US3707912A

US3707912A - Mechanical fuze with self-destruct mechanism

Info

Publication number: US3707912A
Application number: US00173446A
Authority: US
Inventors: C Duncan; J Mcnelia; W Pickler
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1971-08-20
Filing date: 1971-08-20
Publication date: 1973-01-02
Anticipated expiration: 1990-01-02

Abstract

A mechanical fuze for aerial ordnance devices having an extendable probe, and impact sensor mounted on the probe, an impact responsive inertia weight operable with an auxiliary firing pin as a backup for the probe sensor, and a self-destruct assembly. The self-destruct assembly includes a percussion primer actuated during extension of the probe and coupled to a thin column of deflagrating material sheathed in a flexible metal and having an explosive charge at its terminal portion for driving a piston against the inertia weight if both the probe sensor and inertia weight remain unactivated when the column burn front reaches the explosive charge, thereby detonating the device through the auxiliary firing pin.

Description

United States Patent 1 1 Duncan et al. 1 Jan. 2, 1973 s41 MECHANICAL FUZE WITH SELF- 2,960,036 11 1960 Curl 6:61 ..102/7.4

DESTRUCT MECHANISM 3,388,664 6/1968 Kelly etal. 3,604,357 9/1971 Duncan i 1 lnventOfSI g t: 3 f a vf g 3,633,510 1 1972 Bernardin 102/856 0 o 1ver prmg; I 1am Picklel', Fulton 0f Primary Examiner-Samuel W. Engle [73] Assignee: The United States of America as Atmmey"'R'S'Smasc1a ted b th S tar f th i ff y e we y 0 e 57 ABSTRACT [22] Filed Aug 20 1971 A mechanical fuze for aerial ordnance devices having an extendable probe, and impact sensor mounted on [21] Appl- N0: 1 3,446 the probe, an impact responsive inertia weight operable with an auxiliary firing pin as a backup for the [52] U S Cl 102/7 4 102/78 102/84 probe sensor, and a self-destruct assembly. The self- /85 destruct assembly includes a percussion primer actu- [51] Int Cl F42c l 4 ated during extension of the probe and coupled to a [58] Fie'ld 84 85 6 thin column of deflagrating material sheathed in a flexible metal and having an explosive charge at its terminal portion for driving a piston against the inertia weight if both the probe sensor and inertia weight [56] References Cited remain unactivated when the column burn front UNITED STATES PATENTS reaches the explosive charge, thereby detonating the device through the auxiliary firing pin. 2,412,695 l2/l946 Rost et al. ..l02/7.4 2,725,01 l l l/l955 Sundermann et al ..l02/85.6 8 Claims, 3 Drawing Figures 12 l )2 32 i, T l4 l5 l0 2111 Z07 ///,I/ fl/ 5 /S4 4 M v g2 W s 7 /Il8 1 5 Fig. 1

INVENTORS Cecil L.Duncan John F. McNelia William (LPickler ATTORNEY PATENTED 2 I975 3.707.912

SHEET 2 OF 2 IN VENTORS Ceczl L.Duncan John F. McNelia William G.Pickler MECHANICAL FUZE WITH SELF-DESTRUCT MECHANISM BACKGROUND OF THE INVENTION This invention relates generally to ordnance fuzes and more particularly to a mechanical proximity fuze having a self-destruct mechanism incorporated therein and intended for use in an aerial ordnance device.

A widespread problem encountered with fuzes for aerial ordnance devices such as bombs, rockets, projectiles and the like, is their inability to function with 100 percent reliability under the diverse conditions which they frequently encounter. Considering aerial launched bombs having a point contact detonator, for example, such detonators often malfunction if the bomb lands in water or upon very soft terrain because the fuze does not receive sufficient impact to effect detonation. Under other conditions, such as when the bomb must penetrate a heavy jungle canopy, the bomb may be deflected from its normal trajectory in such a manner as to result in a bomb impact angle which exceeds the sensitivity limit of the primary fuze mechanism. In other instances, particularly in a parachute retarded bomb for which the parachute failed to separate from the bomb, the bomb may become suspended in the jun gle canopy. Moreover, in fuzes having forwardly extending probes intended to detonate the device at a standoff distance above the ground level, such probes are frequently damaged or completely broken as the bomb passes through dense foliage and tree limbs. In all of these instances, failure of the bomb to detonate not only results in an expensive piece of equipment being deployed without achieving its tactical mission but a I further problem is that such devices may be recovered by unfriendly forces. These recovered devices may be subsequently used directly against friendly personnel or may be disassembled and its explosive contents be used against friendly personnel.

Previous attempts to minimize the number of duds, or undetonated ordnance devices, has involved a guest for new fuze designs which hopefully have a higher degree of reliability but unfortunately these usually are much more costly. An alternative approach to the problem was to provide the bomb with double fuzing systems which is also a costly technique.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is to provide a new and improved fuze for aerial ordnance device capable of assuring reliable detonation of the device.

Another object of the present invention is to provide a new and improved mechanical fuze for an aerial ordnance device having improved reliability at a minimal increase in cost.

A further object of the instant invention is to provide an improved fuze for aerial ordnance device having the capability of detonating the device regardless of its angle of target impact or the hardness of the material encountered by device.

Briefly, in accordance with the present invention, these and other objects are attained by a fuze having a forwardly extendable probe having an impact sensor mounted thereon, an impact responsive inertia weight operable with an auxiliary firing pin as a backup for the probe sensor, and a pyrotechnic delay column initiated upon extension of the probe and adapted to drive the inertia weight to its firing position upon completion of a predetermined time delay. The burning time of the pyrotechnic delay is sufficient to permit normal fuze detonation initiated by either the probe mounted impact sensor or the inertia weight but, in the event that neither of these primary detonating means are actuated when the bomb reaches its target, the pyrotechnic delay column causes the bomb to self-destruct at the end of a predetermined time delay determined by the length of the pyrotechnic delay column.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and its many attendant advantages will develop as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a side elevation, partially in section, of the fuze according to the present invention; and

FIG. 2 is a transverse sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a partial sectional side view taken along line 3-3 ofFIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like reference characters designate identical or corresponding parts throughout the views and more particularly to FIG. 1 whereon the ordnance fuze is shown as having a generally cylindrical tubular casing 10 with an integral annular flange 12 at the rear end thereof by means of which the fuze may be attached to an aerial ordnance device, such as a bomb, projectile or the like by conventional means, such as bolts, screws, welds or other fasteners. The forward end of the fuze casing 10 is closed by a removable lid 14 having a rim portion 16 crimped into an annular circumferential groove formed in the tubular fuze casing. The lid 14 has attached thereto a tab 18 by which the lid may be wrenched off from the casing.

The central axial bore of the fuze casing 10 has a tubular insert 20 received therein which is open at its forward end and closed at its rearward end by a closure plate 22. Concentrically disposed within the tubular insert is an extendable probe 22 having one end thereof secured to the tubular insert. Probe 24 is formed of a volute spring, such as the Stacer" made by Hunter Spring Company of Hatfield, Pa. In the telescoped position illustrated, the probe is stressed and requires the axial restraining force supplied by the crimped-on lid 14 to maintain it in that position. When the lid or cover 14 is removed, the probe immediately extends itself forward to its fully relaxed unstressed position. As the probe extends, the diameter of its base or rear portion decreases and when it is telescopically retracted, the diameter increases and this change in base diameter is utilized to enhance the rigidity and axial strength of the extended probe through the action of a constrictive locking clamp (not shown) which constrictively engages a peripheral portion of the probe base when it is extended, thereby inhibiting any tendency for the base to expand and thereby maintain the probe in its extended position.

Attached to the forward inner turn of the volute spring probe 24 is a fuze actuator assembly generally indicated by reference numeral 26. The fuze actuator assembly and the previously mentioned constrictive clamp are preferably constructed substantially as shown and described in application, Ser. No. 821,174, filed May 2, 1969. As described in application, Ser. No. 821,174, the fuze actuator assembly 26, which is attached to the inner turn of volute spring probe 24 and is carried to an extended position near the forward portion of the extended probe, preferably includes a piezoelectric crystal assembly generally shown by numeral 28 adapted to be stressed upon fuze impact with a target and being electrically connected to a detonator mounted within an arming rotor positioned in the rearward portion of the fuze casing, as more fully described hereinafter. Upon impact with a target, stressing of the piezoelectric crystal is caused by an explosively driven anvil which is activated by a striker pin driven into the explosive charge upon the crushing of a protective crush cup such as when the probe impacts loose dirt, sand or mud, or alternatively driven into the explosive by the severance of a frangible link in the housing such as when the probe impacts a hard .solid surface. Although the fuze actuator assembly 26 is preferably constructed in accordance with the invention disclosed in Ser. No. 821,174, it will be understood that details thereof do not form an essential part of this invention and that the piezoelectric crystal may be activated by any suitable impact receiving member mounted on the forward portion of the probe 24.

Received within the rear portion of fuze casing is a mounting block 30 for a safety and arming device, the mounting block being secured to the casing 10 by screws 32. Formed in the main body of the mounting block 30 is a central compartment 34 which is defined on three sides and the bottom by the mounting block and on the fourth side by a base plate 36 of an escapement mechanism or timer assembly shown generally at 38. An arming rotor 40 is positioned within the compartment 34 and journaled for rotational movement at one end in the base plate 36 of the timer assembly and at the other end in a socket 42 in the mounting block 30. The arming rotor has a transverse bore 44 formed therethrough for receiving an electrically initiated explosive detonator 46 which is shown in its safe or outof-line position with respect to a transverse explosive lead charge 48 formed in the mounting block 30 which communicates with the booster charge in the ordnance device to be detonated by the fuze assembly. A helical torsion spring 52 is positioned about a shaft 54 on the arming rotor, having one end attached to the shaft and the other end attached to the mounting block. The spring 52 biases the arming rotor 40 for a 90 rotational movement from the out-of-line position shown in FIG. 1 to the armed position wherein detonator 46 is coaxially aligned with the explosive lead charge 48 in the mounting block. The rate of rotational movement of the arming rotor is controlled by the timer assembly 38 in a well known manner. However, prior to extension of the probe 24, the arming rotor is locked in its out-ofline position by means of an arming pin 56 which is attached at its forward end to the fuze actuator assembly 26 and which has its rearward end extending into a slot 58 formed in the arming rotor 40. When the probe cover or lid 14 is removed from the fuze housing, the probe automatically extends and carries with it the fuze actuator assembly 26 and the arming pin 56 connected thereto, thereby withdrawing the end of pin 56 from its locking engagement with rotor slot 58 to free the rotor for rotational movement by spring 52 to the armed position. In this position, detonator 46 is aligned with the bombs booster charge and is electrically connected by conductor (not shown) to the piezoelectric crystal assembly 28 so that upon suitable target impact, the piezoelectric crystal is stressed and a voltage produced thereby will detonate the detonator 46.

If, for some reason, the piezoelectric crystal fails to generate an electrical impulse or the detonator 46 is not initiated thereby, the fuze is provided with an auxiliary detonating mechanism consisting of an inertia weight 64 slidably positioned in a bore 66 formed in the mounting block 30. The inertia weight has a first annular groove 68 formed near the forward end thereof to receive a tang 72 which is formed on the rotor 40 and which extends through a arcuate slot 74 formed in the mounting block. When the rotor is in the unarmed position shown in FIG. 1, the tang 72 projects into angular groove 68 to lock the inertia weight against movement; but when the rotor has moved to its armed position, the tang 72 is withdrawn from its locking engagement with the inertia weight. An auxiliary L-shaped firing pin 76 is pivotally mounted on a pin 78 and has a cam 82 formed thereon which extends into a second annular groove 84 formed in the inertia weight. A helical compression spring 86 received in the forward end of the bore 66 biases the inertia weight toward the rear portion of the bore. With the rotor 40 in its armed position and tang 72 withdrawn from the groove 68, impact with a target develops an inertia force acting on weight 64 which will overcome the restraining force exerted thereon by spring 86 and the weight will slide forward in bore 66 causing the rear edge angular groove 84 to strike the cam 82, thereby driving the point of the auxiliary firing pin 76 into an auxiliary stab detonator. The auxiliary detonator (not shown) is brought into alignment with auxiliary firing pin 76 when the rotor is in its armed position and provides explosive communication with the electric detonator 46.

In the event that the bomb is deflected from its normal trajectory by trees or a heavy jungle canopy to the extent that its impact angle is such as to prevent actuation of the fuze through either the'piezoelectric crystal or the inertia weight, the fuze is further provided with a pyrotechnic delay column positioned within a base plate 88 secured to the base of the mounting block 30 by screws 89 or other suitable fasteners. The forward surface of the base plate 88 has a continuous generally spiral groove 92 formed therein for the purpose of receiving a plurality of turns of a continuous length delay cord 94. The delay cord consists of a thin column of deflagrating pyrotechnic material encased in a flexible protective metal jacket or sheath. Although various suitable delay cords may be employed, one suitable delay cord, for example, includes a thin column of pyrotechnic consisting of a mixture having 38 percent by weight of tungsten, 57 percent by weight of barium chromate and 5 percent by weight of potassium perchlorate encased in a lead alloy sheath. These delay cords have a known burning rate and therefore any desired time delay may be achieved by selecting the length of delay cord necessary to produce the desired time delay.

The burning of the delay cord is initiated by the withdrawal of a pull pin 96 from an initiator housing 98 by tension being applied to a lanyard 102 which is secured at one end to a tab 104 connected to the pull pin and which is secured at its other end to the tab 18 on the fuze housing cover 14. Upon deployment of the ordnance device, tension applied to lanyard 102 will remove the fuze housing cover 14 to extend the probe and also simultaneously withdraw the pull pin 96 from the initiator housing to initiate the delay column.

The initiation of the delay column by withdrawal of the pull pin 96 will be more clearly understood by reference to FIG. 2 wherein the initiator housing is shown as having an elongate bore 106 formed therein and having the pull pin 96 received in a transverse bore 108. The pull pin is provided with a conically tapered peripheral groove 110. A striker pin 112 received within bore 106 is seated against groove 110 of the pull pin and is resiliently biased against the pin by a compression spring 114 surrounding the pin shaft. On the other side of the pull pin and received within the bore 106 is an end coupling 116 positioned in axial alignment with the striker pin. The hollow end coupling housing has positioned at one end thereof adjacent the pull pin a percussion primer 118 and has threadedly secured in the opposite end thereof an adapter 122 in which a body of igniter mix 124 is received in a complementary shaped recess. The igniter mix is in explosive coupling position with respect to the input end of the delay cord 94 received coaxially within adapter 122.

As will be seen therefore, a tension force applied to lanyard 102 will withdraw the pull pin 96 from the igniter housing 98 and as the pin is withdrawn, the conically tapered groove 110 of the pull pin acts as a cam against the tapered point of the striker pin 112 to deplace the striker pin against the force of the compression spring 114, and when the pull pin has been fully withdrawn, the compression spring 114 drives the striker pin into the percussion primer 118. Initiation of the primer causes the igniter mix 124 to burn and this burning is transmitted to the pyrotechnic column within the delay cord 94. The burning or deflagration of the delay cord progresses at a known rate throughout the continuous length of the spiral cord until it reaches a terminal block 126. Referring back to FIG. 1, terminal block 126 is received within a complementary recess formed in the base plate 88 and provides a housing for an explosive charge 128 and a piston 130. Although various suitable materials may be used as the explosive charge 128, a typical explosive would be barium styphenate. Piston 130 is coaxially aligned with the inertia weight 64 so that when explosive charge 128 is initiated, piston 130 is driven against inertia weight 64 thereby causing the inertia weight to slide forwardly within its bore 66 against the force of spring 86 and this sliding movement of the inertia weight causes the rearward surface of the annular groove 84 to engage cam 82 and drive the auxiliary firing pin 76 into the auxiliary detonator contained within the arming rotor 40.

In operation, when the bomb or other fuzed aerial ordnance device is deployed, a tether line 132 attached to lanyard 102 effects the simultaneous withdrawal of striker pin 96 from the initiator housing 98 and the removal of the cover 14 from the fuze housing 10. When the cover 14 is removed, the probe 24 is permitted to extend, thereby causing withdrawal of arming pin 56 from its locking engagement with rotor 40 to permit the rotor to be driven by spring 52 to its armed position, which also withdraws tang 72 from its locking engagement with the inertia weight 64. Since pull pin 96 was withdrawn simultaneously with the removal of the probe cover, the pyrotechnic delay column was initiated by the action of striker pin 112 and the pyrotechnic delay column commenced to burn at a constant rate. The length of the delay column is sufficient to permit descent of the bomb to its target zone and to permit activation of the bomb by the piezoelectric crystal assembly or through the auxiliary firing pin operated by inertia weight 64. In the event, however, that the bomb is deflected from its normal trajectory so that its impact angle is such as to prevent initiation either through the piezoelectric crystal or the inertia weight, the explosive charge 128 will be detonated upon completion of the predetermined time delay required for the burning front to progress through the entire length of column 94 and, upon detonation of explosive charge 128, piston is driven against inertia weight 64 to displace inertia weight 64 into its operative engagement with the auxiliary firing pin 76 to thereby assure detonation of the bomb.

From the foregoing, it will be appreciated that the present invention provides a new and improved fuzing arrangement which will provide stand-off detonation by proper activation of the probe mounted impact sensor or alternatively by the inertia weight under normal operating conditions and, even in the event that the device encounters abnormal conditions, the incorporation of the self-destruct pyrotechnic delay mechanism positively assures proper detonation of the device after a predetermined time sufficient to allow normal fuzing operations. it will be further appreciated that the selfdestruct pyrotechnic delay column of this invention is designed such as to initiate the fuze in a manner identi cal to that which occurs during its normal functions, that is, the terminal block 126 of the delay charge drives the inertia weight against the auxiliary firing pin. Moreover, the column of deflagrating pyrotechnic encased in a protective metal sheath enables the fabrication of columns having small diameter to length ratios which exhibit extremely reliable uniformity in grain distribution. This construction enables the achievement of long delay periods without the generation of large heat concentrations, which are a typically encountered problem in conventional delay designs. Moreover, the pyrotechnic delay column of this invention is susceptible to incorporation in various fuze designs because of its extreme flexibility in obtaining variable delays. Also, rather than being contained within a spiral groove formed in a base plate, these compliant delay columns could be conveniently wrapped around any available spindle contained within the internal fuze housing where space is available.

Obviously, numerous variations and modifications of the present invention are possible in light of the above teachings. lt is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a fuze for an aerial ordnance device, a fuze actuating means comprising:

a fuze housing,

a forwardly extendable probe resiliently' biased toward an extended position forward of the housing,

a probe restraining means detachably secured to said housing for normally restraining said probe within said housing,

an impact responsive detonator mounted on the forward portion of said probe for detonating the ordnance device upon impact with a target,

an auxiliary firing pin operably positioned within said housing,

an inertia weight mounted within said housing for slidable movement from a first position to a second position, said inertia weight being operably associated with said auxiliary firing pin,

resilient biasing means for resiliently maintaining said inertia weight in said first position, and

pyrotechnic delay means initiable upon extension of said probe from said housing and operably associated with said inertia weight to drive said weight from said first position to said second position after a predetermined time delay.

2. The apparatus of claim 1 wherein said pyrotechnic delay means includes:

a thin column of pyrotechnic material encased in a flexible metal sheath,

an igniter operatively coupled to a first end of said column, and

an output housing containing an explosive charge operatively coupled to a second end of said column.

3. The apparatus of claim 2 wherein said pyrotechnic delay means further includes:

a piston contained within said output housing and positioned coaxially with said inertia weight.

4. The apparatus of claim 2 wherein said igniter ineludes:

an igniter housing,

an igniter material positioned within a first end of said housing adjacent said first end of said column,

a percussion primer positioned within the other end of said igniter housing, and

a percussion striker operatively associated with said percussion primer and adapted to be driven into said percussion primer during extension of said probe.

5. The apparatus of claim 4 wherein said percussion striker includes:

means for resiliently biasing said striker into operative engagement with said percussion primer, and

interruptor means positioned between said striker and said percussion primer for normally blocking movement of said striker into said percussion primer.

6. The apparatus of claim 5 further including:

a lanyard connectable to both said interruptor means and to said probe restraining means,

whereby an actuating force applied to said lanyard affects extension of said probe my removal of said probe restraining means and causes initiation of said pyrotechnic delay by removal of said interruptor means permitting said striker to impact said ercussion primer. 7. he apparatus of claim 6 wherein said interruptor means includes:

a pull pin having a conically tapered peripheral groove for cam engagement with said striker, whereby removal of said pull pin displaces said striker against said resilient biasing means as said interruptor is withdrawn from its blocking position within said igniter housing. 8. The apparatus of claim 7 wherein said pyrotechnic delay means further includes:

Claims

1. In a fuze for an aerial ordnance device, a fuze actuating means comprising: a fuze housing, a forwardly extendable probe resiliently biased toward an extended position forward of the housing, a probe restraining means detachably secured to said housing for normally restraining said probe within said housing, an impact responsive detonator mounted on the forward portion of said probe for detonating the ordnance device upon impact with a target, an auxiliary firing pin operably positioned within said housing, an inertia weight mounted within said housing for slidable movement from a first position to a second position, said inertia weight being operably associated with said auxiliary firing pin, resilient biasing means for resiliently maintaining said inertia weight in said first position, and pyrotechnic delay means initiable upon extension of said probe from said housing and operably associated with said inertia weight to drive said weight from said first position to said second position after a predetermined time delay.

2. The apparatus of claim 1 wherein said pyrotechnic delay means includes: a thin column of pyrotechnic material encased in a flexible metal sheath, an igniter operatively coupled to a first end of said column, and an output housing containing an explosive charge operatively coupled to a second end of said column.

3. The apparatus of claim 2 wherein said pyrotechnic delay means further includes: a piston contained within said output housing and positioned coaxially with said inertia weight.

4. The apparatus of claim 2 wherein said igniter includes: an igniter housing, an igniter material positioned within a first end of said housing adjacent said first end of said column, a percussion primer positioned within the other end of said igniter housing, and a percussion striker operatively associated with said percussion primer and adapted to be driven into said percussion primer during extension of said probe.

5. The apparatus of claim 4 wherein said percussion striker includes: means for resiliently biasing said striker into operative engagement with said percussion primer, and interruptor means positioned between said striker and said percUssion primer for normally blocking movement of said striker into said percussion primer.

6. The apparatus of claim 5 further including: a lanyard connectable to both said interruptor means and to said probe restraining means, whereby an actuating force applied to said lanyard affects extension of said probe my removal of said probe restraining means and causes initiation of said pyrotechnic delay by removal of said interruptor means permitting said striker to impact said percussion primer.

7. The apparatus of claim 6 wherein said interruptor means includes: a pull pin having a conically tapered peripheral groove for cam engagement with said striker, whereby removal of said pull pin displaces said striker against said resilient biasing means as said interruptor is withdrawn from its blocking position within said igniter housing.

8. The apparatus of claim 7 wherein said pyrotechnic delay means further includes: a piston contained within said output housing and positioned coaxially with said inertia weight.