Submunition fuse with an inertion-operated and a self-destruct firing mode

Abstract: A submunition fuse (1) presenting a tubular body (17); a support (23) housed in sliding manner in the tubular body (17); a firing element (35) housed in sliding manner in the support (23); a detonating element (7) mounted facing the firing element (35) in the armed position of the fuse; a strip (27) fitted to the top of the support (23), projecting from the tubular body, and which, during descent of the fuse, exerts aerodynamic force on the support in a direction away from the detonating element (7); a first thrust spring (31) acting on the support (23) to generate a first thrust, in the direction of the detonating element (7), not exceeding the aerodynamic force; a second thrust spring (40) acting on the firing element (35) to generate a second thrust in the direction of the detonating element (7); and lock balls (30) retained by the tubular body (17) in such a position as to interfere with and lock the firing element (35) in a withdrawn position. The first thrust spring (31) is disabled, during descent, by the aerodynamic force to maintain the fuse in the arming position, and is activated at the end of descent in the event of failure of the impact-initiating system, by virtue of no longer being counteracted by the aerodynamic force. The support (23) is therefore pushed into such a position as to release the balls (30) and hence the firing element (35) which is pushed by the second spring (40) against the detonating element (7).

Description: The present invention relates to a submunition fuze with an inertial and a self-destruct firing mode, as defined in the preamble of claim 1. As is known, use has been made for many years of artillery projectiles and rockets containing a number of submunitions or bombs, and a time fuze which, when activated at a given height over the target, bursts the so-called carrier or cargo projectile or rocket to fire the bombs over a given surface area. The submunitions feature respective fuzes by which they are exploded on impact at the end of their fall. At present, the most commonly used fuzes operate solely on impact, and present the drawback of possibly misfiring on impact with soft ground and /or at a small angle of descent, thus resulting in submunitions with "armed" fuzes, i.e. with an aligned explosive train, and which may still explode, being left lying on the ground. To overcome the above drawback, fuzes have been devised which, in addition to the primary impact operating mode, also present a secondary self-destruct mode. In this case, when the fuze is armed or the carrier burst, a time mechanism is activated to ensure operation of the fuze in the event it misfires on impact; and, as the submunition, for it to be effective, must of course explode after reaching the target, a lapse of several seconds must be allowed between activation and operation of the self-destruct mechanism. As of yet, two types of self-destruct mechanisms - fire-delay and electronic-delay - have been used or proposed, neither of which, however, has proved altogether satisfactory. The fire-delay type, in fact, presents the disadvantage of being sensitive to ageing and storage conditions; while the electronic-delay type features electronic components, is also affected by prolonged storage and storage conditions if battery powered, and is of complex, high-cost design if powered by electromagnetic generators exploiting relative rotation of the firing pin and fuze. A submunition fuze of the type defined in the preamble of claim 1 is disclosed in US-A-3,998,194, wherein the self-destruct firing mode is obtained through a timer including a shaft and a paddle forming part of a retarding dashpot and connected to the firing element by a camming pin and a helical slot connection. A chamber between the timer and the support is completely filled with a highly-viscous liquid, and the time between fuze arming and self-destruction depends on the dashpot geometry and on the viscosity and pressure of the liquid. This solution shares the disadvantages of the fire-delay self-distruct mechanisms. It is an object of the present invention to provide a submunition fuze designed to overcome the aforementioned drawbacks, and which is therefore reliable, low-cost, and, in particular, is extremely compact and capable of operating reliably within a wide temperature range and even after many years' storage. According to the present invention, there is provided a submunition fuze with an inertial and a self-destruct firing mode, as defined in the appended claims. Two preferred, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figures 1 to 4 show cross sections of a first embodiment of the fuze according to the present invention, at four different stages; Figures 5 and 6 show cross sections of a second embodiment of the fuze according to the present invention, at two different stages corresponding to those of Figures 2 and 4. With reference to Figures 1 to 4, the fuze according to the invention is indicated as a whole by 1, and comprises a casing 2 presenting a transverse bottom channel 3 housing a detonating assembly 4, and an axial channel 5 perpendicular to and communicating with transverse channel 3. Detonating assembly 4 comprises a slide 6 supporting a capsule 7 and presenting two transverse holes 8, 9; and, between slide 6 and a stop 10 integral with casing 2, there is interposed a compressed coil spring 11 for pushing slide 6 outwards of transverse channel 3 (to the right in the drawings). Casing 2 also presents an annular extension 12 (forming an axial chamber 12a) at the top; and a peripheral through hole 13 which, in the withdrawn position of slide 6 (shown in Figure 1 and corresponding to the unarmed position of fuze 1), is aligned with hole 9 and houses a safety pin 14. At the top, axial channel 5 of casing 2 presents a thread 15 which, in the unarmed position of fuze 1 (Figure 1), engages an externally threaded upper portion 16 of a bush 17 housed inside axial channel 5. At the bottom, bush 17 presents a wider portion 18 separated from threaded portion 16 by a smaller-diameter intermediate portion 19, so that, when threaded portion 16 is detached from thread 15, bush 17 is permitted to move in relation to container 2 but not to withdraw fully from axial channel 5. Bush 17 presents an axial hole 20 in turn presenting a minimum diameter at its top end, a medium diameter over most of its length, and a maximum diameter at the bottom end (at wider portion 18 of bush 17), so as to form two stop shoulders 21, 22. A firing pin support or holder 23 is housed inside axial hole 20 so as to slide but not to rotate in relation to bush 17, which rotation lock may be achieved, for example, by means of prismatic sections (not shown) at one end of hole 20 and on the facing portion of holder 23, or by means of lock pins (not shown). Holder 23 is substantially in the form of an upside down cup comprising a closed top end 24, and a dead hole 25 with its open end facing detonating assembly 4. The top end 24 of holder 23 also projects from axial hole 20 in the safe (unarmed) position of fuze 1, and is fixed - in the example shown, by riveting - at 26 to a known strip 27 for arming fuze 1. The bottom end 28 of holder 23 is flared, and presents two or more radial chambers 29, each housing a ball 30. Between shoulder 21 and the flared end 28 of holder 23, axial hole 20 houses a compression spring 31 defining second thrust means for pushing holder 23 towards detonating assembly 4, and the force of which is so calibrated as not to exceed the aerodynamic force to which strip 27 is subjected during descent of the fuze, as described in more detail later on. Dead hole 25 of holder 23 houses in sliding manner a firing pin 35 comprising a tip 36 projecting from dead hole 25, an intermediate lock portion 37, and a small-diameter rod 38. More specifically, lock portion 37 presents substantially the same diameter as dead hole 25, with the exception of an annular groove 39 which, prior to activation of fuze 1, is engaged by balls 30; and groove 39, balls 30, and hole 20 at the wider portion 18 of bush 17 are so sized that, in the unarmed position and the armed (pre-activation) position of the fuze, the inner wall of bush 17 holds balls 30 against lock portion 37 and inside groove 39, to lock the firing pin 35 in position. A compression spring 40, fitted about rod 38 inside dead hole 25, acts between the bottom of dead hole 25 and lock portion 37, and defines first thrust means acting on and for pushing firing pin 35 towards detonating assembly 4; which thrust is normally disabled by the locking action of balls 30, with the exception of the self-destruct condition described later on. Finally, the top end 24 of holder 23 presents a radial hole 41 housing part of a loosely fitted pin 42 projecting inside chamber 12a and held in place by annular extension 12, and which provides for maintaining holder 23 integral with bush 17 when this is rotated and unscrewed, and which is expelled automatically when bush 17 is unscrewed by a given amount, as explained later on. Fuze 1 operates as follows. To begin with, when fuze 1 is unarmed (Figure 1), slide 6 is in the withdrawn position with hole 9 aligned with hole 13 and safety pin 14 inserted; tip 36 of firing pin 35 is housed inside hole 8 to hold slide 6 in place; and threaded portion 16 of bush 17 engages thread 15 of casing 2. Following assembly of fuze 1 to the bomb (not shown), removal of safety pin 14, and bursting in known manner of the projectile in flight, strip 27 begins to unwind. At this stage, due to rotation of the bomb about its axis and/or the air brake to which strip 27 is subjected, relative rotation occurs between casing 2 and holder 23, which rotation is transmitted to bush 17 so that threaded portion 16 unscrews from thread 15 of casing 2, and the whole comprising bush 17, holder 23 and firing pin 35 is raised. In the case of bombs with arming strips 27 that take some time to unwind, the drag on the strip at this first stage may not yet be sufficient to counteract the thrust exerted by compression spring 31, so that holder 23 tends to slide downwards in relation to bush 17. This is prevented, however, by pin 42 retained inside radial hole 41 by the annular extension of casing 2. Pin 42 is expelled by centrifugal force before bush 17 unscrews completely, and upon radial hole 41 passing the top edge of casing 2. At which point, the drag on the arming strip is undoubtedly greater than the force exerted by spring 31, so that no danger of malfunctioning exists and the firing assembly may thus be set to operate. The assembly comprising bush 17, holder 23 and firing pin 35 thus moves into the extracted position with wider portion 18 of bush 17 contacting thread 15; and slide 6, no longer retained by tip 36 of firing pin 35 inside hole 8, is pushed by spring 11 into the extracted position to set capsule 7 beneath firing pin 35, and the fuze to the armed position shown in Figure 2. In the case of violent impact (Figure 3), i.e. with a firm target, holder 23 falls by inertia towards slide 6, taking with it firing pin 35, the tip 36 of which penetrates and initiates capsule 7. Conversely, in the event of impact with soft ground or such that the kinetic energy accumulated is insufficient to move holder 23 by inertia, the self-destruct mechanism comes into play. More specifically, when the aerodynamic force exerted on strip 27 during descent is cut off, spring 31 is free to push holder 23 axially downwards; balls 30, no longer retained by the inner wall of hole 20, are pushed radially outwards by firing pin 35 in turn subjected to the action of spring 40; and firing pin 35, which is now free, is pushed by spring 40 against capsule 7 (Figure 4) to explode the fuze. Figures 5 and 6 show a variation of the fuze according to the invention, in the unarmed and self-destruct position respectively. The Figure 5 and 6 fuze, indicated by 1', presents substantially the same structure as fuze 1 in Figures 1 to 4, with the exception of the second thrust means. More specifically, fuze 1' in Figures 5 and 6 presents no spring 31, and the downward thrust action on holder 23 is achieved by a conical surface 45 defining the bottom portion of hole 20 at the wider portion 18 of bush 17. Since spring 31 is eliminated, hole 20 of fuze 1' presents one diameter, with the exception of the bottom portion referred to above, so that shoulder 21 is also eliminated. The downward thrust action on holder 23 of fuze 1' is achieved by virtue of firing pin 35, via spring 40, subjecting balls 30 to a force presenting a transverse component, i.e. perpendicular to the axial direction of casing 2, which pushes balls 30 against conical surface 45; conical surface 45 thus subjects balls 30 to a reaction force presenting a downward axial component which is transmitted by balls 30 to radial projections 28 and from there to holder 23 in the same way as spring 31 in the first embodiment. During descent, the downward thrust on holder 23 is compensated and eliminated by the drag on strip 27 and, initially if necessary, by pin 42 as in the previous example. During descent, fuze 1', when armed, is positioned as shown in Figure 5. In the event of violent impact, the assembly comprising holder 23 and firing pin 35 moves axially downwards, by virtue of the kinetic energy accumulated and in exactly the same way as for fuze 1, to initiate capsule 7. Conversely, in the event of soft impact or at any rate not strong enough to initiate the capsule, the thrust exerted by conical surface 45 on holder 23, and no longer counteracted by aerodynamic force, slides holder 23 downwards so that radial chambers 29 come out of axial hole 20; balls 30, due to the radial thrust exerted by firing pin 35 via spring 40, release groove 39 on the firing pin; and firing pin 35, which is now free, is pushed by spring 40 against capsule 7 to initiate it and so self-destruct the fuze. The fuzes described therefore present a self-destruct mechanism which is activated independently of descent time and immediately after impact in the event of failure of the primary initiating system, with no need for predetermined-delay mechanisms, and hence with no risk of the self-destruct mechanism coming into play too soon or too late. Moreover, the solutions described are unaffected by ageing or storage conditions, are straightforward in design, and are comparable costwise with known impact-only solutions.

Claims: A submunition fuze (1, 1') with an inertial and a self-destruct firing mode, comprising a tubular arming body (17); a support (23) housed in sliding manner in said tubular arming body (17); a firing pin (35) supported in sliding manner in said support (23); a detonating element (7) mounted facing said firing pin (35), at least in the armed position of said firing pin; vertical-force generating means (27, 42) for generating, during descent of said fuze, a vertical force acting on said support in a direction away from said detonating element (7); first thrust means (40) acting on said firing pin (35) for generating on said firing pin a first thrust in the direction of said detonating element (7), whereby, in case direction of said detonating element (7), whereby, in case of impact with inertial firing, said support (23) and said firing pin (35) fall together by inertia and said firing pin (35) initiates said detonating element (7); characterized in that it comprises second thrust means (31; 45) acting on said support (23) for generating a second thrust, in the direction of said detonating element (7), of a value not exceeding said vertical force and lock means (30) acting on said firing pin (35) for locking said firing pin in a withdrawn position against the action of said first thrust means; said second thrust means (31; 45) defining disabling means for disabling said lock means (30) and active in the arming position of said fuze and in the absence of said vertical force, thereby, in case of impact with self-destructing firing, said second thrust means (31; 45) disables said lock means (30) and said first thrust means (40) pushes said firing pin (35) toward said detonating element (7) for initiation. A fuze as claimed in Claim 1, characterized in that said lock means comprise at least one locking body (30) which, in said arming position, is locked in such a position as to interfere with said firing pin (35). A fuze as claimed in Claim 2, characterized in that said support (23) comprises at least one radial chamber (29) housing said locking body (30) and defined internally by said firing pin (35); said support (23) being movable, in relation to said tubular body (17), between a first disabled position corresponding to said unarmed and armed positions of said fuze (1, 1') and wherein said radial chamber (29) is defined externally by a portion (18) of said tubular body, and an enabled position in the absence of said vertical force and wherein said radial chamber is externally open and permits radial movement of said locking body (30). A fuze as claimed in Claim 2 or 3, characterized in that said locking body comprises at least one ball (30). A fuze as claimed in any one of the foregoing Claims from 2 to 4, characterized in that said firing pin (35) presents a grooved element (39) engaging said locking body (30) in said unarmed and armed positions of said fuze (1, 1'). A fuze as claimed in any one of the foregoing Claims, characterized in that said first thrust means comprise a first elastic element (40). A fuze as claimed in Claim 5, characterized in that said support (23) is cup-shaped and presents a dead hole (25) open towards said detonating element (7) and housing at least one portion (37, 38) of said firing pin (35); said first elastic element (40) being interposed between the bottom surface of said dead hole (25) and a mating surface (37) of said firing pin. A fuze as claimed in any one of the foregoing Claims, characterized in that said second thrust means comprise a second elastic element (31) interposed between said tubular body (17) and said support (23). A fuze as claimed in any one of the foregoing Claims from 1 to 7, characterized in that said second thrust means comprise an inclined surface (45) formed inside said tubular body (17) and acting on said locking body (30) in said unarmed and armed positions of said fuze (1'). A fuze as claimed in any one of the foregoing Claims, characterized in that said vertical-force generating means (27, 42) comprise an air brake element (27). A fuze as claimed in Claim 10, characterized in that said vertical-force generating means (27, 42) also comprise a stop element (42) fitted removably to said support (23) and cooperating with said tubular body (17) to prevent said support (23) from sliding in relation to said tubular body (17) when arming said fuze (1, 1'). A fuze as claimed in Claim 11, characterized in that said stop element comprises a pin (42) housed loosely in and projecting from a cavity (41) in said support (23); and in that it comprises a casing (2) housing said tubular body (17) and presenting a portion (12) for retaining said pin in said cavity (41) when arming said fuze.

Inventors: BORGNI ROBERTO, BORGNI, ROBERTO
Applicants: SIMMEL DIFESA SPA, SIMMEL DIFESA S.P.A.
Application year: 1995
Main classification: F42C9
IPC codes: F42C9