Fuze Arming Device

Abstract

1. In a fuze for a bomb adapted to be dropped from an aircraft and armed in ree fall flight, A casing, An arming rotor rotatably mounted in saId casing for movement from an initial safe position to an armed position in incremental distances, A time delay mechanism connected to the rotor for preventing movement of the rotor for a predetermined time interval, Said time delay mechanism including a stored energy spring means for moving the rotor through a first incremental distance prior to said time interval and for moving the rotor through a second incremental distance at the expiration of said time interval, A rotor locking means connected to said rotor for releasing said rotor for movement through said first incremental distance by said stored energy means when the bomb is subjected to a predetermined minimum air velocity and for starting said time delay mechanism, and An environmentally powered driving means mounted upon said casing and positioned for driving engagement with the rotor when the rotor has been moved through said second incremental distance for driving the rotor to said armed position, Whereby said bomb is armed after the expiration of a predetermined time interval subsequent to release of the bomb by the aircraft at normal launching air speeds.

Description

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a fuze arming device for a free falling bomb and more particularly to a safety and arming system for a tail fuze in a shaped charge bomb such as the type employed with a cluster missile.

Previously known fuzes for bombs of this type have not been entirely satisfactory due to the lack of sufficient safety features to prevent arming of the bomb until a predetermined period of time after the bomb has been launched by the aircraft. The conventional practice is to employ a misaligned explosive train in the bomb fuze and to drive the explosive train into its armed position by means of a direct connection to an air driven impeller. The arming time required to align the fuze train is a function of the distance traversed by the bomb after being released by the aircraft. It therefore becomes apparent that when such bombs are launched by very high speed aircraft, the entire arming operation occurs while the bomb is still in the substantially horizontal portion of its trajectory and in close proximity to the aircraft. The present invention overcomes this problem by providing the fuze arming device with a built-in timing system to prevent arming of the fuze prior to the expiration of a predetermined constant time interval subsequent to launching by the aircraft, thus permitting the aircraft to reach a safe distance from the weapon before the weapon is armed. To insure the safety of the deck crew or ground crew, it is necessary to provide an air launched weapon of this type with a means to discriminate between the launch velocities and the on-deck velocities and take-off or landing velocities. While previously known safety and arming devices have attempted to provide such discriminating means by using centrifugal clutches, it has been found that such clutches do not have a sufficient degree of reliability to provide the safety required. The present invention provides an air speed discriminating means which is of simpler construction than previously known means and is more reliable in its operation.

The present invention provides a safety and arming device for a tail fuze of a free falling bomb adapted to be dropped from an aircraft in flight and to be exploded upon impact with a target or in response to extreme deceleration of the bomb. The safety and arming device has an explosive train, a portion of which is misaligned with the remainder of the train when the fuze is in an unarmed position. The misaligned portion of the explosive train is releasably locked in its unarmed position by means of an air speed discriminating means and releasably restrained in that position by a timing device. The air speed discriminating means comprises a centrifugal weight assembly rotatably driven by an impeller so that the rotor locking means is released upon the attainment of a predetermined rpm of the impeller at which time the timing mechanism is actuated. At the expiration of a predetermined time interval, the timing mechanism releases the rotor restraining means to permit the misaligned portion of the explosive train to be reorientated into alignment with the remainder of the explosive train while closing an electrical firing circuit for the electrical responsive explosive in said misaligned portion. Upon impact with the target, a voltage generator secured to the nose of the bomb detonates the electro-responsive explosive which detonates the main charge of the bomb. In the event of a malfunction of the electrical firing circuit or the impact of the bomb with a soft substance such that the voltage generator fails to generate a voltage of sufficient magnitude to ignite the electro-responsive explosive, the device is provided with a mechanical firing system comprising an inertial weight resiliently held in a position to strike a stab detonator upon deceleration of the bomb. The mechanical firing of the fuze is considerably slower in operation than the electrical firing system to thereby assure detonation of the bomb by the electrical firing system before the mechanical firing cycle has been completed under normal circumstances.

An object of the present invention is to provide a fuze for an aerial bomb having a normally locked arming means for maintaining the fuze in an initial safe position and being adapted to be released and arm the fuze during the free flight of the bomb toward the target.

Another object of the present invention is to provide a fuze arming device for a bomb adapted to be dropped by an aircraft which will prevent arming of the bomb until the bomb has been exposed to air velocity in excess of the landing and take-off velocity of the aircraft.

Another object is to provide a safety and arming device for an air dropped bomb which will prevent arming of the bomb until the expiration of a predetermined time interval after release of the bomb by the aircraft.

Still another object is to provide a safety and arming mechanism for an air dropped bomb which will prevent arming of the bomb until the expiration of a predetermined time interval subsequent to movement of the bomb towards the target at its normal launching speed and which will detonate the bomb electrically upon impact with the target or mechanically in the event the electrical firing system should fail to function.

Other objects and many of the attendant advantages of this invention will be readily appreciated 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 an elevational view partially in section of a shaped charge bomb according to a preferred embodiment of the present invention;

FIG. 2 is a sectional view showing the fuze in an unarmed position;

FIG. 3 is a sectional view of the fuze taken along lines 3--3 of FIG. 2;

FIG. 4 is a sectional view taken on lines 4--4 of FIG. 3 showing the centrifugal weight assembly;

FIG. 5 is an elevational view partially in section of the escapement mechanism; and

FIG. 6 is a plan view of the rotor.

Referring now to the drawings wherein like characters designate like parts throughout the several views and more particularly to FIG. 1 thereof, the shaped charge bomb is indicated generally at 10. The bomb has a main body casing 11 within which is positioned a shaped explosive charge 12. The forward portion of the casing is formed into an elongated hollow stand-off tube 13 within which is positioned an impact responsive voltage generator 14. The voltage generator may be any one of a plurality of conventional piezoelectric crystals arranged to generate a voltage when subjected to mechanical shock when the bomb strikes the target. The bomb is further provided with a tail fuze assembly 15 arranged for detonating a booster charge 16 within the base of the shaped charge 12. The fuze is operated by an impeller 17 rotatably mounted upon the fuze assembly and the bomb is provided with tail fins 18 to enhance the stability of the bomb in flight.

The details of the fuze assembly may be more clearly seen by reference to FIGS 2 and 3. The body of the fuze assembly has a cylindrical recess 19 formed therein to receive a cylindrical arming rotor 21 which is shown in its unarmed position. The arming rotor has a transverse bore 22 formed therein to receive an electroresponsive detonator 23 at one end thereof and an electrical contact assembly 24 which will be described later. The arming rotor is supported upon trunnions for rotative movement from its unarmed position, shown in FIG. 2, to an armed position wherein the electroresponsive detonator 23 will be aligned with the booster charge 16 and in close proximity thereto for detonation of the booster charge and the main charge 12 when the electroresponsive detonator is initiated by an electrical impulse received from the voltage generator 14 upon impact with the target. The electrical contact assembly 24 has a pair of contacts therein which are adapted to shunt the bridge wire of the electroresponsive explosive when the rotor is in its unarmed position. The ball 25 is resiliently biased outwardly for contact with a cam wall portion 26 of the fuze body. The cam wall 26 is a curved wall of decreasing radius from the point of contact with the ball 25 as shown in the FIG. 2 to a point adjacent a contact plate 27 mounted across an opening in the rear wall of the fuze body. The contact plate 27 is mounted upon the fuze body by any suitable means and is provided with a central aperture formed therein to receive a rotor locking pin or detent 29 which extends into a recess 31 formed in the rotor to prevent rotation of the rotor prior to the release of the pin 29 in response to certain conditions, hereinafter described.

As seen in FIG. 3, the fuze assembly is surrounded by a shell 32 to enclose and protect the assembly, the fuze shell having an inwardly directed annular flange 33 formed on one end thereof to engage an outwardly directed annular flange formed on one end of an annular bearing support 34 within which is rotatably mounted an annular hub 35 to which the impeller 17 is fixedly secured. The hub 35 is rotatably supported by a plurality of plastic ball bearings 36 positioned between an outer bearing race 37 defined by a inwardly directed beveled flange formed on the bearing support 34 and an inner race 38 defined by an outwardly beveled annular flange formed on the hub 35. A hub extension 39 is mounted upon the hub for rotation therewith and has an axial bore formed therethrough to receive the shaft of the rotor locking pin 29 and has a counter bore formed therein to receive an enlarged piston head 41 which is integrally formed with the rotor locking pin. A helical compression spring 40 is seated upon the annular shoulder formed by the counter bore in the hub extension and engages the piston head on the rotor locking pin to resiliently bias the piston in a direction away from the rotor to withdraw the rotor locking pin from the recess formed in the rotor. The rotor locking pin and helical compression spring are releasably held in their positions shown in FIG. 3 by means of a centrifugal weight assembly comprised of a pair of centrifugally actuated weights 42, more clearly shown in FIG. 4. Each of the centrifugal weights is rotatably mounted on a support pin 43, the support pins being located equidistantly from the axis of the hub 35 and each of the centrifugal weights being mounted off center with respect to said support pins. Each of the centrifugal weights is provided with a resilient flat spring 44 to resiliently bias the centrifugal weights 42 toward one another into mutual contact, as shown in FIG. 4, to obstruct the axial bore formed in the hub 35. When the bomb is subjected to an air stream of predetermined velocity and the impeller 17 reaches sufficient rpms, the angular moments of force developed by the centrifugal weights overcome the resilient bias force of the springs 44 and the weights are permitted to pivot outwardly in opposite directions to create a void therebetween and thus release the rotor locking pin for movement by the helical compression spring. When the centrifugal weights are separated, the helical compression spring 40 forces the rotor locking pin 29 into the axial bore formed in the hub 35 and thereby withdraws the pin 29 from the rotor locking recess 31 to free the rotor for control by a time based escapement mechanism driven by a stored energy torsion spring 45.

The gear train employed in the escapement mechanism is more clearly illustrated in FIG. 5 while the connection of the arming rotor 21 to the escapement mechanism requires reference to both FIGS. 3 and 5. The prewound torsion spring 45 drives a runaway clutter gear train formed by gears 46, 47, 48 and 49, the rate of rotation thereof being controlled by an oscillating balance bar 51. The final gear 49 of the gear train has a cylindrical drum 52 connected thereto having a contoured groove 53 formed therein to receive a pin 54 which, as seen in FIG. 3, depends downwardly from the arming rotor 21 through an arcuate slot 55 formed in one of a pair of parallel plates 56 between which the escapement gear train is mounted. The contoured groove 53 is formed arcuately about the axis of the drum 52 at a substantially uniform radius of curvature except for the extreme ends of the groove. The stored energy torsion spring 45 transmits its force through the gear train 46 through 49 and drum 52 to the pin 54 to tend to rotate the rotor and pin 54 but the rotor locking pin 29 prevents movement of the rotor and operation of the timing mechanism. When the rotor locking pin 29 is released by the centrifugal weights, the stored energy torsion spring 45 causes the pin 54 to be moved out of the detent portion 61 of the groove 53 and into that portion of the groove 53 having a constant arcuate radius, thus starting the timing cycle. The torsion spring continues to drive the gear train at a constant rate to rotate the drum 52 and arcuate groove 53 relative to pin 54 which is restrained by groove 53 from movement through the arcuate slot 55 in plate 56. When, however, the drum 52 has rotated a sufficient amount that an outwardly directed groove portion 57 comes into contact with the pin 54, the outwardly directed portion of the groove frees the pin 54 from restraint by the groove 53 and thereby causes the pin 54 to be moved radially outwardly from the axis of the drum 52 to a point adjacent the periphery of the drum and imparts an additional amount of rotative movement to the arming rotor. A flat sector 58 mounted upon the rotor and extending radially outwardly beyond the periphery of the rotor is brought into engagement with a friction wheel 59 when the rotor is rotated by the grooved drum 52. The friction wheel is mounted upon the hub extension for rotation with the impeller and the sector 58 may be provided by a knurled or rough surface for engagement with the rotating friction wheel to assure a positive drive connection therebetween. The friction wheel is rotatably driven by the air-driven impeller to rotate the arming rotor 21 to its armed position. Having been driven forward to its armed position, the electroresponsive explosive detonator 23 positioned within the arming rotor 21 is in alignment with the booster charge 16 and the spring loaded ball 25 forming a portion of the electrical switch circuit has been moved into electrical contact with the contact plate 27 and has seated itself in the aperture formed in said contact plate. During the movement of the rotor 21 from the position shown in FIG. 2 to its fully armed position, the spring loaded ball 25 had been forced into the switch assembly 24 by means of its sliding contact with the cam surface 26 thus removing the shunt scross the bridge wire of the electroresponsive explosive 23 and completing the firing circuit. When the rotor has been driven to its fully armed position, a ratchet 62 is caused to move into registry with a pawl, not shown, to lock the rotor in its fully armed position.

In the event that the electrical firing system should fail to function, the device of this invention is provided with a secondary mechanical firing means responsive to the decleration of the bomb upon impact with a target. The secondary mechanical firing system comprises a stab detonator 63 positioned in an aperture formed in the fuze housing for communication with the main charge of the bomb via port 67 in the casing and port 68 in the rotor and the electroresponsive explosive 23. An inertial weight plunger 64 is positioned within a bore for sliding movement along an axis parallel to the axis of the bomb for impact with the stab detonator 63 upon impact with a target. A helical compression spring 65 is positioned within the bore between the stab detonator and the plunger to resiliently bias the plunger in a direction away from the stab detonator. The plunger is provided with a reduced diameter portion 66 to define an annular shoulder for engagement with the ratchet 62 on the arming rotor, the ratchet serving the additional function of a stop means to prevent movement of the inertial weight plunger 64 while the rotor is in its unarmed position as shown in FIG. 3. When the rotor has been moved to its fully armed position, the ratchet 62 moves out of engagement with the plunger 64 and thus frees the plunger for movement into contact with the stab detonator upon deceleration of the bomb, thus enabling the mechanical firing system to detonate the main charge in the event that the electrical firing system should malfunction.

In operation, a plurality of shaped charge bombs are released from a cluster bomb which is released by an aircraft over the target. Upon exposure to the air stream, the impeller 17 begins to rotate by its reaction with the air stream. Until the impeller reaches a predetermined rpm, the centrifugal weights 42 obstruct the axial bore in the hub 35 and therefore retain the rotor locking pin 29 in the position shown in FIG. 3 where the pin engages the rotor locking recess 31 to prevent rotation of the rotor. In its unarmed position, the normally open electrical contacts in the switch assembly 24 are held upon to interrupt the firing circuit. The firing circuit is further interrupted by virtue of the fact that the spring loaded ball 25 is not in contact with the electrical contact plate 27. With the rotor in the unarmed position, the electrically responsive detonator 23 is not aligned with the booster charge 16 and therefore could not detonate the charge even if the electroresponsive detonator were inadvertently actuated. In addition to preventing firing of the primary detonating system, the secondary mechanical firing system is prevented from actuation when the rotor is in its unarmed position by virtue of the stop means provided by the ratchet 62 which engages the reduced diameter portion of the inertial plunger 64 to lock the plunger from movement into contact with the stab detonator. When the impeller 17 reaches a predetermined rpm, the centrifugal weights 42 spread apart radially to permit the compression spring 40 to drive the rotor locking pin 29 into the axial bore formed in the hub 35, thus withdrawing the rotor locking pin from the rotor locking recess. The construction of the centrifugal weights and their resilient springs may be so designed that actuation of the centrifugal weight assembly will not occur until the impeller has been exposed to an airstream having a velocity in excess of the landing and takeoff velocities of the launching aircraft. It is therefore apparent that the rotor locking pin cannot be accidentally withdrawn from the rotor locking recess if the impeller is exposed to only those wind velocities normally encountered on the deck of an aircraft carrier. It will also be appreciated that it would not be possible for the rotor to be manipulated by hand at a speed sufficient to actuate the centrifugal weight assembly. Prior to the release of the rotor locking pin 29, the pin 54 formed on the rotor is positioned within the detent portion 61 of the groove formed in the drum 52, thus locking the drum and preventing operation of the escapement assembly by the stored energy torsion spring. However, when the rotor locking pin is released, the stored energy torsion spring 45 causes the rotor to move an incremental amount thus causing the rotor pin 54 to move out of the detent portion 61 of the groove 53 in the escapement drum and permitting the torsion spring 45 to operate the escapement assembly. As the escapement assembly is driven by the torsion spring, the arcuate groove 53 in the drum prevents further rotation of the arming rotor 51 by virtue of its engagement with the rotor pin 54 until a predetermined time interval has elapsed to permit the bomb to reach a safe distance from the launching aircraft before arming, at which time the outwardly curved portion 57 of the groove 53 releases the rotor pin 54 and causes the rotor to be rotated a second incremental amount towards its fully armed position. The second incremental rotation of the rotor moves the sector 58 into driving connection with the friction driving wheel 59 which moves the rotor 21 to its fully armed position wherein the electrical firing circuit is completed and the fuze train is aligned and the secondary mechanical firing system is released for actuation upon impact with the target. It is important that the final driving force for the arming rotor to its fully armed position is derived from the rotating impeller 17 to eliminate the danger of bombs being armed in the event of a landing accident. For example, it has been found that sometimes the bombs break away from the aircraft when the aircraft lands on the carrier deck and the bomb then slides along the deck. In such cases, the rotating impeller of this invention would be torn off or deformed to prevent rotation of the hub 35 and therefore the final force required to drive the rotor to its fully armed position is eliminated and the bomb remains unarmed.

From the foregoing description it will be apparent that a new and improved fuze arming system for a shaped charge bomb has been disclosed wherein the bomb cannot be armed by the air velocities encountered on the deck of an aircraft carrier but can only be armed by air speeds in excess of the landing and takeoff speeds of the launching aircraft and that the bomb does not arm until a predetermined time interval has been expired subsequent to release of the bomb by the aircraft. The bomb senses the environmental speed to begin the arming cycle and relies upon the environmental driving force to complete the arming cycle after the expiration of a predetermined duration of time. The use of plastic bearings to support the impeller hub eliminates the problem of bearing wear and breakdown known as fretting which occurs to steel bearings subjected to aircraft vibrations. The design of the present invention eliminates the need for an arming wire or jump pin connection to each bomb in the cluster weapon, as required in previously known systems, and therefore vastly simplifies stacking of the bombs and enhances the safety of the weapon. It is recognized that the fuze of the present invention is not to be limited solely to shaped charge applications but rather may be used in any air dropped bomb to be launched in free flight.

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

Claims

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

1. In a fuze for a bomb adapted to be dropped from an aircraft and armed in free fall flight,

a casing,

an arming rotor rotatably mounted in said casing for movement from an initial safe position to an armed position in incremental distances,

a time delay mechanism connected to the rotor for preventing movement of the rotor for a predetermined time interval,

said time delay mechanism including a stored energy spring means for moving the rotor through a first incremental distance prior to said time interval and for moving the rotor through a second incremental distance at the expiration of said time interval,

a rotor locking means connected to said rotor for releasing said rotor for movement through said first incremental distance by said stored energy means when the bomb is subjected to a predetermined minimum air velocity and for starting said time delay mechanism, and

an environmentally powered driving means mounted upon said casing and positioned for driving engagement with the rotor when the rotor has been moved through said second incremental distance for driving the rotor to said armed position,

whereby said bomb is armed after the expiration of a predetermined time interval subsequent to release of the bomb by the aircraft at normal launching air speeds.

2. The device of claim 1 wherein said rotor locking means comprises

a detent disposed in said casing for locking engagement with said rotor and being spring biased out of locking engagement with the rotor,

a centrifugal weight assembly mounted in said housing for releasably holding said detent in locking engagement with said rotor,

said centrifugal weight assembly being connected to said environmentally powered driving means for rotation thereby,

whereby the centrifugal weight assembly releases said detent and rotor when said assembly is rotated at a predetermined rpm commensurate with a predetermined air speed.

3. The device of claim 1 wherein said environmentally powered driving means comprises

an impeller mounted upon said casing for movement by the air stream around the bomb,

a friction wheel connected to said impeller for rotation therewith, and

a friction member mounted upon said rotor for driving engagement with said friction wheel.

4. The device of claim 1 wherein said time delay means comprises,

a gear train powered by a stored energy spring and controlled by an oscillatory balance bar,

a drum driven by said gear train and having an arcuate groove formed therein,

a pin mounted upon said rotor and received within said groove,

said groove having a substantially uniform radius of curvature throughout its median portion and having a closed end terminating adjacent the axis of the drum and further having an open end which opens to the periphery of the drum,

whereby rotation of the drum moves the pin and rotor through the first incremental distance and prevents further movement of the rotor until the open portion of the groove in the drum acts upon said pin to move said rotor a second incremental distance after the time delay.

5. The device of claim 2 wherein said environmentally powered driving means comprises

an impeller mounted upon said casing for movement by the air stream around the bomb,

a friction wheel connected to said impeller for rotation therewith, and

a friction member mounted upon said rotor for driving engagement with said friction wheel.

6. The device of claim 2 wherein said time delay means comprises,

a gear train powered by a stored energy spring and controlled by an oscillatory balance bar,

a drum driven by said gear train and having an arcuate groove formed therein,

a pin mounted upon said rotor and received within said groove,

said groove having a substantially uniform radius of curvature throughout its median portion and having a closed end terminating adjacent the axis of the drum and further having an open end which opens to the periphery of the drum,

whereby rotation of the drum moves the pin and rotor through the first incremental distance and prevents further movement of the rotor until the open portion of the groove in the drum acts upon said pin to move said rotor a second incremental distance after the time delay.

7. The device of claim 1 further comprising,

a fuze train disposed in said casing for detonation of a main charge in the bomb,

a portion of said fuze train being mounted in said rotor for movement from a misaligned to an aligned position with the remainder of the fuze train when the rotor moves from its safe position to its armed position.

8. The device of claim 7 wherein said fuze train portion comprises

an electroresponsive explosive detonator for firing the main charge in response to an electrical signal received from a signal generator in the nose of the bomb,

said rotor having a movable electrical contact mounted thereon to engagement with an electrical contact positioned on said casing when the rotor is in its armed position,

whereby the firing circuit of the bomb is interrupted until the rotor is in its armed position.

9. The device of claim 8 further comprising

a stab detonator mounted in said casing for detonation of the main bomb charge,

an inertial plunger mounted in said casing for sliding movement into contact with said stab detonator, and

resilient plunger bias means mounted in the casing and contacting said plunger to permit actuation of the stab detonation by said plunger only upon impact of the bomb with an object such as a target.

10. The device of claim 9 further comprising

a stop means mounted on said rotor and engaging said plunger to prevent movement of the plunger unless the rotor is in its armed position.

11. The device of claim 10 further comprising

a pawl mounted upon said casing for engagement with a ratchet on said rotor to lock the rotor in its armed position when the rotor is driven to the armed position.