Arrangement for locking arming conditions

Abstract

An arrangement for locking arming conditions to prevent unintentional arming of SAI-units of ammunition units when the ammunition unit is subjected to external threats. A ring shaped shape memory alloy is provided in cooperation with a recess in a plunger arranged 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.

Claims

1. An arrangement for locking arming conditions to prevent unintentional arming of Safety, Arming and Ignition units (SAI-units) of ammunition units when the ammunition unit is subjected to external threats, wherein an essentially ring-shaped shape memory alloy is provided which can assume a locking position to prevent a plunger from moving axially when subjected to heating by changing the shape of the essentially ring-shaped shape memory allowy whereby the essentially ring-shaped shape memory alloy by expansion or contraction becomes partly accommodated in a recess in the plunger and partly accommodated in a fixed recess in a SAI-holder whereby the plunger is locked relative to the fixed recess; said plunger being arranged partly in the SAI-unit or built-in in the SAI-unit.

2. The arrangement as claimed in claim 1, wherein 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. The arrangement as claimed in claim 1, wherein the pressure plunger is provided with first and second circular recesses provided in an envelope surface of the pressure plunger, said first circular recess accommodating a sealing ring and said second circular recess cooperating with the ring-shaped shape memory alloy.

4. The arrangement as claimed in claim 1, wherein 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. The arrangement as claimed in claim 1, wherein the essentially ring-shaped shape memory alloy is designed to expand radially when subjected to heating.

6. The arrangement as claimed in claim 1, wherein the essentially ring-shaped shape memory alloy is designed to contract radially when subjected to heating.

7. The arrangement according to claim 1, wherein the essentially ring-shaped shape memory alloy originally has an essentially rectangular cross section.

8. The arrangement as claimed in claim 1, wherein the essentially ring-shaped shape memory alloy originally has an essentially square-shaped cross section.

9. The arrangement as claimed in claim 1, wherein the essentially ring-shaped shape memory alloy originally has an essentially round cross section.

10. The arrangement as claimed in claim 1, wherein the essentially ring-shaped shape memory alloy is provided with a break.

11. The arrangement as claimed in claim 1, wherein the essentially ring-shaped shape memory alloy has a closed formation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in more detail with reference to the accompanying drawings in which:

(2) FIG. 1 schematically, partly in cross section, shows a known arrangement with a pressure plunger.

(3) FIG. 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.

(4) FIG. 2b schematically, partly in cross section, shows the arrangement of FIG. 2a following the normal function to fulfill the arming pressure conditions.

(5) FIG. 2c schematically, partly in cross section, shows the arrangement of FIG. 2a when the arrangement has been subjected to heating.

(6) FIG. 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.

(7) FIG. 3b schematically, partly in cross section, shows the arrangement of FIG. 3a when the arrangement has been subjected to heating.

(8) FIG. 4a schematically shows an example of a ring shaped shape memory alloy with a break and suitable for the arrangement in a constricted condition.

(9) FIG. 4b schematically shows the ring shaped shape memory alloy of FIG. 4a in an expanded position.

(10) FIG. 4c schematically shows the ring shaped shape memory alloy in a closed formation in a constricted condition.

(11) FIG. 4d schematically shows the ring shaped shape memory alloy of FIG. 4c in a closed formation in an expanded condition.

(12) FIGS. 5a-5c schematically shows three examples of cross sections of the shape memory alloy suitable for the arrangement according to the invention.

DETAILED DESCRIPTION

(13) In the prior art arrangement shown in FIG. 1 there 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.

(14) According to a first arrangement according to the invention and shown in FIGS. 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 FIG. 1 and found in FIGS. 2a-2c have been given the same reference numbers. In comparison with the prior art arrangement described with reference to FIG. 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.

(15) The operation of the arrangement is as follows.

(16) Starting from FIG. 2a the pressure plunger is in its initial position with a sealing O-ring 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.

(17) 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 fulfill 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 FIG. 2b.

(18) 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 FIG. 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.

(19) 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.

(20) A second arrangement is shown in FIGS. 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.

(21) FIG. 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 11 to be set aside. If however the SAI-unit 10 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.

(22) FIGS. 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.

(23) FIGS. 4c and 4d schematically show a ring shaped shape memory alloy 8 as a closed component in constricted condition, FIG. 4c, and in expanded condition, FIG. 4d.

(24) In FIG. 5a-5c three different cross sections for a ring shaped shape memory alloy 8 are shown. In FIG. 5a a rectangular cross section 13 is proposed. In FIG. 5b a square cross section 14 is shown and in FIG. 5c a circular cross section 15 is shown.

(25) 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.