In-line annular piston fixed bolt regenerative variable charge liquid propellant gun with variable hydraulic control of piston

This invention relates to liquid propellant guns utilizing differential area pistons to provide continued or regenerative injection of a liquid propellant into the combustion chamber and, particularly, to such guns in which there are a plurality of coaxial elements, including at least one differential area piston, arranged so as to provide for relative action between elements as a means for controlling regenerative propellant injection.

An extensive summary of the prior art appears in the "Description of the Prior Art" of U.S.-A-4,341,147 to R. E. Mayer. U.S.-A-3,138,990, 4,023,463 and 4,050,349 cited in that document and U.S.-A-4,341,147 itself are exemplary of that prior art. In general, the references cited show differential pressure pistons for forcing liquid propellant from a reservoir chamber into a combustion chamber responsive to combustion pressures. Also pertinent to the present invention are the descriptions of our copending European Patent Applications No. 84112792.1 and 84112793.9 in which a moving differential area piston cooperates with another member, i.e., the fixed bolt 5 in Figure 1 to control the flow rate or dispersion pattern or both of the propellant as it is pumped to the combustion chamber.

US-A-4 099 445 describes a gun structure in which the various propellant components are forced from fixed volume reservoir into the combustion chamber by means of a differential area piston to which an additional moving force is provided at the initial stage of its working stroke movement.

US-A-4 281 582 describes an injection piston of a regenerative liquid propellant gun which is attached to a second piston that has a programmed hydraulic resistance which controls its motion.

US-A-4341 147 describes a regenerative liquid propellant gun according to the preamble of claim 1 and having a structure which reacts to combustion pressure to dispense and regulate the flow of liquid propellant from an included reservoir. Said structure includes a first differential area piston and a second differential area piston in a bore in the first piston, said second piston opening and closing injection ducts in the first piston and being hydraulically controlled.

This invention pertains a novel breech, receiver and combustion chamber structure for a liquid propellant gun of the regenerative injection monopropellant type and pertains to improvements in structures in which a moveable differential area piston cooperates with at least one other structural element to control propellant flow rate or dispersion pattern or both as the propellant is pumped from a reservoir chamber to a combustion chamber by a piston responsive to combustion pressures. The invention contemplates an in-line annular piston (i.e. axially aligned with the gun bore, surrounding a reservoir space and moving in direct reaction to the projectile) supported within the breech mechanism section for reciprocal overrunning motion axially of a fixed central bolt member wherein the cylindro-annular space between the cylindrical differential area piston wall and the bolt constitutes a reservoir chamber having a capacity between the head of the piston and a moveable third member which is variable from zero to a selected full charge capacity. The zero capacity capability provides a starting position for an air free rapid fill to avoid ullage. An annular opening between the bolt and the annular disk-like piston head constitutes an injector for transfer of propellant from the reservoir to the combustion chamber as the piston is displaced responsive to combustion pressure. In particular, the invention contemplates use of a variable orifice hydraulic resistance to movement of the differential area piston by itself or in addition to other means for controlling the flow rate of propellant from a reservoir to a combustion chamber. The moveable third member provides shot-to-shot variable charge capability. The variable orifice hydraulic system permits shot-to-shot programmable mass flow rate of propellant into the combustion chamber. The invention disclosure also contains structural refinements facilitating loading, sealing, ignition and survival. The principal configuration has been tested to demonstrate the efficacy of the structure for obtaining desired ballistic results from predetermined breech pressure and time relationships as a result of controlled injection and burn rates.

More specifically, the present invention provides regenerative injection liquid propellant gun structure wherein a first portion of a moveable differential area piston in the breech casing is interposed between a liquid propellant reservoir and a combustion chamber and moves relative to another structural component in said casing defining a portion of the boundary of the reservoir during firing to collapse said reservoir, characterized by

• a. a recess in said other structural component facing said differential area piston;
• b. a second portion of said differential area piston forming a secondary piston mating with said recess to form a dashpot;
• c. an accumulator structure for charging the dashpot with a suitable operating fluid; and
• d. variable capacity fluid conduit means interconnecting said dashpot and said accumulator structure;

whereby said dashpot and accumulator structure when charged with a suitable fluid resists movement of said differential area piston during firing as a function of pressures created and the flow capacity of said variable capacity fluid conduit means and whereby said dashpot and accumulator structure constitute at least a part of the means for controlling the mass flow rate of liquid propellant from said reservoir to said combustion chamber.

• Figure 1 is a longitudinal sectional view of a fully charged breech section of a variable charge regenerative liquid propellant gun in accordance with this invention.
• Figure 2 is a longitudinal section view of the same gun structure having only half a charge as compared to that of Figure 1.

The implementation of the breech or chamber section of a liquid propellant gun according to the invention and as illustrated in Figures 1 and 2 of the drawings includes, as common to most fire arms and cannon, a gun barrel 1 attached to an enlarged breech mechanism section 2 which includes provisions for the introduction, ignition and burning of a propellant material to create a gas to drive a projectile through the barrel. The breech section 2 of this gun includes a casing 21 surrounding and defining a chamber 3, a breech plug structure 4 restraining two moveable pistons 6 and 7, and a fixed bolt structure 5. The moveable pistons cooperate with the bolt to accept, retain and dispense liquid propellant in a metered fashion in response to pressure created by combustion acting on differential area pressure piston 6.

Chamber 3 as defined by the interior wall 30 of the casing is cylindrical with one closed end wall 31 interrupted by the opening to the bore 11 of barrel 1 and two threaded portions 32 and 34 representing a facility for positioning and securing a breech closure mechanism, as for example, the breech plug structure 4, to provide reaction to propulsion pressures and a facility for securing the fixed bolt structure 5 in place. Casing 21 is illustrated as merely abutting the enlarged barrel base 13 to constitute end wall 31 of the chamber without defined restraining means. Any of the well known structures, e.g. drop block, pivoted block, etc., which are outside the scope of this invention may be used to join this novel breech to the barrel while permitting loading of projectiles 12. Breech plug structure 4 is representative of a wide range of possible designs and is illustrated as having plug portion 42, interconnection means 43 constituting in this case a screw threads for securing the plug to the threaded portion 32 of breech casing 21, spring buffer assembly 44 and internal bore 46 supporting a block or fill piston block 7 by means of a cylindrical portion 72. There is no reason to preclude the use of interrupted screw threads at 32.to provide for quick removal and adjustment.

. Bolt structure 5 is fixed in place in the breech structure axially of the gun by a web structure 50 which has a threaded portion for attaching it to the threaded portion 34 of casing 21 and a reduced cylindrical portion 53 providing support for the annular forward portion 70 of moveable block or fill piston 7 which slides between the reduced cylindrical portion 53 and the casing wall 30. The shaped or contoured portion of the bolt which, as shown in Figure 1, has a cylindrical ledge portion 52 at the junction of the web structure 50, and the reduced radius shaft portion 51 of the bolt which is within the propellant reservoir 35. The cylindrical surface at 52 may carry a seal 54 and interfaces with the annular piston head 60 of the piston 6 in the position shown in Figure 1. The web portion 50 of bolt 5 also contains an axial cup-like combustion chamber 55 facing the opening to barrel bore 11 and multiple passages 56 between the rear shoulder 57 of portion 53 and the combustion chamber. As illustrated, passages 56 are merely holes drilled through the monolithic portion 53 of bolt 5.

The differential area annular piston 6 has a cylindrical skirt portion 63 which serves as a piston rod and primarily defines cylindro-annular reservoir 35 about the shaft portion 51 of bolt 5 which varies in capacity as pistons 6 and 7 are moved relative to each other within the operating cylinder portion of chamber 3. Piston head 60, which separates reservoir 35 from the entrances to passages 56 to combustion chamber 55 and acts as a valve to control flow of propellant from the reservoir, is disk-like and annular in that it has a central hole defined by the cylindrical surface 62 dimensioned to the diameter of bolt ledge 52 to permit seating on the ledge. The interior surface 64 of cylinder head 60 which may be shaped as illustrated to facilitate propellant flow and to provide appropriate strength has, because of the thickness of skirt wall 63, a lesser area than the exterior head surface and causes annular piston 6 to be a differential area piston acting between the combustion chamber and reservoir 35. Piston head 60 also has an exterior rim portion 61 journaled to the interior surface 71 of the cylindro-annular forward portion 70 of piston 7 which could be fitted with a piston ring. The exterior of piston 6 has a slightly reduced portion 66 which creates a narrow annular space 33 between the piston skirt 63 and the interior surface of the forward portion of piston 7.

The face of piston head 60 is shaped to provide a stop surface 65 which abuts the surface of shoulder 57 of bolt 5 when surface 62 is seated on bolt ledge 52. The central aperture of the piston head adjoining cylindrical surface 62 is also shaped to provide a conical surface 67 flaring away from cylindrical surface 62 so that the annular gap between the piston head and ledge 52 which constitutes an injection annulus increases gradually in size as piston 6 moves rearwardly during firing. The maximum size of the injection annulus is the difference in radii of the cylindrical surface 62 and the bolt shaft 51 which is reached as soon as the flared conical surface of the piston head clears the ledge 52. Although both the ledge 52 and the piston head annulus surface 62 are defined here as cylindrical, it may be advantageous under certain conditions to have those surfaces made slightly conical, but less conical than surface 67, to facilitate seating and unseating.

The block or fill piston 7 of a liquid propellant gun according to this invention performs the same functions as that of Co-pending European Patent Application 84112792.1 but also includes a structure which is specific to the present invention. The block or fill piston 7 is fitted in chamber 3 for reciprocal motion and, as already noted, has a cylindro-annular forward portion 70 projecting from its main body 73 which surrounds the annular differential area pressure piston 6 and overruns the reduced cylindrical portion 53 of the bolt structure. A rear cylindrical portion 72 is journaled in bore 46 in the breech plug 4, both supporting the piston and sealing the opening in the breech plug. The main body 73 of piston 7 includes an annular nose portion 74 surrounding and defining a partial axial bore 75 journaled on the stem portion 51 of bolt 5. The nose portion is recessed with respect to the forward portion 70, is defined by an annular recess 76 in the body 73 contoured to receive the annular skirt 63 of annular piston 6 to constitute an annular dashpot and is shaped to mate with the internal surface 64 of the pressure piston 6 so that the capacity of reservoir 35 can be reduced to zero on firing and prior to fill.

Piston 7 in the illustrated embodiment also has an internal accumulator cylinder 78 (which could be external if desired) interconnected with annular recess 76 by multiple conduits 77 and is provided with feed line conduits 17 and 27 for charging the cylinder 78. Free piston separator 79 with appropriate seals is located within cylinder 78 and serves to separate, and balance pressures between, the fluids in cylinder volumes 37 and 47 as they are charged through conduits 27 and 17 and respond to the results of relative movement between pistons 6 and 7, It is contemplated that cylinder portion 37, conduits 77 and annular recess 76 would be charged with water or a hydraulic fluid and cylinder portion 47 charged with air or gas pressure. The accumulator structure is an essential component of the invention and with the strategic locations of the interconnections between the multiple conduits 77 and annular recess 76 and with the optional valves 87 in conduits 77 constitutes a variable or programmed orifice hydraulic damper provides a shot-to-shot programmable mass flow rate capability which includes use of different charge quantities of propellant in reservoir 35.

The gun breech structure illustrated also contains features more fully disclosed and explained in co-pending European Patent Application 84112792.1 including, for example, the annular space 33 closed off by aligned seals carried by pistoh 7 as shown which also accommodate a variable capacity charge capability while retaining seal integrity. When charged with an appropriate fluid through conduit 36, annulus 33 can hydraulically support skirt 63 against firing pressures and can dispense lubricants, preservatives or combustion enhancements or combinations thereof past the piston head ring projection 61 into the combustion area. The breech structure 4 in this embodiment of gun is principally an annular breech block 42 which is adjust- ably retained in the casing by a threaded connection at 32 which as noted could be interrupted threads. It includes a spring buffer assembly 44 made up of Belleville washers 14, pressure ring 15 and pins 16 for positioning piston 7 and for allowing a set back movement of the combined structure of pistons 6 and 7 and the included reservoir 35 to unseat piston head 60 from ledge 52 to initiate feed of propellant from reservoir 35 to the combustion chamber. Other structure, e.g. a liquid spring, liquid damper, coil springs, etc., could be substituted for some of these elements. The structure also includes a drive cylinder 10 with conduit 28 for the insertion of fluid under pressure to drive piston 7 toward the barrel to reseat piston 6 onto the ledge 52 of bolt 5 in preparation for filling the reservoir. The structure also includes fill conduit 45 for the insertion of the liquid propellant and vent conduit 49 communicating with the enclosed cylindrical volume 78. In the embodiment illustrated, the flexible connections required to connect conduits 36, 45, 49,17 and 27 to their proper supplies, valves, etc., are not shown because they are elements readily selected from available technology. The Figures include an igniter 26 communicating with combustion chamber 55 which can be of any convenient design but must have, or be accompanied by, a means for providing a sufficient charge to move pistons 6 and 7 to unseat piston head 60 from ledge 52 to open the annular injector.

The gun mechanism illustrated in Figure 2 is the same mechanism as that in Figure 1 but charged with only half of the amount of liquid propellant present in Figure 1. This shows the adaptability of the structure, a prime feature of the design, and the slightly changed positions of the components with respect to one another to accommodate a half charge. Most noticeable are the smaller capacity of reservoir 35, the smaller volume of empty chamber at 3 between the forward end of piston 7 and chamber end wall 31, and the exposure of a length of screw threads 32 at 22 indicating that the adjustment of the mechanism to determine load charge is made by turning breech plug 4 farther into the chamber to reduce the distance between the nose portion 74 of piston 7 and piston head 60 in the loaded position. Less obvious is the volume reduction of annular recess 76 and a corresponding volume increase of the accumulator hydraulic cylinder 37. In addition in Figure 2, some of the conduits 77 are obstructed by the bottom of skirt 63 of the annular piston 6. The number and location of conduits 77, as already noted, must be determined to produce the desired throttling of flow of hydraulic fluid as it is forced from recess 76 to accumulator 78 to produce the desired hydraulic resistance. The amount of hydraulic resistance to be applied is determined by taking into account all factors including the design of piston head 60, the size of the injection annulus, the burning characteristics of the particular propellant etc., to produce the desired pressure/time curve on firing. The location of conduits 77 to cause some to be blocked off by piston skirt 63 prior to firing a partial charge is a part of this determination. Other mechanical means could be used as a substitute for valves 87 to change the flow capacity of conduits 77 as, for example, a rotating sleeve structure to move identically shaped and aligned apertures into and out of registry or to move skewed elongated apertures through a range of partially coincident positions.

Operation

Firing

The gun structure as illustrated in Figure 1 is fully charged and ready for firing with reservoir 35 filled with the liquid propellant to the maximum capacity and with annular ring 62 of the annular piston 6 seated on ledge surface 52 of the bolt so as to preclude leaking of the liquid propellant into the passages 56 leading to the combustion chamber 55. Space 33 is charged with an inert liquid to provide a hydraulic support for annular piston wall 63 during firing. The liquid in 33 as already noted may be very viscous, may have lubricant properties, or may contain materials chemically similar to those added to powders in conventional ammunitions for the treatment or preservation of barrels. The valve in conduit 45 is closed against backflow of the liquid propellant. Any existing pressure in space 10 and conduit 28 is relieved. Firing is initiated by means of activation of ignitor 26 which is provided with a charge or other means sufficient to create enough pressure in the combustion chamber 55 and communicating passages 56 to unseat piston head 60 from its mating position with the ledge on bolt 5 by driving the reservoir and fill piston 7 rearwardly against pins 16 partially collapsing belleville washers 14. The action of the igniter will both cause an initial injection of liquid propellant from reservoir 35 into combustion chamber 55 and ignite the injected liquid propellant. Ignition of the liquid propellant flowing from reservoir 35 will increase the pressure in the combustion chamber and passages 56 and produce a regenerative feeding of liquid propellant from reservoir 35 into the combustion chamber because of the differential area piston head 60 of the annular piston. As the pressure in combustion chamber 55 increases, it reaches the point of causing the obturation band portion of the projectile 12 to become deformed and permit the projectile to move.

The conical surface of the portion of the annular piston head 60 indicated at 67 causes the annular space between that surface and the edge of ledge 52 to increase during early movement of the piston 6 to produce an ever increasing thickness of the annular sheet of liquid propellant injected into the combustion chamber until all of the surface 67 clears ledge 52 after which the thickness of the annular sheet is a function of the difference in diameters of bolt shaft 51 and annular surface 62. The initial flow rate of liquid propellant produces an increased burn rate with an attendant pressure increase which is adequate to overcome the increased volume of the combustion chamber caused both by displacement of the annular piston and by the accompanying displacement of the projectile 12. The continued flow and burn rate after the injection annulus reaches full size, as already noted, is a function of the design of piston 6, the relative sizes and volumes of components and the characteristics of damping introduced by the variable orifice hydraulic damper which includes the dashpot recess 76, restrictive conduits 77, valves 87 and the accumulator structure 37, 47, 49. As piston head 60 approaches the nose portion 74 of fill piston 7, the injection piston 6 is brought to a halt hydraulically by the closing down of conduits 77 by piston skirt 63. The variable orifice hydraulic damper also provides tailored combustion chamber pressure rises to accommodate acceleration sensitive projectiles and projectiles of different weights.

Charging

At the completion of the firing, annular piston 6 is seated onto fill piston 7 with piston 7 being located against or near the stops 16, depending on the relationship of the reaction of the buffer assembly and dissipation of the chamber pressures. After the insertion of a new projectile 12 by whatever breech action means has been incorporated into the specific gun using this invention, hydraulic or pneumatic pressure, whichever is used, may be inserted through conduit 28 to expand annular space 10 to dirve both pistons, in register, toward the gun barrel until piston 6 seats onto the bolt ledge portion surface 52. The pressure on conduit 28 is then relieved and, if appropriate, breech plug 4 rotated, or reset if an interrupted screw is used, to obtain the proper position of stops 16 to provide for the proper capacity of reservoir 35 for the next firing. The valve in conduit 45 is then opened to admit liquid propellant under pressure into the collapsed reservoir at 35.

As liquid propellant is inserted into and expands reservoir 35 by forcing fill piston 7 away from piston 6, if necessary, against a residual pressure in cylinder 10, to prevent, or at least reduce, the amount of ullage in the liquid propellant in the reservoir. The fill process is continued until the fill piston seats onto pins 16. The gun mechanism is then charged for a subsequent firing and the annular space 33 can be filled if the charging system does not cause that to be effected as a result of the rearward movement of piston 7 which automatically expands space 33.

The foregoing describes the structure and operation of a regenerative monopropellant liquid propellant gun structure according to this invention employing the cooperation of a fixed axial bolt and an annular piston wherein the cylindro-annular piston rod cooperates with other members to define a reservoir for liquid propellant, wherein the annular planar piston head overruns part of bolt as it moves in response to combustion pressure, cooperates with a shaped portion of bolt and with variable orifice hydraulic means for applying a variable resistance back pressure to the piston to deliver a predetermined pattern and flow rate of propellant to the combustion chamber. An additional moveable piston member cooperates with the annular piston and with positioning means to limit travel of the additional moveable piston member to cause the propellant reservoir to have a variable capacity to provide a variable charge capability and shot-to-shot programmable mass flow rate of propellant and to facilitate charging of the gun by permitting the capacity of the reservoir to be increased from zero to a desire content as the liquid propellant is introduced to provide for aid free rapid propellant fill. Structural integrity is enhanced by use of a hydraulic pressure support of the annular piston rod which also facilitates lubrication and cooling of the structure.