US2854540A - Electric switch - Google Patents

Description

p 30, 1953 L. L. CUNNINGHAM 2,854,540

ELECTRIC SWITCH Filed Aug. 15, 1957 ELECTRIC SWITQH Lewis L. Cunningham, Los Altos, fiat-if. Application August 15, 1957, eriai No. 678,423 14 Claims. (Cl. Nil-67) This invention relates generally to small enclosed plunger operated electric switches of the type commonly called unit switches in the electric control industry.

More particularly this invention relates to such a device which will alternately first open at two places one electric circuit then close at two other places another electric circuit, the device including a first spaced pair of stationary contacts for the one of the circuits, a second spaced pair of stationary contacts for the other of the circuits and a contact bridging means for first unbridging one of the pair of contacts and then bridging the other of the pair of contacts.

It is a principal object of. this invention to provide such a switch which is snap acting, which can. easily be made'to provide any desired contact pressure and in which aminimum of contact bounce will be experienced in the operation thereof.

It. is a second object to provide such a switch in which substantially no circuit current is carried by any'part of the switch' entering into the mechanical action thereof.

It is a third object to provide such a switch inwhich the open circuit voltage of acircuit is precisely divided between two simultaneously opened gaps when the switch is, opened.

It is a fourth object to provide such a switch in. which a singleresilient moving contact carrying blade is deformed for over center action and loosely held to limit contact bounce.

It is a fifth object to provide such a switch in which the moving contact carrying blade is held rockably about its longitudinal centerline normal to a plane including its; moving contacts whenever the moving contact carrying blade is in motion to open one circuit and close another circuit.

It. is a sixth object to provide such a switch having a single moving contact blade structure with a shorter part in tension longitudinally of the bladeopposed by a longer part in compression longitudinally ofthe blade so that the longer part will be bowed away from the plane of the. shorter part, together with means for alternately transversely pressing the longer part near its midlength through the plane of the shorter part in opposite directions to reverse the forces acting transversely on said structure at its ends on said shorter part and at its mid length on said longer part.

It isa seventh object to provide such a switch having atmoving contact blade structure with a shorter part in tension longitudinally of the blade opposed by a longer part in-cornpressionlongitudinally of the blade so that the: longer part will be bowed away from the plane of the shorter part, the blade having a pair .of laterally spaced. moving contacts on an unstressed extension at one. end. thereof pressedv against a mating pair of stationary contacts and an other unstressed end extension of the blade. pressed against a. first support pivot on the same side of the blade as the. stationary contactsby a second support pivot at the midpoint of said blade-pressing/the outwardly bowedsiderofthe longer part. of the Patented Sept. 30, 1958 ice 2. blade toward the plane of the shorter part of the blade whereby additional pressure on the blade in one direction by the first support pivot or in. the other direction by the second support pivot will cause the blade to go over center and remove the moving contacts from bridgmg contact with the stationary contacts.

It is an eighth object to provide such a switch with three operating support fulcrum means positioned to limit the bow of the compression part away from the plane of the tension part whereby by movement of any of said three fulcrum means toward said blade said compression part may be moved through the plane of the tension part to relieve all three of said fulcrum means of pressure from said bladeparts.

It is a ninth object to provide such a switch having blade supporting means only on one side of the movable blade at any fulcrum point thereof so the blade can not operate as a reed to generate contact bounce.

It is a tenth object to provide such a switch having a moving blade with a supporting pivot means near the midlength thereof, the blade having unequal moments of inertia of the two ends about said midlength pivot means to dampen any natural vibration of the blade ends about said midlength pivot means.

How these and other objects are attained is explained in the following description referring to the attached drawing in which Fig. 1 is a plan view of a preferred form in which my invention may be practiced.

Fig. 2 is side sectional elevation along the line 2--2 of Fig; 1.

Fig. 3 is a plan view in of Fig. 2.

Fig. 4 is a perspective view of the moving contact blade of the switch of' Figs. 1,2 and 3 Fig. 5 is a side sectional elevation, similar to Fig. 2, of an optional form in which my invention may be practiced.

Fig. 6 is a plan View in section along the line -66 of Fig. 5.

Fig. 7 is a perspective view of the moving contact blade of the switch of Figs. 5 and 6.

Like reference numerals,- referto like parts in the several figures of the drawing.

Referring now to Figs.v l, 2, 3, and 4 there is shown a form of unit switch 11 having a hollow molded plastic insulating case split. horizontally along line 3-3 into an upper case part 12 and a lower case part 13 and held together by screws 14 passed through holes, as shown, in part 12 and threaded into part 13.

Electrically conducting contact rivets 15 are riveted as. shown to switch terminals 16 and molded into upper case part 12 with silver contact faces 17 welded to rivets 15 and extending into the hollow space. 18 formed in case parts 12, 13.

Similarly, electrically conducting contact rivets 19 are riveted as shown to switch terminals 20'and molded into lower case part Iii-withv silver contact faces 21 welded to rivets 19 and extending into the hollow space 18 formed in case parts 12, 13.

As shown in Figs. 2, 3 and 4; movable contact blade 22 isformed of a thin sheet of resilient. metal like spring steel, Phosphor bronze or berylliumv copper and. is split longitudinally on spaced parallel lines .23, 24 with holes 25 at the ends of lines 23, 24' to preventcracking of "the blade in use. Lines 23, 2'4 divide blade 22 into a center section 26, two side. sections 27 andtwo end sections.28, 29. Side sections 27 are shortened with respect to center section 26 by creasing side sections 27 as shown at 30. The-sameefiect has been accomplished by swaging center. sectiorn26. to lengthen it, but it has been found that precise: control. of the relative lengths of the parts is section along the line 3-3 3 obtained more easily by creasing side sections 27 rather than to swage center section 26.

With side sections 27 creased as shown at 30, center section 26 is longer and isforcedto bow in longitudinal compression out of the plane of side sections 27 now maintained in .longitudinal tension. Pressure against the convex side of bowed center section 26 will cause it 'to pass through the plane of sections 27 and change to concave the face of section 26 which was previously convex.

Conducting bar 31 is welded to end 28 of blade 22 and movable switch contacts 32 extending through holes, not shown, in bar 31 and end 28 of blade 22 are riveted in place as shown. End 29 of blade 22 is slotted as shown at 45 and a hole 33 is formed, as shown, through section 26 of blade 22. Longitudinally of blade 22, slot 45 and hole 33 are on the centerline of blade 22 perpendicular to a plane including the centers of the four contact faces of contacts 32. Polished metal pin 34, Fig. 2, is near enough to the diameter of hole 33, Fig. 4, in blade 22 to prevent any substantial lateral or longitudinal movement of blade 22 but does not interfere with or add friction to the operating movement of blade 22. The ends of pin 34 closely fit in holes provided for them in case parts 12, 13; see Fig. 2. a

Surrounding the ends of pin 34 as they emerge from case parts 12, 13 into case interior space 18 are carefully positioned pivot points 35, 36 formed on the inner surfaces of case parts 12, 13 as shown. Operating stem 37 is formed with a pair of spaced pivot points 38, 39 carefully spaced by a fixed spacing rod 40 adapted loosely to engage blade 22 at slot 45 to prevent rotation of blade 22 about pin 34. As seen in Fig. 2 the reduced diameter upper end of stem 37 is freely slidably guided in case part 12 and its full diameter lower end is freely slidably guided in hole- 41 formed into case part 13. Biasing spring 42 in hole 41 normally holds stem 37 upward and the switch operating parts in their positions shown in Fig. 2. Shoulder 43 is carefully positioned on stem 37 and together with the length of rod 40, the spacing of pivot points 35, 36, the spring rate of spring 42, the spacing between contacts 32 and contacts 17 and 21, the size of grooves 30 in blade members 27, and the dimensions of blade 22, determines the switchsensitivity and contact pressure. All of these thingsare determinedby test for a desired operating condition and these variables are then fixed for production- It is to be noted that the switch of Figs. 1 to 4, as particularly shown in Figs. 2 and 3, has its blade 22 supported entirely on pivot point 36 which presses upwardly on the compression blade section 26 and causes the movable switch contacts 32 at the ends of conducting bar 31 to press against stationary contacts 17 which are thereby electrically connected. Also the support of blade 22 by pivot point 36 presses the right end of blade 22, around notch 45, up against pivot point 38 on stem,37. It is seen that blade 22 is held entirely by three fulcrum supports each spaced from the other and each transversely centered on the same center line along which they. are each spaced from the other. One of the fulcrum supports of blade 22 when in the position shown in Fig. 2 is made up of the two transversely aligned stationary. contacts 17 another is the fixed pivot point 36 and the third is the movable pivot point 38.

When it is desired to open movable contacts 32 from stationary contacts 17, stem 37 is pushed downward to cause pivot point 38 to push downward aroundrod 40 on the right end of blade 22 and thus to push side sections 27 of blade 22 downward along the sides of section 26 of blade 22 which of course increases the contact pressure uniformly of each of the contacts 32 on the stationary contacts 17. Further increase of pressure on stem 37 will increase the contact pressures of both contacts 32 on contacts 17 uniformly until the plane of side sections 27 of blade 22 are in the plane of the center section 26 of blade 22 at which time the plane of side sections 22 will suddenly pass to the opposite side of the plane of center section 26 due to the potential energy stored in center section 26 by the deformation thereof.

It should be particularly noted that as contacts 32 are ready to leave contacts 17, blade 22 is free to teeter laterally about its longitudinal centerline and equal pressures will be holding contacts 32 against contacts 17 respectively. This condition therefore causes contacts 32 to leave their respective mating contacts 17 simultaneously thus breaking the open circuit voltage across contacts 17 equally divided between the two gaps formed between the two sets of contacts. It is not known that any prior art device precisely divides this voltage as does this device. I

When the plane of side sections 27 of blade 22 passes the plane of center section 26 center section 26 suddenly goes over center" and snaps upwardly to contact fixed pivot point 35. As the center of center section 26 throws itself upwards the reaction thereof tends to throw the ends of center section 26 downward and carry along with the ends the remainder of blade 22. But the center section 26 being lighter in weight than the rest of blade 22 the center section at its center moves upward against pivot point 35 first then held by pivot point 35 at its middle section 26 presses down at its ends to move then downward. Again since the weight of blade 22 will not be balanced longitudinally over a transverse center line at pivot point 35 the two ends of blade 22 (contacts 32 on one end and the blade around slot 45 at the other), will not strike their new end fulcrum supports (stationary contacts 21 at one end and pivot point 39 at the other) at the same time. With either end striking first any natural vibration of the blade on its resilient part 26 will be impeded by the striking of the other end and it has been found that contact bounce or erratic contact action is not sensibly present in the operation of this switch. It should of course be noted that if in design test contact bounce or erratic contact action is noted, adding or subtracting small weights to a selected end of blade 22 will eliminate the trouble.

In the form of switch shown in Figs. 1 to 4 it is apparent that the switch is designed to open one circuit, terminals 16, and-then to close another circuit, terminals 20, and alternately to open the terminal 20 circuit and close the terminal 16 circuit. As shown in Fig. 2, this alternating operation of the switch is accomplished by alternately pressing down on operating stem 37 against the bias of spring 42 and then releasing stem 37 so that spring 42 can return stem 42 and the switch blade to its original condition.

But it is also apparent the switch could also be alternately operated by alternately moving terminals 16 downward to cause section 26 of blade 22 to go over center and then to move terminals 20 upward to cause section 26 to go back over center. And again the switch could as well be operated by pivot points 35, 36 if they were free to move and pivot point 36 were first moved upward to throw contacts 32 downward and then pivot point 35 is moved downward to throw blade section 26 back over center to return the switch to the condition shown in Fig. 2. A switch having the last described operation is shown in Figs. 5, 6, and 7 wherein moving contacts 321/are connected by bar 311 on end 281 of blade 221 and blade 221 is designed to be laterally tiltable. over pivot point 391 of operating stem 372 and fixed pivot point 351 unless prevented from tilting. laterally by contacts'32l pressing on stationary contacts 171 of circuit terminals 161. In this form of my switch blade 221 is loosely and without operational friction prevented from lateral or longitudinal horizontal movement in interior space 181 by polished pins 341, 342 pressed into case halves 121, 131 and passing loosely through holes 331, 332 in part 261 of blade 221.

When, in Fig. 5, stem 372 is pressed upward, section 261 of blade 221 will go over center first striking pivot point 381' of stem 371 and carrying it to the: position shown in Fig. 5 then bladeend 291 will leave'pivot'point 351 and move to pivot point 361 while blade end 281 moves contacts 321 away from stationary contacts 171 and into contact with stationary contacts 211 where they will stay until stem 372 is released and stem 371 is pressed downward to returnblade 221 with'jcontacts 321 to their positions shown in Fig. 5.

Finally it should be' noted that for clear description the switch gap lengths are exaggerated'in the drawing. In actual practice my entire switch maybe small with blade 22 only one-half inch wide, three quarters long and about five mils thick. On open circuit the gap between the moving contacts and the stationary contacts may be four mils or less since there are always two gaps in series. In operation'the-blademovement is small therefore the velocity of the moving contacts will be small which is an ideal condition for allowing analternating current to stop atzero voltage without restriking as the voltage rises. It should also benotedthat maydouble break contact arrangement is best for breaking a direct current since the current paths through the two series gaps are parallel but opposite and the magnetic fields of the currents in the two g-aps repel each other to blow out the arcs at thegaps as the-switch opens. Tests have shown unexpectedly high circuit breakingcapacity for my switch on both A. C. and D; C. loads.

Having recited some of the objects of my invention, illustrated and described two formsin which my invention may be practiced and explained their" operation; I claim: I

l. Anelectric switch comprising a base memberv having a pair of stationary electric circuit-1contactsinsulatedly secured thereon transversely symmetrically on opposite sides of a longitudinal center line thereof, av movingcontact carrying. blade symmetrically aligned about'its longitudinal center line transversely 'symmetrically with: said center line of said base member, a painof: electrically connected moving contacts carried on said, blade in..respective contact with said stationary'contacts, a first pair of pivot point memberscarried onsaidbase spaced from each other and from-said stationarycontacts on: said longitudinal center line ofsaidbase, said 'bladeaincluding a resilientv section= maintainedv bowed; in: longitudinal compression by an approximately planarztension section thereof, said blade being loosely held against: substantial lateral or. longitudinal movement in the.pl ane-' of said tension section by pin means through said blade approximately perpendicularly thereto-and: secured-in said base member, said pivot points individually and said stationary contacts together forming three longitudinally spaced fulcrum supports for said blade with one of saidsupports pressing against the center of said blade, on theconvex side of said bowed compression member and theother two of said supports pressing the other side of said.blade at its respective ends, one of said'supports beingrnova'ble towards said blade to increase the. pressures. onisaid blade at said three supports to cause said bowed, section to go over center and b'owin the opposite direction, thereby relieving all of said' fulcrumsupports. of. load and withdrawing both said'moving' contacts from;contact with their respective mating contacts simultaneously.

2. The electric switch of claim 1 including a second pair of stationary contacts carried on said base and spaced from said moving contacts on the opposite side of said blade from said first pair of stationary contacts and a second pair of pivot point members carried on said base and positioned on the opposite sides of said blade respectively from said first pair of pivot point members whereby when said movable one of said first supports is moved to cause said bowed section of said blade to go over center said blade will lift said moving contacts from said first pair of stationary contacts and move said moving contacts into respective contact with said second pair of stationary contacts and said blade. will be sup-. ported on three other longitudinally. spaced fulcrum supiports'one determined by said second pair ofi'stationary contacts and the other two determined respectively by said second pair of pivot'point members.

3. The electric switch. ofclaim' 2' in .which one of said three other longitudinally spaced fulcrum supports is movable towards said blade to cause said bowedacompression'member to go back over center to' return-said moving contacts into contact'with'said first pair of stationary contacts and to return said blade to the support of said firstpair Qf'stationary contacts and" said first pair of pivot point members.

4. Anelectric switch including a first pair of stationary contacts, a pair ofinovable contacts in contact respectively with said first pair of stationary contacts, a second. pair of stationarycontact's' spaced respectively fromsaid movablecontacts on theopposite sideof said movable contacts from 'saidJfirst' pair of stationary: contacts, a base. insulatedly supporting allsaid stationary contacts, a movableresilient. blade carrying said' movable contacts and having a center line in a plane midway betweenthe respective contacts of' each of saidpairs of'con-' tacts, said blade including, a resilientsection' and a tensionsection for compressive endwise loading of said resilient section of said blade to bow said resilient section between its ends, a firstpair of pivot supportsfor said blade carried on said base aligned in saidplane on opposite sides of said blade, a second pair of pivot supports for said' blade carried. onjsaid basealigned in said plane on opposite sides of said; blade. and one pivot sup port ofeach. f said pairs being, spaced along said center line from the other pivot; support of each of said pairs and from said contacts whereby when said blade is bowed in onedirection it will be supported near its'mid length on, its convex side and near its respective ends on its concave side. by said first. pairof stationary contacts and the individual ones of said first pair ofpivot supports and when said blade is bowed in the. other direction it will. be supported by said second pair of stationary contacts and said individual ones of said' second. pair. of pivot supports.

5. An electric switch structureincluding an electric switch and a switchcase therefore: said electr-icswitch comprising a resilient movable contact carrying blade formed with a pair of end sections, connected by. a pair of'side sections and a center-section laterally separated from said side sections, said side. sections being shorter than said center section to bow said center section outwardly. from: the plane of saidsid'e sections, said blade including a pair of electrically connected movable contacts carried on one end thereof laterally symmetrically spaced about the longitudinal center line thereof; said case including a first set of three fulcrum supports for said blade when said center section thereofis convexly bowedon one side of'said plane of said side sections and a second set of three fulcrum supports for said blade whensaid center section is convexly bowed on the other side of said plane, said first set of three fulcrum supports. including. a first set of two stationary contacts insulatedly secured insaid case on saidone side. of said blade for respective contact with said movable contacts on; said blade when said center'section of said blade is convex in one direction and a first pair of pivot points longitudinal ly spaced from each other and said first set of two stationary contacts, said second set of three fulcrum supports including a second set of two stationary contacts insulatedly secured in said case on said other side of said blade for respective contact with said movable contacts on said blade when said center section is convex in the opposite direction and a second pair of pivot points longitudinally spaced from each other and said second set of stationary contacts.

6. The electric switch structure of claim 5 in which said case includes a polished pin set/therein perpendicularly to said blade and said blade is formed with a hole therethrough frictionlessly to receive said pin to maintain said blade loosely rockable about both its longitudinal and transverse centerlines on one of said pivots at the junction of said centerlines.

7. The switch of claim including operating means for passing said bowed center section of said blade through the plane of said side sections to reverse the side of said blade from which the center section is convexly bowed and thereby to move said blade from the support of one of said sets of three fulcrum supports to the support of the other of said set of three fulcrum supports and move said movable contacts from contact with said first set of two stationary contacts to contact with said second set of two stationary contacts.

8. An electric switch structure including an electric case and an electric switch operationally supported thereon, said electric switch including a resilient movable blade carrying a pair of electrically connected movable contacts transversely spaced on one end of said blade symmetrically about the longitudinal center line thereof, said blade being separated by two laterally symmetrically spaced longitudinal slits shorter than said blade into a center section and a surrounding section having two opposite end sections and two opposite side sections, said two opposite side sections being shorter than said center section to place said center section in longitudinal compression bowed convexly away from one side of the plane of said surrounding section, a first pair of stationary contacts insulatedly secured in said case for mating contact respectively with said movable contacts on the side of said blade opposite the convexly bowed side of said center section, said case including a first end pivot point positioned to contact said blade on its centerline on its same side with said stationary contacts and on its end opposite said contacts, a first center pivot point positioned to contact said blade between its ends on itscenterline on the convexly bowed side of said center section, whereby said blade will be supported on said case by said first center pivot point on one side of said blade and on theother side of said blade at one end by said first end pivot point and at the other end by said first two laterally spaced stationary contacts, said blade being prevented from rocking about its longitudinal centerline only by said first pair of stationary contacts.

9. The electric switch of claim 8 including first stern means for mounting one of said pivot points in said case movably toward said blade to pass said bowed center section through the plane of said surrounding section to move said movable contacts away from said stationary contacts simultaneously.

10. The electric switch of claim 9 including a second pair of stationary contacts secured on said case on the opposite side of said blade for said first pair, a second end pivot point on said case on the opposite side of said blade from said first end pivot point, a second center pivot point on said case on the opposite side of said blade from said first center pivot point, whereby when said first stern means is operated to pass said bowed center section through the plane of said surrounding section said blade will be stably supported on said one side of said blade by said second end support and said second 8 pair of stationary contacts and on the said other side of said blade by said second center pivot point.

11. The electric switch of claim 10 including a second stem means for mounting one of said pivot points in said case movably toward said blade to pass said bowed center section through the plane of said surrounding section from said'other side to said one side of blade.

12. The electric switch of claim 8 including means for preventing any substantial movement of said blade in its plane with respect to said case without interfering with the frictionless operation of said switch, which comprises a polished pin secured in said case approximately perpendicular to said blade and said pin positioned loosely through a hole formed in said blade to receive said pin.

13. In a substantially flat switch blade for overcenter operation to move a pair of movable contacts carried on said blade from contact with one pair of stationary contacts to contact with another pair of contacts, means for lifting said moving contacts from their respectively mating stationary contacts simultaneously which comprises a three point isosceles triangular support means for said blade on one side thereof and a one point support means for said blade on the other side thereof, said triangular support means including said pair of stationary contacts and a first pivot point equidistant from said stationary contacts, said one point support means including a second pivot point on a line from said first pivot point to the midpoint of a line connecting said secondary contacts, and one of said pivot points being mounted movably toward said blade to cause the overcenter operation thereof whereby when said one of said pivot points is moved toward said blade the pressure is increased on the other of said pivot points and said contacts thereby to keep said blade from lifting away from either of said stationary contacts until it goes overcenter to lift away from both of said contacts at the same instant.

14. In the arrangement of claim 13 for lifting a pair of electrically connected moving contacts from a mating pair of stationary contacts for breaking the circuit of said stationary contacts simultaneously at two places the operationally frictionless means of stabilizing a switch blade in its plane while said blade is moved normal to said plane, said frictionless means comprising a stationary polished pin extending substantially perpendicular to the plane of said blade and extending loosely through a hole formed through said blade to receive said pin.

References Cited in the file of this patent UNITED STATES PATENTS 2,190,299 Valkenburg Feb. 13, 1940 2,197,230 Waddell Apr. 16, 1940 2,444,529 Puster July 6, 1948 2,545,264 Davis Mar. 13, 1951 2,584,460 Jacobs Feb. 5, 1952 2,595,967 McCloy May 6, 1952 2,616,996 Beeman Nov. 4, 1952 2,657,288 Hubble Oct. 27, 1953 2,669,618 Bradley Feb. 16, 1954 2,700,079 Haydon Jan. 18, 1955

Images