Abstract:
An ETC igniter and compatible electrical connector for enabling an ETC gun to be used in a battlefield setting in close proximity with personnel and sensitive electronic equipment. This is accomplished by providing a current path to and from the igniter that is electrically isolated from all other portions of the gun. The connector and igniter are adapted to be capable of withstanding the high connection forces necessary to prevent arcing and the extreme stresses imposed during firing of the gun.

Description:
RELATED APPLICATION  
       [0001]    This application is a division of application Ser. No. 10/373,882 filed Feb. 12, 2003. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to electro-thermal chemical guns, and more particularly, to high-energy igniters and power connectors for electro-thermal chemical cartridges. 
       BACKGROUND OF THE INVENTION 
       [0003]    Electro-thermal chemical (ETC) gun systems have been developed in response to a need for improved medium and large caliber gun performance. Typically, an ETC ammunition round has an igniter assembly. The igniter assembly serves to generate a high-energy plasma from electrical energy supplied to the igniter, and to inject the plasma into a mass of chemical propellant, which is then ignited by the high-temperature plasma. The very high energy and temperature of the plasma enables the use of multi-layer and higher density chemical propellants. Such propellants, although harder to ignite, enable a stronger and more lengthy useful pressure pulse to the projectile, thereby improving gun system performance. One example of such a propellant system is disclosed in U.S. Pat. No. 6,167,810, which is assigned to the owner of the present invention, and which is hereby fully incorporated herein by reference. In addition, the plasma energy itself may serve to provide an additional accelerating force to the projectile, thereby improving gun performance. 
         [0004]    Examples of plasma igniter apparatus for ETC gun systems are disclosed in U.S. Pat. Nos. 5,231,242, 5,287,791, 5,503,081, 5,767,439, 5,444,208, 5,830,377, all assigned to the owner of the present invention, and each of which is hereby fully incorporated by reference herein. In addition, further examples of an ETC plasma igniter are disclosed in co-pending U.S. patent application Ser. No. 09/767,542, assigned to the owner of the present invention, and fully incorporated herein by reference. 
         [0005]    Generally, it is desirable that an ETC igniter apparatus supply about 100 kJ or more of plasma energy to the mass of chemical propellant in an ETC cartridge. As a consequence, it is necessary to supply a slightly greater amount of electrical energy to the igniter. Moreover, for effective plasma formation, the electrical energy must be supplied over a time period measured in milliseconds. As a result, very high electrical currents at very high voltages are necessary to transfer the energy in the requisite amount of time. Currents over 50 kA or more are often necessary. 
         [0006]    Transmission of electrical power at very high current levels presents unique challenges in the design of conductors and connection equipment. Excessive resistance in the current path will cause very rapid and destructive heating effects. In addition, strong magnetic fields may be created which can cause catastrophic failure of conductors and connectors. Moreover, connection interfaces between components in the conductive path may be prone to arcing if contaminated or if insufficient force holds the components together. As a result, it is necessary to provide a strong biasing force to press together components in the current path. This biasing force may reach levels over 1000 pounds of force, imposing high stress loads on components. 
         [0007]    Transmission of electrical power at high currents to a plasma igniter in an ETC gun application presents even greater challenges due to the extreme physical loading characteristics of the application. The breech assembly of a typical 120 mm ETC gun may be subjected to a load of more than 2,000,000 pounds upon firing, resulting in instantaneous stress loads of more than 100,000 p.s.i. in certain components. In addition, the gun and breech assembly must be designed to permit recoil. Thus, power cables must be sufficiently flexible to enable recoil, which may exceed two feet in some cases. 
         [0008]    Specialized coaxial cables and connectors have been developed in response to the above challenges. For example, a high energy flexible coaxial cable and connector suitable for use in ETC gun applications are disclosed in U.S. Pat. No. 5,656,796, assigned to the owner of the present invention, and fully incorporated herein by reference. In addition, embodiments of another high energy power connector usable in ETC gun applications are disclosed in U.S. Pat. No. 5,220,126, assigned to the owner of the present invention, also fully incorporated herein by reference. 
         [0009]    Past solutions, although generally successful in conveying power to an ETC gun plasma igniter while overcoming some of the electrical and physical problems described above, have not been fully suitable for practical use in a battlefield setting for a variety of reasons. The current return path in prior solutions typically leads through portions of the gun that may be exposed to human contact. Due to the high voltages and current present in the return path, such exposed portions can present an extreme life safety hazard to personnel operating the gun, particularly where the gun may be located in a confined space such as a tank turret. Moreover, sensitive electronic devices, which may be used for communication, fire control, or other purposes, are subject to damage from stray currents or strong magnetic fields generated by the current. 
         [0010]    In addition, the power connection in some prior art devices relies on permanent deformation of the connection components or on cumbersome and complicated connectors in order to achieve sufficient connection force to avoid arcing. These methods and devices are generally unsuitable for a battlefield device which must be capable of repeated, reliable, and rapid connection and disconnection so that a relatively high rate of fire may be achieved. 
         [0011]    What is still needed is a high-energy power connection apparatus, especially adapted for use in a battlefield setting, that is suitable for connecting an ETC igniter apparatus in an ETC gun with a high-energy power source. 
       SUMMARY OF THE INVENTION 
       [0012]    The ETC igniter and compatible electrical connector hereof, enable an ETC gun to be used in a battlefield setting in close proximity with personnel and sensitive electronic equipment. This is accomplished by providing a current path to and from the igniter that is electrically isolated from all other portions of the gun. The connector and igniter are adapted to be capable of withstanding the high connection forces necessary to prevent arcing and the extreme stresses imposed during firing of the gun. 
         [0013]    A combination high-energy electrical connector and electro-thermal chemical igniter includes an igniter having a base portion adapted to be operably coupled with an ammunition cartridge case. An electrical connector located in the igniter base portion includes a supply conductor, a return conductor, and a plurality of insulators arranged so as to electrically isolate the supply and return conductors from the base portion. The connector includes a body portion adapted to be operably coupled with a gun breech, a supply conductor having a distal portion adapted to engage and electrically connect with the supply conductor of the igniter, and a return conductor having a distal portion adapted to engage and electrically connect with the return conductor of the igniter. Insulators are arranged so as to electrically isolate the supply and return conductors from the body portion. The connector and electrical connector portion of the igniter may be coaxial. In such a coaxial arrangement, the electrical connector portion of the igniter may have a center supply conductor and an annular outer return conductor surrounding the center supply conductor. The connector may have a center supply conductor having a distal portion adapted to engage and electrically connect with the center supply conductor of the igniter, and an annular outer return conductor surrounding the center supply conductor. The connector further includes a distal portion adapted to engage and electrically connect with the outer supply conductor of the igniter. The supply conductor of the connector may be longitudinally slidable, with a pre-load spring arranged so as to resist proximal sliding of the supply conductor when the igniter is connected with the connector. 
         [0014]    An electro-thermal chemical gun system according to the invention may include an ammunition round having an electro-thermal chemical igniter, a gun adapted to receive and fire the ammunition round, a high-energy power source, a cable connected to the high-energy power source, and a connector for connecting the cable to the igniter. The igniter, connector, and cable are adapted to provide a current supply path and a current return path, each electrically isolated from the gun. 
         [0015]    A method of connecting a power cable from a high energy power source with an igniter in an electro-thermal chemical gun is also disclosed. The method may include the steps of: 
         [0016]    (a) providing the igniter with an electrical connector portion including a pair of conductors, one of the conductors connected with an anode of the igniter, the other conductor connected with a cathode of the igniter, each of the conductors being insulated so as to be electrically isolated from all other portions of the igniter; 
         [0017]    (b) forming an electrical connector having a pair of conductors and a body portion, the body portion operably coupleable to the gun, each of the pair of conductors adapted to engage and connect with a separate one of the pair of conductors of the igniter when the electrical connector is engaged with the igniter, each of the pair of conductors being insulated so as to be electrically isolated from all other portions of the electrical connector and the gun; 
         [0018]    (c) connecting each of the pair of conductors of the electrical connector with a separate conductor of the power cable; 
         [0019]    (d) connecting the electrical connector with the electrical connector portion of the igniter; and 
         [0020]    (e) forcing the electrical connector and the igniter together with a first biasing force of sufficient magnitude to prevent arcing between the conductors of the igniter and the conductors of the electrical connector. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0021]      FIG. 1  is a side elevation view of an ETC gun system; 
           [0022]      FIG. 2  is a cross-sectional view of an electrical connector and ETC igniter in a cartridge case; 
           [0023]      FIG. 2A  is an end view of the igniter depicted in  FIG. 2 ; and 
           [0024]      FIG. 3  is a cross-sectional view of an alternative embodiment of an igniter. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    An electro-thermal chemical gun system  4  is depicted in  FIG. 1 . Gun system  4  generally includes gun  5  and high-energy power source  6 . Gun  5  generally includes barrel  7  with breech portion  8 , chassis portion  9 , and power cable  10 . Chassis portion  9  may have wheels  11  for mobility. 
         [0026]    A power connector and electro-thermal chemical (ETC) igniter assembly  10   a  according to the present invention is depicted in  FIG. 2 . The assembly  10   a  generally includes coaxial power cable  10 , power connector  12 , and basepad igniter  14 . 
         [0027]    Coaxial cable  10  generally includes a center conductor  16 , and an outer conductor  18 , separated by insulation layer  20 , and covered by insulation jacket  22 . One example of a suitable coaxial cable assembly is also disclosed in U.S. Pat. No. 5,656,796, previously incorporated herein by reference. 
         [0028]    Power connector  12 , generally includes center conductor assembly  24 , outer conductor assembly  26 , and outer sleeve  28 . Connector  12  is generally cylindrical and presents a longitudinal axis, annotated A-A in the drawings. 
         [0029]    Center conductor assembly  24  of power connector  12  generally includes center pin  30 , insulating sleeves  32 ,  34 , and preload spring  36 . Proximal end  38  of center pin  30  has an enlarged portion  40  with a socket  42  for receiving the distal end  44  of center conductor  16  of coaxial cable  10 . Distal end  46  of center pin  30  may be conically shaped, as depicted in the drawings, for improved electrical conductivity. Insulating sleeve  32 , which may be formed from a material having a high compressive strength such as ceramic, is slidably disposed around insulation layer  20 . Preload spring  36  bears on the proximal end  48  of insulating sleeve  32  and supplies a biasing force which presses insulating sleeve  32  against the proximal end  38  of center pin  30 , thereby biasing center pin  30  distally. Pre-load spring  36  is depicted as a Belleville washer, but may also be any other suitable resilient member. Insulating sleeve  34  is slidably disposed over center pin  30  so as to enable slight longitudinal movement of center pin  30 . Insulating sleeve  30  may be made from any suitable relatively high strength material such as polycarbonate plastic. 
         [0030]    Outer conductor assembly  26  of power connector  12  generally includes conductor portion  50 , annular sleeve  52 , insulator  54 , and insulating sleeves  56 ,  58 . Conductor portion  50  is generally tubular and may have an interior threaded portion  60  engaged with corresponding threads  62  of annular sleeve  52 . Annular sleeve  52  has a frusto-conical wedge portion  64 , which projects distally through insulator  54 . Insulating sleeve  56 , which again may be formed from a high compressive strength material such as ceramic, is disposed around insulation jacket  22  and is longitudinally sandwiched between shoulder portion  66  of conductor portion  50  and outer sleeve  28 . Insulating sleeve  58  electrically separates shoulder portion  66  from outer sleeve  28 . 
         [0031]    Outer sleeve  28 , which may be formed from high strength material such as high-carbon nickel-chromium-molybdenum alloy steel, may have an exterior threaded portion  68  so that connector  10  may be threaded into a bore  70  formed in a gun breech  72 . Flats  74  may be provided at the proximal end  76  of outer sleeve  28  to facilitate manual threading of the connector. Alternatively, connector  10  may be forced into bore  70  by a hydraulic or other machine capable of supplying a force, as will be further explained hereinbelow. 
         [0032]    Basepad igniter  14  generally includes base  78 , power connector portion  80 , plasma containment portion  82 , and vent cover  84 . Base  78  has a threaded portion  86  so that the igniter  14  may be threaded into a cartridge case  88  of an ammunition round from the inside. 
         [0033]    Power connector portion  80  generally includes anode  90 , cathode  92 , wire  93 , and insulating sleeves  94 ,  96 ,  98 ,  100 . Anode  90  has a conical socket  102  for receiving the conical shaped distal end  46  of center pin  30 . Anode  90  is electrically connected with cathode  92  by wire  93 , but is otherwise electrically isolated from cathode  92  by cooperating insulating sleeves  94 ,  96 . Insulating sleeve  94  may be made from a high compressive strength insulating material such as ceramic, while insulating sleeve  96  may be made from any suitable relatively high-strength material such as polycarbonate plastic. 
         [0034]    Cathode  92  has a frusto-conical socket portion  104  for receiving wedge portion  64  of power connector  12 . Cathode  92  is electrically isolated from base  78  by insulating sleeves  98 ,  100 . Again, insulating sleeve  98  may be made from ceramic or other similar material having a high compressive strength. 
         [0035]    Plasma containment portion  82  fits over base  78  and has a generally spiral shaped plasma channel  106  connecting anode  90  and cathode  92 . Plasma containment portion  82  is formed from a generally insulative material such as plastic. Vent cover  84  is disposed over plasma containment portion  82 , and has vent apertures  105  leading from plasma channel  106  to the interior of the cartridge case, which contains chemical propellant  108 . 
         [0036]    The operation of the invention may now be understood with reference to  FIG. 1 . Outer sleeve  28  is threaded into bore  70  of gun breech  72 , causing the conical shaped distal end  46  of center pin  30  to engage and wedge into conical socket  102  of anode  90 . As outer sleeve  28  is threaded further, outer conductor assembly  26  continues to advance with it, wedging frusto-conical wedge portion  64  into socket portion  104  of cathode  92 . Center pin  30 , being already in contact with conical socket  102 , is stationary, but is wedged with steadily increasing pressure into conical socket  102  through the compression of pre-load spring  36 . Outer sleeve  28  is advanced until a desired contact force is reached at both the connections between center pin  30  and socket  102  and between wedge portion  64  and socket portion  104 . These compressive forces in the current path inhibit arcing, which can result in rapid heating and destruction of the components. The compressive force may preferably be in the range of 800 to 1400 pounds. The high compressive strength insulators  32 ,  56 ,  94  and  98  transmit the compressive force between the metallic components while also providing the desired electrical isolation. 
         [0037]    Once power connector  12  is fully engaged with basepad igniter  14  as described above, a power pulse may be applied to center conductor  16  of coaxial cable  10 . The power is conducted through center pin  30  to anode  90 . Wire  93  vaporizes, forming a plasma arc in plasma channel  106  as current flows to cathode  92 , and plasma is vented into the chemical propellant  108  through vent apertures  105 . The current returns through cathode  92 , outer conductor assembly  28  and outer conductor  18 . 
         [0038]    The current return path is electrically isolated from the cartridge case  88  and gun breech  72  by insulators including plasma containment portion  82 , insulating sleeves  98  and  100 , insulator  54 , insulating sleeves  56  and  58 , and insulation jacket  22 . Thus, personnel and sensitive electronic devices may be located proximate the gun during firing without deleterious effects from high voltage and current. 
         [0039]    The high strength outer sleeve  28  serves as a containment structure for power connector  12 , preventing destruction of the connector from the strong magnetic forces caused by the proximity of the supply and return current paths. The high compressive strength insulators used at critical locations in the connector and igniter serve to transmit the necessary compressive forces to prevent arcing while also resisting the extreme recoil forces resulting from firing the gun. 
         [0040]    An alternative embodiment of an ETC igniter, known as a low-volume injector (LVI) igniter is depicted in  FIG. 3 . Igniter  110  generally includes base portion  112 , electrical connector portion  114 , and plasma rod  116 . The igniter  110  presents a longitudinal axis annotated B-B in the drawings, which is generally coincident with the longitudinal axis of a cartridge case (not depicted). 
         [0041]    Base portion  112  has a threaded portion  118  for threading into the cartridge case of an ammunition round from the inside. Base portion  112  also includes retainer ring  120  and insulating outer cone  122  for retaining electrical connector portion  114 . 
         [0042]    Electrical connector portion  114  generally includes center conductor  124 , anode  126 , cathode  128 , and outer conductor  130 . Wire  131  connects anode  126  and cathode  128 . High compressive strength insulating sleeves  132 ,  134 , as well as insulating sleeve  136 , serve to isolate center conductor  124  from cathode  128  and outer conductor  130 . Outer cone  122 , high compressive strength insulating sleeves  138 ,  140 , and insulating sleeves  142 ,  144 , electrically isolate cathode  128  and outer conductor  130  from base portion  112  and portions of the gun connected with it. Again, center conductor  124  has a conical socket  146  for receiving the conical distal end  46  of electrical connector  12 , while outer conductor  130  has a socket portion  148  for receiving wedge portion  64 . 
         [0043]    Plasma rod  116  generally includes tubular portion  150  enclosing a plasma generation region  151  in the form of plasma channel  152 . Wire  131  is contained in plasma channel  152 . Insulator  153  insulates wire  131  from center conductor  124 . Vent apertures  154  are provided to vent plasma into a chemical propellant mixture as before. End cap  156  is disposed over the end of plasma rod  116  and is secured with fastener  158 . 
         [0044]    In operation, the electrical connector  12  may be engaged with igniter  110  in the same manner as previously described. Once engaged, a high energy current pulse may be supplied through center pin  30  to center conductor  124  and anode  126 . Wire  131  vaporizes, forming a plasma arc in plasma channel  152  as current flows to the cathode  128 , and plasma is vented into chemical propellant through vent apertures  154 , igniting the propellant. Current returns through cathode  128 , and outer conductor  130  to outer conductor assembly  26  of electrical connector  12  and outer conductor  18  of coaxial cable  10 . 
         [0045]    In the embodiment of  FIG. 3 , the return current is isolated from base portion  112  and all portions of the gun connected with it by outer cone  122 , high compressive strength insulating sleeves  138 ,  140 , and insulating sleeves  142 ,  144 . Thus, a gun wherein the LVI ETC igniter is employed may be fired in proximity with personnel and sensitive electronic devices without negative effect. Moreover, the high compressive strength insulating sleeves  132 ,  134 ,  138 , and  140 , serve to effectively transmit the necessary compressive forces between metallic components necessary to prevent arcing, while also withstanding the extreme loads imposed during gun discharge. 
         [0046]    Referring again to  FIG. 2 , for most uniform ignition of a chemical propellant charge  108 , it is generally preferred that the plasma arc be exposed to the chemical propellant  108  over a relatively large area. In the depicted basepad igniter  14 , this is achieved by forming a generally spiral plasma channel  106  with vent apertures  105  distributed along the length of channel  106 . The spiral configuration and relative length of the channel  106  provide a plasma ignition source that is distributed over a relatively large area at the end of a cartridge case  88 . Plasma itself is conductive, however, and as the plasma escapes into the chemical propellant  108  from the vent apertures  105  closest to anode  90  in the incipient stages of plasma formation, a lower resistance current path may be formed directly from anode  90  to cathode  92  through plasma in the chemical propellant  108 . If the bulk of the current short-circuits through such a direct path, the result is a more concentrated plasma arc with a relatively less uniform ignition of the chemical propellant. 
         [0047]    In another embodiment of basepad igniter  14 , depicted in plan view in  FIG. 2A , the above described short-circuiting is advantageously minimized. As depicted, vent cover  84  has been removed, exposing plasma containment portion  82 . A first primary electrode  160  is connected with anode  90  and a second primary electrode  92  is connected with cathode  92 . The primary electrodes  160 ,  162 , are spaced apart a distance annotated X 1 . Wire  93 , which is disposed in plasma channel  106 , electrically connects primary electrodes  160  and  162 . In this embodiment, a plurality of secondary electrodes  164  are located along the length of wire  93 . Each secondary electrode  164  is spaced apart a distance, annotated X 2 , from each immediately adjacent primary electrode  160 ,  162 , and immediately adjacent secondary electrode  164 . The plasma channel  106  is configured, and the secondary electrodes  164  are positioned, so that distance X 1  is at least slightly greater than distance X 2 . The distances X 2  between adjacent electrodes  164  along wire  93  need not be equal, so long as each is at least slightly less than distance X 1 . In operation, when a current pulse is supplied to anode  90 , and the connected primary electrode  160 , the shorter path and resultantly lower resistance between primary electrode  160  and adjacent secondary electrode  164  causes the bulk of current to flow between those two electrodes, rather than directly to cathode  92  through any plasma that may be present in chemical propellant  108 . In similar fashion thereafter, the relatively closer spacing of each adjacent secondary electrode  164  causes the current to flow to it, rather than directly through plasma in the chemical propellant  108 . The plasma arc is thereby propagated along the entire length of plasma channel  106  as preferred.