Abstract:
A modified gas delivery cartridge. A conventional straight-sided brass cartridge case is primed and then filled with solid propellant. A burst cup is then inserted in the case mouth. The burst cup is embossed with a cross or other shape to promote predictable rupture. Once the burst cup is in place, the upper edges of the cartridge case are rolled over the burst cup. In operation, the propellant is ignited to produce pressure within the sealed case. This pressure builds steadily until the embossed cross in the burst cup ruptures. The propellant gases are then vented in a metered fashion through the ruptured burst cup. However, the burst cup is retained by the case so that no solid object escapes the high pressure cartridge. In addition, by carefully designing the shape of the burst cup and the components surrounding it, it is possible to create an efficient expansion nozzle to better meter the propellant gases.

Description:
This invention relates to the field of propellant gas delivery systems. More specifically, the invention comprises an energy delivery cartridge with a burst cap that allows controlled discharge of the propellant gases generated within said cartridge. 
   DESCRIPTION OF THE RELATED ART 
   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. 
   A representative metallic cartridge design is found in the NATO 5.56×45 mm rifle cartridge. In that design, 24 grains of propellant are used to accelerate a 62 grain projectile to a velocity of 3100 feet per second. A more complex system is used where the intention is to accelerate a relatively large mass (relative to the amount of propellant involved) to a relatively low velocity. Such a system is disclosed in U.S. Pat. No. 5,086,703 to Klein (1992). The Klein device is a low-velocity riot control projectile. A metallic cartridge is used to contain a charge of solid propellant in the base of the projectile. The propellant is held within the metallic cartridge by the seating of a disc over the top of the propellant (commonly called a “wad”). Such a cartridge—having no projectile other than the wad—is often called a “blank.” When the cartridge is fired, high pressure propellant gases expel the wad and the cartridge then vents the gases into the space beneath the projectile. The gases then force the projectile forward with respect to the metallic cartridge. The result is the creation of a high pressure chamber within the metallic cartridge and a low pressure chamber within the space behind the projectile—as the projectile moves forward to exit the weapon. Such a system is often referred to as a “Hi/Low” gas delivery system. 
   U.S. Pat. No. 5,259,319 to Dravecky et.al. (1993) discloses another type of Hi/Low system. The Dravecky invention is a reusable practice round for 37 mm and 40 mm grenade launching weapons. It used a .38 caliber “blank” cartridge as the high pressure component (see  FIG. 2 ). The blunt-nosed object projecting from the end of the .38 caliber metallic cartridge is the sealing wad. As those skilled in the art will know, the use of such a wad has traditionally been essential to the function of a blank cartridge. Normal cartridge cases have bullets seated in their mouths (either via an interference fit, crimping, or both). When the propellant is ignited, pressure within the case builds to many atmospheres before the bullet begins to move. This elevated pressure is an essential component of reliable ignition. If, as an example, a case having no obstruction at the mouth is ignited, it will burn erratically or often not at all (sometimes called a “chuff”). Thus, the use of a pressure containment wad is essential. 
   Traditional wads are capable of providing reliable ignition, but less than ideal for a Hi/Low system. Once the wad clears the mouth of the case, the pressure drop within the case is substantial. This fact causes most of the propellant gases to be expelled in a short period, and may also promote incomplete burning of the propellant. A system for metering the expulsion of the gases is therefore desirable. U.S. Pat. No. 5,402,729 to Richert discloses such a system. With respect to  FIG. 1  of the Richert specification, the reader will note that a blank cartridge ( 2 ) is placed within a diffusing device ( 3 ). Although not clearly described, the blank cartridge ( 2 ) appears to be of the molded-propellant type, wherein a solid propellant with an added plasticizer is molded into the shape of a cartridge without the use of a case. This is possible since diffusing device ( 3 ) essentially serves the purpose of a traditional case. Diffusing device ( 3 ) has a series of radial metering holes ( 3   b ) which meter the propellant gases into the low pressure chamber. 
   The Richert device thus solves the metering problem and has the added advantage of not expelling a wad (since it has no wad). The expulsion of a wad is a decided drawback to the other devices. The wad tends to follow an erratic flight path and can strike unintended targets. In addition, many wads will accumulate in the area of a practice range introducing a pollution problem. However, the Richert device has the disadvantage of using unconventional components. The blank cartridge and the diffusing device must be specially manufactured, adding to the cost. The use of more conventional munitions components is preferable. 
   U.S. Pat. No. 6,041,712 to Lyon (2000) discloses a Hi/Low system using a standard .38 caliber cartridge. However, the .38 caliber cartridge is contained within a metal sleeve with a metering hole (see  FIG. 3 ). The metering hole is initially covered by a diaphragm ( 18 ). This combination serves to replace the wad and provides sufficient pressure containment for reliable ignition.  FIG. 4  illustrates an embodiment using a standard .38 caliber blank cartridge, including a wad—plug ( 19 ). The embodiment shown in  FIG. 3  has the benefit of improved gas metering, but it also requires the use of the additional metal sleeve. This is a non-standard component which increases the cost of the device. The embodiment showing in  FIG. 4  suffers from the drawbacks previously discussed—poor gas metering and the ejection of a wad. 
   Finally, the reader should be aware that Hi/Low gas cartridge systems are used in many fields other than munitions. As one example, consider U.S. Pat. No. 6,189,926 to Smith (2001). The Smith device uses a complex high pressure cartridge to vent propellant gases into a low pressure chamber. The low pressure chamber is then used to inflate an automotive air bag. The propellant containing case is designed to rupture—thereby venting the gas. A close inspection of the drawings reveals that the device is quite complex, and consequently quite expensive. It is therefore unsuitable for use in a projectile practice round. However, it does serve to illustrate the fact that cartridge gas venting systems have many different applications. These would additionally include, without limitation:
         1. Turbine and piston engine starters;   2. Parachute inflation devices;   3. Mechanical deployment device;   4. Life vest inflation devices;   5. Life boat inflation devices; and   6. Explosive bolt cutting device.       

   BRIEF SUMMARY OF THE INVENTION 
   The present invention is a modified fluid delivery cartridge.  FIGS. 5 through 8  illustrate the primary features. A conventional straight-sided brass cartridge case is primed and then filled with solid propellant. A burst cap is then inserted in the case mouth. The burst cap is scribed with a cross, as shown in  FIG. 6 . Once the burst cap is in place, the upper edges of the cartridge case are rolled over the burst cap, as shown in  FIG. 8 . 
   In operation, the propellant is ignited to produce pressure within the sealed case. This pressure builds steadily until the scribed cross in the burst cap ruptures. The propellant gases are then vented in a metered fashion through the ruptured burst cap. However, the burst cap is retained by the case so that no solid object escapes the high pressure cartridge. In addition, by carefully designing the shape of the burst cap and the components of the low pressure chamber, it is possible to create an efficient expansion nozzle to better meter the propellant gases. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is an isometric view, showing a prior art practice round. 
       FIG. 2  is an isometric view, showing a prior art practice round. 
       FIG. 3  is a section view, showing the internal features of a prior art practice round. 
       FIG. 4  is an isometric view, showing the internal features of a blank cartridge. 
       FIG. 5  is an isometric view, showing the burst cap in its relation to the high pressure cartridge. 
       FIG. 6  is an isometric view, showing more features of the burst cap. 
       FIG. 7  is an isometric view, showing the burst cap installed within the high pressure cartridge. 
       FIG. 8  is a section view, showing the burst cap installed within the high pressure cartridge. 
       FIG. 9  is a section view, showing the components of the present invention. 
       FIG. 10  is a section view, showing the components of he present invention after the burst cap has ruptured. 
       FIG. 11  is an isometric view, showing the ruptured burst cap. 
       FIG. 12  is a section view, showing an improvement to the prior art charge hole. 
       FIG. 13  is a section view, showing the interaction between the burst cap and the improved charge hole. 
       FIG. 14  is a section view, showing an uncrimped embodiment of the invention. 
       FIG. 15  is a section view, illustrating the present invention being used as an air bag inflation device. 
       FIG. 16  is a section view, showing a necked version of the present invention. 
       FIG. 17  is a section view showing the necked version installed in a modified low pressure case. 
       FIG. 18  is a section view, showing the necked version after firing. 
       FIG. 19  is a section view, showing an M583 low pressure case. 
       FIG. 20  is a section view, showing a complete M583 round. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 REFERENCE NUMERALS IN THE DRAWINGS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 10 
                 practice round 
                 12 
                 low pressure case 
               
               
                   
                 14 
                 projectile body 
                 16 
                 rifling ring 
               
               
                   
                 18 
                 nose cone 
                 20 
                 dye charge 
               
               
                   
                 22 
                 extraction flange 
                 24 
                 base 
               
               
                   
                 26 
                 side wall 
                 28 
                 charge casing 
               
               
                   
                 30 
                 low pressure chamber 
                 32 
                 blank cartridge 
               
               
                   
                 34 
                 percussion primer 
                 36 
                 propellant 
               
               
                   
                 38 
                 filler plug 
                 40 
                 wad 
               
               
                   
                 42 
                 high pressure cartridge 
                 44 
                 roll crimp 
               
               
                   
                 46 
                 burst cup 
                 48 
                 embossed lines 
               
               
                   
                 50 
                 modified crimp 
                 52 
                 charge vent hole 
               
               
                   
                 54 
                 burst petal 
                 56 
                 expansion nozzle 
               
               
                   
                 58 
                 uncrimped case 
                 60 
                 bulkhead 
               
               
                   
                 62 
                 modified blank cartridge 
                 64 
                 air bag cartridge 
               
               
                   
                 66 
                 low pressure case 
                 68 
                 diffuser 
               
               
                   
                 70 
                 vent holes 
                 72 
                 mounting flange 
               
               
                   
                 74 
                 electrical primer 
                 76 
                 necked cartridge 
               
               
                   
                 78 
                 neck 
                 80 
                 low wall case 
               
               
                   
                 82 
                 M583 case 
                 84 
                 projectile container 
               
               
                   
                 86 
                 cap 
                 88 
                 container base 
               
               
                   
                 90 
                 delay charge 
                 92 
                 output charge 
               
               
                   
                   
               
             
          
         
       
     
   

   DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a prior art practice round  10  (containing marking dye) for a grenade launching weapon. It has three major inert components: case  12 , projectile body  14 , and nose cone  18 .  FIG. 2  shows the components assembled as they normally would be prior to firing.  FIG. 3  is a section view, showing some internal features of the prior art practice round  10 . Low pressure case  12  is formed of base  24  with an attached cylindrical side wall  26 . Extraction flange  22  extends out from base  24 . It provides an engagement point for an extracting mechanism to pull the round free of the weapon. 
   Charge casing  28  extends upward from base  24 . Bulkhead  60  closes the upper portion of charge casing  28 . It is pierced by charge vent hole  52 . Low pressure case  12  is typically formed as one integral piece—either as a metallic casting or as molded plastic. 
   Charge casing  28  and bulkhead  60  combine to form a structure to support blank cartridge  32 . Blank cartridge  32  supplies high pressure propellant gases which are fed through charge vent hole  52  into low pressure chamber  30 . Low pressure chamber  30  is formed by seating projectile body  14  into low pressure case  12 . Projectile body  14  has a cavity in its base which tends to receive the hot pressurized propellant gases escaping from charge vent hole  52 . Projectile body  14  is typically formed from a metal capable of withstanding the hot propellant gases. Nose cone  18  is bonded onto the top of projectile body  14 . It contains dye charge  20 , which ejects a dye marking at the point of impact, thereby allowing the operator to observe the fall of the shot. 
   In operation, practice round  10  is placed within a grenade launcher, which typically consists of a firing chamber connected to a short, rifled barrel. Once secured within the launcher, blank cartridge  32  is detonated. The ejection of propellant gases forces projectile body  14 , along with nose cone  18  and the contained dye charge  20  through the rifled bore. Returning briefly to  FIG. 1 , the reader will observe that rifling ring  16  extends outward from projectile body  14 . Its purpose is to engage the rifling within the barrel, thereby spin-stabilizing the projectile in flight. 
     FIG. 4  is a section view illustrating the internal features of the prior art blank cartridge  32 . High pressure cartridge  42  has a base and a base cylindrical vertical side wall. The use of a .38 caliber case is shown. The choice of this case is merely one of expedience, as many types of blank cartridges would work. However, as the .38 caliber case is a very common pistol round, it is cheap and readily available. The case is charged with propellant  36  (such as the solid flake type). This would typically be a nitrocellulose powder, in either spherical or cylindrical form. A percussion primer  34  is seated in the base of blank cartridge  32 . 
   Those skilled in the art will know that the placement of the powder charge within a case has a significant effect on the ignition and burning of the powder. The volume of powder used is set by the ballistic result required; i.e., within a reasonable range, more powder means more velocity to the projectile. It is often true that the powder charge required does not fill the volume of the case. This is particularly true with blank cartridges, since the bullet volume is unoccupied. If the powder is left free in the case, it may settle away from percussion primer  34 , especially when the case is oriented horizontally. In such a situation, unreliable ignition may occur. 
   Looking at  FIG. 4 , the reader will observe that propellant  36  does not occupy the entire volume of the case. Thus, filler plug  38  is used to hold propellant  36  in place proximate percussion primer  34 . Wad  40  is placed over filler plug  38 . The upper portion of the case side walls are then deformed to create roll crimp  44 . This crimp holds the wad and filler in the desired location. 
   Wad  40  is typically formed of heavy card stock, while filler plug  38  is often a softer material—such as an open celled foam. When the practice round is fired, wad  40  and filler plug  38  are ejected into the rifled bore. Most of the mass is ejected downrange. However, it is important to realize that wad  40  and filler plug  38  will be broken into smaller particles that intermingle with the very hot propellant gases. Some of these solids then become attached to the firing chamber and barrel wall (commonly called “fouling”). Such fouling tends to build up rapidly, requiring the frequent cleaning of the weapon. 
   In addition, while wad  40  does serve to keep the components oriented, it cannot withstand significant pressure. It is, in fact, a poor substitute for a bullet. In a conventional cartridge, the bullet&#39;s mass retards its forward motion and allows the pressure within the case to build gradually. In a blank cartridge such as shown in  FIG. 4 , wad  40  has very little mass. As a consequence it is rapidly ejected before the pressure can build evenly. This phenomenon produces an unwanted variation in the burning of the propellant. Such a variation produces variations in the projectile velocity, which limits the device&#39;s effectiveness as a training aid since the operator is unable to determine whether a missed shot was caused by poor aim or poor blank cartridge performance. 
   The present invention produces a much more stable ignition and burn sequence, thereby producing more consistent velocities. In addition, the present invention eliminates the ejection of solid objects which can foul the weapon&#39;s bore.  FIG. 5  shows the major components of modified blank cartridge  62 . High pressure cartridge  42  is the same as for the prior art, including the use of a percussive primer and a propellant charge (also typically solid flake). Burst cup  46  is a hollow, thin-walled object having the approximate external appearance of a bullet. 
     FIG. 6  illustrates the hollow nature of burst cup  46 . The interior surface of burst cup  46  is embossed with embossed lines  48  (the external surface could be scribed instead, or both surfaces could be scribed).  FIG. 7  shows burst cup  46  placed within high pressure cartridge  42 . The upper portion of the side wall of the case has been rolled over to form modified crimp  50 . This feature retains burst cup  46  within high pressure cartridge  42 . 
     FIG. 8  is a sectional view showing how burst cup  46  is secured by modified crimp  50 . Burst cup  46  is essentially a thin cylindrical side wall joined to a hemispherical dome. The cylindrical side wall is sized to slide within but tightly frictional engage the inner cylindrical side wall of high pressure cartridge  42 . This frictional engagement prevents burst cup  46  from seating too deep within high pressure cartridge  42 . The reader will note in  FIG. 8  that some air space is left within high pressure cartridge  42 . As explained previously, unoccupied propellant volume can produce erratic ignition in blank cartridges. However, because burst cup  46  forces a dramatic rise in pressure within the case prior to rupturing, no erratic ignition occurs. In a conventional cartridge with a seated bullet, air space often remains. This does not tend to produce a problem in that circumstance because—again—the bullet&#39;s mass allows the build-up of high pressure. 
   Embossed lines  48  allow burst cap  46  to rupture in a consistent and predictable manner.  FIG. 9  is a section view through case  12  with modified blank cartridge  62  in place. As with the prior art, the blank cartridge is surrounded by charge casing  28  and bulkhead  60 , with bulkhead  60  being pierced by charge vent hole  52 . The upper portion of burst cup  46  lies directly beneath charge vent hole  52 . When the blank cartridge is ignited, the burning propellant causes a sharp rise in the pressure within the case. Burst cup  46  is retained by modified crimp  50  and bulkhead  60 . Thus, the pressure within the case builds and creates even ignition. Once the desired pressure is reached, embossed lines  48  rupture (Those skilled in the art will know that many patterns could be used for embossed lines  48 , depending on the number of resulting petals desired).  FIG. 10  shows burst cup  46  after this rupture, with its upper portions having split into burst petals  54 . Burst cup  46  thereby forms a nozzle which releases the high pressure propellant gases from high pressure cartridge  42 . It is important to note that no solid matter is ejected from modified blank cartridge  62 .  FIG. 11  shows an isometric view of the ruptured burst cup  46  retained within high pressure cartridge  42  (with burst petals  54  protruding out the top). 
   In order to facilitate a complete understanding, it is helpful to compare the entire ignition and burn sequences for the prior art blank cartridge and the present invention. The prior art follows the following sequence: (1) Ignition of the primer; (2) Propellant ignition with initial pressure rise; (3) Expulsion of the filler and wad with a consequent sharp pressure drop; (4) Erratic burning of the remaining propellant. 
   The present invention follows the following sequence: (1) Ignition of the primer; (2) Propellant ignition with initial pressure rise; (3) Additional pressure rise to promote complete ignition; (4) Rupture of the burst disk, creating a metering nozzle; and (5) Sustained burning at even and elevated pressure until the propellant is completely consumed. 
   Those skilled in the art will realize that the metering of the high pressure propellant gases through the throat created by burst cup  46  and charge vent hole  52  is similar to the expansion of burning gases through a rocket nozzle. It is therefore advantageous to optimize the shape of charge hole  52  to create more consistent expansion and acceleration of the gases. One optimum configuration for such a nozzle is known as a DeLaval nozzle.  FIG. 12  shows a modified version of case  12 , wherein charge hole  52  has been modified into expansion nozzle  56 .  FIG. 13  shows this configuration with burst cup  46  in the ruptured state. Burst petals  54  tend to conform to the shape of the wall of expansion nozzle  56 . The reader will recall that low pressure case  12  may be molded of plastic material in order to minimize expense. Thus, if unprotected, expansion nozzle  56  would tend to melt when exposed to the hot propellant gases. The overlay of petals  54  around the throat of expansion nozzle  56  allow it to survive the metering process substantially intact. 
   Having reviewed the preceding, those skilled in the art will realize that the use of modified crimp  50  with modified blank cartridge  62  is not strictly necessary. Burst cup  46  can be placed within high pressure cartridge  42  and externally retained.  FIG. 14  shows such an embodiment loaded into case  12 . Burst cup  46  is shown in the ruptured state. The reader will observe that the throat of expansion nozzle  56  has retained burst cup  46  without the use of modified crimp  50 . Modified crimp  50  does, however, produce added stability to modified blank cartridge  62 , especially prior to loading in low pressure case  12 . Thus, the use of modified crimp  50  is preferable. 
   Although the invention has been primarily illustrated as a component in a projectile round, those skilled in the art will realize that the invention has many other applications.  FIG. 15  illustrates the use of the invention in air bag cartridge  64 . Modified blank cartridge  62  is placed into low pressure case  66 . Low pressure case  66  is mated to an airbag mount by mounting flange  72 . Electrical primer  74  is substituted for the percussion primer ordinarily used, since the means of triggering an air bag to inflate are typically electrical. 
   Diffuser  68 , which opens into a series of vent holes  70 , is mated to low pressure case  66 . Air bag cartridge  64  would typically be placed within an uninflated air bag. When the air bag must be inflated, an electrical signal is sent to ignite electrical primer  74 . This action ignites the propellant, ruptures the burst cap, and causes a rapid but metered flow of gas into and through diffuser  68 . The gas then escaping through vent holes  70  inflates the air bag. 
     FIG. 16  shows yet another embodiment for retaining burst cup  46  within a cartridge. Necked cartridge  76  is firmed by the following steps: (1) a straight-walled case is primed and charged with propellant  36 ; (2) Burst cup  46  is then inserted; and (3) neck  78  is formed to retain burst cup  46  in the appropriate position. 
   The addition of neck  78  considerably reinforces the side walls of necked cartridge  76 . This additional strength reduces the need for surrounding reinforcement of the cartridge.  FIG. 17  shows a modified low pressure case designed to utilize necked cartridge  76 . Low wall casing  80  only encloses the head of necked cartridge  76 . It is also possible—if brass of sufficient thickness is used to form necked cartridge  76  to eliminate low wall casing  80  altogether. 
     FIG. 18  shows necked cartridge  76  after it has been fired. The reader will observe that the mechanical strength of neck  78  is sufficient to retain burst cup  46  without additional surrounding material. 
   Many additional applications are possible for the cartridge.  FIG. 19  shows a shortened low pressure case that is used in a type of projectile designated M583. The reader will observe that M583 case  82  has shortened side walls. High pressure cartridge  82  is seated within charge casing  28 —just as for the embodiment shown in  FIG. 10 . 
     FIG. 20  shows the balance of the M583 cartridge. Projectile container  84  is seated within the open mouth of M583 case  82 . Container base  88  of projectile container  84  opens into a hole. In this hole is inserted necked cartridge  76 . Necked cartridge  76  is modified from the embodiment shown in  FIG. 16 . First, it contains no primer. The primer pocket is simply left open. Second, the propellant is replaced with a duplex charge. The lower portion of the case is filled with delay charge  90 . On top of this is deposited output charge  92 . 
   Projectile container  84  is hollow it is sealed at its upper end by cap  86 , which interlocks with the side walls of projectile container  84 . The container typically contains a payload to be delivered for some purpose. One example would be a flare attached to a parachute (sometimes called a “star shell”). 
   The operation of the device proceeds as follows: (1) The entire round is loaded into a firing chamber; (2) Percussion primer  34  in high pressure cartridge  42  is ignited; (3) The lower burst cup  46  ruptures, venting the pressurized propellant gases; (4) At the same time, the venting propellant gases ignite delay charge  90  in necked cartridge  76  (which burns slowly in a controlled fashion—for up to 5 seconds, or longer); (5) The venting propellant gases accelerate projectile container  84  down a rifled bore, sending it flying into space; (6) While projectile container  84  is arcing through its trajectory, delay charge  90  burns from the base of the cartridge up to output charge  92 , whereupon it detonates output charge  92 ; (7) Output charge  92  ruptures he upper burst cup  46 , throwing pressurized gases into the interior of projectile container  84 ; (8) Cap  86  blows free of projectile container  84 ; and (9) The contents of projectile container  84  (the “payload”) are ejected. 
   If a flare with attached parachute is the payload, the hot gases flowing from necked cartridge  76  can also be used to ignite the flare. The embodiment shown in  FIGS. 19 and 20  serves to illustrate the many different applications for the proposed invention. 
   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.