US3014105A - Thermostatic controls - Google Patents

Description

1961 D- J. SCHMITT 3,

THERMOSTATIC CONTROLS Filed June 29, 1959 33 as F|G.2

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IINVENTOR. DONALD J. SQHMITT BY ATTORNEY United States Patent Ofiticc 3,014,105 Patented Dec. 19, 1961 3,014,1tl THERMIGSTATHC CGNTROLS Donald J. Schmit t, lvlansfieid, Ghio, assignor to Them G-Disc, Incorporated, Mansfield, Ohio, a corporation of Ohio i Filed June 29, 1959, Ser. No. 23,697 8 Claims. (Ct. 208 133) This invention relates to electric switches and more particularly to a new and improved thermostatically controlled switch.

In United States Letters Patent, No. 2,717,936 to John D. Bolesky, there is disclosed a thermostatically controlled switch which is particularly well adapted for controlling the heating current in small household appliances. While the switch of that patent has been found eminently well suited for a wide variety of such applications, situations have arisen where it has become necessary to provide a switch capable of carrying current substantially in excess of what the switch was originally designed for. Because of the exceptionally good performance of the switch of said patent, it was'dee'rned desirable to extend the'practical applications of the switch to devices having higher current-ratings. At the same time, retaining the desirable characteristics of the original switch.

When it was attempted-to operate the switch at such higher current values, difficulties were encountered, due to the tendency for arcing between one of the currentcarrying elements in the switch and the bi-metallic disc or the retaining ring which holds the bi-metallic disc in place on the switch housing. Tests have demonstrated that such undesirable arcing could not be reliably prevented merely by increasing the spacing between the current-carrying elements and the bi-metallic disc, or the retaining ring. i

In accordance with the present invention such arcing is positively prevented by providing a thin wafer of suitable dielectric material engaged between the switch housing and the bi-metallicdisc and the retaining ring therefo'r. By the provision of such an are preventing wafer a switch construction substantially identical to that of said patent may be employed for operation at currents conside'rably' in excess of what was previously considered the maximum tolerable limit. Thus, by this inexpensive expedient, it is possible to' extend the practical utility of the switch to applications which previously were considered impossible.

Accordingly, it is an object of this invention to provide a novel and improved thermostatic switch. Another object of this invention is to provide a thermostatic switch of the bi-metallic disc type which has novel provision for preventing arcing between the currentcarrying member s in the switch and the bi-me'tallic disc,

' or the retaining ring for the disc.

Another object of this invention is to provide a novel thermostatic switch which is capable of safely handling considerably higher currents than was possible heretofore with the same size and type of switch.

These and other objects and advantageous features of the invention, not "at this time more particularly pointed out, will become more apparent as the nature of the invention is better understood from the following detailed description takenin conjunction with the accompanying drawing, wherein like reference characters denote corresponding parts, and wherein:

FIGURE 1 is a top plan view of the switch, with par-ts broken away for purposes of clarity in illustration,

FIGURE 2 is a sectional view taken centrally through theswi'tch, along the line 2-2 of FIGURE 1,

FIGURE 3 is a sectional View taken centrally through the'switch, along the'line 3-3 of FIGURE 1, and

FIGURE 4 is a fragmentary perspective view of the arc suppressing Wafer employed in the present invention. With reference to FIGURES 1 to 3 inclusive of the drawing, the switch proper comprises a substantially cylindrical housing 8, having an upstanding annular sidewall 9 and a generally flat bottom wall 10. Preferably this housing is made of an electrical insulating material which is also heat resistant to a fair degree, such as a phenolic condensation product. At its upper end, the housing sidewall 9 is formed with a laterally outwardly protruding flange 11.

The inner surface of the housing sidewall 9 is formed with diametrically opposed,.inwardly projecting wall portions 13, 14, 15 and 16. The wall portions 13 and 14 and the wall portions 15 and 16, respectively, define therebetween diametrically opposed arcuate recesses 17 and 18. At their lower ends the respective recesses 17 and 18 are provided with slots 19 which extend through the housing bottom wall 10. The exterior surface of the housing bottom wall 10 is cut away at the lower ends of the slot 19 to form substantially rectangular notches 22 which extend inwardly from the periphery of the housing and its'bottorn wall. Conductor straps 23 have their inner ends received in the notches 22. The outer ends of these conductor straps are to be connected in the electric heating circuit of the device with which the present switchis associated, such as a small household appliance. The housing wall portions 14 and 15 and the wall portions 13 and 16, respectively, define there/between, diametrically opposed vertical slots 24 and 25 which at their lower ends terminate at the upper, inner surface of the housing bottom wall 10. The upper, inner surface of the housing bottom wall 10 is formed with a recess 26 at its center.

Mounted on the housing bottom wall iii is an angular spring'mernber 27 which has diametrically extending cars 28, received within the vertical slots 24 and 25. The spring member 27 is suitably arched upwardly at the middle to provide the requisite amount of spring pressure. The arched central portion of spring member 27 is formed with a flat, upwardly facing surface which bears against the lower face of a fiat angular Washer 50 of suitable metal, such as stainless steel. The washer 50 in turn bear against the bottom of a circular bridging contact member 20 which is formed with ears 29 which are received within theslots 24 and 25 andare freely slidable up and down therein. Theseears 29 are disposed above the ears 28 of the spring member 27 and serve to maintain the bridging contact member 20 in proper operative posi' tion within the housing 8. As best'seen in FIGURE 3, the bridging contact member 20 is formed with pressed out dimples 20a and 20b which are engaged by the washer 50. Intermediate the cars 29 and adjacent the periphery thereof bridging contact member 20'is provided with pressed out buttons 30 which serve ascon'tacts. Mounted centrally on the bridging contact member 20 is a bumper button 31 of suitable insulation material. This bumper button has a depending shank portion 31a which extends down through the central opening in the bridging contact member 20 and through the corresponding central openings in the spring washer 50 and the spring member 27. This shank portion 31a of the bumper button is adapted to extend into the recess 26 in the housing bottom wall when it and the bridging contact member 20 areimoved downthe spring contact member and is arranged to be engaged by a contact button formed thereon. Each stationary contact member 32 is formed with a depending shank portion 35 which extends downwardly through the respective opening 19 in the housing bottom wall and is secured to the inner end of the corresponding conductor strap 23 situated within the notch 22 in the housing bottom wall. The shank portion 35 of each stationary contact member is suitably formed so that when attached to the terminal strap 23 it is secured thereto with a mechanical and electrical joint which is not dependent for its current-carrying characteristics on the housing in which it is disposed. The joint between these two parts is independent of the molded switch housing in which the elements are assembled and will not become loose in use, which would tend to cause high resistance to the flow of current thereacross.

The upper end of the switch housing 8 is counterbored to form a flat, angular, upwardly facing seat 37 which receives a disc-like composite thermostatic disc 40. Preferably the thermostatic disc is a dished, bi-metallic, snap acting, thermostatic element which is characterized by having its bowed central portion in one position of. stable equilibrium when the plate is cold or at normal low temperature and in an oppositely disposed stable position of equilibrium when it is hot, the hot and cold positions having opposite curvatures. In the illustrated embodiment, the bi-metallic disc is shown as having an outward curvature when it is cold, or at normal room temperature. When the bi-metallic disc is hot it is curved inwardly and engages the flat upper end of the bumper button 31. The

edge of the thermostatic disc or plate 40 is received within the shoulder portion 37 of the switch housing and is maintained therein by a metal retaining ring 42 which has a circular opening therein, the edge portions 43 of which overlap and confine the periphery of the bi-metallic disc 40. The retaining ring 42 is formed with 21 depending side flange 44 which has its lower edge turned inwardly and seated below the outwardly protruding flange 11 on the switch housing sidewall, thereby securing the bi-metallic disc 40 on the switch housing.

In the operation of the switch, the central portion of the bi-metallic disc 40 is free to move between its equilibrium positions of opposite concavity in response to changes in the temperatures to which it is exposed. When moving from its cold position to its hot position, the bi-metallic disc 40 moves with a snap action against the bumper button 31. This movement is imparted to the movable bridging contact member 2% which moves downwardly against the bias exerted by the spring 27 and disengages from the fixed contact members 32 thereby breaking the electrical circuit in which the switch is connected. When the bimetallic disc 4% is in its normal, cold position (concaved upwardly) the spring 27 maintains the movable bridging contact member 2% in engagement with the stationary switch contact members 32 thereby closing the circuit through the switch.

Thus far, the switch is essentially similar to the switch described and claimed in United States Letters Patent No. 2,717,936 to John D. Bolesky.

In accordance with the present invention, there is provided a novel arrangement for positively preventing arcing between any of the switch contacts and the bimetallic disc 4-0 or its retaining ring 42. In the preferred em bodiment this are preventing means is in the form of a thin wafer of tetrafluoroethylene, this being a material sold under the name Teflon. This material is characterized by high dielectric strength, extreme flexibility, and toughness. As shown in FIGURES 2 and 3 this are suppressing member is engaged between the upper end of the switch housing 8 and the bi-metallic disc 40 and the retaining ring 42 therefor. The wafer 66 has a generally flat central portion 60a and an upwardly oilset angular peripheral flange 60b which is joined to the central portion 60a through an upstanding angular segment 600. As shown in FIGURES 2 and 3, the upwardly 0H- set peripheral segment 69]) rests on top of the flat upper face of the housing sidewall 10 and is engaged by the overlying angular segment of the retaining ring 42. The central portion Giia of this are preventing wafer is seated at its periphery on top of the shoulder 37 of the housing side wall and is engaged beneath the peripheral portion of the bi-metallic disc ill there. The central portion 60a of the are preventing wafer extends completely across the inner face of the bi-metallic disc 4t), as best shown in FIGURES 2 and 3. In one practical embodiment the tetrafluorocthylene wafer 6t? has a uniform thickness of .002 inch.

Because of its high dielectric strength, the tetrafluoroethylene wafer 66 provides a complete dielectric seal for both the bi-metallic disc 40 and its retaining ring 42. Therefore, the occurrence of arcing between any of the switch contacts and the bi-metallic disc or its retaining ring is substantially completely eliminated. Also, because of the fact that the wafer 60 is extremely thin and is composed of material which is inherently flexible, this water is extremely flexible and does not increase materially the force required to operate the switch. Moreover, since the wafer material has a high degree of toughness, it will maintain its physical and electrical properties over the entire useful life of the switch.

While tetrafluoroethylene is considered the preferred material for the are preventing wafer 60, other materials having equivalent properties may be used, if desired. Moreover, the principles of the present invention may be embodied in switch devices which differ in construction from the particular embodiment shown.

Therefore, while there has been described in detail herein and illustrated in the accompanying drawing a particular presently preferred embodiment of this invention, it is to be understood that various modifications, omissions and refinements which depart from the disclosed embodiment, may be adopted without departing from the spirit and scope of this invention as described in the appended claims.

I claim:

1. In a thermostatic switch a housing defining an open end chamber having current carrying switch contacts mounted therein and a bi-metallic disc for actuating said switch contacts, the improvement which comprises a flexible member of dielectric material serving as a closure member for the open end of said chamber interposed between and shielding the bi-metallic disc from said switch contacts to prevent arcing from any of the switch contacts to the bi-metallic disc, said disc arranged to exert pressure through said flexible member to actuate the switch contacts.

2. In a thermostatic switch a housing formed with an open end cylindrical chamber therein, switch contacts mounted in said chamber, a flexible member of dielectric material forming a closure member for the open end of said chamber, a bi-metallic disc superimposed upon said flexible member and coextensive therewith. said disc adapted to exert pressure through the flexible member to actuate the switch contacts, said flexible member serving to shield the bi-metallic disc from said switch contacts to prevent arcing from the switch contacts to the bi-metallic disc.

3. In a thermostatic switch which has a housing with a switch chamber therein, switch contacts in said chamher, and a bi-metallic disc for operating said switch contacts, which is supported by said switch housing extending across one end of said chamber, the improvement which comprises a thin flexible wafer of dielectric material superimposed on the said disc and movable therewith which is interposed between the switch housing and the bi-metallic disc and which extends across the inner face of the bi-metallic disc to shield the bi-metallic disc from the switch contacts.

4. The switch of claim 3 wherein said disc is composed of tetrafluoroethylene.

5. In a thermostatic switch which comprises a hollow, cylindrical housing having an open end and a closed end, inwardly projecting wall portion defining diametrically opposed slots in the interior wall of said housing, spaced stationary contact members mounted within said housing intermediate said slots, a movable contact member bridging the space between said stationary contact members and having opposed extensions engaging within said slots, spring means for maintaining said movable contact member in engagement with said stationary contact members, a snap acting thermostatic disc having its peripheral edge portion confined in the open end'of said housing and having two positions of stability, said thermostatic disc passing automatically from its first position to its second position of stability upon change of temperature to a pre-determined degree and in its second position being adapted to having its central portion move said movable contact out of engagement with said stationary contacts, the improvement which comprises a thin wafer of material having high dielectric strength which is superimposed on said disc and movable therewith to actuate the movable contact and disposed between said closed end of the housing and said thermostatic disc and which extends completely across the inner face of said thermostatic plate to shield the thermostatic disc from the switch contacts.

6. The switch of claim 5 wherein said wafer is composed of tetrafiuoroethylene.

7. The switch of claim 5 wherein said switch housing is formed with a counter-bore at said one end and presents an angular shoulder at said counter-bore at which the peripheral edge of the thermostatic disc is located and wherein there is provided a retaining ring for the thermostatic disc which extends across said one end of the switch housing beyond said counter-bore therein, and said wafer overlies said. shoulder and overlies said one end of the switch housing beyond the counter-bore at the inner side of said retaining ring to shield the retaining ring, as well as the thermostatic disc, from the switch contacts.

8. A thermostatic switch comprising a hollow housing having an open end and a closed end and defining a switch chamber therewithin, switch contacts mounted in said switch chamber, a closure member for the open end of said switch chamber made of a thin flexible dielectric material, a bi-metallic disc mounted on the exterior of said closure member and adapted to exert pressure through said closure member and means serving to hold the bi-metallic disc and closure member in assembled relation on the open end of said housing.

References Cited in the file of this patent UNITED STATES PATENTS ,572,162 Koonz Oct. 23, 1951 2,689,895 Ingwersen Sept. 21, 1954 2,717,936 Bolesky Sept. 13, 1955

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