U.S. patent application number 13/784737 was filed with the patent office on 2014-09-04 for compact and mechanical inertial igniters for thermal batteries and the like for munitions with short duration firing setback shock.
This patent application is currently assigned to Omnitek Partners LLC. The applicant listed for this patent is Jacques Fischer, Jahangir S. Rastegar. Invention is credited to Jacques Fischer, Jahangir S. Rastegar.
Application Number | 20140248522 13/784737 |
Document ID | / |
Family ID | 51421079 |
Filed Date | 2014-09-04 |
United States Patent
Application |
20140248522 |
Kind Code |
A1 |
Fischer; Jacques ; et
al. |
September 4, 2014 |
Compact and Mechanical Inertial Igniters For Thermal Batteries and
the like for Munitions With Short Duration Firing Setback Shock
Abstract
An inertial igniter including: a body having a base; a striker
release element rotatably disposed on the body, the striker release
element having a first surface; a first biasing element for biasing
the striker release element away from the base; a striker mass
rotatably disposed on the base along a second axis, the striker
mass having a second surface corresponding to the first surface of
the striker release element, the first surface obstructing rotation
of the striker mass; and a second biasing element for biasing the
striker mass such that the second surface is biased towards the
first surface; wherein when the body experiences an acceleration
profile of a predetermined magnitude and duration, the striker
release element rotates towards the base to release an engagement
between the first and second surfaces and allow the striker mass to
rotate under a biasing force of the second biasing element.
Inventors: |
Fischer; Jacques; (Sound
Beach, NY) ; Rastegar; Jahangir S.; (Stony Brook,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fischer; Jacques
Rastegar; Jahangir S. |
Sound Beach
Stony Brook |
NY
NY |
US
US |
|
|
Assignee: |
Omnitek Partners LLC
Ronkonkoma
NY
|
Family ID: |
51421079 |
Appl. No.: |
13/784737 |
Filed: |
March 4, 2013 |
Current U.S.
Class: |
429/112 ;
102/275.11 |
Current CPC
Class: |
F42C 15/20 20130101;
F42C 15/24 20130101; F42B 3/10 20130101 |
Class at
Publication: |
429/112 ;
102/275.11 |
International
Class: |
F42B 3/10 20060101
F42B003/10 |
Claims
1. An inertial igniter comprising: a body having a base; a striker
release element rotatably disposed on the body, the striker release
element having a first surface; a first biasing element for biasing
the striker release element away from the base; a striker mass
rotatably disposed on the base along a second axis, the striker
mass having a second surface corresponding to the first surface of
the striker release element, the first surface obstructing rotation
of the striker mass; and a second biasing element for biasing the
striker mass such that the second surface is biased towards the
first surface; wherein when the body experiences an acceleration
profile of a predetermined magnitude and duration, the striker
release element rotates towards the base to release an engagement
between the first and second surfaces and allow the striker mass to
rotate under a biasing force of the second biasing element.
2. The inertial igniter of claim 1, wherein the striker mass
includes a striker surface and the body includes a striken surface,
the inertial igniter further comprising a pyrotechnic material
disposed on at least one of the striker surface and striken
surface, such that release of the engagement between the first and
second surfaces further allows the striker surface to strike the
striken surface to activate the pyrotechnic material.
3. The inertial igniter of claim 2, wherein the striker surface and
striken surface comprise rectangular surfaces in which a length of
the striker surface is non-parallel to a length of the striken
surface.
4. The inertial igniter of claim 3, wherein the length of the
striker surface is orthogonal to the length of the striken
surface.
5. The inertial igniter of claim 2, wherein the base further
includes a hole proximate to the striken surface for passage of
sparks resulting from the activated pyrotechnic material.
6. The inertial igniter of claim 1, wherein the first surface is on
a recess formed in the striker release element and the second
surface is on a projection formed on the striker mass.
7. The inertial igniter of claim 6, wherein the striker release
element includes an additional recess for allowing the projection
to pass when the striker mass rotates under a biasing force of the
second biasing element.
8. The inertial igniter of claim 1, wherein the first biasing
element is selected from a torsion spring, compression spring and
leaf spring.
9. The inertial igniter of claim 1, wherein the second biasing
element is a torsion spring.
10. The inertial igniter of claim 9, wherein the torsion spring is
connected at one end to the body and at another end to the striker
mass.
11. The inertial igniter of claim 10, wherein the base having a
post upon which the striker mass rotates, the post having a slot
for accommodating the one end of the torsion spring.
12. The inertial igniter of claim 1, wherein the striker release
element is rotatable about a first axis and the striker mass is
rotatable about a second axis orthogonal to the first axis.
13. The inertial igniter of claim 1, further comprising a rolling
element disposed between the first and second surfaces.
14. The inertial igniter of claim 13, wherein the rolling element
is one of a ball and cylinder.
15. The inertial igniter of claim 13, wherein at least one of the
first and second surfaces includes a dimple for retaining the ball
element.
16. The inertial igniter of claim 1, wherein the body further
includes a stop for limiting a rotation of the striker release
element away from the base.
17. The inertial igniter of claim 16, wherein the stop comprises a
top plate.
18. The inertial igniter of claim 1, wherein at least one of the
first and second surfaces include a reduced friction material
disposed thereon.
19. A thermal battery assembly comprising: a thermal battery; and
an inertial igniter comprising: a body having a base; a striker
release element rotatably disposed on the body, the striker release
element having a first surface; a first biasing element for biasing
the striker release element away from the base; a striker mass
rotatably disposed on the base along a second axis, the striker
mass having a second surface corresponding to the first surface of
the striker release element, the first surface obstructing rotation
of the striker mass; and a second biasing element for biasing the
striker mass such that the second surface is biased towards the
first surface; wherein when the body experiences an acceleration
profile of a predetermined magnitude and duration, the striker
release element rotates towards the base to release an engagement
between the first and second surfaces and allow the striker mass to
rotate under a biasing force of the second biasing element; the
striker mass includes a striker surface and the body includes a
striken surface, the inertial igniter further comprising a
pyrotechnic material disposed on at least one of the striker
surface and striken surface, such that release of the engagement
between the first and second surfaces further allows the striker
surface to strike the striken surface to activate the pyrotechnic
material; and a hole for passage of sparks resulting from the
activated pyrotechnic material into the thermal battery.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to mechanical
inertial igniters, and more particularly to compact, low-volume,
reliable and easy to manufacture mechanical inertial igniters and
ignition systems for thermal batteries and the like used in
munitions with relatively short duration firing setback
acceleration (shock).
[0003] 2. Prior Art
[0004] 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.sub.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.sub.2 or Li(Si)/CoS.sub.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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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 can be thought of as
a mechanical delay mechanism, after which a separate initiation
system is actuated or released to provide ignition of the inertial
igniter pyrotechnics. An inertial igniter that combines such a
safety system with an impact based initiation system and its
alternative embodiments are described herein.
[0009] Inertia-based igniters must therefore comprise two
components so that together they provide the aforementioned
mechanical safety (delay mechanism) and to provide the required
striking 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 with long enough duration, i.e., to a prescribed
impulse level threshold, corresponding to the firing setback
acceleration event. The prescribed impulse level threshold
requirement is generally accompanied also with a minimum
acceleration level requirement to ensure that the inertial igniter
is safe, i.e., the striker element stays fixed to the inertial
igniter structure, when subjected to relatively low acceleration
levels for relatively long duration. Once the all-fire event, i.e.,
the said minimum acceleration level and the prescribed impulse
level threshold has been reached, the said 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.
[0010] A schematic of a cross-section of a conventional thermal
battery and inertial igniter assembly is shown in FIG. 1. In
thermal battery applications, the inertial igniter 10 (as assembled
in a housing) is generally positioned above the thermal battery
housing 11 as shown in FIG. 1. Upon ignition, the igniter initiates
the thermal battery pyrotechnics positioned inside the thermal
battery through a provided access 12. The total volume that the
thermal battery assembly 16 occupies within munitions is determined
by the diameter 17 of the thermal battery housing 11 (assuming it
is cylindrical) and the total height 15 of the thermal battery
assembly 16. The height 14 of the thermal battery for a given
battery diameter 17 is generally determined by the amount of energy
that it has to produce over the required period of time. For a
given thermal battery height 14, the height 13 of the inertial
igniter 10 would therefore determine the total height 15 of the
thermal battery assembly 16. To reduce the total volume that the
thermal battery assembly 16 occupies within a munitions housing, it
is therefore important to reduce the height of the inertial igniter
10. This is particularly important for small thermal batteries
since in such cases the inertial igniter height with currently
available inertial igniters can be almost the same order of
magnitude as the thermal battery height.
[0011] The isometric cross-sectional view of a currently available
inertia igniter is shown in FIG. 2, referred to generally with
reference numeral 200. The full isometric view of the inertial
igniter 200 is shown in FIG. 3. The inertial igniter 200 is
constructed with igniter body 201, consisting of a base 202 and at
least three posts 203. The base 202 and the at least three posts
203, can be integrally formed as a single piece but may also be
constructed as separate pieces and joined together, for example by
welding or press fitting or other methods commonly used in the art.
The base 202 of the housing can also be provided with at least one
opening 204 (with a corresponding opening(s) in the thermal
battery--not shown) to allow ignited sparks and fire to exit the
inertial igniter and enter into the thermal battery positioned
under the inertial igniter 200 upon initiation of the inertial
igniter pyrotechnics 215, or percussion cap primer when used in
place of the pyrotechnics 215 (not shown). Although illustrated
with the opening 204 in the base, the opening (or openings) can
alternatively be formed in a side wall or in the striker mass as
described in U.S. Patent Application Publication No. 2011/0171511
filed on Jul. 13, 2010, the entire contents thereof is incorporated
herein by reference.
[0012] A striker mass 205 is shown in its locked position in FIG.
2. The striker mass 205 is provided with guides for the posts 203,
such as vertical surfaces 206, that are used to engage the
corresponding (inner) surfaces of the posts 203 and serve as guides
to allow the striker mass 205 to ride down along the length of the
posts 203 without rotation with an essentially pure up and down
translational motion.
[0013] In its illustrated position in FIGS. 2 and 3, the striker
mass 205 is locked in its axial position to the posts 203 by at
least one setback locking ball 207. The setback locking ball 207
locks the striker mass 205 to the posts 203 of the inertial igniter
body 201 through the holes 208 provided in the posts 203 and a
concave portion such as a dimple (or groove) 209 on the striker
mass 205 as shown in FIG. 2. A setback spring 210, which is
preferably in compression, is also provided around but close to the
posts 203 as shown in FIGS. 2 and 3. In the configuration shown in
FIG. 2, the locking balls 207 are prevented from moving away from
their aforementioned locking position by the collar 211. The
setback spring 210 is preferably a wave spring with rectangular
cross-section. The collar 211 is usually provided with partial
guide 212 ("pocket"), which are open on the top as indicated by the
numeral 213. The guide 212 may be provided only at the location of
the locking balls 207 as shown in FIGS. 2 and 3, or may be provided
as an internal surface over the entire inner surface of the collar
211 (not shown).
[0014] The collar 211 rides up and down on the posts 203 as can be
seen in FIGS. 2 and 3, but is biased to stay in its upper most
position as shown in FIGS. 2 and 3 by the setback spring 210. The
guides 212 are provided with bottom ends 214, so that when the
inertial igniter is assembled as shown in FIGS. 2 and 3, the
setback spring 210 which is biased (preloaded) to push the collar
211 upward away from the igniter base 201, would "lock" the collar
211 in its uppermost position against the locking balls 207. As a
result, the assembled inertial igniter 200 stays in its assembled
state and would not require a top cap to prevent the collar 211
from being pushed up and allowing the locking balls 207 from moving
out and releasing the striker mass 205.
[0015] In the inertial igniters of the type shown in FIGS. 2 and 3,
a one part pyrotechnics compound 215 (such as lead styphnate or
other similar compound) is used as shown in FIG. 2. The striker
mass 205 is usually provided with a relatively sharp tip 216 and
the igniter base surface 202 is provided with a protruding tip 217
which is covered with the pyrotechnics compound 215, such that as
the striker mass 205 is released during an all-fire event and is
accelerated down (opposite to the arrow 218 illustrated in FIG. 2),
impact occurs mostly between the surfaces of the tips 216 and 217,
thereby pinching the pyrotechnics compound 215, thereby providing
the means to obtain a reliable initiation of the pyrotechnics
compound 215. Alternatively, a two-part pyrotechnics compound
consisting, for example, one being based on potassium chlorate used
in place of the pyrotechnics 215 and the other based on red
phosphorous which is positions over a (generally larger) tip 216 of
the striker mass 206, may be used. In another alternative design,
instead of using the pyrotechnics compound 215, FIG. 2, a
percussion cap primer or the like (not shown) is used. In such
inertial igniters, the tip 216 of the striker mass 205 is
appropriately sized for initiating the percussion cap primer being
used.
[0016] The basic operation of the inertial igniter 200 shown in
FIG. 2 and is as follows. Any non-trivial acceleration in the axial
direction 218 which can cause the collar 211 to overcome the
resisting force of the setback spring 210 will initiate and sustain
some downward motion of the collar 211. The force due to the
acceleration on the striker mass 205 is supported at the dimples
209 by the locking balls 207 which are constrained inside the holes
208 in the posts 203. If an acceleration time in the axial
direction 218 imparts a sufficient impulse to the collar 211 (i.e.,
if an acceleration time profile is greater than a predetermined
threshold), it will translate down along the axis of the assembly
until the setback locking balls 205 are no longer constrained to
engage the striker mass 205 to the posts 203. If the acceleration
event is not sufficient to provide this motion (i.e., the
acceleration time profile provides less impulse than the
predetermined threshold), the collar 211 will return to its start
(top) position under the force of the setback spring 210.
[0017] 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.
[0018] In the inertial igniter 200 of FIGS. 2 and 3, following
ignition of the pyrotechnics compound 215, the generated flames and
sparks are designed to exit downward through the opening 204 to
initiate the thermal battery below. Alternatively, if the thermal
battery is positioned above the inertial igniter 200, the opening
204 can be eliminated and the striker mass could be provided with
at least one (not shown) to guide the ignition flame and sparks up
through the striker mass 205 to allow the pyrotechnic materials (or
the like) of a thermal battery (or the like) positioned above the
inertial igniter 200 to be initiated.
[0019] In the inertial igniter 200 of FIGS. 2 and 3, by varying the
mass of the striker 205, the mass of the collar 211, the spring
rate of the setback spring 210, the distance that the collar 211
has to travel downward to release the locking balls 207 and thereby
release the striker mass 205, and the distance between the tip 216
of the striker mass 205 and the pyrotechnic compound 215 (and the
tip of the protrusion 217), the designer of the disclosed inertial
igniter 200 can match the all-fire and no-fire impulse level
requirements for various applications as well as the safety (delay
or dwell action) protection against accidental dropping of the
inertial igniter and/or the munitions or the like within which it
is assembled.
[0020] 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.
[0021] In general, the required 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.
[0022] It is appreciated by those skilled in the art that when the
inertial igniter 200 of FIGS. 2 and 3 is subjected to the
aforementioned all-fire acceleration profile threshold, the collar
211 is first caused to be displaced downward under the force caused
by the acceleration in the direction of the arrow 218 acting on the
inertia (mass) of the collar 211, until the striker mass 205 is
released as was described above and accelerated downward to towards
the base 202 of the inertial igniter until the tip 216 of the
striker mass 205 strikes the pyrotechnic material 215 over the
protruding tip 217 and causing it to ignite. It is also appreciated
by those skilled in the art that the process of downward travel of
the collar 211 takes a certain amount of time, hereinafter
indicated as .DELTA.t.sub.1, the amount of which is dependent on
the mass of the collar 211 and the aforementioned preloading level
of the compressive spring 210 and the distance that it has to
travel downward before the balls 207 and thereby the striker mass
205 is released. Similarly, once the striker mass 205 is released,
the process of downward travel of the striker mass 205 until its
tip 216 strikes the pyrotechnic material 215 over the protruding
tip 217 takes a certain amount of time for, hereinafter indicates
as .DELTA.t.sub.2, the amount of which is dependent on the level of
acceleration in the direction of the arrow 218.
[0023] 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 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.
[0024] 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 .DELTA.t.sub.1 and .DELTA.t.sub.2,
hereinafter indicated as .DELTA.t=.DELTA.t.sub.1+.DELTA.t.sub.2.
For example, for the aforementioned case of all-fire (setback)
acceleration being 1000 G for 15 milliseconds, the total time
.DELTA.t must be less than the indicated acceleration duration of
15 milliseconds.
[0025] In certain applications, the aforementioned total time
.DELTA.t is small enough that even by optimizing the parameters
design of the inertial igniter of the type shown in FIGS. 2 and 3
to minimize the required aforementioned time periods .DELTA.t.sub.1
and .DELTA.t.sub.2, the required total time .DELTA.t cannot be
reduced to below the all-fire acceleration period.
[0026] In certain other case, 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.
SUMMARY OF THE INVENTION
[0027] A need therefore exists for novel miniature inertial
igniters that can be used in munitions or the like for initiation
of pyrotechnic materials in thermal batteries or the like in which
the aforementioned all-fire acceleration profile is very short in
duration as is described above for inertial igniters of the type
shown in FIGS. 2 and 3 to be used.
[0028] A need also exists for small inertial igniters that can
initiate thermal batteries used in munitions with relatively low
firing setback acceleration levels that may also be of short
duration.
[0029] There is also a need 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 FIGS. 2 and 3 to
be used.
[0030] 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.
[0031] 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.
[0032] 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:
[0033] provide small inertial igniters that can be initiated when
subjected to very short duration firing setback acceleration
(shock);
[0034] provide small inertial igniters that can be initiated when
subjected to relatively low firing setback acceleration
(shock);
[0035] provide small inertial igniters that can be initiated when
subjected to relatively low firing setback acceleration (shock)
with relatively short duration;
[0036] provide inertial igniters that are significantly shorter
than currently available inertial igniters for thermal batteries or
the like;
[0037] provide inertia igniters that could be constructed to guide
the pyrotechnic flame essentially downward (in the direction
opposite to the direction of the firing acceleration--usually for
mounting on the top of the thermal battery as shown in FIG. 1), or
essentially upward (in the direction opposite of the firing
acceleration--usually for mounting at the bottom of the thermal
battery);
[0038] Accordingly, inertial igniters and ignition systems for use
with thermal batteries or the like upon subjection to firing
setback acceleration, in particular short duration and/or
relatively low peak acceleration levels, are provided. Provided are
also inertial igniters that are very low height for small thermal
batteries.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] 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:
[0040] FIG. 1 illustrates a schematic of a cross-section of a
thermal battery and inertial igniter assembly.
[0041] FIG. 2 illustrates an isometric cut away view of an inertial
igniter assembly known in the art.
[0042] FIG. 3 illustrates a full isometric view of the prior art
inertial igniter of FIG. 2.
[0043] FIG. 4 illustrates a full isometric view of a first
embodiment of an inertial igniter in a locked position.
[0044] FIG. 5 illustrates a blow up view of the first embodiment of
the inertial igniter of FIG. 4 showing all its individual
components.
[0045] FIGS. 6a and 6b illustrate first and second variations of
thermal battery and inertial igniter assemblies.
[0046] FIG. 7 illustrates the alternative options for the biasing
compressive springs for the striker release element of the inertial
igniter embodiment of FIG. 4.
[0047] FIG. 8 illustrates the pyrotechnic region of the inertial
igniter of FIG. 4 with impacting ridges that ensure reliable
initiation of the pyrotechnic material.
[0048] FIG. 9 illustrates the inertial igniter embodiment of FIG. 4
with a provided cover element with a ignition flame and spark exit
hole.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0049] A schematic of the isometric view of a first embodiment of
an inertia igniter is shown in FIG. 4, referred to generally with
reference numeral 250. In the isometric view of FIG. 4 the inertial
igniter body 251 of the inertial igniter 250 is shown as being
transparent to enable the internal components of the device to be
seen. A lever type striker release element 252 is provided which is
rotationally hinged to the inertial igniter body 251 by the pins
253 and 254. One or both pins 253 and 254 may be fixed to the
inertial igniter body 251, preferably through press fitting or
otherwise using adhesives such as epoxy or by soldering or brazing
or by welding or the like, particularly if the joint needs to be
hermetically sealed. When any one of the pins 253 or 254 is fixed
to the inertial igniter body, then the corresponding hole 252a in
the striker release element 252 is provided with enough clearance
to allow free rotation of the striker release element 252 relative
to the inertial igniter body about the long axes of the pins 253
and 254. In an embodiment, the pins 253 and 254 are fixed to the
inertial igniter body, where the fixing process can be achieved by
press fitting the pins into holes 256 provided in the inertial
igniter body 251 during the inertial igniter assembly process.
Alternatively, one or both pins 253 and 254 are fixed to the
striker release element 252 using one of the aforementioned methods
and enough clearance is provided in the holes 256 in the inertial
igniter body to allow free rotation of the striker release element
252 relative to the inertial igniter body about the long axes of
the pins 253 and 254.
[0050] The striker release element 252 is rotationally biased
upward by at least one preloaded torsion spring 255, which is
positioned at one or both rotating joints with pins 253 and/or 254
as shown in FIG. 4. The upward rotation of the striker release
element 252 past the top surface 257 of the inertial igniter 250
can be prevented by a stop (not shown) for ease of inertial igniter
assembly into the intended device (usually a thermal battery or the
like), or by a top inertial igniter cover (not shown), which can be
provided by the thermal battery assembly itself to minimize the
total height of the inertial igniter.
[0051] The inertial igniter 250 is provided with a rotating striker
mass 258, which is free to rotate about the cylindrical post 259,
which is provided on the base 260 of the inertial igniter body 251
as shown in FIGS. 4 and 5.
[0052] The rotating striker mass 258 is provided with a tip portion
261 with a vertical face 262, which faces a matching (vertical)
face 263 provided in the recess 265 on the striker release element
252. In the pre-activation state, the two surfaces 262 and 263 are
pressed against each other (sometimes via a ball element 264--as
later described) by a preloaded torsion spring 266. A dimple 275 is
provided on the contact surface 263 of the striker release element
252 to keep the ball 264 in its indicated position on the contact
surface 263. The dimple 275 can be provided on the contact surface
263 of the striker release element 252, but could alternatively be
provided on the contact surface 262 of the rotating striker mass
258. The inner end of the spring 266 is fixed to the cylindrical
post 259, by fitting its extended end 267, FIG. 5, inside the slot
268 provided on the cylindrical post 259 as can be seen in FIGS. 4
and 5. The other end 269 of the torsion spring 266 is positioned
against a vertical surface 270 that is provided under the rotating
striker mass 258. In the pre-activation state shown in FIG. 4, the
torsion spring is preloaded (wound) such that it would tend to
rotate the rotating striker mass in the counterclockwise direction
as seen in FIG. 4, thereby causing the surfaces 262 and 263 to be
pressed against each other. In an embodiment, the torsion spring
266 is designed and assembled in the inertial igniter 250 such that
the preloading action causes the torsion spring spiral to close.
Such a direction of preloading of the torsion spring 266 is
preferred since in such a preloading state the spring element is
more stable.
[0053] As shown in FIGS. 4 and 5, the rotating striker mass 258 is
also provided with a sharp vertical ridge 271, with a relatively
small flat face, which can run along an entire length (downward) of
the rotating striker mass 258. Inside the igniter body 251 is also
provided with an opposing and preferably horizontal ridge 272,
which is also provided with a relatively small flat face. The
inertial igniter (one part) pyrotechnic material 273 (shown with
dashed lines in FIG. 8) is used to cover the surface of the
horizontal ridge 272 with a relatively thin layer, with the bulk of
pyrotechnic material being deposited on the surfaces around the
horizontal ridge 272 shown in FIG. 5.
[0054] The basic operation of the inertial igniter 250 will now be
described with reference to FIGS. 4 and 5. Any non-trivial
acceleration in the axial direction in the direction or opposite to
the direction of the arrow 274 acts on the inertia of the striker
release element 252, generating a torque that would tend to rotate
the striker release element 252 downward or upward, respectively.
If the acceleration in the direction of the arrow 274 is high
enough to generate a torque that overcomes the preloaded torque of
the torsion spring 255, then the striker release element 252 would
rotate certain amount downwards. The upward rotation of the striker
release element 252 is prevented by the aforementioned stop element
(not shown) or the top cover of the inertial igniter 250 (not
shown). However, if the non-trivial acceleration in the direction
of the arrow 274 is not high enough and its duration is not long
enough, i.e., if it is not at or above the prescribed all-fire
event, then the striker release element 252 would return to its
pre-acceleration (original) position shown in FIG. 4.
[0055] If an acceleration in the direction of the arrow 274 at or
above the all-fire acceleration level and its duration is also at
or above the all-fire acceleration duration, then a sufficient
impulse is imparted to rotate the striker release element 252
downward enough to cause the contact surface 263 of the striker
release element 252 to move below the contact surface 262 of the
rotating striker mass 258. The torque of the preloaded torsion
spring 266 will then cause the rotating striker mass 258 to be
accelerated rotationally in the counterclockwise direction as
observed from the top of the inertial igniter 250, FIG. 4. The
rotating striker mass will keep gaining rotational velocity,
thereby rotational energy, until its sharp vertical ridge 271
strikes the pyrotechnic material 273 covering the horizontal ridge
272 provided inside the igniter body 251. The level of preloading
of the torsion spring 266 and the moment of inertia of the rotating
striker mass 258 are selected such that as the sharp vertical ridge
271 strikes the pyrotechnic material 273 covering the horizontal
ridge 272, it has an appropriate level of energy to ignite the
pyrotechnic material. The resulting flames and sparks will then
exit from the provided exit hole 278.
[0056] In general, a recess 301 is provided in the top surface of
the striker release element 252 over which the released rotating
striker mass 258 travels as shown in FIGS. 4 and 5 to minimize the
total height of the inertial igniter 250.
[0057] In FIG. 4, the inertial igniter embodiment 250 is shown
without any outside housing. In many applications, as shown in the
schematics of FIG. 6a, the inertial igniter 250 (FIG. 4) is placed
securely inside a top housing 283 of the thermal battery 281. Here,
the thermal battery is considered to be subjected to all-fire
setback firing acceleration in the direction of the arrow 276. In
such a thermal battery assembly, the top surface of the inertial
igniter is covered (either by the top cap 277 of the thermal
battery, FIG. 6a, or an inertial igniter top cover--not shown in
FIG. 4), and the ignition flame and sparks are routed through the
opening 278 provided on the bottom surface 260 of the inertial
igniter 250 as shown in FIG. 4. In addition, depending on the
location of the opening 285 in the bottom surface 284 of the
inertial igniter compartment 283 relative to the inertial igniter
flame and spark exit opening 278, a strip of intermediate ignitable
material 279 such as so-called heat paper may be used to facilitate
ignition of the thermal battery heat generating pyrotechnic
material inside the housing 282 of the thermal battery cell
286.
[0058] In other applications, as shown in the schematics of FIG.
6b, the inertial igniter 250 (FIG. 4) is placed securely inside a
bottom housing 293 of the thermal battery 291. Here, the thermal
battery is also considered to be subjected to all-fire setback
firing acceleration in the direction of the arrow 276. In such a
thermal battery assembly, the top surface of the inertial igniter
is covered by bottom surface 297 of the thermal battery, FIG. 6b,
and the ignition flame and sparks are routed through an opening
provided 298 on the inertial igniter top cover 299 (shown in FIG.
9). In addition, depending on the location of the opening 295 on
the surface 294 of the inertial igniter compartment 293 relative to
the inertial igniter flame and spark exit opening 298, a strip of
intermediate ignitable material 300 such as so-called heat paper
may be used to facilitate ignition of the thermal battery heat
generating pyrotechnic material inside the housing 292 of the
thermal battery cell 296.
[0059] In the inertial igniter embodiment 250 of FIG. 4, the at
least one preloaded torsion spring 255, which is positioned at one
or both rotating joints with pins 253 and/or 254, was described as
being used to bias the striker release element 252 upward rotation
against a stop (not shown) for ease of inertial igniter assembly
into the intended device (usually a thermal battery or the like),
or against a top inertial igniter cover (not shown). It is,
however, appreciated by those skilled in the art that
alternatively, the torsion spring 255 may be replaced by a
compressively preloaded spring as is shown in FIG. 7. In FIG. 7, a
simplified side view (as viewed in the direction of the axis of
rotation of the rotary joints with pins 253 and 254) is shown with
only a partial view of the housing 251 (302 in FIG. 7) of the
inertial igniter 250 of FIG. 4, with most of the housing wall
removed except the portion containing the rotary joint
accommodating the joint pin 253 (303 in FIG. 7) for simplification
of the view. In FIG. 7, the simplified view of the striker release
element 304 (252 in FIG. 4) is shown in its normal (in
non-initiated inertial igniter) position. The striker release
element 304 attached to the inertial igniter housing side wall 309
by the rotary joint pin 303. The stop element that prevents further
clockwise rotation of the striker release element 304 from its
position seen in FIG. 7 is not shown for clarity.
[0060] The aforementioned upward biasing compressively loaded
spring may be a regular helical spring (which can be a wave spring
type) 306 or a flat spring 305 formed of a strip of spring steel or
the like. Either compressively preloaded springs 305 or 306 are
positioned between the bottom surface 307 of the striker release
element 304 and the top surface 308 of the inertial igniter housing
302. In general, the compressively preloaded springs 305 or 306 are
mounted within provided detents and/or protrusions on one or both
surfaces 307 and 308 (not shown) to keep the springs 305 or 306 in
place and prevent them from moving inside the inertial igniter
assembly. An advantage of using such compressively preloaded
biasing springs 305 or 306 (such as a formed flat spring 305 type)
is that they would exert an upward force to the bottom surface 307
of the striker release element 304, thereby generating a nearly
pure rotating torque to the striker release element 304, thereby
minimizing the chances of generating increased friction forces at
its rotating joints. The other advantage is that it significantly
reduces assembling complexity, thereby the production cost of the
inertial igniter.
[0061] In FIG. 4, in the schematic of the inertial igniter 250, the
rotating striker mass 258 is shown to be provided with a tip
portion 261 with a vertical face 262, which faces the matching
(vertical) face 263 provided in the recess 265 on the striker
release element 252. As it was previously described, in the
pre-activation state, the two surfaces 262 and 263 are pressed
against each other by the preloaded torsion spring 266. In the
schematic of FIG. 4, a ball 264 is shown to be positioned (on one
side within the dimple 275) between the surfaces 262 and 263, the
reason of which is to facilitate the relative sliding motion
between the two surfaces by minimizing friction between the two
surfaces as the inertial igniter is subjected to all-fire
condition. It is, however, appreciated by those skilled in the art
that other means and methods may also be used to minimize friction
between the sliding surfaces 262 and 263 to facilitate downward
rotation of the striker release element 252, including the
following.
[0062] In one alternative embodiment, a rolling element (shown in
dashed lines in FIG. 5 and enumerated as 310) is used in place of
the aforementioned ball 264. A dimple similar to the dimple 275
shown in FIG. 5 but shaped to accommodate the roller 300 is also
provided to secure the roller in the inertial igniter assembly.
[0063] In another alternative embodiment, the aforementioned ball
264 is not used and the two surfaces 262 and 263, FIG. 4, are
allowed to come into contact. In this embodiment, the two surfaces
262 and 263 can be provided with certain curvature (not shown) to
avoid sharp corners scraping between the two surfaces as the
striker release element 252 rotates downward to release the
rotating striker mass 258. The contacting surfaces may further be
coated by friction reducing materials (lubricants) such as
graphite, Teflon or the like (liquid lubricants are usually not
desirable due to the required very long shelf life of up to 20
years). One or both surfaces may also be coated with hard materials
such as tungsten or the like.
[0064] In yet another alternative embodiment, the aforementioned
ball 264 is not used between the two surfaces 262 and 263, FIG. 4.
To facilitate sliding action between the two surfaces, a thin sheet
of friction reducing material (not shown) such as one made out of
Teflon or a hard and polished metal or ceramic or the like is
provided between the two surfaces 262 and 263. The provided
friction reducing material may be fixed to one of the surfaces 262
or 263 to prevent it from being pushed out or fall off.
[0065] The alternative embodiments of the inertial igniter 250
designs have the purpose of reducing friction to the downward
rotation of the striker release element 252 as it is rotated under
the prescribed all-fire condition to release the rotating striker
mass 258. Other sources of friction that resist the downward
rotation of the striker release element 252 are friction at the
rotating joints with pins 253 and 254, where friction exists
between the pin surfaces and the mating joint surfaces as well as
between the side surfaces of the striker release element 252 and
their contacting surfaces on the inertial igniter housing. To
reduce the effects (i.e., the generated resisting torque to the
downward rotation of the striker release element 252), the
diameters of the pins 253 and 254 can be small and the contacting
surfaces can be coated with friction reducing "lubricating"
materials and/or provided with intermediate low friction "washer"
type relatively thin members.
[0066] As is shown in FIGS. 4 and 5, the rotating striker mass 258
is provided with a sharp vertical ridge 271, which can have a
relatively small flat face 311, which can run along the entire
length of the rotating striker mass 258 as shown in the partial
view FIG. 8. Inside the igniter body 251 was also shown to be
provided with an opposing and preferably horizontal ridge 272,
which is also provided with a relatively small flat face 312. In
FIG. 8, a partial view of the inertial igniter 250, FIGS. 4 and 5,
showing the ridges 271 and 272 with their frontal flat surface 311
and 312, respectively, is shown. In the schematic of FIG. 8 the one
part pyrotechnic material 273, which can be based on lead styphnate
or other similar compounds, and is used to cover the surface of the
horizontal ridge 272 (shown in FIG. 5 but not shown in FIG. 4 for
clarity) is not shown. In general, the portion of the pyrotechnic
material covering the flat surface portion 312 of the horizontal
ridge 272 is in a relatively thin layer. Then as the rotating
striker mass 258 is released, its ridge 271 portion is accelerated
towards the ridge 272 and impacts it at a certain point. In this
design, since the two flat surfaces 311 and 312 are positioned at
about 90 degrees relative to each other, the resulting impacting
surface is always close to a rectangle with sides equal to the
widths of the two flat surfaces 311 and 312. As a result, the
inertial igniter parts do not have to have extremely high precision
to allow the pyrotechnic igniting impact to occur over a relatively
small area. In general, it is highly desirable to have a relatively
small area of impact, within which a thin layer of pyrotechnic
material is impinged during impact to ensure reliable pyrotechnic
initiation.
[0067] In the schematics of FIGS. 4, 5 and 8, the impacting ridges
271 and 272 of the inertial igniter 250 were shown to be vertical
and horizontal, respectively, as viewed in the drawings, to ensure
impact over a relatively small area without requiring extremely
high manufacturing precision of the inertial igniter parts. It is,
however, appreciated by those skilled in the art that the flat
ridge surface 311 and 312 of the impacting ridges 271 and 272,
respectively, do not have to be vertically and horizontally
directed to achieve the goal of small impact surfaces even when the
inertial igniter parts are not very high in geometrical precision.
The only requirement to achieve the goal is that the two surface
strips 311 and 312 are not parallel and make a considerable angle
(such as 90 degrees) with each other.
[0068] While the one-part pyrotechnic material 273 is shown the
body 251, it can alternatively be provided on the striker mass 258.
Alternatively, a two-part pyrotechnic can be used in which one part
is provided on each of the body 251 and striker mass 258.
[0069] 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.
* * * * *