US 3781502 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
United States Patent Schumacher et a1.
MERCURY SWITCH WITH HEAT SINK CONTACT Inventors: Walter C. Schumacher, Warwick;
Ralph L. Graves, East Greenwich, both of RI.
General Electric Company, Providence, RI.
Filed: Apr. 28, 1972 Appl. No.: 248,407
US. Cl 200/226, 200/166 K, 200/221 Int. Cl. H01h 29/20 Field of Search 200/226, 227, 228,
References Cited UNITED STATES PATENTS 1/1939 Sumbleson 200/222 X Dec. 25, 1973 1,857,202 5/1932 Lee 200/166 K 1,149,054 8/1915 Hoppe et al. 200/166 K 3,415,965 10/1968 Coutant 200/222 Primary Examinerl-Ierman J. Hohauser Attorney-Paul E. Rochford et a1.
[ 5 7] ABSTRACT 16 Claims, 17 Drawing Figures 1 1/Z8 32 52 l I l i 60 MERCURY SWITCH WITH HEAT SINK CONTACT CROSS REFERENCE TO RELATED APPLICATION This application relates to application Ser. No. 248456 filed Apr. 28, 1972, Attorneys Docket 58WD- 1105 of Walter C. Schumacher, owned by the same assignee' as this application.
BACKGROUND OF THE INVENTION Many types of mercury switches are known in the art including small switches employed in switching signal levels of current and large mercury relays having magnetically operated plungers used in switching electric power supply to large industrial equipment.
The switches most closely related to the present invention employ a mercury button as the circuit control element. The switches have an insulating casing attached. to a metal mounting strap for mounting the switch within awall box. The insulating casing also has externalscrew terminals and internal contacts, with a mercury button held between the contacts, and a pivot mechanism controlled by an externally extending trigger.
The. mercury buttons have liquid mercury sealed within an hermetically sealed envelope made up a cylindrical metal shell having one closed end, and a three element closure element welded to and sealing the other end. The closure element is made up of an axially extending electrode or contact extending through and bondedto an annular glass insulator, and a metal rim bonded to the outer perimeter of theannular glass insulator.
An internal liner bonded to the glass insulator can divide. the mercury into two pools when the button is placed in operating position. When the button is rotatedto its open position the mercury is separated by the liner into two pools one contacting the metal shell, which serves as one electrode, and the other contacting the electrode extending through the glass insulator. When rotated to its closed position the mercury extends through a hole through the liner and forms a single continuous pool which completes the circuit betweenthe electrode and metal shell.
Control over the separation or joining of the mercury pools is typically exercised by an operating means such as one having a trigger'extending from the insulating casing-of the switch which means can be employed to pivot the mercury button about its cylindrical axis between the switch open and switch closed positions.
Mercury buttons and mercury switches have been known in the art for a number of years extending back to patents such as US. Pat. 3,101,093 and several others which were granted in the 1930s. Improvements have been made in mercury buttons and in the switches in which mercury buttons are employed since their early introduction in commerce to improve product performance in response to the changing functions which these and other switches must perform. Some improvements in mercurey buttons and mercury switches are concerned with the control of higher levels of electric power as for example the power normally supplied for use within residences or commercial buildings. It is well known that the level of use of electric power within homes, factories, schools, banks, etc. is continuously increasing as the level of lighting and the use of apparatus run by electric power is increasing.
Accordingly, there has been a need over a period of years to increase the power switching capabilities of switches employed in buildings from the lower values which were satisfactory when mercury buttons wer first developed in the 1930s to the present time when the higher loads of air-conditioners, heaters, office machines, and other conveniences are employed within buildings. The improvement in the electric power switching capacity of mercury switches and of mercury buttons within mercuryswitches has been a particularly difficult technological problem to solve. In part this is due to restrictions on the size of the switch, and accordingly on the size of the button within the switch, which restrictions are imposed by the standardization of electric supply and distribution devices used within buildings. I
Devices such as switches installed within buildings to be used by occupants in control of lighting and other electrical apparatus are preferably of a size which permits them to be included together with electric wires and connectors within the conventional metal wall boxes. These metal wall boxes are themselves quite small and of a standard size so that the wiring devices of any manufacturer will fit into the wall box of any other manufacturer based on the standards established and used in the industry. The actual opening within a conventional metal wall box is a rectanguloid about 1.75 inches wide by 2.75 inches high by 1.5 to 2.5 inches deep. Were it not for this restriction, it might be feasible to increase the switching capacity of mercury switches by enlarging the switches and the amount of mercury contained therein to a larger size which'can accommodate the higher power.
Larger mercury switches such-as relay switches and the like can be used in industrial applications where size is of no importance. However, such larger switches used for control of higher levels of electric power are very costly and are not economically useable within the walls of residences or buildings which are subject to conventional building codes.
It is known in the art that there are commercially available mercury tilt switches of recent manufacture which have a stepped switching capacity,which capacity increases in steps both with the size of the switch structure and also the amount of mercury contained within the tilt switch structure. Such a switch is conventionally formed with an open ended generally cylindrical outer shell of steel and an insulating enclosure for the open end having an electrode extending through the insulating enclosure. Such a conventional switch which has a switching capacity for 1,600 watt load will be approximately 2 and 9/64th inches in length and 0.600 inches in diameter. By contrast, a US. Pat. 3,451,965 assigned to the same assignee as this application teaches a cylindrical button having an axial length of only one half of an inch and having an outer diamter of three quarters of an inch to be capable of handling a 1S00 watt Ianip load and aEcordingly to have a switching capability of the much larger conventional mercury tilt switch.
A central problem in the improvement of mercury switches is that of increasing their capacity for the switching of electric power without at the same time increasing their size to a point where they no longer fit within the conventional wall boxes of standard buildings. While some increase in size is possible, it is undesirable because less room is then available for the wires and wire connectors which must extend from the wall box during installation of the switch and which must be folded back into the box when the switch is mounted into operating position in the box. v
In the past ten years, several patents have issued to the assignee of this invention directed to improvements in the fabrication or construction of mercury switches and mercury buttons designed to improve the capability and reliability of operation of these products within the restrictions imposed by building codes and electrical codes. Such U.S. Pats. include: 2,916,589; 2,929,902; 2,956,656; 3,032,633; 3,109,079; 3,089,937; 7 3,229,354; 3,265,844; 3,327,084; 3,415,965.
It was known from experience gained in conducting tests on the mercury button disclosed and claimed in the US Pat. No. 3,415,965 assigned to the same assignee as the subject application that the mercury button having the features described and claimed in the patent could switch currents of 15 amperes at voltages of 277 volts through extended periods of time with little more than 3 grams of mercury. This higher power operation represented significant improvements over buttons which had the capacity for switching alternating current power at ratings of 10 amperes at 277 volts where the amount of mercury contained was slightly less than 4 grams. Expressed in terms of watts per gram, the improvement in switch performance is from about 700 watts per gram to over 1,300 watts per gram.
Another requirement which a mercury button and mercury switch must meet in qualifying for commercial use as a wall switch in residences or in other buildings is that of being produced at a reasonable cost but also with a high level of reliability of performance. With particular reference to the factors affecting costs, one of these factors is the produceability on a large scale with a relatively low number of reject of defective units. Efforts to produce the mercury button substantially of the construction disclosed in US. Pat. No. 3,415,965 in large quantities by manufacturing processes having reasonable costs, and to use these buttons in me'rcury switches such as the switch dislosed and taught in US. Pat. 3,265,844 of the same assignee, proved to be difficult and to lead to higher costs and lower performance capabilities than are acceptable in switches produced for use in conventional wall boxes.
In particular it was found that excessively large numbers of such buttons when tested in wall switches such as that of the'3,265,844 patent led to excessive rise in temperature of the button and switch and eventually led to failure of the button due to an are or prolonged flow of arcing current through the switch. It should be emphasized that while it remains possible to form mercury buttons having the structure taught in the 3,415,965 patent which buttons have the capability described in the patent, that the cost of producing buttons having this capability was found to be excessive when the factor of defective buttons or buttons of substandard performance capability is taken into account in computing cost.
While numerous buttons of the 3,415,965 patent, when tested in the switch of the 3,265,844 patent, gave unique results in demonstrating the capability to switch ampere currents of 277 volts on a sustained basis there were still fewer of such button which could pass additional Underwriters Laboratory tests for a switch rating of 15 amperes and 277 volts. For a switch to have this rating it must be capable of performing on-off switching cycles with a voltage of 277 volts and SUMMARY OF THE INVENTION It is accordingly one object of the present invention to provide a mercury switch of improved power switching capability.
Another object is to provide a high performance mercury switch of smaller overall size.
Still another object is to provide a switch capable of a large number of switching cycles.
A further object is to provide a switch capable of reducing the level of arcing which occurs in a mercury button used therein.
Still a further object is to provide a mercury switch which affords a higher power switching capability at lower cost. 1
One way in which the invention may be carried out is by providing an insulating housing'having bottom, end, and side walls, and by providing two contact strips mounted within the housing proximate its side walls. The contacts have disposed between them in spring biased relation a generally cylindrical mercury button, the axis of the cylinder being aligned generally normal to the side walls of the housing. The mercury button has an electrical contact axially extending from an annular insulating closure in one of its end faces into pressure contact with a generally conforming recess in the proximate portion of a first of the contact strips. The button also has a substantial-flat area of its opposite end face and this flat area is biased into pressure contact with a conformingly flat area of the second of the contact strips. The portion of the second strip extending between the flat area and the screw terminal provides a path for the flow of heat energy at a high rate.
Other objects and advantages of theinvention will be in part apparent and in part pointed out in the description which follows.
The manner in which these and other objects of the invention may be achieved will be made clearer in the description which follows by reference to the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exterior side elevation of one form of switch housing showing part in phantom and illustrating a manner of affixing a mounting strap to a housing.
FIG. 2 is a front elevation a switch as illustrated in FIG. 1 with the mounting strap and trigger removed showing the relation of one form of a mercury button to contact strips.
FIG. 3 is an enlarged vertical section in part in phantom of a switch as shown in FIG. 1 illustrating the internal positioning of several elements of the switch.
FIG. 4 is a horrizontal section of a switch as illustrated of FIG. 2 with the strap and trigger removed.
FIG. 5 is a perspective view of a portion of a switch as in FIG. 3 with parts cut away to show the relationship of internal portions of the trigger to the contact strips.
FIG. 6 is an exploded perspective view of certain internal elements of the switch.
FIG. 7 is an exploded perspective view showing the relation of the internalstructure of the mercury button to the heat receiving portion of another form of contact strip usable in the switchof the present invention.
FIG. 8 is a perspective view of a modified contact element having a shortened heat path.
FIG. 9 is a profile view of a mercury button for mounting between contact strips.
FIG. 10 is a similar view of a button illustrating its relation to contact strips shown in section.
FIG. '11 is a front elevation of a modified form of switch.
FIG. 1.2 is a side elevation of the modified switch of FIG. 11. 2
FIG. '13 is an enlarged front elevation of the modified -switch with strap and trigger omitted as in FIG. 2.
-FIG. 14 is an enlarged side elevation with the casing in part broken away to illustrate the relation of some parts FIG. 15 is an exploded perspective view of a modified form of heat sink contact shown in relation to a button.
FIG. 16 is a horizontal section similar to that of FIG. 4 showing some switch elements assembled within the insulating casing.
FIG. 17 is a perspective view of a spring element employed in the modified switch.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1 an external view of a switch is given in its normal operating position when mounted in.a wall. The switch is shown in actual size and a compactness, achieved as is explained below, is evident by comparison to switch housings of other mercury switches particularly prior art switches of lower or equivalent power rating. The switch includes an insulating housing 12, a mounting strap 16, and a trigger 22.
One screw terminal 14 is evident on the side of the switch shown and another is also located catercornered to that shown on the opposite side of the switch. An economical means for mounting the strap l6to the switch housing 12 is by the conventional bosses 18 folded over conforming recesses 20 in the end walls of the housing.
Trigger 22 is shown in the at-rest OFF position and is shown in phantom in the at-rest ON position. Through use of a mercury button such as that taught in US. Pat. No. 3,415,965 the switch is rendered invertible and in such case the up position of the trigger will be the ON position in either orientation and similarly the down position will be the'OFF position.
Turning now to FIG. 2, the strap 16 and trigger 22 of .FIG. 1 are omitted and the placement of some of the other elements within a switch is shown.
The insulating housing 12 is seen to have side walls 13 and end walls 15 defining a chamber within the housing. Two contact strips 24L and 24R are mounted in the chamber with their long dimension extending along the longer side walls 13 of the housing, and are spaced from side walls 13 sufficiently to permit the strips 24R and 24L to be flexed outwardly in a direction generally normal to their long axis. The strips 24R and 24L are mounted in insulated relation in said chamber in conventional recesses and slots formed integrally with the side, bottom, and end walls of the housing.
The screw terminals 14 are located at side openings 11 in the housing walls to provide tool access to the screws thereof to permit electric supply wires to be securely fastened to the terminals.
Fiber inserts 28 seen in FIGS. 2 and 3 are mounted in slots 30 in side walls 13 and serve to hold the contact strips 24R and 24L in place in the housing. The inserts 28 are retained in place by the mounting strap 16 and this retaining ensures against contact of either contact strip with the mounting strap 16. Alternatively the holding down of contact strips 24R and 24L may be accomplished by hold down bosses built onto the trigger as explained more fully below and in such case the inserts 28 may be omitted.
A mercury button 32 as sused in this switch has a generally cylindrical metal shell 33 with a closed end 38, giving it a general cup shape seen best perhaps in the perspective view of FIG. 6.
A closure for the open end of the cup shaped shell 33 of button 32 includes an electrode 34 protruding axially from an annular glass insulator held within a metal rim 36 as more fully described in the US. Pats. 3,327,084 and 3,415,965 of the same assignee as this invention.
The outer end of electrode 34 maybe seen from FIGS. 2 and 4 to extend beyond the outermost reach of the rim 36 of the button closure. Accordingly, when the button is inserted in place between the contact strips 24L and 24R the srip 24R is indirect electrical contact with the closed end 38 of button 32 but is maintained at an air gap insulating distance from the rim 36 of button 32.
The contact of the closed end 38 of the cup shaped shell 33 of the button 32 with the contact strip 24L may be seen to be quite different from the contact of the stem like electrode 34 with strip 24R. This contact of the fiat surface of closed end 38 with the flat portion of strip 24L, and the maintenance of effective heat transfer contact between the surfaces, has been found surprisingly to be vitally important to the capability of the switch to operate at higher levels of power and particularly to interrupt current flow at higher levels of voltage and amperage.
What is deemed unique is the finding that a mercury button which has lower power switching capability when employed in the switch of paten t 3,265,844 has ii substantially higher switching capacity when employed in the switch of this invention. What is more the higher switch rating, i.e., the capability for switching higher wattages, is accomplished within a switch having appreciably smaller overall volume for its switch housing than the switch of the 3,265,844 patent. In large part, the improvements in switch operation are due to improvements made in the transfer of heat generated within the button.
Regarding transfer of heat pursuant to the present invention improved heat transfer may be provided in part by the provision of an improved electrically conductive heat sink directly against one surface of the button. By itself, provision of this electrically conductive heat sink is important because it places a metal element of high heat conductivity directly against a surface of the shell where heat is produced as a result of operation of the switch. This relation of heat sink to shell surface effectively reduces concentrations of heat at localized hot spots of the shell where it has been found that such hot spots are likely to be formed.
It has been found possible through use of heat sinks persuant to this invention to remove heat from such hot spots at such a rate that the spot does not become ex cessively hot. By excessively hot is meant a heating which results in decreased operating efficiency or damage to the button, including eventual failure of the button through its destruction or otherwise. Further it has been observed that there is greater probability of arcing and continuation of arcing to destruction of the button where heat is not removed from locally overheated spots of the button shell than where such spots are in contact with heat sinks providing for more effective transfer and dissipation of heat from such hot spots and in this way reduction in the temperature of button metal exposed to internal arcing as a result of button operation.
This removal of heat and resultant improvement in operation has been found to be possible for buttons of a construction which had been shown through tests to become excessively heated in switches which did not utilize such heat sinks.
An important guide in the provision of a heat sink for the button is. based on the discovery that there are certain portions of the metal shell which ae more likely to be intensely heated than others, and that preservation of the button from the destructive effects of such heating, as by arcing, can be accomplished by providing more effective removal of heat from these spots.
With reference to the button of FIG. 6 for example, it has been found that one portion of the steel shell most likely to be overheated locally is a portion directly opposite the through hole 41 of the ceramic liner 43 of the button.
The through hole 41 is the hole through the ceramic liner 43 of the button into which the two bodies of mercury flow in making contact when the switch is closed and from which they flow when the switch is opened and the single mercury pool is separated into two separate pools, one on either side of the ceramic liner.
For a button constructed similarly to that described in US. Pat. 3,415,965 (but omitting any nipple from closed end 38) the through hole is located opposite approximately the position 40 shown in dotted outline on the closed end 38 of the button 32.
While the structure of the contact as shown in FIGS. 2, 4, and 6 is fully adequate to provide removal of heat for operation at appreciable levels of amperages and voltages, it is preferred that the heat sink portion such as 42 of strip 24L be enlarged, and particularly be large enough to cover the area,such as area 40 of closed end '38, which is swept by the portion of the shell opposite a through hole of the contained ceramic liner as the button is rotated from its ON to its OFF position.
It will be understood that the present invention contemplates a heat sink disposed in direct contact with that portion of the steel shell of a mercury button such as portion 40 of FIG. 6 which is aligned with the through hole within the button. Further the heat sink is formed to providesuch direct contact in all positions in which a portion such as 40 of H6. 6 may be disposed as the button is pivoted to perform actual switching action.
It will further be understood that this relationship of the disposition of the heat sink in close thermal contact with the indicated portion of the steel shell will yield the improved switching performance of the button without limitation to a particular button construction of to a particular through hole placement. Also improved heattransfer may be attained by providing a heat shunt, or shortened heat path, from the wire terminal to the indicated portion of the heat sink without limitation to a particular form of mercury button employed or location of through hole in the ceramic liner of the button.
A mercury button such as thatillustrated in FIGS. 2, 4, and 6 is seen to have a closed end 38 which is the flat bottom face or surface of the cup shaped metal shell 33 of button 32. It is also evident that in these figures not all of this surface of closed end 38 is in direct contact with the heat sink portion 42 of contract strip 24L. While it is desirable as is explained above that the strip have appreciable mass proximate the button for heat sink purposes, it is not necessary that the entire flat surface of the closed end 38 of the button be contacted. Rather what can be done to provide effective heat dissipation by selectively contacting those areas of the surface of closed end 38 most likely to be overheated.
In order to obtain more effective heat transfer it is desirable that the metal through which the heat is to be transferred have a high heat transfer coefficient. A -30 brass as normally used as the brass of a contact strip, for example, has a higher heat transfer coefficient than the steel normally employed in the button. Use of brass in the contact strip is desirable for transfer of heat. Use of copper-iron, or other copper alloys including brasses such as -15 brass with higher electrical conductivity is contemplated in carrying out the present invention.
Further it is desirable to have a relatively high contact pressure between the button and the contact strip heat sink. However, as the pressure between the strip and button is increased, and also as the area of contact is increased, there is a tendency to increase the friction between the button and contact strip to a level at which the smooth low effort motion of the trigger is reduced.
This increased friction can be in part reduced by use of very flat surfaces and also by use of lubricants on such surfaces. High load, high temperature greases with high thermal stability and melting points above about 500F are useful for this purpose.
Alternatively where the contact pressure and friction between button and heat sink surfaces result in reduction is smooth motion of the trigger, what can be done to reduce friction is to reduce the area of contact of the heat sink against the button without reducing of the heat sink mass and without extending the length of the heat flow path to the binding post.
An important factor here is that, pursuant to one aspect of this invention, maintenance of contact at a higher pressure can be accomplished on those portions of the button face left in contact with the heat sink where the contact is between heat sink and those portions of the button face most likely to receive the higher heating as a result of switching operation of the button.
In other words, the total pressure between the contact strip and button surface can actually be reduced while at the same time increasing the pressure between the portions of the heat sink and button which are in contact. This contact pressure can be increased by forming the heat sink to permit pressure to 'be applied selectively at those portions of the closed end 38 of button.32 where higher heating is most likely to occur.
Forexample with reference to reducing the contact area without reducingthe effectiveness of heat transfer, portions of the heat sink surface confronting the button may be depressed so as to be spaced from the button surface. When the actual area of a contact strip making. contact with a closed end such as 38 of mercuryrbutton 32 is reduced in this way, the metal of the sinkout of contact with the buttons still performs the .heat absorbing and heat transmission and dissipation function. This is so because heat received by heat sink portions in contact with the button may be quickly transmitted to the adjoining portions spaced from and out of direct thermal contact with the mercury button particularly where the heat sink itself is formed of a materialhaving a higher coefficient of heat transfer.
Where areasof the heat sink are formed so as to be depressed out of contact with the button, care must be exercised to avoid having the button or heat sink shift within the switch so that the heat receiving areas of .the button and heat absorbing contact areas of the sink are .not in registry. Also, it is important that neither the button nor .the heat sink be tilted where the tilting results in the flat contact portions of the heat sink being out ofgoodithermal contact with corresponding portions of the button. In order to optomize the effectiveness of the heat transfer contact .at least three spaced contact zones are formed on the heat sink. This form of heat sink surface is illustrated in FIG. 7.
Referring to FIG. 7 a round enlarged heat sink portionr80of a contact strip is seen to be formed in a central portion of a contact strip 24A. This portion 80 may have, for example, essentially the same effective diameterasthat of a button closed end 39 surface to be contacted. Only three areas are formed on the heat sink portion 80 for contact with the flat surface. These are thecrescent shaped larger raised flat area 82 and the two additional smaller flat areas 843 and 86 which, in this case, are shown to be circular in shape.
One consequence of providing the three raised flat area for contact with the flat surface of closed end 38 .of button .32 is that inasmuch as three points determine a'plane assistance in automatic paralleling of the flat .areas of the button to the flat of the heat sink is achieved. This isin part the result of the suspending of the button under spring pressure from one point along its axis on one side and from three points on the opposite side between spring biased contact strips such as 24A on onesie and another strip, not shown, on the opposite side of button 32.
Another advantage of this mode of mounting a button in :the switch structure of this invention is the in- :creased contact pressure between the button and the heat sink in those areas where the contact is most needed.
Inthis-regard, and with reference to the form of heat sink shown in FIG. 7, the crescent shaped raised area 82 corresponds to the area of the heat sink which is contacted-by the portion of closed end 38 of button 32 aligned with the through hole extending through the ceramic liner of the button. Accordingly, no matter what position the switcy trigger is in, anywhere between a full ON and full OFF position, the portion of the closed end 38 aligned with through hole 42 of button 32 will be in closepressure contact with the same part of crescent shaped raised area 82 of the heat sink.
It is not essential that the heat sink surface he parallel to the internal side surface of the switch housing so long as there is a close contact of the flat 'surface'of the closed end 38 of button 32 with the corresponding heat receiving flat surface of a heat sink.
To improve positioning ofthe heat sink in the switch housing and particularly to give the heat sink good spring support in the housing the contact strip may be given an H form by including an H pattem'of support arms extending out from an enlarged central heat sink portion. Such a contact strip 90 having the H configuration of arms is shown in FIG. 8.
As is evident from FIG. 8 two of the arms 92 and 94 occupy positions extending out to each side of the central heat sink. Of the two remaining .arms, a first arm 96 may serve as heat shunt and may-for this purpose be connected directly to the binding post 97 of the switch. The remaining support arm 98 completes the H configuration of support arms of the contact strip 90. S upport arm 94 is provided with a brace 100 and support arm 92 with a brace 104, each of'which is stepped back out of the plane of the strip 90 to brace the central sink 93 for spring deflection toward the wall of the switch housing. Contact strip 90 and its various arms and braces may be supported from appropriate'pedestals, slots, or
bosses formed integrally with an insulating housing not shown. For the form of contact strip 90 shown, however, there would be no support of the housing directly behind the central heat sink portion 93 but this central portion is formed to be supported by its arms 92, 94, 96, and 98 and will be able to deflect slightly in a direction generally normal to the plane of central heat sink portion 93.
With regard to the spring pressure developed between'the contact strips and a mercury buttonit will'be appreciated that it is not necessary that both strips be capable of spring deflection. Adequate pressure for both heat transfer and electrical conductivity purposes may be derived from the spring bias of a single contact strip imparting a sufficient spring pressure to the button to make it bear against both contact strips with the needed pressure.
It will also be clearthat other spring biasing means may be used to develop the needed pressure. However, the use of the contact strips for'this purpose has the advantage of low cost coupled with simplicity of construction and reliability of operation.
With further reference to FIG. 8 three raised flat areas including crescent shaped'flat area 106 and two smaller and generally round flat areas 108 and 110, serve essentially the same purposes as the raised flat areas 82, 84, and 86 of heat sink of FIG. 7. The areas in FIG. 8 are seen from the side of heat sink contacted by a closed end 38 of .a mercury button whereas heat sink 80 is seen from its opposite side.
The heat sink 80 of FIG. 7 and heat sink 93 of FIG. 8 are not usable as shown in making contact with the opposite electrode of a mercury button such as 32 of FIG. 7. This electrode has the form of a stem such as H12 of FIG. 9 and it is preferable that a contact strip which makes contact with such an electrode have a groove in its face to guide'the electrode into place during switch assembly and tohold the electrode in place in an assembled switch. A form of groove 59 which may serve this purpose is illustrated in contact strip 24R of FIGS. 4 and S. The button electrode 34 rides down the chute 59 formed in the contact strip 24R and remains in pivot channel 57 where it can pivot under the urging of a-trigger such as 54 best seen in its relation to a button and strip 24R in FIG. 3.
Where the strips such as 24R and 24L are employed there'is an additional economy of switch construction inasmuch as these two parts are interchangeable as either contact strip 24L or strip 24R may be used on either side of a mercury button such as 32 of FIG. 6. Such an interchangeable strip is provided with both an enlarged heat sink portion 42 and with the chute 59 and channel 57 for guiding the axially extending electrode 34 to its proper position relative to the housing and contact strips. The heat sink portion 42 of such an interchangeable strip is principally useful in relation to the flat surface of the closed end 38 of a mercury button and the chute and channel portion formed within the heat sink portion are mainly useful in relation to the electrode such as 34 protruding from the closure element' of a button such as 32.
However, the closed end of a button need not be as flat as the buttons 32 shown in FIGS. 2, 4, 6, and 7 but may be provided on its steel shell surface with a nipple such as that disclosed in U .S. Pat. 3,415,965 and shown in FIG. 9 of the present application as a nipple 116 of button 132.
What has been found feasible in one mode of practice of the present invention is the formation of a button with a nipple 116 which is only half or other appropriate fractional part as high as the electrode 112 extending from the button closure in the opposite direction as shown in FIGS. 9 and 10. Pursuant to this mode of construction, a channel 157 of the contact strip is made of a depth and length to prevent any contact of the outer surface of the nipple 116 with the' contact strip surface in the depth of the channel 157 However, the depth of the channel 157 below the chute 159 is also of such depth that the electrode 112 of FIGS. 9 and 10 displaces the strip 124R outward under spring pressure. This outward displacement establishes and maintains an insulating air gap separation between the rim 1360f the button 132 and the contact strip 124R. Thus although each channel 157 is of equal depth the different length of the nipple 116 and electrode 112 extending into the channels results in the heat sink flat of the strip 124L contacting the flat of the button while the heat sink flat of strip 124R is held spaced from the flange, of the closure rim 136 by an insulating air gap sufficient to maintain an electrical potential of 1,500 volts therebetween as is conventionally required for such switch structures.
The nipple 116 of button 132 can serve the purpose of preventing lateral motion of the button as for example during rotation of the button accompanying the switching action.
For smooth rotary action neither the nipple 116 nor the protruding electrode 112 should strike bottom in the channel 157 formed in an enlarged heat sink portion of a contact strip. Rather for best trigger action the button should be maintained in a constrained floating position with the nipple 116 and electrode 112 held above the bottom of the channel 157 but constrained from side to side movement by the sidewalls of channel 157 acting on the nipple 116 and electrode 112 as needed.
To give the switch a smooth action and to provide a cushioned stop at the end of the stroke a spring may be provided between a button and some portion of the insulating casing as the back wall or bottom of the insulated housing.
Turning back again to FIGS. 2 through 6, it will be seen that a trunion portion 65 of toggle 54 has two relatively flat bearing surfaces 62 and 66 which can register with the underside of the mounting strap 16 to impart to the finger of the user of the switch the sensation of two at rest positions. These positions are analagous to the at-rest positions of an overcenter switch. Inactuality, however, there is no spring pressure on the toggle sufficient by itself to advance the trigger to its at-rest position ahead of the motion resulting from the action of the finger of the operator of the trigger portion 22 of the toggle 54. Rather the action of a spring 50 on button 32 and toggle S4 is that of assisting the user to lodge the trigger 22 in one of its two at-rest positions. The overall smoothness of the switch action is such that the trigger may actually be left in essentially any intermediate position between the two at-rest positions to which the operator may choose to move it.
With reference again to FIG. 3 a wire spring 50 is supported between two bosses 52 formed integrally with and extending out from the back wall 17 of the switch housing. The wire spring ends are received in conforming notches in the forward end of the bosses 52 and the spring is held in place by the pressure .of button 32 pressing inwardly against it. Button 32 is in turn held in place laterally between the contact strips, only one of which 24R is seen in FIG. 3, as explained more fully above.
The button 32 is also confined-to its operating position by an inward push of toggle 54. Toggle S4 accordingly bears outwardly at its trunion surfaces 62, 64, and 66 against the underside of mounting strap 16 and presses button 32 inwardly against wire spring 50. i Very limited in and out motion of the button 32 takes place. What motion does take place occurs mainly when the trigger passes through about the mid-point between its at-rest positions, i.e., when trunion bearing surface 64 engages the underside of strap 16, and when the trigger arrives at the end of its stroke at the full ON or full OFF positions.
The spring action which accompanies action of the toggle 54 is now described. Referring again to FIGS. 2 through 6 it will be evident that rotation of the button 32 by movement of the trigger 22 to various positions does not interrupt close thermal and electrical contact of the flat surface of closed end 38 of button 32 with the flat portion of contact strip 24L. As viewed in FIG. 2 it may also be seen that slight in and out motion of button 32 relative to casing 12 and against the wire spring 50 (a seen in FIG. 3) does not dislodge or separate the flat surface of closed end 38 of button 32 from its close thermal contact with the confrontingflat surface of heat sink portion 42 of contact strip 24L.
The continued contact of the closed end 38 of button 32 with heat sink 42 is important of course in assuring that no over heating of the button surface occurs during any of the buttonmotions which must be made in operating the button. Even a momentary separation of button surface from the heat sink can cause localized over heating and even breakdown of the button where the'higher amperage and voltage level are being controlled by the mercury switch. This overheating can occur because the energy generated by an arc in the button is very high and the localized overheating can cause the arc to be continued thus leading to further overheating and breakdown of the button. An important relationship made possible by this new switch structure is a continued contact of that portion of the flat surface of closed end 38 of button 32 and particularly at that portion wherelocalized overheating has beenfound to 'be mostlikely to take place.
'As the toggle handle 22 ismoved from an OFF positionas shown in FIG. 3 toward an ON position the flat bearingsurface62 of the trunion 65 is separated from the underside of the-mounting strap 16 and the crest 64 comes into contact with the undersurface strap. Because the crest is further from the center of rotation of the button (generally at the electrode 34) the toggle 54 .andaccordingly the button 32 are displaced slightly into the housing as the crest 64 comes into contact with the'underside of strap 16. As this occurs wire pring 50 is "put under further spring bias as it is bent further toward=the back wall 17 of the housing 12.
After the trigger 22 has passed the mid-point of its travel to'the ON position the pressure on the spring 50 is relieved slightly as a second relatively flat portion 66 of the trigger trunion 65 is brought into contact with the underside of the strap 16. This arrival of flat portion 66 into contact with the underside of strap 16 is the motion which gives the sensation to the finger of the switch operator of the arrival of the switch handle at a second at-rest position familiar in overcenter trigger actions.
As the trigger moves through the course recited above or through the reverse course from ON to OFF .the button moves in and out slightly with the electrode 34'travelling a slight distance along channel 57 in thermal and electrical contact therewith.
At the end of the normal course of travel the trigger is given a soft stop due to a similar set of motions of toggle 54, button 34 and spring 50. Again this soft stop does not result in or involve a thermal disengagement of the flat surface of closed end 38 of button 32 from the flat surface of heat sink portion 42 of the contact strip 24L.
In this soft stop motion the trigger overtravels slightly past-the normal at-rest position, i.e., the position in whichthe flat bearing surface 62 or 66 of the trunion 65 is flush with the underside of the strap 16.
Considering for purposes of illustration flat bearing surface-62, the soft stop effect is achieved when the outer end 60 of flat bearing surface 62 engages the strap16 and urges the toggle 54 and button 32 further into the housing 12. The motion of button 32 further into the housing is resisted by the increased biasing of the spring 50. Accordingly, this overtravel of the trig- .get 22 results in increased spring bias and increased tendency of the trigger 22 to be returned to the at-rest postion. The trigger does not strike a stop but rather the end of the stroke is cushioned and rendered silent by the translation of the rotary motion of the trigger and button into an increased bending of biasing of the spring 50 in a direction away from the strap against which the outer end 60 of the bearing surface 62 acts. The position in which the trigger 22 and trunion 65 is illustrated in FIG. 3 is the overtravel position in which the spring return of the trigger 22 to its at-rest position is induced. The outer end of flat bearing surface 62- and a similar outer end 68 of of flat surface66 are effective in inducing soft stop as the trigger travels past the full ON position, or past the full OFF position.
Accordingly there is an actual spring return of the trigger toward one of the at-rest positions from an overtravel as distinct from the action induced by the deflection of the spring 50 as crest 64 passes against strap 16.
Referring next to FIG. 5 an alternative means for holding the contact strips in place in the switch housing is shown in greater detail.
The trigger 22 is shown in a normal position extending from trigger opening 26 in mounting strap 16.
As is evident the trigger is in a position which may for convenience of reference be referred to as an OFF position. The trigger can be pivoted to the vacant portion of trigger opening 26 which corresponds to an ON position.
In the OFF position shown it will be seen that trunion 65 has a bottom trunion stop surface 68 which is poised immediately above or is in contact with contact strip 24R.
Normally contact strip 24R is held in position in insulating body 12 by a wire affixed to a screw terminal such as 14 of FIG. 3. The terminal strip cannot normally rise in housing toward a mounting strap such as 16 when the screw of a screw terminal is backed out or.
where a wire is attached. But it will be evident from FIG. 5 that because trunion 65 underlies strap 16 and overlies contact strip 24R the contact strip not only cannot rise into contact with strap 16 even in the absence fiber inserts 28, but in addition will be driven or depressed down into the switch body by normal operation of the switch toggle 65.
Turning now to FIG. 11 through 17 an alternative form of switch is described.
Referring first to FIGS. 11 and 12 a mounting strap 160 of the switch is shown assembled to a switch housing 170 by bosses 158 formed integrally with strap 160 and extending through opening 153, to grip conforming slots, not shown, in the housing wall.
A trigger 122 emerges through a trigger opening 124 and is pivoted between an OFF position shown in solid lines and an ON position shown in dashed outline 125.
A conventional screw terminal 126 and screw 128 permit power supply wires not shown to be joined to the switch.
In FIG. 13 a front elevation reveals internal details of the switch as the toggle mounting strap 160 and spring are omitted. Contact strips 142 and 144 are disposed internally along the longer side walls 145 and 147 of the insulating housing and communicate with the housing exterior at the terminals such as 126.
Strip 142 is held at is end in positioning slots 146 in end walls 150, and strip 144 is held in similar positioning slots 148.
Contact strip 144 is spaced along its length, and particularly at chute 167 and pivot channel 169, away from side wall 145. In fact a set back such as 143 in side wall 145 may be provided to ensure against contact of the strip 144 with the side wall 145. o
By contrast two ribs 152 are formed integrally on the inner surface of side wall 147.'These ribs stand out from side wall 147 and lie flush in contact with contact strip 142 when strip 142 is in place in the switch housing. The ribs accordingly prevent any outward deflection of strip 142 and particularly any outward pivoting of outward deflection of the enlarged heat sink portion 154 of strip 142. The relationship of ribs 152 to heat sink 154 of strip 142 may be seen in FIG. 15 where the portion of the heat sink 154 contacted by the ribs is shown by dashed lines 153 lying approximately along the lines of contact between ribs and heat sink.
Mercury button 162 is positioned in housing 170 between contact strips 142 and 144 so that the closed and 162 of button 162 is in flush planar contact with heat sink portion 154 of contact strip 142. Also electrode 164 is in pressure contact in pivot channel 167 with contact strip 144 so that the electrode 164 can pivot in channel 167 and maintain electrical and thermal contact with contact strip 144.
The distance between contact strips 142 and 144 is preferably slightly less than the thickness dimension of button 162 from flat closed end 163 to the end of electrode 164. Accordingly, button 162 is maintained between contact strips 142 and 144 under spring bias and more specifically under a spring bias generated by a slight outward bowing of the contact strips, particularly strip 144 which is unrestricted in its outward movement. Good thermal and electrical contact is maintained between the contact strips and button due to this spring pressure. 7
Referring next to FIG. 14 an elevational view in part in section of a switch having elements as shown in FIG..
13 is illustrated. The insulating housing 170 has a strap 160 mounted to it. The strap 160 has a trigger opening 124 and a trigger portion 122 of a toggle extending through the opening 124 from the switch interior. The toggle 130 has a trunion 134 showing, and a second showing, not showning, on the opposite side of toggle 130. The trunion bears at its upper surface 172, 174, and 176 against the longer sides 178 of a generally rectangular leaf spring 140. The two flat bearing surfaces 172 and 176 are the trunion surfaces in contact with spring 178 when the trigger is at its at-rest ON position or at its at-rest OFF position.
Two flat under surfaces 182 and 184 of trunion 134 stand spaced respectively a small distance from the upper edge 186 of strap 142 when the trigger is in its ON and OFF positions.
Normally the upper surfaces 172, 174, or 176 of trunion l34.are in contact with leaf spring 178. As the trigger moves to the end of its stroke, as for example to the position shown in FIG. 14, the surface of trunion 134 bearing against leaf spring 178 will apply increasing pressure on the spring until the spring is bowed up toward strap 160 as shown. Spring 178 bears at its ends 179 against the under side of strap 160 and particularly at a land portion 161 of strap 160. However, the midsection 165 of spring 178 is located beneath a bridge 188 on each side of trigger opening 124 and does not strike the underside of thestrap until the spring 178 is bowed out of its normal configuration in applying pressure on trunion 134.
Normally the spring 178 bears on the bearing surfaces 172, 174, and'176 of trunion 134 with sufficient pressure to provide a frictional engagement between toggle trunion 134 and spring 178 such that the trigger 122 will remain in any positon to which it is set by the user.
When flat bearing surface 172 is in contact with spring 178 the flat under surface 184 of trunion 134 is not normally in contact with the upper edge 186 of contact strip 142. However, as contact pressure of trunion 134 against spring 178 increases and causes an upward bowing of spring 178 toward bridge 188, a further descent of flat under surface 184 toward and into contact with edge 186 of contact strip 142 occurs.
This contact of trunion 134 with contact strip 142 and with 144 prevents the strips 142 and 144 from rising to a point where any contact can be made with strap 160.
Referring back now to FIG. 5 the relation of the contact strips to the toggle is further explained.
An unusual compactness of themercury switch of this invention is achieved partly because an appreciable portion of the toggle body moves down between the contact strips in the normal switch operation. In other words it has been found possible to bring the contact strips up closer to the mounting strap, or conversely to bring the trigger down further into the switch body by spacing the contact strips by a width greater than than the width of the trigger opening of the strap and by forming the body of the toggle so that substantially the entire trigger opening is occupied by the toggle body at any position to which the trigger may be moved.
This shaping of the toggle to fill the trigger opening is a safety feature of the switch in that it prevents injury to children who might otherwise push a wire or nail into the trigger opening of the switch and receive injury when the metal article touches a live contact within the switch. One would be led to expect that a mercury switch which is provided with toggle of such full dimensions would require an enlarged switch housing.
However, by spacing the contact strips and by providing a narrow central portion of the toggle body to conform to the width of the trigger opening which it must occupy, a compact switch construction is achieved in which portions of the trigger opening guards 194 and 196 are able to move down into the switch between the contact strips.
What is claimed as new and desired to be secured by Letters Patent of the United States is:
l. A mercury switch of improved switching capacity which comprises an insulating housing a mercury button mounted for pivoting motion in continuous contact with and between two electrical contacts within said housing, said pivoting motion producing a switching action with respect to electrical current flowing between electrical conductors extending from said contacts to the housing exterior and a heat sink in thermal contact with said mercury button,
said switch being of a size smaller than a standard wall box.
2. The switch of claim 1 'in which the switch includes means for conducting heat from said heat sink to the exterior of said housing.
3. The mercury switch of claim 2 in which the heat conducting means is an electrical conductor of said switch.
4. The mercury switch of claim 1 in which the heat sink is an electrical conductor of said switch.
5. A mercury switch which comprises,
an insulating housing,
a mercury button within said housing mounted in pivoting relation between two contact strips,
said button comprising a cylindrical metal shell having a closed end and having an electrode insulatedly mountedthrough a closure for the other end,
a heat sink in thermal contact with the portion of said metal shell which receives the greatest heat during switch operation.
6. The switch of claim in which said heat sink provides both electrical and thermal contact between said metal shell of said button and one of said contact strips.
7. The switch of claim 5 in which the heat sink is disposed in the area contacted by the portion of the mercury button shell opposite the through hole of said button.
8. The switch of claim 5 in which the heat sink is integral with a contact strip of said switch.
9. The switch of claim 5 in which the heat sink is an enlarged section of the contact strip of said switch.
10. A mercury switch which comprises an insulating housing having two contact strips in insulated relation to each other in said housing a mercury button mounted between said two electrical contact strips to pass and interrupt flow of electric power between said strips in said housing in response to the pivoting of said button,
said button comprising a cylindrical shell having a flat closed end and having an electrode insulatedly mounted through a closure for the other end, electrical contacts for said button extending into contact with said flat closed end and electrode a heat sink disposed against the metal shell of said button.
11. The switch of claim in which one of said contact strips has a flat metal contact in planar contact with the flat surface of the closed end of said button.
12. The switch of claim 10 in which the heat sink is integral with the contact strip of said switch.
13. The switch of claim 10 in which the two contact strips have identical form.
14. A compact mercury switch comprising an insulating housing a mercury button disposed in pivotaing relation in said housing a mounting bracket affixed to said housing and hav- I ing a trigger opening therein,
contact strips spaced within said housing by a distance greater than the width of said trigger opening,
a toggle having a body embracing said mercury button, a trigger extending through said opening, and opening guards abutting said trigger and aligned with the opening to limit entry of foreign matter through said opening,
a trunion on each side of said toggle extending laterally from the body thereof a distance greater than the width of said trigger opening said guards having depending end portions extending below said trunion,
and said end portions being disposed to extend below the upper level of said contact strips on pivoting of said toggle.
15. The switch of claim 14 in which the contact strips communicate with the housing exterior.
16. The switch of claim 14 in which the mercury button is held in pivoting relation between said contact strips under spring bias thereof.