GB2103340A - Projectile fuze with heat-responsive safety element - Google Patents

Abstract

A projectile fuze is provided with an unlocking element which, when a specific temperature is reached, suddenly experiences a specific predetermined change in shape. The unlocking element may be a 'memory' metal which shrinks, or a snap-action bimetallic strip. The heating is caused by dynamic air pressure or is derived from an after burner of the projectile. In one embodiment, Figure 2, inertia bolts 17 & 20 set back upon firing the projectile and enable a sleeve 15 and the parts of the fuze forward of surface 28 to be lifted by a spring 24. Air passages 30 are thus unblocked and an unlocking element 38 is heated by the flow of air, whereupon it shrinks and enables a firing pin 16 to be lifted out of blocking engagement with a detonator-carrying rotor 14. In another embodiment, Figure 7, air passages 54 are unblocked by the set back of an inertia member 51 whereupon a rod 41 of 'memory' metal shrinks to withdraw a firing pin 16 from rotor 8. A self-destruction mechanism, comprises a second element 64 of 'memory' metal which shrinks out of blocking engagement beneath a spring- loaded striker 66 if the fuze fails to fire within a predetermined time. <IMAGE>

Description

SPECIFICATION A safety mechanism for a projectile fuze, a fuze including such a safety mechanism and a projectile having such a fuze The invention relates to a safety mechanism for a projectile fuze comprising a first safety element, for partial arming under the influence of launch acceleration, and a second safety element for arming a bursting-cap booster-charge ignition chain of the fuze, which mechanism has an unlocking mechanism which, after launch, is, preferably, exposed to the air dynamic-pressure friction heat in free flight of a projectile having a fuze with the safety mechanism.

Such a safety mechanism is shown in German Patent No. 1 578 496. As shown, to guarantee the so-called in-front-of-the barrel safety (the fuze is in the live position only after traversing a safety distance in free projectile flight in front of the muzzle opening of the launching weapon barrel) is a second safety element in the form of a melting body which, during the free flight of the projectile, is exposed with its end surface to the dynamic pressure heat.

When the body is heated up to melting temperature it melts and makes possible the advance of a spring-loaded plunger, whereby the fuze is put into the live position.

This safety mechanism tends to be disadvantageous in that the unlocking of the second safety element, ensuing by way of the melting body, is constructionally difficult to define, because the melting body, in the course of heating before finally melting, has a plastic consistency in which it no longer represents a constructional part having defined mechanical and geometrical properties and also no longer guarantees an unequivocal locking function; whilst the material of the melting body may upon further heating finally be deposited in a non-predeterminable manner in the functional region of the second safety element of the fuze and this can lead to malfunctions there. A further criterion which goes against the use of such melting safety devices is the possibility of relatively simple acts of sabotage which are difficult to discover.

Shown in United States Patent No. 2 937 596 is a safety mechanism in which the air dynamic-pressure heating during free flight of the projectile is made use of to evaporate a liquid filling in an expansion vessel. The filling displaces a piston-shaped contact piece for closing an electrical circuit against the force of a restoring spring having adjustable bias. This safety mechanism tends to be disadvantageous more particularly because of the expenditure pertaining to apparatus and the mode of operation of such a liquid-filled expansion vessel, which tends to be troublesome.Also there tends to be poorly defined electrical contact, since the contact piece is a sliding one, because the adjustable spring tension merely determines the minimum pressure and after the minimum pressure is reached evaporation of the liquid filling in the expansion vessel leads to the start of displacement of the contact piece, but after which start the filling no longer has any influence on a specific contact-making in the case of specific heating factors.

According to the present invention there is provided a safety mechanism for a projectile fuze comprising a first safety element, for partial arming under the influence of launch acceleration, and a second safety element for arming a bursting-cap booster-charge ignition chain of the fuze, which mechanism has an unlocking mechanism which, after launch, is, preferably, exposed to the air dynamic-pressure friction heat in free flight of a projectile having a fuze with the safety mechanism, characterized in that the unlocking mechanism has a constructional element of a material which, when a specific temperature is exceeded, substantially suddenly experiences a specific predetermined change in shape.

Further according to the present invention there is provided a projectile fuze including a safety mechanism as described in the immediately preceding paragraph.

Still further according to the present invention there is provided a projectile including a fuze as described in the immediately preceding paragraph.

In the knowledge of the disadvantages mentioned in the case of conventional safety mechanisms whose second safety element is intended to unlock during the free flight of the projectile in a manner caused by air dynamic-pressure heating, embodiments of the invention may advantageously provide an improved or more reliable safety mechanism such that an unequivocal unlocking function for the live position of the fuze, at a specific predetermined temperature at the unlocking mechanism is ensured, by means of the constructional element which has specific mechanical factors not only before but also after response to this critical temperature.

Embodiments of the invention may ensure that non-specific or unpredicted creeping functions do not occur in the course of the unlocking of the second safety element. The live position of the fuze will then occur only upon specific predeterminable heating of the crucial unlocking constructional element and then occurs suddenly, after which, the constructional element again has specific geometrical and mechanical properties. This may enable the constructional element to undertake constructive functions later, for example, projectile ignition or detonation in the target or in self-destruction of the projectile.

As such a constructional element there could basically be used, for example, a bimetal having a snap-transition change of state (U MSCHLAG- SCHNAPPVERHALTEN). Upon a temperature rise in the bimetal, there build up bending stresses which leads to a snapping-over from a first geometrical configuration into a second one only after a constructionally predetermined specific temperature is exceeded. The snap-over may be, for example, a sudden transition from one direction of a curvature to the opposite direction of curvature, in order to release the locking ensured up until then and thus to release orto bring about a movement of the blasting cap into the line of action of the fuze.It maybe, however, more favourable to use a constructional element within the second safety element in accord ance with claim 2, i.e. an element of a material having a power of recollection of shape (for example, so-called "memory alloy") which, is known per se (see for example H. Rissman in METALL vol. 28, No.

10, pages 976 to 978; L. Delaey et alia in METALL vol.

31, No. 12, pages 1325 to 1331). When a structure transformation temperature which is predeterminable in a manner specific to the material is exceeded, the element is converted from one geometrical shape, impressed upon production, as a result of the release of shape-recollection crystal-lattice forces into its originally-given geometrical shape Upon this change in shape, it may, depending on the pretreatment factors during production of the constructional element, be a matter of mainly onedimensional or two-dimensional enlargements or diminutions (lengthening or shortening of a cylinder or expansion of shrinkage of the inside or outside diameter of a ring). Alternatively, it could be a matter of torsion or bending phenomena.The particular advantage of using material temperature-dependent shape recollection memory or ability for the construction element, in the second safety element of a projectile-fuze safety mechanism lies in that, when the transformation temperature is exceeded and even with a small-scale construction element, comparatively large forces are released. Large forces are released because of the effect of the crystal-lattice forces, so that in very restricted space specific mechanical procedures can (even under unfavourable ambient conditions - for example lock-bolt shift also increases under the influence of friction coefficients as a result of acceleration or as a result of heating) be suddenly initiated and carried out.

Advantageously, the constructional element made from this material has, not only before, but after occurrence of the shape transformation, extensively the same mechanical properties. Therefore, in each case, the element has specific predeterminable geometrical configurations, i.e. even after the transformation procedures initiated in a temperaturedependent manner have become effective, a fully functional constructional element continues to be provided in the projectile fuze.The onset of the shape transformation can be influenced constructively by way of heat introduction by means of coupling elements, taking into account heat transfer factors and heat-absorption surfaces related to the volume of the transformation material; in which respect, more particularly by a large ratio of heattransfer surface to volume of the constructional element made from shape memory material, rapid and approximately homogeneous or uniform heating-up of the entire structure in the interests of substantially sudden crystal-lattice transformation and thus shape change is realisable.

Within the scope of claim 3, inside the second safety element an unlocking mechanism similarto that shown in German Patent No. 1 578496 may be provided. That is to say, a bolt or pin may be supported by a fuze-fast spring-loading by way of a circular constructional element, exposed to the air friction heating, as unlocking mechanism in the region of the front part of the fuze.However, in this instance the circular unlocking mechanism has not only a locking function, but after release of the shape recollection forces as a result of the transformation temperature being exceeded, the ring itself, as a result of reduced outside diameter now no longer supported in the locking position, serves as advance stop of the bolt or pin advanced under the influence of the compression spring and thus as a pressure transfer element for the latter triggering of the fuse then made live.

A modified embodiment of the invention as brought out in claim 4 has more particularly the advantage of smaller radial dimensions of the unlocking mechanism with at the same time increased operating safety or reliability. This is because there is no longer an advance orforward thrust element which has to be released by a radially-acting unlocking, but the axial shortening of the unlocking mechanism when made from shape memory material directly frees the spring-loaded axial movement for arming the fuze.

A further development brought out in claim 5 uses an axially-shrinking plunger within the second safety system not only to release the unlocking thereof, but also for applying the unlocking force itself, and has the quite considerable addtional safety-technique advantage (in keeping with the NATO standardisation agreement regarding general constructional guidelines and features for the safety of ammunition ignition systems) of no longer needing, for the unlocking of the second safety element, a device which contains stored energy in the formed of a tensioned spring, after launch-occasioned partial arming or even in the safe position of the fuze.This is because the crystal-lattice forces, released when the transformation temperature is exceeded and leading to the change in shape, are now utilized directly to release, for example, the swinging-in of the blasting cap into the ignition line, or alternatively, (for instance by setting-free torsion movements in the course of the shape-recollection transformation) even utilised directly themselves for the swinging-in of the blasting cap into the ignition line.

German Patent No. 1 578496 discloses the idea of causing the dynamic-pressure airflow generated in the region of the front part of the fuze to enter under the hollow-frustum-shaped jacket surface thereof and to cause the air to emerge again after flow conduction through guiding ducts in this walling, in order to heat-up the corresponding constructional element of the unlocking mechanism during free projectile flight. In accordance with the further developments in accordance with claim 6 or claim 7, it promotes the inherent safety of a projectile which is equipped with such a fuze and safety mechanism if such guiding ducts serving for the thermal activation of the unlocking mechanism of the second safety element are freed for air through-flow only when they have been freed in a launch-occasioned manner, in other words in particular during the course of the unlocking action of the first safety element.

More particularly in connection with this additional safety measure provision may advantageously be made, in accordance with an embodiment within the scope of claim 8, to arrange for the unlocking constructional element, consisting of material having shape recollection ability (memory metal), of the second safety element to be thermally-insulated by a stationary air envelope in the fuze and to connect same thermally to the heat absorber or heat coupler only as a result of the launch acceleration (for example in the course of the opening of the air-flow guiding ducts), so that mere ambient heating of the fuze in itself (for example as a result of a dump fire) is made safe and still cannot lead to critical heating to transformation temperature; and in this way, in any event up to the occurrence of a launch acceleration (unlocking of the first safety element), the thermally-responding second safety element remains reliably locked.

In accordance with the further development as per claim 9, the safety mechanism in accordance with the invention may advantageously at the same time also be utilized (in the case of self-destructing ammunition -for instance practice ammunition or ammunition to be used on flying targets) to unlock a self-destruction unlocking in a time-dependent manner after the fuze is in the live position and thus to initiate self-destruction to render the ammunition harmless. This functional coupling to the fuze live position by establishment of the ignition line is advantageously effected by a thermal series connection in accordance with claim 10, whereby it is ensured that self-destruction can only occur outside the in-front-of-the barrel safety distance, in other words, in free projectile flight at a non-critical distance from the launching weapon barrel.

The present invention will now be described, by way of example only, in the following description of preferred exemplified embodiments, with reference to the accompanying simplified drawings; in which respect, the drawings represent primarily only basic examples which may, more especially in accordance with the heating factors in the dynamic-pressure air flow and in accordance with the heat transfer factors, be the object of abundantly geometrically modified embodiments, in which drawings:: Figure 1 shows, in accordance with the present invention, in central longitudinal section, an article of ammunition - in this case spin-stabilised - with an embodiment of a fuze superimposed but without the propellant charge; Figure 2 in more detail shows the fuze having a thermally-triggerable shrink-ring unlocking mechanism of a second safety element, with air-flow release from a first safety element, in the safe position; Figure 3 shows the fuze in accordance with Figure 2 after release of the first safety element; Figure 4 shows the fuze in accordance with Figure 2/Figure 3 after unlocking of its second safety element; Figure 5 shows, in modification of the fuze in accordance with Figure 2 to Figure 4, a fuze having a shrinkage-piston unlocking mechanism for its second safety element in the safe position of the fuze;; Figure 6 shows the incorporation of the unlocking mechanism with a constructional element made of metal having shape recollection memory into the second safety element of a fuze in accordance with Figure 5; Figure 7shows, in modification of the development of the second safety element in accordance with Figure 2 or respectively Figure 5, a fuze which, within its second safety element, does not need a spring force for the unlocking for the ignition-line release, in thermal series connection with regard to the second safety element; Figure 8 shows the fuze in accordance with Figure 7 with the second safety element unlocked but with the self-destruction unlocking member still not released; and Figure 9 shows, in enlarged detail representation, a fragmentary view from Figure 7/Figure 8, but with the self-destruction unlocking member released.

Figure 1 shows in axial longitudinal section a projectile 1 having a fuze 3 inserted into its end opening 2. In this example an explosive or bursting (SPRENG) projectile is shown, i.e. a projectile body 5 which is substantially completely filled with explosive 4 and which is equipped with a propellant charge case (not shown in the drawing) for launching the projectile 1, which case is located behind a driving band 6 for stabilising spin in the course of propulsion of the projectile through a weapon barrel which is provided with appropriate spin rifling.

When the ignition system is armed, in other words made live, a release mechanism 7 which responds, for instance, to target approach orto impact, initiates piercing of a bursting cap or capsule 8, which in turn triggers a booster charge 9 in order to ignite the explosive 4 and thus to trigger, in the target, the splinter effect of the projectile body 5 and the explosive gas impact effect.

So that the explosive 4 does not ignite on handling the projectile 1 before launching or upon, or immediately after, launching, the fuze 3 contains a multiplyacting safety mechanism 10. Safety mechanism 10 makes possible the fuze effect chain by way of the blasting cap 8 and booster charge 9 on the explosive 4 only when - because of at least two independent environmentally-occasioned physical phenomena it is quite certain that the launching of the projectile 1 in the weapon barrel (not shown in the drawing) has taken place and that the projectile 1 has also left the muzzle of the weapon barrel and has flown through a safety distance, guaranteeing the barrel safety, in front of the muzzle.

Such a safety mechanism 10 is shown in detailed manner in Figure 2. Used as first safety element 11 ensuring the launching and barrel safety therein is a so-called double backfire bolt system 12, which, in the safe position (Figure 2), initially locks a swivel lever 13. In the safe position the swivel lever 13 is in engagement in form-locking manner with a locking sleeve 15, which engages into the rotor 14 or a component part connected thereto, in order initially to prevent any swinging-in of the rotor 14 into the described ignition line. Guided in the interior of the locking sleeve 15 is a puncture needle 16 which, in the safe position of the fuze 3, would also block the rotor 14 swinging-in into the live position.

Upon launching of the projectile 1 from a weapon barrel, the severe and persisting acceleration under the effect of the propellant charge causes the first safety element 11 to unlock for partial arming of the fuze 3, i.e., in the case of the double backfire bolt system 12, initially the first bolt 17 slides back, because of its inertial mass, against the effect of a spring 18, whereupon a blocking sphere 19 is released and also the second bolt 20 can, as a result of its inertial mass, slide back in the forwardlymoved projectile fuze 3 against the action of a spring 21 and pull a blocking pin 22 out of the swivel lever 13, which lever thus passes under the influence (Figure 3) of a swivel spring 23 out of engagement with the locking sleeve 15.As shown in Figure 3, sleeve 15 is thus raised under the influence of a spring 24 out of the blocking position for the rotor 14, as far as the engagement of a stop 25 and the rotor is after that prevented from swinging into the ignition effect line only by the remaining engagement with the puncture needle 16.

With this launch-occasioned release of the locking sleeve 15 by the first safety element 11, the base surface 26 of a frusto-conical fuze front part 27 is lifted off from a sealing surface 28 in order to free outlet openings 29 of air guide ducts 30 which extend inclined to the fuze longitudinal axis 31 (Figure 4). The ducts 30 emanate from a distribution chamber 32 and are azimuthally mutually offset, through the frusto-conical front part 27 of the fuze.

Formed in the frustum end surface 33 are openings 34 through which, in free flight of the projectile 1 outside the weapon barrel and under the effect of the dynamic pressure, air can enter into the distribution chamber 32, in order thereupon to flow through the guide ducts 30 and to emerge at the frustum base surface 26.

In this frusto-conical front part 27 of the fuze the puncture needle 16, displaceable coaxially in the locking sleeve 15 and thus relative to this front part 27, is spring loaded by a spring 35 in the direction of the fuze tip (frustum end surface 33); a supporting plate 36 of a needle holder 37 abuts a radial shrink ring 38 having a frusto-conical outer jacket surface 39 abutting against an encircling supporting shoulder 40.

The shrink-ring 38 lies in the region of the distribution chamber 32 in the flow path of the dynamic-pressure air flow entering through the openings 34 and leaving the guide ducts 30 through the outlet openings 29, so that, in free flight of the rapidly-flying projectile 1, because of the air friction along the outer jacket surface 39 a rapid-severe or intense heating of the shrink ring 38 is effected.

The radial shrink ring 38 acts as unlocking mechanism 41 of a second safety element 42, by means of which under the influence of the air frictional heat, occurring at the shrink ring 38, the ignition chain for arming is unlocked. For this, the unlocking mechanism 41 in the form of the shrink ring 38 comprises a material which suddenly experiences a predetermined change in shape when a specific temperature is exceeded; in this case a radial shrinkage to a smaller outside diameter.

Suitable for this purpose is in particular the material, described at the beginning hereof, having shape recollection power (so-called "memory" alloys), which, when a transformation temperature is exceeded, releases crystal-lattice forces which compel the body to assume once more a previously-given geometrical shape. This shape transformation namely radial shrinkage of the ring 38 - occurs suddenly in practice when the transformation temperature is exceeded, because the ring 38 having a conical outer surface 39 has, in relation to the ring volume, a large effective outer surface which is exposed to the air friction heating, i.e. in the ring 38 itself only slight temperature differences occur.

The handling safety, barrel safety and in-front-ofthe barrel safety of the fuze 3 is thus ensured in that the first safety element 11 is released only as a result of the launching acceleration in the weapon barrel, whereupon only by freeing or uncovering of the outlet openings 29 - in other words by advancing of the locking sleeve 15, released by the swivel lever 13, with the front part 27 of the fuze fastened thereto - is the second safety element 42 put into operational readiness; and the unlocking mechanism 41 of the element 42 is released only after elapsing of a free flight time of the projectile which is sufficient for the heating of the ring material having shape recollection power to shrink the ring 38 to such a diameter that the tensioned spring 35 can advance the ring in the free space between the supporting shoulder 40 until it abuts against a baffle plate 43. Thus the puncture needle 16 is drawn out of the arresting opening in the bursting cap rotor 14, which needle can now - in the case of spin-stabilised projectile 1 under the effect of centrifugal force or in the case of fin-stabilised projectiles 1 under the effect of a stored force such as for instance that of the swivel spring 23 by means of the swivel lever 13 - be swung into the ignition line, and the fuze 3 is then armed (Figure 4).

The puncture needle 16 is now supported by way of its supporting plate 36 and the shrunken ring 38 directly axially against the baffle plate 43, so that, when the front region of the fuze 3 encounters a target, the puncture needle 16 ignites the bursting cap 8 lying, as a result of the swung-in rotor 14, in front of its tip (see also Figure 1) and, by way of this cap, the booster charge 9 and thus the explosive filling of the projectile 1 is ignited.

Thus, as the relevant safety construction regulations require, two environmental criteria which become effective independently of one another as from launching of the projectile 1 are utilised in order to arm the projectile 1 only after flying through a safety zone in front of the muzzle of the weapon barrel. The second safety criterion for this arming is the exceeding of a specific, relatively high temperature, which is brought about in practice only in free flight of the projectile because of the dynamic pressure effect of the air flowing through the guide ducts 30, and these guide ducts 30 are only made available for air through-flow when the first safety element 11 has triggered on launching.

The time span up to unlocking of the second safety element 42 can be predetermined; apart from by way of the material choice, and the transformation temperature prescription connected therewith, for the arming mechanism 41 in the form of shrink ring 38, also by way of in particular the wall thickness of the shrink ring. In general the time span can be predetermined by way of the time behaviour of the penetration of the heating, caused by air friction, from the outer surface 39 into the interior of the material, until the transformation temperature is exceeded over the entire structure.The time behaviour of the unlocking itself - in other words, for example, creeping or sudden movement of the spring-loaded supporting of the needle-holder plate 36 to move ring 38 from the shoulder 40 against the baffle plate 43 - can be predetermined constructionally within wide limits by way of the outer wall geometry of the shrink ring 38.

Constructionally it may be more advantageous to select a geometry which is as simple as possible for the operational element consisting of a memory alloy. In the case of the exemplified embodiment in accordance with Figure 5, the central, heatcontrolled operational elementforthe unlocking mechanism 41 consists of a flat cylindrical shrink plunger 44, which is axially clamped in the region of the air-flow distribution chamber 32 between two heat absorbers 45, 46, for example, made of copper or other good heat-conducting material. The plunger 44 is biassed by the action of an unlocking spring 35.

The front heat absorber 45 is supported by way of an insulating layer 47 in contact with the baffle plate 43 and, for air passage from the openings to the guide ducts 30 the absorber 45 has located rearwardly against the flat shrink plunger 44 an encircling edge or periphery which is of crown-shaped form as shown in Figure 6. The heat absorber 46 opposite (rearward of) absorber 45 butts against the shrink plunger 44 and has, opposite edge 48, a groove 49, in order to predetermine specific axial pressure zones on the shrink plunger 44.

With sufficient air-flow occasioned heating of the heat absorbers 45,46 and thus of the shrink plunger 44 for exceeding the transformation temperature (if previously as described in connection with Figure 2 the first safety element 11 has raised the front part 27 of the fuze to free the guide-duct outlet openings) the shrink plunger 44 is reduced virtually suddenly in axial length (disc thickness), so that, under the action of the unlocking spring 35, as described in connection with Figure 4, the puncture needle 16 is drawn out of the rotor 14 and the latter is swung into the arming line, in order, upon target impact on the front part 27 of the fuze, to be triggered by puncture needle 16 being pushed-back to the rotor.

In the case of the above-described exemplified embodiments of a safety mechanism 10 in accordance with the invention, the barrel safety and the in-front-of-the barrel safety as well as dump safety (even against a dump fire) are indeed ensured, because the second safety element 42 is placed into operational readiness after launch-occasioned activation of the first safety element 11 and the unlocking mechanism 41 thereof is released for arming the ignition chain only after the expiry of sufficiently long free4lightfactors. Nevertheless, in view of the safety standard to be aspired to, it is basically undesirable that the preparation function and the unlocking function connected with the effectiveness of the second safety element 42, even under dump factors, stand under the influence of a biassing force in the form of the lifting spring 24 or respectively the unlocking spring 35.

In the case of the modified exemplified embodiment regarding the safety mechanism in accordance with Figure 7/Figure 8 the action preparation of the second safety element 52 is therefore not effected indirectly by virtue of the launching acceleration namely by releasing of a locking of a lifting spring 24, see Figure 3-; on the contrary, now, parallel to the acceleration-occasioned function of the first safety element 11 and also directly as a result of the launch acceleration a shear element 50, is perforated. Element 50, in the safe position of the fuze 3, still keeps a hollow-frustum-shaped heat coupler 51, which is made from thermally good-conductive material, thermally separated from the unlocking mechanism 41 (see Figure 7).In this safe position, the heat coupler 51 butts with its cone outer walling 52 in such a way on the inside against the hollowfrustum-shaped fuze inner walling 53 that air passage apertures 54 situated there in the fuze 3 are initially closed. The conical region, lying therebefore, of the fuze tip 55 has an air inlet opening 56 in the centre of the frustum end surface 33 and the inlet is preferably also initially blocked in the safe position of the fuze 3, namely by a frusto-conical flow barrier 57, which is inserted coaxially in a form-locking manner into the conically-tapering front region of the fuze tip jacket 58.

The unlocking mechanism 41 has a bar made of material having shape recollection power which is adjusted in such a way that its length is considerably shortened when the transformation temperature is exceeded. In the interior of the hollow-frustumshaped heat coupler 51, this unlocking mechanism 41 is fastened to a frusto-conical heat absorber 59 which is held in a fuze-fast manner and is in particular axially supported. In the rearward (related to the flight direction of a projectile with this fuze 3) extension, the puncture needle 16 is fastened to the unlocking mechanism 41.

By reason of launch-occasioned acceleration of the fuze 3, there is effected not only a partial arming of the blasting cap rotor 14 (for example by means of a first safety element 11 in accordance with Figure 2/Figure 3; not shown in more detail in the case of Figure 8/Figure 9), but (as shown in Figure 8) also a rearward movement of the heat coupler 51 along with consequential breakage of the shear element 50 (for instance designed as a shear bolt or as a shear ring). In Figure 8 the heat coupler 51 is located with its inner surface on the outer surface of the heat absorber 59 and, as a result of the axial displacement relative to the fuze inner walling 53, frees or uncovers the air passage openings 54 as well as a cone-shaped guide duct 30. At the same time, as a result of the launch acceleration, the frusto-conical flow barrier 57 is shifted back, in order also to free, at its outer surface, a cone-shaped guide duct 30 for the air inlet opening 56. In the shifted back position, the flow barrier 57 butts with its base surface 60 (with interpolation of a thermal insulating layer 61) against the end surface of the heat coupler 51 and urges the coupler 51 in dynamic-pressure-impinged manner, with even more pressure against the conical heat absorber 59.

In the safe position in accordance with Figure 7, the cone-jacket-shaped air space about the heat absorber 59 represents a thermal insulating layer which preventsthe heat absorber 59 from heating up as a result of environmental heating; for instance in the case of a dump fire; but in Figure 8 the operationally-prepared second safety element 42 ensures, as a result of the insulating layer 61 between the flow barrier 57 and the heat coupler 51 (as well as through the cone-jacket-shaped air gap along the fuze inner walling 53) that mere environmental heating - for instance in the event of a dump fire - does not lead to critical heating of the heat absorber 59 and thus to the response of the unlocking mechanism 41.Only the dynamic-pressure of air entering under free flight conditions, in other words the air flow along the cone outer walling 52, leads to heating the heat coupler 51 and thus to the heat absorber 59 being heated and emission of this heat to the unlocking mechanism 41. When, after a specific free-flight interval, the shape-recollection transformation temperature of the memory material of this rod-shaped unlocking mechanism 41 is exceeded, the transformation crystal forces are released with the effect of a distinct axial shortening of the unlocking mechanism 41; this leads to the puncture needle 16 being lifted out of the bursting cap rotor 14 which is additionally swung out of the ignition chain; the rotor is now swung by centrifugal force or under the influence of a swivel lever, into the ignition line, whereby the fuze 3 is made live, as described above.Upon impact of the fuze tip 55 on a target, the flow barrier 57, the heat coupler 51, the heat absorber 59 and the unlocking mechanism 41 are pushed back axially in the fuze 3, so that the puncture needle 16 fastened to the unlocking mechanism 41 now triggers or punctures the bursting cap swung into the line of the ignition action chain.

If the fuze 3 shown in Figure 7/Figure 8 is also intended to be used for self-destructor ammunition, which has to be made harmless by self-destruction after a certain interval of time after launching, for example, in the event of a missed target, it is advantageous to thermally connect a further constructional element having shape recollection power in series with the memory component part in the form ofthe unlocking mechanism 41.

In accordance with a preferred exemplified embodiment within the framework of the present invention, for this purpose, as is shown in detail in Figure 9, a needle holder 37' communicating mechanically as well as thermally with the unlocking mechanism 41 is tightened in the unlocking position of the ignition cap carrier (for example of the rotor 14) with a preferably conical supporting surface 62 against a further heat absorber 63. This ensures that a heat transfer takes place from the heat coupler 51 (heated up under free flight by the air flow, by way of the heat absorber 59, the unlocking mechanism 41, the needle holder 37' and the conical supporting surface 62 thereof) to a further heat absorber 63, which is thermally coupled with an unlocking member 64 which also consists of memory material.In this case member 64 is a U-shaped or O-shaped component part similar to the unlocking mechanism 41 shown in Figure 2 .... Figure 4, which, here, is prepared in such a way that the crystal forces released when the transformation temperature is exceeded lead to a widening of the clear or open inside diameter.

In the locked position (see Figure 7 and Figure 8), the unlocking member 64, by reason of its small clear or open inside diameter, axially supports a holder sleeve 65 for a self-destructor initiating needle 66. Needle 66 can be driven into the bursting cap 8 parallel to the puncture needle 16, against the force provided by a tensioned propulsion spring 67; the spring 67 is axially supported in a fuze-fast manner in the interior of the heat absorber 63.

If the self-destructor unlocking member 64 is heated up (by way of the needle holder 37 and the heat absorber 63, in a manner caused by free flight flow) until the transformation temperature is exceeded, the inside clear diameter of member 64 is enlarged and thereby passes out of engagement with a notch or (as shown in Figure 9) with a collar on the holder sleeve 65, so that the spring 67 is released and drives the self-destructor needle 66 into the bursting cap 8, in order to make the projectile equipped with the fuze harmless by self-destruction in flight.

As a result of this thermal series connection of the two unlocking elements 41,65 it is ensured that the self-destructor mechanism can then, and only then, come into operation when, caused by launch acceleration, the second safety element 42 has been made operationally ready and, caused by free flight, has armed the ignition chain, but on the other hand, after a constructionally-predetermined flight time, still no hit-occasioned fuze triggering has been effected. This further flight interval of time after traversing the in-front-of-the barrel safety region, in other words after arming of the fuze 3, is constructionally predeterminable within wide limits by way of the heat coupling from the first heated memory element to the memory element heating up thereafter and by the heat shaping characteristic of the second memory element in the form of the unlocking member 64.

Within the scope of the invention, the use, in accordance with the invention, of a functional part made of memory material for unlocking the second safety element and/or of a self-destruction mechanism, (possibly for arming the fuze or respectively for initiating self-destruction) can however also be effected in the case of projectiles whose construction and/or lowfree-flight speed makes heating a specific region of a safety mechanism accommodated in the projectile nose non-realisable, for instance, in the case of an armour-piercing hollow-charge ammunition with afterburner. Here the fuze is arranged behind the explosive charge in the projectile, so that the thermal influencing for unlocking the second safety element can be effected from the combustion chamber of the afterburner arranged therebehind, for instance in a tail unit, during the free-flight phase of the projectile.

Claims (18)

1. A safety mechanism for a projectile fuze comprising a first safety element, for partial arming under the influence of launch acceleration, and a second safety element for arming a bursting-cap booster-charge ignition chain of the fuze, which mechanism has an unlocking mechanism which, after launch, is, preferably, exposed to the air dynamic-pressure friction heat in free flight of a projectile having a fuze with the safety mechanism, characterised in that the unlocking mechanism has a constructional element of a material which, when a specific temperature is exceeded, substantially suddenly experiences a specific predetermined change in shape.

2. A safety mechanism as claimed in claim 1, characterised in that the constructional element is made from a material having shape recollection power (for example, so-called "memory metal") which, as a result of its transformation temperature being exceeded, frees shape-change crystal-lattice forces.

3. A safety mechanism as claimed in one of the preceding claims, characterised in that the constructional element comprises a radial shrink ring which in use is supported in the direction of the fuze longitudinal axis by an unlocking spring against a supporting shoulder.

4. A safety mechanism as claimed in claim 1 or 2, characterised in that the constructional element comprises an axial shrink plunger which is axially supported in the front part of the fuze by an unlocking spring.

5. A safety mechanism as claimed in claim 1 or 2, characterised in that the constructional element comprises a tie rod or bar which is suspended in the front part of the fuze.

6. A safety mechanism as claimed in one of the preceding claims, characterised in that the constructional element is arranged in the region of dynamicpressure air-flow guide ducts which are formed in the front part of the fuze and which are closed in the safe position of the fuze and, caused by launch acceleration, can be freed or opened by the first safety element.

7. A safety mechanism as claimed in claim 6, characterised in that the guide ducts open out in the base surface of a front part which is axially advanceable on the fuze.

8. A safety mechanism as claimed in one of the preceding claims, characterised in that at least one closure element (for example heat coupler 51; flow barrier 57) is provided in the front part of the fuze and is capable of freeing, on launch acceleration, dynamic-pressure air-flow guide ducts or said guide ducts.

9. A safety mechanism as claimed in claim 8, characterised in that the at least one closure element is a heat coupler which, caused by launch acceleration, ensures the thermal coupling between dynamic-pressure air-flow guide ducts and the unlocking mechanism and is provided in the front part of the fuze.

10. A safety mechanism as claimed in one of the preceding claims, characterised in that a selfdestruction unlocking member is provided, which, when a specifically predeterminable crystal-lattice transformation temperature is exceeded, experiences a predetermined unlocking shape change and can be coupled thermally with the constructional element of the unlocking mechanism of the second safety element.

11. A projectile fuze including a safety mechanism as claimed in any one of the preceding claims.

12. A fuze substantially as herein described with reference to figures 1 to 4, orwhen modified substantially as herein described with reference to figure 5, or 6, or 7 to 9 of the accompanying drawings.

13. A safety mechanism as claimed in claim 1 substantially as herein described with reference to figures 2 to 4, or 5, or 6, or 7 to 9 of the accompanying drawings.

14. A projectile including a fuze as claimed in claim 11 or claim 12.

15. A safety mechanism for a projectile fuze comprising a first safety element, for partial arming under the influence of launch acceleration, and a second safety element for arming a burster-cap booster-charge ignition chain of the fuze, which mechanism has an unlocking mechanism which, after launch, is exposed to heat in free flight of a projectile having a fuze with the safety mechanism, characterised in the provision of a constructional element of a material which, when a specific temperature is exceeded, substantially suddenly experiences a specific predetermined change in shape, said constructional element being part of a selfdestruction mechanism.

16. A safety mechanism for a projectile fuze comprising a first safety element, for partial arming under the influence of launch acceleration, and a second safety element for arming a bursting-cap booster-charge ignition chain of the fuze, which mechanism has an unlocking mechanism which is heated during and because of free flight of a projectile having a fuze with the safety mechanism, characterised in that the unlocking mechanism has a constructional element of a material which, when a specific temperature is exceeded, substantially suddenly experiences a specific predetermined change in shape.

17. Asafetymechanismfora projectilefuze comprising a first safety element, for partial arming under the influence of launch acceleration, and a second safety element for arming a bursting-cap booster-charge ignition chain of the fuze, which mechanism has an unlocking mechanism which, after launch, is, exposed to heat occurring in free flight of a projectile having a fuze with the safety mechanism, said heat being from an afterburner in the projectile and in which the unlocking mechanism has a constructional element of a material which, when a specific temperature is exceeded, substantially suddenly experiences a specific predetermined change in shape.

18. A projectile including a safety mechanism as claimed in Claim 15 or Claim 17.