Patent Grant
10234254
1. Field of the Invention
The present invention relates generally to mechanical inertial igniters and G-switches, and more particularly to compact, low-volume, reliable and easy to manufacture mechanical inertial igniters, ignition systems for thermal batteries and for G-switches used in munitions for initiation and the like as a result of setback acceleration (shock) or the like.
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 KClO4. 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)/FeS2 or Li(Si)/CoS2 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 or semi-automatically. Other manufacturing processes have also been recently developed that are more amenable to automation. 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, however, require electrical energy, thereby requiring an onboard battery or other power sources with related shelf life and/or complexity and volume requirements to operate and initiate the thermal battery. 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 firing setback or the like acceleration (shock) 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.
The need to differentiate accidental and other so-called no-fire events from the so-called all-fire event, i.e., the firing setback acceleration (shock) event necessitates the employment of a safety system which is capable of allowing initiation of the inertial igniter only when the inertial igniter is subjected to the impulse level threshold corresponding to or above the minimum all-fire impulse levels. The safety mechanism is preferably provided with a mechanism that provides for a preset (safety) impulse level threshold, which must be reached before the safety mechanism is activated. The safety mechanism can be thought of as a mechanical delay mechanism, which is usually and preferably provided with certain acceleration threshold detection mechanisms, such that after the safety acceleration threshold has been reached and after a certain amount of time delay, a separate initiation system is actuated or released to provide ignition of the inertial igniter pyrotechnics. The inertial igniter pyrotechnic material may have been directly loaded into the ignition mechanism or may be a separately installed percussion primer. An inertial igniter that combines such a safety system with an impact based initiation system and its alternative embodiments are described herein.
Inertia-based igniters must therefore comprise two components so that together they provide the aforementioned mechanical safety (delay mechanism that is activated after a prescribed acceleration threshold has been reached) and to provide the required striking (percussion) action to achieve ignition of the pyrotechnic element(s) of the inertial igniter. The function of the safety system (mechanism) is to hold the striker element fixed to the igniter structure until the inertial igniter is subjected to a high enough acceleration level above the aforementioned acceleration threshold level and with long enough duration, i.e., to a prescribed impulse level threshold after the aforementioned safety acceleration threshold has been reached, corresponding to the firing setback acceleration event. The prescribed safety acceleration threshold provides a minimum acceleration level to ensure that the inertial igniter is safe, i.e., the striker element stays fixed to the inertial igniter structure, when subjected to acceleration levels below the safety acceleration threshold even for long duration. Once the all-fire event, i.e., the minimum (safety threshold) acceleration level and the prescribed impulse level threshold has been reached, the safety system (mechanism) releases the striker element, allowing it to accelerate toward its target. The ignition itself may take place as a result of striker impact, or simply contact or proximity. For example, the striker may be akin to a firing pin and the target akin to a standard percussion cap primer. Alternately, the striker-target pair may bring together one or more chemical compounds whose combination with or without impact will set off a reaction resulting in the desired ignition.
A schematic of a cross-section of a conventional thermal battery and inertial igniter assembly is shown in
The isometric cross-sectional view of a currently available inertia igniter is shown in
A striker mass 205 is shown in its locked position in
In its illustrated position in
The collar 211 rides up and down on the posts 203 as can be seen in
In the inertial igniters of the type shown in
The basic operation of the inertial igniter 200 shown in
Assuming that the acceleration time profile was at or above the specified “all-fire” profile, the collar 211 will have translated down past the locking balls 207, allowing the striker mass 205 to accelerate down towards the base 202. In such a situation, since the locking balls 207 are no longer constrained by the collar 211, the downward force that the striker mass 205 has been exerting on the locking balls 207 will force the locking balls 207 to move outward in the radial direction. Once the locking balls 207 are out of the way of the dimples 209, the downward motion of the striker mass 205 is no longer impeded. As a result, the striker mass 205 moves downward, causing the tip 216 of the striker mass 205 to strike the pyrotechnic compound 215 on the surface of the protrusion 217 with the requisite energy to initiate ignition.
In the inertial igniter 200 of
In the inertial igniter 200 of
Briefly, the safety system parameters, i.e., the mass of the collar 211, the spring rate of the setback spring 210 and the dwell stroke (the distance that the collar 210 has to travel downward to release the locking balls 207 and thereby release the striker mass 205) must be tuned to provide the required actuation performance characteristics. Similarly, to provide the requisite impact energy, the mass of the striker 205 and the aforementioned separation distance between the tip 216 of the striker mass and the pyrotechnic compound 215 (and the tip of the protrusion 217) must work together to provide the specified impact energy to initiate the pyrotechnic compound when subjected to the remaining portion of the prescribed initiation acceleration profile after the safety system has been actuated.
In general, the required aforementioned acceleration time profile threshold for inertial igniter initiation, i.e., the so-called all-fire condition, is described in terms of an acceleration pulse of certain amplitude and duration. For example, the all-fire acceleration pulse may be given as being 1000 G for 15 milliseconds. The no-fire (no-initiation) condition may be indicated similarly with certain acceleration pulse (or half-sine) amplitude and duration. For example, the no-fire condition may be indicated as being an acceleration pulse of 2000 G for 0.5 milliseconds. Other no-fire conditions may include transportation induced vibration, usually around 10 G with a range of frequencies.
It is appreciated by those skilled in the art that when the inertial igniter 200 of
In addition, in recent years new improved chemistries and manufacturing processes have been developed that promise the development of lower cost and higher performance thermal batteries that could be produced in various shapes and sizes, including their small and miniaturized versions. However, inertial igniters are relatively large and not suitable for small and low power thermal batteries, particularly those that are being developed for use in miniaturized fuzing, future smart munitions, and other similar applications. This is in general the case for munitions with relatively low firing setback acceleration, particularly those in which the firing setback acceleration pulse (shock) has relatively short duration.
It is therefore appreciated by those skilled in the art that the duration of the all fire acceleration must at least be the sum of the above two time periods Δt1 and Δt2, hereinafter indicated as Δt=Δt1+Δt2. For example, for the aforementioned case of all-fire (setback) acceleration being 1000 G for 15 milliseconds, the total time Δt must be less than the indicated acceleration duration of 15 milliseconds.
In certain cases, due to the small size or geometry of the thermal battery or the like, the height of the inertial igniter that can be used is so small that the striker mass 205 upon its release does not have enough distance to travel downward to gain enough velocity (i.e., enough kinetic energy) before its tip 216 strikes the pyrotechnic material 215 over the protruding tip 217 in order to be able to cause the pyrotechnic material 215 to be reliably ignited.
Inertial igniter all-fire and no-fire requirements generally vary significantly from one application to the other. Therefore it is highly desirable to develop inertial igniters which are provided with the means of independently varying the aforementioned safety acceleration threshold level that has been to be reached and the amount of time delay before which the inertial igniter striker element is released.
It is also highly desirable to provide inertial igniter mechanisms and designs which would minimize the effects of friction and stiction between the parts, which would increase initiation reliability, which would reduce the range of acceleration within which initiation is certain to occur.
It is also highly desirable that the inertial igniter mechanisms and designs would result in devices that can be fabricated inexpensively.
In certain applications, the aforementioned firing setback acceleration duration is very short thereby the said acceleration cannot be relied upon to both actuate the aforementioned safety mechanism and then accelerate the inertial igniter striker element to the required speed (energy) to achieve pyrotechnic initiation.
A need therefore exists for inertial igniters that can be used to initiate thermal batteries or the like in munitions or the like when the height available in munitions is too small as is described above for inertial igniters of the type shown in
A need also exists for inertial igniter mechanisms that would provide the means of independently varying the safety acceleration threshold level of the inertial igniter that has to be reached and the amount of time delay before which the inertial igniter striker element is released to ignite the device pyrotechnics.
A need also exists for inertial igniter mechanisms and designs which would minimize the effects of friction and stiction between the parts.
A need also exists for inertial igniter mechanisms and designs that would significantly increase operational reliability of the inertial igniter.
A need also exists for inertial igniter mechanisms and designs that would reduce the range of setback or the like acceleration level within which initiation certainty may occur.
A need also exists for inertial igniter mechanisms and designs that would make the inertial igniter manufactured at lower cost by reducing the number of parts and/or by reducing the complexity and manufacturing cost of the inertial igniter parts and their quality control and assembly costs.
A need also exists for inertial igniters that can be used in applications in which the setback acceleration level is relatively low and/or the setback acceleration duration is relatively short.
Such inertial igniters must be safe and do not initiate when subjected no-fire conditions. In general, such inertial igniters are also required to withstand the harsh firing environment, while being able to be designed to ignite at specified acceleration levels when subjected to such accelerations for a specified amount of time to match the firing acceleration experienced. Very high reliability is also of much concern. The inertial igniters must also usually have a shelf life of up to 20 years and could generally be stored at temperatures of sometimes in the range of −65 to 165 degrees F. This requirement is usually satisfied best if the igniter pyrotechnic is in a sealed compartment. The inertial igniters must also consider the manufacturing costs and simplicity in design to make them cost effective for munitions applications.
To ensure safety and reliability, inertial igniters should not initiate during acceleration events which may occur during manufacture, assembly, handling, transport, accidental drops, etc. Additionally, once under the influence of an acceleration profile particular to the firing of ordinance from a gun, the device should initiate with high reliability. It is also conceivable that the igniter will experience incidental low but long-duration accelerations, whether accidental or as part of normal handling, which must be guarded against initiation.
Those skilled in the art will appreciate that the inertial igniters disclosed herein may provide one or more of the following advantages over prior art inertial igniters:
In view of such objects, inertial igniters and ignition systems for use with thermal batteries or the like upon subjection to firing setback acceleration, in particular low friction and stiction with independently adjustable no-fire (safety) acceleration threshold and all-fire acceleration activation levels and those that can be fabricated at relatively low cost are provided. Provided are also inertial igniters that are very low height for small thermal batteries. Still yet provided are G-switches based on the disclosed inertial igniters.
Accordingly, a device is provided. The device comprising: an impact mass movably restrained relative to a base; and a release mechanism configured to be movable between a restrained position for preventing movement of the impact mass and a released position for permitting movement of the impact mass when the release mechanism is subjected to an acceleration greater than a predetermined magnitude and duration; wherein the release mechanism having a release mass movable when subjected to the acceleration, the movement of the release mass not being influenced by movement of the impact mass.
The release mass can be separated from the impact mass in a lateral direction relative to a direction of the acceleration.
The impact mass can be rotatably movable relative to the base.
The device can further comprise a flame producing means for outputting a flame upon movement of the impact mass. The flame producing means can comprise: a first protrusion provided to protrude from a surface of the impact mass; a second protrusion provided to protrude from the base, the second protrusion being positioned such that movement of the impact mass causes contact between the first and second protrusions; a pyrotechnic provided proximate to one of the first and second protrusions such that the contact between the first and second protrusions ignites the pyrotechnic; and an opening in the base for outputting the flame from the base.
The impact means can include a biasing member for biasing the impact mass in a direction opposite to the direction of the acceleration.
The device can further comprise a circuit means for one of opening or closing an electrical circuit upon movement of the impact mass. The circuit means can comprise: an electrically conductive member provided to a surface of the impact mass; and first and second electrical contacts, electrically isolated from each other, provided to the base, the first and second electrical contacts being positioned such that movement of the impact mass causes the electrically conductive member to contact and close the electrical circuit between the first and second electrical contacts. The circuit means can comprise: an electrically non-conductive member provided to protrude from a surface of the impact mass; and first and second electrical contacts, electrically connected to each other, provided to the base, the first and second electrical contacts being biased in an electrically closed position and movable to an electrically open position, the first and second electrical contacts being positioned such that movement of the impact mass causes the electrically non-conductive member to move the first and second electrical contacts to the electrically open position.
The release mechanism can comprise: a shaft having one end engaged with a portion of the impact mass and an other end engaged with the release mass, the shaft being movable to the released position upon movement of the release mass when the release mass is subjected to the acceleration; and a shaft biasing element for biasing the shaft into the released position when the release mass moves and is no longer engaged with the other end of the shaft. The device can further comprise a release mass biasing element for biasing the release mass into a position of engagement with the other end of the shaft. The release mass can move in translation. The release mass can move in rotation. The device can further comprise a housing including the base.
Also provided is a method for moving an impact mass upon the impact mass experiencing an acceleration greater than a predetermined magnitude and duration. The method comprising: movably restraining the impact mass relative to a base; moving a release mechanism between a restrained position for preventing movement of the impact mass and a released position for permitting movement of the impact mass when the release mechanism is subjected to the acceleration; and configuring the release mechanism to have a release mass movable when subjected to the acceleration, wherein the movement of the release mass is not influenced by movement of the impact mass.
The method can further comprise separating the release mass from the impact mass in a lateral direction relative to a direction of the acceleration.
The method can further comprise outputting a flame upon movement of the impact mass.
The method can further comprise one of opening or closing an electrical circuit upon movement of the impact mass.
The release mass can move in translation.
The release mass can move in rotation.
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:
A schematic of a cross-sectional view of a first embodiment 50 of an inertia igniter is shown in
A post 54, which is fixed to the base element 51 is provided with a hole 55. A shaft 57 is positioned in the hole 55 and is movable within the hole from a position engaging the striker mass 52 to a position not engaging the striker mass 52. Attached to the shaft 57 is the head 59 which in the pre-initiation configuration shown in
In the configuration of
The sliding member 58 is free to slide down against a member 68, if necessary via rolling elements 69. However, sliding contact between the member 68 and sliding member 58 may also be utilized, particularly if the contacting surfaces are low friction surfaces. However, it will be appreciated by those skilled in the art that the rolling elements 69 would provide a means of reducing sliding friction between the sliding member 58 and the member 68 and minimize the possibility of stiction between the moving surfaces. As a result, a level of force needed to move the sliding member down become highly predictable, which in turn makes the level of acceleration needed to release the inertial ignite striker mass 52 more predictable as is described later. Similar roller elements (not shown) may also be positioned between the contacting surfaces of the sliding member 58 and the head 59 of the shaft 57. The rolling elements 69 can be housed in retaining cavities (not shown) in the sliding member 58 or similarly held onto the sliding member 58 via a commonly used cage element (not shown).
The member 68 is fixed to the base element 51. A spring element 70 resists downward motion of the sliding member 58, and can be preloaded in compression so that if a downward force that is less than the compressive preload is applied to the sliding member 58, the applied force would not cause the sliding element 58 to move downwards. A stop 71 fixed to the member 68, is provided to allow the spring element 70 to be preloaded in compression by preventing the sliding member 58 from moving further up (in the direction of arrow 68) from the configuration shown in
During the firing, the inertial igniter 50 is considered to be subjected to setback acceleration in the direction of the arrow 63. The acceleration in the direction of the arrow 63 acts on the inertia of the sliding element 58 and generates a downward force that tends to slide the sliding element 58 downwards (opposite to the direction of acceleration). The compression preloading of the spring element 70 is generally selected such that with the no-fire acceleration levels, the inertia force acting on the sliding element 58 would not overcome (or at most be equal to) the preloading force of the spring element 70. As a result, the inertial igniter 50 is ensured to satisfy its prescribed no-fire requirement. Alternatively, and particularly when the peak no-fire acceleration level is higher than the peak all-fire (setback) acceleration levels but is very short duration as compared to the duration of the all-fire acceleration, then the time that it takes for the sliding element 58 to move down enough to clear the head 59 of the shaft 57 is designed to be less than the duration of the no-fire acceleration events.
Now if the acceleration level in the direction of the arrow 63 is high enough, then the aforementioned inertia force acting on the sliding element 58 will overcome the preloading force of the spring element 70, and will begin to travel downward. If the acceleration level is applied over a long enough period of time (duration) as well, i.e., if the all-fire condition is satisfied and the sliding element 58 will have enough time to travel down far enough and clears the head 59 of the shaft 57, then the compressively preloaded spring 72 would push the head 59 and the shaft 57 away from the striker mass 52, thereby disengaging the tip 60 of the shaft 57 from the tip 61 of the striker mass 52. As a result, the striker mass 52 is released and is allowed to be accelerated in the clockwise rotation as indicated by the arrow 62 (the release mechanism takes a release portion where it is no longer engaged with the mass 52). As a result, for a properly designed inertial igniter 50 (i.e., by selecting a proper mass and moment of inertial for the striker mass 52 and the range of clockwise rotation for the striker mass 52 so that it would gain enough energy), the striker mass 52 will gain enough kinetic energy to initiate the pyrotechnic material 64 between the pinching points provided by the protrusions 65 and 66 on the base element 51 and the bottom surface of the striker mass 52, respectively, as shown in
It will be appreciated by those skilled in the art that the duration of the all-fire acceleration level can also be important for the operation of the inertial igniter 50 by ensuring that the all-fire acceleration level is available long enough to accelerate the striker mass 52 towards the base element 51 to gain enough energy to initiate the pyrotechnic material 64 as described above by the pinching action between the protruding elements 65 and 66.
It will be appreciated by those skilled in the art that when the inertial igniter 50 (
It will be appreciated by those skilled in the art that in the inertial igniter embodiment 50 of
It will also be appreciated by those skilled in the art that by providing a preloaded compressive force level in the spring 72 that is greater than the maximum friction and stiction forces between the tip 61 of the striker mass 52 and the tip 60 of the shaft 57 as well as between the shaft 57 and the hole 55 in the post 54, then once the sliding element 58 has cleared the head 59 of the shaft 57, then the tip 60 of the shaft 57 is ensured to be pulled away from the top 61 of the striker mass 52 to initiate its accelerated clockwise rotation in the direction of the arrow 62, thereby initiating the pyrotechnic material 64 as was previously described.
In the embodiment of
It will be appreciated by those skilled in the art that the hole 55 and the cross-section of the mating shaft 57 do not have to be circular. For example, the designer may choose to use non-circular shapes instead to provide the means of preventing and/or minimizing the rotation of the shaft 57 about its long axis. For example, the designer may choose a trapezoidal mating shape or a shape close to or similar to a trapezoidal shape so that during assembly the two parts could be mated only in the correct orientation and thereby eliminate assembly mistakes and the need for post assembly inspection.
In certain applications, the all-fire setback acceleration level is either not high enough to impart enough kinetic energy to the striker mass 52 or its duration is not long enough to allow the striker mass be released by the downward motion of the sliding element 58 and the clockwise rotation of the striker mass in the direction of the arrow 62. As a result, the striker mass 52 is released as a result of setback firing acceleration or other prescribed acceleration events, but the striker mass is not capable to reliably ignite the pyrotechnic material 64 by the resulting impact (pinching) between the protruding elements 65 and 66. In such applications, additional kinetic energy may be provided by the potential energy stored in appropriately positioned preloaded spring element(s). An example of such an inertial igniter is shown in the schematic of the cross-sectional view of the inertial igniter embodiment 80 of
All components of the inertial igniter embodiment 80 of
A third embodiment 90 of the inertial igniter of the present invention is shown in the cross-sectional view of
Then when the inertial igniter is accelerated in the direction of the arrow 63, the force resulting by the action of the acceleration on the mass of the link 82 and its end 85 will tend to rotate the link 82 in the clockwise direction as seen in the view “A” of
It will be appreciated by those skilled in the art that the link 82 may be fixedly attached to the base plate 51 and be provided with a rotary (flexural) living joint to serve the same purposed as is described above for the link 82 and its end 85. In such an arrangement, the flexibility of the said flexural living joint may be used to serve the purpose of the spring 86. In which case the aforementioned preloading of the spring 86 may also be achieved by designing the flexural element such that in normal conditions the link 82 positions the end 85 passed the head 59 of the shaft 57. Then the prescribed preloading level is achieved by rotating the link in the clockwise direction and bringing it to stop against the provided stop element (elements 87 or 88 in
In the embodiments 50, 80 and 90 of
In the above embodiments, the disclosed devices are intended to actuate, i.e., release their striker mass 52 in response to an all-fire acceleration level to accelerate downwards to impact the provided pyrotechnics materials causing them to ignite. The same mechanisms used for the release of the striker mass due to an all-fire acceleration can be used to provide the means of opening or closing an electrical circuit, i.e., act as a so-called G-switch, that is actuated only if it is subjected to an all-fire acceleration profile, while staying inactive during all no-fire conditions, even if the acceleration level is higher than the all-fire acceleration level but significantly shorter in duration. As a result, this novel G-switch device would satisfy all no-fire (safety) requirements of the device in which it is used while activating in the prescribed all-fire condition.
Schematics of such G-switches are shown in
Turning first to the G-switch 100 of
As discussed above with regard to
As also discussed above with regard to
The G-switch 100 of
As was described for the embodiment 100 of
As discussed above with regard to
As also discussed above with regard to
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.
This application claims the benefit of U.S. Provisional Application No. 62/152,578, filed on Apr. 24, 2015, the entire contents of which is incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4716830 | Davis | Jan 1988 | A |
| 6240848 | Specht | Jun 2001 | B1 |
| 20110252994 | Murray | Oct 2011 | A1 |
| 20120132097 | Rastegar | May 2012 | A1 |
| 20120205225 | Rastegar | Aug 2012 | A1 |
| 20130284044 | Rastegar | Oct 2013 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20160313106 A1 | Oct 2016 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62152578 | Apr 2015 | US |
