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, at least one gas exit aperture ( 44 ), sealed prior to gas generator ( 10 ) activation, is opened as the gas release member ( 40 ) slidably engages an inner wall ( 11 ) of the housing ( 12 ). After gas generator ( 10 ) activation, the spring energy of the spring ( 50 ) gradually equalizes and then exceeds 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 housing ( 12 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of U.S. Provisional Application Ser. No. 60/656,049 having a filing date of Feb. 24, 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 inflator 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. Thus, it is 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 internal pressure and compressing the spring attached to the gas release member. As the spring is compressed, at least one gas exit aperture, sealed prior to gas generator activation, is opened as the gas release member slidably engages an inner wall of the gas generator. After gas generator activation, as the gas pressure gradually decreases, the spring energy of the spring gradually equalizes and then exceeds 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 housing. Accordingly, the spring-biased gas release member regulates pressure thereby affecting a resilient seal and at least partially sealing the gas exit orifice(s) as combustion pressure dissipates. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional side view of an inflator in accordance with the present invention prior to inflator activation; 
       FIG. 2  is a cross-sectional side view of the inflator of  FIG. 1  after inflator activation; and 
       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 a gas generator or an inflator 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 . At least one gas exit orifice or aperture, and more preferably a first plurality of inflation gas exit apertures, generally designated  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). A second plurality of inflation gas exit apertures, generally designated  44 , are formed along inflator body  12  to enable fluid communication between an interior of the inflator body and an exterior of the body. In a first embodiment, gas exit apertures  44  are in the form of substantially identical longitudinal slots  44 - a ,  44 - b  extending substantially parallel with inflator body longitudinal axis  100 . In this embodiment, apertures  44 - a ,  44 - b  are circumferentially spaced substantially evenly around a periphery of housing or inflator body  12 . In addition, apertures  44 - a ,  44 - b  are equilaterally or circumferentially aligned along inflator body  12  such that the lengths of the apertures are substantially coextensive along the inflator body. That is, aperture first ends  44 - a l,  44 - b   1  are each spaced apart from inflator body first end  12 - 1  a distance D 1 , while aperture second ends  44 - a   2 ,  44 - b   2  are each spaced apart from inflator body second end  12 - 1  a distance D 2 . Stated another way, apertures  44   a  and  44   b  are collateral whereby corresponding ends  44 - a   1  and  44 - b   1 , and corresponding ends  44 - a   2  and  44 - b   2  are laterally or circumferentially aligned, respectively. 
   Inflator body  12  may be cast, stamped, extruded, or otherwise metal-formed. Apertures  44  may be formed along the inflator body by, for example, punching or piercing. In  FIGS. 1 and 2 , two apertures  44  are shown to illustrate the principles of the present invention. However, any desired number of apertures may be used, depending on design requirements. 
   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. 
   A perforated internal wall  14  is disposed within inflator body  12  intermediate the ends thereof, defining first and second inflator chambers  20  and  30 , respectively. Wall  14  is preferably formed from metal or ceramic and is substantially oriented along a plane perpendicular to a longitudinal axis  100  of inflator body  12 . Wall  14  is roll-crimped or otherwise secured within inflator body  12  so as to maintain the wall in its position within the inflator body when the wall is subjected to pressures generated by combustion of gas generants stored within the inflator body. In a first embodiment, wall  14  is a substantially cylindrical member having a plurality of inflation gas exit apertures  15  formed therein. 
   A quantity of a propellant or gas generant composition  16  is positioned in chamber  20 . Any suitable propellant might be used and exemplary compounds are disclosed, for example, 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 described gas generator herein. 
   Referring again to  FIG. 1 , end cap  26  supports an igniter  62  operably associated with first chamber  20  such that it can ignite gas generant composition  16  in chamber  20  in a conventional manner. The illustrated position and orientation of igniter  62  might be varied without departing from the scope of the present invention, depending on space and manufacturing requirements. Further, 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 communication with chamber  20  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 along internal walls of first chamber  20  and at an end of combustion first chamber  20 , adjacent internal wall  14 , to help ensure that inflation gas passes through the buffer before exiting first chamber  20 . In a first embodiment, buffer  52  is formed from one or more layers of a compressed knitted metal wire, which is commercially available from vendors such as Metex Corp. of Edison, N.J. Other, suitable materials may also be used. 
   A piston  40  having a face  41  is positioned within chamber  30  to facilitate slidable engagement with an interior wall  11  of inflator body  12 . A pliable seal  43  (for example, an O-ring seal) is secured along an outer surface of the piston so as to form a substantially gas-tight seal between piston  40  and the housing interior wall. Seal  43  is configured to slide freely within chamber  30  along the housing interior wall, in conjunction with piston  40 . Accordingly, upon operation of the inflator  10 , the piston or spring-biased gas release member  40 , is slidably engaged within housing  12  as pressure increases upon combustion of the propellant  16 . Concurrently therewith, the sliding action of the piston  40  opens apertures  44  thereby permitting release of the combustion gas therethrough. As a result, pressure begins to decrease, and piston  40  begins to again move to its pre-operation position, thereby affecting a relative increase in the pressure as the openings or open area of the apertures  40  are/is attenuated. Piston  40  and its associated seal  43  effectively fluidly divide chamber  30  into a pair of sub-chambers  30 - 1  and  30 - 2 . Alternative types of seals or gaskets may be employed provided the alternative seals for a substantially gas-tight barrier between sub-chambers  30 - 1  and  30 - 2  that is movable in conjunction with piston  40 . 
   Piston  40  may be cast, stamped, extruded, or otherwise metal-formed. Alternatively, piston  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 piston  40  and the material from which the piston is formed be selected to minimize the mass of the piston. It is believed that these features reduce the static and dynamic inertia of the piston during actuation, thereby enhancing the responsiveness of the pressure regulation mechanism described herein. It will be appreciated that any spring-biased gas release member such as the piston  40 , that essentially facilitates the same function as a spring-biased pressure regulator (further described below) may be utilized. 
   A spring member  50  is operably coupled to endcap  28  and to piston  40  for exerting a biasing force on piston  40  acting in the direction indicated by arrow “B” ( FIG. 2 ). 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 sub-chamber  30 - 2 . Spring member  50  is configured to have a spring constant that enables piston  40  to move along inflator housing  12  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 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 piston  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 orifices may be iteratively harmonized to result in a desired average pressure within the pressured vessel  10 . As such, when properly equipped 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, 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 spring  50  and the total gas exit aperture area sealed by the piston  40  may be either singularly or jointly evaluated on a trial and error basis depending on the propellant composition desired. 
   In an alternative embodiment, spring member  50  is not coupled to piston  40 , but is rather positioned to contact and exert force on piston  40  after the piston 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, piston  40  rests in the position shown in  FIG. 1 . In this position, seal  43  prevents fluid residing in the inflator between igniter  62  and seal  43  from exiting housing  12  through apertures  44 . In operation, when deployment of the vehicle inflatable restraint system is desired, an activation signal is sent to igniter  62  operably associated with first chamber  20  of the inflator. Gas generant  16  positioned in first chamber  20  is consequently ignited, directly or via a booster propellant such as is known in the art. Ignition of the gas generant causes a rapid production of hot inflation gases in first chamber  20 . Inflation gases flow through apertures  42  to inflate an associated airbag. The inflation gases also flow through buffer  52 , then through internal wall  14  into second chamber  30 . 
   As inflation gases flow into second chamber  30 , the internal pressure in chamber  30 - 1  increases, causing piston  40  to move in the direction indicated by arrow “A”, against the biasing force exerted on the piston by spring member  50 . The spring constant of spring member  50  may be specified to enable piston  40  to move in direction “A” in response to a predetermined minimum inflation gas pressure acting on piston  40 . In the embodiment shown in  FIGS. 1 and 2 , the spring constant is specified to enable piston to move in direction “A” when the inflator internal pressure reaches a pressure residing at a midpoint of an ideal pressure range for combustion of gas generant  16  within the inflator. When the product of this predetermined inflation gas pressure and the area of piston face  41  becomes greater than the force exerted on piston by spring member  50 , piston  40  will begin to move in direction “A”. Pressure values much beyond this predetermined value of internal pressure may lie outside the desired pressure range. Thus, the pressure regulation mechanism is designed such that movement of piston  40  a certain distance in direction “A” opens apertures  44  to allow exit of inflation gas, thereby relieving pressure to prevent the inflation gas pressure from exceeding the desired pressure range. A greater pressure increase within the inflator produces a correspondingly greater movement of piston in direction “A”, thereby uncovering more of apertures  44  and enabling a greater volumetric flowrate of inflation gas through the apertures, thereby further relieving the inflator internal pressure. Thus, the total open area of pressure regulation apertures  44  is proportional to the inflator internal pressure. 
   In addition, as the combustion reaction progresses and the internal inflator pressure begins to drop, spring member  50  forces piston  40  in direction “B”, thereby covering more of apertures  44  and reducing the volumetric flowrate of inflation gas through the apertures, and correspondingly compressing the gas remaining in the inflator to maintain the inflator internal pressure within the optimum range for the combustion reaction. 
   In another embodiment (not shown), a torsion spring is used to rotationally bias the piston into a position in which it blocks the pressure regulation apertures prior to inflator activation. After inflator activation, a suitable increase in pressure produces a rotational motion of the piston against the torsion force exerted by the spring, which gradually uncovers the pressure regulation apertures to relieve excess internal gas pressure. As the pressure drops, the torsion spring acts on the piston to counter-rotate the piston, again gradually covering the apertures to block gas flow therethrough. 
   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. Also, apertures  44  may have shapes (for example, holes) other than slots. In addition, the number and sizes of apertures  44  may be varied according to the pressure regulation requirements for the inflator. 
   The present invention helps to maintain 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 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 of 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  160  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. 
   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.