Abstract:
An inflator  10  of a vehicle occupant protection system, for example, contains an elongated housing  12  having a first end  14  and a second  16 . The gas generator  10  includes a sealed pressurized gas supply or gas tank  18  in fluid communication with the first end  14  upon inflator  10  operation. A first seal  36  seals the first end  14  prior to gas generator  10  operation. A notched support member  56  is wedged within the housing  12  and fixes the first seal  36  against a sealed opening  24  of the gas tank  18 , thereby preventing fluid flow during gas generator  10  inactivity. Upon gas generator  10  activation, the support member  56  is fractured by a force produced by an initiator  68  thereby releasing pressurized gas into the first end  14  and through the housing  12.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of provisional application Ser. No. 60/426,538 filed on Nov. 14, 2002. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to gas generators used to inflate air bags in an automobile occupant protection system and, more particularly, to a stored gas inflator. In accordance with the present invention, an improved release system for stored gas within a pressurized canister is provided.  
         [0003]     Inflation systems for deploying an air bag in a motor vehicle generally employ a gas generator in fluid communication with an uninflated air bag. The gas generator is typically triggered by a firing circuit when the sensed vehicle acceleration exceeds a predetermined threshold value, as through the use of an acceleration-responsive inertial switch.  
         [0004]     Air bag inflation systems often utilize a stored gas generator housed within the B-pillar of the car, for example. Hybrid gas generators are typical and contain pressurized gas that is released upon receipt of a predetermined signal. An ongoing challenge is to reduce the time required to release the stored gas upon a crash event. Furthermore, improved safety and reduced manufacturing costs are also ongoing concerns. Improvements in any of these areas would provide an advantage over state-of-the-art gas release systems.  
         [0005]     Other stored gas release systems are known. For example, U.S. Pat. No. 6,206,420, herein incorporated by reference, describes a device for the introduction of pressurized gas into an airbag.  
       SUMMARY  
       [0006]     In accordance with the present invention, a gas generator includes a housing having a first end and a second end, and an inner peripheral wall defining a plenum for passage of a pressurized gas upon gas generator activation. The first end of the housing fluidly communicates with a pressurized gas supply or gas tank upon gas generator activation, thereby supplying pressurized fluid flow through the housing. Prior to gas generator activation, a first seal covering the first end prevents pressurized fluid flow through the housing prior to activation of the gas generator. A notched support member is fixed within the plenum and against the first seal thereby countering an outer bias on the seal from the pressurized gas, and thus preventing pressurized fluid flow prior to the gas generator activation.  
         [0007]     An initiator is fixed within the housing and fluidly communicates with the plenum upon gas generator activation. Upon gas generator activation, the initiator produces a sharp blast of gas thereby creating a force sufficient to fracture the notched support member and thus release pressurized gas into the first end. Fracture of the notched support member eliminates the support&#39;s bias against the first seal, thereby facilitating rupture of the first seal as the gas pressure is exerted thereagainst. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0008]      FIG. 1  is a side view of a first portion of a pressurized gas generator and a gas release mechanism in accordance with the present invention.  
         [0009]      FIG. 2  is cross-sectional view of a front portion of a pressurized gas generator and a gas release mechanism in accordance with the present invention.  
         [0010]      FIG. 3  is an alternate design of the support member shown in  FIG. 2 .  
         [0011]      FIG. 4  is a view of a preferred second seal covering the gas tank as shown in  FIG. 2 .  
         [0012]      FIG. 5  is a side view of a second portion of a pressurized gas generator and a gas release mechanism in accordance with the present invention.  
         [0013]      FIG. 6  is a sectional view of an annular insert forming a support member across the plenum. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     As shown in the figures, a pressurized gas release mechanism  10  comprises an elongated housing  12  formed, for example, from a stamped rigid material such as carbon steel or stainless steel. The housing  12  contains a first end  14  and a second  16 . A pressurized or stored gas bottle  18  is fixed to the first end  14  and upon activation, is in fluid communication therewith. An annular plate  20  is welded or otherwise fixed to the housing  12  at first end  14 . A stamped or otherwise formed burst disc or seal  22  covers an opening  24  of the gas bottle, tank, or pressurized supply  18 , thereby sealing and preventing release of pressurized gas during normal vehicular operation. In one aspect of the present invention, the burst disc  22  is preferably welded at four points along its diameter. Two of the welds  26  are formed along an outer circle  28  of the disc  22  and connect the disc  22  to the weld plate  20 . Two additional welds  30  are formed along an inner circle  32  concentrically oriented within outer circle  28 , thereby connecting the burst disc  22  to a support member  56  (described below). Although optional, the circular portion  32  may be perforated or formed as a weakened portion of disc  22 . Upon inflator activation, rupture of portion  32  from disc  22  is therefore promoted, thereby creating an annular conduit but minimizing metallic shards when releasing pressurized gas into the housing  12 . Typical state of the art burst discs often feature a plurality of weakened portions that form petals once gas is exerted thereagainst. A concern is that the petals of this design may fracture and therefore require enhanced or more robust filtering as compared to the present burst disc  20 .  
         [0015]     An annular wall  34  is formed within the annular plate  20 . A cylindrical retainer or seal  36  is seated within and against the annular wall  34  and provides a bias or support to interface with an outer face  38  of the burst disc  22 . One advantage of forming a weakened circular portion  32  and then supporting it by the cylindrical retainer  36  is to reduce the strength requirements of disc  22 . In practice then, stainless steel rather than the conventional and more expensive proprietary INCONEL™ may be employed. Gas pressure exerted upon an inner face  40  of the burst disc  22  is thereby retained again during normal vehicular operation. An integral vent  42  is preferably axially machined within the retainer  36  thereby providing a vent in the case of over-pressurization of the gas bottle  18 , during a fire for example.  
         [0016]     A hollow diffuser  44  is machined or otherwise formed from steel or other suitable materials, and then welded or otherwise fixed within the housing  12 . Diffuser  44  functions to distribute gas flowing from first end  14  through the diffuser  44  and out the second end  16 . Diffuser  44  preferably telescopes from the first end  14  toward the second end  16 , from a first wider circumference  46  to a narrower circumference  48 , thereby resulting in a first larger plenum  50  and a second smaller plenum  52 , respectively. A plurality of gas discharge orifices  54  is spaced about circumference  48 . As shown in the figures, a preferred embodiment contains four gas discharge orifices  54  evenly spaced about the circumference  48 .  
         [0017]     A notched support member or wall  56 , preferably extruded or made from aluminum, is laterally fixed across the relatively larger diameter of plenum  50  adjacent the first end  14 . As used herein, the term “fixed” is meant to relate to any embodiment that provides a support member  56  spanning across plenum  50  during normal vehicular operation or prior to a crash event. When buttressed against the cylindrical retainer seal  36 , support wall  56  prevents pressurized gas within the bottle  18  from rupturing the burst disc  22  during normal vehicular operation. As shown in  FIGS. 2 and 3 , in one embodiment a pair of opposing detents  58  is formed along an inner wall  60  of the larger plenum  50  thereby providing a structural support by engaging each end of the support member  56 . Alternatively, as shown in  FIG. 6 , support member  56  may be formed integral to an annular insert  59 , whereby the second periphery  61  of insert  59  is contoured to fit snugly within inner wall  60 . This may for example present certain structural and manufacturing advantages. In yet another embodiment, support member  56  may be formed integral with inner wall  60  again presenting certain structural and manufacturing advantages.  
         [0018]     However formed, support member  56  preferably has a first notched surface  62  and a second notched surface  64  opposite the first surface  62 , whereby pressure exerted upon either surface results in ready fracture of the wall  56 , thereby releasing the cylindrical retainer  36  and therefore the pressurized gas once the burst disc  22  gives way. As shown in  FIG. 2 , the support member  56  may of course be notched on one surface rather than both.  
         [0019]     A micro gas generator  66  is crimped about the outer periphery of plenum  50  and extends through wall  60 . An igniter or pyrotechnic initiator  68  is contained within the generator  66  and ignitably communicates with a gas generant  70  also contained within generator  66 . Upon a crash event, the igniter  68  receives a signal from a crash sensor or accelerometer (not shown), for example, and then ignites the gas generant  70  to produce gas within the plenum  50 . The gas pressure produced from the micro gas generator  66  thereby fractures the support wall  60  in fluid communication therewith and allows the gas pressure within the bottle  18  to fracture the burst disc  22 , thereby driving the cylindrical retainer  36  through the annular wall  34 . Gas pressure within the bottle  18  therefore is routed through the diffuser  44  and out the housing  12  into an airbag (not shown).  
         [0020]     The propellant  70  may comprise any gas generant composition known for its utility in vehicle occupant protection systems. Co-owned U.S. Pat. Nos. 5,035,757, 5,756,929, 5,872,329, 6,077,371, 6,074,502, and 6,210,505 are herein incorporated by reference and exemplify, but do not limit gas generant compositions contemplated in accordance with the present invention.  
         [0021]     In a preferred embodiment, the propellant  70  comprises a mixture of silicone as a fuel at about 10-25% by weight, and an oxidizer such as ammonium or potassium perchlorate at about 75-90% by weight. Silicone not only functions as a fuel but also functions as a binder thereby facilitating the formation of pliant cylindrical propellant extrusions.  
         [0022]     The propellant  70  more preferably comprises silicone as a fuel at about 10-25% by weight; a perchlorate oxidizer such as ammonium, lithium, or potassium perchlorate; and a strontium salt such as strontium nitrate or strontium carbonate as a coolant, wherein the oxidizer and coolant comprise about 75-90% by weight of the propellant. The silicone may be purchased, for example, from General Electric or other well-known suppliers. The other gas generant constituents may be provided by suppliers or by manufacturing methods well known in the art.  
         [0023]     The propellant composition  70  yet more preferably comprises, in percents by weight, 10-25% silicone, 75-90% oxidizer, 1-30% coolant, and 1-20% of a slag-forming constituent. The oxidizer may for example be selected from inorganic perchlorates and nitrates such as sodium perchlorate, potassium perchlorate, ammonium perchlorate, potassium nitrate, ammonium nitrate, and phase stabilized ammonium nitrate. The coolant may for example be selected from metal hydroxides such as aluminum hydroxide; metal carbonates such as calcium carbonate, magnesium carbonate, strontium carbonate, and sodium carbonate; and inorganic oxalates such as calcium oxalate, strontium oxalate, and ammonium oxalate. The slag-forming constituent may for example be selected from metal oxides such as aluminum oxide and iron oxide. It has been found that gas generating compositions containing silicone and a perchlorate oxidizer burn at relatively lower temperatures when a coolant, in accordance with the present invention, is added to the mixture. As a result, cooling requirements of gas generated within the gas release mechanism  10  can be substantially minimized.  
         [0024]     If necessary, a filter or heat sink  72  made from expanded metal or carbon yarn for example, is housed at second end  16  within plenum  52  to filter the gas effluent travelling from plenum  50 . A perforated tube  74  extends from the second end  16  such that upon inflator activation, the airbag (not shown) fluidly communicates therewith. A welded wire mesh filter  72  may be provided by Wayne Wire, Inc. of Kalkaska, Mich., for example.  
         [0025]     It will be understood that the foregoing description of the present invention is for illustrative purposes only, and that the various structural and operational features herein disclosed are susceptible to a number of modifications, none of which departs from the spirit and scope of the present invention.