US2737557A - Silent switches - Google Patents

Description

March 6, 1956 C, w, JOHNSON 2,737,557

SILENT SWITCHES Filed NOV. 12, 1953 i ,Il Il III/II United States Patent This invention relates -to Switches for controlling elecvtric circuits, and particularly to wall switches of the socalled toggle type'used in homes and 'oliices for controlling lighting circuits.

I The main 'object'of "the `present invention is Vto provide a switch of 'this type which will be practically noiseless in operation, -while retaining the vessentialfeature kof quick make and break of the circuit, and avoiding the faults of 4stopping of the parts in intermediate position between -th'e oi 'and on extremes of y"their movementfof intermittent or trembling vcontact in the "on position with Kresultant arc- ,ing constituting "a tire hazard, 'and of vreverse vcreep of the parts out of their intended 'on 'or ofi" position. Other objects of the invention include kthe provision of a simple structure which 'can be feasily and rapidly assembled out of 'inexpensive components of `wide availability to make a switch having long life and'fre'edomfrom failure' in action.

A Vnovel principle exemplified the improved switch to 'attain noiseless actionis `the checking 'of the moving 'parts and 'ending their travelby utilizing the actuating Yspringsown resistanceto bending out of its normal shape.

vvIn this manner of operation, the 'spring yperforms its usual vfunction of 'accelerating and 'completing vthe movement of the parts begun 4by vthe users fingers, to-close oropen the circuit, but thereafter 'such spring opposes resistance to"continued movement lof 'the 1parts 'and thus brings them to 'rest silently. No striking againststops lor stiff con- 'tacts after the vusual inanneris needed 'to arrest the moving parts, and the spring itself makesno audible sound.

The invention also includes anovel'manner of utilizing 'another principle of operation, also characterized by 'noiseless action, namely that of checking themoving'parts and ending their travel I'by-the 'We'dging' or ljamming-action and resultant friction of a surface traveling with'the movl'ing parts against other stationary parts 'disposed in nonparal'lel lrelation to 'the 'path of 'travel yof the `moving part, set forth in my co-pen'ding 'application Serial No. 315,- 929, 'filed October 21,1195'2.

Other objects of the invention, and 'the manner of Ya'ttainment of these aim's'a'nd 'those already indicated, are -`set forth hereinafter.

Illustrative embodiments of the invention are shown in the accompanyingdrawings,lin which Fig. '1 is a side elevation of the no'vel switch, Fig. 2 an end elevation thereof, andfFig 3 afp'lan view, with the 4rthumb piece, th'e Casing, or the mounting vplate 'partly broken aw'ay.

Fig. 4 is 'a perspective view showing the thumb piece and -c'ontactor together-withfth'e pivotal support for such parts, and the actuator spring with its mounting, of lthe switch of Fig.' 1.

.thumb piece .1, of `plastic or yother suitable non-conducting 2,737,557 vatented Mar. 6, 1956 material, in which vis fixed, as by imbedding during the molding, the shank 3 of an L-'shaped contactor 5 forming the main working part of the switch.

The thumb lever thus comprised is pivotally mounted on a 'pivot pin 7 of brass or other conducting material having one of its ends 'fixed as by riveting in a plate 9 which is received in a slot 1'1 formed in one side wall of a switch case V13 of molded plastic or other dielectric ma- 'terial.

Plate 9 is xed in 'place by a screw 15 put through a hole in the .case 13 and threaded through 'the plate, and constitutes a bindingpost for one of the leads (not shown) 'carrying the current through the switch. The *other end of pivot 7 is received 'in a slot 17 molded in the top `edge of the opposite side wall of case 13.

Pivot pin 7 extends through a hole formed in contactor 5 and through fa downwardly yopening groove 8 molded vin the bottomof thumb piece 1 and also in the lateral ing capacity for heavier duty if desired.

An actuator spring 23 in the form of an expanding spring wire coil is attached 'to the extremity lof the substantially horizontal portion of contactor 5, by means of a stud 25 having an enlarged lower portion which is screw-threaded 4externally and a reduced portion or shank which isput through ahole in the foot of contactor 5 and headed over at the upper surface thereof to fix yit'securely thereon. The spring -23 is formed with a closed helix of ytwo or three turns at its upper end, which are screwed around the threads on the exterior of stud 25 to tix the spring securely and permanently thereon. The diameter 4of the threaded portion of stud 25 is sufficiently larger than the internal diameter of the closed helix of the top end of spring 23 to anchor such top end immovably on the stud. lThe Vrest of the coils'of spring 23 are expanded Vinto an open helix, Vthe coils of which lmust be wide apart for silent action, and the end of thecomponent wire is bent to provide 'a foot 2'7 which lies at right angles to lthel axis of the helix. This foot is stepped in a transverse fgroove 29 molded in a pad or abutment formed on the bottom of case 13, such groove running into a second groove y31 extending lengthwise of the switch case. This simple arrangement holds the foot of the springsecurely in positionlin the case against escape in any direction, `while permitting free rocking movement about the axis yof the-foot 27, theadjacent portion of the wire swinging Vlever is at rest. In'its natural relaxed state, the spring is of cylindrical contour with all turns of the helix con- 'centri'callydisposed about a single axis, i. e., it is a straight coil spring.

Spring 23 'is in effect one arm of a toggle linkage, push- `ing upward 'at all times against the other arm, the part of the thumb lever formed by contactor 5, to which it is linked at 'stud 25. Hence when the axis of such stud is .at either side of the line joining the centers 7 and 27, the 4'spring tilts contactor 5 and thus the entire thumb lever in the corresponding direction, through rotation about pivot 7. Thus the movement imparted toy the thumb lever by 3 the users iingers in tilting thumb piece 1 to work the switch is accelerated the instant the axis of stud 25, i. e., the transverse plane of the thumb lever, passes the line joining centers 7 and 27, and the thumb lever proceeds rapidly under the impulse of spring 23 to the limit of its movement.

The checking of this movement of the thumb lever is effected by the resistance of the spring 23 to being bent laterally out of its natural straight or cylindrical extent. Because the top two or three turns of the spring rigidly fixed on stud 25 are forced to remain coaxial with such stud as the latter swings in an arc about pivot 7, while foot 27 remains in fixed location in its step in groove 29, or the coiled lower end is held by the prong referred to, the rest of the turns of the spring below the stud are forced out of coaxial relation with the top turns on the stud, and the bending stress transversely of the axis of the spring increases as the stud travels farther from, the line joining centers 7 and 27 until it exceeds the expansive force of the spring exerted lengthwise thereof, thus checking further longitudinal expansion and also overcoming the momentum of the thumb lever and bringing all moving parts to rest. The nature of this action is completely silent, since it involves solely internal stresses in the spring, and thus the moving parts are brought to rest without a sound.

It is also contemplated in certain instances, as for reduced cost of construction to meet competition, to replace the coil spring by a simple straight spring wire or flat spring blade rigidly fixed to the shank or lower end of contactor 5, while the other end of such spring is stepped in a recess in the bottom of the case with capacity for rocking movement. This spring bends to one side or the other, like the coil spring 23. Such spring is slightly longer than the distance from the arc dened by its point of attachment to the contactor measured to the step, so

that the spring buckles and reverses its lateral bend in Y passing through the line joining centers. The spring is coated with rubber, plastic, or other sound-deadening material to silence its vibration.

To close the electrical circuit in which the switch is to serve, a contact 33 is formed of a bent strip of phosphor bronze or other suitable metal having a widened portion 35 received in a slot 37 in one end wall of case 13, where it is held by a screw 39 put through a hole in the wall of the case and threaded into the portion 35, such screw forming the binding post for the other lead (not shown) carrying the current through the switch. The blade of contact 33 extending inwardly of the case has its transversely flat surface disposed parallel to the axis of pivot 7, and is bent into an arc, and a contact shoe 41 made of a length of half round stock of silver or other metal of high conductivity and long life is fixed on contactor in position to make wiping contact with the flat surface of member 33 when the thumb lever is tilted to bring shoe 41 thereover. The blade of contact 33 is shaped and positioned in such manner that its curvature does not parallel and coincide with the arcuate path of the bottom surface of shoe 41, but instead its concave surface converges toward and is intersected by such path as the contactor 5 reaches the limit of its upward sweep at this end of its travel. While this curve need not be an arc of a circle, an easy way of obtaining the desired relation is to curve the blade on the arc of a circle having its center slightly below the axis of pivot 7 and in substantially the common plane through the pivot 7 and the foot 27, and of shorter radius than that of the arcuate path of shoe 41, after the manner shown in Fig. 6 in relation with the form of Fig. 5. The arcs are so related that shoe 41 makes and breaks its contact with the blade of contact 33 a substantial distance backfrom the free end of the latter; also, since the blade flexes slightly (see dotted lines, Fig. 6) when engaged by shoe 41, there is no bounce or vibration, so that the engagement is both noiseless and greatly reduces u or entirely suppresses arcing at either make or break.

4 The prolonged travel of'shoe 41 along the blade effects a wiping or cleaning action of the coengaging surfaces, which coupled with the increasing pressure toward the end of the stroke ensures good conductivity as well as greatly prolonged life.

In this form the checking of the moving parts in the on position is mainly eected bythe described transverse bending of the spring 23, though the wiping action of the blade against the contactors shoe 41 does have a cooperating braking effect useful in itself and noiseless also, as will be seen in connection with the form of Fig. 5.

When the thumb lever is moved to the olf position the shoe 41 leaves the blade of contact 33 smoothly with gradually descreasing pressure, the blade iiexing upward again to the point where shoe 41 clears it, again with practically no electric arc as shoe 41 does notslide off the end of the blade to draw such arc.

As will be understood, the thumb lever and spring 23 are in such unstable `relation when the thumb lever is at mid-stroke and the axis of stud 25 is in the line joining centers 7 and 27, with spring 23 stressed to its full extent, that the parts cannot remain in this position, or in any other position between the off and on extremes of their movement.

To guard against heavy-handed forcing of the thumb piece far enough beyond its normal stopping points to strain the spring or pull it out of its step in the pad on the bottom of the case, or off of its prong, the lateral extensions 19, 21, have their respective outward surfaces eccentric to the axis of the groove 8 receiving pivot 7, so as to form cams displaced from each other about such axis. These cams are arranged to bear against the under side of the sheet of fiber insulation 43 backed up by switch cover 45 fastened to the case 13 by screws 47, whenever the thumb piece is rocked beyond its normal position of equilibrium determined by spring 23. That is, these cams have no effect on the movement of the thumb piece or other parts unless it is tilted beyond its normal stopping points, but when such occurs one or the other of the cams jams against the insulating sheet 43 to prevent further angular displacement of the thumb piece.

These extensions 19, 21, also serve to insulate further the current-carrying pivot 7 from electrical contact with the metal switch cover 47.

For convenience in finding the switch in the dark, a miniature glow tube or bulb 49, of neon or other type, is cemented in seats formed therefor in the free ends of fins 51 molded on one side wall of the case, such tube being connected permanently across the line, i. e., between binding posts 15 and 39. Transparent or translucent pins 53 of suitable plastic inserted in and extending through the shoulders of thumb piece 1 transmit the light from such tube out from the switch case interior, to form glowing dots showing the locality of the switch.

When a 3way switch is desired, the described structure requires only the addition of a second contact identical to 33, inserted in a slot 55, Figs. 1 and 3, in the other end of switch case 13, and provided with a combined retaining and binding screw identical to 39. The arrangement of these contacts is as shown in Fig. 5.

Fig. 5 shows another form of the invention, which uses solely the principle of arresting the moving parts by forces arising from extended or prolonged engagement of the moving thumb lever or parts thereon with an interfering surface disposed in non-parallel relation to their travel, which tends to direct their movement out of their fixed path and thus gradually retards and finally jams their progress. These forces arise in the form of Figs. l to 4 through contact between shoe 41 of contactor 5 and the curved blade of contact 33, as already noted, and aid in arresting the moving parts. In Fig. 5 these forces are utilized alone to arrest the thumb lever 57, and are created by providing two identical contacts 59-similar to 33 of Fig. l, identically mounted in slots in switch ejzamw case 61 by retaining and binding screws 6,3. The curved blades `of such contacts are engagedby 2a f'c'otitact jsfhoe 55 similar to 41 mounted 'on an L-s'lrapetl contacter-*67 similar to S imbedded ina thumb piece 69 lcorresponding to 1, the blades exerting pressure against Vv"the shoe in directions solely in the plane aof 1"the arcxrf movement of the shoes surface. Actuator spring 71 hereingisga' cylindrical or straight" helix seatedH-:fon a '.,pronggf molded integral with case 61, withthevtop en d V )fthe spring wire extendedparallel to l`thesprings.:ntisrasga tinger A75. This linger is received inglajcup 77 -s t ruck. np from the metal of the end-portion of the laterally extending foot of contacter 61, i. e., in a location corresponding to that of stud 25. "7-

The position and relation of the blades of the two contacts 59 to the arcuate path of element 65 is as already described in re Figs. l to 4, and is easily attained as shown diagrammatically in Fig. 6, with the radius'rof curvature of the blades less than the radius s of the: said arcuate path, and with the center of radius r betweenfand in the plane containing prong 75 and pivot 79 of thumb lever 57.

As before, shoe 65 makes and breaks contactwith with either blade of contacts 59 a substantial distance back from the free end thereof. (Both blades are connected into the circuits for a 3way switch, and onlyione for a 2-Way switch.) After it makes contact, the progressive and gradual increase of pressure applied by the blade to shoe 65 creates a force directed towardrA the pivot 79 which builds up increasing frictional resistance to further movement and eventually arrests the thumb lever without shock and hence noiselessly. The same virtues iiowing from this type of engagement as already pointed out are realized.

The curvature of the blades of contacts 59 both prolongs the impact and distributes the wear along the blades, and the yielding of the blade from the initial dotted-line position to the solid-line position of Fig. 6 further softens the impact, because further prolonging it. This s oft impact naturally reduces rebound and vibration and resultant arcing. Thus the arresting of the moving parts is extended through a greater period of time and distance of travel.

The rest of this switch is as described in relation to Figs. l-4.

In this connection, it is noted that the contacts such as 33, 59 do not need to be arcuate or curved, in all instances, as they will work satisfactorily when formed as fiat spring blades disposed as chords of the part-circular path defined by the bottom surface of shoe 65. These blades because of their resilience will yield and recede, the point of Contact between the shoe and the blade still tracing an arcuate path. The main difference is that the stopping of the moving parts is slightly more abrupt.

Preferably in all forms the contacts such as 33 and 59 are made of Phosphor bronze with a rolled-on coat about .005" thick of coin silver covering the concave surface. The shoe 41 or 65 is made out of pure silver, which is softer than the coin silver on the blade, so that practically all the wear and erosion falls on the relatively thick shoe, thus giving an extremely long life to the parts coupled with maximum conductivity.

An advantageous feature of the improved construction in either form is that it can be made to have relatively very high current-carrying capacity, even up to 30 amperes, without any increase in the size of the case over conventional dimensions, and hence fitting the regular switch outlet boxes. This is done by merely using broader contact blades 33, 59, and a shoe 41, 65 correspondingly lengthened along the foot of the contactor 5, 67, to match the increased width of the blade. The parts need no increase in length, thus keeping down the ,resistance and resultant heat rise within the switch case. This is in contrast with prior switch constructions, where in many instances, notably in mercury type switches, a recent change in official Standardsrequiring an increase in mini- Imuurcarrying@capacity from il 0 f-amperes fto `I51amperes on v. circuits has compelled `an increase `the ydimen- :sionsfof the contact `relements :which .in turn has .forced 7the eexilargement fof the entire Vswitch `mechanism fincluding rth'ecasev f While-1 havesillustrated and describedcertain forms-in whichlthefinventionmay be embodied, I am aware :that

.manyfmodicationsrmaybe made thereinby-any person Askilled.i. nthe art, without departing v.fromthe `scope of the inventionas -expressed in the claims. lIlT'herefore, I do not wish to be limited to the particular form shown, or to the details of construction thereof, but what I do claim is:

1. An electric switch having in combination a thumb lever, a pivot therefor, an abutment, a spring stepped on the abutment and ever pushing against the thumb lever, and a resilient blade having a transversely flat surface which surface is disposed parallel to the axis of the pivot and engaged by a surface travelling with the thumb lever to complete the electric circuit and also check the movement of the thumb lever.

2. An electric switch having in combination a thumb lever, a pivot therefor, an abutment, a spring stepped on the abutment and ever pushing against the thumb lever, and a resilient blade having a longitudinally curved and transversely at surface which surface is disposed parallel to the axis of the pivot and engaged by an electrically charged surface travelling with the thumb lever to complete the electric circuit, the curve of the blade approximating and intersecting the arc defined by the movement of the said surface on the thumb lever.

3. An electric switch having in combination a thumb lever, a pivot therefor, an abutment, a spring stepped on the abutment and ever pushing against the thumb lever, and a resilient blade having a transversely tlat surface which surface is disposed parallel to the axis of the pivot and engaged by a surface travelling with the thumb lever to complete the electric circuit, the blade being curved and intersecting the arc defined by the movement of the coengaging surface on the thumb lever.

4. An electric switch having in combination a thumb lever, a pivot therefor, an abutment, a spring stepped on the abutment and ever pushing against the thumb lever, and a resilient blade engaged by a surface travelling with the thumb lever and curved substantially on an arc of a circle having its center substantially between and in the plane containing the pivot and the spring step and having a radius less than that of the arcuate path of the coengaging surface on the thumb lever.

5. An electric switch having in combination a switch case, a thumb lever, a pivot therefor, a fixed abutment, a spring engaging the thumb lever and stepped on the abutment and held under compression between the thumb lever and the abutment, a resilient contact member disposed in a curve lying in the plane of movement of the thumb lever but eccentric to the latter's pivot and engaged by a surface travelling with the thumb lever to complete an electrical circuit, and applying a force to the said s`urface mainly directed toward the pivot and increasing as the spring expands, the thumb lever having at least one cam surface engaging with a surface in connection with the case and limiting the angular movement of the thumb lever.

6. An electric switch having in combination a switch case, a thumb lever, a pivot therefor, a spring acting both to move the thumb lever and to limit the extent of its movement, a contact element acting to close an electrical circuit when engaged by a surface travelling with the thumb lever and also serving through friction and resistance to displacement in a direction at right angles to the pivot to limit the movement of the thumb lever, and surfaces in connection with the thumb lever entering into wedging engagement with parts in fixed connection with thesvvitch case at the limits of the thumb levers movement gradually arresting the travel thereof.

A'7. An electric switch having in combination a switch case, a thumb lever, a pivot for the latter', a spring acting to move the thumb lever through a limited arc about'the pivotand thereafter resisting further movement, and a resilient contact engaged by a surface traveling with-the thumb lever to complete an electrical circuit, displacedin a direction at right angles to the pivot by, and opposing resistance to, the travel of the thumb lever and the said v d I-lefeenceS/Cited inthe file of this patent I. UNITED STATES PATENTS Dnle Aug. 8, 1922 *Barnitz'v Nov. 3, 1936 -fSh'rrard f va. June 27, 1950 Wiggins .z Dec. 11, 1951 wire-f, sept. 14, 1954

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