The present invention is concerned with a firing mechanism for activation of a
pneumatic stored energy system, and a method 5 of activating a pneumatic stored
energy system.
Pneumatic stored energy systems have many applications. In transport safety they may
be used to rapidly inflate various devices such as car air bags, aircraft passenger
10 escape slides and helicopter flotation systems, in the case of an emergency incident.
Due to their use in emergency incidents, rapid activation of the pneumatic stored
energy system is necessary.
A pneumatic stored energy system may comprise, for example, a sealed vessel filled
15 with a compressed helium-nitrogen (He/N) mixture, and some sort of firing
mechanism to puncture a region of the vessel wall. A collection nozzle arranged about
the vessel fluidly connects an inflatable device, folded in its uninflated state, to the
vessel. In use, the firing mechanism causes a region of the vessel wall to puncture so
as to supply the compressed He/N mixture via the nozzle to inflate the inflatable
20 device.
Typically, pyrotechnic actuators have been used as a firing mechanism to trigger the
pneumatic stored energy systems to inflate the specific device.
25 In use, an electric current is passed through a wire buried in a chemically reactive
substance (the pyrotechnic), causing the pyrotechnic to burn. As the pyrotechnic
burns, it produces a gas. The burn is contained within a sealed cavity of a container,
and the pressure caused by the generation of exhaust gasses is applied to a piston
fitted in the cavity at the end of the container. The piston moves due to the applied gas
30 pressure and the linear movement can be used to shear through a diaphragm, or to
bend and break a hollow pillar, thus releasing the stored pneumatic energy.
3
The use of pyrotechnic actuators is highly regulated. The potentially hazardous
substances used in pyrotechnic actuators are difficult to handle and store. These
potentially hazardous substances also require expensive and time consuming checks,
for both the producer and end user. The potentially hazardous substances may also
5 have a limited life-span, requiring replacement.
An alternate firing mechanism for activating a pneumatic stored energy system is
through the use of shape memory alloys. The shape memory alloy may be caused to
pull on a hollow break-off pillar and break it, thus releasing the stored pneumatic
10 energy.
In this case the shape memory alloy is stretched during heat treatment such that it
retains its stretched dimension during operation at normal, ambient, temperature.
When the alloy is heated, for instance by passing an electrical current through it, it
15 reverts to its unstretched dimensions. The change in length and resulting linear force
can be used to break a hollow pillar.
However, shape memory alloy firing mechanisms often perform unreliably.
Furthermore there remains the risk of unscheduled operation should the local
20 environment conditions change.
It is an aim of the present invention to provide a firing mechanism for activation of a
pneumatic stored energy system that is simple, reliable, re-useable, lightweight, of
relatively small size, low cost, and which may be activated rapidly.
25
According to the first aspect of the invention there is provided a firing mechanism for
activation of a pneumatic stored energy system, the firing mechanism comprising: a
motor having a drive coupling; a vessel having an attachment region; and a tether; a
first part of the tether being attached to the drive coupling of the motor and a second
30 part of the tether being attached to the attachment region of the vessel, wherein
activation of the motor to rotate the drive coupling causes the tether to wind, applying
a linear force to the attachment region of the vessel, fracturing the vessel to activate
the pneumatic stored energy system.
4
The firing mechanism imparts a known linear force to the vessel, as regulated by the
rotation of the motor and the dimensions of the tether. The firing mechanism therefore
may be used reliably and repeatably. The use of a positively controlled motor reduces
the risk of accidental deployment, as the case 5 may be, for example, with shape
memory alloys activated by altering local environmental conditions. Furthermore, the
use of pyrotechnics is not required.
Preferably the vessel includes a sensor, arranged to sense when the vessel is fractured,
10 to provide a signal to deactivate the motor.
Advantageously this prevents the motor from continuing to operate unnecessarily once
the pneumatic stored energy system has been activated.
15 Preferably the sensor is a fuse arranged so as to break when the vessel is fractured, to
deactivate the motor.
The fuse provides a fail-safe cut out for the motor only once the firing mechanism has
activated the pneumatic stored energy system.
20
Preferably the fuse is a wire arranged across the attachment region of the vessel.
Alternatively the fuse is an electrical contact, arranged across the attachment region of
the vessel.
25 Preferably the attachment region of the vessel is a region of weakness.
Advantageously this reduces the requisite linear force that must be applied to the
attachment region of the vessel to ensure fracturing of the vessel. This reduction may
beneficially be realised through the use of lighter components in the firing
30 mechanism, a reduced motor speed (rotation per minute, (rpm)) or indeed a reduced
number of rotations needed before fracture, resulting in a more rapid activation of the
pneumatic stored energy system.
5
Preferably the attachment region of the vessel is a hollow break-off pillar.
The hollow break-off pillar advantageously provides both a region of weakness and
predetermined fracture region of the vessel, such that the gasses expelled by the
fracture of the vessel may be 5 readily collected for, or directed to, their use.
Alternatively the attachment region of the vessel is a tear panel.
The tear panel advantageously provides both a region of weakness and predetermined
10 fracture region of the vessel.
Preferably the tether is a continuous loop.
Advantageously the tether may therefore be attached to the first and or second region
15 by hooking the loop around that region. This arrangement provides a simple
attachment of the firing mechanism parts. It reduces the number of components
required for the firing mechanism, reducing weight, cost and potential failure modes.
Preferably the first part of the tether is attached to the drive coupling by clamping the
20 first part of the tether between a pair of abutting jaws of the drive coupling.
This arrangement advantageously provides a controlled wind as the motor causes the
drive coupling to rotate. Furthermore, after use, a new tether may be fitted such that
the firing mechanism may be used multiple times.
25
Preferably the motor is an electric motor. Preferably electric motor is a DC motor.
Advantageously an electric motor can impart an instant torque to initiate winding of
the ribbon.
30
Preferably the tether is a ribbon.
6
Advantageously the ribbon, extending perpendicularly to the axis of rotation of the
motor, to define an aspect ratio, imparts a greater force per wind, (or full rotation of
the motor), proportional to its aspect ratio. Therefore a reduced number of rotations
are needed before fracture.
5
Preferably the ribbon is made from a woven fabric. Preferably the woven fabric is an
aramid fibre braid. Alternatively the woven fabric is cotton. Alternatively the woven
fabric is an aramid fibre cloth. Alternatively the woven fabric is carbon fibre.
10 Such materials provide a lightweight connection to the vessel. A relatively low inertia
is therefore required to initiate winding of the ribbon by the motor, meaning a
comparatively smaller motor may be used than with heavier ribbon materials.
Preferably the firing mechanism is triggered by a remote switch.
15
According to a second aspect of the present invention there is provided a method of
activating a pneumatic stored energy system, the method comprising the steps of:
providing a motor having a drive coupling; a vessel having an attachment region; and
a tether; a first part of the tether being attached to the drive coupling of the motor and
20 a second part of the tether being attached to the attachment region of the vessel;
activating the motor to rotate the drive coupling, causing the tether to wind, which
applies a linear force to the vessel, fracturing the vessel to activate the pneumatic
stored energy system.
25 Preferably the method includes the step of providing a sensor arranged to sense when
the vessel is fractured, the sensor providing a signal to deactivate the motor when the
vessel is fractured.
According to a further aspect of the present invention there is provided an actuator
30 comprising:
a motor having a drive coupling;
a tether;
7
a first part of the tether being attached to the drive coupling of the motor and a second
part of the tether being remote from the drive coupling, wherein actuation of the motor
to rotate the drive coupling causes the tether to wind, thereby drawing the second part
towards the first part to effect actuation of the actuator.
5
Preferably the drive coupling is rotatable relative to a body of the motor and the
second part is fixed non-rotatable relative to the body.
Preferably the tether winds about a longitudinal axis of the tether.
10
An example of the firing mechanism for activation of a pneumatic stored energy
system in accordance with the present invention will now be described with reference
to the appended drawings in which:
15 Figure 1a is a perspective view of a vessel with a hollow break-off pillar;
Figure 1b is a partial enlarged cross-sectional view of a hollow break-off pillar of
figure 1a;
20 Figure 1c is a partial enlarged cross-sectional view of a hollow break-off pillar of
figure 1a in a fractured state;
Figure 2 is a schematic plan view of the firing mechanism installed with the
pneumatic stored energy system;
25
Figures 3a to 3d are schematic plan views of the firing mechanism of figure 2
isolation, various stages of operation.
In figures 1a to 1c, a sealed cylindrical vessel 2, filled with a high pressure gas, has a
30 hollow break-off pillar 10 arranged protruding perpendicularly from the vessel wall
20. The hollow break-off pillar 10 comprises a cylindrical tube 12 having break-off
pillar axis 16, fitted within a circular opening 24 of a vessel wall 20. The cylindrical
8
tube 12 defines a lumen 14 which is capped at one end by cap 18. The lumen 14 is in
fluid communication with the interior space 22 defined within the vessel wall 20.
The cylindrical tube 12 is designed to fracture under a force applied perpendicular to
its axis 16. Fracture will commonly occur 5 at the junction between the vessel wall
opening 24 and the cylindrical tube 12 as shown in figure 1b. Fracture of the
cylindrical tube 12 therefore allows escape of the high pressure gases held within
interior space 22.
10 Referring to figure 2, a pneumatic stored energy system 1 comprises a sealed vessel
20 defining interior space 22 having a compressed helium-nitrogen mixture therein.
A firing mechanism 25 is arranged alongside the vessel 2. The firing mechanism 25
comprises a motor 50, a tether and a hollow break-off pillar 10. In this embodiment
15 the tether is a ribbon 70.
The motor 50 is arranged within a motor chassis 40. A body 51 of the motor is fixed
to the motor chassis 40. The motor has a drive shaft 55, which passes through a
circular aperture 45 in a wall of the motor chassis 40. The drive shaft 55 terminates in
20 a drive coupling 60.
The drive coupling 60 has an L-shaped main body part 62 and a jaw part 64 (as shown
in figure 3b). The jaw part 64 is sized to fit in a recess defined by the L-shaped main
body part 62. The jaw part 64 is connectable to the main body part 62 by fastening
25 arrangement 65.
The ribbon 70 is a substantially inextensible loop of woven aramid fibre braid. The
ribbon is flexible so that it may be wound. It has an overall length of 210mm. It has a
width of 30mm. It has an aspect ratio, calculated as the length divided by the width,
30 of 7.
The ribbon 70 is clamped between the jaw part 64 and the main body part 64 of the
drive coupling 60. The fastening arrangement 65 comprises a bolt that passes through
9
the main body part 64, the ribbon 70 and the jaw part 64 and is secured by a nut. The
other end of the ribbon 70 is looped around the hollow break-off pillar 10. The ribbon
70 therefore extends between the drive coupling 60 and the hollow break-off pillar 10,
bridging a gap of less than 155mm. The flexible nature of the ribbon 70 allows it to
be looped around the hollow break-off pillar 5 10 without imparting a force sufficient to
break the hollow break-off pillar 10.
A collection nozzle 35 is arranged adjacent the hollow break-off pillar. An inflatable
helicopter flotation system is fluidly attached to nozzle 35 (not shown).
10
A fuse wire 80 is arranged along the cylindrical tube 12 of the hollow break-off pillar
10, in the region of anticipated fracture. The fuse wire 80 is electrically connected to
the motor 50.
15 Referring to figures 3a to 3d, the firing mechanism 25 is shown viewed in direction III
in figure 2. Figures 3a to 3d show the firing mechanism 25 in four stages of the firing
process, as will be explained below.
With the firing mechanism 25 set up so that the ribbon 70 is clamped at one end
20 between the jaw part 64 and the main body part 64 of the drive coupling 60, and
looped around the hollow break-off pillar 10 at the other end, the device is ready to
fire, (figure 3a).
In the instance of a crash or impact scenario requiring deployment of the pneumatic
25 stored energy system, a remote switch is activated by an impact detection alarm
signal. Such an impact detection alarm signal could be raised manually, for example
by a pilot, or automatically, as is known in the art. For example, the impact detection
alarm signal could be initiated by a positive reading on a water sensor, an impact
sensor or a sensor monitoring the instant flight characteristics of the vehicle to which
30 the pneumatic stored energy system is fitted, or a combination of more than one of the
above.
10
The remote switch causes current to be passed through motor 50. The motor starts to
rotate drive shaft 55 causing a quarter turn pivot of the drive coupling 60, and ribbon
70 begins to wind (figure 3b).
As the drive shaft 55 and drive coupling 5 60 complete one full revolution, the winding
of ribbon 70 and associated shortening thereof causes linear force F parallel with the
drive shaft axis 35 and perpendicular to the break-off pillar axis 16, to pull the breakoff
pillar 10 towards the drive coupling 60, (figure 3c).
10 Following three and one quarter full revolutions of the drive shaft 55 and drive
coupling 60, (figure 3d), the ribbon 70 has been wound such that the linear force on
the hollow break-off pillar 10 is sufficient to fracture the hollow break-off pillar 10 as
already described with reference to figures 1b and 1c. The fuse wire 80 is also broken,
which arrests the supply of current to the motor 50.
15
The firing mechanism 25 has therefore activated the pneumatic stored energy system
1, as compressed helium-nitrogen mixture contained within the vessel 20 is able to
escape via the now fractured hollow break-off pillar 10, and be collected to inflate the
inflatable helicopter flotation system via nozzle 35.
20
It is to be understood that the number of rotations required to fracture the hollow
break-off pillar is exemplary in nature only, and could be more or less depending of
the strength of the hollow break-off pillar and the dimensions of the tether.
25 The tether could, for example, comprise one or more single stands of fibre arranged
between the drive coupling 60 and the hollow break-off pillar 10.
In alternative embodiments, the tether could be secured to the drive coupling by
gluing or through the use of further fasteners, or both.
30
In alternate embodiments, the tether could be made of cotton or from an aramid fibre
cloth or from carbon fibre.
11
In the disclosed embodiment, the hollow break-off pillar extends perpendicularly from
a wall of the vessel and both the motor drive axis and the ribbon extend
perpendicularly to the hollow break-off pillar. Other configurations are also
envisaged, limited only to the extent that a force sufficient to fracture the hollow
break-off pillar is applied by winding of 5 the tether. Alternate or additional means for
ensuring that fracture occurs at a specific location under a pre-determined force
includes providing a notch in the cylindrical tube 20, of the hollow break-off pillar 10.
In the disclosed embodiment, an inflatable helicopter flotation system is fluidly
10 attached to nozzle 35. As described above, alternate inflatable devices may be fluidly
attached to nozzle 35, such as an emergency escape slide for an aircraft, or a vehicle
airbag.
In the disclosed embodiment, a compressed helium-nitrogen mixture is given as an
15 exemplary gas contained within vessel 20. Other gases are envisaged for use with the
device of the present invention.
The firing mechanism described can be considered to be an actuator. As will be
appreciated the first part of the tether is attached to the drive coupling of the motor
20 and the second part of the tether is remote from the drive coupling. Activation of
motor to rotate the drive coupling causes the tether to wind, thereby drawing the
second part of the tether towards the first part of the tether to effect actuation of the
actuator. Accordingly, an actuator according to the present invention is not limited to
being used to apply a linear force to an attachment region of a pressure vessel thereby
25 fracturing the pressure vessel to actuate the pneumatic stored energy system.
Actuators according to the present invention can be used to apply a force to any other
type of component. The tether of actuators according to the present invention may be
a continuous loop and/or a ribbon. The ribbon may be made from a woven fabric.
The motor of an actuator according to the present invention may be an electric motor.
30 The drive coupling of the motor may be rotatable relative to a body of he motor.

We Claim:
1. A firing mechanism for activation of a pneumatic stored energy system, the
firing mechanism comprising:
a motor having a drive coupling;
a 5 vessel having an attachment region; and
a tether;
a first part of the tether being attached to the drive coupling of the
motor and a second part of the tether being attached to the attachment region of
the vessel, wherein activation of the motor to rotate the drive coupling causes
10 the tether to wind, applying a linear force to the attachment region of the vessel,
fracturing the vessel to activate the pneumatic stored energy system.
2. A firing mechanism according to claim 1, wherein the vessel includes a sensor
arranged to sense when the vessel is fractured, to provide a signal to deactivate
15 the motor.
3. A firing mechanism according to claim 2, wherein the sensor is a fuse arranged
so as to break when the vessel is fractured, to deactivate the motor.
20 4. A firing mechanism according to claim 3, wherein the fuse is a wire arranged
across the attachment region of the vessel.
5. A firing mechanism according claim 3, wherein the fuse is an electrical contact
arranged across the attachment region of the vessel.
25
6 A firing mechanism according to any preceding claim, wherein the attachment
region of the vessel is a region of weakness.
7. A firing mechanism according to any preceding claim, wherein the attachment
30 region of the vessel is a hollow break-off pillar.
13
8. A firing mechanism according to any of claims 1 to 6, wherein the attachment
region of the vessel is a tear panel.
9. A firing mechanism according to any preceding claim, wherein the tether is a
5 continuous loop.
10. A firing mechanism according to any preceding claim, wherein the first part of
the tether is attached to the drive coupling by clamping the first part of the tether
between a pair of opposed jaws of the drive coupling.
10
11. A firing mechanism according to any preceding claim, wherein the attachment
region of the vessel is disposed within a loop of the second part of the tether.
12. A firing mechanism according to any preceding claim, wherein the motor is an
15 electric motor.
13. A firing mechanism according to any preceding claim, wherein the tether is a
ribbon.
20 14. A firing mechanism according to claim 13, wherein the ribbon is made from a
woven fabric.
15. A firing mechanism according to any preceding claim, wherein the firing
mechanism is triggered by a remote switch.
25
16. A method of activating a pneumatic stored energy system, the method
comprising the steps of: providing a motor having a drive coupling; a vessel
having an attachment region; and a tether; a first part of the tether being attached
to the drive coupling of the motor and a second part of the tether being attached
30 to the attachment region of the vessel; activating the motor to rotate the drive
coupling, causing the tether to wind, which applies a linear force to the vessel,
fracturing the vessel to activate the pneumatic stored energy system.
14
17. A method of activating a pneumatic stored energy system according to claim 16,
comprising the further step of providing a sensor arranged to sense when the
vessel is fractured, the sensor providing a signal to deactivate the motor when
the vessel is fractured.
5
18. A firing mechanism as hereinbefore described with reference to figures 2 to 3d.
19. An actuator comprising:
a motor having a drive coupling;
10 a tether;
a first part of the tether being attached to the drive coupling of the motor and a second
part of the tether being remote from the drive coupling, wherein actuation of the
motor to rotate the drive coupling causes the tether to wind, thereby drawing the
second part towards the first part to effect actuation of the actuator.
15 20. An actuator as defined in claim 19 wherein the drive coupling is rotatable
relative to a body of the motor and the second part is fixed non-rotatable relative to the
body.