Abstract:
A modified fluid delivery cartridge. A conventional straight-sided high pressure cartridge case is primed and then filled with solid propellant. A burst cup is inserted in the case mouth. The burst cup is preferably embossed with a cross or other shape to promote predictable rupture. A charge casing is provided which opens into a high pressure cartridge receiver bounded by an inner charge casing wall. The inner charge casing wall is provided with a step, in which the diameter of the high pressure cartridge receiver is reduced. The high pressure cartridge case is pressed into the receiver in the charge casing wall. As the high pressure cartridge case is being pressed into place, the straight wall of the case passes over the step in the inner charge casing wall, which deforms the straight wall to form a neck. This neck captured the burst cup within the high pressure cartridge case.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       MICROFICHE APPENDIX 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    This invention relates to the field of propellant gas delivery systems. More specifically, the invention comprises an improved energy delivery cartridge with a burst cup that allows controlled discharge of the propellant gases generated within said cartridge. The invention further comprises a method for forming said improved energy delivery cartridge during an assembly process. 
         [0006]    2. Description of the Related Art 
         [0007]    Although the present invention can be applied to any application requiring the use of metered propellant gases, it was primarily developed as part of a propellant system for launching 40 mm grenades (such as the U.S. Army&#39;s M433). The invention is an improvement to a prior design reduced to practice by the same inventor. The prior design is disclosed and claimed in U.S. Pat. No. 7,004,074 to Van Stratum (2006), which is hereby expressly incorporated by reference. 
         [0008]    Metallic cartridges have been used to encapsulate solid propellants for many years. In recent years other materials have been substituted for the traditional brass, but the principles of operation remain the same: A projectile is seated in the open mouth of a cartridge case containing solid propellant. Ignition of the propellant is provided by percussive or electrical means. The burning propellant generates pressurized gas which forces the projectile out of the mouth of the case and then typically through a barrel bore. 
         [0009]    The launching of a 40 mm grenade involves the same principles. The main difference, however, is the size and mass of the projectile. A typical shoulder-fired military weapon launches a projectile weighing less than 30 grams at a relatively high velocity (700-1,000 meters per second). In contrast, a 40 mm grenade weapon launches a projectile weighing over 200 grams at a relatively low velocity (70-80 meters per second). Thus, while the operating principles between the two types of weapons are the same, they can be said to operate in different regimes. 
         [0010]    Since the human operator can only withstand a fixed amount of recoil, one cannot merely scale up the cartridge of a shoulder-fired rifle and create a useable weapon for launching 40 mm grenades. The design considerations are different. The incorporated U.S. Pat. No. 7,004,074 illustrates and describes an effective approach to the problem of launching large masses at low velocities. The &#39;074 invention uses a high-pressure cartridge embedded within a low-pressure larger cartridge. A burst cup metering system is used to meter propellant gases from the high pressure cartridge into the low pressure cartridge, thereby accelerating the projectile in a smooth and controlled fashion. This approach helps to reduce the peak recoil loads experienced by a user. The high pressure found within the high pressure cartridge also ensures the reliable ignition and combustion of the propellant it contains. 
         [0011]    The present invention seeks to simplify the construction and assembly of a suitable High-Low gas pressure cartridge. Although the illustrations and descriptions pertain to 40 mm grenade launchers, the reader should bear in mind that the invention applies to many fields beyond military munitions. A good example is disclosed in U.S. Pat. No. 6,189,926 to Smith (2001), which uses a High-Low pressure cartridge to inflate an airbag. Additional applications would include, without limitation: 
         [0012]    1. Turbine and piston engine starters; 
         [0013]    2. Parachute inflation devices; 
         [0014]    3. Mechanical deployment device; 
         [0015]    4. Life vest inflation devices; 
         [0016]    5. Life boat inflation devices; and 
         [0017]    6. Explosive bolt cutting devices. 
       BRIEF SUMMARY OF THE INVENTION 
       [0018]    The present invention is a modified fluid delivery cartridge.  FIGS. 2 and 3  illustrate most of the invention&#39;s features.  FIG. 2  shows a projectile assembly using a High-Low gas pressure cartridge to launch projectile  14 . High pressure chamber  31  is formed within high pressure cartridge  42 . Low pressure chamber  30  is formed within low pressure cartridge  38 . Burst cup  46  closes the open mouth of the high pressure cartridge. The burst cup is preferably embossed with rupture lines so that it ruptures in a predictable fashion when the high pressure cartridge is ignited. 
         [0019]      FIG. 3  shows the high pressure cartridge in greater detail. High pressure cartridge wall  61  is preferably surrounded and reinforced by charge casing  28  (which is a part of the low pressure cartridge). The charge casing includes step  44 , which is a region in which the charge casing&#39;s inner surface narrows to a smaller diameter. High pressure cartridge wall  61  is deformed to follow the step, resulting in a neck  78 . The neck retains the burst cup in place when it is fired. 
         [0020]    The neck in the high pressure cartridge wall is preferably created when the high pressure cartridge is pressed into the low pressure cartridge. The high pressure cartridge wall actually starts as a conventional straight wall. As the high pressure cartridge is pressed into the low pressure cartridge, step  44  actually creates the neck in the high pressure cartridge wall. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0021]      FIG. 1  is an exploded perspective view, showing a projectile assembly. 
           [0022]      FIG. 2  is a perspective view with a cutaway, showing internal details of the High-Low cartridge. 
           [0023]      FIG. 3  is a sectioned elevation view, showing details of the charge casing and high pressure cartridge wall. 
           [0024]      FIG. 3B  is an elevation view, showing how the step in the charge casing forms the neck in the cartridge wall. 
           [0025]      FIG. 4  is an exploded perspective view, showing how the burst cup is pressed into the high pressure cartridge wall. 
           [0026]      FIG. 5  is a perspective view, showing the components of  FIG. 4  in an assembled state. 
           [0027]      FIG. 6  is a sectioned elevation view, showing details of the step in the inner charge casing wall. 
           [0028]      FIG. 7  is a sectioned elevation view, showing the pressing of the high pressure cartridge into the low pressure cartridge. 
           [0029]      FIG. 8  is a sectioned elevation view, showing the pressing of the high pressure cartridge into the low pressure cartridge. 
           [0030]      FIG. 9  is a sectioned elevation view, showing the high pressure cartridge after it has ignited and expelled its propellant. 
           [0031]      FIG. 10  is a graph of recoil load versus time, during a single firing cycle. 
       
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
       [0032]      
         [0000]    
       
         
               
               
               
               
             
           
               
                   
               
             
             
               
                 11 
                 projectile assembly  
                 12 
                 low pressure cartridge 
               
               
                 14 
                 projectile 
                 16 
                 rifling ring 
               
               
                 22 
                 extraction flange 
                 24 
                 base 
               
               
                 25 
                 high pressure cartridge  
                   
                   
               
               
                   
                 receiver 
                   
                   
               
               
                 28 
                 charge casing 
                 30 
                 low pressure chamber 
               
               
                 31 
                 high pressure chamber 
                 34 
                 percussion primer 
               
               
                 36 
                 propellant 
                 38 
                 low pressure cartridge wall 
               
               
                 40 
                 projectile base 
                 42 
                 high pressure cartridge 
               
               
                 44 
                 step 
                 46 
                 burst cup 
               
               
                 48 
                 embossed lines 
                 52 
                 charge vent hole 
               
               
                 54 
                 burst petal 
                 56 
                 expansion nozzle 
               
               
                 60 
                 bulkhead 
                 61 
                 high pressure cartridge wall 
               
               
                 63 
                 high pressure cartridge base 
                 65 
                 inner charge casing wall 
               
               
                 67 
                 ram 
                 78 
                 neck 
               
               
                 80 
                 low volume curve 
                 82 
                 high volume curve 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0033]      FIG. 1  shows the major components of a 40 mm grenade round. Projectile  14  is mated with low pressure cartridge  12  to form projectile assembly  11 . Those skilled in the art will know that projectile  14  can assume many forms, including a fragmentation grenade, a smoke round, a flare round, etc. It generally includes a rifling ring  16  sized to engage the rifling on the bore of the grenade launching weapon. Nose cone  18  provides an aerodynamically efficient shape. 
         [0034]      FIG. 2  shows projectile assembly  11  with a cutaway through low pressure cartridge  12  to reveal its internal details. The reader will observe that high pressure cartridge  42  is located in the base  24  of low pressure cartridge  12 . It is surrounded and reinforced by charge casing  28 . Bulkhead  60  lies over the top of the high pressure cartridge. It opens into charge vent hole  52 . 
         [0035]    The high pressure cartridge is preferably closed via a burst cup  46 . The high pressure cartridge contains a quantity of propellant  36 , which is ignited by striking percussion primer  34 . Thus, the burst cup divides the assembly into high pressure chamber  31  (within the high pressure cartridge) and low pressure chamber  30  (the enclosure formed by base  24 , low pressure cartridge wall  38 , and projectile base  40 ). When the percussion primer is struck, it ignites the propellants within the high pressure cartridge and ruptures burst cup  46 . The burst cup then forms an expansion nozzle which meters the hot propellant gases from the high pressure chamber into the low pressure chamber. 
         [0036]      FIG. 3  shows the high pressure cartridge in greater detail. The cartridge case preferably assumes the form of a conventional pistol cartridge—such as the .38 Automatic Colt Pistol (“ACP”) or the .45 ACP. The high pressure cartridge has high pressure cartridge base  63  and a cylindrical high pressure cartridge wall  61  attached thereto. The open end of the cartridge is closed by the insertion of burst cup  46 . Burst cup  46  is held in position by neck  78  in high pressure cartridge wall  61 . 
         [0037]    Turning briefly to  FIG. 3B , the reader will observe that the inward facing wall of charge casing  28  includes step  44 , which is positioned to bear against neck  78 . Returning now to FIG.  3 , the reader will appreciate how neck  78  retains burst cup  46  in position, and how step  44  reinforces neck  78 . The high pressure cartridge contains a suitable quantity of propellant  36 , which is ignited by percussion primer  63  in a manner well known in the art. 
         [0038]      FIGS. 4 and 5  illustrate how the high pressure cartridge is loaded and assembled. First, a percussion primer is pressed into the cartridge base. Then a suitable amount of propellant (such as M9 ball powder) is placed into the open mouth of the cartridge case. Next—as shown in FIG.  4 —burst cup  46  is slipped into the open mouth of the case, over the top of the propellant. The reader will observe that one end of the burst cup is cylindrical. The outward facing surface of this cylindrical portion is a sliding fit within the inward facing surface of high pressure cylinder wall  61 . 
         [0039]      FIG. 5  shows burst cup  46  pressed into position. The top of the burst cup preferably includes a pattern of embossed lines  48 . These weaken the dome of the burst cup so that it will rupture in a predictable fashion. It is also preferable to seat the burst cup a fixed distance into the cartridge. This can be done with a seating fixture. However, if a propellant of appropriate density is used, the propellant charge itself can properly locate the burst cup. Once the burst cup has expelled the air in the cartridge and pressed against the solid propellant, it will go no further. 
         [0040]    The assembly shown in  FIG. 5  is ready to be completed by adding the neck in the high pressure cartridge wall. Assuming that the cartridge wall is made of a reasonably ductile material—such as brass—this operation can be done by a conventional forming die. However, if the components are properly configured, the low pressure cartridge case itself can serve as a sort of forming die. Since this eliminates a step in the manufacturing process, it represents the preferred embodiment. 
         [0041]      FIG. 6  shows base  24  of low pressure cartridge  12  in more detail. Base  24  opens into high pressure cartridge receiver  25 . The high pressure cartridge receiver is surrounded by charge casing  28  and bulkhead  60 . The inward facing wall of the charge casing is designated as inner charge casing wall  65 . The reader will observe that the diameter of the inner charge casing wall is abruptly reduced in the region of step  44 , resulting in the transition to charge vent hole  52 . The step can take many forms, including a simple fillet radius (as shown) or an angled chamfer. It could also simply be a sharp-edged step, though this is not preferable for reasons which will become apparent. 
         [0042]    The inner charge casing wall, the step, and the charge vent hole preferably act as a sort of forming die when the high pressure cartridge is placed into the low pressure cartridge.  FIGS. 7 and 8  illustrate this process. In  FIG. 7 , high pressure cartridge  42  is being forced into the high pressure cartridge receiver using a suitable tool. Ram  67  forces the high pressure cartridge into the receiver without placing pressure on the percussion cap. The reader will note in  FIG. 7  that high pressure cartridge wall  61  is undeformed. It is simply advancing along the cylindrical portion of inner charge casing wall  65 . 
         [0043]    In  FIG. 8 , the high pressure cartridge has been pressed further into the receiver in the low pressure cartridge. The reader will observe how neck  44  has deformed high pressure cartridge wall  61  inward to form neck  78 . As the insertion continues, the ductile wall material of the high pressure cartridge will continue to flow over step  44  and neck  78  will move lower and lower with respect to the base of the high pressure cartridge. When the cartridge is fully seated, it will assume the appearance shown in  FIG. 3 . Thus, the reader will appreciate how the high pressure cartridge has been advantageously altered during its assembly into the low pressure cartridge. 
         [0044]    Looking still at  FIG. 3 , the reader will note how the step in the charge casing wall bears against and reinforces the neck in the low pressure cartridge case, holding the high pressure case firmly in position. Of course, the high pressure case may tend to back out of the low pressure case upon firing (move downward in the orientation shown in the view). For this reason, it is preferable to deform some portion of the low pressure cartridge case into the extractor groove surrounding the base of the high pressure cartridge case. This can be done by peening or other suitable processes. The same techniques are preferably applied to the percussion primer so that it will not back out of the high pressure cartridge case. 
         [0045]    When the high pressure cartridge case is detonated, the burst cup ruptures and meters the propellant gases into the low pressure chamber.  FIG. 9  shows a sectioned elevation view after the cartridge has detonated. The hemispherical portion of burst cup  46  has fractured into a plurality of burst petals  54 . Expansion nozzle  56  has thereby been formed between high pressure chamber  31  and low pressure chamber  30 . The interference between the neck in the high pressure cartridge case and the step in the charge casing wall has retained the high pressure cartridge and the burst cup in position. 
         [0046]    Although the neck is preferably formed when the high pressure cartridge is inserted into the low pressure cartridge, this is by no mean the invention&#39;s only embodiment. The neck could obviously be formed in a separate die and the formed case could then be inserted into the high pressure case receiver. The function of the completed device would then be the same. 
         [0047]    The amount of gas volume contained within the low pressure chamber prior to ignition of the high pressure cartridge has a significant impact on the recoil forces generated.  FIG. 2  shows the free volume trapped between the base of the projectile and the inward facing walls of the low pressure cartridge. Those skilled in the art will realize that design variations could easily alter this volume. As one example, reducing the length of low pressure cartridge  38  would reduce the free volume. 
         [0048]    Greater volume tends to prevent a rapid rise in pressure within the low pressure chamber, which in turn tends to spread the recoil forces generated out over a longer period of time. Of course, the low pressure chamber volume enlarges once the projectile starts moving down the bore. However, rifling ring  36  largely seals the gap between the projectile and the bore, so that the projectile acts like a gas-driven piston. 
         [0049]    The presence of a large volume in the low pressure chamber prior to the point where the projectile begins to move tends to act as an energy absorber which prevents a rapid spike in gas pressure. This will tend to reduce the peak low pressure chamber pressure experienced during firing. This reduction in peak low pressure chamber pressure will also reduce peak recoil forces experienced by the person firing the weapon. 
         [0050]      FIG. 10  provides some explanation of this phenomenon.  FIG. 10  shows two test firings, one using a relatively low initial gas volume within the low pressure chamber and one using a relatively high volume. The Y-axis shows recoil force in pounds (lbf). The X-axis shows time (in seconds). Low volume curve  80  plots the force experienced during a test using a low free volume in the low pressure chamber. High volume curve  82  is the same test using a large free volume in the low pressure chamber. 
         [0051]    The area under each curve represents the impulse imparted to each projectile. The area under each curve is very nearly equal, which must be true if the two projectiles are to achieve the same muzzle velocity (which is true for the test). However, the reader will observe that the peak recoil load for the high volume test is significantly lower. The recoil forces are also experienced over a longer period of time. In subjective terms, the use of a larger free volume in the low pressure chamber has taken a sharp jab and converted it into a longer shove. This shift makes the recoil forces much more tolerable for the shooter. 
         [0052]    Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiment of the invention. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.