Electronics unit

Abstract

An electronic unit for a missile comprising a potted electronics in a housing: the unit being adapted to compensate for a difference in coefficient of thermal expansion between the potted electronics and the housing, the unit further comprising: a first ramp; and a second ramp slidably arranged against the first ramp, wherein the first and second ramps are disposed within the housing, the first or the second ramp abutting the potted electronics so as to provide an interference fit between the potted electronics and the housing; wherein the first ramp and second ramp each comprise a coefficient of thermal expansion selected to maintain the interference fit between the potted electronics and the housing throughout a temperature range.

Claims

1. An electronics unit for a missile comprising a potted electronics in a housing, the unit being adapted to compensate for a difference in coefficient of thermal expansion between the potted electronics and the housing; the unit comprising a ramp arrangement disposed within the housing, and the unit having an axis in the direction from the potted electronics to the ramp arrangement; the ramp arrangement comprising a first ramp, and a second ramp slidably arranged against the first ramp at a ramp interface, which ramp interface is angled relative to the axis; the first and second ramps being formed of different materials having different coefficients of thermal expansion; wherein the ramp arrangement abuts the potted electronics so as to provide an interference fit between the potted electronics and the housing, and is at least partially bounded by the housing such that, when the temperature changes and the different materials expand or contract by different amounts, the first and second ramps are constrained to move axially relative to one another within the housing so as to maintain the interference fit between the potted electronics and the housing; and wherein the materials of the first and second ramps are selected such that, when the temperature changes by an expected amount, the relative movement of the first and second ramps, is substantially equal in magnitude, and opposite in direction, to the size of a change in the axial length of the potted electronics in the housing, thereby maintaining the interference fit between the potted electronics and the housing.

2. The unit of claim 1 wherein the axis aligns with the roll axis of the missile and said ramp interface is configured to translate shocks along the roll axis of the missile through the angle into the housing thereby isolating the potted electronics.

3. The unit of claim 1 wherein the first ramp is a toroid and the second ramp is cone shaped.

4. The unit of claim 3 wherein the first and second ramp are concentrically arranged such that the toroid is slidably mounted on the cone.

5. The unit of claim 1 wherein the temperature range is in the range of from 60 C. to 100 C.

6. The unit of claim 1 wherein one of the first or second ramps is integral to the housing.

7. The unit of claim 1 wherein the potted electronics is potted in an epoxy compound.

8. The unit of claim 1 wherein the first ramp is made from a polymer.

9. The unit of claim 1 wherein the first ramp is made from polyoxymethylene.

10. The unit of claim 1 wherein the second ramp is made from aluminium.

11. The unit of claim 1 wherein the first or second ramp angle profile is tailored to ensure abutment of the first or second ramp to the potted electronics throughout the temperature range.

12. The unit of claim 1 wherein the unit further comprises a compressible membrane arranged between the first or second ramp and the potted electronics.

13. The unit of claim 1 wherein the first ramp comprises a coefficient of thermal expansion in the range of from 75 to 13010.sup.6 m/mK.

14. The unit of claim 1 wherein the second ramp comprises a coefficient of thermal expansion in the range of from 10 to 3010.sup.6m/mK.

15. The unit of claim 1 wherein the unit is a safe arm unit for a missile.

16. A missile comprising the unit of claim 1.

Description

FIGURES

(1) Several arrangements of the invention will now be described by way of example and with reference to the accompanying drawings of which:

(2) FIGS. 1a & 1b show an example arrangement of the device.

(3) FIG. 2 shows a force diagram of the example arrangement of FIG. 1a.

(4) FIG. 3 shows a missile comprising the device.

(5) FIGS. 1a & 1b show an example of the electronics unit 100 according to an embodiment of the invention, respectively in a cold temperature and a hot temperature state. The unit 100 comprises a potted electronics 102 in a housing 104. The unit 100 is adapted to compensate for a difference in coefficient of thermal expansion between the potted electronics 102 and the housing 104, the unit further comprising a first ramp 106 and a second ramp 108 slidably arranged against the first ramp 106. The first and second ramps meet at an interface 118. Both the first and second ramps are disposed within the housing 104 wherein the first ramp 106 or the second ramp 108 abuts the potted electronics 102 so as to provide an interference fit between the potted electronics 102 and the housing 104. The first ramp 106 and second ramp 108 each comprise a coefficient of thermal expansion selected to maintain the interference fit between the potted electronics and the housing throughout a temperature range.

(6) An axis of the unit 100 can be defined as being in a direction to or from the potted electronics to the ramp arrangement. The axis is aligned with the direction indicated by arrows 110 and 114 in FIGS. 1a and 1b. The interface between first and second ramps 106 and 108 is at an angle to this axis. In the present example the angle is approximately 30 to the axis in the direction from the potted electronics to the ramp arrangement.

(7) In the present arrangement, the electronics are potted in Eccobond 45 to form the potted electronics 102. The housing is an aluminium housing in the form of a hollow cylindrical container. As the housing 104 comprises a coefficient of thermal expansion lesser than the potted electronics 102, there is a mismatch in CTE, and the housing 104 expands to a lesser extent than the potted electronics 102.

(8) In the present arrangement, the first ramp 106 is a toroid concentrically mounted on the second ramp 108 which is a cone. The first ramp 106 is made from acetal having a CTE of 12010.sup.6 m/mK. The second ramp 108 is made from aluminium 2014A having a CTE of 2310.sup.6 m/mK. In this example, the first ramp comprises a CTE greater than the second ramp, and so the first ramp will expand or contract to a greater extent than the second ramp.

(9) Whilst in this example the first ramp 106 is made from acetal and the second ramp 108 is made from aluminium 2014A, it may be appreciated that the exact material selection of the first ramp 106 and second ramp 108 may be selected according to the maximum and minimum axial length of an expected temperature induced gap. As such, the first and second ramp may be made from a group of materials comprising metal, metal alloys, metalloids, polymers such as nylon, isoprene, polypropelene, polyoxymethylene (Delrin) or hydroxyacetone (acetal). Preferably, the first ramp is made from a polymer. More preferably, the first ramp is made from polyoxymethylene (Delrin). Preferably, the second ramp is made from aluminium. More preferably, the second ramp is made from aluminium 2014A.

(10) As the temperature cools, the potted electronics 102 contracts thereby vacating a volume to create a temperature induced gap indicated by arrow 110 in FIG. 1a. The first ramp 106 contracts more than the second ramp 108 as indicated by arrows 112. As the first ramp 106 contracts, it exerts a compressive force on the second ramp 108, which is resolved into a linear force by sliding against the second ramp 108. It can be seen that the axial length of the ramp arrangement is extended. Because the ramp arrangement is constrained by the walls of the housing, the ramp arrangement pushes into the temperature induced gap vacated by the potted electronics 102. The ramp arrangement thus exerts a securing force against the potted electronics 102, preventing vibration and unwanted movement of the potted electronics 102 within the housing 104 and maintaining an interference fit between the potted electronics 102 and housing 104.

(11) Conversely, as the temperature increases, the first ramp 106 expands more than the second ramp 108 as indicated by arrows 116. The compression of the first ramp on the cone of the second ramp 108 is released. As the potted electronics expand to push against the ramp arrangement, the first ramp 106 therefore slides against the second ramp 108, reducing the axial length of the ramp arrangement. The ramp arrangement remains constrained by the walls of the housing, and continues to maintain the interference fit between the potted electronics 102 and the housing 104.

(12) It can therefore readily be seen that the ramp arrangement (first ramp 106 and second ramp 108) changes its axial length in a cold temperature state indicated by distance x in FIG. 1a versus the axial length in a hot temperature state indicated by distance y in FIG. 1b.

(13) Turning to FIG. 2, there is provided a force diagram of an electronics unit 200 undergoing a high acceleration event indicated by Force F. In this arrangement, the electronics unit 200 oriented within the missile (not shown) such that the axis of roll of the missile is collinear with force vector F. In this arrangement, the second ramp 208 is integral to the housing 204, i.e. it is machined from a single body. In this arrangement, the interface between the first ramp 206 and second ramp 208, i.e. the ramp angle profile is linear and at 45.

(14) In this example, Force F is a force resulting from impact of the missile onto a target. Force F is directly transmitted through the housing 204 to the second ramp 208 as they are integral. The second ramp 208 is slidably mounted against the first ramp 206 therefore the Force F is translated through 45 defined by the ramp angle profile (45) to become Force F. The first ramp 206 is also abutted against the housing 204 therefore Force F is further translated through another 45 into Force F. Force F in turn acts against the side walls of the housing 204. Incoming Force F is therefore translated through 90 thereby converting the incoming impact force from a wholly axial force vector into a wholly lateral force. Force F is therefore not transmitted into the potted electronics 202. The arrangement thereby protects said electronics from damage.

(15) Turning to FIG. 3, there is provided a missile 300 comprising an electronics unit 301, the electronics unit further comprising a housing (not shown) wherein the housing contains the potted electronics 302. The potted electronics 302 is held in an interference fit with the housing by two ramp arrangements 318 disposed either side of the potted electronics component 302. Each ramp arrangement comprises a first ramp 306 and a second ramp 308 slidably arranged against the first ramp 306. In this example, it will be seen that an axis can be defined in the direction from the electronics unit to either of the ramp arrangements 318. The axis is schematically indicated in FIG. 3 by arrow 316. It will also be seen that, in this example, the axis aligns with the roll axis of the missile. The electronics unit 301 further comprises a compressible membrane 320 disposed either side of the electronics component between the ramp arrangement 318 and the potted electronics unit 302. In this arrangement, the compressible membrane 320 is in the form of a rubber disc in order to further aide in the isolation of the potted electronics 302 within the housing. In this arrangement, the electronics unit 301 is a safe arm unit for the missile 300.

(16) Whilst a number of specific embodiments have been described in the above, it will of course be appreciated that variations and modifications to those embodiments are possible. For example, whilst it in the above an embodiment has been described in which the axis of the unit aligns with the roll axis of a missile, it will be appreciated that other orientations of the unit within a missile will be possible. In particular it will be appreciated that in general missile designs are subject to space constraints, and the orientation of the unit may need to be selected so as to fit with such space constraints.