US2404179A - Electrical switching device - Google Patents

Description

E. B. KING 44,179

ELECTRICAL SWITCHING DEVICE Filed June 28, 1943 8 InveJor I B v fiyti iajli fim Attorney Patented July 16, 1946 UNITED STATES PATENT OFFICE Application June 28, 1943, Serial No. 492,616 In Great Britain April 17, 1942 4 Claims. 1

This invention relates to electrical switching arrangements and has as its main object the production of a, switching arrangement, for example, for controlling a relay device, which is responsive to changes in velocity of apparatus carrying the arrangement.

The improved switching arrangement, according to the invention, comprises an acceleration switch arranged to operate its contacts due to the inertia of a moving part during acceleration in a predetermined direction and a deceleration switch arranged to operate its contacts due to the inertia of a moving part during deceleration, one of the switches being irreversible, that is. remaining closed (or open) after operation, so that both switches are in their operated positions after an acceleration period followed by a deceleration peried, or vice versa.

Preferably the irreversible switch consists of a switch of the type employing a conducting liquid, such as mercury, and including a. capillary tube substantially parallel to the direction of motion along which the liquid is forced to close contacts at the remote end of the tube when the rate of change of velocity (the acceleration or the deceleration) exceeds a predetermined value for a predetermined time. Conveniently one or more intermediate traps or bulbs are provided between the ends of the capillary tube to prevent closing of the switch due to accidental shocks or to vibration.

The switch which is not irreversible may comprise a tubular non-capillary switch employing a conducting liquid, such as mercury, and arranged substantially parallel to the direction of motion with the contacts to be closed at the app end of the tube.

The capillary switch may be so arranged and dimensioned that it closes when the force is a large multiple of the force required to close the non-capillary switch, or the switches may be so dimensioned and the conducting liquids so chosen that the forces which cause closing of the respective switches may be of substantially the same order of magnitude.

In a convenient practical arrangement a capillary acceleration switch and a non-capillary deceleration switch have their contacts connected in series in a circuit of a relay, for example, in the anode circuit of a gas-filled triode relay, whereby the circuit is prepared by closing of the capillary switch during acceleration and completed by closing of the non-capillary switch when deceleration begins.

Such a switching arrangement may be combined with a relay for initiating detonation of the charge of a rocket or other non-rotated projectile, in which case the switches are so constructed and supported as to withstand the stresses due to the high acceleration of the projectile. Another application of such arrangement is in combination with a relay for controlling elevators and/or steering mechanism of an aircraft, the relay being energised to efiect a control operation when the aircraft decelerates following a high speed evolution; for example, a steep dive. Such an arrangement can also be used for con trolling the detonation of a projectile or bomb when it reaches a predetermined depth below the surface of the water, the acceleration switch being operated during an initial acceleration period whilst the deceleration switch operates when the projectile slows up immediately following its immersion in the water.

A construction of the switch arrangement according to the invention which is particularly suitable for controlling the arming of a proximity fuze for rockets or other non-rotating projectiles will now be described by way of example with reference to the accompanying drawing in which Fig. 1 shows a preferred form of capillary switch;

Fig. 2 shows a preferred form of non-capillary switch; and

Fig, 3 shows the method of assembling the switches.

The function of a switching arrangement, ac cording to the invention, in a proximity fuze is mainly as a two-stage arming device to ensure that the projectile is safe to handle before it is fired, that electrical apparatus, such as thermionic valves, forming part of the fuze is prepared for operation during the preliminary part of the flight of the proectile without the fuze being completely armed whilst it is close to and therefore sensitive to the ground, and, finally, that complete arming is efiected when the projectile is at a sufiicient distance from the ground to b substantially immune from ground eiiects.

In such fuzes, detonation is controlled by a relay which preferably comprises a gas-filled ionic valve, such, for example, as a valve sold under the registered trade-mark Thyratrcn, having a control grid by means of which the relay is triggered. The triggering impulse may be supplied, preferably through an amplifier, from a photoelectric cell arrangement responsive to changes in illumination caused by the target or by a radio receiver responsive to radio-frequency os- 3 cillations reflected from the target or transmitted from the ground.

The switching arrangement according to the invention is so arranged that the acceleration switch A, which is the irreversible switch, when it operates completes the filament and anode circuits of any thermionic valves employed in the amplifier and other apparatus and also closes a point in the anode circuit of the gas-filled relay. The circuits are thus prepared for operation during the initial acceleration of the projectile.

Complete arming of the fuze during this period is prevented by the open contacts of the deceleration switch B, these contacts being included in the anode circuit of the gas-filled relay. Thus, when the projectile begins to deceler-ate, that is, when, in the case of a rocket, the propelling charge is fully burnt, the deceleration switch B closes and the fuze is then fully armed so that it responds to the reflected radiations from the target as soon as the projectile approaches suf ficiently close thereto.

In such an arrangement a separat acceleration switch is provided for each of the independent circuits to be closed, each switch convenient-- 1y consisting of a glass capillary tube having an internal bore A! (Fig. 1) of between 0.12 and 0.16 millimetre in diameter. The tube, which is about centimetres overall length, has at its lower end, that is the end nearest to the rear end of the projectile, a small bulb A2 of between 3 and 4 millimetres in diameter through the wall of which are sealed two metal Wires A3 of a suitable alloy to form a vacuum-tight seal with the glass, the inner ends of these wires, which project into the bulb, being spaced apart from one another. At the upper end of the tube there is another bulb A4 containing a small amount of mercury. The tube is evacuated to a low pressure and sealed at its upper end. The amount of mercury and the bor of the capillary are such that, due to surface tension, the mercury will not enter the capillary as a result of accidental shocks or normal vibration, but, when the switch is subjected to high acceleration, for example an acceleration of the order of 40 g., the thrust due to the inertia of the mercury is sufiicient to force mercury along the bore of the tube. If such acceleration is maintained for a suflicient time, which depends on the length of the tube, the mercury will fill the bulb at the lower end of the tube and thus complete a low resistance contact between the wires projecting into the bulb. The switch thus closed will remain closed unless it is subjected to a correspondingly high acceleration in the opposite direction.

In order to ensure that vibration will not cause mercury to reach the lower bulb, an intermediate trap or bulb A5 may be formed in the capillary about midway between the ends.

If mercury should penetrate to such trap due to vibration, it is likely to return to the upper bulb as a result of further vibration.

A preferred construction of deceleration switch is shown in Fig. 2 and comprises a glass tube having a length of approximately 4 centimetres and an internal diameter of between 4 and 5 millimetres. In this case, contact wires Bl B2 project into the upper end of the tube which is preferably of slightly reduced internal diameter, the inner ends of the contact wires preferably project ing beyond the point at which the diameter of the tube is reduced, for example, from the upper end of the tube to a. distance of between a. half and a third of the length of the tube. The

tube contains suflicient mercury B3 to produce adequate low-resistance contact between the two wires when the tube is inverted, but the'amount of mercury should not be such as to prevent free movement thereof in the wider portion of the tube. A small quantity of a. suitable powder such as aluminium oxide, may be added to the mercury to facilitate free movement thereof. The tube may be exhausted or may be filled with air or other gas at a suitable pressure.

The dimensions of the acceleration and deceleration switches described above are such that the acceleration switch will be operated by an acceleration of the order of 40 times that of gravity averaged over a period of from 0.4 to 1 second, whilst the deceleration switch is sensitive to a deceleration force of approximately 0.3 times that of gravity for a very short period.

The several switches are mounted with their axes parallel to one another and to the axis of the projectile, as shown in Fig. 3. In order that they will withstand the high stresses due to the rapid acceleration of the projectile, they are assembled and bound together in a suitable plastic or semi-plastic material such as paraflin-wax. Alternatively, they can be mounted in grooves in a former of ebonite or other synthetic insulating material, and enclosed in a varnished paper tube, the complete assembly being, if desired, impregnated with a suitable bonding material.

It is to be understood that the specific construction of switching arrangement described above is by way of example only and that the dimensions and the mounting of the individual switch elements can be varied as desired to suit the use of the switching arrangement. It will also be appreciated that whilst various applications of an arrangement according to the invention have been specifically referred to, such an arrangement can be used in any apparatus or vehicle where it is desired to complete (or to open) an electric circuit as a result of successive acceleration-decal eration periods or vice versa. When the circuit is to be opened the capillary switch or switches will, of course, be arranged so that normally the conducting liquid closes the contacts but moves under the influence of the appropriate acceleration or deceleration to an empty bulb at the remote end of the capillary.

I claim as my invention:

1. In a body subject to changes of velocity, an electrical switching arrangement for controlling electrical circuits carried by the body comprising a first switch adapted to operate in response t a change in velocity of one sign and thereafter to remain locked in the operative position and a second switch adapted to operate in response to a change in velocity of the opposite sign said first switch comprising a capillary tube for each pair of contacts to be operated, a bulb at each end of said capillary, a pair of said cont-acts protruding through the wall into one bulb and a conducting fluid in one bulb, and said second switch comprises a non-capillary tube for each pair of contacts to be operated, a pair of said contacts protruding through the wall into one end thereof and a conducting fluid at one end thereof.

2. In a body subject to changes of velocity an electrical switching arrangement for closing in two stages electrical circuits carried by the body comprising for each pair of contacts to be closed in the first stage a capillary tube, a bulb at one end of said tube, a pair of said contacts in the bulb and a mercury reservoir at the other end of said tube, said mercury flowing through said tube into the bulb in response to a change of velocity of one sign to bridge said pair of contacts and to complete the first stage of closure of said circuits, and for each pair of contacts to be closed in said second stage a non-capillary tube, a pair of said contacts protruding into one end of the bore of the tube, a globule of mercury adapted to move freely in the bore in response to a change of velocity of the opposite sign to bridge the contacts and to complete the second stage of closure of said circuits.

3. An electrical switching arrangement according to claim 2 wherein each capillary tube iS provided with an intermediate bulb substantially midway between its ends, said intermediate bulb acting as a trap to prevent mercury reaching the contacts as a result of vibration.

4. In a body subject to changes of velocity, an

electrical switching arrangement for controlling electrical circuits carried by the body comprising.

a first switch adapted to operate in response to a change of velocity of one sign and thereafter to remain locked in the operative position, and a second switch adapted to operate in response to a change in velocity of the opposite sign, said first switch including a pair of contacts to be operated, a mass of material arranged to move freely in one direction from one position to another and to close said contacts in one of said positions and means for preventing the return of the mass in the opposite direction, and said second switch includes non-capillary tube, a pair of contacts to be operated protruding through the Wall into one end thereof, and a conducting fluid at one end thereof.

EDWARD BOLTON IHNG.

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