Abstract:
A fuse plug pyrotechnic firing device includes a body, a pyrotechnic train, firing pin and a driving device. The body has an axis and a bore disposed along the axis. The pyrotechnic train is disposed along the axis and includes an upper part and a lower part. The firing pin has a firing pin axis and is disposed within the bore between the upper part and the lower part. The firing pin is also disposed to ignite the lower part. The driving device is coupled to the firing pin and to the upper part. The driving device drives the firing pin to move along the firing pin axis and to ignite the lower part, the firing pin rotating about the firing pin axis under pressure of gases generated by the ignition of the lower part. As a result, safe and effective operation of the fuse plug pyrotechnic firing device is ensured.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the technical area of pyrotechnic charge firing devices of the fuse plug type, notably for hand grenades, that include a pyrotechnic circuit detonated conventionally by a firing pin operated by the movement of a handle associated with a cotter pin. 
     This firing device must meet the requirements of safety, reliability and low production cost. In particular, for safety during storage and transit, the pyrotechnic train must be configured so that it can be disabled. 
     This device must also allow the user to select one of the following three firing modes for the pyrotechnic charge: delay, impact mode, or an impact-delay mode. 
     It must be possible for all the component parts to be manufactured using an automated production process. Their assembly should permit the use of robotic production equipment. In this technical field a number of designs have been proposed. 
     French Patent FR 2.517.048 discloses a fuse plug for a hand grenade having three modes of operation with storage and operational safeties that interrupt the pyrotechnic train and lock the firing pins. This plug has two pyrotechnic trains having one part in common, one train being related to one firing pin specifically for delayed operation and the other train working with a second firing pin specifically for impact operation. The grenade operating mode is selected using an outer ring fitted with a stud against which a plate turns under rotary motion from a timer. This plate also determines the alignment of the pyrotechnic train which results after the cotter pin is removed and a delay is determined by the timer. 
     This fuse plug has several disadvantages. In particular, it incorporates two principal non-aligned firing pins that collaborate with two pyrotechnic trains, leading to complex manufacture and operation. 
     Another disadvantage lies in the fact that the alignment of the pyrotechnic train and the arming of the operating modes both depend on a timer, which can have an adverse effect on safety and on the functional reliability of such a fuse plug. A fire, kinetic energy impact or nearby explosion can lead to the accidental ejection of the cotter pin followed by rotation of the plate, leading to an irreversible alignment of the pyrotechnic train. 
     In addition, the impact-delay function is equivalent to self-destruction of the grenade in the absence of percussion, and not to a delay function triggered by the impact function. 
     French Patent FR 2.458.790 discloses a multi-purpose fuse plug with a throwing safety. This plug, which is very similar to that described in the previous patent, can operate in four different ways, and includes two independent, principal firing pins each corresponding to different modes of operation, and a selector having two rotating discs controlled by a timer movement in storage and operation of the throwing safety. This fuse plug also includes an impact detector coupled to one of the firing pins which is configured in an armed position directly after release of the handle, which necessitates the throwing safety. 
     Most of the disadvantages mentioned above are also found here. Notably, the use of a timer mechanism, which may become faulty, to control the alignment of the pyrotechnic train, as well as to ensure ignition safety, is disadvantageous. 
     With regard to the impact-delay mode, the delay function is not triggered by the impact function. 
     French Patent FR 2.682.471 also discloses a storage safety for a fuse plug that interrupts the pyrotechnic train. This interruption is obtained by a pivoting element with a radial orifice positioned between a delay module and a primer composition. Rotation of this part, caused indirectly by the release of the handle, automatically aligns the pyrotechnic train. 
     French Patent FR 2.465.189 also shows a fuse plug for a grenade that includes a pyrotechnic train interrupted by a rotating device operated by a delay mechanism involving the release of glass beads, which allows definitive alignment of the train after a predetermined time interval following initiation of the train. 
     The operating principle of the pyrotechnic train interruptions described in these two patents and in the patents mentioned earlier have the major drawback of resulting in an automatic and irreversible alignment of the train during storage in a hostile environment. 
     Moreover, if any single component essential to locking should fail, which could, for example, occur by accident with no persons present (due to fire, explosion or impact), the firing procedure is inevitably initiated. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to counter the disadvantages mentioned above by proposing a device for firing a pyrotechnic charge of the ignition plug type applicable notably, but not exclusively, to hand grenades, giving enhanced safety during storage, transport and utilization, high operational reliability, low manufacturing and assembly costs and being perfectly suitable for industrial mass-production. 
     Another purpose of the invention is to ensure safety during storage and transport in fully primed sections by interrupting the pyrotechnic train. 
     Another objective of the invention is to provide a fuse plug that is directly adaptable to different types of pyrotechnic device and more particularly to several types of hand grenade (offensive, defensive, tear gas, smoke or practice), while retaining conventional means of initiation such as the combination of handle and cotter pin. 
     Another aim is to allow the user to select, on the fuse plug, one of the three following operating modes of the pyrotechnic charge:delay mode, impact mode or impact-delay mode. 
     To this end, the subject of the invention is a device for firing a pyrotechnic charge, of the fuse plug type notably for a hand grenade, comprising, accommodated in an axial bore made in the body of the plug, a pyrotechnic train in two parts upper and lower, the lower part being initiated by an axial firing pin positioned between the two parts of the train and associated with means of operation collaborating with a means of locking. This device has mechanical means for operating the firing pin, which are introduced between the upper part of the train and the pin in order to displace the firing pin axially and in rotation about its axis under the pressure of gas generated by the initiation of the upper part. 
     The mechanical means of operating the firing pin preferably collaborate with a guide device in a channel in the bore of the plug body. 
     The means of operating the hollow cylindrical firing pin preferably consist of a spring and a piston sliding axially with respect to the central bore, housed in a fixed internal cylindrical casing containing the upper part of the pyrotechnic train, this casing being partially fitted into the firing pin. 
     The means of locking the firing pin to the internal casing may consist of a ball projecting into a recess in the casing and allowing the firing pin to move from an initial safe position, in which the piston traps the ball in a circular groove inside the firing pin, to an armed position, following axial displacement of the piston, in which the ball positioned opposite a circular groove on the outside of the piston escapes from the circular groove inside the firing pin and releases said pin. 
     The guide system preferably consists of a ball projecting into the central bore engaged in the channel made on the outer wall of the firing pin, this channel comprising a longitudinal part extended by a spiral part, so as to accomplish an initial axial displacement of the firing pin followed by a second displacement of the same firing pin which is both rotational and axial. 
     The device may comprise a firing pin locking module positioned between the pin and the lower part of the pyrotechnic train. 
     This locking module of .cylindrical shape may have three series of openings of different lengths arranged around the circumference of the module, to accommodate at least one stud on the firing pin. 
     The firing pin may comprise three external studs arranged at 120° intervals around its circumference and positioned opposite one of the three sets of openings also arranged on the module in order to accomplish either the locking of the firing pin in a safety position for storage and transport, or a functional locking of the pin in the armed position, or the ignition of the lower part of the train. 
     The device preferably comprises a self-destruct module comprising a gas generating composition contained inside the piston and initiated by the upper part of the train, an exhaust vent made in the piston which, after displacement of the piston, is positioned opposite an axial volute attached to the firing pin, in order to cause the pin to rotate and be axially displaced under the effect of the means of operation, followed by ignition of the lower part of the train. 
     The gas generating composition contained inside the piston may consist of a delay composition associated with a reinforcing composition. 
     According to a preferred embodiment, the ignition device according to the invention, comprising an axial system for interrupting the pyrotechnic train placed in the lower part of the train housed in a cylindrical casing, comprises mechanical means to drive the axial interruption element operated simply by rotating the head of the fuse plug, thus allowing the train to be aligned and misaligned by hand. 
     This interruption element may consist of a cylinder with an axial bore, mounted on an alignment drum rotated by mechanical means from the cylinder being in a radial position to an axial position and conversely. 
     The mechanical means of rotating the drum may consist of an internal rotatable cylindrical part partially housed in the casing and connected at its lower end to the drum, its upper end being driven by the rotation of the body and head of the plug. 
     According to a first embodiment, the drum is fitted with a pin engaged in a spiral groove made in the cylindrical casing, which rotates the cylinder through 90°. 
     According to a second embodiment, the drum comprises teeth engaged in a rack in the casing to rotate the cylinder through 90°. 
     The lower part of the pyrotechnic train preferably comprises in turn a percussion cap, a lead azide charge, a further hexagon primer, the cylindrical interruption device and then a principal hexagon relay charge. 
     According to a preferred embodiment, the interruption cylinder also contains an intermediate relay charge of secondary explosive of the hexagon type. 
     The pyrotechnic charge firing device according to the invention applied to a three-function fuse plug allowing delayed, impact or impact-delay operation of the charge, of the type comprising an operating mode selector, an impact detector module and a delay module, is preferably fitted with a selector consisting of the outer cylindrical wall of the plug head, which can be rotated about the cylindrical body of the plug pierced by the central bore. 
     The delay module integrated with the selector can comprise a mechanical rocker controlling the rotation of at least one gear wheel engaged in at least one axial rack attached to the outer wall of the firing pin, to produce a percussion delay in the impact-delay mode. 
     According to a variant embodiment, the outer wall of the firing pin carries four parallel racks of different lengths each corresponding to percussion delays of one second, seven tenths, four tenths and one tenth of a second. 
     For preference, an omnidirectional impact detector module with adjustable sensitivity will be used, for the impact and impact-delay modes, housed in an axial bore of the cylindrical body of the plug, comprising a master cylinder associated with a first spring, a second cylinder associated with a second spring, a transverse detection ball inserted between the master cylinder and the second cylinder, two locking and unlocking balls for the module operated by the axial displacement of the firing pin and another functional locking and unlocking ball for the module preventing or permitting its operation through the action of the selector. 
     The transverse detection ball in the impact detector module is preferably made of a dense material such as tungsten. The selector preferably comprises in the safe position means that prevent the extraction of a cotter pin locking a handle and an upper firing pin controlling the initiation of the upper part of the train. 
     In a preferred mode of operation, the rotary selector occupies an initial safe position and adopts, in successive 90° rotations, at least three different positions, each corresponding to one of the modes of operation: 
     in the safe position, the cotter pin is locked, the pyrotechnic train is interrupted by the element held in the radial position, the firing pin, whose three studs are opposite the three short safety openings, is locked by the ball being trapped in the circular groove inside the firing pin, the gear wheel of the delay module is separated from the firing pin racks, and the impact detector module is locked by the two balls that respectively lock the master cylinder and the second cylinder under the action of the firing pin in the initial position, moreover the functional locking ball held by the selector also locks the master cylinder; 
     an initial rotation of the selector through 90°, corresponding to the delayed operation of the charge, results in turn in the unlocking of the cotter pin to allow it to be extracted, alignment of the pyrotechnic train by rotating the interruption device through 90° and the rotation of the locking module relative to the firing pin by positioning the three longest openings in the module opposite the three firing pin studs corresponding to the firing pin functional locking position, the delay and impact detector modules remaining inactive; 
     a second rotation of the selector through 90°, corresponding to impact operation, also causing the release of the functional locking ball of the impact detector module, this then entering a circular groove inside the selector in order to activate this module; 
     a third rotation of the selector through 90°, corresponding to impact-delay operation, leading in addition to alignment of the gear wheels of the delay module with the first rack of the firing pin corresponding to a percussion delay of one second, the impact detector module remaining active. 
     According to an operational variant, with the selector in the impact-delay position, three additional rotations of the selector in the same direction bring about the alignment of the gear wheel of the delay module with, in turn, the second rack of the firing pin corresponding to a percussion delay of seven tenths, the third rack of the firing pin corresponding to a percussion delay of four tenths and the fourth rack of the firing pin corresponding to a percussion delay of one tenth of a second. 
     According to another operational variant, with the selector in the impact and impact-delay positions and in the absence of the operation of the impact detector module, the self-destruct module together with the firing pin operating means ignite the lower part of the train followed by the explosion of the device. 
     One advantage of the fuse plug according to the invention lies in the compactness of its structure and the modular design of its component parts, significantly simplifying the firing conditions and the manufacturing stages encountered during largely automated production. 
     This fuse plug with several operating modes offers optimal safety in firing and storage. In particular, the element that interrupts the pyrotechnic train judiciously arranged within the lower part of the said train is independent of the environment thus giving improved efficiency in case of accidental initiation of the upper part of the train, during transport or storage of the plug associated with the pyrotechnic charge. 
     This interruption element can be displaced only by the deliberate action of the operator. Consequently the purely manual alignment and misalignment of the pyrotechnic train cannot result from a conjunction of external hostile elements. 
     This has the advantage that the fuse plug mounted on a fully primed hand grenade for example can be stored in complete safety, which is not the case at present with existing fuse plugs. Another advantage stems from the fact that the principal initiation relay is positioned at the center of the main initiating charge, thus ensuring isotropic detonation of the pyrotechnic charge. 
     Other characteristics and advantages of the invention will be evident from the detailed, non-limiting description of one embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This description will make reference to the attached drawings wherein: 
     FIG. 1 is an axial section of a three-function fuse plug according to the invention, in the safe position; 
     FIG. 2 is an enlarged view along 2--2 of FIG. 1 of the locking module associated with the firing pin in the storage or transport position; 
     FIG. 2A is a view showing only the locking module of FIG. 1; 
     FIG. 3 is a side view of the firing pin showing on a larger scale the path followed by the guide device in the longitudinal and spiral channel involved in the displacement of the firing pin; 
     FIG. 4 is a side view of the firing pin associated with the delay module; 
     FIG. 5 is an axial section of an offensive-defensive hand grenade fitted with a fuse plug according to the invention, showing more particularly the lower part of the pyrotechnic train with its interruption device, in the safe position, together with the means of locking the cotter pin; 
     FIG. 6 is a larger scale view of the pyrotechnic train interruption device of FIG. 5, according to a first embodiment; 
     FIG. 7 is a view identical to FIG. 6 of a second embodiment of this device; 
     FIGS. 8 and 8A represent a top view of the selector with an indication of the different modes of operation, showing the means of locking the cotter pin in the safe position; 
     FIGS. 9, 9A, 9B and 9C are radial sections along 9--9 of FIG. 1 at the fixed casing, the selector, the plug body and the top of the internal part enclosing the locking module respectively; 
     FIGS. 10, 10A, 10B, 10C and 10D are partial schematic views relating to FIG. 1, showing the different positions of certain moving parts in the safe, pyrotechnic train alignment, delay, impact and impact-delay positions respectively; 
     FIGS. 11, 11A and 11B are partial views according to FIG. 1, illustrating the movements of the piston and firing pin up to the armed position of the said pin, in the impact-delay operating mode; 
     FIG. 12 represents a view according to FIGS. 11 and 11B following ignition resulting from the operation of the impact detector module; and 
     FIG. 13 represents a view according to FIGS. 11 and 11B following ignition resulting from the operation of the self-destruct module. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1 to 3 show a three-function fuse plug substantially cylindrical in shape that includes, in its lower part, a casing 26 threaded on the outside for fitting the plug, for example, to a hand grenade (not shown). The main part of the plug is attached to the lower part and is free to rotate. The head of the plug is attached to the top of the main part and includes a conventional device for initiating a pyrotechnic train, such as a cotter pin 34 and a handle 22 operating an upper firing pin 29. 
     The main part of the plug includes three superimposed, coaxial, hollow, cylindrical parts 23, 24 and 25 which can rotate with respect to one another. The cylindrical parts have two axial bores 2 and 37. The axial bore 2 extends into the fixed casing 26 so that the main part can be screwed into the grenade. 
     The following are fitted into this central bore 2 made in the cylindrical part 24, from top to bottom: 
     an internal casing 1, attached to the cylindrical part 24, with a solid upper part in which a central cylindrical housing is made containing an upper part 3 of a pyrotechnic train in two parts, and a hollow lower part; 
     a primer cap 3a, a pyrotechnic delay 3b and a gas generating booster charge 3c, constituting the upper part 3 of the train; 
     a hollow cylindrical piston 5 sliding axially which has an external circular groove 5d and an axial gas exhaust vent 5c at its bottom, the piston being held in the upper position by a spring 6, the piston and the spring being housed in the hollow bottom of the casing 1; 
     a gas generating composition that includes a delay composition 5a with a booster composition 5b contained in the piston 5; 
     a hollow cylindrical firing pin 7 having a U-shaped axial section and being disposed to move axially in translation and in rotation about its axis with respect to the fixed internal casing 1 partially contained in the firing pin; 
     a ball 8 for locking and unlocking the firing pin to/from the casing 1 projecting into a recess at the bottom of this casing such that when the piston is in the upper position, the ball contacts the outer wall of the piston and is engaged in an internal circular groove 7f of the firing pin; and 
     a firing pin locking module 20 (FIG. 2) arranged under the firing pin and formed as a single piece with the cylindrical part 25 having a hollow cylinder with three series of axial openings 20a, 20b and 20c arranged at 120° intervals around its circumference, a first series having three short openings 20a for storage and transport safety, a second series having three longer openings 20b for functional safety and a third series having three through openings 20c allowing the firing pin to pass freely. 
     The lower end of the bore 2 communicates with a coaxial hole in the fixed casing 26 containing the lower part 4 of the pyrotechnic train. 
     The bottom of the firing pin 7 has three external studs 7e arranged at 120° intervals around its circumference capable of penetrating the three series of openings 20a, 20b and 20c in the locking module. On the inner surface of the lower part of the firing pin 7, an axial volute 7d is attached in communication with the exhaust vent 5c of the piston 5 in the lower position to cause the firing pin to rotate under the effect of the gases produced by the combustion of the pyrotechnic composition 5a and 5b contained in the piston 5. 
     The locking module also includes an axial locking indication stud 21 projecting to the outside of the module through an opening 26a in the module when one of the three studs 7e of the firing pin is bearing against its top. In the extended position, the stud acts as a stop to prevent relative rotation of the module 20 and the selector 23 with respect to the fixed casing 26 and to indicate to the operator that the firing pin is in the safe position. 
     A channel 7a, 7b (FIG. 3) is made in the outer cylindrical wall of the firing pin 7. The channel 7a, 7b includes a longitudinal part 7a extended by a spiral part 7b in which is engaged a guide device consisting of a ball 9 that rotates in an open recess made in the casing 24 of the plug and projects into the central bore 2 of the plug. 
     In FIG. 3, the different positions of the ball 9 in the longitudinal channel 7a and the spiral channel 7b during the movement of the firing pin are shown as dotted lines. The ball successively occupies the positions 9a, 9b, 9c and 9d after, respectively, an initial axial displacement of the firing pin, a second rotary and axial displacement corresponding to the armed position of the firing pin, a third displacement caused by the action of the self-destruct module, and a fourth displacement leading to the self-destruct percussion or to that of the delayed operating mode. 
     The configuration of the guide device and of the channel described above is not limiting. A different embodiment in which the channel is made in the body 24 of the plug at the bore and the guide device is placed on the cylindrical wall of the firing pin 7, for example, is also covered by the present invention. 
     Four parallel axial racks 7c, 7c2, 7c3 and 7c4 (FIG. 4) with different lengths are attached to an area of the outer cylindrical wall of the firing pin diametrically opposite to the position of the channel described above. In the impact-delay mode of operation of the charge, as will be described below, these racks provide percussion delays of one second, seven tenths, four tenths and one tenth of a second (FIG. 4), respectively. 
     A delay module is placed through an opening made in the body 24 of the plug in the outer cylindrical part 23 forming the head of the plug for selecting the different operating modes of the pyrotechnic device. The delay module, which is integrated with the selector 23 by any known means, is rotated by the said selector around the firing pin into alignment with one of the four axial racks on the firing pin in the impact-delay mode. 
     This entirely mechanical delay module comprises a rocker 19 controlling the position of one or more gear wheels 18 capable of engaging one of the four racks according to the length of percussion delay chosen by the operator using the selector 23. 
     An omnidirectional impact detector module with adjustable sensitivity is fitted in the second axial bore 37, the diameter of which may or may not be equal to that of the central bore 2. 
     This second bore 37 is made in the body 24 of the plug at a short distance from the central bore 2. 
     This impact detector module, used in impact mode and in impact-delay mode, includes: 
     a master cylinder 10 associated with a first spring 11 that contacts the bottom of the bore 37 and the bottom of the master cylinder; 
     a secondary cylinder 12 associated with a second spring 13 that contacts the top end of the bore 37 and on the top of the secondary cylinder; 
     a transverse tungsten detection ball 14, interposed between the master cylinder and the secondary cylinder and disposed to move radially in a housing inside the body 24 of the plug and the selector 23; 
     two balls 15 and 16, moving radially in two recesses in the part of the body 24 situated between the two bores 2 and 37 and each projecting into these two bores, respectively locking the master cylinder 10 and the secondary cylinder 12 in the upper position of the firing pin 7 and unlocking the master cylinder and secondary cylinder after the axial displacement of the firing pin; and 
     a ball 17 which can move radially in a recess in the body 24, providing functional locking of the module under the action of a selector 23 which keeps it engaged in a groove in the master cylinder 10, and functional unlocking allowing the module to operate after rotation of the selector about the body 24 allowing this ball to escape from the groove in the master cylinder and enter an internal circular groove 23b in the selector. 
     When the firing pin 7 is in the upper position, the locking functions of these two parts of the module are provided by the firing pin which keeps each of the balls 15 and 16 engaged in the corresponding groove in the master cylinder and secondary cylinder. The master cylinder 10 is in contact with the ball 9 and keeps it engaged in the channel 7a, 7b of the firing pin. 
     The master cylinder has two necked zones 10a which, following axial displacement of the master cylinder cause, by a longitudinal or transverse impact, allow the ball 9 to escape from the channel, releasing the firing pin. 
     The lower part of the selector 23 formed by the cylindrical top of the plug includes a flexible ratchet 23a which snaps into a circular notch made in the fixed casing 26. Around the circumference of the top of the selector 23 (FIG. 8A) are four principal markers corresponding to the positions of safety, delayed operation, impact operation and impact-delay operation. The operator selects one of the four markers by successive 90° rotations. In the impact-delay position, the selector shows three secondary markers, accessible by successive rotations of 20A for example, corresponding to the different percussion delays described above. 
     An outer part of the circumference of the top of the casing 26 includes a circular rib 26e (FIGS. 5 and 8) which traps, with the flexible ratchet 23a of the selector in the safe position, part of a ring 34a connected to the cotter pin 34 to prevent the cotter pin from being extracted only when the selector is in the safe position. 
     The fixed cylindrical casing 26 screwed into the grenade contains the lower part 4 of the pyrotechnic train. From top to bottom, the lower part 4 includes: a percussion cap 4a, a lead azide charge 4b, a hexagon primer 4c, a train interruption cylinder 27 and a principal hexagon relay charge 4d (FIGS. 5 to 7). 
     The train interruption cylinder 27 for interrupting or misaligning the pyrotechnic train consists of a cylinder with an axial orifice and preferably containing an intermediate relay charge of a secondary explosive of the hexagon type. The train interruption cylinder is attached in any known manner to a cylindrical drum 28 that rotates between a radial position to an axial position of the device. 
     The cylindrical drum is caused to rotate by a mechanical device that is actuated by the manual rotation of the selector 23 and formed by the head of the plug. The mechanical device includes an internal cylindrical part 25 the bottom part of which 25a is housed in the casing 26 and the upper part of which contains the locking module, that is rotated by the body 24 of the plug enclosed by the selector 23. 
     According to a first embodiment (FIG. 6), the mechanical device includes a spiral groove 31 made in the casing 26 associated with a pin 30 on the drum 28 and disposed to rotate in the lower end 25a of the internal part 25, so as to produce a rotation of 90° of the interruption device 27 by a conjoint rotation of 45° of the body 24 and of the selector in the initial safe position. Beyond 45°, the upper part of the part 25 is locked to the fixed casing 26 to keep the pyrotechnic train aligned for the three modes of operation. 
     Returning the selector 23 to the safe position unlocks the part 25 from the casing 26 and skews the pyrotechnic train into misalignment returning the device 27 to the radial position. 
     According to a second embodiment (FIG. 7), the system of spiral groove 31 and pin 30 is replaced by a gear wheel 32 of the drum 28 engaging a circular rack 33 of the casing 26 to align and misalign the pyrotechnic train by rotating the interruption device 27 through 90°. 
     The ignition device according to the invention is operated as follows. 
     With the fuse plug mounted in the safe position on an explosive device such as a hand grenade, for example, the operator selects one of the three modes of operation by manually rotating the head 23 of the plug around the fixed casing 26 screwed on the device. 
     In the initial safe position, the cotter pin 34 cannot be withdrawn, the device 27 in the radial position interrupts the pyrotechnic train, the three studs 7e of the firing pin 7 locked in the upper position are opposite the three short openings 20a, and the delay and impact detector modules are inactive (FIG. 10). 
     So long as the locking indicator pin 21 has not entered the recess 26a, the operator can rotate the selector 23 in one direction only by pressing on the flexible ratchet 23a engaged in the circular gear wheel of the fixed casing 26, in order to select the desired mode of operation. 
     During the angular displacement of the selector 23 from 0° to 45°, the three cylindrical parts 23, 24 and 25 can rotate simultaneously with respect to the fixed casing 26, by two cams 23d and 24b, which are respectively disposed at the ends of parts 23 and 24, fitted with two pins 23c and 24a sliding in corresponding grooves 26b and 26c of the casing (FIGS. 9 to 9B). 
     When the selector is in the 45° non-indexed position, the pyrotechnic train is aligned (FIG. 10A) by the rotation through 90° of the interruption device 27 produced by the rotation of the internal part 25, the internal part being locked to the casing 26 to keep the train in alignment while the mode of operation is selected. This locking function is provided by a flexible stud 25b mounted on the end of part 25, sliding in the groove 26d of the casing 26, where it locks in position at the end of the groove (FIGS. 9 and 9C). 
     It will be noted that the pyrotechnic train can again be placed out of alignment by rotating the selector in the opposite direction and returning it to the safe position. During the angular displacement from 45° to 90°, the two cylindrical parts 23 and 24 remain together and rotate simultaneously with respect to the locked internal part 25. 
     It will be noted that the firing pin 7 rotates with the cylindrical part 24 being connected to it by the ball 9 engaged in the channel 7a, 7b of the firing pin. 
     In the 90° position, corresponding to the delayed operating mode (FIG. 10B), the rotation of the part 24 and hence of the firing pin 7 places the three studs 7e of the firing pin opposite the three longer functional locking openings 20b, the impact detector module remains locked by the functional locking ball 17 that remains engaged in the groove of the master cylinder 10 by the selector, and the delay module is still separated from the firing pin racks 7c. 
     In this position, the operator can extract the cotter pin 34 by pulling on the ring 34a released by the withdrawal of the circular groove 26e on the casing 26, the cylindrical part 24 being locked to the top of the internal part 25 by engagement between the rib 26c and the flexible cam 24b associated with its pin 24a. 
     In this position, corresponding to the impact mode of operation (FIG. 10C), the functional locking ball 17 escapes from the groove on the master cylinder 10 and engages in the internal circular groove 23b of the selector to activate the impact detector module. 
     In this position, as in the previous position, the delay module is separate from the firing pin racks 7c. The part 24 is locked on the casing 26 by a stud 24c in the groove 26f on the casing. 
     During the angular displacement from 180° to 270°, the selector 23 associated with the delay module rotates about the body 24 of the plug. 
     In the 270° position, corresponding to the impact-delay mode of operation (FIG. 10D), the gear wheel 18 of the delay module is aligned with the first rack 7c of the firing pin corresponding to a percussion delay of one second, and the functional locking ball 17 remains free so the impact detector module remains active. 
     The other angular positions of the selector which may, for example, be 300°, 320° and 340° correspond respectively to the alignment of the gear wheel 18 with the racks 7c2, 7c3 and 7c4 for percussion delays of seven tenths, four tenths and one tenth of a second. In these last three positions, the impact detector module is also active. Each of these four positions is indexed by the cam 23c. 
     The operation of the device in impact-delay mode mounted on a hand grenade is described below (FIGS. 11, 11B and 12). 
     Differences in operation according to the other two modes can easily be deduced from this description. 
     The description assumes the configuration relating to this particular mode of operation, determined by the corresponding position of the selector, described above. The user extracts the cotter pin 34 and throws the grenade. 
     The handle 22 releases the upper firing pin 29 which strikes the cap 3a in the upper part 3 of the pyrotechnic train (FIG. 11). The sequence of actions is then as follows. 
     Combustion of the pyrotechnic delay 3b ignites the booster charge 3c, which generates gases causing the axial displacement of the piston 5 and compressing the spring 6. 
     Once the outer circular groove 5d on the piston 5 is opposite the ball 8, the ball releases the firing pin 7. The firing pin then moves axially under the action of the compressed spring 6. 
     The longitudinal part 7a of the channel in the firing pin slides past the ball 9 until it encounters the spiral part 7b of the channel (FIG. 11A). 
     The spiral form of this part of the channel causes the firing pin to rotate through a few degrees. At the end of the spiral part 7b, the firing pin is immobilized because it is held captive by the ball 9 (FIG. 11B). 
     It should be noted that the firing pin 7 forced to rotate by the spiral part of the channel allows the three studs 7e on the firing pin to separate from the three long functional locking openings 20b on the locking module and to move to a position opposite the three through openings 20c, thus effectively arming the device. This design provides a check on the presence of the ball 9 guiding the firing pin and on the initiation of impact, and the integrity of the impact detector module. If one of these elements is faulty, the firing pin descends into the functional safety openings 20b. 
     During its motion, the firing pin releases the two balls 15 and 16 and thus unlocks the impact detector module. 
     A longitudinal impact producing an axial displacement of the assembly of master cylinder 10, ball 14 and secondary cylinder 12, or a transverse impact displacing the ball 14 radially, which necessarily causes the axial displacement of the master cylinder 10 of which one of the two necks 10a, allows the ball 9 to escape from the spiral part 7b of the channel, thus releasing the firing pin (FIG. 12). 
     During its motion towards the lower part 4 of the pyrotechnic train, the firing pin is delayed by the delay module. The rack 7c of the firing pin (or one of the shorter racks 7c2, 7c3 or 7c4, depending upon the percussion delay selected) contacts the gear wheel 18 which strongly brakes the firing pin (FIGS. 11B and 12). 
     Following a delay depending on the length of the rack, the firing pin is released and ignites the lower part 4 of the train by striking the cap 4a. 
     If the impact detector module does not release the ball 9 within the required time, the self-destruct module contained in the piston 5 becomes active (FIG. 13). 
     The propellant charge 3c ignites the delay composition 5a. On completion of combustion, the booster composition 5b generates gases which flow through the volute 7d and force the firing pin to rotate again. The upper end of the spiral part 7b of the channel is then presented to the ball 9 which enters (FIG. 3). 
     This further rotation of the firing pin moves the rack 7c out of alignment with the gear wheel 18 on the delay module such that the self-destruct percussion is instantaneous. 
     Operation in the impact mode is identical with the impact-delay mode, except that rotation of the selector 23 through 180° leaves the firing pin racks separated from the delay module. 
     Operation in the delay mode is identical to the impact-delay mode, except that rotation of the selector 23 through 90° also leaves the firing pin racks separated from the delay module and does not release the functional locking ball 17 from the impact detector module. As a result, self-destruction of the grenade is ensured.