Methods and apparatuses for projectile fuze setback generator power source and projectiles including same

Projectile fuze setback generator power source apparatuses and methods of use and manufacture are disclosed. An explosive projectile contains a fuze with a setback generator and associated fuze electronics. Upon initiation of projectile launch, the setback generator produces a voltage for use by the fuze electronics during flight. The setback generator includes a magnet maintained in place within a surrounding coil by a fastener. When a projectile is fired, rapid acceleration thereof causes the fastener to break and the magnet to be displaced longitudinally within the surrounding coil, which decreases the magnetic field and induces a current in the surrounding coil. The induced current produces a voltage that is stored in a capacitor operably coupled to the setback generators which then is used to power the fuze electronics during flight.

FIELD OF THE INVENTION

This invention, in various embodiments, relates generally to fuzes for projectile-type explosive devices and, more specifically, to apparatuses and methods for an improved setback generator power source used with projectile fuzing electronics.

BACKGROUND OF THE INVENTION

State of the Art: Electronic fuzing systems for controlling projectile warheads are well known in the art. Conventionally, projectile fuzes contain either a setback generator or a reserve battery to provide power to the fuze electronics during flight. Fuze electronics may include controllers, timing circuitry, and various sensors. Additionally, the fuze electronics may include a safing and arming module to ensure that both the arming and detonation of the projectile occur only at a desired moment.

FIG. 1illustrates a conventional explosive projectile60(also referred to as a warhead). As illustrated inFIG. 1, the explosive projectile60includes a fuze62and an explosive material64encased by a body66. Fuze62may comprise, among other parts, a faze electronics module, a power source, and a safing and arming module.

Reserve batteries, which have commonly been used as a power source for fuze electronics, may include a glass ampoule with electrolytes contained therein. Upon projectile launch, ideally the glass ampoule breaks and the electrolytic fluid flows into a cell stack and produces a battery voltage that powers the fuze electronics.

FIG. 2illustrates a conventional reserve battery assembly20that includes a reservoir22with a liquid electrolyte24contained therein, and a voltage producing cell stack26. Upon launch of a projectile, inner and outer drive disks41,42, respectively, are moved by the acceleration forces (shown by arrow25), and, in doing so, reservoir22is crushed and the electrolyte24is forced into cell stack26producing a voltage that powers an electronics module of a projectile fuze during flight. Problems associated with reserve batteries include long delay times for fuze power-up and the use of toxic materials and expensive components. Additionally, the force required to break the glass ampoule may be inconsistent, thus resulting in inconsistent unit-to-unit output energy characteristics.

Setback generators, which are also used as power sources for projectile fuzes, generate a pulse of electricity when a projectile is fired and rapidly accelerates down a launch barrel. The pulse of electricity charges a capacitor and the energy stored in the capacitor is then used to power the fuze electronics.

FIG. 3illustrates a conventional setback generator10that comprises a base cup27, a top cap18and an inner frame21that contains a woven coil23. A magnet12fits within inner frame21and rests against the base cup27. The magnet12is initially held against the base cup27by a thin shear disc14. Upon the firing of a projectile, setback generator10is subjected to a rapid acceleration (shown by arrows29), which causes magnet12to shear through shear disc14and move to the right (as the drawing is oriented) until it rests against the top cap18of the setback generator10assembly. This sudden movement of the magnet12causes the magnetic field within the setback generator10to decrease, which then induces a current within coil23. Terminal post16conducts the induced current away from the setback generator10and a corresponding voltage charges a capacitor, which powers an electronics module of the fuze during flight.

Like reserve batteries, conventional setback generators suffer from high unit-to-unit variances during setback as a result of unpredictable shearing properties of any shear disc design. Conventional setback generators using a shear disc design have high ductility and thickness tolerance properties, which may cause the setback generator to experience effects of friction on the periphery of the magnet against the shear disc edges upon shearing. Additionally, setback generators implementing a shear disc design may also experience plastic deformation and stretching of the discs upon setback, rather than a complete shear of the discs. As a result, the shear disc design suffers from high unit-to-unit output variances during projectile setback. Conventional setback generators also suffer from low energy output as well as from slow response times due to inefficient magnetic circuits. Additionally, conventional setback generators have a high unit product cost due to complex component parts, and lack packaging flexibility within the fuze.

There is a need for methods and apparatuses that simplify, improve the performance of, and increase the speed of setback generators, all while reducing the unit product cost of fuze power sources.

BRIEF SUMMARY OF THE INVENTION

An embodiment of the present invention comprises a setback generator power supply comprising a stator assembly including a coil and an armature assembly including a magnet disposed therein. The armature assembly has a first side, and a second side that is spaced therefrom along the axis relative to the first side. The setback generator power supply further includes a fastener that extends substantially from the first side of the armature assembly toward the second side of the armature assembly through the magnet received within the armature assembly and is configured to be sheared by a launch force of a projectile incorporating the setback generator power supply. The armature assembly is displaced upon the shearing of the fastener, responsive to which displacement of the armature assembly a current is induced in a coil of the stator assembly that surrounds the magnet.

Another embodiment of the present invention includes a method of generating power in a projectile faze comprising providing a magnet contained within an armature assembly of a setback generator. The armature assembly is coupled to the stator assembly by a fastener extending substantially from a first side of the armature assembly to a second side of the armature assembly. The method further includes shearing the fastener using a force of a projectile launch and displacing the armature assembly to generate a current in a surrounding coil of the stator assembly from inductive coupling between the coil and the displaced armature assembly.

Another embodiment of the present invention includes a projectile fuze comprising fuze electronics and a setback generator power supply according to an embodiment of the present invention.

Another embodiment of the present invention includes an explosive projectile comprising an encasement, an explosive material disposed within the encasement and configured for detonation. Additionally, the explosive projectile includes a fuze disposed within the encasement comprising faze electronics and a setback generator power supply according to an embodiment of the present invention.

Yet another embodiment of the present invention includes a method of making a setback generator comprising selecting a magnet with a potentially suitable diameter given a size constraint of the setback generator, wherein the magnet has sufficient length to drive a magnetic flux around a magnetic circuit linked to a coil. The method further includes selecting the coil comprising a number of windings for a desired output voltage, and determining the output voltage of the setback generator. The method further includes varying the selected magnet diameter within the size constraint to achieve an optimized output energy.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, in various embodiments, comprises apparatuses and methods of operation for a fuze setback generator power source that simplify a shearing mechanism employed in the generator, increase the speed of generation and magnitude of the output energy, and reduce the unit product cost of the power source.

In describing embodiments of the present invention, the systems and elements incorporating embodiments of the invention are described to better understand the function of the described embodiments of the invention as it may be implemented within these systems and elements.

FIG. 4illustrates a setback generator power source110in a pre-launch position which operates on a moving magnet principle during setback of a cannon-fired projectile fuze, the term “cannon” as used herein encompassing any and all apparatus for throwing a projectile using force of a controlled detonation of explosive material within a confined space to launch a projectile from a gun barrel. Setback generator110provides for, as described in detail below, a simple shearing mechanism, a minimal amount of component parts, component parts of simplified design, and a high level of magnetic efficiency. Setback generator110includes an elongated fastener146with a first end portion148, a middle portion145and an enlarged, second end portion147comprising a head. Fastener146may be any suitable attachment device, such as a screw, bolt, rivet, and the like. For brevity and ease of description, fastener146will be referred to herein as a screw. The middle portion145of screw146is surrounded by magnet140, which is peripherally encased by a bobbin assembly150and stator ring144. The stator ring144, bobbin assembly150, armature disk152, first end portion148of screw146and a top portion141of magnet140are all substantially surrounded by a stator cup142(also referred to as a housing). The armature disc152peripherally surrounds the second end portion147of screw146and is longitudinally slidably movable, but for the constraint provided by screw146, with respect to the stator cup142, stator ring144and bobbin assembly150. In addition, armature disc152includes a recessed shoulder153abutting end portion147of screw146and configured to secure magnet140to armature disc152. Recessed shoulder153provides a safety feature by ensuring that armature disc152does not separate from magnet140and, therefore, demagnetize magnet140prematurely. Bobbin assembly150includes coil151wound therein, and an output terminal158which extends though the wall of stator cup142and may be used to conduct an electrical pulse from setback generator110. The ferromagnetic components of setback generator110make up a magnetic circuit which includes the magnet140, stator cup142, stator ring144, and armature disc152. Setback generator110also includes an air gap160that exists outside of the magnetic circuit. Magnet140, screw146and armature disc152may together be referred to as an armature assembly and stator ring144, stator cup142, and coil151may together be referred to as a stator assembly.

For example, and without limitation, magnet140may be an Alnico 5 alloy magnet which comprises primarily aluminum, nickel, and cobalt. Alnico 5 alloy magnets exhibit a high flux density (amount of flux over a given area) and a low coercive force or demagnetizing force. As a result, demagnetization of an Alnico 5 alloy magnet is achieved quickly and easily. Although an Alnico 5 alloy magnet is disclosed for use in the described embodiment, the use of any type of permanent magnet is contemplated as within the scope of the invention. Additionally, screw146may be, for example only, and not limitation, a simple polymer screw such as a polyetheretherketone (PEEK) screw.

After initial assembly of setback generator110, magnet140may be magnetized in situ. Magnetization of magnet140may be enhanced by first lowering the reluctance of the magnetic circuit as described in the preceding paragraph by decreasing any low permeability air gaps in the flux path which may cause flux leakage of the magnetic circuit. Additionally, the armature disc152and stator ring144function to reduce flux leakage and saturation effects of the magnetic circuit. After lowering the reluctance of the magnetic circuit, the magnetic circuit is magnetized by means of a capacitive discharge magnetizer.

FIG. 5illustrates setback generator110in a pre-launch position after magnetization, illustrating the magnetic flux path162of the magnetic circuit within setback generator110. The armature disc152, stator ring144and stator cup142make up the magnetic flux return path and direct the lines of flux around coil151within bobbin assembly150. The magnetic flux path162travels from the north pole N of magnet140, along and down the stator cup142, through the stator ring144and armature disc152, into magnet140at the south pole S, and back to the north pole N through the inside of magnet140.

FIG. 6illustrates setback generator110in a post-launch position. Upon the tiring of the projectile containing it, setback generator110is subjected to a rapid acceleration (shown by arrow156). After projectile launch, at a point on a g-force versus time curve (seeFIG. 7), the mass of the magnet140shears the first end portion148of the screw146from middle portion145(seeFIG. 4) and second end portion147of screw146responsive to the acceleration force. Shearing of screw146may be defined as a tensile failure of the screw146in a direction substantially perpendicular to the longitudinal axis L of the screw146. This shearing process enables displacement of magnet140under the acceleration and creates an air gap154within the coil151that extends across the diameter of magnet140. The increased air gap reluctance due to air gap154causes the magnetic flux density to go from high to low and results in demagnetization of magnet140. Demagnetization of magnet140induces a current in the surrounding coil151by virtue of the collapsing magnetic field. Subsequently, output terminal158conducts a voltage, corresponding to the induced current, away from setback generator110through rectifier28and into electrical storage device30(seeFIG. 8). As a result, the induced current produces a voltage that is stored in electrical storage device30, which then is used to power the fuze electronics132during projectile flight. For brevity and ease of description, electrical storage device30will be referred to herein as a capacitor.

As opposed to conventional setback generator designs, the distance between magnetic poles of magnet140is less or, in other words, the length of magnet140is shorter. A shorter magnet requires less of an air gap in order to demagnetize the magnet, which results in a greater rate of change of the magnetic flux with respect to time. Quicker demagnetization of magnet140results in a response time in which the fuze electronics receives power that may be many orders of magnitude faster than when a reserve battery is employed. By way of nonlimiting example only, operation of setback generator110may provide a response time of approximately 100 microseconds. The increased response time enables “in-tube” activation of the fuze electronics for sating and arming circuit processing. Stated another way, due to the faster response time provided by setback generators according to embodiments of the present invention, the safing and arming module may receive power from the setback generator and be activated before a projectile has exited the barrel of a cannon or any other similar projectile launching device.

Additionally, due to a better balance of component parts in comparison to conventional setback generators, including an improved parametric relationship of the magnetic volume, copper volume, and the magnetic circuit volume, the setback generator embodied by the present invention exhibits lower loss and provides increased energy output power per unit volume. To achieve a preferred parametric relationship between the magnetic volume, copper volume, and magnetic circuit volume an optimization process may be carried out. The optimization process includes maximizing the magnetic flux by using an Alnico 5 alloy magnet with the largest possible diameter provided the given size constraints of stator cup142, stator ring144and armature disc152which, in turn, are governed by the diameter of the projectile in which setback generator110is to be used. Also, a sufficient magnetic length must be provided to drive the magnetic flux around the magnetic circuit. For the given stator and armature disc dimensions, a coil with a selected number of windings may then be chosen to provide a desired output voltage. If excessive winding resistance is encountered, or insufficient output voltage results from the available size and volume constraints, the magnet diameter may be varied until an optimized output energy is realized. This design process can be accomplished using hand calculations or computer-aided design (CAD) modeling.

The shearing process of setback generator110is simplified by using only a minimal number of low-cost component parts, in the form of a single fastener146, configured, by way of example only, as a screw. As opposed to conventional setback generators, setback generator110offers a high level of predictability and repeatability due to the simplicity and precision of the configuration and the material consistency of screw146. The shearing process is further simplified by employing only two moving parts within the magnetic circuit, including the magnet140and armature disc152. The lower ductility and thickness tolerance properties of the shear screw design, as opposed to the shear disc design of conventional setback generators, contributes to lower unit-to-unit output variances during projectile setback. In all, using fewer parts, which are simplified in design and more consistent in dimensions and material properties, results in a simplified shearing mechanism that provides better controlled shearing properties, more consistent unit-to-unit output characteristics, and lower per-unit product costs.

FIG. 7is a g-force versus time curve illustrating projectile launch data and the shearing point of screw146(FIGS. 4-6). G-forces of a projectile, including a setback generator contained therein, are represented by curve172and a shearing point is represented by line180at an acceleration value of 25,000 g-forces. As shown, the shear point170of screw146is approximately 25,000 g-forces at a time of approximately 0.13 milliseconds from initiation of projectile movement during launch. The time/acceleration relationship depicted inFIG. 7is only an example of operation of an embodiment of the present invention and by no means limits any embodiment thereof.

FIG. 8is a schematic of a circuit connection of setback generator (SBG)110and fuze electronics132. As described above, upon projectile launch and responsive to acceleration forces, setback generator10provides an electrical pulse via output terminal158(FIGS. 4-6) through rectifier28and a corresponding voltage is stored in capacitor30. Capacitor30is operably coupled to fuze electronics132and the energy stored in capacitor30is used to power fuze electronics132during projectile flight. The circuit configuration illustrated inFIG. 8is used only as an example of one suitable circuit connection between setback generator110and fuze electronics132, and other configurations are encompassed within the scope of the invention.

FIG. 9illustrates a setback generator110including an aft loading configuration and forward-based electrical output terminal158which results in greater packaging flexibility of the flue electronics132. Setback generator110is configured to allow the setback generator110to be located in the back, or aft end, of projectile60with the more sensitive devices, including the fuze electronics132and the safing and arming module134, to be on top of or in front of setback generator110. Output terminal158is located at the front, or forward end, of setback generator110and extends in the same direction as a projectile launch. The aft loading configuration along with the forward-based electrical output terminal158enables easier assembly and simplified routing of power to fuze electronics132. However, while the aft location for the setback generator110is used inFIG. 9, other locations and configurations are contemplated within the scope of the invention.

Whereas one design and size of an embodiment of setback generator110may be employed with a number of different flues, within the scope of the present invention, the configuration of the setback generator embodied in the present invention may be rescaled to provide a range of output energy levels for significantly different fuze applications and sizes.

Specific embodiments have been shown by way of example in the drawings and have been described in detail herein; however, the invention may be susceptible to various modifications and alternative forms. It should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.