Patent Document

FIELD OF THE INVENTION 
       [0001]    This invention relates to an igniter assembly with a mechanical piston to open a sealed pressurized inflator for an airbag assembly. 
       BACKGROUND OF THE INVENTION 
       [0002]    Hybrid or pressurized inflation devices, commonly referred to as inflators, have been used to inflate airbags for years. These devices can be combined with gas generant to form a hybrid inflator that releases pressurized gas and simultaneously burns propellant to generate additional inflation gas. 
         [0003]    Alternatively, no propellant or generant can be used in the inflation device and only the pressurized gas stored will be used. 
         [0004]    In both these style inflators, an igniter or squib receives an electrical signal from a crash sensor and the igniter fires to rupture a seal to release the gas and optionally to ignite generant in the hybrid inflators. 
         [0005]    To improve reliability, mechanical devices can be used to break a seal as taught in U.S. Pat. No. 5,076,607; U.S. Pat. No. 5,462,307 and U.S. Pat. No. 5,584,505; all using a mechanical piston. These pistons will reliably break a seal during impact, but can cause an erratic release of gases when the piston is moved into an opening blocking arrangement with the diffuser passages. This can cause an obstruction in one or more openings which can result in a problem with uniform gas flow and create thrust effects not anticipated in a normally thrust neutral diffuser. To avoid this, the diffuser has been positioned on a side or even at a far end. However, this makes the inflator bulky or longer than otherwise needed. 
         [0006]    The present invention overcomes these short comings in a simpler and more efficient manner, that not only avoids any chance of an obstruction of flow openings, it also allows the inflator to use higher pressures and less expensive gases. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention has an inflator housing, a diffuser, a frangible closure and an igniter assembly. 
         [0008]    The inflator housing stores inflation gases under pressure. The frangible closure seals the pressurized inflation gas inside the inflator housing. The diffuser has a plurality of holes for directing gas flow. 
         [0009]    The igniter assembly has an igniter housing, a squib electrically actuated and fitted in an end of the igniter housing and a retractable piston affixed to the igniter housing. Upon actuation of the squib, the retractable piston propels impacting and breaking the frangible closure releasing gases pushing the piston retractably back into or over the igniter housing as the pressurized gas releases out of the diffuser. 
         [0010]    The igniter assembly has the igniter housing configured to accept the squib at one first end. The squib has electrical connectors extending to attach to wiring connections for actuating the squib. The assembly is affixed to an end of the diffuser and has the retractable piston attached to the igniter housing at a second end opposite the first end and aligned with the frangible closure. The igniter housing has an open passage or chamber between the squib and the retractable piston. The retractable piston is adapted to fit into the chamber internally or over the chamber externally closing the chamber at said second end. 
         [0011]    The retractable piston has a striker or impact portion of a decreasing diameter. The impact portion extends from the base at the igniter housing to an impact end or tip. The impact portion has a length of at least a few millimeters. On assembly, the impact end is fixed a distance (d) from a rupture portion of the frangible closure. The retractable piston has a hollow venting sleeve portion sized to fit over the igniter housing or, preferably, to fit inside the chamber of the igniter housing. The sleeve portion and the igniter housing can be formed as cylindrical tubes sized to fit together on assembly. The sleeve portion extends from the base of the piston and has a length (e) greater than the distance (d) between the impact end and the rupture portion of the frangible closure. This allows the piston to be propelled by the firing of the squib to rupture or break the frangible closure on impact and to travel a distance less than (e) while being stopped by the ruptured closure or inflator housing. This control of impact and distance of travel keeps the sleeve at least partially over or in the igniter housing. The sleeve has one or more, preferably two, vent holes to release the gas pressure generated by the squib. As that gas is vented outwardly, the pressurized inflator gas pushes the piston back over or into the igniter housing to a retracted position. 
         [0012]    The retractable piston is guided by the igniter housing and remains centered in the inflator at the diffuser location. This prevents the retractable piston from dislodging and being an obstruction to any gas flow opening. 
         [0013]    In a preferred embodiment, the retractable piston may include peripheral slots at or near the base, these slots provide a means to hold the piston and igniter housing locally in a press fit to allow a more predictable separation when the squib is activated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0015]      FIG. 1  is a plan view of the inflator of the present invention showing in cross section the portions of the igniter assembly, the diffuser and frangible closure. 
           [0016]      FIG. 2  is a cross-sectional view of the diffuser and igniter assembly of the present invention. 
           [0017]      FIG. 3  is a perspective view of the diffuser and igniter assembly of the present invention. 
           [0018]      FIG. 4  is a cross-sectional view of the diffuser. 
           [0019]      FIG. 5  is a perspective view of the frangible closure. 
           [0020]      FIG. 6A  is a perspective view of the top of the retractable piston. 
           [0021]      FIG. 6B  is a perspective view of the retractable piston looking in the open end of the sleeve portion. 
           [0022]      FIG. 6C  is a plan view of the retractable piston. 
           [0023]      FIGS. 7A-7C  show how the piston moves on actuation without dislodging from the igniter housing. 
           [0024]      FIG. 8  is an alternative embodiment wherein the retractable piston fits over the igniter housing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    With reference to  FIG. 1 , an inflator is illustrated. The inflator  10  is shown having a pressure vessel  12  into which a pressurized gas is contained and held in the pressure vessel  12  sealed by a frangible closure  40 . As shown, the frangible closure  40  separates the inflation gases from a diffuser  30  and an igniter assembly  20 . The igniter assembly  20 , as illustrated, has a squib  60  with electrical connectors  62  that can be attached to wiring connectors to receive an electric signal to activate the squib  60 . The igniter assembly  20  further has an igniter housing  22 ; placed inside the igniter housing  22  is a retractable piston  50 , as illustrated. 
         [0026]    The entire assembly is firmly fixed in the diffuser  30  as further shown in  FIG. 2 . In  FIG. 2  a partial cross-sectional view is taken wherein the igniter housing  22  has been cut away exposing the retractable piston  50  and a portion of the squib  60 . Externally surrounding the igniter assembly  20  in  FIG. 2  is shown a wire mesh filter screen  70 . This filter screen  70  will trap any propellant or debris that projects from the diffuser  30 . 
         [0027]      FIG. 3  is a perspective view of the igniter assembly  20  fully assembled showing the igniter housing  22  with the retractable piston  50  inserted inside a chamber and fixed thereto in such a fashion that the entire assembly makes one compact device for rupturing the frangible closure  40 . 
         [0028]    With reference to  FIG. 4 , the diffuser  30  is shown having a plurality of openings  32  which allow for gases to be vented to fill an airbag, for example. The diffuser  30  has a large end  34  pressure vessel  12  that is rolled about an adjacent end of the igniter housing  22 . At an opposite small end  36  of the diffuser  30  is an opening  36   a . End  26  is inserted into an open end of the pressure vessel  12 . This construction securely mounts the diffuser  30  to the pressure vessel  12 ; the diffuser  30  can be welded or otherwise secured to the pressure vessel  12  at the location shown at location  14 . 
         [0029]    With reference to  FIG. 5 , the frangible closure  40  is shown in a perspective view having a flange  42  which fits over the diffuser as illustrated in  FIGS. 1 and 2 . This flange  42  seals against the diffuser  30  and prevents gases from being released from the housing prematurely. As shown, the frangible closure  40  extends inwardly into the diffuser  30  having a cylindrical portion  44  extending into the diffuser  30  with a conical portion  46  extending to a rupture portion  48 , the rupture portion  48  being of a diameter sufficiently small that it enables the frangible closure  40  to be easily broken on impact by the retractable piston  50  upon actuation of the squib  60 . As illustrated, the frangible closure  40  provides a unique mechanical structure that is able to absorb the impact load of the retractable piston  50  in such a way that the rupture portion  48  breaks cleanly upon impact, but prevents the piston  50  from moving any further due to the structural integrity of the remaining portion of the frangible closure  40 . 
         [0030]    With reference to  FIGS. 6A, 6B and 6C , the retractable piston  50  is shown. The retractable piston  50  has a cylindrical sleeve  52 . The cylindrical sleeve  52  has a plurality of openings  54  which allow gases generated by the squib on actuation to vent out from inside the sleeve  52  thereby reducing internal pressure and allowing the retractable piston  50  to be  [KM1] moved by the pressurized gas leaving the pressure vessel  12  when the rupture occurs at the frangible closure  40 . The impact end  55  of the retractable piston  50  is sized of a diameter to correspond with the rupture portion  48  of the frangible closure  40 . As shown, the diameter is slightly smaller than the rupture portion  48 , therefore on impact, the retractable piston  50  can enter into the frangible closure  40  a short distance. As shown, the impact end  55  is somewhat cylindrical then flares out to an increasing diameter to the base portion  58  of the retractable piston  50 . Around the outer periphery of the base portion  58  is a projecting ring  59 . This projecting ring  59  as shown fits tightly into the igniter housing  22  in a press fit relationship such that when the squib  60  is activated, this portion of the device holding the piston  50  and igniter housing  22  together are overcome by the pressure allowing the retractable piston  50  to propel forward to break the frangible closure  40 . As shown, when the closure  40  is broken the piston  50  limits the amount of travel due to the increasing diameter along the curved or conical section  57  between the base  58  and the end  55 . This stops the device from extending any further than a fixed distance. Once this distance is achieved, the piston  50  stops. As the retractable piston  50  is moving forward the openings  54  are exposed as the piston  50  moves relative to the igniter housing  22 . As the openings  54  are exposed, internal gases are released, and as previously described, allows the piston  50  to be retracted due to the oncoming inrush of gases from the pressure vessel  12  into the diffuser  30 . Since the retractable piston  50  never leaves contact with the internal surface of the igniter housing  22 , it is perfectly centered and upon the release of stored gas [KM2]  will move back into its original or close to its original position inside the igniter housing  22 . This ensures that the retractable piston  50  cannot become dislodged or move into a position to block any of the openings  32  of the diffuser  30 . This uniquely allows the diffuser  30  to operate with high reliability of performance without causing any unusual obstructions on the gas flow emitted from the hybrid or gas filled inflator. 
         [0031]      FIGS. 7A, 7B and 7C  show a view of the igniter assembly  20  with the piston  50  as described above fitted into the igniter housing  22  and show the distance (d) between the frangible closure  60  and the impact end  55 . In step one,  FIG. 7A , pre-ignition of the squib  60 , the inflator  10  is shown in its fully loaded position. Upon actuation of the squib  60  the propellant in the squib  60  pushes the retractable piston  50  forward, see  FIG. 7B , breaking the rupture portion  48  of the frangible closure  40 . Gases generated by the squib propellant are ejected through the openings  54  in the sleeve  52  of the retractable piston  50  as the impact end  55  of the piston  50  penetrates through the frangible closure  40 . As the gases expel from inside the igniter housing  22 , and retractable piston  50  experiences a drop in pressure inside the pressure vessel  12 , the inflation gases push the retractable piston  50  back, see  FIG. 7C , into the igniter housing  22  back into a fully or almost fully retracted position; at this point the inflation gases are also being displaced and released through vent openings  32  of the diffuser  30  to inflate an airbag (not shown). As illustrated, the retractable piston  50  never leaves contact with the igniter housing  22  and as such it is completely centered throughout the actuation process. This ensures that the entire igniter assembly  20  can perform its function of penetrating and breaking the rupture portion  48  of the frangible closure  40  caused by the impact of the retractable piston  50  which is then pushed back into the housing concentrically in such a fashion that it cannot block any of the diffuser openings  32  or impede any of the gas flow as shown. 
         [0032]    With reference to  FIG. 8 , an alternative embodiment of the present invention is shown where the retractable piston  50  is mounted over the external surface of an igniter housing  22  in such a fashion that the igniter housing  22  acts as a cylinder post or guide for the retractable piston  50  to sit over. The function is basically the same as that of the other igniter housing  22 , as it also prevents the retractable piston  50  from dislodging from the igniter housing  22  and therefore prevents any potential obstruction of the diffuser gas vent openings  32 . 
         [0033]    With further reference to  FIG. 7 , it is important to notice the gap between the impact end  55  of the retractable piston  50  and the frangible closure  40  is set a distance (d). The sleeve  52  has a length extending a distance (e). The distance (e) is substantially longer than the distance (d), therefore, on penetration of the rupture portion  48 , the surface  57  of increasing diameter between the base  58  and the impact end  55  of the retractable piston  50  pushes against the closure  40  as previously described. This prevents further movement and limits that movement such that it is always less than the dimension (e). In these circumstances, the pressure applied from the inside of the inflator  10  pushes against the piston  50  forcing it back into or over the igniter housing  22  as previously discussed. 
         [0034]    As shown, it is important to note the closure  40  shape and the piston impact end  55  have been designed in such a way that the closure  40  is not just a semi-sphere or a dome, but it contains a flat area in the top to be impacted by the piston end  55  and a conical area  57  immediately after. This flat area must be in the path of the end  55  impacting the flat area in the closure  40  to rupture in and bend a circular corner where the material is weaker due to the stamping stress, so to detach systematically as a regular disk. Then the piston penetrates inside the closure  40 , through the radius between end  55 , and piston body  50  is able to deform the cone in the opposite side stressing the second circular corner up to the detachment of a crown, which often remains trapped in the piston end  55 . In conclusion, the piston  50  normally detaches from the closure  40  the central disk and a crown which can be a full crown or fractured crown. The idea is to generate a standard behavior in the opening mechanism, reducing the fragmentation of the closure  40  to avoid projection of metal particles. 
         [0035]    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.

Technology Category: b