US2777392A

US2777392A - Striker mechanism for a fuse

Info

Publication number: US2777392A
Application number: US327735A
Authority: US
Inventors: Laakso Aaro Kalevi
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-12-24
Filing date: 1952-12-24
Publication date: 1957-01-15
Anticipated expiration: 1974-01-15

Description

1957 K. LAAKSO 2,777,392

STRIKER MECHANISM FOR A FUSE Filed Dec. 24, 1952 HWGWHM. AA/{O KABLYEV/ LAAKSO yak/12.90 4,

ATTORNEX This invention relates to a striker mechanism of such Un e States at fi v r 2,777,392 Patented Jan. .15.,v 1.95?

air current behind the firing pin member is very much smaller than that of the air current at the nose thereof and consequently the pressure behind the firing pin membe: will increaseli The pressure difierence thus produced acts as" a springpushing the firing pi'n into forward position immediately when an air current is generated at the nose of the firing pin member.

According to a preferred embodiment of the invention the area of the central. hole (or the, sum total of the area of; the holes is, smaller than the cross sectional area of the firing pin member'in' the plane perpendicular to the sensitivity that it will operate upon encountering the slightest resistanc 6. g., after impact with snow. As is well known, snow provides; good protection against flying metal fragments. Even fragments of great projectiles are incapable of-penetrating more than some few meters only into snow. Consequently a projectile exploding in snow produces fragments all of which will be practically smothered in; the snow at aradius' of a few meters from the point of explosion. "For this reasonprojectiles have been designed to explodequ-ite on the surface of snow. For great falling speeds it is easy to design fuses which operate after impacting the snow surface. ever falling speed drops the provision of an effective fuse becomes more and more difficult None of'the heretofore striker mechanisms operate positively" and with sutficient sensitivity at all the falling speeds coming into question. The resistance of light weight frigid snow is so small that at low falling speeds even theweakest of effective safety elements is incapable of overcoming the resistance and the firing pin remains in inoperative posi, tion. Hence, insofar as aspring or a pin isused the safety element as" is the case in known strikermechanisms, it is quite impossible to produce a fuse which will operate with sufiicient sensitivity-iinthe top layers ofsnowi This invention'has for its object the} provision of novel means in the striker mechanism of a projectile including a firing pin: mounted to move longitudinally ofthe fuse and adapted,'upor 1 impact, to makecontact againsta primer. In stfikenmechanifsmof theikind described it has been customary to use, as has been mentioned; a pin or a spring as a safety element during flight, the impact energy requiring for shearing off or overcoming the pin or spring, respectively, being so great that the firing pin will not function, e. g;, after impact with the surface of But 'whenfiring pin,

I A preferred embodiment. of the invention is shownrin Figs. land 2 oftheaccompanying drawing. 'Fig; 1 illustrates a striker mechanism when the projectile is ready to be fired ,and Fig. 2 illustrates the same during the flight of the projectile.

Fig." 3' shows agmodified form of striker head. Allthe figures are longitudinal sectional views of the striker mechanism. In. Figs. 1 and 2 the reference numeral 11 denotes a detonator shell to which is fixed a primer 6 and a booster charge 14. The shell 11 is in prior known manner supported by ball heads 7 so it cannot move forward and so the .fi'ringpin {cannot make-impact against the primer 6 Moreover, the booster charge 14 is housed within a casing 15 provided for the purpose ofpreventing explosion from spreading into the, projectile should the booster charge function during transportation or the firing or dropping phase.

On firing the projectile a sleeve 9 encircling the shell 11' slides backwards while a spring 10 arranged within the space between the "body part Sand the shell" 11 contacts. Then, the ball heads 7 seated in the annular recess between the fore end of the; sleeve 9, the body part 5 and the detonator shell 11 will be released and will, due

to the bevelled surfaces on the detonator shell 11 and in case of rotating projectiles also centrifugal force, fiy outwardly into the recess between the exterior part-of the sleeve 9 and the body" partfll. ,As long as: the pro jectile has linear acceleration the detonatorshell ;sta-ys positively in. the rear andithe boostercharge-within: the casing 15. Upon cessation of linear acceleration the spring 10 moves the sl'eeve49 back into forward position the means used in the striker mechanism for ensuring safety during the flight of the projectile is dependent upon air current created during flight and consequent pressure differences produced withinthe striker mechanism. Because the air current directedagainst the striker mechanism stops immediately when the. same strikes the surface of snow, also fli'ghtsafety provided by the currentstops without use of impact energy, for releasin-gthe same. l l

The basic idea of the invention lies in the provision of a sheet-like member rigidly secured to the firing pin or striker and adapted to freely move with clearance, and together with the firing pin within a cavity in the fore part of the body and in the provision of a central hole or group of holes in the striker head opposite the firing pin member in question. The clearance between the interior surface of the cavity and the periphery of the firing pin member permits entry of air behind the firing pin member and during the flight of the projectile to form there an air cushion which holds the firing pin member and firing pin in their forward positions. The velocity suresinks due. to; the. rapid flow of air.

preventing; the ball. heads 7 fromregaining their previous positions; The; detonator shell. 11 which now is; quite free-movesvforward due; toair pressure on theprojectile. Already prior to this and in consequence of the flow of air the firing pin has moved forward. According to. the invention, to the firing, pin-A. is secured asheet-like; member 3' adapted; to move. freely together with, the firingpin within a cavity 17 in the head part 2 of the fuse. A borehole-.16 in. theendmember closing the fore end ofv the body: Part 5 is. adapted to guide the firing-pin. A clearance is. arrangedbetween the outer periphery of the member 3.- and the inner surface of the cavity 17. The striker-headis provided with a central hole 18. As" the projectile flies throughwthe air a strong flow of air is, produced throughand past the central holelS. Airflows into. the: cavity 17, and outthrough the fiow slots 1. Then an air; cushion. is. produced behind. the member 3 of the firing; pinwhile at the nose of the member 3 the. pres. In consequence of; thispressure difference the; firing pin 4 immediatelymoves forward when the lifting force directed at the firing pin member and due to the said pressure difierence overcomes the counter force due to linear acceleration.

Fig. 2 shows the positions of the various parts of the striker mechanism during the flight of the projectile. As soon as the projectile comes into contact with any object capable of closing the hole 18 in the fore end of the head part 2 the pressure will equalize itself on either side of the firing pin member 3. Then, no impact-resisting-force is directed at the firing pin 4 wherefore even a very slight impact is capable of giving it the speed requisite for igniting the primer 6. When the primer 6 is ignited the flare strikes through the-channel 12 in the detonator. shell 11 igniting the booster charge 14 which explodes the detonator 13 causing the projectile to explode. Y The sensitivity of the firing pin depends solely upon the constructional details of the head parts thereof and it is to be appreciated that the head structure may be applied to a plurality of striker mechanisms in use at the present time.

The locking of the detonator shell 11 by means of the sleeve 9 and the ball heads 7 is prior known as such and has been describedby way of example only and is not the object of the present invention.

Depending on the degree of sensitivity and flight safety efiiciency desired some modifications can even be made in the structure of the head. By changing the size and position of the flow slots 1 as also the shape of the

parts

2 and 3 the pressure difference produced on either side of the firing pin member 3 can be varied within certain limits as also the therefrom resulting lifting force directed at the firing pin member. By making the firing pin member 3 appreciably greater than the hole 18 the aforementioned lifting force can be made so great it is capable of tensioning the (not shown) spring arranged between the firing pin member and the striker head hole and adapted to make impact against the primer of the striker mechanism immediately when the hole 18 in front of the head part 2 is closed in which case the striker mechanism operates without impact proper. In this way is obtained a highly sensitive striker mechanism. The use of a spring is generally unnecessary in practice because even without such an arrangement the firing pin is sufliciently sensitive to operate, e. g. in all snow conditions with even the'lowest speeds coming into question.

The resistance of air can be computed from the follow ing equation:

wherein I C=constant (in practise 0.005)

s=air density kg./m. 1.29

V=maximum speed of projectile m./sec. within the range of use of striker mechanism F=surface area of the striker head hole in cm.

On employing outflow slots attention is here drawn to the positioning of the same. Even the use of one slot, hence asymmetrical in respect of the longitudinal axis of the fuse, is possible but in this case the movement of the firing pin must be guided by means of the hereinabove mentioned longitudinal bore hole 16. If the outfiow slots are, on the other hand, positioned symmetrically practise has shown that guidance of the firing pin is unnecessary above that given by the bore hole for the firing pin made in the fore end of the body part even in the case the material thickness is not as great as that of the construction shown in the drawing.

Fig. 3 shows a slightly modified structure. In this modification the firing pin member 3 is secured to a point at a spaced distance from the fore end of the firing pin so that the same when the member 3 is in the forward position protrudes from the central hole 21 in the head part 2. In this case the firing pin is advantageously so long that the same is always guided by the longitudinal bore hole 16 and the hole 21 independently of the position of the firing pin 4. In this structure the air flow inlet holes 22 are positioned symmetrically about the central hole 21. The outflow slots 20 are symmetrically positioned also.

Although all the structures hereinabove described show that the surface of the firing pin member is greater or substantially as great as the area of the striker head hole, practise has shown that this fact is not an absolute prerequisite for the satisfactory function of the mechanism. So e. g., a firing pin member of an order smaller than that of the striker head hole can be employed.

What I claim is: i

1. A fuse of the sensitive type comprising a fixed head part, a firing pin movably mounted in said head part and adapted to make impact against a primer, a sheet-like member rigidly secured to said firing pin and adapted freely to move with clearance together with said firing pin within said head part of the fuse body and at least one central aperture and one transverse aperture in said head, said apertures providing for the flow of air therebetween forwardly of said sheet-like member and co-operating with said clearance to produce an air cushion behind said firing pin member for maintaining the firing pin in a forward position during flight of the projectile.

2. A fuse as in claim 1, wherein the area of said central aperture is smaller than the cross sectional area of said sheet-like member in a plane perpendicular to said firing pin.

3. A fuse as in claim- 1, wherein saidsheet-like memher is perforated.

4. A fuse comprising a body, a longitudinally displaceable detonator within said body, a head part on said body having a central aperture in the nose thereof and at least one transverse aperture for the flow of air therebetween, a firing pin slidably movable within said head part, and an imperforate sheet-like member surrounding said firing pin and carried thereby, said member being spaced from the walls of said head part and movable with said pin from a rearward position to a point spaced rearwardly from said transverse aperture.

5. In a fuse, a body part, a tubular head part secured to said body part, a firing pin slidably movable into and out of said body part, said head part including a central aperture in the nose thereof and at least one transverse aperture in the wall adjacent said nose for the fiow of air therebetween and a relatively thin sheet-like member secured to said firing pin with the periphery spaced from the inner wall surface of said head and having an area greater than said central aperture, whereby the flow of air through said apertures during the flight of said fuse creates a reduced pressure in front of said sheet-like member causing it to move'forwardly within said head, said sheet-like member and pin being movable rearwardly upon impact to detonate said fuse.

References Cited in the file of this patent UNITED STATES PATENTS