US2939925A - Electric switches - Google Patents

Description

June 7, 1960 E. L. COLE ELECTRIC SWITCHES Filed Jan. 9, 1958 2 Sheets-Sheet l ATTQRNEYQ June 7, 1960 E. L. COLE 2,939,925

ELECTRIC SWITCHES Filed Jan. 9, 1958 2 Sheets-Sheet 2 m9 (/65) R Q BY v.

ATTQRNEVI United States Patent ELECTRIC SWITCHES Eric Laurence Cole, London, England, assignor of onehalf to Graviner Manufacturing Company Limited and one-half to Wilkinson Sword Limited, both of London, England, both British companies Filed Jan. 9, 1958, Ser. No. 707,919

Claims priority, application Great Britain Jan. 11, 1957 7 Claims. (Cl. ZOO-61.44)

This invention relates to electric switches of the kind in which the switch is enclosed in a housing and operation of the switch is effected by pressure exerted from outside the housing.

One use of such switches is on aircraft where they are used for automatically operating equipment in the event of a crash or wheels-up landing. The switch is mounted upon or adjacent the skin of the aircraft body or wings and in the event of a crash or wheels-up landing is operated by contact with the ground or obstructions. Operation of the switch may be used to automatically discharge fire extinguishers, cool hot parts of the engines, switchoif the ignition circuits and other electrical circuits and close fuel and other fluid cocks.

Switches of the general kind to which this invention relates are described and illustrated in Patent No. 2,638,286.

Whilst the present invention is not limited to switches for aircraft use, it is particularly adapted to meet oflicial requirements which are designed to avoid inadvertent operation of the associated equipment operated by the switch. These requirements specify that two such switches must be operated at the same time before the emergency equipment controlled by the switches is rendered operative. This is because accidental depression of one switch during flight, for example by collision with a bird, would otherwise render all the emergency equipment operative, possibly with disastrous results if the aircraft was close to the ground.

These requirements are met by means of the present invention which provides an electric switch comprising a casing, two independent electric switch elements housed in said casing, said elements being spaced a substantial distance from one another and each switch element being operated by the application of pressure thereto, at least a part of the wall of said casing adjacent each switch element being flexible whereby either switch element can be operated by the action of pressure exerted from outside the casing.

The invention also provides an electric switch comprising a casing, two electric switch elements housed in said casing at a substantial distance from one another, each switch element comprising a plurality of electrically conductive strips normally insulated from one another but which can be brought into electrical contact with one another by the application of pressure, at least a part of the wall of said casing adjacent each switch element being flexible whereby said pressure can be exerted from outside the casing.

The invention further provides an electric switch comprising an elongated casing at least part of the walls of which are flexible, two elongated electric switch elements each housed in said casing and extending from adjacent a respective end of the casing towards the other element but separated therefrom by a distance at least as great as the length of an element, each of said switch elements being operable by the application of pressure exerted from outside the casing through a flexible part of the wall.

One construction of electric switch in accordance with the present invention will now be described, by way of example only, reference being made to the accompanying drawings in which:

Figure l is a sectional side elevation of the switch;

Figure 2 is a view in the direction of the arrow II in Figure 1, some parts being shown broken away;

Figure 3 is a view of one switch element before insertion in the switch, the view being taken in the direction of the arrow II in Figure 1;

Figure 4 is an end view of the switch element shown in Figure 3, taken in the direction of the arrow IV, and

Figure 5 shows the insulating strip of a switch element.

The switch shown in the drawings is designed for use on aircraft for the operation of emergency equipment, and at the same time to meet the aforesaid ofiicial requirements.

The switch comprises a casing 10 of resilient insulating material, which may for example be an extrusion of natural or synthetic rubber. This casing 10 is mounted on a metal base 11, the sides of which are doubled back upon themselves to clamp sidepieces 10a of the casing 10 (visible in Figure 2 where parts of the doubled-back portions of the base 11 are shown broken away). Each end of the casing 10 is closed by a metal end cap 12 which like the casing 10 has sidepieces 12a clamped between the doubled back sides of the base 11. Holes which extend through the sidepieces 10a and 12a and the overlapping parts of the base 11 may be provided at intervals therealong, for receiving rivets or other means by which the switch can be secured to the surface of an aircraft with the base 11 bearing against the surface.

Two independent switch elements are provided one at each end of the casing 10 and with a non-sensitive section in a mid-portion 10b of the casing 10, this non-sensitive portion not containing any switch element. In one typical construction of this form the switch elements are each of four inches and are spaced by a non-sensitive section of eight inches.

Each switch element comprises an outer conductive strip 13, 13' an intermediate conductive strip 14, 14' and an inner conductive strip 15, 15' the three strips of each switch element lying in parallel planes and at least the outer strip 13, 13 and the intermediate strip 14, 14' being of resilent material. The three trips 13, 14 and 15 or 13', 14' and 15' are normally spaced from one another by a continuous strip 16, 16 of insulating material, for example of silicone rubber. This insulating strip 16, 16' is threaded through transverse apertures in the intermediate conductive strip 14, 14' so that alternate portions of the insulating strip 16, 16' lie between the outer conductive strip 13, 13 and the intermediate conductive strip 14, 14 and the other portions of the insulating strip 16, 16 lie between the inner conductive strip 15, 15' and the intermediate conductive strip 14, 14. Where the insulating strip 16, 16' passes through the apertures in the intermediate strip 14, 14, notches 16a 16a are provided (Figure 5) in order to assist location, and so that the active portion of the insulating strip 16, 16' shall extend for the full width of the conductive strips. At the end of each switch element where the electrical connections are made, the conductive strips are each formed with tongues 13a, 13'a, 14a, 14'a, 15a, 15'a respectively which extend from the active portions of the conductive strips. As shown in Figures 3 and 4 the tongues 13a, 13'a and 15a, 15'a of the outer and inner strips 13, 13 and 15, 15' respectively extend from the same side of the conductive strips so that they can be bent towards one another and brought together in superimposed relationship. The tongue 14a, 14a from the intermediate strip 14, 14' extends from the other side so that it spaced from the other two tongues. To locate the tongues 13a, 13a,

14a, 1411, a, '1'5'21 an insulating member 17, 17' is provided having two slots 17a, 17b therein, the tongue 14a, 14a fitting in the slot 17a and the other two superimposed tongues 13a, 13aand15a, 15'a fitting in the slot 171:.

At the other end of each switch element the insulating strip 16, 16 is carried round the end of the intermediate conductive strip 14, 14 and extends for a short distance back on the other side of the strip 14, 14" in order to support and space the end of the intermediate conductive strip 14, 14' from the other two conductive strips '13, 13' and 15, 15.

Connection is made to the tongue 14a, 14'a and the superimposed tongues 13a, 13"21 and 15a, 15'a by the two conductors of twin-conductor cables 18, 18' respectively, the cables 18, 18" each being brought through an insulating sleeve 19, 19' and flexible insulating bush '20, 20 which fit in a respective one of two openings 11a, in the base 11. The space within each end cap 12 may be sealed with a filling 21 of insulating compound to exclude moisture.

It will be understood that closure of either switch element can be effected by pressure exerted from outside the casing, which will bring the intermediate conductive Strip into engagement with either the inner conductive strip or the outer conductive strip depending upon the location of the insulation strip at the place where the pressure is applied. By use of an appropriate electrical circuit it can be assured that a desired operation is only etteeted when both switch elements are operated simultaneously. Thus, by suitable spacingof the two switch elements in the case/of an aircraft, it can be ensured that collision with a bird, for example, will not operate both switch elements simultaneously.

or course, the switch can be used for many other purposes, tor example as a foot operated switch connected to apparatus for counting the number of persons passing over it. In this case the switch can be rendered directional so as to count people moving in one direction only, for example people entering a shop but not those leaving, by arranging that the counting apparatus is only operated whenone switch element is first operated and the other switch element operated shortly thereafter. If operation occurs in the reverse sequence no count is made.

What I claim is:

1. An electric switch comprising an elongated casing of electrically insulating material, at least part of the walls of said casing being flexible, and two elongated pressure operable electric switch elements, each switch element comprising three electrically conductive strips lying in parallel planes, the centre conductive strip having apertures therein at spaced intervals along its length, and a strip of insulating material threaded through said at strip is doubled back over the end of the centre strip so that at this end of the switch element there is insulating strip on both sides of the centre strip. 3. An electric switch according to claiml, wherein the insulating strip is of generally the same width as the conductive strips but has notches on both sides at interapertures with portions of insulating strip between adjacent apertures alternately on one side and on the other side of the centre strip, each switch element extending from adjacent a respective end of the casing towards the other element but being separated therefrom by a distance at least as great as the length of an element, each switch element being located adjacent a part of the walls of the casing which is flexible whereby'pressure can be exerted from outside the casing to bring the centre conductive strip into electrical contact with one of the other two conductive strips. 7

2. An electric switch according to claim 1, wherein V at one end of a switch element, the end of the insulating lower strips lying on the same side of a plane which passes through the strips at right angles thereto, and the tongue from the centre strip lying on the other side of said plane.

5. An electric switch according to claim 4, wherein the tongues from the upper and ,lower strips respectively are brought together in superimposed relationship.

6. An electric switch according to claim 5, further comprising an insulating member having two spaced apertures therein, the superimposed tongues from the upper and lower strips being brought through one aperture and the tongue from the centre strip being brought through the other aperture. H

7. An electric switch comprising an elongated casing of electrically insulating material, at least part of the walls oft-said casing being flexible, and two elongated pressure operable electric switch elements, each switch element comprising three electrically conductive strips lying parallel planes, the centre conductive strip having apertures therein at spaced intervals along its length, and a strip of insulating material threaded through said apertures with portions of insulating strip between adjacent apertures alternately on one side and on the other side of the centre strip, said insulating strip being of generally the same width as the conductive strips but has notches on both sides at intervals corresponding to the spacing of the apertures in the centre strip, the width of the insulating strip at said intervals being less than the width of said apertures, each switch element extending from adjacent a respective end of the casing towards the other element but being separated therefrom by a distance at least as great as the length of an element, each switch element being located adjacent a part 'of the wa l-ls of the casing which is flexible.

References Cited in the file of this patent UNlTED STATES PATENTS 1,376,166 Rosenberg Apr. 26, 1921 1,855,581 Meade Apr. 26, 1932 2,052,795 ,Rapis'adra t Sept. 1, 1936 2,173,105 Gear et a1. Sept. I9, 1939 2,594,520 Tiedman Apr. 29, I952 2,638,286 Mathisen May 12, 1953 2,790,872 Hel'sper Apr. 30, 1957 2,885,509 Wilcox May 5-, 1959 FOREIGN PATENTS 432,567 Great Britain July 30, 639,212 Great Britain -a June 21, 1950 692,020 Great Britain a- May 27, 1953

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