Arrangement for locking arming conditions.
Technical field
The present invention relates to an arrangement for locking arming conditions to
prevent unintentional arming of SAI-units of ammunition units, such as projectiles,
when the ammunition unit is subjected to external threats. In this connection SAI
stands for Safety, Arming and Ignition and is a well-known component in the
ammunition field.
Background
Within the Insensitive Munitions (IM) field there are activities going on to find
efficient solutions to protect weapon systems from external threats. In order to
measure the IM-ability of a weapon system there are a number of standardized tests
and threats available. The solution proposed is intended to prevent arming of an
ammunition unit such as a projectile when subjected to a selected such standardized
test to test "Slow cook-off.
The invention is primary intended to be used for preventing arming of projectiles of
disposable one-man carried weapons. However, the invention could also be used in
other existing ammunition types or ammunition types to come.
Summary of the invention
The main objects of the invention is to obtain an arrangement for locking arming
conditions that is non-complicated in construction, reliable, cost effective, applicable
to different types of SAI-units and fulfils the requirements of standardized heating
tests.
The objects are obtained by an arrangement according to the first paragraph
characterized in that an essentially ring shaped shape memory alloy is provided in
cooperation with a recess in a plunger comprised in connection to the SAI-unit and a
fixed recess to prevent the plunger from axial movement when subjected to heating by
changing the shape of the essentially ring shaped shape memory alloy to lock the
plunger relative to the fixed recess. The use of shape memory alloy to lock arming in
connection to a SAI-unit when the ammunition unit is subjected to heating effectively
fulfils the objects mentioned in the previous paragraph.
In this connection it can per se be observed that it is known to use shape memory
alloys (SMA:s) to prevent undesired reactions within the insensitive munition field.
One such example is known from FR 2 742 221 Al disclosing ejection of a cap when
a retaining member made from a material with shape memory effect is actuated by an
excessive temperature. Another example is known from SE 519561 C2 disclosing a
shape memory alloy designed to open up different parts of a casing when the
surrounding temperature approaches the ignition temperature of an explosive.
It is also referred to US 5 445 077 A disclosing an ignition device for a pyrotechnic
system. The device provides an arming condition or fuse activated by a shape memory
alloy when the temperature reaches a sufficiently high temperature. It is now a
requirement that the fuse has been activated before the device can initiate (set fire to)
the pyro technic. On the contrary our invention prevents an arming condition from
being activated.
According to a favourable embodiment of the invention the arrangement is
characterized in that the essentially ring shaped shape memory alloy is provided in
cooperation with a pressure plunger controlling the pressure condition when arming
the SAI-unit. Arranging the ring shaped shape memory alloy admits a compact
construction and involves few reconstructions of constructions on the market.
In particular in a further embodiment according to the invention it is proposed that the
pressure plunger is provided with a first and a second circular recesses provided in the
envelope surface of the pressure plunger, the first circular recess accommodating a
sealing ring and the second circular recess cooperating with the ring shaped shape
memory alloy.
According to another favourable embodiment of the invention the arrangement is
characterized in that the essentially ring shaped shape memory alloy and the plunger
are provided inside the SAI-unit, the essentially ring shaped shape memory alloy in
cooperation with the recess in the plunger and the fixed recess preventing the plunger
from movement when subjected to heating by changing the shape of the essentially
ring shaped shape memory alloy to lock the plunger relative to the fixed recess
preventing activation of an external pressure plunger. This embodiment offers a
complete and competent SAI-unit easy to accommodate in ammunition units.
The ring shaped shape memory alloy can be designed in different ways. According to
one embodiment of the arrangement, the essentially ring shaped memory alloy is
designed to expand radially when subjected to heating. According to another
embodiment of the arrangement, the essentially ring shaped shape memory alloy is
designed to contract radially when subjected to heating.
Furthermore the cross section of the essentially ring shaped shape memory alloy
comprised in the arrangement can vary. In particular it is proposed that the essentially
ring shaped shape memory alloy comprised in the arrangement originally has an
essentially rectangular cross section, an essentially square cross section and/or an
essentially round cross section.
According to still another favourable embodiment, the essentially ring shaped shape
memory alloy comprised in the arrangement is provided with a break. Such a break
can facilitate the expansion and contraction of the shape memory alloy.
In a common embodiment the essentially ring shaped shape memory alloy has a
closed formation.
Brief description of the drawings
The invention will now be described in more detail with reference to the
accompanying drawings in which:
Figure 1 schematically, partly in cross section, shows a known arrangement with a
pressure plunger.
Figure 2a schematically, partly in cross section, shows a first arrangement in
accordance with the invention with a shape memory alloy in cooperation with a
pressure plunger in an initial position.
Figure 2b schematically, partly in cross section, shows the arrangement of figure 2a
following the normal function to fulfil the arming pressure conditions.
Figure 2c schematically, partly in cross section, shows the arrangement of figure 2a
when the arrangement has been subjected to heating.
Figure 3a schematically, partly in cross section, shows a second arrangement in
accordance with the invention accommodating the shape memory alloy and plunger
inside an SAI-unit.
Figure 3b schematically, partly in cross section, shows the arrangement of figure 3a
when the arrangement has been subjected to heating.
Figure 4a schematically shows an example of a ring shaped shape memory alloy with
a break and suitable for the arrangement in a constricted condition.
Figure 4b schematically shows the ring shaped shape memory alloy of figure 4a in an
expanded position.
Figure 4c schematically shows the ring shaped shape memory alloy in a closed
formation in a constricted condition.
Figure 4d schematically shows the ring shaped shape memory alloy of figure 4c in a
closed formation in an expanded condition.
Figures 5a-5c schematically shows three examples of cross sections of the shape
memory alloy suitable for the arrangement according to the invention.
Detailed description
In the prior art arrangement shown in figure 1there is a pressure plunger 1 provided in
a SAI-holder, such as a fin holder 2. The pressure plunger is arranged to be moved
further into the SAI- holder 2 by a pressure generated by propellant and indicated by
an arrow 17. Within the SAI- holder 2 a SAI-unit has been indicated by dashed lines
given reference number 10. The pressure plunger comprises a circular recess 3
accommodating a sealing O-ring 4. Under normal function, the pressure plunger 1
moves in a space 5 under control of a bearing 6 to a position fulfilling the arming
pressure conditions.
According to a first arrangement according to the invention and shown in figures 2a-
2c a further circular recess 7 is provided to accommodate at least parts of a ring
shaped shape memory alloy 8. There is also a circular recess 9 in the SAI-holder 2
initially at the same level as the recess 7 in the pressure plunger 1. Components
described with reference to figure 1 and found in figures 2a-2c have been given the
same reference numbers. In comparison with the prior art arrangement described with
reference to figure 1, the first arrangement according to the invention, has an
extended plunger height and the space 5 has been adapted to the extended height of
the plunger.
The operation of the arrangement is as follows.
Starting from figure 2a the pressure plunger is in its initial position with a sealing Oring
4 to obtain a sealing between the pressure plunger 1 and the space 5. The ring
shaped shape memory alloy 8 is in position in the recess 7 and does not prevent
movement of the pressure plunger 1.
When subjecting the pressure plunger 1 to pressure generated by propellant, the
pressure plunger 1 under normal function strikes a SAI-unit 10 indicated by dashed
lines inside the SAI-holder 2 to fulfil the arming pressure conditions. It could be
observed that the position of the shape memory alloy 8 don't have any noticeable
effect on the movement of the pressure plunger 1, see figure 2b.
When subjected to heating according to a standardized test for example by raising the
temperature around the arrangement by for example 3.3 °C/h up to about 100°C, or by
a comparable unintended temperature raise, the ring shaped shape memory alloy 8
will expand and assume a position as shown in figure 2c resulting in that the pressure
plunger 1 is locket to a recess 9 in the SAI-holder 2 by the shape memory alloy 8 .
Above a shape memory alloy 8 has been described that expands radially when
subjected to heating. It is however also possible to use a shape memory alloy that
initially is in an expanded condition outside the recess 7 of the pressure plunger 1 and
that partly contradict into the recess 7 of the pressure plunger 1 when subjected to
heating.
A second arrangement is shown in figures 3a-3b. In this case the plunger 1 is built in
in the SAI-unit 10. In accordance with the first arrangement the plunger 1 is provided
with a recess 7 accommodating a ring shaped shape memory alloy 8.
Figure 3a shows the SAI-unit 10 in its initial position, the shape memory alloy being
totally within the recess 7 so that the plunger 1 is free to move downwards in the
shown figure if other arming requirements are fulfilled inter alia involving the
component to be set aside. If however the SAI-unit 0 is subjected to heating above
levels set, the shape memory alloy 8 will expand into a recess 9, locking the pressure
plunger 1 to the recess 9.
Figure 4a and 4b schematically show a ring shaped shape memory alloy 8 provided
with a break 12 in two different conditions illustrating how the shape memory alloy
can be expanded or contradicted.
Figure 4c and 4d schematically show a ring shaped shape memory alloy 8 as a closed
component in constricted condition, figure 4c, and in expanded condition, figure 4d.
In figure 5a-5c three different cross sections for a ring shaped shape memory alloy 8
are shown. In figure 5a a rectangular cross section 13 is proposed. In figure 5b a
square cross section 14 is shown and in figure 5c a circular cross section 15 is shown.
The arrangement for locking arming conditions is not limited to the examples
described above but may be modified within the scope of the attached claims.

Patent Claims
. An arrangement for locking arming conditions to prevent unintentional arming
of SAI-units of ammunition units, such as a projectiles, when the ammunition unit is
subjected to external threats, characterized in that an essentially ring shaped shape
memory alloy is provided in cooperation with a recess in a plunger comprised in
connection to the SAI-unit and a fixed recess to prevent the plunger from axial
movement when subjected to heating by changing the shape of the essentially ring
shaped shape memory alloy to lock the plunger relative to the fixed recess.
2. An arrangement as claimed in claim 1, characterized in that the essentially
ring shaped shape memory alloy is provided in cooperation with a pressure plunger
controlling the pressure condition when arming the SAI-unit.
3. An arrangement as claimed in claim 2, characterized in that the pressure
plunger is provided with a first and a second circular recesses provided in the
envelope surface of the pressure plunger, the first circular recess accommodating a
sealing ring and the second circular recess cooperating with the ring shaped shape
memory alloy.
4. An arrangement as claimed in claim 1, characterized in that the essentially
ring shaped shape memory alloy and the plunger are provided inside the SAI-unit, the
essentially ring shaped shape memory alloy in cooperation with the recess in the
plunger and the fixed recess preventing the plunger from movement when subjected to
heating by changing the shape of the essentially ring shaped shape memory alloy to
lock the piston relative to the fixed recess preventing activation of an external pressure
plunger.
5. An arrangement as claimed in any of the preceding claims, characterized in
that the essentially ring shaped shape memory alloy is designed to expand radially
when subjected to heating.
6. An arrangement as claimed in any of the preceding claims 1-4, characterized
in that the essentially ring shaped shape memory alloy is designed to contract radially
when subjected to heating.
7. An arrangement according to any of the preceding claims, characterized in
that the essentially ring shaped shape memory alloy originally has an essentially
rectangular cross section.
8. An arrangement as claimed in claim 7, characterized in that the essentially
ring shaped shape memory alloy originally has an essentially square cross section.
9. An arrangement as claimed in any of the preceding claims 1-6, characterized
in that the essentially ring shaped shape memory alloy originally has an essentially
round cross section.
10. Arrangement as claimed in any of the preceding claims, characterized in that
that the essentially ring shaped shape memory alloy is provided with a break.
1. Arrangement as claimed in any of the preceding claims 1-9, characterized in
that the essentially ring shaped shape memory alloy has a closed formation.