US2858385A - Electrical switch - Google Patents

Description

Oct. 28, 1958 w. J. SCHULTZ ET AL ELECTRICAL SWITCH H 6 Sheets-Sheet 1 Filed Dec. 30, 1955 Invemors William J. Schuhz Carl F. VanBennekom m4 5% Their AHorney 1958 w.,.|. SCHULTZ ET AL 2,858,385

ELECTRICAL SWITCH I Filed Dec. 50(1955 I e Sheets-Sheet 2 ors illicm J. SchuHz rl F Van Bennekom Aa;{ Their AHorney w. J. SCHULTZ ETAL 2,858,385

Oct. 28, 1958 ELECTRICAL SWITCH s Sheet s- Sheet 3 Filed Dec. 50, 1955 Fig.

Their Atro W. J. SCHULTZ ETAL Oct. 28, 1958 ELECTRICAL SWITCH .6 Sheets-Sheet 4 Filed Dec. 30, 1955 Fig.6

I lnveMors:

William J. SchuHz Carl E VonBennekom by, 4

,4 4 Their AHorney Oct. 28,

Filed Dec. 50, 1955 w. J. SCHULTZ EI'AL ELECTRICAL SWITCH e Sheets- Sheet 5 lnvenrors: William J. Schuhz Carl F. VcmBennekom Their AHor ney Oc't- 1958 w. J. SCHULTZ ETAL 2,

ELECTRICAL SWITCH 6 Sheets-Sheet 6 Filed Dec. 30, 1955 United States Patent ELECTRICAL SWITCH William J. Schultz and Carl F. Van Bennekorn, Lynnfield, Mass., assignors to General Electric Company, a corpo ration of New York Application December 30, 1955, Serial No. 556,583

6 Claims. ((ii. Nil-27) The present invention relates generally to electrical switches and in particular relates to an improved electrical switch capable of handling realtively high circuit loads and having novel arrangements for reliably separating the switch contacts in the event such contacts become welded together upon closure thereof.

In the use of electrical switches for controlling electrical circuits in which relatively high current flows, it is relatively common for the switch contacts to become welded together during the closure of the switch. For example, in the case of an electrical circuit including a tungsten filament load drawing a current of 35 amperes, it is not unusual for the switches to have an inrush current traversing their contacts at the moment of closure as high as 8 or 10 times the normal load current in the circuit. Thus, it is possible that a current as high as 350 amperes could traverse the switch contacts in which event it is not unusual for the contacts to become welded together during closure thereof.

If the contacts become welded together, there is no problem in connection therewith so long as the switch remains closed. However, when it is necessary to open the switch, particularly in those instances where the switch is a part of an automatic time switch normally unattended and relying upon a timing motor to provide the necessary power for opening the switch, it is extremely important that the contacts open when required. If they are welded together and cannot open, great damage could occur and the switch would be totally ineffective and unreliable as a circuit controller.

In,the past and in connection with switches having their contacts carried by deflectable spring members, it has been the usual practice to obtain separation of the con-- tacts by storing sufiicient energy in the spring blades during closure thereof so that the stored energy can be used to break any contact welds and thus allow the contacts to open. In the case of a switch rated for 35 amperes tungsten load, it has been found that a force of 20 ounces must be available in each contact carrying member to break any welds encountered during the use of the switch. Obviously the energy required for separation of the contacts must be stored in the deflectable spring member each time the contacts are closed whether or not a weld occurs at any particular instant of closure.

In the case of a single-pole, double-throw switch, a total of 40 ounces must be stored in the contact carrying members each time the contacts are closed and, in a like manner, for a double-pole, double-throw switch, a total of 80 ounces must be stored in the contact carrying members at the time of closure thereof.

In order to store the aforementioned large amounts of energy in the deflectable spring members, it has been found that such spring members must be deflected to a considerable extent upon closure of the switch, resulting in very high bending moments which produce high stresses and severe wearing on the spring members, as well as other parts of the switch. Moreovenin the case of a time switch having a timing motor for the source of its actuating power, the motor must be able to develop the required high level of energy which, of course, results in high loading in the motor.

It has been found that in relying upon the energy stored in the contact carrying members for separating welded contacts, there are often practical limitations that prevent the use of this type of switch actuation without adding materially and significantly to the complexity, size and cost of the resultant switch. Moreover, it has been demonstrated that separation of the contacts resulting from the energy stored in the contact carrying members causes the contacts to physically pull apart from each other, which effect, over any extended period of time, will ultimately completely deteriorate the contact surfaces.

Therefore, it is a primary object of this invention to provide new and novel means for separating contacts of an electrical switch that may have become welded together during closure of the switch.

It is another object of the invention to provide simple and effective means for separating contacts of a switch that may have become welded together during the closure of the switch wherein the loading of the contact carrying members has been substantially reduced.

It is yet another object of the invention to provide novel contact separating means for a switch that may have its contacts welded together upon closure thereof wherein the forces for separation are developed only as required and with a consequent reduction in the size of any power source utilized to effect switch operation.

It is still a further object of the invention to provide novel contact separating means for a switch that may have its contacts welded together upon closure thereof wherein the welds are separated without any resultant deterioration of the contact surfaces.

In one aspect of the invention the improved electrical switch comprises a pair of electrical contacts adapted to move reciprocally relative to each other to open and close the contacts and mounted on a pair of closely spaced deflectable contact carrying spring blades. The blades have corresponding inner ends anchored to a fixed support and have corresponding outer ends free to move relative to each other for cooperation with a suitable switch actuating mechanism that produces the relative movement of the blades which causes the switch to open and close. A timing motor is utilized to drive the bladeactuating mechanism and this motor functions to deflect the spring blades relative to each other to cause the contacts to close.

After the contacts have been closed and some time prior to opening, the timing motor operates to further drive the blade actuating mechanism so that the blades are further deflected relative to each other to cause the contacts to move transversely relatively to each other. This transverse action produces a shearing force across the face of the contacts and in the event the contacts have become welded during closure, the shearing force so developed will effectively break the welds and permit the contacts to readily open.

All of the energy required for breaking the weld is furnished by the timing motor and is only furnished by this motor when so required. In this way, the switch could function for a prolonged period of operation without overloading the motor or the switch itself if no welds occur during such a period of operation.

in the case of those switches utilizing energy stored in the contact carrying members for weld breaking. It is true that when there is a weld, the timing motor has an addi-- tional load imposed thereon, but it has beenfound much more practical and less costly to use a smaller motor capable of handling intermittent high loads than to use a larger motor that is continuously loaded at all times.

The objects of the invention together with the benefits and advantages attendant thereto will be more fully understood upon reference to the detailed description following, particularly when taken in conjunction with the drawingsannexed hereto in which:

Figure 1 is a front view of a program timing device embodying the improved electrical switch forming the subject invention;

Figures 2 and 3 are partial end views of the programming device shown in Figure 1 illustrating the manner in Whichthe programming dial functions to select alternate switchpositions;

Figure 4 is an exploded view of the programming device shown in Figure 1 taken fromthe rear thereof;

Figures 5, 6, 7 and8 are similar views of the programmingdevice shown in Figure 1 taken from the front thereof'with a number of parts removed to show a single-pole, double-throw switch associated with the programming timer and which functions in accordance with the teachings of the subject invention, each view showing a different relative position of the switch.

Referring now to Figure 1, the programming timer device comprises a main supporting plate 9 having an electrical switch terminal block 11' secured to the bottom thereof by means of suitable screws 12 andon which is carried the rotatably mounted programming dial 13. The dial 13 is mounted in any convenient manner and is arranged to be driven by a gear train coupled to a timing motor afiixed to the rear of the plate 9. On the face of the programming dial, there is a 24-hour clock scale 14 surrounding which is a series of spaced radial slots 15 which are provided to removably receive a plurality of switch position selectors 16 which, as shown in Figures 2 and3, are in the form of key members that have their inner ends inserted through the apertures 15 and extending within the radial slots provided in an annular supportingmember 17 located behind the programming dial and spaced therefrom. The selectors 16 have inner and outer projections 18, 19 respectively, intended to cooperate with the inner ends of a pair of switch actuating cranks 21, 22 pivotally mounted on the rear of plate 9 and'having their inner ends extending through a suitable aperture in the plate. referred to asthe o crank, whereas the crank 22 may be referred-to as the on crank. As is shown in Figure 2, the selector 16 has been pushed downwardly so that its projection 18'will cooperate with the crank-21 to lift it as the selector-moves relative thereto. In Figure 3 the'selector is-shown in its alternate horizontal position wherein its outer projection 19 is in a position to cooperatewith the on crank to lift it as the selector moves relative tothe inner end of the crank.

Thus, the selector in either position will cause a limited pivotal motion of the cranks, the particular crank actuateddepending upon the position of the selector.

An indicating pointer 23 may be conveniently mounted on the programming dial to cooperate with the clock scale and function as an indicator of time.

The arrangement described so far is in all respects similar to the arrangement shown and described in the copending application in the name of Ralph M. Manning, filed December 27, 1954, Serial No. 477,903, entitled, Timing Mechanism, and issued April 29, 1958, as U. S. Patent No. 2,832,408, assigned to the same assignee to which the subject application is assigned. For a further description of this portion of the pro graming timer, reference'will be had to the aforesaid copending application.

Turning now to Figure 4, attention is first called to the cylindrical member 24 shown on the rear of plate 9 and this member is the sealed rotor and gear reduction unit forming a part of the well known Telechron synchronous The crank 21 may be convenientlymotor, the remainder of which has been omitted in the interests of clarity since such motors are well understood by those skilled in the art. The posts 25 on opposite sides of the member 24 serve as mounting arrangements for the motor. A pinion protrudes from the inner end of member 24 and extends through the plate where it engages the gear train utilized to drive the programming dial 13.

The cranks 21, 22 are pivoted about a stud shaft 26 and are biased by means of the springs 27, 23 respectively i such that the inner ends of the cranks are urged downwardly relative to the selectors 15.

A pair of slides 29, 31 are mounted for limited sliding motion in the grooved posts 32, each of the slides having notches 33 at its opposite edges surrounding grooves in the posts 32 and functioning as stops limiting motion in either direction transversely of the plate.

A driving arm 34 is pivotally mounted on slide 29 and has its pivot shaft 35 extending through slide 29 to lie within the notch 36 provided in slide 31. The outer end of arm 34- has a flange portion 37 extending through an aperture 38 provided in plate 9 and a spring 39 is provided to bias the arm 34 upwardly along the plate.

Mounted on the rear of switch terminal block 11 are a plurality of cantilever spring blades 41, 42, 43, 44 and 45 having their inner ends rigidly secured to the terminal block by means of similar base sections 46 and having their outer ends freely movable relative to each other and adapted to carry similar electrical contacts 47. The base sections 46 have been shown fully in Figure 4 only in connection with blade 41, the others being cut away or only partially shown in the interests of clarity. Such base sections comprise the bottom strip 46:: having its outer end turned up to form the outer mounting flange 46b adapted to overlie the terminal block 11 at the front thereof, and its inner end turned upon along one of its edges to form the blade 41 on which is formed the inner mounting flange 460. The inner flange an is adapted to overlie the terminal block at the rear thereof, and both of the flanges have suitable apertures 46d aligned with apertures in the terminal block to permit the base sections to be securely attached to the terminal block by means of rivets 4oe or. the like. The blades and their associated base sections are thus formed as a single piece and, if

desired, the blade portion may be ribbed to give added ruggedness to this part of the switch.

The tips of the blades 41, 43and 44 are notched and.

are intended to lie within the notches 43, 49. and 51 provided in the lower edge of slide 31 and in a like manner the tips of blades 42. and 45' are notched and are intended to lie within the notches 52', 56 provided in the lower edge of slide 29. All of the blades are biasedto the left of the plate 9 as viewed in Figure 4, which, in the absence of any restraining force on the slides 29, 31, will carry both of the slides to their extreme left position within the grooves of the posts 32. An auxiliary biasing spring adds further bias in this direction for slide 29.

A steeply inclined cam 53 is attached along the upper edge of slide 31 by suitable screws 53a or the like for cooperation with the transversely extending pawl 54 The arrangement of parts described so far, except forthe configuration of cam 53, is similar to the mechanism shown and described in the copending'application filed December 20, 1955, Serial No. 554,201, in the name of Manning et al., entitled, Time Switch, issued December 10, 1957, as U. S. Patent No. 2,816,184 and assigned to the same assignee to which the subject application is assigned. For a more detailed description of this portion of the programming timer, reference will be had to the aforesaid Manning et al. copending application.

The switches mounted on the terminal block 11 and intended to be controlled by the programming device may mechanism for the switch, including the slides and steep cam 53, has been devised to produce a positive shearing action prior to opening of the contacts such that any welds formed between the contacts are easily separated.

As an indication of the effectiveness of the switch, it

is to be noted that the Underwriters Laboratories requirements for a switch rated at 35 amperes tungsten load call for 6000 successful operations at the rated load. The switch forming the subject invention has been successfully operated at 50 amperes tungsten load for as many as 7800 continuous switch operations without once having switch failure because of welded contacts, and there is no reason to believe that welds occurring at even higher currents (on the order of 100 amperes) could not be effectively separated in accordance with the teachings of the present invention. The manner in which the shearing action effectively separates any contact welds will be best understood upon reference to Figures 5 and 8 inclusive. Thus, in Figure 5 the switch blades 41, 42, 43 are shown as forming a single-pole, double-throw switch and the position of the switch is such that the contacts on blades 42, 43 are closed and contacts on blades 41, 42 are open. The driving arm has moved upward to its normal position adjacent to the lower end of crank 21 and the pawl 54 is resting on the upper edge of cam 53. In this position, it is possible that the contacts carried by blades 42 and 43 have become welded together. In this position of the switch the ofl? crank 21 will be ineffective to cause switch actuation, but the on crank 22 when actuated by one of the selectors on the programming dial 13 will move the driving arm 34 to the left as viewed in Figure 5, carrying with it both of the slides through the interconnection of the driving arm shaft 35. It is well to point out here that the designations on," off have little meaning in connection with a single-pole, double-throw switch, but since the terms are helpful in describing the action of the switch, it is believed that continued use of these terms is in order.

The next position of the switch is shown in Figure 6 illustrating the relative positions of the switch blades after the blades have been driven to the left by the arm 34. Both of the blades 43 and 42 have been further deflected relative to each other and in so doing, their contacts 47 have moved transversely relative to each other to develop a shearing force which effectively separates any welds therebetween. The contacts carried by blades 41 and 42 are open in this position of the switch.

Upon further motion of crank 22, the slides will be moved together slightly further to the left in which event the pawl 54 drops off of cam 53,'disengages the driving arm 34 from crank 22, holds the slide 31 and lets the slide 29 return to its original position under the driving force furnished by the biasing action of spring blade 42. The slides have thus been moved relative to each other and this position of the switch is shown in Figure 7 wherein the contacts carried by blades 42, 43 are now open and those carried by blades 41, 42 are now closed. Here again, the contacts that are closed may become welded together and it is noted that in this position of the switch, crank 22 is ineffective to cause actuation since the driving arm is held out of engagement therewith by pawl 54.

The next switching action will be under the control of selectors 16 that have been set in the off position to cooperate with the off crank, and when the program-"1 ming dial moves such a selector to so cooperate with crank 21, the crank will be rotated clockwise as viewed in Figure 8 and attempt to lift its pawl out of its holding position. However, as is seen in Figure 8, the slope of cam 53 is such that the cam surface interferes with the normal lifting action of the pawl, and the pawl must positively drive the cam 53 out of its path before it can be lifted to its normal position on top of cam 53. In so driving cam 53, the blade 41 is deflected further toward blade 42, carrying with it blade 42, which in turn is also deflected to the left, the relative deflecting action between the two blades creating a transverse mation of the contacts carried thereby relative to each other such that a shearing force is developed to separate any welds formed between the contacts. Since the blade 43 also deflects to the left, the contacts carried by blades 42 and 43 will remain open during this phase of switch operation.

Upon further actuation of crank 21, the pawl 54 will ultimately clear the cam 53, thus permitting the switch to return to the position shown in Figure 5.

From the above, it is seen that for either set of contacts mounted in the single-pole, double-throw switch, there is a positive shearing force developed just prior to opening of these contacts. Moreover, the shearing force so developed is quite substantial in view of the mechanical advantage derived from the arrangement of the blade actuating members relative to the blades. That is, the relatively small force applied transversely to the tips of the blades to cause a relatively large deflection thereof will result in a relatively large force applied transversely along the face of the contacts to cause a relatively small weld separating transverse displacement of the contacts.

Since the contact blades are securely mounted on the terminal block, being literally wrapped around the edge thereof and having the inner and outer mounting flanges riveted together through the block, and, further, since the blades themselves are sufliciently rugged, being ribbed for added strength if so desired, the shearing force de- Of course, if there are no contact welds produced, there will be no shearing forces developed and, the contacts will simply slide relative to each other upon actuation of the switch. In other words, the shearing force is only .developed when required to separate welded contacts,

and for this reason, the switch components are not continuously loaded during operation thereof, but only when necessary to separate welds.

With the arrangement described above, and in the case of a single-pole, double-throw switch, it has been found that for normal operation of the switch, and in the absence of any welds, the timing motor will have to furnish a force of approximately 4 ounces to the contact blades when the contacts are closed, such 4 ounces being sufficient for maintaining proper contact pressure- In contrast, if the switch were functioning such that any contact welds were to be separated by pulling forces developed by energy stored in the blades upon closure of the contacts, it has been found that the timing motor would have to furnish a force of approximately 40 ounces to the contact blades each time the contacts are closed, whether or not any welds result upon closure.

Therefore, under normal conditions of operation and without any welds occurring upon contact closure, the loading on the blades and the timing motor has been reduced to one-tenth of the normal loading required when the blades themselves must function to separate contact welds.

Of course, as and when welds occur, there is a momentary increase in the loading on the timing motor and the blades, but such increased loading can be adequately handled with the use of a smaller motor and less rugged blades than would be required were the loading present for each closure of the switch contacts. That is, if the blades themselves must have energy stored therein to separate contact welds, it would be necessary to use a substantially larger motor and 'more rugged blades to achieve a switch life that is comparable to the switch life achieved. with the present invention.

In other words, the timing motor and the switch blades, together with other associated structure utilized in accordance with the teachings herein could probably be adapted to providevweld separations by the use of energy stored inthe blades, but in such event, the switch would rapidly wear out because of the continuous sustained loading thereof.

It is thus an inherent advantage of the present invention to provide a smaller and less rugged overall switch design than was heretofore possible to handle currents producing contact welds upon closure of the switch, resulting' in a smaller, more compact, and substantially less costly switch.

As has been demonstrated above, the shearing action provided to separate contact welds is effective for any combination of switch blades, from the simple singlethrow arrangement to the more complex double-throw arrangements, with single or. plural poles.

Moreover, although the invention has been illustrated in connection with a switch forming a part of a programming timer, it is to be understood that the invention is not limited in its application to such anarrangement, it being capable of use with any time switch having a blade actuating mechanism similar in principle to that shown and described. Furthermore, although the switch has been shown herein with a pair of relatively movable slides provided to cause deflection of the blades, it is to be understood that other forms of blade deflecting members could be used so long as the force of deflection is applied substantially transversely relative to the tips of the blades, and that such deflection can be effectively utilized to produce a shearing force that will separate contact welds.

Therefore, while a particular embodiment of the subject invention has been shown and described herein, it is in the nature of description rather than limitation, and it will occur to those skilled in the art that various changes, modifications, and combinations may be made within the province of the appended claims, and without departing either in spirit or scope from this invention in its broader aspects.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical switch including a pair of electrical contacts adapted to move reciprocally relative to each other to cause closing and opening of the contacts, a pair of contiguous deflectable cantilever spring blades on which said contacts are mounted, corresponding inner ends of said blades being fixed and corresponding outer ends of said blades being free to move relative to each other, means movably engaging said blades at said outer ends comprising a movable member adapted to move at substantially right angles to said blades to deflect said blades and the contacts mounted thereon and having associated therewith holding means for. restraining said movable member after said electrical contacts are moved thereby to a closed position, said movable member having associated therewith switch actuating means operating after closure of said contacts and just prior to opening thereof to move said blade engaging means to deflect one of said pair of blades toward the other blade and then away from said other blade to cause said contacts to move transversely relative to each other to shear any weld produced therebetween upon closure thereof.

2. The timeswitch as defined in claim 1 wherein said switch actuating means includes a cam member in operative connection with saidimovable member and a relatively movable switch actuator adapted to provide in cooperation with said cam member said holding means and to provide the said relative blade movement through movable engagement therebetween.

3. An electrical switch including at least two electrical contacts adapted to move reciprocally relative to each other to cause closing and opening of the contacts, at least two contiguous deflectable cantilever spring blades on which said contacts are mounted, corresponding inner ends of said blades being fixed and corresponding outer ends of said blades being closely spaced from each other and free to move relative to each other, said contacts being mounted on said free ends, a pair of movably mounted members each engaging at least one corresponding tip of said free ends of said blades and adapted to move relative to each other and at right angles to said free ends to deflect one of the blades toward one other to cause two of said contacts to close, and driving means including a timing motor for moving said blade engaging members, said driving means operating after closure of said contacts and just prior to opening thereof to further deflect said one of said blades toward the other of said blades to cause said contacts to move transversely relative to each other to shear any weld produced therebetween upon closure thereof.

4. Thetime switch as defined in claim 3 wherein said blade engaging members are adapted to be moved to a position wherein said contacts are in a closed position and retained thereby by holding means comprising a cam secured to one of said blade engaging members and a switch actuating member whereby upon subsequent actuation of said switch actuating member just prior to the opening of said contacts said switch actuating member cooperates with said cam to move said one blade engaging member and the blade engaged thereby toward the other blade so as to cause the said movement of said contacts transversely relative to one another, and upon further movement of said switch actuating member relative to said cam said blade engaging members are actuated so as to move said blades away from each other to an open contact position.

5. The time switch as defined in claim 4 wherein said switch actuating member comprises a pivotally mounted pawl actuated by adjustable switch selectors with the slope of said cam surface being such that the cam surface interferes with themovement of the pawl from said closed position todrive the cam and the associated blade engagi relative to each other, said first pair of contacts being mounted on the free ends of said first and second blades and second pair of contacts being mounted on the free ends of said second and third blades, a pair of members engaging the free ends of said blades and adapted to move at right angles thereto with one of said members engaging the tips of said first and third blades and the other of said members engaging the tips of said second blade to deflect said blades relative to each other to either close said first pair of contacts and open said second pair of contacts or open said first pair of contacts and close said second pair of contacts, and driving means in cluding a timing motor for moving said blade engaging means, said driving means operating after closure and prior to opening of either pair of contacts to further defiect said blades relative to each other to cause the closed contacts to move transversely relative to each other to shear any weld produced therebetween upon closure thereof.

(References on fell-swing page) 9 10 References Cited in the file of this patent 1,303,161 Cavanagh May 6, 1919 2,142,462 Teeple Jan. 3, 1939 UNITED STATES PATENTS 2,270,513 Dettar Jan. 20, 1942 1,048,670 Fessenden Dec. 31, 1912 2,308,729 Walter Jan. 19, 1943 1,299,457 Gray Apr. 8, 1919 6 2,690,526 Morrison -2 Sept. 28, 1954

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