of the gas generant composition; and   3) modulating the open area of the gas exit aperture to maintain a predetermined pressure range within the gas generator upon combustion of the gas generant composition.
 
It will be appreciated that the clause “resiliently sealing” refers to a seal provided in the gas exit aperture that initially seals the combustion chamber and then, upon gas generator activation, at least partially seals the gas exit aperture at some point thereafter. Stated another way, the seal of the gas exit aperture is therefore at least partially restored after gas generator activation. It should also be recognized that “modulating the open area” refers to the ability to tailor the open area of the gas exit aperture at a given moment after gas generator activation and during the combustion process, and thus maintain a predetermined pressure range within the gas generator. As described above, the exemplary embodiments contemplate a spring-biased gas release member that is movably positioned within the gas exit aperture of the combustion chamber, thereby facilitating steps 2 and 3 enumerated above. A gas generator, a gas generating system, and a vehicle occupant protection system implementing the method described above are also contemplated.
   

   It will be understood that the foregoing descriptions of embodiments of the present invention are for illustrative purposes only. As such, the various structural and operational features herein disclosed are susceptible to a number of modifications commensurate with the abilities of one of ordinary skill in the art, none of which departs from the scope of the present invention as defined in the appended claims.