Abstract:
An inflator bottle adapted for controlled release of product gas to deploy an inflatable cushion and a method thereof is provided. The inflator bottle comprises a compartment filled with a combustible gas mixture having a partition that divides the compartment into a first region and a second region. Upon a crash event, an igniter on the inflator bottle ignites initiating combustion in the first region. Combustion propagates in the first region toward a nozzle building pressure in the first region sufficient to rupture a burst disk over the passage of the nozzle releasing product gas through the nozzle. The release of product gas through the nozzle draws combustible gas mixture from the second region flowing through the gas portal on the partition into the first region for combustion. The area of the gas portal between the regions is sized in relation to the size of the minimum area of the passage of the nozzle to supply the combustible gas mixture to the first region at a rate that maintains the flame front while preventing it from propagating out into the second region or out the nozzle until the remaining combustible gas mixture in the compartment is consumed.

Description:
TECHNICAL FIELD 
     This invention relates to an inflator bottle for deploying an automotive airbag or the like. More particularly, this invention relates to such inflator bottle having a compartment containing a combustible gas mixture and comprising a partition that divides the compartment into a first region that confines the flame front and draws gas mixture from a second region after rupture of the burst disk, wherein the gas portal between the regions is sized to supply the gas mixture at a rate that maintains the flame front in the first region while preventing it from propagating into the second region or out through the nozzle. 
     BACKGROUND OF INVENTION 
     It is known in an automotive vehicle, in a collision event, to deploy an inflatable cushion, commonly referred to as an airbag, to protect vehicle occupants. Gas for deploying the airbag is supplied by an inflator bottle. One type of inflator bottle comprises a combustible gas mixture. A suitable combustible gas mixture comprises hydrogen, oxygen, argon, and helium gases. During deployment, the combustible gas mixture is ignited to form a product gas that is released through a nozzle into the airbag. Prior to deployment, a burst disk blocks a passage in the nozzle to contain the gas in the inflator bottle. During the early stages of ignition, the increase in pressure ruptures the burst disk to release the product gas. However, it is found that uncontrolled combustion of the combustible gas mixture requires a housing having thicker walls in order to prevent rupture due to the high pressures and the resultant improper deployment of the airbag due to the loss of inflation or product gas. Thicker housing walls undesirably add cost and weight to the inflator bottle. Also, uncontrolled combustion tends to increase the temperature of the product gas beyond limits for safe deployment in contact with the occupant. Moreover, in some applications, it may be desired to provide a more controlled release of product gas over an extended period of time as opposed to a rapid release such as would be produced by uncontrolled combustion of the combustible gas mixture. 
     Therefore, what is needed is an improved inflator bottle that is reliable to ignite the combustible gas mixture to produce an initial pressure effective to rupture the burst disk and release product gas through the nozzle, and thereafter to provide a controlled, sustained release of product gas at lower pressures and temperatures to deploy the airbag. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the invention, an inflator bottle is adapted to release product gas and comprises a housing that defines a compartment. A combustible gas mixture fills the compartment and is combustible to form a product gas. A partition disposed in the housing divides the compartment into a first and second region. The partition includes a gas portal comprising one or more openings having a total portal area. The portal provides fluid communication between the first region and the second region. An igniter located in the first region is effective to initiate combustion of the combustible gas mixture producing product gas. A nozzle is located in the housing having a passage with a cross section area that communicates with the first region releasing the product gas. The gas portal is disposed intermediate the igniter and the nozzle, and the ratio of the total portal area of the gas portal to the minimum cross section area of the passage is less than or equal to about 8:1, preferably less than about 5:1. 
     In accordance with another embodiment of the invention, a method is provided for releasing a product gas. The method includes providing an inflator bottle comprising a compartment filled with a combustible gas mixture. The method further includes partitioning the compartment into a first region and a second region with a partition having a gas portal to provide fluid communication between the first and the second region. The method also includes igniting the combustible gas mixture at an ignition point within the first region to form a flame front that propagates through the first region at a flame speed and forms a product gas. The method yet further includes releasing the product gas through a nozzle that is spaced apart from the ignition point wherein the gas portal is disposed between the nozzle and the ignition point. As product gas is released through the nozzle, combustible gas mixture is drawn from the second region flowing through the gas portal into the first region at a rate effective to prevent the flame front from propagating into the second region or out the nozzle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This invention will be further described with reference to the accompanying drawings in which: 
         FIG. 1  is a view in cross section of a vehicle showing a airbag system that includes an inflator bottle in accordance with the present invention; 
         FIG. 2  shows a cross section view of an inflator bottle in accordance with the present invention; 
         FIG. 2A  is a cross section view of a portion of the inflator bottle in  FIG. 2 , showing details thereof; 
         FIG. 3  shows a cross section view of the inflator bottle in  FIG. 2 , taken along line  3 - 3  in the direction of the arrows; 
         FIG. 4  is a cross section view of a portion of the inflator bottle in  FIG. 2A , showing an alternate embodiment of a gas portal with openings of triangular shape; 
         FIG. 5  is a cross section view of a portion of the inflator bottle in  FIG. 2A , showing an alternate embodiment of a gas portal with numerous openings of circular shape; and 
         FIG. 6  shows a graph of inflator bottle internal pressure as a function of time. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with a preferred embodiment, referring to  FIG. 1 , an inflator bottle  10  for releasing a product gas is employed in an airbag system  12  in a vehicle  14  to deploy an airbag or inflatable cushion  16  in the event of a collision to protect an adult occupant  18  sitting in a seat  20  in vehicle  14 . A sensing diagnostic module (SDM) controller  22  is connected to inflator bottle  10 . Inflator bottle  10  is in fluid communication with inflatable cushion  16 . In the example shown in  FIG. 1 , airbag system  12  is located for side protection. In this arrangement, inflator bottle  10  and inflatable cushion  16  are mounted in a headliner  24  of a vehicle interior  26  and sensing diagnostic module controller  22  is mounted underneath an instrument panel  28  in the front of vehicle interior  26 . In a collision event, controller  22  provides a signal  30  to inflator bottle  10  that ignites the combustible gas mixture in inflator bottle  10  and releases product gas to deploy inflatable cushion  16  protecting occupant  18 . Alternately, the inflator bottle may be employed in a frontal airbag system that protects driver and passenger occupants in the event of frontal collisions. 
     Referring to  FIGS. 2-5 , inflator bottle  10  includes a housing  32  that defines a compartment  34 . Compartment  34  is divided into a first region  36  and a second region  38  by a partition  40 , which in this embodiment is formed by a tube  42  having a wall  44  symmetrical about a longitudinal axis A. Alternately, partition  40  may be a wall that bisects compartment  34  and is attached to housing  32 . First region  36  is an interior region defined by wall  44  and second region  38  is an exterior region surrounding wall  44  of tube  42  within housing  32 . As shown in  FIG. 2 , first region  36  is smaller by volume than second region  38 . Preferably, the volume in first region  36  is less than or equal to about 7% of combustible gas mixture contained in compartment  34  of inflator bottle  10 . Housing  32  is preferably formed of a metal, but could be formed of polymeric or other material that is gas impermeable so the combustible gas mixture does not escape through the housing  32  of inflator bottle  10  before activation of the combustible gas mixture, yet capable of containing gas at high pressures and temperatures associated with combustion of the combustible gas mixture. Tube  42  is preferably formed of a metal, but could be formed of polymeric or other material that is gas impermeable so combustion of the combustible gas mixture is contained with first region  36  along with the pressures and temperatures associated with combustion of the combustible gas mixture. Tube  42  is welded to first axial end  50  of inflator bottle  10 . 
     Partition  40  includes a gas portal  46  providing fluid communication between first region  36  and second region  38 . Gas portal  46  comprises one or more openings  48 . As shown in  FIGS. 2-2A , openings  48  are circular having a diameter that is a maximum dimension d for the circular shape. Preferably, maximum dimension d is less than or equal to about 7 millimeters. As used herein, the total portal area of gas portal  46  refers to the sum of the areas of the openings  48  comprising gas portal  46 . 
     A first axial end  50  comprises a nozzle  52  having an orifice or passage  54  disposed in first region  36  within tube  42 . Tube  42  is welded to housing  32  at end  50 . Nozzle  52  is welded to first axial end  50 . Passage  54  communicates with first region  36  for releasing product gas from first region  36  of compartment  34 . As used herein, the cross section area of passage  54  is defined by the minimum cross section area through which product gas flows to exit first region  36  out through nozzle  52 . As shown in the example in  FIG. 2 , the minimum cross section area through which product gas flows to exit first region  36  through nozzle  52  is defined by the cross section area perpendicular to axis A of the space defining passage  54 . 
     A burst disk  56  is disposed over passage  54  at end  50  within first region  36 . Burst disk  56  is effective to contain combustible gas mixture in compartment  34  and prevent product gas from leaving first region  36  in compartment  34  through nozzle  52  until burst disk  56  is ruptured after combustion is initiated. First region  36  defines a volume of combustible gas mixture in an amount sufficient to produce product gas having a pressure effective to rupture burst disk  56 . After combustion is initiated in first region  36 , pressure builds in first region  36  to a level effective to rupture burst disk  56 . Once burst disk  56  ruptures, product gas is released through passage  54  of nozzle  52 . The amount of unreacted combustible gas mixture released with the product gas through passage  54  after rupture of burst disk  56  less than or equal to the volume of combustible gas mixture contained within first region  36 . 
     A second axial end  58  comprises an igniter  60  disposed in first region  36  opposite nozzle  52  at first axial end  50 . Igniter  60  is effective to initiate combustion of combustible gas mixture to produce product gas. A suitable igniter is a pyrotechnic igniter that generates sufficient heat to initiate a chemical reaction in the combustible gas mixture. Alternately, the igniter may produce an electric spark to ignite the combustible gas mixture. An ignition point  62  on igniter  60  is adapted to produce an electric spark to produce a flame front that initiates combustion of the combustible gas mixture. The flame front travels at a flame speed in first region  36  defined by tube  42 . As combustion is initiated and confined to first region  36 , a smaller igniter  60  that fits within the internal diameter area of tube  42  may be utilized. Tube  42  may be flared (not shown) at an end opposite first axial end  50  and fitted over igniter  60  during manufacturing. 
     Gas portal  46  is disposed on tube  42  intermediate nozzle  52  at end  50  and igniter  60  at end  58  within compartment  34 . As shown in  FIG. 2 , gas portal  46  including the openings  48  in gas portal  46 , have a distance D from the ignition point  62  of igniter  60  that is less than or equal to about 50% of the total length of tube  42 . Preferably, the openings  48  of portal  46  are greater than or equal to about 3 millimeters from ignition point  62  to prevent igniter enclosure material about igniter  60  from blocking the openings  48  after igniter  60  ignites. 
     A combustible gas mixture is contained in compartment  34  of inflator bottle  10 . Combustible gas mixture is combustible to form product gas. A suitable combustible gas mixture comprises hydrogen, oxygen, argon, and helium gases. The combustible gas mixture regulates the combustion reaction rate within first region  36  and generates product gas that exits nozzle  52  to fill inflatable cushion  16 . 
     Housing  32  includes a fill port  64  to fill inflator bottle  10  with combustible gas mixture. As shown in  FIG. 2 , fill port  64  is in communication with second region  38  of inflator bottle  10 . As combustible gas mixture is injected into inflator bottle  10  at fill port  64 , combustible gas mixture fills second region  38  and flows into first region  36  through openings  48  of gas portal  46 . 
     During operation, in the absence of a crash event, inflator bottle  10  in a non-active state with burst disk  56  containing combustible gas mixture within compartment  34 . If a vehicle collision event occurs, controller  22  senses the collision event and sends signal  30  to activate inflator bottle  10 . Signal  30  ignites igniter  60  to produce an electric spark in the combustible gas mixture that results in a flame front within first region  36 . When igniter  60  ignites, combustion is confined to first region  36  by tube  42 . The flame front propagates towards nozzle  52  combusting combustible gas mixture along the flame front producing product gas. As flame front proceeds past gas portal  46 , combustion moves through openings  48  of gas portal  46  into second region  38  about openings  48 . As combustion proceeds past gas portal  46  in first region  36  towards nozzle  52 , the pressure in first region  36  builds to a level effective to rupture burst disk  56  blocking passage  54 . As product gas is produced and pressure effective to rupture burst disk  56  in first region  36  is attained, burst disk  56  ruptures in response to the pressure releasing product gas through passage  54  and out nozzle  52 . 
     Once burst disk  56  ruptures and product gas is released, combustible gas mixture in second region  38  of compartment  34  flows from second region  38  through openings  48  in gas portal  46  into first region  36 . Any incidental combustion about openings  48  is also drawn into first region  36  and flame front settles at a location F in first region  36  intermediate nozzle  52  and gas portal  46 . The flame front settles at location F as passage  54  in nozzle  52  in relation to openings  48  of gas portal  46  is sized and shaped to release product gas at a rate sufficient to draw combustible gas mixture from second region  38  through gas portal  46  into first region  36  at a rate greater than the flame speed of the flame front. The flame front is maintained in first region  36  intermediate nozzle  52  and gas portal  46  and product gas continues to release through passage  54  of nozzle  52  until the combustible gas mixture is consumed in compartment  34 . Since the flame front is maintained at location F in first region  36 , combustion is prevented from reaching second region  38  through openings  48  in gas portal  46  or propagating out through nozzle  52 . 
       FIG. 6  shows a graph contrasting the inflator bottle internal pressure (psi) over time (seconds) for an inflator bottle that includes a partition that is a tube according to the present invention and an inflator bottle of comparable size and shape with no tube partition. As shown in  FIG. 6 , the inflator bottle that includes the partition that is a tube contains the combustion within the first region and shows a lower maximum pressure over time versus an inflator bottle with no partition that contains the combustion within the housing. 
     While not limited to any particular theory, it is believed that, upon ignition of the combustible gas mixture by the igniter, a flame front is formed in the first region and propagates along the tube to a location F in the first region after the rupture of the burst disk. It is desired to maintain the flame front at location F in the first region and prevent it from propagating out of the nozzle at the first axial end or retreating out the gas portal on the partition and into the second region. For this purpose, the total portal area of the openings of the gas portal to the minimum cross section area of the passage in the nozzle is adjusted to have a ratio that is less than or equal to about 8:1. The ratio is preferably less than 5:1 and more preferably, between about 1.5:1 and 3:1. A ratio that is less than or equal to about 8:1 is effective to provide adequate flow of the combustible gas mixture from the second region into the first region and not so great as to allow large combustion reaction to occur outside of the first region. Moreover, the openings in the gas portal have a maximum dimension d that is less than or equal to about 7 millimeters to effectively allow the combustible gas mixture to flow from the second region into the first region at a velocity and a mass flow rate that is compatible with the minimum cross section area of the passage and not so great to allow combustion to occur outside of the first region. Preferably, the maximum dimension d is between about 3 and 7 millimeters. In general, it is preferred to locate the gas portal including the openings of the gas portal within distance D of the ignition point of the igniter that is less than or equal to about 50% of the total length of the partition in millimeters to establish an initial stable combustion and not so great to establish initial stable combustion that occurs outside of the first region into the second region or out through the nozzle after rupture of the burst disk. Additionally, the first region preferably contains a volume of combustible gas mixture that is less than or equal to about 7% of the combustible gas mixture in the compartment that is sufficient to establish and maintain combustion of the combustible gas mixture in the first region and not so great as to enable a large quantity of unreacted combustible gas mixture to be released along with product gas from the first region through the passage in the nozzle after rupture of the burst disk before combustion is fully established in the first region. Preferably, the volume in the first region is between about 4% and 7% of the total gas volume of the compartment. 
     Thus, this invention provides an inflator bottle that is reliable to provide a sustained release of product gas over a longer time interval. Containing combustion within the interior region surrounded by the wall of the tube allows for a more controlled combustion in the compartment, thus reducing the pressure build-up in the exterior region of the inflator bottle along the housing wall and lowering the combustion temperature of the inflator bottle. A lower maximum pressure within the compartment allows for a thinner housing wall to be utilized. A lower internal combustion temperature provides a higher safety factor for vehicle occupants in the interior of the vehicle following a crash event. Utilizing thinner housing walls means less material is needed to manufacture the inflator bottle with a decreased cost. An inflator bottle manufactured with less material has a lower overall weight. Lower inflator bottle weight contributes to a lower vehicle weight allowing for improved vehicle fuel economy desired by vehicle manufacturers. A lighter weight inflator bottle may provide additional packaging options to vehicle manufacturers when integrating the inflator bottle in an airbag system. An inflator bottle utilizing a partition that is a tube may allow a smaller igniter that fits within the inner diameter area of the tube to be utilized to initiate combustion that has less weight and a reduced cost. 
     In the embodiment shown in  FIGS. 2-2A , openings  48  in gas portal  46  are circles. The embodiment in  FIG. 2  also shows four circular openings  48  in gas portal  46 . In an alternate embodiment as shown in  FIG. 4 , a tube  42  may comprise openings  48  in gas portal  46  of triangular shape that have maximum dimension d. In an alternate embodiment shown in  FIG. 5 , gas portal  46  of tube  42  is perforated with numerous openings of circular shape that cooperate to have a total portal area. Alternately, the portal may comprise any number of openings  48  comprising any suitable shape that allows sufficient gas flow into the first region to provide combustible gas mixture for the flame front at a rate effective to maintain the flame front within first region  36  that is governed by the relationship of the ratio of the total portal area of the portal  46  to the minimum cross section area of passage  54  is less than or equal to about 8:1. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.