Patent Publication Number: US-8122829-B2

Title: Safety lighter for pyrotechnic device

Description:
CROSS-REFERENCE TO PRIOR APPLICATION 
     This is a U.S. National Phase Application under 35 U.S.C. §371 of International Application No. PCT/EP07/055876, filed Jun. 14, 2007 and claims benefit of French Patent Application No. 06/04816, filed on Jun. 16, 2006 both of which are incorporated herein. The International Application was published in French on Dec. 21, 2007 as WO 2007/144396 under PCT Article 21(2). 
     FIELD OF THE INVENTION 
     The present invention relates to a safety lighter to initiate the combustion of any type of pyrotechnic device after a determined delay time, such as, for example, the pyrotechnic engines of missiles lit at a safe distance. 
     BACKGROUND OF THE INVENTION 
     The pyrotechnic initiator, the first component of the pyrotechnic lighting chain, can be activated by various means such as electrical, mechanical, thermal, optical means. These means provide stimuli, more often than not of low amplitude, to activate the initiator. These stimuli, which can be in the normal or accidental environment of the pyrotechnic device, can inopportunely activate the lighter provoking the nominal operation of the pyrotechnic device. 
     The regulations concerning the ignition of pyrotechnic lighting devices, notably missiles, are constantly changing toward greater safety, for example by the application of NATO standards. 
     The main safety criterion is that the pyrotechnic device should not be triggered inopportunely. An uncontrolled triggering can involve serious risks to personnel and significant equipment damage. 
     To avoid the effects of inopportune triggerings, the lighters of the prior art whose lighting chain contains sensitive pyrotechnic compounds, normally comprise a safety switch, for example toggle, slider, rotor, which separates these sensitive compounds from the rest of the pyrotechnic chain, and which can be opened when the lighter is deliberately operated only by the activation of at least one safety device. 
     Ignition delays are often introduced into the lighters according to parameters associated with the use of the pyrotechnic device, for example to ensure a sufficient safety distance relative to the personnel and equipment to be protected. 
     These ignition delays can easily be obtained and managed by an electronic circuit receiving an activation signal and supplying an electrical signal delayed by a time t predetermined according to the use of the pyrotechnic device. Such electronic activation-delay generating devices require an electrical energy source and occupy a volume that is sometimes incompatible with the available bulk constraints for certain applications. 
     SUMMARY OF THE INVENTION 
     In order to overcome the drawbacks of the lighters of the prior art, embodiments of the invention propose a safety lighter intended to initiate the combustion of a pyrotechnic device, characterized in that it comprises:
         a lighter body having a cylindrical void of axis XX′;   a pyrotechnic slide-in module comprising pyrotechnic means of initiating the combustion of the pyrotechnic device, the pyrotechnic slide-in module being able to be displaced in the cylindrical void of the lighter body from a so-called safety position, providing isolation between the pyrotechnic means of the slide-in module and the pyrotechnic device to be initiated, to a so-called initiation position, intended to provoke the combustion of the pyrotechnic device;   sealing means between the pyrotechnic slide-in module and the lighter body to isolate, in the safety position, the pyrotechnic slide-in module from the pyrotechnic device to be initiated;   mechanical means for maintaining the pyrotechnic slide-in module in the safety position.       

     Advantageously, the pyrotechnic means of the pyrotechnic slide-in module comprise an igniter, a pyrotechnic delay initiated by the igniter and an intermediate lighting relay initiated by the pyrotechnic delay. 
     In another embodiment, the safety lighter comprises an output lighting relay initiated by the intermediate lighting relay. 
     A main objective of the invention is to obtain pyrotechnic lighters that have a greater operating safety and reliability. 
     Another objective is to produce compact lighters compatible with pyrotechnic devices that have only little space for the lighter. 
     Another objective is to reduce the costs of such pyrotechnic lighters by reducing the number of components needed for their operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will be better understood using exemplary embodiments of the lighter according to the invention, with reference to the indexed drawings in which  FIGS. 1 ,  2  and  3  represent an exemplary embodiment of a safety lighter according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The lighter of  FIG. 1  comprises a lighter body  10  having a cylindrical void  12  of axis XX′, into which a pyrotechnic slide-in module  14  can slide. 
     The pyrotechnic slide-in module  14  can be displaced in the cylindrical void  12  of the lighter body  10 , from a so-called safety position Ps, providing isolation between the pyrotechnic means of the lighter and the pyrotechnic device, to a so-called initiation position Pi, to provoke the initiation of the combustion of the pyrotechnic device (not represented in the figures). 
     The pyrotechnic slide-in module  14  comprises a pyrotechnic chamber  20  in tube form closed at one of the ends by a closure wall  22  perpendicular to the axis XX′ comprising a first hole  24  for passage of the gases between the pyrotechnic chamber  20  and a cell  26  of a cap  28  for closing the pyrotechnic chamber  20 . The cell  26  of the cap  28  includes an intermediate lighting relay  30  that can be activated by hot gases originating from the pyrotechnic chamber  20  through the first hole  24  for passage of the gases. 
     The closure cap  28  comprises two opposite ends of cylindrical form, a first end  32  in tube form, of the same diameter D 1  as that of the pyrotechnic chamber  20 , joined to the end of the pyrotechnic chamber comprising the closure wall  22  and a second cylindrical end  34  of smaller diameter D 2  than the first. The connection between the two ends  32 ,  34  of different diameters D 1  and D 2  of the cap  28  forms at least one shoulder  36  of the cap. 
     Second holes  38  for passage of the gases pass through the cylindrical walls of the cap  28  opening out on one side into the cell  26  of the cap and on the other side level with the shoulder  36  of the cap. 
     The pyrotechnic slide-in module  14  is closed at its other end opposite to the end comprising the cap  28 , by an end-stop  50  in tube form comprising a first end  52  of the end-stop joined to the pyrotechnic chamber  20  and a second end  54  of the end-stop intended to bear on an element  60  of a safety lock  62  to prevent the displacement of the pyrotechnic slide-in module  14  in the lighter body  10 , from the safety position Ps to the initiation position Pi. 
     The pyrotechnic chamber  20 , in tube form, closed at one end by the closure wall  22  and at the other end by the end-stop  50 , comprises, inside the tube, on the side of the end-stop  50 , an electrically-controlled igniter  70  and, facing the igniter  70 , against the closure wall  22  of the pyrotechnic chamber  20 , a pyrotechnic delay  74 . 
     The igniter  70 , inside the pyrotechnic chamber  20 , comprises an active part  72  facing the pyrotechnic delay  74  and a hermetic bushing  76  in contact with the end-stop  50  hermetically closing the pyrotechnic chamber. The hermetic bushing  76  comprises two electrical contacts  80  to supply an electric current to activate the igniter  70 . 
     The cylindrical void  12  of the lighter body  10  comprises a first cylindrical area  90  of the same diameter D 1  as the diameter of the pyrotechnic chamber  20  enabling the pyrotechnic slide-in module to slide inside the lighter body  10 , and a second cylindrical area  92  of the same diameter D 2  as the diameter of the second end  34  of the cap  28 . The two cylindrical areas  90 ,  92  of the lighter body are connected by a shoulder  94  of the lighter body. 
     The lighter body  10  comprises, at the end of the second cylindrical area  92 , a third hole  96  opening out into another cell  97  of the lighter body  10 , this other cell  97  being open toward the charge of the pyrotechnic device to be initiated. 
     The lighter comprises a damper  108  in washer form positioned between the cylindrical surface of the end-stop  50  and a fixed cylindrical end-stop  110  joined to the lighter body  10  on the axis XX′. The damper  108  can, for example, be a spring, an elastomer washer, or similar. 
     In a variant of the safety lighter, the other cell  97  of the lighter body  10  comprises an output lighting relay  110  intended to initiate the combustion of the charge of the pyrotechnic device. 
     The igniter  70 , the pyrotechnic delay  74  and the intermediate lighting relay  30  are positioned in a closed volume comprising the pyrotechnic chamber  20 , the hermetic bushing  76 , the cap  28  and the lighter body  10 , its seal-tightness being ensured by three o-ring seals: 
     a first o-ring seal  100  in a circular groove  102  around the second cylindrical end  34  of diameter D 2  of the cap  28  in contact with the lighter body  10 ; 
     a second o-ring seal  104  in a circular groove  106  around the pyrotechnic chamber  20  in contact with the lighter body  10 ; 
     a third o-ring seal  105  in a circular groove  107  around the hermetic bushing  76 . 
     The element  60  of the safety lock  62  can be fixed by control means of the lock, either in a closed position Pf preventing the passage of the mobile chamber from the safety position Ps to the initiation position Pi, or in an open position Po allowing the passage of the pyrotechnic slide-in module  14  from the safety position Ps to the initiation position Pi. 
     The safety lighter comprises another means of maintaining the slide-in module  14  in the safety position Ps comprising a shearable pin  120  joined by one of its ends to the lighter body  10  and by the other end to the pyrotechnic slide-in module  14 . 
     There now follows an explanation of how the lighter works with the help of  FIGS. 1 to 3  in different configurations. 
     Storage configuration, represented in  FIG. 1  (or in the so-called safety position). 
     In this safety configuration, the pyrotechnic chain is said to be disaligned. The pyrotechnic slide-in module  14  comprising the initiation chain is isolated from the output lighting relay  110  and from the pyrotechnic device, for example the lighting charge of a thruster, thanks to the o-ring seal  100 . 
     The pyrotechnic slide-in module  14  is maintained in the safety position Ps in the lighter body  10  by the shearable pin  120  and the mechanical element  60  of the safety lock  62  in the closed position Pf.
         Inopportune lighting configuration represented in  FIG. 2 .       

     The slide-in module is in the so-called safety position Ps. 
     In case of untimely initiation of the igniter  72 , of the pyrotechnic delay  74  or of the intermediate lighting relay  30  of the initiation pyrotechnic chain, the pyrotechnic slide-in module can be displaced (or retracted) in the lighter body  10  under the effect of the combustion gases from the pyrotechnic delay and/or from the intermediate lighting relay  30  only to bear on the mechanical element  60  of the safety lock  62 . 
     The pyrotechnic chain is still disaligned, the hot gases gz obtained from the combustion of the initiation chain remain contained in the pyrotechnic slide-in module  14  and in the areas of the lighter isolated from the pyrotechnic device by the seal  100 . No hot gas can activate the pyrotechnic device to be initiated or the output pyrotechnic relay  110 .
         Normal (intentional) lighting configuration represented in  FIG. 3 .       

     When the control device of the safety lock  62  detects the specific event or events that allow the pyrotechnic device, for example a thruster, to be lit, it unblocks and clears the safety lock  62  that ensures the safety of the lighter. The mechanical element  60  of the lock passes from the closed position Pf to the open position Po. 
     Simultaneously, an electrical signal activates the igniter  72  which lights the pyrotechnic delay  74  in the slide-in module  14 . 
     On completion of its combustion, after a predetermined time t, the pyrotechnic delay  74  lights the intermediate lighting relay  30  by the hot gases passing through the first hole  24  from the pyrotechnic chamber to the cell  26 . 
     The hot gases produced by the combustion of the intermediate lighting relay  30  pass through the second holes  38  of the cap  28  from the pyrotechnic chamber to the lighter body  10  causing the pyrotechnic slide-in module  14  to retract in the lighter body  10  under the pressure of the hot gases gz. 
     The pyrotechnic slide-in module  14  is no longer prevented in its movement by the mechanical element  60  of the safety lock  62 , so it is freed from the safety position Ps to the initiation position Pi after having sheared the pin  120  until it bears on the fixed end-stop  110 . The damper  108  mitigates the effect of the impact of the pyrotechnic slide-in module  14  on the fixed end-stop  110  joined to the lighter body  10 . 
     The hot gases gz produced by the intermediate lighting relay  30  pass through the holes for passage of the gases  38  to the second cylindrical area  92  of the lighter body  10  and initiate the output lighting relay  110  in the other cell  97  and finally the charge of the pyrotechnic device to be initiated (thruster for example). 
     One main benefit of the invention is to obtain pyrotechnic lighters that have a far greater safety and reliability and allow for risk-free storage. In the case where the lighter is mounted in a pyrotechnic device, the inopportune lighting of the pyrotechnic chain does not cause the charge of the pyrotechnic device to be accidentally lit. 
     The safety lighter according to the invention can be used for numerous civilian or military applications, such as, for example, for lighting rockets, missile engines, gas generators for pressurizing tanks, pyromechanisms such as apogee motor initiators or squibs.