Patent Publication Number: US-6659009-B1

Title: Drilled-in filter for gas generating initiator

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates in general to gas generating initiators and in particular to gas generating initiators including a filter that prevents large particles from entering the generated gas stream. 
     FIG. 1 is a sectional view of a prior art gas generating initiator  10 . Initiator  10  may be used in applications such as the launching of sonobuoys from aircraft, ejector seats in aircraft and the initiation of ballistic munitions. 
     Initiator  10  includes a generally cylindrical body  12  that defines an initiator chamber  14 . The body  12  is open at one end  11  and closed at a second end by a base  13 . The body  12  has a central longitudinal axis A—A. The base  13  includes a generally centrally located passage  15 . Passage  15  has one end on an interior surface  17  of the base and a second end on an exterior surface  19  of the base. A longitudinal axis of the first passage  15  is substantially coincident with the axis A—A of the body  12 . Adhesive is applied to the threads of a filter  30 , discussed in more detail below, which is then threaded into passage  15 . Body  12  and filter  30  may be made of, for example, aluminum, aluminum alloy, steel or steel alloy. 
     Initiator  10  includes a charge holder  16  disposed in the open end  11  of the body  12 . The charge holder  16  includes a consumable membrane  18  at one end and gas generating propellant  20  disposed in the charge holder  16 . Charge holder  16  may be made of plastic and snap fit into chamber  14 . Consumable membrane  18  may be made of nitrocellulose. A cap  22  is attached to the open end  11  of the body  12 , by, for example, threaded engagement. An igniter  24  is disposed in an opening in the cap  22  and extends into the charge holder  16 . The igniter  24  ignites the propellant  20  in the charge holder  16 . A firing mechanism  26  is connected to the igniter  24  for firing the igniter. The firing mechanism may be activated, for example, manually or by a variety of switches, such as inertial switches, accelerometers, etc. 
     In ballistic applications, gas exiting the passage  15  is routed to a munition by using a nipple  28  attached (for example, with threads) to the base end  13  of the initiator body  12 . The nipple  28  includes a passageway  29  therethrough to provide a conduit for gas generated by the initiator. 
     FIGS. 2 a - 2   c  show details of a prior art filter  30 . FIG. 2 a  is a top view of the filter  30  showing a hexagonal head  32 . FIG. 2 b  is a sectional view along the line b—b of FIG. 2 a . FIG. 2 c  is a sectional view along the line c—c of FIG. 2 b . Head  32  is joined to a shank  34 . The shank  34  is threaded and threads into passage  15 . Head  32  includes five radial gas passages  36  that intersect in the center of head  32 . The five radial passages  32  join an axial passage  38 . 
     In use, the initiator  10  is operated by firing the firing mechanism  26  which sends an electric signal to igniter  24 . Igniter  24  ignites propellant  20  thereby generating gas. Consumable membrane  18  bursts and/or burns and the generated gas enters the filter  30  via the five radial passages  32 , then enters the axial passage  38  and then exits the initiator via passage  15 . The radial passages  32  in filter  30  are small enough to prevent any large particles of propellant or pieces of charge holder  16  from entering passage  15 . 
     Because of the relatively small size of initiator chamber  14  (diameter may be as small as 0.035 inches), it is difficult to machine the even smaller filter  30 . In addition, adhesive must be applied to the threads on filter  30  and then the filter must be threaded into the passage  15 . The present invention eliminates the separate filter  30 , thereby saving the time and money of fabricating filter  30  and assembling filter  30  into initiator  10 . 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a gas generating initiator having a drilled-in integral multi-port filter. 
     It is another object of the invention to provide a gas generating initiator with fewer parts than the prior art to thereby simplify manufacture and assembly. 
    
    
     The invention will be better understood, and further objects, features, and advantages thereof will become more apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
     FIG. 1 is a sectional view of a prior art gas generating initiator. 
     FIG. 2 a  is a top view of a prior art filter. 
     FIG. 2 b  is a sectional view along the line b—b of FIG. 2 a.    
     FIG. 2 c  is a sectional view along the line c—c of FIG. 2 b.    
     FIG. 3 is a partial section view of an initiator according to the invention. 
     FIG. 4 is a bottom view of the body of the initiator of FIG.  3 . 
     FIG. 5 is a top view of the body of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention includes a drilled-in integral multi-port filter that reduces the number of parts in an initiator. The reduction in parts simplifies manufacture and assembly. The separate filter  30  described above is eliminated. In its place are drilled-in holes in the base of the initiator body. FIG. 3 is a partial section view of an initiator  50  according to the invention. The separate filter  30  is eliminated. With the exception of the body  52 , the other parts of the initiator  50  (charge holder, consumable membrane, propellant, cap, igniter, firing mechanism and nipple) are as described above with reference to FIG.  1 . 
     The initiator  50  includes a generally cylindrical body  52  that defines an initiator chamber  14  therein. The body  52  is open at one end and closed at a second end by a base  54 . The body  52  has a longitudinal axis B—B. The base  54  includes a generally centrally located first passage  56  therethrough. The first passage  56  has one end on an interior surface  60  of the base  54  and a second end on an exterior surface  62  of the base  54 . A longitudinal axis of the first passage  56  is substantially coincident with the axis B—B of the body  52 . 
     Base  52  also includes a plurality of second passages  58 . The second passages  58  have one end on an interior surface  60  of the base  54  and a second end that intersects the first passage  56  at the second end of the first passage. Longitudinal axes of the second passages  58  form angles C with the longitudinal axis B—B of the first passage  56 . A diameter of the first passage  56  is greater than diameters of the second passages  58 . The number of the second passages  58  may vary, but the number is preferably in a range of two to ten. 
     The angles C between the longitudinal axes of the second passages  58  and the longitudinal axis B—B of the first passage  56  are in a range of about fifteen to about fifty degrees. The diameter of the first passage  56  is in range of about 0.05 to about 0.1 inches. The diameters of the second passages  58  are in a range of about 0.04 to about 0.07 inches. In a preferred embodiment, the diameter of the first passage  56  is about 0.078 inches and diameters of the second passages  58  are about 0.062 inches. 
     It is noted that the larger the angles C between the longitudinal axes of the second passages  58  and the longitudinal axis B—B of the first passage  56 , the smaller the diameters of the second passages  58 . This is required to keep the first passage  56  from becoming too large and allowing large particles to pass. Because of the small size of initiator  50 , the second passages  58  must be drilled in the base  54  from the exterior surface  62  of the base. The diameter of the initiator chamber  14  is in a range of about 0.35 to about 1.5 inches. The diameter and angles C of second passages  58  are selected such that the opening of first passage  56  on the exterior surface  62  remains a circle. That is, the drill bit is inserted in first passage  56  at an angle to drill second passages  58 . 
     FIG. 4 is a bottom view of the base  54  of the body  52  of FIG.  3 . As shown in FIG. 4, only the opening of first passage  56  actually penetrates the exterior surface  62 . FIG. 5 is a top view of the base  54  of the body  52  showing the central first passage  56  and six second passages  58 . 
     While the invention has been described with reference to certain preferred embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.