Patent Publication Number: US-6336407-B1

Title: Pyrotechnic slide assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of co-pending U.S. provisional application Ser. No. 60/181,496, filed on Feb. 10, 2000, which is incorporated herein by reference. 
     This application also relates to co-pending U.S. patent application titled “Self Destruct Fuze with Improved Slide Assembly”, Ser. No. 09/511,641, filed on Feb. 22, 2000, which, in turn, claims the priority of U.S. provisional application Ser. No. 60/128,431, filed on Apr. 5, 1999, both of which are commonly assigned to the same assignee as the present invention, and are incorporated herein by reference. 
    
    
     GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of munitions, and more particularly to an improved design for a secondary self-destruct fuze that functions in the event the primary fuze mode fails to function, and that meets the design requirements for low cost, highly producible, and a non-spin/low velocity operating environment. 
     BACKGROUND OF THE INVENTION 
     Dual Purpose Improved Conventional Munitions (DPICM) must have either a self-destruct capability or they must show dud rates not to exceed 1 in 500 as an operational requirement. To this end, several engineering studies were undertaken in an attempt to address the low reliability of the conventional M223 mechanical fuze. However, these studies did not change the basic design of the M223 mechanical fuze. Instead, they generally considered modifying the materials and the manufacturing processes to reduce the dud rate problem. 
     Conventional designs proposed the development of a hybrid electromechanical fuze which is relatively complex with approximately 40 to 50 parts, with a costly production line. In addition, the no-spin/low velocity operational environments of grenades jeopardize the fuze reliability. Several projectiles have unique operational requirements that the current fuze design might not meet readily. 
     Some of the concerns facing current self-destruct fuze designs are listed below: 
     (1) The threads between the arming screw and the weight can be overtorqued. 
     (2) The fuze components may suffer collateral damage during ejection from the carrier. 
     (3) The fuze may impact the ground at oblique angles and the firing pin might not provide sufficient energy to the detonator. 
     (4) The fuze may operate poorly in a no-spin/low velocity environment. 
     Therefore, there is a still unsatisfied need for a fuze which, among other features, solves the no-spin/low velocity environment, significantly reduces the number of components, improves producibilty, and increases the operational reliability of the primary arming mode. 
     Several engineering studies were conducted in the past two decades in an attempt to address the low reliability of existing mechanical fuzes. Although these ‘mechanical only’ solutions did improve the overall functional reliability of the fuze, there is still room for an improved design that fully addresses the no-spin/low velocity operational environment, and that significantly reduces the dud rate to the present ordnance requirements for self destruct fuzing of grenades. 
     A design that proposes a secondary self-destruct electrical mode of operation is described in U.S. Pat. No. 5,387,257. While the patented fuze provides an improvement in the relevant field, the activation of this self-destruct mode requires forces that are not available from non-spin/low velocity environment. In addition, it&#39;s high cost makes it unaffordable. 
     SUMMARY OF THE INVENTION 
     The present invention contemplates an improved design for a secondary self-destruct fuze that functions in the event the primary fuze mode fails to function, and that meets the design requirements for low cost, highly producible, and a non-spin/low velocity operating environment. 
     The fuze offers several features and advantages, among which are the following: 
     (1) It significantly improves the performance of traditional M223 mechanical fuzes by providing a redundant mode of operation, which adds a self-destruct capability and leads to a tactical destruction of the grenade at impact angles greater than 60 degrees relative to the vertical, on all types of terrain. 
     (2) It significantly simplifies conventional designs and the production process. It uses the main firing mode of the M223 fuze, and adds a few components to the M223 fuze, to add a relatively simple secondary mode of operation through a back up independent firing pin. These additional components can be made of readily available materials that are fabricated for example, by means of stamping, die casting, or precision molding techniques. 
     (3) It solves the functional reliability problems when operating in a no-spin/low spin environment. 
     (4) It uses a unique low cost mechanical/pyrotechnic design to provide a high functional reliability, in almost all operating environments. It uses a unique aerodynamic safety release (ASR) to function the secondary mode feature providing self-destruct fuzing capability. 
     (5) It meets all MIL-STD-1316D standards. 
     (6) It is compatible with almost all grenade configurations. 
     (7) It provides a self destruct delay of between 30-45 seconds. 
     The foregoing and other features and advantages of the present invention are realized by a fuze that includes an improved slide assembly that incorporates a pyrotechnic delay mechanism with a minimum number of components. The fuze operates in two modes. In a primary mode, the fuze can function similarly to a conventional M223 fuze. In a secondary, self-destruct mode, a pyrotechnic delay mechanism is initiated. The slide assembly is comprised of an aerodynamic safety release (ASR), a safety pin, a rotational firing pin fitted with a resilient member such as a spring, an M55 detonator, a pyrotechnic initiator, a pyrotechnic delay mix and an end cap. 
     In use, the fuze is fitted to a munition or grenade. As the grenade is dispensed from its carrier, a grenade stabilizer starts to oscillate and sense drag. The oscillation and drag results in an arming screw and an inertial weight to back out from a slide assembly, allowing the slide assembly to move to an in-line position relative to a main M55 detonator in-line with the arming screw (firing pin). Concurrently, the unique aerodynamic safety release is lifted in the upward direction under the force of the airstream, releasing the safety pin. This releases the rotational firing pin, which forces the rotational firing pin to contact the pyrotechnic initiator. 
     The pyrotechnic delay mix burns to the end cap and propagates to the M55 detonator. The initiation of the M55 detonator causes the fuze to function in the primary mode or, if for any reason the primary mode fails to function the grenade, the grenade is rendered safe to handle by the secondary mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features of the present invention and the manner of attaining them will be described in greater detail with reference to the following description, claims, and drawings, wherein reference numerals are reused, where appropriate, to indicate a correspondence between the referenced items. 
     FIG. 1 is a perspective view of a fuze incorporating an improved slide assembly according to the present invention, shown secured to a grenade or munition; 
     FIG. 2 is an enlarged perspective view of the fuze of FIG. 1 
     FIG. 3 is an exploded view of the fuze of FIGS. 1 and 2; 
     FIG. 4 is a perspective view of the slide assembly of FIGS. 1-3, shown unassembled; 
     FIG. 5 is a perspective view of the slide assembly of FIG. 4, shown assembled; 
     FIG. 6 is an enlarged, perspective, bottom view of an aerodynamic safety release (ASR) forming part of the slide assembly of FIGS. 4 and 5; 
     FIG. 7 is an enlarged, perspective, bottom view of a rotational firing pin forming part of the slide assembly of FIGS. 4 and 5; 
     FIG. 8 is an enlarged perspective view of a rotational firing spring forming part of the slide assembly of FIGS. 4 and 5; 
     FIG. 9 is an enlarged perspective view of a pivot pin that supports the rotational firing pin of FIG.  7  and the rotational firing spring of FIG. 8, for containing the rotation of the rotational firing pin; 
     FIG. 10 is an enlarged perspective, view of a pin that forms part of the rotational firing pin of FIG. 7, used to lock the rotational firing spring of FIG. 8 in position; and 
     FIG. 11 is a perspective bottom view of the slide body and aerodynamic safety release. 
    
    
     As used herein, the directional terms, such as “upright”, “longitudinal”, lateral, and so forth do not imply absolute directions, but rather connote that an angular disposition exists between the related components. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a fuze  10  according to the present invention shown secured to a grenade  12 . With reference to FIG. 2, the fuze  10  generally includes an arming screw and weight assembly  14 , a housing  16 , a cover  18 , and a slide assembly  70 . In an unarmed condition, the slide assembly  70  is secured to the housing  16  and the cover  18 . In an armed condition, the slide assembly  70  moves between the housing  16  and the cover  18 . 
     The fuze  10  operates in two modes: a primary mode and a secondary mode. In the primary mode, the fuze functions similarly to a conventional M223 fuze. The slide assembly  70  is spring-loaded from below, and in a primary mode, when it is released by the fuze safety system and free to move, it places a main detonator  19  (FIG. 3) in line between a main firing pin (combined with the arming screw of the fuze  10 ), and an opening  25  in the cover  18 . This will expose a main charge of the grenade  12  to the action of the main firing pin and the detonator. 
     With reference to FIGS. 3 and 4, the slide assembly  70  is comprised of an aerodynamic safety release (ASR)  100 , a safety pin  200 , a rotational firing pin  300  fitted with a spring  400 , and a pyrotechnic delay mechanism  500 . The spring  400  is attached to the rotational firing pin  300  by means of a spiral pin  410 . With further reference to FIG. 7, the spiral pin  410  is force fitted through a hole  415  formed in the body  418  of the rotational firing pin  300 . A pivot pin  420  is inserted along the center of the rotational firing pin  300  through a hole  425 . The pivot pin  420  passes through the center of the spring  400  and then through the hole  425  of the rotational firing pin  300 , and is force fitted into a hole  440  at the bottom of the slide  600 . 
     The aerodynamic safety release  100  is preferably made of, for example, polycarbonate, using an injection molding process. The safety pin  200  can be made of metal, using a corrosion resistant steel. The rotational firing pin  300  is made of metal, using a corrosion resistant steel. The spring  400  of the rotational firing pin  300  is formed of resilient material. 
     The pyrotechnic delay mechanism  500  is comprised of an initiator  510 , a pyrotechnic delay mix  520 , and an end cap  530 . The initiator  510  is made of match tip material or miniature detonator, and receives the initial stimulus from the rotational firing pin  300  in order to initiate the delay pyrotechnic mix  520 . The pyrotechnic delay mix  520  can be made of a conventional or available composition, and is designed to burn at a rate of approximately 1 inch per 40 seconds, to initiate the end cap  530 . The end cap  530  will detonate when exposed to the burning pyrotechnic delay mix  520 , and, in turn, initiates the main detonator  19 . 
     The slide assembly  70  includes a slide  600  which is preferably made of polycarbonate, using an injection molding process. The slide  600  includes several features and accommodates the remaining components of the slide assembly  70 . 
     In use, the fuze  10  is fitted to a munition such as the grenade  12 . As the grenade  12  is dispensed from its carrier (not shown), a grenade stabilizer (not shown) starts to oscillate and sense drag. This oscillation and drag causes the arming screw and weight assembly  14  to back out from both the housing and the slide assembly, allowing the slide assembly  70  to move to an in-line position relative to the center axis of the grenade and fuze and also in-line with the main detonator of the fuze. Concurrently, the aerodynamic safety release  100  is lifted in the upward direction under the force of the airstream, releasing the safety pin  200 . This releases the rotational firing pin  300 , which rotates until it strikes the pyrotechnic initiator  510 , which, in turn, ignites the pyrotechnic delay mix  520 . 
     The pyrotechnic delay mix  520  continues to burn for a prescribed time, until it initiates the end cap  530 , which causes the main detonator  19  to detonate. If the slide assembly  70  is released and moves to the fully armed position, then the pyrotechnic delay mix  520  results in the initiation of the main detonator  19  and the functioning of the grenade  12 . 
     However, if the primary arming mode fails and the slide assembly  70  does not move to the fully armed position, but rather remains in the unarmed position, the pyrotechnic delay mix  520  still initiates the main detonator  19  and results in the sterilization of the grenade  12 , rendering it safe to handle. 
     Having described the main components and operation of the fuze  10 , the improved slide assembly  70  will now be described in greater detail in connection with FIGS. 4 through 11. With reference to FIGS. 4,  5  and  11 , the slide  600  includes several features and retains the remaining components of the slide assembly  70 . The slide  600  includes a generally rectangularly shaped slide body  603  which is defined by a base  604  and an upper surface  605 . An upright opening  610  (FIG. 4) is formed in the slide body  603 , and extends through the upper surface  605  to the base  604 , in order to accommodate the main detonator  19  (FIG. 3) and to cause it to be retained against the base  604 . The opening  605  is typically as deep as the height of the detonator  19 . 
     A longitudinal blind hole  620  is formed in the slide body  603 , and receives the pyrotechnic delay mechanism  500 , with the end cap  530  fitted first to be in very close proximity to the main detonator  19 , and in contact with the opening  610  via a lateral channel  624 . The pyrotechnic delay mechanism  500  is forced fitted or pressed into the hole  620 . 
     A hole  680  extends through the entire depth of the side  665  to nest the safety pin  200 . A channel  690  having a generally rectangular cross-section, is formed along one side of the slide  600  to receive the rotational firing pin  300 . With reference to FIG. 7, the body  418  of the rotational firing pin  300  includes a crescent shape cutout  727  at one of its side, a generally semi-circular cutout  730  at another end, and a bottom flat face  733 . 
     During assembly, the bottom flat face  733 , which is typically in a plane that is orthogonal to the two holes  415  and  425 , rests against one side  665  of the channel  661 . A side  735  of the rotational firing pin  300  contacts a back surface  670  of the channel  690 , so that the pivot pin  420  can be inserted through the rotational spring  400  and through the rotational firing pin  300 , and into the hole  440  in the slide  600 . 
     With reference to FIG. 8, the rotational spring  400  includes a spirally wound coil  401  that terminates in an outer hook-shaped end  402  that engages the spiral pin  410 . The rotational spring  400  also includes an inner end  404  that engages the pivot pin  420  as described herein. 
     The rotational spring  400  is nested against an upper flat face  734  of the rotational firing pin  300 , and biases against the spiral pin  410  so that the rotational spring  400  is in a pre-loaded condition when the fuze  10  is in the armed position. The crescent cutout  727  is located farthest away from the pyrotechnic delay mechanism  500 , and defines a firing pin tip  810 . The spring  400  spring loads the rotational firing pin  300  in the firing position, with the firing pin tip  810  at a maximum rotational distance from the initiator  510 , so that when the rotational firing pin  300  is released, the pin tip  810  rotates around the pivot pin  420  and strikes the initiator  510 , initiating the pyrotechnic delay mechanism  500  as described above. 
     With reference to FIG. 9, the pivot pin  420  is comprised of three integrally formed sections: a cap  820  that extends into a larger shaft  830 , which, in turn, extends into a smaller shaft  840 . The smaller shaft  840  is inserted into the hole  440  of the slide  600 . The larger shaft  830  is inserted through the rotational spring  400  and the rotational firing pin  300 . The cap  820  rests on the surface of the upper rotational spring  400 . 
     With reference to FIG. 10, the spiral pin  410  is cylindrically shaped, and is force fitted into the hole  415  of the rotational firing pin  300 . The spiral pin  410  provides a counter-balance support for the rotational spring  400 . The spiral pin  410  can be made of the same material as the safety pin  200 , for example, metal. 
     An upright opening  640  extends through the slide body  603 , and allows the main firing pin to nest in the slide body  603 , and to lock the movement of the slide  600  within the housing  16 . Two upright tabs  650  are located on opposite sides of the opening  640 , and extend at an angle from and relative to the upper surface  605 . The tabs  650  provide a stop to the slide assembly  70  once it has moved into the in-line position with the center axis of the grenade  12  and fuze, by butting against the inner surface of the housing  16 . 
     A pivotal slot  660  (FIG. 4) is provided to accommodate a cylindrically shaped bracket  110  of the aerodynamic safety release  100  as it will be explained later. A channel  670  allows an upright member  210  (FIG. 4) of the safety pin  200  to be inserted in, and retained by the slide  600 . A step or channel  661  (FIG. 11) is formed in the slide body  603  to accept a spring similar to the slide spring found in the M223 Fuze. 
     With reference to FIG. 6, the aerodynamic safety release  100  is designed to catch the airstream after the grenade  12  has been ejected from its carrier, which causes the safety pin  200  to be lifted up from its nested position in the slide  600 . The aerodynamic safety release  100  is comprised of the bracket  110  that fits in the pivotal slot  660  of the slide  600 , a wing  140 , and a connecting member  144  that connects the bracket  110  and the wing  140 . 
     A lateral member  220  of the safety pin  200  rests in and a lateral groove  120  formed in the connecting member  144  of the aerodynamic safety release  100 , to ensure proper seating of the safety pin  200  against the aerodynamic safety release  100 . A through opening  130  is generally disposed along a central axis of the connecting member  144 , and is preferably positioned in registration with the hole  680  of the slide  600 , so that the upright member  210  of the safety pin  200  can be inserted simultaneously through both the opening  130  and the semi-circular hole  730  of the rotational firing pin  300  and into hole  440 . 
     The wing  140  is slightly curved so that it is folded inward toward the slide  600 , so that it is deployed in the direction of the arrow A, when it catches the airstream. 
     The safety pin  200  is generally T-shaped, and is designed to be inserted in the slide  600 , as explained earlier, to limit or prevent the movement of the rotational firing pin  300 . 
     It should be understood that the geometry and dimensions of the components described herein may not be to scale, and may be modified within the scope of the invention. The embodiments described herein are included for the purposes of illustration, and are not intended to be the exclusive; rather, they can be modified within the scope of the invention. Other modifications may be made when implementing the invention for a particular application.