IL143620A - Submunition fuze compatible with cargo insensitive munitions - Google Patents

Description

GNm&ri tnmn-roi anna SUBMUNITION FUZE COMPATIBLE WITH CARGO INSENSITIVE MUNITIONS 143620/2 The present invention relates to fuzes for submunitions, to be carried in cargo ammunition such as rocket warheads, aircraft dispensers, mortar bombs, artillery shells and quite generally any type of ground or air launched warhead adapted to carry submunitions.

BACKGROUND OF THE INVENTION Submunitions of various kinds, such as grenades and bomblets, have long been known in the art. Typically, the fuze of a cargo warhead grenade includes a arming screw (functioning also as the main firing pin) or arming screw assembly and a detonator on a slider, adapted to move from an unarmed, or safe ppsition, where the detonator is out of alignment with the arming screw, to an armed position. For arming, the shaft of the arming screw assembly has a portion which protrudes outside the fuze housing and is fitted at its protruding end with drag producing means of stabilization such as, for example, a drag tape. When the grenade is expelled from the cargo ammunition, during its spin around its longitudinal axis and in consequence of this spin, the drag producing means retracts the arming screw assembly from the slider, whereby the fuze is armed. At the same time, the slider moves so that the detonator is brought into alignment with the arming screw, and the arming screw assembly remains in the retracted position until the grenade hits the target. When the grenade hits a target, the inertial forces acting on the arming screw assembly drive it into the striking position with a force which, as a rule, is sufficient to detonate the fuze detonator.

With the known existing submunition fuzes, when there are duds, fuzes can be detonated at a later time are liable to endanger friendly units. Many conventional fuzes can be armed by inadvertent movement of one of the elements of the fuze, or by using a manipulated simple tool, such as a nail, screw driver, pliers or the like, and thus, endanger civilian lives or friendly soldiers moving through the area where the submunitions fell. In addition, such duds can be used as booby traps, for later explosion.

Thus, many conventional fuzes now include a back-up detonating mechanism, also known as a self-destruct mechanism. One example of such a fuze is shown in US patent 4,811,664, to the same assignee. These fuzes generally include a pyrotechnic or other delay mechanism, which is activated at the time of expulsion, and which initiates the delay detonator in the fuze and then activates the main charge in the submunition, in the event that there is no detonation upon impact. Many conventional fuzes are not very reliable in the impact mode or the self-destruct mode, resulting in a high rate of duds, which are still dangerous for friendly forces and civilians.

On the other hand, there are some cases where the submunitions are detonated close to the expulsion process. Such unintended detonations can be induced under a multitude of circumstances, such as when submunitions collide with one another in free fall. Another deficiency of the existing cargo submunitions is the danger during storage, if fire breaks through and causes an expulsion of grenades out of the cargo ammunition (as simulated in cook-off tests). The grenade fuzes can be armed and then a wide area is covered with dangerous armed duds. Those armed grenades can be detonated during this dispersion in the storage place by impact or by self-destruction. This may cause detonation of other ammunitions lying in the armed grenades covered area, and damage to equipment, weapon or sea crafts.

A variety of safety mechanisms have been provided on submunitions and submunition fuzes. The main safety mechanism is the slider, which provides an out-of-line detonator. However, none of the conventional safety systems provide a failsafe fuze for a submunition under all the required conditions.

Accordingly, there is a long felt need for an efficient submunition fuze which has a high level of functional reliability during conditions when detonation is desired, but cannot be detonated except under the desired firing conditions.

SUMMARY OF THE INVENTION The present invention provides a fuze for a submunition which includes four separate, independent safety systems, each of which must be overcome in a certain order and in the proper fashion in order for the arming screw to initiate the detonator. This arrangement provides a fuze which passes the safety conventional tests, including the "Cook Off Test, as well as providing a high level of functional reliability with a corresponding low dud rate.

There is thus provided in accordance with the present invention a fuze for a submunition including a slider holding a detonator, the fuze comprising a safety mechanism engaging the slider and releasable only under certain environmental conditions generated upon firing the cargo ammunition from the launcher.

According to one embodiment of the invention, the fuze includes a slider which is substantially the length of the diameter of the submunition; and a centrifugal pin, an arming screw, and a set-back pin, each mounted in the fuze in engagement with the slider, so as independently to prevent movement of the slider to an in line position except under pre-selected firing conditions.

According to one embodiment of the invention, the fuze includes a pyrotechnic delay for self-destruction of the detonator and all the submunition in the event that it does not detonate upon impact. 143620/3 BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be further understood from the following detailed description taken in conjunction with the drawings in which: Fig. 1 is a top view of a submunition fuze constructed and operative in accordance with one embodiment of the present invention, as assembled.

Fig. 2a is a sectional view of the submunition fuze of Fig. 1 taken through line A-A.

Fig. 2b is a sectional view of the submunition fuze of Fig. 1 taken through line B-B.

Fig. 2c is a sectional view of the submunition fuze of Fig. 1 taken through line C-C.

Fig. 3a is a side view of the submunition fuze of Fig. 1, including a stabilizing ribbon.

Fig. 3b is a side view of the submunition fuze of Fig. 1, including a cover.

Fig. 4 is a sectional view through a typical carrier projectile constructed and operative in accordance with the present invention, including a payload of submunitions; Figs. 5a and 5b are schematic sectional and detail views, respectively, of the release of a set-back pin in the submunition fuze of the present invention; Figs. 6a and 6b are sectional views of the arming screw in an unscrewed position; Figs. 7a and 7b are respective side and top sectional view of the fuze of one embodiment of the present invention is a fully armed state; and Fig. 8 is an exploded view of a submunition constructed and operative in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuze for a submunition warhead which is fired from a rifled barrel. The fuze includes a stab detonator, for detonation upon impact, and includes a back-up self-destruct mechanism which may be activated by a pyrotechnic delay detonator. The fuze is particularly suitable for Insensitive Munitions (IM), by means of meeting the requirements of slow and fast cook-off tests, and can be used, for example, in an Israel Military Industries Hornet-5 (CL 3161) submunition, as well as other submunitions adapted to be assembled in any cargo ammunition. The fuze of the invention fulfills all the requirements of the various safety standards, operates under firing conditions, i.e., high acceleration and high rate of spin, while also providing the level of reliability of functional requirements of submunitions.

The fuze of the present invention meets all the safety requirements of Insensitive Munitions (IM). In particular, the fuze cannot be armed after ejection from the carrier unless the carrier was launched from a barrel under conditions of the intended use. The fuze is capable of arming only after the following sequence of safety feature release has occurred, in the order listed: 1) Firing acceleration from a barrel adapted for use with such cargo carrier containing submunitions, which releases the set-back pin; 2) Ejection from inside the carrier projectile, which releases the geometric-space confinement safety feature; 3) Spin of the submunition, thereby releasing a centrifugal pin safety mechanism; (The spin must be continued until the next safety feature is released.) 4) Aerodynamic drag forces overcome the stationary safety clip and spread the ribbon, cause the unscrewing of the arming screw, and release it from the slider central bore.

It is a particular feature of the invention that the fuze cannot be armed except after the appropriate or anticipated firing acceleration from a barrel. In addition, four different, independent physical conditions must be met sequentially, all of which will always exist in the desired arming situation, but not all of which will exist at times when the submunition must not function properly.

Referring now to Figs. 1 , 2a, 2b, and 2c, there are shown respective top, and sectional views of a submunition fuze 50 constructed and operative in accordance with one embodiment of the present invention, as assembled. The fuze 50 includes a fuze housing 1, in which a slider 4 is mounted. It is a particular feature of the present invention that the length of slider 4 is substantially the same as the diameter of the submunition, as best seen in Fig. 8, a view of the submunition. This permits the use of bore riding, wherein the slider 4 is prevented from moving due to the geometric arrangement of a plurality of submunitions inside a projectile, as described in greater detail below.

With further reference to Figs. 1 , 2a, 2b, and 2c, mounted on slider 4 is a stab detonator 3, and a pyrotechnic delay detonator 2. A striker 7 is also provided on the slider 4 and arranged to pivot about a pivot axis 8 so as to ignite pyrotechnic delay detonator 2. Alternatively, any other suitable self-destruct mechanism can be utilized, rather than a delay detonator.

A centrifugal safety pin 6 is mounted inside housing 1 and urged into engagement with slider 4 by a spring 5, also mounted within housing 1. Operation of these elements will be explained in detail below.

Referring now to Figs. 2a and 2b, side sectional views of the fuze 50, additional safety features of the fuze can be seen. As in conventional fuzes, an arming screw 10 is mounted in the housing 1, as by screw threads. The arming screw 10 is shown in Fig. 2b in the safe position, wherein it engages a bore 17 in the slider 4, thereby preventing movement of the slider. A weight 1 1 , in which the arming screw 10 is screwed, is installed by sliding into housing 1.

A set-back pin 12 is mounted in housing 1 and engages a groove 19 in slider 4, thereby preventing sliding movement of slider 4 in the fuze 50. The set-back pin 12 acts independently of arming screw 10 to retain slider 4 in the safe position. In the illustrated embodiment, set-back pin 12 is held in place by a set-back disc 16, on the outer surface of the fuze 50, seen in Fig. 1. Set-back disc 16 engages a shoulder 12' on set-back pin 12, thereby physically retaining set-back pin 12 in place in the fuze 50. Set-back pin 12 and set-back disc 16 can only be released by acceleration forces acting for the appropriate duration on the fuze 50. Once the disc opens, set-back pin 12 is pulled out of engagement with the groove in slider 4, and the remaining arming procedure can continue. The disc 16 is designed such that the set-back pin 12 cannot be pushed back into the slider engagement, under forces less than the maximum which can be applied in the specific cargo carrier. Alternatively, any other suitable set-back mechanism can be utilized. A locking pin 14 and a locking spring 15 are provided to lock the slider 4, once it has moved to the armed position, to prevent its return to an unarmed position. A closure element 13 is provided to close the fuze 50.

Once the fuze 50 has been assembled in the submunition, a stabilizing folded ribbon 18 is affixed to the arming screw 10, as known. See Figs. 3a and 3b. A stationary safety clip 20 is placed over the folded ribbon 18 to hold it in place until expulsion and separation occur.

Operation of the fuze 50 of the present invention is as follows. A carrier shell 30 is loaded with a payload containing submunitions 32 in a specific geometric arrangement, shown schematically in Fig. 4, which is a sectional view of an example of a loaded carrier projectile. In the illustrated arrangement, by way of example only, a central submunition 32' is loaded coaxially with the longitudinal axis of the projectile, and surrounded by a ring of other submunitions 32, tangentially engaging one another. In this way, there is no room inside the projectile for any of the sliders to slide outwards (to move to the armed position), while the submunitions are inside the carrier shell, which is known in the art as bore riding.

When the carrier projectile is fired, the resultant acceleration forces acting for the appropriate duration on the fuze 50 cause set-back pin 12 to be released. As shown in Figs. 5a and 5b, once disc 16 opens, set-back pin 12 is pushed out of the slider 4 by the acceleration during set back, and the remaining arming procedure can continue.

It is a particular feature of the invention that the conditions under which the set-back disc 16 can open exist only during firing from a barrel. Thus, if this condition is not met, the set-back pin 12 will not be released from the slider 4, and none of the following physical arming conditions can be met. This safety feature ensures that only under the expected, pre-selected firing conditions will the fuze 50 be capable of being armed.

While still in the barrel, or during expulsion and flight, centrifugal forces act on the safety pin 6, and pull it outwards against the action of the spring 5, thereby disengaging from slider 4. It will be appreciated that the slider 4 is still not free to move to the armed position, since the arming screw 10 is still engaged in the bore in the slider.

After firing the carrier projectile from a barrel, the main (projectile) fuze is activated and ignites the expulsion charge at the appropriate height above the target. The pressure generated as a result of ignition of the expulsion charge, shears the threading at the base, and ejects the pay load. The submunitions are separated and dispersed onto the target.

After the separation of a submunition during flight, the stationary clip 20 over stabilizing ribbon 18 is released, as shown in Fig. 6a, and stabilizing ribbon 18 is spread, causing arming screw 10 to unscrew from the weight 11 to the extended position, as shown in Figs. 6a and 6b. Extending of the arming screw 10 also serves to release slider 4, which had been locked in the safe position by the tip of the arming screw. As shown in Figs. 7a and 7b, once the slider 4 has been released, centrifugal forces cause the slider to slide outwards into the armed position, as known. Stab detonator 3 is now aligned with the lead charge, and detonation occurs upon impact of the submunition with a target. Slider 4 is locked in position by the spring-loaded locking pin 14, which engages a shoulder on the warhead, and prevents the slider from sliding back inside the fuze 50. At the same time, striker 7 pivots around pivot 8 and initiates the delay detonator 2.

At this stage, all the conditions for arming the fuze 50 set forth above have been met. If even one of the following safety conditions has not been met in the proper order, the fuze will be incapable of being completely armed: - the set-back pin 12 is released by the acceleration forces during firing; - only after the submunition has been ejected it is physically possible to move the slider 4 to the armed position. (There is not enough room inside the carrier - "bore riding".); - the centrifugal safety system is retracted during spin of the carrier containing the submunition, the centrifugal forces also causing the slider 4 to move into the armed ("in-line") position, depends on the existence of these forces after the next condition is met (arming screw unscrews and extends); - the arming screw 10 unscrews and extends after the submunition was expelled from the carrier shell, due to the drag forces acting on it via the stabilizing ribbon 18.

Once all these four conditions have been met, in this order, the fuze 50 is armed, and locked in the armed ("in-line") position. When the submunition hits the target, it explodes in the impact (main) mode, by striking of the arming screw 10 into the detonator 2, which detonates the warhead main charge through the lead charge. If the submunition does not detonate upon impact, for any reason, the self-destruct mechanism will cause detonation of the warhead after a delay of about 15 seconds from ejection from the carrier projectile.

After firing, no dangerous duds, and generally a very small number of "safe" duds remain on the target area. As stated above, it is impossible to arm these duds, so there remains no danger from unexploded submunitions on the target area.

Referring now to Figure. 8, there is shown a submunition 40 constructed and operative in accordance with one embodiment of the invention, in respective perspective and exploded views. Submunition 40 includes a cover 42 and fuze 50 is mounted together on a warhead 43, as by three rivets 57. In the illustrated embodiment, cover 42 has an H-shaped cross-section. The fuze 50 is seated within the cover 42, and is substantially covered by it. A radial slot 54 is provided in the cover 42 and arranged in register with the slider 4 of the fuze 50, to permit the arming of slider 4, into the armed position.

The fuze housing 1 protrudes through a bridging portion 46, enabling the striking system to extend and the stabilizing ribbon 18 to spread out. The stationary safety clip 20 retains the folded stabilizing ribbon in the submunition until released by centrifugal and drag forces.

It is a particular feature of this embodiment of the present invention that the fuze is protected by a cover, which protects against mechanical damage if the submunition is hit by neighbor submunitions during expulsion, or by il fragments produced by detonation of submunitions after separation, so as to substantially reduce the number of submunitions which are damaged, and consequently reduce the number of duds. In addition, the cover prevents any access, from outside the submunition, to the centrifugal pin, which is recessed inside the cover, and avoids manual release of the slider of a dud submunition. Such an arrangement is not known in conventional submunitions, which do not include any protective fuze cover, and wherein the centrifugal pin is externally accessible and can be released manually by using simple tools.

The fuze of the present invention has several advantages that do not exist in known submunitions or submunition fuzes: a. Meeting the requirements of fast and slow cook-off tests; b. A geometric safety inside the carrier shell is provided by bore riding, and not by coverage by other submunitions or adapters; c. A cover for protection against hits or fragments; d. Use of substantially the entire submunition diameter for slider packing, for detonator safety and an additional geometric safety factor; e. No access to the centrifugal locking system, that prevents any intentional, manual attempt to release it in order to arm the fuze; and f. Four independent safety conditions, released only by sequential physical conditions in a specific order to reach the armed position.

All these give the user a safety level that has never been reached before for submunitions and their fuzes during the following processes: assembly, disassembly of submunition carrier, storage, fast and slow cook-off events, firing, functioning with high reliability, safe duds that cannot be armed or operated by civilians or friendly soldiers passing the target area or enemy forces trying to set a trap for friendly troops.

It will be appreciated that the invention is not limited to what has been described hereinabove merely by way of example. Rather, the invention is limited solely by the claims which follow.

Claims (10)

143620/4

1. A fuze for a submunition having a slider incorporating a stab detonator, comprising: four separate independent safety systems, each of which independently engage the slider and are released in a specific order, only under accelerations and forces generated during conditions of firing followed by expulsion and separation, including: a set-back mechanism, and means for arming same; a centrifugal locking mechanism, and means for retracting the centrifugal locking mechanism; an arming-screw mechanism, and means for activating same; a stationary safety clip, and means for activating same; and means for activating the safety systems sequentially, whereby only by sequentially arming the set-back mechanism, retracting the centrifugal locking mechanism and arming both the arming screw mechanism and the stationary safety clip while the centrifugal locking mechanism is still open, will the fuze be ignited.

2. The fuze for a submunition according to claim 1, and wherein the slider is substantially the length of a diameter of the submunition, and capable of sliding to an armed position only after release from a carrier shell.

3. The fuze according to any of the preceding claims, wherein said set back mechanism includes: a set-back pin having a shoulder, the set-back pin being mounted in a fuze housing and engaging the slider; and a set-back disc mounted in the fuze housing and engaging the shoulder of said setback pin, said set-back disc releasing said set-back pin only under acceleration forces generated during firing the submunition from a barrel.

4. The fuze according to any of the preceding claims, further comprising a self-destruct mechanism. 14 G43705 143620/2

5. An IM submunition comprising a warhead having lead charge and main charge comprising a fuze as defined in any of the preceding claims and a cover coupled to the warhead and substantially covering the fuze protecting it from hits and fragments.

6. The submunition according to claim 5, wherein said cover is arranged to make said centrifugal mechanism inaccessible to any intentional manual arming attempts.

7. The submunition according to claim 5 or 6, wherein: said set-back mechanism is arranged to be released by acceleration forces during firing through a barrel; said slider is arranged to be released from space confinement by expulsion from inside a carrier projectile in which the submunition is loaded; said centrifugal locking mechanism is arranged for release by spin of the submunition; and said arming-screw mechanism is arranged to unscrew until it is free of a central bore in the slider, when aerodynamic drag forces overcome a stationary safety clip or spread a ribbon during free-flight of the submunition.

8. The submunition according to any of claims 5 to 7, wherein said cover includes a fuze receiving cup adapted to receive said fuze of the submunition, said fuze receiving cup including a radial slot in register with said slider

9. The submunition according to any of claims 5 to 8, wherein the slider is substantially the length of a diameter of the submunition.

10. The submunition according to any of claims 5 to 9, wherein said set-back mechanism includes: a set-back pin having a shoulder, the set-back pin being mounted in a fuze housing and engaging the slider; and a set-back disc mounted in the fuze housing and engaging the shoulder of said set-back pin, said set-back disc releasing said set-back pin only under acceleration forces generated upon firing the submunition from a barrel. AGENT FOR APPLICANT D- 12 1 193-00ap.doc