U.S. patent application number 13/048254 was filed with the patent office on 2012-09-20 for pyrotechnic actuator and method of actuating a pyrotechnic actuator.
This patent application is currently assigned to SPECIAL DEVICES, INC.. Invention is credited to Abrar A. Tirmizi.
Application Number | 20120234162 13/048254 |
Document ID | / |
Family ID | 46827397 |
Filed Date | 2012-09-20 |
United States Patent
Application |
20120234162 |
Kind Code |
A1 |
Tirmizi; Abrar A. |
September 20, 2012 |
PYROTECHNIC ACTUATOR AND METHOD OF ACTUATING A PYROTECHNIC
ACTUATOR
Abstract
A pyrotechnic actuator and a method of actuating the same are
described. The actuator comprises a pressure chamber and a piston
having such an outer diameter that it is snugly fitted into the
pressure chamber. A gas generating ignition and output charge
generates gas that pressurizes the pressure chamber and the piston
when ignited. The piston is designed such that at least part of its
outer diameter expands under the pressure in the pressure chamber
such that at least a part of the external piston surface is forced
into a press fit against the internal wall of the pressure chamber
and therefore seals the pressure chamber. This prevents exhaust gas
and flames from escaping from the device in an uncontrolled
manner.
Inventors: |
Tirmizi; Abrar A.; (Simi
Valley, CA) |
Assignee: |
SPECIAL DEVICES, INC.
Moorpark
CA
|
Family ID: |
46827397 |
Appl. No.: |
13/048254 |
Filed: |
March 15, 2011 |
Current U.S.
Class: |
89/1.14 |
Current CPC
Class: |
F42B 3/006 20130101 |
Class at
Publication: |
89/1.14 |
International
Class: |
F42B 99/00 20060101
F42B099/00 |
Claims
1. A pyrotechnic actuator comprising: a pressure chamber that is
defined by an internal pressure chamber wall and an outer piston
wall; a piston having such an outer diameter that it is snugly
fitted into the pressure chamber such that at least a part of an
external piston surface extends in close proximity to or abuts
against at least a part of the internal pressure chamber wall; a
gas generating ignition and output charge generating gas that
pressurizes the pressure chamber and the piston when ignited; and
an igniter for igniting the gas generating ignition and output
charge; wherein the piston is designed such that at least part of
its outer diameter expands under the pressure in the pressure
chamber such that at least a part of the external piston surface is
forced into a press fit against the internal wall of the pressure
chamber.
2. The pyrotechnic actuator of claim 1, wherein the piston is at
least in part hollow comprising an internal piston wall that forms
a part of a piston surface defining the pressure chamber together
with the internal pressure chamber wall.
3. The pyrotechnic actuator of claim 1, wherein the internal piston
wall is formed as a depression in a rear end face of the
piston.
4. The pyrotechnic actuator of claim 3, wherein the depression has
such a shape and size that it determines which part of the piston
expands in its outer diameter and to what extent it expands.
5. The pyrotechnic actuator of claim 4, wherein the depression
starts from the rear end face as a cylindrical depression that is
followed towards a front end face of the piston by a conical
section narrowing towards the front end face.
6. The pyrotechnic actuator of claim 4, wherein the depression
starts from the rear end face as a cylindrical depression that is
followed towards a front end face of the piston by a semi-spherical
section narrowing towards the front end face.
7. The pyrotechnic actuator of claim 4, wherein the depression
starts from the rear end face as a cylindrical depression that
comprises a dome-shaped bottom that deepens from an intersection
with a piston center line towards an outer circumference of the
bottom.
8. The pyrotechnic actuator of claim 3, wherein the depression in
the rear end face of the piston comprises an inner diameter that is
at least half of the outer diameter of the piston and extends over
at least one third of a length of the piston.
9. The pyrotechnic actuator of claim 3, wherein the gas generating
ignition and output charge is provided in an output can that is
ignited by electrical contacts and the output can is accommodated
in the depression before the ignition and output charge is
ignited.
10. The pyrotechnic actuator of claim 1, wherein the external
piston surface comprises a plurality of semicircular ridges which
are press-fitted into the internal pressure chamber wall.
11. The pyrotechnic actuator of claim 1, further comprising a stop
limiting the maximum movement of the piston along the pressure
chamber such that the press-fit between the external piston surface
and the internal wall of the pressure chamber is maintained.
12. The pyrotechnic actuator of claim 1, wherein the press-fit
between the external piston surface and the internal wall of the
pressure chamber substantially seals the pressure chamber retaining
the generated gas within the pressure chamber.
13. The pyrotechnic actuator of claim 1, wherein the pyrotechnic
actuator is a part of one of the group consisting of: pyrotechnic
power disconnect devices, pyrotechnic battery disconnect devices,
pyrotechnic fuses, pyrotechnic switches, pyrotechnic cable cutters,
pyrotechnic release devices, pyrotechnic locking devices,
pyrotechnic interrupters, and pyrotechnic dislodging devices.
14. The pyrotechnic actuator of claim 1, wherein a front end face
of the piston is connected to at least one of a latch and a
knife.
15. A method of actuating a pyrotechnic actuator that comprises a
pressure chamber that is defined by an internal wall and a piston
having such an outer diameter that the piston is fitted snugly into
the internal wall of the pressure chamber such that at least a part
of an external piston surface extends in close proximity to or
abuts against at least a part of the internal wall surface; the
method comprising: igniting a gas generating charge of an
explosive; pressurizing the pressure chamber and at least one
surface of the piston with the gas generated by the ignited charge
of an explosive; expanding the piston in its outer diameter by
pressure within the pressurized pressure chamber such that at least
a part of the external piston surface is forced into a press-fit
against the internal wall of the pressure chamber; and propelling
the piston by the pressure in the pressure chamber along the same
while maintaining the press fit created by the pressure induced
piston expansion.
16. The method of claim 15, further comprising stopping the piston
at a maximum traveling range by running the piston against a
stop.
17. The method of claim 15, further comprising at least one of
cutting, latching and releasing by the moving piston.
18. The method of claim 15, further comprising substantially
sealing the pressure chamber by expanding the piston into the
press-fit.
19. The method of claim 15, further comprising imperfectly sealing
the pressure chamber by expanding the piston into the press-fit
such that a gradual releasing of the pressure within the pressure
chamber takes at least 1 minute.
Description
FIELD OF THE INVENTION
[0001] The invention is in the field of controlling the release of
primer/initiator exhaust gases and flames from pyrotechnic
actuators to improve operational safety and to meet regulatory
requirements. The invention is in particular in the field of
pyrotechnic actuators such as pyrotechnic power disconnect devices,
pyrotechnic battery disconnect devices, pyrotechnic fuses,
pyrotechnic switches, pyrotechnic cable cutters, pyrotechnic
release devices, pyrotechnic locking devices, and pyrotechnic
interrupters.
BACKGROUND OF THE INVENTION
[0002] Pyrotechnics have been used in break, sever, disconnect or
release devices and mechanisms for a long time. As an example, for
instance applicant's U.S. Pat. Nos. 7,123,124 and 7,239,225 can be
named, the content of which is herewith incorporated by reference.
When some of these devices were actuated, the primer exhaust gases
and/or flames were released to the surroundings. In some
applications the release of hot gases, smoke and/or flames may not
be a problem. However, in many applications the release of hot
gases and/or flames during device functioning may create a safety
hazard for equipment and/or personnel near such devices. Devices
that do not control the release of hot gases or flames are also
considered hazardous by regulatory agencies in US and worldwide and
require special packaging, storage and regulatory permits for
transportation and the use of the product throughout the life of
the product. The requirements are stringent enough that they may
prevent the use of such devices in certain applications especially
some cost sensitive applications due to the additional costs
involved. It will also prevent the product from being distributed
as ordinary consumer product such as automotive parts and keep the
general public and industry from the benefits of using such
devices.
[0003] Certain device configurations are more conducive to sealing
the exhaust gases and flames than others. Devices primarily made
from metals in tubular shapes using a piston, cylinder and O-rings
(such as Reefing Line Cutters) tend to be relatively easy to seal
as to gases and flames during the device functioning and have been
known art for a long time. It is not practical to make all such
devices out of metals such as in this case of electrical
power/battery disconnects or to have a tubular piston-cylinder with
O-ring configuration. Some applications require odd shapes for
device configuration that are much more difficult to seal than
simple O-ring type designs. Low cost applications such as
automotive or consumer products require minimizing the costs of
sealing apparatuses (gaskets, O-rings, sealants). It is sometimes
impossible or not practical to verify if the seal is in place and
installed correctly once the device is closed. For parts that are
expected to be used over many years of service the useful life of
gaskets, O-ring or sealant is also a limiting factor especially in
harsh installation and operating environments.
SUMMARY OF THE INVENTION
[0004] It is an object of the invention to alleviate or remove
entirely the hazards created by firing pyrotechnic actuators,
particularly the hazards created by flames and/or exhaust gases
escaping from the device after firing.
[0005] According to a first aspect of the invention, this is
achieved by a pyrotechnic actuator comprising: a pressure chamber
that is defined by an internal pressure chamber wall and an outer
piston wall; a piston having such an outer diameter that it is
snugly fitted into the pressure chamber such that at least a part
of an external piston surface extends in close proximity to or
abuts against at least a part of the internal pressure chamber
wall; a gas generating ignition and output charge generating gas
that pressurizes the pressure chamber and the piston when ignited;
and an igniter for igniting the gas generating ignition and output
charge; wherein the piston is designed such that at least part of
its outer diameter expands under the pressure in the pressure
chamber such that at least a part of the external piston surface is
forced into a press fit against the internal wall of the pressure
chamber.
[0006] According to a second aspect of the invention, this is
achieved by a method of actuating a pyrotechnic actuator that
comprises a pressure chamber that is defined by an internal wall
and a piston having such an outer diameter that the piston is
fitted snugly into the internal wall of the pressure chamber such
that at least a part of an external piston surface extends in close
proximity to or abuts against at least a part of the internal wall
surface; the method comprising: igniting a gas generating charge of
an explosive; pressurizing the pressure chamber and at least one
surface of the piston with the gas generated by the ignited charge
of an explosive; expanding the piston in its outer diameter by
pressure within the pressurized pressure chamber such that at least
a part of the external piston surface is forced into a press-fit
against the internal wall of the pressure chamber; and propelling
the piston by the pressure in the pressure chamber along the same
while maintaining the press fit created by the pressure induced
piston expansion.
DETAILED DESCRIPTION OF THE INVENTION
[0007] According to a preferred embodiment of the pyrotechnic
actuator, the piston is at least in part hollow comprising an
internal piston wall that forms a part of a piston surface defining
the pressure chamber together with the internal pressure chamber
wall. The hollow design can be of any kind as long as the hollow
space formed within the piston is connected to the pressure
generated by the gas after firing.
[0008] Preferably, the internal piston wall is formed as a
depression in a rear end face of the piston. This is particularly
easy to manufacture. However, it may be desirable to have the
pressure access a larger hollow space via a smaller channel so that
the pressure inside the piston is built in a controlled manner more
slowly, allowing the piston to be propelled easier along the
pressure chamber while sealing action gets stronger when the piston
comes closer to reaching its end position.
[0009] According to another preferred embodiment of the pyrotechnic
actuator the depression has such a shape and size that it
determines which part of the piston expands in its outer diameter
and to what extent it expands. This is a valuable design feature
for controlling the sealing forces and what parts of the piston
should generate the sealing forces. One such preferred shape is for
instance to have the depression start from the rear end face as a
cylindrical depression that is followed towards a front end face of
the piston by a conical section narrowing towards the front end
face. In this configuration, the rear end of the piston expands
more than the front end. Preferably, it would for instance be
possible to provide an additional sealing member like an O-ring at
the front part of the piston where the depression is narrow and
therefore where the piston expands less so that in addition to the
pressure induced sealing action by piston expansion also some
independent sealing irrespective of any gas pressure induced
sealing action is provided.
[0010] Another preferred shape of the depression is to have it
start from the rear end face as a cylindrical depression that is
followed towards a front end face of the piston by a semi-spherical
section narrowing towards the front end face. The semi-spherical
shape prevents stress peaks at the outer circumference of the
bottom of the depression where the bottom connects to the
cylindrical depression wall since the spherical bottom shape
prevents a sharp annular corner between the bottom and the
cylindrical wall of the piston.
[0011] According to another preferred shape of the depression it
starts from the rear end face as a cylindrical depression that
comprises a dome-shaped bottom that deepens from an intersection
with a piston center line towards an outer circumference of the
bottom. The connection between the dome-shaped bottom and the
cylindrical wall of the depression can be rounded for avoiding
stress peaks. This shape provides the advantage of facilitating
sort of an annular joint that allows the piston wall to be
deflected more easily to the outside, i.e. facilitates letting the
piston expand where the depression is provided.
[0012] According to another preferred embodiment, the depression in
a rear end face of the piston comprises an inner diameter that is
at least half of the outer diameter of the piston and extends over
at least one third of a length of the piston. As already discussed
above, the inner diameter of the depression and the outer diameter
of the piston determine the wall thickness as one parameter
determining how big a force the piston exerts on the pressure
chamber wall. Another parameter is the length of the depression
from the rear towards the front of the piston, and therefore over
what length the piston may expand in its diameter. In most
applications, it will not be necessary to have the depression
extend over almost the entire length of the piston since the front
end of the piston may extend outside the pressure chamber after the
piston has reached its end position. Therefore, a pressure induced
sealing action might only be desirable closer to the rear end of
the piston.
[0013] According to another preferred embodiment of the pyrotechnic
actuator the gas generating ignition and output charge is provided
in an output can that is ignited by electrical contacts and the
output can is accommodated in the depression before the ignition
and output charge is ignited. This has the advantage of reducing
the entire length and in addition of accommodating the output can
with its explosive securely within the piston as an additional
protection. However, it would also be possible to accommodate the
output charge and igniter at any other position as long as it is
somehow connected to the pressure chamber and can transmit the
pressurized gas into the pressure chamber after firing.
[0014] According to another preferred embodiment of the pyrotechnic
actuator the external piston surface comprises a plurality of
semicircular ridges which are press-fitted into the internal
pressure chamber wall. The advantage of this design is to hold the
piston in place by the press-fit, but at the same time prevent too
strong a press-fit for allowing the piston to move easily along the
pressure chamber after firing. While such a press-fit would also be
possible without the semicircular ridges or other shapes such as
barbs, these help particularly to control the press-fit forces
especially when exposed to extreme temperature swings in the field
and provide better sealing capability over wider temperatures.
[0015] According to another preferred embodiment of the pyrotechnic
actuator a stop limiting the maximum movement of the piston along
the pressure chamber is provided such that the press-fit between
the external piston surface and the internal wall of the pressure
chamber is maintained. The stop allows the piston to be propelled
forward only up to the point where the rear end is not released
from the pressure chamber and therefore may still provide
sufficient sealing. This feature positively wedges/locks the piston
in between the severed ends of the conductor increasing disconnect
reliability.
[0016] According to another preferred embodiment of the pyrotechnic
actuator the press-fit between the external piston surface and the
internal wall of the pressure chamber substantially seals the
pressure chamber retaining the generated gas within the pressure
chamber. Substantially sealing is understood that it takes a long
time until the pressure is released. A hermetical, 100% sealing is
practically impossible as pressurized gas diffuses, in particular
if a plastic is used as the material for the housing and the
pressure chamber and/or piston, but even if metal is used. Also,
though the pressure-induced sealing forces provide a relatively
good sealing, gas may nevertheless over time gradually diffuse or
leak between the contact surfaces of the pressure chamber and the
external piston surface. However, a release of the pressure over
time is not only acceptable but even desirable in most environments
for safety reasons. In the alternative, it is also possible to
provide an extra valve allowing releasing the pressure when
desired. The gas can also be released under these controlled
circumstances through a filter or a reaction column adsorbing or
chemically altering the exhaust gas.
[0017] According to another preferred embodiment of the pyrotechnic
actuator the pyrotechnic actuator is a part of one of the group
consisting of: pyrotechnic power disconnect devices, pyrotechnic
battery disconnect devices, pyrotechnic fuses, pyrotechnic
switches, pyrotechnic cable cutters, pyrotechnic release devices,
pyrotechnic locking devices, pyrotechnic interrupters, and
pyrotechnic dislodging devices. The list of possible applications
for the pyrotechnic actuator is not to be understood as limited by
the above applications. The actuator can be used for any
application where a reliable, fast and strong action is required
that can be performed by an explosive propelling a piston forward.
The actuating parameters such as speed and force can be determined
by the type and quantity of the used charge of explosive.
[0018] According to another preferred embodiment of the pyrotechnic
actuator the front end face of the piston is connected to at least
one of a latch and a knife. However, many other alternatives are
possible, for instance by a planar front end face capable of either
pushing any target element aside or capable of shearing off any
element over a shearing edge such as for instance an electrical
conductor that should be interrupted. Other alternatives might be a
pointed end for puncturing an element or container as desired.
Accordingly, preferred actions performed by the method of actuating
a pyrotechnic actuator are cutting, latching, releasing,
puncturing, coining, shearing etc.
[0019] According to another preferred embodiment of the method of
actuating a pyrotechnic actuator the piston is stopped at a maximum
traveling range by running the piston against a stop. This stopping
action has already been described above. There might be many
reasons why the maximum traveling range of the piston should be
limited, for instance for holding the rear end of the piston within
the pressure chamber and therefore maintaining a tight sealing.
[0020] According to another preferred embodiment of the method of
actuating a pyrotechnic actuator the pressure chamber may be
imperfectly sealed by expanding the piston into the press-fit such
that a gradual releasing of the pressure within the pressure
chamber takes place over time. As discussed above, the imperfect
sealing might be desired so that the pressure is automatically
released within a reasonable time, but so slowly that it does not
create a hazard. A controlled release serves the purpose of
removing the pressure and therefore avoids any dangers that might
otherwise result from a highly pressured chamber, for instance if
parts fail or an unauthorized dissembling is carried out, for
instance by maintenance personnel.
[0021] The invention achieves a method of sealing exhaust gases and
flames from uncontrolled release to the surroundings in tubular
and/or odd shaped actuator devices without the use of additional
components such as gaskets, O-ring or sealants with high
reliability and for mistake-proofing the device assembly. The
design and the materials used in the construction of the piston,
actuator, thruster, pusher is configured such that it also acts as
a sealing apparatus inside the pressure cavity during device
functioning and prevents the uncontrolled release of the exhaust
gases and/or flames to the surrounding. The design is flexible
enough to accommodate a variety of applications involving a range
of conductors, strips, cables, lines, ropes, etc. that can be
severed, disconnected, displaced, dislodged or actuated, captured,
engaged or locked in place.
[0022] The actuator may be cylindrical in shape or may have more
than two sides to it. It may have a flat actuation/cutting end or
may have application specific features to facilitate orientation,
force concentration, guillotine cutting edge or ability to lock in
place. The space for primer inside the piston/actuator may be
cylindrical or have some other desirable shape. The individual
piston/actuator could be any combination of features specified here
depending on application. The pressure cavity may be configured to
accommodate the piston as required by the application. A number of
materials may be suitable for making the actuator/piston. This
includes but is not limited to Hot Melts, a variety of fiber filled
and unfilled thermoplastics (Polyethylene, Polypropylene,
Polyurethane, Polyamides, Polyimide, Polyester, PEEK, PPS, LCP and
many more) or thermoset polymers (natural and artificial
rubber/elastomers), single or multiple part epoxies/sealants or
metals and alloys. Various types of ceramics may also be used. The
piston may have a hexagonal shape. This shape and similar alignment
features (i.e. tongue and groove, square) will prevent the actuator
from rotating during deployment and direct the guillotine-shaped
knife or locking feature exactly at the location where it is
needed. As another alternative, a cylindrical shaped actuator can
be used. Ridges having a semicircular profile can be provided on
the outer diameter of the actuator or piston and pressed fit to the
inside diameter of the pressure cavity providing excellent pressure
sealing capability without the use of O-rings. The cutting face may
or may not have a guillotine-shaped knife or may use a locking
feature depending on application.
[0023] As another alternative, a rectangular actuator with a
locking/capturing element can be used. The outer perimeter is
closely matched with that of the pressure cavity with little
clearance between the two. When the device is fired the actuator
may move and lock itself into a slot on the mating part.
[0024] According to still another alternative, a cylindrical
actuator with an option to install an O-ring can be used. The
cutting face may be flat or have a guillotine-shaped knife, or a
locking feature as required by the application. The outer diameter
of the actuator is closely matched with the inner diameter of the
pressure cavity. The optional O-ring provides a double redundant
sealing system to increase reliability.
[0025] The primer cavity inside the actuator has multiple purposes.
The primer sits inside the cavity to reduce the overall length of
the assembly. Once the primer is fired, the thinner actuator walls
surrounding the primer expand due to primer pressure and seal the
pressure which in turn generates the force or thrust to do work.
Once the actuator has fully stroked, enough of the piston is left
in the pressure chamber to prevent any uncontrolled leaks around
the actuator. The actuator is designed to be tight fitting inside
the pressure chamber and when it is fully stroked it will deform
and swell up due to firing energy and heat and will not retract
back into pressure chamber under service loads. This locking
feature is desirable in applications such as power/battery
disconnects to prevent reconnect due shock or vibration.
[0026] The component parts of the pyrotechnic actuator including
its housing, the pressure chamber and the piston may be molded,
machined, forged, stamped or deep drawn as required by
application.
[0027] If non-cylindrical type actuators are used, the cutting edge
or locking or dislodging feature can be oriented with high
reliability as required by the application. A preferred concept as
to the manufacturing costs and the flexibility in possible shapes
and modifications is a plastic housing concept. However, metallic
housing of circular or irregular shapes may also be used by
applying the aforementioned concepts. The ideas are not limited to
disconnect devices but can be adapted to any product that requires
an actuator to move for serving a specific function.
[0028] The design can be made mistake proof during manufacturing
and installation. This can be done by using symmetrical parts such
that flipping around parts that will not impact form, fit or
functionality of the device is possible. In areas where part
symmetry was not possible or practical, parts are designed such
that it is impossible to assemble the device if the part
orientation is not correct.
[0029] In the prior art the sealing was primarily achieved with the
use of O-rings, gaskets and sealant. In sealed devices like these,
it is very difficult if not impossible to inspect for presence of
an O-ring or gaskets after the assembly is completed. Not using
O-rings or gaskets according to the present invention increased the
reliability of the device.
[0030] The bottom housing may carry according to a preferred
embodiment a shearing edge that acts as a secondary barricade to
prevent the uncontrolled release of primer gases and flames to the
surroundings which could start fires causing equipment damage
and/or harm to personnel in close proximity of the device. This is
double redundant safety. Sealing the primer exhaust with the
actuator opens up the possibility of using a variety of conductor
strips without compromising reliability or limiting the number of
applications.
[0031] The piston can preferably only be installed one way such
that if it is reversed it will not fit inside the pressure cavity
and the assembly cannot be completed. The piston's cutting edge
preferably always faces the strip to be severed in this embodiment.
The conductor strip can only be installed one way such that the
width that needs to be severed is always lined up with the shearing
edge of the piston and housing. This is done with unique features
in the molded housing and conductor. Putting the conductor upside
will not change form, fit or function. The top housing with
pressure chamber can be rotated 180.degree. without changing form,
fit and function. The firing reliability of the device is
independent of primer pin polarity or lead wire orientation. The
fully assembled device can be installed in the field in any
orientation without impacting form, fit, functionality or
reliability of the device.
[0032] The aforementioned concepts can be easily adapted to various
sizes and configurations depending on application. Plastic or
metallic housings (or a combination of either) of circular, square
or irregular shapes may also be used using these concepts.
[0033] The present invention provides reliable and cost effective
mistake proof solutions to address the aforementioned requirements
and overall device safety.
[0034] In the following, the present invention and its advantages
and equivalents are discussed in more detail by describing
exemplary embodiments implementing the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 shows a pre-firing sectional view of a preferred
device implementing the pyrotechnic actuator according to the
present invention.
[0036] FIG. 2 shows a post-firing sectional view of the same device
as shown in FIG. 1.
[0037] FIG. 3 shows a sectional view and a rear end view of a first
embodiment of a piston forming a part of the pyrotechnic actuator
according to the present invention.
[0038] FIG. 4 shows a sectional view and a rear end view of a
second embodiment of a piston forming a part of the pyrotechnic
actuator according to the present invention.
[0039] FIG. 5 shows a sectional view and a rear end view of a third
embodiment of a piston forming a part of the pyrotechnic actuator
according to the present invention.
[0040] FIG. 6 shows a sectional view and a rear end view of a
fourth embodiment of a piston forming a part of the pyrotechnic
actuator according to the present invention.
[0041] FIG. 7 shows a perspective view of a fifth embodiment of a
piston forming a part of the pyrotechnic actuator according to the
present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1 shows a sectional view of one embodiment of the
present invention in the pre-firing state. The shown embodiment
demonstrates a pyrotechnic power disconnect device. A housing 1
comprises an upper housing part 2 and a lower housing part 3 which
can, during assembly, be joined along a separation line 4. During
assembly, an electrical conductor 5 can be inserted on top of the
lower housing part 3. In parallel, the upper housing part can be
pre-assembled by inserting the piston 6 and an output can 7
comprising according to this embodiment an ignition and output
charge that can be ignited via electrical contacts 8. In the
pre-firing state, the output can 7 is accommodated in a depression
9 that is formed in a rear end face 10 of the piston 6. For the
purpose of pre-assembling the upper housing part 2, the piston 6
can be press-fitted into an internal pressure chamber wall 11. Only
a relatively light press-fit is necessary, just for holding the
piston in place within the internal pressure chamber wall. For the
purpose of creating a controlled press-fit, according to the shown
embodiments, a plurality of semicircular ridges 15 are provided on
the external piston surface 16, meaning that these do of course
extend around the entire circumference of the piston but have a
semicircular or similar shape, for instance the profile of a
segment of a circle. In the alternative, the piston 6 can be held
in place by means of a small bead of glue or any other suitable
means.
[0043] After pre-assembly, the upper housing part 2 can then be
positioned on top of the lower housing part 3, sandwiching the
electrical conductor 5 between the upper and lower housing parts 2
and 3. Both housing parts 2, 3 can then be fastened together by
rivets 12. These rivets 12 and their swaged end 13 are selected
such that these have sufficient strength in order to withstand the
force from the piston 6 when propelled forward in direction of the
lower housing part 3 after firing the output charge. The rivets
make the device temper resistant and difficult to disassemble and
access the small explosive charge inside. In an alternate
embodiment the housing parts 2, 3 can be bolted together using
plastic, wooden, sheet metal or machined screws. At least the upper
housing part 2 is preferably made from plastic. Preferably both the
upper housing part 2 and the lower housing part 3 are made from
plastic. For providing a sufficient reaction force to keep the
upper and lower housing parts together after firing, it is also
possible to make the lower housing part from a metal in order to
provide stronger threads 13. In the alternative to rivets, it is
also possible to provide a metal bolt screwed into a metal nut that
can be tightened against a bottom 14. For preventing unauthorized
disassembly, glue can be provided on the threads immediately prior
to screwing the bolt and the nut together, or a weld bead can be
placed to prohibit unauthorized unscrewing.
[0044] FIG. 2 shows the same sectional view as FIG. 1, but in the
post-firing state. The same elements as shown in FIG. 2 are
provided with the same reference numerals, but not all reference
numerals are repeated, only those elements that are discussed in
the following. After igniting the ignition and output charge
provided in the output can 7, the output can 7 explodes, releasing
the generated gas into the pressure chamber 17. As it becomes
apparent from FIG. 2, the piston 6 has been propelled forward, i.e.
in the drawing downward and has ruptured the electrical conductor
5. For facilitating this rupturing action provided by the piston 6
that has been propelled forward, a shearing edge 18 is provided. An
internal bottom 19 of a cavity 20 accommodating a substantial
partial length of the piston 6 in the post-firing state effectively
forms a stop that limits the maximum travelling range along which
the piston 6 can be propelled forward. This internal bottom 19 also
provides the additional function of a counter pressure surface
against which of the ruptured conductor 5 is pressed by a front end
face 21 of the piston 6. This provides another safety feature for
preventing that the two parts of the now ruptured electrical
conductor 5 can inadvertently reconnect and re-establish an
electrical contact that has on purpose been interrupted in the
post-firing state.
[0045] It becomes also apparent from FIG. 2 that the depression 9
that is formed in the rear end face 10 of the piston 6 is part of
the pressure chamber 17 and is therefore filled with pressurized
gas in the post-firing state. This pressure expands the outer
diameter of the piston 6 so that the external piston surface 16 is
pressed against the internal pressure chamber wall 11 and
establishes a sealing that retains the pressurized gas within the
pressure chamber 17. Depending on the circumstances, it might be
desirable to contain the pressurized gas within the pressure
chamber 17 for some period of time, or in the alternative, it might
be acceptable if the pressurized gas gradually releases by creeping
or diffusing through the press-fit between the external piston
surface 16 and the internal pressure chamber wall 11.
[0046] The sealing quality and sealing force between the external
piston surface 16 and the internal pressure chamber wall 11 depends
on several factors, for instance on the material that is chosen for
the piston 16 and the size of the depression 9, and therefore by
the thickness of a wall 22 which thickness is determined by a
diameter difference between an inner diameter of the depression 9
and an outer diameter of the piston 6.
[0047] FIGS. 3 to 7 demonstrate different shapes and designs of
various pistons, depending on the various utilities. Turning to
FIG. 3, the forward end of the piston 6 is provided with a
guillotine-like knife edge 23 for cutting a cable. This knife edge
23 transitions into a hexagonal cross section of the piston 6
having an external diameter 24, while the depression 9 has a
cylindrical cross-section of an inner diameter 25. In this
connection, for the purpose of this patent application, the
expression "diameter" is understood as the widest measurement of a
cross section and is not restricted to circular cross-sections. The
partial figure on top of FIG. 3 shows the rear end face 10 of the
piston 6 as viewed when the knife edge 23 in the drawing below is
moved into the drawing plane by 90 degrees while the rear end face
10 is moved out of the drawing plane by 90 degrees. Similar
combinations of piston sectional views in combination with piston
rear end views as shown in FIG. 3 are also shown in FIGS. 4-6. In
the embodiment shown in FIG. 3, the depression 9 comprises a
cone-shaped bottom 26 that is deeper in its outer circumference
than in the middle. This shape may help expanding the outer
diameter 24 of the piston 6 when the depression 9 is pressurized by
gas.
[0048] The piston shown in FIG. 4 has already been described in the
embodiments shown in FIGS. 1 and 2. The same reference numerals are
used as in the remaining figures. It is pointed out that the
depression 9 has a square shape, while the cross-section of the
piston 6 has a circular shape. Semicircular ridges 15 are provided
on a front portion 27 of the piston 6, while a rear portion 28 of
the piston 6 is substantially cylindrical. This cylindrical part is
the part that is widened in its diameter 24 and therefore pressed
against the internal wall 11 of the pressure chamber (see FIGS. 1
and 2) when filled with pressurized gas. The front face 21 of the
piston 6 is flat since it has only the function of shearing the
electrical conductor 5 (FIG. 2) by pressing it against the shearing
edge 18 (FIG. 2).
[0049] The piston shown in FIG. 5 has a substantially rectangular
shape that transitions into a male latching portion 29 that
likewise has a rectangular shape, but much smaller than the cross
section of a rear part 31 of the piston 6. The depression 9
comprises a spherical bottom 30. When the piston is pushed forward,
the male latching portion 29 may engage a respective female
latching portion.
[0050] FIG. 6 shows another variance of the piston 6 wherein the
depression 9 comprises a rear portion 32 and a front portion 33.
While the rear portion 32 is cylindrical, the front portion 33 is
conical having the deepest spot of this front portion 33 where a
center line of the entire piston intersects with the depression 9.
In addition, an annular groove 34 can be provided for holding an
O-ring providing additional sealing. As can be seen, the thickness
35 of a wall portion at the rear of the piston 6 is relatively
small in comparison to the wall thickness at the front portion 33.
Since the O-ring is provided at the front, less expansion is needed
at the front of the piston in comparison to the rear for providing
a sealing under pressure. The shape of the depression takes this
into account. Therefore, the shape of the depression 9 can be
adapted to control which part of the piston 6 should expand the
most.
[0051] FIG. 7 shows a perspective view of a piston 6 similar to
FIG. 4, but comprising a depression 9 that has a circular cross
section, and in contrast to the embodiments shown in FIG. 4, the
semicircular ridges 15 are provided over the entire length of the
piston 6 and not just in the front part.
[0052] All embodiments shown and discussed are just exemplary
embodiments and the invention is to be understood as not being
limited to these exemplary embodiments. Many modifications are
possible and within the scope of the present invention.
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