GB2347734A - Safety devices for ammunition - Google Patents

Abstract

A safety device for ammunition with a mechanically triggered switch element (S1) for an electrical power supply (6). The switch element (S1) can be actuated reversibly by the weight of the ammunition itself from a safe position into an armed position and wherein the switch element (S1) connects the power supply eg a lithium battery (16) to an energy storage device eg a capacitor, from which the ammunition thus prepared for firing draws its power. When the ammunition is placed in a launcher (11), a pin (8) is pressed in against the bias of a spring (9) to actuate the switch (S1).

Description

SAFETY DEVICES FOR AMMUNITION AS WELL AS AMMUNITION WITH SUCH SAFETY DEVICES The present invention relates to a safety device according to the pre-characterizing part of claim 1 and to ammunition with such a safety device according to claim 6.

Modern ammunition systems are frequently equipped with electronic circuits for firing, firing delay or for target location. Such electronic circuits must however be provided with a power supply. As a rule the power supply comprises electrochemical cells, especially batteries. In many cases lithium cells, i. e. cells whose anode material consists essentially of lithium, are especially well suited on account of their high energy density.

In ammunition systems which are supplied by batteries, high demands have to be imposed on safety. This it must be ensured in all cases that, for example, the firing electronics are not actuated inadvertently during handling, in order not to endanger personnel operating the weapon system.

A number of safety devices are known from the state of the art. Thus DE 4 105 271 Cl for example describes a safety device for preventing premature firing of an active charge of a missile, which is fired from a launcher barrel by a launching charge, relying on a mechanical and a pyrotechnic safety element. The ignition path between a delay part which can be ignited only on launching and the active charge of the missile can be blocked by a barrel sensor movable transverse to the launching direction, which can be arrested in its position blocking the ignition path by an acceleration sensor slidable against the launching direction and, so long as the missile is in the launching barrel, by the missile barrel wall. A second delay part which can likewise be ignited on launching, with a shorter delay time than the first delay part, loads the barrel sensor by gas pressure in the direction of its removal of safety position, after expiry of its delay time.

Furthermore DE 4 127 020 Al describes a safety switch for a missile for switching on the power supply of missile components after launching, with an insulating element which is spring biassed axially in the launching direction and is retained by a ball movable transverse to the axis and holds two contacts separated up to launching, wherein the ball is secured against movement up to launching by a pin spring biassed in the launching direction and a detent acting against displacement of the insulating element between the contacts after they have made contact is provided.

Moreover DE 4 240 809 Al describes a safety device for ammunition, wherein the safety device has a housing, in which a slider member is guided for adjusting movement between a safe position and an armed position. The slider member is provided with a firing medium, which is contacted in the armed position by a firing electronics device. It is formed with contact pins, which make contact with the firing medium and are short-circuited in the safe position by means of a short-circuit element. In the armed position the contact pins are contacted by contact elements which are provided on the housing remote from the short-circuit element and can be or are connected to the firing electronics device.

Metal foils, reed contacts and a self-conducting field effect transistor are considered as short-circuit elements in this state of the art.

The cited safety devices of the state of the art have in common that they detect on the one hand whether ignition of an ignition charge has actually taken place and then determine, for example by acceleration measurement, whether a specially designed firing chain should be set in operation or not, in other words, they determine whether the armed position of the ammunition is appropriate or not.

If however such a safety means is first inadvertently released and the system determines that there should be no initiation of the firing sequence, the ammunition is unusable and has to be repaired to be capable of further use.

Moreover the state of the art does not contemplate special problems which are bound up with batteries and especially with lithium batteries.

The powering of an ammunition system by means of batteries introduces the following problems: -the internal resistance of the batteries is so high that pulsed drawing of current is only possible to a limited extent. Also, at low temperatures, pulsed drawing of current is likewise only possible to a limited extent.

-in order to ensure long storage times of the ammunition often only lithium batteries can be used.

However lithium cells passivate over long storage times and are thus no longer usable for high energy demands after a long storage time. The current supply of the ammunition systems must further be so designed that inadvertent triggering of the ammunition is not possible.

Developing from the initially cited state of the art, the object of the present invention was to be able to use batteries, especially lithium batteries for military devices, safely and reliably, with at least significant avoidance of the problems mentioned above.

A solution to this object can be effected in relation to a safety device by the characterizing features of claim 1.

In relation to ammunition itself this object is met by the features of claim 6.

The safety device for ammunition according to the invention comprises a switch element for an electrical power supply which can be triggered mechanically, wherein the circuit element can be actuated reversibly by the weight of the ammunition itself from a safe position into an armed position; the switch element being operable to connect the power supply to an energy storage device from which the ammunition thus prepared for firing draws its power.

In accordance with the invention, ammunition, especially a shell, which is operated by a battery is typically put in a projector. On reaching the projector bottom a spring-biassed projector sensor, for example, which projects somewhat from the shell, is moved into the shell by the weight of the shell itself. This sensor can in turn actuate a switch element, which closes an electrical contact and connects an energy storage device to the battery or batteries. This energy storage device is charged from the batteries in this operation. The following advantages are exploited: The battery, especially a lithium battery, is depassivated by the charging current flowing in the charging operation of the energy storage device.

The energy of the storage device and its availability are largely independent of temperature.

When the ammunition is fired the total power of the energy storage device is immediately available.

The ammunition is partially prepared for firing by the charging.

Un-fired ammunition can be discharged again, the energy storage device being disconnected from the battery and discharging, e. g. through the discharge resistance itself, whereby the ammunition is again made safe. This operation is thus reversible and the ammunition can be charged and discharged several times.

Using an electrochemical cell, especially a battery, preferably a lithium battery, as the power supply according to claim 2 has the advantage that long storage times are obtained especially with lithium batteries, without significant self-discharge of the lithium battery occurring.

According to claim 3, spring actuated switch elements, especially barrel sensors, have proved especially suitable, because they are in the first place commercially obtainable and in the second place they operate robustly and reliably.

Using a capacitor as the energy storage device according to claim 4 has the advantage that the internal resistance of capacitors is far smaller than that of batteries and especially of lithium batteries. Furthermore capacitors can supply large currents, so that they are best suited for pulse operation.

Discharging the energy storage device through a discharge resistor according to claim 5 for rendering unfired ammunition safe again has the advantage of ensuring in a simple and inexpensive way that the energy storage device is completely discharged again, in order to render the ammunition safe again.

Further advantages and features appear on the basis of the following detailed description of an embodiment of the invention, by way of example, with reference to the drawings, in which: Fig. 1 is a partial longitudinal section through a shell with a safety device according to the invention and through the projector bottom; and Fig. 2 is circuit diagram of the safety device according to the invention.

A partial longitudinal section through a shell 2 as ammunition is shown in the loaded state in Fig. 1, denoted 1. The peripheral tube of the shell 2 is denoted 3. A projector sensor base unit as a safety device 4 is arranged in Fig. 1 at the lower end 5 of the shell 2.

In the example there is a lithium battery 6 shown schematically in Fig. 1 in the interior of the safety device 4. A spring contact projector sensor 7 is provided as a mechanically triggered switch element in the left part in Fig. 1 of the safety device 4.

The spring actuated switch element 7 is in the form of a barrel sensor. The switch element 7 comprises a pin 8 as a mechanical sensor, which projects out of a bottom plate 10 of the shell 2 with the switch element S1, on account of the force provided by a spring 9.

If the shell 2 is placed in a projector, the projector bottom 11 presses the pin 8 in against the spring bias of the spring 9, by virtue of the weight of the shell 2 itself. A switch S1 at the upper end 12 in Figure 1 is brought into a closed position by this movement, whereby the lithium battery 6 is brought into contact with a capacitor Cl (cf. Fig. 2). The capacitor 2 is now charged by the battery 6 and the lithium battery 6 is de-passivated by the charging current flowing in the operation of charging the capacitor Cl. The energy of the capacitor Cl is largely independent of temperature and the internal resistance of the capacitor Cl is far smaller than that of the lithium battery 6. The capacitor Cl can supply large currents in pulsed operation and when the ammunition 2 is fired, the total power of the capacitor Cl is immediately available.

The actual firing of the ammunition is effected inductively through a shell coil 13, which then causes operation of the firing electronics connected to the capacitor C1.

If the ammunition is unloaded from the projector, the pin 8 moves out of the shell again through the force of the spring 9 and opens the switch S1, which interrupts the voltage supply to the capacitor Cl from the lithium battery 6, and a switch S2 is simultaneously closed, so that the capacitor Cl is discharged through the discharge resistor RE in Fig. 2 and the ammunition is again rendered safe. The switch S2 can be dispensed withif required-by a high ohm value of the discharge resistance.

Conversely, to arm the ammunition, it is necessary for the switch S1 to be closed and the switch S2 simultaneously opened, so that the capacitor Cl can be charged by means of the lithium battery 6 so that the power needed by the firing electronics for firing is available.

The ammunition according to the invention can thus be charged and discharged reversibly several times and can be stored safely over a long period, without the passivation of the lithium batteries occurring through this having a disadvantageous effect on the reliability of the ammunition.

Claims (6)

1. CLAIMS 1. A safety device for ammunition with a switch element (Sl, 7) for an electrical power supply (6) which can be triggered mechanically, characterized in that the switch element (S1, 7) can be reversibly actuated by the weight of the ammunition itself from a safe position into an armed position ; and in that the switch element (S1, 7) connects the power supply to an energy storage device (C1), from which the ammunition thus prepared for firing draws its power.
2. 2. A safety device according to claim 1, characterized in that the power supply (6) is an electrochemical cell, especially a battery, preferably a lithium battery.
3. 3. A safety device according to claim 1 or 2, characterized in that the switch element (S1, 7) is a spring actuated switch element (7), especially a barrel sensor.
4. 4. A safety device according to any of claims 1 to 3, characterized in that the energy store is a capacitor (C1).
5. 5. A safety device according to any of claims 1 to 4, characterized in that the energy store (Cl) is discharged through a discharge resistance (RE) for rendering unfired ammunition safe again.
6. 6. Ammunition with a safety device according to at least one of claims 1 to 5.