Mechanical self-percussion fuze for a non-gyrating ammunition

A mechanical self-percussion fuze for a non-gyrating ammunition includes a firing pin disposed along a central axis and a primer provided in a primer holder. The primer holder is movable about an axis of rotation that is parallel and off-centered with respect to the central axis between a storage position in which the primer is off-centered with respect to the firing pin and an armed position in which the primer is aligned with the firing pin and safety devices coupled to the primer holder in order to keep the fuze in a safe state until at least two mutually independent physical phenomena linked to the firing of the ammunition occur. The fuze has a wind turbine designed to be driven in rotation by the relative movement of the air during the flight of the ammunition and to transmit this rotational movement to the primer holder only after the safety devices have been removed.

TECHNICAL FIELD

The present invention relates to a mechanical self-percussion fuze for a non-gyratory ammunition, said fuze comprising a fuze body extending along a central axis between a distal end provided with a cap and a proximal end provided with a connector to assemble said fuze to an ammunition, said fuze comprising a firing pin disposed along said central axis, a primer provided in a primer holder arranged to be rotatably movable about an axis of rotation, parallel and off-centered with respect to said central axis between at least one storage position, in which said primer is off-centered with respect to said firing pin and an armed position, in which said primer is aligned with said firing pin and the pyrotechnical chain of the ammunition, and a mechanism provided with at least two safety devices coupled to said primer holder to keep said fuze in a safe state until at least two mutually independent physical phenomena linked to the firing of said round occur.

BACKGROUND

Mechanical fuzes for rounds are mechanisms having the main function of ensuring rounds are kept safe in their different life phases (storage, handling, transport, manoeuvres in operation zones, loading the ammunition and firing), then ensuring the operation of these rounds as soon as the required conditions are met, and this by way of purely mechanical safety devices. More specifically, at the time of firing the ammunition, the safety of the ammunition must be guaranteed from the time when it is loaded into a weapon to be fired, and up to a distance called “safety distance”, beyond which the fired round can no longer have any damaging effect on the personnel having used it. The fuze must further enable the operation of the ammunition (moving from the safe state to the armed state) from a distance called “certain weapon distance”. Yet, weapons are provided to fire different loads, making it possible to reach targets which are farther away or closer. These loads are characterised, among others, by a quicker or slower linear speed of the ammunition.

The development of safety standards applicable to rounds has shown the requirement of a dual storage safety device, which must only be able to be removed through the occurrence of two physical phenomena linked to the firing of the ammunition, but which are mutually independent (Stanag 4187). The effect of the linear acceleration of the ammunition linked to starting firing constitutes the first physical phenomenon which can be used to remove a first storage safety device. On weapons operating with rotation of the ammunition, the effect of the centrifugal force of the gyrating ammunition linked to the rotation speed in flight constitutes the second physical phenomenon which can be used to remove a second storage safety device. But, on weapons operating without rotation of the ammunition, therefore not generating the centrifugal force, it is particularly difficult to obtain a second storage safety device independent of the linear acceleration of the non-gyratory ammunition linked to starting firing.

Current mechanical solutions are of different types: implementation of a finger for the presence of the ammunition in the gun, detection of the flight deceleration of the ammunition or detection of the gas pressure in the gun. These solutions all have disadvantages linked to their implementation, their reliability, even their feasibility according to the type of fuze in question. Some of these solutions do not meet the standards on the independence of events to enable arming with the ammunition. Furthermore, these solutions are not satisfactory, given that they do not integrate an adaptive function which enables them to ensure a certain arming distance and a safety distance, which are fixed or constant, whatever the load at which the ammunition is fired.

Other mechanical solutions implement a wind turbine to utilise the effect of the aerodynamic force linked to the relative movement of the air, when the ammunition is in flight and achieve the second storage safety device. Publication FR 2 927 695 A1 describes one of these solutions, which is used to release a lock. However, this solution integrates no adaptive function. Consequently, the greater the load is, the quicker the lock will be released, and the shorter the certain and safety arming distances will be. There is, in this case, a high risk for personnel on the ground, if the fired round explodes at a short distance.

Publication WO 03/095933 A1 describes another solution of a fuze equipped with a wind turbine also used to release a safety lock. Upon starting firing, the wind turbine is unscrewed, rises, and releases the primer holder which can rotate and align the firing pin on the primer. As in the preceding example, this solution integrates no adaptive function. Publication U.S. Pat. No. 1,916,244 A describes a similar device.

Publication U.S. Pat. No. 2,644,398 A describes an electrical fuze comprising a wind turbine arranged to drive a generator provided to supply the detonator of the electrical fuze with current, and a friction clutch coupled to a clock. This old technology no longer meets the standards in force, and is very far away from the invention.

SUMMARY OF THE DISCLOSURE

The present invention aims to overcome these disadvantages by proposing a fuze provided with an exclusively mechanical, reliable and efficient solution for keeping safe for a non-gyratory ammunition, which utilises the relative movement of the air with respect to the ammunition during its flight as a second physical phenomenon independent from the first physical phenomenon linked to the linear acceleration upon starting firing, this solution being applicable whatever the type of fuze, and having an adaptive function making it possible to guarantee a certain arming distance and a constant safety distance, whatever the load at which the ammunition is fired.

For this purpose, the invention relates to a fuze of the type indicated in the preamble, characterised in that it comprises a wind turbine arranged to be driven in rotation by the relative movement of the air with respect to the ammunition during its flight, and to generate the rotational torque necessary for the operation of said mechanism, which regulates the time necessary for the fuze to move from the secure state to an armed state, thus guaranteeing an expected safety distance, whatever the load with which the ammunition is fired.

The invention is advantageous in that it proposes the use of the relative movement of the air by a wind turbine to achieve the second storage security lock in the sense of the standard Stanag 4187 for a weapon which does not generate a centrifugal effect.

In a preferred embodiment of the invention, said wind turbine is provided with a drive shaft, combined with the central axis of said fuze body and secured to said firing pin. Said turbine advantageously comprises blades which extend radially from a central zone, and the cap of said fuze comprises at least one axial air inlet orifice to the right of said central zone and several radial air flow orifices at the outlet of said blades to cause a rotation of said wind turbine in a direction of rotation.

Preferably, said fuze comprises a locking system arranged to, in the locked position, prevent the rotation of the wind turbine and keep the fuze in a safe state before firing the ammunition, and in the unlocked position, enabling the rotation of the wind turbine after firing the ammunition.

In the preferred embodiment of the invention, said locking system comprises an inertial socket associated with a return member, said inertial socket being slidingly mounted in the central axis of said fuze body, to be movable between said locked position, in which said inertial socket is subjected by said return member in a high position, and rotatably blocks said wind turbine, and said unlocked position, in which said inertial socket is moved into a low position under the effect of the linear acceleration upon starting firing, constrains said return member and releases the rotation of said wind turbine.

Said locking system can further comprise at least one axial indexing finger provided on one of the parts of said wind turbine or of said inertial socket and an axial orifice provided on the other of the parts of said inertial socket or of said wind turbine, said axial indexing finger being housed in said axial orifice, when said inertial socket is in high position in said locked position, to rotatably block said wind turbine.

Said locking system can also comprise at least one radial guiding finger, provided on one of the parts of said fuze body or of said inertial socket, and an axial groove provided on the other of the parts of said inertial socket or of said fuze body, said radial guiding finger being housed in said axial groove, when said inertial socket is in high position in said locked position, to rotatably block said inertial socket.

Said locking system can finally comprise a blocking element arranged to keep said inertial socket in a low position in said unlocked position. Said blocking element can comprise at least one ball in a lateral housing provided in one of the parts of said inertial socket or of said fuze body, and a lateral opening provided in the other of the parts of said fuze body or of said inertial socket, said ball being arranged to be moved between said lateral housing and said lateral opening when they face one another.

In the preferred embodiment of the invention, said fuze comprises at least one inertial lock arranged to link said primer holder to said fuze body, and keep said primer holder in the storage position, said inertial lock forming part of the other of said safety devices, which has the advantage of reacting to the linear acceleration upon starting firing.

Said fuze advantageously comprises at least one locking member arranged to link said primer holder to said fuze body and keep said primer holder in the storage position, said locking member forming part of one of said safety devices which has the advantage of reacting to the linear speed of the ammunition during its flight. Said locking member can comprise a ball in said primer holder, encased with a hemispherical footprint of said fuze body.

Advantageously, said fuze comprises a rotor superposed to said primer holder, and the drive shaft of said wind turbine comprises a motor pinion arranged to mesh a receiver pinion of said rotor and drive it in rotation about said axis of rotation.

Preferably, said rotor comprises a hemispherical footprint arranged to be positioned facing the ball in said primer holder and enable it to rise to release said primer holder.

Said primer holder and said rotor are advantageously coupled to one another by a coupling device on a determined angular sector, during which the rotation of said rotor drives the rotation of said primer holder moving from said storage position to said armed position. Said coupling device comprises a coupling finger provided on one of the parts of said primer holder or of said rotor, and a circular oblong space on the other of the parts of said rotor or of said primer holder. Said rotor is further provided to mesh a chronometric gear train arranged to regulate the movement of said rotor.

Advantageously, said fuze comprises a collar, secured to the drive shaft of said wind turbine, arranged to break under the effect of an impact transmitted by said cap and enable said firing pin to descend and ram said primer and initiate the pyrotechnical chain, leading to the destruction of the ammunition.

DETAILED DESCRIPTION

In the embodiments illustrated, identical elements or parts have the same reference numbers. Furthermore, the terms which have a relative meaning, such as vertical, horizontal, right, left, front, rear, above, below, top part, bottom part, etc. must be interpreted under the conditions of representation of the invention according to the FIGURES. Moreover, the geometric positions indicated in the description and the claims, such as “perpendicular”, “parallel”, “symmetrical” are not limited in the strict sense defined in geometry, but extend to geometric positions which are close, i.e. which accept a certain tolerance in the technical field in question, without impact on the result obtained. This tolerance is, in particular, introduced by the adverb “substantially”, without this term necessarily being repeated before each adjective.

The invention particularly relates to non-gyratory ammunitions, which are rounds of extended shape along a central axis, being moved without rotating on themselves and are stabilised by feathering. Below in the description, the generic term “round” is used, which applies to any type of rounds, projectiles, rockets, and similar. The ammunition (not represented) is not described as such, as it does not form part of the invention. It mainly contains explosive loads.

The invention more specifically relates to the fuze which is assembled at the top of the ammunition. The fuze contains, in a known manner, a mechanical firing pin and a percussion primer containing a pyrotechnical component such as a detonator. It makes it possible, during the impact of the ammunition on a target, to initiate a polytechnical chain which will activate the explosive loads and cause the destruction of the ammunition.

In reference to the FIGURES, the mechanical self-percussion fuze1for a non-gyratory ammunition according to the invention comprises a substantially truncated fuze body2, extending along a central axis A. The fuze body2is constituted of a base3provided with a connector4to be assembled to the ammunition and with a central housing5passing through to receive the top part of the ammunition and connect the explosive loads to the percussion primer. The fuze body2further comprises a cap holder6surmounted by a cap7able to be deformed in case of impact. The cap7is linked to the cap holder6by radial pins8through spaces9provided in the cap7, or by any other equivalent assembly means.

The fuze1comprises a mechanical10with several safety levels to keep the ammunition in a safe state, until at least two mutually independent phenomena linked to the firing of the ammunition occur. The mechanism10is represented inFIG.3and comprises, from top to bottom:—a wind turbine11provided with a drive shaft12combined with the central axis A of the fuze,an inertial socket13disposed under the wind turbine11,a firing pin14secured to the drive shaft12, and disposed at the opposite end of the wind turbine11,a rotor15driven in rotation by the wind turbine11about an axis of rotation B, off-centered and parallel to the central axis A,a chronometric gear train16to regulate the movement of the rotor15,a primer holder17disposed under the rotor15, and arranged to be driven in rotation by the rotor15about the axis of rotation B, andan inertial lock18disposed on an axis C parallel to the axis of rotation B and housed in a lateral notch19of the rotor15and of the primer holder17.

The top part of the mechanism10is mounted in the cap holder6. The cap holder6comprises a central bore20of axis combined with the central axis A of the fuze, arranged to guide in axial rotation and in axial translation, the drive shaft12of the wind turbine11. It also comprises an annular housing21under the wind turbine11to receive the inertial socket13. The low part of the mechanism10is mounted in a safety device holder22, itself mounted in the base3of the fuze.

The wind turbine11, also called turbine11below, extends perpendicularly to the drive shaft12and comprises blades23which extend radially from a central zone24combined with the drive shaft12. The blades23have a curved shape to generate a rotation of the turbine in the direction of the arrow R (FIG.3). The central zone24has a substantially conic shape, provided with a top centred on the central axis A and oriented in the direction of the end of the cap7, forming the distal end25of the fuze1. The cap7comprises an axial air inlet orifice26to the right of the central zone24of the turbine11and several radial air flow orifices27at the outlet of the blades23. The drive shaft12of the turbine11comprises a toothed pinion, called motor pinion28, arranged to mesh a receiver pinion29secured to the rotor15of the primer holder17. Naturally, any other technically equivalent wind turbine shape can be suitable.

More specifically, in reference toFIGS.4and5, the fuze1comprises a locking system30arranged to, in the locked position, prevent the rotation of the turbine11when the fuze1is in the storage position before firing the ammunition, and in the unlocked position, enable the rotation of the turbine11after firing the ammunition. This locking system30comprises the inertial socket13, which is axially slidingly mounted in the annular housing21provided in the cap holder6to be movable between the locked position and the unlocked position. It comprises a return member31, such as a helical spring, without this example being limiting, disposed in the annular housing21of the cap holder6under the inertial socket13to constrain it in the locked position, in which it is in the high position flattened against the turbine11, which turbine11is in high abutment against the cap7. The locking system30further comprises at least one axial indexing finger32provided on the body of the turbine11and projecting inside at least one axial orifice33provided in the inertial socket13to prevent the wind turbine11to rotate in this locked position. It also comprises a radial guiding finger34provided in the cap holder6and opening into an axial groove35of the inertial socket13to prevent the inertial socket13to rotate. Naturally, the different solutions described and illustrated in reference to the FIGURES are non-limiting examples of embodiments, and any other technical solution fulfilling the same blocking function in rotation can be suitable.

Under the effect of the linear acceleration, upon starting firing, the inertial socket13is axially retracted and moves from the locked position to the unlocked position, in which it is in the low position, constrains the return member31and releases the turbine11which can rotate. The locking system30further comprises a blocking element36arranged to block the inertial socket13in the low position when it is in the unlocked position. This blocking element36comprises a ball37provided in a lateral housing38of the socket and a lateral opening39provided in the cap holder6. When the inertial socket13is retracted, it drives the ball37with it, and when the ball37arrives facing the lateral housing38, it is housed there and prevents the socket from rising. Naturally, any other technical solution fulfilling the same blocking function in the locked position can be suitable.

The wind turbine11thus released is kept in its initial high position by a collar40projecting radially from its drive shaft12which bears on the cap holder6, also keeping the firing pin14in the high position.

The primer holder17has a safety function and makes it possible to keep a primer17′ off-centered or misaligned with respect to the pyrotechnical chain and to the firing pin14. The axis of the pyrotechnical chain is combined with the central axis A. The primer holder17is associated with safety devices provided in the mechanism10to keep the ammunition in a safe state during phases of storing, transporting, handling and loading the ammunition in a weapon until starting firing, and even after starting firing over a predetermined safety distance. This position of the primer holder17is called a storage position. It is only after having detected and reacted to at least two ballistic firing events (linear acceleration of the ammunition and relative movement of the air with respect to the ammunition) that the safety devices provided in the mechanism10enable the primer holder17to be moved to align the primer17′ with the firing pin14and the pyrotechnical chain. This position of the primer holder is called an armed position.

In reference toFIGS.2and6, the primer holder17is kept in the storage position by two independent safety elements: the inertial lock18of axis C on the one hand, and a locking member41on the other hand. The principle of an inertial lock18is commonly used in the field of rounds. In the example represented inFIGS.2and3, the inertial lock18comprises an inner mass50, subjected in a high position by an inner spring51, a ball52radially housed between the inertial lock18and the inner mass50, and an outer spring54to subject the inertial lock18in the high position corresponding to the storage position. Upon starting firing, under the effect of acceleration, the inner mass50descends and compresses the inner spring51. The inner mass50being in the low position, the ball52is removed in a peripheral clearance53of the inner mass50and releases the inertial lock18. Under the effect of acceleration, the inertial lock18descends, compresses the outer spring54and unlocks the primer holder17. At the end of acceleration, the inner mass50rises and locks the inertial lock18in the low position by way of the ball52which is radially housed between the inertial lock18and a radial clearance55provided in the safety device holder22. Any other technically equivalent inertial means can be suitable.

In the example illustrated inFIGS.6to8, the locking member41is arranged to link the primer holder17to the safety device holder22, itself linked to the fuze body2. It comprises a ball42provided in a passing through axial housing43provided in the primer holder17and encased with a hemispherical footprint44provided in the safety device holder22. Any other technically equivalent locking means can be suitable.

Upon starting firing, and under the effect of linear acceleration of the ammunition, the wind turbine11is released and the inertial lock18releases the primer holder17and simultaneously, the rotor15. However, the primer holder17remains fixed, in the storage position, until the rotor15driven by the turbine11travels a determined angular course, and that a hemispherical footprint45provided in the rotor15is positioned facing the ball42housed in the primer holder17, to enable it to rise and release the primer holder17. Naturally, any other technically equivalent indexing means can be suitable.

The primer holder17is then coupled to the rotor15by a coupling device46, such that the rotation of the rotor15drives the rotation of the primer holder17which moves from the storage position (FIG.6) to the armed position (FIG.8). In the example illustrated inFIGS.12to14, the coupling device46comprises a coupling finger47provided on the primer holder17and a circular oblong space48provided on the rotor15. The inverse configuration could also be suitable, in which the coupling finger is on the rotor and the circular oblong space is on the primer holder. The coupling finger47is arranged to circulate in the circular oblong space48on the determined angular sector during which the rotation of the rotor15does not drive the rotation of the primer holder17. When the space48abuts against the coupling finger47, then the primer holder17is coupled to the rotor15and can be driven in rotation. Naturally, any other technically equivalent coupling means can be suitable.

The operation of the fuze1according to the invention is described below.

Storage Position

In the storage position, such as represented inFIGS.2to4,6and12, the fuze1assembled to an ammunition is in a safe state, since the primer17′ integrated in the primer holder17is misaligned from the pyrotechnical chain and from the firing pin14. The primer holder17constitutes the switch of the pyrotechnical chain, and is itself kept in a misaligned position by the two independent safety elements:the inertial lock18,the locking member41which links the primer holder17to the safety device holder22. As the rotor15does not rotate, the ball42of the locking member41is not released from the hemispherical footprint44of the safety device holder22, and the primer holder17cannot move. The rotor15is kept in the storage position by the axis of the firing pin14with which it meshes and which corresponds to the drive shaft12of the wind turbine11. As the drive shaft12is immovable, the mechanism10cannot initiate any movement. The wind turbine11is itself kept fixed over two degrees of freedom: in axial translation, by the return member31of the locking system30which keeps it flattened towards the top against the cap11, via the inertial socket13, and in rotation by the axial indexing finger32housed in the corresponding axial orifice33of the inertial socket13, itself rotatably blocked via the radial guiding finger34.
Starting Firing

Upon starting firing, such as illustrated inFIG.5, under the effect of linear acceleration of the ammunition, the inertial lock18is retracted and releases the primer holder17and the rotor15. Simultaneously, the inertial socket13of the locking system30of the turbine is moved towards the bottom in the annular housing21of the cap holder6. The ball37of the blocking element36, located in the lateral housing38of the inertial socket13descends at the same time, and, as soon as it meets the lateral opening39provided in the cap holder6, is housed there. When the linear acceleration stops, the ball37acts like a lock and blocks the raising of the inertial socket13. The wind turbine11is released and driven in rotation by the airflow generated by the flight of the ammunition.

In Flight to the Armed Position

The rotation of the wind turbine11creates the motor energy of the rotor15and transmits it to it via the drive shaft12of the turbine with which it meshes. The chronometric gear train16regulates the rotation movement of the rotor15. The primer holder17is still kept in the storage position by the action of the ball42of the locking member41, positioned in the hemispherical footprint44of the safety device holder22(FIGS.6and12). When the rotor15has travelled a sufficient angular sector, which is determined by the abutment of the coupling finger47of the coupling device46, secured to the primer holder17, with the corresponding end of the circular oblong space48of the rotor15, the hemispherical footprint45provided in the rotor15appears above the ball42(FIGS.7and13). The ball42is thus free to rise in this footprint. The primer holder17is released from its connection with the safety device holder22and is now driven in rotation by the rotor15. It is the wind turbine11which drives the final movement via its drive shaft12which meshes with the rotor15. The drive shaft12brings the primer holder17into the armed position, the latter now being linked to the rotor15by way of the coupling finger47and of the ball42. In the meantime, the rotor15is no longer connected to the chronometric gear train16, and the alignment of the primer holder16is instantaneous (FIGS.8and14).

Upon Impact on a Target

The drive shaft12of the turbine11, which is found to be combined with the firing pin14, faces the primer17′ which contains the detonator of the pyrotechnical chain. During the impact of the ammunition on a target, the deformation of the cap7makes the entire wind turbine11descend. The collar40which keeps the drive shaft12from the turbine and from the firing pin14at its initial height, is sized in order to remain integrated during the storage, starting firing and flight of the ammunition phases, but not to resist an impact on a target. Under the effect of the impact transmitted by the cap7, the collar40breaks and enables the firing pin14to descend to ram the primer17′ and initiate the pyrotechnical chain, leading to the destruction of the ammunition by explosion.

It clearly appears from the description, that the invention makes it possible to achieve the aims set. In particular, the relative movement of the air during the flight of the ammunition generates the motor torque necessary for the alignment of the primer holder17with the firing pin14and the pyrotechnical chain. The rotation torque transmitted by the wind turbine11is directly linked to the movement speed of the ammunition. Thus, when the speed increases, the torque increases, and the alignment time reduces. This kinematic chain enables the mechanism10to have the same safety distance and the same certain arming distance, whatever the load at which the ammunition is fired. Furthermore, the drive shaft12of the wind turbine11fulfils three functions: keeping the mechanism10in the safety position, transmission of the rotation torque to the primer holder17and percussion of the primer17′.

The present invention is naturally not limited to the examples of embodiments described, but extends to any modification and variant which are clear for a person skilled in the art by remaining within the limit of the accompanying claims. Furthermore, the invention extends to any other non-gyratory ammunition or projectile, as an example, illumination rounds, etc.