Arming Fuze for Artillery Shell

This application is related to my copending and commonly owned patent application Ser. No. 638,077 filed Dec. 5, 1975.

This application relates to a fuze for an artillery projectile or the like. More particularly this invention concerns a detonator fuze for a projectile that is spun about an axis parallel to its direction of travel, as for instance a projectile fired from a rifled barrel.

A detonator fuze is known having a rotor which is aligned centrifugally when the shell is spun at high speeds. A contact or primer pin is engageable against this rotor axially by spring pressure when it has been released by a ball-type detent which is normally held shut by a spring wound about an axis parallel to the direction of displacement. When the shell is fired the rifling of the gun barrel imparts considerable spin to the shell so that the spring pulls away from the ball-type detent, allowing the pin to move into alignment with the centrifugally oriented rotor and arm the projectile. Before the projectile is spun in this manner it is bore safe, that is even accidental dropping or shaking up of the projectile cannot explode it.

This bore safety of the detonator must exist not only prior to firing the projectile, but also for a brief time after it is fired, as the projectile must not explode as soon as it leaves the muzzle of the gun or even be able to explode immediately as it leaves the muzzle. To this end a relatively long spring is wound around the ball-type detent so that a certain period of time is necessary in order for the entire length of spring to unwind and allow the pin to move into the armed position. As a result of this multiturn construction there is considerable friction force so that it is almost impossible to calculate just when the projectile will be armed after it is fired. Furthermore the balls of the detent are themselves urged centrifugally outwardly with considerable force, and frequently press on and deform the inner turns of the spring. This deformation again increases the arming time so that it is not rare in such arrangements that a projectile strikes a given target before it is armed.

It has been suggested to avoid this latter inconvenience, deformation of the inner turns of the spring, by providing a relatively hard split sleeve or the like within the spring, so that a relatively soft spring, for instance made of synthetic-resin material, may be employed. Such an arrangement increases the construction cost of the fuze and adds to its size and bulkiness. Since the fuze must be fitted within a given projectile which is intended to explode and destroy itself, it is essential that the size of the fuze be reduced to a minimum in order to maximize the amount of powder that can be accommodated in the bursting explosive.

It is an object of the present invention to provide an improved fuze for an artillery shell or the like.

Another object is the provision of such a fuze which arms the projectile a predetermined fixed time after the projectile is fired.

Yet another object is the provision of an improved fuze which is relatively compact and inexpensive to manufacture.

These objects are attained according to the present invention in a fuze of the above-described general type wherein the spiral spring means is wound in the fuze chamber around the sleeve in which the pin-locking ball or balls are radially displaceable, the spring comprising inner, outer, and intermediate spring elements or sections. The inner section lies against the sleeve and normally presses the ball against the pin and is made of a very hard material not deformable by the ball. The outer section has a surface with a high coefficient of friction so as to insure that it engages the inside wall of the spring-containing chamber and unwinds it at a predetermined rate after firing of the shell. The intermediate section is of substantially more turns than both the inner and outer sections and serves almost exclusively to establish the time delay before the projectile is armed after it is fired.

According to other features of this invention the inner and outer sections are wound about the sleeve in the direction of spin of the projectile imparted to this projectile by the rifling of the gun. The intermediate section is wound in the opposite direction. The inner and outer sections are made in accordance with this invention of spring steel and the intermediate section of softer material, such as a high-density polyethylene or a polyamide.

With the system according to the present invention the outer spring section ensures the bore safety and transport safety of the shell as it tightly holds the entire spring packet together. At the same time the inner section is not damaged by the balls holding the operating pin in place so that the unwinding of this inner section can be counted on to take a predetermined length of time. The intermediate section, however, is relatively long, at least twice as long as either of the other two sections, and of easily determined characteristics so that its unwinding can be exactly calculated to take a predetermined length of time. In this manner a relatively inexpensive construction allows a fuze to be employed which renders the shell completely safe before firing and insures that it will be armed a readily ascertainable interval after firing.

The above and other features, objects and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a section through a fuze in accordance with this invention in the unarmed position;

FIG. 2 is a view similar to FIG. 1 showing the fuze in the armed position; and

FIGS. 3 and 4 are sections taken along lines III-- III and IV-- IV of FIGS. 1 and 2, respectively.

The fuze according to the present invention as shown in FIGS. 1-4, has a housing I in which a pin 3 is displaceable along the axis A within an internal sleeve 4. A spring 2 urges the pin 3, which is formed with a circumferential groove 3a, upwardly along the axis A. The sleeve 4 is formed with three radially extending holes 6 in each of which is normally received a ball 5 engageable within the groove 3a in order to lock the pin 3 axially in position. A spring packet indicated generally at 7 holds the balls in the groove 3a normally to maintain the fuze in the unarmed position as shown in FIGS. 1 and 3.

The housing is formed with an annular generally cylindrical chamber 8 surrounding the sleeve 4 and having an inside surface 8a turned toward the sleeve 4. The spring pack 7 is received in this chamber 8 and comprises an inner section 7a resting against the balls 5, an intermediate section 7b, and an outer section 7c. The inner and outer sections 7a and 7c have a relatively short overall length so that they have much fewer turns than the intermediate section 7b. Sections 7a and 7c are both made of spring steel and the section 7c is provided on all of its outside surfaces with a synthetic-resin coating that increases its coefficient of friction with the surface 8a and with the intermediate section 7b. This surface is also roughened in order to increase its coefficient of friction. Section 7b is made of synthetic-resin material, a hard resin of the nylon or polyamide family being employed. The section 7a is, as mentioned above, made of spring steel and of sufficient hardness that the steel balls 5 cannot deform it. The sections 7a and 7c are shown in FIGS. 3 and 4 wound against the direction of spin D of the projectile carrying the fuze housing 1 and the section 7b is wound in this direction D.

The sleeve 4 is insulated from the housing 1 by elements 9 and 10. The housing is also provided with a rotor 11 carried on radially extending pins 11a received in journals 12 in the housing 1. When spun at high speed about the axis A the rotor 11 tends to twist about its transverse axis A' from the position shown in FIG. 1 to the position shown in FIG. 2. The pin 3, however, normally rests in a recess 16 formed in the rotor 11 so as to prevent the rotor 11 from moving into the position of FIG. 2 in which the contact pin 13a of a primer 13 is aligned along the axis A with the pin 3. A foil 15 is provided over a window above the rotor 11 to allow the primer 13 to be connected to a conventional fuze or operated in any other manner and also to allow the detonator to be withdrawn from its bore 14 in the rotor 11.

The fuze operates as follows:

Prior to firing, that is during transport, loading, and when in position in the gun bore, the fuze is in the position shown in FIGS. 1 and 3 with the pin 3 seated in the recess 16. The balls 5 lock the pin 3 in this predetermined axial position and prevent the rotor 11 from rotating about its axis A'. Even if the projectile carrying this fuze is dropped or grossly mishandled the elements will remain in this position as only high-speed spinning of the housing 1 about the axis A can unlock these elements relative to one another.

When the shell is fired it is spun about this axis A at a very high speed so that first the outer section 7c of the spring packet 7 will suddenly unwind and engage the surface 8a of the chamber 8, very quickly unwinding and lying against this surface 8a. This frees the spring 7b which now unwinds at a very readily determined rate, as it is wound in the direction of spin of the housing 1, and it is in engagement with the surface of the section 7c which has a very high coefficient of friction. Once the section 7b has fully unwound, taking a relatively long time, the inner section will also very quickly unwind, as it is wound opposite to the direction D. This allows the balls 5 to move radially out of their bores 6 as indicated in FIG. 2.

The pin 3 is now free to move in the direction of axis A. Since the rotor 11 is being urged by centrifugal force to move into position of FIG. 2 it will depress this pin 3, causing it to leave the recess 16, until the contact pin 13a is directly axially aligned with the pin 3 whereupon the spring 2 will push the pin 3 up against this pin 13a. An electrical connection is now made between the pin 3 and the contact pin 13a so that the primer 13 is armed. Firing of this primer 13 can be effected by an electrical current passed between the sleeve 4 and the primer 13 by an impact fuze or the like such as described in the above-cited commonly filed patent application.

Since the intermediate section 7b is relatively long and is wound in the direction of rotation of the fuze, its unwinding time can be relatively easily ascertained and controlled within very strict limits. Thus the shell can be counted on to become armed at a predetermined instant after it leaves the muzzle of the gun. At the same time the relatively hard section 7a is not marred by the balls so that it also unwinds rapidly, and the section 7c having a high coefficient of friction also unwinds rapidly. Both of these sections 7a and 7c are wound against the direction of rotation D of the fuze so that their unwinding time is nominal compared to the unwinding time of the intermediate multiturn section 7b.

It is noted that in FIGS. 3 and 4 the spiral springs 7a-7c are shown with their individual turns spaced apart for clarity of view. In reality in both positions corresponding to FIGS. 3 and 4 the turns of each spring 7a, 7b and 7 c lie on one another and each such spring lies directly on the neighboring spring.