Abstract:
An apparatus and method for sealing the barrel of an underwater gun between firings is disclosed. The apparatus comprises an adapter that attaches to the barrel and includes a physical adaptation that is capable of sealing the barrel. In some embodiments, the physical adaptation is actuated to un-seal the barrel via combustion gases from firing of a round.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This case is related to the following U.S. patent application Ser. Nos. 12/165,060 (Underwater Gun Comprising a Valve-Type Barrel-Seal), 12/165,071 (Underwater Gun Comprising a Plate-Type Barrel Seal), 12/165,079 (Underwater Gun Comprising a Passive Fluidic Barrel Seal), and 12/165,090 (Underwater Gun Comprising a Turbine-Based Barrel Seal), all of which were filed on even date herewith and all of which are incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The present invention relates to underwater guns. 
     BACKGROUND OF THE INVENTION 
     Underwater guns are useful as anti-mine and anti-torpedo devices. Recently, autonomous underwater vehicles (AUVs) have been fitted with underwater guns for torpedo defense and underwater “hunter-killer” CONOPs. 
     A gun, especially one with a high muzzle velocity, cannot be fired when water is in its barrel. If a firing where to incur in a water-filled barrel, a very high breach pressure would result as the ignited propellant charge forces (or tries to force) the water out of the barrel. The likely result would be material failure of the barrel. 
     The prior art is replete with approaches for waterproofing the barrel of an underwater gun, or for clearing water from its barrel before firing. U.S. Pat. No. 5,639,982 discloses a means for firing a fully automatic gun underwater using a blank barrel-clearance round. Blank barrel-clearance rounds are alternated with live rounds of ammunition. To begin the process, a blank barrel-clearance round is first detonated. This creates gas and steam within the chamber that forms a bubble at the muzzle end of the barrel, thereby displacing water from the chamber. A live round is then immediately fired. The process is repeated, whereby the subsequent detonation of a blank barrel-clearance round displaces any water that has re-entered the barrel subsequent to the firing of the live round. 
     U.S. Pat. No. 5,648,631 discloses a spooled tape seal for sealing the barrel of an underwater gun. The system includes a tap that covers the opening of the gun barrel and sprockets for advancing the tape across the opening. Hydrostatic pressure keeps the tape pressed to the end of the barrel to create an effective seal. When a bullet is fired, it perforates the tape. During this brief period of egress, the exhaust gases from combustion of the propellant charge keep water from entering the barrel. Almost immediately, a non-perforated portion of the tape is advanced by the sprockets to cover the barrel opening. External hydrostatic pressure re-seats the tape, thereby preventing water from entering the barrel. 
     U.S. Pat. No. 5,687,501 discloses a sealing plate for providing a watertight seal for a multi- or single-barreled underwater gun. The sealing plate provides one or more firing apertures in an otherwise solid surface. Between firings, the gun muzzle is sealed by a solid surface of the sealing plate. To fire a bullet, the sealing plate or muzzle rotates to align the gun muzzle with one of the firing apertures. This permits unimpeded egress. After the bullet fires, the plate or muzzle again rotates so that a solid portion of the sealing plate covers the muzzle. 
     These are but a few of the many patents pertaining to various aspects of underwater gun design in general, and to the water-in-the-barrel problem, in particular. Notwithstanding the many approaches to the problem, no truly satisfactory approach has been developed for keeping water out of the barrel of an underwater gun between and during operation. 
     SUMMARY OF THE INVENTION 
     The present invention provides an underwater gun having a barrel seal for preventing water from entering the barrel between the firing of rounds. 
     In the illustrative embodiment, a barrel adapter couples to the barrel of a gun. A barrel seal is housed in the barrel adapter or otherwise functions in conjunction therewith. The barrel seal has two primary states: one state in which it is “closed” and another state in which it is “open.” When the barrel seal is closed, it prevents water from advancing past the seal into the gun&#39;s barrel. When the barrel seal is open, it permits a round to be fired. 
     In one embodiment, the barrel seal comprises a plurality of sealing flaps. Each sealing flap comprises two overlapping plates. Each plate is pivotably attached to an interior wall that defines the bore of the barrel adapter. This pivotable attachment enables each plate to rotate between a first position in which it is substantially perpendicular to the longitudinal axis of the bore (thereby blocking the bore) and a second position in which it is substantially parallel thereto. 
     The sealing flaps remain closed until forced open due to the increase in pressure in gun as a consequence of the combustion of the chemical propellant in a round that is fired. The increased pressure is sufficient to cause the plates to lie substantially flush against the interior wall of the barrel adapter. Repetitive firing keeps the sealing flaps in the open state. 
     Each pivotable attachment that attaches the plates of the sealing flaps to the interior wall includes an element that generates a torsional bias that causes the plates to return to the closed state in the absence of increased pressure (i.e., cessation of firing). 
     In a second embodiment, the barrel seal comprises a plurality of serrations and a stopper round. The serrations extend radially inward from the interior wall of the barrel adapter. The serrations extend over a substantial length of interior wall and are directed toward an outlet end of barrel adapter. 
     The bore of the barrel adapter is effectively reduced in size by the presence of the serrations to the extent that it has a diameter that is somewhat smaller than the diameter of the stopper round. As a consequence, there will be contact between serrations and the stopper round when the stopper round is fired. 
     The stopper round comprises an amount of chemical propellant that is insufficient to enable the stopper round to fully transit the serrations within the barrel adapter. Thus, stopper round is trapped (i.e., stopped) by the serrations, thereby sealing the bore of the barrel adapter and, hence, the barrel. A live round is fired to dislodge the stopper round (the pressure rise due to combustion gases in the barrel and barrel adapter dislodges the stopper round). Water is kept out of the bore as firing continues (due to the combustion gases). A subsequent stopper round is fired to reseal the barrel. 
     In a third embodiment, the barrel seal comprises an electromagnet and a stopper round. The electromagnetic comprises a coil of wire running through the barrel adapter. The stopper round includes a detachable, magnetically attracted tail section. 
     In operation, the gun&#39;s fire-control system sends a signal to a controller at an appropriate time (based on the transit time of the stopper round, the time it takes to energize the electromagnet, etc.) to direct a controlled current source to energize the electromagnet. As the stopper round exits the barrel adapter, a magnetic field that is generated by the electromagnet dislodges the tail section from the stopper round. 
     The tail section of the stopper round “unfolds” once dislodged. In its unfolded state, the tail section has an enlarged diameter that prevents it from exiting the barrel adapter. The electromagnet remains energized and, as a consequence, the unfolded tail section remains magnetically bound to barrel adapter, thereby sealing the barrel adapter and the gun&#39;s barrel. A live round is fired to dislodge the stopper round (the pressure rise due to combustion gases in the barrel and barrel adapter dislodges the stopper round). Water is kept out of the bore as firing continues (due to the combustion gases). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an underwater gun comprising a barrel adapter including a barrel seal in accordance with the illustrative embodiment of the present invention. 
         FIG. 2  depicts, via a cross-sectional view, the barrel adapter of  FIG. 1  and a first embodiment of a barrel seal. In this first embodiment, the barrel seal comprises a plurality of one-way flaps, each of which flaps comprises two plates that are pivotably coupled to an inner surface of the barrel adapter. The flaps are shown in a sealing state wherein one of the plates in each pair overlies the other plate in the pair. 
         FIG. 3  depicts, via a side cross-sectional view, the barrel adapter and barrel seal of  FIG. 2 , wherein the plates are partially rotated about their pivot point as the barrel is being unsealed. 
         FIG. 4  depicts, via a side cross-sectional view, the barrel adapter and barrel seal of  FIG. 2 , wherein the plates are fully rotated about their pivot points and lie against the inner surface of the barrel adapter, thereby unsealing the barrel. 
         FIG. 5A  depicts, via an end-on view, one of the plates in the sealing flap. 
         FIG. 5B  depicts, via an end-on view, the companion plate to the plate depicted in  FIG. 5A . 
         FIG. 5C  depicts together, via an end-on view, the plates depicted in  FIGS. 5A and 5B , wherein one of the plates overlies the other plate, as in  FIG. 2 . 
         FIG. 6  depicts, via a cross-sectional view, the barrel adapter of  FIG. 1  and a second embodiment of a barrel seal. In this second embodiment, the barrel seal comprises a stopper round and plurality of serrations that extend radially inward along a length of the interior of the barrel adapter. 
         FIG. 7  depicts, via a cross-sectional view, the barrel adapter and barrel seal of  FIG. 6 , wherein the stopper round has been fired and is captured by the plurality serrations, thereby sealing the barrel. 
         FIG. 8  depicts, via a cross-sectional view, the barrel adapter of  FIG. 1  and a third embodiment of a barrel seal. In this third embodiment, the barrel seal comprises an electromagnet and a stopper round. 
         FIG. 9  depicts, via a cross-sectional view, the barrel adapter and barrel seal of  FIG. 8 , wherein the electromagnet is energized and a detachable tail section of the stopper round is lodged in the barrel adapter. 
     
    
    
     DETAILED DESCRIPTION 
     The terms appearing below are defined for use in this specification, including the appended claims, as follows:
         Axially-oriented (or axial orientation) refers to an orientation that aligns with the longitudinal axis of an element. This orientation is orthogonal to a radial orientation.   Barrel is a narrow, hollow cylindrical portion of a firearm through which a projectile travels.   Bore is the hollow portion of the barrel through which a projectile travels during its acceleration phase.   Breech is an opening in the rear of a barrel of a gun where projectiles can be loaded.   Chamber is the portion of a barrel where a projectile is placed just prior to being fired. This is a high pressure containment area which is very precisely aligned with the bore of the barrel.   Fluidically coupled or fluidic communication means that liquid, gas, or vapor from a first region can flow to or otherwise affect a second region. For example, if two regions are fluidically coupled (or in fluidic communication), a pressure change in one of those regions might result in a pressure change in the other of the regions.   Muzzle is the opening at an end of the barrel where a projectile that has been fired exits the barrel.   Operatively coupled means that the operation of one device affects another device, wherein the devices need not be physical attached to one another. For example, a laser and a mirror are operatively coupled if a laser directs a beam of light to the mirror. An actuator and a valve are operatively coupled if the actuator actuates the valve, regardless of whether there other intermediary mechanisms between the actuator and the valve. Operatively-coupled devices can be coupled through any medium (e.g., semiconductor, air, vacuum, water, copper, optical fiber, etc.) and involve any type of force. Consequently, operatively-coupled objects can be electrically-coupled, hydraulically-coupled, magnetically-coupled, mechanically-coupled, optically-coupled, pneumatically-coupled, thermally-coupled, etc.   Radially-oriented (or radial orientation) refers to an orientation that is coincident with the radial direction of an element. See “axially-oriented.”       

     The present invention pertains to guns that are intended for (1) use in an underwater environment and (2) firing rounds that include a chemical propellant. The underwater guns described herein will typically, although not necessarily, be fitted to AUVs. For clarity, gun  100  is typically depicted in the Figures as having a single round in the chamber or bore. It is to be understood, however, that gun  100  is typically a multi-shot weapon. 
       FIG. 1  depicts underwater gun  100  having a barrel seal in a barrel adapter in accordance with the illustrative embodiment of the present invention. Gun  100  includes barrel  102 , chamber  104 , bore  108 , fire-control system  110 , optional controlled current source  113 , optional controller  111 , barrel adapter  114 , and barrel seal  116 , interrelated as shown. A live round  112  is depicted in bore  108 . 
     Barrel  102 , chamber  104 , and bore  108  are conventional features of most guns. Fire-control system  110  is basically a computer and ancillary elements that enable gun  100  to hit a target. The relative sophistication of any particular embodiment of fire-control system  110  is primarily a function of the intended application for gun  100 . That is, a relatively more sophisticated fire-control system is required for a relatively more autonomous application (e.g., for use in conjunction with an AUV, etc.). 
     In a typical embodiment, fire-control system  110  interfaces with one or more sensors (e.g., sonar, radar, infra-red search and track, laser range-finders, water current, thermometers, etc.). The sensor input is used to develop a firing solution for a target. To the extent that gun  100  is located on an AUV, etc., fire-control system  110  advantageously takes into account movements of the AUV itself. And, when associated with an AUV, fire-control system  110  is operatively coupled to aiming and firing mechanisms. 
     The fire-control system is not particularly germane to an understanding of the invention and, furthermore, is well understood by those skilled in the art. As a consequence, fire-control system  110  will not be described in further detail. 
     Barrel adapter  114 , which in the illustrative embodiment is coupled to the muzzle end  106  of barrel  102 , includes barrel seal  116 . The barrel seal, which is depicted figuratively in  FIG. 1 , is a physical adaptation (of the barrel adapter) that permits barrel  102  to be temporarily sealed against water intrusion. The barrel seal takes any one of a variety of different forms in various embodiments, a few of which are described later in this specification. 
     In the illustrative embodiment that is depicted in  FIG. 1 , muzzle end  106  of barrel  102  and the portion of barrel adapter  114  that abuts the muzzle end are threaded so that they can be “screwed” together. This type of fit permits barrel adapter  114  to be readily removed for maintenance, etc. Alternatively, barrel adapter  114  can be attached to muzzle end  106  of barrel  102  in any convenient manner (e.g., welding, bolted, etc.). 
     Barrel seal  116  has two primary states: one state in which it is “closed” and another state in which it is “open.” When barrel seal  116  is closed, it prevents water from advancing past the seal into barrel  102 . When barrel seal  116  is open, it permits round  112  to be fired. 
     This specification now proceeds with a description of several embodiments of underwater gun  100 . These embodiments are distinguished from one another by differences in barrel seal  116 . 
       FIGS. 2-4  depict an embodiment wherein the barrel seal comprises a plurality sealing flaps  216 . In the embodiment that is depicted in these Figures, sealing flaps  216  are regularly arranged within barrel adapter  214 .  FIG. 2  depicts sealing flaps  216  in a closed state in which they seal barrel  102 , thereby preventing water intrusion.  FIG. 3  depicts sealing flaps  216  during the process of opening and  FIG. 4  depicts sealing flaps  216  when they are fully open. 
     Referring now to  FIGS. 2-4 , barrel adapter  114  has bore  215  which is axially-aligned to and concentric with bore  108  of barrel  102  (see  FIG. 1 ). As depicted in  FIG. 2 , the diameter D B   A  of bore  215  of barrel adapter  114  is greater than the diameter D B   B  of bore  108  of barrel  102 . As will become clearer below, the larger bore of barrel adapter  114  accommodates certain structural aspects of the barrel seal. 
     As depicted in  FIG. 2 , each sealing flap  216  comprises two overlapping plates  218 A and  218 B. Each plate is pivotably attached, such as by hinge  220 , to interior wall  219  of barrel adapter  114 . This pivotable attachment enables each plate to rotate between a position in which it is substantially perpendicular to interior wall  219  ( FIG. 2 ) and a position in which it is substantially parallel to interior wall  219  ( FIG. 4 ). 
       FIG. 2  depicts sealing flaps  216  in a closed state, wherein plates  218 A and  218 B partially overlap and are substantially perpendicular to interior wall  219 . In this state, the plural sealing flaps provide a barrier that substantially prevents water from entering the barrel. 
       FIG. 3  depicts sealing flaps  216  in the process of opening. The sealing flaps are forced open due to the increase in pressure in bores  108  and  215  as a consequence of the combustion of the chemical propellant in round  112 . 
       FIG. 4  depicts sealing flaps  216  in a fully open state, wherein plates  218  A and  218 B are substantially flush against interior wall  219 . In this state, the plates are out of the path of round  112  in the region designated in  FIG. 4  as “Gap.” This region is created by providing bore  215  with a diameter D B   A  that is larger than diameter D B   B  of bore  108 . 
     Thus, prior to firing round  112 , sealing flaps  216  are in their quiescent and closed state, as depicted in  FIG. 2 . As round  112  fires, the increase in pressure within bore  108  (of barrel  102 ) and within bore  215  (of barrel adapter  114 ) due to the combustion of chemical propellant causes plates  218 A and  218 B to partially rotate or pivot about hinge  220 . The pressure is sufficient to cause the plates to lie substantially flush against interior wall  219  of barrel adapter  114 . Repetitive firing keeps sealing flaps  216  in the open state. 
     Hinges  220  include a spring or other element that generates a torsional bias that causes plates  218 A and  218 B to return to the closed state in the absence of increased pressure (i.e., upon cessation of firing). 
     Actuation of sealing flaps  216  is effectively “automatic” based on the firing of round  112 . It can be readily determined how much time is required for the round to reach barrel adapter  114  and sealing flaps  216  and how much force will be required to cause plates  218 A and  218 B to rotate with the requisite speed. As a function of the chemical propellant used in the round, the torsional restoring force provided by the spring, etc., the weight of the plates, and other factors, in some embodiments, a separate charge (in addition to the round&#39;s chemical propellant) will be required to open sealing flaps  216 . 
     In fact, it is possible that the separate charge will need to be pre-fired (before the live round), so that pressure can build to a sufficient extent to open sealing flaps  216 . 
       FIGS. 5A through 5C  depict an embodiment of sealing flap  216  including plate  218 A, plate  218 B, and hinge  220 .  FIG. 5A  depicts one of the plates, plate  218 A and further depicts hinge  220  by which the plate is pivotably coupled to the interior of the barrel adapter.  FIG. 5B  depicts second plate  218 B of sealing flap  216  and its hinge  220 .  FIG. 5C  depicts both of plates  218 A and  218 B, the plates collectively defining sealing flap  216 . In this embodiment, the plates are coupled to diametrically opposed portions of interior wall  219 . In the embodiment that is shown in  FIGS. 5A through 5C , plate  218 A has an area that is somewhat larger than a semicircle and plate  218 B has an area of at least a semicircle to ensure that the plates will overlap (when the sealing flap is in the closed position) to prevent water from entering barrel  102 . 
     The use of a plurality of sealing flaps  216 , as opposed to a single flap, is to provide redundant seals against the external pressure, which can be significant, as a function of the depth of gun  100  below the water. 
       FIGS. 6 and 7  depict an embodiment wherein the barrel seal comprises a plurality of serrations  618  and stopper round  624 . 
     As depicted in these Figures, serrations  618  extend radially inward from interior wall  219  of barrel adapter  114 . The serrations extend over a substantial length of interior wall  219 . Serrations  618  are directed toward an outlet end of barrel adapter  114 , thereby presenting a series of discrete, inwardly-tapering surfaces  622  to an exiting live round. 
     The diameter D S   A  of the opening formed by serrations  618  is somewhat smaller than the diameter D B   B  of bore of the barrel or of the diameter of stopper round  624 . As a consequence, there will be contact between serrations  618  and stopper round  624  when the stopper round is fired. 
     Stopper round  624  comprises an amount of charge that is insufficient to enable the stopper round, when fired, to fully transit the serrations within the barrel adapter. Thus, stopper round  624  is trapped by serrations  618 . 
     The serrations are formed from a resilient material, such as a hard rubber, etc., that will permit repeated contact without substantial degradation and will be sufficiently deformable to create an effective water seal in conjunction with a captured stopper round. 
     In operation, a live round is fired to dislodge stopper round  624  from serrations  618 . The pressure increase due the combustion gases (from firing the live round) dislodges the stopper round. Contact with the transiting live round might facilitate removal of the stopper round as well. Water is kept out of the bore as firing continues. A subsequent stopper round is fired to reseal the barrel. 
     In some embodiments, stopper round  624  is interspersed with live rounds, such as one stopper round per every 20 rounds, etc. In such embodiments, fire-control system  110  would fire  20  rounds and then stop. The twentieth round, being a stopper round, would seal the barrel. If firing is to resume, the next round, which is a live round, would dislodge the stopper round. 
       FIGS. 8 and 9  depict an embodiment wherein the barrel seal comprises an electromagnet and a stopper round. 
     Electromagnet  818  comprises a coil of wire running through barrel adapter  114 . Stopper round  824  comprises a detachable, magnetically attracted, tail section  826 . 
     Electromagnet  818  is coupled to controlled current source  113 , which, in turn, is coupled to controller  111 . The controller is coupled to fire-control system  110 . In the previous embodiments, actuation of the barrel seal is “automatic” in the sense that it is driven by combustion gases. But for the embodiment depicted in  FIGS. 8 and 9 , the actuation of the barrel seal is responsive to information coming from fire-control system  110 . 
     More particularly, fire-control system  110  sends a signal to controller  111  at an appropriate time to direct controlled current source  113  to energize electromagnet  818 . As stopper round  824  exits barrel adapter  114 , a magnetic field that is generated by electromagnet  818  dislodges tail section  826  from the stopper round. 
     Tail section  826  “unfolds” once dislodged from stopper round  824 . In its unfolded state, tail section  826  has an enlarged diameter. Barrel adapter  114  has a reduced-size opening  928 , relative to bore  915 . This reduced-size opening prevents the unfolded tail section  826  from exiting barrel adapter  114 . Electromagnet  818  remains energized and, as a consequence, the unfolded tail section remains magnetically bound to barrel adapter  114 . 
     In operation, a live round is fired to tail section  826 . The pressure increase due the combustion gases (from firing the live round) dislodges the tail section. Contact with the transiting live round might facilitate removal of tail section  826  as well. Water is kept out of the bore as firing continues. 
     It is to be understood that the disclosure teaches just one example of the illustrative embodiment and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims.