Abstract:
A gas generator  10  for an inflatable occupant restraint system is provided. The gas generator  10  includes a projectile firing barrel  20  having a touch hole  26  on a side thereof for ignition of a propellant  24  within the barrel  20 . Ignition of the propellant  24  drives a projectile  50  through the barrel  20  and into a rupturable seal  36  on a stored gas canister  32 . After rupturing the seal  36 , the projectile  50  is positively retained between a base end  21  of the barrel  20  and the gas canister  32.

Description:
This Application claims the Benefit of the Filing Date of U.S. Provisional Patent Application Ser. No. 60/426,894 Filed Nov. 15, 2002 and Incorporated By Reference Herein 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to inflatable occupant restraint systems for use in motor vehicles, and more particularly to a gas generator in such a system utilizing a pyrotechnically driven projectile for releasing inflation gas from a stored gas vessel for inflation of an airbag. 
     BACKGROUND OF THE INVENTION 
     Inflatable safety restraint devices have become standard equipment on many new automobiles. Many designs have developed over the years, incorporating a wide variety of components. In a typical design, an inflatable airbag or cushion is mounted in a folded state, and inflated to protect a vehicle occupant in response to an activation signal from an onboard electrical activation system. The gas generator or inflator commonly associated with the system supplies an inflation gas for filling the airbag. The inflator is typically the heaviest and most complex component in such a system. A reduction in weight and manufacturing complexity are often desirable in the automotive industry, and thus it is desirable to reduce the number and complexity of inflator parts. 
     Various inflator designs and methods have been utilized, for example, many systems employ an ignitable gas generant or pyrotechnic that combusts to rapidly supply inflation gases that are directed into the airbag. Many effective designs are known, however, the inherently hot gases associated with pyrotechnics and particulate material resulting from combustion thereof can present unique concerns. The hot combustion gases must, for example, be cooled to prevent damage to the system materials, particularly the airbag, and also to mitigate potential harm to vehicle occupants. Combustion of the gas generant can create noxious smoke and therefore, the gas generant compositions must be tailored to produce levels in compliance with regulatory and industry standards. 
     Other systems utilize a stored, pressurized gas in a canister or bottle that is released by rupturing a seal, then directed into the airbag. Advantages of the stored gas systems include lower temperatures of the inflation gases, and the lack of particulates. However, developing a fast-response, reliable system for controllably releasing the pressurized gas has proven difficult. One approach has been to combine a pyrotechnically driven projectile for rupturing the seal on the pressurized gas canister. In such a system, an onboard activation system ignites gas generants to provide an actuation gas for driving the projectile into the subject seal. These systems provide an effective means for quickly and reliably releasing the stored gas, however, relatively high velocities are required of the projectile, and after the projectile has performed its intended function, deflection and bouncing of the projectile in the apparatus may, for example, irreparably damage the associated equipment. 
     A further challenge to designers relates to igniting the pyrotechnic charge used to drive the projectile. Where the successful deployment of the airbag depends upon accurately and reliably igniting a relatively small pyrotechnic charge to drive a projectile, it is desirable to design a system providing reliable, repeatable performance. 
     SUMMARY OF THE INVENTION 
     The present invention provides a gas generator for an inflatable occupant protection system in a motor vehicle. The gas generator preferably includes a gas canister having pressurized gas stored therein and a rupturable seal at an end. An elongate projectile firing barrel having a touch hole, preferably formed in a side thereof, is also provided, and includes a quantity of propellant positioned therein. A projectile is positioned in the barrel and movable therein upon an ignition of the propellant. Ignition of the propellant drives the projectile into the rupturable seal, allowing pressurized gas to exit the canister for inflation of an airbag. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially sectioned side view of an inflator according to a preferred embodiment of the present invention; 
         FIG. 2  is a sectioned side view of a projectile firing barrel according to the present invention; 
         FIG. 3  is an end view of a projectile firing barrel according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown an inflator  10  according to a preferred constructed embodiment of the present invention. Inflator  10  is operable to supply gas to rapidly inflate an airbag (not shown) for cushioning a vehicle occupant in the event of a crash or sudden vehicle deceleration, in a manner well known in the art. All the component parts of inflator  10  are either readily commercially available or are formed from known materials and by known processes. Inflator  10  includes a first body portion  12 , preferably a substantially cylindrical hollow metallic tube, and a second body portion  32  that comprises a pressurized gas canister or bottle, also preferably substantially cylindrical. Canister  32  can be any of many known pressurized gas canisters, all commercially available. A connector  34 , also preferably substantially cylindrical, and having an inwardly extending wall is preferably positioned between body portions  12  and  32 , and preferably friction welded to the respective portions, via a process well known in the art. It should be appreciated that embodiments are contemplated wherein first body portion  12  is attached directly to second portion  32 , rather than utilizing a connector therebetween. The various components  12 ,  32 , and  34  can be assembled in any order and attached in any fashion, such as any type of weld, threads, press fitting, etc. A partition or nozzle sealing member  36  preferably separates the pressurized interior of canister  32  from an interior  13  of first body portion  12 . In a preferred embodiment, partition  36  is laser welded to connector  34 , however, it should be appreciated that some other connection means might be employed without departing from the scope of the present invention. Moreover, those skilled in the art will appreciate that because the present invention is applicable to a variety of pressurized gas canisters, the shape of the canister attached to connector  12 , and the manner in which it is sealed might vary significantly from the illustrated version in  FIG. 2 . 
     A firing barrel  20  is positioned within first body portion  12 , and preferably comprises a flange  21  and tube  22 . Firing barrel  20  is preferably formed by deep draw stamping, or another suitable known process. Firing barrel  20  is preferably press fit into body portion  12 , abutting a ledge  35 , although it might be welded thereto or attached by some other means such as by threaded engagement. 
     Referring now to  FIGS. 2 and 3 , there are shown side and end views, respectively, of firing barrel  20 . Flange  21  preferably includes a plurality of apertures  26 , radially arranged around tube  22 . In  FIG. 1 , tube  22  is illustrated as cylindrical in cross-section, however, it should be appreciated that it might be constructed having other shapes without departing from the scope of the present invention. Returning to  FIG. 1 , a projectile  50  is positioned in tube  22  of firing barrel  20 , and is preferably positioned adjacent a pyrotechnic charge  24 . Projectile  50  is preferably metallic and includes a pointed or otherwise sharpened end  51 , however, different configurations and materials might be utilized without departing from the scope of the present invention. Pyrotechnic charge  24  may be any known gas generator booster propellant, preferably cured in situ. U.S. Publication No. 2002-0079680-A1 incorporated herein by reference describes an exemplary process. Gas generant  24  is positioned within tube  22  and is preferably ignitable via a touch hole  26  that connects an interior of tube  22  with interior space  13  of first body portion  12 . Embodiments are contemplated in which the gas generant, preferably in tablet form, is placed within a container or metallic mesh filter in barrel  20 . 
     An initiator assembly  14  is preferably positioned in a body bore  15  in the side of first body portion  12 . In a preferred embodiment, initiator assembly  14  comprises an igniter or squib  16 , any known suitable igniter, and a retainer  18 . Initiator assembly  14  is preferably retained in bore  15  with a weld, for instance a resistance weld, and positioned such that igniter  16  extends into an interior  13  of first body portion  12 . It should be appreciated that rather than welding initiator assembly  14  in bore  15 , it might be press fit in place or secured by an adhesive or some other means. Igniter  16  is preferably connected to a vehicle electrical activation system in a conventional manner, allowing inflator  10  to be activated in response to a signal from an onboard computer. 
     In a preferred embodiment, activation of igniter  16  ignites propellant placed in igniter  16  itself or positioned nearby in space  13 . Ignition of the propellant creates a flame front that traverses or fluidly communicates with touch hole  26  to ignite the booster propellant  24  in tube  22 . Upon activation of gas generant  24 , the rapid generation of gas in tube  22  supplies a force that drives projectile  50  through tube  22  toward partition  36 . Partition  36  is preferably formed from a relatively thin metallic material capable of being punctured by projectile  50 . The pointed end  51  of projectile  50  pierces partition  36 , thereby establishing fluid communications between the interior of canister  32  and the interior  13  of body portion  12  via an aperture  38  in connector  34  and the apertures in flange  21 . Consequently, pressurized gas for inflation of an associated airbag is supplied from canister  32 . In a preferred embodiment, inflation apertures (not shown) in body portion  12  fluidly connect space  13  with an interior of an airbag. Various filters, burst shims, output enhancers, etc., all known in the art may be positioned in the path of the exiting inflation gas as desired. In addition, a wide variety of aperture patterns and means for dispersing the inflation gas might be formed integrally with body portion  12 . 
     The present invention further provides an integral flange trap for capturing the spent projectile  50  after inflator activation. After projectile  50  is driven into and ruptures partition  36 , the projectile is preferably positively retained in the space between flange  21  and connector  34 . 
     In one embodiment, flange  21  is keyed relative to body portion  12 , allowing insertion therein in a single orientation. In such an embodiment, flange  21  is preferably shaped relative to tube  22  such that upon insertion in body portion  12 , touch hole  26  is oriented toward igniter  16 . This feature facilitates proper positioning of barrel  20 , in turn facilitating ignition of gas generant  24  by positioning touch hole  26  proximate igniter  16 , allowing the flame front from activation of igniter  16  to reach gas generant  24  relatively easily. Flange  21  might be formed, for instance, having a non-circular periphery, allowing engagement with body portion  12  in only one, desired orientation. Alternatively, in an embodiment utilizing a threaded engagement between barrel  20  and body portion  12 , the components may be threaded such that touch hole  26  is aligned with igniter  16  when barrel  20  is fully screwed into body portion  12 . 
     By positioning initiator assembly  14  in the side of inflator  10  in bore  15 , and utilizing a resistance weld, the present invention allows the inflator to be manufactured without a weld joint between the initiator housing and an end of the tube. Moreover, the present invention uses fewer parts than earlier designs, and positively captures the spent projectile. Finally, the design is relatively low cost, simple to assemble, and more reliable in operation than earlier designs. 
     It should be understood that the present description is for illustrative purposes only, and should not be construed to limit the scope of the present invention in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the scope of the present invention as described above and in the appended claims.