EP2943740B1

EP2943740B1 - Safety assembly for an ammunition fuze

Info

Publication number: EP2943740B1
Application number: EP14705581.8A
Authority: EP
Inventors: Herzel ALON
Original assignee: Elbit Systems Land and C4I Ltd
Current assignee: Elbit Systems Land and C4I Ltd
Priority date: 2013-01-13
Filing date: 2014-01-12
Publication date: 2018-08-15
Anticipated expiration: 2034-01-12
Also published as: WO2014108904A1; EP2943740A1; IL224201A; LT2943740T

Description

FIELD OF THE INVENTION

The present invention relates to a safety assembly for ammunition and more particularly, to a safety assembly that includes an interrupter.

BACKGROUND OF THE INVENTION

Explosive mortar projectiles are usually equipped with a fuze assembly which is armed after the launch, and ignited in response to target impact. In order to increase safety and to avoid accidents prior to the launch or shortly thereafter, many mortar fuzes comprise a mechanism for arming the projectile only responsive to the setback forces applied during the launch of the mortar projectile and after predefined delay.
Figure 1A is a cutaway diagram of an exemplary fuze according to the prior art. Prior art fuze 10 includes a housing 1 which defines a cavity in which a firing pin 2 is located together with a compression spring device 3 arranged such that compression spring device 3 is configured to push firing pin 2 towards the direction of advancement of the mortar projectile upon launch (referred herein in this disclosure as "upwards", while "downwards" refers to the opposite direction).
In another cavity of prior art fuze 10 there is provided an interrupter 4 rotatably attached to a shaft 5 which is affixed via a torsion spring 6 to housing 1. Interrupter 4 has a cavity configured to accommodate a detonator 8. In a safe position, firing pin 2 cannot accidently reach detonator 8 in case firing pin 2 is pressed downwards as detonator 8 is not located along the line of firing pin 2. Cavity 7 is configured to house a secondary detonator.
Upon launch of the mortar projectile, setback forces applied to prior art fuze 10 press firing pin 2 downwards so that the tip of firing pin 2 activates the rotation of interrupter 4, for example, by piercing a protective foil (not shown) or by removing any other stopper which maintains interrupter 4 at its location in the safe position. Once the setback forces caused by the launch-acceleration cease, spring device 3 pushes firing pin 2 upwards, thus enabling interrupter 4 to rotate around shaft 5. Upon completion of the rotation of interrupter 4 forced by torsion spring 6, detonator 8 is aligned with firing pin 2 and prior art fuze 10 shifts to an armed position.
Figure 1B is perspective view diagram 20 illustrating a safe and arm (S&A) mechanism 20 used in mortar fuzes to provide a safety measure. Mortar fuzes may be provided with a safely assembly configured to lock the rotational movement of interrupter 150 in the safe position and to enable the rotational movement of interrupter 150 responsive to the setback forces and a subsequent cease thereof. In one exemplary embodiment S&A assembly 20 includes: a first safety plunger 330 having a cone-shaped top; a second safety plunger 320 having a radially protruding shoulder and a stopper 322 configured to lock the radial movement of interrupter 150 in the safe mode (possibly by interacting with a teeth wheel 340 surrounding interrupter 150). S&A assembly further includes a locking member 350 that rests, in the safe mode, on the shoulder of second safety plunger 320 so that it locks its movement.
In operation, first safety plunger 330 is configured, responsive to the setback forces, to move downwards so that locking member 350 moves from the shoulder of second safely plunger 320 and reaches the cone-shaped top thus unlocking second safety plunger 320. Additionally, second safety plunger 320 is configured, responsive to the same setback forces and upon being unlocked, to move downwards so that stopper 322 is released from interrupter 150 allowing the clockwork piece 310 to rotate the interrupter to the armed position.
While the aforementioned S&A mechanism provides some level of safely, it would be advantageous to provide another safety mechanism that overcomes the drawbacks of the mortar fuze safety mechanism of the prior art.
GB1017380A discloses an arming device for a projectile or missile fuze. When the projectile is launched, a striker pin is thrust further into a hole by acceleration forces and wedging balls move rearwards and away from the pin. As the acceleration decreases a spring forces the striking pin clear of a drum which then rotates in co-operation with a rocker until a passage and priming charge are aligned with the striker pin.
DE102008053990 discloses a fuze for a projectile, having a fuze train, having an interruptor for interrupting the fuze train, the interruptor being designed to snap from a safety position into a live position when unlocked, and having a locking means to lock the interruptor in the safety position and to unlock the interruptor by means of an unlocking movement.
EP0235005A1 discloses a fuse in which in that the striker is guided in its middle part in the body and its head in the nose, whilst an axial weight sliding round the striker is stressed towards the head of the striker.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an improved safety assembly for ammunition, such as mortar ammunition, which significantly reduces both unintentional detonation and failure mode and further overcomes the aforementioned drawbacks of the prior art. The present invention, in embodiments thereof, provides a and additional secondary safely assembly that enables a firing pin to enter more deeply into the interrupter in the safe position to increase safety provided by the S&A locking mechanism for the interrupter that is activated and deactivated responsive to similar conditions as the proposed secondary safety assembly. Advantageously, both S&A and secondary safety assemblies have to operate properly so that the fuze switches from a 'safe' into an 'armed' position.
According to the present invention, there is provided a secondary safety assembly for ammunition. The secondary safety assembly in accordance with independent claim 1 includes: a housing defining a cavity with an opening at its top; a nose cap which covers the opening wherein the nose cap is connected to the housing by a compression spring; a firing pin with a head having a radially protruding shoulder, wherein the firing pin is directed downwards; a locking means which when in a safe position, rests between the shoulder of the head and the inner walls of the housing; and an interrupter rotatably attached to a shaft that is affixed to the housing wherein the shaft is located along an axis parallel to the firing pin, wherein the interrupter comprises a first cavity located, in the safe position, along the axis of the firing pin and shaped to accommodate a portion of the firing pin, and wherein the interrupter further comprises a second cavity configured to accommodate a detonator, wherein the firing pin is configured to move downwards responsive to setback forces during launch of the ammunition so that the locking means is released from its location between the shoulder of the head and the housing and so that a portion of the firing pin enters the first cavity, and wherein the firing pin is further configured to move upwards responsive to a cease of the setback forces so that the shoulder of the head moves towards the housing and so that the firing pin exits the first cavity entirely.
According to the present invention, there is provided a fuse comprising, in addition to the aforementioned secondary safety mechanism, an S&A safety assembly configured to lock a rotational movement of the interrupter in the safe position and to unlock the rotational movement of the interrupter responsive to the setback forces and a subsequent cease thereof, wherein the operation of the S&A assembly is coordinated with the operation of the secondary safety assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of embodiments of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout.
In the accompanying drawings:

Figure 1A is a cut through diagram of a fuze according to the prior art;
Figure 1B is a perspective diagram showing an S&A mechanism of a fuze according to the prior art;
Figure 2A-2E illustrate a sequence of cutaway diagrams presenting the operation of a fuze according to some embodiments of the present invention; and
Figure 3 is a cut through diagram illustrating the fuze according to some embodiments of the present invention showing the S&A mechanism combined with the secondary safety mechanism.

The drawings together with the following detailed description make apparent to those skilled in the art how the invention may be embodied in practice.

DETAILED DESCRIPTION OF THE INVENTION

With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
Figures 2A-2E illustrate a sequence of cutaway diagrams demonstrating the operation of the safety assembly in a step by step manner, according to some embodiments of the present invention. Fuze 100 includes a housing 110 defining a cavity with an opening at its top. The opening may be covered by a suitably shaped nose cap 130 which is coupled to a first compression spring 124. A firing pin 140 has a bulky head 132 which is coupled to housing 110 via second compression spring 122. Firing pin 140 is free to move back and forth (when uninterrupted).
In the safe position, a locking means 146, possibly in a form of a ball rests between the shoulder of head 132 and housing 110. Fuze 100 further includes an interrupter 150 rotatably attached to a shaft 152 that is affixed to housing 110 such that shaft 152 is located along an axis parallel to that of firing pin 140. Additionally, interrupter 150 includes a first cavity 154 located, in the safe position, along the axis of firing pin 140 and shaped to accommodate a portion of firing pin 140. Interrupter 150 further includes a second cavity 160 configured to accommodate a detonator. In the pre-launched position shown in Figure 2A , a safety wire 112 cuts through housing 110 and overlaps the bottom of head 132 such that it serves as a stopper so that firing pin 140 is locked in the safe position.
Figure 2B shows fuze 100 with safety wire 112 removed. In this position, firing pin 140 is free to move back and forth within the cavity together with the nose cap 130 affixed to it and subject to the force applied to first compression spring device 124 that connects nose cap 130 to housing 110. Thus, any unintentional force applied to the cap nose 130 of fuze 100 in the safe mode will not switch the fuze form the safe position. Additionally, any failure of first compression spring device 124 will not affect the safe position of fuze 100.
Figure 2C shows fuze 100 upon launching, when launch-acceleration setback forces are applied to head 132 pulling it and firing pin 140 sufficiently downwards so that locking means 146 is released from its location between the shoulder of head 132 and housing 110. Consequently, a portion of the firing pin 140 enters first cavity 154 as long as the setback forces are applied at a level that overcomes the expansion forces of second compression spring device 122. In this position, firing pin 140 serves as a locking mechanism to interrupter 150 by preventing any rotary movement thereof.
Figure 2D shows fuze 100 after the setback forces have ceased. Head 132 and firing pin are pushed upwards by second compression spring device 122 so that the shoulder of head 132 reaches housing 100, so that firing pin 140 exits first cavity 154 entirely. In this position, firing pin 140 no longer serves as a locking mechanism to interrupter 150. Additionally, any target impact affecting nose cap 130 will be transferred to firing pin 140 directly. The fuze is however not yet armed in this position (which lasts a very short period) as firing pin 140 is still aligned with first cavity 154.
Figure 2E shows fuze 100 in an armed position after interrupter 150 has been rotated approximately 180° by some rotating means such as a clockwork piece (not shown here). It is understood that such clockwork pieces are well known in the art and are used herein to provide a further delay (possibly of approximately 1 second) from the moment the setback forces cease and the arming of the fuze, which occur once interrupter 150 completes its rotary movements so that second cavity 160 (with a detonator within) aligns with firing pin 140.
Figure 3 is another cutaway diagram and used herein to focus on the combined S&A and secondary safety mechanism aspect of the fuze according to some embodiments of the present invention. Fuze 100 is shown here in the safe position with safety wire 112 inserted. Additionally, S&A mechanism 20 which has been discussed above is also shown (with most of its component obscured). The inventors have found it advantageous to use, as a secondary safety measure, safety mechanism 100 in conjunction with the S&A mechanism 20. These two mechanisms operate independently of each other in the sense that in a case that one of them fails, the other one is not affected by the failure. Additionally, each proper operation of these two mechanisms is solely dependent on the setback forces and their increase or decrease over time. For a proper cooperation of the two mechanisms it would be advantageous to adjust the compression springs so that corresponding components in the two mechanisms such as locking member 350 of S&A mechanism 20 and locking means 146 of the secondary safety mechanism unlock the mechanism approximately at the same time, so that the delay of the clockwork can be properly defined. The robustness as well as the simplicity of use of the secondary mechanism 100 namely due to the bulky head firing pin 140 makes it an effective complementary safety mechanism on top of the S&A mechanism.
In accordance with some embodiments of the present invention, other implementations of the aforementioned structure may achieve the increased safety effect by combining two independent safety mechanisms as illustrated above. In accordance with independent method claim 9 the method of increasing safety for ammunition may include the following steps: providing a mortar fuze having a safety assembly in accordance with the independent assembly claim 1 including a firing pin with a head having a radially protruding shoulder, wherein the firing pin is directed downwards; providing a locking means which when in a safe position, rests between the shoulder of the head and the housing; and providing an interrupter rotatably attached to a shaft that is affixed to the housing wherein the shaft is located along an axis parallel to the firing pin, wherein the interrupter comprises a first cavity located, in the safe position, along the axis of the firing pin and shaped to accommodate a portion of the firing pin, and wherein the interrupter further comprises a second cavity configured to accommodate a detonator; enabling the firing pin to move downwards responsive to setback forces during launch of the ammunition so that the locking means is released from its location between the shoulder of the head and the housing and so that a portion of the firing pin enters the first cavity, and enabling the firing pin to move upwards responsive to a cease of the setback forces so that the shoulder of the head moved towards the housing and so that the firing pin exits the first cavity entirely.

Claims

A safety assembly for ammunition comprising:
a housing (110) defining a cavity with an opening at its top;

a nose cap (130) which covers the opening, wherein the nose cap is connected to the housing by a first compression spring (124);

a firing pin (140) with a head (132) having a radially protruding shoulder, wherein the firing pin is directed downwards;

a locking means (146) which when in a safe position, rests between the shoulder of the head (132) and the housing (110); and

an interrupter (150) rotatably attached to a shaft (152) that is affixed to the housing (110) wherein the shaft is located along an axis parallel to the firing pin (140), wherein the interrupter comprises a first cavity (154) located, in the safe position, along the axis of the firing pin and shaped to accommodate a portion of the firing pin, and wherein the interrupter further comprises a second cavity (160) configured to accommodate a detonator,

wherein the firing pin (140) is configured to move downwards responsive to setback forces during launch of the ammunition so that the locking means (146) is released from its location between the shoulder of the head (132) and the housing (110) and so that a portion of the firing pin (140) enters the first cavity (154), and

wherein the firing pin (140) is further configured to move upwards responsive to a cease of the setback forces so that the shoulder of the head (132) moves towards the housing (110) and so that the firing pin (140) exits the first cavity (154) entirely,

wherein the safety assembly further comprising a second compression spring (122) connecting the bottom of the head (132) and the housing (110),
wherein the second compression spring (122) is configured, in the safe position, to push the head (132) upwards so that the locking means (146) is maintained on the shoulder of the head (132) until the set back forces overcome an expansion force of the second compression spring (122).
The safety assembly of claim 1 configured such that when the firing pin (140) exits the first cavity (154) entirely, any target impact affecting nose cap (130) is transferred to firing pin (140) directly.
The safety assembly according to claim 1 or claim 2, further comprising a clockwork mechanism configured to rotate the interrupter (150) from the safe position into an armed position in which the second cavity (160) within the interrupter aligns with the firing pin (140).
The safety assembly according to any of the preceding claims, wherein the second compression spring (122) is configured to push the head (132) upwards after the locking means (146) is released and the setback forces cease, so that the head (132) reaches the housing (110) and the firing pin (140) exits the first cavity (154) entirely.
The safety assembly according to any of the preceding claims, further comprising a safety wire (112) that cuts through the housing (110) and overlaps the bottom of the head (132) so that the firing pin (140) is locked in the safe mode.
The safety assembly according to any of the preceding claims, wherein the locking means is a ball (146).
An ammunition fuze comprising a safety assembly according to any of claims 1 to 6, further comprising a safe and arm "S&A" assembly (20) configured to lock a rotary movement of the interrupter (150) in the safe position and to unlock the rotary movement of the interrupter (150) responsive to the setback forces and a subsequent cease thereof, wherein the operation of the S&A assembly is coordinated with the operation of the safety assembly.
The fuze according to claim 7, wherein the S&A assembly comprises:
a first safety plunger (330) having a cone-shaped top;

a second safety plunger (320) having a radially protruding shoulder and a stopper (322) configured to lock the radial movement of the interrupter (150) in the safe mode; and

a locking member (350) that rests, in the safe mode, on the shoulder of the second safety plunger so that it locks its movement,

wherein the a first safety plunger (320) is configured, responsive to the setback forces, to move downwards so that the locking member (350) moves from the shoulder of the second safely plunger (320) and reaches the cone-shaped top thus unlocking the second safety plunger (320), and

wherein the a second safety plunger (320) is configured, responsive to the setback forces and upon being unlocked, to move downwards so that the stopper (322) is released from the interrupter allowing the clockwork piece to rotate the interrupter (150) to the armed position, provided that the firing pin (140) has exited the first cavity (154) entirely.
A method of increasing safety for ammunition comprising:
providing a mortar fuze having a safety assembly in accordance with the independent assembly claim 1 including a firing pin (140) with a head (132) having a radially protruding shoulder, wherein the firing pin is directed downwards, wherein the mortar fuze comprises a housing (110) defining a cavity with an opening at its top, and a nose cap (130) which covers the opening, wherein the nose cap (130) is coupled to a first compression spring (124) which is connected to an inner wall of the housing;

providing a locking means (146) which when in a safe position, rests between the shoulder of the head and the housing; and

providing an interrupter (150) rotatably attached to a shaft that is affixed to the housing wherein the shaft is located along an axis parallel to the firing pin, wherein the interrupter comprises a first cavity located, in the safe position, along the axis of the firing pin and shaped to accommodate a portion of the firing pin, and wherein the interrupter further comprises a second cavity configured to accommodate a detonator;

enabling the firing pin (140) to move downwards responsive to setback forces during launch of the ammunition so that the locking means is released from its location between the shoulder of the head and the housing and so that a portion of the firing pin enters the first cavity, and

enabling the firing pin (140) to move upwards responsive to a cease of the setback forces so that the shoulder of the head moved towards the housing and so that the firing pin (140) exits the first cavity (154) entirely,

wherein the safety assembly further comprising a second compression spring (122) connecting the bottom of the head (132) and the housing (110),
wherein the second compression spring (122) is configured, in the safe position, to push the head (132) upwards so that the locking means (146) is maintained on the shoulder of the head (132) until the set back forces overcome an expansion force of the second compression spring (122).