Abstract:
An inflator for producing inflation gas from a propellant has a housing for storing the propellant, a diffuser for attachment to the inflator housing and a sealing member. The diffuser has one or more open passages for passing inflation gas upon ignition of the propellant and a plurality of sealed passages oriented opposite to the one or more open passages. The sealing member covers the sealed passages. The sealing member is consumed when exposed to an open flame thereby opening the sealed passages to vent inflation gases opposite the opposed one or more open passages to create a thrust neutral exhaust upon an inadvertent ignition of the propellant due to exposure to fire.

Description:
FIELD OF THE INVENTION 
     This invention relates to an inflator assembly particularly a propellant filled inflator assembly with a diffuser or endcap attached that provides a safer shipping and storage feature in the event of a fire. 
     BACKGROUND OF THE INVENTION 
     Inflation of a typical airbag cushion in a vehicle is achieved by igniting a propellant stored in an inflator. Once ignited, the propellant rapidly generates large volumes of gas which fill the airbag inflating the cushion to protect the vehicle occupants. These devices are credited for saving numerous lives in the event of a vehicle crash. 
     During the manufacture of these propellant filled inflators, special care is used to insure proper handling and safety precautions are followed to avoid inadvertent ignition of the propellant. 
     Once assembled, the inflators laden with propellant are moved to an assembly location wherein the inflator can be placed in a module housing along with the airbag cushion. In the case of a side curtain airbag, the inflator may be attached to a fill tube connected to a curtain airbag or directly to the cushion. Alternatively, the inflators could be boxed and stored for later assembly or shipment. In any event, large numbers of the inflators are routinely shipped and transported to vehicle assembly plants. 
     It is during storage and transportation that these propellant filled inflators can pose a risk in the event of an inadvertent ignition. The situation is generally remote, but in the event of a fire in shipping or storage, the propellant could be ignited causing a release of gases which could cause a condition of high thrust making the unrestrained inflator a projectile or missile causing a risk to personnel standing nearby or those trying to put out the fire. 
     As a result of this risk, the United States Department of Transportation requires inflators to be subjected to a bonfire test wherein the inflator when placed directly in a fire cannot become a projectile upon ignition of the stored propellant. 
     To pass this test, inflator manufacturers have devised ways to balance the exhausting gases to create a “thrust neutral” or “zero thrust” inflator. 
     In U.S. Pat. No. 7,938,443 B a patent entitled “Shipping Safe Inflator For An Airbag Module” discloses a distal end portion of an inflator with a thrust balancing feature having a plurality of elongated secondary apertures with deflection vanes open to exhaust the gases in a thrust balance configuration. This distal end can discharge gases exiting along the axis through the primary discharge opening and the elongated secondary passages redirect part of the flow longitudinally aft oppositely directed to cancel thrust and has a plurality of radially oriented openings to exhaust more of the gas radially in such a fashion the inflator has no thrust capability due to inadvertent ignition. 
     Others have simply designed inflators with a plurality of holes radially around the circumference of a housing to create a thrust neutral inflator. This technique is most simple and easy to employ in passenger side inflators and other applications wherein the inflator is stored in a housing assembly. 
     In side curtain airbags, the inflator is generally not in a module housing, but is secured directly onto the vehicle along with the airbag curtain connected via a hose or tubing assembly. In this case, the inflator needed to be designed in such a way that the propellant gases are captured to fill the curtain. Ideally the gases are not lost or vented to atmosphere to achieve a thrust neutral condition when in use. This is true because to vent large amounts of the inflation gases means even more propellant must be used so the remaining captured gases are sufficient to fill the airbag. Accordingly, to insure the inflator achieves a thrust neutral balanced exhaust when exposed to fire during shipping and storage, but when assembled for normal use this safety feature does not waste the inflation gases a new a superior way to manufacture a thrust neutral inflator assembly is needed. Preferably, the new way is accomplished in a cost efficient and very reliable way. These and other beneficial objectives are satisfied by the present inventive design described herein. 
     SUMMARY OF THE INVENTION 
     An inflator  30  for producing inflation gas from a propellant  31  has a housing for storing the propellant  31 , a diffuser  10  for attachment to the inflator  30  housing and a sealing member  20 . The diffuser  10  has one or more open passages  14  for passing inflation gas upon ignition of the propellant  31  and a plurality of sealed passages  12  oriented opposite to the one or more open passages  14 . The sealing member  20  covers the sealed passages  12 . The sealing member  20  is consumed when exposed to an open flame thereby opening the sealed passages  12  to vent inflation gases opposite the opposed one or more open passages  14  to create a thrust neutral exhaust upon an inadvertent ignition of the propellant  31  due to exposure to fire. The plurality of sealed passages  12  have an area relative to the area of the opposed one or more open passages  14  of the diffuser  10  balanced in size to ensure thrust neutrality. The sealed passages  12  are four or more openings in the diffuser  10 . The sealed openings  12  are one of circular, square, rectangular, triangular holes or rectangular slots or any combination of these shapes covered by the sealing member  20 . 
     The sealing member  20  is preferably made of a thermo plastic or elastomeric material. The material from which the sealing member  20  is made is consumed by exposure to flame. 
     The diffuser  10  is made of metal. The diffuser  10  has an inlet portion of circular cross section  15  having an open inflation channel  1  and the sealing member  20  is attached internally along an arcuate segment of an internal surface  11  of the diffuser  10 . The sealing member  20  has a yield strength, an ultimate strength and a percent elongation set to exceed the inflation pressure and temperatures of the ignited inflator  30  in normal use of inflating an airbag. The sealing member  20  when assembled into the diffuser preferably has at a minimum a yield strength of 33 MPa, ultimate strength of 35 MPa and percent elongation of 50 percent. The sealing member  20  can withstand the maximum inflation pressure and maximum temperature generated by the normally ignited inflator  30  without losing seal integrity in the absence of exposure to external flames or fire related temperatures which are adapted to consume the sealing member  20  exposing the sealed passages  12  . The sealing member  20  when assembled into the diffuser  10  preferably can withstand 2600 psi at 90 degrees C. The sealing member  20  material can be DELRIN 100 NC010, an acetal material. 
     The sealing member  20  has a plurality of short cylindrical projections  21  adapted to plug the sealed passages  12 ; and wherein two or more of the projections  21  are used to secure the sealing member  20  to the diffuser  10 . Preferably, the two or more projections  21  extending through the openings  12  of the diffuser  10  are heat staked or ultrasonically welded  23  onto the diffuser  10  to secure the sealing member  20 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described by way of example and with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of the inflator with a thrust neutral diffuser according to the present invention with a plurality of sealed passages sealed by a sealing member. 
         FIG. 2  is a perspective view of the igniter delay cartridge device of the present invention. 
         FIG. 3  is a perspective view of the diffuser showing the sealing member attached to the internal surface of the diffuser. 
         FIG. 4  is a perspective view of the sealing member. 
         FIG. 5  is perspective view of an alternative construction showing an endcap of the present invention. 
         FIG. 6  is a view of the present invention inflator with a flame consumable sealing member in the diffuser shown in a side curtain airbag application. 
         FIG. 7  is a second view of the present invention inflator with a flame consumable sealing member in the diffuser used in a vehicle seat for connection to an inflatable seatbelt. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , an inflator  30  is shown with a diffuser  10  attached to a discharge end  33  of the inflator  30 . The inflator  30  has a longitudinal shaped housing  32  inside of which is stored a solid propellant  31  for generation of inflation gases for filling an airbag cushion. The propellant  31  is ignited by an ignition device (not shown) that can be activated in the event of a vehicle crash. The overall structure of the inflator  30  can be of any style or shape as long as it has a discharge end  33  to which the diffuser  10  can be securely attached. 
     As shown, the diffuser  10  has a cylindrical inlet end  15  which surrounds and is secured onto the discharge end  33  of the inflator  30 . Once assembled, the inflator  30  and diffuser  10  become one assembly. 
     As illustrated in  FIG. 2 , the diffuser  10  has a plurality of passages or holes  12 . As shown, the holes  12  are circular openings. Alternatively, the passages or openings  12  can be configured square, triangular, rectangular holes or open slots or any combination of these. Along a 180 degree opposite orientation to the plurality of openings  12  is shown a cylindrical discharge portion  10 A of the diffuser  10 . This discharge portion  10 A has an opening or passageway  14  which is orthogonal to an axis of the inflator  30  and upon ignition of the propellant  31 ; the generated gases are directed into the inlet end  15  of the diffuser  10  along an inlet channel  1  and turned along the passageway  14  which is connected to a tube airbag assembly or directly on an airbag to inflate it. 
     As shown in  FIGS. 1 and 3 , the plurality of openings  12  are closed and sealed by a sealing member  20 . This sealing member  20  is designed to keep the openings  12  sealed even under normal ignition of the inflator  30 . In this way all the generated inflation gases are directed to fill the airbag cushion and virtually none of these gases are lost to atmosphere. This feature enables the inflator  30  to be filled with only the necessary amount of propellant  31  needed to fill the cushion. The sealing member  20  as shown in  FIG. 3  is arcuately shaped and closely seals itself along the interior surface  11  of the diffuser  10 . As shown in  FIG. 3 , the diffuser  10  has a closed end  17 . Accordingly, this forces the inflation gases to turn in the direction of passage  14 . 
     As shown in  FIG. 4 , the sealing member  20  is molded or otherwise formed with an arcuate shaped base  25  and projecting outward from the base  25  and projecting outward from the base  25  are a plurality of projections  21 ,  23  shaped to correspondingly fit into the passageways  14  of the diffuser  10 . In the preferred embodiment two or more of the projections  23  are diagonally opposed and shown extending further than projections  21 . These projections  23  can be used to secure the sealing member  20  tightly to the diffuser  10  as shown in  FIG. 1  the projections  23  can be heat staked or ultrasonically welded to the diffuser opening  12 . 
     As further illustrated in  FIG. 4 , the gas inflation pressure is demonstrated by the arrows  100  radially striking the inside surface  27  of the sealing member  20 . When assembled to the diffuser  10  the base  25  is fully supported by the diffuser  10  along the inner surface  11  except at the sealed passages  12 . The sealing member  20  is designed to withstand this pressure and temperature without rupturing or losing seal integrity. Nevertheless, the sealing member  20  is also designed to be easily and rapidly consumed when exposed to fire. The flames generated by fire greatly exceed the temperatures generated by the ignited propellant  31  inside the inflator  30 . This difference in temperature and the fact the flames can rapidly consume the sealing member  20  has enabled the sealing member  20  to rapidly disappear exposing the sealed openings  12  and thus providing a thrust neutral or balanced thrust to be established in the event of exposure to fire. To accomplish this, the total cumulative area of the openings  12  must approximate the open area of the passageway  14  in the discharge channel portion  10 A of the diffuser  10 , preferably the opposing areas are substantially equal. As shown, the diffuser  10  is preferably made of metal of a metal alloy capable of withstanding the heat and pressures exposed during use and in the event of a fire. Metals such as steel or aluminum are generally sufficient. 
     The sealing member  20  similarly must have a strength exceeding the normal use pressures and temperatures, but must be easily and rapidly consumed when exposed to flames in the event of a fire. Thermoplastic or elastomeric materials can satisfy this condition. The sealing member  20  has a yield strength, an ultimate strength and a percent elongation set to exceed the inflation pressure and temperatures of the ignited inflator  30  in normal use of inflating an airbag. The sealing member  20  when assembled into the diffuser  10  preferably has a yield strength of 33 MPa, ultimate strength of 35 MPa and percent elongation of 50 percent. The sealing member  20  can withstand the maximum inflation pressure and maximum temperature generated by the normally ignited inflator  30  without losing seal integrity in the absence of exposure to external flames or fire related temperatures which are adapted to consume the sealing member  20  exposing the sealed passages  12 . The sealing member  20  when assembled into the diffuser  10  preferably can withstand 2600 psi at 90 degrees C. The sealing member  20  material can be preferably made from DELRIN 100 NC010, an acetal material. 
     While the preferred invention shows the thrust balancing feature for shipping can be integrally built into the diffuser  10 , it must be appreciated the diffuser  10  can be substituted with a simple endcap if so desired. 
     In  FIG. 5  an alternative embodiment is shown wherein an endcap  50  has a pair of opposing sealing members  20 . The two opposing sealing members  20  when exposed to flame create the described zero thrust or thrust neutral condition. The endcap is a desirable alternative in applications wherein the airbag inflator does not use a diffuser. This and various other modifications employing the flame consumable sealing member  20  are considered within the scope of the appended claims. 
     With reference to  FIGS. 6 and 7 , the present invention inflator  30  with a diffuser  10  having the sealing member  20  is shown. The  FIG. 6  depicts the inflator  30  mounted in a bracket assembly  72  with a tube or hose  73  connected to the diffuser  10  and extending to an assembly with a curtain airbag module  74  attached to a bracket  76  with a fill tube  75  connected to hose or tube  73 . This results in an assembly  70  that is pre-manufactured at a facility and shipped for later assembly into a vehicle. 
     With reference to  FIG. 7 , the inflator  30  with a diffuser  10  having a sealing member  20  is shown as an inflation assembly  80  for an inflatable seat belt. That assembly  80  includes the inflator  30  mounted in a bracket  82  with the diffuser  10  connected to a tube or hose  81  that extends to a fill tube  83  and secondary seat bracket  84 . The assembly  80  is adapted to be connected to an inflatable seat belt (not shown). The entire assembly  80  is pre-assembled and shipped to a vehicle manufacturing facility for attachment to seat frame  90  as shown. The inflator  30  when assembled and shipped needs the thrust neutral feature provided by the diffuser  10  with a flame consumable sealing member  20 . 
     As shown, the present invention provides a thrust neutral feature in a unique way to insure safe transport, but additionally in the event of a car or vehicle fire the sealing member  20  can also safely provide this thrust neutral feature. It being understood that in the event of a crash preceding a fire, the inflator  30  will already be activated and the airbag properly deployed before the sealing member  20  is consumed. This provides a beneficial fail safe feature that insures the airbags always deploy as designed without having the flame consumable sealing member  20  interfering with deployment. 
     Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.