Patent Publication Number: US-11022414-B2

Title: Triggering device with safety valve and linkage

Description:
FIELD OF THE INVENTION 
     The invention is in the field of triggering devices, such as for triggering explosive charges. 
     DESCRIPTION OF THE RELATED ART 
     One concern with munitions is behavior of stored munitions in the case of fire or environmental thermal runaway. It is desirable to have a safety mechanism to prevent problems in slow cook-off, where the temperature rises in the munition, for example to prevent a rocket motor from being activated to propel a missile in such a circumstance. 
     SUMMARY OF THE INVENTION 
     A heat-activated triggering device includes a valve that selective blocks or allows passage through an outlet passage used for travel of hot products from detonation/combustion of a primer and booster. 
     A heat-activated triggering device includes a valve that is mechanically coupled by a linkage to a firing pin. The valve acts as a safety device for a primer and booster configured to expel detonation products from the trigger device, ensuring that the products exit the device only if the firing pin has move sufficiently to impact the primer. 
     According to an aspect of the invention, a triggering device includes: a firing pin configured to impact a primer; and a valve mechanically coupled to the firing pin, wherein the valve selectively allows output from firing of the primer pass to an output port of the triggering device. 
     According to an embodiment of any paragraph(s) of this summary, the valve is a barrel valve, with a through hole that selectively lines up with a passage between the firing pin and the output port. 
     According to an embodiment of any paragraph(s) of this summary, the barrel valve rotates to align with the passage just as the firing pin reaches the primer. 
     According to an embodiment of any paragraph(s) of this summary, a linkage mechanically couples the valve to the firing pin. 
     According to an embodiment of any paragraph(s) of this summary, the linkage includes a linking member that translates along with the firing pin, and a cam mechanism that converts translation of the linking member to rotation of the barrel valve. 
     According to an embodiment of any paragraph(s) of this summary, the linkage further includes a dowel pin coupling together firing pin and the linking member. 
     According to an embodiment of any paragraph(s) of this summary, the linking member has a slot therein that receives a follower of the barrel valve. 
     According to an embodiment of any paragraph(s) of this summary, the slot is substantially parallel to a direction of travel of the linking member. 
     According to an embodiment of any paragraph(s) of this summary, the triggering device further comprises a casing that defines cavities that are parallel to one another. 
     According to an embodiment of any paragraph(s) of this summary, the linking member and the firing pin move in respective of the cavities. 
     According to an embodiment of any paragraph(s) of this summary, the triggering device further includes a lockout configured to selectively prevent movement of the firing pin. 
     According to an embodiment of any paragraph(s) of this summary, the lockout includes an inertial mass that moves in a recess coaxial with a recess in which the linking member is located. 
     According to an embodiment of any paragraph(s) of this summary, the triggering device is part of a munition, with the triggering device operatively coupled to a shaped charge of the munition such that detonation products from a primer of the triggering device that is operatively coupled to the firing pin, detonate the shaped charge. 
     According to another aspect of the invention, a method of operating a triggering device, includes the steps of: moving a firing pin toward a primer; and rotating a barrel valve while the firing pin is moving, through the action of a linkage mechanically coupling the firing pin and the barrel valve. 
     According to an embodiment of any paragraph(s) of this summary, a through hole of the barrel valve aligns with an output passage to an outlet port of the device, as the firing pin reaches the primer. 
     According to an embodiment of any paragraph(s) of this summary, the method further includes expelling output from firing of the primer through the outlet port. 
     According to an embodiment of any paragraph(s) of this summary, the rotating the barrel valve includes a follower on the barrel valve moving in a slot of a linking member that translates along with the firing pin. 
     According to an embodiment of any paragraph(s) of this summary, the linking member and the firing pin translate in respective passages of a housing of the triggering device, with moving of the firing pin moving a the linking member and a dowel pin that connects together the firing pin and the linking member. 
     To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The annexed drawings, which are not necessarily to scale, show various aspects of the invention. 
         FIG. 1  is an oblique view of a munition that includes a triggering device in accordance with an embodiment of the invention. 
         FIG. 2  is another oblique view of a munition that includes a triggering device in accordance with an embodiment of the invention. 
         FIG. 3  is an oblique view of the triggering device of the munition of  FIG. 1 . 
         FIG. 4  is a sectional view of the triggering device of  FIG. 3 . 
         FIG. 5  is an oblique view showing some of the working parts of the triggering device of  FIG. 3 . 
         FIG. 6  is an end view of the triggering device of  FIG. 3  in a first step in the triggering process. 
         FIG. 7  is a side view of the triggering device of  FIG. 3  in the first step in the triggering process. 
         FIG. 8  is an end view of the triggering device of  FIG. 3  in a second step in the triggering process. 
         FIG. 9  is a side view of the triggering device of  FIG. 3  in the second step in the triggering process. 
         FIG. 10  is an end view of the triggering device of  FIG. 3  in a third step in the triggering process. 
         FIG. 11  is a side view of the triggering device of  FIG. 3  in the third step in the triggering process. 
         FIG. 12  is a schematic diagram of an alternate embodiment triggering device of the present invention. 
         FIG. 13  is a high-level flow chart of steps in the operation of the triggering device of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     A heat-activated triggering device, such as for a missile or munition, includes a firing pin that is driven into a primer, to initiate a detonation and/or combustion reaction. The firing pin may be mechanically coupled to a linkage that prevents egress of output from the primer if the firing pin has not been moved. The linkage may include, for example, a cylindrical valve element with a through hole, the through hole being alignable with an output channel from the primer when the firing pin has been moved sufficiently. The movement of the firing pin slides a dowel pin that is attached to the firing pin. This in turn translates a cam element that turns the cylindrical element. Partial movement of the firing pin still may leave the valve closed. Preventing the primer from prematurely operating to trigger explosion, for example preventing full operation due to a primer being heated. 
     The movement of the firing pin may be effected in one embodiment by a bi-metal trigger element, with a breakable pin of a first metal surrounded by a sleeve made of a second metal that is different than the first metal. The sleeve may be made of a shape memory alloy, such as a single-crystal shape memory alloy, that is pre-compresses around part of the pin. The sleeve may be configured to put a tension force on the pin as the sleeve passes a predetermined temperature, for instance a temperature at which the shape memory feature of the sleeve is activated. The pin may have a weakened portion, such as a notched portion, at which the pin breaks. The breaking of the pin may be used to drive the firing pin into the primer, to initiate the detonation and/or combustion reaction. 
     The firing pin may be mechanically coupled to a linkage that prevents egress of output from the primer if the firing pin has not been moved. The linkage may include a cylindrical valve element with a through hole, the through hole being alignable with an output channel from the primer when the firing pin has been moved sufficiently. The movement of the firing pin slides a dowel pin that is attached to the firing pin. This in turn translates a cam element that turns the cylindrical element. Partial movement of the firing pin still may leave the valve closed. Preventing the primer from prematurely operating to trigger explosion, for example preventing full operation due to a primer being heated. 
       FIGS. 1 and 2  show a missile or munition  10  that includes a triggering device  12 , for triggering a shaped charge  14  for scoring a motor casing  16  of the missile  10 . This is done to prevent firing of a rocket motor, or explosion of propellant, when the missile or munition is subjected to a slow cook-off event, for example a fire. Upon occurrence of a triggering event, such as reaching a predetermined elevated temperature, the triggering device  12  triggers detonation of the shaped charge  14 , scoring and splitting the motor casing  16 , as shown in  FIG. 2 . This prevents explosion or a propulsive event, which would be a safety hazard. 
     The triggering device  12  also needs to avoid detonation of the shaped charge  14  from other types of heating, for example avoiding triggering from aero-thermal heating during flight of the missile or munition  10 . Accordingly the triggering device  12  may have one or more safety features to prevent undesired triggering of the shaped charge  14 . 
       FIGS. 3 and 4  show some details of the triggering device  12 . The device  12  has three general parts: a triggering element  22  which is used to move a firing pin  24  toward a primer  26 ; an inertial lock-out  28  used to prevent movement of the firing pin  24  once the missile  10  ( FIG. 1 ) has been launched; and a linkage  32  that is used to selectively open or close a passageway (output port)  34  through which products from the primer  26  pass. The operative general parts are located within a casing  38 . 
     The triggering element  22  includes a metal pin  42  made of a first metal, surrounded by a sleeve  44  made of a second metal that is different from the first metal. The term “metal,” as used herein, should be interpreted broadly to include elemental metal, as well as metal alloys. The sleeve  44  is configured to put a force on the metal pin  42  when sufficient heat is applied. This force may be used break the pin  42  at a weakened portion  46  of the pin  42 . In the illustrated embodiment the weakened portion  46  is a notched portion of the pin  42 , but may be a portion otherwise having been thinned. For example a notch may be uniformly cut or otherwise formed around the pin  42  to create the weakened portion  46 . The depth of the notch may be selected in order to cause the pin  42  to break at a predetermined temperature. 
     The sleeve  44  may be made of a shape memory alloy, such as a single-crystal shape memory alloy, such as a copper-aluminum alloy. The sleeve  44  may be pre-compressed against the pin  42 , with a memory shape puts stresses against the pin  42 . As the temperature rises, the sleeve  44  eventually passes its transition temperature, undergoing a phase transformation between different structures. This may occur, for example at around 160° C. The causes the sleeve  44  to produce a force tending to change its shape. This force is transmitted to the pin  42 , for example placing a force on the pin  42  that causes a tension within the pin  42 . This force may be used to sever the pin  42  at the weakened section or portion  46  of the pin  42 , where the pin  42  preferentially breaks. 
     One end  52  of the pin  42  is secured to the firing pin  24 , with the firing pin  24  being hollow and receiving the pin end  52 . An opposite end  54  of the pin  42  extends out of a cavity  58  in which the firing pin  24  and the sleeve  44  are located. The pin end  54  compresses a stack of springs  62 , such as a stack of Belleville washers, that is in a recess  64  in the casing  38 . When the pin  42  breaks at the weakened portion  48 , a force separates the portions of the metal pin on opposite sides of the weakened portion  46 . This force comes mainly from the energy stored in the sleeve  44  that becomes kinetic energy pushing the pin end  52  and the firing pin  24  to slide within the cavity  58  toward the primer  26 . In addition some of the force moving the pin end  52  and the firing pin  24  may come as a result of recoil from the breakage of the pin  42 . The compressed springs  62  provide an even loading on the pin  42 . This provides more consistency in the fracture temperature and the force of the firing pin  24 . 
     A stay spring  66  is also located within the cavity  58 , with the stay spring  66  being a coil spring that is between a ledge of the casing  38  bordering the cavity  58 . One function of the stay spring  66  is to keep loose parts, such as the firing pin  24 , from moving around within the cavity  58  after the breakage of the pin  42 . The spring  66  may also function to provide an additional and/or back-up force to move the firing pin  24  toward the primer  26 , after breakage of the pin  42 . 
     The primer  26  is activated when impacted by the firing pin  24 . This in turn may fire a booster  68  that produces detonation/combustion products, such as flames, hot gasses, and/or molten material. These products are described herein as being products of the detonation of the primer  26 , even though the booster  68  is also involved in creating the products that exit the triggering element  22  to detonate the shaped charge  14  ( FIG. 1 ). 
     A dowel pin  82  is located in and moves with the firing pin  24 , providing a mechanical connection between the triggering element  22  and the linkage  32 . The dowel pin  82  links the firing pin  24  to a linking member  84  that in turn converts translational motion to rotational motion. The linking member  84  slides within a cavity  88  in the casing  38 , and relative to a fixed sleeve  90  that is also within the cavity  88 . With reference in addition to  FIG. 5 , the linking member  84  includes a cam slot  92  that receives a cam follower protrusion  94  on an end of a barrel valve  96 . The barrel valve  96  has a through hole  98  that needs to be aligned with the outlet port  34  for output (hot gasses and other detonation products) to exit the device  12  through the outlet port  34 . These products are used to detonate the shaped charge  14  ( FIG. 1 ). The barrel valve  96  is used as a safety device to prevent exit of the detonation products unless the firing pin  24  has indeed been activated to move. The movement of the firing pin  24  moves in translation the dowel pin  82  and the linking member  84  as well. The movement of the linking member  84  causes rotation of the barrel valve  84  about the axis of the barrel valve  84 . This occurs through the interaction of the cam slot  92  and the follower protrusion  94 . 
       FIGS. 6-11  show the process of triggering the device  12 .  FIGS. 6 and 7  show the device  12  in its initial safe state, before breakage at the weakened portion  46  of the pin  42 . In this condition the barrel valve through hole  98  is not aligned at all with the outlet port  34 , and the solid parts of the barrel valve  96  fully blocks the outlet port  34 . 
       FIGS. 8 and 9  shows an intermediate step, where the pin  42  has broken and the firing pin  24  has started to move. The barrel valve  96  has rotated to the point where the through hole  98  has begun to align with the outlet port  34 . However the barrel valve  96  still mostly blocks the outlet port  34 . The device  12  is thus still in a safe condition, with the primer  26  unable to detonate the shaped charge  14  ( FIG. 1 ). 
       FIGS. 10 and 11  show the situation just before the firing pin  24  impacts the primer  26 . The linkage  32  has now turned the barrel valve  96  so that the through hole  98  is aligned with the outlet port  34 . In this condition the products from the detonation of the primer  26  by the firing pin  24  can leave the casing  38  through the outlet port  34  to detonate the shaped charge  14  ( FIG. 1 ). 
     Returning now to  FIG. 4 , the triggering device  12  also includes the inertial lock-out  28 , which is used to prevent movement of the firing pin  24  once the missile  10  ( FIG. 1 ) has been launched. The components of the lock-out  28  are in a cavity  110  of the device  12 . The cavity  110  may be aligned with the cavity  88 , although other orientations are possible. 
     The lock-out  28  includes an inertial mass  114  that is configured to shift its position in reaction to acceleration from the launch of the missile  10  ( FIG. 1 ). The mass  114  moves against a spring force from a spring  116 , which biases the position of the inertial mass  114  to one side of the cavity  110 , in the illustrated embodiment against the fixed sleeve  90 . The mass  114  is hollow, and has a damping orifice  118  inserted in one of its ends, between the mass  114  and the spring  116 . The damping orifice  118  has air passages therethrough configured to control the movement of the inertial mass  114  through air resistance. 
     Other components are also within the hollow inside the inertial mass  114 : a lockout plunger  122 , a plunger spring  124 , and a ball  126 . A second ball  128  also initially partially rests in a groove  134  in the inertial mass  114 . The second ball  128  also is initially in a hole  136  that is between the cavities  58  and  110 , aligned with a groove  138  in the firing pin  24 . 
     Inertia from the launch of the missile  10  ( FIG. 1 ) causes the inertial mass  114  to move rightward in the diagram. The movement of the inertial mass  114  pushes the ball  128  out of the inertial mass groove  134  and into the firing pin groove  138 . The rightward movement of the inertial mass  114  also allows the ball  126  to emerge from the central hollow of the inertial mass  114 , being pushed by a tip of the lockout plunger  122 , under the force of the plunger spring  124 . The ball  126  drops down in the space left by movement of the inertial mass  114 , blocking the inertial mass  114  from returning to its original position. This blockage of return movement of the inertial mass  114  keeps the ball  128  engaged in and indeed locked in the firing pin groove  138 . This prevents movement of the firing pin  24 , thereby also preventing the firing pin  24  from engaging the primer  26 . 
     Many variations are possible, in that some of the features described above may be modified or in some instance omitted altogether. For instance the inertial lock-out  28  ( FIG. 4 ) may have a different configuration than what is shown. Alternatively or in addition the linkage  32  ( FIG. 4 ) may have a different configuration, or may be omitted altogether. In the latter case the outlet port  34  ( FIG. 4 ) may allow passage of detonation/combustion products without any blockage. Alternatively a differently-configured safety device may be employed in the outlet port  34 . 
       FIG. 12  shows a generalized alternative embodiment triggering device  212 , with a trigger element or mechanism  222  used to move a firing pin  224  toward a primer  226 ; an inertial lockout  228  used to prevent movement of the firing pin  224  once the missile has been launched; and a linkage  232  that is used to selectively open or close a passageway (output port)  234  through which products from the primer  226  pass. The operative general parts are located within a casing  238 . 
     The parts or elements  222 ,  228 , and  232  may have different configurations from those described earlier with regard to the triggering device  12  ( FIG. 4 ). The trigger element  222  may provide other sorts of forces for selectively moving the firing pin  224  when a temperature threshold is reach, for example by using a shape memory alloy spring. The inertial lockout  228  may have other forms for locking out movement of the firing pin  224  when the missile or munition accelerates during launch or flight, for example utilizing mechanical lockout mechanisms other than that in the lockout  28  ( FIG. 4 ). The linkage  232  may use any of a variety of mechanical components, such as sliding elements, pivoting elements, and/or rotating elements, such as gears or cams/followers, coupled together in any of a variety of suitable ways to mechanically link the firing pin  224  to a valve (of any of a variety of sorts) that selectively allows detonation/combustion products to exit the device  212 . 
     In operation, with reference now in addition to  FIG. 13 , a method  300  of firing the triggering device  12  ( FIG. 1 ) begins in step  302  with the device  12  being heated until the forces from the sleeve  44  ( FIG. 4 ) cause the metal pin  42  ( FIG. 4 ) to break, such as at the notched or weakened portion  46  ( FIG. 4 ). 
     In step  304  the breakage of the pin  42  ( FIG. 4 ) causes the firing pin  24  ( FIG. 4 ) to move toward the primer  26  ( FIG. 4 ). At the same time, in step  306 , the movement of the firing pin  24  acts through the linkage  32  ( FIG. 4 ) to rotate the barrel valve  96  ( FIG. 4 ), eventually opening the valve  96 . Finally in step  308  the firing pin  24  strikes the primer  26  ( FIG. 4 ), resulting in detonation products from the primer  26  and the booster  68  ( FIG. 4 ) exiting the triggering device  12  ( FIG. 1 ) through the outlet port  34  ( FIG. 4 ). 
     The triggering devices  12  and  212  provides many advantages over prior devices. The linkage between the firing pin  24  ( FIG. 4 ) and the valve  96  ( FIG. 4 ) provides a robust safety device, low in cost and reliable in operation, for preventing undesired triggering of the shaped charge  14  ( FIG. 1 ). 
     Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.