GB2123217A - Inductive electric couplings - Google Patents

Abstract

Inductive couplings for, for example, electrically coupling electrically initiated explosive devices. An electric coupling includes a transformer having primary and secondary windings, (12, 11, respectively), which may, for example be mounted for relative rotation or linear displacement means for moving or permitting the movement of the primary or secondary winding, between a first position wherein in use there is substantially no inductive coupling between the windings, and a second position wherein inductive coupling between the windings is maximised.

Description

SPECIFICATION Improvements in or relating to electric couplings The present invention relates to electric couplings and particularly to inductive couplings. The invention particularly, though not exclusively, relates to electric couplings for electrically initiated explosive devices such as bombs and shells.

Electrically initiated explosive devices are prone to premature or accidental initiation by spurious radio frequency signals, electrostatic discharges and other radio frequency generators. A known solution to this problem is to include a radio frequency (rf) filter in the electrical initiation circuit of the device. In many cases the inclusion of an rf filter is impractical on grounds of cost and because rf filters which have been stored for a period of years may not perform sufficiently well.

Afurther known solution to the problem of premature or accidental initiation is to provide an inductive coupling comprising primary and secon darytransformerswhich couple an igniter circuit with a firing circuit of an explosive device. The inductive coupling isolates the device from radio frequency and electrostatic hazards.

The present invention provides an improved form of inductive coupling having a safety feature.

According to the present invention an electric coupling comprises a transformer having primary and secondary windings, means for moving or permitting the movement of the primary of secondary windings between a first position wherein in use there is substantially no inductive coupling between the windings, and a second position wherein inductive coupling between the windings is maximised.

Preferably the primary or the secondary winding is fixed and the other winding is rotatable or linearly displaceable from the fixed winding.

The means for permitting the movement of the primary or secondary winding may comprise a mechanical latch or lock which holds the winding in the first position and which may be unlatched or unlocked to permit movement of the winding or windings to the second position.

The movable winding may be mounted in a guide or on a pivot carried in a bomb, shell or other missile and may be moved from the first position to the second position by, for example, the action of a spring, or by acceleration forces on the movable winding when the bomb, shell, or missile is fired or released from its carrier.

Where, for example, the winding are mounted in a missile carried by an aircraft, the means for moving the winding may be a lanyard attached to the aircraft and the movable winding or windings, wherein the lanyard exerts a pull on the movable winding as the missile separates from the aircraft. In further arrangements the means for moving the winding may be solenoid or a pneumatically or hydraulic operated piston.

Embodiments of the invention will now be described, by way of example only, with reference to the drawings which are schematic, and of which Figure 1 is a side elevation of a known inductive coupling.

Figure 2 is a side elevation of an inductive coupling in accordance with the invention shown in a position wherein there is substantially no inductive coupling.

Figures 3 and 4 are side elevations of an inductive coupling in accordance with the invention, shown in a position of maximum and minimum inductive coupling positions in Figures 3 and 4 respectively.

Figure 5 is a further embodiment of the invention for use in an airborne weapon system.

Figure 1 shown a coupling which comprises a transformer primary and secondary, 1 and 2, respectively. The primary 1 includes a winding 3 which has an input from a square wave inverter 6 connected to a 28V dc source (not shown), the output frequency of the inverter being 80 kHz. The secondary 2 includes a winding 4 which has an igniter filament 5 connected across its ends. There is a small gap 7 between adjacent ends of the primary and secondary as seen in Figure 1. The coupling is intended to provide link between the power supply and an electrically initiated explosive (not shown) packed around the igniter wire 5. The link provides protection from radio frequency and electrostatic hazards which in direct linked arrangements can cause premature firing.

Figure 2 shows a coupling in according with the invention which comprises a transformer primary 9 and secondary 10 and associated windings, and an igniter 31 connected to the secondary mounted in a guide tube 8. The secondary 10 is fixed in the guide tube 8 and its windings feed an igniter wire 31. The primary 9 is slidable in the tube 8 and is positioned along the elongitudinal axis of the tube by a pushrod 30. In the position shown with the primary and secondary spaced apart by a distance greater than the internal diameter of the tube, the application of a electric signal, deliberately or otherwise, to the coil of the primary 9 cannot result in current flow in the secondary since the spacing of the primary and secondary is too great for inductive coupling between them.When it is desired to arm the coupling, the primary is pushed by the pushrod 30 in the direction of the arrow A in the drawing until the primary and secondary are closely spaced as in the embodiment of Figure 1. When in the armed position the coupling may be energised and the igniter 31 fired as described for the embodiment of Figure 1.

Figure 3 shows a further embodiment of the invention in which a coupling includes a primary 12 which is rotatable with respect to a secondary 11.

The primary 12 is similar in construction to that of the primary 9 of Figure 2, but has a convex end which is partly cylindrical and centred and mounted for rotation on an axis 16. The secondary 11, which is fixed, has a concave end which is partly cylindrical and also centred on the axis 16. There is a small annular gap 13 between the concave and convex ends of the primary and secondary. The primary 12 and the secondary 11 include windings 15 and 14, respectively.

In the armed position shown in Figure 3, there is a maximum inductive coupling between the primary and secondary. When the primary is rotated through 90 in the direction of the arrow B shown in Figure 3, to the position shown in Figure 4, the inductive coupling is reduced to zero possibility of inadvertent firing correspondingly reduced.

Figure 5 shows another embodiment of the invention, which comprises a coupling which is part of an airborne weapon. A primary transformer 29, similar in construction to the transformer primary 9 of Figure 2 is mounted on an annular steel plate 26 which is fixed in a tube 20. The primary 29 carries, and is supplied by, a square wave inverter 27. A secondary transformer 23 is mounted on a ring 24 of magnetised samarium cobalt which is slidable in the tube 20 and is free to slide in the direction of the arrow C in the drawing, against the action of a light helical spring 25, towards the primary 29. The secondary transformer carries an electro mechanical fuzing system 22 having an ouptut connected to an igniter wire 21.

In the position shown in Figure 5, there is no inductive coupling between the primary 29 and the secondary 23 and the possibility of inadvertent operation of the fuzing mechanism is reduced. When the weapon is released and accelerates in the opposite direction to the arrow C, the secondary 23 and its ring 24 together with the fuzing system 22 slide in the direction of arrow C until the adjacent effaces of the primary and secondary are closely spaced, and are helf in this position by magnetic attraction between the ring 24 and the annular plate 26. If dc current is then supplied to the inverter 27 via wires 28 the primary and secondary will be inductively coupled and the fuzing system 22 actuated to give current flow in the igniter 21.

Claims (9)

1. An electric coupling comprising a transformer having primary and secondary windings, means for moving or permitting the movement of the primary or secondary windings between a first position wherein in use there is substantially no inductive coupling between the windings, and a second position wherein inductive coupling between the windings is maximised.

2. An electric coupling according to claim 1 wherein the primary or secondary winding is fixed and the other winding is rotatable relative to the fixed winding so that the other winding may be rotated or allowed to rotate from the first to the second position.

3. An electric coupling according to claim 1 wherein the primary or secondary winding is fixed and the other winding is linearly displaceable from the fixed winding.

4. An electric coupling as claimed in any of the preceding claims wherein the means for permitting the movement of the primary or secondary winding comprises a mechanical latch or lock which holds the winding or windings in the first position and which is unlatchable or unlockable to permit move ment of the winding to the second position.

5. An electric coupling as claimed in claim 4 wherein the movable winding is mounted in a guide or on a pivot and spring means for urging the movable winding from the first position to the second position when unlatched or unlocked.

6. A missile arming system for a missile having an explosive device, including an electric coupling as claimed in any of claims 1 to 5 arranged to couple an igniter circuit with a firing circuit of the missile explosive device.

7. A missile arming system as claimed in claim 6 wherein the movable winding is mounted in an linear guide which when installed in the missile is aligned with the missile longitudinal axis, and wherein during missile firing or release guides the movable winding under acceleration forces on the winding from the first position to the second position to electrically couple the igniter and firing circuits.

8. A missile arming system as claimed in claim 6 for an aircarft wherein the movable winding is attached by means of a lanyard attached to the aircraft and wherein, in use, the lanyard exerts a pull on the movable winding as the missile separates from the aircraft to move the winding from the first position to the second position.

9. An electric coupling substantially as described herein with reference to the drawings.