US2451176A - Moisture-proofed plunger snap switch - Google Patents

Description

Oct. 12, 1948, J. H. scr-:ELLMAN 2,451,176

vHOISTURB-PROOFED PLUNGER SNAP SWITCH Filed uarcn 27, 1945 A J(6.14; Miwg/ \\\m www ATTORNEYJ Patented Oct. 12, 1948 UNITED STATES. PATaNT. OFFICE Joseph H. Schellman, Ridley Park, Pa.; asslgnor to Robert Hetherington & Son, Ine., `Wilmington, Del., a corporation of Delaware Application- March 27, 1945, Serial No. 585.080

, 4 claims. (emot- 168)V My invention relates to switches of plunger type.

A purpose of my invention is to protect a switch from injury by moisture.

A further purpose is to cover the press button of a switch by a moisture proof cap which is exible enough to permit the button to be pushed through the protecting cap and in which the cap is sealed against the switch casing by axial clamping of the border of the cap.

A further purpose is to provide a plunger switch with a complete water-tight protection which shall not interfere with proper operation of the switch.

A further purpose is to maintain approximately atmospheric pressure upon the switch contacts to be broken, even at high altitudes.

A further purpose is to cut off oxygen supply from switch contacts to be broken.

A further purpose is to limit exactly the forward and rearward strokes of the plunger so as to maintain cam or wedge pressure upon a shorting bar at either or at both ends of the plunger stroke.

Further purposes will appear in the specication and in the claims.

Figure 1 is a longitudinal, central section of one form of my invention applied to a plunger switch, in open position. The size is greatly exaggerated as compared with that of the present product.

Figure 1a is a fragmentary, longitudinal section of a modied form.,

Figure 2 is a section of Figure 1 taken upon line 2 2, enlarged as compared with Figure 1.

Figure 3 is a fragmentary section corresponding generally with Figure 1, but showing to a. reduced scale the switch parts in closed position.

Figure 4 ls a front end elevation to reduced scale of the structure of Figure 1.

In the drawings similar numerals indicate like parts.

It makes but little difference in the use of the iexibie and resilient cap or cover features of my invention as to the character of the interior of the switch, provided the casing terminates in an outwardly aring ilange to which the cap is clamped and, contain radially within this flange. an automatically retracted button, plunger or lever which can be operated through the flexible cover, so that the only hand or machine operation required is the 'movement by which the switch is thrown.

The invention has been illustrated` in connection with a simple form of fully operative springintention to ground the casing, this casing willx be electrically conducting; if it is to be insulated, the material of the casing need not be electrical- 1y conducting; This same`threadin'g is used in applying the present invention.

The switch is held vagainst the panel between two nuts I4 and I5 in connection with whichon one side or other of the panel, but preferably on the forward side, a washer I8 may be used. The

'panel opening will ordinarily be threaded, in

which case the nuts will be lock nuts and in Figures 1 and 1a the washer may be a lock washer. In the figures, the front of the casing is provided with a circular dare or ange I1 against the rear wall of which and about which is clamped the border I`8 near the edge I9 of a ilexible and resilient waterproof cap or cover vIl), which is preferably made of rubber, natural or synthetic. The border at and near the edge is sprung over the ilange`s'o as by its retraction to fit within and against the inner diameters -of the ilange springing into the annular space 2i axially back of the flange. This space has been' accentuated by grooving the casing at 22 immediately back 4of the flange, in order to enlarge the area oi the back or rear face 23 of the flange to which the cap border is to be clamped.

i The border is clamped against the rear face of the ange by a nut 24. In Figure l the nut eective for this purpose is shown at Il'.

Clamping the cap against the ange of the outer casing effectively seals the front end of the switch, protecting the interior oi the cap and all within lt against moisture. In additionb to this mechanical clamping of the resilient cover to the casing, this joint between the parts is additionally protected by bridging the. clamped joint by an insulation type seal about what I have called a plunger 25. v another type of switch operating mechanism than a, direct plunger, though not to the same advantage.

In order that I may show a complete switch operating mechanism--even though it be one only of many switch mechanisms that can be protected by the cap and sealing-I describe it in connection with a plunger type of switch shown.

In' the structure of the figures, the body of the The cap might be thrown about `ture 88.

ing is at the rear.

vlihe body is desirably metallic. It is insulated 'at the rear by the insulating block 83 andrearwardly-open cup insulation 8d. both within the bore. The forwardly facing bottom 3B of the cup closes the bore. forwardly except for aper- The two of the insulation indicated are separate because of requirements for assemblage. The iront about the cap and clampf ing nut and permissibly about theentire mount is'sealed against moisture by latex or synthetic rubber or other similar protective material in the form of a coating 8l, which most desirably is vulcanized in place. A carboxyl polyvinyl chloride acetate is excellent for this purpose.

The cup insulation is nxed in position at its front edge by shoulder 80. The rear block Si is set by engagement of the outer danse 3s with the rear' end of the casing or 4 The connection between the rear block and the casing and the connection between' the molded-in terminals 39, l and the rear block are protected against moisture by a coating, 4i

` oflatex' or synthetic rubberor other suitable compound, which with latex or rubber is vulcanized in place. Y

The terminals are supported by block 35 and araturned radially across toward each other as at 42, 43,so as to be' connected by the front plate M of a shuttle or shortening bar 4B, mov'- ing longitudinally of the .casing within a. space et. The shorting'bar comprises said electrically conducting front face plate Ii, apertured at el in line with aperture 36. The plate is turned rearwardly at its ends I8, 48 and in rear position of the bar, engages the front face of the block insulation by the ends 8B, Il! to limit the rearward movement of the bar.

Both side edges B0 of-eachof the rearwardly 'turned ends .sa se are armed, one toward the other, to constrict or at least limit the side movement, away from each other, of the ends El of transversely extending parallel spiral springs 52.

'The extent of this constriction or restriction is capable of adjustment during assemblage by' turning the side edges to diierent extents so as to accommodate the same shorting bar size f' and construction to switches in which the lateral pressure of the springs against the cams of a hill and valley plunger may be quite different, making it possible by adjustment of the extent of inturning of the edges to Vmake quite a considerable difference in the resistances offered by the side springs to lateral ilexure of the springs by engagement of the plunger cam. v

The rear of the shuttle o r shorting bar is preferably formed by a plate of insulation, apertured at 53'.

In considering the plunger 26 above, I havev contemplated the entire plunger system, from the push button 54 to the plunger shaft 5B, which carries the hill and valley'v operating cam e8.

The pushbutton is externally flanged at the -rear at B1 to slide within the middle counterbore vand the bodyof the button is guided within the front counterbore. k'Ihe piston-:like plunger guide l is rigid with shaft 55 and provided with a cylindrical stem 58 and front collar 80. fitting within the recess of the button and isreduced in diameter at Si at the front end so asfto ilt within the overtravel spring B2.

After the parts are assembled, the rear end of 4 the button about the recess is peened at to hold the collar within the button. Travel of the button il'rst moves the plunger stem against the resistance of the retraction spring Bil until the plunger is stopped.

This movement of the plunger must be enough to'pass the crest of the hill and valley cam between the centers 'of the shorting bar springs, causing the snorting bar to shift forwardly and close the switch. Travel of the button beyond the point at which the plunger stops causes compression of the overtravel spring 62 to begin. The crest of the double cam Se is located at the point where the two truncated cones come together,

base to base. The slopes of'I the two cams are diierent.

During movement of the plunger rearwardly, to' cause forward (switch closing) movement of the ehorting bar, when the double cam is pushed so that the crest of the cam passes downwardly, rearwardly in Figure 2, past the plane between the center lines of the snorting bar springs, the snorting .bar lshifts forwardly and travels down the long forwardly facing slope to closure, giving a relatively slow movement and providing conveniently for overthrow of the plunger after the snorting .bar has been seated against the contacts.

j On the retraction stroke the piston-like guide engages'the shoulder 3i at the front end of the guides travel, preventing excessive forward travel of the stem.

The plunger shaft is guided at its rear end by i vthe walls of the recess 6d whose bottom 66 can be used to limit the extent of travel of the plunger. The travel can be limited also by complete compression of the retraction spring or, where the s'eat of the spring is deep enough to permit the spring to compress within it, the travel can be limited by engagement of the rear face 51 of the pistonlike guide with the front face 68 of the cupped insulation.

. Positivev limitation of the rearward movement of the plunger shaft permits the shaft to be stopped reliably while the snorting bar transverse springs are still engaged by the front slope of the hill and valley cam, thus maintaining ypressure upon the snorting bar to hold it rmly against the contacts 42 and 43, holding the switch closed.

. Both of the means for limiting the plunger stroke stop it where the piston-like guideengages the shoulder at 3|. On the rear stroke the plunger is stopped by the bottom of the guide opening. g Complete protection against moisture, involving as it does complete protection against admission and outward ow to and from the interior of the switch has several distinct advantages. Wherever used the maintenance of a u niform atmosphere about the arc is quite desirable, not only as regards the moisture, but as regards the oxygen content. Where the space is closed, the oxygen is soon completely burned out leaving an inert gas in-which ythe spark cannot nd fuel.

When the switch is surrounded by raried atmosphere,` as in high altitude airplane use, the inert gals, even without its oxygen content, maintains a pressure within the enclosure greatly in excess of the pressure of the surrounding air and which is maintained at nearly the same reduced pressure by the resistance of the cap expansion.

The protection against moisture means also form upon the contacts. It also avoids ignition actieve of dangerous gases by contact of the gases with the switch arc.

. When the rubber cap is slightly collapsed dur ing the pushing of the plunger from the outside of the cap, the pressure about the hill and valley switch contacts is relatively slightly increased, this additional pressure is maintained while arcing takes place. At high altitudes the one pushing upon the button through the rubber cap thus slightly corrects and makes more nearly normal the pressure at the time the switch is closed and hence continues to maintain the higher pressure during the time when the push button pressure is released and at the beginning of which releas.

ing the arc is made.

It will be evident that various forces are at worl; in determining the conditions inside of the switch. This pressure will be less in rariried atmospheres because the outside pressure is very much less than the approximately 15 pounds pressure per square inch at normal atmospheric pressure.

The reduction in pressure is offset by the resistance of the cap material to stretching, by the burning out of the oxygen from the atmosphereon the other hand it is increased by the reduction of volume of the space inside of the switch by collapse of the cap when the plunger is thrown rearwardly, which relative compression continues when the button is released and the switch is opened.

it is to be noted that on the reverse movement, when the pressure upon the push .button is released the short and relatively steep rearwardlyfacing slope of the came becomes effective.

h1 Figure le the cap and the manner oi' cap fastening as well as the'structure inside the casing is intended to be the same asthat shown in Figure l. The casing is flared and grooved and externally threaded, as in Figure 1, the only difference being in the manner of the attachment to the panel. In this case the panelis not threaded, the cap is held in place by a nut I4' threaded upon the casing and compressing the border end of the cap adjacent its edge.

When the acetate is used the sealing material is not vulcanized.

VThe forwardly facing slope of the hill and valley switch is more gradual (i. e. less steep). than the rearwardly facing slope. At the' switch c105- ing end of the shorting bar movement, the springs 62 rest upon the forwardly facing slope so u to maintain forward pressure upon the shox-ting bar to keep the contact nrmly closed.

In view of my invention and disclosure varia.-

tions and modlncations to meet individual whim switch having a threaded exterior and an outwardly :flaring ange upon the front and a springretracted operating member moving forward and baci: at the front, a waterproof, flexible and elas- I tic cup surrounding the iange and operating member-and engaging the rear of the flange and a nut mounted upon the casing and pressing the edge of the cup against the rear of the nange.

2. In a switch, a casing having a threaded ex? terior flanged at the front, a resilient, moistureprooi cap of smaller edge circumference than that oi' the inside of the front ange, a nut mounted by the casing, axially engaging the edge of the cap and pressing it tightly axially against the rear lace of the flange and switch mechanism terminating in an operating plunger within the cap, adapted to be operated from the outside through the cap, thus taking advantage of the exure of the cap.

3. In a switch', an automatically retractable switch having a threaded exterior and an outwardly flaring ange upon the front and a springretracted operating member moving forward and back at the front, a waterproof, flexible and elastic cup surrounding the ange and operatingv member and engaging the rearl of the nance, a

nut mounted upon the casing and pressing the edge of the cup against the rear of the flange. and a waterproof coating extending from the nut to the cup and over the joint between the nut and the cup to seal the same. l

i. In a switch, a cas vhaving a threaded er1- terior flanged on the iront, a resilient, moistureproof cap of smaller edge circumfere than that of the inside of the iront iiange, e, nut mounted on the casing, axially engaging the edge of the cap, and pressing it tightly axially agaimt the rear face of the harige, switch mechanism ter minating in an operating plunger within the cap, adapted to be operated from the outsidethrough the cap, thus taking advantage of the flexure of the cap, and a. waterproof coating of vulcanizable material extending over the outside of the nut and over the cap, sealing the joint between the nut and th'e cap and vulcanized in place.

JOSEPH H. SCHELLMAN.

REFERENCES The following references are of record in the me of this patent:

STATES PATENTS Number Name Date 450,292 Johnston Apr. 14, 1891 809,262 Hood Jan. 2, 1908 1,222,214 Klein Apr. 10, 1917 1,837,185 Jones Dec. 15, 1981 2,202,207 Johnson May 28, 1940 2,301,874 Hetherington Nov. 10, 1942 2,367,441 Schwinn Jan. 15, 1945 2,388,162 Hetherington Oct. 2. 1945 FOREIGN PATENTE Number Country i Date 198,595 Germany Dec. 18. 1907

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