US2794889A - Hermetically sealed switch - Google Patents

Description

June 4, 1957 EQBACHMAN EI'AL 2,794,389

HERMETICALLY SEALED SWITCH I Filed Nov. 20, 1953 IN EN 0R. Eu ene ac man F 00K 5. B o/fa y Frank B. HICKS Q @fmg m;

4 TTOFNEYS nite HERMETIQALLY SEALED SWITCH Application November 20, 1953, Serial No. 393,392

1 Claim. (Cl. 200-168) The present invention relates to electric switches and more particularly to certain new and useful improvements in hermetically sealed electric switching devices of the type particularly designed for use in high altitude aircraft.

Hermetically sealed electric switching devices are not broadly new and many such devices have been designed and constructed for use in high altitude aircraft where low temperatures will cause a condensation and icing problem which will adversely affect the operation of the device and the electrical contacts of the switch unit. In such devices a shaft is usually passed through or cooperates with a simple diaphragm or bellows in the wall of a casing in such a manner as to permit an electrical switch mounted and hermetically sealed in the casing to be actuated by movement of the shaft externally of the casing and fiexion of the diaphragm or bellows.

Hermetically sealed electric switching devices of the above type have not, however, proved generally satisfactory, particularly where the switching device is subject to numerous and repeated actuations. Under such conditions the devices have encountered fatigue problems after a relatively small number of operations with the result that the flexible bellows fails, breaking the hermetic seal provided thereby and permitting the entry of moisture or dirt into the housing.

The above noted defect of the prior art is remedied in accordance with the present invention wherein certain new and useful improvements are provided in an hermetically sealed electric switching device of the type described, which is of both simple and sturdy construction and is inexpensive to manufacture; and in which the electrical switching unit may be continuously and repeatedly actuated externally of the casing without encountering fatigue problems in the hermetic sealing means provided for the actuating mechanism.

More specifically, the present invention contemplates the provision in a hermetically sealed electric switching device, including a casing having an opening and an electric switch supported in the casing having a contact member and a movable member adapted to be moved into and out of electrical engagement with the contact member: of a novel actuating means cooperating through the opening in the casing for operating the electrical switch from the exterior of the casing and for hermetically sealing the opening.

In accordance with the preferred embodiment of the invention, the operating means comprises a rod having an inner portion which extends through the opening in the casing in spaced relation with respect thereto. Means are provided for rockably mounting the rod in and hermetically sealing the opening including a flexible bellows carried by the casing in surrounding relation with respect to a portion of the rod intermediate its end portions, one end of the bellows being secured to the wall of the casing in surrounding relation to the opening, and the other end of the bellows having an aperture therein through which an end portion of the rod is secured. A non-fluid semirigid plastic material is provided which is contained with- States Patent M in the bellows and is adapted to hermetically seal the bellows both with respect to the casing and the portion of the rod extending therethrough, and, further, in cooperation with the bellows to provide a rockable pivot for the rod. The inner end of the rod is adapted, upon rocking movement of the rod in the aperture located in the casing, to operate through an actuating means the movable switch member to move the same into and out of electrical engagement with the electrical contact memher.

The above, as well as other novel features of the hermetically sealed electric switching device, will be more readily understood from the following description of the accompanying drawings illustrating the invention in accordance with its preferred embodiment, in which drawmgs:

Figure 1 is a sectional view of a hermetically sealed electric switching device showing the novel actuating and sealing means according to the preferred embodiment of the invention;

Figure 2 is a top end view of the switching device shown in Figure 1; and

Figure 3 is a sectional view along line 3-3 of Figure 1.

As shown in Figure 1 of the drawings, the electric switching device includes a casing, generally designated as 10, in which is mounted one or more conventional electric switch units, generally designated as 11a and 11b, respectively. The upper wall of the casing is provided with an opening or aperture 12 through which extends the actuating mechanism, generally designated as 13, which serves both to operate the switch units 11:: and 11b from the exterior of the casing and to seal hermetically the aperture 12.

In accordance with the preferred embodiment of the present invention illustrated, the actuating mechanism 13 comprises a rod 14 extending in the manner shown through the aperture 12 in spaced relation with respect to the walls thereof. The rod 14 is rockably mounted in the aperture 12 by means of a flexible bellows 15 carried within the casing in surrounding relation with respect to the inner portion of the rod; one end of the bellows 15 being secured, as at 16, by soldering or otherwise to the inner wall of the casing 10 in surrounding relation to the aperture 12, and the other end of the bellows being provided with an opening or aperture 17. The rod 14 is shown as provided with a threaded end portion 18 of lesser diameter than the central portion of the rod, which end portion extends through the bellows opening 17 with the shoulder 19 abutting the inner side of the end wall 20 of the bellows 15. Contained within the bellows is a non-liquid flexible plastic material 20, such as rubber or a silicone compound, which is poured into the bellows in liquid form and then sets to non-liquid form. It thus fills and hermetically seals the bellows 15 with respect to the rod 14 and casing 10 and serves to provide, in cooperation with the bellows 15, a supporting means for the rod 14 in which there is no fixed physical pivot but which is such that the rod may be rocked within the aperture 12 as though the rod 14 were pivoted at approximately the point at which it passes through the casing.

The actuating mechanism 13 preferably includes an operating member such as lever 26 located exteriorly of the casing and secured at one end by means of the screw 27 to the outer end of the rod 14, and a switch actuating member such as lever 28 located within the housing 10 and secured at one end to the threaded end portion 18 of the rod 14 by means of the nut 29, said end of the actuating lever 28 being fixed in spaced relation from the outer side of the end wall 20 of the bellows 15 by means of the washer 30. As will be observed from member 26 will cause the rod 14 to pivot at approximately the point where it passes through the casing 10, as described hereinbefore, and the actuating lever 28 to be rocked to depress the plunger 31a of the switch unit 11a.

The electric switch unit or units to be operated by the actuating lever 28 may be of any suitable type in which a movable member is adapted to be moved into and out of electrical contact with a contact member. As shown in Figure 1, the two electric switch units (11a and 11b, respectively) presently illustrated, are of the type generally referred to as double acting microswitches, requiring relatively small actuating movements for operation. Each of the switches includes a supporting frame or housing 32 secured to the back wall of the casing 10, stationary contact members 3333 and 34-34, a movable doubleacting resilient snap blade 35 adapted to engage at its end portions the stationary contact members 33-33 and 3434, respectively, an operating plunger 31:; and 31b, and a spring 36 adapted to normally urge and maintain the operating plunger and snap blade in the position shown. As will be observed, switch unit 11b is so positioned below switch unit 11a that downward movement of the plunger 31a of switch unit 11a will be transmitted directly to plunger 31b of switch unit 11b and the two plungers 31a and 31b will, therefore, operate simultaneously upon rocking movement of the actuating lever 28 to effect an upward snapping action of the snap blades 35 which breaks electrical contact between contact members 3333 and establishes electrical contact between contact members 3434.

As shown in Figures 2 and 3, the bottom of the casing is provided with inner and outer insulating plates 40 and 41 which serve to close the casing and to provide a supporting means for the electrical terminals, generally designated as 42, the inner ends of which terminals are connected by means of lead wires 43 to the stationary contact members 3434 and 35-35 of the microswitches 11a and 11b, respectively. In order to seal hermetrically the insulating plates with respect to the casing and the terminals 42, the lower edge portion of the casing 10 is tightly secured to the outer insulating plate 40 by means of screws 44 and a resilient bushing 45 is provided between the inner end of each of the terminals 43 and the inner insulating plate 41. As will be observed, each of the terminals 42 is secured in the outer insulating plate .40 by means of their flange portion 46 which is engaged in a corresponding circumferal groove located in the wall of the hole formed in the outer insulating plate 40 for reception of the terminal 42.

As is apparent from the foregoing, the switching device according to the preferred embodiment of the invention as described is of both simple and sturdy constrution and is distinguished by the fact that the switch units 11a and 11b may be repeatedly actuated by movement of the rod 14 externally of the casing without occasioning a failure in the hermetically sealing means provided for the actuating mechanism. If, after repeated actuation and flexing of the bellows 15, an opening should develop in the wall of the bellows, the plastic material contained within the bellows will continue to provide a hermetic seal between the rod 14 and the casing 107 As will also be apparent, the plastic material 20 in cooperation with the bellows 15 provides a supporting means for the rod 14 in which there is no necessity for any fixed physical pivot but which is such that the rod may be rocked within the aperture 12 as though the rod were pivoted at approximately the point at which it passes through the casing. The plastic material also serves to prevent any water or moisture from entering into the bellows 15 where it might freeze or otherwise cause damage or trouble.

What is claimed is:

An hermetically sealed switch unit of the character described including a casing forming an envelope from which air may be excluded; said casing having an end wall provided with an aperture, electrical switching means mounted within said casing and having an actuating plunger, means for operating said plunger from the exterior of said casing comprising a rod rockably carried by said casing and extending through said casing aperture, an operating arm fixed to said rod exteriorly of said casing and extending from said rod in such spaced relationship to the apertured end wall of said casing as to constitute said wall a limit stop for arresting movement of said arm and rod in one direction, a switch actuating arm fixed to said rod interiorly of said casing; said switch actuating arm having the major portion of its length disposed parallel to the major portion of said operating arm and the end portion thereof remote from said rod disposed in contiguous relation with said switch plunger, and flexible means for maintaining an hermetic seal between said rod and said casing where said rod extends through said casing aperture, comprising a flexible bellows carried by the interior of said casing wall in surrounding relation with respect to a portion of said rod intermediate its end portions; one end of said bellows being secured to the interior of said casing wall in surrounding relation to said aperture and the opposite end of said bellows having an opening through which an end portion of said rod passes, and a non-fluid semi-rigid plastic material cast in situ within said bellows in contact with the inner wall thereof, with a portion of the interior wall of said casing, and with a portion of the surface of said rod.

References Cited in the file of this patent UNITED STATES PATENTS 627,671 Kelly June 27, 1899 2,468,512 Riche Apr. 26, 1949 2,527,475 Bates Oct. 24, 1950 2,532,000 West Nov. 28, 1950 2,650,964 Razdow Sept. 1, 1953 2,677,741 Martin May 4, 1954

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