Abstract:
The present invention provides a self destruction impact fuse for fail-proof detonating a projectile, preferably a low velocity projectile. The present invention further provides a projectile that can be detonated reliably even at low velocity.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to the technologies of ammunition detonation, and more particularly to a self destructing impact fuze that can detonate ammunition reliably when the ammunition is delivered by projectiles, especially the low velocity projectiles. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ammunition comprises two main components, namely projectile and primed cartridge case; the projectile further comprises a fuze and shell body. One type of fuzes commonly used in ammunition is impact fuze that detonates the ammunition by the resultant impact from the hitting of the ammunition to its target. However, when ammunition with an impact fuze is delivered, it may fail to explode due to insufficient impact. The insufficient impact may be caused by a variety of reasons including: (1) it misses the target and lands on soft grounds such as a swamp or a snow covered area; or (2) it lands on a suboptimal angle with respect to the point of impact. Unexploded ammunition poses hazards for the civilians and the military alike and operation to remove such unexploded ammunition is dangerous, costly and labor intensive. 
         [0003]    Self destructing impact fuzes are employed to detonate ammunition delivered with projectiles when the ammunition fails to explode upon impact. Prior art self destructing impact fuzes can be generalized into three categories: (1) chemical, (2) mechanical and (3) electronic. Exemplary of a chemical self destructing delay impact is U.S. Pat. No. 3,998,164 issued to Hadfield. &#39;164 described a self destructing fuze illustrating the use of a timing chamber containing liquid in combination with a weight and tubular spring mechanism for releasing the firing pin onto the detonator. 
         [0004]    An example of a mechanical self destructing fuze for sub-munition is U.S. Pat. No. 4,653,401 issued to Gatti. &#39;401 relies on the plastic deformation of a wire element which holds and delays the exertion of a secondary striker member onto the detonator. 
         [0005]    Recently electronic self destructing fuzes are also developed to detonate projectiles via electronic timing circuitry after they fail to explode upon impact. 
         [0006]    The inventors of the present invention have disclosed a self destructing impact fuze in U.S. Pat. No. 6,237,495, where the disclosed self destructing impact fuze incorporated into a self destructing impact fuze the key components which respond to physical forces exerted on the ammunition during the flight of the projectiles, resulting in the enhanced reliability of self destructing fuze without significantly increasing the unit production cost. However, the disclosed self destructing impact fuze is not functioning as well in low velocity projectiles as in high velocity projectiles. Therefore, there is a need to have a self destructing impact fuze that can function reliably in low velocity projectiles. 
       SUMMARY OF THE INVENTION 
       [0007]    One embodiment of the present invention provides a self destructing impact fuze employed in a low velocity projectile for detonating explosive charge coupled thereto. The self destructing impact fuze comprises a frame, a self destructing (SD) firing pin assembly disposed concentrically within said frame, said SD firing pin assembly comprising a SD head on one end for receiving a SD spring, a SD firing pin on the opposite end for striking a detonator, and a centrifugal chamber for holding a plurality of spheres therein, said chamber further communicating with a plurality of radial openings and exposing portion of said spheres when the fuze is spun, a groove disposed on the surface of said SD firing pin assembly for receiving two centrifugal locks, said locks having a pivot offset from the longitudinal axis of said frame and having a symmetric configuration, a setback pin assembly for each of the centrifugal locks for controlling the release of said centrifugal locks from said SD firing pin assembly, said setback assembly having a setback pin retractable upon experiencing acceleration of said projectile; and a support ring disposed concentrically within said frame for balancing the forces exerted radially on said centrifugal chamber with forces exerted axially on said SD firing pin assembly by said SD spring, whereby when centrifugal forces on said projectile push said spheres against said support ring, said support ring prevents said SD firing pin assembly from being lowered onto said detonator so that the detonation is initiated by impact, but when said projectile fails to explode upon impact and reaches the maximum tactical distance, and the compression forces overcome the centrifugal forces on said spheres, said SD spring lowers said SD firing pin assembly onto said detonator so that said projectile is reliably detonated. 
         [0008]    Another embodiment of the present invention provides a projectile with a self destructing impact fuze. The projectile comprises a self destructing impact fuze, an escapement assembly comprising at least a rotor assembly and a detonator; and a conical spring disposed between the self destructing impact fuze and the escapement assembly; wherein the self destructing impact fuze comprises a frame, a self destructing (SD) firing pin assembly disposed concentrically within said frame, said SD firing pin assembly comprising a SD head on one end for receiving a SD spring, a SD firing pin on the opposite end for striking a detonator, and a centrifugal chamber for holding a plurality of spheres therein, said chamber further communicating with a plurality of radial openings and exposing portion of said spheres when the fuze is spun, a base disposed at the end of the SD firing pin, said base comprising a point detonation (PD) firing pin near the center of the base, wherein the PD firing pin has a SD firing pin opening for allowing the SD firing pin to pass through, a groove disposed on the surface of said SD firing pin assembly for receiving two centrifugal locks, said locks having a pivot offset from the longitudinal axis of said frame and having a symmetric configuration, a setback pin assembly for each of the centrifugal locks for controlling the release of said centrifugal locks from said SD firing pin assembly, said setback assembly having a setback pin retractable upon experiencing acceleration of said projectile; and a support ring disposed concentrically within said frame for balancing the forces exerted radially on said centrifugal chamber with forces exerted axially on said SD firing pin assembly by said SD spring; whereby after the projectile is launched, the escapement assembly aligns said detonator with the PD firing pin; whereby when centrifugal forces on said projectile push said spheres against said support ring, said support ring prevents said SD firing pin assembly from being lowered onto said detonator so that the detonation is initiated by impact via the PD firing pin, but when said projectile fails to explode upon impact and reaches the maximum tactical distance, and the compression forces overcome the centrifugal forces on said spheres, said SD spring lowers said SD firing pin assembly onto said detonator and the SD firing pin passes through the SD firing pin opening so that said projectile is reliably detonated by the SD firing pin. 
         [0009]    The objectives and advantages of the invention will become apparent from the following detailed description of preferred embodiments thereof in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Preferred embodiments according to the present invention will now be described with reference to the Figures, in which like reference numerals denote like elements. 
           [0011]      FIG. 1A  is a perspective, partial cut away, elevational view of the self destructing impact fuze in accordance with one embodiment of the present invention, showing it being in a “SAFE” position prior to the projectile being propelled through the muzzle. 
           [0012]      FIG. 1B  is a bottom, perspective, elevational view of the escapement assembly  5  of the projectile according to  FIG. 1A . 
           [0013]      FIG. 2A  is a perspective, partial cut away, elevational view of the self destructing impact fuze in accordance with one embodiment of the present invention, showing the retraction of the setback pin during the initial launch of the projectile. 
           [0014]      FIG. 2B  is a bottom, perspective, elevational view of the escapement assembly  5  of the projectile, showing retraction of the detent and initiation of the timing function of the fuze. 
           [0015]      FIG. 3A  is a perspective, partial cut away, elevational view of the self destructing impact fuze in accordance with one embodiment of the present invention, showing the full extent of the centrifugal lock and of the centrifugal balls at the maximum acceleration of the projectile. 
           [0016]      FIG. 3B  is a bottom, perspective, elevational view of the escapement assembly  5  of the projectile, showing the gradual alignment of the rotor assembly into an “ARMED” position. 
           [0017]      FIG. 4A  is a perspective, partial cut away, elevational view of the self destructing impact fuze in accordance with one embodiment of the present invention, showing the alignment of the point detonation (PD) firing pin with the detonator and full extent of the arming lock pin. 
           [0018]      FIG. 4B  is a bottom, perspective, elevational view of the escapement assembly  5  of the projectile, showing the extension of the arming lock pin, thereby locking the rotor in the “ARMED” position. 
           [0019]      FIG. 5  is a perspective, partial cut away, elevational view of the self destructing impact fuze in accordance with one embodiment of the present invention, showing the lowering of the self destructing (SD) firing pin onto the detonator when the self destructing (SD) spring overcomes the centrifugal force acting on the centrifugal balls. 
           [0020]      FIG. 6  is a perspective, partial cut away, elevational view of the self destructing impact fuze in accordance with one embodiment of the present invention, showing the self destructing (SD) firing pin striking the detonator of the escapement assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The present invention may be understood more readily by reference to the following detailed description of certain embodiments of the invention. 
         [0022]    Throughout this application, where publications are referenced, the disclosures of these publications are hereby incorporated by reference, in their entireties, into this application in order to more fully describe the state of art to which this invention pertains. 
         [0023]    In the following detailed description, specific details are set forth in order to provide a thorough understanding of the invention. However, in the following description, numerous specific details are set forth such as centrifugal chamber and firing pin in order to provide a thorough understanding of the present invention. It will be obvious to one skilled in the art that the present invention may be practiced without these specific details. In other instances, description of well-known parts such as those involved with explosive charges and the external structure of a projectile is omitted in order not to obscure the presentation of the present invention. 
         [0024]    The present invention provides a self destructing impact fuze that is preferably suitable for low velocity projectiles so that it can reliably detonate explosive charges attached to the low velocity projectiles. The inventors of the present invention have disclosed a self destructing impact fuze with a single centrifugal lock in U.S. Pat. No. 6,237,495, but it is not suitable for low velocity projectiles. Because a low velocity projectile experiences lower rotational forces as compared to a high velocity projectile, the lower rotational forces may fail to release of the single centrifugal lock due to the self destruct spring compressive load exerted on the single centrifugal lock. The self destructing impact fuze of the present invention comprises a dual centrifugal lock design with two centrifugal locks working at the same time, allowing the smooth and swift release of the centrifugal locks of low velocity projectiles. Without wish to be bound by any specific theory or explanation, inventors of the present invention believe that the dual centrifugal lock design results in less compressive load for each of the two centrifugal locks because the compressive load exerted by the SD spring is evenly distributed between the two centrifugal locks. In addition, the dual centrifugal design improves the dynamic stability of the spinning projectiles during the flight. 
         [0025]    Referring to  FIG. 1A , there is provided a self destructing impact fuze in accordance with one embodiment of the present invention.  FIG. 1A  is a perspective, partial cut away, elevational view of the self destructing impact fuze, where the self destructing impact fuze is in the “SAFE” position and prior to the projectile being propelled through a muzzle As shown in  FIG. 1A , the self destructing impact fuze  1  is a mechanical fuze for initiating explosive charge upon impact of the projectile. The fuze  1  comprises a self destructing fuze  10 , an escapement assembly  5 , and a conical spring  28  which separates the self destruction fuze  10  and the escapement assembly  5 . 
         [0026]    Still referring to  FIG. 1A , the self destructing fuze  10  comprises a frame  30  having an enclosure  32 , a base  34 , a self destructing (SD) firing pin subassembly, two centrifugal locks  40   a,    40   b,  two self destructing (SD) setback pin subassemblies  42   a,    42   b  and a support ring  60 . The frame  30  with the enclosure  32  and the base  34  form a cave of the self destructing fuze  10 ; the SD firing pin subassembly is disposed in the cave. A point detonation (PD) firing pin  36  is disposed near the center of the base  34  for initiating the explosive charge once the projectile impacts the target. At the same time, the PD firing pin  36  has a SD firing pin opening  37  permitting the SD firing pin assembly to be lowered therethrough when the projectile fails to explode upon impact (to be described in detail with respect to  FIGS. 5 and 6 ). 
         [0027]    Referring again to  FIG. 1A , the SD firing pin subassembly comprises a self destructing (SD) spring  54 , a SD head  44 , a SD groove  46 , a SD centrifugal chamber  48  and a SD firing pin  52 . The SD firing pin subassembly provides fail safe detonation of the explosive charge of the projectile should the projectile fail to explode for reasons given in the background section above. The SD centrifugal chamber  48  is hollow and holds a plurality of spheres  50 ; the chamber further communicates with a plurality of radial openings  49  disposed on the surface of the chamber  48 . When the projectile and the chamber is subjected to centrifugal force, the spheres  50  will be pushed outwards and a portion thereof expose through the radial openings  49 . Disposed between the SD head  44  and the SD centrifugal chamber  48  is the SD groove  46  for the purpose of receiving the centrifugal locks  40   a;    40   b.  The centrifugal locks  40   a,    40   b  have a pivot  56   a,    56   b  respectively offset from the longitudinal axis of the frame  30 ; the centrifugal locks  40   a,    40   b  lock the SD firing pin subassembly in place with the assistance of the SD setback pin subassemblies  42   a,    42   b.  The SD setback pin subassemblies  42   a,    42   b  comprise a SD setback pin  58   a,    58   b  and a spring (not shown in any of the figures) respectively. 
         [0028]      FIG. 1B  is a bottom, perspective, elevational view of the escapement assembly  5  as shown in  FIG. 1A . The escapement assembly  5  comprises a body  12 , a detent  14 , a spring  16 , a pinion assembly  18 , a verge assembly  20  and a rotor assembly  22  for aligning the detonator after a predetermined interval. The rotor assembly  22  comprises an arming lock pin  24  and a detonator  26 . It is to be noted that the escapement assembly  5  has been described in detail in U.S. Pat. No. 6,237,495, which is incorporated herein in its entirety, thus no detailed description of the escapement assembly  5  will be provided herein. 
         [0029]      FIGS. 1A and 1B  describe the unaligned “SAFE” position of the self destructing fuze  10  when the projectile has not yet been launched. Here, the detent  14  locks the rotor assembly  22  in place, while the SD setback pin subassemblies  42   a,    42   b  also locks the centrifugal locks  40   a,    40   b  against the SD firing pin subassembly. 
         [0030]    Now there is provided a detailed description of the operation of the self destructing impact fuze. 
         [0031]      FIG. 2A  is a perspective, partial cut away, elevational view of the self destructing impact fuze  1  as shown in  FIG. 1A , showing the retraction of the SD setback pins  58   a ′,  58   b ′ during the initial launch of the projectile. Once the projectile is subjected to a setback force, the springs (not shown) of the SD setback pin subassemblies  42   a,    42   b  are deflected allowing the SD setback pins  58   a ′,  58   b ′ to retract. At the same time the centrifugal force (as result of the projectile making its way through the gun barrel and out of the muzzle) is exerted on the SD centrifugal locks  40   a,    40   b  and the SD spheres  50 ′. Centrifugal Locks  40   a,    40   b  lose their contacts with SD groove  46  and move over the SD setback pin subassemblies  42   a,    42   b  respectively, while the spheres  50 ′ within the SD centrifugal chamber  48  are moved outwards inside the radial openings  49  shown in the drawing. The spheres  50 ′ are urged against the support ring  60  such that the SD firing pin subassembly remains unchanged in its position; therefore, the fuze remains secured and barrel safety is assured. The centrifugal force also acts on the detent  14 ′ and the spring  16 ′ such that they retract and allow the rotor assembly  22  of the escapement assembly in  FIGS. 2A and 2B  to initiate the arming sequence. 
         [0032]      FIG. 3A  is a perspective, partial cut away, elevational view of the self destructing impact fuze  1  as shown in  FIG. 1A , showing the fuze as the projectile reaches maximum acceleration. Here, the centrifugal locks  40   a ′,  40   b ′ are fully retracted and the spheres  50 ″ fully extended through the radial openings  49 . In combination with the contact with the support ring  60 , the spheres  50 ″ are able to overcome the compression force exerted axially by the SD spring  54 ′ on the SD firing pin subassembly.  FIG. 3B  is a bottom, perspective, elevational view of the escapement assembly  5  as shown in  FIG. 1A , showing the gradual alignment of the rotor assembly into an “ARMED” position. Under the influence of radially acting centrifugal forces, the detent  14 ′ and spring  16 ′ continue to be retracted and the rotor assembly  22 ′ rotates into position. The pinion assembly  18 ′ and the verge assembly  20 ′ prevent the rotor assembly  22 ′ from rotating to the “ARMED” position until after the prescribed arming delay time is reached. 
         [0033]      FIG. 4A  is a perspective, partial cut away, elevational view of the the self destructing impact fuze  1  as shown in  FIG. 1A , showing the alignment of the point detonation (PD) firing pin  36  with the detonator  26 ′ and full extent of the arming lock pin  24 ′. The rotor assembly  22 ″ is shown to align the detonator  26 ′ directly over the PD firing pin  36 . In  FIG. 4B , the escapement assembly  5  shows the extension of the arming lock pin  24 ′. Here, the projectile has traveled beyond the muzzle safety distance and before the tactical distance. The arming lock pin  24 ′ prevents the rotor assembly  22 ″ from unarming itself when it fails to hit the target and lands on a soft ground. In other words, the self destructing fuze  10  is armed. Should the projectile impact the target, the escapement assembly  5  accelerates towards the frame. As the detonator  26 ′ is aligned with the PD firing pin  36 , it detonates the explosive charge. 
         [0034]      FIGS. 5 and 6  describe the sequence of detonation of the self destructing impact fuze  1  as shown in  FIG. 1A  when the projectile fails to explode upon impact but reaches the maximum tactical distance. Due to resistance of the air, the rotational speed of the projectile decreases continuously throughout its flight, so that the centrifugal force acting on the fuze  10  is reduced continuously. After a certain flight time, the force exerted by the SD spring  54 ′ on the SD firing pin subassembly in  FIGS. 5 and 6  is greater than that of the centrifugal force acting on the spheres  50 ″. The spheres  50 ″ retract from the support ring  60  via the radial openings  49 . The SD firing pin subassembly and the SD firing pin  52 ″ are lowered onto the detonator  26 ″ and set off the explosive charge. 
         [0035]    The present invention as described in  FIGS. 1-6  uses few components and thus results in a compact design for a self destructing impact fuze. Furthermore, the SD firing pin subassembly used in combination with the SD setback pin subassembly ensure that each of the components interact responsively with the physical forces (whether be it acceleration, deceleration and centrifugal) exerted on the fuze. As such, the self destructing fuze of the present invention is reliable. Moreover, each of the components of the present invention is mechanical and used extensively. Therefore, the unit cost of production of the present invention can be minimised. 
         [0036]    While the preferred embodiment of the present invention shows a SD firing pin subassembly with a hollow centrifugal chamber and a plurality of spheres, it should be understood that other equivalent configurations are possible. For instance, a plurality of radiating flaps disposed on the centrifugal chamber can be used instead of the spheres to prevent the SD firing pin subassembly from being lowered onto the detonator. 
         [0037]    While the present invention has been described with reference to particular embodiments, it will be understood that the embodiments are illustrative and that the invention scope is not so limited. Alternative embodiments of the present invention will become apparent to those having ordinary skill in the art to which the present invention pertains. Such alternate embodiments are considered to be encompassed within the spirit and scope of the present invention. Accordingly, the scope of the present invention is described by the appended claims and is supported by the foregoing description.