Abstract:
A method of igniting one of a pyrotechnic material and primer during or after an all fire setback acceleration. The method including: positioning a mass element along an inclined surface; biasing the mass element in a direction into the inclined surface such that the mass element traverses the inclined surface upon the all fire setback acceleration against the biasing; drawing the mass element toward one of a pyrotechnic material and primer with the biasing after the mass element traverses the inclined surface. The method can further include delaying the drawing until the mass element experiences a set forward acceleration. The delaying can include drawing the mass element into a delay well after the mass element traverses the inclined surface and drawing the mass element across a delay wedge when the mass element experiences the set forward acceleration.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit to U.S. Provisional Application 61/175,775 filed on May 5, 2009, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to inertial igniters for thermal batteries or other pyrotechnic type initiated devices for gun-fired munitions and mortars that are initiated as a result of either firing setback acceleration or set-forward acceleration and for electrical switches that are activated (opened or closed) as a result of either firing setback acceleration or set-forward acceleration. 
     2. Prior Art 
     Thermal batteries represent a class of reserve batteries that operate at high temperature. Unlike liquid reserve batteries, in thermal batteries the electrolyte is already in the cells and therefore does not require a distribution mechanism such as spinning. The electrolyte is dry, solid and non-conductive, thereby leaving the battery in a non-operational and inert condition. These batteries incorporate pyrotechnic heat sources to melt the electrolyte just prior to use in order to make them electrically conductive and thereby making the battery active. The most common internal pyrotechnic is a blend of Fe and KClO 4 . Thermal batteries utilize a molten salt to serve as the electrolyte upon activation. The electrolytes are usually mixtures of alkali-halide salts and are used with the Li(Si)/FeS 2  or Li(Si)/CoS 2  couples. Some batteries also employ anodes of Li(Al) in place of the Li(Si) anodes. Insulation and internal heat sinks are used to maintain the electrolyte in its molten and conductive condition during the time of use. Reserve batteries are inactive and inert when manufactured and become active and begin to produce power only when they are activated. 
     Thermal batteries have long been used in munitions and other similar applications to provide a relatively large amount of power during a relatively short period of time, mainly during the munitions flight. Thermal batteries have high power density and can provide a large amount of power as long as the electrolyte of the thermal battery stays liquid, thereby conductive. The process of manufacturing thermal batteries is highly labor intensive and requires relatively expensive facilities. Fabrication usually involves costly batch processes, including pressing electrodes and electrolytes into rigid wafers, and assembling batteries by hand. The batteries are encased in a hermetically-sealed metal container that is usually cylindrical in shape. Thermal batteries, however, have the advantage of very long shelf life of up to 20 years that is required for munitions applications. 
     Thermal batteries generally use some type of igniter to provide a controlled pyrotechnic reaction to produce output gas, flame or hot particles to ignite the heating elements of the thermal battery. There are currently two distinct classes of igniters that are available for use in thermal batteries. The first class of igniter operates based on electrical energy. Such electrical igniters require electrical energy, thereby requiring an onboard battery or other power sources. The second class of igniters, commonly called “inertial igniters”, operates based on the firing acceleration. The inertial igniters do not require onboard batteries for their operation and are thereby often used in high-G munitions applications such as in gun-fired munitions and mortars. 
     In general, the inertial igniters, particularly those that are designed to operate at relatively low impact levels, have to be provided with the means for distinguishing events such as accidental drops or explosions in their vicinity from the firing acceleration levels above which they are designed to be activated. This means that safety in terms of prevention of accidental ignition is one of the main concerns in inertial igniters. 
     SUMMARY OF THE INVENTION 
     Accordingly, an inertial igniter is provided. The inertial igniter comprising: a body; a mass element; a spring element attached at one end to the body and at another end, at least indirectly, to the mass element; and an inclined surface upon which the mass element moves from a resting position to an all-fire position; wherein upon the body experiencing a firing setback acceleration, the mass element travels at least across the inclined surface against a force of the spring element to ignite one of a pyrotechnic material and a primer. 
     The body can include a channel in communication with the inclined surface and positioned under the inclined surface in a direction opposite to the firing setback acceleration, the mass element traveling in the channel towards the one of the pyrotechnic material and primer with the force of the spring element. The channel can include the one of the pyrotechnic material and primer. The mass element can include a first pyrotechnic material and the channel includes a second pyrotechnic material. The channel can include one or more flame exit ports for directing flames resulting from contact between the first and second pyrotechnic materials. 
     The spring element can be a tensile spring or a compression spring. 
     The channel can further include a delay well and delay wedge, the delay well being between the inclined surface and delay wedge such that the mass element enters the delay well during the all fire setback acceleration and cannot traverse the delay wedge until the body experiences a set forward acceleration, after traversing the delay wedge, the mass element contacting the one of the pyrotechnic material and primer. 
     The mass element can be connected to the spring element through a link, the link being connected at one end by the mass element and at another end by a rotary joint, the spring element being connected to the link along a length of the link. 
     The spring element can be a torsional spring and the mass element comprises two mass elements disposed on each end of a link member which rotates about a rotary joint positioned along a length of the link member, the torsional spring being connected at one end to the link member, the inclined surface comprising two inclined surfaces corresponding to the two mass elements, wherein the torsional spring biases the mass elements up the inclined surfaces in a direction of the all fire setback acceleration. 
     Each of the inclined surfaces can include a stop for limiting movement of the mass elements up the inclined surfaces in the direction of the all fire setback acceleration. 
     The mass element can be connected to the spring element through a link, the link being connected at one end by the mass element and having first and second rotary joints, the spring element being connected to the link along a length of the link and the first rotary joint having a female portion and male portion positioned along an edge of the link member when the body is at rest, the second rotary joint having one of a female portion male portion positioned along the edge of the link member and the other of the female portion and male portion offset from the edge when the body is at rest. 
     Also provided is a method of igniting one of a pyrotechnic material and primer during or after an all fire setback acceleration. The method comprising: positioning a mass element along an inclined surface; biasing the mass element in a direction into the inclined surface such that the mass element traverses the inclined surface upon the all fire setback acceleration against the biasing; and drawing the mass element toward one of a pyrotechnic material and primer with the biasing after the mass element traverses the inclined surface. 
     The method can further comprise delaying the drawing until the mass element experiences a set forward acceleration. The delaying can comprise drawing the mass element into a delay well after the mass element traverses the inclined surface and drawing the mass element across a delay wedge when the mass element experiences the set forward acceleration. 
     The method can further comprise directing a flame resulting from the mass element contact with one of the pyrotechnic material and primer to a thermal battery. 
     Still further provided is an electrical switch comprising: a body; a mass element; a spring element attached at one end to the body and at another end, at least indirectly, to the mass element; and an inclined surface upon which the mass element moves from a resting position to an all-fire position; wherein upon the body experiencing a firing setback acceleration, the mass element travels at least across the inclined surface against a force of the spring element to contact an electrical contact and close a circuit. 
     The mass element can be at least partially formed of a conductive material and the spring element is conductive. 
     The body can include a channel in communication with the inclined surface and positioned under the inclined surface in a direction opposite to the firing setback acceleration, the mass element traveling in the channel towards the electrical contact with the force of the spring element. 
     The spring element can a compression spring or tension spring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the apparatus of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG. 1  illustrates a first embodiment of an inertial igniter. 
         FIG. 2  illustrates a variation of the inertial igniter of  FIG. 1 . 
         FIG. 3  illustrates another variation of the inertial igniter of  FIG. 1 . 
         FIG. 4  illustrates a first embodiment of an electrical switch. 
         FIG. 5  illustrates a second embodiment of an inertial igniter. 
         FIGS. 6   a  and  6   b  illustrate a perspective and plan view, respectively, of a third embodiment of an inertial igniter. 
         FIG. 7  illustrates a first variation of the inertial igniter of  FIGS. 6   a  and  6   b.    
         FIGS. 8   a  and  8   b  illustrate a side view and plan view, respectively, of a second variation of the inertial igniter of  FIGS. 6   a  and  6   b.    
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A first embodiment of an inertial igniter is shown in  FIG. 1 , the inertial igniter of the first embodiment generally being referred to with reference numeral  100 . In the first embodiment, a mass element  102  (striker mass) is attached to a body  104  of the inertial igniter  100  via a spring element  106 . The spring element  106  can be preloaded in tension so that it would not freely or upon the application of a threshold force would not extend enough to allow the mass element  102  to move down along the indicated path A. As a result, the mass element  102  is essentially positioned as shown in  FIG. 1  at rest or upon the application of less than all-fire (setback) acceleration level in the direction of the indicated arrow B. Upon all-fire acceleration, the setback acceleration acts upon the inertia of the mass element  102 , and if it lasts long enough, it overcomes the resistance of the spring element and the wedge interface  108 , to extend the spring  106  enough to allow the mass element to follow the indicated path A downwards along the wedge interface  108 . Once the mass element  102  reaches the bottom surface  110  of the body  104  of the inertial igniter  100 , the force exerted by the spring element  106  acts on the mass element  102  to pull the same into the provided corridor  112 . During the latter process, the potential energy stored in the spring element is (partially or wholly) transferred to the mass element  102  as kinetic energy. 
     The mass element  102  then initiates a pyrotechnic material  114  positioned in the corridor  112 . When the process of initiating the pyrotechnic material  114  is by a rubbing action, a first part of the pyrotechnic is provided on the mass element  102  and the second part of the pyrotechnic material is disposed in the corridor  112 . Then as the mass element passes through the corridor  112 , the two parts of the pyrotechnic material rub against each other, thereby initiating the pyrotechnic material  114 . The generated flame and sparks, etc., are then channeled through one or more ports  116  into a thermal battery, or the like (not shown) for its activation. 
     Alternatively, the mass element  102  can acts as a striker mass. The mass element  102  can be provided with one part  114   a  of a two part pyrotechnic material as shown in  FIG. 2 . The second part  114   b  of the two parts pyrotechnic is provided in the corridor  112 , such as at the end of the corridor  112 . Then once the mass element  102  is released into the corridor  112  as a result of the applied setback acceleration over a long enough length of time, the first pyrotechnic part  114   a  on the striker mass  102  strikes the second pyrotechnic part  114   b , thereby initiating the igniter. Pinching points are preferably provided on the striker mass and inside the second pyrotechnic part (not shown) to facilitate ignition. The generated flame and sparks are then channeled through the port  116  into the thermal battery, or the like (not shown) for its activation. 
     Alternatively, the mass element  102  ( FIGS. 1 and 2 ) may strike a primer, thereby initiating the primer. The generated flame and sparks are then channeled through the port  116  into the thermal battery, or the like (not shown) for its activation. 
     Alternatively, the tensile spring element  106  shown in the embodiments of  FIGS. 1 and 2  can be replaced by a compressive spring element  118 . The compressive spring element  118  can be attached on one side to the mass element  102  and on the other end attached to a wall  120  of the inertial igniter housing  104  as shown in  FIG. 3 . The wall  120  can be opposite from a wall  122  which supports the second pyrotechnic material  114   b . Once the mass element  102  is released into the corridor  112  as a result of the applied setback acceleration over a long enough length of time, the first pyrotechnic part  114   a  on the striker mass  102  strikes the second pyrotechnic part  114   b , thereby initiating the igniter. The generated flame and sparks are then channeled through the port  116  into the thermal battery, or the like (not shown) for its activation. 
     The design of the inertial igniter embodiments of  FIG. 1-3  may also be used to construct electrical switches which are activated similarly by the firing setback acceleration. The design and operation of such electrical switches is shown by its application to the embodiment of  FIG. 3  as observed in the schematic of  FIG. 4 . It is however appreciated that the embodiments of  FIGS. 1 and 2  may be similarly used to construct similar electrical switches. Similar features from  FIGS. 1-3  are denoted with similar reference numerals, except with a 200 series. 
     In the electrical switch  200 , the mass element  202  also acts as a first electrical contact  2 , which is released into the corridor  212  as a result of the applied setback acceleration over a long enough length of time. The first electrical contact, which can be the mass element  202  itself or a portion thereof, reaches a second electrical contact  222  shown in  FIG. 4 , thereby allowing electrical current to flow to/from the first switching wire  224  through the first and second electrical contacts  202 ,  222  to/from the second switching wire  226 . The second electrical contact  222  can be provided with adequate insulation material  228  to ensure that it stays insulated from the body of the electrical switch  200 , which may be electrically conductive but is preferably made of electrically nonconductive material. In this embodiment, the compressive spring  218  is considered to be electrically conductive but can alternatively be provided with a conductive component. 
     The embodiments of  FIGS. 1-3  are designed for initiation as a result of the firing setback acceleration that the inertial igniter is subjected over a long enough period of time, usually around 4-10 msec. In certain applications, particularly in munitions applications that involve very high firing setback accelerations, it is highly desirable to delay ignition until the round has exited or has nearly exited the barrel. Such a delay will ensure that the thermal battery is still in its full solid state during the entire setback acceleration, which would in turn ensure survival of very high G setback acceleration levels. 
     The inertial igniter  300  embodiment shown schematically in  FIG. 5  is similar to the embodiment of  FIG. 1  is designed to delay ignition until the round experiences its set-forward acceleration upon exiting the gun barrel. The embodiment of  FIG. 5  is similar to the embodiment of  FIG. 1 , with similar features from the inertial igniter of  FIG. 1  being denoted with similar reference numerals, except with a 300 series. In the inertial igniter  300  of  FIG. 5 , after overcoming the first wedge interface  308  as a result of the setback acceleration, the mass element  302  travels to a delay well  330  and is held there by the setback acceleration. Then when the round begins to experience a set-forward acceleration in the direction opposite to that of the setback acceleration ( FIG. 5 ), the mass element  302  is able to overcome a delay wedge  332  in communication with the delay well  330  and be pulled into the corridor  312  containing the pyrotechnics  314  by the stretched tensile spring element  306 . It is noted that while the mass element  302  is “trapped” in the delay well  330  by the setback acceleration, its positioning beneath a portion  308   a  of the primary wedge  308  ensures that the mass element  302  is not ejected back to its start position above the primary wedge  308  upon the application of the set-forward acceleration. As discussed with regard to the inertial igniter of  FIG. 1 , when the process of initiating the pyrotechnic material  314  is by a rubbing action, a first part of the pyrotechnic is provided on the mass element  302  and a second part of the pyrotechnic material  314  is disposed in the corridor  312 . Then as the mass element  302  passes through the corridor  312 , the two parts of the pyrotechnic material rub against each other, thereby initiating the pyrotechnic material  314 . The generated flame and sparks, etc., are then channeled through the port  316  into the thermal battery, or the like (not shown) for its activation. 
     Alternatively, the mass element  302  can act as a striker mass similar to that shown in the schematic of  FIG. 2 . The second part of the two parts pyrotechnic is provided in the corridor  312 , preferably at the end of the corridor  314  and is activated as was previously described for the embodiment of  FIG. 2 . 
     Alternatively, as also discussed with the first embodiment of inertial igniters above, the mass element  302  may strike a primer, thereby initiating the primer. The generated flame and sparks are then channeled through the port  316  into the thermal battery, or the like (not shown) for its activation. 
     Alternatively, the tensile spring element  306  shown in the embodiment of  FIG. 5  can be replaced by a compressive spring element as shown and described for the embodiment of  FIG. 3 . 
     As still yet another alternative, the inertial igniter of  FIG. 5  can be used as an electrical switch, similar to that described above with regard to  FIG. 4  to provide a time delay for closing the circuit. 
     Another embodiment of an inertial igniter is shown in a perspective schematic of  FIG. 6   a  (a plan view of the device is shown on in  FIG. 6   b ). In this embodiment, the mass element  402  is connected to a link  404 , which is allowed to rotate sideways and downward at its double rotary joint connection  406  to the body  408  of the inertial igniter (here shown as the ground). A tensile spring element  410  is used to maintain the link  404 , thereby the mass element  402  at its rest position shown in  FIG. 6   a  at its right hand most position on an inclined surface  412 . The spring element  410  can be preloaded in tension so that during all no-fire (accidental) accelerations in the direction of the setback acceleration and corresponding time durations (accidental impulse levels and acceleration profiles), the mass element  402  does not travel all the way down the inclined surface  412 . However, upon the application of all-fire setback acceleration profile, the mass element  402  overcomes the resistance of the inclined surface  412  and tensile force of the spring element  410  and follows the path A indicated in  FIG. 6   a  to pass beneath the wedge  414 . At this point, the potential energy stored in the spring element  410  begins to accelerate the mass element (and the link  404 ) to the right. The mass element (with first part pyrotechnic material) can then initiate the inertial igniter by either rubbing against the second part pyrotechnic material (similarly to that shown in  FIG. 1 ) or by impacting the second part pyrotechnic material (similarly to that shown in  FIG. 2 ) or by impacting a primer. The generated flame and sparks are then channeled through a port into the thermal battery, or the like for activation thereof (similarly to that shown in  FIGS. 1-3 ). 
     An variation of the embodiment of  FIG. 6  is shown in the schematic of  FIG. 7 . In the embodiment of  FIG. 7 , as compared to the embodiment of  FIG. 6   b , at rest, a female portion  416   a  of a primary rotating joint  416  on the link element  404  is engaged with its male counterpart  416   b . Then as a result of the setback acceleration, the mass element  404  rotates essentially on a circle centered at the primary joint  416  and downward over the inclined surface  412  of the wedge element  414 . During this time, the tensile spring element  410  (which can be preloaded in tension at rest) is further extended, thereby further storing potential energy. Once the mass element  402  passes the wedge element  414 , the mass element  402  moves under the wedge element  414  and the spring element  410  begins accelerating it to the right as previously described for the embodiment of  FIG. 6   a . At some point, however, a female portion  418   a  of a secondary rotary joint  418  on the link  404  reaches a fixed male portion  418   b  of the secondary rotary joint  418 . Then from that point on, the link  404  begins rotating about the secondary rotary joint  418 . Thus, the radius of the link  404  and mass element  402  rotation is reduced, therefore proportionally increasing the rotational speed of the link  402  and thereby the velocity of the mass element  402 . As a result, a smaller mass element  402  can be used to achieve initiation of the pyrotechnic materials as compared to the embodiment of  FIG. 6   a.    
     Alternatively, the tensile spring element shown in the embodiments of  FIGS. 6   a  and  7  can be replaced by a compressive spring element similar to that shown and described for the embodiment of  FIG. 3 . 
     A second variant of the embodiment of  FIG. 6   a  is shown in  FIGS. 8   a  and  8   b . The embodiment of  FIGS. 8   a  and  8   b  differs from the embodiment of  FIG. 6   a  for at least the following two reasons. Firstly, the tension spring element of  FIG. 6   a  is replaced by a torsional spring  420 . Secondly, instead of one wedge surface, two (or more) wedge surfaces  412  are each used for a striker mass  402  to ride as the inertial igniter is subjected to setback acceleration in the direction of the indicated arrow B (alternatively, only one wedge element may also be used). The link element  404   a  is similarly attached to the body  408  of the inertial igniter by a joint  406   a  that allows for rotation of the link about the vertical axis (perpendicular to the plane of the illustration) as well as displace up and down (in and out of the plane of the illustration), thereby constituting a so-called “cylindrical joint”. The torsional spring element  420  is used to maintain the link  404   a , thereby the mass element  402  at its rest position shown in  FIG. 8   a , resting against a striker stop  414   a  on the inclined surface  412 . The torsional spring element  420  can be preloaded so that during all no-fire (accidental) accelerations in the direction of the setback acceleration B and corresponding time durations (accidental impulse levels and acceleration profiles), the mass elements  402  do not travel all the way down the wedge inclined surface  412 . However, upon the application of all-fire setback acceleration profile, the mass elements  402  overcome the resistance of the wedge  414  and the resisting torque of the torsional spring element  420  and follow the path A indicated by the arrow in  FIG. 8   a  and pass beneath the wedge  414 . As the mass elements  402  travel down the wedge slope, the link  404   a  is forced to rotate in the counterclockwise direction and more potential energy is stored in the torsional spring  420 . At this point, the potential energy stored in the torsional spring element  420  begins to accelerate the mass elements  402  towards the second part pyrotechnic materials  414   b  (as the link is accelerated in rotation in the clockwise direction). The mass elements  402  (with first part pyrotechnic material  414   a ) can then initiate the inertial igniter by either rubbing against the second part pyrotechnic material  414   b  (as shown in  FIG. 1 ) or by impacting the second part pyrotechnic material  414   b  (as shown in  FIG. 8   a ) or by impacting a primer. The generated flame and sparks can then be channeled through a port(s)  116  into the thermal battery, or the like for activation thereof. 
     In a manner similar to those of the embodiment of  FIG. 4 , the inertial igniter of the embodiments of  FIGS. 6   a ,  7  and  8   a  may be converted into an electrical switch that is activated by the firing setback acceleration. 
     In alternative embodiments to those of  FIGS. 6   a ,  7  and  8   a , by providing delay wells and delay well wedges similar to that shown in the embodiment of  FIG. 5 , these embodiments can be constructed to initiate during the set-forward acceleration of the round as was previously described for the embodiment of  FIG. 5 . 
     It is noted that in all the embodiments shown, the spring elements may be preloaded (in tension for the tensile springs and in compression for the compression springs) at rest. However, the spring elements in these embodiments can be substantially at their free lengths at rest. The latter spring element state can be safer and prevent accidental activation. In addition, the level and duration of the acceleration in the direction of the setback acceleration (impulse level) that would actuate these devices, i.e., move the mass elements past the indicated wedge surface and thereby initiate activation, are designed to be higher that all no-fire (no-actuation for the electrical switch embodiments) acceleration and duration (impulse) levels to satisfy the device safety requirements against accidental initiation, such as due to accidental dropping of the devices on hard surfaces from heights of usually 5-7 feet. 
     While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.